JOURNAL OF SCIENCES (ISLAMIC AZAD UNIVERSITY)
Year:2010 | Volume:20 | Issue:75 (PHYSICS ISSUE)|Papers Count:13

Introduction: Experimental and theoretical studies of electrical conductance through magnetic nanostructures have extensively attracted much interest during the last years. Spin dependent transport phenomena in magnetic nanostructures such as magnetic quantum wire have received more attention from both scientific and technological view. The transport properties of magnetic quantum wire can be measured by coupling it to leads and passing current through the set up. In the present work we study spin dependent transport in a magnetic nanocrystal connected between two three dimensional metal leads.Aim: The study of spin polarized transport in a nanocrystal with magnetic layers in the presence of electrical and magnetic fields due to landuer formalism.Materials and Methods: In this paper, the spin polarized transport in a three dimensional quantum wire with magnetic layers attached to two metal three dimensional electrodes has been investigated in the tight-binding approach and assuming nearest –neighbor interaction by Green's function method and landuer formalism.Results: The transport of up & down spin to be accomplished in the separate channels, electrons with spin down have less share in the transport and the transport amplitude will be decreased by means of electrical field.Conclusion: some different possible results because of its directly effect on magnetic layers make strengthen the essence of reviewing in the presence or absence of external magnetic field. The magnetic layers couple ferromagnetically in an external magnetic field but couple antiferromagnetically in the absence of the magnetic field. Also the in – plane electrical field suppresses the transport amplitude and it has been predicted that the spin polarized transport amplitude can be controlled externally through this system by means of this electric field.

Introduction: Viristors are seramical electrical species that primary work of them is limitation of temporary voltages in amount that was unsafe for system. oxide Viristors have symetric and non-linear I-V (voltage-current) characteristics.one of the most important component that used for visitor preparation is ZnO-Bi2O3. Although it is shown that intergranular material probably for due to existence potential barriers in grain boundaries, details of mechanisms is not known now.Aim: Study electrical properties of thin layer ZnO-Bi2O3 and sandwich structure of Al- Zno -Al and measurment evaluation with 4point probe and 2point probe in vacuity cell.Materials and Methods: in this study ZnO-Bi2O3 and sandwich structure Al-Zno-Al on basis of single grain boundary model were evaluated. Conductivity mechanisms with study properties of I-V characteristics evaluated in vacuum. For samples preparation, R-F sputtering for ZnO deposition and Vacuum evaporation method for Bi2O3 and Al films. Effect of vacuity and increasing of temperatue in I-V characteristic were evaluated.Results: In ZnO measuring with 4point probe for high amount resistance of ZnO, voltage and probe permanently changed and were not measurable. This shows that our contacts on tip of the probes were nonohmic but in measuring with 4point probes, touches must be ohmic and for this reasons and 4 point probe limitation this probe was no valuable and only trust to sandwich structure that measured in vacuum. From evaluation sandwich structures two paradox results earned. Separation of the connection Ag forincreasing temperature probably shows that I-V characterizes is not related to ZnO. sandwich structure can be shows electrical conductive from volume of sample. Measuring of the electrical conductive of ZnO-Bi2O3 in this research probably related to conduction from the surface of sample. Furthermore usage of the sandwich structures in papers lead to measuring of the electrical conductive from the volume of sample.with evaluation measuring, measuring with 4point probes for reason humidity and surface conductive, shows more electrical conductive in comparison in vacuum and vacuum and increasing of the sample temperature decrease conductivity.Conclusion: Measuring of the electrical conductive of ZnO-Bi2O3 two layers and sandwich structure Al-ZnO-Al shows that with attention to the four point probe limitation, contacts must be ohmic and point contact of probes must be minimum resistance, but for easuring were not done in vaccum and it may be contacts were not ohmic, for this reason it is not measuring conditions, only measuing from sandwich structures is trustbles.

Introduction: High power laser interaction with metal targets produces a high temperature plasma (hundreds ev to several kev) which is a good source of x-ray radiation.The produced x-ray is suitable for different applications including lithography, medical science, biology, (Inertial Confinement Fusion) ICF and space sciences. In practical uses, enhancement of x-ray yield or higher conversion of laser energy into x-ray yield is efficient.For such reasons, there is a great deal of interest in producing x-ray from plasmas and also in methods that could enhance the x-ray yield.Aim: Simulation of x-ray radiation from laser plasma and inspecting the effect of using laser prepulse on the x-ray yield.Materials and Methods: This investigation is made using atomic physics simulations.Firstly, plasma formation from high power laser interaction with metal target is simulated.Secondly, after the plasma parameters especially electron density and temperature are found, x-ray radiation is simulated using the corresponding equations of different mechanisms.Finally, the effect of laser prepulse is studied by correcting computer codes.Results: It was seen that deeper layers of the target are affected at greater times by the laser interaction and their temperature and density increase. For a laser pulse of 50 ps and 1015 W/cm2 the temperature and density across the target are about several hundred ev and 1023 cm-3, respectively. X-ray production is higher from the layers with higher electron density and especially electron temperature. In addition, the produced x-ray pulse duration (FWHM) approximately the same as the laser pulse i.e.50 ps. It was seen that by using prepulse, there is an optimum delay time (time separation between main pulse and prepulse) at which maximum x-ray yield is produced. The optimum delay time was about 400 ps and 1700 ps when the ratio of the prepulse to the main pulse intensities was 0.01 and 0.001, respectively.Also, calculations showed that decreasing the prepulse intensity increases the x-ray yield enhancement.Conclusion: The x-ray pulse duration emitted from laser plasma is about the same as the laser pulse. It was shown that using a prepulse with proper intensity and delay time can enhance the x-ray yield considerably. There is an optimum delay time at which maximum xray yield can be produced. The optimum delay time depends on the prepulse intensity.

Introduction: Polymer matrix composites have been thought as insulating materials.Recently, the electrical and optical properties of polymers have been extensively investigated.Polymeric materials with positive nonlinear refractive index are very important in optics.Changes of light-induced refractive index are commonly described by the relationship n=n0+n2I, where n0 is the linear refractive index, I is the intensity of the light and n2 is the nonlinear refractive index coefficient. This phenomenon have considerable effects on the propagation of electromagnetic waves through the medium, which leads to well known effects such as self focusing or defocusing, self phase modulation, self bending and so on.Aim: In this work the effect of RF plasma on the nonlinear optical parameters of red lake doped Polyvinyl Chloride (PVC) polymer film is studied experimentally. Positive nonlinear refractive index of red lake doped PVC and decreasing of this index after RF plasma treatment are two important and interesting phenomena.Materials and Methods: In this experiment red lake doped PVC films are exposed to low pressure RF plasma for 5 to 15 minutes. Different experiments are done to study the effect of RF plasma treatment on the nonlinear optical properties of red lake doped PVC film, include beam broadening measurement, optical limiting measurement and open and closed Zscan experiments.Results: By obtaining the beam profile propagated through treated samples, nonlinear refractive index of red lake doped PVC films is found to be positive. This magnitude is decreased due to plasma treatment. The optical limiting behavior of samples is investigated by measurement of transmission through the sample, which is remained unchanged in comparison with pristine sample. The third order nonlinearity of plasma treated samples is measured using Z-scan method. Experimental results show that real and imaginary parts of nonlinear susceptibility decrease with increasing the time of treatment.Conclusion: Effect of plasma treatment on the nonlinear optical properties of red lake doped commercial PVC film is studied which is a very common way to improve the surface characteristics of polymer films.The nonlinear refractive index and absorption coefficient of this material as well as its third order nonlinear susceptibility are changed where the linear optical parameters of this polymer are remaining unchanged.

Introduction: Energy sources are the most problem in world today, The every day increase of feul price and decrease in its resoures and increase in demands for energy, cuased the attentions change into away to produce more energy with lowest expences, Muon catalyzed fusion is the new and stable source for future.Aim: In this article we determined the Muon catalized fusion in three layer system D/T, T2, D2 and Muon stripping effect that no considered in previous researches.In resent observation find that fusion could be occur from semi stable molecule(dt m)*.Material and Method: in this research we used the all fusin branch in this system and solve equations with Rung Kutta 45-Maple software, that results are in (3), (4), (5) and (6) tables.Results: In this research we use of this branch of fusion and Muon stripping effect, too, that no considered in previous systems [14].Conclusion: calculations show that 82.6 fusion be occur per one Muon and Muon cycling coefficient for the suggested system is compared to the D/T homogeneous system and is shown that which has 18% enhancement to convensional homogeneous D/T system.

Introduction: According to use of neutron capture therapy in treatment of some cancer diseases, controlling and protection instances is unavoidable in use of it.Aim: Whereas the fast neutrons have strong destroyer effects and also for protection against additional absorbed energy (absorbed dose) by tissue during neutron capture therapy and also naught damaging to rest of healthy tissues, and because of destroyer effects of fast neutrons are almost quintuple more than gamma photons, therefore the absorbed energy by tissue must be measured accurately.Material and Method: In this article for neutron capture therapy of a sample tissue such as male’s liver a system by the Monte Carlo method (MCNP4C code) has been simulated and its results with analytical method have been compared.Results: The absorbed dose in the sample liver tissue and absorbed energy in the other component of related system have been obtained accurately for a sample source with energy 17MeV. Also the volumetric flux of determined neutrons in the tissue and other component of system have been obtained.Conclusion: From the obtained information of sample liver tissue which is related to male, the requirement duration of act for achievement to desirable absorbed dose by considering of energy and flux of used neutron source for each liver tissue that must be under neutron capture therapy can be computed.

Introduction: In particle physics, CP violation is a violation of the postulated CP symmetry of the laws of physics. CP violation represents the most delicately broken symmetry observed so far in nature and provides physicists with a powerful phenomenological probe. The violation of CP symmetry is one of the most intriguing aspects of high-energy physics which plays an important role in the theories of cosmology that attempt to explain the dominance of matter over antimatter in the present universe. The study of CP violation remains a vibrant area of theoretical and experimental work today. From 1964, experimenters have searched for CP violation in mesons. Mesons are essential to CP violation. A meson contains one quark and one antiquark, in an equal mixture of matter and antimatter. Family of mesons involves particles like pions, kaons, B and D mesons and etc.Aim: A theoretical tool for CP symmetry breaking has been used and the violation of this symmetry in b quark decays has been investigated.Materials and Methods: In this research, the decay rates of b quark and`b antiquark in tree-level and penguin based on effective Hamiltonian theory have been calculated and the values of CP violation in b quark decays have been obtained by means of them.Results: Relying on quark model of b and`b decays, we have compared theoretical results with experimental ones for CP violation in B meson decays. We consider that b→ ud`u and b →cs`c decays have greatest and smallest values of CP violation, respectively.Conclusion: Various b quark and`b antiquark decay rates in tree-level and penguin, based on effective Hamiltonian theory, calculated. Obviously, when calculating the decay rates of those four decays which only contain tree-level, b → ud`c, b → us`c, b → cd`u and b→ cs`u, Wilson coefficients C3, ..., 6 that carry the gluonic penguin contributions, have been taken equal to zero and hence, there is no difference between quark and antiquark decay rates for these decays. Making use of CP asymmetry relation and using the values of the decay rates in, we calculate CP violation for those b quark decays which have different rate from the corresponding antiquark due to the effect of penguin contribution and presence of Wilson coefficients C3, ..., 6 in effective Hamiltonian formalism.

Introduction: Many of unique phenomenons in atmosphere and ocean are deduced by air-sea interaction that one of them is gravity currents that are occurred in the semi-closed marine environment. These currents as a component of sea waters circulation have effective role on some of the marine activities such as military, communications, fishing, researching and ….Aim: The aim of this paper is: - survey of presence of the outflow gravity currents from Persian Gulf as the component of sea waters circulation- survey of some of characteristics of these currents in Persian Gulf Material and Method: Presence of the outflow gravity currents from Persian Gulf is surveyed by comparison of water salinity and density profile of Persian Gulf with another seas such as Spencer Gulf that Presence of these currents are confirmed by measurements in there. Also, some of characteristics of the outflow gravity currents from Persian Gulf such as velocity, direction and … are determined by solving motion equations under ageostrophic steady condition by dynamical geometrical method of forces projection and using diagrams resulting of collected data by Mount Mitchell ship cruise in February – June 1992 corresponding to ROPME project.Results: This study shows that outflow gravity current from Persian Gulf is a permanent current that amplifies in during February – June and peaks on March.Conclusion: This current with the thickness about 35m, mean velocity about 0.4 m/sec and friction coefficient of order0.783 × 10−3 slips down the slope at an angle of about 7.84o to the isobaths.

Introduction: In the recent years, importance of protection and modification of river water quality has been distinguished, more than last decades. One of the most important rivers in Iran is Karun River. This River is divided to two branches in the end part which have named: Bahmanshir River and Haffar River. Because of establish of water control projects in upstream of Karun River especially in Iran, Turkey and Iraq and existence of tidal currents in downstream of this river, condition of river in salinity point of view is critical and scientific investigation on it should be accomplished.Aim: The main aim of this research is comparison of salinity condition of Karun River in real condition and the results of simulation by MIKE11 model. Salinity front moves toward river in flow condition and moves backward sea in ebb condition. Mixing of fresh water and sea water is occurred because of this phenomenon.Results: The results of modeling show that there isn’t any salinity in the Darkhovein station resulting of tidal currents. There is a low salinity concentration in the Soleimanieh station in 1000 m3/hr river flow according to model results and local measurements. The maximum measured salinity in 200 m3/hr river flow was 960 PSU and results of model show 880 PSU for this condition.Conclusion: Comparison between data of measurement and modeling shows that modeling can be apply as a reliable tool for prediction of behavior of salinity in two phase rivers.

Introduction: Semiconductor nanostructures have attracted much attention due to its application in the development of optoelectronic devices. In these structures the electron spectrum comprises a set of discrete levels. On the other hand, donor impurity in quantum dots can alter the properties of a quantum devices.Aim: Study of the effect of external electric field on the impurity binding energy in a spherical quantum dot.Materials and Method: The energy levels are investigated using variational method within the effective mass approximation and finite barrier potential.Results: The energy of impurity and binding energy are calculated in terms of radius of quantum dot. The binding energy is reduced with increases the radius of dot. The ground state energy of electron, impurity energy, and normalized binding energy versus electric field for different dot radii in finite quantum dot are also calculated.Conclusion: The results show the energies decrease with increases the strength of electric field.

Introduction: Nowadays extraordinary properties of nano world and economical problems are the reasons for directing techniques toward micro implements, electronic circuits dimensions have been reduced to 10 to 100 nano meters. Moreover microstructures in cells with nano meter dimensions have been investigated by biologists, there are structures in electronic and biology which are very similar to the billiards and the electromagnetic waveguides but their dimensions are in nano meter range, therefore they were called quantum waveguides and billiards.Aim: In this research billiards and quantum waveguides at any arbitrary cross sectional area have been investigated.Method: A considerable effort was devoted in solving Helmholtz’s equation with two dimensional cross sectional areas. Linear combinations of plane waves or Heller methods for several types of connective and no connective billiards with regular and irregular shapes have been used. Then eigenvalues and eigenvectors were calculated. At the final part by applying a simple method billiard type (chaotic or quiet) in a quantum scale has been realized.Results and Discussions: In this paper two types of circular and stadium billiards have been studied and by using Heller’s method and applying the numerical solution, energy levels together with the function forms have been attained.Conclusions: This paper shows that Heller’s method despite its quickness and simplicity is a very accurate method for finding eigenvalues and eigenvectors. Although in high eigenvalues the calculation is weighted, nevertheless this method is an acceptable computational method for the investigation of quantum nanobilliards such as quantum points.