Plasma lens experiment at the final focus test beam

The proposed plasma lens experiment at the Final focus Test Beam (FFTB) facility of the Stanford Linear Accelerator Center has been approved by the adminstration. The experiment would allow the examination of plasma focusing devices for particle beams in the parameter regime of interest to future high-energy colliders. It is expected to lead to compact plasma lens designs capable of focusing the beam to unprecedented small spot sizes.     

Interaction of relativistic electrons with ultrashort laser pulses:generation of femtosecond X-rays and microprobing of electron beams

The interaction of relativistic electrons with terawatt femtosecond laser pulses is reviewed with emphasis on how the scattering process can be used as a source of ultrashort X-ray pulses and as a time-resolved diagnostic for measuring transverse and longitudinal phase space distributions of an electron beam with microns spatial and subpicosecond temporal resolution. Recent experimental results are presented in which 90° Thomson scattering was utilized to generate 300 fs duration pulses of X-rays with peak energy of 30 keV. It is shown that, through analysis of the scattered X-ray beam properties, transverse and longitudinal distributions of the electron beam can be obtained     

T cell apoptosis in human heart allografts: association with lack of co-stimulation?

It is unclear whether the intracardial immune reactivity after heart transplantation influences the peripheral immunological status (activation or nonresponsiveness) of the patient. Co-stimulation and activation-induced cell death (AICD) or apoptosis play an important role in determining the balance between lymphocyte reactivity and nonreactivity. Therefore, we studied the expression of co-stimulatory molecules and the process of apoptosis in biopsies of human heart allografts, using immunohistochemistry. Although a normal expression of co-stimulatory molecules on antigen-presenting cells was observed, the expression of their counter-structures on T cells was absent. This may be due to chronic T cell activation, which can lead to the induction of apoptosis via the Fas/Fas ligand pathway. In the infiltrates, a considerable percentage of the lymphocytes, but not the macrophages, were apoptotic. Apoptosis was confirmed by DNA fragmentation analysis. Increased numbers of Bax-expressing versus decreased numbers of Bcl2-expressing lymphocytes in comparison with normal lymphoid tissue confirmed a imbalance in favor of apoptosis. Apoptosis was biased towards CD4+ T cells (65.7% versus 26.6% in CD8+ T cells). Fas was expressed on most of the infiltrating cells. Fas ligand expression was also observed, not only on most of the T cells but also on all macrophages. Because macrophages were often detected in close contact with T cells, they may play a role in T cell regulation via the Fas/Fas ligand pathway. This study indicates that, during rejection, not only is tissue damage induced by infiltrating T cells, but also the infiltrating lymphocytes themselves are actively down-regulated (eg, AICD) by one another and by macrophages in the infiltrate. This regulatory process may affect the immunological status of the patient after heart transplantation.     

Spectroscopy of betatron radiation emitted from laser-produced wakefield accelerated electrons

X-ray betatron radiation is produced by oscillations of electrons in the intense focusing field of a laser-plasma accelerator. These hard x-rays show promise for use in femtosecond-scale time-resolved radiography of ultrafast processes. However, the spectral characteristics of betatron radiation have only been inferred from filter pack measurements. In order to achieve higher resolution spectral information about the betatron emission, we used an x-ray charge-coupled device to record the spectrum of betatron radiation, with a full width at half maximum resolution of 225 eV. In addition, we have recorded simultaneous electron and x-ray spectra along with x-ray images that allow for a determination of the betatron emission source size, as well as differences in the x-ray spectra as a function of the energy spectrum of accelerated electrons.     

Proteolysis during ensilage of forages varying in soluble sugar content

The nuclear shielding constants in OCS are studied using ab initio theoretical methods and gas-phase NMR measurements. The shielding surfaces are calculated and the rovibrational effects and the resulting temperature dependence are analyzed. The temperature dependence of 13C shielding in the gas phase is determined experimentally in the range 278-373 K. 13C is the single nucleus for which the experimental data for the temperature dependence can be converted to a reference-independent scale, and good agreement of the measured and calculated ab initio results is observed. For 33S, we discuss a new, more accurate absolute shielding scale.     

Complex processing–morphology interrelationships during the reactive compatibilization of blends of poly(butylene terephthalate) with epoxide‐ containing rubber

Reactive processing of blends of poly(butylene terephthalate) (PBT) with the ethene–(methyl acrylate)–(glycidyl methacrylate) terpolymer (E–MA–GMA) is known to present a very complex reactivity since two competitive reactions take place spontaneously during melt blending, that is, blend compatibilization and rubber‐phase crosslinking. In this article, the effects of several processing parameters, such as the shear rate, the processing temperature, and the matrix viscosity, on the reactive processing of those blends were investigated in terms of the blend morphology and of the amount of copolymer formed at the blend interface. It was shown that the morphology development could be divided in two successive regimes: In the early stages of the mixing process, the particle size is essentially determined by the physical dispersion process, that is, breakup and coalescence, while, at longer mixing times, a further decrease in particle size is obtained as a result of the compatibilization reactions. The shift between the two regimes is progressive and intimately related to the processing conditions. Despite such a complexity, not only the blend morphology but also the elastic properties of the rubber particles can be controlled in a broad range by an adequate adjustment of the relative kinetics between both physical and chemical processes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 703–718, 2004     

Laser guiding for GeV laser-plasma accelerators

Guiding of relativistically intense laser beams in preformed plasma channels is discussed for development of GeV-class laser accelerators. Experiments using a channel guided laser wakefield accelerator at Lawrence Berkeley National Laboratory (LBNL) have demonstrated that near mono-energetic 100 MeV-class electron beams can be produced with a 10 TW laser system. Analysis, aided by particle-in-cell simulations, as well as experiments with various plasma lengths and densities, indicate that tailoring the length of the accelerator, together with loading of the accelerating structure with beam, is the key to production of mono-energetic electron beams. Increasing the energy towards a GeV and beyond will require reducing the plasma density and design criteria are discussed for an optimized accelerator module. The current progress and future directions are summarized through comparison with conventional accelerators, highlighting the unique short-term prospects for intense radiation sources based on laser-driven plasma accelerators.     

Solid solution softening and strain-rate sensitivity of Fe-Re and Fe-Mo alloys

The resolved shear stress and strain-rate sensitivity of Fe-Mo and Fe-Re alloys, well within the solid solution range, were measured versus temperature and compared with previous results for Fe-Ti alloys. The strain-rate sensitivity-temperature curves shifted systematically to lower temperatures as solute was added. The resolved shear stress was divided into two parts, a dynamic part which is a function of strain-rate and a static part which is not. The strain-rate sensitivity data were inverted to give the dynamic part of the flow stress and this was subtracted from the resolved shear stress to give the static part of the flow stress. Significant solid solution softening occurred in the dynamic part of the flow stress at 166 and 196 K. This is due to intrinsic effects and not to scavenging of im-purities. The static part of the flow stress is made up of two parts, a peaking effect super-imposed on normal solid solution hardening.     

Combination gas chromatography-mass spectrometry

The direct combination of gas-liquid chromatography with mass spectrometry represents one of the most powerful techniques available for the analysis of complex mixtures of lipids. Principal advantages are the extremely small amounts of material required, the relative speed of analysis, and the wealth of molecular structural information available. The ability to record rapidly several mass spectra of one emerging chromatographic peak may also frequently be of use in detecting impurities, unresolved mixtures, or thermal decomposition of the sample. In the development of new gas chromatographic analytical procedures, the combination instrument may frequently prove highly useful for following chemical reactions in the preparation of new types of derivatives for GLC.