Renormalization group analysis of the three-dimensional Gross-Neveu model at finite temperature and density

The Renormalization Group flow equations obtained by means of a proper time regulator are used to analyze the restoration of the discrete chiral symmetry at non-zero density and temperature in the Gross-Neveu model in d=2+1 dimensions. The effects of the wave function renormalization of the auxiliary scalar field on the transition have been studied. The analysis is performed for a number of fermion flavors N_f=12 and the limit of large N_f is also considered. The results are compared with those coming from lattice simulations.Comment: Latex file, 12 pages, 2 eps figures, minor changes, added references, published versio

A universal scaling law for the evolution of granular gases

Dry, freely evolving granular materials in a dilute gaseous state coalesce into dense clusters only due to dissipative interactions. This clustering transition is important for a number of problems ranging from geophysics to cosmology. Here we show that the evolution of a dilute, freely cooling granular gas is determined in a universal way by the ratio of inertial flow and thermal velocities, that is, the Mach number. Theoretical calculations and direct numerical simulations of the granular Navier--Stokes equations show that irrespective of the coefficient of restitution, density or initial velocity distribution, the density fluctuations follow a universal quadratic dependence on the system's Mach number. We find that the clustering exhibits a scale-free dynamics but the clustered state becomes observable when the Mach number is approximately of $\mathcal{O}(1)$. Our results provide a method to determine the age of a granular gas and predict the macroscopic appearance of clusters

The Development of a Novel Silicon on Insulator Microdosimeter with Sensitive Volumes Modeled after Living Cells

Purpose: The purpose of this work was to test the feasibility of using a silicon on insulator microdosimeter, which mimics the size and shape of particular cells within the human body, to determine dose equivalent from a 239PuBe neutron source with uncertainty less than 10%. Methods: A batch of microdosimeters were analyzed in terms of their physical surface conditions and basic diode characteristics such as leakage current as a function of bias voltage, to select those with the best performance. A calibration protocol was developed utilizing an 241Am alpha particle source and a reference tail pulse generator. Neutron spectra were acquired using two different converter layers placed atop the microdosimeter: a tissue-substitute converter made from high-density polyethylene, and a boron converter consisting of epoxy coated with boron powder. To compare the experimental results, a Monte Carlo code was written to simulate the alpha particle and neutron irradiations. Dose equivalent was determined using an average quality factor calculated for each spectrum on the basis of the ICRU definition (1986). Results: Using the tissue-substitute converter, the cell-shaped microdosimeters were able to determine dose equivalent with uncertainty less than 10%. However, uncertainties were 13.5% when using the boron converter. Conclusion: The cell-shaped silicon on insulator microdosimeters proved feasible for further research and development. With higher quality silicon chips, this type of microdosimeter could become a simple, small, and lightweight device to determine dose equivalent in real-time and to provide improved radiation protection for radiotherapy patients and personnel who are occupationally exposed to radiation

Software/Hardware Tradeoffs in the Speedup of Color Image Processing Algorithms

Data parallel image processing algorithms have numerous uses in many real time applications. Depending on the complexity of the computations involved, these algorithms may take considerable amounts of time to complete. Since the algorithms are performed in real time, the end user is negatively impacted by the extended execution times. Fortunately, there are many different ways available in hardware and software to improve the speed of these algorithms. This thesis looks at several different methods of improving the speedup of color image processing algorithms and compares the tradeoffs among them. The methods for increasing the execution time of an algorithm include implementing Single Input Multiple Data (SIMD) instructions, using Posix threads to code across several processors, and using a stream based multichannel framework to implement the algorithms on an FPGA. Each of the above methods had advantages and disadvantages, yet all approaches were found to introduce a significant speedup over the single core baseline tests. These methods were completed on a number of different images to examine the effects of workload on the efficiency of the implementations. The application of these speedup techniques yielded excellent results leading to speedups of greater than 3.85 times in software and 5.8 times in hardware. In each of the software tests, the output image had a 2-d correlation coefficient (CORR2) of 1.0000. When implementing the algorithms in hardware using implementation specific approximations, the correlation coefficient of the output image was still an acceptable 0.99 or higher

Majorana Quasi-Particles Protected by Z2\mathbb{Z}_2 Angular Momentum Conservation

We show how angular momentum conservation can stabilise a symmetry-protected quasi-topological phase of matter supporting Majorana quasi-particles as edge modes in one-dimensional cold atom gases. We investigate a number-conserving four-species Hubbard model in the presence of spin-orbit coupling. The latter reduces the global spin symmetry to an angular momentum parity symmetry, which provides an extremely robust protection mechanism that does not rely on any coupling to additional reservoirs. The emergence of Majorana edge modes is elucidated using field theory techniques, and corroborated by density-matrix-renormalization-group simulations. Our results pave the way toward the observation of Majorana edge modes with alkaline-earth-like fermions in optical lattices, where all basic ingredients for our recipe - spin-orbit coupling and strong inter-orbital interactions - have been experimentally realized over the last two years.Comment: 12 pages (6 + 6 supplementary material

Overlap distributions for quantum quenches in the anisotropic Heisenberg chain

The dynamics after a quantum quench is determined by the weights of the initial state in the eigenspectrum of the final Hamiltonian, i.e., by the distribution of overlaps in the energy spectrum. We present an analysis of such overlap distributions for quenches of the anisotropy parameter in the one-dimensional anisotropic spin-1/2 Heisenberg model (XXZ chain). We provide an overview of the form of the overlap distribution for quenches from various initial anisotropies to various final ones, using numerical exact diagonalization. We show that if the system is prepared in the antiferromagnetic N\'eel state (infinite anisotropy) and released into a non-interacting setup (zero anisotropy, XX point) only a small fraction of the final eigenstates gives contributions to the post-quench dynamics, and that these eigenstates have identical overlap magnitudes. We derive expressions for the overlaps, and present the selection rules that determine the final eigenstates having nonzero overlap. We use these results to derive concise expressions for time-dependent quantities (Loschmidt echo, longitudinal and transverse correlators) after the quench. We use perturbative analyses to understand the overlap distribution for quenches from infinite to small nonzero anisotropies, and for quenches from large to zero anisotropy.Comment: 23 pages, 8 figure

The Abruzzo-Apulian (Central and Southeastern Italy) fossil fauna, new challenges for paleontologists and paleobiogeographers

The Abruzzo-Apulian Platform was an endemic Neogene paleobioprovince. Its relics can be found at the south-east of the Italian Peninsula. Geological and paleontological traces of this past land crop out both in the central Apennines, Maiella (Scontrone fossiliferous site), as well as in the Gargano Promontory. The Scontrone paleofauna -Scontrone is placed on the southern borderline of the Abruzzo National Park, Central-Southern Apennine. The bone-bearing sediments are coastaltidal-flat calcarenites stratigraphically dated to the Lower Tortonian. They yielded remains of terrestrial mammals, which include the bizarre ruminant Hoplitomeryx and the giant insectivore Deinogalerix, of a large terrestrial bird, and of large crocodilians and chelonians. At present, Hoplitomeryx, Deinogalerix and the crocodilians represent the elements in common with the Gargano community. The fauna is endemic and quite unbalanced. Six species of Hoplitomeryx have been described until now, but other species are adding to the list as new specimens are being freed from the calcarenites. Deinogalerix seems also represented by more than a single species. No mammal carnivores nor small mammals were found until now. The Gargano paleofauna - A very diversified endemic fauna is contained in soil deposits (Terre Rosse) that fill an extensive karst system at the north-western slopes of Mount Gargano (Southern Italy). The fossil assemblages include both large and small mammals, birds, reptiles, and amphibians, and are highly unbalanced. The small mammal component is mainly made of rodents, lagomorphs, and insectivores. Larger mammalian taxa are less abundant and are represented by Hoplitomericidae, Deinogalerix. And the sea otter Paralutra garganensis. The fissure fillings have been arranged in a biochronological sequence based on their different faunal composition and evolutionary degree. During the time period documented by the fissure deposits the faunal diversity changed and several taxa underwent significant evolutionary modifications, giving rise to numerous adaptive radiations. Taxa weakly- or non-modified compared to their continental counterparts characterize the oldest assemblages. They likely represent the youngest dispersal phase from the mainland into the insular domain, suggesting a polyphasic origin of the community.Evidence of apparently the oldest faunal settlement in Gargano was found in the recently discovered fissure M013. It contains remains of a new murid, which is manifestly the ancestor of Mikrotia (the endemic and widespread murid of the Terre Rosse), together with those of a new Cricetodontinae, which resembles primitive early Miocene representatives. These occurrences, in addition to the absence of Apodemus and Prolagus, two ubiquitous taxa of the Terre Rosse fillings, confirm that the assemblages are the result of a set of successive bioevents. The age and paleogeography of Scontrone and Gargano: the Abruzzo-Apulian domain - The Early Tortonian age of the Scontrone fauna is unequivocally proven not only by solid geologic evidence, but also by the Hoplitomeryx representatives, which are comparatively more primitive than their Gargano counterparts. The same might apply to the Deinogalerix specimens from the two localities, but analyses are still under way to check this aspect. The Gargano fissure fillings are tentatively dated to the Late Miocene on the basis of paleontological inferences, namely the occurrence of Apodemus, which is supposed to be not older than MN12 in the European mainland. The Gargano’s younger age possibly reflects the fact that the Gargano palaeo-islands formed stable structural high, while the Scontrone area was involved in the Apennine build-up and gradually sunk. Thus, the faunas from Scontrone and Gargano represent two different time slices within the same bioprovince. The colonization of the Abruzzo-Apulia domain - The existence, from the Late Oligocene to the Langhian, of a trans-Adriatic structural high between Dalmatia and the Gargano Peninsula, through the present day Tremiti Islands, was ascertained based on the seismostratigraphic analysis of more than 6000 kilometers of reflection seismic profiles from the Adriatic offshore, but also on several tens of deep wells. The major 29-30 Ma global sea-level fall caused the generalized surfacing of this structure across the Adriatic. The trans-Adriatic isthmus was originally in the form of stripe of land. Then, as the sea level turned growing at the transition to the Early Miocene, the structural high likely gave rise to an archipelago of gradually shrinking islands. The isthmus definitively sank at the end of the Langhian, i.e. around 14.8 Ma, and the Abruzzo-Apulian area remained cut off from any near mainland for the next 7 million years. Dalmatia and the Gargano were connected again during the Messinian sea lowstand. Thereafter, the sea level turned gradually to rise again, at first isolating the Abruzzo-Apulian area and then finally submerging it entirely at the very end of the Messinian. The possible ways of colonization used by the Messinian colonizers is still passionately debated. Although many steps have been made in the direction of improving our understanding of the history of the Abruzzo-Apulian Platform and of its faunal communities, yet many issues are still unanswered. Settling these issues will not only give us a better insight into the development of the Abruzzo-Apulian faunas per se, but will also lead us to a better understanding of the geo– and biodynamics of paleoislands in general