6,651 research outputs found
Ultra-heavy cosmic rays: Theoretical implications of recent observations
Extreme ultraheavy cosmic ray observations (Z greater or equal 70) are compared with r-process models. A detailed cosmic ray propagation calculation is used to transform the calculated source distributions to those observed at the earth. The r-process production abundances are calculated using different mass formulae and beta-rate formulae; an empirical estimate based on the observed solar system abundances is used also. There is the continued strong indication of an r-process dominance in the extreme ultra-heavy cosmic rays. However it is shown that the observed high actinide/Pt ratio in the cosmic rays cannot be fit with the same r-process calculation which also fits the solar system material. This result suggests that the cosmic rays probably undergo some preferential acceleration in addition to the apparent general enrichment in heavy (r-process) material. As estimate also is made of the expected relative abundance of superheavy elements in the cosmic rays if the anomalous heavy xenon in carbonaceous chondrites is due to a fissioning superheavy element
Design guidelines for use of adhesives and organic coatings in hybrid microcircuits
A study was conducted to investigate the reliability of organic adhesives in hybrid microcircuits. The objectives were twofold: (1) to identify and investigate problem areas that could result from the use of organic adhesives and (2) to develop evaluation tests to quantify the extent to which these problems occur for commercially available adhesives. Efforts were focused on electrically conductive adhesives. Also, a study was made to evaluate selected organic coatings for contamination protection for hybrid microcircuits
Rotating Neutron Stars in a Chiral SU(3) Model
We study the properties of rotating neutron stars within a generalized chiral
SU(3)-flavor model. The influence of the rotation on the inner structure and
the hyperon matter content of the star is discussed. We calculate the Kepler
frequency and moments of inertia of the neutron star sequences. An estimate for
the braking index of the associated pulsars is given.Comment: 14 pages, 9 figure
From FAIR to RHIC, hyper clusters and an effective strange EoS for QCD
Two major aspects of strange particle physics at the upcoming FAIR and NICA
facilities and the RHIC low energy scan will be discussed. A new distinct
production mechanism for hypernuclei will be presented, namely the production
abundances for hypernuclei from 's absorbed in the spectator matter in
peripheral heavy ion collisions. As strangeness is not uniformly distributed in
the fireball of a heavy ion collision, the properties of the equation of state
therefore depend on the local strangeness fraction. The same, inside neutron
stars strangeness is not conserved and lattice studies on the properties of
finite density QCD usually rely on an expansion of thermodynamic quantities at
zero strange chemical potential, hence at non-zero strange-densities. We will
therefore discuss recent investigations on the EoS of strange-QCD and present
results from an effective EoS of QCD that includes the correct asymptotic
degrees of freedom and a deconfinement and chiral phase transition.Comment: Talk given at the international conference on Strangeness in Quark
Matter 2011 in Krako
Hybrid Stars in an SU(3) Parity Doublet Model
We apply an extended version of the SU(3) parity model, containing quark
degrees of freedom, to study neutron stars. The model successfully reproduces
the main thermodynamic features of QCD which allows us to describe the
composition of dense matter. Chiral symmetry restoration is realized inside the
star and the chiral partners of the baryons appear, their masses becoming
degenerate. Furthermore, quark degrees of freedom appear in a transition to a
deconfined state. Performing an investigation of the macroscopic properties of
neutron stars, we show that observational constraints, like mass and thermal
evolution, are satisfied and new predictions can be made
Fractal dimension of domain walls in the Edwards-Anderson spin glass model
We study directly the length of the domain walls (DW) obtained by comparing
the ground states of the Edwards-Anderson spin glass model subject to periodic
and antiperiodic boundary conditions. For the bimodal and Gaussian bond
distributions, we have isolated the DW and have calculated directly its fractal
dimension . Our results show that, even though in three dimensions
is the same for both distributions of bonds, this is clearly not the case for
two-dimensional (2D) systems. In addition, contrary to what happens in the case
of the 2D Edwards-Anderson spin glass with Gaussian distribution of bonds, we
find no evidence that the DW for the bimodal distribution of bonds can be
described as a Schramm-Loewner evolution processes.Comment: 6 pages, 5 figures. Accepted for publication in PR
Estimating novel potential drug targets of Plasmodium falciparum by analysing the metabolic network of knock-out strains in silico
Malaria is one of the world’s most common and serious diseases causing death of about 3 million people
each year. Its most severe occurrence is caused by the protozoan Plasmodium falciparum. Biomedical
research could enable treating the disease by effectively and specifically targeting essential enzymes of
this parasite. However, the parasite has developed resistance to existing drugsmaking it indispensable to
discover new drugs. We have established a simple computational tool which analyses the topology of the
metabolic network of P. falciparum to identify essential enzymes as possible drug targets.Weinvestigated
the essentiality of a reaction in the metabolic network by deleting (knocking-out) such a reaction in silico.
The algorithmselected neighbouring compounds of the investigated reaction that had to be produced by
alternative biochemical pathways. Using breadth first searches, we tested qualitatively if these products
could be generated by reactions that serve as potential deviations of the metabolic flux. With this we
identified 70 essential reactions. Our results were compared with a comprehensive list of 38 targets of
approved malaria drugs. When combining our approach with an in silico analysis performed recently
[Yeh, I., Hanekamp, T., Tsoka, S., Karp, P.D., Altman, R.B., 2004. Computational analysis of Plasmodium
falciparum metabolism: organizing genomic information to facilitate drug discovery. Genome Res. 14,
917–924] we could improve the precision of the prediction results. Finally we present a refined list of 22
new potential candidate targets for P. falciparum, half of which have reasonable evidence to be valid
targets against micro-organisms and cancer
Calogero-Sutherland eigenfunctions with mixed boundary conditions and conformal field theory correlators
We construct certain eigenfunctions of the Calogero-Sutherland hamiltonian
for particles on a circle, with mixed boundary conditions. That is, the
behavior of the eigenfunction, as neighbouring particles collide, depend on the
pair of colliding particles. This behavior is generically a linear combination
of two types of power laws, depending on the statistics of the particles
involved. For fixed ratio of each type at each pair of neighboring particles,
there is an eigenfunction, the ground state, with lowest energy, and there is a
discrete set of eigenstates and eigenvalues, the excited states and the
energies above this ground state. We find the ground state and special excited
states along with their energies in a certain class of mixed boundary
conditions, interpreted as having pairs of neighboring bosons and other
particles being fermions. These particular eigenfunctions are characterised by
the fact that they are in direct correspondence with correlation functions in
boundary conformal field theory. We expect that they have applications to
measures on certain configurations of curves in the statistical O(n) loop
model. The derivation, although completely independent from results of
conformal field theory, uses ideas from the "Coulomb gas" formulation.Comment: 35 pages, 9 figure
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