8,410 research outputs found
Quantum thermal machines with single nonequilibrium environments
We propose a scheme for a quantum thermal machine made by atoms interacting
with a single non-equilibrium electromagnetic field. The field is produced by a
simple configuration of macroscopic objects held at thermal equilibrium at
different temperatures. We show that these machines can deliver all
thermodynamic tasks (cooling, heating and population inversion), and this by
establishing quantum coherence with the body on which they act. Remarkably,
this system allows to reach efficiencies at maximum power very close to the
Carnot limit, much more than in existing models. Our findings offer a new
paradigm for efficient quantum energy flux management, and can be relevant for
both experimental and technological purposes.Comment: 10 pages, 6 figure
Non equilibrium dissipation-driven steady many-body entanglement
We study an ensemble of two-level quantum systems (qubits) interacting with a
common electromagnetic field in proximity of a dielectric slab whose
temperature is held different from that of some far surrounding walls. We show
that the dissipative dynamics of the qubits driven by this stationary and out
of thermal equilibrium (OTE) field, allows the production of steady many-body
entangled states, differently from the case at thermal equilibrium where steady
states are always non-entangled. By studying up to ten qubits, we point out the
role of symmetry in the entanglement production, which is exalted in the case
of permutationally invariant configurations. In the case of three qubits, we
find a strong dependence of tripartite entanglement on the spatial disposition
of the qubits, and in the case of six qubits, we find several highly entangled
bipartitions where entanglement can, remarkably, survive for large qubit-qubit
distances up to 100 m.Comment: 10 pages, 5 figures, updated version accepted for publication in
Phys. Rev.
Social representations theory and critical: Constructionism: Insights from Caillaud's article
he aim of this paper is to highlight therole that Social Representations Theory (SRT) could play in the debate on the criticalpotential of social constructionist perspectives. Wedraw upon some of the arguments raised by Caillaud (this issue), mainly concerning such a sensitive topic as environmental issues, to highlightsomecrucial points of that debate. As is well known, one of the goals of the social constructionist movement has been to takea more critical stance towards taken-for-granted knowledge (Gergen,1985; Burr,1995). It aimsto show that our understanding of the world is by no means neutral or value-free;it is instead the result of historical and cultural specificities, which operate ideologically. In this vein, the social constructionist approach raises the question of social transformation and emancipation, as well as the problems of power and social inequality, in close consonance with the scope of the more general critical approach in psychology (Tolman&Maiers, 1991)
Thermally-activated non-local amplification in quantum energy transport
We study energy-transport efficiency in light-harvesting planar and 3D
complexes of two-level atomic quantum systems, embedded in a common thermal
blackbody radiation. We show that the collective non-local dissipation induced
by the thermal bath plays a fundamental role in energy transport. It gives rise
to a dramatic enhancement of the energy-transport efficiency, which may largely
overcome . This effect, which improves the understanding of transport
phenomena in experimentally relevant complexes, suggests a particularly
promising mechanism for quantum energy management.Comment: 7 pages, 4 figures. New version in which the RP line of Figure 1 has
been amended with the correct parameter
Distributed thermal tasks on many-body systems through a single quantum machine
We propose a configuration of a single three-level quantum emitter embedded
in a non-equilibrium steady electromagnetic environment, able to stabilize and
control the local temperatures of a target system it interacts with, consisting
of a collection of coupled two-level systems. The temperatures are induced by
dissipative processes only, without the need of further external couplings for
each qubit. Moreover, by acting on a set of easily tunable geometric
parameters, we demonstrate the possibility to manipulate and tune each qubit
temperature independently over a remarkably broad range of values. These
findings address one standard problem in quantum-scale thermodynamics,
providing a way to induce a desired distribution of temperature among
interacting qubits and to protect it from external noise sources.Comment: 6 pages, 5 figure
Promising approaches to optimize the biological properties of the antimicrobial peptide esculentin-1a(1-21)NH2. amino acids substitution and conjugation to nanoparticles
Antimicrobial peptides (AMPs) represent an interesting class of molecules with expanding biological properties which make them a viable alternative for the development of future antibiotic drugs. However, for this purpose, some limitations must be overcome: (i) the poor biostability due to enzymatic degradation; (ii) the cytotoxicity at concentrations slightly higher than the therapeutic dosages; and (iii) the inefficient delivery to the target site at effective concentrations. Recently, a derivative of the frog skin AMP esculentin-1a, named esculentin-1a(1-21)NH2, [Esc(1-21): GIFSKLAGKKIKNLLISGLKG-NH2] has been found to have a potent activity against the Gram-negative bacterium Pseudomonas aeruginosa; a slightly weaker activity against Gram-positive bacteria and interesting immunomodulatory properties. With the aim to optimize the antimicrobial features of Esc(1-21) and to circumvent the limitations described above, two different approaches were followed: (i) substitutions by non-coded amino acids, i.e., α-aminoisobutyric acid or d-amino acids; and (ii) peptide conjugation to gold nanoparticles. In this mini-review, we summarized the structural and functional properties of the resulting Esc(1-21)-derived compounds. Overall, our data may assist researchers in the rational design and optimization of AMPs for the development of future drugs to fight the worldwide problem of antibiotic resistance
Settling distances of benthic invertebrates in a sediment mobilization simulation in semi-natural flumes
Drift time and distance depend on the ability of the drifting invertebrates to alter their body posture or by swimming, and these behaviors may change according to the local hydraulic environment, resulting in different distances travelled before exiting the drift. Such drift and settlement mediated invertebrate movement determine dispersal processes and ultimately generates distribution patterns within streams. We conducted an experiment in an open-air, artificial flume system directly fed by an Alpine stream, where we disturbed the sediment in the flumes, inducing catastrophic drift in the benthic community, and then assessed the settlement distances of benthic invertebrates. For each flume, we collected drift samples by disturbing the substrate at 1.5 m intervals, at increasing distance from the downstream end, for a total of 7 disturbances and a maximum settling distance of 10 m in each flume, with five replicates (i.e., five flumes) for each disturbance. The disturbances induced a massive catastrophic drift in Ephemeroptera, Plecoptera and Trichoptera, always higher than the behaviorally-occurring basedrift. The Settling Index calculated over the total drift collected at each distance increased with increasing distance, and after 10 m, 90% of the drifting animals had settled. Evenness and taxa richness progressively decrease with increasing settling distance. All drifting taxa were represented mainly by young instars. We used the drift collected at 1 m from the disturbance to standardize the remaining samples, based on the assumption that 1 m is not a distance long enough to allow animals to settle at that water velocity. We calculated the percentage of possible drifters which settled by computing a Settling Index for each taxon. The drifting taxa listed by decreasing Settling Index scores were Epeorus sp., Rhithrogena semicolorata, Isoperla spp., Sericostoma spp., Ecdyonurus spp., Nemoura spp., Leuctra spp., Baetis spp., Hydropsyche spp., Rhyacophila spp. We have shown, in accordance with numerous other studies, that entrained EPT nymphs travel only short distances before returning to the substratum, and that the actual distance travelled while drifting and the total time spent in drift varies between species. The results of this study can provide suggestions to assess taxon-specific availability to colonization which generates distribution patterns within streams and, on a smaller scale (i.e., flume simulations), our results can be extrapolated to other studies conducted in artificial flumes, or to support evidences from field studies.</p
Steady entanglement out of thermal equilibrium
We study two two-level atomic quantum systems (qubits) placed close to a body
held at a temperature different from that of the surrounding walls. While at
thermal equilibrium the two-qubit dynamics is characterized by not entangled
steady thermal states, we show that absence of thermal equilibrium may bring to
the generation of entangled steady states. Remarkably, this entanglement
emerges from the two-qubit dissipative dynamic itself, without any further
external action on the two qubits, suggesting a new protocol to produce and
protect entanglement which is intrinsically robust to environmental effects.Comment: 6 pages, 4 figures, some typos corrected with respect to both the
previous arXiv and published version
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