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.     

Development of motion-defined figure-ground segregation in preschool and older children, using a letter-identification task

BACKGROUND: Three-month-old infants can discriminate motion-defined (MD) form, but we do not know the age at which this ability reaches adult levels. Previous psychophysical evidence suggests that different neural mechanisms are involved in the processing of luminance-defined (LD) and MD spatial form in adults. This difference may be reflected in the development of LD versus MD form identification in children. METHODS: We measured speed threshold for identifying MD letters, letter-chart (i.e, Snellen) acuity for high-contrast LD letters and single-letter acuity for high- and low-contrast LD letters. Forty-seven children between 3 and 12 years of age and 20 adult subjects were tested. RESULTS: Development to the adult level was observed as follows: low-contrast single-letter acuity before 3 years; high-contrast single-letter acuity by 5 to 6 years; the ability to identify MD letters by 7 to 8 years; letter-chart acuity by 9 to 10 years. CONCLUSIONS: MD form identification continues to mature in preschool children. LD form identification also matures in this age group but with a different time course. MD letters are not equivalent to low-contrast letters developmentally. Our findings provide further support for the hypothesis that the spatial aspects of MD and LD form are processed separately to some extent.     

On closure properties of bounded two-sided error complexity classes

We show that if a complexity classC is closed downward under polynomial-time majority truth-table reductions ( _mtt ^p ), then practically every other polynomial closure property it enjoys is inherited by the corresponding bounded two-sided error class BP[C]. For instance, the Arthur-Merlin game class AM [B1] enjoys practically every closure property of NP. Our main lemma shows that, for any relativizable classD which meets two fairly transparent technical conditions, we haveC ^BP[C] BP[D ^C]. Among our applications, we simplify the proof by Toda [Tol], [To2] that the polynomial hierarchy PH is contained in BP[P]. We also show that relative to a random oracleR, PH ^R is properly contained in P ^R .The first author was supported in part by NSF Grant CCR-9011248 and the second author was supported in part by NSF Grant CCR-89011154.     

Video-assisted coronary bypass surgery: clinical results

The pesticide residues 1-(o-chlorophenyl)-1-(p-chlorophenyl)-2,2,2-trichloroethane (o,p'-DDT) and beta-hexachlorocyclohexane (beta-HCH) act as weak estrogens, producing uterotrophic responses in ovariectomized rodents and stimulating human breast cancer cells in culture. Such activity suggests that these compounds may act as tumor promoters in estrogen-responsive tissues. Organochlorine compounds such as o,p'-DDT and beta-HCH are concentrated in body fat. The present report tests whether sufficient compound can be released from fat depots to produce estrogenic effects in uteri of ovariectomized mice. Adult animals were "loaded" with test compound by three daily injections of vehicle (DMSO), 17beta-estradiol (E2), beta-HCH, or o,p'-DDT. Uterotrophic effects were assessed at 24 h after the last loading dose of test compound and at 2 weeks after the loading regimen, with or without a prior 2-day period of fasting. The initial 3-day treatment with either beta-HCH or o,p'-DDT doubled the relative dry weight of the uterus: 102 +/- 8.6 mg/kg body weight (BW) and 104 +/- 4.4 mg/kg BW for beta-HCH and o,p'-DDT, respectively, compared to 49 +/- 1.9 mg/kg BW for vehicle-treated animals. E2-treated animals had uterine dry weights of 228 +/- 11 mg/kg BW. After 2 weeks without further treatment, a 2-day fast produced a decrease in body mass of 4.1 g/animal (fasted, 25.9 +/- 1.89 g versus fed, 30.0 +/- 2.82 g). Animals that had been loaded with beta-HCH and fasted had uterine weights (88 +/- 12 mg/kg BW) significantly greater (P < 0.05) than those of vehicle-loaded, fasted animals (51 +/- 2.9 mg/kg BW) or of beta-HCH-loaded, fed animals (59 +/- 4.6 mg/kg BW). The uterine weights of the fasted and fed o,p'-DDT-loaded or E2-loaded animals were not different from those of control weights. The difference between wet and dry weights showed that fasting of beta-HCH-loaded animals also increased water imbibition in the uterus; there was no effect from fasting in the other groups. Generally, epithelial cell height reflected the same responses as uterine weight with the exception that cell heights of beta-HCH-loaded, fed animals were slightly higher (P < 0.05) than corresponding controls, indicating that there may have been some active compound available to the tissues even without fasting. The effects of fasting show that during periods of lipolysis beta-HCH can be released in quantities sufficient to stimulate estrogen target tissues, suggesting a novel mechanism linking obesity and the progression of estrogen-responsive tumors. The lack of effect from fasting in o,p'-DDT-loaded animals indicates that these compounds are differentially mobilized from fat depots.     

Orientation‐Controlled Selective‐Area Epitaxy of III–V Nanowires on (001) Silicon for Silicon Photonics

Monolithic integration of III–V nanowires on silicon platforms has been regarded as a promising building block for many on‐chip optoelectronic, nanophotonic, and electronic applications. Although great advances have been made from fundamental material engineering to realizing functional devices, one of the remaining challenges for on‐chip applications is that the growth direction of nanowires on Si(001) substrates is difficult to control. Here, catalyst‐free selective‐area epitaxy of nanowires on (001)‐oriented silicon‐on‐insulator (SOI) substrates with the nanowires aligned to desired directions is proposed and demonstrated. This is enabled by exposing {111} planes on (001) substrates using wet chemical etching, followed by growing nanowires on the exposed planes. The formation of nanowire array‐based bottom‐up photonic crystal cavities on SOI(001) and their coupling to silicon waveguides and grating couplers, which support the feasibility for on‐chip photonic applications are demonstrated. The proposed method of integrating position‐ and orientation‐controllable nanowires on Si(001) provides a new degree of freedom in combining functional and ultracompact III–V devices with mature silicon platforms.     

Extracellular reduced glutathione increases neuronal vulnerability to combined chemical hypoxia and glucose deprivation

In addition to its intracellular antioxidant role, reduced glutathione (GSH) is released by CNS cells and may mediate or modulate excitatory neurotransmission. Although extracellular GSH levels rise in the ischemic cortex, its effect on the viability of energy-compromised neurons has not been defined. In this study, we tested the hypothesis that exogenous GSH would increase the vulnerability of cultured cortical neurons to azide-induced chemical hypoxia combined with glucose deprivation. Thirty minutes azide exposure in a glucose-free buffer was tolerated by most neurons, with release of less than 10% of neuronal LDH over the subsequent 21-25 h. Concomitant treatment with 10-100 microM GSH increased cell death in a concentration-dependent fashion, to 71.6+/-5.1% of neurons at 100 microM; GSH alone was nontoxic. Injury was blocked by the selective N-methyl-d-aspartate (NMDA) antagonist MK-801 but not by the AMPA/kainate antagonist NBQX. The sulfhydryl reducing agent mercaptoethanol (10-100 microM) mimicked the action of GSH; however, the zinc chelator ethylenediaminetetraacetic acid (EDTA) was ineffective. Two GSH analogues that lack a sulfhydryl group, S-hexylglutathione (SHG) and oxidized glutathione (GSSG), were inactive per se but attenuated the effect of both GSH and mercaptoethanol. These results suggest that micromolar concentrations of GSH enhance neuronal loss due to energy depletion by altering the extracellular redox state, resulting in increased NMDA receptor activation.     

A surrogate-based multiobjective metaheuristic and network degradation simulation model for robust toll pricing

Robust transportation network design problems generally rely on systems engineering methods that share common research gaps. First, problem sizes are constrained due to the use of multi-objective solution algorithms that are notoriously inefficient due to computationally expensive function evaluations. Second, link disruptions at a network level are difficult to model realistically. In this paper, a stochastic search metaheuristic based on radial basis functions is proposed for constrained multiobjective problems. It is proven to converge, and compared with conventional metaheuristics for four representative test problems. A scenario simulation method based on multivariate Bernoulli random variables that accounts for correlations between link failures is proposed to sample scenarios for a mean-variance toll pricing problem. Four tests are conducted on the classical Sioux Falls network to gain some insights into the algorithm, the simulation model, and to the robust toll pricing problem. The first test empirically measures the efficiency of the simulation algorithm and approximate Pareto set by obtaining a standard error in the ε-indicator measure for a given number of scenarios and iterations. The second test compares the dominance of the proposed heuristic’s solutions with a conventional multiobjective genetic algorithm by comparing the average ε-indicator. The third test quantifies the gap due to falsely assuming that link failures are independent of each other when they are not. The last test quantifies the value of having the flexibility to adapt a Pareto set of toll pricing solutions to changing probability regimes such as peak and off-peak hurricane or snow seasons.     

Health Risks and Adverse Reactions to Functional Foods

Functional foods have become increasingly popular with consumers anxious to mitigate the effects of an unhealthy lifestyle or aging. In spite of attractive health claims, these products do not have legal or regulatory status in most countries and are regulated through their health claims. Regulation of functional foods by health claims does not address health risks and adverse effects of these products. In this essay regulatory aspects of functional foods are reviewed along with adverse effects published in the peer-reviewed literature. We detail why the lack of an internationally accepted definition of functional foods places consumers at risk of adverse outcomes. Our review will assist regulatory agencies, manufacturers and consumer groups to assess the benefits and reduce the risks associated with these products.     

LunchTime: a slow-casual game for long-term dietary behavior change

Eating out has recently become part of our lifestyle. However, when eating out in restaurants, many people find it difficult to make meal choices consistent with their health goals. Bad eating choices and habits are in part responsible for the alarming increase in the prevalence of chronic diseases such as obesity, diabetes, and high blood pressure, which burden the health care system. Therefore, there is a need for an intervention that educates the public on how to make healthy choices while eating away from home. In this paper, we propose a goal-based slow-casual game approach that addresses this need. This approach acknowledges different groups of users with varying health goals and adopts slow technology to promote learning and reflection. We model two recognized determinants of well-being into dietary interventions and provide feedback accordingly. To demonstrate the suitability of our approach for long-term sustained learning, reflection, and attitude and/or behavior change, we develop and evaluate LunchTime—a goal-based slow-casual game that educates players on how to make healthier meal choices. The result from the evaluation shows that LunchTime facilitates learning and reflection and promotes positive dietary attitude change.