6,645 research outputs found
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)-2Ă1. 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
Relationships between Texas tortoise carapace length, home range size, and habitat selection at sites with invasive grass
Invasive grasses in south Texas have the potential to negatively impact the threatened Texas tortoise (Gopherus berlandieri) by reducing the availability of preferred foods (forbs) and may cause tortoises to travel farther, lead to reduced carapace length, and reduce the availability of refugia from heat stress. I used compositional analysis, regression, and ANOVA to explore relationships between invasive grasses and habitat use, home range size, and carapace length, as well as compared daily maximum temperatures between tussocks of an invasive and native grass. Forbs were ranked higher in use over invasive grasses in compositional analysis, but not strongly so (p\u3e0.05), and there was no correlation between home range size and invasive grass or forb cover. Female tortoise carapace length was positively correlated with forb cover (R2=0.106; p=0.005). Temperatures inside invasive grass tussocks were warmer and exceeded the stress point of tortoises more often than in native grass
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
Entangled Wavefunctions from Classical Oscillator Amplitudes
In the first days of quantum mechanics Dirac pointed out an analogy between
the time-dependent coefficients of an expansion of the Schr\"odinger equation
and the classical position and momentum variables solving Hamilton's equations.
Here it is shown that the analogy can be made an equivalence in that, in
principle, systems of classical oscillators can be constructed whose position
and momenta variables form time-dependent amplitudes which are identical to the
complex quantum amplitudes of the coupled wavefunction of an N-level quantum
system with real coupling matrix elements. Hence classical motion can reproduce
quantum coherence.Comment: extended versio
Probing the Interior Environment of Carbon Nano-test-tubes
We report the filling of single walled carbon nanotubes with an electron
spin-active fullerene species where a nitroxide radical is functionalized on
the fullerene cage. High resolution transmission electron microscopy (HRTEM),
optical absorption and electron spin resonance (ESR) are used to determine the
rotational behavior of the encapsulated molecules and determine the polar
nature of the nanotube interior
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 Pronyâs 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
- âŠ