Antiresonance and Localization in Quantum Dynamics

The phenomenon of quantum antiresonance (QAR), i.e., exactly periodic recurrences in quantum dynamics, is studied in a large class of nonintegrable systems, the modulated kicked rotors (MKRs). It is shown that asymptotic exponential localization generally occurs for $\eta$ (a scaled $\hbar$) in the infinitesimal vicinity of QAR points $\eta_0$. The localization length $\xi_0$ is determined from the analytical properties of the kicking potential. This ``QAR-localization" is associated in some cases with an integrable limit of the corresponding classical systems. The MKR dynamical problem is mapped into pseudorandom tight-binding models, exhibiting dynamical localization (DL). By considering exactly-solvable cases, numerical evidence is given that QAR-localization is an excellent approximation to DL sufficiently close to QAR. The transition from QAR-localization to DL in a semiclassical regime, as $\eta$ is varied, is studied. It is shown that this transition takes place via a gradual reduction of the influence of the analyticity of the potential on the analyticity of the eigenstates, as the level of chaos is increased.Comment: To appear in Physical Review E. 51 pre-print pages + 9 postscript figure

Trumpler 20 - an old and rich open cluster

We show that the open cluster Trumpler 20, contrary to the earlier findings, is actually an old Galactic open cluster. New CCD photometry and high-resolution spectroscopy are used to derive the main parameters of this cluster. At [Fe/H]=-0.11 for a single red giant star, the metallicity is slightly subsolar. The best fit to the color-magnitude diagrams is achieved using a 1.3 Gyr isochrone with convective overshoot. The cluster appears to have a significant reddening at E(B-V)=0.46 (for B0 spectral type), although for red giants this high reddening yields the color temperature exceeding the spectroscopic T_eff by about 200 K. Trumpler 20 is a very rich open cluster, containing at least 700 members brighter than M_V=+4. It may extend over the field-of-view available in our study at 20'x20'.Comment: 7 pages, 5 figures; accepted for publication in MNRA

Very large scale correlations in the galaxy distribution

We characterize galaxy correlations in the Sloan Digital Sky Survey by measuring several moments of galaxy counts in spheres. We firstly find that the average counts grows as a power-law function of the distance with an exponent D= 2.1+- 0.05 for r in [0.5,20] Mpc/h and D = 2.8+-0.05 for r in [30,150] Mpc/h. In order to estimate the systematic errors in these measurements we consider the counts variance finding that it shows systematic finite size effects which depend on the samples sizes. We clarify, by making specific tests, that these are due to galaxy long-range correlations extending up to the largest scales of the sample. The analysis of mock galaxy catalogs, generated from cosmological N-body simulations of the standard LCDM model, shows that for r<20 Mpc/h the counts exponent is D~2.0, weakly dependent on galaxy luminosity, while D=3 at larger scales. In addition, contrary to the case of the observed galaxy samples, no systematic finite size effects in the counts variance are found at large scales, a result that agrees with the absence of large scale, r~100 Mpc/h, correlations in the mock catalogs. We thus conclude that the observed galaxy distribution is characterized by correlations, fluctuations and hence structures, which are larger, both in amplitude and in spatial extension, than those predicted by the standard model LCDM of galaxy formation.Comment: 6 pages, 7 figures to be published in Europhysics Letter

Quantum Revivals in Periodically Driven Systems close to nonlinear resonance

We calculate the quantum revival time for a wave-packet initially well localized in a one-dimensional potential in the presence of an external periodic modulating field. The dependence of the revival time on various parameters of the driven system is shown analytically. As an example of application of our approach, we compare the analytically obtained values of the revival time for various modulation strengths with the numerically computed ones in the case of a driven gravitational cavity. We show that they are in very good agreement.Comment: 14 pages, 1 figur

An Empirical Mass Function Distribution

The halo mass function, encoding the comoving number density of dark matter halos of a given mass, plays a key role in understanding the formation and evolution of galaxies. As such, it is a key goal of current and future deep optical surveys to constrain the mass function down to mass scales that typically host ${L}_{\star }$ galaxies. Motivated by the proven accuracy of Press–Schechter-type mass functions, we introduce a related but purely empirical form consistent with standard formulae to better than 4% in the medium-mass regime, {10}^{10}\mbox{--}{10}^{13}\,{h}^{-1}M☉. In particular, our form consists of four parameters, each of which has a simple interpretation, and can be directly related to parameters of the galaxy distribution, such as {L}_{\star }$. Using this form within a hierarchical Bayesian likelihood model, we show how individual mass-measurement errors can be successfully included in a typical analysis, while accounting for Eddington bias. We apply our form to a question of survey design in the context of a semi-realistic data model, illustrating how it can be used to obtain optimal balance between survey depth and angular coverage for constraints on mass function parameters. Open-source Python and R codes to apply our new form are provided at http://mrpy.readthedocs.org and https://cran.r-project.org/web/packages/tggd/index.html respectively

An experimental investigation of the impact of personality disorder diagnosis on clinicians:can we see past the borderline?

Background: There is concern that diagnostic labels for psychiatric disorders may invoke damaging stigma, stereotypes and misunderstanding. Aims: This study investigated clinicians’ reactions to diagnostic labelling by examining their positive and negative reactions to the label borderline personality disorder (BPD). Method: Mental health professionals (n = 265) viewed a videotape of a patient suffering from panic disorder and agoraphobia undergoing assessment. Prior to viewing the videotape, participants were randomly allocated to one of three conditions and were given the following information about the patient: (a) general background information; (b) additional descriptive information about behaviour corresponding to BPD; and (c) additional descriptive information about behaviour corresponding to BPD, but explicitly adding BPD as a possible comorbid diagnostic label. All participants were then asked to note things they had seen in the videotape that made them feel optimistic or pessimistic about treatment outcome. Results: Participants in the group that were explicitly informed that the patient had a BPD diagnostic label reported significantly fewer reasons to be optimistic than the other two groups. Conclusions: Diagnostic labels may negatively impact on clinicians’ judgments and perceptions of individuals and therefore clinicians should think carefully about whether, and how, they use diagnoses and efforts should be made to destigmatize diagnostic terms.</jats:p

The very bright SCUBA galaxy count: looking for SCUBA galaxies with the Mexican Hat Wavelet

We present the results of a search for bright high-redshift galaxies in two large SCUBA scan-maps of Galactic regions. A Mexican Hat Wavelet technique was used to locate point sources in these maps, which suffer high foreground contamination as well as typical scan-map noise signatures. A catalogue of point source objects was selected and observed again in the submillimetre continuum, and in HCO+ (3->2) at zero redshift to rule out Galactic sources. No extragalactic sources were found. Simulations show that the survey was sensitive to sources with fluxes > 50 mJy, depending on the local background. These simulations result in upper limits on the 850-micron counts of SCUBA galaxies of 53 per square degree at 50 mJy and 2.9 per square degree at 100 mJy.Comment: Accepted by MNRA

Vegetation and peat characteristics of restiad bogs on Chatham Island (Rekohu), New Zealand

Restiad bogs dominated by Sporadanthus traversii on Chatham Island, New Zealand, were sampled to correlate vegetation patterns and peat properties, and to compare with restiad systems dominated by Sporadanthus ferrugineus and Empodisma minus in the Waikato region, North Island, New Zealand. Classification and ordination resulted in five groups that reflected a disturbance gradient. The largest S. traversii group, which comprised plots from central, relatively intact bogs, had the lowest levels of total nitrogen (mean 1.20 mg cm-3), total phosphorus (mean 0.057 mg cm-3), total potassium (mean 0.083 mg cm-3), and available phosphorus (mean 18.6 μg cm-3). Modification by drainage, stock, and fires resulted in a decline of S. traversii and an increase of Gleichenia dicarpa fern cover, together with elevated peat nutrient levels and higher bulk density. Compared with peat dominated by Sporadanthus ferrugineus or Empodisma minus in relatively unmodified Waikato restiad bogs, Chatham Island peat under S. traversii has significantly higher total potassium, total nitrogen, available phosphorus, bulk density, and von Post decomposition indices, and significantly lower pH. Sporadanthus traversii and Empodisma minus have similar ecological roles in restiad bog development, occupying a relatively wide nutrient range, and regenerating readily from seed after fire. Despite differences in root morphology, S. traversii and E. minus are the major peat formers in raised restiad bogs on Chatham Island and in Waikato, respectively, and could be regarded as ecological equivalents

LTB solutions in Newtonian gauge: from strong to weak fields

Lemaitre-Tolman-Bondi (LTB) solutions are used frequently to describe the collapse or expansion of spherically symmetric inhomogeneous mass distributions in the Universe. These exact solutions are obtained in the synchronous gauge where nonlinear dynamics (with respect to the FLRW background) induce large deviations from the FLRW metric. In this paper we show explicitly that this is a gauge artefact (for realistic sub-horizon inhomogeneities). We write down the nonlinear gauge transformation from synchronous to Newtonian gauge for a general LTB solution using the fact that the peculiar velocities are small. In the latter gauge we recover the solution in the form of a weakly perturbed FLRW metric that is assumed in standard cosmology. Furthermore we show how to obtain the LTB solutions directly in Newtonian gauge and illustrate how the Newtonian approximation remains valid in the nonlinear regime where cosmological perturbation theory breaks down. Finally we discuss the implications of our results for the backreaction scenario.Comment: 17 page

High-energy neutrino conversion and the lepton asymmetry in the universe

We study matter effects on oscillations of high-energy neutrinos in the Universe. Substantial effect can be produced by scattering of the neutrinos from cosmological sources (z\gta 1) on the relic neutrino background, provided that the latter has large CP-asymmetry: \eta\equiv (n_\nu-n_{\bar{\nu}})/n_\gamma\gta 1, where $n_\nu$, $n_{\bar{\nu}}$ and $n_\gamma$ are the concentrations of neutrinos, antineutrinos and photons. We consider in details the dynamics of conversion in the expanding neutrino background. Applications are given to the diffuse fluxes of neutrinos from GRBs, AGN, and the decay of super-heavy relics. We find that the vacuum oscillation probability can be modified by $\sim (10-20)$ and in extreme cases allowed by present bounds on $\eta$ the effect can reach $\sim 100$. Signatures of matter effects would consist (i) for both active-active and active-sterile conversion, in a deviation of the numbers of events produced in a detector by neutrinos of different flavours, $N_{\alpha}~(\alpha=e,\mu,\tau)$, and of their ratios from the values given by vacuum oscillations; such deviations can reach $\sim 5-15$, (ii) for active-sterile conversion, in a characteristic energy dependence of the ratios $N_{e}/N_{\mu},N_{e}/N_{\tau},N_{\mu}/N_{\tau}$. Searches for these matter effects will probe large CP and lepton asymmetries in the universe.Comment: 32 pages, RevTeX, 16 figures. Substantial changes in the treatment of conversion effects in the relic neutrino background and of active-active oscillations of high-energy neutrinos. Figures and references added; conclusions partially modifie