CERN Document Server: Published Articles
https://cds.cern.ch
CERN Document Server latest documents in Published ArticlesenSat, 19 Apr 2014 05:20:21 GMTInvenio 1.1.0.156-1d5a9cds.support@cern.ch360345093125https://cds.cern.ch/img/site_logo_rss.pngCERN Document Server
https://cds.cern.ch
Search Search this site:p
https://cds.cern.ch/search
Optimising a Muon Spectrometer for Measurements at the ISIS Pulsed Muon Source
https://cds.cern.ch/record/1696442
This work describes the development of a state-of-the-art muon spectrometer for the ISIS pulsed muon source. Conceived as a major upgrade of the highly successful EMU instrument, emphasis has been placed on making effective use of the enhanced flux now available at the ISIS source. This has been achieved both through the development of a highly segmented detector array and enhanced data acquisition electronics. The pulsed nature of the ISIS beam is particularly suited to the development of novel experiments involving external stimuli, and therefore the ability to sequence external equipment has been added to the acquisition system. Finally, the opportunity has also been taken to improve both the magnetic field and temperature range provided by the spectrometer, to better equip the instrument for running the future ISIS user programme.Giblin, S RFri, 18 Apr 2014 02:34:02 GMThttps://cds.cern.ch/record/1696442The Single-Channel Regime of Transport through Random Media
https://cds.cern.ch/record/1696424
The propagation of light through samples with random inhomogeneities can be described by way of transmission eigenchannels, which connect incoming and outgoing external propagating modes. Although the detailed structure of a disordered sample can generally not be fully specified, these transmission eigenchannels can nonetheless be successfully controlled and utilized for focusing and imaging light through random media. Here we demonstrate that in deeply localized quasi-1D systems, the single dominant transmission eigenchannel is formed by an individual Anderson localized mode or by a "necklace state". In this single-channel regime, the disordered sample can be treated as an effective 1D system with a renormalized localization length, coupled through all the external modes to its surroundings. Using statistical criteria of the single-channel regime and pulsed excitations of the disordered samples allows us to identify long-lived localized modes and short-lived necklace states at long and short time delays, respectively.Peña, AFri, 18 Apr 2014 02:33:59 GMThttps://cds.cern.ch/record/1696424Proton capture by 14N at astrophysical energies
https://cds.cern.ch/record/1696423
Calculations are reported for low energy, proton capture by 14N with the recoil corrected continuum shell model. An interaction from a fit to Cohen and Kurath (6-16) p-shell matrix elements and Reid soft core g-matrix elements is employed. The prediction for 14N(p,{\gamma})15O, based on this model and available data, is that S(0) equals 1.632 and S(30) is 1.625 keV b. Good agreement with available cross section data support this result. No evidence is found for significant contributions from the subthreshold resonance.Grineviciute, JFri, 18 Apr 2014 02:33:47 GMThttps://cds.cern.ch/record/1696423Dirac oscillators and the relativistic R matrix
https://cds.cern.ch/record/1696422
The Dirac oscillators are shown to be an excellent expansion basis for solutions of the Dirac equation by $R$-matrix techniques. The combination of the Dirac oscillator and the $R$-matrix approach provides a convenient formalism for reactions as well as bound state problems. The utility of the $R$-matrix approach is demonstrated in relativistic impulse approximation calculations where exchange terms can be calculated exactly, and scattering waves made orthogonal to bound state wave functions.Grineviciute, JFri, 18 Apr 2014 02:33:47 GMThttps://cds.cern.ch/record/1696422Quantum Local Symmetry of the D-Dimensional Non-Linear Sigma Model: A Functional Approach
https://cds.cern.ch/record/1696401
We summarize recent progress on the symmetric subtraction of the Non-Linear Sigma Model in $D$ dimensions, based on the validity of a certain Local Functional Equation (LFE) encoding the invariance of the SU(2) Haar measure under local left transformations. The deformation of the classical non-linearly realized symmetry at the quantum level is analyzed by cohomological tools. It is shown that all the divergences of the one-particle irreducible (1-PI) amplitudes (both on-shell and off-shell) can be classified according to the solutions of the LFE. Applications to the non-linearly realized Yang-Mills theory and to the electroweak theory, which is directly relevant to the model-independent analysis of LHC data, are briefly addressed.Quadri, AndreaFri, 18 Apr 2014 02:32:51 GMThttps://cds.cern.ch/record/1696401On the origin of stars with and without planets. Tc trends and clues to Galactic evolution
https://cds.cern.ch/record/1696372
We explore a sample of 148 solar-like stars to search for a possible correlation between the slopes of the abundance trends versus condensation temperature (known as the Tc slope) with stellar parameters and Galactic orbital parameters in order to understand the nature of the peculiar chemical signatures of these stars and the possible connection with planet formation. We find that the Tc slope significantly correlates (at more than 4sigma) with the stellar age and the stellar surface gravity. We also find tentative evidence that the Tc slope correlates with the mean galactocentric distance of the stars (Rmean), suggesting that those stars that originated in the inner Galaxy have fewer refractory elements relative to the volatiles. While the average Tc slope for planet-hosting solar analogs is steeper than that of their counterparts without planets, this difference probably reflects the difference in their age and Rmean. We conclude that the age and probably the Galactic birth place are determinant to establish the star's chemical properties. Old stars (and stars with inner disk origin) have a lower refractory-to-volatile ratio.Adibekyan, V ZhFri, 18 Apr 2014 02:28:57 GMThttps://cds.cern.ch/record/1696372Perspectives of current-layer diagnostics in solar flares
https://cds.cern.ch/record/1696364
A reconnecting current layer is a `heart' of a solar flare, because it is a place of magnetic-field energy release. However there are no direct observations of these layers. The aim of our work is to understand why we actually do not directly observe current layers and what we need to do it in the future. The method is based on a simple mathematical model of a super-hot (T ~ 1E8 K) turbulent-current layer (SHTCL) and a model of plasma heating by the layer. The models allow us to study a correspondence between the main characteristics of the layer, such as temperature and dimensions, and the observational features, such as differential and integral emission measure of heated plasma, intensity of spectral lines Fe XXVI (1.78 and 1.51A) and Ni XXVII (1.59 A). This method provides a theoretical basis for determining parameters of the current layer from observations. Observations of SHTCLs are difficult, because the spectral line intensities are faint, but it is theoretically possible in the future. Observations in X-ray range 1.5--1.8 A with high spectral resolution (better than 0.01 A) and high temporal resolution (seconds) are needed. It is also very important to interpret the observations using a multi-temperature approach instead of the usual single or double temperature method.Oreshina, A VFri, 18 Apr 2014 02:28:51 GMThttps://cds.cern.ch/record/1696364Companions of Stars: From Other Stars to Brown Dwarfs to Planets: The Discovery of the First Methane Brown Dwarf
https://cds.cern.ch/record/1696362
The discovery of the first methane brown dwarf provides a framework for describing the important advances in both fundamental physics and astrophysics that are due to the study of companions of stars. I present a few highlights of the history of this subject along with details of the discovery of the brown dwarf Gliese 229B. The nature of companions of stars is discussed with an attempt to avoid biases induced by anthropocentric nomenclature. With the newer types of remote reconnaissance of nearby stars and their systems of companions, an exciting and perhaps even more profound set of contributions to science is within reach in the near future. This includes an exploration of the diversity of planets in the universe and perhaps soon the first solid evidence for biological activity outside our Solar System.Oppenheimer, B RFri, 18 Apr 2014 02:28:49 GMThttps://cds.cern.ch/record/1696362Ab initio geometry and bright excitation of carotenoids: Quantum Monte Carlo and Many Body Green's Function Theory calculations on peridinin
https://cds.cern.ch/record/1695760
In this letter we report the singlet ground state structure of the full carotenoid peridinin by means of variational Monte Carlo (VMC) calculations. The VMC relaxed geometry has an average bond length alternation of 0.1165(10) {\AA}, larger than the values obtained by DFT (PBE, B3LYP and CAM-B3LYP) and shorter than that calculated at the Hartree-Fock (HF) level. TDDFT and EOM-CCSD calculations on a reduced peridinin model confirm the HOMO-LUMO major contribution of the Bu+-like (S2) bright excited state. Many Body Green's Function Theory (MBGFT) calculations of the vertical excitation energy of the Bu+-like state for the VMC structure (VMC/MBGFT) provide excitation energy of 2.62 eV, in agreement with experimental results in n-hexane (2.72 eV). The dependence of the excitation energy on the bond length alternation in the MBGFT and TDDFT calculations with different functionals is discussed.Coccia, EmanueleThu, 17 Apr 2014 03:09:42 GMThttps://cds.cern.ch/record/1695760Flood avalanches in a semiarid basin with a dense reservoir network
https://cds.cern.ch/record/1695759
This study investigates flood avalanches in a dense reservoir network in the semiarid north-eastern Brazil. The population living in this area strongly depends on the availability of the water from this network. Water is stored during intense wet-season rainfall events and evaporates from the reservoir surface during the dry season. These seasonal changes are the driving forces behind the water dynamics in the network. The reservoir network and its connectivity properties during flood avalanches are investigated with a model called ResNetM, which simulates each reservoir explicitly. It runs on the basis of daily calculated water balances for each reservoir. A spilling reservoir contributes with water to the reservoir downstream, which can trigger avalanches affecting, in some cases, large fractions of the network. The main focus is on the study of the relation between the total amount of water stored and the largest observable cluster of connected reservoirs that overspill in the same day. It is shown that the thousands of small and middle-sized reservoirs are eminent for the retention of water upstream the large ones. Therefore, they prevent large clusters at a low level of water. Concerning connectivity measures, the actual reservoir network, which evolved without an integrated plan, performed better (i.e., generated smaller avalanches for similar amount of stored water) than numerous stochastically generated artificial reservoir networks on the same river network.Peter, Samuel JThu, 17 Apr 2014 03:09:42 GMThttps://cds.cern.ch/record/1695759The Dynamics of Emotional Chats with Bots: Experiment and Agent-Based Simulations
https://cds.cern.ch/record/1695756
Quantitative research of emotions in psychology and machine-learning methods for extracting emotion components from text messages open an avenue for physical science to explore the nature of stochastic processes in which emotions play a role, e.g., in human dynamics online. Here, we investigate the occurrence of collective behavior of users that is induced by chats with emotional Bots. The Bots, designed in an experimental environment, are considered. Furthermore, using the agent-based modeling approach, the activity of these experimental Bots is simulated within a social network of interacting emotional agents. Quantitative analysis of time series carrying emotional messages by agents suggests temporal correlations and persistent fluctuations with clustering according to emotion similarity. {All data used in this study are fully anonymized.}Tadic, BosiljkaThu, 17 Apr 2014 03:09:41 GMThttps://cds.cern.ch/record/1695756Spatial Coherence Properties of Organic Molecules Coupled to Plasmonic Surface Lattice Resonances in the Weak and Strong Coupling Regimes
https://cds.cern.ch/record/1695753
We study spatial coherence properties of a system composed of periodic silver nanoparticle arrays covered with a fluorescent organic molecule (DiD) film. The evolution of spatial coherence of this composite structure from the weak to the strong coupling regime is investigated by systematically varying the coupling strength between the localized DiD excitons and the collective, delocalized modes of the nanoparticle array known as surface lattice resonances. A gradual evolution of coherence from the weak to the strong coupling regime is observed, with the strong coupling features clearly visible in interference fringes. A high degree of spatial coherence is demonstrated in the strong coupling regime, even when the mode is very excitonlike (80%), in contrast to the purely localized nature of molecular excitons. We show that coherence appears in proportion to the weight of the plasmonic component of the mode throughout the weak-to-strong coupling crossover, providing evidence for the hybrid nature of the normal modes.Shi, LThu, 17 Apr 2014 03:09:41 GMThttps://cds.cern.ch/record/1695753All optical diode based on dipole modes of Kerr microcavity in asymmetric L-shaped photonic crystal waveguide
https://cds.cern.ch/record/1695750
A design of all optical diode in $L$-shaped photonic crystal waveguide is proposed that uses the multistability of single nonlinear Kerr microcavity with two dipole modes. Asymmetry of the waveguide is achieved by difference in coupling of the dipole modes with the left and right legs of waveguide. By use of coupled mode theory we present domains in axis of light frequency and amplitude where an extremely high transmission contrast can be achieved. The direction of optical diode transmission can be governed by power and frequency of injecting light. The theory agrees with numerical solution of the Maxwell equations.Bulgakov, E NThu, 17 Apr 2014 03:09:41 GMThttps://cds.cern.ch/record/1695750Relativistic R matrix and continuum shell model
https://cds.cern.ch/record/1695739
Background: The $R$ matrix formalism of Lane and Thomas has proven to be a convenient reaction theory for solving many-coupled channel systems. The theory provides solutions to bound states, scattering states, and resonances for microscopic models in one formalism. Purpose: The first purpose is to extend this formalism to the relativistic case so that the many-coupled channels problem may be solved for systems in which binary breakup channels satisfy a relative Dirac equation. The second purpose is to employ this formalism in a relativistic continuum shell model. Methods: Expressions for the collision matrix and the scattering amplitude, from which observables may be calculated, are derived. The formalism is applied to the 1p-1h relativistic continuum shell model with an interaction extracted from relativistic mean-field theory. Results: The simplest of the $\sigma +\omega +\rho$ exchange interactions produces a good description of the single-particle energies in $^{16}$O and $^{90}$Zr and a reasonable description of proton scattering from $^{15}$N. Conclusions: The development of a calculable, relativistic $R$ matrix and its implementation in a $1p-1h$ relativistic continuum shell model provide a simple relatively self-consist, physically justifiable model for use in knockout reactions.Grineviciute, JThu, 17 Apr 2014 03:09:29 GMThttps://cds.cern.ch/record/1695739Noncommutativity and Humanity -- Julius Wess and his Legacy
https://cds.cern.ch/record/1695733
A personal view on Julius Wess's human and scientific legacy in Serbia and the Balkan region is given. Motivation for using noncommutative and nonarchimedean geometry on very short distances is presented. In addition to some mathematical preliminaries, we present a short introduction in adelic quantum mechanics in a way suitable for its noncommutative generalization. We also review the basic ideas and tools embedded in $q$-deformed and noncommutative quantum mechanics. A rather fundamental approach, called deformation quantization, is noted. A few relations between noncommutativity and nonarchimedean spaces, as well as similarities between corresponding quantum theories, in particular, quantum cosmology are pointed out. An extended Moyal product in a frame of an adelic noncommutative quantum mechanics is also considered.Djordjevic, Goran SThu, 17 Apr 2014 03:09:03 GMThttps://cds.cern.ch/record/1695733Massive Jackiw-Rebbi Model
https://cds.cern.ch/record/1695732
In this paper we analyze a generalized Jackiw-Rebbi (J-R) model in which a massive fermion is coupled to the kink of the $\lambda\phi^4$ model as a prescribed background field. We solve this massive J-R model exactly and analytically and obtain the whole spectrum of the fermion, including the bound and continuum states. The mass term of the fermion makes the potential of the decoupled second order Schrodinger-like equations asymmetric in a way that their asymptotic values at two spatial infinities are different. Therefore, we encounter the unusual problem in which two kinds of continuum states are possible for the fermion: reflecting and scattering states. We then show the energies of all the states as a function of the parameters of the kink, i.e. its value at spatial infinity ($\theta_0$) and its slope at $x=0$ ($\mu$). The graph of the energies as a function of $\theta_0$, where the bound state energies and the two kinds of continuum states are depicted, shows peculiar features including an energy gap in the form of a triangle where no bound states exist. That is the zero mode exists only for $\theta_0$ larger than a critical value $(\theta_0^{\textrm{c}})$. This is in sharp contrast to the usual (massless) J-R model where the zero mode and hence the fermion number $\pm1/2$ for the ground state is ever present. This also makes the origin of the zero mode very clear: It is formed from the union of the two threshold bound states at $\theta_0^{\textrm{c}}$, which is zero in the massless J-R model.Charmchi, FaridThu, 17 Apr 2014 03:09:03 GMThttps://cds.cern.ch/record/1695732Halo-independent comparison of direct dark matter detection data: a review
https://cds.cern.ch/record/1695711
We review the halo-independent formalism, that allows to compare data from different direct dark matter detection experiments without making assumptions on the properties of the dark matter halo. We apply this method to spin-independent WIMP-nuclei interactions, for both isospin-conserving and isospin-violating couplings, and to WIMPs interacting through an anomalous magnetic moment.Del Nobile, EugenioThu, 17 Apr 2014 03:08:32 GMThttps://cds.cern.ch/record/1695711Emergent Weyl fermions and the origin of $i=\sqrt{-1}$ in quantum mechanics
https://cds.cern.ch/record/1695707
Conventional quantum mechanics is described in terms of complex numbers. However, all physical quantities are real. This indicates, that the appearance of complex numbers in quantum mechanics may be the emergent phenomenon, i.e. complex numbers appear in the low energy description of the underlined high energy theory. We suggest a possible explanation of how this may occur. Namely, we consider the system of multi - component Majorana fermions. There is a natural description of this system in terms of real numbers only. In the vicinity of the topologically protected Fermi point this system is described by the effective low energy theory with Weyl fermions. These Weyl fermions interact with the emergent gauge field and the emergent gravitational field.Volovik, G EThu, 17 Apr 2014 03:08:32 GMThttps://cds.cern.ch/record/1695707Breakdown of the equivalence between gravitational mass and energy for a composite quantum body
https://cds.cern.ch/record/1695683
The simplest quantum composite body, a hydrogen atom, is considered in the presence of a weak external gravitational field. We define an operator for the passive gravitational mass of the atom in the post-Newtonian approximation of the general relativity and show that it does not commute with its energy operator. Nevertheless, the equivalence between the expectation values of the mass and energy is shown to survive at a macroscopic level for stationary quantum states. Breakdown of the equivalence between passive gravitational mass and energy at a microscopic level for stationary quantum states can be experimentally detected by studying unusual electromagnetic radiation, emitted by the atoms, supported by and moving in the Earth's gravitational field with constant velocity, using spacecraft or satelliteLebed, Andrei GThu, 17 Apr 2014 03:06:56 GMThttps://cds.cern.ch/record/1695683Classifying orbits in galaxy models with a prolate or an oblate dark matter halo component
https://cds.cern.ch/record/1695667
We explore the nature of orbits of stars moving in the meridional plane $(R,z)$ of an axially symmetric galactic model with a disk, a spherical nucleus, and a flat biaxial dark matter halo component. In particular, we study the influence of all the involved parameters of the dynamical system, by computing both the percentage of chaotic orbits and the percentages of orbits of the main regular resonant families in each case. To distinguish between ordered and chaotic motion, we use the smaller alignment index (SALI) method to extensive samples of orbits by numerically integrating the equations of motion as well as the variational equations. Moreover, a method based on the concept of spectral dynamics that utilizes the Fourier transform of the time series of each coordinate is used to identify the various families of regular orbits and also to recognize the secondary resonances that bifurcate from them. Two cases are studied for every parameter: (i) the case where the halo component is prolate and (ii) the case where an oblate dark halo is present. Our numerical investigation indicates that all the dynamical quantities affect, more or less, the overall orbital structure. It was observed that the mass of the nucleus, the halo flattening parameter, the scale length of the halo, the angular momentum, and the orbital energy are the most influential quantities, while the effect of all the other parameters is much weaker. It was also found that all the parameters corresponding to the disk only have a minor influence on the nature of orbits. Furthermore, some other quantities, such as the minimum distance to the origin, the horizontal, and the vertical force, were tested as potential chaos detectors. Our analysis revealed that only general information can be obtained from these quantities. We also compared our results with early related work.Zotos, Euaggelos EThu, 17 Apr 2014 03:03:14 GMThttps://cds.cern.ch/record/1695667Bending and Breathing Modes of the Galactic Disk
https://cds.cern.ch/record/1695657
We explore the hypothesis that a passing satellite or dark matter subhalo has excited coherent oscillations of the Milky Way's stellar disk in the direction perpendicular to the Galactic midplane. This work is motivated by recent observations of spatially dependent bulk vertical motions within ~ kpc of the Sun. A satellite can transfer a fraction of its orbital energy to the disk stars as it plunges through the Galactic midplane thereby heating and thickening the disk. Bulk motions arise during the early stages of such an event when the disk is still in an unrelaxed state. We present simple toy-model calculations and simulations of disk-satellite interactions, which show that the response of the disk depends on the relative velocity of the satellite. When the component of the satellite's velocity perpendicular to the disk is small compared with that of the stars, the perturbation is predominantly a bending mode. Conversely, breathing and higher order modes are excited when the vertical velocity of the satellite is larger than that of the stars. We argue that the compression and rarefaction motions seen in three different surveys are in fact breathing mode perturbations of the Galactic disk.Widrow, Lawrence MThu, 17 Apr 2014 03:03:12 GMThttps://cds.cern.ch/record/1695657Smart Diabetic Socks: Embedded device for diabetic foot prevention
https://cds.cern.ch/record/1695571
1) Objectives Most foot ulcers are the consequence of a trauma (repetitive high stress, ill-fitting footwear, or an object inside the shoe) associated to diabetes. They are often followed by amputation and shorten life expectancy. This paper describes the prototype of the Smart Diabetic Socks that has been developed in the context of the French ANR TecSan project. The objective is to prevent pressure foot ulcers for diabetic persons. 2) Material and methods A fully wireless, customizable and washable "smart sock" has been designed. It is made of a textile which fibers are knitted in a way they provide measurements of the pressure exerted under and all around the foot in real-life conditions. This device is coupled with a subject-specific Finite Element foot model that simulates the internal strains within the soft tissues of the foot. 3) Results A number of derived stress indicators can be computed based on that analysis, such as the accumulated stress dose, high internal strains or peak pressures near bony prominences during gait. In case of risks for pressure ulcer, an alert is sent to the person and/or to the clinician. A watch, a smart-phone or a distant laptop can be used for providing such alert.Perrier, AntoineWed, 16 Apr 2014 02:42:20 GMThttps://cds.cern.ch/record/1695571Vertically coupled polymer microracetrack resonators for Label-Free Biochemical sensors
https://cds.cern.ch/record/1695567
We report on the efficient design and fabrication of polymeric microracetrack optical resonators for label-free biosensing purposes. Vertically-coupled microresonators immersed in deionised water display high Q-factors (>35000) and finesses up to 25. A surface sensing experiment performed with these microresonators using 5-TAMRA cadaverine as a test molecule demonstrated both the high sensitivity and low detection limit of our device.Delezoide, CamilleWed, 16 Apr 2014 02:42:20 GMThttps://cds.cern.ch/record/1695567General Approach for the Sensitivity Analysis and Optimization of Integrated Optical Evanescent-Wave Sensors
https://cds.cern.ch/record/1695563
The optimization of integrated optical evanescent-wave sensors is dual. For optimal performances, we require waveguides with both maximal sensitivity to the measurand, the quantity intended to be measured, and minimal sensitivities to perturbations. In this context, fully numerical approaches are extremely powerful, but demand huge computer resources. We address this issue by introducing a general and efficient approach, based on the formal derivation of analytical dispersion equations, to express and evaluate all waveguide sensitivities. In particular, we apply this approach to rectangular waveguides, to discuss its accuracy and its use within sensitivity optimization procedures.Delezoide, CamilleWed, 16 Apr 2014 02:42:18 GMThttps://cds.cern.ch/record/1695563Generalized $su(2)$ coherent states for the Landau levels and their nonclassical properties
https://cds.cern.ch/record/1695553
Following the lines of the recent papers [J. Phys. A: Math. Theor. 44, 495201 (2012); Eur. Phys. J. D 67, 179 (2013)], we construct here a new class of generalized coherent states related to the Landau levels, which can be used as the finite Fock subspaces for the representation of the $su(2)$ Lie algebra. We establish the relationship between them and the deformed truncated coherent states. We have, also, shown that they satisfy the resolution of the identity property through a positive definite measures on the complex plane. Their nonclassical and quantum statistical properties such as quadrature squeezing, higher order `$su(2)$' squeezing, anti-bunching and anti-correlation effects are studied in details. Particularly, the influence of the generalization on the nonclassical properties of two modes is clarified.Dehghani, AWed, 16 Apr 2014 02:42:16 GMThttps://cds.cern.ch/record/1695553