Anomalous response to gate voltage application in mesoscopic LaAlO_3/SrTiO_3 devices

We report on resistivity and Hall measurements performed on a series of narrow mesa devices fabricated from LaAlO_3/SrTiO_3 single interface heterostructure with a bridge width range of 1.5-10 microns. Upon applying back-gate voltage of the order of a few Volts, a strong increase in the sample resistance (up to factor of 35) is observed, suggesting a relatively large capacitance between the Hall-bar and the gate. The high value of this capacitance is due to the device geometry, and can be explained within an electrostatic model using the Thomas Fermi approximation. The Hall coefficient is sometimes a non-monotonic function of the gate voltage. This behavior is inconsistent with a single conduction band model. We show that a theoretical two-band model is consistent with this transport behavior, and indicates a metal to insulator transition in at least one of these bands.Comment: 5 pages, 4 figure

Nasopharyngeal Carriage of Streptococcus pneumoniae Shortly before Vaccination with a Pneumococcal Conjugate Vaccine Causes Serotype-Specific Hyporesponsiveness in Early Infancy

Background. The antibody response to pneumococcal conjugate vaccines (PCVs) in infants is variable. Factors responsible for this variability have not been fully elucidated. The objective of this study was to investigate whether pneumococcal carriage around the time of the first dose of 7-valent PCV (PCV7) affects serotype-specific immunologic response. Methods. Healthy 2-month old infants were randomized to receive 2 (at the ages of 4 and 6 months) or 3 (at the ages of 2, 4, and 6 months) PCV7 doses and a booster dose (at the age of 12 months). Nasopharyngeal or oropharyngeal specimens were obtained for culture shortly before the first PCV7 dose. Serotype-specific immunoglobulin (Ig) G levels were measured at ages 2, 7, and 13 months. Results. Of 545 children studied, 332 received a booster dose. The most common serotypes carried around the time of the first PCV7 dose were 6B (n = 37), 19F (n = 22), and 23F (n = 14). In carriers before the first dose, the IgG response to the carried serotype after 2 or 3 doses was significantly lower than in noncarriers. In contrast, response to the noncarried serotypes was not affected. Although all children responded to the booster dose, the response to the originally carried serotype was generally lower. Conclusions. Serotype-specific hyporesponsiveness to PCV7 after pneumococcal carriage in infants is demonstrated for the first time. This phenomenon was common, lasted for at least several months, and was only partially overcome by the 12-month booster. Trial registration. isrctn.org identifier: ISRCTN2844584

High-order harmonic transient grating spectroscopy of SF6 molecular vibrations

special issue : Ultrafast electron and molecular dynamicsInternational audienceStrong field transient grating spectroscopy has shown to be a very versatile tool in time-resolved molecular spectroscopy. Here we use this technique to investigate the high-order harmonic generation from SF6 molecules vibrationally excited by impulsive stimulated Raman scattering. Transient grating spectroscopy enables us to reveal clear modulations of the harmonic emission. This heterodyne detection shows that the harmonic emission generated between 14 to 26 eV is mainly sensitive to two among the three active Raman modes in SF6, i.e. the strongest and fully symmetric nu 1-A1g mode (774 cm-1, 43 fs) and the slowest mode nu5-T2g (524 cm-1, 63 fs). A time-frequency analysis of the harmonic emission reveals additional dynamics: the strength and central frequency of the nu 1 mode oscillate with a frequency of 52 cm-1 (640 fs). This could be a signature of the vibration of dimers in the generating medium. Harmonic 11 shows a remarkable behavior, oscillating in opposite phase, both on the fast (774 cm-1) and slow (52 cm-1) timescales, which indicates a strong modulation of the recombination matrix element as a function of the nuclear geometry. These results demonstrate that the high sensitivity of high-order harmonic generation to molecularvibrations, associated to the high sensitivity of transient grating spectroscopy, make their combination a unique tool to probe vibrational dynamics

Point contact spectroscopy of the electron-doped cuprate superconductor Pr{2-x}Ce{x}CuO4: The dependence of conductance-voltage spectra on cerium doping, barrier strength and magnetic field

We present conductance-voltage (G-V) data for point contact junctions between a normal metal and the electron doped cuprate superconductor Pr{2-x}Ce{x}CuO4 (PCCO). We observe a zero bias conductance peak (ZBCP) for the under-doped composition of this cuprate (x=0.13) which is consistent with d-wave pairing symmetry. For optimally-doped (x=0.15) and over-doped (x=0.17) PCCO, we find that the G-V characteristics indicate the presence of an order parameter without nodes. We investigate this further by obtaining point contact spectroscopy data for different barrier strengths and as a function of magnetic field.Comment: 13 pages, 9 figure

Linear-T resistivity and change in Fermi surface at the pseudogap critical point of a high-Tc superconductor

A fundamental question of high-temperature superconductors is the nature of the pseudogap phase which lies between the Mott insulator at zero doping and the Fermi liquid at high doping p. Here we report on the behaviour of charge carriers near the zero-temperature onset of that phase, namely at the critical doping p* where the pseudogap temperature T* goes to zero, accessed by investigating a material in which superconductivity can be fully suppressed by a steady magnetic field. Just below p*, the normal-state resistivity and Hall coefficient of La1.6-xNd0.4SrxCuO4 are found to rise simultaneously as the temperature drops below T*, revealing a change in the Fermi surface with a large associated drop in conductivity. At p*, the resistivity shows a linear temperature dependence as T goes to zero, a typical signature of a quantum critical point. These findings impose new constraints on the mechanisms responsible for inelastic scattering and Fermi surface transformation in theories of the pseudogap phase.Comment: 24 pages, 6 figures. Published in Nature Physics. Online at http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys1109.htm

Do we have an alternative methodology for teaching design?

The study reported here is a research project aimed to examine the relationship between alternative approaches towards design teaching (structural or functional), and the students’ mental modelling of the design process and the quality of their design process. The structural approach emphasizes the need for an ordered learning of the stages of the design process, while the functional approach emphasizes the teaching and study of design functions (rather than stages). 80 seventh graders, divided in two groups, were taught a unit on technological problem solving by either approach for fourteen classes (21 hours). Before, during and after the design process of a technological solution the students had to generate representations of this process and make portfolios representing their problem solving process. The results were analysed looking for: (a) The differences between the groups in the mental models which were constructed during the instruction process. (b) The differences between the groups in the quality of the process and the design functions implemented. Significant differences between the groups observed for many of the variables studied indicate that the functional approach represents a promising methodology for teaching design

Analysis of vadose zone inhomogeneity toward distinguishing recharge rates: Solving the nonlinear interface problem with Newton method

Citation: Steward, D. R. (2016). Analysis of vadose zone inhomogeneity toward distinguishing recharge rates: Solving the nonlinear interface problem with Newton method. Water Resources Research, 52(11), 8756-8774. doi:10.1002/2016wr019222Recharge from surface to groundwater is an important component of the hydrological cycle, yet its rate is difficult to quantify. Percolation through two-dimensional circular inhomogeneities in the vadose zone is studied where one soil type is embedded within a uniform background, and nonlinear interface conditions in the quasilinear formulation are solved using Newton's method with the Analytic Element Method. This numerical laboratory identifies detectable variations in pathline and pressure head distributions that manifest due to a shift in recharge rate through in a heterogeneous media. Pathlines either diverge about or converge through coarser and finer grained materials with inverse patterns forming across lower and upper elevations; however, pathline geometry is not significantly altered by recharge. Analysis of pressure head in lower regions near groundwater identifies a new phenomenon: its distribution is not significantly impacted by an inhomogeneity soil type, nor by its placement nor by recharge rate. Another revelation is that pressure head for coarser grained inhomogeneities in upper regions is completely controlled by geometry and conductivity contrasts; a shift in recharge generates a difference Dp that becomes an additive constant with the same value throughout this region. In contrast, shifts in recharge for finer grained inhomogeneities reveal patterns with abrupt variations across their interfaces. Consequently, measurements aimed at detecting shifts in recharge in a heterogeneous vadose zone by deciphering the corresponding patterns of change in pressure head should focus on finer grained inclusions well above a groundwater table

Exploring the evidence base for national and regional policy interventions to combat resistance

The effectiveness of existing policies to control antimicrobial resistance is not yet fully understood. A strengthened evidence base is needed to inform effective policy interventions across countries with different income levels and the human health and animal sectors. We examine three policy domains—responsible use, surveillance, and infection prevention and control—and consider which will be the most effective at national and regional levels. Many complexities exist in the implementation of such policies across sectors and in varying political and regulatory environments. Therefore, we make recommendations for policy action, calling for comprehensive policy assessments, using standardised frameworks, of cost-effectiveness and generalisability. Such assessments are especially important in low-income and middle-income countries, and in the animal and environmental sectors. We also advocate a One Health approach that will enable the development of sensitive policies, accommodating the needs of each sector involved, and addressing concerns of specific countries and regions

Image reconstruction of fluorescent molecular tomography based on the tree structured Schur complement decomposition

<p>Abstract</p> <p>Background</p> <p>The inverse problem of fluorescent molecular tomography (FMT) often involves complex large-scale matrix operations, which may lead to unacceptable computational errors and complexity. In this research, a tree structured Schur complement decomposition strategy is proposed to accelerate the reconstruction process and reduce the computational complexity. Additionally, an adaptive regularization scheme is developed to improve the ill-posedness of the inverse problem.</p> <p>Methods</p> <p>The global system is decomposed level by level with the Schur complement system along two paths in the tree structure. The resultant subsystems are solved in combination with the biconjugate gradient method. The mesh for the inverse problem is generated incorporating the prior information. During the reconstruction, the regularization parameters are adaptive not only to the spatial variations but also to the variations of the objective function to tackle the ill-posed nature of the inverse problem.</p> <p>Results</p> <p>Simulation results demonstrate that the strategy of the tree structured Schur complement decomposition obviously outperforms the previous methods, such as the conventional Conjugate-Gradient (CG) and the Schur CG methods, in both reconstruction accuracy and speed. As compared with the Tikhonov regularization method, the adaptive regularization scheme can significantly improve ill-posedness of the inverse problem.</p> <p>Conclusions</p> <p>The methods proposed in this paper can significantly improve the reconstructed image quality of FMT and accelerate the reconstruction process.</p