bluuebunny/crossref_metadata_2025 huggingface dataset:
Acute administration of a single dose of valsartan improves left ventricular functions: a pilot study to assess the role of tissue velocity echocardiography in patients with systemic arterial hypertension in the TVE‐valsartan study I
Authors: Govind Satish C. , Brodin Lars‐Åke , Nowak Jacek , Ramesh S. S. , Saha Samir K.
Published: October 2006

Background  The advent of colour‐coded tissue velocity echocardiography (TVE) has now made it possible to quantify left ventricular (LV) functions in patients with systemic arterial hypertension (HTN).

Hypothesis  In this project, we have studied the cardiac effects of a single dose of orally administered valsartan in patients with known HTN.

Methods  Fifty‐five patients with HTN with a mean age of 56 ± 10 years were given an early morning dose of 80 mg valsartan withholding regular antihypertensive medications on the day of investigation. TVE images, acquired on VIVID systems were digitized for postprocessing of longitudinal and radial peak systolic velocities, strain rate, and systolic and diastolic time intervals before (pre) and 5 h after (post) administration of the drug.

Results  Blood pressure (mmHg) pre and post, respectively, were 147 ± 15 versus 137 ± 14 systolic and 90 ± 7 versus 86 ± 7 diastolic (all P<0·01). LV longitudinal systolic velocities (cm s−1) were significantly higher post in LV septum (5·7 ± 1·1 versus 6·4 ± 1·6; P<0·001) with similar results obtained in other LV walls. Radial strain rate (1 s−1) was significantly higher post compared with pre valsartan (2·1 ± 0·6 versus 2·3 ± 0·9; P<0·01). Regional diastolic filling and ejection times (ms) were significantly shorter post (390 ± 122 versus 370 ± 120 and 275 ± 32 versus 163 ± 36 respectively; all P<0·05).

Conclusions  Within 5 h after oral administration of valsartan, improvement in regional myocardial systolic functions could be registered. Although the changes could well be secondary to afterload reduction, additional effects of the drug, evidenced by improved strain rate that is relatively load‐independent, may have contributed in this improvement.
Range of Applicability of the Method of Caustics around Holes
Authors: Badalouka B. G. , Papadopoulos G. A.
Published: October 2006

Abstract:  The range of applicability of the optical method of caustics, which is based on plane stress conditions, around cylindrical holes in plane specimens is investigated. The position of the generatrix curve of the caustic and the conditions, which influence its size, are defined. The dimensions of the specimen, the ratio of the thickness to the diameter of the hole, the applied stress and the dimensions of the optical set‐up influence the position of the generatrix curve of the caustic. At a critical distance from the boundary of the hole the state of stress degenerates from three‐dimensional to plane stress. In this paper, the extent of this region was defined by finite element analysis, in case of uniaxial tension. The defined critical distance was correlated with the condition, which influence the caustic, thus the range of applicability of the method of caustic around hole was defined. The validity of this range was experimentally checked.
Ethical, Legal, and Social Dimensions of Epilepsy Genetics
Authors: Shostak Sara , Ottman Ruth
Published: October 2006

Summary:  Purpose: Emerging genetic information and the availability of genetic testing has the potential to increase understanding of the disease and improve clinical management of some types of epilepsy. However, genetic testing is also likely to raise significant ethical, legal, and social issues for people with epilepsy, their family members, and their health care providers. We review the genetic and social dimensions of epilepsy relevant to understanding the complex questions raised by epilepsy genetics.

Methods: We reviewed two literatures: (a) research on the genetics of epilepsy, and (b) social science research on the social experience and social consequences of epilepsy. For each, we note key empiric findings and discuss their implications with regard to the consequences of emerging genetic information about epilepsy. We also briefly review available principles and guidelines from professional and advocacy groups that might help to direct efforts to ascertain and address the ethical, legal, and social dimensions of genetic testing for epilepsy.

Results: Genetic information about epilepsy may pose significant challenges for people with epilepsy and their family members. Although some general resources are available for navigating this complex new terrain, no guidelines specific to epilepsy have yet been developed to assist people with epilepsy, their family members, or their health care providers.

Conclusions: Research is needed on the ethical, legal, and social concerns raised by genetic research on epilepsy and the advent of genetic testing. This research should include the perspectives of people with epilepsy and their family members, as well as those of health care professionals, policymakers, and bioethicists.
Functional Impairment, Race, and Family Expectations of Death
Authors: Williams Brie A. , Lindquist Karla , Moody‐Ayers Sandra Y. , Walter Louise C. , Covinsky Kenneth E.
Published: October 2006

OBJECTIVES: To assess the effect of functional impairment on family expectations of death and to examine how this association varies by race.

DESIGN: Cross‐sectional.

SETTING: Community based.

PARTICIPANTS: Two thousand two hundred thirty‐seven family members of decedents from the Health and Retirement Survey (HRS), a national study of persons aged 50 and older.

MEASUREMENTS: Families were interviewed within 2 years of the HRS participant's death. The primary outcome was whether death was expected. The primary predictors were the decedent's functional status (impairment in any activity of daily living (ADL; eating, dressing, transferring, toileting, or bathing) during the last 3 months of life and the decedent's race.

RESULTS: Overall, 58% of families reported that their family member's death was expected. Expecting death was strongly associated with functional impairment; 71% of families of decedents with ADL disability expected death, compared with 24% of those without ADL disability (P<.01). Death was expected more often in families of white decedents (60%) than African Americans (49%) (P<.01), although the effect of ADL disability was similar in both groups. After adjustment for potentially confounding factors, there were still significant associations between expecting death and functional impairment (odds ratio (OR)=3.58, 95% confidence interval (CI) 2.73–4.70), and families of African Americans expected death less often than families of white decedents (OR=0.63, 95% CI=0.46–0.86).

CONCLUSION: Family members of older adults expected death only 58% of the time. Families of functionally impaired older people were more likely to expect death when it occurred than were families of older people who were not functionally impaired, and the expectation of death was lower for families of African Americans than for whites.
A Molecular Phylogenetic Investigation of Zoothamnium (Ciliophora, Peritrichia, Sessilida)1
Authors: CLAMP JOHN C. , WILLIAMS DANIEL
Published: October 2006

ABSTRACT. The gene coding for 18S small subunit ribosomal RNA (ssu rRNA) was sequenced in seven free‐living, marine species of the sessiline peritrich genus Zoothamnium. These were Zoothamnium niveum, Zoothamnium alternans, Zoothamnium pelagicum, and four unidentified species. The ssu rRNA gene also was sequenced in Vorticella convallaria, Vorticella microstoma, and in an unidentified, freshwater species of Vorticella. Phylogenetic trees were constructed using these new sequences to test a previously published phylogenetic association between Zoothamnium arbuscula, currently in the family Zoothamniidae, and peritrichs in the family Vorticellidae. Trees constructed by means of neighbor‐joining, maximum parsimony, maximum likelihood, and Bayesian inference methods all had similar topologies. The seven new sequences of Zoothamnium species grouped into three well‐supported clades, each of which contained a diversity of morphological types. The three clades formed a poorly supported, larger clade that was deeply divergent from Z. arbuscula, which remained more closely associated with vorticellid peritrichs. It is apparent that Zoothamnium is a richly diverse genus and that a much more intensive investigation, involving both morphological and molecular data and a wider selection of species, will be necessary to resolve its phylogeny. A greater amount of molecular diversity than is predicted by morphological data exists within all major clades of sessiline peritrichs that have been included in molecular phylogenies, indicating that characteristics of stalk and peristomial structure traditionally used to differentiate taxa at the generic level and above may not be uniformly reliable.
FPSO Conference—Estimating Wind-Sea and Swell for FPSO Operability
Authors: Ewans K. C. , Vanderschuren L. , Tromans P. S.
Published: October 2006

The motion response of an FPSO is sensitive to the relative intensities and directions of the wind-sea and swell components in a sea state, and the operability of the FPSO is a function of the long-term variation in these components. Estimations of the operability are therefore dependent both on how the sea state is described in terms of its constituent wind-sea and swell components, and on how the long-term variability of the sea state is captured. However, there is currently no consensus on how either the sea state or its long-term variability should be described. We investigate these issues by means of a study of the responses of a typical FPSO to the wave fields at a location offshore Namibia and a location off the west coast of New Zealand. We make use of a state-of-the-art program for splitting a directional wave spectrum into wind-sea and swell components, and we examine the effect on the motion responses of allowing the spectra to be split into many swell partitions or constraining the spectral split to a maximum of two partitions, as is often assumed in response calculations. The resulting decompositions are used to examine the effects of swell on hull motions and, hence, to identify methods for generating sea state criteria for operability. In addition, one-year metocean conditions are estimated; these are relevant for analysis of the limits on operations.
Kinematic Laplacian Equation Method: A Velocity-Vorticity Formulation for the Navier-Stokes Equations
Authors: Ponta Fernando L.
Published: October 2006

In this work, a novel procedure to solve the Navier-Stokes equations in the vorticity-velocity formulation is presented. The vorticity transport equation is solved as an ordinary differential equation (ODE) problem on each node of the spatial discretization. Evaluation of the right-hand side of the ODE system is computed from the spatial solution for the velocity field provided by a new partial differential equation expression called the kinematic Laplacian equation (KLE). This complete decoupling of the two variables in a vorticity-in-time/velocity-in-space split algorithm reduces the number of unknowns to solve in the time-integration process and also favors the use of advanced ODE algorithms, enhancing the efficiency and robustness of time integration. The issue of the imposition of vorticity boundary conditions is addressed, and details of the implementation of the KLE by isoparametric finite element discretization are given. Validation results of the KLE method applied to the study of the classical case of a circular cylinder in impulsive-started pure-translational steady motion are presented. The problem is solved at several Reynolds numbers in the range 5<Re<180 comparing numerical results with experimental measurements and flow visualization plates. Finally, a recent result from a study on periodic vortex-array structures produced in the wake of forced-oscillating cylinders is included.
Initial Imperfection Models for Segments of Line Pipe
Authors: Dorey Alfred B. , Murray David W. , Cheng J. J. Roger
Published: October 2006

Initial imperfections have long been acknowledged as having an effect on the behavior of shell structures, affecting both the global and local behavior. Yet, despite their significance, initial imperfections are rarely included in analytical models for pipelines. This is usually because of the complicated nature of initial imperfections, the difficulty in measuring them, and the small amount of available literature that describes their geometry. Some recent investigations at the University of Alberta in Edmonton have focused on the effect of initial imperfections on the behavior of segments of line pipe. Imperfections measured across the inside surface of pipe test specimens were incorporated into a finite element model that was developed to predict the experimental behavior of the specimens tested under combined loads of internal pressure, axial load and bending moment. Test-to-predicted ratios for the load carrying capacity of the test specimens had a mean value of 1.035 with a coefficient of variation of 0.047. The improvements in the accuracy of the finite element analysis models that include the initial imperfection pattern indicate their importance in modeling the experimental behavior. Once the importance of initial imperfections was established, idealized patterns were developed to simplify numerical modeling. This paper presents the results of different patterns investigated for both plain and girth-welded segments of line pipe and provides recommended simplified assumed initial imperfection patterns.
Finite Mixture Models for Nonidentical Multiple Tooled Manufacturing
Authors: Bracken Allen T.
Published: October 2006

This paper presents a novel method to assess nonidentical multiple tooled (NIMT) manufacturing processes (like multiple cavity injection molding) using finite mixture distribution (FMD) models. A stepwise methodology is presented, including supporting mathematics and statistics. The methodology is illustrated and supported by its application to two sets of real multicavity injection molding data. The method is commercially relevant and is significant in that it allows enhanced examination of the fraction of the parts nonconforming or better setting of the specification level. Included are discussions of FMD models versus normal models and novel tail probability comparison methods (ratio of tail probabilities and log PDF comparisons). The methodology is recommended for NIMT processes, and is thought to better address the adequacy evaluation of processes where there are multiple nonidentical distributions mixing in production.
Understanding Limits on Fin Aspect Ratios in Counterflow Microchannel Arrays Produced by Diffusion Bonding
Authors: Paul Brian K. , Kwon Patrick , Subramanian Ramkumar
Published: October 2006

This paper investigates the manufacturability limits of fin aspect ratios within two-fluid counter-flow microchannel arrays based on the stress state between laminae during diffusion bonding. In prior papers, it has been shown that the diffusion bonding of two-fluid systems by microlamination can result in regions of the device that do not directly transmit bonding pressure and, consequently, result in unbonded regions leading to device leakage. A finite element model is used to analyze the stress state between laminae during diffusion bonding. The stress state is used to determine the critical stress necessary for diffusion bonding to occur in areas not receiving direct bonding pressure. Model results are compared with experimental results over a wide range of counter-flow geometries. It has been found generally that a compressive stress state must exist in every part of the geometry in order to produce leak-free bonds. Implications of this finding on the design of two-fluid microchannel arrays are discussed.
A Fuzzy Adaptive Network Model for Waviness Removal in Grinding of Wire-Sawn Silicon Wafers
Authors: Jiao Yue , Pei Z. J. , Lei Shuting , Lee E. Stanley , Fisher Graham R.
Published: October 2006

Silicon is the primary semiconductor material used to fabricate microchips, and the quality of microchips depends directly upon the quality of the starting silicon wafers. One of the manufacturing problems in silicon wafer manufacturing is the presence of waviness on the surface as a result of wire-saw slicing. Various factors influence the waviness reduction capacity during soft-pad grinding; the grinding process is very complicated and difficult to define. In this research, fuzzy adaptive network, which is ideally suited to the modeling of vague phenomena, is used to model the waviness problem. Fuzzy adaptive network has the learning ability of a neural network and the linguistic representation of a complex, not well understood phenomenon. Simulation data are used to illustrate the applicability of fuzzy adaptive network. The results, even though based on some very limited data, indicate the influences of the independent parameters clearly.
Identification and Characterization of the
Bacillus thuringiensi
s
phaZ
Gene, Encoding New Intracellular Poly-3-Hydroxybutyrate Depolymerase
Authors: Tseng Chi-Ling , Chen Hui-Ju , Shaw Gwo-Chyuan
Published: October 2006

A gene that codes for a novel intracellular poly-3-hydroxybutyrate (PHB) depolymerase has now been identified in the genome of
Bacillus thuringiensis
subsp.
israelensis
ATCC 35646. This gene, previously annotated as a hypothetical 3-oxoadipate enol-lactonase (PcaD) gene and now designated
phaZ
, encodes a protein that shows no significant similarity with any known PHB depolymerase. Purified His-tagged PhaZ could efficiently degrade trypsin-activated native PHB granules as well as artificial amorphous PHB granules and release 3-hydroxybutyrate monomer as a hydrolytic product, but it could not hydrolyze denatured semicrystalline PHB. In contrast, purified His-tagged PcaD of
Pseudomonas putida
was unable to degrade trypsin-activated native PHB granules and artificial amorphous PHB granules. The
B. thuringiensis
PhaZ was inactive against
p
-nitrophenylpalmitate, tributyrin, and triolein. Sonication supernatants of the wild-type
B. thuringiensis
cells exhibited a PHB-hydrolyzing activity in vitro, whereas those prepared from a
phaZ
mutant lost this activity. The
phaZ
mutant showed a higher PHB content than the wild type at late stationary phase of growth in a nutrient-rich medium, indicating that this PhaZ can function as a PHB depolymerase in vivo. PhaZ contains a lipase box-like sequence (G-W-S
102
-M-G) but lacks a signal peptide. A purified His-tagged S102A variant had lost the PHB-hydrolyzing activity. Taken together, these results indicate that
B. thuringiensis
harbors a new type of intracellular PHB depolymerase.
TheEscherichia coliK-12 NarL and NarP Proteins Insulate thenrfPromoter from the Effects of Integration Host Factor
Authors: Browning Douglas F. , Lee David J. , Wolfe Alan J. , Cole Jeffrey A. , Busby Stephen J. W.
Published: October 2006

TheEscherichia coliK-12nrfoperon promoter can be activated fully by the FNR protein (regulator of fumarate and nitrate reduction) binding to a site centered at position −41.5. FNR-dependent transcription is suppressed by integration host factor (IHF) binding at position −54, and this suppression is counteracted by binding of the NarL or NarP response regulator at position −74.5. TheE. coli acsgene is transcribed from a divergent promoter upstream from thenrfoperon promoter. Transcription from the majoracsP2 promoter is dependent on the cyclic AMP receptor protein and is modulated by IHF and Fis binding at multiple sites. We show that IHF binding to one of these sites, located at position −127 with respect to thenrfpromoter, has a positive effect onnrfpromoter activity. This activation is dependent on the face of the DNA helix, independent of IHF binding at other locations, and found only when NarL/NarP are not bound at position −74.5. Binding of NarL/NarP appears to insulate thenrfpromoter from the effects of IHF. Theacs-nrfregulatory region is conserved in other pathogenicE. colistrains and related enteric bacteria but differs inSalmonella entericaserovar Typhimurium.
A FRAMEWORK FOR THE PRAGMATIC QUALITY OF Z SPECIFICATIONS
Authors: KAMTHAN PANKAJ
Published: October 2006

Z is a formal specification language for describing sequential software systems. As the use of Z increases, the quality of Z specifications as effective means of communication arises. The aim of this paper is to contribute to a systematic assessment of the quality of Z specifications as perceived by their stakeholders. A pragmatic quality framework for Z specifications using notions from semiotics, cognitive psychology, and information system quality is proposed. The goals for pragmatic quality, and manageable criteria and mechanisms to address them in a feasible manner are identified. The utility and trade-offs of the mechanisms in achieving the quality goals of the framework are analyzed. Examples that lead to compromise of pragmatic quality in a Z specification, and techniques for improvement, are given.
CYCLODEXTRIN NANOTUBE INDUCED BY 4,4′-BIS(2-BENZOXAZOLYL) STILBENE
Authors: WU AIHUA , SHEN XINGHAI , GAO HONGCHENG
Published: October 2006

The formation of β- and γ-cyclodextrin (CD) nanotubes induced by the molecule 4,4′-bis(2-benzoxazolyl) stilbene (BOS) was investigated by fluorescence anisotropy. Using the Perrin–Webber formula, the average number of cyclodextrin (n CD ) in each nanotube was estimated and the results suggested that the n CD value in the γ-CD system is larger than that in the β-CD system. Hydrogen-bonding between the hydroxyl groups of neighboring CDs was found to be an important contribution to the formation of cyclodextrin nanotube on the basis of the pH effect study. The temperature effect study showed that this nanotube was thermostable at T ≤ 303 K , while it was gradually collapsed at higher temperature.
CHEMICAL PREPARATION OF MgO WHISKERS
Authors: WANG XIAOLI , YAN CHENGLIN , ZOU LONGJIANG , XUE DONGFENG
Published: October 2006

A useful method is described for the chemical synthesis of high length-radius ratio magnesium oxide ( MgO ) whiskers at ambient temperature. The diameter of MgO whiskers falls in the range of 2–5 μm with a length of 30–50 μm. The length-radius ratio generally falls in the range of 10–30. Energy-dispersive X-ray spectrometer analysis reveals that the whiskers are composed of Mg and O elements. Microscopic morphologies and structures are well studied by scanning electron microscopy and X-ray diffraction. The growth mechanism of MgO whiskers is also proposed on the basis of crystallographic characteristics.
FABRICATION AND PROPERTIES OF Ni-YSZ AND Ni-Co-YSZ CERMETS
Authors: SHAO GANG-QIN , LI YONG , DUAN XING-LONG , CAI HU , LI JIA , SHI XIAO-LIANG , GUO JING-KUN
Published: October 2006

Ni -YSZ and Ni - Co -YSZ cermets were fabricated by hot-press-sintering from nanocomposite powders. The structure, morphology, relative density, hardness, specific heat capacity and thermal conductivity were measured. Results show that the crystalline grains are much homogeneous. Their size distribution is quite narrow and between 0.2–0.4 μm (200–400 nm). The Ni - Co -YSZ cermet reaches a maximum relative density (96.2%) at 1350°C and a maximum Rockwell hardness (70.5) at 1400°C. The specific heat capacity of Ni -YSZ cermet is larger than that of Ni - Co -YSZ cermet. The thermal conductivity of Ni -YSZ cermet is smaller than that of Ni - Co -YSZ cermet.
DIAMOND NANORODS FROM CARBON NANOTUBES BY HYDROGEN PLASMA TREATMENT
Authors: GONG J. L. , SUN L. T. , ZHU D. Z. , ZHU Z. Y. , HE S. X. , YUE T. , WANG Z. X.
Published: October 2006

Single crystalline diamond nanorods with diameters of 4–8 nm and with lengths up to 200 nm have been synthesized by hydrogen plasma post-treatment of multiwalled carbon nanotubes. The diamond nanorods were identified to have a core-sheath structure with inner core being diamond crystal and outer shell being amorphous carbon. A growth mechanism for the diamond nanorods was proposed.
FABRICATION OF COMPOSITE STRUCTURE OF HONEYCOMB FILM AND LUMINESCENT NANOPARTICLES CONTAINING LANTHANIDE COMPLEXES
Authors: TAMAKI KOICHI , ISOSHIMA TAKASHI , HARA MASAHIKO , SHIMOMURA MASATSUGU
Published: October 2006

Micropatterned films are attractive materials with potentials applicable in the fields of photonics, electronics, biotechnology, and so on. Fabrication of honeycomb-patterned microporous films ("honeycomb films") by casting dilute solution of various types of polymers under high humidity has been already reported. Introduction of luminescent nanoparticles into micropores of the film is investigated to realize photofunctional materials. Novel luminescent monodisperse nanoparticles containing europium or terbium complexes have been prepared for this experiment. By a scanning electron microscope (SEM), many wrinkles were observed on the surface of lanthanide-containing nanoparticles. Zeta potential of the lanthanide-containing nanoparticles was positive. Composites of honeycomb film and the nanoparticles, the latter embedded in the micropores, were fabricated by dropping water dispersion of mixture of the europium-, terbium-, and no-dye-containing nanoparticles on the films. The number of the nanoparticles in a micropore was estimated no less than 400 by analyzing SEM images. The ratio of emission intensity of terbium to that of europium in the individual micropores of the composites fluctuated and deviated from the intensity ratio in bulk. Numerical simulation confirmed this tendency qualitatively.
The semi-regenerative method of simulation output analysis
Authors: Calvin James M. , Glynn Peter W. , Nakayama Marvin K.
Published: October 2006

We develop a class of techniques for analyzing the output of simulations of a semi-regenerative process. Called the semi-regenerative method, the approach is a generalization of the regenerative method, and it can increase efficiency. We consider the estimation of various performance measures, including steady-state means, expected cumulative reward until hitting a set of states, derivatives of steady-state means, and time-average variance constants. We also discuss importance sampling and a bias-reduction technique. In each case, we develop two estimators: one based on a simulation of a single sample path, and the other a type of stratified estimator in which trajectories are generated in an independent and identically distributed manner. We establish a central limit theorem for each estimator so confidence intervals can be constructed.
Scientific formats for object-relational database systems
Authors: Cohen Shirley , Hurley Patrick , Schulz Karl W. , Barth William L. , Benton Brad
Published: October 2006

Commercial database management systems (DBMSs) have historically seen very limited use within the scientific computing community. One reason for this absence is that previous database systems lacked support for the extensible data structures and performance features required within a high-performance computing context. However, database vendors have recently enhanced the functionality of their systems by adding object extensions to the relational engine. In principle, these extensions allow for the representation of a rich collection of scientific datatypes and common statistical operations. Utilizing these new extensions, this paper presents a study of the suitability of incorporating two popular scientific formats, NetCDF and HDF, into an object-relational system. To assess the performance of the database approach, a series of solution variables from a regional weather forecast model are used to build representative small, medium and large databases. Common statistical operations and array element queries are then performed using the object-relational database, and the execution timings are compared against native NetCDF and HDF operations.
Report on the 7
th
Workshop on Distributed Data and Structures
Authors: Schwarz Thomas , Manasse Mark
Published: October 2006

The seventh Workshop on Distributed Data and Structures (WDAS) took place on the campus of Santa Clara University on January 4 and 5, 2006 and drew participants actively working in research on distributed data, structures, and their applications. WDAS aims to stimulate the exchange of ideas and to be a forum for work in progress. The electronic version of the Proceedings contains all papers accepted at the conference [WDAS]. In addition, the workshop presentations helped to select a subset that will appear revised in the Proceedings in Informatics Series at Carleton Scientific. Two papers could not be presented by authors because of the difficulties of obtaining an entry visa to the United States, unfortunately a more and more common phenomenon. We now give an overview of the topics discussed at the workshop and the related presentations.
Changes to the
TODS
editorial board
Authors: Snodgrass Richard
Published: October 2006

Mike Franklin left the Editorial Board on March 1 after five years of very active service, handling an even two dozen
TODS
submissions. I especially appreciate Mike's cogent advice on the many policy issues that arose over the last five years.
Too Much Information
Authors: Christensen Jim , Sussman Jeremy , Levy Stephen , Bennett William E. , Wolf Tracee Vetting , Kellogg Wendy A.
Published: October 2006

As mobile computing devices and a variety of sensors become ubiquitous, new resources for applications and services - often collectively referred to under the rubric of context-aware computing - are becoming available to designers and developers. In this article, we consider the potential benefits and issues that arise from leveraging context awareness in new communication services that include the convergence of VoIP (voice over IP) and traditional information technology.
The generalized two-server problem
Authors: Sitters René A. , Stougie Leen
Published: October 2006

We consider the generalized on-line two-server problem in which each server moves in its own metric space. Requests for service arrive one-by-one and every request is represented by two points: one in each metric space. The problem is to move, at every request, one of the two servers to its request-point such that the total distance travelled by the two servers is minimized.The special case in which both metric spaces are the real line is known as the CNN-problem. It has been a well-known open question in on-line optimization if an algorithm with a constant-competitive ratio exists for this problem. We answer this question in the affirmative by providing a constant-competitive algorithm for the generalized two-server problem on any metric space.The basic result in this article is a characterization of competitiveness for metrical service systems that seems much easier to use when looking for a competitive algorithm. The existence of a competitive algorithm for the generalized two-server problem follows rather easily from this result.
An improved algorithm for loop dead optimization
Authors: Behera Chandan Kumar , Kumar Pawan
Published: October 2006

Loop dead variables are the variables, which are defined in a loop, but not used in that loop. On successive execution of loop, these get different value, however all values (except last value) are not used. Hence in optimized program, the definition of a loop dead variable can be moved outside the loop (after the loop), rather than computing every time, inside the loop. In our discussion, we have assumed only simple loop. Every loop has one entry and one exit point.
Bulk Disambiguation of Speculative Threads in Multiprocessors
Authors: Ceze Luis , Tuck James , Torrellas Josep , Cascaval Calin
Published: October 2006

Transactional Memory (TM), Thread-Level Speculation (TLS), and Checkpointed multiprocessors are three popular architectural techniques based on the execution of multiple, cooperating speculative threads. In these environments, correctly maintaining data dependences across threads requires mechanisms for disambiguating addresses across threads, invalidating stale cache state, and making committed state visible. These mechanisms are both conceptually involved and hard to implement. In this paper, we present Bulk, a novel approach to simplify these mechanisms. The idea is to hash-encode a thread's access information in a concise signature, and then support in hardware signature operations that efficiently process sets of addresses. Such operations implement the mechanisms described. Bulk operations are inexact but correct, and provide substantial conceptual and implementation simplicity. We evaluate Bulk in the context of TLS using SPECint2000 codes and TM using multithreaded Java workloads. Despite its simplicity, Bulk has competitive performance with more complex schemes. We also find that signature configuration is a key design parameter.
Reducing Startup Time in Co-Designed Virtual Machines
Authors: Hu Shiliang , Smith James E.
Published: October 2006

A Co-Designed Virtual Machine allows designers to implement a processor via a combination of hardware and software. Dynamic binary translation converts code written for a conventional (legacy) ISA into optimized code for an underlying implementation-specific ISA. Because translation is done dynamically, an important consideration in such systems is the startup time for performing the initial translations. Beginning with a previously proposed co-designed VM that implements the x86 ISA, we study runtime binary translation overhead effects. The co-designed x86 virtual machine is based on an adaptive translation system that uses a basic block translator for initial emulation and a superblock translator for hotspot optimization. We analyze and model VM startup performance via simulation. We observe that non-hotspot emulation via basic block translation is the major part of the startup overhead. To reduce startup translation overhead, we follow the co-designed hardware / software philosophy and propose hardware assists to dramatically accelerate basic block translations. By combining hardware assists with balanced translation strategies, the co-designed translation system reduces runtime overhead significantly and demonstrates very competitive startup performance when compared with conventional processors running a set of Windows application benchmarks.
Program Demultiplexing
Authors: Balakrishnan Saisanthosh , Sohi Gurindar S.
Published: October 2006

We present Program Demultiplexing (PD), an execution paradigm that creates concurrency in sequential programs by "demultiplexing" methods (functions or subroutines). Call sites of a demultiplexed method in the program are associated with handlers that allow the method to be separated from the sequential program and executed on an auxiliary processor. The demultiplexed execution of a method (and its handler) is speculative and occurs when the inputs of the method are (speculatively) available, which is typically far in advance of when the method is actually called in the sequential execution. A trigger, composed of predicates that are based on program counters and memory write addresses, launches the speculative execution of the method on another processor. Our implementation of PD is based on a full-system execution-based chip multi-processor simulator with software to generate triggers and handlers from an x86- program binary. We evaluate eight integer benchmarks from the SPEC2000 suite .programs written in C with no explicit concurrency and/or motivation to create concurrency. and achieve a harmonic mean speedup of 1.8x with our implementation of PD.
Flexible Snooping
Authors: Strauss Karin , Shen Xiaowei , Torrellas Josep
Published: October 2006

A simple and low-cost approach to supporting snoopy cache coherence is to logically embed a unidirectional ring in the network of a multiprocessor, and use it to transfer snoop messages. Other messages can use any link in the network. While this scheme works for any network topology, a naive implementation may result in long response times or in many snoop messages and snoop operations. To address this problem, this paper proposes Flexible Snooping algorithms, a family of adaptive forwarding and filtering snooping algorithms. In these algorithms, a node receiving a snoop request may either forward it to another node and then perform the snoop, or snoop and then forward it, or simply forward it without snooping. The resulting design space offers trade-offs in number of snoop operations and messages, response time, and energy consumption. Our analysis using SPLASH-2, SPECjbb, and SPECweb workloads finds several snooping algorithms that are more costeffective than current ones. Specifically, our choice for a highperformance snooping algorithm is faster than the currently fastest algorithm while consuming 9-17% less energy; our choice for an energy-efficient algorithm is only 3-6% slower than the previous one while consuming 36-42% less energy.
A loopless Gray code for rooted trees
Authors: Korsh James , Lafollette Paul
Published: October 2006

Beyer and Hedetniemi [1980] gave the first constant average-time algorithm for the generation of all rooted trees with
n
nodes. This article presents the first combinatorial Gray code for these trees and a loopless algorithm for its generation.
Robust subgraphs for trees and paths
Authors: Hassin Refael , Segev Danny
Published: October 2006

Consider a graph problem which is associated with a parameter, for example, that of finding a longest tour spanning
k
vertices. The following question is natural: Is there a small subgraph that contains an optimal or near optimal solution for every possible value of the given parameter? Such a subgraph is said to be
robust
. In this article we consider the problems of finding heavy paths and heavy trees of
k
edges. In these two cases, we prove surprising bounds on the size of a robust subgraph for a variety of approximation ratios. For both problems, we show that in every complete weighted graph on
n
vertices there exists a subgraph with approximately α/1−α
2
n
edges that contains an α-approximate solution for every
k
= 1,…,
n
− 1. In the analysis of the tree problem, we also describe a new result regarding balanced decomposition of trees. In addition, we consider variants in which the subgraph itself is restricted to be a path or a tree. For these problems, we describe polynomial time algorithms and corresponding proofs of negative results.
Polaris
Authors: Stiegler Marc , Karp Alan H. , Yee Ka-Ping , Close Tyler , Miller Mark S.
Published: October 2006

It limits the damage a virus can do by using the operating system's own security mechanisms to enforce the Principle of Least Authority on individual applications.
A Wiki for discussing and promoting best practices in research
Authors: Hill Mark D. , Gaudiot Jean-Luc , Hall Mary , Marks Joe , Prinetto Paolo , Baglio Donna
Published: October 2006

Dealing with the demands of escalating paper submissions is a daunting challenge for conference organizers and program chairs. ACM and IEEE have joined forces to create a forum for sharing ideas on the best ways to handle it all.
Cache coherence tradeoffs in shared-memory MPSoCs
Authors: Loghi Mirko , Poncino Massimo , Benini Luca
Published: October 2006

Shared memory is a common interprocessor communication paradigm for single-chip multiprocessor platforms. Snoop-based cache coherence is a very successful technique that provides a clean shared-memory programming abstraction in general-purpose chip multiprocessors, but there is no consensus on its usage in resource-constrained multiprocessor systems on chips (MPSoCs) for embedded applications. This work aims at providing a comparative energy and performance analysis of cache-coherence support schemes in MPSoCs. Thanks to the use of a complete multiprocessor simulation platform, which relies on accurate technology-homogeneous power models, we were able to explore different cache-coherent shared-memory communication schemes for a number of cache configurations and workloads.
Evaluating Network Processors using NetBench
Authors: Memik Gokhan , Mangione-Smith William H.
Published: October 2006

The Network Processor market is one of the fastest growing segments of the microprocessor industry today. In spite of this increasing market importance, there does not exist a common framework to compare the performance of different Network Processor designs. Our primary goal in this study is to fill this gap by creating the NetBench benchmarking suite. NetBench is designed to represent Network Processor workloads. It contains 11 programs that form 18 different applications. The programs are selected from all levels of packet processing: Small, low-level code fragments as well as large application-level programs are included in the suite. These applications are representative of the Network Processor applications in the market. Using the SimpleScalar simulator to model an ARM processor, we study these programs in detail and compare key characteristics, such as instructions per cycle, instruction distribution, cache behavior, and branch prediction accuracy with the programs from MediaBench. Using statistical analysis, we show that the simulation results for the programs in NetBench have significantly different characteristics than programs in MediaBench. Finally, we present performance measurements from Intel IXP1200 Network Processor to show how NetBench can be utilized.
It's all about the concept...
Authors: Arnowitz Jonathan , Dykstra-Erickson Elizabeth
Published: October 2006

How can a design review be conducted on static interfaces? What constitutes good design?
Introduction
Authors: Sirer Emin Gün
Published: October 2006

This issue of the Operating Systems Review focuses on self-organizing systems; that is, systems whose functionality emerges through the autonomous activities of their components. Self-organization is a powerful paradigm for structuring systems ranging from stand-alone operating systems all the way up to planetary-scale distributed systems. Unlike the previously dominant organizational paradigms, self-organization has the potential to be much more robust because the individual components can autonomously compensate for the failures of other components, to scale to much larger systems because they avoid centralized components that pose bottlenecks, and to provide much better performance because they draw on the resources of a great many components distributed in many different places.This issue of the OSR brings together various papers on the application of the self-organizing design paradigm to various contexts. The vast majority of the papers in this issue relate to peer-to-peer (P2P) systems, a newly emerging class of distributed systems in which self-organization has played a foundational role. Peer-to-peer systems can be characterized by the ability of clients to also function as servers. This ability to shift traditional service functionality from dedicated servers (which provide resources) to a collection of self-organizing nodes that would otherwise serve solely as consumers has enabled a new and broad class of systems with unprecedented performance, robustness, and scale. There has been a huge outpouring of research on self-organizing peer-to-peer systems, whose applications include content delivery, naming systems, messaging, publish-subscribe, data repositories, just to name a few. While a recent panel at SOSP asked the question of whether P2P is "still useless," the overwhelming evidence at the panel was that self-organization techniques are now a standard part of the distributed system designer's tool chest, and have enabled our community, with the aid of PlanetLab, to tackle and address some of the outstanding problems in Internet-scale systems. Planetary scale systems are no longer just a theoretical endeavor; practical self-organizing systems seem to be here to stay.The papers in this issue cover foundations of self-organizing systems, such as elementary building blocks, such as clouds, for managing large scale networks, as well as basic techniques for reconciling quality of service with P2P, and for bridging the gap between centralized and peer-to-peer systems. A primary concern in any self-organizing system is whether the participants have incentives to autonomously follow a protocol, so some of the papers examine mechanism design and incentive-compatibility. Finally, a few of the papers examine self-organization within the context of a single, stand-alone operating system, examining, for instance, self-repair in componentized OSes. I hope you will enjoy reading this issue.
A study of Nash equilibrium in contribution games for peer-to-peer networks
Authors: Corbo Jacomo , Calvó-Armengol Antoni , Parkes David
Published: October 2006

We consider a stylized model of content contribution in a peer-to-peer network. The model is appealing because it allows for linear-quadratic payoff functions and for very general interaction patterns among agents. Furthermore, when the model has a unique Nash equilibrium (NE) we find that it is defined by a network centrality measure (Bonacich 1987), with
L1
and
L2
norms of the Bonacich index vector providing aggregate contribution and social welfare. Furthermore, we find that NE are always (even when they are non-unique) computable by solving a linear complementarity problem. We study the network designer's problem of engineering the most efficient equilibrium outcome, proving that maximizing aggregate contribution can be reconciled with maximizing aggregate welfare. We also provide a partial characterization of optimal NE graphs and suggest different approaches for how a network designer can promote more efficient graph structures.
A framework for password-based authenticated key exchange
1
Authors: Gennaro Rosario , Lindell Yehuda
Published: October 2006

In this paper, we present a general framework for password-based authenticated key exchange protocols, in the common reference string model. Our protocol is actually an abstraction of the key exchange protocol of Katz et al. and is based on the recently introduced notion of smooth projective hashing by Cramer and Shoup. We gain a number of benefits from this abstraction. First, we obtain a modular protocol that can be described using just three high-level cryptographic tools. This allows a simple and intuitive understanding of its security. Second, our proof of security is significantly simpler and more modular. Third, we are able to derive analogs to the Katz et al. protocol under additional cryptographic assumptions. Specifically, in addition to the DDH assumption used by Katz et al., we obtain protocols under both the quadratic and
N
-residuosity assumptions. In order to achieve this, we construct new smooth projective hash functions.
XORs in the air
Authors: Katti Sachin , Rahul Hariharan , Hu Wenjun , Katabi Dina , Médard Muriel , Crowcroft Jon
Published: October 2006

This paper proposes COPE, a new architecture for wireless mesh networks. In addition to forwarding packets, routers mix (i.e., code) packets from different sources to increase the information content of each transmission. We show that intelligently mixing packets increases network throughput. Our design is rooted in the theory of network coding. Prior work on network coding is mainly theoretical and focuses on multicast traffic. This paper aims to bridge theory with practice; it addresses the common case of unicast traffic, dynamic and potentially bursty flows, and practical issues facing the integration of network coding in the current network stack. We evaluate our design on a 20-node wireless network, and discuss the results of the first testbed deployment of wireless network coding. The results show that COPE largely increases network throughput. The gains vary from a few percent to several folds depending on the traffic pattern, congestion level, and transport protocol.