bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutron diffraction and dielectric anomalies in YMn2−xFexO5
Authors: Kim Dong Hyun , Kim Sung Baek , Kim Chul Sung
Published: May 2007

The multiferroic YMn2−xFexO5 (x=0.00,0.01,0.02,0.04) system has been studied by neutron diffraction and Mössbauer spectroscopy, focusing on the dielectric constant anomaly near 18K. We found that the electric Curie temperature (TCE) decreased and the second transition anomaly temperature (T2) smeared from the ε∕ε0 curves with higher Fe concentrations in YMn2−xFexO5. The temperature dependence of the dielectric constant (ε∕ε0) shows a peak at 41K and a second transition near 18K for polycrystalline YMn2O5. TCE of YMn1.96Fe0.04O5 was observed at 34K. The temperature dependence of the lattice parameters for YMn2O5 shows a discontinuous jump at 18K, which is the same anomaly temperature obtained from the dielectric constant curve. The Mössbauer electric quadrupole splitting value also changed at 21K for YMn1.99Fe0.01O5. Our data indicate that the changes in the lattice and Mössbauer parameters occur simultaneously with the anomaly of dielectric constant.
An ab initio investigation on the endohedral metallofullerene Gd3N–C80
Authors: Qian M. C. , Khanna S. N.
Published: May 2007

First-principles electronic structure studies on the ground state geometry and electronic and magnetic properties of bare and hydrogen coated metallofullerene Gd3N–C80 have been carried out within a density functional formalism. The correlation effects are incorporated either through a generalized gradient corrected functional or through an on-site Coulomb interaction (LDA+U). It is shown that the bare Gd3N–C80 possess a ferromagnetic ground state with a large spin moment of 21μB that is highly stable against spin fluctuations. The simulated Raman spectrum shows that the low-energy peaks are contributed by the floppy movement of N atom. As to the effect of addition of hydrogens, it is shown that the most favorable site for the hydrogen adsorption is an on-top site where the H atom is located above a five-member carbon ring with a binding energy of 1.92eV, while the least stable site corresponds to an on-top absorption above a six-member ring. A study of the energetics upon multiple adsorption of H shows that the binding energy of the H to metallofullerene drops after 11 H atoms. This shows that it should be possible to attach multiple ligands offering the potential that the Gd3N–C80 can be functionalized with ligands or assembled in cluster assemblies.
Stress dependence of magnetic domains in FeCoSiB amorphous films
Authors: Peng B. , Xie Q. Y. , Zhang W. L. , Zhong Z. Y.
Published: May 2007

The work reports the effect of a tensile stress on the magnetic domain of FeCoSiB amorphous films. The domain structures of the unstressed and stressed FeCoSiB amorphous films with different tensile strains have been studied by magnetic force microscopy (MFM). With the increase of the tensile stress in the samples, it has been observed that the domain structures transform from irregular domains into parallel strip domains, and magnetic contrasts decrease. The MFM image disappears when the tensile stress is strong enough. A model has been presented to explain the evolution of the domain structures under the tensile stress. The effects of the stress on the domain of the films have been discussed.
Study of individual ferromagnetic disks with femtosecond optical pulses
Authors: Laraoui A. , Vénuat J. , Halté V. , Albrecht M. , Beaurepaire E. , Bigot J.-Y.
Published: May 2007

The magnetization dynamics of ferromagnetic disks made of CoPt3 and Ni80Fe20 has been investigated using a time resolved magneto-optical Kerr microscope. The spatial resolution of 500nm combined to the pump and probe femtosecond laser pulses allows us to explore the magnetization dynamics of individual disks over a broad temporal regime ranging from 100fsto1ns. In addition, our experimental configuration allows us to perform a dynamical imaging of the magnetization for a fixed delay between the pump and probe pulses. Such imaging has also been performed when the disk is initially switched to the reversed magnetization by the pump pulse.
Influence of substrate roughness on the magnetic properties of thin fcc Co films
Authors: Steinmuller S. J. , Vaz C. A. F. , Ström V. , Moutafis C. , Gürtler C. M. , Kläui M. , Bland J. A. C. , Cui Z.
Published: May 2007

We present a study of the influence of substrate roughness on the magnetic properties of thin fcc Co films (7 and 17nm thick) grown on Cu(001)∕Si(001). A significant decrease in cubic anisotropy with increasing film roughness was observed with Brillouin light scattering. In addition, the rougher samples exhibited a substantial broadening of the spin wave peaks. Both effects were found to be more pronounced for the thinner Co layers. We propose a magnetic configuration with the magnetization following coherently the substrate morphology (“undulating” state) resulting in the absence of magnetic surface charges. This configuration gives rise to a reduction in the magnetic anisotropy of epitaxial thin films, in good qualitative agreement with the experimental observations.
Magnetomechanical performance of directionally solidified Fe–Ga alloys
Authors: Zhao X. , Mellors N. , Lord D. G.
Published: May 2007

Iron-gallium alloys can produce magnetostrictions of ∼400ppm and might serve as mechanically robust actuator/sensing materials. However, for polycrystalline Fe–Ga alloys, the magnetostrictive performance decreases with the increasing deviations from the ideal ⟨100⟩ texture. In this paper, three directionally solidified Fe–Ga alloys with gallium contents of 17, 18.4, and 19.5at.% were characterized at ambient temperature. These specimens exhibit high d33 and magnetic permeability when subjected to applied magnetic fields, indicating their suitability for light weight actuator applications but not for high force applications due to their low saturation magnetostriction and hence low blocking force. All the alloys produce significant changes in magnetization, around 0.7Ms–0.8Ms when subjected to cyclic compressive stresses of 51MPa, making them promising candidate materials for sensing and energy harvesting applications. However, eddy current effects may easily become a problem when such materials are subjected to a high frequency vibration or magnetic field due to their intrinsic high magnetic permeability.
Ultrafast optical modification of magnetic anisotropy and stimulated precession in an epitaxial Co2MnAl thin film
Authors: Liu Y. , Shelford L. R. , Kruglyak V. V. , Hicken R. J. , Sakuraba Y. , Oogane M. , Ando Y. , Miyazaki T.
Published: May 2007

An all-optical pump-probe method was used to study magnetization precession in an epitaxial Co2MnAl Heusler alloy thin film. The frequency and amplitude of precession showed a clear fourfold variation as the orientation of the static field was applied in different directions within the plane of the film, revealing that the precession is induced by an ultrafast modification of the magnetocrystalline anisotropy field. The effective fields acting upon the magnetization have been determined and the damping parameter is found to decrease rapidly as the strength of the applied field is increased.
Effect of polarization and uniaxial stress on the R-line luminescence of single crystal sapphire
Authors: Margueron Samuel H. , Clarke David R.
Published: May 2007

The polarization dependence of the optical absorption and R-line emission of a Cr3+-doped sapphire single crystal have been characterized. The absorption bands, U(T42) and Y(T41), as well as the R-line emission are determined to be dipole-like transitions associated with three incoherent dipoles oriented along the sapphire principal crystallographic axes (a,m,c). From measurements using the Muller method, it is found that the polarization of the R lines does not depend on either the polarization of the incident excitation or its wavelength. The σ emission is also an order of magnitude stronger than π emission. The R2-R1 peak separation and the ratio of the R2∕R1 peak areas are found to be dependent on both the polarization and the stress directions. Stress in the basal plane breaks the symmetry of α polarization with the R2∕R1 ratio increasing along the stress direction and decreasing in the perpendicular direction in the basal plane. The π emission also decreases with stress in the basal plane. However, in both polarizations the ratio R2∕R1 does not depend on stress applied along the c axis. The value of the R2∕R1 peak area ratio can be understood in terms of a piezoelectric-like effect on the dipole transition.
The role of helicity and stretching in forced kinematic dynamos in a spherical shell
Authors: Livermore P. W. , Hughes D. W. , Tobias S. M.
Published: May 2007

Considerations of mean-field theory suggest that small-scale helical flows are an effective means of generating large-scale (mean) magnetic fields, whereas fast dynamo considerations reveal the importance of Lagrangian chaos in the flow for generating small-scale magnetic fields in the limit of high magnetic Reynolds number. We explore these ideas further by considering the kinematic magnetic fields generated by three forced steady flows in a spherical shell that differ both in their helicity and in their stretching properties. The full magnetic induction equation is solved numerically, with no a priori assumptions about the nature of the generated magnetic field. There are two surprising aspects to our results. One is that the most significant mean field is generated by a flow with zero net helicity; the other is that the flow with the “best” stretching properties turns out to be the most inefficient dynamo. Our results, therefore, suggest that it may not be possible to determine the nature of a kinematic-dynamo generated magnetic field simply from the knowledge of certain flow properties.
Vortex magnetization reversal in double-layer ferromagnetic/antiferromagnetic dots
Authors: Guslienko K. Y. , Hoffmann A.
Published: May 2007

We investigated theoretically the magnetization reversal via vortex nucleation and annihilation in double-layer ferromagnetic/antiferromagnetic cylindrical dots. The influence of the antiferromagnetic layer on the magnetization reversal is accounted for by means of an interfacial, unidirectional exchange field. We consider explicitly a nonuniformity of the magnetization reversal mode along the direction perpendicular to the layers, which gives rise to a nonuniform Bloch line. The vortex annihilation fields, the vortex trajectory, and the average dot magnetization are calculated as functions of the dot geometrical parameters and the external field direction with respect to the exchange-bias field. The calculations are compared with recent experiments.
Charge and momentum transfer in supercooled melts: Why should their relaxation times differ?
Authors: Lubchenko Vassiliy
Published: May 2007

The steady-state values of the viscosity and the intrinsic ionic conductivity of quenched melts are computed, in terms of independently measurable quantities. The frequency dependence of the ac dielectric response is estimated. The discrepancy between the corresponding characteristic relaxation times is only apparent; it does not imply distinct mechanisms, but stems from the intrinsic barrier distribution for α-relaxation in supercooled fluids and glasses. This type of intrinsic “decoupling” is argued not to exceed four orders in magnitude for known glassformers. The origin of the discrepancy between the stretching exponent β, as extracted from ε(ω) and the dielectric modulus data, is explained. The actual width of the barrier distribution always grows with lowering the temperature. The contrary is an artifact of the large contribution of the dc-conductivity component to the modulus data. The methodology allows one to single out other contributions to the conductivity, as in “superionic” liquids or when charge carriers are delocalized, implying that in those systems, charge transfer does not require structural reconfiguration.
Electron transport in n-doped Si/SiGe quantum cascade structures
Authors: Lazic I. , Ikonic Z. , Milanovic V. , Kelsall R. W. , Indjin D. , Harrison P.
Published: May 2007

An electron transport model in n-Si/SiGe quantum cascade or superlattice structures is described. The model uses the electronic structure calculated within the effective-mass complex-energy framework, separately for perpendicular (Xz) and in-plane (Xxy) valleys, the degeneracy of which is lifted by strain, and additionally by size quantization. The transport is then described via scattering between quantized states, using a rate equations approach and tight-binding expansion, taking the coupling with two nearest-neighbor periods. Acoustic phonon, optical phonon, alloy disorder, and interface roughness scattering are taken into account. The calculated current/voltage dependence and gain profiles are presented for two simple superlattice structures.
Critical adsorption on nonspherical colloidal particles
Authors: Kondrat S. , Harnau L. , Dietrich S.
Published: May 2007

We consider a nonspherical colloidal particle immersed in a fluid close to its critical point. The temperature dependence of the corresponding order parameter profile is calculated explicitly. We perform a systematic expansion of the order parameter profile in powers of the local curvatures of the surface of the colloidal particle. This curvature expansion reduces to the short distance expansion of the order parameter profile in the case that the solvent is at the critical composition.
Short-range and long-range solvent effects on charge-transfer-to-solvent transitions of I− and K+I− contact ion pair dissolved in supercritical ammonia
Authors: Sciaini G. , Fernández-Prini R. , Estrin D. A. , Marceca E.
Published: May 2007

Vertical excitation and electron detachment energies associated with the optical absorption of iodide ions dissolved in supercritical ammonia at 420K have been calculated in two limiting scenarios: as a solvated free I− ion and forming a K+I− contact ion pair (CIP). The evolution of the transition energies as a result of the gradual building up of the solvation structure was studied for each absorbing species as the solvent’s density increased, i.e., changing the NH3 supercritical thermodynamic state. In both cases, if the solvent density is sufficiently high, photon absorption produces a spatially extended electron charge beyond the volume occupied by the solvated solute core; this excited state resembles a typical charge-transfer-to-solvent (CTTS) state. A combination of classical molecular dynamics simulations followed by quantum mechanical calculations for the ground, first-excited, and electron-detached electronic states have been carried out for the system consisting of one donor species (free I− ion or K+I− CIP) surrounded by ammonia molecules. Vertical excitation and electron detachment energies were obtained by averaging 100 randomly chosen microconfigurations along the molecular dynamics trajectory computed for each thermodynamic condition (fluid density). Short- and long-range contributions of the solvent−donor interaction upon the CTTS states of I− and K+I− were identified by performing additional electronic structure calculations where only the solvent interaction due to the first neighbor molecules was taken into account. These computations, together with previous experimental evidence that we collected for the system, have been used to analyze the solvent effects on the CTTS transition. In this paper we have established the following: (i) the CTTS electron of free I− ion or K+I− CIP presents similar features, and it gradually localizes in close proximity of the iodine parent atom when the ammonia density is increased; (ii) for the free I− ion, the short-range solvent interaction contributes to the stabilization of the ground state more than it does for the CTTS excited state, which is evidenced experimentally as a blueshift in the maximum absorption of the CTTS transition when the density is increased; (iii) this effect is less noticeable for the K+I− ion pair, because in this case a tight solvation structure, formed by four NH3 molecules wedged between the ions, appears at very low density and is very little affected by changes in the density; (iv) the long-range contribution to the solvent stabilization can be neglected for the K+I− CIP, since the main features of its electronic transition can be explained on the basis of the vicinity of the cation; (v) however, the long-range solvent field contribution is essential for the free I− ion to become an efficient CTTS donor upon photoexcitation, and this establishes a difference in the CTTS behavior of I− in bulk and in clusters.
Probing the valence character of O 1s→Rydberg excited O2 by participator Auger decay measurements and partial ion yield spectroscopy following x-ray absorption
Authors: Feifel R. , Tanaka T. , Kitajima M. , Tanaka H. , De Fanis A. , Sankari R. , Karlsson L. , Sorensen S. , Piancastelli M. -N. , Prümper G. , Hergenhahn U. , Ueda K.
Published: May 2007

The valence character of O 1s→Rydberg excited O2 is investigated by means of participator Auger decay spectroscopy, performed at selected photon energies across the K-shell resonance region, and by means of partial ion yield x-ray absorption spectroscopy. For several of the excitation energies studied, the authors find substantial σ*(Σu−4,Σu−2) valence character being mixed with nsσ and npσ (Σu−4,Σu−2) Rydberg states. An experimental indication of a coupling between the channels associated with quartet and doublet ion cores is considered and discussed. New spectroscopic constants are derived for the singly ionized XΠg2 state of O2 based on the observation of at least 20 vibrational sublevels.
Characterization of multicapillary dielectric cathodes
Authors: Gleizer J. Z. , Hadas Y. , Yarmolich D. , Felsteiner J. , Krasik Ya. E.
Published: May 2007

Parameters of the plasma and electron beam produced by a multicapillary cathode in a diode powered by a ∼200kV, ∼300ns pulse are presented. It was found that the source of electrons is the plasma ejected from the capillaries. Inside the capillaries this plasma obtains electron density and temperature of ∼8×1015cm−3 and ∼5eV, respectively. In the vicinity of the cathode, the density and temperature of the plasma electrons were found to be 2×1014cm−3 and 4.5eV, respectively, for electron current density of ∼40A∕cm2. It was shown that the plasma expansion velocity is in the range of (1–2)×106cm∕s for current density of >12A∕cm2.
Electron interferometry in the proximity of amorphous ultrathin SiO2∕Si
Authors: Xue K. , Ho H. P. , Xu J. B. , Wang R. Z.
Published: May 2007

Electron standing waves (ESWs) have been excited in the proximity of amorphous ultrathin SiO2∕Si using ultrahigh vacuum scanning tunneling microscope. Distinct ESW characteristics have been discerned in conductance spectra obtained in the vicinity of ultrathin (∼1nm) SiO2 films. And these features are similar to those obtained on Si surface, showing that both the interference and coherence of electron waves degrade only slightly due to the oxide presence. In a thicker oxide (>1.5nm), no ESW features are observed. The results indicate that the ESW is a very locally confined phenomenon and attainable in amorphous films with sufficiently slender thickness and low defect density.
Electric field mediated breakdown of thin liquid films separating microscopic emulsion droplets
Authors: Mostowfi Farshid , Khristov Khristo , Czarnecki Jan , Masliyah Jacob , Bhattacharjee Subir
Published: May 2007

The authors present a microfluidic technique for electrically induced breakup of thin films formed between microscopic emulsion droplets. The method involves creating a stationary film at the intersection of two microchannels etched onto a glass substrate. After stabilizing the film, a ramped potential is applied across it. The electrical stresses developed at the film interfaces lead to its rupture above a threshold potential. The potential difference at which the film ruptures assesses the film stability. This approach is employed to demonstrate how surfactant (lecithin) adsorption imparts stability to an ultrathin oil film formed between two water droplets.
Lead-free In2O3-doped (Bi0.5Na0.5)0.93Ba0.07TiO3 ceramics synthesized by direct reaction sintering
Authors: Zhou Tao-Sheng , Huang Rong-Xia , Shang Xun-Zhong , Peng Fei , Guo Jian-Yong , Chai Li-Ying , Gu Hao-Shuang , He Yun-Bin
Published: May 2007

Lead-free (Bi0.5Na0.5)0.93Ba0.07TiO3–xwt%In2O3 ceramics synthesized by direct reaction sintering have been studied. X-ray diffraction reveals that all (Bi0.5Na0.5)0.93Ba0.07TiO3–xwt%In2O3 ceramics are of a perovskite structure with coexistence of rhombohedral and tetragonal phases. It is found that the direct reaction sintering promotes growing of ceramic grains while doping of In2O3 contributes to inhibit and homogenize the grain growth, as shown by scanning electron microscopy. The ceramics show excellent piezoelectric and dielectric properties with thickness electromechanical coupling factor kt=0.503, piezoelectric constant d33=205pC∕N, dielectric constant ε33T∕ε0=1046, and loss tangent tanδ=0.036.
Epitaxial lateral overgrowth of (112¯2) semipolar GaN on (11¯00) m-plane sapphire by metalorganic chemical vapor deposition
Authors: Ni X. , Özgür Ü. , Baski A. A. , Morkoç H. , Zhou Lin , Smith David J. , Tran C. A.
Published: May 2007

The authors report the growth of semipolar (112¯2) GaN films on nominally on-axis (101¯0) m-plane sapphire substrates using metal organic chemical vapor deposition. High-resolution x-ray diffraction (XRD) results indicate a preferred (112¯2) GaN orientation. Moreover, epitaxial lateral overgrowth (ELO) of GaN was carried out on the (112¯2) oriented GaN templates. When the ELO stripes were aligned along [112¯0]sapphire, the Ga-polar wings were inclined by 32° with respect to the substrate plane with smooth extended nonpolar a-plane GaN surfaces and polar c-plane GaN growth fronts. When compared with the template, the on-axis and off-axis XRD rocking curves indicated significant improvement in the crystalline quality by ELO for this mask orientation (on-axis 1700arcsec for the template, 380arcsec for the ELO sample, when rocked toward the GaN m axis), as verified by transmission electron microscopy (TEM). For growth mask stripes aligned along [0001]sapphire with GaN m-plane as growth fronts, the surface was composed of two {101¯1} planes making a 26° angle with the substrate plane. For this mask orientation XRD and TEM showed no improvement in the crystalline quality by ELO when compared to the non-ELO template.
Optofluidic transport in liquid core waveguiding structures
Authors: Mandal Sudeep , Erickson David
Published: May 2007

Here the authors introduce a method to achieve optofluidically based particle transport using liquid core waveguiding structures. Optically driven transport of 3μm polystyrene particles through a liquid core photonic crystal fiber is demonstrated and the resulting velocity distribution is characterized. The authors also show that dielectric particles can form highly concentrated bands within the liquid core with negligible transport based dispersion. They anticipate that this approach could lay the groundwork for an innovative class of optically driven particle concentration and separation devices.
Observation of largely enhanced hardness in nanomultilayers of the Ag–Nb system with positive enthalpy of formation
Authors: Lai W. S. , Yang M. J.
Published: May 2007

Ag ∕ Nb nanomultilayers with different modulation wavelengths Λ were prepared on silicon wafers by electron beam evaporation. Nanoindenter measurements show that with decreasing Λ of the multilayers, the nanohardness increases up to ∼80% for Λ=4nm, whereas the modulus is almost unchanged. This unusual behavior originates from a unique microstructure where amorphous Ag–Nb alloys form at the interfaces and grain boundaries of silver nanoparticles, as observed by cross-section high resolution transmission electron microscopy. The amorphous phases favor hardness enhancement by preventing dislocation emission and movement, whereas they have a negative contribution to the modulus because of their free volume.
Temperature dependence of the tunneling current in metal-oxide-semiconductor devices due to the coupling between the longitudinal and transverse components of the electron thermal energy
Authors: Mao Ling-Feng
Published: May 2007

Based on the analysis of the Schrödinger equation, the coupling between the longitudinal and transverse components of the thermal energy of tunneling electrons gives a physical explanation of the temperature-dependent tunneling current. The difference of the effective electron mass between the oxide and the substrate (gate) results in a reduction in the barrier height of metal-oxide-semiconductor devices. Such a reduction strongly depends on the energy of tunneling electrons. The calculated Fowler-Nordheim tunneling currents agree well with the experimental data in the literature. The calculations also show that the temperature sensitivity of the tunneling current strongly depends on the effective electron mass.
High-mobility window for two-dimensional electron gases at ultrathin AlN∕GaN heterojunctions
Authors: Cao Yu , Jena Debdeep
Published: May 2007

High-conductivity two-dimensional electron gases at AlN∕GaN heterojunctions are reported. The sheet densities can be tuned from ∼5×1012∕cm2to∼5×1013∕cm2 by varying the AlN thickness from 2to7nm. A critical thickness is observed beyond which biaxial strain relaxation and cracking of AlN occur, and a degradation of carrier mobility is seen to occur at extremely high sheet densities. A high-mobility window is identified, within which room-temperature mobility exceeding 1000cm2∕Vs. and sheet densities in the (1–3)×1013∕cm2 are obtained, yielding record low sheet resistances in the range of ∼170Ω∕◻. Interface roughness scattering and strain relaxation are identified as the factors preventing lower sheet resistances at present.
Fluorescence telescopes observe the predicted ultrahigh-energy cutoff of the cosmic-ray spectrum
Authors: Schwarzschild Bertram
Published: May 2007

When a cosmic-ray proton has as much kinetic energy as a well-hit tennis ball, it can create pions and thus lose energy in intergalactic space simply by plowing through the cosmic microwave background.
Time-resolved electric-field measurements probe plasma breakdown
Authors: Miller Johanna
Published: May 2007

A spectroscopic experiment offers a new look at a plasma in the first few instants of its formation.
EU hammers out pact to cut greenhouse gas emissions
Authors: Kaplan Karen H.
Published: May 2007

The threat of global warming's effects has already spurred some multinational companies to cut emissions. Meanwhile, in the US, grassroots efforts are growing.
New chief vows to reinvigorate Italian space activities
Authors: Feder Toni
Published: May 2007

As president of Italy's space agency, Giovanni Bignami aims to revive the country's satellite program and strengthen ties to other space agencies.
NASA cancels science flight, ditches international partners
Authors: Guinnessy Paul
Published: May 2007

A 12-year project to build a billion-dollar particle-physics lab in space is grounded unless someone comes up with at least $380 million.
Russian academy of sciences weathers round of attacks
Authors: Feder Toni
Published: May 2007

Russian scientists say their academy's woes are symptomatic of a broader undermining of science in their country.
Special report: Budget boosts physical sciences in FY 2008, most other research down
Authors: Dawson Jim
Published: May 2007

For the second year, President Bush's American Competitiveness Initiative would significantly increase funding for research at NSF, Department of Energy, and NIST laboratories. Other agencies aren't so lucky.
Dan Haneman 1931 - 2002
Authors: Read M. N. , Miller D. J.
Published: May 2007

Dan Haneman died in Sydney as a result of Parkinson's disease on 13 December 2002. He made fundamental contributions to the study of clean semiconductor surfaces from the beginning of such studies in the 1950s. Perhaps his most important contributions were the Haneman model for semiconductor surfaces and the invention of novel experimental methods for the study of surfaces produced by cleavage in ultrahigh vacuum. Numerous PhD students benefited from his careful supervision over many years.
Appointing a Professor: Reflections on Filling the Chair of Organic Chemistry at the University of Sydney in 1948
Authors: Rae Ian D.
Published: May 2007

Chemistry Departments, like other sections of Australian universities, long looked to Britain as the source of their senior appointees. None more so than the University of Sydney, where an attempt to fill the chair of organic chemistry in 1948 went badly awry. The selected candidate, an English chemist with a modest research record but qualities of leadership that were valued by the Head of School at Sydney, Professor Raymond Le Fèvre, at first accepted but then declined the appointment. The main cause for his change of heart was the support in the university, which came to the attention of the popular press, for the appointment of an internal candidate. This was Dr Francis Lions, a graduate of the university and a staff member for two decades who had a strong record of chemical research. Le Fèvre expressed a preference for someone more co-operative than Lions, with whom he had already clashed. The chair remained vacant for several years but was eventually filled by the appointment of an Australian, Arthur Birch. Australian universities at that time were slowly moving to appoint more local candidates to chairs whereas in the past they had almost automatically looked to Britain for their recruits. As well as noting this shift, this account of the 1948 incident also raises questions about the implicit and explicit criteria on which appointments are made and compares the case study with other contentious appointments in a range of disciplines in Australian universities.
Kenneth Baillieu Myer 1921 - 1992
Authors: Denton Derek
Published: May 2007

Kenneth Baillieu Myer was elected to the Fellowship of the Australian Academy in April 1992, under the provision for special election of people who are not scientists but have rendered conspicuous service to the cause of science. Myer was a significant figure in Australian history by virtue of his contribution to the origins or early development of major national institutions, most notably the Howard Florey Laboratories of Experimental Physiology and Medicine, the School of Oriental Studies at the University of Melbourne, the Victorian Arts Centre and the National Library of Australia. He successfully fostered new research in organizations such as the Division of Plant Industry of the CSIRO and helped build the Oriental Collection of the Art Gallery of New South Wales.
Insights into the nature of the transition zone from physically constrained inversion of long-period seismic data
Authors: Cammarano Fabio , Romanowicz Barbara
Published: May 2007

Imposing a thermal and compositional significance to the outcome of the inversion of seismic data facilitates their interpretation. Using long-period seismic waveforms and an inversion approach that includes constraints from mineral physics, we find that lateral variations of temperature can explain a large part of the data in the upper mantle. The additional compositional signature of cratons emerges in the global model as well. Above 300 km, we obtain seismic geotherms that span the range of expected temperatures in various tectonic regions. Absolute velocities and gradients with depth are well constrained by the seismic data throughout the upper mantle, except near discontinuities. The seismic data are consistent with a slower transition zone and an overall faster shallow upper mantle, which is not compatible with a homogenous dry pyrolite composition. A gradual enrichment with depth in a garnet-rich component helps to reduce the observed discrepancies. A hydrated transition zone would help to lower the velocities in the transition zone, but it does not explain the seismic structure above it.
A-803467, a potent and selective Na
v
1.8 sodium channel blocker, attenuates neuropathic and inflammatory pain in the rat
Authors: Jarvis Michael F. , Honore Prisca , Shieh Char-Chang , Chapman Mark , Joshi Shailen , Zhang Xu-Feng , Kort Michael , Carroll William , Marron Brian , Atkinson Robert , Thomas James , Liu Dong , Krambis Michael , Liu Yi , McGaraughty Steve , Chu Katharine , Roeloffs Rosemarie , Zhong Chengmin , Mikusa Joseph P. , Hernandez Gricelda , Gauvin Donna , Wade Carrie , Zhu Chang , Pai Madhavi , Scanio Marc , Shi Lei , Drizin Irene , Gregg Robert , Matulenko Mark , Hakeem Ahmed , Gross Michael , Johnson Matthew , Marsh Kennan , Wagoner P. Kay , Sullivan James P. , Faltynek Connie R. , Krafte Douglas S.
Published: May 2007

Activation of tetrodotoxin-resistant sodium channels contributes to action potential electrogenesis in neurons. Antisense oligonucleotide studies directed against Na
v
1.8 have shown that this channel contributes to experimental inflammatory and neuropathic pain. We report here the discovery of A-803467, a sodium channel blocker that potently blocks tetrodotoxin-resistant currents (IC
50
= 140 nM) and the generation of spontaneous and electrically evoked action potentials
in vitro
in rat dorsal root ganglion neurons. In recombinant cell lines, A-803467 potently blocked human Na
v
1.8 (IC
50
= 8 nM) and was >100-fold selective vs. human Na
v
1.2, Na
v
1.3, Na
v
1.5, and Na
v
1.7 (IC
50
values ≥1 μM). A-803467 (20 mg/kg, i.v.) blocked mechanically evoked firing of wide dynamic range neurons in the rat spinal dorsal horn. A-803467 also dose-dependently reduced mechanical allodynia in a variety of rat pain models including: spinal nerve ligation (ED
50
= 47 mg/kg, i.p.), sciatic nerve injury (ED
50
= 85 mg/kg, i.p.), capsaicin-induced secondary mechanical allodynia (ED
50
≈ 100 mg/kg, i.p.), and thermal hyperalgesia after intraplantar complete Freund's adjuvant injection (ED
50
= 41 mg/kg, i.p.). A-803467 was inactive against formalin-induced nociception and acute thermal and postoperative pain. These data demonstrate that acute and selective pharmacological blockade of Na
v
1.8 sodium channels
in vivo
produces significant antinociception in animal models of neuropathic and inflammatory pain.
Cryopyrin/NALP3 binds ATP/dATP, is an ATPase, and requires ATP binding to mediate inflammatory signaling
Authors: Duncan Joseph A. , Bergstralh Daniel T. , Wang Yanhong , Willingham Stephen B. , Ye Zhengmao , Zimmermann Albert G. , Ting Jenny Pan-Yun
Published: May 2007

The CATERPILLER (CLR/NLR) gene family encodes a family of putative nucleotide-binding proteins important for host defense. Although nucleotide binding is thought to be central to this family, this aspect is largely unstudied. The CATERPILLER protein cryopyrin/NALP3 regulates IL-1β processing by assembling the multimeric inflammasome complex. Mutations within the exon encoding the nucleotide-binding domain are associated with hereditary periodic fevers characterized by constitutive IL-1β production. We demonstrate that purified cryopyrin binds ATP, dATP, and ATP-agarose, but not CTP, GTP, or UTP, and exhibits ATPase activity. Mutation of the nucleotide-binding domain reduces ATP binding, caspase-1 activation, IL-1β production, cell death, macromolecular complex formation, self-association, and association with the inflammasome component ASC. Disruption of nucleotide binding abolishes the constitutive activation of disease-associated mutants, identifying nucleotide binding by cryopyrin as a potential target for antiinflammatory pharmacologic intervention.
Assessing risks of climate variability and climate change for Indonesian rice agriculture
Authors: Naylor Rosamond L. , Battisti David S. , Vimont Daniel J. , Falcon Walter P. , Burke Marshall B.
Published: May 2007

El Niño events typically lead to delayed rainfall and decreased rice planting in Indonesia's main rice-growing regions, thus prolonging the hungry season and increasing the risk of annual rice deficits. Here we use a risk assessment framework to examine the potential impact of El Niño events and natural variability on rice agriculture in 2050 under conditions of climate change, with a focus on two main rice-producing areas: Java and Bali. We select a 30-day delay in monsoon onset as a threshold beyond which significant impact on the country's rice economy is likely to occur. To project the future probability of monsoon delay and changes in the annual cycle of rainfall, we use output from the Intergovernmental Panel on Climate Change AR4 suite of climate models, forced by increasing greenhouse gases, and scale it to the regional level by using empirical downscaling models. Our results reveal a marked increase in the probability of a 30-day delay in monsoon onset in 2050, as a result of changes in the mean climate, from 9–18% today (depending on the region) to 30–40% at the upper tail of the distribution. Predictions of the annual cycle of precipitation suggest an increase in precipitation later in the crop year (April–June) of ≈10% but a substantial decrease (up to 75% at the tail) in precipitation later in the dry season (July–September). These results indicate a need for adaptation strategies in Indonesian rice agriculture, including increased investments in water storage, drought-tolerant crops, crop diversification, and early warning systems.
The conserved transcriptome in human and rodent male gametogenesis
Authors: Chalmel Frédéric , Rolland Antoine D. , Niederhauser-Wiederkehr Christa , Chung Sanny S. W. , Demougin Philippe , Gattiker Alexandre , Moore James , Patard Jean-Jacques , Wolgemuth Debra J. , Jégou Bernard , Primig Michael
Published: May 2007

We report a cross-species expression profiling analysis of the human, mouse, and rat male meiotic transcriptional program, using enriched germ cell populations, whole gonads, and high-density oligonucleotide microarrays (GeneChips). Among 35% of the protein-coding genes present in rodent and human genomes that were found to be differentially expressed between germ cells and somatic controls, a key group of 357 conserved core loci was identified that displays highly similar meiotic and postmeiotic patterns of transcriptional induction across all three species. Genes known to be important for sexual reproduction are significantly enriched among differentially expressed core loci and a smaller group of conserved genes not detected in 17 nontesticular somatic tissues, correlating transcriptional activation and essential function in the male germ line. Some genes implicated in the etiology of cancer are found to be strongly transcribed in testis, suggesting that these genes may play unexpected roles in sexual reproduction. Expression profiling data further identified numerous conserved genes of biological and clinical interest previously unassociated with the mammalian male germ line.
Gene–gene interaction associated with neural reward sensitivity
Authors: Yacubian Juliana , Sommer Tobias , Schroeder Katrin , Gläscher Jan , Kalisch Raffael , Leuenberger Boris , Braus Dieter F. , Büchel Christian
Published: May 2007

Reward processing depends on dopaminergic neurotransmission and is modulated by factors affecting dopamine (DA) reuptake and degradation. We used fMRI and a guessing task sensitive to reward-related activation in the prefrontal cortex and ventral striatum to study how individual variation in genes contributing to DA reuptake [DA transporter (DAT)] and degradation [catechol-o-methyltransferase (COMT)] influences reward processing. Prefrontal activity, evoked by anticipation of reward irrespective of reward probability and magnitude, was COMT genotype-dependent. Volunteers homozygous for the Met allele, associated with lower enzyme activity and presumably greater DA availability, showed larger responses compared with volunteers homozygous for the Val allele. A similar COMT effect was observed in the ventral striatum. As reported previously, the ventral striatum was also found to code gain-related expected value, i.e., the product of reward magnitude and gain probability. Individual differences in ventral striatal sensitivity for value were in part explained by an epistatic gene–gene interaction between COMT and DAT. Although most genotype combinations exhibited the expected activity increase with more likely and larger rewards, two genotype combinations (COMT Met/Met DAT 10R and COMT Val/Val 9R) were associated with blunted ventral striatal responses. In view of a consistent relationship between reduced reward sensitivity and addiction, our findings point to a potential genetic basis for vulnerability to addiction.
Identification of a human CD8+regulatory T cell subset that mediates suppression through the chemokine CC chemokine ligand 4
Authors: Joosten Simone A. , van Meijgaarden Krista E. , Savage Nigel D. L. , de Boer Tjitske , Triebel Frédéric , van der Wal Annemieke , de Heer Emile , Klein Michèl R. , Geluk Annemieke , Ottenhoff Tom H. M.
Published: May 2007

Regulatory T cells (Treg) comprise multiple subsets and are important in controlling immunity and inflammation. However, the induction and mode of action of the various distinct Treg subsets remain ill defined, particularly in humans. Here, we describe a human CD8+lymphocyte activation gene-3 (LAG-3)+CD25+FoxP3+Treg subset, which suppresses T cells partly through the secretion of CC chemokine ligand 4 (CCL4), which can inhibit T cell activation by interfering with T cell receptor signaling. CD8+Tregs are expanded by antigen inin vivo-primed donors, and can be detected in pathogen-infected human tissue. This CD8+LAG-3+CD25+FoxP3+CCL4+Treg subset thus may play a role in immunoregulation in humans, including infectious diseases.
Ena/VASP Proteins Have an Anti-Capping Independent Function in Filopodia Formation
Authors: Applewhite Derek A. , Barzik Melanie , Kojima Shin-ichiro , Svitkina Tatyana M. , Gertler Frank B. , Borisy Gary G.
Published: May 2007

Filopodia have been implicated in a number of diverse cellular processes including growth-cone path finding, wound healing, and metastasis. The Ena/VASP family of proteins has emerged as key to filopodia formation but the exact mechanism for how they function has yet to be fully elucidated. Using cell spreading as a model system in combination with small interfering RNA depletion of Capping Protein, we determined that Ena/VASP proteins have a role beyond anticapping activity in filopodia formation. Analysis of mutant Ena/VASP proteins demonstrated that the entire EVH2 domain was the minimal domain required for filopodia formation. Fluorescent recovery after photobleaching data indicate that Ena/VASP proteins rapidly exchange at the leading edge of lamellipodia, whereas virtually no exchange occurred at filopodial tips. Mutation of the G-actin–binding motif (GAB) partially compromised stabilization of Ena/VASP at filopodia tips. These observations led us to propose a model where the EVH2 domain of Ena/VASP induces and maintains clustering of the barbed ends of actin filaments, which putatively corresponds to a transition from lamellipodial to filopodial localization. Furthermore, the EVH1 domain, together with the GAB motif in the EVH2 domain, helps to maintain Ena/VASP at the growing barbed ends.
Inhibition of the Ubiquitin-Proteasome System Induces Stress Granule Formation
Authors: Mazroui Rachid , Di Marco Sergio , Kaufman Randal J. , Gallouzi Imed-Eddine
Published: May 2007

The inhibition of the ubiquitin-dependent proteasome system (UPS) via specific drugs is one type of approach used to combat cancer. Although it has been suggested that UPS inhibition prevents the rapid decay of AU-rich element (ARE)-containing messages, very little is known about the cellular mechanisms leading to this effect. Here we establish a link between the inhibition of UPS activity, the formation of cytoplasmic stress granules (SGs), and mRNA metabolism. The assembly of the SGs requires the phosphorylation of the translation initiation factor eIF2α by a mechanism involving the stress kinase GCN2. On prolonged UPS inhibition and despite the maintenance of eIF2α phosphorylation, SGs disassemble and translation recovers in an Hsp72 protein-dependent manner. The formation of these SGs coincides with the disassembly of processing bodies (PBs), known as mRNA decay entities. As soon as the SGs assemble, they recruit ARE-containing messages such as p21cip1mRNA, which are stabilized under these conditions. Hence, our findings suggest that SGs could be considered as one of the players that mediate the early response of the cell to proteasome inhibitors by interfering temporarily with mRNA decay pathways.
Rapid and Reversible Nuclear Accumulation of Cytoplasmic tRNA in Response to Nutrient Availability
Authors: Whitney Michael L. , Hurto Rebecca L. , Shaheen Hussam H. , Hopper Anita K.
Published: May 2007

Cytoplasmic tRNAs have recently been found to accumulate in the nucleus during amino acid starvation in yeast. The mechanism and regulation by which tRNAs return to the nucleus are unclear. Here, we show accumulation of cytoplasmic tRNA in the nucleus also occurs during glucose starvation. Nuclear accumulation of tRNA in response to acute glucose or amino acid starvation is rapid, reversible, requires no new transcription, and is independent of the aminoacylation status of tRNA. Gradual depletion of nutrients also results in the accrual of tRNA in the nucleus. Distinct signal transduction pathways seem to be involved in the accumulation of cytoplasmic tRNA in the nucleus in response to amino acid versus glucose starvation. These findings suggest tRNA nucleocytoplasmic distribution may play a role in gene expression in response to nutritional stress.
Biomechanics of male erectile function
Authors: Udelson Daniel
Published: May 2007

Two major branches of engineering mechanics are fluid mechanics and structural mechanics, with many practical problems involving the effect of the first on the second. An example is the design of an aircraft's wings to bend within reasonable limits without breaking under the action of lift forces exerted by the air flowing over them; another is the maintenance of the structural integrity of a dam designed to hold back a water reservoir which would exert very large forces on it. Similarly, fluid and structural mechanics are involved in the engineering analysis of erectile function: it is the hydraulic action of increased blood flow into the corpora cavernosa that creates the structural rigidity necessary to prevent collapse of the penile column.