1,593 research outputs found
A Magnetohydrodynamic Model of the M87 Jet I: Superluminal Knot Ejections from HST-1 as Trails of Quad Relativistic MHD Shocks
This is the first in a series of papers that introduces a new paradigm for
understanding the jet in M87: a collimated relativistic flow in which strong
magnetic fields play a dominant dynamical role. Here wefocus on the flow
downstream of HST-1 - an essentially stationary flaring feature that ejects
trails of superluminal components. We propose that these components are quad
relativistic magnetohydrodynamic shock fronts (forward/reverse fast and slow
modes) in a narrow jet with a helically twisted magnetic structure. And we
demonstrate the properties of such shocks with simple one-dimensional numerical
simulations. Quasi-periodic ejections of similar component trails may be
responsible for the M87 jet substructures observed further downstream on 100 -
1,000 pc scales. This new paradigm requires the assimilation of some new
concepts into the astrophysical jet community, particularly the behavior of
slow/fast-mode waves/shocks and of current-driven helical kink instabilities.
However, the prospects of these ideas applying to a large number of other jet
systems may make this worth the effort.Comment: 7 pages, 4 figures, Accepted for Publication in Ap
Dynamin-related protein 1 is required for normal mitochondrial bioenergetic and synaptic function in CA1 hippocampal neurons.
Disrupting particular mitochondrial fission and fusion proteins leads to the death of specific neuronal populations; however, the normal functions of mitochondrial fission in neurons are poorly understood, especially in vivo, which limits the understanding of mitochondrial changes in disease. Altered activity of the central mitochondrial fission protein dynamin-related protein 1 (Drp1) may contribute to the pathophysiology of several neurologic diseases. To study Drp1 in a neuronal population affected by Alzheimer's disease (AD), stroke, and seizure disorders, we postnatally deleted Drp1 from CA1 and other forebrain neurons in mice (CamKII-Cre, Drp1lox/lox (Drp1cKO)). Although most CA1 neurons survived for more than 1 year, their synaptic transmission was impaired, and Drp1cKO mice had impaired memory. In Drp1cKO cell bodies, we observed marked mitochondrial swelling but no change in the number of mitochondria in individual synaptic terminals. Using ATP FRET sensors, we found that cultured neurons lacking Drp1 (Drp1KO) could not maintain normal levels of mitochondrial-derived ATP when energy consumption was increased by neural activity. These deficits occurred specifically at the nerve terminal, but not the cell body, and were sufficient to impair synaptic vesicle cycling. Although Drp1KO increased the distance between axonal mitochondria, mitochondrial-derived ATP still decreased similarly in Drp1KO boutons with and without mitochondria. This indicates that mitochondrial-derived ATP is rapidly dispersed in Drp1KO axons, and that the deficits in axonal bioenergetics and function are not caused by regional energy gradients. Instead, loss of Drp1 compromises the intrinsic bioenergetic function of axonal mitochondria, thus revealing a mechanism by which disrupting mitochondrial dynamics can cause dysfunction of axons
The Wyoming Survey for H-alpha. III. H-alpha Luminosity Functions at z ~ 0.16, 0.24, 0.32, and 0.40
The Wyoming Survey for H-alpha, or WySH, is a large-area, ground-based
imaging survey for H-alpha-emitting galaxies at redshifts of z ~ 0.16, 0.24,
0.32, and 0.40. The survey spans up to four square degrees in a set of fields
of low Galactic cirrus emission, using twin narrowband filters at each epoch
for improved stellar continuum subtraction. H-alpha luminosity functions are
presented for each Delta(z) ~ 0.02 epoch based on a total of nearly 1200
galaxies. These data clearly show an evolution with lookback time in the
volume-averaged cosmic star formation rate. Integrals of Schechter fits to the
incompleteness- and extinction-corrected H-alpha luminosity functions indicate
star formation rates per co-moving volume of 0.010, 0.013, 0.020, 0.022 h_70
M_sun yr^{-1} Mpc^{-3} at z ~ 0.16, 0.24, 0.32, and 0.40, respectively.
Statistical and systematic measurement uncertainties combined are on the order
of 25% while the effects of cosmic variance are at the 20% level. The bulk of
this evolution is driven by changes in the characteristic luminosity L_* of the
H-alpha luminosity functions, with L_* for the earlier two epochs being a
factor of two larger than L_* at the latter two epochs; it is more difficult
with this data set to decipher systematic evolutionary differences in the
luminosity function amplitude and faint-end slope. Coupling these results with
a comprehensive compilation of results from the literature on emission line
surveys, the evolution in the cosmic star formation rate density over 0 < z <
1.5 is measured to be rho_dot_SFR(z) = rho_dot_SFR(0) (1+z)^{3.4+/-0.4}.Comment: Accepted for publication in ApJ Letter
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Implementation of an Ultraviolet Phototherapy Service at a National Referral Hospital in Western Kenya: Reflections on Challenges and Lessons Learned.
IntroductionIn order to manage skin conditions at a national referral hospital level in Kenya, specialized dermatology services, such as dermatologic surgery, dermatopathology, phototherapy, and sub-specialty care, should be offered, as is typically available in referral hospitals around the world. A Kenyan patient with prurigo nodularis, whose severe itch remitted after phototherapy treatment at the University of California, San Francisco (UCSF), inspired the development of a phototherapy service at Academic Model Providing Access to Healthcare (AMPATH), a partnership in Western Kenya between Moi Teaching and Referral Hospital, Moi University College of Health Sciences, and a consortium of North American academic medical centers.MethodsInitial project funds were raised through a crowdfunding campaign and fundraising events. A new narrowband ultraviolet B phototherapy unit and replacement bulbs were donated and air shipped to Eldoret, Kenya. A team of dermatologists and phototherapy nurses from UCSF conducted a 2-day training session. US-based dermatologists affiliated with AMPATH provide ongoing support through regular communication and on-site visits.ResultsEarly in implementation, challenges faced included training clinical staff with limited experience in phototherapy and improving communication between nurses and clinicians. More recent challenges include frequent rotation of specialty clinic nurses in the dermatology clinic, adaptation of phototherapy guidelines to balance patient volume with service delivery capacity, and training assessment of disease activity in darkly pigmented skin.ConclusionStrategies that have been helpful in addressing implementation challenges include: increasing on-site and remote training opportunities for clinicians and nurses, developing a tiered payment schema, educating patients to combat misconceptions about phototherapy, dynamic phototherapy referral guidelines to accommodate service delivery capacity, and prioritizing the engagement of a multidisciplinary team
Nebular Attenuation in H\alpha-selected Star-forming Galaxies at z=0.8 from the NewH\alpha\ Survey
We present measurements of the dust attenuation of H\alpha-selected
emission-line galaxies at z=0.8 from the NewH\alpha\ narrowband survey. The
analysis is based on deep follow-up spectroscopy with Magellan/IMACS, which
captures the strong rest-frame optical emission lines from [OII] \lambda 3727
to [OIII] \lambda 5007. The spectroscopic sample used in this analysis consists
of 341 confirmed H\alpha\ emitters. We place constraints on the AGN fraction
using diagnostics which can be applied at intermediate redshift. We find that
at least 5% of the objects in our spectroscopic sample can be classified as AGN
and 2% are composite, i.e. powered by a combination of star-formation and AGN
activity. We measure the dust attenuation for individual objects from the
ratios of the higher order Balmer lines. The H\beta\ and H\gamma\ pair of lines
is detected with S/N>5 in 55 individual objects and the H\beta\ and H\delta\
pair is detected in 50 individual objects. We also create stacked spectra to
probe the attenuation in objects without individual detections. The median
attenuation at H\alpha\ based on the objects with individually detected lines
is A(H\alpha)=0.9+-1.0 magnitudes, in good agreement with the attenuation found
in local samples of star-forming galaxies. We find that the z=0.8 galaxies
occupy a similar locus of attenuation as a function of magnitude, mass and SFR
as a comparison sample drawn from the SDSS DR4. Both the results from the
individual z=0.8 galaxies and from the stacked spectra show consistency with
the mass -- attenuation and SFR -- attenuation relations found in the local
Universe, indicating that these relations are also applicable at intermediate
redshift.Comment: Submitted to AJ. Revised per referee's comment
Global Star Formation Rate Density over 0.7<z<1.9
We determine the global star formation rate density at 0.7<z<1.9 using
emission-line selected galaxies identified in Hubble Space Telescope Near
Infrared Camera and Multi-Object Spectrograph (HST-NICMOS) grism spectroscopy
observations. Observing in pure parallel mode throughout HST Cycles 12 and 13,
our survey covers ~104 arcmin2 from which we select 80 galaxies with likely
redshifted Ha emission lines. In several cases, a somewhat weaker [OIII]
doublet emission is also detected. The Ha luminosity range of the emission-line
galaxy sample is 4.4 x 10^41 < L(Ha) < 1.5 x 10^43 erg/s. In this range, the
luminosity function is well described by a Schechter function with phi* =
(4.24\pm3.55) x 10^-3 Mpc^-3, L* = (2.88\pm1.58) x 10^42 erg/s, and alpha =
-1.39\pm0.43. We derive a volume-averaged star formation rate density of
0.138\pm0.058 Msun/yr/Mpc3 at z=1.4 without an extinction correction.
Subdividing the redshift range, we find star formation rate densities of
0.088\pm0.056 Msun/yr/Mpc3 at z=1.1 and 0.265\pm0.174 Msun/yr/Mpc3 at z=1.6.
The overall star formation rate density is consistent with previous studies
using Ha when the same average extinction correction is applied, confirming
that the cosmic peak of star formation occurs at z>1.5.Comment: Accepted for publication in Ap
Using honey to heal diabetic foot ulcers
Diabetic ulcers seem to be arrested in the inflammatory/proliferative stage of the healing process, allowing infection and inflammation to preclude healing. Antibiotic-resistant bacteria have become a major cause of infections, including diabetic foot infections. It is proposed here that the modern developments of an ancient and traditional treatment for wounds, dressing them with honey, provide the solution to the problem of getting diabetic ulcers to move on from the arrested state of healing. Honeys selected to have a high level of antibacterial activity have been shown to be very effective against antibiotic-resistant strains of bacteria in laboratory and clinical studies. The potent anti-inflammatory action of honey is also likely to play an important part in overcoming the impediment to healing that inflammation causes in diabetic ulcers, as is the antioxidant activity of honey. The action of honey in promotion of tissue regeneration through stimulation of angiogenesis and the growth of fibroblasts and epithelial cells, and its insulin-mimetic effect, would also be of benefit in stimulating the healing of diabetic ulcers. The availability of honey-impregnated dressings which conveniently hold honey in place on ulcers has provided a means of rapidly debriding ulcers and removing the bacterial burden so that good healing rates can be achieved with neuropathic ulcers. With ischemic ulcers, where healing cannot occur because of lack of tissue viability, these honey dressings keep the ulcers clean and prevent infection occurring
Mechanisms controlling anaemia in Trypanosoma congolense infected mice.
Trypanosoma congolense are extracellular protozoan parasites of the blood stream of artiodactyls and are one of the main constraints on cattle production in Africa. In cattle, anaemia is the key feature of disease and persists after parasitaemia has declined to low or undetectable levels, but treatment to clear the parasites usually resolves the anaemia. The progress of anaemia after Trypanosoma congolense infection was followed in three mouse strains. Anaemia developed rapidly in all three strains until the peak of the first wave of parasitaemia. This was followed by a second phase, characterized by slower progress to severe anaemia in C57BL/6, by slow recovery in surviving A/J and a rapid recovery in BALB/c. There was no association between parasitaemia and severity of anaemia. Furthermore, functional T lymphocytes are not required for the induction of anaemia, since suppression of T cell activity with Cyclosporin A had neither an effect on the course of infection nor on anaemia. Expression of genes involved in erythropoiesis and iron metabolism was followed in spleen, liver and kidney tissues in the three strains of mice using microarrays. There was no evidence for a response to erythropoietin, consistent with anaemia of chronic disease, which is erythropoietin insensitive. However, the expression of transcription factors and genes involved in erythropoiesis and haemolysis did correlate with the expression of the inflammatory cytokines Il6 and Ifng. The innate immune response appears to be the major contributor to the inflammation associated with anaemia since suppression of T cells with CsA had no observable effect. Several transcription factors regulating haematopoiesis, Tal1, Gata1, Zfpm1 and Klf1 were expressed at consistently lower levels in C57BL/6 mice suggesting that these mice have a lower haematopoietic capacity and therefore less ability to recover from haemolysis induced anaemia after infection
Baryonic Popcorn
In the large N limit cold dense nuclear matter must be in a lattice phase.
This applies also to holographic models of hadron physics. In a class of such
models, like the generalized Sakai-Sugimoto model, baryons take the form of
instantons of the effective flavor gauge theory that resides on probe flavor
branes. In this paper we study the phase structure of baryonic crystals by
analyzing discrete periodic configurations of such instantons. We find that
instanton configurations exhibit a series of "popcorn" transitions upon
increasing the density. Through these transitions normal (3D) lattices expand
into the transverse dimension, eventually becoming a higher dimensional (4D)
multi-layer lattice at large densities.
We consider 3D lattices of zero size instantons as well as 1D periodic chains
of finite size instantons, which serve as toy models of the full holographic
systems. In particular, for the finite-size case we determine solutions of the
corresponding ADHM equations for both a straight chain and for a 2D zigzag
configuration where instantons pop up into the holographic dimension. At low
density the system takes the form of an "abelian anti-ferromagnetic" straight
periodic chain. Above a critical density there is a second order phase
transition into a zigzag structure. An even higher density yields a rich phase
space characterized by the formation of multi-layer zigzag structures. The
finite size of the lattices in the transverse dimension is a signal of an
emerging Fermi sea of quarks. We thus propose that the popcorn transitions
indicate the onset of the "quarkyonic" phase of the cold dense nuclear matter.Comment: v3, 80 pages, 18 figures, footnotes 5 and 7 added, version to appear
in the JHE
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