946 research outputs found

    Energy Distribution in f(R) Gravity

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    The well-known energy problem is discussed in f(R) theory of gravity. We use the generalized Landau-Lifshitz energy-momentum complex in the framework of metric f(R) gravity to evaluate the energy density of plane symmetric solutions for some general f(R) models. In particular, this quantity is found for some popular choices of f(R) models. The constant scalar curvature condition and the stability condition for these models are also discussed. Further, we investigate the energy distribution of cosmic string spacetime.Comment: 15 pages, accepted for publication in Gen. Relativ. & Gra

    Quantum Critical Kondo Quasiparticles Probed By Esr In β-ybalb 4

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    Electron spin resonance (ESR) can probe conduction electrons (CE) and local moment (LM) spin systems in different materials. A CE spin resonance (CESR) is observed in metallic systems based on light elements or with enhanced Pauli susceptibility. LM ESR can be seen in compounds with paramagnetic ions and localized d or f electrons. Here we report a remarkable and unprecedented ESR signal in the heavy-fermion superconductor β-YbAlB4 which behaves as a CESR at high temperatures and acquires characteristics of the Yb3 LM ESR at low temperature. This dual behavior strikes as an in situ unique observation of the Kondo quasiparticles in a quantum critical regime. The proximity to a quantum critical point may favor the appearance of this dual character of the ESR signal in β-YbAlB4. © 2011 American Physical Society.1072Tien, C., Yu, J., Duh, H., (1993) Jpn. J. Appl. Phys., 32, p. 2658. , JAPNDE 0021-4922 10.1143/JJAP.32.2658Sichelschmidt, J., (2003) Phys. Rev. Lett., 91, p. 156401. , PRLTAO 0031-9007 10.1103/PhysRevLett.91.156401Sichelschmidt, J., (2007) J. Phys. Condens. Matter, 19, p. 016211. , JCOMEL 0953-8984 10.1088/0953-8984/19/1/016211Krellner, C., Forster, T., Jeevan, H., Geibel, C., Sichelschmidt, J., Relevance of ferromagnetic correlations for the electron spin resonance in kondo lattice systems (2008) Physical Review Letters, 100 (6), p. 066401. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.100.066401&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.100.066401Abrahams, E., Wolfle, P., (2008) Phys. Rev. B, 78, p. 104423. , PRBMDO 1098-0121 10.1103/PhysRevB.78.104423Schlottmann, P., (2009) Phys. Rev. B, 79, p. 045104. , PRBMDO 1098-0121 10.1103/PhysRevB.79.045104Macaluso, R.T., Nakatsuji, S., Kuga, K., Thomas, E.L., Machida, Y., Maeno, Y., Fisk, Z., Chan, J.Y., Crystal structure and physical properties of polymorphs of LnAlB 4 (Ln = Yb, Lu) (2007) Chemistry of Materials, 19 (8), pp. 1918-1922. , DOI 10.1021/cm062244+Nakatsuji, S., (2008) Nature Phys., 4, p. 603. , NPAHAX 1745-2473 10.1038/nphys1002Duque, J.G.S., (2009) Phys. Rev. B, 79, p. 035122. , PRBMDO 1098-0121 10.1103/PhysRevB.79.035122Trovarelli, O., (2000) Phys. Rev. Lett., 85, p. 626. , PRLTAO 0031-9007 10.1103/PhysRevLett.85.626Gegenwart, P., (2002) Phys. Rev. Lett., 89, p. 056402. , PRLTAO 0031-9007 10.1103/PhysRevLett.89.056402Dyson, F.J., (1955) Phys. Rev., 98, p. 349. , PHRVAO 0031-899X 10.1103/PhysRev.98.349Tao, L.J., (1971) Phys. Rev. B, 4, p. 5. , PRBMDO 0556-2805 10.1103/PhysRevB.4.5Abragam, A., Bleaney, B., (1970) EPR of Transitions Ions, , Clarendon, OxfordSattler, J.P., Nemarich, J., (1970) Phys. Rev. B, 1, p. 4249. , PRBMDO 0556-2805 10.1103/PhysRevB.1.4249Rettori, C., (1981) Physica (Amsterdam), 107, p. 359. , PHYBE3 0378-4363 10.1016/0378-4363(81)90485-XHuber, D.L., (2004) Phys. Rev. B, 70, p. 125417. , PRBMDO 1098-0121 10.1103/PhysRevB.70.125417Oseroff, S.B., (1977) Phys. Rev. B, 15, p. 1283. , PRBMDO 0556-2805 10.1103/PhysRevB.15.1283Continetino, M., (2005) Braz. J. Phys., 35, p. 197. , BJPHE6 0103-9733 10.1590/S0103-97332005000100018Coleman, P., Pepin, C., Si, Q., Ramazashvili, R., How do Fermi liquids get heavy and die? (2001) Journal of Physics Condensed Matter, 13 (35), pp. R723-R738. , DOI 10.1088/0953-8984/13/35/202, PII S095389840124853XMonod, P., (1978) J. Phys. (Paris), 39, pp. 6-1472. , JOPQAG 0302-0738 10.1051/jphyscol:19786589Rettori, C., (1997) Phys. Rev. B, 55, p. 1016. , PRBMDO 0163-1829 10.1103/PhysRevB.55.1016Pagliuso, P.G., (1997) Phys. Rev. B, 56, p. 8933. , PRBMDO 0163-1829 10.1103/PhysRevB.56.8933Urbano, R.R., (2002) Phys. Rev. Lett., 89, p. 087602. , PRLTAO 0031-9007 10.1103/PhysRevLett.89.087602Likodimos, V., Koutandos, S., Pissas, M., Papavassiliou, G., Prassides, K., Conduction electron spin resonance in Mg1-xAl xB2 (2003) Europhysics Letters, 61 (1), pp. 116-121. , DOI 10.1209/epl/i2003-00257-1Sercheli, M.S., Kopelevich, Y., Ricardo Da Silva, R., Torres, J.H.S., Rettori, C., Evidence for internal field in graphite: A conduction electron spin-resonance study (2002) Solid State Communications, 121 (9-10), pp. 579-583. , DOI 10.1016/S0038-1098(01)00465-3, PII S0038109801004653Walmsley, L., Rettori, C., C-Axis resistivity in graphite-AlCl3 as found by CESR measurements (1990) Synthetic Metals, 36 (2), pp. 235-239. , DOI 10.1016/0379-6779(90)90056-QPfluger, P., (1983) Synth. Met., 8, p. 15. , SYMEDZ 0379-6779 10.1016/0379-6779(83)90004-8Nevidomskyy, A.H., Coleman, P., (2009) Phys. Rev. Lett., 102, p. 077202. , PRLTAO 0031-9007 10.1103/PhysRevLett.102.077202Si, Q., Rabello, S., Ingersent, K., Smith, J.L., Locally critical quantum phase transitions in strongly correlated metals (2001) Nature, 413 (6858), pp. 804-808. , DOI 10.1038/3510150

    300 GHz CMOS video detection using broadband and active planar antennas

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    Using CMOS transistors for terahertz detection is currently a disruptive technology that offers the direct integration of a terahertz detector with video preamplifiers. The detectors are based on the resistive mixer concept and performance mainly depends on the following parameters: type of antenna, electrical parameters (gate to drain capacitor and channel length of the CMOS device) and foundry. Two different 300 GHz detectors are discussed: a single transistor detector with a broadband antenna and a differential pair driven by a resonant patch antenna

    Bergmann-Thomson energy-momentum complex for solutions more general than the Kerr-Schild class

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    In a very well-known paper, Virbhadra's research group proved that the Weinberg, Papapetrou, Landau and Lifshitz, and Einstein energy-momentum complexes ``coincide'' for all metrics of Kerr-Schild class. A few years later, Virbhadra clarified that this ``coincidence'' in fact holds for metrics more general than the Kerr-Schild class. In the present paper, this study is extended for the Bergmann-Thomson complex and it is proved that this complex also ``coincides'' with those complexes for a more general than the Kerr-Schild class metric.Comment: RevTex, 12 page

    Energy and Momentum densities of cosmological models, with equation of state ρ=μ\rho=\mu, in general relativity and teleparallel gravity

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    We calculated the energy and momentum densities of stiff fluid solutions, using Einstein, Bergmann-Thomson and Landau-Lifshitz energy-momentum complexes, in both general relativity and teleparallel gravity. In our analysis we get different results comparing the aforementioned complexes with each other when calculated in the same gravitational theory, either this is in general relativity and teleparallel gravity. However, interestingly enough, each complex's value is the same either in general relativity or teleparallel gravity. Our results sustain that (i) general relativity or teleparallel gravity are equivalent theories (ii) different energy-momentum complexes do not provide the same energy and momentum densities neither in general relativity nor in teleparallel gravity. In the context of the theory of teleparallel gravity, the vector and axial-vector parts of the torsion are obtained. We show that the axial-vector torsion vanishes for the space-time under study.Comment: 15 pages, no figures, Minor typos corrected; version to appear in International Journal of Theoretical Physic

    Teleparallel Energy-Momentum Distribution of Spatially Homogeneous Rotating Spacetimes

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    The energy-momentum distribution of spatially homogeneous rotating spacetimes in the context of teleparallel theory of gravity is investigated. For this purpose, we use the teleparallel version of Moller prescription. It is found that the components of energy-momentum density are finite and well-defined but are different from General Relativity. However, the energy-momentum density components become the same in both theories under certain assumptions. We also analyse these quantities for some special solutions of the spatially homogeneous rotating spacetimes.Comment: 12 pages, accepted for publication in Int. J. Theor. Phy

    The impact of flooding on aquatic ecosystem services

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    Flooding is a major disturbance that impacts aquatic ecosystems and the ecosystem services that they provide. Predicted increases in global flood risk due to land use change and water cycle intensification will likely only increase the frequency and severity of these impacts. Extreme flooding events can cause loss of life and significant destruction to property and infrastructure, effects that are easily recognized and frequently reported in the media. However, flooding also has many other effects on people through freshwater aquatic ecosystem services, which often go unrecognized because they are less evident and can be difficult to evaluate. Here, we identify the effects that small magnitude frequently occurring floods ( 100-year recurrence interval) have on ten aquatic ecosystem services through a systematic literature review. We focused on ecosystem services considered by the Millennium Ecosystem Assessment including: (1) supporting services (primary production, soil formation), (2) regulating services (water regulation, water quality, disease regulation, climate regulation), (3) provisioning services (drinking water, food supply), and (4) cultural services (aesthetic value, recreation and tourism). The literature search resulted in 117 studies and each of the ten ecosystem services was represented by an average of 12 ± 4 studies. Extreme floods resulted in losses in almost every ecosystem service considered in this study. However, small floods had neutral or positive effects on half of the ecosystem services we considered. For example, small floods led to increases in primary production, water regulation, and recreation and tourism. Decision-making that preserves small floods while reducing the impacts of extreme floods can increase ecosystem service provision and minimize losses
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