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Sample records for fermi energy domain

  1. Heavy-ion peripheral collisions in the Fermi energy domain : Fragmentation processes or dissipative collisions ?

    NASA Astrophysics Data System (ADS)

    Borderie, B.; Rivet, M. F.; Tassan-Got, L.

    For several years a new field in nuclear physics has been opened by the opportunity to accelerate heavy ions through an energy domain including the Fermi energy of nucleons. The new domain has to be seen as a link between dissipative processes observed at low energies, dominated by mean field considerations, and high energy collisions for which nucleon-nucleon collisions play an important role. This paper reviews our present knowledge on peripheral collisions. A reminder of contiguous energy domains is done as well as their extension in the new field. Specific calculations are also presented. Finally a wide comparison between experiments and calculations is performed. A fast dissipative stage proves to be responsible for the dominant mechanisms involved, at least when the incident energy is lower than 50 MeV/nucleon. Un nouveau champ d'études de la physique nucléaire s'est ouvert depuis quelques années avec la possibilité de réaliser des collisions noyau-noyau dans un domaine en énergie franchissant l'énergie de Fermi des nucléons. Ce nouveau domaine constitue le lien entre les processus dissipatifs observés à basse énergie, dominés par le concept de champ moyen, et les réactions à grande énergie pour lesquelles les collisions nucléon-nucléon jouent un rôle important. Cet article sur les collisions périphériques fait le point sur l'état actuel de nos connaissances. Après un rappel des domaines en énergie connexes, de leurs eventuelles extensions dans le domaine considéré, des calculs spécifiques au domaine sont décrits. Enfin une importante comparaison calculs théoriques-expériences est présentée. Une dissipation en énergie très rapide est responsable des processus dominants observés jusqu'à des énergies incidentes d'environ 50 MeV/nucléon.

  2. Dependence of the Fermi energy upon neutron excess

    NASA Astrophysics Data System (ADS)

    Jeukenne, J.-P.; Mahaux, C.; Sartor, R.

    1991-05-01

    The Fermi energy EF is defined as the negative of the average between the separation energies of a nucleon from the (A+1)- and A-nucleon systems. In the independent-particle limit, EF is the average between the energies of the last occupied and of the first unoccupied shell-model orbits. For mass numbers 40<~A<~208, the experimental neutron Fermi energies EFn increase approximately linearly with increasing asymmetry parameter η=(N-Z)/A. In contrast, the experimental proton Fermi energies EFp are, on the average, nearly independent of η when the average single-particle Coulomb energy EC is subtracted, the quantity EFp-EC decreases linearly with increasing η, with a slope whose modulus differs from that found for EFn. These features are analyzed in the framework of two mean-field models; they both include an isoscalar and an isovector central component, as well as a Coulomb correction in the case of protons. From the comparison between the n-208Pb and p-208Pb mean fields, it is derived that the depth of the symmetry potential is nearly independent of energy in the domain 15<~E<~50 MeV, in close agreement with a recent phenomenological study of the global optical-model potential for nuclei with mass numbers 40<=A<=208. In the vicinity of the Fermi energy, the isoscalar and isovector components are assumed to have Woods-Saxon radial shapes and linearly energy-dependent depths. In both models, the depth of the symmetry potential is taken equal to (23.2-0.46E) MeV. In the first model, all the parameters are extracted from a recent dispersion relation analysis of the mean fields felt by neutrons and protons in 208Pb; then, the calculated neutron Fermi energies are in good agreement with the experimental values but the calculated proton Fermi energies are larger than the experimental values, except for the lead isotopes. The second model incorporates, in addition, information derived from dispersion relation analyses of the n-40Ca and n-90Zr potentials; its main

  3. High Energy Neutrinos from the Fermi Bubbles

    SciTech Connect

    Lunardini, Cecilia; Razzaque, Soebur

    2012-06-01

    Recently the Fermi-LAT data have revealed two gamma-ray emitting bubble-shaped structures at the Galactic center. If the observed gamma rays have hadronic origin (collisions of accelerated protons), the bubbles must emit high energy neutrinos as well. This new, Galactic, neutrino flux should trace the gamma-ray emission in spectrum and spatial extent. Its highest energy part, above 20–50 TeV, is observable at a kilometer-scale detector in the northern hemisphere, such as the planned KM3NeT, while interesting constraints on it could be obtained by the IceCube Neutrino Observatory at the South Pole. The detection or exclusion of neutrinos from the Fermi bubbles will discriminate between hadronic and leptonic models, thus bringing unique information on the still mysterious origin of these objects and on the time scale of their formation.

  4. High energy neutrinos from the Fermi bubbles.

    PubMed

    Lunardini, Cecilia; Razzaque, Soebur

    2012-06-01

    Recently the Fermi-LAT data have revealed two gamma-ray emitting bubble-shaped structures at the Galactic center. If the observed gamma rays have hadronic origin (collisions of accelerated protons), the bubbles must emit high energy neutrinos as well. This new, Galactic, neutrino flux should trace the gamma-ray emission in spectrum and spatial extent. Its highest energy part, above 20-50 TeV, is observable at a kilometer-scale detector in the northern hemisphere, such as the planned KM3NeT, while interesting constraints on it could be obtained by the IceCube Neutrino Observatory at the South Pole. The detection or exclusion of neutrinos from the Fermi bubbles will discriminate between hadronic and leptonic models, thus bringing unique information on the still mysterious origin of these objects and on the time scale of their formation.

  5. Fermi energy instability in resonant tunneling

    NASA Astrophysics Data System (ADS)

    Claro, Francisco; Inkoferer, Jutta; Obermeir, Gustav

    2001-03-01

    In resonant tunneling two different instabilities may arise induced by the electron-electron interaction, depending on whether the conduction channel is at the emitter Fermi energy, or at the bottom of the emitter Fermi sea. The latter leads to a well understood multistable regime in the device characteristics. The former was found in the past for the case when a magnetic field is present in the direction of the current flow*. We shall show that the external field is not required, and that actually the instability can take place in the presence of zero, one and two dimensional quantum wells. Supported in part by FONDECYT 1990425 and Catedra Presidencial en Ciencias *P.Orellana, E.Anda and F.Claro, Phys.Rev.Lett. 79, 1118 (1997)

  6. Fermi level stabilization energy in cadmium oxide

    SciTech Connect

    Speaks, D. T.; Mayer, M. A.; Yu, K. M.; Mao, S. S.; Haller, E. E.; Walukiewicz, W.

    2010-04-08

    We have studied the effects of high concentrations of native point defects on the electrical and optical properties of CdO. The defects were introduced by irradiation with high energy He+, Ne+, Ar+ and C+ ions. Increasing the irradiation damage with particles heavier than He+ increases the electron concentration until a saturation level of 5x1020 cm-3 is reached. In contrast, due to the ionic character and hence strong dynamic annealing of CdO, irradiation with much lighter He+ stabilizes the electron concentration at a much lower level of 1.7x1020 cm-3. A large shift of the optical absorption edge with increasing electron concentration in irradiated samples is explained by the Burstein-Moss shift corrected for electron-electron and electron-ion interactions. The saturation of the electron concentration and the optical absorption edge energy are consistent with a defect induced stabilization of the Fermi energy at 1 eV above the conduction band edge. The result is in a good agreement with previously determined Fermi level pinning energies on CdO surfaces. The results indicate that CdO shares many similarities with InN, as both materials exhibit extremely large electron affinities and an unprecedented propensity for n-type conductivity.

  7. High Energy Neutrinos from the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Razzaque, Soebur; Lunardini, Cecilia

    2012-03-01

    Recent discovery of two gamma-ray emitting bubble-shaped structures (Fermi Bubbles) at the Galactic center opens up a possibility to detect high-energy neutrinos from them as well, if the observed gamma rays have hadronic origin. This new predicted Galactic neutrino flux is hard, following gamma-ray data, compared to the atmospheric neutrino flux and can be detected with a kilometer scale neutrino telescope in the northern hemisphere, such as the planned KM3NeT, above 20-50 TeV. IceCube Neutrino Observatory at the South pole can also provide interesting constraints on the flux model. A detection or exclusion of this neutrino flux can discriminate between a leptonic or hadronic origin of the gamma-rays, as well as bring unique information on the activities at the Galactic center.

  8. Angular correlations near the Fermi energy

    SciTech Connect

    Fox, D.; Cebra, D.A.; Karn, J.; Parks, C.; Pradhan, A.; Vander Molen, A.; van der Plicht, J.; Westfall, G.D.; Wilson, W.K.; Tickle, R.S.; and others

    1988-07-01

    Angular correlations between light particles have been studied to probe the extent to which a thermally equilibrated system is formed in heavy ion collisions near the Fermi energy. Single-light-particle inclusive energy spectra and two-particle large-angle correlations were measured for 40 and 50 MeV/nucleon C+C, Ag, and Au. The single-particle inclusive energy spectra are well fit by a three moving source parametrization. Two-particle large-angle correlations are shown to be consistent with emission from a thermally equilibrated source when the effects of momentum conservation are considered. Single-particle inclusive spectra and light-particle correlations at small relative momentum were measured for 35 MeV/nucleon N+Ag. Source radii were extracted from the two-particle correlation functions and were found to be consistent with previous measurements using two-particle correlations and the coalescence model. The temperature of the emitting source was extracted from the relative populations of states using the quantum statistical model and was found to be 4.8/sub -2.4//sup +2.8/ MeV, compared to the 14 MeV temperature extracted from the slopes of the kinetic energy spectra.

  9. Domain-averaged Fermi-hole analysis for solids.

    PubMed

    Baranov, Alexey I; Ponec, Robert; Kohout, Miroslav

    2012-12-07

    The domain-averaged Fermi hole (DAFH) orbitals provide highly visual representation of bonding in terms of orbital-like functions with attributed occupation numbers. It was successfully applied on many molecular systems including those with non-trivial bonding patterns. This article reports for the first time the extension of the DAFH analysis to the realm of extended periodic systems. Simple analytical model of DAFH orbital for single-band solids is introduced which allows to rationalize typical features that DAFH orbitals for extended systems may possess. In particular, a connection between Wannier and DAFH orbitals has been analyzed. The analysis of DAFH orbitals on the basis of DFT calculations is applied to hydrogen lattices of different dimensions as well as to the solids diamond, graphite, Na, Cu and NaCl. In case of hydrogen lattices, remarkable similarity is found between the DAFH orbitals evaluated with both the analytical approach and DFT. In case of the selected ionic and covalent solids the DAFH orbitals deliver bonding descriptions, which are compatible with classical orbital interpretation. For metals the DAFH analysis shows essential multicenter nature of bonding.

  10. Domain-averaged Fermi-hole analysis for solids

    NASA Astrophysics Data System (ADS)

    Baranov, Alexey I.; Ponec, Robert; Kohout, Miroslav

    2012-12-01

    The domain-averaged Fermi hole (DAFH) orbitals provide highly visual representation of bonding in terms of orbital-like functions with attributed occupation numbers. It was successfully applied on many molecular systems including those with non-trivial bonding patterns. This article reports for the first time the extension of the DAFH analysis to the realm of extended periodic systems. Simple analytical model of DAFH orbital for single-band solids is introduced which allows to rationalize typical features that DAFH orbitals for extended systems may possess. In particular, a connection between Wannier and DAFH orbitals has been analyzed. The analysis of DAFH orbitals on the basis of DFT calculations is applied to hydrogen lattices of different dimensions as well as to the solids diamond, graphite, Na, Cu and NaCl. In case of hydrogen lattices, remarkable similarity is found between the DAFH orbitals evaluated with both the analytical approach and DFT. In case of the selected ionic and covalent solids the DAFH orbitals deliver bonding descriptions, which are compatible with classical orbital interpretation. For metals the DAFH analysis shows essential multicenter nature of bonding.

  11. The Spectral Energy Distributions of Fermi Blazars

    NASA Astrophysics Data System (ADS)

    Fan, J. H.; Yang, J. H.; Liu, Y.; Luo, G. Y.; Lin, C.; Yuan, Y. H.; Xiao, H. B.; Zhou, A. Y.; Hua, T. X.; Pei, Z. Y.

    2016-10-01

    In this paper, multiwavelength data are compiled for a sample of 1425 Fermi blazars to calculate their spectral energy distributions (SEDs). A parabolic function, {{log}}{(ν {F}ν )={P}1({{log}}ν -{P}2)}2+{P}3, is used for SED fitting. Synchrotron peak frequency ({log}{ν }{{p}}), spectral curvature (P1), peak flux ({ν }{{p}}{F}{ν {{p}}}), and integrated flux (ν {F}ν ) are successfully obtained for 1392 blazars (461 flat-spectrum radio quasars [FSRQs], 620 BL Lacs [BLs], and 311 blazars of uncertain type [BCUs]; 999 sources have known redshifts). Monochromatic luminosity at radio 1.4 GHz, optical R band, X-ray at 1 keV and γ-ray at 1 GeV, peak luminosity, integrated luminosity, and effective spectral indices of radio to optical ({α }{{RO}}) and optical to X-ray ({α }{{OX}}) are calculated. The “Bayesian classification” is employed to log {ν }{{p}} in the rest frame for 999 blazars with available redshift, and the results show that three components are enough to fit the log {ν }{{p}} distribution; there is no ultra-high peaked subclass. Based on the three components, the subclasses of blazars using the acronyms of Abdo et al. are classified, and some mutual correlations are also studied. Conclusions are finally drawn as follows: (1) SEDs are successfully obtained for 1392 blazars. The fitted peak frequencies are compared with common sources from available samples. (2) Blazars are classified as low synchrotron peak sources if log {ν }{{p}}({Hz})≤slant 14.0, intermediate synchrotron peak sources if 14.0\\lt {log} {ν }{{p}}({Hz})≤slant 15.3, and high synchrotron peak sources if {log} {ν }{{p}}({Hz})\\gt 15.3. (3) Gamma-ray emissions are strongly correlated with radio emissions. Gamma-ray luminosity is also correlated with synchrotron peak luminosity and integrated luminosity. (4) There is an anticorrelation between peak frequency and peak luminosity within the whole blazar sample. However, there is a marginally positive correlation for high

  12. FERMI: A Flexible Expert Reasoner with Multi-Domain Inferencing.

    DTIC Science & Technology

    2014-09-26

    representation systems. In particular, FERMI uses schemas, (Brachman, 1979, Minsky, 1975, 1975, Fox , 1979, Bobrow, 1977)data structures composed of...if-added demons in the CONNIVER system (Sussman, 1975), and continuing through KAL (Bobrow, 1977) and SRL (Wright & Fox , 1983, 1983). FERMI’s schemas...language SRL ( Fox , 1979, Wright & Fox , 1983, 1983) in which isa links cause automatic inheritance of all the slots and their associated knowledge

  13. Fermi level stabilization energy in group III-nitrides

    SciTech Connect

    Li, S.X.; Yu, K.M.; Wu, J.; Jones, R.E.; Walukiewicz, W.; AgerIII, J.W.; Shan, W.; Haller, E.E.; Lu, Hai; Schaff, William J.

    2005-01-07

    Energetic particle irradiation is used to systematically introduce point defects into In{sub 1-x}Ga{sub x}N alloys over the entire composition range. Three types of energetic particles (electrons, protons, and {sup 4}He{sup +}) are used to produce a displacement damage dose spanning five decades. In InN and In-rich InGaN the free electron concentration increases with increasing irradiation dose but saturates at a sufficiently high dose. The saturation is due to Fermi level pinning at the Fermi Stabilization Energy (E{sub FS}), which is located at 4.9 eV below the vacuum level. Electrochemical capacitance-voltage (ECV) measurements show that the pinning of the surface Fermi energy at E{sub FS} is also responsible for the surface electron accumulation in as-grown InN and In-rich InGaN alloys. The results are in agreement with the amphoteric defect model that predicts that the same type of native defects are responsible for the Fermi level pinning in both cases.

  14. Diagnosing alternative conceptions of Fermi energy among undergraduate students

    NASA Astrophysics Data System (ADS)

    Sharma, Sapna; Ahluwalia, Pardeep Kumar

    2012-07-01

    Physics education researchers have scientifically established the fact that the understanding of new concepts and interpretation of incoming information are strongly influenced by the preexisting knowledge and beliefs of students, called epistemological beliefs. This can lead to a gap between what students actually learn and what the teacher expects them to learn. In a classroom, as a teacher, it is desirable that one tries to bridge this gap at least on the key concepts of a particular field which is being taught. One such key concept which crops up in statistical physics/solid-state physics courses, and around which the behaviour of materials is described, is Fermi energy (εF). In this paper, we present the results which emerged about misconceptions on Fermi energy in the process of administering a diagnostic tool called the Statistical Physics Concept Survey developed by the authors. It deals with eight themes of basic importance in learning undergraduate solid-state physics and statistical physics. The question items of the tool were put through well-established sequential processes: definition of themes, Delphi study, interview with students, drafting questions, administration, validity and reliability of the tool. The tool was administered to a group of undergraduate students and postgraduate students, in a pre-test and post-test design. In this paper, we have taken one of the themes i.e. Fermi energy of the diagnostic tool for our analysis and discussion. Students’ responses and reasoning comments given during interview were analysed. This analysis helped us to identify prevailing misconceptions/learning gaps among students on this topic. How spreadsheets can be effectively used to remove the identified misconceptions and help appreciate the finer nuances while visualizing the behaviour of the system around Fermi energy, normally sidestepped both by the teachers and learners, is also presented in this paper.

  15. Fractional processes and nuclear disassembly in very-heavy-ion collisions in the Fermi energy regime

    SciTech Connect

    Schroeder, W.U.

    1991-01-01

    Exclusive measurements of charged products and neutrons were performed for the reactions {sup 197}Au + (29 MeV/u) {sup 208}Pb and {sup 209}Bi + (28.2 MeV/u) {sup 136}Xe. The multiplicities of neutrons and charged particles are found to indicate collision impact parameters with different sensitivities. Characteristic correlations observed between massive products and light particles suggest the dominance of the damped-reaction mechanism in the Fermi energy domain. For central collisions, massive fragments are no longer observed, and a considerable fraction of the mass of the system is found disassembled into light particles and clusters. 75 refs., 19 figs.

  16. Enhanced photogalvanic current in topological insulators via Fermi energy tuning

    NASA Astrophysics Data System (ADS)

    Okada, Ken N.; Ogawa, Naoki; Yoshimi, Ryutaro; Tsukazaki, Atsushi; Takahashi, Kei S.; Kawasaki, Masashi; Tokura, Yoshinori

    2016-02-01

    We achieve the enhancement of the circular photogalvanic effect arising from the photoinjection of spins in topological insulator thin films by tuning the Fermi level (EF) . A series of (Bi1-xSbx) 2Te3 thin films were tailored so that the Fermi energy ranges above 0.34 eV to below 0.29 eV of the Dirac point, i.e., from the bulk conduction band bottom to the valence band top through the bulk in-gap surface-Dirac cone. The circular photogalvanic current, indicating a flow of spin-polarized surface-Dirac electrons, shows a pronounced peak when the EF is set near the Dirac point and is also correlated with the carrier mobility. Our observation reveals that there are substantial scatterings between the surface-Dirac and bulk state electrons in the generation process of spin-polarized photocurrent, which can be avoided by designing the electronic structure in topological insulators.

  17. The Spectral Energy Distribution of Fermi Bright Blazars

    NASA Technical Reports Server (NTRS)

    Abdo, A. A.; Ackermann, M.; Agudo, I.; Ajello, M.; Aller, H. D.; Aller, M. F.; Angelakis, E.; Arkharov, A. A.; Axelsson, M.; Bach, U.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B. M.; Bechtol, K.; Bellazzini, R.; Benitiez, E.; Berdyugin, A.; Gehrels, N.; Harding, A. K.; Hays, E.; Marshall, F.; Scargle, J. D.; Thompson, D. J.

    2010-01-01

    We have conducted a detailed investigation of the broadband spectral properties of the gamma-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi gamma-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray /gamma-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these gamma-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log v-log v Fv representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, alpha(sub ro) , and optical to X-ray, alpha(sub ox), spectral slopes) and from the gamma-ray spectral index. Our data show that the synchrotron peak frequency (v(sup S) (sub peak)) is positioned between 10(exp 12.5) and 10(exp 14) Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10(exp 13) and 10(exp 17) Hz in featureless BL Lacertae objects. We find that the gamma-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than

  18. Multi-Messenger Time-Domain Astronomy with the Fermi Gamma-ray Burst Monitor

    NASA Astrophysics Data System (ADS)

    Goldstein, Adam; Fermi GBM Team

    2017-01-01

    With exciting new detections of gravitational waves by LIGO and astrophysical neutrinos by IceCube and ANTARES, the era of multi-messenger time-domain astronomy has arrived. The Fermi Gamma-ray Burst Monitor (GBM) continuously observes the entire sky that is not occulted by the Earth in gamma-rays from 8 keV - 40 MeV with 2 microsecond temporal resolution, and that continuous data is downlinked every few hours. This wealth of near-real-time all-sky data has lead to the development of continuous data searches for gamma-ray events, such as Gamma-Ray Bursts (GRBs), in coincidence with astrophysical neutrinos and gravitational wave events. Additionally, GBM has the ability to localize triggered and un-triggered transient events to a few-degree accuracy, rapidly disseminate the alerts and localization sky maps, and there have been several successful follow-up attempts by wide-field optical telescopes, such as the Palomar Transient Factory, to catch the fading optical afterglow of GBM-triggered GRBs. We discuss the current applications and importance of Fermi GBM in leading multi-messenger time-domain astronomy in the gamma-ray regime.

  19. Multi-Messenger Time-Domain Astronomy with the Fermi Gamma-ray Burst Monitor

    NASA Astrophysics Data System (ADS)

    Connaughton, Valerie; Goldstein, Adam; Fermi GBM - LIGO Group

    2017-01-01

    With exciting new detections of gravitational waves by LIGO and astrophysical neutrinos by IceCube and ANTARES, the era of multi-messenger time-domain astronomy has arrived. The Fermi Gamma-ray Burst Monitor (GBM) continuously observes the entire sky that is not occulted by the Earth in gamma-rays from 8 keV - 40 MeV with 2 microsecond temporal resolution, with regular data downlinks every few hours. This wealth of near-realtime all-sky data has lead to the development of continuous data searches for gamma-ray events, such as Gamma-Ray Bursts (GRBs), in coincidence with astrophysical neutrinos and gravitational wave events. Additionally, GBM has the ability to localize triggered and untriggered transient events to a few-degree accuracy, rapidly disseminate the alerts and localization sky maps within tens of seconds, and there have been several successful follow-up attempts by wide-field optical telescopes, such as the Palomar Transient Factory, to catch the fading optical afterglow of GBM-triggered GRBs. We discuss the current applications and importance of Fermi GBM in leading multi-messenger time-domain astronomy in the gamma-ray regime.

  20. Shape analysis applied in heavy ion reactions near Fermi energy

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Huang, M.; Wada, R.; Liu, X.; Lin, W.; Wang, J.

    2017-03-01

    A new method is proposed to perform shape analyses and to evaluate their validity in heavy ion collisions near the Fermi energy. In order to avoid erroneous values of shape parameters in the calculation, a test particle method is utilized in which each nucleon is represented by n test particles, similar to that used in the Boltzmann–Uehling–Uhlenbeck (BUU) calculations. The method is applied to the events simulated by an antisymmetrized molecular dynamics model. The geometrical shape of fragments is reasonably extracted when n = 100 is used. A significant deformation is observed for all fragments created in the multifragmentation process. The method is also applied to the shape of the momentum distribution for event classification. In the momentum case, the errors in the eigenvalue calculation become much smaller than those of the geometrical shape analysis and the results become similar between those with and without the test particle method, indicating that in intermediate heavy ion collisions the shape analysis of momentum distribution can be used for the event classification without the test particle method.

  1. High-energy proton emission and Fermi motion in intermediate-energy heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Lin, W.; Liu, X.; Wada, R.; Huang, M.; Ren, P.; Tian, G.; Luo, F.; Sun, Q.; Chen, Z.; Xiao, G. Q.; Han, R.; Shi, F.; Liu, J.; Gou, B.

    2016-12-01

    An antisymmetrized molecular dynamics model (AMD-FM), modified to take into account the Fermi motion explicitly in its nucleon-nucleon collision process, is presented. Calculated high-energy proton spectra are compared with those of 40Ar+51V at 44 MeV/nucleon from Coniglione et al. [Phys. Lett. B 471, 339 (2000), 10.1016/S0370-2693(99)01383-0] and those of 36Ar+181Ta at 94 MeV/nucleon from Germain et al. [Nucl. Phys. A 620, 81 (1997), 10.1016/S0375-9474(97)00146-2]. Both of the experimental data are reasonably well reproduced by the newly added Fermi boost in the nucleon-nucleon collision process without additional processes, such as a three-body collision or a short-range correlation. The production mechanism of high-energy protons in intermediate-energy heavy-ion collisions is discussed.

  2. A one-electron approximation to domain-averaged Fermi hole analysis.

    PubMed

    Cooper, David L; Ponec, Robert

    2008-03-07

    In general, full domain-averaged Fermi hole (DAFH) analysis for correlated wavefunctions requires explicit use of the correlated pair density, but such a quantity is not always readily available. We propose instead a simple one-electron approximation, which we call pseudo-DAFH or pDAFH, and which requires instead only the natural orbitals (and their occupation numbers). From comparisons of the DAFH and pDAFH modes of analysis for the bond dissociation processes in H2, N2 and LiH, as well as for the electronic structure of more complex bonding patterns, such as in CH2Li2 and Li4, we conclude that pDAFH analysis could indeed prove to be very useful when the correlated pair density is not available. Detailed comparisons are also presented of values of the shared-electron distribution index (SEDI), a proposed one-electron approximation to it (pSEDI) and a generalized Wiberg index.

  3. Fermi-motion effect on the intermediate energy nucleus-nucleus collision

    NASA Astrophysics Data System (ADS)

    Fan, G. W.; Kong, W. Y.; Han, T. F.; Li, X. C.; Ma, J. B.; Sheng, Z. Q.; Shi, G. Z.; Tian, F.; Wang, J.; Zhang, C.

    2016-11-01

    The Glauber model is modified with the Fermi-motion effect in the calculation of elastic differential cross-sections and momentum distributions of a fragment from mother nucleus. Different reaction systems at low energies are calculated with the modified Glauber model. It is found that calculations including the Fermi-motion provide a better prescription relating the model to a proper nuclear density distribution by comparing with the experimental data. On the basis of the studies, the influence of the correction on the extracted nuclear radius is quantified. The results further confirm the importance of the Fermi-motion in the nucleus-nucleus collision reactions at low energies.

  4. First Results on the High Energy Cosmic Ray Electron Spectrum from Fermi Lat

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2009-01-01

    This viewgraph presentation addresses energy reconstruction, electron-hadron separation, validation of Monte Carlo with flight data and an assessment of systematic errors from the Fermi Large Area Telescope.

  5. High Energy Astrophysics with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2009-01-01

    This slide presentation reviews some of the findings of the Large Area Telescope (LAT) aboard the Fermi Observatory. It includes information about the LAT, and the Gamma-Ray Burst Monitor (GBM), detection of the quiet sun and the moon in gamma rays, Pulsars observed by the observatory, Globular Star Clusters, Active Galactic Nucleus, and Gamma-Ray Bursts, with specific information about GRB 080916C.

  6. On the interpretation of domain averaged Fermi hole analyses of correlated wavefunctions.

    PubMed

    Francisco, E; Martín Pendás, A; Costales, Aurora

    2014-03-14

    Few methods allow for a physically sound analysis of chemical bonds in cases where electron correlation may be a relevant factor. The domain averaged Fermi hole (DAFH) analysis, a tool firstly proposed by Robert Ponec in the 1990's to provide interpretations of the chemical bonding existing between two fragments Ω and Ω' that divide the real space exhaustively, is one of them. This method allows for a partition of the delocalization index or bond order between Ω and Ω' into one electron contributions, but the chemical interpretation of its parameters has been firmly established only for single determinant wavefunctions. In this paper we report a general interpretation based on the concept of excluded density that is also valid for correlated descriptions. Both analytical models and actual computations on a set of simple molecules (H2, N2, LiH, and CO) are discussed, and a classification of the possible DAFH situations is presented. Our results show that this kind of analysis may reveal several correlated assisted bonding patterns that might be difficult to detect using other methods. In agreement with previous knowledge, we find that the effective bond order in covalent links decreases due to localization of electrons driven by Coulomb correlation.

  7. Modeling High-Energy Gamma-Rays from the Fermi Bubbles - Oral Presentation

    SciTech Connect

    Splettstoesser, Megan

    2015-08-25

    In 2010, the Fermi Bubbles were discovered at the galactic center of the Milky Way. These giant gamma-ray structures, extending 50 degrees in galactic latitude and 20-30 degrees in galactic longitude, were not predicted. We wish to develop a model for the gamma-ray emission of the Fermi Bubbles. To do so, we assume that second order Fermi acceleration is responsible for the high-energy emission of the bubbles. Second order Fermi acceleration requires charged particles and irregular magnetic fields—both of which are present in the disk of the Milky Way galaxy. I use the assumption of second order Fermi acceleration in the transport equation, which describes the diffusion of particles. By solving the steady-state case of the transport equation, I compute the proton spectrum due to Fermi second order acceleration and compare this analytical solution to a numerical solution provided by Dr. P. Mertsch. Analytical solutions to the transport equation are taken from Becker, Le, & Dermer and are used to further test the numerical solution. I find that the numerical solution converges to the analytical solution in all cases. Thus, we know the numerical solution accurately calculates the proton spectrum. The gamma-ray spectrum follows the proton spectrum, and will be computed in the future.

  8. Modeling high-energy gamma-rays from the Fermi Bubbles

    SciTech Connect

    Splettstoesser, Megan

    2015-09-17

    In 2010, the Fermi Bubbles were discovered at the galactic center of the Milky Way. These giant gamma-ray structures, extending 55° in galactic latitude and 20°-30° in galactic longitude, were not predicted. We wish to develop a model for the gamma-ray emission of the Fermi Bubbles. To do so, we assume that second order Fermi acceleration requires charged particles and irregular magnetic fields- both of which are present in the disk of the Milky Way galaxy. By solving the steady-state case of the transport equation, I compute the proton spectrum due to second order Fermi acceleration. I compare the analytical solutions of the proton spectrum to a numerical solution. I find that the numerical solution to the transport equation converges to the analytical solution in all cases. The gamma-ray spectrum due to proton-proton interaction is compared to Fermi Bubble data (from Ackermann et al. 2014), and I find that second order Fermi acceleration is a good fit for the gamma-ray spectrum of the Fermi Bubbles at low energies with an injection source term of S = 1.5 x 10⁻¹⁰ GeV⁻¹cm⁻³yr⁻¹. I find that a non-steady-state solution to the gamma-ray spectrum with an injection source term of S = 2 x 10⁻¹⁰ GeV⁻¹cm⁻³yr⁻¹ matches the bubble data at high energies.

  9. Fermi γ-ray Pulsars: Towards the Understanding of the Pulsed High-Energy Emission

    NASA Astrophysics Data System (ADS)

    Kalapotharakos, Constantinos; Kust Harding, Alice; Kazanas, Demosthenes; Brambilla, Gabriele

    2016-04-01

    Based on the Fermi observational data we reveal meaningful constraints for the dependence of the macroscopic parameters of dissipative pulsar magnetosphere models on the corresponding spin-down rate. Our models are specifications of the FIDO (Force-Free Inside, Dissipative Outside) model where the dissipative regions are outside the light-cylinder near the equatorial current sheet. These models provide not only the field geometry but also the necessary particle accelerating electric fields. Assuming emission due to curvature radiation, the FIDO models reproduce the observed light-curve phenomenology as depicted in the radio-lag vs peak-separation diagram obtained by Fermi. A direct and detailed comparison of the model spectral properties (cutoff energies and total γ-ray luminosities) with those observed by Fermi reveals the dependence of the macroscopic conductivity parameter on the spin-down rate providing a unique insight for the understanding of the physical mechanisms behind the high-energy emission in pulsar magnetospheres.

  10. On the ground state energy of the delta-function Fermi gas

    NASA Astrophysics Data System (ADS)

    Tracy, Craig A.; Widom, Harold

    2016-10-01

    The weak coupling asymptotics to order γ of the ground state energy of the delta-function Fermi gas, derived heuristically in the literature, is here made rigorous. Further asymptotics are in principle computable. The analysis applies to the Gaudin integral equation, a method previously used by one of the authors for the asymptotics of large Toeplitz matrices.

  11. A Method for Calculating Fermi Energy and Carrier Concentrations in Semiconducts

    ERIC Educational Resources Information Center

    Gaylord, T. K.; Linxwiler, J. N., Jr.

    1976-01-01

    An efficient numerical method for calculating the Fermi energy, the free electron and free hole concentrations, and the ionized impurity conductors in a semiconductor material is described. The method allows freedom with respect to type of material, temperature, and amount and type of donor and acceptor impurities. (Author/CP)

  12. GRBs as Ultra-High Energy Cosmic Ray Sources: Clues From Fermi

    DTIC Science & Technology

    2010-03-27

    implications for neutrino and γ-ray production are considered in [24]. 7 Summary In this contribution, we have sketched the energy requirements for GRBs to be...holes. Future Fermi observations and the possibility of detecting PeV neutrinos from GRBs with IceCube could establish whether GRBs are the sources of

  13. Fermi energy control of vacancy coalescence and dislocation density in melt-grown GaAs

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Gatos, H. C.; Lin, D. G.; Aoyama, T.

    1984-01-01

    A striking effect of the Fermi energy on the dislocation density in melt-grown GaAs has been discovered. Thus, a shift of the Fermi energy from 0.1 eV above to 0.2 eV below its intrinsic value (at high temperature, i.e., near 1100 K) increases the dislocation density by as much as five orders of magnitude. The Fermi energy shift was brought about by n-type and p-type doping at a level of about 10 to the 17th per cu cm (under conditions of optimum partial pressure of As, i.e., under optimum melt stoichiometry). This effect must be associated with the fact that the Fermi energy controls the charge state of vacancies (i.e., the occupancy of the associated electronic states) which in turn must control their tendency to coalesce and thus the dislocation density. It appears most likely that gallium vacancies are the critical species.

  14. Fractionally Charged Zero-Energy Single-Particle Excitations in a Driven Fermi Sea

    NASA Astrophysics Data System (ADS)

    Moskalets, Michael

    2016-07-01

    A voltage pulse of a Lorentzian shape carrying half of the flux quantum excites out of a zero-temperature Fermi sea an electron in a mixed state, which looks like a quasiparticle with an effectively fractional charge e /2 . A prominent feature of such an excitation is a narrow peak in the energy distribution function lying exactly at the Fermi energy μ . Another spectacular feature is that the distribution function has symmetric tails around μ , which results in a zero-energy excitation. This sounds improbable since at zero temperature all available states below μ are fully occupied. The resolution lies in the fact that such a voltage pulse also excites electron-hole pairs, which free some space below μ and thus allow a zero-energy quasiparticle to exist. I discuss also how to address separately electron-hole pairs and a fractionally charged zero-energy excitation in an experiment.

  15. Ferromagnetism of the repulsive atomic Fermi gas: three-body recombination and domain formation

    NASA Astrophysics Data System (ADS)

    Zintchenko, Ilia; Wang, Lei; Troyer, Matthias

    2016-08-01

    The simplest model for itinerant ferromagnetism, the Stoner model, has so far eluded experimental observation in repulsive ultracold fermions due to rapid three-body recombination at large scattering lengths. Here we show that a ferromagnetic phase can be stabilised by imposing a moderate optical lattice. The reduced kinetic energy drop upon formation of a polarized phase in an optical lattice extends the ferromagnetic phase to smaller scattering lengths where three-body recombination is small enough to permit experimental detection of the phase. We also show, using time dependent density functional theory, that in such a setup ferromagnetic domains emerge rapidly from a paramagnetic initial state.

  16. A connection between domain-averaged Fermi hole orbitals and electron number distribution functions in real space

    NASA Astrophysics Data System (ADS)

    Francisco, E.; Martín Pendás, A.; Blanco, M. A.

    2009-09-01

    We show in this article how for single-determinant wave functions the one-electron functions derived from the diagonalization of the Fermi hole, averaged over an arbitrary domain Ω of real space, and expressed in terms of the occupied canonical orbitals, describe coarse-grained statistically independent electrons. With these domain-averaged Fermi hole (DAFH) orbitals, the full electron number distribution function (EDF) is given by a simple product of one-electron events. This useful property follows from the simultaneous orthogonality of the DAFH orbitals in Ω, Ω'=R3-Ω, and R3. We also show how the interfragment (shared electron) delocalization index, δΩ,Ω', transforms into a sum of one-electron DAFH contributions. Description of chemical bonding in terms of DAFH orbitals provides a vivid picture relating bonding and delocalization in real space. DAFH and EDF analyses are performed on several test systems to illustrate the close relationship between both concepts. Finally, these analyses clearly prove how DAFH orbitals well localized in Ω or Ω' can be simply ignored in computing the EDFs and/or δΩ,Ω', and thus do not contribute to the chemical bonding between the two fragments.

  17. Numerically fitting the electron Fermi energy and the electron fraction in a neutron star

    NASA Astrophysics Data System (ADS)

    Li, Xing Hu; Gao, Zhi Fu; Li, Xiang Dong; Xu, Yan; Wang, Pei; Wang, Na; Peng, Qiu He

    2016-10-01

    Based on the basic definition of the Fermi energy of degenerate and relativistic electrons, we obtain a special solution to the electron Fermi energy, EF(e), and express EF(e) as a function of the electron fraction, Ye, and matter density, ρ. We obtain several useful analytical formula for Ye and ρ within classical models and the work of Dutra et al. (2014) (Type-2) in relativistic mean-field theory are obtained using numerically fitting. When describing the mean-field Lagrangian, density, we adopt the TMA parameter set, which is remarkably consistent with the updated astrophysical observations of neutron stars (NSs). Due to the importance of the density dependence of the symmetry energy, J, in nuclear astrophysics, a brief discussion on J and its slop is presented. Combining these fitting formula with boundary conditions for different density regions, we can evaluate the value of EF(e) in any given matter density, and obtain a schematic diagram of EF(e) as a continuous function of ρ. Compared with previous studies on the electron Fermi energy in other studies models, our methods of calculating EF(e) are more simple and convenient, and can be universally suitable for the relativistic electron regions in the circumstances of common neutron stars. We have deduced a general expression of EF(e) and ne, which could be used to indirectly test whether one equation of state of a NS is correct in our future studies on neutron star matter properties. Since URCA reactions are expected in the center of a massive star due to high-value electron Fermi energy and electron fraction, this study could be useful in the future studies on the NS thermal evolution.

  18. Possible Interpretations of the High Energy Cosmic Ray Electron Spectrum Measured with the Fermi Space Telescope

    SciTech Connect

    Grasso, D.; Profumo, S.; Strong, A.W.; Baldini, L.; Bellazzini, R.; Bloom, E.D.; Bregeon, J.; Di Bernardo, G.; Gaggero, D.; Giglietto, N.; Kamae, T.; Latronico, L.; Longo, F.; Mazziotta, M.N.; Moiseev, A.A.; Morselli, A.; Ormes, J.F.; Pesce-Rollins, M.; Pohl, M.; Razzano, M.; Sgro, C.; /INFN, Pisa /INFN, Pisa /NASA, Ames

    2012-04-25

    The Fermi Large Area Telescope has provided the measurement of the high energy (20 GeV to 1 TeV) cosmic ray electrons and positrons spectrum with unprecedented accuracy. This measurement represents a unique probe for studying the origin and diffusive propagation of cosmic rays as well as for looking for possible evidences of Dark Matter. In this contribution we focus mainly on astrophysical sources of cosmic ray electrons and positrons which include the standard primary and secondary diffuse galactic contribution, as well as nearby point-sources which are expected to contribute more significantly to higher energies. In this framework, we discuss possible interpretations of Fermi results in relation with other recent experimental data on energetic electrons and positrons (specifically the most recent ones reported by PAMELA, ATIC, PPB-BETS and H.E.S.S.).

  19. Beam energy spread in FERMI@elettra gun and linac induced by intrabeam scattering

    SciTech Connect

    Zholents, Alexander A; Zholents, Alexander A; Zolotorev, Max S.; Penco, Giuseppe

    2008-07-11

    Intrabeam scattering (IBS) of electrons in the pre-cathode area in the electron guns know in the literature as Boersh effect is responsible for a growth of the electron beam energy spread there. Albeit most visible within the electron gun where the electron beam density is large and the energy spread is small, the IBS acts all along the entire electron beam pass through the Linac. In this report we calculate the energy spread induced by IBS in the FERMI@elettra electron gun.

  20. Fermi energy 5f spectral weight variation in uranium alloys

    SciTech Connect

    Denlinger, J.D.; Clack, J.; Allen, J.W.

    1997-04-01

    Uranium materials display a wide range of thermal, electrical and magnetic properties, often exotic. For more than a decade there have been efforts to use photoemission spectroscopy to develop a systematic and unified understanding of the 5f electron states giving rise to this behavior. These efforts have been hampered by a paucity of systems where changes in transport properties are accompanied by substantial spectral changes, so as to allow an attempt to correlate the two kinds of properties within some model. The authors have made resonant photoemission measurements to extract the 5f spectral weight in three systems which show varying degrees of promise of permitting such an attempt, Y{sub 1{minus}x}U{sub x}Pd{sub 3}, U(Pd{sub x}Pt{sub 1{minus}x}){sub 3} and U(Pd{sub x}Cu{sub 1{minus}x}){sub 5}. They have also measured U 4f core level spectra. The 4f spectra can be modeled with some success by the impurity Anderson model (IAM), and the 5f spectra are currently being analyzed in that framework. The IAM characterizes the 5f-electrons of a single site by an f binding energy {epsilon}{sub f}, an f Coulomb interaction and a hybridization V to conduction electrons. Latent in the model are the phenomena of 5f mixed valence and the Kondo effect.

  1. New Results on High Energy Cosmic Ray Electrons Observed with Fermi LAT and Their Implications on the Models of Pulsars

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    This viewgraph presentation describes, in detail, the Fermi Large Area Telescope (LAT) and GLAST Burst Monitor (GBM). Observations made from the June 11, 2008 launch and a discussion of observations made of high energy cosmic ray electrons is also presented.

  2. Fermi Large Area Telescope observations of high-energy gamma-ray emission from Solar flares

    NASA Astrophysics Data System (ADS)

    Pesce Rollins, Melissa

    2017-01-01

    The Fermi Large Area Telescope (LAT) observations of the active Sun provide the largest sample of detected solar flares with emission greater than 30 MeV to date. These include detections of impulsive and sustained emission, extending up to 20 hours in the case of the 2012 March 7 X-class flares. These high-energy flares are coincident with GOES X-ray flares of X, M and C classes as well as very fast Coronal Mass Ejections (CME). We will present results from the First Fermi-LAT solar flare catalog covering the majority of Solar Cycle 24 including correlation studies with the associated Solar Energetic Particles (SEP) and CMEs.

  3. On directly measuring relative Fermi energies of noble metals and their alloys

    NASA Astrophysics Data System (ADS)

    Kleiman, G. G.; Sundaram, V. S.; Rogers, J. D.

    1981-09-01

    We present the first evidence of direct measurement of relative Fermi energies in alloys and between pure metals. From applying the "atomic" concept of core hole final state screening, the Auger energy shift of noble metal A equals EFA- EF( x). High resolution Auger shifts in P1- xtCux, AuxCu1- x and AuxAg1- x demonstrate experimental verification of this simple relation. We find E FCuE FAu ≅ - 0.2 eV, and E FPt ≅ E FCu and E FAg ≅ E FAu.

  4. FAINT HIGH-ENERGY GAMMA-RAY PHOTON EMISSION OF GRB 081006A FROM FERMI OBSERVATIONS

    SciTech Connect

    Zheng Weikang; Akerlof, Carl W.; Pandey, Shashi B.; McKay, Timothy A.; Zhang Binbin; Zhang Bing

    2012-01-20

    Since the launch of the Fermi Gamma-ray Space Telescope on 2008 June 11, the Large Area Telescope (LAT) instrument has firmly detected more than 20 gamma-ray bursts (GRBs) with high-energy photon emission above 100 MeV. Using the matched filter technique, three more GRBs have also shown evidence of correlation with high-energy photon emission as demonstrated by Akerlof et al. In this paper, we present another GRB, GRB 081006A, unambiguously detected by the matched filter technique. This event is associated with more than 13 high-energy photons above 100 MeV. The likelihood analysis code provided by the Fermi Science Support Center generated an independent verification of this detection using a comparison of the test statistics value with similar calculations for random LAT data fields. We have performed detailed temporal and spectral analysis of photons from 8 keV up to 0.8 GeV from the Gamma-ray Burst Monitor and the LAT. The properties of GRB 081006A can be compared to those of the other two long-duration GRBs detected at similar significance, GRB 080825C and GRB 090217A. We find that GRB 081006A is more similar to GRB 080825C with comparable appearances of late high-energy photon emission. As demonstrated previously, there appears to be a surprising dearth of faint LAT GRBs, with only one additional GRB identified in a sample of 74. In this unique period when both Swift and Fermi are operational, there is some urgency to explore this aspect of GRBs as fully as possible.

  5. Effect of the Fermi surface reconstruction on the self-energy of the copper-oxide superconductors

    NASA Astrophysics Data System (ADS)

    Bellafi, B.; Azzouz, M.; Charfi-Kaddour, S.

    2014-11-01

    We calculated the self-energy corrections beyond the mean-field solution of the rotating antiferromagnetism theory using the functional integral approach. The frequency dependence of the scattering rate 1 / τ is evaluated for different temperatures and doping levels, and is compared with other approaches. The general trends we found are fairly consistent with the nearly antiferromagnetic Fermi liquid as far as the k -anisotropy and some aspects of the marginal-Fermi liquid behavior are concerned. The present approach provides the justification from the microscopic point of view for the phenomenology of the marginal Fermi liquid ansatz, which was used in the calculation of several physical properties of the high-TC cuprates within the rotating antiferromagnetism theory. In addition, the expression of self-energy we calculated takes into account the two currently hot issues of the high-TC cuprate superconductors, namely the Fermi surface reconstruction and the hidden symmetry, which are closely related to the pseudogap.

  6. Fermi-LAT Observations of High-energy Behind-the-limb Solar Flares

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Allafort, A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Bonino, R.; Bottacini, E.; Bregeon, J.; Bruel, P.; Buehler, R.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Ciprini, S.; Costanza, F.; Cutini, S.; D’Ammando, F.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Drell, P. S.; Favuzzi, C.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Giglietto, N.; Giordano, F.; Giroletti, M.; Grenier, I. A.; Guillemot, L.; Guiriec, S.; Jogler, T.; Jóhannesson, G.; Kashapova, L.; Krucker, S.; Kuss, M.; La Mura, G.; Larsson, S.; Latronico, L.; Li, J.; Liu, W.; Longo, F.; Loparco, F.; Lubrano, P.; Magill, J. D.; Maldera, S.; Manfreda, A.; Mazziotta, M. N.; Mitthumsiri, W.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Negro, M.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orlando, E.; Pal’shin, V.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Principe, G.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, O.; Rubio da Costa, F.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Tajima, H.; Thayer, J. B.; Torres, D. F.; Troja, E.; Vianello, G.

    2017-02-01

    We report on the Fermi-LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi-LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO. All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwave spectra. We also provide a comparison of the BTL flares detected by Fermi-LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. The protons are believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.

  7. Fermi level pinning and the charge transfer contribution to the energy of adsorption at semiconducting surfaces

    SciTech Connect

    Krukowski, Stanisław; Kempisty, Paweł; Strak, Paweł; Sakowski, Konrad

    2014-01-28

    It is shown that charge transfer, the process analogous to formation of semiconductor p-n junction, contributes significantly to adsorption energy at semiconductor surfaces. For the processes without the charge transfer, such as molecular adsorption of closed shell systems, the adsorption energy is determined by the bonding only. In the case involving charge transfer, such as open shell systems like metal atoms or the dissociating molecules, the energy attains different value for the Fermi level differently pinned. The Density Functional Theory (DFT) simulation of species adsorption at different surfaces, such as SiC(0001) or GaN(0001) confirms these predictions: the molecular adsorption is independent on the coverage, while the dissociative process adsorption energy varies by several electronvolts.

  8. Fermi energy tuning with light to control doping profiles during epitaxy

    SciTech Connect

    Sanders, C. E.; Beaton, D. A.; Reedy, R. C.; Alberi, K.

    2015-05-04

    The influence of light stimulation and photogenerated carriers on the process of dopant surface segregation during growth is studied in molecular beam epitaxially grown Si-doped GaAs structures. The magnitude of surface segregation decreases under illumination by above-bandgap photons, wherein splitting of the quasi Fermi levels reduces the band bending at the growth surface and raises the formation energy of compensating defects that can enhance atomic diffusion. We further show that light-stimulated epitaxy can be used as a practical approach to diminish dopant carry-forward in device structures and improve the performance of inverted modulation-doped quantum wells.

  9. Stochastic Fermi Energization of Coronal Plasma during Explosive Magnetic Energy Release

    NASA Astrophysics Data System (ADS)

    Pisokas, Theophilos; Vlahos, Loukas; Isliker, Heinz; Tsiolis, Vassilis; Anastasiadis, Anastasios

    2017-02-01

    The aim of this study is to analyze the interaction of charged particles (ions and electrons) with randomly formed particle scatterers (e.g., large-scale local “magnetic fluctuations” or “coherent magnetic irregularities”) using the setup proposed initially by Fermi. These scatterers are formed by the explosive magnetic energy release and propagate with the Alfvén speed along the irregular magnetic fields. They are large-scale local fluctuations (δB/B ≈ 1) randomly distributed inside the unstable magnetic topology and will here be called Alfvénic Scatterers (AS). We constructed a 3D grid on which a small fraction of randomly chosen grid points are acting as AS. In particular, we study how a large number of test particles evolves inside a collection of AS, analyzing the evolution of their energy distribution and their escape-time distribution. We use a well-established method to estimate the transport coefficients directly from the trajectories of the particles. Using the estimated transport coefficients and solving the Fokker–Planck equation numerically, we can recover the energy distribution of the particles. We have shown that the stochastic Fermi energization of mildly relativistic and relativistic plasma can heat and accelerate the tail of the ambient particle distribution as predicted by Parker & Tidman and Ramaty. The temperature of the hot plasma and the tail of the energetic particles depend on the mean free path (λsc) of the particles between the scatterers inside the energization volume.

  10. A Method for Localizing Energy Dissipation in Blazars Using Fermi Variability

    NASA Technical Reports Server (NTRS)

    Dotson, Amanda; Georganopoulos, Markos; Kazanas, Demosthenes; Perlman, Eric S.

    2013-01-01

    The distance of the Fermi-detected blazar gamma-ray emission site from the supermassive black hole is a matter of active debate. Here we present a method for testing if the GeV emission of powerful blazars is produced within the sub-pc scale broad line region (BLR) or farther out in the pc-scale molecular torus (MT) environment. If the GeV emission takes place within the BLR, the inverse Compton (IC) scattering of the BLR ultraviolet (UV) seed photons that produces the gamma-rays takes place at the onset of the Klein-Nishina regime. This causes the electron cooling time to become practically energy independent and the variation of the gamma-ray emission to be almost achromatic. If on the other hand the -ray emission is produced farther out in the pc-scale MT, the IC scattering of the infrared (IR) MT seed photons that produces the gamma-rays takes place in the Thomson regime, resulting to energy-dependent electron cooling times, manifested as faster cooling times for higher Fermi energies. We demonstrate these characteristics and discuss the applicability and limitations of our method.

  11. A MULTIWAVELENGTH STUDY ON THE HIGH-ENERGY BEHAVIOR OF THE FERMI/LAT PULSARS

    SciTech Connect

    Marelli, Martino; Luca, Andrea De; Caraveo, Patrizia A.

    2011-06-01

    Using archival as well as freshly acquired data, we assess the X-ray behavior of the Fermi/Large Area Telescope {gamma}-ray pulsars listed in the First Fermi source catalog. After revisiting the relationships between the pulsars' rotational energy losses and their X-ray and {gamma}-ray luminosities, we focus on the distance-independent {gamma}-to-X-ray flux ratios. When plotting our F{sub {gamma}}/F{sub X} values as a function of the pulsars' rotational energy losses, one immediately sees that pulsars with similar energetics have F{sub {gamma}}/F{sub X} spanning three decades. Such spread, most probably stemming from vastly different geometrical configurations of the X-ray and {gamma}-ray emitting regions, defies any straightforward interpretation of the plot. Indeed, while energetic pulsars do have low F{sub {gamma}}/F{sub X} values, little can be said for the bulk of the Fermi neutron stars. Dividing our pulsar sample into radio-loud and radio-quiet subsamples, we find that, on average, radio-quiet pulsars do have higher values of F{sub {gamma}}/F{sub X}, implying an intrinsic faintness of their X-ray emission and/or a different geometrical configuration. Moreover, despite the large spread mentioned above, statistical tests show a lower scatter in the radio-quiet data set with respect to the radio-loud one, pointing to a somewhat more constrained geometry for the radio-quiet objects with respect to the radio-loud ones.

  12. FERMI-LAT OBSERVATIONS OF HIGH-ENERGY γ-RAY EMISSION TOWARD THE GALACTIC CENTER

    SciTech Connect

    Ajello, M.; Albert, A.; Blandford, R. D.; Bloom, E. D.; Bottacini, E.; Caliandro, G. A.; Cameron, R. A.; Atwood, W. B.; Caputo, R.; Barbiellini, G.; Bastieri, D.; Buson, S.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Bonino, R.; Brandt, T. J.; Bregeon, J.; and others

    2016-03-01

    The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy γ-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1–100 GeV from a 15° × 15° region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the γ-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner ∼1 kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15° × 15° region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC are used to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM.

  13. Pulsar Astrophysics at Very High Energies in the Fermi-HAWC Era

    NASA Astrophysics Data System (ADS)

    Saz Parkinson, Pablo; Belfiore, A.; HAWC Collaboration; Fermi LAT Collaboration

    2013-04-01

    Pulsar astrophysics has received a major boost in recent years with the tremendous progress achieved in the gamma-ray regime. In the 0.1-100 GeV energy range, where pulsars emit a large fraction of their energy, the Fermi Large Area Telescope (LAT) is providing an abundance of high-quality data, greatly improving our understanding of the pulsar mechanism. In addition to detecting over 120 pulsars, the improved statistics from the LAT have enabled studies of some of the brightest pulsars with exquisite detail, up to unprecedented energies (in some cases above 25 GeV), finally bridging the gap with ground-based instruments. At very high energies (VHE, > 100 GeV), recent detections by VERITAS and MAGIC of pulsations from the Crab pose a serious challenge to pulsar models. It is unclear whether the Crab is unique in this respect, or whether VHE emission is common in other pulsars. Some models predict that such emission should smoothly connect with the standard GeV emission seen by the LAT, while others point instead to a different spectral (e.g. inverse Compton) component altogether. If present in other pulsars, such a component might be found at higher energies (> 1 TeV), but its flux is highly uncertain. Further VHE observations of pulsars are crucial to distinguish between (and constrain) the competing scenarios. The High Altitude Water Cherenkov Observatory (HAWC), currently under construction in Mexico, is well-suited to perform observations of pulsars above 100 GeV. The HAWC detector has a wide field of view, high duty cycle, and excellent sensitivity 15 times better than its predecessor Milagro), and its contemporaneous operation with Fermi should enable it to carry out the first comprehensive survey of northern-hemisphere gamma-ray pulsars above 100 GeV. I will discuss the motivations, goals, timeline, and sensitivity of HAWC searches for VHE emission from pulsars.

  14. Fermi Large Area Telescope Observations of Markarian 421: The Missing Piece of its Spectral Energy Distribution

    NASA Astrophysics Data System (ADS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Cannon, A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Escande, L.; Favuzzi, C.; Fegan, S. J.; Finke, J.; Focke, W. B.; Fortin, P.; Frailis, M.; Fuhrmann, L.; Fukazawa, Y.; Fukuyama, T.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Georganopoulos, M.; Germani, S.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Guiriec, S.; Hadasch, D.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kadler, M.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S.-H.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Max-Moerbeck, W.; Mazziotta, M. N.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann-Godo, M.; Nishino, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Pavlidou, V.; Pearson, T. J.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Readhead, A.; Reimer, A.; Reimer, O.; Reyes, L. C.; Richards, J. L.; Ritz, S.; Roth, M.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stawarz, Ł.; Stevenson, M.; Strickman, M. S.; Suson, D. J.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Wehrle, A. E.; Winer, B. L.; Wood, K. S.; Yang, Z.; Yatsu, Y.; Ylinen, T.; Zensus, J. A.; Ziegler, M.; Fermi LAT Collaboration; Aleksić, J.; Antonelli, L. A.; Antoranz, P.; Backes, M.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Berdyugin, A.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R. K.; Boller, A.; Bonnoli, G.; Bordas, P.; Borla Tridon, D.; Bosch-Ramon, V.; Bose, D.; Braun, I.; Bretz, T.; Camara, M.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Dazzi, F.; de Angelis, A.; De Cea del Pozo, E.; Delgado Mendez, C.; De Lotto, B.; De Maria, M.; De Sabata, F.; Diago Ortega, A.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Elsaesser, D.; Ferenc, D.; Fonseca, M. V.; Font, L.; García López, R. J.; Garczarczyk, M.; Gaug, M.; Giavitto, G.; Godinovi, N.; Hadasch, D.; Herrero, A.; Hildebrand, D.; Höhne-Mönch, D.; Hose, J.; Hrupec, D.; Jogler, T.; Klepser, S.; Krähenbühl, T.; Kranich, D.; Krause, J.; La Barbera, A.; Leonardo, E.; Lindfors, E.; Lombardi, S.; López, M.; Lorenz, E.; Majumdar, P.; Makariev, E.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Miyamoto, H.; Moldón, J.; Moralejo, A.; Nieto, D.; Nilsson, K.; Orito, R.; Oya, I.; Paoletti, R.; Paredes, J. M.; Partini, S.; Pasanen, M.; Pauss, F.; Pegna, R. G.; Perez-Torres, M. A.; Persic, M.; Peruzzo, J.; Pochon, J.; Prada, F.; Prada Moroni, P. G.; Prandini, E.; Puchades, N.; Puljak, I.; Reichardt, T.; Rhode, W.; Ribó, M.; Rico, J.; Rissi, M.; Rügamer, S.; Saggion, A.; Saito, K.; Saito, T. Y.; Salvati, M.; Sánchez-Conde, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shayduk, M.; Shore, S. N.; Sierpowska-Bartosik, A.; Sillanpää, A.; Sitarek, J.; Sobczynska, D.; Spanier, F.; Spiro, S.; Stamerra, A.; Steinke, B.; Storz, J.; Strah, N.; Struebig, J. C.; Suric, T.; Takalo, L. O.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Vankov, H.; Wagner, R. M.; Weitzel, Q.; Zabalza, V.; Zandanel, F.; Zanin, R.; MAGIC Collaboration; Villata, M.; Raiteri, C.; Aller, H. D.; Aller, M. F.; Chen, W. P.; Jordan, B.; Koptelova, E.; Kurtanidze, O. M.; Lähteenmäki, A.; McBreen, B.; Larionov, V. M.; Lin, C. S.; Nikolashvili, M. G.; Reinthal, R.; Angelakis, E.; Capalbi, M.; Carramiñana, A.; Carrasco, L.; Cassaro, P.; Cesarini, A.; Falcone, A.; Gurwell, M. A.; Hovatta, T.; Kovalev, Yu. A.; Kovalev, Y. Y.; Krichbaum, T. P.; Krimm, H. A.; Lister, M. L.; Moody, J. W.; Maccaferri, G.; Mori, Y.; Nestoras, I.; Orlati, A.; Pace, C.; Pagani, C.; Pearson, R.; Perri, M.; Piner, B. G.; Ros, E.; Sadun, A. C.; Sakamoto, T.; Tammi, J.; Zook, A.

    2011-08-01

    We report on the γ-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) γ-ray spectrum above 0.3 GeV can be well described by a power-law function with photon index Γ = 1.78 ± 0.02 and average photon flux F(> 0.3 GeV) = (7.23 ± 0.16) × 10-8 ph cm-2 s-1. Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor ~3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in γ-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.

  15. Searches for correlation between UHECR events and high-energy gamma­ray Fermi-LAT data

    NASA Astrophysics Data System (ADS)

    Mirabal, Nestor; Alvarez, Ezequiel; Cuoco, Alessandro; Zaharijas, Gabrijela; Fermi Collaboration

    2017-01-01

    The sources responsible for ultra high-energy cosmic rays (UHECRs) continue to be one of the most intriguing mysteries in astrophysics.We present a comprehensive search for correlations between high-energy (>= 1 GeV) gamma-ray events from the Fermi Large Area Telescope (LAT) and UHECRs (>= 60 EeV) detected by the Telescope Array and the Pierre Auger Observatory. We perform two separate searches. First, we conduct a standard cross-correlation analysis between the arrival directions of UHECRs and gamma-ray sources in the Second Catalog of Hard Fermi-LAT sources (2FHL). Second,we search for a possible correlation between UHECR directions and unresolved Fermi-LAT gamma-ray emission. We report our findings and their implications in the search for the origin of UHECRs.

  16. Statistical multifragmentation model with discretized energy and the generalized Fermi breakup: Formulation of the model

    NASA Astrophysics Data System (ADS)

    Souza, S. R.; Carlson, B. V.; Donangelo, R.; Lynch, W. G.; Tsang, M. B.

    2013-07-01

    The generalized Fermi breakup model, recently demonstrated to be formally equivalent to the statistical multifragmentation model, if the contribution of excited states is included in the state densities of the former, is implemented. Because this treatment requires application of the statistical multifragmentation model repeatedly on hot fragments until they have decayed to their ground states, it becomes extremely computationally demanding, making its application to the systems of interest extremely difficult. Based on exact recursion formulas previously developed by Chase and Mekjian to calculate statistical weights very efficiently, we present an implementation which is efficient enough to allow it to be applied to large systems at high excitation energies. Comparison with the gemini++ sequential decay code and the Weisskopf-Ewing evaporation model shows that the predictions obtained with our treatment are fairly similar to those obtained with these more traditional models.

  17. Constraining the High-Energy Emission from Gamma-Ray Bursts with Fermi

    NASA Technical Reports Server (NTRS)

    Gehrels, Neil; Harding, A. K.; Hays, E.; Racusin, J. L.; Sonbas, E.; Stamatikos, M.; Guirec, S.

    2012-01-01

    We examine 288 GRBs detected by the Fermi Gamma-ray Space Telescope's Gamma-ray Burst Monitor (GBM) that fell within the field-of-view of Fermi's Large Area Telescope (LAT) during the first 2.5 years of observations, which showed no evidence for emission above 100 MeV. We report the photon flux upper limits in the 0.1-10 GeV range during the prompt emission phase as well as for fixed 30 s and 100 s integrations starting from the trigger time for each burst. We compare these limits with the fluxes that would be expected from extrapolations of spectral fits presented in the first GBM spectral catalog and infer that roughly half of the GBM-detected bursts either require spectral breaks between the GBM and LAT energy bands or have intrinsically steeper spectra above the peak of the nuF(sub v) spectra (E(sub pk)). In order to distinguish between these two scenarios, we perform joint GBM and LAT spectral fits to the 30 brightest GBM-detected bursts and find that a majority of these bursts are indeed softer above E(sub pk) than would be inferred from fitting the GBM data alone. Approximately 20% of this spectroscopic subsample show statistically significant evidence for a cut-off in their high-energy spectra, which if assumed to be due to gamma gamma attenuation, places limits on the maximum Lorentz factor associated with the relativistic outflow producing this emission. All of these latter bursts have maximum Lorentz factor estimates that are well below the minimum Lorentz factors calculated for LAT-detected GRBs, revealing a wide distribution in the bulk Lorentz factor of GRB outflows and indicating that LAT-detected bursts may represent the high end of this distribution.

  18. In-Flight Measurement of the Absolute Energy Scale of the Fermi Large Area Telescope

    SciTech Connect

    Ackermann, M.; Ajello, M.; Allafort, A.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bloom, E.D.; Bonamente, E.; Borgland, A.W.; Bouvier, A.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; /more authors..

    2012-09-20

    The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between {approx}6 and {approx}13 GeV with an estimated uncertainty of {approx}2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.

  19. In-Flight Measurement of the Absolute Energy Scale of the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Allafort, A.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Barbielini, G; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B,; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Gehrels, N.; Hays, E.; McEnery, J. E.; Thompson, D. J.; Troja, E. J.

    2012-01-01

    The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron- plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between approx. 6 and approx. 13 GeV with an estimated uncertainty of approx. 2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.

  20. Data cleaning in the energy domain

    NASA Astrophysics Data System (ADS)

    Akouemo Kengmo Kenfack, Hermine N.

    This dissertation addresses the problem of data cleaning in the energy domain, especially for natural gas and electric time series. The detection and imputation of anomalies improves the performance of forecasting models necessary to lower purchasing and storage costs for utilities and plan for peak energy loads or distribution shortages. There are various types of anomalies, each induced by diverse causes and sources depending on the field of study. The definition of false positives also depends on the context. The analysis is focused on energy data because of the availability of data and information to make a theoretical and practical contribution to the field. A probabilistic approach based on hypothesis testing is developed to decide if a data point is anomalous based on the level of significance. Furthermore, the probabilistic approach is combined with statistical regression models to handle time series data. Domain knowledge of energy data and the survey of causes and sources of anomalies in energy are incorporated into the data cleaning algorithm to improve the accuracy of the results. The data cleaning method is evaluated on simulated data sets in which anomalies were artificially inserted and on natural gas and electric data sets. In the simulation study, the performance of the method is evaluated for both detection and imputation on all identified causes of anomalies in energy data. The testing on utilities' data evaluates the percentage of improvement brought to forecasting accuracy by data cleaning. A cross-validation study of the results is also performed to demonstrate the performance of the data cleaning algorithm on smaller data sets and to calculate an interval of confidence for the results. The data cleaning algorithm is able to successfully identify energy time series anomalies. The replacement of those anomalies provides improvement to forecasting models accuracy. The process is automatic, which is important because many data cleaning processes

  1. Characterizing high-energy light curves of Fermi/LatGRBs - Oral Presentation

    SciTech Connect

    Gillette, Jarred

    2015-08-23

    A systematic analysis of the light curves of Gamma-Ray Burst (GRBs) with redshift and detected at high-energy (> 100 MeV) by Fermi/LAT has never been done before our work, because there were only a handful of detections. Now we have 20 of those, which we can use to characterize the GRBs in their rest frame. We compared a characteristic decay times Tc of GRBs with redshifts using the new "Pass8" data, and used a Crystal Ball function to parametrize GRB characteristics. An unexpected anti-correlation between Tc and the peak flux was observed. This means that brighter peaked GRBs have shorter durations. There is also no correlation between Tc and the decay index, which is one of the competing hypothesis on the origin of the high-energy emission. We did not observe any bimodality, which is seen in GRBs at lower energies.

  2. Characterizing high-energy light curves of Fermi/Lat GRBs

    SciTech Connect

    Gillette, Jarred

    2015-08-21

    A systematic analysis of the light curves of Gamma-Ray Burst (GRBs) with redshift and detected at high-energy (> 100 MeV) by Fermi/LAT has never been done before our work, because there were only a handful of detections. Now we have 20 of those, which we can use to characterize the GRBs in their rest frame. We compared a characteristic decay times Tc of GRBs with redshifts using the new “Pass 8” data, and used a Crystal Ball function to parametrize GRB characteristics. An unexpected anti-correlation between Tc and the peak flux was observed. This means that brighter peaked GRBs have shorter durations. There is also no correlation between the Tc and the decay index, which makes the anti-correlation with brightness more clear. This results appears to be consistent with the External Shock model, which is one of the competing hypothesis on the origin of the high-energy emission. We did not observe any bimodality, which is seen in GRBs at lower energies.

  3. High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars

    NASA Astrophysics Data System (ADS)

    Giroletti, M.; Massaro, F.; D'Abrusco, R.; Lico, R.; Burlon, D.; Hurley-Walker, N.; Johnston-Hollitt, M.; Morgan, J.; Pavlidou, V.; Bell, M.; Bernardi, G.; Bhat, R.; Bowman, J. D.; Briggs, F.; Cappallo, R. J.; Corey, B. E.; Deshpande, A. A.; Ewall-Rice, A.; Emrich, D.; Gaensler, B. M.; Goeke, R.; Greenhill, L. J.; Hazelton, B. J.; Hindson, L.; Kaplan, D. L.; Kasper, J. C.; Kratzenberg, E.; Feng, L.; Jacobs, D.; Kudryavtseva, N.; Lenc, E.; Lonsdale, C. J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Pindor, B.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, A. E. E.; Roshi, A.; Udaya Shankar, N.; Srivani, K. S.; Subrahmanyan, R.; Tingay, S. J.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.

    2016-04-01

    Context. Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies. Aims: We characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources. Methods: We cross-correlated the 6100 deg2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detected by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. Results: We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120-180 MHz) blazar spectral index is ⟨αlow⟩ = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources. Conclusions: Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population. Tables 5-7 are only available at the CDS via anonymous ftp to http

  4. Self-energy of an impurity in an ideal Fermi gas to second order in the interaction strength

    NASA Astrophysics Data System (ADS)

    Trefzger, Christian; Castin, Yvan

    2014-09-01

    We study in three dimensions the problem of a spatially homogeneous zero-temperature ideal Fermi gas of spin-polarized particles of mass m perturbed by the presence of a single distinguishable impurity of mass M. The interaction between the impurity and the fermions involves only the partial s wave through the scattering length a and has negligible range b compared to the inverse Fermi wave number 1/kF of the gas. Through the interactions with the Fermi gas the impurity gives birth to a quasiparticle, which will be here a Fermi polaron (or more precisely a monomeron). We consider the general case of an impurity moving with wave vector K ≠0: Then the quasiparticle acquires a finite lifetime in its initial momentum channel because it can radiate particle-hole pairs in the Fermi sea. A description of the system using a variational approach, based on a finite number of particle-hole excitations of the Fermi sea, then becomes inappropriate around K =0. We rely thus upon perturbation theory, where the small and negative parameter kFa→0- excludes any branches other than the monomeronic one in the ground state (as, e.g., the dimeronic one), and allows us a systematic study of the system. We calculate the impurity self-energy Σ(2)(K,ω) up to second order included in a. Remarkably, we obtain an analytical explicit expression for Σ(2)(K,ω), allowing us to study its derivatives in the plane (K,ω). These present interesting singularities, which in general appear in the third-order derivatives ∂3Σ(2)(K,ω). In the special case of equal masses, M =m, singularities appear already in the physically more accessible second-order derivatives ∂2Σ(2)(K,ω); using a self-consistent heuristic approach based on Σ(2) we then regularize the divergence of the second-order derivative ∂K2ΔE(K) of the complex energy of the quasiparticle found in Trefzger and Castin [Europhys. Lett. 104, 50005 (2013), 10.1209/0295-5075/104/50005] at K =kF, and we predict an interesting scaling

  5. UV/IR mixing in non-Fermi liquids: higher-loop corrections in different energy ranges

    NASA Astrophysics Data System (ADS)

    Mandal, Ipsita

    2016-12-01

    We revisit the Ising-nematic quantum critical point with an m-dimensional Fermi surface by applying a dimensional regularization scheme, introduced in [I. Mandal, S.S. Lee, Phys. Rev. B 92, 035141 (2015)]. We compute the contribution from two-loop and three-loop diagrams in the intermediate energy range controlled by a crossover scale. We find that for m = 2, the corrections continue to be one-loop exact for both the infrared and intermediate energy regimes.

  6. Testing the nonlocal kinetic energy functional of an inhomogeneous, two-dimensional degenerate Fermi gas within the average density approximation

    NASA Astrophysics Data System (ADS)

    Towers, J.; van Zyl, B. P.; Kirkby, W.

    2015-08-01

    In a recent paper [B. P. van Zyl et al., Phys. Rev. A 89, 022503 (2014), 10.1103/PhysRevA.89.022503], the average density approximation (ADA) was implemented to develop a parameter-free, nonlocal kinetic energy functional to be used in the orbital-free density functional theory of an inhomogeneous, two-dimensional (2D) Fermi gas. In this work, we provide a detailed comparison of self-consistent calculations within the ADA with the exact results of the Kohn-Sham density functional theory and the elementary Thomas-Fermi (TF) approximation. We demonstrate that the ADA for the 2D kinetic energy functional works very well under a wide variety of confinement potentials, even for relatively small particle numbers. Remarkably, the TF approximation for the kinetic energy functional, without any gradient corrections, also yields good agreement with the exact kinetic energy for all confining potentials considered, although at the expense of the spatial and kinetic energy densities exhibiting poor pointwise agreement, particularly near the TF radius. Our findings illustrate that the ADA kinetic energy functional yields accurate results for both the local and global equilibrium properties of an inhomogeneous 2D Fermi gas, without the need for any fitting parameters.

  7. Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoT e2

    NASA Astrophysics Data System (ADS)

    Sakano, M.; Bahramy, M. S.; Tsuji, H.; Araya, I.; Ikeura, K.; Sakai, H.; Ishiwata, S.; Yaji, K.; Kuroda, K.; Harasawa, A.; Shin, S.; Ishizaka, K.

    2017-03-01

    We investigate the surface electronic structures of polar 1 T'-MoT e2 , the Weyl semimetal candidate realized through the nonpolar-polar structural phase transition, by utilizing the laser angle-resolved photoemission spectroscopy combined with first-principles calculations. Two kinds of domains with different surface band dispersions are observed from a single-crystalline sample. The spin-resolved measurements further reveal that the spin polarizations of the surface and the bulk-derived states show the different domain dependences, indicating the opposite bulk polarity. For both domains, some segmentlike band features resembling the Fermi arcs are clearly observed. The patterns of the arcs present the marked contrast between the two domains, respectively agreeing well with the slab calculation of (0 0 1) and (0 0 -1) surfaces. The present result strongly suggests that the Fermi arc connects the identical pair of Weyl nodes on one side of the polar crystal surface, whereas it connects between the different pairs of Weyl nodes on the other side.

  8. Crystal growth nucleation and Fermi energy equalization of intrinsic spherical nuclei in glass-forming melts.

    PubMed

    Tournier, Robert F

    2009-02-01

    The energy saving resulting from the equalization of Fermi energies of a crystal and its melt is added to the Gibbs free-energy change ΔG2ls associated with a crystal formation in glass-forming melts. This negative contribution being a fraction ε ls(T) of the fusion heat is created by the electrostatic potential energy -U0 resulting from the electron transfer from the crystal to the melt and is maximum at the melting temperature Tm in agreement with a thermodynamics constraint. The homogeneous nucleation critical temperature T2, the nucleation critical barrier ΔG2ls∗/kBT and the critical radius R∗2ls are determined as functions of εls(T). In bulk metallic glass forming melts, εls(T) and T2 only depend on the free-volume disappearance temperature T0l, and εls(Tm) is larger than 1 (T0l>Tm/3); in conventional undercooled melts εls(Tm) is smaller than 1 (T0l>Tm/3). Unmelted intrinsic crystals act as growth nuclei reducing ΔG2ls∗/kBT and the nucleation time. The temperature-time transformation diagrams of Mg65Y10Cu25, Zr41.2Ti13.8Cu12.5Ni10Be22.5, Pd43Cu27 Ni10P20, Fe83B17 and Ni melts are predicted using classic nucleation models including time lags in transient nucleation, by varying the intrinsic nucleus contribution to the reduction of ΔG2ls∗/kBT. The energy-saving coefficient ε nm(T) of an unmelted crystal of radius Rnm is reduced when Rnm ≪R∗2ls; εnm is quantified and corresponds to the first energy level of one s-electron moving in vacuum in the same spherical attractive potential -U0 despite the fact that the charge screening is built by many-body effects.

  9. Energy localization on q-tori, long-term stability, and the interpretation of Fermi-Pasta-Ulam recurrences.

    PubMed

    Christodoulidi, H; Efthymiopoulos, C; Bountis, T

    2010-01-01

    We focus on two approaches that have been proposed in recent years for the explanation of the so-called Fermi-Pasta-Ulam (FPU) paradox, i.e., the persistence of energy localization in the "low-q " Fourier modes of Fermi-Pasta-Ulam nonlinear lattices, preventing equipartition among all modes at low energies. In the first approach, a low-frequency fraction of the spectrum is initially excited leading to the formation of "natural packets" exhibiting exponential stability, while in the second, emphasis is placed on the existence of "q breathers," i.e., periodic continuations of the linear modes of the lattice, which are exponentially localized in Fourier space. Following ideas of the latter, we introduce in this paper the concept of " q-tori" representing exponentially localized solutions on low-dimensional tori and use their stability properties to reconcile these two approaches and provide a more complete explanation of the FPU paradox.

  10. Enrico Fermi

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Enrico Fermi was, of all the great physicists of the 20th century, among the most respected and admired. He was respected and admired because of his contributions to both theoretical and experimental physics, because of his leadership in discovering for mankind a powerful new source of energy, and above all, because of his personal character. He was always reliable and trustworthy. He had both of his feet on the ground all the time. He had great strength, but never threw his weight around. He did not play to the gallery. He did not practise one-up-manship. He exemplified, I always believe, the perfect Confucian gentleman...

  11. A CORRELATION BETWEEN THE HIGHEST ENERGY COSMIC RAYS AND NEARBY ACTIVE GALACTIC NUCLEI DETECTED BY FERMI

    SciTech Connect

    Nemmen, Rodrigo S.; Bonatto, Charles; Storchi-Bergmann, Thaisa

    2010-10-10

    We analyze the correlation of the positions of {gamma}-ray sources in the Fermi Large Area Telescope (LAT) First Source Catalog (1FGL) and the First LAT Active Galactic Nuclei (AGNs) Catalog (1LAC) with the arrival directions of ultra-high-energy cosmic rays (UHECRs) observed with the Pierre Auger Observatory, in order to investigate the origin of UHECRs. We find that Galactic sources and blazars identified in the 1FGL are not significantly correlated with UHECRs, while the 1LAC sources display a mild correlation (2.6{sigma} level) on an {approx}2.{sup 0}4 angular scale. When selecting only the 1LAC AGNs closer than 200 Mpc, we find a strong association (5.4{sigma}) between their positions and the directions of UHECRs on an {approx}17{sup 0} angular scale; the probability of the observed configuration being due to an isotropic flux of cosmic rays is 5 x 10{sup -8}. There is also a 5{sigma} correlation with nearby 1LAC sources on a 6.{sup 0}5 scale. We identify seven '{gamma}-ray loud' AGNs which are associated with UHECRs within {approx}17{sup 0} and are likely candidates for the production sites of UHECRs: Centaurus A, NGC 4945, ESO 323-G77, 4C+04.77, NGC 1218, RX J0008.0+1450, and NGC 253. We interpret these results as providing additional support to the hypothesis of the origin of UHECRs in nearby extragalactic objects. As the angular scales of the correlations are large, we discuss the possibility that intervening magnetic fields might be considerably deflecting the trajectories of the particles on their way to Earth.

  12. Isobaric yield ratios and the symmetry energy in heavy-ion reactions near the Fermi energy

    SciTech Connect

    Huang, M.; Chen, Z.; Kowalski, S.; Ma, Y. G.; Wada, R.; Hagel, K.; Barbui, M.; Bottosso, C.; Materna, T.; Natowitz, J. B.; Qin, L.; Rodrigues, M. R. D.; Sahu, P. K.; Keutgen, T.; Bonasera, A.; Wang, J.

    2010-04-15

    The relative isobaric yields of fragments produced in a series of heavy-ion-induced multifragmentation reactions have been analyzed in the framework of a modified Fisher model, primarily to determine the ratio of the symmetry energy coefficient to the temperature, a{sub sym}/T, as a function of fragment mass A. The extracted values increase from 5 to approx16 as A increases from 9 to 37. These values have been compared to the results of calculations using the antisymmetrized molecular dynamics (AMD) model together with the statistical decay code gemini. The calculated ratios are in good agreement with those extracted from the experiment. In contrast, the values extracted from the ratios of the primary isobars from the AMD model calculation are approx4 to 5 and show little variation with A. This observation indicates that the value of the symmetry energy coefficient derived from final fragment observables may be significantly different than the actual value at the time of fragment formation. The experimentally observed pairing effect is also studied within the same simulations. The Coulomb coefficient is also discussed.

  13. Searches for correlation between UHECR events and high-energy gamma-ray Fermi-LAT data

    NASA Astrophysics Data System (ADS)

    Álvarez, Ezequiel; Cuoco, Alessandro; Mirabal, Nestor; Zaharijas, Gabrijela

    2016-12-01

    The astrophysical sources responsible for ultra high-energy cosmic rays (UHECRs) continue to be one of the most intriguing mysteries in astrophysics. We present a comprehensive search for correlations between high-energy (gtrsim 1 GeV) gamma-ray events from the Fermi Large Area Telescope (LAT) and UHECRs (gtrsim 60 EeV) detected by the Telescope Array and the Pierre Auger Observatory. We perform two separate searches. First, we conduct a standard cross-correlation analysis between the arrival directions of 148 UHECRs and 360 gamma-ray sources in the Second Catalog of Hard Fermi-LAT sources (2FHL). Second, we search for a possible correlation between UHECR directions and unresolved Fermi-LAT gamma-ray emission. For the latter, we use three different methods: a stacking technique with both a model-dependent and model-independent background estimate, and a cross-correlation function analysis. We also test for statistically significant excesses in gamma rays from signal regions centered on Cen A and the Telescope Array hotspot. No significant correlation is found in any of the analyses performed, except a weak (lesssim 2σ) hint of signal with the correlation function method on scales ~ 1°. Upper limits on the flux of possible power-law gamma-ray sources of UHECRs are derived.

  14. Exploring biases in the measurement of Isotropic Equivalent Energies of Gamma-ray Bursts with the Fermi Telescope

    NASA Astrophysics Data System (ADS)

    Zoldak, Kimberly; Racusin, Judith L.; Kennefick, Julia D.

    2015-01-01

    This study is being performed to determine if isotropic equivalent energies, Eiso, measured for gamma-ray bursts are significantly biased by lack of high-energy gamma-ray photon data, leading to inconsistent best-fit spectral models which diverge at high energies. Isotropic equivalent energies are often measured between energies of 10 keV to 10 MeV and prior to the 2008 launch of Fermi, the BATSE gamma-ray burst telescope was limited to observable energies below 700 keV, missing ~90% of the integrated energy band. The brightest bursts often peak at energies exceeding previous detector thresholds, therefore missing large portions of a burst's fluence and leading to incorrect modeling of the spectral shape. Despite these limitations on accurately measuring the full energy output, correlations have emerged, treating Eiso as an intrinsic property with physical application to gamma-ray burst physics rather than an observational quantity. We explore the impact of detector truncation on Eiso by performing time-integrated analysis both with and without spectra from Fermi's high-energy Large Area Telescope (LAT). Preliminary results show that multiple models, providing good statistics, measure inconsistent isotropic equivalent energies for the same burst, and consistently underestimate the energy output when LAT data is excluded from the analysis. Exclusion of the LAT data leads to unconstrained high-energy spectral slopes of the Band function allowing for observer influence on the choice of how to constrain the slope or to accept a cutoff power-law as the better fit. This proves that correlations involving Eiso are currently biased by detector limitations and the true meaning of Eiso has yet to be determined.

  15. Kinetic-energy density functionals with nonlocal terms with the structure of the Thomas-Fermi functional

    SciTech Connect

    Garcia-Aldea, David; Alvarellos, J. E.

    2007-11-15

    We study two families of approximate nonlocal kinetic-energy functionals that include a full von Weizsaecker functional, and that have nonlocal terms with the mathematical structure of the Thomas-Fermi functional. The functionals recover the exact kinetic energy and the linear response function of a homogeneous electron system. The first family is a generalization of a successful previous nonlocal functional. The second family is proposed in the paper, and is designed to obtain functionals suitable for use in both localized and extended systems. Furthermore, this family has been designed to be evaluated by a single integration in momentum space when a constant reference density is used. The atomic total kinetic energies are in good agreement with the exact calculations. The kinetic-energy density corresponding to each functional has been assessed to control its quality. The results show that, in general, these functionals behave better than both the Thomas-Fermi and all semilocal generalized gradient approximation functionals when describing the kinetic-energy density of atoms, providing a better description of the nonlocal effects of the kinetic energy of electron systems.

  16. THE FERMI BUBBLE AS A SOURCE OF COSMIC RAYS IN THE ENERGY RANGE >10{sup 15} eV

    SciTech Connect

    Cheng, K.-S.; Chernyshov, D. O.; Dogiel, V. A.; Ko, C.-M.; Wang, Y.; Ip, W.-H.

    2012-02-20

    The Fermi Large Area Telescope has recently discovered two giant gamma-ray bubbles that extend north and south of the Galactic center with diameters and heights of the order of H {approx} 10 kpc. We suggest that the periodic star capture processes by the Galactic supermassive black hole Sgr A*, with a capture rate of {tau}{sup -1}{sub cap} {approx} 3 Multiplication-Sign 10{sup -5} yr{sup -1} and an energy release of W {approx} 3 Multiplication-Sign 10{sup 52} erg per capture, can result in hot plasma injecting into the Galactic halo at a wind velocity of u {approx} 10{sup 8} cm s{sup -1}. The periodic injection of hot plasma can produce a series of shocks. Energetic protons in the bubble are re-accelerated when they interact with these shocks. We show that for energy larger than E > 10{sup 15} eV, the acceleration process can be better described by the stochastic second-order Fermi acceleration. We propose that hadronic cosmic rays (CRs) within the 'knee' of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Re-acceleration of these particles in the Fermi Bubble produces CRs beyond the knee. With a mean CR diffusion coefficient in this energy range in the bubble D{sub B} {approx} 3 Multiplication-Sign 10{sup 30} cm{sup 2} s{sup -1}, we can reproduce the spectral index of the spectrum beyond the knee and within it. The conversion efficiency from shock energy of the bubble into CR energy is about 10%. This model provides a natural explanation of the observed CR flux, spectral indices, and matching of spectra at the knee.

  17. The Search for High Energy Extended Emission by Fermi-LAT from Swift-Localized Gamma-Ray Bursts

    SciTech Connect

    Chiang, J.; Racusin, J.L.; /NASA, Goddard

    2012-05-01

    The brighter Fermi-LAT bursts have exhibited emission at energies >0.1 GeV that persists as late as {approx}2 ks after the prompt phase has nominally ended. This so-called 'extended emission' could arise from continued activity of the prompt burst mechanism or it could be the start of a high energy afterglow component. The high energy extended emission seen by the LAT has typically followed a t{sup -}{gamma} power-law temporal decay where {gamma} {approx} 1.2-1.7 and has shown no strong indication of spectral evolution. In contrast, the prompt burst emission generally displays strong spectral variability and more complex temporal changes in the LAT band. This differing behavior suggests that the extended emission likely corresponds to an early afterglow phase produced by an external shock. In this study, we look for evidence of high energy extended emission from 145 Swift-localized GRBs that have occurred since the launch of Fermi. A majority of these bursts were either outside of the LAT field-of-view or were otherwise not detected by the LAT during the prompt phase. However, because of the scanning operation of the Fermi satellite, the long-lived extended emission of these bursts may be detectable in the LAT data on the {approx}few ks time scale. We will look for emission from individual bursts and will perform a stacking analysis in order to set bounds on this emission for the sample as a whole. The detection of such emission would have implications for afterglow models and for the overall energy budget of GRBs.

  18. Spectroscopic evidence for Fermi liquid-like energy and temperature dependence of the relaxation rate in the pseudogap phase of the cuprates.

    PubMed

    Mirzaei, Seyed Iman; Stricker, Damien; Hancock, Jason N; Berthod, Christophe; Georges, Antoine; van Heumen, Erik; Chan, Mun K; Zhao, Xudong; Li, Yuan; Greven, Martin; Barišić, Neven; van der Marel, Dirk

    2013-04-09

    Cuprate high-Tc superconductors exhibit enigmatic behavior in the nonsuperconducting state. For carrier concentrations near "optimal doping" (with respect to the highest Tcs) the transport and spectroscopic properties are unlike those of a Landau-Fermi liquid. On the Mott-insulating side of the optimal carrier concentration, which corresponds to underdoping, a pseudogap removes quasi-particle spectral weight from parts of the Fermi surface and causes a breakup of the Fermi surface into disconnected nodal and antinodal sectors. Here, we show that the near-nodal excitations of underdoped cuprates obey Fermi liquid behavior. The lifetime τ(ω, T) of a quasi-particle depends on its energy ω as well as on the temperature T. For a Fermi liquid, 1/τ(ω, T) is expected to collapse on a universal function proportional to (ℏω)(2) + (pπk(B)T)(2). Magneto-transport experiments, which probe the properties in the limit ω = 0, have provided indications for the presence of a T(2) dependence of the dc (ω = 0) resistivity of different cuprate materials. However, Fermi liquid behavior is very much about the energy dependence of the lifetime, and this can only be addressed by spectroscopic techniques. Our optical experiments confirm the aforementioned universal ω- and T dependence of 1/τ(ω, T), with p ∼ 1.5. Our data thus provide a piece of evidence in favor of a Fermi liquid-like scenario of the pseudogap phase of the cuprates.

  19. Fermi LAT Results and Perspectives in Measurements of High Energy Galactic Cosmic Rays

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    Real breakthrough during last 1-1.5 years in cosmic ray electrons: ATIC, HESS, Pamela, and finally Fermi-LAT. New quality data have made it possible to start quantitative modeling. With the new data more puzzles than before on CR electrons origin. Need "multi-messenger" campaign: electrons, positrons, gammas, X-ray, radio, neutrino... It is viable that we are dealing with at least two distinct mechanisms of "primary" electron (both signs) production: a softer spectrum of negative electrons, and a harder spectrum of both e(+)+e(-). Exotic (e.g. DM) origin is not ruled out. Upper limits on CR electrons anisotropy are set. Good perspectives to have the Fermi LAT results on proton spectrum and positron fraction.

  20. Multimessenger study of the Fermi bubbles: Very high energy gamma rays and neutrinos

    NASA Astrophysics Data System (ADS)

    Lunardini, Cecilia; Razzaque, Soebur; Yang, Lili

    2015-07-01

    The Fermi bubbles have been imaged in sub-TeV gamma rays at Fermi-LAT, and, if their origin is hadronic, they might have been seen with low statistics in ˜0.1 - 1 PeV neutrinos at IceCube. We discuss the detectability of these objects at the new High Altitude Water Cherenkov (HAWC) gamma-ray detector. HAWC will view the north bubble for ˜2 - 3 hours a day and will map its spectrum at 0.1-100 TeV. For the hard primary proton spectrum required to explain five events at IceCube, a high significance detection at HAWC will be achieved in less than 30 days. The combination of results at HAWC and IceCube will substantiate the hadronic model, or constrain its spectral parameters.

  1. A new type of vanadium carbide V5C3 and its hardening by tuning Fermi energy

    NASA Astrophysics Data System (ADS)

    Xing, Wandong; Meng, Fanyan; Yu, Rong

    2016-03-01

    Transition metal compounds usually have various stoichiometries and crystal structures due to the coexistence of metallic, covalent, and ionic bonds in them. This flexibility provides a lot of candidates for materials design. Taking the V-C binary system as an example, here we report the first-principles prediction of a new type of vanadium carbide, V5C3, which has an unprecedented stoichiometry in the V-C system, and is energetically and mechanically stable. The material is abnormally much harder than neighboring compounds in the V-C phase diagram, and can be further hardened by tuning the Fermi energy.

  2. A new type of vanadium carbide V5C3 and its hardening by tuning Fermi energy

    PubMed Central

    Xing, Wandong; Meng, Fanyan; Yu, Rong

    2016-01-01

    Transition metal compounds usually have various stoichiometries and crystal structures due to the coexistence of metallic, covalent, and ionic bonds in them. This flexibility provides a lot of candidates for materials design. Taking the V-C binary system as an example, here we report the first-principles prediction of a new type of vanadium carbide, V5C3, which has an unprecedented stoichiometry in the V-C system, and is energetically and mechanically stable. The material is abnormally much harder than neighboring compounds in the V-C phase diagram, and can be further hardened by tuning the Fermi energy. PMID:26928719

  3. Millisecond Pulsars at Gamma-Ray Energies: Fermi Detections and Implications

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2011-01-01

    The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the discovery of new populations of radio quiet and millisecond gamma-ray pulsars. The Fermi Large Area Telescope has so far discovered approx.20 new gamma-ray millisecond pulsars (MSPs) by both folding at periods of known radio MSPs or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -30 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. Many of the newly discovered MSPs may be suitable for addition to the collection of very stable MSPs used for gravitational wave detection. Detection of such a large number of MSPs was surprising, given that most have relatively low spin-down luminosity and surface field strength. I will discuss their properties and the implications for pulsar particle acceleration and emission, as well as their potential contribution to gamma-ray backgrounds and Galactic cosmic rays.

  4. Microscopic calculations of heavy-residue formation in quasielastic and deep-inelastic collisions below the Fermi energy.

    NASA Astrophysics Data System (ADS)

    Souliotis, G. A.; Shetty, D. V.; Galanopoulos, S.; Yennello, S. J.

    2007-10-01

    During the last several years we have undertaken a systematic study of heavy residues formed in quasi-elastic and deep- inelastic collisions near and below the Fermi energy [1,2]. Presently, we are exploring the possibility of extracting information on the dynamics by comparing our heavy residue data to calculations using microscopic models based on the quantum molecular dynamics approach (QMD). We have performed detailed calculations of QMD type using the recent version of the constrained molecular dynamics code CoMD of M. Papa [3]. CoMD is especially designed for reactions near the Fermi energy. It implements an effective interaction with a nuclear-matter compressibility of K=200 (soft EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential. CoMD imposes a constraint in the phase space occupation for each nucleon, thus restoring the Pauli principle at each time step of the collision. Results of the calculations and comparisons with our residue data will be presented and discussed in detail. [1] G.A. Souliotis et al., Phys. Rev. Lett. 91, 022701 (2003); Nucl. Instrum. Methods B 204 166 (2003). [2] G.A. Souliotis et al., Phys. Lett. B 588, 35 (2004). [3] M. Papa et al., Phys. Rev. C 64, 024612 (2001).

  5. Energy localization on q -tori, long-term stability, and the interpretation of Fermi-Pasta-Ulam recurrences

    NASA Astrophysics Data System (ADS)

    Christodoulidi, H.; Efthymiopoulos, C.; Bountis, T.

    2010-01-01

    We focus on two approaches that have been proposed in recent years for the explanation of the so-called Fermi-Pasta-Ulam (FPU) paradox, i.e., the persistence of energy localization in the “low- q ” Fourier modes of Fermi-Pasta-Ulam nonlinear lattices, preventing equipartition among all modes at low energies. In the first approach, a low-frequency fraction of the spectrum is initially excited leading to the formation of “natural packets” exhibiting exponential stability, while in the second, emphasis is placed on the existence of “ q breathers,” i.e., periodic continuations of the linear modes of the lattice, which are exponentially localized in Fourier space. Following ideas of the latter, we introduce in this paper the concept of “ q -tori” representing exponentially localized solutions on low-dimensional tori and use their stability properties to reconcile these two approaches and provide a more complete explanation of the FPU paradox.

  6. Looking for blazars in a sample of unidentified high-energy emitting Fermi sources

    NASA Astrophysics Data System (ADS)

    Marchesini, E. J.; Masetti, N.; Chavushyan, V.; Cellone, S. A.; Andruchow, I.; Bassani, L.; Bazzano, A.; Jiménez-Bailón, E.; Landi, R.; Malizia, A.; Palazzi, E.; Patiño-Álvarez, V.; Rodríguez-Castillo, G. A.; Stephen, J. B.; Ubertini, P.

    2016-11-01

    Context. Based on their overwhelming dominance among associated Fermi γ-ray catalogue sources, it is expected that a large fraction of the unidentified Fermi objects are blazars. Through crossmatching between the positions of unidentified γ-ray sources from the First Fermi Catalog of γ-ray sources emitting above 10 GeV (1FHL) and the ROSAT and Swift/XRT catalogues of X-ray objects and between pointed XRT observations, a sample of 36 potential associations was found in previous works with less than 15 arcsec of positional offset. One-third of them have recently been classified; the remainder, though believed to belong to the blazar class, still lack spectroscopic classifications. Aims: We study the optical spectrum of the putative counterparts of these unidentified gamma-ray sources in order to find their redshifts and to determine their nature and main spectral characteristics. Methods: An observational campaign was carried out on the putative counterparts of 13 1FHL sources using medium-resolution optical spectroscopy from the Osservatorio Astronomico di Bologna in Loiano, Italy; the Telescopio Nazionale Galileo and the Nordic Optical Telescope, both in the Canary Islands, Spain; and the Observatorio Astronómico Nacional San Pedro Mártir in Baja California, Mexico. Results: We were able to classify 14 new objects based on their continuum shapes and spectral features. Conclusions: Twelve new blazars were found, along with one new quasar and one new narrow line Seyfert 1 (NLS1) to be potentially associated with the 1FHL sources of our sample. Redshifts or lower limits were obtained when possible alongside central black hole mass and luminosity estimates for the NLS1 and the quasar.

  7. A New View of the High Energy Gamma-ray Sky with the Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2010-01-01

    This slide presentation reviews some of the findings that have been made possible by the use of the Fermi Gamma-ray Space Telescope. It describes the current status of the Fermi Telescope and reviews some of the science highlights.

  8. Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate

    PubMed Central

    Nataf, G. F.; Grysan, P.; Guennou, M.; Kreisel, J.; Martinotti, D.; Rountree, C. L.; Mathieu, C.; Barrett, N.

    2016-01-01

    The understanding of domain structures, specifically domain walls, currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM – electrons reflected) to Low Energy Electron Microscopy (LEEM – electrons backscattered) gives rise to a robust contrast between domains with upwards (Pup) and downwards (Pdown) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces, and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field. PMID:27608605

  9. Interaction energy and itinerant ferromagnetism in a strongly interacting Fermi gas in the absence of molecule formation

    SciTech Connect

    He, Lianyi

    2014-11-26

    In this study, we investigate the interaction energy and the possibility of itinerant ferromagnetism in a strongly interacting Fermi gas at zero temperature in the absence of molecule formation. The interaction energy is obtained by summing the perturbative contributions of Galitskii-Feynman type to all orders in the gas parameter. It can be expressed by a simple phase-space integral of an in-medium scattering phase shift. In both three and two dimensions (3D and 2D), the interaction energy shows a maximum before reaching the resonance from the Bose-Einstein condensate side, which provides a possible explanation of the experimental measurements of the interaction energy. This phenomenon can be theoretically explained by the qualitative change of the nature of the binary interaction in the medium. The appearance of an energy maximum has significant effects on the itinerant ferromagnetism. In 3D, the ferromagnetic transition is reentrant and itinerant ferromagnetism exists in a narrow window around the energy maximum. In 2D, the present theoretical approach suggests that itinerant ferromagnetism does not exist, which reflects the fact that the energy maximum becomes much lower than the energy of the fully polarized state.

  10. Interaction energy and itinerant ferromagnetism in a strongly interacting Fermi gas in the absence of molecule formation

    DOE PAGES

    He, Lianyi

    2014-11-26

    In this study, we investigate the interaction energy and the possibility of itinerant ferromagnetism in a strongly interacting Fermi gas at zero temperature in the absence of molecule formation. The interaction energy is obtained by summing the perturbative contributions of Galitskii-Feynman type to all orders in the gas parameter. It can be expressed by a simple phase-space integral of an in-medium scattering phase shift. In both three and two dimensions (3D and 2D), the interaction energy shows a maximum before reaching the resonance from the Bose-Einstein condensate side, which provides a possible explanation of the experimental measurements of the interactionmore » energy. This phenomenon can be theoretically explained by the qualitative change of the nature of the binary interaction in the medium. The appearance of an energy maximum has significant effects on the itinerant ferromagnetism. In 3D, the ferromagnetic transition is reentrant and itinerant ferromagnetism exists in a narrow window around the energy maximum. In 2D, the present theoretical approach suggests that itinerant ferromagnetism does not exist, which reflects the fact that the energy maximum becomes much lower than the energy of the fully polarized state.« less

  11. The spectral energy distribution of the core of Cen A with H.E.S.S. and Fermi-LAT

    NASA Astrophysics Data System (ADS)

    Magill, Jeff; Prokhorov, Dmitry; Becherini, Yvonne; Buson, Sara; Gasparini, Dario; Perkins, Jeremy; Tanaka, Yasuyuki; H. E. S. S. Collaboration; Fermi-LAT Collaboration

    2017-01-01

    Cen A, the nearest radio galaxy, was detected as a faint emitter of very high energy (VHE) gamma rays by the H.E.S.S. telescopes in Namibia. The flux derived from the H.E.S.S. data is much higher than that expected from a single zone synchrotron self-Compton model, which adequately describes the emission from Cen A at lower frequencies. New observations with H.E.S.S. were performed to clarify the spectral characteristics of the VHE emission from Cen A. We report the results of the analysis of the complete H.E.S.S. dataset with twice the live time of the previously published spectrum and an update of the Cen A spectrum obtained with Fermi-LAT at GeV energies.

  12. Gamma-ray astronomy: From Fermi up to the HAWC high-energy γ-ray observatory in Sierra Negra

    NASA Astrophysics Data System (ADS)

    Carramiñana, Alberto; HAWC Collaboration

    2013-06-01

    Gamma-rays represent the most energetic electromagnetic window for the study of the Universe. They are studied both from space at MeV and GeV energies, with instruments like the Fermi γ-ray Space Telescope, and at TeV energies with ground based instruments profiting of particle cascades in the atmosphere and of the Čerenkov radiation of charged particles in the air or in water. The Milagro gamma-ray observatory represented the first instrument to successfully implement the water Čerenkov technique for γ-ray astronomy, opening the ground for the more sensitive HAWC γ-ray observatory, currently under development in the Sierra Negra site and already providing early science results.

  13. Gamma-ray astronomy: From Fermi up to the HAWC high-energy {gamma}-ray observatory in Sierra Negra

    SciTech Connect

    Carraminana, Alberto; Collaboration: HAWC Collaboration

    2013-06-12

    Gamma-rays represent the most energetic electromagnetic window for the study of the Universe. They are studied both from space at MeV and GeV energies, with instruments like the Fermi{gamma}-ray Space Telescope, and at TeV energies with ground based instruments profiting of particle cascades in the atmosphere and of the Cerenkov radiation of charged particles in the air or in water. The Milagro gamma-ray observatory represented the first instrument to successfully implement the water Cerenkov technique for {gamma}-ray astronomy, opening the ground for the more sensitive HAWC {gamma}-ray observatory, currently under development in the Sierra Negra site and already providing early science results.

  14. Fermi Large Area Telescope Observations of High-Energy Gamma-ray Emission From Behind-the-limb Solar Flares

    NASA Astrophysics Data System (ADS)

    Omodei, Nicola; Pesce-Rollins, Melissa; Petrosian, Vahe; Liu, Wei; Rubio da Costa, Fatima; Golenetskii, Sergei; Kashapova, Larisa; Krucker, Sam; Palshin, Valentin; Fermi Large Area Telescope Collaboration

    2017-01-01

    Fermi LAT >30 MeV observations of the active Sun have increased the number of detected solar flares by almost a factor of 10 with respect to previous space observations. Of particular interest are the recent detections of three solar flares whose position behind the limb was confirmed by the STEREO-B spacecraft. These observations sample flares from active regions originating from behind both the eastern and western limbs and include an event associated with the second ground level enhancement event (GLE) of the 24th Solar Cycle. While gamma-ray emission up to tens of MeV resulting from proton interactions has been detected before from occulted solar flares, the significance of these particular events lies in the fact that these are the first detections of >100 MeV gamma-ray emission from footpoint-occulted flares. These detections present an unique opportunity to diagnose the mechanisms of high-energy emission and particle acceleration and transport in solar flares. We will present the Fermi-LAT, RHESSI and STEREO observations of these flares and discuss the various emission scenarios for these sources.

  15. Fermi at Six Months

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2009-01-01

    An overview of the Fermi Gamma-ray Space Telescope's first 6 months in operation is provided. The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy rage 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. It contains a Large Area Telescope capable of viewing the entire sky every 3 hours and a Gamma-ray Burst Monitor for viewing the entire unocculted sky. Since its launch on June 11, 2008 Fermi has provided information on pulsars, gamma ray bursts, relativistic jets, the active galactic nucleus, and a globular star cluster. This presentation describes Fermi's development, mission, instruments and recent findings.

  16. Discussion on the energy content of the galactic dark matter Bose-Einstein condensate halo in the Thomas-Fermi approximation

    SciTech Connect

    De Souza, J.C.C.; Pires, M.O.C. E-mail: marcelo.pires@ufabc.edu.br

    2014-03-01

    We show that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate [6] trapped by a self-graviting potential [5], may be stable in the Thomas-Fermi approximation since appropriate choices for the dark matter particle mass and scattering length are made. The demonstration is performed by means of the calculation of the potential, kinetic and self-interaction energy terms of a galactic halo described by a Boehmer-Harko density profile. We discuss the validity of the Thomas-Fermi approximation for the halo system, and show that the kinetic energy contribution is indeed negligible.

  17. Chiral non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Sur, Shouvik; Lee, Sung-Sik

    2014-07-01

    A non-Fermi liquid state without time-reversal and parity symmetries arises when a chiral Fermi surface is coupled with a soft collective mode in two space dimensions. The full Fermi surface is described by a direct sum of chiral patch theories, which are decoupled from each other in the low-energy limit. Each patch includes low-energy excitations near a set of points on the Fermi surface with a common tangent vector. General patch theories are classified by the local shape of the Fermi surface, the dispersion of the critical boson, and the symmetry group, which form the data for distinct universality classes. We prove that a large class of chiral non-Fermi liquid states exists as stable critical states of matter. For this, we use a renormalization group scheme where low-energy excitations of the Fermi surface are interpreted as a collection of (1+1)-dimensional chiral fermions with a continuous flavor labeling the momentum along the Fermi surface. Due to chirality, the Wilsonian effective action is strictly UV finite. This allows one to extract the exact scaling exponents although the theories flow to strongly interacting field theories at low energies. In general, the low-energy effective theory of the full Fermi surface includes patch theories of more than one universality classes. As a result, physical responses include multiple universal components at low temperatures. We also point out that, in quantum field theories with extended Fermi surface, a noncommutative structure naturally emerges between a coordinate and a momentum which are orthogonal to each other. We show that the invalidity of patch description for Fermi liquid states is tied with the presence of UV/IR mixing associated with the emergent noncommutativity. On the other hand, UV/IR mixing is suppressed in non-Fermi liquid states due to UV insensitivity, and the patch description is valid.

  18. Remembering Fermi

    SciTech Connect

    Cronin, James

    2005-03-30

    A combination of the discovery of nuclear fission and the circumstances of the 2nd World War brought Enrico Fermi to Chicago, where he led the team that produced the first controlled, self-sustained nuclear chain reaction. Following the war in 1945 Chancellor Hutchins, William Zachariasen, and Walter Bartky convinced Fermi to accept a professorship at the University of Chicago, where the Institute for Nuclear Studies was established. Fermi served as the leading figure in surely the greatest collection of scientists the world has ever seen. Fermi's tenure at Chicago was cut short by his death in 1954. My talk will concentrate on the years 1945-54. Examples of his research notebooks, his speeches, his teaching, and his correspondence will be discussed.

  19. NEW FERMI-LAT EVENT RECONSTRUCTION REVEALS MORE HIGH-ENERGY GAMMA RAYS FROM GAMMA-RAY BURSTS

    SciTech Connect

    Atwood, W. B.; Baldini, L.; Bregeon, J.; Pesce-Rollins, M.; Sgro, C.; Tinivella, M.; Bruel, P.; Cohen-Tanugi, J.; Granot, J.; Longo, F.; Razzaque, S.; Zimmer, S. E-mail: nicola.omodei@stanford.edu

    2013-09-01

    Based on the experience gained during the four and a half years of the mission, the Fermi-LAT Collaboration has undertaken a comprehensive revision of the event-level analysis going under the name of Pass 8. Although it is not yet finalized, we can test the improvements in the new event reconstruction with the special case of the prompt phase of bright gamma-ray bursts (GRBs), where the signal-to-noise ratio is large enough that loose selection cuts are sufficient to identify gamma rays associated with the source. Using the new event reconstruction, we have re-analyzed 10 GRBs previously detected by the Large Area Telescope (LAT) for which an X-ray/optical follow-up was possible and found four new gamma rays with energies greater than 10 GeV in addition to the seven previously known. Among these four is a 27.4 GeV gamma ray from GRB 080916C, which has a redshift of 4.35, thus making it the gamma ray with the highest intrinsic energy ({approx}147 GeV) detected from a GRB. We present here the salient aspects of the new event reconstruction and discuss the scientific implications of these new high-energy gamma rays, such as constraining extragalactic background light models, Lorentz invariance violation tests, the prompt emission mechanism, and the bulk Lorentz factor of the emitting region.

  20. Automatic Cloud Bursting under FermiCloud

    SciTech Connect

    Wu, Hao; Shangping, Ren; Garzoglio, Gabriele; Timm, Steven; Bernabeu, Gerard; Kim, Hyun Woo; Chadwick, Keith; Jang, Haengjin; Noh, Seo-Young

    2013-01-01

    Cloud computing is changing the infrastructure upon which scientific computing depends from supercomputers and distributed computing clusters to a more elastic cloud-based structure. The service-oriented focus and elasticity of clouds can not only facilitate technology needs of emerging business but also shorten response time and reduce operational costs of traditional scientific applications. Fermi National Accelerator Laboratory (Fermilab) is currently in the process of building its own private cloud, FermiCloud, which allows the existing grid infrastructure to use dynamically provisioned resources on FermiCloud to accommodate increased but dynamic computation demand from scientists in the domains of High Energy Physics (HEP) and other research areas. Cloud infrastructure also allows to increase a private cloud’s resource capacity through “bursting” by borrowing or renting resources from other community or commercial clouds when needed. This paper introduces a joint project on building a cloud federation to support HEP applications between Fermi National Accelerator Laboratory and Korea Institution of Science and Technology Information, with technical contributions from the Illinois Institute of Technology. In particular, this paper presents two recent accomplishments of the joint project: (a) cloud bursting automation and (b) load balancer. Automatic cloud bursting allows computer resources to be dynamically reconfigured to meet users’ demands. The load balance algorithm which the cloud bursting depends on decides when and where new resources need to be allocated. Our preliminary prototyping and experiments have shown promising success, yet, they also have opened new challenges to be studied

  1. Pauli-blocking effect in two-body collisions dominates the in-medium effects in heavy-ion reactions near Fermi energy

    NASA Astrophysics Data System (ADS)

    Xing, Yong-Zhong; Zhang, H. F.; Liu, Xiao-Bin; Zheng, Yu-Ming

    2017-01-01

    The dissipation phenomenon in the heavy-ion reaction at incident energy near Fermi energy is studied by simulating the reactions 129Xe + 129Sn and 58Ni + 58Ni with isospin-dependent quantum molecular dynamics model (IQMD). The isotropy ratio in terms of transverse and longitudinal energies of the free protons emitted in the final states of these reactions is quantitatively analyzed to explore the in-medium correlation of the binary collisions. Comparison of the calculations with the experimental data recently released by INDRA collaboration exhibits that the ratio is very sensitive to the Pauli blocking effect in two-body collisions and Pauli exclusion principle is indispensable in the theoretical simulations for the heavy-ion reactions near the Fermi energy.

  2. Theory of the Carrier Fermi Energy and Density of States of n- and p-TYPE SnTe

    NASA Astrophysics Data System (ADS)

    Das, R. K.; Mohapatro, S.

    In the present work we theoretically develop a kṡπ model to calculate the carrier electronic structure for both n- and p-type SnTe. Here π is the momentum operator in the presence of the spin-orbit interaction. The work is an extension of the theory developed for n- and p-PbTe earlier by one of the authors to evaluate the Fermi energy and the density of states (DOS). We consider a six-level energy basis for SnTe, as proposed by Bernick and Kleinman. One set of calculations was done by diagonalizing the kṡπ Hamiltonian matrix for the band-edge states and treating the far bands using perturbation theory. In the second set we have rediagonalized the kṡπ Hamiltonian matrix for the band edge states, treating the first diagonalization as the basis. The far bands are, as usual, included through perturbation. We have compared the results of both the sets. Results obtained for n- and p-type SnTe are also compared with that of n- and p-type PbTe. The similarities and contrasts are discussed. An indirect comparison with the DOS of the metallic tin suggests that the calculations are fairly reasonable. The results are also compared with some recent results for SnTe.

  3. Synchrotron Radiation from Ultra-High Energy Protons and the Fermi Observations of GRB 080916C

    DTIC Science & Technology

    2010-01-01

    when photopion processes are important, which will require IceCube neutrino detections [40] to establish. In GRB 080916C, where multi-GeV radiation...energy neutrinos from gamma ray bursts. Phys Rev Lett 2003; 91: 071102. [26] Asano K, Guiriec S, Mészáros P. Hadronic models for the extra spectral...of gamma-ray burst high-energy lags. Astrophys J 2009; 707: 404-16. [37] Murase K, Ioka K, Nagataki S, Nakamura T. High-Energy neutrinos and cosmic

  4. AHEAD: Integrated Activities in the High Energy Astrophysics Domain

    NASA Astrophysics Data System (ADS)

    Piro, Luigi; Natalucci, Lorenzo; Ahead Consortium

    2015-09-01

    AHEAD (Integrated Activities in the High Energy Astrophysics Domain) is a forthcoming project approved in the framework of the European Horizon 2020 program (Research Infrastructures for High Energy Astrophysics). The overall objective of AHEAD is to integrate national efforts in high-energy Astrophysics and to promote the domain at the European level, to keep its community at the cutting edge of science and technology and ensure that space observatories for high-energy astrophysics, with particular regard to Athena, are at the state of the art. AHEAD will integrate key research infrastructures for on-ground test and calibration of space-based sensors and electronics and promote their coordinated use. In parallel, the best facilities for data analysis of high-energy astrophysical observatories will be made available to the European community. The technological development will focus on the improvement of selected critical technologies, background modeling, cross calibration, and feasibility studies of space-based instrumentation for the benefit of future high energy missions like Athena, and the best exploitation of existing observatories. AHEAD will support the community via grants for collaborative studies, dissemination of results, and promotion of workshops. A strong public outreach package will ensure that the domain is well publicized at national, European and International level. Networking, joint research activities and access to infrastructures as devised in AHEAD, will serve to establish strong connections between institutes and industry to create the basis for a more rapid advancement of high-energy astrophysical science, space oriented instrumentation and cutting-edge sensor technology in Europe. This enables the development of new technologies and the associated growth of the European technology market with a dedicated technology innovation package, as well as the creation of a new generation of researchers.

  5. FermiGrid

    SciTech Connect

    Yocum, D.R.; Berman, E.; Canal, P.; Chadwick, K.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Sharma, N.; Timm, S.; /Fermilab

    2007-05-01

    As one of the founding members of the Open Science Grid Consortium (OSG), Fermilab enables coherent access to its production resources through the Grid infrastructure system called FermiGrid. This system successfully provides for centrally managed grid services, opportunistic resource access, development of OSG Interfaces for Fermilab, and an interface to the Fermilab dCache system. FermiGrid supports virtual organizations (VOs) including high energy physics experiments (USCMS, MINOS, D0, CDF, ILC), astrophysics experiments (SDSS, Auger, DES), biology experiments (GADU, Nanohub) and educational activities.

  6. Particle and light fragment emission in peripheral heavy ion collisions at Fermi energies

    SciTech Connect

    Piantelli, S.; Maurenzig, P. R.; Olmi, A.; Bardelli, L.; Bartoli, A.; Bini, M.; Casini, G.; Coppi, C.; Mangiarotti, A.; Pasquali, G.; Poggi, G.; Stefanini, A. A.; Taccetti, N.; Vanzi, E.

    2006-09-15

    A systematic investigation of the average multiplicities of light charged particles and intermediate mass fragments emitted in peripheral and semiperipheral collisions is presented as a function of the beam energy, violence of the collision, and mass of the system. The data have been collected with the FIASCO setup in the reactions {sup 93}Nb+{sup 93}Nb at (17,23,30,38)A MeV and {sup 116}Sn+{sup 116}Sn at (30,38)A MeV. The midvelocity emission has been separated from the emission of the projectile-like fragment. This last component appears to be compatible with an evaporation from an equilibrated source at normal density, as described by the statistical code GEMINI at the appropriate excitation energy. On the contrary, the midvelocity emission presents remarkable differences in both the dependence of the multiplicities on the energy deposited in the midvelocity region and the isotopic composition of the emitted light charged particles.

  7. Energetics of midvelocity emissions in peripheral heavy ion collisions at Fermi energies.

    PubMed

    Mangiarotti, A; Maurenzig, P R; Olmi, A; Piantelli, S; Bardelli, L; Bartoli, A; Bini, M; Casini, G; Coppi, C; Gobbi, A; Pasquali, G; Poggi, G; Stefanini, A A; Taccetti, N; Vanzi, E

    2004-12-03

    Peripheral and semiperipheral collisions have been studied in the system 93Nb+93Nb at 38A MeV. The evaporative and midvelocity components of the light charged particle and intermediate mass fragment emissions have been carefully disentangled. In this way it was possible to obtain the average amount not only of charge and mass, but also of energy, pertaining to the midvelocity emission, as a function of an impact parameter estimator. This emission has a very important role in the overall balance of the reaction, as it accounts for a large fraction of the emitted mass and for more than half of the dissipated energy. As such, it may give precious clues on the microscopic mechanism of energy transport from the interaction zone toward the target and projectile remnants.

  8. Production of exotic nuclei in projectile fragmentation at relativistic and Fermi energies

    NASA Astrophysics Data System (ADS)

    Ogul, R.; Ergun, A.; Buyukcizmeci, N.

    2017-02-01

    Isotopic distributions of projectile fragmentation in peripheral heavy ion collisions of 86Kr on 112Sn are calculated within the statistical multifragmentation model. Obtained data are compared to the experimental cross section measurements. We show the enhancement in the production of neutron-rich isotopes close to the projectile, observed in the experiments. Our results show the universality of the limitation of the excitation energy induced in the projectile residues.

  9. Apparent Low-Energy Scale Invariance in Two-Dimensional Fermi Gases

    NASA Astrophysics Data System (ADS)

    Taylor, Edward

    2013-05-01

    Strongly-interacting systems in two dimensions have occupied a central position in the study of quantum materials. From high temperature superconductors to the Hall effect in two-dimensional electron gases, strong quantum and thermal fluctuations conspire to make this an extremely rich yet poorly-understood regime to work in. Several remarkable and surprising recent experiments in ultracold atomic gases show us that there are puzzles to be understood even in the simplest nontrivial two-dimensional system: a dilute quantum gas with strong s-wave interactions. Amongst these is an experiment that finds an undamped breathing mode oscillating at twice the trap frequency over a wide range of parameters, behaviour nominally associated with scale invariance, even though scale invariance is strictly broken in this system by a finite s-wave scattering length. This apparent scale symmetry is all the more remarkable given that the mean-field BCS theory for the 2D gas predicts an exact low-energy scale invariance, relevant to the low-energy breathing mode, meaning that only quantum and thermal fluctuations can break this low-energy scale symmetry. Understanding why the symmetry breaking is so weak may give insight into how to make reliable theoretical predictions in systems with strong fluctuation effects, where there is no obvious small parameter from which a perturbation expansion can be formulated. Supported by NSF Grant No. DMR-1006532 (Mohit Randeria), NSERC, and the Canadian Institute for Advanced Research.

  10. Systematic study of neutron-rich rare isotope production in peripheral heavy-ion collisions below the Fermi energy

    NASA Astrophysics Data System (ADS)

    Fountas, P. N.; Souliotis, G. A.; Veselsky, M.; Bonasera, A.

    2014-12-01

    Detailed calculations of the yields of projectilelike fragments (with focus on the neutron-rich isotopes) are presented for the interaction of 86Kr (15 MeV/nucleon) with 64Ni, 58Ni, and 124Sn, 112Sn, as well as 86Kr (25 MeV/nucleon) with 124Sn and compared with our recently published experimental data for these reactions. The calculations are based on a two-step approach: the dynamical stage of the collision was described with the microscopic constrained molecular dynamics (CoMD) model, as well as the phenomenological deep-inelastic transfer (DIT) model and its modified (DITm) version. The deexcitation of the hot projectile fragments was performed with the statistical multifragmentation model (SMM) and the binary-decay model gemini, which provided nearly similar results for the neutron-rich products from the reactions studied. An overall good agreement of the calculations with the experimental results, especially for near-projectile isotopes was observed using both the CoMD model and the DITm model for the dynamical stage. The successful description of the production of neutron-rich isotopes with the CoMD model is of particular importance, due to the predictive power of the microscopic approach that essentially does not depend on the reaction dynamics. Our studies to date suggest that peripheral heavy-ion collisions at this energy range (i.e., well above the Coulomb barrier, but below the Fermi energy), if induced by neutron-rich rare-isotope beams of adequate intensity may offer a unique route to access extremely neutron-rich rare isotopes toward the astrophysical r -process path and the presently uncharted neutron drip line.

  11. Fermi LAT Observation of Diffuse Gamma-Rays Produced through Interactions Between Local Interstellar Matter and High Energy Cosmic Rays

    SciTech Connect

    Abdo, A.A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B.M.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bloom, E.D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Burnett, T.H.; /more authors..

    2012-03-30

    Observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse {gamma}-rays in a mid-latitude region in the third quadrant (Galactic longitude l from 200{sup o} to 260{sup o} and latitude |b| from 22{sup o} to 60{sup o}) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of {gamma}-ray point sources and inverse Compton scattering are estimated and subtracted. The residual {gamma}-ray intensity exhibits a linear correlation with the atomic gas column density in energy from 100 MeV to 10 GeV. The measured integrated {gamma}-ray emissivity is (1.63 {+-} 0.05) x 10{sup -26} photons s{sup -1}sr{sup -1} H-atom{sup -1} and (0.66 {+-} 0.02) x 10{sup -26} photons s{sup -1}sr{sup -1} H-atom{sup -1} above 100 MeV and above 300 MeV, respectively, with an additional systematic error of {approx}10%. The differential emissivity from 100 MeV to 10 GeV agrees with calculations based on cosmic ray spectra consistent with those directly measured, at the 10% level. The results obtained indicate that cosmic ray nuclei spectra within 1 kpc from the solar system in regions studied are close to the local interstellar spectra inferred from direct measurements at the Earth within {approx}10%.

  12. A non-Boltzmannian behavior of the energy distribution for quasi-stationary regimes of the Fermi-Pasta-Ulam β system

    NASA Astrophysics Data System (ADS)

    Leo, Mario; Leo, Rosario Antonio; Tempesta, Piergiulio

    2013-06-01

    In a recent paper [M. Leo, R.A. Leo, P. Tempesta, C. Tsallis, Phys. Rev. E 85 (2012) 031149], the existence of quasi-stationary states for the Fermi-Pasta-Ulam β system has been shown numerically, by analyzing the stability properties of the N/4-mode exact nonlinear solution. Here we study the energy distribution of the modes N/4, N/3 and N/2, when they are unstable, as a function of N and of the initial excitation energy. We observe that the classical Boltzmann weight is replaced by a different weight, expressed by a q-exponential function.

  13. 75 FR 24755 - DTE ENERGY; Enrico Fermi Atomic Power Plant Unit 1; Exemption From Certain Low-Level Waste...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-05

    .... DTE is in the process of decommissioning Fermi-1 and radioactive waste shipments from the site are... offsite low-level radioactive waste disposal sites. Experience at other decommissioning nuclear power facilities has shown that, due primarily to the volume of radioactive waste; licensees have encountered...

  14. Anisotropic non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Sur, Shouvik; Lee, Sung-Sik

    2016-11-01

    We study non-Fermi-liquid states that arise at the quantum critical points associated with the spin density wave (SDW) and charge density wave (CDW) transitions in metals with twofold rotational symmetry. We use the dimensional regularization scheme, where a one-dimensional Fermi surface is embedded in (3 -ɛ ) -dimensional momentum space. In three dimensions, quasilocal marginal Fermi liquids arise both at the SDW and CDW critical points: the speed of the collective mode along the ordering wave vector is logarithmically renormalized to zero compared to that of Fermi velocity. Below three dimensions, however, the SDW and CDW critical points exhibit drastically different behaviors. At the SDW critical point, a stable anisotropic non-Fermi-liquid state is realized for small ɛ , where not only time but also different spatial coordinates develop distinct anomalous dimensions. The non-Fermi liquid exhibits an emergent algebraic nesting as the patches of Fermi surface are deformed into a universal power-law shape near the hot spots. Due to the anisotropic scaling, the energy of incoherent spin fluctuations disperse with different power laws in different momentum directions. At the CDW critical point, on the other hand, the perturbative expansion breaks down immediately below three dimensions as the interaction renormalizes the speed of charge fluctuations to zero within a finite renormalization group scale through a two-loop effect. The difference originates from the fact that the vertex correction antiscreens the coupling at the SDW critical point whereas it screens at the CDW critical point.

  15. New Results on High Energy Cosmic Ray Electrons Observed with Fermi LAT and Their Implications on the Origin of Cosmic Rays

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    The Large Area Telescope on-board the Fermi Gamma-Ray Space Telescope has collected more than 10 million cosmic ray electrons with energy above 7 GeV since its science operation on orbit. High energy electrons rapidly lose their energy by synchrotron radiation on Galactic magnetic fields and by inverse Compton scattering on the interstellar radiation field. The typical distance over which a 1 TeV electron loses half its total energy is estimated to be 300-400 pc.This makes them a unique tool for probing nearby Galactic space. Observed spectrum has a harder spectral index than was previously reported and suggests the presence of nearby sources of high energy electrons. One of viable candidates are nearby pulsars, possibly some of recently discovered by Fermi. At the same time the dark matter origin of such sources cannot be ruled out. I will also report our current upper limits on cosmic ray electrons anisotropy which helps to set constraints on their local sources.

  16. GRB 110709A, 111117A, AND 120107A: FAINT HIGH-ENERGY GAMMA-RAY PHOTON EMISSION FROM FERMI-LAT OBSERVATIONS AND DEMOGRAPHIC IMPLICATIONS

    SciTech Connect

    Zheng Weikang; Akerlof, Carl W.; McKay, Timothy A.; Pandey, Shashi B.; Zhang Binbin; Zhang Bing; Sakamoto, Takanori

    2012-09-01

    Launched on 2008 June 11, the Large Area Telescope (LAT) instrument on board the Fermi Gamma-ray Space Telescope has provided a rare opportunity to study high-energy photon emission from gamma-ray bursts (GRBs). Although the majority of such events (27) have been identified by the Fermi-LAT Collaboration, four were uncovered by using more sensitive statistical techniques. In this paper, we continue our earlier work by finding three more GRBs associated with high-energy photon emission, GRB 110709A, 111117A, and 120107A. To systematize our matched filter approach, a pipeline has been developed to identify these objects in nearly real time. GRB 120107A is the first product of this analysis procedure. Despite the reduced threshold for identification, the number of GRB events has not increased significantly. This relative dearth of events with low photon number prompted a study of the apparent photon number distribution. We find an extremely good fit to a simple power law with an exponent of -1.8 {+-} 0.3 for the differential distribution. As might be expected, there is a substantial correlation between the number of lower energy photons detected by the Gamma-ray Burst Monitor (GBM) and the number observed by LAT. Thus, high-energy photon emission is associated with some but not all of the brighter GBM events. Deeper studies of the properties of the small population of high-energy emitting bursts may eventually yield a better understanding of these entire phenomena.

  17. Importance of Fermi energy for understanding the intermixing behavior at the LaAlO{sub 3}/SrTiO{sub 3} heterointerface

    SciTech Connect

    Yamamoto, Takashi; Mizoguchi, Teruyasu

    2014-11-17

    We investigated the migration energy and vacancy formation energy of La and Sr ions at a LaAlO{sub 3}/SrTiO{sub 3} heterointerface using first-principles calculations. Our study reveal that the migration energies at the p-type interface are lower than those at the n-type interface, and the formation energies of Sr and La vacancies are relatively high when we assume a reduction atmosphere and insulator conditions. To explain the experimental evidence that intermixing is preferentially taking place at the n-type interface, considering the Fermi energy is critical. We find that the presence of electron carriers plays an important role in the intermixing behaviors at the LaAlO{sub 3}/SrTiO{sub 3} heterointerface.

  18. Non-thermal insights on mass and energy flows through the Galactic Centre and into the Fermi bubbles

    NASA Astrophysics Data System (ADS)

    Crocker, R. M.

    2012-07-01

    We construct a simple model of the star-formation- (and resultant supernova-) driven mass and energy flows through the inner ˜200 pc (in diameter) of the Galaxy. Our modelling is constrained, in particular, by the non-thermal radio continuum and γ-ray signals detected from the region. The modelling points to a current star formation rate of 0.04-0.12 M⊙ yr-1 at 2σ confidence within the region with best-fitting value in the range 0.08-0.12 M⊙ yr-1 which - if sustained over 10 Gyr - would fill out the ˜109 M⊙ stellar population of the nuclear bulge. Mass is being accreted on to the Galactic Centre (GC) region at a rate ? yr-1. The region's star formation activity drives an outflow of plasma, cosmic rays and entrained, cooler gas. Neither the plasma nor the entrained gas reaches the gravitational escape speed, however, and all this material fountains back on to the inner Galaxy. The system we model can naturally account for the recently observed ≳106 M⊙'halo' of molecular gas surrounding the Central Molecular Zone out to 100-200 pc heights. The injection of cooler, high-metallicity material into the Galactic halo above the GC may catalyze the subsequent cooling and condensation of hot plasma out of this region and explain the presence of relatively pristine, nuclear-unprocessed gas in the GC. This process may also be an important ingredient in understanding the long-term stability of the GC star formation rate. The plasma outflow from the GC reaches a height of a few kpc and is compellingly related to the recently discovered Fermi bubbles by a number of pieces of evidence. These include that the outflow advects precisely (i) the power in cosmic rays required to sustain the bubbles'γ-ray luminosity in saturation; (ii) the hot gas required to compensate for gas cooling and drop-out from the bubbles and (iii) the magnetic field required to stabilize the walls of these structures. Our modelling demonstrates that ˜109 M⊙ of hot gas is processed through

  19. Enhanced high-energy gamma-ray emission from the microquasar Cygnus X-3 detected by Fermi/LAT

    NASA Astrophysics Data System (ADS)

    Loh, Alan; Corbel, Stephane

    2017-02-01

    Following the recent decrease of the hard X-ray emission from the high-mass X-ray binary Cygnus X-3 as seen by the Swift/Burst Alert Telescope (https://swift.gsfc.nasa.gov/results/transients/CygX-3/), the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed significant gamma-ray emission originating from the microquasar.

  20. The GAMMA Ray Sky as Seen by Fermi: Opening a New Window on the High Energy Space Environment

    DTIC Science & Technology

    2009-01-01

    pulsars , stars whose repeating emissions can be used as ultra-precise chronometers. Measurement of gamma radiation provides unique insight...diffuse glow are a number of bright point sources, mostly gamma ray pulsars — rotating, magnetized neutron stars — as discussed below. The bright sources...important early discoveries of Fermi have been from objects in our galaxy. The LAT has discovered 12 new pulsars that seem to be visible only in gamma

  1. Optical characterization of semi-insulating GaAs - Determination of the Fermi energy, the concentraion of the midgap EL2 level and its occupancy

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Bugajski, M.; Matsui, M.; Gatos, H. C.

    1987-01-01

    The key electronic characteristics of semiinsulating GaAs, i.e., the Fermi energy, concentration, and occupancy of the midgap donor EL2, and the net concentration of ionized acceptors can all be determined from high-resolution measurements of the EL2 intracenter absorption. The procedure is based on the measurement of zero-phonon line intensity before and after the complete transfer of EL2 to its metastable state followed by thermal recovery. The procedure is quantitative, involves no fitting parameters, and unlike existing methods, is applicable even when a significant part of the EL2 is ionized.

  2. Fermi LAT detection of increasing GeV gamma-ray activity from the high-energy peaked BL Lac object 1ES 1959+650

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano; Fermi Large Area Telescope Collaboration

    2015-10-01

    The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray emission from a source positionally consistent with the very-high energy peaked BL Lac object 1ES 1959+650 (also known as TXS 1959+650 and 3FGL J2000.0+6509, Acero et al. 2015, ApJS 218, 23) with radio coordinates (J2000) R.A.: 299.999384 deg, Dec.: 65.148514 deg (Beasley et al. 2002, ApJS, 141, 13). This source has a redshift z=0.047 (Schachter et al. 1993, ApJ, 412, 541).

  3. Fermi-LAT, FACT, MAGIC and VERITAS detection of increasing gamma-ray activity from the high-energy peaked BL Lac object 1ES 1959+650

    NASA Astrophysics Data System (ADS)

    Buson, S.; Magill, J. D.; Dorner, D.; Biland, A.; Mirzoyan, R.; Mukherjee, R.

    2016-04-01

    The Fermi-LAT, FACT, MAGIC and VERITAS collaborations report the detection of enhanced gamma-ray activity from a source positionally consistent with the very-high-energy peaked BL Lac object 1ES 1959+650 (a.k.a 3FGL J2000.0+6509, in the 3rd LAT source catalog, 3FGL, Acero et al. 2015, ApJS 218, 23) with radio coordinates (J2000) R.A.: 299.999384 deg, Dec.: 65.148514 deg (Beasley et al. 2002, ApJS, 141, 13). This source has a redshift z=0.047 (Schachter et al. 1993, ApJ, 412, 541).

  4. Fermi level stabilization and band edge energies in Cd{sub x}Zn{sub 1−x}O alloys

    SciTech Connect

    Detert, Douglas M.; Tom, Kyle B.; Dubon, Oscar D.; Battaglia, Corsin; Javey, Ali; Denlinger, Jonathan D.; Lim, Sunnie H. N.; Anders, André; Yu, Kin M.; Walukiewicz, Wladek

    2014-06-21

    We have measured the band edge energies of Cd{sub x}Zn{sub 1−x}O thin films as a function of composition by three independent techniques: we determine the Fermi level stabilization energy by pinning the Fermi level with ion irradiation, measure the binding energy of valence band states and core levels by X-ray photoelectron spectroscopy, and probe shifts in the conduction band and valence band density of states using soft X-ray absorption and emission spectroscopy, respectively. The three techniques find consensus in explaining the origin of compositional trends in the optical-bandgap narrowing upon Cd incorporation in wurtzite ZnO and widening upon Zn incorporation in rocksalt CdO. The conduction band minimum is found to be stationary for both wurtzite and rocksalt alloys, and a significant upward rise of the valence band maximum accounts for the majority of these observed bandgap changes. Given these band alignments, alloy disorder scattering is found to play a negligible role in decreasing the electron mobility for all alloys. These band alignment details, combined with the unique optical and electrical properties of the two phase regimes, make CdZnO alloys attractive candidates for photoelectrochemical water splitting applications.

  5. Quantum Oscillations from Fermi Arcs

    NASA Astrophysics Data System (ADS)

    Pereg-Barnea, Tamar; Refael, Gil; Franz, Marcel; Weber, Heidi; Seradjeh, Babak

    2009-03-01

    Recent experiments[1] in a variety of High Tc superconductors revel 1/B oscillations in the vortex-liquid state. The period of oscillations in underdoped samples is short and can be translated, via the Onsager relation to an area in k-space which makes up a few percents of the Brillouin zone. Quantum oscillations are usually thought of as arising from closed orbits in momentum space along the Fermi surface and are used to measure the Fermi vector. Thus, the observation of quantum oscillations in the cuprates seems to be at odds with the observation of Fermi arcs in ARPES experiments[2] due to their fragmented Fermi surface topology. In this talk we show that quantum oscillations can arise from a partially gapped Fermi surface. We adopt a phenomenological model of arcs which terminate at a regime with a superconducting gap of d-wave symmetry to describe the pseudo gap phase. Without invoking any additional order, quantization of energy is found well below the gap maximum. Semiclassically the quantization condition arises from closed orbits in real-space. When translated to momentum space, the area enclosed by the orbits is much smaller than that of the full Fermi surface. [1]N. Doiron-Leyaraud et al. nature 447, 565 (2007) [2]Kanigel et al. Nature Physics 2 447 (2006)

  6. Enrico Fermi Awards Ceremony for Dr. Mildred S. Dresselhaus and Dr. Burton Richter, May 2012 (Presentations, including remarks by Energy Secretary, Dr. Steven Chu)

    SciTech Connect

    Chu, Steven

    2012-05-07

    The Fermi Award is a Presidential award and is one of the oldest and most prestigious science and technology honors bestowed by the U.S. Government. On May 7, 2012 it was conferred upon two exceptional scientists: Dr. Mildred Dresselhaus, 'for her scientific leadership, her major contributions to science and energy policy, her selfless work in science education and the advancement of diversity in the scientific workplace, and her highly original and impactful research,' and Dr. Burton Richter, 'for the breadth of his influence in the multiple disciplines of accelerator physics and particle physics, his profound scientific discoveries, his visionary leadership as SLAC Director, his leadership of science, and his notable contributions in energy and public policy.' Dr. John Holder, Director of the White House Office of Science and Technology Policy, opened the ceremony, and Dr. Bill Brinkman, Director of DOE's Office of Science introduced the main speaker, Dr. Steven Chu, U.S. Energy Secretary.

  7. Enrico Fermi Awards Ceremony for Dr. Mildred S. Dresselhaus and Dr. Burton Richter, May 2012 (Presentations, including remarks by Energy Secretary, Dr. Steven Chu)

    ScienceCinema

    Chu, Steven (U.S. Energy Secretary)

    2016-07-12

    The Fermi Award is a Presidential award and is one of the oldest and most prestigious science and technology honors bestowed by the U.S. Government. On May 7, 2012 it was conferred upon two exceptional scientists: Dr. Mildred Dresselhaus, 'for her scientific leadership, her major contributions to science and energy policy, her selfless work in science education and the advancement of diversity in the scientific workplace, and her highly original and impactful research,' and Dr. Burton Richter, 'for the breadth of his influence in the multiple disciplines of accelerator physics and particle physics, his profound scientific discoveries, his visionary leadership as SLAC Director, his leadership of science, and his notable contributions in energy and public policy.' Dr. John Holder, Director of the White House Office of Science and Technology Policy, opened the ceremony, and Dr. Bill Brinkman, Director of DOE's Office of Science introduced the main speaker, Dr. Steven Chu, U.S. Energy Secretary.

  8. High-Energy Gamma-Ray Emission From Solar Flares: Summary of Fermi LAT Detections and Analysis of Two M-Class Flares

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Albert, A.; Allafort, A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Brandt, T. J.; Guiriec, S.; Hays, E.; McEnery, J. E.; Nemmen, R.; Perkins, J. S.; Thompson, D. J.

    2013-01-01

    We present the detections of 19 solar flares detected in high-energy gamma rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its rst four years of operation. Interestingly, all ares are associated with fairly fast Coronal Mass Ejections (CMEs) and are not all powerful X-ray ares. We then describe the detailed temporal, spatial and spectral characteristics of the rst two long-lasting events: the 2011 March 7 are, a moderate (M3.7) impulsive are followed by slowly varying gamma-ray emission over 13 hours, and the 2011 June 7 M2.5 are, which was followed by gamma-ray emission lasting for 2 hours. We compare the Fermi-LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that a hadronic origin of the gamma rays is more likely than a leptonic origin and nd that the energy spectrum of the proton distribution softens after the 2011 March 7 are, favoring a scenario with continuous acceleration at the are site. This work suggests that proton acceleration in solar ares is more common than previously thought, occurring for even modest X-ray ares, and for longer durations.

  9. Low-energy physics of the t -J model in d =∞ using extremely correlated Fermi liquid theory: Cutoff second-order equations

    NASA Astrophysics Data System (ADS)

    Shastry, B. Sriram; Perepelitsky, Edward

    2016-07-01

    We present the results for the low-energy properties of the infinite-dimensional t -J model with J =0 , using O (λ2) equations of the extremely correlated Fermi liquid formalism. The parameter λ ∈[0 ,1 ] is analogous to the inverse spin parameter 1 /(2 S ) in quantum magnets. The present analytical scheme allows us to approach the physically most interesting regime near the Mott insulating state n ≲1 . It overcomes the limitation to low densities n ≲0.7 of earlier calculations, by employing a variant of the skeleton graph expansion, and a high-frequency cutoff that is essential for maintaining the known high-T entropy. The resulting quasiparticle weight Z , the low ω ,T self-energy, and the resistivity are reported. These are quite close at all densities to the exact numerical results of the U =∞ Hubbard model, obtained using the dynamical mean field theory. The present calculation offers the advantage of generalizing to finite T rather easily, and allows the visualization of the loss of coherence of Fermi liquid quasiparticles by raising T . The present scheme is generalizable to finite dimensions and a nonvanishing J .

  10. Energy Fluctuation of Ideal Fermi Gas Trapped under Generic Power Law Potential U=\\sum_{i=1}^{d} c_i\\vert x_{i}/a_{i}\\vert^{n_{i} } in d Dimensions

    NASA Astrophysics Data System (ADS)

    Mehedi Faruk, Mir; Muktadir Rahman, Md.; Debnath, Dwaipayan; Sakhawat Hossain Himel, Md.

    2016-04-01

    Energy fluctuation of ideal Fermi gas trapped under generic power law potential U=\\sumi=1d ci \\vertxi/ai \\vert n_i has been calculated in arbitrary dimensions. Energy fluctuation is scrutinized further in the degenerate limit μ ≫ KBT with the help of Sommerfeld expansion. The dependence of energy fluctuation on dimensionality and power law potential is studied in detail. Most importantly our general result can not only exactly reproduce the recently published result regarding free and harmonically trapped ideal Fermi gas in d = 3 but also can describe the outcome for any power law potential in arbitrary dimension.

  11. Fermi and Swift observations of correlated and high-energy activity from the FSRQ TXS 0059+581

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano; Pacciani, Luigi; Pivato, Giovanna

    2016-04-01

    The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed hard-spectrum gamma rays from a source positionally consistent with the FSRQ TXS 0059+581 (also known as GB6 J0102+5824, 7C 0059+5808, 5BZU J0102+5824 and 3FGL J0102.8+5825) with radio coordinates (J2000), R.A.: 15.69068 deg, Dec.: 58.40309 deg (Johnston et al. 1995, AJ, 110, 880).

  12. Detection of high-energy gamma-ray emission from the globular cluster 47 Tucanae with Fermi.

    PubMed

    Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cecchi, C; Celik, O; Charles, E; Chaty, S; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cutini, S; Dermer, C D; de Palma, F; Digel, S W; Dormody, M; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Farnier, C; Favuzzi, C; Fegan, S J; Focke, W B; Frailis, M; Fukazawa, Y; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Horan, D; Hughes, R E; Jóhannesson, G; Johnson, A S; Johnson, R P; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kawai, N; Kerr, M; Knödlseder, J; Kuehn, F; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Panetta, J H; Parent, D; Pelassa, V; Pepe, M; Pierbattista, M; Piron, F; Porter, T A; Rainò, S; Rando, R; Razzano, M; Rea, N; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rochester, L S; Rodriguez, A Y; Romani, R W; Roth, M; Ryde, F; Sadrozinski, H F-W; Sanchez, D; Sander, A; Saz Parkinson, P M; Sgrò, C; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Strickman, M S; Suson, D J; Tajima, H; Takahashi, H; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Wang, P; Webb, N; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M

    2009-08-14

    We report the detection of gamma-ray emissions above 200 megaelectron volts at a significance level of 17sigma from the globular cluster 47 Tucanae, using data obtained with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. Globular clusters are expected to emit gamma rays because of the large populations of millisecond pulsars that they contain. The spectral shape of 47 Tucanae is consistent with gamma-ray emission from a population of millisecond pulsars. The observed gamma-ray luminosity implies an upper limit of 60 millisecond pulsars present in 47 Tucanae.

  13. Effective pinning energy landscape perturbations for propagating magnetic domain walls

    NASA Astrophysics Data System (ADS)

    Burn, D. M.; Atkinson, D.

    2016-10-01

    The interaction between a magnetic domain wall and a pinning site is explored in a planar nanowire using micromagnetics to reveal perturbations of the pinning energetics for propagating domain walls. Numerical simulations in the high damping ’quasi-static’ and low damping ’dynamic’ regimes are compared and show clear differences in de-pinning fields, indicating that dynamical micromagnetic models, which incorporate precessionally limited magnetization processes, are needed to understand domain wall pinning. Differences in the micromagnetic domain wall structure strongly influence the pinning and show periodic behaviour with increasing applied field associated with Walker breakdown. In the propagating regime pinning is complicated.

  14. Effective pinning energy landscape perturbations for propagating magnetic domain walls

    PubMed Central

    Burn, D. M.; Atkinson, D.

    2016-01-01

    The interaction between a magnetic domain wall and a pinning site is explored in a planar nanowire using micromagnetics to reveal perturbations of the pinning energetics for propagating domain walls. Numerical simulations in the high damping ’quasi-static’ and low damping ’dynamic’ regimes are compared and show clear differences in de-pinning fields, indicating that dynamical micromagnetic models, which incorporate precessionally limited magnetization processes, are needed to understand domain wall pinning. Differences in the micromagnetic domain wall structure strongly influence the pinning and show periodic behaviour with increasing applied field associated with Walker breakdown. In the propagating regime pinning is complicated. PMID:27694953

  15. Effective pinning energy landscape perturbations for propagating magnetic domain walls.

    PubMed

    Burn, D M; Atkinson, D

    2016-10-03

    The interaction between a magnetic domain wall and a pinning site is explored in a planar nanowire using micromagnetics to reveal perturbations of the pinning energetics for propagating domain walls. Numerical simulations in the high damping 'quasi-static' and low damping 'dynamic' regimes are compared and show clear differences in de-pinning fields, indicating that dynamical micromagnetic models, which incorporate precessionally limited magnetization processes, are needed to understand domain wall pinning. Differences in the micromagnetic domain wall structure strongly influence the pinning and show periodic behaviour with increasing applied field associated with Walker breakdown. In the propagating regime pinning is complicated.

  16. Conserved residues in the HAMP domain define a new family of proposed bipartite energy taxis receptors.

    PubMed

    Elliott, Kathryn T; Zhulin, Igor B; Stuckey, Jeanne A; DiRita, Victor J

    2009-01-01

    HAMP domains, found in many bacterial signal transduction proteins, generally transmit an intramolecular signal between an extracellular sensory domain and an intracellular signaling domain. Studies of HAMP domains in proteins where both the input and output signals occur intracellularly are limited to those of the Aer energy taxis receptor of Escherichia coli, which has both a HAMP domain and a sensory PAS domain. Campylobacter jejuni has an energy taxis system consisting of the domains of Aer divided between two proteins, CetA (HAMP domain containing) and CetB (PAS domain containing). In this study, we found that the CetA HAMP domain differs significantly from that of Aer in the predicted secondary structure. Using similarity searches, we identified 55 pairs of HAMP/PAS proteins encoded by adjacent genes in a diverse group of microorganisms. We propose that these HAMP/PAS pairs form a new family of bipartite energy taxis receptors. Within these proteins, we identified nine residues in the HAMP domain and proximal signaling domain that are highly conserved, at least three of which are required for CetA function. Additionally, we demonstrated that CetA contributes to the invasion of human epithelial cells by C. jejuni, while CetB does not. This finding supports the hypothesis that members of HAMP/PAS pairs possess the capacity to act independently of each other in cellular traits other than energy taxis.

  17. Cut-off characterisation of energy spectra of bright fermi sources: Current instrument limits and future possibilities

    NASA Astrophysics Data System (ADS)

    Romoli, C.; Taylor, A. M.; Aharonian, F.

    2017-02-01

    In this paper some of the brightest GeV sources observed by the Fermi-LAT were analysed, focusing on their spectral cut-off region. The sources chosen for this investigation were the brightest blazar flares of 3C 454.3 and 3C 279 and the Vela pulsar with a reanalysis with the latest Fermi-LAT software. For the study of the spectral cut-off we first explored the Vela pulsar spectrum, whose statistics in the time interval of the 3FGL catalog allowed strong constraints to be obtained on the parameters. We subsequently performed a new analysis of the flaring blazar SEDs. For these sources we obtained constraints on the cut-off parameters under the assumption that their underlying spectral distribution is described by a power-law with a stretched exponential cut-off. We then highlighted the significant potential improvements on such constraints by observations with next generation ground based Cherenkov telescopes, represented in our study by the Cherenkov Telescope Array (CTA). Adopting currently available simulations for this future observatory, we demonstrate the considerable improvement in cut-off constraints achievable by observations with this new instrument when compared with that achievable by satellite observations.

  18. Insights into the High-energy γ-ray Emission of Markarian 501 from Extensive Multifrequency Observations in the Fermi Era

    NASA Astrophysics Data System (ADS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Cannon, A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; Dermer, C. D.; de Palma, F.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Frailis, M.; Fuhrmann, L.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Guillemot, L.; Guiriec, S.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kadler, M.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S.-H.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Max-Moerbeck, W.; Mazziotta, M. N.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Nishino, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Parent, D.; Pavlidou, V.; Pearson, T. J.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Readhead, A.; Reimer, A.; Reimer, O.; Richards, J. L.; Ripken, J.; Ritz, S.; Roth, M.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Scargle, J. D.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stawarz, Ł.; Stevenson, M.; Strickman, M. S.; Sokolovsky, K. V.; Suson, D. J.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Wehrle, A. E.; Winer, B. L.; Wood, K. S.; Yang, Z.; Ylinen, T.; Zensus, J. A.; Ziegler, M.; Fermi LAT Collaboration; Aleksić, J.; Antonelli, L. A.; Antoranz, P.; Backes, M.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Berdyugin, A.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R. K.; Boller, A.; Bonnoli, G.; Bordas, P.; Borla Tridon, D.; Bosch-Ramon, V.; Bose, D.; Braun, I.; Bretz, T.; Camara, M.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Dazzi, F.; de Angelis, A.; De Cea del Pozo, E.; De Lotto, B.; De Maria, M.; De Sabata, F.; Delgado Mendez, C.; Diago Ortega, A.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Elsaesser, D.; Ferenc, D.; Fonseca, M. V.; Font, L.; García López, R. J.; Garczarczyk, M.; Gaug, M.; Giavitto, G.; Godinovi, N.; Hadasch, D.; Herrero, A.; Hildebrand, D.; Höhne-Mönch, D.; Hose, J.; Hrupec, D.; Jogler, T.; Klepser, S.; Krähenbühl, T.; Kranich, D.; Krause, J.; La Barbera, A.; Leonardo, E.; Lindfors, E.; Lombardi, S.; López, M.; Lorenz, E.; Majumdar, P.; Makariev, E.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Miyamoto, H.; Moldón, J.; Moralejo, A.; Nieto, D.; Nilsson, K.; Orito, R.; Oya, I.; Paoletti, R.; Paredes, J. M.; Partini, S.; Pasanen, M.; Pauss, F.; Pegna, R. G.; Perez-Torres, M. A.; Persic, M.; Peruzzo, J.; Pochon, J.; Prada Moroni, P. G.; Prada, F.; Prandini, E.; Puchades, N.; Puljak, I.; Reichardt, T.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rissi, M.; Rügamer, S.; Saggion, A.; Saito, K.; Saito, T. Y.; Salvati, M.; Sánchez-Conde, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shayduk, M.; Shore, S. N.; Sierpowska-Bartosik, A.; Sillanpää, A.; Sitarek, J.; Sobczynska, D.; Spanier, F.; Spiro, S.; Stamerra, A.; Steinke, B.; Storz, J.; Strah, N.; Struebig, J. C.; Suric, T.; Takalo, L. O.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Vankov, H.; Wagner, R. M.; Weitzel, Q.; Zabalza, V.; Zandanel, F.; Zanin, R.; MAGIC Collaboration; Acciari, V. A.; Arlen, T.; Aune, T.; Benbow, W.; Boltuch, D.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Cannon, A.; Cesarini, A.; Ciupik, L.; Cui, W.; Dickherber, R.; Errando, M.; Falcone, A.; Finley, J. P.; Finnegan, G.; Fortson, L.; Furniss, A.; Galante, N.; Gall, D.; Gillanders, G. H.; Godambe, S.; Grube, J.; Guenette, R.; Gyuk, G.; Hanna, D.; Holder, J.; Huang, D.; Hui, C. M.; Humensky, T. B.; Kaaret, P.; Karlsson, N.; Kertzman, M.; Kieda, D.; Konopelko, A.; Krawczynski, H.; Krennrich, F.; Lang, M. J.; Maier, G.; McArthur, S.; McCann, A.; McCutcheon, M.; Moriarty, P.; Mukherjee, R.; Ong, R.; Otte, A. N.; Pandel, D.; Perkins, J. S.; Pichel, A.; Pohl, M.; Quinn, J.; Ragan, K.; Reyes, L. C.; Reynolds, P. T.; Roache, E.; Rose, H. J.; Rovero, A. C.; Schroedter, M.; Sembroski, G. H.; Senturk, G. D.; Steele, D.; Swordy, S. P.; Tešić, G.; Theiling, M.; Thibadeau, S.; Varlotta, A.; Vincent, S.; Wakely, S. P.; Ward, J. E.; Weekes, T. C.; Weinstein, A.; Weisgarber, T.; Williams, D. A.; Wood, M.; Zitzer, B.; VERITAS Collaboration; Villata, M.; Raiteri, C. M.; Aller, H. D.; Aller, M. F.; Arkharov, A. A.; Blinov, D. A.; Calcidese, P.; Chen, W. P.; Efimova, N. V.; Kimeridze, G.; Konstantinova, T. S.; Kopatskaya, E. N.; Koptelova, E.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lähteenmäki, A.; Larionov, V. M.; Larionova, E. G.; Larionova, L. V.; Ligustri, R.; Morozova, D. A.; Nikolashvili, M. G.; Sigua, L. A.; Troitsky, I. S.; Angelakis, E.; Capalbi, M.; Carramiñana, A.; Carrasco, L.; Cassaro, P.; de la Fuente, E.; Gurwell, M. A.; Kovalev, Y. Y.; Kovalev, Yu. A.; Krichbaum, T. P.; Krimm, H. A.; Leto, P.; Lister, M. L.; Maccaferri, G.; Moody, J. W.; Mori, Y.; Nestoras, I.; Orlati, A.; Pagani, C.; Pace, C.; Pearson, R., III; Perri, M.; Piner, B. G.; Pushkarev, A. B.; Ros, E.; Sadun, A. C.; Sakamoto, T.; Tornikoski, M.; Yatsu, Y.; Zook, A.

    2011-02-01

    We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15—August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size lsim0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (sime1044 erg s-1) constitutes only a small fraction (~10-3) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk

  19. A possible explanation of low energy γ-ray excess from galactic centre and Fermi bubble by a Dark Matter model with two real scalars

    SciTech Connect

    Modak, Kamakshya Prasad; Majumdar, Debasish

    2015-03-09

    We promote the idea of multi-component Dark Matter (DM) to explain results from both direct and indirect detection experiments. In these models as contribution of each DM candidate to relic abundance is summed up to meet WMAP/Planck measurements of Ω{sub DM}, these candidates have larger annihilation cross-sections compared to the single-component DM models. We illustrate this fact by introducing an extra scalar to the popular single real scalar DM model. We also present detailed calculations for the vacuum stability bounds, perturbative unitarity and triviality constraints on this model. As direct detection experimental results still show some conflict, we kept our options open, discussing different scenarios with different DM mass zones. In the framework of our model we make an interesting observation: the existing direct detection experiments like CDMS II, CoGeNT, CRESST II, XENON 100 or LUX together with the observation of excess low energy γ-ray from galactic centre and Fermi bubble by Fermi Gamma-ray Space Telescope (FGST) already have the capability to distinguish between different DM halo profiles.

  20. A possible explanation of low energy γ-ray excess from galactic centre and Fermi bubble by a Dark Matter model with two real scalars

    SciTech Connect

    Modak, Kamakshya Prasad; Majumdar, Debasish

    2015-03-01

    We promote the idea of multi-component Dark Matter (DM) to explain results from both direct and indirect detection experiments. In these models as contribution of each DM candidate to relic abundance is summed up to meet WMAP/Planck measurements of Ω{sub DM}, these candidates have larger annihilation cross-sections compared to the single-component DM models. We illustrate this fact by introducing an extra scalar to the popular single real scalar DM model. We also present detailed calculations for the vacuum stability bounds, perturbative unitarity and triviality constraints on this model. As direct detection experimental results still show some conflict, we kept our options open, discussing different scenarios with different DM mass zones. In the framework of our model we make an interesting observation: the existing direct detection experiments like CDMS II, CoGeNT, CRESST II, XENON 100 or LUX together with the observation of excess low energy γ-ray from galactic centre and Fermi bubble by Fermi Gamma-ray Space Telescope (FGST) already have the capability to distinguish between different DM halo profiles.

  1. Energy landscape scheme for an intuitive understanding of complex domain dynamics in ferroelectric thin films.

    PubMed

    Kim, Tae Heon; Yoon, Jong-Gul; Baek, Seung Hyub; Park, Woong-kyu; Yang, Sang Mo; Yup Jang, Seung; Min, Taeyuun; Chung, Jin-Seok; Eom, Chang-Beom; Noh, Tae Won

    2015-07-01

    Fundamental understanding of domain dynamics in ferroic materials has been a longstanding issue because of its relevance to many systems and to the design of nanoscale domain-wall devices. Despite many theoretical and experimental studies, a full understanding of domain dynamics still remains incomplete, partly due to complex interactions between domain-walls and disorder. We report domain-shape-preserving deterministic domain-wall motion, which directly confirms microscopic return point memory, by observing domain-wall breathing motion in ferroelectric BiFeO3 thin film using stroboscopic piezoresponse force microscopy. Spatial energy landscape that provides new insights into domain dynamics is also mapped based on the breathing motion of domain walls. The evolution of complex domain structure can be understood by the process of occupying the lowest available energy states of polarization in the energy landscape which is determined by defect-induced internal fields. Our result highlights a pathway for the novel design of ferroelectric domain-wall devices through the engineering of energy landscape using defect-induced internal fields such as flexoelectric fields.

  2. Ultrafast many-body interferometry of impurities coupled to a Fermi sea

    NASA Astrophysics Data System (ADS)

    Cetina, Marko; Jag, Michael; Lous, Rianne S.; Fritsche, Isabella; Walraven, Jook T. M.; Grimm, Rudolf; Levinsen, Jesper; Parish, Meera M.; Schmidt, Richard; Knap, Michael; Demler, Eugene

    2016-10-01

    The fastest possible collective response of a quantum many-body system is related to its excitations at the highest possible energy. In condensed matter systems, the time scale for such “ultrafast” processes is typically set by the Fermi energy. Taking advantage of fast and precise control of interactions between ultracold atoms, we observed nonequilibrium dynamics of impurities coupled to an atomic Fermi sea. Our interferometric measurements track the nonperturbative quantum evolution of a fermionic many-body system, revealing in real time the formation dynamics of quasi-particles and the quantum interference between attractive and repulsive states throughout the full depth of the Fermi sea. Ultrafast time-domain methods applied to strongly interacting quantum gases enable the study of the dynamics of quantum matter under extreme nonequilibrium conditions.

  3. Iterative image-domain decomposition for dual-energy CT

    SciTech Connect

    Niu, Tianye; Dong, Xue; Petrongolo, Michael; Zhu, Lei

    2014-04-15

    Purpose: Dual energy CT (DECT) imaging plays an important role in advanced imaging applications due to its capability of material decomposition. Direct decomposition via matrix inversion suffers from significant degradation of image signal-to-noise ratios, which reduces clinical values of DECT. Existing denoising algorithms achieve suboptimal performance since they suppress image noise either before or after the decomposition and do not fully explore the noise statistical properties of the decomposition process. In this work, the authors propose an iterative image-domain decomposition method for noise suppression in DECT, using the full variance-covariance matrix of the decomposed images. Methods: The proposed algorithm is formulated in the form of least-square estimation with smoothness regularization. Based on the design principles of a best linear unbiased estimator, the authors include the inverse of the estimated variance-covariance matrix of the decomposed images as the penalty weight in the least-square term. The regularization term enforces the image smoothness by calculating the square sum of neighboring pixel value differences. To retain the boundary sharpness of the decomposed images, the authors detect the edges in the CT images before decomposition. These edge pixels have small weights in the calculation of the regularization term. Distinct from the existing denoising algorithms applied on the images before or after decomposition, the method has an iterative process for noise suppression, with decomposition performed in each iteration. The authors implement the proposed algorithm using a standard conjugate gradient algorithm. The method performance is evaluated using an evaluation phantom (Catphan©600) and an anthropomorphic head phantom. The results are compared with those generated using direct matrix inversion with no noise suppression, a denoising method applied on the decomposed images, and an existing algorithm with similar formulation as the

  4. High-energy gamma-ray emission from solar flares: Summary of Fermi large area telescope detections and analysis of two M-class flares

    SciTech Connect

    Ackermann, M.; Ajello, M.; Albert, A.; Allafort, A.; Bechtol, K.; Bottacini, E.; Buehler, R.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Buson, S.; Bellazzini, R.; Bregeon, J.; Bissaldi, E.; Bonamente, E.; Bouvier, A.; Brandt, T. J.; Brigida, M.; Bruel, P.; and others

    2014-05-20

    We present the detections of 18 solar flares detected in high-energy γ-rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its first 4 yr of operation. This work suggests that particle acceleration up to very high energies in solar flares is more common than previously thought, occurring even in modest flares, and for longer durations. Interestingly, all these flares are associated with fairly fast coronal mass ejections (CMEs). We then describe the detailed temporal, spatial, and spectral characteristics of the first two long-lasting events: the 2011 March 7 flare, a moderate (M3.7) impulsive flare followed by slowly varying γ-ray emission over 13 hr, and the 2011 June 7 M2.5 flare, which was followed by γ-ray emission lasting for 2 hr. We compare the Fermi LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that the γ-rays are more likely produced through pion decay than electron bremsstrahlung, and we find that the energy spectrum of the proton distribution softens during the extended emission of the 2011 March 7 flare. This would disfavor a trapping scenario for particles accelerated during the impulsive phase of the flare and point to a continuous acceleration process at play for the duration of the flares. CME shocks are known for accelerating the solar energetic particles (SEPs) observed in situ on similar timescales, but it might be challenging to explain the production of γ-rays at the surface of the Sun while the CME is halfway to the Earth. A stochastic turbulence acceleration process occurring in the solar corona is another likely scenario. Detailed comparison of characteristics of SEPs and γ-ray-emitting particles for several flares will be helpful to distinguish between these two possibilities.

  5. Fermi Pulsar Analysis

    NASA Video Gallery

    This animation illustrates how analysis of Fermi data reveals new pulsars. Fermi's LAT records the precise arrival time and approximate direction of the gamma rays it detects, but to identify a pul...

  6. Fermi surface of YBCO by DHVA

    SciTech Connect

    Smith, J.L.; Fowler, C.M.; Freeman, B.L.; Hults, W.L.; King, J.C.; Mueller, F.M.

    1991-01-01

    These proceedings demonstrate how far scientist have come in the last four years of high temperature superconductivity. Knowledge of the energy bands and Fermi surfaces from experiment has come rather late. Photoemission, first showed proof of the validity of the energy band calculations. Positron annihilation, presented by West, after a rough start, is now giving evidence of the Fermi surface. Both of these techniques involve electronic excitations and hence, although they show the Fermi surface, do not put as severe a constraint on various models for superconductivity as does the de Haas-van Alphen (dHvA) effect. This is a true measurement of the electronic ground state in an applied magnetic field where the frequency of oscillatory magnetization yields extremal cross-sectional areas of the Fermi surface. The authors have already reported some of their Fermi surface work at two conferences but present here discussion of several more important aspects of the work. 11 refs., 2 figs.

  7. SIMULTANEOUS OBSERVATIONS OF PKS 2155-304 WITH HESS, FERMI, RXTE, AND ATOM: SPECTRAL ENERGY DISTRIBUTIONS AND VARIABILITY IN A LOW STATE

    SciTech Connect

    Aharonian, F.; Bernloehr, K.; Bochow, A.; Buehler, R.; Akhperjanian, A. G.; Anton, G.; Brucker, J.; Barres de Almeida, U.; Chadwick, P. M.; Bazer-Bachi, A. R.; Borrel, V.; Behera, B.; Boisson, C.; Brion, E.; Brun, P.; Buesching, I.; Boutelier, T. E-mail: berrie@in2p3.fr E-mail: jchiang@slac.stanford.edu

    2009-05-10

    We report on the first simultaneous observations that cover the optical, X-ray, and high-energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 2008 August 25 and 2008 September 6 (MJD 54704-54715), jointly with the Fermi Gamma-ray Space Telescope and the HESS atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution (SED) with the new generation of {gamma}-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time period. The object was close to the lowest archival X-ray and very high energy (VHE; >100 GeV) state, whereas the optical flux was much higher. The light curves show relatively little ({approx}30%) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high-energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155-304.

  8. Simultaneous Observations of PKS 2155--304 with H.E.S.S., Fermi, RXTE and ATOM: Spectral Energy Distributions and Variability in a Low State

    SciTech Connect

    Aharonian, F.; Akhperjanian, A.G.; Anton, G.; Barres de Almeida, U.; Bazer-Bachi, A.R.; Becherini, Y.; Behera, B.; Bernlohr, K.; Boisson, C.; Bochow, A.; Borrel, V.; Brion, E.; Brucker, J.; Brun, P.; Buhler, R.; Bulik, T.; Busching, I.; Boutelier, T.; Chadwick, P.M.; Charbonnier, A.; Chaves, R.C.G.; /more authors..

    2009-05-07

    We report on the first simultaneous observations that cover the optical, X-ray, and high-energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 2008 August 25 and 2008 September 6 (MJD 54704-54715), jointly with the Fermi Gamma-ray Space Telescope and the HESS atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution (SED) with the new generation of {gamma}-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time period. The object was close to the lowest archival X-ray and very high energy (VHE; >100 GeV) state, whereas the optical flux was much higher. The light curves show relatively little ({approx}30%) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high-energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155-304.

  9. Enrico Fermi Awards Ceremony for Dr. Allen J. Bard and Dr. Andrew Sessler, February 2014 (Presentations, including remarks by Energy Secretary, Dr. Ernest Moniz)

    SciTech Connect

    Moniz, Ernest

    2014-02-03

    The Fermi Award is a Presidential award and is one of the oldest and most prestigious science and technology honors bestowed by the U.S. Government. On February 3, 2014 it was conferred upon two exceptional scientists. The first to be recognized is Dr. Allen J. Bard, 'for international leadership in electrochemical science and technology, for advances in photoelectrochemistry and photocatalytic materials, processes, and devices, and for discovery and development of electrochemical methods including electrogenerated chemiluminescence and scanning electrochemical microscopy.' The other honoree is Dr. Andrew Sessler, 'for advancing accelerators as powerful tools of scientific discovery, for visionary direction of the research enterprise focused on challenges in energy and the environment, and for championing outreach and freedom of scientific inquiry worldwide.' Dr. Patricia Dehmer opened the ceremony, and Dr. Ernest Moniz presented the awards.

  10. Large Fermi energy modulation in graphene transistors with high-pressure O{sub 2}-annealed Y{sub 2}O{sub 3} topgate insulators

    SciTech Connect

    Kanayama, Kaoru; Nagashio, Kosuke Nishimura, Tomonori; Toriumi, Akira

    2014-02-24

    We demonstrate a considerable suppression of the low-field leakage through a Y{sub 2}O{sub 3} topgate insulator on graphene by applying high-pressure O{sub 2} at 100 atm during post-deposition annealing (HP-PDA). Consequently, the quantum capacitance measurement for the monolayer graphene reveals the largest Fermi energy modulation (E{sub F} = ∼0.52 eV, i.e., the carrier density of ∼2 × 10{sup 13} cm{sup −2}) in the solid-state topgate insulators reported so far. HP-PDA is the robust method to improve the electrical quality of high-k insulators on graphene.

  11. Enrico Fermi Awards Ceremony for Dr. Allen J. Bard and Dr. Andrew Sessler, February 2014 (Presentations, including remarks by Energy Secretary, Dr. Ernest Moniz)

    ScienceCinema

    Moniz, Ernest [U.S. Energy Secretary

    2016-07-12

    The Fermi Award is a Presidential award and is one of the oldest and most prestigious science and technology honors bestowed by the U.S. Government. On February 3, 2014 it was conferred upon two exceptional scientists. The first to be recognized is Dr. Allen J. Bard, 'for international leadership in electrochemical science and technology, for advances in photoelectrochemistry and photocatalytic materials, processes, and devices, and for discovery and development of electrochemical methods including electrogenerated chemiluminescence and scanning electrochemical microscopy.' The other honoree is Dr. Andrew Sessler, 'for advancing accelerators as powerful tools of scientific discovery, for visionary direction of the research enterprise focused on challenges in energy and the environment, and for championing outreach and freedom of scientific inquiry worldwide.' Dr. Patricia Dehmer opened the ceremony, and Dr. Ernest Moniz presented the awards.

  12. Energy-efficient writing scheme for magnetic domain-wall motion memory

    NASA Astrophysics Data System (ADS)

    Kim, Kab-Jin; Yoshimura, Yoko; Ham, Woo Seung; Ernst, Rick; Hirata, Yuushou; Li, Tian; Kim, Sanghoon; Moriyama, Takahiro; Nakatani, Yoshinobu; Ono, Teruo

    2017-04-01

    We present an energy-efficient magnetic domain-writing scheme for domain wall (DW) motion-based memory devices. A cross-shaped nanowire is employed to inject a domain into the nanowire through current-induced DW propagation. The energy required for injecting the magnetic domain is more than one order of magnitude lower than that for the conventional field-based writing scheme. The proposed scheme is beneficial for device miniaturization because the threshold current for DW propagation scales with the device size, which cannot be achieved in the conventional field-based technique.

  13. Dynamics of magnetic domain wall motion after nucleation: dependence on the wall energy.

    PubMed

    Fukumoto, K; Kuch, W; Vogel, J; Romanens, F; Pizzini, S; Camarero, J; Bonfim, M; Kirschner, J

    2006-03-10

    The dynamics of magnetic domain wall motion in the FeNi layer of a FeNi/Al2O3/Co trilayer has been investigated by a combination of x-ray magnetic circular dichroism, photoelectron emission microscopy, and a stroboscopic pump-probe technique. The nucleation of domains and subsequent expansion by domain wall motion in the FeNi layer during nanosecond-long magnetic field pulses was observed in the viscous regime up to the Walker limit field. We attribute an observed delay of domain expansion to the influence of the domain wall energy that acts against the domain expansion and that plays an important role when domains are small.

  14. Tunable conductance of magnetic nanowires with structured domain walls.

    PubMed

    Dugaev, V K; Berakdar, J; Barnaś, J

    2006-02-03

    We show that in a magnetic nanowire with double magnetic domain walls, quantum interference results in spin-split quasistationary states localized mainly between the domain walls. Spin-flip-assisted transmission through the domain structure increases strongly when these size-quantized states are tuned on resonance with the Fermi energy, e.g., upon varying the distance between the domain walls which results in resonance-type peaks of the wire conductance. This novel phenomenon is shown to be utilizable to manipulate the spin density in the domain vicinity. The domain wall parameters are readily controllable, and the predicted effect is hence exploitable in spintronic devices.

  15. Ground-state energy, density profiles, and momentum distribution of attractively interacting 1D Fermi gases with hard-wall boundaries: a Monte Carlo study

    NASA Astrophysics Data System (ADS)

    McKenney, J. R.; Shill, C. R.; Porter, W. J.; Drut, J. E.

    2016-11-01

    Motivated by the realization of hard-wall boundary conditions in experiments with ultracold atoms, we investigate the ground-state properties of spin-1/2 fermions with attractive interactions in a one-dimensional box. We use lattice Monte Carlo methods to determine essential quantities like the energy, which we compute as a function of coupling strength and particle number in the regime from few to many particles. Many-fermion systems bound by hard walls display non-trivial density profiles characterized by so-called Friedel oscillations (which are similar to those observed in harmonic traps). In non-interacting systems, the characteristic length scale of the oscillations is set by {(2{k}{{F}})}-1, where {k}{{F}} is the Fermi momentum, while repulsive interactions tend to generate Wigner-crystal oscillations of period {(4{k}{{F}})}-1. Based on the non-interacting result, we find a remarkably simple parametrization of the density profiles of the attractively interacting case, which we generalize to the one-body density matrix. While the total momentum is not a conserved quantity in the presence of hard walls, the magnitude of the momentum does provide a good quantum number. We are therefore able to provide a detailed characterization of the (quasi-)momentum distribution, which displays rather robust discontinuity at the Fermi surface. In addition, we determine the spatially varying on-site density-density correlation, which in turn yields Tan’s contact density and, upon integration, Tan’s contact. As is well known, the latter fully determines the short-range correlations and plays a crucial role in a multitude of equilibrium and non-equilibrium sum rules.

  16. Investigations of the output energy deviation and other parameters during commissioning of the four-rod radio frequency quadrupole at the Fermi National Accelerator Laboratory

    SciTech Connect

    Schmidt, J. S.; et al.,

    2014-03-01

    After 30 years of operation, the Cockcroft-Walton based injector at FNAL (Fermi National Accelerator Laboratory) has been replaced by a new beam line including a dimpled magnetron 35 keV source in combination with a 750 keV 4-rod Radio Frequency Quadrupole (RFQ). The new injector is followed by the existing drift tube linac (DTL). Prior to installation, a test beam line was built which included the magnetron source and the 4-rod RFQ with a number of beam measurement instrumentation. The first beam test with the RFQ showed an output energy deviation greater than 2.5%. Other problems also showed up which led to investigations of the output energy, power consumption and transmission properties using RF simulations which were complemented with additional beam measurements. The sources of this deviation and the mechanical modifications of the RFQ to solve this matter will be presented in this paper. Meanwhile, the nominal output energy of 750 keV has been confirmed and the new injector with the 4-rod RFQ is in full operation.

  17. Homogeneous Atomic Fermi Gases

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Yan, Zhenjie; Patel, Parth B.; Hadzibabic, Zoran; Yefsah, Tarik; Struck, Julian; Zwierlein, Martin W.

    2017-03-01

    We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state: the striking consequence of Pauli blocking in momentum space for a degenerate gas. Cooling a spin-balanced Fermi gas at unitarity, we create homogeneous superfluids and observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas.

  18. Measurement of magnetic domain wall width using energy-filtered Fresnel images.

    PubMed

    Lloyd, S J; Loudon, J C; Midgley, P A

    2002-08-01

    Magnetic domain walls in Nd2Fe14B have been examined using a series of energy-filtered Fresnel images in the field emission gun transmission electron microscope (FEGTEM). We describe the changes in the intensity distribution of the convergent wall image as a function of defocus, foil thickness and domain wall width. The effect of tilted domain walls and beam convergence on the fringe pattern is also discussed. A comparison of the experimental intensity profile with that from simulations allows the domain wall width to be determined. Measurement of very narrow walls is made possible only by using a relatively thick foil, which necessitates energy-filtering to allow quantitative comparison with simulations. The magnetic domain wall width in Nd2Fe14B was found to be 3 +/- 2 nm.

  19. Fermi level pinning characterisation on ammonium fluoride-treated surfaces of silicon by energy-filtered doping contrast in the scanning electron microscope

    PubMed Central

    Chee, Augustus K. W.

    2016-01-01

    Two-dimensional dopant profiling using the secondary electron (SE) signal in the scanning electron microscope (SEM) is a technique gaining impulse for its ability to enable rapid and contactless low-cost diagnostics for integrated device manufacturing. The basis is doping contrast from electrical p-n junctions, which can be influenced by wet-chemical processing methods typically adopted in ULSI technology. This paper describes the results of doping contrast studies by energy-filtering in the SEM from silicon p-n junction specimens that were etched in ammonium fluoride solution. Experimental SE micro-spectroscopy and numerical simulations indicate that Fermi level pinning occurred on the surface of the treated-specimen, and that the doping contrast can be explained in terms of the ionisation energy integral for SEs, which is a function of the dopant concentration, and surface band-bending effects that prevail in the mechanism for doping contrast as patch fields from the specimen are suppressed. PMID:27576347

  20. Extended Thomas-Fermi kinetic energy density functional with spatially varying effective mass in d=1,2,3 dimensions

    SciTech Connect

    Berkane, K.; Bencheikh, K.

    2005-08-15

    For first-principles density functional theory of a many fermion system, the determination of the kinetic energy functional is important. We consider N independent fermions with spatially varying effective mass in two dimensions, we derive the corresponding kinetic energy density using the ({Dirac_h}/2{pi}) semiclassical approach. Our result reduces, as expected, to the one obtained in the literature for a constant effective mass. We examine the analytical expressions of the position dependent effective mass terms in the kinetic energy density functional with respect to the dimensionality d=1,2,3 of the space.

  1. Quantum Mechanical Models Of The Fermi Shuttle

    SciTech Connect

    Sternberg, James

    2011-06-01

    The Fermi shuttle is a mechanism in which high energy electrons are produced in an atomic collision by multiple collisions with a target and a projectile atom. It is normally explained purely classically in terms of the electron's orbits prescribed in the collision. Common calculations to predict the Fermi shuttle use semi-classical methods, but these methods still rely on classical orbits. In reality such collisions belong to the realm of quantum mechanics, however. In this paper we discuss several purely quantum mechanical calculations which can produce the Fermi shuttle. Being quantum mechanical in nature, these calculations produce these features by wave interference, rather than by classical orbits.

  2. Fermi-liquid theory for unconventional superconductors

    SciTech Connect

    Sauls, J.A.

    1994-12-31

    Fermi liquid theory is used to generate the Ginzburg-Landau free energy functionals for unconventional superconductors belonging to various representations. The parameters defining the GL functional depend on Fermi surface anisotropy, impurity scattering and the symmetry class of the pairing interaction. As applications the author considers the basic models for the multiple superconducting phases of UPt{sub 3}. An important prediction of the leading order Fermi liquid theory for the two-dimensional representations of the hexagonal symmetry group is that the zero-field equilibrium state exhibits spontaneously broken time-reversal symmetry.

  3. Quantum chaos on a critical Fermi surface.

    PubMed

    Patel, Aavishkar A; Sachdev, Subir

    2017-02-21

    We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of [Formula: see text] species of fermions at nonzero density coupled to a [Formula: see text] gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent of [Formula: see text], the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details.

  4. A new approach for modelling lattice energy in finite crystal domains

    NASA Astrophysics Data System (ADS)

    Bilotsky, Y.; Gasik, M.

    2015-09-01

    Evaluation of internal energy in a crystal lattice requires precise calculation of lattice sums. Such evaluation is a problem in the case of small (nano) particles because the traditional methods are usually effective only for infinite lattices and are adapted to certain specific potentials. In this work, a new method has been developed for calculation of lattice energy. The method is a generalisation of conventional geometric probability techniques for arbitrary fixed lattices in a finite crystal domain. In our model, the lattice energy for wide range of two- body central interaction potentials (including long-range Coulomb potential) has been constructed using absolutely convergent sums. No artificial cut-off potential or periodical extension of the domain (which usually involved for such calculations) have been made for calculation of the lattice energy under this approach. To exemplify the applications of these techniques, the energy of Coulomb potential has been plotted as the function of the domain size.

  5. Fermi's Conundrum: Proliferation and Closed Societies

    NASA Astrophysics Data System (ADS)

    Teller, Wendy; Westfall, Catherine

    2007-04-01

    On January 1, 1946 Emily Taft Douglas, a freshman Representative at Large for Illinois, sent a letter to Enrico Fermi. She wanted to know whether, if atomic energy was used for peaceful purposes, it might be possible to clandestinely divert some material for bombs. Douglas first learned about the bomb not quite five months before when Hiroshima was bombed. Even though she was not a scientist she identified a key problem of the nuclear age. Fermi responded with requirements to allow peaceful uses of atomic energy and still outlaw nuclear weapons. First, free interchange of information between people was required, and second, people who reported possible violations had to be protected. Fermi had lived in Mussolini's Italy and worked under the war time secrecy restrictions of the Manhattan Project. He was not optimistic that these conditions could be met. This paper discusses how Douglas came to recognize the proliferation issue and what led Fermi to his solution and his pessimism about its practicality.

  6. Note on Generalized Fermi-Dirac Function and Its Derivatives

    NASA Astrophysics Data System (ADS)

    Gong, Zhigang; Zejda, Ladislav; Däppen, Werner

    2000-04-01

    Generalized Fermi-Dirac function and its derivatives are important in evaluating the thermodynamic functions of partially degenerate electrons in hot stellar plasmas. Because of the nature of the Fermi-Dirac functions, analytic expressions are only available for certain extreme cases, and regular numeric methods fail when degeneracy and temperature are relatively high (but not high enough to use approximative formulae). In this paper, recursion relations of the generalized Fermi-Dirac function are discussed, and an effective numerical method to evaluate the derivatives of the generalized Fermi-Dirac function is given, following the Aparicio (1998) scheme. Finally, accuracy and domain of reliability of some popular analytic approximations are investigated.

  7. Wind energy system time-domain (WEST) analyzers

    NASA Technical Reports Server (NTRS)

    Dreier, M. E.; Hoffman, J. A.

    1981-01-01

    A portable analyzer which simulates in real time the complex nonlinear dynamics of horizontal axis wind energy systems was constructed. Math models for an aeroelastic rotor featuring nonlinear aerodynamic and inertial terms were implemented with high speed digital controllers and analog calculation. This model was combined with other math models of elastic supports, control systems, a power train and gimballed rotor kinematics. A stroboscopic display system graphically depicting distributed blade loads, motion, and other aerodynamic functions on a cathode ray tube is included. Limited correlation efforts showed good comparison between the results of this analyzer and other sophisticated digital simulations. The digital simulation results were successfully correlated with test data.

  8. Energy Band Gap, Intrinsic Carrier Concentration and Fermi Level of CdTe Bulk Crystal between 304 K and 1067 K

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    2007-01-01

    Optical transmission measurements were performed on CdTe bulk single crystal. It was found that when a sliced and polished CdTe wafer was used, a white film started to develop when the sample was heated above 530 K and the sample became opaque. Therefore, a bulk crystal of CdTe was first grown in the window area by physical vapor transport; the optical transmission was then measured and from which the energy band gap was derived between 304 and 1067 K. The band gaps of CdTe can be fit well as a function of temperature using the Varshini expression: Eg (e V) = 1.5860 - 5.9117xl0(exp -4) T(sup 2)/(T + 160). Using the band gap data, the high temperature electron-hole equilibrium was calculated numerically by assuming the Kane's conduction band structure and a heavy-hole parabolic valance band. The calculated intrinsic carrier concentrations agree well with the experimental data reported previously. The calculated intrinsic Fermi levels between 270 and 1200 K were also presented.

  9. Point contact spectroscopy in oriented La[sub 2-x]Sr[sub x]CuO[sub 4] superconductors; energy gap and Fermi velocity

    SciTech Connect

    Hass, N. ); Deutscher, G. ); Revcolevschi, A.; Dhalenne, G. )

    1994-08-01

    Point contact measurements in oriented La[sub 2-x]Sr[sub x]CuO[sub 4] samples were performed using metal tips. The current-voltage curves measured along the CuO plane direction (ab) are characteristic of the Andreev reflection phenomenon. The superconducting energy gap in the ab plane is determined, [Delta][sub ab] = 6 [+-] 1 meV, with a possibility for the existence of a lower subgap in the plane. A lower limit for the Fermi velocity in the CuO planes is also set by the measurements; V[sub F] [ge] 6 [times] 10[sup 7] cm/sec, which is significantly higher than the average velocity obtained by band calculations. The results are discussed in the context of different models for superconductivity in the layered oxides. In particular, the authors raise the possibility of an anisotropic gap parameter which may indicate a nonstandard s-wave pairing in La[sub 2-x]Sr[sub x]CuO[sub 4]. A comparison with previous results obtained on YBa[sub 2]Cu[sub 3]O[sub 7-[delta

  10. High-performance giant-magnetoresistance junctions based on the all-Heusler architecture with matched energy bands and Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Bai, Zhaoqiang; Cai, Yongqing; Shen, Lei; Han, Guchang; Feng, Yuanping

    2013-04-01

    We present an all-Heusler architecture which could be used as a rational design scheme for achieving high spin-filter efficiency in the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. A Co2MnSi/Ni2NiSi/Co2MnSi trilayer stack is chosen as the prototype of such an architecture, of which the electronic structure and magnetotransport properties are systematically investigated by first principles approaches. Well matched energy bands and Fermi surfaces between the all-Heusler electrode-spacer pair are found, which, in combination with the electrode half-metallicity, indicate large bulk and interfacial spin-asymmetry, high spin-filter efficiency, and consequently good magnetoresistance performance. Transport calculations further confirm the superiority of the all-Heusler architecture over the conventional Heusler/transition-metal structure by comparing their transmission coefficients and interfacial resistances of parallel conduction electrons, as well as the macroscopic current-voltage characteristics. We suggest future theoretical and experimental efforts in developing high-performance all-Heusler CPP-GMR junctions for the read heads of the next generation high-density hard disk drives.

  11. Functional Domain Walls as Active Elements for Energy Technology

    SciTech Connect

    Wu, Junqiao

    2016-10-12

    In the past five years in the duration of this project (July 2011-July 2016), we have made a wide range of achievements in both basic research and energy applications along the direction planned in the original proposal. These achievements were reflected by 13 articles published in peer-reviewed journals including Nature Communications, Nano Letters, etc., and one currently in revision at Science. These papers have been accumulatively cited for more than 660 times as of October 2016, according to Web of Science statistics. Specifically, we have made impactful discoveries in the following fields. Basic Research. We have investigated in depth the materials physics of the representative quantum material, VO2, on which most of our project is anchored. We have discovered that independent diffusion of heat and charge in the absence of quasiparticles in metallic VO2 leads to an anomalously low electronic thermal conductivity, dramatically violating the Wiedemann-Franz law, which is a robust law governing behavior of normal conductors stating that free electrons transport heat proportionally to the charge they transport. In addition, we have discovered a peculiar thermal rectification effect based on its phase transition, as well as a gating response of the phase transition. In parallel to the work on VO2, we have also made breakthroughs in investigation of transition metal dichalcogenides (TMDs): we have experimentally demonstrate a strong anisotropy in in-plane thermal conductivity of black phosphorous, discovered a new, unusual member of the TMDs family, ReS2, where the bulk behaves as monolayers due to electronic and vibrational decoupling, unusual interaction between physi-sorbed molecules and 2D semiconductors, and thermally driven crossover from indirect toward direct bandgap in some 2D TMDs. Applications. Based on the understanding and knowledge gained from the basic investigation, we have developed novel tools and

  12. Pseudogap-generated a coexistence of Fermi arcs and Fermi pockets in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Zhao, Huaisong; Gao, Deheng; Feng, Shiping

    2017-03-01

    One of the most intriguing puzzle is why there is a coexistence of Fermi arcs and Fermi pockets in the pseudogap phase of cuprate superconductors? This puzzle is calling for an explanation. Based on the t - J model in the fermion-spin representation, the coexistence of the Fermi arcs and Fermi pockets in cuprate superconductors is studied by taking into account the pseudogap effect. It is shown that the pseudogap induces an energy band splitting, and then the poles of the electron Green's function at zero energy form two contours in momentum space, however, the electron spectral weight on these two contours around the antinodal region is gapped out by the pseudogap, leaving behind the low-energy electron spectral weight only located at the disconnected segments around the nodal region. In particular, the tips of these disconnected segments converge on the hot spots to form the closed Fermi pockets, generating a coexistence of the Fermi arcs and Fermi pockets. Moreover, the single-particle coherent weight is directly related to the pseudogap, and grows linearly with doping. The calculated result of the overall dispersion of the electron excitations is in qualitative agreement with the experimental data. The theory also predicts that the pseudogap-induced peak-dip-hump structure in the electron spectrum is absent from the hot-spot directions.

  13. Ground state energy of the δ-Bose and Fermi gas at weak coupling from double extrapolation

    NASA Astrophysics Data System (ADS)

    Prolhac, Sylvain

    2017-04-01

    We consider the ground state energy of the Lieb–Liniger gas with δ interaction in the weak coupling regime γ \\to 0 . For bosons with repulsive interaction, previous studies gave the expansion {{e}\\text{B}}≤ft(γ \\right)≃ γ -4{γ3/2}/3π +≤ft(1/6-1/{π2}\\right){γ2} . Using a numerical solution of the Lieb–Liniger integral equation discretized with M points and finite strength γ of the interaction, we obtain very accurate numerics for the next orders after extrapolation on M and γ. The coefficient of {γ5/2} in the expansion is found to be approximately equal to -0.001 587 699 865 505 944 989 29 , accurate within all digits shown. This value is supported by a numerical solution of the Bethe equations with N particles, followed by extrapolation on N and γ. It was identified as ≤ft(3\\zeta (3)/8-1/2\\right)/{π3} by G Lang. The next two coefficients are also guessed from the numerics. For balanced spin 1/2 fermions with attractive interaction, the best result so far for the ground state energy has been {{e}\\text{F}}≤ft(γ \\right)≃ {π2}/12-γ /2+{γ2}/6 . An analogue double extrapolation scheme leads to the value -\\zeta (3)/{π4} for the coefficient of {γ3} .

  14. Fermi resonance in optical microcavities

    NASA Astrophysics Data System (ADS)

    Yi, Chang-Hwan; Yu, Hyeon-Hye; Lee, Ji-Won; Kim, Chil-Min

    2015-04-01

    Fermi resonance is a phenomenon of quantum mechanical superposition, which most often occurs between normal and overtone modes in molecular systems that are nearly coincident in energy. We find that scarred resonances in deformed dielectric microcavities are the very phenomenon of Fermi resonance, that is, a pair of quasinormal modes interact with each other due to coupling and a pair of resonances are generated through an avoided resonance crossing. Then the quantum number difference of a pair of quasinormal modes, which is a consequence of quantum mechanical superposition, equals periodic orbits, whereby the resonances are localized on the periodic orbits. We derive the relation between the quantum number difference and the periodic orbits and confirm it in an elliptic, a rectangular, and a stadium-shaped dielectric microcavity.

  15. Fermi Surface of the Most Dilute Superconductor

    NASA Astrophysics Data System (ADS)

    Lin, Xiao; Zhu, Zengwei; Fauqué, Benoît; Behnia, Kamran

    2013-04-01

    The origin of superconductivity in bulk SrTiO3 is a mystery since the nonmonotonous variation of the critical transition with carrier concentration defies the expectations of the crudest version of the BCS theory. Here, employing the Nernst effect, an extremely sensitive probe of tiny bulk Fermi surfaces, we show that, down to concentrations as low as 5.5×1017cm-3, the system has both a sharp Fermi surface and a superconducting ground state. The most dilute superconductor currently known therefore has a metallic normal state with a Fermi energy as little as 1.1 meV on top of a band gap as large as 3 eV. The occurrence of a superconducting instability in an extremely small, single-component, and barely anisotropic Fermi surface implies strong constraints for the identification of the pairing mechanism.

  16. New semi-automatic method for reaction product charge and mass identification in heavy-ion collisions at Fermi energies

    NASA Astrophysics Data System (ADS)

    Gruyer, D.; Bonnet, E.; Chbihi, A.; Frankland, J. D.; Barlini, S.; Borderie, B.; Bougault, R.; Dueñas, J. A.; Galichet, E.; Kordyasz, A.; Kozik, T.; Le Neindre, N.; Lopez, O.; Pârlog, M.; Pastore, G.; Piantelli, S.; Valdré, S.; Verde, G.; Vient, E.

    2017-03-01

    This article presents a new semi-automatic method for charge and mass identification of charged nuclear fragments using either ΔE - E correlations between measured energy losses in two successive detectors or correlations between charge signal amplitude and rise time in a single silicon detector, derived from digital pulse shape analysis techniques. In both cases different nuclear species (defined by their atomic number Z and mass number A) can be visually identified from such correlations if they are presented as a two-dimensional histogram ('identification matrix'), in which case correlations for different species populate different ridge lines ('identification lines') in the matrix. The proposed algorithm is based on the identification matrix's properties and uses as little information as possible on the global form of the identification lines, making it applicable to a large variety of matrices. Particular attention has been paid to the implementation in a suitable graphical environment, so that only two mouse-clicks are required from the user to calculate all initialization parameters. Example applications to recent data from both INDRA and FAZIA telescopes are presented.

  17. Fermi Galactic Center Zoom

    NASA Video Gallery

    This animation zooms into an image of the Milky Way, shown in visible light, and superimposes a gamma-ray map of the galactic center from NASA's Fermi. Raw data transitions to a view with all known...

  18. Fermi, Szilard and Trinity

    ERIC Educational Resources Information Center

    Anderson, Herbert L.

    1974-01-01

    The final installment of the author's recollections of his work with physicists Enrico Fermi, Leo Szilard and others in developing the first controlled nuclear chain reaction and in preparing the test explosion of the first atomic bomb. (GS)

  19. Hidden Fermi liquid; the moral: a good effective low-energy theory is worth all of Monte Carlo with Las Vegas thrown in

    NASA Astrophysics Data System (ADS)

    Anderson, Philip W.; Casey, Philip A.

    2010-04-01

    We present a formalism for dealing directly with the effects of the Gutzwiller projection implicit in the t-J model which is widely believed to underlie the phenomenology of the high-Tc cuprates. We suggest that a true Bardeen-Cooper-Schrieffer condensation from a Fermi liquid state takes place, but in the unphysical space prior to projection. At low doping, however, instead of a hidden Fermi liquid one gets a 'hidden' non-superconducting resonating valence bond state which develops hole pockets upon doping. The theory which results upon projection does not follow conventional rules of diagram theory and in fact in the normal state is a Z = 0 non-Fermi liquid. Anomalous properties of the 'strange metal' normal state are predicted and compared against experimental findings.

  20. Universal Pinning Energy Barrier for Driven Domain Walls in Thin Ferromagnetic Films

    NASA Astrophysics Data System (ADS)

    Jeudy, V.; Mougin, A.; Bustingorry, S.; Savero Torres, W.; Gorchon, J.; Kolton, A. B.; Lemaître, A.; Jamet, J.-P.

    2016-07-01

    We report a comparative study of magnetic field driven domain wall motion in thin films made of different magnetic materials for a wide range of field and temperature. The full thermally activated creep motion, observed below the depinning threshold, is shown to be described by a unique universal energy barrier function. Our findings should be relevant for other systems whose dynamics can be modeled by elastic interfaces moving on disordered energy landscapes.

  1. Universal Pinning Energy Barrier for Driven Domain Walls in Thin Ferromagnetic Films.

    PubMed

    Jeudy, V; Mougin, A; Bustingorry, S; Savero Torres, W; Gorchon, J; Kolton, A B; Lemaître, A; Jamet, J-P

    2016-07-29

    We report a comparative study of magnetic field driven domain wall motion in thin films made of different magnetic materials for a wide range of field and temperature. The full thermally activated creep motion, observed below the depinning threshold, is shown to be described by a unique universal energy barrier function. Our findings should be relevant for other systems whose dynamics can be modeled by elastic interfaces moving on disordered energy landscapes.

  2. High-energy water sites determine peptide binding affinity and specificity of PDZ domains.

    PubMed

    Beuming, Thijs; Farid, Ramy; Sherman, Woody

    2009-08-01

    PDZ domains have well known binding preferences for distinct C-terminal peptide motifs. For most PDZ domains, these motifs are of the form [S/T]-W-[I/L/V]. Although the preference for S/T has been explained by a specific hydrogen bond interaction with a histidine in the PDZ domain and the (I/L/V) is buried in a hydrophobic pocket, the mechanism for Trp specificity at the second to last position has thus far remained unknown. Here, we apply a method to compute the free energies of explicit water molecules and predict that potency gained by Trp binding is due to a favorable release of high-energy water molecules into bulk. The affinities of a series of peptides for both wild-type and mutant forms of the PDZ domain of Erbin correlate very well with the computed free energy of binding of displaced waters, suggesting a direct relationship between water displacement and peptide affinity. Finally, we show a correlation between the magnitude of the displaced water free energy and the degree of Trp-sensitivity among subtypes of the HTRA PDZ family, indicating a water-mediated mechanism for specificity of peptide binding.

  3. Time-domain electromagnetic energy in a frequency-dispersive left-handed medium

    NASA Astrophysics Data System (ADS)

    Cui, Tie Jun; Kong, Jin Au

    2004-11-01

    From Maxwell’s equations and the Poynting theorem, the time-domain electric and magnetic energy densities are generally defined in the frequency-dispersive media based on the conservation of energy. As a consequence, a general definition of electric and magnetic energy is proposed. Comparing with existing formulations of electric and magnetic energy in frequency-dispersive media, the new definition is more reasonable and is valid in any case. Using the new definition and staring from the equation of motion, we have shown rigorously that the total energy density and the individual electric and magnetic energy densities are always positive in a realistic artificial left-handed medium (LHM) [

    R. A. Shelby, D. R. Smith, and S. Schultz, Science 292, 77 (2001)
    ], which obeys actually the Lorentz medium model, although such a LHM has negative permittivity and negative permeability simultaneously in a certain frequency range. We have also shown that the conservation of energy is not violated in LHM. The earlier conclusions can be easily extended to the Drude medium model and the cold plasma medium model. Through an exact analysis of a one-dimensional transient current source radiating in LHM, numerical results are given to demonstrate that the work done by source, the power flowing outwards a surface, and the electric and magnetic energy stored in a volume are all positive in the time domain.

  4. Nonlocal Poisson-Fermi model for ionic solvent.

    PubMed

    Xie, Dexuan; Liu, Jinn-Liang; Eisenberg, Bob

    2016-07-01

    We propose a nonlocal Poisson-Fermi model for ionic solvent that includes ion size effects and polarization correlations among water molecules in the calculation of electrostatic potential. It includes the previous Poisson-Fermi models as special cases, and its solution is the convolution of a solution of the corresponding nonlocal Poisson dielectric model with a Yukawa-like kernel function. The Fermi distribution is shown to be a set of optimal ionic concentration functions in the sense of minimizing an electrostatic potential free energy. Numerical results are reported to show the difference between a Poisson-Fermi solution and a corresponding Poisson solution.

  5. Nonlocal Poisson-Fermi model for ionic solvent

    NASA Astrophysics Data System (ADS)

    Xie, Dexuan; Liu, Jinn-Liang; Eisenberg, Bob

    2016-07-01

    We propose a nonlocal Poisson-Fermi model for ionic solvent that includes ion size effects and polarization correlations among water molecules in the calculation of electrostatic potential. It includes the previous Poisson-Fermi models as special cases, and its solution is the convolution of a solution of the corresponding nonlocal Poisson dielectric model with a Yukawa-like kernel function. The Fermi distribution is shown to be a set of optimal ionic concentration functions in the sense of minimizing an electrostatic potential free energy. Numerical results are reported to show the difference between a Poisson-Fermi solution and a corresponding Poisson solution.

  6. Probing the Contact Locally in a Trapped Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Paudel, Rabin; Sagi, Yoav; Drake, Tara; Jin, Deborah

    2013-03-01

    The inherent density inhomogeneity of a trapped gas can complicate interpretation of experiments and can wash out sharp features. This is especially important for a Fermi gas, where interaction effects as well as the local Fermi energy, or Fermi momentum, depend on the density. We report on experiments that use optical pumping with shaped light beams to spatially select the center part of a trapped gas for probing. This technique is compatible with momentum resolved measurements. For a weakly interacting Fermi gas of 40K atoms, we present measurements of the momentum distribution that reveal for the first time a sharp Fermi surface. We then apply this technique to a strongly interacting Fermi gas at the Feshbach resonance, where we measured the temperature dependence of the Tan's contact locally in the trapped gas.

  7. [Analysis of spectral intensity of fermi resonance of molecules].

    PubMed

    Jiang, Yong-heng; Gao, Shu-qin; Li, Zhan-long; Cao, Biao; Li, Zuo-wei

    2010-01-01

    Raman spectra of liquid carbon disulfide (CS) and carbon tetrachloride (CCl4) were measured. And the spectral intensity was analyzed using the J. F. Bertran theory and the group theory. The rule about Fermi resonance was obtained from the Raman spectra of carbon disulfide (CS) and carbon tetrachloride (CCL4): (1) The energy can transfer between a fundamental and an overtone frequency about Fermi resonance; the two spectra have the same intensity. The spectral intensity of the two spectra was equal (R=1) about Fermi resonance, when the difference between fundamental of Fermi resonance and overtone of Fermi resonance was very small. (2) The intensity of overtone is stronger than that of fundamental's. (3) The spectrum of Fermi resonance was observed, but the fundamental frequency was not. This article has very good reference value for the assignments in the molecular structure and the research of contents.

  8. A time domain energy theorem for scattering of plane electromagnetic waves

    NASA Astrophysics Data System (ADS)

    de Hoop, A. T.

    1984-10-01

    A time domain analysis of the scattering problem reveals the more general conditions under which the relevant theorems in the theory of the scattering of electromagnetic waves by an obstacle of bounded extent may also hold in the time domain. The present investigation is concerned with the energy theorem for plane wave scattering. Three different kinds of time behavior are considered, taking into account transient fields, time-periodic fields, and perpetuating fields. The derived energy theorem relates the energy which is both absorbed and scattered by the object to the spherical-wave amplitude of the scattered field in the far-field region, when observed in the direction of propagation of the incident plane wave.

  9. Decomposing Fuel Economy and Greenhouse Gas Regulatory Standards in the Energy Conversion Efficiency and Tractive Energy Domain

    SciTech Connect

    Pannone, Greg; Thomas, John F; Reale, Michael; Betz, Brian

    2017-01-01

    The three foundational elements that determine mobile source energy use and tailpipe carbon dioxide (CO2) emissions are the tractive energy requirements of the vehicle, the on-cycle energy conversion efficiency of the propulsion system, and the energy source. The tractive energy requirements are determined by the vehicle's mass, aerodynamic drag, tire rolling resistance, and parasitic drag. Oncycle energy conversion of the propulsion system is dictated by the tractive efficiency, non-tractive energy use, kinetic energy recovery, and parasitic losses. The energy source determines the mobile source CO2 emissions. For current vehicles, tractive energy requirements and overall energy conversion efficiency are readily available from the decomposition of test data. For future applications, plausible levels of mass reduction, aerodynamic drag improvements, and tire rolling resistance can be transposed into the tractive energy domain. Similarly, by combining thermodynamic, mechanical efficiency, and kinetic energy recovery fundamentals with logical proxies, achievable levels of energy conversion efficiency can be established to allow for the evaluation of future powertrain requirements. Combining the plausible levels of tractive energy and on-cycle efficiency provides a means to compute sustainable vehicle and propulsion system scenarios that can achieve future regulations. Using these principles, the regulations established in the United States (U.S.) for fuel consumption and CO2 emissions are evaluated. Fleet-level scenarios are generated and compared to the technology deployment assumptions made during rule-making. When compared to the rule-making assumptions, the results indicate that a greater level of advanced vehicle and propulsion system technology deployment will be required to achieve the model year 2025 U.S. standards for fuel economy and CO2 emissions.

  10. Upgrading Fermi Without Traveling to Space

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-02-01

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has received an upgrade that increased its sensitivity by a whopping 40% and nobody had to travel to space to make it happen! The difference instead stems from remarkable improvement to the software used to analyze Fermi-LATs data, and it has resulted in a new high-energy map of our sky.Animation (click to watch!) comparing the Pass 7 to the Pass 8 Fermi-LAT analysis, in a region in the constellation Carina. Pass 8 provides more accurate directions for incoming gamma rays, so more of them fall closer to their sources, creating taller spikes and a sharper image. [NASA/DOE/Fermi LAT Collaboration]Pass 8Fermi-LAT has been surveying the whole sky since August 2008. It detects gamma-ray photons by converting them into electron-positron pairs and tracking the paths of these charged particles. But differentiating this signal from the charged cosmic rays that also pass through the detector with a flux that can be 10,000 times larger! is a challenging process. Making this distinction and rebuilding the path of the original gamma ray relies on complex analysis software.Pass 8 is a complete reprocessing of all data collected by Fermi-LAT. The software has gone through many revisions before now, but this is the first revision that has taken into account all of the experience that the Fermi team has gained operating the LAT in its orbital environment.The improvements made in Pass 8 include better background rejection of misclassified charged particles, improvements to the point spread function and effective area of the detector, and an extension of the effective energy range from below 100 MeV to beyond a few hundred GeV. The changes made in Pass 8 have increased the sensitivity of Fermi-LAT by an astonishing 40%.Map of the High-Energy SkySky map of the sources in the 2FHL catalog, classified by their most likely association. Click for a better look! [Ackermann et al. 2016]The first result from the

  11. Fermi surface instabilities in CeRh2Si2 at high magnetic field and pressure

    NASA Astrophysics Data System (ADS)

    Palacio Morales, A.; Pourret, A.; Seyfarth, G.; Suzuki, M.-T.; Braithwaite, D.; Knebel, G.; Aoki, D.; Flouquet, J.

    2015-06-01

    We present thermoelectric power (TEP) studies under pressure and high magnetic field in the antiferromagnet CeRh2Si2 at low temperature. Under a magnetic field, large quantum oscillations are observed in the TEP, S (H ) , in the antiferromagnetic phase. They suddenly disappear when entering in the polarized paramagnetic state at Hc, pointing out an important reconstruction of the Fermi surface. Under pressure, S /T increases strongly at low temperature near the critical pressure Pc, where the antiferromagnetic (AF) order is suppressed, implying the interplay of a Fermi surface change and low-energy excitations driven by spin and valence fluctuations. The difference between the TEP signal in the polarized paramagnetic state above Hc at ambient pressure and in the pressure-induced paramagnetic state above Pc can be explained by different Fermi surfaces. Band-structure calculations at P =0 stress that in the AF phase the 4 f contribution at the Fermi level (EF) is weak, while it is the main contribution in the paramagnetic domain. In the polarized paramagnetic phase the 4 f contribution at EF drops. Large quantum oscillations are observed in the antiferromagnetic state while these disappear in the polarized state above Hc. Comparison is made to the CeRu2Si2 series highly studied for its (H ,T ) phase diagram.

  12. Simultaneous prediction of binding free energy and specificity for PDZ domain-peptide interactions

    NASA Astrophysics Data System (ADS)

    Crivelli, Joseph J.; Lemmon, Gordon; Kaufmann, Kristian W.; Meiler, Jens

    2013-12-01

    Interactions between protein domains and linear peptides underlie many biological processes. Among these interactions, the recognition of C-terminal peptides by PDZ domains is one of the most ubiquitous. In this work, we present a mathematical model for PDZ domain-peptide interactions capable of predicting both affinity and specificity of binding based on X-ray crystal structures and comparative modeling with R osetta. We developed our mathematical model using a large phage display dataset describing binding specificity for a wild type PDZ domain and 91 single mutants, as well as binding affinity data for a wild type PDZ domain binding to 28 different peptides. Structural refinement was carried out through several R osetta protocols, the most accurate of which included flexible peptide docking and several iterations of side chain repacking and backbone minimization. Our findings emphasize the importance of backbone flexibility and the energetic contributions of side chain-side chain hydrogen bonds in accurately predicting interactions. We also determined that predicting PDZ domain-peptide interactions became increasingly challenging as the length of the peptide increased in the N-terminal direction. In the training dataset, predicted binding energies correlated with those derived through calorimetry and specificity switches introduced through single mutations at interface positions were recapitulated. In independent tests, our best performing protocol was capable of predicting dissociation constants well within one order of magnitude of the experimental values and specificity profiles at the level of accuracy of previous studies. To our knowledge, this approach represents the first integrated protocol for predicting both affinity and specificity for PDZ domain-peptide interactions.

  13. Supernova Remnants with Fermi Large Area Telescope

    NASA Astrophysics Data System (ADS)

    Caragiulo, M.; Di Venere, L.

    2017-03-01

    The Large Area Telescope (LAT), on-board the Fermi satellite, proved to be, after 8 years of data taking, an excellent instrument to detect and observe Supernova Remnants (SNRs) in a range of energies running from few hundred MeV up to few hundred GeV. It provides essential information on physical processes that occur at the source, involving both accelerated leptons and hadrons, in order to understand the mechanisms responsible for the primary Cosmic Ray (CR) acceleration. We show the latest results in the observation of Galactic SNRs by Fermi-LAT.

  14. Fermi TGF detection map

    NASA Video Gallery

    Fermi’s Gamma-ray Burst Monitor detected 130 TGFs from August 2008 to the end of 2010. Thanks to instrument tweaks, the team has been able to improve the detection rate to several TGFs per week. ...

  15. The Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    Thompson, Dave; McEnery, Julie

    2011-01-01

    This slide presentation reviews the Gamma Ray Astronomy as enhanced by the Fermi Gamma Ray Space Telescope and Radio Astronomy as a synergistic relationship. Gamma rays often represent a significant part of the energy budget of a source; therefore, gamma-ray studies can be critical to understanding physical processes in such sources. Radio observations offer timing and spatial resolutions vastly superior to anything possible with gamma-ray telescopes; therefore radio is often the key to understanding source structure. Gamma-ray and radio observations can complement each other, making a great team. It reviews the Fermi Guest Investigator (GI) program, and calls for more cooperative work that involves Fermi and the Very Long Baseline Array (VLBA), a system of ten radio telescopes.

  16. Interaction quenches of Fermi gases

    SciTech Connect

    Uhrig, Goetz S.

    2009-12-15

    It is shown that the jump in the momentum distribution of Fermi gases evolves smoothly for small and intermediate times once an interaction between the fermions is suddenly switched on. The jump does not vanish abruptly. The loci in momentum space where the jumps occur are those of the noninteracting Fermi sea. No relaxation of the Fermi surface geometry takes place.

  17. Fermi LARGE AREA TELESCOPE DETECTION OF TWO VERY-HIGH-ENERGY (E > 100 GeV) γ-RAY PHOTONS FROM THE z = 1.1 BLAZAR PKS 0426–380

    SciTech Connect

    Tanaka, Y. T.; Mizuno, T.; Cheung, C. C.; Dermer, C. D.; Inoue, Y.; Stawarz, Ł.; Ajello, M.; Wood, D. L.; Chekhtman, A.; Fukazawa, Y.; Ohno, M.; Paneque, D.; Thompson, D. J.

    2013-11-01

    We report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E > 100 GeV) γ-ray photons from the directional vicinity of the distant (redshift, z = 1.1) blazar PKS 0426–380. The null hypothesis that both the 134 and 122 GeV photons originate from unrelated sources can be rejected at the 5.5σ confidence level. We therefore claim that at least one of the two VHE photons is securely associated with PKS 0426–380, making it the most distant VHE emitter known to date. The results are in agreement with recent Fermi-LAT constraints on the extragalactic background light (EBL) intensity, which imply a z ≅ 1 horizon for ≅ 100 GeV photons. The LAT detection of the two VHE γ-rays coincided roughly with flaring states of the source, although we did not find an exact correspondence between the VHE photon arrival times and the flux maxima at lower γ-ray energies. Modeling the γ-ray continuum of PKS 0426–380 with daily bins revealed a significant spectral hardening around the time of the first VHE event detection (LAT photon index Γ ≅ 1.4) but on the other hand no pronounced spectral changes near the detection time of the second one. This combination implies a rather complex variability pattern of the source in γ-rays during the flaring epochs. An additional flat component is possibly present above several tens of GeV in the EBL-corrected Fermi-LAT spectrum accumulated over the ∼8 month high state.

  18. Fermi and Non-Fermi Liquid Behavior in Quantum Impurity Systems: Conserving Slave Boson Theory

    NASA Astrophysics Data System (ADS)

    Kroha, Johann; Woelfle, Peter

    1998-12-01

    The question of Fermi liquid vs. non-Fermi liquid behavior induced by strong correlations is one of the prominent problems in metallic local moment systems. As standard models for such systems, the SU(N)× SU(M) Anderson impurity models exhibit both Fermi liquid and non-Fermi liquid behavior, depending on their symmetry. Taking the Anderson model as an example, these lectures first give an introduction to the auxiliary boson method to describe correlated systems governed by a strong, short-range electronic repulsion. It is then shown how to include the relevant low-lying excitations (coherent spin flip and charge fluctuation processes), while preserving the local gauge symmetry of the model. This amounts to a conserving T-matrix approximation (CTMA). We prove a cancellation theorem showing that the CTMA incorporates all leading and subleading infrared singularities at any given order in a self-consistent loop expansion of the free energy. As a result, the CTMA recovers the correct infrared behavior of the auxiliary particle propagators, indicating that it correctly describes both the Fermi and the non-Fermi liquid regimes of the Anderson model.

  19. Continuous transitions between composite Fermi liquid and Landau Fermi liquid: A route to fractionalized Mott insulators

    NASA Astrophysics Data System (ADS)

    Barkeshli, Maissam; McGreevy, John

    2012-08-01

    One of the most successful theories of a non-Fermi-liquid metallic state is the composite Fermi-liquid (CFL) theory of the half-filled Landau level. In this paper, we study continuous quantum phase transitions out of the CFL state and into a Landau Fermi liquid, in the limit of no disorder and fixed particle number. This transition can be induced by tuning the bandwidth of the Landau level relative to the interaction energy, for instance through an externally applied periodic potential. We find a transition to the Landau Fermi liquid through a gapless Mott insulator with a Fermi surface of neutral fermionic excitations. In the presence of spatial symmetries, we also find a direct continuous transition between the CFL and the Landau Fermi liquid. The transitions have a number of characteristic observable signatures, including the presence of two crossover temperature scales, resistivity jumps, and vanishing compressibility. When the composite fermions are paired instead, our results imply quantum critical points between various non-Abelian topological states, including the ν=1/2 Moore-Read Pfaffian [Ising × U(1) topological order], a version of the Kitaev B phase (Ising topological order), and paired electronic superconductors. To study such transitions, we use a projective construction of the CFL, which goes beyond the conventional framework of flux attachment to include a broader set of quantum fluctuations. These considerations suggest a possible route to fractionalized Mott insulators by starting with fractional quantum Hall states and tuning the Landau-level bandwidth.

  20. Mathematical methods for restricted domain ternary liquid mixture free energy determination using light scattering.

    PubMed

    Wahle, Chris W; Ross, David S; Thurston, George M

    2013-09-28

    We extend methods of solution of a light scattering partial differential equation for the free energy of mixing to apply to connected, isotropic ternary liquid composition domains that do not touch all three binary axes. To do so we mathematically analyze the problem of inferring needed Dirichlet boundary data, and solving for the free energy, with use of hypothetical static light scattering measurements that correspond to dielectric composition gradient vectors that have distinct directions. The physical idea behind the technique is that contrasting absorption properties of mixture components can result in such distinctly directed dielectric composition gradient vectors, due to their differing wavelength dependences of dielectric response. At suitably chosen wavelengths, contrasting light scattering efficiency patterns in the ternary composition triangle can then correspond to the same underlying free energy, and enlarge the scope of available information about the free energy, as shown here. We show how to use distinctly directed dielectric gradients to measure the free energy on both straight lines and curves within the ternary composition triangle, so as to provide needed Dirichlet conditions for light scattering partial differential equation solution. With use of Monte Carlo simulations of noisy light scattering data, we provide estimates of the overall system measurement time and sample spacing needed to determine the free energy to a desired degree of accuracy, for various angles between the assumed dielectric gradient vectors, and indicate how the measurement time depends on instrumental throughput parameters. The present analysis methods provide a way to use static light scattering to measure, directly, mixing free energies of many systems that contain such restricted liquid domains, including aqueous solutions of biological macromolecules, micellar mixtures and microemulsions, and many small molecule systems that are important in separation technology.

  1. Mathematical methods for restricted domain ternary liquid mixture free energy determination using light scattering

    NASA Astrophysics Data System (ADS)

    Wahle, Chris W.; Ross, David S.; Thurston, George M.

    2013-09-01

    We extend methods of solution of a light scattering partial differential equation for the free energy of mixing to apply to connected, isotropic ternary liquid composition domains that do not touch all three binary axes. To do so we mathematically analyze the problem of inferring needed Dirichlet boundary data, and solving for the free energy, with use of hypothetical static light scattering measurements that correspond to dielectric composition gradient vectors that have distinct directions. The physical idea behind the technique is that contrasting absorption properties of mixture components can result in such distinctly directed dielectric composition gradient vectors, due to their differing wavelength dependences of dielectric response. At suitably chosen wavelengths, contrasting light scattering efficiency patterns in the ternary composition triangle can then correspond to the same underlying free energy, and enlarge the scope of available information about the free energy, as shown here. We show how to use distinctly directed dielectric gradients to measure the free energy on both straight lines and curves within the ternary composition triangle, so as to provide needed Dirichlet conditions for light scattering partial differential equation solution. With use of Monte Carlo simulations of noisy light scattering data, we provide estimates of the overall system measurement time and sample spacing needed to determine the free energy to a desired degree of accuracy, for various angles between the assumed dielectric gradient vectors, and indicate how the measurement time depends on instrumental throughput parameters. The present analysis methods provide a way to use static light scattering to measure, directly, mixing free energies of many systems that contain such restricted liquid domains, including aqueous solutions of biological macromolecules, micellar mixtures and microemulsions, and many small molecule systems that are important in separation technology.

  2. Fermi Gamma-Ray Space Telescope Science Overview

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2010-01-01

    After more than 2 years of science operations, the Fermi Gamma-ray Space Telescope continues to survey the high-energy sky on a daily basis. In addition to the more than 1400 sources found in the first Fermi Large Area Telescope Catalog (I FGL), new results continue to emerge. Some of these are: (1) Large-scale diffuse emission suggests possible activity from the Galactic Center region in the past; (2) a gamma-ray nova was found, indicating particle acceleration in this binary system; and (3) the Crab Nebula, long thought to be a steady source, has varied in the energy ranges seen by both Fermi instruments.

  3. Energy of the interaction between membrane lipid domains calculated from splay and tilt deformations

    NASA Astrophysics Data System (ADS)

    Galimzyanov, T. R.; Molotkovsky, R. J.; Kheyfets, B. B.; Akimov, S. A.

    2013-01-01

    Specific domains, called rafts, are formed in cell membranes. Similar lipid domains can be formed in model membranes as a result of phase separation with raft size may remaining small (˜10-100 nm) for a long time. The characteristic lifetime of a nanoraft ensemble strongly depends on the nature of mutual raft interactions. The interaction energy between the boundaries of two rafts has been calculated under the assumption that the thickness of the raft bilayer is greater than that of the surrounding membrane, and elastic deformations appear in order to smooth the thickness mismatch at the boundary. When rafts approach each other, deformations from their boundaries overlap, making interaction energy profile sophisticated. It has been shown that raft merger occurs in two stages: rafts first merge in one monolayer of the lipid bilayer and then in another monolayer. Each merger stage requires overcoming of an energy barrier of about 0.08-0.12 k BT per 1 nm of boundary length. These results allow us to explain the stability of the ensemble of finite sized rafts.

  4. FERMI LARGE AREA TELESCOPE SECOND SOURCE CATALOG

    SciTech Connect

    Nolan, P. L.; Ajello, M.; Allafort, A.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Abdo, A. A.; Ackermann, M.; Antolini, E.; Bonamente, E.; Atwood, W. B.; Belfiore, A.; Axelsson, M.; Baldini, L.; Bellazzini, R.; Ballet, J.; Bastieri, D.; Bignami, G. F. E-mail: Gino.Tosti@pg.infn.it E-mail: tburnett@u.washington.edu; and others

    2012-04-01

    We present the second catalog of high-energy {gamma}-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely {gamma}-ray-producing source classes.

  5. Fermi Large Area Telescope Second Source Catalog

    NASA Technical Reports Server (NTRS)

    Nolan, P. L.; Abdo, A. A.; Ackermann, M.; Ajello, M; Allafort, A.; Antolini, E; Bonnell, J.; Cannon, A.; Celik O.; Corbet, R.; Davis, D. S.; DeCesar, M. E.; Ferrara, E. C.; Gehrels, N.; Harding, A. K.; Hays, E.; Johnson, T. E.; McConville, W.; McEnery, J. E; Perkins, J. S.; Racusin, J. L; Scargle, J. D.; Stephens, T. E.; Thompson, D. J.; Troja, E.

    2012-01-01

    We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24-month period. The Second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in 5 energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 11eV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely gamma-ray-producing source classes.

  6. Nonlinear Cascades of Surface Oceanic Geostrophic Kinetic Energy in the Frequency Domain

    DTIC Science & Technology

    2012-09-01

    spectral transfers T(v) 5 2 › ›v P(v) of kinetic energy in frequency v space, as diagnostics of the impact of nonlinearity on the frequency spectra of...surface ocean geostrophic flows. Our analysis of non- linearities in the frequency domain is somewhat similar to the diagnostics employed by Sheng and...transfers T(v) could be useful diagnostics of the role of non- linearity in maintaining low-frequency variability in the climate system. In ocean models, T

  7. Nodal to nodeless superconducting energy-gap structure change concomitant with Fermi-surface reconstruction in the heavy-fermion compound CeCoIn5

    DOE PAGES

    Kim, Hyunsoo; Tanatar, M. A.; Flint, R.; ...

    2015-01-15

    The London penetration depth λ(T) was measured in single crystals of Ce1–xRxCoIn₅, R=La, Nd, and Yb down to Tmin ≈ 50 mK (Tc/Tmin ~50) using a tunnel-diode resonator. In the cleanest samples Δλ(T) is best described by the power law, Δλ(T) ∝ Tn, with n ~ 1, consistent with line nodes. Substitutions of Ce with La, Nd, and Yb lead to similar monotonic suppressions of Tc, however, the effects on Δλ(T) differ. While La and Nd dopings lead to increase of the exponent n and saturation at n ~ 2, as expected for a dirty nodal superconductor, Yb doping leadsmore » to n > 3, suggesting a change from nodal to nodeless superconductivity. As a result, this superconducting gap structure change happens in the same doping range where changes of the Fermi surface topology were reported, implying that the nodal structure and Fermi surface topology are closely linked.« less

  8. Generalized Fermi-Dirac functions and derivatives: properties and evaluation

    NASA Astrophysics Data System (ADS)

    Gong, Z.; Zejda, L.; Däppen, W.; Aparicio, J. M.

    2001-05-01

    The generalized Fermi-Dirac functions and their derivatives are important in evaluating the thermodynamic quantities of partially degenerate electrons in hot dense stellar plasmas. New recursion relations of the generalized Fermi-Dirac functions have been found. An effective numerical method to evaluate the derivatives of the generalized Fermi-Dirac functions up to third order with respect to both degeneracy and temperature is then proposed, following Aparicio [Ap.J.S.S. 117 (1998) 627]. A Fortran program based on this method, together with a sample test case, is provided. Accuracy and domain of reliability of some other, popularly used analytic approximations of the generalized Fermi-Dirac functions for extreme conditions are investigated and compared with our results.

  9. Electric current effect on the energy barrier of magnetic domain wall depinning: origin of the quadratic contribution.

    PubMed

    Kim, Kab-Jin; Ryu, Jisu; Gim, Gi-Hong; Lee, Jae-Chul; Shin, Kyung-Ho; Lee, Hyun-Woo; Choe, Sug-Bong

    2011-11-18

    The energy barrier of a magnetic domain wall trapped at a defect is measured experimentally. When the domain wall is pushed by an electric current and/or a magnetic field, the depinning time from the barrier exhibits perfect exponential distribution, indicating that a single energy barrier governs the depinning. The electric current is found to generate linear and quadratic contributions to the energy barrier, which are attributed to the nonadiabatic and adiabatic spin-transfer torques, respectively. The adiabatic spin-transfer torque reduces the energy barrier and, consequently, causes depinning at lower current densities, promising a way toward low-power current-controlled magnetic applications.

  10. Adaptive ferroelectric states in systems with low domain wall energy: Tetragonal microdomains

    NASA Astrophysics Data System (ADS)

    Jin, Y. M.; Wang, Y. U.; Khachaturyan, A. G.; Li, J. F.; Viehland, D.

    2003-09-01

    Ferroelectric and ferroelastic phases with very low domain wall energies have been shown to form miniaturized microdomain structures. A theory of an adaptive ferroelectric phase has been developed to predict the microdomain-averaged crystal lattice parameters of this structurally inhomogeneous state. The theory is an extension of conventional martensite theory, applied to ferroelectric systems with very low domain wall energies. The case of ferroelectric microdomains of tetragonal symmetry is considered. It is shown for such a case that a nanoscale coherent mixture of microdomains can be interpreted as an adaptive ferroelectric phase, whose microdomain-averaged crystal lattice is monoclinic. The crystal lattice parameters of this monoclinic phase are self-adjusting parameters, which minimize the transformation stress. Self-adjustment is achieved by application of the invariant plane strain to the parent cubic lattice, and the value of the self-adjusted parameters is a linear superposition of the lattice constants of the parent and product phases. Experimental investigations of Pb(Mg1/3Nb2/3)O3-PbTiO3 and Pb(Zn1/3Nb2/3)O3-PbTiO3 single crystals confirm many of the predictions of this theory.

  11. Looking for the Northern Fermi Bubble with HAWC

    NASA Astrophysics Data System (ADS)

    Ayala, Hugo; Zhou, Hao; Huentemeyer, Petra; HAWC Collaboration

    2016-03-01

    The Fermi Bubbles were discovered in the GeV gamma-ray data from the Fermi Telescope in 2010. They extend up to 55° above and below the Galactic Center forming two large and homogeneous regions of spectrally hard gamma-ray emission. Understanding the mechanisms which produce the observed hard spectrum will help understand the origin of the Fermi Bubbles. Both hadronic and leptonic models can describe the spectrum of the bubbles, though the leptonic model can explain similar structures observed in microwave data from the WMAP and Planck satellites. Recent publications show that the spectrum of the Fermi Bubbles is well described by a power law with an exponential cutoff between 100MeV to 500GeV. Observing the Fermi Bubbles at higher gamma-ray energies will help constrain their spectrum. A steeper cutoff will favor a leptonic model. The High Altitude Water Cherenkov (HAWC) Observatory, located 4100m above sea level in Mexico, is designed to measure high-energy gamma rays between 100GeV to 100TeV. With a large field of view and good sensitivity to spatially extended sources, HAWC is the ground-based observatory best suited to detect extended regions like the Fermi Bubbles. We present a search for emission from the Fermi Bubble visible to HAWC.

  12. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    DOE PAGES

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; ...

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  13. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    SciTech Connect

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; Markiewicz, R. S.; Bansil, A.; Wilson, S. D.; He, Rui -Hua

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  14. Increased monolayer domain size and patterned growth of tungsten disulfide through controlling surface energy of substrates

    NASA Astrophysics Data System (ADS)

    Godin, Kyle; Kang, Kyungnam; Fu, Shichen; Yang, Eui-Hyeok

    2016-08-01

    We report a surface energy-controlled low-pressure chemical vapor deposition growth of WS2 monolayers on SiO2 using pre-growth oxygen plasma treatment of substrates, facilitating increased monolayer surface coverage and patterned growth without lithography. Oxygen plasma treatment of the substrate caused an increase in the average domain size of WS2 monolayers by 78%  ±  2% while having a slight reduction in nucleation density, which translates to increased monolayer surface coverage. This substrate effect on growth was exploited to grow patterned WS2 monolayers by patterned plasma treatment on patterned substrates and by patterned source material with resolutions less than 10 µm. Contact angle-based surface energy measurements revealed a dramatic increase in polar surface energy. A growth model was proposed with lowered activation energies for growth and increased surface diffusion length consistent with the range of results observed. WS2 samples grown with and without oxygen plasma were similar high quality monolayers verified through transmission electron microscopy, selected area electron diffraction, atomic force microscopy, Raman, and photoluminescence measurements. This technique enables the production of large-grain size, patterned WS2 without a post-growth lithography process, thereby providing clean surfaces for device applications.

  15. Berry Fermi liquid theory

    NASA Astrophysics Data System (ADS)

    Chen, Jing-Yuan; Son, Dam Thanh

    2017-02-01

    We develop an extension of the Landau Fermi liquid theory to systems of interacting fermions with non-trivial Berry curvature. We propose a kinetic equation and a constitutive relation for the electromagnetic current that together encode the linear response of such systems to external electromagnetic perturbations, to leading and next-to-leading orders in the expansion over the frequency and wave number of the perturbations. We analyze the Feynman diagrams in a large class of interacting quantum field theories and show that, after summing up all orders in perturbation theory, the current-current correlator exactly matches with the result obtained from the kinetic theory.

  16. Fermi Large Area Telescope Bright Gamma-ray Source List

    SciTech Connect

    Abdo, Aous A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Ballet, J.; Band, D.L.; Barbiellini, Guido; Bastieri, Denis; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bignami, G.F.; Bloom, Elliott D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brigida, M.; Bruel, P.; Burnett, Thompson H.; /more authors..

    2009-05-15

    Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than {approx}10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.

  17. First Light on GRBs with Fermi

    DTIC Science & Technology

    2010-08-04

    components at LAT energies, and the line-of-death problem [21] cannot be easily explained within the framework of such a model , as noted already in...30] using a GRB model [31] with different star formation rate factors for GRBs [31, 32, 33]. If UHECRs originate from long duration GRBs, then the...leptonic models are pitted against hadronic models , and found to be energetically favored. Interpretation of the Fermi data on GRBs helps establish

  18. FERMI-LAT Observations of Galatic Transients

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2010-01-01

    This slide presentation reviews the use of the Large Area Telescope on the Fermi Observatory observations of Galactic Transients. LAT all-sky monitoring is producing spectacular results for the GeV transient sky: (1) New blazars and unidentified transients (2) Probing the jet of the Cygnus X-3 microquasar (3) Discovery of gamma rays from V407 Cygni nova (4) Fast high-energy gamma-ray flares from the Crab Nebula.

  19. Conformal Fermi Coordinates

    SciTech Connect

    Dai, Liang; Pajer, Enrico; Schmidt, Fabian E-mail: Enrico.pajer@gmail.com

    2015-11-01

    Fermi Normal Coordinates (FNC) are a useful frame for isolating the locally observable, physical effects of a long-wavelength spacetime perturbation. Their cosmological application, however, is hampered by the fact that they are only valid on scales much smaller than the horizon. We introduce a generalization that we call Conformal Fermi Coordinates (CFC). CFC preserve all the advantages of FNC, but in addition are valid outside the horizon. They allow us to calculate the coupling of long- and short-wavelength modes on all scales larger than the sound horizon of the cosmological fluid, starting from the epoch of inflation until today, by removing the complications of the second order Einstein equations to a large extent, and eliminating all gauge ambiguities. As an application, we present a calculation of the effect of long-wavelength tensor modes on small scale density fluctuations. We recover previous results, but clarify the physical content of the individual contributions in terms of locally measurable effects and ''projection'' terms.

  20. Superconductivity versus bound-state formation in a two-band superconductor with small Fermi energy: Applications to Fe pnictides/chalcogenides and doped SrTiO3

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey V.; Eremin, Ilya; Efremov, Dmitri V.

    2016-05-01

    We analyze the interplay between superconductivity and the formation of bound pairs of fermions (BCS-BEC crossover) in a 2D model of interacting fermions with small Fermi energy EF and weak attractive interaction, which extends to energies well above EF. The 2D case is special because a two-particle bound state forms at arbitrary weak interaction, and already at weak coupling, one has to distinguish between the bound-state formation and superconductivity. We briefly review the situation in the one-band model and then consider two different two-band models: one with one hole band and one electron band and another with two hole or two electron bands. In each case, we obtain the bound-state energy 2 E0 for two fermions in a vacuum and solve the set of coupled equations for the pairing gaps and the chemical potentials to obtain the onset temperature of the pairing Tins and the quasiparticle dispersion at T =0 . We then compute the superfluid stiffness ρs(T =0 ) and obtain the actual Tc. For definiteness, we set EF in one band to be near zero and consider different ratios of E0 and EF in the other band. We show that at EF≫E0 , the behavior of both two-band models is BCS-like in the sense that Tc≈Tins≪EF and Δ ˜Tc . At EF≪E0 , the two models behave differently: in the model with two hole/two electron bands, Tins˜E0/lnE/0EF , Δ ˜(E0EF) 1 /2 , and Tc˜EF , like in the one-band model. In between Tins and Tc, the system displays a preformed pair behavior. In the model with one hole and one electron bands, Tc remains of order Tins, and both remain finite at EF=0 and of the order of E0. The preformed pair behavior still does exist in this model because Tc is numerically smaller than Tins. For both models, we reexpress Tins in terms of the fully renormalized two-particle scattering amplitude by extending to the two-band case (the method pioneered by Gorkov and Melik-Barkhudarov back in 1961). We apply our results for the model with a hole and an electron band to

  1. Insulating behavior of a trapped ideal Fermi gas.

    PubMed

    Pezzè, L; Pitaevskii, L; Smerzi, A; Stringari, S; Modugno, G; de Mirandes, E; Ferlaino, F; Ott, H; Roati, G; Inguscio, M

    2004-09-17

    We investigate theoretically and experimentally the center-of-mass motion of an ideal Fermi gas in a combined periodic and harmonic potential. We find a crossover from a conducting to an insulating regime as the Fermi energy moves from the first Bloch band into the band gap of the lattice. The conducting regime is characterized by an oscillation of the cloud about the potential minimum, while in the insulating case the center of mass remains on one side of the potential.

  2. Full-waveform inversion in the time domain with an energy-weighted gradient

    SciTech Connect

    Zhang, Zhigang; Huang, Lianjie; Lin, Youzuo

    2011-01-01

    When applying full-waveform inversion to surface seismic reflection data, one difficulty is that the deep region of the model is usually not reconstructed as well as the shallow region. We develop an energy-weighted gradient method for the time-domain full-waveform inversion to accelerate the convergence rate and improve reconstruction of the entire model without increasing the computational cost. Three different methods can alleviate the problem of poor reconstruction in the deep region of the model: the layer stripping, depth-weighting and pseudo-Hessian schemes. The first two approaches need to subjectively choose stripping depths and weighting functions. The third one scales the gradient with only the forward propagation wavefields from sources. However, the Hessian depends on wavefields from both sources and receivers. Our new energy-weighted method makes use of the energies of both forward and backward propagated wavefields from sources and receivers as weights to compute the gradient. We compare the reconstruction of our new method with those of the conjugate gradient and pseudo-Hessian methods, and demonstrate that our new method significantly improves the reconstruction of both the shallow and deep regions of the model.

  3. The Fermi Paradox Is Neither Fermi's Nor a Paradox

    NASA Astrophysics Data System (ADS)

    Gray, Robert H.

    2015-03-01

    The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth-and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked 'where is everybody?'- apparently suggesting that we don't see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist, or suggesting its absence is paradoxical. The claim 'they are not here; therefore they do not exist' was first published by Michael Hart, claiming that interstellar travel and colonization of the galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence-cited in the U. S. Congress as a reason for killing NASA's SETI program on one occasion-but evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox. Keywords: Astrobiology, SETI, Fermi paradox, extraterrestrial life

  4. High-redshift Fermi blazars

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Tagliaferri, G.; Foschini, L.; Ghirlanda, G.; Tavecchio, F.; Della Ceca, R.; Haardt, F.; Volonteri, M.; Gehrels, N.

    2011-02-01

    With the release of the first-year Fermi catalogue, the number of blazars detected above 100 MeV lying at high redshift has been largely increased. There are 28 blazars at z > 2 in the `clean' sample. All of them are flat spectrum radio quasars. We study and model their overall spectral energy distribution in order to find the physical parameters of the jet-emitting region, and for all of them, we estimate their black hole masses and accretion rates. We then compare the jet with the accretion disc properties, setting these sources in the broader context of all the other bright γ-ray or hard X-ray blazars. We confirm that the jet power correlates with the accretion luminosity. We find that the high-energy emission peak shifts to smaller frequencies as the observed luminosity increases, according to the blazar sequence, making the hard X-ray band the most suitable for searching the most-luminous and distant blazars.

  5. Signatures of an annular Fermi sea

    NASA Astrophysics Data System (ADS)

    Jo, Insun; Liu, Yang; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.; Winkler, R.

    2017-01-01

    The concept of a Fermi surface, the constant-energy surface containing all the occupied electron states in momentum, or wave-vector (k ) , space plays a key role in determining electronic properties of conductors. In two-dimensional (2D) carrier systems, the Fermi surface becomes a contour which, in the simplest case, encircles the occupied states. In this case, the area enclosed by the contour, which we refer to as the Fermi sea (FS), is a simple disk. Here we report the observation of an FS with a new topology, namely, an FS in the shape of an annulus. Such an FS is expected in a variety of 2D systems where the energy band dispersion supports a ring of extrema at finite k , but its experimental observation has been elusive. Our study provides (1) theoretical evidence for the presence of an annular FS in 2D hole systems confined to wide GaAs quantum wells and (2) experimental signatures of the onset of its occupation as an abrupt rise in the sample resistance, accompanied by a sudden appearance of Shubnikov-de Haas oscillations at an unexpectedly high frequency whose value does not simply correspond to the (negligible) density of holes contained within the annular FS.

  6. GRBs in the Era of Swift and Fermi

    NASA Technical Reports Server (NTRS)

    Racusin, Judy

    2011-01-01

    Utilizing both Swift and Fermi to study GRBs provides us with a unique broad spectral and temporal window into both prompt emission and afterglow studies. Swift has provided key information from GRB follow-up of LAT detected bursts) that has led to ground-based redshift measurements and afterglow broadband light curves and SEDs. We study the X-ray and optical afterglows of Fermi-LAT detected bursts in the context of the hundreds of GRBs discovered by Swift over the last 7 years) in order to better understand the origin of the high-energy gamma-rays. We also briefly describe the efforts to best facilitate joint Swift-Fermi observations. These initial results demonstrate the synergy between Swift and Fermi) and hint at the many interesting discoveries to come.

  7. Renormalization group and the superconducting susceptibility of a Fermi liquid

    SciTech Connect

    Parameswaran, S. A.; Sondhi, S. L.; Shankar, R.

    2010-11-15

    A free Fermi gas has, famously, a superconducting susceptibility that diverges logarithmically at zero temperature. In this paper we ask whether this is still true for a Fermi liquid and find that the answer is that it does not. From the perspective of the renormalization group for interacting fermions, the question arises because a repulsive interaction in the Cooper channel is a marginally irrelevant operator at the Fermi liquid fixed point and thus is also expected to infect various physical quantities with logarithms. Somewhat surprisingly, at least from the renormalization group viewpoint, the result for the superconducting susceptibility is that two logarithms are not better than one. In the course of this investigation we derive a Callan-Symanzik equation for the repulsive Fermi liquid using the momentum-shell renormalization group, and use it to compute the long-wavelength behavior of the superconducting correlation function in the emergent low-energy theory. We expect this technique to be of broader interest.

  8. TU-F-18A-02: Iterative Image-Domain Decomposition for Dual-Energy CT

    SciTech Connect

    Niu, T; Dong, X; Petrongolo, M; Zhu, L

    2014-06-15

    Purpose: Dual energy CT (DECT) imaging plays an important role in advanced imaging applications due to its material decomposition capability. Direct decomposition via matrix inversion suffers from significant degradation of image signal-to-noise ratios, which reduces clinical value. Existing de-noising algorithms achieve suboptimal performance since they suppress image noise either before or after the decomposition and do not fully explore the noise statistical properties of the decomposition process. We propose an iterative image-domain decomposition method for noise suppression in DECT, using the full variance-covariance matrix of the decomposed images. Methods: The proposed algorithm is formulated in the form of least-square estimation with smoothness regularization. It includes the inverse of the estimated variance-covariance matrix of the decomposed images as the penalty weight in the least-square term. Performance is evaluated using an evaluation phantom (Catphan 600) and an anthropomorphic head phantom. Results are compared to those generated using direct matrix inversion with no noise suppression, a de-noising method applied on the decomposed images, and an existing algorithm with similar formulation but with an edge-preserving regularization term. Results: On the Catphan phantom, our method retains the same spatial resolution as the CT images before decomposition while reducing the noise standard deviation of decomposed images by over 98%. The other methods either degrade spatial resolution or achieve less low-contrast detectability. Also, our method yields lower electron density measurement error than direct matrix inversion and reduces error variation by over 97%. On the head phantom, it reduces the noise standard deviation of decomposed images by over 97% without blurring the sinus structures. Conclusion: We propose an iterative image-domain decomposition method for DECT. The method combines noise suppression and material decomposition into an iterative

  9. Free-energy landscape of ion-channel voltage-sensor-domain activation.

    PubMed

    Delemotte, Lucie; Kasimova, Marina A; Klein, Michael L; Tarek, Mounir; Carnevale, Vincenzo

    2015-01-06

    Voltage sensor domains (VSDs) are membrane-bound protein modules that confer voltage sensitivity to membrane proteins. VSDs sense changes in the transmembrane voltage and convert the electrical signal into a conformational change called activation. Activation involves a reorganization of the membrane protein charges that is detected experimentally as transient currents. These so-called gating currents have been investigated extensively within the theoretical framework of so-called discrete-state Markov models (DMMs), whereby activation is conceptualized as a series of transitions across a discrete set of states. Historically, the interpretation of DMM transition rates in terms of transition state theory has been instrumental in shaping our view of the activation process, whose free-energy profile is currently envisioned as composed of a few local minima separated by steep barriers. Here we use atomistic level modeling and well-tempered metadynamics to calculate the configurational free energy along a single transition from first principles. We show that this transition is intrinsically multidimensional and described by a rough free-energy landscape. Remarkably, a coarse-grained description of the system, based on the use of the gating charge as reaction coordinate, reveals a smooth profile with a single barrier, consistent with phenomenological models. Our results bridge the gap between microscopic and macroscopic descriptions of activation dynamics and show that choosing the gating charge as reaction coordinate masks the topological complexity of the network of microstates participating in the transition. Importantly, full characterization of the latter is a prerequisite to rationalize modulation of this process by lipids, toxins, drugs, and genetic mutations.

  10. Free-energy landscape of ion-channel voltage-sensor–domain activation

    PubMed Central

    Delemotte, Lucie; Kasimova, Marina A.; Klein, Michael L.; Tarek, Mounir; Carnevale, Vincenzo

    2015-01-01

    Voltage sensor domains (VSDs) are membrane-bound protein modules that confer voltage sensitivity to membrane proteins. VSDs sense changes in the transmembrane voltage and convert the electrical signal into a conformational change called activation. Activation involves a reorganization of the membrane protein charges that is detected experimentally as transient currents. These so-called gating currents have been investigated extensively within the theoretical framework of so-called discrete-state Markov models (DMMs), whereby activation is conceptualized as a series of transitions across a discrete set of states. Historically, the interpretation of DMM transition rates in terms of transition state theory has been instrumental in shaping our view of the activation process, whose free-energy profile is currently envisioned as composed of a few local minima separated by steep barriers. Here we use atomistic level modeling and well-tempered metadynamics to calculate the configurational free energy along a single transition from first principles. We show that this transition is intrinsically multidimensional and described by a rough free-energy landscape. Remarkably, a coarse-grained description of the system, based on the use of the gating charge as reaction coordinate, reveals a smooth profile with a single barrier, consistent with phenomenological models. Our results bridge the gap between microscopic and macroscopic descriptions of activation dynamics and show that choosing the gating charge as reaction coordinate masks the topological complexity of the network of microstates participating in the transition. Importantly, full characterization of the latter is a prerequisite to rationalize modulation of this process by lipids, toxins, drugs, and genetic mutations. PMID:25535341

  11. Fermi GBM Observations of Terrestrial Gamma Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R. D.; Kippen, R. M.; vonKienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

    2010-01-01

    In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed 79 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds.

  12. The Statistical Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Maccone, C.

    In this paper is provided the statistical generalization of the Fermi paradox. The statistics of habitable planets may be based on a set of ten (and possibly more) astrobiological requirements first pointed out by Stephen H. Dole in his book Habitable planets for man (1964). The statistical generalization of the original and by now too simplistic Dole equation is provided by replacing a product of ten positive numbers by the product of ten positive random variables. This is denoted the SEH, an acronym standing for “Statistical Equation for Habitables”. The proof in this paper is based on the Central Limit Theorem (CLT) of Statistics, stating that the sum of any number of independent random variables, each of which may be ARBITRARILY distributed, approaches a Gaussian (i.e. normal) random variable (Lyapunov form of the CLT). It is then shown that: 1. The new random variable NHab, yielding the number of habitables (i.e. habitable planets) in the Galaxy, follows the log- normal distribution. By construction, the mean value of this log-normal distribution is the total number of habitable planets as given by the statistical Dole equation. 2. The ten (or more) astrobiological factors are now positive random variables. The probability distribution of each random variable may be arbitrary. The CLT in the so-called Lyapunov or Lindeberg forms (that both do not assume the factors to be identically distributed) allows for that. In other words, the CLT "translates" into the SEH by allowing an arbitrary probability distribution for each factor. This is both astrobiologically realistic and useful for any further investigations. 3. By applying the SEH it is shown that the (average) distance between any two nearby habitable planets in the Galaxy may be shown to be inversely proportional to the cubic root of NHab. This distance is denoted by new random variable D. The relevant probability density function is derived, which was named the "Maccone distribution" by Paul Davies in

  13. The fermi paradox is neither Fermi's nor a paradox.

    PubMed

    Gray, Robert H

    2015-03-01

    The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth--and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked "Where is everybody?"--apparently suggesting that we do not see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist or suggesting its absence is paradoxical. The claim "they are not here; therefore they do not exist" was first published by Michael Hart, claiming that interstellar travel and colonization of the Galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence--cited in the U.S. Congress as a reason for killing NASA's SETI program on one occasion. But evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox.

  14. BiFeO3 Domain Wall Energies and Structures: A Combined Experimental and Density Functional Theory+U Study

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Nelson, Chris; Melville, Alexander; Winchester, Benjamin; Shang, Shunli; Liu, Zi-Kui; Schlom, Darrell G.; Pan, Xiaoqing; Chen, Long-Qing

    2013-06-01

    We determined the atomic structures and energies of 109°, 180°, and 71° domain walls in BiFeO3, combining density functional theory+U calculations and aberration-corrected transmission electron microscopy images. We find a substantial Bi sublattice shift and a rather uniform Fe sublattice across the walls. The calculated wall energies (γ) follow the sequence γ109<γ180<γ71 for the 109°, 180°, and 71° walls. We attribute the high 71° wall energy to an opposite tilting rotation of the oxygen octahedra and the low 109° wall energy to the opposite twisting rotation of the oxygen octahedra across the domain walls.

  15. Fermi's New Pulsar Detection Technique

    NASA Video Gallery

    To locate a pulsar in Fermi LAT data requires knowledge of the object’s sky position, its pulse period, and how the pulse rate slows over time. Computers check many different combinations of posi...

  16. Directed Magnetic Particle Transport above Artificial Magnetic Domains Due to Dynamic Magnetic Potential Energy Landscape Transformation.

    PubMed

    Holzinger, Dennis; Koch, Iris; Burgard, Stefan; Ehresmann, Arno

    2015-07-28

    An approach for a remotely controllable transport of magnetic micro- and/or nanoparticles above a topographically flat exchange-bias (EB) thin film system, magnetically patterned into parallel stripe domains, is presented where the particle manipulation is achieved by sub-mT external magnetic field pulses. Superparamagnetic core-shell particles are moved stepwise by the dynamic transformation of the particles' magnetic potential energy landscape due to the external magnetic field pulses without affecting the magnetic state of the thin film system. The magnetic particle velocity is adjustable in the range of 1-100 μm/s by the design of the substrate's magnetic field landscape (MFL), the particle-substrate distance, and the magnitude of the applied external magnetic field pulses. The agglomeration of magnetic particles is avoided by the intrinsic magnetostatic repulsion of particles due to the parallel alignment of the particles' magnetic moments perpendicular to the transport direction and parallel to the surface normal of the substrate during the particle motion. The transport mechanism is modeled by a quantitative theory based on the precise knowledge of the sample's MFL and the particle-substrate distance.

  17. Representing situation awareness in collaborative systems: a case study in the energy distribution domain.

    PubMed

    Salmon, P M; Stanton, N A; Walker, G H; Jenkins, D; Baber, C; McMaster, R

    2008-03-01

    The concept of distributed situation awareness (DSA) is currently receiving increasing attention from the human factors community. This article investigates DSA in a collaborative real-world industrial setting by discussing the results derived from a recent naturalistic study undertaken within the UK energy distribution domain. The results describe the DSA-related information used by the networks of agents involved in the scenarios analysed, the sharing of this information between the agents and the salience of different information elements used. Thus, the structure, quality and content of each network's DSA is discussed, along with the implications for DSA theory. The findings reinforce the notion that when viewing situation awareness (SA) in collaborative systems, it is useful to focus on the coordinated behaviour of the system itself, rather than on the individual as the unit of analysis and suggest that the findings from such assessments can potentially be used to inform system, procedure and training design. SA is a critical commodity for teams working in industrial systems and systems, procedures and training programmes should be designed to facilitate efficient system SA acquisition and maintenance. This article presents approaches for describing and understanding SA during real-world collaborative tasks, the outputs from which can potentially be used to inform system, training programmes and procedure design.

  18. The Onset of Nonlinear Flow in Three-Dimensional Heterogeneous Flow Domains Based on Energy Dissipation Measures

    NASA Astrophysics Data System (ADS)

    Meakin, P.; Basagaoglu, H.; Succi, S.; Welhan, J.

    2005-12-01

    The onset of nonlinear flow in three-dimensional random disordered porous flow domains was analyzed using participation numbers based on local kinetic energies, and energy dissipation rates computed via non-equilibrium kinetic tensors. A three-dimensional lattice Boltzmann model was used to simulate gravity-driven single-phase flow over a range of Reynolds numbers that included the crossover from linear to nonlinear flow. The simulations results indicated that the kinetic energy participation number characterized the onset of nonlinear flow in terms of transition to a more dispersed (uniform) distribution of kinetic energy densities as the flow rate increased. However, the energy dissipation participation number characterized the onset of nonlinear flow in terms of a transition to a more locally concentrated distribution of energy dissipation densities at higher flows. The flow regime transition characterized by the energy dissipation participation number occurred over a nearly equal or a narrower range of Reynolds numbers compared to the transition characterized by the kinetic energy participation number. The results also revealed that the boundary conditions (periodic vs. no-slip) parallel to the main flow direction have an insignificant effect on the magnitude of the critical Reynolds number, that characterizes the onset of nonlinear effects, although they did influence the spatial correlations of the pore-scale kinetic energy and the energy dissipation densities in all Cartesian directions. Flow domains with periodic boundaries resulted in less-localized (more dispersed) steady-state flows than domains with no-slip boundaries. These results should be useful for designing future experiment like those of Zeria et al. 2005 (Transport in Porous Media, 60:159-181) that would have significant potential implications in diverse fields.

  19. Self-annihilation of inversion domains by high energy defects in III-Nitrides

    SciTech Connect

    Koukoula, T.; Kioseoglou, J. Kehagias, Th.; Komninou, Ph.; Ajagunna, A. O.; Georgakilas, A.

    2014-04-07

    Low-defect density InN films were grown on Si(111) by molecular beam epitaxy over an ∼1 μm thick GaN/AlN buffer/nucleation layer. Electron microscopy observations revealed the presence of inverse polarity domains propagating across the GaN layer and terminating at the sharp GaN/InN (0001{sup ¯}) interface, whereas no inversion domains were detected in InN. The systematic annihilation of GaN inversion domains at the GaN/InN interface is explained in terms of indium incorporation on the Ga-terminated inversion domains forming a metal bonded In-Ga bilayer, a structural instability known as the basal inversion domain boundary, during the initial stages of InN growth on GaN.

  20. Fermi-LAT Observations of Galactic Transients

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2011-01-01

    This slide presentation reviews the observations of Galactic transients by the Large Area Telescope (LAT) on the Fermi Gamma Ray Space Telescope. The LAT is producing spectacular results for the GeV transient sky, some of which are shown and reviewed. Some of the results in the GeV range that are discussed in this presentation are: (1) New blazars and unidentified transients (2) the jet of the Cygnus X-3 microquasar (3) gamma rays from V407 Cygni nova (4) Fast high-energy gamma-ray flares from the Crab Nebula

  1. The first Fermi LAT supernova remnant catalog

    DOE PAGES

    Acero, F.

    2016-05-16

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope. Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude, allows us to determine an upper limit of 22% on the number of GeV candidatesmore » falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, demonstrates the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. As a result, we model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.« less

  2. Pulsars above 10 GeV: Fermi LAT Observations and Questions

    NASA Technical Reports Server (NTRS)

    Thomson, Dave

    2012-01-01

    The success of the Fermi Large Area Telescope in studying gamma-ray pulsars offers hints about future work above 10 GeV. The infrastructure for discovering pulsars will be similar between LAT and any future telescope. Some of the Fermi LAT results suggest intriguing questions about the future of high-energy pulsar studies.

  3. Targeting domain-III hinging of dengue envelope (DENV-2) protein by MD simulations, docking and free energy calculations.

    PubMed

    Dubey, Kshatresh Dutta; Tiwari, Gargi; Ojha, Rajendra Prasad

    2017-04-01

    The entry of the dengue virus is mediated by the conformational change in the envelope protein due to change in the endosomal pH. The structural study reveals that domain-III of the dengue envelope protein (DENV) shows the largest shift in its position during the entry of the virus. Therefore, targeting the hinge region of the domain-III may block the conformational changes in the DENV. In the present work, we have targeted the domain I/III hinge region using four known ligands used for the dengue envelope protein (serotype-2) and have intended to explore the specificity of one ligand R1 (5-(3-chlorophenyl)-N-(2-phenyl-2H-benzo[d][1,2,3]triazol-6-yl)furan-2-carboxamide) that succeeded the dengue inhibition by the molecular dynamics (MD) simulations in conjunction of the molecular docking and the binding free energy calculations. The residue interactions map shows Lys 296 of domain-III of the DENV-2, which might be responsible for binding small molecules between domain I/III interface, as an important residue conserved in all the dengue serotypes.

  4. Fermi Large Area Telescope First Source Catalog

    NASA Astrophysics Data System (ADS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Antolini, E.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B. M.; Bechtol, K.; Bellazzini, R.; Belli, F.; Berenji, B.; Bisello, D.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Burnett, T. H.; Busetto, G.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Campana, R.; Canadas, B.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cavazzuti, E.; Ceccanti, M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Cillis, A. N.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Corbet, R.; Davis, D. S.; DeKlotz, M.; den Hartog, P. R.; Dermer, C. D.; de Angelis, A.; de Luca, A.; de Palma, F.; Digel, S. W.; Dormody, M.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Fabiani, D.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giavitto, G.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Healey, S. E.; Hill, A. B.; Horan, D.; Hughes, R. E.; Iafrate, G.; Jóhannesson, G.; Johnson, A. S.; Johnson, R. P.; Johnson, T. J.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kerr, M.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Landriu, D.; Latronico, L.; Lee, S.-H.; Lemoine-Goumard, M.; Lionetto, A. M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Marangelli, B.; Marelli, M.; Massaro, E.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Michelson, P. F.; Minuti, M.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Mongelli, M.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakajima, H.; Nakamori, T.; Naumann-Godo, M.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paccagnella, A.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Pinchera, M.; Piron, F.; Porter, T. A.; Poupard, L.; Rainò, S.; Rando, R.; Ray, P. S.; Razzano, M.; Razzaque, S.; Rea, N.; Reimer, A.; Reimer, O.; Reposeur, T.; Ripken, J.; Ritz, S.; Rochester, L. S.; Rodriguez, A. Y.; Romani, R. W.; Roth, M.; Sadrozinski, H. F.-W.; Salvetti, D.; Sanchez, D.; Sander, A.; Saz Parkinson, P. M.; Scargle, J. D.; Schalk, T. L.; Scolieri, G.; Sgrò, C.; Shaw, M. S.; Siskind, E. J.; Smith, D. A.; Smith, P. D.; Spandre, G.; Spinelli, P.; Starck, J.-L.; Stephens, T. E.; Striani, E.; Strickman, M. S.; Strong, A. W.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Tibolla, O.; Tinebra, F.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Van Etten, A.; Vasileiou, V.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wallace, E.; Wang, P.; Watters, K.; Winer, B. L.; Wood, K. S.; Yang, Z.; Ylinen, T.; Ziegler, M.; Fermi LAT Collaboration

    2010-06-01

    We present a catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), during the first 11 months of the science phase of the mission, which began on 2008 August 4. The First Fermi-LAT catalog (1FGL) contains 1451 sources detected and characterized in the 100 MeV to 100 GeV range. Source detection was based on the average flux over the 11 month period, and the threshold likelihood Test Statistic is 25, corresponding to a significance of just over 4σ. The 1FGL catalog includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and power-law spectral fits as well as flux measurements in five energy bands for each source. In addition, monthly light curves are provided. Using a protocol defined before launch we have tested for several populations of gamma-ray sources among the sources in the catalog. For individual LAT-detected sources we provide firm identifications or plausible associations with sources in other astronomical catalogs. Identifications are based on correlated variability with counterparts at other wavelengths, or on spin or orbital periodicity. For the catalogs and association criteria that we have selected, 630 of the sources are unassociated. Care was taken to characterize the sensitivity of the results to the model of interstellar diffuse gamma-ray emission used to model the bright foreground, with the result that 161 sources at low Galactic latitudes and toward bright local interstellar clouds are flagged as having properties that are strongly dependent on the model or as potentially being due to incorrectly modeled structure in the Galactic diffuse emission.

  5. The ground states of iron(III) porphines: role of entropy-enthalpy compensation, Fermi correlation, dispersion, and zero-point energies.

    PubMed

    Kepp, Kasper P

    2011-10-01

    Porphyrins are much studied due to their biochemical relevance and many applications. The density functional TPSSh has previously accurately described the energy of close-lying electronic states of transition metal systems such as porphyrins. However, a recent study questioned this conclusion based on calculations of five iron(III) porphines. Here, we compute the geometries of 80 different electronic configurations and the free energies of the most stable configurations with the functionals TPSSh, TPSS, and B3LYP. Zero-point energies and entropy favor high-spin by ~4kJ/mol and 0-10kJ/mol, respectively. When these effects are included, and all electronic configurations are evaluated, TPSSh correctly predicts the spin of all the four difficult phenylporphine cases and is within the lower bound of uncertainty of any known theoretical method for the fifth, iron(III) chloroporphine. Dispersion computed with DFT-D3 favors low-spin by 3-53kJ/mol (TPSSh) or 4-15kJ/mol (B3LYP) due to the attractive r(-6) term and the shorter distances in low-spin. The very large and diverse corrections from TPSS and TPSSh seem less consistent with the similarity of the systems than when calculated from B3LYP. If the functional-specific corrections are used, B3LYP and TPSSh are of equal accuracy, and TPSS is much worse, whereas if the physically reasonable B3LYP-computed dispersion effect is used for all functionals, TPSSh is accurate for all systems. B3LYP is significantly more accurate when dispersion is added, confirming previous results.

  6. The Fermiac or Fermi's Trolley

    NASA Astrophysics Data System (ADS)

    Coccetti, F.

    2016-03-01

    The Fermiac, known also as Fermi's trolley or Monte Carlo trolley, is an analog computer used to determine the change in time of the neutron population in a nuclear device, via the Monte Carlo method. It was invented by Enrico Fermi and constructed by Percy King at Los Alamos in 1947, and used for about two years. A replica of the Fermiac was built at INFN mechanical workshops of Bologna in 2015, on behalf of the Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", thanks to the original drawings made available by Los Alamos National Laboratory (LANL). This reproduction of the Fermiac was put in use, and a simulation was developed.

  7. Fermi Observations of GRB 090510: A Short-Hard Gamma-ray Burst with an Additional, Hard Power-law Component from 10 keV TO GeV Energies

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Asano, K.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bhat, P. N.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Briggs, M. S.; Brigida, M.; Bruel, P.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Connaughton, V.; Conrad, J.; Dermer, C. D.; de Palma, F.; Dingus, B. L.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Finke, J.; Focke, W. B.; Frailis, M.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Glanzman, T.; Godfrey, G.; Granot, J.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Harding, A. K.; Hays, E.; Horan, D.; Hughes, R. E.; Jóhannesson, G.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kippen, R. M.; Knödlseder, J.; Kocevski, D.; Kouveliotou, C.; Kuss, M.; Lande, J.; Latronico, L.; Lemoine-Goumard, M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Makeev, A.; Mazziotta, M. N.; McEnery, J. E.; McGlynn, S.; Meegan, C.; Mészáros, P.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakajima, H.; Nakamori, T.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paciesas, W. S.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Preece, R.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Ritz, S.; Rodriguez, A. Y.; Roth, M.; Ryde, F.; Sadrozinski, H. F.-W.; Sander, A.; Scargle, J. D.; Schalk, T. L.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stamatikos, M.; Stecker, F. W.; Strickman, M. S.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Toma, K.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Uehara, T.; Usher, T. L.; van der Horst, A. J.; Vasileiou, V.; Vilchez, N.; Vitale, V.; von Kienlin, A.; Waite, A. P.; Wang, P.; Wilson-Hodge, C.; Winer, B. L.; Wu, X. F.; Yamazaki, R.; Yang, Z.; Ylinen, T.; Ziegler, M.

    2010-06-01

    We present detailed observations of the bright short-hard gamma-ray burst GRB 090510 made with the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) on board the Fermi observatory. GRB 090510 is the first burst detected by the LAT that shows strong evidence for a deviation from a Band spectral fitting function during the prompt emission phase. The time-integrated spectrum is fit by the sum of a Band function with E peak = 3.9 ± 0.3 MeV, which is the highest yet measured, and a hard power-law component with photon index -1.62 ± 0.03 that dominates the emission below ≈20 keV and above ≈100 MeV. The onset of the high-energy spectral component appears to be delayed by ~0.1 s with respect to the onset of a component well fit with a single Band function. A faint GBM pulse and a LAT photon are detected 0.5 s before the main pulse. During the prompt phase, the LAT detected a photon with energy 30.5+5.8 -2.6 GeV, the highest ever measured from a short GRB. Observation of this photon sets a minimum bulk outflow Lorentz factor, Γgsim 1200, using simple γγ opacity arguments for this GRB at redshift z = 0.903 and a variability timescale on the order of tens of ms for the ≈100 keV-few MeV flux. Stricter high confidence estimates imply Γ >~ 1000 and still require that the outflows powering short GRBs are at least as highly relativistic as those of long-duration GRBs. Implications of the temporal behavior and power-law shape of the additional component on synchrotron/synchrotron self-Compton, external-shock synchrotron, and hadronic models are considered.

  8. Fermi GBM Observations of Terrestrial Gamma Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R.; Kippen, R. M.; von Kienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

    2010-01-01

    In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed more than 77 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds. The energy spectra of some TGFs have strong 511 keV positron annihilation lines, indicating that these TGFs contain a large fraction of positrons

  9. Fermi (nee GLAST) at Six Months

    NASA Technical Reports Server (NTRS)

    Ritz, Steve

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  10. Fermi (Formerly GLAST) at Six Months

    NASA Technical Reports Server (NTRS)

    Ritz, Steven M.

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  11. Fermi Mission Results, Status, and Plans

    NASA Technical Reports Server (NTRS)

    Ritz, Steven M.

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  12. Blue Fermi flat spectrum radio quasars

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Tavecchio, F.; Foschini, L.; Sbarrato, T.; Ghirlanda, G.; Maraschi, L.

    2012-09-01

    Many blazars detected by the Fermi satellite, observed spectroscopically in the optical, are line-less, and have been classified as BL Lac objects. Optical-ultraviolet (UV) photometry of nearly 100 of them allowed us to determine the redshift for a handful of objects and redshift upper limits in the great majority. A few of these are candidates to be 'blue quasars', namely flat spectrum radio quasars whose broad emission lines are hidden by an overwhelming synchrotron emission peaking in the UV. This implies that the emitting electrons have high energies. In turn, this requires relatively weak radiative cooling, a condition that can be met if the main radiative dissipation of the jet power occurs outside the broad-line region. We confirm this hypothesis by studying and modelling the spectral energy distributions of the four 'blue quasars' recently discovered. Furthermore, we discuss the distribution of Fermi blazars in the γ-ray spectral index-γ-ray luminosity plane, and argue that 'blue quasars' objects are a minority within the blazar populations.

  13. Fermi Finds Youthful Pulsar Among Ancient Stars

    NASA Video Gallery

    In three years, NASA's Fermi has detected more than 100 gamma-ray pulsars, but something new has appeared. Among a type of pulsar with ages typically numbering a billion years or more, Fermi has fo...

  14. Superfluidity of heated Fermi systems in the static fluctuation approximation

    SciTech Connect

    Khamzin, A. A.; Nikitin, A. S.; Sitdikov, A. S.

    2015-10-15

    Superfluidity properties of heated finite Fermi systems are studied in the static fluctuation approximation, which is an original method. This method relies on a single and controlled approximation, which permits taking correctly into account quasiparticle correlations and thereby going beyond the independent-quasiparticle model. A closed self-consistent set of equations for calculating correlation functions at finite temperature is obtained for a finite Fermi system described by the Bardeen–Cooper–Schrieffer Hamiltonian. An equation for the energy gap is found with allowance for fluctuation effects. It is shown that the phase transition to the supefluid state is smeared upon the inclusion of fluctuations.

  15. Harper Operator, Fermi Curves and Picard-Fuchs Equation

    NASA Astrophysics Data System (ADS)

    Li, Dan

    2014-05-01

    This paper is a continuation of the work on the spectral problem of the Harper operator using algebraic geometry. We continue to discuss the local monodromy of algebraic Fermi curves based on Picard-Lefschetz formula. The density of states over approximating components of Fermi curves satisfies a Picard-Fuchs equation. By the property of Landen transformation, the density of states has a Lambert series as the quarter period. A q-expansion of the energy is derived from a mirror map as in the B-model.

  16. Fermi's β-DECAY Theory

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Throughout his lifetime Enrico Fermi (1901-1954) had considered his 1934 β-decay theory as his most important contribution to theoretical physics. E. Segrè (1905-1989) had vividly written about an episode at the inception of that paper:1...

  17. CCC and the Fermi paradox

    NASA Astrophysics Data System (ADS)

    Gurzadyan, V. G.; Penrose, R.

    2016-01-01

    Within the scheme of conformal cyclic cosmology (CCC), information can be transmitted from aeon to aeon. Accordingly, the "Fermi paradox" and the SETI programme --of communication by remote civilizations-- may be examined from a novel perspective: such information could, in principle, be encoded in the cosmic microwave background. The current empirical status of CCC is also discussed.

  18. Economics and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Hosek, W. R.

    A resolution of the Fermi paradox is proposed using common economic assumptions that should apply to all intelligent, planet-bound civilizations. It is argued that seemingly rational decisions about resource allocation will lead all civilizations to forego the commitment to interstellar exploration and colonization. Consequently humans have not, and will not, be visited by them and humans will not visit other civilizations.

  19. Fermi's Large Area Telescope (LAT)

    NASA Video Gallery

    Fermi’s Large Area Telescope (LAT) is the spacecraft’s main scientificinstrument. This animation shows a gamma ray (purple) entering the LAT,where it is converted into an electron (red) and a...

  20. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    DOE PAGES

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes amore » phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.« less

  1. Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase

    NASA Astrophysics Data System (ADS)

    Yamamoto, Seiji; Si, Qimiao

    2006-03-01

    We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.

  2. Bosonic models with Fermi-liquid kinematics: realizations and properties

    NASA Astrophysics Data System (ADS)

    Goldbart, Paul; Gopalakrishnan, Sarang; Lamacraft, Austen

    2011-03-01

    We consider models of interacting bosons in which the single-particle kinetic energy achieves its minimum on a surface in momentum space. The kinematics of such models resembles that resulting from Pauli blocking in Fermi liquids; therefore, Shankar's renormalization-group treatment of Fermi liquids can be adapted to investigate phase transitions in these bosonic systems. We explore possible experimental realizations of such models in cold atomic gases: e.g., via spin-orbit coupling, multimode-cavity-mediated interactions, and Cooper pairing of Fermi gases in spin-dependent lattices. We address the phase structure and critical behavior of the resulting models within the framework of Ref., focusing in particular on Bose-Einstein condensation and on quantum versions of the Brazovskii transition from a superfluid to a supersolid.

  3. Time evolution of excitations in normal Fermi liquids

    NASA Astrophysics Data System (ADS)

    Pavlyukh, Y.; Rubio, A.; Berakdar, J.

    2013-05-01

    We inspect the initial and the long-time evolution of excitations in Fermi liquids by analyzing the time structure of the electron spectral function. Focusing on the short-time limit we study the electron-boson model for the homogeneous electron gas and apply the first-order (in boson propagator) cumulant expansion of the electron Green's function. In addition to a quadratic decay in time upon triggering the excitation, we identify nonanalytic terms in the time expansion similar to those found in the Fermi edge singularity phenomenon. We also demonstrate that the exponential decay in time in the long-time limit is inconsistent with the GW approximation for the self-energy. The background for this is the Paley-Wiener theorem of complex analysis. To reconcile with the Fermi liquid behavior an inclusion of higher order diagrams (in the screened Coulomb interaction) is required.

  4. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    SciTech Connect

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes a phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.

  5. FERMI@Elettra FEL Design Technical Optimization Final Report

    SciTech Connect

    Fawley, William; Penn, Gregory; Allaria, Enrico; De Ninno,Giovanni; Graves, William

    2006-07-31

    This is the final report of the FEL Design Group for the Technical Optimization Study for the FERMI{at}ELETTRA project. The FERMI{at}ELETTRA project is based on the principle of harmonic upshifting of an initial ''seed'' signal in a single pass, FEL amplifier employing multiple undulators. There are a number of FEL physics principles which underlie this approach to obtaining short wavelength output: (1) the energy modulation of the electron beam via the resonant interaction with an external laser seed (2) the use of a chromatic dispersive section to then develop a strong density modulation with large harmonic overtones (3) the production of coherent radiation by the microbunched beam in a downstream radiator. Within the context of the FERMI project, we discuss each of these elements in turn.

  6. STEM education and Fermi problems

    NASA Astrophysics Data System (ADS)

    Holubova, Renata

    2017-01-01

    One of the research areas of Physics education is the study of the educational process. Investigations in this area are aimed for example on the teaching and learning process and its results. The conception of STEM education (Science, Technology, Engineering, and Mathematics) is discussed - it is one possible approach to the preparation of the curriculum and the focus on the educational process at basic and secondary schools. At schools in the Czech Republic STEM is much more realized by the application of interdisciplinary relations between subjects Physics-Nature-Technique. In both conceptions the aim is to support pupils' creativity, critical thinking, cross-curricular links. In this context the possibility of using Fermi problems in teaching Physics was discussed (as an interdisciplinary and constructivist activity). The aim of our research was the analysis of Fermi problems solving strategies, the ability of pupils to solve Fermi problems. The outcome of our analysis was to find out methods and teaching strategies which are important to use in teaching - how to solve qualitative and interdisciplinary tasks in physics. In this paper the theoretical basis of STEM education and Fermi problems will be presented. The outcome of our findings based on the research activities will be discussed so as our experiences from 10 years of Fermi problems competition that takes place at the Science Faculty, Palacky University in Olomouc. Changes in competencies of solving tasks by our students (from the point of view in terms of modern, activating teaching methods recommended by theory of Physics education and other science subjects) will be identified.

  7. Formulation and implementation of a high-order 3-D domain integral method for the extraction of energy release rates

    NASA Astrophysics Data System (ADS)

    Ozer, H.; Duarte, C. A.; Al-Qadi, I. L.

    2012-04-01

    This article presents a three dimensional (3-D) formulation and implementation of a high-order domain integral method for the computation of energy release rate. The method is derived using surface and domain formulations of the J-integral and the weighted residual method. The J-integral along 3-D crack fronts is approximated by high-order Legendre polynomials. The proposed implementation is tailored for the Generalized/eXtended Finite Element Method and can handle discontinuities arbitrarily located within a finite element mesh. The domain integral calculations are based on the same integration elements used for the computation of the stiffness matrix. Discontinuities of the integrands across crack surfaces and across computational element boundaries are fully accounted for. The proposed method is able to deliver smooth approximations and to capture the boundary layer behavior of the J-integral using tetrahedral meshes. Numerical simulations of mode-I and mixed mode benchmark fracture mechanics examples verify expected convergence rates for the computed energy release rates. The results are also in good agreement with other numerical solutions available in the literature.

  8. Fermi's golden rule in the Wigner representation

    NASA Astrophysics Data System (ADS)

    Segev, Bilha

    2003-06-01

    When Fermi's golden rule (FGR) is studied in the Wigner representation, the transition rate from an initial pure state or from an initial thermal distribution into a quasicontinuum manifold of degenerate states is given by an overlap integral of Wigner functions in phase space. In the semiclassical limit the transition rate is obtained by integrating over the regions in phase space where the energy difference between the initial and final potential surfaces is equal to the available energy. The integral is weighted by the initial probability density to be at that phase-space region. The classical limit of FGR is thus both simple and intuitive. In one dimension a relation to the Landau-Zener-Stuckelberg formula is established. The multi-dimensional case is considered by induction, proving that for separable multi-dimensional systems deviations of the logarithm of the transition rate from its classical limit scale at worst linearly with the dimension.

  9. The Mirage of the Fermi Scale

    NASA Astrophysics Data System (ADS)

    Antipin, Oleg; Sannino, Francesco; Tuominen, Kimmo

    2013-09-01

    The discovery of a light Higgs boson at Large Hadron Collider may be suggesting that we need to revise our model building paradigms to understand the origin of the weak scale. We explore the possibility that the Fermi scale is not fundamental but rather a derived one, i.e. a low energy mirage. We show that this scenario emerges in a very natural way in models previously used to break the electroweak symmetry dynamically and suggest a simple dynamical framework for this idea. In our model the electroweak scale results from the interplay between two very high energy scales, one typically of the order of ΛUV 1010GeV and the other around MU 1016GeV, although other values are also possible.

  10. Constraining decaying dark matter with Fermi LAT gamma-rays

    SciTech Connect

    Zhang, Le; Sigl, Günter; Weniger, Christoph; Maccione, Luca; Redondo, Javier E-mail: christoph.weniger@desy.de E-mail: redondo@mppmm.mpg.de

    2010-06-01

    High energy electrons and positrons from decaying dark matter can produce a significant flux of gamma rays by inverse Compton off low energy photons in the interstellar radiation field. This possibility is inevitably related with the dark matter interpretation of the observed PAMELA and FERMI excesses. The aim of this paper is providing a simple and universal method to constrain dark matter models which produce electrons and positrons in their decay by using the Fermi LAT gamma-ray observations in the energy range between 0.5 GeV and 300 GeV. We provide a set of universal response functions that, once convolved with a specific dark matter model produce the desired constraints. Our response functions contain all the astrophysical inputs such as the electron propagation in the galaxy, the dark matter profile, the gamma-ray fluxes of known origin, and the Fermi LAT data. We study the uncertainties in the determination of the response functions and apply them to place constraints on some specific dark matter decay models that can well fit the positron and electron fluxes observed by PAMELA and Fermi LAT. To this end we also take into account prompt radiation from the dark matter decay. We find that with the available data decaying dark matter cannot be excluded as source of the PAMELA positron excess.

  11. Magnetic breakdown in an array of overlapping Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Kadigrobov, A. M.; Radić, D.; Bjeliš, A.

    2015-03-01

    We develop a theoretical framework for a magnetic breakdown in an array of circular two-dimensional bands with a finite overlap of neighboring Fermi surfaces due to the presence of a presumably weak periodic potential, and apply the obtained results to the electron bands in carbon honeycomb structures of doped graphene and intercalated graphite compounds. In contrast to the standard treatment, inaugurated more than fifty years ago by Slutskin and Kadigrobov, with electron semiclassical trajectories encircling significantly overlapping Fermi surfaces, we examine a configuration in which bands are related in a way that the Fermi surfaces only slightly overlap, forming internal band pockets with areas of the size comparable to the area of the quantum magnetic flux for a given external magnetic field. Such band configuration has to be treated quantum mechanically. The calculation leads to the results for magnetic breakdown coefficients comprising an additional large factor with respect to the standard results, proportional to the ratio of the Fermi energy and the cyclotron energy. Also, these coefficients show oscillating dependence on energy, as well as on the wave number of periodic potential. Both mentioned elements enable the adjustment of the preferred wave vector of possible magnetic breakdown induced density wave instability at the highest possible critical temperature.

  12. Nonlinear Cascades of Surface Oceanic Geostrophic Kinetic Energy in the Frequency Domain

    DTIC Science & Technology

    2012-09-01

    in frequency ai space, as diagnostics of the impact of nonlinearity on the frequency spectra of surface ocean geostrophic flows. Our analysis of...non- linearities in the frequency domain is somewhat similar to the diagnostics employed by Sheng and Hayashi (1990a,b) on realistic atmospheric...results in Fig. 8c, we also anticipate that the spectral transfers T(ai) could be useful diagnostics of the role of non- linearity in maintaining

  13. Fermi LAT Observations of LS 5039

    SciTech Connect

    Abdo, A.A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B.M.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R.D.; Bloom, E.D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; /more authors..

    2012-03-29

    The first results from observations of the high-mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented. Our results indicate variability that is consistent with the binary period, with the emission being modulated with a period of 3.903 {+-} 0.005 days; the first detection of this modulation at GeV energies. The light curve is characterized by a broad peak around superior conjunction in agreement with inverse Compton scattering models. The spectrum is represented by a power law with an exponential cutoff, yielding an overall flux (100 MeV-300 GeV) of 4.9 {+-} 0.5(stat) {+-} 1.8(syst) x 10{sup -7} photon cm{sup -2} s{sup -1}, with a cutoff at 2.1 {+-} 0.3(stat) {+-} 1.1(syst) GeV and photon index {Gamma} = 1.9 {+-} 0.1(stat) {+-} 0.3(syst). The spectrum is observed to vary with orbital phase, specifically between inferior and superior conjunction. We suggest that the presence of a cutoff in the spectrum may be indicative of magnetospheric emission similar to the emission seen in many pulsars by Fermi.

  14. Repulsive Fermi Polarons in a Resonant Mixture of Ultracold ^{6}Li Atoms.

    PubMed

    Scazza, F; Valtolina, G; Massignan, P; Recati, A; Amico, A; Burchianti, A; Fort, C; Inguscio, M; Zaccanti, M; Roati, G

    2017-02-24

    We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold ^{6}Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E_{+}, the effective mass m^{*}, the residue Z, and the decay rate Γ. Above a critical interaction, E_{+} is found to exceed the Fermi energy of the bath, while m^{*} diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.

  15. Repulsive Fermi Polarons in a Resonant Mixture of Ultracold 6Li Atoms

    NASA Astrophysics Data System (ADS)

    Scazza, F.; Valtolina, G.; Massignan, P.; Recati, A.; Amico, A.; Burchianti, A.; Fort, C.; Inguscio, M.; Zaccanti, M.; Roati, G.

    2017-02-01

    We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold 6Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E+, the effective mass m*, the residue Z , and the decay rate Γ . Above a critical interaction, E+ is found to exceed the Fermi energy of the bath, while m* diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.

  16. Temperature equilibration rate with Fermi-Dirac statistics

    NASA Astrophysics Data System (ADS)

    Brown, Lowell S.; Singleton, Robert L., Jr.

    2007-12-01

    We calculate analytically the electron-ion temperature equilibration rate in a fully ionized, weakly to moderately coupled plasma, using an exact treatment of the Fermi-Dirac electrons. The temperature is sufficiently high so that the quantum-mechanical Born approximation to the scattering is valid. It should be emphasized that we do not build a model of the energy exchange mechanism, but rather, we perform a systematic first principles calculation of the energy exchange. At the heart of this calculation lies the method of dimensional continuation, a technique that we borrow from quantum field theory and use in a different fashion to regulate the kinetic equations in a consistent manner. We can then perform a systematic perturbation expansion and thereby obtain a finite first-principles result to leading and next-to-leading order. Unlike model building, this systematic calculation yields an estimate of its own error and thus prescribes its domain of applicability. The calculational error is small for a weakly to moderately coupled plasma, for which our result is nearly exact. It should also be emphasized that our calculation becomes unreliable for a strongly coupled plasma, where the perturbative expansion that we employ breaks down, and one must then utilize model building and computer simulations. Besides providing different and potentially useful results, we use this calculation as an opportunity to explain the method of dimensional continuation in a pedagogical fashion. Interestingly, in the regime of relevance for many inertial confinement fusion experiments, the degeneracy corrections are comparable in size to the subleading quantum correction below the Born approximation. For consistency, we therefore present this subleading quantum-to-classical transition correction in addition to the degeneracy correction.

  17. Split Fermi Surface Properties based on the Relativistic Effect in Superconductor PdBiSe with the Cubic Chiral Crystal Structure

    NASA Astrophysics Data System (ADS)

    Kakihana, Masashi; Nakamura, Ai; Teruya, Atsushi; Harima, Hisatomo; Haga, Yoshinori; Hedo, Masato; Nakama, Takao; Ōnuki, Yoshichika

    2015-03-01

    We grew single crystals of PdBiSe with the ullmannite-type cubic chiral structure and carried out de Haas-van Alphen (dHvA) experiments to clarify the Fermi surface properties. The Fermi surfaces are found to split into two different Fermi surfaces, reflecting the non-centrosymmetric crystal structure. A splitting energy between two nearly spherical Fermi surfaces named α and α' is determined as 1050-1260 K. These Fermi surfaces are identified to be due the band-149 and -150 electron Fermi surfaces centered at the Γ point from the results of full-potential linearized augmented plane wave (FLAPW) energy band calculations under consideration of a mass correction in the spin-orbit interaction for Bi-6p electrons based on the relativistic effect. The theoretical splitting energy between these Fermi surfaces is 1080-1150 K, which is in good agreement with the experimental value.

  18. Assessment of Energy Removal Impacts on Physical Systems: Hydrodynamic Model Domain Expansion and Refinement, and Online Dissemination of Model Results

    SciTech Connect

    Yang, Zhaoqing; Khangaonkar, Tarang; Wang, Taiping

    2010-08-01

    In this report we describe the 1) the expansion of the PNNL hydrodynamic model domain to include the continental shelf along the coasts of Washington, Oregon, and Vancouver Island; and 2) the approach and progress in developing the online/Internet disseminations of model results and outreach efforts in support of the Puget Sound Operational Forecast System (PS-OPF). Submittal of this report completes the work on Task 2.1.2, Effects of Physical Systems, Subtask 2.1.2.1, Hydrodynamics, for fiscal year 2010 of the Environmental Effects of Marine and Hydrokinetic Energy project.

  19. The existence of energy solutions to 2-dimensional non-Lipschitz stochastic Navier-Stokes equations in unbounded domains

    NASA Astrophysics Data System (ADS)

    Taniguchi, Takeshi

    In this paper we consider the existence and uniqueness of weak energy solutions to a stochastic 2-dimensional non-Lipschitz Navier-Stokes equation perturbed by the cylindrical Wiener process W(t) in a bounded or unbounded domain D with the smooth boundary ∂ D or D=R: dX(t)=[-νAX(t)+B(X(t))] dt+f(t,X(t)) dt+g(t,X(t)) dW(t), where A is the Stokes operator and f, g satisfy the non-Lipschitz condition.

  20. Surface to bulk Fermi arcs via Weyl nodes as topological defects

    PubMed Central

    Kim, Kun Woo; Lee, Woo-Ram; Kim, Yong Baek; Park, Kwon

    2016-01-01

    A hallmark of Weyl semimetal is the existence of surface Fermi arcs. An intriguing question is what determines the connectivity of surface Fermi arcs, when multiple pairs of Weyl nodes are present. To answer this question, we show that the locations of surface Fermi arcs are predominantly determined by the condition that the Zak phase integrated along the normal-to-surface direction is . The Zak phase can reveal the peculiar topological structure of Weyl semimetal directly in the bulk. Here, we show that the winding of the Zak phase around each projected Weyl node manifests itself as a topological defect of the Wannier–Stark ladder, energy eigenstates under an electric field. Remarkably, this leads to bulk Fermi arcs, open-line segments in the bulk spectra. Bulk Fermi arcs should exist in conjunction with surface counterparts to conserve the Weyl fermion number under an electric field, which is supported by explicit numerical evidence. PMID:27845342

  1. Surface to bulk Fermi arcs via Weyl nodes as topological defects

    NASA Astrophysics Data System (ADS)

    Kim, Kun Woo; Lee, Woo-Ram; Kim, Yong Baek; Park, Kwon

    2016-11-01

    A hallmark of Weyl semimetal is the existence of surface Fermi arcs. An intriguing question is what determines the connectivity of surface Fermi arcs, when multiple pairs of Weyl nodes are present. To answer this question, we show that the locations of surface Fermi arcs are predominantly determined by the condition that the Zak phase integrated along the normal-to-surface direction is . The Zak phase can reveal the peculiar topological structure of Weyl semimetal directly in the bulk. Here, we show that the winding of the Zak phase around each projected Weyl node manifests itself as a topological defect of the Wannier-Stark ladder, energy eigenstates under an electric field. Remarkably, this leads to bulk Fermi arcs, open-line segments in the bulk spectra. Bulk Fermi arcs should exist in conjunction with surface counterparts to conserve the Weyl fermion number under an electric field, which is supported by explicit numerical evidence.

  2. Unidentified EGRET sources and their possible Fermi counterparts

    NASA Astrophysics Data System (ADS)

    Lyapin, A. R.; Arkhangelskaja, I. V.; Larin, D. S.

    2017-01-01

    Unidentified EGRET sources from 3EG catalog have been analyzed. Preliminary data analysis has shown at least 23 of these sources coincide with those in 3FGL Fermi catalogue within 1, 2 and 3 sigma error intervals of the coordinates and fluxes. Their properties are discussed in the presented work. Even 3-sigma difference allows supposing sources similarity because of more than 3-sigma distinctions in values of fluxes between identified EGRET sources and their Fermi counterparts. For instance, the coincidence between 3EG J1255-0549 and 3FGL J1256.1-0547 was reported in Fermi catalogues 1FGL, 2FGL, 3FGL. However, these sources fluxes (in units of 10‑8 photons × cm‑2 × s‑1) in the energy band E > 100 MeV were 179.7 ± 6.7 (3EG), 44.711 ± 0.724 (3FGL), 53.611 ± 0.997 (2FGL) and 67.939 ± 1.861 (1FGL). Such effect was observed for sufficient portion of identified EGRET sources. It could cause by troubles of particles identification by Fermi/LAT trigger system. Very often charged particles recognized as gamma-quanta because of wrong backsplash analysis. Nevertheless, gammas counts as charged particles due analogous reason and rejected during ground data processing. For example, it appears as geomagnetic modulation presence on gamma-quanta count rate latitudinal profiles in energy band E > 20 MeV.

  3. Landau quantization and Fermi velocity renormalization in twisted graphene bilayers

    NASA Astrophysics Data System (ADS)

    Yin, Long-Jing; Qiao, Jia-Bin; Wang, Wen-Xiao; Zuo, Wei-Jie; Yan, Wei; Xu, Rui; Dou, Rui-Fen; Nie, Jia-Cai; He, Lin

    2015-11-01

    Currently there is a lively discussion concerning Fermi velocity renormalization in twisted bilayers and several contradicted experimental results are reported. Here we study electronic structures of the twisted bilayers by scanning tunneling microscopy (STM) and spectroscopy (STS). The interlayer coupling strengths between the adjacent bilayers are measured according to energy separations of two pronounced low-energy van Hove singularities (VHSs) in the STS spectra. We demonstrate that there is a large range of values for the interlayer interaction not only in different twisted bilayers, but also in twisted bilayers with the same rotation angle. Below the VHSs, the observed Landau quantization in the twisted bilayers is identical to that of massless Dirac fermions in graphene monolayer, which allows us to measure the Fermi velocity directly. Our result indicates that the Fermi velocity of the twisted bilayers depends remarkably on both the twisted angles and the interlayer coupling strengths. This removes the discrepancy about the Fermi velocity renormalization in the twisted bilayers and provides a consistent interpretation of all current data.

  4. Enrico Fermi and the Dolomites

    NASA Astrophysics Data System (ADS)

    Battimelli, Giovanni; de Angelis, Alessandro

    2014-11-01

    Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.

  5. Fermi Timing and Synchronization System

    SciTech Connect

    Wilcox, R.; Staples, J.; Doolittle, L.; Byrd, J.; Ratti, A.; Kaertner, F.X.; Kim, J.; Chen, J.; Ilday, F.O.; Ludwig, F.; Winter, A.; Ferianis, M.; Danailov, M.; D'Auria, G.

    2006-07-19

    The Fermi FEL will depend critically on precise timing of its RF, laser and diagnostic subsystems. The timing subsystem to coordinate these functions will need to reliably maintain sub-100fs synchronicity between distant points up to 300m apart in the Fermi facility. The technology to do this is not commercially available, and has not been experimentally demonstrated in a working facility. Therefore, new technology must be developed to meet these needs. Two approaches have been researched by different groups working with the Fermi staff. At MIT, a pulse transmission scheme has been developed for synchronization of RF and laser devices. And at LBL, a CW transmission scheme has been developed for RF and laser synchronization. These respective schemes have advantages and disadvantages that will become better understood in coming years. This document presents the work done by both teams, and suggests a possible system design which integrates them both. The integrated system design provides an example of how choices can be made between the different approaches without significantly changing the basic infrastructure of the system. Overall system issues common to any synchronization scheme are also discussed.

  6. Wavelet domain analysis of EEG data for emotion recognition: evaluation of recoursing energy efficiency

    NASA Astrophysics Data System (ADS)

    Aspiras, Theus H.; Asari, Vijayan K.

    2011-06-01

    In this paper, we evaluate the feature extraction technique of Recoursing Energy Efficiency on electroencephalograph data for human emotion recognition. A protocol has been established to elicit five distinct emotions (joy, sadness, disgust, fear, surprise, and neutral). EEG signals are collected using a 256-channel system, preprocessed using band-pass filters and Laplacian Montage, and decomposed into five frequency bands using Discrete Wavelet Transform. The Recoursing Energy Efficiency (REE) is calculated and applied to a Multi-Layer Perceptron network for classification. We compare the performance of REE features with conventional energy based features.

  7. Numerical Investigation and Experimental Reproduction of Fermi Acceleration in Laboratory Scale

    NASA Astrophysics Data System (ADS)

    Zhou, M.; Zhai, C.

    2015-12-01

    Fermi acceleration is widely accepted as the mechanism to explain power law of cosmic ray spectrum. Now this mechanism has been developed to first order Fermi acceleration and second order Fermi acceleration. In first order Fermi acceleration, also known as diffusive shock acceleration, particles are confined around the shock through scattering and accelerated by repeatedly crossing shock front. In second order Fermi acceleration, particles gain energy through statistical collisions with interstellar clouds. In this proposed work, we plan to carefully study these two kinds of acceleration numerically and experimentally. We first consider a single relativistic particle and investigate how it gains energy in Fermi-Ulam model and shock wave acceleration model respectively. We investigate collective behavior of particles with different kinds of wall-oscillation functions and try to find an optimal one in terms of efficiency of acceleration. Then, we plan to go further and consider a group of particles statistically, during which we borrow the correct generalization of Maxwell's velocity distribution in special relativity and compare the results with those in cases where we simply use Maxwell-Boltzmann distribution. To this end, we try to provide a scheme to build an accelerator applying both laser technology and mirror effect in Laboratory to reproduce Fermi acceleration, which might be a promising source to obtain high energy particles and further study the mechanism of cosmic rays acceleration.

  8. A study of the structure and energy of the Néel domain wall by the numerical method

    NASA Astrophysics Data System (ADS)

    Semenov, V. S.

    2016-02-01

    The Brown-LaBonte variation numerical method has been used to investigate the structure and energy of the Néel domain wall (DW) in a thin magnetic film of the Permalloy type. The equilibrium structure of the DW corresponds to the minimum of the total energy and to the Aharoni criterion close to unity. It has been shown that, when moving from the center of the DW, variations in the magnetization occur in an oscillating manner with a period that increases upon approaching the edge of the DW. At the edge of the DW, the period reaches a maximum value and, in this region, a sharp decrease occurs in the magnetization. In the region of the extended side tails of the DW, a larger gradient of the change in the magnetization is obtained, compared to the model of a logarithmic variation.

  9. The Second Fermi Large Area Telescope GRB Catalog

    NASA Astrophysics Data System (ADS)

    Kocevski, Daniel; Fermi Large Area Telescope Collaboration

    2017-01-01

    The high-energy emission from gamma-ray bursts (GRBs) is a formidable probe of extreme physics, requiring rapid variability from highly relativistic sources. Despite the advancements in our understanding of GRBs through observations by NASA's Swift and Fermi spacecraft, many fundemental questions regarding the particle acceleration and radiative processes associated with these events remain unanswered. Here we present the most extensive search for emission from GRBs above 40 MeV performed by the Fermi Large Area Telescope (LAT). The resulting catalog includes more than 130 detections and represents an improvement in the detection efficency of GRBs at high-energies of over 50% compared to the first LAT GRB catalog. We utilize this improved sensativity to characterize the high-energy emission from GRBs and review how these observations further our understanding of the nature of these events.

  10. Momentum sharing in imbalanced Fermi systems

    DOE PAGES

    Hen, O.; Sargsian, M.; Weinstein, L. B.; ...

    2014-10-16

    The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron starsmore » and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems.« less

  11. Momentum sharing in imbalanced Fermi systems

    SciTech Connect

    Hen, O.; Sargsian, M.; Weinstein, L. B.; Piasetzky, E.

    2014-10-16

    The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron stars and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems.

  12. Pairing phenomena in strongly correlated Fermi liquids

    NASA Astrophysics Data System (ADS)

    Krotscheck, E.; Smith, R. A.; Jackson, A. D.

    1981-12-01

    The correlated-basis-function method is extended to deal with pairing phenomena in strongly correlated Fermi liquids. With a variational ansatz for the model wave function we derive the "correlated" analog of the conventional Bardeen-Cooper-Schrieffer (or Balian-Werthamer), Anderson-Brinkman-Morel theory of pairing. A suitable (and well-controlled) set of approximations brings the theory into a form identical to the conventional theories, but with the bare interaction replaced by a weak effective interaction and the bare single-particle energies replaced by an effective single-particle spectrum. As usual, liquid 3He provides a very stringent test of the theory, as both the interaction and the experimental facts are pretty clear. The variational estimates for the pairing interaction are improved by nonorthogonal perturbation theory. We find the expected enhancement of the attraction in P waves, although the restriction to effective two-body interactions appears to be insufficient to generate P-wave pairing.

  13. Repulsive Fermi gas in a harmonic trap: Ferromagnetism and spin textures

    NASA Astrophysics Data System (ADS)

    Leblanc, L. J.; Thywissen, J. H.; Burkov, A. A.; Paramekanti, A.

    2009-07-01

    We study ferromagnetism in a repulsively interacting two-component Fermi gas in a harmonic trap. Within a local density approximation, the two components phase separate beyond a critical interaction strength, with one species having a higher density at the trap center. We discuss several easily observable experimental signatures of this transition. The mean-field release energy, its separate kinetic and interaction contributions, as well as the potential energy all depend on the interaction strength and contain a sharp signature of this transition. In addition, the conversion rate of atoms to molecules, arising from three-body collisions, peaks at an interaction strength just beyond the ferromagnetic transition point. We then go beyond the local density approximation and derive an energy functional that includes a term that depends on the local magnetization gradient and acts as a “surface tension.” Using this energy functional, we numerically study the energetics of some candidate spin textures that may be stabilized in a harmonic trapping potential at zero net magnetization. We find that a hedgehog state has a lower energy than an “in-out” domain-wall state in an isotropic trap. Upon inclusion of trap anisotropy we find that the hedgehog magnetization profile gets distorted due to the surface tension term, this distortion being more apparent for small atom numbers. We estimate that the magnetic dipole interaction does not play a significant role in this system. We consider possible implications for experiments on trapped L6i and K40 gases.

  14. Potential to kinetic energy conversion in wave number domain for the Southern Hemisphere

    NASA Technical Reports Server (NTRS)

    Huang, H.-J.; Vincent, D. G.

    1984-01-01

    Preliminary results of a wave number study conducted for the South Pacific Convergence Zone (SPCZ) using FGGE data for the period January 10-27, 1979 are reported. In particular, three variables (geomagnetic height, z, vertical p-velocity, omega, and temperature, T) and one energy conversion quantity, omega-alpha (where alpha is the specific volume), are shown. It is demonstrated that wave number 4 plays an important role in the conversion from available potential energy to kinetic energy in the Southern Hemisphere tropics, particularly in the vicinity of the SPCZ. It is therefore suggested that the development and movement of wave number 4 waves be carefully monitored in making forecasts for the South Pacific region.

  15. Energy Drinks: Topical Domain in the Emerging Literature and Neglected Areas of Research

    ERIC Educational Resources Information Center

    Piotrowski, Chris

    2014-01-01

    Prevalence statistics indicate that consumption of Energy drinks (EDs), often in combination with alcohol, is quite popular in the younger generation and particularly with college students. As literature on this topic is advancing at a rapid pace, it seemed instructive to examine which topics are emphasized in emerging EDs research. To that end, a…

  16. The Energy Retrofit of a Building: A Journey Through Bloom's Learning Domains

    ERIC Educational Resources Information Center

    Morgenstern, Mark; Meyer, Sally; Whitten, Barbara; Reuer, Matt

    2008-01-01

    At Colorado College, the energy retrofit of a building is used as a service-learning research project to teach physics and chemistry in a variety of courses. In introductory courses for nonscience majors, the project helps students appreciate the scientific method and quantitative reasoning. Within the physical-chemistry course, students see that…

  17. Landau Theory of Helical Fermi Liquids.

    PubMed

    Lundgren, Rex; Maciejko, Joseph

    2015-08-07

    We construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator. In the presence of rotation symmetry, interactions between quasiparticles are described by ten independent Landau parameters per angular momentum channel, by contrast with the two (symmetric and antisymmetric) Landau parameters for a conventional spin-degenerate Fermi liquid. We project quasiparticle states onto the Fermi surface and obtain an effectively spinless, projected Landau theory with a single projected Landau parameter per angular momentum channel that captures the spin-momentum locking or nontrivial Berry phase of the Fermi surface. As a result of this nontrivial Berry phase, projection to the Fermi surface can increase or lower the angular momentum of the quasiparticle interactions. We derive equilibrium properties, criteria for Fermi surface instabilities, and collective mode dispersions in terms of the projected Landau parameters. We briefly discuss experimental means of measuring projected Landau parameters.

  18. Wind Energy Potential: Current representation and projections for the European domain

    NASA Astrophysics Data System (ADS)

    Davy, Richard; Gnatiuk, Natalia; Bobylev, Leonid; Pettersson, Lasse

    2016-04-01

    We have used the publically available CORDEX datasets to quantify the ability of a current regional climate model (SMHI-RCA4) to simulate the wind energy potential in the Black sea region using 5 different global climate models for the boundary conditions. The regional climate model results are compared to the ERA-Interim reanalyses over a common period, 1979-2005, and we use Taylor plots to demonstrate the effect of different global climate models on the regional climate simulations. Wind energy potential is calculated from the daily hub-height (120 m) wind speeds by extrapolating the available 10 m wind speeds using a power-law wind profile approximation. In general we find that the regional climate model produces stronger surface winds over the Black Sea region as compared to the ERA-Interim reanalysis, which we relate to the difference in model resolution. We also assess the projected changes to the wind energy potential in the CORDEX EUR-11 region from the current period to the near future (2021-2050), and to the late 21st century (2061-2090). We use a single model ensemble approach to assess the robustness of the projected changes, depending upon the choice of global climate model used for the boundary conditions. To understand the context of the changes in wind energy potential in the region, we include the changing climatology of the upper level (850 hPa) winds over these periods. This work was supported by the EU FP7 Project, Grant agreement No.: 287844. "Towards COast to COast NETworks of marine protected areas (from the shore to the high and deep sea), coupled with sea-based wind energy potential (CoCoNet)".

  19. Modeling of piezoelectric energy extraction in a thermoacoustic engine with multi-pole time-domain impedance

    NASA Astrophysics Data System (ADS)

    Lin, Jeffrey; Scalo, Carlo; Hesselink, Lambertus

    2015-11-01

    We have carried out the first high-fidelity Navier-Stokes simulation of a complete thermoacoustic engine with piezoelectric energy extraction. The standing-wave thermoacoustic piezoelectric (TAP) engine model comprises a 51 cm long cylindrical resonator, containing a thermoacoustic stack on one end and capped by a PZT-5A piezoelectric diaphragm on the other end, tuned to the frequency of the thermoacoustically-amplified mode (388 Hz). A multi-pole broadband time-domain impedance model has been adopted to accurately simulate the measured electromechanical properties of the piezoelectric diaphragm. Simulations are first carried out from quasi-quiescent conditions to a limit cycle, with varying temperature gradients and stack configurations. Stack geometry and boundary layers are fully resolved. Acoustic energy extraction is then activated, achieving a new limit cycle at lower pressure amplitudes. The scaling of the modeled electrical power output and attainable thermal-to-electric energy conversion efficiencies are discussed. Limitations of extending a quasi-one-dimensional linear approximation based on Rott's theory to a (low amplitude) limit cycle are discussed, as well as nonlinear effects such as thermoacoustic energy transport and viscous dissipation.

  20. Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La)2CuO6+δ (Bi2201)

    PubMed Central

    Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; Bansil, Arun

    2015-01-01

    Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. We show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping. PMID:26084605

  1. Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La)2CuO6+δ (Bi2201)

    DOE PAGES

    Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; ...

    2015-06-18

    Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. Here, we show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Finally, our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping.

  2. Pulsar Timing with the Fermi LAT

    DTIC Science & Technology

    2010-12-01

    Pulsar Timing with the Fermi LAT Paul S. Ray∗, Matthew Kerr†, Damien Parent∗∗ and the Fermi PSC‡ ∗Naval Research Laboratory, 4555 Overlook Ave., SW...Laboratory, Washington, DC 20375, USA ‡Fermi Pulsar Search Consortium Abstract. We present an overview of precise pulsar timing using data from the Large...unbinned photon data. In addition to determining the spindown behavior of the pulsars and detecting glitches and timing noise, such timing analyses al

  3. Fermi surface behavior in the ABJM M2-brane theory

    NASA Astrophysics Data System (ADS)

    DeWolfe, Oliver; Henriksson, Oscar; Rosen, Christopher

    2015-06-01

    We calculate fermionic Green's functions for states of the three-dimensional Aharony-Bergman-Jafferis-Maldacena M2-brane theory at large N using the gauge-gravity correspondence. We embed extremal black brane solutions in four-dimensional maximally supersymmetric gauged supergravity, obtain the linearized Dirac equations for each spin-1 /2 mode that cannot mix with a gravitino, and solve these equations with infalling boundary conditions to calculate retarded Green's functions. For generic values of the chemical potentials, we find Fermi surfaces with universally non-Fermi liquid behavior, matching the situation for four-dimensional N =4 super-Yang-Mills. Fermi surface singularities appear and disappear discontinuously at the point where all chemical potentials are equal, reminiscent of a quantum critical point. One limit of parameter space has zero entropy at zero temperature, and fermionic fluctuations are perfectly stable inside an energy region around the Fermi surface. An ambiguity in the quantization of the fermions is resolved by supersymmetry.

  4. Bioterrorism and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Cooper, Joshua

    2013-04-01

    We proffer a contemporary solution to the so-called Fermi Paradox, which is concerned with conflict between Copernicanism and the apparent paucity of evidence for intelligent alien civilizations. In particular, we argue that every community of organisms that reaches its space-faring age will (1) almost immediately use its rocket-building computers to reverse-engineer its genetic chemistry and (2) self-destruct when some individual uses said technology to design an omnicidal pathogen. We discuss some of the possible approaches to prevention with regard to Homo sapiens' vulnerability to bioterrorism, particularly on a short-term basis.

  5. Fermi surface, charge-density-wave gap, and kinks in 2H- TaSe2

    NASA Astrophysics Data System (ADS)

    Rossnagel, K.; Rotenberg, Eli; Koh, H.; Smith, N. V.; Kipp, L.

    2005-09-01

    The Fermi surface of the layered charge-density-wave compound 2H-TaSe2 is measured by angle-resolved photoemission as a function of temperature. A surprising Fermi-surface topology and a Fermi-surface branch-dependent charge-density-wave gap are found. In the charge-density-wave state band hybridization effects are strong and responsible for kinks in the band dispersions at relatively high binding energy. The implications of the results on the charge-density-wave mechanism are discussed.

  6. THE FERMI GBM GAMMA-RAY BURST CATALOG: THE FIRST TWO YEARS

    SciTech Connect

    Paciesas, William S.; Bhat, P. N.; Briggs, Michael S.; Burgess, J. Michael; Chaplin, Vandiver; Connaughton, Valerie; Goldstein, Adam; Guiriec, Sylvain; Meegan, Charles A.; Van der Horst, Alexander J.; Von Kienlin, Andreas; Diehl, Roland; Foley, Suzanne; Greiner, Jochen; Gruber, David; Bissaldi, Elisabetta; Fishman, Gerald J.; Gibby, Melissa; Giles, Misty; and others

    2012-03-01

    The Fermi Gamma-ray Burst Monitor (GBM) is designed to enhance the scientific return from Fermi in studying gamma-ray bursts (GRBs). In its first two years of operation GBM triggered on 491 GRBs. We summarize the criteria used for triggering and quantify the general characteristics of the triggered GRBs, including their locations, durations, peak flux, and fluence. This catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.

  7. The VELA-X-Pulsar Wind Nebula Revisited with Four Years of Fermi Large Area Telescope Observations

    NASA Technical Reports Server (NTRS)

    Grondin, M. -H.; Romani, R. W.; Lemoine-Goumard, M.; Guillemot, L.; Harding, Alice K.; Reposeur, T.

    2013-01-01

    The Vela supernova remnant (SNR) is the closest SNR to Earth containing an active pulsar, the Vela pulsar (PSR B0833-45). This pulsar is an archetype of the middle-aged pulsar class and powers a bright pulsar wind nebula (PWN), Vela-X, spanning a region of 2deg × 3deg south of the pulsar and observed in the radio, X-ray, and very high energy ?-ray domains. The detection of the Vela-X PWN by the Fermi Large Area Telescope (LAT) was reported in the first year of the mission. Subsequently, we have reinvestigated this complex region and performed a detailed morphological and spectral analysis of this source using 4 yr of Fermi-LAT observations. This study lowers the threshold for morphological analysis of the nebula from 0.8 GeV to 0.3 GeV, allowing for the inspection of distinct energy bands by the LAT for the first time. We describe the recent results obtained on this PWN and discuss the origin of the newly detected spatial features.

  8. THE VELA-X PULSAR WIND NEBULA REVISITED WITH FOUR YEARS OF FERMI LARGE AREA TELESCOPE OBSERVATIONS

    SciTech Connect

    Grondin, M.-H.; Romani, R. W.; Lemoine-Goumard, M.; Reposeur, T.; Harding, A. K.

    2013-09-10

    The Vela supernova remnant (SNR) is the closest SNR to Earth containing an active pulsar, the Vela pulsar (PSR B0833-45). This pulsar is an archetype of the middle-aged pulsar class and powers a bright pulsar wind nebula (PWN), Vela-X, spanning a region of 2 Degree-Sign Multiplication-Sign 3 Degree-Sign south of the pulsar and observed in the radio, X-ray, and very high energy {gamma}-ray domains. The detection of the Vela-X PWN by the Fermi Large Area Telescope (LAT) was reported in the first year of the mission. Subsequently, we have reinvestigated this complex region and performed a detailed morphological and spectral analysis of this source using 4 yr of Fermi-LAT observations. This study lowers the threshold for morphological analysis of the nebula from 0.8 GeV to 0.3 GeV, allowing for the inspection of distinct energy bands by the LAT for the first time. We describe the recent results obtained on this PWN and discuss the origin of the newly detected spatial features.

  9. Vibrational lifetime and Fermi resonance in polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Fendt, A.; Fischer, S. F.; Kaiser, W.

    1981-05-01

    The energy decay of CH-stretching modes of the molecules CHCl 3 ,CH 2Cl 2, CH 3COCH 3, CH 3OH, and CH 3CH 2OH is measured in the liquid state. The observed lifetime very between 1.5 and 65 ps. A theoretical analysis points to the importance of Fermi resonance in the vibrational relaxation process. Quantitative comparison between theory and experiments is presented for the individual molecules. The strong variation of the lifetime for CH-stretching modes of various molecules may be understood if several effects are taken into account. First and most important is the influence of the Fermi resonances. Without the anharmonic mixing of the initial state, the overtone of the CH-bending modes and/or a higher order combination tone, one would predict lifetimes which are more than an order of magnitude longer than the observed lifetimes. This effect has been discussed earlier in detail for methylhalides by Zygan-Maus and Fischer [11] and, more recently, it has been incorporated in elaborate discussions for triatomic molecules like CO 2 by several authors [12]. A second factor to be considered for the interpretation is the rapi energy redistribution between different CH-stretching states was found theoretically to be faster than the further decay process by an order of magnitude [6, 11]. Experimentally, this effect was verified in this note for CH 2Cl 2 by the observation that the decay time was the same regardl whether the symmetric or the asymmetric CH-stretching mode was excited. This effect leads to a lengthening of the observed decay process. There is a bottleneck effect. Finally, we have shown that location and width of the final state are important parameters for the interpretation of the depopulatio lifetime. The empirical determination of these effects is not free of uncertainties. Very strong Fermi resonance can lead to rapid energy exchange during the exc process. In this case there is no bottleneck effect and it is difficult to detect the pathway of the energy

  10. Fermi Science Support Center Data Servers and Archive

    NASA Astrophysics Data System (ADS)

    Reustle, Alexander; FSSC, LAT Collaboration

    2017-01-01

    The Fermi Science Support Center (FSSC) provides the scientific community with access to Fermi data and other products. The Gamma-Ray Burst Monitor (GBM) data is stored at NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) and is accessible through their searchable Browse web interface. The Large Area Telescope (LAT) data is distributed through a custom FSSC interface where users can request all photons detected from a region on the sky over a specified time and energy range. Through its website the FSSC also provides planning and scheduling products, such as long and short term observing timelines, spacecraft position and attitude histories, and exposure maps. We present an overview of the different data products provided by the FSSC, how they can be accessed, and statistics on the archive usage since launch.

  11. Hierarchy of simulation models in predicting molecular recognition mechanisms from the binding energy landscapes: structural analysis of the peptide complexes with SH2 domains.

    PubMed

    Verkhivker, G M; Bouzida, D; Gehlhaar, D K; Rejto, P A; Schaffer, L; Arthurs, S; Colson, A B; Freer, S T; Larson, V; Luty, B A; Marrone, T; Rose, P W

    2001-12-01

    Computer simulations using the simplified energy function and simulated tempering dynamics have accurately determined the native structure of the pYVPML, SVLpYTAVQPNE, and SPGEpYVNIEF peptides in the complexes with SH2 domains. Structural and equilibrium aspects of the peptide binding with SH2 domains have been studied by generating temperature-dependent binding free energy landscapes. Once some native peptide-SH2 domain contacts are constrained, the underlying binding free energy profile has the funnel-like shape that leads to a rapid and consistent acquisition of the native structure. The dominant native topology of the peptide-SH2 domain complexes represents an extended peptide conformation with strong specific interactions in the phosphotyrosine pocket and hydrophobic interactions of the peptide residues C-terminal to the pTyr group. The topological features of the peptide-protein interface are primarily determined by the thermodynamically stable phosphotyrosyl group. A diversity of structurally different binding orientations has been observed for the amino-terminal residues to the phosphotyrosine. The dominant native topology for the peptide residues carboxy-terminal to the phosphotyrosine is tolerant to flexibility in this region of the peptide-SH2 domain interface observed in equilibrium simulations. The energy landscape analysis has revealed a broad, entropically favorable topology of the native binding mode for the bound peptides, which is robust to structural perturbations. This could provide an additional positive mechanism underlying tolerance of the SH2 domains to hydrophobic conservative substitutions in the peptide specificity region.

  12. Determination of magnetic anisotropy constants and domain wall pinning energy of Fe/MgO(001) ultrathin film by anisotropic magnetoresistance.

    PubMed

    Hu, Bo; He, Wei; Ye, Jun; Tang, Jin; Zhang, Yong-Sheng; Ahmad, Syed Sheraz; Zhang, Xiang-Qun; Cheng, Zhao-Hua

    2015-09-15

    It is challenging to determine domain wall pinning energy and magnetic anisotropy since both coherent rotation and domain wall displacement coexist during magnetization switching process. Here, angular dependence anisotropic magnetoresistance (AMR) measurements at different magnetic fields were employed to determine magnetic anisotropy constants and domain wall pinning energy of Fe/MgO(001) ultrathin film. The AMR curves at magnetic fields which are high enough to ensure the coherent rotation of magnetization indicate a smooth behavior without hysteresis between clockwise (CW) and counter-clockwise (CCW) rotations. By analyzing magnetic torque, the magnetic anisotropy constants can be obtained. On the other hand, the AMR curves at low fields show abrupt transitions with hysteresis between CW and CCW rotations, suggesting the presence of multi-domain structures. The domain wall pinning energy can be obtained by analyzing different behaviors of AMR. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of magnetic anisotropy and domain wall pinning energy, which is still a critical issue for spintronics.

  13. Wind Energy System Time-domain (WEST) analyzers using hybrid simulation techniques

    NASA Technical Reports Server (NTRS)

    Hoffman, J. A.

    1979-01-01

    Two stand-alone analyzers constructed for real time simulation of the complex dynamic characteristics of horizontal-axis wind energy systems are described. Mathematical models for an aeroelastic rotor, including nonlinear aerodynamic and elastic loads, are implemented with high speed digital and analog circuitry. Models for elastic supports, a power train, a control system, and a rotor gimbal system are also included. Limited correlation efforts show good comparisons between results produced by the analyzers and results produced by a large digital simulation. The digital simulation results correlate well with test data.

  14. Ferromagnetism in the upper branch of the Feshbach resonance and the hard-sphere Fermi gas

    PubMed Central

    Chang, Soon-Yong; Randeria, Mohit; Trivedi, Nandini

    2011-01-01

    We address the question of ferromagnetism in repulsive Fermi gas, a problem of fundamental interest, using quantum Monte Carlo simulations that include backflow corrections. We investigate a two-component Fermi gas on the upper branch of a Feshbach resonance and contrast it with the hard-sphere gas. We find that, in both cases, the Fermi liquid becomes unstable to ferromagnetism at a kFa smaller than the mean field result, where kF is the Fermi wavevector and a is the scattering length. Even though the total energies E(kFa) are similar in the two cases, their pair correlations and kinetic energies are completely different, reflecting the underlying potentials. We discuss the extent to which our calculations shed light on recent experiments.

  15. Energy-efficient optical network units for OFDM PON based on time-domain interleaved OFDM technique.

    PubMed

    Hu, Xiaofeng; Cao, Pan; Zhang, Liang; Jiang, Lipeng; Su, Yikai

    2014-06-02

    We propose and experimentally demonstrate a new scheme to reduce the energy consumption of optical network units (ONUs) in orthogonal frequency division multiplexing passive optical networks (OFDM PONs) by using time-domain interleaved OFDM (TI-OFDM) technique. In a conventional OFDM PON, each ONU has to process the complete downstream broadcast OFDM signal with a high sampling rate and a large FFT size to retrieve its required data, even if it employs a portion of OFDM subcarriers. However, in our scheme, the ONU only needs to sample and process one data group from the downlink TI-OFDM signal, effectively reducing the sampling rate and the FFT size of the ONU. Thus, the energy efficiency of ONUs in OFDM PONs can be greatly improved. A proof-of-concept experiment is conducted to verify the feasibility of the proposed scheme. Compared to the conventional OFDM PON, our proposal can save 17.1% and 26.7% energy consumption of ONUs by halving and quartering the sampling rate and the FFT size of ONUs with the use of the TI-OFDM technology.

  16. Hydrodynamic modeling of the deconfinement phase transition in heavy-ion collisions in the NICA-FAIR energy domain

    SciTech Connect

    Merdeev, A. V.; Satarov, L. M.; Mishustin, I. N.

    2011-07-15

    We use (3 + 1) dimensional ideal hydrodynamics to describe the space-time evolution of strongly interacting matter created in Au + Au and Pb + Pb collisions. The model is applied for the domain of bombarding energies 1-160 GeV/nucleon which includes future NICA (Dubna) and FAIR (Darmstadt) experiments. Two equations of state are used, the first one corresponding to resonance hadron gas and the second one including the deconfinement phase transition. The initial state is represented by two Lorentz-boosted nuclei. Dynamic trajectories of matter in the central box of the system are analyzed. They can be well represented by a fast shock-wave compression followed by a relatively slow isentropic expansion. The parameters of collective flows and hadronic spectra are calculated under assumption of the isochronous freeze-out. It is shown that the deconfinement phase transition leads to broadening of proton rapidity distributions, increase of elliptic flows, and formation of the directed antiflow in the central rapidity region. These effects are most pronounced at bombarding energies around 10 GeV/nucleon, when the system spends the longest time in the mixed phase. From the comparison with three-fluid calculations we conclude that the transparency effects are not so important in central collisions at NICA-FAIR energies (below 30 GeV/nucleon).

  17. Fully discrete energy stable high order finite difference methods for hyperbolic problems in deforming domains

    NASA Astrophysics Data System (ADS)

    Nikkar, Samira; Nordström, Jan

    2015-06-01

    A time-dependent coordinate transformation of a constant coefficient hyperbolic system of equations which results in a variable coefficient system of equations is considered. By applying the energy method, well-posed boundary conditions for the continuous problem are derived. Summation-by-Parts (SBP) operators for the space and time discretization, together with a weak imposition of boundary and initial conditions using Simultaneously Approximation Terms (SATs) lead to a provable fully-discrete energy-stable conservative finite difference scheme. We show how to construct a time-dependent SAT formulation that automatically imposes boundary conditions, when and where they are required. We also prove that a uniform flow field is preserved, i.e. the Numerical Geometric Conservation Law (NGCL) holds automatically by using SBP-SAT in time and space. The developed technique is illustrated by considering an application using the linearized Euler equations: the sound generated by moving boundaries. Numerical calculations corroborate the stability and accuracy of the new fully discrete approximations.

  18. Inhomogeneous atomic Bose-Fermi mixtures in cubic lattices.

    PubMed

    Cramer, M; Eisert, J; Illuminati, F

    2004-11-05

    We determine the ground state properties of inhomogeneous mixtures of bosons and fermions in cubic lattices and parabolic confining potentials. For finite hopping we determine the domain boundaries between Mott-insulator plateaux and hopping-dominated regions for lattices of arbitrary dimension within mean-field and perturbation theory. The results are compared with a new numerical method that is based on a Gutzwiller variational approach for the bosons and an exact treatment for the fermions. The findings can be applied as a guideline for future experiments with trapped atomic Bose-Fermi mixtures in optical lattices.

  19. Fermi: The Gamma-Ray Large Area Space Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  20. Fermi: The Gamma-Ray Large Area Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2015-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  1. Fermi: The Gamma-Ray Large Area Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10 seconds of gigaelectronvolts from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as super-symmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  2. Fermi: The Gamma-Ray Large Area Telescope Mission Status

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  3. Dark Matter Searches with the Fermi Large Area Telescope

    SciTech Connect

    Meurer, Christine

    2008-12-24

    The Fermi Gamma-Ray Space Telescope, successfully launched on June 11th, 2008, is the next generation satellite experiment for high-energy gamma-ray astronomy. The main instrument, the Fermi Large Area Telescope (LAT), with a wide field of view (>2 sr), a large effective area (>8000 cm{sup 2} at 1 GeV), sub-arcminute source localization, a large energy range (20 MeV-300 GeV) and a good energy resolution (close to 8% at 1 GeV), has excellent potential to either discover or to constrain a Dark Matter signal. The Fermi LAT team pursues complementary searches for signatures of particle Dark Matter in different search regions such as the galactic center, galactic satellites and subhalos, the milky way halo, extragalactic regions as well as the search for spectral lines. In these proceedings we examine the potential of the LAT to detect gamma-rays coming from Weakly Interacting Massive Particle annihilations in these regions with special focus on the galactic center region.

  4. Superfluid Thomas—Fermi approximation for trapped fermi gases

    NASA Astrophysics Data System (ADS)

    Hernández, E. S.; Capuzzi, P.; Szybisz, L.

    2009-02-01

    We present a generalization of fermionic fluiddynamics to the case of two trapped fermion species with a contact interaction. Within a mean field approximation, we derive coupled equations of motion for the particle densities, particle currents, and anomalous pair density. For an inhomogeneous system, the equilibrium situation with vanishing currents is described by a generalized Thomas-Fermi relation that includes the superfluid gap, together with a new nonlocal gap equation that replaces the usual BCS one. These equations are numericaly solved resorting to a local density approximation (LDA). Density and gap profiles are analyzed in terms of the scattering length, revealing that the current frame can exhibit microscopic details of quantum origin that are frequently absent in more macroscopic scenarios.

  5. The Fermi-Pasta-Ulam Problem in the Thermodynamic Limit

    NASA Astrophysics Data System (ADS)

    Ponno, Antonio

    In the present contribution we justify and discuss the scaling laws characterizing the first phase of the energy transfer from large to small spatial scales in a chain of nonlinear oscillators (the so-called Fermi-Pasta-Ulam α-model). By means of qualitative estimates, we show that large scale initial excitations (long wavelength Fourier modes) produce injection of energy into smaller scales on times t > τc ˜ ɛ-3/4 and up to a cutoff spatial scale ell c ˜ ɛ-1/4, where ɛ is the energy per degree of freedom of the system.

  6. Fermi acceleration in the randomized driven Lorentz gas and the Fermi-Ulam model.

    PubMed

    Karlis, A K; Papachristou, P K; Diakonos, F K; Constantoudis, V; Schmelcher, P

    2007-07-01

    Fermi acceleration of an ensemble of noninteracting particles evolving in a stochastic two-moving wall variant of the Fermi-Ulam model (FUM) and the phase randomized harmonically driven periodic Lorentz gas is investigated. As shown in [A. K. Karlis, P. K. Papachristou, F. K. Diakonos, V. Constantoudis, and P. Schmelcher, Phys. Rev. Lett. 97, 194102 (2006)], the static wall approximation, which ignores scatterer displacement upon collision, leads to a substantial underestimation of the mean energy gain per collision. In this paper, we clarify the mechanism leading to the increased acceleration. Furthermore, the recently introduced hopping wall approximation is generalized for application in the randomized driven Lorentz gas. Utilizing the hopping approximation the asymptotic probability distribution function of the particle velocity is derived. Moreover, it is shown that, for harmonic driving, scatterer displacement upon collision increases the acceleration in both the driven Lorentz gas and the FUM by the same amount. On the other hand, the investigation of a randomized FUM, comprising one fixed and one moving wall driven by a sawtooth force function, reveals that the presence of a particular asymmetry of the driving function leads to an increase of acceleration that is different from that gained when symmetrical force functions are considered, for all finite number of collisions. This fact helps open up the prospect of designing accelerator devices by combining driving laws with specific symmetries to acquire a desired acceleration behavior for the ensemble of particles.

  7. Universal Fermi liquid crossover and quantum criticality in a mesoscopic system.

    PubMed

    Keller, A J; Peeters, L; Moca, C P; Weymann, I; Mahalu, D; Umansky, V; Zaránd, G; Goldhaber-Gordon, D

    2015-10-08

    Quantum critical systems derive their finite-temperature properties from the influence of a zero-temperature quantum phase transition. The paradigm is essential for understanding unconventional high-Tc superconductors and the non-Fermi liquid properties of heavy fermion compounds. However, the microscopic origins of quantum phase transitions in complex materials are often debated. Here we demonstrate experimentally, with support from numerical renormalization group calculations, a universal crossover from quantum critical non-Fermi liquid behaviour to distinct Fermi liquid ground states in a highly controllable quantum dot device. Our device realizes the non-Fermi liquid two-channel Kondo state, based on a spin-1/2 impurity exchange-coupled equally to two independent electronic reservoirs. On detuning the exchange couplings we observe the Fermi liquid scale T*, at energies below which the spin is screened conventionally by the more strongly coupled channel. We extract a quadratic dependence of T* on gate voltage close to criticality, and validate an asymptotically exact description of the universal crossover between strongly correlated non-Fermi liquid and Fermi liquid states.

  8. Distinct Evolutions of Weyl Fermion Quasiparticles and Fermi Arcs with Bulk Band Topology in Weyl Semimetals

    NASA Astrophysics Data System (ADS)

    Xu, N.; Autès, G.; Matt, C. E.; Lv, B. Q.; Yao, M. Y.; Bisti, F.; Strocov, V. N.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Plumb, N. C.; Radovic, M.; Qian, T.; Yazyev, O. V.; Mesot, J.; Ding, H.; Shi, M.

    2017-03-01

    The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence of topologically protected degeneracies near the Fermi level. These degeneracies are the source of exotic phenomena, including the realization of chiral Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with the bulk band topology by performing angle-resolved photoemission spectroscopy, supported by first-principles calculations, on transition-metal monophosphides. While Weyl fermion quasiparticles exist only when the chemical potential is located between two saddle points of the Weyl cone features, the Fermi arc states extend in a larger energy scale and are robust across the bulk Lifshitz transitions associated with the recombination of two nontrivial Fermi surfaces enclosing one Weyl point into a single trivial Fermi surface enclosing two Weyl points of opposite chirality. Therefore, in some systems (e.g., NbP), topological Fermi arc states are preserved even if Weyl fermion quasiparticles are absent in the bulk. Our findings not only provide insight into the relationship between the exotic physical phenomena and the intrinsic bulk band topology in Weyl semimetals, but also resolve the apparent puzzle of the different magnetotransport properties observed in TaAs, TaP, and NbP, where the Fermi arc states are similar.

  9. Distinct Evolutions of Weyl Fermion Quasiparticles and Fermi Arcs with Bulk Band Topology in Weyl Semimetals.

    PubMed

    Xu, N; Autès, G; Matt, C E; Lv, B Q; Yao, M Y; Bisti, F; Strocov, V N; Gawryluk, D; Pomjakushina, E; Conder, K; Plumb, N C; Radovic, M; Qian, T; Yazyev, O V; Mesot, J; Ding, H; Shi, M

    2017-03-10

    The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence of topologically protected degeneracies near the Fermi level. These degeneracies are the source of exotic phenomena, including the realization of chiral Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with the bulk band topology by performing angle-resolved photoemission spectroscopy, supported by first-principles calculations, on transition-metal monophosphides. While Weyl fermion quasiparticles exist only when the chemical potential is located between two saddle points of the Weyl cone features, the Fermi arc states extend in a larger energy scale and are robust across the bulk Lifshitz transitions associated with the recombination of two nontrivial Fermi surfaces enclosing one Weyl point into a single trivial Fermi surface enclosing two Weyl points of opposite chirality. Therefore, in some systems (e.g., NbP), topological Fermi arc states are preserved even if Weyl fermion quasiparticles are absent in the bulk. Our findings not only provide insight into the relationship between the exotic physical phenomena and the intrinsic bulk band topology in Weyl semimetals, but also resolve the apparent puzzle of the different magnetotransport properties observed in TaAs, TaP, and NbP, where the Fermi arc states are similar.

  10. Log-Gabor energy based multimodal medical image fusion in NSCT domain.

    PubMed

    Yang, Yong; Tong, Song; Huang, Shuying; Lin, Pan

    2014-01-01

    Multimodal medical image fusion is a powerful tool in clinical applications such as noninvasive diagnosis, image-guided radiotherapy, and treatment planning. In this paper, a novel nonsubsampled Contourlet transform (NSCT) based method for multimodal medical image fusion is presented, which is approximately shift invariant and can effectively suppress the pseudo-Gibbs phenomena. The source medical images are initially transformed by NSCT followed by fusing low- and high-frequency components. The phase congruency that can provide a contrast and brightness-invariant representation is applied to fuse low-frequency coefficients, whereas the Log-Gabor energy that can efficiently determine the frequency coefficients from the clear and detail parts is employed to fuse the high-frequency coefficients. The proposed fusion method has been compared with the discrete wavelet transform (DWT), the fast discrete curvelet transform (FDCT), and the dual tree complex wavelet transform (DTCWT) based image fusion methods and other NSCT-based methods. Visually and quantitatively experimental results indicate that the proposed fusion method can obtain more effective and accurate fusion results of multimodal medical images than other algorithms. Further, the applicability of the proposed method has been testified by carrying out a clinical example on a woman affected with recurrent tumor images.

  11. Sensitivity of the KM3NeT detector to a neutrino flux from the Fermi bubbles

    SciTech Connect

    Coniglione, R.; Piattelli, P.; Sapienza, P.; Trovato, A.; Collaboration: KM3NeT Collaboration

    2014-11-18

    The Fermi Large Area Telescope data has provided evidence for a high-intensity emission of high-energy gamma rays with a E{sup −2} spectrum from two large bubbles above and below the Galactic Center. Hadronic mechanisms were proposed for this gamma-ray emission making the Fermi bubbles promising source candidates of high-energy neutrino emission. In this work preliminary simulation results regarding the detectability of high-energy neutrinos from the Fermi bubbles with the future multi-km{sup 3} neutrino telescope KM3NeT are presented.

  12. A study of diquark and meson condensation in the Nambu-Jona-Lasinio model and Fermi momentum

    NASA Astrophysics Data System (ADS)

    Ghosh, R.; Bhattacharya, A.; Chakrabarti, B.

    2017-01-01

    Using a three- and four-dimensional Pauli-Villars regularization scheme, we investigate quark-antiquark and diquark condensation in the framework of the Nambu-Jona-Lasinio model. Using the particle Fermi momentum as a cutoff parameter, we study the energy gap width and coherence length for the meson condensate . We also study the energy gap width and critical coherence length ( the distance over which there would be no diquark condensation) for the diquark < qq> and the dependence on the Fermi momentum. We obtain an estimate of the Fermi momentum value for meson and diquark condensates with an energy gap width of the order of 100 MeV.

  13. Cooling and thermometry of atomic Fermi gases

    NASA Astrophysics Data System (ADS)

    Onofrio, R.

    2016-11-01

    We review the status of cooling techniques aimed at achieving the deepest quantum degeneracy for atomic Fermi gases. We first discuss some physics motivations, providing a quantitative assessment of the need for deep quantum degeneracy in relevant physics cases, such as the search for unconventional superfluid states. Attention is then focused on the most widespread technique to reach deep quantum degeneracy for Fermi systems, sympathetic cooling of Bose - Fermi mixtures, organizing the discussion according to the specific species involved. Various proposals to circumvent some of the limitations on achieving the deepest Fermi degeneracy, and their experimental realizations, are then reviewed. Finally, we discuss the extension of these techniques to optical lattices and the implementation of precision thermometry crucial to the understanding of the phase diagram of classical and quantum phase transitions in Fermi gases.

  14. Reversible switching of in-plane polarized ferroelectric domains in BaTiO3(001) with very low energy electrons

    PubMed Central

    Rault, J. E.; Menteş, T. O.; Locatelli, A.; Barrett, N.

    2014-01-01

    The switchable bipolar ground state is at the heart of research into ferroelectrics for future, low-energy electronics. Polarization switching by an applied field is a complex phenomenon which depends on the initial domain ordering, defect concentration, electrical boundary conditions and charge screening. Injected free charge may also to be used to reversibly switch in-plane polarized domains. We show that the interaction between the initial domain order and the bulk screening provided by very low energy electrons switches the polarization without the collateral radiation damage which occurs when employing a beam of high energy electrons. Polarization switching during charge injection adds a new dimension to the multifunctionality of ferroelectric oxides. PMID:25354723

  15. Low energy constants of SU(2) partially quenched chiral perturbation theory from Nf=2+1 domain wall QCD

    DOE PAGES

    Boyle, P. A.; Christ, N. H.; Garron, N.; ...

    2016-03-09

    Here, we have performed fits of the pseudoscalar masses and decay constants, from a variety of the RBC-UKQCD Collaboration’s domain wall fermion ensembles, to SU(2) partially quenched chiral perturbation theory at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO). We report values for 9 NLO and 8 linearly independent combinations of NNLO partially quenched low-energy constants, which we compare to other lattice and phenomenological determinations. We discuss the size of successive terms in the chiral expansion and use our large set of low-energy constants to make predictions for mass splittings due to QCD isospin-breaking effects and the S-wave ππ scattering lengths.more » Lastly, we conclude that, for the range of pseudoscalar masses explored in this work, 115 MeV≲mPS≲430 MeV, the NNLO SU(2) expansion is quite robust and can fit lattice data with percent-scale accuracy.« less

  16. Fermi surface measurements of lutetium

    NASA Astrophysics Data System (ADS)

    Johanson, W. R.; Crabtree, G. W.; Schmidt, F. A.

    1982-03-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (101¯0) and (112¯0) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  17. Fermi surface measurements of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1982-03-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  18. Fermi surface measurements of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1982-01-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of Lutetium at temperatures down to .3K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a non-magnetic prototype of the structurally similar (hcp), trivalent, heavy rare-earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  19. Deformation quantization of fermi fields

    SciTech Connect

    Galaviz, I. Garcia-Compean, H. Przanowski, M. Turrubiates, F.J.

    2008-04-15

    Deformation quantization for any Grassmann scalar free field is described via the Weyl-Wigner-Moyal formalism. The Stratonovich-Weyl quantizer, the Moyal *-product and the Wigner functional are obtained by extending the formalism proposed recently in [I. Galaviz, H. Garcia-Compean, M. Przanowski, F.J. Turrubiates, Weyl-Wigner-Moyal Formalism for Fermi Classical Systems, arXiv:hep-th/0612245] to the fermionic systems of infinite number of degrees of freedom. In particular, this formalism is applied to quantize the Dirac free field. It is observed that the use of suitable oscillator variables facilitates considerably the procedure. The Stratonovich-Weyl quantizer, the Moyal *-product, the Wigner functional, the normal ordering operator, and finally, the Dirac propagator have been found with the use of these variables.

  20. Spectral properties of 438 GRBs detected by Fermi/GBM

    NASA Astrophysics Data System (ADS)

    Nava, L.; Ghirlanda, G.; Ghisellini, G.; Celotti, A.

    2011-06-01

    We present the results of the spectral analysis of the public data of 438 gamma ray bursts (GRBs) detected by the Fermi Gamma ray Burst Monitor (GBM) up to March 2010. For 432 bursts we could fit the time-integrated spectrum. In 318 cases we could reliably constrain the peak energy Eobs_peak of their νFν spectrum by analyzing their time-integrated spectrum between 8 keV and 35 MeV. Eighty percent of these spectra are fitted by a power-law with an exponential cutoff, and the remaining with the Band function. Among these 318 GRBs, 274 belong to the long GRB class and 44 to the short. Long GRBs have a typical peak energy Eobs_peak ~ 160 keV and low-energy spectral index α ~ - 0.92. Short GRBs have a harder peak energy (Eobs_peak ~ 490 keV) and a harder low-energy spectral index (α ~ -0.50) than long bursts. For each Fermi GRB we also analyzed the spectrum corresponding to the peak flux of the burst. On average, the peak spectrum has a harder low-energy spectral index than the corresponding time-integrated spectrum for the same burst, but similar Eobs_peakṪhe spectral parameters derived in our analysis of Fermi/GBM bursts are globally consistent with those reported in the GRB Cicular Network (GCN) archive after December 2008, while we found systematic differences in the low-energy power-law index for earlier bursts. Tables 2-5 are available in electronic form at http://www.aanda.org

  1. FERMI view of the TeV blazar Markarian 421

    SciTech Connect

    Paneque, D; Raino, S.; Chiang, J.; Mazziotta, M.N.; Tramacere, A.; /SLAC /KIPAC, Menlo Park /CIFS, Turin

    2010-08-26

    The high energy component of the TeV blazar Markarian 421 has been extensively studied since the beginning of the 90s, when the source was first detected at gamma-rays with EGRET and the Whipple Telescope, yet the source is still far from being understood. The high sensitivity, large dynamic range, and excellent time coverage of the Fermi Large Area Telescope (LAT), all representing significant advances over previous gamma-ray observations, will play a key role in the elucidation of the physical processes underlying the high energy emission of this blazar. In this presentation we show the results from almost 6 months (4 August 2008 to 20 January 2009) of observation with LAT. We report significant flux/spectral variability on a range of time scales from weeks to days, and an energy spectrum from 0.1 GeV to 300 GeV, overlapping with the energy ranges covered by the current generation of Cherenkov Telescopes. Results on the observations of the BLLac object Markarian 421 collected in the first months of operation of the Fermi satellite have been presented. Light curves on weekly and daily timescales have been shown, as well as the results of the spectral analysis in the energy range between 100 MeV and 300 GeV, covered for the first time by a satellite experiment overlapping the lower energy observations from Cherenkov telescopes on earth. These results are still preliminary and will be enriched and completed soon by a forthcoming publication. The results shown here demonstrate the great performance of Fermi-LAT to study the gamma-emission from Mrk421 (and blazars in general) over a large dynamic range and also on short timescales, which is expected to be of key importance for the study of the emission of the source in a coordinated way with other instruments covering other energy ranges.

  2. Twelve Years of Education and Public Outreach with the Fermi Gamma-ray Space Telescope

    NASA Astrophysics Data System (ADS)

    Cominsky, Lynn R.; McLin, K. M.; Simonnet, A.; Fermi E/PO Team

    2013-04-01

    During the past twelve years, NASA's Fermi Gamma-ray Space Telescope has supported a wide range of Education and Public Outreach (E/PO) activities, targeting K-14 students and the general public. The purpose of the Fermi E/PO program is to increase student and public understanding of the science of the high-energy Universe, through inspiring, engaging and educational activities linked to the mission’s science objectives. The E/PO program has additional more general goals, including increasing the diversity of students in the Science, Technology, Engineering and Mathematics (STEM) pipeline, and increasing public awareness and understanding of Fermi science and technology. Fermi's multi-faceted E/PO program includes elements in each major outcome category: ● Higher Education: Fermi E/PO promotes STEM careers through the use of NASA data including research experiences for students and teachers (Global Telescope Network), education through STEM curriculum development projects (Cosmology curriculum) and through enrichment activities (Large Area Telescope simulator). ● Elementary and Secondary education: Fermi E/PO links the science objectives of the Fermi mission to well-tested, customer-focused and NASA-approved standards-aligned classroom materials (Black Hole Resources, Active Galaxy Education Unit and Pop-up book, TOPS guides, Supernova Education Unit). These materials have been distributed through (Educator Ambassador and on-line) teacher training workshops and through programs involving under-represented students (after-school clubs and Astro 4 Girls). ● Informal education and public outreach: Fermi E/PO engages the public in sharing the experience of exploration and discovery through high-leverage multi-media experiences (Black Holes planetarium and PBS NOVA shows), through popular websites (Gamma-ray Burst Skymap, Epo's Chronicles), social media (Facebook, MySpace), interactive web-based activities (Space Mysteries, Einstein@Home) and activities by

  3. A low energy electron microscopy study of the initial growth, structure, and thermal stability of 4,4'-biphenyldicarboxylic acid domains on Cu(001)

    NASA Astrophysics Data System (ADS)

    Khokhar, Fawad S.; van Gastel, Raoul; Schwarz, Daniel; Zandvliet, Harold J. W.; Poelsema, Bene

    2011-09-01

    The growth of 4,4'-biphenyldicarboxylic acid (BDA) on Cu(001) has been studied using low energy electron microscopy and selective area low energy electron diffraction. The emergence of large islands and hydrogen bonding to perpendicularly oriented, adjacent molecules is confirmed. The two benzene rings of adsorbed BDA are twisted along the molecular axis. Unconventional growth of the domains, followed by a second nucleation stage, is observed at room temperature. This unanticipated feature is attributed to the accumulation of stress in the islands. Ostwald ripening in the films and the decay of BDA domains at 448 K exhibits features that are consistent with diffusion limited behavior.

  4. Radio-weak BL Lac Objects in the Fermi Era

    NASA Astrophysics Data System (ADS)

    Massaro, F.; Marchesini, E. J.; D’Abrusco, R.; Masetti, N.; Andruchow, I.; Smith, Howard A.

    2017-01-01

    The existence of “radio-weak BL Lac objects” (RWBLs) has been an open question, and has remained unsolved since the discovery that quasars could be radio-quiet or radio-loud. Recently, several groups identified RWBL candidates, mostly found while searching for low-energy counterparts of the unidentified or unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs (WDs) or weak emission line quasars (WELQs) when there are not sufficient data to precisely draw their broadband spectral energy distribution, and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs, and BL Lacs using the [3.4]–[4.6]–[12] μm color–color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with that of the BL Lac population.

  5. The First FERMI-LAT Gamma-Ray Burst Catalog

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Asano, K.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bhat, P. N.; Bissaldi, E.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Burgess, J. Michael; Buson, S.; Byrne, D.; Caliandro, G. A.; Ferrara, E. C.; Gehrels, N.; Guiriec, S.; McEnery, J. E.; Nemmen, R.; Perkins, J. S.; Racusin, J. L.; Thompson, D. J.; Kouveliotou, C.

    2013-01-01

    In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy great than (20 MeV) gamma-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above approximately 20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

  6. Observation of Weyl nodes and Fermi arcs in tantalum phosphide

    PubMed Central

    Xu, N.; Weng, H. M.; Lv, B. Q.; Matt, C. E.; Park, J.; Bisti, F.; Strocov, V. N.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Plumb, N. C.; Radovic, M.; Autès, G.; Yazyev, O. V.; Fang, Z.; Dai, X.; Qian, T.; Mesot, J.; Ding, H.; Shi, M.

    2016-01-01

    A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs. PMID:26983910

  7. DPA Cross Section Library FermiDPA 1.0

    SciTech Connect

    Pronskikh, V. S.; Mokhov, N. V.

    2013-06-05

    DPA cross section library FermiDPA 1.0 based on the industry standard NRT model calculations is described. The library contains DPA cross sections for neutrons in the energy range 10$^{-5}$ eV 20 (150) MeV. Calculations used neutron-induced reaction cross sections from ENDFB-VII database of evaluated nuclear data. The NJOY99 nuclear data processing system's module HEATR was applied to calculate NRT model radiation damage cross sections. The FermiDPA 1.0 library is a database of 395 text files (for 395 known isotopes) with DPA cross sections. It is code-independent and can be implemented in any transport code.

  8. Strongly Correlated States of Ultracold Rotating Dipolar Fermi Gases

    SciTech Connect

    Osterloh, Klaus; Barberan, Nuria; Lewenstein, Maciej

    2007-10-19

    We study strongly correlated ground and excited states of rotating quasi-2D Fermi gases constituted of a small number of dipole-dipole interacting particles with dipole moments polarized perpendicular to the plane of motion. As the number of atoms grows, the system enters an intermediate regime, where ground states are subject to a competition between distinct bulk-edge configurations. This effect obscures their description in terms of composite fermions and leads to the appearance of novel quasihole ground states. In the presence of dipolar interactions, the principal Laughlin state at filling {nu}=1/3 exhibits a substantial energy gap for neutral (total angular momentum conserving) excitations and is well-described as an incompressible Fermi liquid. Instead, at lower fillings, the ground state structure favors crystalline order.

  9. Unconventional fermi surface instabilities in the kagome Hubbard model.

    PubMed

    Kiesel, Maximilian L; Platt, Christian; Thomale, Ronny

    2013-03-22

    We investigate the competing Fermi surface instabilities in the kagome tight-binding model. Specifically, we consider on-site and short-range Hubbard interactions in the vicinity of van Hove filling of the dispersive kagome bands where the fermiology promotes the joint effect of enlarged density of states and nesting. The sublattice interference mechanism devised by Kiesel and Thomale [Phys. Rev. B 86, 121105 (2012)] allows us to explain the intricate interplay between ferromagnetic fluctuations and other ordering tendencies. On the basis of the functional renormalization group used to obtain an adequate low-energy theory description, we discover finite angular momentum spin and charge density wave order, a twofold degenerate d-wave Pomeranchuk instability, and f-wave superconductivity away from van Hove filling. Together, this makes the kagome Hubbard model the prototypical scenario for several unconventional Fermi surface instabilities.

  10. Quasi-two-dimensional Fermi gases at finite temperatures

    NASA Astrophysics Data System (ADS)

    Fischer, Andrea M.; Parish, Meera M.

    2014-12-01

    We consider a Fermi gas with short-range attractive interactions that is confined along one direction by a tight harmonic potential. For this quasi-two-dimensional (quasi-2D) Fermi gas, we compute the pressure equation of state, radiofrequency spectrum, and the superfluid critical temperature Tc using a mean-field theory that accounts for all the energy levels of the harmonic confinement. Our calculation for Tc provides a natural generalization of the Thouless criterion to the quasi-2D geometry, and it correctly reduces to the 3D expression derived from the local density approximation in the limit where the confinement frequency ωz→0 . Furthermore, our results suggest that Tc can be enhanced by relaxing the confinement and perturbing away from the 2D limit.

  11. Magnetic description of the Fermi arc in type-I and type-II Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Tchoumakov, Serguei; Civelli, Marcello; Goerbig, Mark O.

    2017-03-01

    We consider finite-sized interfaces of a Weyl semimetal and show that the corresponding confinement potential is similar to the application of a magnetic field. Among the numerous states, which can be labeled by indices n like in Landau levels, the n =0 surface state describes the Weyl semimetal Fermi arc at a given chemical potential. Moreover, the analogy with a magnetic field shows that an external in-plane magnetic field can be used to distort the Fermi arc and would explain some features of magnetotransport in Weyl semimetals. We derive the Fermi arc for type-I and type-II Weyl semimetals where we deal with the tilt anisotropy by the use of Lorentz boosts. In the case of type-II Weyl semimetals, this leads to many additional topologically trivial surface states at low energy. Finally, we extend the Aharonov-Casher argument and demonstrate the stability of the Fermi arc over fluctuations of the surface potential.

  12. Sharper Fermi LAT images: instrument response functions for an improved event selection

    SciTech Connect

    Portillo, Stephen K. N.; Finkbeiner, Douglas P.

    2014-11-20

    The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope has a point-spread function (PSF) with large tails, consisting of events affected by tracker inefficiencies, inactive volumes, and hard scattering; these tails can make source confusion a limiting factor. The parameter CTBCORE, available in the publicly available Extended Fermi LAT data (available at http://fermi.gsfc.nasa.gov/ssc/data/access/), estimates the quality of each event's direction reconstruction; by implementing a cut in this parameter, the tails of the PSF can be suppressed at the cost of losing effective area. We implement cuts on CTBCORE and present updated instrument response functions derived from the Fermi LAT data itself, along with all-sky maps generated with these cuts. Having shown the effectiveness of these cuts, especially at low energies, we encourage their use in analyses where angular resolution is more important than Poisson noise.

  13. Virial expansion for a strongly correlated Fermi gas with imbalanced spin populations

    NASA Astrophysics Data System (ADS)

    Liu, Xia-Ji; Hu, Hui

    2010-10-01

    Quantum virial expansion provides an ideal tool to investigate the high-temperature properties of a strongly correlated Fermi gas. Here, we construct the virial expansion in the presence of spin-population imbalance. Up to the third order, we calculate the high-temperature free energy of a unitary Fermi gas as a function of spin imbalance, with infinitely large attractive or repulsive interactions. In the latter repulsive case, we show that there is no itinerant ferromagnetism when quantum virial expansion is applicable. We therefore estimate an upper bound for the ferromagnetic transition temperature Tc. For a harmonically trapped Fermi gas at unitarity, we find that (Tc)upperFermi temperature at the center of the trap. Our result for the high-temperature equations of state may confront future high-precision thermodynamic measurements.

  14. Sharper Fermi LAT Images: Instrument Response Functions for an Improved Event Selection

    NASA Astrophysics Data System (ADS)

    Portillo, Stephen K. N.; Finkbeiner, Douglas P.

    2014-11-01

    The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope has a point-spread function (PSF) with large tails, consisting of events affected by tracker inefficiencies, inactive volumes, and hard scattering; these tails can make source confusion a limiting factor. The parameter CTBCORE, available in the publicly available Extended Fermi LAT data (available at http://fermi.gsfc.nasa.gov/ssc/data/access/), estimates the quality of each event's direction reconstruction; by implementing a cut in this parameter, the tails of the PSF can be suppressed at the cost of losing effective area. We implement cuts on CTBCORE and present updated instrument response functions derived from the Fermi LAT data itself, along with all-sky maps generated with these cuts. Having shown the effectiveness of these cuts, especially at low energies, we encourage their use in analyses where angular resolution is more important than Poisson noise.

  15. Emergence of a Metallic Quantum Solid Phase in a Rydberg-Dressed Fermi Gas.

    PubMed

    Li, Wei-Han; Hsieh, Tzu-Chi; Mou, Chung-Yu; Wang, Daw-Wei

    2016-07-15

    We examine possible low-temperature phases of a repulsively Rydberg-dressed Fermi gas in a three-dimensional free space. It is shown that the collective density excitations develop a roton minimum, which is softened at a wave vector smaller than the Fermi wave vector when the particle density is above a critical value. The mean field calculation shows that, unlike the insulating density wave states often observed in conventional condensed matters, a self-assembled metallic density wave state emerges at low temperatures. In particular, the density wave state supports a Fermi surface and a body-centered-cubic crystal order at the same time with the estimated critical temperature being about one tenth of the noninteracting Fermi energy. Our results suggest the emergence of a fermionic quantum solid that should be observable in the current experimental setup.

  16. Fermi-liquid theory for the single-impurity Anderson model

    NASA Astrophysics Data System (ADS)

    Mora, Christophe; Moca, Cǎtǎlin Paşcu; von Delft, Jan; Zaránd, Gergely

    2015-08-01

    We generalize Nozières' Fermi-liquid theory for the low-energy behavior of the Kondo model to that of the single-impurity Anderson model. In addition to the electrons' phase shift at the Fermi energy, the low-energy Fermi-liquid theory is characterized by four Fermi-liquid parameters: the two given by Nozières that enter to first order in the excitation energy, and two additional ones that enter to second order and are needed away from particle-hole symmetry. We express all four parameters in terms of zero-temperature physical observables, namely the local charge and spin susceptibilities and their derivatives with respect to the local level position. We determine these in terms of the bare parameters of the Anderson model using Bethe ansatz and numerical renormalization group (NRG) calculations. Our low-energy Fermi-liquid theory applies throughout the crossover from the strong-coupling Kondo regime via the mixed-valence regime to the empty-orbital regime. From the Fermi-liquid theory, we determine the conductance through a quantum dot symmetrically coupled to two leads in the regime of small magnetic field, low temperature, and small bias voltage, and compute the coefficients of the ˜B2 , ˜T2 , and ˜V2 terms exactly in terms of the Fermi-liquid parameters. The coefficients of T2, V2, and B2 are found to change sign during the Kondo to empty-orbital crossover. The crossover becomes universal in the limit that the local interaction is much larger than the level width. For completeness, we also compute the shot noise and discuss the resulting Fano factor.

  17. Fermi bubbles as a source of cosmic rays above 1015 eV

    NASA Astrophysics Data System (ADS)

    Chernyshov, D. O.; Cheng, K. S.; Dogiel, V. A.; Ko, C. M.

    2014-11-01

    Fermi bubbles are giant gamma-ray structures extended north and south of the Galactic center with characteristic sizes of order of 10 kpc recently discovered by Fermi Large Area Telescope. Good correlation between radio and gamma-ray emission in the region covered by Fermi bubbles implies the presence of high-energy electrons in this region. Since it is relatively difficult for relativistic electrons of this energy to travel all the way from the Galactic sources toward Fermi bubbles one can assume that they accelerated in-situ. The corresponding acceleration mechanism should also affect the distribution of the relativistic protons in the Galaxy. Since protons have much larger lifetimes the effect may even be observed near the Earth. In our model we suggest that Fermi bubbles are created by acceleration of electrons on series of shocks born due to periodic star accretions by supermassive black hole Sgr A*. We propose that hadronic CR within the 'knee' of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Reacceleration of these particles in the Fermi Bubble produces CRs beyond the knee. This model provides a natural explanation of the observed CR flux, spectral indexes, and matching of spectra at the knee.

  18. REFINING THE ASSOCIATIONS OF THE FERMI LARGE AREA TELESCOPE SOURCE CATALOGS

    SciTech Connect

    Massaro, F.; D’Abrusco, R.; Paggi, A.; Smith, Howard A.; Landoni, M.; Masetti, N.; Giroletti, M.; Otí-Floranes, H.; Jiménez-Bailón, E.; Chavushyan, V.; Patiño-Álvarez, V.; Digel, S. W.; Tosti, G.

    2015-03-15

    The Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) was released in 2010 February and the Fermi-LAT 2-Year Source Catalog (2FGL) appeared in 2012 April, based on data from 24 months of operation. Since they were released, many follow up observations of unidentified γ-ray sources have been performed and new procedures for associating γ-ray sources with potential counterparts at other wavelengths have been developed. Here we review and characterize all of the associations as published in the 1FGL and 2FGL catalogs on the basis of multifrequency archival observations. In particular, we located 177 spectra for the low-energy counterparts that were not listed in the previous Fermi catalogs, and in addition we present new spectroscopic observations of eight γ-ray blazar candidates. Based on our investigations, we introduce a new counterpart category of “candidate associations” and propose a refined classification for the candidate low-energy counterparts of the Fermi sources. We compare the 1FGL-assigned counterparts with those listed in 2FGL to determine which unassociated sources became associated in later releases of the Fermi catalogs. We also search for potential counterparts to all of the remaining unassociated Fermi sources. Finally, we prepare a refined and merged list of all of the associations of 1FGL plus 2FGL that includes 2219 unique Fermi objects. This is the most comprehensive and systematic study of all the associations collected for the γ-ray sources available to date. We conclude that 80% of the Fermi sources have at least one known plausible γ-ray emitter within their positional uncertainty regions.

  19. VizieR Online Data Catalog: Refined associations of Fermi/LAT sources (Massaro+, 2015)

    NASA Astrophysics Data System (ADS)

    Massaro, F.; D'Abrusco, R.; Landoni, M.; Paggi, A.; Masetti, N.; Giroletti, M.; Oti-Floranes, H.; Chavushyan, V.; Jimenez-Bailon, E.; Patino-Alvarez, V.; Digel, S. W.; Smith, H. A.; Tosti, G.

    2015-04-01

    The Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) was released in 2010 February and the Fermi-LAT 2-Year Source Catalog (2FGL) appeared in 2012 April, based on data from 24 months of operation. Since they were released, many follow up observations of unidentified γ-ray sources have been performed and new procedures for associating γ-ray sources with potential counterparts at other wavelengths have been developed. Here we review and characterize all of the associations as published in the 1FGL and 2FGL catalogs on the basis of multifrequency archival observations. In particular, we located 177 spectra for the low-energy counterparts that were not listed in the previous Fermi catalogs, and in addition we present new spectroscopic observations of eight γ-ray blazar candidates. Based on our investigations, we introduce a new counterpart category of "candidate associations" and propose a refined classification for the candidate low-energy counterparts of the Fermi sources. We compare the 1FGL-assigned counterparts with those listed in 2FGL to determine which unassociated sources became associated in later releases of the Fermi catalogs. We also search for potential counterparts to all of the remaining unassociated Fermi sources. Finally, we prepare a refined and merged list of all of the associations of 1FGL plus 2FGL that includes 2219 unique Fermi objects. This is the most comprehensive and systematic study of all the associations collected for the γ-ray sources available to date. We conclude that 80% of the Fermi sources have at least one known plausible γ-ray emitter within their positional uncertainty regions. (2 data files).

  20. Quantum oscillations from inside the Fermi sea

    NASA Astrophysics Data System (ADS)

    Pal, Hridis K.

    2017-02-01

    Quantum oscillations are conventionally understood to arise from the Fermi level; hence, they are considered to be a proof of the existence of an underlying Fermi surface. In this article we show that in certain situations quantum oscillations can also arise from inside the Fermi sea. We establish this analytically, supporting it with numerical calculations. Possible scenarios where such unusual behavior can occur are pointed out. In particular, in strongly particle-hole asymmetric insulators, models of which have been recently used in the context of the topological Kondo insulator SmB6, we show that the oscillations arise from inside the filled band, and are not related to the gap.

  1. Dependence of Kambersky damping on Fermi level and spin orientation

    SciTech Connect

    Qu, T.; Victora, R. H.

    2014-05-07

    Kambersky damping represents the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction. It is demonstrated that, for bcc Fe-based transition metal alloys, the logarithm of the energy loss is proportional to the density of states at the Fermi level. Both inter and intraband damping are calculated for spins at arbitrary angle to the previously examined [001] direction. Although the easy axis 〈100〉 shows isotropic relaxation and achieves the minimum damping value of 0.002, other directions, such as 〈110〉, show substantial anisotropic damping.

  2. Minimax rational approximation of the Fermi-Dirac distribution

    DOE PAGES

    Moussa, Jonathan E.

    2016-10-27

    Accurate rational approximations of the Fermi-Dirac distribution are a useful component in many numerical algorithms for electronic structure calculations. The best known approximations use O(log(βΔ)log(ϵ–1)) poles to achieve an error tolerance ϵ at temperature β–1 over an energy interval Δ. We apply minimax approximation to reduce the number of poles by a factor of four and replace Δ with Δocc, the occupied energy interval. Furthermore, this is particularly beneficial when Δ >> Δocc, such as in electronic structure calculations that use a large basis set.

  3. Minimax rational approximation of the Fermi-Dirac distribution

    SciTech Connect

    Moussa, Jonathan E.

    2016-10-27

    Accurate rational approximations of the Fermi-Dirac distribution are a useful component in many numerical algorithms for electronic structure calculations. The best known approximations use O(log(βΔ)log(ϵ–1)) poles to achieve an error tolerance ϵ at temperature β–1 over an energy interval Δ. We apply minimax approximation to reduce the number of poles by a factor of four and replace Δ with Δocc, the occupied energy interval. Furthermore, this is particularly beneficial when Δ >> Δocc, such as in electronic structure calculations that use a large basis set.

  4. Condensate fraction of a two-dimensional attractive Fermi gas

    SciTech Connect

    Salasnich, Luca

    2007-07-15

    We investigate the Bose-Einstein condensation of fermionic pairs in a two-dimensional uniform two-component Fermi superfluid obtaining an explicit formula for the condensate density as a function of the chemical potential and the energy gap. By using the mean-field extended Bardeen-Cooper-Schrieffer theory, we analyze, as a function of the bound-state energy, the off-diagonal long-range order in the crossover from the Bardeen-Cooper-Schrieffer state of weakly bound Cooper pairs to the Bose-Einstein condensate of strongly-bound molecular dimers.

  5. Optical response of Sr2RuO4 reveals universal fermi-liquid scaling and quasiparticles beyond Landau theory.

    PubMed

    Stricker, D; Mravlje, J; Berthod, C; Fittipaldi, R; Vecchione, A; Georges, A; van der Marel, D

    2014-08-22

    We report optical measurements demonstrating that the low-energy relaxation rate (1/τ) of the conduction electrons in Sr(2)RuO(4) obeys scaling relations for its frequency (ω) and temperature (T) dependence in accordance with Fermi-liquid theory. In the thermal relaxation regime, 1/τ ∝ (ħω)(2)+(pπk(B)T)(2) with p = 2, and ω/T scaling applies. Many-body electronic structure calculations using dynamical mean-field theory confirm the low-energy Fermi-liquid scaling and provide quantitative understanding of the deviations from Fermi-liquid behavior at higher energy and temperature. The excess optical spectral weight in this regime provides evidence for strongly dispersing "resilient" quasiparticle excitations above the Fermi energy.

  6. Modeling a thermionic energy converter using finite-difference time-domain particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Lo, F. S.; Lu, P. S.; Ragan-Kelley, B.; Minnich, A. J.; Lee, T. H.; Lin, M. C.; Verboncoeur, J. P.

    2014-02-01

    A thermionic energy converter (TEC) is a static device that converts heat directly into electricity by boiling electrons off a hot emitter surface across a small inter-electrode gap to a cooler collector surface. The main challenge in TECs is overcoming the space charge limit, which limits the current transmitted across a gap of a given voltage and width. We have verified the feasibility of studying and developing a TEC using a bounded finite-difference time-domain particle-in-cell plasma simulation code, OOPD1, developed by Plasma Theory and Simulation Group, formerly at UC Berkeley and now at Michigan State University. In this preliminary work, a TEC has been modeled kinetically using OOPD1, and the accuracy has been verified by comparing with an analytically solvable case, giving good agreement. With further improvement of the code, one will be able to quickly and cheaply analyze space charge effects, and seek designs that mitigate the space charge effect, allowing TECs to become more efficient and cost-effective.

  7. Hierarchies, multiple energy barriers, and robustness govern the fracture mechanics of alpha-helical and beta-sheet protein domains.

    PubMed

    Ackbarow, Theodor; Chen, Xuefeng; Keten, Sinan; Buehler, Markus J

    2007-10-16

    The fundamental fracture mechanisms of biological protein materials remain largely unknown, in part, because of a lack of understanding of how individual protein building blocks respond to mechanical load. For instance, it remains controversial whether the free energy landscape of the unfolding behavior of proteins consists of multiple, discrete transition states or the location of the transition state changes continuously with the pulling velocity. This lack in understanding has thus far prevented us from developing predictive strength models of protein materials. Here, we report direct atomistic simulation that over four orders of magnitude in time scales of the unfolding behavior of alpha-helical (AH) and beta-sheet (BS) domains, the key building blocks of hair, hoof, and wool as well as spider silk, amyloids, and titin. We find that two discrete transition states corresponding to two fracture mechanisms exist. Whereas the unfolding mechanism at fast pulling rates is sequential rupture of individual hydrogen bonds (HBs), unfolding at slow pulling rates proceeds by simultaneous rupture of several HBs. We derive the hierarchical Bell model, a theory that explicitly considers the hierarchical architecture of proteins, providing a rigorous structure-property relationship. We exemplify our model in a study of AHs, and show that 3-4 parallel HBs per turn are favorable in light of the protein's mechanical and thermodynamical stability, in agreement with experimental findings that AHs feature 3.6 HBs per turn. Our results provide evidence that the molecular structure of AHs maximizes its robustness at minimal use of building materials.

  8. Variation of free‐energy landscape of the p53 C‐terminal domain induced by acetylation: Enhanced conformational sampling

    PubMed Central

    Iida, Shinji; Mashimo, Tadaaki; Kurosawa, Takashi; Hojo, Hironobu; Muta, Hiroya; Goto, Yuji; Fukunishi, Yoshifumi; Nakamura, Haruki

    2016-01-01

    The C‐terminal domain (CTD) of tumor suppressor protein p53 is an intrinsically disordered region that binds to various partner proteins, where lysine of CTD is acetylated/nonacetylated and histidine neutralized/non‐neutralized. Because of the flexibility of the unbound CTD, a free‐energy landscape (FEL) is a useful quantity for determining its statistical properties. We conducted enhanced conformational sampling of CTD in the unbound state via virtual system coupled multicanonical molecular dynamics, in which the lysine was acetylated or nonacetylated and histidine was charged or neutralized. The fragments were expressed by an all‐atom model and were immersed in an explicit solvent. The acetylation and charge‐neutralization varied FEL greatly, which might be convenient to exert a hub property. The acetylation slightly enhanced alpha‐helix structures that are more compact than sheet/loop conformations. The charge‐neutralization produced hairpins. Additionally, circular dichroism experiments confirmed the computational results. We propose possible binding mechanisms of CTD to partners by investigating FEL. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc. PMID:27735058

  9. Electron Energy-Loss Spectroscopy (EELS)Calculation in Finite-Difference Time-Domain (FDTD) Package: EELS-FDTD

    NASA Astrophysics Data System (ADS)

    Large, Nicolas; Cao, Yang; Manjavacas, Alejandro; Nordlander, Peter

    2015-03-01

    Electron energy-loss spectroscopy (EELS) is a unique tool that is extensively used to investigate the plasmonic response of metallic nanostructures since the early works in the '50s. To be able to interpret and theoretically investigate EELS results, a myriad of different numerical techniques have been developed for EELS simulations (BEM, DDA, FEM, GDTD, Green dyadic functions). Although these techniques are able to predict and reproduce experimental results, they possess significant drawbacks and are often limited to highly symmetrical geometries, non-penetrating trajectories, small nanostructures, and free standing nanostructures. We present here a novel approach for EELS calculations using the Finite-difference time-domain (FDTD) method: EELS-FDTD. We benchmark our approach by direct comparison with results from the well-established boundary element method (BEM) and published experimental results. In particular, we compute EELS spectra for spherical nanoparticles, nanoparticle dimers, nanodisks supported by various substrates, and gold bowtie antennas on a silicon nitride substrate. Our EELS-FDTD implementation can be easily extended to more complex geometries and configurations and can be directly implemented within other numerical methods. Work funded by the Welch Foundation (C-1222, L-C-004), and the NSF (CNS-0821727, OCI-0959097).

  10. Measurement techniques for the characterization in the frequency domain of regulated energy-storage DC-to-DC converters. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Bahler, D. D.

    1978-01-01

    Procedures are presented for obtaining valid frequency-domain transfer functions of regulated reactor energy-storage dc-to-dc converters. These procedures are for measuring loop gain, closed loop gain, output impedance, and audio susceptibility. The applications of these measurements are discussed.

  11. No indications of axionlike particles from Fermi

    SciTech Connect

    Belikov, Alexander V.; Goodenough, Lisa; Hooper, Dan

    2011-03-15

    As very high energy (> or approx. 100 GeV) gamma rays travel over cosmological distances, their flux is attenuated through interactions with the extragalactic background light. Observations of distant gamma ray sources at energies between {approx}200 GeV and a few TeV by ground-based gamma-ray telescopes such as HESS, however, have motivated the possibility that the universe is more transparent to very high energy photons than had been anticipated. One proposed explanation for this is the existence of axionlike particles (ALPs) which gamma rays can efficiently oscillate into, enabling them to travel cosmological distances without attenuation. In this article, we use a state-of-the-art model for the extragalactic background light (which is somewhat lower at {approx}{mu}m wavelengths than in previous models) and data from the Fermi Gamma Ray Space Telescope to calculate the spectra at 1-100 GeV of two gamma-ray sources, 1ES1101-232 at redshift z=0.186 and H2356-309 at z=0.165, in conjunction with the measurements of ground-based telescopes, to test the ALP hypothesis. We find that these observations can be well fit by an intrinsic power-law source spectrum with indices of -1.72 and -2.1 for 1ES1101-232 and H2356-309, respectively, and that no ALPs or other exotic physics is necessary to explain the observed degree of attenuation. While this does not exclude the possibility that ALPs are involved in the cosmological propagation of gamma rays, it does reduce the motivation for such new physics.

  12. The nuclear Thomas-Fermi model

    SciTech Connect

    Myers, W.D.; Swiatecki, W.J.

    1994-08-01

    The statistical Thomas-Fermi model is applied to a comprehensive survey of macroscopic nuclear properties. The model uses a Seyler-Blanchard effective nucleon-nucleon interaction, generalized by the addition of one momentum-dependent and one density-dependent term. The adjustable parameters of the interaction were fitted to shell-corrected masses of 1654 nuclei, to the diffuseness of the nuclear surface and to the measured depths of the optical model potential. With these parameters nuclear sizes are well reproduced, and only relatively minor deviations between measured and calculated fission barriers of 36 nuclei are found. The model determines the principal bulk and surface properties of nuclear matter and provides estimates for the more subtle, Droplet Model, properties. The predicted energy vs density relation for neutron matter is in striking correspondence with the 1981 theoretical estimate of Friedman and Pandharipande. Other extreme situations to which the model is applied are a study of Sn isotopes from {sup 82}Sn to {sup 170}Sn, and the rupture into a bubble configuration of a nucleus (constrained to spherical symmetry) which takes place when Z{sup 2}/A exceeds about 100.

  13. The Nuclear Thomas-Fermi Model

    DOE R&D Accomplishments Database

    Myers, W. D.; Swiatecki, W. J.

    1994-08-01

    The statistical Thomas-Fermi model is applied to a comprehensive survey of macroscopic nuclear properties. The model uses a Seyler-Blanchard effective nucleon-nucleon interaction, generalized by the addition of one momentum-dependent and one density-dependent term. The adjustable parameters of the interaction were fitted to shell-corrected masses of 1654 nuclei, to the diffuseness of the nuclear surface and to the measured depths of the optical model potential. With these parameters nuclear sizes are well reproduced, and only relatively minor deviations between measured and calculated fission barriers of 36 nuclei are found. The model determines the principal bulk and surface properties of nuclear matter and provides estimates for the more subtle, Droplet Model, properties. The predicted energy vs density relation for neutron matter is in striking correspondence with the 1981 theoretical estimate of Friedman and Pandharipande. Other extreme situations to which the model is applied are a study of Sn isotopes from {sup 82}Sn to {sup 170}Sn, and the rupture into a bubble configuration of a nucleus (constrained to spherical symmetry) which takes place when Z{sup 2}/A exceeds about 100.

  14. General physical properties of bright Fermi blazars

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Tavecchio, F.; Foschini, L.; Ghirlanda, G.; Maraschi, L.; Celotti, A.

    2010-02-01

    We studied all blazars of known redshift detected by the Fermi satellite during its first 3-month survey. For the majority of them, pointed Swift observations ensure a good multiwavelength coverage, enabling us to reliably construct their spectral energy distributions (SEDs). We model the SEDs using a one-zone leptonic model and study the distributions of the derived interesting physical parameters as a function of the observed γ-ray luminosity. We confirm previous findings concerning the relation of the physical parameters with source luminosity which are at the origin of the blazar sequence. The SEDs allow to estimate the luminosity of the accretion disc for the majority of broad emitting line blazars, while for the lineless BL Lac objects in the sample upper limits can be derived. We find a positive correlation between the jet power and the luminosity of the accretion disc in broad-line blazars. In these objects, we argue that the jet must be proton dominated, and that the total jet power is of the same order of (or slightly larger than) the disc luminosity. We discuss two alternative scenarios to explain this result.

  15. Fermi: physicist with a capital F

    NASA Astrophysics Data System (ADS)

    Cobal, Marina

    2016-12-01

    Enrico Fermi – one of the great physicists of the 21st century – was a beacon for every Italian student of physics. This is wonderfully captured in The Pope of Physics by Gino Segrè and Bettina Hoerlin.

  16. Fermi Proves Supernova Remnants Make Cosmic Rays

    NASA Video Gallery

    The husks of exploded stars produce some of the fastest particles in the cosmos. New findings by NASA's Fermi show that two supernova remnants accelerate protons to near the speed of light. The pro...

  17. Fermi Sees Antimatter-Hurling Thunderstorms

    NASA Video Gallery

    NASA's Fermi Gamma-ray Space Telescope has detected beams of antimatter launched by thunderstorms. Acting like enormous particle accelerators, the storms can emit gamma-ray flashes, called TGFs, an...

  18. Fermi discovers giant bubbles in Milky Way

    NASA Video Gallery

    Using data from NASA's Fermi Gamma-ray Space Telescope, scientists have recently discovered a gigantic, mysterious structure in our galaxy. This feature looks like a pair of bubbles extending above...

  19. A fast algorithm for finding point sources in the Fermi data stream: FermiFAST

    NASA Astrophysics Data System (ADS)

    Asvathaman, Asha; Omand, Conor; Barton, Alistair; Heyl, Jeremy S.

    2017-04-01

    We present a new and efficient algorithm for finding point sources in the photon event data stream from the Fermi Gamma-Ray Space Telescope, FermiFAST. The key advantage of FermiFAST is that it constructs a catalogue of potential sources very fast by arranging the photon data in a hierarchical data structure. Using this structure, FermiFAST rapidly finds the photons that could have originated from a potential gamma-ray source. It calculates a likelihood ratio for the contribution of the potential source using the angular distribution of the photons within the region of interest. It can find within a few minutes the most significant half of the Fermi Third Point Source catalogue (3FGL) with nearly 80 per cent purity from the 4 yr of data used to construct the catalogue. If a higher purity sample is desirable, one can achieve a sample that includes the most significant third of the Fermi 3FGL with only 5 per cent of the sources unassociated with Fermi sources. Outside the Galactic plane, all but eight of the 580 FermiFAST detections are associated with 3FGL sources. And of these eight, six yield significant detections of greater than 5σ when a further binned likelihood analysis is performed. This software allows for rapid exploration of the Fermi data, simulation of the source detection to calculate the selection function of various sources and the errors in the obtained parameters of the sources detected.

  20. Fermi LAT Limits on Primordial Black Hole Evaporation

    NASA Astrophysics Data System (ADS)

    Johnson, Chistian; Malyshev, Dmitry; Funk, Stefan; Ritz, Steven; Fermi LAT Collaboration

    2017-01-01

    Primordial black holes (PBHs) of sufficiently small mass emit gamma rays in the Fermi Large Area Telescope (LAT) energy range. PBHs with lifetimes shorter than the Fermi observation time will appear as moving point sources with gamma-ray emission that becomes harder and brighter with time until the PBH completely evaporates. Previous searches for gamma rays from PBHs have focused on either short time scale bursts or the contribution of PBH bursts to the isotropic diffuse emission. Here we use Fermi LAT point source catalogs to search for PBH candidates that evaporate on a time scale of several years. In addition to looking for the spectral signatures of a PBH, we also develop an algorithm to detect proper motion. There are a few unassociated point sources with spectra consistent with PBH evaporation; however, none of these sources show significant proper motion. We derive a conservative limit on PBH evaporation rate in the vicinity of the Earth by using a threshold on the gamma-ray flux above 10 GeV such that there are no sources above this threshold with spectra consistent with Hawking radiation from PBHs. The derived limit is more stringent than the limits obtained with ground-based gamma-ray observatories.

  1. Quadratic Fermi node in a 3D strongly correlated semimetal

    DOE PAGES

    Kondo, Takeshi; Nakayama, M.; Chen, R.; ...

    2015-12-07

    We report that strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour ismore » predicted, for which we observe some evidence. Lastly, our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states.« less

  2. Quadratic Fermi node in a 3D strongly correlated semimetal

    SciTech Connect

    Kondo, Takeshi; Nakayama, M.; Chen, R.; Ishikawa, J. J.; Moon, E. -G.; Yamamoto, T.; Ota, Y.; Malaeb, W.; Kanai, H.; Nakashima, Y.; Ishida, Y.; Yoshida, R.; Yamamoto, H.; Matsunami, M.; Kimura, S.; Inami, N.; Ono, K.; Kumigashira, H.; Nakatsuji, S.; Balents, L.; Shin, S.

    2015-12-07

    We report that strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour is predicted, for which we observe some evidence. Lastly, our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states.

  3. Quadratic Fermi node in a 3D strongly correlated semimetal

    PubMed Central

    Kondo, Takeshi; Nakayama, M.; Chen, R.; Ishikawa, J. J.; Moon, E.-G.; Yamamoto, T.; Ota, Y.; Malaeb, W.; Kanai, H.; Nakashima, Y.; Ishida, Y.; Yoshida, R.; Yamamoto, H.; Matsunami, M.; Kimura, S.; Inami, N.; Ono, K.; Kumigashira, H.; Nakatsuji, S.; Balents, L.; Shin, S.

    2015-01-01

    Strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour is predicted, for which we observe some evidence. Our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states. PMID:26640114

  4. FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE ACTIVE GALAXY 4C +55.17: STEADY, HARD GAMMA-RAY EMISSION AND ITS IMPLICATIONS

    SciTech Connect

    McConville, W.; McEnery, J. E.; Ostorero, L.; Moderski, R.; Stawarz, L.; Cheung, C. C.; Ajello, M.; Monzani, M. E.; Bouvier, A.; Bregeon, J.; Donato, D.; Finke, J.; Furniss, A.; Williams, D. A.; Orienti, M.; Reyes, L. C.; Rossetti, A. E-mail: stawarz@astro.isas.jaxa.jp

    2011-09-10

    We report Fermi Large Area Telescope (LAT) observations and broadband spectral modeling of the radio-loud active galaxy 4C +55.17 (z = 0.896), formally classified as a flat-spectrum radio quasar. Using 19 months of all-sky survey Fermi-LAT data, we detect a {gamma}-ray continuum extending up to an observed energy of 145 GeV, and furthermore we find no evidence of {gamma}-ray variability in the source over its observed history. We illustrate the implications of these results in two different domains. First, we investigate the origin of the steady {gamma}-ray emission, where we re-examine the common classification of 4C +55.17 as a quasar-hosted blazar and consider instead its possible nature as a young radio source. We analyze and compare constraints on the source physical parameters in both blazar and young radio source scenarios by means of a detailed multiwavelength analysis and theoretical modeling of its broadband spectrum. Second, we show that the {gamma}-ray spectrum may be formally extrapolated into the very high energy (VHE, {>=}100 GeV) range at a flux level detectable by the current generation of ground-based Cherenkov telescopes. This enables us to place constraints on models of extragalactic background light within LAT energies and features the source as a promising candidate for VHE studies of the universe at an unprecedented redshift of z = 0.896.

  5. Nonperturbative effects on the ferromagnetic transition in repulsive Fermi gases

    NASA Astrophysics Data System (ADS)

    He, Lianyi; Huang, Xu-Guang

    2012-04-01

    It is generally believed that a dilute spin-(1)/(2) Fermi gas with repulsive interactions can undergo a ferromagnetic phase transition to a spin-polarized state at a critical gas parameter (kFa)c. Previous theoretical predictions of the ferromagnetic phase transition have been based on the perturbation theory, which treats the gas parameter as a small number. On the other hand, Belitz, Kirkpatrick, and Vojta (BKV) have argued that the phase transition in clean itinerant ferromagnets is generically of first order at low temperatures, due to the correlation effects that lead to a nonanalytic term in the free energy. The second-order perturbation theory predicts a first-order phase transition at (kFa)c=1.054, consistent with the BKV argument. However, since the critical gas parameter is expected to be of order O(1), perturbative predictions may be unreliable. In this paper we study the nonperturbative effects on the ferromagnetic phase transition by summing the particle-particle ladder diagrams to all orders in the gas parameter. We consider a universal repulsive Fermi gas where the effective range effects can be neglected, which can be realized in a two-component Fermi gas of 6Li atoms by using a nonadiabatic field switch to the upper branch of a Feshbach resonance with a positive s-wave scattering length. Our theory predicts a second-order phase transition, which indicates that ferromagnetic transition in dilute Fermi gases is possibly a counterexample to the BKV argument. The predicted critical gas parameter (kFa)c=0.858 is in good agreement with the recent quantum Monte Carlo result (kFa)c=0.86 for a nearly zero-range potential [S. Pilati , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.030405 105, 030405 (2010)]. We also compare the spin susceptibility with the quantum Monte Carlo result and find good agreement.

  6. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center

    2017-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.

  7. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center Team

    2016-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.

  8. Strain-induced Fermi contour anisotropy of GaAs (311)A 2D holes

    NASA Astrophysics Data System (ADS)

    Shabani, Javad; Shayegan, Mansour; Winkler, Roland

    2008-03-01

    There is considerable current interest in electronic properties of two-dimensional (2D) carriers whose energy bands are spin-split at finite values of in-plane wave vector, thanks to the spin-orbit interaction and the lack of inversion symmetry. We report experimental and theoretical results revealing that the spin-subband Fermi contours of the heavy and light heavy-holes (HHh and HHl) can be tuned in high mobility GaAs (311)A 2D hole systems via the application of symmetry-breaking in-plane strain. Our calculations show that the HHl spin-subband Fermi contour is circular but the HHh spin-subband Fermi contour is distorted. Experimentally, we probe the Fermi contour anisotropy by measuring the magneto-resistance commensurability peaks induced by square arrays of antidots. When the spin splitting is sufficiently large, the magneto-resistance trace exhibits two peaks, providing clear evidence for spin-resolved ballistic transport. The experimental results are in good agreement with the calculations, and confirm that the majority spin-subband (HHh) has a severely distorted Fermi contour whose anisotropy can be tuned with strain while Fermi contour of the minority spin-subband (HHl) remains nearly isotropic.

  9. Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions

    PubMed Central

    Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

    2016-01-01

    Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes. PMID:27551687

  10. Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions.

    PubMed

    Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

    2016-08-01

    Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes.

  11. Bimodal intramolecular excitation energy transfer in a multichromophore photosynthetic model system: hybrid fusion proteins comprising natural phycobilin- and artificial chlorophyll-binding domains.

    PubMed

    Zeng, Xiao-Li; Tang, Kun; Zhou, Nan; Zhou, Ming; Hou, Harvey J M; Scheer, Hugo; Zhao, Kai-Hong; Noy, Dror

    2013-09-11

    The phycobilisomes of cyanobacteria and red-algae are highly efficient peripheral light-harvesting complexes that capture and transfer light energy in a cascade of excitation energy transfer steps through multiple phycobilin chromophores to the chlorophylls of core photosystems. In this work, we focus on the last step of this process by constructing simple functional analogs of natural phycobilisome-photosystem complexes that are based on bichromophoric protein complexes comprising a phycobilin- and a chlorophyll- or porphyrin-binding domain. The former is based on ApcE(1-240), the N-terminal chromophore-binding domain of the phycobilisome's L(CM) core-membrane linker, and the latter on HP7, a de novo designed four-helix bundle protein that was originally planned as a high-affinity heme-binding protein, analogous to b-type cytochromes. We fused a modified HP7 protein sequence to ApcEΔ, a water-soluble fragment of ApcE(1-240) obtained by excising a putative hydrophobic loop sequence of residues 77-153. HP7 was fused either to the N- or the C-terminus of ApcEΔ or inserted between residues 76 and 78, thereby replacing the native hydrophobic loop domain. We describe the assembly, spectral characteristics, and intramolecular excitation energy transfer of two unique systems: in the first, the short-wavelength absorbing zinc-mesoporphyrin is bound to the HP7 domain and serves as an excitation-energy donor to the long-wavelength absorbing phycocyanobilin bound to the ApcE domain; in the second, the short-wavelength absorbing phycoerythrobilin is bound to the ApcE domain and serves as an excitation energy donor to the long-wavelength absorbing zinc-bacteriochlorophyllide bound to the HP7 domain. All the systems that were constructed and tested exhibited significant intramolecular fluorescence resonance energy transfer with yields ranging from 21% to 50%. This confirms that our modular, covalent approach for studying EET between the cyclic and open chain tetrapyrroles is

  12. Cell survival fraction estimation based on the probability densities of domain and cell nucleus specific energies using improved microdosimetric kinetic models.

    PubMed

    Sato, Tatsuhiko; Furusawa, Yoshiya

    2012-10-01

    Estimation of the survival fractions of cells irradiated with various particles over a wide linear energy transfer (LET) range is of great importance in the treatment planning of charged-particle therapy. Two computational models were developed for estimating survival fractions based on the concept of the microdosimetric kinetic model. They were designated as the double-stochastic microdosimetric kinetic and stochastic microdosimetric kinetic models. The former model takes into account the stochastic natures of both domain and cell nucleus specific energies, whereas the latter model represents the stochastic nature of domain specific energy by its approximated mean value and variance to reduce the computational time. The probability densities of the domain and cell nucleus specific energies are the fundamental quantities for expressing survival fractions in these models. These densities are calculated using the microdosimetric and LET-estimator functions implemented in the Particle and Heavy Ion Transport code System (PHITS) in combination with the convolution or database method. Both the double-stochastic microdosimetric kinetic and stochastic microdosimetric kinetic models can reproduce the measured survival fractions for high-LET and high-dose irradiations, whereas a previously proposed microdosimetric kinetic model predicts lower values for these fractions, mainly due to intrinsic ignorance of the stochastic nature of cell nucleus specific energies in the calculation. The models we developed should contribute to a better understanding of the mechanism of cell inactivation, as well as improve the accuracy of treatment planning of charged-particle therapy.

  13. Conformational Changes in the Epidermal Growth Factor Receptor: Role of the Transmembrane Domain Investigated by Coarse-Grained MetaDynamics Free Energy Calculations

    PubMed Central

    2016-01-01

    The epidermal growth factor receptor (EGFR) is a dimeric membrane protein that regulates key aspects of cellular function. Activation of the EGFR is linked to changes in the conformation of the transmembrane (TM) domain, brought about by changes in interactions of the TM helices of the membrane lipid bilayer. Using an advanced computational approach that combines Coarse-Grained molecular dynamics and well-tempered MetaDynamics (CG-MetaD), we characterize the large-scale motions of the TM helices, simulating multiple association and dissociation events between the helices in membrane, thus leading to a free energy landscape of the dimerization process. The lowest energy state of the TM domain is a right-handed dimer structure in which the TM helices interact through the N-terminal small-X3-small sequence motif. In addition to this state, which is thought to correspond to the active form of the receptor, we have identified further low-energy states that allow us to integrate with a high level of detail a range of previous experimental observations. These conformations may lead to the active state via two possible activation pathways, which involve pivoting and rotational motions of the helices, respectively. Molecular dynamics also reveals correlation between the conformational changes of the TM domains and of the intracellular juxtamembrane domains, paving the way for a comprehensive understanding of EGFR signaling at the cell membrane. PMID:27459426

  14. Fermi level dependent native defect formation: Consequences for metal-semiconductor and semiconductor-semiconductor interfaces

    SciTech Connect

    Walukiewicz, W.

    1988-02-01

    The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration. 33 refs., 6 figs.

  15. Fermi/LAT search for counterpart to the IceCube event 67093193 (run 127853)

    NASA Astrophysics Data System (ADS)

    Vianello, G.; Magill, J. D.; Omodei, N.; Kocevski, D.; Ajello, M.; Buson, S.; Krauss, F.; Chiang, J.

    2016-04-01

    on behalf of the Fermi-LAT team: We have searched the Fermi Large Area Telescope data for a high-energy gamma-ray counterpart for the IceCube High Energy Starting Event (HESE) 67093193, detected in run 127853 on 2016-04-27 05:52:32.00 UT (AMON GCN notice rev. 2, http://gcn.gsfc.nasa.gov/notices_amon/67093193_127853.amon . See http://gcn.gsfc.nasa.gov/doc/Public_Doc_AMON_IceCube_GCN_Alerts_v2.pdf for a description of HESE events and related GCN notices).

  16. Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La)2CuO6+δ (Bi2201)

    SciTech Connect

    Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; Bansil, Arun

    2015-06-18

    Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. Here, we show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Finally, our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping.

  17. Unconventional bulk three-dimensional Fermi surface in Kondo insulating SmB6

    NASA Astrophysics Data System (ADS)

    Tan, Beng

    We report the observation of a paradoxical insulator with a bulk state which is electrically insulating and simultaneously yields quantum oscillations typical of good metals. We present high field measurements of conductivity and magnetic torque in high purity single crystals of the Kondo insulator SmB6 which reveal an activated behavior characteristics of an insulator with an energy gap at the Fermi energy in the former and quantum oscillation of frequencies characteristics of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6 in the latter. The quantum oscillations observed in the magnetic torque measurements are characteristic of an unconventional Fermi liquid - the amplitude strongly increases at low temperatures in a stark contrast to the saturating Lifshitz-Kosevich behavior in conventional metallic states.

  18. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center

    2015-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. The reference manual gives details of the options available for each tool. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide information on recent updates incorporated in the Science Tools as well as upcoming changes that will be included in the upcoming release of the Science Tools in early 2015.

  19. Revised Thomas-Fermi approximation for singular potentials

    NASA Astrophysics Data System (ADS)

    Dufty, James W.; Trickey, S. B.

    2016-08-01

    Approximations for the many-fermion free-energy density functional that include the Thomas-Fermi (TF) form for the noninteracting part lead to singular densities for singular external potentials (e.g., attractive Coulomb). This limitation of the TF approximation is addressed here by a formal map of the exact Euler equation for the density onto an equivalent TF form characterized by a modified Kohn-Sham potential. It is shown to be a "regularized" version of the Kohn-Sham potential, tempered by convolution with a finite-temperature response function. The resulting density is nonsingular, with the equilibrium properties obtained from the total free-energy functional evaluated at this density. This new representation is formally exact. Approximate expressions for the regularized potential are given to leading order in a nonlocality parameter, and the limiting behavior at high and low temperatures is described. The noninteracting part of the free energy in this approximation is the usual Thomas-Fermi functional. These results generalize and extend to finite temperatures the ground-state regularization by R. G. Parr and S. Ghosh [Proc. Natl. Acad. Sci. U.S.A. 83, 3577 (1986), 10.1073/pnas.83.11.3577] and by L. R. Pratt, G. G. Hoffman, and R. A. Harris [J. Chem. Phys. 88, 1818 (1988), 10.1063/1.454105] and formally systematize the finite-temperature regularization given by the latter authors.

  20. The first Fermi LAT supernova remnant catalog

    SciTech Connect

    Acero, F.

    2016-05-16

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope. Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude, allows us to determine an upper limit of 22% on the number of GeV candidates falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, demonstrates the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. As a result, we model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.

  1. Detecting superlight dark matter with Fermi-degenerate materials

    NASA Astrophysics Data System (ADS)

    Hochberg, Yonit; Pyle, Matt; Zhao, Yue; Zurek, Kathryn M.

    2016-08-01

    We examine in greater detail the recent proposal of using superconductors for detecting dark matter as light as the warm dark matter limit of O (keV). Detection of suc light dark matter is possible if the entire kinetic energy of the dark matter is extracted in the scattering, and if the experiment is sensitive to O (meV) energy depositions. This is the case for Fermi-degenerate materials in which the Fermi velocity exceeds the dark matter velocity dispersion in the Milky Way of ˜ 10-3. We focus on a concrete experimental proposal using a superconducting target with a transition edge sensor in order to detect the small energy deposits from the dark matter scatterings. Considering a wide variety of constraints, from dark matter self-interactions to the cosmic microwave background, we show that models consistent with cosmological/astrophysical and terrestrial constraints are observable with such detectors. A wider range of viable models with dark matter mass below an MeV is available if dark matter or mediator properties (such as couplings or masses) differ at BBN epoch or in stellar interiors from those in superconductors. We also show that metal targets pay a strong in-medium suppression for kinetically mixed mediators; this suppression is alleviated with insulating targets.

  2. Prospects for Fermi Particle Acceleration at Coronal Magnetic Reconnection Sites

    NASA Astrophysics Data System (ADS)

    Provornikova, E.; Laming, J. M.; Lukin, V.

    2015-12-01

    The mechanism of first order Fermi acceleration of particles interacting with the converging magnetized flows at a reconnection site was introduced recently in an attempt to predict the energy distribution of particles resulting from violent reconnection in galactic microquasars. More careful consideration of this mechanism showed that the spectral index of accelerated particles is related to the total plasma compression within a reconnection region, similar to that in the formulation for diffusive shock acceleration. In the solar context, reconnection regions producing strong compression could be the source of suprathermal "seed particles". A hard spectrum of such suprathermal particles is believed to be necessary to initiate the particle acceleration process at low Mach number coronal mass ejection shocks close to the Sun where the gradual solar energetic particle events originate. As a first step to investigate the efficiency of Fermi acceleration, we explore the degree of plasma compression that can be achieved at reconnection sites in the solar corona. This work presents a set of 2D two-temperature resistive MHD simulations of the dynamics of several magnetic configurations within a range of lower corona plasma parameters. Energy transport processes in the MHD model include anisotropic thermal conduction for electrons and ions and radiative cooling. Magnetic configurations considered are a Harris current sheet, a force-free current sheet, a flux rope sitting above an arcade of magnetic loops, and two merging flux ropes. We demonstrate that only for some magnetic topologies, corresponding in particular to 3D magnetic nulls, the compression ratio, sufficient for first order Fermi acceleration in the reconnection region, can be achieved. These represent the potential sites in the solar corona where a hard seed particle energetic spectrum could be produced.

  3. Critical Zeeman splitting of a unitary Fermi superfluid

    SciTech Connect

    He Lianyi; Zhuang Pengfei

    2011-05-01

    We determine the critical Zeeman energy splitting of a homogeneous Fermi superfluid at unitary in terms of the Fermi energy {epsilon}{sub F} according to recent experimental results in Laboratoire Kastler Brossel (LKB)-Lhomond. Based on the universal equations of state for the superfluid and normal phases, we show that there exist two critical fields H{sub c1} and H{sub c2}, between which a superfluid-normal mixed phase is energetically favored. Universal formulas for the critical fields and the critical population imbalance P{sub c} are derived. We have found a universal relation between the critical fields and the critical imbalances: H{sub c1}={gamma}{xi}{epsilon}{sub F} and H{sub c2}=(1+{gamma}P{sub c}){sup 2/3}H{sub c1}, where {xi} is the universal constant and {gamma} is the critical value of the chemical potential imbalance in the grand canonical ensemble. Since {xi}, {gamma}, and P{sub c} have been measured in the experiments, we can determine the critical Zeeman fields without the detailed information of the equation of state for the polarized normal phase. Using the experimental data from LKB-Lhomond, we have found H{sub c1{approx_equal}}0.37{epsilon}{sub F} and H{sub c2{approx_equal}}0.44{epsilon}{sub F}. Our result of the polarization P as a function of the Zeeman field H/{epsilon}{sub F} is in good agreement with the data extracted from the experiments. We also give an estimation of the critical magnetic field for dilute neutron matter at which the matter gets spin polarized, assuming the properties of the dilute neutron matter are close to those of the unitary Fermi gas.

  4. Pairing in a dry Fermi sea

    NASA Astrophysics Data System (ADS)

    Maier, T. A.; Staar, P.; Mishra, V.; Chatterjee, U.; Campuzano, J. C.; Scalapino, D. J.

    2016-06-01

    In the traditional Bardeen-Cooper-Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin-fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.

  5. Topology of Fermi surfaces and anomaly inflows

    NASA Astrophysics Data System (ADS)

    Adem, Alejandro; Camarena, Omar Antolín; Semenoff, Gordon W.; Sheinbaum, Daniel

    2016-11-01

    We derive a rigorous classification of topologically stable Fermi surfaces of non-interacting, discrete translation-invariant systems from electronic band theory, adiabatic evolution and their topological interpretations. For systems on an infinite crystal it is shown that there can only be topologically unstable Fermi surfaces. For systems on a half- space and with a gapped bulk, our derivation naturally yields a K -theory classification. Given the d - 1-dimensional surface Brillouin zone X s of a d-dimensional half-space, our result implies that different classes of globally stable Fermi surfaces belong in K -1 (Xs) for systems with only discrete translation-invariance. This result has a chiral anomaly inflow interpretation, as it reduces to the spectral flow for d = 2. Through equivariant homotopy methods we extend these results for symmetry classes AI, AII, C and D and discuss their corresponding anomaly inflow interpretation.

  6. Renormalization group flow for noncommutative Fermi liquids

    SciTech Connect

    Estrada-Jimenez, Sendic; Garcia-Compean, Hugo; Wu Yongshi

    2011-06-15

    Some recent studies of the AdS/CFT correspondence for condensed matter systems involve the Fermi liquid theory as a boundary field theory. Adding B-flux to the boundary D-branes leads in a certain limit to the noncommutative Fermi liquid, which calls for a field theory description of its critical behavior. As a preliminary step to more general consideration, the modification of the Landau's Fermi liquid theory due to noncommutativity of spatial coordinates is studied in this paper. We carry out the renormalization of interactions at tree level and one loop in a weakly coupled fermion system in two spatial dimensions. Channels ZS, ZS' and BCS are discussed in detail. It is shown that while the Gaussian fixed-point remains unchanged, the BCS instability is modified due to the space noncommutativity.

  7. Fermi surface determination from momentum density projections

    NASA Astrophysics Data System (ADS)

    Leitner, Michael; Weber, Josef Andreas; Ceeh, Hubert

    2016-06-01

    The problem of determining a metal’s Fermi surface from measured projections of the electron or electron/positron momentum densities, such as those obtained by Compton scattering or angular correlation of positron annihilation radiation, respectively, is examined in a Bayesian formulation. A consistent approach with an explicit treatment of the Fermi surface already at the reconstruction stage is presented, and its advantages compared to previous practice are discussed. A validation of the proposed method on simulated data shows its systematic accuracy to be very satisfactory and its statistical precision on modest experimental data to be surprisingly good.

  8. Information-driven societies and Fermi's paradox

    NASA Astrophysics Data System (ADS)

    Lampton, Michael

    2013-10-01

    Fermi's paradox is founded on the idea that one or more Galactic extraterrestrial civilizations (ETCs) existed long ago and sustained exploration for millions of years, but in spite of their advanced knowledge, they could not find a way to explore the Galaxy other than with fleets of starships or self replicating probes. Here, I question this second assumption: if advanced technology generally allows long-distance remote sensing, and if ETCs were motivated by gaining information rather than conquest or commerce, then such voyages would be unnecessary, thereby resolving Fermi's paradox.

  9. MASTER: OT detection during Fermi trigger inspection

    NASA Astrophysics Data System (ADS)

    Popova, E.; Lipunov, V.; Buckley, D.; Gorbovskoy, E.; Tiurina, N.; Balanutsa, P.; Kuznetsov, A.; Kornilov, V.; Chazov, V.; Vlasenko, D.; Vladimirov, V.; Gress, O.; Ivanov, K.; Potter, S.; Gabovich, A.

    2016-11-01

    During inspection of Fermi trigger 501261070 ( (Ra,Dec)=47.190,-47.210; GRB_ERROR_radius=3.27deg, GRB_TIME=2016/11/19 15:11:06.40UT http://gcn.gsfc.nasa.gov/other/501261070.fermi ) MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source at (RA, Dec) = 03h 22m 52.70s -48d 29m 10.9s on 2016-11-19 21:17:17.878UT with unfiltered m_OT=17.8 (mlim=19.7).

  10. Fermi gamma-ray imaging of a radio galaxy.

    PubMed

    Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cavazzuti, E; Cecchi, C; Celik, O; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Colafrancesco, S; Cominsky, L R; Conrad, J; Costamante, L; Cutini, S; Davis, D S; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Farnier, C; Favuzzi, C; Fegan, S J; Finke, J; Focke, W B; Fortin, P; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Georganopoulos, M; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hughes, R E; Jackson, M S; Jóhannesson, G; Johnson, A S; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocian, M L; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rochester, L S; Rodriguez, A Y; Romani, R W; Roth, M; Ryde, F; Sadrozinski, H F-W; Sambruna, R; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Sgrò, C; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stawarz, Ł; Strickman, M S; Suson, D J; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wallace, E; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M; Hardcastle, M J; Kazanas, D

    2010-05-07

    The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.

  11. Unitary Fermi Gas, ɛ Expansion, and Nonrelativistic Conformal Field Theories

    NASA Astrophysics Data System (ADS)

    Nishida, Yusuke; Son, Dam Thanh

    We review theoretical aspects of unitary Fermi gas (UFG), which has been realized in ultracold atom experiments. We first introduce the ɛ expansion technique based on a systematic expansion in terms of the dimensionality of space. We apply this technique to compute the thermodynamic quantities, the quasiparticle cum, and the criticl temperature of UFG. We then discuss consequences of the scale and conformal invariance of UFG. We prove a correspondence between primary operators in nonrelativistic conformal field theories and energy eigenstates in a harmonic potential. We use this correspondence to compute energies of fermions at unitarity in a harmonic potential. The scale and conformal invariance together with the general coordinate invariance constrains the properties of UFG. We show the vanishing bulk viscosities of UFG and derive the low-energy effective Lagrangian for the superfluid UFG. Finally we propose other systems exhibiting the nonrelativistic scaling and conformal symmetries that can be in principle realized in ultracold atom experiments.

  12. Conformational change path between closed and open forms of C2 domain of coagulation factor V on a two-dimensional free-energy surface.

    PubMed

    Wu, Sangwook; Lee, Chang Jun; Pedersen, Lee G

    2009-04-01

    We test a hypothesis that the closed form of the C2 domain of coagulation factor V is more stable than the open form in an aqueous environment using a two-dimensional free-energy calculation with a simple dielectric solvent model. Our result shows that while the free-energy difference between two forms is small, favoring the closed form, a two-dimensional free-energy surface (FES) reveals that a transition state (1.53 kcal/mol) exists between the two conformations. By mapping the one-dimensional order parameter DeltaQ onto the two-dimensional FES, we search the conformational change path with the highest Boltzmann weighting factor between the closed and open form of the factor V C2 domain. The predicted transition path from the closed to open form is not that of simple side chain movements, but instead concerted movements of several loops. We also present a one-dimensional free-energy profile using a collective order parameter, which in a coarse manner locates the energy barriers found on the two-dimensional FES.

  13. Quantum properties of charged ferroelectric domain walls

    NASA Astrophysics Data System (ADS)

    Sturman, B.; Podivilov, E.; Stepanov, M.; Tagantsev, A.; Setter, N.

    2015-12-01

    We consider the properties of charged domain walls in ferroelectrics as a quantum problem. This includes determination of self-consistent attracting 1D potential for compensating charge carriers, the number and positions of discrete energy levels in this potential, dependencies on the ferroelectric characteristics, as well as the spatial structure and formation energy of the wall. Our description is based on the Hartree and Thomas-Fermi methods and Landau theory for the ferroelectric transitions. Changeover from a few to many quantum levels (with the electron binding energies ˜1 eV) is controlled by a single characteristic parameter. The quantum models well describe the core of the wall, whose width is typically ˜10 nm. Additionally, the walls possess pronounced long-range tails which are due to trap recharging. For the trap concentration Nt=(1017-1018) cm-3 , the tail length ℓ is of the μ m scale. On the distances much larger than ℓ the walls are electrically uncoupled from each other and the crystal faces.

  14. Correlations in the low-density Fermi gas: Fermi-liquid state, dimerization, and Bardeen-Cooper-Schrieffer pairing

    NASA Astrophysics Data System (ADS)

    Fan, H. H.; Krotscheck, E.; Lichtenegger, T.; Mateo, D.; Zillich, R. E.

    2015-08-01

    We present ground-state calculations for low-density Fermi gases described by two model interactions, an attractive square-well potential and a Lennard-Jones potential, of varying strength. We use the optimized Fermi-hypernetted chain integral equation method, which has been proved to provide, in the density regimes of interest here, an accuracy of better than 1%. We first examine the low-density expansion of the energy and compare it with the exact answer of H. Huang and C. N. Yang [Phys. Rev. 105, 767 (1957), 10.1103/PhysRev.105.767]. It is shown that a locally correlated wave function of the Jastrow-Feenberg type does not recover the quadratic term in the expansion of the energy in powers of a0kF , where a0 is the vacuum s -wave scattering length and kF the Fermi wave number. The problem is cured by adding second-order perturbation corrections in a correlated basis. Going to higher densities and/or more strongly coupled systems, we encounter an instability of the normal state of the system which is characterized by a divergence of the in-medium scattering length. We interpret this divergence as a phonon-exchange-driven dimerization of the system, similar to what occurs at zero density when the vacuum scattering length a0 diverges. We then study, in the stable regime, the superfluid gap and its dependence on the density and the interaction strength. We identify two corrections to low-density expansions: One is medium corrections to the pairing interaction, and the other is finite-range corrections. We show that the most important finite-range corrections are a direct manifestation of the many-body nature of the system.

  15. Exciting Quantized Vortex Rings in a Superfluid Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Bulgac, Aurel

    2014-03-01

    In a recent article, Yefsah et al., Nature 499, 426 (2013) report the observation of an unusual quantum excitation mode in an elongated harmonically trapped unitary Fermi gas. After phase imprinting a domain wall, they observe collective oscillations of the superfluid atomic cloud with a period almost an order of magnitude larger than that predicted by any theory of domain walls, which they interpret as a possible new quantum phenomenon dubbed ``a heavy soliton'' with an inertial mass some 50 times larger than one expected for a domain wall. We present compelling evidence that this ``heavy soliton'' is instead a quantized vortex ring by showing that the main aspects of the experiment can be naturally explained within an extension of the time-dependent density functional theory (TDDFT) to superfluid systems. The numerical simulations required the solution of some 260,000 nonlinear coupled time-dependent 3-dimensional partial differential equations and was implemented on 2048 GPUs on the Cray XK7 supercomputer Titan of the Oak Ridge Leadership Computing Facility.

  16. Intrinsic Correlations for Flaring Blazars Detected by Fermi

    NASA Astrophysics Data System (ADS)

    Fan, J. H.; Yang, J. H.; Xiao, H. B.; Lin, C.; Constantin, D.; Luo, G. Y.; Pei, Z. Y.; Hao, J. M.; Mao, Y. W.

    2017-02-01

    Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between γ-ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi, we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic γ-ray luminosity is strongly correlated with other intrinsic luminosities.

  17. FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE VELA PULSAR

    SciTech Connect

    Abdo, A. A.; Ackermann, M.; Bartelt, J.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bogart, J. R.; Atwood, W. B.; Bagagli, R.; Baldini, L.; Bellardi, F.; Bellazzini, R.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bisello, D.; Baughman, B. M. E-mail: massimiliano.razzano@pi.infn.it

    2009-05-10

    The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new {gamma}-ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high-quality pulse profile, with some 32,400 pulsed photons at E {>=} 0.03 GeV, shows new features, including pulse structure as fine as 0.3 ms and a distinct third peak, which shifts in phase with energy. We examine the high-energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power-law index of {gamma} = 1.51{sup +0.05} {sub -0.04} with an exponential cutoff at E{sub c} = 2.9 {+-} 0.1 GeV. Spectral fits with generalized cutoffs of the form e{sup -(E/E{sub c}){sup b}} require b {<=} 1, which is inconsistent with magnetic pair attenuation, and thus favor outer-magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding pulsar wind nebula.

  18. Shells, orbit bifurcations, and symmetry restorations in Fermi systems

    NASA Astrophysics Data System (ADS)

    Magner, A. G.; Koliesnik, M. V.; Arita, K.

    2016-11-01

    The periodic-orbit theory based on the improved stationary-phase method within the phase-space path integral approach is presented for the semiclassical description of the nuclear shell structure, concerning themain topics of the fruitful activity ofV.G. Soloviev. We apply this theory to study bifurcations and symmetry breaking phenomena in a radial power-law potential which is close to the realistic Woods-Saxon one up to about the Fermi energy. Using the realistic parametrization of nuclear shapes we explain the origin of the double-humped fission barrier and the asymmetry in the fission isomer shapes by the bifurcations of periodic orbits. The semiclassical origin of the oblate-prolate shape asymmetry and tetrahedral shapes is also suggested within the improved periodic-orbit approach. The enhancement of shell structures at some surface diffuseness and deformation parameters of such shapes are explained by existence of the simple local bifurcations and new non-local bridge-orbit bifurcations in integrable and partially integrable Fermi-systems. We obtained good agreement between the semiclassical and quantum shell-structure components of the level density and energy for several surface diffuseness and deformation parameters of the potentials, including their symmetry breaking and bifurcation values.

  19. Enrico: Python package to simplify Fermi-LAT analysis

    NASA Astrophysics Data System (ADS)

    Sanchez, David; Deil, Christoph

    2015-01-01

    Enrico analyzes Fermi data. It produces spectra (model fit and flux points), maps and lightcurves for a target by editing a config file and running a python script which executes the Fermi science tool chain.

  20. Fermi LAT Gamma-ray Observations of IceCube-160731

    NASA Astrophysics Data System (ADS)

    Cheung, C. C.; Toomey, M. W.; Kocevski, D.; Buson, S.

    2016-08-01

    We report follow-up of the extremely high-energy (EHE) IceCube-160731 neutrino event (AMON GCN notice; http://gcn.gsfc.nasa.gov/notices_amon/6888376_128290.amon) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope.

  1. Indirect searches for dark matter with the Fermi large area telescope

    DOE PAGES

    Albert, Andrea

    2015-03-24

    There is overwhelming evidence that non-baryonic dark matter constitutes ~ 27% of the energy density of the Universe. Weakly Interacting Massive Particles (WIMPs) are promising dark matter candidates that may produce γ rays via annihilation or decay detectable by the Fermi Large Area Telescope (LAT). A detection of WIMPs would also indicate the existence of physics beyond the Standard Model. We present recent results from the two cleanest indirect WIMP searches by the Fermi-LAT Collaboration: searches for γ-ray spectral lines and γ-ray emission associated with Milky Way dwarf spheroidal satellite galaxies.

  2. Indirect searches for dark matter with the Fermi large area telescope

    SciTech Connect

    Albert, Andrea

    2015-03-24

    There is overwhelming evidence that non-baryonic dark matter constitutes ~ 27% of the energy density of the Universe. Weakly Interacting Massive Particles (WIMPs) are promising dark matter candidates that may produce γ rays via annihilation or decay detectable by the Fermi Large Area Telescope (LAT). A detection of WIMPs would also indicate the existence of physics beyond the Standard Model. We present recent results from the two cleanest indirect WIMP searches by the Fermi-LAT Collaboration: searches for γ-ray spectral lines and γ-ray emission associated with Milky Way dwarf spheroidal satellite galaxies.

  3. Topological change of the Fermi surface in low-density Rashba gases: application to superconductivity.

    PubMed

    Cappelluti, E; Grimaldi, C; Marsiglio, F

    2007-04-20

    In this Letter we show how, for small values of the Fermi energy compared to the spin-orbit splitting of Rashba type, a topological change of the Fermi surface leads to an effective reduction of the dimensionality in the electronic density of states in the low charge density regime. We investigate its consequences on the onset of the superconducting instability. We show that the superconducting critical temperature is significantly tuned in this regime by the spin-orbit coupling. We suggest that materials with strong spin-orbit coupling are good candidates for enhanced superconductivity.

  4. Connecting the dots: Time-reversal symmetric Weyl semimetals with tunable Fermi arcs

    NASA Astrophysics Data System (ADS)

    Dwivedi, Vatsal; Ramamurthy, Srinidhi T.

    2016-12-01

    We propose a one-parameter family of noninteracting lattice models for Weyl semimetals with four Weyl nodes and tunable Fermi arcs. These two-band model Hamiltonians are time-reversal symmetric with T2=+1 , and tuning the parameter changes the connectivity of the Fermi arcs continuously without affecting the location and chiralities of the Weyl nodes in the bulk Brillouin zone. The bulk polarization and magnetization are shown to vary with this parameter, a dependence inaccessible to the low energy effective field theory.

  5. Fermi Level Pinning at Electrical Metal Contacts of Monolayer Molybdenum Dichalcogenides.

    PubMed

    Kim, Changsik; Moon, Inyong; Lee, Daeyeong; Choi, Min Sup; Ahmed, Faisal; Nam, Seunggeol; Cho, Yeonchoo; Shin, Hyeon-Jin; Park, Seongjun; Yoo, Won Jong

    2017-02-28

    Electrical metal contacts to two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) are found to be the key bottleneck to the realization of high device performance due to strong Fermi level pinning and high contact resistances (Rc). Until now, Fermi level pinning of monolayer TMDCs has been reported only theoretically, although that of bulk TMDCs has been reported experimentally. Here, we report the experimental study on Fermi level pinning of monolayer MoS2 and MoTe2 by interpreting the thermionic emission results. We also quantitatively compared our results with the theoretical simulation results of the monolayer structure as well as the experimental results of the bulk structure. We measured the pinning factor S to be 0.11 and -0.07 for monolayer MoS2 and MoTe2, respectively, suggesting a much stronger Fermi level pinning effect, a Schottky barrier height (SBH) lower than that by theoretical prediction, and interestingly similar pinning energy levels between monolayer and bulk MoS2. Our results further imply that metal work functions have very little influence on contact properties of 2D-material-based devices. Moreover, we found that Rc is exponentially proportional to SBH, and these processing parameters can be controlled sensitively upon chemical doping into the 2D materials. These findings provide a practical guideline for depinning Fermi level at the 2D interfaces so that polarity control of TMDC-based semiconductors can be achieved efficiently.

  6. Spin Texture on the Fermi Surface of Strained HgTe

    NASA Astrophysics Data System (ADS)

    Zaheer, Saad; Young, Steve; Cellucci, Daniel; Teo, Jeffrey; Kane, Charles; Mele, Eugene; Rappe, Andrew

    2012-02-01

    We present ab initio and k.p calculations of the Fermi surface of strained HgTe obtained by stretching the Zinc-Blende lattice along the (111) axis. Near the Fermi level, strained HgTe exhibits point-like accidental degeneracies between a two-fold degenerate and two non-degenerate bands along the (111) axis. The three bands disperse linearly in all directions about the degenerate points and their low energy physics is described by an effective four band k.p Hamiltonian. The Fermi surface consists of two ellipsoids which contact only at the point where the Fermi level crosses the two-fold degenerate band along the (111) axis. The spin expectation value on both ellipsoids is constrained to vanish along the (111) axis due to mirror symmetry about a plane that contains that axis. Furthermore the winding number of spins around the two ellipsoids changes from one end to the other indicating the existence of singular points in the spin texture. Indeed, the ab initio and k.p calculations confirm the existence of such spin singularities on the Fermi ellipsoids. We show that doping HgTe with Zinc atoms chemically strains the HgTe Zinc-Blende lattice and present ab initio calculations on HgZnTe that confirm the above results.

  7. The detection of Fermi AGN above 100 GeV using clustering analysis

    NASA Astrophysics Data System (ADS)

    Armstrong, Thomas; Brown, Anthony M.; Chadwick, Paula M.; Nolan, S. J.

    2015-09-01

    The density-based clustering algorithm DBSCAN has been applied to the Fermi Large Area Telescope (LAT) data set of Eγ ≥ 100 GeV events with |b| > 10°, in order to search for new very high energy (VHE) γ-ray sources. The clustering analysis returned 49 clusters, of which 21 correspond to already known VHE-emitting active galactic nuclei (AGN) within the TeVCat catalogue and a further 11 were found to be significant in a full Fermi analysis. Of these, two are previously detected Fermi VHE AGN, and nine represent new VHE sources consisting of six BL Lac objects, one blazar of unknown type and two unassociated sources. Comparing these, along with the VHE AGN RBS 0679 and RBS 0970 previously detected with Fermi-LAT, to the current populations of AGN detected with ground-based instruments and Fermi suggests that the VHE-emitting AGN discovered in this study are very similar to the TeVCat AGN and therefore further observations with ground-based imaging atmospheric Cherenkov telescopes are recommended.

  8. Spin Polarization and Texture of the Fermi Arcs in the Weyl Fermion Semimetal TaAs.

    PubMed

    Xu, Su-Yang; Belopolski, Ilya; Sanchez, Daniel S; Neupane, Madhab; Chang, Guoqing; Yaji, Koichiro; Yuan, Zhujun; Zhang, Chenglong; Kuroda, Kenta; Bian, Guang; Guo, Cheng; Lu, Hong; Chang, Tay-Rong; Alidoust, Nasser; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Neupert, Titus; Komori, Fumio; Kondo, Takeshi; Shin, Shik; Lin, Hsin; Jia, Shuang; Hasan, M Zahid

    2016-03-04

    A Weyl semimetal is a new state of matter that hosts Weyl fermions as quasiparticle excitations. The Weyl fermions at zero energy correspond to points of bulk-band degeneracy, called Weyl nodes, which are separated in momentum space and are connected only through the crystal's boundary by an exotic Fermi arc surface state. We experimentally measure the spin polarization of the Fermi arcs in the first experimentally discovered Weyl semimetal TaAs. Our spin data, for the first time, reveal that the Fermi arcs' spin-polarization magnitude is as large as 80% and lies completely in the plane of the surface. Moreover, we demonstrate that the chirality of the Weyl nodes in TaAs cannot be inferred by the spin texture of the Fermi arcs. The observed nondegenerate property of the Fermi arcs is important for establishing its exact topological nature, which reveals that spins on the arc form a novel type of 2D matter. Additionally, the nearly full spin polarization we observed (∼80%) may be useful in spintronic applications.

  9. Study of the properties of dilute Fermi gases in the strongly interacting regime

    NASA Astrophysics Data System (ADS)

    Chang, Soon Yong

    Quantum degenerate Fermi gases can be created in the laboratories using alkali atoms. These gases can be in different regimes of density and interaction strength and provide an ideal test bed for the basic properties of the quantum and statistical mechanics. Also some astrophysical objects such as neutron stars can be idealized as interacting fermion systems. In this thesis work, the ground state properties of dilute Fermi gases with attractive short range two-body interactions are reported. Main results of this work are produced by application of quantum Monte Carlo methods. We introduce variational nodal structure to the trial wave function in order to deal with the fermion sign problem. We consider the possibility of Cooper pairing between fermions of different species. The strength of the interaction is varied to study different pairing regimes which are characterized by the product of the s-wave scattering length a and the Fermi wave vector k F. We also review some of the conventional variational methods such as the Lowest Order Constrained Variational which is suitable for Fermi fluids without pairing correlation. The ground state energy, pairing gap Delta, quasi-particle spectrum, two-body distribution function, and momentum distribution of the superfluid were studied with greater accuracy using ab initio quantum Monte Carlo techniques. In the case of the two component Fermi fluid, we find that in the weak coupling regime, 1/akF < -1, the system is a Bardeen-Cooper-Schrieffer type superfluid and the energy gap Delta is much smaller than the Fermi gas energy EFG. For 1/akF ≥ 0.5 we find that weakly interacting composite bosons or molecules are formed in the superfluid gas with Delta and gas energy per particle approaching half of the molecular energy |Emol|/2. In this region we seem to have Bose-Einstein condensation of molecules. The behavior of the energy, chemical potential and energy gap in the transition region, -0.5 < 1/ak F < 0.5, is discussed. The

  10. Pairing, pseudogap and Fermi arcs in cuprates

    DOE PAGES

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; ...

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scatteringmore » creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.« less

  11. Pairing, pseudogap and Fermi arcs in cuprates

    SciTech Connect

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; Gu, Genda

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scattering creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.

  12. Relativistic equation of state at subnuclear densities in the Thomas-Fermi approximation

    SciTech Connect

    Zhang, Z. W.; Shen, H.

    2014-06-20

    We study the non-uniform nuclear matter using the self-consistent Thomas-Fermi approximation with a relativistic mean-field model. The non-uniform matter is assumed to be composed of a lattice of heavy nuclei surrounded by dripped nucleons. At each temperature T, proton fraction Y{sub p} , and baryon mass density ρ {sub B}, we determine the thermodynamically favored state by minimizing the free energy with respect to the radius of the Wigner-Seitz cell, while the nucleon distribution in the cell can be determined self-consistently in the Thomas-Fermi approximation. A detailed comparison is made between the present results and previous calculations in the Thomas-Fermi approximation with a parameterized nucleon distribution that has been adopted in the widely used Shen equation of state.

  13. FFLO Superfluids in 2D Spin-Orbit Coupled Fermi Gases

    PubMed Central

    Zheng, Zhen; Gong, Ming; Zhang, Yichao; Zou, Xubo; Zhang, Chuanwei; Guo, Guangcan

    2014-01-01

    We show that the combination of spin-orbit coupling and in-plane Zeeman field in a two-dimensional degenerate Fermi gas can lead to a larger parameter region for Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases than that using spin-imbalanced Fermi gases. The resulting FFLO superfluids are also more stable due to the enhanced energy difference between FFLO and conventional Bardeen-Cooper-Schrieffer (BCS) excited states. We clarify the crucial role of the symmetry of Fermi surface on the formation of finite momentum pairing. The phase diagram for FFLO superfluids is obtained in the BCS-BEC crossover region and possible experimental observations of FFLO phases are discussed. PMID:25288379

  14. Hall Effect in the Vortex Lattice of d-Wave Superconductors with Anisotropic Fermi Surfaces

    NASA Astrophysics Data System (ADS)

    Kohno, Wataru; Ueki, Hikaru; Kita, Takafumi

    2017-02-01

    On the basis of the augmented quasiclassical theory of superconductivity with the Lorentz force, we study the magnetic field dependence of the charge distribution due to the Lorentz force in a d-wave vortex lattice with anisotropic Fermi surfaces. Owing to the competition between the energy-gap and Fermi surface anisotropies, the charge profile in the vortex lattice changes dramatically with increasing magnetic field because of the overlaps of each nearest vortex-core charge. In addition, the accumulated charge in the core region may reverse its sign as a function of magnetic field. This strong field dependence of the vortex-core charge cannot be observed in the model with an isotropic Fermi surface.

  15. Quantum Oscillations, Thermoelectric Coefficients, and the Fermi Surface of Semimetallic WTe2

    NASA Astrophysics Data System (ADS)

    Zhu, Zengwei; Lin, Xiao; Liu, Juan; Fauqué, Benoît; Tao, Qian; Yang, Chongli; Shi, Youguo; Behnia, Kamran

    2015-05-01

    We present a study of angle-resolved quantum oscillations of electric and thermoelectric transport coefficients in semimetallic WTe2, which has the particularity of displaying a large B2 magnetoresistance. The Fermi surface consists of two pairs of electronlike and holelike pockets of equal volumes in a "Russian doll" structure. The carrier density, Fermi energy, mobility, and the mean-free path of the system are quantified. An additional frequency is observed above a threshold field and attributed to the magnetic breakdown across two orbits. In contrast to all other dilute metals, the Nernst signal remains linear in the magnetic field even in the high-field (ωcτ ≫1 ) regime. Surprisingly, none of the pockets extend across the c axis of the first Brillouin zone, making the system a three-dimensional metal with moderate anisotropy in Fermi velocity, yet a large anisotropy in the mean-free path.

  16. Optical spectroscopic classification of a selection of Southern Hemisphere Fermi-LAT unclassified blazars

    NASA Astrophysics Data System (ADS)

    Klindt, L.; van Soelen, B.; Meintjes, P. J.; Väisänen, P.

    2017-01-01

    The Fermi-LAT has detected more than 3000 sources in the GeV γ-ray regime. The majority are extra-galactic and these sources are dominated by blazars. However, ˜28 per cent of the sources in Fermi 3LAC are listed as blazar candidates of uncertain type (BCU). Increasing the number of classified Fermi-LAT sources is important for improving our understanding of extra-galactic γ-ray sources and can be used to search for new very high energy sources. We report on the optical spectroscopy of seven selected unclassified BCU sources during 2014 and 2015 undertaken using the SAAO 1.9-m and Southern African Large Telescope (SALT). Based on the identified spectral lines we have classified three of the sources as FSRQs and the remaining four as BL Lac objects, determining the redshift for four sources.

  17. The Spectrum and Morphology of the Fermi Bubbles

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazini, R.; Bissaldi, E.; Brandt, T. J.; Ferrara, E. C.; Guiriec, S.; Harding, A. K.; Hayes, E.; Kocevski, D.; McEnery, J. E.; Nemmen, R.; Perkins, J. S.; Troja, E.

    2014-01-01

    The Fermi bubbles are two large structures in the gamma-ray sky extending to 55 deg above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and 500 GeV above 10 deg in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7 sigma significance. The power law with an exponential cutoff has an index of 1.90+/-0.2 and a cutoff energy of 110+/- 50 GeV. We find that the gamma-ray luminosity of the bubbles is 4.4(+)2.4(-0.9 ) 10(exp 37) erg s-1. We confirm a significant enhancement of gamma-ray emission in the south-eastern part of the bubbles, but we do not find significant evidence for a jet. No significant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be 3.4(+)3.7(-)2.6 deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons t the gamma-ray data well. In the IC scenario, the synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic field between 5 and 20 micro-G.

  18. The spectrum and morphology of the Fermi bubbles

    SciTech Connect

    Ackermann, M.; Buehler, R.; Albert, A.; Blandford, R. D.; Bloom, E. D.; Bottacini, E.; Caliandro, G. A.; Cameron, R. A.; Atwood, W. B.; Baldini, L.; Bellazzini, R.; Ballet, J.; Bastieri, D.; Buson, S.; Bissaldi, E.; Brandt, T. J.; Bregeon, J.; and others

    2014-09-20

    The Fermi bubbles are two large structures in the gamma-ray sky extending to 55° above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and 500 GeV above 10° in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7σ significance. The power law with an exponential cutoff has an index of 1.9 ± 0.2 and a cutoff energy of 110 ± 50 GeV. We find that the gamma-ray luminosity of the bubbles is 4.4{sub −0.9}{sup +2.4}×10{sup 37} erg s{sup –1}. We confirm a significant enhancement of gamma-ray emission in the southeastern part of the bubbles, but we do not find significant evidence for a jet. No significant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be 3.4{sub −2.6}{sup +3.7} deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons fit the gamma-ray data well. In the IC scenario, synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic field between 5 and 20 μG.

  19. CLUSTERING OF γ-RAY-SELECTED 2LAC FERMI BLAZARS

    SciTech Connect

    Allevato, V.; Finoguenov, A.; Cappelluti, N.

    2014-12-20

    We present the first measurement of the projected correlation function of 485 γ-ray-selected blazars, divided into 175 BL Lacertae (BL Lacs) and 310 flat-spectrum radio quasars (FSRQs) detected in the 2 year all-sky survey by the Fermi-Large Area Telescope. We find that Fermi BL Lacs and FSRQs reside in massive dark matter halos (DMHs) with log M{sub h} = 13.35{sub −0.14}{sup +0.20} and log M{sub h} = 13.40{sub −0.19}{sup +0.15} h {sup –1} M {sub ☉}, respectively, at low (z ∼ 0.4) and high (z ∼ 1.2) redshift. In terms of clustering properties, these results suggest that BL Lacs and FSRQs are similar objects residing in the same dense environment typical of galaxy groups, despite their different spectral energy distributions, power, and accretion rates. We find no difference in the typical bias and hosting halo mass between Fermi blazars and radio-loud active galactic nuclei (AGNs), supporting the unification scheme simply equating radio-loud objects with misaligned blazar counterparts. This similarity in terms of the typical environment they preferentially live in, suggests that blazars tend to occupy the center of DMHs, as already pointed out for radio-loud AGNs. This implies, in light of several projects looking for the γ-ray emission from DM annihilation in galaxy clusters, a strong contamination from blazars to the expected signal from DM annihilation.

  20. Observations of supernova remnants and molecular clouds from the mm to the gamma-ray domain: bridging low and high energy cosmic rays

    NASA Astrophysics Data System (ADS)

    Gabici, Stefano; Montmerle, Thierry

    2015-10-01

    New evidence that cosmic rays (hadronic component) are accelerated by supernova remnant shocks all the way from low energies to high energies, has come from recent works combining gamma-ray observations in the sub-GeV to TeV domain on the one hand, and in the submm-mm domain on the other hand. These observations concern the specific cases of supernova remnants interacting with molecular cloud complexes, that have long been suspected to be ideal laboratories to study in situ cosmic ray acceleration and diffusion. Indeed, enhanced gamma-ray emission from neutral pion decay, as well as enhanced ionization (both by at least one order of magnitude with respect to average galactic values) have been observed in several regions of massive star formation housing supernova remnants interacting with molecular cloud complexes. This paper summarizes the main physical and chemical processes at work, as well as recent observations, that further support the paradigm of cosmic ray acceleration by supernova remnants all the way from the MeV domain up to several tens of TeV, although much work remains to be done to understand cosmic ray penetration and diffusion inside and around molecular clouds, and reveal the actual spectrum of the accelerated cosmic rays.

  1. Radio core dominance of Fermi blazars

    NASA Astrophysics Data System (ADS)

    Pei, Zhi-Yuan; Fan, Jun-Hui; Liu, Yi; Yuan, Yi-Hai; Cai, Wei; Xiao, Hu-Bing; Lin, Chao; Yang, Jiang-He

    2016-07-01

    During the first 4 years of mission, Fermi/LAT detected 1444 blazars (3FGL) (Ackermann et al. in Astrophys. J. 810:14, 2015). Fermi/LAT observations of blazars indicate that Fermi blazars are luminous and strongly variable with variability time scales, for some cases, as short as hours. Those observations suggest a strong beaming effect in Fermi/LAT blazars. In the present work, we will investigate the beaming effect in Fermi/LAT blazars using a core-dominance parameter, R = S_{core}/ S_{ext.}, where S_{core} is the core emission, while S_{ext.} is the extended emission. We compiled 1335 blazars with available core-dominance parameter, out of which 169 blazars have γ-ray emission (from 3FGL). We compared the core-dominance parameters, log R, between the 169 Fermi-detected blazars (FDBs) and the rest non-Fermi-detected blazars (non-FDBs), and we found that the averaged values are < log Rrangle = 0.99±0.87 for FDBs and < log Rrangle = -0.62±1.15 for the non-FDBs. A K-S test shows that the probability for the two distributions of FDBs and non-FDBs to come from the same parent distribution is near zero (P =9.12×10^{-52}). Secondly, we also investigated the variability index (V.I.) in the γ-ray band for FDBs, and we found V.I.=(0.12 ±0.07) log R+(2.25±0.10), suggesting that a source with larger log R has larger V.I. value. Thirdly, we compared the mean values of radio spectral index for FDBs and non-FDBs, and we obtained < α_{radio}rangle =0.06±0.35 for FDBs and < α_{radio}rangle =0.57±0.46 for non-FDBs. If γ-rays are composed of two components like radio emission (core and extended components), then we can expect a correlation between log R and the γ-ray spectral index. When we used the radio core-dominance parameter, log R, to investigate the relationship, we found that the spectral index for the core component is α_{γ}|_{core} = 1.11 (a photon spectral index of α_{γ}^{ph}|_{core} = 2.11) and that for the extended component is α_{γ}|_{ext.} = 0

  2. A PP2C phosphatase containing a PAS domain is required to convey signals of energy stress to the sigmaB transcription factor of Bacillus subtilis.

    PubMed

    Vijay, K; Brody, M S; Fredlund, E; Price, C W

    2000-01-01

    The sigmaB transcription factor of the bacterium Bacillus subtilis is activated by growth-limiting energy or environmental challenge to direct the synthesis of more than 100 general stress proteins. Although the signal transduction pathway that conveys these stress signals to sigmaB is becoming increasingly well understood, how environmental or energy stress signals enter this pathway remains unknown. We show here that two PP2C serine phosphatases - RsbP, which is required for response to energy stress, and RsbU, which is required for response to environmental stress - each converge on the RsbV regulator of sigmaB. According to the current understanding of sigmaB regulation, in unstressed cells the phosphorylated RsbV anti-anti-sigma is unable to complex the RsbW anti-sigma, which is then free to bind and inactivate sigmaB. We can now advance the model that either PP2C phosphatase, when triggered by its particular class of stress, can remove the phosphate from RsbV and thereby activate sigmaB. The action of the previously described RsbU is known to be controlled by dedicated upstream signalling components that are activated by environmental stress. The action of the RsbP phosphatase described here requires an energy stress, which we suggest is sensed, at least in part, by the PAS domain in the amino-terminal region of the RsbP phosphatase. In other bacterial signalling proteins, similar PAS domains and their associated chromophores directly sense changes in intracellular redox potential to control the activity of a linked output domain.

  3. FermiGrid - experience and future plans

    SciTech Connect

    Chadwick, K.; Berman, E.; Canal, P.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Timm, S.; Yocum, D.; /Fermilab

    2007-09-01

    Fermilab supports a scientific program that includes experiments and scientists located across the globe. In order to better serve this community, Fermilab has placed its production computer resources in a Campus Grid infrastructure called 'FermiGrid'. The FermiGrid infrastructure allows the large experiments at Fermilab to have priority access to their own resources, enables sharing of these resources in an opportunistic fashion, and movement of work (jobs, data) between the Campus Grid and National Grids such as Open Science Grid and the WLCG. FermiGrid resources support multiple Virtual Organizations (VOs), including VOs from the Open Science Grid (OSG), EGEE and the Worldwide LHC Computing Grid Collaboration (WLCG). Fermilab also makes leading contributions to the Open Science Grid in the areas of accounting, batch computing, grid security, job management, resource selection, site infrastructure, storage management, and VO services. Through the FermiGrid interfaces, authenticated and authorized VOs and individuals may access our core grid services, the 10,000+ Fermilab resident CPUs, near-petabyte (including CMS) online disk pools and the multi-petabyte Fermilab Mass Storage System. These core grid services include a site wide Globus gatekeeper, VO management services for several VOs, Fermilab site authorization services, grid user mapping services, as well as job accounting and monitoring, resource selection and data movement services. Access to these services is via standard and well-supported grid interfaces. We will report on the user experience of using the FermiGrid campus infrastructure interfaced to a national cyberinfrastructure--the successes and the problems.

  4. Semi empirical formula for electronic stopping power determination of 24Mg, 27Al and 28Si ions crossing Formvar foil in the ion energy domain of LSS theory

    NASA Astrophysics Data System (ADS)

    Guesmia, A.; Ammi, H.; Mammeri, S.; Dib, A.; Pineda-Vargas, C. A.; Msimanga, M.; Hedibel, M.

    2014-03-01

    We have determined continuous stopping power of heavy ions in thin Formvar foil for 28Si, 27Al and 24Mg ions over an energy range of (0.1-0.5) MeV/nucleon. Heavy Ions Elastic Recoil Detection Analysis (HI-ERDA) technique coupled with time of flight (ToF) spectrometer has been used to measure energy loss of charged particles in this thin absorber. Lindhard, Scharff and Schiott (LSS) theory compared with the corresponding determined stopping values in Formvar, shows significantly large deviations. However, a novel semi empirical expression has been proposed here and tested for better stopping power calculations at low velocity in the ion energy domain of LSS theory for 28Si, 27Al and 24Mg ions crossing thin Formvar foil. The results were compared to the obtained experimental stopping power data, predictions of LSS theory and also to those generated by SRIM-2010 computer code. The obtained results exhibit good agreement with experimental data.

  5. Spectral probes of the holographic Fermi ground state: Dialing between the electron star and AdS Dirac hair

    SciTech Connect

    Cubrovic, Mihailo; Liu Yan; Schalm, Koenraad; Sun Yawen; Zaanen, Jan

    2011-10-15

    We argue that the electron star and the anti-de Sitter (AdS) Dirac hair solution are two limits of the free charged Fermi gas in AdS. Spectral functions of holographic duals to probe fermions in the background of electron stars have a free parameter that quantifies the number of constituent fermions that make up the charge and energy density characterizing the electron star solution. The strict electron star limit takes this number to be infinite. The Dirac hair solution is the limit where this number is unity. This is evident in the behavior of the distribution of holographically dual Fermi surfaces. As we decrease the number of constituents in a fixed electron star background the number of Fermi surfaces also decreases. An improved holographic Fermi ground state should be a configuration that shares the qualitative properties of both limits.

  6. SLAC All Access: Fermi Gamma-ray Space Telescope

    SciTech Connect

    Romani, Roger

    2013-05-31

    Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

  7. SLAC All Access: Fermi Gamma-ray Space Telescope

    ScienceCinema

    Romani, Roger

    2016-07-12

    Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

  8. Structure of a Quantized Vortex in Fermi Atom Gas

    SciTech Connect

    Machida, Masahiko; Koyama, Tomio

    2006-09-07

    In atomic Fermi gases, the pairing character changes from BCS-like to BEC-like when one decreases the threshold energy of the Feshbach resonance. With this crossover, the system enters the strong-coupling regime through the population enhancement of diatom molecules, and the vortex structure becomes much different from well-known core structures in BCS superfluid since the superfluid order parameter is given by a sum of BCS pairs and BEC molecular condensates. In this paper, we study the structure of a vortex by numerically solving the generalized Bogoliubov-de Gennes equation derived from the fermion-boson model and clarify how the vortex structure changes with the threshold energy of the Feshbach resonance. We find that the diatom boson condensate enhances the matter density depletion inside the vortex core and the discreteness of localized quasi-particle spectrum.

  9. Quantum solitons in the Fermi-Pasta-Ulam model

    NASA Astrophysics Data System (ADS)

    Li, De-Jun; Tang, Bing

    2014-03-01

    In this paper, quantum solitons in the Fermi-Pasta-Ulam (FPU) model are investigated analytically. By using the canonical transform method and number-conserving approximation, we obtain the normal form of the phonon-conserving quantized Hamiltonian. In order to convert the quantized Hamiltonian into the coordinate space, we employ the inverse Fourier transform. With the help of the Hartree approximate and the semidiscrete multiple-scale method, the nonlinear Schrödinger (NLS) equation is derived. The results show that quantum solitons may exist in the FPU model. Moreover, it is found that moving quantum solitons become quantum intrinsic localized modes under certain condition. In addition, we obtain the energy level of quantum solitons, which indicates that the energy of such quantum solitons is quantized.

  10. Criterion for stability of Goldstone modes and Fermi liquid behavior in a metal with broken symmetry

    PubMed Central

    Watanabe, Haruki; Vishwanath, Ashvin

    2014-01-01

    There are few general physical principles that protect the low-energy excitations of a quantum phase. Of these, Goldstone’s theorem and Landau–Fermi liquid theory are the most relevant to solids. We investigate the stability of the resulting gapless excitations—Nambu–Goldstone bosons (NGBs) and Landau quasiparticles—when coupled to one another, which is of direct relevance to metals with a broken continuous symmetry. Typically, the coupling between NGBs and Landau quasiparticles vanishes at low energies, leaving the gapless modes unaffected. If, however, the low-energy coupling is nonvanishing, non-Fermi liquid behavior and overdamped bosons are expected. Here we prove a general criterion that specifies when the coupling is nonvanishing. It is satisfied by the case of a nematic Fermi fluid, consistent with earlier microscopic calculations. In addition, the criterion identifies a new kind of symmetry breaking—of magnetic translations—where nonvanishing couplings should arise, opening a previously unidentified route to realizing non-Fermi liquid phases. PMID:25349386

  11. Detroit Edison's Fermi 1 - Preparation for Reactor Removal

    SciTech Connect

    Swindle, Danny

    2008-01-15

    This paper is intended to provide information about the ongoing decommissioning tasks at Detroit Edison's Fermi 1 plant, and in particular, the work being performed to prepare the reactor for removal and disposal. In 1972 Fermi 1 was shutdown and the fuel returned to the Atomic Energy Commission. By the end of 1975, a retirement plan was prepared, the bulk sodium removed, and the plant placed in a safe store condition. The plant systems were left isolated with the sodium containing systems inert with carbon dioxide in an attempt to form a carbonate layer, thus passivating the underlying reactive sodium. In 1996, Detroit Edison determined to evaluate the condition of the plant and to make recommendations in relation to the Fermi 1 future plans. At the end of 1997 approval was obtained to remove the bulk asbestos and residual alkali-metals (i.e., sodium and sodium potassium (NaK)). In 2000, full nuclear decommissioning of the plant was approved. To date, the bulk asbestos insulation has been removed, and the only NaK remaining is located in six capillary instrument tubes. The remaining sodium is contained within the reactor, two of the three primary loops, and miscellaneous removed pipes and equipment to be processed. The preferred method for removing or reacting sodium at Fermi 1 is by injecting superheated steam into a heated, nitrogen inert system. The byproducts of this reaction are caustic sodium hydroxide, hydrogen gas, and heat. The decision was made to separate the three primary loops from the reactor for better control prior to processing each loop and the reactor separately. The first loop has already been processed. The main focus is now to process the reactor to allow removal and disposal of the Class C waste prior to the anticipated June 2008 closure of the Barnwell radioactive waste disposal facility located in South Carolina. Lessons learnt are summarized and concern: the realistic schedule and adherence to the schedule, time estimates, personnel

  12. Composite Fermi liquids in the lowest Landau level

    NASA Astrophysics Data System (ADS)

    Wang, Chong; Senthil, T.

    2016-12-01

    We study composite Fermi liquid (CFL) states in the lowest Landau level (LLL) limit at a generic filling ν =1/n . We begin with the old observation that, in compressible states, the composite fermion in the lowest Landau level should be viewed as a charge-neutral particle carrying vorticity. This leads to the absence of a Chern-Simons term in the effective theory of the CFL. We argue here that instead a Berry curvature should be enclosed by the Fermi surface of composite fermions, with the total Berry phase fixed by the filling fraction ϕB=-2 π ν . We illustrate this point with the CFL of fermions at filling fractions ν =1 /2 q and (single and two-component) bosons at ν =1 /(2 q +1 ) . The Berry phase leads to sharp consequences in the transport properties including thermal and spin Hall conductances. We emphasize that these results only rely on the LLL limit and do not require particle-hole symmetry, which is present microscopically only for fermions at ν =1 /2 . Nevertheless, we show that the existing LLL theory of the composite Fermi liquid for bosons at ν =1 does have an emergent particle-hole symmetry. We interpret this particle-hole symmetry as a transformation between the empty state at ν =0 and the boson integer quantum hall state at ν =2 . This understanding enables us to define particle-hole conjugates of various bosonic quantum Hall states which we illustrate with the bosonic Jain and Pfaffian states. For bosons at ν =1 we construct paired non-Abelian states distinct from both the standard bosonic Pfaffian and its particle hole conjugate and show how they may arise naturally out of the neutral vortex composite Fermi liquid. The bosonic particle-hole symmetry can be realized exactly on the surface of a three-dimensional boson topological insulator. We also show that with the particle-hole and spin S U (2 ) rotation symmetries, there is no gapped topological phase for bosons at ν =1 . Finally we comment on systems that are not strictly in the

  13. Fully nonlinear time-domain simulation of a backward bent duct buoy floating wave energy converter using an acceleration potential method

    NASA Astrophysics Data System (ADS)

    Lee, Kyoung-Rok; Koo, Weoncheol; Kim, Moo-Hyun

    2013-12-01

    A floating Oscillating Water Column (OWC) wave energy converter, a Backward Bent Duct Buoy (BBDB), was simulated using a state-of-the-art, two-dimensional, fully-nonlinear Numerical Wave Tank (NWT) technique. The hydrodynamic performance of the floating OWC device was evaluated in the time domain. The acceleration potential method, with a full-updated kernel matrix calculation associated with a mode decomposition scheme, was implemented to obtain accurate estimates of the hydrodynamic force and displacement of a freely floating BBDB. The developed NWT was based on the potential theory and the boundary element method with constant panels on the boundaries. The mixed Eulerian-Lagrangian (MEL) approach was employed to capture the nonlinear free surfaces inside the chamber that interacted with a pneumatic pressure, induced by the time-varying airflow velocity at the air duct. A special viscous damping was applied to the chamber free surface to represent the viscous energy loss due to the BBDB's shape and motions. The viscous damping coefficient was properly selected using a comparison of the experimental data. The calculated surface elevation, inside and outside the chamber, with a tuned viscous damping correlated reasonably well with the experimental data for various incident wave conditions. The conservation of the total wave energy in the computational domain was confirmed over the entire range of wave frequencies.

  14. Multi-wavelength emission from the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Ko, Chung-Ming; Dogiel, V. A.; Chernyshov, Dmitry; Cheng, K. S.

    The source of electrons responsible for the nonthermal emissions from the Fermi Bubbles, such as gamma rays and microwave, still awaits successful explanation. These electrons should be accelerated in-situ because of the efficient energy loss by inverse Compton and synchrotron processes. In this contribution, we analyse electron acceleration or re-acceleration by the shocks and turbulence produced by tidal disruption of stars by the supermassive black hole at the Galactic center. We consider two different scenarios. The first involved stochastic acceleration of electrons directly from the background plasma (in which the seeds are KeV electrons). The model can explain the observed gamma-ray microwave fluxes but only in a very restricted parameter space. The second is the re-acceleration of GeV electrons originated from the supernova remnants in the Galactic plane that diffuse into the Bubbles. This model produces the Fermi-LAT gamma-ray result but the microwave spectrum is steeper than the observed one.

  15. Two-fluid hydrodynamics in strongly interacting Fermi gases

    NASA Astrophysics Data System (ADS)

    Taylor, Edward

    2010-03-01

    Landau's theory of two-fluid hydrodynamics provides an exact description of the finite-temperature, low-energy dynamics of all strongly interacting superfluids described by a two-component order parameter. Reliable solutions of the two-fluid equations in trapped Fermi gases through the BCS-BEC crossover are crucial for extracting information about the equation of state and transport coefficients from experiments in the superfluid phase. In this talk, I will present new accurate variational solutions for the first and second sound frequencies in a trapped Fermi gas at unitarity, highlighting similarities with superfluid Helium-4 as well as some surprising differences [1.]. I will also discuss proposals to detect these modes in experiments. For the uniform gas, we show that at temperatures of order 0.7Tc and higher, second sound enters with comparable weight to first sound in the dynamic structure factor, in agreement with the recent results of Arahata and Nikuni on the propagation of density pulses [2.].[1.] E. Taylor, H. Hu, X.-J. Liu, L. P. Pitaevskii, A. Griffin, and S. Stringari, Phys. Rev. A 80, 053601 (2009).[2.] E. Arahata and T. Nikuni, Phys. Rev. A 80, 043613 (2009).

  16. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, J. L.; Oates, S. R.; Schady, P.; Burrows, D. N.; de Pasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; Roming, P.; Sakamoto, T.; Swenson, C.; Virgili, F.; Wanderman, D.; Zhang, B.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi-LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT GRBs and the well studied, fainter, less energetic GRBs detected by Swift-BAT is only beginning to be explored by multiwavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi-GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  17. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, Judith L.; Oates, S. R.; Schady, P.; Burrows, D. N.; dePasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; Roming, P.; Sakamoto, T.; Swenson, C.; Troja, E.; Vasileiou, V.; Virgili, F.; Wanderman, D.; Zhang, B.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi -LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust dataset of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT detected GRBs and the well studied, fainter, less energetic GRBs detected by Swift -BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi -GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  18. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, Judith I.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi-LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT GRBs and the well studied, fainter, less energetic GRBs detected by Swift-BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi-GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  19. The likely Fermi detection of the supernova remnant RCW 103

    SciTech Connect

    Xing, Yi; Wang, Zhongxiang; Zhang, Xiao; Chen, Yang

    2014-02-01

    We report on the results from our γ-ray analysis of the supernova remnant (SNR) RCW 103 region. The data were taken with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. An extended source is found at a position consistent with that of RCW 103 and its emission was only detected above 1 GeV (10σ significance), with a power-law spectrum with a photon index of 2.0 ± 0.1. We obtain its 1-300 GeV spectrum and the total flux gives a luminosity of 8.3 × 10{sup 33} erg s{sup –1} at a source distance of 3.3 kpc. Given the positional coincidence and property similarities of this source with other SNRs, we identify it as the likely Fermi γ-ray counterpart to RCW 103. Including radio measurements of RCW 103, the spectral energy distribution (SED) is modeled by considering emission mechanisms based on both hadronic and leptonic scenarios. We find that models in the two scenarios can reproduce the observed SED, while in the hadronic scenario the existence of SNR-molecular cloud interactions is suggested as a high density of the target protons is required.

  20. Low-lying excitations in a strongly interacting Fermi gas

    NASA Astrophysics Data System (ADS)

    Vale, Christopher; Hoinka, Sascha; Dyke, Paul; Lingham, Marcus

    2016-05-01

    We present measurements of the low-lying excitation spectrum of a strongly interacting Fermi gas across the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover using Bragg spectroscopy. By focussing the Bragg lasers onto the central volume of the cloud we can probe atoms at near-uniform density allowing measurement of the homogeneous density-density response function. The Bragg wavevector is set to be approximately half of the Fermi wavevector to probe the collective response. Below the superfluid transition temperature the Bragg spectra dominated by the Bogoliubov-Anderson phonon mode. Single particle excitations become visible at energies greater than twice the pairing gap. As interactions are tuned from the BCS to BEC regime the phonon and single particle modes separate apart and both the pairing gap and speed of sound can be directly read off in certain regions of the crossover. Single particle pair-breaking excitations become heavily suppressed as interactions are tuned from the BCS to BEC regimes.

  1. High-redshift Fermi blazars observed by GROND and Swift

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Nardini, M.; Tagliaferri, Greiner, J.; Schady, P.; Rau, A.; Foschini, L.; Tavecchio, F.; Ghirlanda, G.; Sbarrato, T.

    2013-01-01

    We observed five γ-ray-loud blazars at redshift greater than 2 with the X-Ray Telescope (XRT) and the UltraViolet and Optical Telescope (UVOT) on-board the Swift satellite, and the Gamma-Ray burst Optical Near-Infrared Detector (GROND) instrument. These observations were quasi-simultaneous, usually within a few hours. For four of these blazars, the near-IR to UV data show the presence of an accretion disc, and we could reliably estimate its accretion rate and black hole mass. One of them, PKS 1348+007, was found in an extraordinarily high IR-optical state, almost two orders of magnitude brighter than at the epoch of the Sloan Digital Sky Survey observations. For all the five quasars, the physical parameters of the jet-emitting zone, derived by applying a one-zone emission model, are similar to that found for the bulk of other γ-ray-loud quasars. With our observations, we have X-ray data for the full sample of blazars at z > 2 present in the Fermi 2-year (2LAC) catalogue. This allows us to have a rather complete view of the spectral energy distribution of all high-redshift Fermi blazars, and to draw some conclusions about their properties, and especially about the relation between the accretion rate and the jet power.

  2. Kondo temperature when the Fermi level is near a step in the conduction density of states

    NASA Astrophysics Data System (ADS)

    Fernández, J.; Aligia, A. A.; Roura-Bas, P.; Andrade, J. A.

    2017-01-01

    The (111) surface of Cu, Ag, and Au is characterized by a band of surface Shockley states with a constant density of states beginning slightly below the Fermi energy. These states as well as bulk states hybridize with magnetic impurities which can be placed above the surface. We calculate the characteristic low-temperature energy scale, the Kondo temperature TK of the impurity Anderson model, as the bottom of the conduction band Ds crosses the Fermi energy ɛF. We find simple power laws TK≃|Ds-ɛF| η , where η depends on the sign of Ds-ɛF , the ratio between surface and bulk hybridizations with the impurity Δs/Δb , and the ratio between on-site and Coulomb energy Ed/U in the model.

  3. Trapped unitary two-component Fermi gases with up to ten particles

    NASA Astrophysics Data System (ADS)

    Yin, X. Y.; Blume, D.

    2015-05-01

    The properties of two-component Fermi gases with zero-range interactions are universal. We use an explicitly correlated Gaussian basis set expansion approach to investigate small equal-mass two-component Fermi gases under spherically symmetric external harmonic confinement. At unitarity, we determine the ground state energy for systems with up to ten particles interacting through finite-range two-body potentials for both even and odd number of particles. We extrapolate the energies to the zero-range limit using a novel scheme that removes the linear and quadratic dependence of the ground state energies on the two-body range. Our extrapolated zero-range energies are compared with results from the literature. We also calculate structural properties and the two-body Tan contact. We acknowledge support by the NSF through Grant No. PHY-1205443. This work used the XSEDE, which is supported by NSF Grant No. ACI-1053575.

  4. Signals of Bose Einstein condensation and Fermi quenching in the decay of hot nuclear systems

    NASA Astrophysics Data System (ADS)

    Marini, P.; Zheng, H.; Boisjoli, M.; Verde, G.; Chbihi, A.; Napolitani, P.; Ademard, G.; Augey, L.; Bhattacharya, C.; Borderie, B.; Bougault, R.; Frankland, J. D.; Fable, Q.; Galichet, E.; Gruyer, D.; Kundu, S.; La Commara, M.; Lombardo, I.; Lopez, O.; Mukherjee, G.; Parlog, M.; Rivet, M. F.; Rosato, E.; Roy, R.; Spadaccini, G.; Vigilante, M.; Wigg, P. C.; Bonasera, A.

    2016-05-01

    We report on first experimental observations of nuclear fermionic and bosonic components displaying different behaviours in the decay of hot Ca projectile-like sources produced in mid-peripheral collisions at sub-Fermi energies. The experimental setup, constituted by the coupling of the INDRA 4π detector array to the forward angle VAMOS magnetic spectrometer, allowed to reconstruct the mass, charge and excitation energy of the decaying hot projectile-like sources. By means of quantum-fluctuation analysis techniques, temperatures and local partial densities of bosons and fermions could be correlated to the excitation energy of the reconstructed system. The results are consistent with the production of dilute mixed systems of bosons and fermions, where bosons experience higher phase-space and energy density as compared to the surrounding fermionic gas. Our findings recall phenomena observed in the study of Bose condensates and Fermi gases in atomic traps despite the different scales.

  5. Time-domain measurement of a self-amplified spontaneous emission free-electron laser with an energy-chirped electron beam and undulator tapering

    SciTech Connect

    Marcus, G.; Rosenzweig, J. B.; Artioli, M.; Ciocci, F.; Del Franco, M.; Giannessi, L.; Petralia, A.; Quattromini, M.; Bacci, A.; Bellaveglia, M.; Chiadroni, E.; Di Pirro, G.; Ferrario, M.; Filippetto, D.; Gatti, G.; Rossi, A. R.; Cianchi, A.; Labat, M.; Mostacci, A.; Petrillo, V.; and others

    2012-09-24

    We report, with an unequivocal time-domain measurement, that an appropriately chosen undulator taper can compensate for an electron beam longitudinal energy-chirp in a free-electron laser amplifier, leading to the generation of single-spike radiation close to the Fourier limit. The measurements were taken using the frequency-resolved optical gating technique by employing an advanced transient-grating diagnostic geometry. The reconstructed longitudinal radiation characteristics are compared in detail to prediction from time-dependent three-dimensional simulations.

  6. Onset and Rapid Increase of Gamma-Ray activity from the Binary System PSR B1259-63 detected by Fermi LAT

    NASA Astrophysics Data System (ADS)

    Wood, K. S.; Caliandro, G. A.; Cheung, C. C.; Li, J.; Torres, D. F.; Fermi LAT Collaboration

    2014-06-01

    The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, is measuring rapid brightening of the binary system PSR B1259-63/SS 2883 in the GeV energy range. ...

  7. Magnetic domain and domain wall in Co/Pt multilayer

    NASA Astrophysics Data System (ADS)

    Talapatra, A.; Mohanty, J.

    2016-05-01

    We report systematic micromagnetic investigation of formation of magnetic domains in perpendicularly magnetized Co/Pt multilayer with the variation in magnetic anisotropy and stack thickness. The lowering of anisotropy makes the domain wall broader and domain formation less efficient. Domain sizeincreases with increasing thickness of the stack to minimize the stray field energy.The minimization of energy of the system due to domain formation makes the M-H loop narrower whereas, lower stack thickness results in a wider loop. The magnetization reversalin this system occurs due tothe nucleation and growth of reverse domains.

  8. Gamma-Ray Observations of Tycho’s Supernova Remnant with VERITAS and Fermi

    NASA Astrophysics Data System (ADS)

    Archambault, S.; Archer, A.; Benbow, W.; Bird, R.; Bourbeau, E.; Buchovecky, M.; Buckley, J. H.; Bugaev, V.; Cerruti, M.; Connolly, M. P.; Cui, W.; Dwarkadas, V. V.; Errando, M.; Falcone, A.; Feng, Q.; Finley, J. P.; Fleischhack, H.; Fortson, L.; Furniss, A.; Griffin, S.; Hütten, M.; Hanna, D.; Holder, J.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kelley-Hoskins, N.; Kertzman, M.; Kieda, D.; Krause, M.; Kumar, S.; Lang, M. J.; Maier, G.; McArthur, S.; McCann, A.; Moriarty, P.; Mukherjee, R.; Nieto, D.; O’Brien, S.; Ong, R. A.; Otte, A. N.; Park, N.; Pohl, M.; Popkow, A.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Sadeh, I.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Slane, P.; Staszak, D.; Telezhinsky, I.; Trepanier, S.; Tyler, J.; Wakely, S. P.; Weinstein, A.; Weisgarber, T.; Wilcox, P.; Wilhelm, A.; Williams, D. A.; Zitzer, B.

    2017-02-01

    High-energy gamma-ray emission from supernova remnants (SNRs) has provided a unique perspective for studies of Galactic cosmic-ray acceleration. Tycho’s SNR is a particularly good target because it is a young, type Ia SNR that has been well-studied over a wide range of energies and located in a relatively clean environment. Since the detection of gamma-ray emission from Tycho’s SNR by VERITAS and Fermi-LAT, there have been several theoretical models proposed to explain its broadband emission and high-energy morphology. We report on an update to the gamma-ray measurements of Tycho’s SNR with 147 hr of VERITAS and 84 months of Fermi-LAT observations, which represent about a factor of two increase in exposure over previously published data. About half of the VERITAS data benefited from a camera upgrade, which has made it possible to extend the TeV measurements toward lower energies. The TeV spectral index measured by VERITAS is consistent with previous results, but the expanded energy range softens a straight power-law fit. At energies higher than 400 GeV, the power-law index is 2.92 ± 0.42stat ± 0.20sys. It is also softer than the spectral index in the GeV energy range, 2.14 ± 0.09stat ± 0.02sys, measured in this study using Fermi-LAT data. The centroid position of the gamma-ray emission is coincident with the center of the remnant, as well as with the centroid measurement of Fermi-LAT above 1 GeV. The results are consistent with an SNR shell origin of the emission, as many models assume. The updated spectrum points to a lower maximum particle energy than has been suggested previously.

  9. A Family of Convective-Like Energy-Stable Outflow Boundary Conditions for Incompressible Flow Simulations on Severely-Truncated Unbounded Domains

    NASA Astrophysics Data System (ADS)

    Dong, Suchuan

    2016-11-01

    A large class of flow problems are spatially developing and involves physically unbounded domains, e.g. wakes, jets, and shear layers. To numerically simulate such problems, it is necessary to truncate the domain to a finite size, and some open boundary condition (a.k.a. outflow boundary condition) will be required at the artificial boundary. Backflow instability is a commonly encountered issue with outflows or open boundaries at moderate and high Reynolds numbers. Simulations have been observed to instantly blow up when strong vortices or backflows occur at the outflow/open boundary. In this talk we present a family of convective-like open boundary conditions that effectively overcomes the backflow instability. A prominent feature of these boundary conditions is that they all ensure the energy stability of the system, even in situations where strong vortices or backflows occur at the outflow/open boundary. The proposed boundary conditions unify and provide an underlying connection between the usual convective boundary condition and the traction-free boundary condition. Several canonical wake and jet problems in open domains will be presented to demonstrate the accuracy and effectiveness of the method for overcoming backflow instability. This work is partially supported by NSF (DMS-1318820 and DMS-1522537).

  10. Stokes paradox in electronic Fermi liquids

    NASA Astrophysics Data System (ADS)

    Lucas, Andrew

    2017-03-01

    The Stokes paradox is the statement that in a viscous two-dimensional fluid, the "linear response" problem of fluid flow around an obstacle is ill posed. We present a simple consequence of this paradox in the hydrodynamic regime of a Fermi liquid of electrons in two-dimensional metals. Using hydrodynamics and kinetic theory, we estimate the contribution of a single cylindrical obstacle to the global electrical resistance of a material, within linear response. Momentum relaxation, present in any realistic electron liquid, resolves the classical paradox. Nonetheless, this paradox imprints itself in the resistance, which can be parametrically larger than predicted by Ohmic transport theory. We find a remarkably rich set of behaviors, depending on whether or not the quasiparticle dynamics in the Fermi liquid should be treated as diffusive, hydrodynamic, or ballistic on the length scale of the obstacle. We argue that all three types of behavior are observable in present day experiments.

  11. Operation of FERMI FELs for users

    NASA Astrophysics Data System (ADS)

    Svandrlik, M.

    2015-05-01

    The FERMI seeded free electron laser facility, located at the Elettra laboratory in Trieste (Italy), has been operated for user experiments in the past years using the first FEL line, FEL-1, covering the VUV - EVU spectral range (100 - 20 nm). After the conclusion of the commissioning for the soft-X ray FEL line, FEL-2, the facility is now ready to provide the scientific community with intense FEL pulses (<10 μJ) characterized by a high degree of coherence and spectral stability in the whole range from 100 nm down to 4 nm. We report about the recent achievement of FERMI FELs and our experience with operations for user requiring specific FEL configurations.

  12. Unconventional Fermi surface in an insulating state

    NASA Astrophysics Data System (ADS)

    Tan, B. S.; Hsu, Y.-T.; Zeng, B.; Hatnean, M. Ciomaga; Harrison, N.; Zhu, Z.; Hartstein, M.; Kiourlappou, M.; Srivastava, A.; Johannes, M. D.; Murphy, T. P.; Park, J.-H.; Balicas, L.; Lonzarich, G. G.; Balakrishnan, G.; Sebastian, Suchitra E.

    2015-07-01

    Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.

  13. Probing Magnetized Turbulence in the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Lund, Kelsey; Hales, Christopher A.; Su, Meng

    2017-01-01

    Fermi-LAT observations have revealed giant, sharply defined gamma-ray structures emanating from the Galactic center known as the Fermi bubbles. They extend ~50 degrees (~8.5 kpc) above and below the plane of the Milky Way. Their origin is uncertain but thought to be related to an energetic event such as accretion onto Sgr A* or a burst of nuclear star formation. We analyzed archival radio measurements of Faraday rotation toward extragalactic sources and detected a signature of the bubbles at the shock boundary to the Galactic halo. To confirm these preliminary findings we performed new radio observations with the Karl G. Jansky Very Large Array (JVLA). We discuss the findings of our observations, the shock energetics of the bubbles and their implications for nuclear Galactic activity.

  14. Unconventional Fermi surface in an insulating state

    SciTech Connect

    Harrison, Neil; Tan, B. S.; Hsu, Y. -T.; Zeng, B.; Hatnean, M. Ciomaga; Zhu, Z.; Hartstein, M.; Kiourlappou, M.; Srivastava, A.; Johannes, M. D.; Murphy, T. P.; Park, J. -H.; Balicas, L.; Lonzarich, G. G.; Balakrishnan, G.; Sebastian, Suchitra E.

    2015-07-17

    Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. As a result, the quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.

  15. The Thomas–Fermi quark model: Non-relativistic aspects

    SciTech Connect

    Liu, Quan Wilcox, Walter

    2014-02-15

    The first numerical investigation of non-relativistic aspects of the Thomas–Fermi (TF) statistical multi-quark model is given. We begin with a review of the traditional TF model without an explicit spin interaction and find that the spin splittings are too small in this approach. An explicit spin interaction is then introduced which entails the definition of a generalized spin “flavor”. We investigate baryonic states in this approach which can be described with two inequivalent wave functions; such states can however apply to multiple degenerate flavors. We find that the model requires a spatial separation of quark flavors, even if completely degenerate. Although the TF model is designed to investigate the possibility of many-quark states, we find surprisingly that it may be used to fit the low energy spectrum of almost all ground state octet and decuplet baryons. The charge radii of such states are determined and compared with lattice calculations and other models. The low energy fit obtained allows us to extrapolate to the six-quark doubly strange H-dibaryon state, flavor symmetric strange states of higher quark content and possible six quark nucleon–nucleon resonances. The emphasis here is on the systematics revealed in this approach. We view our model as a versatile and convenient tool for quickly assessing the characteristics of new, possibly bound, particle states of higher quark number content. -- Highlights: • First application of the statistical Thomas–Fermi quark model to baryonic systems. • Novel aspects: spin as generalized flavor; spatial separation of quark flavor phases. • The model is statistical, but the low energy baryonic spectrum is successfully fit. • Numerical applications include the H-dibaryon, strange states and nucleon resonances. • The statistical point of view does not encourage the idea of bound many-quark baryons.

  16. HESS-II reconstruction strategy and performance in the low-energy (20-150 GeV) domain

    SciTech Connect

    Becherini, Y.; Djannati-Atai, A.; Punch, M.; Bernloehr, K.; Ehlert, S.; Masbou, J.; Moulin, E.

    2008-12-24

    In mid-2009 a notable upgrade of the H.E.S.S. telescope system will take place: a new telescope with a 600 m{sup 2} mirror area and very-high-resolution camera (0.07 deg.) will be positioned at the centre of the present configuration, with the aim of lowering the threshold and enhance its sensitivity in the 100 GeV to several TeV energy range. HESS-II will permit the investigation of the lower energy {gamma}-ray spectra in various cosmic accelerators, giving information on the origin of the {gamma}-rays observed, and will detect AGNs with a redshift greater than 0.2 (being less affected by absorption by Extragalactic Background Light--EBL--in this energy range) and will search for new classes of very high energy {gamma}-ray emitters (pulsars, microquasars, GRB, and dark matter candidates)

  17. "Permanence" - An Adaptationist Solution to Fermi's Paradox?

    NASA Astrophysics Data System (ADS)

    Cirkovic, Milan M.

    A new solution of Fermi's paradox sketched by SF writer Karl Schroeder in his 2002. novel Permanence is investigated. It is argued that this solution is tightly connected with adaptationism - a widely discussed working hypothesis in evolutionary biology. Schroeder's hypothesis has important ramifications for astrobiology, SETI projects, and future studies. Its weaknesses should be explored without succumbing to the emotional reactions often accompanying adaptationist explanations.

  18. Ideas by Szilard, physics by Fermi

    SciTech Connect

    Lanouette, W.

    1992-12-01

    An excerpt from William Lanouette's book Genius in the shadows: A biography of Leo Szilard, the man behind the bomb (with Bela Silard). This article covers Szilard's life from early 1933, when he first began contemplating fleeing Germany, to the first self-sustaining nuclear chain reaction on December 2, 1942, and includes a description of his partnership with Enrico Fermi. Part of a series of articles in this magazine commemorating the 50th anniversary of the first controlled chain reaction.

  19. The Fermi Large Area Telescope on Orbit: Event Classification, Instrument Response Functions, and Calibration

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Albert, A.; Allafort, A.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Celik, Q.; Cobet, R.; Davis, D. S.; Ferrara, E. C.; Gehrels, N.; Guiriec, S.; McConville, W.; McEnery, J. E.; Nemmen, R.; Perkins, J. S.; Thompson, D. J.

    2012-01-01

    The Fermi Large Area Telescope (Fermi-LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy -ray telescope, covering the energy range from 20 MeV to more than 300 GeV. During the first years of the mission the LAT team has gained considerable insight into the in-flight performance of the instrument. Accordingly, we have updated the analysis used to reduce LAT data for public release as well as the Instrument Response Functions (IRFs), the description of the instrument performance provided for data analysis. In this paper we describe the effects that motivated these updates. Furthermore, we discuss how we originally derived IRFs from Monte Carlo simulations and later corrected those IRFs for discrepancies observed between flight and simulated data. We also give details of the validations performed using flight data and quantify the residual uncertainties in the IRFs. Finally, we describe techniques the LAT team has developed to propagate those uncertainties into estimates of the systematic errors on common measurements such as fluxes and spectra of astrophysical sources.

  20. Fermi polaron-polaritons in charge-tunable atomically thin semiconductors

    NASA Astrophysics Data System (ADS)

    Sidler, Meinrad; Back, Patrick; Cotlet, Ovidiu; Srivastava, Ajit; Fink, Thomas; Kroner, Martin; Demler, Eugene; Imamoglu, Atac

    2016-10-01

    The dynamics of a mobile quantum impurity in a degenerate Fermi system is a fundamental problem in many-body physics. The interest in this field has been renewed due to recent ground-breaking experiments with ultracold Fermi gases. Optical creation of an exciton or a polariton in a two-dimensional electron system embedded in a microcavity constitutes a new frontier for this field due to an interplay between cavity coupling favouring ultralow-mass polariton formation and exciton-electron interactions leading to polaron or trion formation. Here, we present cavity spectroscopy of gate-tunable monolayer MoSe2 (ref. ) exhibiting strongly bound trion and polaron resonances, as well as non-perturbative coupling to a single microcavity mode. As the electron density is increased, the oscillator strength determined from the polariton splitting is gradually transferred from the higher-energy repulsive exciton-polaron resonance to the lower-energy attractive exciton-polaron state. Simultaneous observation of polariton formation in both attractive and repulsive branches indicates a new regime of polaron physics where the polariton impurity mass can be much smaller than that of the electrons. Our findings shed new light on optical response of semiconductors in the presence of free carriers by identifying the Fermi polaron nature of excitonic resonances and constitute a first step in investigation of a new class of degenerate Bose-Fermi mixtures.

  1. THE FERMI LARGE AREA TELESCOPE ON ORBIT: EVENT CLASSIFICATION, INSTRUMENT RESPONSE FUNCTIONS, AND CALIBRATION

    SciTech Connect

    Ackermann, M.; Ajello, M.; Allafort, A.; Bechtol, K.; Blandford, R. D.; Bloom, E. D.; Bogart, J. R.; Borgland, A. W.; Bottacini, E.; Albert, A.; Atwood, W. B.; Bouvier, A.; Axelsson, M.; Baldini, L.; Ballet, J.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Bonamente, E. E-mail: luca.baldini@pi.infn.it; and others

    2012-11-15

    The Fermi Large Area Telescope (Fermi-LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy {gamma}-ray telescope, covering the energy range from 20 MeV to more than 300 GeV. During the first years of the mission, the LAT team has gained considerable insight into the in-flight performance of the instrument. Accordingly, we have updated the analysis used to reduce LAT data for public release as well as the instrument response functions (IRFs), the description of the instrument performance provided for data analysis. In this paper, we describe the effects that motivated these updates. Furthermore, we discuss how we originally derived IRFs from Monte Carlo simulations and later corrected those IRFs for discrepancies observed between flight and simulated data. We also give details of the validations performed using flight data and quantify the residual uncertainties in the IRFs. Finally, we describe techniques the LAT team has developed to propagate those uncertainties into estimates of the systematic errors on common measurements such as fluxes and spectra of astrophysical sources.

  2. Pairing in a dry Fermi sea

    SciTech Connect

    Maier, Thomas A.; Staar, Peter; Mishra, V.; Chatterjee, Utpal; Campuzano, J. C.; Scalapino, Douglas J.

    2016-06-17

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.

  3. Cinema, Fermi problems and general education

    NASA Astrophysics Data System (ADS)

    Efthimiou, C. J.; Llewellyn, R. A.

    2007-05-01

    During the past few years the authors have developed a new approach to the teaching of physical science, a general education course typically found in the curricula of nearly every college and university. This approach, called Physics in Films (Efthimiou and Llewellyn 2006 Phys. Teach. 44 28-33), uses scenes from popular films to illustrate physical principles and has excited student interest and improved student performance. A similar approach at the senior/high-school level, nicknamed Hollywood Physics, has been developed by Chandler (2006 Phys. Teach. 44 290-2 2002 Phys. Teach. 40 420-4). The two approaches may be considered complementary as they target different student groups. The analyses of many of the scenes in Physics in Films are a direct application of Fermi calculations—estimates and approximations designed to make solutions of complex and seemingly intractable problems understandable to the student non-specialist. The intent of this paper is to provide instructors with examples they can use to develop skill in recognizing Fermi problems and making Fermi calculations in their own courses.

  4. Fermi/GBM Results of Magnetars

    NASA Technical Reports Server (NTRS)

    Kouveliotou, chryssa

    2011-01-01

    Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 18) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11,2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from four magnetar sources. Two of these were brand new sources, SGR J0501 +4516, discovered with Swift and extensively monitored with Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN). A third was SGR Jl550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP IEI547.0-5408), but exhibiting a very prolific outburst with over 400 events recorded in January 2009. In my talk I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the exciting new results of Fermi in this field and the current status of our knowledge of the magnetar population properties and magnetic fields.

  5. A Probabilistic Analysis of the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Solomonides, Evan; Terzian, Yervant

    2016-06-01

    The Fermi paradox uses an appeal to the mediocrity principle to make it seem counterintuitive that humanity has not been contacted by extraterrestrial intelligence. A numerical, statistical analysis was conducted to determine whether this apparent loneliness is, in fact, unexpected. An inequality was derived to relate the frequency of life arising and developing technology on a suitable planet in the galaxy; the average length of time since the first broadcast of such a civilization; and a constant term. An analysis of the sphere reached thus far by human communication was also conducted, considering our local neighborhood and planets of particular interest. These analyses both conclude that the Fermi paradox is not, in fact, unexpected. By the mediocrity principle and numerical modeling, it is actually unlikely that the Earth would have been reached by extraterrestrial communication at this point. We predict that under 1% of the galaxy has been reached at all thus far, and we do not anticipate to be reached until approximately 50% of stars/planets have been reached. We offer a prediction that we should not expect this until at least 1,500 years in the future. Thus the Fermi paradox is not a shocking observation- or lack thereof- and humanity may very well be contacted within our species’ lifespan (we can begin to expect to be contacted 1,500 years in the future).

  6. The Sustainability Solution To The Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Haqq-Misra, J. D.; Baum, S. D.

    No present observations suggest a technologically advanced extraterrestrial intelligence (ETI) has spread through the galaxy. However, under commonplace assumptions about galactic civilization formation and expansion, this absence of observation is highly unlikely. This improbability is the heart of the Fermi Paradox. The Fermi Paradox leads some to conclude that humans have the only advanced civilization in this galaxy, either because civilization formation is very rare or because intelligent civilizations inevitably destroy themselves. In this paper, we argue that this conclusion is premature by introducing the “Sustainability Solution” to the Fermi Paradox, which questions the Paradox's assumption of faster ( e.g. exponential) civilization growth. Drawing on insights from the sustainability of human civilization on Earth, we propose that faster-growth may not be sustainable on the galactic scale. If this is the case, then there may exist ETI that have not expanded throughout the galaxy or have done so but collapsed. These possibilities have implications for both searches for ETI and for human civilization management.

  7. Pairing in a dry Fermi sea

    PubMed Central

    Maier, T. A; Staar, P.; Mishra, V.; Chatterjee, U.; Campuzano, J. C.; Scalapino, D. J.

    2016-01-01

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and −k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability. PMID:27312569

  8. Pairing in a dry Fermi sea

    DOE PAGES

    Maier, Thomas A.; Staar, Peter; Mishra, V.; ...

    2016-06-17

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, wemore » report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.« less

  9. Using edge-preserving algorithm with non-local mean for significantly improved image-domain material decomposition in dual-energy CT

    NASA Astrophysics Data System (ADS)

    Zhao, Wei; Niu, Tianye; Xing, Lei; Xie, Yaoqin; Xiong, Guanglei; Elmore, Kimberly; Zhu, Jun; Wang, Luyao; Min, James K.

    2016-02-01

    Increased noise is a general concern for dual-energy material decomposition. Here, we develop an image-domain material decomposition algorithm for dual-energy CT (DECT) by incorporating an edge-preserving filter into the Local HighlY constrained backPRojection reconstruction (HYPR-LR) framework. With effective use of the non-local mean, the proposed algorithm, which is referred to as HYPR-NLM, reduces the noise in dual-energy decomposition while preserving the accuracy of quantitative measurement and spatial resolution of the material-specific dual-energy images. We demonstrate the noise reduction and resolution preservation of the algorithm with an iodine concentrate numerical phantom by comparing the HYPR-NLM algorithm to the direct matrix inversion, HYPR-LR and iterative image-domain material decomposition (Iter-DECT). We also show the superior performance of the HYPR-NLM over the existing methods by using two sets of cardiac perfusing imaging data. The DECT material decomposition comparison study shows that all four algorithms yield acceptable quantitative measurements of iodine concentrate. Direct matrix inversion yields the highest noise level, followed by HYPR-LR and Iter-DECT. HYPR-NLM in an iterative formulation significantly reduces image noise and the image noise is comparable to or even lower than that generated using Iter-DECT. For the HYPR-NLM method, there are marginal edge effects in the difference image, suggesting the high-frequency details are well preserved. In addition, when the search window size increases from 11× 11 to 19× 19 , there are no significant changes or marginal edge effects in the HYPR-NLM difference images. The reference drawn from the comparison study includes: (1) HYPR-NLM significantly reduces the DECT material decomposition noise while preserving quantitative measurements and high-frequency edge information, and (2) HYPR-NLM is robust with respect to parameter selection.

  10. Scaling analysis of domain-wall free energy in the Edwards-Anderson Ising spin glass in a magnetic field.

    PubMed

    Sasaki, M; Hukushima, K; Yoshino, H; Takayama, H

    2007-09-28

    The stability of the spin-glass phase against a magnetic field is studied in the three- and four-dimensional Edwards-Anderson Ising spin glasses. Effective couplings J(eff) and effective fields H(eff) associated with length scale L are measured by a numerical domain-wall renormalization-group method. The results obtained by scaling analysis of the data strongly indicate the existence of a crossover length beyond which the spin-glass order is destroyed by field H. The crossover length well obeys a power law of H which diverges as H --> 0 but remains finite for any nonzero H, implying that the spin-glass phase is absent even in an infinitesimal field. These results are well consistent with the droplet theory for short-range spin glasses.

  11. Fermi Gamma-Ray Space Telescope: Science Highlights for the First 8 Months

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    The Fermi Gamma-ray Space Telescope was launched on June 11, 2008 and since August 2008 has successfully been conducting routine science observations of high energy phenomena in the gamma-ray sky. A number of exciting discoveries have been made during its first year of operation, including blazar flares, high-energy gamma-ray bursts, and numerous new,gamma-ray sources of different types, among them pulsars and Active Galactic Nuclei (AGN). fermi-LAT also performed accurate mea.<;urement of the diffuse gamma-radiation which clarifies the Ge V excess reported by EGRET almost 10 years ago, high precision measurement of the high energy electron spectrum, and other observations. An overview of the observatory status and recent results as of April 30, 2009, are presented. Key words: gamma-ray astronomy, cosmic rays, gamma-ray burst, pulsar, blazar. diffuse gamma-radiation

  12. Fermi Gamma-Ray Space Telescope - Science Highlights for the First Two Years on Orbit

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2011-01-01

    Fermi science objectives cover probably everything in high energy astrophysics: How do super massive black holes in Active Galactic Nuclei create powerful jets of material moving at nearly light speed? What are the jets made of? What are the mechanisms that produce Gamma-Ray Burst (GRB) explosions? What is the energy budget? How does the Sun generate high-energy gamma-rays in flares? How do the pulsars operate? How many of them are around and how different are they? What are the unidentified gamma-ray sources found by EGRET? What is the origin of the cosmic rays that pervade the Galaxy? What is the nature of dark matter? Fermi LAT successfully operates on the orbit for more than 2 years and demonstrates excellent performance, which is continuously monitored and calibrated. LAT collected> 100 billion on-orbit triggers

  13. Interacting preformed Cooper pairs in resonant Fermi gases

    SciTech Connect

    Gubbels, K. B.; Stoof, H. T. C.

    2011-07-15

    We consider the normal phase of a strongly interacting Fermi gas, which can have either an equal or an unequal number of atoms in its two accessible spin states. Due to the unitarity-limited attractive interaction between particles with different spin, noncondensed Cooper pairs are formed. The starting point in treating preformed pairs is the Nozieres-Schmitt-Rink (NSR) theory, which approximates the pairs as being noninteracting. Here, we consider the effects of the interactions between the Cooper pairs in a Wilsonian renormalization-group scheme. Starting from the exact bosonic action for the pairs, we calculate the Cooper-pair self-energy by combining the NSR formalism with the Wilsonian approach. We compare our findings with the recent experiments by Harikoshi et al. [Science 327, 442 (2010)] and Nascimbene et al. [Nature (London) 463, 1057 (2010)], and find very good agreement. We also make predictions for the population-imbalanced case, which can be tested in experiments.

  14. Non-uniform drag force on the Fermi accelerator model

    NASA Astrophysics Data System (ADS)

    Tavares, Danila F.; Leonel, Edson D.; Costa Filho, R. N.

    2012-11-01

    Some dynamical properties of a particle suffering the action of a generic drag force are obtained for a dissipative Fermi Acceleration model. The dissipation is introduced via a viscous drag force, like a gas, and is assumed to be proportional to a power of the velocity: F∝-vγ. The dynamics is described by a two-dimensional nonlinear area-contracting mapping obtained via the solution of Newton’s second law of motion. We prove analytically that the decay of high energy is given by a continued fraction which recovers the following expressions: (i) linear for γ=1; (ii) exponential for γ=2; and (iii) second-degree polynomial type for γ=1.5. Our results are discussed for both the complete version and the simplified version. The procedure used in the present paper can be extended to many different kinds of system, including a class of billiards problems.

  15. q-Breathers and the Fermi-Pasta-Ulam problem.

    PubMed

    Flach, S; Ivanchenko, M V; Kanakov, O I

    2005-08-05

    The Fermi-Pasta-Ulam (FPU) paradox consists of the non-equipartition of energy among normal modes of a weakly anharmonic atomic chain model. In the harmonic limit each normal mode corresponds to a periodic orbit in phase space and is characterized by its wave number q. We continue normal modes from the harmonic limit into the FPU parameter regime and obtain persistence of these periodic orbits, termed here q-breathers (QB). They are characterized by time periodicity, exponential localization in the q-space of normal modes and linear stability up to a size-dependent threshold amplitude. Trajectories computed in the original FPU setting are perturbations around these exact QB solutions. The QB concept is applicable to other nonlinear lattices as well.

  16. Nuclear physics. Momentum sharing in imbalanced Fermi systems.

    PubMed

    Hen, O; Sargsian, M; Weinstein, L B; Piasetzky, E; Hakobyan, H; Higinbotham, D W; Braverman, M; Brooks, W K; Gilad, S; Adhikari, K P; Arrington, J; Asryan, G; Avakian, H; Ball, J; Baltzell, N A; Battaglieri, M; Beck, A; May-Tal Beck, S; Bedlinskiy, I; Bertozzi, W; Biselli, A; Burkert, V D; Cao, T; Carman, D S; Celentano, A; Chandavar, S; Colaneri, L; Cole, P L; Crede, V; D'Angelo, A; De Vita, R; Deur, A; Djalali, C; Doughty, D; Dugger, M; Dupre, R; Egiyan, H; El Alaoui, A; El Fassi, L; Elouadrhiri, L; Fedotov, G; Fegan, S; Forest, T; Garillon, B; Garcon, M; Gevorgyan, N; Ghandilyan, Y; Gilfoyle, G P; Girod, F X; Goetz, J T; Gothe, R W; Griffioen, K A; Guidal, M; Guo, L; Hafidi, K; Hanretty, C; Hattawy, M; Hicks, K; Holtrop, M; Hyde, C E; Ilieva, Y; Ireland, D G; Ishkanov, B I; Isupov, E L; Jiang, H; Jo, H S; Joo, K; Keller, D; Khandaker, M; Kim, A; Kim, W; Klein, F J; Koirala, S; Korover, I; Kuhn, S E; Kubarovsky, V; Lenisa, P; Levine, W I; Livingston, K; Lowry, M; Lu, H Y; MacGregor, I J D; Markov, N; Mayer, M; McKinnon, B; Mineeva, T; Mokeev, V; Movsisyan, A; Munoz Camacho, C; Mustapha, B; Nadel-Turonski, P; Niccolai, S; Niculescu, G; Niculescu, I; Osipenko, M; Pappalardo, L L; Paremuzyan, R; Park, K; Pasyuk, E; Phelps, W; Pisano, S; Pogorelko, O; Price, J W; Procureur, S; Prok, Y; Protopopescu, D; Puckett, A J R; Rimal, D; Ripani, M; Ritchie, B G; Rizzo, A; Rosner, G; Roy, P; Rossi, P; Sabatié, F; Schott, D; Schumacher, R A; Sharabian, Y G; Smith, G D; Shneor, R; Sokhan, D; Stepanyan, S S; Stepanyan, S; Stoler, P; Strauch, S; Sytnik, V; Taiuti, M; Tkachenko, S; Ungaro, M; Vlassov, A V; Voutier, E; Walford, N K; Wei, X; Wood, M H; Wood, S A; Zachariou, N; Zana, L; Zhao, Z W; Zheng, X; Zonta, I

    2014-10-31

    The atomic nucleus is composed of two different kinds of fermions: protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority of fermions (usually neutrons) to have a higher average momentum. Our high-energy electron-scattering measurements using (12)C, (27)Al, (56)Fe, and (208)Pb targets show that even in heavy, neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few-body systems to neutron stars and may also be observable experimentally in two-spin-state, ultracold atomic gas systems.

  17. Environmental Survey preliminary report, Fermi National Accelerator Laboratory, Batavia, Illinois

    SciTech Connect

    Not Available

    1988-10-01

    This report presents the preliminary findings from the first phase of the Environmental Survey of the US Department of Energy (DOE) Fermi National Accelerator Laboratory (Fermilab), conducted September 14 through 25, 1987. The Survey is being conducted by an interdisciplinary team of environmental specialists led and managed by the Office of Environment, Safety and Health's Office of Environmental Audit. Individual participants for the Survey team are being supplied by a private contractor. The objective of the Survey is to identify environmental problems and areas of environmental risk associated with Fermilab. The Survey covers all environmental media and all areas of environmental regulation. It is being performed in accordance with the DOE Environmental Survey Manual. This phase of the Survey involves the review of existing site environmental data, observations of the operations performed at Fermilab, and interviews with site personnel. 110 refs., 26 figs., 41 tabs.

  18. Eta Carinae's first full orbit in the Fermi era

    NASA Astrophysics Data System (ADS)

    Reimer, Olaf; Reitberger, Klaus; Reimer, Anita; Takahashi, Hiromitsu

    2015-08-01

    Eta Carinae, the so-far only colliding wind binary system shining brightly at high-energy gamma-rays, has been observed over the first complete orbit since launch of the Fermi Gamma-ray Space Telescope. This allows us to compare the spatial, temporal and spectral characteristics of the gamma-ray emission to earlier studies and confront predictions about anticipated observational signatures when concluding the full orbit and entering into the next. By analyzing 2024 days of LAT data we were able to improve the spatial association between the nominal location of eta Carinae and the observed gamma-ray location, confirming the two-component spectrum, as well as the spectro-variability seen predominatly above 10 GeV. The observed source characteristics strengthens the case that eta Car remains unique for the otherwise elusive class of gamma-ray sources whose emission can be related to a colliding stellar wind scenario.

  19. Trapped 173Yb Fermi gas across an orbital Feshbach resonance

    NASA Astrophysics Data System (ADS)

    Iskin, M.

    2017-01-01

    Starting with the two-band description of an orbital Feshbach resonance, we study superfluid properties of a trapped 173Yb Fermi gas under the assumptions of a local-density approximation for the trapping potential and a mean-field approximation for the intraband Cooper pairings. In particular, we investigate the competition and interplay between the pair-breaking effect that is caused by the interband detuning energy, and the pair-breaking and thermal-broadening effects that are simultaneously caused by the temperature. We predict several experimental signatures that are directly caused by this interplay including a spatial separation of superfluid and normal phases within the trap, and could play decisive roles in probing two-band superfluidity in these systems.

  20. Observations of Accreting Pulsars with the FERMI-GBM

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen

    2012-01-01

    The Gamma-ray Burst Monitor (GBM) on-board Fermi comprises 12 NaI detectors spanning the 8-1000 keV band and 2 BGO detectors spanning the 100 keV to 40 MeV band. These detectors view the entire unocculted sky, providing long (approximately 40 ks/day) observations of accreting pulsars daily, which allow long-term monitoring of spin-frequencies and pulsed uxes via epoch-folded searches plus daily blind searches for new pulsars. Phase averaged uxes can be measured using the Earth occultation technique. In this talk I will present highlights of GBM accretion-powered pulsar monitoring such as the discovery of a torque reversal in 4U1626-67, a high-energy QPO in A0535+26, and evidence for a stable accretion disk in OAO 1657-415.