High quantum efficiency and narrow absorption bandwidth of thewafer-fused resonant In0.53Ga0.47As photodetectors

We demonstrate greater than 90% quantum efficiency in an In_0.53Ga_0.47As photodetector with a thin (900 Å) absorbing layer. This was achieved by inserting the In_0.53 Ga_0.47As/InP epitaxial layer into a microcavity composed of a GaAs/AlAs quarter-wavelength stack (QWS) and a Si/SiO₂ dielectric mirror. The 900-Å-thick In_0.53 Ga_0.47As layer was wafer fused to a GaAs/AlAs mirror, having nearly 100% power reflectivity. A Si/SiO₂ dielectric mirror was subsequently deposited onto the wafer-fused photodiode to form an asymmetric Fabry-Perot cavity. The external quantum efficiency and absorption bandwidth for the wafer-fused RCE photodiodes were measured to be 94±3% and 14 nm, respectively. To our knowledge, these wafer-fused RCE photodetectors have the highest external quantum efficiency and narrowest absorption bandwidth ever reported on the long-wavelength resonant-cavity-enhanced photodetectors     

Interferometric measurements of dispersion-spectra variations in a single-mode fiber

Previous work has demonstrated that group-delay spectra in single-mode fibers can be measured with 0.1-ps resolution by a white-light cross-correlation technique. An application would be to pretest short fibers before drawing an entire preform. This could be particularly useful for achieving high draw yield for fibers whose dispersion spectra are sensitive to core diameter. This paper describes measurements of minimum-dispersion spectra that were obtained using 4-m lengths of fiber that were cut from each end of kilometer-long quadruple-clad, triangular-index, and step-index depressed-clad fibers. The axial uniformity of fiber dispersion was found to be very good. Results show that averaging dispersion spectra using short fiber segments from each end produces excellent agreement when compared with the dispersion spectrum determined from conventional pulse-delay measurements on a long length of fiber.     

Mixed methods for complex kinematic constraints in dynamic figure animation

Advances for achieving user control of a dynamic simulation of linked figures is presented. The formulation integrates forward and inverse kinematics specification within a mixed method of forward and inverse dynamics simulation. Kinematic specifications can be imposed through kinematic constraints embedded within the dynamics framework. Kinematic constraints may be simple (functions of one degree of freedom), or complex (functions of multiple interrelated degrees of freedom). Thus, keyframed paths, closed loops, point-to-path constraints, and collisions between links and the environment can be simulated. A simultaneous solution for unknown motion and forces of constraint is performed. A Lagrange multiplier method is outlined for incorporating these general constraints into the mathematical formulation of the equations of motion. Results from three example simulations are presented and discussed.     

Carbide precipitation during stage I tempering of Fe-Ni-C martensites

Microstructural changes which accompany the first stage of tempering have been studied by transmission electron microscopy (TEM) and electrical resistometry in two Fe-Ni-C alloys that form platelike martensite. The ε-carbide transition phase in these alloys adopts a platelike shape with a habit plane near {012=_α. Electron diffraction data indicate that the carbide may be partially ordered, resulting in orthorhombic symmetry, and therefore, this phase is designated as ε′- carbide. The carbide particles contain a fine internal substructure which appears to represent an internal accommodation deformation (faulting) on the carbide basal plane. Detailed analysis of the kinematics of carbide precipitation suggests that the observed habit plane and accommodation deformation permit an invariant-plane strain transformation which minimizes elastic strain energy. The apparent selection of only a limited number of possible orientation variants is explained in terms of the symmetry of the parent martensitic phase, which is known to undergo spinodal decomposition prior to the nucleation of the transition carbide. The martensitic substructure is not found to exert any significant influence on this overall precipitation behavior. formerly with the Massachusetts Institute of Technology formerly with the Massachusetts Institute of Technology     

An evaluation of transovarian uptake of metabolites using arterio-venous difference methods in dairy cattle

Arterio-venous (A-V) difference techniques were used in cattle to examine ovarian energy metabolism, cholesterol uptake and steroid hormone outputs. Catheters were inserted into the ovarian vein and facial artery, and Transonic flow transducers were placed around the ovarian A-V plexus. Further, in some cows, the effects of a challenge with GnRH were examined. Glucose uptake and lactate output were significant in most individual cows. Nonesterified fatty acids (NEFA) uptake were not significant in any cow in dioestrus. Ovarian uptake of beta-Hydroxy-butyrate (3-OHB) was significant in 4 cows in dioestrus. Cholesterol uptake was significant in only 1 cow. Oxygen uptake was significant in all cows at all stages of the oestrous cycle. All cows had significant output of progesterone and oestradiol-17 beta. These data show that the bovine ovary utilises significant amounts of glucose, and Respiratory quotient (RQ) estimates demonstrated that glucose was the primary fuel used by the ovary. The significant output of lactate suggested that anaerobic pathways were mainly used for glucose oxidation. The observed uptakes of 3-OHB indicated that the ovary utilises 3-OHB as a source of energy. Cholesterol uptake was not a rate-limiting factor for steroid hormone production in the ovary. Despite the high metabolic rate in the luteal ovary, the small difference in PO2 between arterial and ovarian venous blood indicated that the ovary consumes only a small proportion of available oxygen. GnRH had no significant effect on the uptake of metabolites and energy metabolism, but it increased OBF and the output of progesterone and oestradiol-17 beta. The use of A-V methods to determine the metabolic needs of the ovary is useful in understanding the means by which nutrition can influence fertility.     

Protection of low density lipoprotein oxidation at chemical and cellular level by the antioxidant drug dipyridamole

1. The oxidative modification of low density lipoprotein (LDL) is thought to be an important factor in the initiation and development of atherosclerosis. Natural and synthetic antioxidants have been shown to protect LDL from oxidation and to inhibit atherosclerosis development in animals. Synthetic antioxidants are currently being tested, by they are not necessarily safe for human use. 2. We have previously reported that dipyridamole, currently used in clinical practice, is a potent scavenger of free radicals. Thus, we tested whether dipyridamole could affect LDL oxidation at chemical and cellular level. 3. Chemically induced LDL oxidation was made by Cu(II), Cu(II) plus hydrogen peroxide or peroxyl radicals generated by thermolysis of 2,2'-azo-bis(2-amidino propane). Dipyridamole, (1-10 microM), inhibited LDL oxidation as monitored by diene formation, evolution of hydroperoxides and thiobarbituric acid reactive substances, apoprotein modification and by the fluorescence of cis-parinaric acid. 4. The physiological relevance of the antioxidant activity was validated by experiments at the cellular level where dipyridamole inhibited endothelial cell-mediated LDL oxidation, their degradation by monocytes, and cytotoxicity. 5. In comparison with ascorbic acid, alpha-tocopherol and probucol, dipyridamole was the more efficient antioxidant with the following order of activity: dipyridamole > probucol > ascorbic acid > alpha-tocopherol. The present study shows that dipyridamole inhibits oxidation of LDL at pharmacologically relevant concentrations. The inhibition of LDL oxidation is unequivocally confirmed by use of three different methods of chemical oxidation, by several methods of oxidation monitoring, and the pharmacological relevance is demonstrated by the superiority of dipyridamole over the naturally occurring antioxidants, ascorbic acid and alpha-tocopherol and the synthetic antioxidant probucol.     

Ischemic heart disease and stroke mortality in African-American, Hispanic, and non-Hispanic white men and women, 1985 to 1991

Electrochemiluminescence (ECL) of 200 ppm 2,3-diaminonaphthalene (2,3-DAN) was studied alone and in conjunction with 100 ppm of 34 different metal and non-metal ions and revealed three relatively intense ECL responses from interactions of 2,3-DAN with Au+, Fe+3 and V+5. ECL responses from Cr+6 or Ru+3 with 2,3-DAN were less intense, but noteworthy, as was the coloured fluorescent product of the non-metal ion Se+4 interaction with 2,3-DAN. Several intense 2,3-DAN-metal ion ECL reactions were studied in greater detail and revealed various titration curves with ionic detection limits in the low ppm range, using a fixed level (200 ppm) of 2,3-DAN.