Nonlinear self-guiding and switching in an all-fiber device

We study the nonlinear propagation of light in optical fibers in the strong nonlinearity limit. In this limit, the transverse guiding properties are altered and cannot be decoupled from the longitudinal part of the wave equation. We consider a refractive index profile with no bound modes at low intensities and show that stable self-guiding occurs at a critical intensity. This critical intensity is a property of the guide and can be made much lower than the threshold for unstable self-focusing. We consider a particular design for which self-guiding occurs at three orders of magnitude lower than the self-focusing threshold.     

A comparative study of human skin thermal response to sapphirecontact and cryogen spray cooling

Surface cooling, in conjunction with various thermally mediated therapeutic procedures, can provide a means to protect superficial tissues from injury while achieving destruction of deeper targeted structures. We have investigated the thermal response of in-vivo human skin to: (1) contact cooling with a sapphire window (6-12°C); and (2) spray cooling with a freon substitute cryogen [tetrafluoroethane; boiling point ≈-26°C at 1 atmospheric pressure (atm)]. Measurements utilizing infrared radiometry show surface temperature reductions from 30°C to 14-19°C are obtained within approximately is in response to sapphire contact cooling. Surface temperature reductions to values between 5°C and -9°C are obtained in response to 20-100-ms cryogen spurts. Computational results, based on fitting the measured radiometric surface temperature to estimate heat transfer parameters, show: (1) temperature reductions remain localized to approximately 200 μm of superficial tissue; and (2) values of heat flux and total energy removed per unit skin surface area at least doubled when using cryogen spray cooling     

High-transconductance n-type Si/SiGe modulation-doped field-effecttransistors

The authors report on the fabrication and the resultant device characteristics of the first 0.25-μm gate-length field-effect transistor based on n-type modulation-doped Si/SiGe. Prepared using ultrahigh vacuum/chemical vapor deposition (UHV/CVD), the mobility and electron sheet charge density in the strained Si channel are 1500 (9500) cm²/V-s and 2.5×10¹² (1.5×10¹² ) cm^-2 at 300 K (77 K). At 77 K, the devices have a current and transconductance of 325 mA/mm and 600 mS/mm, respectively. These values far exceed those found in Si MESFETs and are comparable to the best results achieved in GaAs/AlGaAs modulation-doped transistors     

A novel four-point bend test for strength measurement of opticalfibers and thin beams. II. Statistical analysis

In the first part of this work, a novel implementation of the well-known four-point bend test is described that determines the strength of thin beams and optical fibers by measuring the loading pin displacement, rather than the applied load. This paper extends the analysis of the nonlinear bending behavior to account for the stochastic nature of strength. A statistical analysis is presented that determines the effective tested length in bending and the tension to bending strength ratio. Results are given for both surface and volume flaws as well as for specimens of both circular and rectangular section. Strength measurements on a deliberately weakened silica optical fiber are consistent with the predictions of the analysis     

CHEMILUMINESCENCE FROM THE OXIDATION OF AUXIN DERIVATIVES

Abstract— The thiophenyl ester of indole-3-acetic acid and indole-3-acetonitrile produce chemiluminescence in aerated dimethylsulfoxide in the presence of potassium t -butoxide. The emitter is the aromatic aldehyde. In the case of acetonitrile, the other product expected from the cleavage of an intermediate dioxetane, cyanate/isocyanate, has also been identified. Other auxins also chemiluminesce under similar conditions, but the emitters have not been properly identified.
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route.     

Degradation of ²-O-4 lignin model and related compounds by the ascomyceteChrysonilia sitophila (TFB 27441 strain)

Growth of the ascomyceteChrysonilia sitophila during degradation of lignin model dimers and monomers was compared to a glucose control. An inhibition of growth by Cα-carbonyl monomers and stimulation by β-O-4 lignin model and vanillyl alcohol were observed. A comparison of the degradation by this ascomycete with the basidiomycetePhanerochaete chrysosoporium showed similarities in relation to the type of degradation caused.     

Voltammetry of copper species in estuarine waters: Part I. Electrochemistry of copper species in chloride media

Theoretical and experimental voltammetric studies of copper reduction in chloride media show that electrodeposition on the hanging mercury drop electrode (HMDE) is controlled by competitive reduction between Cu(II) organic species and the Cu(I)Cl₂^? intermediate. For reversible Cu(II) species reduction, the change from organic ligand to chloride control of the final reduction step can be predicted by thermodynamic calculation. On the other hand in irreversible systems (e.g. estuarine waters) involvement of the CuCl₂^? intermedite in the electrodeposition is more complex and can occur both before and after amalgamation.