Growth of calcium carbonate on non-covalently modified carbon nanotubes

The crystallization of calcium carbonate was investigated on pristine and non-covalently modified carbon nanotubes (CNTs) using the vapor diffusion technique in a calcium chloride solution. Non-covalent modification was accomplished by treating the carbon nanostructures with the amphiphilic copolymer poly(isoprene-b-acrylic acid). Calcium carbonate crystals grown on the surface and in the interstitial channels of CNT buckypapers were observed in both cases. Scanning electron microscopy analysis of the untreated CNTs showed the characteristic rhombohedral morphology of calcite crystals, while in the case of modified material spherical and ellipsoidal crystals, consisted of nanocrystallites, were observed. X-ray diffraction analysis showed the presence of calcite crystals in both cases.     

Harmonic oscillators realized using current amplifiers and grounded capacitors

New configurations of harmonic oscillators, realized using current amplifier blocks and only grounded capacitors, are introduced in this article. The proposed configurations are based on a grounded inductor simulator scheme and on a loop constructed from first‐order sections, respectively. Comparison with the already published topologies shows that the new configurations have attractive characteristics concerning their implementation in integrated form. Copyright © 2006 John Wiley & Sons, Ltd.     

Controlled Drug Release and Chemotherapy Response in a Novel Acoustofluidic 3D Tumor Platform

Overcoming transport barriers to delivery of therapeutic agents in tumors remains a major challenge. Focused ultrasound (FUS), in combination with modern nanomedicine drug formulations, offers the ability to maximize drug transport to tumor tissue while minimizing toxicity to normal tissue. This potential remains unfulfilled due to the limitations of current approaches in accurately assessing and quantifying how FUS modulates drug transport in solid tumors. A novel acoustofluidic platform is developed by integrating a physiologically relevant 3D microfluidic device and a FUS system with a closed‐loop controller to study drug transport and assess the response of cancer cells to chemotherapy in real time using live cell microscopy. FUS‐induced heating triggers local release of the chemotherapeutic agent doxorubicin from a liposomal carrier and results in higher cellular drug uptake in the FUS focal region. This differential drug uptake induces locally confined DNA damage and glioblastoma cell death in the 3D environment. The capabilities of acoustofluidics for accurate control of drug release and monitoring of localized cell response are demonstrated in a 3D in vitro tumor mode. This has important implications for developing novel strategies to deliver therapeutic agents directly to the tumor tissue while sparing healthy tissue.     

Global behavior of the diffusion coefficient for the Van Der Waals binary mixture

We describe the general dependence of the diffusion coefficient associated with the Van der Waals binary mixture on the temperature, number densities, and relative strengths of molecular interaction parameters. The task is facilitated by the fact that for Kac-type intermolecular potentials, in the long-range limit, the diffusion coefficient becomes simply related to the product of a partial compressibility and the curvature of the equilibrium free energy in the space of number densities. Therefore the different kinds of behavior found can be classified according to the scheme of Scott and Van Konynenburg for the global phase diagram of the same model mixture.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Monte Carlo circuits for the abelian permutation group intersection problem

Summary We show that the problem of computing a basis for an abelian transitive permutation group is in N C ^k and also we show that the problem of computing a basis for an abelian permutation group and the problem of computing the intersection of two abelian groups acting on n points, can be solved in depth (log n)^k on a Monte Carlo Boolean circuit of polynomial size. Moreover the latter two problems are shown to be in N C ^k in the restricted case of bounded number of generators.     

On the estimation of characteristic indoor air quality parameters using analytical and numerical methods

Indoor exposure to air contaminants penetrating from the outdoor environment depends on a number of key processes and parameters such as the ventilation rate, the geometric characteristics of the indoor environment, the outdoor concentration and the indoor removal mechanisms. In this study two alternative methods are used, an analytical and a numerical one, in order to study the time lag and the reduction of the variances of the indoor concentrations, and to estimate the deposition rate of the air contaminants in the indoor environment employing both indoor and outdoor measurements of air contaminants. The analytical method is based on a solution of the mass balance equation involving an outdoor concentration pulse which varies sinusoidally with the time, while the numerical method involves the application of the MIAQ indoor air quality model assuming a triangular pulse. The ratio of the fluctuation of the indoor concentrations to the outdoor ones and the time lag were estimated for different values of the deposition velocity, the ventilation rate and the duration of the outdoor pulse. Results have showed that the time lag between the indoor and outdoor concentrations is inversely proportional to the deposition and ventilation rates, while is proportional to the duration of the outdoor pulse. The decrease of the ventilation and the deposition rate results in a rapid decrement of the variance ratio of indoor to outdoor concentrations and to an increment of the variance ratio, respectively. The methods presented here can be applied for gaseous species as well as for particulate matter. The nomograms and theoretical relationships that resulted from the simulation results and the analytical methods respectively were used in order to study indoor air phenomena. In particular they were used for the estimation of SO2 deposition rate. Implications of the studied parameters to exposure studies were estimated by calculating the ratio of the indoor exposure to the exposure outdoors. Limitations of the methods were explored by testing various scenarios which are usually met in the indoor environment. Strong indoor emissions, intense chemistry and varying ventilation rates (opening and closing of the windows) were found to radically influence the time lag and fluctuation ratios.     

Experimental solid–liquid equilibria and solid formation kinetics for carbon dioxide in methane for LNG processing

In cryogenic liquefaction processes, CO₂ poses a solid-formation risk even in trace concentrations. We present solid–fluid equilibrium (SFE) data for CO₂ in liquid methane at CO₂ concentrations from (52 to 500) ppm, extending the available data and indicating that models tuned to existing data over predict the solubility of CO₂ at LNG storage temperatures (~112 K) by nearly a factor of 3. The new data are used to improve the SFE model in the ThermoFAST software package. The formation kinetics of CO₂ solids in liquid methane are elucidated at conditions relevant to cryogenic gas processing. Repeated, ramped-temperature formation measurements provide a statistical basis for quantifying solidification risk. Nucleation rates extracted from the ramped-temperature data, consistent with those measured at fixed temperature, were used to extract parameters describing CO₂ solid formation in methane. These results significantly improve the ability to predict CO₂ solid formation risk in cryogenic natural gas processing.     

Fe(PyTACN)‐Catalyzed cis‐Dihydroxylation of Olefins with Hydrogen Peroxide

A family of iron complexes with general formula [Fe(II)(^R,Y,XPyTACN)(CF₃SO₃)₂], where ^R,Y,XPyTACN=1‐[2′‐(4‐Y‐6‐X‐pyridyl)methyl]‐4,7‐dialkyl‐1,4,7‐triazacyclononane, X and Y refer to the groups at positions 4 and 6 of the pyridine, respectively, and R refers to the alkyl substitution at N‐4 and N‐7 of the triazacyclononane ring, are shown to be catalysts for efficient and selective alkene oxidation (epoxidation and cis‐dihydroxylation) employing hydrogen peroxide as oxidant. Complex [Fe(II)(^Me,Me,HPyTACN)(CF₃SO₃)₂] ( 7 ), was identified as the most efficient and selective cis‐dihydroxylation catalyst among the family. The high activity of 7 allows the oxidation of alkenes to proceed rapidly (30 min) at room temperature and under conditions where the olefin is not used in large amounts but instead is the limiting reagent. In the presence of 3 mol% of 7 , 2 equiv. of H₂O₂ as oxidant and 15 equiv. of water, in acetonitrile solution, alkenes are cis‐dihydroxylated reaching yields that might be interesting for synthetic purposes. Competition experiments show that 7 exhibits preferential selectivity towards the oxidation of cis olefins over the trans analogues, and also affords better yields and high [syn‐diol]/[epoxide] ratios when cis olefins are oxidized. For aliphatic substrates, reaction yields attained with the present system compare favourably with state of the art Fe‐catalyzed cis‐dihydroxylation systems, and it can be regarded as an attractive complement to the iron and manganese systems described recently and which show optimum activity against electron‐deficient and aromatic olefins.     

A collision resolution algorithm for clump-free fast moving cloth

Cloth animation is an important area of computer graphics due to its numerous applications. However, so far a fast moving cloth with multiple wrinkles has been difficult to animate because of the cloth clump problem. Cloth clumps are the frozen areas where cloth pieces are clustered unnaturally — an obstacle in making a realistic cloth animation. Hence we present a novel cloth collision resolution algorithm that prevents clump formation during fast cloth motions. The goal of our resolution algorithm is to make cloth move swiftly without having any unnatural frozen cloth clumps, while preventing any cloth-cloth and rigid-cloth penetrations at any moment of a simulation. The non-penetration status of cloth is maintained without the formation of cloth clumps regardless of the speed of cloth motion. Our algorithm is based on a particular order that we found in the resolution of cloth collisions, and can be used with any structural modeling approaches such as spring-masses or finite elements. This paper includes several realistic simulation examples involving fast motions that are clump-free.