Iranian Journal of Physics Research
Year:2002 | Volume:3 | Issue:2|Papers Count:10

Over the past few years, nano-science and its associated nano-technology have emerged into prominence in research institutions across the world. They have brought about new scientific and engineering paradigms, allowing for the manipulation of single atoms and molecules, designing and fabricating new materials, atom-by-atom, and devices that operate on significantly reduced time and length scales. One important area of research in nano-science and nanotechnology is carbon-based physics in the form of fullerene physics. The C60 molecule, and other cage-like fullerenes, together with carbon nano-tubes provide objects that can be combined to generate three-dimensional functional structures for use in the anticipated nano-technology of future. The unique properties of C60 can also be exploited in designing nano-phase thin films with applications in nano-scopic device technology and processes such as nano-lithography this requires a deep understanding of the highly complex process of adsorption of this molecule on a variety of substrates. We review the field of nano-scale nucleation and growth of C60 molecules on some of the technologically important substrates. In addition to experimental results, the results of a set of highly accurate computational simulations are also reported.

We report on an experimental comparison of the characteristics of quark-induced jets based on an analysis of jet events selected from hadronic events at c.m. energy of 60 GeV in e+ e-annihilations. The triangle plot shows that the majority are two-jet events. The three-jet events are also present but not as many as two-jet events. The mean transverse momentum is larger for three-jet events than the corresponding value for the two-jet events. This is in qualitative agreement with QCD theory, which predicts a greater probability for gluon radiation in three-jet events. Furthermore, the particles in the gluon-enriched sample have a higher multiplicity than its counterpart in quark jet sample. The ratio of the multiplicities is 1.506±0.067. This numerical value is in good quantitative agreement with the OPAL experiment. Possible explanation for all these features will be presented in this paper.

In order to determine the fusion energy gain in a target due to inertial confinement fusion, it is necessary to solve hydrodynamic equations governed on plasma behavior during confinement time. To compress spherical multilayer targets having fuel in the central part, they are irradiated by laser or heavy ion beams. A suitable mass ratio of a pusher is used to ignite the central part of the target. When compression is maximum, fuel density exceeds from 500 to 1000 times of the cold density. Temperature in the cold fuel region rises rapidly and cause the plasma and fusion reaction to take place. Calculations of density, temperature and pressure profiles in the plasma are necessary to obtain the energy flux of neutrons, electrons and radiations coming out from the target. Using numerical solutions for continuity, the momentum and energy equations based on a defined continuity equation we prepared a computer program to calculate density, temperature and pressure profiles. The gain of the target as .output to input energy is determined; using this procedure to a designed target with deuterium-tritium (DT) fuel derived by heavy ion beams gives an energy gain over 400.

In this project the neutron spectra from the reaction of deutron on beryllium muclei is measured. The energies of deuterons were 7, 10, 13 and 15 MeV, and these measurements are performed at 10, 30 and 50 degrees relative to the beam of deutrons. The detector used is 76 by 76 mm right circular cylender of NE-213 liquid scintillator. The zero crossing technique is used for gamma discrimination. For the elimination of the background radiation, a Polyethylene block, 40 cm in thickness, with inserted cadmium sheets, and a lead block, 5 cm in thickness, were used. In order to obtain the background radiation spectrum, the latter blocks were placed between the target and the detector to eliminate neutron and gamma radiations reaching the detector directly. "FORIST" code is used to unfold the neutron spectra from the measured pulse height spectra and "O5S" and "RESPMG" codes are used to obtain the detector response matrix.

In this paper we present a detailed theoretical treatment of the 3-D temperature distribution induced by laser beam in photothermal displacement spectroscopy. We assume that a solid sample, which is deposited on-a substrate and is in contact with a fluid, is irradiated by an intensity modulated cw laser source. By using a technique based on Green's function and integral transformations we find the explicit expression for temperature distribution function. This function which depends on the properties of the laser beam and optical and thermal properties of the sample, the substrate and the fluid, exhibits the characteristics of a damped thermal wave. Numerical analysis of the temperature distribution for a certain sample (GaAs) reveals that the behavior of thermal wave is not so sensitive with respect to the variation of the modulation frequency. On the other hand; we find that the temperature of the sample surface decreases with increasing modulation frequency because of the thermal inertia of the sample. Furthermore, the effective thermal length decreases with increasing modulation frequency, thereby making the decay of photothermal signal faster.

In the present work, the fundamental behavior of four body molecule formations of ptμμ, pdμμ, dtμμ, ttμμ, and ppμμ in a D/T fusion are considered. Their higher fusion rate, specially the available data for dtμμ, encouraged us to study the muon cycling rate in D/T fusion in the temperature range of (100-1400 K), density and deuterium-tritium concentration ratio. For this purpose, various values for the doubly muonic molecule formation are chosen and with the comparison to the experimental results, the doubly muonic formation rate of 109 S-1 is predicted theoretically. Our calculated cycling rate has shown that having not considered the doubly muonic formation in previous calculations had made no serious changes in the previously calculated values.

There are several observational evidences for the existence of dark matter in the universe. More than about 90% of the matter in the universe is in a form which is not directly observable. If the dark matter is in the form of weakly interacting massive particles (WIMPs) or cosmions, part of it is captured by the Sun, other stars, and even planets. In this paper, some basic ideas of the cosmion hypothesis are presented and the abundance and the coefficient of thermal energy transport by WIMPs are calculated, using an approximate method.

In this paper we try to formulate the Berezin quantization on projective Hilbert space P(H) and use its geometric structure to construct a correspondence between a given classical theory and a given quantum theory. It will be shown that the star product in Berezin quantization is equivalent to the Poisson bracket on coherent states manifold M, embedded in P(H), and the Berezin method is used to define a classical limit for geometric quantum mechanics. With this construction to all of the quantum observables are associated their covariant symbols, which form a poisson algebra on P(H) and since the corresponding classical phase space has a natural Poisson structure, the Berezin quantization is then a systematic procedure to relate these two piosson algebras.

Single phase polycrystalline Gd1-xPrxBa2Cu3O7-δ samples with x= 0.05, 0.10, and 0.15 have been prepared by standard solid state reaction technique and characterized by XRD and SEM analysis. The electrical resistivity, Hall effect and magnetoresistance measurements have been made on the samples. The electrical resistivity measurements indicate a reduction of transition temperature (Tc) and an increase of superconducting transition width with increasing x. Hall measurements show anomalous temperature dependence for Hall coefficient (RH) in the normal state. In Gd0.90Pr0.10Ba2Cu3O7-δ sample, we have seen an anomalous sign reversal in the Hall coefficient with respect to temperature. The magnetoresistance measurements in the range of 0 to 10 kOe also show small changes in the normal states, although the changes are large in the superconducting state. An anomaly at 260 K appears in the transverse magnetoresistance for x=0.1 sample, which is related to the presence of magnetic Gd ion. The superconducting transition width also increases with the magnetic field in all of the samples. An exponent behavior for Hc2 versus (1- T/T0(H)) and superconducting transition width versus H have been derived. Pinning energy (U) has also been calculated from these measurements. Results show the reduction of pinning energy with the increase of magnetic field and x. Our results show that the exponent behavior of U ∞ HV, where v is independent of x.