459 research outputs found
Enrichment Activities and Materials for the Intermediate Grades\u27 Arithmetic Program
What are some worthwhile enrichment activities and materials for the intermediate grades\u27 arithmetic program
The evolution of M 2-9 from 2000 to 2010
M 2-9, the Butterfly nebula, is an outstanding representative of extreme
aspherical flows. It presents unique features such as a pair of high-velocity
dusty polar blobs and a mirror-symmetric rotating pattern in the inner lobes.
Imaging monitoring of the evolution of the nebula in the past decade is
presented. We determine the proper motions of the dusty blobs, which infer a
new distance estimate of 1.3+-0.2 kpc, a total nebular size of 0.8 pc, a speed
of 147 km/s, and a kinematical age of 2500 yr. The corkscrew geometry of the
inner rotating pattern is quantified. Different recombination timescales for
different ions explain the observed surface brightness distribution. According
to the images taken after 1999, the pattern rotates with a period of 92+-4 yr.
On the other hand, the analysis of images taken between 1952 and 1977 measures
a faster angular velocity. If the phenomenon were related to orbital motion,
this would correspond to a modest orbital eccentricity (e=0.10+-0.05), and a
slightly shorter period (86+-5 yr). New features have appeared after 2005 on
the west side of the lobes and at the base of the pattern. The geometry and
travelling times of the rotating pattern support our previous proposal that the
phenomenon is produced by a collimated spray of high velocity particles (jet)
from the central source, which excites the walls of the inner cavity of M 2-9,
rather than by a ionizing photon beam. The speed of such a jet would be
remarkable: between 11000 and 16000 km/s. The rotating-jet scenario may explain
the formation and excitation of most of the features observed in the inner
nebula, with no need for additional mechanisms, winds, or ionization sources.
All properties point to a symbiotic-like interacting binary as the central
source of M 2-9.Comment: Accepted for publication on Astronomy and Astrophysics (10 pages, 8
figures
HST Snapshot Survey of Post-AGB Objects
The results from a Hubble Space Telescope (HST) snapshot survey of post-AGB
objects are shown. The aim of the survey is to complement existing HST images
of PPN and to connect various types of nebulosities with physical and chemical
properties of their central stars. Nebulosities are detected in 15 of 33
sources. Images and photometric and geometric measurements are presented. For
sources with nebulosities we see a morphological bifurcation into two groups,
DUPLEX and SOLE, as previous studies have found. We find further support to the
previous results suggesting that this dichotomy is caused by a difference in
optical thickness of the dust shell. The remaining 18 sources are classified as
stellar post-AGB objects, because our observations indicate a lack of
nebulosity. We show that some stellar sources may in fact be DUPLEX or SOLE
based on their infrared colors. The cause of the differences among the groups
are investigated. We discuss some evidence suggesting that high progenitor-mass
AGB stars tend to become DUPLEX post-AGB objects. Intermediate progenitor-mass
AGB stars tend to be SOLE post-AGB objects. Most of the stellar sources
probably have low mass progenitors and do not seem to develop nebulosities
during the post-AGB phase and therefore do not become planetary nebulae.Comment: 21 pages, 11 figure
HST NICMOS Observations of the Polarization of NGC 1068
We have observed the polarized light at 2 micron in the center of NGC 1068
with HST NICMOS Camera 2. The nucleus is dominated by a bright, unresolved
source, polarized at a level of 6.0 pm 1.2% with a position angle of 122degr pm
1.5degr. There are two polarized lobes extending up to 8'' northeast and
southwest of the nucleus. The polarized flux in both lobes is quite clumpy,
with the maximum polarization occurring in the southwest lobe at a level of 17%
when smoothed to 0.23'' resolution. The perpendiculars to the polarization
vectors in these two lobes point back to the intense unresolved nuclear source
to within one 0.076'' Camera 2 pixel, thereby confirming that this is the
illuminating source of the scattered light and therefore the probable AGN
central engine. Whereas the polarization of the nucleus is probably caused by
dichroic absorption, the polarization in the lobes is almost certainly caused
by scattering, with very little contribution from dichroic absorption. Features
in the polarized lobes include a gap at a distance of about 1'' from the
nucleus toward the southwest lobe and a ``knot'' of emission about 5''
northeast of the nucleus. Both features had been discussed by ground-based
observers, but they are much better defined with the high spatial resolution of
NICMOS. The northeast knot may be the side of a molecular cloud that is facing
the nucleus, which cloud may be preventing the expansion of the northeast radio
lobe at the head of the radio synchrotron-radiation-emitting jet. We also
report the presence of two ghosts in the Camera 2 polarizers. These had not
been detected previously (Hines et al. 2000) because they are relatively faint
and require observations of a source with a large dynamic range.Comment: 17 pages, 4 figure
Self-assembled photosystem-I biophotovoltaics on nanostructured TiO2 and ZnO
The abundant pigment-protein membrane complex photosystem-I (PS-I) is at the heart of the Earth’s energy cycle. It is the central molecule in the “Z-scheme” of photosynthesis, converting sunlight into the chemical energy of life. Commandeering this intricately organized photosynthetic nanocircuitry and re-wiring it to produce electricity carries the promise of inexpensive and environmentally friendly solar power. We here report that dry PS-I stabilized by surfactant peptides functioned as both the light-harvester and charge separator in solar cells self-assembled on nanostructured semiconductors. Contrary to previous attempts at biophotovoltaics requiring elaborate surface chemistries, thin film deposition, and illumination concentrated into narrow wavelength ranges the devices described here are straightforward and inexpensive to fabricate and perform well under standard sunlight yielding open circuit photovoltage of 0.5 V, fill factor of 71%, electrical power density of 81 µW/cm2 and photocurrent density of 362 µA/cm2, over four orders of magnitude higher than any photosystem-based biophotovoltaic to date
Behavioral and neuroanatomical consequences of cell-type specific loss of dopamine D2 receptors in the mouse cerebral cortex
Developmental dysregulation of dopamine D2 receptors (D2Rs) alters neuronal migration, differentiation, and behavior and contributes to the psychopathology of neurological and psychiatric disorders. The current study is aimed at identifying how cell-specific loss of D2Rs in the cerebral cortex may impact neurobehavioral and cellular development, in order to better understand the roles of this receptor in cortical circuit formation and brain disorders. We deleted D2R from developing cortical GABAergic interneurons (Nkx2.1-Cre) or from developing telencephalic glutamatergic neurons (Emx1-Cre). Conditional knockouts (cKO) from both lines, Drd2fl/fl, Nkx2.1-Cre+ (referred to as GABA-D2R-cKO mice) or Drd2fl/fl, Emx1-Cre+ (referred to as Glu-D2R-cKO mice), exhibited no differences in simple tests of anxiety-related or depression-related behaviors, or spatial or nonspatial working memory. Both GABA-D2R-cKO and Glu-D2R-cKO mice also had normal basal locomotor activity, but GABA-D2R-cKO mice expressed blunted locomotor responses to the psychotomimetic drug MK-801. GABA-D2R-cKO mice exhibited improved motor coordination on a rotarod whereas Glu-D2R-cKO mice were normal. GABA-D2R-cKO mice also exhibited spatial learning deficits without changes in reversal learning on a Barnes maze. At the cellular level, we observed an increase in PV+ cells in the frontal cortex of GABA-D2R-cKO mice and no noticeable changes in Glu-D2R-cKO mice. These data point toward unique and distinct roles for D2Rs within excitatory and inhibitory neurons in the regulation of behavior and interneuron development, and suggest that location-biased D2R pharmacology may be clinically advantageous to achieve higher efficacy and help avoid unwanted effects.Fil: Lee, Gloria S.. Florida State University; Estados UnidosFil: Graham, Devon L.. Florida State University; Estados UnidosFil: Noble, Brenda L.. Florida State University; Estados UnidosFil: Trammell, Taylor S.. Florida State University; Estados UnidosFil: McCarthy, Deirdre M.. Florida State University; Estados UnidosFil: Anderson, Lisa R.. Florida State University; Estados UnidosFil: Rubinstein, Marcelo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Investigaciones en IngenierĂa GenĂ©tica y BiologĂa Molecular "Dr. HĂ©ctor N. Torres"; ArgentinaFil: Bhide, Pradeep G.. Florida State University; Estados UnidosFil: Stanwood, Gregg D.. Florida State University; Estados Unido
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