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Search Results: 1 - 10 of 144491 matches for " Melchert F "
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HIV-Infektion und assistierte Reproduktion - heute schon medizinisch und ethisch vertretbar?
Weigel M,Beichert M,Melchert F
Journal für Fertilit?t und Reproduktion , 2001,
Abstract: Die Fortschritte der antiretroviralen Therapie haben in den letzten Jahren die Lebensperspektive vieler HIV-infizierter Menschen soweit verbessert, da vielfach auch der Wunsch nach einem eigenen Kind erw chst. Dessen Erfüllung steht aber das Infektionsrisiko für den gesunden Partner bzw. die gesunde Partnerin entgegen. Verfahren der assistierten Reproduktion weisen zwar einen Ausweg aus diesem Dilemma, ihrer Anwendung bei HIV-diskordanten Paaren stehen aber teilweise medizinische, ethische und juristische Bedenken entgegen. Bei HIV-positiven Frauen scheint diese Zurückhaltung insbesondere aus haftungsrechtlichen Erw gungen wegen des Risikos einer materno-fetalen Virustransmission gegenw rtig noch gerechtfertigt. Bei HIV-Infektion des Ehemannes besteht dagegen eine medizinische Indikation für Verfahren der assistierten Reproduktion. Denn durch standardisierte Aufbereitungstechniken k nnen motile Spermien von im Ejakulat enthaltenen HI-Viren separiert werden und stehen nach Testung mittels hochempfindlicher Nachweisverfahren für eine Behandlung der gesunden Partnerin zur Verfügung. Die dabei heute erreichten Standards k nnen medizinische, ethische und rechtliche Bedenken weitgehend ausr umen.
Emergent loop current order from pair density wave superconductivity
Daniel F. Agterberg,Drew S. Melchert,Manoj K. Kashyap
Physics , 2014, DOI: 10.1103/PhysRevB.91.054502
Abstract: There is evidence that the pseudogap phase in the cuprates breaks time-reversal symmetry. Here we show that pair density wave (PDW) states give rise to a translational invariant nonsuperconducting order parameter that breaks time-reversal and parity symmetries, but preserves their product. This secondary order parameter has a different origin, but shares the same symmetry properties as a magnetoelectric loop current order that has been proposed earlier in the context of the cuprates to explain the appearance of intracell magnetic order. We further show that, due to fluctuations, this secondary loop current order, which breaks only discrete symmetries, can preempt PDW order, which breaks both continuous and discrete symmetries. In such a phase, the emergent loop current order coexists with spatial short-range superconducting order and possibly short-range charge density wave (CDW) order. Finally, we propose a PDW phase that accounts for intracell magnetic order and the Kerr effect, has CDW order consistent with x-ray scattering and nuclear magnetic resonance observations, and quasi-particle properties consistent with angle-resolved photoemission scattering.
The Life and Works of Abū Dāwūd al-Sijistānī
Melchert, Christopher
Al-Qantara : Revista de Estudios Arabes , 2008,
Abstract: Abū Dāwūd al-Sijistānī (m. en Basora, 275/889) fue un eminente recopilador de hadices proféticos. Parece que esa labor de compilación la hizo en Iraq, La Meca y Siria entre los a os 220-35 H.; en Jorasán hasta principios de la siguiente década y, ya nuevamente en Iraq y Siria, además de Egipto, hasta el a o 250 H. Afirmó haber recopilado 500.000 hadices en total. Entre 250 y 270 H. permaneció fundamentalmente en Tarso, componiendo su famosa al-Sunan y dedicó los cinco últimos a os de su vida a ense ar cerca de Basora. Este artículo revisa los trabajos conocidos del autor, especialmente al-Sunan, que llegará a ser uno de los “Seis libros” (compilaciones canónicas de hadiz). Esta obra fue transmitida, con peque as variaciones, por nueve tradicionistas que la tomaron de él. Casi el 90% de las tradiciones se remontan al Profeta. Esta obra se diferencia de otras colecciones porque se centra en hadices que clasifican acciones (a kām). Los comentarios expresos de Abū Dāwūd dentro de la obra se refieren a versiones alternativas, aplicaciones legales y la ciencia del rijāl. Dado que pocas veces repite un mismo hadiz bajo diferentes epígrafes, se trata probablemente de la más larga de las seis colecciones canónicas de hadices. Debe reconocerse que Abū Dāwūd era bastante descuidado a la hora de identificar individuos en las cadenas de transmisión. Su colección independiente de hadices relativos a la renuncia ascética, al-Zuhd, comprende fundamentalmente dichos de los Compa eros del Profeta. Por lo que se refiere al derecho, Abū Dāwūd estaba cerca de A mad b. anbal (m. 241/855). En teología se adhirió al movimiento de los ahl al-sunnah wa-l- amā‘a del siglo IX. Se dice que admiraba y era admirado por el proto-sufi Sahl al-Tustarī (m. 283/896?). Abū Dāwūd al-Sijistānī (d. Basra, 275/889) was a prominent collector of prophetic hadith. He seems to have collected in Iraq, Mecca, and Syria A.H. 220-35, then Khurasan till the early 240s, then Iraq, Syria, and Egypt till around 250. He claimed to have collected 500,000 in all. He spent most of the years 250-70 in Tarsus, composing his famous Sunan, then the last five years of his life teaching near Basra. This article reviews Abū Dāwūd's known works, especially al-Sunan, which became one of the Six Books. The Sunan was transmitted from him in slightly different versions by nine named traditionists. A little under 90 percent of it goes back to the Prophet. It is distinguished from other collections by its concentration on hadith that classify actions (a kām). Abū Dāwūd's express comments within the Sunan concern alternati
autoScale.py - A program for automatic finite-size scaling analyses: A user's guide
O. Melchert
Physics , 2009,
Abstract: autoScale.py is a program that performs an automatic finite-size scaling analysis for given sets of simulated data. It implements a quite general scaling assumption and optimizes an initial set of scaling parameters that enforce a data collapse of the different data sets. The presented guide describes how the program works, it presents a detailed example and finally gives some hints on how to improve the results of a scaling analysis.
Encryption dynamics and avalanche parameter for "delayed dynamics"-based cryptosystems
O. Melchert
Physics , 2012,
Abstract: The presented article attempts to characterize the encryption dynamics of delayed dynamics based block ciphers, designed for the encryption of binary data. For such encryption algorithms, the encryption process relies on a coupling dynamics with time delay between different bits in the plaintext (i.e.\ the "initial" message to be encrypted). Here, the principal dynamics of the encryption process is examined and the Hammingdistance is used to quantify the change in ciphertext (i.e.\ the plaintext after encryption) upon changing a single bit in the plaintext message or slightly perturbing the key used during encryption. More precisely, the previously proposed "encryption via delayed dynamics" (in short: EDDy) algorithm as well as its extended version (termed ExEDDy) are analyzed by means of numerical simulations. As a result it is found that while EDDy exhibits a rather poor perfomance, ExEDDy performes considerably better and hence constitutes a significant improvement over EDDy. Consequently, the results are contrasted with those obtained for a block cipher that implements the encryption/decryption dynamics by means of reversible cellular automata.
Minimum weight spanning trees of weighted scale free networks
O. Melchert
Physics , 2012,
Abstract: In this lecture we will consider the minimum weight spanning tree (MST) problem, i.e., one of the simplest and most vital combinatorial optimization problems. We will discuss a particular greedy algorithm that allows to compute a MST for undirected weighted graphs, namely Kruskal's algorithm, and we will study the structure of MSTs obtained for weighted scale free random graphs. This is meant to clarify whether the structure of MSTs is sensitive to correlations between edge weights and topology of the underlying scale free graphs.
The universality class of the continuous phase transition in the 2D "Touch and Stop" cluster growth percolation model
O. Melchert
Physics , 2012, DOI: 10.1103/PhysRevE.87.022115
Abstract: We consider the "Touch and Stop" cluster growth percolation (CGP) model on the two dimensional square lattice. A key-parameter in the model is the fraction p of occupied "seed" sites that act as nucleation centers from which a particular cluster growth procedure is started. Here, we consider two growth-styles: rhombic and disk-shaped cluster growth. For intermediate values of p the final state, attained by the growth procedure, exhibits a cluster of occupied sites that spans the entire lattice. Using numerical simulations we investigate the percolation probability and the order parameter and perform a finite-size scaling analysis for lattices of side length up to L=1024 in order to carefully determine the critical exponents that govern the respective transition. In contrast to previous studies, reported in [Tsakiris et al., Phys. Rev. E 82 (2010) 041108], we find strong numerical evidence that the CGP model is in the standard percolation universality class.
Percolation thresholds on planar Euclidean relative neighborhood graphs
O. Melchert
Physics , 2013, DOI: 10.1103/PhysRevE.87.042106
Abstract: In the presented article, statistical properties regarding the topology and standard percolation on relative neighborhood graphs (RNGs) for planar sets of points, considering the Euclidean metric, are put under scrutiny. RNGs belong to the family of ``proximity graphs'', i.e. their edge-set encodes proximity information regarding the close neighbors for the terminal nodes of a given edge. Therefore they are, e.g., discussed in the context of the construction of backbones for wireless ad-hoc networks that guarantee connectedness of all underlying nodes. Here, by means of numerical simulations, we determine the asymptotic degree and diameter of RNGs and we estimate their bond and site percolation thresholds, which were previously conjectured to be nontrivial. We compare the results to regular 2D graphs for which the degree is close to that of the RNG. Finally, we deduce the common percolation critical exponents from the RNG data to verify that the associated universality class is that of standard 2D percolation.
Basic Data Analysis and More - A Guided Tour Using Python
O. Melchert
Physics , 2012,
Abstract: In these lecture notes, a selection of frequently required statistical tools will be introduced and illustrated. They allow to post-process data that stem from, e.g., large-scale numerical simulations (aka sequence of random experiments). From a point of view of data analysis, the concepts and techniques introduced here are of general interest and are, at best, employed by computational aid. Consequently, an exemplary implementation of the presented techniques using the Python programming language is provided. The contents of these lecture notes is rather selective and represents a computational experimentalist's view on the subject of basic data analysis, ranging from the simple computation of moments for distributions of random variables to more involved topics such as hierarchical cluster analysis and the parallelization of Python code.
Constru??o de uma cela de fluxo de longo caminho óptico para medidas espectrofotométricas
Melchert, Wanessa Roberto;Rocha, Fábio R. P.;Raimundo Jr., Ivo M.;Reis, Boaventura F.;
Química Nova , 2008, DOI: 10.1590/S0100-40422008000200042
Abstract: a simple and low-cost flow cell with 30 cm optical path for spectrophotometric measurements is described. it presents desirable characteristics such as low attenuation of the radiation beam and internal volume (75 μl) comparable to that of a 1-cm conventional cell (80 μl). despite the increase in optical path, the effect on sample dispersion was also similar to that attained in the commercial cell. the performance of the cell was assessed by the determination of phosphate based on the molybdenum blue method, yielding a linear response range between 0.05 and 0.8 mg l-1 phosphorus (r=0.999). the increase in sensitivity (30.4-fold) in comparison with that obtained with a conventional 1-cm flow cell agreed with that estimated by the lambert-beer law.
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