718 research outputs found
Photonuclear reactions with Zinc: A case for clinical linacs
The use of bremsstrahlung photons produced by a linac to induce photonuclear
reactions is wide spread. However, using a clinical linac to produce the
photons is a new concept. We aimed to induce photonuclear reactions on zinc
isotopes and measure the subsequent transition energies and half-lives. For
this purpose, a bremsstrahlung photon beam of 18 MeV endpoint energy produced
by the Philips SLI-25 linac has been used. The subsequent decay has been
measured with a well-shielded single HPGe detector. The results obtained for
transition energies are in good agreement with the literature data and in many
cases surpass these in accuracy. For the half-lives, we are in agreement with
the literature data, but do not achieve their precision. The obtained accuracy
for the transition energies show what is achievable in an experiment such as
ours. We demonstrate the usefulness and benefits of employing clinical linacs
for nuclear physics experiments
Bottom Production
We review the prospects for bottom production physics at the LHC.Comment: 74 pages, Latex, 71 figures, to appear in the Report of the ``1999
CERN Workshop on SM physics (and more) at the LHC'', P. Nason, G. Ridolfi, O.
Schneider G.F. Tartarelli, P. Vikas (conveners
Optical character recognition on heterogeneous SoC for HD automatic number plate recognition system
Automatic number plate recognition (ANPR) systems are becoming vital for safety and security purposes. Typical ANPR systems are based on three stages: number plate localization (NPL), character segmentation (CS), and optical character recognition (OCR). Recently, high definition (HD) cameras have been used to improve their recognition rates. In this paper, four algorithms are proposed for the OCR stage of a real-time HD ANPR system. The proposed algorithms are based on feature extraction (vector crossing, zoning, combined zoning, and vector crossing) and template matching techniques. All proposed algorithms have been implemented using MATLAB as a proof of concept and the best one has been selected for hardware implementation using a heterogeneous system on chip (SoC) platform. The selected platform is the Xilinx Zynq-7000 All Programmable SoC, which consists of an ARM processor and programmable logic. Obtained hardware implementation results have shown that the proposed system can recognize one character in 0.63 ms, with an accuracy of 99.5% while utilizing around 6% of the programmable logic resources. In addition, the use of the heterogenous SoC consumes 36 W which is equivalent to saving around 80% of the energy consumed by the PC used in this work, whereas it is smaller in size by 95%
Estudo da evolução dos processos de alteração supergênica de rocha granítica - Granito Independência - Morro do IPA, Porto Alegre, RS
The rocks of the earth's surface are constantly exposed to the action of natural agents such as water, temperature variations, atmospheric gases and the action of living beings. Among the action of living beings, in the urban centers highlight the anthropogenic, which often ends up by degrading natural resources. In this context, understanding the processes of transformation of the rocks, you can understand the genesis and evolution of soils, and improve methods for their recovery. This study was conducted in a profile altered granitic rock located in the urban area of Porto Alegre, where eight samples were collected representing different levels, from rock to soil. The samples were analyzed by X-ray diffraction, by the powder method on whole rock and in the fraction <4 micrometers. The composition was determined by X-ray fluorescence. Fragments of the samples were observed by scanning electron microscopy (secondary electrons). Petrographic and mineralogical studies showed that there is little variation in the mineralogical composition of the vertical profiles, mainly composed of quartz, feldspar, and kaolinite, identified in all horizons, and illite/biotite, identified in saprolitic horizons. Analyzes whit secondary electron images allowed to identify even the presence of halloysite. The exudation of the iron plates of biotite observed in the optical microscope marking the beginning of supergene alteration in granite. X-ray fluorescence data show that the choice of the reference element property to check whether or not the enrichment of elements along the profile is very important since this paper was verified that Aluminum has a movable behavior probably associated with conditions soil acidity.As rochas da superfície terrestre estão permanentemente expostas à ação de agentes naturais, como a água, as variações de temperatura, os gases atmosféricos e a ação dos seres vivos. Dentre a ação dos seres vivos, nos centros urbanos destaca-se a ação antrópica, que por vezes acaba por degradar os recursos naturais. Nesse contexto, entender os processos de transformação das rochas, para que se possa compreender a gênese e evolução dos solos, e assim, aperfeiçoar métodos para sua recuperação, torna-se imprescindível. Este estudo foi desenvolvido em um perfil de alteração de rocha granítica localizado na área urbana de Porto Alegre, onde foram coletadas oito amostras representativas dos diferentes níveis, da rocha ao solo. As amostras foram analisadas por difratometria de raios X (DRX), pelo método do pó na rocha total e na fração < 4 μm. A composição química foi determinada por fluorescência de raios X (FRX). Fragmentos das amostras foram observados no microscópio eletrônico de varredura (elétrons secundários) e no microscópio ótico. Os estudos mineralógicos e petrográficos mostraram a existência de pequena variação composicional vertical no perfil, essencialmente composto por quartzo, feldspato alcalino e caolinita, identificados em todos os horizontes, e ilita/biotita identificadas nos horizontes saprolíticos. As análises através de imagens de elétrons secundários permitiram identificar ainda a presença de haloisita. A exsudação de ferro pelas lamelas da biotita observada no microscópio óptico marca o início da alteração supergênica no granito. Os dados de FRX mostram que a escolha do elemento imóvel de referência para verificar a existência ou não de enriquecimento dos elementos ao longo do perfil é muito importante, pois neste trabalho verificou-se que o alumínio tem um comportamento móvel, provavelmente associado às condições de acidez do solo
Search for a Fourth-Generation Quark More Massive than the Z0 Boson in ppbar Collisions at sqrt(s) = 1.8 TeV
We present the results of a search for pair production of a fourth-generation
charge -1/3 quark (b') in sqrt(s)=1.8 TeV ppbar collisions using 88 pb^(-1) of
data obtained with the Collider Detector at Fermilab. We assume that both
quarks decay via the flavor-changing neutral current process b' -> bZ and that
the b' mass is greater than m_Z + m_b. We studied the decay mode b'b'bar -> ZZ
b bbar where one Z0 decays into e^+e^- or mu^+ mu^- and the other decays
hadronically, giving a signature of two leptons plus jets. An upper limit on
the cross section of ppbar -> b'b'bar times [BR (b' -> bZ)]^2 is established as
a function of the b' mass. We exclude at 95% confidence level a b' quark with
mass between 100 and 199 GeV/c^2 for BR(b' -> bZ) = 100%.Comment: 12 pages, 2 figures, submitted to Phys. Rev. Letters on 9/12/9
Search for charged Higgs decays of the top quark using hadronic tau decays
We present the result of a search for charged Higgs decays of the top quark,
produced in collisions at 1.8 TeV. When the charged
Higgs is heavy and decays to a tau lepton, which subsequently decays
hadronically, the resulting events have a unique signature: large missing
transverse energy and the low-charged-multiplicity tau. Data collected in the
period 1992-1993 at the Collider Detector at Fermilab, corresponding to
18.70.7~pb, exclude new regions of combined top quark and charged
Higgs mass, in extensions to the standard model with two Higgs doublets.Comment: uuencoded, gzipped tar file of LaTeX and 6 Postscript figures; 11 pp;
submitted to Phys. Rev.
Inclusive jet cross section in collisions at TeV
The inclusive jet differential cross section has been measured for jet
transverse energies, , from 15 to 440 GeV, in the pseudorapidity region
0.10.7. The results are based on 19.5 pb of data
collected by the CDF collaboration at the Fermilab Tevatron collider. The data
are compared with QCD predictions for various sets of parton distribution
functions. The cross section for jets with GeV is significantly
higher than current predictions based on O() perturbative QCD
calculations. Various possible explanations for the high- excess are
discussed.Comment: 8 pages with 2 eps uu-encoded figures Submitted to Physical Review
Letter
Observation of Hadronic W Decays in t-tbar Events with the Collider Detector at Fermilab
We observe hadronic W decays in t-tbar -> W (-> l nu) + >= 4 jet events using
a 109 pb-1 data sample of p-pbar collisions at sqrt{s} = 1.8 TeV collected with
the Collider Detector at Fermilab (CDF). A peak in the dijet invariant mass
distribution is obtained that is consistent with W decay and inconsistent with
the background prediction by 3.3 standard deviations. From this peak we measure
the W mass to be 77.2 +- 4.6 (stat+syst) GeV/c^2. This result demonstrates the
presence of two W bosons in t-tbar candidates in the W (-> l nu) + >= 4 jet
channel.Comment: 20 pages, 4 figures, submitted to PR
Measurement of the B0 anti-B0 oscillation frequency using l- D*+ pairs and lepton flavor tags
The oscillation frequency Delta-md of B0 anti-B0 mixing is measured using the
partially reconstructed semileptonic decay anti-B0 -> l- nubar D*+ X. The data
sample was collected with the CDF detector at the Fermilab Tevatron collider
during 1992 - 1995 by triggering on the existence of two lepton candidates in
an event, and corresponds to about 110 pb-1 of pbar p collisions at sqrt(s) =
1.8 TeV. We estimate the proper decay time of the anti-B0 meson from the
measured decay length and reconstructed momentum of the l- D*+ system. The
charge of the lepton in the final state identifies the flavor of the anti-B0
meson at its decay. The second lepton in the event is used to infer the flavor
of the anti-B0 meson at production. We measure the oscillation frequency to be
Delta-md = 0.516 +/- 0.099 +0.029 -0.035 ps-1, where the first uncertainty is
statistical and the second is systematic.Comment: 30 pages, 7 figures. Submitted to Physical Review
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