10,274 research outputs found
Quantum Diffusion and Delocalization for Band Matrices with General Distribution
We consider Hermitian and symmetric random band matrices in
dimensions. The matrix elements , indexed by , are independent and their variances satisfy \sigma_{xy}^2:=\E
\abs{H_{xy}}^2 = W^{-d} f((x - y)/W) for some probability density . We
assume that the law of each matrix element is symmetric and exhibits
subexponential decay. We prove that the time evolution of a quantum particle
subject to the Hamiltonian is diffusive on time scales . We
also show that the localization length of the eigenvectors of is larger
than a factor times the band width . All results are uniform in
the size \abs{\Lambda} of the matrix. This extends our recent result
\cite{erdosknowles} to general band matrices. As another consequence of our
proof we show that, for a larger class of random matrices satisfying
for all , the largest eigenvalue of is bounded
with high probability by for any ,
where M \deq 1 / (\max_{x,y} \sigma_{xy}^2).Comment: Corrected typos and some inaccuracies in appendix
Narratives that nudge: Raising theoretical questions about reflective practice
The narratives of pre-service teachers in this paper tell a story which interrupts the notion that reflective practice necessarily produces a transformative self. Although this argument is not new, the extent to which the utility of reflective practice is taken for granted in the current context of teacher education (beginning and continuing) remains greater than ever. We show how this normative construction of reflective practice and the understandings of self that it produces in the narratives of pre-service teachers are undermined in the context of schooling. We suggest that further research is needed in this area. Through this effort we raise questions about the spaces in which reflective practice is assumed to operate and the ways in which the reflective self it assumes has been disconnected from society and relations of power. We situate ourselves as teachers, teacher educators and researchers who desire theoretically informed positions from which we can begin to critically address, extend or displace our current understandings of these issues. This paper raises questions about reflective practice and its relationship to pedagogy within the current context of schooling
Analytic nuclear forces and molecular properties from full configuration interaction quantum Monte Carlo
Unbiased stochastic sampling of the one- and two-body reduced density
matrices is achieved in full configuration interaction quantum Monte Carlo with
the introduction of a second, "replica" ensemble of walkers, whose population
evolves in imaginary time independently from the first, and which entails only
modest additional computational overheads. The matrices obtained from this
approach are shown to be representative of full configuration-interaction
quality, and hence provide a realistic opportunity to achieve high-quality
results for a range of properties whose operators do not necessarily commute
with the hamiltonian. A density-matrix formulated quasi-variational energy
estimator having been already proposed and investigated, the present work
extends the scope of the theory to take in studies of analytic nuclear forces,
molecular dipole moments and polarisabilities, with extensive comparison to
exact results where possible. These new results confirm the suitability of the
sampling technique and, where sufficiently large basis sets are available,
achieve close agreement with experimental values, expanding the scope of the
method to new areas of investigation.Comment: 11 page
Gene expression during preimplantation mouse development
To develop a resource for the identification and isolation of genes expressed in the early mammalian embryo, large and representative cDNA libraries were constructed from unfertilized eggs, and two-cell, eight-cell, and blastocyst-stage mouse embryos. Using these libraries, we now report the first stages at which the cytokines interleukin (IL)-6, IL-1 beta, and interferon (IFN)-gamma are transcribed in the developing embryo and the presence of IL-7 transcripts in the unfertilized egg. Transcripts for IL-1 alpha, -2, -3, -4, or -5 were not detected at these stages. To identify novel genes expressed on activation of the embryonic genome, the egg and eight-cell stage-specific cDNA libraries were subtracted from the two-cell library, yielding a specialized cDNA library enriched for transcripts expressed at the two-cell stage. Sequence and Southern blot analysis of several of these cDNAs expressed predominantly at the two-cell stage of embryogenesis revealed them to be from novel genes, thereby providing the first molecular tools with which to approach the study of gene expression in the early mammalian embryo
Deep Optimisation:Solving Combinatorial Optimisation Problems using Deep Neural Networks
Deep Optimisation (DO) combines evolutionary search with Deep Neural Networks
(DNNs) in a novel way - not for optimising a learning algorithm, but for
finding a solution to an optimisation problem. Deep learning has been
successfully applied to classification, regression, decision and generative
tasks and in this paper we extend its application to solving optimisation
problems. Model Building Optimisation Algorithms (MBOAs), a branch of
evolutionary algorithms, have been successful in combining machine learning
methods and evolutionary search but, until now, they have not utilised DNNs. DO
is the first algorithm to use a DNN to learn and exploit the problem structure
to adapt the variation operator (changing the neighbourhood structure of the
search process). We demonstrate the performance of DO using two theoretical
optimisation problems within the MAXSAT class. The Hierarchical Transformation
Optimisation Problem (HTOP) has controllable deep structure that provides a
clear evaluation of how DO works and why using a layerwise technique is
essential for learning and exploiting problem structure. The Parity Modular
Constraint Problem (MCparity) is a simplistic example of a problem containing
higher-order dependencies (greater than pairwise) which DO can solve and state
of the art MBOAs cannot. Further, we show that DO can exploit deep structure in
TSP instances. Together these results show that there exists problems that DO
can find and exploit deep problem structure that other algorithms cannot.
Making this connection between DNNs and optimisation allows for the utilisation
of advanced tools applicable to DNNs that current MBOAs are unable to use
Dry-mass sensing for microfluidics
We present an approach for interfacing an electromechanical sensor with a microfluidic device for the accurate quantification of the dry mass of analytes within microchannels. We show that depositing solutes onto the active surface of a quartz crystal microbalance by means of an on-chip microfluidic spray nozzle and subsequent solvent removal provides the basis for the real-time determination of dry solute mass. Moreover, this detection scheme does not suffer from the decrease in the sensor’s quality factor and the viscous drag present if the measurement is performed in a liquid environment, yet allows solutions to be analysed. We demonstrate the sensitivity and reliability of our approach by controlled deposition of nanogram levels of salt and protein from a micrometer-sized channel.We thank Alexander K. Buell, Igor Efimov, and Victor Ostanin for valuable discussions on QCM sensors and gratefully acknowledge financial support from the Swiss National Science Foundation (SNF), the Engineering and Physical Sciences Research Council (EPSRC), the Biotechnology and Biological Sciences Research Council (BBSRC), the European Research Council (ERC), as well as the Frances and Augustus Newman Foundation.Permission is granted to quote from an AIP publication with the customary acknowledgment of the source. Republication of an article or portions thereof (e.g., excerpts of greater than 400 words, figures, tables, etc.) in original form or in translation, as well as other types of reuse (such as use in course packs or electronic reserves) require formal permission from AIP and may be subject to fees. Although it is not a legal requirement for permission, as a courtesy, an author of the original article should be informed of any request for republication/reuse
Controlling unsteady cavity flows using internal structures
We report experimental measurements and preliminary analysis on a series of geometric modifications to a rectangular cavity, aimed at alleviating the severity of the aeroacoustic environment. The cavity had a length-to-depth ratio of 5 and a width-to-depth ratio of 1, and featured a simplified representation of a generic missile on the centre line. The modifications consisted of full width and depth ribs or “collars” with a cutout for the missile. Collars could be fitted at various combinations of locations in the cavity and were either straight (i.e. perpendicular to the cavity centre line), leaned or yawed. The cavity flowfield was characterised by surface pressure measurements along the ceiling. Judging from the available measurements the presence of collars modified the mean pressure distribution, and appeared to reduce the acoustic tones and generally lower the broadband noise
Discovery of 6.035GHz Hydroxyl Maser Flares in IRAS18566+0408
We report the discovery of 6.035GHz hydroxyl (OH) maser flares toward the
massive star forming region IRAS18566+0408 (G37.55+0.20), which is the only
region known to show periodic formaldehyde (4.8 GHz H2CO) and methanol (6.7 GHz
CH3OH) maser flares. The observations were conducted between October 2008 and
January 2010 with the 305m Arecibo Telescope in Puerto Rico. We detected two
flare events, one in March 2009, and one in September to November 2009. The OH
maser flares are not simultaneous with the H2CO flares, but may be correlated
with CH3OH flares from a component at corresponding velocities. A possible
correlated variability of OH and CH3OH masers in IRAS18566+0408 is consistent
with a common excitation mechanism (IR pumping) as predicted by theory.Comment: Accepted for publication in the Astrophysical Journa
A recombinant bovine herpesvirus-4 vectored vaccine delivered via intranasal nebulization elicits viral neutralizing antibody titers in cattle
Recombinant herpesvirus vaccine vectors offer distinct advantages in next-generation vaccine development, primarily due to the ability to establish persistent infections to provide sustainable antigen responses in the host. Recombinant bovine herpesvirus-4 (BoHV-4) has been previously shown to elicit protective immunity in model laboratory animal species against a variety of pathogens. For the first time, we describe the induction of antigen-specific immune responses to two delivered antigens in the host species after intranasal nebulization of recombinant BoHV-4 expressing the chimeric peptide containing the bovine viral diarrhea virus (BVDV) glycoprotein E2 and the bovine herpesvirus 1 (BoHV-1) glycoprotein D (BoHV-4-A-CMV-IgK-gE2gD-TM). In this study, four cattle were immunized via intranasal nebulization with the recombinant BoHV-4 construct. Two of the cattle were previously infected with wild-type BoHV-4, and both developed detectable serologic responses to BVDV and BoHV-1. All four immunized cattle developed detectable viral neutralizing antibody responses to BVDV, and one steer developed a transient viral neutralizing response to BoHV-1. Approximately one year after immunization, immunosuppressive doses of the glu-cocorticoid dexamethasone were administered intravenously to all four cattle. Within two weeks of immunosuppression, all animals developed viral neutralizing antibody responses to BoHV-1, and all animals maintained BVDV viral neutralizing capacity. Overall, nebulization of BoHV-4-A-CMV-IgK-gE2gD-TM persistently infects cattle, is capable of eliciting antigen-specific immunity following immunization, including in the presence of pre-existing BoHV-4 immunity, and recrudescence of the virus boosts the immune response to BoHV-4-vectored antigens. These results indicate that BoHV-4 is a viable and attractive vaccine delivery platform for use in cattle
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