bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin-wave excitation in ultrathin Co and Fe films on Cu(001) by spin-polarized electron energy loss spectroscopy (invited)
Authors: Vollmer R. , Etzkorn M. , Kumar P. S. Anil , Ibach H. , Kirschner J.
Published: May 2004

We demonstrate, that spin-polarized electron energy loss spectroscopy is a unique tool to determine spin-wave dispersion curves of ultrathin films and surfaces over the whole Brillouin zone. For ultrathin Co films on Cu(001) the excitation of a spin wave appears as a well defined peak in the loss spectrum. 3 ML Fe films on 1 ML Co/Cu(001) films show spin-wave excitation peaks as well though much broader compared to the Co case. The spin-wave energy at the surface zone boundary of about 140 meV for the Fe film is nearly a factor of 2 smaller than that of the Co films.
Study of thiol-induced adhesion of stressed III–V semiconductor on wax using thin film elastic relaxation
Authors: Bessueille F. , Kostrzewa M. , Leclercq J.-L. , Grenet G.
Published: May 2004

In this paper we underline the role played by octadecylthiols as adhesion promoters on the elastic relaxation of a compressively-prestressed (0.8%) In0.65Ga0.35As thin film stuck on Apiezon-W wax. Surface morphologies by Nomarski Optical Microscopy and Atomic Force Microscopy reveal drastic changes when octadecylthiols are involved in the sticking process. In the “no-thiol” case, the surface morphology displays closely joined regularly distributed undulations (wavelength ≈4.8 μm, height ≈0.18 μm). On the contrary, in the “thiol” case, the wrinkling looks like a large-meshed wire lattice [wire–wire distance ≈(10–40 μm), height ≈0.4 μm]. These thiol-induced changes in morphology are explained as due to an energy compromise between relaxing the film stress on the one hand and stressing the self-assembled monolayer organization at the wax/film interface on the other hand.
Calculated half-metallic behavior in dilute magnetically doped ZnS
Authors: Stern R. A. , Schuler T. M. , MacLaren J. M. , Ederer D. L. , Perez-Dieste V. , Himpsel F. J.
Published: May 2004

First principles calculations of Zn11X1S12 supercells in the zincblende structure, where X is a magnetic ion, show that when X=Cr, Fe, and Ni the materials are calculated to be half metallic and ferromagnetic, i.e., the densities of states of these bulk materials at the Fermi energy is calculated to be 100% spin polarized and the exchange interaction is ferromagnetic. This behavior persists even when on-site Coulomb “Hubbard U” potentials are applied.
Light emission from Al/HfO2/silicon diodes
Authors: Chen T. C. , Lai W. Z. , Liang C. Y. , Chen M. J. , Lee L. S. , Liu C. W.
Published: May 2004

The metal–insulator–silicon light-emitting diode (MIS LED) using a high-dielectric-constant material (HfO2) is studied. The external quantum efficiency for light emission at room temperature from the MIS LED was observed to be 2.0×10−6, as compared to 0.5×10−6 for the metal–oxide–silicon (MOS) LED. The large hole concentration at the Si/HfO2 interface created by the high dielectric constant of HfO2 may be responsible for the enhancement. The emission line shape of the MIS LED can be fitted by the electron-hole plasma recombination model, similar to the MOS LED. The Al/HfO2/silicon LED with a high interface trap density has a continuous spectrum below the Si gap beside the electron-hole plasma emission, probably due to the radiative recombination between the electrons and holes via the interface states.
Influence of the growth conditions on the ridge morphology during GaAs deposition on GaAs (001) patterned substrates
Authors: Williams R. S. , Ashwin M. J. , Jones T. S. , Neave J. H.
Published: May 2004

The formation of ridge structures on 〈100〉 aligned mesa stripes defined on GaAs (001) substrates has been investigated as a function of the substrate temperature, V/III flux ratio, and GaAs deposition quantity. Across the entire range of deposition conditions employed, the ridge structures were observed to form with {110} facets, indicating a similar growth mechanism in all cases. The {110} facet lengths on the ridge structures were accurately reproduced using a simple one-dimensional geometric model that included the effects of Ga adatom migration from the {110} facets to the upper ridge surface and resulting in an additional Ga flux. The results have important implications for the controlled growth of micron-scale ridge structures on patterned substrates.
Fractional revivals in the rovibrational motion of I2
Authors: Lohmüller T. , Engel V. , Beswick J. A. , Meier C.
Published: May 2004

Motivated by pump–probe experiments of I2 in a room-temperature sample, the detection of fractional revivals is investigated using full-dimensional quantum wave packet calculations. It is shown that the structures observed in the pump–probe signal depend sensitively on the probe parameters employed and that the observed signal reflects a particular phase effect between fractional revivals.
Recovery of the carrier density in arsenic-doped silicon after high energy (2 MeV) Si+ implantation
Authors: Nobili D. , Solmi S. , Ferri M. , Attari M.
Published: May 2004

Carrier density and mobility measurements were performed on heavily arsenic-doped silicon-on-insulator specimens after 2 MeV implantation of Si+ ions. It is found that implantation induces a marked reduction of the electron density, which increases with the concentration of active dopant, and approaches saturation for a Si+ fluence of 5×1015 cm−2. Recovery of the carriers was studied by isothermal annealing at temperatures in the range of 550–800 °C. It is shown that this phenomenon can be separated by As deactivation, which takes place at the same time, and that the kinetics of carrier recovery can be expressed by the rate equation: −dn/dt=nγC exp(−Ea/kT), with Ea=2.3 eV and γ=2.32. The recovery rate increases with As concentration, and values of C that account for this phenomenon are reported. These results and the annealing behavior of the carrier mobility in the damaged and undamaged reference samples indicate that the decrease of the carrier density upon irradiation can be attributed to acceptor centers, probably due to point defects clusters.
Lifetime evaluation of weakly ionized plasma channel by accumulation effect of charged particles by means of laser absorption
Authors: Yamaura Michiteru , Hayashi Nobuya , Ihara Satoshi , Satoh Saburoh , Yamabe Chobei
Published: May 2004

The density of weakly ionized plasma and the lifetime for laser-triggered lightning are improved by using a KrF excimer laser with a high repetition rate of the order of kilohertz. We have studied how to create a weakly ionized plasma channel with the plasma density of 1013 cm−3 and the long lifetime of the order of milliseconds in order to trigger and guide lightning discharge efficiently. The density of a weakly ionized plasma channel is 1013 cm−3 and the plasma channel has a long lifetime of the order of milliseconds, which were achieved by utilizing the accumulation effect of charged particles generated by the high-repetition-rate laser. Moreover, it is clarified that the dominant mechanism of decay of plasma generated the high-repetition-rate laser was ion-ion recombination between N+ and O−.
The use of nitrogen to disorder GaInP
Authors: Chapman D. C. , Rieth L. W. , Stringfellow G. B. , Lee J. W. , Seong T. Y.
Published: May 2004

Significant changes in microstructure, surface structure, and alloy composition have been observed in GaInP with the addition of nitrogen. These effects occur due to surface changes induced by small concentrations of nitrogen. Transmission electron microscopy and photoluminescence experiments indicate that the use of the surfactant N nearly eliminates the CuPtB ordered structure typically seen in organometallic vapor phase epitaxially grown Ga0.5In0.5P lattice matched to GaAs. In situ surface photoabsorption measurements show a large change in the surface structure indicating that N reduces the concentration of P dimers on the surface, decreasing the driving force for ordering. Nitrogen also has a significant effect on the Ga/In ratio in the bulk. The indium content in the solid is decreased by 71% with a DMHy/III ratio of 60 (DMHy—1,1 dimethyl hydrazine). Nitrogen roughens the surface causing the formation of hillocks and small rectangular features that can be up to 50 nm tall.
Alternating and direct current characterization and photoinduced absorption studies of modified conjugated polymer thin films
Authors: Lipson S. M. , Coleman J. N. , Drury A. , O’Brien D. F. , Blau W. J. , Cadby A. J. , Lane P. A. , Bradley D. D. C.
Published: May 2004

Control of interchain separation enables the optical properties of polymer thin films to be altered. We present a thin film preparation technique that increases the free volume fraction in spin coated polymer thin films resulting in reduced interchain interaction. The polaron yield, measured using photoinduced absorption, was significantly reduced as a direct result of the increased interchain separation, leading to a higher value for the measured photoluminescence efficiency. Impedance spectroscopy showed an increase in permittivity, probably due to greater polarizability. Increases approaching one order of magnitude were observed for direct current hole conductivity and mobility values. Space charge limited conduction analysis suggests a narrowing of the highest occupied molecular orbital band tail on treatment resulting in reduced trapping. Single layer light emitting devices prepared using this technique were found to be significantly brighter and to have longer operating lifetimes.
Time-resolved reflectance studies of silicon during laser thermal processing of amorphous silicon gates on ultrathin gate oxides
Authors: Chong Y. F. , Gossmann H.-J. L. , Thompson M. O. , Yang S. , Pey K. L. , Wee A. T. S.
Published: May 2004

In this paper, we report the systematic investigation on the melt characteristics of silicon during laser thermal processing (LTP) of amorphous silicon (a-Si) gates on ultrathin gate oxides. LTP is used to reduce the gate depletion effect in advanced semiconductor devices. The influence of implantation-induced damage and chemical inhomogeneities on the melt behavior of ion-implanted a-Si is studied using in situ time-resolved reflectance (TRR) measurements and ex situ secondary ion mass spectrometry. The results from TRR measurements indicate the presence of a buried melt for a-Si implanted with B+ at a subamorphizing dose. In contrast, such a melt behavior is not observed during LTP of undoped a-Si and a-Si implanted with As+ at an amorphizing dose. We attribute the marked difference in the melt characteristics to the competitive effects between compositional inhomogeneities and the extent of amorphization in the a-Si layer. It should be noted that the as-deposited a-Si gate is not really “amorphous” in the sense of an ion beam-induced amorphous layer. This postulation is verified by the absence of a buried melt in a-Si films implanted with Si+ prior to B+ implantation, where the dose of the Si+ implant is sufficient to cause amorphization in silicon and the amorphization depth greatly exceeds the projected range of the boron implant.
Evidence of nitric-oxide-induced surface band bending of indium tin oxide
Authors: Hu Jianqiao , Pan Jisheng , Zhu Furong , Gong Hao
Published: May 2004

The interaction of indium tin oxide (ITO) film with nitric oxide (NO) has been investigated in situ by a four-point probe and x-ray photoelectron spectroscopy (XPS). The XPS N 1s peak emerged at a high binding energy of 404 eV indicating that NO was molecularly adsorbed on ITO surface. The adsorption of NO on ITO surface also induced a 0.2 eV shift in its valence band maximum to the low binding energy side leading to an upward surface band bending. We have shown that the increase in the ITO sheet resistance was attributed to its surface band bending.
Anomalous nonlinear photoresponse in a InGaN/GaN heterostructure
Authors: Zeller J. , Rudolph W. , Sheik-Bahae M.
Published: May 2004

The nonlinear (third to fourth order) as well as linear photoconductivity in a Gallium nitride/Indium-Gallium nitride (GaN/InGaN) heterostructure is investigated using femtosecond pulses in the infrared (IR) and near ultraviolet (UV). An anomalous IR photoresponse is explained by a four level model for the GaN region including defect density fluctuations and nonlinear carrier transport phenomena. The same model also explains the observed subpicosecond noninstantaneous IR response of the photodetector. The linear UV photoresponse originates in the InGaN region. Design guidelines for GaN-based nonlinear photodetectors used in autocorrelation measurements are suggested.
Acrylic-based resin with favorable properties for three-dimensional two-photon polymerization
Authors: Baldacchini Tommaso , LaFratta Christopher N. , Farrer Richard A. , Teich Malvin C. , Saleh Bahaa E. A. , Naughton Michael J. , Fourkas John T.
Published: May 2004

We describe an acrylic-based prepolymer resin that is ideally suited for the fabrication of three-dimensional structures with two-photon polymerization. We characterize the photochemical and photophysical properties of the photoinitiator and present representative structures that demonstrate the favorable mechanical and optical properties of the polymer.
Effects of postanneal conditions on the dielectric properties of CaCu3Ti4O12 thin films prepared on Pt/Ti/SiO2/Si substrates
Authors: Fang Liang , Shen Mingrong , Cao Wenwu
Published: May 2004

High-dielectric-constant CaCu3Ti4O12 (CCTO) thin films were prepared on Pt/Ti/SiO2/Si(100) substrates by pulsed-laser deposition (PLD). The 480 nm thick polycrystalline films have preferred orientation and show obvious crystallization on the surface. The temperature dependence of dielectric constant and loss of the Pt/CCTO/Pt capacitors is comparable with that obtained in the epitaxial CCTO films grown on oxides substrates. We found that the dielectric properties are very sensitive to the postannealing atmosphere and temperature. Postannealing in nitrogen atmosphere produces larger low-frequency dielectric relaxation as the annealing temperature increases, while annealing in oxygen atmosphere at high temperature suppresses the relaxation and decreases the dielectric constant of the thin films. Such results are attributed to the presence of insulating grain-boundary barrier layers.
Structural and optical properties of titanium dioxide films deposited by reactive magnetron sputtering in pure oxygen plasma
Authors: Asanuma T. , Matsutani T. , Liu C. , Mihara T. , Kiuchi M.
Published: May 2004

Titanium dioxide (TiO2) thin films were deposited on unheated quartz (SiO2) substrates in “pure oxygen” plasma by reactive radio-frequency (rf) magnetron sputtering. The structural and optical properties of deposited films were systematically studied by changing the deposition parameters, and it was very recently found that crystalline TiO2 films grew effectively in pure O2 atmosphere. For TiO2 films deposited at a rf power Prf of 200 W, x-ray diffraction patterns show the following features: (a) no diffraction peak was observed at a total sputtering pressure ptot of 1.3 Pa; (b) rutile (110) diffraction was observed at 4.0 Pa, (c) the dominant diffraction was from anatase (101) planes, with additional diffraction from (200), under ptot between 6.7 and 13 Pa. For the deposition at 140 W, however, crystalline films with mixed phases were observed only between 4.0 and 6.7 Pa. The peaks of both the deposition rate and the anatase weight ratio for the films produced at 140 W were found at ptot of approximately 6.7 Pa. This suggests that the nucleation and growth of TiO2 films were affected by the composition, density, and kinetic energy of the particles impinging on the substrate surface. The optical absorption edge analysis showed that the optical band gap Eg and the constant B could sensitively detect the film growth behavior, and determine the film structure and optical absorption. The change in the shape of the fundamental absorption edge is considered to reflect the variation of density and the short-range structural modifications.
Orientational and interaction induced dynamics in the isotropic phase of a liquid crystal: Polarization resolved ultrafast optical Kerr effect spectroscopy
Authors: Hunt Neil T. , Meech Stephen R.
Published: May 2004

The ultrafast dynamics of the isotropic phase of a liquid crystal 4′-pentyl-4-p-biphenylcarbonitrile (5CB) have been investigated using polarization resolved optical Kerr effect spectroscopy. Measurements were made as a function of both temperature and dilution in nonpolar solvents. To separate single molecule and interaction induced components to the relaxation of the induced birefringence, measurements of both the anisotropic and isotropic response were made. The isotropic response was found to be dominated by a damped low-frequency mode of intramolecular origin. There is a minor additional component assigned to an interaction induced contribution. There is at most an extremely weak isotropic signal beyond 1 ps, showing that the picosecond time scale dynamics of 5CB are dominated by orientational relaxation. The isotropic response is independent of temperature in the range studied (0.2–50 K above the nematic to isotropic phase-transition temperature). The anisotropic response exhibits relaxation dynamics on time scales spanning subpicosecond to several hundred picoseconds and beyond. The fastest components are dominated by a librational response, but there are smaller contributions from three low-frequency intramolecular modes, and a contribution from interaction induced effects. The low-frequency spectral density extracted from these data are independent of temperature in the range studied, 0.2–30 K above the phase-transition temperature, but shift to lower frequency on dilution in alkane solvents. In neat 5CB the picosecond time scale orientational dynamics are dominated by temperature-independent reorientation within the pseudonematic domains, while in solution these are disrupted, and the orientational response becomes faster and temperature dependent.
Imaging water on Ag(111): Field induced reorientation and contrast inversion
Authors: Morgenstern Karina , Nieminen Jouko
Published: May 2004

Water adsorbed on Ag(111) at 70 K forms circular clusters that consist of six molecules. In scanning tunneling microscopy, this cyclic hexamer is imaged as a protrusion for voltages below VSS=−93 meV and as a depression for voltages above VSS. The electronic density of states, however, increases around VSS. We explain this counterintuitive result with the aid of calculated images by a change from constructive to destructive interference between different tunneling channels due to a field induced reorientation of the molecule under the tunneling tip.
Bridging continuum and statistical thermodynamics via equations of state and the density of states
Authors: Gospodinov Ivan D. , Escobedo Fernando A.
Published: May 2004

The connection between molecular force fields and equations of state (EoS) is typically established at the level of predicted quantities, e.g., by comparing simulation data and EoS data. In this paper we show how an EoS can be used to extract the density of states (Ω) of a system thus establishing a deeper connection between EoSs and statistical thermodynamics. We also show how such an EoS Ω can be used to aid molecular simulation methods designed to map out Ω (like the multicanonical approach). Central to the implementation of these ideas is the fact that the configurational Ω is related to thermodynamic properties accessible by an EoS via Boltzmann’s equation. Sample calculations are presented for the Ωemph relevant to isothermal-isobaric and grand canonical ensemble simulations using the hard-sphere system and the Lennard–Jones system as model fluids, and the Carnahan–Starling EoS and a cubic EoS, respectively, as thermodynamic models.
Basis set effects on frontier molecular orbital energies and energy gaps: A comparative study between plane waves and localized basis functions in molecular systems
Authors: Matus Myrna H. , Garza Jorge , Galván Marcelo
Published: May 2004

In order to study the Kohn–Sham frontier molecular orbital energies in the complete basis limit, a comparative study between localized functions and plane waves, obtained with the local density approximation exchange-correlation functional is made. The analyzed systems are ethylene and butadiene, since they are theoretical and experimentally well characterized. The localized basis sets used are those developed by Dunning. For the plane-waves method, the pseudopotential approximation is employed. The results obtained by the localized basis sets suggest that it is possible to get an estimation of the orbital energies in the limit of the complete basis set, when the basis set size is large. It is shown that the frontier molecular orbital energies and the energy gaps obtained with plane waves are similar to those obtained with a large localized basis set, when the size of the supercell and the plane-wave expansion have been appropriately calibrated.
A vibrational spectroscopic study of structure evolution of water dissolved in supercritical carbon dioxide under isobaric heating
Authors: Oparin R. , Tassaing T. , Danten Y. , Besnard M.
Published: May 2004

A combination of Raman scattering spectroscopy and infrared absorption was applied to investigate the structural evolution of water dissolved in supercritical carbon dioxide under isobaric heating (T=40–340 °C, P=250 bar). Quantitative analysis of experimental spectra allowed us to determine that at relatively moderate temperatures water dissolved in CO2-rich phase exists only under monomeric form (solitary water surrounding by CO2 molecules), but hydrogen-bonded species, namely, dimers, begin to appear upon heating. At the same time, the ratio of dimers to monomers concentration increases with further temperature increase and at temperatures close to the temperature of total miscibility of the mixture (T=366 °C, P=250 bar), water dimers only are present in the CO2-rich phase.
Adam–Gibbs model for the supercooled dynamics in the ortho-terphenyl ortho-phenylphenol mixture
Authors: Roland C. M. , Capaccioli S. , Lucchesi M. , Casalini R.
Published: May 2004

Dielectric measurements of the α-relaxation time were carried out on a mixture of ortho-terphenyl (OTP) with ortho-phenylphenol, over a range of temperatures at two pressures, 0.1 and 28.8 MPa. These are the same conditions for which heat capacity, thermal expansivity, and compressibility measurements were reported by Takahara et al. [S. Takahara, M. Ishikawa, O. Yamamuro, and T. Matsuo, J. Phys. Chem. B 103, 3288 (1999)] for the same mixture. From the combined dynamic and thermodynamic data, we determine that density and temperature govern to an equivalent degree the variation of the relaxation times with temperature. Over the measured range, the dependence of the relaxation times on configurational entropy is in accord with the Adam–Gibbs model, and this dependence is invariant to pressure. Consistent with the implied connection between relaxation and thermodynamic properties, the kinetic and thermodynamic fragilities are found to have the same pressure independence. In comparing the relaxation properties of the mixture to those of neat OTP, density effects are stronger in the former, perhaps suggestive of less efficient packing.
Stabilizing the Herd: Fixing the Identity of Nonhumans
Authors: Lulka David
Published: May 2004

Supported by scientific modes of representation, wildlife-management agencies commonly adopt policies that subordinate nonhuman species and resubstantiate human–nonhuman hierarchies. In this paper I illustrate the inadequacy of current management policies by drawing upon Deleuzian notions of immanence and movement and applying them to the specific case of Yellowstone bison. Modes of representation that define nonhuman ontology in terms of genetics are shown to be inadequate for they separate essence from experience and facilitate the removal and exclusion of nonhumans. In contrast, a Deleuzian theory of wildlife accentuates the importance of movement, contact, and contingency in the constitution of nonhuman ontology, thus outlining an approach that can also lead to a revision of human–nonhuman relations. In particular, movement provides a physical mechanism to bridge the theoretical gap that separates human from nonhuman, and suggests a means to link together ethical and evolutionary concerns regarding nonhumans. With the distinctions between Deleuzian theory and common wildlife-management practices in mind, the paradigm of sustainability is criticized for prioritizing demographic and genetic stability over spatial transgression, thereby minimizing the developmental capacities of nonhumans and legitimizing existing spatial structures of exclusion and control.
Cycle of the seminiferous epithelium in a marsupial species, the brushtail possum (Trichosurus vulpecula), and estimation of its duration
Authors: Lin Minjie , Harman Amanda , Fletcher Terry P.
Published: May 2004

We investigated the cycle of the seminiferous epithelium in a marsupial, namely the brushtail possum (Trichosurus vulpecula), using semithin sections of seminiferous tubules embedded in Spurr’s resin. Using 14 steps of spermatid development as markers, we were able to class tubular cross-sections into 10 well-defined stages of the seminiferous epithelial cycle. The duration of one cycle was 13.5 days, as determined by injections of [3H]-thymidine and autoradiographic examination of the most advanced sperm cells at 2 h and 17 days after injection. The durations of stages I–X were 21.4, 66.4, 54.1, 47.0, 29.8, 28.5, 25.3, 25.0, 12.0 and 15.9 h, respectively, estimated by the relative percentage of occurrence of each stage. It was estimated that the life spans of the main germ cells were as follows: type B spermatogonia, 5.4 days; primary spermatocytes, 16.7 days; secondary spermatocytes, 0.7 days; and spermatids, 21.4 days. The results suggest that the kinetics of spermatogenesis in marsupials show a similar pattern to that in eutherians.
Noc2 is essential in normal regulation of exocytosis in endocrine and exocrine cells
Authors: Matsumoto Masanari , Miki Takashi , Shibasaki Tadao , Kawaguchi Miho , Shinozaki Hidehiro , Nio Junko , Saraya Atsunori , Koseki Haruhiko , Miyazaki Masaru , Iwanaga Toshihiko , Seino Susumu
Published: May 2004

Rab3 is a subfamily of the small GTP-binding protein Rab family and plays an important role in exocytosis. Several potential effectors of Rab3, including rabphilin3 and Rims (Rim1 and Rim2), have been isolated and characterized. Noc2 was identified originally in endocrine pancreas as a molecule homologous to rabphilin3, but its role in exocytosis is unclear. To clarify the physiological function of Noc2 directly, we have generated Noc2 knockout (Noc2
-/-
) mice. Glucose intolerance with impaired insulin secretion was induced
in vivo
by acute stress in Noc2
-/-
mice, but not in wild-type (Noc2
+/+
) mice. Ca
2+
-triggered insulin secretion from pancreatic isles of Noc2
-/-
mice was markedly impaired, but was completely restored by treatment with pertussis toxin, which inhibits inhibitory G protein Gi/o signaling. In addition, the inhibitory effect of clonidine, an α
2
-adrenoreceptor agonist, on insulin secretion was significantly greater in Noc2
-/-
islets than in Noc2
+/+
islets. Impaired Ca
2+
-triggered insulin secretion was rescued by adenovirus gene transfer of wild-type Noc2 but not by that of mutant Noc2, which does not bind to Rab3. Accordingly, Noc2 positively regulates insulin secretion from endocrine pancreas by inhibiting Gi/o signaling, and the interaction of Noc2 and Rab3 is required for the effect. Interestingly, we also found a marked accumulation of secretory granules in various exocrine cells of Noc2
-/-
mice, especially in exocrine pancreas with no amylase response to stimuli. Thus, Noc2, a critical effector of Rab3, is essential in normal regulation of exocytosis in both endocrine and exocrine cells.
NMDA receptor hypofunction produces concomitant firing rate potentiation and burst activity reduction in the prefrontal cortex
Authors: Jackson Mark E. , Homayoun Houman , Moghaddam Bita
Published: May 2004

Cognitive deficits associated with frontal lobe dysfunction are a determinant of long-term disability in schizophrenia and are not effectively treated with available medications. Clinical studies show that many aspects of these deficits are transiently induced in healthy individuals treated with
N
-methyl-
d
-aspartate (NMDA) antagonists. These findings and recent genetic linkage studies strongly implicate NMDA receptor deficiency in schizophrenia and suggest that reversing this deficiency is pertinent to treating the cognitive symptoms of schizophrenia. Despite the wealth of behavioral data on the effects of NMDA antagonist treatment in humans and laboratory animals, there is a fundamental lack of understanding about the mechanisms by which a general state of NMDA deficiency influences the function of cortical neurons. Using ensemble recording in freely moving rats, we found that NMDA antagonist treatment, at doses that impaired working memory, potentiated the firing rate of most prefrontal cortex neurons. This potentiation, which correlated with expression of behavioral stereotypy, resulted from an increased number of irregularly discharged single spikes. Concurrent with the increase in spike activity, there was a significant reduction in organized bursting activity. These results identify two distinct mechanisms by which NMDA receptor deficiency may disrupt frontal lobe function: an increase in disorganized spike activity, which may enhance cortical noise and transmission of disinformation; and a decrease in burst activity, which reduces transmission efficacy of cortical neurons. These findings provide a physiological basis for the NMDA receptor deficiency model of schizophrenia and may clarify the nature of cortical dysfunction in this disease.
A high-affinity interaction between NusA and the
rrn nut
site in
Mycobacterium tuberculosis
Authors: Arnvig Kristine B. , Pennell S. , Gopal B. , Colston M. J.
Published: May 2004

The bacterial NusA protein enhances transcriptional pausing and termination and is known to play an essential role in antitermination. Antitermination is signaled by a nut-like cis-acting RNA sequence comprising
boxB
,
boxA
, and
boxC
. In the present study, we demonstrate a direct, specific high-affinity interaction between the
rrn
leader nut-like sites and the NusA proteins of
Mycobacterium tuberculosis
and
Escherichia coli
. This NusA–RNA interaction relies on the conserved region downstream of
boxA
, the
boxC
region, thus demonstrating a key function of this element. We have established an
in vivo
assay for antitermination in mycobacteria and use this to show that the
M
.
tuberculosis rrn
nut-like site enhances transcriptional read-through of untranslated RNA consistent with an antitermination signal within this site. Finally, we present evidence that this NusA–RNA interaction affects transcriptional events further downstream.
Programmable cells: Interfacing natural and engineered gene networks
Authors: Kobayashi Hideki , Kærn Mads , Araki Michihiro , Chung Kristy , Gardner Timothy S. , Cantor Charles R. , Collins James J.
Published: May 2004

Novel cellular behaviors and characteristics can be obtained by coupling engineered gene networks to the cell's natural regulatory circuitry through appropriately designed input and output interfaces. Here, we demonstrate how an engineered genetic circuit can be used to construct cells that respond to biological signals in a predetermined and programmable fashion. We employ a modular design strategy to create
Escherichia coli
strains where a genetic toggle switch is interfaced with: (
i
) the SOS signaling pathway responding to DNA damage, and (
ii
) a transgenic quorum sensing signaling pathway from
Vibrio fischeri.
The genetic toggle switch endows these strains with binary response dynamics and an epigenetic inheritance that supports a persistent phenotypic alteration in response to transient signals. These features are exploited to engineer cells that form biofilms in response to DNA-damaging agents and cells that activate protein synthesis when the cell population reaches a critical density. Our work represents a step toward the development of “plug-and-play” genetic circuitry that can be used to create cells with programmable behaviors.
Prevalence of overweight and obesity among young people in Great Britain
Authors: Jebb Susan A , Rennie Kirsten L , Cole Tim J
Published: May 2004

Objective:

To determine the prevalence of overweight and obesity in British young people (4–18 years) in 1997.

Design:

Cross-sectional analysis of the National Diet and Nutrition Survey of young people.

Setting:

Great Britain.

Subjects:

Nationally representative sample of 1836 young people (age 4–18 years).

Results:

The prevalence of obesity based on body mass index (weight/height2) and the International Obesity Task Force cut–offs was 4.0%, with a further 15.4% identified as overweight. Asians were almost four times as likely to be obese as white subjects (13.6 vs. 3.5%, P < 0.001). Among white subjects there was no significant difference in the prevalence of obesity between girls and boys, or with age. The risk of obesity was significantly higher in subjects from social classes IV and V than from social classes I–III (6.5 vs. 2.7%, P = 0.003). Subjects living in Scotland and Wales were significantly more likely to be obese than those in England (7.6 and 6.5 vs. 2.9%, respectively, P < 0.01). Multiple logistic regression showed that, among white subjects, those in social classes IV and V living in Wales and Scotland were three times more likely to be obese than the other children in the survey (odds ratio 3.3, 95% confidence interval 1.1–9.8).

Conclusion:

These data provide information on the national prevalence of overweight and obesity in Great Britain and baseline data from which to monitor future trends. This analysis provides important demographic information on those most at risk of obesity, which may be used to inform public health strategies to prevent obesity in young people.
How feasible are healthy eating and physical activity for young women?
Authors: Ball Kylie , Crawford David , Warren Narelle
Published: May 2004

Objective:

This study investigated young women's perceptions of the feasibility of physical activity and healthy eating behaviours, and how these vary by socio-economic status, domestic characteristics and weight status.

Design:

This population-based study used a mailed questionnaire to investigate perceptions of the feasibility of commonly recommended healthy eating and physical activity behaviours among a sample of young women. The feasibility of 29 physical activity behaviours (e.g. relating to frequency, intensity, duration, domain/setting) and 15 healthy eating behaviours (e.g. relating to location/setting, fruit and vegetable intake, fat/sugar intake) was assessed. Height, weight and sociodemographic details were also obtained.

Setting:

Nation-wide community-based survey.

Subjects:

A total of 445 women aged 18–32 years selected randomly from the Australian electoral roll.

Results:

Most women reported that they either were already engaged in many of the healthy eating behaviours or saw these as highly feasible. Many physical activity behaviours, on the other hand, were perceived as less feasible, particularly among women with children and women who were overweight.

Conclusions:

Health promotion messages and strategies aimed at increasing physical activity and healthy eating are unlikely to succeed unless they take into account perceptions that these behaviours are not feasible. For young women, this may involve promoting more time-effective, flexible ways of achieving recommended physical activity. Messages specifically targeted to women with children, and women who are overweight, are required.
Large heterogeneity of the obesity epidemic in Danish adults
Authors: Heitmann Berit L , Strøger Ulla , Mikkelsen Kim L , Holst Claus , Sørensen Thorkild IA
Published: May 2004

Objective:

To examine to what extent the obesity epidemic is a general phenomenon in adults by assessing the secular change, by birth cohort and age, in the prevalence of obesity and median body mass index (BMI) in Danish men and women measured between 1964 and 1994.

Design:

Multiple cross-sectional population surveys.

Setting:

The greater Copenhagen area of Denmark.

Subjects:

The study included 17 065 men (30 336 observations) and 13 417 women (24 065 observations), aged 20–84 years.

Main outcome measures:

Trends in median BMI and prevalence of obesity estimated from measured height and weight in 10-year age groups.

Results:

In general the prevalence of obesity was increasing, although in an irregular way: among men in two phases, during the 1970s and 1990s and among women only during the 1990s. Great heterogeneity was observed between birth cohorts and age groups. There was only little indication of an increasing trend in obesity prevalence for women, except for the 55–64-year-olds. In men, the prevalence of obesity was increasing in all age groups except in the youngest ones, and it was statistically significant only for men aged 35–74 years. There was no significant linear change in median BMI in any group, except for an increasing trend among men aged 50 years and above.

Conclusion:

Although the overall Danish trend for obesity prevalence, similar to trends world-wide, showed a marked increase, the trend was very heterogeneous and generally neither uniform nor significantly positive; the changes were irregular, different among men and women, and different in the different age and birth cohorts. The obesity problem in middle-aged and older men of certain birth cohorts poses a specific public health challenge. Future studies of determinants behind the heterogeneity in the development of the obesity epidemic may provide clues to its causes.
A review of the epidemiological evidence for the ‘antioxidant hypothesis’
Authors: Stanner SA , Hughes J , Kelly CNM , Buttriss J
Published: May 2004

Objective:

The British Nutrition Foundation was recently commissioned by the Food Standards Agency to conduct a review of the government's research programme onAntioxidants in Food. Part of this work involved an independent review of the scientific literature on the role of antioxidants in chronic disease prevention, which is presented in this paper.

Background:

There is consistent evidence that diets rich in fruit and vegetables and other plant foods are associated with moderately lower overall mortality rates and lower death rates from cardiovascular disease and some types of cancer. The ‘antioxidant hypothesis’ proposes that vitamin C, vitamin E, carotenoids and other antioxidant nutrients afford protection against chronic diseases by decreasing oxidative damage.

Results:

Although scientific rationale and observational studies have been convincing, randomised primary and secondary intervention trials have failed to show any consistent benefit from the use of antioxidant supplements on cardiovascular disease or cancer risk, with some trials even suggesting possible harm in certain subgroups. These trials have usually involved the administration of single antioxidant nutrients given at relatively high doses. The results of trials investigating the effect of a balanced combination of antioxidants at levels achievable by diet are awaited.

Conclusion:

The suggestion that antioxidant supplements can prevent chronic diseases has not been proved or consistently supported by the findings of published intervention trials. Further evidence regarding the efficacy, safety and appropriate dosage of antioxidants in relation to chronic disease is needed. The most prudent public health advice remains to increase the consumption of plant foods, as such dietary patterns are associated with reduced risk of chronic disease.
Grandparents as family stabilizers during economic hardship in Bulgaria
Authors: Botcheva Luba B. , Feldman S. Shirley
Published: May 2004

The present study of three generations' families living together during a period of marked economic dislocation investigates whether supportive grandparents can ameliorate the negative effects of economic stress on parenting and on teen outcomes. The study focuses on harsh parenting and adolescent depression, which has been shown to be especially responsive to economic stress. Three hypotheses were investigated: (1) in extended families there is a link between economic adversity and adolescent depression that is mediated by harsh parenting; (2) grandparent support diminishes the relationship between economic pressure and harsh parenting; and (3) grandparent support diminishes the relationship between harsh parenting and adolescent depression. Data were collected from a community sample of 62 extended families with an adolescent during a period of marked economic dislocation in Bulgaria. Mothers, fathers, and adolescents completed questionnaires about perceived economic pressure, parents' harsh parenting, and perceived support of grandparents. Adolescents also completed a measure of self‐reported depression. Additional interviews were conducted with every eligible family member about family relations. Results showed that even though there was significant economic stress reported by parents, adolescents reported moderate levels of depression and low levels of harsh parenting by mothers and fathers. Correlation and regression analyses revealed that whenever respondents experienced support by grandparents, it made a difference for family members. More specifically, despite economic stress, mothers who experienced the support of grandparents tended to exercise less harsh parenting practices than mothers who lacked such support. Furthermore, when grandparents were supportive, harsh parenting was not associated with adolescent depression. These findings are discussed in the light of existing studies of families under economic pressure with a special focus on extended family relations and the role of cultural context.
Uteroglobin Represses Allergen-induced Inflammatory Response by Blocking PGD2 Receptor–mediated Functions
Authors: Mandal Asim K. , Zhang Zhongjian , Ray Rabindranath , Choi Moonsuk S. , Chowdhury Bhabadeb , Pattabiraman Nagarajan , Mukherjee Anil B.
Published: May 2004

Uteroglobin (UG) is an antiinflammatory protein secreted by the epithelial lining of all organs communicating with the external environment. We reported previously that UG-knockout mice manifest exaggerated inflammatory response to allergen, characterized by increased eotaxin and Th2 cytokine gene expression, and eosinophil infiltration in the lungs. In this study, we uncovered that the airway epithelia of these mice also express high levels of cyclooxygenase (COX)-2, a key enzyme for the production of proinflammatory lipid mediators, and the bronchoalveolar lavage fluid (BALF) contain elevated levels of prostaglandin D2. These effects are abrogated by recombinant UG treatment. Although it has been reported that prostaglandin D2 mediates allergic inflammation via its receptor, DP, neither the molecular mechanism(s) of DP signaling nor the mechanism by which UG suppresses DP-mediated inflammatory response are clearly understood. Here we report that DP signaling is mediated via p38 mitogen–activated protein kinase, p44/42 mitogen–activated protein kinase, and protein kinase C pathways in a cell type–specific manner leading to nuclear factor–κB activation stimulating COX-2 gene expression. Further, we found that recombinant UG blocks DP-mediated nuclear factor–κB activation and suppresses COX-2 gene expression. We propose that UG is an essential component of a novel innate homeostatic mechanism in the mammalian airways to repress allergen-induced inflammatory responses.
Application of hyperbolic dynamics to physics: Some problems and conjectures
Authors: Ruelle David
Published: May 2004

The long time behavior of smooth dynamical systems is, in good cases, given by an SRB measure

ρ
\rho

. The measure

ρ
\rho

is expected often to have very discontinuous dependence on parameters of the dynamical system. This is a very unsatisfactory situation for physical applications, where one would like to differentiate

ρ
\rho

with respect to parameters. Here we propose a solution to this difficulty, based on analytic continuation in a frequency variable

ω
\omega

.
The Lipid Binding Pleckstrin Homology Domain in UNC-104 Kinesin is Necessary for Synaptic Vesicle Transport inCaenorhabditis elegans
Authors: Klopfenstein Dieter R. , Vale Ronald D.
Published: May 2004

UNC-104 (KIF1A) is a kinesin motor that transports synaptic vesicles from the neuronal cell body to the terminal. Previous in vitro studies have shown that a Dictyostelium relative of UNC-104 transports liposomes containing acidic phospholipids, but whether this interaction is needed for the recognition and transport of synaptic vesicles in metazoans remains unexplored. Here, we have introduced mutations in the nonmotor domain of UNC-104 and examined whether these mutant motors can rescue an unc-104 Caenorhabditis elegans strain. We show that a pleckstrin homology (PH) domain in UNC-104 is essential for membrane transport in living C. elegans, that this PH domain binds specifically to phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2), and that point mutants in the PH domain that interfere with PI(4,5)P2binding in vitro also interfere with UNC-104 function in vivo. Several other lipid-binding modules could not effectively substitute for the UNC-104 PH domain in this in vivo assay. Real time imaging also revealed that a lipid-binding point mutation in the PH domain reduced movement velocity and processivity of individual UNC-104::GFP punctae in neurites. These results reveal a critical role for PI(4,5)P2binding in UNC-104–mediated axonal transport and shows that the cargo-binding properties of the distal PH domain can affect motor output.
Reoxygenation after severe hypoxia induces cardiomyocyte hypertrophy in vitro: activation of CREB downstream of GSK3β
Authors: Jamali Amina El , Freund Christian , Rechner Cindy , Scheidereit Claus , Dietz Rainer , Bergmann Martin W.
Published: May 2004

In vivo, left ventricular remodeling after myocardial infarction involves hypertrophy generally attributed to increased cardiac workload. We hypothesized that hypoxia/reoxygenation directly induces cardiomyocyte hypertrophy and studied several participating kinases and transcription factors in isolated cardiomyocytes. Hypoxia for 6 h followed by 42 h reoxygenation induced cardiomyocyte hypertrophy assessed by 3H leucine incorporation and immunohistochemistry. Inhibition of reactive oxygen species (ROS), serine/threonine kinase AKT, and ERK abolished reoxygenation‐induced hypertrophy. In addition, a β2‐adrenergic receptor (β2‐AR) antagonist, as well as Gi inhibitor pertussis toxin, blocked reoxygenation‐induced hypertrophy. Hypoxia for 6 h increased transcription factors CREB, NF‐κ B, and GATA DNA binding activities. However, only CREB DNA‐binding was sustained during reoxygenation. Inhibition of PI3‐kinase, ERK, and PKA abrogated reoxygenation‐induced CREB DNA‐binding without affecting CREB serine‐133 phosphorylation. These same pathways were found to regulate hypoxia/reoxygenation‐induced GSK3β kinase activity and CREB serine‐129 de‐phosphorylation. GSK3β mutants resistant to phosphorylation blocked the stimulation of CRE‐dependent transcription induced by hypoxia/reoxygenation. Transfection of cardiomyocytes with a dominant‐negative mutant of CREB abrogated hypoxia/reoxygenation‐induced hypertrophy. We suggest that hypoxia/reoxygenation induces cardiomyocyte hypertrophy through CREB activation. Inactivation of GSK3β by hypoxia/reoxygenation, possibly integrating PI3‐kinase and ERK pathways downstream of β2‐AR and ROS, is a prerequisite for CRE‐dependent transcription. Transient hypoxia may contribute to cardiac hypertrophy in ischemic heart disease independent of cardiac workload.