291 research outputs found
Modeling and Control of Quantum Systems: An Introduction
No full textThe scope of this work is to provide a self-contained introduction to a selection of basic theoretical aspects in the modeling and control of quantum mechanical systems, as well as a brief survey on the main approaches to control synthesis. While part of the existing theory, especially in the open-loop setting, stems directly from classical control theory (most notably geometric control and optimal control), a number of tools specifically tailored for quantum systems have been developed since the 1980s, in order to take into account their distinctive features: the probabilistic nature of atomic-scale physical systems, the effect of dissipation and the irreversible character of the measurements have all proved to be critical in feedback-design problems. The relevant dynamical models for both closed and open quantum systems are presented, along with the main results on their controllability and stability. A brief review of several currently available control design methods is meant to provide the interested reader with a roadmap for further studies
Stabilization Via Feedback Switching for Quantum Stochastic Dynamics
No full textWe propose a new method for pure-state and subspace preparation in quantum systems, which employs the output of a continuous measurement process and switching dissipative control to improve convergence speed, as well as robustness with respect to the initial conditions. In particular, we prove that the proposed closed-loop strategy makes the desired target globally asymptotically stable both in mean and almost surely, and we show it compares favorably against a time-based and a state-based switching control law, with significant improvements in the case of faulty initialization
Environment-assisted and feedback-assisted stabilization of quantum stochastic evolutions
No full textWe consider a class of pure-state preparation problems for stochastic quantum dynamics, by means of Hamiltonian control, continuous measurement and quantum feedback, in the presence of a Markovian environment. We prove that, whenever suitable dissipative effects are induced either by the unmonitored environment or by continuous-time measurements, open-loop time-invariant control is in principle sufficient to achieve stabilization of the target state (in probability). When this is not sufficient, we show that state stabilization can be attained for a wide class of models by the addition of a switching, filtering-based feedback control Hamiltonian
Amyotrophic lateral sclerosis: Epidemiology and risk factors
No full textAmyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of motor neurons, invariably leading to progressive paralysis and death in 3–5 years from onset. ALS has an annual incidence of 2/100,000 and a prevalence of 6/100,000. The disease is more common in males and in Caucasian ethnicities and its incidence rises with advancing age. Age at onset and site of onset (bulbar vs. spinal) are the two main prognostic factors in ALS. The only certain risk factors for ALS are positive family history, male gender, and advancing age; among environmental factors, cigarette smoking is supported by the most robust evidence, whereas others are less well documented. However, most epidemiological studies on environmental risk factors in ALS are limited by methodological flaws. Future researches should be performed according to more stringent criteria and on larger cohorts, and they should also aim to capture the complex interplay between genetic and environmental factors in ALS pathogenesis
Characterizing limits and opportunities in speeding up Markov chain mixing
No full textA variety of paradigms have been proposed to speed up Markov chain mixing, ranging from non-backtracking random walks to simulated annealing and lifted Metropolis–Hastings. We provide a general characterization of the limits and opportunities of different approaches for designing fast mixing dynamics on graphs using the framework of “lifted Markov chains”. This common framework allows to prove lower and upper bounds on the mixing behavior of these approaches, depending on a limited set of assumptions on the dynamics. We find that some approaches can speed up the mixing time to diameter time, or a time inversely proportional to the graph conductance, while others allow for no speedup at all
Amyotrophic Lateral Sclerosis: Neurochemical Biomarkers
No full textAmyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive loss of upper and lower motor neurons, causing relentless paralysis. There is a need for ALS biomarkers in order to facilitate early and differential diagnosis and prediction of disease course. The most promising ALS biomarkers are neurofilaments (phosphorylated heavy chain [pNFH] and light chain [NFL]), for which increasing evidence probably warrants their introduction in the clinical scenario in the near future. Their levels are raised in the CSF of ALS patients as a consequence of release from degenerating motor neuron axons, therefore enabling differentiation from most other conditions. Neurofilaments also have prognostic value, predicting survival and correlating with disease progression rate. Thanks to technological advances, neurofilaments can now be measured also in the blood, providing information which is similar to that given by their CSF counterparts. As neurofilament levels are stable over time and blood sampling makes longitudinal measurements easy, they are particularly promising as pharmacodynamic biomarkers for trials of experimental therapeutics. Another class of ALS biomarkers is that of neuroinflammatory molecules, among which the chitinases, and particularly chitotriosidase (Chit1), have been most studied in the last years. Though significantly raised in the CSF in ALS, the diagnostic performance of Chit1 is actually lower than that of neurofilaments; its potential usefulness is rather due to the fact that it presumably reflects microglial inflammation occurring in the non-cell-autonomous neurodegenerative process, which, together with the longitudinal stability of CSF levels, would enable its use as a pharmacodynamic biomarker in future trials targeting neuroinflammation
Investigation on the mechanisms involved in the central protective effect of amylin on gastric ulcers in rats
No full text1. The mechanisms involved in the protective effect of amylin (administered into the brain ventricle, i.c.v.) on gastric ulcers induced by the oral administration of ethanol 50% (EtOH, 2 ml/rat) or indomethacin (indomethacin, 20 mg kg(-1), at a dosing volume of 5 ml) were investigated in rats. 2. The possible involvement of endogenous nitric oxide (NO) in the beneficial effect of amylin against EtOH-induced ulcers was examined. The inhibitor of NO-synthesis, NG-nitro-L-arginine methyl ester (L-NAME, 70 mg kg(-1), s.c.) was injected 30 min before amylin (2.2 microg/rat, i.c.v.) followed by EtOH after a further 30 min. Rats were sacrificed 1 h after EtOH. L-NAME completely removed the protective effect of amylin. 3. The interaction between amylin and gastric nonprotein sulfhydryl groups was studied. The rats were treated with N-ethyl-maleimide (NEM, 25 mg kg(-1), s.c.) 30 min before amylin (2.2 microg/rat, i.c.v.) followed by EtOH 30 min after or by indomethacin 5 min after amylin. Rats were sacrificed 1 h or 6 h respectively after EtOH or indomethacin. NEM counteracted the protective effect of amylin against EtOH-induced ulcers but not against those provoked by indomethacin. 4. To determine whether amylin was able to promote ulcer healing, the peptide was injected 5 min after EtOH or 1 h after indomethacin. In the case of EtOH, the beneficial effect of amylin was lost whereas it was still effective on indomethacin-induced ulcers. 5. The results indicate that: the mechanisms involved in the antiulcer effects of amylin are different in these two types of gastric lesions probably because of the different etiopathology of various types of ulcers. Endogenous NO and nonprotein sulfhydryl groups are involved in the mucosal protective effects of amylin on EtOH and not on indomethacin-induced ulcers. Furthermore the effectiveness of amylin against indomethacin-induced lesions when administered after the ulcerogenic process has started suggests that amylin is involved not only in the protection but also in the healing mechanisms in this type of ulcer
Stabilization of stochastic quantum dynamics via open and closed loop control.
No full textIn this paper we investigate parametrization free solutions of the problem of quantum pure state preparation
and subspace stabilization by means of Hamiltonian control, continuous measurement and quantum feedback, in the presence of a Markovian environment. In particular,
we show that whenever suitable dissipative effects are induced either by the unmonitored environment, or by non Hermitian measurements, there is no need for feedback, as open-loop time-invariant control is sufficient to achieve stabilization of the target set in probability. Constructive necessary and sufficient conditions on the form of the control Hamiltonian can be provided in this case. When time-invariant control is not sufficient, state stabilization in expectation can be attained by the addition of filteringbased
feedback control
The role of bisphosphonates in the treatment of painful metastatic bone disease: A review of phase III trials
No full textMetastatic bone disease is a frequent cause of morbidity in advanced cancer patients with a subsequent high incidence of skeletal complications (fractures, hypercalcemia, spinal cord compression) and severe pain. The osteolytic process is mainly characterized by an osteoclastic activity of bone resorption and inflammatory activity provoked by various cytokines and prostaglandins. Bisphosphonates represent a new class of drugs with inhibitory activity on bone resorption and on inflammatory processes which revealed themselves to be efficacious in a series of clinical conditions such as tumour-induced hypercalcemia, Paget's disease, osteoporosis and metastatic bone disease. The aim of this review of the literature is to show the analgesic efficacy of the different bisphosphonates in phase III studies carried out on patients with metastatic bone disease. Medline and Cancerlit database from January 1984 to February 1998 have been considered. From the analysis of the published studies it appears that bisphosphonates and, in particular, intravenous Disodium Pamidronate, are not only able to slow down the progression of the disease and to reduce the onset of skeletal complications but also have an analgesic effect and the possibility of improving the quality of life, above all in patients with osteolytic metastases due to breast cancer and multiple myeloma. Bisphosphonates represent a further valid therapy to add to an already consolidated list of therapies such as radio, chemo and endocrine therapy, analgesic drugs, orthopaedic and physiatric in the pain management of patients with bone metastases. These drugs meet with the patients' compliance, are well-tolerated as well as having a good cost/efficacy profile. It still remains to be seen if the newer and more potent bisphosphonates such as Ibandronate and Zoledronate can be administered differently from the intravenous route such as by mouth or by patch which are readily accepted by the patient and, moreover, if these more potent drugs are able to prevent or delay the onset and/or the progression of bone metastases. Copyright (C) 1998 International Association for the Study of Pain. Published by Elsevier Science B.V
Exact and approximate solutions for the quantum minimum-Kullback-entropy estimation problem
No full textThe minimum-Kullback-entropy principle (mKE) is a useful tool to estimate quantum states and operations from incomplete data and prior information. In general, the solution of an mKE problem is analytically challenging and an approximate solution has been proposed and employed in different contexts. Recently, the form and a way to compute the exact solution for finite dimensional systems has been found, and a question naturally arises on whether the approximate solution could be an effective substitute for the exact solution, and in which regimes this substitution can be performed. Here, we provide a systematic comparison between the exact and the approximate mKE solutions for a qubit system when average data from a single observable are available. We address both mKE estimation of states and weak Hamiltonians, and compare the two solutions in terms of state fidelity and operator distance. We find that the approximate solution is generally close to the exact one unless the initial state is near an eigenstate of the measured observable. Our results provide a rigorous justification for the use of the approximate solution whenever the above condition does not occur, and extend its range of application beyond those situations satisfying the assumptions used for its derivation
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