654 research outputs found
Role of the sampling weight in evaluating classical time autocorrelation functions
We analyze how the choice of the sampling weight affects the efficiency of
the Monte Carlo evaluation of classical time autocorrelation functions.
Assuming uncorrelated sampling or sampling with constant correlation length, we
propose a sampling weight for which the number of trajectories needed for
convergence is independent of the correlated quantity, dimensionality,
dynamics, and phase-space density. In contrast, it is shown that the
computational cost of the "standard" intuitive algorithm which samples directly
from the phase-space density may scale exponentially with the number of degrees
of freedom. Yet, for the stationary Gaussian distribution of harmonic systems
and for the autocorrelation function of a linear function of phase-space
coordinates, the computational cost of this standard algorithm is also
independent of dimensionality.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Let
Evaluation of the nondiabaticity of quantum molecular dynamics with the dephasing representation of quantum fidelity
We propose an approximate method for evaluating the importance of
non-Born-Oppenheimer effects on the quantum dynamics of nuclei. The method uses
a generalization of the dephasing representation (DR) of quantum fidelity to
several diabatic potential energy surfaces and its computational cost is the
cost of dynamics of a classical phase space distribution. It can be implemented
easily into any molecular dynamics program and also can utilize on-the-fly ab
initio electronic structure information. We test the methodology on three model
problems introduced by Tully and on the photodissociation of NaI. The results
show that for dynamics close to the diabatic limit the decay of fidelity due to
nondiabatic effects is described accurately by the DR. In this regime, unlike
the mixed quantum-classical methods such as surface hopping or Ehrenfest
dynamics, the DR can capture more subtle quantum effects than the population
transfer between potential energy surfaces. Hence we propose using the DR to
estimate the dynamical importance of diabatic, spin-orbit, or other couplings
between potential energy surfaces. The acquired information can help reduce the
complexity of a studied system without affecting the accuracy of the quantum
simulation.Comment: 5 pages, 3 figures, section Theory extended(v2), small textual
improvements(v2), added reference(v2 & v3), added acknowledgement(v3),
submitted to J. Chem. Phy
Breaking the exponential wall in classical simulations of fidelity
We analyze the efficiency of available algorithms for the simulation of
classical fidelity and show that their computational costs increase
exponentially with the number of degrees of freedom for almost all initial
states. Then we present an algorithm whose cost is independent of the system's
dimensionality and show that, within a continuous family of algorithms, our
algorithm is the only one with this property. Simultaneously we propose a
general analytical approach to estimate efficiency of trajectory-based methods.Comment: 5 pages, 3 figure
Zustand und Entwicklung ausgewählter Fischbestände Einschätzung und Empfehlungen des ICES im Jahr 2004
The state of North Atlantic, Baltic Sea and North Sea commercially exploited fish stocks are assessed annually by the International Council for the Exploration of the Sea (ICES). Estimates of the stock size (biomass), recruitment, landings, current exploitation rates and of future harvesting possibilities are provided for those stocks where sufficient information is available to conduct a full analytical assessment. For all other stocks, only landings and stock trends can be given. This paper presents the development of north-east Atlantic fish stocks which are of general or specific interest for the German fishery and fish industry. Generally, it may be concluded that most pelagic fish stocks, such as herring, sprat, mackerel, and blue whiting, are in good condition, while the majority of the demersal stocks, like cod, plaice or whiting are in critical state. There are, however, a number of remarkable exceptions to this pattern
Aktuelle Entwicklung der Herings- und Sprottenbestände südlich des 62. Breitengrades
Information is given about the last meeting of the ICES “Herring Assessment Working Group for the Area South of 62° N”, conducted from 9.-18. March 1998 in Copenhagen. The actual stock development and the catch option estimations for different assessment units of herring and sprat are presented. The spawning stock size of North Sea herring was in 1997 still below the “Minimum Biological Acceptable Level” (MBAL) of 800 000 t. Keeping the fishing mortalities at the present level, the spawning stock size should reach a level of about 1.1 million tons by end of 1998. For the Western Baltic pring spawning herring stock no actual stock parameters were estimated. Due to uncertainties in splitting the catches in North sea autumn and Baltic spring spawners no analytical assessment was accepted
Die Lage der Fischbestände in Nordostatlantik, Nord- und Ostsee. Einschätzungen des Internationalen Rates für Meeresforschung im Frühjahr 2001
The spring session of ACFM gave advice for a number of stocks in the North Atlantic, North Sea and Baltic. The present assessment of the situation is given here for stocks of importance for the German fishery. These are: Blue Whiting: the stock size is rapidly decreasing due to high catches; ICES recommends a closure of the fishery. Herring (Atlanto-Scandian, Norwegian spring spawner): Stock is within save biological limits, weak recruitment of the recent years will lead to a further reduction of biomass. Herring (North Sea): revision of the assessment led to a different perception of the stock: SSB was in 2000 below Blim. Excellent recruitment will lead to an increase of SSB over Blim within this year, but ICES recommends to reduce fishing mortality on adults significantly. Herring (Baltic spring spawner in 22–24, IIIa): Still no increasing tendency is detectable. Herring (VIaNorth): stable. Redfish: generally further decreasing tendency observed, a reduction of the fishery is recommended. Signs of recovery visible only for two units. Greenland Halibut: State of the stock not quite clear, but slightly positive tendencies. The present fishing intensity should be reduced. Cod (Kattegat): Weak recruitment, outside safe biological limits. ICES recommends a closure of the fishery. Cod (22–24, Western Baltic): Stock situation unclear due to extensive migrations. F should be reduced by at least 10%
Zustand und Entwicklung ausgewählter Fischbestände: Einschätzung des ICES im Frühjahr 2003
During the spring session of the ICES Advisory Committee for Fisheries Management (ACFM) 48 stocks assessed by 7 Working Groups have been analyzed and reviewed, among these all herring stocks in the ICES area, blue whiting and most demersal stocks in the Baltic, Arctic and North-Western area. As in previous years, ICES recommends a reduction in fishing mortality for a number of stocks or even the establishment of recovery and management plans, to safeguard a continuous development of the stocks towards safe biological limits. ICES recommended a 90% reduction of the cod fishery in the Baltic Sea, while most of the herring stocks are in good condition
Die lage der Fischbestände in Nordostatlantik, Nord- und Ostsee. Einschätzungen des Internationalen Rates für Meeresforschung im Frühjahr 2000
The spring session of ACFM gave advice for a number
of stocks in the North Atlantic, North Sea and Baltic.
The present assessment of the situation is given here for
stocks of higher importance for the German fishery.
These are: Blue Whiting: the stock is still relatively high,
this, however, will not last very long, due to too intense
fishing. Cod in Kattegat: stock is outside safe biological
limits. No immediate recovery in sight. Cod in 22–24
(Baltic): stock is inside save biological limits. F, however, is above the recommendation of the IBSFC. Greenland
Halibut: state of the stock not quite clear. The present
fishing intensity seems to be sustainable. Herring (Atlanto-
scandian, Norwegian spring spawner): stock is within safe biological limits, weak recruitment of the recent years will lead to a reduction of biomass. Herring: for Baltic spring spawner in 22–24 and IIIa still no increasing tendency detectable. North Sea Herring: further
increasing tendency, with 900 000 t over B lim, good
recruitment. Herring in VIa: stable. Redfish: generally
decreasing tendency observed, a reduction of the fishery
is recommended. Signs of recovery, however, visible for some unit
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