11,411 research outputs found
Reduction of Lie-Jordan Banach algebras and quantum states
A theory of reduction of Lie-Jordan Banach algebras with respect to either a
Jordan ideal or a Lie-Jordan subalgebra is presented. This theory is compared
with the standard reduction of C*-algebras of observables of a quantum system
in the presence of quantum constraints. It is shown that the later corresponds
to the particular instance of the reduction of Lie-Jordan Banach algebras with
respect to a Lie-Jordan subalgebra as described in this paper. The space of
states of the reduced Lie-Jordan Banach algebras is described in terms of
equivalence classes of extensions to the full algebra and their GNS
representations are characterized in the same way. A few simple examples are
discussed that illustrates some of the main results
Variable stars in the open cluster NGC 6791 and its surrounding field
Aims: This work presents a high--precision variability survey in the field of
the old, super metal-rich open cluster NGC 6791.
Methods: The data sample consists of more than 75,000 high-precision CCD time
series measurements in the V band obtained mainly at the Canada-France-Hawaii
Telescope, with additional data from S. Pedro Martir and Loiano observatories,
over a time span of ten nights. The field covers an area of 42x28 arcmin^2.
Results: We have discovered 260 new variables and re-determined periods and
amplitudes of 70 known variable stars. By means of a photometric evaluation of
the membership in NGC 6791, and a preliminary membership based on the proper
motions, we give a full description of the variable content of the cluster and
surrounding field in the range 16<V<23.5. Accurate periods can be given for the
variables with P<4.0 d, while for ones with longer periods the limited
time-baseline hampered precise determinations. We categorized the entire sample
as follows: 6 pulsating, 3 irregular, 3 cataclysmic, 89 rotational variables
and 61 eclipsing systems; moreover, we detected 168 candidate variables for
which we cannot give a variability class since their periods are much longer
than our time baseline.
Conclusions: On the basis of photometric considerations, and of the positions
of the stars with respect to the center of the cluster, we inferred that 11 new
variable stars are likely members of the cluster, for 22 stars the membership
is doubtful and 137 are likely non-members. We also detected an outburst of
about 3 mag in the light curve of a very faint blue star belonging to the
cluster and we suggest that this star could be a new U Gem (dwarf nova)
cataclysmic variable.Comment: 24 pages, 19 Figures, A&A accepte
Collisional cross sections and momentum distributions in astrophysical plasmas: dynamics and statistical mechanics link
We show that, in stellar core plasmas, the one-body momentum distribution
function is strongly dependent, at least in the high velocity regime, on the
microscopic dynamics of ion elastic collisions and therefore on the effective
collisional cross sections, if a random force field is present. We take into
account two cross sections describing ion-dipole and ion-ion screened
interactions. Furthermore we introduce a third unusual cross section, to link
statistical distributions and a quantum effect originated by the
energy-momentum uncertainty owing to many-body collisions, and propose a
possible physical interpretation in terms of a tidal-like force. We show that
each collisional cross section gives rise to a slight peculiar correction on
the Maxwellian momentum distribution function in a well defined velocity
interval. We also find a possible link between microscopical dynamics of ions
and statistical mechanics interpreting our results in the framework of
non-extensive statistical mechanics.Comment: 8 page
A worm gel-based 3D model to elucidate the paracrine interaction between multiple myeloma and mesenchymal stem cells
Multiple myeloma (MM) is a malignancy of terminally-differentiated plasma cells that develops mainly inside the bone marrow (BM) microenvironment. It is well known that autocrine and paracrine signals are responsible for the progression of this disease but the precise mechanism and contributions from single cell remain largely unknown. Mesenchymal stem cells (MSC) are an important cellular component of the BM: they support MM growth by increasing its survival and chemo-resistance, but little is known about the paracrine signaling pathways. Three-dimensional (3D) models of MM-MSC paracrine interactions are much more biologically-relevant than simple 2D models and are considered essential for detailed studies of MM pathogenesis.
Herein we present a novel 3D co-culture model designed to mimic the paracrine interaction between MSC and MM cells. MSC were embedded within a previously characterized thermoresponsive block copolymer worm gel that can induce stasis in human pluripotent stem cells (hPSC) and then co-cultured with MM cells. Transcriptional phenotyping of co-cultured cells indicated the dysregulation of genes that code for known disease-relevant factors, and also revealed IL-6 and IL-10 as upstream regulators. Importantly, we have identified a synergistic paracrine signaling pathway between IL-6 and IL-10 that plays a critical role in sustaining MM cell proliferation.
Our findings indicate that this 3D co-culture system is a useful model to investigate the paracrine interaction between MM cells and the BM microenvironment in vitro. This approach has revealed a new mechanism that promotes the proliferation of MM cells and suggested a new therapeutic target
Avaliação de soluções fixadoras e tempo de fixação na análise morfológica dos espermatozoides de tambaqui Colossoma macropomum.
Extracellular circulating viral microRNAs: Current knowledge and perspectives
MicroRNAs (miRNAs) are small non-coding RNAs responsible of post-transcriptional regulation of gene expression through interaction with messenger RNAs (mRNAs). They are involved in important biological processes and are often dysregulated in a variety of diseases, including cancer and infections. Viruses also encode their own sets of miRNAs, which they use to control the expression of either the host's genes and/or their own. In the past few years evidence of the presence of cellular miRNAs in extracellular human body fluids such as serum, plasma, saliva, and urine has accumulated. They have been found either cofractionate with the Argonaute2 protein or in membrane-bound vesicles such as exosomes. Although little is known about the role of circulating miRNAs, it has been demonstrated that miRNAs secreted by virus-infected cells are transferred to and act in uninfected recipient cells. In this work we summarize the current knowledge on viral circulating miRNAs and provide a few examples of computational prediction of their functio
Fundamental parameters of Cepheids. V. Additional photometry and radial velocity for southern Cepheids
I present photometric and radial velocity data for Galactic Cepheids, most of
them being in the southern hemisphere. There are 1250 Geneva 7-color
photometric measurements for 62 Cepheids, the average uncertainty per
measurement is better than 0.01 mag. A total of 832 velocity measurements have
been obtained with the CORAVEL radial velocity spectrograph for 46 Cepheids.
The average accuracy of the radial velocity data is 0.38 km/s. There are 33
stars with both photometry and radial velocity data. I discuss the possible
binarity or period change that these new data reveal. I also present reddenings
for all Cepheids with photometry. The data are available electronically.Comment: To appear in ApJS. Data available electronically at
ftp://cfa-ftp.harvard.edu/pub/dbersier
A knowledge base for the discovery of function, diagnostic potential and drug effects on cellular and extracellular miRNAs
Background: MicroRNAs (miRNAs) are small noncoding RNAs that play an important role in the regulation of various biological processes through their interaction with cellular mRNAs. A significant amount of miRNAs has been found in extracellular human body fluids (e.g. plasma and serum) and some circulating miRNAs in the blood have been successfully revealed as biomarkers for diseases including cardiovascular diseases and cancer. Released miRNAs do not necessarily reflect the abundance of miRNAs in the cell of origin. It is claimed that release of miRNAs from cells into blood and ductal fluids is selective and that the selection of released miRNAs may correlate with malignancy. Moreover, miRNAs play a significant role in pharmacogenomics by down-regulating genes that are important for drug function. In particular, the use of drugs should be taken into consideration while analyzing plasma miRNA levels as drug treatment. This may impair their employment as biomarkers. Description: We enriched our manually curated extracellular/circulating microRNAs database, miRandola, by providing (i) a systematic comparison of expression profiles of cellular and extracellular miRNAs, (ii) a miRNA targets enrichment analysis procedure, (iii) information on drugs and their effect on miRNA expression, obtained by applying a natural language processing algorithm to abstracts obtained from PubMed. Conclusions: This allows users to improve the knowledge about the function, diagnostic potential, and the drug effects on cellular and circulating miRNAs
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