Advanced technology applications for second and third general coal gasification systems

The historical background of coal conversion is reviewed and the programmatic status (operational, construction, design, proposed) of coal gasification processes is tabulated for both commercial and demonstration projects as well as for large and small pilot plants. Both second and third generation processes typically operate at higher temperatures and pressures than first generation methods. Much of the equipment that has been tested has failed. The most difficult problems are in process control. The mechanics of three-phase flow are not fully understood. Companies participating in coal conversion projects are ordering duplicates of failure prone units. No real solutions to any of the significant problems in technology development have been developed in recent years

Fermi Level Position at Semiconductor Surfaces

There have been several recent reports of barrier height studies on metal-semiconductor interfaces. Metals of widely different work functions evaporated onto Si and GaAs surfaces indicated that in each case the energy difference between the semiconductor conduction band edge and Fermi level at the interface,φ_(Bn), was essentially independent of the metal, which indicates that the Fermi level is fixed by surface states. In the present work barrier height measurements have been made on a number of zinc-blende semiconductors to determine (a) if the barriers are in all cases determined by surface states, and (b) the relation between the Fermi energy at the interface and the band gap E_g

Conduction Band Minima in AlAs and AlSb

The photoresponse of surface barrier rectifiers made by evaporating a metal such as gold or platinum on a cleaved surface of AlAs and AlSb has been measured in the front wall configuration. The photoresponse of such units for hv > E_g, where E_g is the energy gap, will be proportional to the absorption coefficient as long as the optical attenuation length is large compared to both the width of the space-charge region and the minority carrier diffusion length. The analysis is essentially the same as that for p-n junctions with the exception that the barrier is at the surface and hence more sensitive to photons of high absorption coefficient. Photoinjection of carriers from the metal into the semiconductor for photon energies where hv < E_g can also be observed

Voltage Dependence of Barrier Height in AIN Tunnel Junctions

We report measurements of barrier heights on AI-AIN-Mg thin-film structures as a function of applied voltage and insulator thickness. These results are in disagreement with currently accepted theories based upon image potential and/or field penetration of the electrodes

Photoemission from Au and Cu into CdS

Many metal-semiconductor surface barrier rectifiers show photosensitivity for photon energies (hv) less than the semiconductor energy gap (E_g). Cases in the literature include metals evaporated or electrodeposited on elemental and III-V compound semiconductor surfaces. In these studies the source of the low-energy photocurrent, when hv < E_g, was shown to be the photoemission of carriers over the Schottky barrier between the metal film and the semiconductor. An extensive investigation has been reported for a series of metals, particularly Cu and Au, electroplated on n-type CdS with the conclusion that here also photoemission from the metal is responsible for most of the low-energy photovoltage. However, recent studies have questioned this conclusion for the CdS case. One study proposed that the origin of the low-energy photovoltaic response is electron photoexcitation from Cu impurities located in the CdS and within a diffusion length of the space charge region. Hole conduction probably in the 3d Cu levels was postulated for these samples, which had ≈ 30-ppm Cu. A second study interpreted the results as a p·n junction photovoltaic effect

Conduction Band Minima of Ga(As_(1−x)P_x)

Photoresponse of surface barriers on samples of Ga(As_(1−x_P_x) covering the range 0≤x≤1 has been measured. Thresholds corresponding to both direct and indirect band-to-band excitations within the semiconductor and also photoinjection from the metal have been identified. The threshold of the direct transition varies with composition from 1.37 eV in GaAs to 2.65 eV in GaP. The indirect transition was followed for x≳0.38 and again varied linearly from 2.2 eV in GaP to an extrapolated value in 1.62 eV in GaAs. The energy separation of the two conduction band minima in GaAs is in disagreement with previously reported values

Fermi Level Position at Metal-Semiconductor Interfaces

The position of the Fermi level at a metal-semiconductor interface relative to the conduction band has been found to be a constant fraction of the semiconductor band gap for all but 3 of the 14 group IV or III-V semiconductors studied. In all cases, the position was essentially independent of the metal work function. This general result is not inconsistent with the limited theories of surface state energies now available. The three exceptional cases can be understood in terms of a first-order perturbation to the surface state energies correlated with a similar perturbation observed in the energy gap at the (111) zone edge. Experiments are also reported on Ga(As-P) alloys, and two II-VI materials showing distinctly different behavior

Vaginal-rectal colonization with group A streptococci in late pregnancy.

OBJECTIVE: To determine the vaginal-rectal colonization rate with group A streptococci in late pregnancy. METHODS: All patients delivering at a northern New England hospital over a 38 month period had 35-37 week vaginal-rectal swabs cultured for group A and group B streptococci, using selective media and slide agglutination. RESULTS: Six thousand nine hundred forty-four screening cultures were obtained. Among these 1,393 were positive for group B streptococci and 2 for group A streptococci, yielding colonization rates of 20.1% and 0.03%, respectively. CONCLUSIONS: Vaginal-rectal colonization with group A streptococci is rare, arguing against the need for establishing group A streptococcal screening programs in pregnancy. An approach for managing this uncommon finding is presented

Final report of the Committee on Depreciation; Dissenting opinion to the final report of the Committee on Depreciation

Losses of value which are complete, and fully demonstrated by proper abandonment or necessary replacement of the whole or a unit part of a property, are a matter of history and fact, and require only proper accounting to determine their occurrence and amount. Losses of value, which are partial or incomplete, always require prophecy as to future need, usefulness, and service, in order to properly divide that portion of the value which still exists from that which is lost. This function necessitates much more judgment than accounting. It requires the careful analysis of a broadly trained, experienced, and practical mind, thoroughly familiar with the business in question. Original item in Boxno. 0409