bluuebunny/crossref_metadata_2025 huggingface dataset:
Felsic highland crust on Venus suggested by Galileo Near‐Infrared Mapping Spectrometer data
Authors: Hashimoto George L. , Roos‐Serote Maarten , Sugita Seiji , Gilmore Martha S. , Kamp Lucas W. , Carlson Robert W. , Baines Kevin H.
Published: December 2008

We evaluated the spatial variation of Venusian surface emissivity at 1.18 μm wavelength and that of near‐surface atmospheric temperature using multispectral images obtained by the Near‐Infrared Mapping Spectrometer (NIMS) on board the Galileo spacecraft. The Galileo NIMS observed the nightside thermal emission from the surface and the deep atmosphere of Venus, which is attenuated by scattering from the overlying clouds. To analyze the NIMS data, we used a radiative transfer model based on the adding method. Although there is still an uncertainty in the results owing to the not well known parameters of the atmosphere, our analysis revealed that the horizontal temperature variation in the near‐surface atmosphere is no more than ±2 K on the Venusian nightside and also suggests that the majority of lowlands likely has higher emissivity compared to the majority of highlands. One interpretation for the latter result is that highland materials are generally composed of felsic rocks. Since formation of a large body of granitic magmas requires water, the presence of granitic terrains would imply that Venus may have had an ocean and a mechanism to recycle water into the mantle in the past.
IS Integration and Business Performance: The Mediation Effect of Organizational Absorptive Capacity in SMEs
Authors: Francalanci Chiara , Morabito Vincenzo
Published: December 2008

A fundamental result of the information technology (IT) and business performance literature is that IT is not a driver of performance per se. However, it can be associated with higher performance if accompanied by organizational change. The identification of the variables describing organizational change is still on-going work. This paper focuses on organizational absorptive capacity and analyses its effects on the relationship between IT and business performance in small and medium enterprises (SMEs). Organizational absorptive capacity measures the ability of an organization to complete a learning process. A significant learning effort is typically associated with IT, as it represents a complex technology. To cope with IT's complexity, implementation is typically incremental and is accompanied by a continuous integration effort of data and applications. The degree of integration of a company's information system (IS), called IS integration, is a proxy of IT maturity and quality. In this study, we explore the effect of IS integration on business performance through absorptive capacity, that is, we hypothesize that absorptive capacity has a mediation role between IS integration and business performance. The proposed research model is tested with data surveyed from 466 SMEs sited in Italy, for which exports constitute more than half of their revenues. Results indicate that organizational absorptive capacity has a mediation effect. Alternative models attributing to absorptive capacity a role different from mediation are found to be non-significant.
A note on the Pulay force at finite electronic temperatures
Authors: Niklasson Anders M. N.
Published: December 2008

Pulay’s original expression for the basis-set dependent adjustment term to the Hellmann–Feynman force in electronic structure theory, which occurs for nonorthogonal local basis-set representations, is based on the idempotency condition of a pure ensemble. At finite electronic temperatures with a fractional occupation of the states, the conventional expression of the Pulay force is therefore no longer valid. Here we derive a simple and computationally efficient expression for a generalized Pulay force, which is suitable for large-scale ab initio simulations at finite electronic temperatures using local nonorthogonal basis-set representations. The generalized Pulay force expression is given in terms of the temperature-dependent density matrix. For the construction of the density matrix, we propose a recursive Fermi operator expansion algorithm that automatically converges to the correct chemical potential.
Dipole allowed transitions in GdF: A four-component relativistic general open-shell configuration interaction study
Authors: Yamamoto Shigeyoshi , Tatewaki Hiroshi , Saue Trond
Published: December 2008

A four-component relativistic study of electronic transitions in the gadolinium monofluoride molecule (GdF) is presented. The electronic spectra of GdF have been investigated with a general open-shell configuration interaction method, where active electrons are distributed among molecular spinors mainly consisting of the Gd 4f, 5d, and 6s atomic spinors. The near-degeneracy effects of these spinors on the molecular electronic structure are considered by the valence full-CI-like approach. By the magnitudes of calculated transition dipole moments, the candidates for the observable transitions were selected. The present result is complementary to our previous study based on multireference configuration interaction singles and doubles calculations, which identified the electronic excited states of GdF by comparing the calculated excitation energies and angular momenta with those given by the laser spectroscopy. The spectra of the excited states less than 3.0 eV have been refined with the help of the calculated transition probabilities. The transitions between the excited states are newly analyzed and a rearrangement is proposed.
Pathways and reduced-dimension five-dimensional potential energy surface for the reactions H3++CO→H2+HCO+ and H3++CO→H2+HOC+
Authors: Li Hui , Hirano Tsuneo , Amano Takayoshi , Le Roy Robert J.
Published: December 2008

To obtain theoretical insight regarding the stability and formation dynamics of the interstellar ions HCO+ and HOC+, stationary points and the associated vibrational frequencies on the full nine-dimensional potential energy surface for the electronic ground state have been calculated using coupled-cluster theory with both single and double substitutions (CCSD). The energetics were refined with a higher-level coupled-cluster method CCSD(T), with core-valence electron correlation treated at the complete basis set limit. To elucidate the formation mechanism and internal relaxation processes, the reaction paths for the reactions H3++CO→H2+HCO+ and H3++CO→H2+HOC+ were calculated at the second-order Møller–Plesset (MP2) level, and corresponding single-point energies were obtained at the higher CCSD(T)/aug-cc-pVTZ level. Based on the analysis of the main reaction processes, a reduced-dimension five-dimensional potential energy surface for this system was constructed from 128 440 ab initio points calculated at the CCSD(T)/aug-cc-pVTZ level.
Gas sensing properties of defect-controlled ZnO-nanowire gas sensor
Authors: Ahn M.-W. , Park K.-S. , Heo J.-H. , Park J.-G. , Kim D.-W. , Choi K. J. , Lee J.-H. , Hong S.-H.
Published: December 2008

The effect of oxygen-vacancy-related defects on gas-sensing properties of ZnO-nanowire gas sensors was investigated. Gas sensors were fabricated by growing ZnO nanowires bridging the gap between two prepatterned Au catalysts. The sensor displayed fast response and recovery behavior with a maximum sensitivity to NO2 gas at 225 °C. Gas sensitivity was found to be linearly proportional to the photoluminescence intensity of oxygen-vacancy-related defects in both as-fabricated and defect-controlled gas sensors by postannealing in Ar and H2 atmosphere. This result agrees well with previous theoretical prediction that oxygen vacancies play a role of preferential adsorption sites for NO2 molecules.
A continuous kilohertz Cu Kα source produced by submillijoule femtosecond laser pulses for phase contrast imaging
Authors: Chakera J. A. , Ali A. , Tsui Y. Y. , Fedosejevs R.
Published: December 2008

We report a continuously operated Cu Kα x-ray source produced by a commercial kilohertz submillijoule femtosecond laser system. The source has an x-ray conversion of ∼4×10−5 into Kα line emission at 8.05 keV. The microplasma x-ray source has a size of 8 μm (full width at half maximum) produced by focusing 260 μJ laser pulses on a moving Cu-wire target. An average photon flux of ∼1.1×109 photons/sr/s is obtained using the above laser pulses. The source has been used to record phase contrast images of test samples. This compact x-ray source can serve as a low cost operating system for phase contrast imaging in clinical applications.
Quantum dynamics of small H2 and D2 clusters in the large cage of structure II clathrate hydrate: Energetics, occupancy, and vibrationally averaged cluster structures
Authors: Sebastianelli Francesco , Xu Minzhong , Bačić Zlatko
Published: December 2008

We report diffusion Monte Carlo (DMC) calculations of the quantum translation-rotation (T-R) dynamics of one to five para-H2 (p-H2) and ortho-D2 (o-D2) molecules inside the large hexakaidecahedral (51264) cage of the structure II clathrate hydrate, which was taken to be rigid. These calculations provide a quantitative description of the size evolution of the ground-state properties, energetics, and the vibrationally averaged geometries, of small (p-H2)n and (o-D2)n clusters, n=1–5, in nanoconfinement. The zero-point energy (ZPE) of the T-R motions rises steeply with the cluster size, reaching 74% of the potential well depth for the caged (p-H2)4. At low temperatures, the rapid increase of the cluster ZPE as a function of n is the main factor that limits the occupancy of the large cage to at most four H2 or D2 molecules, in agreement with experiments. Our DMC results concerning the vibrationally averaged spatial distribution of four D2 molecules, their mean distance from the cage center, the D2–D2 separation, and the specific orientation and localization of the tetrahedral (D2)4 cluster relative to the framework of the large cage, agree very well with the low-temperature neutron diffraction experiments involving the large cage with the quadruple D2 occupancy.
Analytical ballistic theory of carbon nanotube transistors: Experimental validation, device physics, parameter extraction, and performance projection
Authors: Akinwande Deji , Liang Jiale , Chong Soogine , Nishi Yoshio , Wong H.-S. Philip
Published: December 2008

We developed a fully analytical ballistic theory of carbon nanotube field effect transistors enabled by the development of an analytical surface potential capturing the temperature dependence and gate and quantum capacitance electrostatics. The analytical ballistic theory is compared to the experimental results of a ballistic transistor with good agreement. The validated analytical theory enables intuitive circuit design, provides techniques for parameter extraction of the bandgap and surface potential, and elucidates on the device physics of drain optical phonon scattering and its role in reducing the linear conductance and intrinsic gain of the transistor. Furthermore, a threshold voltage definition is proposed reflecting the bandgap-diameter dependence. Projections for key analog and digital performances are discussed.
Matrix replacement route to vertically aligned nickel nanowire array/polydimethylsiloxane nanocomposite film
Authors: Meng Xin , Zhou Liang-Tian , Zhu Ji-Xiang , Song Jie , Wang Xuan-Rui , Qiao Zheng-Ping
Published: December 2008

Vertically aligned magnetic anisotropic nickel (Ni) nanowire (NW) array/polydimethylsiloxane (PDMS) film was prepared from (Ni NW array)/anodic aluminum oxide by a simple matrix replacement route. The main challenge is to preserve the parallelly aligned Ni NW during replacement. The diameter and thickness of the as-prepared Ni NW and the Ni NW array/PDMS film are 8 mm and 60 μm, respectively. The magnetic property measurement shows that the film has remarkably enhanced coercivity and remanence ratio compared to that of bulk nickel and exhibits perpendicular magnetic anisotropy.
Ti
x
Si
1
−
x
O
2
optical coatings with tunable index and their response to intense subpicosecond laser pulse irradiation
Authors: Nguyen D. , Emmert L. A. , Cravetchi I. V. , Mero M. , Rudolph W. , Jupe M. , Lappschies M. , Starke K. , Ristau D.
Published: December 2008

Ion-beam sputtered TixSi1−xO2 binary-oxide films of high optical quality with tunable bandgap and refractive index were produced using zone targets. The suitability of the films for high-power subpicosecond laser applications is explored by laser breakdown measurements. The observed scaling laws of the single-pulse breakdown threshold—a power law with respect to pulse duration and a linear law with respect to bandgap energy—are similar to results obtained with high-quality simple oxides. The single- and multiple-pulse breakdown behaviors of these binary films indicate only slightly larger defect densities than found in simple oxides.
Bubble velocity, diameter, and void fraction measurements in a multiphase flow using fiber optic reflectometer
Authors: Lim Ho-Joon , Chang Kuang-An , Su Chin B. , Chen Chi-Yueh
Published: December 2008

A fiber optic reflectometer (FOR) technique featuring a single fiber probe is investigated for its feasibility of measuring the bubble velocity, diameter, and void fraction in a multiphase flow. The method is based on the interference of the scattered signal from the bubble surface with the Fresnel reflection signal from the tip of the optical fiber. Void fraction is obtained with a high accuracy if an appropriate correction is applied to compensate the underestimated measurement value. Velocity information is accurately obtained from the reflected signals before the fiber tip touches the bubble surface so that several factors affecting the traditional dual-tip probes such as blinding, crawling, and drifting effects due to the interaction between the probe and bubbles can be prevented. The coherent signals reflected from both the front and rear ends of a bubble can provide velocity information. Deceleration of rising bubbles and particles due to the presence of the fiber probe is observed when they are very close to the fiber tip. With the residence time obtained, the bubble chord length can be determined by analyzing the coherent signal for velocity determination before the deceleration starts. The bubble diameters are directly obtained from analyzing the signals of the bubbles that contain velocity information. The chord lengths of these bubbles measured by FOR represent the bubble diameters when the bubble shape is spherical or represent the minor axes when the bubble shape is ellipsoidal. The velocity and size of bubbles obtained from the FOR measurements are compared with those obtained simultaneously using a high speed camera.
High-quality InGaN∕GaN heterojunctions and their photovoltaic effects
Authors: Zheng Xinhe , Horng Ray-Hua , Wuu Dong-Sing , Chu Mu-Tao , Liao Wen-Yih , Wu Ming-Hsien , Lin Ray-Ming , Lu Yuan-Chieh
Published: December 2008

High-quality p-GaN∕i-In0.1Ga0.9N∕n-GaN heterojunctional epilayers are grown on (0001)-oriented sapphire substrates by metal organic chemical vapor deposition. The Pendellösung fringes around the InGaN peak in high-resolution x-ray diffraction (HRXRD) confirm a sharp interface between InGaN and GaN films. The corresponding HRXRD and photoluminescence measurements demonstrate that there is no observable phase separation. The improvement in crystal quality yields high-performance photovoltaic cells with open-circuit voltage of around 2.1eV and fill factor up to 81% under standard AM 1.5 condition. The dark current-voltage measurements show very large shunt resistance, implying an insignificant leakage current in the devices and therefore achieving the high fill factor in the illuminated case.
Early stage formation of graphene on the C face of 6H-SiC
Authors: Camara N. , Rius G. , Huntzinger J.-R. , Tiberj A. , Magaud L. , Mestres N. , Godignon P. , Camassel J.
Published: December 2008

An investigation of the early stage formation of graphene on the C face of 6H-silicon carbide (SiC) is presented. We show that the sublimation of few atomic layers of Si out of the SiC substrate is not homogeneous. In good agreement with the results of theoretical calculations it starts from defective sites, mainly dislocations that define nearly circular graphene layers, which have a pyramidal, volcanolike shape with a center chimney where the original defect was located. At higher temperatures, complete conversion occurs but, again, it is not homogeneous. Within the sample surface, the intensity of the Raman bands evidences inhomogeneous thickness.
The radial distribution of defects in a percolation path
Authors: Li X. , Tung C. H. , Pey K. L.
Published: December 2008

Our results show that the defect distribution within a nanometer size percolation path is nonuniform. The defects, which are shown as oxygen vacancies, spread out radially from the center of the percolation path. The conduction band edges of the defective oxide are lowered for 0.14–0.78eV when the Si–O composition changes from SiO1.76 to SiO0.7.
Transistor threshold voltage modulation by Dy2O3 rare-earth oxide capping: The role of bulk dielectrics charge
Authors: Yu H. Y. , Chang S. Z. , Aoulaiche M. , Wang X. P. , Adelmann C. , Kazer B. , Absil P. , Lauwers A. , Biesemans S.
Published: December 2008

The mechanism governing threshold voltage (Vt) modulation in NiSi/SiON n-channel metal-oxide-semiconductor field-effect transistors when doping with rare-earth elements (dysprosium or Dy in this work) is studied. In addition to the widely reported interface dipole theory, this letter provides additional evidence that the bulk trapping charges (related to the unintermixed Dy2O3 layer after device fabrication) can play an important role in determining the device Vt for the above-mentioned gate stacks. It is thus suggested that a careful design of the capping layer thickness and the thermal budget for intermixing the capping layer with host dielectrics is necessary to eliminate the impact from bulk trapping charges to the device performance.
Low-loss nonselectively oxidized AlxGa1−xAs heterostructure waveguides
Authors: Lou Y. , Hall D. C.
Published: December 2008

The use of nonselective AlGaAs oxidation (i.e., via the use of controlled, dilute O2 addition during wet thermal oxidation) enables a significant propagation loss reduction in fully oxidized Al0.3Ga0.7As/Al0.85Ga0.15As planar oxide single heterostructure waveguides. Prism coupling measurements are utilized to characterize the oxidized waveguide cladding and core layer thicknesses, refractive indices, and propagation loss. At a wavelength of 633 nm, above the Al0.3Ga0.7As core’s bandgap energy, the strongly absorbing semiconductor heterostructure waveguide is converted by nonselective oxidation to a transparent oxide heterostructure waveguide with a propagation loss of only 5.0 dB/cm (1.15 cm−1). A low loss of 3.6 dB/cm (0.83 cm−1) is obtained at 1.3 μm.
Heterostructured DNA templates: A combined magnetic force microscopy and circular dichroism study
Authors: Jaganathan Hamsa , Ivanisevic Albena
Published: December 2008

The effect of nanoparticle (NP) concentration was examined on the formation of heterostructured nanowires fabricated using DNA as a template. At mass ratios of 1:1 DNA:NP, the circular dichroism (CD) data showed a distinct characteristic, a plateau at 260 nm. The magnetic force microscopy (MFM) data revealed segments that showed variable interaction with the magnetized tip. At high NP concentrations both the CD and MFM data confirmed that the DNA template denatures and the control over the assembly process is poor.
Absorption characteristics of a quantum dot array induced intermediate band: Implications for solar cell design
Authors: Tomić Stanko , Jones Tim S. , Harrison Nicholas M.
Published: December 2008

We present a theoretical study of the electronic and absorption properties of the intermediate band (IB) formed by a three dimensional structure of InAs/GaAs quantum dots (QDs) arranged in a periodic array. Analysis of the electronic and absorption structures suggests that the most promising design for an IB solar cell material, which will exhibit its own quasi-Fermi level, is to employ small QDs (~6–12 nm QD lateral size). The use of larger QDs leads to extension of the absorption spectra into a longer wavelength region but does not provide a separate IB in the forbidden energy gap.
Stochastic optimization of a cold atom experiment using a genetic algorithm
Authors: Rohringer W. , Bücker R. , Manz S. , Betz T. , Koller Ch. , Göbel M. , Perrin A. , Schmiedmayer J. , Schumm T.
Published: December 2008

We employ an evolutionary algorithm to automatically optimize different stages of a cold atom experiment without human intervention. This approach closes the loop between computer based experimental control systems and automatic real time analysis and can be applied to a wide range of experimental situations. The genetic algorithm quickly and reliably converges to the most performing parameter set independent of the starting population. Especially in many-dimensional or connected parameter spaces, the automatic optimization outperforms a manual search.
Coupling of surface plasmons between two silver films in a Ag/SiO2/Ag plasmonic thermal emitter with grating structure
Authors: Ye Yi-Han , Jiang Yu-Wei , Tsai Ming-Wei , Chang Yi-Tsung , Chen Chia-Yi , Tzuang Dah-Ching , Wu Yi-Ting , Lee Si-Chen
Published: December 2008

The reflection and emission spectra of Ag/SiO2/Ag trilayer plasmonic thermal emitters with different SiO2 thicknesses are investigated. The top Ag film is perforated with periodic slits. It is found that the coupling of surface plasmons at the top and bottom Ag/SiO2 interface results in the redshift in thermal emission peaks. In this Ag/SiO2/Ag plasmonic thermal emitter, the electromagnetic field exhibits either Fabry–Pérot resonance or propagating surface plasmons depending on the thickness of SiO2 layer. By varying the thickness of SiO2 layer, transition from localized to grating-coupled propagating surface plasmon modes is observed.
Subnanosecond time-resolved x-ray measurements using an organic-inorganic perovskite scintillator
Authors: Kishimoto S. , Shibuya K. , Nishikido F. , Koshimizu M. , Haruki R. , Yoda Y.
Published: December 2008

We have developed a fast x-ray detector using an organic-inorganic perovskite scintillator of phenethylamine lead bromide (PhE-PbBr4). The scintillator had a dominant light emission with a fast decay time of 9.9 ns. An x-ray detector equipped with a 0.9-mm-thick PhE-PbBr4 crystal was used to detect nuclear resonant scattering in N61i (the first excited level: 67.41 keV; lifetime: 7.6 ns) by using synchrotron radiation. With this detector, we could successfully record the decaying gamma rays emitted from N61i with a time resolution of 0.7 ns (full width at half maximum) and a relatively high detection efficiency of 24%.
Simple prediction of interaction strengths in complex food webs
Authors: Berlow Eric L. , Dunne Jennifer A. , Martinez Neo D. , Stark Philip B. , Williams Richard J. , Brose Ulrich
Published: December 2008

Darwin's classic image of an “entangled bank” of interdependencies among species has long suggested that it is difficult to predict how the loss of one species affects the abundance of others. We show that for dynamical models of realistically structured ecological networks in which pair-wise consumer-resource interactions allometrically scale to the ¾ power—as suggested by metabolic theory—the effect of losing one species on another can be predicted well by simple functions of variables easily observed in nature. By systematically removing individual species from 600 networks ranging from 10–30 species, we analyzed how the strength of 254,032 possible pair-wise species interactions depended on 90 stochastically varied species, link, and network attributes. We found that the interaction strength between a pair of species is predicted well by simple functions of the two species' biomasses and the body mass of the species removed. On average, prediction accuracy increases with network size, suggesting that greater web complexity simplifies predicting interaction strengths. Applied to field data, our model successfully predicts interactions dominated by trophic effects and illuminates the sign and magnitude of important nontrophic interactions.
Viral RNA polymerase complex promotes optimal growth of 1918 virus in the lower respiratory tract of ferrets
Authors: Watanabe Tokiko , Watanabe Shinji , Shinya Kyoko , Kim Jin Hyun , Hatta Masato , Kawaoka Yoshihiro
Published: December 2008

The 1918 influenza pandemic was the most devastating outbreak of infectious disease in human history, accounting for about 50 million deaths worldwide. In addition to a significant number of cases of secondary bacterial pneumonia, this highly pathogenic strain of influenza A virus caused fatal primary viral pneumonia. To identify the viral gene(s) chiefly responsible for the high virulence of the 1918 virus, we generated a series of reassortants between the 1918 virus and a contemporary human H1N1 virus (A/Kawasaki/173/2001; K173) using reverse genetics. We then assessed their virulence properties in ferrets, a model closely resembling humans in terms of sensitivity to influenza virus infection and pattern of spread after intranasal inoculation. Substitution of single genes from the 1918 virus in the genetic background of K173 virus did not markedly alter the pattern of infection. That is, the reassortants grew well in nasal turbinates, but only sporadically (if at all) in the trachea and lungs. One exception was the 1918PB1/K173 reassortant, which replicated efficiently in lung tissues as well as the upper respiratory tract. A reassortant virus expressing the 1918 viral RNA polymerase complex (PA, PB1, and PB2) and nucleoprotein showed virulence properties in the upper and lower respiratory tracts of ferrets that closely resembled those of wild-type 1918 virus. Our findings strongly implicate the viral RNA polymerase complex as a major determinant of the pathogenicity of the 1918 pandemic virus. This new insight may aid in identifying virulence factors in future pandemic viruses that could be targeted with antiviral compounds.
Whole-genome association study identifies
STK39
as a hypertension susceptibility gene
Authors: Wang Ying , O'Connell Jeffrey R. , McArdle Patrick F. , Wade James B. , Dorff Sarah E. , Shah Sanjiv J. , Shi Xiaolian , Pan Lin , Rampersaud Evadnie , Shen Haiqing , Kim James D. , Subramanya Arohan R. , Steinle Nanette I. , Parsa Afshin , Ober Carole C. , Welling Paul A. , Chakravarti Aravinda , Weder Alan B. , Cooper Richard S. , Mitchell Braxton D. , Shuldiner Alan R. , Chang Yen-Pei C.
Published: December 2008

Hypertension places a major burden on individual and public health, but the genetic basis of this complex disorder is poorly understood. We conducted a genome-wide association study of systolic and diastolic blood pressure (SBP and DBP) in Amish subjects and found strong association signals with common variants in a serine/threonine kinase gene,
STK39
. We confirmed this association in an independent Amish and 4 non-Amish Caucasian samples including the Diabetes Genetics Initiative, Framingham Heart Study, GenNet, and Hutterites (meta-analysis combining all studies:
n
= 7,125,
P
< 10
−6
). The higher BP-associated alleles have frequencies > 0.09 and were associated with increases of 3.3/1.3 mm Hg in SBP/DBP, respectively, in the Amish subjects and with smaller but consistent effects across the non-Amish studies. Cell-based functional studies showed that
STK39
interacts with WNK kinases and cation-chloride cotransporters, mutations in which cause monogenic forms of BP dysregulation. We demonstrate that in vivo,
STK39
is expressed in the distal nephron, where it may interact with these proteins. Although none of the associated SNPs alter protein structure, we identified and experimentally confirmed a highly conserved intronic element with allele-specific in vitro transcription activity as a functional candidate for this association. Thus, variants in
STK39
may influence BP by increasing STK39 expression and consequently altering renal Na
+
excretion, thus unifying rare and common BP-regulating alleles in the same physiological pathway.
RETRACTED: A primitive Late Pliocene cheetah, and evolution of the cheetah lineage
Authors: Christiansen Per , Mazák Ji H.
Published: December 2008

The cheetah lineage is a group of large, slender, and long-limbed cats with a distinctive skull and dental morphology, of which only the extant cheetah (
Acinonyx jubatus
) is present today. The lineage is characterized by having abbreviated, tall, and domed crania, and a trenchant dentition with a much reduced, posteriorly placed protocone on the upper carnassial. In this article, we report on a new discovery of a Late Pliocene specimen from China with an estimated age of ≈2.2–2.5 million years, making it one of the oldest specimens known to date. A cladistic analysis confirmed that it is the most primitive cheetah known, and it shares a number of unambiguous derived cranial traits with the
Acinonyx
lineage, but has more primitive dentition than previously known cheetahs, demonstrating that the many unusual skull and dental characters hitherto considered characteristic of cheetahs evolved in a gradual fashion. Isolated teeth of primitive cheetahs may not be recognizable as such, but can be confused with, for instance, those of leopards or other similar-sized pantherine cats or pumas. The age and morphology of the new specimen supports an Old World origin of the cheetah lineage, not a New World one, as has been suggested. We name the new species
Acinonyx kurteni
in honor of the late Björn Kurtén.
DGCR8-dependent microRNA biogenesis is essential for skin development
Authors: Yi Rui , Pasolli H. Amalia , Landthaler Markus , Hafner Markus , Ojo Tolulope , Sheridan Robert , Sander Chris , O'Carroll Donal , Stoffel Markus , Tuschl Thomas , Fuchs Elaine
Published: December 2008

MicroRNAs play important roles in animal development. Numerous conditional knockout (cKO) studies of
Dicer
have been performed to interrogate the functions of microRNA during mammalian development. However, because Dicer was recently implicated in the biogenesis of endogenous siRNAs in mammals, it raises the question whether the
Dicer
cKO defects can be attributable to the loss of microRNAs. Previously, we and others conditionally targeted
Dicer
and identified its critical roles in embryonic skin morphogenesis. Here, we focus explicitly on microRNAs by taking a parallel strategy with
Dgcr8
, encoding an essential component of the microprocessor complex that is exclusively required for microRNA biogenesis. With this comparative analysis, we show definitively that the
Dicer
- and
Dgcr8
-null skin defects are both striking and indistinguishable. By deep sequencing analysis of microRNA depletion in both
Dicer
- and
Dgcr8
-null skin, we demonstrate that most abundantly expressed skin microRNAs are dependent on both Dicer and DGCR8. Our results underscore a specific importance of microRNAs in controlling mammalian skin development.
A phosphorylation-dependent intramolecular interaction regulates the membrane association and activity of the tumor suppressor PTEN
Authors: Rahdar Meghdad , Inoue Takanari , Meyer Tobias , Zhang Jin , Vazquez Francisca , Devreotes Peter N.
Published: December 2008

The PI 3-phosphatase PTEN (phosphatase and tensin homologue deleted on chromosome 10), one of the most important tumor suppressors, must associate with the plasma membrane to maintain appropriate steady-state levels of phosphatidylinositol 3,4,5-triphosphate. Yet the mechanism of membrane binding has received little attention and the key determinants that regulate localization, a phosphatidylinositol 4,5-bisphosphate (PIP
2
) binding motif and a cluster of phosphorylated C-terminal residues, were not included in the crystal structure. We report that membrane binding requires PIP
2
and show that phosphorylation regulates an intramolecular interaction. A truncated version of the enzyme, PTEN
1–351
, bound strongly to the membrane, an effect that was reversed by co-expression of the remainder of the molecule, PTEN
352–403
. The separate fragments associated in vitro, an interaction dependent on phosphorylation of the C-terminal cluster, a portion of the PIP
2
binding motif, integrity of the phosphatase domain, and the CBR3 loop. Our investigation provides direct evidence for a model in which PTEN switches between open and closed states and phosphorylation favors the closed conformation, thereby regulating localization and function. Small molecules targeting these interactions could potentially serve as therapeutic agents in antagonizing Ras or PI3K-driven tumors. The study also stresses the importance of determining the structure of the native enzyme.
Resolving cadherin interactions and binding cooperativity at the single-molecule level
Authors: Zhang Yunxiang , Sivasankar Sanjeevi , Nelson W. James , Chu Steven
Published: December 2008

The cadherin family of Ca
2+
-dependent cell adhesion proteins are critical for the morphogenesis and functional organization of tissues in multicellular organisms, but the molecular interactions between cadherins that are at the core of cell–cell adhesion are a matter of considerable debate. A widely-accepted model is that cadherins adhere in 3 stages. First, the functional unit of cadherin adhesion is a
cis
dimer formed by the binding of the extracellular regions of 2 cadherins on the same cell surface. Second, formation of low-affinity
trans
interactions between cadherin
cis
dimers on opposing cell surfaces initiates cell–cell adhesion. Third, lateral clustering of cadherins cooperatively strengthens intercellular adhesion. Evidence of these cadherin binding states during adhesion is, however, contradictory, and evidence for cooperativity is lacking. We used single-molecule structural (fluorescence resonance energy transfer) and functional (atomic force microscopy) assays to demonstrate directly that cadherin monomers interact via their N-terminal EC1 domain to form
trans
adhesive complexes. We could not detect the formation of cadherin
cis
dimers, but found that increasing the density of cadherin monomers cooperatively increased the probability of
trans
adhesive binding.
An empirical explanation of aperture effects
Authors: Sung Kyongje , Wojtach William T. , Purves Dale
Published: December 2008

The perceived direction of a moving line changes, often markedly, when viewed through an aperture. Although several explanations of this remarkable effect have been proposed, these accounts typically focus on the percepts elicited by a particular type of aperture and offer no biological rationale. Here, we test the hypothesis that to contend with the inherently ambiguous nature of motion stimuli the perceived direction of objects moving behind apertures of different shapes is determined by a wholly empirical strategy of visual processing. An analysis of moving line stimuli generated by objects projected through apertures shows that the directions of motion subjects report in psychophysical testing is accounted for by the frequency of occurrence of the 2D directions of stimuli generated by simulated 3D sources. The completeness of these predictions supports the conclusion that the direction of perceived motion is fully determined by accumulated behavioral experience with sources whose physical motions cannot be conveyed by image sequences as such.
Lymphoid tissue inducer–like cells are an innate source of IL-17 and IL-22
Authors: Takatori Hiroaki , Kanno Yuka , Watford Wendy T. , Tato Cristina M. , Weiss Greta , Ivanov Ivaylo I. , Littman Dan R. , O'Shea John J.
Published: December 2008

The interleukin (IL) 17 family of cytokines has emerged to be critical for host defense as well as the pathogenesis of autoimmune and autoinflammatory disorders, and serves to link adaptive and innate responses. Recent studies have identified a new subset of T cells that selectively produce IL-17 (Th17 cells; Bettelli, E., T. Korn, and V.K. Kuchroo. 2007. Curr. Opin. Immunol. 19:652–657; Kolls, J.K., and A. Linden. 2004. Immunity. 21:467–476), but the regulation of IL-17 production by innate immune cells is less well understood. We report that in vitro stimulation with IL-23 induced IL-17 production by recombination activating gene (Rag) 2−/− splenocytes but not Rag2−/− common γ chain−/− splenocytes. We found that a major source of IL-17 was CD4+CD3−NK1.1−CD11b−Gr1−CD11c−B220− cells, a phenotype that corresponds to lymphoid tissue inducer–like cells (LTi-like cells), which constitutively expressed the IL-23 receptor, aryl hydrocarbon receptor, and CCR6. In vivo challenge with the yeast cell wall product zymosan rapidly induced IL-17 production in these cells. Genetic deletion of signal transducer and activator of transcription 3 reduced but did not abrogate IL-17 production in LTi-like cells. Thus, it appears that splenic LTi-like cells are a rapid source of IL-17 and IL-22, which might contribute to dynamic organization of secondary lymphoid organ structure or host defense.
Mutations at the Signature Sequence of CFTR Create a Cd2+-gated Chloride Channel
Authors: Wang Xiaohui , Bompadre Silvia G. , Li Min , Hwang Tzyh-Chang
Published: December 2008

The canonical sequence LSGGQ, also known as the signature sequence, defines the adenosine triphosphate (ATP)-binding cassette transporter superfamily. Crystallographic studies reveal that the signature sequence, together with the Walker A and Walker B motifs, forms the ATP-binding pocket upon dimerization of the two nucleotide-binding domains (NBDs) in a head-to-tail configuration. The importance of the signature sequence is attested by the fact that a glycine to aspartate mutation (i.e., G551D) in cystic fibrosis transmembrane conductance regulator (CFTR) results in a severe phenotype of cystic fibrosis. We previously showed that the G551D mutation completely eliminates ATP-dependent gating of the CFTR chloride channel. Here, we report that micromolar [Cd2+] can dramatically increase the activity of G551D-CFTR in the absence of ATP. This effect of Cd2+ is not seen in wild-type channels or in G551A. Pretreatment of G551D-CFTR with the cysteine modification reagent 2-aminoethyl methane thiosulfonate hydrobromide protects the channel from Cd2+ activation, suggesting an involvement of endogenous cysteine residue(s) in mediating this effect of Cd2+. The mutants G551C, L548C, and S549C, all in the signature sequence of CFTR's NBD1, show robust response to Cd2+. On the other hand, negligible effects of Cd2+ were seen with T547C, Q552C, and R553C, indicating that a specific region of the signature sequence is involved in transmitting the signal of Cd2+ binding to the gate. Collectively, these results suggest that the effect of Cd2+ is mediated by a metal bridge formation between yet to be identified cysteine residue(s) and the engineered aspartate or cysteine in the signature sequence. We propose that the signature sequence serves as a switch that transduces the signal of ligand binding to the channel gate.
The Skeletal L-type Ca2+ Current Is a Major Contributor to Excitation-coupled Ca2+ entry
Authors: Bannister Roger A. , Pessah Isaac N. , Beam Kurt G.
Published: December 2008

The term excitation-coupled Ca2+ entry (ECCE) designates the entry of extracellular Ca2+ into skeletal muscle cells, which occurs in response to prolonged depolarization or pulse trains and depends on the presence of both the 1,4-dihydropyridine receptor (DHPR) in the plasma membrane and the type 1 ryanodine receptor in the sarcoplasmic reticulum (SR) membrane. The ECCE pathway is blocked by pharmacological agents that also block store-operated Ca2+ entry, is inhibited by dantrolene, is relatively insensitive to the DHP antagonist nifedipine (1 μM), and is permeable to Mn2+. Here, we have examined the effects of these agents on the L-type Ca2+ current conducted via the DHPR. We found that the nonspecific cation channel antagonists (2-APB, SKF 96356, La3+, and Gd3+) and dantrolene all inhibited the L-type Ca2+ current. In addition, complete (>97%) block of the L-type current required concentrations of nifedipine >10 μM. Like ECCE, the L-type Ca2+ channel displays permeability to Mn2+ in the absence of external Ca2+ and produces a Ca2+ current that persists during prolonged (∼10-second) depolarization. This current appears to contribute to the Ca2+ transient observed during prolonged KCl depolarization of intact myotubes because (1) the transients in normal myotubes decayed more rapidly in the absence of external Ca2+; (2) the transients in dysgenic myotubes expressing SkEIIIK (a DHPR α1S pore mutant thought to conduct only monovalent cations) had a time course like that of normal myotubes in Ca2+-free solution and were unaffected by Ca2+ removal; and (3) after block of SR Ca2+ release by 200 μM ryanodine, normal myotubes still displayed a large Ca2+ transient, whereas no transient was detectable in SkEIIIK-expressing dysgenic myotubes. Collectively, these results indicate that the skeletal muscle L-type channel is a major contributor to the Ca2+ entry attributed to ECCE.
Breeding programme for Horned guan Oreophasis derbianus at Africam Safari, Mexico
Authors: CORNEJO J.
Published: December 2008

The Horned guan Oreophasis derbianus is one of the most threat cracids but the species has always been scarce in captivity. By the end of 2007, the International Studbook registered a global population of 70 individuals in human care. This population is genetically compromised, as most of the potential founders are not yet represented. In the last 6 years, Africam Safari's breeding programme has hatched nearly 50% of the individuals bred in collections, contributing to the knowledge about husbandry and the biology of the species.
Differences in husbandry and management systems across ten facilities housing Asian elephants Elephas maximas in India
Authors: MALLAPUR A. , RAMANATHAN A.
Published: December 2008

A face‐to‐face questionnaire survey was conducted to document the husbandry and management systems followed by ten facilities housing Asian elephants Elephas maximas in India. Eighty‐two Asian elephants at these ten facilities were surveyed between November 2004 and February 2005. A significantly greater percentage of the elephants managed by zoos (n=4 zoos; 13 elephants surveyed) and the forest elephant camp (n=1 forest elephant camp; five elephants surveyed) were housed in pairs or groups; whereas animals maintained by tourist camps (n=2 tourist camps; 40 elephants surveyed) and temples (n=3 temples; 24 elephants surveyed) were permanently restrained with minimal social contact (physical contact with other elephants). A considerably larger proportion of elephants from tourist camps and temples were housed in environments devoid of natural features, such as trees, shrubs and water bodies. Forest elephant camp and zoo elephants, on the other hand, were housed in complex species‐specific environments, which included water bodies, trees/shrubs and a substrate of compacted mud. From this paper, it is evident that the husbandry and management protocols vary significantly across the degrees of captivity, with some facilities (e.g. zoos and a forest elephant camp) being more conducive for housing elephants than others (e.g. temples and tourist camps).
1997 Best Paper Award—Controls and Diagnostics Committee: Active Stabilization of Rotating Stall and Surge in a Transonic Single-Stage Axial Compressor
Authors: Weigl H. J. , Paduano J. D. , Fre´chette L. G. , Epstein A. H. , Greitzer E. M. , Bright M. M. , Strazisar A. J.
Published: December 2008

Rotating stall and surge have been stabilized in a transonic single-stage axial compressor using active feedback control. The control strategy is to sense upstream wall static pressure patterns and feed back the signal to an annular array of twelve separately modulated air injectors. At tip relative Mach numbers of 1.0 and 1.5 the control achieved 11 and 3.5 percent reductions in stalling mass flow, respectively, with injection adding 3.6 percent of the design compressor mass flow. The aerodynamic effects of the injection have also been examined. At a tip Mach number, Mtip, of 1.0, the stall inception dynamics and effective active control strategies are similar to results for low-speed axial compressors. The range extension was achieved by individually damping the first and second spatial harmonics of the prestall perturbations using constant gain feedback. At a Mtip of 1.5 (design rotor speed), the prestall dynamics are different than at the lower speed. Both one-dimensional (surge) and two-dimensional (rotating stall) perturbations needed to be stabilized to increase the compressor operating range. At design speed, the instability was initiated by approximately ten rotor revolutions of rotating stall followed by classic surge cycles. In accord with the results from a compressible stall inception analysis, the zeroth, first, and second spatial harmonics each include more than one lightly damped mode, which can grow into the large amplitude instability. Forced response testing identified several modes traveling up to 150 percent of rotor speed for the first three spatial harmonics; simple constant gain control cannot damp all of these modes and thus cannot stabilize the compressor at this speed. A dynamic, model-based robust controller was therefore used to stabilize the multiple modes that comprise the first three harmonic perturbations in this transonic region of operation.
Reduction of Unsteady Blade Loading by Beneficial Use of Vortical and Potential Disturbances in an Axial Compressor With Rotor Clocking
Authors: Hsu S. T. , Wo A. M.
Published: December 2008

This paper demonstrates reduction of stator unsteady loading due to forced response in a large-scale, low-speed, rotor/stator/rotor axial compressor rig by clocking the downstream rotor. Data from the rotor/stator configuration showed that the stator response due to the upstream vortical disturbance reaches a maximum when the wake impinges against the suction surface immediately downstream of the leading edge. Results from the stator/rotor configuration revealed that the stator response due to the downstream potential disturbance reaches a minimum with a slight time delay after the rotor sweeps pass the stator trailing edge. For the rotor/stator/rotor configuration, with Gap1 = 10 percent chord and Gap2 = 30 percent chord, results showed a 60 percent reduction in the stator force amplitude by clocking the downstream rotor so that the time occurrence of the maximum force due to the upstream vortical disturbance coincides with that of the minimum force due to the downstream potential disturbance. This is the first time, the authors believe, that beneficial use of flow unsteadiness is definitively demonstrated to reduce the blade unsteady loading.