Simulations of Contrail Optical Properties and Radiative Forcing for Various Crystal Shapes

The aim of this study is to investigate the sensitivity of radiative-forcing computations to various contrail crystal shape models. Contrail optical properties in the shortwave and longwave ranges are derived using a ray-tracing geometric method and the discrete dipole approximation method, respectively. Both methods present good correspondence of the single-scattering albedo and the asymmetry parameter in a transition range (3–8 µm). There are substantial differences in single-scattering properties among 10 crystal models investigated here (e.g., hexagonal columns and plates with different aspect ratios, and spherical particles). The single-scattering albedo and the asymmetry parameter both vary by up to 0.1 among various crystal shapes. The computed single-scattering properties are incorporated in the moderate-resolution atmospheric radiance and transmittance model(MODTRAN) radiative transfer code to simulate solar and infrared fluxes at the top of the atmosphere. Particle shapes have a strong impact on the contrail radiative forcing in both the shortwave and longwave ranges. The differences in the net radiative forcing among optical models reach 50% with respect to the mean model value. The hexagonal-column and hexagonal-plate particles show the smallest net radiative forcing, and the largest forcing is obtained for the spheres. The balance between the shortwave forcing and longwave forcing is highly sensitive with respect to the assumed crystal shape and may even change the sign of the net forcing. The optical depth at which the mean diurnal radiative forcing changes sign from positive to negative varies from 4.5 to 10 for a surface albedo of 0.2 and from 2 to 6.5 for a surface albedo of 0.05. Contrails are probably never that optically thick (except for some aged contrail cirrus), however, and so will not have a cooling effect on climate

VELO-TT track reconstruction

The paper describes the track reconstruction in the system of VELO and TT detectors. Two separate algorithms for off-line and on-line approaches were merged. The single algorithm consists of the common code for pattern recognition and two parts specific to off-line and on-line functionalities. The note presents the performance in terms of track reconstruction efficiency and ghost rate

Numerical relativity in higher dimensions

We give a status report on our project targeted at performing numerical simulations of a head-on collision of non-spinning black holes in higher dimensional non-compact space-times. These simulations should help us understand black objects in higher dimensions and their stability properties. They are also relevant for the problem of black hole formation and evaporation in particle accelerators and cosmic rays. We use the symmetries of the system to reduce the problem to an effective 3+1 problem, allowing the use of existing numerical codes. As a simple application of the formalism, we present the results for the evolution of a five dimensional single black hole space-time. © 2010 IOP Publishing Ltd

Measurement of g-factor tensor in a quantum dot and disentanglement of exciton spins

We perform polarization-resolved magneto-optical measurements on single InAsP quantum dots embedded in an InP nanowire. In order to determine all elements of the electron and hole $g$-factor tensors, we measure in magnetic field with different orientations. The results of these measurements are in good agreement with a model based on exchange terms and Zeeman interaction. In our experiment, polarization analysis delivers a powerful tool that not only significantly increases the precision of the measurements, but also enables us to probe the exciton spin state evolution in magnetic fields. We propose a disentangling scheme of heavy-hole exciton spins enabling a measurement of the electron spin $T_2$ time

Primary vertex reconstruction

This report reviews the improved method of primary vertex off-line reconstruction. The new method for primary vertex seed finding as well as modified procedure for vertex fit have been briefly described. Results of the primary vertex reconstruction performance are presented and compared to the previous version of the package. Improvement in the primary vertex reconstruction efficiencies is observed. Small but statistically significant bias, coming mostly from the long-living tracks as well as from a bias of the Velo measurements present in the DC06 simulation, affects the determination of the primary vertex position along the beam direction

Head-on collisions of unequal mass black holes in D=5 dimensions

We study head-on collisions of unequal mass black hole binaries in D=5 space-time dimensions, with mass ratios between 1:1 and 1:4. Information about gravitational radiation is extracted by using the Kodama-Ishibashi gauge-invariant formalism and details of the apparent horizon of the final black hole. For the first time, we present waveforms, total integrated energy and momentum for this process. Our results show surprisingly good agreement, within 5% or less, with those extrapolated from linearized, point-particle calculations. Our results also show that consistency with the area theorem bound requires that the same process in a large number of spacetime dimensions must display new features.Comment: 10 pages, 5 figures, RevTex4. v2: Published versio

Spin-induced dynamical scalarization, de-scalarization and stealthness in scalar-Gauss-Bonnet gravity during black hole coalescence

Particular couplings between a scalar field and the Gauss-Bonnet invariant lead to spontaneous scalarization of black holes. Here we continue our work on simulating this phenomenon in the context of binary black hole systems. We consider a negative coupling for which the black-hole spin plays a major role in the scalarization process. We find two main phenomena: (i) dynamical descalarization, in which initially scalarized black holes form an unscalarized remnant, and (ii) dynamical scalarization, whereby the late merger of initially unscalarized black holes can cause scalar hair to grow. An important consequence of the latter case is that modifications to the gravitational waveform due to the scalar field may only occur post-merger, as its presence is hidden during the entirety of the inspiral. However, with a sufficiently strong coupling, we find that scalarization can occur before the remnant has even formed. We close with a discussion of observational implications for gravitational-wave tests of general relativity

Numerical relativity for D dimensional axially symmetric space-times: formalism and code tests

The numerical evolution of Einstein's field equations in a generic background has the potential to answer a variety of important questions in physics: from applications to the gauge-gravity duality, to modelling black hole production in TeV gravity scenarios, analysis of the stability of exact solutions and tests of Cosmic Censorship. In order to investigate these questions, we extend numerical relativity to more general space-times than those investigated hitherto, by developing a framework to study the numerical evolution of D dimensional vacuum space-times with an SO(D-2) isometry group for D\ge 5, or SO(D-3) for D\ge 6. Performing a dimensional reduction on a (D-4)-sphere, the D dimensional vacuum Einstein equations are rewritten as a 3+1 dimensional system with source terms, and presented in the Baumgarte, Shapiro, Shibata and Nakamura (BSSN) formulation. This allows the use of existing 3+1 dimensional numerical codes with small adaptations. Brill-Lindquist initial data are constructed in D dimensions and a procedure to match them to our 3+1 dimensional evolution equations is given. We have implemented our framework by adapting the LEAN code and perform a variety of simulations of non-spinning black hole space-times. Specifically, we present a modified moving puncture gauge which facilitates long term stable simulations in D=5. We further demonstrate the internal consistency of the code by studying convergence and comparing numerical versus analytic results in the case of geodesic slicing for D=5,6.Comment: 31 pages, 6 figures; v2 Minor changes and added two references. Matches the published version in PRD