59 research outputs found
Critical Spectral Statistics at the Metal-Insulator Transition in Interacting Fermionic Systems
The spectral properties of a disordered system with few interacting
three-dimensional spinless fermions are investigated. We show the existence of
a critical spacings distribution which is invariant upon increase of the system
size, but strongly depends on the number of particles. At the critical point,
we report a substantial decrease of the degree of level repulsion as the number
of particles increases indicating a decrease of nearest level correlations
associated with the sparsity of the Hamiltonian matrix.Comment: Revtex, 4 pages, 3 encapsulated postscript figures appended Final
version as accepted for publication in PR
Constraining the properties of delta Scuti stars using spectroscopic eclipsing binary systems
Many stars exhibit stellar pulsations, favoring them for asteroseismic
analyses. Interpreting the oscillations requires some knowledge of the
oscillation mode geometry (spherical degree, radial and azimuthal orders). The
delta Scuti stars (1.5 - 2.5 M_sol) often show just one or few pulsation
frequencies. Although this may promise a successful seismological analysis, we
may not know enough about either the mode or the star to use the oscillation
frequency to improve the determination of the stellar model, or probe the
star's structure. For the observed frequencies to be used successfully as
seismic probes of these objects, we need to concentrate on stars for which we
can reduce the number of free parameters in the problem, such as binary systems
or open clusters. We investigate how much our understanding of a delta Scuti
star is improved when it is in a detached eclipsing binary system instead of
being a single field star. We use singular value decomposition to explore the
precision we expect in stellar parameters (mass, age and chemical composition)
for both cases. We examine how the parameter uncertainties propagate to the
luminosity - effective temperature diagram and determine when the effort of
obtaining a new measurement is justified. We show that for the single star, a
correct identification of the oscillation mode is necessary to produce strong
constraints on the stellar model properties, while for the binary system the
observations without the pulsation mode provide the same or better constraints
on the stellar parameters. In the latter case, ...Comment: emulateapj 16 pages, accepted Ap
Magnetic Field Effect for Two Electrons in a Two Dimensional Random Potential
We study the problem of two particles with Coulomb repulsion in a
two-dimensional disordered potential in the presence of a magnetic field. For
the regime, when without interaction all states are well localized, it is shown
that above a critical excitation energy electron pairs become delocalized by
interaction. The transition between the localized and delocalized regimes goes
in the same way as the metal-insulator transition at the mobility edge in the
three dimensional Anderson model with broken time reversal symmetry.Comment: revtex, 7 pages, 6 figure
Do interactions increase or reduce the conductance of disordered electrons? It depends!
We investigate the influence of electron-electron interactions on the
conductance of two-dimensional disordered spinless electrons. By using an
efficient numerical method which is based on exact diagonalization in a
truncated basis of Hartree-Fock states we are able to determine the exact
low-energy properties of comparatively large systems in the diffusive as well
as in the localized regimes. We find that weak interactions increase the d.c.
conductance in the localized regime while they decrease the d.c. conductance in
the diffusive regime. Strong interactions always decrease the conductance. We
also study the localization of single-particle excitations close to the Fermi
energy which turns out to be only weakly influenced by the interactions.Comment: final version as publsihed, 4 pages REVTEX, 6 EPS figures include
Non-ergodic effects in the Coulomb glass: specific heat
We present a numerical method for the investigation of non-ergodic effects in
the Coulomb glass. For that, an almost complete set of low-energy many-particle
states is obtained by a new algorithm. The dynamics of the sample is mapped to
the graph formed by the relevant transitions between these states, that means
by transitions with rates larger than the inverse of the duration of the
measurement. The formation of isolated clusters in the graph indicates
non-ergodicity. We analyze the connectivity of this graph in dependence on
temperature, duration of measurement, degree of disorder, and dimensionality,
studying how non-ergodicity is reflected in the specific heat.Comment: Submited Phys. Rev.
Assessment of Elder Mistreatment in Two American Indian Samples: Psychometric Characteristics of the HS-EAST and the Native Elder Life–Financial Exploitation and –Neglect Measures
Although elder mistreatment among ethnic minorities is increasingly gaining attention, our empirical knowledge of this phenomenon among American Indians remains quite limited, especially with respect to measurement. The Shielding American Indian Elders (SAIE) Project used a collaborative approach to explore culturally informed measurement of elder mistreatment in two American Indian elder samples (a Northern Plains reservation and a South Central metropolitan area). The project sought to investigate the performance characteristics of the commonly used Hwalek-Sengstock Elder Abuse Screening Test (HS-EAST), as well as to examine the psychometric properties of a new measure developed to capture culturally salient aspects of mistreatment in American Indian contexts—the Native Elder Life Scale (NELS). Using methods and samples comparable to those in the literature, the HS-EAST performed adequately in these Native samples. The NELS also shows promise for use with this population and assesses different aspects of elder mistreatment than does the HS-EAST.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Insulin-like growth factor (IGF)-I obliterates the pregnancy-associated protection against mammary carcinogenesis in rats: evidence that IGF-I enhances cancer progression through estrogen receptor-α activation via the mitogen-activated protein kinase pathway
INTRODUCTION: Pregnancy protects against breast cancer development in humans and rats. Parous rats have persistently reduced circulating levels of growth hormone, which may affect the activity of the growth hormone/insulin-like growth factor (IGF)-I axis. We investigated the effects of IGF-I on parity-associated protection against mammary cancer. METHODS: Three groups of rats were evaluated in the present study: IGF-I-treated parous rats; parous rats that did not receive IGF-I treatment; and age-matched virgin animals, which also did not receive IGF-I treatment. Approximately 60 days after N-methyl-N-nitrosourea injection, IGF-I treatment was discontinued and all of the animal groups were implanted with a silastic capsule containing 17β-estradiol and progesterone. The 17β-estradiol plus progesterone treatment continued for 135 days, after which the animals were killed. RESULTS: IGF-I treatment of parous rats increased mammary tumor incidence to 83%, as compared with 16% in parous rats treated with 17β-estradiol plus progesterone only. Tumor incidence and average number of tumors per animal did not differ between IGF-I-treated parous rats and age-matched virgin rats. At the time of N-methyl-N-nitrosourea exposure, DNA content was lowest but the α-lactalbumin concentration highest in the mammary glands of untreated parous rats in comparison with age-matched virgin and IGF-I-treated parous rats. The protein levels of estrogen receptor-α in the mammary gland was significantly higher in the age-matched virgin animals than in untreated parous and IGF-I-treated parous rats. Phosphorylation (activation) of the extracellular signal-regulated kinase-1/2 (ERK1/2) and expression of the progesterone receptor were both increased in IGF-I-treated parous rats, as compared with those in untreated parous and age-matched virgin rats. Expressions of cyclin D(1 )and transforming growth factor-β(3 )in the mammary gland were lower in the age-matched virgin rats than in the untreated parous and IGF-I-treated parous rats. CONCLUSION: We argue that tumor initiation (transformation and fixation of mutations) may be similar in parous and age-matched virgin animals, suggesting that the main differences in tumor formation lie in differences in tumor progression caused by the altered hormonal environment associated with parity. Furthermore, we provide evidence supporting the notion that tumor growth promotion seen in IGF-I-treated parous rats is caused by activation of estrogen receptor-α via the Raf/Ras/mitogen-activated protein kinase cascade
Verdadero Retrato del Santo Cristo del Paño, venerado en el Convento de la Merced de Cadiz
La p. [1] Ă©s el grav. xil. orlat del VÂş. R. del StÂş. Christo del Paño. La p. [2] Ă©s una oraciĂł en vers a les tres caigudes de Jesucrist, el primer vers de la qual Ă©s: "Fuiste por Judas vendido"El tĂt. Ă©s el text que acompanya al grav. de la p. [1La p. [1] amb el grav. orladaEl grav. xil. "B. T.". Pot ser Baltasar Talamantes?El text de la oraciĂł de la p. [2] a dues col. separades per band
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Multi-modal simulation for microstructural and property prediction for Al alloy hot rolling
This study presents the application of FE modelling and intelligent systems techniques to the prediction of microstructural mapping for aluminium alloys. Here, the material within each finite element is defined using a set of non-linear physically-based equations. These are then solved in real-time using a semi-physical grey-box model. This model is based on a neuro-fuzzy approach and it has been embedded within the FE technique. The model maps the evolution of the internal state variables (i.e. dislocation density, subgrain size and subgrain boundary misorientation) and their effect on the recrystallisation behaviour of the stock. This paper presents the model development, the integration between the numerical techniques, and the application of the technique to a hot rolling operation using an Aluminium, 1wt% Magnesium alloy. In addition, the developed model includes a CA (Cellular Automata) level to represent inhomogeneous nature of microstructural beheviour
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