Evolutionary approach for finding the atomic structure of steps on stable crystal surfaces

The problem addressed here can be concisely formulated as follows: Given a stable surface orientation with a known reconstruction and given a direction in the plane of this surface, find the atomic structure of the steps oriented along that direction. We report a robust and generally applicable variable-number genetic algorithm for determining the atomic configuration of crystallographic steps, and exemplify it by finding structures for several types of monatomic steps on Si(114)-2×1. We show that the location of the step edge with respect to the terrace reconstructions, the step width (number of atoms), and the positions of the atoms in the step region can all be simultaneously determined

The stability of strained H:Si(105) and H:Ge(105) surfaces

We report atomic scale studies of the effect of applied strain and hydrogen environment on the reconstructions of the (105) Si and Ge surfaces. Surface energy calculations for monohydride-terminated (001) and (105) reconstructions reveal that the recently established single-height rebonded model is unstable not only with respect to (001), but also in comparison to other monohydride (105) structures. This finding persists for both Si and Ge, for applied biaxial strains from -4% to 4%, and for nearly the entire relevant domain of the chemical potential of hydrogen, thus providing an explanation for the recently observed H-induced destabilization of the Ge(105) surface

Harnessing Intellectual Resources in a Collaborative Context to Create Value

The value of electronic collaboration has arisen as successful organisations recognize that they need to convert their intellectual resources into customized services. The shift from personal computing to interpersonal or collaborative computing has given rise to ways of working that may bring about better and more effective use of intellectual resources. Current efforts in managing knowledge have concentrated on producing; sharing and storing knowledge while business problems require the combined use of these intellectual resources to enable organisations to provide innovative and customized services. In this chapter the collaborative context is developed using a model for electronic collaboration through the use of which organisations may mobilse collaborative technologies and intellectual resources towards achieving joint effect.electronic collaboration;value creation;collaborative computing;knowledge management and intellectual resources

From infall to rotation around young stellar objects: A transitional phase with a 2000 AU radius contracting disk?

Evidence for a transitional stage in the formation of a low-mass star is reported, intermediate between the fully embedded and the T Tauri phases. Millimeter aperture synthesis observations in the HCO+ J=1-0 and 3-2, HCN 1-0, 13CO 1-0, and C18O 1-0 transitions reveal distinctly different velocity fields around two embedded, low-mass young stellar objects. The 0.6 M(sun) of material around TMC 1 (IRAS 04381+2517) closely follows inside-out collapse in the presence of a small amount of rotation (~3 km/s/pc), while L1489 IRS (IRAS 04016+2610) is surrounded by a 2000 AU radius, flared disk containing 0.02 M(sun). This disk shows Keplerian rotation around a ~0.65 M(sun) star and infall at 1.3 (r/100 AU)^-0.5 km/s, or, equivalently, sub-Keplerian motions around a central object between 0.65 and 1.4 M(sun). Its density is characterized by a radial power law and an exponential vertical scale height. The different relative importance of infall and rotation around these two objects suggests that rotationally supported structures grow from collapsing envelopes over a few times 10^5 yr to sizes of a few thousand AU, and then decrease over a few times 10^4 yr to several hundred AU typical for T Tauri disks. In this scenario, L1489 IRS represents a transitional phase between embedded YSOs and T Tauri stars with disks. The expected duration of this phase of ~5% of the embedded stage is consistent with the current lack of other known objects like L1489 IRS. Alternative explanations cannot explain L1489 IRS's large disk, such as formation from a cloud core with an unusually large velocity gradient or a binary companion that prevents mass accretion onto small scales. It follows that the transfer and dissipation of angular momentum is key to understanding the formation of disks from infalling envelopes.Comment: Accepted ApJ. 33 pages, including 10 B/W figures and 1 color figure. Uses AASTe

Reading on the Ropes: A Pilot Study of an Accelerated Remediation Program with Alternative High School Students

High school students must read to learn curriculum, yet few interventions are proven to substantially help close literacy gaps for older students with reading deficits. Students with large literacy deficits particularly benefit from explicit, systematic instruction of interventions emphasizing the structure of language (i.e., phonology, orthography, syntax, morphology, semantics, pragmatics), aspects of cognition (i.e., problem solving, attention, reasoning, and inferencing), and organization of spoken and written language. A 14-week pilot study of Readable English, a reading intervention using these structured literacy elements, provided embedded interactive orthography to scaffold online grade level content for students at two alternative high schools (N = 25). Students in the treatment group showed significant and meaningful increases in standardized tests of reading accuracy, fluency, and reading comprehension compared to minimal or no gains in the control group. Transfer effects from students using the Readable English markup to reading in standard English were demonstrated. Implications for use as accelerated remediation intervention for older adolescents are discussed

Simultaneous Inversion of cross-dipole acoustic waveforms in anisotropic media for azimuthal angle and dispersion of fast and slow shear waves

A method to jointly invert for azimuthal angle and dispersion relations from cross-dipole data is presented. Dispersion curves from the joint inversion are compared to both Prony’s method and a simple back propagation schema and an agrrement is found. The azimuthal angle estimate is shown to differ from a frequency domain rotaion that takes no account of dispersion within the waveforms indicating the importance of joint inversion.Massachusetts Institute of Technology. Earth Resources LaboratoryMassachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu

FermiFermi GBM Observations of V404 Cyg During its 2015 Outburst

V404 Cygni was discovered in 1989 by the $Ginga$ X-ray satellite during its only previously observed X-ray outburst and soon after confirmed as a black hole binary. On June 15, 2015, the Gamma Ray Burst Monitor (GBM) triggered on a new outburst of V404 Cygni. We present 13 days of GBM observations of this outburst including Earth occultation flux measurements, spectral and temporal analysis. The Earth occultation fluxes reached 30 Crab with detected emission to 100 keV and determined, via hardness ratios, that the source was in a hard state. At high luminosity, spectral analysis between 8 and 300 keV showed that the electron temperature decreased with increasing luminosity. This is expected if the protons and electrons are in thermal equilibrium during an outburst with the electrons cooled by the Compton scattering of softer seed photons from the disk. However, the implied seed photon temperatures are unusually high, suggesting a contribution from another source, such as the jet. No evidence of state transitions is seen during this time period. The temporal analysis reveals power spectra that can be modeled with two or three strong, broad Lorentzians, similar to the power spectra of black hole binaries in their hard state

Equivalence of the Path Integral for Fermions in Cartesian and Spherical Coordinates

The path-integral calculation for the free energy of a spin-1/2 Dirac-fermion gas is performed in spherical polar coordinates for a flat spacetime geometry. Its equivalence with the Cartesian-coordinate representation is explicitly established. This evaluation involves a relevant limiting case of the fermionic path integral in a Schwarzschild background, whose near-horizon limit has been shown to be related to black hole thermodynamics.Comment: 16 page