Mars low albedo regions: Possible map of near-surface

A freeze/thaw desorption mechanism is proposed in certain low albedo areas which could be the factor that instigated dust storms. It is widely accepted that the bulk of the episodic gas evolution (not necessarily the oxygen release) experienced during the humidification process in the Viking Gas Exhange Experiment (GEX) was caused by a familiar process in which more polar H2O molecules replace large quantities of other preadsorbed gas molecules on adsorption sites. The author suggests that a similar process could produce high pore pressures in soil that could disrupt the soil and eject dust at high velocity. The author also argued that association of sites of dust storms initiated with high thermal inertial areas may simply reflect repeated dust depletion

Photochemical weathering and contemporary volatile loss on Mars

In an earlier series of papers by the author it was proposed that photochemical weathering of Fe(2+) in magnetite and in mafic silicates may be occurring in the contemporary surface environment with a resultant loss of O2 from the atmosphere. Morris and Lauer challenged the photochemical weathering model, proposing that oxidation by radiant heating rather than UV photoelectron emission induced oxidation may have dominated in the authors experiments. Subsequent laboratory studies of photochemical weathering of magnetite described here support the authors original proposal that UV illunimation can indeed drive the oxidation of magnetite under contemporary Martian surface conditions. The negative results of the Morris and Lauer study can now be explained

Chemical frost weathering of olivine: Experimental study and implications

New experimental results are reported on the frost weathering of olivine. After first weathering, a decrease in Fe sup 2(+)M(2) absorption bands were noted. This decrease is related to the protonation of O(+) in the mineral. It is contented that this reaction may result in the regolith storage of 100 to 1000 m of H(sub 2) over the history of Mars

Microwave Gaseous Disharges

Contains reports on seven research projects.Atomic Energy Commission under Contract AT(30-1)184

Plant diversity greatly enhances weed suppression in intensively managed grasslands

Weed suppression was investigated in a field experiment across 31 international sites. The study included 15 plant communities at each site, based on two grasses and two legumes, each sown in monoculture and 11 four-species mixtures varying in the relative proportions of the four species. At each site, one grass and one legume species was selected as fast establishing and the other two species were selected for persistence. Average weed biomass in mixtures over the whole experiment was 52% less (95% confidence interval, 30 to 75%) than in the most suppressive monoculture (transgressive suppression). Transgressive suppression of weed biomass persisted over each year for each mixture. Weed biomass was consistently low and relatively similar across all mixtures and years. Average sown species biomass was greater in all mixtures than in any monoculture. The suppressive effect of sown forage species on weeds in mixtures was achieved without any herbicide use. At each site, weed biomass for almost every mixture was lower than the average across the four monocultures. The average proportion of weed biomass in mixtures was less than in the most suppressive monoculture in two thirds of sites. Mixtures outyielded monocultures, and mixture yield comprised far lower weed biomass

Interstellar Plasma Turbulence Spectrum Toward the Pulsars PSR B0809+74 and B0950+08

Interstellar scintillations of pulsars PSR B0809+74 and B0950+08 have been studied using observations at low frequencies (41, 62, 89, and 112 MHz). Characteristic temporal and frequency scales of diffractive scintillations at these frequencies have been determined. The comprehensive analysis of the frequency and temporal structure functions reduced to the same frequency has shown that the spectrum of interstellar plasma inhomogeneities toward both pulsars is described by a power law. The exponent of the spectrum of fluctuations of interstellar plasma inhomogeneities toward PSR B0950+08 (n = 3.00 +- 0.05) appreciably differs from the Kolmogorov exponent. Toward PSR B0809+74 the spectrum is a power law with an exponent n = 3.7 +- 0.1. A strong angular refraction has been detected toward PSR B0950+08. The distribution of inhomogeneities along the line of sight has been analyzed; it has been shown that the scintillations of PSR B0950+08 take place on a turbulent layer with enhanced electron density, which is localized at approximately 10 pc from the observer. For PSR B0809+74 the distribution of inhomogeneities is quasi-uniform. Mean-square fluctuations of electron density on inhomogeneities with a characteristic scale rho_0 = 10^7 m toward four pulsars have been estimated. On this scale the local turbulence level in the 10-pc layer is 20 times higher than in an extended region responsible for the scintillations of PSR B0809+74.Comment: 13 pages, 11 figure

Intensity-modulated radiotherapy of nasopharyngeal carcinoma: a comparative treatment planning study of photons and protons

<p>Abstract</p> <p>Background</p> <p>The aim of this treatment planning study was to investigate the potential advantages of intensity-modulated (IM) proton therapy (IMPT) compared with IM photon therapy (IMRT) in nasopharyngeal carcinoma (NPC).</p> <p>Methods</p> <p>Eight NPC patients were chosen. The dose prescriptions in cobalt Gray equivalent (Gy_E) for gross tumor volumes of the primary tumor (GTV-T), planning target volumes of GTV-T and metastatic (PTV-TN) and elective (PTV-N) lymph node stations were 72.6 Gy_E, 66 Gy_E, and 52.8 Gy_E, respectively. For each patient, nine coplanar fields IMRT with step-and-shoot technique and 3D spot-scanned three coplanar fields IMPT plans were prepared. Both modalities were planned in 33 fractions to be delivered with a simultaneous integrated boost technique. All plans were prepared and optimized by using the research version of the inverse treatment planning system KonRad (DKFZ, Heidelberg).</p> <p>Results</p> <p>Both treatment techniques were equal in terms of averaged mean dose to target volumes. IMPT plans significantly improved the tumor coverage and conformation (<it>P </it>< 0.05) and they reduced the averaged mean dose to several organs at risk (OARs) by a factor of 2–3. The low-to-medium dose volumes (0.33–13.2 Gy_E) were more than doubled by IMRT plans.</p> <p>Conclusion</p> <p>In radiotherapy of NPC patients, three-field IMPT has greater potential than nine-field IMRT with respect to tumor coverage and reduction of the integral dose to OARs and non-specific normal tissues. The practicality of IMPT in NPC deserves further exploration when this technique becomes available on wider clinical scale.</p