2,467 research outputs found
Development of a sub-miniature rubidium oscillator for SEEKTALK application
Warm-up and size challenges to oscillator construction are presented as well as the problems involved in these tasks. The performance of M-100 military rubidium oscillator is compared to that of a subminiture rubididum oscillator (M-1000). Methods of achieving 1.5 minute warm-up are discussed as well as improvements in performance under adverse environmental conditions, including temperature, vibration, and magnetics. An attempt is made to construct an oscillator error budget under a set of arbitrary mission conditions
Prime diagnosticity in short-term repetition priming: Is primed evidence discounted, even when it reliably indicates the correct answer?
The authors conducted 4 repetition priming experiments that manipulated prime duration and prime diagnosticity in a visual forced-choice perceptual identification task. The strength and direction of prime diagnosticity produced marked effects on identification accuracy, but those effects were resistant to subsequent changes of diagnosticity. Participants learned to associate different diagnosticities with primes of different durations but not with primes presented in different colors. Regardless of prime diagnosticity, preference for a primed alternative covaried negatively with prime duration, suggesting that even for diagnostic primes, evidence discounting remains an important factor. A computational model, with the assumption that adaptation to the statistics of the experiment modulates the level of evidence discounting, accounted for these results
Low Luminosity Companions to White Dwarfs
This paper presents results of a near-infrared imaging survey for low mass
stellar and substellar companions to white dwarfs. A wide field proper motion
survey of 261 white dwarfs was capable of directly detecting companions at
orbital separations between and 5000 AU with masses as low as 0.05
, while a deep near field search of 86 white dwarfs was capable of
directly detecting companions at separations between and 1100 AU with
masses as low as 0.02 . Additionally, all white dwarf targets were
examined for near-infrared excess emission, a technique capable of detecting
companions at arbitrarily close separations down to masses of 0.05 .
No brown dwarf candidates were detected, which implies a brown dwarf
companion fraction of % for white dwarfs. In contrast, the stellar
companion fraction of white dwarfs as measured by this survey is 22%,
uncorrected for bias. Moreover, most of the known and suspected stellar
companions to white dwarfs are low mass stars whose masses are only slightly
greater than the masses of brown dwarfs. Twenty previously unknown stellar
companions were detected, five of which are confirmed or likely white dwarfs
themselves, while fifteen are confirmed or likely low mass stars.
Similar to the distribution of cool field dwarfs as a function of spectral
type, the number of cool unevolved dwarf companions peaks at mid-M type. Based
on the present work, relative to this peak, field L dwarfs appear to be roughly
2-3 times more abundant than companion L dwarfs. Additionally, there is no
evidence that the initial companion masses have been altered by post main
sequence binary interactions.Comment: 149 pages, 59 figures, 11 tables, accepted to ApJ Supplement
Mid Infrared Observations of Van Maanen 2: No Substellar Companion
The results of a comprehensive infrared imaging search for the putative 0.06
solar mass astrometric companion to the 4.4 pc white dwarf van Mannen 2 are
reported. Adaptive optics images acquired at 3.8 microns reveal a diffraction
limited core of 0.09" and no direct evidence of a secondary. Models predict
that at 5 Gyr, a 50 jupiter mass brown dwarf would be only 1 magnitude fainter
than van Maanen 2 at this wavelength and the astrometric analysis suggested a
separation of 0.2". In the case of a chance alignment along the line of sight,
a 0.4 mag excess should be measured. An independent photometric observation at
the same wavelength reveals no excess. In addition, there exist published ISO
observations of van Maanen 2 at 6.8 and 15.0 microns which are consistent with
photospheric flux of a 6750 K white dwarf. If recent brown dwarf models are
correct, there is no substellar companion with T > 500 K.Comment: 11 pages, 3 figures, 1 table, accepted to ApJ Letter
A Dusty Disk Around WD1150-153: Explaining the Metals in White Dwarfs by Accretion from the Interstellar Medium versus Debris Disks
We report the discovery of excess K-band radiation from a metal-rich DAV
white dwarf star, WD1150-153. Our near infrared spectroscopic observations show
that the excess radiation cannot be explained by a (sub)stellar companion, and
is likely to be caused by a debris disk similar to the other DAZ white dwarfs
with circumstellar debris disks. We find that the fraction of DAZ white dwarfs
with detectable debris disks is at least 14%. We also revisit the problem of
explaining the metals in white dwarf photospheres by accretion from the
interstellar medium (ISM). We use the observed interstellar column densities
toward stars in close angular proximity and similar distance as DAZ white
dwarfs to constrain the contribution of accretion from the ISM. We find no
correlation between the accretion density required to supply metals observed in
DAZs with the densities observed in their interstellar environment, indicating
that ISM accretion alone cannot explain the presence of metals in nearby DAZ
white dwarfs. Although ISM accretion will certainly contribute, our analysis
indicates that it is not the dominant source of metals for most DAZ white
dwarfs. Instead, the growing number of circumstellar debris disks around DAZs
suggests that circumstellar material may play a more dominant role in polluting
the white dwarf atmospheres.Comment: ApJ, in pres
A Dusty Disk Around GD 362, a White Dwarf With a Uniquely High Photospheric Metal Abundance
Eighteen years after an infrared excess was discovered associated with the
white dwarf G29-38, we report ground-based measurements (JHKL'N') with
mJy-level sensitivity of GD 362 that show it to be a second single white dwarf
with an infrared excess. As a first approximation, the excess around GD 362,
which amounts to about 3% of the total stellar luminosity, can be explained by
emission from a passive, flat, opaque dust disk that lies within the Roche
radius of the white dwarf. The dust may have been produced by the tidal
disruption of a large parent body such as an asteroid. Accretion from this
circumstellar disk could account for the remarkably high abundance of metals in
the star's photosphere.Comment: 12 pages, 2 figures. ApJ Letters, in pres
Cool Customers in the Stellar Graveyard I: Limits to Extrasolar Planets Around the White Dwarf G29-38
We present high contrast images of the hydrogen white dwarf G 29-38 taken in
the near infrared with the Hubble Space Telescope and the Gemini North
Telescope as part of a high contrast imaging search for substellar objects in
orbit around nearby white dwarfs.
We review the current limits on planetary companions for G29-38, the only
nearby white dwarf with an infrared excess due to a dust disk. We add our
recent observations to these limits to produce extremely tight constraints on
the types of possible companions that could be present. No objects 6
M are detected in our data at projected separations 12 AU, and no
objects 16 M are detected for separations from 3 to 12 AU, assuming
a total system age of 1 Gyr. Limits for companions at separations 3 AU come
from a combination of 2MASS photometry and previous studies of G29-38's
pulsations. Our imaging with Gemini cannot confirm a tentative claim for the
presence of a low mass brown dwarf. These observations demonstrate that a
careful combination of several techniques can probe nearby white dwarfs for
large planets and low mass brown dwarfs.Comment: 20 pages, 4 figures, Accepted to Ap
Electrophysiological correlates of high-level perception during spatial navigation
We studied the electrophysiological basis of object recognition by recording scalp\ud
electroencephalograms while participants played a virtual-reality taxi driver game.\ud
Participants searched for passengers and stores during virtual navigation in simulated\ud
towns. We compared oscillatory brain activity in response to store views that were targets or\ud
nontargets (during store search) or neutral (during passenger search). Even though store\ud
category was solely defined by task context (rather than by sensory cues), frontal ...\ud
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Detailed Spectroscopic and Photometric Analysis of DQ White Dwarfs
We present an analysis of spectroscopic and photometric data for cool DQ
white dwarfs based on improved model atmosphere calculations. In particular, we
revise the atmospheric parameters of the trigonometric parallax sample of
Bergeron et al.(2001), and discuss the astrophysical implications on the
temperature scale and mean mass, as well as the chemical evolution of these
stars. We also analyze 40 new DQ stars discovered in the first data release of
the Sloan Digital Sky Survey.Comment: 6 pages,3 figures, 14th European Workshop on White Dwarfs, ASP
Conference Series, in pres
MEWUJUDKAN NILAI-NILAI SOLIDARITAS ANTAR WARGA MELALUI PELAKSANAAN UPACARA BANCAKAN : Studi Deskriptif Analitis tentang Community Civics di Desa Gegesik Lor Kabupaten Cirebon
Globalisasi yang mengakar telah mengubah karakter warga dalam kehidupan bermasyarakat. Hubungan antar warga yang erat dan intens menjadi terhambat karena perubahan sikap warga yang cenderung individualis. Dalam proses interaksi dan sosialisasi warga, mulai sulit menjumpai warga yang saling bersosialisasi di lingkungan rumah. Bahkan sering dijumpai fenomena dalam masyarakat dimana antar tetangga tidak saling mengenal. Sebagai akibat dari tidak saling mengenal bahkan cenderung acuh tersebut maka rentan terjadi konflik sosial. Kenyataan ini tentu saja harus dicari solusinya, salah satu solusi yang hendak dikembangkan yaitu dengan mewujudkan nilai-nilai solidaritas antar warga melalui upacara bancakan. Penelitian ini bertujuan untuk mengetahui cara mewujudkan nilai-nilai solidaritas antar warga melalui upacara bancakan sehingga dalam masyarakat lain dapat dikembangan nilai-nilai community civics. Dengan menggunakan pendekatan kualitatif dan menggunakan metode deskriptif analitis serta subjek penelitian utama warga Gegesik Lor, diharapkan penelitian ini berhasil menemukan cara mewujudkan nilai-nilai solidaritas antar warga melalui upacara bancakan. Temuan dalam penelitian ini adalah sebagai berikut: 1) Pelaksanaan upacara bancakan yang biasa dilakukan oleh masyarakat desa Gegesik Lor, Kabupaten Cirebon ternyata banyak mengandung nilai-nilai community civics. Nilai-nilai tersebut tampak dari berbagai kegiatan, antara lain: bersyukur melalui wujud kepedulian sosial, menjaga kerukunan antar warga, menjaga silaturahmi, kebersamaan, solidaritas, menghormati orang lain dan saling berbagi; 2) Mewujudkan nilai-nilai solidaritas antar warga dalam upacara bancakan dilakukan dengan cara, sebagai berikut: mengundang warga, ngobeng, rubungan, dan makan bersama; 3) Hambatan dalam mewujudkan nilai-nilai solidaritas antar warga melalui upacara bancakan sangat minim bahkan cenderung tidak ada. Hambatan hanya terjadi karena dua faktor teknis, yaitu karena warga yang diundang sudah terlebih dahulu makan dan warga yang diundang berhalangan untuk ikut bancak; 4) Kaitan nilai-nilai solidaritas antar warga pada upacara bancakan dengan community civics pada warga desa Gegesik Lor antara lain: nilai kebersamaan, nilai gotong royong, dan nilai tolong menolong
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