8,156 research outputs found
Transforming carbon nanotubes by silylation: An ab initio study
We use ab initio density functional calculations to study the chemical
functionalization of single-wall carbon nanotubes and graphene monolayers by
silyl (SiH3) radicals and hydrogen. We find that silyl radicals form strong
covalent bonds with graphene and nanotube walls, causing local structural
relaxations that enhance the sp3 character of these graphitic nanostructures.
Silylation transforms all carbon nanotubes into semiconductors, independent of
their chirality. Calculated vibrational spectra suggest that specific frequency
shifts can be used as a signature of successful silylation.Comment: 4 pages, 3 figure
Preliminary evaluation of radar imagery of Yellowstone Park, Wyoming
Evaluation of radar imagery of Yellowstone Park, Wyomin
Prospects for Mirage Mediation
Mirage mediation reduces the fine-tuning in the minimal supersymmetric
standard model by dynamically arranging a cancellation between anomaly-mediated
and modulus-mediated supersymmetry breaking. We explore the conditions under
which a mirage "messenger scale" is generated near the weak scale and the
little hierarchy problem is solved. We do this by explicitly including the
dynamics of the SUSY-breaking sector needed to cancel the cosmological
constant. The most plausible scenario for generating a low mirage scale does
not readily admit an extra-dimensional interpretation. We also review the
possibilities for solving the mu/Bmu problem in such theories, a potential
hidden source of fine-tuning.Comment: 14 page
Quantum Films Adsorbed on Graphite: Third and Fourth Helium Layers
Using a path-integral Monte Carlo method for simulating superfluid quantum
films, we investigate helium layers adsorbed on a substrate consisting of
graphite plus two solid helium layers. Our results for the promotion densities
and the dependence of the superfluid density on coverage are in agreement with
experiment. We can also explain certain features of the measured heat capacity
as a function of temperature and coverage.Comment: 13 pages in the Phys. Rev. two-column format, 16 Figure
On the validity of mean-field amplitude equations for counterpropagating wavetrains
We rigorously establish the validity of the equations describing the
evolution of one-dimensional long wavelength modulations of counterpropagating
wavetrains for a hyperbolic model equation, namely the sine-Gordon equation. We
consider both periodic amplitude functions and localized wavepackets. For the
localized case, the wavetrains are completely decoupled at leading order, while
in the periodic case the amplitude equations take the form of mean-field
(nonlocal) Schr\"odinger equations rather than locally coupled partial
differential equations. The origin of this weakened coupling is traced to a
hidden translation symmetry in the linear problem, which is related to the
existence of a characteristic frame traveling at the group velocity of each
wavetrain. It is proved that solutions to the amplitude equations dominate the
dynamics of the governing equations on asymptotically long time scales. While
the details of the discussion are restricted to the class of model equations
having a leading cubic nonlinearity, the results strongly indicate that
mean-field evolution equations are generic for bimodal disturbances in
dispersive systems with \O(1) group velocity.Comment: 16 pages, uuencoded, tar-compressed Postscript fil
A preliminary report on the contact-independent antagonism of Pseudogymnoascus destructans by Rhodococcus rhodochrous strain DAP96253.
BackgroundThe recently-identified causative agent of White-Nose Syndrome (WNS), Pseudogymnoascus destructans, has been responsible for the mortality of an estimated 5.5 million North American bats since its emergence in 2006. A primary focus of the National Response Plan, established by multiple state, federal and tribal agencies in 2011, was the identification of biological control options for WNS. In an effort to identify potential biological control options for WNS, multiply induced cells of Rhodococcus rhodochrous strain DAP96253 was screened for anti-P. destructans activity.ResultsConidia and mycelial plugs of P. destructans were exposed to induced R. rhodochrous in a closed air-space at 15°C, 7°C and 4°C and were evaluated for contact-independent inhibition of conidia germination and mycelial extension with positive results. Additionally, in situ application methods for induced R. rhodochrous, such as fixed-cell catalyst and fermentation cell-paste in non-growth conditions, were screened with positive results. R. rhodochrous was assayed for ex vivo activity via exposure to bat tissue explants inoculated with P. destructans conidia. Induced R. rhodochrous completely inhibited growth from conidia at 15°C and had a strong fungistatic effect at 4°C. Induced R. rhodochrous inhibited P. destructans growth from conidia when cultured in a shared air-space with bat tissue explants inoculated with P. destructans conidia.ConclusionThe identification of inducible biological agents with contact-independent anti- P. destructans activity is a major milestone in the development of viable biological control options for in situ application and provides the first example of contact-independent antagonism of this devastating wildlife pathogen
What Does Written Reflection Reveal About Novice Teachers’ Knowledge, Beliefs, and Skills Related to Literacy Assessment?
Assessment of literacy learning has been a long-standing focus for future teachers in elementary education. Teacher educators use ongoing written reflection to promote learning before, during, and after coursework and field experiences. In this study, the researchers examined the effects of ongoing written reflection on two groups of novice teachers’ knowledge, beliefs, and skills about literacy assessment in a semester-long graduate-level literacy assessment course with embedded fieldwork. First, the researchers conducted qualitative and descriptive analyses to examine what novice teachers reflected about in their ongoing written reflections. Second, they conducted comparative analyses to examine the extent to which the two groups differed in what they reflected about. Qualitative and descriptive analysis of written reflections revealed four prominent categories in which novice teachers reflected: (a) content knowledge related to literacy assessment, (b) beliefs about literacy assessment, (c) empathy and perspective-taking in the literacy assessment and instruction process, and (d) instructional planning and decision making. Comparative analyses revealed significant differences between the two groups of novice teachers in all four categories
Calibration of a polarimetric imaging SAR
Calibration of polarimetric imaging Synthetic Aperture Radars (SAR's) using point calibration targets is discussed. The four-port network calibration technique is used to describe the radar error model. The polarimetric ambiguity function of the SAR is then found using a single point target, namely a trihedral corner reflector. Based on this, an estimate for the backscattering coefficient of the terrain is found by a deconvolution process. A radar image taken by the JPL Airborne SAR (AIRSAR) is used for verification of the deconvolution calibration method. The calibrated responses of point targets in the image are compared both with theory and the POLCAL technique. Also, response of a distributed target are compared using the deconvolution and POLCAL techniques
Is There a Peccei-Quinn Phase Transition?
The nature of axion cosmology is usually said to depend on whether the
Peccei-Quinn (PQ) symmetry breaks before or after inflation. The PQ symmetry
itself is believed to be an accident, so there is not necessarily a symmetry
during inflation at all. We explore these issues in some simple models, which
provide examples of symmetry breaking before and after inflation, or in which
there is no symmetry during inflation and no phase transition at all. One
effect of these observations is to relax the constraints from isocurvature
fluctuations due to the axion during inflation. We also observe new
possibilities for evading the constraints due to cosmic strings and domain
walls, but they seem less generic.Comment: 14 pages. Several references adde
Childhood poly-victimization and perceived family environment
There is a growing body of evidence demonstrating the necessity of examining multiple victimizations when studying childhood victimization histories. Several studies have found poly-victimization (i.e., high cumulative levels of victimization) common in non-clinical samples and associated with greater trauma symptomatology than experiencing a single type of victimization (Finkelhor, Ormrod, & Turner, 2007; Richmond, Elliott, Pierce, Aspelmeier, & Alexander, 2009; Saunders, 2003). This study examined the relative contribution of six different categories of childhood victimization and poly-victimization in predicting the Conflict and Cohesion subscale scores of the Family Environment Scale (FES). In a sample of 330 female college undergraduates, the results showed that victimization was common in a non-clinical sample, and most participants who endorsed one type of victimization also endorsed multiple types. Poly-victimization accounted for significant proportions of variability in participants\u27 perceptions of their family conflict and cohesion, but these contributions were small to moderate. Finally, polyvictimization and the simultaneous entry of all six categories of victimization accounted for large, and statistically significant, amounts of variance for perceived family conflict and cohesion
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