988 research outputs found
The Distance to the M31 Globular Cluster System
The distance to the centroid of the M31 globular cluster system is determined
by fitting theoretical isochrones to the observed red-giant branches of
fourteen globular clusters in M31. The mean true distance modulus of the M31
globular clusters is found to be 24.47 +/- 0.07 mag. This is consistent with
distance modulii for M31 that have been obtained using other distance
indicators.Comment: 11 pages, 2 postscript figures, uses aaspp4.sty, to be published in
the May 1998 Astronomical Journa
A self-filling microfluidic device for noninvasive and time-resolved single red blood cell experiments
Existing approaches to red blood cell (RBC) experiments on the single-cell level usually rely on chemical or physical manipulations that often cause difficulties with preserving the RBC's integrity in a controlled microenvironment. Here, we introduce a straightforward, self-filling microfluidic device that autonomously separates and isolates single RBCs directly from unprocessed human blood samples and confines them in diffusion-controlled microchambers by solely exploiting their unique intrinsic properties. We were able to study the photo-induced oxygenation cycle of single functional RBCs by Raman microscopy without the limitations typically observed in optical tweezers based methods. Using bright-field microscopy, our noninvasive approach further enabled the time-resolved analysis of RBC flickering during the reversible shape evolution from the discocyte to the echinocyte morphology. Due to its specialized geometry, our device is particularly suited for studying the temporal behavior of single RBCs under precise control of their environment that will provide important insights into the RBC's biomedical and biophysical properties
Surface Enhanced Second Harmonic Generation from Macrocycle, Catenane, and Rotaxane Thin Films: Experiments and Theory
Surface enhanced second harmonic generation (SE SHG) experiments on molecular structures, macrocycles, catenanes, and rotaxanes, deposited as monolayers and multilayers by vacuum sublimation on silver, are reported. The measurements show that the molecules form ordered thin films, where the highest degree of order is observed in the case of macrocycle monolayers and the lowest in the case of rotaxane multilayers. The second harmonic generation activity is interpreted in terms of electric field induced second harmonic (EFISH) generation where the electric field is created by the substrate silver atoms. The measured second order nonlinear optical susceptibility for a rotaxane thin film is compared with that obtained by considering only EFISH contribution to SHG intensity. The electric field on the surface of a silver layer is calculated by using the Delphi4 program for structures obtained with TINKER molecular mechanics/dynamics simulations. An excellent agreement is observed between the calculated and the measured SHG susceptibilities.
The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
The Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM) is a
dedicated multi-object RM experiment that has spectroscopically monitored a
sample of 849 broad-line quasars in a single 7 deg field with the SDSS-III
BOSS spectrograph. The RM quasar sample is flux-limited to i_psf=21.7 mag, and
covers a redshift range of 0.1<z<4.5. Optical spectroscopy was performed during
2014 Jan-Jul dark/grey time, with an average cadence of ~4 days, totaling more
than 30 epochs. Supporting photometric monitoring in the g and i bands was
conducted at multiple facilities including the CFHT and the Steward Observatory
Bok telescopes in 2014, with a cadence of ~2 days and covering all lunar
phases. The RM field (RA, DEC=14:14:49.00, +53:05:00.0) lies within the CFHT-LS
W3 field, and coincides with the Pan-STARRS 1 (PS1) Medium Deep Field MD07,
with three prior years of multi-band PS1 light curves. The SDSS-RM 6-month
baseline program aims to detect time lags between the quasar continuum and
broad line region (BLR) variability on timescales of up to several months (in
the observed frame) for ~10% of the sample, and to anchor the time baseline for
continued monitoring in the future to detect lags on longer timescales and at
higher redshift. SDSS-RM is the first major program to systematically explore
the potential of RM for broad-line quasars at z>0.3, and will investigate the
prospects of RM with all major broad lines covered in optical spectroscopy.
SDSS-RM will provide guidance on future multi-object RM campaigns on larger
scales, and is aiming to deliver more than tens of BLR lag detections for a
homogeneous sample of quasars. We describe the motivation, design and
implementation of this program, and outline the science impact expected from
the resulting data for RM and general quasar science.Comment: 25 pages, submitted to ApJS; project website at http://www.sdssrm.or
52. Development of network of cancer family syndrome registries in eastern Europe
It has been proven that organizing the registries of families affected by CFS is very helpful in research leading to: 1. Identification of new genes of CFS, 2. Better knowledge of correlations in CFS, 3. Identification of external factors having impact on mutated genes, 4. Description of mutation characteristic for particular populations.Thus, development of CFS registries is very important for increasing pre-clinical and clinical research facilities. Direct positive consequence will also be the improvement of quality of life by better management of patients affected by CFS. Without registries these patients are very often not identified and deprived of appropriate recommendations concerning prophylactics, surveillance and treatment. Development of CFS registries leads also to further improvement of quality of life by progress in management in families with these tumours which can be achieved by better organizing of research on CFS. Better management in CFS families decreases also health-care costs by lowering the number of cancers and increasing the number of tumours detected at their earliest clinical stage when the treatment is less expensive.The scientific objectives of the project include:-elaboration of standards for a model cancer family syndrome registries in Eastern Europe-registration of ⌠2000 families with different types of CFS in populations of East European countries (Czech, Hungary, Latvia, Lithuania, Poland)-initiation of European collaborative studies with the use of material collected by East European CFS registries
Free Energy Simulations of a GTPase: GTP and GDP Binding to Archaeal Initiation Factor 2
International audienceArchaeal initiation factor 2 (aIF2) is a protein involved in the initiation of protein biosynthesis. In its GTP-bound, "ON" conformation, aIF2 binds an initiator tRNA and carries it to the ribosome. In its GDP-bound, "OFF" conformation, it dissociates from tRNA. To understand the specific binding of GTP and GDP and its dependence on the ON or OFF conformational state of aIF2, molecular dynamics free energy simulations (MDFE) are a tool of choice. However, the validity of the computed free energies depends on the simulation model, including the force field and the boundary conditions, and on the extent of conformational sampling in the simulations. aIF2 and other GTPases present specific difficulties; in particular, the nucleotide ligand coordinates a divalent Mg(2+) ion, which can polarize the electronic distribution of its environment. Thus, a force field with an explicit treatment of electronic polarizability could be necessary, rather than a simpler, fixed charge force field. Here, we begin by comparing a fixed charge force field to quantum chemical calculations and experiment for Mg(2+):phosphate binding in solution, with the force field giving large errors. Next, we consider GTP and GDP bound to aIF2 and we compare two fixed charge force fields to the recent, polarizable, AMOEBA force field, extended here in a simple, approximate manner to include GTP. We focus on a quantity that approximates the free energy to change GTP into GDP. Despite the errors seen for Mg(2+):phosphate binding in solution, we observe a substantial cancellation of errors when we compare the free energy change in the protein to that in solution, or when we compare the protein ON and OFF states. Finally, we have used the fixed charge force field to perform MDFE simulations and alchemically transform GTP into GDP in the protein and in solution. With a total of about 200 ns of molecular dynamics, we obtain good convergence and a reasonable statistical uncertainty, comparable to the force field uncertainty, and somewhat lower than the predicted GTP/GDP binding free energy differences. The sign and magnitudes of the differences can thus be interpreted at a semiquantitative level, and are found to be consistent with the experimental binding preferences of ON- and OFF-aIF2
PS18kh: A New Tidal Disruption Event with a Non-Axisymmetric Accretion Disk
We present the discovery of PS18kh, a tidal disruption event (TDE) discovered
at the center of SDSS J075654.53+341543.6 ( Mpc) by the Pan-STARRS
Survey for Transients. Our dataset includes pre-discovery survey data from
Pan-STARRS, the All-Sky Automated Survey for Supernovae (ASAS-SN), and the
Asteroid Terrestrial-impact Last Alert System (ATLAS) as well as high-cadence,
multi-wavelength follow-up data from ground-based telescopes and Swift,
spanning from 56 days before peak light until 75 days after. The optical/UV
emission from PS18kh is well-fit as a blackbody with temperatures ranging from
K to K and it peaked at a luminosity of
ergs s. PS18kh radiated
ergs over the period of observation, with
ergs being released during the rise to peak.
Spectra of PS18kh show a changing, boxy/double-peaked H emission
feature, which becomes more prominent over time. We use models of
non-axisymmetric accretion disks to describe the profile of the H line
and its evolution. We find that at early times the high accretion rate leads
the disk to emit a wind which modifies the shape of the line profile and makes
it bell-shaped. At late times, the wind becomes optically thin, allowing the
non-axisymmetric perturbations to show up in the line profile. The
line-emitting portion of the disk extends from to
an outer radius of and the perturbations can be
represented either as an eccentricity in the outer rings of the disk or as a
spiral arm in the inner disk.Comment: 27 pages, 13 figures, 8 tables. Updated to reflect changes made in
the published version. A table containing the host-subtracted photometry
presented in this manuscript is included in machine-readable format as an
ancillary fil
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