2,744 research outputs found

    Dimensional perturbation theory for vibration-rotation spectra of linear triatomic molecules

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    A very efficient large-order perturbation theory is formulated for the nuclear motion of a linear triatomic molecule. To demonstrate the method, all of the experimentally observed rotational energies, with values of JJ almost up to 100, for the ground and first excited vibrational states of CO2_2 and for the ground vibrational states of N2_2O and of OCS are calculated. All coupling between vibration and rotation is included. The perturbation expansions reported here are rapidly convergent. The perturbation parameter is D−1/2D^{-1/2}, where DD is the dimensionality of space. Increasing DD is qualitatively similar to increasing the angular momentum quantum number JJ. Therefore, this approach is especially suited for states with high rotational excitation. The computational cost of the method scales only as JNv5/3JN_v^{5/3}, where NvN_v is the size of the vibrational basis set.Comment: submitted to Journal of Chemical Physics, 23 pages, REVTeX, no figure

    Distributed variance regularized Multitask Learning

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    Past research on Multitask Learning (MTL) has focused mainly on devising adequate regularizers and less on their scalability. In this paper, we present a method to scale up MTL methods which penalize the variance of the task weight vectors. The method builds upon the alternating direction method of multipliers to decouple the variance regularizer. It can be efficiently implemented by a distributed algorithm, in which the tasks are first independently solved and subsequently corrected to pool information from other tasks. We show that the method works well in practice and convergences in few distributed iterations. Furthermore, we empirically observe that the number of iterations is nearly independent of the number of tasks, yielding a computational gain of O(T) over standard solvers. We also present experiments on a large URL classification dataset, which is challenging both in terms of volume of data points and dimensionality. Our results confirm that MTL can obtain superior performance over either learning a common model or independent task learning

    Invariance of the correlation energy at high density and large dimension in two-electron systems

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    We prove that, in the large-dimension limit, the high-density correlation energy \Ec of two opposite-spin electrons confined in a DD-dimensional space and interacting {\em via} a Coulomb potential is given by \Ec \sim -1/(8D^2) for any radial confining potential V(r)V(r). This result explains the observed similarity of \Ec in a variety of two-electron systems in three-dimensional space.Comment: 4 pages, 1 figure, to appear in Phys. Rev. Let

    Using Raman Spectroscopy to Improve Hyperpolarized Noble Gas Production for Clinical Lung Imaging Techniques

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    Spin-exchange optical pumping (SEOP) can be used to “hyperpolarize” 129Xe for human lung MRI. SEOP involves transfer of angular momentum from light to an alkali metal (Rb) vapor, and then onto 129Xe nuclear spins during collisions; collisions between excited Rb and N2 ensure that incident optical energy is nonradiatively converted into heat. However, because variables that govern SEOP are temperature-dependent, the excess heat can complicate efforts to maximize spin polarization—particularly at high laser fluxes and xenon densities. Ultra-low frequency Raman spectroscopy may be used to perform in situ gas temperature measurements to investigate the interplay of energy thermalization and SEOP dynamics. Experimental configurations include an “orthogonal” pump-and-probe design and a newer “inline” design (with source and detector on the same axis) that has provided a >20-fold improvement in SNR. The relationship between 129Xe polarization and the spatiotemporal distribution of N2 rotational temperatures has been investigated as a function of incident laser flux, exterior cell temperature, and gas composition. Significantly elevated gas temperatures have been observed—hundreds of degrees hotter than exterior cell surfaces—and variances with position and time can indicate underlying energy transport, convection, and Rb mass-transport processes that, if not controlled, can negatively impact 129Xe hyperpolarization

    Enhanced X-ray variability from V1647 Ori, the young star in outburst illuminating McNeil's Nebula

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    We report a ~38 ks X-ray observation of McNeil's Nebula obtained with XMM on 2004 April 4. V1647 Ori, the young star in outburst illuminating McNeil's Nebula, is detected with XMM and appears variable in X-rays. We investigate the hardness ratio variability and time variations of the event energy distribution with quantile analysis, and show that the large increase of the count rate from V1647 Ori observed during the second half of the observation is not associated with any large plasma temperature variations as for typical X-ray flares from young low-mass stars. X-ray spectral fitting shows that the bulk (~75%) of the intrinsic X-ray emission in the 0.5-8 keV energy band comes from a soft plasma component (0.9 keV) reminiscent of the X-ray spectrum of the classical T Tauri star TW Hya, for which X-ray emission is believed to be generated by an accretion shock onto the photosphere of a low-mass star. The hard plasma component (4.2 keV) contributes ~25% of the total X-ray emission, and can be understood only in the framework of plasma heating sustained by magnetic reconnection events. We find a hydrogen column density of NH=4.1E22 cm-2, which points out a significant excess of hydrogen column density compared to the value derived from optical/IR observations, consistent with the picture of the rise of a wind/jet unveiled from ground optical spectroscopy. The X-ray flux observed with XMM ranges from roughly the flux observed by Chandra on 2004 March 22 (~10 times greater than the pre-outburst X-ray flux) to a value two times greater than that caught by Chandra on 2004 March 7 (~200 times greater than the pre-outburst X-ray flux). We have investigated the possibility that V1647 Ori displays a periodic variation in X-ray brightness as suggested by the combined Chandra+XMM data set (abridged).Comment: 11 pages and 8 Figures. Accepted for publication by Astronomy & Astrophysic

    Academic training in oral and maxillofacial surgery - when and how to enter the pathway

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    Entering into surgical academia can seem a daunting prospect for an oral and maxillofacial surgery (OMFS) trainee. However, the streamlining of academic training by the NIHR to create the integrated academic training (IAT) pathway has simplified academic training and more clearly defined academic positions and entry points for trainees. In this article we review the current NIHR IAT pathway and the various grades and entry points available to OMF surgeons, both pre- and post-doctoral. We highlight the unique challenges facing OMF trainees and provide advice and insight from both junior and senior OMFS academics. Finally, we focus on the planning and application for a doctoral research fellowship - discussing funding streams available to OMF surgeons

    Depression and anxiety symptoms at TNF inhibitor initiation are associated with impaired treatment response in axial spondyloarthritis

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    Acknowledgment We are grateful to Professor Gary Macfarlane for commenting on the manuscript. We are grateful to the staff of the BSRBR-AS register and to the recruiting staff at the clinical centres, details of which are available at: www.abdn.ac.uk/bsrbr-as. We also thank Dr Lewis Carpenter for suggesting splines for modelling time. Contribution: SSZ analysed the data and wrote the manuscript with significant input from all co- authors. GTJ is the Deputy Chief Investigator on BSRBR-AS and designed the study and oversaw its conduct. In the current project they discussed results and provided input into drafts of the manuscript. Funding: The BSRBR-AS is funded by the British Society for Rheumatology (BSR) who have received funding for this from Pfizer, AbbVie and UCB. These companies receive advance copies of manuscripts for comments. They have no input in determining the topics for analysis or work involved in undertaking it.Peer reviewedPublisher PD

    The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System

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    We describe the layout and unique features of the focal plane system for MIRI. We begin with the detector array and its readout integrated circuit (combining the amplifier unit cells and the multiplexer), the electronics, and the steps by which the data collection is controlled and the output signals are digitized and delivered to the JWST spacecraft electronics system. We then discuss the operation of this MIRI data system, including detector readout patterns, operation of subarrays, and data formats. Finally, we summarize the performance of the system, including remaining anomalies that need to be corrected in the data pipeline

    Furthering alternative cultures of valuation in higher education research

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    The value of higher education is often implicit or assumed in educational research. The underlying and antecedent premises that shape and influence debates about value remain unchallenged which perpetuates the dominant, but limiting, terms of the debate and fosters reductionism. I proceed on the premise that analyses of value are not self–supporting or self-referential but are embedded within prevailing cultures of valuation. I contend that challenging, and providing alternatives to, dominant narratives of higher education requires an appreciation of those cultures. I therefore highlight some of the existing cultures of valuation and their influence. I then propose Sayer’s concept of lay normativity as a culture of valuation and discuss how it translates into the practices of research into higher education, specifically the practice of analysis. I animate the discussion by detecting the presence of lay normativity in the evaluative space of the capability approach
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