Modeling of Lake Ice Characteristics in North America Using Climate, Geography, and Lake Bathymetry

Ice cover records from 128 freshwater lakes in the United States and Canada were analyzed. Multivariable linear regression models, log-transform models, and a combination of the two (the “hybrid” form) were used to express ice-in date, ice-out date, and maximum ice thickness as functions of mean air temperature, latitude, average depth, elevation, and surface area of each lake. Mean air temperatures are for periods from September 1 to December 31 for ice-in dates, February 1 to June 30 for ice-out dates, and September 1 to June 30 for maximum ice thickness. Data for individual years as well as averages (over the record length) for each lake were analyzed. The log-transform formulas proved best for estimating ice-in date, while the hybrid form provided the best models of maximum ice thickness. The linear regression model estimated the ice-out date best. In most cases, mean air temperature and/or latitude were the most influential parameters, followed by elevation. Lake surface area and depth had a small or no influence. R2 values of all equations ranged from 0.50 to 0.92.     

Mechanisms of Enzyme-Catalyzed Reduction of Two Carcinogenic Nitro-Aromatics, 3-Nitrobenzanthrone and Aristolochic Acid I: Experimental and Theoretical Approaches

This review summarizes the results found in studies investigating the enzymatic activation of two genotoxic nitro-aromatics, an environmental pollutant and carcinogen 3-nitrobenzanthrone (3-NBA) and a natural plant nephrotoxin and carcinogen aristolochic acid I (AAI), to reactive species forming covalent DNA adducts. Experimental and theoretical approaches determined the reasons why human NAD(P)H:quinone oxidoreductase (NQO1) and cytochromes P450 (CYP) 1A1 and 1A2 have the potential to reductively activate both nitro-aromatics. The results also contributed to the elucidation of the molecular mechanisms of these reactions. The contribution of conjugation enzymes such as N,O-acetyltransferases (NATs) and sulfotransferases (SULTs) to the activation of 3-NBA and AAI was also examined. The results indicated differences in the abilities of 3-NBA and AAI metabolites to be further activated by these conjugation enzymes. The formation of DNA adducts generated by both carcinogens during their reductive activation by the NOQ1 and CYP1A1/2 enzymes was investigated with pure enzymes, enzymes present in subcellular cytosolic and microsomal fractions, selective inhibitors, and animal models (including knock-out and humanized animals). For the theoretical approaches, flexible in silico docking methods as well as ab initio calculations were employed. The results summarized in this review demonstrate that a combination of experimental and theoretical approaches is a useful tool to study the enzyme-mediated reaction mechanisms of 3-NBA and AAI reduction.     

Self‐Assembly of Ferromagnetic Organic–Inorganic Perovskite‐Like Films

Perovskite‐based organic–inorganic hybrids hold great potential as active layers in electronics or optoelectronics or as components of biosensors. However, many of these applications require thin films grown with good control over structure and thickness—a major challenge that needs to be addressed. The work presented here is an effort towards this goal and concerns the layer‐by‐layer deposition at ambient conditions of ferromagnetic organic–inorganic hybrids consisting of alternating CuCl₄‐octahedra and organic layers. The Langmuir‐Blodgett technique used to assemble these structures provides intrinsic control over the molecular organization and film thickness down to the molecular level. Magnetic characterization reveals that the coercive field for these thin films is larger than that for solution‐grown layered bulk crystals. The strategy presented here suggests a promising cost effective route to facilitate the excellently controlled growth of sophisticated materials on a wide variety of substrates that have properties relevant for the high density storage media and spintronic devices.     

Development of Synthetic Platelet‐Activating Hydrogel Matrices to Induce Local Hemostasis

Several hemostatic strategies rely on the use of blood components such as fibrinogen and thrombin, which suffer from high cost and short shelf‐life. Here, a cost‐effective synthetic biomaterial is developed for rapid local hemostasis. Instead of using thrombin, thrombin‐receptor‐agonist‐peptide‐6 (TRAP6) is covalently engineered in polyvinyl alcohol (PVA) hydrogels. Soluble PVA‐TRAP6 is first prepared by covalent attachment of cysteine‐containing TRAP6 onto the backbone of PVA‐norbornenes (PVA‐NB) through photoconjugation. Cytotoxicity studies using C2C12 myoblasts indicate that PVA‐NB and PVA‐TRAP6 are nontoxic. Thromboelastography reveals that hemostatic activity of TRAP6 is retained in conjugated form, which is comparable to free TRAP6 solutions with equal concentrations. A 0.1% PVA‐TRAP6 solution can shorten the clotting time (CT) to ca. 45% of the physiological CT. High platelet‐activating efficiency is further confirmed by platelet aggregation assay and flow cytometry (FACS). For potential clinical applications, TRAP6‐presenting hydrogel particulates (PVA‐TRAP6‐P) are developed for local platelet activation and hemostasis. PVA‐TRAP6‐P is prepared by biofunctionalization of photopolymerized PVA‐NB hydrogel particulates (PVA‐NB‐P) with TRAP6. It is demonstrated that PVA‐TRAP6‐P can effectively shorten the CT to ca. 50%. FACS shows that PVA‐TRAP6‐P can activate platelets to a comparable extent as soluble TRAP6 control. Altogether, PVA‐TRAP6‐P represents a promising class of biomaterials for safe hemostasis and wound healing.     

Stabilizing the optimal carrier concentration for high thermoelectric efficiency

The band structure of PbTe can be manipulated by alloying with MgTe to control the band degeneracy. This is used to stabilize the optimal carrier concentration, making it less temperature dependent, demonstrating a new strategy to improve overall thermoelectric efficiency over a broad temperature range.     

Optical tweezers for synchrotron radiation probing of trapped biological and soft matter objects in aqueous environments

Investigations of single fragile objects manipulated by optical forces with high brilliance X-ray beams may initiate the development of new research fields such as protein crystallography in an aqueous environment. We have developed a dedicated optical tweezers setup with a compact, portable, and versatile geometry for the customary manipulation of objects for synchrotron radiation applications. Objects of a few micrometers up to a few tens of micrometers size can be trapped for extended periods of time. The selection and positioning of single objects out of a batch of many can be performed semi-automatically by software routines. The performance of the setup has been tested by wide-angle and small-angle X-ray scattering experiments on single optically trapped starch granules, using a synchrotron radiation microbeam. We demonstrate here for the first time the feasibility of microdiffraction on optically trapped protein crystals. Starch granules and insulin crystals were repeatedly raster-scanned at about 50 ms exposure/raster-point up to the complete loss of the structural order. Radiation damage in starch granules results in the appearance of low-angle scattering due to the breakdown of the polysaccharide matrix. For insulin crystals, order along the densely packed [110] direction is preferentially maintained until complete loss of long-range order.     

A new constitutive model for textured geomembrane/geotextile interfaces

The paper presents a study of the frictional behaviour of geosynthetics used for municipal solid waste landfills. Direct shear tests of several geomembrane/geotextile interfaces were performed to investigate the shear behaviour. Furthermore, analytical and numerical models were developed to describe the observed behaviour, especially to simulate progressive geomembrane/geotextile interface failure and the factors controlling its significance.     

Compatibility and molecular structure of rubbers

Compatibility of 17 pairs of rubbers has been investigated by means of phase separation, glass transition measurements and electron microscopy. Influence of structural details like side chains, configuration of monomer units and distance between double bonds in the chain on the compatibility of polymers has been elucidated. Experimental data lead to following results: Side chains have the strongest influence on compatibility; poly(isobutene) and poly(pentenamer), e.g., are highly incompatible. With decreasing influence on compatibility follows the configuration of the double bond in the polymer chain. Polymers with equal configuration are more compatible than polymers with different configuration. The structural detail with the weakest influence on compatibility is the distance between double bonds along the polymer chain. Poly(octenamer) and poly(pentenamer), e.g., with 6 and 3 methylene groups between the double bonds are less compatible than poly(butadiene) and poly(pentenamer) with a distance of 2 and 3 methylene groups. Cis-poly(pentenamer) and natural rubber were found to be highly compatible although electron micrographs show domains with an average diameter of 50 Å.