Analysis of insecticidal proteins from Bacillus thuringiensis and recombinant Escherichia coli by capillary electrokinetic chromatography

Bacillus thuringiensis and recombinant Escherichia coli proteinaceous protoxins were subject to proteolysis and analyzed by capillary electrokinetic chromatography. Three resulting toxins (65 kDa) were baseline-resolved within 22 min using a 10 mM borate, pH 11 separation buffer consisting of 25 mM sodium dodecyl sulfate (SDS) and 30 mM phytic acid. The toxins displayed differential interactions with the SDS and phytic acid phases to effect their separation. The ion-pairing interaction between the analyte and phytic acid was also useful in preventing adsorption to the capillary walls and thus enhanced separation resolution and efficiency. The use of electrokinetic chromatography allows achievement of the separation in a significantly shorter time than conventional high-performance liquid chromatography (HPLC) using a diethylaminoethyl (DEAE) weak-anion exchanger.     

Exciton-exciton interaction in quantum wells

Il Nuovo Cimento D - Fast initial decays of both the luminescence intensity and the circular luminescence polarization at high exciton densities, under resonant excitation, are reported for the...     

Evidences for Auger recombination in electron-hole droplets (silicon)

The microwave absorption technique was used to measure the transient free carrier density following an electric injection in silicon at 4°K. The experiment agrees with the idea that droplets are obtained by free carrier condensation directly, without a preliminary formation of free excitons.¹ An Auger recombination process in droplets explains the observed kinetics; parameters are measured.     

Use of stable isotopes as surrogates for radionuclides for security studies

During the past decade, interest has increased in qualifying and quantifying the threat posed to the public by the illegal use of radionuclides. In order to take investigations beyond the laboratory bench into more realistic scenarios, environmental and safety considerations dictate that these studies be performed on stable and benign surrogates. This paper discusses some of these studies, specifically the use of cerium dioxide for actinide ceramics and calcium and natural strontium ceramics for those based on ⁹⁰Sr.     

Hysteresis effect and surface energy of drops in silicon

We report here the observation of the hysteresis effect of the drop luminescence in silicon at the temperature of 6.6 K. Hysteresis ratios up to 2.1 have been registered. The surface energy σ of drops is deduced from the measurement of the energy shift of the drops luminescence at low pumping level. The results yield: σ = (125±60) × 10^?4ergcm^?2.     

Binding probability of free electrons and free holes into Wannier-Mott exciton in non-polar semiconductors

A free electron and a free hole in a crystal may be bound together due to the attractive coulomb field: in semiconductors such an electron-hole pair is similar to the Wannier-Mott exciton. The probability of binding into the fundamental state has been calculated by Lipnik[1]. Lipnik's model does not predict our recent low temperature measurements[2]. Actually the binding probabilities of excited states of excitons must be considered. This is the purpose of the present paper: a quantum model, (adequate in the low temperature limit) and a semi-classical model (adequate when the temperature rises) are presented.     

Identification of a set of genes showing regionally enriched expression in the mouse brain

Background

We have recorded responses from single neurons in murine visual cortex to determine the effectiveness of the input from the two murine cone photoreceptor mechanisms and whether there is any unique selectivity for cone inputs at this higher region of the visual system that would support the possibility of colour vision in mice. Each eye was stimulated by diffuse light, either 370 (strong stimulus for the ultra-violet (UV) cone opsin) or 505 nm (exclusively stimulating the middle wavelength sensitive (M) cone opsin), obtained from light emitting diodes (LEDs) in the presence of a strong adapting light that suppressed the responses of rods.

Results

Single cells responded to these diffuse stimuli in all areas of striate cortex. Two types of responsive cells were encountered. One type (135/323 – 42%) had little to no spontaneous activity and responded at either the on and/or the off phase of the light stimulus with a few impulses often of relatively large amplitude. A second type (166/323 – 51%) had spontaneous activity and responded tonically to light stimuli with impulses often of small amplitude. Most of the cells responded similarly to both spectral stimuli. A few (18/323 – 6%) responded strongly or exclusively to one or the other spectral stimulus and rarely in a spectrally opponent manner.

Conclusion

Most cells in murine striate cortex receive excitatory inputs from both UV- and M-cones. A small fraction shows either strong selectivity for one or the other cone mechanism and occasionally cone opponent responses. Cells that could underlie chromatic contrast detection are present but extremely rare in murine striate cortex.     

Exciton cooling and localization in GaAs/AlGaAs multiquantum well structures

We report experimental and theoretical results on picosecond time resolved photoluminescence spectroscopy of 2D-excitons in multiquantum well structures. A theoretical model is formulated which includes the cooling of the free exciton gas by acoustical phonon emission and the localization of excitons due to interface defects. The cooling rate of 2D excitons is shown to be enhanced with respect to the 3D case.     

Rheological properties of suspensions of polyethylene-coated aluminum nanoparticles

Ultrafine aluminum powder was identified as very promising fuels for novel energetic materials formulations. However, the large specific surface area of this powder facilitates its oxidation and greatly reduces its shelf life. Therefore, different coating processes were proposed to solve this problem. The rheology of viscous suspensions of nanoparticles still remains poorly understood and the effect of the coating of such particles on the flow behavior is even more difficult to assess. We have studied the rheology of ultrafine aluminum suspensions in three low molecular weight polymers of different viscosities: a hydroxy-terminated polybutadiene, a polypropylene glycol, and a polysiloxane. The nanosize aluminum powder was previously coated by a thin layer of high-density polyethylene using an in situ polymerization process. The rheological characterization of the suspensions was conducted by the means of steady and oscillatory shear flow measurements for noncoated and coated particles. The effect of the coating process on the rheology of the suspensions is discussed in terms of the interactions between the particles and the suspending fluids.