Barbaetis: A New Genus of Eastern Nearctic Mayflies (Ephemeroptera: Baetidae)

The new genus Barbaetis Waltz and McCafferty, and new species Barbaetis benfieldi Kennedy are described from larvae collected from the New River, Virginia. Barbaetis is easily told from Baetis by the presence of procoxal osmobranchia. Cladistics of B. benfieldi, related Pseudocloeon species, and the lutheri and pavidus complexes of Baetis are presented and indicate the need for further taxonomic revision. The habitat of B. benfieldi is described in terms of several ecological parameters. The new species demonstrates a univoltine life history with postembryonic development restricted to a short springtime period

Correction of Optical Aberrations in Elliptic Neutron Guides

Modern, nonlinear ballistic neutron guides are an attractive concept in neutron beam delivery and instrumentation, because they offer increased performance over straight or linearly tapered guides. However, like other ballistic geometries they have the potential to create significantly non-trivial instrumental resolution functions. We address the source of the most prominent optical aberration, namely coma, and we show that for extended sources the off-axis rays have a different focal length from on-axis rays, leading to multiple reflections in the guide system. We illustrate how the interplay between coma, sources of finite size, and mirrors with non-perfect reflectivity can therefore conspire to produce uneven distributions in the neutron beam divergence, the source of complicated resolution functions. To solve these problems, we propose a hybrid elliptic-parabolic guide geometry. Using this new kind of neutron guide shape, it is possible to condition the neutron beam and remove almost all of the aberrations, whilst providing the same performance in beam current as a standard elliptic neutron guide. We highlight the positive implications for a number of neutron scattering instrument types that this new shape can bring.Comment: Presented at NOP2010 Conference in Alpe d'Huez, France, in March 201

Phase Diagram of the Spin-One Heisenberg System with Dimerization and Frustration

We use the density matrix renormalization group method to study the ground state properties of an antiferromagnetic spin-$1$ chain with a next-nearest neighbor exchange $J_2 ~$ and an alternation $\delta$ of the nearest neighbor exchanges. We find a line running from a gapless point at $(J_2 , \delta) = (0, 0.25 \pm 0.01)$ upto an almost gapless point at $(0.725 \pm 0.01, 0$ such that the open chain ground state is $4$-fold degenerate below the line and is unique above it. A disorder line $2 J_2 + \delta = 1$ runs from $\delta =0$ to about $\delta =0.136$. To the left of this line, the peak in the structure factor $S(q)$ is at $\pi$, while to the right of the line, it is at less than $\pi$.Comment: 11 pages, plain TeX, 3 figures available on reques

The motivating operation and negatively reinforced problem behavior. A systematic review.

The concept of motivational operations exerts an increasing influence on the understanding and assessment of problem behavior in people with intellectual and developmental disability. In this systematic review of 59 methodologically robust studies of the influence of motivational operations in negative reinforcement paradigms in this population, we identify themes related to situational and biological variables that have implications for assessment, intervention, and further research. There is now good evidence that motivational operations of differing origins influence negatively reinforced problem behavior, and that these might be subject to manipulation to facilitate favorable outcomes. There is also good evidence that some biological variables warrant consideration in assessment procedures as they predispose the person's behavior to be influenced by specific motivational operations. The implications for assessment and intervention are made explicit with reference to variables that are open to manipulation or that require further research and conceptualization within causal models

Radiation and shielding study for the International Ultraviolet Explorer

Technical advisory services to ensure integrity of parts and material exposed to energetic particle radiation for the IUE scientific instruments, spacecraft, and subsystems are provided. A significant potential for interference, degradation, or failure for unprotected or sensitive items was found. Vulnerable items were identified, and appropriate tests, changes, and shields were defined

The Woods-Saxon Potential in the Dirac Equation

The two-component approach to the one-dimensional Dirac equation is applied to the Woods-Saxon potential. The scattering and bound state solutions are derived and the conditions for a transmission resonance (when the transmission coefficient is unity) and supercriticality (when the particle bound state is at E=-m) are then derived. The square potential limit is discussed. The recent result that a finite-range symmetric potential barrier will have a transmission resonance of zero-momentum when the corresponding well supports a half-bound state at E=-m is demonstrated.Comment: 8 pages, 4 figures. Submitted to JPhys

Diethyl 3,4-dimethylthieno[2,3-it b]thiophene-2,5-dicarboxylate

In the title compound, C14H16O4S2, the thieno[2,3-b]thiophene ring systems are planar [maximum deviation = 0.008 (2) Å]. The molecular conformation is stabilized by intramolecular C-HO hydrogen bonds, while the crystal packing is stabilized by C-HO, C-H and - stacking [centroid-centroid distance = 3.6605 (14) Å] interactions, which lead to supramolecular layers in the ab plane