591 research outputs found
Neutrons from multiplicity-selected Au-Au collisions at 150, 250, 400, and 650 AMeV
We measured neutron triple-differential cross sections from
multiplicity-selected Au-Au collisions at 150, 250, 400, and 650 \AMeV. The
reaction plane for each collision was estimated from the summed transverse
velocity vector of the charged fragments emitted in the collision. We examined
the azimuthal distribution of the triple-differential cross sections as a
function of the polar angle and the neutron rapidity. We extracted the average
in--plane transverse momentum and the normalized
observable , where is the neutron
transverse momentum, as a function of the neutron center-of-mass rapidity, and
we examined the dependence of these observables on beam energy. These
collective flow observables for neutrons, which are consistent with those of
protons plus bound nucleons from the Plastic Ball Group, agree with the
Boltzmann--Uehling--Uhlenbeck (BUU) calculations with a momentum--dependent
interaction. Also, we calculated the polar-angle-integrated maximum azimuthal
anisotropy ratio R from the value of .Comment: 20 LaTeX pages. 11 figures to be faxed on request, send email to
sender's addres
Fragment Flow and the Nuclear Equation of State
We use the Boltzmann-Uehling-Uhlenbeck model with a momentum-dependent
nuclear mean field to simulate the dynamical evolution of heavy ion collisions.
We re-examine the azimuthal anisotropy observable, proposed as sensitive to the
equation of state of nuclear matter. We obtain that this sensitivity is maximal
when the azimuthal anisotropy is calculated for nuclear composite fragments, in
agreement with some previous calculations. As a test case we concentrate on
semi-central collisions at 400 MeV.Comment: 12 pages, ReVTeX 3.0. 12 Postscript figures, uuencoded and appende
Who bullies whom at a garden feeder? Interspecific agonistic interactions of small passerines during a cold winter
Interspecific agonistic interactions are important
selective factors for maintaining ecological niches of
different species, but their outcome is difficult to predict
a priori. Here, we examined the direction and intensity of
interspecific interactions in an assemblage of small passerines
at a garden feeder, focussing on three finch species
of various body sizes. We found that large and mediumsized
birds usually initiated and won agonistic interactions
with smaller species. Also, the frequency of fights increased
with decreasing differences in body size between
the participants. Finally, the probability of engaging in a
fight increased with the number of birds at the feeder
Effects of Compression and Collective Expansion on Particle Emission from Central Heavy-Ion Reactions
Conditions under which compression occurs and collective expansion develops
in energetic reactions of heavy nuclei, are analyzed, together with their
effects on emitted light baryons and pions. Within transport simulations, it is
shown that shock fronts perpendicular to beam axis form in head-on reactions.
The fronts separate hot compressed matter from normal. As impact parameter
increases, the angle of inclination of the fronts relative to beam axis
decreases, and in-between the fronts a weak tangential discontinuity develops.
Hot matter exposed to the vacuum in directions perpendicular to shock motion
(and parallel to fronts), starts to expand sideways, early within reactions.
Expansion in the direction of shock motion follows after the shocks propagate
through nuclei, but due to the delay does not acquire same strength. Expansion
affects angular distributions, mean-energy components, shapes of spectra and
mean energies of different particles emitted into any one direction, and
further particle yields. Both the expansion and a collective motion associated
with the weak discontinuity, affect the magnitude of sideward flow within
reaction plane. Differences in mean particle energy components in and out of
the reaction plane in semicentral collisions, depend sensitively on the
relative magnitude of shock speed in normal matter and speed of sound in hot
matter.Comment: 71 pages, 33 figures (available on request), report MSUCL-94
Towards a tensionless string field theory for the N=(2,0) CFT in d=6
We describe progress in using the field theory of tensionless strings to
arrive at a Lagrangian for the six-dimensional conformal
theory. We construct the free part of the theory and propose an ansatz for the
cubic vertex in light-cone superspace. By requiring closure of the
supersymmetry algebra, we fix the cubic vertex up to two parameters.Comment: 46 pages, 2 figures. V2: references added; minor changes and
improvement
Adenovirus DNA in Guthrie cards from children who develop acute lymphoblastic leukaemia (ALL)
Aims: The aim of this thesis was to increase understanding of how molecular processes influence
the development and risk assessment of childhood leukemia. Studies I and II investigates whether a
specific virus infection in utero could be involved in a “first hit” in leukemogenesis. Studies III and
IV examine whether alterations in protein expression from cell cycle regulating genes may predict
a relapse in children with myeloid malignancies undergoing hematopoietic stem cell
transplantation (HSCT).
Background: Genetic alterations, analyzed at time of diagnosis in children who develop leukemia,
have been traced back to neonatal dried blood spots (DBS). This suggests that the majority of
chromosome translocations occur in utero during fetal hematopoiesis, generating a “first hit”. A
“second hit” is then required to generate a leukemic clone. Today, experiments in vitro, animal
models, and clinical observations have revealed that several viruses are oncogenic and capable of
initiating a genetic alteration. Smith M postulated the theory that an in utero infection might be the
“first hit”, causing genetic aberrations that could later lead to the development of the leukemic
clone, which is supported by the early age of onset and space-time clustering data, based on time,
place of birth, and diagnosis.
Leukemia develops as a result of hematopoietic or lymphoid tissue with uncontrolled cell division.
Normally cell division is controlled by the cell cycle, the network of which is complex with
numerous regulating proteins both up and down stream, but also containing several feedback
loops. The important regulators of this process are tumor suppressor genes, essential for normal
cell proliferation and differentiation as well as for controlling DNA integrity. Errors in these genes
or their protein expression affect the ability of the cell to check for DNA damage, thus tumors may
occur. Proteins from these genes could serve as prognostic markers and predict relapse.
Methods: In studies I and II we investigated neonatal DBS by PCR for the presence of adenovirus
DNA (243 samples) and the three newly discovered polyomaviruses (50 samples) from children
who later developed leukemia but also from controls (486 and 100 samples respectively). In
studies III and IV we explored the expression of one (p53) respectively four (p53, p21, p16 and
PTEN) cell cycle regulating proteins in bone marrow at diagnosis as well as pre and post HSCT in
myeloid malignancies in children. We retrospectively collected clinical data and bone marrow
samples from 33 children diagnosed with chronic myeloid malignancies (MDS, JMML and CML),
34 children diagnosed with AML as well as 55 controls. The samples were prepared by tissue
micro array (TMA) as well as immunohistochemistry and examined for protein expression in a
light microscope.
Results: In study I we detected adenovirus DNA in only two patients who later developed
leukemia, but in none of the controls. In study II all the samples were negative for KIPyV, WUPyV
and MCPyV DNA in both patients and controls. In study III we found an overexpression of p53
protein at diagnosis that significantly predicted relapse after HSCT in children with rare chronic
myeloid malignancies. In study IV a significantly higher p53 expression was found in the relapse
compared to the non-relapse group at six months post HSCT in children with AML, suggesting
that p53 may be used as prognostic markers for predicting a relapse. In addition, the calculated cut
off level for p53 at diagnosis (study III) and at six months (study IV) post HSCT was
approximately 20%, which indicates that a p53 expression over 20% may predict relapse in
children with myeloid malignancies.
Conclusion: Although we did not find an association between adenoviruses or the three newly
discovered polyomaviruses and the development of childhood leukemia, a virus could still be
involved in this process; the virus may have escaped detection, other new viruses could be
involved or a virus could precipitate the “second hit”.
We suggest that evaluation of p53 protein expression may be used as a supplement to regular
prognostic markers both pre and post HSCT. To further evaluate this, a prospective multicenter
study has been started
Regulatory network modelling of iron acquisition by a fungal pathogen in contact with epithelial cells
Peer reviewedPublisher PD
Two chemically similar stellar overdensities on opposite sides of the plane of the Galaxy
Our Galaxy is thought to have undergone an active evolutionary history
dominated by star formation, the accretion of cold gas, and, in particular,
mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of
these interactions in the form of stellar streams, substructures, and
chemically distinct stellar components. The impact of dwarf galaxy mergers on
the content and morphology of the Galactic disk is still being explored. Recent
studies have identified kinematically distinct stellar substructures and moving
groups, which may have extragalactic origin. However, there is mounting
evidence that stellar overdensities at the outer disk/halo interface could have
been caused by the interaction of a dwarf galaxy with the disk. Here we report
detailed spectroscopic analysis of 14 stars drawn from two stellar
overdensities, each lying about 5 kiloparsecs above and below the Galactic
plane - locations suggestive of association with the stellar halo. However, we
find that the chemical compositions of these stars are almost identical, both
within and between these groups, and closely match the abundance patterns of
the Milky Way disk stars. This study hence provides compelling evidence that
these stars originate from the disk and the overdensities they are part of were
created by tidal interactions of the disk with passing or merging dwarf
galaxies.Comment: accepted for publication in Natur
Hypercholesterolemia downregulates autophagy in the rat heart
Background: We have previously shown that efficiency of ischemic conditioning is diminished in hypercholesterolemia and that autophagy is necessary for cardioprotection. However, it is unknown whether isolated hypercholesterolemia disturbs autophagy or the mammalian target of rapamycin (mTOR) pathways. Therefore, we investigated whether isolated hypercholesterolemia modulates cardiac autophagy-related pathways or programmed cell death mechanisms such as apoptosis and necroptosis in rat heart.
Methods: Male Wistar rats were fed either normal chow (NORM; n=9) or with 2% cholesterol and 0.25% cholic acid-enriched diet (CHOL; n=9) for 12 weeks. CHOL rats exhibited a 41% increase in plasma total cholesterol level over that of NORM rats (4.09mmol/L vs. 2.89mmol/L) at the end of diet period. Animals were sacrificed, hearts were excised and briefly washed out. Left ventricles were snap-frozen for determination of markers of autophagy, mTOR pathway, apoptosis, and necroptosis by Western blot.
Results: Isolated hypercholesterolemia was associated with a significant reduction in expression of cardiac autophagy markers such as LC3-II, Beclin-1, Rubicon and RAB7 as compared to controls. Phosphorylation of ribosomal S6, a surrogate marker for mTOR activity, was increased in CHOL samples. Cleaved caspase-3, a marker of apoptosis, increased in CHOL hearts, while no difference in the expression of necroptotic marker RIP1, RIP3 and MLKL was detected between treatments.
Conclusions: This is the first comprehensive analysis of autophagy and programmed cell death pathways of apoptosis and necroptosis in hearts of hypercholesterolemic rats. Our data show that isolated hypercholesterolemia suppresses basal cardiac autophagy and that the decrease in autophagy may be a result of an activated mTOR pathway. Reduced autophagy was accompanied by increased apoptosis, while cardiac necroptosis was not modulated by isolated hypercholesterolemia. Decreased basal autophagy and elevated apoptosis may be responsible for the loss of cardioprotection reported in hypercholesterolemic animals
Effective Dark Matter Model: Relic density, CDMS II, Fermi LAT and LHC
The Cryogenic Dark Matter Search recently announced the observation of two
signal events with a 77% confidence level. Although statistically inconclusive,
it is nevertheless suggestive. In this work we present a model-independent
analysis on the implication of a positive signal in dark matter scattering off
nuclei. Assuming the interaction between (scalar, fermion or vector) dark
matter and the standard model induced by unknown new physics at the scale
, we examine various dimension-6 tree-level induced operators and
constrain them using the current experimental data, e.g. the WMAP data of the
relic abundance, CDMS II direct detection of the spin-independent scattering,
and indirect detection data (Fermi LAT cosmic gamma-ray), etc. Finally, the LHC
reach is also explored
- …