bluuebunny/crossref_metadata_2025 huggingface dataset:
Construction and evaluation of near-isogenic lines for major QTLs of basal root thickness and 1000-grain-weight in lowland and upland rice
Authors: Li-Feng Liu , Hong-Liang Zhang , Ping Mu , Yan-Ying Qu , Zi-Chao Li
Published: February 2008

The development of near-isogenic lines (NILs) is an important fundamental step in the cloning of quantitative trait loci (QTL) and molecular marker assisted breeding. In the present study, NILs for two major QTLs of basal root thickness (BRT) and 1000-grain-weight (TGW) were obtained by molecular marker-assisted selection (MAS) through foreground selection for target QTL and background selection in three backcross generations (BC1F1, BC2F1and BC3F1). After phenotypic evaluation in the BC3F2generation, nine BRT QTL-NILs with BRT ranges of 1.07–1.16 mm (6.11–15.18% greater than the recurrent parent) and an average recovery ratio of genetic background (RRGB) of 97.22%, and 11 TGW QTL-NILs with ranges of 21.25–26.25 g (7.05–32.16% greater than the recurrent parent) and 95.97% of RRGB, were selected.
Seasonal geophysical monitoring of biogenic gases in a northern peatland: Implications for temporal and spatial variability in free phase gas production rates
Authors: Comas Xavier , Slater Lee , Reeve Andrew
Published: February 2008

A set of high resolution surface ground penetrating radar (GPR) surveys, combined with elevation rod (to monitor surface deformation) and gas flux measurements, were used to investigate in situ biogenic gas dynamics within a northern peatland (Caribou Bog, Maine). Gas production rates were directly estimated from the time series of GPR measurements. Spatial variability in gas production was also investigated by comparing two sites with different geological and ecological attributes, showing differences and/or similarities depending on season. One site characterized by thick highly humified peat deposits (5–6 m), wooded heath vegetation and open pools showed large ebullition events during the summer season, with estimated emissions (based on an assumed range of CH4 concentration) between 100 and 172 g CH4 m−2 during a single event. The other site characterized by thinner less humified peat deposits (2–3 m) and shrub vegetation showed much smaller ebullition events during the same season (between 13 and 23 g CH4 m−2). A consistent period of free‐phase gas (FPG) accumulation during the fall and winter, enhanced by the frozen surficial peat acting as a confining layer, was followed by a decrease in FPG after the snow/ice melt that released estimated fluxes between 100 and 200 g CH4 m−2 from both sites. Estimated FPG production rates during periods of biogenic gas accumulation ranged between 0.22 and 2.00 g CH4 m3 d−1 and reflected strong seasonal and spatial variability associated with differences in temperature, peat soil properties, and/or depositional attributes (e.g., stratigraphy). Periods of decreased atmospheric pressure coincided with short‐period increases in biogenic gas flux, including a very rapid decrease in FPG content associated with an ebullition event that released an estimated 39 and 67 g CH4 m−2 in less than 3.5 hours. These results provide insights into the spatial and seasonal variability in production and emission of biogenic gases from northern peatlands.
Enhanced antithrombotic effects of unfractionated heparin in rats after repeated oral doses and its relationship to endothelial heparin concentration
Authors: Hiebert L M , Ping T , Wice S M
Published: February 2008

Background and purpose:

An oral, single dose of 7.5 mg kg−1 of unfractionated heparin (UFH) reduces thrombosis by 50% in a rat model of venous thrombosis. As long‐term use is required clinically, our objectives were to study the antithrombotic effects following repeated oral UFH administration.

Experimental approach:

Bovine lung UFH was administered by oral gavage to rats in 3 doses of 7.5 mg kg−1 each 12, 24, 48, and 72 h apart; and in 3 or 15 doses of 1 mg kg−1 every 48 h. The last dose was given immediately after thrombus initiation where 10% formalin in methanol was applied to the jugular vein. The vessel was examined for thrombosis 4 h later. Amounts of heparin in tissue and endothelium, and plasma anticoagulant activity were measured.

Key results:

When 3 × 7.5 mg kg−1 heparin was given, thrombotic incidence was most reduced at 48 h dose‐intervals and was significantly less than single dose treatment. There was a negative correlation between endothelial heparin content and thrombotic incidence, but not anticoagulant activity. When 3 doses of 1 mg kg−1 every 48 h were given, thrombotic incidence was similar to single dose treatment. When 15 doses were given, total thrombotic incidence was less than for 3 doses and was similar to that after s.c. administration.

Conclusions and implications:

Antithrombotic activity increased with repeated doses of oral UFH, with antithrombotic effects similar to s.c. administration. Antithrombotic activity was related to heparin on endothelium.

British Journal of Pharmacology (2008) 153, 1177–1184; doi:10.1038/bjp.2008.14; published online 11 February 2008
Enhanced nitric oxide and cyclic GMP formation plays a role in the anti‐platelet activity of simvastatin
Authors: Chou T‐C , Lin Y‐F , Wu W‐C , Chu K‐M
Published: February 2008

Background and purpose:

It has been found that 3‐hydroxy‐3‐methyl‐glutaryl coenzyme A (HMG‐CoA) reductase inhibitors (statins) exert various vascular protective effects, beyond their cholesterol‐lowering property, including inhibition of platelet‐dependent thrombus formation. The objective of the present study was to determine whether the nitric oxide (NO)/cyclic GMP‐mediated processes in platelets contribute to the anti‐aggregatory activity of simvastatin.

Experimental approach:

After rabbit platelets were incubated with simvastatin for 5 min, aggregation was induced and the platelet aggregation, nitric oxide synthase activity, guanylyl cyclase activity, NO and cyclic GMP formation were measured appropriately.

Key results:

Treatment with simvastatin concentration‐dependently inhibited platelet aggregation induced by collagen or arachidonic acid with an IC50 range of 52–158 μM. We also demonstrated that simvastatin (20–80 μM) concentration‐dependently further enhanced collagen‐induced NO and cyclic GMP formation through increasing NOS activity (from 2.64±0.12 to 3.52±0.21–5.10±0.14 μmol min−1 mg protein−1) and guanylyl cyclase activity (from 142.9±7.2 to 163.5±17.5–283.8±19.5 pmol min−1 mg protein−1) in the platelets. On the contrary, inhibition of platelet aggregation by simvastatin was markedly attenuated (by about 50%) by addition of a nitric oxide synthase inhibitor, a NO scavenger or a NO‐sensitive guanylyl cyclase inhibitor. The anti‐aggregatory effects of simvastatin were significantly increased by addition of a selective inhibitor of cyclic GMP phosphodiesterase.

Conclusions and implications:

Our findings indicate that enhancement of a NO/cyclic GMP‐mediated process plays an important role in the anti‐aggregatory activity of simvastatin.

British Journal of Pharmacology (2008) 153, 1281–1287; doi:10.1038/bjp.2008.19; published online 11 February 2008
A model explaining some bryozoan colonies
Authors: Mazurek Dawid
Published: February 2008

Although the colonialism surely developed independently in Graptolithoidea and Bryozoa, both groups share similar patterns of astogeny. One of the common features is the presence of morphological gradients. Many attempts at its explanation were made for more than a half of the century. This paper discusses a new model of the late astogeny in some bryozoan colonies, showing a cyclic reappearance of secondary zones of astogenetic change and astogenetic repetition that cannot be explained by the single morphogen gradient theory.
Small-angle-neutron-scattering from giant water-in-oil microemulsion droplets. II. Polymer-decorated droplets in a quaternary system
Authors: Foster Tobias , Sottmann Thomas , Schweins Ralf , Strey Reinhard
Published: February 2008

Amphiphilic block copolymers of the type poly(ethylenepropylene)-co-poly(ethyleneoxide) dramatically enhance the solubilisation efficiency of non-ionic surfactants in microemulsions that contain equal volumes of water in oil. Consequently, the length scale of the microstructure of such bicontinuous microemulsions is dramatically increased up to the order of a few 100nm. In this paper, we show that this so-called efficiency boosting effect can also be applied to water-in-oil microemulsions with droplet microstructure. Such giant water-in-oil microemulsions would provide confined compartments in which chemical reactions of biological macromolecules can be performed on a single molecule level. With this motivation we investigated the phase behavior and the microstructure of oil-rich microemulsions containing D2O, n-decane(d22), C10E4 and the amphiphilic block copolymer PEP5-PEO5 [poly(ethylenepropylene)-co-poly(ethyleneoxide), weight per block of 5000g∕mol]. We found that 15wt% of water can be solubilised by 5wt% of surfactant and block copolymer when about 6wt% of surfactant is replaced by the block copolymer. Small-angle-neutron-scattering experiments were performed to determine the length scales and microstructure topologies of the oil-rich microemulsions. To analyze the scattering data, we derived a novel form factor that also takes into account the scattering contribution of the hydrophobic part of the block copolymer molecules that reside in the surfactant shell. The quantitative analysis of the scattering data with this form factor shows that the radius of the largest droplets amounts up to 30nm. The novel form factor also yielded qualitative information on the stretching of the polymer chains in dependence on the polymer surface density and the droplet radius.
Contracted auxiliary Gaussian basis integral and derivative evaluation
Authors: Giese Timothy J. , York Darrin M.
Published: February 2008

The rapid evaluation of two-center Coulomb and overlap integrals between contracted auxiliary solid harmonic Gaussian functions is examined. Integral expressions are derived from the application of Hobson’s theorem and Dunlap’s product and differentiation rules of the spherical tensor gradient operator. It is shown that inclusion of the primitive normalization constants greatly simplifies the calculation of contracted functions corresponding to a Gaussian multipole expansion of a diffuse charge density. Derivative expressions are presented and it is shown that chain rules are avoided by expressing the derivatives as a linear combination of auxiliary integrals involving no more than five terms. Calculation of integrals and derivatives requires the contraction of a single vector corresponding to the monopolar result and its scalar derivatives. Implementation of the method is discussed and comparison is made with a Cartesian Gaussian-based method. The current method is superior for the evaluation of both integrals and derivatives using either primitive or contracted functions.
An integrate-over-temperature approach for enhanced sampling
Authors: Gao Yi Qin
Published: February 2008

A simple method is introduced to achieve efficient random walking in the energy space in molecular dynamics simulations which thus enhances the sampling over a large energy range. The approach is closely related to multicanonical and replica exchange simulation methods in that it allows configurations of the system to be sampled in a wide energy range by making use of Boltzmann distribution functions at multiple temperatures. A biased potential is quickly generated using this method and is then used in accelerated molecular dynamics simulations.
Transferability of coarse-grained force fields: The polymer case
Authors: Carbone Paola , Varzaneh Hossein Ali Karimi , Chen Xiaoyu , Müller-Plathe Florian
Published: February 2008

A key question for all coarse-graining methodologies is the degree of transferability of the resulting force field between various systems and thermodynamic conditions. Here we present a detailed study of the transferability over different thermodynamic states of a coarse-grained (CG) force field developed using the iterative Boltzmann inversion method. The force field is optimized against distribution functions obtained from atomistic simulations. We analyze the polymer case by investigating the bulk of polystyrene and polyamide-6,6 whose coarse-grained models differ in the chain length and in the number of atoms lumped in one bead. The effect of temperature and pressure on static, dynamic, and thermodynamic properties is tested by comparing systematically the coarse-grain results with the atomistic ones. We find that the CG model describing the polystyrene is transferable only in a narrow range of temperature and it fails in describing the change of the bulk density when temperature is 80K lower than the optimization one. Moreover the calculation of the self-diffusion coefficient shows that the CG model is characterized by a faster dynamics than the atomistic one and that it overestimates the isothermal compressibility. On the contrary, the polyamide-6,6 CG model turns out to be fully transferable between different thermodynamic conditions. The transferability is checked by changing either the temperature or the pressure of the simulation. We find that, in this case, the CG model is able to follow all the intra- and interstructural rearrangements caused by the temperature changes. In addition, while at low temperature the difference between the CG and atomistic dynamics is remarkable due to the presence of hydrogen bonds in the atomistic systems, for high temperatures, the speedup of the CG dynamics is strongly reduced, leading to a CG diffusion coefficient only six times bigger than the atomistic one. Moreover, the isothermal compressibility calculated at different temperatures agrees very well with the experimental one. We find that the polymer chain length does not affect the transferability of the force field and we attribute such transferability mainly to the finer model used in describing the polyamide-6,6 than the polystyrene.
Effects of d0 substitution on phase competition in Pr0.50Ca0.50Mn1−xTixO3
Authors: Frontera C. , Beran P. , Bellido N. , Hernández–Velasco J. , García–Muñoz J. L.
Published: February 2008

We study the effect of the substitution of Mn by d0 nonmagnetic ions in Pr0.50Ca0.50Mn1−xTixO3 (x=0.01, 0.03, and 0.05) manganites. Synchrotron and neutron powder diffractions have allowed us to characterize the dependence of the coexisting phases, the evolution of their relative fractions, and magnetic structures with the Ti substitution level. In consistence with the Ti4+ valence state (d0), the proportion of microdomains exhibiting pseudo-CE-type magnetic order increases with the Ti content at expenses of the CE-type regions in the material. The magnetic disorder greatly increases with Ti contents. The absence of ferromagnetism is confirmed in zero field. The apparition of magnetization steps has been further characterized by neutron powder diffraction under magnetic field.
The two-spin model with dipolar interactions for the exchange coupled composite media
Authors: Vokoun D. , Beleggia M. , Rahman T. , Hou H. C. , Lai C. H.
Published: February 2008

We study exchange coupled composite (ECC) media where both the hard and soft coupled layers possess perpendicular anisotropy or one of the layers is superparamagnetic. Our model is used to demonstrate the effect of the dipolar interactions on the coercive field. A series of ECC samples with various thicknesses of Ru spacer is manufactured and analyzed. The structure of the samples prepared is CoPtCr-SiO2∕Ru∕CoPtCr-SiO2, with the composition varied around that of (CoPt17Cr10)90-(SiO2)10. The acquired experimental data are used to illustrate the significance of magnetostatic interactions between the two coupled magnetic layers.
Vibrational effects on the dynamic electric properties of hydrogen peroxide
Authors: Santiago Emílio , Castro Marcos A. , Fonseca Tertius L. , Mukherjee Prasanta K.
Published: February 2008

In this work we present a method based on the perturbation theoretic approach of Bishop and co-workers [J. Chem. Phys. 95, 2646 (1991); 97, 5255 (1992); 108, 10013 (1998)] to calculate the effect of torsional motion on the polarizability and hyperpolarizabilities of hydrogen peroxide. The frequency dependence has been evaluated using the time-dependent Hartree–Fock method. The results obtained show that the zero-point vibrational averaging contributions are small compared to the corresponding electronic contributions. In the static limit the pure vibrational contributions are very large, specially for β and γ. These contributions are significant for the hyperpolarizabilities even in the visible region, except for the second harmonic generation and third harmonic generation processes.
Spin waves in CuFeO2
Authors: Fishman Randy S.
Published: February 2008

One of the most fascinating frustrated antiferromagnets, CuFeO2, contains stacked hexagonal layers, each with an ↑↑↓↓ magnetic structure. Recent neutron-scattering studies have found that the spin-wave spectrum softens with increasing magnetic field or by substituting Al for Fe. We present a theory of the spin-wave excitations that fits the observed frequencies quite well and explains this softening.
Thermodiffusion in model nanofluids by molecular dynamics simulations
Authors: Galliero G. , Volz S.
Published: February 2008

In this work, a new algorithm is proposed to compute single particle (infinite dilution) thermodiffusion using nonequilibrium molecular dynamics simulations through the estimation of the thermophoretic force that applies on a solute particle. This scheme is shown to provide consistent results for model nanofluids in the liquid state (spherical nonmetallic nanoparticles+Lennard–Jones fluid) where it appears that thermodiffusion amplitude, as well as thermal conductivity, decreases with nanoparticle concentration. Then, by changing the nature of the nanoparticle (size, mass, and internal stiffness) and that of the solvent (quality and viscosity), various trends are exhibited. In all cases, the single particle thermodiffusion is positive, i.e., the nanoparticle tends to migrate toward the cold area. The single particle thermal diffusion coefficient is shown to be independent of the size of the nanoparticle (diameter of 0.8–4nm), whereas it increases with the quality of the solvent and is inversely proportional to the viscosity of the fluid. In addition, this coefficient is shown to be independent of the mass of the nanoparticle and to increase with the stiffness of the nanoparticle internal bonds. Besides, for these configurations, the mass diffusion coefficient behavior appears to be consistent with a Stokes–Einstein-like law.
Magnetic properties of ilmenite-hematite films and bulk samples
Authors: Dou J. , Navarrete L. , Schad R. , Padmini P. , Pandey R. K. , Guo H. , Gupta A.
Published: February 2008

Ilmenite-hematite [(FeTiO3)1−x–(Fe2O3)x] is a solid solution system with intrinsic ferrimagnetic and semiconducting properties. Bulk ceramic samples and epitaxial thin films have been prepared with magnetization values of up to 1500G (bulk) and 700G (thin films) at room temperature. Superparamagnetic behavior was discriminated from ferrimagnetic properties using field cooled and zero field cooled measurements. The blocking temperature exceeds room temperature for samples with composition x>0.25. Using magnetic force microscopy, the domain structure in the thin ilmenite-hematite films was detected.
Broadband polarizing films by photopolymerization-induced phase separation and in situ Swelling
Authors: Fan B. , Vartak S. , Eakin J. N. , Faris S. M.
Published: February 2008

This letter describes the spectral broadening of cholesteric liquid crystal films prepared from a blend comprising a cross-linkable liquid crystal polymer and a noncross-linkable low-molecular-weight liquid crystal. The bandwidth of the broadened reflection band can be increased by several times upon photopolymerization. The spectral broadening arises from the formation of gradient pitch across the film thickness. It is shown that both phase separation and in situ swelling are important mechanisms for the resulting film structure.
The self-referential method combined with thermodynamic integration
Authors: Sweatman Martin B. , Atamas Alexander A. , Leyssale Jean-Marc
Published: February 2008

The self-referential method [M. B. Sweatman, Phys. Rev. E 72, 016711 (2005)] for calculating the free energy of crystalline solids via molecular simulation is combined with thermodynamic integration to produce a technique that is convenient and efficient. Results are presented for the chemical potential of hard sphere and Lennard-Jones face centered cubic crystals that agree well with this previous work. For the small system sizes studied, this technique is about 100 times more efficient than the parameter hopping technique used previously.
Ripple rotation, pattern transitions, and long range ordered dots on silicon by ion beam erosion
Authors: Ziberi B. , Frost F. , Tartz M. , Neumann H. , Rauschenbach B.
Published: February 2008

The importance of the ion incidence angle in self-organized pattern formation during low energy Xe+ ion beam erosion of silicon is elaborated. By a small step variation of the ion incidence angle, a variety of nanostructured patterns can develop. In this context, the angular distribution of ions within the ion beam is explored as an additional parameter controlling the evolution of the surface topography. Due to a controlled variation of these two parameters, hitherto unknown phenomena are found: (i) formation of rotated ripples, (ii) continuous transitions between patterns, and (iii) long range square ordered dot pattern.
Alignment layer effects on thin liquid crystal cells
Authors: Jiao Meizi , Ge Zhibing , Song Qiong , Wu Shin-Tson
Published: February 2008

Factors affecting the thin cell performance of a liquid crystal cell are analyzed. Examples based on vertically aligned thin cells are given to illustrate these effects. When the cell gap is below ∼2μm, the liquid crystal alignment material, layer thickness, and anchoring energy all play important roles. The first two factors affect the threshold and on-state voltage, while the last one affects the operating voltage and response time. Three reflective liquid crystal cells are studied experimentally. Good agreement between experiment and theory is obtained.
Fabrication of single-walled carbon nanotube flexible strain sensors with high sensitivity
Authors: Chang Neng-Kai , Su Chi-Chung , Chang Shuo-Hung
Published: February 2008

This work demonstrates a fabrication technique of high sensitivity flexible strain sensors at room temperature. The grown well-aligned millimeter-long single-walled carbon nanotube (SWCNT) was transferred from the silicon substrate to the pretrenched flexible substrate. The sensor design allows effective adhesion between SWCNT and flexible substrate for SWCNT lengthwise strain and piezoresistivity change. Experimental results show that the sensor achieves a high strain resolution of 0.004%. The measured piezoresistive gauge factor of the flexible sensor is 269. The demonstrated fabrication technique of flexible sensors shows advantage of high sensitivity, high quality, and is suitable for mass production.
Urban Environmental Externalities, Agglomeration Forces, and the Technological ‘Deus ex Machina’
Authors: Verhoef Erik , Nijkamp Peter
Published: February 2008

The aim of this paper is to analyze and depict urban equilibrium from the perspective of a complex force field between (positive) agglomeration economies and (negative) environmental externalities. Based on a simplified representation of a linear urban economy, a general-equilibrium model is designed and its properties are investigated by using numerical simulations. The model includes a spacious industrial centre, in which agglomeration externalities are differentiated over space, and a residential area that suffers from pollution, which is also differentiated over space. For the sake of simplicity urban environmental externalities are analyzed as being proportional to fossil fuel use, so that energy taxes would be a logical instrument. Environmental technology choice by firms is used as a tool for coping with environmental externalities, and is endogenized. Using this model we are able to generate interesting and sometimes surprising results for the city under consideration.
Are Immigrants' Earnings Influenced by the Characteristics of Their Neighbours?
Authors: Musterd Sako , Andersson Roger , Galster George , Kauppinen Timo M
Published: February 2008

Differences in immigrant economic trajectories have been attributed to a wide variety of factors. One of these is the local spatial context where immigrants reside. This spatial context assumes special salience in light of expanding public exposure to and scholarly interest in the potential impacts of spatial concentrations of immigrants. A crucial question is whether immigrants' opportunities are influenced by their neighbours. In this paper we contribute statistical evidence relevant to answering this vital question. We develop multiple measures of the spatial context in which immigrants reside and assess their contribution to the average earnings of immigrant individuals in the three large Swedish metropolitan areas, controlling for individual and regional labour-market characteristics. We use unusually rich longitudinal information about Swedish immigrants during the 1995–2002 period. We find evidence that immigrant men and women paid a substantial penalty during 1999–2002 if in 1999 they resided in areas where a substantial number of their neighbours were members of the same ethnic group. The evidence suggests that own-group concentrations can initially pay dividends for immigrants, but these benefits quickly turn into net disadvantages over time.
Explaining Continuity and Change in International Policies: Issue Linkage, Venue Change, and Learning on Policies for the River Scheldt Estuary 1967–2005
Authors: Meijerink Sander
Published: February 2008

This paper aims to assess the explanatory power and to explore the compatibility of three major accounts of policy continuity and change in cross-border policy domains: negotiation analysis (NA), the advocacy coalition framework (ACF), and the punctuated-equilibrium (PE) framework. These frameworks are used to analyze policies for the river Scheldt estuary between 1967 and 2005. The estuary of the river Scheldt is situated partly in the Belgian region of Flanders and partly in the Netherlands. Major international policy issues in this estuary are the maritime access to the port of Antwerp, water and sediment pollution, and estuarine rehabilitation. It will be shown that the negotiations on these issues are characterized by complex issue linkages, and that NA does very well in explaining both deadlocks and international policy agreement. However, unlike the ACF, NA does not specify how actors come to define their interests. Moreover, we will argue that learning across the prodevelopment Antwerp coalition and the cross-border environmentalist coalition accounts for a gradual convergence of Dutch and Flemish perceived interests. Finally, PE offers useful complementary insights as Scheldt estuary policies cannot be understood without addressing the interrelations between the processes of negotiation, learning, the creation and enforcement of game rules, which have been going on in different venues simultaneously.
Reverse wave propagation in the cochlea
Authors: He Wenxuan , Fridberger Anders , Porsov Edward , Grosh Karl , Ren Tianying
Published: February 2008

Otoacoustic emissions, sounds generated by the inner ear, are widely used for diagnosing hearing disorders and studying cochlear mechanics. However, it remains unclear how emissions travel from their generation sites to the cochlear base. The prevailing view is that emissions reach the cochlear base via a backward-traveling wave, a slow-propagating transverse wave, along the cochlear partition. A different view is that emissions propagate to the cochlear base via the cochlear fluids as a compressional wave, a fast longitudinal wave. These theories were experimentally tested in this study by measuring basilar membrane (BM) vibrations at the cubic distortion product (DP) frequency from two longitudinal locations with a laser interferometer. Generation sites of DPs were varied by changing frequencies of primary tones while keeping the frequency ratio constant. Here, we show that BM vibration amplitude and phase at the DP frequency are very similar to responses evoked by external tones. Importantly, the BM vibration phase at a basal location leads that at a more apical location, indicating a traveling wave that propagates in the forward direction. These data are in conflict with the backward- traveling-wave theory but are consistent with the idea that the emission comes out of the cochlea predominantly through compressional waves in the cochlear fluids.
Heart failure drug digitoxin induces calcium uptake into cells by forming transmembrane calcium channels
Authors: Arispe Nelson , Diaz Juan Carlos , Simakova Olga , Pollard Harvey B.
Published: February 2008

Digitoxin and other cardiac glycosides are important, centuries-old drugs for treating congestive heart failure. However, the mechanism of action of these compounds is still being elucidated. Calcium is known to potentiate the toxicity of these drugs, and we have hypothesized that digitoxin might mediate calcium entry into cells. We report here that digitoxin molecules mediate calcium entry into intact cells. Multimers of digitoxin molecules also are able to form calcium channels in pure planar phospholipid bilayers. These digitoxin channels are blocked by Al
3+
and La
3+
but not by Mg
2+
or the classical
l
-type calcium channel blocker, nitrendipine. In bilayers, we find that the chemistry of the lipid affects the kinetics of the digitoxin channel activity, but not the cation selectivity. Antibodies against digitoxin promptly neutralize digitoxin channels in both cells and bilayers. We propose that these digitoxin calcium channels may be part of the mechanism by which digitoxin and other active cardiac glycosides, such as digoxin, exert system-wide actions at and above the therapeutic concentration range.
From Universal Laws of Cognition to Specific Cognitive Models
Authors: Chater Nick , Brown Gordon D. A.
Published: February 2008

The remarkable successes of the physical sciences have been built on highly general quantitative laws, which serve as the basis for understanding an enormous variety of specific physical systems. How far is it possible to construct universal principles in the cognitive sciences, in terms of which specific aspects of perception, memory, or decision making might be modelled? Following Shepard (e.g., ), it is argued that some universal principles may be attainable in cognitive science. Here, 2 examples are proposed: the simplicity principle (which states that the cognitive system prefers patterns that provide simpler explanations of available data); and the scale‐invariance principle, which states that many cognitive phenomena are independent of the scale of relevant underlying physical variables, such as time, space, luminance, or sound pressure. This article illustrates how principles may be combined to explain specific cognitive processes by using these principles to derive SIMPLE, a formal model of memory for serial order (), and briefly mentions some extensions to models of identification and categorization. This article also considers the scope and limitations of universal laws in cognitive science.
A Rational Analysis of Rule‐Based Concept Learning
Authors: Goodman Noah D. , Tenenbaum Joshua B. , Feldman Jacob , Griffiths Thomas L.
Published: February 2008

This article proposes a new model of human concept learning that provides a rational analysis of learning feature‐based concepts. This model is built upon Bayesian inference for a grammatically structured hypothesis space—a concept language of logical rules. This article compares the model predictions to human generalization judgments in several well‐known category learning experiments, and finds good agreement for both average and individual participant generalizations. This article further investigates judgments for a broad set of 7‐feature concepts—a more natural setting in several ways—and again finds that the model explains human performance.
Is a Single‐Bladed Knife Enough to Dissect Human Cognition? Commentary on Griffiths et al.
Authors: Fu Wai‐Tat
Published: February 2008

Griffiths, Christian, and Kalish (this issue) present an iterative‐learning paradigm applying a Bayesian model to understand inductive biases in categorization. The authors argue that the paradigm is useful as an exploratory tool to understand inductive biases in situations where little is known about the task. It is argued that a theory developed only at the computational level is much like a single‐bladed knife that is only useful in highly idealized situations. To be useful as a general tool that cuts through the complex fabric of cognition, we need at least two‐bladed scissors that combine both computational and psychological constraints to characterize human behavior. To temper its sometimes expansive claims, it is time to show what a Bayesian model cannot explain. Insight as to how human reality may differ from the Bayesian predictions may shed more light on human cognition than the simpler focus on what the Bayesian approach can explain. There remains much to be done in terms of integrating Bayesian approaches and other approaches in modeling human cognition.
Microtubule stabilization specifies initial neuronal polarization
Authors: Witte Harald , Neukirchen Dorothee , Bradke Frank
Published: February 2008

Axon formation is the initial step in establishing neuronal polarity. We examine here the role of microtubule dynamics in neuronal polarization using hippocampal neurons in culture. We see increased microtubule stability along the shaft in a single neurite before axon formation and in the axon of morphologically polarized cells. Loss of polarity or formation of multiple axons after manipulation of neuronal polarity regulators, synapses of amphids defective (SAD) kinases, and glycogen synthase kinase-3β correlates with characteristic changes in microtubule turnover. Consistently, changing the microtubule dynamics is sufficient to alter neuronal polarization. Application of low doses of the microtubule-destabilizing drug nocodazole selectively reduces the formation of future dendrites. Conversely, low doses of the microtubule-stabilizing drug taxol shift polymerizing microtubules from neurite shafts to process tips and lead to the formation of multiple axons. Finally, local stabilization of microtubules using a photoactivatable analogue of taxol induces axon formation from the activated area. Thus, local microtubule stabilization in one neurite is a physiological signal specifying neuronal polarization.
Stable hZW10 kinetochore residency, mediated by hZwint-1 interaction, is essential for the mitotic checkpoint
Authors: Famulski Jakub K. , Vos Larissa , Sun Xuejun , Chan Gordon
Published: February 2008

The mitotic checkpoint is an essential surveillance mechanism that ensures high fidelity chromosome segregation during mitosis. Mitotic checkpoint function depends on numerous kinetochore proteins, including ZW10, ROD, and Zwilch (the ROD–ZW10–Zwilch complex). Through an extensive mutagenesis screen of hZW10, we have mapped the kinetochore localization domain of hZW10 as well as the hZwint-1 interaction domain. We find that hZwint-1–noninteracting mutants still localize to kinetochores. In addition, using fluorescence recovery after photobleaching, we have found that hZW10 residency at metaphase kinetochores is brief (half-time of 13 s). However, during prometaphase or at unattached kinetochores, enhanced green fluorescent protein–hZW10 becomes a stable component of the kinetochore. Moreover, we find that stable hZW10 kinetochore residency at prometaphase kinetochores is dependent on its interaction with hZwint-1, and is essential for mitotic checkpoint arrest.
Cripto promotes A–P axis specification independently of its stimulatory effect on Nodal autoinduction
Authors: D'Andrea Daniela , Liguori Giovanna L. , Le Good J. Ann , Lonardo Enza , Andersson Olov , Constam Daniel B. , Persico Maria G. , Minchiotti Gabriella
Published: February 2008

The EGF-CFC gene cripto governs anterior–posterior (A–P) axis specification in the vertebrate embryo. Existing models suggest that Cripto facilitates binding of Nodal to an ActRII–activin-like kinase (ALK) 4 receptor complex. Cripto also has a crucial function in cellular transformation that is independent of Nodal and ALK4. However, how ALK4-independent Cripto pathways function in vivo has remained unclear. We have generated cripto mutants carrying the amino acid substitution F78A, which blocks the Nodal–ALK4–Smad2 signaling both in embryonic stem cells and cell-based assays. In criptoF78A/F78A mouse embryos, Nodal fails to expand its own expression domain and that of cripto, indicating that F78 is essential in vivo to stimulate Smad-dependent Nodal autoinduction. In sharp contrast to cripto-null mutants, criptoF78A/F78A embryos establish an A–P axis and initiate gastrulation movements. Our findings provide in vivo evidence that Cripto is required in the Nodal–Smad2 pathway to activate an autoinductive feedback loop, whereas it can promote A–P axis formation and initiate gastrulation movements independently of its stimulatory effect on the canonical Nodal–ALK4–Smad2 signaling pathway.
Legislative Productivity of the U.S. Congress, 1789–2004
Authors: Grant J. Tobin , Kelly Nathan J.
Published: February 2008

We measure legislative productivity for the entire history of the U.S. Congress. Current measures of legislative productivity are problematic because they measure productivity for a limited number of decades and because they are based on different aspects of productivity. We provide a methodology for measuring (1) a Legislative Productivity Index (LPI) and (2) a Major Legislation Index (MLI). We use the W-CALC algorithm of Stimson (1999, Public opinion in America: Moods, cycles, and swings. 2nd ed. Boulder, CO: Westview Press) to combine information from previously used indicators of productivity into measures of the LPI and the MLI. We provide examinations of content, convergent, and construct validity. The construct validity model includes potential determinants of legislative productivity. We conclude that the LPI and the MLI are superior measures of productivity than other measures used in the literature.
An MHC-restricted CD8+ T-cell response is induced in cattle by foot-and-mouth disease virus (FMDV) infection and also following vaccination with inactivated FMDV
Authors: Guzman Efrain , Taylor Geraldine , Charleston Bryan , Skinner Michael A. , Ellis Shirley A.
Published: February 2008

Foot-and-mouth disease virus (FMDV) causes a highly contagious disease of cloven-hooved animals that carries enormous economic consequences. CD8+cytotoxic T lymphocytes play an important role in protection and disease outcome in viral infections but, to date, the role of the CD8+T-cell immune response to FMDV remains unclear. This study aimed to investigate major histocompatibility complex (MHC) class I-restricted CD8+T-cell responses to FMDV in vaccinated and in infected cattle. Anin vitroassay was used to detect antigen-specific gamma interferon release by CD8+T cells in FMDV-infected cattle of known MHC class I genotypes. A significant MHC class I-restricted CD8+T-cell response was detected to both FMDV strain O1 BFS and a recombinant fowlpox virus expressing the structural proteins of FMDV. Antigen-specific MHC class I-restricted CD8+T-cell responses were also detected in cattle vaccinated with inactivated FMDV. These responses were shown to be directed, at least in part, to epitopes within the structural proteins (P12A region) of the virus. By using mouse cells expressing single cattle MHC class I alleles, it was possible to identify the restriction elements in each case. Identification of these epitopes will facilitate the quantitative and qualitative analysis of FMDV-specific memory CD8+T cells in cattle and help to ensure that potential vaccines induce a qualitatively appropriate CD8+T-cell response.
H5N1 avian influenza re-emergence of Lake Qinghai: phylogenetic and antigenic analyses of the newly isolated viruses and roles of migratory birds in virus circulation
Authors: Wang Guihua , Zhan Dawei , Li Laixing , Lei Fumin , Liu Bohua , Liu Di , Xiao Haixia , Feng Youjun , Li Jing , Yang Baoan , Yin Zuohua , Song Xiaohui , Zhu Xiaojia , Cong Yanlong , Pu Juan , Wang Jian , Liu Jinhua , Gao George F. , Zhu Qingyu
Published: February 2008

Highly pathogenic avian influenza H5N1 virus has swept west across the globe and caused serious debates on the roles of migratory birds in virus circulation since the first large-scale outbreak in migratory birds of Lake Qinghai, 2005. In May 2006, another outbreak struck Lake Qinghai and six novel strains were isolated. To elucidate these QH06 viruses, the six isolates were subjected to whole-genome sequencing. Phylogenetic analyses show that QH06 viruses are derived from the lineages of Lake Qinghai, 2005. Five of the six novel isolates are adjacent to the strain A/Cygnus olor/Croatia/1/05, and the last one is related to the strain A/duck/Novosibirsk/02/05, an isolate of the flyway. Antigenic analyses suggest that QH06 and QH05 viruses are similar to each other. These findings implicate that QH06 viruses of Lake Qinghai may travel back via migratory birds, though not ruling out the possibility of local circulation of viruses of Lake Qinghai.
The F protein of Helicoverpa armigera single nucleopolyhedrovirus can be substituted functionally with its homologue from Spodoptera exigua multiple nucleopolyhedrovirus
Authors: Wang Manli , Tan Ying , Yin Feifei , Deng Fei , Vlak Just M. , Hu Zhihong , Wang Hualin
Published: February 2008

F proteins of group II nucleopolyhedroviruses (NPVs) are envelope fusion proteins essential for virus entry and egress. An F-nullHelicoverpa armigerasingle nucleocapsid NPV (HearNPV) bacmid, HaBacΔF, was constructed. This bacmid could not produce infectious budded virus (BV) when transfected into HzAM1 cells, showing that F protein is essential for cell-to-cell transmission of BVs. When HaBacΔF was pseudotyped with the homologous F protein (HaBacΔF-HaF, positive control) or with the heterologous F protein fromSpodoptera exiguamultinucleocapsid NPV (SeMNPV) (HaBacΔF-SeF), infectious BVs were produced with similar kinetics. In the late phase of infection, the BV titre of HaBacΔF-SeF virus was about ten times lower than that of HaBacΔF-HaF virus. Both pseudotyped viruses were able to fuse HzAM1 cells in a similar fashion. The F proteins of both HearNPV and SeMNPV were completely cleaved into F1and F2in the BVs of vHaBacΔF-HaF and vHaBacΔF-SeF, respectively, but the cleavage of SeF in vHaBacΔF-SeF-infected HzAM1 cells was incomplete, explaining the lower BV titre of vHaBacΔF-SeF. Polyclonal antisera against HaF1and SeF1specifically neutralized the infection of vHaBacΔF-HaF and vHaBacΔF-SeF, respectively. HaF1antiserum showed some cross-neutralization with vHaBacΔF-SeF. These results demonstrate that group II NPV F proteins can be functionally replaced with a homologue of other group II NPVs, suggesting that the interaction of F with other viral or host proteins is not absolutely species-specific.
Multiple maternity in black‐headed gull Larus ridibundus clutches as revealed by protein fingerprinting
Authors: Duda Norbert , Ch ętnicki Wlodzimierz , Waldeck Peter , Andersson Malte
Published: February 2008

Social monogamy with biparental care is the norm in gulls Laridae, but egg colour variation suggests that some nests may contain mixed clutches laid by more than one female. Here we use protein fingerprinting of egg albumen to assess the occurrence of mixed maternity clutches in three colonies of black‐headed gulls. Among 160 analysed clutches with >1 egg, 34% contained eggs from more than one female, and 15% of the eggs in clutches >1 came from other females than the major female (laying most eggs in nest). Among clutches with 2–3 eggs 28% were mixed, and among clutches with 4 or more eggs 89% contained eggs from two or more females. There were significantly fewer eggs from the major female in mixed nests (mean=2.06±0.63 SD) than in non‐mixed nests (mean=2.82±0.43 SD). In nests without evidence of female conflict, hatching success of minority eggs was similar to that of eggs from the major female (12.5 and 8.4%, respectively). In 21% of mixed maternity nests, one or more minority eggs was buried or punctured, and 25% of eggs from major females were also found evicted, suggesting conflict between females and rejection of eggs. Intra‐specific nest parasitism seems the most likely cause of mixed clutches, but there are also other possible causes.
Sex biased natal dispersal in a closed, saturated population of Seychelles warblersAcrocephalus sechellensis
Authors: Eikenaar Cas , Richardson David S. , Brouwer Lyanne , Komdeur Jan
Published: February 2008

The distances that individuals disperse, from their natal site to the site of first breeding and between breeding sites, have important consequences for the dynamics and genetic structure of a population. Nearly all previous studies on dispersal have the problem that, because the study area encompassed only a part of the population, emigration may have been confounded with mortality. As a result long‐distance dispersers may have been overlooked and dispersal data biased towards short distances. By studying a virtually closed population of Seychelles warblersAcrocephalus sechellensiswe obtained almost unbiased results on several aspects of dispersal. As in the majority of other avian species, natal dispersal distance was female biased in the Seychelles warbler. Female offspring also forayed further from the natal territory in search of breeding vacancies than male offspring. The sex bias in natal dispersal distance did, however, depend on local breeding density. In males, dispersal distance decreased as the number of territories bordering the natal territory increased, while in females, dispersal distance did not vary with local density. Dispersal by breeders was rare and, unlike in most species, distances did not differ between the sexes. We argue that our results favour the idea that the sex bias in natal dispersal distance in the Seychelles warbler is due to inbreeding avoidance and not resource competition or intrasexual competition for mates.