1,297 research outputs found
Cloning transformations in spin networks without external control
In this paper we present an approach to quantum cloning with unmodulated spin
networks. The cloner is realized by a proper design of the network and a choice
of the coupling between the qubits. We show that in the case of phase covariant
cloner the XY coupling gives the best results. In the 1->2 cloning we find that
the value for the fidelity of the optimal cloner is achieved, and values
comparable to the optimal ones in the general N->M case can be attained. If a
suitable set of network symmetries are satisfied, the output fidelity of the
clones does not depend on the specific choice of the graph. We show that spin
network cloning is robust against the presence of static imperfections.
Moreover, in the presence of noise, it outperforms the conventional approach.
In this case the fidelity exceeds the corresponding value obtained by quantum
gates even for a very small amount of noise. Furthermore we show how to use
this method to clone qutrits and qudits. By means of the Heisenberg coupling it
is also possible to implement the universal cloner although in this case the
fidelity is 10% off that of the optimal cloner.Comment: 12 pages, 13 figures, published versio
Adiabatic quantum dynamics of a random Ising chain across its quantum critical point
We present here our study of the adiabatic quantum dynamics of a random Ising
chain across its quantum critical point. The model investigated is an Ising
chain in a transverse field with disorder present both in the exchange coupling
and in the transverse field. The transverse field term is proportional to a
function which, as in the Kibble-Zurek mechanism, is linearly
reduced to zero in time with a rate , , starting
at from the quantum disordered phase () and ending
at in the classical ferromagnetic phase (). We first analyze
the distribution of the gaps -- occurring at the critical point --
which are relevant for breaking the adiabaticity of the dynamics. We then
present extensive numerical simulations for the residual energy
and density of defects at the end of the annealing, as a function of
the annealing inverse rate . %for different lenghts of the chain. Both
the average and are found to behave
logarithmically for large , but with different exponents, with , and
. We propose a mechanism for
-behavior of based on the Landau-Zener
tunneling theory and on a Fisher's type real-space renormalization group
analysis of the relevant gaps. The model proposed shows therefore a
paradigmatic example of how an adiabatic quantum computation can become very
slow when disorder is at play, even in absence of any source of frustration.Comment: 10 pages, 11 figures; v2: added references, published versio
From perfect to fractal transmission in spin chains
Perfect state transfer is possible in modulated spin chains, imperfections
however are likely to corrupt the state transfer. We study the robustness of
this quantum communication protocol in the presence of disorder both in the
exchange couplings between the spins and in the local magnetic field. The
degradation of the fidelity can be suitably expressed, as a function of the
level of imperfection and the length of the chain, in a scaling form. In
addition the time signal of fidelity becomes fractal. We further characterize
the state transfer by analyzing the spectral properties of the Hamiltonian of
the spin chain.Comment: 8 pages, 10 figures, published versio
Online region computations for Euler Diagrams with relaxed drawing conventions
AbstractEuler diagrams are an accessible and effective visualisation of data involving simple set-theoretic relationships. Efficient algorithms to quickly compute the abstract regions of an Euler diagram upon curve addition and removal have previously been developed (the single marked point approach, SMPA), but a strict set of drawing conventions (called well-formedness conditions) were enforced, meaning that some abstract diagrams are not representable as concrete diagrams. We present a new methodology (the multiple marked point approach, MMPA) enabling online region computation for Euler diagrams under the relaxation of the drawing convention that zones must be connected regions. Furthermore, we indicate how to extend the methods to deal with the relaxation of any of the drawing conventions, with the use of concurrent line segments case being of particular importance. We provide complexity analysis and compare the MMPA with the SMPA. We show that these methods are theoretically no worse than other comparators, whilst our methods apply to any case, and are likely to be faster in practise due to their online nature. The machinery developed for the concurrency case could be of use in Euler diagram drawing techniques (in the context of the Euler Graph), and in computer graphics (e.g. the development of an advanced variation of a winged edge data structure that deals with concurrency). The algorithms are presented for generic curves; specialisations such as utilising fixed geometric shapes for curves may occur in applications which can enhance capabilities for fast computations of the algorithms' input structures. We provide an implementation of these algorithms, utilising ellipses, and provide time-based experimental data for benchmarking purposes
Effectiveness of mixtures of vivianite and organic materials in preventing iron chlorosis in strawberry
Application of Fe salts with different organic matter sources has been demonstrated to be effective in preventing
Fe deficiency chlorosis. The main objective of this work was to study the effectiveness of different Fe sources based
on mixtures of humic substances or compost with vivianite in preventing this nutritional disorder in strawberry
(Fragaria × ananassa cv Camarosa). To this end, a randomised block experiment involving four replications (3 plants
per replication) and one factor (Fe source) was performed in a greenhouse using a calcareous growing medium. Iron
sources studied were: (i) control without Fe, (ii) control with an effective Fe source in calcareous media (EDDHA-Fe,
0.1 g kg–1), (iii) vivianite (1 g kg–1 medium, which is the recommended rate), (iv) vivianite (1 g kg–1) + humic substances
(HS 0.06 g kg–1), (v) vivianite (0.5 g kg–1) + HS (0.06 g kg–1) and (vi) a mixture of composted cork residue and vivianite
at a 6:1 mass ratio (CORVIV) applied at a dose of 6 g kg–1 medium. All Fe sources were effective in increasing SPAD
readings when compared with control without Fe. Treatments based on vivianite provided non-significantly different
SPAD readings from that obtained with EDDHA-Fe. However, only CORVIV showed non-significantly different dry
matter (DM) production, leaf area index, and total Fe content in the aerial part than EDDHA-Fe. Humic substances
and vivianite at 1 g kg–1 increased DM yield in plants when compared with vivianite without HS, results with this last
treatment being similar to those obtained with vivianite at 0.5 g kg–1 with HS. It can be concluded that studied sources
of organic matter increased the efficiency of vivianite in preventing Fe chlorosis in strawberry, especially vivianite
enriched cork compost which was as effective as EDDHA-Fe
Preventive medicine center and health care for students of medicine and health professions at the Sapienza University of Rome: a research protocol
This project aims to develop a Center of Preventive Medicine and Health Care for the students of Medicine and Health profession
at Sapienza University of Rome. At the beginning of the university career students, both residents and nonresident s, have to face
several difficulties such as: starting smoking or the increase in cigarette consumption ; the independent management of their own
health (especially for non residents consequently to the distance of the family doctor) ; unhealthy diet; tuberculosis (TB) biological
risk during their university training. These aspects , especially if present at the same time, act as a source stress and adversely affect
the quality of life and the academic performance. Specific aims of the project will be: implementing an ambulatory of Preventive
Medicine; implementing a virtual ambulatory of general medicine; creating a website on the problems mentioned above. Data
collected will be computerized to keep an electronic health record (HER) and to use the information for the purposes of scientific
research. The Centre will act in close relationship with the Central Administration, with the Headmasters of the Medical Faculties,
and in close collaboration with the Center of Occupational Medicine of Sapienza University
Chemical Profiling of Astragalus membranaceus Roots (Fish.) Bunge Herbal Preparation and Evaluation of Its Bioactivity
Astragalus membranaceus (Fish.) Bunge is a perennial herb distributed in the northern part of China, and its roots, namely, Hang qi, are included as a natural ingredient in dietary supplement formulations commonly used to treat different disorders such as respiratory infections, diabetes, and heart failure. The availability of a simple method for the determination of the quality of Astragalus herbal preparations could be a challenging issue for commercial purposes. In this study, a liquid chromatography–mass spectrometry (LC–MS)/MS based approach was used to characterize specialized metabolite recovery of 3 commercial hydroalcoholic extracts of A. membranaceus (AMG1, AMG2, AMG3) in addition to a hydroalcoholic extract of A. membranaceus root (AST). The hypoglycemic effect, cholinesterase inhibition, and antioxidant activities were also evaluated. Thirty-one compounds, of which 19 polyphenols and 12 saponins, were identified. The extracts were also quantified by using a sensitive and selective Q-Trap system for their content in flavonoids and astragalosides, selecting astragaloside I and IV as chemical markers. From our results, AMG3 preparation (Axtragyl) was the most abundant in terms of both specialized classes of metabolites, showing a fingerprint similar to that of AST. Interestingly, tested enzyme inhibition ability of flavonoids, daidzein (11) and formononetin (19), reported a higher α-glucosidase inhibition in comparison with that of acarbose used as positive control. The in silico study clarified the interactions among the molecules and the importance of having a free hydroxy group. Moreover, Axtragyl was able to exert protective effects in Caco-2 cells treated with hydrogen peroxide, confirming its ability as a potential protective agent in intestinal injury
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