5,660 research outputs found
Competing interactions in semiconductor quantum dots
We introduce an integrability-based method enabling the study of
semiconductor quantum dot models incorporating both the full hyperfine
interaction as well as a mean-field treatment of dipole-dipole interactions in
the nuclear spin bath. By performing free induction decay and spin echo
simulations we characterize the combined effect of both types of interactions
on the decoherence of the electron spin, for external fields ranging from low
to high values. We show that for spin echo simulations the hyperfine
interaction is the dominant source of decoherence at short times for low
fields, and competes with the dipole-dipole interactions at longer times. On
the contrary, at high fields the main source of decay is due to the
dipole-dipole interactions. In the latter regime an asymmetry in the echo is
observed. Furthermore, the non-decaying fraction previously observed for zero
field free induction decay simulations in quantum dots with only hyperfine
interactions, is destroyed for longer times by the mean-field treatment of the
dipolar interactions.Comment: 10 pages, 5 figures [v2: subsection and references added
URL-BERT: Training Webpage Representations via Social Media Engagements
Understanding and representing webpages is crucial to online social networks
where users may share and engage with URLs. Common language model (LM) encoders
such as BERT can be used to understand and represent the textual content of
webpages. However, these representations may not model thematic information of
web domains and URLs or accurately capture their appeal to social media users.
In this work, we introduce a new pre-training objective that can be used to
adapt LMs to understand URLs and webpages. Our proposed framework consists of
two steps: (1) scalable graph embeddings to learn shallow representations of
URLs based on user engagement on social media and (2) a contrastive objective
that aligns LM representations with the aforementioned graph-based
representation. We apply our framework to the multilingual version of BERT to
obtain the model URL-BERT. We experimentally demonstrate that our continued
pre-training approach improves webpage understanding on a variety of tasks and
Twitter internal and external benchmarks
Reduced transforming growth factor-beta signaling in cartilage of old mice: role in impaired repair capacity
Osteoarthritis (OA) is a common joint disease, mainly effecting the elderly population. The cause of OA seems to be an imbalance in catabolic and anabolic factors that develops with age. IL-1 is a catabolic factor known to induce cartilage damage, and transforming growth factor (TGF)-beta is an anabolic factor that can counteract many IL-1-induced effects. In old mice, we observed reduced responsiveness to TGF-beta-induced IL-1 counteraction. We investigated whether expression of TGF-beta and its signaling molecules altered with age. To mimic the TGF-beta deprived conditions in aged mice, we assessed the functional consequence of TGF-beta blocking. We isolated knee joints of mice aged 5 months or 2 years, half of which were exposed to IL-1 by intra-articular injection 24 h prior to knee joint isolation. Immunohistochemistry was performed, staining for TGF-beta1, -2 or -3, TGF-betaRI or -RII, Smad2, -3, -4, -6 and -7 and Smad-2P. The percentage of cells staining positive was determined in tibial cartilage. To mimic the lack of TGF-beta signaling in old mice, young mice were injected with IL-1 and after 2 days Ad-LAP (TGF-beta inhibitor) or a control virus were injected. Proteoglycan (PG) synthesis ((35)S-sulfate incorporation) and PG content of the cartilage were determined. Our experiments revealed that TGF-beta2 and -3 expression decreased with age, as did the TGF-beta receptors. Although the number of cells positive for the Smad proteins was not altered, the number of cells expressing Smad2P strongly dropped in old mice. IL-1 did not alter the expression patterns. We mimicked the lack of TGF-beta signaling in old mice by TGF-beta inhibition with LAP. This resulted in a reduced level of PG synthesis and aggravation of PG depletion. The limited response of old mice to TGF-beta induced-IL-1 counteraction is not due to a diminished level of intracellular signaling molecules or an upregulation of intracellular inhibitors, but is likely due to an intrinsic absence of sufficient TGF-beta receptor expression. Blocking TGF-beta distorted the natural repair response after IL-1 injection. In conclusion, TGF-beta appears to play an important role in repair of cartilage and a lack of TGF-beta responsiveness in old mice might be at the root of OA development
A Precise Determination of the Running Coupling in the SU(3) Yang-Mills Theory
A non-perturbative finite-size scaling technique is used to study the
evolution of the running coupling (in a certain adapted scheme) in the SU(3)
Yang-Mills theory. At low energies contact is made with the fundamental
dynamical scales, such as the string tension K, while at larger energies the
coupling is shown to evolve according to perturbation theory. In that regime
the coupling in the MS-bar scheme of dimensional regularization is obtained
with an estimated total error of a few percent.Comment: pages 0-27, ps-file 255491 bytes, preprint DESY 93-114 (CERN-TH
6996/93
Characterizations of quasitrivial symmetric nondecreasing associative operations
We provide a description of the class of n-ary operations on an arbitrary
chain that are quasitrivial, symmetric, nondecreasing, and associative. We also
prove that associativity can be replaced with bisymmetry in the definition of
this class. Finally we investigate the special situation where the chain is
finite
Beyond the MSSM Higgs with d=6 effective operators
We continue a previous study of the MSSM Higgs Lagrangian extended by all
effective operators of dimension d=6 that can be present beyond the MSSM,
consistent with its symmetries. By supersymmetry, such operators also extend
the neutralino and chargino sectors, and the corresponding component fields
Lagrangian is computed onshell. The corrections to the neutralino and chargino
masses, due to these operators, are computed analytically in function of the
MSSM corresponding values. For individual operators, the corrections are small,
of few GeV for the constrained MSSM (CMSSM) viable parameter space. We
investigate the correction to the lightest Higgs mass, which receives, from
individual operators, a supersymmetric correction of up to 4 (6) GeV above the
2-loop leading-log CMSSM value, from those CMSSM phase space points with: EW
fine tuning Delta<200, consistent with WMAP relic density (3), and for
a scale of the operators of M=10 (8) TeV, respectively. Applied to the CMSSM
point of minimal fine tuning (Delta=18), such increase gives an upper limit
GeV, respectively. The increase of m_h from individual
operators can be larger ( 10-30 GeV) for those CMSSM phase space points
with Delta>200; these can now be phenomenologically viable, with reduced Delta,
and this includes those points that would have otherwise violated the LEP2
bound by this value. The neutralino/chargino Lagrangian extended by the
effective operators can be used in studies of dark matter relic density within
extensions of the MSSM, by implementing it in public codes like micrOMEGAs.Comment: 36 pages, Latex, 16 figures (v2: minor changes, corrected typos
A Monte Carlo study of old, new and tadpole improved actions
Scaling of mass ratios in intermediate volumes, obtained with improved SU(2)
lattice actions is tested against analytic results for the Wilson and continuum
action. A new improved action is introduced by adding a 2X2 plaquette to the
Symanzik action. Completing a square leads to a covariant propagator that
simplifies perturbative calculations. Data is presented on lattices of size
4**3X128, with lattice spacings of approximately 0.02 and 0.12 fermi. For the
latter case no further improvement as compared to the tree-level action was
observed when including the Lepage-Mackenzie tadpole correction to the one-loop
improved Luscher-Weisz Symanzik action.Comment: 12 pages, including 2 tables and 2 figures, late
Properties of Classical and Quantum Jensen-Shannon Divergence
Jensen-Shannon divergence (JD) is a symmetrized and smoothed version of the
most important divergence measure of information theory, Kullback divergence.
As opposed to Kullback divergence it determines in a very direct way a metric;
indeed, it is the square of a metric. We consider a family of divergence
measures (JD_alpha for alpha>0), the Jensen divergences of order alpha, which
generalize JD as JD_1=JD. Using a result of Schoenberg, we prove that JD_alpha
is the square of a metric for alpha lies in the interval (0,2], and that the
resulting metric space of probability distributions can be isometrically
embedded in a real Hilbert space. Quantum Jensen-Shannon divergence (QJD) is a
symmetrized and smoothed version of quantum relative entropy and can be
extended to a family of quantum Jensen divergences of order alpha (QJD_alpha).
We strengthen results by Lamberti et al. by proving that for qubits and pure
states, QJD_alpha^1/2 is a metric space which can be isometrically embedded in
a real Hilbert space when alpha lies in the interval (0,2]. In analogy with
Burbea and Rao's generalization of JD, we also define general QJD by
associating a Jensen-type quantity to any weighted family of states.
Appropriate interpretations of quantities introduced are discussed and bounds
are derived in terms of the total variation and trace distance.Comment: 13 pages, LaTeX, expanded contents, added references and corrected
typo
HLA antibody testing: a tool to facilitate not to prevent organ transplantation
The introduction of very sensitive HLA antibody screening assays has destroyed the old dogma that pre-existence of donor specific HLA antibodies in the patient is a contra-indication for transplantation. The challenge is now to reach consensus on the parameters which predict the clinical relevance of donor specific HLA antibodies. Antibody screening assays should not only be used to prevent transplantation of patients with donor specific antibodies but also to facilitate transplantation of highly sensitized patients, both by defining acceptable HLA mismatches and non-detrimental donor specific HLA antibodies
Low lopinavir plasma or hair concentrations explain second-line protease inhibitor failures in a resource-limited setting.
In resource-limited settings, many patients, with no prior protease inhibitor (PI) treatment on a second-line, high genetic barrier, ritonavir-boosted PI-containing regimen have virologic failure
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