Influence of Heat Input, Working Fluid and Evacuation Level on the Performance of Pulsating Heat Pipe

An experimental study on pulsating heat pipe (PHP) is presented in this work. A closed loop PHP with a single U turn is fabricated and tested. The transient and steady state experiments are conducted and operating temperatures are measured. The experiments are carried out for different working fluids, heat input and for different evacuation levels. The derived parameters include thermal resistance and heat transfer coefficient of PHP. The results of these experiments show an intermittent motion of the working fluid at lower heat input. The temperature difference between evaporator and condenser at steady state is found lower for acetone compared to water, ethanol and methanol. Lower value of thermal resistance and higher value of heat transfer coefficient are observed in case of acetone compared to water, ethanol and methanol. Lower values of temperature difference between evaporator and condenser and thermal resistance and higher value of heat transfer coefficient are observed at atmospheric conditions of operation of PHP compared to evacuation conditions. The Power Spectral Density Analysis is also carried out on the results of these experiments using FFT technique to analyse the pulsating motion of the fluid in a PHP. In the Power Spectral Density analysis, the frequency distribution of temperature variation in PHP was observed over a wider range, signifying the periodic motion in the fluid flow of the liquid slug and vapour plug. This characteristic frequency corresponded to the characteristic time for a couple of adjacent vapour plug and liquid slug passing through a specific local wall surface in a PHP

Constraints on the uncertainties of entangled symmetric qubits

We derive necessary and sufficient inseparability conditions imposed on the variance matrix of symmetric qubits. These constraints are identified by examining a structural parallelism between continuous variable states and two qubit states. Pairwise entangled symmetric multiqubit states are shown here to obey these constraints. We also bring out an elegant local invariant structure exhibited by our constraints.Comment: 5 pages, REVTEX, Improved presentation; Theorem on neccessary and sufficient condition included; To appear in Phys. Lett.

Quantum discord evolution of three-qubit states under noisy channels

We investigated the dissipative dynamics of quantum discord for correlated qubits under Markovian environments. The basic idea in the present scheme is that quantum discord is more general, and possibly more robust and fundamental, than entanglement. We provide three initially correlated qubits in pure Greenberger-Horne-Zeilinger (GHZ) or W state and analyse the time evolution of the quantum discord under various dissipative channels such as: Pauli channels $\sigma_{x}$, $\sigma_{y}$, and $\sigma_{z}$, as well as depolarising channels. Surprisingly, we find that under the action of Pauli channel $\sigma_{x}$, the quantum discord of GHZ state is not affected by decoherence. For the remaining dissipative channels, the W state is more robust than the GHZ state against decoherence. Moreover, we compare the dynamics of entanglement with that of the quantum discord under the conditions in which disentanglement occurs and show that quantum discord is more robust than entanglement except for phase flip coupling of the three qubits system to the environment.Comment: 17 pages, 4 figures, accepted for publication in EPJ

Large scale magnetogenesis from a non-equilibrium phase transition in the radiation dominated era

We study the generation of large scale primordial magnetic fields by a cosmological phase transition during the radiation dominated era. The setting is a theory of N charged scalar fields coupled to an abelian gauge field, that undergoes a phase transition at a critical temperature much larger than the electroweak scale. The dynamics after the transition features two distinct stages: a spinodal regime dominated by linear long-wavelength instabilities, and a scaling stage in which the non-linearities and backreaction of the scalar fields are dominant. This second stage describes the growth of horizon sized domains. We implement a recently introduced formulation to obtain the spectrum of magnetic fields that includes the dissipative effects of the plasma. We find that large scale magnetogenesis is very efficient during the scaling regime. The ratio between the energy density on scales larger than L and that in the background radiation r(L,T) = rho_B(L,T)/rho_{cmb}(T) is r(L,T) \sim 10^{-34} at the Electroweak scale and r(L,T) \sim 10^{-14} at the QCD scale for L \sim 1 Mpc. The resulting spectrum is insensitive to the magnetic diffusion length. We conjecture that a similar mechanism could be operative after the QCD chiral phase transition.Comment: LaTex, 25 pages, no figures, to appear in Phys. Rev.

Quark Stars: Features and Findings

Under extreme conditions of temperature and/or density, quarks and gluons are expected to undergo a deconfinement phase transition. While this is an ephemeral phenomenon at the ultra-relativistic heavy-ion collider (BNL-RHIC), quark matter may exist naturally in the dense interior of neutron stars. Herein, we present an appraisal of the possible phase structure of dense quark matter inside neutron stars, and the likelihood of its existence given the current status of neutron star observations. We conclude that quark matter inside neutron stars cannot be dismissed as a possibility, although recent observational evidence rules out most soft equations of state.Comment: Contribution to proceedings of Hot Quarks 2006, Villasimius, Italy; 5 pages (TeX), 2 .eps figure

Particle Physics Approach to Dark Matter

We review the main proposals of particle physics for the composition of the cold dark matter in the universe. Strong axion contribution to cold dark matter is not favored if the Peccei-Quinn field emerges with non-zero value at the end of inflation and the inflationary scale is superheavy since, under these circumstances, it leads to unacceptably large isocurvature perturbations. The lightest neutralino is the most popular candidate constituent of cold dark matter. Its relic abundance in the constrained minimal supersymmetric standard model can be reduced to acceptable values by pole annihilation of neutralinos or neutralino-stau coannihilation. Axinos can also contribute to cold dark matter provided that the reheat temperature is adequately low. Gravitinos can constitute the cold dark matter only in limited regions of the parameter space. We present a supersymmetric grand unified model leading to violation of Yukawa unification and, thus, allowing an acceptable b-quark mass within the constrained minimal supersymmetric standard model with mu>0. The model possesses a wide range of parameters consistent with the data on the cold dark matter abundance as well as other phenomenological constraints. Also, it leads to a new version of shifted hybrid inflation.Comment: 32 pages including 6 figures, uses svmult.cls, some clarifications added, lectures given at the Third Aegean Summer School "The Invisible Universe: Dark Matter and Dark Energy", 26 September-1 October 2005, Karfas, Island of Chios, Greece (to appear in the proceedings

Present Status and Future of DCC Analysis

Disoriented Chiral Condensates (DCC) have been predicted to form in high energy heavy ion collisions where the approximate chiral symmetry of QCD has been restored. This leads to large imbalances in the production of charged to neutral pions. Sophisticated analysis methods are being developed to disentangle DCC events out of the large background of events with conventionally produced particles. We present a short review of current analysis methods and future prospects.Comment: 12 pages, 5 figures. Invited talk presented at the 13th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 97), Tsukuba, Japan, 1-5 Dec 199

Particle density fluctuations

Event-by-event fluctuations in the multiplicities of charged particles and photons at SPS energies are discussed. Fluctuations are studied by controlling the centrality of the reaction and rapidity acceptance of the detectors. Results are also presented on the event-by-event study of correlations between the multiplicity of charged particles and photons to search for DCC-like signals.Comment: Talk presented at Quark Matter 2002, Nantes, Franc

Search for DCC in 158A GeV Pb+Pb Collisions

A detailed analysis of the phase space distributions of charged particles and photons have been carried out using two independent methods. The results indicate the presence of nonstatistical fluctuations in localized regions of phase space.Comment: Talk at the PANIC99 Conference, June 9-16, 199

Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration

Extensive experimental data from high-energy nucleus-nucleus collisions were recorded using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The comprehensive set of measurements from the first three years of RHIC operation includes charged particle multiplicities, transverse energy, yield ratios and spectra of identified hadrons in a wide range of transverse momenta (p_T), elliptic flow, two-particle correlations, non-statistical fluctuations, and suppression of particle production at high p_T. The results are examined with an emphasis on implications for the formation of a new state of dense matter. We find that the state of matter created at RHIC cannot be described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted to Nuclear Physics A as a regular article; v3 has minor changes in response to referee comments. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm