bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Habitat Loss and Fragmentation on Population Dynamics
Authors: WIEGAND THORSTEN , REVILLA ELOY , MOLONEY KIRK A.
Published: January 2005

Abstract:  We used a spatially explicit population model that was generalized to produce nine ecological profiles of long‐lived species with stable home ranges and natal dispersal to investigate the effects of habitat loss and fragmentation on population dynamics. We simulated population dynamics in landscapes composed of three habitat types (good‐quality habitat ranging from 10–25%, poor‐quality habitat ranging from 10–70%, and matrix). Landscape structures varied from highly fragmented to completely contiguous. The specific aims of our model were (1) to investigate under which biological circumstances the traditional approach of using two types only (habitat and matrix) failed and assess the potential impact of restoring matrix to poor‐quality habitat, (2) to investigate how much of the variation in population size was explained by landscape composition alone and which key attributes of landscape structure can serve as predictors of population response, and (3) to estimate the maximum fragmentation effects expressed in equivalent pure loss of good‐quality habitat. Poor‐quality habitat mattered most in situations when it was generally not considered (i.e., for metapopulations or spatially structured populations when it provides dispersal habitat). Population size increased up to 3 times after restoring matrix to poor‐quality habitat. Overall, habitat amount accounted for 68% of the variation in population size, whereas ecological profile and fragmentation accounted for approximately 13% each. The maximal effect of (good‐quality) habitat fragmentation was equivalent to a pure loss of up to 15% of good‐quality habitat, and the maximal loss of individuals resulting from maximal fragmentation reached 80%. Abundant dispersal habitat and sufficiently large dispersal potential, however, resulted in functionally connected landscapes, and maximal fragmentation had no effect at all. Our findings suggest that predicting fragmentation effects requires a good understanding of the biology and habitat use of the species in question and that the uniqueness of species and the landscapes in which they live confound simple analysis.
Increasing the Accuracy of Productivity and Survival Estimates in Assessing Landbird Population Status
Authors: ANDERS ANGELA D. , MARSHALL MATTHEW R.
Published: January 2005

Abstract:  The conservation of species with declining populations requires information on population demography and identification of factors that limit population growth. For landbird species, an understanding of large‐scale population declines often requires assessment of local population processes, including the production of offspring, the survival of those offspring, and adult survival. Population growth has been modeled for several species of landbirds to date, and these studies have provided important information on relationships between population status and population‐limiting factors. Several recent studies have illuminated field methods and analytical techniques that can aid in increasing the accuracy of productivity and survival estimates for population models. We reviewed these methods and recommend their implementation, including quantification of the season‐long productivity of individuals, collection of empirical data on juvenile survival during the postfledging and overwintering periods, and incorporation of adult breeding dispersal into annual adult survival estimates. Such methods will allow for more accurate assessment of population status and provide a better understanding of the factors on which to focus our conservation efforts.
Conservation Genetics of Potentially Endangered Mutualisms: Reduced Levels of Genetic Variation in Specialist versus Generalist Bees
Authors: PACKER LAURENCE , ZAYED AMRO , GRIXTI JENNIFER C. , RUZ LUISA , OWEN ROBIN E. , VIVALLO FELIPE , TORO HAROLDO
Published: January 2005

Abstract: Oligolectic bees collect pollen from one or a few closely related species of plants, whereas polylectic bees visit a variety of flowers for pollen. Because of their more restricted range of host plants, it maybe expected that specialists exist in smaller, more isolated populations, with lower effective population sizes than generalists. Consequently, we hypothesized that oligolectic bees have reduced levels of genetic variation relative to related polylectic species. To test this hypothesis, we used five phylogenetically independent pairs of species in which one member was oligolectic and the other was polylectic. We assayed genetic variation in our species pairs at an average of 32 allozyme loci. Within each species pair, the oligolectic member had fewer polymorphic loci, lower average allelic richness, and lower average expected heterozygosity than its polylectic relative. Averaged over all species pairs, this corresponds to a 21% reduction in allelic richness, a 72% reduction in the proportion of polymorphic loci, and an 83% reduction in expected heterozygosity in specialists compared with generalists. Our data support the hypothesis of reduced effective population size in oligolectic bees and suggest that they may be more prone to extinction as a result. We suggest that in instances in which bee specialists are involved in mutually codependent relationships with their floral hosts, these mutualisms may be endangered for genetic and ecological reasons.
Primary Annular Plaque‐Type Psoriasis
Authors: Guill Carrie Lynn , Hoang Mai P. , Carder K. Robin
Published: January 2005

Abstract:  We described two adolescent girls with untreated, consistently annular, plaque‐type psoriasis without pustules, a presentation that is to our knowledge, not previously described. No typical confluent plaque‐type lesions were present. The plaques in our patients resembled other entities such as tinea corporis and erythema annulare centrifugum, given the erythematous, scaling borders and central clearing. Biopsy specimens from our patients showed features characteristic of psoriasis vulgaris. Both patients responded to combination therapy with calcipotriene and a mid‐potency steroid. We conclude that primary annular plaque‐type psoriasis shares features of both typical plaque‐type and annular pustular psoriasis, suggesting that these entities represent a spectrum of psoriatic disease.
Blood collection and transfusion in the United States in 1999
Authors: Sullivan Marian T. , Wallace Edward L.
Published: January 2005

BACKGROUND:  Collection, processing, and transfusion of blood and blood components in the US in 1999 were measured and compared with prior years.

STUDY DESIGN AND METHODS:  Questionnaires were completed by 2040 blood centers and hospitals. Statistical procedures were used to verify the representativeness of the sample and to estimate national totals.

RESULTS:  The total US blood supply in 1999 was 13,876,000 units (before testing), 10.1 percent greater than in 1997. It included 13,109,000 allogeneic units, 651,000 autologous units, and 116,000 red cell (RBC) units collected by apheresis. Transfusion of whole blood and RBCs increased by 7.6 percent to 12,389,000 units. Platelet (PLT) transfusions totaled 9,052,000 PLT concentrate equivalent units, of which 66.5 percent were PLTs from apheresis. In comparison with 1997, the total number of PLT units transfused was unchanged, whereas single‐donor PLT units transfused increased by 6.7 percent and the transfusion of PLTs from whole blood (PLT concentrates) declined by 10.6 percent (a difference of approximately 400,000 units in each case).

CONCLUSIONS:  The margin between transfusion demand and the total allogeneic supply in 1999 was 1,203,000 units, 9.1 percent of the supply. By comparison, the margin in 1997 was 7.2 percent, whereas in 1989 it was 13.8 percent. Similarly, the rate of blood collection in 1999 per 1000 population was 11.9 percent higher than the 1997 rate. During the same period, however, the rate of transfusion per 1000 population increased by 5.8 percent. Risk in the future lies primarily in the increasing demand for RBCs and further shrinkage of the supply‐and‐demand margin.
Understanding Canadian student motivations and beliefs about giving blood
Authors: Hupfer M.E. , Taylor D.W. , Letwin J.A.
Published: January 2005

BACKGROUND:  A better understanding of Canadian blood donor beliefs and motivations is needed to develop targeted interventions. Recruiters must know how motivation variables and correlation patterns differ with donor experience and sex.

STUDY DESIGN AND METHODS:  Data addressing reasons for donating, statements about the blood supply, beliefs about donation consequences, and reasons for avoiding donation were collected from 450 undergraduates. Principal components analysis was used to investigate the underlying factorial structure of each domain. Men‐women and donor‐nondonor differences were explored with multivariate analysis of variance techniques.

RESULTS:  A bivariate model better represented donor beliefs than did a bipolar conceptualization. Negative beliefs distinguished donors and nondonors more so than did positive factors. Altruism dominated reasons for donating, whereas logistic factors accounted for the most variance in donation avoidance. Women were more concerned about adverse physical consequences, and nondonors expressed higher levels of groundless donation‐related fears.

CONCLUSION:  Recruiters should consider the sex and donation experience of targets when they develop recruitment and retention strategies. Education programs aimed at overcoming fears and heightening awareness of need are recommended, as are operational improvements aimed at reducing barriers posed by time and inconvenience.
Slip-Rate Measurements on the Karakorum Fault May Imply Secular Variations in Fault Motion
Authors: Chevalier M.-L. , Ryerson F. J. , Tapponnier P. , Finkel R. C. , Van Der Woerd J. , Haibing Li , Qing Liu
Published: January 2005

Beryllium-10 surface exposure dating of offset moraines on one branch of the Karakorum Fault west of the Gar basin yields a long-term (140- to 20-thousand-year) right-lateral slip rate of ∼10.7 ± 0.7 millimeters per year. This rate is 10 times larger than that inferred from recent InSAR analyses (∼1 ± 3 millimeters per year) that span ∼8 years and sample all branches of the fault. The difference in slip-rate determinations suggests that large rate fluctuations may exist over centennial or millennial time scales. Such fluctuations would be consistent with mechanical coupling between the seismogenic, brittle-creep, and ductile shear sections of faults that reach deep into the crust.
Cardiovascular Risk Factors Emerge After Artificial Selection for Low Aerobic Capacity
Authors: Wisløff Ulrik , Najjar Sonia M. , Ellingsen Øyvind , Haram Per Magnus , Swoap Steven , Al-Share Qusai , Fernström Mats , Rezaei Khadijeh , Lee Sang Jun , Koch Lauren Gerard , Britton Steven L.
Published: January 2005

In humans, the strong statistical association between fitness and survival suggests a link between impaired oxygen metabolism and disease. We hypothesized that artificial selection of rats based on low and high intrinsic exercise capacity would yield models that also contrast for disease risk. After 11 generations, rats with low aerobic capacity scored high on cardiovascular risk factors that constitute the metabolic syndrome. The decrease in aerobic capacity was associated with decreases in the amounts of transcription factors required for mitochondrial biogenesis and in the amounts of oxidative enzymes in skeletal muscle. Impairment of mitochondrial function may link reduced fitness to cardiovascular and metabolic disease.
Isolation and Characterization of an Aldehyde Dehydrogenase Encoded by thealdBGene ofEscherichia coli
Authors: Ho Kwok Ki , Weiner Henry
Published: January 2005

An aldehyde dehydrogenase was detected in crude cell extracts ofEscherichia coliDH5α. Growth studies indicated that the aldehyde dehydrogenase activity was growth phase dependent and increased in cells grown with ethanol. The N-terminal amino acid sequence of the purified enzyme identified the latter as an aldehyde dehydrogenase encoded byaldB, which was thought to play a role in the removal of aldehydes and alcohols in cells that were under stress. The purified enzyme showed an estimated molecular mass of 220 ± 8 kDa, consisting of four identical subunits, and preferred to use NADP and acetaldehyde. MgCl2increased the activity of the NADP-dependent enzyme with various substrates. A comparison of the effect of Mg2+ions on the bacterial enzyme with the effect of Mg2+ions on human liver mitochondrial aldehyde dehydrogenase revealed that the bacterial enzyme shared kinetic properties with the mammalian enzyme. An R197E mutant of the bacterial enzyme appeared to retain very little NADP-dependent activity on acetaldehyde.
Sulfur and Nitrogen Limitation inEscherichia coliK-12: Specific Homeostatic Responses
Authors: Gyaneshwar Prasad , Paliy Oleg , McAuliffe Jon , Popham David L. , Jordan Michael I. , Kustu Sydney
Published: January 2005

We determined global transcriptional responses ofEscherichia coliK-12 to sulfur (S)- or nitrogen (N)-limited growth in adapted batch cultures and cultures subjected to nutrient shifts. Using two limitations helped to distinguish between nutrient-specific changes in mRNA levels and common changes related to the growth rate. Both homeostatic and slow growth responses were amplified upon shifts. This made detection of these responses more reliable and increased the number of genes that were differentially expressed. We analyzed microarray data in several ways: by determining expression changes after use of a statistical normalization algorithm, by hierarchical and k-means clustering, and by visual inspection of aligned genome images. Using these tools, we confirmed known homeostatic responses to global S limitation, which are controlled by the activators CysB and Cbl, and found that S limitation propagated into methionine metabolism, synthesis of FeS clusters, and oxidative stress. In addition, we identified several open reading frames likely to respond specifically to S availability. As predicted from the fact that theddpoperon is activated by NtrC, synthesis of cross-links between diaminopimelate residues in the murein layer was increased under N-limiting conditions, as was the proportion of tripeptides. Both of these effects may allow increased scavenging of N from the dipeptided-alanine-d-alanine, the substrate of the Ddp system.
Site-Directed Mutagenesis Analysis of Amino Acids Critical for Activity of the Type I Signal Peptidase of the Archaeon
Methanococcus voltae
Authors: Bardy Sonia L. , Ng Sandy Y. M. , Carnegie David S. , Jarrell Ken F.
Published: January 2005

Site-directed mutagenesis studies of the signal peptidase of the methanogenic archaeon
Methanococcus voltae
identified three conserved residues (Ser
52
, His
122
, and Asp
148
) critical for activity. The requirement for one conserved aspartic acid residue distinguishes the archaeal enzyme from both the
Escherichia coli
and yeast Sec11 enzymes.
Characterization of the RokA and HexA Broad-Substrate-Specificity Hexokinases from
Bacteroides fragilis
and Their Role in Hexose and
N
-Acetylglucosamine Utilization
Authors: Brigham Christopher J. , Malamy Michael H.
Published: January 2005

Bacteroides fragilis
, a human gastrointestinal commensal and an opportunistic pathogen, utilizes simple and complex sugars and polysaccharides for growth in the large intestine and at sites of infection. Because
B. fragilis
lacks transport-linked sugar phosphorylation systems, cytoplasmic kinase(s) was expected to be required for the phosphorylation of hexoses and hexosamines. We have now identified two hexose kinases that are important for growth of
B. fragilis
on glucose, mannose, and other sugars. One kinase (RokA), a member of the ROK family of proteins, was found to be the sole kinase for activation of
N
-acetyl-
d
-glucosamine (NAG). The other kinase (HexA) is responsible for the majority of the glucose kinase activity in the cell, although a
hexA
deletion mutant strain was not defective for growth on any substrate tested. Deletion of both the
rokA
and
hexA
kinase genes resulted in inability of the cell to use glucose, mannose, NAG, and many other sugars. We purified RokA and determined its approximate molecular mass to be 36.5 kDa. The purified RokA protein was shown to phosphorylate several substrates, including glucose, NAG, and mannose, but not
N
-acetylmannosamine or
N
-acetylneuraminic acid. Phylogenetic analysis of RokA showed that it is most similar to kinases from the
Cytophaga-Flavibacterium-Bacteroides
group, while HexA was most similar to other bacterial hexokinases and eukaryotic hexokinases.
Growth Kinetics of Extremely Halophilic
Archaea
(Family
Halobacteriaceae
) as Revealed by Arrhenius Plots
Authors: Robinson Jessie L. , Pyzyna Brandy , Atrasz Rachelle G. , Henderson Christine A. , Morrill Kira L. , Burd Anna Mae , DeSoucy Erik , Fogleman Rex E. , Naylor John B. , Steele Sarah M. , Elliott Dawn R. , Leyva Kathryn J. , Shand Richard F.
Published: January 2005

Members of the family
Halobacteriaceae
in the domain
Archaea
are obligate extreme halophiles. They occupy a variety of hypersaline environments, and their cellular biochemistry functions in a nearly saturated salty milieu. Despite extensive study, a detailed analysis of their growth kinetics is missing. To remedy this, Arrhenius plots for 14 type species of the family were generated. These organisms had maximum growth temperatures ranging from 49 to 58°C. Nine of the organisms exhibited a single temperature optimum, while five grew optimally at more than one temperature. Generation times at these optimal temperatures ranged from 1.5 h (
Haloterrigena turkmenica
) to 3.0 h (
Haloarcula vallismortis
and
Halorubrum saccharovorum
). All shared an inflection point at 31 ± 4°C, and the temperature characteristics for 12 of the 14 type species were nearly parallel. The other two species (
Natronomonas pharaonis
and
Natronorubrum bangense
) had significantly different temperature characteristics, suggesting that the physiology of these strains is different. In addition, these data show that the type species for the family
Halobacteriaceae
share similar growth kinetics and are capable of much faster growth at higher temperatures than those previously reported.
Role of Integration Host Factor in the Transcriptional Activation of Flagellar Gene Expression in
Caulobacter crescentus
Authors: Muir Rachel E. , Gober James W.
Published: January 2005

In the
Caulobacter crescentus
predivisional cell, class III and IV flagellar genes, encoding the extracytoplasmic components of the flagellum, are transcribed in the nascent swarmer compartment. This asymmetric expression pattern is attributable to the compartmentalized activity of the σ
54
-dependent transcriptional activator FlbD. Additionally, these temporally transcribed flagellar promoters possess a consensus sequence for the DNA-binding protein integration host factor (IHF), located between the upstream FlbD binding site and the promoter sequences. Here, we deleted the
C. crescentus
gene encoding the β-subunit of the IHF,
ihfB
(
himD
), and examined the effect on flagellar gene expression. The Δ
ihfB
strain exhibited a mild defect in cell morphology and impaired motility. Using flagellar promoter reporter fusions, we observed that expression levels of a subset of class III flagellar promoters were decreased by the loss of IHF. However, one of these promoters,
fliK-lacZ
, exhibited a wild-type cell cycle-regulated pattern of expression in the absence of IHF. Thus, IHF is required for maximal transcription of several late flagellar genes. The Δ
ihfB
strain was found to express significantly reduced amounts of the class IV flagellin, FljL, as a consequence of reduced transcriptional activity. Our results indicate that the motility defect exhibited by the Δ
ihfB
strain is most likely attributable to its failure to accumulate the class IV-encoded 27-kDa flagellin subunit, FljL.
STUDY OF THE MEDIUM MESSAGE PERFORMANCE OF BIP/MYRINET
Authors: TOURANCHEAU BERNARD , WESTRELIN ROLAND
Published: January 2005

The Basic Interface for Parallelism (BIP) [1] is a low-level communication system for Myrinet programmable network interface cards (NIC). On one hand BIP has proven that a very small latency and a very large throughput can be delivered. On another hand hardware implementations, like Giganet or NICs that implement the Scalable Coherent Interface (SCI), demonstrate very good performance for medium-sized messages. Our aim in this paper is to study how the programmable NICs can compare with the hardware solutions for medium-sized messages. We built a very precise model of the pipeline behavior driven by the NIC program in order to identify the bottlenecks. The results show that the pipeline quality is critical. We have developed an adaptive strategy as in [2] and then introduced it in BIP. Experiments show up to a two-fold gain over the previous BIP results and reach performances above the hardware solutions.
MUSCULAR CONTRACTION MIMICED BY MAGNETIC GELS
Authors: Zrínyi Miklós , Szabó Dénes
Published: January 2005

The ability of magnetic-field-sensitive gels to undergo a quick controllable change of shape can be used to create an artificially designed system possessing sensor- and actuator functions internally in the gel itself. The peculiar magneto-elastic properties may be used to create a wide range of motion and to control the shape change and movement, that are smooth and gentle similar to that observed in muscle. Magnetic field sensitive gels provide attractive means of actuation as artificial muscle for biomechanics and biomimetic applications.
ELECTROACTIVE AND ELECTROSTRUCTURED ELASTOMERS
Authors: Bossis G. , Abbo C. , Cutillas S. , Lacis S. , Métayer C.
Published: January 2005

Electroactive elastomers are composites made of solid particles embedded in an elastomeric network whose mechanical or optical properties can be changed by the application of an electric or a magnetic field. These materials have obviously a strong connection with ER and MR fluids and can be more appropriated for some applications. We present recent results concerning two kinds of filled elastomer, one based on carbonyl iron particles and the second one on silica particles. In the first case we show that that change of elastic properties obtained by the application of a magnetic field depend dramatically on the way we have structured the suspension before the polymerization. We explain quantitatively these experimental results with the help of finite element calculation to predict the magnetic forces between the particles. In the second case we show how it is possible to modulate the transmission of a laser beam by shearing a thin elastomeric film whose particles have been initially aligned with the help of an electric field. Some applications related to the organization of the filler particles by the application of a field or a combination of a field and a flow before polymerization will be discussed.
FIELD-INDUCED RHEOLOGY IN UNIAXIAL AND BIAXIAL FIELDS
Authors: MARTIN JAMES E.
Published: January 2005

Steady and oscillatory shear 3-D simulations of electro- and magnetorheology in uniaxial and biaxial fields are presented, and compared to the predictions of the chain model. These large scale simulations are three dimensional, and include the effect of Brownian motion. In the absence of thermal fluctuations, the expected shear thinning viscosity is observed in steady shear, and a striped phase is seen to rapidly form in a uniaxial field, with a shear slip zone in each sheet. However, as the influence of Brownian motion increases, the fluid stress decreases, especially at lower Mason numbers, and the striped phase eventually disappears, even when the fluid stress is still high. In a biaxial field, an opposite trend is seen, where Brownian motion decreases the stress most significantly at higher Mason numbers. To account for the uniaxial steady shear data we propose a microscopic chain model of the role played by thermal fluctuations on the rheology of ER and MR fluids that delineates the regimes where an applied field can impact the fluid viscosity, and gives an analytical prediction for the thermal effect. In oscillatory shear, a striped phase again appears in a uniaxial field, at strain amplitudes greater than ~0.15, and the presence of a shear slip zone creates strong stress nonlinearities at low strain amplitudes. In a biaxial field, a shear slip zone is not created, and so the stress nonlinearities develop only at expected strain amplitudes. The nonlinear dynamics of these systems is shown to be in good agreeement with the Kinetic Chain Model.
PARAMETERS AFFECTING LAMELLAR FORMATIONS IN ER FLUIDS: AN ALTERNATIVE MODEL FOR ER ACTIVITY
Authors: FILISKO F. E. , HENLEY S.
Published: January 2005

Under static conditions, ER suspensions form columns under electric field. However under the combined stimulii of a shear and electric field, the particles assemble into lamellar structures. The morphology of these structures are complex functions of electric field, shear rate, time of shear, electrode gap, particle concentration, and others. In this paper we present information regarding the field dependence, the concentration dependence, and the sequence of application of the electric and shear fields. A alternative model for ER activity, other than chain breaking, is presented which incorporates this lamellar texture.
MINIMUM ENERGY CONFIGURATIONS OF ER-FLUIDS
Authors: LUKKARINEN ARI , KASKI KIMMO
Published: January 2005

The dynamics of the structure formation of an electrorheological fluid consisting of either one type of particles or with two types of particles is studied numerically. In the latter case half of the suspension particles have dielectric constants greater and the other half smaller than that of the base fluid. In such a system the potential energy between interacting particles depends also on the type of the particles such that the direction of the force between different types of particles is complementary to the force between identical particles. The simulation model is based on a dipole model by utilizing an Ewald method for taking long range interactions into account. The dipoles are not fixed but they are allowed to adapt to local surroundings.
Dependence of the shear stress on particle properties in electrorheological fluids
Authors: Lu Kunquan , Lan Yucheng , Men Shouqiang , Xu Xiaoyu , Xianpeng Zhao , Xu Sujuan
Published: January 2005

By measuring the shear stress of a ferroelectric particle/silicone oil ER fluid varying with the temperature across Tc, the dependence of ER effect on permittivity mismatch is quantitatively obtained. The dielectric property of ferroelectric material behaves a dramatic change at Curie temperature (Tc) either in the dielectric constant and the conductivity. TGS and KNO 3 ferroelectric particles are chosen for studying the dielectric constant and conductivity dependence of the shear stress in ER fluids respectively. The measured results are more reliable, because the conditions, such as size, shape, composition of particles, especially chemical nature of particles and interface property between particles and liquid, all are same. The available theoretical calculations can not well fit our measured results. In order to consider the properties of whole suspensions, the orientation of the particles with spontaneous polarization under an electric field was studied in advance.
The Effect of Activation Time of Phosphoric Ester Cellulose Particles on the Electrorheological Properties of Anhydrous ER Fluids
Authors: Ahn B. G. , Choi U. S. , Kim C. H. , Kwon O. K.
Published: January 2005

The electrorheological (ER) behavior of suspensions in silicone oil of phosphoric ester cellulose powder (average particle size: 17.77 μm) was investigated at room temperature with electric fields up to 2.5 kV/mm. For development of anhydrous ER fluids using at wide temperature range, it was sought the effect of activation time of phosphoric ester cellulose particles on the ER activities. Anhydrous ER fluids based on the phosphoric ester cellulose particles made from cellulose particles treating in chemical solution of 2M phosphoric acid and 4M urea and heating at 150°C were measured. After activating the phosphoric ester cellulose anhydrous ER fluids at 120°C, not only analysis of dispersing cellulose particles but also electroroheological characteristics of ER fluids such as dielectric constant, current density, electrical conductivity and rheological properties were studied. Activation time had a large influence to ER properties of anhydrous ER fluids based on phosphoric ester cellulose. As the activation time went by, particle size and number of dispersing particles, electrical properties, dynamic yield stress on electric field, initial apparent viscosity (η0) and electrorheological effect (τA/τ0) of phosphoric ester cellulose ER fluids increased with increasing activation time at 120°C till activation time over 5 hours.
STATIC YIELD STRESS IN MAGNETORHEOLOGICAL FLUID
Authors: KORDONSKI W. , GORODKIN S. , ZHURAVSKI N.
Published: January 2005

A method and a device for measuring a true static yield stress in magnetorheological (MR) fluids are proposed. The data obtained by means of this device are compared with the measured values of the dynamic yield stress for similar compositions as well as with the quantities calculated by the reported models. It is shown that the dynamic yield stress exceeds the static one. The experimental data better agree with Rosensweig's model.
COMPUTER SIMULATION STUDY OF A NEMATOGENIC LATTICE-GAS MODEL BASED ON THE NEHRING–SAUPE INTERACTION POTENTIAL
Authors: ROMANO S.
Published: January 2005

Over 25 years ago, Nehring and Saupe proposed an anisotropic nematogenic lattice model, whose restriction to nearest neighbours has the form [Formula: see text] Here the three-component vectors xj∈Z3define centre-of-mass coordinates of the particles, and ukare three-component unit vectors defining their orientations; ∊ is a positive quantity setting energy and temperature scales (i.e. T*=kBT/∊); this model is seen to be the anisotropic counterpart to the generic Lebwohl–Lasher lattice model. It has often been used for approximate calculations of elastic properties, and has recently been studied by simulation [Hashim and Romano, Int. J. Mod. Phys.B13, 3879 (1999)]. We study here its lattice-gas extension, whose Hamiltonian is defined by [Formula: see text] where νk=0,1 denote occupation numbers, ∑{j<k}denotes sum over all distinct nearest-neighbouring pairs of lattice sites, and μ is the chemical potential. The model has been addressed by Monte Carlo simulation; comparisons are reported with Mean Field theory as well as with the Lebwohl–Lasher counterpart.
NEW INSIGHTS TO THE FUNCTION OF PHYTOPATHOGENIC BACTERIAL TYPE III EFFECTORS IN PLANTS
Authors: Beth Mudgett Mary
Published: January 2005

Phytopathogenic bacteria use the type III secretion system ( TTSS type III secretion system ) to inject effector proteins into plant cells. This system is essential for bacteria to multiply in plant tissue and to promote the development of disease symptoms. Until recently, little was known about the function of TTSS effectors in bacterial-plant interactions. New studies dissecting the molecular and biochemical action of TTSS effectors show that these proteins contribute to bacterial pathogenicity by interfering with plant defense signal transduction. These investigations provide us with a fresh view of how bacteria manipulate plant physiology to colonize their hosts.
Cloning and characterization of the human soluble adenylyl cyclase
Authors: Geng Weidong , Wang Zenglu , Zhang Jianning , Reed Berenice Y. , Pak Charles Y. C. , Moe Orson W.
Published: January 2005

We identified the human ortholog of soluble adenylyl cyclase (hsAC) in a locus linked to familial absorptive hypercalciuria and cloned it from a human cDNA library. hsAC transcripts were expressed in multiple tissues using RT-PCR and RNA blotting. RNA blot analysis revealed a predominant 5.1-kb band in a multiple human tissue blot, but three splice transcript variants were detected using RT-PCR and confirmed by performing sequence analysis. Immunoblot analysis showed 190- and 80-kDa bands in multiple human cell lines from gut, renal, and bone origins in both cytosol and membrane fractions, including Caco-2 colorectal adenocarcinomas, HEK-293 cells, HOS cells, and primary human osteoblasts, as well as in vitro induced osteoclast-like cells. The specificity of the antiserum was verified by peptide blocking and reduction using sequence-specific small interfering RNA. Confocal immunofluorescence cytochemistry localized hsAC primarily in cytoplasm, but some labeling was observed in the nucleus and the plasma membrane. Cytoplasmic hsAC colocalized with microtubules but not with microfilaments. To test the function of hsAC, four constructs containing catalytic domains I and II (aa 1–802), catalytic domain II (aa 231–802), noncatalytic domain (aa 648–1,610), and full-length protein (aa 1–1,610) were expressed in Sf9 insect cells. Only catalytic domains I and II or full-length proteins showed adenylyl cyclase activity. Mg2+, Mn2+, and Ca2+ all increased adenylyl cyclase activity in a dose-dependent manner. While hsAC had a minimal response to HCO3− in the absence of divalent cations, HCO3− robustly stimulated Mg2+-bound hsAC but inhibited Mn2+-bound hsAC in a dose-dependent manner. In summary, hsAC is a divalent cation and HCO3− sensor, and its HCO3− sensitivity is modulated by divalent cations.
Whole body and forearm substrate metabolism in hyperthyroidism: evidence of increased basal muscle protein breakdown
Authors: Riis Anne Lene Dalkjær , Jørgensen Jens Otto Lunde , Gjedde Signe , Nørrelund Helene , Jurik Anne Grethe , Nair K. S. , Ivarsen Per , Weeke Jørgen , Møller Niels
Published: January 2005

Thyroid hormones have significant metabolic effects, and muscle wasting and weakness are prominent clinical features of chronic hyperthyroidism. To assess the underlying mechanisms, we examined seven hyperthyroid women with Graves' disease before (Ht) and after (Eut) medical treatment and seven control subjects (Ctr). All subjects underwent a 3-h study in the postabsorptive state. After regional catheterization, protein dynamics of the whole body and of the forearm muscles were measured by amino acid tracer dilution technique using [15N]phenylalanine and [2H4]tyrosine. Before treatment, triiodothyronine was elevated (6.6 nmol/l) and whole body protein breakdown was icreased 40%. The net forearm release of phenylalanine was increased in hyperthyroidism (μg·100 ml−1·min−1): −7.0 ± 1.2 Ht vs. −3.8 ± 0.8 Eut ( P = 0.04), −4.2 ± 0.3 Ctr ( P = 0.048). Muscle protein breakdown, assessed by phenylalanine rate of appearance, was increased (μg·100 ml−1·min−1): 15.5 ± 2.0 Ht vs. 9.6 ± 1.4 Eut ( P = 0.03), 9.9 ± 0.6 Ctr ( P = 0.02). Muscle protein synthesis rate did not differ significantly. Muscle mass and muscle function were decreased 10–20% before treatment. All abnormalities were normalized after therapy. In conclusion, our results show that hyperthyroidism is associated with increased muscle amino acid release resulting from increased muscle protein breakdown. These abnormalities can explain the clinical manifestations of sarcopenia and myopathy.
Encoding of Virtual Acoustic Space Stimuli by Neurons in Ferret Primary Auditory Cortex
Authors: Mrsic-Flogel Thomas D. , King Andrew J. , Schnupp Jan W. H.
Published: January 2005

Recent studies from our laboratory have indicated that the spatial response fields (SRFs) of neurons in the ferret primary auditory cortex (A1) with best frequencies ≥4 kHz may arise from a largely linear processing of binaural level and spectral localization cues. Here we extend this analysis to investigate how well the linear model can predict the SRFs of neurons with different binaural response properties and the manner in which SRFs change with increases in sound level. We also consider whether temporal features of the response (e.g., response latency) vary with sound direction and whether such variations can be explained by linear processing. In keeping with previous studies, we show that A1 SRFs, which we measured with individualized virtual acoustic space stimuli, expand and shift in direction with increasing sound level. We found that these changes are, in most cases, in good agreement with predictions from a linear threshold model. However, changes in spatial tuning with increasing sound level were generally less well predicted for neurons whose binaural frequency-time receptive field (FTRF) exhibited strong excitatory inputs from both ears than for those in which the binaural FTRF revealed either a predominantly inhibitory effect or no clear contribution from the ipsilateral ear. Finally, we found (in agreement with other authors) that many A1 neurons exhibit systematic response latency shifts as a function of sound-source direction, although these temporal details could usually not be predicted from the neuron's binaural FTRF.
Effect of Haemodialysis on Regional and Transmural Inhomogeneities of the Ventricular Repolarisation Phase
Authors: Jaroszyński Andrzej J. , Załuska Wojciech T. , Książek Andrzej
Published: January 2005

Recent studies have indicated increased ventricular repolarisation dispersion in haemodialysis (HD) patients. The purpose of this study was to estimate the effect of the HD process on parameters of regional and transmyocardial repolarisation inhomogeneities. Thirty-two selected HD patients (without relevant diseases and medication known to affect the QT interval) were included. Dispersion of the QT corrected interval (QT-c-D) and the corrected interval between the peak and the end of the T wave (Tpe-c-D) were evaluated before and after HD, and in controls. Blood chemistry and extracellular body water (ECW) were evaluated before and after HD. Predialysis QT-c-D and Tpe-c-D were higher in patients (53.40 ± 17.39 and 47.50 ± 13.68 ms, respectively) than in controls (34.91 ± 17.70 ms, p < 0.001 and 31.9 ± 16.76 ms, p < 0.001, respectively). HD induced an increase in the QT-c-D (67.59 ± 19.40 ms; p < 0.001) and Tpe-c-D (62.89 ± 14.33 ms; p < 0.001). Stepwise multiple regression identified the independent risk factors of QT-c-D (the differences between pre- and postdialysis phosphorus, potassium and calcium levels and ECW values) and Tpe-c-D (the differences between pre- and postdialysis phosphorus levels, calcium levels and ECW values) increases, induced by the HD process. The HD process increases regional and transmyocardial repolarisation phase inhomogeneities in HD patients. Changes of phosphorus, calcium and potassium levels plus ECW values seem to be important predisposing factors as far as the increase in ventricular inhomogeneities in HD patients is concerned.
Effects of S1P on Myoblastic Cell Contraction: Possible Involvement of Ca2+-Independent Mechanisms
Authors: Nosi D. , Vassalli M. , Polidori L. , Giannini R. , Tani A. , Chellini F. , Paternostro F.
Published: January 2005

Sphingosine-1-phosphate (S1P) is a lipid mediator, which affects many essential processes such as cell proliferation, differentiation and contraction in many cell types. We have previously demonstrated that the lipid mediator elicits Ca2+ transients in a myoblastic cell line (C2C12) by interacting with its specific receptors (S1PRs). In the present study, we wanted to correlate the Ca2+ response with activation of myoblastic cell contractility. C2C12 cells were first investigated for the expression and cellular organization of cytoskeletal proteins by immunoconfocal microscopy. We found that myoblasts exhibited a quite immature cytoskeleton, with filamentous actin dispersed as a web-like structure within the cytoplasm. To evaluate intracellular Ca2+ mobilization, the cells were loaded with a fluorescent Ca2+ indicator (Fluo-3), stimulated with S1P and simultaneously observed with differential interference contrast and fluorescence optics. Exogenous S1P-induced myoblastic cell contraction was temporally unrelated to S1P-induced intracellular Ca2+ increase; cell contraction occurred within 5–8 s from stimulation, whereas intracellular Ca2+ increase was evident only after 15–25 s. To support the Ca2+ independence of myoblastic cell contraction, the cells were pretreated with a Ca2+ chelator, BAPTA/AM, prior to stimulation with S1P. In these experimental conditions, the myoblasts were still able to contract, whereas the S1P-induced Ca2+ transients were completely abolished. On the contrary, when C2C12 cells were induced to differentiate into skeletal myotubes, they responded to S1P with a rapid cell contraction concurrent with an increase in the intracellular Ca2+. These data suggest that Ca2+-independent mechanism of cell contraction may be replaced by Ca2+-dependent ones during skeletal muscle differentiation.
Altered ATP-Sensitive P2 Receptor Subtype Expression in the Han:SPRD cy/+ Rat, a Model of Autosomal Dominant Polycystic Kidney Disease
Authors: Turner C.M. , Ramesh B. , Srai S.K.S. , Burnstock G. , Unwin R.J.
Published: January 2005

The effects of extracellular ATP on fluid secretion and reabsorption by renal epithelial cells, as well as its known effects on cell proliferation and death, are potentially important contributory factors in the development and growth of renal cysts. In this study, we have investigated the protein and mRNA expression of several P2Y receptor subtypes (P2Y1,2,4,6), as well as the P2X5 and P2X7 receptors, in kidney tissue from the Han:SPRD (cy/+) rat model of polycystic kidney disease. All of the P2Y receptors tested for, and the P2X5 and P2X7 subtypes, were located on the cyst-lining cells of Han:SPRD (cy/+) rat polycystic kidneys; most immunostaining was cytosolic and we could not confidently localize it to one or other membrane. However, the staining pattern for P2Y6 was uniquely granular when compared with the other P2 receptors. P2Y2 and P2Y6 receptor mRNA was increased in both homozygote (cy/cy) and heterozygote (cy/+) rat kidneys when compared with unaffected littermates. The protein levels of P2Y2 and P2Y6 receptors were also increased, being undetectable or at a low level, respectively, in control tissue. Finally, P2X7 receptor mRNA was increased in cy/+, but not in cy/cy rat kidneys. Our results show that a number of P2Y receptor subtypes, as well as the P2X5 and P2X7 receptors, are clearly expressed in cyst-lining cells in the Han:SPRD (cy/+) rat model of renal cystic disease. Furthermore, P2Y2 and P2Y6 receptor mRNA and protein levels are markedly increased in cystic rat kidneys compared with normal rats of the same genetic background. Thus, the most consistent findings were an increase in the expression of P2Y2, P2Y6 and P2X7 receptors in cystic tissue. Given the widely reported effects of stimulating these P2 receptor subtypes in epithelial and other renal cells, they could contribute to the development and growth of renal cysts: extracellular ATP and its products ‘trapped’ in cyst fluid may activate P2 receptors expressed by cyst-lining cells, causing cyst expansion from increased fluid secretion and/or reduced reabsorption, as well as an increase in cell turnover (re-modeling).
Mechanism of VEGF-Induced Uterine Venous Hyperpermeability
Authors: Celia Gerard , Osol George
Published: January 2005

Background: Transfer of molecular signals from veins to adjacent arteries is an established mechanism of vascular communication in the uterine circulation, which ultimately depends on venous permeability. This study tests the hypotheses that: (1) uterine veins are permeable to intravenous solutes, using a 3-kDa dextran tracer and (2) this permeability is enhanced in response to vascular endothelial growth factor (VEGF). Additionally, the involvement of nitric oxide (NO), calcium, and the phospholipase C-protein kinase C (PLC-PKC) cascade in VEGF-enhanced permeability were investigated, and the impact of pregnancy-induced uterine vascular remodeling on permeability was evaluated. Methods: Studies utilized fluorimetry to quantitate solute flux in isolated segments of rat uterine vein as a function of endothelial surface area and time under basal and VEGF-stimulated conditions. VEGF signaling was probed using NO synthase inhibition (L-NNA), calcium channel blockade (lanthanum chloride) and withdrawal (calcium-free solution), and inhibitors of the PLC-PKC cascade (U-73122 and chelerythrine chloride, respectively). Gestational effects were assessed using vessels from late pregnant (day 20) rats. Results: Basal flux (control) in nonpregnant animals was 26 ± 2.5 molecules/µm²/min × 1,000 and was increased significantly by VEGF in a concentration-dependent manner (1 nM ≈ 3.3-fold, 10 nM ≈ 4.6-fold). Inhibition of PLC, PKC, and calcium signaling, but not NO, attenuated the response to VEGF. Gestation significantly increased flux (78 ± 9.3 molecules/µm²/min × 1,000), and maintained responsiveness to VEGF. Conclusions: These results demonstrate uterine venous permeability to intermediate-sized solutes through a VEGF-sensitive pathway involving calcium and PLC-PKC, but not NO, and further substantiate a role for veno-arterial communication in uterine blood flow regulation during pregnancy.
Analysis of Interactions between Serotonin and Gabapentin or Adenosine in the Spinal Cord of Rats
Authors: Yoon Myung Ha , Choi Jeong Il , Park Heon Chang , Bae Hong Beom , Jeong Seong Wook , Jeong Chang Young
Published: January 2005

We evaluated the nature of the pharmacologic interaction after concurrent administration of 5-HT–gabapentin and 5-HT–adenosine at the spinal level. Intrathecal catheters were placed in the subarachnoid space of male Sprague-Dawley rats. Nociception was induced by subcutaneous injection of formalin solution (5%, 50 µl) into the hind paw. A fixed dose analysis and an isobolographic analysis were used to determine the properties of interaction. Intrathecal 5-HT dose-dependently suppressed the flinching response during phase 1 of the formalin test, while neither gabapentin nor adenosine affected the phase-1 flinching response. All three intrathecal drugs attenuated the phase-2 flinching response in a dose-dependent manner. The intrathecal combination of 5-HT with a fixed dose of gabapentin or adenosine in phase 1 had little effect or increased the antinociception of 5-HT alone. Isobolographic analysis in phase 2 revealed an additive or a synergistic interaction after intrathecal delivery of 5-HT–gabapentin or 5-HT–adenosine mixture. Taken together, the combination of 5-HT with either gabapentin or adenosine may offer a potential remedy in the treatment of the facilitated state as well as acute pain in the spinal cord.