Investigation of Heat Transfer From

The convective heat transfer from the surface of an ellipsoidal forebody of fineness ratio 3 and 20-inch maximum diameter was investigated in clear air for both stationary and rotating operation over a range of conditions including air speeds up to 240 knots, rotational speeds up to 1200 rpm, and angles of attack of 0 deg, 3 deg, and 6 deg. The results are presented in the form of heat-transfer coefficients and the correlation of Nusselt and Reynolds numbers. Both a uniform surface temperature and a uniform input heater density distribution were used. The experimental results agree well with theoretical predictions for uniform surface temperature distribution. Complete agreement was not obtained with uniform input heat density in the laminar-flow region because of conduction effects. No significant effects of rotation were obtained over the range of airstream and rotational speeds investigated. Operation at angle of attack had only minor effects on the local heat transfer. Transition from laminar to turbulent heat transfer occurred over a wide range of Reynolds numbers. The location of transition depended primarily on surface roughness and pressure and temperature gradients. Limited transient heating data indicate that the variation of surface temperature with time followed closely an exponential relation

Investigation of Heat Transfer from a Stationary and Rotating Conical Forebody

The convective heat transfer from the surface of a conical forebody having a hemispherical nose, an included angle of approximately 30 deg, and. a maximum diameter of 18.9 inches was investigated in a wind tunnel for both stationary and. rotating operation. The range of test conditions included free-stream velocities up to 400 feet per second, rotational speeds up to 1200 rpm, and. angles of attack of 0 deg and 6 deg. Both a uniform surface temperature and a uniform heater input power density were used. The Nusselt-Reynolds number relations provided good correlation of the heat-transfer data for the complete operating range at 0 deg angle of attack with and without spinner rotation, and for 6deg angle of attack with rotation. Rotational speeds up to 1200 rpm had no apparent effect on the heat-transfer characteristics of the spinner. The results obtained at 6 deg angle of attack with rotation were essentially the same as those obtained at 0 deg angle of attack without rotation. The experimental heat-transfer characteristics in the turbulent flow region were consistently in closer agreement with the results predicted for a two-dimensional body than with those predicted. for a cone. For stationary operation at 60 angle of attack, the measured heat-transfer coefficients in the turbulent flow region were from 6 to 13 percent greater on the lower surface (windward. side) than on the upper surface (sheltered side) for corresponding surface locations. The spinner-nose geometry appeared to cause early boundary-layer transition. Transition was initiated at a fairly constant Reynolds number (based on surface distance from nose) of 8.0 x 10(exp 4). Transition was completed at Reynolds numbers less than 5.0 x 10(exp 5) for all conditions investigated

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH_3-Si(111) and CD_3-Si(111) surfaces

The surface structure and vibrational dynamics of CH_3–Si(111) and CD_3–Si(111) surfaces were measured using helium atom scattering. The elastic diffraction patterns exhibited a lattice constant of 3.82 Å, in accordance with the spacing of the silicon underlayer. The excellent quality of the observed diffraction patterns, along with minimal diffuse background, indicated a high degree of long-range ordering and a low defect density for this interface. The vibrational dynamics were investigated by measurement of the Debye–Waller attenuation of the elastic diffraction peaks as the surface temperature was increased. The angular dependence of the specular (θ_i=θ_f) decay revealed perpendicular mean-square displacements of 1.0 x 10^(−5) Å^2 K^(−1) for the CH_3–Si(111) surface and 1.2 x 10^(−5) Å^2 K^(−1) for the CD_3–Si(111) surface, and a He-surface attractive well depth of ~7 meV. The effective surface Debye temperatures were calculated to be 983 K for the CH_3–Si(111) surface and 824 K for the CD_3–Si(111) surface. These relatively large Debye temperatures suggest that collisional energy accommodation at the surface occurs primarily through the Si–C local molecular modes. The parallel mean-square displacements were 7.1 x 10^(−4) and 7.2 x 10^(−4) Å^2 K^(−1) for the CH_3–Si(111) and CD_3–Si(111) surfaces, respectively. The observed increase in thermal motion is consistent with the interaction between the helium atoms and Si–CH_3 bending modes. These experiments have thus yielded detailed information on the dynamical properties of these robust and technologically interesting semiconductor interfaces

7.2% efficient polycrystalline silicon photoelectrode

After etching, n-type cast polycrystalline silicon photoanodes immersed in a solution of methanol and a substituted ferrocene reagent exhibit photoelectrode efficiencies of 7.2%±0.7% under simulated AM2 illumination. Scanning laser spot data indicate that the grain boundaries are active; however, the semiconductor/liquid contact does not display the severe shunting effects which are observed at a polycrystalline Si/Pt Schottky barrier. Evidence for an interfacial oxide on the operating polycrystalline Si photoanode is presented. Some losses in short circuit current can be ascribed to bulk semiconductor properties; however, despite these losses, photoanodes fabricated from polycrystalline substrates exhibit efficiencies comparable to those of single crystal material. Two major conclusions of our studies are that improved photoelectrode behavior in the polycrystalline silicon/methanol system will primarily result from changes in bulk electrode properties and from grain boundary passivation, and that Fermi level pinning by surface states does not prevent the design of efficient silicon-based liquid junctions

A 14% efficient nonaqueous semiconductor/liquid junction solar cell

We describe the most efficient semiconductor/liquid junction solar cell reported to date. Under W‐halogen (ELH) illumination, the device is a 14% efficient two‐electrode solar cell fabricated from an n‐type silicon photoanode in contact with a nonaqueous electrolyte solution. The cell′s central feature is an ultrathin electrolyte layer which simultaneously reduces losses which result from electrode polarization, electrolyte light absorption, and electrolyte resistance. The thin electrolyte layer also eliminates the need for forced convection of the redox couple and allows for precise control over the amount of water (and other electrolyte impurities) exposed to the semiconductor. After one month of continuous operation under ELH light at 100 mW/cm^2, which corresponds to the passage of over 70 000 C/cm^2, thin‐layer cells retained over 90% of their efficiency. In addition, when made with Wacker Silso cast polycrystalline Si, cells yield an efficiency of 9.8% under simulated AMl illumination. The thin‐layer cells employ no external compensation yet surpass their corresponding experimental (three‐electrode) predecessors in efficiency

Evaluation of Pt, Ni, and Ni–Mo electrocatalysts for hydrogen evolution on crystalline Si electrodes

The dark electrocatalytic and light photocathodic hydrogen evolution properties of Ni, Ni–Mo alloys, and Pt on Si electrodes have been measured, to assess the viability of earth-abundant electrocatalysts for integrated, semiconductor coupled fuel formation. In the dark, the activities of these catalysts deposited on degenerately doped p^+-Si electrodes increased in the order Ni < Ni–Mo ≤ Pt. Ni–Mo deposited on degenerately doped Si microwires exhibited activity that was very similar to that of Pt deposited by metal evaporation on planar Si electrodes. Under 100 mW cm^(−2) of Air Mass 1.5 solar simulation, the energy conversion efficiencies of p-type Si/catalyst photoelectrodes ranged from 0.2–1%, and increased in the order Ni ≈ Ni–Mo < Pt, due to somewhat lower photovoltages and photocurrents for p-Si/Ni–Mo relative to p-Si/Ni and p-Si/Pt photoelectrodes. Deposition of the catalysts onto microwire arrays resulted in higher apparent catalytic activities and similar photoelectrode efficiencies than were observed on planar p-Si photocathodes, despite lower light absorption by p-Si in the microwire structures

Solar Water Splitting Cells

No abstract

Dalbavancin in the treatment of complicated skin and soft-tissue infections: a review

Increasing rates of antimicrobial resistance among strains of Streptococcus, Staphylococcus, and Enterococcus spp. have been widely documented. At least 50% of nosocomial Staphylococcus aureus infections in intensive care units in the US and UK are due methicillin-resistant S. aureus (MRSA). Drug resistance is not confined to hospitals, and community-acquired MRSA (CA-MRSA) strains are now common causes of complicated skin and soft-tissue infections (cSSTIs) in many regions. Dalbavancin is a novel parenterally administered semisynthetic lipoglycopeptide similar to the naturally produced glycopeptides vancomycin and teicoplanin. Dalbavancin features a multifaceted mechanism of action that inhibits bacterial cell wall formation by two different mechanisms that enhances its activity against a wide range of gram-positive bacteria including staphylococci, streptococci, enterococci, and some anaerobes. Additionally, dalbavancin possesses unique pharmacokinetic properties, the most significant of which is a long terminal half-life that allows for once weekly dosing. This attribute may prove to yield clinical and cost benefit. Overall, clinical trials indicate that dalbavancin is a safe, well-tolerated, and effective antimicrobial agent. In the largest investigation evaluating dalbavancin for the treatment of cSSTIs, it appeared to be as effective as linezolid. Dalbavancin, which is expected to receive FDA approval in 2008, appears to be a promising new antimicrobial agent for the treatment of cSSTIs