Approximate closed-form formulas for the zeros of the Bessel Polynomials

We find approximate expressions x(k,n) and y(k,n) for the real and imaginary parts of the kth zero z_k=x_k+i y_k of the Bessel polynomial y_n(x). To obtain these closed-form formulas we use the fact that the points of well-defined curves in the complex plane are limit points of the zeros of the normalized Bessel polynomials. Thus, these zeros are first computed numerically through an implementation of the electrostatic interpretation formulas and then, a fit to the real and imaginary parts as functions of k and n is obtained. It is shown that the resulting complex number x(k,n)+i y(k,n) is O(1/n^2)-convergent to z_k for fixed kComment: 9 pages, 2 figure

Chopping Logs: A Look at the History and Uses of Logarithms

Logarithms are an integral part of many forms of technology, and their history and development help to see their importance and relevance. This paper surveys the origins of logarithms and their usefulness both in ancient and modern times

Access to land-based resources under the influence of land reform: a case study from an agrarian community in Mexico

This study provides important empirical and analytical insights that represent a step forward towards a deeper and better understanding of the effects of land reform and land policies on the distribution of access to land-based resources. It explores the extent to which the process of land reform during the early 1990s, and the subsequent implementation of complementary land policies and programmes brought deep modifications to the way in which agrarian communities obtain benefits from resources. The empirical evidence on which this research is based consists of both qualitative and quantitative data elicited by a combination of research methods applied to a case study design. The case study chosen is San Francisco Oxtotilpan, an agrarian community in Mexico‟s central highlands that is home to the smallest indigenous group in the region: the Matlatzinca. The theoretical and analytical framework designed takes into account the main scholarship on access to natural resources. This extended analytical framework of access to land-based resources provides a characterization of access mechanisms that disentangle the complex set of cultural, socio-economic and political processes underlying access to land-based resources. It enables an assessment of the effects of the implementation of land reform-related policies and programmes over the different ways in which members of the agrarian community benefit from land-based resources. The study concludes that the implementation of land policies in Mexico since the early 1990s has brought deep modifications in the local governance of land-based resources. It illustrates that the differential distribution of benefits from land-based resources depends on households‟ ability to use a set of access mechanisms to gain, control or maintain the flux of benefits from land-based resources. Results show that when it comes to land-based resource governance, the implementation of land policies and programmes has produced conflicts between the agrarian community and external politico-legal institutions –especially from the State. Furthermore, it modified the internal structure of the agrarian community, and consequently, the complex set of mechanisms that shape the distribution of access to land-based resources available

Parasitization of Callinectes rathbunae and Callinectes sapidus by the Rhizocephalan Barnacle Loxothylacus texanus in Alvarado Lagoon, Veracruz, Mexico

Callinectes rathbunae and CalIinectes sapidus in Alvarado Lagoon, Mexico, were sampled monthly for one year to determine the extent of parasitization by the rhizocephalan cirripede Loxothylacus texanus. Prevalence levels. host sex ratio, carapace width-weight variation, and distribution of the number of parasites among hosts were analyzed. Loxothylacus texanus was present almost exclusively in C. rathbunae with a mean prevalence of 7.58%, while less than 1% of all C. sapidus were parasitized. Callinectes rathbunae constitutes a new host record for this parasite. A study of infection revealed significant variation in prevalence and host size throughout the study period. The sex ratio of parasitized crabs differed from that of the total sample with mares being parasitized more often, and the comparison of carapace width-weight relationships revealed lower weights of parasitized crabs

Parasitization of Callinectes rathbunae and Callinectes sapidus by the Rhizocephalan Barnacle Loxothylacus texanus in Alvarado Lagoon, Veracruz, Mexico

Callinectes rathbunae and CalIinectes sapidus in Alvarado Lagoon, Mexico, were sampled monthly for one year to determine the extent of parasitization by the rhizocephalan cirripede Loxothylacus texanus. Prevalence levels. host sex ratio, carapace width-weight variation, and distribution of the number of parasites among hosts were analyzed. Loxothylacus texanus was present almost exclusively in C. rathbunae with a mean prevalence of 7.58%, while less than 1% of all C. sapidus were parasitized. Callinectes rathbunae constitutes a new host record for this parasite. A study of infection revealed significant variation in prevalence and host size throughout the study period. The sex ratio of parasitized crabs differed from that of the total sample with mares being parasitized more often, and the comparison of carapace width-weight relationships revealed lower weights of parasitized crabs

Aplicación del modelo de difusión de Bass para estimar el ciclo de vida de una tienda minorista

This article presents a practical application of Lifecycle estimation using the Bass Diffusion Model in the case of a retail store. The results from the application of the model show that the probability that a person will buy driven by advertising is 5%, whereas the probability of buying based on the recommendation of another customer is 23%. According to the sales Lifecycle results, the store’s monthly sales have stabilized and its market share is near its peak.En el presente artículo se presenta una aplicación práctica para la estimación del ciclo de vida de una tienda minorista a través de la implementación del modelo de difusión de Bass. Al aplicar el modelo se obtiene que la probabilidad que una persona compre impulsado por publicidad es del 5%, mientras que la que compre por recomendación de otro cliente es del 23%. Al analizar el ciclo de venta del negocio se observa que este llegó a un nivel estable de ventas mensuales y se encuentra en auge dentro de la cuota de mercado que se tiene hasta el momento

Multibody Dynamics Model of a Human Hand for Haptics Interaction

In this paper we propose a strategy for modelling a human hand for Haptics interaction. The strategy consists in a parallel computing architecture that calculates the dynamics of a hand; this is accomplished by computing the dynamics of each finger in a parallel manner. In this approach multiple threads (e.g. haptics thread, graphics thread, collision detection thread, etc.) run concurrently and therefore we developed a synchronization mechanism for data exchange. We describe in detail the elements of the developed software

RNA microarray analysis in prenatal mouse cochlea reveals novel IGF-I target genes: implication of MEF2 and FOXM1 transcription factors

Background: Insulin-like growth factor-I (IGF-I) provides pivotal cell survival and differentiation signals during inner ear development throughout evolution. Homozygous mutations of human IGF1 cause syndromic sensorineural deafness, decreased intrauterine and postnatal growth rates, and mental retardation. In the mouse, deficits in IGF-I result in profound hearing loss associated with reduced survival, differentiation and maturation of auditory neurons. Nevertheless, little is known about the molecular basis of IGF-I activity in hearing and deafness. Methodology/Principal Findings: A combination of quantitative RT-PCR, subcellular fractionation and Western blotting, along with in situ hybridization studies show IGF-I and its high affinity receptor to be strongly expressed in the embryonic and postnatal mouse cochlea. The expression of both proteins decreases after birth and in the cochlea of E18.5 embryonic Igf1(-/-) null mice, the balance of the main IGF related signalling pathways is altered, with lower activation of Akt and ERK1/2 and stronger activation of p38 kinase. By comparing the Igf1(-/-) and Igf1(+/+) transcriptomes in E18.5 mouse cochleae using RNA microchips and validating their results, we demonstrate the up-regulation of the FoxM1 transcription factor and the misexpression of the neural progenitor transcription factors Six6 and Mash1 associated with the loss of IGF-I. Parallel, in silico promoter analysis of the genes modulated in conjunction with the loss of IGF-I revealed the possible involvement of MEF2 in cochlear development. E18.5 Igf1(+/+) mouse auditory ganglion neurons showed intense MEF2A and MEF2D nuclear staining and MEF2A was also evident in the organ of Corti. At P15, MEF2A and MEF2D expression were shown in neurons and sensory cells. In the absence of IGF-I, nuclear levels of MEF2 were diminished, indicating less transcriptional MEF2 activity. By contrast, there was an increase in the nuclear accumulation of FoxM1 and a corresponding decrease in the nuclear cyclin-dependent kinase inhibitor p27(Kip1). Conclusions/Significance: We have defined the spatiotemporal expression of elements involved in IGF signalling during inner ear development and reveal novel regulatory mechanisms that are modulated by IGF-I in promoting sensory cell and neural survival and differentiation. These data will help us to understand the molecular bases of human sensorineural deafness associated to deficits in IGF-I

Efecto de confinamiento espacial y de núcleo de tamaño finito en sistemas atómicos

Se estudia el comportamiento de distintos sistemas atómicos cuando son sometidos a altas presiones externas: átomos hidrogenoides, de helio y litio. La presión ejercida se modela mediante el confinamiento espacial de los átomos, dentro de un pozo de potencial con simetría esférica, tanto de paredes impenetrables como penetrables. Se estudian diversas propiedades de los sistemas cuánticos confinados. En el átomo de hidrógeno: la polarizabilidad, la presión, el desdoblamiento hiperfino, el apantallamiento magnético y la probabilidad de tunelamiento (en el caso de confinamiento dentro de paredes penetrables). En el átomo de helio: la polarizabilidad y los potenciales de ionización. En el átomo de litio: el efecto producido por el confinamiento sobre el estado base del sistema. Para hallar la energía del estado base de los sistemas descritos anteriormente, se hace uso del método variacional de Rayleigh-Ritz. Para el átomo hidrogenoide confinado, también se resuelve de forma exacta la ecuación de Schrödinger, escribiendo la solución en términos de funciones hipergeométricas confluentes, y se calculan soluciones numéricas con muy alta precisión. Además estudiamos algunas propiedades poco consideradas en la literatura. Por ejemplo, para el átomo de hidrógeno confinado: el espectro de estructura fina para el estado base y algunos estados excitados, y correcciones relativistas. Estudiamos el efecto de considerar un núcleo de volumen finito, en lugar de un núcleo de tamaño puntual (como habitualmente se utiliza), sobre la energía del estado base de sistemas atómicos confinados de uno, dos y tres electrones. También estudiamos átomos exóticos confinados: los llamados átomos muónicos. Se analiza el comportamiento de la entropía informática de Shannon en el espacio de coordenadas en los sistemas cuánticos confinados, y su posible aplicación como medida de la calidad de la función de onda, así como su uso como medida de la localización (o deslocalización) de las partículas dentro de un sistema confinado.We study the behavior of different atomic systems (hydrogen-like atoms, helium and lithium) when they are subjected to high external pressures. The exerted pressure is modeled by spatial confinement of the atoms, inside a spherical potential for both impenetrable and penetrable walls. We study different properties of the confined quantum systems. For a hydrogen atom, polarizability, pressure, hyperfine splitting, magnetic screening and the tunneling probability (for the case of confinement inside penetrable walls) are analyzed, whereas for helium, polarizability and ionization potentials. Also, confinement induced effects are studied for lithium ground state. In order to analyze such effects for the above described systems, we use the Rayleigh-Ritz variational method. For a confined hydrogen-like atom, we solve the Schrödinger equation in an exact manner by writing the solution in terms of confluent hypergeometric functions, and we calculate numerical solutions with a very high accuracy. We also study some properties seldom considered in the literature. For example, for the confined hydrogen atom, the fine structure spectrum for the ground and some excited states, in conjunction with relativistic corrections. In addition, we study effects arising from spatially extending the nuclear region through a finite volume occupied by the nucleus, instead of considering it a point size particle (as it is usually assumed), when analyzing the ground state energy of atomic systems of one, two and three electrons. We also study exotic confined atoms, the so called muonic atoms. We analyze the Shannon information entropy behavior in the coordinate space for quantum confined systems, viewed as an application for measuring the quality of the wave function, as well as its use as a measure of localization and delocalization of particles inside a confined system