30 research outputs found
Influence of shower fluctuations and primary composition on studies of the shower longitudinal development
We study the influence of shower fluctuations, and the possible presence of
different nuclear species in the primary cosmic ray spectrum, on the
experimental determination of both shower energy and the proton air inelastic
cross section from studies of the longitudinal development of atmospheric
showers in fluorescence experiments. We investigate the potential of track
length integral and shower size at maximum as estimators of shower energy. We
find that at very high energy (~10^19-10^20 eV) the error of the total energy
assignment is dominated by the dependence on the hadronic interaction model,
and is of the order of 5%. At lower energy (~10^17-10^18 eV), the uncertainty
of the energy determination due to the limited knowledge of the primary cosmic
ray composition is more important. The distribution of depth of shower maximum
is discussed as a measure of the proton-air cross section. Uncertainties in a
possible experimental measurement of this cross section introduced by intrinsic
shower fluctuations, the model of hadronic interactions, and the unknown
mixture of primary nuclei in the cosmic radiation are numerically evaluated.Comment: 12 pages, 11 figures, 4 table
Constraints on the Ultra High Energy Photon flux using inclined showers from the Haverah Park array
We describe a method to analyse inclined air showers produced by ultra high
energy cosmic rays using an analytical description of the muon densities. We
report the results obtained using data from inclined events
(60^{\circ}<\theta<80^{\circ}) recorded by the Haverah Park shower detector for
energies above 10^19 eV. Using mass independent knowledge of the UHECR spectrum
obtained from vertical air shower measurements and comparing the expected
horizontal shower rate to the reported measurements we show that above 10^19 eV
less than 48 % of the primary cosmic rays can be photons at the 95 % confidence
level and above 4 X 10^19 eV less than 50 % of the cosmic rays can be photonic
at the same confidence level. These limits place important constraints on some
models of the origin of ultra high-energy cosmic rays.Comment: 45 pages, 25 figure
New hadrons as ultra-high energy cosmic rays
Ultra-high energy cosmic ray (UHECR) protons produced by uniformly
distributed astrophysical sources contradict the energy spectrum measured by
both the AGASA and HiRes experiments, assuming the small scale clustering of
UHECR observed by AGASA is caused by point-like sources. In that case, the
small number of sources leads to a sharp exponential cutoff at the energy
E<10^{20} eV in the UHECR spectrum. New hadrons with mass 1.5-3 GeV can solve
this cutoff problem. For the first time we discuss the production of such
hadrons in proton collisions with infrared/optical photons in astrophysical
sources. This production mechanism, in contrast to proton-proton collisions,
requires the acceleration of protons only to energies E<10^{21} eV. The diffuse
gamma-ray and neutrino fluxes in this model obey all existing experimental
limits. We predict large UHE neutrino fluxes well above the sensitivity of the
next generation of high-energy neutrino experiments. As an example we study
hadrons containing a light bottom squark. These models can be tested by
accelerator experiments, UHECR observatories and neutrino telescopes.Comment: 17 pages, revtex style; v2: shortened, as to appear in PR
Avaliação do potencial antioxidante frente Ă oxidação lipĂdica e da toxicidade preliminar do extrato e fraçÔes obtidas das frondes de Dicksonia sellowiana (Presl.) Hook
A large-scale RNAi screen in human cells identifies new components of the p53 pathway
RNA interference (RNAi) is a powerful new tool with which to
perform loss-of-function genetic screens in lower organisms and
can greatly facilitate the identification of components of cellular
signalling pathways. In mammalian cells, such screens have
been hampered by a lack of suitable tools that can be used on a
large scale. We and others have recently developed expression
vectors to direct the synthesis of short hairpin RNAs (shRNAs)
that act as short interfering RNA (siRNA)-like molecules to stably
suppress gene expression. Here we report the construction of a
set of retroviral vectors encoding 23,742 distinct shRNAs, which
target 7,914 different human genes for suppression. We use this
RNAi library in human cells to identify one known and five new
modulators of p53-dependent proliferation arrest. Suppression
of these genes confers resistance to both p53-dependent and
p19ARF-dependent proliferation arrest, and abolishes a DNAdamage-
induced G1 cell-cycle arrest. Furthermore, we describe
siRNA bar-code screens to rapidly identify individual siRNA
vectors associated with a specific phenotype. These new tools
will greatly facilitate large-scale loss-of-function genetic screens
in mammalian cells
Gene expression profiling predicts clinical outcome of breast cancer
Breast cancer patients with the same stage of disease can have
markedly different treatment responses and overall outcome. The
strongest predictors for metastases (for example, lymph node
status and histological grade) fail to classify accurately breast
tumours according to their clinical behaviour. Chemotherapy
or hormonal therapy reduces the risk of distant metastases by
approximately one-third; however, 70 â 80% of patients receiving
this treatment would have survived without it. None of the
signatures of breast cancer gene expression reported to date
allow for patient-tailored therapy strategies. Here we used DNA
microarray analysis on primary breast tumours of 117 young
patients, and applied supervised classification to identify a gene
expression signature strongly predictive of a short interval to
distant metastases ('poor prognosis' signature) in patients without
tumour cells in local lymph nodes at diagnosis (lymph node
negative). In addition, we established a signature that identifies
tumours of BRCAI carriers. The poor prognosis signature consists
of genes regulating cell cycle, invasion, metastasis and angiogenesis. This gene expression profile will outperform all
currently used clinical parameters in predicting disease outcome.
Our findings provide a strategy to select patients who would
benefit from adjuvant therapy