200 research outputs found
Slave-Boson Functional-Integral Approach to the Hubbard Model with Orbital Degeneracy
A slave-boson functional-integral method has been developed for the Hubbard
model with arbitrary, orbital degeneracy . Its saddle-point mean-field
theory is equivalent to the Gutzwiller approximation, as in the case of
single-band Hubbard model. Our theory is applied to the doubly degenerate () model, and numerical calculations have been performed for this model in the
paramagnetic states. The effect of the exchange interaction on the
metal-insulator (MI) transition is discussed. The critical interaction for the
MI transition is analytically calculated as functions of orbital degeneracy and
electron occupancy.Comment: Latex 20 pages, 9 figures available on request to
[email protected] Note: published in J. Physical Society of Japan with
some minor modification
Interplay of Mott Transition and Ferromagnetism in the Orbitally Degenerate Hubbard Model
A slave boson representation for the degenerate Hubbard model is introduced.
The location of the metal to insulator transition that occurs at commensurate
densities is shown to depend weakly on the band degeneracy M. The relative
weights of the Hubbard sub-bands depend strongly on M, as well as the magnetic
properties. It is also shown that a sizable Hund's rule coupling is required in
order to have a ferromagnetic instability appearing. The metal to insulator
transition driven by an increase in temperature is a strong function of it.Comment: 5 pages, revtex, 5 postscript figures, submitted to Phys. Rev.
Bisphenol A shapes children’s brain and behavior: towards an integrated neurotoxicity assessment including human data
The authors gratefully acknowledge editorial assistance provided by Richard
Davies. VM is under contract within the Human Biomonitoring for Europe
Project (European Union Commission H2020-EJP-HBM4EU). The authors acknowledge the funding received from the Biomedical Research Networking
Center-CIBER de Epidemiología y Salud Pública (CIBERESP), and the Instituto
de Salud Carlos III (ISCIII) (FIS-PI16/01820 and FIS-PI16/01812). The funders
had no role in the study design, data.Concerns about the effects of bisphenol A (BPA) on human brain and behavior are not novel; however, Grohs and
colleagues have contributed groundbreaking data on this topic in a recent issue of Environmental Health. For the first time,
associations were reported between prenatal BPA exposure and differences in children’s brain microstructure, which
appeared to mediate the association between this exposure and children’s behavioral symptoms. Findings in numerous
previous mother-child cohorts have pointed in a similar worrying direction, linking higher BPA exposure during pregnancy
to more behavioral problems throughout childhood as assessed by neuropsychological questionnaires. Notwithstanding, this
body of work has not been adequately considered in risk assessment. From a toxicological perspective, results are now
available from the CLARITY-BPA consortium, designed to reconcile academic and regulatory toxicology findings. In fact, the
brain has consistently emerged as one of the most sensitive organs disrupted by BPA, even at doses below those
considered safe by regulatory agencies such as the European Food Safety Authority (EFSA). In this Commentary, we
contextualize the results of Grohs et al. within the setting of previous epidemiologic and CLARITY-BPA data and express our
disquiet about the “all-or-nothing” criterion adopted to select human data in a recent EFSA report on the appraisal
methodology for their upcoming BPA risk assessment. We discuss the most relevant human studies, identify emerging
patterns, and highlight the need for adequate assessment and interpretation of the increasing epidemiologic literature in this
field in order to support decision-making. With the aim of avoiding a myopic or biased selection of a few studies in
traditional risk assessment procedures, we propose a future reevaluation of BPA focused on neurotoxicity and based on a
systematic and comprehensive integration of available mechanistic, animal, and human data. Taken together, the
experimental and epidemiologic evidence converge in the same direction: BPA is a probable developmental neurotoxicant
at low doses. Accordingly, the precautionary principle should be followed, progressively implementing stringent preventive
policies worldwide, including the banning of BPA in food contact materials and thermal receipts, with a focus on the
utilization of safer substitutes.European Union (EU): H2020-EJP-HBM4EUBiomedical Research Networking Center-CIBER de Epidemiologia y Salud Publica (CIBERESP)Instituto de Salud Carlos III
FIS-PI16/01820
FIS-PI16/0181
Metal-insulator transition in a doubly orbitally degenerate model with correlated hopping
In the present paper we propose a doubly orbitally degenerate narrow-band
model with correlated hopping. The peculiarity of the model is taking into
account the matrix element of electron-electron interaction which describes
intersite hoppings of electrons. In particular, this leads to the concentration
dependence of the effective hopping integral. The cases of the strong and weak
Hund's coupling are considered. By means of a generalized mean-field
approximation the single-particle Green function and quasiparticle energy
spectrum are calculated. Metal-insulator transition is studied in the model at
different integer values of the electron concentration. With the help of the
obtained energy spectrum we find energy gap width and criteria of
metal-insulator transition.Comment: minor revisions, published in Phys. Rev.
Interferon β-1a in relapsing multiple sclerosis: four-year extension of the European IFNβ-1a Dose-C omparison Study
Background: Multiple sclerosis (MS) is a chronic disease requiring long-term monitoring of treatment. Objective: To assess the four-year clinical efficacy of intramuscular (IM) IFNb-1a in patients with relapsing MS from the European IFNb-1a Dose-C omparison Study. Methods: Patients who completed 36 months of treatment (Part 1) of the European IFNb-1a Dose-C omparison Study were given the option to continue double-blind treatment with IFNb-1a 30 mcg or 60 mcg IM once weekly (Part 2). Analyses of 48-month data were performed on sustained disability progression, relapses, and neutralizing antibody (NA b) formation. Results: O f 608/802 subjects who completed 36 months of treatment, 493 subjects continued treatment and 446 completed 48 months of treatment and follow-up. IFNb-1a 30 mcg and 60 mcg IM once weekly were equally effective for up to 48 months. There were no significant differences between doses over 48 months on any of the clinical endpoints, including rate of disability progression, cumulative percentage of patients who progressed (48 and 43, respectively), and annual relapse rates; relapses tended to decrease over 48 months. The incidence of patients who were positive for NAbs at any time during the study was low in both treatment groups. Conclusion: C ompared with 60-mcg IM IFNb-1a once weekly, a dose of 30 mcg IM IFNb-1a once weekly maintains the same clinical efficacy over four years
GPS constraints on deformation in northern Central America from 1999 to 2017, Part 1 – Time-dependent modelling of large regional earthquakes and their post-seismic effects
We use continuous and campaign measurements from 215 GPS sites in northern Central America and southern Mexico to estimate coseismic and afterslip solutions for the 2009 Mw = 7.3 Swan Islands fault strike-slip earthquake and the 2012 Mw = 7.3 El Salvador and Mw = 7.4 Guatemala thrust-faulting earthquakes on the Middle America trench. Our simultaneous, time-dependent inversion of more than 350 000 daily GPS site positions gives the first jointly consistent estimates of the coseismic slips for all three earthquakes, their combined time-dependent post-seismic effects and secular station velocities corrected for both the coseismic and post-seismic deformation. Our geodetic slip solutions for all three earthquakes agree with previous estimates that were derived via static coseismic-offset modelling. Our time-dependent model, which attributes all transient post-seismic deformation to earthquake afterslip, fits nearly all of the continuous GPS site position time-series within their severalmillimetre position noise. Afterslip moments for the three earthquakes range from 35 to 140 per cent of the geodetic coseismic moments, with the largest afterslip estimated for the 2012 El Salvador earthquake along the weakly coupled El Salvador trench segment. Forward modelling of viscoelastic deformation triggered by all three earthquakes for a range of assumed mantle and lower crustal viscosities suggests that it accounts for under 20 per cent of the observed post-seismic deformation and possibly under 10 per cent
The Corinth Rift Laboratory, Greece (CRL): A Multidisciplinary Near Fault Observatory (NFO) on a Fast Rifting System
The western rift of Corinth (Greece) is one of the most active tectonic structures of the euro-mediterranean area. Its NS opening rate is 1.5 cm/yr ( strain rate of 10-6/yr) results into a high microseismicity level and a few destructive, M>6 earthquakes per century, activating a system of mostly north dipping normal faults. Since 2001, monitoring arrays of the European Corinth Rift Laboratory (CRL, www.crlab.eu) allowed to better track the mechanical processes at work, with short period and broad band seismometers, cGPS, borehole strainmeters, EM stations, …). The recent (300 kyr) tectonic history has been revealed by onland (uplifted fan deltas and terraces) and offshore geological studies (mapping, shallow seismic, coring), showing a fast evolution of the normal fault system. The microseismicity, dominated by swarms lasting from days to months, mostly clusters in a layer 1 to 3 km thick, between 6 and 9 km in depth, dipping towards north, on which most faults are rooting. The diffusion of the microseismicity suggests its triggering by pore pressure transients, with no or barely detected strain. Despite a large proportion of multiplets, true repeaters seem seldom, suggesting a minor contribution of creep in their triggering, although transient or steady creep is clearly detected on the shallow part of some majors faults. The microseismic layer may thus be an immature, downward growing detachment, and the dominant rifting mechanism might be a mode I, anelastic strain beneath the rift axis , for which a mechanical model is under development. Paleoseismological (trenching, paleoshorelines, turbidites), archeological and historical studies completed the catalogues of instrumental seismicity, motivating attempts of time dependent hazard assessment. The Near Fault Observatory of CRL is thus a multidisciplinary research infrastructure aiming at a better understanding and modeling of multiscale, coupled seismic/aseismic processes on fault systems.Grant for Researchers (CC) ID 188753
Equations for the estimation of strong ground motions from shallow crustal earthquakes using data from Europe and the Middle East : vertical peak ground acceleration and spectral acceleration
This article presents equations for the estimation of vertical strong ground motions caused by shallow crustal earthquakes with magnitudes M w 5 and distance to the surface projection of the fault less than 100km. These equations were derived by weighted regression analysis, used to remove observed magnitude-dependent variance, on a set of 595 strong-motion records recorded in Europe and the Middle East. Coefficients are included to model the effect of local site effects and faulting mechanism on the observed ground motions. The equations include coefficients to model the observed magnitude-dependent decay rate. The main findings of this study are that: short-period ground motions from small and moderate magnitude earthquakes decay faster than the commonly assumed 1/r, the average effect of differing faulting mechanisms is similar to that observed for horizontal motions and is not large and corresponds to factors between 0.7 (normal and odd) and 1.4 (thrust) with respect to strike-slip motions and that the average long-period amplification caused by soft soil deposits is about 2.1 over those on rock sites
Plio‐Quaternary exhumation history of the central Nepalese Himalaya: 2. Thermokinematic and thermochronometer age prediction model
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95647/1/tect1875.pd
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