447 research outputs found
RAPID THERMAL-DIFFUSION OF SN FROM SPIN-ON-GLASS INTO GAAS
Diffusion of dopants into semiconductors from a spin-on-glass (SOG) source is of great interest because of its versatility, simplicity, and relatively low cost. SiO2 SOG films doped with Sn and/or Ga were used as a diffusion source on GaAs. Diffusion was studied during rapid thermal annealing with or without an As over-pressure ambient, which was produced by either the proximity over-pressure or the enhanced over-pressure proximity techniques. Diffusivity of Sn was observed to decrease as As over-pressure increases. Modifying the Sn doped SOG to contain 4 mole percent Ga slightly reduced the Sn diffusivity. An explanation of these results is proposed based on the chemical reactions between the SOG and GaAs. Highly doped layers (1-3 x 10(18) cm(-3)) with good electron mobility (>1000 cm(2)/V . s) resulting in abrupt shallow junctions (<0.5 mu m) were obtained.14282829283
Holographic Metamagnetism, Quantum Criticality, and Crossover Behavior
Using high-precision numerical analysis, we show that 3+1 dimensional gauge
theories holographically dual to 4+1 dimensional Einstein-Maxwell-Chern-Simons
theory undergo a quantum phase transition in the presence of a finite charge
density and magnetic field. The quantum critical theory has dynamical scaling
exponent z=3, and is reached by tuning a relevant operator of scaling dimension
2. For magnetic field B above the critical value B_c, the system behaves as a
Fermi liquid. As the magnetic field approaches B_c from the high field side,
the specific heat coefficient diverges as 1/(B-B_c), and non-Fermi liquid
behavior sets in. For B<B_c the entropy density s becomes non-vanishing at zero
temperature, and scales according to s \sim \sqrt{B_c - B}. At B=B_c, and for
small non-zero temperature T, a new scaling law sets in for which s\sim
T^{1/3}. Throughout a small region surrounding the quantum critical point, the
ratio s/T^{1/3} is given by a universal scaling function which depends only on
the ratio (B-B_c)/T^{2/3}.
The quantum phase transition involves non-analytic behavior of the specific
heat and magnetization but no change of symmetry. Above the critical field, our
numerical results are consistent with those predicted by the Hertz/Millis
theory applied to metamagnetic quantum phase transitions, which also describe
non-analytic changes in magnetization without change of symmetry. Such
transitions have been the subject of much experimental investigation recently,
especially in the compound Sr_3 Ru_2 O_7, and we comment on the connections.Comment: 23 pages, 8 figures v2: added ref
Thermodynamic instability of doubly spinning black objects
We investigate the thermodynamic stability of neutral black objects with (at
least) two angular momenta. We use the quasilocal formalism to compute the
grand canonical potential and show that the doubly spinning black ring is
thermodynamically unstable. We consider the thermodynamic instabilities of
ultra-spinning black objects and point out a subtle relation between the
microcanonical and grand canonical ensembles. We also find the location of the
black string/membrane phases of doubly spinning black objects.Comment: 25 pages, 7 figures v2: matches the published versio
Gauge gravity duality for d-wave superconductors: prospects and challenges
We write down an action for a charged, massive spin two field in a fixed
Einstein background. Despite some technical problems, we argue that in an
effective field theory framework and in the context of the AdS/CFT
correspondence, this action can be used to study the properties of a superfluid
phase transition with a d-wave order parameter in a dual strongly interacting
field theory. We investigate the phase diagram and the charge conductivity of
the superfluid phase. We also explain how possible couplings between the spin
two field and bulk fermions affect the fermion spectral function.Comment: 42 pages, 6 figure
Universality and exactness of Schrodinger geometries in string and M-theory
We propose an organizing principle for classifying and constructing
Schrodinger-invariant solutions within string theory and M-theory, based on the
idea that such solutions represent nonlinear completions of linearized vector
and graviton Kaluza-Klein excitations of AdS compactifications. A crucial
simplification, derived from the symmetry of AdS, is that the nonlinearities
appear only quadratically. Accordingly, every AdS vacuum admits infinite
families of Schrodinger deformations parameterized by the dynamical exponent z.
We exhibit the ease of finding these solutions by presenting three new
constructions: two from M5 branes, both wrapped and extended, and one from the
D1-D5 (and S-dual F1-NS5) system. From the boundary perspective, perturbing a
CFT by a null vector operator can lead to nonzero beta-functions for spin-2
operators; however, symmetry restricts them to be at most quadratic in
couplings. This point of view also allows us to easily prove nonrenormalization
theorems: for any Sch(z) solution of two-derivative supergravity constructed in
the above manner, z is uncorrected to all orders in higher derivative
corrections if the deforming KK mode lies in a short multiplet of an AdS
supergroup. Furthermore, we find infinite classes of 1/4 BPS solutions with
4-,5- and 7-dimensional Schrodinger symmetry that are exact.Comment: 31 pages, plus appendices; v2, minor corrections, added refs, slight
change in interpretation in section 2.3, new Schrodinger and Lifshitz
solutions included; v3, clarifications in sections 2 and 3 regarding
existence of solutions and multi-trace operator
Recommended from our members
Cosmogenic neutron production at the Sudbury Neutrino Observatory
Neutrons produced in nuclear interactions initiated by cosmic-ray muons present an irreducible background to many rare-event searches, even in detectors located deep underground. Models for the production of these neutrons have been tested against previous experimental data, but the extrapolation to deeper sites is not well understood. Here we report results from an analysis of cosmogenically produced neutrons at the Sudbury Neutrino Observatory. A specific set of observables are presented, which can be used to benchmark the validity of geant4 physics models. In addition, the cosmogenic neutron yield, in units of 10-4 cm2/(g·μ), is measured to be 7.28±0.09(stat)-1.12+1.59(syst) in pure heavy water and 7.30±0.07(stat)-1.02+1.40(syst) in NaCl-loaded heavy water. These results provide unique insights into this potential background source for experiments at SNOLAB
Analysis of a panel of antibodies to APC reveals consistent activity towards an unidentified protein
Acquisition of truncating mutations in the adenomatous polyposis coli (APC) protein underlies the progression of the majority of sporadic and familial colorectal cancers. As such, the localisation patterns and interacting partners of APC have been extensively studied in a range of systems, relying on the use of a broad panel of antibodies. Until recently, antibodies to APC have been used largely unchecked. However, several recent reports have been invaluable in clarifying the use of a number of antibodies commonly used to detect APC. Here, we analyse the specificity of a further subset of antibodies to APC. We used a panel of six commercially available antibodies (directed to the amino and carboxy termini of APC) and confirm the detection of full-length APC by immunoblotting. We demonstrate that a 150 kDa protein, also reproducibly detected by this panel of antibodies, is unlikely to be APC. We present data for the immunological staining patterns of the APC antibodies and validate the results through RNAi. Using this approach, we confirm that the apical staining pattern, observed by immunofluorescence and previously reported in cell systems, is unlikely to be APC. Finally, we present our data as a summary of APC-antibody specificities for APC
Entrepreneurial orientation and the business performance of SMEs: a quantitative study from the Netherlands
Entrepreneurial Orientation (EO) is often mentioned as an antecedent of growth, competitive advantage and superior performance, and prior empirical research has often shown a positive relationship between EO and performance appears to exist. However, an important question that remains unanswered is what effect EO might have on firm performance during periods of economic crisis, and the severe environmental turbulence that accompany such crises. This research is a first investigation towards the effects of EO on the performance of small and medium sized firms during the current global economic crisis. In this study we use the multidimensional model of EO and test a series of hypotheses pertaining to its performance effects using survey data gathered from 164 Dutch SMEs. The present research shows that proactive firm behavior positively contributes to SME performance during the economic crisis. We further show that innovative SMEs do perform better in turbulent environments, but those innovative SMEs should minimize the level of risk and should take action to avoid projects that are too risky
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
Effective Rheology of Bubbles Moving in a Capillary Tube
We calculate the average volumetric flux versus pressure drop of bubbles
moving in a single capillary tube with varying diameter, finding a square-root
relation from mapping the flow equations onto that of a driven overdamped
pendulum. The calculation is based on a derivation of the equation of motion of
a bubble train from considering the capillary forces and the entropy production
associated with the viscous flow. We also calculate the configurational
probability of the positions of the bubbles.Comment: 4 pages, 1 figur
- …