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Search Results: 1 - 10 of 20002 matches for " Eric Nelson "
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Density Functional Theory Meta-GGA+U Study of Water Incorporation in the Metal Organic Framework Material Cu-BTC
Eric Cockayne,Eric B. Nelson
Physics , 2015, DOI: 10.1063/1.4923461
Abstract: Water absorption in the metal-organic framework (MOF) material Cu-BTC, up to a concentration of 3.5 H$_2$O per Cu ion, is studied via density functional theory at the meta-GGA+U level. The stable arrangements of water molecules show chains of hydrogen-bonded water molecules and a tendency to form closed cages at high concentration. Water clusters are stabilized primarily by a combination of water-water hydrogen bonding and Cu-water oxygen interactions. Stability is further enhanced by van der Waals interactions, electric field enhancement of water-water bonding, and hydrogen bonding of water to framework oxygens. We hypothesize that the tendency to form such stable clusters explains the particularly strong affinity of water to Cu-BTC and related MOFs with exposed metal sites.
Diverse roles for RNA in gene regulation
Nelson C Lau, Eric C Lai
Genome Biology , 2005, DOI: 10.1186/gb-2005-6-4-315
Abstract: The recent Keystone Symposium on the role of RNA in gene regulation brought together a diverse and highly interactive group of biochemists, geneticists, crystallographers, and bioinformaticians to discuss the next frontier - how RNA regulates gene output at the transcriptional, translational, and mRNA-stability level. Many new developments concerned the biochemical mechanism of RNA interference (RNAi) and the endogenous biological processes regulated by microRNAs (miRNAs) and small interfering RNAs (siRNAs). There was, however, also a strong appreciation of previously unannotated RNA genes lurking in the genome and other novel mechanisms by which RNA regulates gene expression. Participants also heard about the fruition of efforts to exploit RNAi for genome-wide functional studies and progress in the use of the technology to develop human therapeutics.The most hotly pursued class of non-coding RNA (ncRNA) in recent years has been the miRNAs. Although research still continues on miRNA discovery, the field has largely made the transition to studying the endogenous biological functions of miRNAs. In particular, speakers discussed computational or experimental approaches to identifying the specific targets of miRNA regulation, as well as genetic approaches to identifying mutant phenotypes associated with altered miRNA activity.David Bartel (Whitehead Institute, Massachusetts Institute of Technology, Cambridge, USA) presented TargetScanS, his group's animal miRNA-target-finding algorithm. It predicts potential targets of miRNAs by searching for 3' untranslated region (UTR) sequences with highly and specifically conserved Watson-Crick matches to positions 2-7 or 2-8 (the 'seed') of the query miRNA; increased confidence is assigned to target sites with an adenosine at position 1 of the miRNA interaction site. Bartel predicted that at least one third of the genes in the human genome are miRNA targets. Lee Lim (Rosetta Inpharmatics, Seattle, USA) challenged the dogma that the
Detecting very long-lived gravitational-wave transients lasting hours to weeks
Eric Thrane,Vuk Mandic,Nelson Christensen
Physics , 2015, DOI: 10.1103/PhysRevD.91.104021
Abstract: We explore the possibility of very long-lived gravitational-wave transients (and detector artifacts) lasting hours to weeks. Such very long signals are both interesting in their own right and as a potential source of systematic error in searches for persistent signals, e.g., from a stochastic gravitational-wave background. We review possible mechanisms for emission on these time scales and discuss computational challenges associated with their detection: namely, the substantial volume of data involved in a search for very long transients can require vast computer memory and processing time. These computational difficulties can be addressed through a form of data compression known as coarse-graining, in which information about short time spans is discarded in order to reduce the computational requirements of a search. Using data compression, we demonstrate an efficient radiometer (cross-correlation) algorithm for the detection of very long transients. In the process, we identify features of a very long transient search (related to the rotation of the Earth) that make it more complicated than a search for shorter transient signals. We implement suitable solutions.
Correlated magnetic noise in global networks of gravitational-wave interferometers: observations and implications
Eric Thrane,Nelson Christensen,Robert Schofield
Physics , 2013, DOI: 10.1103/PhysRevD.87.123009
Abstract: One of the most ambitious goals of gravitational-wave astronomy is to observe the stochastic gravitational-wave background. Correlated noise in two or more detectors can introduce a systematic error, which limits the sensitivity of stochastic searches. We report on measurements of correlated magnetic noise from Schumann resonances at the widely separated LIGO and Virgo detectors. We investigate the effect of this noise on a global network of interferometers and derive a constraint on the allowable coupling of environmental magnetic fields to test mass motion in gravitational-wave detectors. We find that while correlated noise from global electromagnetic fields could be safely ignored for initial LIGO stochastic searches, it could severely impact Advanced LIGO and third-generation detectors.
Detecting compact binary coalescences with seedless clustering
Michael Coughlin,Eric Thrane,Nelson Christensen
Physics , 2014, DOI: 10.1103/PhysRevD.90.083005
Abstract: Compact binary coalescences are a promising source of gravitational waves for second-generation interferometric gravitational-wave detectors. Although matched filtering is the optimal search method for well-modeled systems, alternative detection strategies can be used to guard against theoretical errors (e.g., involving new physics and/or assumptions about spin/eccentricity) while providing a measure of redundancy. In previous work, we showed how "seedless clustering" can be used to detect long-lived gravitational-wave transients in both targeted and all-sky searches. In this paper, we apply seedless clustering to the problem of low-mass ($M_\text{total}\leq10M_\odot$) compact binary coalescences for both spinning and eccentric systems. We show that seedless clustering provides a robust and computationally efficient method for detecting low-mass compact binaries.
New constructions of RIP matrices with fast multiplication and fewer rows
Jelani Nelson,Eric Price,Mary Wootters
Computer Science , 2012,
Abstract: In compressed sensing, the "restricted isometry property" (RIP) is a sufficient condition for the efficient reconstruction of a nearly k-sparse vector x in C^d from m linear measurements Phi x. It is desirable for m to be small, and for Phi to support fast matrix-vector multiplication. In this work, we give a randomized construction of RIP matrices Phi in C^{m x d}, preserving the L_2 norms of all k-sparse vectors with distortion 1+eps, where the matrix-vector multiply Phi x can be computed in nearly linear time. The number of rows m is on the order of eps^{-2}klog dlog^2(klog d). Previous analyses of constructions of RIP matrices supporting fast matrix-vector multiplies, such as the sampled discrete Fourier matrix, required m to be larger by roughly a log k factor. Supporting fast matrix-vector multiplication is useful for iterative recovery algorithms which repeatedly multiply by Phi or Phi^*. Furthermore, our construction, together with a connection between RIP matrices and the Johnson-Lindenstrauss lemma in [Krahmer-Ward, SIAM. J. Math. Anal. 2011], implies fast Johnson-Lindenstrauss embeddings with asymptotically fewer rows than previously known. Our approach is a simple twist on previous constructions. Rather than choosing the rows for the embedding matrix to be rows sampled from some larger structured matrix (such as the discrete Fourier transform or a random circulant matrix), we instead choose each row of the embedding matrix to be a linear combination of a small number of rows of the original matrix, with random sign flips as coefficients. The main tool in our analysis is a recent bound for the supremum of certain types of Rademacher chaos processes in [Krahmer-Mendelson-Rauhut, arXiv:1207.0235].
A diagnosis-based clinical decision rule for spinal pain part 2: review of the literature
Donald R Murphy, Eric L Hurwitz, Craig F Nelson
Chiropractic & Manual Therapies , 2008, DOI: 10.1186/1746-1340-16-7
Abstract: The databases of Medline, Cinahl, Embase and MANTIS were searched for studies that evaluated the reliability and validity of clinic-based diagnostic procedures for patients with spinal pain that have relevance for questions 2 (which investigates characteristics of the pain source) and 3 (which investigates perpetuating factors of the pain experience). In addition, the reference list of identified papers and authors' libraries were searched.A total of 1769 articles were retrieved, of which 138 were deemed relevant. Fifty-one studies related to reliability and 76 related to validity. One study evaluated both reliability and validity.Regarding some aspects of the DBCDR, there are a number of studies that allow the clinician to have a reasonable degree of confidence in his or her findings. This is particularly true for centralization signs, neurodynamic signs and psychological perpetuating factors. There are other aspects of the DBCDR in which a lesser degree of confidence is warranted, and in which further research is needed.Accurate diagnosis or classification of patients with spinal pain has been identified as a research priority [1]. We presented in Part 1 the theoretical model of an approach to diagnosis in patients with spinal pain [2]. This approach incorporated the various factors that have been found, or in some cases theorized, to be of importance in the generation and perpetuation of neck or back pain into an organized scheme upon which a management strategy can be based. The authors termed this approach a diagnosis-based clinical decision rule (DBCDR). The DBCDR is not a clinical prediction rule. It is an attempt to identify aspects of the clinical picture in each patient that are relevant to the perpetuation of pain and disability so that these factors can be addressed with interventions designed to improve them. The purpose of this paper is to review the literature on the methods involved in the DBCDR regarding reliability and validity and to identify thos
Introducing the Photometric Maximum Likelihood Method: Galaxy Luminosity Functions at z<1.2 in MUSYC-ECDFS
Daniel Christlein,Eric Gawiser,Danilo Marchesini,Nelson Padilla
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15474.x
Abstract: We present a new maximum likelihood method for the calculation of galaxy luminosity functions from multi-band photometric surveys without spectroscopic data. The method evaluates the likelihood of a trial luminosity function by directly comparing the predicted distribution of fluxes in a multi-dimensional photometric space to the observations, and thus does not require the intermediate step of calculating photometric redshifts. We apply this algorithm to ~27,000 galaxies with m_R<=25 in the MUSYC-ECDFS field, with a focus on recovering the luminosity function of field galaxies at z<1.2. Our deepest LFs reach M_r=-14 and show that the field galaxy LF deviates from a Schechter function, exhibiting a steep upturn at intermediate magnitudes that is due to galaxies of late spectral types.
All-sky, narrowband, gravitational-wave radiometry with folded data
Eric Thrane,Sanjit Mitra,Nelson Christensen,Vuk Mandic,Anirban Ain
Physics , 2015, DOI: 10.1103/PhysRevD.91.124012
Abstract: Gravitational-wave radiometry is a powerful tool by which weak signals with unknown signal morphologies are recovered through a process of cross correlation. Radiometry has been used, e.g., to search for persistent signals from known neutron stars such as Scorpius X-1. In this paper, we demonstrate how a more ambitious search--for persistent signals from unknown neutron stars--can be efficiently carried out using folded data, in which an entire ~year-long observing run is represented as a single sidereal day. The all-sky, narrowband radiometer search described here will provide a computationally tractable means to uncover gravitational-wave signals from unknown, nearby neutron stars in binary systems, which can have modulation depths of ~0.1-2 Hz. It will simultaneously provide a sensitive search algorithm for other persistent, narrowband signals from unexpected sources.
The Evolution of Early-type Galaxies Selected by Their Spatial Clustering
Nelson Padilla,Daniel Christlein,Eric Gawiser,Danilo Marchesini
Physics , 2011, DOI: 10.1051/0004-6361/201116926
Abstract: Aims: We present a new method that uses luminosity or stellar mass functions combined with clustering measurements to select samples of galaxies at different redshifts likely to follow a progenitor-to-descendant relationship. As the method uses clustering information, we refer to galaxy samples selected this way as clustering-selected samples. We apply this method to infer the number of mergers during the evolution of MUSYC early-type galaxies (ETGs) from z~1 to the present-day. Methods: The method consists in using clustering information to infer the typical dark-matter halo mass of the hosts of the selected progenitor galaxies. Using LambdaCDM predictions, it is then possible to follow these haloes to a later time where the sample of descendants will be that with the clustering of these descendant haloes. Results: This technique shows that ETGs at a given redshift evolve into brighter galaxies at lower redshifts (considering rest-frame, passively evolved optical luminosities). This indicates that the stellar mass of these galaxies increases with time and that, in principle, a stellar mass selection at different redshifts does not provide samples of galaxies in a progenitor-descendant relationship. Conclusions: The comparison between high redshift ETGs and their likely descendants at z=0 points to a higher number density for the progenitors by a factor 5.5+-4.0, implying the need for mergers to decrease their number density by today. Because the luminosity densities of progenitors and descendants are consistent, our results show no need for significant star-formation in ETGs since z=1, which indicates that the needed mergers are dry, i.e. gas free.
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