1,005 research outputs found
Measurement of the Omega_c Lifetime
We present the measurement of the lifetime of the Omega_c we have performed
using three independent data samples from two different decay modes. Using a
Sigma- beam of 340 GeV/c we have obtained clean signals for the Omega_c
decaying into Xi- K- pi+ pi+ and Omega- pi+ pi- pi+, avoiding topological cuts
normally used in charm analysis. The short but measurable lifetime of the
Omega_c is demonstrated by a clear enhancement of the signals at short but
finite decay lengths. Using a continuous maximum likelihood method we
determined the lifetime to be tau(Omega_c) = 55 +13-11(stat) +18-23(syst) fs.
This makes the Omega_c the shortest living weakly decaying particle observed so
far. The short value of the lifetime confirms the predicted pattern of the
charmed baryon lifetimes and demonstrates that the strong interaction plays a
vital role in the lifetimes of charmed hadrons.Comment: 15 pages, including 7 figures; gzipped, uuencoded postscrip
Nuclei, Superheavy Nuclei and Hypermatter in a chiral SU(3)-Modell
A model based on chiral SU(3)-symmetry in nonlinear realisation is used for
the investigation of nuclei, superheavy nuclei, hypernuclei and multistrange
nuclear objects (so called MEMOs). The model works very well in the case of
nuclei and hypernuclei with one Lambda-particle and rules out MEMOs. Basic
observables which are known for nuclei and hypernuclei are reproduced
satisfactorily. The model predicts Z=120 and N=172, 184 and 198 as the next
shell closures in the region of superheavy nuclei. The calculations have been
performed in self-consistent relativistic mean field approximation assuming
spherical symmetry. The parameters were adapted to known nuclei.Comment: 19 pages, 11 figure
The amino acid and hydrocarbon contents of the Paris meteorite: Insights into the most primitive CM chondrite
International audienc
Elaia, Pergamon's maritime satellite:The rise and fall of an ancient harbour city shaped by shoreline migration
Throughout human history, communication and trade have been key to society. Because maritime trade facilitated the rapid transportation of passengers and freight at relatively low cost, harbours became hubs for traffic, trade and exchange. This general statement holds true for the Pergamenian kingdom, which ruled wide parts of today's western Turkey during Hellenistic times. Its harbour, located at the city of Elaia on the eastern Aegean shore, was used extensively for commercial and military purposes. This study reconstructs the coastal evolution in and around the ancient harbour of Elaia and compares the observed environmental modifications with archaeological and historical findings. We use micropalaeontological, sedimentological and geochemical proxies to reconstruct the palaeoenvironmental dynamics and evolution of the ancient harbour. The geoarchaeological results confirm the archaeological and historical evidence for Elaia's primacy during Hellenistic and early Roman times, and the city's gradual decline during the late Roman period. Furthermore, our study demonstrates that Elaia holds a unique position as a harbour city during ancient times in the eastern Aegean region, because it was not greatly influenced by the high sediment supply associated with river deltas. Consequently, no dredging of the harbour basins is documented, creating exceptional geo-bioarchives for palaeoenvironmental reconstructions
Promoting Photocatalytic Hydrogen Evolution Activity of Graphitic Carbon Nitride with Hole-Transfer Agents
Density dependent hadron field theory for hypernuclei
The Density Dependent Relativistic Hadron Field (DDRH) theory, previously
introduced and applied to isospin nuclei, is extended to hypernuclei by
including the octet hyperons. Infinite matter Dirac-Brueckner theory for octet
baryons and the derivation of in-medium DDRH baryon-meson vertices is
discussed. From the properties of Dirac-Brueckner interactions it is found that
hyperon and nucleon self-energies and vertices are related by the ratios of
free space coupling constants. This leads to simple scaling laws for the
in-medium hyperon and nucleon vertices. The model is applied in relativistic
DDRH mean-field calculations to singl$\Lambda nuclei. Free space N-Lambda
T-matrix results are used for the scalar vertex. As the only free parameter the
hyperon vector vertex scaling factor is adjusted to a selected set of
hypernuclear data. Spectroscopic data of single Lambda hypernuclei over the
full mass range are well described. The reduced Lambda spin-orbit splitting is
reproduced and found to be related closely the medium dependence of scalar and
vector interactions.Comment: 38 pages, 9 figure
In silico evolution of diauxic growth
The glucose effect is a well known phenomenon whereby cells, when presented with two different nutrients, show a diauxic growth pattern, i.e. an episode of exponential growth followed by a lag phase of reduced growth followed by a second phase of exponential growth. Diauxic growth is usually thought of as a an adaptation to maximise biomass production in an environment offering two or more carbon sources. While diauxic growth has been studied widely both experimentally and theoretically, the hypothesis that diauxic growth is a strategy to increase overall growth has remained an unconfirmed conjecture. Here, we present a minimal mathematical model of a bacterial nutrient uptake system and metabolism. We subject this model to artificial evolution to test under which conditions diauxic growth evolves. As a result, we find that, indeed, sequential uptake of nutrients emerges if there is competition for nutrients and the metabolism/uptake system is capacity limited. However, we also find that diauxic growth is a secondary effect of this system and that the speed-up of nutrient uptake is a much larger effect. Notably, this speed-up of nutrient uptake coincides with an overall reduction of efficiency. Our two main conclusions are: (i) Cells competing for the same nutrients evolve rapid but inefficient growth dynamics. (ii) In the deterministic models we use here no substantial lag-phase evolves. This suggests that the lag-phase is a consequence of stochastic gene expression
Frequency dependent specific heat of viscous silica
We apply the Mori-Zwanzig projection operator formalism to obtain an
expression for the frequency dependent specific heat c(z) of a liquid. By using
an exact transformation formula due to Lebowitz et al., we derive a relation
between c(z) and K(t), the autocorrelation function of temperature fluctuations
in the microcanonical ensemble. This connection thus allows to determine c(z)
from computer simulations in equilibrium, i.e. without an external
perturbation. By considering the generalization of K(t) to finite wave-vectors,
we derive an expression to determine the thermal conductivity \lambda from such
simulations. We present the results of extensive computer simulations in which
we use the derived relations to determine c(z) over eight decades in frequency,
as well as \lambda. The system investigated is a simple but realistic model for
amorphous silica. We find that at high frequencies the real part of c(z) has
the value of an ideal gas. c'(\omega) increases quickly at those frequencies
which correspond to the vibrational excitations of the system. At low
temperatures c'(\omega) shows a second step. The frequency at which this step
is observed is comparable to the one at which the \alpha-relaxation peak is
observed in the intermediate scattering function. Also the temperature
dependence of the location of this second step is the same as the one of the
peak, thus showing that these quantities are intimately connected to
each other. From c'(\omega) we estimate the temperature dependence of the
vibrational and configurational part of the specific heat. We find that the
static value of c(z) as well as \lambda are in good agreement with experimental
data.Comment: 27 pages of Latex, 8 figure
Detection of chromosome aberrations in the human interphase nucleus by visualization of specific target DNAs with radioactive and non-radioactive in situ hybridization techniques: diagnosis of trisomy 18 with probe L1.84
The localization of chromosome 18 in human interphase nuclei is demonstrated by use of radioactive and nonradioactive in situ hybridization techniques with a DNA clone designated L1.84. This clone represents a distinct subpopulation of the repetitive human alphoid DNA family, located in the centric region of chromosome 18. Under stringent hybridization conditions hybridization of L1.84 is restricted to chromosome 18 and reflects the number of these chromosomes present in the nuclei, namely, two in normal diploid human cells and three in nuclei from cells with trisomy 18. Under conditions of low stringency, cross-hybridization with other subpopulations of the alphoid DNA family occurs in the centromeric regions of the whole chromosome complement, and numerous hybridization sites are detected over interphase nuclei. Detection of chromosome-specific target DNAs by non-radioactive in situ hybridization with appropriate DNA probes cloned from individual chromosomal subregions presents a rapid means of identifying directly numerical or even structural chromosome aberrations in the interphase nucleus. Present limitations and future applications of interphase cytogenetics are discussed
Airborne observations of Arctic air mass transformations during the HALO-(AC)3 campaign
The HALO-(AC)3 campaign was conducted in March and April 2022
to investigate warm air intrusions into the Arctic and marine cold air outbreaks. In
coordinated flights over the Arctic, the High Altitude and Long Range Research Aircraft
(HALO), equipped with a remote sensing payload and dropsondes, investigated these
air mass transformations together with the research aircraft Polar 5 and Polar 6. In
this report, we give an overview about the research flights and preliminary results from
projects, which are carried out by employees of the Leipzig Institute for Meteorology
(LIM).Die HALO-(AC)3 Kampagne wurde im März und April 2022
durchgeführt, umWarmlufteinbrüche in die Arktis und marine Kaltluftausbrüche zu untersuchen.
Das 'High Altitude and Long Range Research Aircraft' (HALO), ausgestattet
mit Instrumenten zur Fernerkundung und Standardmeteorologiesonden, untersuchte
zusammen mit den Forschungsflugzeugen Polar 5 und Polar 6, in koordinierten Flügen
über der Arktis, diese Veränderungen der Luftmassen. In diesem Bericht wird eine
Übersicht über die durchgeführten Forschungsflüge gegeben und Forschungsprojekte
werden vorgestellt, welche von Mitarbeitern des Leipziger Instituts für Meteorologie
(LIM) durchgeführt werden
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