The usability of the optical parametric amplification of light for high-angular-resolution imaging and fast astrometry

High-angular-resolution imaging is crucial for many applications in modern astronomy and astrophysics. The fundamental diffraction limit constrains the resolving power of both ground-based and spaceborne telescopes. The recent idea of a quantum telescope based on the optical parametric amplification (OPA) of light aims to bypass this limit for the imaging of extended sources by an order of magnitude or more. We present an updated scheme of an OPA-based device and a more accurate model of the signal amplification by such a device. The semiclassical model that we present predicts that the noise in such a system will form so-called light speckles as a result of light interference in the optical path. Based on this model, we analysed the efficiency of OPA in increasing the angular resolution of the imaging of extended targets and the precise localization of a distant point source. According to our new model, OPA offers a gain in resolved imaging in comparison to classical optics. For a given time-span, we found that OPA can be more efficient in localizing a single distant point source than classical telescopes.Comment: Received: 11 November 2017, revision received: 31 January 2018, accepted: 31 January 201

Quantum channels and their entropic characteristics

One of the major achievements of the recently emerged quantum information theory is the introduction and thorough investigation of the notion of quantum channel which is a basic building block of any data-transmitting or data-processing system. This development resulted in an elaborated structural theory and was accompanied by the discovery of a whole spectrum of entropic quantities, notably the channel capacities, characterizing information-processing performance of the channels. This paper gives a survey of the main properties of quantum channels and of their entropic characterization, with a variety of examples for finite dimensional quantum systems. We also touch upon the "continuous-variables" case, which provides an arena for quantum Gaussian systems. Most of the practical realizations of quantum information processing were implemented in such systems, in particular based on principles of quantum optics. Several important entropic quantities are introduced and used to describe the basic channel capacity formulas. The remarkable role of the specific quantum correlations - entanglement - as a novel communication resource, is stressed.Comment: review article, 60 pages, 5 figures, 194 references; Rep. Prog. Phys. (in press

Rotation sensing at the ultimate limit

Conventional classical sensors are approaching their maximum sensitivity levels in many areas. Yet these levels are still far from the ultimate limits dictated by quantum mechanics. Quantum sensors promise a substantial step ahead by taking advantage of the salient sensitivity of quantum states to the environment. Here, we focus on sensing rotations, a topic of broad application. By resorting to the basic tools of estimation theory, we derive states that achieve the ultimate sensitivities in estimating both the orientation of an unknown rotation axis and the angle rotated about it. The critical enhancement obtained with these optimal states should make of them an indispensable ingredient in the next generation of rotation sensors that is now blossoming

Performance analysis of the parallel acquisition of weak GPS signals

This thesis provides a comprehensive analysis of the acquisition performance of the mobile-embedded Global Positioning System (GPS) receiver. Particular emphasis is given to the analysis of differentially coherent processing techniques and parallel acquisition strategies. New analytical expressions for the distribution of the decision variable of differentially coherent detectors are derived. In addition, new Gaussian approximations are derived and shown to be more accurate than existing approximations. Using these Gaussian approximations it is demonstrated that the traditional noncoherent combining detector is the best choice when the signal to noise ratio is large, but that differentially coherent combining is a superior choice at low signal to noise ratios. An analysis of the effects of carrier Doppler, code Doppler and data modulation on detector performance is also conducted. For the noncoherent combining detector, new expressions are obtained for the mean and worst case power attenuation due to the combined effects of carrier Doppler and data modulation. Approximate expressions are also derived for the differentially coherent combining detector. New expressions are also obtained for the mean and variance of the time to first hit using a Markov chain model and matrix methods. These models permit the use of numerical techniques to determine the optimal choice of receiver parameters for a given performance requirement. Finally the effect of unknown power levels and multi-access interference (MAI) are considered. A novel technique for detecting MAI, referred to as the power level detector, is introduced and its performance analysed. All results are verified by Monte Carlo computer simulation using a simplified signal model. The simulations were implemented on a 100 processor computer cluster

Data transmission through channels pertubed by impulsive noise

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New Directions for Contact Integrators

Contact integrators are a family of geometric numerical schemes which guarantee the conservation of the contact structure. In this work we review the construction of both the variational and Hamiltonian versions of these methods. We illustrate some of the advantages of geometric integration in the dissipative setting by focusing on models inspired by recent studies in celestial mechanics and cosmology.Comment: To appear as Chapter 24 in GSI 2021, Springer LNCS 1282

Evaluating the evidence base in pharmacovigilance decision making

Introduction It has been said that through monitoring of drug safety, pharmacovigilance (PV) systems have been instrumental in assisting regulatory decisions on product safety. However, there has been no, systematic, in-depth study of this role. This thesis reports such a study conducted in the UK. On the basis of the results, suggestions are made on how PV data might be produced and used more effectively. Methods In Phase 1, a scoping study was conducted to document all changes made to UK product labelling on safety grounds over a 10 year period (September 1st 1995 to August 31st 2005). In Phase 2, all product withdrawals and major labelling changes made during the 10 year study above, were investigated in depth to determine the therapeutic group, source of ADR data cited as the reason for the change; and product survival probability, using Kaplan-Meier modelling. Phase 3, informed by Phases 1 and 2, used a web-based survey (150 respondents) and structured interviews (13 subjects) with healthcare professionals and scientists with a PV role in the NHS, pharmaceutical companies and the UK regulator, to gain views on the current procedures for handling safety issues in the UK and how these might be improved. Inferences were drawn using interpretative henomenological analysis with NVivo 8 software. Key findings Phases 1 and 2 revealed the fragmentary nature of information in the public domain and the difficulties of obtaining unpublished information. Based on public information, Phase 1 showed that 2,630 safety notices were issued affecting 688 individual products. The two main safety notice categories were drug interactions (841;32%) and side effects (537;20%). The rank order of the four most common therapeutic areas in which safety notices occurred was: CNS (23.5%)> anti-infectives (21.6%) > cardiovascular (15.2%) > cancer chemotherapy (10.8%). The ratio of Type A : Type B side effects (ADRs) was 1:3.3. Phase 2 found that of 518 eligible products launched during the study period, 9 (1.7%) were licensed and withdrawn for safety reasons. The ten-year Kaplan-Meier probability of adverse drug reactions causing the withdrawal of a new product, postmarketingwas 2.2%. All decisions were based on more than one safety data type and all involved UK yellow cards. One decision considered prescription event monitoring (PEM) data. A total of 164 important safety notices affecting 818 individual products were identified. Of 518 products launched during the study period, 56 experienced at least one major labelling change for safety reasons. The ten-year Kaplan-Meier risk of a product experiencing at least one major labelling change on safety grounds was 13.8%. As with product withdrawals, safety decisions were based on a wide range of data sources of variable quality and quantity. Variation in dissemination of the new safety information was observed. Only one fifth of safety notices warranting a ‘Dear Healthcare Professional’ letter or a monograph in ‘Current Problems in Pharmacovigilance’, were accompanied by a boxed warning in the BNF, representing an important inconsistency in notifying prescribers. As with interview participants, respondents to the on-line questionnaire had difficulties placing the yellow card reports in a formal hierarchy of evidence whilst acknowledging that the data were valuable in the decision making process. Suggested ways of improving the quality of such reports included making the reporting more accessible and training all those eligible to report. PEM studies were cited by the majority of respondents as a means of generating credible safety data and raising the general quality of the drug safety database. In terms of dissemination and education about ADRs, Drug Safety Updates (which replaced the ‘Current Problems’ publication from the MHRA in August 2007) were highly thought of; they appeared to be more popular than ‘Dear Healthcare Professional’ letters and because they were web-based, ought to be accessible by a wider audience. Conclusions Safeguarding public health is of utmost importance when making a decision whether or not to withdraw a product or amend its labelling upon the emergence of new safety data. Labelling changes should be made only on the best evidence available at the time and appropriate risk management strategies should be instigated where feasible; not only when a safety signal arises post-marketing, but when a drug is first granted a marketing authorisation. There is no general consensus on what constitutes ‘best evidence’ and rating evidence using traditional hierarchies is problematic, The GRADE hierarchy may be an exception. Improving ADR reporting should lead to improved data bases from which to draw safety conclusions. Methods of improving reporting include early instigation and enforcement of risk management plans by the regulator, education of all those eligible to report, greater transparency of regulatory decisions and better and more rapid dissemination of safety change information.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Cognitive Radio Systems

Cognitive radio is a hot research area for future wireless communications in the recent years. In order to increase the spectrum utilization, cognitive radio makes it possible for unlicensed users to access the spectrum unoccupied by licensed users. Cognitive radio let the equipments more intelligent to communicate with each other in a spectrum-aware manner and provide a new approach for the co-existence of multiple wireless systems. The goal of this book is to provide highlights of the current research topics in the field of cognitive radio systems. The book consists of 17 chapters, addressing various problems in cognitive radio systems

Application of diversity techniques for solving the problems of the effects impurities in optical fibers on the performance of optical systems

We analyzed the methods for reducing the impact of noise and interference, the performance of digital optical IM-DD system. Performances of digital optical telecommunication systems, as well as their improvement, were analyzed using standard criteria for evaluation: outage probability, average probability, channel capacity, and average fading duration. These performance measures are determined on the basis of statistical characteristics of the first and second rows of signal reception and are part of the technical documentation accompanying each of the realized digital optical communication system. Therefore, the closed form of expressions, derived in this dissertation, which can be used to calculate the statistical characteristics of signal reception, represent a significant contribution, in terms of design of digital optical transmission systems. Our analysis is placed on theoretical consideration on so far untreated cases, and therefore the theoretical basis of physical phenomena that affect the transmission through the digital optical systems, well known from the literature, are not further elaborated. We included a procedure for determining the expression for the multidimensional joint probability density distribution with correlated and uncorrelated random variables. The derived expressions have a wide range of applicability and are an excellent basis for further performance analysis of optical digital transmission systems, in terms of correlated channels, as well as the characteristics of the connection by using multiple-input receiver. Their practical use is demonstrated especially in the section that deals λSK optical systems, as well as the part of that processes - the relay optical systems. Improving the transmission reliability and reducing the impact of noise and interference on the performance of digital optical telecommunication systems, with a reduction in power transmission and increasing the distance between the transmitter and receiver, is analyzed through the applying of techniques using spatial diversity reception. The dissertation discussed the various techniques of spatial combining receiving signals from the receiving branches of optical systems, in terms of reducing impact noise and interference. Ratios were formed and interference signals at the entrance combiner branches and under the terms of the previous chapter are determined by the joint probability density of these relationships for all incoming branches and the corresponding joint cumulative probability. Using this statistical feature of the incoming signal and interference are determined and statistical characteristics of signal-to-interference at the output of given combiner, which represents the next significant contribution to the dissertation. The contribution of these derived expressions can be seen from the aspect of using the results obtained for the case of the proposed statistical modeling of the channel model when considering the reduction of the impact of various types of noise and interference, and examination performance enhancements of digital optical telecommunication systems using diversity reception techniques. Specifically, by assigning appropriate values of parameters in the corresponding expressions, which describe the statistical characteristics of the first order of receipt, an analysis of the value of standard measures of performance of optical telecommunication systems, as well as improve their use of spatial diversity techniques, for cases when the communication channel is exposed to various types of interference and noises. Using the derived expressions can be shown to improve all the standard measure of performance of optical telecommunication systems. Also, when transferred unchanged forces the useful signal and interference, and at the same range of connections, get better system performance (lower values of the probability of cancellation, less the value of average bet error probability, lower average fading duration...). Based on these facts can be concluded that the required the outage probability values (ABEP) for the reception, when we apply the described techniques of receipt, in the same range of connections and the same noise power, can achieve the necessary reduction of the useful signal power in transmission, that is, at the same useful signal power, the same level of interference in the channel, the required the outage probability (ASEP) at the reception, when we apply the described techniques of receipt, can be achieved at larger distances from the transmitting terminal