6,923 research outputs found
Modified Empirical Parametrization of Fragmentation Cross Sections
New experimental data obtained mainly at the GSI/FRS facility allow to modify
the empirical parametrization of fragmentation cross sections, EPAX. It will be
shown that minor modifications of the parameters lead to a much better
reproduction of measured cross sections. The most significant changes refer to
the description of fragmentation yields close to the projectile and of the
memory effect of neutron-deficient projectiles.Comment: 10 pages, latex file, 11 postscript figures, submitted to Phys. Rev.
Thruster Allocation for Dynamical Positioning
Positioning a vessel at a fixed position in deep water is of great importance when working offshore. In recent years a Dynamical Positioning (DP) system was developed at Marin [2]. After the measurement of the current position and external forces (like waves, wind etc.), each thruster of the vessel is actively controlled to hold the desired location.
In this paper we focus on the allocation process to determine the settings for each thruster that results in the minimal total power and thus fuel consumption. The mathematical formulation of this situation leads to a nonlinear optimization problem with equality and inequality constraints, which can be solved by applying Lagrange multipliers.
We give three approaches: first of all, the full problem was solved using the MATLAB fmincon routine with the solution from the linearised problem as a starting point. This implementation, with robust handling of the situations where the thrusters are overloaded, lead to promising results: an average reduction in fuel consumption of approximately two percent. However, further analysis proved useful. A second approach changes the set of variables and so reduces the number of equations. The third and last approach solves the Lagrange equations with an iterative method on the linearized Lagrange problem
Hysteresis phenomenon in deterministic traffic flows
We study phase transitions of a system of particles on the one-dimensional
integer lattice moving with constant acceleration, with a collision law
respecting slower particles. This simple deterministic ``particle-hopping''
traffic flow model being a straightforward generalization to the well known
Nagel-Schreckenberg model covers also a more recent slow-to-start model as a
special case. The model has two distinct ergodic (unmixed) phases with two
critical values. When traffic density is below the lowest critical value, the
steady state of the model corresponds to the ``free-flowing'' (or ``gaseous'')
phase. When the density exceeds the second critical value the model produces
large, persistent, well-defined traffic jams, which correspond to the
``jammed'' (or ``liquid'') phase. Between the two critical values each of these
phases may take place, which can be interpreted as an ``overcooled gas'' phase
when a small perturbation can change drastically gas into liquid. Mathematical
analysis is accomplished in part by the exact derivation of the life-time of
individual traffic jams for a given configuration of particles.Comment: 22 pages, 6 figures, corrected and improved version, to appear in the
Journal of Statistical Physic
False memory ≠ false memory: DRM errors are unrelated to the misinformation effect
The DRM method has proved to be a popular and powerful, if controversial, way to study 'false memories'. One reason for the controversy is that the extent to which the DRM effect generalises to other kinds of memory error has been neither satisfactorily established nor subject to much empirical attention. In the present paper we contribute data to this ongoing debate. One hundred and twenty participants took part in a standard misinformation effect experiment, in which they watched some CCTV footage, were exposed to misleading post-event information about events depicted in the footage, and then completed free recall and recognition tests. Participants also completed a DRM test as an ostensibly unrelated filler task. Despite obtaining robust misinformation and DRM effects, there were no correlations between a broad range of misinformation and DRM effect measures (mean r = -.01). This was not due to reliability issues with our measures or a lack of power. Thus DRM 'false memories' and misinformation effect 'false memories' do not appear to be equivalent
Proseuctor v. Ntaganda – The International Criminal Court’s Dangerous Foray into the Shades of Lochner
Article published in the Michigan State International Law Review
Does dynamics reflect topology in directed networks?
We present and analyze a topologically induced transition from ordered,
synchronized to disordered dynamics in directed networks of oscillators. The
analysis reveals where in the space of networks this transition occurs and its
underlying mechanisms. If disordered, the dynamics of the units is precisely
determined by the topology of the network and thus characteristic for it. We
develop a method to predict the disordered dynamics from topology. The results
suggest a new route towards understanding how the precise dynamics of the units
of a directed network may encode information about its topology.Comment: 7 pages, 4 figures, Europhysics Letters, accepte
Clues to the nature of dark matter from first galaxies
We use thirty-eight high-resolution simulations of galaxy formation between
redshift 10 and 5 to study the impact of a 3 keV warm dark matter (WDM)
candidate on the high-redshift Universe. We focus our attention on the stellar
mass function and the global star formation rate and consider the consequences
for reionization, namely the neutral hydrogen fraction evolution and the
electron scattering optical depth. We find that three different effects
contribute to differentiate warm and cold dark matter (CDM) predictions: WDM
suppresses the number of haloes with mass less than few M; at
a fixed halo mass, WDM produces fewer stars than CDM; and finally at halo
masses below M, WDM has a larger fraction of dark haloes than
CDM post-reionization. These three effects combine to produce a lower stellar
mass function in WDM for galaxies with stellar masses at and below
M. For , the global star formation density is lower by a
factor of two in the WDM scenario, and for a fixed escape fraction, the
fraction of neutral hydrogen is higher by 0.3 at . This latter
quantity can be partially reconciled with CDM and observations only by
increasing the escape fraction from 23 per cent to 34 per cent. Overall, our
study shows that galaxy formation simulations at high redshift are a key tool
to differentiate between dark matter candidates given a model for baryonic
physics.Comment: 11 pages, 8 figures, submitted to MNRA
REGIONAL CHANGES IN THE DISTRIBUTION OF NET VALUE ADDED IN U.S. AGRICULTURE, 1960-2002
This paper examines the effects of structural changes on the distribution of net value added and the difference between net value added and agricultural income over time. We present and discuss the changes in the distribution of net value added (land, labor, capital, and farm operator income) over time. Net value added by U.S. agriculture grew significantly from 95 billion in 1996. We examine regional differences in net value added using the Theil entropy measure. The inequality (dispersion) of net value added increased over time. The increased inequality represented both increases in regional dispersion in net value added and increases in the average inequality in net value added in each region. Thus, the net value added is becoming less alike across the U.S. We also examined the inequality in the components of net value added. The greatest dispersion occurred in returns to land followed by returns to capital. Therefore, changes in the dispersion of net value added by agriculture are explained by differences in the payments to non-operator landlords and to capital.Agricultural Finance,
- …