4,784 research outputs found
Gravitational Lensing and the Hubble Deep Field
We calculate the expected number of multiply-imaged galaxies in the Hubble
Deep Field (HDF), using photometric redshift information for galaxies with m_I
< 27 that were detected in all four HDF passbands. A comparison of these
expectations with the observed number of strongly lensed galaxies constrains
the current value of Omega_m-Omega_Lambda, where Omega_m is the mean mass
density of the universe and Omega_Lambda is the normalized cosmological
constant. Based on current estimates of the HDF luminosity function and
associated uncertainties in individual parameters, our 95% confidence lower
limit on Omega_m-Omega_Lambda ranges between -0.44, if there are no strongly
lensed galaxies in the HDF, and -0.73, if there are two strongly lensed
galaxies in the HDF. If the only lensed galaxy in the HDF is the one presently
viable candidate, then, in a flat universe (Omega_m+Omega_Lambda=1),
Omega_Lambda < 0.79 (95% C.L.). These limits are compatible with estimates
based on high-redshift supernovae and with previous limits based on
gravitational lensing.Comment: 4 pages (aipproc.sty), 2 figures. To appear in "After the dark ages:
when galaxies were young," proceedings of the 9th Annual October Astrophysics
Conference, eds. S. S. Holt & E. P. Smit
Dubious decision evidence and criterion flexibility in recognition memory.
When old-new recognition judgments must be based on ambiguous memory evidence, a proper criterion for responding "old" can substantially improve accuracy, but participants are typically suboptimal in their placement of decision criteria. Various accounts of suboptimal criterion placement have been proposed. The most parsimonious, however, is that subjects simply over-rely on memory evidence - however faulty - as a basis for decisions. We tested this account with a novel recognition paradigm in which old-new discrimination was minimal and critical errors were avoided by adopting highly liberal or conservative biases. In Experiment 1, criterion shifts were necessary to adapt to changing target probabilities or, in a "security patrol" scenario, to avoid either letting dangerous people go free (misses) or harming innocent people (false alarms). Experiment 2 added a condition in which financial incentives drove criterion shifts. Critical errors were frequent, similar across sources of motivation, and only moderately reduced by feedback. In Experiment 3, critical errors were only modestly reduced in a version of the security patrol with no study phase. These findings indicate that participants use even transparently non-probative information as an alternative to heavy reliance on a decision rule, a strategy that precludes optimal criterion placement
Are eccentricity fluctuations able to explain the centrality dependence of ?
The fourth harmonic of the azimuthal distribution of particles has been
measured for Au-Au collisions at the Relativistic Heavy Ion Collider (RHIC).
The centrality dependence of does not agree with the prediction from
hydrodynamics. In particular, the ratio , where denotes the
second harmonic of the azimuthal distribution of particles, is significantly
larger than predicted by hydrodynamics. We argue that this discrepancy is
mostly due to elliptic flow () fluctuations. We evaluate these
fluctuations on the basis of a Monte Carlo Glauber calculation. The effect of
deviations from local thermal equilibrium is also studied, but appears to be
only a small correction. Combining these two effects allows us to reproduce
experimental data for peripheral and midcentral collisions. However, we are
unable to explain the large magnitude of observed for the most
central collisions.Comment: talk presented at the Strangeness in Quark Matter Conference, Buzios,
Brazil, Sept. 27 - oct. 2, 200
The homotopy type of the loops on -connected -manifolds
For we compute the homotopy groups of -connected closed
manifolds of dimension . Away from the finite set of primes dividing
the order of the torsion subgroup in homology, the -local homotopy groups of
are determined by the rank of the free Abelian part of the homology.
Moreover, we show that these -local homotopy groups can be expressed as a
direct sum of -local homotopy groups of spheres. The integral homotopy type
of the loop space is also computed and shown to depend only on the rank of the
free Abelian part and the torsion subgroup.Comment: Trends in Algebraic Topology and Related Topics, Trends Math.,
Birkhauser/Springer, 2018. arXiv admin note: text overlap with
arXiv:1510.0519
Optical and mechanical design of the extreme AO coronagraphic instrument MagAO-X
Here we review the current optical mechanical design of MagAO-X. The project
is post-PDR and has finished the design phase. The design presented here is the
baseline to which all the optics and mechanics have been fabricated. The
optical/mechanical performance of this novel extreme AO design will be
presented here for the first time. Some highlights of the design are: 1) a
floating, but height stabilized, optical table; 2) a Woofer tweeter (2040
actuator BMC MEMS DM) design where the Woofer can be the current f/16 MagAO ASM
or, more likely, fed by the facility f/11 static secondary to an ALPAO DM97
woofer; 3) 22 very compact optical mounts that have a novel locking clamp for
additional thermal and vibrational stability; 4) A series of four pairs of
super-polished off-axis parabolic (OAP) mirrors with a relatively wide FOV by
matched OAP clocking; 5) an advanced very broadband (0.5-1.7micron) ADC design;
6) A Pyramid (PWFS), and post-coronagraphic LOWFS NCP wavefront sensor; 7) a
vAPP coronagraph for starlight suppression. Currently all the OAPs have just
been delivered, and all the rest of the optics are in the lab. Most of the
major mechanical parts are in the lab or instrument, and alignment of the
optics has occurred for some of the optics (like the PWFS) and most of the
mounts. First light should be in 2019A.Comment: 10 pages, proc. SPIE 10703, Adaptive Optics IV, Austin TX, June 201
A faster pseudo-primality test
We propose a pseudo-primality test using cyclic extensions of . For every positive integer , this test achieves the
security of Miller-Rabin tests at the cost of Miller-Rabin
tests.Comment: Published in Rendiconti del Circolo Matematico di Palermo Journal,
Springe
MicroRNA profiling reveals marker of motor neuron disease in ALS models
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder marked by the loss of motor neurons (MNs) in the brain and spinal cord, leading to fatally debilitating weakness. Because this disease predominantly affects MNs, we aimed to characterize the distinct expression profile of that cell type to elucidate underlying disease mechanisms and to identify novel targets that inform on MN health during ALS disease time course. microRNAs (miRNAs) are short, noncoding RNAs that can shape the expression profile of a cell and thus often exhibit cell-type-enriched expression. To determine MN-enriched miRNA expression, we used Cre recombinase-dependent miRNA tagging and affinity purification in mice. By defining thein vivomiRNA expression of MNs, all neurons, astrocytes, and microglia, we then focused on MN-enriched miRNAs via a comparative analysis and found that they may functionally distinguish MNs postnatally from other spinal neurons. Characterizing the levels of the MN-enriched miRNAs in CSF harvested from ALS models of MN disease demonstrated that one miRNA (miR-218) tracked with MN loss and was responsive to an ALS therapy in rodent models. Therefore, we have used cellular expression profiling tools to define the distinct miRNA expression of MNs, which is likely to enrich future studies of MN disease. This approach enabled the development of a novel, drug-responsive marker of MN disease in ALS rodents.SIGNIFICANCE STATEMENTAmyotrophic lateral sclerosis (ALS) is a neurodegenerative disease in which motor neurons (MNs) in the brain and spinal cord are selectively lost. To develop tools to aid in our understanding of the distinct expression profiles of MNs and, ultimately, to monitor MN disease progression, we identified small regulatory microRNAs (miRNAs) that were highly enriched or exclusive in MNs. The signal for one of these MN-enriched miRNAs is detectable in spinal tap biofluid from an ALS rat model, where its levels change as disease progresses, suggesting that it may be a clinically useful marker of disease status. Furthermore, rats treated with ALS therapy have restored expression of this MN RNA marker, making it an MN-specific and drug-responsive marker for ALS rodents.</jats:p
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