Effect of pressure on an intramolecular electron-transfer reaction induced by pulse-radiolysis

Abstract

The pressure dependence of an intramolecular electron-transfer reaction between p-nitrobenzoate and the pentaamminecobalt (III) species was studied with the aid of a combined high-pressure pulse-radiolysis technique. The resulting volume of activation of +7.5±0.3 cm³mol^?1 is ascribed to an intrinsic volume increase due to the reduction of Co(III) to Co(II) and some desolvation of the coordinated ligand during the electron-transfer process. The results are compared with related data obtained using conventional kinetic techniques.     

Simple Proofs of Classical Theorems in Discrete Geometry via the Guth–Katz Polynomial Partitioning Technique

Recently Guth and Katz (arXiv:1011.4105, 2010) invented, as a step in their nearly complete solution of Erd?s??s distinct distances problem, a new method for partitioning finite point sets in ? ^d , based on the Stone?CTukey polynomial ham-sandwich theorem. We apply this method to obtain new and simple proofs of two well known results: the Szemerédi?CTrotter theorem on incidences of points and lines, and the existence of spanning trees with low crossing numbers. Since we consider these proofs particularly suitable for teaching, we aim at self-contained, expository treatment. We also mention some generalizations and extensions, such as the Pach?CSharir bound on the number of incidences with algebraic curves of bounded degree.     

Search for Z' --> e+ e- using dielectron mass and angular distribution

We search for Z' bosons in dielectron events produced in pp collisions at square root of s = 1.96 TeV, using 0.45 fb(-1) of data accumulated with the Collider Detector at Fermilab II detector at the Fermilab Tevatron. To identify the Z' --> e+ e- signal, both the dielectron invariant mass distribution and the angular distribution of the electron pair are used. No evidence of a signal is found, and 95% confidence level lower limits are set on the Z' mass for several models. Limits are also placed on the mass and gauge coupling of a generic Z', as well as on the contact-interaction mass scales for different helicity structure scenarios.     

Scalar modifications to gravity from unparticle effects may be testable

Interest has focused recently on low energy implications of a nontrivial scale invariant sector of an effective field theory with an IR fixed point, manifest in terms of "unparticles" with peculiar properties. If unparticle stuff exists it could couple to the stress tensor and mediate a new "fifth" force ("ungravity"). Under the assumption of strict conformal invariance in the hidden sector down to low energies, we compute the lowest order ungravity correction to the Newtonian gravitational potential and find scale invariant power law corrections of type (R_(G)/r)(2d)_(U)(-1), where d_(U) is an anomalous unparticle dimension and R_(G) is a characteristic length scale where the ungravity interactions become significant. It is shown that a discrimination between extra dimension models and ungravity is possible in future improved submillimeter tests of gravity.     

半导体激光器的线宽压窄及频率连续调谐

我们利用共焦F—P腔光学弱反馈技术，实现了单模GaAlAs半导体激光器线宽压窄、频率锁定及连续调谐。其线宽从自由运转时的10MHz被压窄到45kHz，并可将频率锁定于共焦F—P腔。实验证明，在弱反馈情况下，激光器的频率连续调谐范围与共焦FP腔的光强反馈量近似成正比，实现了在铷原子D2线附近1．2GHz的频率连续调谐，