Maxwell's theory on a post-Riemannian spacetime and the equivalence principle

The form of Maxwell's theory is well known in the framework of general relativity, a fact that is related to the applicability of the principle of equivalence to electromagnetic phenomena. We pose the question whether this form changes if torsion and/or nonmetricity fields are allowed for in spacetime. Starting from the conservation laws of electric charge and magnetic flux, we recognize that the Maxwell equations themselves remain the same, but the constitutive law must depend on the metric and, additionally, may depend on quantities related to torsion and/or nonmetricity. We illustrate our results by putting an electric charge on top of a spherically symmetric exact solution of the metric-affine gauge theory of gravity (comprising torsion and nonmetricity). All this is compared to the recent results of Vandyck.Comment: 9 pages, REVTeX, no figures; minor changes, version to be published in Class. Quantum Gra

Symposium: New Trends in Unconventional Approaches to Magnetic Fusion

An extensive review of the meeting is given. The concepts discussed included reverse-field pinches, compact tori, advanced stellarators, multipoles, surface magnetic confinement systems, the bumpy torus, and a collection of mirror-based approaches. (MOW

Fusion research: the past is prologue

At this juncture fusion research can be viewed as being at a turning point, a time to review its past and to imagine its future. Today, almost 50 years since the first serious attempts to address the daunting problem of achieving controlled fusion, we have both an opportunity and a challenge. Some predictions place fusion research today at a point midway between its first inception and its eventual maturation - in the middle of the 21st century - when fusion would become a major source of energy. Our opportunity therefore is to assess what we have learned from 50 years of hard work and use that knowledge as a starting point for new and better approaches to solving the fusion problem. Our challenge is to prove the "50 more years" prophesy wrong, by finding ways to shorten the time when fusion power becomes a reality. The thesis will be advanced that in the magnetic confinement approach to fusion open-ended magnetic confinement geometries offer much in responding to the challenge. A major advantage of open systems is that, owing to their theoretically and experimentally demonstrated ability to suppress plasma instabilities of both the MHD and the high-frequency wave-particle variety, the confinement becomes predictable from "classical," i.e., Fokker-Planck-type analysis. In a time of straitened budgetary circumstances for magnetic fusion research now being faced in the United States, the theoretical tractability of mirror-based systems is a substantial asset. In pursuing this avenue it is also necessary to keep an open mind as to the forms that mirror-based fusion power plants might take. For example, one can look to the high-energy physics community for a possible model: This community has shown the feasibility of constructing large and complex particle accelerators using superconducting magnets, vacuum chambers and complicated particle-handling technology, housed in underground tunnels that are 20 or more kilometers long. In the paper examples of mirror-based fusion power systems resembling long "linear colliders" will be discussed. It is not the intent of this paper to present detailed proposals for next-generation experiments in magnetic fusion research, but rather to encourage a return to the ambiance of an earlier era of fusion research, when innovative thinking and a spirit of scientific adventure prevailed. In that way we can realistically build a new era of fusion research, an era that would be firmly undergirded by the scientific and technological foundation that was laid in fusion's first half-century

Renal health after long-term exposure to tenofovir disoproxil fumarate (TDF) in HIV/HBV positive adults in Ghana

Objectives: The study assessed markers of renal health in HIV/HBV co-infected patients receiving TDF- containing antiretroviral therapy in Ghana. Methods: Urinary protein-to-creatinine ratio (uPCR) and albumin-to-protein ratio (uAPR) were measured cross-sectionally after a median of four years of TDF. At this time, alongside extensive laboratory testing, patients underwent evaluation of liver stiffness and blood pressure. The estimated glomerular filtration rate (eGFR) was measured longitudinally before and during TDF therapy. Results: Among 101 participants (66% women, median age 44 years, median CD4 count 572 cells/mm 3 ) 21% and 17% had detectable HIV-1 RNA and HBV DNA, respectively. Overall 35% showed hypertension, 6% diabetes, 7% liver stiffness indicative of cirrhosis, and 18% urinary excretion of Schistosoma antigen. Tubular proteinuria occurred in 16% of patients and was independently predicted by female gender and hypertension. The eGFR declined by median 1.8 ml/min/year during TDF exposure (IQR −4.4, −0.0); more pronounced declines ( ≥5 ml/min/year) occurred in 22% of patients and were associated with receiv-ing ritonavir-boosted lopinavir rather than efavirenz. HBV DNA, HBeAg, transaminases, and liver stiffness were not predictive of renal function abnormalities. Conclusions: The findings mandate improved diagnosis and management of hypertension and suggest targeted laboratory monitoring of patients receiving TDF alongside a booster in sub-Saharan Africa

Estudio farmacocinético de propofol en equinos

Se estudian las características farmacocinéticas de propofol en 6 caballos. Se determinaron parámetros farmacocinéticos de propofol cuantificando sus concentraciones sanguíneas en función del tiempo por HPLC, tras su administración de 2.4 mg/kg por vía endovenosa al grupo de animales. Los datos de concentración se interpretaron por un modelo abierto de 2 compartimentos, obteniéndose, entre otros, los valores de t1/2a, t1/2b,Vdc, Vdss, Vdb, Cltotaly MRT. Las variables farmacodinámicas se encuentran acordes a la disposición cinética de este fármaco. El análisisde los parámetros farmacocinéticos del propofol indica que éste posee una rápida y pronta distribución a los tejidos y una rápida eliminación del organismo. El propofol se presenta como una alternativa anestésica factible de ser incorporada dentro de un protocolo anestésico en caballos. Los parámetros farmacocinéticos obtenidos contribuyen para una correcta dosificación ya sea para mantener un estado de anestesia por infusión continua o por inyecciones repetidasPharmacokinetic variables of propofol were studied in 6 horses. Blood concentration of propofol at different times, after a single dose of 2.4mg/kg bw, was determined by HPLC. An open two compartment model was used to evaluate blood concentrations of propofol. Values of t1/2a,t1/2b, Vdc, Vdss,Vdb, Cltotal y MRT were obtained.The pharmacodynamic values show a narrow relationship with the pharmacokinetic disposition of this drug. Propofol s pharmacokinetic disposition presented a rapid distribution and removal from organic tissues. It is concluded that propofol is an alternative to be considered in anaesthetic protocolsin horses, and the pharmacokinetic variables presented contribute to determinethe appropriate dose to be give

Farmacocinética de propofol en potrillos de 10 a 15 días de edad

Se estudian las características farmacocinéticas de propofol en 6 potrillos de 10 a 15 días de edad. Se determinaron parámetros farmacocinéticos de propofol, cuantificando sus concentraciones sanguíneas en función del tiempo por HPLC, tras su administración de 2,4 mg/kg por vía endovenosa al grupo de animales. Los datos de concentración se interpretaron por un modelo abierto de 2 compartimentos, obteniéndose, entre otros, los valores de t1/2a, t1/2b, Vdc, Vdss, Vdb, Cltotal y MRT. El análisis de los parámetros farmacocinéticos del propofol, indican que éste posee una rápida y pronta distribución a los tejidos y una rápida eliminación del organismo. Los parámetros farmacocinéticos obtenidos contribuyen a efectuar cálculos para una correcta dosificaciónPharmacokinetic variables of propofol were studied in 8 foals. Plasma levels of propofol at different time after a single intravenous dose of 2.4 mg/kg bw, were determined by HPLC. An open two compartments model was used to evaluate plasma levels of propofol and values of t1/2a, t1/2b, Vdc, Vdss, Vdb, Cltotal y MRT were obtained. Propofol pharmacokinetic disposition showed a rapid distribution and removal from organic tissues, and the reported pharmacokinetic variables contribute to determine the appropriate dose to be give

Determination of electromagnetic medium from the Fresnel surface

We study Maxwell's equations on a 4-manifold where the electromagnetic medium is described by an antisymmetric $2\choose 2$-tensor $\kappa$. In this setting, the Tamm-Rubilar tensor density determines a polynomial surface of fourth order in each cotangent space. This surface is called the Fresnel surface and acts as a generalisation of the light-cone determined by a Lorentz metric; the Fresnel surface parameterises electromagnetic wave-speed as a function of direction. Favaro and Bergamin have recently proven that if $\kappa$ has only a principal part and if the Fresnel surface of $\kappa$ coincides with the light cone for a Lorentz metric $g$, then $\kappa$ is proportional to the Hodge star operator of $g$. That is, under additional assumptions, the Fresnel surface of $\kappa$ determines the conformal class of $\kappa$. The purpose of this paper is twofold. First, we provide a new proof of this result using Gr\"obner bases. Second, we describe a number of cases where the Fresnel surface does not determine the conformal class of the original $2\choose 2$-tensor $\kappa$. For example, if $\kappa$ is invertible we show that $\kappa$ and $\kappa^{-1}$ have the same Fresnel surfaces.Comment: 23 pages, 1 figur

A superintegrable finite oscillator in two dimensions with SU(2) symmetry

A superintegrable finite model of the quantum isotropic oscillator in two dimensions is introduced. It is defined on a uniform lattice of triangular shape. The constants of the motion for the model form an SU(2) symmetry algebra. It is found that the dynamical difference eigenvalue equation can be written in terms of creation and annihilation operators. The wavefunctions of the Hamiltonian are expressed in terms of two known families of bivariate Krawtchouk polynomials; those of Rahman and those of Tratnik. These polynomials form bases for SU(2) irreducible representations. It is further shown that the pair of eigenvalue equations for each of these families are related to each other by an SU(2) automorphism. A finite model of the anisotropic oscillator that has wavefunctions expressed in terms of the same Rahman polynomials is also introduced. In the continuum limit, when the number of grid points goes to infinity, standard two-dimensional harmonic oscillators are obtained. The analysis provides the $N\rightarrow \infty$ limit of the bivariate Krawtchouk polynomials as a product of one-variable Hermite polynomials