Observations of Lunar Swirls by the Diviner Lunar Radiometer Experiment

The presence of anomalous, high albedo markings on the lunar surface has been known since the Apollo era. These features, collectively known as lunar swirls, occur on both the mare and highlands. Some swirls are associated with the antipodes of major impact basins, while all are associated with magnetic field anomalies of varying strength. Three mechanisms have been proposed for the formation of the swirls: (1) solar wind standoff due to the presence of magnetic fields, (2) micrometeoroid or comet swarms impacting and disturbing the lunar surface, revealing unweathered regolith, and (3) transport and deposition of fine-grained feldspathic material. Diviner s unique capabilities to determine silicate composition and degree of space weathering of the lunar surface, in addition to its capabilities to determine thermophysical properties from night-time temperature measurements, make it an ideal instrument to examine the swirls and help differentiate among the three proposed formation mechanisms

Probing the potential landscape inside a two-dimensional electron-gas

We report direct observations of the scattering potentials in a two-dimensional electron-gas using electron-beam diffaction-experiments. The diffracting objects are local density-fluctuations caused by the spatial and charge-state distribution of the donors in the GaAs-(Al,Ga)As heterostructures. The scatterers can be manipulated externally by sample illumination, or by cooling the sample down under depleted conditions.Comment: 4 pages, 4 figure

Lunar Flashlight: Illuminating the Lunar South Pole

Recent reflectance data from LRO instruments suggest water ice and other volatiles may be present on the surface in lunar permanentlyshadowed regions, though the detection is not yet definitive. Understanding the composition, quantity, distribution, and form of water and other volatiles associated with lunar permanently shadowed regions (PSRs) is identified as a NASA Strategic Knowledge Gap (SKG) for Human Exploration. These polar volatile deposits are also scientifically interesting, having the potential to reveal important information about the delivery of water to the Earth- Moon system

Lunar Flashlight: Illuminating the Moon's South Pole

Recent reflectance data from LRO instruments suggest water ice and other volatiles may be present on the surface in lunar permanently shadowed regions, though the detection is not yet definitive. Understanding the composition, quantity, distribution, and form of water and other volatiles associated with lunar permanently shadowed regions (PSRs) is identified as a NASA Strategic Knowledge Gap (SKG) for Human Exploration. These polar volatile deposits are also scientifically interesting, having the potential to reveal important information about the delivery of water to the Earth-Moon system

Stability of trions in strongly spin-polarized two-dimensional electron gases

Low-temperature magneto-photoluminescence studies of negatively charged excitons (X- trions) are reported for n-type modulation-doped ZnSe/Zn(Cd,Mn)Se quantum wells over a wide range of Fermi energy and spin-splitting. The magnetic composition is chosen such that these magnetic two-dimensional electron gases (2DEGs) are highly spin-polarized even at low magnetic fields, throughout the entire range of electron densities studied (5e10 to 6.5e11 cm^-2). This spin polarization has a pronounced effect on the formation and energy of X-, with the striking result that the trion ionization energy (the energy separating X- from the neutral exciton) follows the temperature- and magnetic field-tunable Fermi energy. The large Zeeman energy destabilizes X- at the nu=1 quantum limit, beyond which a new PL peak appears and persists to 60 Tesla, suggesting the formation of spin-triplet charged excitons.Comment: 5 pages (RevTex), 4 embedded EPS figs. Submitted to PRB-R

Landau Level Crossings and Extended-State Mapping in Magnetic Two-dimensional Electron Gases

We present longitudinal and Hall magneto-resistance measurements of a ``magnetic'' two-dimensional electron gas (2DEG) formed in modulation-doped Zn$_{1-x-y}$Cd$_{x}$Mn$_{y}$Se quantum wells. The electron spin splitting is temperature and magnetic field dependent, resulting in striking features as Landau levels of opposite spin cross near the Fermi level. Magnetization measurements on the same sample probe the total density of states and Fermi energy, allowing us to fit the transport data using a model involving extended states centered at each Landau level and two-channel conduction for spin-up and spin-down electrons. A mapping of the extended states over the whole quantum Hall effect regime shows no floating of extended states as Landau levels cross near the Fermi level.Comment: 10 pages, 4 figures, submitted to Phys. Rev.

Selecting and Certifying a Landing Site for Moonrise in South Pole-Aitken Basin

MoonRise is a New Frontiers mission concept to land in the South Pole-Aitken (SPA) basin, collect samples, and return the samples to Earth for detailed mineral, chemical, petrologic, geochronologic, and physical properties analyses to address science questions relevant to the early evolution of the Solar System and the Moon. Science associated with this mission concept is described elsewhere; here we discuss selection of sites within SPA to address science objectives using recent scientific studies (orbital spectroscopy, gravity, topography), and the use of new data (LRO) to certify safe landing sites for a robotic sample return mission such as MoonRise

Decay constants of P and D-wave heavy-light mesons

We investigate decay constants of P and D-wave heavy-light mesons within the mock-meson approach. Numerical estimates are obtained using the relativistic quark model. We also comment on recent calculations of heavy-light pseudo-scalar and vector decay constants.Comment: REVTeX, 22 pages, uses epsf macro, 8 postscript figures include

Excitons and charged excitons in semiconductor quantum wells

A variational calculation of the ground-state energy of neutral excitons and of positively and negatively charged excitons (trions) confined in a single-quantum well is presented. We study the dependence of the correlation energy and of the binding energy on the well width and on the hole mass. The conditional probability distribution for positively and negatively charged excitons is obtained, providing information on the correlation and the charge distribution in the system. A comparison is made with available experimental data on trion binding energies in GaAs-, ZnSe-, and CdTe-based quantum well structures, which indicates that trions become localized with decreasing quantum well width.Comment: 9 pages, 11 figure