665 research outputs found
A Superbubble Feedback Model for Galaxy Simulations
We present a new stellar feedback model that reproduces superbubbles.
Superbubbles from clustered young stars evolve quite differently to individual
supernovae and are substantially more efficient at generating gas motions. The
essential new components of the model are thermal conduction, sub-grid
evaporation and a sub-grid multi-phase treatment for cases where the simulation
mass resolution is insufficient to model the early stages of the superbubble.
The multi-phase stage is short compared to superbubble lifetimes. Thermal
conduction physically regulates the hot gas mass without requiring a free
parameter. Accurately following the hot component naturally avoids overcooling.
Prior approaches tend to heat too much mass, leaving the hot ISM below K
and susceptible to rapid cooling unless ad-hoc fixes were used. The hot phase
also allows feedback energy to correctly accumulate from multiple, clustered
sources, including stellar winds and supernovae.
We employ high-resolution simulations of a single star cluster to show the
model is insensitive to numerical resolution, unresolved ISM structure and
suppression of conduction by magnetic fields. We also simulate a Milky Way
analog and a dwarf galaxy. Both galaxies show regulated star formation and
produce strong outflows.Comment: 13 pages, 13 figures; replaced with version accepted to MNRA
Conservazione e valorizzazione delle grotte sarde: biodiversit\ue0 e ruolo socio-economico-culturale
Stima del valore economico del bene grotta e individuazione del target di fruitore; studio dei percorsi turistici per ottimizzare il numero dei visitatori per la salvaguardia del bene ambientale grotta, Stima della Capacit\ue0 di Carico turistica. Modello di una ottima fruizione di una grotta modello. Modello complesso di integrazione tra beni culturali, enogastronomici, ambientali e demo-etno-antropologici. Studio e creazione di network degli interessi
Quantum Information Processing and Relativistic Quantum Fields
It is shown that an ideal measurement of a one-particle wave packet state of
a relativistic quantum field in Minkowski spacetime enables superluminal
signalling. The result holds for a measurement that takes place over an
intervention region in spacetime whose extent in time in some frame is longer
than the light-crossing time of the packet in that frame. Moreover, these
results are shown to apply not only to ideal measurements but also to unitary
transformations that rotate two orthogonal one-particle states into each other.
In light of these observations, possible restrictions on the allowed types of
intervention are considered. A more physical approach to such questions is to
construct explicit models of the interventions as interactions between the
field and other quantum systems such as detectors. The prototypical
Unruh-DeWitt detector couples to the field operator itself and so most likely
respects relativistic causality. On the other hand, detector models which
couple to a finite set of frequencies of field modes are shown to lead to
superluminal signalling. Such detectors do, however, provide successful
phenomenological models of atom-qubits interacting with quantum fields in a
cavity but are valid only on time scales many orders of magnitude larger than
the light-crossing time of the cavity.Comment: 16 pages, 2 figures. Improved abstract and discussion of 'ideal'
measurements. References to previous work adde
Worldline approach to vector and antisymmetric tensor fields
The N=2 spinning particle action describes the propagation of antisymmetric
tensor fields, including vector fields as a special case. In this paper we
study the path integral quantization on a one-dimensional torus of the N=2
spinning particle coupled to spacetime gravity. The action has a local N=2
worldline supersymmetry with a gauged U(1) symmetry that includes a
Chern-Simons coupling. Its quantization on the torus produces the one-loop
effective action for a single antisymmetric tensor. We use this worldline
representation to calculate the first few Seeley-DeWitt coefficients for
antisymmetric tensor fields of arbitrary rank in arbitrary dimensions. As side
results we obtain the correct trace anomaly of a spin 1 particle in four
dimensions as well as exact duality relations between differential form gauge
fields. This approach yields a drastic simplification over standard heat-kernel
methods. It contains on top of the usual proper time a new modular parameter
implementing the reduction to a single tensor field. Worldline methods are
generically simpler and more efficient in perturbative computations then
standard QFT Feynman rules. This is particularly evident when the coupling to
gravity is considered.Comment: 30 pages, 5 figures, references adde
Tree amplitudes of noncommutative U(N) Yang-Mills Theory
Following the spirit of S-matrix program, we proposed a modified
Britto-Cachazo-Feng-Witten recursion relation for tree amplitudes of
noncommutative U(N) Yang-Mills theory. Starting from three-point amplitudes,
one can use this modified BCFW recursion relation to compute or analyze
color-ordered tree amplitudes without relying on any detail information of
noncommutative Yang-Mills theory. After clarifying the color structure of
noncommutative tree amplitudes, we wrote down the noncommutative analogies of
U(1)-decoupling, Kleiss-Kuijf and Bern-Carrasco-Johansson relations for
color-ordered tree amplitudes, and proved them using the modified BCFW
recursion relation.Comment: 24 pages, 3 figures. v2 References added. v3 some typos correcte
Sars-cov-2 detection in fecal sample from a patient with typical findings of covid-19 pneumonia on ct but negative to multiple sars-cov-2 rt-pcr tests on oropharyngeal and nasopharyngeal swab samples
Reverse transcriptase polymerase chain reaction (RT-PCR) negative results in the upper respiratory tract represent a major concern for the clinical management of coronavirus disease 2019 (COVID-19) patients. Herein, we report the case of a 43-years-old man with a strong clinical suspicion of COVID-19, who resulted in being negative to multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RT-PCR tests performed on different oropharyngeal and nasopharyngeal swabs, despite serology having confirmed the presence of SARS-CoV-2 IgM. The patient underwent a chest computed tomography (CT) that showed typical imaging findings of COVID-19 pneumonia. The presence of viral SARS-CoV-2 was confirmed only by performing a SARS-CoV-2 RT-PCR test on stool. Performing of SARS-CoV-2 RT-PCR test on fecal samples can be a rapid and useful approach to confirm COVID-19 diagnosis in cases where there is an apparent discrepancy between COVID-19 clinical symptoms coupled with chest CT and SARS-CoV-2 RT-PCR tests’ results on samples from the upper respiratory tract
Exosomes from human periapical Cyst-MSCs: Theranostic application in Parkinson’s disease
The scientific community continuously strives to get new disease models, to discover early markers or novel therapeutic approaches, improving the diagnosis and prognosis of several human pathologies. Parkinson’s Disease (PD) is characterized by a long asymptomatic phase, characterized by a selective loss of dopaminergic neurons. Recently, the human Periapical Cyst-Mesenchymal Stem Cells (hPCy-MSCs) have been differentiated in functional dopaminergic neurons: such oral-derived MSCs and the hPCy-MSCs-derived exosomes may represent a strategic and useful in vitro study-model, as well as intriguing therapeutic carriers. Circadian rhythm (CR) alteration variously impacts on PD pathways: an interesting research target is represented by the analysis of the exosomes released by dopaminergic neurons, derived from neural-differentiated hPCy-MSCs, after having reproduced in-vitro PD-like conditions. This review aims to describe the crosstalk among some aspects of circadian rhythm related to the onset of PD and the exosomes released by cells of PD patients. More in detail: the first part of this article will describe the main characteristics of circadian rhythm and the involvement of the exosomes found to be effective in the pathogenesis of PD. Finally, the authors will suggest how those exosomes derived from dopaminergic neurons, obtained by oral-derived stem cells (hPCy-MSCs) may represent a smart model for the in vitro research on PD, to find new biomarkers, to test new drugs or, fatally, to find new pathways applicable in future therapeutic approaches
Boundary Contributions Using Fermion Pair Deformation
Continuing the study of boundary BCFW recursion relation of tree level
amplitudes initiated in \cite{Feng:2009ei}, we consider boundary contributions
coming from fermion pair deformation. We present the general strategy for these
boundary contributions and demonstrate calculations using two examples, i.e,
the standard QCD and deformed QCD with anomalous magnetic momentum coupling. As
a by-product, we have extended BCFW recursion relation to off-shell gluon
current, where because off-shell gluon current is not gauge invariant, a new
feature must be cooperated.Comment: 26 pages, 4 figure
The Random Discrete Action for 2-Dimensional Spacetime
A one-parameter family of random variables, called the Discrete Action, is
defined for a 2-dimensional Lorentzian spacetime of finite volume. The single
parameter is a discreteness scale. The expectation value of this Discrete
Action is calculated for various regions of 2D Minkowski spacetime. When a
causally convex region of 2D Minkowski spacetime is divided into subregions
using null lines the mean of the Discrete Action is equal to the alternating
sum of the numbers of vertices, edges and faces of the null tiling, up to
corrections that tend to zero as the discreteness scale is taken to zero. This
result is used to predict that the mean of the Discrete Action of the flat
Lorentzian cylinder is zero up to corrections, which is verified. The
``topological'' character of the Discrete Action breaks down for causally
convex regions of the flat trousers spacetime that contain the singularity and
for non-causally convex rectangles.Comment: 20 pages, 10 figures, Typos correcte
- …