Oscillation of the scattering time in a 2D electron system with oval antidots

Electron scattering by a single barrier is predicted to reveal singularities as the magnetic field is changed, because the number of electron collisions with the barrier dramatically increases as chaotic orbits around the barrier are changed into periodic orbits. To test this experimentally we have measured the magnetoresistance of AlGaAs/GaAs heterostructures with a two-dimensional electron gas and a lateral lattice containing a macroscopic number of oval-shaped antidots fabricated using electron lithography. Reproducible fluctuations in the magnetoresistance are observed at low field, which are due to the oscillations of the number of electron collisions with the antidots. The number of collisions N before the electron escapes from the antidot has been calculated as a function of B in an electric field. The position of the maxima in N(B) obtained from calculations and experiment are in reasonable agreement.     

Measuring interdiffusion at an interface between two elastomers with tapping-mode and contact-resonance atomic force microscopy imaging

Despite the common use of tapping-mode atomic force microscopy to image composites or polymer blends, very few studies have focused on the measurement of the interdiffusion at an interface between two polymers in contact. In this study, we show how to assess the interphase between two polymers with two methods. First, stable and robust tapping conditions are established, and the problem of the phase contrast is discussed. Second, a contact-resonance method is presented: the tip in contact with the sample is electrostatically excited at its resonance frequency by a self-controlled oscillator. The gain and frequency images allow us to measure the interdiffusion width. Both methods (using high and weak mechanical solicitation) give the same assessment of the interdiffusion width. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Anisotropic Magnetoresistance of GaMnAs Ferromagnetic Semiconductors

The angular dependence of the magnetoresistance has been studied for two sets of samples: annealed and hydrogenated, respectively. Different behavior of magnetoresistance anisotropy has been discussed in terms of change of scattering rate and/or introduction of strain during treatment.     

Les passions de l'ame: On obsessive and harmonious passion.

Passion is defined as a strong inclination toward an activity that people like, that they find important, and in which they invest time and energy. Two types of passion are proposed: obsessive and harmonious. Obsessive passion (OP) refers to a controlled internalization of an activity in one's identity that creates an internal pressure to engage in the activity that the person likes. Harmonious passion (HP) refers to an autonomous internalization that leads individuals to choose to engage in the activity that they like. HP promotes healthy adaptation whereas OP thwarts it by causing negative affect and rigid persistence. Results from four studies involving more than 900 participants from different populations supported the proposed conceptualization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

HIV-1 disease progression and AIDS-defining disorders in rural Uganda

BACKGROUND: The majority of people infected with HIV-1 live in Africa, yet little is known about the natural history of the disease in that continent. We studied survival times, disease progression, and AIDS-defining disorders, according to the proposed WHO staging system, in a population-based, rural cohort in Uganda. METHODS: In 1990 we recruited a random sample of people already infected with HIV-1 (as prevalent cases) detected during the initial survey round of a general-population study to form a natural-history cohort. Individuals from the general-population cohort who seroconverted between 1990 and 1995 (incident cases) were also invited to enroll. Participants were seen routinely every 3 months and when they were III. FINDINGS: By the end of 1995, 93 prevalent cases and 86 incident cases had been enrolled. Four patients in the prevalent group were in stage 4 (AIDS) at the initial visit. During the next 5 years, 37 prevalent cases progressed to AIDS. Seven incident cases progressed to AIDS and the cumulative progression to AIDS at 1, 3, and 5 years after seroconversion was 2%, 6%, and 22%, respectively. The cumulative probability of AIDS at 4 years from entering stages 1, 2, and 3 was 11%, 33%, and 58%, respectively. There were 47 deaths among prevalent cases and seven among incident cases during follow-up. The cumulative mortality 4 years after patients entered stages 1, 2, 3, and 4 was 9%, 33%, 56%, and 86%, respectively. The median survival after the onset of AIDS was 9.3 months. INTERPRETATION: Our results are important for the setting of priorities and rationalisation of treatment availability in countries with poor resources. We found that progression rates to AIDS are similar to those in developed countries for homosexual cohorts and greater than for cohorts infected by other modes of transmission. However, we have found that the rates of all-cause mortality are much higher and the progression times to death are shorter than in developed countries.     

Electron tunneling between two-dimensional electronic systems in a heterostructure with a single doped barrier

Electron tunneling in a heterostructure with a single doped barrier was investigated. Analysis of the experimental data showed that all features in the tunneling conductance are due to electron tunneling between two-dimensional electron sheets which appear on different sides of the barrier as a result of ionization of impurities in the barrier. Electron transport between the two-dimensional electron sheets and three-dimensional contact regions does not introduce significant distortions in the measured tunneling characteristics. In such structures there is no current flow along the two-dimensional electron gas; such a current ordinarily makes it difficult to investigate tunneling between two-dimensional electronic systems in magnetic fields. Fiz. Tekh. Poluprovodn. 32, 602–606 (May 1998)     

Effect of diet on the fatty acid and molecular species composition of dog retina phospholipids

Dogs were born to mothers fed commercial diets low or enriched in n-3 fatty acids and raised on those diets until they were about 50 d old. Retinas were removed, lipids were extracted, and total phospholipids were analyzed for fatty acid and molecular species composition. Animals from the low n-3 group had significantly lower retinal levels of 22:6n-3 and higher levels of n-6 fatty acids, especially 20:4n-6 and 22:5n-6. There was no difference in the retinal levels of 18:2n-6, and only small differences were found in saturated and monounsaturated fatty acids. The most dramatic differences in molecular species occurred in 22:6n-3-22:6n-3 (4.7 vs. 0.8%) and 18:0-22:6n-3 (27.6 vs. 14.4%); total molecular species containing 22:6n-3 were significantly lower in the low n-3 group (45.5 vs. 24.0%). Molecular species containing 20:4n-6 and 22:5n-6 were greater in the low n-3 animals (13.0 vs. 25.7%), as were molecular species containing only saturated and monounsaturated fatty acids (40.8 vs. 35.4%). These results show that modest differences in the amount of n-3 fatty acids in the diets of dogs can have profound effects on the fatty acid and molecular species composition of their retinas.     

Aging of the flame‐retardant properties of polycarbonate and polypropylene protected by an intumescent coating

Flame retardancy (FR) in polycarbonate (PC) and polypropylene (PP) was obtained through the application of an intumescent coating on the polymeric substrate. A better performance was obtained with PC, a char former and highly viscous polymer, compared to with PP. Indeed, whereas 61 μm was required to obtain good FR (by the UL94 V0 rating, in particular) in the case of PC, at least 158 μm needed to be used to give FR to PP. The aging of the coated materials induced by UV‐filtered light radiation was then studied. This exposure led to a decrease in the FR. This effect was more pronounced in the case of PP compared to that of PC. The decrease in the FR was attributed to a decrease in the adhesion of the coating on the polymeric substrate because of its suspected physical aging. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39566.