Hilf, E
Hohlfeld, M
Severiens, T
Zimmermann, K
Distributed Information Services in Physics
High Energy Phys. Libr. Webzine
2
4
The concept of distributed information services maintained by a distributed work force for scientific information is described. Realizations and experiences for Physics (since 1995), Marine Sciences, and dissertation theses in physics are presented. Technically the information is gathered from the local web servers of the worldwide distributed research institutes and departments, by distributed Harvest-gatherers, under the control of national learned societies or regional other institutions. Queries are answered by a network of mirrors of Harvest-brokers. For PhysNet, a Charter sets the rules to assure a noncommercial, free full-text access service, under the control of the set of national national learned societies involved, but unbiased to any single one.
eng
2001
Imported from Invenio.
Borrmann, P
Gloski, D
Hilf, E R
Specific heat in the thermodynamics of clusters
The thermodynamic properties such as the specific heat are uniquely determined by the second moments of the energy distribution for a given ensemble averaging. However for small particle numbers the results depend on the ensemble chosen. We calculated the higher moments of the distributions of some observables for both the canonical and the microcanonical ensemble of the same van der Waals clusters. The differences of the resulting thermodynamic observables for the two ensembles are calculated in terms of the higher moments. We demonstrate how for increasing particle number these terms decrease to vanish for bulk material. For the calculation of the specific heat within the microcanonical ensemble we give a new method based on an analysis of histograms.
eng
1994
http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=chem-ph&id=9412003;
Imported from Invenio.
Borrmann, P
Stamerjohanns, H
Hilf, E R
Tománek, D
Paradoxical Magnetic Cooling in a Structural Transition Model
Eur. Phys. J. B
117-119
19
In contrast to the experimentally widely used isentropic demagnetization process for cooling to ultra-low temperatures we examine a particular classical model system that does not cool, but rather heats up with isentropic demagnetization. This system consists of several magnetite particles in a colloidal suspension, and shows the uncommon behavior of disordering structurally while ordering magnetically in an increasing magnetic field. For a six-particle system, we report an uncommon structural transition from a ring to a chain as a function of magnetic field and temperature.
eng
2001
http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cond-mat&id=0009048;
Imported from Invenio.
Borrmann, P
Harting, J
Mülken, O
Hilf, E R
Calculation of thermodynamic properties of finite Bose-Einstein systems
Phys. Rev. A
1519
60
We derive an exact recursion formula for the calculation of thermodynamic functions of finite systems obeying Bose-Einstein statistics. The formula is applicable for canonical systems where the particles can be treated as noninteracting in some approximation, e.g. like Bose-Einstein condensates in magnetic traps. The numerical effort of our computation scheme grows only linear with the number of particles. As an example we calculate the relative ground state fluctuations and specific heats for ideal Bose gases with a finite numbers of particles enclosed in containers of different shapes.
eng
1999
http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cond-mat&id=0008071;
Imported from Invenio.
Küpper, W A
Hilf, E R
Wegmann, G
Thermostatic properties of nuclear matter
Nucl. Phys.
We use Monte Carlo simulations to investigate the thermodynamical behaviour of aggregates consisting of few superparamagnetic particles in a colloidal suspension. The potential energy surface of this classical two-level system with a stable and a metastable `ring' and `chain' configuration is tunable by an external magnetic field and temperature. We determine the complex `phase diagram' of this intriguing system and analyze thermodynamically the nature of the transition between the ring and the chain `phase'.
eng
1996
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=cond-mat&id=9601138;
Imported from Invenio.
Dullweber, A
Hilf, E R
Mendel, E
Simple quantum mechanical phenomena and the Feynman real time path integral
The path integral formalism gives a very illustrative and intuitive understanding of quantum mechanics but due to its difficult sum over phases one usually prefers Schr\"odinger's approach. We will show that it is possible to calculate simple quantum phenomena by performing Feynman's sum over all paths staying entirely in real time. Once the propagator is obtained it is particularly easy to get the energy spectrum or the evolution of any wavefunction.
eng
1995
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=quant-ph&id=9511042;
http://cds.cern.ch/record/292190/files/9511042.pdf;
Imported from Invenio.
Diekmann, B
Borrmann, P
Hilf, E R
Structures and stabilities of H3+(H2)n clusters (n=1-11)
Geometries and energies for H3+(H2)n clusters (n = 0, ..., 11) have been calculated using standard "ab initio" methods. Up to clusters with n = 6, four different Pople basis sets (DZ, TZ, TZP) have been used in the calculations. For larger cluster sizes, the calculations have been carried out with one basis set (DZ) using the HF/CISD method. We discuss here only the nice counterplay of polarisation effects between the central H3+ ion and the adsorbed H2 molecules, which naturally governs both the geometric structure and the energy of the clusters.
eng
1994
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=cond-mat&id=9412123;
Imported from Invenio.
Borrmann, P
Diekmann, B
Hilf, E R
Tománek, D
Magnetism of small transition metal clusters and the effects of isomerisation
We investigate the magnetic properties of small transition metal clusters using a simple statistical model, which requires some input data from ab initio spin-density functional calculations. In our study we consider a thermodynamically equilibrated ensemble of clusters with different structures, spin multiplicities, and ground state energies. We calculate the physical properties of this system by weighting the individual configurations according to the Boltzmann statistics. We find that presence of isomers with very similar ground state energies, yet very different magnetic properties, gives rise to a rich magnetic behaviour of the system which differs significantly from what would be expected for single configurations. We apply the present model to to determine the magnetic susceptibility of a cluster ensemble of Langevin paramagnets. Our results show that some of the anomalies in the magnetic behaviour of transition metal clusters might be understood in the framework of our model which is, of course, limited by the extremely high computational effort needed to obtain the input data.
eng
1994
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=cond-mat&id=9412121;
Imported from Invenio.
Borrmann, P
Hilf, E R
New enhancements to Feynman's path integral for fermions
We show that the computational effort for the numerical solution of fermionic quantum systems, occurring e.g., in quantum chemistry, solid state physics, field theory in principle grows with less than the square of the particle number for problems stated in one space dimension and with less than the cube of the particle number for problems stated in three space dimensions. This is proven by representation of effective algorithms for fermion systems in the framework of the Feynman Path Integral.
eng
1994
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=cond-mat&id=9412113;
Imported from Invenio.
Kleihaus, B
Polley, L
Wendel, M H
Hilf, E R
Wilson action in terms of the Kogut-Susskind fermion matrix