Accounting for hotels

Thesis (M.B.A.)—Boston Universit

Subquotients of Hecke C*-algebras

We realize the Hecke C*-algebra CQ of Bost and Connes as a direct limit of Hecke C*-algebras which are semigroup crossed products by NF, for F a finite set of primes. For each approximating Hecke C*-algebra we describe a composition series of ideals. In all cases there is a large type I ideal and a commutative quotient, and the intermediate subquotients are direct sums of simple C*-algebras. We can describe the simple summands as ordinary crossed products by actions of ZS for S a finite set of primes. When |S|=1, these actions are odometers and the crossed products are Bunce–Deddens algebras; when |S|\u3e1, the actions are an apparently new class of higher-rank odometer actions, and the crossed products are an apparently new class of classifiable AT-algebras

Growth of vertically aligned Si wire arrays over large areas (>1 cm^2) with Au and Cu catalysts

Arrays of vertically oriented Si wires with diameters of 1.5 µm and lengths of up to 75 µm were grown over areas >1 cm^2 by photolithographically patterning an oxide buffer layer, followed by vapor-liquid-solid growth with either Au or Cu as the growth catalyst. The pattern fidelity depended critically on the presence of the oxide layer, which prevented migration of the catalyst on the surface during annealing and in the early stages of wire growth. These arrays can be used as the absorber material in novel photovoltaic architectures and potentially in photonic crystals in which large areas are needed

10 µm minority-carrier diffusion lengths in Si wires synthesized by Cu-catalyzed vapor-liquid-solid growth

The effective electron minority-carrier diffusion length, L_(n,eff), for 2.0 µm diameter Si wires that were synthesized by Cu-catalyzed vapor-liquid-solid growth was measured by scanning photocurrent microscopy. In dark, ambient conditions, L_(n,eff) was limited by surface recombination to a value of ≤ 0.7 µm. However, a value of L_(n,eff) = 10.5±1 µm was measured under broad-area illumination in low-level injection. The relatively long minority-carrier diffusion length observed under illumination is consistent with an increased surface passivation resulting from filling of the surface states of the Si wires by photogenerated carriers. These relatively large L_(n,eff) values have important implications for the design of high-efficiency, radial-junction photovoltaic cells from arrays of Si wires synthesized by metal-catalyzed growth processes

A comparison of productivity for whole tree, tree length, and log length skyline thinning in 35 year old Douglas-fir stands of western Oregon

Whole tree and tree length thinning are two alternatives which are likely to be more productive and may prove to be more cost effective than conventional log length thinning. The purpose of this study was to evaluate and compare log length, tree length, and whole tree thinning techniques in terms of productivity and harvesting costs. The thinning operation took place in a second-growth Douglas-fir stand [Pseudotsuga menziesii (Mirb.) Franco] (average dbh = 12.8") using a small skyline yarder (28' tower, 120 HP) in a gravity return configuration. The treatments were defined by the amount of work done by the faller prior to yarding. Log length implies that felling, limbing, bucking and topping occured at the stump. Tree length indicates that trees were felled, limbed and topped only, and finally, whole trees were felled only prior to yarding. A rubber-tired cable skidder was used to swing material from the landing chute to a processing area. Here the skidder operator Forest Engineering presented on April 14, 1983 completed any limbing and bucking which was necessary. He then sorted and decked the logs prior to loading. During log length thinning, logs were either cold decked in front of the yarder or swung with the skidder to a loading deck. Detailed time studies were used to evaluate the felling and yarding operations for each of the three thinning techniques. Multiple linear regression was then used to develop predictive models for felling and yarding work cycles. An analysis of the delays on this study made it possible to separate out delays which were affected by a particular thinning technique, rather than having a single prorated delay time as is usually done. By combining results from the regression and delay analyses, estimates of productivity for each thinning technique were obtained. Finally, harvesting costs in dollars per cunit at the loading deck were generated and used to compare log length, tree length, and whole tree thinning. Results indicated that where cold decking is feasible and will not overly hamper the operation it will probably still be the cheapest alternative since a skidder is not required. The cost per cunit for this method was $8.24 or 11whole tree system. However, where cold decking is not feasible, as is often the case on steep slopes with narrow roads, the whole tree technique will be the most cost effective alternative. It has a per cunit cost which is$10.06 or 12% less expensive than conventional log length thinning with a skidder swing. The advantage to the whole tree system results primarily from transferring limbing and bucking from the stump to the landing where it is not only done more efficiently, but also reduces operator idle time on the skidder swing

Volume 30, Number 1, March 2010 OLAC Newsletter

Digitized March 2010 issue of the OLAC Newsletter

Secondary ion mass spectrometry of vapor−liquid−solid grown, Au-catalyzed, Si wires

Knowledge of the catalyst concentration within vapor-liquid-solid (VLS) grown semiconductor wires is needed in order to assess potential limits to electrical and optical device performance imposed by the VLS growth mechanism. We report herein the use of secondary ion mass spectrometry to characterize the Au catalyst concentration within individual, VLS-grown, Si wires. For Si wires grown by chemical vapor deposition from SiCl_4 at 1000 °C, an upper limit on the bulk Au concentration was observed to be 1.7 x 10^16 atoms/cm^3, similar to the thermodynamic equilibrium concentration at the growth temperature. However, a higher concentration of Au was observed on the sidewalls of the wires

Volume 31, Number 2, June 2011 OLAC Newsletter

Digitized June 2011 issue of the OLAC Newsletter

Volume 31, Number 1, March 2011 OLAC Newsletter

Digitized March 2011 issue of the OLAC Newsletter