Dilatonic global strings

We examine the field equations of a self-gravitating global string in low energy superstring gravity, allowing for an arbitrary coupling of the global string to the dilaton. Massive and massless dilatons are considered. For the massive dilaton the spacetime is similar to the recently discovered non-singular time-dependent Einstein self-gravitating global string, but the massless dilaton generically gives a singular spacetime, even allowing for time-dependence. We also demonstrate a time-dependent non-singular string/anti-string configuration, in which the string pair causes a compactification of two of the spatial dimensions, albeit on a very large scale.Comment: 18 pages RevTeX, 3 figures, references amende

Acoustic Detection Of The Magnetocaloric Effect: Application To Gd And Gd5.09 Ge2.03 Si1.88

In this paper we present a simple method for the determination of the total magnetocaloric effect based on the acoustic detection of the adiabatic temperature rise caused by the application of an ac magnetic field of small amplitude. The continuous scanning of a superimposed dc magnetic field allows, by numerical integration, the determination of large temperature variations caused by magnetic field steps from zero to tens of kOe. Absolute values of temperature rise are easily acquired after the calibration of the microphone signal using an appropriate reference sample. Once the calibration is done, no further information about the sample's thermal properties is necessary since the measured signal is directly proportional to the temperature variation. Measurements were made in Gd and Gd5.09 Ge2.03 Si1.88 samples in the temperature range from 240 to 320 K. The technique shows to be suitable for the investigation of materials undergoing both purely magnetic phase transitions, as in the case of Gd, and magnetic-crystallographic first-order ones, as observed for Gd5.09 Ge2.03 Si1.88. Besides the ability to determine the temperature variation due to a large magnetic field step through the continuous scanning of the magnetic field, the technique is also very suitable for measuring the magnetocaloric effect under very small magnetic field steps since it has sensitivity below millikelvin. Moreover, it is able to detect temperature variations in very small amount of sample, leading to its potential application in magnetocaloric thin films. © 2009 The American Physical Society.8013Foldeaki, M., Schnelle, W., Gmelin, E., Benard, P., Koszegi, B., Giguere, A., Chahine, R., Bose, T.K., (1997) J. Appl. Phys., 82, p. 309. , 10.1063/1.365813Pecharsky, V.K., Gschneidner, Jr.K.A., (1999) J. Appl. Phys., 86, p. 565. , 10.1063/1.370767Gopal, B.R., Chahine, R., Bose, T.K., (1997) Rev. Sci. Instrum., 68, p. 1818. , 10.1063/1.1147999Pecharsky, V.K., Gschneidner, Jr.K.A., (1999) J. Magn. Magn. Mater., 200, p. 44. , 10.1016/S0304-8853(99)00397-2Pecharsky, V.K., Gschneidner, Jr.K.A., (1997) Phys. Rev. Lett., 78, p. 4494. , 10.1103/PhysRevLett.78.4494Otowski, W., Glorieux, C., Hofman, R., Thoen, J., (1993) Thermochim. Acta, 218, p. 123. , 10.1016/0040-6031(93)80416-8Gopal, B.R., Chahine, R., Földeàki, M., Bose, T.K., (1995) Rev. Sci. Instrum., 66, p. 232. , 10.1063/1.1145264Rosencwaig, A., Gersho, A., (1976) J. Appl. Phys., 47, p. 64. , 10.1063/1.322296Pecharsky, V.K., Gschneidner, Jr.K.A., (2001) Adv. Mater., 13, p. 683. , 10.1002/1521-4095(200105)13:93.0.CO;2-OVon Ranke, P.J., De Oliveira, N.A., Gama, S., (2004) J. Magn. Magn. Mater., 277, p. 78. , 10.1016/j.jmmm.2003.10.013Carvalho, A.M.G., Alves, C.S., Campos, A., Coelho, A.A., Gama, S., Gandra, F.C.G., Von Ranke, P.J., Oliveira, N.A., (2005) J. Appl. Phys., 97, pp. 10M320. , 10.1063/1.1860932Pecharsky, A.O., Gschneidner, Jr.K.A., Pecharsky, V.K., (2003) J. Magn. Magn. Mater., 267, p. 60. , 10.1016/S0304-8853(03)00305-6Gama, S., Alves, C.S., Coelho, A.A., Ribeiro, C.A., Persiano, A.I.C., Silva, D., (2004) J. Magn. Magn. Mater., 272-276, p. 848. , 10.1016/j.jmmm.2003.12.1260Pires, M.J.M., Carvalho, A.M.G., Gama, S., Da Silva, E.C., Coelho, A.A., Mansanares, A.M., (2005) Phys. Rev. B, 72, p. 224435. , 10.1103/PhysRevB.72.224435Glorieux, C., Thoen, J., Bednarz, G., White, M.A., Geldart, D.J.W., (1995) Phys. Rev. B, 52, p. 12770. , 10.1103/PhysRevB.52.12770Bednarz, G., Geldart, D.J.W., White, M.A., (1993) Phys. Rev. B, 47, p. 14247. , 10.1103/PhysRevB.47.14247Yu. Dan'Kov, S., Tishin, A.M., Pecharsky, V.K., Gschneidner, Jr.K.A., (1998) Phys. Rev. B, 57, p. 3478. , 10.1103/PhysRevB.57.3478Glorieux, C., Caerels, J., Thoen, J., (1996) J. Appl. Phys., 80, p. 3412. , 10.1063/1.363208Pecharsky, V.K., Gschneidner, Jr.K.A., (1999) J. Appl. Phys., 86, p. 6315. , 10.1063/1.371734Giguere, A., Foldeaki, M., Ravi Gopal, B., Chahine, R., Bose, T.K., Frydman, A., Barclay, J.A., (1999) Phys. Rev. Lett., 83, p. 2262. , 10.1103/PhysRevLett.83.2262Yue, M., Zhang, J., Zeng, H., Chen, H., Liu, X.B., (2006) J. Appl. Phys., 99, pp. 08Q104. , 10.1063/1.2158971Tocado, L., Palacios, E., Burriel, R., (2006) J. Therm Anal. Calorim., 84, p. 213. , 10.1007/s10973-005-7180-zGschneidner, Jr.K.A., Pecharsky, V.K., Brück, E., Duijn, H.G.M., Levin, E.M., (2000) Phys. Rev. Lett., 85, p. 4190. , 10.1103/PhysRevLett.85.419

Light propagation in statistically homogeneous and isotropic universes with general matter content

We derive the relationship of the redshift and the angular diameter distance to the average expansion rate for universes which are statistically homogeneous and isotropic and where the distribution evolves slowly, but which have otherwise arbitrary geometry and matter content. The relevant average expansion rate is selected by the observable redshift and the assumed symmetry properties of the spacetime. We show why light deflection and shear remain small. We write down the evolution equations for the average expansion rate and discuss the validity of the dust approximation.Comment: 42 pages, no figures. v2: Corrected one detail about the angular diameter distance and two typos. No change in result

Does accelerating universe indicates Brans-Dicke theory

The evolution of universe in Brans-Dicke (BD) theory is discussed in this paper. Considering a parameterized scenario for BD scalar field $\phi=\phi_{0}a^{\alpha}$ which plays the role of gravitational "constant" $G$, we apply the Markov Chain Monte Carlo method to investigate a global constraints on BD theory with a self-interacting potential according to the current observational data: Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs) data, observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. It is shown that an expanded universe from deceleration to acceleration is given in this theory, and the constraint results of dimensionless matter density $\Omega_{0m}$ and parameter $\alpha$ are, $\Omega_{0m}=0.286^{+0.037+0.050}_{-0.039-0.047}$ and $\alpha=0.0046^{+0.0149+0.0171}_{-0.0171-0.0206}$ which is consistent with the result of current experiment exploration, $\mid\alpha\mid \leq 0.132124$. In addition, we use the geometrical diagnostic method, jerk parameter $j$, to distinguish the BD theory and cosmological constant model in Einstein's theory of general relativity.Comment: 16 pages, 3 figure

Plasma Wakefield Acceleration with a Modulated Proton Bunch

The plasma wakefield amplitudes which could be achieved via the modulation of a long proton bunch are investigated. We find that in the limit of long bunches compared to the plasma wavelength, the strength of the accelerating fields is directly proportional to the number of particles in the drive bunch and inversely proportional to the square of the transverse bunch size. The scaling laws were tested and verified in detailed simulations using parameters of existing proton accelerators, and large electric fields were achieved, reaching 1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found in this case.Comment: 9 pages, 7 figure

The energy dependence of ptp_t angular correlations inferred from mean-ptp_{t} fluctuation scale dependence in heavy ion collisions at the SPS and RHIC

We present the first study of the energy dependence of $p_t$ angular correlations inferred from event-wise mean transverse momentum fluctuations in heavy ion collisions. We compare our large-acceptance measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure suggests that the principal source of $p_t$ correlations and fluctuations is minijets (minimum-bias parton fragments). We observe a dramatic increase in correlations and fluctuations from SPS to RHIC energies, increasing linearly with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related fluctuations near 10 GeV.Comment: 10 pages, 4 figure

Partonic flow and ϕ\phi-meson production in Au+Au collisions at sNN\sqrt{s_{NN}} = 200 GeV

We present first measurements of the $\phi$-meson elliptic flow ($v_{2}(p_{T})$) and high statistics $p_{T}$ distributions for different centralities from $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at RHIC. In minimum bias collisions the $v_{2}$ of the $\phi$ meson is consistent with the trend observed for mesons. The ratio of the yields of the $\Omega$ to those of the $\phi$ as a function of transverse momentum is consistent with a model based on the recombination of thermal $s$ quarks up to $p_{T}\sim 4$ GeV/$c$, but disagrees at higher momenta. The nuclear modification factor ($R_{CP}$) of $\phi$ follows the trend observed in the $K^{0}_{S}$ mesons rather than in $\Lambda$ baryons, supporting baryon-meson scaling. Since $\phi$-mesons are made via coalescence of seemingly thermalized $s$ quarks in central Au+Au collisions, the observations imply hot and dense matter with partonic collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR

Measurement of Transverse Single-Spin Asymmetries for Di-Jet Production in Proton-Proton Collisions at s=200\sqrt{s} = 200 GeV

We report the first measurement of the opening angle distribution between pairs of jets produced in high-energy collisions of transversely polarized protons. The measurement probes (Sivers) correlations between the transverse spin orientation of a proton and the transverse momentum directions of its partons. With both beams polarized, the wide pseudorapidity ($-1 \leq \eta \leq +2$) coverage for jets permits separation of Sivers functions for the valence and sea regions. The resulting asymmetries are all consistent with zero and considerably smaller than Sivers effects observed in semi-inclusive deep inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the new results with the sizable transverse spin effects seen in SIDIS and forward hadron production in pp collisions.Comment: 6 pages total, 1 Latex file, 3 PS files with figure

Energy and system size dependence of \phi meson production in Cu+Cu and Au+Au collisions

We study the beam-energy and system-size dependence of \phi meson production (using the hadronic decay mode \phi -- K+K-) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the transverse momentum distributions for \phi mesons are observed to be similar in yield and shape for Cu+Cu and Au+Au colliding systems with similar average numbers of participating nucleons. The \phi meson yields in nucleus-nucleus collisions, normalised by the average number of participating nucleons, are found to be enhanced relative to those from p+p collisions with a different trend compared to strange baryons. The enhancement for \phi mesons is observed to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems.Comment: 20 pages and 5 figure

Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya

Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization