6,544 research outputs found
Top Quarks, Axigluons and Charge Asymmetries at Hadron Colliders
Axigluons are colored heavy neutral gauge boson that couple to quarks through
an axial vector current and the same strong coupling as gluons. The most
important model-independent manifestation of axigluons is the generation of a
forward--backward asymmetry in top-antitop quark production at
collisions which originates from the charge asymmetry. We update our previous
analysis for the inclusive QCD induced forward--backward asymmetry and define a
new observable which is more sensitive to the effect than the forward--backward
asymmetry. Furthermore, we find a lower limit of 1.2 TeV at 90% C.L. on the
axigluon mass from recent measurements of the asymmetry at Tevatron. Also at
LHC, the charge asymmetry is sizable in suitably selected samples. We evaluate
this asymmetry in the central region for different selection cuts and show
that, like at Tevatron, the charge asymmetry can probe larger values of the
axigluon mass than the dijet mass distribution.Comment: 13 pages, 9 figure
An Efficient All-Parses Systolic Algorithm for General Context-Free Parsing
The problem of outputting all parse trees of a string accepted by a context-free grammar is considered. A systolic algorithm is presented that operates in O (m n) time, where m is the number of distinct parse traces and n is the length of the input. The systolic array uses n2 processors, each of which requires at most O(log n) bits of storage. This is much more space-efficient than a previously reported systolic algorithm for the same problem, which required O (n log n) space per processor. The algorithm also extends previous algorithms that only output a single parse tree of the input
Localizing gravity on exotic thick 3-branes
We consider localization of gravity on thick branes with a non trivial
structure. Double walls that generalize the thick Randall-Sundrum solution, and
asymmetric walls that arise from a Z_2-symmetric scalar potential, are
considered. We present a new asymmetric solution: a thick brane interpolating
between two AdS_5 spacetimes with different cosmological constants, which can
be derived from a ``fake supergravity'' superpotential, and show that it is
possible to confine gravity on such branes.Comment: Final version, minor changes, references adde
Exponential Decay for Small Non-Linear Perturbations of Expanding Flat Homogeneous Cosmologies
It is shown that during expanding phases of flat homogeneous cosmologies all
small enough non-linear perturbations decay exponentially. This result holds
for a large class of perfect fluid equations of state, but notably not for very
``stiff'' fluids as the pure radiation case
Three-frequency resonances in dynamical systems
We investigate numerically and experimentally dynamical systems having three
interacting frequencies: a discrete mapping (a circle map), an exactly solvable
model (a system of coupled ordinary differential equations), and an
experimental device (an electronic oscillator). We compare the hierarchies of
three-frequency resonances we find in each of these systems. All three show
similar qualitative behaviour, suggesting the existence of generic features in
the parameter-space organization of three-frequency resonances.Comment: See home page http://lec.ugr.es/~julya
UHE tau neutrino flux regeneration while skimming the Earth
The detection of Earth-skimming tau neutrinos has turned into a very
promising strategy for the observation of ultra-high energy cosmic neutrinos.
The sensitivity of this channel crucially depends on the parameters of the
propagation of the tau neutrinos through the terrestrial crust, which governs
the flux of emerging tau leptons that can be detected. One of the
characteristics of this propagation is the possibility of regeneration through
multiple conversions, which are often neglected
in the standard picture. In this paper, we solve the transport equations
governing the propagation and compare the flux of emerging tau
leptons obtained allowing regeneration or not. We discuss the validity of the
approximation of neglecting the regeneration using different
scenarios for the neutrino-nucleon cross-sections and the tau energy losses.Comment: 8 pages, 8 figure
The Initial-Boundary Value Problem in General Relativity
In this article we summarize what is known about the initial-boundary value
problem for general relativity and discuss present problems related to it.Comment: 11 pages, 2 figures. Contribution to a special volume for Mario
Castagnino's seventy fifth birthda
Unique growth pattern of human mammary epithelial cells induced by polymeric nanoparticles.
Due to their unique properties, engineered nanoparticles (NPs) have found broad use in industry, technology, and medicine, including as a vehicle for drug delivery. However, the understanding of NPs' interaction with different types of mammalian cells lags significantly behind their increasing adoption in drug delivery. In this study, we show unique responses of human epithelial breast cells when exposed to polymeric Eudragit® RS NPs (ENPs) for 1-3 days. Cells displayed dose-dependent increases in metabolic activity and growth, but lower proliferation rates, than control cells, as evidenced in tetrazolium salt (WST-1) and 5-bromo-2'-deoxyuridine (BrdU) assays, respectively. Those effects did not affect cell death or mitochondrial fragmentation. We attribute the increase in metabolic activity and growth of cells culture with ENPs to three factors: (1) high affinity of proteins present in the serum for ENPs, (2) adhesion of ENPs to cells, and (3) activation of proliferation and growth pathways. The proteins and genes responsible for stimulating cell adhesion and growth were identified by mass spectrometry and Microarray analyses. We demonstrate a novel property of ENPs, which act to increase cell metabolic activity and growth and organize epithelial cells in the epithelium as determined by Microarray analysis
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