# Showing papers in "Physical Review Letters in 2001"

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TL;DR: A dynamical model for the spreading of infections on scale-free networks is defined, finding the absence of an epidemic threshold and its associated critical behavior and this new epidemiological framework rationalizes data of computer viruses and could help in the understanding of other spreading phenomena on communication and social networks.

Abstract: The Internet has a very complex connectivity recently modeled by the class of scale-free networks. This feature, which appears to be very efficient for a communications network, favors at the same time the spreading of computer viruses. We analyze real data from computer virus infections and find the average lifetime and persistence of viral strains on the Internet. We define a dynamical model for the spreading of infections on scale-free networks, finding the absence of an epidemic threshold and its associated critical behavior. This new epidemiological framework rationalizes data of computer viruses and could help in the understanding of other spreading phenomena on communication and social networks.

4,926 citations

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TL;DR: It is shown that the underlying general principle of their construction is in fact a small-world principle of high efficiency, which gives a clear physical meaning to the concept of "small world," and also a precise quantitative analysis of both weighted and unweighted networks.

Abstract: We introduce the concept of efficiency of a network as a measure of how efficiently it exchanges information. By using this simple measure, small-world networks are seen as systems that are both globally and locally efficient. This gives a clear physical meaning to the concept of "small world," and also a precise quantitative analysis of both weighted and unweighted networks. We study neural networks and man-made communication and transportation systems and we show that the underlying general principle of their construction is in fact a small-world principle of high efficiency.

3,619 citations

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TL;DR: A scheme of quantum computation that consists entirely of one-qubit measurements on a particular class of entangled states, the cluster states, which are thus one-way quantum computers and the measurements form the program.

Abstract: We present a scheme of quantum computation that consists entirely of one-qubit measurements on a particular class of entangled states, the cluster states. The measurements are used to imprint a quantum logic circuit on the state, thereby destroying its entanglement at the same time. Cluster states are thus one-way quantum computers and the measurements form the program.

2,961 citations

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TL;DR: The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device and shows linear temperature dependence with a value of 80 microV/K at room temperature.

Abstract: The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device. The observed thermal conductivity is more than 3000 W/K m at room temperature, which is 2 orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. The temperature dependence of the thermal conductivity of nanotubes exhibits a peak at 320 K due to the onset of umklapp phonon scattering. The measured thermoelectric power shows linear temperature dependence with a value of 80 microV/K at room temperature.

2,960 citations

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TL;DR: This work shows that absence of entanglement does not imply classicality, and considers the vanishing of discord as a criterion for the preferred effectively classical states of a system, i.e., the pointer states.

Abstract: Two classically identical expressions for the mutual information generally differ when the systems involved are quantum. This difference defines the quantum discord. It can be used as a measure of the quantumness of correlations. Separability of the density matrix describing a pair of systems does not guarantee vanishing of the discord, thus showing that absence of entanglement does not imply classicality. We relate this to the quantum superposition principle, and consider the vanishing of discord as a criterion for the preferred effectively classical states of a system, i.e., the pointer states.

2,873 citations

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TL;DR: A new Monte Carlo algorithm is presented that permits us to directly access the free energy and entropy, is independent of temperature, and is efficient for the study of both 1st order and 2nd order phase transitions.

Abstract: We present a new Monte Carlo algorithm that produces results of high accuracy with reduced simulational effort. Independent random walks are performed (concurrently or serially) in different, restricted ranges of energy, and the resultant density of states is modified continuously to produce locally flat histograms. This method permits us to directly access the free energy and entropy, is independent of temperature, and is efficient for the study of both 1st order and 2nd order phase transitions. It should also be useful for the study of complex systems with a rough energy landscape.

2,429 citations

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TL;DR: It is shown that a microfluidic device designed to produce reverse micelles can generate complex, ordered patterns as it is continuously operated far from thermodynamic equilibrium.

Abstract: Spatiotemporal pattern formation occurs in a variety of nonequilibrium physical and chemical systems. Here we show that a microfluidic device designed to produce reverse micelles can generate complex, ordered patterns as it is continuously operated far from thermodynamic equilibrium. Flow in a microfluidic system is usually simple—viscous effects dominate and the low Reynolds number leads to laminar flow. Self-assembly of the vesicles into patterns depends on channel geometry and relative fluid pressures, enabling the production of motifs ranging from monodisperse droplets to helices and ribbons.

1,946 citations

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TL;DR: An experiment is reported in which a light pulse is effectively decelerated and trapped in a vapor of Rb atoms, stored for a controlled period of time, and then released on demand.

Abstract: We report an experiment in which a light pulse is effectively decelerated and trapped in a vapor of Rb atoms, stored for a controlled period of time, and then released on demand. We accomplish this ``storage of light'' by dynamically reducing the group velocity of the light pulse to zero, so that the coherent excitation of the light is reversibly mapped into a Zeeman (spin) coherence of the Rb vapor.

1,564 citations

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TL;DR: In this article, the authors derived the shear viscosity of the finite-temperature N = 4 supersymmetric Yang-Mills theory in the large N, strong-coupling regime with the absorption cross section of low-energy gravitons by a near-extremal black three-brane.

Abstract: Using the anti–de Sitter/conformal field theory correspondence, we relate the shear viscosity ? of the finite-temperature N = 4 supersymmetric Yang-Mills theory in the large N, strong-coupling regime with the absorption cross section of low-energy gravitons by a near-extremal black three-brane. We show that in the limit of zero frequency this cross section coincides with the area of the horizon. From this result we find ? = ? / 8N2T3. We conjecture that for finite ’t Hooft coupling gYM2N the shear viscosity is ? = f(gYM2N)N2T3, where f(x) is a monotonic function that decreases from O(x-2ln-1(1/x)) at small x to ?/8 when x??.

1,556 citations

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TL;DR: A fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interface.

Abstract: We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interface. Different regimes of tunneling (resonant through a ``surface plasmon molecule,'' or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system.

1,552 citations

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TL;DR: In this paper, the total flux of 8B neutrinos was determined to be (5.44±0.99)×106 cm−2 s−1, in close agreement with the predictions of solar models.

Abstract: Solar neutrinos from the decay of 8B have been detected at the Sudbury Neutrino Observatory (SNO) via the charged current (CC) reaction on deuterium and by the elastic scattering (ES) of electrons. The CC reaction is sensitive exclusively to νe, while the ES reaction also has a small sensitivity to νμ and ντ. The flux of νe from 8B decay measured by the CC reaction rate is φCC(ν e )=[1.75±0.07(stat.) −0.11 +0.12 (syst.)×0.05(theor.)]×106cm−2s−1. Assuming no flavor transformation, the flux inferred from the ES reaction rate is φES(ν x )=[2.39±0.34(stat.) −0.14 +0.16 (syst.)]×106cm−2s−1. Comparison of φCC(νe) to the Super-Kamiokande collaboration’s precision value of φES(νx) yields a 3.3σ difference, assuming the systematic uncertainties are normally distributed, providing evidence that there is a nonelectron flavor active neutrino component in the solar flux. The total flux of active 8B neutrinos is thus determined to be (5.44±0.99)×106 cm−2 s−1, in close agreement with the predictions of solar models.

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TL;DR: These states can be regarded as an entanglement resource since one can generate a family of other multiparticle entangled states such as the generalized Greenberger-Horne-Zeilinger states of

Abstract: We study the entanglement properties of a class of $N$-qubit quantum states that are generated in arrays of qubits with an Ising-type interaction. These states contain a large amount of entanglement as given by their Schmidt measure. They also have a high persistency of entanglement which means that $\ensuremath{\sim}N/2$ qubits have to be measured to disentangle the state. These states can be regarded as an entanglement resource since one can generate a family of other multiparticle entangled states such as the generalized Greenberger-Horne-Zeilinger states of $lN/2$ qubits by simple measurements and classical communication.

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TL;DR: In this paper, the authors focus on the topological and dynamical properties of real Internet maps in a three-year time interval and find that the Internet is characterized by nontrivial correlations among nodes and different dynamical regimes.

Abstract: The description of the Internet topology is an important open problem, recently tackled with the introduction of scale-free networks. We focus on the topological and dynamical properties of real Internet maps in a three-year time interval. We study higher order correlation functions as well as the dynamics of several quantities. We find that the Internet is characterized by nontrivial correlations among nodes and different dynamical regimes. We point out the importance of node hierarchy and aging in the Internet structure and growth. Our results provide hints towards the realistic modeling of the Internet evolution. Complex networks play an important role in the under- standing of many natural systems (1,2). A network is a set of nodes and links, representing individuals and the interactions among them, respectively. Despite this simple definition, growing networks can exhibit a high degree of complexity, due to the inherent wiring entanglement occur- ring during their growth. The Internet is a capital example of growing network with technological and economical relevance; however, the recollection of router-level maps of the Internet has received the attention of the research community only very recently (3-5). The statistical analysis performed so far has revealed that the Internet ex- hibits several nontrivial topological properties (wiring redundancy, clustering, etc.). Among them, the presence of a power-law connectivity distribution (6,7) makes the Internet an example of the recently identified class of scale-free networks (8). In this Letter, we focus on the dynamical properties of the Internet. We shall consider the evolution of real In- ternet maps from 1997 to 2000, collected by the National Laboratory for Applied Network Research (NLANR) (3). In particular, we will inspect the correlation properties of nodes' connectivity, as well as the time behavior of several quantities related to the growth dynamics of new nodes. Our analysis shows dynamical behavior with dif- ferent growth regimes depending on the node's age and connectivity. The analysis points out two distinct wiring processes: the first one concerns newly added nodes, while the second is related to already existing nodes increasing their interconnections. A feature introduced in this pa- per refers to the Internet hierarchical structure, reflected in a nontrivial scale-free connectivity correlation function. Finally, we discuss recent models for the generation of scale-free networks in the light of the present analysis of real Internet maps. The results presented in this Letter could help develop more accurate models of the Internet.

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TL;DR: It is shown that the Raman scattering technique can give complete structural information for one-dimensional systems, such as carbon nanotubes, by measuring one radial breathing mode frequency omega(RBM) and using the theory of resonant transitions.

Abstract: We show that the Raman scattering technique can give complete structural information for one-dimensional systems, such as carbon nanotubes. Resonant confocal micro-Raman spectroscopy of an (n,m) individual single-wall nanotube makes it possible to assign its chirality uniquely by measuring one radial breathing mode frequency omega(RBM) and using the theory of resonant transitions. A unique chirality assignment can be made for both metallic and semiconducting nanotubes of diameter d(t), using the parameters gamma(0) = 2.9 eV and omega(RBM) = 248/d(t). For example, the strong RBM intensity observed at 156 cm(-1) for 785 nm laser excitation is assigned to the (13,10) metallic chiral nanotube on a Si/SiO2 surface.

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ETH Zurich

^{1}TL;DR: From the properties of the solutions to Bogoliubov-de Gennes equations in the vortex core, the non-Abelian statistics of vortices are derived identical to that for the Moore-Read (Pfaffian) quantum Hall state.

Abstract: Excitation spectrum of a half-quantum vortex in a $p$-wave superconductor contains a zero-energy Majorana fermion. This results in a degeneracy of the ground state of the system of several vortices. From the properties of the solutions to Bogoliubov--de Gennes equations in the vortex core we derive the non-Abelian statistics of vortices identical to that for the Moore-Read (Pfaffian) quantum Hall state.

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TL;DR: It is argued that, near criticality, the average distance between sites in the spanning (largest) cluster scales with its mass, M, as square root of [M], rather than as log (k)M, as expected for random networks away from criticality.

Abstract: We study the tolerance of random networks to intentional attack, whereby a fraction $p$ of the most connected sites is removed. We focus on scale-free networks, having connectivity distribution $P(k)\ensuremath{\sim}{k}^{\ensuremath{-}\ensuremath{\alpha}}$, and use percolation theory to study analytically and numerically the critical fraction ${p}_{c}$ needed for the disintegration of the network, as well as the size of the largest connected cluster. We find that even networks with $\ensuremath{\alpha}\ensuremath{\le}3$, known to be resilient to random removal of sites, are sensitive to intentional attack. We also argue that, near criticality, the average distance between sites in the spanning (largest) cluster scales with its mass, $M$, as $\sqrt{M}$, rather than as ${log}_{k}M$, as expected for random networks away from criticality.

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TL;DR: A technique for manipulating quantum information stored in collective states of mesoscopic ensembles by optical excitation into states with strong dipole-dipole interactions that can be employed for controlled generation of collective atomic spin states as well as nonclassical photonic states and for scalable quantum logic gates is described.

Abstract: We describe a technique for manipulating quantum information stored in collective states of mesoscopic ensembles. Quantum processing is accomplished by optical excitation into states with strong dipole-dipole interactions. The resulting "dipole blockade" can be used to inhibit transitions into all but singly excited collective states. This can be employed for a controlled generation of collective atomic spin states as well as nonclassical photonic states and for scalable quantum logic gates. An example involving a cold Rydberg gas is analyzed.

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TL;DR: A scaling law is reported that governs both the elastic and frictional properties of a wide variety of living cell types, over a wide range of time scales and under a variety of biological interventions, and implies that cytoskeletal proteins may regulate cell mechanical properties mainly by modulating the effective noise temperature of the matrix.

Abstract: We report a scaling law that governs both the elastic and frictional properties of a wide variety of living cell types, over a wide range of time scales and under a variety of biological interventions. This scaling identifies these cells as soft glassy materials existing close to a glass transition, and implies that cytoskeletal proteins may regulate cell mechanical properties mainly by modulating the effective noise temperature of the matrix. The practical implications are that the effective noise temperature is an easily quantified measure of the ability of the cytoskeleton to deform, flow, and reorganize.

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TL;DR: An intense proton beam to achieve fast ignition is proposed, produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF.

Abstract: The concept of fast ignition with inertial confinement fusion (ICF) is a way to reduce the energy required for ignition and burn and to maximize the gain produced by a single implosion. Based on recent experimental findings at the PETAWATT laser at Lawrence Livermore National Laboratory, an intense proton beam to achieve fast ignition is proposed. It is produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF.

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TL;DR: It is conjecture that the load exponent is a universal quantity to characterize scale-free networks and valid for both undirected and directed cases.

Abstract: We study a problem of data packet transport in scale-free networks whose degree distribution follows a power law with the exponent $\ensuremath{\gamma}$. Load, or ``betweenness centrality,'' of a vertex is the accumulated total number of data packets passing through that vertex when every pair of vertices sends and receives a data packet along the shortest path connecting the pair. It is found that the load distribution follows a power law with the exponent $\ensuremath{\delta}\ensuremath{\approx}2.2(1)$, insensitive to different values of $\ensuremath{\gamma}$ in the range, $2l\ensuremath{\gamma}\ensuremath{\le}3$, and different mean degrees, which is valid for both undirected and directed cases. Thus, we conjecture that the load exponent is a universal quantity to characterize scale-free networks.

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TL;DR: Waveguiding characteristics and group-velocity dispersion of line defects in photonic crystal slabs as a function of defect widths reveal that they can be tuned by controlling the defect width, and the results agree well with theoretical calculations, indicating that light paths with made-to-order dispersion can be designed.

Abstract: We reveal experimentally waveguiding characteristics and group-velocity dispersion of line defects in photonic crystal slabs as a function of defect widths. The defects have waveguiding modes with two types of cutoff within the photonic band gap. Interference measurements show that they exhibit extraordinarily large group dispersion, and we found waveguiding modes whose traveling speed is 2 orders of magnitude slower than that in air. These characteristics can be tuned by controlling the defect width, and the results agree well with theoretical calculations, indicating that we can design light paths with made-to-order dispersion.

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TL;DR: Femtosecond x-ray and visible pulses were used to probe structural and electronic dynamics during an optically driven, solid-solid phase transition in VO, suggesting that, in this regime, the structural transition may not be thermally initiated.

Abstract: Femtosecond x-ray and visible pulses were used to probe structural and electronic dynamics during an optically driven, solid-solid phase transition in VO(2). For high interband electronic excitation (approximately 5 x 10(21) cm(-3)), a subpicosecond transformation into the high-T, rutile phase of the material is observed, simultaneous with an insulator-to-metal transition. The fast time scale observed suggests that, in this regime, the structural transition may not be thermally initiated.

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TL;DR: Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals, and MgB2 can be viewed as an analog of the long sought, but still hypothetical, superconducting metallic hydrogen.

Abstract: Boron in MgB2 forms stacks of honeycomb layers with magnesium as a space filler. Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals. Strong bonding with an ionic component and considerable metallic density of states yield a sizable electron-phonon coupling. Together with high phonon frequencies, which we estimate via zone-center frozen phonon calculations to be between 300 and 700 cm(-1), this produces a high critical temperature, consistent with recent experiments. Thus MgB2 can be viewed as an analog of the long sought, but still hypothetical, superconducting metallic hydrogen.

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TL;DR: In this paper, it was shown that the correlation between the BH mass and its temperature, deduced from the energy spectrum of the decay products, can test Hawking's evaporation law and determine the number of large new dimensions and the scale of quantum gravity.

Abstract: If the scale of quantum gravity is near TeV, the CERN Large Hadron Collider will be producing one black hole (BH) about every second. The decays of the BHs into the final states with prompt, hard photons, electrons, or muons provide a clean signature with low background. The correlation between the BH mass and its temperature, deduced from the energy spectrum of the decay products, can test Hawking's evaporation law and determine the number of large new dimensions and the scale of quantum gravity.

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TL;DR: In this article, the gravity solution corresponding to a large number of Neveu-Schwarz or D5-branes wrapped on a two-sphere sphere was found.

Abstract: We find the gravity solution corresponding to a large number of Neveu-Schwarz or D5-branes wrapped on a two sphere so that we have pure $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ super Yang-Mills in the IR. The supergravity solution is smooth, it shows confinement, and it breaks the $\mathrm{U}(1{)}_{R}$ chiral symmetry in the appropriate way. When the gravity approximation is valid the masses of glueballs are comparable to the masses of Kaluza-Klein (KK) states on the 5-brane, but if we could quantize strings on this background it looks like we should be able to decouple the KK states.

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TL;DR: Current blockade and time distributions for single-stranded DNA polymers during voltage-driven translocations through a single alpha-hemolysin pore imply that, while polymers longer than the pore are translocated at a constant speed, the velocity of shorter polymers increases with decreasing length.

Abstract: We measure current blockade and time distributions for single-stranded DNA polymers during voltage-driven translocations through a single alpha-hemolysin pore. We use these data to determine the velocity of the polymers in the pore. Our measurements imply that, while polymers longer than the pore are translocated at a constant speed, the velocity of shorter polymers increases with decreasing length. This velocity is nonlinear with the applied field. Based on this data, we estimate the effective diffusion coefficient and the energy penalty for extending a molecule into the pore.

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TL;DR: Between 7 and 100 K the polarization decay has two distinct components resulting in a non-Lorentzian line shape with a lifetime-limited zero-phonon line and a broadband from elastic exciton-acoustic phonon interactions.

Abstract: We measure a dephasing time of several hundred picoseconds at low temperature in the ground-state transition of strongly confined InGaAs quantum dots, using a highly sensitive four-wave mixing technique. Between 7 and 100 K the polarization decay has two distinct components resulting in a non-Lorentzian line shape with a lifetime-limited zero-phonon line and a broadband from elastic exciton-acoustic phonon interactions.

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TL;DR: Measurements of the temperature dependence of the critical current, I(c), in Josephson junctions consisting of conventional superconducting banks of Nb and a weakly ferromagnetic interlayer of a CuxNi1-x alloy show a sharp cusp with decreasing temperature.

Abstract: We report measurements of the temperature dependence of the critical current, Ic, in Josephson junctions consisting of conventional superconducting banks of Nb and a weakly ferromagnetic interlayer of a CuxNi1-x alloy, with x around 0.5. With decreasing temperature Ic generally increases, but for specific thicknesses of the ferromagnetic interlayer, a maximum is found followed by a strong decrease down to zero, after which Ic rises again. Such a sharp cusp can be explained only by assuming that the junction changes from a 0-phase state at high temperatures to a I� phase state at low temperatures.

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University of Tokyo

^{1}, Boston University^{2}, Massachusetts Institute of Technology^{3}, Brookhaven National Laboratory^{4}, University of California, Irvine^{5}, California State University, Dominguez Hills^{6}, George Mason University^{7}, Gifu University^{8}, Kobe University^{9}, Kyoto University^{10}, Louisiana State University^{11}, University of Maryland, College Park^{12}, University of Minnesota^{13}, Stony Brook University^{14}, University of Utah^{15}, Niigata University^{16}, Osaka University^{17}, Seoul National University^{18}, Shizuoka University^{19}, Tohoku University^{20}, Tokai University^{21}, Tokyo Institute of Technology^{22}, University of Warsaw^{23}, University of Washington^{24}TL;DR: Solar neutrino measurements from 1258 days of data from the Super-Kamiokande detector are presented and the recoil electron energy spectrum is consistent with no spectral distortion.

Abstract: Solar neutrino measurements from 1258days of data from the Super-Kamiokande detector are presented. The measurements are based on recoil electrons in the energy range 5.0{endash}20.0MeV. The measured solar neutrino flux is 2.32{+-}0.03(stat){sup +0.08}{sub {minus}0.07}(syst){times}10{sup 6} cm{sup {minus}2}s{sup {minus}1} , which is 45.1{+-}0.5(stat ){sup +1.6}{sub {minus}1.4}(syst) % of that predicted by the BP2000 SSM. The day vs night flux asymmetry ({Phi}{sub n}{minus}{Phi}{sub d})/ {Phi}{sub average} is 0.033{+-}0.022(stat){sup +0.013}{sub {minus}0.012}(syst) . The recoil electron energy spectrum is consistent with no spectral distortion. For the hep neutrino flux, we set a 90% C.L.upper limit of 40{times}10{sup 3} cm{sup {minus}2}s{sup {minus}1} , which is 4.3times the BP2000 SSM prediction.

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TL;DR: It is shown that renormalizable, asymptotically free, four-dimensional gauge theories that dynamically generate a fifth dimension are constructed.

Abstract: We construct renormalizable, asymptotically free, four-dimensional gauge theories that dynamically generate a fifth dimension.