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Search Results: 1 - 10 of 30755 matches for " Robert Werner "
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Bowen-York Tensors
Robert Beig,Werner Krammer
Physics , 2004, DOI: 10.1088/0264-9381/21/3/005
Abstract: There is derived, for a conformally flat three-space, a family of linear second-order partial differential operators which send vectors into tracefree, symmetric two-tensors. These maps, which are parametrized by conformal Killing vectors on the three-space, are such that the divergence of the resulting tensor field depends only on the divergence of the original vector field. In particular these maps send source-free electric fields into TT-tensors. Moreover, if the original vector field is the Coulomb field on $\mathbb{R}^3\backslash \lbrace0\rbrace$, the resulting tensor fields on $\mathbb{R}^3\backslash \lbrace0\rbrace$ are nothing but the family of TT-tensors originally written down by Bowen and York.
Introduction: Racial and Ethnic Conflict and Violence
Werner Bergmann,Robert D. Crutchfield
International Journal of Conflict and Violence , 2009,
Abstract: Racial and ethnic violence takes many forms. Genocides, ethnic cleansing, pogroms, civil wars, and violent separatist movements are the most obvious and extreme expressions, but less organized violence such as rioting, and hate crimes by individuals or small groups are products of racial and ethnic conflict as well. Also, the distribution of criminal violence within societies, which may or may not be aimed at members of another group, is in some places a by-product of ongoing conflicts between superior and subordinated racial or ethnic groups. Although estimates of the number of deaths attributable to ethnic violence vary widely, range of eleven to twenty million given for the period between 1945 and the early 1990s show the gravity of this type of conflict (Williams 1994, 50). So it comes as no surprise that scholars have paid increasing attention to such conflicts over the last decades.
Organic carbon dynamics and enzyme activities in agricultural soils amended with biogas slurry, liquid manure and sewage sludge  [PDF]
Britta Stumpe, Steffen Werner, Robert Jung, Stefanie Heinze, Elisabeth Jüschke, Christian Strippel, Bernd Marschner
Agricultural Sciences (AS) , 2012, DOI: 10.4236/as.2012.31014
Abstract: The application of organic soil amendments is a common practice for increasing soil fertility and soil organic carbon (SOC) content. In recent years, a new product from biogas production, biogas slurry is increasingly applied to agricultural soils, although little is known about its effects on soil properties. In this study, the influence of this new product in comparison with liquid manure and sewage sludge on the organic carbon dynamics and enzyme activities were investigated in two different agricultural soils in short-term incubation studies. As a control, biologically inert sand was also amended with these organic wastes. In sand, biogas slurry degraded to 10.4% within 14 days, while no differences were found between the degradability of liquid manure and sewage sludge with 6.6% and 5.4%, respectively. However, although the degradability of biogas slurry was highest among the organic amendments, liquid manure application resulted in the highest respiration rates in the soil samples. This was likely due to the organic waste borne easily decomposable substrates which were most dominant in liquid manure. Organic waste applications were found to generally increase the activity of numerous enzymes but did not change the soil enzyme patterns. Thus, in general it was shown that the microbial population of the organic wastes will not become prominent when introduced with the manures to soils. Thus, an inoculation with organic waste borne microorganisms could likely be neglected when discussing the extent of organic carbon dynamics after organic waste application to agricultural soils.
Self tolerance in a minimal model of the idiotypic network
Robert Schulz,Benjamin Werner,Ulrich Behn
Quantitative Biology , 2013,
Abstract: We consider the problem of self tolerance in the frame of a minimalistic model of the idiotypic network. A node of this network represents a population of B lymphocytes of the same idiotype which is encoded by a bit string. The links of the network connect nodes with (nearly) complementary strings. The population of a node survives if the number of occupied neighbours is not too small and not too large. There is an influx of lymphocytes with random idiotype from the bone marrow. Previous investigations have shown that this system evolves toward highly organized architectures, where the nodes can be classified into groups according to their statistical properties. The building principles of these architectures can be analytically described and the statistical results of simulations agree very well with results of a modular mean field theory. In this paper we present simulation results for the case that one or several nodes, playing the role of self, are permanently occupied. We observe that the group structure of the architecture is very similar to the case without self antigen, but organized such that the neighbours of the self are only weakly occupied, thus providing self tolerance. We also treat this situation in mean field theory which give results in good agreement with data from simulation.
Werner Seebacher,Robert Weis,Robert Saf,Ferdinand Belaj
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810013619
Abstract: The title compound, C24H18N2, is the first structural example containing the 3,4-dihydrobenzo[b][1,6]naphthyridine fragment. It was synthesized from 2,4,6,8-tetraphenyl-3,7-diazabicyclo[3.3.1]nonan-9-one and was crystallized from a methanol–ethanol solution over two years as a racemate. The C=N double bond [1.2868 (15) ] is bent significantly out of the plane of the aromatic bicyclic ring system [N—C—C—C = 157.63 (12)°] and out of the plane of the phenyl ring bonded at the 1-position [N—C—C—C = 41.15 (16)°].
Asymptotic behavior of quantum walks with spatio-temporal coin fluctuations
Andre Ahlbrecht,Christopher Cedzich,Robert Matjeschk,Volkher B. Scholz,Albert H. Werner,Reinhard F. Werner
Physics , 2012, DOI: 10.1007/s11128-012-0389-4
Abstract: Quantum walks subject to decoherence generically suffer the loss of their genuine quantum feature, a quadratically faster spreading compared to classical random walks. This intuitive statement has been verified analytically for certain models and is also supported by numerical studies of a variety of examples. In this paper we analyze the long-time behavior of a particular class of decoherent quantum walks, which, to the best of our knowledge, was only studied at the level of numerical simulations before. We consider a local coin operation which is randomly and independently chosen for each time step and each lattice site and prove that, under rather mild conditions, this leads to classical behavior: With the same scaling as needed for a classical diffusion the position distribution converges to a Gaussian, which is independent of the initial state. Our method is based on non-degenerate perturbation theory and yields an explicit expression for the covariance matrix of the asymptotic Gaussian in terms of the randomness parameters.
Compliance with referral of sick children: a survey in five districts of Afghanistan
William Newbrander, Paul Ickx, Robert Werner, Farooq Mujadidi
BMC Pediatrics , 2012, DOI: 10.1186/1471-2431-12-46
Abstract: The study was conducted in 5 rural districts of 5 Afghan provinces using interviews with parents or caretakers in 492 randomly selected households with a child from 0 to 2 years old who had been sick within the previous 2 weeks with diarrhea, acute respiratory infection (ARI), or fever. Data collectors from local nongovernmental organizations used a questionnaire to assess compliance with a referral recommendation and identify barriers to compliance.The number of referrals, 99 out of 492 cases, was reasonable. We found a high number of referrals by community health workers (CHWs), especially for ARI. Caretakers were more likely to comply with referral recommendations from community members (relative, friend, CHW, traditional healer) than with recommendations from health workers (at public clinics and hospitals or private clinics and pharmacies). Distance and transportation costs did not create barriers for most families of referred sick children. Although the average cost of transportation in a subsample of 75 cases was relatively high (US$11.28), most families (63%) who went to the referral site walked and hence paid nothing. Most caretakers (75%) complied with referral advice. Use of referral slips by health care providers was higher for urgent referrals, and receiving a referral slip significantly increased caretakers’ compliance with referral.Use of referral slips is important to increase compliance with referral recommendations in rural Afghanistan.Child survival efforts in developing countries focus on applying basic lifesaving interventions to health problems faced by newborns, infants, and young children. These interventions are often applied by mothers or caretakers in the home, first-line health care providers such as community health workers (CHWs), or health care providers at the lowest-level health facility who have been trained to recognize common illnesses and provide basic treatment, such as oral rehydration solution and zinc for diarrhea. The import
The Proper Motion of the Central Compact Object RX J0822-4300 in the Supernova Remnant Puppis A
Werner Becker,Tobias Prinz,P. Frank Winkler,Robert Petre
Physics , 2012, DOI: 10.1088/0004-637X/755/2/141
Abstract: Using the High Resolution Camera (HRC) aboard the Chandra X-ray Observatory, we have re-examined the proper motion of the central compact object RX J0822-4300 in the supernova remnant Puppis A. New data from 2010 August, combined with three archival data sets from as early as 1999 December, provide a baseline of 3886 days (more than 10 1/2 years) to perform the measurement. Correlating the four positions of RX J0822-4300 measured in each data set implies a projected proper motion of mu 71 \pm 12 masy. For a distance of 2 kpc this proper motion is equivalent to a recoil velocity of 672 \pm 115 km/s. The position angle is found to be 244 \pm 11 degrees. Both the magnitude and direction of the proper motion are in agreement with RX J0822-4300 originating near the optical expansion center of the supernova remnant. For a displacement of 371 \pm 31 arcsec between its birth place and today's position we deduce an age of (5.2 \pm 1.0) 10^3 yrs for RX J0822-4300. The age inferred from the neutron star proper motion and filament motions can be considered as two independent measurements of the same quantity. They average to 4450 \pm 750 yrs for the age of the supernova remnant Puppis A.
Evolution of the stripe phase as a function of doping from a theoretical analysis of angle-resolved photoemission data
Marc G. Zacher,Robert Eder,Enrico Arrigoni,Werner Hanke
Physics , 2001, DOI: 10.1103/PhysRevB.65.045109
Abstract: By comparing single-particle spectral functions of t-J and Hubbard models with recent angle-resolved photoemission (ARPES) results for LSCO and Nd-LSCO, we can decide where holes go as a function of doping, and more specifically, which type of stripe (bond-, site-centered) is present in these materials at a given doping. For dopings greater than about 12% our calculation shows furthermore that the holes prefer to proliferate out of the metallic stripes into the neighboring antiferromagnetic domains. The spectra were calculated by a cluster perturbation technique, for which we present an alternative formulation. Implications for the theory for high-Tc superconductivity are discussed.
Stripes in Doped Antiferromagnets: Single-Particle Spectral Weight
Marc G. Zacher,Robert Eder,Enrico Arrigoni,Werner Hanke
Physics , 2000, DOI: 10.1103/PhysRevLett.85.2585
Abstract: Recent photoemission (ARPES) experiments on cuprate superconductors provide important guidelines for a theory of electronic excitations in the stripe phase. Using a cluster perturbation theory, where short-distance effects are accounted for by exact cluster diagonalization and long-distance effects by perturbation (in the hopping), we calculate the single-particle Green's function for a striped t-J model. The data obtained quantitatively reproduce salient (ARPES-) features and may serve to rule out "bond-centered" in favor of "site-centered" stripes.
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