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Search Results: 1 - 10 of 50608 matches for " Y. Hama "
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Coulomb Effect: A Possible Probe for the Evolution of Hadronic Matter
T. Osada,Y. Hama
Physics , 1999, DOI: 10.1103/PhysRevC.60.034904
Abstract: Electromagnetic field produced in high-energy heavy-ion collisions contains much useful information, because the field can be directly related to the motion of the matter in the whole stage of the reaction. One can divide the total electromagnetic field into three parts, i.e., the contributions from the incident nuclei, non-participating nucleons and charged fluid, the latter consisting of strongly interacting hadrons or quarks. Parametrizing the space-time evolution of the charged fluid based on hydrodynamic model, we study the development of the electromagnetic field which accompanies the high-energy heavy-ion collisions. We found that the incident nuclei bring a rather strong electromagnetic field to the interaction region of hadrons or quarks over a few fm after the collision. On the other hand, the observed charged hadrons' spectra are mostly affected (Coulomb effect) by the field of the charged fluid. We compare the result of our model with experimental data and found that the model reproduces them well. The pion yield ratio pi^-/pi+ at a RHIC energy, Au+Au 100+100 GeV/nucleon, is also predicted.
A new scheme for calculation of the multiplicity distributions in hadronic interactions
Beggio, P. C.;Hama, Y.;
Brazilian Journal of Physics , 2007, DOI: 10.1590/S0103-97332007000700016
Abstract: we generalize an existing geometrical approach for multiparticle production in hadronic interactions, in which the overall multiplicity distribution is given by summing contributions coming from each impact parameter b of the incident hadronic system. in the previous work, the process occurring at a fixed impact parameter b was interpreted as due to an elementary collision with formation of an object similar to the one in e- e+ annihilations. here, we extend the model allowing the possibility of formation of more than just one string. the output seems to be more consistent with data.
Antihyperon polarization in inclusive processes at high energies
Barros, Jr., C. C.;Hama, Y.;
Brazilian Journal of Physics , 2004, DOI: 10.1590/S0103-97332004000200030
Abstract: we propose a model that we believe is the main source of the antihyperon polarization in high-energy protonnucleus inclusive reactions. the polarization is originated by the final-state interactions between the antihyperons and other produced particles in these collisions (predominantly pions). the model is based on two elements: the low-energy pion-hyperon interaction (described by chiral effective lagrangians) and the statistical fluctuations plus expansion of the background matter.
Topics on hydrodynamic model of nucleus-nucleus collisions
Hama, Y.;Kodama, T.;Socolowski Jr., O.;
Brazilian Journal of Physics , 2005, DOI: 10.1590/S0103-97332005000100003
Abstract: a survey is given on the applications of hydrodynamic model of nucleus-nucleus collisons, focusing especially on i) the resolution of hydrodynamic equations for arbitrary configurations, by using the smoothed-particle hydrodynamic approach; ii) effects of the event-by-event fluctuation of the initial conditions on the observables; iii) decoupling criteria; iv) analytical solutions; and others.
Antihyperon polarization in inclusive processes at high energies
Barros Jr.,C. C.,Hama Y.
Brazilian Journal of Physics , 2004,
Abstract: We propose a model that we believe is the main source of the antihyperon polarization in high-energy protonnucleus inclusive reactions. The polarization is originated by the final-state interactions between the antihyperons and other produced particles in these collisions (predominantly pions). The model is based on two elements: the low-energy pion-hyperon interaction (described by chiral effective Lagrangians) and the statistical fluctuations plus expansion of the background matter.
Carotid Body Tumour: The Second Case Series from Baghdad, Iraq  [PDF]
Waleed M. Hussen, Abdulsalam Y. Taha, Diar S. Hama-Kareem
International Journal of Clinical Medicine (IJCM) , 2015, DOI: 10.4236/ijcm.2015.63019
Abstract:
Background: Carotid body tumour (CBT) is a rare neoplasm, yet it is the commonest head and neck paraganglioma. In Iraq, relevant literature is sparse. Herein, we present our second case series. Methodology: Patients with CBTs that were operated upon in the Department of Thoracic and Vascular Surgery, Baghdad Medical City from 2010 to 2014 were enrolled. History and examination were followed by a workup of duplex ultrasonography, CT scan, magnetic resonance imaging, CT or conventional carotid angiography. Surgical exploration via a standard anterolateral cervical incision and subadventitial dissection was used to resect the tumours with preservation of carotid arteries. Intra-luminal carotid shunts and vein grafts were prepared to be used if necessary. Results: There were 5 males and 2 females aging 17 - 46 with a mean of 32.9 ± 9.8 year. All patients had slowly growing painless pulsatile swelling below mandiblular angle for long durations (1 - 25 years) and a positive Fontaine’s sign. All tumours were benign, unilateral (right n = 4, left n = 3) and ranging in size from 3 × 3 cm to 6.4 × 3.2 cm. Beside US neck exam, carotid angiography was done in 5 patients. According to Shamblin classification, 4 were class II, 2 class I and 1 class III. All tumours were successfully resected with preservation of ICA. However, the ECA was safely ligated twice due to severe involvement. Tongue deviation occurred once (14.3%) but no patient died and none had stroke or recurrence. Conclusions: Our results of surgery for CBT compare very well with the international standards.
HBT Interferometry for Sonoluminescence Bubble
Y. Hama,T. Kodama,Sandra S. Padula
Physics , 1996, DOI: 10.1103/PhysRevA.56.2233
Abstract: The two-photon correlation of the light pulse emitted from a sonoluminescence bubble is discussed. It is shown that several important information about the mechanism of light emission, such as the time-scale and the shape of the emission region could be obtained from the HBT interferometry. We also argue that such a measurement may serve to reject one of the two currently suggested emission mechanisms, i.e., thermal process versus dynamical Casimir effect.
Fluctuations in Hadronic and Nuclear Collisions
Y. Hama,T. Kodama,Samya Paiva
Physics , 1997, DOI: 10.1007/BF02551503
Abstract: We investigate several fluctuation effects in high-energy hadronic and nuclear collisions through the analysis of different observables. To introduce fluctuations in the initial stage of collisions, we use the Interacting Gluon Model (IGM) modified by the inclusion of the impact parameter. The inelasticity and leading-particle distributions follow directly from this model. The fluctuation effects on rapidity distributions are then studied by using Landau's Hydrodynamic Model in one dimension. To investigate further the effects of the multiplicity fluctuation, we use the Longitudinal Phase-Space Model, with the multiplicity distribution calculated within the hydrodynamic model, and the initial conditions given by the IGM. Forward-backward correlation is obtained in this way.
The Study of Goldstone Modes in $ν$=2 Bilayer Quantum Hall Systems
Y. Hama,Y. Hidaka,G. Tsitsishvili,Z. F. Ezawa
Physics , 2012, DOI: 10.1140/epjb/e2012-30559-2
Abstract: At the filling factor $\nu$=2, the bilayer quantum Hall system has three phases, the spin-ferromagnet phase, the spin singlet phase and the canted antiferromagnet (CAF) phase, depending on the relative strength between the Zeeman energy and interlayer tunneling energy. We present a systematic method to derive the effective Hamiltonian for the Goldstone modes in these three phases. We then investigate the dispersion relations and the coherence lengths of the Goldstone modes. To explore a possible emergence of the interlayer phase coherence, we analyze the dispersion relations in the zero tunneling energy limit. We find one gapless mode with the linear dispersion relation in the CAF phase.
Hydrodynamic evolution near QCD critical point
Aguiar, C. E.;Kodama, T.;Koide, T.;Hama, Y.;
Brazilian Journal of Physics , 2007, DOI: 10.1590/S0103-97332007000100028
Abstract: some consequences of the presence of critical point in the equation of state on the hydrodynamical evolution of the strongly interacting matter are discussed. for this purpose, we apply the low energy effective theory of qcd, the nambu-jona-lasinio model and show some examples.
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