Life history and production of Capitella capitata (Polychaeta: Capitellidae) in Río de la Plata Estuary (Argentina)

A benthic survey was carried out from November 1998 to December 1999 in the tidal flats of Bahía Samborombón (Río de la Plata estuary, Argentina), in order to study the population structure, reproductive aspects, growth and secondary production of Capitella capitata (Fabricius, 1780). Growth was analyzed using ELEFAN routine, and the secondary production was estimated by Hynes and Coleman's method (1968). C. capitata did not present periods of very important recruitments throughout the year; however, the abundance of smallest size classes was higher during summer and autumn. The summer cohort showed a growth rate (K) of 2.05 and a seasonal growth oscillation (C) of 0.6, pointing out that worms grew very slowly during winter months. The life span of this cohort was 13 months. The autumn cohort showed a lower growth rate (K= 1.5) and its growth was lowest during winter. The life span was 15 months for this cohort. C. capitata in Punta Rasa presented an extended reproductive period, with absence of activity during winter months. The type of eggs and larvae suggest that C. capitata has benthic larval development in the study area, destining its reproductive effort to the production of a low number of eggs, and assuring larvae survival through incubation in brooding tubes. The annual mean biomass in Punta Rasa was 0.117 g m-2 (AFDW), with a mean secondary production of 0.23 g m-2 y-1 and a P/B ratio of 1.96 y-1. The relatively low density, biomass production and P/B ratio of C. capitata in Punta Rasa can be considered as reference values for this species inhabiting undisturbed or moderately disturbed areas

Non-Abelian Tensor Multiplet Equations from Twistor Space

We establish a Penrose-Ward transform yielding a bijection between holomorphic principal 2-bundles over a twistor space and non-Abelian self-dual tensor fields on six-dimensional flat space-time. Extending the twistor space to supertwistor space, we derive sets of manifestly N=(1,0) and N=(2,0) supersymmetric non-Abelian constraint equations containing the tensor multiplet. We also demonstrate how this construction leads to constraint equations for non-Abelian supersymmetric self-dual strings.Comment: v3: 23 pages, revised version published in Commun. Math. Phy

Magnetic anisotropy terms in [110] MBE grown REFe2 films involving the strain term ???

The magnetic anisotropy parameters in [110] MBE grown films of REFe2 compounds are not the same as those in the bulk. This is due to the presence of a shear strain εxy, frozen in during crystal growth. In this paper, calculated magnetic anisotropy parameters for [110] MBE grown REFe2 films, that directly involve the shear strain εxy, are presented and discussed. In addition to the usual first order Callen and Callen term K˜'2, there are nine second order terms six of which involve cross terms between εxy and the cubic crystal field terms B4 and B6. Two of the second order cross terms are identified as being important: K˜"242(T) and K˜"262(T). Of these, the rank-two term K˜"242(T) dominates over a large temperature range. It has the same angular dependence as the first order term K˜'2, but with a more rapid temperature dependence. The correction at T = 0K for TbFe2, DyFe2, HoFe2, ErFe2, and TmFe2, amounts to ~+9.2%, -13.9%, -11.6%, +22.7%, and 27.1%, respectively. Similar comments are made concerning the rank-four K˜"264(T) term

Results from the 4PI Effective Action in 2- and 3-dimensions

We consider a symmetric scalar theory with quartic coupling and solve the equations of motion from the 4PI effective action in 2- and 3-dimensions using an iterative numerical lattice method. For coupling less than 10 (in dimensionless units) good convergence is obtained in less than 10 iterations. We use lattice size up to 16 in 2-dimensions and 10 in 3-dimensions and demonstrate the convergence of the results with increasing lattice size. The self-consistent solutions for the 2-point and 4-point functions agree well with the perturbative ones when the coupling is small and deviate when the coupling is large.Comment: 14 pages, 11 figures; v5: added numerical calculations in 3D; version accepted for publication in EPJ

Soft Gluon Approach for Diffractive Photoproduction of J/psi

We study diffractive photoproduction of $J/\psi$ by taking the charm quark as a heavy quark. A description of nonperturbative effect related to $J/\psi$ can be made by using NRQCD. In the forward region of the kinematics, the interaction between the $c\bar c$-pair and the initial hadron is due to exchange of soft gluons. The effect of the exchange can be studied by using the expansion in the inverse of the quark mass $m_c$. At the leading order we find that the nonperturbative effect related to the initial hadron is represented by a matrix element of field strength operators, which are separated in the moving direction of $J/\psi$ in the space-time. The S-matrix element is then obtained without using perturbative QCD and the results are not based on any model. Corrections to the results can be systematically added. Keeping the dominant contribution of the S-matrix element in the large energy limit we find that the imaginary part of the S-matrix element is related to the gluon distribution for $x\to 0$ with a reasonable assumption, the real part can be obtained with another approximation or with dispersion relation. Our approach is different than previous approaches and also our results are different than those in these approaches. The differences are discussed in detail. A comparison with experiment is also made and a qualitative agreement is found.Comment: 25 pages, 6 figures. Tiny changes in two figures, conclusion and text unchanged, accpeted by Nucl. Phys.

Corrections to the Central Limit Theorem for Heavy-Tailed Probability Densities

Classical Edgeworth expansions provide asymptotic correction terms to the Central Limit Theorem (CLT) up to an order that depends on the number of moments available. In this paper, we provide subsequent correction terms beyond those given by a standard Edgeworth expansion in the general case of regularly varying distributions with diverging moments (beyond the second). The subsequent terms can be expressed in a simple closed form in terms of certain special functions (Dawson's integral and parabolic cylinder functions), and there are qualitative differences depending on whether the number of moments available is even, odd or not an integer, and whether the distributions are symmetric or not. If the increments have an even number of moments, then additional logarithmic corrections must also be incorporated in the expansion parameter. An interesting feature of our correction terms for the CLT is that they become dominant outside the central region and blend naturally with known large-deviation asymptotics when these are applied formally to the spatial scales of the CLT

On the stability and spectrum of non-supersymmetric AdS(5) solutions of M-theory compactified on Kahler-Einstein spaces

Eleven-dimensional supergravity admits non-supersymmetric solutions of the form AdS(5)xM(6) where M(6) is a positive Kahler-Einstein space. We show that the necessary and sufficient condition for such solutions to be stable against linearized bosonic supergravity perturbations can be expressed as a condition on the spectrum of the Laplacian acting on (1,1)-forms on M(6). For M(6)=CP(3), this condition is satisfied, although there are scalars saturating the Breitenlohner-Freedman bound. If M(6) is a product S(2)xM(4) (where M(4) is Kahler-Einstein) then there is an instability if M(4) has a continuous isometry. We show that a potential non-perturbative instability due to 5-brane nucleation does not occur. The bosonic Kaluza-Klein spectrum is determined in terms of eigenvalues of operators on M(6).Comment: 21 pages. v2: Includes SU(4) quantum numbers for CP3 case, typos fixed, refs adde

Spin-Peierls and Antiferromagnetic Phases in Cu{1-x}Zn{x}GeO{3}: A Neutron Scattering Study

Comprehensive neutron scattering studies were carried out on a series of high-quality single crystals of Cu_{1-x}Zn_xGeO_3. The Zn concentration, x, was determined for each sample using Electron Probe Micro-Analysis. The measured Zn concentrations were found to be 40-80% lower than the nominal values. Nevertheless the measured concentrations cover a wide range which enables a systematic study of the effects due to Zn-doping. We have confirmed the coexistence of spin-Peierls (SP) and antiferromagnetic (AF) orderings at low temperatures and the measured phase diagram is presented. Most surprisingly, long-range AF ordering occurs even in the lowest available Zn concentration, x=0.42%, which places important constraints on theoretical models of the AF-SP coexistence. Magnetic excitations are also examined in detail. The AF excitations are sharp at low energies and show no considerable broadening as x increases indicating that the AF ordering remains long ranged for x up to 4.7%. On the other hand, the SP phase exhibits increasing disorder as x increases, as shown from the broadening of the SP excitations as well as the dimer reflection peaks.Comment: 17 preprint style pages, 9 postscript files included. Submitted to Phys. Rev. B. Also available from http://insti.physics.sunysb.edu/~mmartin/pubs.htm