The shear modulus of the human vocal fold in a transverse direction

The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3g was applied to the epithelium, and the resultant displacement logged at a rate of 1kHz. Force measurement accuracy was 20microg and position measurement accuracy was 4microm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796Pa. These data demonstrate that it is possible to obtain estimates for the shear modulus of the vocal fold while preserving anatomical context. The modulus values reported here are higher than those reported using parallel plate rheometry. This is to be expected as the tissue is attached to surrounding structures, and is under natural tension.     

Photoinduced radical processes on the spinel (MgAl2O4) surface involving methane, ammonia, and methane/ammonia

The present study explored photoinduced radical processes caused by interaction of CH(4) and NH(3) with a photoexcited surface of a complex metal oxide: magnesium-aluminum spinel (MgAl(2)O(4); MAS). UV irradiation of MAS in vacuo yielded V-type color centers as evidenced by the 360 nm band in difference diffuse reflectance spectra. Interaction of these H-bearing molecules with photogenerated surface-active hole states (O(S)(-)?) yielded radical species which on recombination produced more complex molecules (including heteroatomic species) relative to the initial molecules. For the MAS/CH(4) system, photoinduced dissociative adsorption of CH(4) on surface-active hole centers produced ?CH(3) radicals that recombined to yield CH(3)CH(3). For MAS/NH(3), a similar dissociative adsorption process led to formation of ?NH(2) radicals with formation of NH(2)NH(2) as an intermediate product; continued UV irradiation ultimately yielded N(2). For the mixed MAS/CH(4)/NH(3) system, however, interaction of adsorbed NH(3) and CH(4) on the UV-activated surface of MAS yielded ?NH(2) and ?CH(3) radicals, respectively, which produced CH(3)-NH(2) followed by loss of the remaining hydrogens to form a surface-adsorbed cyanide, CN(S), species. Recombination of photochemically produced radicals released sufficient energy to re-excite the solid spinel, generating new surface-active sites and a flash luminescence (emission decay time at 520 nm, τ ~ 6 s for the MAS/NH(3) case) referred to as the PhICL effect.     

Mechanistic studies of the formation of different states of oxygen on irradiated ZrO2 and the photocatalytic nature of photoprocesses from determination of turnover numbers

The photoadsorption of oxygen (photoreduction on electron surface-active centers) and the photoadsorption of hydrogen (photooxidation on hole surface-active centers) as well as the photooxidation of hydrogen in the presence of oxygen were examined over irradiated zirconia (ZrO2) specimens by thermoprogrammed desorption spectroscopy (TPD) and kinetically to assess the states (forms) of oxygen species formed on the surface of zirconia. The three TPD spectral maxima observed inferred three oxygen species of varying activity in the photooxidation of hydrogen. The number of surface-active sites on the zirconia surface were quantitatively estimated (ca. 1 x 10(16) centers), thereby permitting an estimate of the turnover numbers (TON) for the photooxidation of hydrogen (TON > 14.5) and for the photoreduction of oxygen (TON > 6.6). These demonstrate for the first time that a photoreaction occurring on the surface of a metal-oxide photocatalyst is truly photocatalytic.     

Hydrodynamic Properties of “Pseudo-Dendrimer”

Summary: Hyperbranched polycarbosilane with terminal butyl groups is obtained by chemical modification of hyperbranched polyallylcarbosilane using the reaction of hydrosilylation with methyldichlorosilane, followed by treatment of the polychlorosilyl derivative with butyllithium. Its hydrodynamic and conformational properties are studied by the methods of light scattering, sedimentation-diffusion analysis, and viscosimetry in dilute solutions of methyl-tert-butyl ether, hexane, THF, chloroform, and toluene. The results obtained are compared with the data for the initial polyallylcarbosilane and carbosilane dendrimer with butyl terminal groups. It is demonstrated that branching regularity is the decisive factor determining the solution properties at fixed degree of the branching.     

Rheological properties of nonfunctional derivatives of hyperbranched polycarbosilanes

The rheological properties of melts of nonfunctional hyperbranched polycarbosilane polymers differed in regularity of the structure and chain length between the branch points were studied for the first time. Unlike melts of linear polymers, the studied hyperbranched systems are Newtonian fluids, and the viscosity and activation energy of their viscous flow depend substantially on the molecular parameters and regularity of the molecular structure.     

Effect of surface photoreactions on the photocoloration of a wide band gap metal oxide: probing whether surface reactions are photocatalytic

A nonphotocatalytic reaction occurring on the surface of an irradiated wide band gap metal oxide, such as ZrO2, can affect the process of photoinduced formation of Zr3+, F- and V-type color centers. The effect of such reactions is seen as the influence of photostimulated adsorption on the photocoloration of the metal oxide specimen. In particular, photoadsorption of electron donor molecules leads to an increase of electron color centers, whereas photoadsorption of electron acceptor molecules leads to an increase of hole color centers. Monitoring the photocoloration of a metal oxide during a surface photochemical reaction probes whether the reaction is photocatalytic: accordingly, the influence of simple photoreactions on the photocoloration of ZrO2, reactions that involved the photoreduction of molecular oxygen, the photooxidation of molecular hydrogen, the photooxidation of hydrogen by adsorbed oxygen, and the photoinduced transformation of ammonia and carbon dioxide. Kinetics of the photoprocesses are reported, as well as the photoinduced chesorluminscence (PhICL effect) of ammonia. Thermoprogrammed desorption and mass spectral monitoring of the photoreaction involving NH3 identified hydrazine as an intermediate and molecular nitrogen as the final product. The photoreactions involving NH3 and CO2 are nonphotocatalytic processes, in contrast to the photooxidation of hydrogen which is photocatalytic. Carbon dioxide and carbonate radical anions are formed by interaction of CO2 with Zr3+ centers and hole states (OS-*), respectively. Mechanistic implications are discussed.     

Synthesis and properties of carbosilane dendrimers with perfluorohexyl groups in the outer layer of the molecular structure

Branched perfluorohydrosiloxane with CF₃CF₂CF₂C(CF₃)₂(CH₂)₃ groups at the silicon atom was synthesized by a sequence of chemical reactions. The resulting compound was used as a modifying agent for carbosilane dendrimers of the 3rd and 6th generations. Dendrimers with perfluorohexyl terminal groups in surface layer are characterized by a complex of physicochemical methods. It is demonstrated that due to the branching of perfluoroalkyl terminal groups, obtained carbosilane dendrimers are soluble in organic and inorganic media. Differences in the solubility of small and large dendrimers are caused by the formation of the outer fluoride shell of different densities.     

COMPOSITION OF INDOOR AEROSOLS AT EMPEROR QIN''''S TERRA-COTTA MUSEUM, XI''''AN, CHINA, DURING SUMMER, 2004

Particle samples were collected in August 2004 both inside and outside Emperor Qin's Terra-Cotta Museum in Xi'an, China. Mass and chemical composition of total suspended particles (JSP, particles with aerodynamic diameter less than-30μm), PM2.5(particles with aerodynamic diameter <2.5μm) were determined. The average levels of indoor PM2.5 and TSP were 108.4 and 172.4 μg·m-3, respectively, with PM2.5 constituting 62.9% of the TSP mass. Sulfate ((32.4±6.2)%), organics ((27.7±8.0)%), and geological material ((12.5±3.4)%) dominated indoor PM2.5, followed by ammonium ((8.9±2.8)%), nitrate ((7.0±2.9)%), and elemental carbon (EC, (3.9±1.5)%). Particle size distribution varied with the number of tourists in the museum. The size of sulfate, organics, EC, nitrate, and ammonium was found to vary in the range of 0.43 to 3.3 μm in fraction. Ion balance indicated that the aerosol was acidic, with insufficient ammonium ions to neutralize the sulfuric and nitric acids. High concentrations of acidic aerosols will erode the Terra-cotta warriors and horses especially in the summer season with high temperature (30℃) and relative humidity (70%) and undesirable solar radiation inside the museum. More attention should be paid to protecting these precious antiques made 2000 years ago.     

Temperature Dependence of the Hydrodynamic and Conformational Properties of Hyperbranched Polycarbosilanes

Three types of carbosilane hyperbranched polymers were studied in dilute solution in toluene. The samples had different lengths of chains between branch points and the structure of terminal groups (butyl, undecenyl, or fluorine containing). The temperature dependences of intrinsic viscosity and second virial coefficient values were determined by viscometry and static light scattering methods. It is shown that conformational characteristics of hyperbranched polycarbosilanes do not depend on the thermodynamic quality of a solution in the wide range of temperatures.