Optical-induced spectral tuning in grating-assisted nonlinearcouplers

The spectral (wavelength) properties of the grating-assisted nonlinear coupler are investigated theoretically. The interaction of linear and nonlinear wavelength-dependent phase detuning leads to a rich display of new and useful characteristics. Among these are bandpass tuning and spectral shaping. The grating frequency is viewed as a `free design parameter' which may be judiciously chosen to bring about an optimum behavior for a given application. As a wavelength processing element, the coupler behaves as an extended and continuously tunable wavelength filter, with tuning proportional to the input power. As an an-optical switch, a broadened and virtually transparent passband is easily achieved, which has desirable consequences for ultra-fast (large bandwidth) switching. The coupler may be operated in two complimentary modes: The active mode, where the power level of an input pulse or signal interacts in a nonlinear fashion with the passband of the coupler; and the passive mode, where a separate idler input is used to bias the device for a desired response to a smaller injected signal     

Procedures for analysis of strain transfer in the acetabular region in vitro

The failure of acetabular cups via loosening, migration or fracture is partially related to the stress distribution existing in the acetabular region. The complexity of the investigation of these stresses demands the application of a variety of model testing techniques involving combined embedded strain gauging, finite element analysis, transmission and reflective photoelasticity and crack propagation studies. The application of these procedures are described and the difficulties of obtaining representative loadings and restraints are commented upon.     

Continuous and discontinuous fatigue crack growth of irradiated ultrahigh molecular mass polyethylene in saline solution at 37°C

To provide data for prosthesis design, the fatigue crack growth resistance of irradiated ultrahigh molecular mass polyethylene (UHMMPE) in saline solution at 37°C was determined from tests performed on compact tension specimens, comparable in size to the components in knee prostheses. The specimens were cyclically loaded by using a sinusoidal wave form at 1 Hz with a minimum-to-maximum load ratio of 0.1. Scanning electron microscopic fractography was used to examine the fracture surfaces. At higher stress levels, the Paris's Law was used to analyse the data, and a striation pattern with each striation corresponding to multi-cycles was observed. At lower stress levels, discontinuous fatigue crack growth was found, a phenomenon which dominated the fatigue life of the material and had not been reported previously in this material. A craze zone ahead of the crack tip was observed, which formed the discontinuous crack growth band with a length relevant to the Dugdale plastic zone length.     

Very high-order microring resonator filters for WDM applications

High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications.     

Individuation, peers, and adolescent alcohol use: A latent growth analysis.

The study used latent growth modeling to investigate longitudinal relationships between individuation, peer alcohol use, and adolescent alcohol use among African American, Mexican American, and non-Hispanic White adolescents (N=6,048) from 7th, 8th, and 9th grades over a 3-year period. Initial levels of peer alcohol use were significantly related to changes in adolescents' alcohol use, whereas initial adolescent alcohol use also significantly related to changes in peers' alcohol use, suggesting a bidirectional relationship. Higher levels of intergenerational individuation were related to smaller increases in adolescent alcohol use and higher levels of separation were related to larger increases in youth drinking. The findings were similar across ethnic groups. Implications for development of prevention and intervention programs are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reducing energy-related CO2 emissions using accelerated weathering of limestone

The use and impacts of accelerated weathering of limestone (AWL; reaction: CO₂+H₂O+CaCO₃→Ca²⁺+2(HCO₃⁻) is explored as a CO₂ capture and sequestration method. It is shown that significant limestone resources are relatively close to a majority of CO₂-emitting power plants along the coastal US, a favored siting location for AWL. Waste fines, representing more than 20% of current US crushed limestone production (>10⁹ tonnes/yr), could provide an inexpensive or free source of AWL carbonate. With limestone transportation then as the dominant cost variable, CO₂ mitigation costs of $3-$4/tonne appear to be possible in certain locations. Perhaps 10–20% of US point–source CO₂ emissions could be mitigated in this fashion. It is experimentally shown that CO₂ sequestration rates of 10⁻⁶ to 10⁻⁵ moles/sec per m² of limestone surface area are achievable, with reaction densities on the order of 10⁻² tonnes CO₂ m⁻³day⁻¹, highly dependent on limestone particle size, solution turbulence and flow, and CO₂ concentration. Modeling shows that AWL would allow carbon storage in the ocean with significantly reduced impacts to seawater pH relative to direct CO₂ disposal into the atmosphere or sea. The addition of AWL-derived alkalinity to the ocean may itself be beneficial for marine biota.     

Exfoliation and related microstructures in 2024 aluminum body skins on aging aircraft

Exfoliation, a directional attack along elongated grain boundaries, has been examined in some detail in rolled 2024 aluminum sheet and plate for KC-135 aging aircraft body skin samples utilizing optical (light) metallography, scanning electron microscopy, and transmission electron microscopy. A detailed analysis and comparison of precipitates within the grains and in the grain boundaries were performed, as well as an examination of elemental depletion profiles across grain boundaries. These observations suggest that corrosion-related anodic sites play a far less significant role in the propagation of exfoliation than do the hard corrosion products creating wedging stresses within the elongated grain boundaries, which seem to demonstrate unique and unusual structural or energetic features or both.     

Cell-associated viral RNA expression during acute infection with HIV type 1

The mechanism of decline in viremia following acute infection with HIV is unknown. To characterize this process virologically, the expression of viral RNAs was analyzed in samples of peripheral blood mononuclear cells (PBMCs) from a patient who experienced a 100-fold decline in plasma viremia over a 13-day period prior to the initiation of antiretroviral therapy. Cell-associated viral RNA declined in association with the decline in plasma virus. During the initial 7 days of observation, plasma viremia declined more than 10-fold with no change in the ratio of unspliced to multiply spliced mRNAs. The efficiency of viral gene expression did not decline during the study period and varied from 380 to 2800 unspliced RNA copies per productively infected cell. Together, these data indicate no change in the relative proportion of cells in late- and early-stage gene expression during the initial decline and provide evidence against shortening of the viral replication cycle by immune surveillance. However, the prevalence of productively infected cells declined markedly during the 13 days of observation, from 1 in 250 to 1 in 25,000 PBMCs. These data are compatible with depletion of available target cells during the initial decline in viremia. As the level of plasma virus stabilized after 8 days of observation, the ratio of unspliced to multiply spliced mRNAs rose; this rise was due to a relatively greater decline in multiply spliced mRNA. These data suggest the possible onset of a blockade to new infection events (for example, by neutralizing antibody or chemokines), causing an increase in the relative proportion of cells in late-stage gene expression. They may also be explained, however, by the persistence of cell-associated virions together with the near disappearance of productively infected cells from the circulation.