1,659 research outputs found
Explaining LIGO's observations via isolated binary evolution with natal kicks
We compare binary evolution models with different assumptions about
black-hole natal kicks to the first gravitational-wave observations performed
by the LIGO detectors. Our comparisons attempt to reconcile merger rate,
masses, spins, and spin-orbit misalignments of all current observations with
state-of-the-art formation scenarios of binary black holes formed in isolation.
We estimate that black holes (BHs) should receive natal kicks at birth of the
order of (50) km/s if tidal processes do (not) realign
stellar spins. Our estimate is driven by two simple factors. The natal kick
dispersion is bounded from above because large kicks disrupt too many
binaries (reducing the merger rate below the observed value). Conversely, the
natal kick distribution is bounded from below because modest kicks are needed
to produce a range of spin-orbit misalignments. A distribution of misalignments
increases our models' compatibility with LIGO's observations, if all BHs are
likely to have natal spins. Unlike related work which adopts a concrete BH
natal spin prescription, we explore a range of possible BH natal spin
distributions. Within the context of our models, for all of the choices of
used here and within the context of one simple fiducial parameterized
spin distribution, observations favor low BH natal spin.Comment: 19 pages, 14 figures, as published in PR
PHENIX first measurement of the J/psi elliptic flow parameter v2 in Au+Au collisions at sqrt(sNN) = 200 GeV
Recent results indicate that the J/psi suppression pattern differs with
rapidity showing a larger suppression at forward rapidity. J/psi suppression
mechanisms based on energy density (such as color screening, interaction with
co-movers, etc.) predict the opposite trend. On the other hand, it is expected
that more c\bar{c} pairs should be available to form quarkonia at mid-rapidity
via recombination. Some models provide a way to differentiate J/psi production
from initially produced c\bar{c} pairs and final state recombination of
uncorrelated pairs, via the rapidity and transverse momentum dependence of the
elliptic flow (v2).
During 2007 data taking at RHIC, a large sample of Au+Au collisions at
sqrt(sNN)=200 GeV was collected. The statistics has been increased compared to
previous 2004 data set, thus allowing a more precise measurement of the J/psi
production at both mid and forward rapidity. Furthermore, the PHENIX experiment
benefited from the addition of a new detector, which improves the reaction
plane resolution and allows us to measure the J/psi v2. Comparing this
measurement to the positive D-mesons v2 (through non-photonic electron decays)
will help constraining the J/psi production mechanisms and getting a more
precise picture of the proportion of J/psi coming from direct production or
charm quark coalescence.
Details on how the J/psi v2 is measured at both rapidities are presented. The
J/psi v2 as a function of transverse momentum are compared to existing models.Comment: 4 pages, 3 figures, Quark Matter 2008 proceeding
Dynamics of lane formation in driven binary complex plasmas
The dynamical onset of lane formation is studied in experiments with binary
complex plasmas under microgravity conditions. Small microparticles are driven
and penetrate into a cloud of big particles, revealing a strong tendency
towards lane formation. The observed time-resolved lane formation process is in
good agreement with computer simulations of a binary Yukawa model with Langevin
dynamics. The laning is quantified in terms of the anisotropic scaling index,
leading to a universal order parameter for driven systems.Comment: 4 pages, 3 figures, movies available at
http://www.mpe.mpg.de/pke/lane-formation
Multi-Objective and Financial Portfolio Optimization of Carrier-Sense Multiple Access Protocols with Cooperative Diversity
8th International Workshop on Multiple Access Communications (MACOM2015), Helsinki, Finland.This paper presents a trade-off design and optimization of a class of wireless carrier-sense multiple access protocols where collision-free transmissions are assisted by the potential cooperative retransmissions of inactive terminals with a correct copy of the original transmission. Terminals are enabled with a decode-and-forward relaying protocol. The analysis is focused on asymmetrical settings, where terminals experience different channel and queuing statistics. This work is based on multi-objective and financial portfolio optimization tools. Each packet transmission is thus regarded not only as a network resource, but also as a financial asset with different values of return and risk (or variance of the return). The objective of this financial optimization is to find the transmission policy that simultaneously maximizes return and minimizes risk in the network. The work is focused on the characterization of the boundaries (envelope) of different types of trade-off performance regions: the conventional throughput region, sum-throughput vs. fairness, sum-throughput vs. power, and return vs. risk regions. Fairness is evaluated by means of the Gini-index, which is a metric commonly used in economics to measure income inequality. Transmit power is directly linked to the global transmission rate. The protocol is shown to outperform non-cooperative solutions under different network conditions that are here discussed
Topoisomer Differentiation of Molecular Knots by FTICR MS: Lessons from Class II Lasso Peptides
Lasso peptides constitute a class of bioactive peptides sharing a knotted
structure where the C-terminal tail of the peptide is threaded through and
trapped within an N-terminalmacrolactamring. The structural characterization of
lasso structures and differentiation from their unthreaded topoisomers is not
trivial and generally requires the use of complementary biochemical and
spectroscopic methods. Here we investigated two antimicrobial peptides
belonging to the class II lasso peptide family and their corresponding
unthreaded topoisomers: microcin J25 (MccJ25), which is known to yield
two-peptide product ions specific of the lasso structure under collisioninduced
dissociation (CID), and capistruin, for which CID does not permit to
unambiguously assign the lasso structure. The two pairs of topoisomers were
analyzed by electrospray ionization Fourier transform ion cyclotron resonance
mass spectrometry (ESI-FTICR MS) upon CID, infrared multiple photon
dissociation (IRMPD), and electron capture dissociation (ECD). CID and
ECDspectra clearly permitted to differentiate MccJ25 from its non-lasso
topoisomer MccJ25-Icm, while for capistruin, only ECD was informative and
showed different extent of hydrogen migration (formation of c\bullet/z from
c/z\bullet) for the threaded and unthreaded topoisomers. The ECD spectra of the
triply-charged MccJ25 and MccJ25-lcm showed a series of radical b-type product
ions {\eth}b0In{\TH}. We proposed that these ions are specific of
cyclic-branched peptides and result from a dual c/z\bullet and y/b
dissociation, in the ring and in the tail, respectively. This work shows the
potentiality of ECD for structural characterization of peptide topoisomers, as
well as the effect of conformation on hydrogen migration subsequent to electron
capture
Recommended from our members
Computational and experimental investigation of magnetized target fusion
In Magnetized Target Fusion (MTF), a preheated and magnetized target plasma is hydrodynamically compressed to fusion conditions. Because the magnetic field suppresses losses by electron thermal conduction in the fuel during the target implosion heating process, the compression may be over a much longer time scale than in traditional inertial confinement fusion (ICF). Bigger targets and much lower initial target densities than in ICF can be used, reducing radiative energy losses. Therefore, ``liner-on-plasma`` compressions, driven by relatively inexpensive electrical pulsed power, may be practical. Potential MTF target plasmas must meet minimum temperature, density, and magnetic field starting conditions, and must remain relatively free of high-Z radiation-cooling-enhancing contaminants. At Los Alamos National Laboratory, computational and experimental research is being pursued into MTF target plasmas, such as deuterium-fiber-initiated Z-pinches, and the Russian-originated MAGO plasma. In addition, liner-on-plasma compressions of such target plasmas to fusion conditions are being computationally modeled, and experimental investigation of such heavy liner implosions has begun. The status of the research will be presented
Chemoreception Regulates Chemical Access to Mouse Vomeronasal Organ: Role of Solitary Chemosensory Cells
Controlling stimulus access to sensory organs allows animals to optimize sensory reception and prevent damage. The vomeronasal organ (VNO) detects pheromones and other semiochemicals to regulate innate social and sexual behaviors. This semiochemical detection generally requires the VNO to draw in chemical fluids, such as bodily secretions, which are complex in composition and can be contaminated. Little is known about whether and how chemical constituents are monitored to regulate the fluid access to the VNO. Using transgenic mice and immunolabeling, we found that solitary chemosensory cells (SCCs) reside densely at the entrance duct of the VNO. In this region, most of the intraepithelial trigeminal fibers innervate the SCCs, indicating that SCCs relay sensory information onto the trigeminal fibers. These SCCs express transient receptor potential channel M5 (TRPM5) and the phospholipase C (PLC) β2 signaling pathway. Additionally, the SCCs express choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) for synthesizing and packaging acetylcholine, a potential transmitter. In intracellular Ca2+ imaging, the SCCs responded to various chemical stimuli including high concentrations of odorants and bitter compounds. The responses were suppressed significantly by a PLC inhibitor, suggesting involvement of the PLC pathway. Further, we developed a quantitative dye assay to show that the amount of stimulus fluid that entered the VNOs of behaving mice is inversely correlated to the concentration of odorous and bitter substances in the fluid. Genetic knockout and pharmacological inhibition of TRPM5 resulted in larger amounts of bitter compounds entering the VNOs. Our data uncovered that chemoreception of fluid constituents regulates chemical access to the VNO and plays an important role in limiting the access of non-specific irritating and harmful substances. Our results also provide new insight into the emerging role of SCCs in chemoreception and regulation of physiological actions
- …