Ab Initio Calculations of Pristine and Doped Zirconia Σ5 (310)/[001] Tilt Grain Boundaries

The structure of the cubic-ZrO₂ symmetrical tilt Σ5 (310)/[001] grain boundary is examined using density functional theory within the local density and pseudopotential approximations. Several pristine stoichiometric grain-boundary structures are investigated and compared with Z-contrast scanning transmission electron microscopy and electron energy loss spectroscopy results. The lowest-energy grain-boundary structure is found to agree well with the experimental data. When Y³⁺ is substituted for Zr⁴⁺ at various sites in the lowest-energy grain-boundary structure, the calculations indicate that Y³⁺ segregation to the grain boundary is energetically preferred to bulk doping, in agreement with experimental results.     

Continuous and discrete time response analysis of the backflow cell model for linear interphase mass transfer on a distillation plate

An analysis of the backflow cell model of a distillation plate with linear interphase mass transfer is given. The steady state character is discussed in terms of liquid phase concentration profiles and plate efficiencies. The dynamics due to liquid and vapor phase concentration perturbations are derived for continuous time and discrete times based upon two point time difference methods of numerical solution. The moments of the discrete impulse response are related to those for continuous time. Stability and convergence are discussed. For the liquid on a valve plate, the backflow cell model outlet response due to a measured inlet response is compared to the monitored outlet response resulting from upstream salt tracer injection.     

Diameter dependent growth rate and interfacial abruptness in vapor-liquid-solid Si/Si1-xGex heterostructure nanowires

A strong diameter dependence is observed in the interfacial abruptness and growth rates in Si/Si 1- x Ge x axial heterostructure nanowires grown via Au-mediated low pressure CVD using silane and germane precursors. The growth of these nanowires has similarities to that of heterostructure thin films with similar compositional interfacial broadening, which increases with and is on the order with diameter. This broadening may reveal a fundamental challenge to fabrication of abrupt heterostructures via VLS growth.     

Theory of optimal beam splitting by phase gratings. II. Square and hexagonal gratings

We use the calculus of variations to give a general theory for finding optimal square and hexagonal phase gratings for doing beam splitting.     

A frequent activated smoothened mutation in sporadic basal cell carcinomas

Basal-cell carcinomas (BCCs) are the most common cancer in Caucasians. It has been reported that the patched gene is inactivated in 30-40% sporadic BCCs and 20% sporadic medulloblastomas via loss of heterozygosity and nonsense mutations. Recently, two activating smoothened mutations have been found in the sporadic basal cell carcinomas. One, at base pair 1604 (G-to-T transversion) of exon 9, changes codon 535 from tryptophan to leucine, and the other, at base pair 1685 (G-to-A transition) of exon 10, changes codon 562 from arginine to glutamine (Xie et al., 1998). In our study, 1604G-->T was found in 20 out of 97 (20.6%) sporadic BCCs. The high prevalence indicates that 1604G is the mutation hot spot in our tumor samples. This mutation was detected in all three histological subtypes of BCCs, suggesting that smoothened mutation is an early event during the development of the tumor. Our finding of a high smoothened mutation rate, together with high frequent patched gene mutations reported recently, indicates that activation of the hedgehog signal transduction pathway is the most common and early event in the development of sporadic BCCs. Additionally, to determine whether smoothened, like patched, is also involved in the carcinogenesis of medulloblastomas, we screened medulloblastoma samples for these two mutations by restriction analysis. We have found the 1604G-->T mutation in 1 out of 21 medulloblastomas. This result confirmed smoothened gene involvement in the carcinogenesis of medulloblastoma.     

Dynamic equilibrium unfolding pathway of human tumor necrosis factor-alpha induced by guanidine hydrochloride

The dynamic equilibrium unfolding pathway of human tumor necrosis factor-alpha (TNF-alpha) during denaturation at different guanidine hydrochloride (GdnHCl) concentrations (0-4.2 M) was investigated by steady-state fluorescence spectroscopy, potassium iodide (KI) fluorescence quenching, far-UV circular dichroism (CD), picosecond time-resolved fluorescence lifetime, and anisotropy decay measurements. We utilized the intrinsic fluorescence of Trp-28 and Trp-114 to characterize the conformational changes involved in the equilibrium unfolding pathway. The detailed unfolding pathway under equilibrium conditions was discussed with respect to motional dynamics and partially folded structures. At 0-0.9 M [GdnHCl], the rotational correlation times of 22-25 ns were obtained from fluorescence anisotropy decay measurements and assigned to those of trimeric states by hydrodynamic calculation. In this range, the solvent accessibility of Trp residues increased with increasing [GdnHCl], suggesting the slight expansion of the trimeric structure. At 1.2-2.1 M [GdnHCl], the enhanced solvent accessibility and the rotational degree of freedom of Trp residues were observed, implying the loosening of the internal structure. In this [GdnHCl] region, TNF-alpha was thought to be in soluble aggregates having distinct conformational characteristics from a native (N) or fully unfolded state (U). At 4.2 M [GdnHCl], TNF-alpha unfolded to a U-state. From these results, the equilibrium unfolding pathway of TNF-alpha, trimeric and all beta-sheet protein, could not be viewed from the simple two state model (N-->U).     

In situ optical variability and relationships in the Santa Barbara Channel: implications for remote sensing

Relationships and variability of bio-optical properties in coastal waters are investigated. Optical proxies indicate that these coastal waters are optically complex and highly variable and are categorized as follows: (1) relatively clear and dominated by high index of refraction, biogenic particles, (2) more turbid, consisting of mostly inorganic particles and little phytoplankton, (3) extremely turbid with high concentrations of inorganic particles, and (4) more turbid and dominated by biogenic particles. We present a method, alternative to traditional remote-sensing algorithms, of classifying coastal waters [the Spectral Angle Mapper (SAM)] and utilize the SAM to successfully isolate plume conditions in time series of downwelling irradiance and total absorption coefficient. We conclude with a discussion of the use of the SAM for coastal management operations.     

Transistors Formed from a Single Lithography Step Using Information Encoded in Topography

This paper describes a strategy for the fabrication of functional electronic components (transistors, capacitors, resistors, conductors, and logic gates but not, at present, inductors) that combines a single layer of lithography with angle‐dependent physical vapor deposition; this approach is named topographically encoded microlithography (abbreviated as TEMIL). This strategy extends the simple concept of ‘shadow evaporation’ to reduce the number and complexity of the steps required to produce isolated devices and arrays of devices, and eliminates the need for registration (the sequential stacking of patterns with correct alignment) entirely. The defining advantage of this strategy is that it extracts information from the 3D topography of features in photoresist, and combines this information with the 3D information from the angle‐dependent deposition (the angle and orientation used for deposition from a collimated source of material), to create ‘shadowed’ and ‘illuminated’ regions on the underlying substrate. It also takes advantage of the ability of replica molding techniques to produce 3D topography in polymeric resists. A single layer of patterned resist can thus direct the fabrication of a nearly unlimited number of possible shapes, composed of layers of any materials that can be deposited by vapor deposition. The sequential deposition of various shapes (by changing orientation and material source) makes it possible to fabricate complex structures—including interconnected transistors—using a single layer of topography. The complexity of structures that can be fabricated using simple lithographic features distinguishes this procedure from other techniques based on shadow evaporation.