The geology of the Venera/Vega landing sites

We have performed a photogeological analysis of the Venera Vega landing sites using Magellan radar images. These seven sites are the only places on Venus where geochemistry measurements were taken. In this study, the updated coordinates of the landing sites are used and the landing circle has a radius with an admissible error of about 150 km

Soil hydraulic controls over nitrogen oxide emissions and nitrogen cycling in tropical agriculture

Soils are the major natural source of nitrous oxide (N2O). Intensive land use increased atmospheric concentrations of this greenhouse gas. Soil microbes produce and consume nitrogen oxides (NO, N2O) during the processes of nitrification (aerobic) and denitrification (anaerobic). Micro-scale variability of controlling factors cause nitrification and denitrification to occur simultaneously in soils, resulting in high spatial variability of nitrogen oxide emissions. Fertilization increases nutrient availability and thus N2O fluxes. Forest soils in the humid tropics account for 20--50% of all N2O sources. Expansion and intensification of tropical agriculture is expected to increase atmospheric N2O concentrations. We measured N2O fluxes from secondary humid tropical forest soils in Costa Rica, followed fluxes during forest conversion and studied emissions from unfertilized and fertilized agricultural soils. We related fluxes to soil moisture dynamics and agricultural practice. Gases were measured using manual and automated chamber techniques. Soil moisture content was measured using manual (auger) and automated (Time Domain Reflectrometry; TDR) sampling techniques. A 3-phase-mixing model was found suitable to calibrate TDR technique for the studied soils. The field experiment was based on a split-plot design, comparing clay versus loam, each under fertilized and unfertilized annual and perennial crop. Soils feature relatively low bulk density, high hydraulic conductivity and high organic matter content. Mean soil moisture content was above 70% water-filled-pore-space (WFPS) in both soils and land uses. N 2O was emitted throughout the year. Fluxes from forest soils showed no seasonality. Forest conversion caused fluxes to increase temporarily. Fertilization was the dominant source for temporal variability under agricultural use, differences in flux dynamics were large between individual post-fertilization phases. N2O-loss as % of applied fertilizer-N increased with soil moisture. Spatial variability was generally high, especially post-fertilization. Repeated fertilization increased mean and variation of fluxes. Emissions simulated by regression models and by the physically based Denitrification-Decomposition model matched field measured fluxes well. Both modeling techniques confirmed that nutrient availability and soil moisture content were the dominant flux controls. In aggregated soils differences in soil structure between the surface layer and soil at 0.05 m depth may affect moisture content and consequently soil N 2O fluxes

Largest impact craters on Venus

High-resolution radar images from the Magellan spacecraft have allowed us to perform a detailed study on 25 large impact craters on Venus with diameters from 70 to 280 km. The dimension of these large craters is comparable with the characteristic thickness of the venusian lithosphere and the atmospheric scale height. Some physical parameters for the largest impact craters on Venus (LICV), such as depth, ring/diameter ratio, and range of ballistic ejecta deposits, have been obtained from the SAR images and the altimetry dataset produced by MIT. Data related to each of these parameters is discussed

Skating on a Film of Air: Drops Impacting on a Surface

Drops impacting on a surface are ubiquitous in our everyday experience. This impact is understood within a commonly accepted hydrodynamic picture: it is initiated by a rapid shock and a subsequent ejection of a sheet leading to beautiful splashing patterns. However, this picture ignores the essential role of the air that is trapped between the impacting drop and the surface. Here we describe a new imaging modality that is sensitive to the behavior right at the surface. We show that a very thin film of air, only a few tens of nanometers thick, remains trapped between the falling drop and the surface as the drop spreads. The thin film of air serves to lubricate the drop enabling the fluid to skate on the air film laterally outward at surprisingly high velocities, consistent with theoretical predictions. Eventually this thin film of air must break down as the fluid wets the surface. We suggest that this occurs in a spinodal-like fashion, and causes a very rapid spreading of a wetting front outwards; simultaneously the wetting fluid spreads inward much more slowly, trapping a bubble of air within the drop. Our results show that the dynamics of impacting drops are much more complex than previously thought and exhibit a rich array of unexpected phenomena that require rethinking classical paradigms.Comment: 4 pages, 4 figure

Activity driven fluctuations in living cells

We propose a model for the dynamics of a probe embedded in a living cell, where both thermal fluctuations and nonequilibrium activity coexist. The model is based on a confining harmonic potential describing the elastic cytoskeletal matrix, which undergoes random active hops as a result of the nonequilibrium rearrangements within the cell. We describe the probe's statistics and we bring forth quantities affected by the nonequilibrium activity. We find an excellent agreement between the predictions of our model and experimental results for tracers inside living cells. Finally, we exploit our model to arrive at quantitative predictions for the parameters characterizing nonequilibrium activity, such as the typical time scale of the activity and the amplitude of the active fluctuations.Comment: 6 pages, 4 figure

A lottery incentive system to facilitate dialogue and social support for workplace HIV counselling and testing: A qualitative inquiry

Despite South African mid-sized companies’ efforts to offer HIV counselling and testing (HCT) in the workplace, companies report relatively poor uptake rates. An urgent need for a range of different interventions aimed at increasing participation in workplace HCT has been identified. The aim of this study was to explore qualitatively the influence of a lottery incentive system (LIS) as an intervention to influence shop-floor workers’ workplace HIV testing behaviour. A qualitative study was conducted among 17 shop-floor workers via convenience sampling in two mid-sized South African automotive manufacturing companies in which an LIS for HCT was implemented. The in-depth interviews employed a semi-structured interview schedule and thematic analysis was used to analyse the data. The interviews revealed that the LIS created excitement in the companies and renewed employees’ personal interest in HCT. The excitement facilitated social interactions that resulted in a strong group cohesion pertaining to HCT that mitigated the burden of HIV stigma in the workplace. Open discussions allowed for the development of supportive social group pressure to seek HCT as a collective in anticipation of a reward. Lotteries were perceived as a supportive and innovative company approach to workplace HCT. The study identified important aspects for consideration by companies when using an LIS to enhance workplace HIV testing. The significance of inter- and intra-player dialogue in activating supportive social norms for HIV testing in collectivist African contexts was highlighted.Keywords: HCT, company, collectivist, group pressure, norm, South AfricaMalgre´ les efforts que font les petites et moyennes entreprises sud-africaines pour offrir le conseil et de´pistage volontaire du VIH (CDV) en milieu de travail, les entreprises font e´tat de taux de participation relativement bas. Un besoin urgent pour une gamme de diffe´rentes interventions visant a` accroıˆtre la participation au CDV en milieu de travail a e´te´ identifie´e. Le but de cette e´tude e´tait d’e´tudier qualitativement l’influence d’un syste`me d’incitation a` la loterie comme intervention pour influencer le comportement CDV des ouvriers en milieu de travail. Une e´tude qualitative a e´te´ mene´e aupre`s de 17 ouvriers choisis par e´chantillonnage de commodite´ dans 2 entreprises de fabrication automobile en Afrique du Sud. Dans ces 2 entreprises de taille moyenne, un syste`me d’incitation a` la loterie a e´te´ mis en oeuvre pour encourager le CDV en milieu de travail. Un guide d’interviews semistructure ´es a e´te´ employe´ pour mener des entretiens approfondis. L’analyse the´matique a e´te´ utilise´e pour analyser les donne´es. Les entrevues ont re´ve´le´ que les syste`mes d’incitation ont cre´e´ de l’excitation dans les entreprises et ont renouvele´ l’inte´reˆt personnel des employe´s pour le CDV. L’excitation a facilite´ des interactions sociales qui ont abouti a` une forte cohe´sion du groupe d’ouvriers concernant le CDV et atte´nuant ainsi la stigmatisation lie´e au VIH en milieu de travail. Des discussions ouvertes ont permis l’e´laboration de pression sociale de groupe en support a` la participation collective au CDV en pre´vision d’une re´compense. Les loteries ont e´te´ perc¸ues comme une approche soutenante et innovante de la part des entreprises pour le CDV en milieu de travail. L’e´tude a identifie´ des aspects importants a` prendre en compte par les entreprises lors de l’utilisation d’un syste`me d’incitation a` la loterie pour augmenter le taux de de´pistage VIH en milieu de travail. L’importance du dialogue inter- et intra-joueur dans l’activation de normes sociales favorables pour le de´pistage VIH dans les contextes collectivistesafricains a e´te´ souligne´e.Mots cle´s: CDV, entreprise, collectiviste, pression de groupe, norme, Afrique du Su

Microwave Dielectric Heating of Drops in Microfluidic Devices

We present a technique to locally and rapidly heat water drops in microfluidic devices with microwave dielectric heating. Water absorbs microwave power more efficiently than polymers, glass, and oils due to its permanent molecular dipole moment that has a large dielectric loss at GHz frequencies. The relevant heat capacity of the system is a single thermally isolated picoliter drop of water and this enables very fast thermal cycling. We demonstrate microwave dielectric heating in a microfluidic device that integrates a flow-focusing drop maker, drop splitters, and metal electrodes to locally deliver microwave power from an inexpensive, commercially available 3.0 GHz source and amplifier. The temperature of the drops is measured by observing the temperature dependent fluorescence intensity of cadmium selenide nanocrystals suspended in the water drops. We demonstrate characteristic heating times as short as 15 ms to steady-state temperatures as large as 30 degrees C above the base temperature of the microfluidic device. Many common biological and chemical applications require rapid and local control of temperature, such as PCR amplification of DNA, and can benefit from this new technique.Comment: 6 pages, 4 figure