Design and testing of liquid hydrogen-cooled, ultrahigh-speed ball bearings

Large-bore, liquid hydrogen-cooled, ultrahigh-speed, rolling contact bearings of an optimum design allow optimization of large rocket engine turbopumps in which bearing speed is a limiting factor. Optimum design for the bearings resulted from an application of liquid hydrogen used as a coolant

Methane fluxes, microbial activities and community structures in a wet tundra of the Lena Delta

Wet tundra environments of the Arctic are natural sources of the climate relevant trace gas methane. The underlying biogeochemical processes are not yet well understood. The field investigations were carried out on the island Samoylov (N 72°, E 126°) located in the Lena Delta, Siberia. The study site represented an area of typical polygonal patterned grounds with ice-wedges, which were considered for analyses of methane fluxes, organic matter quality and microbial communities.The mean flux rate of the depression was 53.2 ± 8.7 mg CH4 m-2 d-1, whereas the mean flux rate of the dryer rim part of the polygon was 4.7 ± 2.5 CH4 m-2 d-1. The quantity of dissolved organic matter (DOM), which represents an important C pool for microbial communities, correlated significant with the total concentrations of phospholipid fatty acids and ether lipids (PLFA and PLEL) a measure for microbial biomass. Although permafrost soils represent a large carbon pool, it was shown, that the reduced quality of organic matter leads to a substrate limitation of the microbial metabolism. This is an important finding for modelling and calculating trace gas fluxes from permafrost environments, because the known models are consider only the total carbon amount.It can be concluded by the presented results firstly that microbial communities in permafrost environments are composed by members of all three domains of life at numbers comparable to temperate soil ecosystems and secondly that the permafrost microorganisms are well adapted to the extreme temperature gradient of their environment

Light Stop Searches at the LHC in Events with One Hard Photon or Jet and Missing Energy

Low energy supersymmetric models provide a solution to the hierarchy problem and also have the necessary ingredients to solve two of the most outstanding issues in cosmology: the origin of the baryon asymmetry and the source of dark matter. In the MSSM, weak scale generation of the baryon asymmetry may be achieved in the presence of light stops, with masses lower than about 130 GeV. Moreover, the proper dark matter density may be obtained in the stop-neutralino co-annihilation region, where the stop-neutralino mass difference is smaller than a few tens of GeV. Searches for scalar top quarks (stops) in pair production processes at the Tevatron and at the Large Hadron Collider (LHC) become very challenging in this region of parameters. At the LHC, however, light stops proceeding from the decay of gluino pairs may be identified, provided the gluino mass is smaller than about 900 GeV. In this article we propose an alternative method for stop searches in the co-annihilation region, based on the search for these particles in events with missing energy plus one hard photon or jet. We show that this method is quite efficient and, when complemented with ongoing Tevatron searches, allows to probe stop masses up to about 160 GeV, fully probing the region of parameters consistent with electroweak baryogenesis in the MSSM.Comment: 17 pages, 6 figure

Fluid dynamics video of domains with spiral dislocations formed in the wake of an enslaved phase-separation front

Enslaved phase-separation fronts that move with a speed just smaller than that of a free front will leave in their wake a morphology of alternating domains that are roughly aligned with the front. However, these alternating domains will typically not be in phase initially. Instead there are defects. Here we present novel phase-separation morphologies that are formed in such systems where the defects are reminiscent of spiral dislocations in crystal growth.Comment: 1 pag

Evolution of Feedback Loops in Oscillatory Systems

Feedback loops are major components of biochemical systems. Many systems show multiple such (positive or negative) feedback loops. Nevertheless, very few quantitative analyses address the question how such multiple feedback loops evolved. Based on published models from the mitotic cycle in embryogenesis, we build a few case studies. Using a simple core architecture (transcription, phosphorylation and degradation), we define oscillatory models having either one positive feedback or one negative feedback, or both loops. With these models, we address the following questions about evolvability: could a system evolve from a simple model to a more complex one with a continuous transition in the parameter space? How do new feedback loops emerge without disrupting the proper function of the system? Our results show that progressive formation of a second feedback loop is possible without disturbing existing oscillatory behavior. For this process, the parameters of the system have to change during evolution to maintain predefined properties of oscillations like period and amplitude.Comment: Proceedings of the 2009 FOSBE conference in Denver, CO, USA. 4 page

Challenges for MSSM Higgs searches at Hadron Colliders

In this article we analyze the impact of B-physics and Higgs physics at LEP on standard and non-standard Higgs bosons searches at the Tevatron and the LHC, within the framework of minimal flavor violating supersymmetric models. The B-physics constraints we consider come from the experimental measurements of the rare B-decays b -> s gamma and B_u -> tau nu and the experimental limit on the B_s -> mu+ mu- branching ratio. We show that these constraints are severe for large values of the trilinear soft breaking parameter A_t, rendering the non-standard Higgs searches at hadron colliders less promising. On the contrary these bounds are relaxed for small values of A_t and large values of the Higgsino mass parameter mu, enhancing the prospects for the direct detection of non-standard Higgs bosons at both colliders. We also consider the available ATLAS and CMS projected sensitivities in the standard model Higgs search channels, and we discuss the LHC's ability in probing the whole MSSM parameter space. In addition we also consider the expected Tevatron collider sensitivities in the standard model Higgs h -> b bbar channel to show that it may be able to find 3 sigma evidence in the B-physics allowed regions for small or moderate values of the stop mixing parameter.Comment: 22 pages, 5 figures. Added references and acknowledgements. Submitted to PR

Kaon and Pion production in relativistic heavy-ion collisions

The BUU transport model is applied to study strangeness and pion production in nucleus-nucleus collisions. Starting from proton induced reactions, we further investigate Si+Au, Au+Au and Pb+Pb collisions in the energy range between 2 and 40 A$\cdot$GeV and compare with data and with other transport calculations. The $q \bar q$ annihilation, or resonance, channel simulated by the string model in meson-nucleon collisions at $\sqrt{s} > 2$ GeV is introduced. The importance of this channel for a good description of the proton-nucleus data on $K^+$ production is demonstrated. We, furthermore, show that the meson-meson collisions contribute significantly to the $K \bar K$ production in heavy-ion collisions above 5 A GeV and improve an agreement with data on the $K^+/\pi^+$ ratio. Finally, we study the influence of the in-medium modifications of the FRITIOF model on the pion and kaon production.Comment: 20 pages, 25 figures, added statistical errors in figure

Kaon production from 1 to 40 A GeV

Kaon production is studied within the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) model. Results are compared with experiment and with other models. The influence of the kaon potential on the kaon azimuthal distributions at SIS energies is considered. We also discuss the role of the many-body collisions at high-density phase of reaction.Comment: 6 pages, 4 figures, Proc. of the Int. Workshop on Hot and Dense Matter in Relativistic Heavy Ion Collisions, 09-12.04.2006, Budapes