Analysis of scalar and fermion quantum field theory on anti-de Sitter spacetime

We study vacuum and thermal expectation values of quantum scalar and fermion fields on anti-de Sitter space-time. Anti-de Sitter space-time is maximally symmetric and this enables expressions for the scalar and fermion vacuum Feynman Green's functions to be derived in closed form. We employ Hadamard renormalization to find the vacuum expectation values. The thermal Feynman Green's functions are constructed from the vacuum Feynman Green's functions using the imaginary time periodicity/anti-periodicity property for scalars/fermions. Focussing on massless fields with either conformal or minimal coupling to the space-time curvature (these two cases being the same for fermions) we compute the differences between the thermal and vacuum expectation values. We compare the resulting energy densities, pressures and pressure deviators with the corresponding classical quantities calculated using relativistic kinetic theory

Establishing the Range of Applicability of Hydrodynamics in High-Energy Collisions

We simulate the space-time dynamics of high-energy collisions based on a microscopic kinetic description in the conformal relaxation time approximation, in order to determine the range of applicability of an effective description in relativistic viscous hydrodynamics. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number is sufficiently small and the early pre-equilibrium stage is properly accounted for. We further discuss the implications of our findings for the (in)applicability of hydrodynamics in proton-proton, proton-nucleus and light nucleus collisions.Comment: 9 pages, 4 figures v2: Several minor changes to spelling, notation, affiliations, acknowledgements, references. Moved Supplemental Material to end of document. Equivalent to version published in PR

A low-cost test-bed for real-time landmark tracking

A low-cost vehicle test-bed system was developed to iteratively test, refine and demonstrate navigation algorithms before attempting to transfer the algorithms to more advanced rover prototypes. The platform used here was a modified radio controlled (RC) car. A microcontroller board and onboard laptop computer allow for either autonomous or remote operation via a computer workstation. The sensors onboard the vehicle represent the types currently used on NASA-JPL rover prototypes. For dead-reckoning navigation, optical wheel encoders, a single axis gyroscope, and 2-axis accelerometer were used. An ultrasound ranger is available to calculate distance as a substitute for the stereo vision systems presently used on rovers. The prototype also carries a small laptop computer with a USB camera and wireless transmitter to send real time video to an off-board computer. A real-time user interface was implemented that combines an automatic image feature selector, tracking parameter controls, streaming video viewer, and user generated or autonomous driving commands. Using the test-bed, real-time landmark tracking was demonstrated by autonomously driving the vehicle through the JPL Mars yard. The algorithms tracked rocks as waypoints. This generated coordinates calculating relative motion and visually servoing to science targets. A limitation for the current system is serial computing−each additional landmark is tracked in order−but since each landmark is tracked independently, if transferred to appropriate parallel hardware, adding targets would not significantly diminish system speed

BIPHASIC PATTERN OF THYMUS REGENERATION AFTER WHOLE-BODY IRRADIATION

Whole-body irradiation of mice with 300 or 400 R causes a precipitous fall in thymus weight, followed by an increase in the mitotic index and an almost complete restoration of thymus mass. This phase is followed by a secondary fall in thymus weight and gradual recovery. This secondary fall can be prevented by intravenous injection of bone marrow or shielding of the hind limbs during irradiation. The hypothesis is proposed that the thymus depends on the migration of cells from the bone marrow to the thymus for the maintenance of its cell population. Bone marrow cells with chromosome markers injected intravenously into normal or lightly irradiated (150 R) animals do not populate the host bone marrow to any significant degree. After whole-body irradiation with heavy doses (400 R), donor cells dominate the marrow. There may be a competition between dividing cells in the bone marrow which regulates proliferation of hemic cells. Bone marrow cells with marker chromosomes do not repopulate the thymus in irradiated animals until long after repopulating the bone marrow. It is possible that these cells have to pass through the marrow or the blood-marrow barrier to acquire characteristics needed for entering the thymus. After whole-body irradiation with 500 R or more, the first phase of regeneration of the thymus, represented by an increase in the mitotic index, does not occur to a significant degree. Apparently cells in the thymus capable of proliferation have been largely eliminated, and restoration of organ mass depends chiefly on seeding from other sources, probably the bone marrow. After whole-body irradiation with 200 R, only the first phase of thymus weight loss and regeneration takes place. Probably bone marrow injury is too small to interfere with the supply of cells repopulating the thymus

Structure and Magnetic Properties of the Radical Cation Salt of a TTF-based NiII Complex

Chemical oxidation of a TTF-based NiII complex with I2 produces the corresponding radical cation salt 1, [Ni2Cl2(L)2](I3)2(I5)2(I2)(H2O)2(C4H8O)3, (L=4,5-bis(2-pyridylmethylsulfanyl)-4',5'-ethylenedithiotetrathiafulvalene). The results of magnetic susceptibility measurements show the occurrence of intramolecular magnetic exchange interactions in 1. The lack of close S···S contacts, confirmed by crystal structure analysis, results in an insulating behavio

Quantum superposition principle and gravitational collapse: Scattering times for spherical shells

A quantum theory of spherically symmetric thin shells of null dust and their gravitational field is studied. In Nucl. Phys. 603 (2001) 515 (hep-th/0007005), it has been shown how superpositions of quantum states with different geometries can lead to a solution of the singularity problem and black hole information paradox: the shells bounce and re-expand and the evolution is unitary. The corresponding scattering times will be defined in the present paper. To this aim, a spherical mirror of radius R_m is introduced. The classical formula for scattering times of the shell reflected from the mirror is extended to quantum theory. The scattering times and their spreads are calculated. They have a regular limit for R_m\to 0 and they reveal a resonance at E_m = c^4R_m/2G. Except for the resonance, they are roughly of the order of the time the light needs to cross the flat space distance between the observer and the mirror. Some ideas are discussed of how the construction of the quantum theory could be changed so that the scattering times become considerably longer.Comment: 30 pages and 5 figures; the post-referee version: shortened and some formulations improved; to be published in Physical Revie

Robot-Assisted Hybrid Esophagectomy Is Associated with a Shorter Length of Stay Compared to Conventional Transthoracic Esophagectomy:A Retrospective Study

Aim. To compare the peri- and postoperative data between a hybrid minimally invasive esophagectomy (HMIE) and the conventional Ivor Lewis esophagectomy. Methods. Retrospective comparison of perioperative characteristics, postoperative complications, and survival between HMIE and Ivor Lewis esophagectomy. Results. 216 patients were included, with 160 procedures performed with the conventional and 56 with the HMIE approach. Lower perioperative blood loss was found in the HMIE group (600 ml versus 200 ml, p<0.001). Also, a higher median number of lymph nodes were harvested in the HMIE group (median 28) than in the conventional group (median 23) (p=0.002). The median length of stay was longer in the conventional group compared to the HMIE group (11.5 days versus 10.0 days, p=0.03). Patients in the HMIE group experienced fewer grade 2 or higher complications than the conventional group (39% versus 57%, p=0.03). The rate of all pulmonary (51% versus 43%, p=0.32) and severe pulmonary complications (38% versus 18%, p = 0.23) was not statistically different between the groups. Conclusions. The HMIE was associated with lower intraoperative blood loss, a higher lymph node harvest, and a shorter hospital stay. However, the inborn limitations with the retrospective design stress a need for prospective randomized studies. Registration number is DRKS00013023

Embedding variables in finite dimensional models

Global problems associated with the transformation from the Arnowitt, Deser and Misner (ADM) to the Kucha\v{r} variables are studied. Two models are considered: The Friedmann cosmology with scalar matter and the torus sector of the 2+1 gravity. For the Friedmann model, the transformations to the Kucha\v{r} description corresponding to three different popular time coordinates are shown to exist on the whole ADM phase space, which becomes a proper subset of the Kucha\v{r} phase spaces. The 2+1 gravity model is shown to admit a description by embedding variables everywhere, even at the points with additional symmetry. The transformation from the Kucha\v{r} to the ADM description is, however, many-to-one there, and so the two descriptions are inequivalent for this model, too. The most interesting result is that the new constraint surface is free from the conical singularity and the new dynamical equations are linearization stable. However, some residual pathology persists in the Kucha\v{r} description.Comment: Latex 2e, 29 pages, no figure