2,960 research outputs found
Detection of the Red Giant Branch Stars in M82 Using the Hubble Space Telescope
We present color-magnitude diagrams and luminosity functions of stars in two
halo regions of the irregular galaxy in M82, based on F555W and F814W
photometry taken with the Hubble Space Telescope and Wide Field Planetary
Camera 2. The I-band luminosity function shows a sudden jump at I~23.95 mag,
which is identified as the tip of the red giant branch (TRGB). Adopting the Lee
et al. (1993) calibration of the TRGB based on the RR Lyrae distances to
Galactic globular clusters, we obtain the distance modulus of (m-M)_0=27.95 +-
0.14 (random) +- 0.16 (systematic) mag. This corresponds to a linear distance
of 3.9 +- 0.3 (random) +- 0.3 (systematicf) Mpc, which agrees well with the
distance of M81 deteremined from the HST observations of the Cepheid variable
stars. In addition, we observe a significant number of stars apparently
brighter than the TRGB. However, with the current data, we cannot rule out
whether these stars are blends of fainter stars, or are indeed intermediate-age
asymptotic giant branch stars.Comment: 8 figure
Photometric Calibration of the Supernova Legacy Survey Fields
We present the photometric calibration of the Supernova Legacy Survey (SNLS)
fields. The SNLS aims at measuring the distances to SNe Ia at (0.3<z<1) using
MegaCam, the 1 deg^2 imager on the Canada-France-Hawaii Telescope (CFHT). The
uncertainty affecting the photometric calibration of the survey dominates the
systematic uncertainty of the key measurement of the survey, namely the dark
energy equation of state. The photometric calibration of the SNLS requires
obtaining a uniform response across the imager, calibrating the science field
stars in each survey band (SDSS-like ugriz bands) with respect to standards
with known flux in the same bands, and binding the calibration to the UBVRI
Landolt standards used to calibrate the nearby SNe from the literature
necessary to produce cosmological constraints. The spatial non-uniformities of
the imager photometric response are mapped using dithered observations of dense
stellar fields. Photometric zero-points against Landolt standards are obtained.
The linearity of the instrument is studied. We show that the imager filters and
photometric response are not uniform and publish correction maps. We present
models of the effective passbands of the instrument as a function of the
position on the focal plane. We define a natural magnitude system for MegaCam.
We show that the systematics affecting the magnitude-to-flux relations can be
reduced if we use the spectrophotometric standard star BD +17 4708 instead of
Vega as a fundamental flux standard. We publish ugriz catalogs of tertiary
standards for all the SNLS fields.Comment: 46 pages, 23 figures. Accepted by Astronomy and Astrophysics. Online
material available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ or
alternatively from: http://supernovae.in2p3.fr/snls3/regnault09_cds.tar.g
Snowfall Simulator Quick-Release Retrofit
In the early 1990s, UCAR fabricated a snowfall simulator that they have used to test deicing fluids for aircraft, among other applications. Ice cores are actuated by a stepper motor and travel along a linear guide rail feeding it into an auger bit. This bit shaves the ice core, creating conditions that simulate snowfall. Currently, the simulator is in satisfactory operating condition, however upgrades have been proposed to make the simulator more user friendly. When one ice core has been exhausted, the motor controlling the carriage must be actuated in reverse to move the mount along a lead screw back to reloading position, which can take upwards of three minutes. The purpose of this project is to retrofit the simulator with a quick release system that allows for the user to manually unlock the carriage and quickly pull it back into the reloading position, decreasing turn around time in the testing process. The final design is a symmetric 2-clamp system that is installed directly onto the ice core mount. The two clamps engage the lead screw from the left and the right. To reload the ice cores, the user must simply lift the Destaco clamps on each side and pull the entire carriage back to the original position at the front of the simulator
CaCu_3Ti_4O_12/CaTiO_3 Composite Dielectrics: A Ba/Pb-free Ceramics with High Dielectric Constants
We have measured dielectric properties of CaCuTiO
( = 0, 0.1, 0.5, 1, 1.5, 2, 2.9 and 3), and have found that
CaCuTiO (a composite of CaCuTiO and
CaTiO) exhibits a high dielectric constant of 1800 with a low dissipation
factor of 0.02 below 100 kHz from 220 to 300 K. These are comparable to (or
even better than) those of the Pb/Ba-based ceramics, which could be attributed
to a barrier layer of CaTiO on the surface of the CaCuTiO
grains. The composite dielectric ceramics reported here are environmentally
benign as they do not contain Ba/Pb.Comment: 4 pages, 4 figures, Appl. Phys. Lett. (scheduled on July 25, 2005
Huge Seebeck coefficients in non-aqueous electrolytes
The Seeebeck coefficients of the non-aqueous electrolytes tetrabutylammonium
nitrate, tetraoctylphosphonium bromide and tetradodecylammonium nitrate in
1-octanol, 1-dodecanol and ethylene-glycol are measured in a temperature range
from T=30 to T=45 C. The Seebeck coefficient is generally of the order of a few
hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here
we report huge values of 7 mV/K at 0.1M concentration for tetrabutylammonium
nitrate in 1-dodecanol. These striking results open the question of
unexpectedly large kosmotrope or "structure making" effects of
tetraalkylammonium ions on the structure of alcohols.Comment: Submitted to J. Chem. Phy
Methodological challenges in following up patients of a hospital child protection team: is there a recruitment bias?
BACKGROUND: The aims of this study are to describe the methodological challenges in recruiting a follow-up sample of children referred to an interdisciplinary hospital child protection team (CPT) and to compare participating versus non-participating groups on several demographic variables and maltreatment characteristics.
METHODS: Of the 319 in- and outpatients referred to the CPT at University Children's Hospital Zurich from 2005-2006 a sample of 180 children was drawn to contact for a follow-up. The children and their parents were asked to participate in a face-to-face interview at the hospital; in 42 cases the children and parents consented to do so. Alternatively, the parents could take part in a telephone interview (n = 39). Non-participation resulted because no contact or adequate communication in German, French, or English could be established (n = 49) or because the parents or children refused to participate (n = 50).
RESULTS: Participants and non-participants did not differ significantly in mean child age at follow-up, gender, family status, place of residence, certainty and type of maltreatment, and type of perpetrator. However, the child's nationality had a significant impact: Percentages of foreign nationals were higher in the fully participating group (45%; n = 19) and the non-contactable group (53%; n = 26) and significantly lower in the refusal (26%; n = 10) and the telephone interview group (18%; n = 9). Although a high percentage of families had moved in the few years since the CPT intervention (32%; n = 57), the percentage of moves was not significantly higher in non-participants compared to participants.
CONCLUSIONS: Further research is needed to support these results in different national backgrounds and to test for biases in variables not included - especially socioeconomic status. This includes gathering more detailed information on non-participants, while respecting ethical boundaries. Overall, the fact that only child's nationality was unevenly distributed between participants and non-participants is encouraging
Posttraumatic stress and behavior problems in infants and toddlers with burns
This study assessed posttraumatic stress disorder (PTSD) and behavior problems in young children with burns and examined individual, injury-related, and family-related determinants. Seventy-six children, aged 12-49 months, were assessed at an average of 15 months after their burn injury, using parents as informants on the posttraumatic stress disorder semi-structured interview and observational record for infants and young children and the child behavior checklist. Ten children (13.2%) met the alternative criteria for PTSD proposed by Scheeringa et al. Number of PTSD symptoms were associated with family-related variables (maternal PTSD, quality of family relations). Compared to community norms, children with burns showed less externalizing behavior problems, and internalizing behavior problems were within the normal range. Overall, behavioral adjustment was associated with the quality of family relations (cohesion, expressiveness, conflicts). Whereas behavior was found to be normal in young children with burns, this study provides evidence for a substantial prevalence of PTS
Interatomic potentials for the vibrational properties of III-V semiconductor nanostructures
We derive interatomic potentials for zinc blende InAs, InP, GaAs and GaP
semiconductors with possible applications in the realm of nanostructures. The
potentials include bond stretching interaction between the nearest and
next-nearest neighbors, a three body term and a long-range Coulomb interaction.
The optimized potential parameters are obtained by (i) fitting to bulk phonon
dispersions and elastic properties and (ii) constraining the parameter space to
deliver well behaved potentials for the structural relaxation and vibrational
properties of nanostructure clusters. The targets are thereby calculated by
density functional theory for clusters of up to 633 atoms. We illustrate the
new capability by the calculation Kleinman and Gr\"uneisen parameters and of
the vibrational properties of nanostructures with 3 to 5.5 nm diameter.Comment: 22 pages, 5 figures; Phys. Rev. B 201
Magnetic properties of HO2 thin films
We report on the magnetic and transport studies of hafnium oxide thin films
grown by pulsed-laser deposition on sapphire substrates under different oxygen
pressures, ranging from 10-7 to 10-1 mbar. Some physical properties of these
thin films appear to depend on the oxygen pressure during growth: the film
grown at low oxygen pressure (P ~= 10-7 mbar) has a metallic aspect and is
conducting, with a positive Hall signal, while those grown under higher oxygen
pressures (7 x 10-5 <= P <= 0.4 mbar) are insulating. However, no intrinsic
ferromagnetic signal could be attributed to the HfO2 films, irrespective of the
oxygen pressure during the deposition.Comment: 1
- âŠ