Planar Dirac Electron in Coulomb and Magnetic Fields

The Dirac equation for an electron in two spatial dimensions in the Coulomb and homogeneous magnetic fields is discussed. For weak magnetic fields, the approximate energy values are obtained by semiclassical method. In the case with strong magnetic fields, we present the exact recursion relations that determine the coefficients of the series expansion of wave functions, the possible energies and the magnetic fields. It is found that analytic solutions are possible for a denumerably infinite set of magnetic field strengths. This system thus furnishes an example of the so-called quasi-exactly solvable models. A distinctive feature in the Dirac case is that, depending on the strength of the Coulomb field, not all total angular momentum quantum number allow exact solutions with wavefunctions in reasonable polynomial forms. Solutions in the nonrelativistic limit with both attractive and repulsive Coulomb fields are briefly discussed by means of the method of factorization.Comment: 18 pages, RevTex, no figure

Opioids activate brain analgesic circuits through cytochrome P450/epoxygenase signaling.

To assess the importance of brain cytochrome P450 (P450) activity in opioid analgesic action, we generated a mutant mouse with brain neuron-specific reductions in P450 activity; these mice showed highly attenuated morphine antinociception compared with controls. Pharmacological inhibition of brain P450 arachidonate epoxygenases also blocked morphine antinociception in mice and rats. Our findings indicate that a neuronal P450 epoxygenase mediates the pain-relieving properties of morphine. © 2010 Nature America, Inc. All rights reserved

The Radiation Assessment Detector (RAD) Investigation

The Radiation Assessment Detector (RAD) on the Mars Science Laboratory (MSL) is an energetic particle detector designed to measure a broad spectrum of energetic particle radiation. It will make the first-ever direct radiation measurements on the surface of Mars, detecting galactic cosmic rays, solar energetic particles, secondary neutrons, and other secondary particles created both in the atmosphere and in the Martian regolith. The radiation environment on Mars, both past and present, may have implications for habitability and the ability to sustain life. Radiation exposure is also a major concern for future human missions. The RAD instrument combines charged- and neutral-particle detection capability over a wide dynamic range in a compact, low-mass, low-power instrument. These capabilities are required in order to measure all the important components of the radiation environment. RAD consists of the RAD Sensor Head (RSH) and the RAD Electronics Box (REB) integrated together in a small, compact volume. The RSH contains a solid-state detector telescope with three silicon PIN diodes for charged particle detection, a thallium doped Cesium Iodide scintillator, plastic scintillators for neutron detection and anti-coincidence shielding, and the front-end electronics. The REB contains three circuit boards, one with a novel mixed-signal ASIC for processing analog signals and an associated control FPGA, another with a second FPGA to communicate with the rover and perform onboard analysis of science data, and a third board with power supplies and power cycling or "sleep"-control electronics. The latter enables autonomous operation, independent of commands from the rover. RAD is a highly capable and highly configurable instrument that paves the way for future compact energetic particle detectors in space