Modeling resonator frequency fluctuations induced by adsorbing and desorbing surface molecules

Resonator frequency fluctuations due to adsorption and desorption of molecules on plate electrodes are studied using the principle of mass-loading effects of adsorbed molecules. The study is based on a 525 MHz, AT-cut quartz resonator enclosed in a small crystal holder. Equations relating the surface adsorption rates of the crystal holder to pressure were derived and found to be quadratic polynomial functions of the adsorption rates. Calculations based on these equations show that a contaminant gas with a higher desorption energy creates larger changes in pressure when the temperature is varied. The function describing the frequency fluctuations due to any one contaminant site is a continuous-time Markov chain. Kolmogorov equations and an autocorrelation function for the Markov chain are derived. The autocorrelation and spectral density function of resonator frequency fluctuations are derived. The spectral density of frequency fluctuations at 1 Hz is studied as a function of pressure, temperature, and desorption energy of molecules. The noise levels for a contaminant gas with one type of molecules are found to be lower for lower desorption energies, and higher at lower pressures.     

Resonator surface contamination-a cause of frequency fluctuations?

The mass loading effects of adsorbing and desorbing contaminant molecules on the magnitude and characteristics of frequency fluctuations in a thickness-shear resonator are studied. The study is motivated by the observation that the frequency of a thickness-shear resonator is determined predominantly by such mechanical parameters as the thickness of the resonator, elastic stiffnesses, mass loading of the electrodes, and energy trapping. An equation was derived relating the spectral density of frequency fluctuations to: (1) rates of adsorption and desorption of one species of contaminant molecules; (2) mass per unit area of a monolayer of molecules: (3) frequency constant; (4) thickness of resonator; and (5) number of molecular sites on one resonator surface. The induced phase noises were found to be significant in very-high-frequency resonators and are not simple functions of the percentage of area contaminated. The spectral density of frequency fluctuations was inversely proportional to the fourth power of the thickness if other parameters were held constant.     

Synthesis and characterization of photopolymerizable hydrogels based on poly (ethylene glycol) for biomedical applications

Hydrogels are polymeric materials widely used in medicine due to their similarity with the biological components of the body. Hydrogels are biocompatible materials that have the potential to promote cell proliferation and tissue support because of their hydrophilic nature, porous structure, and elastic mechanical properties. In this work, we demonstrate the microwave-assisted synthesis of three molecular weight varieties of poly(ethylene glycol) dimethacrylate (PEGDMA) with different mechanical and thermal properties and the rapid photo of them using 1-hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184) as UV photoinitiator. The effects of the poly(ethylene glycol) molecular weight and degree of acrylation on swelling, mechanical, and rheological properties of hydrogels were investigated. The biodegradability of the PEGDMA hydrogels, as well as the ability to grow and proliferate cells, was examined for its viability as a scaffold in tissue engineering. Altogether, the biomaterial hydrogel properties open the way for applications in the field of regenerative medicine for functional scaffolds and tissues.     

Nitrophosphates and DAP are equally effective as P fertilizers for various crop species grown in rotation on a Typic Haplustept

In two long-term field experiments using wheat-maize and potato-sunflower-pearl millet (fodder) cropping systems on Typic Haplustept loamy sand, three different water-soluble P fertilizers [diammonium phosphate (DAP, water-soluble phosphorus content (WSPC) of 89.1%), ammonium nitrophosphate (ANP, WSPC 59%) and suphala (ammonium nitrophosphate, WSPC 26.7%)] were compared. Five amounts of P (0, 8.75, 17.5, 26 and 35 kg P/ha) were applied to wheat and (0, 13, 26, 39 and 52 kg P/ha) to potato. The succeeding crops under both the rotations used residual P from the P applied to wheat and potato crops. Grain yield and P content of wheat increased significantly up to an applied P level of 26 kg P/ha while the residual effect on maize crop was significant up to 17.5 kg P/ha. Tuber yield and P content of potato increased significantly up to an applied P level of 39 kg P/ha while the residual effect on sunflower and pearl millet (fodder) crops was significant up to 26 kg P/ha. Total profits in a year from wheat-maize and potato-sunflower-pearl millet (fodder) cropping systems increased significantly up to an applied P level of 26 and 39 kg P/ha, respectively. However, at all the levels of applied P and under both the cropping systems, the three P fertilizers used were found to be equally effective for plant yields, P contents, relative agronomic efficiencies and total profits in a year. Hence, it was concluded that the two nitrophosphates can be used instead of DAP as P fertilizers for the soil, plant species and crop rotations studied.     

Synthesis and antitumor activity of 1-β-D-arabinofuranosylcytosine conjugates of optical isomers of ether and thioether lipids

Four 1-β-D-arabinofuranosylcytosine conjugates (ara-C) (1a, b and 2a, b) ofsn−1 andsn−3 isomers of 1-O-octadecyl-2-O-palmitoylglycerol and its 1-S-alkyl analogue have been synthesized, and their antitumor activity against L1210 lymphoid leukemia in mice were compared with those of the previous conjugates (3a, b) of racemates in order to determine the significance of chirality of the glycerol moieties for activity. Administration (i.p.) of a single dose (300 mg/kg) of conjugates ofsn−1 (1a),sn−3 (2a) andrac (3a) isomers of the ether lipid increased lifespan of i.p. implanted L1210 lymphoid leukemic DBA/2J mice by 169, 175 and 236%, respectively. Thesn−1 (1b),sn−3 (2b), andrac (3b) isomers of the thioether lipid with a single dose of 300 mg/kg produced an increase in lifespan values of 238, 263 and 250%, respectively. The results indicate that chirality of the glycerol moieties appears not to be critical for the activity, and racemates 3a and 3b are promising prodrugs of ara-C for further clinical investigations. This material was presented in part at the 81 st Annual Meeting of the American Association for Cancer Research in Washington, D.C., May, 1990 (Abstract No. 2493).     

Impact of Variable Packet Length on the Performance of Heterogeneous Multimedia Wireless Sensor Networks

Wireless Personal Communications - Performance valuation of wireless sensor network (WSN) routing protocols calls for realistic data traffic models because of their application specific nature....     

Efficient photodegradation of methylene blue (MB) under solar radiation by ZrC nanoparticles

Due to increase in water pollution, there is a need to dwindle this problem for a clean and green future. Photocatalysts like ZnO, CaO and TiO₂ have proved to be triumphant in removal of environmental contaminants. In this present work, ZrC nanopowder has been synthesized using a single-step reduction technique by heating zirconium oxide (ZrO₂) and hexane (C₆H₁₄) in metallic Mg powder and is used as a photocatalyst for the degradation of methylene blue (MB) dye under solar radiation. Optimization of synthesis parameters (temperature, holding time and carbon content) has been done to obtain single phase ZrC. Various characterization techniques like X-ray diffraction (XRD), transmission electron microscope (TEM), differential scanning calorimetry/thermal gravimetric analysis (DSC/TGA) and X-ray photoelectron spectroscopy (XPS) were studied for various structural, thermal and surface characteristics of as-synthesized samples. The effect of synthesis parameters on crystal distortion of ZrC particles was studied with the help of Double Voigt analysis. Further, the comparative catalytic activity as photodegradation of MB dye with the help of optimized sample was studied under UV and solar radiations. As an effect of illumination source with the same concentration of catalyst and dye, 80% degradation was observed under solar radiations which is quite higher than that observed under UV in 5?h.