Element Calculations Research Articles

Large magnetic anisotropy and tunneling anisotropic magnetoresistance in layered bimetallic nanostructures: Case study of Mn/W(001)

We predict large magnetic anisotropy energy (MAE) and tunneling anisotropic magnetoresistance in bimetallic $3d\text{\ensuremath{-}}4(5)d$ transition-metal structures which properly balance conditions to maximize moment on the magnetic $3d$ atom, exchange coupling between the $3d$ and $4(5)d$ elements, and magnetic susceptibility and spin-orbit coupling of the $4(5)d$ metal. Our ab initio MAE value of 5.57 meV/Mn atom and relative density-of-states anisotropies of $\ensuremath{\sim}100%$ in the ferromagnetic state of Mn overlayer on W(001) surface demonstrate that the optimal structures may contain unconventional combinations of transition metals. Results are interpreted by employing element and layer specific torque calculations of the MAE. It is shown that large MAE mainly comes from itinerant $5d(\text{W})\text{-atom}$ magnetic moments at the interface and subinterface which are induced by exchange coupling with localized $3d(\text{Mn})\text{-atom}$ moments. To relate these highly anisotropic transition-metal structures to potential applications we also provide estimates of the Curie temperature and the magnetic recording density that can be achieved for system parameters corresponding to our model ferromagnetic Mn/W(001) structure.

An iterative algorithm for magnetic induction modulus inversion

An iterative algorithm is proposed for magnetic induction modulus inversion. The iterative process is based on a recurrence relation for the squared induction modulus, which can be represented at each iteration step by a system of linear algebraic equations for components of the magnetization vector. Formulas for the calculation of matrix elements of this system and the determination of the magnetization at the next iteration step are given. Model and practical examples illustrating the reconstruction of magnetization and anomalous field components are presented.

Muon capture rates in Se and Cd isotopes

Energy and time spectra of γ rays following nuclear capture of negative muons in natural Se and Cd and isotopically enriched 76Se and 106Cd targets have been measured with HPGe detectors. Total muon lifetimes in Se and Cd isotopes and partial μ capture rates to excited levels of 76As and 106Ag are obtained. These results are necessary for calculation of nuclear matrix elements of the 2β decay of 76Ge and 106Cd respectively.

Preliminary orbit determination of a tethered satellite using the f and g series

A renewed interest in the deployment of tethered satellites has led to a need for a preliminary orbit determination method which is capable of distinguishing tethered satellites from untethered ones. Several of the classical preliminary orbit determination methods, which are used for Keplerian satellites, generally require two or more position vectors along with their respective observation times in order to determine a preliminary orbital element set. These conventional methods, however, are unable to distinguish between Keplerian and tethered satellites, whose motion is modified due to the presence of a tether force. The use of these conventional methods will result in the calculation of inaccurate orbital elements if the observed satellite is part of a tethered satellite system. Modifications have been made to the f and g series preliminary orbit determination method in order to allow for the identification of tethered satellites. These modifications allow for the calculation of a gravitational parameter, in addition to a set of orbital elements, which can be used to distinguish between a tethered satellite and an untethered one. This paper applies this modified f and g series method to the problem of the quick identification of a tethered satellite. The performance of this method is evaluated through scenarios of differing tether lengths, levels of observation error, and orbital eccentricities. Due to the desire for the preliminary orbit determination to be achieved quickly, only short time intervals between observations were considered. A description of how this preliminary orbit information can be used to obtain tether parameters for the subsequent differential correction process is also provided.

Fatigue crack propagation in tensile shear stainless steel spot welded specimens

ABSTRACTFatigue tests were carried out on 4 mm thick spot welded joints; the material was stainless steel AISI 301, quarter hard. Some specimens were instrumented with a strain gauge bonded in correspondence with one of the edges of the spot weld. Strain gauge output was demonstrated to be a reliable instrument to monitor the nucleation and propagation of fatigue cracks. A good correlation was found between strain gauge output and spent fatigue life. Some fatigue tests were suspended when the strain gauge output was equal to pre‐fixed values, corresponding to fatigue life in the range from 15 to 85%. Subsequently, the specimens were dissected to observe fatigue cracks. The same correlation existed between crack depth and fatigue life. Small cracks were observed in specimens fatigue tested up to 15% of the mean fatigue life; fatigue cracks in the joints under examination would be nucleated between 5 and 10% of fatigue life.Finite Element calculations were carried out, introducing in the models cracks similar to those observed in the fatigue tests. Calculated strain at the external surface compared well with the measured strain as a function of crack depth. Calculations demonstrated that small errors in strain gauge position can be tolerated without appreciable deterioration in crack dimension prediction.

Fast Algorithm to Extract the Singularity of Higher Order Moment Method

The higher order moment method has far fewer unknowns compared to the low order methods. However, the computation of the self-term matrix elements is extremely time-consuming. This paper presents an algorithm to extract the singularity by dividing the integrand into two parts on account of Taylor's formula. The integrand of the first part with a removable discontinuity is easy to be integrated. The rest part consists of three principal singular functions. Their singularities are canceled by the Jacobian of a simple transformation. This singularity extraction leads to a rapid non-redundant integration. Numerical results prove that this algorithm is more than 20 times faster than the old method.

Single top-quark production by strong and electroweak supersymmetric flavor-changing interactions at the LHC

We report on a complete study of the single top-quark production by direct supersymmetric flavor-changing neutral-current (FCNC) processes at the LHC. The total cross section, σ(pp(gg) → + ), is computed at the 1-loop order within the unconstrained Minimal Supersymmetric Standard Model (MSSM). The present study extends the results of the supersymmetric strong effects (SUSY-QCD), which were advanced by some of us in a previous work, and includes the computation of the full supersymmetric electroweak corrections (SUSY-EW). Our analysis of σ(pp(gg) → + ) in the MSSM has been performed in correspondence with the stringent low-energy constraints from b → sγ. In the most favorable scenarios, the SUSY-QCD contribution can give rise to production rates of around 105 events per 100 fb−1 of integrated luminosity. Furthermore, we show that there exist regions of the MSSM parameter space where the SUSY-EW correction becomes sizeable. This could be important, especially if the SUSY-QCD effects would be suppressed. In the SUSY-EW favored regions, one obtains lower, but still appreciable, event production rates that can reach the 103 level for the same range of integrated luminosity. We study also the possible reduction in the maximum event rate obtained from the full MSSM contribution if we additionally include the constraints from the B0s−0s. However, we treat these restrictions at a different level from the b → sγ ones, due to the higher uncertainties inherent in the calculation of the matrix element associated to that mixing. In view of the fact that the FCNC production of heavy quark pairs of different flavors, such as or , is extremely suppressed in the SM, the detection of a significant number of these events could lead to evidence of new physics — of likely supersymmetric origin.

Stress Distribution in Be Compact Tension Specimen

Beryllium (Be) is susceptible to introduce stress because it is a brittle metal with a high elastic modular. The compact tension (CT) specimens of beryllium were designed to determinate stress and fracture behaviors. Stress distribution near notch in CT beryllium was measured by the combination of an X-ray stress analysis and a custom-designed load device. The results show that local stresses near notch tip are much higher than those on other area. Thus, stress concentration lead the CT specimens fracture along the notch direction. Residual stresses due to machining are remained. A finite element ( FE ) calculation on the same loaded geometry was made, and the result is agreement with the measured stress distribution near notch.

Microstructure Reconstruction and Numerical Simulation of Deformation in Particle-Reinforced Composites

A new methodology of computer simulation is proposed to perform finite element (FE) calculations of uniaxial tensile deformation on the three-dimensional (3D) complex microstructures, through its application to the microstructure of aluminum matrix containing randomly distributed and oriented SiC particles of highly variable and angular geometry. Compared with the simplified microstructure model, the complex microstructure model shows significant differences in terms of micromechanical fields and macroscopic uniaxial deformation. The results reveal that a quantitative and convenient reconstruction of microstructure of particulate composites is crucial for both the prediction and design of material properties.

Eligibility of spherical-well approximation for calculations of nucleon-transfer matrix elements

Single-particle matrix elements of nucleon transfer were calculated by the Woods-Saxon potential wave functions. The results are compared with the ones calculated by the spherical-well approximation. The eligibility of the approximation of the mean field of nuclei by the spherical well to study the initial stage of nuclear reactions at heavy-ion collisions is demonstrated.

Novel carbonaceous coupling products containing sulphur

The coupling of alkali ethynides with CSCl2, SOCl2, or SO2Cl2 results in new carbonaceous polymeric products; their structures were studied by FTIR and XPS spectra, and the assumptions on reaction mechanism were made with respect to the found elemental composition and model calculations. These macromolecular products, obtained in the yields of 80–92%, contain chlorine in the chain terminals, and alkyne sequences along with inserted C=S, S=O or SO2 groups. These inserted sulphur groups contribute to the stability of alkyne sequences as evidenced by FTIR spectra. Soluble thioketone iPr3SiC≡C–CS–C≡CSiiPr3 (2) prepared by similar coupling of iPr3SiC≡CLi (1) with CSCl2 in the yield of 72%, was considered as a support of the suggested coupling mechanism. Similarly monomolecular sulfoxide iPr3SiC≡C–SO–C≡CSiiPr3 (3) was prepared by coupling of iPr3SiC≡CLi (1) with SOCl2 in the yield 75%.

Unique second-forbidden β transitions: Decay of 137Cs

The intensity of the 283.4-keV γ line in the decay of 137Cs has been measured. The value obtained is used to determine the probability of the unique second-forbidden β transition of the 7/2+ → 1/2+ type: (8.7 ± 2.0) × 10−4% of the number of decays; this value corresponds to log f2unt = 16.45 ± 0.12. The intensity of the possible E5 transition at 378.3 keV is estimated to be < 0.9 × 10−4%. The technique for determining the values of log f2unt in calculations of the tensor matrix elements in the Cartesian and spherical coordinate systems is discussed. The possible intensity of the unique second-forbidden β transition between the ground states of 129I and 129Xe is estimated to be Iβ ≈ 0.1% of the number of decays of 129I.

Simplified mesh techniques for design of beam-shaping diffractive optical elements

This paper describes a simplified mesh generation technique that is based on the finite element method of calculation of beam-shaping diffractive optical elements (DOEs). The mesh generation technique uses the inherent symmetry of the incident beam to generate a mesh. Using the meshes so generated, DOEs that convert a Gaussian intensity beam to one of a specified shape, are calculated. Simulations of the results of such beam-shaping elements will be presented. Such elements have uses in industrial and medical applications where both the shape as well as the intensity distribution on the material that is to be processed is very important. For example, in industrial applications the beam may be used to uniformly heat up a specific area in which case the intensity has to be uniform across the beam. The Gaussian intensity variation of a laser has to be converted to a flat-top beam in order to achieve this. To reiterate, beam shaping refers to changing both the intensity distribution and the shape of the beam. Experimental results of the fabricated gratings will also be presented. These results will include experimental data on the method of additive lithography which can be used to improve the efficiency of DOEs.

Excited baryons and heavy pentaquarks in large- Nc QCD

We briefly discuss the large-N c picture for excited baryons, present a new method for the calculation of matrix elements and illustrate it by computing the strong decays of heavy exotic states.

A symbolic-numerical algorithm for the computation of matrix elements in the parametric eigenvalue problem

A symbolic-numerical algorithm for the computation of the matrix elements in the parametric eigenvalue problem to a prescribed accuracy is presented. A procedure for calculating the oblate angular spheroidal functions that depend on a parameter is discussed. This procedure also yields the corresponding eigenvalues and the matrix elements (integrals of the eigenfunctions multiplied by their derivatives with respect to the parameter). The efficiency of the algorithm is confirmed by the computation of the eigenvalues, eigenfunctions, and the matrix elements and by the comparison with the known data and the asymptotic expansions for small and large values of the parameter. The algorithm is implemented as a package of programs in Maple-Fortran and is used for the reduction of a singular two-dimensional boundary value problem for the elliptic second-order partial differential equation to a regular boundary value problem for a system of second-order ordinary differential equations using the Kantorovich method.

Speeding Up PEEC Partial Inductance Computations Using a QR-Based Algorithm

The partial element equivalent circuit (PEEC) approach has been used in different forms for the computation of equivalent circuit elements for quasi-static and full-wave electromagnetic models. In this paper, we focus on the topic of large scale inductance computations. For many problems as part of PEEC modeling, partial inductances need to be computed to model interactions between a large numbers of objects. These computations can be very time and memory consuming. To date, several techniques have been devised to reduce the memory and time required to compute the partial inductance entities, as well as the time required to use them in a circuit analysis compute step. Some of the existing methods use hierarchical compression while some others are based on issues like properties of the inverse of the partial inductance matrix. However, because of inherent limitations, most of these methods are less suitable for PEEC applications. In this paper, we present an approach which is based on the compression of the partial inductance matrix utilizing the QR decomposition of the far coefficients submatrices. The QR-decomposed form is represented as a compressed SPICE-compatible circuit. This yields an efficient and mathematically consistent approach for reducing the storage and time requirements

Preliminary orbit determination of a tethered satellite

Interest in the deployment of tethered satellites has led to a need for preliminary orbit determination methods which are capable of distinguishing tethered satellites from untethered ones. Classical preliminary orbit determination methods, which are used for Keplerian satellites, generally require two or more position vectors along with their respective observation times in order to determine a preliminary orbital element set. These conventional methods, however, are unable to distinguish between Keplerian and tethered satellites, whose motion is modified due to the presence of a tether force. The use of conventional methods result in the calculation of inaccurate orbital elements if the observed satellite is part of a tethered satellite system. Modifications have been made to four classical preliminary orbit determination methods in order to allow for the identification of tethered satellites. These modifications provide the ability to distinguish between a tethered satellite and an untethered one. This paper applies these modified preliminary orbit determination methods to the problem of the identification of a tethered satellite. The performance of these methods is evaluated through scenarios of differing tether lengths and levels of observation error, and results are compared in order to determine the most accurate method.

Grating coupling elements for high-Q resonators and rectangular waveguides of the millimeter wave band

Techniques for electrodynamic-level calculation of slot-grating wideband coupling elements for single-mode waveguides are developed. New coupling devices that ensure the obtaining of a voltage standing-wave ratio of 1.6 in the entire tuning range of a resonator without readjustment of the coupling element are designed and tested experimentally. It is found that application of new coupling devices in resonators do not deteriorate the loaded Q factor of the resonator.

Analysis of Extra-Solar Planetary Transits Using Tools from Eclipsing Binaries

Analytical formulae for the computation of the photometric elements of extra-solar planetary transits are presented. They were initially derived for the study of well-detached eclipsing binaries and are valid for any degree of limb darkening and type of transit as well as for eccentric orbits. The only assumption is that the projections of the star and the planet on the plane of the sky are well represented by circular discs. The procedure to get valid ranges for the involved parameters, as well as to make precise estimations of initial parameters, using the analytical nature of the equations is given together with some discussion on their practical application. Examples are shown for OGLE-TR-113, representative of a light curve obtained with ground-based telescopes, and HD 209458 with a precise light curve obtained with the Hubble Space Telescope.

Temperature dependence of the inelastic electron tunneling

The property of the anomalous inverted region in the energy gap law which was found in the recent non-Condon theory of the electron transfer (ET) in protein media is investigated in more detail in relation to the inelastic electron tunneling. The physical aspect of the inelastic electron tunneling is theoretically discussed and schematically explained. Since it was previously shown that the inelastic electron tunneling mechanism worked significantly due to an exponential-like decay of the autocorrelation function of the electron tunneling matrix element with a small correlation time at 300 K, we investigated whether the similar exponential-like decay of the autocorrelation function is obtained or not and how the correlation time is changed at low temperatures. For this purpose, numerical calculations for the electron tunneling matrix element in the ET at 77 K from bacteriopheophytin (Bph) anion to the primary quinone in the reaction center of photosynthetic bacteria Rhodobacter sphaeroides are made. The results are that almost exponential-like decay of the autocorrelation function was obtained even at 77 K and the half decay time was of the similar magnitude to that at 300 K. Physical meaning of this temperature dependence is discussed.