bluuebunny/crossref_metadata_2025 huggingface dataset:
Meeting school food standards – students’ food choice and free school meals
Authors: Ensaff Hannah , Russell Jean , Barker Margo E
Published: January 2013

Objective

To examine students’ school food choice in relation to school food standards and entitlement to free school meals (FSM).

Design

Cross-sectional analysis of students’ school food choices.

Setting

Two large secondary schools in Yorkshire, England.

Subjects

Students (n 2660) aged 11–18 years.

Results

Sandwiches and pizza were the most popular main food items: 40·4 % and 31·2 %, respectively, in School A; 48·3 % and 27·3 %, respectively, in School B. More nutritionally valuable ‘dishes of the day’ accounted for 8·7 % and 8·3 % of main foods for School A and School B, respectively. FSM students were more likely (P < 0·0 0 1) to choose main foods (School A: FSM 87·04 %, non-FSM 70·28 %; School B: FSM 75·43 %, non-FSM 56·13 %). Dishes of the day were chosen on a significantly greater (P < 0·0 0 1) percentage of days by FSM v. non-FSM students (School A: FSM 15·67 %, non-FSM 7·11 %; School B: FSM 19·42 %, non-FSM 5·17 %).

Conclusions

Despite the availability of nutritionally valuable dishes of the day, the most popular food items were sandwiches, pizza and desserts. FSM students were more likely to choose the more nutritionally valuable dish of the day. School food standards should be reassessed in light of students’ preferences.
Intestinal epithelial cells as mediators of the commensal–host immune crosstalk
Authors: Goto Yoshiyuki , Ivanov Ivaylo I
Published: January 2013

Commensal bacteria regulate the homeostasis of host effector immune cell subsets. The mechanisms involved in this commensal–host crosstalk are not well understood. Intestinal epithelial cells (IECs) not only create a physical barrier between the commensals and immune cells in host tissues, but also facilitate interactions between them. Perturbations of epithelial homeostasis or function lead to the development of intestinal disorders such as inflammatory bowel diseases (IBD) and intestinal cancer. IECs receive signals from commensals and produce effector immune molecules. IECs also affect the function of immune cells in the lamina propria. Here we discuss some of these properties of IECs that define them as innate immune cells. We focus on how IECs may integrate and transmit signals from individual commensal bacteria to mucosal innate and adaptive immune cells for the establishment of the unique mucosal immunological equilibrium.
Autophagy and inflammatory diseases
Authors: Jones Sarah A , Mills Kingston H G , Harris James
Published: January 2013

Autophagy is a cellular mechanism for the sequestration and degradation of intracellular pathogens and compromised organelles, particularly damaged mitochondria. Autophagy also clears other cellular components, such as inflammasomes and cytokines, thus providing an important means of regulating inflammation. Defects in autophagy have been found by genetic association studies to confer susceptibility to several autoimmune and inflammatory disorders, particularly inflammatory bowel disease. Thus, the manipulation of autophagy in disease situations is of growing interest for therapeutic targeting; however, the involvement of autophagy in cellular homoeostasis, in normal immune function and in inflammation is manifold. An appreciation of the intricacies of the contributions of this process to inflammation, and how these are altered by various immune and environmental stimuli, is essential for the understanding and interpretation of studies of inflammation and the design of therapeutics exploiting the manipulation of autophagy. This review focuses on the known roles of autophagy in the induction and maintenance of inflammation and on its role in the aetiology and regulation of inflammatory and autoimmune disorders.
Structure of Plasmodium falciparum TRAP (thrombospondin-related anonymous protein) A domain highlights distinct features in apicomplexan von Willebrand factor A homologues
Authors: Pihlajamaa Tero , Kajander Tommi , Knuuti Juho , Horkka Kaisa , Sharma Amit , Permi Perttu
Published: January 2013

TRAP (thrombospondin-related anonymous protein), localized in the micronemes and on the surface of sporozoites of the notorious malaria parasite Plasmodium, is a key molecule upon infection of mammalian host hepatocytes and invasion of mosquito salivary glands. TRAP contains two adhesive domains responsible for host cell recognition and invasion, and is known to be essential for infectivity. In the present paper, we report high-resolution crystal structures of the A domain of Plasmodium falciparum TRAP with and without bound Mg2+. The structure reveals a vWA (von Willebrand factor A)-like fold and a functional MIDAS (metal-ion-dependent adhesion site), as well as a potential heparan sulfate-binding site. Site-directed mutagenesis and cell-attachment assays were used to investigate the functional roles of the surface epitopes discovered. The reported structures are the first determined for a complete vWA domain of parasitic origin, highlighting unique features among homologous domains from other proteins characterized hitherto. Some of these are conserved among Plasmodiae exclusively, whereas others may be common to apicomplexan organisms in general.
Independent and combined effects of acute physiological hyperglycaemia and hyperinsulinaemia on metabolic gene expression in human skeletal muscle
Authors: Tsintzas Kostas , Norton Luke , Chokkalingam Kamal , Nizamani Nusrat , Cooper Scott , Stephens Francis , Billeter Rudolf , Bennett Andrew
Published: January 2013

Physiological hyperglycaemia and hyperinsulinaemia are strong modulators of gene expression, which underpins some of their well-known effects on insulin action and energy metabolism. The aim of the present study was to examine whether acute in vivo exposure of healthy humans to hyperinsulinaemia and hyperglycaemia have independent or additive effects on expression of key metabolic genes in skeletal muscle. On three randomized occasions, seven young subjects underwent a 4 h (i) hyperinsulinaemic (50 m-units·m−2·min−1) hyperglycaemic (10 mmol/l) clamp (HIHG), (ii) hyperglycaemic (10 mmol/l) euinsulinaemic (5 m-units·m−2·min−1) clamp (LIHG) and (iii) hyperinsulinaemic (50 m-units·m−2·min−1) euglycaemic (4.5 mmol/l) clamp (HING). Muscle biopsies were obtained before and after each clamp for the determination of expression of genes involved in energy metabolism, and phosphorylation of key insulin signalling proteins. Hyperinsulinaemia and hyperglycaemia exerted independent effects with similar direction of modulation on PI3KR1 (phosphatidylinositol 3-kinase, regulatory 1), LXRα (liver X receptor α), PDK4 (pyruvate dehydrogenase kinase 4) and FOXO1 (forkhead box O1A) and produced an additive effect on PI3KR1, the gene that encodes the p85α subunit of PI3K in human skeletal muscle. Acute hyperglycaemia itself altered the expression of genes involved in fatty acid transport and oxidation [fatty acid transporter (CD36), LCAD (long-chain acyl-CoA dehydrogenase) and FOXO1], and lipogenesis [LXRα, ChREBP (carbohydrate-responseelement-binding protein), ABCA1 (ATP-binding cassette transporter A1) and G6PD (glucose-6-phosphate dehydrogenase). Surperimposing hyperinsulinaemia on hyperglycaemia modulated a number of genes involved in insulin signalling, glucose metabolism and intracellular lipid accumulation and exerted an additive effect on PI3KR1. These may be early molecular events that precede the development of glucolipotoxicity and insulin resistance normally associated with more prolonged periods of hyperglycaemia and hyperinsulinaemia.
A tri-atomic Renner-Teller system entangled with Jahn-Teller conical intersections
Authors: Csehi A. , Bende A. , Halász G. J. , Vibók Á. , Das A. , Mukhopadhyay D. , Baer M.
Published: January 2013

The present study concentrates on a situation where a Renner-Teller (RT) system is entangled with Jahn-Teller (JT) conical intersections. Studies of this type were performed in the past for contours that surround the RT seam located along the collinear axis [see, for instance, G. J. Halász, Á. Vibók, R. Baer, and M. Baer, J. Chem. Phys. 125, 094102 (2006)]. The present study is characterized by planar contours that intersect the collinear axis, thus, forming a unique type of RT-non-adiabatic coupling terms (NACT) expressed in terms of Dirac-δ functions. Consequently, to calculate the required adiabatic-to-diabatic (mixing) angles, a new approach is developed. During this study we revealed the existence of a novel molecular parameter, η, which yields the coupling between the RT and the JT NACTs. This parameter was found to be a pure number η = $2\sqrt 2 /\pi$22/π (and therefore independent of any particular molecular system) and is designated as Renner-Jahn coupling parameter. The present study also reveals an unexpected result of the following kind: It is well known that each (complete) group of states, responsible for either the JT-effect or the RT-effect, forms a Hilbert space of its own. However, the entanglement between these two effects forms a third effect, namely, the RT/JT effect and the states that take part in it form a different Hilbert space.
Optical conductivity of highly mismatched GaP alloys
Authors: Gohda Yoshihiro , Tsuneyuki Shinji
Published: January 2013

Highly mismatched alloys are promising for applications to intermediate-band (IB) solar cells. Here, we report first-principles prediction of intermediate bands in GaP on the basis of hybrid-density-functional theory, which enables to handle large supercells including defects with much better accuracy than semilocal functionals. Calculated optical conductivity reveals that the intermediate states due to co-doped Mg and O have sufficiently high optical transition probability. The multiple gaps are robust against thermalization. Intermediate-band states become more delocalized by hybridization with phosphorus-vacancy states, increasing the optical transition probability.
Area of contact and thermal transport across transfer-printed metal-dielectric interfaces
Authors: Seong M. , Singh P. K. , Sinha S.
Published: January 2013

Recent experiments suggest that the interfacial thermal conductance of transfer printed metal-dielectric interfaces is ∼45 MW/m2K at 300 K, approaching that of interfaces formed using physical vapor deposition. We investigate this anomalous result using a combination of theoretical deformation mechanics and nanoscale thermal transport. Our analysis shows that plastic deformation and capillary forces lead to significantly large fractional areal coverage of ∼0.25. The conductance predicted from theory is on the same order of magnitude (∼18 MW/m2K) as the experimental data and partially explains the temperature trend. There remains a quantitative discrepancy between data and theory that is not explained through deformation of the asperities alone. We suggest that capillary bridges formed in the small asperities contribute significantly to heat conduction. A preliminary analysis shows this to be plausible based on available data. This work shows that metallic interconnects formed using transfer printing are not at a disadvantage compared to ones formed using vapor deposition, in terms of heat flow characteristics.
Detailed analysis of the vibration induced instability of a liquid film flow
Authors: Garih H. , Strzelecki A. , Casalis G. , Estivalezes J. L.
Published: January 2013

The problem of the vibration induced instability of a liquid film flow is formulated, thanks to a linear approach. For the solution of the problem, the disturbances are expanded using a spectral method based on Chebyshev polynomials leading to a system of ordinary differential equations. This system is solved by using Floquet theory. The natural and vibration induced instabilities are studied in terms of frequency, temporal growth rate, and eigenfunction. Numerical results show that the mean flow velocity alters the surface wave frequency, which is not predictable by Mathieu's equation model (which assumes that the fluid is at rest). Above a threshold amplitude, multiple vibration induced instability modes are triggered. At specific amplitudes above the latter, two wavenumbers coexist at the free surface. A relation between the eigenfunction shape and the instability mode is observed.
Effects of interleaflet coupling on the morphologies of multicomponent lipid bilayer membranes
Authors: Funkhouser Chloe M. , Mayer Michael , Solis Francisco J. , Thornton K.
Published: January 2013

We investigate dynamical and stationary compositional and surface morphologies in macroscopically phase-separating multicomponent lipid bilayer membranes using a computational model. We employ a phase-field method for the description of the coexisting phases and treat the two leaflets individually while including interleaflet interactions. The compositional evolution of the two leaflets is coupled to the shape evolution of the membrane via a Helfrich free energy with a composition-dependent spontaneous curvature. We investigate the effects of the interleaflet interaction on the dynamics and stationary states of a system favoring nonzero spontaneous curvatures. Morphological phase diagrams are mapped in composition space using three different interleaflet coupling strengths. We find that characteristics sensitive to the coupling strength include the time required to develop regions of fully separated phases, the prevalence of a stripe morphology, and the shifting of phase compositions to accommodate energetically favorable interactions across leaflets. Characteristics found to be robust with respect to coupling strength include (1) the stripe morphology is favored at nearly equal mixtures and (2) phase separation is prevented in systems where a pair of phases that preferentially interact across leaflets together occupy nearly all or none of the membrane.
Surface temperature effects on the dynamics of N2 Eley-Rideal recombination on W(100)
Authors: Quintas-Sánchez E. , Crespos C. , Larrégaray P. , Rayez J-C. , Martin-Gondre L. , Rubayo-Soneira J.
Published: January 2013

Quasiclassical trajectories simulations are performed to study the influence of surface temperature on the dynamics of a N atom colliding a N-preadsorbed W(100) surface under normal incidence. A generalized Langevin surface oscillator scheme is used to allow energy transfer between the nitrogen atoms and the surface. The influence of the surface temperature on the N2 formed molecules via Eley-Rideal recombination is analyzed at T = 300, 800, and 1500 K. Ro-vibrational distributions of the N2 molecules are only slightly affected by the presence of the thermal bath whereas kinetic energy is rather strongly decreased when going from a static surface model to a moving surface one. In terms of reactivity, the moving surface model leads to an increase of atomic trapping cross section yielding to an increase of the so-called hot atoms population and a decrease of the direct Eley-Rideal cross section. The energy exchange between the surface and the nitrogen atoms is semi-quantitatively interpreted by a simple binary collision model.
Mechanics of swimming of multi-body bacterial swarmers using non-labeled cell tracking algorithm
Authors: Phuyal Kiran , Kim Min Jun
Published: January 2013

To better understand the survival strategy of bacterial swarmers and the mechanical advantages offered by the linear chain (head-tail) attachment of the multiple bacterial bodies in an individual swarmer cell at low Reynolds number, a non-labeled cell tracking algorithm was used to quantify the mechanics of multi-body flagellated bacteria, Serratia marcescens, swimming in a motility buffer that originally exhibited the swarming motility. Swarming is a type of bacterial motility that is characterized by the collective coordinated motion of differentiated swarmer cells on a two-dimensional surface such as agar. In this study, the bacterial swarmers with multiple cell bodies (2, 3, and 4) were extracted from the swarm plate, and then tracked individually after resuspending in the motility medium. Their motion was investigated and compared with individual undifferentiated swimming bacterial cells. The swarmers when released into the motility buffer swam actively without tumbles. Their speeds, orientations, and the diffusive properties were studied by tracking the individual cell trajectories over a short distance in two-dimensional field when the cells are swimming at a constant depth in a bulk aqueous environment. At short time scales, the ballistic trajectory was dominant for both multi-body swarmers and undifferentiated cells.
Optofluidic cell manipulation for a biological microbeam
Authors: Grad Michael , Bigelow Alan W. , Garty Guy , Attinger Daniel , Brenner David J.
Published: January 2013

This paper describes the fabrication and integration of light-induced dielectrophoresis for cellular manipulation in biological microbeams. An optoelectronic tweezers (OET) cellular manipulation platform was designed, fabricated, and tested at Columbia University's Radiological Research Accelerator Facility (RARAF). The platform involves a light induced dielectrophoretic surface and a microfluidic chamber with channels for easy input and output of cells. The electrical conductivity of the particle-laden medium was optimized to maximize the dielectrophoretic force. To experimentally validate the operation of the OET device, we demonstrate UV-microspot irradiation of cells containing green fluorescent protein (GFP) tagged DNA single-strand break repair protein, targeted in suspension. We demonstrate the optofluidic control of single cells and groups of cells before, during, and after irradiation. The integration of optofluidic cellular manipulation into a biological microbeam enhances the facility's ability to handle non-adherent cells such as lymphocytes. To the best of our knowledge, this is the first time that OET cell handling is successfully implemented in a biological microbeam.
Current density distributions and sputter marks in electron cyclotron resonance ion sources
Authors: Panitzsch Lauri , Peleikis Thies , Böttcher Stephan , Stalder Michael , Wimmer-Schweingruber Robert F.
Published: January 2013

Most electron cyclotron resonance ion sources use hexapolar magnetic fields for the radial confinement of the plasma. The geometry of this magnetic structure is then—induced by charged particles—mapped onto the inner side of the plasma electrode via sputtering and deposition. The resulting structures usually show two different patterns: a sharp triangular one in the central region which in some cases is even sputtered deep into the material (referred to as thin groove or sharp structure), and a blurred but still triangular-like one in the surroundings (referred to as broad halo). Therefore, both patterns seem to have different sources. To investigate their origins we replaced the standard plasma electrode by a custom-built plasma electrode acting as a planar, multi-segment current-detector. For different biased disc voltages, detector positions, and source biases (referred to the detector) we measured the electrical current density distributions in the plane of the plasma electrode. The results show a strong and sharply confined electron population with triangular shape surrounded by less intense and spatially less confined ions. Observed sputter- and deposition marks are related to the analysis of the results. Our measurements suggest that the two different patterns (thin and broad) indeed originate from different particle populations. The thin structures seem to be caused by the hot electron population while the broad marks seem to stem from the medium to highly charged ions. In this paper we present our measurements together with theoretical considerations and substantiate the conclusions drawn above. The validity of these results is also discussed.
Global existence for a coupled system of Schrödinger equations with power-type nonlinearities
Authors: Nguyen Nghiem V. , Tian Rushun , Deconinck Bernard , Sheils Natalie
Published: January 2013

In this manuscript, we consider the Cauchy problem for a Schrödinger system with power-type nonlinearities\documentclass[12pt]{minimal}\begin{document}$\left\lbrace \begin{array}{l}i\frac{\partial }{\partial t}u_j+ \triangle u_j + \sum _{k=1}^m a_{jk} |u_k|^{p}|u_j|^{p-2} u_j=0,\\u_j(x,0) = \psi _{j0}(x), \end{array} \right.$\end{document}i∂∂tuj+▵uj+∑k=1majk|uk|p|uj|p−2uj=0,uj(x,0)=ψj0(x),where \documentclass[12pt]{minimal}\begin{document}$u_j: \mathbb {R}^N\times \mathbb {R} \rightarrow \mathbb {C}$\end{document}uj:RN×R→C, \documentclass[12pt]{minimal}\begin{document}$\psi _{j0}:\mathbb {R}^N \rightarrow \mathbb {C}$\end{document}ψj0:RN→C for j = 1, 2, …, m and ajk = akj are positive real numbers. Global existence for the Cauchy problem is established for a certain range of p. A sharp form of a vector-valued Gagliardo-Nirenberg inequality is deduced, which yields the minimal embedding constant for the inequality. Using this minimal embedding constant, global existence for small initial data is shown for the critical case p = 1 + 2/N. Finite-time blow-up, as well as stability of solutions in the critical case, is discussed.
A classical density-functional theory for describing water interfaces
Authors: Hughes Jessica , Krebs Eric J. , Roundy David
Published: January 2013

We develop a classical density functional for water which combines the White Bear fundamental-measure theory (FMT) functional for the hard sphere fluid with attractive interactions based on the statistical associating fluid theory variable range (SAFT-VR). This functional reproduces the properties of water at both long and short length scales over a wide range of temperatures and is computationally efficient, comparable to the cost of FMT itself. We demonstrate our functional by applying it to systems composed of two hard rods, four hard rods arranged in a square, and hard spheres in water.
Vortical control of forced two-dimensional turbulence
Authors: Fontane Jérôme , Dritschel David G. , Scott Richard K.
Published: January 2013

A new numerical technique for the simulation of forced two-dimensional turbulence [D. Dritschel and J. Fontane, “The combined Lagrangian advection method,” J. Comput. Phys. 229, 5408–5417 (2010)10.1016/j.jcp.2010.03.048] is used to examine the validity of Kraichnan-Batchelor scaling laws at higher Reynolds number than previously accessible with classical pseudo-spectral methods, making use of large simulation ensembles to allow a detailed consideration of the inverse cascade in a quasi-steady state. Our results support the recent finding of Scott [R. Scott, “Nonrobustness of the two-dimensional turbulent inverse cascade,” Phys. Rev. E 75, 046301 (2007)10.1103/PhysRevE.75.046301], namely that when a direct enstrophy cascading range is well-represented numerically, a steeper energy spectrum proportional to k−2 is obtained in place of the classical k−5/3 prediction. It is further shown that this steep spectrum is associated with a faster growth of energy at large scales, scaling like t−1 rather than Kraichnan's prediction of t−3/2. The deviation from Kraichnan's theory is related to the emergence of a population of vortices that dominate the distribution of energy across scales, and whose number density and vorticity distribution with respect to vortex area are related to the shape of the enstrophy spectrum. An analytical model is proposed which closely matches the numerical spectra between the large scales and the forcing scale.
Threshold criteria for incipient sediment motion on an inclined bedform in the presence of oscillating-grid turbulence
Authors: Wan Mohtar W. H. M. , Munro R. J.
Published: January 2013

Here, we report laboratory experiments to investigate the threshold criteria for incipient sediment motion in the presence of oscillating-grid turbulence, with the bed slope inclined at angles between the horizontal and the repose limit for the sediment. A set of nine mono-disperse sediment types was used with size ranges normally associated with either the hydraulically-smooth or transitional regimes. Measurements of the (turbulent) fluid velocity field, in the region between the grid and bedform's surface, were obtained using two-dimensional particle imaging velocimetry. Statistical analysis of the velocity data showed that the turbulence had a anisotropic structure, due to the net transfer of energy from the normal to the tangential velocity components in the near-bed region, and that the fluctuations were dominant compared to the secondary mean flow. The sediment threshold criteria for horizontal bedforms were compared with, and found to be in good qualitative agreement with the standard Shields curve. For non-horizontal bedforms, the bed mobility was found to increase with increasing bed slope, and the threshold criteria were compared with previously-reported theoretical models, based on simple force-balance arguments.
High-fidelity Hugoniot analysis of porous materials
Authors: Fredenburg D. A. , Koller D. D. , Rigg P. A. , Scharff R. J.
Published: January 2013

An experimental technique and analysis methodology for obtaining high-fidelity Hugoniot measurements with defined uncertainty bounds on powder compacts using optical velocimetry is presented. Impedance matching is used to calculate the shocked state in the powder from the measured initial compact density, ρ00, impact velocity, VImp, and shock velocity, US. Detailed characterization of the powder thicknesses at precise locations results in improvements in characterization of the initial density state and accurate measurements of the powder thickness at locations corresponding to shock velocity measurements. These measurements result in high accuracies in the equilibrium Hugoniot state and reduced uncertainties in the measured and calculated Hugoniot parameters. Assumptions in this analysis include a constant and homogeneous initial porous density, and steady state wave propagation. The approach is applied to a system of CeO2 powder pressed to 4.0 g/cm3 (55% theoretical maximum density), and results indicate a complex dynamic response.
Dynamic non-equilibrium wall-modeling for large eddy simulation at high Reynolds numbers
Authors: Kawai Soshi , Larsson Johan
Published: January 2013

A dynamic non-equilibrium wall-model for large-eddy simulation at arbitrarily high Reynolds numbers is proposed and validated on equilibrium boundary layers and a non-equilibrium shock/boundary-layer interaction problem. The proposed method builds on the prior non-equilibrium wall-models of Balaras et al. [AIAA J. 34, 1111–1119 (1996)]10.2514/3.13200 and Wang and Moin [Phys. Fluids 14, 2043–2051 (2002)]10.1063/1.1476668: the failure of these wall-models to accurately predict the skin friction in equilibrium boundary layers is shown and analyzed, and an improved wall-model that solves this issue is proposed. The improvement stems directly from reasoning about how the turbulence length scale changes with wall distance in the inertial sublayer, the grid resolution, and the resolution-characteristics of numerical methods. The proposed model yields accurate resolved turbulence, both in terms of structure and statistics for both the equilibrium and non-equilibrium flows without the use of ad hoc corrections. Crucially, the model accurately predicts the skin friction, something that existing non-equilibrium wall-models fail to do robustly.
Study of creep/relaxation mechanisms in thin freestanding nanocrystalline palladium films through the lab-on-chip technology
Authors: Guisbiers G. , Colla M.-S. , Coulombier M. , Raskin J.-P. , Pardoen T.
Published: January 2013

A nanomechanical lab-on-chip set-up has been used to study the creep/relaxation response of thin palladium films with temperature. The basic idea is to use residual stresses present in a silicon nitride thin beam to load the test film after etching the underneath sacrificial layer. The main advantage of this experimental method is that we can simultaneously perform thousands of creep/relaxation tests without monopolizing any external actuating/loading equipment and without using any time consuming calibration procedures. A signature of the dominant relaxation mechanism is given by the activation volume which has been determined for different levels of plastic deformation and different temperatures. The activation volume is equal to ∼15-40 b3 at room temperature and tends to decrease with increasing plastic deformation. The activation volume decreases when relaxation takes place at 50 °C down to ∼7-20 b3. These variations of the activation volume indicate the competition between two different thermally activated deformation mechanisms in the temperature range between 20 °C and 50 °C.
Energy barriers to magnetization reversal in perpendicularly magnetized thin film nanomagnets
Authors: Chaves-O'Flynn Gabriel D. , Vanden-Eijnden Eric , Stein D. L. , Kent A. D.
Published: January 2013

Understanding the stability of thin film nanomagnets with perpendicular magnetic anisotropy (PMA) against thermally induced magnetization reversal is important when designing perpendicularly magnetized patterned media and magnetic random access memories. The magnetization reversal rate depends primarily on the energy barrier the system needs to surmount in order for reversal to proceed. In this paper, we study the reversal dynamics of these systems and compute the relevant barriers using the string method of E, Vanden-Eijnden, and Ren. We find the reversal to be often spatially incoherent; that is, rather than all parts of the element switching simultaneously, reversal proceeds instead through a soliton-like domain wall sweeping through the system. We show that for square nanomagnetic elements, the energy barrier increases with element size up to a critical length scale, beyond which the energy barrier is constant. For circular elements, the energy barrier continues to increase indefinitely, albeit more slowly beyond a critical size. In both cases, the energy barriers are smaller than those expected for coherent magnetization reversal.
Fast modeling of flux trapping cascaded explosively driven magnetic flux compression generators
Authors: Wang Yuwei , Zhang Jiande , Chen Dongqun , Cao Shengguang , Li Da , Liu Chebo
Published: January 2013

To predict the performance of flux trapping cascaded flux compression generators, a calculation model based on an equivalent circuit is investigated. The system circuit is analyzed according to its operation characteristics in different steps. Flux conservation coefficients are added to the driving terms of circuit differential equations to account for intrinsic flux losses. To calculate the currents in the circuit by solving the circuit equations, a simple zero-dimensional model is used to calculate the time-varying inductance and dc resistance of the generator. Then a fast computer code is programmed based on this calculation model. As an example, a two-staged flux trapping generator is simulated by using this computer code. Good agreements are achieved by comparing the simulation results with the measurements. Furthermore, it is obvious that this fast calculation model can be easily applied to predict performances of other flux trapping cascaded flux compression generators with complex structures such as conical stator or conical armature sections and so on for design purpose.
Interfacial properties and electronic structure of β-SiC(111)/α-Ti(0001): A first principle study
Authors: Li Jian , Yang Yanqing , Li Lili , Lou Juhong , Luo Xian , Huang Bin
Published: January 2013

First-principles calculations of β-SiC(111)/α-Ti(0001) interface have been performed and the adhesion strength, interface energy, interfacial fracture toughness, and electronic structure are obtained. Six C-terminated β-SiC(111)/α-Ti(0001) interface models are investigated to clarify the influence of stacking sites and Ti atoms tilt direction on the interface bonding and fracture toughness. The hollow-site-stacked interfaces, in which Ti atoms locate on the hollow site of interfacial C atoms (cases III and IV), are more thermodynamically stable with larger work of adhesion, and interfacial fracture toughness. The center-site-stacked (cases I and II) and top-site-stacked (cases V and VI) interfaces have a decreasing interface adhesion as the order. The electronic structure of hollow-site-stacked interface (case IV) gives the evidence that atomic bonding exists between interfacial C, Si, and Ti atoms, and the C-Ti bonds exhibit more covalent features than Si-Ti. The tilt direction of Ti atoms, namely the stacking style of Ti, has a subtle and secondary effect on the interface stability.
Probing antiferromagnetism in NiMn/Ni/(Co)/Cu3Au(001) single-crystalline epitaxial thin films
Authors: Yaqoob Khan M. , Wu Chii-Bin , Erkovan Mustafa , Kuch Wolfgang
Published: January 2013

Antiferromagnetism of equi-atomic single-crystalline NiMn thin film alloys grown on Ni/Cu3Au(001) is probed by means of magneto-optical Kerr effect (MOKE). Thickness-dependent coercivity (HC) enhancement of polar MOKE measurements in NiMn/Ni/Cu3Au(001) shows that ∼7 atomic monolayers (MLs) NiMn order antiferromagnetically at room temperature. It is found that NiMn can couple to out-of-plane (OoP) as well as in-plane (IP) magnetized Ni films, the latter stabilized by Co under-layer deposition. The antiferromagnetic (AFM) ordering temperature (TAFM) of NiMn coupled to OoP Ni is found to be much higher (up to 110 K difference) than in the IP case, for similar interfacial conditions. This is attributed to a magnetic proximity effect in which the ferromagnetic (FM) layer substantially influences TAFM of the adjacent AFM layer, and can be explained by either (i) a higher interfacial coupling strength and/or (ii) a thermally more stable NiMn spin structure when coupled to Ni magnetized in OoP direction than in IP. An exchange-bias effect could only be observed for the thickest NiMn film studied (35.7 ML); the exchange-bias field is higher in the OoP exchange-coupled system than in the IP one, possibly due to the same reason/s.
Influence of Pb doping on the electrical transport properties of BiCuSeO
Authors: Pan Lin , Bérardan David , Zhao Lidong , Barreteau Céline , Dragoe Nita
Published: January 2013

The effect of Pb doping on the thermoelectric properties of p-type BiCuSeO from 25 K to 873 K has been studied. The electrical resistivity and Seebeck coefficient of Bi1−xPbxCuSeO both decreased monotonically in all temperature range with increasing Pb content due to the increased carrier concentration. The power factor of Bi1−xPbxCuSeO (x = 0.03) reaches 5.3 μW cm−1 K−2 at 873 K. The influence of Pb2+ doping on the electronic structure is the same as the one obtained with Sr2+, however, the decrease of the holes mobility is reduced as compared to Sr2+ doping, which could be beneficial to the thermoelectric performances.
Structural and mechanical stability of dilute yttrium doped chromium
Authors: Lei Jialin , Chen Bin , Guo Shengmin , Wang Kaiyang , Tan Liuxi , Khosravi Ebrahim , Yan Jinyuan , Vennila Raju Selva , Yang Shizhong
Published: January 2013

Rare earth element doping of chromium is much desired for various applications, but is technically difficult because of dopant segregation. Using a room temperature mechanical alloying method, dilute yttrium doping into nanosized chromium was achieved. Synchrotron-based high-pressure X-ray diffraction indicated that the Cr-Y alloy (Cr0.97Y0.03) was stable at up to 39 GPa, and the bulk modulus was 203 ± 2.6 GPa. The experimental results were consistent with first-principles density functional theory simulation. The diffraction line broadening profiles indicated the deformation anisotropy of the nanoalloy. This study suggests that Cr0.97Y0.03 alloy is promising for ultrahigh stress applications such as airplane engines and land-based turbines.
Tunneling spectroscopy of graphene using planar Pb probes
Authors: Li Yanjing , Mason Nadya
Published: January 2013

We show that evaporating lead (Pb) directly on graphene can create high-yield, high-quality tunnel probes, and we demonstrate high magnetic field/low temperature spectroscopy using these probes. Comparisons of Pb, Al, and Ti/Au probes show that after oxidation a well-formed self-limited tunnel barrier is created only between the Pb and the graphene. Tunneling spectroscopy using the Pb probes manifests energy-dependent features such as scattering resonances and localization behavior and can thus be used to probe the microscopic electronics of graphene.
Surface-normal second harmonic emission from AlGaAs high-contrast gratings
Authors: Tran T. , Karagodsky V. , Rao Y. , Yang W. , Chen R. , Chase C. , Chuang L. C. , Chang-Hasnain C. J.
Published: January 2013

Second harmonic (SH) generation from AlGaAs near-wavelength high-contrast gratings was studied in polarization-dependent reflection measurements. The grating design is critical in determining the strength and polarization of the second harmonic signal. The second harmonic response was enhanced by more than 3 orders of magnitude compared to flat AlGaAs surfaces without the gratings. These enhancements are due to the diffractive nature of the gratings, specifically their ability to change the direction of light waves.
Active terahertz quantum-cascade composite right/left-handed metamaterial
Authors: Tavallaee Amir A. , Hon Philip W. C. , Chen Qi-Sheng , Itoh Tatsuo , Williams Benjamin S.
Published: January 2013

We report the demonstration of a composite right/left-handed (CRLH) metamaterial waveguide for terahertz quantum-cascade (QC) lasers. By incorporating gap capacitors (∼250 nm) in the top metallization of a metal-metal waveguide operating in a higher order lateral mode, we have realized a CRLH transmission line that supports traveling modes with negative effective phase indices (i.e., left-handed or backward-wave propagation). The CRLH metamaterial waveguide is employed as an active leaky-wave antenna for a terahertz QC-laser. Directional single-lobed beams launched in the backwards direction at angles of −4° and −63° were experimentally observed at excitation frequencies 2.59 and 2.48 THz, respectively.
A nanoelectromechanical systems optical switch driven by optical gradient force
Authors: Cai H. , Dong B. , Tao J. F. , Ding L. , Tsai J. M. , Lo G. Q. , Liu A. Q. , Kwong D. L.
Published: January 2013

A nanoelectromechanical systems (NEMS) optical switch driven by optical gradient force is demonstrated. The switch consists of a free-standing ring resonator and two bus waveguides. When the free-standing ring is bended by the optical gradient force, the output transmission signal is tuned from the on-state to the off-state of the switch. The NEMS optical switch shows a switching time of 43.5 ns and a switching contrast of more than 25 dB. With its chip-scale integrability, the optical switch has potential applications in signal processing and high-speed optical communication networks.
Half-metallic ferromagnetism in wurtzite ScM (M=C, Si, Ge, and Sn): Ab initio calculations
Authors: Fan S. W. , Ding L. J. , Wang Z. L. , Yao K. L.
Published: January 2013

Using the full potential linearized augment plane wave method with the modified Becke and Johnson (mBJ) potential, the half-metallicity and electronic structure for the wurtzite ScM (M = C, Si, Ge, and Sn) compounds are investigated. The ScM series compounds are found to be excellent half-metallic ferromagnets (HMFs) with large half-metallic gaps (0.76–0.33 eV). The magnetic moments are 2.00 μB per cell, and p-d hybridization mechanism plays crucial role in forming the half-metallic ferromagnetism. The ferromagnetic ground states, larger half metallic gaps, the robust half-metallicity with respect to the lattice compression, negative cohesive energy, and heat of formation indicate ScM compounds would be promising HMFs.
Low-temperature large magnetocaloric effect in the antiferromagnetic ErNi0.6Cu0.4Al compound
Authors: Wang L. C. , Dong Q. Y. , Xu Z. Y. , Hu F. X. , Sun J. R. , Shen B. G.
Published: January 2013

Magnetic properties and magnetocaloric effects (MCEs) of the ErNi0.6Cu0.4Al compound are investigated. The compound is found to be antiferromagnet with the Néel temperature TN = 4 K. An antiferromagnetic (AFM)-to-ferromagnetic (FM) transition below TN occurs under an applied magnetic field of 0.8 kOe. The field-induced AFM-FM transition leads to a large MCE and no magnetic hysteresis loss is observed. The maximum values of magnetic entropy change (ΔS) are found to be −15.5 J/kg K and −22.5 J/kg K with a refrigerant capacity value of 122 and 354 J/kg for the field changes of 0–20 kOe and 0–50 kOe, respectively. The large ΔS as well as no hysteresis loss make ErNi0.6Cu0.4Al an attractive candidate for low temperature magnetic refrigerant.
Dynamic loading characteristics of an intradural spinal cord stimulator
Authors: Oliynyk M. S. , Gillies G. T. , Oya H. , Wilson S. , Reddy C. G. , Howard M. A.
Published: January 2013

We have measured the forces that act on the electrode-bearing surface of an intradural neuromodulator designed to be in direct contact with the pial surface of the spinal cord, as part of our effort to develop a new method for treating intractable pain. The goal was to investigate the pressures produced by this device on the spinal cord and compare them with normal intrathecal pressure. For this purpose, we employed a dual-sensor arrangement that allowed us to measure the response of a custom-designed silicone spinal cord surrogate to the forces applied by the device. We found that the device had a mean compliance of ≈63 μN μm−1, and that over a 3 mm range of compression, the mid-span pressure it exerted on the spinal cord was ≈1.88 × 103 Pa = 14.1 mm Hg, which lies within the range of normal intrathecal pressure in humans.
Effects of Ni Particle Size on Hydrogen Storage of Ni-Doped High Surface Area Activated Carbon
Authors: Yang Lufeng , Xie Chunlin , Hu Chaofan , Zheng Mingtao , Wang Haibo , Cui Jianghu , Xiao Yong , Lei Bingfu , Liu Yingliang , Sun Lixian
Published: January 2013

A type of activated carbon that is further chemically activated to obtain a high surface area (~3322 m2 g–1) (hsAC), is loaded with nickel nanoparticles by a direct hydrothermal method, and tested for hydrogen storage. The chemical composition, crystal structure, and microstructure of hsAC with or without Ni loading are characterised in addition to the nitrogen absorbance isotherms. Hydrogen storage studies showed that metal doping has no effect on the cryogenic storage, and the maximum room temperature (RT) storage capacity through spillover on the Ni-doped hsAC materials achieved 0.79 wt-% at 30 Pa with enhancement factors of 2.93. The smaller catalyst size was a critical factor that determined the enhancement of RT storage capacity of the materials. The Ni catalyst size was controlled by the doped Ni content. Tuning the Ni catalyst size together with an optimum carbon spillover receptor should play an effective role in further enhancement by the spillover effect.
Notch signaling in chondrocytes modulates endochondral ossification and osteoarthritis development
Authors: Hosaka Yoko , Saito Taku , Sugita Shurei , Hikata Tomohiro , Kobayashi Hiroshi , Fukai Atsushi , Taniguchi Yuki , Hirata Makoto , Akiyama Haruhiko , Chung Ung-il , Kawaguchi Hiroshi
Published: January 2013

Here we examined the involvement of Notch signaling in the endochondral ossification process, which is crucial for osteoarthritis (OA) development. Intracellular domains of Notch1 and -2 were translocated into the nucleus of chondrocytes with their differentiation in mouse limb cartilage and in mouse and human OA articular cartilage. A tissue-specific inactivation of the Notch transcriptional effector recombination signal binding protein for Ig kappa J (RBPjκ) in chondroprogenitor cells of SRY-box containing gene 9 (Sox9)-Cre;Rbpjfl/flmouse embryos caused an impaired terminal stage of endochondral ossification in the limb cartilage. The RBPjκ inactivation in adult articular cartilage after normal skeletal growth using type II collagen (Col2a1)-CreERT;Rbpjfl/flmice by tamoxifen injection caused resistance to OA development in the knee joint. Notch intracellular domain with the effector RBPjκ stimulated endochondral ossification through induction of the target gene Hes1 in chondrocytes. Among the Notch ligands, Jagged1 was strongly induced during OA development. Finally, intraarticular injection ofN-[N-(3,5-diflurophenylacetate)-l-alanyl]-(S)-phenylglycine t-butyl ester (DAPT), a small compound Notch inhibitor, to the mouse knee joint prevented OA development. The RBPjκ-dependent Notch signaling in chondrocytes modulates the terminal stage of endochondral ossification and OA development, representing an extracellular therapeutic target of OA.
Evolution of multicellularity coincided with increased diversification of cyanobacteria and the Great Oxidation Event
Authors: Schirrmeister Bettina E. , de Vos Jurriaan M. , Antonelli Alexandre , Bagheri Homayoun C.
Published: January 2013

Cyanobacteria are among the most diverse prokaryotic phyla, with morphotypes ranging from unicellular to multicellular filamentous forms, including those able to terminally (i.e., irreversibly) differentiate in form and function. It has been suggested that cyanobacteria raised oxygen levels in the atmosphere around 2.45–2.32 billion y ago during the Great Oxidation Event (GOE), hence dramatically changing life on the planet. However, little is known about the temporal evolution of cyanobacterial lineages, and possible interplay between the origin of multicellularity, diversification of cyanobacteria, and the rise of atmospheric oxygen. We estimated divergence times of extant cyanobacterial lineages under Bayesian relaxed clocks for a dataset of 16S rRNA sequences representing the entire known diversity of this phylum. We tested whether the evolution of multicellularity overlaps with the GOE, and whether multicellularity is associated with significant shifts in diversification rates in cyanobacteria. Our results indicate an origin of cyanobacteria before the rise of atmospheric oxygen. The evolution of multicellular forms coincides with the onset of the GOE and an increase in diversification rates. These results suggest that multicellularity could have played a key role in triggering cyanobacterial evolution around the GOE.
Quantum phase transition from triangular to stripe charge order in NbSe
2
Authors: Soumyanarayanan Anjan , Yee Michael M. , He Yang , van Wezel Jasper , Rahn Dirk J. , Rossnagel Kai , Hudson E. W. , Norman Michael R. , Hoffman Jennifer E.
Published: January 2013

The competition between proximate electronic phases produces a complex phenomenology in strongly correlated systems. In particular, fluctuations associated with periodic charge or spin modulations, known as density waves, may lead to exotic superconductivity in several correlated materials. However, density waves have been difficult to isolate in the presence of chemical disorder, and the suspected causal link between competing density wave orders and high-temperature superconductivity is not understood. Here we used scanning tunneling microscopy to image a previously unknown unidirectional (stripe) charge-density wave (CDW) smoothly interfacing with the familiar tridirectional (triangular) CDW on the surface of the stoichiometric superconductor NbSe
2
. Our low-temperature measurements rule out thermal fluctuations and point to local strain as the tuning parameter for this quantum phase transition. We use this quantum interface to resolve two longstanding debates about the anomalous spectroscopic gap and the role of Fermi surface nesting in the CDW phase of NbSe
2
. Our results highlight the importance of local strain in governing phase transitions and competing phenomena, and suggest a promising direction of inquiry for resolving similarly longstanding debates in cuprate superconductors and other strongly correlated materials.