On nuclear matrix element uncertainties in short range 0vBB decay

The evaluation of short range contributions to neutrinoless double beta decay has been challenged due to critics of the ansatz of the nuclear matrix element calculations. We comment on the critics and uncertainties of these calculations and the effect on the derived limits.Comment: 3 pages, Latex, new arguments adde

New Leptoquark Mechanism of Neutrinoless Double Beta Decay

A new mechanism for neutrinoless double beta (\znbb) decay based on leptoquark exchange is discussed. Due to the specific helicity structure of the effective four-fermion interaction this contribution is strongly enhanced compared to the well-known mass mechanism of \znbb decay. As a result the corresponding leptoquark parameters are severely constrained from non-observation of \znbb-decay. These constraints are more stringent than those derived from other experiments.Comment: LaTeX, 6 pages, 1 figur

Computing periodic orbits using the anti-integrable limit

Chaotic dynamics can be effectively studied by continuation from an anti-integrable limit. Using the Henon map as an example, we obtain a simple analytical bound on the domain of existence of the horseshoe that is equivalent to the well-known bound of Devaney and Nitecki. We also reformulate the popular method for finding periodic orbits introduced by Biham and Wenzel. Near an anti-integrable limit, we show that this method is guaranteed to converge. This formulation puts the choice of symbolic dynamics, required for the algorithm, on a firm foundation.Comment: 11 Pages Latex2e + 1 Figure (eps). Accepted for publication in Physics Lettes

Constraints on Leptoquark Masses and Couplings from Rare Processes and Unification

Motivated by the recent experimental data at HERA and ZEUS, which have reported evidence for leptoqark production at Sqrt{s}=314 GeV with a mass at M_D=200 GeV we consider its implications in unified supersymmetric theories. We also present calculations for leptoquark production incorporating the existing limits from other exotic reactions on its couplings and other relevant parameters.Comment: Latex file, 10pages, reference adde

Singularly Perturbed Monotone Systems and an Application to Double Phosphorylation Cycles

The theory of monotone dynamical systems has been found very useful in the modeling of some gene, protein, and signaling networks. In monotone systems, every net feedback loop is positive. On the other hand, negative feedback loops are important features of many systems, since they are required for adaptation and precision. This paper shows that, provided that these negative loops act at a comparatively fast time scale, the main dynamical property of (strongly) monotone systems, convergence to steady states, is still valid. An application is worked out to a double-phosphorylation ``futile cycle'' motif which plays a central role in eukaryotic cell signaling.Comment: 21 pages, 3 figures, corrected typos, references remove

Spin diffusion at finite electric and magnetic fields

Spin transport properties at finite electric and magnetic fields are studied by using the generalized semiclassical Boltzmann equation. It is found that the spin diffusion equation for non-equilibrium spin density and spin currents involves a number of length scales that explicitly depend on the electric and magnetic fields. The set of macroscopic equations can be used to address a broad range of the spin transport problems in magnetic multilayers as well as in semiconductor heterostructure. A specific example of spin injection into semiconductors at arbitrary electric and magnetic fields is illustrated

Additional Nucleon Current Contributions to Neutrinoless Double Beta Decay

We have examined the importance of momentum dependent induced nucleon currents such as weak-magnetism and pseudoscalar couplings to the amplitude of neutrinoless double beta decay in the mechanisms of light and heavy Majorana neutrino as well as in that of Majoron emission. Such effects are expected to occur in all nuclear models in the direction of reducing the light neutrino matrix elements by about 30%. To test this we have performed a calculation of the nuclear matrix elements of the experimentally interesting nuclei A = 76, 82, 96, 100, 116, 128, 130, 136 and 150 within the pn-RQRPA. We have found that indeed such corrections vary somewhat from nucleus to nucleus, but in all cases they are greater than 25 percent. In the case of heavy neutrino the effect is much larger (a factor of 3). Combining out results with the best presently available experimental limits on the half-life of the neutrinoless double beta decay we have extracted new limits on the effective neutrino mass (light and heavy) and the effective Majoron coupling constant.Comment: 31 pages, RevTex, 3 Postscript figures, submitted to Phys. Rev.

Assessing the impact of the physical properties of industrially produced carbon nanotubes on their interaction with human primary macrophages in vitro

Currently it is not fully understood how carbon nanotubes (CNTs) may affect human health. Despite this, CNTs are produced at a tonne mass scale yearly. Due to their large production and intended use within a variety of applications it is imperative that a clear understanding of the hazard potential of CNTs is gained. The aim of this study therefore was to assess the impact of five different industrially produced CNTs which varied in their physical properties on the viability of human monocyte derived macrophages (MDM), and subsequently, at sub-lethal concentrations (0.005-0.02 mg/mL), their ability to cause oxidative stress and a pro-inflammatory response in these important immune cells over a 24-h period. None of the CNTs caused significant cytotoxicity up to 0.02 mg/mL after 24 h. Only the long multi-walled CNTs (MWNCTs) caused a significant, dose-dependent (0.005-0.02 mg/mL) reactive oxygen species production, whilst bundled MWCNTs showed a significant tumor necrosis factor alpha release after 24 h exposure at 0.02 mg/mL. No effects were observed for either tangled MWCNTs or short MWCNTs. It can be concluded from the findings of the present study that the industrially produced CNTs studied can cause hazardous effects in vitro that may be associated with their physical propertie

Order-Disorder Transition in a Two-Layer Quantum Antiferromagnet

We have studied the antiferromagnetic order -- disorder transition occurring at $T=0$ in a 2-layer quantum Heisenberg antiferromagnet as the inter-plane coupling is increased. Quantum Monte Carlo results for the staggered structure factor in combination with finite-size scaling theory give the critical ratio $J_c = 2.51 \pm 0.02$ between the inter-plane and in-plane coupling constants. The critical behavior is consistent with the 3D classical Heisenberg universality class. Results for the uniform magnetic susceptibility and the correlation length at finite temperature are compared with recent predictions for the 2+1-dimensional nonlinear $\sigma$-model. The susceptibility is found to exhibit quantum critical behavior at temperatures significantly higher than the correlation length.Comment: 11 pages (5 postscript figures available upon request), Revtex 3.

Surface Effects in Magnetic Microtraps

We have investigated Bose-Einstein condensates and ultra cold atoms in the vicinity of a surface of a magnetic microtrap. The atoms are prepared along copper conductors at distances to the surface between 300 um and 20 um. In this range, the lifetime decreases from 20 s to 0.7 s showing a linear dependence on the distance to the surface. The atoms manifest a weak thermal coupling to the surface, with measured heating rates remaining below 500 nK/s. In addition, we observe a periodic fragmentation of the condensate and thermal clouds when the surface is approached.Comment: 4 pages, 4 figures; v2: corrected references; v3: final versio