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Modeling Shows (modeling + shows)

Distribution by Scientific Domains

Polymers and Materials Science	40%

Selected Abstracts

Synthesis of Poly(4-vinylpyridine) Thin Films by Initiated Chemical Vapor Deposition (iCVD) for Selective Nanotrench-Based Sensing of Nitroaromatics

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010
Wyatt E. Tenhaeff
Abstract A new nanoscale sensing concept for the detection of nitroaromatic explosives is described. The design consists of nitroaromatic-selective polymeric layers deposited inside microfabricated trenches. As the layers are exposed to nitroaromatic vapors, they swell and contact each other to close an electrical circuit. The nitroaromatic selective polymer, poly(4-vinylpyridine) (P4VP), is deposited in the trenches using initiated chemical vapor deposition (iCVD). P4VP is characterized for the first time as a selective layer for the absorption of nitroaromatic vapors. The Flory,Huggins equation is used to model the swelling response to nitroaromatic vapors. The Flory,Huggins interaction parameter for the P4VP,nitrobenzene system at 40,°C is 0.71 and 0.25 for P4VP,4-nitrotoluene at 60,°C. Sensing of nitrobenzene vapors is demonstrated in a prototype device, while techniques to improve the performance of the design in terms of response time and sensitivities are described. Modeling shows that concentration and mass limits of detection of 0.95,ppb and 3 fg, respectively, can be achieved. [source]

Par j 1 and Par j 2, the two major allergens in Parietaria judaica, bind preferentially to monoacylated negative lipids

FEBS JOURNAL, Issue 6 2009
Roberto González-Rioja
Par j 1 and Par j 2 proteins are the two major allergens in Parietaria judaica pollen, one of the main causes of allergic diseases in the Mediterranean area. Each of them contains eight cysteine residues organized in a pattern identical to that found in plant nonspecific lipid transfer proteins. The 139- and 102-residue recombinant allergens, corresponding respectively to Par j 1 and Par j 2, refold properly to fully functional forms, whose immunological properties resemble those of the molecules purified from the natural source. Molecular modeling shows that, despite the lack of extensive primary structure homology with nonspecific lipid transfer proteins, both allergens contain a hydrophobic cavity suited to accommodate a lipid ligand. In the present study, we present novel evidence for the formation of complexes of these natural and recombinant proteins from Parietaria pollen with lipidic molecules. The dissociation constant of oleyl-lyso-phosphatidylcholine is 9.1 ± 1.2 ,m for recombinant Par j 1, whereas pyrenedodecanoic acid shows a much higher affinity, with a dissociation constant of approximately 1 ,m for both recombinant proteins, as well as for the natural mixture. Lipid binding does not alter the secondary structure content of the protein but is very efficient in protecting disulfide bonds from reduction by dithiothreitol. We show that Par j 1 and Par j 2 not only bind lipids from micellar dispersions, but also are able to extract and transfer negative phospholipids from bilayers. [source]

Atomistic Modeling Study of Surface Segregation in Nd:YAG

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006
Ulrich Aschauer
This study investigates the composition of free surfaces of neodymium-doped yttrium,aluminum,garnet, using energy minimization techniques. Atomistic modeling shows that the dopant is concentrated in a zone within 5 Å of the surface, the enrichment factor being around 1300 when comparing surfaces with bulk concentrations. It is shown that the (111) surface can incorporate 1.8 times as much Nd as the (110) surface, the latter commonly found in YAG morphologies. Our results indicate that by using nanocrystalline ceramics and by modifying crystal growth to form (111) surfaces, the Nd content and thus the laser power may be significantly increased. [source]

Mathematical modeling of 980-nm and 1320-nm endovenous laser treatment

LASERS IN SURGERY AND MEDICINE, Issue 3 2007
Serge R. Mordon PhD
Abstract Background and Objectives Endovenous laser treatment (ELT) has been proposed as an alternative in the treatment of reflux of the great saphenous vein (GSV) and small saphenous vein (SSV). Numerous studies have since demonstrated that this technique is both safe and efficacious. ELT was presented initially using diode lasers of 810 nm, 940 nm, and 980 nm. Recently, a 1,320-nm Nd:YAG laser was introduced for ELT. This study aims to provide mathematical modeling of ELT in order to compare 980 nm and 1,320 nm laser-induced damage of saphenous veins. Study Design/Materials and Methods The model is based on calculations describing light distribution using the diffusion approximation of the transport theory, the temperature rise using the bioheat equation, and the laser-induced injury using the Arrhenius damage model. The geometry to simulate ELT was based on a 2D model consisting of a cylindrically symmetric blood vessel including a vessel wall and surrounded by an infinite homogenous tissue. The mathematical model was implemented using the Macsyma-Pdease2D software (Macsyma, Inc., Arlington, MA). Calculations were performed so as to determine the damage induced in the intima tunica, the externa tunica and inside the peri-venous tissue for 3 mm and 5 mm vessels (considered after tumescent anesthesia) and different linear endovenous energy densities (LEED) usually reported in the literature. Results Calculations were performed for two different vein diameters: 3 mm and 5 mm and with LEED typically reported in the literature. For 980 nm, LEED: 50 to 160 J/cm (CW mode, 2 mm/second pullback speed, power: 10 W to 32 W) and for 1,320 nm, LEED: 50 to 80 J/cm (pulsed mode, pulse duration 1.2 milliseconds, peak power: 135 W, repetition rate 30 Hz to 50 Hz). Discussion and Conclusion Numerical simulations are in agreement with LEED reported in clinical studies. Mathematical modeling shows clearly that 1,320 nm, with a better absorption by the vessel wall, requires less energy to achieve wall damage. In the 810,1,320-nm range, blood plays only a minor role. Consequently, the classification of these lasers into hemoglobin-specific laser wavelengths (810, 940, 980 nm) and water-specific laser wavelengths (1,320 nm) is inappropriate. In terms of closure rate, 980 nm and 1,320 nm can lead to similar results and, as reported by the literature, to similar side effects. This model should serve as a useful tool to simulate and better understand the mechanism of action of the ELT. Lasers Surg. Med. 39:256,265, 2007. © 2007 Wiley-Liss, Inc. [source]

The effect of oxygen on interface microstructure evolution in CdS/CdTe solar cells

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2002
D.S. Albin
Microstructural changes at the CdS/CdTe solar cell interface where close-spaced sublimation (CSS) is used as the growth technique to deposit the p -type CdTe absorber layer are studied by systematic layer characterization at various stages during heterojunction growth. CdS layers grown by both chemical bath deposition (CBD) and CSS provide a basis for determining the effects of CdS crystallinity, grain size, and oxygen content on the subsequent CdTe layer. As-grown CBD CdS films exhibit small grains and variations in optical properties attributed to film impurities. In contrast, CSS yields CdS films with good crystallinity, larger grains, and nearly ideal optical properties. The hexagonal nature of CSS-grown CdS is seen to nucleate hexagonal CdTe during the initial stages of CdTe film growth. Cubic CdS deposited by CBD in contrast promotes cubic CdTe nucleation. Oxygen anneals in the latter case can aid hexagonal CdTe nucleation. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) of the CdS/CdTe interface show CdS-dependent differences in interdiffusion at the interface. This interdiffusion appears to be determined by the oxygen level in the CdS. When low-oxygen-containing CSS CdS films are used, sulfur diffusion is substantial, leading to significant consumption of the CdS layer. When these same films are annealed in oxygen, the consumption is reduced. Te diffusion into the CdS layer is also observed to decrease with oxygen anneals. Optical modeling shows that Te alloying with the CdS layer can greatly reduce the short-circuit current of CdS/CdTe devices. Copyright © 2002 John Wiley & Sons, Ltd. [source]