191 research outputs found
Enhancement of stability of metastable states in the presence of L\'{e}vy noise
The barrier crossing event for superdiffusion in the form of symmetric
L\'{e}vy flights is investigated. We derive from the fractional Fokker-Planck
equation a general differential equation with the corresponding conditions
useful to calculate the mean residence time of a particle in a fixed interval
for an arbitrary smooth potential profile, in particular metastable, with a
sink and a L\'{e}vy noise with an arbitrary index . A closed expression
in quadrature of the nonlinear relaxation time for L\'{e}vy flights with the
index in cubic metastable potential is obtained. Enhancement of the
mean residence time in the metastable state, analytically derived, due to
L\'{e}vy noise is found.Comment: 7 pages, 3 figure
Hysteretic Superconducting Heat-Flux Quantum Modulator
We discuss heat transport in a thermally biased superconducting quantum-interference device (SQUID) in the presence of an external magnetic flux, when a non-negligible inductance of the SQUID ring is taken into account. A properly sweeping driving flux causes the thermal current to modulate and behave hysteretically. The response of this device is analyzed as a function of both the hysteresis parameter and the degree of asymmetry of the SQUID, highlighting the parameter range over which hysteretic behavior is observable. Markedly, the temperature of the SQUID also shows hysteretic evolution, with sharp transitions characterized by temperature jumps up to, e.g., approximately 0.02 K for a realistic Al-based setup. In view of these results, the proposed device can effectively find an application as a temperature-based superconducting memory element, working even at gigahertz frequencies by suitably choosing the superconductor on which the device is based
Phase-coherent solitonic Josephson heat oscillator
Since its recent foundation, phase-coherent caloritronics has sparkled continuous interest giving rise to numerous concrete applications. This research field deals with the coherent manipulation of heat currents in mesoscopic superconducting devices by mastering the Josephson phase difference. Here, we introduce a new generation of devices for fast caloritronics able to control local heat power and temperature through manipulation of Josephson vortices, i.e., solitons. Although most salient features concerning Josephson vortices in long Josephson junctions were comprehensively hitherto explored, little is known about soliton-sustained coherent thermal transport. We demonstrate that the soliton configuration determines the temperature profile in the junction, so that, in correspondence of each magnetically induced soliton, both the flowing thermal power and the temperature significantly enhance. Finally, we thoroughly discuss a fast solitonic Josephson heat oscillator, whose frequency is in tune with the oscillation frequency of the magnetic drive. Notably, the proposed heat oscillator can effectively find application as a tunable thermal source for nanoscale heat engines and coherent thermal machines
Solitonic Josephson-based meminductive systems
Memristors, memcapacitors, and meminductors represent an innovative generation of circuit elements whose properties depend on the state and history of the system. The hysteretic behavior of one of their constituent variables, is their distinctive fingerprint. This feature endows them with the ability to store and process information on the same physical location, a property that is expected to benefit many applications ranging from unconventional computing to adaptive electronics to robotics. Therefore, it is important to find appropriate memory elements that combine a wide range of memory states, long memory retention times, and protection against unavoidable noise. Although several physical systems belong to the general class of memelements, few of them combine these important physical features in a single component. Here, we demonstrate theoretically a superconducting memory based on solitonic long Josephson junctions. Moreover, since solitons are at the core of its operation, this system provides an intrinsic topological protection against external perturbations. We show that the Josephson critical current behaves hysteretically as an external magnetic field is properly swept. Accordingly, long Josephson junctions can be used as multi-state memories, with a controllable number of available states, and in other emerging areas such as memcomputing, i.e., computing directly in/by the memory
Yeast ecology of vineyards within Marsala wine area (western Sicily) in two consecutive vintages and selection of autochthonous Saccharomyces cerevisiae strains
In this work, the yeast ecology associated with the spontaneous fermentation of Grillo cultivar grapes from 10
vineyards was analyzed from grape harvest till complete consumption of must sugars. The microbiological investigation
started with the plate count onto two culture media to distinguish total yeasts (TY) and presumptive Saccharomyces (PS).
Yeasts were randomly isolated and identified by a combined genotypic approach consisting of restriction fragment
length polymorphism (RFLP) of 5.8S rRNA gene and 26S rRNA and sequencing of D1/D2 domain of the 26S rRNA gene,
which resulted in the recognition of 14 species belonging to 10 genera. The distribution of the yeasts within the vineyards
showed some differences in species composition and concentration levels among 2008 and 2009 vintages. Due to
the enological relevance, all Saccharomyces cerevisiae isolates were differentiated applying two genotypic tools (interdelta
analysis and microsatellite multiplex PCR of polymorphic microsatellite loci) that recognized 51 strains. Based on
the low production of H2S, acetic acid and foam, ethanol resistance, growth in presence of high concentrations of
potassium metabisulphite (KMBS) and CuSO4 and at low temperatures, 14 strains were selected and used as starter to
ferment grape must at 13 C and 17 C in presence of 100 mg/L of KMBS. Three strains (CS160, CS165 and CS182) showed
optimal technological aptitudes
CSI 2264: Simultaneous optical and X-ray variability in pre-Main Sequence stars. I: Time resolved X-ray spectral analysis during optical dips and accretion bursts in stars with disks
Pre-main sequence stars are variable sources. In stars with disks, this
variability is related to the morphology of the inner circumstellar region
(<0.1 AU) and that of the photosphere and corona, all impossible to be
spatially resolved with present day techniques. This has been the main
motivation for the Coordinated Synoptic Investigation of NGC 2264. In this
paper, we focus on the stars with disks. We analyze the X-ray spectral
properties extracted during optical bursts and dips in order to unveil the
nature of these phenomena. We analyze simultaneous CoRoT and Chandra/ACIS-I
observations to search for coherent optical and X-ray flux variability in stars
with disks. Then, stars are analyzed in two different samples. In stars with
variable extinction, we look for a simultaneous increase of optical extinction
and X-ray absorption during the optical dips; in stars with accretion bursts,
we search for soft X-ray emission and increasing X-ray absorption during the
bursts. Results. We find evidence for coherent optical and X-ray flux
variability among the stars with variable extinction. In 9/24 stars with
optical dips, we observe a simultaneous increase of X-ray absorption and
optical extinction. In seven dips, it is possible to calculate the NH/AV ratio
in order to infer the composition of the obscuring material. In 5/20 stars with
optical accretion bursts, we observe increasing soft X-ray emission during the
bursts that we associate to the emission of accreting gas. It is not surprising
that these properties are not observed in all the stars with dips and bursts,
since favorable geometric configurations are required. The observed variable
absorption during the dips is mainly due to dust-free material in accretion
streams. In stars with accretion bursts, we observe on average a larger soft
X-ray spectral component not observed in non accreting stars.Comment: Accepted for publication by Astronomy & Astrophysic
Coupled quantum pendula as a possible model for Josephson-junction-based axion detection
The model of two coupled quantum pendula is studied and its suitability to describe Josephson junctions interacting with axions is analysed. It is shown that some physical features of one pendulum, not directly accessible, can be deduced by local measures on the other one, which is experimentally available. Such an effect can be exploited for the axion (the invisible pendulum) detection based on Josephson junctions (the accessible pendulum). The interaction between axion and Josephson junction can be enhanced at the resonance, if the axion and the junction frequencies match, and if the accessible system is prepared in the most convenient initial quantum state
Nonlinear relaxation phenomena in metastable condensed matter systems
Nonlinear relaxation phenomena in three different systems of condensed matter are investigated. (i) First, the phase dynamics in Josephson junctions is analyzed. Specifically, a superconductor-graphene-superconductor (SGS) system exhibits quantum metastable states, and the average escape time from these metastable states in the presence of Gaussian and correlated fluctuations is calculated, accounting for variations in the the noise source intensity and the bias frequency. Moreover, the transient dynamics of a long-overlap Josephson junction (JJ) subject to thermal fluctuations and non-Gaussian noise sources is investigated. Noise induced phenomena are observed, such as the noise enhanced stability and the stochastic resonant activation. (ii) Second, the electron spin relaxation process in a n-type GaAs bulk driven by a fluctuating electric field is investigated. In particular, by using a Monte Carlo approach, we study the influence of a random telegraph noise on the spin polarized transport. Our findings show the possibility to raise the spin relaxation length by increasing the amplitude of the external fluctuations. Moreover, we find that, crucially, depending on the value of the external field strength, the electron spin depolarization length versus the noise correlation time increases up to a plateau. (iii) Finally, the stabilization of quantum metastable states by dissipation is presented. Normally, quantum fluctuations enhance the escape from metastable states in the presence of dissipation. We show that dissipation can enhance the stability of a quantum metastable system, consisting of a particle moving in a strongly asymmetric double well potential, interacting with a thermal bath. We find that the escape time from the metastable region has a nonmonotonic behavior versus the system- bath coupling and the temperature, producing a stabilizing effect
Selected lactic acid bacteria as a hurdle to the microbial spoilage of cheese: application on a traditional raw ewes’ milk cheese.
To evaluate the efficacy of lactic acid bacteria (LAB) to improve the hygienic safety of a traditional raw
milk cheese, the raw ewes’ milk protected denomination of origin (PDO) Pecorino Siciliano cheese was
used as a model system. Different Pecorino Siciliano curds and cheeses were used as sources of
autochthonous LAB subsequently used as starter and non-starter LAB. These were screened for their
acidification capacity and autolysis. Starter LAB showing the best performance were genotypically
differentiated and identified: two strains of Lactococcus lactis subsp. lactis were selected. From the nonstarter
LAB, Enterococcus faecalis, Lactococcus garvieae and Streptococcus macedonicus strains were
selected. The five cultures were used in individual or dual inocula to produce experimental cheeses in a
dairy factory for which production was characterised by high numbers of undesirable bacteria. At 5-
month of ripening, the experimental cheeses produced with LAB were characterised by undetectable
levels of enterobacteria and pseudomonads and the typical sensory attributes
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