Optical transition radiation used in the diagnostic of low energy and low current electron beams in particle accelerators.

Optical transition radiation (OTR) plays an important role in beam diagnostics for high energy particle accelerators. Its linear intensity with beam current is a great advantage as compared to fluorescent screens, which are subject to saturation. Moreover, the measurement of the angular distribution of the emitted radiation enables the determination of many beam parameters in a single observation point. However, few works deals with the application of OTR to monitor low energy beams. In this work we describe the design of an OTR based beam monitor used to measure the transverse beam charge distribution of the 1.9-MeV electron beam of the linac injector of the IFUSP microtron using a standard vision machine camera. The average beam current in pulsed operation mode is of the order of tens of nano-Amps. Low energy and low beam current make OTR observation difficult. To improve sensitivity, the beam incidence angle on the target was chosen to maximize the photon flux in the camera field-of-view. Measurements that assess OTR observation (linearity with beam current, polarization, and spectrum shape) are presented, as well as a typical 1.9-MeV electron beam charge distribution obtained from OTR. Some aspects of emittance measurement using this device are also discussed.

Evaluation of new leptin fragments on food intake and body weight of normal rats.

Leptin, a protein hormone originating from adipose tissue, circulates in the plasma and affects the energy balance by interacting with the hypothalamus. Leptin plays an important role in the regulation of a variety of physiological functions, including food intake, body temperature and body weight maintenance. Tertiary structure of the leptin molecule reveals the existence of a four-helix bundle that is characteristic of the short-helix cytokines. To identify regions of the leptin molecule responsible for its bioactivity, we have recently synthesized six peptides based on the protein three-dimensional structure. Our results indicated that the fragments Ac-hLEP(92-115)-NH(2) (IV) and Ac-[Ser(117)]-hLEP(116-140)-NH(2) (V) were recognized by leptin receptor present in hp-75 cells validating that this region of the molecule contain the functional epitope of the leptin molecule. In the present study, a new series of decapeptides encompassing the region of fragments IV and V of leptin were synthesized, and their effects on body weight and food intake were assessed when administered into the lateral cerbroventricle of normal rats. Peptides were synthesized by SPPS, purified by RP-HPLC and characterized by LC/ESI-MS. We also performed a conformational study of the peptides by circular dichroism in order to correlate the biological activity and secondary structure of the leptin fragments. Among the fragments tested, we found that Ac-hLEP(110-119)-NH(2) (VI) induce a significant reduction in both body weight and food intake. The use of synthetic leptin-derivate fragments may offer the basis for the development of compounds with potential application in human obesity or to its related metabolic dysfunctions.

Long-term accumulation and microdistribution of uranium in the bone and marrow of beagle dog.

The accumulation and microdistribution of uranium in the bone and marrow of Beagle dogs were determined by both neutron activation and neutron-fission analysis. The experiment started immediately after the weaning period, lasting till maturity. Two animal groups were fed daily with uranyl nitrate at concentrations of 20 and 100 microg g(-1) food. Of the two measuring techniques, uranium accumulated along the marrow as much as in the bone, contrary to the results obtained with single, acute doses. The role played by this finding for the evaluation of radiobiological long-term risks is discussed. It was demonstrated, by means of a biokinetical approach, that the long-term accumulation of uranium in bone and marrow could be described by a piling up of single dose daily incorporation.

Transfer coefficient measurements of uranium to the organs of Wistar rats, as a function of the uranium content in the food.

Groups of animals (Wistar rats) were fed with rations doped with uranyl nitrate at concentrations ranging from 0.5 to 100 ppm. The uranium content in the ashes of the organs was measured by the neutron-fission track counting technique. The most striking result is that the transfer coefficients, as a function of the uranium concentration, exhibit a concave shape with a minimum around 20 ppm-U for all organs. Explanations to interpret this finding are tentatively given.