2,254 research outputs found
Results of a partial cycloplegic on the visual system
Results of a partial cycloplegic on the visual syste
Second harmonic beam analysis, a sensitive technique to determine the duration of single ultrashort laser pulses
The second harmonic beam generated in a noncollinear arrangement allows the observation of the autocorrelation functio: A compact optical beam splitter and imaging system eliminates alignment problems. Single pulses of 1 ps duration and approximately 10â8 joule energy are readily observed using an optical multichannel analyser
Mechanisms of doping graphene
We distinguish three mechanisms of doping graphene. Density functional theory
is used to show that electronegative molecule like F4-TCNQ and electropositive
metals like K dope graphene p- and n-type respectively. These dopants are
expected to lead to a decrease in carrier mobility arising from Coulomb
scattering but without any hysteresis effects. Secondly, a novel doping
mechanism is exhibited by Au which dopes bilayer graphene but not single layer.
Thirdly, electrochemical doping is effected by redox reactions and can result
in p-doping by humid atmospheres and n-doping by NH3 and toluene.Comment: submitted to Physica Status Solid
CLASH-VLT: The stellar mass function and stellar mass density profile of the z=0.44 cluster of galaxies MACS J1206.2-0847
Context. The study of the galaxy stellar mass function (SMF) in relation to
the galaxy environment and the stellar mass density profile, rho(r), is a
powerful tool to constrain models of galaxy evolution. Aims. We determine the
SMF of the z=0.44 cluster of galaxies MACS J1206.2-0847 separately for passive
and star-forming (SF) galaxies, in different regions of the cluster, from the
center out to approximately 2 virial radii. We also determine rho(r) to compare
it to the number density and total mass density profiles. Methods. We use the
dataset from the CLASH-VLT survey. Stellar masses are obtained by SED fitting
on 5-band photometric data obtained at the Subaru telescope. We identify 1363
cluster members down to a stellar mass of 10^9.5 Msolar. Results. The whole
cluster SMF is well fitted by a double Schechter function. The SMFs of cluster
SF and passive galaxies are statistically different. The SMF of the SF cluster
galaxies does not depend on the environment. The SMF of the passive population
has a significantly smaller slope (in absolute value) in the innermost (<0.50
Mpc), highest density cluster region, than in more external, lower density
regions. The number ratio of giant/subgiant galaxies is maximum in this
innermost region and minimum in the adjacent region, but then gently increases
again toward the cluster outskirts. This is also reflected in a decreasing
radial trend of the average stellar mass per cluster galaxy. On the other hand,
the stellar mass fraction, i.e., the ratio of stellar to total cluster mass,
does not show any significant radial trend. Conclusions. Our results appear
consistent with a scenario in which SF galaxies evolve into passive galaxies
due to density-dependent environmental processes, and eventually get destroyed
very near the cluster center to become part of a diffuse intracluster medium.Comment: A&A accepted, 15 pages, 13 figure
CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z=0.44 galaxy cluster MACS 1206.2-0847
We use an unprecedented data-set of about 600 redshifts for cluster members,
obtained as part of a VLT/VIMOS large programme, to constrain the mass profile
of the z=0.44 cluster MACS J1206.2-0847 over the radial range 0-5 Mpc (0-2.5
virial radii) using the MAMPOSSt and Caustic methods. We then add external
constraints from our previous gravitational lensing analysis. We invert the
Jeans equation to obtain the velocity-anisotropy profiles of cluster members.
With the mass-density and velocity-anisotropy profiles we then obtain the first
determination of a cluster pseudo-phase-space density profile. The kinematics
and lensing determinations of the cluster mass profile are in excellent
agreement. This is very well fitted by a NFW model with mass M200=(1.4 +- 0.2)
10^15 Msun and concentration c200=6 +- 1, only slightly higher than theoretical
expectations. Other mass profile models also provide acceptable fits to our
data, of (slightly) lower (Burkert, Hernquist, and Softened Isothermal Sphere)
or comparable (Einasto) quality than NFW. The velocity anisotropy profiles of
the passive and star-forming cluster members are similar, close to isotropic
near the center and increasingly radial outside. Passive cluster members follow
extremely well the theoretical expectations for the pseudo-phase-space density
profile and the relation between the slope of the mass-density profile and the
velocity anisotropy. Star-forming cluster members show marginal deviations from
theoretical expectations. This is the most accurate determination of a cluster
mass profile out to a radius of 5 Mpc, and the only determination of the
velocity-anisotropy and pseudo-phase-space density profiles of both passive and
star-forming galaxies for an individual cluster [abridged]Comment: A&A in press; 22 pages, 19 figure
Atom Chips
Atoms can be trapped and guided using nano-fabricated wires on surfaces,
achieving the scales required by quantum information proposals. These Atom
Chips form the basis for robust and widespread applications of cold atoms
ranging from atom optics to fundamental questions in mesoscopic physics, and
possibly quantum information systems
CLASH-VLT: spectroscopic confirmation of a z=6.11 quintuply lensed galaxy in the Frontier Fields Cluster RXC J2248.7-4431
We present VIsible Multi-Object Spectrograph (VIMOS) observations of a z 6
galaxy quintuply imaged by the Frontier Fields galaxy cluster RXC J2248.7-4431
(z=0.348). This sub-L^*, high-z galaxy has been recently discovered by Monna et
al. (2013) using dropout techniques with the 16-band HST photometry acquired as
part of the Cluster Lensing And Supernova survey with Hubble (CLASH). Obtained
as part of the CLASH-VLT survey, the VIMOS medium-resolution spectra of this
source show a very faint continuum between ~8700A and ~9300A and a prominent
emission line at 8643A, which can be readily identified with Lyman-alpha at
z=6.110. The emission line exhibits an asymmetric profile, with a more
pronounced red wing. The rest-frame equivalent width of the line is EW=79+-10A.
After correcting for magnification, the star-formation rate (SFR) estimated
from the Lya line is SFR(Lya)=11 M_{sol}/yr and that estimated from the UV data
is SFR(UV)=3 M_{sol}/yr. We estimate that the effective radius of the source is
R_e6
M_{sol}/yr/kpc^2 and, using the Kennicutt-Schmidt relation, a gas surface mass
density Sigma_{gas}>10^3 M_{sol}/pc^2. Our results support the idea that this
magnified, distant galaxy is a young and compact object with 0.4 L^* at z=6,
with comparable amount of mass in gas and stars. Future follow-up observations
with ALMA will provide valuable insight into the SFR and molecular gas content
of this source. In the spirit of the Frontier Fields initiative, we also
publish the redshifts of several multiply imaged sources and other background
objects which will help improving the strong lensing model of this galaxy
cluster.Comment: 4 pages, 3 figures, 1 table, Accepted for publication in A&A (minor
changes, published version
CLASH-VLT: The stellar mass function and stellar mass density profile of the z = 0.44 cluster of galaxies MACS J1206.2-0847
Context. The study of the galaxy stellar mass function (SMF) in relation to the galaxy environment and the stellar mass density profile, (r), is a powerful tool to constrain models of galaxy evolution. Aims. We determine the SMF of the z = 0.44 cluster of galaxies MACS J1206.2-0847 separately for passive and star-forming (SF) galaxies, in different regions of the cluster, from the center out to approximately 2 virial radii. We also determine (r) to compare it to the number density and total mass density profiles. Methods. We use the dataset from the CLASH-VLT survey. Stellar masses are obtained by spectral energy distribution fitting with the MAGPHYS technique on 5-band photometric data obtained at the Subaru telescope. We identify 1363 cluster members down to a stellar mass of 109.5 M, selected on the basis of their spectroscopic (~1/3 of the total) and photometric redshifts. We correct our sample for incompleteness and contamination by non members. Cluster member environments are defined using either the clustercentric radius or the local galaxy number density. Results. The whole cluster SMF is well fitted by a double Schechter function, which is the sum of the two Schechter functions that provide good fits to the SMFs of, separately, the passive and SF cluster populations. The SMF of SF galaxies is significantly steeper than the SMF of passive galaxies at the faint end. The SMF of the SF cluster galaxies does not depend on the environment. The SMF of the passive cluster galaxies has a significantly smaller slope (in absolute value) in the innermost (= 0.50 Mpc, i.e., ~0.25 virial radii), and in the highest density cluster region than in more external, lower density regions. The number ratio of giant/subgiant galaxies is maximum in this innermost region and minimum in the adjacent region, but then gently increases again toward the clusteroutskirts. This is also reflected in a decreasing radial trend of the average stellar mass per cluster galaxy. On the other hand, the stellar mass fraction, i.e., the ratio of stellar to total cluster mass, does not show any significant radial trend. Conclusions. Our results appear consistent with a scenario in which SF galaxies evolve into passive galaxies due to density-dependent environmental processes and eventually get destroyed very near the cluster center to become part of a diffuse intracluster medium. Dynamical friction, on the other hand, does not seem to play an important role. Future investigations of other clusters of the CLASH-VLT sample will allow us to confirm our interpretation
- âŠ