243 research outputs found
Recursiveness, Switching, and Fluctuations in a Replicating Catalytic Network
A protocell model consisting of mutually catalyzing molecules is studied in
order to investigate how chemical compositions are transferred recursively
through cell divisions under replication errors. Depending on the path rate,
the numbers of molecules and species, three phases are found: fast switching
state without recursive production, recursive production, and itinerancy
between the above two states. The number distributions of the molecules in the
recursive states are shown to be log-normal except for those species that form
a core hypercycle, and are explained with the help of a heuristic argument.Comment: 4 pages (with 7 figures (6 color)), submitted to PR
Large-scale periodicity in the distribution of QSO absorption-line systems
The spatial-temporal distribution of absorption-line systems (ALSs) observed
in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is
investigated on the base of our updated catalog of absorption systems. We
consider so called metallic systems including basically lines of heavy
elements. The sample of the data displays regular variations (with amplitudes ~
15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution,
where eta is a dimensionless line-of-sight comoving distance, relatively to
smoother dependences. The eta-distribution reveals the periodicity with period
Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic
scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20)
h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a
spatial interpretation of the results treating the pattern obtained as a trace
of an order imprinted on the galaxy clustering in the early Universe.Comment: AASTeX, 13 pages, with 9 figures, Accepted for publication in
Astrophysics & Space Scienc
Deviation From \Lambda CDM With Cosmic Strings Networks
In this work, we consider a network of cosmic strings to explain possible
deviation from \Lambda CDM behaviour. We use different observational data to
constrain the model and show that a small but non zero contribution from the
string network is allowed by the observational data which can result in a
reasonable departure from \Lambda CDM evolution. But by calculating the
Bayesian Evidence, we show that the present data still strongly favour the
concordance \Lambda CDM model irrespective of the choice of the prior.Comment: 15 Pages, Latex Style, 4 eps figures, Revised Version, Accepted for
publication in European Physical Journal
Study of the production of and hadrons in collisions and first measurement of the branching fraction
The product of the () differential production
cross-section and the branching fraction of the decay () is
measured as a function of the beauty hadron transverse momentum, ,
and rapidity, . The kinematic region of the measurements is and . The measurements use a data sample
corresponding to an integrated luminosity of collected by the
LHCb detector in collisions at centre-of-mass energies in 2011 and in 2012. Based on previous LHCb
results of the fragmentation fraction ratio, , the
branching fraction of the decay is
measured to be \begin{equation*} \mathcal{B}(\Lambda_b^0\rightarrow J/\psi
pK^-)= (3.17\pm0.04\pm0.07\pm0.34^{+0.45}_{-0.28})\times10^{-4},
\end{equation*} where the first uncertainty is statistical, the second is
systematic, the third is due to the uncertainty on the branching fraction of
the decay , and the
fourth is due to the knowledge of . The sum of the
asymmetries in the production and decay between and
is also measured as a function of and .
The previously published branching fraction of , relative to that of , is updated.
The branching fractions of are determined.Comment: 29 pages, 19figures. All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-032.htm
Clustering of dark matter tracers: generalizing bias for the coming era of precision LSS
On very large scales, density fluctuations in the Universe are small,
suggesting a perturbative model for large-scale clustering of galaxies (or
other dark matter tracers), in which the galaxy density is written as a Taylor
series in the local mass density, delta, with the unknown coefficients in the
series treated as free "bias" parameters. We extend this model to include
dependence of the galaxy density on the local values of nabla_i nabla_j phi and
nabla_i v_j, where phi is the potential and v is the peculiar velocity. We show
that only two new free parameters are needed to model the power spectrum and
bispectrum up to 4th order in the initial density perturbations, once symmetry
considerations and equivalences between possible terms are accounted for. One
of the new parameters is a bias multiplying s_ij s_ji, where s_ij=[nabla_i
nabla_j \nabla^-2 - 1/3 delta^K_ij] delta. The other multiplies s_ij t_ji,
where t_ij=[nabla_i nabla_j nabla^-2 - 1/3 delta^K_ij](theta-delta), with
theta=-(a H dlnD/dlna)^-1 nabla_i v_i. (There are other, observationally
equivalent, ways to write the two terms, e.g., using theta-delta instead of
s_ij s_ji.) We show how short-range (non-gravitational) non-locality can be
included through a controlled series of higher derivative terms, starting with
R^2 nabla^2 delta, where R is the scale of non-locality (this term will be a
small correction as long as k^2 R^2 is small, where k is the observed
wavenumber). We suggest that there will be much more information in future huge
redshift surveys in the range of scales where beyond-linear perturbation theory
is both necessary and sufficient than in the fully linear regime.Comment: 24 pg., 5 fi
Evaluating the stable isotopic composition of phosphate oxygen as a tracer of phosphorus from waste water treatment works
Eutrophication is a globally significant challenge facing freshwater ecosystems and is closely associated with anthropogenic enrichment of phosphorus (P) in the aquatic environment. Phosphorus inputs to rivers are usually dominated by diffuse sources related to farming activities and point sources such as waste water treatment works (WwTW). The limited availability of inherent labels for different P sources has constrained understanding of these triggers for eutrophication in natural systems. There have been substantial recent advances in the use of phosphate oxygen isotopes (ÎŽ18OPO4) as a way of understanding phosphate sources and processing. Results from all previous studies of the ÎŽ18OPO4 composition of WwTW effluent and septic tanks are combined together with significant new data from the UK to assess ÎŽ18OPO4 compositions in waste water sources. The overall average ÎŽ18OPO4 value is 13.9â°, ranging from 8.4 to 19.7â°. Values measured in the USA are much lower than those measured in Europe. A strong positive correlation exists between ÎŽ18OPO4 and ÎŽ18OH2O, suggesting biologically-mediated exchange between the water molecules and the phosphate ions. A comparison of ÎŽ18OPO4 and the offset from isotopic equilibrium showed a strong positive linear correlation (Ï = 0.94) for the data from Europe but no relationship for the historic USA data which may be due to recent advances in the extraction procedure or to a relative paucity of data. This offset is most strongly controlled by the ÎŽ18OH2O rather than temperature, with greater offsets occurring with lower ÎŽ18OH2O. Time series data collected over 8-24 hours for three sites showed that, although there were significant changes in the phosphate concentration, for a given WwTW the ÎŽ18OPO4 stayed relatively constant. Two new studies that considered instream processing of ÎŽ18OPO4 downstream of WwTWs showed mixing of the upstream source with effluent water but no evidence of biological cycling 3 km downstream. It is suggested that ÎŽ18OPO4 can be an effective tool to trace P from WwTWs provided the source of the effluent is known and samples are collected within a day
Formation, evolution and multiplicity of brown dwarfs and giant exoplanets
This proceeding summarises the talk of the awardee of the Spanish
Astronomical Society award to the the best Spanish thesis in Astronomy and
Astrophysics in the two-year period 2006-2007. The thesis required a tremendous
observational effort and covered many different topics related to brown dwarfs
and exoplanets, such as the study of the mass function in the substellar domain
of the young sigma Orionis cluster down to a few Jupiter masses, the relation
between the cluster stellar and substellar populations, the accretion discs in
cluster brown dwarfs, the frequency of very low-mass companions to nearby young
stars at intermediate and wide separations, or the detectability of Earth-like
planets in habitable zones around ultracool (L- and T-type) dwarfs in the solar
neighbourhood.Comment: "Highlights of Spanish Astrophysics V", Proceedings of the VIII
Scientific Meeting of the Spanish Astronomical Society (SEA) held in
Santander, 7-11 July, 2008. Edited by J. Gorgas, L. J. Goicoechea, J. I.
Gonzalez-Serrano, J. M. Diego. Invited oral contribution to plenary sessio
Nanoparticles for Applications in Cellular Imaging
In the following review we discuss several types of nanoparticles (such as TiO2, quantum dots, and gold nanoparticles) and their impact on the ability to image biological components in fixed cells. The review also discusses factors influencing nanoparticle imaging and uptake in live cells in vitro. Due to their unique size-dependent properties nanoparticles offer numerous advantages over traditional dyes and proteins. For example, the photostability, narrow emission peak, and ability to rationally modify both the size and surface chemistry of Quantum Dots allow for simultaneous analyses of multiple targets within the same cell. On the other hand, the surface characteristics of nanometer sized TiO2allow efficient conjugation to nucleic acids which enables their retention in specific subcellular compartments. We discuss cellular uptake mechanisms for the internalization of nanoparticles and studies showing the influence of nanoparticle size and charge and the cell type targeted on nanoparticle uptake. The predominant nanoparticle uptake mechanisms include clathrin-dependent mechanisms, macropinocytosis, and phagocytosis
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