An ontology-based universal design knowledge support system An effective and efficient knowledge support system is crucial for universal design process, as it has become a major design issue in the last decade with the growth of the elderly population and disabled people. There are a limited number of CAD investigations on the nature of knowledge processing that supports the cognitive activities of universal design process. Therefore, this paper proposes an ontology-based computer-assisted universal design (CAUD) plug-in tool that supports designers in developing satisfactory universal design solutions in the conceptual design phase. The required knowledge processing and representation of the developed tool is motivated by the ontological language. It is based on the multiple divergence-convergence cognitive strategies and cognitive needs of designers in the analysis/ synthesis/evaluation operations. The CAUD plug-in tool is the first attempt to interface the universal design knowledge ontologically and respond to the requirements of conceptual design phase. According to the user acceptance study, the tool is assessed as useful, understandable, efficient, supportive and satisfactory. Architectural design process is composed of a series of goal oriented cognitive activities. Although the final goal is ill-defined initially, the subgoals have to be well-defined throughout the design process [13] . The suitability of the design strategy and the efficiency of the knowledge support system determine the level of creativity and the quality of the design process [26] . Since ''designers cannot retain all the information they need to solve complex design problems in their heads, so they must retrieve that information from external sources, including colleagues, documents, drawings, models and databases'' [7, p. 173] . In the last 20 years, there had been attempts to develop an ideal knowledge-based computational design support system that assists designers by providing databases, storing design goals and predicting the performances of alternative solutions [10] . However, there are many discussions on the suitability of these support systems to the conceptual design phase [25, 38, 59] . Commercially available CAD tools were far from being promising for covering the requirements for conceptual design phases since they were more suitable for the detailed design phase in the early years [43] . Nowadays, the conceptual phase as the most vigorous, dynamic, informal, complex and creative phase is the least understood and supported by the CAD systems. ''Current CAD tools push designers in precisely the wrong direction, encouraging users to bypass the refinement process of creative and critical thought and go straight to the finished work'' [11, p. 592] . Most CAD users are contended with the same tools in the conceptual phase that they use in the detailed design phase. Therefore, there is an urgent need to develop an efficient knowledge-based system that supports conceptual activities.. A suitable knowledge support system is also crucial for designing better built environments. In the last decade, the concept of universal design, which means creating products, environments and systems for all ages, abilities and sizes, has become a major design issue with the growth in the elderly population and disabled people [42] . Furthermore, the needs and demands of diverse population members, who are children, adult or disabled, vary considerably. For Mace [34] , it includes not just people in wheelchairs, but also people with mobility, speech and hearing impairments, and with all diminished abilities, either temporary or permanent, that can be occurred over a person's life span, such as retardation, advanced age, or pregnancy. Thus, to overcome the inclusivity challenge in the design process, universal design has been studied extensively in various fields such as interior and product design, design education and many others [39] . However, there are a limited number of CAD studies on the nature of design cognition that supports an effective universal design knowledge acquisition in the conceptual phase. Most of the developed systems provide support for design representation, manipulation and transformation, but none of them explicitly support cognitive needs of architects. The relevant studies should go beyond specification of human dimensions, visualization of ergonomics data or task analysis tools. The importance of architectural design in the technological arena 0950 shows it has a specific domain for cognitive understanding of all dimensions of the real world. So, this study develops an ontology-based universal design support system for the conceptual phase. Since the ontological approach described as 'an explicit specification of a conceptualization' [22] is suitable for determining the specific features of a certain domain, it appears as a promising integration structure for this study. We propose a computer-assisted universal design (CAUD) plug-in tool that supports real world designers in applying a suitable design strategy for developing satisfactory solutions. In this respect, the overall aim of the research is to focus on how universal design knowledge ontologically relates itself to the methodological flow of design process. To the best of the authors' knowledge, this study is the initial evidence in architectural design literature that an ontologybased universal design knowledge support tool for the conceptual design phase. The research questions addressed by this study are:. 1. How does a designer define a set of requirements, a sequence of design strategies and evaluate alternative solutions in the conceptual phase of the universal design process? 2. How does a designer retrieve and use the information from an ontology-based universal design knowledge domain including experts, design solutions and databases? 3. How does the dynamic nature of a CAD medium provide feedback to the designer in the conceptual design phase?. The outline of this paper is as follows: In Section 2, we review the literature on cognitive strategies of designers and their CAD usage in the conceptual phase. Section 3 addresses universal design knowledge processing and representation where an ontology-based model put forward with respect to an iterative design process. Section 4 introduces the proposed experimental system -CAUD plug-in tool -with user interfaces. In Section 5, the evaluation of the tool is conducted. Finally, Section 6 draws conclusions and mentions future work. In this paper, we present a novel ontology-based approach for universal design concept generation. Today, universal design knowledge appears in various sources changing from technical documents to design representations [39] . However, CAD applications should provide knowledge representations that can flexibly adapt to the requirements of the projects [5] . Therefore, we developed the CAUD plug-in tool that defines ontologies together with the iterative process of analysis-synthesis-evaluation operations. In Section 1, we proposed three explicit research questions and the answers to these questions are as follows:. 1. Our solution to how to deal with design requirements, sequence of strategies and evaluation of alternative designs is achieved by identifying the existing sources of universal design data and integrating them to the requirements of analysis, synthesis and evaluation operations. 2. Ontologies are used to represent universal design database schemas. The ontological language enhances searching, retrieving and using universal design standards, guidelines and use cases within the SketchUp environment. 3. The feedback mechanism of the proposed plug-in tool is achieved through semantic wikis. Semantic wikis with annotations and markup tags could provide strong knowledge representations that do not interrupt designer's creative process. Its web-based and open nature allows the distribution of design process over a group of designers [5] .. The CAUD plug-in tool with its above-explained capabilities coincide with the following five functional requirements of an ideal knowledge-based design support system [40] : (1) support and visualize the evolution of design development, (2) set up a creative support environment, (3) capable of knowledge management functions, (4) support a collaborative work and (5) conduct a design process with analysis, synthesis and evaluation operations.. To sum up, the cognitive needs of a designer for problem solving are highly related with the conducted design activities, and the successes of a designer in each of these activities are dependent on the employed design strategies [14] . Moreover, as psychologists acknowledged there are a number of benefits of using computer technologies to simulate cognitive process of problem solving [58] . In this respect, what is unique in our ontology is that both knowledge processing and representation is based on the most suitable design strategy and cognitive needs of designers in the conceptual design phase. Ontologies in the study provide an essential basis for enhancing designers' cognitive approach to successfully capturing, efficiently organizing, effectively representing and easily modeling of the universal design knowledge. Moreover, compared to the conventional approaches, the ontology-based approach helps to reduce the working time, increases confidence in generated solution, and contributes to the exploration of design alternatives in a short period of time. Therefore, the contribution of the CAUD plug-in tool into scientific knowledge is as follows: (1) the universal design knowledge domain is interfaced for the first time with an ontological knowledge-based approach without hindering the creativity of designer; (2) the plug-in tool overcomes the limitations in architectural design practice by providing an efficient management of universal design knowledge processing and representation. Our future work includes elaboration of an advanced CAUD plug-in tool with improved representation and reasoning capabilities. A higher level semantic web layer could be studied that allows more flexible mechanism for collaborative work and an advanced universal design knowledge processing within a wiki system. It would be also possible to extend the ontological language of the plug-in tool for different built environments as suggested by the respondents, who carried out the acceptability studies. Analysis operation as the initial part of the conceptual design process requires defining a list of objectives as design specifications. Ozkaya and Akin [44] described design specification and development as being parallel activities since design act is a cyclic process, where alternatives are checked against the initial set of objectives, and the set of objectives are redefined for the subsequent steps. Examining the literature on universal design problem-solving emphasized also the importance of analysis operation [13] . As the designer conducts an analysis operation, the user ontologies can be built up by specifying the design objectives that set the limits to the solution space, and indicate the preferred solutions. Since the initial definition of each objective can critically affect the solution in later phases, backtracking of definitions can be achieved by ontological semantics. Ontologies attempt to precisely define each objective (e.g. what space dimensions are, how the space is furnished), and express it through relations. Thus, an ontology-based approach provides formal definitions for problem descriptions and can make automated inferences about relationships among objectives (e.g. how furniture is related to space dimensions).

O O B I O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O B I O O O O O O O O O B I O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Practical

scalable

image

analysis

and

indexing

using

Hadoop

The

ability

to

handle

very

large

amounts

of

image

data

is

important

for

image

analysis,

indexing

and

retrieval

applications.

Sadly,

in

the

literature,

scalability

aspects

are

often

ignored

or

glanced

over,

especially

with

respect

to

the

intricacies

of

actual

implementation

details.

In

this

paper

we

present

a

case-study

showing

how

a

standard

bag-of-visual-words

image

indexing

pipeline

can

be

scaled

across

a

distributed

cluster

of

machines.

In

order

to

achieve

scalability,

we

investigate

the

optimal

combination

of

hybridisations

of

the

MapReduce

distributed

computational

framework

which

allows

the

components

of

the

analysis

and

indexing

pipeline

to

be

effectively

mapped

and

run

on

modern

server

hardware.

We

then

demonstrate

the

scalability

of

the

approach

practically

with

a

set

of

image

analysis

and

indexing

tools

built

on

top

of

the

Apache

Hadoop

MapReduce

framework.

The

tools

used

for

our

experiments

are

freely

available

as

open-source

software,

and

the

paper

fully

describes

the

nuances

of

their

implementation.

This

paper

has

described

in

detail

how

a

typical

image

analysis

and

indexing

pipeline

can

be

efficiently

scaled

across

a

distributed

cluster

of

machines.

In

order

to

achieve

this

we

have

described

a

set

of

hybridisations

of

the

original

MapReduce

framework

that

allow

the

processing

tasks

to

be

performed

effectively

on

modern

server

hardware,

taking

into

accounts

limits

such

as

the

available

amount

of

RAM.

The

theoretical

discussions

of

the

hybridisations

of

the

MapReduce

framework

have

been

backed

up

with

actual

implementations

and

experiments

to

demonstrate

their

worth,

and

in

particular,

we

have

released

the

entire

suite

of

tools

implementing

the

bag-of-visual-words

indexing

pipeline

on

top

of

Apache

Hadoop

as

a

set

of

freely

available

open-source

tools.

We

believe

that

this

is

the

first

work

to

fully

describe

a

complete

scalable

image

indexing

pipeline

and

provide

a

baseline

implementation..

Using

our

indexing

pipeline

tools

we

have

performed

a

number

of

experiments

to

assess

the

actual

performance

increases

we

can

achieve

by

using

a

distributed

system.

The

experimental

results

show

that

the

speedup

achieved

using

a

cluster

of

three

machines

over

a

single

machine

outweighs

the

three-times

speedup

that

might

be

expected.

The

extra

speedup

is

due

to

the

way

the

Hadoop

framework

is

able

to

distribute

I/O

across

multiple

disks

and

data

buses

even

on

a

single

machine.

The

resultant

disk-based

index

created

by

our

pipeline

has

been

shown

to

be

as

effective

as

existing

state-of-the-art

techniques,

whilst

at

the

same

time

being

many

times

more

efficient

and

scalable..

Our

approach

is

based

around

both

commodity

hardware

and

software,

utilising

both

commonly

available

hardware

architectures

and

common

programming

para-digms.

Therefore,

our

approach

scales

cheaply

in

terms

of

hardware.

In

addition,

our

approach

can

be

easily

understood

and

extended

by

researchers

and

other

programmers.

Nevertheless,

the

GP-GPU

hardware

parallelism

solutions

we

discuss

in

Section

have

been

supported

by

Amazon's

Elastic

MapReduce

since

late

(see

Furthermore,

GPUs

themselves

have

been

dropping

in

price,

increasing

in

computational

power

and

GP-GPU

computational

frameworks

have

been

increasing

in

functionality

over

the

last

half

decade.

With

these

factors

in

mind

we

predict

that

hybrid

solutions

that

combine

MapReduce

paradigms

with

more

specialised

hardware

such

as

GPUs

will

become

more

common

over

the

next

decade.

As

a

practical

example,

it

is

easy

to

see

how

a

process

like

the

difference-ofGaussian

interest-point

detection

used

in

the

SIFT

algorithm,

can

be

implemented

on

a

GPU,

and

rolled

into

our

MapReduce

framework,

potentially

offering

the

best

of

both

worlds.

We

are

considering

actively

looking

at

such

a

hybrid

approach

for

future

versions

of

our

tools..

Sina

Samangooei

holds

a

MEng

degree

in

Computer

Science

and

a

PhD

in

Electronic

Engineering,

both

from

the

University

of

Southampton.

He

currently

works

as

a

Research

fellow

in

the

Web

and

Internet

Science

Research

group

at

the

University

of

Southampton.

His

research

interests

include:

biometrics,

multimedia

retrieval

and

large-scale

text

mining..

Paul

H.

Lewis

is

a

Professor

of

Computer

Science

in

the

Web

and

Internet

Science

Research

Group

at

the

University

of

Southampton.

His

main

research

interests

are

in

the

broad

area

of

information

retrieval

and

multimedia

information

handling,

in

image

and

video

processing,

pattern

recognition,

knowledge

processing

and

the

semantic

web.

A

motivating

and

long-term

goal

for

much

of

his

research

is

the

bridging

of

the

semantic

gap

between

low

level

features,

which

can

be

extracted

from

raw

multimedia

objects

(images,

video

etc)

and

the

high

level

semantics

they

represent.

He

has

recently

been

involved

in

the

Living

Knowledge

European

Future

Emerging

Technologies

project

and

the

Live

Memories

project

funded

by

the

Trentino

region

of

Italy.

He

is

currently

involved

in

the

EU

Arcomem

Integrating

Project

and

collaborates

closely

with

other

academics

both

in

the

group

and

internationally.

The

experiments

performed

to

investigate

the

performance

of

the

ImageTerrier

indexes

take

the

form

of

a

traditional

image

retrieval

or

object

recognition

experiments.

The

UKBench

dataset

and

evaluation

protocol

is

used

as

the

basis

for

the

experiments

presented

here;

the

UKBench

dataset

consists

of

images

of

specific

objects

under

varying

orientation

and

illumination

conditions.

There

are

images

of

each

object

in

the

dataset.

The

UKBench

retrieval

protocol

is

to

take

each

image

in

turn

as

a

query

and

calculate

the

four

best

matches

Fig.

Time

taken

for

an

average

query

against

number

of

documents

in

the

index

(one,

usually

the

first,

of

which

should

be

the

query

image

itself).

A

score

is

assigned

based

on

how

many

of

the

top-four

images

are

of

the

same

object

as

the

query

(essentially

this

is

equivalent

to

the

precision

at

four

documents

retrieved).

The

score

is

averaged

over

all

queries,

and

has

a

maximum

value

of

The

indexing

pipeline

is

optimised

for

dealing

with

many

more

images

than

are

present

in

the

UKBench

dataset.

Therefore,

to

properly

test

the

technologies

we

include

a

set

of

distractor

images

into

the

standard

UKBench

corpus.

For

this

purpose

we

use

the

ImageNet

dataset

used

in

the

scalability

experiments.

For

the

retrieval

experiments,

we

include

to

million

distractor

images

in

increments

of

powers

of

to

show

the

effect

of

large

image

sets

on

retrieval

performance.

In

the

experiments

we

perform

the

complete

UKBench

evaluation

protocol

times

for

each

combination

of

valid

and

distractor

images.

The

indexes

generated

are

the

basic

type

(i.e.

without

any

extra

geometric

information).

We

present

retrieval

results

using

score

weighting

schemes

and

TF/IDF)

[see

for

more

details].

Starting

with

distractors

and

adding

more

in

powers

of

up

to

million

distractors

results

in

a

total

of

tests

distractor

combinations

performed

times,

each

with

scoring

strategies).

For

these

experiments

we

elected

to

use

a

general

vocabulary

of

millions

terms

trained

against

the

dataset

unrelated

to

both

UKBench

and

ImageNet;

this

gives

us

a

lower

retrieval

performance,

but

is

more

indicative

of

a

retrieval

scenario

where

the

entire

corpus

is

not

known

prior

to

indexing.

Even

though

the

dataset

is

different,

the

approximate

k-means

clustering

was

still

performed

in

the

distributed

manner

described

in

the

earlier

sections

of

this

paper,

using

our

HadoopFastKMeans

tool.

Results

and

discussions

are

presented

below.

Performance

In

Fig.

we

show

the

average

time

taken

for

queries

per

experiment.

The

first

thing

that

should

be

noted

is

that,

once

the

index

is

loaded

and

initialised,

a

query

is

likely

to

take

under

s

with

indexes

of

up

to

million

documents.

This

is

comparable

to

the

query

times

reported

by

Nistér

and

Stewénius,

but

it

should

be

noted

that

our

inverted

index

is

completely

disk-based,

whereas

Nistér

and

Stewénius's

was

held

in

RAM.

For

comparison,

Philbin

et

al.

report

query

times

of

between

s

and

s

for

a

disk-based

inverted

index

of

million

images

and

s

of

an

in-memory

index

of

images.

This

result

is

very

important

as

it

shows

that

using

our

distributed

indexing

pipeline,

not

only

can

you

build

indexes

quickly

and

efficiently,

but

that

the

resultant

indexes

can

also

be

searched

quickly..

In

more

detail,

the

results

show

that

with

up

to

distractors

the

query

time

is

constant.

Beyond

distractors

there

is

a

near-linear

increase

in

the

time

per

query

as

a

function

of

the

number

of

documents

(note

the

x-axis

is

logarithmic).

This

is

to

be

expected

as

even

in

an

inverted

index,

the

postings

list

of

a

given

term

is

likely

to

increase

linearly

with

number

of

documents

and

in

turn

so

will

the

time

taken

to

score

documents.

However,

the

key

improvement

promised

by

the

inverted

index

approach

comes

not

in

a

reduction

of

the

complexity

of

the

algorithm,

but

rather

the

gradient

of

the

linear

complexity.

The

inverted

index

strategy

promises

a

line

of

much

lower

gradient

than

a

brute

force

strategy.

We

also

expect

a

further

drop

in

this

gradient

if

the

searching

strategy

is

extended

to

work

in

a

distributed

manner

or

the

index

is

placed

on

a

faster

hard-drive..

In

Fig.

we

show

the

UKBench

evaluation

performance

as

distractors

are

added.

Figure

shows

the

average

interpolated

precision

recall

curve

across

all

queries.

We

notice

that

the

scores

fall

as

distractors

are

added.

This

is

to

be

expected;

within

UKBench,

images

which

only

tentatively

achieved

high

scores

with

images

that

did

not

match

very

strongly

can

be

easily

confused

when

more

images

are

added.

An

example

of

such

a

situation

is

shown

in

Fig.

which

shows

the

same

query

with

distractors,

distractors

and

distractors.

It

should

also

be

noted

that

the

best

score

we

demonstrate

without

distractors

is

which

is

slightly

below

the

state

of

the

art.

However,

as

previously

mentioned,

these

experiments

used

a

general

vocabulary

trained

against

a

different

dataset

unrelated

to

both

UKBench

and

ImageNet.

Using

UKBench

itself

to

create

a

vocabulary

from

SIFT

features

we

achieve

scores

near

with

a

term

vocabulary

(compared

to

reported

by

using

a

non-hierarchical

vocabulary

from

MSER-SIFT

features).

We

have

achieved

our

best

results

with

a

score

of

over

by

using

ASIFT

features

quantised

with

a

million

term

vocabulary

(learnt

from

the

ASIFT

features

themselves).

O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


A heterogeneous computing environment to solve the 768-bit RSA challenge In December 2009 the 768-bit, 232-digit number RSA-768 was factored using the number field sieve. Overall, the computational challenge would take more than 1700 years on a single, standard core. In the article we present the heterogeneous computing approach, involving different Scientific calculations in domains such as physics (fluid dynamics, high-energy physics etc.), chemistry (quantum chemistry, molecular modeling, etc.), biology (large scale genomic or proteomics projects), and climate modeling often require massive amounts of computing power. If the kind of problem calls for tightly coupled massively parallel computing, it is often well suited for supercomputers and stands a good chance to attract funding both to get access to the proper hardware and to develop suitable software. In contrast, embarrassingly parallel applications, where any number of stand-alone devices will do, are often not welcome on classical supercomputers but are instead relegated to high-performance computing clusters, Grid infrastructures, or desktop computing environments such as BOINC or Condor.. The latter category includes cryptographic applications. Although they are not less CPU-demanding than other scientific applications, they are not considered to be of much interest by the HPC community. Despite this disregard, many cryptographic problems are computationally, mathematically and algorithmically challenging and non-trivial, and practically relevant for users of cryptography (i.e., almost everyone these days). One of these problems is integer factorization, the subject of this paper: we present the heterogeneous computational infrastructure that was used to set a new integer factorization record by factoring the challenge number RSA-768, a 768-bit, 232-digit composite integer [11] .. We used the approach commonly used to factor large integers since the late 1980s. Thus, we did not aim for a single, homogeneous computing environment or single supercomputer, but used a heterogeneous compute environment consisting of several cluster and Grid environments (in Australia, Japan, and many European countries), different operating systems, job execution environments and technical personnel. Several technical as well as non-technical reasons have led us to a such a heterogeneous approach:. -Single Grid infrastructures such as the European Grid infrastructure: only a limited number of resources (for a limited time) in the European Grid environment have been dedicated to the RSA-factorization problem. Therefore, even though using a Grid-only environment is promising and convenient, we had to look into alternative approaches. -Individual clusters at different sites are available but are managed in different ways (i.e., different local resource management systems, different file systems, different hardware, different site expertise with respect to the RSA application, etc.). Again, standardized Grid protocols and middleware would have helped to address the problem in a more homogeneous way but the clusters we used are not part of a single Grid environment. -A diversified, heterogeneous environment better represents the Internet as a whole than any organized computer infrastructure. It thus allows a more reliable estimate of the havoc miscreants could cause by large surreptitious cryptanalytic efforts.. In brief, the RSA-768 challenge has the following features and computational stages. The first main stage is the most CPU intensive and embarrassingly parallel part of the computation and also created most data. Compressed about 5 TB had to be transferred over the Internet, at a rate of about 10 GB per day, to a central location where, once enough data had been collected, the second main stage was prepared. This stage is not embarrassingly parallel and was traditionally done on a single supercomputer or, later, on a single tightly coupled cluster. Lacking access to sufficiently large clusters for a long enough period of time, we had to adopt a somewhat more complicated approach that allows usage of a limited number of tightly coupled clusters at different locations. As a result, roughly 100 GB of data had to be distributed, using the Internet again, to the contributing clusters (restricting to those in France, Japan, and Switzerland). They worked independently, with the exception of an intermediate step that had to be done on a single tightly coupled cluster with 1 TB of RAM. This implied, yet again, a substantial data exchange. In summary, the RSA-768 challenge was solved using a truly heterogeneous infrastructure with no communication among the contributors nor computational cores except to break the computation into independent tasks.. Given the embarrassingly parallel nature of the first main stage, the most CPU intensive part of the computation, we could have used one of the tools that allow contributions by volunteers on the Internet. That is how it was done in the late 1980s and early 1990s, using crude email and FTP-based precursors of currently popular tools. Indeed, an ongoing integer factorization BOINC project [14] does just that. Having managed several such proof-of-concept projects from 1988 until about 1995, we found that a lot of time goes into addressing simple concerns of the contributors, in particular if considerable RAM resources are required (as was the case for RSA-768 with at least one but preferably two GB RAM per core). We chose to limit our project to a limited set of dedicated and knowledgeable researchers who could be expected to resolve occasional issues themselves.. Section 2 gives the cryptographic motivation, Sect. 3 presents the computational steps in more detail, and Sect. 4 describes the heterogeneous compute infrastructure used. We described the heterogeneous hardware resources and diverse management tools used during a period of about two years at many different locations to solve a cryptanalytic challenge. The computational effort required, though large given the resources available, was considerable though not exceptionally large: it would require a couple of weeks using the full "Ranger" supercomputer at the University of Texas at Austin.. Our result is a good indication for the size cryptanalytic effort that can successfully be undertaken in a more or less acceptable amount of time by a rather loosely coupled, widely scattered and mostly academic team of volunteers. Pulling off a substantially larger effort in comparable or less time would require tighter management or more funding than customary in academic cryptanalytic circles. A greater appreciation of the HPC community for cryptanalytic activities could change this picture overnight.

O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O


Compositional pattern producing networks: A novel abstraction of development Abstract Natural DNA can encode complexity on an enormous scale. Researchers are attempting to achieve the same representational efficiency in computers by implementing developmental encodings, i.e. encodings that map the genotype to the phenotype through a process of growth from a small starting point to a mature form. A major challenge in in this effort is to find the right level of abstraction of biological development to capture its essential properties without introducing unnecessary inefficiencies. In this paper, a novel abstraction of natural development, called Compositional Pattern Producing Networks (CPPNs), is proposed. Unlike currently accepted abstractions such as iterative rewrite systems and cellular growth simulations, CPPNs map to the phenotype without local interaction, that is, each individual component of the phenotype is determined independently of every other component. Results produced with CPPNs through interactive evolution of twodimensional images show that such an encoding can nevertheless produce structural motifs often attributed to more conventional developmental abstractions, suggesting that local interaction may not be essential to the desirable properties of natural encoding in the way that is usually assumed. Research in developmental encoding to this date can be characterized as a search for the right abstraction. Computational abstractions of natural development generally have included, not surprisingly, local interaction and unfolding over time. In this paper, a novel abstraction was proposed that breaks this tradition. Nevertheless, this abstraction, called Compositional Pattern Producing Networks (CPPNs), still captures essential properties of natural developmental encoding. A series of interactive evolutionary experiments with CPPNs demonstrated that they indeed produce patterns and sequences of patterns with properties analogous to those seen in natural evolution and development. Furthermore, an algorithm for evolving increasingly complex CPPNs, called CPPN-NEAT, was introduced. Thus, a promising new encoding that is demonstrably capable of discovering symmetry and repetition with variation is revealed. Future research will focus on converting the patterns output by CPPNs into important substrates such as large-scale neural networks, physical morphologies, and building architectures. This section introduces important concepts in developmental encoding, starting with a review of prior computational abstractions. Following this review, typical patterns produced by natural development are discussed, providing context for evaluating the validity of different abstractions. Finally, an important process in natural evolution called complexification, which also occurs in the experiments in this paper, is described. Developmental encodings are traditionally evaluated for their performance on benchmark tasks [6, 7, 14-19, 21-23, 27, 28, 31, 42, 67] . These tasks range from body-brain evolution [15, 16, 23, 28] , to target object morphologies [6, 17, 22] , to target patterns such as flags [18, 19, 31] . It is also common to compare developmental encodings to direct encodings, usually demonstrating that reuse can be advantageous when the target is sufficiently regular and complex to make direct encoding prohibitive [6, 22, 23, 67, 68] .. For three reasons, this paper takes a significantly different experimental approach. First, the primary aim of this paper is to demonstrate that CPPNs abstract the essential properties of natural development even without local interaction or unfolding over time. Because removing these features significantly distances CPPNs from more traditional abstractions, the aim in this section to establish that CPPNs deserve to be categorized in the same class. Other developmental encodings generally need not establish this link because their relationship to natural development is more explicit.. Second, natural evolution does not evolve to specified targets. Rather, it exploits established regularities in creative ways. Thus, evaluating against a specific target or task does not necessarily reveal CPPNs' ability to similarly establish and then exploit regularities. In the future, it will be informative to measure CPPN performance in a range of domains; however, first it is important to establish that the way evolving CPPNs solve tasks indeed matches with the important mechanisms of natural evolution and development. The major contribution of this paper is thus to establish that a new kind of abstraction of development is admissible.. Third, natural organisms do not appear to be able to take on any arbitrary form. For example, no macroscopic organism has any appendage analogous to a wheel, even though a wheel is a fundamental engineering structure. Thus, if DNA was tasked with representing a car, it would likely fail. Nevertheless, such failure would not be an indictment against its potential for encoding unparalleled complexity. Therefore, rather than focus on whether a CPPN can represent a certain class of object, the following experiments focus on its ability to establish and exploit regularities in general.

O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Sign-preserving of principal eigenfunctions in P1 finite element approximation of eigenvalue problems of second-order elliptic operators This paper is concerned with the P1 finite element approximation of the eigenvalue problem of second-order elliptic operators subject to the Dirichlet boundary condition. The focus is on the preservation of basic properties of the principal eigenvalue and eigenfunctions of continuous problems. It is shown that when the stiffness matrix is an irreducible M -matrix, the algebraic eigenvalue problem maintains those properties such as the smallest eigenvalue being real and simple and the corresponding eigenfunctions being either positive or negative inside the physical domain. Mesh conditions leading to such a stiffness matrix are also studied. A sufficient condition is that the mesh is simplicial, acute when measured in the metric specified by the inverse of the diffusion matrix, and interiorly connected. The acute requirement can be replaced by the Delaunay condition in two dimensions. Numerical results are presented to verify the theoretical findings. We are concerned with the P1 finite element approximation of the eigenvalue problem of a general second-order elliptic operator . Note that the condition (2) is not essential. We can always make them satisfied by adding a large positive number to the function c(x). The original and shifted problems will have the same eigenfunctions and the eigenvalues of the former can be obtained by shifting the eigenvalues of the latter. The eigenvalue problem (1) is not self-adjoint in general. Nevertheless, it is known (e.g., see Lemma 3.1 below or Evans [27, Theorem 2 on Page 336 and Theorem 3 on page 340]) that the principal eigenvalue (that is, the smallest eigenvalue in modulus) is real and simple and the principal eigenfunctions (that is, the eigenfunctions corresponding to the principal eigenvalue) are either positive or negative in Ω. Since the principal eigenvalues typically represent the ground state of a physical system or correspond to the most unstable mode in stability or sensitivity analysis, it is of practical and theoretical importance to study when a numerical approximation preserves these properties of the principal eigenvalue and eigenfunctions and especially the sign of the principal eigenfunctions.. The objective of this paper is to investigate when a P1 finite element approximation of (1) on a simplicial mesh preserves the basic properties of the principal eigenvalue and eigenfunctions of the continuous problem. We shall show that most of the basic properties of the principal eigenvalue and eigenfunctions are preserved in the P1 finite element approximation provided that the resulting stiffness matrix is an irreducible M -matrix (cf. Theorem 3.1). Particularly, the principal eigenvalue of the discrete system is real and algebraically and geometrically simple and the corresponding eigenfunctions are either positive or negative (sign-preserving) in the physical domain. Several sufficient mesh conditions are proposed (Theorem 4.1) for the stiffness matrix to be an irreducible M -matrix.. We point out that there is a vast literature on the finite element approximation of differential eigenvalue problems and most of it is on convergence analysis; e.g., see Babuška and Osborn [2] , Boffi [8] , and Boffi et al. [9] , and references therein. Early work includes Birkhoff et al. [7] , Fix [28] , and Babuška and Osborn [3] . We also point out some interesting recent work [20, 21, 35, 51, 52, 54, 62, 65, 66] .. An outline of the paper is as follows. The P1 finite element approximation of (1) is presented in §2 and the preservation of the basic properties of the principal eigenvalue and eigenfunctions in the P1 finite element approximation is studied in §3. §4 is devoted to the study of mesh conditions under which the stiffness matrix is ensured to be an irreducible M -matrix, followed by numerical examples in §5. The conclusions are drawn in §6.

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Secure and self-stabilizing clock synchronization in sensor networks In sensor networks, correct clocks have arbitrary starting offsets and nondeterministic fluctuating skews. We consider an adversary that aims at tampering with the clock synchronization by intercepting messages, replaying intercepted messages (after the adversary's choice of delay), and capturing nodes (i.e., revealing their secret keys and impersonating them). We present the first self-stabilizing algorithm for secure clock synchronization in sensor networks that is resilient to such an adversary's attacks. Our algorithm tolerates random media noise, guarantees with high probability efficient communication overheads, and facilitates a variety of masking techniques against pulse-delay attacks in the presence of captured nodes. Accurate clock synchronization is imperative for many applications in sensor networks, such as mobile object tracking, detection of duplicates, and TDMA radio scheduling. Broadly speaking, existing clock synchronization protocols are too expensive for sensor networks because of the nature of the hardware and the limited resources that sensor nodes have. The unattended environment, in which sensor nodes typically reside, necessitates secure solutions and autonomous system design criteria that are self-defensive against a malicious adversary.. To illustrate an example of clock synchronization importance, consider a mobile object tracking application that monitors objects that pass through the network area (see [2] ). Nodes detect the passing objects, record the time of detection, and send the estimated trajectory. Inaccurate clock synchronization would result in an estimated trajectory that could differ significantly from the actual one.. We propose the first self-stabilizing algorithm for clock synchronization in sensor networks with security concerns. We consider an adversary that intercepts messages that it later replays. Our algorithm guarantees automatic recovery after the occurrence of arbitrary failures. Moreover, the algorithm tolerates message omission failures that might occur, say, due to the algorithm's message collisions or due to random media noise.. The short propagation delay of messages in close range wireless communications allows nodes to use broadcast transmissions to approximate pulses that mark the time of real physical events (i.e., beacon messages). In the pulse-delay attack, the adversary snoops messages, jams the synchronization pulses, and replays them at the adversary's choice of time (see [9, 10, 20] ).. We are interested in fine-grained clock synchronization, where there are no cryptographic counter measures for such pulse-delay attacks. For example, the nonce techniques strive to verify the freshness of a message by issuing pseudo-random numbers for ensuring that old communications could not be reused in replay attacks (see [19] ). Unfortunately, the lack of fine-grained clock synchronization implies that the round-trip time of message exchange cannot be efficiently estimated. Therefore, it is not clear how the nonce technique can detect pulse-delay attacks.. The system strives to synchronize its clocks while forever monitoring the adversary. We assume that the adversary cannot break existing cryptographic primitives for sensor networks by eavesdropping (e.g., [19, 23] ).. However, we assume that the adversary can capture nodes, reveal their entire state (including private variables), stop their execution, and impersonate them.. We assume that, at any time, the adversary has a distinct location in space and a bounded influence radius, uses omnidirectional broadcasts from that distinct location, and cannot intercept broadcasts for an arbitrarily long period. (Namely, we consider system settings that are comparable to the settings of Gilbert et al. [11] , that consider the minimal requirements for message delivery under broadcast interception attacks.) We explain how, by following these realistic assumptions, we can sift out responses to delayed beacons.. A secure synchronization protocol should mask attacks by an adversary that aims to make the protocol give an erroneous output. Unfortunately, due to the unattended environment and the limited resources, it is unlikely that all the designer's assumptions hold forever, e.g., over time the number of captured nodes becomes sufficiently large for the adversary to tamper with the clock.. We consider systems that have the capability of monitoring the adversary, and then stopping it by external intervention. In this case, the nodes start executing their program from an arbitrary state. From that point on, we require rapid system recovery. Self-stabilizing algorithms [3, 4] cope with the occurrence of transient faults in an elegant way. Self-stabilizing systems can be started in any configuration, that might occur due to the occurrence of an arbitrary combination of failures. From that arbitrary starting point, the algorithm must ensure that it accomplishes its task if the system obeys the designer's assumptions for a sufficiently long period.. We focus on the fault-tolerance aspects of secure clock synchronization protocols in sensor networks. Our objective is to design a distributed algorithm for sampling n clocks in the presence of t incorrect nodes (i.e., faulty or captured). The clock sampling algorithm facilitates clock synchronization using a variety of existing masking techniques to overcome pulse-delay attacks in the presence of captured nodes, e.g., [9, 10] use Byzantine agreement (requires 3t+1 ≤ n), and [20] considers the statistical outliers (requires 2t + ≤ n, where ∈ O(1)).. The execution of a clock synchronization protocol can be classified between two extremes: on-demand and continuous. Nodes that wish to synchronize their clocks can invoke a distributed procedure for clock synchronization on-demand. The procedure terminates as soon as the nodes reach their target precision. An execution of a clock synchronization program is classified as continuous if no node ever stops invoking the clock synchronization procedure.. Our generic design facilitates a trade-off between energy conservation (i.e., on-demand operation) and fine-grained clock synchronization (i.e., continuous operation). The trade-off allows budget policies to balance between application requirements and energy constraints. (More details appear in [16] Section 1.3.2.) Designing secure and self-stabilizing infrastructure for sensor networks narrows the gap between traditional networks and sensor networks by simplifying the design of future systems. In this work, we consider realistic system settings and take a clean slate approach in designing a fundamental component; a clock synchronization protocol.. The designers of sensor networks often implement clock synchronization protocols that assume the system settings of traditional networks. However, sensor networks often require fine-grained clock synchronization for which the traditional protocols are inappropriate.. Alternatively, when the designers do not assume traditional system settings, they turn to reinforce the protocols with masking techniques. Thus, the designers assume that the adversary never violates the assumptions of the masking techniques, e.g., there are at most t captured nodes at all times, where 3t+1 ≤ n. Since sensor networks reside in an unattended environment, the last assumption is unrealistic.. Our design promotes self-defense capabilities once the system returns to following the original designer's assumptions. Interestingly, the selfstabilization design criteria provide an elegant way for designing secure autonomous systems. Sensor networks are particularly vulnerable to interference, whether as a result of hardware malfunction, environmental anomalies, or malicious intervention. When dealing with message collisions, message delays and noise, it is hard to separate malicious from non-malicious causes. For instance, it is hard to distinguish between a pulse delay attack from a combination of failures, e.g., a node that suffers from a hidden terminal failure, but receives an echo of a beacon. Recent studies consider more and more implementations that take security, failures and interference into account when protecting sensor networks (e.g., [11, 5] ). We note that many of the existing implementations assume the existence of a fined grained synchronized clock, which we implement.. Ganeriwal et al. [9, 10] overcome the challenge of delayed beacons using the round-trip synchronization technique, and the Byzantine agreement protocol [13] . Thus, Ganeriwal et al. require 3t + 1 ≤ n. Song et al. [20] consider a different approach that uses the reference broadcasting synchronization technique. Existing statistics models refer to malicious time offsets as outliers. The statistical outlier approach is numerically stable for 2t + ≤ n ≤ 3t + 1, where is a safety constant (see [20] ). We note that both approaches are applicable to our work. However, based on our practical assumptions, we are able to avoid the Byzantine agreement overheads and follow the approach of Song et al. [20] . They assume the existence of a distributed algorithm for sending beacons and collecting their responses. This work presents the first secure and self-stabilizing design of that algorithm.. The generalized extreme studentized deviate (GESD) algorithm [18] can be used to detect outliers. We note that there exists a self-stabilizing version of Song et al.'s [20] strategy. Let B be the set of delivered beacon records within a period of R. The node removes older records from B. The GESD algorithm tests set B for outliers.. Existing implementations of secure clock synchronization protocols [23, 22, 9, 8, 14, 10, 20] are not self-stabilizing. Thus, their specifications are not compatible with security requirements for autonomous systems. In autonomous systems, the self-stabilization design criteria are imperative for secure clock synchronization. For example, many existing implementations require initial clock synchronization prior to the first pulse-delay attack (during the protocol set up). This assumption implies that the system uses global restart for self-defense management, say, using an external intervention. We note that the adversary is capable of intercepting messages continually. Thus, the adversary can risk detection and intercept all pulses for a long period. Assume that the system detects the adversary's location and stops it. Nevertheless, the system cannot synchronize its clocks without a global restart.. Sun et al. [21] describe a cluster-wise synchronization algorithm that is based on synchronous broadcasting rounds. The authors assume that a Byzantine agreement algorithm [13] synchronizes the clocks before the system executes the algorithm. Our algorithm is comparable with the requirements of autonomous systems and makes no assumptions on synchronous broadcasting rounds or start.. Manzo et al. [14] describe several possible attacks on an (unsecured) clock synchronization algorithm and suggest counter measures. For single hop synchronization, the authors suggest using a randomly selected "core" of nodes to minimize the effect of captured nodes. The authors do not consider the cases in which the adversary captures nodes after the core selection. In this work, we make no assumption regarding the distribution of the captured nodes. Farrugia and Simon [8] consider a cross-network spanning tree in which the clock values propagate for global clock synchronization. However, no pulse-delay attacks are considered. Sun et al. [22] investigate how to use multiple clocks from external source nodes (e.g., base stations) to increase the resilience against an attack that compromises source nodes. In this work, there are no source nodes.. In [23] , the authors explain how to implement a secure clock synchronization protocol. Although the protocol is not self-stabilizing, we believe that some of their security primitives could be used in a self-stabilizing manner when implementing our self-stabilizing algorithm.. Herman and Zhang [12] present a self-stabilizing clock synchronization algorithm for sensor networks. The authors present a model for proving the correctness of synchronization algorithms and show that the convergeto-max approach is stabilizing. However, the converge-to-max approach is prone to attacks with a single captured node that introduces the maximal clock value whenever the adversary decides to attack. Thus, the adversary can at once set the clock values "far into the future", preventing the nodes from implementing a continuous time approximation function. This work is the first in the context of self-stabilization to provide security solutions for clock synchronization in sensor networks.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O


Genetic algorithms are suitable for driving microbial ecosystems in desirable directions The behavior of natural, biological ecosystems is for a large part determined by environmental conditions. It should therefore be possible to experimentally manipulate such conditions to drive ecosystems in desirable directions. When a set of environmental conditions can be manipulated to be either present or absent, such an exercise becomes a typical combinatorial optimization problem, and one for which a genetic algorithm should be very suitable. In this work, four exhaustive experimental datasets were assembled, containing growth levels of different natural microbial ecosystem as influenced by all possible combinations of a set of five chemical supplements. The ability of a genetic algorithm to search these datasets for combinations of supplements driving the ecosystems to high levels of growth was compared to that of a random search, a local search, and a hill-climbing algorithm. The results indicate that a genetic algorithm is very suitable for driving microbial ecosystems in desirable directions, which opens opportunities for both applied and fundamental ecology. Ecology is the field of biology that studies the interrelationships of living organisms and their environment. Ecosystem dynamics and functions are influenced by environmental conditions, which can cause shifts in organism composition and activity. By purposefully manipulating environmental conditions, a desirable ecosystem function can be obtained. This is for example attempted in biostimulation, the operation of wastewater treatment plants, and the application of prebiotics. In this work, a genetic algorithm was used to find the combinations of chemical supplements that would result in high levels of growth of natural microbial ecosystems. The performance of a genetic algorithm was compared to that of random search, local search, and hillclimbing, three alternative approaches a human experimenter unaware of genetic algorithms might use. The performance of the algorithms was compared on exhaustive growth datasets of four different microbial ecosystems and results showed that the genetic algorithm outperformed the other optimizers in ten out of twelve instances.. Genetic algorithms have been applied in an experimental microbial context before. They have been used to design mixed microbial cultures from sets of isolated strains [1, 2] and for the optimization of growth media for pure cultures [3] . Our work described here experimentally demonstrates that a genetic algorithm is suitable for driving real-world, undefined microbial ecosystems in desirable directions by manipulating environmental conditions. In this study, a genetic algorithm, random search, local search, and hill-climbing algorithm were used to find combinations of environmental conditions that would lead to optimal levels of growth in a number of natural microbial ecosystems. Statistical comparison of optimization performance revealed that in 10 out of 12 cases, the genetic algorithm outperformed the three competing algorithms. This result experimentally validates the idea that genetic algorithms are suitable for driving microbial ecosystems in desirable directions by optimizing environmental conditions. The three competing algorithms correspond to optimization methods a human experimenter unaware of genetic algorithms might use in the lab to optimize microbial systems: trying random guesses (random search), gradually modifying an existing solution (local search), and changing parameters one at a time (hillclimbing). Even though the genetic algorithm operated with a small population size and low number of generations, comparison of the algorithm to three derivatives demonstrated that selection, crossover, and mutation all contributed to the algorithm's operation. The genetic algorithm performed less well on the stream water dataset, which was the dataset that had the highest correlation between total number of supplements added and overall growth (lower total number of supplements corresponded to higher levels of growth). It is possible that the local search and hill-climbing algorithms exploited an inherent pattern of that dataset by gradually stripping candidate solutions of supplements. This particular result suggests that it may be possible to estimate optimization problem difficulty by a priori analyzing structural properties of the microbial system of interest.. The results obtained here hold promise from both an applied and a fundamental ecological perspective. From a practical point of view, a genetic algorithm could for example be used to design efficient biostimulation treatments, supplements for wastewater treatment plants, or enhanced prebiotics. In fundamental studies, a genetic algorithm could be used to better study ecological functions of interest by selectively inducing them in the lab in samples from a variety of origins. Also, a sample displaying an intermediate level of a function of interest could be driven in radically different functional directions using a genetic algorithm. Molecular genetic analysis of such parallel samples could then help elucidate functionally critical community dynamics or molecular mechanisms. Exhaustive experimental datasets were obtained that contained growth levels of microorganisms in saliva, sludge, soil, and stream water, as influenced by all possible combinations of five chemical supplements. A random search, local search, hillclimbing, and genetic algorithm were used to find the combination of supplements that would result in optimal growth levels described in the datasets of these different microbial ecosystems. Statistical comparison of 5000 runs of each algorithm revealed that in 10 out of 12 cases, the genetic algorithm outperformed the three competing optimizers ( Table 1 ). The standard genetic algorithm was compared on the saliva dataset to three derivative algorithms that had the selection, crossover, and mutation operators disabled. The standard algorithm statistically outperformed each of the three derivatives. R 2 values were calculated for a linear regression between growth levels and total number of supplements present. The following values were obtained, for saliva, sludge, soil, and stream water, respectively: 0.05, 0.10, 0.26, and 0.57. The stream water sample had a much higher R 2 value than the other samples.

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Existence and Computation of Low Kronecker-Rank Approximations for Large Linear Systems of Tensor Product Structure In this paper we construct an approximation to the solution x of a linear system of equations Ax ¼ b of tensor product structure as it typically arises for finite element and finite difference discretisations of partial differential operators on tensor grids. For a right-hand side b of tensor product structure we can prove that the solution x can be approximated by a sum of OðlogðeÞ 2 Þ tensor product vectors where e is the relative approximation error. Numerical examples for systems of size 1024 256 indicate that this method is suitable for high-dimensional problems. A general linear system of equations. can be solved with algorithms of complexity OðN 3 Þ, e.g., by Householder. This complexity can be reduced if, e.g., blockwise Gaussian elimination is possible. In that case Strassen's algorithm [13] yields a better order OðN log 2 ð7Þ Þ. Obviously, OðN 2 Þ is a lower bound if no structure on the matrix A is imposed. For certain sparse systems it is possible to approximate the solution x by iterative schemes of complexity OðN Þ per step. Obviously, OðN Þ is a lower bound if no structure on the right-hand side b is imposed.. In this paper we consider linear systems of equations where the matrix A and the right-hand side b are of a special structure. Let N ¼ n d denote the number of columns and rows of A. The right-hand side is given in tensor structure . The matrix A possesses the tensor structure . with spectrum rðAÞ contained in the left complex halfplane. In the last Section 6 we discuss where such a structure may arise. Our algorithm can solve an equation of the structure (2) for a right-hand side of the form (1) with complexity Oðdn logðnÞ 2 logðeÞ 7=2 Þ such that the approximant fulfils kx Àxk 2 ekxk 2 :. The only known previous works are those for the case d ¼ 2. There, a twodimensional tensor vector b 1 b 2 can be identified with the rank 1 matrix. The system. can be rewritten as a (matrix) Sylvester equation. where the sought solution X and the right-hand side B are matrices. The tensor form (1) of the right-hand side b implies that B is of rank at most 1. In [4] a proof for the existence of a rank k approximant X k to the solution X is given, where the rank k necessary to achieve an approximation error of kX À X k k 2 ekX k 2 is proportional to logðeÞ. Of course, the estimate depends on the spectra of A 1 and A 2 , but it is independent of B.. Although there is an extensive literature on the numerical solution of Sylvester's equation, this is not the case for low rank solvers. A low rank approximation X k to X can, e.g., be computed efficiently by iterative methods like the ADI or Smith iteration (see [11] and more recently [10] ) that perform few iterative steps such that the ith iterate is of rank at most i. An extension to higher dimensions is not evident. Another approach is to use the matrix sign function in combination with hierarchical matrices (see [6] ) to compute a low rank or hierarchical matrix approximation to X . This approach is also limited to d ¼ 2.. The rest of this paper is organised as follows: The main approximation result is derived in Section 3. We prove that the solution x can be approximated by a vectorx which is the sum of vectors in the tensor structure (1) . In Section 5 we address the problem of computing the matrix exponential expðtA i Þ which is needed in the representation formula for the approximantx. The last Section 6 presents numerical results for problems of dimension d ¼ 256 and n ¼ 1024. Since the full solution vector x has 2 2560 entries, we can neither compare our results to methods from the literature nor can we compute the approximation error kx Àxk 2 exactly. Instead, we estimate the approximation error by evaluation in few random entries. We have presented a method for the approximate solution of a linear system where the system matrix is of the tensor structure arising typically from finite element and finite difference discretisations of a partial differential equation on a tensor grid. The inverse stiffness matrix can be approximated in a data sparse format as the sum of matrices in tensor structure. The complexity for the approximation of the inverse is almost linear with respect to the meshwidth h

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Exact enumeration of rooted 3-connected triangular maps on the projective plane We study the relation between rooted 3-connected triangular maps and rooted 2-connected triangular maps on the projective plane. We then use this relation to derive a simple parametric expression for the generating function of rooted 3-connected triangular maps on the projective plane. We believe that this is the ÿrst simple exact result for 3-connected nonplanar maps. ? A map on a surface is a 2-cell embedding of a graph on the surface. A map is rooted by selecting a vertex, an edge incident with the vertex, and a side of the edge in the map. The selected vertex and edge are called the root vertex and root edge of the map, respectively. The face corresponding to the selected side of the root edge is called the root face.. A rooted near-triangular map on a surface is a rooted map on the surface such that each face except possibly the root face has valence three. A rooted triangular map is a rooted near-triangular map whose root face valence is also three. Much work has been done on enumerating various types of rooted planar maps since Tutte's pioneer work in the 1960s [19] [20] [21] [22] . (See also [5] for a survey.). Major developments on enumeration of nonplanar maps occurred in the 1980s mainly because of the connections with modern physics [2, 7, 16, 17, 23] and other branches of mathematics [18] . Simple expressions for all rooted maps on the projective plane, the torus and the Klein Bottle, were ÿrst obtained by Bender et al. [6] . Arques [1] independently obtained the result on the torus. Bender and Canÿeld [4] derived recursions for all rooted maps, which in principle can be used to calculate the exact expressions of the generating functions for all rooted maps on any given surface. The generating functions for all rooted maps on the ÿrst few surfaces were calculated in [4, 10] . Similar recursions for all rooted triangular maps were derived by Gao [13] , and parametric expressions of the generating functions were also given for the projective plane and the torus. However, exact enumeration of nonplanar maps with connectivity higher than one is much more complicated. Brown [9] made the ÿrst attempt in enumerating rooted 2-connected maps in the projective plane, but his result appears quite complicated. A simple parametric expression was obtained in [14] for rooted 2-connected triangular maps on the projective plane. Edelman and Reiner [11] derived a simple expression for the generating function of rooted triangular maps on the Mőbius band where all vertices lie on the boundary. In this paper, we obtain a simple expression for the generating function of rooted 3-connected triangular maps on the projective plane. Our approach is based on the study of the structures of 2-cycles in 2-connected triangular maps on the projective plane, and the well-known fact that a triangular map is 3-connected if and only if it contains no loops or multiple edges. We believe that this is the ÿrst simple exact result for 3-connected nonplanar maps.. Let P(x) be the generating function of rooted 3-connected triangular maps on the projective plane, where x marks the total number of vertices. In the rest of the paper, we use [x n ]f(x) to denote the coe cient of x n in the power series expansion of f(x). Our main result is the following: Theorem 1. Let t = t(x) = x + · · · be the (unique) power series satisfying x = t(1 − t) 3 . Then. Corollary 1. As n → ∞, the number of rooted 3-connected triangular maps with n vertices on the projective plane has the asymptotic expression

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Impossibility of Succinct Quantum Proofs for Collision-Freeness We show that any quantum algorithm to decide whether a function f : [n] → [n] is a permutation or far from a permutation must make Ω n 1/3 /w queries to f , even if the algorithm is given a w-qubit quantum witness in support of f being a permutation. This implies that there exists an oracle A such that SZK A ⊂ QMA A , answering an eight-year-old open question of the author. Indeed, we show that relative to some oracle, SZK is not in the counting class A 0 PP defined by Vyalyi. The proof is a fairly simple extension of the quantum lower bound for the collision problem. The collision problem is to decide whether a black-box function f : [n] → [n] is one-to-one (i.e., a permutation) or two-to-one function, promised that one of these is the case. Together with its close variants, the collision problem is one of the central problems studied in quantum computing theory; it abstractly models numerous other problems such as graph isomorphism and the breaking of cryptographic hash functions.. In this paper, we will mostly deal with a slight generalization of the collision problem that we call the Permutation Testing Problem, or PTP. This is a property testing problem, in which we are promised that f : [n] → [n] is either a permutation or far from any permutation, and are asked to decide which is the case.. In 1997, Brassard, Høyer, and Tapp [8] gave a quantum algorithm for the collision problem that makes O n 1/3 queries to f , an improvement over the Θ ( √ n) randomized query complexity that follows from the birthday paradox. Brassard et al.'s algorithm is easily seen to work for the PTP as well.. Five years later, Aaronson [1] proved the first non-constant lower bound for these problems: namely, any bounded-error quantum algorithm to solve them needs Ω n 1/5 queries to f . Aaronson and Shi [4] subsequently improved the lower bound to Ω n 1/3 , for functions f : [n] → [3n/2]; then Ambainis [5] and Kutin [11] proved the optimal Ω n 1/3 lower bound for functions f : [n] → [n]. All of these lower bounds work for both the collision problem and the PTP, though they are slightly easier to prove for the latter.. The collision problem and the PTP are easily seen to admit Statistical Zero-Knowledge (SZK) proof protocols. Thus, one consequence of the collision lower bound was the existence of an oracle A such that SZK A ⊂ BQP A .. In talks beginning in 2002, 1 the author often raised the following question:. is a permutation, rather than far from a permutation. Is there a small ( polylog (n)-qubit) quantum proof |ϕ f of that fact, which can be verified using polylog (n) quantum queries to f ?. In this paper, we will answer the above question in the negative. As a consequence, we will obtain an oracle A such that SZK A ⊂ QMA A . This implies, for example, that any QMA protocol for graph non-isomorphism would need to exploit something about the problem structure beyond its reducibility to the collision problem.. Given that the relativized SZK versus QMA problem remained open for eight years, our solution is surprisingly simple. We first use the in-place amplification procedure of Marriott and Watrous [12] to "eliminate the witness," and reduce the question to one about quantum algorithms with extremely small acceptance probabilities. We then use a relatively-minor adaptation of the polynomial degree argument that was used to prove the original collision lower bound. Our proof actually yields an oracle A such that SZK A ⊂ A 0 PP A , where A 0 PP is a class defined by Vyalyi [15] that sits between QMA and PP.. Despite the simplicity of our result, to our knowledge it constitutes the first nontrivial lower bound on QMA query complexity, where "nontrivial" means that it doesn't follow immediately from earlier results unrelated to QMA. 2 We hope it will serve as a starting point for stronger results in the same vein.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O B I O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B B I O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O