Cluster algebras in algebraic Lie theory

We survey some recent constructions of cluster algebra structures on coordinate rings of unipotent subgroups and unipotent cells of Kac-Moody groups. We also review a quantized version of these results.Comment: Invited survey; to appear in Transformation Group

Charmonium Suppression with cc~ Dissociation by Strings

We study the production of cc~ pairs in nuclear reactions at SPS energies within the covariant transport approach HSD. The production of cc~ is treated perturbatively employing experimental cross sections while the interactions of cc~ pairs with baryons are included by conventional cascade-type two-body collisions. Adopting 6 mb for the cc~-baryon cross sections the data on J/\Psi suppression in p+A reactions are reproduced in line with calculations based on the Glauber model. Additionally the dissociation of the cc~ pairs by strings is included in a purely geometrical way. We find good agreement with experimental data from the NA38 and NA50 collaboration with an estimate for the string radius of ~0.2-0.3 fm.Comment: 9 pages (LaTeX), 5 PS figure

The interstellar gas experiment

The Interstellar Gas Experiment (IGE) exposed thin metallic foils to collect neutral interstellar gas particles. These particles penetrate the solar system due to their motion relative to the sun. Thus, it is possible to entrap them in the collecting foils along with precipitating magnetospheric and perhaps some ambient atmospheric particles. For the entire duration of the Long Duration Exposure Facility (LDEF) mission, seven of these foils collected particles arriving from seven different directions as seen from the spacecraft. In the mass spectroscopic analysis of the noble gas component of these particles, we have detected the isotopes of He-3, He-4, Ne-20, and Ne-22. In the foil analyses carried out so far, we find a distribution of particle arrival directions which shows that a significant part of the trapped particles are indeed interstellar atoms. The analysis needed to subtract the competing fluxes of magnetospheric and atmospheric particles is still in progress

The Interstellar Gas Experiment: Analysis in progress

The Interstellar Gas Experiment (IGE) exposed thin metallic foils aboard the LDEF spacecraft in low Earth orbit in order to collect neutral interstellar particles which penetrate the solar system due to their motion relative to the sun. By mechanical penetration these atoms were imbedded in the collecting foils along with precipitating magnetospheric ions and, possibly, with ambient atmospheric atoms. During the entire LDEF mission, seven of these foils collected particles arriving from seven different directions as seen from the spacecraft. After the foils were returned to Earth, a mass spectrometric analysis of the noble gas component of the trapped particles was begun. The isotopes of He-3, He-4, Ne-20, and Ne-22 were detected. We have given a first account of the experiment. In order to infer the isotopic ratios in the interstellar medium from the concentrations found in the foils, several lines of investigation had to be initiated. The flux of ambient atmospheric noble gas atoms moving toward the foils due to the orbital motion of LDEF was estimated by detailed calculations. Any of these particles which evaded the baffles in the IGE collector could be entrapped in the foils as a background flux. However, the calculations have shown that this flux is negligible, which was the intent of the experiment hardware design. This conclusion is supported by the measurements. However, both the concentration of trapped helium and its impact energy indicate that the flux of magnetospheric ions which was captured was larger than had been expected. In fact, it appears that the magnetospheric particles constitute the largest fraction of the particles in the foils. Since little is known about this particle flux, their presence in the IGE foils appears fortunate. The analysis of these particles provides information about their isotropic composition and average flux

Big Bang Nucleosynthesis with Long Lived Charged Massive Particles

We consider Big Bang Nucleosynthesis (BBN) with long lived charged massive particles. Before decaying, the long lived charged particle recombines with a light element to form a bound state like a hydrogen atom. This effect modifies the nuclear reaction rates during the BBN epoch through the modifications of the Coulomb field and the kinematics of the captured light elements, which can change the light element abundances. It is possible that the heavier nuclei abundances such as $^7$Li and $^7$Be decrease sizably, while the ratios $Y_p$, D/H, and $^3$He/H remain unchanged. This may solve the current discrepancy between the BBN prediction and the observed abundance of $^7$Li. If future collider experiments found signals of a long-lived charged particle inside the detector, the information of its lifetime and decay properties could provide insights to understand not only the particle physics models but also the phenomena in the early universe in turn.Comment: 20 pages, 6 figures, published version in Physical Review

Skin preparation before hip replacement in emergency setting versus elective scheduled arthroplasty: Bacteriological comparative analysis

SummaryIntroductionHip arthroplasty needs to be performed in an emergency setting after intracapsular femur neck fracture, whereas pain makes preoperative skin preparation of the limb difficult and it may therefore be incomplete. To date no study has analyzed the patient's skin bacteriological status in these surgical conditions.HypothesisThe skin's bacterial flora is quantitatively and qualitatively different in the trauma context compared to an elective scheduled arthroplasty for chronic hip disease.Materials and methodsTwo groups of patients, undergoing hip arthroplasty and having the same preparation at the time of surgery but different skin preparation procedures the day before and the day of surgery, were prospectively compared: 30 patients operated on in an emergency setting for fracture (group A) had no skin preparation and 32 patients operated on in scheduled surgery (group B). Group A had no skin disinfection before going into surgery, whereas group B followed a predefined protocol the day before surgery. Skin samples were taken on gelose at three different stages of skin preparation at the time of surgery (before and after detersive cleaning, and at the end of the surgery) and on two sites (inguinal and greater trochanter). The bacteriological analysis took place after 48hours of incubation.ResultsBefore detersive cleaning, group A had 3.6times more bacteria than group B in the trochanter region and 2.7times more in the inguinal area. After detersive cleaning, the contamination rate in the trochanter area was similar in both groups (group A: 10%; group B: 12.5%), but different in the inguinal region (group A: 33%; group B: 3%; P=0.002). At the end of the surgery, no difference was identified. Coagulase-negative Staphylococcus and Bacillus cereus accounted for 44% and 37%, respectively, of the bacteria isolated. In addition, the frequency of pathogenic non-saprotrophic bacteria was higher in group A (38%) compared to group B (6%). At a mean follow-up of 9.7months (range: 8–11months), no infection of the surgical site was identified.ConclusionThe dermal flora is more abundant and different when the patient is managed in an emergency context. Although effective in the trochanter area, cutaneous detersive cleaning in the operating room is insufficient in the inguinal area and the frequency of pathogenic bacteria warrants identical rigor in preoperative preparation in all situations.Level of evidenceIII. Prospective case – control study

Limitations on suprathermal tails of electrons in the lower solar corona

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95261/1/grl9586.pd

Weak pitch angle scattering of few MV rigidity ions from measurements of anisotropies in the distribution function of interstellar pickup H +

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95477/1/grl8632.pd