bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and magnetostriction of PrxCe1−xFe1.9(0.5≤x≤1.0) alloys
Authors: Wang Y. , Zhai L. , Shi Y. G. , Tang S. L. , Du Y. W.
Published: May 2010

High-pressure synthesis method has been used to synthesize PrxCe1−xFe1.9(0.5≤x≤1.0) magnetostrictive alloys. The x-ray diffraction results show that all the alloys exhibit cubic Laves phase with MgCu2-type structure. The lattice parameter, Curie temperature, magnetization, and magnetostriction of the alloys have been investigated. The Curie temperature, the saturation magnetostriction, and the lattice parameters increase approximately linearly with the increment of Pr concentration. The magnetostriction is mainly attributed to the Pr sublattice. The magnetostriction in the magnetic field direction (λ∥) of PrFe1.9 and Pr0.9Ce0.1Fe1.9 alloy at 5 K reaches up to 3700 and 2800 ppm at the biggest field of 50 kOe, respectively, Pr0.9Ce0.1Fe1.9 possesses lower magnetostriction than PrFe1.9 because of the quenching of the orbital 4f moment of Ce. The magnetostriction of all samples deceases as the temperature increases. The composition dependence of the ratio λ/K1 for PrxCe1−xFe1.9 alloys reaches a maximum value at x=0.8, indicating that Pr0.8Ce0.2Fe1.9 possesses a good magnetostrictive property at room temperature.
Interface depolarization field as common denominator of fatigue and size effect in Pb(Zr0.54Ti0.46)O3 ferroelectric thin film capacitors
Authors: Bouregba R. , Sama N. , Soyer C. , Poullain G. , Remiens D.
Published: May 2010

Dielectric, hysteresis and fatigue measurements are performed on Pb(Zr0.54Ti0.46)O3 (PZT) thin film capacitors with different thicknesses and different electrode configurations, using platinum and LaNiO3 conducting oxide. The data are compared with those collected in a previous work devoted to study of size effect by R. Bouregba et al., [J. Appl. Phys. 106, 044101 (2009)]. Deterioration of the ferroelectric properties, consecutive to fatigue cycling and thickness downscaling, presents very similar characteristics and allows drawing up a direct correlation between the two phenomena. Namely, interface depolarization field (Edep) resulting from interface chemistry is found to be the common denominator, fatigue phenomena is manifestation of strengthen of Edep in the course of time. Change in dielectric permittivity, in remnant and coercive values as well as in the shape of hysteresis loops are mediated by competition between degradation of dielectric properties of the interfaces and possible accumulation of interface space charge. It is proposed that presence in the band gap of trap energy levels with large time constant due to defects in small nonferroelectric regions at the electrode—PZT film interfaces ultimately governs the aging process. Size effect and aging process may be seen as two facets of the same underlying mechanism, the only difference lies in the observation time of the phenomena.
Enhanced piezoelectricity and high temperature poling effect in (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 ceramics via an ethylene glycol route
Authors: Tailor H. N. , Ye Z.-G.
Published: May 2010

A solution chemical method utilizing ethylene glycol as solvent has been developed to prepare the ceramics of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3[(1−x)PMN–xPT] from a precursor powder that can be pressed and fired in one step to produce high quality ceramics with excellent piezoelectric properties. The ceramics reach a relative density of up to 97% of the theoretical value after direct calcinations. This high density is achieved without the need of additional sintering after calcination which is usually required in conventional solid state syntheses to produce ceramics. The ceramics exhibit a unipolar piezoelectric coefficient d33 of 848 pC/N, which is one of the highest values for any unmodified/untextured binary systems reported to date. Since the piezoelectric properties depend on composition and electric field, the effect of poling conditions was investigated. A critical temperature limit has been found, above which poling can dramatically impair the piezoelectric properties due to a field-induced increase in the monoclinic phase component around the morphotropic phase boundary.
Spatial correlation between optical properties and defect formation in GaN thin films laterally overgrown on cone-shaped patterned sapphire substrates
Authors: Lee Kyu-Seung , Kwack Ho-Sang , Hwang Jun-Seok , Roh Tae-Moo , Cho Yong-Hoon , Lee Jae-Hoon , Kim Yong-Chun , Kim Chang Soo
Published: May 2010

This study examines the influence of the growth mode on defect formation and strain relaxation in GaN thin films grown on cone-shaped patterned sapphire (CSPS) substrates by metal-organic chemical vapor deposition. A dramatic reduction in the luminescence dark spot density and a red-shifted excitonic emission were found for GaN on CSPS compared to GaN on planar sapphire substrates. The results also show that both the crystal quality and optical properties are improved in GaN on CSPS with a strong spatial correlation between the dark spots and local structural properties due to the induced-lateral overgrowth on the cone-shaped patterns.
Optical frequency shot-noise suppression in electron beams: Three-dimensional analysis
Authors: Nause A. , Dyunin E. , Gover A.
Published: May 2010

A predicted effect of current shot-noise suppression at optical-frequencies in a drifting charged-particle-beam and the corresponding process of particles self-ordering are analyzed in a one-dimensional (1D) model and verified by three-dimensional numerical simulations. The analysis confirms the prediction of a 1D single mode Langmuir plasma wave model of longitudinal plasma oscillation in the beam, and it defines the regime of beam parameters in which this effect takes place. The suppression of relativistic beam shot noise can be utilized to enhance the coherence of free electron lasers and of any coherent radiation device using an electron beam.
Effect of the indices of crystal plane of gold electrodes on the transport properties of C20 fullerene
Authors: Wang L. H. , Guo Y. , Tian C. F. , Song X. P. , Ding B. J.
Published: May 2010

Using first-principles density functional theory and nonequilibrium Green’s function formalism, we investigate the effect of the indices of crystal plane of electrodes on the electronic transport properties of molecular devices by taking C20 fullerene molecule as conductor component and semi-infinite Au(111)/(100) as electrodes. The results show that the transport behaviors through molecular devices are closely related to the crystallographic orientation of electrodes. Negative differential resistance (NDR) in the current-voltage curve can be observed for the Au(100) electrode case but cannot be observed for the Au(111) case. A mechanism for the NDR phenomenon is proposed.
Influence of two photon absorption induced free carriers on coherent polariton and phonon generation in ZnTe crystals
Authors: Kamaraju N. , Kumar Sunil , Freysz Eric , Sood A. K.
Published: May 2010

Combination of femtosecond Kerr, two photon absorption, and impulsive stimulated Raman scattering (ISRS) experiments have been carried out to investigate the effect of pulse energy and crystal temperature on the generation of coherent polaritons and phonons in ⟨110⟩ cut ZnTe single crystals of three different resistivities. We demonstrate that the effect of two photon induced free carriers on the creation of both the polaritons and phonons is largest at 4 K where the free carrier lifetime is enhanced. The temperature dependant ISRS on high and low purity ZnTe crystals allows us to unambiguously assign the phonon mode at 3.5 THz to the longitudinal acoustic mode at X-point in the Brillouin zone, LA(X).
Vibrational properties and Raman spectra of single-wall carbon nanotubes with divacancy
Authors: Chang Xu , Zhou Jian , Fa Wei , Dong Jinming
Published: May 2010

Using the empirical Brenner potential, we have calculated the structural and vibrational properties of single walled carbon nanotubes (SWNTs) with divacancies, based upon which their nonresonant Raman spectra have been calculated by the empirical bond polarizability model. It is found that the SWNT’s diameter will be changed by the divacancies, depending strongly on the tube’s chirality and the divacancy concentration. More importantly, it is found that the divacancy-induced Raman peaks lie out of the SWNT’s G-band and their positions depend on the tube’s chirality and the divacancy’s symmetry, which can be used to detect the divacancy experimentally.
Note: A frequency modulated wireless interrogation system exploiting narrowband acoustic resonator for remote physical quantity measurement
Authors: Droit C. , Martin G. , Ballandras S. , Friedt J.-M.
Published: May 2010

We demonstrate the wireless conversion of frequency modulation to amplitude modulation by radio frequency resonators as means of accurately determining the resonance frequency of passive acoustoelectronic sensors. The emitted frequency modulated radio frequency pulses are generated by a pulsed radar for probing a surface acoustic wave based sensor. The sharp sign transition of the amplitude modulated received signal provides a signal on which a feedback loop is locked to monitor the resonance signal. The strategy is demonstrated using a full software implementation on a generic hardware, resulting in 2 Hz resolution at 1 s integration time limited by the proportional feedback loop.
Kinetic effects of magnetic field on the γ/α interface controlled reaction in iron
Authors: Garcin Thomas , Rivoirard Sophie , Gaucherand Franck , Beaugnon Eric
Published: May 2010

The effect of magnetic field on the austenite (γ) to ferrite (α) transformation kinetics is studied in iron by means of dilatation measurements under magnetic field. In the frame of the Johnson–Mehl–Avrami-Kolmogorov analysis and considering a spherical growth mode for the ferrite grains, the Avrami exponent and the activation energy for the interface mobility are calculated. These parameters are found to be weakly influenced by the application of a 16 T magnetic field. This indicates that they are related mainly to the total amount of energy available for the transformation whatever its origin (whether magnetic or chemical). Whereas the magnetic field strongly affects the α/γ thermodynamic equilibrium through the Gibbs free energy of phases, it has a non noticeable influence on the transformation kinetics itself.
The strict theory of complex variable function method for sextuple harmonic equation and applications
Authors: Fan Tian You , Tang Zhi Yi , Li Lian He , Li Wu
Published: May 2010

The strict theory of the complex variable function method for the sextuple harmonic equation is given in detail, which is a development of the work on the quadruple harmonic equation of the authors. Both of the above mentioned works develop the well-known Muskhelishvili complex variable function method for solving the biharmonic equation used in the classical theory of elasticity. Meanwhile, some applications to the elasticity, plasticity, and fracture theories of quasicrystalline materials have shown that the theory and method are successful and effective.
Design, development, and evaluation of a simple blackbody radiative source
Authors: Castrejón-García R. , Castrejón-Pita J. R. , Castrejón-Pita A. A.
Published: May 2010

This paper presents a simple design and the testing of a blackbody prototype. The physical properties and geometry of the cavity produce a radiator or blackbody with an emissivity greater than 0.99. The prototype has the advantages of having a traditional spherical cavity made of alumina refractory cement and a radiative emission very close to that of an ideal blackbody. The prototype can be used as a calibration standard for other radiation measuring instruments or sensors. Experimental measurements of radiant flux of the prototype measured with a calibrated infrared radiometer and a wide spectrum radiometer are also presented. The prototype is easy to construct and the material required are available to most research centers, laboratories, industries, and universities.
Effect of two ion species on the propagation of shear Alfvén waves of small transverse scale
Authors: Vincena S. T. , Morales G. J. , Maggs J. E.
Published: May 2010

The results of a theoretical modeling study and experimental investigation of the propagation properties of shear Alfvén waves of small transverse scale in a plasma with two ion species are reported. In the two ion plasma, depending on the mass of the heavier species, ion kinetic effects can become prominent, and significant parallel electric fields result in electron acceleration. The theory predicts the appearance of frequency propagation gaps at the ion-ion hybrid frequency and between harmonics of the lower cyclotron frequency. Within these frequency bands spatial structures arise that mix the cone-propagation characteristics of Alfvén waves with radially expanding ion Bernstein modes. The experiments, performed at the Basic Plasma Science Facility (BaPSF) at UCLA, consist of the spatial mapping of shear waves launched by a loop antenna. Although a variety of two ion-species combinations were explored, only results from a helium-neon mix are reported. A clear signature of a shear wave propagation gap, as well as propagation between multiple harmonics, is found for this gas combination. The evanescence of shear waves beyond the reflection point at the ion-ion hybrid frequency in the presence of an axial magnetic field gradient is also documented.
Nonclassical assembly pathways of anisotropic particles
Authors: Whitelam Stephen
Published: May 2010

Advances in synthetic methods have spawned an array of nanoparticles and bio-inspired molecules of diverse shapes and interaction geometries. Recent experiments indicate that such anisotropic particles exhibit a variety of nonclassical self-assembly pathways, forming ordered assemblies via intermediates that do not share the architecture of the bulk material. Here we apply mean field theory to a prototypical model of interacting anisotropic particles, and find a clear thermodynamic impetus for nonclassical ordering in certain regimes of parameter space. In other parameter regimes, by contrast, assembly pathways are selected by dynamics. This approach suggests a means of predicting when anisotropic particles might assemble in a manner more complicated than that assumed by classical nucleation theory.
Melting of (MgO)n (n=18, 21, and 24) clusters simulated by molecular dynamics
Authors: Zhang Y. , Chen H. S. , Liu B. X. , Zhang C. R. , Li X. F. , Wang Y. C.
Published: May 2010

Molecular dynamics simulations are employed to investigate the melting behavior and thermal stability of magnesium oxide clusters (MgO)n (n=18, 21, and 24). The rocksalt and hexagonal tube structures are two dominant low-energy structural motifs for small (MgO)n clusters and it results in the magic sizes n=3k (k is an integer). For n=6, 9, 12, and 15, the rocksalt and hexagonal tube structures have the same topological geometry, but for n≥18, the two isomers are separated by high energy barriers. The simulations show a one-step melting process for the rocksalt structures of (MgO)18,24 (no perfect rocksalt structure exists for n=21). The melting transition occurs sharply between 1800 and 1950 K for n=24 but gradually from 1400 to 2450 K for n=18. The relative root-mean-square bond length fluctuation reveals a premelting stage from about 700 K to the melting transition for the hexagonal tube structures of all the three clusters. The short-time averages of kinetic energy and a visual molecular dynamics package are used to monitor the structures along the trajectories. The low-energy isomers are identified by the quenching technique and the isomerization processes are traced. The results show that there exists a family of isomers which are only 0.1–0.4 eV higher in energy than the corresponding hexagonal tube structures and separated by low energy barriers. The premelting stage is caused by the isomerizations among these structures. The melting characteristics demonstrated in the simulations are clarified in terms of the energies of the isomers and the energy barriers separating them.
Low-lying excitations of poly-fused thiophene within Pariser–Parr–Pople model: A density matrix renormalization group study
Authors: Das Mousumi
Published: May 2010

We studied the nature of the ground and low-lying excited states of poly-fused thiophene oligomers within long-range Pariser–Parr–Pople (PPP) model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. Our results show that the lowest dipole-allowed state lies below the lowest dipole forbidden two-photon state, indicating that poly-fused thiophenes are strongly fluorescent. The lowest triplet state lies below the two-photon state, which is in agreement with the general trend in conjugated polymers. The charge density and bond order calculations of three low-lying excited states, along with the ground state of fused thiophene oligomers, show a significant transfer of charge from sulfur to adjacent carbon atom in the middle of the largest system size and these excitations are localized. The charge density and bond order calculations on singly and doubly doped states show that bipolarons are not stable entity in these systems. The calculations of low-lying excitations on radical cation and anion of fused thiophene oligomers show a new energy band in the low energy region, which is strongly coupled to its hole and electron conductivity. This implies that poly-fused thiophenes posses novel field-effect transistor properties.
The electronic consequences of multivalent elements in inorganic solar absorbers: Multivalency of Sn in Cu2ZnSnS4
Authors: Biswas Koushik , Lany Stephan , Zunger Alex
Published: May 2010

Multivalent transition metal impurities in semiconductors are known to create deep levels inside the band gap that are associated with changes in the oxidation state. Some emerging functional semiconductor materials now contain multivalent elements not just as impurities, but as part of their structural skeleton (“multivalent semiconductors”). This raises the possibility that the performance of such materials may be affected by those skeleton elements transitioning from one oxidation state to another, in response to charge-altering perturbations such as illumination or doping. Here we address the correlation between multivalency and the electronic properties of these new semiconductor materials.
InGaN-based light-emitting diodes grown and fabricated on nanopatterned Si substrates
Authors: Deng Dongmei , Yu Naisen , Wang Yong , Zou Xinbo , Kuo Hao-Chung , Chen Peng , Lau Kei May
Published: May 2010

InGaN-based light-emitting diodes (LEDs) were grown and fabricated on nanoscale patterned Si (111) substrates (NPSi). Using anodized aluminum oxide as the etch mask, the NPSi was prepared with an average nanopore diameter of 150 nm and interpore distance of 120 nm. LEDs grown on NPSi exhibit relaxed tensile stress relative to the ones grown on microscale patterned Si (111) substrates (MPSi). Nanoheteroepitaxial lateral overgrowth was significantly promoted on NPSi, which led to extensive dislocation bending and annihilation. The devices made on NPSi exhibit lower leakage current and higher light output power as compared with those on MPSi.
Effect of magnetostatic energy on domain structure and magnetization reversal in (Co/Pd) multilayers
Authors: Sbiaa R. , Bilin Z. , Ranjbar M. , Tan H. K. , Wong S. J. , Piramanayagam S. N. , Chong T. C.
Published: May 2010

Magnetization reversal in (Co/Pd) multilayers with perpendicular anisotropy for different numbers of bilayers (N) is investigated experimentally and by theoretical modeling. The focus of this study is on the magnetostatic energy in these structures and its effect on the magnetization reversal behavior and the nature of domain formation. For (Co/Pd) multilayers with small N, sharp magnetization switching and large domains were observed. In contrast, (Co/Pd) multilayers with a large N have long tail in the hysteresis loop that gets more pronounced as N increases. The size of domains becomes considerably smaller as N increases. Based on theoretical modeling that takes into account of the magnetostatic energy from the different magnetic layers, the domain size dependence on the number of bilayers is explained. For large N, the tail in the hysteresis loop is revealed to be the result of an increase in the magnetostatic energy, which at the same time leads to a drastic reduction in domain width.
Estimation method of finger tapping dynamics using simple magnetic detection system
Authors: Kandori Akihiko , Sano Yuko , Miyashita Tsuyoshi , Okada Yoshihisa , Irokawa Masataka , Shima Keisuke , Tsuji Toshio , Yokoe Masaru , Sakoda Saburo
Published: May 2010

We have developed the simple estimation method of a finger tapping dynamics model for investigating muscle resistance and stiffness during tapping movement in normal subjects. We measured finger tapping movements of 207 normal subjects using a magnetic finger tapping detection system. Each subject tapped two fingers in time with a metronome at 1, 2, 3, 4, and 5 Hz. The velocity and acceleration values for both the closing and opening tapping data were used to estimate a finger tapping dynamics model. Using the frequency response of the ratio of acceleration to velocity of the mechanical impedance parameters, we estimated the resistance (friction coefficient) and compliance (stiffness). We found two dynamics models for the maximum open position and tap position. In the maximum open position, the extensor muscle resistance was twice as high as the flexor muscle resistance and males had a higher spring constant. In the tap position, the flexor muscle resistance was much higher than the extensor muscle resistance. This indicates that the tapping dynamics in the maximum open position are controlled by the balance of extensor and flexor muscle friction resistances and the flexor stiffness, and the flexor friction resistance is the main component in the tap position. It can be concluded that our estimation method makes it possible to understand the tapping dynamics.
The importance of hole concentration in establishing carrier-mediated ferromagnetism in Mn doped Ge
Authors: Zhou Shengqiang , Bürger Danilo , Skorupa Wolfgang , Oesterlin Peter , Helm Manfred , Schmidt Heidemarie
Published: May 2010

In the present work, we have prepared Mn-doped Ge using different annealing approaches after Mn ion implantation, and obtained samples with hole concentrations ranging from 1018 to 2.1×1020 cm−3, the latter being the highest reported so far. Based on the magnetotransport properties of Mn doped Ge, we argue that the hole concentration is a decisive parameter in establishing carrier-mediated ferromagnetism in magnetic Ge.
High-order cumulants in the counting statistics of asymmetric quantum dots
Authors: Fricke Christian , Hohls Frank , Sethubalasubramanian Nandhavel , Fricke Lukas , Haug Rolf J.
Published: May 2010

Measurements of single electron tunneling through a quantum dot (QD) using a quantum point contact as charge detector have been performed for very long time traces with very large event counts. This large statistical basis is used for a detailed examination of the counting statistics for varying symmetry of the QD system. From the measured statistics we extract high order cumulants describing the distribution. Oscillations of the high order cumulants are observed when varying the symmetry. We compare this behavior to the observed oscillation in time dependence and show that the variation in both system variables lead to the same kind of oscillating response.
A requirement for diagnosis of the ionization state in opacity measurements
Authors: Xu Yan , Zhang Jiyan
Published: May 2010

An accurate independent diagnosis of the temperature and the ionization state of the sample plasmas is important to get a set of well-characterized opacity data in experiment. An analysis of using x-ray scattering was presented for this purpose. Information of the ionization state of the sample plasmas could only be clearly detected when both the Compton and Rayleigh features of the scattering spectra are detectable in one laser shot. Only those plasmas with a few bounded electrons left can provide such kind of scattering spectra. The requirements for using the x-ray scattering as diagnosis are rigorous. Under a radiation field produced by laser-heated hohlraum, only limited number of sample elements can be heated to the ionization state required. Careful design is needed to achieve an x-ray scattering experiment. This work can be helpful to establish a diagnostic flattop for the opacity experiments.
Electronic structure of wurtzite and rocksalt InN investigated by optical absorption under hydrostatic pressure
Authors: Ibáñez J. , Segura A. , Manjón F. J. , Artús L. , Yamaguchi T. , Nanishi Y.
Published: May 2010

The pressure dependence of the optical absorption edge of InN is investigated. Owing to the strong nonparabolicity of the energy bands, wurtzite InN exhibits enhanced optical absorption well above the absorption edge. The direct band gap of wurtzite InN increases linearly with pressure at 29±1 meV/GPa. The wurtzite-to-rocsksalt phase transition is observed at 15.3±0.5 GPa as a clear change in the absorption edge. We find that rocksalt InN is an indirect semiconductor with a band gap energy of around 1.0 eV. A higher energy direct transition is found at ∼2 eV. These results are discussed in terms of theoretical band-structure calculations.
Valence state dependent room-temperature ferromagnetism in Fe-doped ceria nanocrystals
Authors: Dohčević-Mitrović Z. D. , Paunović N. , Radović M. , Popović Z. V. , Matović B. , Cekić B. , Ivanovski V.
Published: May 2010

Room-temperature ferromagnetism was observed in undoped and Fe2+(3+)-doped CeO2 nanocrystals. In Fe-doped samples the enhancement of ferromagnetic ordering occurs by changing the valence state of Fe ions, whereas Raman spectra demonstrated strong electron-molecular vibrational coupling and increase in oxygen vacancy concentration. Air annealing showed degradation of ferromagnetic ordering and appearance of hematite phase in Fe3+-doped sample. The observed ferromagnetic coupling in Fe-doped samples, associated with the presence of magnetic ions mediated by single charged O2− vacancies, demonstrated that valence state of dopant has a strong influence on magnetic properties of CeO2 nanoparticles.
Potassium-doped BaFe2As2 superconducting thin films with a transition temperature of 40 K
Authors: Lee Nam Hoon , Jung Soon-Gil , Kim Dong Ho , Kang Won Nam
Published: May 2010

We report the growth of potassium-doped BaFe2As2 thin films, where the major charge carriers are holes, on Al2O3 (0001) and LaAlO3 (001) substrates by using an ex situ pulsed laser deposition technique. The measured superconducting transition temperatures are 40 K and 39 K for the films grown on Al2O3 and LaAlO3, respectively, and diamagnetism indicates that the films have good bulk superconducting properties below 36 K and 30 K, respectively. The x-ray diffraction patterns for both films indicated a preferred c-axis orientation, regardless of the substrate structures of LaAlO3 and Al2O3. The upper critical field at zero temperature was estimated to be about 155 T.
Performance of an AuPd micromechanical resonator as a temperature sensor
Authors: Pandey Ashok Kumar , Gottlieb Oded , Shtempluck Oleg , Buks Eyal
Published: May 2010

In this work we study the sensitivity of the primary resonance of an electrically excited microresonator for the possible usage of a temperature sensor. We find a relatively high normalized responsivity factor Rf=|TfdfdT|=0.37 with a quality factor of ∼105. To understand this outcome we perform a theoretical analysis based on experimental observation. We find that the dominant contribution to the responsivity comes from the temperature dependence of the tension in the beam. Subsequently, Rf is found to be inversely proportional to the initial tension. Corresponding to a particular temperature, the tension can be increased by applying a bias voltage.
Estimating lion population variables: prey and disease effects in Kruger National Park, South Africa
Authors: Ferreira Sam M. , Funston Paul J.
Published: May 2010

Context. Lion (Panthera leo Linnaeus, 1758) populations experience a range of ecological and human influences that affect their demography. Few lion populations have reliable estimates of population size, trends in these, or demographic profiles. Threats such as those imposed by diseases are thus hard to evaluate and respond to. Aims. To calibrate call-up stations and define survey effort required to achieve estimates with known precision, and extract age structures and estimate survival rates, to estimate lion numbers, sex and age structure and survival rates, and then to evaluate the effect of bovine tuberculosis (bTB) on estimates of lion density and survival. Methods.By using call-up stations, we developed a statistically robust approach to estimate selected population variables and evaluated the perceived threat of bTB in landscapes of varying prey biomass in the Kruger National Park. Key results. The size of the lion population was stable, although long intervals between present and historical estimates limit this conclusion. Density and survival rates associated positively with prey biomass, and a positive association was detected between the survival rate and bTB prevalence, with survival being higher in areas that had high prevalence of bTB. Male survival was lower than female survival, disregarding the effects of prey biomass or bTB prevalence. Body condition of lions was high, with scores lower at low to medium prey density. Conclusions. The effect of an exotic disease on the Kruger lion population may be negligible at present. Intra-specific competition in areas where lions live at high densities affects survival rate. However, droughts could disrupt the hierarchical influences of prey biomass and bTB prevalence on lion densities and survival. Implications. To evaluate the effect of an exotic disease on lion demography, population surveys should include age- and sex-structure assessments, complemented with focal studies of fecundity. This reflects the importance of understanding host–disease dynamics to inform management options.
Habitat use of remnant forest habitats by the threatened arboreal marsupial Dromiciops gliroides (Microbiotheria) in a rural landscape of southern Chile
Authors: Smith-Ramirez Cecilia , Celis-Diez Juan L. , von Jenstchyk Erik , Jimenez Jaime E. , Armesto Juan J.
Published: May 2010

Context. Remnant forest patches in rural landscapes may be important sites for maintaining viable populations of restricted forest species, especially when these remnant habitats maintain some connectivity, for instance through riparian vegetation strips and other forest patches.

Aims. We assessed the use of remnant forest habitats in a rural landscape of southern Chile (40°S) by the ‘near threatened’ arboreal marsupial Dromiciops gliroides (Microbiotheria), in relation to habitat type (riparian strips, forest fragments and continuous forests), width of the riparian forests, and the presence and abundance of the hemiparasite Tristerix corymbosus, whose fruits are readily eaten by D. gliroides.

Methods. In two summers, 2004 and 2008, we set up grids of 96 live traps for three consecutive nights at each of 16 sites along two riparian forest strips, four additional sites in remnant, non-riparian forest patches, and four more within continuous pre-Andean forest. We counted hemiparasites on trees in the trapping grid area, and estimated their individual volumes.

Key results
. In total, 48 individuals of D. gliroides were captured at all sites during the 2 years. We documented a significant positive relationship between the width of riparian vegetation and the number of individuals captured (r
s = 0.78, P = 0.02, n = 8) for one riparian strip, but not for the second one. Neither habitat type nor the frequency of hemiparasites related statistically to D. gliroides abundance.

Key conclusions. We conclude that in the rural landscape of the Chilean Lake District, narrow riparian forest strips, in a highly inter-connected mosaic of remnant forest patches may be as important as large patches and continuous Andean forests to sustain viable populations of this threatened, strictly arboreal, marsupial.

Implications. The present study reports, for the first time, the presence in narrow riparian forests immersed in a pasture-dominated agricultural matrix of this forest-specialist marsupial, which was previously known only from continuous pre-Andean forests.
Demography of feral horses (Equus caballus): a long-term study in Tornquist Park, Argentina
Authors: Scorolli Alberto L. , Cazorla Andrea C. Lopez
Published: May 2010

Context. All over the world, invasive alien mammals present conservation problems. Feral horses are invasive in many countries and their management is challenging. Aims. To determine the demography of feral horses in Tornquist Park, Argentina, so as to develop a quantitative basis for their management. Methods. Ground counts of individually identified female horses were conducted monthly from 1995 to 1997 and from 2000 to 2002, and seasonally in 1998 and 1999. We calculated the age structure, foaling and survival rates of mares and analysed the effects of adult density and rainfall on demographic parameters. The population trend was calculated by fitting a logistic equation to annual adult mare counts. Key results. The foaling rate averaged 0.55 annually and the survival rate in females averaged 0.89 for adults, 0.91 for juveniles, 0.87 for yearlings and 0.94 for foals. We found adult density, rainfall and the previous year’s rainfall to have a significant effect on fecundity but no effect on adult, juvenile and foal female survival rates. Adult density had a significant negative effect on female yearling survival; however, the effect is probably trivial. The logistic equation parameters gave r = 0.327 and carrying capacity (K) = 240 adult mares. Conclusions. A density-dependent response is suggested. The population growth is mainly limited by low fecundity, with the reduced adult female survival probably also playing a minor role. Implications. It is expected that the present long-term demographic study will contribute to the understanding of feral ungulate ecology and improve the management of feral populations.
Justification for continued conservation efforts following the delisting of a threatened species: a case study of the woylie, Bettongia penicillata ogilbyi (Marsupialia:Potoroidae)
Authors: Groom Christine
Published: May 2010

Context. There are few cases where a species has been removed from a list of threatened species as a result of conservation efforts. One such example is the woylie (also known as the brush-tailed bettong), Bettongia penicillata ogilbyi, which was removed from state (Western Australian), national (Australian) and international lists in 1996, following the successful implementation of the species’ recovery plan. Since downgrading of its conservation status, the woylie has been considered conservation dependent. Conservation efforts continued in the form of toxic baiting to control the species’ principal predator, monitoring to identify trends in distribution and abundance, and translocation to help restore ecosystem function and further secure the conservation status of the species. Recent observations of a decline in abundance of the species have prompted a review of its conservation status. Aims. To assess the conservation status of the woylie in 2006 against IUCN criteria and to investigate the value of continued conservation efforts following the delisting of the species. Methods. Monitoring data were collated and parameters required to assess the conservation status of the woylie against IUCN criteria were investigated. The various processes associated with conserving the species, such as translocation and monitoring, were also assessed. Key results. The species underwent a rapid decline between 2001 and 2006, reducing the population by ~75% to an estimated 10 000 individuals. The decline has not been consistent across occurrences and of particular concern are the declines observed at Perup/Lake Muir, Dryandra and Batalling, which were previously considered amongst the largest and most stable occurrences. In 2006, the species qualified for listing as Endangered using IUCN criteria. The resources allocated to translocation and monitoring the delisted woylie have ultimately resulted in managers being in a much better position to understand and act when an unforeseeable population decline occurred. Conclusion. Conservation efforts and population monitoring of delisted species must continue at a level where changes in distribution or abundance, which are significant enough to support relisting, can be detected. Implications. Threatened species lists should not be the primary consideration in allocation of resources to conservation efforts.
The usefulness of field data and hunting statistics in the assessment of wild rabbit (Oryctolagus cuniculus) conservation status in Portugal
Authors: Ferreira Catarina , Paupério Joana , Alves Paulo Célio
Published: May 2010

Context. The wild rabbit (Oryctolagus cuniculus) is a keystone species from the Iberian Peninsula that has suffered a strong decline in Spain during the past decades. Data on historical and current population trends in Portugal are virtually non-existent.
Aims. To investigate changes in rabbit abundance at the national level so as to inform conservation status assessments, and to evaluate the usefulness of hunting bags as a rabbit abundance index.
Methods. Field surveys based on latrine counts in linear transects were performed in two periods (1995 and 2002) to assess variation in population abundance. Hunting bags were also analysed for the same period to verify whether these data showed the same trends. General trends of rabbit abundance were estimated using TRIM software.
Key results. Field data revealed that most of the sampling units across Portugal have low abundances, despite the observation of local high-density spots. A population reduction of 27% was estimated. Although some fluctuations were observed in hunting bags, global results obtained from these data suggest a slightly increasing trend in rabbit abundance.
Conclusions. A discrepancy between field data and hunting statistics was observed. Because hunting bags may be influenced by sporadic management operations undertaken by hunters and the lack of systematic procedures in data collection, we believe that hunting statistics are not representative of real changes in rabbit populations. Thus, observed reduction in rabbit abundance estimated by field data, combined with the high initial morbidity due to rabbit haemorrhagic disease (RHD) after 1988 and the potential for continuing decline in population trends because of other factors, led to an inference of a reduction of >30% in rabbit abundance in Portugal during the past decade.
Implications. Taking into account the estimated reduction, the species’ biology and socioeconomic implications, wild rabbit in Portugal was listed in 2005 in the Near Threatened category under IUCN criteria. Because of its ecological and economic importance, this classification prompted the definition of several conservation actions aimed at the recovery of the species in Portugal.
Genome-wide survey of
Arabidopsis
natural variation in downy mildew resistance using combined association and linkage mapping
Authors: Nemri Adnane , Atwell Susanna , Tarone Aaron M. , Huang Yu S. , Zhao Keyan , Studholme David J. , Nordborg Magnus , Jones Jonathan D. G.
Published: May 2010

The model plant
Arabidopsis thaliana
exhibits extensive natural variation in resistance to parasites. Immunity is often conferred by resistance (
R
) genes that permit recognition of specific races of a disease. The number of such
R
genes and their distribution are poorly understood. In this study, we investigated the basis for resistance to the downy mildew agent
Hyaloperonospora arabidopsidis
ex
parasitica (Hpa)
in a global sample of
A. thaliana
. We implemented a combined genome-wide mapping of resistance using populations of recombinant inbred lines and a collection of wild
A. thaliana
accessions. We tested the interaction between 96 host genotypes collected worldwide and five strains of
Hpa
. Then, a fraction of the species-wide resistance was genetically dissected using six recently constructed populations of recombinant inbred lines. We found that resistance is usually governed by single dominant
R
genes that are concentrated in four genomic regions only. We show that association genetics of resistance to diseases such as downy mildew enables increased mapping resolution from quantitative trait loci interval to candidate gene level. Association patterns in quantitative trait loci intervals indicate that the pool of
A. thaliana
resistance sources against the tested
Hpa
isolates may be predominantly confined to six
RPP
(Resistance to
Hpa
) loci isolated in previous studies. Our results suggest that combining association and linkage mapping could accelerate resistance gene discovery in plants.
Catalytic promiscuity in the biosynthesis of cyclic peptide secondary metabolites in planktonic marine cyanobacteria
Authors: Li Bo , Sher Daniel , Kelly Libusha , Shi Yanxiang , Huang Katherine , Knerr Patrick J. , Joewono Ike , Rusch Doug , Chisholm Sallie W. , van der Donk Wilfred A.
Published: May 2010

Our understanding of secondary metabolite production in bacteria has been shaped primarily by studies of attached varieties such as symbionts, pathogens, and soil bacteria. Here we show that a strain of the single-celled, planktonic marine cyanobacterium
Prochlorococcus
—which conducts a sizable fraction of photosynthesis in the oceans—produces many cyclic, lanthionine-containing peptides (lantipeptides). Remarkably, in
Prochlorococcus
MIT9313 a single promiscuous enzyme transforms up to 29 different linear ribosomally synthesized peptides into a library of polycyclic, conformationally constrained products with highly diverse ring topologies. Genes encoding this system are found in variable abundances across the oceans—with a hot spot in a Galapagos hypersaline lagoon—suggesting they play a habitat- and/or community-specific role. The extraordinarily efficient pathway for generating structural diversity enables these cyanobacteria to produce as many secondary metabolites as model antibiotic-producing bacteria, but with much smaller genomes.
Signaling properties of a covalent modification cycle are altered by a downstream target
Authors: Ventura Alejandra C. , Jiang Peng , Van Wassenhove Lauren , Del Vecchio Domitilla , Merajver Sofia D. , Ninfa Alexander J.
Published: May 2010

We used a model system of purified components to explore the effects of a downstream target on the signaling properties of a covalent modification cycle, an example of retroactivity. In the experimental system used, a bifunctional enzyme catalyzed the modification and demodification of its substrate protein, with both activities regulated by a small molecule stimulus. Here we examined how a downstream target for one or both forms of the substrate of the covalent modification cycle affected the steady-state output of the system, the sensitivity of the response to the stimulus, and the concentration of the stimulus required to provide the half-maximal response (S
50
). When both the modified and unmodified forms of the substrate protein were sequestered by the downstream target, the sensitivity of the response was dramatically decreased, but the S
50
was only modestly affected. Conversely, when the downstream target only sequestered the unmodified form of the substrate protein, significant effects were observed on both system sensitivity and S
50
. Behaviors of the experimental systems were well approximated both by simple models allowing analytical solutions and by a detailed model based on the known interactions and enzymatic activities. Modeling and experimentation indicated that retroactivity may result in subsensitive responses, even if the covalent modification cycle displays significant ultrasensitivity in the absence of retroactivity. Thus, we provide examples of how a downstream target can alter the signaling properties of an upstream signal transduction covalent modification cycle.
End-Devonian extinction and a bottleneck in the early evolution of modern jawed vertebrates
Authors: Sallan Lauren Cole , Coates Michael I.
Published: May 2010

The Devonian marks a critical stage in the early evolution of vertebrates: It opens with an unprecedented diversity of fishes and closes with the earliest evidence of limbed tetrapods. However, the latter part of the Devonian has also been characterized as a period of global biotic crisis marked by two large extinction pulses: a “Big Five” mass extinction event at the Frasnian-Famennian stage boundary (374 Ma) and the less well-documented Hangenberg event some 15 million years later at the Devonian-Carboniferous boundary (359 Ma). Here, we report the results of a wide-ranging analysis of the impact of these events on early vertebrate evolution, which was obtained from a database of vertebrate occurrences sampling over 1,250 taxa from 66 localities spanning Givetian to Serpukhovian stages (391 to 318 Ma). We show that major vertebrate clades suffered acute and systematic effects centered on the Hangenberg extinction involving long-term losses of over 50% of diversity and the restructuring of vertebrate ecosystems worldwide. Marine and nonmarine faunas were equally affected, precluding the existence of environmental refugia. The subsequent recovery of previously diverse groups (including placoderms, sarcopterygian fish, and acanthodians) was minimal. Tetrapods, actinopterygians, and chondrichthyans, all scarce within the Devonian, undergo large diversification events in the aftermath of the extinction, dominating all subsequent faunas. The Hangenberg event represents a previously unrecognized bottleneck in the evolutionary history of vertebrates as a whole and a historical contingency that shaped the roots of modern biodiversity.
Fabricating nanowire devices on diverse substrates by simple transfer-printing methods
Authors: Lee Chi Hwan , Kim Dong Rip , Zheng Xiaolin
Published: May 2010

The fabrication of nanowire (NW) devices on diverse substrates is necessary for applications such as flexible electronics, conformable sensors, and transparent solar cells. Although NWs have been fabricated on plastic and glass by lithographic methods, the choice of device substrates is severely limited by the lithographic process temperature and substrate properties. Here we report three new transfer-printing methods for fabricating NW devices on diverse substrates including polydimethylsiloxane, Petri dishes, Kapton tapes, thermal release tapes, and many types of adhesive tapes. These transfer-printing methods rely on the differences in adhesion to transfer NWs, metal films, and devices from weakly adhesive donor substrates to more strongly adhesive receiver substrates. Electrical characterization of fabricated NW devices shows that reliable ohmic contacts are formed between NWs and electrodes. Moreover, we demonstrated that Si NW devices fabricated by the transfer-printing methods are robust piezoresistive stress sensors and temperature sensors with reliable performance.