Antihyperon-Production in Relativistic Heavy Ion Collision

Recently it has been shown that the observed antiproton yield in heavy-ion collisions at CERN-SpS energies can be understood by multi-pionic interactions which enforce local chemical equilibrium of the antiprotons with the nucleons and pions. Here we show that antihyperons are driven towards local chemical equilibrium with pions, nucleons and kaons on a timescale of less than 3 fm/c when applying a similar argument for the antihyperons by considering the inverse channel of annihilation reactions anti-Y + p to pions + kaons. These multi-mesonic reactions easily explain the antihyperon yields at CERN-SpS energies as advertised in pure thermal, hadronic models without the need of a quark gluon plasma phase. In addition, the argument also applies for AGS energies.Comment: 4 pages using RevTeX, 1 eps figur

Nanostructures: Physics and Technology

Abstract. Optical and structural properties of self organised InGaAs quantum dots (QD), deposited in Al 0.3 Ga 0.7 As matrix, were investigated. Samples were grown by molecularbeam epitaxy (MBE). It is shown, that deposition of 1.7-4 monolayer of InAs on Al 0.3 Ga 0.7 As surface results in formation of nanoscale QDs on 1-2 monolayer thick wetting layer (Stranski-Krastanov growth mode

Structuring effect of tools conceptualized through initial goal fixedness for work activity

Analysis of work activities in nuclear industry has highlighted a new psycho-cognitive phenomenon: the structuring effect of tools (SET) sometimes leading to unexpected operating deviations; the subject is unable to perform a task concerning object A using or adapting a tool designed and presented to perform the same task concerning object B when object A is expected by the subject. Conditions to isolate and identify the SET were determined and reproduced in experiments for further analysis. Students and seven professional categories of adults (N = 77) were involved in three experimental conditions (control group, group with prior warning, group with final control) while individually performing a task with similar characteristics compared to real operating conditions and under moderate time-pressure. The results were: (1) highest performance with prior warning and (2) demonstration that academic and professional training favor the SET. After discussing different cognitive processes potentially related to the SET, we described (3) the psycho-cognitive process underlying the SET: Initial Goal Fixedness (IGF), a combination of the anchoring of the initial goal of the activity with a focus on the features of the initial goal favored by an Einstellung effect. This suggested coping with the negative effect of the SET by impeding the IGF rather than trying to increase the subjects’ awareness at the expense of their health. Extensions to other high-risk industries were discussed

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Desorption of Emulsifiers From Polystyrene Latices Followed By Spectroscopic Techniques

The desorption of emulsifier from the particle surface of latices prepared by emulsion polymerisation has been followed by spectroscopic techniques: transmission IR, X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS) -fast atom bombardment mass spectrometry (FAB-MS). In IR spectra, the extra band at 1710 cm-1 due to carboxylic groups originating from the emulsifier is fortunately visible because it is located within a window of the polystyrene peaks. XPS is a valuable surface method of analysis (contrary to IR). Nevertheless, for the latices considered here, it is impossible to extract from the very intense carbon peak information concerning variation in the carboxyl groups, which amount to less than 1%. Another important method for surface analysis is static-SIMS, which allows detection of elements and molecular species present in the first few layers with a detection limit which is less than 10(-4)%. FAB-MS permits the detection of the parent ion of the emulsifier employed. Freeze-dried powders of latices extensively purified with mixed-bed ion-exchange resins were studied for us using FAB-MS at UMIST in Manchester (UK). A comparison is made of the results obtained with these three spectroscopic techniques

Neutron Therapy - From Radiobiological Expectation To Clinical Reality

The radiobiological data at present available indicate that high LET radiations could bring a benefit in the treatment of some types of tumours (typically slowly growing. well differentiated). Radiobiology also suggests some mechanisms through which this benefit could be achieved: hypoxic gain factor, kinetics gain factor, etc. However, the need for patient selection is clearly apparent. Among the high LET radiations, fast neutrons are the least expensive and the most widely used in therapy. Seventeen centres are today actively involved in neutron therapy, and more than 15,000 patients have been treated so far. Two main difficulties are encountered when reviewing the clinical results of fast neutron therapy. Firstly, as indicated above, patient selection, which depends on the characteristics of the tumour (and of the normal tissues at risk) is important. A lack of proper selection can obscure or worsen the results. Secondly, there is a need for a high physical selectivity with neutrons. Throughout the history of radiation therapy, physical selectivity has been proved to be essential for the outcome of treatment. It becomes even more important with high LET than with low LET radiations, because of a reduction of the differential effect between the different cell populations when increasing LET. Neutron therapy started in the seventies in rather sub-optimal (or even poor) technical conditions. The situation has been significantly improved with the introduction of high energy, hospital-based cyclotrons, with isocentric mounting and variable collimators. However, in many neutron therapy centres today the level of physical selectivity does not yet fully reach the same level as modem photon therapy. The interpretation of the clinical results is then biased and it is difficult to separate what is really due to the high LET characteristics of the beams from that related to the technical treatment conditions. Among the clinical indications for fast neutrons, the following are most commonly recognised: (1) inoperable or recurrent salivary gland tumours, (2) locally extended tumours of the paranasal sinuses, (3) some other tumours of the head and neck area especially with fixed adenopathies, (4) slowly growing, well differentiated soft tissue sarcomas, osteosarcomas and chondrosarcomas, (5) locally extended prostatic adenocarcinomas, (6) palliative treatment of melanomas. The indications for neutron therapy represent about 10-15% of all patients currently referred to the radiation therapy departments