Constraining the Cosmological Parameters and Transition Redshift with Gamma-Ray Bursts and Supernovae

A new method of measuring cosmology with gamma-ray bursts(GRBs) has been proposed by Liang and Zhang recently. In this method, only observable quantities including the rest frame peak energy of the \nu F_\nu spectrum (E'_p), the isotropic energy of GRB (E_{\gamma,iso}), and the break time of the optical afterglow light curves in the rest frame (t'_b) are used. By considering this method we constrain the cosmological parameters and the redshift at which the universe expanded from the deceleration to acceleration phase. We add five recently-detected GRBs to the sample and derive E_{\gamma, iso}/10^{52} ergs=(0.93\pm 0.25)\times (E'_p/100 keV)^{1.91\pm 0.32}\times (t'_b/day)^{-0.93\pm 0.38} for a flat cosmology with \Omega_M=0.28 and H_0=71.0 km s^{-1} Mpc^{-1}. This relation is independent of the medium density around bursts and the efficiency of conversion of the explosion energy to gamma-ray energy that are difficult to measure. We regard the E_{\gamma,iso}(E'_p, t'_b) relationship as a standard candle and find 0.05<\Omega_M<0.48 and \Omega_\Lambda<1.15 (at the 1\sigma confidence level). In a flat universe with the cosmological constant we obtain 0.25<\Omega_M <0.46 and 0.54<\Omega_\Lambda<0.78 at the 1\sigma confidence level. The transition redshift is z_T=0.69_{-0.12}^{+0.11}. Combining 20 GRBs and 157 type Ia supernovae, we find \Omega_M=0.29 \pm0.03 for a flat universe and the transition redshift is z_T=0.61_{-0.05}^{+0.06}, which is slightly larger than the value found by considering SNe Ia alone. In particular, We also discuss several dark-energy models in which the equation of state w(z) is arameterized and investigate constraints on the cosmological parameters in detail.Comment: Revised version based on the referee's comments, added references, MNRAS in pres

Lost Relatives of the Gumbel Trick

The Gumbel trick is a method to sample from a discrete probability distribution, or to estimate its normalizing partition function. The method re- lies on repeatedly applying a random perturbation to the distribution in a particular way, each time solving for the most likely configuration. We derive an entire family of related methods, of which the Gumbel trick is one member, and show that the new methods have superior properties in several settings with minimal additional computational cost. In particular, for the Gumbel trick to yield computational benefits for discrete graphical models, Gumbel perturbations on all configurations are typically replaced with so- called low-rank perturbations. We show how a subfamily of our new methods adapts to this set- ting, proving new upper and lower bounds on the log partition function and deriving a family of sequential samplers for the Gibbs distribution. Finally, we balance the discussion by showing how the simpler analytical form of the Gumbel trick enables additional theoretical results.Alan Turing Institute under EPSRC grant EP/N510129/1, and by the Leverhulme Trust via the CFI

The weak field limit of quantum matter back-reacting on classical spacetime

Consistent coupling of quantum and classical degrees of freedom exists so long as there is both diffusion of the classical degrees of freedom and decoherence of the quantum system. In this paper, we derive the Newtonian limit of such classical-quantum (CQ) theories of gravity. Our results are obtained both via the gauge fixing of the recently proposed path integral theory of CQ general relativity and via the CQ master equation approach. In each case, we find the same weak field dynamics. We find that the New-tonian potential diffuses by an amount lower bounded by the decoherence rate into mass eigenstates. We also present our results as an unraveled system of stochastic differential equations for the trajectory of the hybrid classical-quantum state and provide a series of kernels for constructing figures of merit, which can be used to rule out part of the parameter space of classical-quantum theories of gravity by experimentally testing it via the decoherence-diffusion trade-off. We compare and contrast the weak field limit to previous models of classical Newtonian gravity coupled to quantum systems. Here, we find that the Newtonian potential and quantum state change in lock-step, with the flow of time being stochastic

Hydrodynamic response of a submerged tunnel element suspended from a twin-barge under random waves

It is possible that the excessive dynamic responses of tunnel elements could jeopardize the safety and accuracy of installation procedures used during subsea tunnel construction. To investigate the motion characteristics of the tunnel element, experimental measurements of a moored tunnel element suspended from a twin-barge were conducted in a wave flume at a geometric scale of 1:50. A corresponding numerical model was developed to simulate the dynamic response of the tunnel-barge system in realistic sea conditions, using hydrodynamic parameters from a radiation/diffraction potential model. Multiple linear wave conditions and three immersion depths were tested. The results indicate that the motion response of the tunnel element increases with decreasing immersion depth, and the natural periods of the tunnel, barge and combined tunnel-barge system play key roles in the influence of wave conditions on the motions of the tunnel. It was found that the low-frequency motion of the tunnel element is large in small wave periods. The mooring system under such conditions needs to be considered carefully during system design in order to safely control the motions of the tunnel-barge system in energetic ocean environments.The work is supported by the National Natural Science Foundation of China (Grant No.11272079), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51221961) and the China Scholarship Council (award to Yang Can for 1 year’s study abroad at the University of Exeter)

Experimental and numerical investigation on coupled motion characteristics of a tunnel element suspended from a twin-barge

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThe coupled motion characteristics of a tunnel element, which is suspended from a twin-barge and moored to the seabed during the installation process, has been investigated using a 1:50 scaled model. Response characteristics are obtained for multiple regular wave conditions and three different immersion depths. Experimental investigation includes studies to identify system properties of individual arrangements (tunnel, twin-barge) and for the coupled tunnel & twin-barge configuration. Investigation of motion characteristics includes i) experimental studies of the tunnel element from a fixed suspension point and barge, ii) experimental studies with and without a mooring arrangement from the tunnel element to the seabed, iii) experimental study of the fully coupled tunnel & twin-barge configuration, and iv) numerical investigation of the fully coupled tunnel & twin-barge configuration using a commercial fully dynamic mooring simulation software (OrcaFlex™). The experimental investigations were carried out in the State Key Laboratory of Coastal and Offshore Engineering at Dalian University of Technology (DUT), using the ‘6-D Measurement System’ (6D-UMS) to obtain six degree of motions for both the tunnel and twin-barge. For the numerical study hydrodynamic properties were obtained from the diffraction/radiation potential code WAMIT for simplified tunnel and twin-barge elements and used to derive fully coupled motion behavior using the time-domain mooring simulation software OrcaFlex™. The results are presented in order to provide insights into the motion characteristics for the different configurations studied. The main findings indicate that the sway and roll motions for the coupled tunnel & twin-barge configuration decrease with increasing wave incidence angle and immersion depths. The use of additional mooring lines to restrain the tunnel element to the seabed played a further role in reducing the motions of the tunnel element, particularly when subjected to large amplitude and long period waves.The study is supported by the National Natural Science Foundation of China (Grant No.11272079) and the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51221961) and the China Scholarship Council (award to Yang Can for 1 year's study abroad at the University of Exeter). The corresponding author has been partly funded through EPSRC grant EP/R007519/1

Singlet Ground State and Magnetization Plateaus in Ba3_3Mn2_2O8_8

Magnetic susceptibility and the magnetization process have been measured in \green polycrystal. In this compound, the magnetic manganese ion exists as Mn$^{5+}$ in a tetrahedral environment, and thus the magnetic interaction can be described by an S=1 Heisenberg model. The ground state was found to be a spin singlet with an excitation gap $\Delta/k_{\rm B}=11.2$ K. Magnetization plateaus were observed at zero and at half of the saturation magnetization. These results indicate that the present system can be represented by a coupled antiferromagnetic dimer model.Comment: 4 pages, 4 figures, jpsj styl

Coherent photonuclear reactions for isotope transmutation

Coherent photonuclear isotope transmutation (CPIT) produces exclusively radioactive isotopes (RIs) by coherent photonuclear reactions via E1 giant resonances. Photons to be used are medium energy photons produced by laser photons backscattered off GeV electrons. The cross sections are as large as 0.2 - 0.6 b, being independent of individual nuclides. A large fraction of photons is effectively used for the photonuclear reactions, while the scattered GeV electrons remain in the storage ring to be re-used. CPIT with medium energy photons provides specific/desired RIs with the high rate and the high density for nuclear science, molecular biology and for nuclear medicines.Comment: 8 pages, 2 figure

One year of aerosol refractive index measurement from a coastal Antarctic site

Climate change model evaluations need a better understanding of the atmo- spheric aerosols' optical properties and with this of the refractive index (RI) of atmospheric aerosols as well. Due to the remoteness of Antarctica only a very few data on the refractive index exists from there. In this paper we calculate the real refractive index of atmospheric aerosols from number size distribution measurements at a coastal Antarctic measurement site. In our calculations we used the overlapping size range (120-340 nm) of a scanning mobility sizer (SMPS), which sizes the particles by their electrical mobility, and a laser aerosol spectrometer (LAS), which sizes the particles by their optical scattering signal. Based on almost a complete year of measurement and 2439 measurement points, the average effective refractive index (RIeff) turned out to be 1.44. This is in a good agreement with the RI value of 1.47 which we derived from the chemical composition filter measurements. At our measurement site the aerosol has a very characteristic seasonal pattern in both number concentration and chemical composition. Despite this, we could not identify any significant sea- sonal variability in the effective refractive index, the monthly averages remain within the range of 1.40-1.50. Two austral winter months June and September has a slightly higher average values (1.50 and 1.47). We could not identify any in uence of the occurring wind direction on the retrieved RIeff either. For the few examples of north winds coming from the Neumayer station (occurs very rarely, this is the reason why the measurement site was built to the south), we don't see different values than for the other wind directions. During an artificial, high contamination episode, when diesel engines were operated right next to the measurement site, we had an hour of constant conditions such that one RI fit was possible. This fit resulted in an unusual high RI of 1.59, which is most probably due to the high black carbon content of the diesel engine emission. Therefore, we also assume that even during northerly wind directions we did not have significant in uence from the Neumayer station. During a shorter period between 2017 December and 2018 January we used the time averaged LAS and SMPS number size distributions to get some in- formation on the size dependency of the refractive index. The RI was fit in 5 different particle size ranges, and we have found a slight decrease of the re- fractive index with the particle size from 1.47 in the 116-168 nm to 1.37 in the 346-478 nm range

Evolution of density perturbations in double exponential quintessence models

In this work we investigate the evolution of matter density perturbations for quintessence models with a self-interaction potential that is a combination of exponentials. One of the models is based on the Einstein theory of gravity, while the other is based on the Brans-Dicke scalar tensor theory. We constrain the parameter space of the models using the determinations for the growth rate of perturbations derived from data of the 2-degree Field Galaxy Redshift Survey.Comment: 5 pages, 3 eps figure

Percolation limited magnetic order in Eu1-xCaxB6

Abstract.: We report the results of measurements of the low-temperature specific heat Cp(T) and the ac susceptibility χac(T) in low applied magnetic fields for a series of samples of Eu1-xCaxB6. The anomalies in Cp(T), together with the results for χac(T) and M(H), confirm the onset of phase transitions to long range magnetic order for x < 0.7 and provide evidence that for x ≥ 0.7, the Eu moments, which are captured in large magnetic clusters with magnetic moments of the order of 260 μB, adopt a spin-glass type ground state. The data set allows to establish the low-temperature [ T,x] phase diagram of this alloy serie