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Search Results: 1 - 10 of 297507 matches for " J. Esser "
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Naar aanleiding van I La Galigo
S.J. Esser
Bijdragen tot de Taal-, Land- en Volkenkunde , 1961,
Non-equilibrium Ionization and FIP Effect Diagnostics
Richard J. Edgar,Ruth Esser
Physics , 2000,
Abstract: We examine the accuracy of a common FIP effect diagnostic, the ratio of Ne VI to Mg VI lines in the solar transition region. Since the two ions have quite similar contribution functions near their maxima in equilibrium, the ratio of these two ions is often taken to be the abundance ratio of Ne and Mg. First we compute non-equilibrium ionization effects on the ratio f(Ne+5)/f(Mg+5) of ion fractions for a variety of simple flows through the transition region. Calculating the spectral line ratios for a few examples, we then show that non-equilibrium effects as well as temperature and density dependence must be evaluated for each line ratio used in the diagnostics.
Dynamics of Domains in Diluted Antiferromagnets
U. Nowak,J. Esser,K. D. Usadel
Physics , 1996, DOI: 10.1016/0378-4371(96)00133-1
Abstract: We investigate the dynamics of two-dimensional site-diluted Ising antiferromagnets. In an external magnetic field these highly disordered magnetic systems have a domain structure which consists of fractal domains with sizes on a broad range of length scales. We focus on the dynamics of these systems during the relaxation from a long-range ordered initial state to the disordered fractal-domain state after applying an external magnetic field. The equilibrium state with applied field consists of fractal domains with a size distribution which follows a power law with an exponential cut-off. The dynamics of the system can be understood as a growth process of this fractal-domain state in such a way that the equilibrium distribution of domains develops during time. Following these ideas quantitatively we derive a simple description of the time dependence of the order parameter. The agreement with simulations is excellent.
Exact Ground State Properties of Disordered Ising-Systems
J. Esser,U. Nowak,K. D. Usadel
Physics , 1996, DOI: 10.1103/PhysRevB.55.5866
Abstract: Exact ground states are calculated with an integer optimization algorithm for two and three dimensional site-diluted Ising antiferromagnets in a field (DAFF) and random field Ising ferromagnets (RFIM). We investigate the structure and the size-distribution of the domains of the ground state and compare it to earlier results from Monte Carlo simulations for finite temperature. Although DAFF and RFIM are thought to be in the same universality class we found essential differences between these systems as far as the domain properties are concerned. For the DAFF the ground states consist of fractal domains with a broad size distribution that can be described by a power law with exponential cut-off. For the RFIM the limiting case of the size distribution and structure of the domains for strong random fields is the size distribution and structure of the clusters of the percolation problem with a field dependent lower cut-off. The domains are fractal and in three dimensions nearly all spins belong to two large infinite domains of up- and down spins - the system is in a two-domain state.
Modified Scaling Relation for the Random-Field Ising Model
U. Nowak,K. D. Usadel,J. Esser
Physics , 1997, DOI: 10.1016/S0378-4371(97)00580-3
Abstract: We investigate the low-temperature critical behavior of the three dimensional random-field Ising ferromagnet. By a scaling analysis we find that in the limit of temperature $T \to 0$ the usual scaling relations have to be modified as far as the exponent $\alpha$ of the specific heat is concerned. At zero temperature, the Rushbrooke equation is modified to $\alpha + 2 \beta + \gamma = 1$, an equation which we expect to be valid also for other systems with similar critical behavior. We test the scaling theory numerically for the three dimensional random field Ising system with Gaussian probability distribution of the random fields by a combination of calculations of exact ground states with an integer optimization algorithm and Monte Carlo methods. By a finite size scaling analysis we calculate the critical exponents $\nu \approx 1.0$, $\beta \approx 0.05$, $\bar{\gamma} \approx 2.9$ $\gamma \approx 1.5$ and $\alpha \approx -0.55$.
Polymorphisme de la phosphoglucomutase (PGM) dans l'espèce bovine
M Ansay, R Hanset, J Esser-Coulon
Genetics Selection Evolution , 1971, DOI: 10.1186/1297-9686-3-4-413
La malate déshydrogénase mitochondriale: variants électrophorétiques de nature héréditaire dans l'espèce bovine
M Ansay, R Hanset, J Esser-coulon
Genetics Selection Evolution , 1971, DOI: 10.1186/1297-9686-3-3-235
Neurodevelopmental status of HIV-exposed but uninfected children: A pilot study
P Springer, B Laughton, M Tomlinson, J Harvey, M Esser
South African Journal of Child Health , 2012,
Abstract: Introduction. HIV affects children both directly and indirectly, with evidence of increased infectious mortality and morbidity in the HIV-exposed but uninfected (HEU) infant. There is little published research on neurodevelopmental outcome of HEU infants in Africa. Following the introduction of successful prevention of mother-to-child transmission programmes, it has become important to determine whether differences exist between HEU infants and infants born to HIV-negative mothers in order to guide current management policies of this rapidly growing group of infants. Objectives. To compare the developmental outcome of infants exposed to HIV in utero who remained uninfected (HEU) with that of infants unexposed to HIV in utero (HUU). Methodology. This was a prospective, blinded, hospital-based study. Infants aged between 17 and 19 months were assessed on the Griffiths Mental Developmental Scales (GMDS). Birth history, previous hospitalisation, maternal and infant characteristics, antiretroviral exposure, anthropometric measurements and abnormal clinical findings were documented. Results. Of the original 55 infants enrolled at 2 weeks of age, 37 (17 HEU and 20 HUU) underwent neurological and developmental assessment. There were no significant differences between the groups with regard to the GMDS general quotient or other subscales, apart from the Personal/social subscale, where the HEU group performed significantly more poorly than the HUU participants (p=0.026). This difference is probably a result of cultural differences between the groups, as 76% of HEU and only 15% of HUU participants were of Xhosa origin. Discussion. There was no difference in neurodevelopmental outcome at 18 months between the HEU and HUU groups.
Genetics of fungi: retrospect and perspective
K. Esser
Micología Aplicada Internacional , 2001,
Abstract: This short survey on fungal genetics in the 20th century reflects the course of development from classical to molecular genetics and its implication to biotechnology.
Dendrochernes cyrneus (Arachnida: Pseudoscorpiones: Chernetidae) in Brandenburg
Esser, Jens
Arachnologische Mitteilungen , 2011, DOI: 10.5431/aramit4203
Abstract: The pseudoscorpion Dendrochernes cyrneus (L. Koch, 1873) is recorded for the first time in Brandenburg (Germany). The specimen was found in the ancient park of Sanssouci under the bark of a branch of a beech tree. The suitability of D. cyrneus as an indicator species for old-growth woodlands is discussed.
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