Inelastic Neutron Scattering from the Spin Ladder Compound (VO)2P2O7

We present results from an inelastic neutron scattering experiment on the candidate Heisenberg spin ladder vanadyl pyrophosphate, (VO)2P2O7. We find evidence for a spin-wave excitation gap of $E_{gap} = 3.7\pm 0.2$ meV, at a band minimum near $Q=0.8 A^{-1}$. This is consistent with expectations for triplet spin waves in (VO)2P2O7 in the spin-ladder model, and is to our knowledge the first confirmation in nature of a Heisenberg antiferromagnetic spin ladder.Comment: 11 pages and 2 figures (available as hard copy or postscript files from the authors, send request to [email protected] or [email protected]), TEX using jnl, reforder and eqnorder, ORNL-CCIP-94-05 / RAL-94-04

Successful explanations start with accurate descriptions:Questionnaire items as personality markers for more accurate predictions

Personality-outcome associations, typically represented using the Big Five personality domains, are ubiquitous, but often weak and possibly driven by the constituents of these domains. We hypothesized that representing the associations using personality questionnaire items (as markers for personality nuances) could increase prediction strength. Using the National Child Development Study (N = 8,719), we predicted 40 diverse outcomes from both the Big Five domains and their 50 items. Models were trained (using penalized regression) and applied for prediction in independent sample partitions (with 100 permutations). Item-models tended to out-predict Big Five-models (explaining on average 30% more variance), regardless of outcomes’ independently-rated breadth versus behavioral specificity. Moreover, the predictive power of Big Five domains per se was at least partly inflated by the unique variance of their constituent items, especially for generally more predictable outcomes. Removing the Big Five variance from items marginally reduced their predictive power. These findings are consistent with the possibility that the associations of personality with outcomes often pertain to (potentially large numbers of) specific behavioral, cognitive, affective and motivational characteristics represented by single questionnaire items rather than to the broader (underlying) traits that these items are ostensibly indicators of. This may also have implications for personality-based interventions

Solar collector cover with temperature-controlled solar light transmittance

Our aim is the development of a solar collector cover with temperature-controlled solar light transmittance in order to protect plastic solar collectors against overheating and to prevent collector damage during stagnation. The temperature-dependent reduction of solar transmittance is based on an increase of backscattering of the incident solar radiation (thermotropism). The thermotropic materials consist of two components: 1) a thermotropic additive, namely submicron-sized core-shell particles containing a phase-change material, and 2) an appropriate transparent matrix polymer. Thermotropic samples based on three different matrix polymers (UV-curable cast resin, EVA and PVB) were prepared as sandwich laminates according to industrially relevant processes. Temperature-dependent measurements of the total solar transmittance reveal absolute differences of up to 28 % between OFF and ON state