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Health economic analysis of screening
Krauth, Christian
GMS Current Topics in Otorhinolaryngology, Head and Neck Surgery , 2008,
Abstract: In this article health economic implications of screening are analysed. First, requirements screening programmes should fulfil are derived, and methodical standards of health economic evaluation are outlined. Using the example of newborn hearing screening, it is then examined if empirical studies meet the methodical requirements of health economic evaluation. Some deficits are realised: Health economic studies of newborn hearing screening are not randomised, most studies are even not controlled. Therefore, most studies do not present incremental, but only average cost-effectiveness ratios (i.e. cost per case identified). Furthermore, evidence on long-term outcomes of screening and early interventions is insufficient. In conclusion, there is a need for controlled trials to examine differences in identified cases, but particularly to examine long-term effects.
Quantum Monte Carlo Calculations for a large number of bosons in a harmonic trap
Werner Krauth
Physics , 1996, DOI: 10.1103/PhysRevLett.77.3695
Abstract: In this paper, I present a precise Quantum Monte Carlo calculation at finite temperature for a very large number (many thousands) of bosons in a harmonic trap, which may be anisotropic. The calculation applies directly to the recent experiments of Bose-Einstein condensation of atomic vapors in magnetic traps. I show that the critical temperature of the system decreases with the interaction. I also present profiles for the overall density and the one of condensed particles, and obtain excellent agreement with solutions of the Gross-Pitaevskii equation.
Introduction To Monte Carlo Algorithms
Werner Krauth
Physics , 1996,
Abstract: In these lectures, given in '96 summer schools in Beg-Rohu (France) and Budapest, I discuss the fundamental principles of thermodynamic and dynamic Monte Carlo methods in a simple light-weight fashion. The keywords are MARKOV CHAINS, SAMPLING, DETAILED BALANCE, A PRIORI PROBABILITIES, REJECTIONS, ERGODICITY, "FASTER THAN THE CLOCK ALGORITHMS". The emphasis is on ORIENTATION, which is difficult to obtain (all the mathematics being simple). A firm sense of orientation helps to avoid getting lost, especially if you want to leave safe trodden-out paths established by common usage. Even though I remain quite basic (and, I hope, readable), I make every effort to drive home the essential messages, which are easily explained: the crystal-clearness of detail balance, the main problem with Markov chains, the great algorithmic freedom, both in thermodynamic and dynamic Monte Carlo, and the fundamental differences between the two problems.
Four lectures on computational statistical physics
Werner Krauth
Physics , 2009,
Abstract: In my lectures at the Les Houches Summer School 2008, I discussed central concepts of computational statistical physics, which I felt would be accessible to the very cross-cultural audience at the school. I started with a discussion of sampling, which lies at the heart of the Monte Carlo approach. I specially emphasized the concept of perfect sampling, which offers a synthesis of the traditional direct and Markov-chain sampling approaches. The second lecture concerned classical hard-sphere systems, which illuminate the foundations of statistical mechanics, but also illustrate the curious difficulties that beset even the most recent simulations. I then moved on, in the third lecture, to quantum Monte Carlo methods, that underly much of the modern work in bosonic systems. Quantum Monte Carlo is an intricate subject. Yet one can discuss it in simplified settings (the single-particle free propagator, ideal bosons) and write direct-sampling algorithms for the two cases in two or three dozen lines of code only. These idealized algorithms illustrate many of the crucial ideas in the field. The fourth lecture attempted to illustrate aspects of the unity of physics as realized in the Ising model simulations of recent years. More details on what I discussed in Les Houches, and wrote up (and somewhat rearranged) here, can be found in my book, "Statistical Mechanics: Algorithms and Computations", as well as in recent papers. Computer programs are available for download and perusal at the book's web site www.smac.lps.ens.fr.
Coming home from a MOOC
Werner Krauth
Physics , 2014,
Abstract: My ten-week Massive Open Online Course "Statistical Mechanics: Algorithms and Computations", in early 2014, focused on subjects such as Monte Carlo sampling, molecular dynamics, transition phases in hard-sphere liquids, simulated annealing, classical spin models, quantum Monte Carlo algorithms, and Bose-Einstein condensation, etc. It familiarized a huge international crowd of students with cutting-edge subjects in computational physics. Here, I present the topics of the course, its basic design ideas, its scope and challenges, and compare it with earlier attempts in online teaching.
Disks on a Sphere and two-dimensional Glasses
Werner Krauth
Physics , 2002,
Abstract: I describe the classic circle-packing problem on a sphere, and the analytic and numerical approaches that have been used to study it. I then present a very simple Markov-chain Monte Carlo algorithm, which succeeds in finding the best solutions known today. The behavior of the algorithm is put into the context of the statistical physics of glasses.
Cluster Monte Carlo algorithms
Werner Krauth
Physics , 2003,
Abstract: In recent years, a better understanding of the Monte Carlo method has provided us with many new techniques in different areas of statistical physics. Of particular interest are so called cluster methods, which exploit the considerable algorithmic freedom given by the detailed balance condition. Cluster algorithms appear, among other systems, in classical spin models, such as the Ising model, in lattice quantum models (bosons, quantum spins and related systems) and in hard spheres and other `entropic' systems for which the configurational energy is either zero or infinite. In this chapter, we discuss the basic idea of cluster algorithms with special emphasis on the pivot cluster method for hard spheres and related systems, for which several recent applications are presented.We provide less technical detail but more context than in the original papers.
Comment on ``Critical temperature of trapped hard-sphere Bose gases''
Werner Krauth
Physics , 1998,
Abstract: In this comment, I discuss a recent path-integral Monte Carlo calculation by Pearson, Pang, and Chen (Phys. Rev. A 58, 4796 (1998)). For bosons with a small hard-core interaction in a harmonic trap, the authors find a critical temperature which does not change with respect to the non-interacting gas. The calculation suffers from a serious discretization error of the many-particle density matrix.
Coexistence of solutions in dynamical mean-field theory of the Mott transition
Werner Krauth
Physics , 1999, DOI: 10.1103/PhysRevB.62.6860
Abstract: In this paper, I discuss the finite-temperature metal-insulator transition of the paramagnetic Hubbard model within dynamical mean-field theory. I show that coexisting solutions, the hallmark of such a transition, can be obtained in a consistent way both from Quantum Monte Carlo (QMC) simulations and from the Exact Diagonalization method. I pay special attention to discretization errors within QMC. These errors explain why it is difficult to obtain the solutions by QMC close to the boundaries of the coexistence region.
Two-Dimensional QCD in the Wu-Mandelstam-Leibbrandt Prescription
Matthias Staudacher,Werner Krauth
Physics , 1997, DOI: 10.1103/PhysRevD.57.2456
Abstract: We find the exact non-perturbative expression for a simple Wilson loop of arbitrary shape for U(N) and SU(N) Euclidean or Minkowskian two-dimensional Yang-Mills theory regulated by the Wu-Mandelstam-Leibbrandt gauge prescription. The result differs from the standard pure exponential area-law of YM_2, but still exhibits confinement as well as invariance under area-preserving diffeomorphisms and generalized axial gauge transformations. We show that the large N limit is NOT a good approximation to the model at finite N and conclude that Wu's N=infinity Bethe-Salpeter equation for QCD_2 should have no bound state solutions. The main significance of our results derives from the importance of the Wu-Mandelstam-Leibbrandt prescription in higher-dimensional perturbative gauge theory.
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