1,428 research outputs found
Head-Tail Clouds: Drops to Probe the Diffuse Galactic Halo
A head-tail high-velocity cloud (HVC) is a neutral hydrogen halo cloud that
appears to be interacting with the diffuse halo medium as evident by its
compressed head trailed by a relatively diffuse tail. This paper presents a
sample of 116 head-tail HVCs across the southern sky (d < 2 deg) from the HI
Parkes All Sky Survey (HIPASS) HVC catalog, which has a spatial resolution of
15.5 arcmin (45 pc at 10 kpc) and a sensitivity of N_HI=2 x 10^(18) cm^(-2) (5
sigma). 35% of the HIPASS compact and semi-compact HVCs (CHVCs and :HVCs) can
be classified as head-tail clouds from their morphology. The clouds have
typical masses of 730 M_sun at 10 kpc (26,000 M_sun at 60 kpc) and the majority
can be associated with larger HVC complexes given their spatial and kinematic
proximity. This proximity, together with their similar properties to CHVCs and
:HVCs without head-tail structure, indicate the head-tail clouds have short
lifetimes, consistent with simulation predictions. Approximately half of the
head-tail clouds can be associated with the Magellanic System, with the
majority in the region of the Leading Arm with position angles pointing in the
general direction of the movement of the Magellanic System. The abundance in
the Leading Arm region is consistent with this feature being closer to the
Galactic disk than the Magellanic Stream and moving through a denser halo
medium. The head-tail clouds will feed the multi-phase halo medium rather than
the Galactic disk directly and provide additional evidence for a diffuse
Galactic halo medium extending to at least the distance of the Magellanic
Clouds.Comment: MNRAS Accepted, 10 figures, 7 in colo
Generators for the hyperelliptic Torelli group and the kernel of the Burau representation at t = -1
We prove that the hyperelliptic Torelli group is generated by Dehn twists about
separating curves that are preserved by the hyperelliptic involution. This verifies a
conjecture of Hain. The hyperelliptic Torelli group can be identified with the kernel
of the Burau representation evaluated at t = −1 and also the fundamental group of
the branch locus of the period mapping, and so we obtain analogous generating sets
for those. One application is that each component in Torelli space of the locus of
hyperelliptic curves becomes simply connected when curves of compact type are added
Picoradian deflection measurement with an interferometric quasi-autocollimator using weak value amplification
We present an "interferometric quasi-autocollimator" that employs weak value
amplification to measure angular deflections of a target mirror. The device has
been designed to be insensitive to all translations of the target. We present a
conceptual explanation of the amplification effect used by the device. An
implementation of the device demonstrates sensitivities better than 10
picoradians per root hertz between 10 and 200 hertz.Comment: To be published in Optics Letter
High-Velocity Clouds in the Nearby Spiral Galaxy M 83
We present deep HI 21-cm and optical observations of the face-on spiral
galaxy M 83 obtained as part of a project to search for high-velocity clouds
(HVCs) in nearby galaxies. Anomalous-velocity neutral gas is detected toward M
83, with 5.6x10^7 Msolar of HI contained in a disk rotating 40-50 km/s more
slowly in projection than the bulk of the gas. We interpret this as a
vertically extended thick disk of neutral material, containing 5.5% of the
total HI within the central 8 kpc. Using an automated source detection
algorithm to search for small-scale HI emission features, we find eight
distinct, anomalous-velocity HI clouds with masses ranging from 7x10^5 to
1.5x10^7 Msolar and velocities differing by up to 200 km/s compared to the HI
disk. Large on-disk structures are coincident with the optical spiral arms,
while unresolved off-disk clouds contain no diffuse optical emission down to a
limit of 27 r' mag per square arcsec. The diversity of the thick HI disk and
larger clouds suggests the influence of multiple formation mechanisms, with a
galactic fountain responsible for the slowly-rotating disk and on-disk discrete
clouds, and tidal effects responsible for off-disk cloud production. The mass
and kinetic energy of the HI clouds are consistent with the mass exchange rate
predicted by the galactic fountain model. If the HVC population in M 83 is
similar to that in our own Galaxy, then the Galactic HVCs must be distributed
within a radius of less than 25 kpc.Comment: 30 pages, 23 figures; accepted for publication in ApJ. Some figures
have been altered to reduce their siz
Westerbork HI observations of high-velocity clouds near M31 and M33
We have undertaken high-resolution follow-up of a sample of high velocity HI
clouds apparently associated with M31. Our sample was chosen from the
population of high-velocity clouds (HVCs) detected out to 50 kpc projected
radius of the Andromeda Galaxy by Thilker et al. (2004) with the Green Bank
Telescope. Nine pointings were observed with the Westerbork Synthesis Radio
Telescope to determine the physical parameters of these objects and to find
clues to their origin. One additional pointing was directed at a similar object
near M33. At 2' resolution we detect 16 individual HVCs around M31 and 1 HVC
near M33 with typical HI masses of a few times 10^5 solar masses and sizes of
the order of 1 kpc. Estimates of the dynamical and virial masses of some of the
HVCs indicate that they are likely gravitationally dominated by additional mass
components such as dark matter or ionised gas. Twelve of the clouds are
concentrated in an area of only 1 by 1 degree at a projected separation of less
than 15 kpc from the disk of M31. This HVC complex has a rather complicated
morphological and kinematical structure and partly overlaps with the giant
stellar stream of M31, suggesting a tidal origin. Another detected feature is
in close proximity, in both position and velocity, with NGC 205, perhaps also
indicative of tidal processes. Other HVCs in our survey are isolated and might
represent primordial, dark-matter dominated clouds.Comment: 18 pages, 16 figures, accepted for publication in Astronomy &
Astrophysic
Biomanufacturing through iGEM-An International Student Competition
The foundations of synthetic biology are built on molecular biology and genetic engineering. One of the purposes of synthetic biology is to make biology easier to engineer by the creation of standardized biological parts and devices. There are a wide range of potential applications for synthetic biology and a variety of approaches to constructing parts and systems. Undergraduate Science, Technology, Engineering, and Mathematics (STEM) students from around the world apply synthetic biology principles at the annual International Genetically Engineered Machine (iGEM) competition to demonstrate functioning biological systems created from standardized parts. The iGEM competition will continue to add to the growing field of synthetic biology and the global bioeconomy through innovations in projects and training of STEM students.
In this study, a survey was conducted of the iGEM team participants at the 2014 competition, specifically to investigate teams that had biomanufacturing as the foundation for their projects. Teams that participated during the 2014 iGEM competition comprised of STEM undergraduate and graduate students from different geographical regions. The primary source of information for this study was from 2014 iGEM team websites.
The results of this study found that many student-led teams are able to build on the fundamentals of synthetic biology to generate a wide range of useful bioproducts. In doing so, students are training themselves for future careers in STEM and expanding the field of synthetic biology
Intrapancreatic delivery of human umbilical cord blood aldehyde dehydrogenase-producing cells promotes islet regeneration
Aims/hypothesis We sought to investigate the stimulation of islet regeneration by transplanted human umbilical cord blood (UCB) cells purified according to high aldehyde dehydrogenase (ALDH) activity (ALDHhi), a conserved characteristic of multiple progenitor lineages. We hypothesised that direct intrapancreatic (iPan) delivery of ALDHhi progenitors would augment islet regeneration via timely and localised exposure to islet-regenerative stimuli. Methods Cells were purified from UCB based on flow cytometry for low ALDH activity (ALDHlo) vs ALDHhi. UCB ALDHlo or ALDHhi cells were compared for surface marker expression, as well as haematopoietic, endothelial and multipotent stromal progenitor content in vitro. UCB ALDHlo or ALDHhi cells were i.v. or iPan injected into streptozotocin-treated non-obese diabetic/severe combined immune-deficient mice temporally monitored for blood glucose, serum insulin and glucose tolerance. Human cell recruitment and survival in the pancreas, insulin content, islet-associated cell proliferation and islet vascularisation were documented in situ. Results UCB-derived ALDHhi cells were highly enriched for haematopoietic and endothelial progenitor frequency, and showed increased expression of progenitor and myeloid cell surface markers. Although i.v. transplantation of ALDHhi cells demonstrated low pancreas engraftment and only transient blood glucose lowering capacity, iPan injected ALDHhi cells reversed established hyperglycaemia, increased serum insulin and improved the response to a glucose challenge. iPan injected ALDHhi cells surrounded damaged islets at early time points and increased islet-associated cell proliferation, resulting in the recovery of beta cell mass. Conclusions/interpretation iPan delivery of UCB ALDHhi cells potentiated islet-associated cell proliferation, insulin production and islet revascularisation, resulting in the recovery of host islet function. Elucidation of the progenitor-specific pathways stimulated during islet regeneration may provide new approaches to promote islet expansion during diabetes. © Springer-Verlag 2012
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