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A Dense Reference Network for Mass-Market Centimeter-Accurate Positioning
The quality of atmospheric corrections provided
by a dense reference network for centimeter-accurate carrierphase
differential GNSS (CDGNSS) positioning is investigated.
A dense reference network (less than 20 km inter-station distance)
offers significant benefits for mass-market users, enabling lowcost
(including single-frequency) CDGNSS positioning with rapid
integer ambiguity resolution. Precise positioning on a massmarket
platform would significantly influence the world economy,
ushering in a host of consumer-focused applications such as
globally-registered augmented and virtual reality and improved
all-weather safety and efficiency for intelligent transportation
systems, applications which have so far been hampered by the
several-meter-level errors in standard GNSS positioning. This
contribution examines CDGNSS integer ambiguity resolution
performance in terms of network correction uncertainty, and
network correction uncertainty, in turn, in terms of network
density. It considers the total error in network corrections: a
sum of ionospheric, tropospheric, and reference station multipath
components. The paper’s primary goal is to identify the network
density beyond which mass-market users would see no further
significant improvement in ambiguity resolution performance. It
finishes by describing development and deployment of a low-cost
dense reference network in Austin, Texas.Aerospace Engineering and Engineering Mechanic
Circumnuclear stellar population, morphology and environment of Seyfert 2 galaxies: an evolutionary scenario
We investigate the relation between the characteristics of the circumnuclear
stellar population and both the galaxy morphology and the presence of close
companions for a sample of 35 Seyfert 2 nuclei. Fifteen galaxies present
unambiguous signatures of recent episodes of star formation within 300
pc from the nucleus. When we relate this property with the Hubble type of the
host galaxy, we find that the incidence of recent circumnuclear star formation
increases along the Hubble sequence, and seems to be larger than in non-Seyfert
galaxies for the early Hubble types S0 and Sa, but similar to that in
non-Seyfert galaxies for later Hubble types. Both in early-type and late-type
Seyferts, the presence of recent star-formation is related to the galaxy
morphology in the inner few kiloparsecs, as observed in HST images through the
filter F606W by Malkan et al., who has assigned a late ``inner Hubble type'' to
most Seyfert 2s with recent nuclear star-formation. This new classification is
due to the presence of dust lanes and spiral structures in the inner region.
The presence of recent star formation in Seyfert 2 nuclei is also related to
interactions: among the 13 galaxies of the sample with close companions or in
mergers, 9 have recent star formation in the nucleus. These correlations
between the presence of companions, inner morphology and the incidence of
recent star formation suggest an evolutionary scenario in which the interaction
is responsible for sending gas inwards which both feeds the AGN and triggers
star-formation. The starburst then fades with time and the composite Seyfert 2
+ Starburst nucleus evolves to a ``pure'' Seyfert 2 nucleus with an old stellar
population.Comment: 12 pages, 6 figures, 2 table
Cdk1 inactivation terminates mitotic checkpoint surveillance and stabilizes kinetochore attachments in anaphase
Two mechanisms safeguard the bipolar attachment of chromosomes in mitosis. A correction mechanism destabilizes erroneous attachments that do not generate tension across sister kinetochores [1]. In response to unattached kinetochores, the mitotic checkpoint delays anaphase onset by inhibiting the anaphase-promoting complex/cyclosome (APC/CCdc20) [2]. Upon satisfaction of both pathways, the APC/CCdc20 elicits the degradation of securin and cyclin B [3]. This liberates separase triggering sister chromatid disjunction and inactivates cyclin-dependent kinase 1 (Cdk1) causing mitotic exit. How eukaryotic cells avoid the engagement of attachment monitoring mechanisms when sister chromatids split and tension is lost at anaphase is poorly understood [4]. Here we show that Cdk1 inactivation disables mitotic checkpoint surveillance at anaphase onset in human cells. Preventing cyclin B1 proteolysis at the time of sister chromatid disjunction destabilizes kinetochore-microtubule attachments and triggers the engagement of the mitotic checkpoint. As a consequence, mitotic checkpoint proteins accumulate at anaphase kinetochores, the APC/CCdc20 is inhibited, and securin reaccumulates. Conversely, acute pharmacological inhibition of Cdk1 abrogates the engagement and maintenance of the mitotic checkpoint upon microtubule depolymerization. We propose that the simultaneous destruction of securin and cyclin B elicited by the APC/CCdc20 couples chromosome segregation to the dissolution of attachment monitoring mechanisms during mitotic exit
On the Origin of Broad Fe K alpha and Hi H alpha Lines in AGN
We examine the properties of the Fe emission lines that arise near 6.4 keV in
the ASCA spectra of AGN. Our emphasis is on the Seyfert 1 galaxies where broad
and apparently complex Fe K alpha emission is observed. We consider various
origins for the line but focus on the pros and cons for line emitting accretion
disk models. We develop a simple model of an illuminated disk capable of
producing both X-ray and optical lines from a disk. The model is able to
reproduce the observed Fe K alpha FWHM ratio as well as the radii of maximum
emissivity implied by the profile redshifts. The overall profile shapes however
do not fit well the predictions of our disk illumination model nor do we derive
always consistent disk inclinations for the two lines. We conclude that the
evidence for and against an accretion disk origin for the Fe K alpha emission
is equal at best. The bulk of the data requires a very disparate set of line
fits which shed little light on a coherent physical model. We briefly consider
alternatives to disk emission models and show that a simple bicone model can
reproduce the FE line profiles equally well.Comment: 29 pages, 6 tables, 6 figures. Submitted for publication in the
Astrophysical Journal part
Persistence of Li Induced Kondo Moments in the Superconducting State of Cuprates
We measure the magnetic susceptibility nearby Li spinless impurities in the
superconducting phase of the high Tc cuprate YBaCuO. The induced moment which
was found to exist above Tc persists below Tc. In the underdoped regime, it
retains its Curie law below Tc. In contrast, near optimal doping, the large
Kondo screening observed above Tc (T_K=135 K) is strongly reduced below Tc as
expected theoretically when the superconducting gap develops. This moment still
extends essentially on its 4 near neighbour Cu, showing the persistence of AF
correlations in the superconducting state. A direct comparison with recent STM
results of Pan et al. is proposed.Comment: accepted for publication in Phys. Rev. Lett. (issue of 30 april 2001)
Revised version : 8 pages including 4 pages of text and 4 figure
An integrative identification guide to the Hydrozoa (Cnidaria) of Bocas del Toro, Panama
This work is the first attempt to assess the biodiversity of the Hydrozoa in the Archipiélago de Bocas del Toro (Panamá, Caribbean Sea) using morphology and molecular taxonomy, and to produce field identification tools to help future identification and monitoring efforts in the area. We sampled, identified, vouchered, and barcoded 112 specimens of Hydrozoa from shallow coastal waters (0–22 m depth) in the Archipiélago de Bocas del Toro. The specimens belong to 70 taxa, of which 53 were identified at the species level, and 17 were identified at the genus or family level. We produced 64 sequences of the large ribosomal subunit of the mitochondrial RNA (mt lsu-rRNA, 16S), the genetic marker generally used for barcoding Hydrozoa. We updated the local checklist that now comprises 118 species, and produced 87 detailed taxon identification tables that display species descriptions augmented with pictures, geographic distribution (worldwide and in Bocas del Toro), GenBank accession numbers for the 16S mitochondrial gene, and a synopsis of the families they belong to
Studying kinetochore kinases
Mitotic kinetochores are signaling network hubs that regulate chromosome movements, attachment error-correction, and the spindle assembly checkpoint. Key switches in these networks are kinases and phosphatases that enable rapid responses to changing conditions. Describing the mechanisms and dynamics of their localized activation and deactivation is therefore instrumental for understanding the spatiotemporal control of chromosome segregation
Intermediate and extreme mass-ratio inspirals — astrophysics, science applications and detection using LISA
Black hole binaries with extreme (gtrsim104:1) or intermediate (~102–104:1) mass ratios are among the most interesting gravitational wave sources that are expected to be detected by the proposed laser interferometer space antenna (LISA). These sources have the potential to tell us much about astrophysics, but are also of unique importance for testing aspects of the general theory of relativity in the strong field regime. Here we discuss these sources from the perspectives of astrophysics, data analysis and applications to testing general relativity, providing both a description of the current state of knowledge and an outline of some of the outstanding questions that still need to be addressed. This review grew out of discussions at a workshop in September 2006 hosted by the Albert Einstein Institute in Golm, Germany
GEMINI 3D spectroscopy of BAL+IR+Fe II QSOs: II. IRAS 04505-2958 an explosive QSO with hypershell and a new scenario for galaxy formation and galaxy end
From a study of BAL + IR + Fe II QSOs (using deep Gemini GMOS-IFU
spectroscopy) new results are presented: for IRAS 04505-2958. Specifically, we
have studied in detail the out flow (OF) process and their associated
structures, mainly at two large galactic scales: (i) two blobs/shells (S1, S2)
at radius r = 1.1 and 2.2 kpc; and (ii) an external hypergiant shell (S3) at r
= 11 kpc. In addition, the presence of two very extended hypergiant shells (S4,
S5) at r = 80 kpc is discussed. From this GMOS study the following main results
were obtained: (i) For the external hypergiant shell S3 the kinematics GMOS
maps of the ionized gas show very similar features to those observed for the
prototype of exploding external supergiant shell: in NGC 5514. (ii) The main
knots K1, K2 and K3 -of this hypergiant shell S3- show a stellar population and
emission line ratios associated with the presence of a starburst + OF/shocks.
(iii) The internal shells S1 and S2 show structures, OF components and
properties very similar to those detected in the nuclear shells of Mrk 231.
(iv) The shells S1+S2 and S3 are aligned at PA = 131: i.e. suggesting that the
OF process is in the blow-out phase with bipolar structure. In addition, the
shells S4 and S5 (at 80-100 kpc scale) are aligned at PA = 40, i.e.: a bipolar
OF perpendicular to the internal OF. Finally, the generation of UHE cosmic rays
and neutrino/ dark-matter -associated with HyNe in BAL + IR + Fe II QSOs- is
discussed.Comment: Submitted MNRAS, 81 pages, 25 Figure
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