7,651 research outputs found
Generation of Closed Timelike Curves with Rotating Superconductors
The spacetime metric around a rotating SuperConductive Ring (SCR) is deduced
from the gravitomagnetic London moment in rotating superconductors. It is shown
that theoretically it is possible to generate Closed Timelike Curves (CTC) with
rotating SCRs. The possibility to use these CTC's to travel in time as
initially idealized by G\"{o}del is investigated. It is shown however, that
from a technology and experimental point of view these ideas are impossible to
implement in the present context.Comment: 9 pages. Submitted to Classical and Quantum Gravit
Oscillatons revisited
In this paper, we study some interesting properties of a spherically
symmetric oscillating soliton star made of a real time-dependent scalar field
which is called an oscillaton. The known final configuration of an oscillaton
consists of a stationary stage in which the scalar field and the metric
coefficients oscillate in time if the scalar potential is quadratic. The
differential equations that arise in the simplest approximation, that of
coherent scalar oscillations, are presented for a quadratic scalar potential.
This allows us to take a closer look at the interesting properties of these
oscillating objects. The leading terms of the solutions considering a quartic
and a cosh scalar potentials are worked in the so called stationary limit
procedure. This procedure reveals the form in which oscillatons and boson stars
may be related and useful information about oscillatons is obtained from the
known results of boson stars. Oscillatons could compete with boson stars as
interesting astrophysical objects, since they would be predicted by scalar
field dark matter models.Comment: 10 pages REVTeX, 10 eps figures. Updated files to match version
published in Classical and Quantum Gravit
Monitoring of antibiotic resistance and contaminants of emerging concern in small-scale wetland-based municipal treatment systems
Human sewage is one of the major sources of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and chemical contaminants of emerging concern (CECs). Wastewater treatment is a crucial barrier to prevent environmental contamination. This study aimed to assess the efficacy of three constructed wetlands (CWs) (<200 p.e.) located in small villages, in Northern Portugal dedicated to the treatment of domestic effluents. Twenty-four hour composite samples of influent and effluent were collected over four campaigns in the winter (March), spring (May), summer (July) and autumn (October) during the year of 2023. Triplicate total DNA extracts from 50-250 ml of sample were used to measure the abundance of biomarkers associated with anthropogenic contamination (intI1; uidA; sul1; crAssphage; ermB, ermF, qacEΔ1, tetX, mefC and aph(3´´)-ib)1 and the bacterial load through 16S rRNA gene quantification by qPCR. Cultivable Escherichia coli and total coliforms were quantified on Chromogenic Coliform Agar (CCA). CECs extracted by solid-phase extraction (SPE) were quantified by liquid chromatography-mass spectrometry (LC–MS). Total coliforms ranged from 4.5 – 6.1 log UFC/mL in influent samples and 1.7 – 3.8 log UFC/mL in effluent samples. Total bacterial abundance, assessed based on the 16S rRNA gene, ranged between 8.0 – 8.9 log-units gene copy/mL in influent and 6.3 – 7.6 log-units in effluent. The biomarkers tested showed removal values of up to 3 log-units gene copy/mL. The chemical analysis of 119 compounds showed that pain killers as acetaminophen, illicit drugs as cocaine, antihyperlipidemic as fenofibric-acid, antihypertensives as irbesartan or psychoactive drugs as oxazepam were present in all samples (1st and 2nd campaigns), persisting after treatment. The results obtained so far suggest that the three CWs have good treatment capacity, with an important role of macrophytes, although dependent on the growth stage along the year, and with limited capacity to remove CECs.info:eu-repo/semantics/publishedVersio
Exactly Thermalised Quantum Dynamics of the Spin-Boson Model coupled to a Dissipative Environment
We present an application of the Extended Stochastic Liouville-von Neumann
equations (ESLN) method introduced earlier [PRB 95, 125124 (2017); PRB 97,
224310 (2018)] which describes the dynamics of an exactly thermalised open
quantum system reduced density matrix coupled to a non-Markovian harmonic
environment. Critically, the combined system of the open system fully coupled
to its environment is thermalised at finite temperature using an imaginary time
evolution procedure before the application of real time evolution. This
initialises the combined system in the correct canonical equilibrium state
rather than being initially decoupled. We apply our theory to the spin-boson
Hamiltonian and develop a number of competing ESLN variants designed to reduce
the numerical divergence of the trace of the open system density matrix. We
find that a careful choice of the driving noises is essential for improving
numerical stability. We also investigate the effect of applying higher order
numerical schemes for solving stochastic differential equations, such as the
Stratonovich-Heun scheme, and conclude that stochastic sampling dominates
convergence with the improvement associated with the numerical scheme being
less important for short times but required for late times. To verify the
method and its numerical implementation, we consider evolution under a fixed
Hamiltonian and show that the system either remains in, or approaches, the
correct canonical equilibrium state at long times. Additionally, evolution of
the open system under non-equilibrium Landau-Zener (LZ) driving is considered
and the asymptotic convergence to the LZ limit was observed for vanishing
system-environment coupling and temperature. When coupling and temperature are
non-zero, initially thermalising the combined system at a finite time in the
past was found to be a better approximation of the true LZ initial state than a
pure state
Edge phonons in black phosphorus
Exfoliated black phosphorus has recently emerged as a new two-dimensional
crystal that, due to its peculiar and anisotropic crystalline and electronic
band structures, may have potentially important applications in electronics,
optoelectronics and photonics. Despite the fact that the edges of layered
crystals host a range of singular properties whose characterization and
exploitation are of utmost importance for device development, the edges of
black phosphorus remain poorly characterized. In this work, the atomic
structure and the behavior of phonons near different black phosphorus edges are
experimentally and theoretically studied using Raman spectroscopy and density
functional theory calculations. Polarized Raman results show the appearance of
new modes at the edges of the sample, and their spectra depend on the atomic
structure of the edges (zigzag or armchair). Theoretical simulations confirm
that the new modes are due to edge phonon states that are forbidden in the
bulk, and originated from the lattice termination rearrangements.Comment: 15 pages, 4 figure
Scalar Field Dark Matter: behavior around black holes
We present the numerical evolution of a massive test scalar fields around a
Schwarzschild space-time. We proceed by using hyperboloidal slices that
approach future null infinity, which is the boundary of scalar fields, and also
demand the slices to penetrate the event horizon of the black hole. This
approach allows the scalar field to be accreted by the black hole and to escape
toward future null infinity. We track the evolution of the energy density of
the scalar field, which determines the rate at which the scalar field is being
diluted. We find polynomial decay of the energy density of the scalar field,
and use it to estimate the rate of dilution of the field in time. Our findings
imply that the energy density of the scalar field decreases even five orders of
magnitude in time scales smaller than a year. This implies that if a
supermassive black hole is the Schwarzschild solution, then scalar field dark
matter would be diluted extremely fastComment: 15 pages, 21 eps figures. Appendix added, accepted for publication in
JCA
- …