1,016 research outputs found
Magnetorotational Instability in a Couette Flow of Plasma
All experiments, which have been proposed so far to model the
magnetorotational instability (MRI) in the laboratory, involve a Couette flow
of liquid metals in a rotating annulus. All liquid metals have small magnetic
Prandtl numbers, Pm, of about 10^{-6} (the ratio of kinematic viscosity to
magnetic diffusivity). With plasmas both large and small Pm are achievable by
varying the temperature and the density of plasma. Compressibility and fast
rotation of the plasma result in radial stratification of the equilibrium
plasma density. Evolution of perturbations in radially stratified viscous and
resistive plasma permeated by an axial uniform magnetic field is considered.
The differential rotation of the plasma is induced by the ExB drift in applied
radial electric field. Global unstable eigenmodes are calculated by our newly
developed matrix code. The plasma is shown to be MRI unstable for parameters
easily achievable in experimental setup.Comment: 6 pages, 2 figures; to be published in the Proceedings of the 3d
Workshop on Non-Neutral Plasmas, July 2003, Santa Fe, US
Flavor Symmetry Breaking and Vacuum Alignment on Orbifolds
Flavor symmetry has been widely studied for figuring out the masses and
mixing angles of standard-model fermions. In this paper we present a framework
for handling flavor symmetry breaking where the symmetry breaking is triggered
by boundary conditions of scalar fields in extra-dimensional space. The
alignment of scalar expectation values is achieved without referring to any
details of scalar potential and its minimization procedure. As applications to
non-abelian discrete flavor symmetries, illustrative lepton mass models are
constructed where the S3 and A4 flavor symmetries are broken down to the
directions leading to the tri-bimaximal form of lepton mixing and realistic
mass patterns.Comment: 21 page
Bottom-Up Approach to Moduli Dynamics in Heavy Gravitino Scenario : Superpotential, Soft Terms and Sparticle Mass Spectrum
The physics of moduli fields is examined in the scenario where the gravitino
is relatively heavy with mass of order 10 TeV, which is favored in view of the
severe gravitino problem. The form of the moduli superpotential is shown to be
determined, if one imposes a phenomenological requirement that no physical CP
phase arise in gaugino masses from conformal anomaly mediation. This bottom-up
approach allows only two types of superpotential, each of which can have its
origins in a fundamental underlying theory such as superstring. One
superpotential is the sum of an exponential and a constant, which is identical
to that obtained by Kachru et al (KKLT), and the other is the racetrack
superpotential with two exponentials. The general form of soft supersymmetry
breaking masses is derived, and the pattern of the superparticle mass spectrum
in the minimal supersymmetric standard model is discussed with the KKLT-type
superpotential. It is shown that the moduli mediation and the anomaly mediation
make comparable contributions to the soft masses. At the weak scale, the
gaugino masses are rather degenerate compared to the minimal supergravity,
which bring characteristic features on the superparticle masses. In particular,
the lightest neutralino, which often constitutes the lightest superparticle and
thus a dark matter candidate, is a considerable admixture of gauginos and
higgsinos. We also find a small mass hierarchy among the moduli, gravitino, and
superpartners of the standard-model fields. Cosmological implications of the
scenario are briefly described.Comment: 45 pages, 10 figures, typos correcte
Principles of the Kenzan Method for Robotic Cell Spheroid-Based Three-Dimensional Bioprinting
Bioprinting is a technology with the prospect to change the way many diseases are treated, by replacing the damaged tissues with live de novo created biosimilar constructs. However, after more than a decade of incubation and many proofs of concept, the field is still in its infancy. The current stagnation is the consequence of its early success: the first bioprinters, and most of those that followed, were modified versions of the three-dimensional printers used in additive manufacturing, redesigned for layer-by-layer dispersion of biomaterials. In all variants (inkjet, microextrusion, or laser assisted), this approach is material (“scaffold”) dependent and energy intensive, making it hardly compatible with some of the intended biological applications. Instead, the future of bioprinting may benefit from the use of gentler scaffold-free bioassembling methods. A substantial body of evidence has accumulated, indicating this is possible by use of preformed cell spheroids, which have been assembled in cartilage, bone, and cardiac muscle-like constructs. However, a commercial instrument capable to directly and precisely “print” spheroids has not been available until the invention of the microneedles-based (“Kenzan”) spheroid assembling and the launching in Japan of a bioprinter based on this method. This robotic platform laces spheroids into predesigned contiguous structures with micron-level precision, using stainless steel microneedles (“kenzans”) as temporary support. These constructs are further cultivated until the spheroids fuse into cellular aggregates and synthesize their own extracellular matrix, thus attaining the needed structural organization and robustness. This novel technology opens wide opportunities for bioengineering of tissues and organs
Neutrino Oscillations in a Supersymmetric SO(10) Model with Type-III See-Saw Mechanism
The neutrino oscillations are studied in the framework of the minimal
supersymmetric SO(10) model with Type-III see-saw mechanism by additionally
introducing a number of SO(10) singlet neutrinos. The light Majorana neutrino
mass matrix is given by a combination of those of the singlet neutrinos and the
active neutrinos. The minimal SO(10) model gives an unambiguous Dirac
neutrino mass matrix, which enables us to predict the masses and the other
parameters for the singlet neutrinos. These predicted masses take the values
accessible and testable by near future collider experiments under the
reasonable assumptions. More comprehensive calculations on these parameters are
also given.Comment: 14 pages, 5 figures; the version to appear in JHE
Gauged Nambu-Jona-Lasinio model with extra dimensions
We investigate phase structure of the D (> 4)-dimensional gauged
Nambu-Jona-Lasinio (NJL) model with extra dimensions
compactified on TeV scale, based on the improved ladder Schwinger-Dyson (SD)
equation in the bulk. We assume that the bulk running gauge coupling in the SD
equation for the SU(N_c) gauge theory with N_f massless flavors is given by the
truncated Kaluza-Klein effective theory and hence has a nontrivial ultraviolet
fixed point (UVFP). We find the critical line in the parameter space of two
couplings, the gauge coupling and the four-fermion coupling, which is similar
to that of the gauged NJL model with fixed (walking) gauge coupling in four
dimensions. It is shown that in the presence of such walking gauge interactions
the four-fermion interactions become ``nontrivial'' even in higher dimensions,
similarly to the four-dimensional gauged NJL model. Such a nontriviality holds
only in the restricted region of the critical line (``nontrivial window'') with
the gauge coupling larger than a non-vanishing value (``marginal triviality
(MT)'' point), in contrast to the four-dimensional case where such a
nontriviality holds for all regions of the critical line except for the pure
NJL point. In the nontrivial window the renormalized effective potential yields
a nontrivial interaction which is conformal invariant. The exisitence of the
nontrivial window implies ``cutoff insensitivity'' of the physics prediction in
spite of the ultraviolet dominance of the dynamics. In the formal limit D -> 4,
the nontrivial window coincides with the known condition of the nontriviality
of the four-dimensional gauged NJL model, .Comment: 34 pages, 6 figures, references added, to appear in Phys.Rev.D. The
title is changed in PR
Effects of Fipronil on Non-target Ants and Other Invertebrates in a Program for Eradication of the Argentine Ant, Linepithema humile
Pesticides are frequently used to eradicate invasive ant species, but pose ecological harm. Previous studies assessed non-target effects only in terms of the increase or decrease of abundance or species richness after pesticide applications. Positive effects of the release from pressure caused by invasive ant species have not been considered so far. To more accurately assess pesticide effects in the field, the non-target effects of pesticides should be considered separately from the positive effects of such releases. Here, we used monitoring data of ants and other invertebrates collected in a program for the eradication of the Argentine ant, Linepithema humile (Mayr), using fipronil. First, we separately assessed the effects of L. humile abundance and fipronil exposure on non-target ants and other invertebrates using generalized linear models. The abundance of L. humile and the number of pesticide treatments were negatively associated with the total number of non-target individuals and taxonomic richness. We also noted negative relationships between the number of individuals of some ant species and other invertebrate taxonomic groups. The L. humile × pesticide interaction was significant, suggesting that the abundance of L. humile affected the level of impact of pesticide treatment on non-target fauna. Second, we evaluated the dynamics of non-target ant communities for 3 years using principal response curve analyses. Non-target ant communities treated with fipronil continuously for 3 years recovered little, whereas those treated for 1 year recovered to the level of the untreated and non-invaded environment
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