Showing papers by "Worcester Polytechnic Institute published in 1970"

Avalanche breakdown in polycrystalline selenium rectifiers

Abstract: Measurements have been made at 113 and 296 °K of the reverse current–voltage and reactance–voltage characteristics of polycrystalline selenium rectifiers with an injecting nickel and a blocking aluminum or cadmium selenide contact. The voltage dependence of the reactance at low applied voltage is characteristic of a step junction at the blocking contact with 1/C proportional to (U + U0). Avalanche breakdown takes place at a field strength of approximately 1.5 × 105 V/cm at room temperature with a positive temperature coefficient. Avalanching is confirmed by the onset of multiplication of the photocurrent at essentially the same field strength as for multiplication of the dark current. Electroluminescence is observed in the avalanche regime. A mean free path for phonon creation of approximately 20 nm is estimated which is sufficiently small that the selenium grain boundaries can be neglected. Die Strom–Spannungs- und die Reaktanz–Spannungs-Kennlinie eines in Sperrichtung gepolten polykristallinen Selengleichrichters mit injizierendem Nickelkontakt und sperrendem Aluminium- oder Kadmiumselenidkontakt wurde bei 113 und 296 °K gemessen. Fur niedrige Spannungen entspricht die Spannungsabhangigkeit der Reaktanz derjenigen eines stufenformigen p–n-Uberganges am Sperrkontakt, wobei 1/C proportional zu (U + U0) ist. Der Lawinendurchbruch findet bei Zimmertemperatur bei einer Feldstarke von etwa 1,5 × 105 V/cm (mit positivem Temperaturkoeffizienten) statt. Das gleichzeitige Auftreten der Multiplikation des Photostromes und des Dunkelstromes fur dieselbe Feldstarke bestatigt den Lawinenprozes. Im Lawinengebiet wurde gleichzeitig Elektrolumineszenz beobachtet. Die freie Weglange fur Phononenproduktion ist ungefahr 20 nm und damit so klein, das Selenkorngrenzen vernachlassigbar sind.

Endomorphism rings of non-abelian groups

Abstract: In 1942 F.W. Levi described those groups in which any two inner automorphic images of an arbitrary element commute. Until recently it was not known whether there existed non-abelian groups with the property that any two endomorphic images of an arbitrary element commute. Now, R. Faudree has given examples of finite p–groups having this property. In this paper we give a necessary and sufficient condition that a torsion group which contains no elements of order 2 has this property. The technique of proof involves looking at certain near rings of functions on the group. The inspiration for the theorem comes from the “halving” technique used by B.H. Neumann in 1940.

Coherent absorption in a homogeneously broadened medium

Abstract: An investigation of the propagation properties of a short pulse in a resonant absorber with a homogeneously broadened transition is presented with two main questions in mind: 1) the influence of the input pulse area on the transitory regime and on the steady-state propagation; 2) the effects of atomic coherence on the pulse shaping and the time delay of the leading edge of the pulse. The transitory regime of a propagating pulse is investigated and the stability of some asymptotic wave form confirmed. As expected, the transversal relaxation mechanism affects critically the major features of the coherent interaction. A detailed analysis of this problem is also presented.

Design of Condenser Cooling Water System for a Nuclear Power Plant Located on a Large Estuary

Abstract: A coordinated program is described for developing information needed for designing a condenser cooling water system for a nuclear power plant located on a large estuary to meet State water quality standards and minimize any adverse effects on aquatic life. The paper discusses estuarine conditions pertinent to the design of the intake and discharge structures, the heat assimilative capacity of the estuary, application of the momentum jet theory to the condenser cooling water discharges, and hydraulic model investigations to determine mixing and dispersion patterns.

Some effects of water vapour on selenium rectifiers

Abstract: The current—voltage and capacitance—voltage characteristics of selenium rectifiers with an evaporated aluminum blocking electrode have been measured immediately upon deposition of the aluminum electrode. Such rectifiers show an extremely low reverse breakdown voltage (<1 V) which excludes an avalanche breakdown mechanism. The characteristic is stable when the sample is exposed to oxygen, nitrogen, or dry air. Upon the introduction of water vapour the breakdown voltage increases to its normal value, being determined by avalanche breakdown. Water vapour has little effect on the doping concentration in the exhaustion region as determined from capacitance—voltage characteristics: its main effects are to increase the surface band-bending and the rate of energy loss of hot electrons to the selenium lattice. Die Strom—Spannungs- und Kapazitat—Spannungskennlinien von Selengleichrichtern mit Aluminium-Sperrelektroden wurden kurz nach dem Aufdampfen der Aluminiumelektroden gemessen. Solche Gleichrichter haben eine sehr niedrige Druchbruchspannung in der Sperrrichtung (<1 V), so das ein Lawinenmechanismus ausgeschlossen werden mus. Stabile Kennlinien werden erhalten, wenn das Material sich in Sauerstoff, Stickstoff oder Trockenluft befindet. Beim Einfuhren von Wasserdampf wird dagegen die Durchbruchspannung auf den normalen Wert, der durch den Lawinenmechanismus bestimmt ist, erhoht. Messungen der Kapazitat—Spannungskennlinien zeigen, das der Einflus von Wasserdampf auf die Dotierungskonzentration verhaltnismasig gering ist, wenigstens fur mittlere Werte der Dotierungsdichten. Von Bedeutung ist dagegen die vergroserte Biegung der Oberflachenenergiebander und die zunehmende Energieabgabe der heisen Elektronen an das Selengitter unter dem Einflus von Wasserdampf.

Control of Thermal Effects at Beaver Valley Station

Abstract: The conceptual design of condenser cooling water system and provisions for control of hydrothermal effects at Beaver Valley Station are discussed. To ensure compliance with required temperature criteria, a once-through system assisted by a supplemental cooling tower is provided. A feature of the site is the local configuration of the Ohio River which branches into a main navigable channel and a smaller back channel, with the plant outlet located on the latter. Field studies and model tests were carried out to investigate means for improving river flow distribution. It was found that the outlet orientation could be optimized to ensure maximum river flow entrainment into the back channel by the discharge jet. Analysis and test results showed that warm water recirculation between discharge and intake structures could be adequately controlled by increasing effluent dilution in the back channel. Temperature patterns at the surface and in cross sections were determined on the model for a two mile long river reach.