Generation of alternating groups by pairs of conjugates

Considering the conjugacy classes of the alternating group of degreen, those classes that contain a pair of generators are in the majority. In fact, the proportion of such classes is 1 –(n), and(n) 0 asn .     

A new approach to reduction of the Neumann problem in acoustic scattering to a non-hypersingular integral equation

The Neumann problem for the propagative Helmholtz equation inthe exterior of several bodies (obstacles) is studied in twoand three dimensions by a special modification of the boundaryintegral equation method. This modification can be called the'method of interior boundaries', because additional boundariesare introduced inside scattering bodies. The solution of theproblem is obtained in the form of a single layer potentialon the whole boundary. The density in the potential satisfiesthe uniquely solvable Fredholm equation of the second kind andcan be computed by standard codes. In fact our method holdsfor any positive wave numbers.     

Beam shear-Alfven instability in two-component tokamak

The authors consider from a theoretical standpoint the excitation of shear-Alfven waves in a tokamak in which the plasma contains a fast ion group. It is assumed that the fast ions are formed as a result of fast neutral atoms injected into the tokamak. An expression is derived for the growth rate of the shear-Alfven oscillations, with an arbitrary relationship between the transverse wave length and the dimension of the Larmor and drift orbits. The authors analyse the part played by the finite orbit effect in the case of a longitudinal beam with a small Maxwellian velocity spread and an arbitrary ratio between the directed velocityV ₀ and the Alfven velocityc _A . It is demonstrated that at a finite ratioV ₀/c _A two physically different types of oscillations may build up, corresponding to the two signs of the ratio/k _¦ ( is the oscillation frequency,k _¦ is the longitudinal wave number). The growth rate for perturbations with /k_¦<0 is greater than for /k>0.     

Ultraviolet Spectral Energy Differences Affect the Ability of Sunscreen Lotions to Prevent Ultraviolet-Radiation-Induced Immunosuppression*

Acute exposure to UV radiation causes immunosuppression of contact hypersensitivity (CH) responses. Past studies conducted with unfiltered sunlamps emitting nonsolar spectrum UV power (wavelengths below 295 nm) or using excessive UV doses have suggested sunscreens may not prevent UV-induced immunosuppression in mice. This study was thus designed to evaluate critically the effects of different UV energy spectra on the immune protection capacity of sunscreen lotions. Minimum immune suppression doses (MISD), i.e. the lowest UV dose to cause~50% suppression of the CH response to dinitrofluorobenzene in C3H mice, were established for three artificial UV sources. The MISD for each UV source was 0.25 kJ/m² for unfiltered FS20 sunlamps (FS), 0.90 kJ/m² for Kodacel-filtered FS20 sunlamps (KFS), which do not emit UV power at wavelengths <290 nm, and 1.35 kJ/m² for a 1000 W filtered xenon arc lamp solar simulator. Using MISD as baseline, sunscreens with labeled sun protection factors (SPF) of 4, 8, 15 and 30 were tested with each UV source to establish their relative immune protection factors. The immune protection factor of each sunscreen exceeded its labeled SPF in tests conducted with the solar simulator, which has a UV power spectrum (295–400 nm) similar to that of sunlight. Conversely, sunscreen immune protection factors were significantly less than the labeled SPF in tests conducted with FS and KFS. Comparison of the immunosuppression effectiveness spectra showed that relatively small amounts of nonsolar spectrum UV energy, i.e. UVC (200–290 nm) and/or shorter wavelength UVB (between 290 and 295 nm), produced by FS and KFS contributes significantly to the induction of immunosuppression. For example, 36.3% and 3.5% of the total immunosuppressive UV energy from FS and KFS, respectively, lies below 295 nm. Sunscreen absorption spectra showed that transmission of immunosuppressive UV energy below 295 nm for FS was at least eight-fold higher than that for KFS. Compared to the solar simulator UV spectrum the transmission of nonsolar immunosuppressive UV energy through sunscreens was >15-fold higher for FS and ≥1.5-fold higher for KFS. These data demonstrate that relevant evaluations of sunscreen immune protection can only be obtained when tests are conducted with UV sources that produce UV power spectra similar to that of sunlight and UV doses are employed that are based on established MISD.     

Locating Benefit Posts in Brazil

In this paper we report on a case study involving the location of benefit distribution facilities (benefit posts) in Brazil. Significant improvements in the distribution of benefits are anticipated as a result of this study.