868 research outputs found
Structure of wavefunctions in (1+2)-body random matrix ensembles
Abstrtact: Random matrix ensembles defined by a mean-field one-body plus a
chaos generating random two-body interaction (called embedded ensembles of
(1+2)-body interactions) predict for wavefunctions, in the chaotic domain, an
essentially one parameter Gaussian forms for the energy dependence of the
number of principal components NPC and the localization length {\boldmath
l}_H (defined by information entropy), which are two important measures of
chaos in finite interacting many particle systems. Numerical embedded ensemble
calculations and nuclear shell model results, for NPC and {\boldmath l}_H,
are compared with the theory. These analysis clearly point out that for
realistic finite interacting many particle systems, in the chaotic domain,
wavefunction structure is given by (1+2)-body embedded random matrix ensembles.Comment: 20 pages, 3 figures (1a-c, 2a-b, 3a-c), prepared for the invited talk
given in the international conference on `Perspectives in Theoretical
Physics', held at Physical Research Laboratory, Ahmedabad during January
8-12, 200
Spin-dependent thermoelectric transport coefficients in near-perfect quantum wires
Thermoelectric transport coefficients are determined for semiconductor
quantum wires with weak thickness fluctuations. Such systems exhibit anomalies
in conductance near 1/4 and 3/4 of 2e^2/h on the rising edge to the first
conductance plateau, explained by singlet and triplet resonances of conducting
electrons with a single weakly bound electron in the wire [T. Rejec, A. Ramsak,
and J.H. Jefferson, Phys. Rev. B 62, 12985 (2000)]. We extend this work to
study the Seebeck thermopower coefficient and linear thermal conductance within
the framework of the Landauer-Buettiker formalism, which also exhibit anomalous
structures. These features are generic and robust, surviving to temperatures of
a few degrees. It is shown quantitatively how at elevated temperatures thermal
conductance progressively deviates from the Wiedemann-Franz law.Comment: To appear in Phys. Rev. B 2002; 3 figure
Genetic and phenotypic characterization of indolent T-cell lymphoproliferative disorders of the gastrointestinal tract.
Indolent T-cell lymphoproliferative disorders of the gastrointestinal tract are rare clonal T-cell diseases that more commonly occur in the intestines and have a protracted clinical course. Different immunophenotypic subsets have been described, but the molecular pathogenesis and cell of origin of these lymphocytic proliferations is poorly understood. Hence, we performed targeted next-generation sequencing and comprehensive immunophenotypic analysis of ten indolent T-cell lymphoproliferative disorders of the gastrointestinal tract, which comprised CD4 <sup>+</sup> (n=4), CD8 <sup>+</sup> (n=4), CD4 <sup>+</sup> /CD8 <sup>+</sup> (n=1) and CD4 <sup>-</sup> /CD8 <sup>-</sup> (n=1) cases. Genetic alterations, including recurrent mutations and novel rearrangements, were identified in 8/10 (80%) of these lymphoproliferative disorders. The CD4 <sup>+</sup> , CD4 <sup>+</sup> /CD8 <sup>+</sup> , and CD4 <sup>-</sup> /CD8 <sup>-</sup> cases harbored frequent alterations of JAK-STAT pathway genes (5/6, 82%); STAT3 mutations (n=3), SOCS1 deletion (n=1) and STAT3-JAK2 rearrangement (n=1), and 4/6 (67%) had concomitant mutations in epigenetic modifier genes (TET2, DNMT3A, KMT2D). Conversely, 2/4 (50%) of the CD8 <sup>+</sup> cases exhibited structural alterations involving the 3' untranslated region of the IL2 gene. Longitudinal genetic analysis revealed stable mutational profiles in 4/5 (80%) cases and acquisition of mutations in one case was a harbinger of disease transformation. The CD4 <sup>+</sup> and CD4 <sup>+</sup> /CD8 <sup>+</sup> lymphoproliferative disorders displayed heterogeneous Th1 (T-bet <sup>+</sup> ), Th2 (GATA3 <sup>+</sup> ) or hybrid Th1/Th2 (T-bet <sup>+</sup> /GATA3 <sup>+</sup> ) profiles, while the majority of CD8 <sup>+</sup> disorders and the CD4 <sup>-</sup> /CD8 <sup>-</sup> disease showed a type-2 polarized (GATA3 <sup>+</sup> ) effector T-cell (Tc2) phenotype. Additionally, CD103 expression was noted in 2/4 CD8 <sup>+</sup> cases. Our findings provide insights into the pathogenetic bases of indolent T-cell lymphoproliferative disorders of the gastrointestinal tract and confirm the heterogeneous nature of these diseases. Detection of shared and distinct genetic alterations of the JAK-STAT pathway in certain immunophenotypic subsets warrants further mechanistic studies to determine whether therapeutic targeting of this signaling cascade is efficacious for a proportion of patients with these recalcitrant diseases
Conductance anomalies and the extended Anderson model for nearly perfect quantum wires
Anomalies near the conductance threshold of nearly perfect semiconductor
quantum wires are explained in terms of singlet and triplet resonances of
conduction electrons with a single weakly-bound electron in the wire. This is
shown to be a universal effect for a wide range of situations in which the
effective single-electron confinement is weak. The robustness of this generic
behavior is investigated numerically for a wide range of shapes and sizes of
cylindrical wires with a bulge. The dependence on gate voltage, source-drain
voltage and magnetic field is discussed within the framework of an extended
Hubbard model. This model is mapped onto an extended Anderson model, which in
the limit of low temperatures is expected to lead to Kondo resonance physics
and pronounced many-body effects
Dynamic nuclear polarization and spin-diffusion in non-conducting solids
There has been much renewed interest in dynamic nuclear polarization (DNP),
particularly in the context of solid state biomolecular NMR and more recently
dissolution DNP techniques for liquids. This paper reviews the role of spin
diffusion in polarizing nuclear spins and discusses the role of the spin
diffusion barrier, before going on to discuss some recent results.Comment: submitted to Applied Magnetic Resonance. The article should appear in
a special issue that is being published in connection with the DNP Symposium
help in Nottingham in August 200
A Solvable Regime of Disorder and Interactions in Ballistic Nanostructures, Part I: Consequences for Coulomb Blockade
We provide a framework for analyzing the problem of interacting electrons in
a ballistic quantum dot with chaotic boundary conditions within an energy
(the Thouless energy) of the Fermi energy. Within this window we show that the
interactions can be characterized by Landau Fermi liquid parameters. When ,
the dimensionless conductance of the dot, is large, we find that the disordered
interacting problem can be solved in a saddle-point approximation which becomes
exact as (as in a large-N theory). The infinite theory shows a
transition to a strong-coupling phase characterized by the same order parameter
as in the Pomeranchuk transition in clean systems (a spontaneous
interaction-induced Fermi surface distortion), but smeared and pinned by
disorder. At finite , the two phases and critical point evolve into three
regimes in the plane -- weak- and strong-coupling regimes separated
by crossover lines from a quantum-critical regime controlled by the quantum
critical point. In the strong-coupling and quantum-critical regions, the
quasiparticle acquires a width of the same order as the level spacing
within a few 's of the Fermi energy due to coupling to collective
excitations. In the strong coupling regime if is odd, the dot will (if
isolated) cross over from the orthogonal to unitary ensemble for an
exponentially small external flux, or will (if strongly coupled to leads) break
time-reversal symmetry spontaneously.Comment: 33 pages, 14 figures. Very minor changes. We have clarified that we
are treating charge-channel instabilities in spinful systems, leaving
spin-channel instabilities for future work. No substantive results are
change
Enhancing Next-Generation Sequencing-Guided Cancer Care Through Cognitive Computing
Background: Using next-generation sequencing (NGS) to guide cancer therapy has created challenges in analyzing and reporting large volumes of genomic data to patients and caregivers. Specifically, providing current, accurate information on newly approved therapies and open clinical trials requires considerable manual curation performed mainly by human âmolecular tumor boardsâ (MTBs). The purpose of this study was to determine the utility of cognitive computing as performed by Watson for Genomics (WfG) compared with a human MTB. Materials and Methods: One thousand eighteen patient cases that previously underwent targeted exon sequencing at the University of North Carolina (UNC) and subsequent analysis by the UNCseq informatics pipeline and the UNC MTB between November 7, 2011, and May 12, 2015, were analyzed with WfG, a cognitive computing technology for genomic analysis. Results: Using a WfG-curated actionable gene list, we identified additional genomic events of potential significance (not discovered by traditional MTB curation) in 323 (32%) patients. The majority of these additional genomic events were considered actionable based upon their ability to qualify patients for biomarker-selected clinical trials. Indeed, the opening of a relevant clinical trial within 1 month prior to WfG analysis provided the rationale for identification of a new actionable event in nearly a quarter of the 323 patients. This automated analysis took <3 minutes per case. Conclusion: These results demonstrate that the interpretation and actionability of somatic NGS results are evolving too rapidly to rely solely on human curation. Molecular tumor boards empowered by cognitive computing could potentially improve patient care by providing a rapid, comprehensive approach for data analysis and consideration of up-to-date availability of clinical trials. Implications for Practice: The results of this study demonstrate that the interpretation and actionability of somatic next-generation sequencing results are evolving too rapidly to rely solely on human curation. Molecular tumor boards empowered by cognitive computing can significantly improve patient care by providing a fast, cost-effective, and comprehensive approach for data analysis in the delivery of precision medicine. Patients and physicians who are considering enrollment in clinical trials may benefit from the support of such tools applied to genomic data
The beam energy measurement system for the Beijing electron-positron collider
The beam energy measurement system (BEMS) for the upgraded Beijing
electron-positron collider BEPC-II is described. The system is based on
measuring the energies of Compton back-scattered photons. The relative
systematic uncertainty of the electron and positron beam energy determination
is estimated as 2 \cdot 10^{-5}. The relative uncertainty of the beam's energy
spread is about 6 %
Measurement of the branching fraction
The branching fraction is measured in a data sample
corresponding to 0.41 of integrated luminosity collected with the LHCb
detector at the LHC. This channel is sensitive to the penguin contributions
affecting the sin2 measurement from The
time-integrated branching fraction is measured to be . This is the most precise measurement to
date
Measurement of the CP-violating phase \phi s in Bs->J/\psi\pi+\pi- decays
Measurement of the mixing-induced CP-violating phase phi_s in Bs decays is of
prime importance in probing new physics. Here 7421 +/- 105 signal events from
the dominantly CP-odd final state J/\psi pi+ pi- are selected in 1/fb of pp
collision data collected at sqrt{s} = 7 TeV with the LHCb detector. A
time-dependent fit to the data yields a value of
phi_s=-0.019^{+0.173+0.004}_{-0.174-0.003} rad, consistent with the Standard
Model expectation. No evidence of direct CP violation is found.Comment: 15 pages, 10 figures; minor revisions on May 23, 201
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