2,316 research outputs found
Astrin regulates Aurora-A localization
Alterations in the expression and activity of the centrosomal kinase, Aurora-A/STK15, affect genomic stability, disrupt the fidelity of centrosome duplication, and induce cellular transformation. A mitotic spindle-associated protein, astrin/DEEPEST, was identified as an Aurora-A interacting protein by a two-hybrid screen. Astrin and Aurora-A co-express at mitosis and co-localize to mitotic spindles. RNAi-mediated depletion of astrin abolishes the localization of Aurora-A on mitotic spindles and leads to a moderate mitotic cell cycle delay, which resembles the mitotic arrest phenotypes in siAurora-A treated cells. However, depletion of Aurora-A does not affect astrin localization, and co-depletion of both astrin and Aurora-A causes a mitotic arrest phenotype similar to depletion of siAurora-A alone. These results suggest that astrin acts upstream of Aurora-A to regulate its mitotic spindle localization
A Technique for Narrowband Time Series Photometry: the X-ray Star V2116 Oph
We have used innovative features of the Taurus Tunable Filter instrument on
the 3.9-m Anglo-Australian Telescope to obtain nearly-continuous,
high-throughput, linear photometry of V2116 Oph in a 7 Angstrom bandpass at the
center of the O I 8446 emission line. This instrumental technique shows promise
for applications requiring precise, rapid, narrowband photometry of faint
objects. The spectrum of V2116 Oph, the counterpart of GX 1+4 (=X1728-247), is
exotic, even among the unusual spectra of other optical counterparts of compact
Galactic X-ray sources. The second strongest emission line is an unusual one,
namely extremely prominent O I 8446, which is likely to result from pumping by
an intense Ly beta radiation field. As the X-radiation from GX 1+4 is steadily
pulsed, with typical pulsed fractions of 0.4, the O I 8446 emission in V2116
Oph may also be strongly modulated with the current 127 s period of the X-ray
source. If so, this may well allow us to obtain high signal-to-noise radial
velocity measurements and thus to determine the system parameters. However, no
such pulsations are detected, and we set an upper limit of ~1% (full-amplitude)
on periodic 8446 oscillations at the X-ray frequency. This value is comparable
to the amplitude of continuum oscillations observed on some nights by other
workers. Thus we rule out an enhancement of the pulsation amplitude in O I
emission, at least at the time of our observations.Comment: 9 pages including 4 figures and no tables. Accepted for publication
in PASP; to appear in Volume 110, August 199
Structural network heterogeneities and network dynamics: a possible dynamical mechanism for hippocampal memory reactivation
The hippocampus has the capacity for reactivating recently acquired memories
[1-3] and it is hypothesized that one of the functions of sleep reactivation is
the facilitation of consolidation of novel memory traces [4-11]. The dynamic
and network processes underlying such a reactivation remain, however, unknown.
We show that such a reactivation characterized by local, self-sustained
activity of a network region may be an inherent property of the recurrent
excitatory-inhibitory network with a heterogeneous structure. The entry into
the reactivation phase is mediated through a physiologically feasible
regulation of global excitability and external input sources, while the
reactivated component of the network is formed through induced network
heterogeneities during learning. We show that structural changes needed for
robust reactivation of a given network region are well within known
physiological parameters [12,13].Comment: 16 pages, 5 figure
Discovery of a Luminous Quasar in the Nearby Universe
In the course of the Pico dos Dias survey (PDS), we identified the stellar
like object PDS456 at coordinates alpha = 17h 28m 19.796s, delta = -14deg 15'
55.87'' (epoch 2000), with a relatively nearby (z = 0.184) and bright (B =
14.69) quasar. Its position at Galactic coordinates l_II = 10.4deg, b_II =
+11.2deg, near the bulge of the Galaxy, may explain why it was not detected
before. The optical spectrum of PDS456 is typical of a luminous quasar, showing
a broad (FWHM ~ 4000 km/s) H_\beta line, very intense FeII lines and a weak
[OIII]\lambda5007 line. PDS456 is associated to the infrared source IRAS
17254-1413 with a 60 \mum infrared luminosity L_{60} = 3.8 x 10^{45} erg/s. The
relatively flat slopes in the infrared (\alpha(25,60) = -0.33 and \alpha(12,25)
= -0.78) and a flat power index in the optical (F_{\nu} \propto \nu^{-0.72})
may indicate a low dust content. A good match between the position of PDS456
and the position of the X-ray source RXS J172819.3-141600 implies an X-ray
luminosity L_x = 2.8 x 10^{44} erg/s. The good correlation between the strength
of the emission lines in the optical and the X-ray luminosity, as well as the
steep optical to X-ray index estimated (\alpha_{ox} = -1.64) suggest that
PDS456 is radio quiet. A radio survey previously performed in this region
yields an upper limit for radio power at ~ 5 GHz of ~ 2.6 x 10^{30} erg/s/Hz.
We estimate the Galactic reddening in this line-of-sight to be A_B \simeq 2.0,
implying an absolute magnitude M_B = -26.7 (using H_0 = 75 km s^{-1} Mpc^{-1}
and q_0 = 0). In the optical, PDS456 is therefore 1.3 times more luminous than
3C 273 and the most luminous quasar in the nearby (z \leq 0.3) Universe.Comment: 12 pages, LaTeX (aasms4.sty) + 3 figures; accepted for publication in
the Astrophysical Journal Letter
Randomized trial of polychromatic blue-enriched light for circadian phase shifting, melatonin suppression, and alerting responses.
Wavelength comparisons have indicated that circadian phase-shifting and enhancement of subjective and EEG-correlates of alertness have a higher sensitivity to short wavelength visible light. The aim of the current study was to test whether polychromatic light enriched in the blue portion of the spectrum (17,000 K) has increased efficacy for melatonin suppression, circadian phase-shifting, and alertness as compared to an equal photon density exposure to a standard white polychromatic light (4000 K). Twenty healthy participants were studied in a time-free environment for 7 days. The protocol included two baseline days followed by a 26-h constant routine (CR1) to assess initial circadian phase. Following CR1, participants were exposed to a full-field fluorescent light (1 × 10 14 photons/cm 2 /s, 4000 K or 17,000 K, n = 10/condition) for 6.5 h during the biological night. Following an 8 h recovery sleep, a second 30-h CR was performed. Melatonin suppression was assessed from the difference during the light exposure and the corresponding clock time 24 h earlier during CR1. Phase-shifts were calculated from the clock time difference in dim light melatonin onset time (DLMO) between CR1 and CR2. Blue-enriched light caused significantly greater suppression of melatonin than standard light ((mean ± SD) 70.9 ± 19.6% and 42.8 ± 29.1%, respectively, p \u3c 0.05). There was no significant difference in the magnitude of phase delay shifts. Blue-enriched light significantly improved subjective alertness (p \u3c 0.05) but no differences were found for objective alertness. These data contribute to the optimization of the short wavelength-enriched spectra and intensities needed for circadian, neuroendocrine and neurobehavioral regulation
Discovery of optical pulsations in V2116 Ophiuchi/GX 1+4
We report the detection of pulsations with s period in V2116 Oph,
the optical counterpart of the low-mass X-ray binary GX 1+4. The pulsations are
sinusoidal with modulation amplitude of up to 4% in blue light and were
observed in ten different observing sessions during 1996 April-August using a
CCD photometer at the 1.6-m and 0.6-m telescopes of Laborat\'orio Nacional de
Astrof\'{\i}sica, in Brazil. The pulsations were also observed with the
fast photometer. With only one exception the observed optical periods are
consistent with those observed by the BATSE instrument on board the Compton
Gamma Ray Observatory at the same epoch. There is a definite correlation
between the observability of pulsations and the optical brightness of the
system: V2116~Oph had magnitude in the range when the pulsed
signal was detected, and when no pulsations were present. The
discovery makes GX 1+4 only the third of accretion-powered X-ray
pulsars to be firmly detected as a pulsating source in the optical. The
presence of flickering and pulsations in V2116 Oph adds strong evidence for an
accretion disk scenario in this system. The absolute magnitude of the pulsed
component on 1996 May 27 is estimated to be . The implied
dimensions for the emitting region are 1.1 R_{\sun}, 3.2 R_{\sun}, and 7.0
R_{\sun}, for black-body spectral distributions with K, K, and K, respectively.Comment: 9 pages, 3 figures in PostScript, latex, accepted for publication on
the Astrophysical Journal Letter
Spin Motion in Electron Transmission through Ultrathin Ferromagnetic Films Accessed by Photoelectron Spectroscopy
Ab initio and model calculations demonstrate that the spin motion of
electrons transmitted through ferromagnetic films can be analyzed in detail by
means of angle- and spin-resolved core-level photoelectron spectroscopy. The
spin motion appears as precession of the photoelectron spin polarization around
and as relaxation towards the magnetization direction. In a systematic study
for ultrathin Fe films on Pd(001) we elucidate its dependence on the Fe film
thickness and on the Fe electronic structure. In addition to elastic and
inelastic scattering, the effect of band gaps on the spin motion is addressed
in particular.Comment: 4 pages, 5 figure
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