bluuebunny/crossref_metadata_2025 huggingface dataset:
Graded ferroelectric capacitors with robust temperature characteristics
Authors: El-Naggar Mohamed Y. , Dayal Kaushik , Goodwin David G. , Bhattacharya Kaushik
Published: December 2006

Ferroelectric thin films offer the possibility of engineering the dielectric response for tunable components in frequency-agile rf and microwave devices. However, this approach often leads to an undesired temperature sensitivity. Compositionally graded ferroelectric films have been explored as a means of redressing this sensitivity, but experimental observations vary depending on geometry and other details. In this paper, we present a continuum model to calculate the capacitive response of graded ferroelectric films with realistic electrode geometries by accurately accounting for the polarization distribution and long-range electrostatic interactions. We show that graded c-axis poled BaxSr1−xTiO3 (BST) parallel plate capacitors are ineffective while graded a-axis poled BST coplanar capacitors with interdigitated electrodes are extremely effective in obtaining high and temperature-stable dielectric properties.
First principles phase diagram calculations for the wurtzite-structure systems AlN–GaN, GaN–InN, and AlN–InN
Authors: Burton B. P. , van de Walle A. , Kattner U.
Published: December 2006

First principles phase diagram calculations were performed for the wurtzite-structure quasibinary systems AlN–GaN, GaN–InN, and AlN–InN. Cluster expansion Hamiltonians that excluded, and included, excess vibrational contributions to the free energy, Fvib, were evaluated. Miscibility gaps are predicted for all three quasibinaries, with consolute points, (XC,TC), for AlN–GaN, GaN–InN, and AlN–InN equal to (0.50, 305K), (0.50, 1850K), and (0.50, 2830K) without Fvib, and (0.40, 247K), (0.50, 1620K), and (0.50, 2600K) with Fvib, respectively. In spite of the very different ionic radii of Al, Ga, and In, the GaN–InN and AlN–GaN diagrams are predicted to be approximately symmetric.
An ultrasensitive radio-frequency single-electron transistor working up to 4.2 K
Authors: Brenning Henrik , Kafanov Sergey , Duty Tim , Kubatkin Sergey , Delsing Per
Published: December 2006

We present the measurement of a radio-frequency single-electron transistor that displays a very high charge sensitivity of 1.9 μe∕Hz at 4.2 K. At 40 mK, the charge sensitivity is 0.9 and 1.0 μe∕Hz in the superconducting and normal state, respectively. The sensitivity was measured as a function of radio frequency amplitude at three different temperatures; 40 mK, 1.8, and 4.2 K.
Light- and bias-induced metastabilities in Cu(In,Ga)Se2 based solar cells caused by the (VSe-VCu) vacancy complex
Authors: Lany Stephan , Zunger Alex
Published: December 2006

We investigate theoretically light- and bias-induced metastabilities in Cu(In,Ga)Se2 (CIGS) based solar cells, suggesting the Se–Cu divacancy complex (VSe-VCu) as the source of this hitherto puzzling phenomena. Due to its amphoteric nature, the (VSe-VCu) complex is able to convert by persistent carrier capture or emission from a shallow donor into a shallow acceptor configuration, and vice versa, thereby changing in a metastable fashion the local net acceptor density inside the CIGS absorber of the solar cell, e.g., a CdS/CIGS heterojunction. In order to establish a comprehensive picture of metastability caused by the (VSe-VCu) complex, we determine defect formation energies from first-principles calculations, employ numerical simulations of equilibrium defect thermodynamics, and develop a model for the transition dynamics after creation of a metastable nonequilibrium state. We find that the (VSe-VCu) complex can account for the light-induced metastabilities, i.e., the “red” and “blue” illumination effects, as well as for the reverse-bias effect. Thus, our (VSe-VCu) model implies that the different metastabilities observed in CIGS share a common origin. A defect state in the band gap caused by (VSe-VCu) in the acceptor configuration creates a potentially detrimental recombination center and may contribute to the saturation of the open circuit voltage in larger-gap Cu(In,Ga)Se2 alloys with higher Ga content. Therefore, the presence of metastable defects should be regarded as a concern for solar cell performance.
Charging and discharging processes of carbon nanotubes probed by electrostatic force microscopy
Authors: Zdrojek M. , Mélin T. , Diesinger H. , Stiévenard D. , Gebicki W. , Adamowicz L.
Published: December 2006

Electrostatic properties of individually separated single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multiwalled carbon nanotubes (MWCNTs) deposited on insulating layers have been investigated by charge injection and electric force microscopy (EFM) experiments. Delocalized charge patterns are observed along the CNTs upon local injection from the EFM tip, corresponding to (i) charge storage in the nanotubes and to (ii) charge trapping in the oxide layer along the nanotubes. The two effects are dissociated easily for CNTs showing abrupt discharge processes in which the charge stored in the CNT are field emitted back to the EFM tip, while trapped oxide charge can subsequently be imaged by EFM, clearly revealing field-enhancement patterns at the CNT caps. The case of continuous discharge processes of SWCNTs, DWCNTs, and MWCNTs is discussed, as well as the evolution of the discharge time constants with respect to the nanotube diameter.
Mobility and charge trapping comparison for crystalline and amorphous HfON and HfSiON gate dielectrics
Authors: Kirsch P. D. , Quevedo-Lopez M. A. , Krishnan S. A. , Lee B. H. , Pant G. , Kim M. J. , Wallace R. M. , Gnade B. E.
Published: December 2006

Mobility and charge trapping results for n-channel transistors gated with HfON and HfSiON are reported as a function of physical thickness (Tphys). HfSiON peak mobility improves with Tphys over the range of 1.8–2.7nm, achieving 260cm2∕Vs at 2.7nm. However, HfSiON mobility degrades at a critical thickness, Tphys⩾3.5nm. HfON mobility response is different. It is a maximum (230cm2∕Vs) at Tphys=1.2nm but degrades with increasing thickness, particularly for the critical thickness ⩾2.5nm. Mobility loss and trapping occur concurrently for both dielectrics when these critical thicknesses are exceeded. These critical thicknesses are the minimum required to achieve dielectric crystallization. Interfacial defects along crystalline grain boundaries may negatively impact electrical performance of both dielectrics.
Thickness profiles through fatigued bulk ceramic lead zirconate titanate
Authors: Balke Nina , Lupascu Doru C. , Blair Thomas , Gruverman Alexei
Published: December 2006

Wedge-cut samples of fatigued ferroelectric lead zirconate titanate ceramics were investigated using piezoresponse force microscopy in conjunction with conventional electrical hysteresis measurements. The local clamping of domains is monitored at different depths in the sample. The coercive fields in grains near the electrodes differ for different materials and preparation methods of the electrodes. For silver, fatigue consistently generates a space charge in the depth of the sample. For platinum electrodes, the fatigue behavior scatters strongly. Microscopically, it either occurs directly underneath the electrodes or resembles the behavior of the silver electrodes in other samples.
Study of the negative resistance phenomenon in transition metal oxide films from a statistical mechanics point of view
Authors: Jeong Doo Seok , Choi Byung Joon , Hwang Cheol Seong
Published: December 2006

The mechanism of the differential negative resistance behavior observable in transition metal oxides such as TiO2, NiO, and Nb2O5 is theoretically developed in terms of the order to disorder transition of local conducting pathways, so called filaments, by applying statistical mechanics. Joule heat is taken as a heat source giving rise to an increase of temperature in the filaments. The free energy of the filaments is evaluated by taking the site percolation model as well as the nonhomogeneity of an order parameter into account. It is concluded that the transition of a filament from the conducting state, which is dominated by the internal bonding energy term, to the nonconducting state is due to an increased contribution of the entropy term to the system’s total energy at a higher temperature. The calculation results also show that the rupture of a filament occurs in the middle of the filament when the filaments are in contact with thermally conducting metal electrodes, such as Pt.
Random polycrystals of grains containing cracks: Model of quasistatic elastic behavior for fractured systems
Authors: Berryman James G. , Grechka Vladimir
Published: December 2006

A model study on fractured systems was performed using a concept that treats isotropic cracked systems as ensembles of cracked grains by analogy to isotropic polycrystalline elastic media. The approach has two advantages: (a) Averaging performed is ensemble averaging, thus avoiding the criticism legitimately leveled at most effective medium theories of quasistatic elastic behavior for cracked media based on volume concentrations of inclusions. Since crack effects are largely independent of the volume they occupy in the composite, such a non-volume-based method offers an appealingly simple modeling alternative. (b) The second advantage is that both polycrystals and fractured media are stiffer than might otherwise be expected, due to natural bridging effects of the strong components. These same effects have also often been interpreted as crack-crack screening in high-crack-density fractured media, but there is no inherent conflict between these two interpretations of this phenomenon. Results of the study are somewhat mixed. The spread in elastic constants observed in a set of numerical experiments is found to be very comparable to the spread in values contained between the Reuss and Voigt bounds for the polycrystal model. Unfortunately, computed Hashin-Shtrikman bounds are much too tight to be in agreement with the numerical data, showing that polycrystals of cracked grains tend to violate some implicit assumptions of the Hashin-Shtrikman bounding approach. However, the self-consistent estimates obtained for the random polycrystal model are nevertheless very good estimators of the observed average behavior.
Spectral matching consideration in the design of a novel x-ray image intensifier
Authors: Yu Chunyu , Chang Benkang , Wei Dianxiu
Published: December 2006

In this article, a novel x-ray image intensifier is introduced. It is mainly composed of an x-ray intensifying screen and a low-light-level (L3) image intensifier. In order to obtain a bright enough image, the spectral compatibility among three different combinations of the x-ray intensifying screen and the photocathode is analyzed. The comparison indicates that a (Zn,Cd)S:Ag screen is superior to either a CaWO4 screen or a Gd2O2S:Tb screen when combined with the Super S25 photocathode and spectral compatibility analysis is a useful guide when designing an optoelectronic imaging device.
Nonlinear modulated dust lattice wave packets in two-dimensional hexagonal dust crystals
Authors: Farokhi B. , Kourakis I. , Shukla P. K.
Published: December 2006

The amplitude modulation of dust lattice waves (DLWs) propagating in a two-dimensional hexagonal dust crystal is investigated in a continuum approximation, accounting for the effect of dust charge polarization (dressed interactions). A dusty plasma crystalline configuration with constant dust grain charge and mass is considered. The dispersion relation and the group velocity for DLWs are determined for wave propagation in both longitudinal and transverse directions. The reductive perturbation method is used to derive a (2+1)-dimensional nonlinear Schrödinger equation (NLSE). New expressions for the coefficients of the NLSE are derived and compared, for a Yukawa-type potential energy and for a “dressed” potential energy, taking into account interaction and geometric nonlinearities.
Physics of the dusty Hall plasmas
Authors: Pandey B. P. , Vranjes J.
Published: December 2006

The presence of the immobile charged dust in the plasma modifies the scale over which the Hall effect becomes important. For a positively charged dusty background this scale can become arbitrarily large. It is shown that the emergence of the Hall effect in an immobile charged background is related to the presence of an electric field that operates over the plasma gyration period. The generalized flux, which is a combination of the magnetic and fluid vortex flux, can decay due to the presence of the charge or the density inhomogeneities. The normal mode behavior of such a dusty plasma could be very different for positively and negatively charged grains. Whereas for negatively charged grains the usual magnetohydrodynamic (MHD) modes are present in the system, for positively charged grains, the Alfvén mode may not exist if Znd∼ne, where Z is the charge of the dust and nd(ne) are the dust (electron) number densities. In the presence of the inhomogeneities, inertialess dusty plasma is subject to the Hall instability. It is shown that the growth rate of the Hall instability is proportional to the whistler frequency. Since Hall drift is nondissipative in nature, this instability can play important role in redistributing the magnetic energy from the large to small scales.
Experimental investigation of the Soret effect in acetone/water and dimethylsulfoxide/water mixtures
Authors: Ning Hui , Wiegand Simone
Published: December 2006

The thermal diffusion behavior of acetone/water and dimethylsulfoxide(DMSO)/water mixtures has been experimentally investigated by a transient holographic grating technique named thermal diffusion forced Rayleigh scattering (TDFRS). For both systems a sign change of the Soret coefficient ST with varying water content has been predicted by simulations [C. Nieto Draghi et al., J. Chem. Phys. 122, 114503 (2005)]. The sign change of ST is confirmed by the experiment. Except for equimolar concentrations of acetone/water the agreement between the experimental and simulation data is reasonable.
Nanofractal structure consisting of nanoparticles produced by ultrashort laser pulses
Authors: Nishikawa Kumiko , Takano Kei , Miyahara Hidekazu , Kawamura Tohru , Okino Akitoshi , Hotta Eiki , Nayuki Takuya , Oishi Yuji , Fujii Takashi , Wang Xiaofang , Nemoto Koshichi
Published: December 2006

By irradiating subpicosecond laser onto an iron plate, a nanofibrous structure consisting of iron nanoparticles with diameters less than 12nm was produced. The nanofibrous structure was found to be three-dimensional fractal, and its fractal dimension measured from field-emission scanning electron microscopy images conserved the same fractal dimension of 1.73 in the wide-scale range from 30nmto60μm, and the smallest fractal structure was less than 10nm. The growth of this fractal is related to the cluster-cluster aggregation model, and it suggests that the fractal structure grew by the attachment of clusters consisting of nanoparticles.
Epitaxial semimetallic HfxZr1−xB2 templates for optoelectronic integration on silicon
Authors: Roucka Radek , An YuJin , Chizmeshya Andrew V. G. , Tolle John , Kouvetakis John , D'Costa Vijay R. , Menéndez José , Crozier Peter
Published: December 2006

High quality heteroepitaxial HfxZr1−xB2 (x=0–1) buffers were grown directly on Si(111). The compositional dependence of the film structure and ab initio elastic constants were used to show that hexagonal HfxZr1−xB2 possess tensile in-plane strain (0.5%) as grown. High quality HfB2 films were also grown on strain compensating ZrB2-buffered Si(111). Initial reflectivity measurements of thick ZrB2 films agree with first principles calculations which predict that the reflectivity of HfB2 increases by 20% relative to ZrB2 in the 2–8eV range. These tunable structural, thermoelastic, and optical properties suggest that HfxZr1−xB2 templates should be suitable for broad integration of III nitrides with Si.
Combining reactive and configurational-bias Monte Carlo: Confinement influence on the propene metathesis reaction system in various zeolites
Authors: Jakobtorweihen S. , Hansen N. , Keil F. J.
Published: December 2006

In order to efficiently calculate chemical equilibria of large molecules in a confined environment the reactive Monte Carlo technique is combined with the configurational-bias Monte Carlo approach. To prove that detailed balance is fulfilled the acceptance rule for this combination of particular Monte Carlo techniques is derived in detail. Notably, by using this derivation all other acceptance rules of any Monte Carlo trial moves usually carried out in combination with the configurational-bias Monte Carlo approach can be deduced from it. As an application of the combination of reactive and configurational-bias Monte Carlo the influence of different zeolitic confinements (MFI, TON, LTL, and FER) on the reaction equilibrium and the selectivity of the propene metathesis reaction system was investigated. Compared to the bulk phase the conversion is increased significantly. The authors study this reaction system in the temperature range between 300 and 600K, and the pressure range from 1to7bars. In contrast to the bulk phase, pressure and temperature have a strong influence on the composition of the reaction mixture in confinement. At low pressures and temperatures both conversion and selectivity are highest. Furthermore, the equilibrium composition is strongly dependent on the type of zeolite. This demonstrates the important role of the host structure in catalytic systems.
Nanofabrication on ZnO nanowires
Authors: Zhan Jinhua , Bando Yoshio , Hu Junqing , Golberg Dmitri
Published: December 2006

ZnO nanowires were subjected to convergent electron beam irradiation in a 300kV transmission electron microscope. The size of perforated hexagonal pores generated by irradiation can vary with the beam size. An irradiated area is denuded layer by layer via removal of Zn and O atoms. The polar ZnO surfaces have a higher resistance to irradiation than the unpolar ones. Ultrathin nanobridges, ∼1nm thick or less, were generated through deliberate removal of Zn and O atomic monolayers.
Growth and thermal stability of GaPO4 epitaxial thin films
Authors: Pedarnig J. D. , Roither S. , Peruzzi M.
Published: December 2006

Thin epitaxial films of gallium orthophosphate (GaPO4) are grown on α-quartz (SiO2) substrates. Here, amorphous stoichiometric precursor layers fabricated by pulsed-laser deposition on (001) SiO2 substrates are transformed to crystalline GaPO4 by postannealing in air at 650–950°C. Epitaxial films with thicknesses up to 300nm exhibit strong in-plane and out-of-plane textures (angular widths <0.6°). Long-term annealing in air at temperatures above the α- to β-phase transition of the quartz substrate (573°C) does not degrade the films.
Quantifying stacking faults and vacancies in thin convectively assembled colloidal crystals
Authors: Wei H. , Meng L. , Jun Y. , Norris D. J.
Published: December 2006

The authors determine the concentration and distribution of stacking faults and vacancies in colloidal crystals between 3 and 11 layers thick grown via convective assembly. The average stacking parameter ⟨α⟩ rises from 0.1 for samples 3 layers thick to 0.8 for ⩾6 layers. For samples ⩾6 layers, the authors also find that the stacking faults are less likely to be near the substrate. The average vacancy concentration is 2.1×10−3 per unit cell. Surprisingly, the layer-averaged vacancy concentration is lowest in the layer nearest the substrate and highest in the next nearest layer.
Optical characterization of intersubband transitions in ZnxCd1−xSe∕Znx′Cdy′Mg1−x′−y′Se multiple quantum well structures by contactless electroreflectance
Authors: Lu H. , Shen A. , Charles W. , Yokomizo I. , Tamargo M. C. , Franz K. J. , Gmachl C. , Muñoz M.
Published: December 2006

Contactless electroreflectance was measured at room temperature to characterize a wide range of the possible optical transitions in ZnxCd1−xSe∕Znx′Cdy′Mg1−x′−y′Se multi-quantum-well structures grown by molecular beam epitaxy. Based on these measurements, the authors predict and then verify the anticipated intersubband transition energies. They investigate a representative Zn0.5Cd0.5Se∕Zn0.20Cd0.19Mg0.61Se structure, for which the E1-E2 transition energy is predicted to be 178meV (6.97μm). Intersubband absorption using Fourier transform infrared spectroscopy exhibits a peak at 180meV (6.89μm), in excellent agreement with the contactless electroreflectance measurements.
Size-dependent Schottky Barrier Height in self-assembled gold nanoparticles
Authors: Ruffino F. , Grimaldi M. G. , Giannazzo F. , Roccaforte F. , Raineri V.
Published: December 2006

(Au nanocluster)/6H-SiC Schottky contacts were electrically characterized by conductive atomic force microscopy, collecting a high number of current-voltage (I-V) curves. The main observed result is the Schottky barrier height (SBH) dependence on the cluster size. The SBH increases from 1.35±0.01to1.77±0.01eV when the cluster size increases from 1.5to6.8nm and it tends, asymptotically, to the theoretical SBH of the macroscopic contact Au∕SiC (∼1.9eV). This behavior is interpreted considering the thermoionic transport theory through the Au cluster/SiC barrier coupled with the concept of ballistic transport within few electron quantum dots.
Athermal crystallization induced by electronic excitations in ion-irradiated silicon carbide
Authors: Benyagoub A. , Audren A. , Thomé L. , Garrido F.
Published: December 2006

Silicon carbide single crystals were irradiated at room temperature with low energy I ions and high energy Pb ions. It is found that the damaged layer formed by the elastic collisions generated during low energy I ion irradiation can readily be removed by the electronic excitations induced by swift Pb ions. This effect occurs at a temperature quite below that at which the conventional ion-beam induced crystallization process is generally achieved by nuclear energy loss. This finding is interesting both from a fundamental point of view for the understanding of the interaction of swift heavy ions with solids and for a large number of technological applications.
Imaging of quantum interference patterns within a quantum point contact
Authors: da Cunha Carlo R. , Aoki Nobuyuki , Morimoto Takahiro , Ochiai Yuichi , Akis Richard , Ferry David K.
Published: December 2006

Visualization of quantum interference patterns has been obtained within a quantum point contact using scanning gate microscopy. The area distribution of the interference pattern is shown to be consistent with the interference area obtained from the magnetoconductance fluctuations of a quantum point contact. Both distributions follow the Gaussian unitary ensemble, corresponding to chaotic behavior. The interference is caused by the random potential fluctuations within the channel, which is modified by the tip-induced potential.
Thin film interference in the optomechanical response of micromechanical silicon cantilevers
Authors: Wilkinson Paul R. , Gimzewski James K.
Published: December 2006

The mechanical response of uncoated silicon microcantilevers is shown to modulate as a function of incident wavelength. Cantilever motion is measured interferometrically, using phase sensitive detection in response to a mechanically chopped excitation source. Thin film interference modeling shows that the fraction of absorbed light within the cantilever varies periodically over the range of 450–1000nm, in excellent agreement with the measurements. The results show that the optomechanical responsivity of these cantilevers can be tuned due to the effect via an appropriate selection of incident wavelength, incidence angle, lever thickness, and optical constants of the lever.
Sheet geometry enhanced giant piezoelectric coefficients
Authors: Shih Wan Y. , Luo Hongyu , Li Huidong , Martorano Christian , Shih Wei-Heng
Published: December 2006

The authors report a giant piezoelectric coefficient, −d31=2000pm∕V in substrate-free polycrystalline (Pb(Mg1∕3Nb2∕3)O3)0.63(PbTiO3)0.37 (PMN-37PT) sheets at E⩾7kV∕cm, larger than the −d31=930pm∕V exhibited by specially cut commercial PMN-PT single crystals and 300–500pm∕V of polycrystalline bulk PMN-37PT. X-ray diffraction indicated due to the thin sheet geometry the present PMN-37PT sheets contained about 60vol% of the tetragonal a and rhombohedral domains even after poling. At large fields, these tetragonal a and rhombohedral domains switched to the tetragonal c domains to result in the giant d31 enhancement at high fields.
Effect of thermal treatment on oxygen stoichiometry and transport properties of SrRuO3 thin films
Authors: Sakai Joe , Ito Nobuaki , Ito Shin-Ichi , Takahashi Kenji , Funakubo Hiroshi
Published: December 2006

The oxygen content was evaluated using the non-Rutherford elastic resonant scattering method for SrRuO3 (SRO) thin films deposited on (001) SrTiO3 substrates by a sputtering technique, followed by postannealing in various conditions. The resistivity of the SRO film annealed in 50mTorr Ar at 500°C was not higher than 4×10−3Ωcm in the range of 5–300K despite its oxygen deficiency (=2.7). On the other hand, the SRO film annealed in an Ar+1% O2 mixture gas of 50mTorr at 700°C retained its oxygen stoichiometry and maintained its resistivity below 5×10−4Ωcm.
Lewis-Base Adducts of Main Group 1 Metal-Compounds. XII. Synthesis and Crystal Structure of (2,2′-Bipyridine)(bromo)(propan-2-ol)lithium(I)
Authors: Skelton BW , Whitaker CR , White AH
Published: December 2006

The title compound is readily crystallized from a 1 : 1 mixture of 2,2′-bipyridine and lithium(I) bromide in propan-2-ol; its structure has been established by single-crystal X-ray methods at c. 295 K. Crystals are monoclinic, P21/c, a 10.942(3), b 15.060(4), c 9.359(3)Ǻ, β 108.57(2)°, Z = 4; R was 0.050 for 1820 'observed' reflections. In the four-coordinate LiBrN2O environment, Li- Br,O are 2.47(1), 1.94(1)Ǻ, and Li-N are 2.05(1), 2.07(1)Ǻ.
Carboxyl-modified single-walled carbon nanotubes selectively induce human telomeric i-motif formation
Authors: Li Xi , Peng Yinghua , Ren Jinsong , Qu Xiaogang
Published: December 2006

As the leading nanodevice candidate, single-walled carbon nanotubes (SWNTs) have potential therapeutic applications in gene therapy and novel drug delivery. We found that SWNTs can inhibit DNA duplex association and selectively induce human telomeric i-motif DNA formation by binding to the 5′-end major groove under physiological conditions or even at pH 8.0. SWNT binding to telomeric DNA was studied by UV melting, NMR, S1 nuclease cleavage, CD, and competitive FRET methods. These results suggest that SWNTs might have the intriguing potential to modulate human telomeric DNA structures
in vivo
, like biologically relevant B-A and B-Z DNA transitions, which is of great interest for drug design and cancer therapy.
Axonal mRNA transport and localized translational regulation of κ-opioid receptor in primary neurons of dorsal root ganglia
Authors: Bi Jing , Tsai Nien-Pei , Lin Ya-Ping , Loh Horace H. , Wei Li-Na
Published: December 2006

κ-opioid receptor (KOR) is detected pre- and postsynaptically, but the subcellular localization, translation, and regulation ofkormRNA in presynaptic compartments of sensory neurons remain elusive.In situhybridization detected axonal distribution ofkormRNA in primary neurons of dorsal root ganglia (DRG). The MS2-fused GFP trackedkormRNA transport from DRG neuronal soma to axons, requiring its 5′ and 3′ UTRs. In Campenot chambers, axonal translation ofkormRNA was demonstrated for DRG neurons, which depended on its 5′ UTR and was stimulated by KCl depolarization. KCl depolarization of DRG neurons rendered redistribution ofkormRNA from the postpolysomal fraction to the translationally active polysomal fraction. This study provided evidence for mRNA transport and regulation of presynaptic protein synthesis of nonstructural proteins like KOR in primary sensory neurons and demonstrated a mechanism of KCl depolarization-stimulated axonal mRNA redistribution for localized translational regulation.
Identification of a biomarker for sleep drive in flies and humans
Authors: Seugnet Laurent , Boero Jaime , Gottschalk Laura , Duntley Stephen P. , Shaw Paul J.
Published: December 2006

It is a common experience to sacrifice sleep to meet the demands of our 24-h society. Current estimates reveal that as a society, we sleep on average 2 h less than we did 40 years ago. This level of sleep restriction results in negative health outcomes and is sufficient to produce cognitive deficits and reduced attention and is associated with increased risk for traffic and occupational accidents. Unfortunately, there is no simple quantifiable marker that can detect an individual who is excessively sleepy before adverse outcomes become evident. To address this issue, we have developed a simple and effective strategy for identifying biomarkers of sleepiness by using genetic and pharmacological tools that dissociate sleep drive from wake time in the model organism
Drosophila melanogaster
. These studies have identified a biomarker,
Amylase
, that is highly correlated with sleep drive. More importantly, both salivary Amylase activity and mRNA levels are also responsive to extended waking in humans. These data indicate that the fly is relevant for human sleep research and represents a first step in developing an effective method for detecting sleepiness in vulnerable populations.
Identification of alterations in DNA copy number in host stromal cells during tumor progression
Authors: Pelham Robert J. , Rodgers Linda , Hall Ira , Lucito Robert , Nguyen Ken C. Q. , Navin Nicholas , Hicks James , Mu David , Powers Scott , Wigler Michael , Botstein David
Published: December 2006

The interactions between cancer cells and the surrounding host stromal tissue play a critical role in tumor progression and metastasis, but the molecular nature of this relationship remains largely uncharacterized. Furthermore, although genetic changes of neoplastic cells in tumors contribute significantly to tumor progression, it is not known whether similar changes occur in the adjacent host stromal microenvironment and whether they contribute to or inhibit tumorigenesis. To address this question in an unbiased and genome-wide manner, we applied high-resolution DNA copy number analysis to murine stromal DNA isolated from human xenograft tumors that were formed in immunodeficient mice. We show that numerous amplifications and deletions are found within the host stromal microenvironment, suggesting that alterations in host DNA copy number can occur and may play a significant role in modifying tumor–stromal interactions.
Combinatorial pattern recognition receptor signaling alters the balance of life and death in macrophages
Authors: Seimon Tracie A. , Obstfeld Amrom , Moore Kathryn J. , Golenbock Douglas T. , Tabas Ira
Published: December 2006

Macrophage pattern recognition receptors (PRRs) play key roles in innate immunity, but they also may contribute to disease processes under certain pathological conditions. We recently showed that engagement of the type A scavenger receptor (SRA), a PRR, triggers JNK-dependent apoptosis in endoplasmic reticulum (ER)-stressed macrophages. In advanced atherosclerotic lesions, the SRA, activated JNK, and ER stress are observed in macrophages, and macrophage death in advanced atheromata leads to plaque necrosis. Herein, we show that SRA ligands trigger apoptosis in ER-stressed macrophages by cooperating with another PRR, Toll-like receptor 4 (TLR4), to redirect TLR4 signaling from prosurvival to proapoptotic. Common SRA ligands activate both TLR4 signaling and engage the SRA. The TLR4 effect results in activation of the proapoptotic MyD88-JNK branch of TLR4, whereas the SRA effect silences the prosurvival IRF-3-IFN-β branch of TLR4. The normal cell-survival effect of LPS-induced TLR4 activation is converted into an apoptosis response by immunoneutralization of IFN-β, and the apoptosis effect of SRA ligands is converted into a cell-survival response by reconstitution with IFN-β. Thus, combinatorial signaling between two distinct PRRs results in a functional outcome-macrophage apoptosis that does not occur with either PRR alone. PRR-induced macrophage death may play important roles in advanced atherosclerosis and in other innate immunity-related processes in which the balance between macrophage survival and death is critical.
The Effects of Cognitive Demand upon Relationships between Working Memory and Cognitive Skills
Authors: St Clair-Thompson Helen L.
Published: December 2006

The present study explored the effects of cognitive demand upon relationships between working memory and cognitive skills. Both children and adults were tested on a measure of short-term memory and three measures of counting span, which varied in cognitive demand. When statistically controlling for short-term memory and the speed of counting operations, the more demanding the counting-span task, the closer its relationship with cognitive skills. The results are discussed in terms of practical and theoretical implications for working memory research.
Roles of type II myosin and a tropomyosin isoform in retrograde actin flow in budding yeast
Authors: Huckaba Thomas M. , Lipkin Thomas , Pon Liza A.
Published: December 2006

Retrograde flow of cortical actin networks and bundles is essential for cell motility and retrograde intracellular movement, and for the formation and maintenance of microvilli, stereocilia, and filopodia. Actin cables, which are F-actin bundles that serve as tracks for anterograde and retrograde cargo movement in budding yeast, undergo retrograde flow that is driven, in part, by actin polymerization and assembly. We find that the actin cable retrograde flow rate is reduced by deletion or delocalization of the type II myosin Myo1p, and by deletion or conditional mutation of the Myo1p motor domain. Deletion of the tropomyosin isoform Tpm2p, but not the Tpm1p isoform, increases the rate of actin cable retrograde flow. Pretreatment of F-actin with Tpm2p, but not Tpm1p, inhibits Myo1p binding to F-actin and Myo1p-dependent F-actin gliding. These data support novel, opposing roles of Myo1p and Tpm2 in regulating retrograde actin flow in budding yeast and an isoform-specific function of Tpm1p in promoting actin cable function in myosin-driven anterograde cargo transport.
Erythropoiesis and Myocardial Energy Requirements Contribute to the Hypermetabolism of Childhood Sickle Cell Anemia
Authors: Hibbert Jacqueline M , Creary Melissa S , Gee Beatrice E , Buchanan Iris D , Quarshie Alexander , Hsu Lewis L
Published: December 2006

Objectives:

We hypothesized that an elevated hemoglobin synthesis rate (SynHb) and myocardial oxygen consumption (MVO2) contribute to the excess protein and energy metabolism reported in children with sickle cell anemia.

Patients and Methods:

Twelve children (6–12 years old) with asymptomatic sickle cell and 9 healthy children matched for age and sex were studied. Measurements were whole‐body protein turnover by [1‐13C]leucine, SynHb by [15N]glycine, resting energy expenditure by indirect calorimetry and the systolic blood pressure–heart rate product used as an index of MVO2. Protein energy cost was calculated from protein turnover. Statistical analysis included Spearman correlations and partial correlation analyses.

Results:

Although body mass index was significantly lower for sickle cell versus controls (P < 0.02), children with asymptomatic sickle cell had 52% higher protein turnover (P < 0.0005). Proportional reticulocyte count, SynHb, MVO2 and resting energy expenditure were also significantly higher in children with sickle cell (P < 0.01). Protein turnover correlated significantly with both SynHb (r = 0.63, P < 0.01) and reticulocyte percentage (r = 0.83, P < 0.0001). Partial correlation of these 3 variables showed reticulocyte percentage as the only variable to be significantly associated with protein turnover, even after adjusting for sickle cell anemia (P = 0.03). Partial correlation of log resting energy expenditure on MVO2 was significant, controlling for protein energy cost, sex and age (P = 0.03).

Conclusion:

These results indicate that metabolic demands of increased erythropoiesis and cardiac energy consumption account for much of the excess protein and energy metabolism in children with sickle cell anemia.
Epithelial Electrical Resistance as a Measure of Permeability Changes in Pediatric Duodenal Biopsies
Authors: Reims Annika , Strandvik Birgitta , Sjövall Henrik
Published: December 2006

Objectives:

Intestinal permeability measured with medium‐sized oral probes is increased in cystic fibrosis (CF) and celiac disease (CD), probably reflecting reduced tight junction resistance. The aim of this study was to evaluate whether square‐pulse analysis of duodenal biopsies from children can be used to determine electrical tight junction resistance.

Methods:

Intestinal biopsies from children with different stages of CD and from patients with CF were studied in a modified Ussing chamber. The epithelium was assumed to act as an electrical circuit consisting of a current generator parallel with a resistance and a capacitance. Subepithelial and epithelial resistances were determined by square‐pulse analysis, and the generated current was calculated.

Results:

Confirming data using permeability probes, reduced epithelial electrical resistance was found both in patients with CF and CD. Only the CF patients had reduced resting current as well. The secretagogues prostaglandin E2, cyclic adenosine monophosphate and acetylcholine increased the current in both control biopsies and biopsies with villous atrophy but had no significant effect on epithelial resistance.

Conclusions:

Measurement of electrical resistance in duodenal biopsies can be used as an alternative method of quantifying permeability in pediatric biopsies.
A New Indirect Chemiluminescent Immunoassay to Measure Anti–tissue Transglutaminase Antibodies
Authors: Basso Daniela , Guariso Graziella , Fasolo Michela , Pittoni Marina , Schiavon Stefania , Fogar Paola , Greco Eliana , Navaglia Filippo , Zambon Carlo‐Federico , Plebani Mario
Published: December 2006

Objectives:

Anti–tissue transglutaminase antibody (anti‐tTG) determination using second‐generation (human antigen) enzyme‐linked immunoassays (ELISAs) is a very accurate test to diagnose celiac disease (CD). In this study, we compared 2 second‐generation ELISAs (Celikey tTG; Pharmacia Diagnostics GmbH & Co, Freiburg, Germany, and QuantaLite; Inova Diagnostics, San Diego, CA) and antiendomysial antibodies (EMAs) with a new indirect chemiluminescence immunoassay (LIAISON tTG; DiaSorin S.p.A., Saluggia, Italy) in diagnosing and monitoring CD in children.

Patients and Methods:

Antiendomysial antibodies, anti‐tTGs and total immunoglobulin A were measured in the sera of 103 control children, 101 children with histologically proven CD and 31 CD children on gluten‐free diet (GFD).

Results:

Anti–tissue transglutaminase antibody mean levels were significantly higher in CD with respect to control or GFD children. The sensitivity value of EMAs, LIAISON tTG, Celikey tTG and QuantaLite in diagnosing CD was 97.7%, 97.0%, 94.1% and 98.0%, respectively, and the corresponding specificity values were 91.1%, 98.1%, 97.1% and 96.1%, respectively. The degree of mucosal destruction (Marsh criteria) was correlated with EMA semiquantification (P < 0.01) and with the circulating levels of anti‐tTGs measured using LIAISON (P < 0.05) or QuantaLite (P < 0.01). Twenty‐six CD children were followed up from 5 to 25 months after GFD. The circulating levels of anti‐tTGs measured with any of the 3 assays significantly dropped after GFD.

Conclusions:

Anti–tissue transglutaminase antibody determination with second‐generation ELISAs is as effective as EMAs for CD diagnosis. The novel chemiluminescent method described in the present paper for the detection of anti‐tTGs in the diagnosis of CD had the highest sensitivity and specificity values. The anti‐tTG test correlates with the degree of mucosal destruction and is suitable for verifying patient compliance to dietary treatment.
The excitation of band systems by electron impact
Authors: Langstroth G. O. , Richardson Owen Willans
Published: December 2006

The relative positions of the more intense bands of a system in the usual square array can be predicted by classical methods (the Frank-Condon principle) from the potential curves for the initial and final states. This procedure is upheld in its essentials by wave mechanics, and a further wave mechanics development permits the calculation of transition probabilities in emission in band systems of symmetric diatomic molecules. The essential features of the theory are that relatively massive nuclei may be assumed not to respond immediately to changes in the electronic arrangement of the molecule, and that one need not evaluate that part of the electric moment directly concerned with such electronic rearrangements. These circumstances reduce the problem to one for simple oscillators with known potential functions. For a
complete
theory of the relative
intensities
, however, the details of the accompanying phenomenon of excitation must be known. While these are necessarily extremely complicated for bands emitted from different initial electronic states, a considerable simplification may be expected for bands emitted from the same electronic state. The problem of the relative excitation probabilities then forms the excitation analogue of the Frank-Condon principle.
The effect of imprisonment of resonance radiation in the decomposition of ammonia and of deutero-ammonia
Authors: Melville Harry Work
Published: December 2006

In three recent papers, the kinetics of the mercury photo-sensitized decomposition of ammonia and of deutero-ammonia have been compared in order (
a
) to obtain the velocity coefficients for the processes occurring in these reactions, (
b
) to establish correlations between these coefficients and the measured quenching radii and zero-point energy content of the molecules participating in the collisions. Calculations made upon simple premises yielded inconsistencies in the numerical values of the coefficients, thus throwing doubt upon the fundamental assumptions in the kinetic treatment of the problem. Evans and Taylor, in a later paper, have sought to surmount these difficulties by postulating the formation of mercury-ammonia complexes which have finite and different lifetimes for the two ammonias and which are subject to various deactivating collisions in the gas phase. There are, however, a number of factors to be taken into account, not hitherto considered, before recourse need be made to assumptions of this nature. It is the purpose of this paper to attempt to estimate quantitatively the magnitude of the corrections to be applied, to see then what discrepancies still exist and what probable explanations need be put forward to effect the necessary modifications to the scheme of reactions. We must distinguish between two separate phenomena occurring in these reactions. In the first place the ammonia molecule is dissociated by a collision with a mercury atom of high energy content and therefore, in order to calculate the velocity of this process, the stationary concentration of the mercury atoms as a function of ammonia and hydrogen pressure and other possible variables must be known. Secondly, the fragments of the dissociated molecule do not necessarily yield molecular hydrogen and nitrogen, for it is known in the direct photo chemical decomposition the quantum yield is less than unity and therefore reverse actions leading to the regeneration of ammonia must come into play. In comparing the behaviour of isotopic molecules, each of these factors may be different and hence they must be separately investigated. In the following pages the phenomena having to do with mercury atom collisions are described first and then the question of secondary reactions is considered in the second part of the paper.
Composite films of oxygen and hydrogen on tungsten
Authors: Roberts John Keith
Published: December 2006

The methods described in the two foregoing papers have been applied to the study of the adsorption of oxygen on a hydrogen-covered surface and of the behaviour of hydrogen when the surface has previously been covered, or nearly covered, with oxygen. 1—The Adsorption of Oxygen on a Hydrogen-Covered Surface Using the accommodation coefficient of neon as an indicator, it has been shown that oxygen can be adsorbed at room temperature on a tungsten surface already covered with hydrogen. The bare tungsten surface was first covered with hydrogen so that the accommodation coefficient rose to 0·16. Oxygen was the introduced and after several admissions the accommodation coefficient rose to 0·36.
Thermal conduction in hydrogen-deuterium mixtures
Authors: Archer C. T.
Published: December 2006

The work to be described here was undertaken by the author in order to provide accurate data on thermal conduction in gaseous mixtures of deuterium and hydrogen at ordinary temperatures, to be applied to the analysis of such mixtures by the thermal conductivity method developed by A. Farkas and L. Farkas (1934) and others; and also to make an accurate direct determination of the thermal conductivity of pure deuterium. With regard to the latter quantity, the values obtained by other workers to date vary widely, showing a maximum difference of the order of 11%.
The mechanism of chain breaking in the thermal decomposition of ethane
Authors: Hobbs J. E. , Hinshelwood Cyril Norman
Published: December 2006

The decomposition of ethane in the neighbourhood of 600° occurs largely by a chain mechanism in which free radicals are formed. In the course of experiments on the inhibition of the reaction by nitric oxide, Staveley (1937) found that the mean chain length diminished with increasing ethane pressure. From this he reached the conclusion that the chains were broken predominantly by a ternary collision process involving two radicles and an ethane molecule. The important question whether chains are ended by binary or by ternary collisions can be approached in another way, the exploration of which is described in the following pages.
The electrical conductivity of the transition metals.
Authors: Wilson Alan Herries
Published: December 2006

1·1. The conductivity of a pure metal depends upon a large number of quantities, and it is difficult to decide the relative importance of the various constants since they often produce compensating effects. It is, however, generally agreed that the low conductivity of the divalent metals, and especially of bismuth, is due to the small effective number of conduction electrons. It has further been suggested by Mott (1935, 1936
a
, 1936
b
) that the low conductivity of the transition elements, which are even worse conductors than the divalent elements, is due to another cause, namely, to the abnormal smallness of the free path. The transition metals possess conduction electrons in an
s
-band and they also have unfilled
d
-bands. Hence, in addition to the normal
s-s
transitions the electrons can also undergo
s-d
transitions, and this results in a shortening of the free path. One of the difficulties in the way of a complete theory is the necessity of separating the normal
s-s
transitions from the
s-d
transitions, and so far it has not proved possible to do this. In the present paper it is shown that the resistances produced by the two different types of transition have different temperature variations, and therefore that it should be possible to estimate their relative importance by measurements over a sufficiently large range of temperature.