Craters as sand traps: Dynamics, history, and morphology of modern sand transport in an active Martian dune field

Aeolian transport of sand is abundant on modern-day Mars, as revealed by remote sensing measurements of the motion of dunes, and of the meter-scale ripples that mantle them. We study a large-scale natural sand trap within the Meroe Patera dune field: a 1.8-km diameter crater which features a dune-free “shadow” in its lee. We compare the volume of sand trapped within this crater to the sand volume that would be expected to cover the area of the crater and its dune-free shadow behind it if the crater were not present. We find that the crater holds less sand than this “missing” volume would predict, implying that sand escapes from the crater over time. Modern day imagery shows an apparent lack of sand escaping from the Meroe crater, however, suggesting that changes in the wind regime at the site may have allowed sand to escape in the past. The persistence of an altered dune morphology all the way to the far downwind edge of the dune field suggests consistent wind conditions over the time of the crater-dune field interaction

Modifications to the Method of Modal Strain Energy for Improved Estimates of Loss Factors for Damped Structures

The method of Modal Strain Energy (MSE) enables predictions of modal loss factors for vibrating systems from finite element analyses without evaluation of a complex-valued frequency response or a complex-valued frequency. While the method is simple, some error results; especially if the dissipative material has the high loss factor characteristic of materials added to increase system damping. Several methods for reducing this error through modifications to MSE have been suggested. In this work, the exact loss factor for a simple mechanical system is found. The method of Modal Strain Energy (MSE) is then used to find the loss factor for that prototype system and errors are evaluated in terms of system parameters. Comparisons are also made to predictions with several modifications to MSE. A modification due to Rongong is found to provide significant improvement. The use of this modification together with MSE is shown to lead to lower and upper bounds for the system loss factor. As the prototype system is shown to be mechanically equivalent to constrained layer damping configurations, the findings are applicable to the analysis and design of optimized sandwich beams, plates, and damping tapes. Results are given for beams and plates with constrained layer treatments

Craters as sand traps: Dynamics, history, and morphology of modern sand transport in an active Martian dune field

Aeolian transport of sand is abundant on modern-day Mars, as revealed by remote sensing measurements of the motion of dunes, and of the meter-scale ripples that mantle them. We study a large-scale natural sand trap within the Meroe Patera dune field: a 1.8-km diameter crater which features a dune-free “shadow” in its lee. We compare the volume of sand trapped within this crater to the sand volume that would be expected to cover the area of the crater and its dune-free shadow behind it if the crater were not present. We find that the crater holds less sand than this “missing” volume would predict, implying that sand escapes from the crater over time. Modern day imagery shows an apparent lack of sand escaping from the Meroe crater, however, suggesting that changes in the wind regime at the site may have allowed sand to escape in the past. The persistence of an altered dune morphology all the way to the far downwind edge of the dune field suggests consistent wind conditions over the time of the crater-dune field interaction

Outcomes in culture positive and culture negative ascitic fluid infection in patients with viral cirrhosis: cohort study

<p>Abstract</p> <p>Background</p> <p>Ascitic fluid infection (AFI) in cirrhotic patients has a high morbidity and mortality. It has two variants namely, spontaneous bacterial peritonitis (SBP) and culture negative neutrocytic ascites (CNNA). The aim of this study was to determine the outcome in cirrhotic patients with culture positive (SBP) and culture negative neutrocytic ascites.</p> <p>Methods</p> <p>We analyzed 675 consecutive hepatitis B and/or C related cirrhosis patients with ascites admitted in our hospital from November 2005 to December 2007. Of these, 187 patients had AFI; clinical and laboratory parameters of these patients including causes of cirrhosis, Child Turcotte Pugh (CTP) score were recorded.</p> <p>Results</p> <p>Out of 187 patients with AFI, 44 (23.5%) had SBP while 143 (76.4%) had CNNA. Hepatitis C virus (HCV) infection was the most common cause of cirrhosis in 139 (74.3%) patients. Patients with SBP had high CTP score as compared to CNNA (12.52 ± 1.45 vs. 11.44 ± 1.66); p < 0.001. Platelets count was low in patients with SBP (101 ± 53 × 10⁹/L) as compared to CNNA (132 ± 91 × 10⁹/L), p = 0.005. We found a high creatinine (mg/dl) (1.95 ± 1.0 vs. 1.44 ± 0.85), (p = 0.003) and high prothrombin time (PT) in seconds (24.8 ± 6.6 vs. 22.4 ± 7.2) (p = 0.04) in SBP as compared to CNNA. More patients with SBP (14/44; 31.8%) had blood culture positivity as compare to CNNA (14/143; 9.8%), p = 0.002. Escherichia. Coli was the commonest organism in blood culture in 15/28 (53.5%) patients. SBP group had a higher mortality (11/44; 25%) as compared to CNNA (12/143; 8.4%), p = 0.003. On multiple logistic regression analysis, creatinine >1.1 mg/dl and positive blood culture were the independent predictors of mortality in patients with SBP.</p> <p>Conclusion</p> <p>Patients with SBP have a higher mortality than CNNA. Independent predictors of mortality in SBP are raised serum creatinine and a positive blood culture.</p

Characterization of the Threshold Response of Initiation of Blood Clotting to Stimulus Patch Size

This article demonstrates that the threshold response of initiation of blood clotting to the size of a patch of stimulus is a robust phenomenon under a wide range of conditions and follows a simple scaling relationship based on the Damkohler number. Human blood and plasma were exposed to surfaces patterned with patches presenting clotting stimuli using microfluidics. Perturbations of the complex network of hemostasis, including temperature, variations in the concentration of stimulus (tissue factor), and the absence or inhibition of individual components of the network (factor IIa, factor V, factor VIII, and thrombomodulin), did not affect the existence of this response. A scaling relationship between the threshold patch size and the timescale of reaction for clotting was supported in numerical simulations, a simple chemical model system, and experiments with human blood plasma. These results may be useful for understanding the spatiotemporal dynamics of other autocatalytic systems and emphasize the relevance of clustering of proteins and lipids in the regulation of signaling processes

Using chemistry and microfluidics to understand the spatial dynamics of complex biological networks

Understanding the spatial dynamics of biochemical networks is both fundamentally important for understanding life at the systems level and also has practical implications for medicine, engineering, biology, and chemistry. Studies at the level of individual reactions provide essential information about the function, interactions, and localization of individual molecular species and reactions in a network. However, analyzing the spatial dynamics of complex biochemical networks at this level is difficult. Biochemical networks are non-equilibrium systems containing dozens to hundreds of reactions with nonlinear and time-dependent interactions, and these interactions are influenced by diffusion, flow, and the relative values of state-dependent kinetic parameters. To achieve an overall understanding of the spatial dynamics of a network and the global mechanisms that drive its function, networks must be analyzed as a whole, where all of the components and influential parameters of a network are simultaneously considered. Here, we describe chemical concepts and microfluidic tools developed for network-level investigations of the spatial dynamics of these networks. Modular approaches can be used to simplify these networks by separating them into modules, and simple experimental or computational models can be created by replacing each module with a single reaction. Microfluidics can be used to implement these models as well as to analyze and perturb the complex network itself with spatial control on the micrometer scale. We also describe the application of these network-level approaches to elucidate the mechanisms governing the spatial dynamics of two networks-hemostasis (blood clotting) and early patterning of the Drosophila embryo. To investigate the dynamics of the complex network of hemostasis, we simplified the network by using a modular mechanism and created a chemical model based on this mechanism by using microfluidics. Then, we used the mechanism and the model to predict the dynamics of initiation and propagation of blood clotting and tested these predictions with human blood plasma by using microfluidics. We discovered that both initiation and propagation of clotting are regulated by a threshold response to the concentration of activators of clotting, and that clotting is sensitive to the spatial localization of stimuli. To understand the dynamics of patterning of the Drosophila embryo, we used microfluidics to perturb the environment around a developing embryo and observe the effects of this perturbation on the expression of Hunchback, a protein whose localization is essential to proper development. We found that the mechanism that is responsible for Hunchback positioning is asymmetric, time-dependent, and more complex than previously proposed by studies of individual reactions. Overall, these approaches provide strategies for simplifying, modeling, and probing complex networks without sacrificing the functionality of the network. Such network-level strategies may be most useful for understanding systems with non-linear interactions where spatial dynamics is essential for function. In addition, microfluidics provides an opportunity to investigate the mechanisms responsible for robust functioning of complex networks. By creating nonideal, stressful, and perturbed environments, microfluidic experiments could reveal the function of pathways thought to be nonessential under ideal conditions

Lunar International Science Coordination/Calibration Targets

A new era of international lunar exploration has begun and will expand over the next four years with data acquired from at least four sophisticated remote sensing missions: KAGUYA (SELENE) [Japan], Chang'E [China], Chandrayaan-l [India], and LRO [United States]. It is recognized that this combined activity at the Moon with modern sophisticated sensors wi II provide unprecedented new information about the Moon and will dramatically improve our understanding of Earth's nearest neighbor. It is anticipated that the blooming of scientific exploration of the Moon by nations involved in space activities will seed and foster peaceful international coordination and cooperation that will benefit all. Summarized here are eight Lunar International Science Coordination/Calibration Targets (L-ISCT) that are intended to a) allow cross-calibration of diverse multi-national instruments and b) provide a focus for training young scientists about a range of lunar science issues. The targets, discussed at several scientific forums, were selected for coordinated science and instrument calibration of orbital data. All instrument teams are encouraged to participate in a coordinated activity of early-release data that will improve calibration and validation of data across independent and diverse instruments