Confluent operator algebras and the closability property

Certain operator algebras A on a Hilbert space have the property that every densely defined linear transformation commuting with A is closable. Such algebras are said to have the closability property. They are important in the study of the transitive algebra problem. More precisely, if A is a two-transitive algebra with the closability property, then A is dense in the algebra of all bounded operators, in the weak operator topology. In this paper we focus on algebras generated by a completely nonunitary contraction, and produce several new classes of algebras with the closability property. We show that this property follows from a certain strict cyclicity property, and we give very detailed information on the class of completely nonunitary contractions satisfying this property, as well as a stronger property which we call confluence.Comment: Preliminary versio

Effect of humidity on transonic flow

An experimental investigation of the effects of humidity-induced condensation on shock/boundary-layer interaction has been conducted in a transonic wind-tunnel test. The test geometry considered was a wall-mounted bump model inserted in the test section of the wind tunnel. The formation of a λ-shape condensation shock wave was shown from schlieren visualization and resulted in a forward movement of the shock wave, reduced shock wave strength, and reduced separation. Empirical correlations of the shock wave strength and humidity/dew point temperature were established. For humidity levels below 0.15 or a dew point temperature of 268 K, the effect of humidity was negligible. The unsteady pressure measurements showed that if a condensation shock wave formed and interacted with a main shock wave, the flow becomes unsteady with periodic flow oscillations occurring at 720 Hz

Contrasting growth habits of some arid-loving southern African aloes

Several species of stemless and shrubby, clump-forming aloes grow in the generally flat, arid areas of western South African and southern Namibia. Their habitats receive very little rain, so plants survive mainly due to the coastal fogs and condensation from the sudden overnight temperature drop. Despite similarities of habitat there are some interesting differences between these species. These are discussed in terms of Aloe arenicola, A. claviflora and A. asperfolia. Plants in cultivation are also briefly described

Differences in the trophic ecology of micronekton driven by diel vertical migration.

Many species of micronekton perform diel vertical migrations (DVMs), which ultimately contributes to carbon export to the deep sea. However, not all micronekton species perform DVM, and the nonmigrators, which are often understudied, have different energetic requirements that might be reflected in their trophic ecology. We analyze bulk tissue and whole animal stable nitrogen isotopic compositions (δ 15N values) of micronekton species collected seasonally between 0 and 1250 m depth to explore differences in the trophic ecology of vertically migrating and nonmigrating micronekton in the central North Pacific. Nonmigrating species exhibit depth-related increases in δ 15N values mirroring their main prey, zooplankton. Higher variance in δ 15N values of bathypelagic species points to the increasing reliance of deeper dwelling micronekton on microbially reworked, very small suspended particles. Migrators have higher δ 15N values than nonmigrators inhabiting the epipelagic zone, suggesting the consumption of material during the day at depth, not only at night when they migrate closer to the surface. Migrating species also appear to eat larger prey and exhibit a higher range of variation in δ 15N values seasonally than nonmigrators, likely because of their higher energy needs. The dependence on material at depth enriched in 15N relative to surface particles is higher in migratory fish that ascend only to the lower epipelagic zone. Our results confirm that stark differences in the food habits and dietary sources of micronekton species are driven by vertical migrations

STAT5A expression in swiss 3T3 cells promotes adipogenesis in vivo in an athymic mice model system

Many studies from our laboratories and others have shown that STAT5 expression and activity are increased during adipogenesis of murine and human adipocytes. Ectopic expression of STAT5A in fibroblasts or preadipocytes can confer or enhance adipogenesis. To determine whether STAT5A also plays a role in adipogenesis in vivo, we injected athymic mice with Swiss 3T3 cells expressing an empty pBABE retrovirus, Swiss cells expressing a pBABE retrovirus-containing STAT5A, or 3T3-F442A preadipocytes. Athymic mice injected with either 3T3-F442A cells or Swiss 3T3 cells expressing STAT5A resulted in fat pad formation at the site of injection. However, mice injected with Swiss cells containing the parent retroviral vector did not have any observable fat pads. An analysis of the ectopic fat pads obtained from the Swiss 3T3 STAT5A mice revealed abundant expression of peroxisome proliferator-activated receptor-γ (PPAR-γ) and adiponectin. The protein levels of both of these fat cell markers were comparable to expression levels in epididymal fat pads. These results demonstrate that STAT5A can promote adipogenesis in vivo in this model system which supports a role of this transcription factor in adipocyte development in the whole animal. © 2011 The Obesity Society

El problema de los subespacios invariantes

El Prof. Carl Pearcy, de la Universidad de Michigan en Ann Arbor, visitó la Escuela de Matemática en noviembre de 1983, y ofreció un minicurso de tres sesiones sobre el problema de los subespacios invariantes. Dicho problema pide averiguar si un operador acotado sobre un espacio de Banach posee un subespacio cerrado no trivial invariante. El Dr. Pearcy era un experto en esta rama del análisis funcional. Estas notas del minicurso, tomados por Joseph Várilly, circularon como manuscrito mecanografiado durante varios años.UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Matemátic

On the structure of contraction operators with applications to invariant subspaces

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26407/1/0000494.pd

The neustonic fauna in coastal waters of the northeast Pacific: abundance, distribution, and utilization by juvenile salmonids

The surface-layer zone, occupying the upper 20 cm of the water column, represents a unique oceanic environment. A diverse assemblage of organisms occupies this zone, either in an obligate or facultative manner (Zaitsev 1970, Hempel and Weikert 1972, Cheng 1975, Peres 1982). Certain animals show morphological or biochemical adaptations to this environment and are generally found in this layer throughout their life cycles. More often, however, species may be found near the surface for only a limited part of their life cycle, as in the case of diel migrants (Zaitsev 1970). These organisms have been collectively referred to as pleuston if they are found at the air-sea interface and neuston if they reside immediately below this interface (Cheng 1975)