Routine sagittal whole-spine magnetic resonance imaging in finding incidental spine lesions

Magnetic Resonance Materials in Physics, Biology and Medicine - To examine the efficacy and feasibility of T2-weighted whole-spine sagittal magnetic resonance imaging (MRI) screening for all...     

Degradation and bioavailability of dried alginate hydrocolloid capsules in simulated soil system

Hydrocolloid capsules are common chemical carriers used in many types of applications in foods, biotechnology, and agriculture. Alginate microbeads and macrobeads are some of the more prevalent types of hydrocolloid capsules. Most studies to date have focused on alginate carrier applications but only a few have looked at their bioavailability after use. In this study, alginate carriers were subjected to simulated field conditions and their biodegradation in the soil was evaluated by respiration measurements, visualization, and volatile solids reduction. Using respiration rate, the degradation rate was calculated at 32 ± 3.1% (w/w) after 2 months. The visually estimated volume and volatile solids reduction gave degradation rates of 40 ± 8.6% (v/v) and 22.5 ± 2.5% (w/w), respectively. Moreover, water-loss calculations suggested that the carriers can serve as a stand-alone soil amendment for water retention. These findings emphasize the importance of studying hydrocolloid bioavailability in the soil and alginate carrier suitability for future applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48142.     

Co-production models with random functionality yields

Production systems with random functionality yields and downward substitutable demand are modeled and investigated. Such systems arise frequently in the electronics and petrochemical industries. We analyze two single-period models. The first models a single production process in which the total yield of usable products is uncertain; furthermore the realized usable products are of two grades, higher and lower, and the portions of each grade products are also uncertain. Demand for lower-grade products can be met, if necessary, by higher-grade units. The second model we analyze has two parallel production processes: one is as in die previous model; the other is attempting to produce lower-grade products only, but their yield is random. In both single-process and two-process scenarios the relative magnitudes of the salvage values of the two product grades lead to somewhat different models that need to be analyzed separately. We prove that all the expected profit functions are concave (jointly concave), and derive me optimality conditions. Some related modeling and managerial issues are discussed.     

The effectiveness of investment in lead time reduction for a make-to-stock product

This paper focuses on a firm selling a make-to-stock product with a constant customer demand rate. The firm follows an exact (Q, r) policy for raw material inventory control and faces a random replenishment lead time. Through this research, we wish to gain a better understanding of the impact of investing in reducing supply lead time when the investment costs have to be borne, partly or fully, by the firm. This work is motivated by the recognition that lead time reduction is now of strategic importance in the successful operation of a firm. We examine different types of investment schemes in replenishment lead time reduction and the different cost models they generate. We present analytical and numerical results and insights for each type of model, compute the optimal (Q, r) policy and the associated investment levels. The work presents new results, and sheds light on some apparently counter-intuitive observations.     

Composite polymer derived ceramic system for oxidizing environments

Preceramic polymers and expansion agents are being investigated to produce composite ceramic coatings for oxidation protection of metallic substrates. In this paper, we present results of a systematic approach to selecting the preceramic polymer and expansion agents and the optimization of the processing parameters to produce composite ceramics. Six commercially available poly(silsesquioxane) polymers and a polysiloxane were studied. In addition, several metals and an intermetallic were considered as potential expansion agents. Based on this study, the most desirable polymer/expansion agent combination and optimal processing parameters have been identified.     

Preceramic polymer pyrolysis

The physicochemical behaviour of characterized polysilazanes has been examined during their pyrolytic transformation into amorphous silicon-based ceramics. Selected polysilazanes bearing different substituents at silicon and nitrogen were synthesized by ruthenium catalysed dehydrocoupling of Si-H bonds with N-H bonds. The relationships between the structure and chemical content of polymers and their pyrolysed ceramic compositions and yields are discussed. Possible reactions occurring during pyrolysis are described in terms of a set of mechanisms based on known behaviour of silazane monomers. The decomposition product patterns at different temperature levels and the compositions of the final ceramics suggest specific kinetically or thermodynamically controlled thermolysis pathways. Additional chemical reactivity has been observed when the amorphous ceramic products at 800° C are heated and crystallized at 1600° C.     

On the Relationship Between the Grain Size and Gas-Sensitivity of Chemo-Resistive Metal-Oxide Gas Sensors with Nanosized Grains

In this work we elaborate the effect of grain size on the sensitivity of chemo-resistive metal-oxide gas sensors with nanosized grains. The effective carrier concentration in nanocrystalline SnO₂ sensors with various grain sizes is calculated as a function of the surface state density. This involves numerical computation of the charge balance equation (i.e., the electroneutrality condition) using approximated analytical solutions of Poissons equation for small spherical crystallites. The calculations demonstrate a sharp decrease in the carrier concentration when the surface state density reaches a critical value that corresponds to a condition of fully depleted grains, namely when nearly all the electrons are trapped at the surface. Assuming that the variations in the surface state density are induced by surface interactions with the gas phase, these calculations enable to simulate the response curves of nanocrystalline SnO₂ gas sensors. The simulations show that the conductivity increases linearly with decreasing trapped charge densities, and that the sensitivity to the gas-induced variations in the trapped charge density is proportional to 1/D, where D is the average grain size.     

Phytoplankton-mediated redox cycle of iron in the epilimnion of Lake Kinneret

The biological-mediated redox cycle of Fe was studied in the epilimnion of Lake Kinneret (Sea of Galilee), a mesotrophic lake in Israel. Multi-annual lake water sampling and incubation experiments were carried out to study Fe(III) reduction by natural phytoplankton populations and their possible role in inhibiting Fe(II) oxidation. The reduction characteristics of the dinoflagellate Peridinium gatunense, the dominant lake alga, were further examined in the laboratory. The steady-state concentration of Fe(II) calculated from the assessed reduction and oxidation rates was compared with Fe(II) measured in the lake in order to evaluate the significance of these processes to the lake Fe redox cycle. Nanomolar concentrations of Fe(II) were measured in the oxygenated, high pH, upper water layer of the lake throughout the year. Reduction rates of Fe by natural phytoplankton assemblages ranged between 0.1 and 10 nM/h. The highest reduction rates, determined in dinoflagellate-dominated lake waters, coincided with the highest concentrations of Fe(II) measured simultaneously in the lake. Iron(II) oxidation rates calculated from the measured lake Fe(II) and the obtained reduction rates were significantly slower than published abiotic Fe(II) oxidation rates. Indeed, Fe(II) oxidation rates measured in algal-enriched lake water were 30-fold slowerthan Fe(II) oxidation rates in natural water, demonstrating the potential for Fe(II) stabilization by the lake phytoplankton.