Aspects of Symmetry in de Sitter Space

We study various aspects of symmetry in four-dimensional de Sitter space (dS$_4$).Physic

The Open Cluster NGC 7789: I. Radial Velocities for Giant Stars

A total of 597 radial-velocity observations for 112 stars in the ~1.6 Gyr old open cluster NGC 7789 have been obtained since 1979 with the radial velocity spectrometer at the Dominion Astrophysical Observatory. The mean cluster radial velocity is -54.9 +/- 0.12 km/s and the dispersion is 0.86 km/s, from 50 constant-velocity stars selected as members from this radial-velocity study and the proper motion study of McNamara and Solomon (1981). Twenty-five stars (32%) among 78 members are possible radial-velocity variable stars, but no orbits are determined because of the sparse sampling. Seventeen stars are radial-velocity non-members, while membership estimates of six stars are uncertain. There is a hint that the observed velocity dispersion falls off at large radius. This may due to the inclusion of long-period binaries preferentially in the central area of the cluster. The known radial-velocity variables also seem to be more concentrated toward the center than members with constant velocity. Although this is significant at only the 85% level, when combined with similar result of Raboud and Mermilliod (1994) for three other clusters, the data strongly support the conclusion that mass segregation is being detected.Comment: 16 pages (including 3 figures) and 3 table

Structural contributions to the pressure-tuned charge-density-wave to superconductor transition in ZrTe3: Raman scattering studies

Superconductivity evolves as functions of pressure or doping from charge-ordered phases in a variety of strongly correlated systems, suggesting that there may be universal characteristics associated with the competition between superconductivity and charge order in these materials. We present an inelastic light (Raman) scattering study of the structural changes that precede the pressure-tuned charge-density-wave (CDW) to superconductor transition in one such system, ZrTe3. In certain phonon bands, we observe dramatic linewidth reductions that accompany CDW formation, indicating that these phonons couple strongly to the electronic degrees of freedom associated with the CDW. The same phonon bands, which represent internal vibrations of ZrTe3 prismatic chains, are suppressed at pressures above ~10 kbar, indicating a loss of long-range order within the chains, specifically amongst intrachain Zr-Te bonds. These results suggest a distinct structural mechanism for the observed pressure-induced suppression of CDW formation and provide insights into the origin of pressure-induced superconductivity in ZrTe3.Comment: 6 pages, 5 figure

State/Operator Correspondence in Higher-Spin dS/CFT

A recently conjectured microscopic realization of the dS$_4$/CFT$_3$ correspondence relating Vasiliev's higher-spin gravity on dS$_4$ to a Euclidean $Sp(N)$ CFT$_3$ is used to illuminate some previously inaccessible aspects of the dS/CFT dictionary. In particular it is argued that states of the boundary CFT$_3$ on $S^2$ are holographically dual to bulk states on geodesically complete, spacelike $R^3$ slices which terminate on an $S^2$ at future infinity. The dictionary is described in detail for the case of free scalar excitations. The ground states of the free or critical $Sp(N)$ model are dual to dS-invariant plane-wave type vacua, while the bulk Euclidean vacuum is dual to a certain mixed state in the CFT$_3$. CFT$_3$ states created by operator insertions are found to be dual to (anti) quasinormal modes in the bulk. A norm is defined on the $R^3$ bulk Hilbert space and shown for the scalar case to be equivalent to both the Zamolodchikov and pseudounitary C-norm of the $Sp(N)$ CFT$_3$.Comment: 24 page

Incompressible Fluids of the de Sitter Horizon and Beyond

There are (at least) two surfaces of particular interest in eternal de Sitter space. One is the timelike hypersurface constituting the lab wall of a static patch observer and the other is the future boundary of global de Sitter space. We study both linear and non-linear deformations of four-dimensional de Sitter space which obey the Einstein equation. Our deformations leave the induced conformal metric and trace of the extrinsic curvature unchanged for a fixed hypersurface. This hypersurface is either timelike within the static patch or spacelike in the future diamond. We require the deformations to be regular at the future horizon of the static patch observer. For linearized perturbations in the future diamond, this corresponds to imposing incoming flux solely from the future horizon of a single static patch observer. When the slices are arbitrarily close to the cosmological horizon, the finite deformations are characterized by solutions to the incompressible Navier-Stokes equation for both spacelike and timelike hypersurfaces. We then study, at the level of linearized gravity, the change in the discrete dispersion relation as we push the timelike hypersurface toward the worldline of the static patch. Finally, we study the spectrum of linearized solutions as the spacelike slices are pushed to future infinity and relate our calculations to analogous ones in the context of massless topological black holes in AdS$_4$.Comment: 27 pages, 8 figure

On the effective Stefan-Boltzmann law and the thermodynamic origin of the initial radiation density in warm inflation

In this presentation, we are going to explain the thermodynamic origin of warm inflation scenarios by using the effetive Stefan-Boltzmann law. In the warm inflation scenarios, radiation always exists to avoid the graceful exit problem, for which the radiation energy density should be assumed to be finite at the starting point of the warm inflation. To find out the origin of the non-vanishing initial radiation energy density, we derive an effective Stefan-Boltzmann law by considering the non-vanishing trace of the total energy-momentum tensors. The effective Stefan-Boltzmann law successfully shows where the initial radiation energy density is thermodynamically originated from. And by using the above effective Stefan-Boltzmann law, we also study the cosmological scalar perturbation, and obtain the sufficient radiation energy density in order for GUT baryogenesis at the end of inflation. This proceeding is based on Ref. [1

Open-end winding induction machine fed by a dual-output indirect matrix converter

Open-ended winding induction machines fed from standard two-level Voltage Source Inverters (VSI) provide an attractive arrangement for AC drives. An alternative approach is to use a dual output Indirect Matrix Converter (IMC). It is well known that the IMC provides fully bidirectional power flow operation, with small input size filter requirements. Whilst a standard IMC consists of an AC-DC matrix converter input stage followed by a single VSI output stage, it is possible to replicate the VSI to produce multiple outputs. In this paper an open-end winding induction machine fed by an IMC with two output stages is presented. The IMC modulation strategy aims to reduce the common-mode voltage whilst compensating any zero sequence voltage fed to the machine. The system is modeled using a PSIM and MATLAB/Simulink platform. Experimental results demonstrating the viability of the method are presented using a 7.5 kW prototype

Cassini RADAR Sequence Planning and Instrument Performance

The Cassini RADAR is a multimode instrument used to map the surface of Titan, the atmosphere of Saturn, the Saturn ring system, and to explore the properties of the icy satellites. Four different active mode bandwidths and a passive radiometer mode provide a wide range of flexibility in taking measurements. The scatterometer mode is used for real aperture imaging of Titan, high-altitude (around 20 000 km) synthetic aperture imaging of Titan and Iapetus, and long range (up to 700 000 km) detection of disk integrated albedos for satellites in the Saturn system. Two SAR modes are used for high- and medium-resolution (300-1000 m) imaging of Titan's surface during close flybys. A high-bandwidth altimeter mode is used for topographic profiling in selected areas with a range resolution of about 35 m. The passive radiometer mode is used to map emission from Titan, from Saturn's atmosphere, from the rings, and from the icy satellites. Repeated scans with differing polarizations using both active and passive data provide data that can usefully constrain models of surface composition and structure. The radar and radiometer receivers show very good stability, and calibration observations have provided an absolute calibration good to about 1.3 dB. Relative uncertainties within a pass and between passes can be even smaller. Data are currently being processed and delivered to the planetary data system at quarterly intervals one year after being acquired

Increased Th17-Related Cytokine Serum Levels in Patients With Multiple Polyps of Unexplained Origin

OBJECTIVES: Most patients with multiple colonic polyps do not have a known genetic or hereditary origin. Our aim was to analyze the presence of inflammatory cytokines and levels of glucose, insulin, and C-reactive protein (CRP) in patients with multiple colonic polyps. METHODS: Eighty-three patients with 10 or more adenomatous or serrated polyps and 53 control people with normal colonoscopy were included. Smoking habits were registered, and glucose, CRP, and basal insulin in the serum/blood were measured. Quantification of IL-2, IL-4, IL-6, IL-10, IL-11, IL-17A, and IL-23 cytokine levels in the serum was performed by a high-sensitivity enzyme-linked immunosorbent assay. RESULTS: Smoking and diabetes were more prevalent in those with colonic polyps than in the control people (67% vs 16%, P = 0.001; 11% vs 2%, P = 0.048). In addition, the cytokine serum levels were higher, i.e., IL-2 (P = 0.001), IL-4 (P = 0.001), IL-6 (P = 0.001), IL-17A (P = 0.001), IL-23 (P = 0.014), and CRP (P = 0.003). Adjusting for sex, smoking, and diabetes in a multivariate analysis, IL-2, IL-4, IL-6, IL-17A, and IL-23 remained independently elevated in cases with multiple polyps. DISCUSSION: These results indicate that immune responses mediated by Th17 cells may be involved in the pathogenesis of multiple colonic polyps