10,823 research outputs found
Particle collisions near a three-dimensional warped AdS black hole
In this paper we consider the warped AdS black hole solution of
topologically massive gravity with a negative cosmological constant, and we
investigate the possibility that it acts as a particle accelerator by analyzing
the energy in the center of mass (CM) frame of two colliding particles in the
vicinity of its horizon, which is known as the Ba\~nados, Silk and West (BSW)
process. Mainly, we show that the critical angular momentum of the
particle decreases when the parameter that controls the stretching deformation
() increases. Also, we show that despite the particle with can exist
for certain values of the conserved energy outside the horizon, it will never
reach the event horizon; therefore, the black hole can not act as a particle
accelerator with arbitrarily high CM energy on the event horizon. However, such
particle could also exist inside the outer horizon being the BSW process
possible on the inner horizon. On the other hand, for the extremal warped
AdS black hole, the particle with and energy could exist
outside the event horizon and the CM energy blows up on the event horizon if
its conserved energy fulfill the condition
, being the BSW process possible.Comment: 11 pages, 6 figure
Fermionic greybody factors of two and five-dimensional dilatonic black holes
We study fermionic perturbations in the background of a two and
five-dimensional dilatonic black holes. Then, we compute the reflection and
transmission coefficients and the absorption cross section for fermionic
fields, and we show numerically that the absorption cross section vanishes in
the low and high frequency limit. Also we find that beyond a certain value of
the horizon radius the absorption cross section for five-dimensional
dilatonic black hole is constant. Besides, we have find that the absorption
cross section decreases for higher angular momentum, and it decreases when the
mass of the fermionic field increases.Comment: Accepted in EPJ
Metabolic engineering: Use of system-level approaches and application to fuel production in Escherichia coli
Metabolic engineering was formally defined more than two decades ago (Bailey, 1991) and it is now an established discipline. Metabolic engineering is generally defined as the directed improvement of product formation or cellular properties through the modification of specific biochemical reactions or the introduction of new ones with the use of recombinant DNA technology (Bailey, 1991; Stephanopoulos et al. 1998). Therefore, the analysis and engineering/synthesis of metabolic pathways is of central importance to metabolic engineering. The analytical part uses a number of experimental and modeling techniques for the systematic study of cellular responses (in terms of RNA, protein and metabolite levels, metabolic fluxes, etc.) to genetic and environmental perturbations. This facilitates a rational design of metabolic modifications, which are implemented using recombinant DNA technology. Both, the analysis and the synthesis of metabolic pathways will be covered in this review. Recent efforts on the engineering of fermentative and biosynthetic pathways for biofuel production in Escherichia coli, as well as those enabling the utilization of novel feedstocks, will be highlighted
Determinantes del interes por instituciones universitarias del estudiante que egresa de la educación diversificada.
Proyecto de Investigación. Instituto Tecnológico de Costa Rica. Vicerrectoría de Vida Estudiantil y Servicios Académicos. Departamento de Orientación y Psicología, 1985En Costa Rica existe un amplio espectro de oportunidad de educación universitaria. Cada año, un gran sector de estudiantes que egresan de la Educación Diversificada consideran la posibilidad de realizar estudios universitarios. Datos de la Oficina de Planificación de la Educación Superior muestran que en los años 1979, 1980 y 1982 se inscribieron en los procesos de admisión de la UCR, UNA e ITCR un promedio de 66, 78% de los estudiantes que terminaron la Educación Diversificada durante dichos años.
Por otra parte, paralelamente y en contradicción con el alto interés del estudiante costarricense por la educación universitaria, existe también en Costa Rica una ausencia seria de información sobre los determinantes de dicho interés
Origin of passivation in hole-selective transition metal oxides for crystalline silicon heterojunction solar cells
Transition metal oxides (TMOs) have recently demonstrated to be a good alternative to boron/phosphorous doped layers in crystalline silicon heterojunction solar cells. In this work, the interface between n-type c-Si (n-Si) and three thermally evaporated TMOs (MoO3, WO3, and V2O5) was investigated by transmission electron microscopy, secondary ion-mass, and x-ray photoelectron spectroscopy. For the oxides studied, surface passivation of n-Si was attributed to an ultra-thin (1.9–2.8 nm) SiOx~1.5 interlayer formed by chemical reaction, leaving oxygen-deficient species (MoO, WO2, and VO2) as by-products. Carrier selectivity was also inferred from the inversion layer induced on the n-Si surface, a result of Fermi level alignment between two materials with dissimilar electrochemical potentials (work function difference ¿¿ = 1 eV). Therefore, the hole-selective and passivating functionality of these TMOs, in addition to their ambient temperature processing, could prove an effective means to lower the cost and simplify solar cell processing.Postprint (author's final draft
Enhanced manufacturing storage management using data mining prediction techniques
Performing an efficient storage management is a key issue for reducing costs in the manufacturing process. And the first step to accomplish this task is to have good estimations of the consumption of every storage component.
For making accurate consumption estimations two main approaches are possible: using past utilization values (time series); and/or considering other external factors affecting the spending rates.
Time series forecasting is the most common approach due to the fact that not always is clear the causes affecting consumption. Several classical methods have extensively been used, mainly ARIMA models.
As an alternative, in this paper it is proposed to use prediction techniques based on the data mining realm.
The use of consumption prediction algorithms clearly increases the storage management efficiency. The predictors based on data mining can offer enhanced solutions in many cases.Telefónica, through the “Cátedra de Telefónica Inteligencia en la Red”Paloma Luna Garrid
- …