Properties of Nucleon Resonances by means of a Genetic Algorithm

We present an optimization scheme that employs a Genetic Algorithm (GA) to determine the properties of low-lying nucleon excitations within a realistic photo-pion production model based upon an effective Lagrangian. We show that with this modern optimization technique it is possible to reliably assess the parameters of the resonances and the associated error bars as well as to identify weaknesses in the models. To illustrate the problems the optimization process may encounter, we provide results obtained for the nucleon resonances $\Delta$(1230) and $\Delta$(1700). The former can be easily isolated and thus has been studied in depth, while the latter is not as well known experimentally.Comment: 12 pages, 10 figures, 3 tables. Minor correction

End of the cosmic neutrino energy spectrum

There may be a high-energy cutoff of neutrino events in IceCube data. In particular, IceCube does not observe either continuum events above 2 PeV, or the Standard Model Glashow-resonance events expected at 6.3 PeV. There are also no higher energy neutrino signatures in the ANITA and Auger experiments. This absence of high-energy neutrino events motivates a fundamental restriction on neutrino energies above a few PeV. We postulate a simple scenario to terminate the neutrino spectrum that is Lorentz-invariance violating, but with a limiting neutrino velocity that is always smaller than the speed of light. If the limiting velocity of the neutrino applies also to its associated charged lepton, then a significant consequence is that the two-body decay modes of the charged pion are forbidden above two times the maximum neutrino energy, while the radiative decay modes are suppressed at higher energies. Such stabilized pions may serve as cosmic ray primaries.Comment: 6 pages. Version to appear in PL

A directed mutation operator for real coded genetic algorithms

Copyright @ Springer-Verlag Berlin Heidelberg 2010.Developing directed mutation methods has been an interesting research topic to improve the performance of genetic algorithms (GAs) for function optimization. This paper introduces a directed mutation (DM) operator for GAs to explore promising areas in the search space. In this DM method, the statistics information regarding the fitness and distribution of individuals over intervals of each dimension is calculated according to the current population and is used to guide the mutation of an individual toward the neighboring interval that has the best statistics result in each dimension. Experiments are carried out to compare the proposed DM technique with an existing directed variation on a set of benchmark test problems. The experimental results show that the proposed DM operator achieves a better performance than the directed variation on most test problems

US-guided laser treatment of parathyroid adenomas

Objective: To determine the clinical efficacy of laser ablation for the tredatment of primary hyperparathyroidism (pHPT). Materials and methods: Twelve patients with pHPT were treated with laser ablation. Energy was administered by means of 1.5 m optical fibers percutaneously placed into the target via 21 G needles. A laser ablation unit (EchoLaser X4, Esaote) applied 3 W power for 400\u2013600 s/fiber/insertion to a total 3600\u20139000 Joules of energy. Patient serum parathyroid hormone (PTH) and calcium levels were checked at baseline and thereafter every 6 months. Patients were followed-up for 2 years with serologic and contrast-enhanced ultrasound. Therapeutic success was defined as normal PTH and calcium levels together with disappearance of nodule-related symptoms. Results: All procedures were performed in single session. Immediately following ablation, contrast enhanced ultrasound confirmed that all but one target had become avascular (technical success rate 11/12; 92%), remaining avascular at all follow-up ultrasound examinations, thereafter. The mean volume of parathyroid nodules decreased from 0.54 cc to 0.36 cc (72.0%). Serum PTH and calcium levels were significantly lower at 1, 12 and 24 m compared to baseline (p < 0.01). By 6 m, PTH and calcium returned to normal and were stable until 24 m in all successfully treated patients. All cases of hyperparathyroid-related symptoms resolved by 6 m (ostealgia [n = 5], repeated renal colic [n = 5], vomiting [n = 3]). Only one patient (8%) reported transient dysphonia as a minor complication. Conclusion: Laser ablation of enlarged, symptomatic parathyroid glands is safe and well-tolerated and can produce long-term, sustained reduction of serum PTH and calcium levels

Gravitational waves from binary systems in circular orbits: Convergence of a dressed multipole truncation

The gravitational radiation originating from a compact binary system in circular orbit is usually expressed as an infinite sum over radiative multipole moments. In a slow-motion approximation, each multipole moment is then expressed as a post-Newtonian expansion in powers of v/c, the ratio of the orbital velocity to the speed of light. The bare multipole truncation of the radiation consists in keeping only the leading-order term in the post-Newtonian expansion of each moment, but summing over all the multipole moments. In the case of binary systems with small mass ratios, the bare multipole series was shown in a previous paper to converge for all values v/c < 2/e, where e is the base of natural logarithms. In this paper, we extend the analysis to a dressed multipole truncation of the radiation, in which the leading-order moments are corrected with terms of relative order (v/c)^2 and (v/c)^3. We find that the dressed multipole series converges also for all values v/c < 2/e, and that it coincides (within 1%) with the numerically ``exact'' results for v/c < 0.2.Comment: 9 pages, ReVTeX, 1 postscript figur

Evidence of Skyrmion excitations about ν=1\nu =1 in n-Modulation Doped Single Quantum Wells by Inter-band Optical Transmission

We observe a dramatic reduction in the degree of spin-polarization of a two-dimensional electron gas in a magnetic field when the Fermi energy moves off the mid-point of the spin-gap of the lowest Landau level, $\nu=1$. This rapid decay of spin alignment to an unpolarized state occurs over small changes to both higher and lower magnetic field. The degree of electron spin polarization as a function of $\nu$ is measured through the magneto-absorption spectra which distinguish the occupancy of the two electron spin states. The data provide experimental evidence for the presence of Skyrmion excitations where exchange energy dominates Zeeman energy in the integer quantum Hall regime at $\nu=1$

Unexpected impact of D waves in low-energy neutral pion photoproduction from the proton and the extraction of multipoles

Contributions of $D$ waves to physical observables for neutral pion photoproduction from the proton in the near-threshold region are studied and means to isolate them are proposed. Various approaches to describe the multipoles are employed --a phenomenological one, a unitary one, and heavy baryon chiral perturbation theory. The results of these approaches are compared and found to yield essentially the same answers. $D$ waves are seen to enter together with $S$ waves in a way that any means which attempt to obtain the $E_{0+}$ multipole accurately must rely on knowledge of $D$ waves and that consequently the latter cannot be dismissed in analyses of low-energy pion photoproduction. It is shown that $D$ waves have a significant impact on double-polarization observables that can be measured. This importance of $D$ waves is due to the soft nature of the $S$ wave and is a direct consequence of chiral symmetry and the Nambu--Goldstone nature of the pion. $F$-wave contributions are shown to be negligible in the near-threshold region.Comment: 38 pages, 13 figures, 19 tables. Version to be published in Physical Review

Gravitational waves from inspiraling compact binaries: Second post-Newtonian waveforms as search templates II

We present further evidence that the second post-Newtonian (pN) approximation to the gravitational waves emitted by inspiraling compact binaries is sufficient for the detection of these systems. This is established by comparing the 2-pN wave forms to signals calculated from black hole perturbation theory. Results are presented for different detector noise curves. We also discuss the validity of this type of analysis.Comment: 5 pages, 3 Figures, RevTe

Predictions for the Cosmogenic Neutrino Flux in Light of New Data from the Pierre Auger Observatory

The Pierre Auger Observatory (PAO) has measured the spectrum and composition of the ultrahigh energy cosmic rays with unprecedented precision. We use these measurements to constrain their spectrum and composition as injected from their sources and, in turn, use these results to estimate the spectrum of cosmogenic neutrinos generated in their propagation through intergalactic space. We find that the PAO measurements can be well fit if the injected cosmic rays consist entirely of nuclei with masses in the intermediate (C, N, O) to heavy (Fe, Si) range. A mixture of protons and heavier species is also acceptable but (on the basis of existing hadronic interaction models) injection of pure light nuclei (p, He) results in unacceptable fits to the new elongation rate data. The expected spectrum of cosmogenic neutrinos can vary considerably, depending on the precise spectrum and chemical composition injected from the cosmic ray sources. In the models where heavy nuclei dominate the cosmic ray spectrum and few dissociated protons exceed GZK energies, the cosmogenic neutrino flux can be suppressed by up to two orders of magnitude relative to the all-proton prediction, making its detection beyond the reach of current and planned neutrino telescopes. Other models consistent with the data, however, are proton-dominated with only a small (1-10%) admixture of heavy nuclei and predict an associated cosmogenic flux within the reach of upcoming experiments. Thus a detection or non-detection of cosmogenic neutrinos can assist in discriminating between these possibilities.Comment: 10 pages, 7 figure