Torque-balanced high-density steady states of single-component plasmas

Electron plasmas in a Penning-Malmberg trap are compressed radially using a rotating electric field (the "rotating-wall technique"). For large electric fields, plasmas can be compressed over a broad range of frequencies. This permits access to a novel high-density regime in which outward transport is insensitive to plasma density. The limiting density occurs when the plasma rotation frequency equals the rotating-wall frequency. Characteristics of the resulting torque-balanced steady states are described, and implications for high-density electron and positron plasma confinement are discussed.     

Critical point in complex plasmas

The occurrence of liquid-vapor phase transition and the possible existence of a critical point in complex plasmas--systems that consist of charged micrograins in a neutralizing plasma background--is investigated theoretically. An analysis based on the consideration of the intergrain interaction potential suggests that under certain conditions systems near and at the critical point should be observable. Measurements under microgravity conditions would appear to be required. The analysis aims at determining the plasma parameter regime most suitable for planned experimental investigations.     

A fixed point for quantum gravity

Using the 1/N expansion a fixed point of the renormalization group is found for quantized gravitational theories which is non-trivial in all dimensions, d, including four. Using the fixed point it is shown how Einstein's theory can be renormalized for 3<d<4. In four dimensions the pure Einstein theory does not exist, but the R + C_μναβ² theory does. It is shown how gravitational theories whose quantum lagrangians are scale invariant may be renormalized such that the scale invariance is broken only by the choice of the critical renormalization group trajectory. A comparison is made with the renormalization of four-fermion and Yukawa theories in 4?? dimensions which suggests that quantum gravity might exist in four dimensions even if those theories do not.     

A Lefschetz fixed point formula for symplectomorphisms

Consider a compact Kähler manifold endowed with a prequantum bundle. Following the geometric quantization scheme, the associated quantum spaces are the spaces of holomorphic sections of the tensor powers of the prequantum bundle. In this paper we construct an asymptotic representation of the prequantum bundle automorphism group in these quantum spaces. We estimate the characters of these representations under some transversality assumption. The formula obtained generalizes in some sense the Lefschetz fixed point formula for the automorphisms of the prequantum bundle preserving its holomorphic structure. Our results will be applied in two forthcoming papers to the quantum representation of the mapping class group.     

改进的固定点图像复原算法（英文）

研究了周期边界条件下,Tikhonov正则化的固定点算法,提出了变化正则化参数的方法。首先对正则化参数取较大值,抑制复原图像中的噪声,通过得出的收敛结果来修正初始梯度;然后对正则化参数取较小值,以增强复原图像中的细节。实验结果表明,与当前求解L1范数正则化函数和全变分正则化函数的流行算法比较,本文算法对于运动模糊与高斯模糊图像的复原效果更佳。     

Quantitative single point imaging with compressed sensing

A novel approach with respect to single point imaging (SPI), compressed sensing, is presented here that is shown to significantly reduce the loss of accuracy of reconstructed images from under-sampled acquisition data. SPI complements compressed sensing extremely well as it allows unconstrained selection of sampling trajectories. Dynamic processes featuring short NMR signal can thus be more rapidly imaged, in our case the absorption of moisture by a cereal-based wafer material, with minimal loss of image quantification. The absolute moisture content distribution is recovered via a series of images acquired with variable phase encoding times allowing extrapolation to time zero for each image pixel and the effective removal of contrast.     

Undecidable hopf bifurcation with undecidable fixed point

We exhibit a polynomial dynamical system where one cannot decide whether a Hopf bifurcation occurs. Therefore one cannot decide whether there will be parameter values such that a stable fixed point becomes an unstable one. Related incompleteness results for previously described axiomatized versions of dynamical systems theory are also discussed.Dedicated to the memory of Leopoldo Nachbin (1922–1993), mathematician, mentor, and friend.     

On the existence of Feigenbaum's fixed point

We give a proof of the existence of aC ², even solution of Feigenbaum's functional equation $$g{\text{(}}x) = - \lambda _0^{ - 1} g{\text{(}}g( - \lambda _0 x)),g{\text{(0) = 1,}}$$ whereg is a map of [?1, 1] into itself. It extends to a real analytic function over ?.     

A nontrivial Renormalization Group fixed point for the Dyson-Baker hierarchical model

We prove the existence of a nontrivial Renormalization Group (RG) fixed point for the Dyson-Baker hierarchical model ind=3 dimensions. The single spin distribution of the fixed point is shown to be entire analytic, and bounded by exp(–const×t ⁶) for large real values of the spint. Our proof is based on estimates for the zeros of a RG fixed point for Gallavotti's hierarchical model. We also present some general results for the heat flow on a space of entire functions, including an order preserving property for zeros, which is used in the RG analysis.Supported in Part by the National Science Foundation under Grant No. DMS-9103590.Supported in Part by the Swiss National Science Foundation.     

Phase coexistence and a critical point in ultracold neutral plasmas

We show the existence of the liquid-vapor phase coexistence and a critical point for strongly coupled ions in ultracold neutral (UCN) plasmas. Expressions for the free energy of UCN plasmas and an equation of state for the ions are obtained in the mean field approximation. A van der Waals-like isotherm shows the existence of a critical point in UCN plasmas. Depending on the ion temperature, the ions are shown to exist in a mixed vapor-liquid phase for a range of the ion Coulomb coupling parameter Γ(i) (defined by the ratio between the ion interaction and the ion kinetic energies), and in a strongly coupled liquid state for values of Γ(i) above this range. The estimates of critical constants show that it may be possible to observe these phenomena in the present day UCN plasmas.     

Nonperturbative fixed point in a nonequilibrium phase transition

We apply the nonperturbative renormalization group method to a class of out-of-equilibrium phase transitions (usually called "parity-conserving" or, more properly, "generalized voter" class) which is out of the reach of perturbative approaches. We show the existence of a genuinely nonperturbative fixed point, i.e., a critical point that does not seem to be Gaussian in any dimension.     

A hierarchical model exhibiting the Kosterlitz-Thouless fixed point

We present a new hierarchical model for 2D Coulomb gases and investigate its behavior under renormalization group transformations. Unlike all previous hierarchical models (including the Migdal-Kadanoff version) for this system our model displays a line of stable fixed points describing the Kosterlitz-Thouless phase transition. For Coulomb gases corresponding to Z_N models these fixed points are stable in an intermediate range of temperatures.     

Strong disorder fixed point in absorbing-state phase transitions

The effect of quenched disorder on nonequilibrium phase transitions in the directed percolation universality class is studied by a strong disorder renormalization group approach and by density matrix renormalization group calculations. We show that for sufficiently strong disorder the critical behavior is controlled by a strong disorder fixed point and in one dimension the critical exponents are conjectured to be exact: beta=(3-sqrt[5])/2 and nu( perpendicular )=2. For disorder strengths outside the attractive region of this fixed point, disorder dependent critical exponents are detected. Existing numerical results in two dimensions can be interpreted within a similar scenario.     

A renormalization group model with non-Gaussian fixed point

We apply short distance scaling to the Wick square of a massive free time zero field and show that the characteristic functionals of the suitably renormalized fields have a short distance limit. The properties of the limiting characteristic functionals allow us to find a class of the other renormalization group invariant processes. They are all non-Gaussian, but can be expressed by superposition of the Gaussians. We also discuss the test function spaces and the pointwise limit of the n-point functions.     

The fermion mass matrices near a fixed point

The structure of the fermion mass matrices is investigated in the neighbourhood of an infrared fixed point with special emphasis on the mixing angles which determine the charged current couplings. We find that it is necessary to introduce a fourth generation of quarks whose masses are predicted. The mass of the top quark is close to 35 GeV. The solution for a two family problem is found, which predicts very small charged current couplings of the very heavy to the lighter quarks.     

From Dynkin diagram symmetries to fixed point structures

Any automorphism of the Dynkin diagram of a symmetrizable Kac-Moody algebra g induces an automorphism of g and a mapping between highest weight modules of g. For a large class of such Dynkin diagram automorphisms, we can describe various aspects of these maps in terms of another Kac-Moody algebra, the orbit Lie algebra . In particular, the generating function for the trace of over weight spaces, which we call the twining character of g (with respect to the automorphism), is equal to a character of . The orbit Lie algebras of untwisted affine Lie algebras turn out to be closely related to the fixed point theories that have been introduced in conformal field theory. Orbit Lie algebras and twining characters constitute a crucial step towards solving the fixed point resolution problem in conformal field theory.     

Interpolation parameter and expansion for a three-dimensional nontrivial scalar infrared fixed point

We compute a nontrivial infraredϕ ₃ ⁴ -fixed point by means of an interpolation expansion in fixed dimension. The expansion is formulated for an infinitesimal momentum-space renormalization group. We choose a coordinate representation for the fixed-point interaction in derivative expansion, and compute its coordinates to high orders by means of computer algebra. We compute the series for the critical exponentv up to order 25 of interpolation expansion in this representation, and evaluate it using Padé, Borel-Padé, Borel-conformal-Padé, andD log -Padé resummation. The resummation returns 0.6262(13) as the value ofv. Our renormalization group uses canonical resealing, for whichη = 0     

A non-Gaussian renormalization group fixed point for hierarchical scalar lattice field theories

A rigorous method is developed to handle the large field problems in the Wilson-Kadanoff renormalization group approach to critical lattice systems of unbounded spins. We use this method to study in a hierarchical approximation the non-Gaussian renormalization group fixed point which governs the infrared behaviour of critical lattice field theories in three dimensions. The method is an improvement of the analyticity techniques of Gawedzki and Kupiainen: using Borel summation techniques we are able to incorporate the large field region into the perturbative region so that the theory is completely described in terms of convergent expansions.Supported in part by the National Science Foundation under Grant No. DMS-8540879Supported in part by the National Science Foundation under Grant No. DMR81-14726Part of this work has been carried out during a visit of the author at the Courant Institute of Mathematical Sciences, NYU     

The effects of gradients on the diagnostic use of spectral features from laser compressed plasmas

The use of spectral features as diagnostics of the plasma temperature and density is studied using a non-LTE radiative transfer model, which solves the coupled statistical equilibrium and radiative transfer equation consistently. The effect of gradients on the hydrodynamic data, i.e. temperature and mass density, is studied to establish the accuracy of the diagnostic procedures.