bluuebunny/crossref_metadata_2025 huggingface dataset:
DEBT POLICY RULE, PRODUCTIVE GOVERNMENT SPENDING, AND MULTIPLE GROWTH PATHS
Authors: Futagami Koichi , Iwaisako Tatsuro , Ohdoi Ryoji
Published: June 2008

This paper constructs an endogenous growth model with productive government spending. In this model, the government can finance its costs through income tax and government debt and has a target level of government debt relative to the size of the economy. We show that there are two steady states. One is associated with high growth and the other with low growth. It is also shown that whether the government uses income taxes or government bonds makes the results differ significantly. In particular, an increase in government bonds reduces the growth rate in the high-growth steady state and raises the growth rate in the low-growth steady state. Conversely, an increase in the income tax rate reduces the growth rate in the low-growth steady state and there exists some tax rate that maximizes the growth rate in the high-growth steady state. Finally, the level of welfare in the low-growth steady state is lower than that in the high-growth steady state.
NOTE ON FINITE APPROXIMATIONS OF THE ASYMPTOTICALLY IDEAL MODEL
Authors: Serletis Apostolos , Shahmoradi Asghar
Published: June 2008

This note builds on recent work by Serletis and Shahmoradi [Macroeconomic Dynamics 9 (2005), 542–559] and estimates the AIM model at different degrees of approximation, using the same optimization procedures as in Gallant and Golub [Journal of Econometrics. 26 (1984), 295–321]. We estimate the models subject to regularity and provide a comparison between the different versions. We argue that the AIM(3) model estimated subject to global curvature currently provides the best specification for research in semiparametric modeling of consumer demand systems.
DYNAMICS OF THE CONSUMPTION–CAPITAL RATIO, THE SAVING RATE, AND THE WEALTH DISTRIBUTION IN THE NEOCLASSICAL GROWTH MODEL
Authors: Guha Subrata
Published: June 2008

The paper utilizes a common approach to derive sufficient conditions for strictly monotonic behavior of three ratios along the transition to the steady state in the Ramsey–Cass–Koopmans model: the consumption–capital ratio, the consumption–output ratio (and the saving rate), and the consumption–wage ratio. These conditions are then applied to derive additional results on the transitional dynamics of the distribution of wealth in the model (when individual consumers are differentiated by their initial wealth endowments).
TASTE FOR VARIETY AND ENDOGENOUS FLUCTUATIONS IN A MONOPOLISTIC COMPETITION MODEL
Authors: Seegmuller Thomas
Published: June 2008

In past years, imperfect competition has been introduced in several dynamic models to show how markup variability, increasing returns (decreasing marginal cost), and monopoly profits affect the occurrence of endogenous fluctuations. In this paper, we focus on another possible feature of imperfectly competitive economies: consumers' taste for variety as a result of endogenous product diversity. Introducing monopolistic competition [Dixit and Stiglitz (1977), Benassy (1996)] in an overlapping generations model in which consumers have taste for variety, we show that local indeterminacy can occur under the three following conditions: a high substitution between capital and labor, increasing returns arbitrarily small, and a not too elastic labor supply. The key mechanism for this result is based on the fact that, because of taste for variety, the aggregate price decreases with the procyclical product diversity, which has a direct influence on the real wage and the real interest rate.
EFFICIENCY–EQUALITY TRADE-OFF OF SOCIAL INSURANCE
Authors: Boháĉek Radim
Published: June 2008

This paper studies the effects of social insurance policies on efficiency and distribution of resources in a general equilibrium model of a closed economy with heterogeneous agents and repeated moral hazard. I compare optimal allocations in stationary recursive equilibria for economies with different guaranteed minimum consumption levels (social insurance). I show that the efficiency–equality trade-off associated with social insurance does not hold: Efficiency and inequality decrease as the minimum guaranteed consumption increases to around one third of the average consumption. However, if social insurance expands even further, the efficiency loss becomes very high and inequality increases.
COMPARATIVE STATICS AND DYNAMICS OF THE ROMER R&D GROWTH MODEL WITH QUALITY UPGRADING
Authors: Arnold Lutz G. , Kornprobst Wolfgang
Published: June 2008

This paper replaces increasing product variety with quality upgrading in the Romer model [Romer, Paul M., Journal of Political Economy 98 (1990), S71–S102]. We show that the range of parameters for which a steady state exists can be divided into two subspaces with well-behaved comparative statics and saddle-point dynamics in one subspace, but with “perverse” comparative-statics properties and either equilibrium indeterminacy or instability in the other subspace. These results for the closed economy can also be used to characterize the dynamics of the M-country open-economy version of the model.
NONLINEARITIES IN THE DYNAMICS OF THE EURO AREA DEMAND FOR M1
Authors: Calza Alessandro , Zaghini Andrea
Published: June 2008

This paper finds evidence of nonlinearities in the dynamics of the euro area demand for the narrow aggregate M1. A long-run money demand relationship is first estimated over a sample period covering the past three decades. Although the parameters of the relationship are jointly stable, there are indications of nonlinearity in the residuals of the error-correction model. This nonlinearity is explicitly modeled using a fairly general Markov switching error-correction model with satisfactory results. The empirical findings of the paper are consistent with theoretical predictions of nonlinearities in the dynamics of adjustment to equilibrium stemming from “buffer stock” and “target-threshold” models and with analogous empirical evidence for European countries and the United States.
Living as a drug addict in Oslo, Norway – a study focusing on nutrition and health
Authors: Sæland M , Haugen M , Eriksen F-L , Smehaugen A , Wandel M , Böhmer T , Oshaug A
Published: June 2008

Objectives

To investigate nutritional status and related living conditions among drug addicts in Oslo.

Design

A cross-sectional study of nutritional status evaluated by anthropometric and biochemical measurements; a structured interview concerning education, living conditions, income source, drug history and sex practice; and biochemical testing of sexually transmitted infections.

Setting

The present study was conducted between November 2001 and April 2003 in locations where the drug addicts reside in Oslo.

Subjects

A total of 123 male and seventy-two female addicts using drugs by injections regularly.

Results

We found that 20 % of the women were moderately underweight (BMI in kg/m2) (16·5 < BMI < 18·5), 7 % were severely underweight (BMI ≤ 16·5) and 3 % of the men were moderately underweight (16·5 < BMI < 18·5). BMI was positively correlated with days institutionalised and number of eating events per day. Respondents sleeping rough had significantly reduced BMI compared to those in hostels and shelters. The concentrations of Hb, serum ferritin and albumin supported a higher prevalence of malnutrition among the women. Hepatitis C was found in 85 %, active hepatitis B in 6 % and less than 2 % were HIV positive. Also, 84 % received public financial support, 38 % of the women had prostitution as a significant income source, while burglary was most prevalent among the men; 20 % were pushing drugs.

Conclusion

Malnutrition among the drug addicts varied from 5 % to 30 %, independent of drug history, education and income. Moderate and severe underweight was most prevalent among the women. Being previously institutionalised and having increased number of eating events increased BMI. Sleeping rough correlated with reduced body weight. Hepatitis C infection was common; hepatitis B and HIV were rare.
Drosophila RalA is essential for the maintenance of Jak/Stat signalling in ovarian follicles
Authors: Ghiglione Christian , Devergne Olivier , Cerezo Delphine , Noselli Stéphane
Published: June 2008

Small GTPases of the Ras‐like (Ral) family are crucial for signalling functions in both normal and cancer cells; however, their role in a developing organism is poorly understood. Here, we identify the Drosophila Ral homologue RalA as a new key regulator of polar‐cell differentiation during oogenesis. Polar cells have a crucial role in patterning the egg chamber and in recruiting border cells, which undergo collective and guided migration. We show that RalA function is essential for the maintenance of anterior and posterior polar‐cell fate and survival. RalA is required cell autonomously to control the expression of polar‐cell‐specific markers, including the Jak/Stat ligand Unpaired. The loss of RalA also causes a cell non‐autonomous phenotype owing to reduced Jak/Stat signalling in neighbouring follicle cells. As a result, border‐cell assembly and migration as well as the polarization of the oocyte are defective. Thus, RalA is required in organizing centres to control proper patterning and migration in vivo.
Dipolophoresis of nanoparticles
Authors: Miloh Touvia
Published: June 2008

A general methodology is presented for evaluating the dielectrophoretic velocity of a freely suspended spherical colloid in an electrolyte solutes under the action of a nonuniform electric field and for a Debye layer of arbitrary thickness. The nonlinear induced charge electrophoretic problem is first considered. General analytic expressions are derived for the mobility of an uncharged particle in the form of products between adjacent modes of the ambient electric field demonstrating a symmetry-breaking-type phenomena. It is shown that the mobility of a conducting (i.e., ideally polarizable) spherical particle vanishes for a quadratic electric field in the limiting case of a thin Debye layer. For an infinitely thick Debye layer it attains asymptotically a positive finite value. Yet, there is another value of a finite Debye length for which the mobility changes sign. This interesting nonintuitive effect may have implications to separation of particles by size. The linear case of a uniformly charged colloid is obtained as a special limit and the classical mobility expressions of Henry [Proc. R. Soc. (London) 4, 106 (1931)], Smulokowski [Handbook of Electricity and Magnetism, edited by L. Graetz (Barth, Leipzig, 1921), p. 2], and Huckel [Physik 25, 204 (1924)] for a spherical colloid are readily recovered. The formulation is based on an extension of Teubner’s integral approach for nonuniform electric fields and on utilizing a variant of the Lorentz reciprocal theorem for Stokes flows. As an example demonstrating the effect of nearby boundaries, the method is finally applied for the radially symmetric case involving a freely suspended colloid within a hollow spherical capsule filled with electrolyte. It can be considered as an extension of Henry’s unbounded solution for a confined three dimensional embodiment.
Thermal resistivity of Si–Ge alloys by molecular-dynamics simulation
Authors: Skye Ashton , Schelling Patrick K.
Published: June 2008

We explore the ability of molecular-dynamics simulation to elucidate thermal transport in Si–Ge alloys. Simulations using Stillinger–Weber potentials yield values for the thermal resistivity significantly higher than experimental measurements. In agreement with experiment and theoretical predictions, we find that scattering from mass disorder is dominant, with bond disorder and strain effects playing a very minor role. To explore the origins of the large discrepancies with experiment, we use theoretical methods suitable for the limit where point-defect scattering dominates the resistivity. We find that point-defect scattering models based on a Debye spectrum cannot be used to fit our simulations, indicating that high-frequency modes may play an important role in the simulation. The results have important implications for using classical molecular-dynamics simulation to predict properties of alloy materials near and below the Debye temperature.
Theoretical study of hydrogenated Mg, Ca@Al12 clusters
Authors: Lu Q. L. , Jalbout A. F. , Luo Q. Q. , Wan J. G. , Wang G. H.
Published: June 2008

The studies on the structure and electronic properties of hydrogenated metal embedded Al12 cage clusters have been performed by density functional theory calculations. We have investigated aluminum cluster hydrides with 12 and 14 hydrogen atoms, respectively. Insertion of the Mg, Ca alkali metals remarkably enhances the stability of the aluminum clusters. The hydrogen atom prefers to occupy on-top sites along the surface of the clusters. Mulliken population analysis indicates that significant charge transfer occurs between the Mg and Ca atoms and the Al atoms. Our computations suggest that these clusters appear to be physically and chemically stable.
Effects of electrostatic screening on the conformation of single DNA molecules confined in a nanochannel
Authors: Zhang Ce , Zhang Fang , van Kan Jeroen A. , van der Maarel Johan R. C.
Published: June 2008

Single T4-DNA molecules were confined in rectangular-shaped channels with a depth of 300nm and a width in the range of 150–300nm casted in a poly(dimethylsiloxane) nanofluidic chip. The extensions of the DNA molecules were measured with fluorescence microscopy as a function of the ionic strength and composition of the buffer as well as the DNA intercalation level by the YOYO-1 dye. The data were interpreted with the scaling theory for a wormlike polymer in good solvent, including the effects of confinement, charge, and self-avoidance. It was found that the elongation of the DNA molecules with decreasing ionic strength can be interpreted in terms of an increase of the persistence length. Self-avoidance effects on the extension are moderate, due to the small correlation length imposed by the channel cross-sectional diameter. Intercalation of the dye results in an increase of the DNA contour length and a partial neutralization of the DNA charge, but besides effects of electrostatic origin it has no significant effect on the bare bending rigidity. In the presence of divalent cations, the DNA molecules were observed to contract, but they do not collapse into a condensed structure. It is proposed that this contraction results from a divalent counterion mediated attractive force between the segments of the DNA molecule.
Transparent and conducting electrodes for organic electronics from reduced graphene oxide
Authors: Eda Goki , Lin Yun-Yue , Miller Steve , Chen Chun-Wei , Su Wei-Fang , Chhowalla Manish
Published: June 2008

The deposition and optoelectronic properties of reduced graphene oxide thin films are described. Thin films with thicknesses ranging from 1–10nm have been deposited by the vacuum filtration method. The conductivity of the thin films can be varied over six orders of magnitude by varying the filtration volume of the graphene oxide aqueous suspension while maintaining the transmittance between 60%–95%. In addition, enhancement in the conductance through Cl doping is demonstrated. The combination of the reduction and Cl treatments make the reduced graphene oxide thin films sufficiently conducting to incorporate them as the hole collecting electrode in proof of concept organic photovoltaic devices.
Single-chain dynamics in a semidilute polymer solution under steady shear
Authors: Jose Prasanth P. , Szamel Grzegorz
Published: June 2008

We use Brownian dynamics computer simulations to investigate single-chain dynamics in a semidilute polymer solution undergoing a steady, uniform shear flow. In the presence of the shear flow, the system used in the present study exhibits anisotropic structure factors, often referred to as butterfly patterns, which rotate with increasing shear rate [P. P. Jose and G. Szamel, J. Chem. Phys. 127, 114905 (2007)]. The rotation of these patterns correlates with shear thinning of the solution. In order to elucidate the microscopic origin of this behavior, we have investigated the change in the single-chain dynamics in the solution: We have focused on the relaxation of the end-to-end vector, the Rouse modes, and the radius of gyration tensor. In equilibrium and for small shear rates, these quantities show double exponential relaxation. With increasing shear rate, they show oscillatory relaxation, which hints at the tumbling motion of the chain. In the high shear rate regime, the frequency of the oscillations of the end-to-end vector autocorrelation function shows a power law dependence on the shear rate. We have compared the single-chain dynamics in the semidilute solution with that in a dilute solution. An analysis of the instantaneous values of the radius of gyration tensor, the end-to-end distance, and the normal stress along the system’s trajectory reveals a synchronization of the fluctuations of these quantities.
Compression behavior of WC and WC-6%Co up to 50 GPa determined by synchrotron x-ray diffraction and ultrasonic techniques
Authors: Amulele George M. , Manghnani Murli H. , Marriappan Sekar , Hong Xinguo , Li Fengung , Qin Xiomei , Liermann Hanns P.
Published: June 2008

The equations of state (pressure-volume relations) for WC and WC-6%Co have been determined by synchrotron x-ray diffraction measurements on polycrystalline powder samples loaded in a diamond anvil cell as well as by ultrasonic measurements on hot-pressed polycrystalline, cylindrical samples loaded in a multianvil high-pressure apparatus. The third-order Birch–Murnaghan equation of state fitted to the x-ray diffraction pressure-density sets of data, collected up to 50 GPa, yields ambient pressure isothermal bulk moduli of KoT=411.8±12.1 GPa and KoT=402.4±14.1 GPa, with pressure derivatives of KoT′=5.45±0.73 and KoT′=7.50±0.86 for WC and WC-6%Co, respectively. The ultrasonic measurements, conducted up to 14 GPa, enabled the determination of the pressure dependences of both bulk and shear moduli. Using Eulerian finite strain equations to fit the ultrasonic data, we obtain for WC an ambient pressure adiabatic bulk modulus of Kos=383.8±0.8 GPa, and Kos′=2.61±0.07 for its pressure derivative, while values of Gos=304.0±0.3 GPa and Gos′=1.50±0.09 were determined for the shear modulus and its pressure derivative, respectively. Meanwhile, for WC-6%Co, we obtain Kos=357.5±1.0 GPa, Kos′=5.18±0.14, Gos=253.5±0.3 GPa, and Gos′=1.09±0.09. The equations of state derived from the ultrasonic data are in good agreement with extrapolated results reported previously by Day and Ruoff [J. Appl. Phys. 44, 2447 (1973)] and Gerlich and Kennedy [J. Appl. Phys. 50, 3331 (1978)] who carried out measurements up to 0.2 and 1.0 GPa, respectively.
Generating multichain configurations of an inhomogeneous melt from the knowledge of single-chain properties
Authors: Hömberg Martin , Müller Marcus
Published: June 2008

Mean-field techniques provide a rather accurate description of single-chain conformations in spatially inhomogeneous polymer systems containing interfaces or surfaces. Intermolecular correlations, however, are not described by the mean-field approach and information about the distribution of distance between different molecules is lost. Based on the knowledge of the exact equilibrium single-chain properties in contact with solid substrates, we generate multichain configurations that serve as nearly equilibrated starting configurations for molecular dynamics simulations by utilizing the packing algorithm of [Auhl et al., J. Chem. Phys. 119, 12718 (2003)] for spatially inhomogeneous systems, i.e., a thin polymer film confined between two solid substrates. The single-chain conformations are packed into the thin film conserving the single-chain properties and simultaneously minimizing local fluctuations of the density. The extent to which enforcing incompressibility of a dense polymer liquid during the packing process is able to re-establish intermolecular correlations is investigated by monitoring intermolecular correlation functions and the structure function of density fluctuations as a function of the distance from the confining solid substrates.
Field electron emission enhancement of amorphous carbon through a niobium buffer layer
Authors: Xu L. , Wang C. , Hu C. Q. , Yu W. X. , Zhao Z. D. , Zheng W. T.
Published: June 2008

Field electron emission for amorphous carbon (a-C) films deposited on Si (100) substrates with a niobium buffer layer is investigated. It is found that the Nb buffer layer can substantially improve the electron field emission properties of the a-C films, which can be attributed to an increase in the enhancement factor β on the surface of the a-C films after insertion of the Nb layer. Moreover, the electron field emission can be further enhanced by annealing a-C∕Nb∕Si, which can be ascribed to the formation of NbC phase at the interface between a-C and Nb layer, revealed by x-ray diffraction for annealed a-C∕Nb∕Si. The first-principles calculated results show that the formation of NbC can lower the interface barrier and improve the back contact between Nb and a-C films, enhancing the field electron emission of a-C.
Control of film morphology and its effects on subthreshold characteristics in dibenzotetrathiafulvalene organic thin-film transistors
Authors: Yamada T. , Hasegawa T. , Hiraoka M. , Matsui H. , Tokura Y. , Saito G.
Published: June 2008

The interface engineering of dibenzotetrathiafulvalene organic thin-film transistors (OTFTs) is reported. Polycrystalline-film morphologies are successfully controlled by surface treatments of silicon dioxide dielectric substrates using hexamethyldisilazane, a silane coupling agent, to tune the average lateral grain sizes between 0.2 and 20μm. The field-effect mobility of the resulting OTFTs is approximately 0.55cm2∕Vs. The effects of the grain sizes on subthreshold properties are discussed in terms of the charge transport against the grain boundaries through the films.
Efficient linear-scaling calculation of response properties: Density matrix-based Laplace-transformed coupled-perturbed self-consistent field theory
Authors: Beer Matthias , Ochsenfeld Christian
Published: June 2008

A density matrix-based Laplace reformulation of coupled-perturbed self-consistent field (CPSCF) theory is presented. It allows a direct, instead of iterative, solution for the integral-independent part of the density matrix-based CPSCF (D-CPSCF) equations [J. Kussmann and C. Ochsenfeld, J. Chem. Phys. 127, 054103 (2007)]. In this way, the matrix-multiplication overhead compared to molecular orbital-based solutions is reduced to a minimum, while at the same time, the linear-scaling behavior of D-CPSCF theory is preserved. The present Laplace-based equation solver is expected to be of general applicability.
A microfocus x-ray source based on a nonmetal liquid-jet anode
Authors: Tuohimaa T. , Ewald J. , Schlie M. , Fernández-Varea J. M. , Hertz H. M. , Vogt U.
Published: June 2008

We demonstrate stable operation of a nonmetallic anode in an electron-impact x-ray source. A high-brightness electron beam is focused on a ∼70m∕s speed, ∼10μm diameter methanol jet producing stable x-ray emission with peak spectral brightness at ∼5.4×105photons∕(s×μm2×sr×0.1%BW). The jet is fully evaporated in the interaction point. The shape of a simulated spectrum using Monte Carlo methods shows good agreement with experimental data, and the theoretical brightness values give an upper limit for the achievable x-ray emission from jets with very high velocities. Using this anode concept, all compounds and elements found in liquid form are potentially usable for x-ray generation.
Linear and nonlinear optical properties of multifunctional PbVO3 thin films
Authors: Kumar Amit , Podraza Nikolas J. , Denev Sava , Li Jian , Martin Lane W. , Chu Ying-Hao , Ramesh R. , Collins Robert W. , Gopalan Venkatraman
Published: June 2008

Lead vanadate (PbVO3) is a multifunctional material which is both polar and magnetic. Its optical properties, important for linear and nonlinear optical spectroscopy of the material, are presented. Using spectroscopic ellipsometry, the refractive index and absorption versus wavelength of lead vanadate thin films at 295K is reported. Using optical second harmonic generation, the nonlinear optical coefficients were determined to be d15∕d31=0.20±0.02, d33∕d31=316.0±4.4, and ∣d33∣=10.40±0.35pm∕V at a fundamental wavelength of 800nm.
Fabrication and characterization of periodically poled lithium niobate waveguide using femtosecond laser pulses
Authors: Zhang Shuanggen , Yao Jianghong , Shi Qing , Liu Yange , Liu Weiwei , Huang Zhangchao , Lu Fuyun , Li Enbang
Published: June 2008

We present in this letter the fabrication and characterization of thermally stable type II waveguides in Z-cut periodically poled lithium niobate crystals. The waveguides were fabricated by using a femtosecond laser and were utilized for second harmonic generation. Our experiments have shown that a quasiphase matching wavelength of 1548.2nm, a tuning bandwidth of 2nm, and a tuning temperature range of 150.4±1.6°C can be achieved.
Investigation on polymer anode design for flexible polymer solar cells
Authors: Zhou Yinhua , Zhang Fengling , Tvingstedt Kristofer , Barrau Sophie , Li Fenghong , Tian Wenjing , Inganäs Olle
Published: June 2008

Bilayer polymer anode composed of poly(3,4-ethylene-dioxythiophene): polystyrenesulfonate (PEDOT:PSS) (PH500) and PEDOT:PSS (Baytron P VP Al 4083) was used to construct flexible polymer solar cells on plastic substrates polyethylene terephthalate (PET) with a device structure of PET/polymer anode/APFO-3:PCBM/LiF∕Al. The power conversion efficiency (PCE) of the indium tin oxide (ITO)-free solar cells achieved 2.2% under illumination of AM1.5 (100mWcm−2), which is 80% of the PCE of the reference cells with ITO on glass. The simplicity of preparing bilayer polymer anode and the comparable performance achieved in the flexible solar cells made the bilayer polymer anode an alternative to ITO for flexible solar cells produced by printing technology.
Molecular simulation of the carbon nanotube growth mode during catalytic synthesis
Authors: Banerjee Soumik , Naha Sayangdev , Puri Ishwar K.
Published: June 2008

Catalyzed growth of carbon nanostructures occurs mainly through two modes, i.e., base growth when the metal nanoparticle remains at the bottom of the nanotube, or when it is lifted by the growing carbon nanostructure due to tip growth. A correct prediction of the dominant growth mode depends on the energy gain due to the addition of C atoms from the carbon-metal catalyst solution to the graphene sheets forming the carbon nanostructures. We determine this energy gain through atomistic scale molecular dynamics simulations. Our results suggest tip growth for Ni and base growth for Fe catalysts.
Egg size and number is influenced by both environmental and social factors in a facultatively social bee
Authors: Kayaalp Pelin , Schwarz Michael P.
Published: June 2008

Social factors influencing the trade-off between egg size and number have been almost entirely neglected in studies of social insects. We examined egg size and number in an Australian allodapine bee where nutritional resource availability and social competition during egg laying vary over colony development. We hypothesised that during August queens should lay many eggs to provide work incentives for subordinates, but because resources are strongly limited these eggs will be small. In spring, resources are less limited but some subordinates also lay eggs, resulting in competition between offspring for communally provided food. Here, we hypothesised that females should attempt to direct resources preferentially to their own offspring by laying large eggs. We analysed egg numbers and weights as functions of colony size. We found that a trade-off existed in August nests but that egg size increased with egg number in October. In November, when larval eclosion was commencing, colonies with larvae had smaller mean egg weights than those with only eggs, suggesting that resources are directed away from oviposition towards larval provisioning. Our analyses suggest that egg size is a function of egg number, rather than colony size per se.
Changes in the physical properties of stomach digesta during fasting in tammar wallabies (Macropus eugenii eugenii)
Authors: Lentle R. G. , Stafford K. J. , Hemar Y. , Aseruvujanon P. , Mellor D. J. , Moughan P. J.
Published: June 2008

We compared changes in the particle size profiles, permeability and elastic shear modulus of digesta in the forestomach and rumen of fasting tammar wallabies (Macropus eugenii eugenii) and fistulated sheep respectively that had been fed chopped lucerne hay. The wet mass of digesta in the tammar wallaby stomach declined curvilinearly over 24 h. The relative proportion of particles >2 mm in size in tammar wallaby digesta increased significantly and that of particles <2 mm in size decreased significantly after 12 h of fasting. This contrasted with the sheep rumen digesta, in which the relative proportions of coarse and fine particles did not change significantly over time. The permeability of wallaby digesta increased significantly after 24 h whilst that of sheep declined. All samples of tammar digesta had a significant elastic component (G′) that was preserved throughout the period of fasting. Interaction between component particles was significant at all times, digesta behaving as a weak gel. The ratio of energy lost to energy stored during flow of digesta tended to decrease during the period of fasting, indicating an increase in behaviour as an elastic solid. The relationship between G′ and dry matter content and mean particle size indicated that these phenomena resulted from progressive loss of finer digesta particles and that digestion in the wallaby stomach, via permeation of the particulate by the fluid phase, was possible for up to 33 h after eating.
Diet and habitat preferences of the Fijian crested iguana (Brachylophus vitiensis) on Yadua Taba, Fiji: implications for conservation
Authors: Morrison Clare , Osborne Tamara , Harlow Peter S. , Thomas Nunia , Biciloa Pita , Niukula Jone
Published: June 2008

The Fijian crested iguana (Brachylophus vitiensis) is restricted to tropical dry forest habitat and has been extirpated from over 80% of its original range primarily because of habitat destruction. A large population on Yadua Taba island has been proposed as a source for iguana translocations. This study aimed to determine the dietary and habitat requirements of the herbivorous B. vitiensis on Yadua Taba to identify essential tree species. Between September 2005 and June 2006 we examined the diet of B. vitiensis using faecal analyses, while perch preferences were examined using field surveys. Faecal analyses identified 26 plant species in the diet of B. vitiensis, while field surveys recorded iguanas in 33 tree species. The most common diet species largely overlapped with the most common perch species. There were no major seasonal shifts, sex differences, or age-class variations in diet or perch preferences. These results suggest that while B. vitiensis occurs in and consumes several plant species on Yadua Taba, it is primarily dependent on only a few species. To improve translocation success, future translocations of B. vitiensis need to ensure that these important tree species are present at new sites.
Evaluating molecular and behavioural sexing methods for the Australasian gannet (Morus serrator)
Authors: Daniel Claire , Millar Craig D. , Ismar Stefanie M. H. , Stephenson Brent M. , Hauber Mark E.
Published: June 2008

The availability of molecular methods for avian sex identification has revolutionised the study of sexual differences in behaviour, morphology, life-history traits and conservation management. We implemented the recommendations of a recent review of DNA-based sex-identification by (1) verifying the sex-specificity and (2) estimating the accuracy of different sex-assignment methods in an apparently monomorphic seabird, the Australasian gannet (Morus serrator). The polymerase chain reaction (PCR) method based on the amplification of the sex-linked chromodomain-helicase-DNA binding gene (CHD) repeatedly assigned the same sex in 96% (n = 27 replicates) and correctly sexed all individuals with known gonadal anatomy (n = 6). PCR and sex-specific restriction fragment length polymorphism (RFLPs) showed agreement for 99.5% of individuals (n = 201). DNA-sexed pairs known to be social mates consisted of a male and a female in 96% of pairs sexed by PCR (n = 77) and 98% of pairs sexed by RFLP (n = 65). DNA-sexed females were in the bottom and males in the top copulatory position in 86% of observed copulations (n = 43 individuals). These results validate assumptions that both membership in social pairs and different copulatory positions can serve as reliable behavioural proxies for field-based sex identification in this colonial and obligately biparental seabird.
A new fossil kangaroo from the Oligocene-Miocene Etadunna Formation of Ngama Quarry, Lake Palankarinna, South Australia
Authors: Kear Benjamin P. , Pledge Neville S.
Published: June 2008

Mandibular and postcranial remains attributable to a new fossil kangaroo (Macropodoidea) are described from the Oligocene-Miocene Etadunna Formation deposits of Ngama Quarry at Lake Palankarinna in north-eastern South Australia. The taxon is uniquely differentiated by its straight bunolophodont molar row, elongate P3 with distinct labial/lingual cingulids and 12–13 fine (shallowly incised) cuspids/transcristids, molars with a rectangular (length at least 0.3 > width) occlusal outline, hypolophid formed by a buccally directed crest from the entoconid, absence of a discrete M1 protostylid, transversely broad trigonid basin on the M1, M4 not markedly smaller than the anterior molars, distal end of humerus with sub-equally sized capitellum and trochlea (the latter also closely abutting the entepicondyle), and ulna with distinctly sinuous ventral edge. Relationships of the Ngama Quarry kangaroo are poorly resolved because of missing data; however, inclusion within the most comprehensive published phylogenetic dataset of Macropodoidea suggests close affinity with the currently extant potoroine/macropodid lineage.
A hybrid zone defined by allozymes and ventral colour in Geocrinia rosea (Anura:Myobatrachidae)
Authors: Driscoll Don A. , Roberts J. Dale
Published: June 2008

The frog Geocrinia rosea is highly genetically subdivided with a major genetic division between northern and southern populations. Previous research did not sample a region spanning 12 km between these two populations. We report the distribution of G. rosea in the unsampled area and identify a geographically restricted hybrid zone. Boundaries of genetic groups were defined using two allozyme loci in 13 populations and ventral colouration. G. rosea was not continuously distributed in the area of parapatry. At the only point where the northern and southern groups met, there was a single hybrid population with genotypes demonstrating substantial interbreeding. Colour patterns implied a slightly broader hybrid zone, with four populations showing ventral colour introgression. Northern populations tended to have pink bellies whereas southern populations generally had orange bellies. We conclude that the two groups have diverged in allopatry and have formed a very narrow hybrid zone after range expansion. The magnitude of allozyme divergence between the four currently recognised species in the G. rosea complex is similar to the divergence between northern and southern G. rosea and is much greater than the divergence between other intraspecific groups. Taxonomic revision may therefore be warranted.
Incorporation of histone deacetylase inhibition into the structure of a nuclear receptor agonist
Authors: Tavera-Mendoza Luz E. , Quach Tan D. , Dabbas Basel , Hudon Jonathan , Liao Xiaohong , Palijan Ana , Gleason James L. , White John H.
Published: June 2008

1,25-dihydroxyvitamin D
3
(1,25D) regulates gene expression by signaling through the nuclear vitamin D receptor (VDR) transcription factor and exhibits calcium homeostatic, anticancer, and immunomodulatory properties. Histone deacetylase inhibitors (HDACis) alter nuclear and cytoplasmic protein acetylation, modify gene expression, and have potential for treatment of cancer and other indications. The function of nuclear receptor ligands, including 1,25D, can be enhanced in combination with HDACi. We designed triciferol, a hybrid molecule in which the 1,25D side chain was replaced with the dienyl hydroxamic acid of HDACi trichostatin A. Triciferol binds directly to the VDR, and functions as an agonist with 1,25D-like potency on several 1,25D target genes. Moreover, unlike 1,25D, triciferol induces marked tubulin hyperacetylation, and augments histone acetylation at concentrations that largely overlap those where VDR agonism is observed. Triciferol also exhibits more efficacious antiproliferative and cytotoxic activities than 1,25D in four cancer cell models
in vitro
. The bifunctionality of triciferol is notable because (
i
) the HDACi activity is generated by modifying the 1,25D side chain without resorting to linker technology and (
ii
) 1,25D and HDACi have sympathetic, but very distinct biochemical targets; the hydrophobic VDR ligand binding domain and the active sites of HDACs, which are zinc metalloenzymes. These studies demonstrate the feasibility of combining HDAC inhibition with nuclear receptor agonism to enhance their therapeutic potential.
The Coffin–Lowry syndrome-associated protein RSK2 is implicated in calcium-regulated exocytosis through the regulation of PLD1
Authors: Zeniou-Meyer Maria , Liu Yuanyuan , Béglé Aurélie , Olanich Mary E. , Hanauer André , Becherer Ute , Rettig Jens , Bader Marie-France , Vitale Nicolas
Published: June 2008

Exocytosis of neurotransmitters and hormones occurs through the fusion of secretory vesicles with the plasma membrane. This highly regulated process involves key proteins, such as SNAREs, and specific lipids at the site of membrane fusion. Phospholipase D (PLD) has recently emerged as a promoter of membrane fusion in various exocytotic events potentially by providing fusogenic cone-shaped phosphatidic acid. We show here that PLD1 is regulated by ribosomal S6 kinase 2 (RSK2)-dependent phosphorylation. RSK2 is activated by a high K
+
-induced rise in cytosolic calcium. Expression of inactive RSK2 mutants or selective knockdown of endogenous RSK2 dramatically affects the different kinetic components of the exocytotic response in chromaffin cells. RSK2 physically interacts with and stimulates PLD activity through the phosphorylation of Thr-147 in the PLD1 amino-terminal phox homology domain. Expression of PLD1 phosphomimetic mutants fully restores secretion in cells depleted of RSK2, suggesting that RSK2 is a critical upstream signaling element in the activation of PLD1 to produce the lipids required for exocytosis. We propose that PLD-related defects in neuronal and endocrine activities could contribute to the effect observed after the loss-of-function mutations in
Rsk2
that lead to Coffin–Lowry syndrome, an X-linked form of growth and mental retardation.
Carboxypeptidase E mediates palmitate-induced β-cell ER stress and apoptosis
Authors: Jeffrey Kristin D. , Alejandro Emilyn U. , Luciani Dan S. , Kalynyak Tatyana B. , Hu Xiaoke , Li Hong , Lin Yalin , Townsend R. Reid , Polonsky Kenneth S. , Johnson James D.
Published: June 2008

Obesity is a principal risk factor for type 2 diabetes, and elevated fatty acids reduce β-cell function and survival. An unbiased proteomic screen was used to identify targets of palmitate in β-cell death. The most significantly altered protein in both human islets and MIN6 β-cells treated with palmitate was carboxypeptidase E (CPE). Palmitate reduced CPE protein levels within 2 h, preceding endoplasmic reticulum (ER) stress and cell death, by a mechanism involving CPE translocation to Golgi and lysosomal degradation. Palmitate metabolism and Ca
2+
flux were also required for CPE proteolysis and β-cell death. Chronic palmitate exposure increased the ratio of proinsulin to insulin. CPE null islets had increased apoptosis
in vivo
and
in vitro
. Reducing CPE by ≈30% using shRNA also increased ER stress and apoptosis. Conversely, overexpression of CPE partially rescued β-cells from palmitate-induced ER stress and apoptosis. Thus, carboxypeptidase E degradation contributes to palmitate-induced β-cell ER stress and apoptosis. CPE is a major link between hyperlipidemia and β-cell death pathways in diabetes.
Nuclear localization of Cdk5 is a key determinant in the postmitotic state of neurons
Authors: Zhang Jie , Cicero Samantha A. , Wang Li , Romito-DiGiacomo Rita R. , Yang Yan , Herrup Karl
Published: June 2008

Cyclin-dependent kinase 5 (Cdk5) is a nontraditional Cdk that is primarily active in postmitotic neurons. Its best known substrates are cytoskeletal proteins. Less appreciated is its role in the maintenance of a postmitotic state. We show here that in cycling cells (NIH 3T3), the localization of Cdk5 changes from predominantly nuclear to cytoplasmic as cells reenter a cell cycle after serum starvation. Similarly, when β-amyloid peptide is used to stimulate cultured primary neurons to reenter a cell cycle, they too show a loss of nuclear Cdk5. Blocking nuclear export pharmacologically abolishes cell cycle reentry in wild-type but not
Cdk5
−/−
neurons, suggesting a Cdk5-specific effect. Cdk5 overexpression targeted to the nucleus of
Cdk5
−/−
neurons effectively blocks the cell cycle, but cytoplasmic targeting is ineffective. Further, in both human Alzheimer's disease as well as in the R1.40 mouse Alzheimer's model and the
E2f1
−/−
mouse, neurons expressing cell cycle markers consistently show reduced nuclear Cdk5. Thus, both
in vivo
and
in vitro
, neurons that reenter a cell cycle lose nuclear Cdk5. We propose that the nuclear Cdk5 plays an active role in allowing neurons to remain postmitotic as they mature and that loss of nuclear Cdk5 leads to cell cycle entry.
Role of catalysts in dehydrogenation of MgH
2
nanoclusters
Authors: Larsson Peter , Araújo C. Moysés , Larsson J. Andreas , Jena Puru , Ahuja Rajeev
Published: June 2008

A fundamental understanding of the role of catalysts in dehydrogenation of MgH
2
nanoclusters is provided by carrying out first-principles calculations based on density functional theory. It is shown that the transition metal atoms Ti, V, Fe, and Ni not only lower desorption energies significantly but also continue to attract at least four hydrogen atoms even when the total hydrogen content of the cluster decreases. In particular, Fe is found to migrate from the surface sites to the interior sites during the dehydrogenation process, releasing more hydrogen as it diffuses. This diffusion mechanism may account for the fact that a small amount of catalysts is sufficient to improve the kinetics of MgH
2
, which is essential for the use of this material for hydrogen storage in fuel-cell applications.
The fold of α-synuclein fibrils
Authors: Vilar Marçal , Chou Hui-Ting , Lührs Thorsten , Maji Samir K. , Riek-Loher Dominique , Verel Rene , Manning Gerard , Stahlberg Henning , Riek Roland
Published: June 2008

The aggregation of proteins into amyloid fibrils is associated with several neurodegenerative diseases. In Parkinson's disease it is believed that the aggregation of α-synuclein (α-syn) from monomers by intermediates into amyloid fibrils is the toxic disease-causative mechanism. Here, we studied the structure of α-syn in its amyloid state by using various biophysical approaches. Quenched hydrogen/deuterium exchange NMR spectroscopy identified five β-strands within the fibril core comprising residues 35–96 and solid-state NMR data from amyloid fibrils comprising the fibril core residues 30–110 confirmed the presence of β-sheet secondary structure. The data suggest that β1-strand interacts with β2, β2 with β3, β3 with β4, and β4 with β5. High-resolution cryoelectron microscopy revealed the protofilament boundaries of ≈2 × 3.5 nm. Based on the combination of these data and published structural studies, a fold of α-syn in the fibrils is proposed and discussed.
Two distinct activity patterns of fast-spiking interneurons during neocortical UP states
Authors: Puig Maria Victoria , Ushimaru Mika , Kawaguchi Yasuo
Published: June 2008

During sleep, neocortical neuronal networks oscillate slowly (<1 Hz) between periods of activity (UP states) and silence (DOWN states). UP states favor the interaction between thalamic-generated spindles (7–14 Hz) and cortically generated gamma (30–80 Hz) waves. We studied how these three nested oscillations modulate fast-spiking interneuron (FSi) activity
in vivo
in VGAT-Venus transgenic rats. Our data describe a population of FSi that discharge “early” within UP states and another population that discharge “late.” Early FSi tended to be silent during epochs of desynchronization, whereas late FSi were active. We hypothesize that late FSi may be responsible for generating the gamma oscillations associated with cognitive processing during wakefulness. Remarkably, FSi populations were differently modulated by spindle and gamma rhythms. Early FSi were robustly coupled to spindles and always discharged earlier than late FSi within spindle and gamma cycles. The preferred firing phase during spindle and gamma waves was strongly correlated in each cell, suggesting a cross-frequency coupling between oscillations. Our results suggest a precise spatiotemporal pattern of FSi activity during UP states, whereby information rapidly flows between early and late cells, initially promoted by spindles and efficiently extended by local gamma oscillations.
Phospholipase D1 is an effector of Rheb in the mTOR pathway
Authors: Sun Y. , Fang Y. , Yoon M.-S. , Zhang C. , Roccio M. , Zwartkruis F. J. , Armstrong M. , Brown H. A. , Chen J.
Published: June 2008

The mammalian target of rapamycin (mTOR) assembles a signaling network essential for the regulation of cell growth, which has emerged as a major target of anticancer therapies. The tuberous sclerosis complex 1 and 2 (TSC1/2) proteins and their target, the small GTPase Rheb, constitute a key regulatory pathway upstream of mTOR. Phospholipase D (PLD) and its product phosphatidic acid are also upstream regulators of the mitogenic mTOR signaling. However, how the TSC/Rheb and PLD pathways interact or integrate in the rapamycin-sensitive signaling network has not been examined before. Here, we find that PLD1, but not PLD2, is required for Rheb activation of the mTOR pathway, as demonstrated by the effects of RNAi. The overexpression of Rheb activates PLD1 in cells in the absence of mitogenic stimulation, and the knockdown of Rheb impairs serum stimulation of PLD activation. Furthermore, the overexpression of TSC2 suppresses PLD1 activation, whereas the knockdown or deletion of TSC2 leads to elevated basal activity of PLD. Consistent with a TSC-Rheb-PLD signaling cascade, AMPK and PI3K, both established regulators of TSC2, appear to lie upstream of PLD as revealed by the effects of pharmacological inhibitors, and serum activation of PLD is also dependent on amino acid sufficiency. Finally, Rheb binds and activates PLD1
in vitro
in a GTP-dependent manner, strongly suggesting that PLD1 is a bona fide effector for Rheb. Hence, our findings reveal an unexpected interaction between two cascades in the mTOR signaling pathways and open up additional possibilities for targeting this important growth-regulating network for the development of anticancer drugs.