Nature and strength of bonding in a crystal of semiconducting nanotubes: van der Waals density functional calculations and analytical results

The dispersive interaction between nanotubes is investigated through ab initio theory calculations and in an analytical approximation. A van der Waals density functional (vdW-DF) [Phys. Rev. Lett. 92, 246401 (2004)] is used to determine and compare the binding of a pair of nanotubes as well as in a nanotube crystal. To analyze the interaction and determine the importance of morphology, we furthermore compare results of our ab initio calculations with a simple analytical result that we obtain for a pair of well-separated nanotubes. In contrast to traditional density functional theory calculations, the vdW-DF study predicts an intertube vdW bonding with a strength that is consistent with recent observations for the interlayer binding in graphitics. It also produce a nanotube wall-to-wall separation which is in very good agreement with experiments. Moreover, we find that the vdW-DF result for the nanotube-crystal binding energy can be approximated by a sum of nanotube-pair interactions when these are calculated in vdW-DF. This observation suggests a framework for an efficient implementation of quantum-physical modeling of the CNT bundling in more general nanotube bundles, including nanotube yarn and rope structures.Comment: 10 pages, 4 figure

On cloud ice induced absorption and polarisation effects in microwave limb sounding

Microwave limb sounding in the presence of ice clouds was studied by detailed simulations, where clouds and other atmospheric variables varied in three dimensions and the full polarisation state was considered. Scattering particles were assumed to be horizontally aligned oblate spheroids with a size distribution parameterized in terms of temperature and ice water content. A general finding was that particle absorption is significant for limb sounding, which is in contrast to the down-looking case, where it is usually insignificant. Another general finding was that single scattering can be assumed for cloud optical paths below about 0.1, which is thus an important threshold with respect to the complexity and accuracy of retrieval algorithms. The representation of particle sizes during the retrieval is also discussed. Concerning polarisation, specific findings were as follows: Firstly, no significant degree of circular polarisation was found for the considered particle type. Secondly, for the ±45° polarisation components, differences of up to 4 K in brightness temperature were found, but differences were much smaller when single scattering conditions applied. Thirdly, the vertically polarised component has the smallest cloud extinction. An important goal of the study was to derive recommendations for future limb sounding instruments, particularly concerning their polarisation setup. If ice water content is among the retrieval targets (and not just trace gas mixing ratios), then the simulations show that it should be best to observe any of the ±45° and circularly polarised components. These pairs of orthogonal components also make it easier to combine information measured from different positions and with different polarisations

The Effect of Statewide Residency Restrictions on Sex Offender Post-Release Housing Mobility

Securing stable housing may be difficult for returning offenders in general, and these concerns may be exacerbated for sex offenders. In addition to the barriers faced by other returning offenders, sex offenders face intense stigma and once released to the community, they are also subject to additional legal restrictions. The current study explores the effect of statewide residency restriction policies on housing mobility using a unique sample of male sex offenders released in a Midwestern state. The research is based on a quasi-experimental cohort control group design and it describes the frequency and correlation of movement for pre- and post-statewide residency restriction legislation samples. Sex offenders released after the implementation of residency restrictions moved more often and had relatively high degrees of housing mobility compared to offenders released prior to the legislation. The results have important implications for reentry programming and post-release services for sex offenders

An Evaluation of Sex Offender Residency Restrictions in Michigan and Missouri

In Michigan, sex offenders are prohibited from living within 1,000 feet of school property and 500 feet from any licensed daycare center. Missouri prohibits sex offenders from living within 1,000 feet of a public or private school up to the 12th grade or childcare facility which existed at the time the offender established his/her residency. In addition, sex offenders are prohibited from working or loitering within 500 feet of a school, childcare facility, or public park with playground equipment or a public swimming pool. Residency restriction policies in both States are universally applied to all registered sex offenders. The current study had three primary goals. First, document the residency locations of sex offenders and non-sex offenders before and after the implementation of the residency restriction laws. Second, examine the change in recidivism patterns before and after the implementation of residency restrictions. Third, describe the collateral consequences of residency restrictions. The study found a decline in the number of registered sex offenders living in restricted areas, including near schools or daycare centers, but the differences were not statistically significant. The study also determined that sex offenders, especially child molesters, moved more often relative to comparable non-sex offenders after the implementation of residency restrictions; those living at addresses within the boundary zones surrounding schools and daycare centers tended to live in more disadvantaged areas. Regarding the impact of residency restrictions on recidivism, the relationship was small. The study recommends reconsidering the universal application of sex offender residency restrictions, an increase in housing services for sex offenders, and the development of reentry programming specific to sex offender populations. 22 tables and 139 reference

FoldIndex©: a simple tool to predict whether a given protein sequence is intrinsically unfolded

Summary: An easy-to-use, versatile and freely available graphic web server, FoldIndex© is described: it predicts if a given protein sequence is intrinsically unfolded implementing the algorithm of Uversky and co-workers, which is based on the average residue hydrophobicity and net charge of the sequence. FoldIndex© has an error rate comparable to that of more sophisticated fold prediction methods. Sliding windows permit identification of large regions within a protein that possess folding propensities different from those of the whole protein. Availability: FoldIndex© can be accessed at http://bioportal.weizmann.ac.il/fldbin/findex Contact: [email protected] Supplementary information: http://www.weizmann.ac.il/sb/faculty_pages/Sussman/papers/suppl/Prilusky_200

Atomic Supersymmetry, Rydberg Wave Packets, and Radial Squeezed States

We study radial wave packets produced by short-pulsed laser fields acting on Rydberg atoms, using analytical tools from supersymmetry-based quantum-defect theory. We begin with a time-dependent perturbative calculation for alkali-metal atoms, incorporating the atomic-excitation process. This provides insight into the general wave packet behavior and demonstrates agreement with conventional theory. We then obtain an alternative analytical description of a radial wave packet as a member of a particular family of squeezed states, which we call radial squeezed states. By construction, these have close to minimum uncertainty in the radial coordinates during the first pass through the outer apsidal point. The properties of radial squeezed states are investigated, and they are shown to provide a description of certain aspects of Rydberg atoms excited by short-pulsed laser fields. We derive expressions for the time evolution and the autocorrelation of the radial squeezed states, and we study numerically and analytically their behavior in several alkali-metal atoms. Full and fractional revivals are observed. Comparisons show agreement with other theoretical results and with experiment.Comment: published in Physical Review