bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum dynamics of H2, D2, and HD in the small dodecahedral cage of clathrate hydrate: Evaluating H2-water nanocage interaction potentials by comparison of theory with inelastic neutron scattering experiments
Authors: Xu Minzhong , Sebastianelli Francesco , Bačić Zlatko
Published: June 2008

We have performed rigorous quantum five-dimensional (5D) calculations and analysis of the translation-rotation (T-R) energy levels of one H2, D2, and HD molecule inside the small dodecahedral (H2O)20 cage of the structure II clathrate hydrate, which was treated as rigid. The H2- cage intermolecular potential energy surface (PES) used previously in the molecular dynamics simulations of the hydrogen hydrates [Alavi et al., J. Chem. Phys. 123, 024507 (2005)] was employed. This PES, denoted here as SPC/E, combines an effective, empirical water-water pair potential [Berendsen et al., J. Phys. Chem. 91, 6269 (1987)] and electrostatic interactions between the partial charges placed on H2O and H2. The 5D T-R eigenstates of HD were calculated also on another 5D H2-cage PES denoted PA-D, used by us earlier to investigate the quantum T-R dynamics of H2 and D2 in the small cage [Xu et al., J. Phys. Chem. B 110, 24806 (2006)]. In the PA-D PES, the hydrogen-water pair potential is described by the ab initio 5D PES of the isolated H2–H2O dimer. The quality of the SPC/E and the PA-D H2-cage PESs was tested by direct comparison of the T-R excitation energies calculated on them to the results of two recent inelastic neutron scattering (INS) studies of H2 and HD inside the small clathrate cage. The translational fundamental and overtone excitations, as well as the triplet splittings of the j=0→j=1 rotational transitions, of H2 and HD in the small cage calculated on the SPC/E PES agree very well with the INS results and represent a significant improvement over the results computed on the PA-D PES. Our calculations on the SPC/E PES also make predictions about several spectroscopic observables for the encapsulated H2, D2, and HD, which have not been measured yet.
Transition from traveling to standing waves as a function of frequency in a reaction-diffusion system
Authors: Cuiñas Daniel , Berenstein Igal , Carballido-Landeira Jorge , Muñuzuri Alberto P.
Published: June 2008

The addition of polyethylene glycol to the Belousov–Zhabotinsky reaction increases the frequency of oscillations, which in an extended system causes a transition from traveling to standing waves. A further increase in frequency causes another transition to bulk oscillations. The standing waves are composed of two domains, which oscillate out of phase with a small delay between them, the delay being smaller as the frequency of oscillations is increased.
Terahertz generation in GaN diodes in the limited space-charge accumulation mode
Authors: Barry E. A. , Sokolov V. N. , Kim K. W. , Trew R. J.
Published: June 2008

The conditions for terahertz power generation are investigated theoretically in a nanoscale GaN-based diode coupled to an external resonant circuit for operation in the limited space-charge accumulation (LSA) mode under the high-field transport regime. The generation criteria are revisited in terms of a phase plane analysis of the diode high-field transport and circuit equations. Based on a Fourier series analysis, the waveforms of the diode voltage and current are examined and the generated power and conversion efficiencies are estimated at the fundamental and lowest harmonic frequencies. The advantages of group-III nitride LSA diodes are elucidated including their ability to simultaneously achieve large output powers (>10 mW) and high dc-to-rf conversion efficiencies (>1%) over a wide range of frequencies near 1 THz.
Room temperature terahertz detection based on bulk plasmons in antenna-coupled GaAs field effect transistors
Authors: Kim Sangwoo , Zimmerman Jeramy D. , Focardi Paolo , Gossard Arthur C. , Wu Dong Ho , Sherwin Mark S.
Published: June 2008

A first generation of antenna-coupled GaAs metal-semiconductor-field-effect-transistors (MESFETs) is fabricated, modeled, and tested for room-temperature terahertz detection. For fixed excitation frequencies between 0.14 and 1THz, the source-drain current (signal) is monitored as the gate and drain voltages are varied. The signal shows resonances when applied voltages sweep the charge density in the MESFET through values at which the bulk plasmon is resonant with the excitation frequency. For these unoptimized devices, the measured system noise-equivalent power is ∼5×10−8W∕Hz1∕2; the electronics-limited response time is 10ns.
Theoretical analysis of coupled oscillator array using resonant tunneling diodes in subterahertz and terahertz range
Authors: Asada M. , Suzuki S.
Published: June 2008

Power combining with array configuration is an effective method for high output power in oscillators with resonant tunneling diodes (RTDs) in subterahertz and terahertz range. In this paper, output power and stability are analyzed for coupled oscillator array of RTDs. The coupled van der Pol equations are derived from the equivalent circuit for two-element oscillator arrays at first, and the condition in which only the fundamental oscillation mode stably oscillates is shown. The oscillation frequency of the array is single due to the mutual injection locking even if the individual frequencies of oscillator elements are different. Minimum difference between the individual frequencies to keep the mutual injection locking is analyzed. Experimental results are explained with theory. The analysis is extended to multielement oscillator arrays, and characteristics of oscillation modes, stability, combined output power, and locking range of the frequency difference between the elements are obtained. Theoretical combined output power increases with element number in proportion roughly to square of the element number if the frequency difference between the elements is small, and decreases with frequency difference. Different array configurations for stable and high-power operation are also discussed briefly.
Spectral investigation of carrier recombination processes in ZnO nanorods at high temperatures
Authors: Gupta A. , Omari M. , Kouklin N.
Published: June 2008

The mechanism of near-band-edge (NBE) emission from crystalline ZnO (c-ZnO) nanorods grown on c-Si by a catalyst-assisted vapor-liquid-solid method has been investigated by performing temperature-, power-, and time-dependent photoluminescence (PL) measurements at a temperature (T) range of 143–503K. In contrast to previous reports, we find that the NBE PL is primarily associated with free exciton emission, whereas the contribution of band-to-band and free-to-bound radiative recombinations remains negligible up to the highest T studied. A spectral evolution of the NBE band with T was further analyzed within the framework of a three-parameter model, proposed recently, with the results presented and discussed. Finally, the ratio of excitonic-to-defect luminescence intensity has been observed to change nonmonotonically with T, which is explained based on the difference in the quenching mechanisms of exciton and defect PL.
InAs nanowire metal-oxide-semiconductor capacitors
Authors: Roddaro Stefano , Nilsson Kristian , Astromskas Gvidas , Samuelson Lars , Wernersson Lars-Erik , Karlström Olov , Wacker Andreas
Published: June 2008

We present a capacitance-voltage study for arrays of vertical InAs nanowires. Metal-oxide-semiconductor (MOS) capacitors are obtained by insulating the nanowires with a conformal 10nm HfO2 layer and using a top Cr∕Au metallization as one of the capacitor’s electrodes. The described fabrication and characterization technique enables a systematic investigation of the carrier density in the nanowires as well as of the quality of the MOS interface.
Latent heat investigation by photopyroelectric calorimetry
Authors: Mercuri F. , Marinelli M. , Paoloni S. , Zammit U. , Scudieri F.
Published: June 2008

We report on an approach for photopyroelectric calorimetry enabling a frequency dependence detection of the specific heat and of the latent heat exchanged over first order transitions. It has been applied to the nematic-isotropic transition of 4-n-octyl-4′-cyanobiphenyl liquid crystal confined in a silica nanoparticles network, where the specific heat shows a double peak structure. The larger strain involved with the nematic nucleating over the low temperature peak induces a considerable lower latent heat than the one involved over the higher temperature peak. The frequency dependent measurements have shown a different dynamics of the nematic nucleating over the two peaks.
Pulsed corona discharge for oxidation of gaseous elemental mercury
Authors: Ko Kyung Bo , Byun Youngchul , Cho Moohyun , Namkung Won , Hamilton Ian P. , Shin Dong Nam , Koh Dong Jun , Kim Kyoung Tae
Published: June 2008

Positive pulsed corona discharge has been applied for the oxidation of gaseous elemental mercury (Hg0) from a simulated flue gas. The oxidation of Hg0 to HgO and HgCl2 can significantly enhance the mercury removal from flue gas. At a gas condition of O2 (10%), H2O (3%), and N2 (balance), Hg0 oxidation efficiency of 84% was achieved at an input energy density of 45J∕l. The presence of NO, however, hinders Hg0 oxidation due to the preferential reaction of NO with O and O3. On the contrary, SO2 shows little effect on Hg0 oxidation due to its preferential reaction with OH. It has been also observed that the HCl in gas stream can be dissociated to Cl and Cl2 and can induce additional Hg0 oxidation to HgCl2.
Reversible switching characteristics of polyfluorene-derivative single layer film for nonvolatile memory devices
Authors: Kim Tae-Wook , Oh Seung-Hwan , Choi Hyejung , Wang Gunuk , Hwang Hyunsang , Kim Dong-Yu , Lee Takhee
Published: June 2008

This letter reports on reversible switching behavior of metal-insulator-metal type nonvolatile organic memory devices using polyfluorene-derivative (WPF-oxy-F) single layer film. The current-voltage (I-V) characteristics showed that the WPF-oxy-F single layer film has two distinguished resistance states, low resistance state and high resistance state, with four orders of on/off ratio (Ion∕Ioff∼104). From the analysis of I-V curves, area dependent I-V characteristics, and current images obtained by conducting atomic force microscopy we propose that the space charge limited current with filamentary conduction is a potential mechanism for the reversible switching behavior of WPF-Oxy-F memory devices.
Achieving 1nm capacitive effective thickness in atomic layer deposited HfO2 on In0.53Ga0.47As
Authors: Lee K. Y. , Lee Y. J. , Chang P. , Huang M. L. , Chang Y. C. , Hong M. , Kwo J.
Published: June 2008

A capacitive effective thickness (CET) value of 1.0nm has been achieved in atomic layer deposited (ALD) high κ dielectrics HfO2 on In0.53Ga0.47As∕InP. The key is a short air exposure under 10min between removal of the freshly grown semiconductor epilayers and loading to the ALD reactor. This has led to minimal formation of the interfacial layer thickness, as confirmed using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The measured electrical characteristics of metal-oxide-semiconductor diodes of Au∕Ti∕HfO2(4.5nm)∕In0.53Ga0.47As showed a low leakage current density of 3.8×10−4A∕cm2 at VFB+1V, which is about eight orders of magnitudes lower than that of SiO2 with the same CET. The capacitance-voltage curves show an overall κ value of 17–18, a nearly zero flatband shift, and an interfacial density of states Dit of 2×1012cm−2eV−1.
High efficiency electrophosphorescence device using a thin cleaving layer in an Ir-complex doped emitter layer
Authors: Yang Dongfang , Li Wenlian , Chu Bei , Zhang Dongyu , Zhu Jianzhuo , Su Zisheng , Su Wenming , Han Liangliang , Bi Defeng , Chen Yiren , Yan Fei , Liu Huihui , Wang Dan
Published: June 2008

The authors demonstrate a considerable increase in current efficiency of fac-tris(2-phenylpyridine) iridium doped phosphorescent organic green-light emitting diode in which a thin 4,7 dipheny-1,10-phenanthroline (Bphen) layer acts as a cleaving layer. As 4nm Bphen layer divides the emitting layer (EML) into two sub-EMLs, a maximum current efficiency of 53cd∕A (corresponding to external efficiency quantum of 15%) is obtained, which is higher for 2.3 folds than that of the device without it, especially the current efficiency increases 64% over the reference device at a luminance of 40000cd∕m2. The increases are demonstrated to the high electron mobility and special energy level alignment of Bphen with 4,4′-N,N′-dicarbazole-biphenyl host. The efficiency improvement attributes to a higher exciton formation probability in the recombination zone and better balance of the carrier injection. The detail enhancement mechanism of the efficiency is also discussed.
Improved resonance characteristics of GaAs beam resonators by epitaxially induced strain
Authors: Yamaguchi H. , Kato K. , Nakai Y. , Onomitsu K. , Warisawa S. , Ishihara S.
Published: June 2008

Micromechanical-beam resonators were fabricated using a strained GaAs film grown on relaxed In0.1Ga0.9As∕In0.1Al0.9As buffer layers. The natural frequency of the fundamental mode was increased 2.5–4 times by applying tensile strain, showing good agreement with the model calculation assuming strain of 0.35% along the beam. In addition, the Q factor of 19 000 was obtained for the best sample, which is one order of magnitude higher than that for the unstrained resonator. This technique can be widely applied for improving the performance of resonator-based micro-/nanoelectromechanical devices.
Thermal tunability of monolithic polymer microcavities
Authors: Regoliosi P. , Guehl M. , Scarpa G. , Lugli P. , Persano L. , Del Carro P. , Camposeo A. , Cingolani R. , Pisignano D. , Bietti S. , Grilli E. , Guzzi M.
Published: June 2008

We demonstrate the thermal tunability of the emission of polymer embedded in microcavities. The large thermo-optic coefficients of a conjugated polymer is combined with the possibility to tailor the emission properties by means of cavities acting as optical filters. Both the transmission and the photoluminescence spectra of the polymer in cavities can be finely tuned with slopes up to about −0.2nm∕°C. Such an effect could be exploited to realize thermally tunable organic light-emitting devices for optical communication or sensing applications.
Effects of Inversion and Negation on Social Inferences from Faces
Authors: Santos Isabel M , Young Andrew W
Published: June 2008

Judgments about personality and other social characteristics based on facial appearance are remarkably consistent across individuals. However, whereas the facial cues that underpin age and sex judgments are already well understood, the physical bases for judgments of characteristics such as intelligence or trustworthiness are still unknown. Inversion and photographic negation are used here to investigate the visual processes underlying social inferences from the face and to explore whether various judgments might rely on different perceptual representations. In experiment 1, the perceptions of age, sex, attractiveness, approachability, intelligence, and trustworthiness, but not distinctiveness, were affected by inversion, and all these characteristics were affected by negation. The effects of inversion and negation were independent, suggesting that they impaired the encoding of different types of information. Moreover, an independent manipulation of hue and luminance in experiment 2 showed that the effects of negation were mainly due to the reversal of luminance values. These results are consistent with the view that information about the configuration of features (the processing of which is impaired by inversion) and information about surface properties (the processing of which is impaired by brightness negation) are both used in the perception of social characteristics from faces. In addition, the fact that there was a similar pattern of impairment across most judgments suggests that there is an initial common perceptual representation of the face, from which most characteristics are inferred.
Visibility bias in aerial survey: mark - recapture, line-transect or both?
Authors: Laake Jeff , Dawson Michelle J. , Hone Jim
Published: June 2008

Mark–recapture and line-transect sampling procedures both provide estimators for visibility bias in aerial surveys, and have coexisted in the literature for decades. Mark–recapture estimators of abundance tend to be negatively biased in this context as a result of unmodelled heterogeneity. Line-transect sampling can also be negatively biased if detection probability on the line is less than 1.0. Numerous papers have described hybrid approaches using mark–recapture and line transect methods but there have been some subtle but important differences that may not be apparent to the practitioner. We have used wild horse survey data collected in south-eastern Australia and some imaginary data to highlight these subtle differences. We demonstrate the advantage of using the hybrid approach, which uses the strengths of both mark–recapture and line-transect procedures by fitting a detection function (with p(0) = 1) to the line-transect data to estimate the shape of the detection function, and uses a separate detection function for the mark–recapture data to estimate the intercept (p(0)).
Evaluating helicopter-based surveys for estimating densities of Himalayan thar
Authors: Choquenot David , Bolton Neil , Woods Darrin
Published: June 2008

Himalayan thar (Hemitragus jemlahicus Smith) inhabit a large area of New Zealand’s southern alps. Since 1993, a control plan for thar has required estimation of thar density within management units (MUs), and across their range. We evaluated helicopter-based survey as an alternative to current ground-based surveys to provide these estimates. Both survey methods sample thar density within predetermined survey-catchments located in MUs. Helicopter- and ground-based surveys undertaken in four survey-catchments (three located in MU4, one located in MU3) contrasted the performance of the two methods. Helicopter-based surveys used a double-count method to estimate the sightability of thar groups. Sightability varied from 0.53 for single thar, to 1.0 for groups of three or more. Correction factors accounting for sightability were applied to helicopter-based counts to estimate thar density within survey-catchments, which were contrasted with estimates from ground-based surveys. Density estimates for three of the survey-catchments were within 25%, and displayed no systematic bias, indicating reasonable convergence of the two methods. The effect of sampling rate on precision of density estimates was explored using helicopter-based survey results for survey-catchments sampled within MU4. Confidence intervals for the density estimate stabilised when 10–15 survey-catchments were sampled, equivalent to a sampling rate of 13–20% of the MU. Compared with ground-based surveys, helicopter-based surveys were 30% cheaper, less logistically constrained, and could be applied randomly across MUs. This suggests that they may be a better option to meet the information requirements for implementation of the thar control plan, at least in MUs where habitat is sufficiently open.
Coping with variation in aerial survey protocol for line-transect sampling
Authors: Laake Jeff , Guenzel Richard J. , Bengtson John L. , Boveng Peter , Cameron Michael , Hanson M. Bradley
Published: June 2008

Altitude and flight speed affect detection probability and they typically vary during the course of most aerial surveys. We demonstrate how these sources of variation can be accommodated with covariates in a line-transect analysis using data from a pronghorn (Antilocapra americana) survey in Wyoming and a survey of Antarctic ice seals (Lobodon carcinophaga, Leptonychotes weddellii, Hydrurga leptonyx, Ommatophoca rossii). We also show how the likelihood for binned distance data can be modified to allow for variation in altitude. As an alternative, we develop an estimator for aerial line-transect sampling based on vertical angles rather than distance. With a small simulation study, we show that our estimators are unbiased and are preferable to using biased estimators based on fixed-distance intervals derived from average altitude.
A comparison of mark - recapture distance-sampling methods applied to aerial surveys of eastern grey kangaroos
Authors: Fewster Rachel M. , Pople Anthony R.
Published: June 2008

Aerial surveys of kangaroos (Macropus spp.) in Queensland are used to make economically important judgements on the levels of viable commercial harvest. Previous analysis methods for aerial kangaroo surveys have used both mark–recapture methodologies and conventional distance-sampling analyses. Conventional distance sampling has the disadvantage that detection is assumed to be perfect on the transect line, while mark–recapture methods are notoriously sensitive to problems with unmodelled heterogeneity in capture probabilities. We introduce three methodologies for combining together mark–recapture and distance-sampling data, aimed at exploiting the strengths of both methodologies and overcoming the weaknesses. Of these methods, two are based on the assumption of full independence between observers in the mark–recapture component, and this appears to introduce more bias in density estimation than it resolves through allowing uncertain trackline detection. Both of these methods give lower density estimates than conventional distance sampling, indicating a clear failure of the independence assumption. The third method, termed point independence, appears to perform very well, giving credible density estimates and good properties in terms of goodness-of-fit and percentage coefficient of variation. Estimated densities of eastern grey kangaroos range from 21 to 36 individuals km–2, with estimated coefficients of variation between 11% and 14% and estimated trackline detection probabilities primarily between 0.7 and 0.9.
Aerial surveys of multiple species: critical assumptions and sources of bias in distance and mark - recapture estimators
Authors: Melville Gavin J. , Tracey John P. , Fleming Peter J. S. , Lukins Brian S.
Published: June 2008

Recent developments in the application of line-transect models to aerial surveys have used double-observer sampling to account for undercounting on the transect line, a crucial step in obtaining correct population estimates. This method is commonly called the mark–recapture line-transect sampling method and estimates the detection probability at zero distance to correct line-transect estimates of abundance. An alternative approach, which uses the same methodology during data collection, is to use a range of covariates, including distance from the transect, in a mark–recapture model. This approach overcomes the implicit assumption of uniform distribution of distances in line-transect estimators. In this paper, we use three alternative approaches (a multiple-covariates distance method, a distance method incorporating adjustment for incomplete detection on the transect line using mark–recapture sampling, and a mark–recapture method with distance as a covariate) to estimate the abundance of several medium-sized mammals in semiarid ecosystems. Densities determined with the three estimators varied considerably within species and sites. In some cases distance estimates were larger than mark–recapture estimates and vice versa. Despite large numbers of observations, distance uniformity was not observed for any species at any site, nor for any species where sites were combined. Possible reasons, which include sampling variability, movement in response to the aircraft and failure of the mark–recapture independence assumption, are discussed in detail.
Some human, aircraft and animal factors affecting aerial surveys: how to enumerate animals from the air
Authors: Fleming Peter J. S. , Tracey John P.
Published: June 2008

Aerial surveys of wildlife involve a noisy platform carrying one or more observers moving over animals in order to quantify their abundance. This simple-sounding system encapsulates limits to human visual acuity and human concentration, visual attention, salience of target objects within the viewed scene, characteristics of survey platforms and facets of animal behaviours that affect the detection of animals by the airborne observers. These facets are too often ignored in aerial surveys, yet are inherent sources of counting error. Here we briefly review factors limiting the ability of observers to detect animals from aerial platforms in a range of sites, including characteristics of the aircraft, observers and target animals. Some of the previously uninvestigated limitations identified in the review were studied in central and western New South Wales, showing that inaccuracies of human memory and enumeration processes are sources of bias in aerial survey estimates. Standard protocols that minimise or account for the reviewed factors in aerial surveys of wildlife are recommended.
Accuracy of some aerial survey estimators: contrasts with known numbers
Authors: Tracey John P. , Fleming Peter J. S. , Melville Gavin J.
Published: June 2008

Density estimates are seldom examined against actual population size, hence the ability of estimators to correct for bias is unknown. Studies that compare techniques are difficult to interpret because of the uncertainty of adherence to their respective assumptions. Factors influencing detection probability, estimators that correct for bias, the validity of their assumptions and how these relate to true density are important considerations for selecting suitable methods. Here we contrasted five estimates of feral goat (Capra hircus) densities obtained from aerial surveys (strip counts, Petersen, stratified Petersen, Chao, Alho) against known densities derived from total counts. After correcting for recounting, the Alho and stratified Petersen estimators applied to helicopter surveys were the most accurate (bias = 0.08 and –0.09 respectively), which suggests that estimates were improved by correcting individual observations according to the characteristics of each observation. An approach using modified Horvitz–Thompson equations for unequal-sized units is described and is recommended to allow for this. Both the Chao (bias = 0.35) and Petersen (bias = 0.22) estimators were positively biased, which is likely to be a consequence of averaging detection probability across all observations. Helicopter survey using capture–recapture with multiple observers is recommended for estimating the density of wildlife populations. However, adjustment for the factors that influence detection probability is required.
Geometric constraints on neuronal connectivity facilitate a concise synaptic adhesive code
Authors: Itzkovitz Shalev , Baruch Leehod , Shapiro Ehud , Segal Eran
Published: June 2008

The nervous system contains trillions of neurons, each forming thousands of synaptic connections. It has been suggested that this complex connectivity is determined by a synaptic “adhesive code,” where connections are dictated by a variable set of cell surface proteins, combinations of which form neuronal addresses. The estimated number of neuronal addresses is orders of magnitude smaller than the number of neurons. Here, we show that the limited number of addresses dictates constraints on the possible neuronal network topologies. We show that to encode arbitrary networks, in which each neuron can potentially connect to any other neuron, the number of neuronal addresses needed scales linearly with network size. In contrast, the number of addresses needed to encode the wiring of geometric networks grows only as the square root of network size. The more efficient encoding in geometric networks is achieved through the reutilization of the same addresses in physically independent portions of the network. We also find that ordered geometric networks, in which the same connectivity patterns are iterated throughout the network, further reduce the required number of addresses. We demonstrate our findings using simulated networks and the
C. elegans
neuronal network. Geometric neuronal connectivity with recurring connectivity patterns have been suggested to confer an evolutionary advantage by saving biochemical resources on the one hand and reutilizing functionally efficient neuronal circuits. Our study suggests an additional advantage of these prominent topological features—the facilitation of the ability to genetically encode neuronal networks given constraints on the number of addresses.
Interplay among side chain sequence, backbone composition, and residue rigidification in polypeptide folding and assembly
Authors: Horne W. Seth , Price Joshua L. , Gellman Samuel H.
Published: June 2008

The extent to which polypeptide conformation depends on side-chain composition and sequence has been widely studied, but less is known about the importance of maintaining an α-amino acid backbone. Here, we examine a series of peptides with backbones that feature different repeating patterns of α- and β-amino acid residues but an invariant side-chain sequence. In the pure α-backbone, this sequence corresponds to the previously studied peptide GCN4-pLI, which forms a very stable four-helix bundle quaternary structure. Physical characterization in solution and crystallographic structure determination show that a variety of α/β-peptide backbones can adopt sequence-encoded quaternary structures similar to that of the α prototype. There is a loss in helix bundle stability upon β-residue incorporation; however, stability of the quaternary structure is not a simple function of β-residue content. We find that cyclically constrained β-amino acid residues can stabilize the folds of α/β-peptide GCN4-pLI analogues and restore quaternary structure formation to backbones that are predominantly unfolded in the absence of cyclic residues. Our results show a surprising degree of plasticity in terms of the backbone compositions that can manifest the structural information encoded in a sequence of amino acid side chains. These findings offer a framework for the design of nonnatural oligomers that mimic the structural and functional properties of proteins.
Multimeric nature of voltage-gated proton channels
Authors: Koch Hans P. , Kurokawa Tatsuki , Okochi Yoshifumi , Sasaki Mari , Okamura Yasushi , Larsson H. Peter
Published: June 2008

Voltage-gated potassium channels are comprised of four subunits, and each subunit has a pore domain and a voltage-sensing domain (VSD). The four pore domains assemble to form one single central pore, and the four individual VSDs control the gate of the pore. Recently, a family of voltage-gated proton channels, such as H
V
or voltage sensor only protein (VSOP), was discovered that contain a single VSD but no pore domain. It has been assumed that VSOP channels are monomeric and contain a single VSD that functions as both the VSD and the pore domain. It remains unclear, however, how a protein that contains only a VSD and no pore domain can conduct ions. Using fluorescence measurements and immunoprecipitation techniques, we show here that VSOP channels are expressed as multimeric channels. Further, FRET experiments on constructs with covalently linked subunits show that VSOP channels are dimers. Truncation of the cytoplasmic regions of VSOP reduced the dimerization, suggesting that the dimerization is caused mainly by cytoplasmic protein–protein interactions. However, these N terminus- and C terminus-deleted channels displayed large proton currents. Therefore, we conclude that even though VSOP channels are expressed mainly as dimers in the cell membrane, single VSOP subunits could function independently as proton channels.
Nucleosome repeat length and linker histone stoichiometry determine chromatin fiber structure
Authors: Routh Andrew , Sandin Sara , Rhodes Daniela
Published: June 2008

To understand how nuclear processes involving DNA are regulated, knowledge of the determinants of chromatin condensation is required. From recent structural studies it has been concluded that the formation of the 30-nm chromatin fiber does not require the linker histone. Here, by comparing the linker histone-dependent compaction of long, reconstituted nucleosome arrays with different nucleosome repeat lengths (NRLs), 167 and 197 bp, we establish that the compaction behavior is both NRL- and linker histone-dependent. Only the 197-bp NRL array can form 30-nm higher-order chromatin structure. Importantly for understanding the regulation of compaction, this array shows a cooperative linker histone-dependent compaction. The 167-bp NRL array displays a limited linker histone-dependent compaction, resulting in a thinner and topologically different fiber. These observations provide an explanation for the distribution of NRLs found in nature.
Registration of Down syndrome in the Medical Birth Registry of Norway: Validity and time trends
Authors: MELVE KARI KLUNGSØYR , LIE ROLV TERJE , SKJAERVEN ROLV , VAN DER HAGEN CARL BIRGER , GRADEK GYRI AASLAND , JONSRUD CHRISTOPHER , BRAATHEN GEIR J. , IRGENS LORENTZ M.
Published: June 2008

Objective. To validate Down syndrome registration in the Medical Birth Registry of Norway (MBRN), 2001–2005, and study time trends and geographical differences in Down syndrome prevalence,1967–2005. Design/setting. Population‐based cohort study, Norway. Population. 2.3 million pregnancies and births registered in the MBRN, 1967–2005. Methods. We linked data from the MBRN during 2001–2005 with data from Norway's four laboratories of medical genetics. We calculated sensitivity and positive predictive values (PPV) of the MBRN registration overall, and by background variables. Prevalence rates from 1967 to 2005, overall and regional, were presented graphically as smoothed lowess estimates, crude and standardized for maternal age. Time trends were evaluated, adjusting for maternal age by logistic regression. Main outcome measures. Sensitivity, PPV, and prevalence rates. Results. Five hundred and seventy‐six verified cases of Down syndrome gave a prevalence of 2.0 per 1,000 among 288,213 births and terminations in the MBRN during 2001–2005. Of verified cases, 470 (81.6%) were registered with Down syndrome in the MBRN, while 470 (90.2%) of 521 MBRN‐registered cases were verified. Sensitivity was higher in the Northern (93.1%; p = 0.005) and Middle (90.6%; p = 0.02) region relative the Southern (76.3%), higher for mothers ≥35 years (92.9%) than younger ones (86.1%; p = 0.01), and higher for live births (88.8%) relative stillbirths (55.6%; p<0.001). When adjusting for maternal age, there were no significant time trends in prevalence rates from 1967 to 2005. Regional differences over time were found, probably representing reporting differences. Conclusions. Validity of registration in the MBRN was satisfactory during 2001–2005. Increasing prevalence rates over time were explained by increasing maternal age.
MMP‐2, TIMP‐1, E‐cadherin, and β‐catenin expression in endometrial serous carcinoma compared with low‐grade endometrial endometrioid carcinoma and proliferative endometrium
Authors: SHACO‐LEVY RUTHY , SHARABI SHALOM , PIURA BENJAMIN , SION‐VARDY NETTA
Published: June 2008

Objective. To investigate the expression of MMP‐2, TIMP‐1, E‐cadherin and β‐catenin in endometrial serous carcinoma (ESC), low‐grade endometrial endometrioid carcinoma (EEC), and proliferative endometrium. Methods. We performed an immunohistochemical study on 14 cases of ESC, 15 cases of low‐grade EEC, and 10 cases of proliferative endometrium. Results. Compared with low‐grade EEC, ESC showed significantly increased MMP‐2 and TIMP‐1 expression, as well as decreased membranous β‐catenin staining. E‐cadherin expression was significantly lower in ESC and EEC as compared with proliferative endometrium. Conclusions. We suggest that MMP‐2 and TIMP‐1 expression and loss of β‐catenin have a role in the pathogenesis and progression of ESC. Decreased E‐cadherin may have an important role in the development of both ESC and EEC. Furthermore, the dissimilarities in MMP‐2, TIMP‐1, E‐cadherin and β‐catenin expressions in ESC compared with EEC may be responsible, along with other factors, for their different biological behavior.
Opportunities missed and/or thwarted? ‘Funds of knowledge’ meet the English national curriculum
Authors: Thomson Pat , Hall Christine
Published: June 2008

North American curriculum theorists Gonzales and Moll and their colleagues have argued that working with children's ‘funds of knowledge’ allows teachers to build on what children already know in order to meet the mandated outcomes. The approach also has the potential to change the knowledges that are valued and which advantage some children over others. In this article we examine three instances in which children's ‘funds of knowledge’ leaked into English classrooms: these were not fully taken up. We suggest that these instances represent opportunities wasted, but that they offer some insight into the challenges of introducing a ‘funds of knowledge’ approach into the English ‘curriculum space’, as well as some of the possibilities. We suggest that while there are current initiatives which do work with children's peer and family knowledges, these are isolated and that coordinated debate is required about the potentials of such an approach in the English context.
Prevalence and correlates of jugular injections among injection drug users
Authors: HODA ZIA , KERR THOMAS , LI KATHY , MONTANER JULIO S. G. , WOOD EVAN
Published: June 2008

Background. Jugular injection of drugs has been reported, although little is known about the prevalence of and risk factors associated with this behaviour. We evaluated factors associated with jugular injection among a cohort of injection drug users (IDU) in Vancouver, Canada. Methods. We used univariate statistics and logistic regression to examine factors associated with jugular injection among participants in the Vancouver Injecting Drug Users Study (VIDUS), a large prospective cohort study of IDU recruited through snowball sampling methods in Vancouver, Canada. Findings. Between December 2004 and November 2005, 780 IDU were followed up as part of VIDUS and 198 (25%) reported jugular injection in the previous 6 months. In multivariate analyses, factors associated independently with jugular injection included: being of the female gender [adjusted odds ratio (aOR) = 1.72, 95% confidence interval (CI): 1.14–2.59; p = 0.010], daily heroin use (aOR = 2.89, 95% CI: 1.93–4.34; p < 0.001), daily cocaine use (aOR = 1.76, 95% CI: 1.12–2.76; p = 0.014], requiring help injecting (aOR = 4.44, 95% CI: 2.64–7.46; p < 0.001), and involvement in the sex‐trade (aOR = 2.71, 95% CI: 1.6–4.55; p < 0.001). Interpretation. Reporting a history of jugular injecting was alarmingly high in the cohort and was associated with several identifiable demographic and drug‐using characteristics. Given previous reports demonstrating the risk of infection and vascular trauma due to this behaviour, these populations should be considered seriously as a target for safer injecting education.
A cross‐sectional survey of young people attending a music festival: associations between drug use and musical preference
Authors: LIM MEGAN S. C. , HELLARD MARGARET E. , HOCKING JANE S. , AITKEN CAMPBELL K.
Published: June 2008

Introduction and Aims. Drug use is becoming normalised among young Australian people involved in music sub‐cultures. We aimed to determine prevalences of illicit drug use in this population and associations between preferences for different music genres and recent use of particular illicit drugs. Design and Methods. A cross‐sectional questionnaire of young people (aged 16–29 years) attending a music festival. Results. Of 939 respondents, 46% had used illicit drugs (principally cannabis) in the past month, a significantly higher proportion than among respondents to the 2004 National Drug Strategy Household Survey (18%). Participants who favoured dance/house or rap music were more likely to have used illicit drugs recently than the remainder of the sample, while those who favoured pop or alternative music were less likely to have used drugs in the past month. Discussion and Conclusions. These data suggest that music festival attendees use illicit drugs more commonly than their age‐matched cohort in the general community, and that music festivals venues (particularly those that cater for dance/house and rap) would be appropriate places for interventions to promote safer drug use.
Patients' help‐seeking behaviours for health problems associated with methadone and buprenorphine treatment
Authors: WINSTOCK ADAM R. , LEA TOBY , SHERIDAN JANIE
Published: June 2008

Introduction and Aims. Clients in opioid substitution therapy often have considerable unmet health‐care needs. The current study aimed to explore health problems related to opioid substitution therapy among clients on methadone and buprenorphine treatment. Design and Methods. A self‐complete, cross‐sectional survey conducted among 508 patients receiving methadone and buprenorphine treatment at community pharmacies in New South Wales (NSW), Australia. Results. The most common problems for which participants had ever sought help were dental (29.9%), constipation (25.0%) and headache (24.0%). The most common problems for which participants would currently like help were dental (41.1%), sweating (26.4%) and reduced sexual enjoyment (24.2%). There were no significant differences between those currently on methadone and those currently on buprenorphine for any of the health problems explored, nor differences for gender or treatment duration. Participants on methadone doses 100 mg or above were significantly more likely to want help currently for sedation. Discussion and Conclusions. The considerable unmet health care needs among participants in this study suggest that treatment providers should consider improving the detection and response to common health problems related to opioid substitution therapy.
Alcohol and suicide in eastern Europe
Authors: LANDBERG JONAS
Published: June 2008

Introduction and Aims. The aim of this paper was to estimate how suicide rates in seven eastern European countries are affected by changes in population drinking and to put the results into a comparative perspective. Design and Methods. The analysis included data on annual suicide mortality rates and per capita consumption for the post‐war period from: Russia, Belarus, Poland, Hungary, Bulgaria, the former Czechoslovakia and the former German Democratic Republic (GDR). Overall and gender‐specific models were estimated using the Box–Jenkins technique for time–series analysis. The estimates were pooled into two groups, i.e. spirits countries (Russia, Belarus and Poland) and non‐spirits countries (Hungary, Bulgaria, former Czechoslovakia and former GDR). Results. All countries obtained positive alcohol effect estimates. The effects on the overall population were largest in the spirits countries, where a 1‐litre increase in per capita consumption was associated with an increase in overall suicide rates of 5.7–7.5%. The effects were somewhat smaller in the non‐spirits countries, 2.7–4.7%. The estimates for males were larger, but showed the same national variations as the overall population estimates. The female estimates were generally smaller than for men and did not differ between the two country groups. Discussion and Conclusions. The results suggest that per capita consumption matters for suicide mortality in these eastern European countries, but that the strength of the relationship is contingent upon the drinking culture, so that it tends to be stronger in countries with detrimental drinking patterns.
Reactivity of Brain Parenchymal Arterioles after Ischemia and Reperfusion
Authors: CIPOLLA MARILYN J. , BULLINGER LISA V.
Published: June 2008

Objective: We investigated the effect of ischemia and reperfusion on the vasoactive function of penetrating brain parenchymal arterioles under pressurized conditions.

Methods: Parenchymal arterioles (<50 μm in diameter) from within the middle cerebral artery territory were dissected from male Wistar rats that were either nonischemic control (n = 16) or ischemic for one hour and reperfused for 24 hours (n = 16) by temporary filament occlusion of the middle cerebral artery. Arterioles were mounted on glass cannulas within an arteriograph chamber that allowed for the measurement of lumen diameter and control over intravascular pressure.

Results: After one hour of equilibration at 10 mmHg, spontaneous myogenic tone developed in both groups of animals, constricting control arterioles from 69 ± 9 to 49 ± 11 μm (29.5 ± 10.2%) and ischemic arterioles from 66 ± 9 to 45 ± 11 μm (33.1 ± 14.1%); p > 0.05. Contraction to the nitric oxide synthase inhibitor nitro‐L‐arginine (10–4M) was significantly diminished in ischemic arterioles, constricting only 3.2 ± 3.3 vs. 15.6 ± 12.5% in control arterioles (p = 0.017). Both groups dilated to nifedipine; however, the response was significantly diminished after ischemia. The EC50 for nifedipine in control arterioles was 3.54 ± 0.11 vs. 9.90 ± 0.71 nM for ischemic arterioles (p = 0.024).

Conclusions: These findings demonstrate that functional changes occur in brain parenchymal arterioles after ischemia and reperfusion, a result that may significantly influence stroke outcome by altering blood flow to an ischemic region.
Central flattening of the fast-ion profile in reversed-shear DIII-D discharges
Authors: Heidbrink W.W. , Van Zeeland M.A. , Austin M.E. , Burrell K.H. , Gorelenkov N.N. , Kramer G.J. , Luo Y. , Makowski M.A. , McKee G.R. , Muscatello C. , Nazikian R. , Ruskov E. , Solomon W.M. , White R.B. , Zhu Y.
Published: June 2008

Neutral beam injection into a plasma with negative central shear produces a rich spectrum of toroidicity-induced and reversed-shear Alfvén eigenmodes in the DIII-D tokamak. The application of fast-ion Dα (FIDA) spectroscopy shows that the central fast-ion profile is flattened in the inner half of the discharge. Neutron and equilibrium measurements corroborate the FIDA data. The temporal evolution of the current profile is also strongly modified. Studies in similar discharges show that flattening of the profile correlates with the mode amplitude and that both types of Alfvén modes correlate with fast-ion transport. Calculations by the ORBIT code do not explain the observed fast-ion transport for the measured mode amplitudes, however. Possible explanations for the discrepancy are considered.