bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientation-dependent multiferroic properties in Pb(Zr0.52Ti0.48)O3–CoFe2O4 nanocomposite thin films derived by a sol-gel processing
Authors: He Hong-cai , Ma Jing , Wang Jing , Nan Ce-Wen
Published: February 2008

Bilayered multiferroic nanocomposite films of preferentially oriented Pb(Zr0.52Ti0.48)O3 (PZT) and CoFe2O4 (CFO) were prepared on general Pt∕Ti∕SiO2∕Si substrate via a simple solution processing. Different annealing processings resulted in different preferential orientations for the PZT layers in the bilayered thin films, on which the dependence of properties, including ferroelectric, ferromagnetic, and magnetoelectric properties, in the PZT-CFO nanocomposite thin films was investigated. Strong ferroelectric and ferromagnetic responses and, in particular, direct magnetoelectric coupling effect were simultaneously observed in these bilayered thin films at room temperature.
Scanning magnetoresistance microscopy of atom chips
Authors: Volk M. , Whitlock S. , Wolff C. H. , Hall B. V. , Sidorov A. I.
Published: February 2008

Surface based geometries of microfabricated wires or patterned magnetic films can be used to magnetically trap and manipulate ultracold neutral atoms or Bose–Einstein condensates. We investigate the magnetic properties of such atom chips using a scanning magnetoresistive (MR) microscope with high spatial resolution and high field sensitivity. By comparing MR scans of a permanent magnetic atom chip to field profiles obtained using ultracold atoms, we show that MR sensors are ideally suited to observe small variations of the magnetic field caused by imperfections in the wires or magnetic materials which ultimately lead to fragmentation of ultracold atom clouds. Measurements are also provided for the magnetic field produced by a thin current-carrying wire with small geometric modulations along the edge. Comparisons of our measurements with a full numeric calculation of the current flow in the wire and the subsequent magnetic field show excellent agreement. Our results highlight the use of scanning MR microscopy as a convenient and powerful technique for precisely characterizing the magnetic fields produced near the surface of atom chips.
Hybrid flow velocimeter measurements of transparent and turbid liquids in a microchannel using a transmission grating
Authors: Kuraya Mitsumasa , Katayama Kenji , Kitamori Takehiko
Published: February 2008

A Doppler velocimeter with a transmission grating was developed for flow rate measurements inside a microchannel. This velocimeter has the same optical setup as a recently developed flow velocimeter for transparent liquids, in which two beams (pump and probe) optically coupled to a fiber were used. Although the principle of the flow velocity measurement was quite different between the two methods, the optical setups used were almost similar; the differences are that only the probe beam is used and fast Fourier transform analysis is utilized for the signal processing in the new technique. This development offers hybrid flow velocimeter for both transparent and turbid liquids.
Broadband dielectric studies on the interfacial dynamics enabled by use of nanostructured electrodes
Authors: Serghei A. , Kremer F.
Published: February 2008

By employing silica nanostructures as spacers, an experimental approach is developed to enable one broadband dielectric measurements on the molecular dynamics taking place in the immediate (nanometric) vicinity of solid interfaces. This development renders to broadband dielectric spectroscopy—traditionally a bulk technique—the character of an interfacial method.
A proposed measurement method for void fraction in lubricant oil based on the image processing technique
Authors: Wang Jianwen , An Qi
Published: February 2008

A new method for measuring void fraction in lubricating oils is presented based on the image processing technique. The problem here differs from the bubbles detection problem in two-phase fluids in that our interest lies in the gross amount of gas voids in oils. Our method is based on an observation that gas voids in oils change the color of the mixed gas-oil material. Therefore, a measurement technique was established based on the change in color. In particular, the relationship between the change in color and amount of voids was established experimentally. The experiment and testing were performed on a particular setup which consists of a pipe, oil, and air. The test result has shown that this method is effective. The method is the simplest and most accurate one among the existing methods.
Aperture tolerances for neutron-imaging systems in inertial confinement fusion
Authors: Ghilea M. C. , Sangster T. C. , Meyerhofer D. D. , Lerche R. A. , Disdier L.
Published: February 2008

Neutron-imaging systems are being considered as an ignition diagnostic for the National Ignition Facility (NIF) [Hogan et al., Nucl. Fusion 41, 567 (2001)]. Given the importance of these systems, a neutron-imaging design tool is being used to quantify the effects of aperture fabrication and alignment tolerances on reconstructed neutron images for inertial confinement fusion. The simulations indicate that alignment tolerances of more than 1mrad would introduce measurable features in a reconstructed image for both pinholes and penumbral aperture systems. These simulations further show that penumbral apertures are several times less sensitive to fabrication errors than pinhole apertures.
Noncontact infrared laser sensing of magnetoresistance
Authors: Mennicke Ralph T. , Matthew James A. D. , Thompson Sarah M.
Published: February 2008

The magnetorefractive effect (MRE) has previously been demonstrated to be an effective method for the remote sensing of magnetoresistance. These studies were made using an infrared (IR) spectrometer, which is ideal for technique development and fundamental material characterization but lacks the simplicity of a fixed-frequency measurement in which the intensity is monitored as a function of applied magnetic field—mimicking a traditional four-point probe electrical measurement. Using a carbon dioxide laser as an IR light source, the design of a fixed-frequency instrument in the reflection geometry is presented and tested. Taking into account both drifts and short-term fluctuations, a light intensity detection signal-to-noise ratio of better than 200:1 is achieved in applied magnetic fields of ±12kOe enabling detection of MRE of 0.15%. The fixed-frequency instrument provides a noncontact probe of magnetoresistance with the potential for spatial resolution and angular variation.
A general approach for fabrication of superhydrophobic and superamphiphobic surfaces
Authors: Xi Jinming , Feng Lin , Jiang Lei
Published: February 2008

A simple one-step electrodeposition process is developed for the fabrication of superhydrophobic surfaces on a series of substrates such as copper, titanium, iron, zinc, aluminum, and stannum. The hierarchical micro- and nanostructures endow these surfaces with excellent super-hydrophobicity and the resulting surfaces show superhydrophobicity even for some corrosive liquids including salt solutions and acidic and basic solutions at all pH values. Importantly, this approach can be easily applied to other systems such as the fabrication of superamphiphobic surfaces as long as the substrates are electrically conductive.
Impurity bound-to-unbound terahertz sensors based on beryllium and silicon δ-doped GaAs∕AlAs multiple quantum wells
Authors: Seliuta D. , Kavaliauskas J. , Čechavičius B. , Balakauskas S. , Valušis G. , Sherliker B. , Halsall M. P. , Harrison P. , Lachab M. , Khanna S. P. , Linfield E. H.
Published: February 2008

Beryllium and silicon δ-doped GaAs∕AlAs multiple quantum wells (MQWs) were designed and fabricated for selective sensing of terahertz radiation. Optical characterization of the structures by photoreflectance spectroscopy has indicated a presence of built-in electric fields–from 18 up to 49kV∕cm depending on the structure design–located mainly in the cap and buffer layers, but do not penetrating into the MQWs region. Terahertz sensing under normal incidence via impurity bound-to-unbound transitions is demonstrated in photocurrent experiments within 0.6–4.2THz in silicon-doped MQWs and 3.5–7.3THz range in beryllium-doped MQWs at low temperatures.
Calibration of magnetic probes in the vicinity of a conducting well
Authors: Howard S. J. , Horton R. D. , Hwang D. Q. , Evans R. W. , Brockington S. J.
Published: February 2008

Measuring magnetic fields near the edge of a plasma device can be complicated by the geometric effects of the ports through which such measurements are made. The primary effect is an attenuation of the magnetic field at the probe coil due to the field expanding into the finite sized conducting well of the port. In addition, it is possible to determine the correspondence between the location of a field line as it intersects the probe coil inside the well, with its location far from the perturbation of the well. Here we explore several methods of experimentally characterizing the magnetic fields in the vicinity of the magnetic probe ports of a vacuum vessel, with the aim of improving the interpretation of magnetic measurements needed for experiments in plasma physics.
Effects of ultraviolet light irradiation on poly(vinlycarbazole)
Authors: Qian Lei , Bera Debasis , Holloway Paul H.
Published: February 2008

In this paper, we present a study of the photophysical and photochemical effects that influence phosphor-doped polymer light-emitting diodes based on poly(vinlycarbazole). With ultraviolet (UV) light irradiation, the relative concentration of partially overlapping carbazole groups [poly(vinlycarbazole), (p-PVK)] to the fully overlapping conformation (f-PVK) is decreased via photoisomerization, which affects both the energies and the probability of forming singlet versus triplet excitons. As a result, phosphor-doped polymer light-emitting diodes fabricated using UV irradiated PVK exhibited higher efficiencies as compared with control devices (doped PVK without UV light irradiation). These data demonstrate a new route for the production of more efficient electrophosphorescent light-emitting diodes.
Inhomogeneous and anisotropic equilibrium state of a swollen hydrogel containing a hard core
Authors: Zhao Xuanhe , Hong Wei , Suo Zhigang
Published: February 2008

A polymer network can imbibe water from environment and swell to an equilibrium state. If the equilibrium is reached when the network is subject to external mechanical constraint, the deformation of the network is typically anisotropic and the concentration of water inhomogeneous. Such an equilibrium state in a network constrained by a hard core is modeled here with a nonlinear differential equation. The presence of the hard core markedly reduces the concentration of water near the interface and causes high stresses.
Two-color pump-probe studies of intraminiband relaxation in doped GaAs∕AlGaAs superlattices
Authors: Stehr D. , Wagner M. , Schneider H. , Helm M. , Andrews A. M. , Roch T. , Strasser G.
Published: February 2008

The miniband relaxation dynamics of electrons in doped GaAs∕AlGaAs superlattices are investigated by two-color infrared pump-probe experiments. By this technique, we are able to separate the different contributions from inter- and intraminiband relaxations to the transient behavior after an ultrafast excitation. In particular, the intraminiband relaxation is studied for different miniband widths below and above the optical phonon energy of GaAs. For minibands wider than this critical value, we find fast relaxation, nearly constant for different excitation intensities, whereas for narrow minibands, a strong temperature and intensity dependence of the relaxation is found. The results are in good agreement with previously published Monte Carlo simulations.
Quantification of the carrier absorption losses in Si-nanocrystal rich rib waveguides at 1.54μm
Authors: Navarro-Urrios D. , Pitanti A. , Daldosso N. , Gourbilleau F. , Rizk R. , Pucker G. , Pavesi L.
Published: February 2008

A detailed study of the carrier absorption (CA) mechanism in multilayered silicon-nanocrystals (Si-nc) rib waveguides is reported. A pump (532nm) and probe (1535nm) technique is used to assess two loss mechanisms due to optical excitation of the system: one characterized by slow (seconds) dynamics related to heating and the other characterized by fast (microsecond) dynamics associated to CA mechanisms within the Si-nc. CA losses increase with pumping flux of up to 6dB∕cm for 3×1020photons∕cm2s. By comparing the temporal dynamics of CA losses and time resolved photoluminescence, we suggest that both are determined by exciton generation and recombination.
Ohmic conduction of sub-10nm P-doped silicon nanowires at cryogenic temperatures
Authors: Rueß F. J. , Micolich A. P. , Pok W. , Goh K. E. J. , Hamilton A. R. , Simmons M. Y.
Published: February 2008

We investigate the conduction properties of an embedded, highly phosphorus-doped nanowire with a width of 8nm lithographically defined by scanning tunneling microscope based patterning of a hydrogen-terminated Si(100):H surface. Four terminal I-V measurements show that ohmic conduction is maintained within the investigated temperature range from 35K down to 1.3K. A prominent resistance increase is observed below ∼4K which is attributed to a crossover into the strong localization regime. The low temperature conductance follows a one-dimensional variable range hopping model accompanied by positive magnetoresistance which dominates over weak localization effects at low temperature.
Modification of the spin state in Sm0.52Sr0.48MnO3 by external magnetic field
Authors: Sarkar P. , Mandal P.
Published: February 2008

The effect of applied magnetic field (H) on the magnetic properties of Sm0.52Sr0.48MnO3 single crystal in the paramagnetic (PM) state has been investigated. We observe a field induced steplike jump in magnetization (M) above TC (110K). The temperature and magnetic field dependence of susceptibility reveal that the PM phase of this system is quite complicated due to the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) interactions. The nature of magnetic interaction changes abruptly from AFM to FM at around 3.5T, above which M ceases the steplike jump.
Nanocrystalline iron nitride films with perpendicular magnetic anisotropy
Authors: Gupta Ajay , Dubey Ranu , Leitenberger W. , Pietsch U.
Published: February 2008

Nanocrystalline α-iron nitride films have been prepared using reactive ion-beam sputtering. Films develop significant perpendicualr magnetic anisotropy (PMA) with increasing thickness. A comparison of x-ray diffraction patterns taken with scattering vectors in the film plane and out of the film plane provides a clear evidence for development of compressive strain in the film plane with thickness. Thermal annealing results in relaxation of the strain, which correlates very well with the relaxation of PMA. This suggests that the observed PMA is a consequence of the breaking of the symmetry of the crystal structure due to the compressive strain.
High contrast radiography using a small dense plasma focus
Authors: Castillo F. , Gamboa-deBuen I. , Herrera J. J. E. , Rangel J. , Villalobos S.
Published: February 2008

Radiographs are obtained with a small (4.6kJ) dense plasma focus machine, using the x-rays which cross a 300μm aluminum window on the axis. Contrast is improved by inserting an iron needle on the tip of the electrode. Measurements with TLD-100 dosimeters have shown the average dose to increase from 0.077±0.006mGy/shot, when a hollow cathode is used, to 0.11±0.01mGy/shot, with the needle. The spectrum is estimated using aluminum filters and the effective equivalent energy is found to be in the range of 20–25keV.
Investigation of an oversized backward wave oscillator as a high power microwave generator
Authors: Li Zheng-Hong
Published: February 2008

An oversized rectangular corrugated backward wave oscillator is designed and theoretically analyzed to produce TM01 high power microwave radiation in the frequency of 8.68GHz without mode competition. The device includes a slow wave structures, a resonant reflector, and an output waveguide. The slow wave structure and the reflector are matched to achieve mode selection and enhance interaction efficiency. Feedback processes from the reflector are introduced to explore mode selection in the configuration. In particle in cell simulation, high power microwaves of TM01 mode are generated with peak power of 2.0GW, frequency of 8.68GHz, and conversion efficiency is 28.6% when beam voltage is 500kV and current 14kA.
Electron density and temperature measurement of an atmospheric pressure plasma by millimeter wave interferometer
Authors: Lu Xin Pei , Laroussi Mounir
Published: February 2008

In this paper, a 105GHz millimeter wave interferometer system is used to measure the electron density and temperature of an atmospheric pressure helium plasma driven by submicrosecond pulses. The peak electron density and electron-neutral collision frequency reach 8×1012cm−3 and 2.1×1012s−1, respectively. According to the electron-helium collision cross section and the measured electron-neutral collision frequency, the electron temperature of the plasma is estimated to reach a peak value of about 8.7eV.
Low operation voltage of inkjet-printed plastic sheet-type micromechanical switches
Authors: Nakano Shintaro , Sekitani Tsuyoshi , Yokota Tomoyuki , Someya Takao
Published: February 2008

We have fabricated plastic micromechanical switches using inkjet printing technologies. By reducing the device dimensions, particularly the spacing between the electrodes for electrostatic attraction, the operation voltage is reduced to 6.6V. The frequency response exceeds 1kHz when the operation voltage is above 20V. When the number of periodic cycles of the rectangular voltage waveforms that are applied to the control electrodes in air exceeds 2×106, the on resistance changes slightly from 25to30Ω, thereby demonstrating the reliability and stability of the present plastic switches.
Proposal of mechanics of liquid crystals and development of liquid crystalline microactuators
Authors: Chono Shigeomi , Tsuji Tomohiro
Published: February 2008

We propose a research field “mechanics of liquid crystals,” in which liquid crystals are studied from a mechanical viewpoint. The unsteady behaviors of a liquid crystal between parallel plates under an electric field are investigated. The imposition of the electric field on the liquid crystal induces flows, whose profile and magnitude strongly depend on the twist angle of the director at the plates. A visualization experiment confirms the generation of flows. The mechanism of such generation can be explained by considering that the rotation of molecules generated by the imposition of the electric field induces a local velocity gradient.
Measurement of the slip length of water flow on graphite surface
Authors: Maali Abdelhamid , Cohen-Bouhacina Touria , Kellay Hamid
Published: February 2008

We present measurements of the hydrodynamic damping of an atomic force microscopy cantilever-tip immersed in water and approaching a mica surface or a graphite surface. Water completely wets the mica surface while it partially wets the graphite surface with a contact angle of 74°. The measurements show that the damping is higher on mica than on graphite giving a slip length of about 8nm on this latter surface.
Elimination of scattering effects in spectral measurement of granulated materials using terahertz pulsed spectroscopy
Authors: Shen Y. C. , Taday P. F. , Pepper M.
Published: February 2008

Spectral distortions are commonly observed in terahertz spectra of granulated materials. These spurious structures in the spectroscopy are caused by scattering due to the refractive index mismatch between the particles and their surrounding medium. We find that the scattering contribution is random across sample positions and could be eliminated by summing and averaging multiple measurements over a sample area. We present experimental results of both absorbing and nonabsorbing particles in the size range 50–250μm and also give an empirical expres-sion to describe the effect of grain size on the scattering-induced extinction as a function of frequency.
First-principles prediction of enhanced magnetic anisotropy in FeCo alloys
Authors: Wu Dangxin , Zhang Qiming , Liu J. Ping , Yuan Dingwang , Wu Ruqian
Published: February 2008

The structural, electronic, and magnetic properties of FeCo alloys were studied by first-principles calculations. It has been found that the alloys prefer chemically noncubic geometries in a wide composition range. This produces appreciable uniaxial magnetic anisotropy, which facilitates interphase magnetic interaction and enhances the overall magnetization in exchange-coupled nanocomposite systems. Large magnetostrictive coefficients provide another venue for manipulations of magnetic anisotropy energies.
Negative differential conductance in two-dimensional electron grids
Authors: Pan W. , Lyo S. K. , Reno J. L. , Simmons J. A. , Li D. , Brueck S. R. J.
Published: February 2008

Negative differential conductance has been observed in grid-shaped surface superlattices, realized in a high mobility two-dimensional electron system. The current-voltage characteristics vary with the modulation strength, indicating that the two-dimensional electronic transport properties can be manipulated in a controllable way. Theoretical modeling yields reasonable agreement with the experimental data.
Highly efficient green organic light-emitting diodes from single exciplex emission
Authors: Wang Dan , Li Wenlian , Chu Bei , Su Zisheng , Bi Defeng , Zhang Dongyu , Zhu Jianzhuo , Yan Fei , Chen Yiren , Tsuboi Taiju
Published: February 2008

Spectral single and stable green exciplex emission was demonstrated from organic light-emitting diodes (OLEDs) with 4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine and 4,7-diphenyl-1,10-phenanthroline that function as electron donor (D) and acceptor (A), respectively. As 8-hydroxyquinoline aluminum (Alq3) was attached to the acceptor layer, electroluminescent (EL) properties of the two exciplex-type OLEDs with D/A-bilayer and D:A mixture layer configurations were markedly improved, i.e., a peak current efficiency of 7.6cd∕A at 2.38mA∕cm2 in three-layer device and a maximum luminance of 6620cd∕m2 at 8.7V in blend layer device were obtained, respectively, without changing the peak position (535nm) and the shape of EL spectrum. Discussion is given on the harvest of the pure green exciplex emission and enhancement of luminance which is obtained by inserting Alq3 layer.
Supersolid behavior in helium coincides with enhanced shear modulus
Authors: Miller Johanna
Published: February 2008

When the temperature is low enough, solid helium seems to acquire superfluid properties. But at the same time, the apparently flowing solid becomes stiffer.
Increased funding for physical sciences evaporates after budget showdown
Authors: Kramer David
Published: February 2008

Particle physics and ITER participation are the losers as Congress wraps up fiscal year 2008 appropriations. NSF growth is slowed.
New UK research council abruptly abandons some major international projects
Authors: Schwarzschild Bertram
Published: February 2008

Withdrawal from the International Linear Collider and from several observatories without peer review or even consultation angers British research communities.
The physics of sailing
Authors: Anderson Bryon D.
Published: February 2008

Sails and keels, like airplane wings, exploit Bernoulli’s principle. Aerodynamic and hydrodynamic insights help designers create faster sailboats.
Electron sources for accelerators
Authors: Hernandez-Garcia Carlos , O’Shea Patrick G. , Stutzman Marcy L.
Published: February 2008

Photoemission shines as a source of the bright electron beams required for free-electron lasers and particle-physics accelerators.
Civil Liberties and the Regulation of Public Space: The Case of Sidewalks in Las Vegas
Authors: Blumenberg Evelyn , Ehrenfeucht Renia
Published: February 2008

Conflicts over the nature of and rights associated with public space have a long history and have prompted numerous regulatory responses. Perhaps nowhere in the USA has the regulation of public space been as far-reaching as in Las Vegas, Nevada, where the financial stakes associated with sidewalks are enormous. This study examines how local officials mediate among varied and competing uses of the sidewalk. In defining the function of the sidewalks narrowly and passively deferring questions of civil liberties, local officials have effectively controlled almost all aspects of public behavior. In recent years, cities have invested in major commercial realization projects. Evidence from this case study suggests that, if successful, these developments will engender more extensive regulation of public life and the further curtailment of the freedoms traditionally guaranteed to citizen activity in public places.
Patterning in Urban Population Densities: A Spatiotemporal Model Compared with Toronto 1971–2001
Authors: Millward Hugh , Bunting Trudi
Published: February 2008

We build on the literature on population-density distributions, but translate the consensus cross-sectional progression into a three-dimensional and six-stage geographic information system (GIS) based ‘volcano’ model. Visual comparison and descriptive statistics show Toronto's recent density patterns to be very similar to those suggested by the model: the central density cluster has reversed its decline, while peripheral clusters have developed at increasing distances from downtown. Local autocorrelation (LISA) allowed areas of significant clustering and diversity to be mapped, and strong conformity was found between the model and Toronto's empirical patterns. Overall, density levels throughout the metropolitan area are homogenizing and randomizing, even while inner-city redensification and peripheral densification proceed.
The orphan G protein-coupled receptor,
Gpr161
, encodes the
vacuolated lens
locus and controls neurulation and lens development
Authors: Matteson Paul G. , Desai Jigar , Korstanje Ron , Lazar Gloria , Borsuk Tanya E. , Rollins Jarod , Kadambi Sindhuja , Joseph Jamie , Rahman Taslima , Wink Jason , Benayed Rym , Paigen Beverly , Millonig James H.
Published: February 2008

The
vacuolated lens
(
vl
) mouse mutant causes congenital cataracts and neural tube defects (NTDs), with the NTDs being caused by abnormal neural fold apposition and fusion. Our positional cloning of
vl
indicates these phenotypes result from a deletion mutation in an uncharacterized orphan G protein-coupled receptor (GPCR),
Gpr161. Gpr161
displays restricted expression to the lateral neural folds, developing lens, retina, limb, and CNS. Characterization of the
vl
mutation indicates that C-terminal tail of Gpr161 is truncated, leading to multiple effects on the protein, including reduced receptor-mediated endocytosis. We have also mapped three modifier quantitative trait loci (QTL) that affect the incidence of either the
vl
cataract or NTD phenotypes. Bioinformatic, sequence, genetic, and functional data have determined that
Foxe3
, a key regulator of lens development, is a gene responsible for the
vl
cataract-modifying phenotype. These studies have extended our understanding of the
vl
locus in three significant ways. One, the cloning of the
vl
locus has identified a previously uncharacterized GPCR-ligand pathway necessary for neural fold fusion and lens development, providing insight into the molecular regulation of these developmental processes. Two, our QTL analysis has established
vl
as a mouse model for studying the multigenic basis of NTDs and cataracts. Three, we have identified
Foxe3
as a genetic modifier that interacts with Gpr161 to regulate lens development.
Cellular components and signals required for the cardiac outflow tract assembly in
Drosophila
Authors: Zmojdzian Monika , Da Ponte Jean Philippe , Jagla Krzysztof
Published: February 2008

Specification of cardiac primordia and formation of the
Drosophila
heart tube is highly reminiscent of the early steps of vertebrate heart development. We previously reported that the final morphogenesis of the
Drosophila
heart involves a group of nonmesodermal cells called heart-anchoring cells and a pair of derived from the pharyngeal mesoderm cardiac outflow muscles. Like the vertebrate cardiac neural crest cells, heart-anchoring cells migrate, interact with the tip of the heart, and participate in shaping the cardiac outflow tract. To better understand this process, we performed an in-depth analysis of how the
Drosophila
outflow tract is formed. We found that the most anterior cardioblasts that form a central outflow tract component, the funnel-shaped heart tip, do not originate from the cardiac primordium. They are initially associated with the pharyngeal cardiac outflow muscles and join the anterior aorta during outflow tract assembly. The particular morphology of the heart tip is disrupted in embryos in which heart-anchoring cells were ablated, revealing their critical role in outflow tract morphogenesis. We also demonstrate that Slit and Robo are required for directed movements of heart-anchoring cells toward the heart tip and that the cell–cell contact between the heart-anchoring cells and the
ladybird
-expressing cardioblasts is critically dependent on
D
E-cadherin Shotgun. Our observations suggest that the similarities between
Drosophila
and vertebrate cardiogenesis extend beyond the early developmental events.
The orphan nuclear receptor chicken ovalbumin upstream promoter-transcription factor II is a critical regulator of adipogenesis
Authors: Xu Zhao , Yu Songtao , Hsu Chung-Hsin , Eguchi Jun , Rosen Evan D.
Published: February 2008

The orphan nuclear receptor chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII; Nr2f2) is expressed in adipose tissue
in vivo
and declines during differentiation. Overexpression of COUP-TFII prevents adipogenesis, whereas shRNA-mediated reduction of COUP-TFII promotes differentiation, as shown by increased lipid accumulation and elevated expression of fat cell marker proteins. Furthermore, reduction of COUP-TFII allows uncommitted fibroblasts to be differentiated into fat cells. COUP-TFII represses the expression of a number of proadipogenic factors in adipocytes, with direct action noted at the CAAT enhancer-binding protein α promoter. We show that COUP-TFII acts downstream of hedgehog signaling and is required for the full antiadipogenic effect of this pathway. This effect is mediated in part by interaction with GATA factors. COUP-TFII and GATA2 are physically associated and repress target gene expression in an additive manner. Taken together, our data demonstrate that COUP-TFII represents an endogenous suppressor of adipogenesis, linking antiadipogenic extracellular signals to the core transcriptional cascade.
Signaling of cell fate determination by the TPD1 small protein and EMS1 receptor kinase
Authors: Jia Gengxiang , Liu Xiaodong , Owen Heather A. , Zhao Dazhong
Published: February 2008

Sexual reproduction requires the specification of cells with distinct fates in plants and animals. The EMS1 (also known as EXS) leucine-rich repeat receptor-like kinase (LRR-RLK) and TPD1 small protein play key roles in regulating somatic and reproductive cell fate determination in
Arabidopsis
anthers. Here, we show that ectopic expression of
TPD1
causes abnormal differentiation of somatic and reproductive cells in anthers. In addition, ectopic TPD1 activity requires functional EMS1. Yeast two-hybrid, pull-down, and coimmunoprecipitation analyses further demonstrate that TPD1 interacts with EMS1
in vitro
and
in vivo
. Moreover, TPD1 induces EMS1 phosphorylation
in planta
. Thus, our results suggest that TPD1 serves as a ligand for the EMS1 receptor kinase to signal cell fate determination during plant sexual reproduction.
A moderately thermophilic ammonia-oxidizing crenarchaeote from a hot spring
Authors: Hatzenpichler Roland , Lebedeva Elena V. , Spieck Eva , Stoecker Kilian , Richter Andreas , Daims Holger , Wagner Michael
Published: February 2008

The recent discovery of ammonia-oxidizing archaea (AOA) dramatically changed our perception of the diversity and evolutionary history of microbes involved in nitrification. In this study, a moderately thermophilic (46°C) ammonia-oxidizing enrichment culture, which had been seeded with biomass from a hot spring, was screened for ammonia oxidizers. Although gene sequences for crenarchaeotal 16S rRNA and two subunits of the ammonia monooxygenase (
amoA
and
amoB
) were detected via PCR, no hints for known ammonia-oxidizing bacteria were obtained. Comparative sequence analyses of these gene fragments demonstrated the presence of a single operational taxonomic unit and thus enabled the assignment of the
amoA
and
amoB
sequences to the respective 16S rRNA phylotype, which belongs to the widely distributed group I.1b (soil group) of the
Crenarchaeota
. Catalyzed reporter deposition (CARD)–FISH combined with microautoradiography (MAR) demonstrated metabolic activity of this archaeon in the presence of ammonium. This finding was corroborated by the detection of
amoA
gene transcripts in the enrichment. CARD-FISH/MAR showed that the moderately thermophilic AOA is highly active at 0.14 and 0.79 mM ammonium and is partially inhibited by a concentration of 3.08 mM. The enriched AOA, which is provisionally classified as “
Candidatus
Nitrososphaera gargensis,” is the first described thermophilic ammonia oxidizer and the first member of the crenarchaeotal group I.1b for which ammonium oxidation has been verified on a cellular level. Its preference for thermophilic conditions reinvigorates the debate on the thermophilic ancestry of AOA.
Decreases in dengue transmission may act to increase the incidence of dengue hemorrhagic fever
Authors: Nagao Yoshiro , Koelle Katia
Published: February 2008

Dengue hemorrhagic fever (DHF) is a potentially fatal manifestation of an infection with the mosquito-borne dengue virus. Because of the social and economic costs of DHF, many countries in Asia and South America have initiated public health measures aimed at vector control. Despite these measures, DHF incidence rates do not appear to be declining. The effectiveness of vector control in reducing dengue transmissibility has thereby been questioned. Here, we revisit this conclusion using epidemiological data from Thailand. We first show, with age incidence data, that dengue transmission rates have fallen since 1981; surprisingly, however, these declines are not associated with decreases in DHF incidence. Instead, district-level analyses indicate a nonmonotonic relationship between the basic reproductive numberR0and DHF incidence. To understand this relationship, we formulated three mathematical models, which differ in their assumptions of transient between-serotype cross-protection. Unlike the first two models, the previously unconsidered third model with clinical cross-protection can reproduce this nonmonotonic relationship. Simulation of this model with nonstationaryR0reproduces several previously unexplained patterns of dengue dynamics, including a transition from a ≈2-year cycle to a ≈4-year cycle and a transient trough in DHF incidence in provinces with rapidR0declines. These results imply that DHF incidence can be effectively controlled with a sufficiently large reduction inR0but that moderate reductions may be counterproductive. More broadly, these results show that assuming parameter stationarity in systems with approximate stationarity in disease incidence is unjustified and may result in missed opportunities to understand the drivers of disease variability.
Evidence for a fundamental and pervasive shift away from nature-based recreation
Authors: Pergams Oliver R. W. , Zaradic Patricia A.
Published: February 2008

After 50 years of steady increase,
per capita
visits to U.S. National Parks have declined since 1987. To evaluate whether we are seeing a fundamental shift away from people's interest in nature, we tested for similar longitudinal declines in 16 time series representing four classes of nature participation variables: (
i
) visitation to various types of public lands in the U.S. and National Parks in Japan and Spain, (
ii
) number of various types of U.S. game licenses issued, (
iii
) indicators of time spent camping, and (
iv
) indicators of time spent backpacking or hiking. The four variables with the greatest
per capita
participation were visits to Japanese National Parks, U.S. State Parks, U.S. National Parks, and U.S. National Forests, with an average individual participating 0.74–2.75 times per year. All four time series are in downtrends, with linear regressions showing ongoing losses of −1.0% to −3.1% per year. The longest and most complete time series tested suggest that typical declines in
per capita
nature recreation began between 1981 and 1991, are proceeding at rates of −1.0% to −1.3% per year, and total to date −18% to −25%. Spearman correlation analyses were performed on untransformed time series and on transformed percentage year-to-year changes. Results showed very highly significant correlations between many of the highest
per capita
participation variables in both untransformed and in difference models, further corroborating the general downtrend in nature recreation. In conclusion, all major lines of evidence point to an ongoing and fundamental shift away from nature-based recreation.
Evolution of polyketide synthases in bacteria
Authors: Ridley Christian P. , Lee Ho Young , Khosla Chaitan
Published: February 2008

The emergence of resistant strains of human pathogens to current antibiotics, along with the demonstrated ability of polyketides as antimicrobial agents, provides strong motivation for understanding how polyketide antibiotics have evolved and diversified in nature. Insights into how bacterial polyketide synthases (PKSs) acquire new metabolic capabilities can guide future laboratory efforts in generating the next generation of polyketide antibiotics. Here, we examine phylogenetic and structural evidence to glean answers to two general questions regarding PKS evolution. How did the exceptionally diverse chemistry of present-day PKSs evolve? And what are the take-home messages for the biosynthetic engineer?
Microneedles permit transdermal delivery of a skin-impermeant medication to humans
Authors: Wermeling Daniel P. , Banks Stan L. , Hudson David A. , Gill Harvinder S. , Gupta Jyoti , Prausnitz Mark R. , Stinchcomb Audra L.
Published: February 2008

Drugs with poor oral bioavailability usually are administered by hypodermic injection, which causes pain, poor patient compliance, the need for trained personnel, and risk of infectious disease transmission. Transdermal (TD) delivery provides an excellent alternative, but the barrier of skin's outer stratum corneum (SC) prevents delivery of most drugs. Micrometer-scale microneedles (MNs) have been used to pierce animal and human cadaver skin and thereby enable TD delivery of small molecules, proteins, DNA, and vaccines for systemic action. Here, we present a clinical study of MN-enhanced delivery of a medication to humans. Naltrexone (NTX) is a potent mu-opioid receptor antagonist used to treat opiate and alcohol dependence. This hydrophilic and skin-impermeant molecule was delivered from a TD patch to healthy human subjects with and without pretreatment of the skin with MNs. Whereas delivery from a standard NTX TD patch over a 72-h period yielded undetectable drug plasma levels, pretreatment of skin with MNs achieved steady-state plasma concentrations within 2 h of patch application and were maintained for at least 48 h. The MNs and NTX patch were well tolerated with mild systemic and application site side effects. The MN arrays were painless upon administration and not damaged during skin insertion, and no MNs were broken off into the skin. This human proof-of-concept study demonstrates systemic administration of a hydrophilic medication by MN-enhanced TD delivery. These findings set the stage for future human studies of skin-impermeant medications and biopharmaceuticals for clinical applications.
The Timothy syndrome mutation differentially affects voltage- and calcium-dependent inactivation of Ca
V
1.2 L-type calcium channels
Authors: Barrett Curtis F. , Tsien Richard W.
Published: February 2008

Calcium entry into excitable cells is an important physiological signal, supported by and highly sensitive to the activity of voltage-gated Ca
2+
channels. After membrane depolarization, Ca
2+
channels first open but then undergo various forms of negative feedback regulation including voltage- and calcium-dependent inactivation (VDI and CDI, respectively). Inactivation of Ca
2+
channel activity is perturbed in a rare yet devastating disorder known as Timothy syndrome (TS), whose features include autism or autism spectrum disorder along with severe cardiac arrhythmia and developmental abnormalities. Most cases of TS arise from a sporadic single nucleotide change that generates a mutation (G406R) in the pore-forming subunit of the L-type Ca
2+
channel Ca
V
1.2. We found that the TS mutation powerfully and selectively slows VDI while sparing or possibly speeding the kinetics of CDI. The deceleration of VDI was observed when the L-type channels were expressed with β
1
subunits prominent in brain, as well as β
2
subunits of importance for the heart. Dissociation of VDI and CDI was further substantiated by measurements of Ca
2+
channel gating currents and by analysis of another channel mutation (I1624A) that hastens VDI, acting upstream of the step involving Gly
406
. As highlighted by the TS mutation, CDI does not proceed to completeness but levels off at ≈50%, consistent with a change in gating modes and not an absorbing inactivation process. Thus, the TS mutation offers a unique perspective on mechanisms of inactivation as well as a promising starting point for exploring the underlying pathophysiology of autism.
Ambient temperature predicts sex ratios and male longevity
Authors: Catalano Ralph , Bruckner Tim , Smith Kirk R.
Published: February 2008

The theory that natural selection has conserved mechanisms by which women subjected to environmental stressors abort frail male fetuses implies that climate change may affect sex ratio at birth and male longevity. Using time series methods, we find that cold ambient temperatures during gestation predict lower secondary sex ratios and longer life span of males in annual birth cohorts composed of Danes, Finns, Norwegians, and Swedes born between 1878 (earliest year with complete life tables) and 1914 (last birth cohort for which male life span can be estimated). We conclude that ambient temperature affects the characteristics of human populations by influencing who survives gestation, a heretofore unrecognized effect of climate on humanity.
Structural identification of the pathway of long-range communication in an allosteric enzyme
Authors: Gandhi Prafull S. , Chen Zhiwei , Mathews F. Scott , Di Cera Enrico
Published: February 2008

Allostery is a common mechanism of regulation of enzyme activity and specificity, and its signatures are readily identified from functional studies. For many allosteric systems, structural evidence exists of long-range communication among protein domains, but rarely has this communication been traced to a detailed pathway. The thrombin mutant D102N is stabilized in a self-inhibited conformation where access to the active site is occluded by a collapse of the entire 215–219 β-strand. Binding of a fragment of the protease activated receptor PAR1 to exosite I, 30-Å away from the active site region, causes a large conformational change that corrects the position of the 215–219 β-strand and restores access to the active site. The crystal structure of the thrombin-PAR1 complex, solved at 2.2-Å resolution, reveals the details of this long-range allosteric communication in terms of a network of polar interactions.
Use of
13
C
α
chemical shifts for accurate determination of β-sheet structures in solution
Authors: Vila Jorge A. , Arnautova Yelena A. , Scheraga Harold A.
Published: February 2008

A physics-based method, aimed at determining protein structures by using NOE-derived distance constraints together with observed and computed
13
C
α
chemical shifts, is applied to determine the structure of a 20-residue all-β peptide (BS2). The approach makes use of
13
C
α
chemical shifts, computed at the density functional level of theory, to derive backbone and side-chain torsional constraints for all of the amino acid residues, without making use of information about residue occupancy in any region of the Ramachandran map. In addition, the torsional constraints are derived dynamically—i.e., they are redefined at each step of the algorithm. It is shown that, starting from randomly generated conformations, the final protein models are more accurate than existing NMR-derived models of the peptide, in terms of the agreement between predicted and observed
13
C
β
chemical shifts, and some stereochemical quality indicators. The accumulated evidence indicates that, for a highly flexible BS2 peptide in solution, it may not be possible to determine a single structure (or a small set of structures) that would satisfy all of the constraints exactly and simultaneously because the observed NOEs and
13
C
α
chemical shifts correspond to a dynamic ensemble of conformations. Analysis of the structural flexibility, carried out by molecular dynamics simulations in explicit water, revealed that the whole peptide can be characterized as having liquid-like behavior, according to the Lindemann criterion. In summary, a β-sheet structure of a highly flexible peptide in solution can be determined by a quantum-chemical-based procedure.
Paternal effects on offspring fitness in a multimale primate society
Authors: Charpentier M. J. E. , Van Horn R. C. , Altmann J. , Alberts S. C.
Published: February 2008

When females mate with multiple males, paternal care is generally expected to be negligible, because it may be difficult or impossible for males to discriminate their own offspring from those of other males, and because engaging in paternal care may reduce male mating opportunities. Consequently, males in multimale societies are not predicted to provide direct benefits to their offspring. We have recently demonstrated, however, that males in a typical multimale primate society (yellow baboons,Papio cynocephalus) discriminate their own offspring from those of other males and provide care to them in the form of repeated support during agonistic encounters. This observation raises the question of whether fathers enhance offspring fitness in this species. Here we use 30 years of data on age at maturity for 118 yellow baboons with known fathers. We show that the father's presence in the offspring's social group during the offspring's immature period accelerated the timing of physiological maturation in daughters. Sons also experienced accelerated maturation if their father was present during their immature period, but only if the father was high ranking at the time of their birth. Because age at reproductive maturity has a large impact on lifetime reproductive success, our results indicate a direct effect of paternal presence on offspring fitness. This relationship in turn suggests that the multiple roles that males play in multimale animal societies have not been sufficiently examined or appreciated and that paternal effects may be more pervasive than previously appreciated.