bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulse-Decay Method for Measuring the Thermal Conductivity of Living Tissues
Authors: Chen M. M. , Holmes K. R. , Rupinskas V.
Published: June 2009

The present communication presents a single microprobe technique for measuring tissue thermal properties based on the dissipation of a measured amount of energy and the observation of the resulting temperature rise a given time later. An advantage of this method is that the effective sampling volume can be varied by varying the measurement time. Using a measurement time of a few seconds, the sampling volume was estimated to be several orders of magnitude greater than the probe volume. Hence artifacts due to probe-induced trauma or stress would be insignificant. Additional advantages of the technique are: the results were independent of the probe shape, size and properties, and hence represents absolute measurements without the need for calibration; the required electronics and computations are simple; the determination of thermal conductivity requires only a single measurement; and comparison of data at different measurement times yields a clear and unequivocal indication of nonconductive contributions of heat transfer, if present.
Oscillatory Compressional Behavior of Articular Cartilage and Its Associated Electromechanical Properties
Authors: Lee R. C. , Frank E. H. , Grodzinsky A. J. , Roylance D. K.
Published: June 2009

The compressive stiffness of articular cartilage was examined in oscillatory confined compression over a wide frequency range including high frequencies relevant to impact loading. Nonlinear behavior was found when the imposed sinusoidal compression amplitude exceeded a threshold value that depended on frequency. Linear behavior was attained only by suitable control of the compression amplitude. This was enabled by real time Fourier analysis of data which provided an accurate assessment of the extent of nonlinearity. For linear viscoelastic behavior, a stiffness could be defined in the usual sense. The dependence of the stiffness on ionic strength and proteoglycan content showed that electrostatic forces between matrix charge groups contribute significantly to cartilage’s compressive stiffness over the 0.001 to 20 Hz frequency range. Sinusoidal streaming potentials were also generated by oscillatory compression. A theory relating the streaming potential field to the fluid velocity field is derived and used to interpret the data. The observed magnitude of the streaming potential suggests that interstitial fluid flow is significant to cartilage behavior over the entire frequency range. The use of simultaneous streaming potential and stiffness data with an appropriate theory appears to be an important tool for assessing the relative contribution of fluid flow, intrinsic matrix viscoelasticity, or other molecular mechanisms to energy dissipation in cartilage. This method is applicable in general to hydrated, charged polymers.
The Time and History-Dependent Viscoelastic Properties of the Canine Medial Collateral Ligament
Authors: Woo S. L.-Y. , Gomez M. A. , Akeson W. H.
Published: June 2009

The viscoelastic properties of the canine medial collateral ligament (MCL) were investigated. Stress-strain relationships at different strain rates, long-term stress relaxation and cyclic stress-strain curves of the MCL were obtained experimentally using a bone-MCL-bone preparation. The experimental data were used in conjunction with the quasi-linear viscoelastic theory as proposed by Fung [15] to characterize the reduced relaxation function, G(t) and elastic response σe (ε) of this tissue. It was found that the quasi-linear viscoelastic theory can adequately describe the time and history-dependent rheological properties of the canine medial collateral ligament.
H.R. Lissner Award Lecture - Bone and Bones
Authors: Evans F. G.
Published: June 2009

A brief review is given of some of the author’s biomechanical research carried out during the past 30 yr. Part of this research was done in collaboration with the late Professor Herbert R. Lissner, after whom the Bioengineering Award is named.
Properties and an Anisotropic Model of Cancellous Bone From the Proximal Tibial Epiphysis
Authors: Williams J. L. , Lewis J. L.
Published: June 2009

An investigation has been made of the source and magnitude of anisotropic material properties of cancellous bone in the proximal epiphysis of the human tibia. Results are reported for stiffness measurements made in three orthogonal directions on 21 cubes of cancellous bone before testing to failure along one of the three principal axes. The structure is approximately transversely isotropic. Strength and stiffness are linear with area fraction for loading along the isotropic axis. Strength is proportional to stiffness for all directions. A finite element model is proposed, based on experimental observations, which enables one to predict the elastic constants of cylindrically structured cancellous bone in the tibia from morphological measurements in the transverse plane.
A Comparison of Steady and Pulsatile Flow in Symmetrically Branched Tubes
Authors: Walburn F. J. , Stein P. D.
Published: June 2009

The purpose of this study was to compare the characteristics of flow in the region of symmetrical bifurcations having branch-to-trunk area ratios of 0.4, 0.8 and 1.2 during steady and pulsatile flow. Flow was visualized with neutrally bouyant particles. Secondary flow was not observed in the branches during either steady or pulsatile flow when the branch-to-trunk area ratio was 0.4. Secondary velocity patterns were not observed in the branches with branch-to-trunk area ratios of 0.8 and 1.2 during pulsatile flow, although they were observed during steady flow. It may be inaccurate, therefore, to characterize pulsatile flow at an instantaneous Reynolds number on the basis of steady flow at the same Reynolds number.
Kinematic Analysis and Simulation of Vertebral Motion Under Static Load—Part II: Simulation Study
Authors: Patwardhan A. G. , Soni A. H. , Sullivan J. A. , Gudavalli M. R. , Srinivasan V.
Published: June 2009

Based on the earlier work by the author on the development of a theoretical motion simulation model of an open-loop, kinematic chain, the present paper examines the motion characteristics of a human spine motion-segment. Based on the experimental data collected from the human cadaver specimens of lumbar spine, a static simulation model of a lumbar segment is proposed. The equivalent motion characteristic of the intervertebral joint is described by a spherical pair which is located for an intervertebral joint by fitting in a least-square sense a cone to a set of motion data describing the axode characteristics of the joint. The intevertebral disk and the ligaments are represented by an equivalent stiffness matrix whose elements are assumed to be constant over the entire range of mobility. The proposed model showed a good agreement with the observed motion data of an intervertebral joint.
A Note on the Application and Evaluation of the Buckle Transducer for Knee Ligament Force Measurement
Authors: Lewis J. L. , Lew W. D. , Schmidt J.
Published: June 2009

Knee ligament forces were directly measured with buckle transducers. Given a collection of buckle transducers with adequate rigidity and a variety of sizes to accommodate different ligamentous geometries, two potential problems remain when using the buckles: 1) impingement of the transducers with bone, producing a false output; 2) ligament shortening due to buckle installation, potentially altering the distribution of ligament forces around the knee. This report describes our current buckle transducer designs and installation procedures, and presents data which demonstrates that the errors due to ligament shortening and bone impingement can be assessed and reduced to acceptable levels.
Numerical Analysis of Blood Flow in the Vertebral Artery
Authors: Fukushima Takayoshi , Azuma Takehiko , Matsuzawa Teruo
Published: June 2009

Abnormal hemodynamic forces associated with distortions of blood vessel lumen have been thought to play an important role in the pathogenesis of focal vascular lesions. In the vertebral artery, segments located between osseous rings are ectatic compared with those surrounded by the rings. Based on the assumption that arterial blood flow was quasi-steady, this work was undertaken to investigate the structure of flow through arterial models with one or two sinusoidal stenoses. Numerical analysis was performed by an integral-momentum method. The validity of the method was examined by comparison of experimental data so far reported with theoretical results. Velocity and wall shear stress distributions were explored in a model with two stenoses simulating a part of the vertebral artery. The ectatic segments of the vertebral artery have been known as predilection sites for atherosclerotic lesions. The present study suggested that the ectatic wall was under unstable shear stresses, the direction of which was dependent upon the magnitude of the Reynolds number.
Predictive Engineering Formulations for Diver Heating
Authors: Johnson C. E. , Collins J. D.
Published: June 2009

Predictive heat transfer equations have been developed to estimate the local supplementary heating necessary to support a resting diver. These formulations consider the diver’s passive thermal protection in the form of a diving dress and the effects of his ambient environment upon the dress thermal resistance. The mathematical model performs a numerical analysis on discrete regions comprised of the skin, dry protective suit, breathing gas mixture and the surrounding fluid environment. The parametric properties associated with the heat transfer correlations were obtained from validated experimental heat flux and skin temperature data collected under specific environmental conditions. The supplementary heating required to maintain a diver is obtained by determining the heat flux that would be lost were he not heated and substracting from this the normal heat flux expected from a resting euthermic subject. Applying this principle to each of the regions, it is possible to predict the supplementary heating necessary to compensate for an excessiveflux.
A Study of the Effects of a Transversely Moving Boundary on Plane Posieuille Flow
Authors: Robertson J. M. , Clark M. E. , Cheng L. C.
Published: June 2009

Numerical (finite-difference) solutions in vorticity-stream function variables using a nonorthogonal geometric transform are found for viscous flow through a plane channel in which a portion of the boundary oscillates to change the flow. Calculations were made for three rates of inflow and for three frequencies of oscillation. The boundary pumpage relative to inflow decreased with inflow Karman number and with the oscillatory period of the boundary. The maximum shear stress, as indicated by the maximum vorticity, increased with Karman number and occurred when the boundary was in the maximum stenotic position. It did not change with boundary period except for the case when the period was the smallest. The channel pressure drop was significantly affected by the pumpage as well as the boundary nonuniformity.
Oscillatory Convective Dispersion in a Branching Tube Network
Authors: Tarbell J. M. , Ultman J. S. , Durlofsky L.
Published: June 2009

The axial dispersion of a nondiffusing dye in water during pure oscillatory flow (zero mean flow) in a five-generation branching tube network has been studied experimentally. The influence of stroke volume and frequency on an effective network dispersion coefficient has been determined for a range of conditions embracing both normal respiration and high-frequency ventilation in human lungs. The oscillatory convective dispersion mechanism results in large dispersion coefficients (on the order of 100–1000 cm2/s for human respiration conditions) with relatively strong dependence on the Reynolds number and weak dependence on the unsteadiness parameter.
Soft Tissue Strain and Facet Face Interaction in the Lumbar Intervertebral Joint—Part II: Calculated Results and Comparison With Experimental Data
Authors: Tencer A. F. , Mayer T. G.
Published: June 2009

A numerical simulation of soft-tissue strain and facet face interaction in the lumbar intervertebral joint under load was performed. The results, compared with a previous experimental sectioning study, showed that disk fiber strain was the main mechanism in shear resistance, except posterior shear, where the facets were main load bearing members. In axial compression, compression of the annulus was found, with a significant decrease in compressive strain resulting from annulus bulging, but no contact was found in the facet joints. The posterior ligaments, except for the facet capsules and ligamentum flavum, were found to be active only in flexion and lateral bending, while the facets and the disk both played major roles in resisting axial torsion moments.
In-Vitro Measurement of Static Pressure Distribution in Synovial Joints—Part II: Retropatellar Surface
Authors: Ahmed A. M. , Burke D. L. , Yu A.
Published: June 2009

This second part of a two-part paper is concerned with the measurement of static pressure distribution on the retropatellar surface. The study has been performed in a loading apparatus designed to simulate individually the lines of action and the magnitudes of the tensions in the components of the quadriceps femoris muscle group. Results have been obtained using 24 specimens in the knee flexion range 0 to 130 deg and employing a net quadriceps tension of 734 N. Particular emphasis has been placed on the evaluation of the sensitivity of the results to variations in the characteristics of the simulated quadriceps tension. The pressure distribution results have been interpreted in terms of variation of the normal force and the average contact stress on the retropatellar surface as a function of flexion angle. It has been shown that the “pulley” model of the patella consistently overestimates the actual patellofemoral joint reaction force throughout the range of flexion. Clinical implications of the results, in terms of etiology of degeneration of patellar cartilage, have been discussed.
Age-Dependent Influence of Strain Rate on the Tensile Failure of Rat-Tail Tendon
Authors: Haut R. C.
Published: June 2009

Sensitivity of tensile strength, failure strain, and failure energy density to strain rate was studied for rat-tail tendon (RTT), a collagen-rich connective tissue. Tendons from animals aged 1–27 months were stretched at a high (720 percent/s) and low (3.6 percent/s) strain rate. Each failure parameter increased with strain rate. However, the sensitivity of tendon failure to rate of strain decreased rapidly during growth and sexual maturation of the animal. The study provides basic data on the rate-sensitive strength of collagen fibers using RTT.
A Pressure Distribution Transducer for In-Vitro Static Measurements in Synovial Joints
Authors: Ahmed A. M.
Published: June 2009

The basic features and the performance characteristics of a transducer to measure in-vitro static pressure distribution at the articular interfaces of intact synovial joints are described. Pressure distribution is interpreted from the microindentation pattern left on a thin plastic material, the indenter and the plastic material having been subjected to load between the articular surfaces. The effects of the finite thickness and compliance of the transducer and the effects of the time-dependent response properties of the articular cartilage on the accuracy of measurement have been estimated by means of specific experiments and analyses.
In-Vitro Head and Neck Response to Impact
Authors: Kabo J. M. , Goldsmith W. , Harris N. M.
Published: June 2009

Two unembalmed and one embalmed human cadaveric head-neck systems were instrumented and subjected to central forehead impact of ballistically suspended 3.07-kg aluminum shell at velocities ranging from 50 to 345 cm/s. Occipital skull accelerations and disk pressures were measured by transducers, while the deformation of the system was determined by framing camera data. The results were found to be in accord with those from corresponding tests in artifical head-neck replica. Initial and terminal X-ray examination of the structure revealed no evidence of either skull or vertebral fractures.
In-Vitro Fluid Dynamic Characteristics of the Abiomed Trileaflet Heart Valve Prosthesis
Authors: Woo Yi-Ren , Williams F. P. , Yoganathan A. P.
Published: June 2009

The need for better and longer lasting trileaflet valves has led to the design and development of the Abiomed polymeric trileaflet valve prosthesis. In-vitro fluid dynamic studies on sizes 25 and 21 mm valves in the aortic position indicate an overall improvement in performance compared to the Carpentier-Edwards and Ionescu-Shiley tissue valves in current clinical use. The pressure drop studies yielded effective orifice areas of 1.99 and 1.54 cm2, and performance indices of 0.41 and 0.45 for the Nos. 25 and 21 valves, respectively. Leaflet photography studies indicated that the two valve sizes had maximum opening areas of 225 and 145 mm2, respectively, at a normal resting cardiac output. Steady and pulsatile flow velocity measurements with a laser-Doppler anemometer (LDA) system indicate that the flow field downstream of the Abiomed valve is jetlike and turbulent. Maximum mean square axial velocity fluctuations of 55 and 83 cm/s, and turbulent shear stresses of 220 and 450 N/m2 were measured in the immediate vicinity of the nos. 25 and 21 valves, respectively. The Abiomed valves studied had been originally configured for use in valved conduits, and it is therefore our opinion that further improvements can be made to the valve and stent design, which would enhance its fluid dynamic performance.
Tribological Behavior of Plasma Nitrided 1Cr18Ni9Ti Austenitic Stainless Steel Under the Effect of Lubricant Additives
Authors: Fang Jian , Xia Yanqiu , Lin Yimin , Liu Weimin
Published: June 2009

To expand the engineering application of stainless steel as tribological material, it is important to study the tribological interaction of the nitrided layer with lubricating additives. The friction and wear properties of plasma nitrided 1Cr18Ni9Ti stainless steel were investigated under lubricated conditions on an Optimol Schwinyung Reibung Versch oscillating friction and wear tester. The lubrication oil was 1,1,1-trihydroxymethylpropyl trioctoate containing zinc dibutyl dithiophosphate, bismuth dibutyl dithiophosphate, and bismuth N, N-dibutyldithiocarbamate as the antiwear and extreme pressure additives. The variations in the nitrided stainless steel and the unnitrided one under the tribological action of the additives were contrasted and the tribological chemical interaction between the nitrided layer and the additives was revealed. The results showed that the selected additives had good synergetic effect with the nitrided layer on tribological performance and the bismuth containing additive had better friction-reducing and antiwear abilities than the zinc containing additive. Meanwhile, under the effect of these additives, the N/(Fe+Cr) ratio rose and the Fe/Cr ratio decreased in the nitrided layer, while the Fe/Cr ratio in the unnitrided stainless steel varied little. Three main elements, N, Cr, and Fe, in nitrided layer had different actions with the additives and contributed to tribological performance by different methods.
An Efficient FE Analysis for Complex Low Flying Air-Bearing Slider Designs in Hard Disk Drives—Part I: Static Solution
Authors: Bhargava Puneet , Bogy David B.
Published: June 2009

Prediction of the steady state flying height and attitude of air-bearing sliders in hard disk drives via simulations is the basis of their design process. Over the past few years air-bearing surfaces have become increasingly complex incorporating deep etches and steep wall profiles. In this paper we present a novel method of solving the inverse problem for air-bearing sliders in hard disk drives that works well for such new designs. We also present a new method for calculating the static air-bearing stiffness by solving three linear systems of equations. The formulation is implemented, and convergence studies are carried out for the method. Mesh refinements based on flux jumps and pressure gradients are found to work better than those based on other criteria.
The Role of Fluid Mechanics in Atherogenesis
Authors: Nerem R. M. , Cornhill J. F.
Published: June 2009

A specialists meeting on “The Role of Fluid Mechanics in Atherogenesis” was held August 24–25, 1978, at The Ohio State University. This meeting was a followup to a similar meeting held in 1974 [1, 2]. The present status of our knowledge of the importance of fluid mechanics in the initiation and progression of arterial lesions is summarized on the basis of the experimental data presented at the meeting; no attempt is made to provide a comprehensive review of the relevant literature. Three basic aspects are addressed: firstly, the localization of arterial lesions; secondly, the local hemodynamics of arterial segments with a high predilection to the development of lesions; and thirdly, the interaction of hemodynamic factors with the arterial wall. The many unresolved questions, apparently conflicting experimental data and areas in need of future research on the role of fluid mechanics in atherogenesis are identified specifically.
Load Elongation Behavior of the Canine Anterior Cruciate Ligament
Authors: Dorlot J.-M. , Ait Ba Sidi M. , Tremblay G. M. , Drouin G.
Published: June 2009

This paper describes the results of an investigation on the mechanical properties of canine anterior cruciate ligaments. A total of 38 ligaments were tested. It is shown that the completely reversible (elastic) range of strain is limited to 14 percent elongation, corresponding to an applied load of 200 N. Within this range each specimen was tested at different strain rates varying from 0.12 percent/s to 220 percent/s and it is demonstrated that the mechanical behavior of the ligaments is not sensitive to strain rate in the range investigated. After completion of tests in the reversible range, of strain ten ligaments were frozen and similar tests were performed after thawing. It is shown that freezing produces alterations of the mechanical properties. The ligaments become more rigid than when they are tested in fresh conditions. From room temperature up to 45C, the load-elongation relationship is not significantly dependent upon test temperature.
Protein Kinase G Is Required for Intrinsic Antibiotic Resistance in Mycobacteria
Authors: Wolff Kerstin A. , Nguyen Hoa T. , Cartabuke Richard H. , Singh Ajay , Ogwang Sam , Nguyen Liem
Published: June 2009

Antibiotic resistance and virulence of pathogenic mycobacteria are phenotypically associated, but the underlying genetic linkage has not been known. Here we show that PknG, a eukaryotic-type protein kinase previously found to support survival of mycobacteria in host cells, is required for the intrinsic resistance of mycobacterial species to multiple antibiotics.
Target Analysis of the Experimental Measles Therapeutic AS-136A
Authors: Yoon Jeong-Joong , Krumm Stefanie A. , Ndungu J. Maina , Hoffman Vanessa , Bankamp Bettina , Rota Paul A. , Sun Aiming , Snyder James P. , Plemper Richard K.
Published: June 2009

No effective therapeutic is currently in place for improved case management of severe measles or the rapid control of outbreaks. Through high-throughput screening, we recently identified a novel small-molecule class that potently blocks activity of the measles virus (MeV) RNA-dependent RNA polymerase (RdRp) complex in transient replicon assays. However, the nature of the block in RdRp activity and the physical target of the compound remained elusive. Through real-time reverse transcription-PCR analysis, we demonstrate that the lead compound AS-136A blocks viral RNA synthesis in the context of an infection. Adaptation of different MeV strains to growth in the presence of the compound identified three candidate hot spots for resistance that are located in conserved domains of the viral polymerase (L protein) subunit of the RdRp complex. Rebuilding of individual mutations in RdRp-driven reporter assays and recombinant MeV traced the molecular basis for resistance to specific mutations in L. Mutations responsible for resistance cluster in the immediate vicinity of the proposed catalytic center for phosphodiester bond formation and neighboring conserved domains of L, providing support for effective inhibition of a paramyxovirus RdRp complex through interaction of a nonnucleoside small-molecule inhibitor with the L protein. Resistance mutations are located in regions of L that are fully conserved among viral isolates, and recombinant MeV harboring individual resistance mutations show some delay in the onset of viral growth in vitro. Taken together, these data support the hypothesis that acquiring mutations in these L domains may reduce virus fitness.
Multiresistance in
Pasteurella multocida
Is Mediated by Coexistence of Small Plasmids
Authors: San Millan Alvaro , Escudero Jose Antonio , Gutierrez Belen , Hidalgo Laura , Garcia Nerea , Llagostera Montserrat , Dominguez Lucas , Gonzalez-Zorn Bruno
Published: June 2009

In most gram-negative bacteria, acquired multiresistance is conferred by large plasmids compiling numerous antimicrobial resistance genes. Here, we show an evolutionary alternative strategy used by
Pasteurella multocida
to become resistant to multiple clinically relevant antibiotics. Thirteen β-lactam-resistant clinical isolates, concomitantly resistant to tetracyclines and/or streptomycin as well as to sulfonamides, were studied. Pulsed-field gel electrophoresis analysis revealed different profiles among the isolates, showing that clonal dissemination was not the sole event responsible for the spread of multiresistance. Each
P. multocida
strain carried two or three small plasmids between 4 and 6 kb in size. A direct association between resistance profile and plasmid content was found. Complete nucleotide sequencing of all plasmids revealed seven different replicons, six of them belonging to the ColE1 superfamily. All plasmids carried one, or a maximum of two, antimicrobial resistance determinants. Plasmids pB1000 and pB1002 bore
bla
ROB-1
, pB1001 carried
tet
(B), pB1003 and pB1005 carried
sul2
and
strA
, pB1006 harbored
tet
(O), and p9956 bore the
tet
(H) gene. All plasmids except pB1002 and pB1006 were successfully transformed into
Escherichia coli
. pB1000, also involved in β-lactam resistance in
Haemophilus parasuis
(A. San Millan et al., Antimicrob. Agents Chemother. 51:2260-2264, 2007), was mobilized in
E. coli
using the conjugation machinery of an IncP plasmid. Stability experiments proved that pB1000 was stable in
P. multocida
but highly unstable in
E. coli
. In conclusion,
bla
ROB-1
is responsible for β-lactam resistance in
P. multocida
in Spain. Coexistence and the spread of small plasmids are used by
P. multocida
to become multiresistant.
Proteomic Investigation of the Time Course Responses of RAW 264.7 Macrophages to Infection with
Salmonella enterica
Authors: Shi Liang , Chowdhury Saiful M. , Smallwood Heather S. , Yoon Hyunjin , Mottaz-Brewer Heather M. , Norbeck Angela D. , McDermott Jason E. , Clauss Therese R. W. , Heffron Fred , Smith Richard D. , Adkins Joshua N.
Published: June 2009

To investigate the extent to which macrophages respond to
Salmonella
infection, we infected RAW 264.7 macrophages with
Salmonella enterica
serotype Typhimurium and analyzed macrophage proteins at various time points following infection by using a global proteomic approach. A total of 1,006 macrophage and 115
Salmonella
proteins were identified with high confidence. Most of the
Salmonella
proteins were observed in the late stage of the infection time course, which is consistent with the fact that the bacterial cells proliferate inside RAW 264.7 macrophages. The peptide abundances of most of the identified macrophage proteins remained relatively constant over the time course of infection. Compared to those of the control, the peptide abundances of 244 macrophage proteins (i.e., 24% of the total identified macrophage proteins) changed significantly after infection. The functions of these
Salmonella
-affected macrophage proteins were diverse, including production of antibacterial nitric oxide (i.e., inducible nitric oxide synthase), production of prostaglandin H
2
(i.e., cyclooxygenase 2), and regulation of intracellular traffic (e.g., sorting nexin 5 [SNX5], SNX6, and SNX9). Diverse functions of the
Salmonella
-affected macrophage proteins demonstrate a global macrophage response to
Salmonella
infection. Western blot analysis not only confirmed the proteomic results for a selected set of proteins but also revealed that (i) the protein abundance of mitochondrial superoxide dismutase increased following macrophage infection, indicating an infection-induced oxidative stress in mitochondria, and (ii) in contrast to infection of macrophages by wild-type
Salmonella
, infection by the
sopB
deletion mutant had no negative impact on the abundance of SNX6, suggesting a role for SopB in regulating the abundance of SNX6.
Suppression of a Novel Hematopoietic Mediator in Children with Severe Malarial Anemia
Authors: Keller Christopher C. , Ouma Collins , Ouma Yamo , Awandare Gordon A. , Davenport Gregory C. , Were Tom , Hittner James B. , Vulule John M. , Ong'echa John M. , Perkins Douglas J.
Published: June 2009

In areas of holoendemicPlasmodium falciparumtransmission, severe malarial anemia (SMA) is a leading cause of pediatric morbidity and mortality. Although many soluble mediators regulate erythropoiesis, it is unclear how these factors contribute to development of SMA. Investigation of novel genes dysregulated in response to malarial pigment (hemozoin [PfHz]) revealed that stem cell growth factor (SCGF; also called C-type lectin domain family member 11A [CLEC11A]), a hematopoietic growth factor important for development of erythroid and myeloid progenitors, was one of the most differentially expressed genes. Additional experiments with cultured peripheral blood mononuclear cells (PBMCs) demonstrated that PfHz decreased SCGF/CLEC11A transcriptional expression in a time-dependent manner. Circulating SCGF levels were then determined for Kenyan children (n= 90; aged 3 to 36 months) presenting at a rural hospital with various severities of malarial anemia. SCGF levels in circulation (P= 0.001) and in cultured PBMCs (P= 0.004) were suppressed in children with SMA. Circulating SCGF also correlated positively with hemoglobin levels (r= 0.241;P= 0.022) and the reticulocyte production index (RPI) (r= 0.280;P= 0.029). In addition, SCGF was decreased in children with reduced erythropoiesis (RPI of <2) (P< 0.001) and in children with elevated levels of naturally acquired monocytic PfHz (P= 0.019). Thus, phagocytosis of PfHz promotes a decrease in SCGF gene products, which may contribute to reduced erythropoiesis in children with SMA.
Vaginal Microbiota of Women with Frequent Vulvovaginal Candidiasis
Authors: Zhou Xia , Westman Rachel , Hickey Roxana , Hansmann Melanie A. , Kennedy Colleen , Osborn Thomas W. , Forney Larry J.
Published: June 2009

Vulvovaginal candidiasis (VVC) is an insidious infection that afflicts a large proportion of women of all ages, and 5 to 8% of affected women experience recurrent VVC (RVVC). The aim of this study was to explore the possible importance of vaginal bacterial communities in reducing the risk of RVVC. The species composition and diversity of microbial communities were evaluated for 42 women with and without frequent VVC based on profiles of terminal restriction fragment polymorphisms of 16S rRNA genes and phylogenetic analysis of cloned 16S rRNA gene sequences from the numerically dominant microbial populations. The data showed that there were no significant differences between the vaginal microbial communities of women in the two groups (likelihood score, 5.948; bootstrap
P
value, 0.26). Moreover, no novel bacteria were found in the communities of women with frequent VVC. The vaginal communities of most women in both groups (38/42; 90%) were dominated by species of
Lactobacillus
. The results of this study failed to provide evidence for the existence of altered or unusual vaginal bacterial communities in women who have frequent VVC compared to women who do not have frequent VVC. The findings suggest that commensal vaginal bacterial species may not be able to prevent VVC.
Night work, long working hours, psychosocial work stress and cortisol secretion in mid-life: evidence from a British birth cohort
Authors: Thomas C , Hertzman C , Power C
Published: June 2009

Objectives:

To examine the relationships between exposure to workplace factors (night work, extended working hours, psychosocial work stress) and cortisol secretion, and to test whether workplace factors interact, resulting in combined effects.

Methods:

Multiple linear and logistic regression was used to test relationships between workplace factors and cortisol secretion in the 1958 British birth cohort at 45 years. Salivary cortisol was measured twice on the same day to capture the post-waking decline, facilitating the analysis of different cortisol patterns: (1) time 1 (T1, 45 minutes post-waking); (2) time 2 (T2, 3 h after T1); (3) average 3 h exposure from T1 to T2 cortisol; and (4) T1 to T2 change. To identify altered diurnal cortisol patterns we calculated: (1) flat T1–T2 change in cortisol; (2) top 5% T1; (3) bottom 5% T1; and (4) T1 hypo-secretion or hyper-secretion. Models were adjusted for socioeconomic position at birth and in adulthood, qualifications, marital status, dependent children, and smoking status.

Results:

25% of men and 8% of women were exposed to >1 workplace factor (night work, extended work hours, job strain). Night work was associated with a 4.28% (95% CI 1.21 to 7.45) increase in average 3 h cortisol secretion independently of job strain or work hours. Night workers not exposed to job strain had elevated T1 cortisol (5.81%, 95% CI 1.61 to 10.19), although for T2 cortisol it was night workers exposed to low job control who had elevated levels (11.72%, 95% CI 4.40 to 19.55). Men (but not women) working >48 h/week had lower average 3 h cortisol secretion (4.55%, 95% CI −8.43 to −0.50). There were no main effects for psychosocial work stress. All associations for T2 and average 3 h cortisol secretion weakened slightly after adjustment for confounding factors, but associations for T1 cortisol were unaffected by adjustment.

Conclusions:

Our study suggests that night work in particular is associated with elevated cortisol secretion and that cortisol dysregulation may exist in subgroups with specific combinations of stressors.
A prospective cohort study of exposure-response relationship for vibration-induced white finger
Authors: Bovenzi M
Published: June 2009

Objectives:

To investigate prospectively the relation between vibration-induced white finger (VWF) and measures of cumulative (lifetime) exposure to hand-transmitted vibration (HTV).

Methods:

Two hundred and forty-nine HTV workers and 138 control men of the same companies participated in a 3-year follow-up study. The diagnosis of VWF (Raynaud’s phenomenon in the controls) was based on the medical history, the administration of colour charts and the results of a cold test. Tool vibration magnitudes were expressed as root-mean-square (r.m.s.) acceleration, frequency-weighted according to international standard ISO 5349-1 and also unweighted over the frequency range 6.3–1250 Hz. From the vibration magnitudes and exposure durations, alternative measures of cumulative vibration dose were calculated for each HTV worker, according to the expression: dose  =  Σaimti, whereaiis the acceleration magnitude on tooli,tiis the lifetime exposure duration (hours) for tooli, andm =  0, 1, 2 or 4.

Results:

The incidence of VWF varied from 5 to 6% in the HTV workers versus 0 to 1.5% for Raynaud’s phenomenon in the controls. After adjusting for potential confounders, measures of cumulative vibration dose derived from total operating hours and high powers of unweighted acceleration (ie,, withm>1) gave better predictions of the occurrence of VWF than dose measures calculated from frequency-weighted acceleration (ie,). These findings were observed in the entire sample of HTV workers, in those with no VWF at the initial investigation, and in those with normal cold test results at baseline.

Conclusions:

This prospective cohort study suggests that measures of cumulative vibration doses constructed from unweighted r.m.s. acceleration perform better for the prediction of VWF than dose measures calculated according to the recommendations of current standards. These findings should contribute to the improvement of the ISO frequency weighting for evaluating the severity of hand-transmitted vibration.
PARAMETER ESTIMATION OF SCHOTTKY-BARRIER DIODE MODEL BY PARTICLE SWARM OPTIMIZATION
Authors: WANG KAIER , YE MEIYING
Published: June 2009

This paper presents particle swarm optimization (PSO) method to solve the parameter estimation problem of the Schottky-barrier diode model. Based on the synthetic and experimental data, we have demonstrated that the proposed method has high parameter estimation accuracy. Besides, the initial guesses for the model parameter values are not required in the PSO method. Also, the performance of the PSO method is compared with that of the genetic algorithm (GA) method. The results indicate that the PSO method outperforms the binary-coded and real-coded GA methods in terms of estimation accuracy and computation efficiency.
A MODIFIED CELLULAR AUTOMATON MODEL FOR RING ROAD TRAFFIC WITH VELOCITY GUIDANCE
Authors: MEI C. Q. , HUANG H. J. , TANG T. Q.
Published: June 2009

We present a modified cellular automaton model to study the traffic flow on a signal controlled ring road with velocity guidance. The velocity guidance is such a strategy that when vehicles approach the traffic light, suggested velocities are provided for avoiding the vehicles' sharp brakes in front of red light. Simulation results show that this strategy may significantly reduce the vehicles' stopping rate and the effect size is dependent upon the traffic density, the detector position, the signal's cycle time and the obedience rate of vehicles to the guidance.
ANALYSIS OF CRITICAL SHORT-TIME LANGEVIN DYNAMICS IN TWO-DIMENSIONAL ϕ4 THEORY ON THE BASIS OF A HIGHER-ORDER ALGORITHM
Authors: OTOBE TSUYOSHI , NAKAZATO HIROMICHI , OKANO KEISUKE , YUASA KAZUYA , HATTORI NOZOMU
Published: June 2009

We investigate the critical short-time scaling of the two-dimensional lattice ϕ4 field theory with a Langevin dynamics. Starting from a "hot" initial configuration but with a small magnetization, the critical initial increase of the magnetization is observed, through which we determine the critical point. From the short-time relaxation dynamics of various quantities at the critical point obtained, the dynamic critical exponents θ, z and the static exponent β/ν are evaluated. In executing a Langevin simulation, an appropriate discretization method with respect to the time degree of freedom becomes essentially important to be adopted and we show that the well-known second-order form of discretized Langevin equation works well to investigate the short-time dynamics.
A FREEZING FERROMAGNETIC MOMENT MODEL FOR EXCHANGE BIAS IN α-Fe2O3 NANOLEAVES
Authors: XU YING-YING , DONG ZHAO , ZHANG XIONG-JIAN , JIN WEN-TAO , KASHKAROV PAVEL , ZHANG HAN
Published: June 2009

We propose a freezing ferromagnetic moment model to explain the exchange bias discovered in α- Fe 2 O 3 antiferromagnetic nanoleaves most recently. The model assumes that in the antiferromagnetic nanosystem, the disorder surface spins are frozen at low temperature along magnetic filed direction, forming a ferromagnetic layer. Then this frozen ferromagnetic surface state couples with the inside antiferromagnetic layers that results in an exchange bias. After some proper simplification, we get the magnetization at different applied field by the minimal energy calculation using MATLAB. Our model computerizing indicates the exchange bias shift of the magnetization curve is -48.2 Oe for n = 100 antiferromagnetic layers, which matches the observed value very well.
SCALING PROPERTIES OF AN EVOLVING NETWORK MODEL WITH AGING MECHANISM
Authors: YANG RENHUAN , SONG AIGUO
Published: June 2009

In this paper, a growing network model with aging mechanism is investigated. Each new node of the network gets attached to the ith existing node with the probability [Formula: see text], where ki is the degree of the ith node and τi is its age at time t. β denotes attraction factor and α represents aging intensity. It is found that the network shows scaling behaviors such as scale-free and exponential distribution of degree. Moreover, the phase diagram in the β - α plane is observed, in which there are three regions plotted by two boundaries.
DISTRIBUTED LEARNING OF EQUILIBRIA IN A ROUTING GAME
Authors: Barth Dominique , Cohen Johanne , Bournez Olivier , Boussaton Octave
Published: June 2009

We focus on the problem of learning equilibria in a particular routing game similar to the Wardrop traffic model. We describe a routing game played by a large number of players and present a distributed learning algorithm that we prove to converge weakly to equilibria for the system. The proof of convergence is based on a differential equation governing the global evolution of the system that is inferred from all the local evolutions of the agents in play. We prove that the differential equation converges with the help of Lyapunov techniques.
COMPUTATIONS AND DECIDABILITY OF ITERATIVE ARRAYS WITH RESTRICTED COMMUNICATION
Authors: KUTRIB MARTIN , MALCHER ANDREAS
Published: June 2009

Iterative arrays (IAs) are linear arrays of interconnected interacting finite state machines, where one distinguished one is equipped with a one-way read-only input tape. We investigate IAs operating in real time whose inter-cell communication is bounded by a constant number of bits not depending on the number of states. Their capabilities are considered in terms of syntactical pattern recognition. It is known [17] that such devices can recognize rather complicated sets of unary patterns with a minimum amount of communication, namely one-bit communication. Some examples are the sets {a2n | n ≥ 1}, {an2 | n ≥ 1}, and {ap | p is prime}. Here, we consider non-unary patterns and it turns out that the non-unary case is quite different. We present several real-time constructions for certain non-unary syntactical patterns. For example, the sets {anbn | n ≥ 1}, {anbncn | n ≥ 1}, {an(bn)m | n, m ≥ 1}, and {anbamb(ba)n·m | n, m ≥ 1} are recognized in real time by IAs. Moreover, it is shown that real-time one-bit IAs can, in some sense, add and multiply integer numbers. Furthermore, decidability questions of communication restricted IAs are dealt with. Due to the constructions provided, undecidability results can be derived. It turns out that emptiness is still not even semidecidable for one-bit IAs despite their restricted communication. Moreover, also the questions of finiteness, infiniteness, inclusion, and equivalence are non-semidecidable.
A 1D CELLULAR AUTOMATON THAT MOVES PARTICLES UNTIL REGULAR SPATIAL PLACEMENT
Authors: MAIGNAN LUIDNEL , GRUAU FRÉDÉRIC
Published: June 2009

We consider a finite cellular automaton with particles where each site can host at most one particle. Starting from an arbitrary initial configuration, our goal is to move the particles between neighbor sites until the distance to the nearest particle is minimized globally. Such a configuration corresponds in fact to a regular placement. This problem is a cellular automata equivalent of load-balancing in parallel computing, where each task is a particle and each processor a connected set of sites. We present a cellular automata rule that solves this problem in the 1D case, and is convergent, i.e. once the regular placement is achieved, the configuration does not change anymore. The rule is inspired from the Lloyd algorithm, computing a centroidal Voronoi tessellation. The dynamic of the rule is described at a higher level, using self-explanatory space-time diagrams. They exhibit signals acting as quantity of movement carrying the energy of system. Each signal bounces or pass through particles, causing their movement, until it eventually reaches the border and vanishes. When signals have all vanished, particles are regularly placed.
A FAMILY OF DISCRETE INTEGRABLE COUPLING SYSTEMS AND ITS LIOUVILLE INTEGRABILITY
Authors: XU XI-XIANG , YANG HONG-XIANG
Published: June 2009

A discrete matrix spectral problem and corresponding family of discrete integrable systems are discussed. A semi-direct sum of Lie algebras of four-by-four matrices is introduced, and the related integrable coupling systems of resulting discrete integrable systems are derived. The obtained discrete integrable coupling systems are all written in their Hamiltonian forms by the discrete variational identity. Finally, Liouville integrability of the family of obtained integrable coupling systems is demonstrated.
ACOUSTIC BAND GAPS TUNED BY TRANSLATION GROUP SYMMETRY IN TWO-DIMENSIONAL PERIODIC COMPOSITES
Authors: MU ZHONGFEI , WU FUGEN
Published: June 2009

The acoustic band structures of two kinds of acoustic crystals (two-dimensional periodic arrays of rigid solid rods embedded in air with two different configurations) have been studied by the plane-wave expansion (PWE) method based on super cell calculation. The translation group symmetry of the acoustic crystal is changed by changing the area of the cross section of adjacent rods. We found that by changing the translation group symmetry, one can effectively adjust the acoustic band gaps (ABGs). In the case that the cross section of scattering rods is square without any rotation, the decrease of translation group symmetry is advantaged to form ABGs. But when the cross section of scattering rods is square with a rotation of 45°, the decrease of translation group symmetry is disadvantaged to form ABGs.
SYNCHRONIZATION AND GENERALIZED SYNCHRONIZATION OF FRACTIONAL ORDER CHAOTIC SYSTEMS
Authors: WANG XING-YUAN , ZHANG JING
Published: June 2009

In this paper, based on the modified state observer method, synchronization and generalized synchronization of a class of fractional order chaotic systems are presented. The two synchronization approaches are theoretically and numerically studied and two simple criterions are proposed. By using the stability theory of linear fractional order systems, suitable conditions for achieving synchronization and generalized synchronization are given. Numerical simulations coincide with the theoretical analysis.