Gaussian-Charge Polarizable Interaction Potential for Carbon Dioxide

A number of simple pair interaction potentials of the carbon dioxide molecule are investigated and found to underestimate the magnitude of the second virial coefficient in the temperature interval 220 K to 448 K by up to 20%. Also the third virial coefficient is underestimated by these models. A rigid, polarizable, three-site interaction potential reproduces the experimental second and third virial coefficients to within a few percent. It is based on the modified Buckingham exp-6 potential, an anisotropic Axilrod-Teller correction and Gaussian charge densities on the atomic sites with an inducible dipole at the center of mass. The electric quadrupole moment, polarizability and bond distances are set to equal experiment. Density of the fluid at 200 and 800 bars pressure is reproduced to within some percent of observation over the temperature range 250 K to 310 K. The dimer structure is in passable agreement with electronically resolved quantum-mechanical calculations in the literature, as are those of the monohydrated monomer and dimer complexes using the polarizable GCPM water potential. Qualitative agreement with experiment is also obtained, when quantum corrections are included, for the relative stability of the trimer conformations, which is not the case for the pair potentials.Comment: Error in the long-range correction fixed and three-body dispersion introduced. 32 pages (incl. title page), 7 figures, 9 tables, double-space

Seasonal Ice Cycle at the Mars Phoenix Landing Site: 2. Postlanding CRISM and Ground Observations

The combination of ground observations from the Mars Phoenix Lander and orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) provided a detailed view of the formation of late summer surface water ice at the landing site and surrounding regions. CRISM observations of the landing site during and immediately after Phoenix operations were analyzed to track the seasonal and diurnal ice cycles during the late spring to late summer, and a nonlinear mixing model was used to estimate grain sizes and relative abundances of water ice and dust. The surface around the Phoenix landing site was ice-free from late spring through midsummer, although transient patches of mobile ices were observed in an 85 m diameter crater to the northeast of the landing site. At the ∼10 km diameter Heimdal Crater, located ∼10 km east of the landing site, permanent patches of water ice were observed to brighten during the late spring and darken during the summer, possibly as fine-grained water ice that was cold trapped onto the ice during late spring sintered into larger grains or finally sublimated, exposing larger-grained ice. CRISM spectra first show evidence of widespread ice during the night at solar longitude (Ls) ∼ 109°, ∼9 sols before Phoenix’s Surface Stereo Imager detected it. CRISM spectra first show evidence of afternoon surface ice and water ice clouds after Ls ∼ 155°, after Phoenix operations ended

Seasonal Ice Cycle at the Mars Phoenix Landing Site: 2. Postlanding CRISM and Ground Observations

The combination of ground observations from the Mars Phoenix Lander and orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) provided a detailed view of the formation of late summer surface water ice at the landing site and surrounding regions. CRISM observations of the landing site during and immediately after Phoenix operations were analyzed to track the seasonal and diurnal ice cycles during the late spring to late summer, and a nonlinear mixing model was used to estimate grain sizes and relative abundances of water ice and dust. The surface around the Phoenix landing site was ice-free from late spring through midsummer, although transient patches of mobile ices were observed in an 85 m diameter crater to the northeast of the landing site. At the ∼10 km diameter Heimdal Crater, located ∼10 km east of the landing site, permanent patches of water ice were observed to brighten during the late spring and darken during the summer, possibly as fine-grained water ice that was cold trapped onto the ice during late spring sintered into larger grains or finally sublimated, exposing larger-grained ice. CRISM spectra first show evidence of widespread ice during the night at solar longitude (Ls) ∼ 109°, ∼9 sols before Phoenix’s Surface Stereo Imager detected it. CRISM spectra first show evidence of afternoon surface ice and water ice clouds after Ls ∼ 155°, after Phoenix operations ended

Multiple chromosomal rearrangements in a hybrid zone between Littorina saxatilis ecotypes

Both classical and recent studies suggest that chromosomal inversion polymorphisms are important in adaptation and speciation. However, biases in discovery and reporting of inversions make it difficult to assess their prevalence and biological importance. Here, we use an approach based on linkage disequilibrium among markers genotyped for samples collected across a transect between contrasting habitats to detect chromosomal rearrangements de novo. We report 17 polymorphic rearrangements in a single locality for the coastal marine snail, Littorina saxatilis. Patterns of diversity in the field and of recombination in controlled crosses provide strong evidence that at least the majority of these rearrangements are inversions. Most show clinal changes in frequency between habitats, suggestive of divergent selection, but only one appears to be fixed for different arrangements in the two habitats. Consistent with widespread evidence for balancing selection on inversion polymorphisms, we argue that a combination of heterosis and divergent selection can explain the observed patterns and should be considered in other systems spanning environmental gradients. This article is protected by copyright. All rights reserved

Determination of dust aerosol particle size at Gale Crater using REMS UVS and Mastcam measurements

We calculate the seasonal and interannual variation in dust aerosol particle size above Gale Crater during the first 1413 Martian solar days (sols = 24.6 h) of the Mars Science Laboratory mission. Measurements of UV radiation made by the Rover Environmental Monitoring Station in combination with atmospheric opacities retrieved from the Mastcam instrument are used for the calculations. Our results indicate that the dust effective radius varies significantly with season, ranging from ~0.6 μm during the low opacity season (Ls = 60°â 140°) to ~2 μm during the high opacity season (Ls = 180°â 360°). Our results suggest that Gale Crater is affected by dust events of high aerosol content originated at various distances from it. Our results improve the accuracy of estimations of ultraviolet radiation fluxes at the Martian surface. Moreover, our results have important implications because the lifetime of suspended dust and its ability to nucleate clouds are affected by particle size.Plain Language SummaryThe Martian atmosphere transports large amounts of dust, which interacts strongly with solar and infrared radiation. The large spatial and temporal variability in atmospheric dust load creates complex feedbacks connecting dust lifting with the evolving atmospheric circulations. The size of suspended aerosols affects the surface and atmospheric heating rates, influencing the Martian climate. In this work, we have calculated the dust aerosol particle size above Gale Crater during the first 1413 sols of the Mars Science Laboratory (MSL) mission using measurements of UV radiation made for the first time from the surface of Mars. Our results indicate that the dust effective radius varies significantly with season, ranging from ~0.6 μm during the clear season to ~2 μm during the dusty season. Our results suggest that Gale Crater is affected by dust events of high aerosol content originated at various distances from it. Our results are important because the lifetime of suspended dust and its ability to nucleate clouds are affected by the particle size.Key PointsWe have developed a novel methodology to retrieve dust aerosol particle size at Gale Crater using Mars Science Laboratory dataThe retrieved dust effective radii range from 0.6 μm during the clear aphelion season to 2 μm during the dusty perihelion seasonOur results improve the estimation of ultraviolet radiation fluxes at the Martian surfacePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/1/grl55782-sup-0001-2017GL072589-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/2/grl55782_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/3/grl55782.pd

Seasonal and interannual variability of solar radiation at Spirit, Opportunity and Curiosity landing sites

In this article we characterize the radiative environment at the landing sites of NASA's Mars Exploration Rover (MER) and Mars Science Laboratory (MSL) missions. We use opacity values obtained at the surface from direct imaging of the Sun and our radiative transfer model COMIMART to analyze the seasonal and interannual variability of the daily irradiation at the MER and MSL landing sites. In addition, we analyze the behavior of the direct and diffuse components of the solar radiation at these landing sites

Statistical Mechanics of Membrane Protein Conformation: A Homopolymer Model

The conformation and the phase diagram of a membrane protein are investigated via grand canonical ensemble approach using a homopolymer model. We discuss the nature and pathway of $\alpha$-helix integration into the membrane that results depending upon membrane permeability and polymer adsorptivity. For a membrane with the permeability larger than a critical value, the integration becomes the second order transition that occurs at the same temperature as that of the adsorption transition. For a nonadsorbing membrane, the integration is of the first order due to the aggregation of $\alpha$-helices.Comment: RevTeX with 5 postscript figure

Large Dust Aerosol Sizes Seen During the 2018 Martian Global Dust Event by the Curiosity Rover

Mars’ atmosphere typically supports dust aerosol with an effective radius near 1.5 μm, varying from ~1 μm during low dust times near northern summer solstice to ~2 μm during higher dust times in southern spring and summer. After global dust events, size variations outside this range have not previously been observed. We report on imaging and spectral observations by the Curiosity rover through the 2018 global dust event. These observations show that the dust effective radius was seasonally normal prior to the local onset of increased opacity, increased rapidly above 4 μm with increasing opacity, remained above 3 μm over a period of ~50 Martian solar days, then returned to seasonal values before the opacity did so. This demonstrates lifting and regionalâ scale transport of a dust population ~3 times the size of typical dust aerosol.Plain Language SummaryDuring the global dust storm of 2018, the Curiosity rover measured the variation of atmospheric dust over time. During the onset of the dust storm, typical Martian dust was enhanced by much larger particles that were freshly lifted off the surface in distant storms and then carried to the rover site at Gale crater. The larger dust particles persisted for weeks, but fell out of the atmosphere faster than the typical dust as normal conditions were restored.Key PointsThe Curiosity rover observed dust aerosol size variations through the 2018 global dust eventThe average dust radius increased above 4 μm, more than double the largest sizes previously seen with Curiosity’s instrumentsThe observations demonstrate the lifting and regionalâ scale transport of dust significantly larger than typical dust aerosolPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151856/1/grl59493.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151856/2/grl59493_am.pd

Coulomb excitation of exotic nuclei at the R3B-LAND setup

Exotic Ni isotopes have been measured at the R3B-LAND setup at GSI in Darmstadt, using Coulomb excitation in inverse kinematics at beam energies around 500 MeV/u. As the experimental setup allows kinematically complete measurements, the excitation energy was reconstructed using the invariant mass method. The GDR and additional low-lying strength have been observed in 68Ni, the latter exhausting 4.1(1.9)% of the E1 energy-weighted sum rule. Also, the branching ratio for the non-statistical decay of the excited 68Ni nuclei was measured and amounts to 24(4)%.Comment: 11 pages, 7 figures. Invited Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS