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1.
Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of 1020 eV and 1013 eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the science reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos. The outline of this review is as follows:
  • Introduction
  • Why kilometer-scale detectors?
  • Cosmic neutrinos associated with the highest energy cosmic rays
  • High energy neutrino telescopes: methodologies of neutrino detection
  • High energy neutrino telescopes: status
  •   相似文献   

    2.
    The influence of frequency modulation of the rf field and modulation of the static magnetic field on NMR-response is investigated. The mathematical treatment using density operator formalism results in a different dynamical behaviour of the nuclei whether frequency—or field modulation is applied. Therefore a general equivalence of the two kinds of modulation does not exist. Explicite solutions for the nuclear magnetization with simultaneous frequency—and field modulation are evaluated for systems obeying Bloch equations. Resonance experiments have been performed using different detection methods:
    1. rf spectrum analysis of the nuclear induction emf from a decoupled (zero leakage) crossed coil setup.
    2. conventional lock-in detection of the signal information from an NMR-detector with single resonant circuit.
      相似文献   

    3.
    Theq states Potts model exhibits a first order phase transition at some inverse temperature β t between “ordered” and “disordered” phases forq large as proved in [1]. In space dimension 2 we use theduality transformation as aninternal symmetry of the partition function at β t to derive an estimate on the probability of a contour. This enables us to prove the preceding result and the following new results:
    1. The discontinuity of the mass gap at β t .
    2. The existence of astrictly positive surface tension between two ordered phases up to β t .
    3. The existence of a non-zero surface tension between an “ordered” and the “disordered” phase at β t .
      相似文献   

    4.
    In a previous paper, “strong” decrease properties of the truncated correlation functions, taking into account the separation of all particles with respect to each other, have been presented and discussed. In this paper, we prove these properties for finite range interactions in various situations, in particular
    1. at low activity for lattice and continuous systems,
    2. at arbitrary activity and high temperature for lattice systems,
    3. at ReH≠0, β arbitrary and atH=0 for appropriate temperatures in the case of ferromagnets.
    We also give some general results, in particular an equivalence, on the links between analyticity and strong cluster properties of the truncated correlation functions.  相似文献   

    5.
    We give mathematically rigorous results on the quantization of the covariant Klein Gordon field with an external stationary scalar interaction in a stationary curved space-time. We show how, following Segal, Weinless etc., the problem reduces to finding a “one particle structure” for the corresponding classical system. Our main result is an existence theorem for such a one-particle structure for a precisely specified class of stationary space-times. Byproducts of our approach are:
    1. A discussion of when a given “equal-time” surface in a given stationary space-time is Cauchy.
    2. A modification and extension of the methods of Chernoff [3] for proving the essential self-adjointness of certain partial differential operators.
      相似文献   

    6.
    Conclusions
    1. The temperature profile of an absorbing film for a given microwave power flux distribution has been considered.
    2. The conditions under which agreement is found between the temperature relief and the flux distribution has been clarified.
    3. An experimental investigation has been carried out of the temperature profile in a matched film for the TE10 mode.
    4. The possibility of using a semiconductor thermal probe to investigate the microwave power flux distribution has been demonstrated.
      相似文献   

    7.
    The exhaustion of the major fossil energy sources on earth in near future and the serious environmental pollution from the fuel combustion processes in the presently applied technologies are the most important problems of modern society. The sustainable development of mankind requests strongly to develop “green” power devices characterized by high fuel energy conversion efficiency, less pollution to the environment and convenience to use. Fuel cells have been commonly accepted to be a kind of clean, safe and convenient power source with high energy efficiency and are on the verge of revolutionizing the electric power industry by offering better ways to produce electricity and to deliver it to the consumers. Among all the advanced fuel cells being developed, which one might be the better choice for ideal green power generators in the 21st century? The answer is solid state fuel cells, particularly the solid oxide fuel cells(SOFCs) but not in the present stage of development. The new generation of SOFCs will certainly be based on all the results and experiences achieved so far in the fuel cell field and a lot of R & D work has to be performed furthermore. This paper attempts to present the current status of the R & D work on fuel cells, especially SOFCs, new concepts and trends, problems and possible measures which may initiate further discussion. The present article includes the following sub-topics:
  • The best electric power plants for the 21st Century
  • R & D on SOFCs: current status, problems and new trends
  • Intermediate temperature SOFCs - what do we need to do?
  • Fabrication techniques - soft chemistry routes
  • What to do for coming up with “green” power plants?
  •   相似文献   

    8.
    9.
    Removal of a wide range of trace organic contaminants from water to concentrations below USEPA Maximum Contaminant Levels (MCL) remains an important goal for the water industry. Design of advanced carbon based adsorption systems represents a unique approach to solving these problems. A number of successful examples are cited in this paper and are briefly summarized in the following section.
    1. Removal of foulants such as humic acid using nanoparticle carbon blacks and chemically activated nanoporous fibers;
    2. Removal of trace organic contaminants such as benzene, toluene, ethylbenzene and p-xylene (BTEX) to levels below USEPA MCL using nanoporous carbon fibers;
    3. Removal of trace chemical warfare simulants such as diisopropylmethyl phosponate and chloroethylethylsulfide using enlarged nanoporous carbon fibers;
    4. Removal of trace chlorinated solvents such as trichloroethylene (TCE) and chloroform using tailored nanoporous carbon fibers;
    5. Removal of the trace herbicide, atrazine, to below USEPA MCL level using nanoporous chemically activated fibers.
    In this paper the enormous improvement of the above systems over commercially available products in static and dynamic adsorption evaluation is described.  相似文献   

    10.
    Broad-area electrodes show electron emission already at electric field strengthsF≈107 V/m. This enhanced field emission (EFE) occurs only for contaminated surfaces. EFE is accompanied by photon emission and gas desorption yielding finally discharges. EFE is caused by dust and contaminants initiating the following effects:
  • an electron is stochastically emitted in a trigger zone
  • the electron gains energyΔE?eΔxF *
  • which excites electronic states
  • which relax by the emission of electrons, photons, and atoms
  • where the positive charges left behind enhanceF *=βF (β?1) initiating so an electron avalanche, i.e., a high conductivity channel. Because of charge migration and neutralization, this avalanche has a life time. This pulsating EFE is accompanied by light emission and gas desorption yielding finally a gas cloud and a discharge.
  • The pulsating, self-sustained EFE has the same root as:
  • the enhanced secondary emission found first by Malter
  • the conductivity switching exhibited by thin (≈ 1 μm) layers of semiconductors or insulators
  • the normal cathode fall and
  • the firing-wave instability in neurodynamics.
  •   相似文献   

    11.
    We study the effects of some of the most important and typical structural changes in two-phase systems on selected structural parameters obtained from small-angle x-ray scattering (SAXS) measurements. To limit the present study, it was assumed that the Phase, 1, embedded in the matrix
    1. is monodispersed and homogeneous,
    2. possesses one of the three most extreme shapes (spherical, fibrillar or lamellar) and
    3. changes its behaviour
    1. through type change (spinodal or nucleotic or coarsening), without changing the shape,
    2. through a change of the shape only, or
    3. through a) (type change) and b) (shape change) simultaneously.
    To find the type of change for three basically different shapes of Phase 1 and to calculate its intensity (amount of the change) the following three SAXS parameters must be compared before and after the treatment of the system:
    1. chord lengthl 1 (and/or radius of gyrationR),
    2. volume partw 1 of the Phase 1, and
    3. relative inner surfaceS v of the system.
    It is shown by this comparison that by the pure type change in the case of
    1. spinodal change, all three SAXRS parameters are increasing or decreasing simultaneously and proportional to a power of the intensity of the change,
    2. nucleotic change,l 1 (and/orR) is unchanged, the other two (w 1 andS v ) are increasing or decreasing simultaneously and directly proportional to the intensity,
    3. coarsening change,w 1 is unchanged and anincreasing ofl 1 is always accompanied by adecreasing ofS v and vice versa.
    In addition to this type change, the cases of mere changes of the shape (“shape change”) and finally of simultaneous type and/or shape change are studied. For the case of pure shape change the alteration of the dimensions (chord lengthl 1 and/or radius of gyrationR) must be followed. The limitations of the analyses of the simultaneous type and/or shape change are discussed in detail.  相似文献   

    12.
    A novel method for measuring magnetostriction constants is presented. A strain, periodic in time, applied to the sample, causes a modulation of the ferromagnetic resonance line position. The height of the signal obtained after phase-sensitive detection is proportional to the strain modulation depth. The appropriate magnetostriction constant λ is obtained by comparing the height of the SMFMR signal with that of the FMR line, as recorded by means of magnetic field modulation. Features of the new technique are:
    1. high sensitivity: λmin? 10?9 forM=100 Oe and linewidth ΔH d=1 Oe;
    2. λ's belonging to distinct precession modes are separately determined;
    3. applicable to thin layers for which strain gauge techniques cannot be used;
    4. wide temperature range: 1.2 K<T<300 K;
    5. uniform stress.
    An illustrative example (YIG layer on GGG substrate) is given.  相似文献   

    13.
    The frequency behaviour of axial modes was investigated during the initial phase of mode competition in case of a helical TEA-CO2 laser. With the help of a homodyne technique single-shot and multi-shot beat spectra were measured. Analysing these under various aspects and combining the results of an earlier investigation it was found that
    1. inferior modes exist only for 100–200 ns.
    2. their spectral width is less than 1 MHz and is determined by lifetime broadening, with the dominant mode narrower than 0.77 MHz,
    3. in the average over many shots the spectral envelope of modes does not follow a Lorentzian shape as expected for the Lorentzian gain curve,
    4. the beat powers change widely from shot to shot, whereas the total laser power remains constant,
    5. no specific phase structures are likely to govern the laser emission, although the maximum emission principle appears to be obeyed with every individual shot. In an appendix relations are derived and summarized which are required for the evaluation of beat mode spectra and for the determination of line width as they apply to the actual time dependence of the laser emission.
      相似文献   

    14.
    A new interferometric method is proposed, using white light fringes of equal chromatic order to determine simultaneously the following paramcters:
    1. The refractive index of a thin dielectric film, and hence its dispersion.
    2. The film thickness.
    3. The correct value of the order of interference.
    4. The phase shift occuring due to reflection at the dielectric/metal interface. In the present work, doubly silvered zinc sulphide (ZnS) thin dielectric film was used as an example in applying the proposed method.
      相似文献   

    15.
    The following new findings are briefly reported:
    1. A consistent quantum theory can be formulated for a free massless scalar field in two-dimensional spacetime.
    2. Satisfactory operator solutions in terms of asymptotic fields can be constructed in the Thirring and Schwinger models.
    3. Gauge invariance is spontaneously broken in the Thirring model as well as in the Schwinger model.
      相似文献   

    16.
    We give a sufficient condition for a self-adjoint operator to have the following properties in a neighborhood of a pointE of its spectrum:
    1. its point spectrum is finite;
    2. its singular continuous spectrum is empty;
    3. its resolvent satisfies a class of a priori estimates.
      相似文献   

    17.
    Starting from the four component Dirac equation for free particles without mass W.Heisenberg und W.Pauli have shown that the interaction term is uniquely defined, if one requires that all symmetries of free particles are preserved. Here we obtain similar results if we start from the eight component Dirac equation for free particles without mass:
    1. The symmetry group of the eight component Dirac equation for free particles without mass has 16 parameters. It is isomorph to the direct product of the SU 4 and a one-parametric group: SU 4× (1).
    2. The interaction operator is uniquely defined if one requires to preserve as many symmetries as possible of those given in (1).
    3. But some of the symmetries in (1) are necessarily broken, in particular that of SU 3. The symmetry of the interaction operator is given by SO 4× (1)× (1).
    These results mean:
    1. The Heisenberg theory is uniquely defined, only if one assumes that the free particle part of the equation is well known.
    2. The theory can be changed without modifying the fundamental idea ofHeisenberg andPauli to deduce an uniquely defined interaction operator if one starts with a modified free particle part.
    3. A special kind of modification of the free particle part leads essentially to the SU 4-symmetry including that of SU 3, which is necessarily broken by the interaction term.
    4. The question arises if this break of the SU 3-symmetry has something to do with the real break. This question is not yet touched in this paper.
      相似文献   

    18.
    New developments and new trends in NMR-ON are presented, especially in the context of precise measurements of nuclear magnetic moments and electric quadrupole moments of short-lived nuclei far off stability with on-line nuclear orientation techniques. The main emphasis is put on the following items:
    1. Quadrupole-interaction-resolved NMR-ON (QI-NMR-ON): It is shown that hcp-Co is an ideal matrix for precise measurements of electric quadrupole moments of radioactive nuclei in the region Hg, Au, Pt, Ir, Os. Recently, the first on-line experiment was performed successfully at NICOLE/ISOLDE-CERN and the very interesting quadrupole moment of186Au could be determined precisely.
    2. General problems with lattice location and NMR-ON line widths in long decay chains, such as “lattice-site conservation” by implantation of a suitable precursor.
    3. β-decay-induced lattice site change. In the context of integral nuclear orientation measurements on nuclei far off stability, where the β-decay energies become large, lattice site changes may occur, which make the interpretation of γ-anisotropies measured by integral and even time-differential techniques difficult or even impossible. A pilot experiment is described, in which such a β-decay-induced lattice site change has been identified by a double-resonance NMR-ON measurement.
      相似文献   

    19.
    An overview of the subject of space plasma physics is attempted. This encompasses a discussion of various ground-based and satellite studies of the near-Earth space environment, with its marked temporal and spatial variations, theoretical investigations, and numerical simulations. The important distinction is drawn between passive studies of elements of the natural system, aimed at the difficult task of understanding the self-consistent evolution of some natural processes, and active investigations, which either probe or modify natural processes, in order to improve understanding of cause and effect (e.g. of energy transformations) within the system. Linear, nonlinear, and chaotic processes can occur. Attention is paid to:
    1. Energetic events on the Sun,
    2. Large-scale features of the interplanetary medium, both observed directly and via scintillations of distant radio stars,
    3. The magnetosphere in general, and the aurora in particular,
    4. Wave-particle interactions, especially cyclotron resonance phenomena, and
    5. The ionosphere, particularly when heated by powerful radio waves.
    The approach adopted is to place these special topics in the context of the Solar Terrestrial Energy Program (STEP) of ICSU's SCOSTEP. Finally, mention is made of some benefits to humanity of studies of space plasma physics phenomena.  相似文献   

    20.
    We prove that the following lattice systems:
    1. anisotropic Heisenberg model,
    2. Ising model with transverse magnetic field,
    3. quantum lattice gas with hard cores extending over nearest neighbours,
    exhibit phase transitions if the temperature is sufficiently low and the transverse (or kinetic) part of the interaction sufficiently small.  相似文献   

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