Helium- and Lithium-like ionic sequences: Critical charges

In non-relativistic quantum mechanics we study the Coulomb systems of infinitely massive center of charge Z and two-three electrons: $(Z,e,e)$ and $(Z,e,e,e)$. It is shown that in both cases the total energy curve in $Z$ is smooth, without any visible irregularities. Thus, for both systems the physical integer charges $Z=1,2,...$ do not play a distinguished role as would be associated with charge quantization. By definition, a critical charge $Z_{cr}$ is a charge which separates a domain of the existence of bound states from a domain of unbound ones (continuum). For both systems the critical charges are found, $Z_{cr,2e}=0.91085$ and $Z_{cr,3e}=2.009$, respectively. Based on numerical analysis, the Puiseux expansion in fractional powers of $(Z-Z_{cr})$ is constructed for both systems. Our results indicate the existence of a square-root branch point singularity at $Z_{cr}$ with exponent 3/2. A connection between the critical charge and the radius of convergence of 1/Z-expansion is briefly discussed.Comment: 10 pages, LaTeX, typos corrected, Fig.1 added, a Note Added with calculated critical charge for $2^1S$ state for $(Z,e,e)$ system, $Z_{cr,2e}^{(2^1S)}\ =\ 1.02

Bifurcation analysis of a normal form for excitable media: Are stable dynamical alternans on a ring possible?

We present a bifurcation analysis of a normal form for travelling waves in one-dimensional excitable media. The normal form which has been recently proposed on phenomenological grounds is given in form of a differential delay equation. The normal form exhibits a symmetry preserving Hopf bifurcation which may coalesce with a saddle-node in a Bogdanov-Takens point, and a symmetry breaking spatially inhomogeneous pitchfork bifurcation. We study here the Hopf bifurcation for the propagation of a single pulse in a ring by means of a center manifold reduction, and for a wave train by means of a multiscale analysis leading to a real Ginzburg-Landau equation as the corresponding amplitude equation. Both, the center manifold reduction and the multiscale analysis show that the Hopf bifurcation is always subcritical independent of the parameters. This may have links to cardiac alternans which have so far been believed to be stable oscillations emanating from a supercritical bifurcation. We discuss the implications for cardiac alternans and revisit the instability in some excitable media where the oscillations had been believed to be stable. In particular, we show that our condition for the onset of the Hopf bifurcation coincides with the well known restitution condition for cardiac alternans.Comment: to be published in Chao

Geological Characterization and Reserve Growth Potential of Spraberry Reservoirs in the Midland Basin, West Texas

Major reservoirs in the Spraberry-Dean play of the Midland Basin, West Texas, initially contained approximately 10.6 billion barrels of oil at discovery. However, current projections indicate that only around 7 percent of this vast resource will be recovered. Despite the significant remaining reserves, a large amount of mobile oil remains trapped in place due to reservoir heterogeneities at abandonment. Consequently, these reservoirs present excellent opportunities for reserve growth through extended conventional recovery methods. Given the substantial volume of movable, nonresidual oil estimated to be present (more than 4 billion barrels), the Spraberry reservoirs were selected for detailed reinvestigation aimed at extended conventional recovery through strategic infield exploration. It was recognized that these reservoirs exhibit significant heterogeneity. Therefore, the primary objective of the project was to determine how an understanding of the genetic stratigraphy of these reservoirs could be leveraged to maximize recovery. Traditionally, Spraberry reservoirs have been perceived as homogeneous "layer cake" oil pools, with development strategies focusing on natural fractures while overlooking the depositional sedimentary architecture of the productive sandstones and siltstones. This reinvestigation seeks to rectify this oversight and explore new approaches to optimize recovery from these complex reservoirs.Bureau of Economic Geolog

Evaluation of Two "in vitro" Digestibility Tests with the "in vivo" Test of Alfalfa (Medicago sativa) in Guinea Pig (Cavia porcellus) Feeding

The purpose of the present study was to compare two types of "in vitro" digestibility assays by using commercial enzymes and guinea pig cecalliquor with the in vivo assay, to identify the assay that most resembles the in vivo response. The alfalfa was used in two cutting times of 30 and 45 days. The "in vivo" digestibility of alfalfa was analyzed, obtaining that after 30 days of cutting the digestibility was 53.64% and at 45 days it was 47.72%, while for the digestibility "in vitro", the DaisyII®-Ankom Technology with cecal liquor and commercial pepsin; for the cecal liquor a value of 55.46% and 49.90% was obtained, for the alfalfa in the two cutting times, while the digestibility with enzymes was 71.01% and 66.34% respectively. It was determined that the method with more relation to the in vivo test corresponds to the trial with cecal liquor, because it presents a lower statistical difference (p <0.05) for both cut-off times. At the same time, it is identified that the protein is the nutrient that has a higher digestibility coefficient, becoming an indicator of the nutritional quality of the food

Diseño, síntesis y evaluación citotóxica de un inhibidor selectivo de la recaptación de serotonina (ISRS) mediante cribado virtual

La depresión es una de las enfermedades mentales más comunes y afecta a casi 300 millones de personas. Según la OMS, la depresión es una de las principales causas de discapacidad y morbilidad en el mundo. Las personas que padecen esta enfermedad requieren tratamiento tanto psicológico como farmacológico, ya que los episodios depresivos graves suelen desembocar en suicidio. Los inhibidores selectivos de la recaptación de serotonina (ISRS) son antidepresivos muy utilizados que actúan sobre el transportador humano de serotonina (hSERT). La cristalización del hSERT y los datos experimentales disponibles permiten utilizar herramientas computacionales de coste y tiempo eficientes, como el cribado virtual (VS), en el desarrollo de agentes terapéuticos. En este trabajo sintetizamos, caracterizamos y evaluamos la actividad biológica de un nuevo análogo ISRS de la paroxetina, diseñado racionalmente mediante la aplicación de un modelo QSAR basado en redes neuronales artificiales y un análisis de acoplamiento molecular sobre hSERT. El análogo N-sustituido 18a mostró mayor afinidad por el transportador (-10,2 kcal/mol), menor valor Ki (1,19 nM) y un perfil toxicológico más seguro que la paroxetina y se sintetizó con un rendimiento del 71%. La citotoxicidad in vitro del análogo se evaluó utilizando líneas celulares de glioblastoma humano (U87 MG), neuroblastoma humano (SH SY5Y) y fibroblastos murinos (L929). También se evaluó la capacidad hemolítica del compuesto en eritrocitos humanos. Los resultados mostraron que el análogo 18a no mostró actividad citotóxica en las líneas celulares utilizadas y no tiene actividad hemolítica en ninguna de las concentraciones ensayadas, mientras que con paroxetina se observó hemólisis a 2,3, 1,29 y 0,67 mM. En base a estos resultados, es posible sugerir que el análogo 18a podría ser un nuevo y prometedor candidato a ISRS para el tratamiento de esta enfermedad.Depression is one of the most common mental illnesses, affecting almost 300 million people. According to the WHO, depression is one of the world's leading causes of disability and morbidity. People with this illness require both psychological and pharmaceutical treatment because severe depressive episodes often result in suicide. Selective serotonin reuptake inhibitors (SSRI) are widely used antidepressants that target the human serotonin transporter (hSERT). The crystallization of hSERT and the experimental data available allows cost and time-efficient computational tools like virtual screening (VS) to be utilized in the development of therapeutic agents. Here, we synthesized, characterized, and evaluated the biological activity of a novel SSRI analog of paroxetine, rationally designed by applying an artificial neural network-based QSAR model and a molecular docking analysis on hSERT. The analog N-substituted 18a showed higher affinity for the transporter (-10.2 kcal/mol), lower Ki value (1.19 nM) and a safer toxicological profile than paroxetine and was synthesized with a 71% yield. The in vitro cytotoxicity of the analog was evaluated using human glioblastoma (U87 MG), human neuroblastoma (SH SY5Y) and murine fibroblast (L929) cell lines. Also, the hemolytic ability of the compound was assessed on human erythrocytes. Results showed that analog 18a did not exhibit cytotoxic activity on the cell lines used and has no hemolytic activity at any of the concentrations tested, whereas with paroxetine, hemolysis was observed at 2.3, 1.29 y 0.67 mM. Based on these results, it is possible to suggest that analog 18a could be a promising new SSRI candidate for the treatment of this illness

Kondo Regime of a Quantum Dot Molecule: A Finite-U Slave-Boson Approach

We study the electronic transport in a double quantum dot structure connected to leads in the Kondo regime for both series and parallel arrangements. By applying a finite-U slave boson technique in the mean field approximation we explore the effect of level degeneracy in the conductance through the system. Our results show that for the series connection, as the energy difference of the localized dot levels increases, the tunneling via the Kondo state is destroyed. For the parallel configuration, we find an interesting interplay of state symmetry and conductance. Our results are in good agrement with those obtained with other methods, and provide additional insights into the physics of the Kondo state in the double dot system.Comment: 4 pages, 5 figures, to appear in Physica