1,935 research outputs found
Slower Speed and Stronger Coupling: Adaptive Mechanisms of Self-Organized Chaos Synchronization
We show that two initially weakly coupled chaotic systems can achieve
self-organized synchronization by adaptively reducing their speed and/or
enhancing the coupling strength. Explicit adaptive algorithms for
speed-reduction and coupling-enhancement are provided. We apply these
algorithms to the self-organized synchronization of two coupled Lorenz systems.
It is found that after a long-time self-organized process, the two coupled
chaotic systems can achieve synchronization with almost minimum required
coupling-speed ratio.Comment: 4 pages, 5 figure
NLO-QCD corrections to e+ e- --> hadrons in models of TeV-scale gravity
We present results on NLO-QCD corrections to the process e+ e- --> hadrons
via photon-, Z- and graviton-exchange in the context of TeV-scale gravity
models. The quantitative impact of these QCD corrections for searches of extra
dimensions at a Linear Collider is briefly discussed.Comment: 10 pages, LaTeX, using axodraw.st
Low-Frequency Optical Conductivity in Inhomogeneous d-wave Superconductors
Motivated by the recent optical conductivity experiments on
Bi_2Sr_2CaCu_2O_{8+delta} films, we examine the possible origin of
low-frequency dissipation in the superconducting state. In the presence of
spatial inhomogeneity of the local phase stiffness rho_s, it is shown that some
spectral weight is removed from omega=0 to finite frequencies and contribute to
dissipation. A case where both rho_s and the local normal fluid density are
inhomogeneous is also considered. We find an enhanced dissipation at low
frequency if the two variations are anti-correlated.Comment: To appear in Phys. Rev.
Rat astroglial somatomedin/insulin-like growth factor binding proteins: characterization and evidence of biologic function
Specific binding proteins (BPs) to somatomedin/insulin-like growth factors (Sm/IGFs) have been identified in conditioned media from a variety of cells in culture. By affinity cross-linking using disuccinimidyl suberate, we have covalently cross-linked radiolabeled somatomedin-C/insulin-like growth factor I (Sm-C/IGF I), insulin-like growth factor II (IGF II) and insulin to BPs in conditioned medium (CM) from cultured astroglial cells derived from cerebral cortices of neonatal rats. Two species of radiolabeled Sm/IGF BP complexes of 40,000 Da (40K) and 45K were identified. Competition with unlabeled Sm- C/IGF I and IGF II demonstrated that the BPs in each complex have similar affinities for Sm-C/IGF I and IGF II. The BP in the 45K complex was about 5-fold more sensitive to competition with unlabeled Sm/IGFs than the BP in the 40K complex, suggesting that it either has a higher affinity for Sm/IGFs or is less abundant. Evidence that the BPs in each complex are distinct includes the following findings: (1) insulin competed with Sm/IGF for binding to the 45K complex, but not the 40K complex, and (2) the BP in the 40K complex, but not the 45K complex, was recognized by antibodies raised against a BP purified from CM of buffalo rat liver (BRL) 3A cells. Growth hormone did not affect the apparent secretion of either BP. The binding activity of both BPs was retained after mild heat treatment, changes to extremes of pH (2–10), and prolonged storage at -20 degrees C, but was destroyed after heating to higher temperatures (80 degrees C and greater), reduction, and proteolytic treatment.(ABSTRACT TRUNCATED AT 250 WORDS
Characterization of somatomedin/insulin-like growth factor receptors and correlation with biologic action in cultured neonatal rat astroglial cells
The role of somatomedin/insulin-like growth factors (Sm/IGFs) in neural growth and development is not clearly defined. To characterize Sm/IGF receptors and to correlate binding with the biologic actions of Sm/IGFs in a homogeneous population of neural cells, we isolated and studied a nearly pure population of cultured astroglial monolayers derived from cerebral cortices of neonatal rats. Binding of radiolabeled Sm/IGFs was specific, saturable, and reversible, with 90% of the binding occurring within 6 hr of incubation at 4 degrees C. Competitive binding studies with Sm-C/IGF I yielded curvilinear Scatchard plots, while studies with IGF II and multiplication stimulating activity (MSA) yielded linear plots, suggesting that 125I-Sm-C/IGF I binds to more than 1 receptor species, and 125I-IGF II and 125I-MSA bind to one only. These findings were supported by affinity-labeling studies with radiolabeled Sm/IGFs using disuccinimidyl suberate as a cross-linking agent. Sm-C/IGF I appeared to bind to both type I and II Sm/IGF receptors, because cross- linked 125I-Sm-C/IGF I-receptor complexes with molecular weight (Mr) of greater than 300,000 (300K) and 130K (type I receptor) were observed under nonreducing and reducing conditions, respectively, as were 220 and 260K complexes (type II receptor) under the same respective conditions. 125I-IGF II and 125I-MSA, however, bound only to the Mr 220 and 260K moieties under nonreducing and reducing conditions, respectively, suggesting that these peptides bind only to the type II receptor. Competitive binding studies of the cross-linked moieties were consistent with this interpretation. In contrast, 125I-insulin bound poorly to astroglia (less than 0.5% specific binding), and cross- linking studies could not definitely distinguish among low-affinity binding to the type I Sm/IGF receptor, binding to a paucity of insulin receptors, or both. In addition, by combining autoradiography to localize 125I-Sm/IGFs binding on astroglial cells and immunocytochemistry with anti-glial fibrillary acidic protein to identify the cell type, we have demonstrated cell-surface binding and apparent internalization of radiolabeled Sm/IGFs. Concurrent studies of Sm/IGF stimulation of 3H-thymidine incorporation revealed that these cells were most sensitive to Sm-C/IGF I, followed by IGF II and MSA, and insulin. MSA and IGF II, however, were the most potent followed by Sm-C/IGF I and then insulin. Half-maximal stimulations of 3H-thymidine incorporation corresponded closely with half-maximal binding displacement for Sm-C/IGF I and less so for IGF II and MSA.(ABSTRACT TRUNCATED AT 400 WORDS
Brain ageing in schizophrenia: evidence from 26 international cohorts via the ENIGMA Schizophrenia consortium
Schizophrenia (SZ) is associated with an increased risk of life-long cognitive impairments, age-related chronic disease, and
premature mortality. We investigated evidence for advanced brain ageing in adult SZ patients, and whether this was associated
with clinical characteristics in a prospective meta-analytic study conducted by the ENIGMA Schizophrenia Working Group. The
study included data from 26 cohorts worldwide, with a total of 2803 SZ patients (mean age 34.2 years; range 18–72 years; 67%
male) and 2598 healthy controls (mean age 33.8 years, range 18–73 years, 55% male). Brain-predicted age was individually
estimated using a model trained on independent data based on 68 measures of cortical thickness and surface area, 7 subcortical
volumes, lateral ventricular volumes and total intracranial volume, all derived from T1-weighted brain magnetic resonance imaging
(MRI) scans. Deviations from a healthy brain ageing trajectory were assessed by the difference between brain-predicted age and
chronological age (brain-predicted age difference [brain-PAD]). On average, SZ patients showed a higher brain-PAD of +3.55 years
(95% CI: 2.91, 4.19; I2 = 57.53%) compared to controls, after adjusting for age, sex and site (Cohen’s d = 0.48). Among SZ patients,
brain-PAD was not associated with specific clinical characteristics (age of onset, duration of illness, symptom severity, or
antipsychotic use and dose). This large-scale collaborative study suggests advanced structural brain ageing in SZ. Longitudinal
studies of SZ and a range of mental and somatic health outcomes will help to further evaluate the clinical implications of increased
brain-PAD and its ability to be influenced by interventions
Models for Enhanced Absorption in Inhomogeneous Superconductors
We discuss the low-frequency absorption arising from quenched inhomogeneity
in the superfluid density rho_s of a model superconductor. Such inhomogeneities
may arise in a high-T_c superconductor from a wide variety of sources,
including quenched random disorder and static charge density waves such as
stripes. Using standard classical methods for treating randomly inhomogeneous
media, we show that both mechanisms produce additional absorption at finite
frequencies. For a two-fluid model with weak mean-square fluctuations <(d
rho_s)^2 > in rho_s and a frequency-independent quasiparticle conductivity, the
extra absorption has oscillator strength proportional to the quantity <(d
rho_s)^2>/rho_s, as observed in some experiments. Similar behavior is found in
a two-fluid model with anticorrelated fluctuations in the superfluid and normal
fluid densities. The extra absorption typically occurs as a Lorentzian centered
at zero frequency. We present simple model calculations for this extra
absorption under conditions of both weak and strong fluctuations. The relation
between our results and other model calculations is briefly discussed
Constraining models of the large scale Galactic magnetic field with WMAP5 polarization data and extragalactic Rotation Measure sources
We introduce a method to quantify the quality-of-fit between data and
observables depending on the large scale Galactic magnetic field. We combine
WMAP5 polarized synchrotron data and Rotation Measures of extragalactic sources
in a joint analysis to obtain best fit parameters and confidence levels for GMF
models common in the literature. None of the existing models provide a good fit
in both the disk and halo regions, and in many instances best-fit parameters
are quite different than the original values. We note that probing a very large
parameter space is necessary to avoid false likelihood maxima. The thermal and
relativistic electron densities are critical for determining the GMF from the
observables but they are not well constrained. We show that some
characteristics of the electron densities can already be constrained using our
method and with future data it may be possible to carry out a self-consistent
analysis in which models of the GMF and electron densities are simultaneously
optimized.Comment: 27 pages, 13 figures. Accepted for publication in JCAP; arXiv version
updated to include minor revision
Non-Abelian Dark Sectors and Their Collider Signatures
Motivated by the recent proliferation of observed astrophysical anomalies,
Arkani-Hamed et al. have proposed a model in which dark matter is charged under
a non-abelian "dark" gauge symmetry that is broken at ~ 1 GeV. In this paper,
we present a survey of concrete models realizing such a scenario, followed by a
largely model-independent study of collider phenomenology relevant to the
Tevatron and the LHC. We address some model building issues that are easily
surmounted to accommodate the astrophysics. While SUSY is not necessary, we
argue that it is theoretically well-motivated because the GeV scale is
automatically generated. Specifically, we propose a novel mechanism by which
mixed D-terms in the dark sector induce either SUSY breaking or a super-Higgs
mechanism precisely at a GeV. Furthermore, we elaborate on the original
proposal of Arkani-Hamed et al. in which the dark matter acts as a messenger of
gauge mediation to the dark sector. In our collider analysis we present
cross-sections for dominant production channels and lifetime estimates for
primary decay modes. We find that dark gauge bosons can be produced at the
Tevatron and the LHC, either through a process analogous to prompt photon
production or through a rare Z decay channel. Dark gauge bosons will decay back
to the SM via "lepton jets" which typically contain >2 and as many as 8
leptons, significantly improving their discovery potential. Since SUSY decays
from the MSSM will eventually cascade down to these lepton jets, the discovery
potential for direct electroweak-ino production may also be improved.
Exploiting the unique kinematics, we find that it is possible to reconstruct
the mass of the MSSM LSP. We also present decay channels with displaced
vertices and multiple leptons with partially correlated impact parameters.Comment: 44 pages, 25 figures, version published in JHE
Infant feeding practices in a multi-ethnic Asian cohort: the GUSTO study
The optimal introduction of complementary foods provides infants with nutritionally balanced diets and establishes healthy eating habits. The documentation of infant feeding practices in multi-ethnic Asian populations is limited. In a Singapore cohort study (GUSTO), 842 mother-infant dyads were interviewed regarding their feeding practices when the infants were aged 9 and 12 months. In the first year, 20.5% of infants were given dietary supplements, while 5.7% took probiotics and 15.7% homeopathic preparations. At age 9 months, 45.8% of infants had seasonings added to their foods, increasing to 56.3% at 12 months. At age 12 months, 32.7% of infants were given blended food, although 92.3% had begun some form of self-feeding. Additionally, 87.4% of infants were fed milk via a bottle, while a third of them had food items added into their bottles. At both time points, more than a third of infants were provided sweetened drinks via the bottle. Infants of Indian ethnicity were more likely to be given dietary supplements, have oil and seasonings added to their foods and consumed sweetened drinks from the bottle (p < 0.001). These findings provide a better understanding of variations in infant feeding practices, so that healthcare professionals can offer more targeted and culturally-appropriate advice
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