Extensions, Levi subgroups and character formulas

This paper consists of three interconnected parts. Parts I,III study the relationship between the cohomology of a reductive group and that of a Levi subgroup. For example, we provide a necessary condition, arising from Kazhdan-Lusztig theory, for the natural map on Ext-groups of irreducible modules to be surjective. In cohomological degree 1, the map is always an isomorphism, under our hypothesis. These results were inspired by recent work of Hemmer obtained for general linear groups, and they both extend and improve upon his work when our condition is met. Part II obtains results on Lusztig character formulas for reductive groups, obtaining new necessary and sufficient conditions for such formulas to hold. In the special case of general linear groups, these conditions can be recast in a striking way completely in terms of explicit representation theoretic properties of the symmetric group (and the results improve upon the sufficient cohomological conditions established recently in the authors)

Violaceous nodules in an HIV-positive man

Plasmablastic lymphoma (PBL) is a rare and aggressive malignancy associated with immunosuppression and the oncogenic effects of the Epstein-Barr virus (EBV). We present an HIV-positive man with PBL that presented as ulcers and violaceous exophytic nodules on the legs. The clinical features, histologic appearance, and differential diagnosis of this malignancy are briefly reviewed

Dicaesium tetra­chlorido­dioxido­plutonate(VI)

The anion of the title complex, Cs2[PuCl4O2], adopts a pseudo-octa­hedral geometry (2/m crystallographic site symmetry) with two plutonyl oxide ligands in axial sites and four chloride ligands occupying the equatorial plane. Charge balance is maintained by two caesium cations per tetra­chlorido­dioxido­plutonate(VI) anion. Principal bond lengths include Pu—O = 1.752 (3) Å and Pu—Cl = 2.6648 (8) Å

The preparation and characterisation of monomeric and linked metal carbonyl clusters containing the closo-Si2Co4 pseudo-octahedral core

PhSiH3 reacts with [Co₄(CO)₁₂] at 50 °C in hydrocarbon solvents to give [(µ₄-SiPh)₂Co₄(CO)₁₁], 2c, shown by an X-ray crystal structure determination to have a pseudo-octahedral Si₂Co₄ core. Substituted aryl-silanes behaved similarly. Mixtures of PhSiH₃, H₃SiC₆H₄SiH₃ and [Co₄(CO)₁₂] in a ca. 2 1 2 ratio gave the dimeric cluster [{Co₄(µ₄-SiPh)(CO)₁₁Si}₂C₆H₄], 3a, which has the two Si₂Co₄ cores linked by a C₆H₄ group to give a rigid molecule which an X-ray structure analysis shows to be over 23 Å long. Related dimers linked by –(CH₂)₈– groups were isolated from mixtures of PhSiH₃, α ,ω-(H₃Si)₂(CH₂)₈ and [Co₄(CO)₁₂]. Electrochemical studies show the two cluster units in 3a do not interact electronically

PORTFOLIOS OF AGRICULTURAL MARKET ADVISORY SERVICES: HOW MUCH DIVERSIFICATION IS ENOUGH?

Agricultural market advisory services offer specific advice to farmers on how to market their commodities. Farmers can subscribe to one or more of these services and follow their advice as a way of managing price risk. According to portfolio theory, a combination of these services may have risk/return benefits compared to individual services. This report analyzes the potential risk reduction gains from naïve diversification among market advisory services for corn and soybeans. Results show that increasing the number of (equal-weighting) services reduces portfolio expected risk, but the marginal decrease in risk from adding a new service decreases rapidly with portfolio size. The risk reduction benefits of naïve diversification among advisory services is relatively small compared to the results obtained in previous studies for stock portfolios, and this is mainly because advisory prices, on average, are highly correlated. A one service portfolio has only a 20%, 16% and 32% higher expected standard deviation than the minimum risk naïve portfolio for corn, soybeans and 50/50 revenue, respectively. Most risk reduction benefits are achieved with small portfolios. For instance, a four service portfolio has only 5%, 4% and 9% higher expected standard deviation than the minimum risk naïve portfolio for corn, soybeans and 50/50 revenue, respectively. Based on these results, there does not appear to be strong justification for farmers adopting portfolios with a large number of advisory services. Farmers may well choose portfolios with as few as two or three programs, since the relatively high total subscription costs associated with larger portfolios can be avoided while obtaining most of the benefits from diversification.Marketing,

An Instructor\u27s Guide to Electronic Databases of Indexed Professional Literature

This document reviews 20 databases that are relevant to psychology but that are used primarily by professionals in other disciplines. Each database is described, any corresponding paper index is indicated, searching tips are provided, and, when available, free Internet access sites are identified