Surface characteristics and blood compatibility of PVDF/PMMA membranes

Poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) membranes have important applications as biomaterials. In this study, PVDF/PMMA with varying ratios is blown into membranes, the surface property and blood compatibility of which are thoroughly investigated. Membrane surface characteristics including composition and topography exert considerable influence on the blood compatibility. Introduction of PMMA disturbs PVDF crystallization, however, favors the β phase crystal formation. PVDF content, crystallization ability, and surface enrichment have decisive effects on the membrane surface composition. Meanwhile, with increased PMMA fraction, the membrane surface roughness is also increased, and subsequently results in decreased hemocompatibility. While the membranes with PMMA content lower than 30 wt% show good blood compatibility, those with higher PMMA fraction exhibit obvious platelet adhesion to the surface. Thermal annealing promotes the formation of β phase PVDF and generates much smoother surface, thus endowing the membranes with greatly enhanced blood compatibility. These results show the prospect for optimization of processability, surface property, and blood compatibility of PVDF/PMMA membranes through facile modulation of PMMA content and fabrication process.     

Invited review: Hispanic-style cheeses and their association with Listeria monocytogenes

The rise in consumption of Hispanic-style cheeses (HSC), due in large part to the increasing Hispanic population in the United States, has not been met with advances in food safety sufficient to prevent the numerous outbreaks and recalls due to Listeria monocytogenes. Hispanic-style cheeses are typically high moisture and have low salt content and low acidity from being subjected to little to no ripening. These conditions necessitate refrigeration to maintain safety and quality, as the majority of traditional extrinsic preservation methods are either ineffective or disrupt the mild sensory attributes of HSC. Unfortunately, the cold-growth of L. monocytogenes presents significant problems from post-pasteurization contamination or insufficient pasteurization. In this review, we discuss the factors affecting listerial contamination and growth in HSC, and present current knowledge of L. monocytogenes incidence in manufacturing settings and commercial prevalence. Furthermore, we differentiate HSC types by processing methods to aid with interpretation of works involving nonstandardized varieties and, finally, summarize research on intervention methods for eliminating listerial contaminants in HSC.     

Carotene Degradation and Isomerization during Thermal Processing: A Review on the Kinetic Aspects

Kinetic models are important tools for process design and optimization to balance desired and undesired reactions taking place in complex food systems during food processing and preservation. This review covers the state of the art on kinetic models available to describe heat-induced conversion of carotenoids, in particular lycopene and β-carotene. First, relevant properties of these carotenoids are discussed. Second, some general aspects of kinetic modeling are introduced, including both empirical single-response modeling and mechanism-based multi-response modeling. The merits of multi-response modeling to simultaneously describe carotene degradation and isomerization are demonstrated. The future challenge in this research field lies in the extension of the current multi-response models to better approach the real reaction pathway and in the integration of kinetic models with mass transfer models in case of reaction in multi-phase food systems.     

Development and testing of an innovative two-arm focal-plane thermal strap (TAFTS)

Temperature control of optical focal planes comes with the intrinsic challenge of creating a pathway that is both extremely flexible mechanically and highly conductive thermally. The task is further complicated because science-caliber optical focal planes are extremely delicate, yet time, cost, and their unique nature means that their mechanical resiliency is rarely tested and documented. The mechanical engineer tasked with the thermo-mechanical design must then create a highly conductive thermal link that minimizes the tensile and shear stresses transmitted to the focal plane without design parameters on an acceptable stiffness and without data on the stiffness of previously implemented thermal links.This paper describes the development and testing of the thermal link developed for the Portable Remote Imaging Spectrometer (PRISM) instrument. It will provide experimentally determined mechanical stiffness plots in the three axes of interest. Analytical and experimental thermal conductance results for the two-arm focal-plane thermal strap (TAFTS), from cryogenic to room temperatures, are also presented. The paper also briefly describes some elements of the fabrication process followed in developing a novel design solution, which provides high conductance and symmetrical mechanical loading, while providing enhanced flexibility in all three dimensions.     

Evolution of microstructure and properties of internal nitride dispersion strengthened alloy before nitriding

Internal nitride dispersion strengthened superalloy is a new type of high performance superalloy for combustion chamber. The background and development of this alloy were firstly introduced. And then the microstructure and properties of NS163 which is a typical internal nitride dispersion strengthened alloy were investigated. The results show that the microstructure of NS163 is simple in the temperature range of 900??1250??, which is composed of austenite matrix and MC carbide. The recrystallization behavior of the cold- rolled sheet under the test condition was studied systematically. It is found that the solid solution temperature of the finished product should be 1200??, and after solid solution at 1200??, the sheet has 5 grade average grain size, excellent cold workability and low tensile strength at high temperature. The above results can help to optimize the microstructure of NS163 alloy sheet before nitriding and provide a basis for the evaluation of the strengthening effect of the alloy after internal nitriding.     

苯胍胺改性三聚氰胺甲醛树脂的合成研究

以NaOH为催化剂,在反应温度不超过90℃下,苯胍胺的加入可以改善三聚氰胺甲醛树脂体系的贮存稳定性,但树脂的固含量、黏度等指标与树脂的贮存稳定性没有明显的规律可循。作为发泡材料用树脂,树脂的固含量为90%左右时,发泡效果最好。     

Allocating reforestation areas for sediment flow minimization: an?integer programming formulation and?a?heuristic solution method

Policy and decision makers dealing with environmental conservation and land use planning often require identifying potential sites for contributing to minimize sediment flow reaching riverbeds. This is the case of reforestation initiatives, which can have sediment flow minimization among their objectives. This paper proposes an Integer Programming (IP) formulation and a Heuristic solution method for selecting a predefined number of locations to be reforested in order to minimize sediment load at a given outlet in a watershed. Although the core structure of both methods can be applied for different sorts of flow, the formulations are targeted to minimization of sediment delivery. The proposed approaches make use of a Single Flow Direction (SFD) raster map covering the watershed in order to construct a tree structure so that the outlet cell corresponds to the root node in the tree. The results obtained with both approaches are in agreement with expert assessments of erosion levels, slopes and distances to the riverbeds, which in turn allows concluding that this approach is suitable for minimizing sediment flow. Since the results obtained with the IP formulation are the same as the ones obtained with the Heuristic approach, an optimality proof is included in the present work. Taking into consideration that the heuristic requires much less computation time, this solution method is more suitable to be applied in large sized problems.