1,179 research outputs found
Sheath parameters for non-Debye plasmas: simulations and arc damage
This paper describes the surface environment of the dense plasma arcs that
damage rf accelerators, tokamaks and other high gradient structures. We
simulate the dense, non-ideal plasma sheath near a metallic surface using
Molecular Dynamics (MD) to evaluate sheaths in the non-Debye region for high
density, low temperature plasmas. We use direct two-component MD simulations
where the interactions between all electrons and ions are computed explicitly.
We find that the non-Debye sheath can be extrapolated from the Debye sheath
parameters with small corrections. We find that these parameters are roughly
consistent with previous PIC code estimates, pointing to densities in the range
. The high surface fields implied by these
results could produce field emission that would short the sheath and cause an
instability in the time evolution of the arc, and this mechanism could limit
the maximum density and surface field in the arc. These results also provide a
way of understanding how the "burn voltage" of an arc is generated, and the
relation between self sputtering and the burn voltage, while not well
understood, seems to be closely correlated. Using these results, and equating
surface tension and plasma pressure, it is possible to infer a range of plasma
densities and sheath potentials from SEM images of arc damage. We find that the
high density plasma these results imply and the level of plasma pressure they
would produce is consistent with arc damage on a scale 100 nm or less, in
examples where the liquid metal would cool before this structure would be lost.
We find that the sub-micron component of arc damage, the burn voltage, and
fluctuations in the visible light production of arcs may be the most direct
indicators of the parameters of the dense plasma arc, and the most useful
diagnostics of the mechanisms limiting gradients in accelerators.Comment: 8 pages, 16 figure
Minimal Gaugino Mediation
We propose Minimal Gaugino Mediation as the simplest known solution to the
supersymmetric flavor and CP problems. The framework predicts a very minimal
structure for the soft parameters at ultra-high energies: gaugino masses are
unified and non-vanishing whereas all other soft supersymmetry breaking
parameters vanish. We show that this boundary condition naturally arises from a
small extra dimension and present a complete model which includes a new
extra-dimensional solution to the mu problem. We briefly discuss the predicted
superpartner spectrum as a function of the two parameters of the model. The
commonly ignored renormalization group evolution above the GUT scale is crucial
to the viability of Minimal Gaugino Mediation but does not introduce new model
dependence.Comment: LaTeX, 16 pages, 4 figures, running of the bottom and tau Yukawas
included, plots revise
Lepton Flavor Violation in Supersymmetric SO(10) Grand Unified Models
The study for lepton flavor violation combined with the neutrino oscillation
may provide more information about the lepton flavor structure of the grand
unified theory. In this paper, we study two lepton flavor violation processes,
and , in the context of supersymmetric SO(10)
grand unified models. We find the two processes are both of phenomenological
interest. In particular the latter may be important in some supersymmetric
parameter space where the former is suppressed. Thus, Z-dacay may offer another
chance for looking for lepton flavor violation.Comment: 26 pages, 10 figure
Regulation of caspase-3 processing by cIAP2 controls the switch between pro-inflammatory activation and cell death in microglia.
Cell Death and Disease is an open-access journal published by Nature Publishing Group. This work is licensed under a Creative Commons Attribution 4.0 International Licence. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons licence, users will need to obtain permission from the licence holder to reproduce the material.The activation of microglia, resident immune cells of the central nervous system, and inflammation-mediated neurotoxicity are typical features of neurodegenerative diseases, for example, Alzheimer's and Parkinson's diseases. An unexpected role of caspase-3, commonly known to have executioner role for apoptosis, was uncovered in the microglia activation process. A central question emerging from this finding is what prevents caspase-3 during the microglia activation from killing those cells? Caspase-3 activation occurs as a two-step process, where the zymogen is first cleaved by upstream caspases, such as caspase-8, to form intermediate, yet still active, p19/p12 complex; thereafter, autocatalytic processing generates the fully mature p17/p12 form of the enzyme. Here, we show that the induction of cellular inhibitor of apoptosis protein 2 (cIAP2) expression upon microglia activation prevents the conversion of caspase-3 p19 subunit to p17 subunit and is responsible for restraining caspase-3 in terms of activity and subcellular localization. We demonstrate that counteracting the repressive effect of cIAP2 on caspase-3 activation, using small interfering RNA targeting cIAP2 or a SMAC mimetic such as the BV6 compound, reduced the pro-inflammatory activation of microglia cells and promoted their death. We propose that the different caspase-3 functions in microglia, and potentially other cell types, reside in the active caspase-3 complexes formed. These results also could indicate cIAP2 as a possible therapeutic target to modulate microglia pro-inflammatory activation and associated neurotoxicity observed in neurodegenerative disorders
Modifying the Sum Over Topological Sectors and Constraints on Supergravity
The standard lore about the sum over topological sectors in quantum field
theory is that locality and cluster decomposition uniquely determine the sum
over such sectors, thus leading to the usual theta-vacua. We show that without
changing the local degrees of freedom, a theory can be modified such that the
sum over instantons should be restricted; e.g. one should include only
instanton numbers which are divisible by some integer p. This conclusion about
the configuration space of quantum field theory allows us to carefully
reconsider the quantization of parameters in supergravity. In particular, we
show that FI-terms and nontrivial Kahler forms are quantized. This analysis
also leads to a new derivation of recent results about linearized supergravity.Comment: 17 pages, minor change
Effects of Supersymmetric Threshold Corrections on High-Scale Flavor Textures
Integration of superpartners out of the spectrum induces potentially large
contributions to Yukawa couplings. These corrections, the supersymmetric
threshold corrections, therefore influence the CKM matrix prediction in a
non-trivial way. We study effects of threshold corrections on high-scale flavor
structures specified at the gauge coupling unification scale in supersymmetry.
In our analysis, we first consider high-scale Yukawa textures which qualify
phenomenologically viable at tree level, and find that they get completely
disqualified after incorporating the threshold corrections. Next, we consider
Yukawa couplings, such as those with five texture zeroes, which are incapable
of explaining flavor-changing proceses. Incorporation of threshold corrections,
however, makes them phenomenologically viable textures. Therefore,
supersymmetric threshold corrections are found to leave observable impact on
Yukawa couplings of quarks, and any confrontation of high-scale textures with
experiments at the weak scale must take into account such corrections.Comment: 25 pages, submitted to JHE
Yukawa Unified Supersymmetric SO(10) Model: Cosmology, Rare Decays and Collider Searches
It has recently been pointed out that viable sparticle mass spectra can be
generated in Yukawa unified SO(10) supersymmetric grand unified models
consistent with radiative breaking of electroweak symmetry. Model solutions are
obtained only if , and positive -term
contributions to scalar masses from SO(10) gauge symmetry breaking are used. In
this paper, we attempt to systematize the parameter space regions where
solutions are obtained. We go on to calculate the relic density of neutralinos
as a function of parameter space. No regions of the parameter space explored
were actually cosmologically excluded, and very reasonable relic densities were
found in much of parameter space. Direct neutralino detection rates could
exceed 1 event/kg/day for a Ge detector, for low values of GUT scale
gaugino mass . We also calculate the branching fraction for decays, and find that it is beyond the 95% CL experimental limits in
much, but not all, of the parameter space regions explored. However, recent
claims have been made that NLO effects can reverse the signs of certain
amplitudes in the calculation, leading to agreement between
theory and experiment in Yukawa unified SUSY models. For the Fermilab Tevatron
collider, significant regions of parameter space can be explored via
and searches. There also exist some limited regions of
parameter space where a trilepton signal can be seen at TeV33. Finally, there
exist significant regions of parameter space where direct detection of bottom
squark pair production can be made, especially for large negative values of the
GUT parameter .Comment: Added comparison to Blazek/Raby results and added Comments on de Boer
et al. b->s gamma result
Silica SHB chiral Pc-L* copper complexes for halogen-free solvent cyclopropanation reactions
The grafting of the preformed Pc-L* (pyridine containing macrocyclic ligands) copper(I) complexes on different ordered and non-ordered silicas, and their use, under heterogeneous batch conditions, as catalysts for the olefin cyclopropanation are reported. High yields (up to 99%), good recyclability in halogen-free solvent reactions were obtained, together with negligible copper leaching (0.1% of total copper)
Higgs Mass Bounds Separate Models of Electroweak Symmetry Breaking
Vacuum stability implies a lower limit on the mass of the higgs boson in the
Standard Model (SM). In contrast, an upper limit on the lightest higgs mass can
be calculated in supersymmetric (susy) models. The main uncertainty in each
limit is the value of the top mass, which may now be fixed by the recent CDF
result. We study the possibility that these bounds do not overlap, and find
that (i) a mass gap emerges at GeV between the SM and the Minimal
Susy Standard Model (MSSM); and between the SM and the Minimal plus Singlet
Susy Model [(M+1)SSM] if the independent scalar self--coupling of the latter is
perturbatively small or if the parameter is large; this gap widens
with increasing ; (ii) there is no overlap between the SM and the MSSM
bounds at even smaller values of for the value (--2)
preferred in Supersymmetric Grand Unified Theories. Thus, if the new top mass
measurement remains valid, a measurement of the first higgs mass will serve to
exclude either the SM or MSSM/(M+1)SSM higgs sectors. In addition, we discuss
the upper bound on the lightest higgs mass in susy models with an extended
higgs sector, and in models with a strongly interacting higgs sector. Finally,
we comment on the discovery potential for the lightest higgses in these models.Comment: 18 pages, 5 figures, VAND-TH-94-1
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