2,285 research outputs found
Simulation of cosmic irradiation conditions in thick target arrangements
One approach to simulate 2-pi irradiation conditions of planetary surfaces which has been widely applied in the past are bombardments of so called thick targets. A very large thick target was exposed recently to 2.1 GeV protons at the Bevatron-Bevalac in Berkeley. In a 100x100x180 cm steel-surrounded granodiorite target radioactive medium and high energy spallation products of the incident primary and of secondary particles were analyzed along the beam axis down to depths of 140 g/cm(2) in targets such as Cu, Ni, Co, Fe, T, Si, SiO2 and Al. Activities of these nuclides were exclusively determined via instrumental gamma-ray spectroscopy. Relative yields of neutron capture and spallation products induced in Co and Cu targets during the thick target bombardment are shown as a function of depth. The majority of the medium energy products such as Co-58 from Co targets exhibit a maximum at shallow depths of 40-60 g/cm(2) and then decrease exponentially. In a comparable 600 MeV proton bombarded thick target such a slight maximum for medium energy products was not observed. Rather, Co-58 activities in Co decreased steadily with the highest activity at the surface. The activities of the n-capture product Co-60 increase steadily starting at the surface. This indicates the rapidly growing flux of low energy neutrons within the target
The structure of borders in a small world
Geographic borders are not only essential for the effective functioning of
government, the distribution of administrative responsibilities and the
allocation of public resources, they also influence the interregional flow of
information, cross-border trade operations, the diffusion of innovation and
technology, and the spatial spread of infectious diseases. However, as growing
interactions and mobility across long distances, cultural, and political
borders continue to amplify the small world effect and effectively decrease the
relative importance of local interactions, it is difficult to assess the
location and structure of effective borders that may play the most significant
role in mobility-driven processes. The paradigm of spatially coherent
communities may no longer be a plausible one, and it is unclear what structures
emerge from the interplay of interactions and activities across spatial scales.
Here we analyse a multi-scale proxy network for human mobility that
incorporates travel across a few to a few thousand kilometres. We determine an
effective system of geographically continuous borders implicitly encoded in
multi-scale mobility patterns. We find that effective large scale boundaries
define spatially coherent subdivisions and only partially coincide with
administrative borders. We find that spatial coherence is partially lost if
only long range traffic is taken into account and show that prevalent models
for multi-scale mobility networks cannot account for the observed patterns.
These results will allow for new types of quantitative, comparative analyses of
multi-scale interaction networks in general and may provide insight into a
multitude of spatiotemporal phenomena generated by human activity.Comment: 9 page
Physical Processes in Star-Gas Systems
First we present a recently developed 3D chemodynamical code for galaxy
evolution from the K**2 collaboration. It follows the evolution of all
components of a galaxy such as dark matter, stars, molecular clouds and diffuse
interstellar matter (ISM). Dark matter and stars are treated as collisionless
N-body systems. The ISM is numerically described by a smoothed particle
hydrodynamics (SPH) approach for the diffuse (hot) gas and a sticky particle
scheme for the (cool) molecular clouds. Physical processs such as star
formation, stellar death or condensation and evaporation processes of clouds
interacting with the ISM are described locally. An example application of the
model to a star forming dwarf galaxy will be shown for comparison with other
codes. Secondly we will discuss new kinds of exotic chemodynamical processes,
as they occur in dense gas-star systems in galactic nuclei, such as
non-standard ``drag''-force interactions, destructive and gas producing stellar
collisions. Their implementation in 1D dynamical models of galactic nuclei is
presented. Future prospects to generalize these to 3D are work in progress and
will be discussed.Comment: 4 pages, 4 figures, "The 5th Workshop on Galactic Chemodynamics" -
Swinburne University (9-11 July 2003). To be published in the Publications of
the Astronomical Society of Australia in 2004 (B.K. Gibson and D. Kawata,
eds.). Accepted version, minor changes relative to origina
Engineering adiabaticity at an avoided crossing with optimal control
We investigate ways to optimize adiabaticity and diabaticity in the
Landau-Zener model with non-uniform sweeps. We show how diabaticity can be
engineered with a pulse consisting of a linear sweep augmented by an
oscillating term. We show that the oscillation leads to jumps in populations
whose value can be accurately modeled using a model of multiple,
photon-assisted Landau-Zener transitions, which generalizes work by Wubs et al.
[New J. Phys. 7, 218 (2005)]. We extend the study on diabaticity using methods
derived from optimal control. We also show how to preserve adiabaticity with
optimal pulses at limited time, finding a non-uniform quantum speed limit
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Long-term follow-up of 22 psoriatic patients treated with ixekizumab after failure of secukinumab
Switching of biologic agents in treatment of plaque psoriasis is a common strategy. Only a few studies are available on switching between IL17A-blockers. In a retrospective study, we identified 22 psoriasis patients who, after failing secukinumab as a first IL17A-blocker received ixekizumab with an observation period of at least 24 weeks. At last observation 10/22 patients had a good response (PASI75 or PASI<3) using ixekizumab therapy. None of five patients with primary non-response to secukinumab reached a good, durable response to ixekizumab. In conclusion, ixekizumab appears to be a therapeutic option as a second IL17A-blocker in psoriasis patients who did not show a primary non-response to secukinumab
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