Simple Mass Model Research Articles

Tunneling through AlAs barriers: Γ–X transfer current

We have investigated Γ–X intervalley transfer tunneling by measuring currents at low temperature in a series of single AlAs barrier samples grown on GaAs substrates. The transfer occurs at AlAs-GaAs interfaces and is intrinsic because the translational symmetry is broken in the growth direction of the epitaxial layered structures. Calculated current-voltage characteristics employing a simple effective mass model which includes Γ–X transfer at heterointerfaces agree reasonably well with experiments, while calculations assuming only the Γ-band potential predict currents several orders of magnitude lower than experiments.

High-resolution neutral hydrogen observations - The barred spiral galaxy NGC 1300

Observations of the barred spiral galaxy NGC 1300 are reported and compared with theoretical models. Strong spiral structure is seen in the H I gas distribution. These neutral hydrogen arms correspond very well with the optical arms and with H II regions. The central region of the galaxy is gas-poor. This region is approximately the one occupied by the bar, suggesting a dynamical origin for the lack of gas. Analysis of the velocity field yields a systematic velocity of 1575.0 km/s, a position angle for the line of nodes of - 85.5 deg, and an inclination of 50.2 deg. The rotation curve derived from this velocity field rises to a maximum of 185 km/s and then drops slowly out to a distance of 3.2 arcmin. No evidence is seen for a truncation signature in the rotation curve. Simple mass models yielded a mass of 4.9 x 10 to the 10th solar mass for the total galaxy mass. 31 references.

Nitrogen Bound Electrons, Excitons, and Multiexcitons in GaP

AbstractBy means of a simple effective mass model the density functional theory is used to calculate the ground state energy of the exciton at the isolate N impurity. For this purpose, the N potential is adjusted and provides the value known from experiment. This potential offers the basis for the computations of the bound multiexciton complexes at the isolated N impurity and of the electron binding energy at the N pairs. The results so obtained are in good qualitative agreement with the experimental ones.

Complex band structure calculations of the electric field dependence of the transmission of holes through a (100) GaAs/AlGaAs/GaAs barrier structure

A pseudopotential complex band structure approach is used to investigate the transmission of heavy and light holes through a (100) GaAs/AlGaAs/GaAs barrier structure in the presence of an electric field. The results can be significantly different from those obtained using a simple effective mass model. In particular, for an incident light hole there is large barrier induced mixing with the spin-split-off states which reduces the light hole transmission and excites the transmission of spin-split off states. Transmission through a quantum well structure is also considered and significant effects are seen due to the presence of resonances.

Working Load on Specimen in Rapid-Fracture Toughness Test

In order to evaluate dynamic fracture toughness of structural steel, three point bending (3 PB-COD) or compact tension (CT) test is usually carried out by using drop weight or high tensile rate testing machine.Since, in static test, applied load to the specimen can easily measured exactly by load cell of test system, but in dynamic test it is difficult to get or decide working load on test specimen because the effect of acceleration affects on the output of load cell in test system.In this paper, the estimation of working load on test specimen was investigated applying a simple mass and spring model to the loading system of test equipment.

Structural models and undamped torsional natural frequencies of a superconducting turbogenerator rotor

Superconducting turbogenerators with a “double rotor structure” have a torsional natural frequency within the generator, the outer rotor moving in opposition to the inner rotor. For large machines this natural frequency may approach 100 Hz. In this paper a finite element model and simple lumped mass and spring models of the rotor, for the calculation of the undamped torsional natural frequencies, are described and compared. A method by which equivalent spring stiffnesses for both the inner and outer rotors can be derived is described, allowing one to use a rotor model with one lumped mass and equivalent spring stiffness for each of the inner and outer rotors. Such a rotor model can be readily used for studying electromagnetic interaction effects and assessing fault torques in the outer rotor and inner rotor torque tubes.

Globular cluster orbits and the galactic mass distribution

view Abstract Citations (155) References (52) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Globular cluster orbits and the galactic mass distribution. Innanen, K. A. ; Harris, W. E. ; Webbink, R. F. Abstract A list of selected globular clusters has been compiled for which measured tidal radii, luminosites, and distances seem currently most reliable. Using this material, an investigation is conducted of the distribution of cluster perigalactica on the basis of simple galactic mass models having either a logarithmic potential or a point-mass potential. The results give mean perigalactic distances too large to be consistent with published analyses of the cluster radial velocities. The most likely source of this systematic discrepancy appears to be an underestimate of the true cluster m/l ratio by a factor of 2-3, and possible observational errors in the measured tidal radii. It is also found that the observed dispersion of cluster densities at a given galactocentric distance is much smaller than that expected for an isotropic velocity dispersion, even though the observed dispersion is plainly generated mostly by random observational errors. Publication: The Astronomical Journal Pub Date: March 1983 DOI: 10.1086/113320 Bibcode: 1983AJ.....88..338I Keywords: Galactic Mass; Galactic Structure; Globular Clusters; Milky Way Galaxy; Density Distribution; Distance; Kinematics; Luminosity; Mass Distribution; Mass To Light Ratios; Radii; Astrophysics full text sources ADS | data products SIMBAD (61)

Strain dependence of the vibrational modes of a diacetylene crystal

AbstractResonance Raman spectroscopy has been used to measure the strain dependence of four high‐frequency vibrational modes in a single crystal of toluene sulfonate diacetylene polymer. The 0.62‐μm thick crystal was stretched elastically to 4% strain before fracture occurred. This was equivalent to an ultimate tensile strength of 2.0 × 109 N m−2. The strain dependence of the vibrational modes has been interpreted using a simple point mass and anharmonic spring constant model. A Fermi resonance was observed for two vibrational modes which are degenerate at 2.1% strain and a 1464 cm−1 frequency.

Pressure and temperature dependence of the electronic and vibrational excitations of a conjugated polymer crystal

The pressure dependence of reflection, absorption and resonant Raman spectra of single crystals of toluene sulphonate dicetylene polymer have been measured under hydrostatic conditions to 5 kbars. The peak of the reflection spectrum near 2 eV shifted to lower energies with increasing pressure at a rate of 7.3+or-0.3 meV per kbar. This result is shown to be in qualitative agreement with the prediction of molecular orbital calculations. The temperature and pressure dependence of the resonant Raman spectra are discussed using a simple point mass and anharmonic spring constant model.

Temperature and angular dependences of upper critical fields for the layer structure superconductor 2H-NbSe2

The temperature and angular dependences of upper critical fieldsH c2 have been measured for several 2H-NbSe2 single crystals by use of an electrical conduction method in magnetic fields up to 150 kOe. As the temperature approaches the transition temperatureT c , the value ofH c2‖ (parallel to the layer planes) decreases with a positive curvature, while the value ofH c2⊥ (perpendicular to the layer planes) decreases almost linearly. The ratio ofH c2‖ toH c2⊥ increases monotonically from 2.4 nearT c with decreasing temperature and reaches the constant value of 3.2 at the lowest temperature. It becomes clear that the simple effective mass model based on the anisotropic Ginzburg-Landau theory does not explain our experimental results. The anisotropic behavior ofH c2 can be accounted for by the Takanaka theory, which includes anisotropies of both the Fermi velocity and the energy gap and the effect of nonlocality. Agreement between experimental results and the theoretical prediction is obtained by the use of values of 0.16≲e ≲0.25 and −0.6≲e 2 ≲−0.3, where e 1 is the mass anisotropy parameter and e 2 the gap anisotropy parameter. The coupling strength between layers is too strong to be explained by the Josephson phase coupling model proposed for quasi-two-dimensional layer superconductors.

On the Sensitivity of the Behaviour of Stellar Orbits to the Parameters of Simple Galactic Mass Models

Some conjectures are given about the sensitivity of the behaviour of the stellar orbits (appearance of resonant orbits, possible interaction of resonances etc.) to the set of parameters characterizing a simple realistic ‘spheroid + nucleus’ mass model of our Galaxy. Connections with a systematic exploration of orbits in Schmidt mass models are mentioned. Finally we present arguments in favour of the existence of a third integral for the whole solar neighbourhood old stellar populations, independently of the chosen model.

Mathematical modeling of spinning elastic bodies for modal analysis.

The problem of modal analysis of an elastic appendage on a rotating base is examined to establish the relative advantages of various mathematical models of elastic structures and to extract general inferences concerning the magnitude and character of the influence of spin on the natural frequencies and mode shapes of rotating structures. In realization of the first objective, it is concluded that except for a small class of very special cases the elastic continuum model is devoid of useful results, while for constant nominal spin rate the distributed-mass finite-element model is quite generally tractable, since in the latter case the governing equations are always linear, constant-coefficient, ordinary differential equations. Although with both of these alternatives the details of the formulation generally obscure the essence of the problem and permit very little engineering insight to be gained without extensive computation, this difficulty is not encountered when dealing with simple concentrated mass models.