bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of central inhibition of sympathetic nervous activity on myocardial metabolism in chronic heart failure: acute effects of the imidazoline I1-receptor agonist moxonidine
Authors: Mobini Reza , Fu Michael , Jansson Per-Anders , Bergh Claes-Håkan , Scharin Täng Margareta , Waagstein Finn , Andersson Bert
Published: November 2007

Although β-adrenergic blockade is beneficial in heart failure, inhibition of central sympathetic outflow using moxonidine has been associated with increased mortality. In the present study, we studied the acute effects of the imidazoline-receptor agonist moxonidine on haemodynamics, NA (noradrenaline) kinetics and myocardial metabolism. Fifteen patients with CHF (chronic heart failure) were randomized to a single dose of 0.6 mg of sustained-release moxonidine or matching placebo. Haemodynamics, NA kinetics and myocardial metabolism were studied over a 2.5 h time period. There was a significant reduction in pulmonary and systemic arterial pressures, together with a decrease in cardiac index in the moxonidine group. Furthermore, there was a simultaneous reduction in systemic and cardiac net spillover of NA in the moxonidine group. Analysis of myocardial consumption of substrates in the moxonidine group showed a significant increase in non-esterified fatty acid consumption and a possible trend towards an increase in myocardial oxygen consumption compared with the placebo group (P=0.16). We conclude that a single dose of moxonidine (0.6 mg) in patients already treated with a β-blocker reduced cardiac and overall sympathetic activity. The finding of increased lipid consumption without decreased myocardial oxygen consumption indicates a lack of positive effects on myocardial metabolism under these conditions. We suggest this might be a reason for the failure of moxonidine to prevent deaths in long-term studies in CHF.
Role of osteoprotegerin (OPG) in cancer
Authors: Holen Ingunn , Shipman Claire M.
Published: November 2007

OPG (osteoprotegerin), a secreted member of the TNF (tumour necrosis factor) receptor superfamily, has a variety of biological functions which include the regulation of bone turnover. OPG is a potent inhibitor of osteoclastic bone resorption and has been investigated as a potential therapeutic for the treatment of both osteoporosis and tumour-induced bone disease. Indeed, in murine models of cancer-induced bone disease, inhibition of osteoclastic activity by OPG was also associated with a reduction in tumour burden. The discovery that OPG can bind to and inhibit the activity of TRAIL (TNF-related apoptosis-inducing ligand) triggered extensive research into the potential role of OPG in the regulation of tumour cell survival. A number of reports from studies using in vitro models have shown that OPG protects tumour cells from the effects of TRAIL, thereby possibly providing tumour cells that produce OPG with a survival advantage. However, the ability of OPG to act as a tumour cell survival factor remains to be verified using appropriate in vivo systems. A third area of interest has been the use of OPG as a prognostic marker in various cancer types, including myeloma, breast and prostate cancer. This review provides an overview of the role of OPG in cancer, both in cancer-induced bone disease and in tumour growth and survival.
Granulocyte apoptosis in the pathogenesis and resolution of lung disease
Authors: Bianchi Stephen M. , Dockrell David H. , Renshaw Stephen A. , Sabroe Ian , Whyte Moira K. B.
Published: November 2007

Apoptosis, programmed cell death, of neutrophil and eosinophil granulocytes is a potential control point in the physiological resolution of innate immune responses. There is also increasing evidence that cellular processes of apoptosis can be dysregulated by pathogens as a mechanism of immune evasion and that delayed apoptosis, resulting in prolonged inflammatory cell survival, is important in persistence of tissue inflammation. The identification of cell-type specific pathways to apoptosis may allow the design of novel anti-inflammatory therapies or agents to augment the innate immune responses to infection. This review will explore the physiological roles of granulocyte apoptosis and their importance in infectious and non-infectious lung disease.
Immune responses toHelicobacter pyloricolonization: mechanisms and clinical outcomes
Authors: Portal-Celhay Cynthia , Perez-Perez Guillermo I.
Published: November 2007

Helicobacter pylori colonizes the stomachs of half of the world's population and usually persists in the gastric mucosa of human hosts for decades or life. Although most H. pylori-positive people are asymptomatic, the presence of H. pylori is associated with increased risk for the development of peptic ulcer disease, gastric adenocarcinoma and gastric lymphoma. The development of a sustained gastric inflammatory and immune response to infection appears to be pivotal for the development of disease. During its long co-existence with humans, H. pylori has evolved complex strategies to maintain a mild inflammation of the gastric epithelium while limiting the extent of immune effector activity. In this review, the nature of the host immune response to H. pylori infection and the mechanism employed by the bacterium to evade them is considered. Understanding the mechanisms of colonization, persistence and virulence factors of the bacterium as well as the innate and adaptive immune responses of the host are critically important for the development of new strategies to prevent the development of H. pylori-induced gastroduodenal disease.
Side-effects of L-dopa on venous tone in Parkinson's disease: a leg-weighing assessment
Authors: Wolf Jean-Pierre , Bouhaddi Malika , Louisy Francis , Mikehiev Andrei , Mourot Laurent , Cappelle Sylvie , Vuillier Fabrice , Andre Pierre , Rumbach Lucien , Regnard Jacques
Published: November 2007

In the present study, the effects of L-dopa treatment on cardiovascular variables and peripheral venous tone were assessed in 13 patients with Parkinson's disease (PD) with Hoehn and Yahr stages 1–4. Patients were investigated once with their regular treatment and once after 12 h of interruption of L-dopa treatment. L-Dopa intake significantly reduced systolic and diastolic blood pressure, heart rate and plasma noradrenaline and adrenaline in both the supine and upright (60°) positions. A significant reduction in stroke volume and cardiac output was also seen with L-dopa. The vascular status of the legs was assessed through thigh compression during leg weighing, a new technique developed in our laboratory. Healthy subjects were used to demonstrate that this technique provided reproducible results, consistent with those provided by strain gauge plethysmography of the calf. When using this technique in patients with PD, L-dopa caused a significant lowering of vascular tone in the lower limbs as shown, in particular, by an increase in venous distensibility. Combined with the results of the orthostatic tilting, these findings support that the treatment-linked lowering of plasma noradrenaline in patients with PD was concomitant with a significant reduction in blood pressure, heart rate and vascular tone in the lower limbs. These pharmacological side-effects contributed to reduce venous return and arterial blood pressure which, together with a lowered heart rate, worsened the haemodynamic status.
Effect of the angiotensin II receptor blocker olmesartan on the development of murine acute myocarditis caused by coxsackievirus B3
Authors: Seko Yoshinori
Published: November 2007

Ang II (Angiotensin II) has been shown to play a pivotal role in the pathophysiology of various organs, especially the cardiovascular system. The effects of ARBs (Ang II receptor blockers) in the treatment of hypertension, congestive heart failure and myocardial fibrosis have been analysed extensively in human trials, as well as animal models, and the focus of interest is now directed to its pleiotropic effects, especially on inflammatory disorders. To investigate the effects of a new ARB, olmesartan, on immune-mediated myocardial injury, the protective effects of olmesartan on the development of murine acute myocarditis caused by CVB3 (coxsackievirus B3) were analysed. Olmesartan and a non-specific vasodilator hydralazine lowered systolic blood pressure of mice on day 7 after virus inoculation to a similar extent. Olmesartan significantly decreased myocardial inflammation compared with controls, whereas hydralazine significantly increased this. Olmesartan significantly decreased the expression of IFN-γ (interferon-γ), FasL (Fas ligand), iNOS (inducible nitric oxide synthase) and PFP (pore-forming protein) in myocardial tissue, indicating that olmesartan suppressed the activation of infiltrating killer lymphocytes. Olmesartan also decreased the expression of CVB3 genomes in myocardial tissue as well as serum levels of 8-OHdG (8-hydroxy-2′-deoxyguanosine), a biomarker of oxidative-stress-induced DNA damage. The findings suggest that olmesartan prevents myocardial damage and may improve the prognosis of patients with acute myocarditis; however, further investigations are needed before clinical use.
TNF-α levels are associated with skin capillary recruitment in humans: a potential explanation for the relationship between TNF-α and insulin resistance
Authors: Ijzerman Richard G. , Voordouw Jasper J. , Van Weissenbruch Mirjam M. , Yudkin John S. , Serné Erik H. , Delemarre-Van De Waal Henriette A. , Stehouwer Coen D. A.
Published: November 2007

The mechanism by which TNF-α (tumour necrosis factor-α) may cause insulin resistance is not clear. On the basis of experiments in rats, TNF-α has been suggested to cause defects in capillary function, with a decreased access of insulin and glucose to tissues. To test this hypothesis in humans, we assessed serum TNF-α concentrations, skin capillary recruitment and insulin sensitivity in a group of 37 healthy adults. In addition, we measured these variables in 21 of their prepubertal children. Serum TNF-α levels were measured by sandwich enzyme immunoassay, and insulin sensitivity was assessed with the hyperinsulinaemic euglycaemic clamp technique. Capillary recruitment during post-occlusive reactive hyperaemia was evaluated by videomicroscopy. In the adults, serum TNF-α levels were associated with both capillary recruitment (r=−0.40, P=0.02) and insulin sensitivity (r=−0.33, P=0.05). In addition, capillary recruitment was associated with insulin sensitivity (r=0.34, P=0.04). Regression analysis showed that the association between TNF-α and insulin sensitivity [−0.527 mg·kg−1 of body weight·min−1 per pmol/l per pg/ml TNF-α (95% confidence interval, −1.066 to 0.011); P=0.05] decreased by 30% after adjustment for capillary recruitment. In the children, neither capillary recruitment (r=0.33, P=0.2) nor insulin sensitivity (r=−0.24, P=0.4) was significantly associated with TNF-α. In conclusion, in adults, but not in children, serum TNF-α levels are associated with capillary recruitment during post-occlusive hyperaemia, which, in part, can explain the relationship between TNF-α and insulin resistance. Our data suggest that these relationships are initiated during growth from childhood to adulthood.
A comparison between active- and reactive-hyperaemia-induced brachial artery vasodilation
Authors: Padilla Jaume , Harris Ryan A. , Fly Alyce D. , Rink Lawrence D. , Wallace Janet P.
Published: November 2007

The measurement of brachial artery vasodilation in response to a hyperaemic stimulus has been used extensively to assess changes in endothelial function. However, whether or not similar changes occur in response to an active hyperaemic stimulus is unknown. The purpose of the present study was to compare brachial artery vasodilation in response to an active compared with a reactive hyperaemic stimulus following a known perturbation of endothelial function. Eight apparently healthy adults were assigned to four treatment conditions in a counter-balanced design: (i) low-fat meal with active hyperaemic stimulus (LFM-A), (ii) high-fat meal with active hyperaemic stimulus (HFM-A), (iii) low-fat meal with reactive hyperaemic stimulus (LFM-R), and (iv) high-fat meal with reactive hyperaemic stimulus (HFM-R). Meals were ingested at 08:00 hours on each treatment day. Brachial artery vasodilation was assessed via ultrasound 4 h after ingestion of each meal. The active hyperaemic stimulus was induced by 5 min of rhythmic handgrip exercise, whereas reactive hyperaemia was induced by 5 min of forearm occlusion. Brachial artery vasodilation was expressed as the percentage change in diameter from baseline to post-active/reactive hyperaemia. Using a 2×2 repeated measures ANOVA, a significant stimulus×meal interaction (P=0.025) was found. Simple main effects revealed no difference (P=0.541) in brachial artery vasodilation between LFM-A (5.75±1.64%) and HFM-A (6.39±1.45%); however, a significant decrease (P=0.014) in brachial artery vasodilation was found in the HFM-R (4.29±1.64%) compared with the LFM-R (7.18±1.13%) treatment. In conclusion, the measurement of brachial artery vasodilation in response to active hyperaemia did not detect a change in endothelial function following a single perturbation meal, whereas reactive hyperaemia did.
Mesenchymal stem cells in rheumatology: a regenerative approach to joint repair
Authors: De Bari Cosimo , Dell'Accio Francesco
Published: November 2007

The advent of biologics in rheumatology has considerably changed the evolution and prognosis of chronic inflammatory arthritis. The success of these new treatments has contributed to steering more attention to research focussed on repair and remodelling of joint tissues. Indeed, when the tissue damage is established, treatment options are very limited and the risk of progression towards joint destruction and failure remains high. Increasing evidence indicates that mesenchymal stem cells persist postnatally within joint tissues. It is postulated that they would function to safeguard joint homoeostasis and guarantee tissue remodelling and repair throughout life. Alterations in mesenchymal stem cell biology in arthritis have indeed been reported but a causal relationship has not been demonstrated, mainly because our current knowledge of mesenchymal stem cell niches and functions within the joint in health and disease is very limited. Nonetheless, mesenchymal stem cell technologies have attracted the attention of the biomedical research community as very promising tools to achieve the repair of joint tissues such as articular cartilage, subchondral bone, menisci and tendons. This review will outline stem-cell-mediated strategies for the repair of joint tissues, spanning from the use of expanded mesenchymal stem cell populations to therapeutic targeting of endogenous stem cells, resident in their native tissues, and related reparative signals in traumatic, degenerative and inflammatory joint disorders.
Beyond the step model: Approximate expressions for the field in the plasma boundary sheath
Authors: Brinkmann Ralf Peter
Published: November 2007

The transition from quasineutrality to charge depletion is one of the characteristic features of the plasma boundary sheath. For modeling purposes, this transition is often described in terms of the so-called step model which assumes a sharp transition point s (electron step) where the electron density ne drops from a value equal to the ion density ni (in the bulk, x>s) to a value of zero (in the sheath, x<s). Inserted into Poisson’s equation, the step model yields an expression for the field which is realistic deep in the sheath (for x≪s) but fails to merge correctly into the ambipolar field of the bulk. This work considers the transition from quasineutrality to charge depletion more rigorously. Within the framework of asymptotic scale analysis, a family of field approximations is derived which, in the limit of weak spatial ion density variation ∂ni∕∂x≪ni∕λD, exhibit convergence to the exact solution of the Boltzmann–Poisson equation. The first of the approximations recovers only the step model. Higher order expressions, however, also include the ambipolar field and are valid for all values of x. The simplest of them is proposed as being the best suited for a self-consistent sheath analysis. This statement is backed by numerical experiments which show good results for the ion density distribution provided by the collision dominated sheath model.
Nonvariational time-dependent multiconfiguration self-consistent field equations for electronic dynamics in laser-driven molecules
Authors: Nguyen-Dang T. Tung , Peters Michel , Wang Sen-Ming , Sinelnikov Evgueni , Dion François
Published: November 2007

A time-dependent multiconfiguration self-consistent field (TDMCSCF) scheme is developed to describe the time-resolved electron dynamics of a laser-driven many-electron atomic or molecular system, starting directly from the time-dependent Schrödinger equation for the system. This nonvariational formulation aims at the full exploitations of concepts, tools, and facilities of existing, well-developed quantum chemical MCSCF codes. The theory uses, in particular, a unitary representation of time-dependent configuration mixings and orbital transformations. Within a short-time, or adiabatic approximation, the TDMCSCF scheme amounts to a second-order split-operator algorithm involving generically the two noncommuting one-electron and two-electron parts of the time-dependent electronic Hamiltonian. We implement the scheme to calculate the laser-induced dynamics of the two-electron H2 molecule described within a minimal basis, and show how electron correlation is affected by the interaction of the molecule with a strong laser field.
Breaking bonds with the left eigenstate completely renormalized coupled-cluster method
Authors: Ge Yingbin , Gordon Mark S. , Piecuch Piotr
Published: November 2007

The recently developed [P. Piecuch and M. Wloch, J. Chem. Phys. 123, 224105 (2005)] size-extensive left eigenstate completely renormalized (CR) coupled-cluster (CC) singles (S), doubles (D), and noniterative triples (T) approach, termed CR-CC(2,3) and abbreviated in this paper as CCL, is compared with the full configuration interaction (FCI) method for all possible types of single bond-breaking reactions between C, H, Si, and Cl (except H2) and the H2SiSiH2 double bond-breaking reaction. The CCL method is in excellent agreement with FCI in the entire region R=1–3Re for all of the studied single bond-breaking reactions, where R and Re are the bond distance and the equilibrium bond length, respectively. The CCL method recovers the FCI results to within approximately 1mhartree in the region R=1–3Re of the H–SiH3, H–Cl, H3Si–SiH3, Cl–CH3, H–CH3, and H3C–SiH3 bonds. The maximum errors are −2.1, 1.6, and 1.6mhartree in the R=1–3Re region of the H3C–CH3, Cl–Cl, and H3Si–Cl bonds, respectively, while the discrepancy for the H2SiSiH2 double bond-breaking reaction is 6.6 (8.5)mhartree at R=2(3)Re. CCL also predicts more accurate relative energies than the conventional CCSD and CCSD(T) approaches, and the predecessor of CR-CC(2,3) termed CR-CCSD(T).
Do supercooled liquids freeze by spinodal decomposition?
Authors: Bartell Lawrence S. , Wu David T.
Published: November 2007

Two questions are addressed in this paper: Is it likely that spinodals occur in the freezing of one-component liquids at degrees of supercooling as moderate as T∕Tmelt=0.6, and are the ramified solidlike structural fluctuations seen in simulations of supercooled liquids the tell-tale harbingers of spinodal decomposition? It has been suggested in several papers that in the freezing of argonlike systems, a spinodal can be expected to be encountered at T∕Tmelt of ∼0.6 or even at a shallower degree of supercooling. Heuristic evidence, particularly that found in molecular dynamics simulations in the system of selenium hexafluoride, a substance with properties similar in several respects to those of argon, suggests that a spinodal does not occur at supercoolings even considerably deeper than T∕Tmelt=0.6. Reinforcing this conclusion are arguments based on nucleation kinetics in the Appendix. It has been found that many of the very thin, ramified solidlike fluctuations encountered in simulations of deeply supercooled liquids do not, in themselves, qualify as true nuclei for freezing but do, nevertheless, significantly influence the properties of the liquids. They contribute to the breakdown of the Stokes-Einstein relation universally found in supercooled liquids, liquids which have not been seen to exhibit a spinodal. Although such ramified fluctuations have been postulated to be precursors of spinodal decomposition, that role has not yet been confirmed.
Solvation shell dynamics studied by molecular dynamics simulation in relation to the translational and rotational dynamics of supercritical water and benzene
Authors: Yoshida Ken , Matubayasi Nobuyuki , Nakahara Masaru
Published: November 2007

The solvation shell dynamics of supercritical water is analyzed by molecular dynamics simulation with emphasis on its relationship to the translational and rotational dynamics. The relaxation times of the solvation number (τS), the velocity autocorrelation function (τD), the angular momentum correlation function (τJ), and the second-order reorientational correlation function (τ2R) are studied at a supercritical temperature of 400°C over a wide density region of 0.01–1.5gcm−3. The relaxation times are decomposed into those conditioned by the solvation number n, and the effect of the short-ranged structure is examined in terms of its probability Pn of occurrence. In the low to medium-density range of 0.01–0.4gcm−3, the time scales of water dynamics are in the following sequence: τD>τS≳τJ≳τ2R. This means that the rotation in supercritical water is of the “in-shell” type while the translational diffusion is not. The comparison to supercritical benzene is also performed and the effect of hydrogen bonding is examined. The water diffusion is not of the in-shell type up to the ambient density of 1.0gcm−3, which corresponds to the absence of the transition from the collision to the Brownian picture, whereas such transition is present in the case of benzene. The absence of the transition in water comes from the fast reorganization of the hydrogen bonds and the enhanced mobility of the solvation shell in supercritical conditions.
Density functional description of adsorption in slitlike pores modified with chain molecules: A simple model for pillaredlike materials
Authors: Matusewicz M. , Patrykiejew A. , Sokołowski S. , Pizio O.
Published: November 2007

We propose a density functional theory to describe adsorption of Lennard-Jones fluid in slitlike pores modified by chain molecules. Specifically, the chains are bonded by their ends to the opposite pore walls, so they can form pillaredlike structure. Two models are studied. In the first model, the nonterminating segments of chains can change their configuration inside the pore upon adsorption of spherical species. In the second model, the chains configuration remains fixed, so that the system is similar to a nonuniform quenched-annealed mixture. We study capillary condensation of fluid species inside such modified pores and compare the results obtained for two models.
Stability study of the floating zone with respect to the Prandtl number value
Authors: Bouizi Othman , Delcarte Claudine , Kasperski Guillaume
Published: November 2007

Thermocapillary convection in a laterally heated liquid bridge is studied numerically, using a Chebyshev spectral method. The stability of the axisymmetric basic state, with respect to 3D perturbations, is characterized over a large range of Prandtl number values (Pr∊[10−3,102]), thanks to the choice of a sufficiently sharp regularizing function of the vorticity singularities. Criteria are established to ensure the compatibility of this function with mass conservation, and to choose a correct model of the lateral heat flux in order to reach a spectral convergence of the results. First 3D nonlinear spectral computations are presented.
Metal-high-k-high-k-oxide-semiconductor capacitors and field effect transistors using Al∕La2O3∕Ta2O5∕SiO2∕Si structure for nonvolatile memory applications
Authors: Cheng Chih-Hao , Lee Joseph Ya-Min
Published: November 2007

A metal-high-k-high-k-oxide-silicon structure was fabricated for nonvolatile memory applications. Al∕La2O3∕Ta2O5∕SiO2∕Si capacitors and field effect transistors were fabricated using Ta2O5 as the charge storage layer and La2O3 as the blocking layer. The programing time of the Al∕La2O3∕Ta2O5∕SiO2∕Si transistors was characterized. With a programing pulse voltage of 6V, a threshold voltage shift of more than 0.5V was achieved in 10ns. As for the retention properties, the Al∕La2O3∕Ta2O5∕SiO2∕Si transistors can keep a ΔVth window of 0.83V for 10yr.
Micromagnetic simulations of current-induced magnetization switching in Co∕Cu∕Co nanopillars
Authors: Xiao Z. H. , Ma X. Q. , Wu P. P. , Zhang J. X. , Chen L. Q. , Shi S. Q.
Published: November 2007

We studied the current-induced magnetic switching in Co∕Cu∕Co nanopillars with an in-plane magnetization traversed by a perpendicular-to-plane spin-polarized current. The Landau-Lifshitz-Gilbert equation incorporating the spin transfer torque (STT) effect was employed. Magnetization switching was found to take place when the current density exceeds a threshold. It is accompanied by drastic oscillations near the magnetic reversal point. The switching time depends on the applied current density. The magnetization can also be switched by a sufficiently long square pulsed current. The roles of anisotropy, exchange, and demagnetization energies in the magnetization switching process of nanopillars are discussed. It is shown that the switching is mainly determined by the competition between STT and the Gilbert damping torque.
Wide band gaps and low-loss waveguiding in ceramic high dielectric constant photonic crystals
Authors: Meisels R. , Oberhumer P. , Kuchar F. , Aldrian F. , Gajic R.
Published: November 2007

Photonic crystals based on dielectric material with very high dielectric constant ε are investigated by transmission experiments in the microwave range and by calculations of the band structure and wave propagation. The material used is a tungsten-bronze-type ceramic (BaO–Nd2O3–4TiO2) with ε≈90. Our results demonstrate the superior properties of such a material, including omnidirectional and complete gaps, and improved waveguiding. This type of photonic crystals opens an additional road for basic research and applications regarding electronic devices in the radio frequency and microwave ranges as well as for spectroscopic techniques in the terahertz range.
Kinetic theory of a confined polymer driven by an external force and pressure-driven flow
Authors: Butler Jason E. , Usta O. Berk , Kekre Rahul , Ladd Anthony J. C.
Published: November 2007

Kinetic theory is used to investigate the mechanisms causing cross-stream migration of confined polymers and polyelectrolytes under the influence of external forces and flow fields. Numerical simulations and experiments have demonstrated that confined polymers migrate towards the center of the channel in response to both external forces and uniaxial flows. Yet, migration towards the walls has been observed with combinations of external force and flow. In this paper, the kinetic theory for an elastic dumbbell developed by Ma and Graham [Phys. Fluids 17, 083103 (2005)] has been extended to account for the effects of an external force. Further modifications account for counterion screening within a Debye-Hückel approximation. This enables qualitative comparison with experimental results [Zheng and Yeung, Anal. Chem. 75, 3675 (2003)] on DNA migration under combined electric and pressure-driven flow fields. The comparison supports the contention [Long et al., Phys. Rev. Lett. 76, 3858 (1996)] that the hydrodynamic interactions in polyelectrolytes decay algebraically, as 1∕r3, rather than exponentially. The theory qualitatively reproduces results of both simulations and experiments for the migration of neutral polymers and polyelectrolytes. Concentration profiles similar to those found in numerical simulations are observed, but the Peclet numbers differ by factors of 2–3.
Extended double-complex linear systems and new multiple infinite-dimensional hidden symmetries for the general symplectic gravity models
Authors: Gao Ya-Jun
Published: November 2007

By using a so-called extended double (ED)-complex method, the previously found doubleness symmetry for each member of the class of general symplectic gravity models is further exploited and extended. A 2(n+1)×2(n+1) matrix double-complex H-potential is constructed for any non-negative integer n, and the motion equations in two dimensions are written in a double-complex formulation. A double-duality mapping is proposed and two pairs of ED-complex Hauser-Ernst-type linear systems [J. Math. Phys. 21, 1126 (1980)] are established. Based on these linear systems, explicit formulations of new multiple hidden symmetry transformations for the studied theories are given. For any fixed n, these symmetry transformations are verified to constitute multiple infinite-dimensional Lie algebras, each of which is a semidirect product of the Kac-Moody sp(2(n+1̂),R) and Virasoro algebras (without center charges). These results demonstrate that the ED-complex method is necessary and more effective, and the general symplectic gravity models under consideration possess much richer symmetry structures than previously expected.
Superconductivity as a tool for solid mechanics
Authors: Antonevici Anca , Villaume Alain , Villard Catherine
Published: November 2007

The critical current, a key parameter characterizing the performances of coated conductors (CCs), can be used to probe the plasticity behavior of their metallic substrates. More generally, transport measurements in the superconducting state improve the usual electrical methods employed in solid mechanics to monitor cracks growth and velocity toward higher precisions without any calibration step. The particular case of the development of Lüder bands in a CC Hastelloy substrate is studied via the damaging of the fragile DyBCO superconducting layer deposited on the top of it. Magneto-optics completes the macroscopic data obtained from transport measurements by local morphological observations.
Interpretation of the nonlinear mode excitation in the ITER gyrotron
Authors: Nusinovich G. S. , Sinitsyn O. V.
Published: November 2007

This study was motivated by an interesting physical effect observed in experiments with a 1MW, 170GHz, continuous-wave gyrotron developed at the Japan Atomic Energy Agency for plasma heating and current drive in ITER [see, e.g., Fusion Eng. Des. 55, issues 2–3 (2001)]. In these experiments, the gyrotron switching from a parasitic mode to the operating one was observed with the increase in external magnetic field in the region of hard self-excitation of the operating mode where it cannot be excited from the noise level in the absence of other modes. Below, the theory describing this effect is developed. The switching mechanism caused by merging and disappearance of two (one stable and another unstable) equilibrium states with nonzero amplitudes of both modes is proposed. It is found that the present theory can correctly interpret experimental results qualitatively, but the lack of experimental data does not let the authors carry out some simulations more adequate to experimental conditions.
Toward the jamming threshold of sphere packings: Tunneled crystals
Authors: Torquato S. , Stillinger F. H.
Published: November 2007

We have discovered a family of three-dimensional crystal sphere packings that are strictly jammed (i.e., mechanically stable) and yet possess an anomalously low density. This family constitutes an uncountably infinite number of crystal packings that are subpackings of the densest crystal packings and are characterized by a high concentration of self-avoiding “tunnels” (chains of vacancies) that permeate the structures. The fundamental geometric characteristics of these tunneled crystals command interest in their own right and are described here in some detail. These include the lattice vectors (that specify the packing configurations), coordination structure, Voronoi cells, and density fluctuations. The tunneled crystals are not only candidate structures for achieving the jamming threshold (lowest-density rigid packing), but may have substantially broader significance for condensed matter physics and materials science.
Structure and magnetic properties of Cu-doped SmCo6.7−xCuxCr0.3 magnets
Authors: Yao Q. , Liu W. , Zhao X. G. , Zhang Z. D.
Published: November 2007

Structure and magnetic properties of mechanically alloyed Cu-doped SmCo6.7−xCuxCr0.3 (x=0.1–0.7) magnets have been systematically studied. The magnetically hard main phase is found to be of Th2Ni17 type in the SmCo6.7−xCuxCr0.3 alloys. A small amount of Cu addition is favorable for the formation of the 2:17 phase/Co nanocomposite structure in the alloys. The increase of Cu doping results in more Cu precipitating in the alloys with separating the grains, which significantly enhances the intrinsic coercivity Hci of the alloys and weakens the exchange coupling between the magnetically hard and soft phases. The magnetization reversal processes of the magnets have been discussed, upon the measurement of the recoil curves.
Recombination and resistive losses at ZnO∕a-Si:H∕c-Si interfaces in heterojunction back contacts for Si solar cells
Authors: Einsele Florian , Rostan Philipp J. , Schubert Markus B. , Rau Uwe
Published: November 2007

We investigate resistive losses at p-type crystalline Si∕hydrogen passivated Si:H∕ZnO:Al heterojunction back contacts for high efficiency silicon solar cells. A low tunneling resistance for the (p-type) Si:H∕(n-type) ZnO part of the junction requires deposition of Si:H with a high hydrogen dilution rate RH>40 resulting in a highly doped microcrystalline (μc) Si:H layer. Such a μc-Si:H layer if deposited directly on a Si wafer yields a surface recombination velocity of S≈180cm∕s. Using the same layer as part of a (p-type) c-Si∕Si:H∕ZnO:Al back contact in a solar cell results in an open circuit voltage VOC=640mV and a fill factor FF=80%. Insertion of an undoped amorphous (i) a-Si:H layer between the μc-Si:H and the wafer leads to a further decrease of S and, for the solar cells, to an increase of VOC. However, if the thickness of this intrinsic layer exceeds a threshold value of 4–5nm, resistive losses degrade the fill factor FF of the solar cells. Temperature dependent measurements of the contact resistance unveil activation energies in a range of 0.49–0.65eV, which we attribute to the valence band offset between a-Si:H and c-Si. The balance of FF losses and VOC gains determines the optimum (i) a-Si:H interlayer thickness for (i) a-Si:H∕(p) μc-Si:H double layer or (i) a-Si:H∕(p) a-Si:H∕(p) μc-Si:H triple layer back contacts.
Design of n-type silicon-based quantum cascade lasers for terahertz light emission
Authors: Driscoll Kristina , Paiella Roberto
Published: November 2007

The design of terahertz quantum cascade lasers based on electronic intersubband transitions in Ge∕SiGe quantum wells is investigated. A detailed theoretical model of the conduction-band lineup of these heterostructures is first presented and used to show that large quantum confinement in the L valleys can be obtained with properly selected layer compositions and thicknesses. Computation of the key laser design parameters is then discussed, including the important role played by the L-valley ellipsoidal constant-energy surfaces. Finally, the main design issues specific to this material system and its potential for high-performance operation are illustrated by means of two exemplary structures, designed for emission near 50 and 25μm.
Volumetric negative-refractive-index metamaterials based upon the shunt-node transmission-line configuration
Authors: Stickel Micah , Elek Francis , Zhu Jiang , Eleftheriades George V.
Published: November 2007

A volumetric negative-refractive-index transmission-line (NRI-TL) metamaterial is presented. This structure constitutes a natural extension of the planar NRI-TL metamaterials1 and maintains the desired features of broad bandwidth and low transmission loss. Unlike their planar counterparts, the proposed volumetric NRI-TL metamaterials can effectively couple incident plane waves from free space. The proposed topology can be readily made by stacking layers that are individually fabricated using standard multilayer printed-circuit board techniques at microwave frequencies. However, the creation of the volumetric structure results in the presence of a parasitic parallel-plate mode. This mode can interfere with the desired backward wave mode of the metamaterial, causing a stop band to appear. To facilitate the rapid analysis of this new design, a multiconductor transmission line model was developed. Through the use of this model and full-wave simulations, it will be demonstrated that this unwanted parallel-plate mode can be eliminated by properly arranging the vertical inductive loading wires. Using this process, it will be shown that a properly designed inductive load can result in a practical NRI metamaterial slab which is matched to free space over a large bandwidth (22%) and with low insertion loss (<−1 dB). This approach can also be used to design NRI-TL metamaterials with backward wave dispersion bandwidths of over 140%.
Electrolyte effects on charge, polarization, and conduction in thin anodic Al2O3 films II. Temperature dependent conduction and a Meyer-Neldel relation
Authors: Hickmott T. W.
Published: November 2007

The effect of anodizing electrolyte on the temperature dependence of current-voltage (I-V) curves of Al–Al2O3–Au diodes is reported. Two aqueous electrolytes, 0.1M ammonium pentaborate (bor-H2O) and 0.1M ammonium citrate (citrate), and one nonaqueous electrolyte, 0.1M ammonium pentaborate per liter of ethylene glycol (bor-gly), have been used. Al2O3 thicknesses are between 12 and 54nm; temperatures are between 100 and 320K. Maximum currents for the applied voltage for VA>0V (IMX+) and for VA<0V (IMX−), and the rectification ratio RR (IMX+∕IMX−) depend on the electrolyte. RR(bor-H2O)>RR(citrate)⪢RR(bor-gly) at 300K; at 100K, the rectification ratios are approximately equal. I-V curves for decreasing VA>0V are reproducible and nearly independent of previous history. They are due to Fowler-Nordheim tunneling, J=CF2exp(−B∕F), where J is current density, F is the electric field, and B and C are constants. B is used to obtain an effective barrier height for tunneling, ϕE. ϕE is 1.3–1.5eV at 300K for all three electrolytes. ϕE increases as temperature decreases. If ΔϕE=[ϕE(100K)−ϕE(300K)], then ΔϕE=1.3–1.5eV for Al2O3 formed in bor-H2O and ΔϕE∼0.5eV for Al2O3 formed in bor-gly. The pre-exponential tunneling factor C increases by orders of magnitude as temperature decreases from 300to100K. There is a Meyer-Neldel relation between C and B, C=r+sB where r and s are constants that depend on the anodizing electrolyte. A model is proposed in which ϕE depends on temperature dependent occupation of defect states in anodic Al2O3. Defect states, in turn, depend on the anodizing electrolyte.
Raman scattering studies of magnetic Co-doped ZnO thin films
Authors: Thakur J. S. , Auner G. W. , Naik V. M. , Sudakar C. , Kharel P. , Lawes G. , Suryanarayanan R. , Naik R.
Published: November 2007

Structural, magnetization, and Raman spectroscopic investigations have been carried out on spin coated Zn1−xCoxO (0⩽x⩽0.1) films. We investigated the broadening of the E2low mode for different values of x in both air and vacuum annealed films, and found a direct correlation of Co ions incorporation at the Zn sites with ferromagnetic order. The magnitudes of the magnetic moment are directly related to the size of the disorder correlation radius. However, for x∼5% where the magnetic moment becomes negligible, the broadening of the E2low Raman mode also becomes negligible, suggesting rejection of the Co ions from the Zn sites. For a given x, Co ions are incorporated at the Zn sites with the same concentration in both the air and vacuum annealed films but the magnetic moment values are much smaller for the air annealed samples. This behavior is directly related to the presence of oxygen vacancies. We also discuss the effects of air and vacuum annealing on the linewidth of E2high and A1 (LO) modes. At higher doping levels, e.g., x>5%, the air annealed films showed a strong phase separation tendency toward Co3O4 as shown by both Raman and high resolution electron microscopy.
Undulation of sub-100nm porous dielectric structures: A mechanical analysis
Authors: Darnon M. , Chevolleau T. , Joubert O. , Maitrejean S. , Barbe J. C. , Torres J.
Published: November 2007

In microelectronics technologies, patterning of sub-100nm width ridges capped with a titanium nitride mask can lead to undulations of the ridges detrimental to performances. This phenomenon is observed with highly compressive residual stress into the mask (>2GPa), with dielectrics with low elastic properties (E<2Gpa) and with high dielectric ridge heights (>230nm). Experiments and simulations show that undulations can originate from buckling which allows the release of the strain energy initially stored in the mask. Simulations predict that the dielectric material undulations can become an issue for porous dielectrics integration in the next generations of integrated circuits (2016 and later).
Mass-based readout for agglutination assays
Authors: Chunara Rumi , Godin Michel , Knudsen Scott M. , Manalis Scott R.
Published: November 2007

We present a mass-based readout for agglutination assays. The suspended microchannel resonator (SMR) is used to classify monomers and dimers that are formed during early stage aggregation, and to relate the total count to the analyte concentration. Using a model system of streptavidin functionalized microspheres and biotinylated antibody as the analyte, we obtain a dose-response curve over a concentration range of 0.63–630nM and show that the results are comparable to what has been previously achieved by image analysis and conventional flow cytometry.
Transmission of single mode ultrathin terahertz photonic crystal slabs
Authors: Yee Cristo , Jukam Nathan , Sherwin Mark
Published: November 2007

Silicon photonic crystal slabs (PCSs) were fabricated using a reactive ion etching technique. The PCSs consist of a triangular lattice of holes with a lattice constant a=64μm, radius r=0.3a, and a thickness of 0.75a. An optical bandgap from 1.15to1.56THz for transverse electric modes was measured using Fourier transform infrared spectroscopy. The optical bandgap is in good agreement with the finite difference time domain and frequency domain predictions.
Circadian rhythmicity mediated by temporal regulation of the activity of p38 MAPK
Authors: Vitalini Michael W. , de Paula Renato M. , Goldsmith Charles S. , Jones Carol A. , Borkovich Katherine A. , Bell-Pedersen Deborah
Published: November 2007

Circadian clocks are composed of central oscillators, input pathways that transduce external information to the oscillators, and output pathways that allow the oscillators to temporally regulate cellular processes. Little is known about the output pathways. In this study, we show that the
Neurospora crassa
osmosensing MAPK pathway, essential for osmotic stress responses, is a circadian output pathway that regulates daily rhythms in the expression of downstream genes. Rhythmic activation of the highly conserved stress-activated p38-type MAPK [Osmotically Sensitive-2 (OS-2)] by the
N. crassa
circadian clock allows anticipation and preparation for hyperosmotic stress and desiccation that begin at sunrise. These results suggest a conserved role for MAPK pathways in circadian rhythmicity.
Specific developmental disruption of disrupted-in-schizophrenia-1 function results in schizophrenia-related phenotypes in mice
Authors: Li Weidong , Zhou Yu , Jentsch J. David , Brown Robert A. M. , Tian Xiaoli , Ehninger Dan , Hennah William , Peltonen Leena , Lönnqvist Jouko , Huttunen Matti O. , Kaprio Jaakko , Trachtenberg Joshua T. , Silva Alcino J. , Cannon Tyrone D.
Published: November 2007

Disrupted-in-schizophrenia 1 (DISC1) was initially discovered through a balanced translocation (1;11)(q42.1;q14.3) that results in loss of the C terminus of the DISC1 protein, a region that is thought to play an important role in brain development. Here, we use an inducible and reversible transgenic system to demonstrate that early postnatal, but not adult induction, of a C-terminal portion of DISC1 in mice results in a cluster of schizophrenia-related phenotypes, including reduced hippocampal dendritic complexity, depressive-like traits, abnormal spatial working memory, and reduced sociability. Accordingly, we report that individuals in a discordant twin sample with a DISC1 haplotype, associating with schizophrenia as well as working memory impairments and reduced gray matter density, were more likely to show deficits in sociability than those without the haplotype. Our findings demonstrate that alterations in DISC1 function during brain development contribute to schizophrenia pathogenesis.
Hydrophilic protein associated with desiccation tolerance exhibits broad protein stabilization function
Authors: Chakrabortee Sohini , Boschetti Chiara , Walton Laura J. , Sarkar Sovan , Rubinsztein David C. , Tunnacliffe Alan
Published: November 2007

The ability of certain plants, invertebrates, and microorganisms to survive almost complete loss of water has long been recognized, but the molecular mechanisms of this phenomenon remain to be defined. One phylogenetically widespread adaptation is the presence of abundant, highly hydrophilic proteins in desiccation-tolerant organisms. The best characterized of these polypeptides are the late embryogenesis abundant (LEA) proteins, first described in plant seeds >20 years ago but recently identified in invertebrates and bacteria. The function of these largely unstructured proteins has been unclear, but we now show that a group 3 LEA protein from the desiccation-tolerant nematode
Aphelenchus avenae
is able to prevent aggregation of a wide range of other proteins both
in vitro
and
in vivo
. The presence of water is essential for maintenance of the structure of many proteins, and therefore desiccation stress induces unfolding and aggregation. The nematode LEA protein is able to abrogate desiccation-induced aggregation of the water-soluble proteomes from nematodes and mammalian cells and affords protection during both dehydration and rehydration. Furthermore, when coexpressed in a human cell line, the LEA protein reduces the propensity of polyglutamine and polyalanine expansion proteins associated with neurodegenerative diseases to form aggregates, demonstrating
in vivo
function of an LEA protein as an antiaggregant. Finally, human cells expressing LEA protein exhibit increased survival of dehydration imposed by osmotic upshift, consistent with a broad protein stabilization function of LEA proteins under conditions of water stress.
Optimal savings and the value of population
Authors: Arrow Kenneth J. , Bensoussan Alain , Feng Qi , Sethi Suresh P.
Published: November 2007

We study a model of economic growth in which an exogenously changing population enters in the objective function under total utilitarianism and into the state dynamics as the labor input to the production function. We consider an arbitrary population growth until it reaches a critical level (resp. saturation level) at which point it starts growing exponentially (resp. it stops growing altogether). This requires population as well as capital as state variables. By letting the population variable serve as the surrogate of time, we are still able to depict the optimal path and its convergence to the long-run equilibrium on a two-dimensional phase diagram. The phase diagram consists of a
transient curve
that reaches the
classical curve
associated with a positive exponential growth at the time the population reaches the critical level. In the case of an asymptotic population saturation, we expect the transient curve to approach the equilibrium as the population approaches its saturation level. Finally, we characterize the approaches to the classical curve and to the equilibrium.