27,456 research outputs found
Stability of the Magnetic Monopole Condensate in three- and four-colour QCD
It is argued that the ground state of three- and four-colour QCD contains a
monopole condensate, necessary for the dual Meissner effect to be the mechanism
of confinement, and support its stability on the grounds that it gives the
off-diagonal gluons an effective mass sufficient to remove the unstable ground
state mode.Comment: jhep.cls, typos corrected, references added, some content delete
Least-squares methods for identifying biochemical regulatory networks from noisy measurements
<b>Background</b>:
We consider the problem of identifying the dynamic interactions in biochemical networks from noisy experimental data. Typically, approaches for solving this problem make use of an estimation algorithm such as the well-known linear Least-Squares (LS) estimation technique. We demonstrate that when time-series measurements are corrupted by white noise and/or drift noise, more accurate and reliable identification of network interactions can be achieved by employing an estimation algorithm known as Constrained Total Least Squares (CTLS). The Total Least Squares (TLS) technique is a generalised least squares method to solve an overdetermined set of equations whose coefficients are noisy. The CTLS is a natural extension of TLS to the case where the noise components of the coefficients are correlated, as is usually the case with time-series measurements of concentrations and expression profiles in gene networks.
<b>Results</b>:
The superior performance of the CTLS method in identifying network interactions is demonstrated on three examples: a genetic network containing four genes, a network describing p53 activity and <i>mdm2</i> messenger RNA interactions, and a recently proposed kinetic model for interleukin (IL)-6 and (IL)-12b messenger RNA expression as a function of ATF3 and NF-κB promoter binding. For the first example, the CTLS significantly reduces the errors in the estimation of the Jacobian for the gene network. For the second, the CTLS reduces the errors from the measurements that are corrupted by white noise and the effect of neglected kinetics. For the third, it allows the correct identification, from noisy data, of the negative regulation of (IL)-6 and (IL)-12b by ATF3.
<b>Conclusion</b>:
The significant improvements in performance demonstrated by the CTLS method under the wide range of conditions tested here, including different levels and types of measurement noise and different numbers of data points, suggests that its application will enable more accurate and reliable identification and modelling of biochemical networks
BRST symmetry of SU(2) Yang-Mills theory in Cho--Faddeev--Niemi decomposition
We determine the nilpotent BRST and anti-BRST transformations for the
Cho--Faddeev-Niemi variables for the SU(2) Yang-Mills theory based on the new
interpretation given in the previous paper of the Cho--Faddeev-Niemi
decomposition. This gives a firm ground for performing the BRST quantization of
the Yang--Mills theory written in terms of the Cho--Faddeev-Niemi variables. We
propose also a modified version of the new Maximal Abelian gauge which could
play an important role in the reduction to the original Yang-Mills theory.Comment: 11 pages, no figure; Introduction improved, 3 references adde
Stability of inflating branes in a texture
We investigate the stability of inflating branes embedded in an O(2) texture
formed in one extra dimension. The model contains two 3-branes of nonzero
tension, and the extra dimension is compact. When the gravitational
perturbation is applied, the vacuum energy which is responsible for inflation
on the branes stabilizes the branes if the symmetry-breaking scale of the
texture is smaller than some critical value. This critical value is determined
by the particle-hierarchy scale between the two branes, and is smaller than the
5D Planck-mass scale. The scale of the vacuum energy can be considerably low in
providing the stability. This stability story is very different from the
flat-brane case which always suffers from the instability due to the
gravitational perturbation.Comment: 16 pages, 5 eps figures, revte
Magnetic Field Structure and Stochastic Reconnection in a Partially Ionized Gas
We consider stochastic reconnection in a magnetized, partially ionized
medium. Stochastic reconnection is a generic effect, due to field line
wandering, in which the speed of reconnection is determined by the ability of
ejected plasma to diffuse away from the current sheet along magnetic field
lines, rather than by the details of current sheet structure. We consider the
limit of weak stochasticity, so that the mean magnetic field energy density is
greater than either the turbulent kinetic energy density or the energy density
associated with the fluctuating component of the field. We consider field line
stochasticity generated through a turbulent cascade, which leads us to consider
the effect of neutral drag on the turbulent cascade of energy. In a
collisionless plasma, neutral particle viscosity and ion-neutral drag will damp
mid-scale turbulent motions, but the power spectrum of the magnetic
perturbations extends below the viscous cutoff scale. We give a simple physical
picture of the magnetic field structure below this cutoff, consistent with
numerical experiments. We provide arguments for the reemergence of the
turbulent cascade well below the viscous cut-off scale and derive estimates for
field line diffusion on all scales. We note that this explains the persistence
of a single power law form for the turbulent power spectrum of the interstellar
medium, from scales of tens of parsecs down to thousands of kilometers. We find
that under typical conditions in the ISM stochastic reconnection speeds are
reduced by the presence of neutrals, but by no more than an order of magnitude.Comment: Astrophysical Journal in pres
Geometrical properties of the trans-spherical solutions in higher dimensions
We investigate the geometrical properties of static vacuum -brane
solutions of Einstein gravity in dimensions, which have spherical
symmetry of orthogonal to the -directions and are invariant under
the translation along them. % The solutions are characterized by mass density
and tension densities. % The causal structure of the higher dimensional
solutions is essentially the same as that of the five dimensional ones. Namely,
a naked singularity appears for most solutions except for the Schwarzschild
black -brane and the Kaluza-Klein bubble. % We show that some important
geometric properties such as the area of and the total spatial volume
are characterized only by the three parameters such as the mass density, the
sum of tension densities and the sum of tension density squares rather than
individual tension densities. These geometric properties are analyzed in detail
in this parameter space and are compared with those of 5-dimensional case.Comment: 14 pages, 2 figures, Title change
Inflating magnetically charged braneworlds
Numerical solutions of Einstein, scalar, and gauge field equations are found
for static and inflating defects in a higher-dimensional spacetime. The defects
have -dimensional core and magnetic monopole configuration in
extra dimensions. For symmetry-breaking scale below the critical value
, the defects are characterized by a flat worldsheet geometry and
asymptotically flat extra dimensions. The critical scale is comparable
to the higher-dimensional Planck scale and has some dependence on the gauge and
scalar couplings. For , the extra dimensions degenerate into a
`cigar', and for all static solutions are singular. The
singularity can be removed if the requirement of staticity is relaxed and
defect cores are allowed to inflate. The inflating solutions have de Sitter
worldsheets and cigar geometry in the extra dimensions. Exact analytic
solutions describing the asymptotic behavior of these inflating monopoles are
found and the parameter space of these solutions is analyzed.Comment: 35 pages, revtex, 18 eps figure
Control of threshold voltage in E-mode and D-mode GaN-on-Si metal-insulator-semiconductor heterostructure field effect transistors by in-situ fluorine doping of atomic layer deposition Al2O3 gate dielectrics
We report the modification and control of threshold voltage in enhancement and depletion mode AlGaN/GaN metal-insulator-semiconductor heterostructure field effect transistors through the use of in-situ fluorine doping of atomic layer deposition Al2O3. Uniform distribution of F ions throughout the oxide thickness are achievable, with a doping level of up to 5.5 × 1019 cm−3 as quantified by secondary ion mass spectrometry. This fluorine doping level reduces capacitive hysteretic effects when exploited in GaN metal-oxide-semiconductor capacitors. The fluorine doping and forming gas anneal also induces an average positive threshold voltage shift of between 0.75 and 1.36 V in both enhancement mode and depletion mode GaN-based transistors compared with the undoped gate oxide via a reduction of positive fixed charge in the gate oxide from +4.67 × 1012 cm−2 to −6.60 × 1012 cm−2. The application of this process in GaN based power transistors advances the realisation of normally off, high power, high speed devices
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