Energetics and vibrational states for hydrogen on Pt(111)

We present a combination of theoretical calculations and experiments for the low-lying vibrational excitations of H and D atoms adsorbed on the Pt(111) surface. The vibrational band states are calculated based on the full three-dimensional adiabatic potential energy surface obtained from first-principles calculations. For coverages less than three quarters of a monolayer, the observed experimental high-resolution electron peaks at 31 and 68 meV are in excellent agreement with the theoretical transitions between selected bands. Our results convincingly demonstrate the need to go beyond the local harmonic oscillator picture to understand the dynamics of this system.     

Q2 Dependence of quadrupole strength in the gamma*p --> Delta(+)(1232) --> p pi(0) transition

Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the gamma*p-->Delta(+)-->p pi(0) transition. We report new experimental values for the ratios E(1+)/M(1+) and S(1+)/M(1+) over the range Q2 = 0.4-1.8 GeV2, extracted from precision p(e,e(')p)pi(0) data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role.     

REDUCING OPERATOR-INDUCED MACHINE VIBRATION USING A COMPLEX POLE/ZERO PREFILTER

A systematic prefilter design process for reducing operator-induced rigid body vibrations of rubber tire mounted machines is presented. The contribution of this work is the development of a systematic prefilter design process and interpretation of the results. The class of heavy equipment considered in this work are those machines having rigid body main frame vibrations dominated by linear dynamics. The reduction in machine vibrations is accomplished through the design of prefilters that reduce the machine resonant frequencies from the operator commands. The machine information required for the design process includes the bandwidth of the electro-hydraulic (E/H) valves and rigid body resonant frequencies of the machine mainframe. The prespecified performance in the design process is the desired attenuation of machine resonant frequencies which is related to the acceptable level of machine vibration. The design methodology has been applied to a telescopic boom lift to illustrate the procedure and the effectiveness of the design.     

Specific heat of single crystal MgB2: a two-band superconductor with two different anisotropies

Heat-capacity measurements of a 39 microg MgB2 single crystal in fields up to 14 T and below 3 K allow the determination of the low-temperature linear term of the specific heat, its field dependence, and its anisotropy. Our results are compatible with two-band superconductivity, the band carrying the smaller gap being isotropic, that carrying the larger gap having an anisotropy of approximately 5. Three different upper critical fields are thus needed to describe the superconducting state of MgB2.     

Synthesis and magnetic properties of Cu0.5Ni0.5Fe2O4 nanoparticles produced by glycothermal and hydrothermal processes

Cu_0.5Ni_0.5Fe₂O₄ nanoparticles have been synthesized in ethylene glycol solution and in deionised water. The glycothermal reaction was carried at 200°C under gauge pressure of 100 psi. The hydrothermal treatment was done at 100°C under zero pressure. Complete single-phase cubic spinel structure in the samples made by glycothermal (sample G) and hydrothermal (sample H) processes formed after annealing at 600°C and 900°C respectively. The coercive field of sample H increases from 72 Oe to 133 Oe after sintering at 700°C and then decrease to 11 Oe on sintering at 1000°C. This variation is attributed to surface effects and crossover from single to multidomain behavior due to increasing particle size.     

Stacking of multilayer InAs quantum dots with combination capping of InAlGaAs and high temperature grown GaAs

We are reporting the growth of multilayer stacks of quantum dots (10 periods) with a combination capping of In_0.21Al_0.21Ga_0.58As (30 Å) and GaAs (70–180 Å) grown by solid source molecular beam epitaxy (MBE). Reflection high energy electron diffraction (RHEED) has been used for the insitu monitoring of quantum dot (QD) formation in heterostructure samples. The samples were also characterized by other exsitu techniques like cross sectional transmission electron microscopy (XTEM) and photoluminescence measurements (PL). For a heterostructure sample with thin barrier thickness (<100 Å), an XTEM image showed the stacking of QDs only up to the 5th layer and in the upper layers there was hardly any formation of dots. We presume the stoppage of dot formation is due to the uneven surface of the InAlGaAs alloy overgrown on the InAs QDs, as a result of the local compositional deviations of the Group-III atoms. Samples grown with thicker barriers (>100 Å of GaAs) showed good stacking of islands until the tenth layer. The thick GaAs layer overgrown on the InAlGaAs at 590 ^°C is believed to remove the surface modifications of the quaternary layer thereby creating a smoother surface front for the growth of subsequent QD layers.     

Ultrasensitive UV-tunable grating in all-solid photonic bandgap fibers

We study the shift of a long period grating’s resonance wavelength with UV induced refractive index changes in an all-solid photonic bandgap fiber. A long period grating is mechanically imprinted in an all-solid photonic bandgap fiber with Germanium doped silica high-index rods in a lower-index silica background. The index of the high-index rods is modified through UV exposure, and we observe that the long period grating’s resonance shifts with the bandgaps. With a sensitivity of 21,000 nanometers per refractive index unit and a 8.8 nm resonance width changes of refractive index of 3 × 10⁻⁶ are in principle detectable