Magnetic properties in different fullerenes Xn nano-structures: Monte Carlo study

The aim of this work is to study the magnetic properties in deferent fullerenes X_n like nano-structures, where the symbol X can be assigned to any magnetic atom and “n” is the number of these magnetic atoms. Our study is based on the fullerenes: C₂₀, C₆₀ and C₇₀, formed by atoms with mixed spins σ = 1 and S = 1/2. We focus our interest on the examination of the influence of the coupling exchange interactions between atoms, the external magnetic and the crystal fields. Also, we present and discuss the nature of the corresponding ground state phase diagrams. The effect of the compensation and critical temperatures is also presented for different magnetization profiles by using the Monte Carlo simulations. The behavior of the total magnetizations as a function of the physical system parameters is also analyzed and discussed, in this study.     

A percolation study of RTS noise in deep sub-micron MOSFET by Monte Carlo simulation

Based on percolation theory and random telegraph signal (RTS) noise generation mechanism, a numerical model for RTS in deep submicron metal-oxide-semiconductor field-effect transistor (MOSFET) was presented, with which the dependence of Tc/Te (where Tc=capture time, Te=emission period ) on energy levels and trap depth with respect to the interface of traps can be simulated. Compared with experimental results, the simulated ones showed a good qualitative agreement.     

A Monte Carlo study for the shielding of γ backgrounds induced by radionuclides for CDEX

The CDEX(China Dark matter EXperiment)Collaboration will carry out a direct search for WIMPs(Weakly Interacting Massive Particles)using an Ultra-Low Energy Threshold High Purity Germanium(ULE-HPGe)detector at the CJPL(China JinPing deep underground Laboratory).A complex shielding system was designed to reduce backgrounds and a detailed GEANT4 Monte Carlo simulation was performed to study the achievable reduction of T rays induced by radionuclides and neutron backgrounds by D(γ,n)p reaction.Furthermore,the upper level of allowed radiopurity of shielding materials was estimated under the constraint of the expected goal.Compared with the radiopurity reported by other low-background rare-event experiments,it indicates that the shielding used in the CDEX can be made out of materials with obtainable radiopurity.     

A Monte Carlo study for the shielding of γ backgrounds induced by radionuclides for CDEX

The CDEX (China Dark matter EXperiment) Collaboration will carry out a direct search for WIMPs (Weakly Interacting Massive Particles) using an Ultra-Low Energy Threshold High Purity Germanium (ULE-HPGe) detector at the CJPL (China JinPing deep underground Laboratory). A complex shielding system was designed to reduce backgrounds and a detailed GEANT4 Monte Carlo simulation was performed to study the achievable reduction of γ rays induced by radionuclides and neutron backgrounds by D(γ,n)p reaction. Furthermore, the upper level of allowed radiopurity of shielding materials was estimated under the constraint of the expected goal. Compared with the radiopurity reported by other low-background rare-event experiments, it indicates that the shielding used in the CDEX can be made out of materials with obtainable radiopurity.     

Self-evolving atomistic kinetic Monte?Carlo: fundamentals and applications

The fundamentals of the framework and the details of each component of the self-evolving atomistic kinetic Monte Carlo (SEAKMC) are presented. The strength of this new technique is the ability to simulate dynamic processes with atomistic fidelity that is comparable to molecular dynamics (MD) but on a much longer time scale. The observation that the dimer method preferentially finds the saddle point (SP) with the lowest energy is investigated and found to be true only for defects with high symmetry. In order to estimate the fidelity of dynamics and accuracy of the simulation time, a general criterion is proposed and applied to two representative problems. Applications of SEAKMC for investigating the diffusion of interstitials and vacancies in bcc iron are presented and compared directly with MD simulations, demonstrating that SEAKMC provides results that formerly could be obtained only through MD. The correlation factor for interstitial diffusion in the dumbbell configuration, which is extremely difficult to obtain using MD, is predicted using SEAKMC. The limitations of SEAKMC are also discussed. The paper presents a comprehensive picture of the SEAKMC method in both its unique predictive capabilities and technically important details.     

Coupled structural and magnetic properties of ferric fluoride nanostructures: Part II,a Monte Carlo–Heisenberg study

We present a numerical study of the magnetic structure of nanostructured iron fluoride, using the Monte Carlo Metropolis simulated annealing technique and a classical Heisenberg Hamiltonian with superexchange angle dependent interactions. The parameters are adjusted on experimental results, and the atomic structure and topology taken from a previous atomistic model of grain boundaries in the same system. We find perfect antiferromagnetic crystalline grains and a disordered magnetic configuration (speromagnetic) at the grain boundary, in agreement with experimental features. Both the lowest magnetic energy and the rate of magnetic frustration are found to be dependent on the relative disorientation of crystalline grains, i.e. on the cationic topology. We conclude on possible extensions of the model.     

A study of fluorescence properties of citrinin in β-cyclodextrin aqueous solution and different solvents

Citrinin (CIT) is a nephrotoxic mycotoxin initially isolated from filamentous fungus Penicilliu citrinum. It was later isolated from several other species, such as Aspergillus and Monascus. It has a conjugated, planar structure that gives it a natural fluorescence ability, which can be used to develop sensitive methods for detecting CIT in food. In this paper, we used the spectro?uorescence technique to study the effects of pH value, β-cyclodextrin (β-CD) and organic solvents on the CIT fluorescence intensity. The results show that lower pH value, aceitc acid, β-CD and acetonitrile can induce a higher fluorescence intensity of CIT, but methanol or H₂O has a decreasing effect on the fluorescence intensity of CIT. Findings in this study provide a theoretical basis for development of a high sensitivity fluorescence-based trace analysis for CIT detection.     

A Monte Carlo Study on the Identification of Quark and Gluon Jets

Three-jet events in e^ e^- collisions at 91.2 GeV are investigated using both HERWIG and JETSET Monte Carlo generators.The angles among the three jets are used to identify the quark and gluon jets.An analysis at the parton level is carried out to ensure the reasonableness of this method and an angular cut is utilized to improve the purity of this identification.The multiplicity inside the identified quark or gluon jets agrees with the quantum chromodynamic predictions qualitatively.     

How universal are the low temperature acoustic properties of glasses?

We evaluated already published data on ultrasound absorption and velocity changes below 1 K for a set of 18 different glasses. By uniformly analysing these data according to the tunnelling model we have calculated the standard spectral density of two-level-systems (TLS) and their coupling energy ₁ and ₁ to longitudinal and transversal phonons. Contrary to literature, we have not observed any correlation between and the glass transition temperatureT _g for our set of 18 glasses. As far asT _g is concerned we only found a relation _min ^0.1K withn2.5 and where _min is the shortest TLS-phonon relaxation time at 0.1 K. Since the values for and _1,t scatter within half an order of magnitude, we conclude that the TLS parameters of a certain glass are only weakly dependent on bulk properties. We find that the ratio _t ² /C ₄₄ (whereC ₄₄ is the shear elastic constant) is a more sensitive parameter for tests on the variation of the TLS spectral density of glasses.     

Numerical study of translational nonequilibrium in an He–Xe mixture by direct simulation Monte Carlo

The distributions of pairs of particles over relative velocities at the shock wave front in He with a small Xe additive have been studied. It has turned out that the values of the distributions over relative velocities for an Xe–Xe atomic pair far (up to 10⁹ times) exceed their equilibrium values behind a shock wave within a narrow part of its front at high velocities of the wave and small Mach numbers (M = 2). This feature is lacking in the distributions of He–Xe atomic pairs over relative velocities.     

How hidden are hidden processes? A primer on crypticity and entropy convergence

We investigate a stationary process's crypticity--a measure of the difference between its hidden state information and its observed information--using the causal states of computational mechanics. Here, we motivate crypticity and cryptic order as physically meaningful quantities that monitor how hidden a hidden process is. This is done by recasting previous results on the convergence of block entropy and block-state entropy in a geometric setting, one that is more intuitive and that leads to a number of new results. For example, we connect crypticity to how an observer synchronizes to a process. We show that the block-causal-state entropy is a convex function of block length. We give a complete analysis of spin chains. We present a classification scheme that surveys stationary processes in terms of their possible cryptic and Markov orders. We illustrate related entropy convergence behaviors using a new form of foliated information diagram. Finally, along the way, we provide a variety of interpretations of crypticity and cryptic order to establish their naturalness and pervasiveness. This is also a first step in developing applications in spatially extended and network dynamical systems.     

A critical behavior of the Lennard–Jones dimeric fluid in two-dimensions.: A Monte Carlo study

Monte Carlo simulation with hyper-parallel tempering, the histogram reweighting and finite-size scaling techniques are used to explore the critical behavior of Lennard-Jones fluids of dimers in the two-dimensional system. The dimers are built of two distinct segments. The critical parameters for selected types of dimers are estimated. We analyze the influence of the bond length and differences in the chemical nature of segments on the critical parameters. The results can be used to predict the critical parameters of dimers whose molecular parameters are known.     

Statistical properties of excited nuclei in the mass range 47 ? A ? 59

Level densities and their energy dependences for nuclei in the mass range of 47 ?? A ?? 59 were determined from the results obtained by measuring neutron-evaporation spectra in respective (p, n) reactions. The spectra of neutrons originating from the (p, n) reactions on ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, ⁵³Cr, ⁵⁴Cr, ⁵⁷Fe, and ⁵⁹Co nuclei were measured in the proton-energy range of 7?C11 MeV. These measurements were performed with the aid of a fast-neutron spectrometer by the time-of-flight method over the base of the EGP-15 pulsed tandem accelerator installed at the Institute for Physics and Power Engineering (Obninsk, Russia). A high resolution of the spectrometer and its stability in the time of flight made it possible to identify reliably discrete low-lying levels along with the continuum part of neutron spectra. Our measured data were analyzed within the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations were performed with the aid of the Hauser-Feshbach formalismof statistical theory supplemented with the generalized model of a superfluid nucleus, the back-shifted Fermi gas model, and the Gilbert-Cameron composite formula for nuclear level densities. Nuclear level densities for ⁴⁷V, ⁴⁸V, ⁴⁹V, ⁵³Mn, ⁵⁴Mn, ⁵⁷Co, and ⁵⁹Ni and their energy dependences were determined. The results are discussed and compared with available experimental data and with recommendations of model-based systematics.     

Calculation of Internal Energy and Pressure of Dense hydrogen Plasma by Direct Path Integral Monte Carlo Approach

The internal energy and pressure of dense hydrogen plasma are calculated by the direct path integral Monte Carlo approach. The Kelbg potential is used as interaction potentials both between electrons and between protons and electrons in the calculation. The complete formulae for internal energy and pressure in dense hydrogen plasma derived [or the simulation are presented. The correctness of the derived formulae are validated by the obtained simulation results. The numerical results are discussed in details.     

How important are columnar cacti as sources of water and nutrients for desert consumers? A review

Succulent CAM plants, such as columnar cacti, are important physiognomic elements of many arid lands. Although, these plans are often ecologically important because they provide abundant resources in the form of nectar and fruit, their contribution to the energy, nutrient and water budgets of consumes has not been quantified. We describe an isotopic approach that allows quantifying the ecological importance of CAM succulents. We first briefly review our work on the interaction between saguaros, an archetypical CAM succulent, and the desert doves that feed on its fruit. We then describe the potential importance of saguaro fruit as a function of its abundance, macronutrient composition, and seasonal availability. We argue that the resources provided by saguaros do much to satisfy the energy and water requirements of the birds that reside in hot subtropical deserts during the summer. We then describe the carbon isotope composition of saguaros and of the plant community in which they are imbedded and use two species of desert doves to illustrate how stable isotopes can reveal the importance of a single plant as a source of carbon and water for consumers. The second section of this review presents new data on the importance of saguaros for the entire community of birds that inhabit the Sonoran Desert during the summer. We show how the resources of saguaro reach across dietary guilds and account for a large proportion of the diet of many insectivorous species as well as that of granivorous and frugivorous species. We demonstrate that many of these species probably obtain significant water as well as nutrients from saguaro fruit. Finally, we point out the current limitations of using deuterium as a water tracer in animal systems.