3,887 research outputs found
Quantum ratchets in dissipative chaotic systems
Using the method of quantum trajectories we study a quantum chaotic
dissipative ratchet appearing for particles in a pulsed asymmetric potential in
the presence of a dissipative environment. The system is characterized by
directed transport emerging from a quantum strange attractor. This model
exhibits, in the limit of small effective Planck constant, a transition from
quantum to classical behavior, in agreement with the correspondence principle.
We also discuss parameter values suitable for implementation of the quantum
ratchet effect with cold atoms in optical lattices.Comment: Significant changes: Several text improvements and new results.
Figure 2 modified. Figure 4 adde
On a non-isothermal model for nematic liquid crystals
A model describing the evolution of a liquid crystal substance in the nematic
phase is investigated in terms of three basic state variables: the {\it
absolute temperature} \teta, the {\it velocity field} \ub, and the {\it
director field} \bd, representing preferred orientation of molecules in a
neighborhood of any point of a reference domain. The time evolution of the
velocity field is governed by the incompressible Navier-Stokes system, with a
non-isotropic stress tensor depending on the gradients of the velocity and of
the director field \bd, where the transport (viscosity) coefficients vary
with temperature. The dynamics of \bd is described by means of a parabolic
equation of Ginzburg-Landau type, with a suitable penalization term to relax
the constraint |\bd | = 1. The system is supplemented by a heat equation,
where the heat flux is given by a variant of Fourier's law, depending also on
the director field \bd. The proposed model is shown compatible with
\emph{First and Second laws} of thermodynamics, and the existence of
global-in-time weak solutions for the resulting PDE system is established,
without any essential restriction on the size of the data
Posidonia Oceanica And Green Tea Extract As Active Agents For Shelf Life Extension Of Fresh Cut Peach
Nowadays the reduction of food waste and the availability of food all over the world areas are priority keys for society. In this context, the shelf life extension of fresh products in a sustainable way may represent one of the main goals. The aim of the present research work was to extend the shelf life of fresh cut peach slices by using extracts of Posidonia oceanica (POS) and green tea (GT), and compared to the control. Total polyphenols content was assessed by Folin-Ciocalteu method and the antioxidant capacity by DPPH (2,2-Diphenyl-1-Picrylhydrazyl) assay. Antimicrobial activity of the two extracts was initially carried out in vitro by determining the Minimal Inhibitory Concentration (MIC) against Escherichia coli, Listeria innocua, Pseudomonas putida, Staphylococcus aureus, Saccharomyces cerevisiae, Aspergillus niger and Penicillium chrysogenum. The two extracts in vivo on peach slices by dipping were applied (only water for the control), than, slices were placed into low-density polyethylene (LDPE) bag and stored at 3 ± 1°C for up to 7 days. Microbiological analyses, color (L*,a*,b*), total soluble solid (TSS) and titratable acidity (TA) on peach slices were carried out every 3 days.
POS showed the highest polyphenols content (615±45 mg Gallic Acid Equivalent/g – mg GAE/g) while GT 526 ± 28 mg GAE/g. The values of EC50, for POS, was 72.42 ± 22.90 mg/L, while for GT 3.80 ± 0.11 mg/L. Trials in vitro showed MIC values of above 2 g/L for POS and above 1 g/L in GT mainly against Gram positive bacteria. POS was also found to lead a growth delay in the case of fungi, approximately 60 h compared to the control.
Results related to the Total Aerobic (TAC) and yeasts and moulds (Y&M) counts highlighted that peach slices dipped with POS maintained in the first 5 days of storage the microbiota at lower or analogous levels than those found at t0 (1.80 ± 0.09 log cfu/g respect 2.30 ± 0.11 log cfu/g and 1.80 ± 0.05 log cfu/g respect 1.70 ± 0.03 log cfu/g of the control, respectively for TAC and Y&M).
Regarding pomological analysis, after seven days, lightness of the peach slices decreased 28% in POS, 24% in GT and 35% in control. During shelf life TSS increased 8% in the control, 2% in POS and remained unchanged in GT, after seven days. At the same time, TA decreased 30% in POS, 20% in GT treatment and 63% in the control. During the experiment TSS increased in all treatments, more rapidly in the control; meanwhile the TA decreased slowly in treated samples compared to the control.
Concluding, Posidonia oceanica and green tea extracts were found able to delay the colour and pomological parameters decay, maintaining a good fruit quality during shelf life. Data already showed evidence a better performance of the Posidonia extract, limiting the growth of microorganisms responsible for fresh fruit deterioration
Quantum Poincar\'e Recurrences
We show that quantum effects modify the decay rate of Poincar\'e recurrences
P(t) in classical chaotic systems with hierarchical structure of phase space.
The exponent p of the algebraic decay P(t) ~ 1/t^p is shown to have the
universal value p=1 due to tunneling and localization effects. Experimental
evidence of such decay should be observable in mesoscopic systems and cold
atoms.Comment: revtex, 4 pages, 4 figure
Covariant quantum measurements which maximize the likelihood
We derive the class of covariant measurements which are optimal according to
the maximum likelihood criterion. The optimization problem is fully resolved in
the case of pure input states, under the physically meaningful hypotheses of
unimodularity of the covariance group and measurability of the stability
subgroup. The general result is applied to the case of covariant state
estimation for finite dimension, and to the Weyl-Heisenberg displacement
estimation in infinite dimension. We also consider estimation with multiple
copies, and compare collective measurements on identical copies with the scheme
of independent measurements on each copy. A "continuous-variables" analogue of
the measurement of direction of the angular momentum with two anti-parallel
spins by Gisin and Popescu is given.Comment: 8 pages, RevTex style, submitted to Phys. Rev.
A Crash Course on Aging
In these lecture notes I describe some of the main theoretical ideas emerged
to explain the aging dynamics. This is meant to be a very short introduction to
aging dynamics and no previous knowledge is assumed. I will go through simple
examples that allow one to grasp the main results and predictions.Comment: Lecture Notes (22 pages) given at "Unifying Concepts in Glass Physics
III", Bangalore (2004); to be published in JSTA
Theoretical framework for quantum networks
We present a framework to treat quantum networks and all possible
transformations thereof, including as special cases all possible manipulations
of quantum states, measurements, and channels, such as, e.g., cloning,
discrimination, estimation, and tomography. Our framework is based on the
concepts of quantum comb-which describes all transformations achievable by a
given quantum network-and link product-the operation of connecting two quantum
networks. Quantum networks are treated both from a constructive point of
view-based on connections of elementary circuits-and from an axiomatic
one-based on a hierarchy of admissible quantum maps. In the axiomatic context a
fundamental property is shown, which we call universality of quantum memory
channels: any admissible transformation of quantum networks can be realized by
a suitable sequence of memory channels. The open problem whether this property
fails for some nonquantum theory, e.g., for no-signaling boxes, is posed.Comment: 23 pages, revtex
Evaluation of the antioxidant/antimicrobial performance of Posidonia oceanica in comparison with three commercial natural extracts and as a treatment on fresh-cut peaches (Prunus persica Batsch)
This research aimed at extending the choice of natural antimicrobials/antioxidants for food applications. Four plant extracts, Posidonia oceanica (PO), Green Tea (GT), Grape seeds (GS) and Grape skin (GK), were analyzed to determine their total phenolic content, antioxidant activity and in vitro antimicrobial performance. PO extract showed the highest total phenolic content (711 mg gallic acid/g extract) and antifungal activity against Aspergillus niger and Penicillium chrysogenum. The highest antioxidant (3.81 mg/L EC50) and antibacterial activities (bactericidal against Gram positives and bacteriostatic against Gram negatives) were found for GT extract.
The best performing extracts (PO and GT) were applied by dipping on peach slices in storage trials. Microbiological and pomological parameters were evaluated during 7 d storage. Total aerobic count, Pseudomonas as well as yeasts and moulds populations, were reduced by about 0.5 log cfu/g, mainly up to 5 d in all treated samples compared to the control. Total soluble solids, titratable acidity and colour (L*a*b*) changes were also delayed in treated fruit
The Frascati Beam Test Facility
From 2004 the Frascati Beam Test Facility (BTF) in the DAFNE accelerator
complex provides to the external user up to 1E10 electrons per bunch or up to
10E9 positrons per bunch to develop their detectors. After an upgrade program
terminated in 2020 of the beam test facility a description of the status and
available beam lines will be done.Comment: Talk presented at the International Workshop on Future Linear
Colliders (LCWS 2023), 15-19 May 2023. C23-05-15.
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