6,766 research outputs found
Ultra peripheral heavy ion collisions and the energy dependence of the nuclear radius
To estimate realistic cross sections in ultra peripheral heavy ion collisions
we must remove effects of strong absorption. One method to eliminate these
effects make use of a Glauber model calculation, where the nucleon-nucleon
energy dependent cross sections at small impact parameter are suppressed. In
another method we impose a geometrical cut on the minimal impact parameter of
the nuclear collision (, where is the radius of ion
""). In this last case the effect of a possible nuclear radius dependence
with the energy has not been considered in detail up to now. Here we introduce
this effect showing that for final states with small invariant mass the effect
is negligible. However when the final state has a relatively large invariant
mass, e.g. an intermediate mass Higgs boson, the cross section can decrease up
to 50%.Comment: To appear in Phys. Lett.
On-Line Instruction-checking in Pipelined Microprocessors
Microprocessors performances have increased by more than five orders of magnitude in the last three decades. As technology scales down, these components become inherently unreliable posing major design and test challenges. This paper proposes an instruction-checking architecture to detect erroneous instruction executions caused by both permanent and transient errors in the internal logic of a microprocessor. Monitoring the correct activation sequence of a set of predefined microprocessor control/status signals allow distinguishing between correctly and not correctly executed instruction
The 125 GeV boson: A composite scalar?
Assuming that the 125 GeV particle observed at the LHC is a composite scalar
and responsible for the electroweak gauge symmetry breaking, we consider the
possibility that the bound state is generated by a non-Abelian gauge theory
with dynamically generated gauge boson masses and a specific chiral symmetry
breaking dynamics motivated by confinement. The scalar mass is computed with
the use of the Bethe-Salpeter equation and its normalization condition as a
function of the SU(N) group and the respective fermionic representation. If the
fermions that form the composite state are in the fundamental representation of
the SU(N) group, we can generate such light boson only for one specific number
of fermions for each group. In the case of small groups, like SU(2) to SU(5),
and two fermions in the adjoint representation we find that is quite improbable
to generate such light composite scalar.Comment: 24 pages, 5 figures, discussion extended, references added; version
to appear in Phys. Rev.
The small behavior of the gluon structure function from total cross sections
Within a QCD-based eikonal model with a dynamical infrared gluon mass scale
we discuss how the small behavior of the gluon distribution function at
moderate is directly related to the rise of total hadronic cross
sections. In this model the rise of total cross sections is driven by
gluon-gluon semihard scattering processes, where the behavior of the small
gluon distribution function exhibits the power law . Assuming that the scale is proportional to the
dynamical gluon mass one, we show that the values of obtained in this
model are compatible with an earlier result based on a specific nonperturbative
Pomeron model. We discuss the implications of this picture for the behavior of
input valence-like gluon distributions at low resolution scales.Comment: 19 pages, 3 figures; revised version; to appear in Int. J. Mod. Phys.
Modeling Changes in Measured Conductance of Thin Boron Carbide Semiconducting Films Under Irradiation
Semiconducting, p-type, amorphous partially dehydrogenated boron carbide films (a-B10C2+x:Hy) were deposited utilizing plasma enhanced chemical vapor deposition (PECVD) onto n-type silicon thus creating a heterojunction diode. A model was developed for the conductance of the device as a function of perturbation frequency (��) that incorporates changes of the electrical properties for both the a-B10C2+x:Hy film and the silicon substrate when irradiated. The virgin model has 3 independent variables (R1, C1, R3), and 1 dependent variable (��). Samples were then irradiated with 200 keV He+ ions, and the conductance model was matched to the measured data. It was found that initial irradiation (0.1 displacements per atom (dpa) equivalent) resulted in a decrease in the parallel junction resistance parameter from 6032 Ω to 2705 Ω. Further irradiation drastically increased the parallel junction resistance parameter to 39000 Ω (0.2 dpa equivalent), 77440 Ω (0.3 dpa equivalent), and 190000 Ω (0.5 dpa equivalent). It is believed that the initial irradiation causes type inversion of the silicon substrate changing the original junction from a p-n to a p-p+ with a much lower barrier height leading to a lower junction resistance component between the a-B10C2+x:Hy and irradiated silicon. Additionally, it was found that after irradiation, a second parallel resistor and capacitor component is required for the model, introducing 2 additional independent variables (R2, C2). This is interpreted as the junction between the irradiated and virgin silicon near ion end of range
Assessment of the conservation status of natural and semi-natural patches associated with urban areas through habitat suitability indices
Urban environments rely on the surrounding natural ecosystems remnants as providers of ecosystem functions, therefore these areas not only support a unique biodiversity but also have a social value for maintaining public health and wellbeing. For this reason, urbanization is considered to be one the biggest threats to ecosystems, leading to native biodiversity simplification and, thus, to a detriment of the provided ecosystem services. Moreover, this change in land use results in high levels of landscape fragmentation and modification in areas surrounding the habitat remnants which, in consequence, become inadequate for many native species. In this context, it is important that urban planners have the information to assess the possible consequences of future changes in land use in order to increase the landscape chances of supporting both, native biodiversity and the needs of a growing human population. The objective of the present work is to evaluate the ecological integrity of natural and semi-natural vegetation patches immersed in an urban area in order to generate a conceptual framework for landscape assessment that allows urban planners to envision the best choice for city development at a given place. To do so, we developed a quantitative integral environmental evaluation index that includes ecological characterization, geological characterization, and environmental characterization (presence of anthropic disturbance) of the assessed area. We conclude that the index we have generated in this work is suitable to be used as a management tool to allow an unbiased valuation and to identify managing situations that require a short term response.Fil: Natale, Evangelina Sandra. Fundación Conservación y Desarrollo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Villalba, G.. Fundación Conservación y Desarrollo; ArgentinaFil: Junquera, J. E.. Fundación Conservación y Desarrollo; ArgentinaFil: Zalba, Sergio Martín. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia. Grupo de Estudios en Conservación y Manejo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
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