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Understanding the interactions between sediment transport and turbulence in a supercritical flow is useful in the study of river hydraulics and fluvial systems and the modeling of such flows in nature. Toward this end, 11 profiles of suspended-sediment concentration and fluid velocity were collected in supercritical conditions over low-relief antidunes in a recirculating laboratory flume. It was found that velocity profiles agreed well with the law of the wall, and that turbulence intensities were similar to those in clear-water flows. The classic Rouse equation was found to under-predict concentration values in the upper 60-80% of the flow depth and a slightly modified version was proposed and successfully tested against experimental data from the present study and others.

Chemiluminescent reactions of ground state (Ca, Sr, and Ba) atoms with (Cl2, Br2, I2, ICl, and IBr) were studied in a beam-gas arrangement. The MX2* pseudo-continua were measured as a function of target gas pressure in the 0.0001−0.25 Pa range. To identify the main reaction channels that contribute to MX2* formation and to obtain their relative contributions, kinetic models were fitted to the data. The following channels were considered:  (1) radiative two-body recombination (R2BR), (2) radiative three-body recombination (R3BR), (3) two consecutive harpooning steps involving MX^† intermediate (two-step chemiluminescent reaction TSCR), and (4) combinations of the above. On their own, none of the mechanisms (1−3) provide satisfactory data fits. The best agreement is obtained by a model involving both R2BR and TSCR. The branching ratios of these channels were determined for p = 0−0.25 Pa. At 0.16 Pa these R2BR fractions vary from 7% (for Ca, Sr + ICl) to 79% (for Ba + IBr). Absolute CL cross sections and lower limits of photon yields were estimated by cross-calibrations. Photon yields for R2BR varied from 0.0004% to 0.037%, depending on the collision partners.

Bipotential oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells, which give rise to oligodendrocytes and type-2 astrocytes in cultures of rat optic nerve, are one of the few cell types in which most aspects of proliferation and differentiation can be manipulated in a defined in vitro environment. Previous studies have shown that O-2A progenitors exposed to platelet-derived growth factor (PDGF) divide as migratory bipolar cells a limited number of times, with a cell cycle time of 18 hr, before clonally related progenitors differentiate into nondividing oligodendrocytes with a timing similar to that seen in vivo. In contrast, O-2A progenitors grown in the absence of mitogen do not divide but instead differentiate prematurely into oligodendrocytes, and progenitors exposed to appropriate inducing factors differentiate into type-2 astrocytes. We now have found that O-2A progenitors can be induced to undergo continuous self-renewal in the absence of oligodendrocytic differentiation by exposure to a combination of PDGF and basic fibroblast growth factor (bFGF). With the exception of the inhibition of differentiation, the O-2A progenitors exposed to PDGF and bFGF behaved similarly to those exposed to PDGF alone. In contrast, progenitors exposed to basic bFGF alone were multipolar, had a cell-cycle length of 45 hr, showed little migratory behavior, underwent premature oligodendrocytic differentiation, and did not cease division upon expression of oligodendrocyte marker antigens. Thus, inhibition of differentiation required the presence of both mitogens. Our results demonstrate that PDGF and bFGF act on O-2A progenitors as both inducers of division and as regulators of differentiation that modulate multiple aspects of O-2A progenitor development and, additionally, reveal a previously unrecognized means of regulating self-renewal processes, wherein cooperation between growth factors promotes continuous division in the absence of differentiation.

The central nervous system of individuals with multiple sclerosis contains lesions specifically characterized by breakdown of myelin sheaths associated with a general failure of repair of demyelinating damage. The cause of myelin breakdown is unknown. Although immune mechanisms have been implicated in this breakdown, no convincing demonstrations of specific immune reaction against myelin have yet been provided in multiple sclerosis patients. Similarly, the cellular biological mechanisms which underlie the failure of myelin repair are unknown. We have found that (i) oligodendrocytes, the cells that produce myelin sheaths in the central nervous system, and (ii) oligodendrocyte/type-2 astrocyte (O/2A) progenitor cells derived from optic nerves of adult rats bind and activate complement in the absence of antibody in vitro, leading to destruction of these cells. Susceptibility to antibody-independent lysis by complement was a cell-type-specific trait of oligodendrocytes and adult O/2A progenitors and was not shared by perinatal O/2A progenitors, type-2 astrocytes, type-1 astrocytes, meningeal cells, or Schwann cells. We suggest that the susceptibility of oligodendrocytes and adult O/2A progenitor cells to complement-induced lysis, combined with other specific properties of adult O/2A progenitors, are consistent with--and may be a contributing factor--both in the generation of demyelinating lesions in multiple sclerosis and also in the failure of these lesions to be successfully repaired in adult multiple sclerosis patients.

The transformation of 4-bromo-2-(2'-acetoxyethyl) cyclopenten-1-one, 2, into hydroxenone 3, has been investigated. Silver oxide was determined to be the reagent of choice.

A short synthesis of 2-formylbicyclo[3.1.1]-hept-2-ene, suitable for multigram preparations, is presented.

We have been studying the differing characteristics of oligodendrocyte-type-2 astrocyte (O-2A) progenitors isolated from optic nerves of perinatal and adult rats. These two cell types display striking differences in their in vitro phenotypes. In addition, the O-2Aperinatal progenitor population appears to have a limited life-span in vivo, while O-2Aadult progenitors appear to be maintained throughout life. O-2Aperinatal progenitors seem to have largely disappeared from the optic nerve by 1 mo after birth, and are not detectable in cultures derived from optic nerves of adult rats. In contrast, O-2Aadult progenitors can first be isolated from optic nerves of 7-d-old rats and are still present in optic nerves of 1-yr-old rats. These observations raise two questions: (a) From what source do O-2Aadult progenitors originate; and (b) how is the O-2Aadult progenitor population maintained in the nerve throughout life? We now provide in vitro evidence indicating that O-2Aadult progenitors are derived directly from a subpopulation of O-2Aperinatal progenitors. We also provide evidence indicating that O-2Aadult progenitors are capable of prolonged self renewal in vitro. In addition, our data suggests that the in vitro generation of oligodendrocytes from O-2Aadult progenitors occurs primarily through asymmetric division and differentiation, in contrast with the self-extinguishing pattern of symmetric division and differentiation displayed by O-2Aperinatal progenitors in vitro. We suggest that O-2Aadult progenitors express at least some properties of stem cells and thus may be able to support the generation of both differentiated progeny cells as well as their own continued replenishment throughout adult life.

Mechanical heart valves are associated with a risk of thromboembolism and anticoagulation is generally recommended. However, this is inevitably associated with a risk of intracranial bleeding. The case of a patient who sustained an intracranial bleed while taking warfarin for a prosthetic aortic valve and a further two intracranial bleeds while on heparin as an inpatient is discussed and the literature on the management of intracranial haemorrhage in patients on warfarin with prosthetic valves is reviewed.

SummaryIn this paper we describe the previously unreported phenomenon of a carbamazepine-induced mucocutaneous syndrome in identical twins. These twins had developed primary generalised epilepsy within 2 months of each other.

Using a Knudson‐cell method with a quadrupole MS as a detector partial as well as absolute vapor pressures of Cs2Te and Cs2TeO3are determined over the range 600 to 1000 °C. Standard enthalpies are measured and the data are used to calculate Gibbs energies of vaporization.

Acylation of the 6‐substituted bicyclic esters (II) is accomplished either by the Vilsmeier‐Haack reaction with the amides (Ia) or by treatment with the appropriate benzoyl chlorides (Ib), yielding the esters (III).