bluuebunny/crossref_metadata_2025 huggingface dataset:
On minimal lengths of expressions of Coxeter group elements as products of reflections
Authors: Dyer Matthew
Published: July 2002

It is shown that the absolute length

l
′

(
w
)

l’(w)

of a Coxeter group element

w
w

(i.e. the minimal length of an expression of

w
w

as a product of reflections) is equal to the minimal number of simple reflections that must be deleted from a fixed reduced expression of

w
w

so that the resulting product is equal to

e
e

, the identity element. Also,

l
′

(
w
)

l’(w)

is the minimal length of a path in the (directed) Bruhat graph from the identity element

e
e

to

w
w

, and

l
′

(
w
)

l’(w)

is determined by the polynomial

R

e
,
w

R_{e,w}

of Kazhdan and Lusztig.
Analysis of PSLQ, an integer relation finding algorithm
Authors: Ferguson Helaman , Bailey David , Arno Steve
Published: July 2002

Let

K

{\mathbb {K}}

be either the real, complex, or quaternion number system and let

O

(

K

)

{\mathbb {O}}({\mathbb {K}})

be the corresponding integers. Let

x
=
(

x

1

,
…
,

x

n

)

x = (x_{1}, \dots , x_{n})

be a vector in

K

n

{\mathbb {K}}^{n}

. The vector

x
x

has an integer relation if there exists a vector

m
=
(

m

1

,
…
,

m

n

)
∈

O

(

K

)

n

m = (m_{1}, \dots , m_{n}) \in {\mathbb {O}}({\mathbb {K}})^{n}

,

m
≠
0

m \ne 0

, such that

m

1

x

1

+

m

2

x

2

+
…
+

m

n

x

n

=
0

m_{1} x_{1} + m_{2} x_{2} + \ldots + m_{n} x_{n} = 0

. In this paper we define the parameterized integer relation construction algorithm PSLQ

(
τ
)

(\tau )

, where the parameter

τ
\tau

can be freely chosen in a certain interval. Beginning with an arbitrary vector

x
=
(

x

1

,
…
,

x

n

)
∈

K

n

x = (x_{1}, \dots , x_{n}) \in {\mathbb {K}}^{n}

, iterations of PSLQ

(
τ
)

(\tau )

will produce lower bounds on the norm of any possible relation for

x
x

. Thus PSLQ

(
τ
)

(\tau )

can be used to prove that there are no relations for

x
x

of norm less than a given size. Let

M

x

M_{x}

be the smallest norm of any relation for

x
x

. For the real and complex case and each fixed parameter

τ
\tau

in a certain interval, we prove that PSLQ

(
τ
)

(\tau )

constructs a relation in less than

O
(

n

3

+

n

2

log
⁡

M

x

)

O(n^{3} + n^{2} \log M_{x})

iterations.
𝑅-equivalence in spinor groups
Authors: Chernousov Vladimir , Merkurjev Alexander
Published: July 2002

The groups of

R
R

-equivalent classes of the spinor groups of non-degenerate quadratic forms over arbitrary fields are computed in terms of certain

K
K

-cohomology groups of corresponding quadric hypersurfaces. As an application, examples of non-rational spinor groups of every dimension

≥
6

\geq 6

are given.
Dirac cohomology, unitary representations and a proof of a conjecture of Vogan
Authors: Huang Jing-Song , Pandžić Pavle
Published: July 2002

Let

G
G

be a connected semisimple Lie group with finite center. Let

K
K

be the maximal compact subgroup of

G
G

corresponding to a fixed Cartan involution

θ
\theta

. We prove a conjecture of Vogan which says that if the Dirac cohomology of an irreducible unitary

(

g

,
K
)

(\mathfrak {g},K)

-module

X
X

contains a

K
K

-type with highest weight

γ
\gamma

, then

X
X

has infinitesimal character

γ
+

ρ

c

\gamma +\rho _{c}

. Here

ρ

c

\rho _{c}

is the half sum of the compact positive roots. As an application of the main result we classify irreducible unitary

(

g

,
K
)

(\mathfrak {g},K)

-modules

X
X

with non-zero Dirac cohomology, provided

X
X

has a strongly regular infinitesimal character. We also mention a generalization to the setting of Kostant’s cubic Dirac operator.
L-series with nonzero central critical value
Authors: James Kevin
Published: July 2002

Given a cusp form

f
f

of even integral weight and its associated

L
L

-function

L
(
f
,
s
)

L(f,s)

, we expect that a positive proportion of the quadratic twists of

L
L

will have nonzero central critical value. In this paper we give examples of weight two newforms whose associated

L
L

-functions have the property that a positive proportion of its quadratic twists have nonzero central critical value.
Decomposing Borel sets and functions and the structure of Baire class 1 functions
Authors: Solecki Sławomir
Published: July 2002

We establish dichotomy results concerning the structure of Baire class 1 functions. We consider decompositions of Baire class 1 functions into continuous functions and into continuous functions with closed domains. Dichotomy results for both of them are proved: a Baire class 1 function decomposes into countably many countinuous functions, or else contains a function which turns out to be as complicated with respect to the decomposition as any other Baire class 1 function; similarly for decompositions into continuous functions with closed domains. These results strengthen a theorem of Jayne and Rogers and answer some questions of Steprāns. Their proofs use effective descriptive set theory as well as infinite Borel games on the integers. An important role in the proofs is played by what we call, in analogy with being Wadge complete, complete semicontinuous functions. As another application of our study of complete semicontinuous functions, we generalize some recent theorems of Jackson and Mauldin, and van Mill and Pol concerning measures viewed as examples of complicated semicontinuous functions. We also prove that a Borel set

A
A

is either

Σ

α

0

\boldsymbol \Sigma ^{0}_{\alpha }

or there is a continuous injection

ϕ
:

ω

ω

→
A

\phi :\; \omega ^{\omega }\to A

such that for any

Σ

α

0

\boldsymbol \Sigma ^{0}_{\alpha }

set

B
⊂
A

B\subset A

,

ϕ

−
1

(
B
)

\phi ^{-1}(B)

is meager. We show analogous results for Borel functions. These theorems give a new proof of a result of Stern, strengthen some results of Laczkovich, and improve the estimates for cardinal coefficients studied by Cichoń, Morayne, Pawlikowski, and the author.
Large Schubert varieties
Authors: Brion Michel , Polo Patrick
Published: July 2002

For a semisimple adjoint algebraic group

G
G

and a Borel subgroup

B
B

, consider the double classes

B
w
B

BwB

in

G
G

and their closures in the canonical compactification of

G
G

; we call these closures large Schubert varieties. We show that these varieties are normal and Cohen-Macaulay; we describe their Picard group and the spaces of sections of their line bundles. As an application, we construct geometrically a filtration à la van der Kallen of the algebra of regular functions on

B
B

. We also construct a degeneration of the flag variety

G

/

B

G/B

embedded diagonally in

G

/

B
×
G

/

B

G/B\times G/B

, into a union of Schubert varieties. This yields formulae for the class of the diagonal of

G

/

B
×
G

/

B

G/B\times G/B

in

T
T

-equivariant

K
K

-theory, where

T
T

is a maximal torus of

B
B

.
The adjoint representation in rings of functions
Authors: Sommers Eric , Trapa Peter
Published: July 2002

Let

G
G

be a connected, simple Lie group of rank

n
n

defined over the complex numbers. To a parabolic subgroup

P
P

in

G
G

of semisimple rank

r
r

, one can associate

n
−
r

n-r

positive integers coming from the theory of hyperplane arrangements (see P. Orlik and L. Solomon, Combinatorics and topology of complements of hyperplanes, Invent. Math. 56 (1980), 167-189; Coxeter arrangements, in Proc. of Symposia in Pure Math., Vol. 40 (1983) Part 2, 269-291). In the case

r
=
0

r=0

, these numbers are just the usual exponents of the Weyl group

W
W

of

G
G

. These

n
−
r

n-r

numbers are called coexponents. Spaltenstein and Lehrer-Shoji have proven the observation of Spaltenstein that the degrees in which the reflection representation of

W
W

occurs in a Springer representation associated to

P
P

are exactly (twice) the coexponents (see N. Spaltenstein, On the reflection representation in Springer’s theory, Comment. Math. Helv. 66 (1991), 618-636 and G. I. Lehrer and T. Shoji, On flag varieties, hyperplane complements and Springer representations of Weyl groups, J. Austral. Math. Soc. (Series A) 49 (1990), 449-485). On the other hand, Kostant has shown that the degrees in which the adjoint representation of

G
G

occurs in the regular functions on the variety of regular nilpotents in

g

:=
Lie
⁡
(
G
)

\mathfrak {g}:=\operatorname {Lie}(G)

are the usual exponents (see B. Kostant, Lie group representations on polynomial rings, Amer. J. Math. 85 (1963), 327-404). In this paper, we extend Kostant’s result to Richardson orbits (or orbit covers) and we get a statement which is dual to Spaltenstein’s. We will show that the degrees in which the adjoint representation of

G
G

occurs in the regular functions on an orbit cover of a Richardson orbit associated to

P
P

are also the coexponents.
DrosophilaMinichromosome Maintenance 6 Is Required for Chorion Gene Amplification and Genomic Replication
Authors: Schwed Gina , May Noah , Pechersky Yana , Calvi Brian R.
Published: July 2002

Duplication of the eukaryotic genome initiates from multiple origins of DNA replication whose activity is coordinated with the cell cycle. We have been studying the origins of DNA replication that control amplification of eggshell (chorion) genes duringDrosophila oogenesis. Mutation of genes required for amplification results in a thin eggshell phenotype, allowing a genetic dissection of origin regulation. Herein, we show that one mutation corresponds to a subunit of the minichromosome maintenance (MCM) complex of proteins, MCM6. The binding of the MCM complex to origins in G1 as part of a prereplicative complex is critical for the cell cycle regulation of origin licensing. We find that MCM6 associates with other MCM subunits during amplification. These results suggest that chorion origins are bound by an amplification complex that contains MCM proteins and therefore resembles the prereplicative complex. Lethal alleles of MCM6 reveal it is essential for mitotic cycles and endocycles, and suggest that its function is mediated by ATP. We discuss the implications of these findings for the role of MCMs in the coordination of DNA replication during the cell cycle.
Association between Ozone and Hospitalization for Acute Respiratory Diseases in Children Less than 2 Years of Age
Authors: Burnett Richard T. , Smith-Doiron Marc , Stieb Dave , Raizenne Mark E. , Brook Jeffrey R. , Dales Robert E. , Leech Judy A. , Cakmak Sabit , Krewski Daniel
Published: July 2002

To clarify the health effects of ozone exposure in young children, the authors studied the association between air pollution and hospital admissions for acute respiratory problems in children less than 2 years of age during the 15-year period from 1980 to 1994 in Toronto, Canada. The daily time series of admissions was adjusted for the influences of day of the week, season, and weather. A 35% (95% confidence interval: 19%, 52%) increase in the daily hospitalization rate for respiratory problems was associated with a 5-day moving average of the daily 1-hour maximum ozone concentration of 45 parts per billion, the May–August average value. The ozone effect persisted after adjustment for other ambient air pollutants or weather variables. Ozone was not associated with hospital admissions during the September–April period. Ambient ozone levels in the summertime should be considered a risk factor for respiratory problems in children less than 2 years of age.
Risk Factors for Proximal Humerus, Forearm, and Wrist Fractures in Elderly Men and Women The Dubbo Osteoporosis Epidemiology Study
Authors: Nguyen Tuan V. , Center Jacqueline R. , Sambrook Philip N. , Eisman John A.
Published: July 2002

Fractures of the proximal humerus, forearm, and wrist account for approximately one third of total osteoporotic fractures in the elderly. Several risk factors for these fractures were evaluated in this prospective study of 739 men and 1,105 women aged ≥60 years in Dubbo, Australia. During follow-up (1989–1996), the respective incidences of humerus and of forearm and wrist fractures, per 10,000 person-years, were 22.6 and 33.8 for men and 54.8 and 124.6 for women. Independent predictors of humerus fracture were femoral neck bone mineral density (FNBMD) (relative risk (RR) = 2.3, 95% confidence interval (CI): 1.2, 4.5) in men and FNBMD (RR = 2.4, 95% CI: 1.7, 3.5) and height loss (RR = 1.1, 95% CI: 1.0, 1.2) in women. For forearm and wrist fractures, risk factors were FNBMD (men: RR = 1.5, 95% CI: 1.0, 2.3; women: RR = 1.5, 95% CI: 1.2, 1.9) and height loss (men: RR = 1.2, 95% CI: 1.0, 1.3; women: RR = 1.1, 95% CI: 1.0, 1.2). In addition, dietary calcium (men: RR = 2.0, 95% CI: 1.0, 3.6) and a history of falls (women: RR = 1.9, 95% CI: 1.4, 2.6) were also significant. These data suggest that elderly men and women largely share common risk factors for upper limb fractures and that FNBMD is the primary risk factor.
Estimation and filtering of potential protein-protein docking positions.
Authors: Ackermann F , Herrmann G , Posch S , Sagerer G
Published: July 2002

MOTIVATION: Software systems predicting automatically whether and how two proteins may interact are highly desirable, both for understanding biological processes and for the rational design of new proteins. As a part of a future complete solution to this problem, a bundle of programs is presented designed (i) to estimate initial docking positions for a given pair of docking candidates, (ii) to adjust them, and (iii) to filter them, thus preparing more detailed computations of free energies. RESULTS: The system is evaluated on a test set of 51 co-crystallized complexes aiming at redocking the subunits. It works completely automatically and the evaluation is performed using one single set of parameters for all complexes in the test set. The number of solutions is fixed to 50 positions with a median CPU time of 26 min. For 30 complexes, these contain a near-correct solution with root mean square deviation ( RMSD ) </=5.0 A, which is ranked first in five cases. For all complexes, the best solution is scored on rank 16 as the worst case, and has a median RMSD of 4.3 A. Alternatively to this initial estimation of docking positions, a global sampling of rotations was tested. Whereas this yields top-ranked solutions with RMSD </=3.0 A for all 51 complexes, the median CPU time increases to 11 h. This shows that this blind sampling is not feasible for most applications. AVAILABILITY: The system and its components are available on request from the authors. Contact: friedric@techfak.uni-bielefeld or posch@techfak.uni-bielefeld.de
An NMR assignment module implemented in the Gifa NMR processing program.
Authors: Malliavin T E , Pons J L , Delsuc M A
Published: July 2002

MOTIVATION: Peptide and protein structures are determined daily using NMR spectroscopy. Assignment of the NMR spectra is an important step within the procedure and is usually the limiting one. Computer-aided assignment tools should be user friendly with open architecture to communicate with other programs involved in the structure determination. RESULTS: Here we present an interactive NMR assignment module which provides numerous graphic tools for the user. The module is composed of a database management system-handling peaks, spins and spin-systems. The assignment information is maintained as a set of interrelated associative arrays, which serve as generic high-level data structures. The module is developed in the macro language embedded in the Gifa NMR processing program (Pons et al. , J. Biomol. NMR, 8 , 445-452, 1996). This provides the user with a consistent interface, a set of sophisticated tools, and an easily extendible and customizable environment. AVAILABILITY: The program is available on request from the authors. The Gifa package can be accessed at: ((http://www.cbs. univ-montp1.fr/GIFA)) CONTACT: Marc-Andre.Delsuc@cbs.univ-montp1.fr
Motif-based searching in TOPS protein topology databases.
Authors: Gilbert D , Westhead D , Nagano N , Thornton J
Published: July 2002

MOTIVATION: TOPS cartoons are a schematic ion of protein three-dimensional structures in two dimensions, and are used for understanding and manual comparison of protein folds. Recently, an algorithm that produces the cartoons automatically from protein structures has been devised and cartoons have been generated to represent all the structures in the structural databank. There is now a need to be able to define target topological patterns and to search the database for matching domains. RESULTS: We have devised a formal language for describing TOPS diagrams and patterns, and have designed an efficient algorithm to match a pattern to a set of diagrams. A pattern-matching system has been implemented, and tested on a database derived from all the current entries in the Protein Data Bank (15,000 domains). Users can search on patterns selected from a library of motifs or, alternatively, they can define their own search patterns. AVAILABILITY: The system is accessible over the Web at http://tops.ebi.ac.uk/tops
STRAP: editor for STRuctural Alignments of Proteins
Authors: Gille Christoph , Frömmel Cornelius
Published: July 2002

Summary: STRAP is a comfortable and extensible tool for the generation and refinement of multiple alignments of protein sequences. Various sequence ordered input file formats are supported. These are the SwissProt-,GenBank-, EMBL-, DSSP- PDB-, MSF-, and plain ASCII text format. The special feature of STRAP is the simple visualization of spatial distances of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(C_{{\alpha}}\) \end{document}-atoms within the alignment. Thus structural information can easily be incorporated into the sequence alignment and can guide the alignment process in cases of low sequence similarities. Further STRAP is able to manage huge alignments comprising a lot of sequences. The protein viewers and modeling programs INSIGHT, RASMOL and WEBMOL are embedded into STRAP. STRAP is written in Java. The well-documented source code can be adapted easily to special requirements. STRAP may become the basis for complex alignment tools in the future.

Availability: The tool is available to academic institutions at http://www.charite.de/bioinf. The source code can be requested via e-mail.

Contact: christoph.gille@charite.de

* To whom correspondence should be addressed.
A data-mining approach to spacer oligonucleotide typing of
Mycobacterium tuberculosis
Authors: Sebban M. , Mokrousov I. , Rastogi N. , Sola C.
Published: July 2002

Motivation: The Direct Repeat (DR) locus of Mycobacterium tuberculosis is a suitable model to study (i) molecular epidemiology and (ii) the evolutionary genetics of tuberculosis. This is achieved by a DNA analysis technique (genotyping), called sp acer oligo nucleotide typing (spoligotyping ). In this paper, we investigated data analysis methods to discover intelligible knowledge rules from spoligotyping, that has not yet been applied on such representation. This processing was achieved by applying the C4.5 induction algorithm and knowledge rules were produced. Finally, a Prototype Selection (PS) procedure was applied to eliminate noisy data. This both simplified decision rules, as well as the number of spacers to be tested to solve classification tasks. In the second part of this paper, the contribution of 25 new additional spacers and the knowledge rules inferred were studied from a machine learning point of view. From a statistical point of view, the correlations between spacers were analyzed and suggested that both negative and positive ones may be related to potential structural constraints within the DR locus that may shape its evolution directly or indirectly.

Results: By generating knowledge rules induced from decision trees, it was shown that not only the expert knowledge may be modeled but also improved and simplified to solve automatic classification tasks on unknown patterns. A practical consequence of this study may be a simplification of the spoligotyping technique, resulting in a reduction of the experimental constraints and an increase in the number of samples processed.

Contact: csola@pasteur.gp

* To whom correspondence should be addressed.
An integrated approach utilizing artificial neural networks and
SELDI mass spectrometry for the classification of human tumours and
rapid identification of potential biomarkers
Authors: Ball G. , Mian S. , Holding F. , Allibone R. O. , Lowe J. , Ali S. , Li G. , McCardle S. , Ellis I. O. , Creaser C. , Rees R. C.
Published: July 2002

Motivation: MALDI mass spectrometry is able to elicit macromolecular expression data from cellular material and when used in conjunction with Ciphergen protein chip technology (also referred to as SELDI—Surface Enhanced Laser Desorption/Ionization), it permits a semi-high throughput approach to be taken with respect to sample processing and data acquisition. Due to the large array of data that is generated from a single analysis (8–10000 variables using a mass range of 2–15 kDa—this paper) it is essential to implement the use of algorithms that can detect expression patterns from such large volumes of data correlating to a given biological/pathological phenotype from multiple samples. If successful, the methodology could be extrapolated to larger data sets to enable the identification of validated biomarkers correlating strongly to disease progression. This would not only serve to enable tumours to be classified according to their molecular expression profile but could also focus attention upon a relatively small number of molecules that might warrant further biochemical/molecular characterization to assess their suitability as potential therapeutic targets.

Results: Using a multi-layer perceptron Artificial Neural Network (ANN) (Neuroshell 2) with a back propagation algorithm we have developed a prototype approach that uses a model system (comprising five low and seven high-grade human astrocytomas) to identify mass spectral peaks whose relative intensity values correlate strongly to tumour grade. Analyzing data derived from MALDI mass spectrometry in conjunction with Ciphergen protein chip technology we have used relative importance values, determined from the weights of trained ANNs (Balls et al. , Water, Air Soil Pollut. , 85, 1467–1472, 1996), to identify masses that accurately predict tumour grade. Implementing a three-stage procedure, we have screened a population of approximately 100000–120000 variables and identified two ions (m/zvalues of 13454 and 13457) whose relative intensity pattern was significantly reduced in high-grade astrocytoma. The data from this initial study suggests that application of ANN-based approaches can identify molecular ion patterns which strongly associate with disease grade and that its application to larger cohorts of patient material could potentially facilitate the rapid identification of validated biomarkers having significant clinical (i.e. diagnostic/prognostic) potential for the field of cancer biology.

Availability: Neuroshell 2 is commercially available from ward systems.

Contact: graham.balls@ntu.ac.uk

* To whom correspondence should be addressed.
The development of the electroreceptors of the platypus (
Ornithorhynchus anatinus
)
Authors: Manger Paul R. , Collins Rita , Pettigrew John D.
Published: July 2002

A series of developmental stages of the platypus were examined to obtain an anatomical description of the development of the periphery of the electroreceptive system. Putative electroreceptors, composed of modified mucous glands, were observed to appear at 10 days post hatching (p.h.). The typical striped arrangement of peripheral electroreceptors in the platypus was seen at 12 days p.h. The arrangement of the stripes was modified during development with a range of additions and divisions of stripes occurring until the adult pattern is obtained, approximately 6 months p.h. After appearing at 10 days p.h., the number of electroreceptors increases rapidly until sometime between 24 and 28 days p.h. when there is massive death of electroreceptors, the number present at 28 days p.h. being 60% of the number present at 24 days p.h. This massive death of receptors is coincident with the appearance of other sensory structures in the epidermis of the bill skin, the push–rod mechanoreceptors and the sensory serous glands. Histological examination of a range of developmental stages demonstrated poorly differentiated innervation at 28 days p.h., which became differentiated and reached the adult configuration between 11 weeks p.h. and 6 months p.h., the time at which nestling platypus leave the burrow. Lamination of the cells lining the duct of the electroreceptors showed a similar developmental profile. This study indicates that the electroreceptive system of the developing platypus is not functional, in a similar manner to the adult, until it is time for the platypus to leave the nesting burrow. However, the system may be functional in the developing platypus, and may be used speculatively in the location of the mammary region for suckling.
The molecular genetics of European ancestry
Authors: Sykes Bryan
Published: July 2002

In an earlier paper we proposed, on the basis of mitochondrial control region variation, that the bulk of modern European mitochondrial DNA (mtDNA) diversity had its roots in the European Upper Palaeolithic. Refining the mtDNA phylogeny and enlarging the sample size both within Europe and the Middle East still support this interpretation and indicate three separate phases of colonization: (i) the Early Upper Palaeolithic about 50,000 BP; (ii) the Late Upper Palaeolithic 11,000–14,000 BP; and (iii) the Neolithic from 8500 BP.
Revolutions in the earth sciences
Authors: Allègre Claude , Courtillot Vincent
Published: July 2002

The 20th century has been a century of scientific revolutions for many disciplines: quantum mechanics in physics, the atomic approach in chemistry, the nonlinear revolution in mathematics, the introduction of statistical physics. The major breakthroughs in these disciplines had all occurred by about 1930. In contrast, the revolutions in the so–called natural sciences, that is in the earth sciences and in biology, waited until the last half of the century. These revolutions were indeed late, but they were no less deep and drastic, and they occurred quite suddenly. Actually, one can say that not one but three revolutions occurred in the earth sciences: in plate tectonics, planetology and the environment. They occurred essentially independently from each other, but as time passed, their effects developed, amplified and started interacting. These effects continue strongly to this day.
Replacement migration, or why everyone is going to have to live in Korea: a fable for our times from the United Nations
Authors: Coleman D. A.
Published: July 2002

This paper considers international migration in the context of population ageing. In many Western countries, the search for appropriate responses to manage future population ageing and population decline has directed attention to international migration. It seems reasonable to believe that international migrants, mostly of young working age, can supply population deficits created by low birth rates, protect European society and economy from the economic costs of elderly dependency, and provide a workforce to care for the elderly. Particular prominence has been given to this option through the publicity attendant on a report from the UN Population Division in 2000 on ‘replacement migration’, which has been widely reported and widely misunderstood. Although immigration can prevent population decline, it is already well known that it can only prevent population ageing at unprecedented, unsustainable and increasing levels of inflow, which would generate rapid population growth and eventually displace the original population from its majority position. This paper reviews these arguments in the context of the causes and inevitability of population ageing, with examples mostly based on UK data. It discusses various options available in response to population ageing through workforce, productivity, pensions reform and other means. It concludes that there can be no ‘solution’ to population ageing, which is to a considerable degree unavoidable. However, if the demographic regime of the United Kingdom continues to be relatively benign, future population ageing can be managed with tolerable inconvenience without recourse to increased immigration for ‘demographic’ purposes. At present (2001), net immigration to the United Kingdom is already running at record levels and is now the main engine behind UK population and household growth. By itself, population stabilization, or even mild reduction, is probably to be welcomed in the United Kingdom, although the issue has attracted little attention since the 1970s.
Protein–Protein Interaction Panel Using Mouse Full-Length cDNAs
Authors: Suzuki Harukazu , Fukunishi Yoshifumi , Kagawa Ikuko , Saito Rintaro , Oda Hiroshi , Endo Toshinori , Kondo Shinji , Bono Hidemasa , Okazaki Yasushi , Hayashizaki Yoshihide
Published: July 2002

We have developed a novel assay system for systematic analysis of protein–protein interactions (PPIs) that is characteristic of a PCR-mediated rapid sample preparation and a high-throughput assay system based on the mammalian two-hybrid method. Using gene-specific primers, we successfully constructed the assay samples by two rounds of PCR with up to 3.6 kb from the first-round PCR fragments. In the assay system, we designed all the steps to be performed by adding only samples, reagents, and cells into 384-well assay plates using two types of semiautomatic multiple dispensers. The system enabled us examine more than 20,000 assay wells per day. We detected 145 interactions in our pilot study using 3500 samples derived from mouse full-length enriched cDNAs. Analysis of the interaction data showed both several significant interaction clusters and predicted functions of a few uncharacterized proteins. In combination with our comprehensive mouse full-length cDNA clone bank covering a large part of the whole genes, our high-throughput assay system will discover many interactions to facilitate understanding of the function of uncharacterized proteins and the molecular mechanism of crucial biological processes, and also enable completion of a rough draft of the entire PPI panel in certain cell types or tissues of mouse within a short time.
Refolding kinetics of cytochrome c551 reveals a mechanistic difference between urea and guanidine
Authors: Gianni Stefano , Brunori Maurizio , Travaglini‐Allocatelli Carlo
Published: July 2002

The energetic parameters for the folding of small globular proteins can be very different if derived from guanidine hydrochloride (GdnHCl) or urea denaturation experiments. A study of the equilibrium and kinetics of the refolding of wild‐type (wt) cytochrome c551 (cyt c551) from Pseudomonas aeruginosa and of two site‐directed mutants (E70Q and E70V) shows that the nonionic nature of urea reveals the role of a salt bridge between residues E70 and K10 on the transition state, which is otherwise completely masked in GdnHCl experiments. Mixed denaturant refolding experiments allow us to conclude that the masking effect of GdnHCl is complete at fairly low GdnHCl concentrations (≅0.1 M). The fact that potassium chloride is unable to reproduce this quenching effect, together with the results obtained on the mutants, suggests a specific binding of the Gdn+ cation, which involves the E70–K10 ion pair in wt cyt c551. We propose, therefore, a simple kinetic test to obtain a mechanistic interpretation of nonlinear dependences of ΔGw on GdnHCl concentration on the basis of kinetic refolding experiments in the presence of both denaturants.
Number and orientations of beams in intensity‐modulated radiation treatments
Authors: Stein Jörg , Mohan Radhe , Wang Xiao‐Hong , Bortfeld Thomas , Wu Qiuwen , Preiser Konrad , Ling C. Clifton , Schlegel Wolfgang
Published: July 2002

The fundamental question of how many equispaced coplanar intensity‐modulated photon beams are required to obtain an optimum treatment plan is investigated in a dose escalation study for a typical prostate tumor. Furthermore, optimization of beam orientations to improve dose distributions is explored. A dose‐based objective function and a fast gradient technique are employed for optimizing the intensity profiles (inverse planning). An exhaustive search and fast simulated annealing techniques (FSA) are used to optimize beam orientations. However, to keep computation times reasonable, the intensity profiles for each beam arrangement are still optimized using inverse planning. A pencil beam convolution algorithm is employed for dose calculation. All calculations are performed in three‐dimensional (3D) geometry for 15 MV photons. DVHs, dose displays, TCP, NTCP, and biological score functions are used for evaluation of treatment plans. It is shown that for the prostate case presented here, the minimum required number of equiangular beams depends on the prescription dose level and ranges from three beams for 70 Gy plans to seven to nine beams for 81 Gy plans. For the highest dose level (81 Gy), beam orientations are optimized and compared to equiangular spaced arrangements. It is shown that (1) optimizing beam orientations is most valuable for a small numbers of beams (⩽5) and the gain diminishes rapidly for higher numbers of beams; (2) if sensitive structures (for example rectum) are partially enclosed by the target volume, beams coming from their direction tend to be preferable, since they allow greater control over dose distributions; (3) while FSA and an exhaustive search lead to the same results, computation times using FSA are reduced by two orders of magnitude to clinically acceptable values. Moreover, characteristics of and demands on biology‐based and dose‐based objective functions for optimization of intensity‐modulated treatments are discussed.
Processor quality control in laser imaging systems
Authors: Bogucki T. M. , Murphy W. R. , Baker C. W. , Piazza S. S. , Haus A. G.
Published: July 2002

Sensitometric techniques for performing processor quality control in laser imaging systems are analyzed in this study. The sensitivity of conventional x‐ray films using simulated screen‐light sensitometry is compared with helium–neon (HeNe) laser film exposed with a simulated red‐light sensitometer, a standalone (reference) laser sensitometer, an experimental (unstable) laser sensitometer, and laser printers. Infrared (IR) laser film exposed with an IR laser diode and a simulated IR sensitometer are also evaluated. It is demonstrated that laser‐generated step tablets provide an easy and reliable method of performing laser film processor quality control.
Physical and dosimetric aspects of a multileaf collimation system used in the dynamic mode for implementing intensity modulated radiotherapy
Authors: LoSasso Thomas , Chui Chen‐Shou , Ling C. Clifton
Published: July 2002

The use of a multileaf collimator in the dynamic mode to perform intensity modulated radiotherapy became a reality at our institution in 1995. Unlike treatment with static fields using a multileaf collimator, there are significant dosimetric issues which must be assessed before dynamic therapy can be implemented. We have performed a series of calculations and measurements to quantify head scatter for small fields, collimator transmission, and the transmission through rounded leaf ends. If not accounted for, these factors affect the delivered dose to the prostate by 5%–20% for a typical plan. Data obtained with ion chambers and radiographic film are presented for both 6 and 15 MV x‐ray beams. The impact on the delivered dose of the mechanical accuracy of the multileaf collimator, achieved during leaf position calibration and maintained during dose delivery, is also discussed.
Experimental evaluation of interface doses in the presence of air cavities compared with treatment planning algorithms
Authors: Shahine B. H. , Al‐Ghazi M. S. A. L. , El‐Khatib E.
Published: July 2002

A series of experiments were carried out to simulate air cavities in a polystyrene phantom. Dose was measured at air/polystyrene interface and as a function of depth. Results of experiments were compared to calculations done using three treatment planning systems. These systems employ Batho, modified Batho, and the equivalent tissue–air‐ratio methods for inhomogeneity corrections. The measured interface dose decreased by 55% for a 5 cm air gap, 5×5 cm2 field size, and 6 MV photons. This has been attributed to a lack of electronic equilibrium and dispersion of secondary particles transported through the air gap. These results are at variance with predictions of calculations using three treatment planning systems, for which only a 10% decrease was calculated. This is because the calculation algorithms employed do not incorporate electron transport. Further experiments were conducted to study the contribution of scatter from sides of the walls of the cavities. Dose measurements as a function of depth were also performed to investigate the effect of primary fluence attenuation. The Batho algorithm did not show any sensitivity to the position of air gap sidewalls. This points to the need for proper inclusion of disequilibrium effects and shape of inhomogeneity.
Tomographic inversion for sediment parameters in shallow water
Authors: Potty Gopu R. , Miller James H. , Lynch James F. , Smith Kevin B.
Published: July 2002

This article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources. The experimental data used for the inversions are SUS charge explosions acquired on a vertical hydrophone array during the Shelf Break Primer Experiment conducted south of New England in the Middle Atlantic Bight in August 1996. The SUS signals were analyzed for their time-frequency behavior using wavelets. The group speed dispersion curves were obtained from the wavelet scalogram of the SUS signals. A genetic algorithm (GA) was used for the inversion of sound speeds in the water column and compressional wave speeds in the sediment layers. The variations in the sound speeds in the water column were represented using empirical orthogonal functions (EOFs). A range-independent normal mode routine was used to construct the replica fields corresponding to the parameters. Comparison of group speeds for modes 1 to 9 and for a range of frequencies 8 to 200 Hz was used to arrive at the best parameter fit. An efficient hybrid optimization scheme using the GA and a Levenberg–Marquardt algorithm is presented. Linear perturbation methods were also used to “fine tune” the inversions and to obtain resolution and variance estimates. Analysis was also done to compute the degree of convergence of each of the parameters by explicitly calculating the Hessian matrices numerically. A posteriori estimation of mean and covariance was also done to obtain error estimates. Group speeds for the inverted sound speed fields provide an excellent match to the experimental data. The inverted sediment compressional speed profile compares well with in situ measurements.
Phase and group velocities of fast and slow compressional waves in trabecular bone
Authors: Padilla Frédéric , Laugier Pascal
Published: July 2002

This Letter is an extension to a multilayer model of porous bone first proposed by Hughes et al. [Ultrasound Med. Biol. 25, 811–821 (1999)]. Both slow and fast compressional waves propagate when the acoustic wave propagation is parallel to the trabecular alignment. However, a slow wave disappears at high refraction angles. To explain this phenomenon, the multilayer model is extended to compute group velocity surface and arrival times with an angle. Two major effects are highlighted as the refraction angle increases. First, the energy of the slow wave is refracted from the phase propagation direction. Second, the signals of fast and slow waves overlap. As a consequence, the slow wave may not be observed for a refraction angle greater than 40°, which is in agreement with previous experimental data published by Hughes et al. and others.
Convergence of poroelastic finite elements based on Biot displacement formulation
Authors: Dauchez Nicolas , Sahraoui Sohbi , Atalla Noureddine
Published: July 2002

The convergence of linear poroelastic elements based on Biot displacement formulation is investigated. The aim is to determine a mesh criterion that provides reliable results under a given frequency limit. The first part deals with 1D applications for which resonance frequencies can be related to Biot wavelengths. Their relative contributions to the motion are given in order to determine if the mesh criteria for monophasic media are suitable for poroelastic media. The imposition of six linear elements per wavelength is found for each Biot wave as a primary condition for convergence. For 3D applications, convergence rules are derived from a generic configuration, i.e., a clamped porous layer. Because of the complex deformation, the previous criterion is shown to be insufficient. Influence of the coupling between the two phases is demonstrated.
Multiple scattering in a reflecting cavity: Application to fish counting in a tank
Authors: De Rosny Julien , Roux Philippe
Published: July 2002

Classical fisheries acoustics techniques are useless in the presence of multiple scattering or reflecting boundaries. A general technique is developed that provides the number and the scattering strength of scatterers in motion placed inside a highly reflecting cavity. This approach is based on multiple scattering theory. The idea is to measure the average effect of the scatterers on the acoustic echoes of the cavity interfaces. This leads to the measure of the scattering mean free path, a typical length that characterizes the scattering strength of the cloud of scatterers. Numerical results are shown to agree with a simple theoretical analysis. Experiments are performed with fish in a tank at two different scales: ultrasonic frequency (400 kHz) in a 1.4-1 beaker with 1-cm-long fish as well as fisheries acoustics frequency (12.8 kHz) in a 30-m3 tank with 35-cm-long fish. These results have interesting applications to fish target strength measurement and fish counting in aquaculture.
Streaming generated by a bubble in an ultrasound field
Authors: Wu Junru , Du Gonghuan
Published: July 2002

A theory has been developed to calculate microstreaming velocity inside and outside an isolated air bubble in a liquid produced by a bubble-scattered sound field, taking account of two predominant modes of the bubble’s motion: a monopole (pulsation), and a dipole (translational harmonic vibrations). It has been demonstrated that the streaming velocity inside a bubble is much greater than that outside the bubble. It has also been shown that the microstreaming is most pronounced for a bubble undergoing volume resonance, which is in agreement with Elder’s experimental observations. If the viscosity of the gas medium in a bubble is neglected in theory, the results obtained agree qualitatively with Davidson and Riley’s.
On the use of matched-field processing and hybrid algorithms for vertical slice tomography
Authors: Taroudakis Michael I. , Markaki Maria G.
Published: July 2002

Matched-field processing and a hybrid scheme for vertical slice tomography are studied in characteristic cases of range-independent and range-dependent ocean environments using simulated data obtained at discrete points in the sound field along a vertical line, representing a vertical array of hydrophones. The matched-field processing is associated with a Genetic Algorithm, while the basic characteristic of the hybrid scheme is the application of matched-field processing for the definition of a reference environment to be subsequently used in connection with a modal-phase inversion scheme. In all cases studied, the sound-speed profiles are reconstructed with the use of empirical orthogonal functions. It is shown that the reconstruction of either the single sound-speed profile characterizing the range-independent environment, or the set of profiles characterizing an eddy in the range-dependent environment is achieved with good accuracy, despite the fact that a very wide search space has been considered. The apparent nonuniqueness in the solution of the inverse problem for the range-dependent case is remedied by applying physical constraints in the structure of the sea eddy and averaging over the admissible solutions obtained by the matched-field inversion scheme.
Electrode discrimination and speech recognition in postlingually deafened adult cochlear implant subjects
Authors: Zwolan Terry A. , Collins Leslie M. , Wakefield Gregory H.
Published: July 2002

This study investigated the relationship between electrode discrimination and speech recognition in 11 postlingually deafened adult cochlear implant subjects who were implanted with the Nucleus/Cochlear Corporation multichannel device. The discriminability of each electrode included in a subject’s clinical map was measured using adaptive and fixed-level discrimination tasks. Considerable variability in electrode discriminability was observed across subjects. Two subjects could discriminate all electrodes, and discrimination performance by the remaining nine subjects varied from near perfect to very poor. In these nine subjects, the results obtained from the discrimination tasks were used to create a map that contained only discriminable electrodes, and subjects’ performance on speech recognition tasks using this experimental map was measured. Four different speech recognition tests were administered: a nine-choice closed-set medial vowel recognition task, a 14-choice closed-set medial consonant recognition task, the NU6 Monosyllabic Words Test [T. W. Tillman and T. Carhart, Tech. Rep. No. SAM-TR-66-55, USAF School of Aerospace Medicine, Brooks Air Force Base, Texas (1966)] scored for both words and phonemes correct, and the Central Institute for the Deaf (CID) Everyday Sentences test [H. Davis and S. R. Silverman, Hearing and Deafness (Holt, Rinehart, and Winston, New York, 1978)]. Seven of the nine subjects tested with the experimental map showed significant improvement on at least one speech recognition measure, even though the experimental map contained fewer electrodes than the original map. Three subjects’ scores improved significantly on the CID Everyday Sentences test, three subjects’ scores improved significantly on the NU6 Monosyllabic Words test, and five subjects’ scores improved significantly on the NU6 Monosyllabic Words test scored for phonemes correct. None of the subjects’ scores improved significantly on either the vowel or consonant tests. No significant correlation was observed between electrode discrimination ability and speech recognition scores or between electrode discrimination ability and improvement in speech recognition scores when programmed with the experimental map. The results of this study suggest that electrode discrimination tasks may be used to improve speech recognition of some cochlear implant subjects, and that each electrode site does not necessarily provide perceptually distinct information.
Surface-controlled drop oscillations in space
Authors: Holt R. Glynn , Tian Yuren , Jankovsky Joseph , Apfel Robert E.
Published: July 2002

Large liquid drops were deformed by an acoustic standing wave in a resonant air chamber called the Drop Physics Module, which was carried on Space Shuttle Columbia as part of the second United States Microgravity Laboratory mission. When this deforming force was suddenly reduced, the drops executed free oscillations about a perfect spherical equilibrium. The complex frequency of these oscillations was measured. The first results from a series of experiments are presented here. Results for pure water compare favorably with fundamental theoretical predictions. Drops containing aqueous solutions of soluble surfactants exhibited remarkable differences in both frequency and damping, and these are explained phenomenologically by a discussion of the multiple time scales introduced by the addition of surfactants.