A Quest for (sila)0-4cyclopentasilylenes and their Arduengo Analogs by DFT

Silicon - Following our interest in exotic silylenes, here we compare and contrast 20 novel five-membered cyclic silylenes, including saturated (sila)0–4 cyclopentasilylenes (1–10) and...     

A New Model for the Thermal Conductivity of Molten Salts

A new model based on rough hard-sphere theory is proposed for the thermal conductivity of molten salts. The model incorporates a smooth hard-sphere contribution using the properties of argon, as well as characteristic parameters based on the melting point of the molten salt. It is demonstrated that it is possible to correlate the thermal conductivity of monovalent and multivalent molten salts within experimental error using this approach. Furthermore, in salts with a common anion, the single adjustable parameter in the model exhibits regular behavior with the molecular weight of the salt. It is also shown that the thermal conductivity of several molten-salt mixtures can be predicted without any mixture parameters.     

Biopolymer nanocomposite films reinforced with nanocellulose whiskers

A xylan nanocomposite film with improved strength and barrier properties was prepared by a solution casting using nanocellulose whiskers as a reinforcing agent. The 13C cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) analysis of the spectral data obtained for the NCW/xylan nanocomposite films indicated the signal intensity originating from xylan-cellulose interactions. Qualitatively, the spectral data obtained for the NCW/xylan nanocomposite films indicated that the amount of xylan adsorbed to cellulose increases with the addition of NCW. In an attempt to quantify this effect, non-linear least-squared spectral line fitting was used to deconvolute the adsorbed xylan peak at -82 ppm. The peak intensity ratio of adsorbed xylan peak and xylan C1 peak, which represents the total amount of xylan increases suggesting that upon the addition of NCW, the amount of adsorbed xylan increases. In an effort to further infer the structure-property relationships associated with the observed strength and barrier properties, 1H NMR T2 relaxation experiments were also conducted to investigate the change in the nature of carbohydrate-water interactions as a result of NCW incorporation. Water adsorbed into the 50% nanocomposite film had significantly shorter relaxation times with respect to the control xylan/sorbitol and all other NCW/xylan nanocomposite films. Additionally, X-ray diffraction of the nanocomposite films showed increased levels of crystalline material in the nanocomposites due to NCW addition.     

Dosimetric comparison of centered and off-centered posterior neck electron fields

The effect of visual skills, such as binocularity, on saccadic eye movement test performance is currently unknown. Therefore, the relationship between performance on commonly used clinical saccadic eye movement tests and visual skill was studied in a masked investigation of 181 kindergartners and first graders (mean age 6.25 years) from a middle class, suburban, elementary school near Cleveland, Ohio. The New York State Optometric Association King-Devick saccade test (NYSOA K-D) and the Developmental Eye Movement test (DEM) were employed because they are two commonly used clinical saccadic eye movement tests. A Modified Clinical Technique (MCT) vision screening and Randot stereoacuity test were performed to evaluate other visual skills. Analysis revealed that for the whole study population, total errors on the NYSOA K-D were significantly related to referral on the MCT screening (p = 0.015) and stereoacuity worse than 100 sec arc (p = 0.011). A trend toward significance was also found between DEM ratio and stereoacuity worse than 50 sec arc for the whole study population. However, in the children who passed the MCT, stereoacuity was not found to be significantly related to performance on NYSOA K-D or DEM. Thus, our findings indicate that visual difficulties may affect performance on the NYSOA K-D in this population.     

Optimized lens-sparing treatment of retinoblastoma with electron beams

PURPOSE: The ideal lens-sparing radiotherapy technique for retinoblastoma calls for 100% dose to the entire retina including the ora serrata and zero dose to the lens. Published techniques, most of which use photons, have not accomplished this ideal treatment. We describe here a technique that approaches this ideal configuration using electron beam therapy. METHODS AND MATERIALS: Dose-modeling calculations were made using a computer program built around a proprietary algorithm. This program calculates 3D dose distribution for electrons and photons and uses the Cimmino feasibility method for the inverse problem of beam weighting to achieve the prescribed dose. The algorithm has been verified in the ocular region by measurements in a RANDO phantom. To search for an ideal lens-sparing beam setup, a stylized phantom of an 8-month-old infant was generated with built-in inhomogeneities, and a phantom of a 5-year-old child was generated from a patient CT series. RESULTS: Of more than 100 different beam setups tested, two 9 MeV electron beams at gantry angles plus and minus 26 degrees from the optic nerve axis achieved the best distribution. Both fields have a lens block and an isocenter between the globe and origin of the optic nerve. When equal doses are given to both fields, the entire extent of the retina (including ora serrata) received 100%, while the lens received 10% or less. CONCLUSION: The two-oblique-electron-beam technique here described appears to meet most of the stringent dosimetry needed to treat retinoblastoma. It is suitable for a range of ages, from infancy to early childhood years.     

The kinetics of interactions between fecapentaene-12 and DNA

Fecapentaene-12 (Fp-12) is a potent colon cancer mutagen, which interacts with DNA. In this study, the kinetics of its interactions with DNA is investigated. Various pHs are used. Three first-order rates are observed at each pH. This suggests that interaction between Fp-12 and DNA occurs through three different mechanisms.     

Substituent Effect On Structure,Stability, and Electronic Properties of the Novel Bicyclic Silylenes at DFT

Silicon - The density functional theory (DFT) calculations are carried out to assay the effects of nitrogen atoms on the stability and reactivity of singlet (s) and triplet (t) forms of novel...