Application of high Tc superconductors asfrequency selective surfaces: experiment and theory

The use of YBa₂Cu₃O_7-x and Tl₂CaBa₂Cu₂O₈ high-temperature superconducting thin films to fabricate frequency selective surfaces (FSS) at millimeter-wave frequencies (75-110 GHz) is discussed. An analytical/numerical model was applied, using a Floquet expansion and the method of moments, to analyze bandstop superconducting frequency selective surfaces. Experimental results were compared with the model, and showed agreement with resonant frequency prediction with an accuracy of better than 1%. The use of the superconducting frequency selective surfaces as quasi-optical millimeter-wave bandpass filters was also demonstrated     

Effect of metabolic acidosis on insulin action and secretion in uremia

BACKGROUND: Metabolic acidosis affects both vitamin D and insulin metabolism. Vitamin D is important in modulation of both insulin secretion and insulin sensitivity in uremia. The present study examines the effect of correction of metabolic acidosis on insulin action and secretion as well as 1,25 vitamin D3 concentrations in uremic patients. METHODS: Eight patients (age 18 +/- 1 year) on maintenance hemodialysis with metabolic acidosis were studied before and after two weeks of oral sodium bicarbonate (NaHCO3) treatment to correct the acidosis. To control for the effect of additional sodium, they were also studied after two weeks of an equivalent amount of oral sodium chloride (NaCl). Controls consisted of 7 healthy controls (age 19 +/- 1 year). Insulin sensitivity was measured by the hyperinsulinemic euglycemic clamp technique. Insulin secretion was measured by the hyperglycemic clamp technique. RESULTS: Oral NaHCO3 treatment led to significant increases in venous pH and serum bicarbonate concentrations but no significant change in intact parathyroid hormone (PTH) concentrations. Circulating 1,25 dihydroxyvitamin [(OH)2] D3 were significantly lower than control values initially and increased significantly after treatment. Oral NaCl did not change any of the biochemical parameters. Before treatment of acidosis, uremic patients had lower insulin sensitivity (insulin resistance) during constant hyperinsulinemia and lower insulin secretion during constant hyperglycemia compared with controls. Following two weeks of NaHCO3 treatment there were significant increases in insulin sensitivity and insulin secretion, although the values did not normalize. There were no changes in insulin sensitivity or insulin secretion following two weeks of NaCl. CONCLUSION: Treatment of metabolic acidosis increased both insulin sensitivity and insulin secretion in patients with uremia. This was accompanied by an increase in the circulating levels of 1,25(OH)2D3 but no change in those of parathyroid hormone.     

A LARGE MANNAN MOLECULE RELEASED FROM ISOLATED YEAST CELL WALLS BY THE ACTION OF SNAIL GUT JUICE

The molecular weight of the mannans dissolved from isolated yeast cell walls by the action of snail gut juice is shown to be about two to three times as large as that of the more familiar type of mannan preparation which has been extracted in the presence of sodium hydroxide. Other types of large mannan molecules are associated with certain intracellular membranes. The availability of the former materials may facilitate the study of the chemistry of the alkali-labile bonds on which the integrity of the yeast cell wall depends.     

Fluorescence lifetime spectroscopy for pH sensing in scattering media

Fluorescence lifetime spectroscopy in the presence of tissuelike scattering is demonstrated from measurements of phase and modulation ratio as a function of modulation frequency using a pH-sensitive dye, Carboxy Seminaphthofluorescein-1 (C-SNAFL-1). From the optical diffusion equation describing the propagation and generation of fluorescence within solutions of 0.5 microM C-SNAFL-1 containing 2.0% (by volume) of Intralipid as a scatterer, the values of the average lifetime of C-SNAFL-1 were determined as the solution pH varied between 5 and 9. Average lifetime values were found to match those measured using traditional phase-modulation measurement in nonscattering media. Furthermore, the robustness of the spectroscopic technique was demonstrated by conducting lifetime measurements at varying scatterer concentrations (1.5-3.0 vol % Intralipid). These results confirm the approach for analytical sensing in scattering media via fluorescence lifetime kinetics in order to track changes in analyte concentrations.     

Polyhedral studies for minimum-span graph labelling with integer distance constraints

This paper studies the polytope of the minimum‐span graph labelling problems with integer distance constraints (DC‐MSGL). We first introduce a few classes of new valid inequalities for the DC‐MSGL defined on general graphs and briefly discuss the separation problems of some of these inequalities. These are the initial steps of a branch‐and‐cut algorithm for solving the DC‐MSGL. Following that, we present our polyhedral results on the dimension of the DC‐MSGL polytope, and that some of the inequalities are facet defining, under reasonable conditions, for the polytope of the DC‐MSGL on triangular graphs.     

A PDES/STEP-based information model for computer-aided process planning

Computer Aided Process Planning (CAPP) constitutes one of the most essential elements in Computer Integrated Manufacturing (CIM). Although many CAPP systems have been reported in literature during the last two decades, few of them are compatible enough to integrate easily with other systems in the CIM environment. One major reason is the lack of an effective method to represent the information required by CAPP, and to unify such information with the information of other systems in the CIM environment. Indeed, this problem has received relatively inadequate attention in the recent research of CAPP systems. In this paper, an information model for CAPP is developed by using the object-oriented modeling and the Product Data Exchange Step/STandard of Exchange Product data (PDES/STEP) techniques. The model consists of the part information model, the process plan information model, and the production resource information model. The EXPRESS language or the EXPRESS-G diagram is used to represent these models. Indeed, the proposed information model will greatly improve the CAPP system's capability of effective integration with other systems in the CIM environment, and, ultimately, to facilitate the implementation of the whole CIM strategy in manufacturing enterprises.     

Taylor vortex flow in presence of internal baffles

We present a study on Taylor vortex flow in between a rotating inner cylinder and a stationary outer cylinder with vertical or horizontal baffles. A mineral oil is used as the working fluid in the annular channel of 60 mm in height and 11.6 mm in gap width. The flow pattern in the annulus is investigated by particle image velocimetry (PIV) and computational fluid dynamics (CFD). Both the experimental and simulation results show that the presence of vertical baffles influences the vertical positions of vortices—it is primarily significant for the bottom vortex. Increasing number of vertical baffles gradually decreases the azimuthal variation in the vertical position. The baffles also lead to the occurrence of a circulation flow immediately upstream and downstream each baffle plate in the radial–azimuthal plane. On the other hand, an annular horizontal baffle with sufficient width alters the vortex structure in the gap, for instance, fewer vortices are observed. With two horizontal baffles in the annulus, the flow pattern is largely affected by the baffle width and the distance between the two baffles. This study provides a better understanding of Taylor vortex in presence of internal baffles, which will be important for practical applications of Taylor vortex devices.     

Direct observations of colloid retention in granular media in the presence of energy barriers, and implications for inferred mechanisms from indirect observations

In this paper we present direct observations of retention of colloids in granular porous media over a large size range (0.21-9.0 μm) and generalize the significance of attachment in grain to grain contacts and attachment on the open surface as a function of colloid:collector ratio. We examine reversibility of attachment via these mechanisms with respect to ionic strength reduction and fluid velocity increase. We relate these direct observations to existing literature, and in some cases offer alternative interpretations of mechanisms of retention drawn from indirect observations (e.g. via column effluent and retained concentrations).