918 research outputs found
Automated three-axis gonioreflectometer for computer graphics applications
We describe an automated three-axis BRDF measurement instrument that can help increase the physical realism of computer graphics images by providing light scattering data for the surfaces within a synthetic scene that is to be rendered. To our knowledge, the instrument is unique in combining wide angular coverage (beyond 85 ° from the surface normal), dense sampling of the visible wavelength spectrum (1024 samples), and rapid operation (less than ten hours for complete measurement of an isotropic sample). The gonioreflectometer employs a broadband light source and a detector with a diffraction grating and linear diode array. Validation was achieved by comparisons against reference surfaces and other instruments. The accuracy and spectral and angular ranges of the BRDFs are appropriate for computer graphics imagery, while reciprocity and energy conservation are preserved. Measured BRDFs on rough aluminum, metallic silver automotive paint, and a glossy yellow paint are reported, and an example rendered automotive image is included
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"The dearest of our possessions": applying Floridi's information privacy concept in models of information behavior and information literacy
This conceptual paper argues for the value of an approach to privacy in the digital information environment informed by Luciano Floridi's philosophy of information and information ethics. This approach involves achieving informational privacy, through the features of anonymity and obscurity, through an optimal balance of ontological frictions. This approach may be used to modify models for information behavior and for information literacy, giving them a fuller and more effective coverage of privacy issues in the infosphere. For information behavior, the Information Seeking and Communication Model, and the Information Grounds conception, are most appropriate for this purpose. For information literacy, the metaliteracy model, using a modification a privacy literacy framework, is most suitable
Welding fume nanoparticles from solid and flux-cored wires: Solubility, toxicity, and role of fluorides
Welding fume particles are hazardous. Their toxicity likely depends on their composition and reactivity. This study aimed at exploring the role of sodium or other fluorides (NaF), which are intentionally added to flux-cored wire electrodes for stainless steel welding, on the solubility (in phosphate buffered saline) and toxicity of the generated welding fume particles. A multi-analytical particle characterization approach along with in-vitro cell assays was undertaken. The release of Cr(VI) and Mn from the particles was tested as a function of fluoride solution concentration. The welding fume particles containing NaF released significantly higher amounts of Cr(VI) compared with solid wire reference fumes, which was associated with increased cytotoxicity and genotoxicity in-vitro. No crystalline Na or potassium (K) containing chromates were observed. Cr(VI) was incorporated in an amorphous mixed oxide. Solution-added fluorides did not increase the solubility of Cr(VI), but contributed to a reduced Mn release from both solid and flux-cored wire fume particles and the reduction of Cr(VI) release from solid wire fume particles. Chemical speciation modeling suggested that metal fluoride complexes were not formed. The presence of NaF in the welding electrodes did not have any direct, but possibly an indirect, role in the Cr(VI) solubility of welding fumes
Adiabatic decaying vacuum model for the universe
We study a model that the entropy per particle in the universe is constant.
The sources for the entropy are the particle creation and a lambda decaying
term. We find exact solutions for the Einstein field equations and show the
compatibilty of the model with respect to the age and the acceleration of the
universe.Comment: 10 pages, 2 figure
The Palomar Testbed Interferometer Calibrator Catalog
The Palomar Testbed Interferometer (PTI) archive of observations between 1998
and 2005 is examined for objects appropriate for calibration of optical
long-baseline interferometer observations - stars that are predictably
point-like and single. Approximately 1,400 nights of data on 1,800 objects were
examined for this investigation. We compare those observations to an
intensively studied object that is a suitable calibrator, HD217014, and
statistically compare each candidate calibrator to that object by computing
both a Mahalanobis distance and a Principal Component Analysis. Our hypothesis
is that the frequency distribution of visibility data associated with
calibrator stars differs from non-calibrator stars such as binary stars.
Spectroscopic binaries resolved by PTI, objects known to be unsuitable for
calibrator use, are similarly tested to establish detection limits of this
approach. From this investigation, we find more than 350 observed stars
suitable for use as calibrators (with an additional being
rejected), corresponding to sky coverage for PTI. This approach
is noteworthy in that it rigorously establishes calibration sources through a
traceable, empirical methodology, leveraging the predictions of spectral energy
distribution modeling but also verifying it with the rich body of PTI's on-sky
observations.Comment: 100 pages, 7 figures, 7 tables; to appear in the May 2008ApJS, v176n
A GLIMPSE into the Nature of Galactic Mid-IR Excesses
We investigate the nature of the mid-IR excess for 31 intermediate-mass stars
that exhibit an 8 micron excess in either the Galactic Legacy Infrared
Mid-Plane Survey Extraordinaire or the Mid-Course Space Experiment using high
resolution optical spectra to identify stars surrounded by warm circumstellar
dust. From these data we determine projected stellar rotational velocities and
estimate stellar effective temperatures for the sample. We estimate stellar
ages from these temperatures, parallactic distances, and evolutionary models.
Using MIPS [24] measurements and stellar parameters we determine the nature of
the infrared excess for 19 GLIMPSE stars. We find that 15 stars exhibit Halpha
emission and four exhibit Halpha absorption. Assuming that the mid-IR excesses
arise in circumstellar disks, we use the Halpha fluxes to model and estimate
the relative contributions of dust and free-free emission. Six stars exhibit
Halpha fluxes that imply free-free emission can plausibly explain the infrared
excess at [24]. These stars are candidate classical Be stars. Nine stars
exhibit Halpha emission, but their Halpha fluxes are insufficient to explain
the infrared excesses at [24], suggesting the presence of a circumstellar dust
component. After the removal of the free-free component in these sources, we
determine probable disk dust temperatures of Tdisk~300-800 K and fractional
infrared luminosities of L(IR)/L(*)~10^-3. These nine stars may be
pre-main-sequence stars with transitional disks undergoing disk clearing. Three
of the four sources showing Halpha absorption exhibit circumstellar disk
temperatures ~300-400 K, L(IR)/L(*)~10^-3, IR colors K-[24]< 3.3, and are warm
debris disk candidates. One of the four Halpha absorption sources has K-[24]>
3.3 implying an optically thick outer disk and is a transition disk candidate.Comment: 17 figures. Accepted for publication in Ap
Debris Disk Evolution Around A Stars
We report 24 and/or 70 um measurements of ~160 A-type main-sequence stars
using the Multiband Imaging Photometer for Spitzer (MIPS). Their ages range
from 5 to 850 Myr based on estimates from the literature (cluster or moving
group associations) or from the H-R diagram and isochrones. The thermal
infrared excess is identified by comparing the deviation (~3% and ~15% at the
1-\sigma level at 24 and 70 um, respectively) between the measurements and the
synthetic Kurucz photospheric predictions. Stars showing excess infrared
emission due to strong emission lines or extended nebulosity seen at 24 um are
excluded from our sample; therefore, the remaining infrared excesses are likely
to arise from circumstellar debris disks. At the 3-sigma confidence level, the
excess rate at 24 and 70 um is 32% and >=33% (with an uncertainty of 5%),
considerably higher than has been found for old solar analogs and M dwarfs. Our
measurements place constraints on the fractional dust luminosities and
temperatures in the disks. We find that older stars tend to have lower
fractional dust luminosity than younger ones. While the fractional luminosity
from the excess infrared emission follows a general 1/t relationship, the
values at a given stellar age vary by at least two orders of magnitude. We also
find that (1) older stars possess a narrow range of temperature distribution
peaking at colder temperatures, and (2) the disk emission at 70 um persists
longer than that at 24 um. Both results suggest that the debris-disk clearing
process is more effective in the inner regions.Comment: 17 pages, accepted for publication in Ap
Migrant participation in Norwegian health care. A qualitative study using key informants
Background Little is known about how migrants adapt to first-world public health systems. In Norway, patients are assigned a registered general practitioner (RGP) to provide basic care and serve as gatekeeper for other medical services. Objectives: To explore determinants of migrant compliance with the RGP scheme and obstacles that migrants may experience. Methods: Individuals in leadership positions within migrant organizations for the 13 largest migrant populations in Norway in 2008 participated in this qualitative study. Semi-structured interviews, with migrants serving as key informants, were used to elucidate possible challenges migrant patients face in navigating the local primary health-care system. Conversations were structured using an interview guide covering the range of challenges that migrant patients meet in the health-care system. Results: According to informants, integration into the RGP scheme and adequacy of patient-physician communication varies according to duration of stay in Norway, the patient's country of origin, the reason for migration, health literacy, intention to establish permanent residence in Norway, language proficiency, and comprehension of information received about the health system. Informants noted as obstacles: doctor-patient interaction patterns, conflicting ideas about the role of the doctor, and language and cultural differences. In addressing noted obstacles, one strategy would be to combine direct intervention by migrant associations with indirect intervention via the public-health system
Abundances in giant stars of the globular cluster NGC 6752
Recent theoretical yields and chemical evolution models demonstrate that
intermediate-mass AGB stars cannot reproduce the observed abundance
distributions of O, Na, Mg, and Al. As a further observational test of this
finding, we present elemental abundance ratios [X/Fe] for 20 elements in 38
bright giants of the globular cluster NGC 6752. Our mean abundance ratios
[X/Fe] are in good agreement with previous studies of this cluster and are also
consistent with other globular clusters and field stars at the same
metallicity. The mean abundance ratios [Ba/Eu] and [La/Eu] exhibit values, in
agreement with field stars at the same metallicity, that lie approximately
midway between the pure r-process and the solar (s-process + r-process) mix,
indicating that AGB stars have played a role in the chemical evolution of the
proto-cluster gas.
For the first time, we find possible evidence for an abundance variation for
elements heavier than Al in this cluster. We find a correlation between [Si/Fe]
and [Al/Fe] which is consistent with the abundance anomalies being synthesized
via proton captures at high temperatures. Leakage from the Mg-Al chain into
28Si may explain the Si excess in stars with the highest [Al/Fe]. We identify
correlations between [Y/Fe] and [Al/Fe], [Zr/Fe] and [Al/Fe], and [Ba/Fe] and
[Al/Fe] suggesting that Y, Zr, and Ba abundances may increase by about 0.1 dex
as Al increases by about 1.3 dex. While the correlations are statistically
significant, the amplitudes of the variations are small. If the small
variations in Y, Zr, and Ba are indeed real, then the synthesis of the Al
anomalies must have taken place within an unknown class of stars that also ran
the s-process. [Abridged]Comment: Accepted for publication in A&
The Psychology of Privacy in the Digital Age
Privacy is a psychological topic suffering from historical neglect – a neglect that is increasingly consequential in an era of social media connectedness, mass surveillance and the permanence of our electronic footprint. Despite fundamental changes in the privacy landscape, social and personality psychology journals remains largely unrepresented in debates on the future of privacy. By contrast, in disciplines like computer science and media and communication studies, engaging directly with socio- technical developments, interest in privacy has grown considerably. In our review of this interdisciplinary literature we suggest four domains of interest to psychologists. These are: sensitivity to individual differences in privacy disposition; a claim that privacy is fundamentally based in social interactions; a claim that privacy is inherently contextual; and a suggestion that privacy is as much about psychological groups as it is about individuals. Moreover, we propose a framework to enable progression to more integrative models of the psychology of privacy in the digital age, and in particular suggest that a group and social relations based approach to privacy is needed
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