Fabrication of SiO2 microdisk arrays for optics and light trapping experiments

We present a simple silicon based microfabrication process that produces an array of SiO₂ microdisks using UV lithography. High-resolution SEM images of these structures indicate a smooth outer microdisk cavity surface. Photoemission measurements were performed at different spots on the microdisk and compared with measurements inside the cavity. A silicon to oxygen atomic concentration ratio of 1:2 obtained during depth profiling confirms that the entire microdisk is made up of stoichiometric SiO₂. In contrast, the inner cavity is mostly silicon with native oxide on top. We discuss the usefulness of SiO₂ microdisks in optics for light trapping experiments.     

Comparison of transesophageal Doppler methods with angiography for evaluation of the severity of mitral regurgitation

Doppler evaluation of mitral regurgitation remains difficult; thus, a head-to-head comparison of the diagnostic accuracy of Doppler methods was undertaken. Fifty patients with native mitral regurgitation underwent multiplane transesophageal echocardiography within 5 days of catheterization. Angiographic grade of mitral regurgitation and, in 20 patients with grade II-IV regurgitation, invasively determined regurgitant stroke volume were compared with color Doppler area, regurgitant jet diameter, ratio of systolic to diastolic peak pulmonary venous flow velocities, and (based on the proximal convergence zone) maximal regurgitant flow rate and regurgitant orifice area. Rank correlation coefficients of angiographic grade with Doppler parameters were 0.61 for color jet area, -0.61 for pulmonary venous flow velocity ratio, 0.69 for color jet diameter, 0.79 for maximal regurgitant flow rate, and 0.78 for regurgitant orifice area (all P < .01). Convergence zone-based parameters also correlated best (r=0.73) with invasively determined regurgitant stroke volume. Receiver operating characteristic curve analysis confirmed higher diagnostic accuracy for proximal jet width and proximal convergence zone parameters than for color jet area or pulmonary venous flow velocity ratio. Proximal convergence zone parameters and proximal color jet diameter best distinguished severe from mild forms of mitral regurgitation.     

Nosocomial colonization, septicemia, and Hickman/Broviac catheter-related infections in bone marrow transplant recipients. A 5-year prospective study

In this 5-year prospective study of 242 bone marrow transplantation (BMT) recipients from whom daily blood cultures via the indwelling Broviac/Hickman catheter were obtained, there was a median of 35 catheter-days during hospitalization, mean of 40 days, and total of 9,667 catheter-days which were divided almost equally between neutropenic (4,771) and non-neutropenic (4,896) days. One hundred twenty (50%) patients had a total of 161 episodes of nosocomial bacterial or candidal infections. Overall, 81 (33%) patients experienced 100 episodes of catheter-related infections and 90 (37%) patients experienced 112 episodes of septicemia, including 51 episodes of catheter-related septicemia. There was an incidence of 11.59 septicemia episodes, including 5.28 catheter-related septicemia episodes, 2.48 colonization only (without subsequent septicemia), and 2.59 exit site infections only, per 1,000 catheter-days. Over a period of a total of 6,593 afebrile days, 34 (14%) patients developed 40 episodes of colonization, a rate of 6.07 per 1,000 afebrile days, of which 16 developed into septicemia. Twenty-five patients had 1 episode each of exit site infection without bacteremia. There were 10 (4%) septicemia-related deaths, 4 of which were catheter-related; 50% of all deaths involved Pseudomonas aeruginosa. The mortality due to catheter-related septicemic episodes was not greater than that of the non-catheter-related episodes. Neutropenia was found to be a significant risk factor in our study: 76% of the septicemia episodes (85/112) and 65% of the catheter-related infectious episodes (65/100) occurred during neutropenia. There was a higher incidence of septicemic episodes during neutropenia than during non-neutropenic periods, 17.82 versus 5.51 per 1,000 days (p < 0.0001), and a higher rate of catheter-related infections during the neutropenic period, 13.62 versus 7.15 during non-neutropenic days per 1,000 days (0.001). Fourteen of 16 colonization episodes developed into septicemia during neutropenia versus 2/24 during non-neutropenic periods, a rate of 5.47 versus 0.47 per 1,000 afebrile days, respectively (p < 0.0001), and 9/10 deaths occurred during neutropenia.     

Human melanoma patients recognize an HLA-A1-restricted CTL epitope from tyrosinase containing two cysteine residues: implications for tumor vaccine development

To identify shared epitopes for melanoma-reactive CTL restricted by MHC molecules other than HLA-A*0201, six human melanoma patient CTL lines expressing HLA-A1 were screened for reactivity against the melanocyte differentiation proteins Pmel-17/gp100, MART-1/Melan-A, and tyrosinase, expressed via recombinant vaccinia virus vectors. CTL from five of the six patients recognized epitopes from tyrosinase, and recognition of HLA-A1+ target cells was strongly correlated with tyrosinase expression. Restriction by HLA-A1 was further demonstrated for two of those tyrosinase-reactive CTL lines. Screening of 119 synthetic tyrosinase peptides with the HLA-A1 binding motif demonstrated that nonamer, decamer, and dodecamer peptides containing the sequence KCDICTDEY (residues 243-251) all reconstituted the CTL epitope in vitro. Epitope reconstitution in vitro required high concentrations of these peptides, which was hypothesized to be a result of spontaneous modification of cysteine residues, interfering with MHC binding. Substitution of serine or alanine for the more N-terminal cysteine prevented modification at that residue and permitted target cell sensitization at peptide concentrations 2 to 3 orders of magnitude lower than that required for the wild-type peptide. Because spontaneous modification of sulfhydryl groups may also occur in vivo, tumor vaccines using this or other cysteine-containing peptides may be improved by amino acid substitutions at cysteine residues.     

Self‐Pulsation in Multisection Distributed Feedback Laser Diode with a Novel Dual Grating Structure

A self‐pulsating multisection distributed‐feedback laser diode (DFB LD) can potentially realize all‐optical clock extraction. This device generally consists of three sections, two DFB sections and one waveguide section. The most important variable in this device is detuning, which is the relative spectral position between the stop bands of two DFB sections. We fabricated a novel structure in which two gratings were located one over and one under the active layers. Each grating structure was independently defined in processing so that detuning, which is the prerequisite for self‐pulsation, could be easily controlled. Observing various self‐pulsating phenomena in these devices under several detuning conditions, we characterized the phenomena as dispersive Q‐switching, mode beating, and self‐mode‐locking.     

Kinetics of refolding and reactivation of rabbit-muscle aldolase after acid dissociation

Tetrameric rabbit muscle aldolase has been dissociated to the monomer at pH 2.3 and fully reassociated and reactivated at pH 7.6 Kinetics of reactivation and refolding were followed by slow and fast kinetic techniques after neutralization of the acidic enzyme solutions by dilution or rapid mixing. Rate constants (k), reaction orders (n), and activation evergies (E) were calculated from measurements on the time, concentration, and temperature dependence of the reactions. The experimental results prove reactivation at high enzyme concentration (c greater than 4mug/ml) to obey first-order kinetics; at lower concentrations a transition to a higher reaction order is observed. Because of concentration-dependent deactivation at low enzyme concentrations reactivation measurements could not be extended below c approximately o.5 mug/ml. In the accessible concentration range incomplete separation of reassociation and transconformation processes as well as intrinsic residual activity of the isolated subunits lead to an average value of n = 1.40 +/- 0.18. Renaturation as monitored by protein fluorescnce is a multi-step process composed of a fast increase in flurescence emission (first-order rate constant k approximately 15 s-1) and a slow concentration-dependent decrease which parallels the recovery of enzyme activity (n = 1.46 +/- 0.12). The activation energy of both processes is of the order of E = 12-16 Kcal/mol (50-67 kJ/mol). Reassociation is a prerequisite of full catalytic function and native fluorescence.     

Effects of tungsten oxide addition on the electrochemical performance of nanoscale tantalum oxide-based electrocatalysts for proton exchange membrane (PEM) fuel cells

In the present study, the properties of non-platinum based nanoscale tantalum oxide/tungsten oxide-carbon composite catalysts were investigated for potential use in catalyzing the oxygen reduction reaction on the cathode side of a PEM fuel cell. All of the tantalum oxide-based catalysts exhibit high ORR on-set potentials, comparable with the commercial Pt/C catalyst even though oxygen reduction current was limited. The tungsten oxide doping to tantalum oxide improved catalytic performance. The performance enhancement was due to a decrease in resistance polarization with increasing tungsten content mainly due to the decrease in resistance polarization. XPS results indicate that the oxidation state of tungsten is +6 and that of the tantalum is +5, suggesting that excess oxygen is generated in the resulting oxide structure. This compositional effect seems to reduce resistance polarization by altering the surface chemistry of the tantalum oxide and enhancing the reaction steps such as surface diffusion. Maximum performance was achieved with a catalyst containing 32 mol% of tungsten oxide, reaching a mass specific current density of ∼7% that of the commercial Pt/C catalyst at 0.6 V vs. NHE and ∼35% at 0.2 V vs. NHE. In term of area-specific current density, five-fold increase in loading of the doped catalyst leads to a 4-4.5 fold increase in area specific current density at 0.6 V vs. NHE, reaching 66% that of the Pt/C catalyst at 100 rpm and 35% at 2400 rpm.