bluuebunny/crossref_metadata_2025 huggingface dataset:
Consistent relationship between global climate and surface nitrate utilization in the western subarctic Pacific throughout the last 500 ka
Authors: Galbraith Eric D. , Kienast Markus , Jaccard Samuel L. , Pedersen Thomas F. , Brunelle Brigitte G. , Sigman Daniel M. , Kiefer Thorsten
Published: May 2008

The open subarctic Pacific is, at present, a high nitrate low chlorophyll (HNLC) region, where nitrate is perennially abundant at the surface. Theoretically, the HNLC status of this region is subject to modification by ocean circulation and/or micronutrient supply, with implications for the effectiveness of the biological pump and hence carbon sequestration in the ocean interior. Records of biogenic detritus in sediments from throughout the subarctic Pacific indicate that export production was generally lower during glacial maxima, while nitrogen isotope measurements from the Bering Sea have shown that nitrate consumption there was more complete during the last glacial period than it is today. Here, nitrogen isotopic analyses of bulk sediments (δ15Nbulk) from three deep water sites in the open subarctic Pacific are evaluated in terms of regional nitrate isotopic composition and local relative nitrate utilization. The eastern subarctic Pacific δ15Nbulk record bears great similarity to δ15Nbulk records from the western margin of North America over the last glacial cycle, suggesting that variability in the isotopic composition of subeuphotic zone nitrate, the growth substrate, is reasonably coherent throughout the northeast Pacific and dominates at these sites. However, the two western subarctic Pacific records, which lie at the heart of the HNLC region, display a different pattern, implying that significant changes in local relative nitrate utilization overlie the regional background variability. After a novel correction intended to remove the background signal associated with denitrification in the eastern tropical North Pacific, these nitrate utilization records are correlated with a benthic oxygen isotope stack reflecting global deep ocean temperature and ice volume (r2 = 0.65). The correlation implies a strong link between global climate and subarctic Pacific nitrate utilization, with nearly complete nitrate consumption during glacial periods when export production was low.
Association of Monosodium Glutamate Intake With Overweight in Chinese Adults: The INTERMAP Study
Authors: He Ka , Zhao Liancheng , Daviglus Martha L. , Dyer Alan R. , Van Horn Linda , Garside Daniel , Zhu Liguang , Guo Dongshuang , Wu Yangfeng , Zhou Beifan , Stamler Jeremiah ,   INTERMAP Cooperative Research Group
Published: May 2008

Animal studies indicate that monosodium glutamate (MSG) can induce hypothalamic lesions and leptin resistance, possibly influencing energy balance, leading to overweight. This study examines the association between MSG intake and overweight in humans. We conducted a cross‐sectional study involving 752 healthy Chinese (48.7% women), aged 40–59 years, randomly sampled from three rural villages in north and south China. The great majority of participants prepared their foods at home, without use of commercially processed foods. Diet was assessed with four in‐depth multipass 24‐h recalls. Participants were asked to demonstrate MSG amounts added in food preparation. Amounts shaken out were weighed by trained interviewers. Overweight was defined as BMI ≥25.0 or ≥23.0 kg/m2(based on World Health Organization recommendations for Asian populations). Eighty‐two percent of participants were MSG users. Average intake was 0.33 g/day (s.d. = 0.40). With adjustment for potential confounders including physical activity and total energy intake, MSG intake was positively related to BMI. Prevalence of overweight was significantly higher in MSG users than nonusers. For users in the highest tertile of MSG intake compared to nonusers, the multivariable‐adjusted odds ratios of overweight (BMI ≥23.0 and ≥25.0) were 2.10 (95% confidence interval, 1.13–3.90, P for trend across four MSG categories = 0.03) and 2.75 (95% confidence interval, 1.28–5.95, P = 0.04). This research provides data that MSG intake may be associated with increased risk of overweight independent of physical activity and total energy intake in humans.
Erratum: “Wavelengths, Transition Probabilities, and Energy Levels for the Spectra of Rubidium (Rb I through Rb XXXVI)” [J. Phys. Chem. Ref. Data 35, 301–421 (2006)]
Authors: Sansonetti J. E.
Published: May 2008

Corrections to configuration, term, and J values for ns and nd levels, with n from 37 to 54, in the table Energy Levels of Rb I.
Interaction between turbulence and a nonlinear tearing mode in the low β regime
Authors: Militello F. , Waelbroeck F. L. , Fitzpatrick R. , Horton W.
Published: May 2008

The interaction between turbulence and a nonlinear tearing mode is investigated numerically using a 2D electrostatic model. Turbulence is found to cause transitions between the different roots for the propagation velocity of the mode. The transitions take the mode towards roots with slower propagation that are characterized by a locally flattened density profile. For sufficiently large islands the transition reduces the drive for the tearing mode.
Very high temperature laser heated furnace for Knudsen cell mass spectrometry
Authors: Colle Jean-Yves , Capone Franco
Published: May 2008

A very high temperature furnace (up to 3000°C) for the Knudsen cell mass spectrometry (KCMS) based on a laser heating technique has been developed. It is demonstrated that this system overcomes some of the typical technological problems encountered by the standard methods and can be more easily handled in special environments such as gloveboxes or hot cells. This paper describes the laser heated KCMS general design. The technology of the laser furnace along with its advantages, disadvantages, and applications is presented. Mechanical designs, some technical details, and the importance of the temperature control are also discussed.
Plasma-sheath instability in Hall thrusters due to periodic modulation of the energy of secondary electrons in cyclotron motion
Authors: Sydorenko D. , Smolyakov A. , Kaganovich I. , Raitses Y.
Published: May 2008

Particle-in-cell simulation of Hall thruster plasmas reveals a plasma-sheath instability manifesting itself as a rearrangement of the plasma sheath near the thruster channel walls accompanied by a sudden change of many discharge parameters. The instability develops when the sheath current as a function of the sheath voltage is in the negative conductivity regime. The major part of the sheath current is produced by beams of secondary electrons counter-streaming between the walls. The negative conductivity is the result of nonlinear dependence of beam-induced secondary electron emission on the plasma potential. The intensity of such emission is defined by the beam energy. The energy of the beam in crossed axial electric and radial magnetic fields is a quasiperiodical function of the phase of cyclotron rotation, which depends on the radial profile of the potential and the thruster channel width. There is a discrete set of stability intervals determined by the final phase of the cyclotron rotation of secondary electrons. As a result, a small variation of the thruster channel width may result in abrupt changes of plasma parameters if the plasma state jumps from one stability interval to another.
Cis
→
trans
, trans→cis isomerizations and N–O bond dissociation of nitrous acid (HONO) on an ab initio potential surface obtained by novelty sampling and feed-forward neural network fitting
Authors: Le Hung M. , Raff Lionel M.
Published: May 2008

The isomerization and dissociation dynamics of HONO are investigated on an ab initio potential surface obtained by fitting the results of electronic structure calculations at 21 584 configurations by using previously described novelty sampling and feed-forward neural network (NN) methods. The electronic structure calculations are executed by using GAUSSIAN 98 with a 6-311G(d) basis set at the MP4(SDQ) level of accuracy. The average absolute error of the NN fits varies from 0.012eV (1.22kJmol−1) to 0.017eV (1.64kJmol−1). The average computation time for a HONO trajectory using a single NN surface is approximately 4.8s. These computation times compare very favorably with those required by other methods primarily because the NN fitting needs to be executed only one time rather than at every integration point. If the average result obtained from a committee of NNs is employed at each point rather than a single NN, increased fitting accuracy can be achieved at the expense of increased computational requirements. In the present investigation, we find that a committee comprising five NN potentials reduces the average absolute interpolation error to 0.0111eV (1.07kJmol−1). Cis-trans isomerization rates with total energy of 1.70eV (including zero point energy) have been computed for a variety of different initial distributions of the internal energy. In contrast to results previously reported by using an empirical potential, where cis→trans to trans→cis rate coefficient ratios at 1.70eV total energy were found to lie in the range of 2.0–12.9 depending on the vibration mode excited, these ratios on the ab initio NN potential lie in the range of 0.63–1.94. It is suggested that this result is a reflection of much larger intramode coupling terms present in the ab initio potential surface. A direct consequence of this increased coupling is a significant decrease in the mode specific rate enhancement when compared to results obtained by using empirical surfaces. All isomerizations are found to be first order in accordance with the results reported by using empirical potentials. The dissociation rate to NO+OH has been investigated at internal HONO energies of 3.10 and 3.30eV for different distributions of this energy among the six vibrational modes of HONO. These dissociations are also found to be first order. The computed dissociation rate coefficients exhibit only modest mode specific rate enhancement that is significantly smaller than that obtained on an empirical surface because of the much larger mode couplings present on the ab initio surface.
Analytical study of turbulent Poiseuille flow with wall transpiration
Authors: Vigdorovich Igor , Oberlack Martin
Published: May 2008

An incompressible, pressure-driven, fully developed turbulent flow between two parallel walls, with an extra constant transverse velocity component, is considered. A closure condition is formulated, which relates the shear stress to the first and the second derivatives of the longitudinal mean velocity. The closure condition is derived without invoking any special hypotheses on the nature of turbulent motion, only taking advantage of the fact that the flow depends on a finite number of governing parameters. By virtue of the closure condition, the momentum equation is reduced to the boundary-value problem for a second-order differential equation, which is solved by the method of matched asymptotic expansions at high values of the logarithm of the Reynolds number based on the friction velocity. There are three characteristic flow regions in the channel: the core region and two wall regions near injection and suction walls. For each region, the solution is constructed. The asymptotic matching gives formulas for the wall shear stress and the maximum mean velocity. A limit transpiration velocity is obtained, such that the shear stress at the injection wall vanishes, while the maximum point on the velocity profile approaches the suction wall. In this case, a sublayer near the suction wall appears where the mean velocity is proportional to the square root of the distance from the wall. A friction law for Poiseuille flow with transpiration is found, which makes it possible to describe the relation between the wall shear stress, the Reynolds number, and the transpiration velocity by a function of one variable. A velocity defect law, which generalizes the classical law for the core region in a channel with impermeable walls to the case of transpiration, is also established. In similarity variables, the mean velocity profiles across the whole channel width outside viscous sublayers can be described by a one-parameter family of curves. The theoretical results obtained are in good agreement with available direct numerical simulation data.
Free enthalpy landscape of SrO
Authors: Schön J. C. , Čančarević Ž. P. , Hannemann A. , Jansen M.
Published: May 2008

Trying to predict thermodynamically stable and metastable solid compounds as function of pressure and temperature requires the global exploration of the enthalpy landscapes of chemical systems and the subsequent construction of their free enthalpy landscapes. In this work, we present a general approach to the determination of a free energy landscape. As an example, we construct the free enthalpy landscape of SrO for two different pressures on the empirical potential level and also compute various thermodynamic and elastic properties of SrO in the NaCl-, CsCl-, NiAs-, NbS-, TiP-, β−BeO, sphalerite-, and wurtzite-structure type on an ab initio level. We employ density functional theory within the hybrid B3LYP approximation. The results show good agreement with experimental and theoretical data.
A density functional study of a twisted nematic cell and its relation to the Frank–Oseen theory
Authors: de Vos Thierri , Baus Marc
Published: May 2008

The numerical results for the twist angle profile ξ(z) across a slab-shaped nematic cell obtained from a density functional theory (DFT) are compared to the predictions of the macroscopic Frank–Oseen theory. The latter theory predicts that ξ″(z)=0, and this is also seen to be the case for the DFT results. These do, however, verify the Frank–Oseen relation, λ±W±=K2, between the de Gennes extrapolation length (λ±), the anchoring energy per unit area of the (±) cell wall (W±), and the elastic constant of the nematic for twist deformations (K2), only if W± is nonlinearly related to the amplitude of the anchoring term of the DFT.
Cholesky decomposition of the two-electron integral matrix in electronic structure calculations
Authors: Røeggen I. , Johansen Tor
Published: May 2008

A standard Cholesky decomposition of the two-electron integral matrix leads to integral tables which have a huge number of very small elements. By neglecting these small elements, it is demonstrated that the recursive part of the Cholesky algorithm is no longer a bottleneck in the procedure. It is shown that a very efficient algorithm can be constructed when family type basis sets are adopted. For subsequent calculations, it is argued that two-electron integrals represented by Cholesky integral tables have the same potential for simplifications as density fitting. Compared to density fitting, a Cholesky decomposition of the two-electron matrix is not subjected to the problem of defining an auxiliary basis for obtaining a fixed accuracy in a calculation since the accuracy simply derives from the choice of a threshold for the decomposition procedure. A particularly robust algorithm for solving the restricted Hartree–Fock (RHF) equations can be speeded up if one has access to an ordered set of integral tables. In a test calculation on a linear chain of beryllium atoms, the advocated RHF algorithm nicely converged, but where the standard direct inversion in iterative space method converged very slowly to an excited state.
Quantum diffusion of hydrogen and muonium atoms in liquid water and hexagonal ice
Authors: Markland Thomas E. , Habershon Scott , Manolopoulos David E.
Published: May 2008

We have used the ring polymer molecular dynamics method to study the diffusion of muonium, hydrogen, and deuterium atoms in liquid water and hexagonal ice over a wide temperature range (8–361 K). Quantum effects are found to dramatically reduce the diffusion of muonium in water relative to that predicted by classical simulation. This leads to a simple explanation for the lack of any significant isotope effect in the observed diffusion coefficients of these species in the room temperature liquid. Our results indicate that the mechanism of the diffusion in liquid water is similar to the intercavity hopping mechanism observed in ice, supplemented by the diffusion of the cavities in the liquid. Within the same model, we have also been able to simulate the observed crossover in the c-axis diffusion coefficients of hydrogen and deuterium in hexagonal ice. Finally, we have been able to obtain good agreement with experimental data on the diffusion of muonium in hexagonal ice at 8 K, where the process is entirely quantum mechanical.
Response to “Comment on ‘Calculation of the mean first passage time tested on simple two-dimensional models’” [J. Chem. Phys. 128, 197102 (2008)]
Authors: Kalinay Pavol
Published: May 2008

Bowles et al. interpreted their simulation results [J. Chem. Phys.121, 10668 (2004)] for two diffusing disks in his Comment. They stressed that there is no support for the −3∕2 exponent of the power law dependence of the hopping time on the width of the bottleneck there. As my calculations [J. Chem. Phys.126, 194708 (2007)] were not contested, the problem remains unresolved.
Mass measuring instrument for use under microgravity conditions
Authors: Fujii Yusaku , Shimada Kazuhito , Yokota Masayuki , Hashimoto Seiji , Sugita Yoichi , Ito Hitomi
Published: May 2008

A prototype instrument for measuring astronaut body mass under microgravity conditions has been developed and its performance was evaluated by parabolic flight tests. The instrument, which is the space scale, is applied as follows. Connect the subject astronaut to the space scale with a rubber cord. Use a force transducer to measure the force acting on the subject and an optical interferometer to measure the velocity of the subject. The subject’s mass is calculated as the impulse divided by the velocity change, i.e., M=∫Fdt∕δv. Parabolic flight by using a jet aircraft produces a zero-gravity condition lasting approximately 20s. The performance of the prototype space scale was evaluated during such a flight by measuring the mass of a sample object.
The origin of the dynamic transition in proteins
Authors: Khodadadi S. , Pawlus S. , Roh J. H. , Garcia Sakai V. , Mamontov E. , Sokolov A. P.
Published: May 2008

Despite extensive efforts in experimental and computational studies, the microscopic understanding of dynamics of biological macromolecules remains a great challenge. It is known that hydrated proteins, DNA and RNA, exhibit a so-called “dynamic transition.” It appears as a sharp rise of their mean-squared atomic displacements ⟨r2⟩ at temperatures above 200–230K. Even after a long history of studies, this sudden activation of biomolecular dynamics remains a puzzle and many contradicting models have been proposed. By combining neutron and dielectric spectroscopy data, we were able to follow protein dynamics over an extremely broad frequency range. Our results show that there is no sudden change in the dynamics of the protein at temperatures around ∼200–230K. The protein’s relaxation time exhibits a smooth temperature variation over the temperature range of 180–300K. Thus the experimentally observed sharp rise in ⟨r2⟩ is just a result of the protein’s structural relaxation reaching the limit of the experimental frequency window. The microscopic mechanism of the protein’s structural relaxation remains unclear.
Superplastic deformation induced by cyclic hydrogen charging
Authors: Choe Heeman , Schuh Christopher A. , Dunand David C.
Published: May 2008

Deformation under the combined action of external stress and cyclic hydrogen charging/discharging is studied in a model material, titanium. Cyclic charging with hydrogen is carried out at 860 °C, which repeatedly triggers the transformation between hydrogen-lean α-Ti and hydrogen-rich β-Ti. Due to bias from the externally applied tensile stress, the internal mismatch strains produced by this isothermal α-β transformation accumulate preferentially along the loading axis. These strain increments are linearly proportional to the applied stress, i.e., flow is ideally Newtonian, at small stress levels (below ∼2 MPa). Therefore, after multiple chemical cycles, a tensile engineering strain of 100% is achieved without fracture, with an average strain rate of 10−5 s−1, which demonstrates for the first time that superplastic elongations can be achieved by chemical cycling. The effect of hydrogen partial pressure, cycle time, and external stress on the value of the superplastic strain increments is experimentally measured and discussed in light of a diffusional phase transformation model. Special attention is paid to understanding the two contributions to the internal mismatch strains from the phase transformation and lattice swelling.
Sub-MeV tunably polarized X-ray production with laser Thomson backscattering
Authors: Kawase K. , Kando M. , Hayakawa T. , Daito I. , Kondo S. , Homma T. , Kameshima T. , Kotaki H. , Chen L.-M. , Fukuda Y. , Faenov A. , Shizuma T. , Fujiwara M. , Bulanov S. V. , Kimura T. , Tajima T.
Published: May 2008

Reported in this article is the generation of unique polarized x-rays in the sub-MeV region by means of the Thomson backscattering of the Nd:YAG laser photon with a wavelength of 1064nm on the 150MeV electron from the microtron accelerator. The maximum energy of the x-ray photons is estimated to be about 400keV. The total energy of the backscattered x-ray pulse is measured with an imaging plate and a LYSO scintillator. The angular divergence of the x-rays is also measured by using the imaging plate. We confirm that the x-ray beam is polarized according to the laser polarization direction with the Compton scattering method. In addition, we demonstrate the imaging of the object shielded by lead with the generated x-rays.
Temperature dependence of polarized electroluminescence side emission from (0001)-oriented blue and violet InGaN∕GaN light-emitting diodes
Authors: Du Xiaozhang , Lu Hai , Han Ping , Zhang Rong , Zheng Youdou
Published: May 2008

Temperature dependent polarized electroluminescence from (0001)-oriented blue and violet InGaN∕GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) has been investigated. The viewing angle dependent light emission is found to be highly polarized perpendicular to the electrical field in the MQWs. The polarization ratio of 410nm LEDs exhibits monotonic decrease with increasing temperature from room temperature to 200°C. In contrast, the polarization ratio of 470nm LEDs initially increases with increasing temperature and then decreases at higher temperatures. This result suggests that carrier localization in quantum-dot-like structures could relax the polarization-related optical selection rule. Meanwhile, polarization ratios of side emission from both LEDs decrease at elevated injection current levels.
Self-aligned inversion-type enhancement-mode GaAs metal-oxide-semiconductor field-effect transistor with Al2O3 gate dielectric
Authors: Shahrjerdi D. , Akyol T. , Ramon M. , Garcia-Gutierrez D. I. , Tutuc E. , Banerjee S. K.
Published: May 2008

In this letter, we report fabrication of self-aligned inversion-type enhancement-mode GaAs metal-oxide-semiconductor (MOS) field-effect transistors with atomic layer deposition of Al2O3 gate dielectric directly on GaAs substrates using a simple ex situ wet clean of GaAs. Thermal stability of the gate stack was examined by monitoring the frequency dispersion behavior of GaAs MOS capacitors under different annealing conditions. A maximum drive current of ∼4.5μA∕μm was obtained for a gate length of 20μm at a gate overdrive of 2.5V. The threshold voltage and subthreshold slope were determined to be ∼0.4V and ∼145mV∕dec from the corresponding Id-Vg characteristics.
Observation of light-induced reorientational effects in periodic structures with planar nematic-liquid-crystal defects
Authors: Laudyn Urszula A. , Miroshnichenko Andrey E. , Krolikowski Wieslaw , Chen Deng Feng , Kivshar Yuri S. , Karpierz Miroslaw A.
Published: May 2008

We report on the experimental studies of the light-induced reorientational effects in a one-dimensional periodic photonic structure with an embedded planar nematic-liquid-crystal defect. We demonstrate that in the presence of a periodic structure, the self-action of light in a liquid-crystal layer demonstrates sharp power-dependent characteristics for the intensity-dependent optical transmission. Robustness of the effect suggests its applications for all-optical tunable photonic devices.
Interpretation of nanoscale conducting paths and their control in nickel oxide (NiO) thin films
Authors: Yoo I. K. , Kang B. S. , Park Y. D. , Lee M. J. , Park Y.
Published: May 2008

The behavior of unipolar resistance switching in NiO thin film was investigated. The switching current and the switching voltage alone did not follow statistical distribution. Instead, it was observed that product of switching current and switching voltage; namely, switching power follows Poisson’s distribution. An electrical manipulation—pulse train, for example—was suggested in order to minimize switching failure based on the above Poisson’s distribution behavior.
Synthesis, and Cyclization to Aurones and Flavones, of Alkoxy-Substituted Aryl, Arylalkynyl Ketones
Authors: Kerr Penelope J. , Pyke Simon M. , Ward A. David
Published: May 2008

Acylation of 1,3,5-tribenzyloxybenzene with alkoxy-substituted phenylpropioloyl chlorides provides the corresponding aryl alkoxylarylalkynyl ketones in which one of the benzyl groups has been removed. Cyclization of these phenolic ketones using basic reagents (potassium carbonate in acetone is best) provides the corresponding aurone system. When the phenolic group of the alkynyl ketones is protected as the t-butyldimethylsilyl ether followed by cyclization, using 18-crown-6 and potassium fluoride, mixtures of the corresponding aurones and flavones are produced. A by-product from the formation of the ketones is the corresponding β-chlorochalcone, which can also be cyclized to an aurone product using basic conditions. Similarly, the t-butyldimethylsilyl ethers of the HCl adducts can also be cyclized to a mixture of the corresponding aurones and flavones.
Synthesis, Optical Properties, and Characterization of New Soluble Conjugated Poly(p-phenylenevinylene) Derivatives Constituted of Alternating Pyrazole and 1,3,4-Oxadiazole Moieties
Authors: Chang En-Ming , Lee Cheng-Tien , Chen Chun-Yen , Wong Fung Fuh , Yeh Mou-Yung
Published: May 2008

Two new soluble poly(p-phenylenevinylene) derivatives with 1,3,4-oxadiazole and pyrazole rings along the main core were successfully synthesized by 1,3-dipolar addition, dehydration, and Heck coupling reaction. The new conjugated polymers are soluble in common organic solvents afforded by the fully conjugated backbone with soluble dedecyloxy side groups. The polymers showed relatively high glass-transition temperatures (~150°C) and good satisfactory thermal stability. Solutions of the polymers emitted bluish-green light with photoluminescence (PL) emission maxima around 530–540 nm. The PL spectrum for polymers of thin films, with a maximum at 570 nm, shows a red-shift (~35 nm) with respect to the solution spectrum. Cyclic voltammetry displayed that both conjugated polymers had reversible reduction and irreversible oxidation, making them n-type electroluminescent materials. The electron affinity of new polymers was estimated as 2.76–2.81 eV. The weight-average molecular weights (Mw) of the new soluble polymers were in the range 3400–3500.
Rapid Synthesis of O,O′-Dialkyl Alkylphosphonates on TLC with Analytical Purity for the Verification Analysis of Chemical Weapons Convention
Authors: Gupta Hemendra K. , Pardasani Deepak , Gupta Arvind K. , Jain Rajiv , Dubey D. K.
Published: May 2008

Reaction parameters for the rapid synthesis of O,O′-dialkyl alkylphosphonates and O-alkyl hydrogen alkylphosphonates were optimized using thin-layer chromatographic plates as a solid-supported platform under microwave irradiation. Immediate synthesis of these compounds with analytical purity is of paramount importance for the verification analysis of the Chemical Weapons Convention.
Synthesis, Characterization, and Ethylene Oligomerization and Polymerization by 2-Quinoxalinyl-6-iminopyridine Chromium Chlorides
Authors: Amolegbe Saliu A. , Asma Maliha , Zhang Min , Li Gang , Sun Wen-Hua
Published: May 2008

A series of chromium(iii) complexes ligated by N^N^N tridentate 2-quinoxalinyl-6-iminopyridine were synthesized and characterized by elemental analysis and infrared spectroscopy. Single-crystal X-ray diffraction analysis for the structure of complex C3 reveals a distorted octahedral geometry. When methylaluminoxane was employed as the co-catalyst, the chromium complexes showed high activities for ethylene oligomerization and polymerization. The distribution of oligomers obtained followed Schulz–Flory rules with high selectivity for α-olefins. Both steric and electronic effects of coordinated ligands affected the catalytic activities as well as the properties of the catalytic products. The parameters of the reaction conditions were also investigated to explore the optimum catalytic potentials of these complexes.
Nanoparticle-Based Photorefractive Polymers
Authors: Li Xiangping , Chon James W. M. , Gu Min
Published: May 2008

Photorefractivity has attracted intense attention owing to its ability to spatially modulate the refractive index under non-uniform light illumination. In particular, photorefractive polymers are appealing materials as they enable the high non-linear performance that underpins many areas of photonics. The incorporation of nanoparticles into photorefractive polymers shows an enormous potential owing to the broad spectroscopic tuning range and the high photogeneration efficiency, which are inaccessible to traditional photorefractive materials. This article reviews the recent developments in the field of nanoparticle-doped photorefractive polymers. The merit and functionality of these hybrid materials are summarized and future challenges are discussed. The application of nanoparticle-doped photorefractive polymers under two-photon excitation is also described, which facilitates a promising new area of high-density optical data storage, the third-generation of optical data storage.
Synthesis of Novel Chiral (Thio)ureas and Their Application as Organocatalysts and Ligands in Asymmetric Synthesis
Authors: Hernández-Rodríguez Marcos , Avila-Ortiz Claudia Gabriela , del Campo Jorge M. , Hernández-Romero Delia , Rosales-Hoz María J. , Juaristi Eusebio
Published: May 2008

The synthesis of novel chiral (thio)ureas 1–10 and 14–26 is described. These (thio)ureas incorporate chiral auxiliaries derived from (R)- or (S)-α-phenylethylamine, (R)-phenylglycine, or (1R,2S)-ephedrine. The phenylethyl group in compounds 1–10 and 21–24 adopts a particular orientation in the molecular structure as a consequence of 1,3-allylic strain with the (thio)carbonyl group. Ureas 1–10 were tested as Lewis basic organocatalysts in epoxide ring opening and in aldolic condensation, and it was found that the tetrasubstituted urea (R,R)-2 afforded the best results in terms of reaction yields. (Thio)ureas 20–26 were examined as ligands in the enantioselective diethylzinc addition to benzaldehyde, observing that C2-symmetric chiral urea (R,S,R,S)-20 provides the expected carbinol in nearly quantitative yield and in up to 62% enantiomeric excess.
Entropic contributions and the influence of the hydrophobic environment in promiscuous protein–protein association
Authors: Chang Chia-en A. , McLaughlin William A. , Baron Riccardo , Wang Wei , McCammon J. Andrew
Published: May 2008

The mechanisms by which a promiscuous protein can strongly interact with several different proteins using the same binding interface are not completely understood. An example is protein kinase A (PKA), which uses a single face on its docking/dimerization domain to interact with multiple A-kinase anchoring proteins (AKAP) that localize it to different parts of the cell. In the current study, the configurational entropy contributions to the binding between the AKAP protein HT31 with the D/D domain of RII α-regulatory subunit of PKA were examined. The results show that the majority of configurational entropy loss for the interaction was due to decreased fluctuations within rotamer states of the side chains. The result is in contrast to the widely held approximation that the decrease in the number of rotamer states available to the side chains forms the major component. Further analysis showed that there was a direct linear relationship between total configurational entropy and the number of favorable, alternative contacts available within hydrophobic environments. The hydrophobic binding pocket of the D/D domain provides alternative contact points for the side chains of AKAP peptides that allow them to adopt different binding conformations. The increase in binding conformations provides an increase in binding entropy and hence binding affinity. We infer that a general strategy for a promiscuous protein is to provide alternative contact points at its interface to increase binding affinity while the plasticity required for binding to multiple partners is retained. Implications are discussed for understanding and treating diseases in which promiscuous protein interactions are used.
Nitrogen fixation island and rhizosphere competence traits in the genome of root-associated
Pseudomonas stutzeri
A1501
Authors: Yan Yongliang , Yang Jian , Dou Yuetan , Chen Ming , Ping Shuzhen , Peng Junping , Lu Wei , Zhang Wei , Yao Ziying , Li Hongquan , Liu Wei , He Sheng , Geng Lizhao , Zhang Xiaobing , Yang Fan , Yu Haiying , Zhan Yuhua , Li Danhua , Lin Zhanglin , Wang Yiping , Elmerich Claudine , Lin Min , Jin Qi
Published: May 2008

The capacity to fix nitrogen is widely distributed in phyla of
Bacteria
and
Archaea
but has long been considered to be absent from the
Pseudomonas
genus. We report here the complete genome sequencing of nitrogen-fixing root-associated
Pseudomonas stutzeri
A1501. The genome consists of a single circular chromosome with 4,567,418 bp. Comparative genomics revealed that, among 4,146 protein-encoding genes, 1,977 have orthologs in each of the five other
Pseudomonas
representative species sequenced to date. The genome contains genes involved in broad utilization of carbon sources, nitrogen fixation, denitrification, degradation of aromatic compounds, biosynthesis of polyhydroxybutyrate, multiple pathways of protection against environmental stress, and other functions that presumably give A1501 an advantage in root colonization. Genetic information on synthesis, maturation, and functioning of nitrogenase is clustered in a 49-kb island, suggesting that this property was acquired by lateral gene transfer. New genes required for the nitrogen fixation process have been identified within the
nif
island. The genome sequence offers the genetic basis for further study of the evolution of the nitrogen fixation property and identification of rhizosphere competence traits required in the interaction with host plants; moreover, it opens up new perspectives for wider application of root-associated diazotrophs in sustainable agriculture.
Neuroprotection via matrix-trophic coupling between cerebral endothelial cells and neurons
Authors: Guo Shuzhen , Kim Woo Jean , Lok Josephine , Lee Sun-Ryung , Besancon Elaine , Luo Bing-Hao , Stins Monique F. , Wang Xiaoying , Dedhar Shoukat , Lo Eng H.
Published: May 2008

The neurovascular unit is an emerging concept that emphasizes homeostatic interactions between endothelium and cerebral parenchyma. Here, we show that cerebral endothelium are not just inert tubes for delivering blood, but they also secrete trophic factors that can be directly neuroprotective. Conditioned media from cerebral endothelial cells broadly protects neurons against oxygen-glucose deprivation, oxidative damage, endoplasmic reticulum stress, hypoxia, and amyloid neurotoxicity. This phenomenon is largely mediated by endothelial-produced brain-derived neurotrophic factor (BDNF) because filtering endothelial-conditioned media with TrkB-Fc eliminates the neuroprotective effect. Endothelial production of BDNF is sustained by β-1 integrin and integrin-linked kinase (ILK) signaling. Noncytotoxic levels of oxidative stress disrupts ILK signaling and reduces endothelial levels of neuroprotective BDNF. These data suggest that cerebral endothelium provides a critical source of homeostatic support for neurons. Targeting these signals of matrix and trophic coupling between endothelium and neurons may provide new therapeutic opportunities for stroke and other CNS disorders.
Synergistic upregulation of erythropoietin receptor (EPO-R) expression by sense and antisense EPO-R transcripts in the canine lung
Authors: Zhang Quiyang , Zhang Jianning , Moe Orson W. , Hsia Connie C. W.
Published: May 2008

We previously found increased erythropoietin receptor (EPO-R) protein levels in vigorously growing canine lungs after pneumonectomy (PNX), suggesting a role for paracrine EPO signaling in lung growth and remodeling. Now we find that sense and antisense EPO-R transcripts (sEPO-R and asEPO-R, respectively) are concordantly up-regulated in the post-PNX remaining lung, leading to the hypothesis that sEPO-R and asEPO-R interactions enhance EPO signaling during lung growth. We cloned a canine asEPO-R cDNA, which is fully complementary to the sense strand of the
EPO-R
gene from 2.5kb 3′ to the sense stop codon, and extends into the 5′ UTR of the sEPO-R transcript. Both asEPO-R and sEPO-R transcripts colocalize with EPO-R protein in the same lung cells. In cultured human embryonic kidney (HEK293) cells, transfection with sEPO-R (+FLAG tag) cDNA alone increased EPO-R protein expression (anti-EPO-R and anti-FLAG). At constant sEPO-R cDNA levels, cotransfection with escalating asEPO-R cDNA further increased recombinant EPO-R protein expression. The asEPO-R transcript harbors two putative opening reading frames (ORFs). Separate transfection of each asEPO-R ORF cDNA resulted in differential stimulatory effects on EPO-R protein expression. We conclude that both sEPO-R and asEPO-R transcripts contribute to
in vivo
up-regulation of EPO-R protein expression in the post-PNX remaining lung. This demonstrates synergism between sense–antisense EPO-R transcripts in response to physiological stimulation in a robust model of induced lung growth.
Indications of a negative impact of herring on recruitment of Norway pout
Authors: Huse Geir , Salthaug Are , Skogen Morten D.
Published: May 2008

Huse, G., Salthaug, A., and Skogen, M. D. 2008. Indications of a negative impact of herring on recruitment of Norway pout. – ICES Journal of Marine Science, 65: 906–911. The Norway pout (Trisopterus esmarkii) stock in the North Sea has experienced poor recruitment recently. Herring (Clupea harengus) has been suggested to be a major predator on fish larvae in the North Sea. We investigated possible interactions between herring and Norway pout using a simple statistical analysis and a modified stock–recruit relationship. There was a significant negative relationship (linear regression, r = −0.44, p < 0.05) between total herring biomass and recruitment of Norway pout. The spawning stock of Norway pout is typically dominated by 2-year-olds, and there was a strong negative relationship (linear regression, r = −0.79, p < 0.01) between herring biomass and Norway pout spawning-stock biomass (SSB) 2 years later. A Beverton–Holt model fitted to stock–recruit data of Norway pout produced a rather poor correlation (r2 = 0.04). However, when only the Norway pout SSB not overlapping with herring is considered, the fit between the model and the stock–recruit data improves (r2 = 0.31). The analyses indicate a negative impact by herring on recruitment of Norway pout, the most plausible cause for this being herring predation on Norway pout larvae, but field studies are needed to verify such predation.
Crammer's Corner
Authors: Riley Ben
Published: May 2008

Each month, Crammer's Corner features information and practical advice to help you learn the core knowledge and skills described in the RCGP curriculum and prepare for the new MRCGP assessments.
Acute Stroke in Primary Care
Authors: Simon Chantal
Published: May 2008

Hippocrates (460–370 BC) provided the first recorded description of the phenomenon of sudden paralysis. He termed the condition ‘apoplexy’ from the Greek meaning ‘struck down with violence’. The modern-day term ‘stroke’ is derived from a literal translation of this. Stroke is the most common cause of adult onset disability in the UK and is a devastating condition.
Prevention of Stroke
Authors: Simon Chantal
Published: May 2008

In England alone, over 100 000 people a year have a stroke. Three-quarters of them are over the age of 65 years. More than one in five of those individuals will die in the period immediately after their stroke. The survivors return to the community and every practice in the UK has a median prevalence of 14.7 patients who have had a stroke or transient ischaemic attack (TIA) per 1000 patients registered ( Fig. 1 ). Ninety per cent of those who survive will be left with some permanent disability as a result of their stroke, making stroke the most common cause of adult onset disability, and costing the nation more than £7 billion every year. This figure is set to rise as the population of the UK ages and people survive in a disabled state for longer.
Audit in Primary Care
Authors: Simon Chantal
Published: May 2008

An attitude of striving for continual improvement is extremely important in primary care. Ongoing monitoring by the practice of its standard of care and willingness to make changes is a fundamental part of good practice. Audit is a form of quality control.
Ethical Issues in Palliative Care
Authors: Simon Chantal
Published: May 2008

Ethics involves critical reflection on morality. Ethical principles are not laws, but guiding principles about what is ‘good’ and what is ‘bad’, that should direct doctors and other health care professionals in their work and decision making. Issues arising over end-of-life care involving decisions that affect the nature and timing of an individual's death raise difficult ethical conflicts for all concerned and can be a source of discord between health professionals within a team, health professionals and family members, or between different family members. It is not possible to explore all aspects of such decisions, so this article aims to address just the common issues likely to affect GPs on a day-to-day basis.
Effects of Nighttime Temperature During Kernel Development on Rice Physicochemical Properties
Authors: Cooper N. T. W. , Siebenmorgen T. J. , Counce P. A.
Published: May 2008

Rice quality can vary inexplicably from one lot to another and from year to year. One cause could be the variable temperatures experienced during the nighttime hours of rice kernel development. During the fall of 2004, a controlled temperature study was conducted using large growth chambers, testing nighttime temperatures of 18, 22, 26, and 30°C from 12 a.m. until 5 a.m. throughout kernel development, using rice cultivars Cypress, LaGrue, XP710, XL8, M204, and Bengal. As nighttime temperature increased, head rice yields (HRY) significantly decreased for all cultivars except Cypress and Bengal, for which HRY did not vary among nighttime temperature treatments. Kernel mass did not vary among temperature treatments for any cultivar. Grain dimensions generally decreased as nighttime temperature increased. The number of chalky kernels increased with an increase in nighttime temperature for all cultivars but Cypress. The amylose content of Cypress and LaGrue was significantly lower at the nighttime temperature of 30°C, while total brown rice lipid and protein contents did not vary among temperature treatments for all cultivars.
Isolation, Fractionation, and Structural Characteristics of Alkali‐Extractable β‐Glucan from Rye Whole Meal
Authors: Ragaee S. M. , Wood P. J. , Wang Q. , Tosh S. M. , Brummer Y. , Huang X.
Published: May 2008

The main nonstarch polysaccharide of rye is arabinoxylan (AX), but rye contains significant levels of (1→3)(1→4)‐β‐d‐glucan, which unlike oat and barley β‐glucan, is not readily extracted by water, possibly because of entrapment within a matrix of AX cross‐linked by phenolics. This study continues objectives to improve understanding of factors controlling the physicochemical behavior of the cereal β‐glucans. Rye β‐glucan was extracted by 1.0N NaOH and increasing concentrations of ammonium sulfate were used to separate the β‐glucan from AX and prepare a series of eight narrow molecular weight (MW) distribution fractions. Composition and structural characteristics of the isolated β‐glucan and the eight fractions were determined. High‐performance size‐exclusion chromatography (HPSEC) with both specific calcofluor binding and a triple detection (light scattering, viscometry, and refractive index) system was used for MW determination. Lichenase digestion followed by high‐performance anion exchange chromatography of released oligosaccharides, was used for structural evaluation. The overall structure of all fractions was similar to that of barley β‐glucan.
Influence of Starch and Gluten Characteristics on Rheological Properties of Wheat Flour Gel at Small and Large Deformation
Authors: Sasaki Tomoko , Yasui Takeshi , Kohyama Kaoru
Published: May 2008

Starch and gluten were isolated from 10 wheat cultivars or lines with varied amylose content. The rheological properties of 30% wheat flour gel, starch gel, and the gel of isolated gluten mixed with common starch were determined in dynamic mechanical testing under shear deformation, creep‐recovery, and compression tests under uniaxial compression. Variation of wheat samples measured as storage shear modulus (G′), loss shear modulus (G″), and loss tangent (tan δ = G″/G′) was similar between flour and starch gels and correlated significantly between flour and starch gel. The proportion of acetic acid soluble glutenin exhibited a significant relationship with tan δ of gluten‐starch mixture gel. The small difference in amylose content strongly affected the rheological parameters of flour gels in creep‐recovery measurement. Wheat flour gel with lower amylose content showed higher creep and recovery compliance that corresponded to the trend in starch gel. Compressive force of flour gel at 50 and 95% strain correlated significantly with that of starch gel. Gel mixed with the isolated gluten from waxy wheat lines appeared to have a weaker gel structure in dynamic viscoelasticity, creep‐recovery, and compression tests. Starch properties of were primarily responsible for rheological changes in wheat flour gel.
Storage of Wheat Grains at Elevated Temperatures Increases Solubilization of Glutenin Subunits
Authors: Wilkes Meredith , Copeland Les
Published: May 2008

Grains of two wheat (Triticum aestivum L.) cultivars, Sunco and Sunsoft, were stored at 4°C and 30°C for 270 days to examine changes in proteins during storage. When whole meal flour extracted from the grains was analyzed using an unfractionated protein extraction procedure, no significant changes were found in protein content or SDS‐PAGE profile for either cultivar in samples stored at 30°C compared with those stored at 4°C. Fractionation of the flour samples from stored grain into soluble and insoluble proteins revealed increases in soluble protein content for both cultivars stored at 30°C compared with 4°C. The soluble protein content, expressed as a percentage of the total protein, increased by 1.5% (P = 0.032) for Sunco and by 8.0 % (P = 0.158) for Sunsoft during storage at 30°C compared with those samples stored at 4°C. Analysis by SDS‐PAGE and subsequent protein identification revealed that the most evident change that occurred during storage at 30°C was an increase in the content of high molecular weight glutenin subunits (HMW‐GS) in the soluble fraction. The potential effect of changes in solubility of HMW‐GS on functional properties is discussed.