bluuebunny/crossref_metadata_2025 huggingface dataset:
Averaged indicators of secondary flow in repeated acoustic Doppler current profiler crossings of bends
Authors: Dinehart R. L. , Burau J. R.
Published: September 2005

Cross‐stream velocity was measured in a large river bend at high spatial resolution over three separate survey episodes. A suite of methods for resolving cross‐stream velocity distributions was tested on data collected using acoustic Doppler current profilers (ADCP) in the sand‐bedded Sacramento River, California. The bend was surveyed with repeated ADCP crossings at eight cross sections during a rising limb of high discharge in February 2004 and twice on recession in March 2004. By translating and interpolating repeated ADCP crossings to planar grids, velocity ensembles at similar positions along irregular boat paths could be averaged. The averaging minimized turbulent fluctuations in streamwise velocities over 1 m/s, enabling the resolution of weaker cross‐stream velocities (~15‐30 cm/s). Secondary‐flow influence on suspended sediment was inferred from a lateral region of acoustic backscatter intensity aligned with outward flow over the point bar. A near‐bed decrease in backscatter intensity across the pool corresponded with inward cross‐stream flow. These suspension indicators were used to orient averaged velocity grids for unambiguously defining the cross‐stream velocity magnitudes. Additional field investigations could test whether the correlation between cross‐stream velocity and backscatter intensity patterns results from helical recirculation of suspended sediment to the inside of the bend. These river measurements, consistent with classic and recent laboratory studies, show that ADCP surveys can provide refined views of secondary flow and sediment movement in large rivers.
Water films and scaling of soil characteristic curves at low water contents
Authors: Tuller Markus , Or Dani
Published: September 2005

Individual contributions of capillarity and adsorptive surface forces to the matric potential are seldom differentiated in determination of soil water characteristic (SWC) curves. Typically, capillary forces dominate at the wet end, whereas adsorptive surface forces dominate at the dry end of a SWC where water is held as thin liquid films. The amount of adsorbed soil water is intimately linked to soil specific surface area (SA) and plays an important role in various biological and transport processes in arid environments. Dominated by van der Waals adsorptive forces, surface‐water interactions give rise to a nearly universal scaling relationship for SWC curves at low water contents. We demonstrate that scaling measured water content at the dry end by soil specific surface area yields remarkable similarity across a range of soil textures and is in good agreement with theoretical predictions based on van der Waals interactions. These scaling relationships are important for accurate description of SWC curves in dry soils and may provide rapid and reliable estimates of soil specific surface area from SWC measurements for matric potentials below ‒10 MPa conveniently measured with the chilled‐mirror dew point technique. Surface area estimates acquired by fitting the scaling relationship to measured SWC data were in good agreement with SA data measured by standard methods. Preliminary results suggest that the proposed method could provide reliable SA estimates for natural soils with hydratable surface areas smaller than 200 m2/g.
TRBP, a regulator of cellular PKR and HIV‐1 virus expression, interacts with Dicer and functions in RNA silencing
Authors: Haase Astrid D , Jaskiewicz Lukasz , Zhang Haidi , Lainé Sébastien , Sack Ragna , Gatignol Anne , Filipowicz Witold
Published: September 2005

Dicer is a key enzyme involved in RNA interference (RNAi) and microRNA (miRNA) pathways. It is required for biogenesis of miRNAs and small interfering RNAs (siRNAs), and also has a role in the effector steps of RNA silencing. Apart from Argonautes, no proteins are known to associate with Dicer in mammalian cells. In this work, we describe the ide.jpgication of TRBP (human immunodeficiency virus (HIV‐1) transactivating response (TAR) RNA‐binding protein) as a protein partner of human Dicer. We show that TRBP is required for optimal RNA silencing mediated by siRNAs and endogenous miRNAs, and that it facilitates cleavage of pre‐miRNA in vitro. TRBP had previously been assigned several functions, including inhibition of the interferon‐induced double‐stranded RNA‐regulated protein kinase PKR and modulation of HIV‐1 gene expression by association with TAR. The TRBP–Dicer interaction shown raises interesting questions about the potential interplay between RNAi and interferon–PKR pathways.
SUMO‐1 represses apoptosis signal‐regulating kinase 1 activation through physical interaction and not through covalent modification
Authors: Lee Yun‐Suk , Jang Moon‐Sun , Lee Jong‐Soo , Choi Eui‐Ju , Kim Eunhee
Published: September 2005

This study examined whether small ubiquitin‐related modifier‐1 (SUMO‐1) regulates apoptosis signal‐regulating kinase 1 (ASK1). ASK1 interacted with SUMO‐1 in vitro as well as in BOSC23 cells. Endogenous ASK1–SUMO‐1 interaction was disrupted following H2O2 signal. SUMO‐1 overexpression suppressed the self‐oligomerization, kinase activity and apoptotic potential of ASK1, whereas SUMO‐1 depletion potentiated such activities. SUMO‐1(ΔC6), a sumoylation‐incompetent mutant lacking carboxy‐terminal six amino acids, suppressed ASK1 activation, implying that the suppressive effect of SUMO‐1 on ASK1 is independent of sumoylation. ASK1(3M), an ASK1 mutant in which all three lysines in the ψKXE m.jpg were substituted with alanines, still retained the kinase activity and activated the Jun amino‐terminal kinase pathway. However, SUMO‐1 failed to interact with ASK1(3M) and to suppress ASK1(3M) activation, indicating that the three lysines are important for regulation by SUMO‐1. This study shows that SUMO‐1 exerts a negative regulatory effect on ASK1 activation through physical interaction and not through covalent modification.
Genetic evidence for selective neurotrophin 3 signalling through TrkC but not TrkB in vivo
Authors: Stenqvist Anna , Agerman Karin , Marmigère Frédéric , Minichiello Liliana , Ernfors Patrik
Published: September 2005

Neurotrophins control neuronal survival in a target‐derived manner during the period of naturally occurring cell death in development. The specificity of this mechanism has been attributed to a restricted spatio‐temporal expression of neurotrophin ligands in target tissues, as well as a selective expression of their cognate tyrosine kinase (Trk) receptors in different neuronal subpopulations. However, several in vitro and in vivo studies of null mutant mice have suggested that neurotrophin 3 (NT3) also signals through the non‐preferred TrkB receptor. In this study, we have directly addressed the in vivo preference of NT3 to signal through TrkB or TrkC, by crossing the NT3 knock‐in mice (BDNFNT3/NT3 mice) with the TrkB‐ or TrkC‐null mutant mice. We find that TrkB is dispensable, whereas TrkC is required for the neuronal rescue by the NT3 allele in the brain‐derived neurotrophic factor‐ and NT3‐dependent cochleovestibular system. Our results show that NT3 maintains survival of cells as well as target innervation only through interactions with TrkC in vivo. TrkB and TrkC receptors are thus not functionally redundant for NT3, even when coexpressed in neurons of the cochleovestibular system.
Reaction dynamics study of O−+C2H2 with crossed beams and density-functional theory calculations
Authors: Liu Li , Li Yue , Farrar James M.
Published: September 2005

The reactions between O− and C2H2 have been studied using the crossed-beam technique and density-functional theory (DFT) calculations in the collision energy range from 0.35 to 1.5 eV (34–145kJ∕mol). Both proton transfer and C–O bond formation are observed. The proton transfer channel forming C2H− is the dominant pathway. The center-of-mass flux distributions of the C2H− product ions are highly asymmetric, with maxima close to the velocity and direction of the precursor acetylene beam, characteristic of direct reactions. The reaction quantitatively transforms the entire reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the proton is transferred in a configuration in which both the breaking and the forming bonds are extended. The C–O bond formation channel producing HC2O− displays a distinctive kinematic picture in which the product distribution switches from predominantly forward scattering with a weak backward peak to sideways scattering as the collision energy increases. At low collision energies, the reaction occurs through an intermediate that lives a significant fraction of a rotational period. The asymmetry in the distribution leads to a lifetime estimate of 600 fs, in reasonable agreement with DFT calculations showing that hydrogen-atom migration is rate limiting. At higher collision energies, the sideways-scattered products arise from repulsive energy release from a bent transition state.
A study of transparent contact to vertical GaN-based light-emitting diodes
Authors: Kim D. W. , Lee H. Y. , Yeom G. Y. , Sung Y. J.
Published: September 2005

In this study, transparent indium tin oxide (ITO) deposited by sputtering was applied to laser lift-off (LLO) GaN-based vertical light-emitting diodes (VLEDs) and the electrical and optical properties of ITO films were measured as a function of annealing conditions. The measured minimum resistivity of ITO film was about 3.78×10−4Ωcm and the measured optical transmittance at 460nm was 96.8% after the annealing process. In this condition, about 1×10−5Ωcm2 of ITO contact resistance to LLO n-GaN could be obtained. By applying the transparent ITO layer to the LLO GaN-based VLEDs, a significant decrease of the forward operating voltage from 3.3to3.8V at 20mA could be obtained.
Phase changes in Lennard-Jones mixed clusters with composition ArnXe6−n (n=,1,2)
Authors: White Ronald P. , Cleary Sean M. , Mayne Howard R.
Published: September 2005

We have carried out parallel tempering Monte Carlo calculations on the binary six-atom mixed Lennard-Jones clusters, ArnXe6−n (n=0,1,2). We have looked at the classical configurational heat capacity CV(T) as a probe of phase behavior. All three clusters show a feature in the heat capacity in the region of 15–20K. The Ar2Xe4 cluster exhibits a further peak in the heat capacity near 7K. We have also investigated dynamical properties of the Ar2Xe4 cluster as a function of temperature using molecular dynamics. We report the interbasin isomerization rate and the bond fluctuation parameter obtained from these calculations. At 7K, the isomerization rate is on the order of 0.01ns−1; at 20K, the isomerization rate is greater than 10ns−1. Furthermore, at 7K, the bond fluctuation parameter is less than 3%; at 20K, it is in the range of 10–15% (depending on the sampling time used). Using this information, together with Monte Carlo quenching data, we assign the 15–20K feature in the heat capacity to a solid-liquid phase change and the 7-K peak to a solid-solid phase change. We believe this is the smallest Lennard-Jones cluster system yet shown to exhibit solid-solid phase change behavior.
D
5
h
C
50
X
10
: Saturn-like fullerene derivatives (X=F, Cl, Br)
Authors: Chang Y. F. , Zhang J. P. , Hong B. , Sun H. , An Z. , Wang R. S.
Published: September 2005

Based on the recently reported D5hC50, the geometries and stabilities of its Saturn-like derivatives C50X10 (X=F, Cl, Br) have been investigated by DFT method. Compared with C50, the equatorial carbon atoms in C50X10 have been saturated by halogens and change to sp3 hybridization to release the large angle strain. Because the equatorial carbon atoms have been taken out of the π system by the halogens “ring,” the C50X10 system has been split into two well-delocalized conjugated annulene subunits, and then the electronic stabilization has been enhanced.
Nanostructured Zr- and Ti-based composite materials with high strength and enhanced plasticity
Authors: Kühn U. , Mattern N. , Gebert A. , Kusy M. , Boström M. , Siegel U. , Schultz L.
Published: September 2005

Multicomponent composite materials with the compositions Zr66Nb13Cu8Ni6.8Al6.2 and Ti66Nb13Cu8Ni6.8Al6.2 were produced by copper mold casting, and their microstructure and their room-temperature mechanical properties were investigated. The specific alloys were developed to circumvent the limited ductility of Zr- and Ti-based bulk metallic glasses by the formation of a heterogeneous microstructure consisting of a nanocrystalline matrix and ductile dendritic bcc precipitates. Comparing the microstructure of both alloys, two significant differences were observed. The volume fraction of the dendritic bcc phase is higher for the Ti-based alloy and the formed interdendritic matrix phase(s) have a different structure. The two alloys show an excellent combination of strength and plastic strain. Especially the Ti-based alloy exhibits exceptional mechanical properties, such as high fracture stress of more than 2000MPa and a plastic elongation to failure of almost 30%.
Temperature study of the spin-transfer switching speed from dc to 100ps
Authors: Devolder T. , Tulapurkar A. , Suzuki Y. , Chappert C. , Crozat P. , Yagami K.
Published: September 2005

We study the speed of the magnetization switching resulting from spin transfer in pillar-shaped CoFe∕Cu∕CoFe spin valves and the temperature dependence thereof. The switching speed was investigated with current pulses of durations from 100ps to dc while the temperature was varied from 50to300K. Quasistatic loops indicate that the reversal events imply transition states with reduced remanences. Their interval of occurrence shrinks gradually to almost null when the temperature is raised to 300K. The curvature of resistance versus current hysteresis loops is different in the antiparallel and parallel branches, which evidences the influence of the Ampere field on the quasistatic micromagnetic configuration. In the dynamical regime, the pulse-induced parallel to antiparallel transition speed is not much temperature dependent from 50to300K. In contrast, the pulse-induced antiparallel to parallel transition is thermally disfavored and much faster at 150K than at 300K. We model the experimental behavior by a competition between thermal fluctuations and the Ampere-field-related C-like bending of the magnetization in the free layer. The contribution of the Ampere field dominates in most cases. These contributions are amplified or damped together by the spin-transfer torque, but since the C-like bending is a response to a magnetic field, it sets in at a gradual pace ruled by the classical Gilbert relaxation. Most of the difference between quasistatic switching and pulse-induced switching results from this complete or incomplete alignment with the total effective field. Our demonstration of 100-ps switching validates spin-transfer switching for fast memory applications.
Rotational motion in the molecular crystals meta- and ortho-carborane studied by deuteron nuclear magnetic resonance
Authors: Winterlich Manfred , Böhmer Roland , Diezemann Gregor , Zimmermann Herbert
Published: September 2005

Spin-lattice and spin-spin-relaxation times, one- and two-dimensional spectra as well as two- and four-time correlation functions were measured for the molecular crystals ortho- and meta-carborane using deuteron nuclear magnetic resonance. It is found that in their noncubic phases these crystals exhibit highly anisotropic motions. In order to allow for a quantitative description of the motional geometry of the carboranes several stochastic models are formulated. By comparison of the model calculations with the experimental results it is found that the dynamics of these quasi-icosahedrally shaped molecules is governed by a composite reorientation process. Here the molecules perform threefold jumps around a molecule-fixed axis which itself can be tilted in four different directions with respect to a crystal-fixed axis. The tilt angle increases significantly with increasing temperature. On the basis of measurements of four-time stimulated-echo functions, implications for dynamic heterogeneity also in comparison with that of supercooled liquids are discussed.
Zn(O,OH) layers in chalcopyrite thin-film solar cells: Valence-band maximum versus composition
Authors: Bär M. , Reichardt J. , Grimm A. , Kötschau I. , Lauermann I. , Rahne K. , Sokoll S. , Lux-Steiner M. C. , Fischer Ch.-H. , Weinhardt L. , Umbach E. , Heske C. , Jung Ch. , Niesen T. P. , Visbeck S.
Published: September 2005

Zn(O,OH) layers deposited by the ion layer gas reaction (ILGAR) technique have the potential to replace the conventionally used CdS buffer layer in Cu(In(1−X)GaX)(SYSe(1−Y))2-based thin-film solar cells. To avoid stability issues, the fraction of metastable Zn(OH)2 should be reduced in the final buffer layer. However, hydroxide-poor or -free ZnO “buffers” result in noncompetitive devices. We have therefore investigated the impact of different oxide/hydroxide ratios on the electronic band alignment at the absorber/buffer heterointerface. The surface composition as well as the position of the valence-band maximum (VBM) of respective ILGAR-Zn(O,OH) samples was determined by photoelectron spectroscopy. The position of the conduction-band minimum (CBM) was estimated using optical band gaps determined from optical reflection/transmission measurements. From the comparison of these VBM and CBM values with the respective values of the absorber surface, predictions are made in terms of valence- and conduction-band offsets at the crucial absorber/buffer interface. The results are compared with previous findings, and the drawn conclusions are correlated with the performance of respective solar cell devices.
Intersubband optical absorption in quantum dots-in-a-well heterostructures
Authors: Han Xiuxun , Li Jiemin , Wu Jiejun , Cong Guangwei , Liu Xianglin , Zhu Qinsheng , Wang Zhanguo
Published: September 2005

The theoretical analysis of intersubband optical transitions for InAs∕InGaAs quantum dots-in-a-well (DWELL) detectors are performed in the framework of effective-mass envelope-function theory. In contrast to InAs∕GaAs quantum dot (QD) structures, the calculated band structure of DWELL quantitatively confirms that an additional InGaAs quantum well effectively lowers the ground state of InAs QDs relative to the conduction-band edge of GaAs and enhances the confinement of electrons. By changing the doping level, the dominant optical transition can occur either between the bound states in the dots or from the ground state in the dots to bound states in the well, which corresponds to the far-infrared and long-wave infrared (LWIR) peaks in the absorption spectra, respectively. Our calculated results also show that it is convenient to tailor the operating wavelength in the LWIR atmospheric window (8–12μm) by adjusting the thickness of the InGaAs layer while keeping the size of the quantum dots fixed. Theoretical predictions agree well with the available experimental data.
Dielectric relaxation in doped SrTiO3: Transition from classical thermal activation to quantum tunnelling
Authors: Lemanov V. V. , Sotnikov A. V. , Smirnova E. P. , Weihnacht M.
Published: September 2005

The transition from the thermally activated regime to quantum tunneling is observed in the dielectric relaxation in SrTiO3 ceramic samples doped with Mn and (MgNb). The relaxation is attributed to MnTi4+ off-center ions and to polaronlike defects coupled to MnTi2+ and NbTi5+ centers. The experimental results are fitted to an Arrhenius relation and to quantum tunneling with the account of damping and phonon-assisted processes.
Electrode specific electropolymerization of ethylenedioxythiophene: Injection enhancement in organic transistors
Authors: Schroeder Raoul , Majewski Leszek A. , Grell Martin , Maunoury Jonathan , Gautrot Julien , Hodge Philip , Turner Mike
Published: September 2005

In this letter, we report on a method of decreasing the injection barrier from metal electrodes to organic semiconductors, namely pentacene and poly(triarylamine) (PTAA). This method involves the electrodeposition of PEDOT∕PSS on to the source electrode of an organic field-effect transistor (OFET) without unintended doping of the channel. In an OFET, the drain current injected at the PEDOT∕PSS coated gold electrode increases (2–6) fold over that of the current injected at the unmodified gold electrode, all else being the same. Furthermore, in the transistor with a polytriarylamine as the semiconductor, a decrease of the threshold voltage is observed.
A mechanism for hole generation by octahedral B6 clusters in silicon
Authors: Ohmori Kengo , Esashi Noboru , Takao Masakazu , Sato Daisuke , Hayafuji Yoshinori
Published: September 2005

The electronic structure and x-ray photoelectron spectra of silicon with octahedral B6 clusters are investigated using first-principles calculations. It is found that the B6 clusters act as double acceptors in silicon and that the simulated chemical shift of the B1s orbital signals of the B6 clusters in x-ray photoelectron spectra coincides with the chemical shift of B1s experimentally observed in as-implanted silicon at an extremely high dose of boron. These results reveal that the B6 clusters are the origin of hole carriers. We propose a mechanism of hole generation and a model of B6 cluster formation at implantation-induced divacancy sites.
Pyroelectric properties of 0.7PbMg1∕3(Nb0.9Ta0.1)2∕3O3–0.3PbTiO3 ceramics
Authors: Wang J. T. , Zhang C.
Published: September 2005

0.7 Pb Mg 1 ∕ 3 ( Nb 0.9 Ta 0.1 ) 2 ∕ 3 O 3 - 0.3 Pb Ti O 3 (PMNT–PT) ceramic was prepared with solid-state reaction method. The sample was characterized with x-ray diffraction and dielectric constant measurement, which ensured the high quality of the sample. The focus of this study is the pyroelectric properties of PMNT–PT ceramics. We measured the hysteresis loops at different temperatures and frequencies. The spontaneous and remnant polarizations as a function of temperature were obtained. An anomaly of remnant polarization as a function of temperature was found and discussed. Particularly, we measured the pyroelectric current with a Keithley 6485 Picoammeter. The maximum of the current is as high as 108nA∕cm2.
Novel phase measurement technique of the heterodyne laser interferometer
Authors: Choi Hyunseung , Park Kyihwan , La Jongpil
Published: September 2005

This article describes a novel phase measurement technique to increase the measurement velocity compared to the previous arc-tangent method in the heterodyne laser interferometer. The proposed method can reduce the calculation load because the pulse width modulation signal has a linear relation between the phase difference, while the nonlinear function such as arc tangent is required to demodulate the sinusoidal interferent signal. The brief analysis and measurement scheme of the system, and the experimental result using a Zeeman-stabilized He–Ne laser are presented. They demonstrate that the proposed phase measurement technique is proven to be three times faster and more robust than previous arc-tangent method.
Tunable multiferroic properties in nanocomposite PbTiO3–CoFe2O4 epitaxial thin films
Authors: Murakami M. , Chang K.-S. , Aronova M. A. , Lin C.-L. , Yu Ming H. , Simpers J. Hattrick , Wuttig M. , Takeuchi I. , Gao C. , Hu B. , Lofland S. E. , Knauss L. A. , Bendersky L. A.
Published: September 2005

We report on the synthesis of PbTiO3–CoFe2O4 multiferroic nanocomposites and continuous tuning of their ferroelectric and magnetic properties as a function of the average composition on thin-film composition spreads. The highest dielectric constant and nonlinear dielectric signal was observed at (PbTiO3)85–(CoFe2O4)15, where robust magnetism was also observed. Transmission electron microscopy revealed a pancake-shaped epitaxial nanostructure of PbTiO3 on the order of 30 nm embedded in the matrix of CoFe2O4 at this composition. Composition dependent ferroics properties observed here indicate that there is considerable interdiffusion of cations into each other.
Formation of InAs wetting layers studied by cross-sectional scanning tunneling microscopy
Authors: Offermans P. , Koenraad P. M. , Nötzel R. , Wolter J. H. , Pierz K.
Published: September 2005

We show that the composition of (segregated) InAs wetting layers (WLs) can be determined by either direct counting of the indium atoms or by analysis of the outward displacement of the cleaved surface as measured by cross-sectional scanning tunneling microscopy. We use this approach to study the effects of the deposited amount of indium, the InAs growth rate, and the host material on the formation of the WLs. We conclude that the formation of (segregated) WLs is a delicate interplay between surface migration, strain-driven segregation, and the dissolution of quantum dots during overgrowth.
Architecture and engineering of a supramolecular functional material by manipulating the nanostructure of fiber network
Authors: Li Jing-Liang , Liu Xiang-Yang
Published: September 2005

Three-dimensional fiber networks were created from an organogel system consisting mainly of elongated fibrils by using a nonionic surfactant as an additive. The presence of the surfactant molecules manipulates the network structure by enhancing the mismatch nucleation on the growing fiber tips. Both the fiber network structure and the rheological properties of the material can be finely tuned by changing the surfactant concentration, which provides a robust approach to the engineering of supramolecular soft functional materials.
A candidate LiBH4 for hydrogen storage: Crystal structures and reaction mechanisms of intermediate phases
Authors: Kang Jeung Ku , Kim Se Yun , Han Young Soo , Muller Richard P. , Goddard William A.
Published: September 2005

First-principles calculation and x-ray diffraction simulation methods have been used to explore crystal structures and reaction mechanisms of the intermediate phases involved in dehydriding of LiBH4. LiBH4 was found to dehydride via two sequential steps: first dehydriding through LiBH, followed by the dehydriding of LiBH through LiB. The first step, which releases 13.1wt.% hydrogen, was calculated to have an activation barrier of 2.33eV per formula unit and was endothermic by 1.28eV per formula unit, while the second step was endothermic by 0.23eV per formula unit. On the other hand, if LiBH4 and LiBH each donated one electron, possibly to the catalyst doped on their surfaces, it was found that the barrier for the first step was reduced to 1.50eV. This implies that the development of the catalyst to induce charge migration from the bulk to the surface is essential to make LiBH4 usable as a hydrogen storage material in a moderate temperature range, which is also important to stabilize the low-temperature structure of Pnma (no. 62) LiBH on dehydrogenation. Consequently, the high 13.1wt.% hydrogen available from the dehydriding of LiBH4 and LiBH and their phase stability on Pnma when specific catalysts were used suggest that LiBH4 has good potential to be developed as the hydrogen storage medium capable of releasing the Department of Energy target of 6.5wt.% for a hydrogen fuel cell car in a moderate temperature range.
Defect dissolution in strain-compensated stacked InAs∕GaAs quantum dots grown by metalorganic chemical vapor deposition
Authors: Nuntawong N. , Huang S. , Jiang Y. B. , Hains C. P. , Huffaker D. L.
Published: September 2005

We report a highly effective growth technique to both dissolve large islands and prevent further defect propagation in closely spaced (15nm) stacked quantum dot (QD) active regions while maintaining an emission wavelength >1.3μm. Island dissolution is accomplished via an In flush, which is an AsH3 pause inserted into the growth sequence just after each QD layer is capped. The low V∕III ratio enables the flushing of surface In atoms from the defect sites while the fully capped QDs remain intact. This technique eliminates the need for in situ annealing that activates the In flush in other growth scenarios and results in large emission blueshift. Strain propagation within the closely spaced QD stacks is reduced by GaP strain-compensation layers. Room-temperature photoluminescence confirms ground-state emission wavelength >1.34μm. Atomic force microscopy and transmission electron microscopy confirm improved surface morphology and crystalline quality of stacked QD active regions. The resulting structures are suitable for long-wavelength lasers, especially vertical cavity surface-emitting laser applications in which high modal gain is attractive.
Iron(III) Fluoride: A Highly Efficient and Versatile Catalyst for the Protection of Carbonyl Compounds under Solvent-Free Conditions
Authors: Bandgar Babasaheb P. , Kamble Vinod T. , Kulkarni Ashwini
Published: September 2005

Carbonyl compounds are successfully converted into oxathioacetals and dithioacetals with 2-mercaptoethanol and ethane-1,2-dithiol using a catalytic amount of iron(iii) fluoride under solvent-free conditions. The catalysts were recovered and reused in various runs without affecting the efficiency of the process.
Lupane-Triterpene Esters from the Leaves of Ceriops decandra (Griff.) Ding Hou
Authors: Ponglimanont Chanita , Thongdeeying Pakakrong
Published: September 2005

Two novel triterpene esters were isolated from the leaves of Ceriops decandra in addition to 16 known triterpenes: lupenone 3, lupeol 4, betulinaldehyde 5, 3β-Z-coumaroyllupeol 6, 3β-E-coumaroyllupeol 7, 3-epi-betulinic acid 8, betulin 9, betulinic acid 10, 3β-E-feruloylbetulin 11, 30-nor-lup-3β-ol-20-one 12, 3β-E-caffeoyllupeol 13, lup-20(29)-en-3β,30-diol 14, 3β-hydroxylupan-29-oic acid 15, 3β,20-dihydroxylupane 16, and a mixture of oleanolic and ursolic acid 17 and 18. The new compounds were determined by spectroscopic methods to be 3β-E-feruloyllupeol 1 and 3β-Z-feruloyllupeol 2. Compounds 3 and 5–16 were reported for the first time as metabolites of C. decandra.
Selective Carbonyl Propargylation Mediated by SnCl2/NiCl2-KI in Water
Authors: Wang Jun , Miao Xiao-Peng , Yuan Gu
Published: September 2005

Propargylation of carbonyl compounds to produce homopropargylic alcohols plays a very important role in synthetic organic and pharmaceutical chemistry. A novel method that carbonyl compounds and propargyl halide were mediated by SnCl2/NiCl2-KI in water at room temperature was developed by us to successfully synthesize homopropargylic alcohols in good yields. The reactions were carried out in an environmentally friendly solution and under mild conditions.
Solventless Rapid Synthesis of Oxime, Semicarbazone, and Phenylhydrazone Derivatives from Carbonyl Compounds under Microwave Conditions
Authors: Kamakshi R. , Reddy Boreddy S. R.
Published: September 2005

A rapid and efficient method for the synthesis of oximes, semicarbazones, and phenylhydrazones has been reported under solventless conditions using microwave irradiation.
A uudd Cyclic Water Tetramer and an Opened Octameric Water Cluster in the Charge-Transfer Salts of the Bipyridinium Cation
Authors: Sun Yan-qiong , Zhang Jie , Ju Zhan-feng , Yang Guo-Yu
Published: September 2005

Two novel charge-transfer salts, [(Bpyph)(SCN)2]·2H2O 1 and {(HBpyph)[Fe(CN)6]}·5.5H2O 2, have been synthesized and characterized using elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction studies. Compound 1 is the first bipyridinium charge-transfer salt containing a cyclic water tetramer, in which the uudd cyclic water tetramers built from four symmetry related water molecules join the Bpyph2+ cations to the dimer by hydrogen bonds between the water molecules and the nitrogen atoms of Bpyph2+. The cooperation of the hydrogen-bonding and π–π stacking interactions between the pyridyl groups results in the formation of an infinite ribbon with a herringbone arrangement. An opened water octamer has been observed in 2. It presents a new association mode of water molecules that is not predicted theoretically nor found experimentally. The water octamer is hydrogen-bonded to two HBpyph3+ cations and two [Fe(CN)6]3− anions to form water octamer-bridged HBpyPh-Fe(CN)6 dimers, which are further connected to each other via π–π offset stacking interactions to generate an infinite one-dimensional ribbon.
Stereoselective Isomerizations of 4-(2´-Chloro-3´-methoxyphenyl)-2,5-dimethyl-1,3-dioxolanes: Stereochemistry and Conformation of the Product 2-Benzopyrans
Authors: Giles Robin G. F. , Green Ivan R. , Li Shuk-Hui
Published: September 2005

Stereoselective isomerization of rel-(2R,4S,5R)-4-(2′-chloro-3′-methoxyphenyl)-2,5-dimethyl-1,3-dioxolane 5 with titanium(iv) chloride afforded solely rel-(1R,3R,4S)-5-chloro-4-hydroxy-6-methoxy-1,3-dimethyl-2-benzopyran 17 in high yield in which the conformation adopted by the dihydropyran ring minimized peri-interactions through stereochemistries that were axial for the C-3 methyl, pseudoaxial for the C-4 hydroxy and pseudoequatorial for the C-1 methyl groups. Similar isomerization of the individual rel-(2S,4R,5R)- and rel-(2R,4R,5R)-diastereoisomeric dioxolanes 6 and 7 gave solely the corresponding rel-(1S,3R,4R)-2-benzopyran 25 in which the orientations of the substituents at C-3, C-4 and C-1 were equatorial, pseudoaxial and pseudoequatorial respectively. These observations differed significantly from those previously made for the related isomerizations of the corresponding 4-(2′-chloro-5′-methoxyphenyl)-2,5-dimethyl-1,3-dioxolanes.
A Simple Approach to Micro-Patterned Surfaces by Breath Figures with Internal Structure Using Thermoresponsive Amphiphilic Block Copolymers
Authors: Nygard Alexandra , Davis Thomas P. , Barner-Kowollik Christopher , Stenzel Martina H.
Published: September 2005

Employing amphiphilic block copolymers in a casting process to obtain honeycomb-structured films via breath figures leads to a suborder of these porous films. A thermoresponsive block copolymer, polystyrene-block-poly(N-isopropyl acrylamide), was synthesized and used to test the arrangement of both blocks within the honeycomb-structured films. Contact angle measurements reveal that the surface of these films has a different composition compared to the structure of the pores. The pores were found to be enriched in hydrophilic sequences showing stimuli-responsive behavior, whereas the surface reacts like a typical hydrophobic porous film.
Nonlinear structured-illumination microscopy: Wide-field fluorescence imaging with theoretically unlimited resolution
Authors: Gustafsson Mats G. L.
Published: September 2005

Contrary to the well known diffraction limit, the fluorescence microscope is in principle capable of unlimited resolution. The necessary elements are spatially structured illumination light and a nonlinear dependence of the fluorescence emission rate on the illumination intensity. As an example of this concept, this article experimentally demonstrates saturated structured-illumination microscopy, a recently proposed method in which the nonlinearity arises from saturation of the excited state. This method can be used in a simple, wide-field (nonscanning) microscope, uses only a single, inexpensive laser, and requires no unusual photophysical properties of the fluorophore. The practical resolving power is determined by the signal-to-noise ratio, which in turn is limited by photobleaching. Experimental results show that a 2D point resolution of <50 nm is possible on sufficiently bright and photostable samples.
Sequential development of hematopoietic and cardiac mesoderm during embryonic stem cell differentiation
Authors: Kouskoff Valerie , Lacaud Georges , Schwantz Staci , Fehling Hans Jöerg , Keller Gordon
Published: September 2005

The ability to generate a wide spectrum of differentiated cell types from ES cells in culture offers a powerful approach for studying lineage induction and specification and a promising source of progenitors for cell replacement therapy. Although significant efforts are being made to optimize culture conditions for the generation of different cell populations from ES cells, the identification and efficient isolation of specific progenitors for many lineages within these cultures remains a major challenge. By specifically tracking hematopoietic and cardiac development, we demonstrate here that these two lineages arise from distinct mesoderm subpopulations that develop in sequential waves from pre-mesoderm cells. Access to these populations provides a unique approach to isolate and characterize the earliest progenitors of these lineages.
Comparative physical mapping links conservation of microsynteny to chromosome structure and recombination in grasses
Authors: Bowers John E. , Arias Miguel A. , Asher Rochelle , Avise Jennifer A. , Ball Robert T. , Brewer Gene A. , Buss Ryan W. , Chen Amy H. , Edwards Thomas M. , Estill James C. , Exum Heather E. , Goff Valorie H. , Herrick Kristen L. , Steele Cassie L. James , Karunakaran Santhosh , Lafayette Gmerice K. , Lemke Cornelia , Marler Barry S. , Masters Shelley L. , McMillan Joana M. , Nelson Lisa K. , Newsome Graham A. , Nwakanma Chike C. , Odeh Rosana N. , Phelps Cynthia A. , Rarick Elizabeth A. , Rogers Carl J. , Ryan Sean P. , Slaughter Keimun A. , Soderlund Carol A. , Tang Haibao , Wing Rod A. , Paterson Andrew H.
Published: September 2005

Nearly finished sequences for model organisms provide a foundation from which to explore genomic diversity among other taxonomic groups. We explore genome-wide microsynteny patterns between the rice sequence and two sorghum physical maps that integrate genetic markers, bacterial artificial chromosome (BAC) fingerprints, and BAC hybridization data. The sorghum maps largely tile a genomic component containing 41% of BACs but 80% of single-copy genes that shows conserved microsynteny with rice and partially tile a nonsyntenic component containing 46% of BACs but only 13% of single-copy genes. The remaining BACs are centromeric (4%) or unassigned (8%). The two genomic components correspond to cytologically discernible “euchromatin” and “heterochromatin.” Gene and repetitive DNA distributions support this classification. Greater microcolinearity in recombinogenic (euchromatic) than nonrecombinogenic (heterochromatic) regions is consistent with the hypothesis that genomic rearrangements are usually deleterious, thus more likely to persist in nonrecombinogenic regions by virtue of Muller's ratchet. Interchromosomal centromeric rearrangements may have fostered diploidization of a polyploid cereal progenitor. Model plant sequences better guide studies of related genomes in recombinogenic than nonrecombinogenic regions. Bridging of 35 physical gaps in the rice sequence by sorghum BAC contigs illustrates reciprocal benefits of comparative approaches that extend at least across the cereals and perhaps beyond.
Expression of activation-induced cytidine deaminase is regulated by cell division, providing a mechanistic basis for division-linked class switch recombination
Authors: Rush James S. , Liu Man , Odegard Valerie H. , Unniraman Shyam , Schatz David G.
Published: September 2005

Class switch recombination (CSR) is the process by which B cells alter the effector function properties of their Ig molecules. The decision to switch to a particular Ig isotype is determined primarily by the mode of B cell activation and cytokine exposure. More recent work indicates that the likelihood or probability of switching increases with successive cell divisions and is largely independent of time. We have analyzed different molecular features of CSR using cell division as a reference point in an attempt to gain insight into the mechanism of division-linked switching. Our results indicated that the accessibility of Ig heavy chain constant regions targeted for CSR was established after the cells had undergone a single cell division and did not vary significantly with subsequent cell divisions. In contrast, expression of activation-induced cytidine deaminase (AID) mRNA was found to increase with successive divisions, exhibiting a striking correlation with the frequency of CSR. Levels of AID in a given division remained constant at different time points, strongly suggesting that the regulation of AID expression was division-linked and independent of time. In addition, constitutive AID expression from a transgene accelerated division-linked CSR. Thus, we propose that the division-linked increase in AID expression provides an underlying molecular explanation for division-linked CSR.
Estrogen down-regulation of the corepressor N-CoR: Mechanism and implications for estrogen derepression of N-CoR-regulated genes
Authors: Frasor Jonna , Danes Jeanne M. , Funk Cory C. , Katzenellenbogen Benita S.
Published: September 2005

The nuclear receptor corepressor N-CoR plays a crucial role in the repressive activity of diverse transcription factors, yet little is known about what regulates its cellular level. We have found that estrogen markedly down-regulates N-CoR protein levels in estrogen receptor (ER)-positive breast cancer cells without affecting N-CoR mRNA levels, whereas levels of the related corepressor SMRT are unaffected. This effect is attributable to estrogen up-regulation of the ubiquitin ligase Siah2, which is a rapid and primary transcriptional response mediated by the ER, and precedes the loss of N-CoR. Treatment with proteasomal inhibitor or with small interfering RNA against Siah2 prevented the down-regulation of N-CoR by estrogen. Furthermore, the expression of 24-hydroxylase, a gene repressed by unliganded vitamin D receptor through its interaction with N-CoR, was up-regulated by estrogen and required Siah2. Our results illustrate a mechanism by which the estrogen–ER complex markedly reduces the level of N-CoR through a process involving the up-regulation of Siah2 and the subsequent targeting of N-CoR for proteasomal degradation. These findings reveal that, although estrogen directly regulates the transcription of many genes, by regulating a gene such as Siah2 it can exert profound “secondary” effects on cellular activity through mechanisms such as targeting regulatory proteins for degradation. This estrogen-evoked down-regulation of N-CoR could have a global derepressive effect on genes whose repression depends on N-CoR and thereby have broad impact on the activity of transcription factors and nuclear receptors whose actions involve N-CoR.
Nitric oxide regulates angiogenesis through a functional switch involving thrombospondin-1
Authors: Ridnour Lisa A. , Isenberg Jeffrey S. , Espey Michael G. , Thomas Douglas D. , Roberts David D. , Wink David A.
Published: September 2005

Nitric oxide (NO) donors have been shown to stimulate and inhibit the proliferation, migration, and differentiation of endothelial cellsin vitroand angiogenesisin vivo. Recently, we have shown distinct thresholds for NO to regulate p53-Ser-15P, phosphorylated extracellular signal-regulated kinase (pERK), and hypoxia inducible factor 1α in tumor cells. Because these signaling pathways also promote the growth and survival of endothelial cells, we examined their roles in angiogenic responses of venous endothelial cells and vascular outgrowth of muscle explants elicited by NO. An additional protein involved in the regulation of angiogenesis is thrombospondin-1 (TSP1), a matricellular glycoprotein known to influence adhesion, migration, and proliferation of endothelial cells. Here we demonstrate a triphasic regulation of TSP1 mediated by a slow and prolonged release of NO that depends on ERK phosphorylation. Under conditions of 5% serum, a 24-h exposure of NO donor (0.1–1,000 μM) mediated a triphasic response in the expression of TSP1 protein: decreasing at 0.1 μM, rebounding at 100 μM, and decreasing again at 1,000 μM. Under the same conditions, we observed a dose-dependent increase in P53 phosphorylation and inverse biphasic responses of pERK and mitogen-activated protein kinase phosphatase-1. Both the growth-stimulating activity of low-dose NO for endothelial cells and suppression of TSP1 expression were ERK-dependent. Conversely, exogenous TSP1 suppressed NO-mediated pERK. These results suggest that dose-dependent positive- and negative-feedback loops exist between NO and TSP1. Limiting TSP1 expression by positive feedback through the ERK mitogen-activated protein kinase pathway may facilitate switching to a proangiogenic state at low doses of NO.
Deletion ofXPCleads to lung tumors in mice and is associated with early events in human lung carcinogenesis
Authors: Hollander M. Christine , Philburn Robyn T. , Patterson Andrew D. , Velasco-Miguel Susana , Friedberg Errol C. , Linnoila R. Ilona , Fornace Albert J.
Published: September 2005

Chromosome 3p and 1p deletions are among the most frequent genetic changes in human lung cancer and although candidate tumor suppressor genes have been identified in these regions, no causative correlations have been drawn between deletion or mutation of these and lung carcinogenesis. We identifyXPCandGadd45aas genes within each of these regions involved in lung tumor initiation and progression, respectively. One hundred percent ofXPC-/- mice develop multiple spontaneous lung tumors with a minority progressing to non-small cell lung adenocarcinoma, occasionally with metastasis to adjacent lymph nodes. Deletion ofGadd45aalone does not lead to increased lung tumors in mice, but coupled with anXPCdeletion, it results in lung tumor progression. Analysis of published data indicated allelic loss ofXPCin most human lung tumors and allelic loss ofGadd45ain some human lung and other cancer types. Because DNA repair capacity is compromised inXPC+/- cells, it is possible that the loss of a singleXPCallele in the human lung might confer a mutator phenotype. Coupled with cigarette carcinogens, decreased DNA repair would lead to additional mutations in genes such as p53 that are frequent targets in lung cancer.
Recognition of peptide–MHC class I complexes by activating killer immunoglobulin-like receptors
Authors: Stewart C. Andrew , Laugier-Anfossi Fanny , Vély Frédéric , Saulquin Xavier , Riedmuller Jenifer , Tisserant Agnès , Gauthier Laurent , Romagné François , Ferracci Géraldine , Arosa Fernando A. , Moretta Alessandro , Sun Peter D. , Ugolini Sophie , Vivier Eric
Published: September 2005

Inhibitory receptors for MHC class I molecules increase the threshold of lymphocyte activation. Natural Killer (NK) cells express a large number of such inhibitory receptors, including the human killer Ig-like receptors (KIR). However, activating members of the KIR family have poorly defined ligands and functions. Here we describe the use of activating KIR tetramer reagents as probes to detect their ligands. Infection of cells with Epstein–Barr virus leads to expression of a detectable ligand for the activating receptor KIR2DS1. In this case, KIR2DS1 interacts with up-regulated peptide–MHC class I complexes on Epstein–Barr virus-infected cells in a transporter associated with antigen processing (TAP)-dependent manner. In tetramer-based cellular assays and direct affinity measurements, this interaction with MHC class I is facilitated by a broad spectrum of peptides. KIR2DS1 and its inhibitory homologue, KIR2DL1, share sensitivity to peptide sequence alterations at positions 7 and 8. These results fit a model in which activating and inhibitory receptors recognize the same sets of self-MHC class I molecules, differing only in their binding affinities. Importantly, KIR2DS1 is not always sufficient to trigger NK effector responses when faced with cognate ligand, consistent with fine control during NK cell activation. We discuss how our results for KIR2DS1 and parallel studies on KIR2DS2 relate to the association between activatingKIRgenes and susceptibility to autoimmune disorders.