Level Repulsion in Constrained Gaussian Random-Matrix Ensembles

Introducing sets of constraints, we define new classes of random-matrix ensembles, the constrained Gaussian unitary (CGUE) and the deformed Gaussian unitary (DGUE) ensembles. The latter interpolate between the GUE and the CGUE. We derive a sufficient condition for GUE-type level repulsion to persist in the presence of constraints. For special classes of constraints, we extend this approach to the orthogonal and to the symplectic ensembles. A generalized Fourier theorem relates the spectral properties of the constraining ensembles with those of the constrained ones. We find that in the DGUEs, level repulsion always prevails at a sufficiently short distance and may be lifted only in the limit of strictly enforced constraints.Comment: 20 pages, no figures. New section adde

Spectral fluctuation properties of constrained unitary ensembles of Gaussian-distributed random matrices

We investigate the spectral fluctuation properties of constrained ensembles of random matrices (defined by the condition that a number N(Q) of matrix elements vanish identically; that condition is imposed in unitarily invariant form) in the limit of large matrix dimension. We show that as long as N(Q) is smaller than a critical value (at which the quadratic level repulsion of the Gaussian unitary ensemble of random matrices may be destroyed) all spectral fluctuation measures have the same form as for the Gaussian unitary ensemble.Comment: 15 page

Pharmacokinetics of orally administered acetaminophen in man

Average and individual sets of plasma concentration-time data for acetaminophen following two oral treatments were simultaneously fitted to the integrated equation describing the two-compartment open model with first-order absorption and lag time. The nonlinear least-squares program NONLIN and an IBM 360/67 digital computer were employed to estimate nine parameters (k A , k B , C A 0 , C B 0 , k 12 , k 21 , k el , and ). When the mean plasma concentrations were weighted according to the inverse of their variances, the parameter estimates more accurately reflected those for individual subjects in the disposition portion of the model. Depending on the relative magnitudes of the disposition rate constants (k 12 , k 21 , and k el ), the one-compartment open model can be used to predict equilibrium-state plasma levels even though the drug is really “two compartment.” Equations are presented which show when the one-compartment approximation is justified. Equations are also presented for calculation of loading doses for multiple dose regimens of any drug obeying the two-compartment open model and the equations are applied to acetaminophen .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45044/1/10928_2005_Article_BF01071309.pd

Cuban scientific production in Medicine and Public Health: Scopus 2003-2011

El objetivo de este trabajo fue analizar la evolución del volumen y la visibilidad de la producción científica cubana en Salud Pública y en Medicina para determinar si siguen los mismos patrones de comunicación, y recomendar buenas prácticas de publicación. Se aplicaron indicadores bibliométricos de volumen, visibilidad y colaboración extraídos del portal SCImago Institutions Rankings a partir de datos de Scopus, para el área temática Medicine y la categoría Public Health, Environmental and Occupational Health, período 2003-2011. Cuba tiene una posición relativamente alta en los rankings de volumen de producción científica tanto en Medicina como en Salud Pública en los contextos internacionales y regionales, mientras que en impacto está entre los últimos países. La tendencia de la producción es al crecimiento, aunque en Salud Pública es más acelerado. El liderazgo es alto, pero la colaboración internacional está por debajo de lo esperado. La publicación en revistas de alto impacto (primer cuartil) y los artículos en el 10% más citado (excelencia) son escasos. Se concluye que el volumen y el impacto de la publicación no están acorde al potencial científico de salud cubana. Se recomienda incrementar la colaboración científica, la publicación de artículos en revistas de alto impacto, la preparación de los recursos humanos y seguir las recomendaciones internacionales sobre las buenas prácticas de edición y publicación científica.The aim of this study was to analyze the evolution of the quantity and visibility of Cuban scientific production in Public Health and Medicine to determine if they follow the same patterns of scientific communication and the recommended best practices for publication. Bibliometric indicators of quantity, visibility and cooperation were extracted from the SCImago Institutions Rankings website, which is based on Scopus data, in the field of Medicine and category of Public Health, Environmental and Occupational Health from 2003 to 2011.Cubahas a relatively high position in the rankings of scientific production in both Medicine and Public Health within the international and regional contexts, but its impact is ranked among the last countries. The production trend of both fields has increased, but public health is increasing faster. Leadership is high, but international collaboration is below expectations. Publication in high impact journals (first quartile) and articles in the set 10% most cited documents (excellence) are scarce. Thus, it may be concluded that the volume and impact of publication are not in accordance with the scientific potential of Cuban health. We recommend increasing scientific cooperation, publishing articles in high impact journals, training human resources and following the international recommendations for good editorial and scientific publication practices

Random matrix ensembles with random interactions: Results for EGUE(2)-SU(4)

We introduce in this paper embedded Gaussian unitary ensemble of random matrices, for $m$ fermions in $\Omega$ number of single particle orbits, generated by random two-body interactions that are SU(4) scalar, called EGUE(2)-SU(4). Here the SU(4) algebra corresponds to Wigner's supermultiplet SU(4) symmetry in nuclei. Formulation based on Wigner-Racah algebra of the embedding algebra $U(4\Omega) \supset U(\Omega) \otimes SU(4)$ allows for analytical treatment of this ensemble and using this analytical formulas are derived for the covariances in energy centroids and spectral variances. It is found that these covariances increase in magnitude as we go from EGUE(2) to EGUE(2)-\cs to EGUE(2)-SU(4) implying that symmetries may be responsible for chaos in finite interacting quantum systems.Comment: 11 pages, 2 figures, some formulas in Table 1 corrected, Table 1 changed to Table 1 and 2, Fig. 2 modifie

Isoniazid hair concentrations in children with tuberculosis: a proof of concept study

Assessing treatment adherence and quantifying tuberculosis drug exposure among children is challenging. We undertook a “proof of concept” study to assess the drug concentrations of isoniazid in hair as a therapeutic drug monitoring tool. Children <12 years of age initiated on thrice-weekly treatment including isoniazid (10 mg/kg) for newly diagnosed tuberculosis were enrolled. Isoniazid concentrations in hair were measured using liquid chromatography-tandem mass spectrometry at 1, 2, 4 and 6 months after tuberculosis treatment initiation. We found that isoniazid hair concentrations in all children on thrice weekly isoniazid were detectable and displayed variability across a dynamic range