X-ray induced electrostatic charging of helium films

It is well known that free electrons can be held onto the free surface of liquid helium through either their own image charges or through the effect of an externally applied electric field. The resultant electrostatic pressure causes films to thin. We have recently measured x-ray reflectivity from static films of isotopic mixtures of helium with an intense x-ray beam in the temperature range between 0.37 K and 1.3 K. Normally, no significant thickness variation with x-ray intensity is expected over a wide range of temperatures when the film is superfluid. We have found that even modest x-ray intensities affect the thickness of films containing only trace amounts of³He. We believe that the effect is due to x-ray produced photoelectrons, which thermalize in the vapor and then reside on the surface, attracted by both the film and a charged substrate. The temperature and concentration dependence is then due to the transport properties of the electrons at the surface. It may be possible to study the 2-D electron gas produced in this way by diffraction techniques.     

Basic fibroblast growth factor expression as a predictor of prognosis in pediatric high-grade gliomas

Clinical and histopathological factors fail to adequately predict outcomes in children with high-grade gliomas, indicating a need to identify relevant biological markers of tumor behavior to guide therapeutic decision-making. Basic fibroblast growth factor (bFGF) is a mitogenic and angiogenic factor that has been observed to be overexpressed in a significant percentage of malignant gliomas, although the prognostic significance of this expression is unknown. To address this issue, the expression status of bFGF was examined immunohistochemically in a series of 27 archival pediatric malignant non-brainstem gliomas treated consecutively at our institution between 1975 and 1992. Tumors were categorized based on expression levels, and the association between expression status and outcome was examined. Sixteen cases showed high levels of expression of bFGF, and 11 showed low levels. There was no correlation between expression status and either tumor histology, patient age, or tumor location. However, there was a significant difference in outcome between patients with high levels of bFGF immunoreactivity and those with low expression. Median progression-free survival was >66 months in the low bFGF group as compared to 6 months in the high bFGF group (P = 0.006). Median overall survival was >66 months in the low bFGF group as compared to 18 months in the high bFGF group (P = 0.03). Tumor bFGF expression seems to be strongly associated with outcome in children with high-grade gliomas and, consequently, may serve as a biological correlate of patient prognosis in conjunction with other prognostic variables.     

The learning curve as a metacognitive tool.

A series of 4 experiments demonstrated that when practicing for a test of problem solving, recognition and selection of a particular stopping signal was shown to depend on the within-set variability (statistical noise) of a problem set. When noise was high, participants used a nondiagnostic stopping signal based on the initial size of the problem set. However, when noise was low, access to evidence of learning was possible, resulting in the operation of a stopping signal based on learning curve characteristics. By blocking access to local segments of the learning curve through the use of variability masking, it was demonstrated that participants were sensitive to changes throughout the entire curve. In spite of a long history associated with the psychological study of the learning curve, these results provide the first demonstration of the learning curve as a source of metacognitive judgment and regulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Angiography with carbon dioxide (CO2)

CO2 possesses many advantages over conventional iodinated contrast agents used for arteriography. It is nonallergic and lacks renal toxicity. Its unique properties permit use of smaller catheters in diagnostic and therapeutic angiographic procedures, allow optimal vascular imaging of various neoplasm, assist in detection of occult gastrointestinal bleeding, and facilitate TIPS procedures. With digital subtraction techniques and stacking programs, CO2 arteriography is as accurate as iodinated contrast studies in most patients and thus is the preferred arterial imaging technique in patients with contrast allergy and renal insufficiency. CO2 is also extremely inexpensive compared with available contrast agents. Understanding of the effects of buoyancy and compressibility is necessary for safe, controlled delivery of CO2 during arteriography, but only rare complications have occurred in our large experience with CO2 angiography. Thus, use of CO2 as an arterial contrast agent significantly expands the safety and utility of arterial imaging in patients with peripheral vascular disease.     

Spin-polarized hydrogen: A weakly interacting boson gas

These lectures on a gas of spin-polarized hydrogen discuss the developments in this field up to the latest results. First, hydrogen is treated as a stable non-recombining gas and many fundamental properties such as Bose-Einstein condensation (BEC), the two-dimensional Kosterlitz-Thouless transition to superfluidity, and interactions with helium are discussed. In the second section the experimental production and handling of spin-polarized hydrogen is treated. This includes theoretical and experimental discussions of two- and three-body recombination as well as relaxation, both in the normal and condensate phase. These processes have so far prevented the experimental observation of degenerate quantum effects, as they either limit the density or the temperatures of samples. In the final section several experimental ideas for BEC, currently under development, are discussed. These include the magnetostatic trap, the microwave trap, compression of hydrogen as bubbles in helium, compression with magnetic field gradients, and the use of the Lyman- laser source in the study of atomic hydrogen.Presented by Isaac F. Silvera.     

Ultra-sensitive bolometers for atomic hydrogen detection

Two different types of bolometers have been developed to be used for spin-polarized atomic hydrogen detection. One of them uses a thin Cu shell as the absorber and a doped Ge chip as the thermometer element. The other uses a silver film as the absorber and a superconductor-insulator-normal metal junction to measure the temperature rise of the electrons in the absorber. These bolometers have a calculated noise equivalent power of 10^–15 WHz^–1/2 and 10^–17 WHz^–1/2, respectively, and can detect down to 6 × 10³ and 800 particles, respectively, at an operating temperature of 100 mK. If these detectors perform as predicted, the minimum number of detectable hydrogen atoms will be improved by several orders of magnitude.     

The protective effect of moderate alcohol consumption on ischemic stroke

Experiments were designed to investigate the influence of estrous cycle and gender of the rat on the effects of a gamma-aminobutyric acid type A (GABA(A)) receptor active neurosteroid, 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone), the benzodiazepine, triazolam, and a GABA(A) receptor antagonistic neurosteroid, delta5-androsten-3beta-ol-17-one sulfate (dehydroepiandrosterone sulfate), on food intake and elevated plus-maze learning behaviors. Allopregnanolone (0.25 mg/kg, s.c.) and triazolam (0.25 mg/kg, i.p.) produced a hyperphagic effect, while dehydroepiandrosterone sulfate (5 mg/kg, s.c.) elicited an anorectic effect. However, allopregnanolone was more potent in diestrous females, whereas triazolam exhibited significantly higher hyperphagic potency in estrus females. The extent of anorexia following dehydroepiandrosterone sulfate was alike in male and female rats. The triazolam- and allopregnanolone-induced hyperphagic effect was blocked by bicuculline (1 mg/kg, i.p.), a selective GABA(A) receptor antagonist. In contrast to triazolam, the hyperphagic effect of allopregnanolone was insensitive to flumazenil (5 mg/kg, i.p.), a benzodiazepine antagonist. Vehicle-treated diestrous rats displayed moderately higher latencies in the elevated plus-maze learning task than estrus or proestrus females. Although allopregnanolone and triazolam elicited equipotent learning deficits in plus-maze learning in male and female rats, the magnitude of impairment-induced by triazolam was significantly higher in diestrous females than proestrus females. Dehydroepiandrosterone sulfate enhanced memory performance only in male rats. Although the use of the elevated plus-maze as a learning paradigm with benzodiazepines and neurosteroids may be sensitive to changes in anxiety, the differential data suggest that neurosteroid-induced effects are at least partly specific to learning behavior. These results confirm the role of estrous cycle and sex of rats in modifying the potency of neurosteroids and benzodiazepines on food consumption and learning and memory processes.     

Multiple regions of human Fc gamma RII (CD32) contribute to the binding of IgG

The low affinity receptor for IgG, Fc gamma RII (CD32), has a wide distribution on hematopoietic cells where it is responsible for a diverse range of cellular responses crucial for immune regulation and resistance to infection. Fc gamma RII is a member of the immunoglobulin superfamily, containing an extracellular region of two Ig-like domains. The IgG binding site of human Fc gamma RII has been localized to an 8-amino acid segment of the second extracellular domain, Asn154-Ser161. In this study, evidence is presented to suggest that domain 1 and two additional regions of domain 2 also contribute to the binding of IgG by Fc gamma RII. Chimeric receptors generated by exchanging the extracellular domains and segments of domain 2 between Fc gamma RII and the structurally related Fc epsilon RI alpha chain were used to demonstrate that substitution of domain 1 in its entirety or the domain 2 regions encompassing residues Ser109-Val116 and Ser130-Thr135 resulted in a loss of the ability of these receptors to bind hIgG1 in dimeric form. Site-directed mutagenesis performed on individual residues within and flanking the Ser109-Val116 and Ser130-Thr135 domain 2 segments indicated that substitution of Lys113, Pro114, Leu115, Val116, Phe129, and His131 profoundly decreased the binding of hIgG1, whereas substitution of Asp133 and Pro134 increased binding. These findings suggest that not only is domain 1 contributing to the affinity of IgG binding by Fc gamma RII but, importantly, that the domain 2 regions Ser109-Val116 and Phe129-Thr135 also play key roles in the binding of hIgG1. The location of these binding regions on a molecular model of the entire extracellular region of Fc gamma RII indicates that they comprise loops that are juxtaposed in domain 2 at the interface with domain 1, with the putative crucial binding residues forming a hydrophobic pocket surrounded by a wall of predominantly aromatic and basic residues.