1,226 research outputs found
Improvement of pulmonary surfactant activity by introducing D-amino acids into highly hydrophobic amphiphilic α-peptide Hel 13-5
AbstractThe high costs of artificial pulmonary surfactants, ranging in hundreds per kilogram of body weight, used for treating the respiratory distress syndrome (RDS) premature babies have limited their applications. We have extensively studied soy lecithins and higher alcohols as lipid alternatives to expensive phospholipids such as DPPC and PG. As a substitute for the proteins, we have synthesized the peptide Hel 13-5D3 by introducing D-amino acids into a highly lipid-soluble, basic amphiphilic peptide, Hel 13-5, composed of 18 amino acid residues. Analysis of the surfactant activities of lipid-amphiphilic artificial peptide mixtures using lung-irrigated rat models revealed that a mixture (Murosurf SLPD3) of dehydrogenated soy lecithin, fractionated soy lecithin, palmitic acid (PA), and peptide Hel 13-5D3 (40:40:17.5:2.5, by weight) superior pulmonary surfactant activity than a commercially available pulmonary surfactant (beractant, Surfacten®). Experiments using ovalbumin-sensitized model animals revealed that the lipid-amphiphilic artificial peptide mixtures provided significant control over an increase in the pulmonary resistance induced by premature allergy reaction and reduced the number of acidocytes and neutrophils in lung-irrigated solution. The newly developed low-cost pulmonary surfactant system may be used for treatment of a wide variety of respiratory diseases
The Animal Model of Spinal Cord Injury as an Experimental Pain Model
Pain, which remains largely unsolved, is one of the most crucial problems for spinal cord injury patients. Due to sensory problems, as well as motor dysfunctions, spinal cord injury research has proven to be complex and difficult. Furthermore, many types of pain are associated with spinal cord injury, such as neuropathic, visceral, and musculoskeletal pain. Many animal models of spinal cord injury exist to emulate clinical situations, which could help to determine common mechanisms of pathology. However, results can be easily misunderstood and falsely interpreted. Therefore, it is important to fully understand the symptoms of human spinal cord injury, as well as the various spinal cord injury models and the possible pathologies. The present paper summarizes results from animal models of spinal cord injury, as well as the most effective use of these models
Observations of a pulse driven cool polar jet by SDO/AIA
Context. We observe a solar jet at north polar coronal hole (NPCH) using SDO
AIA 304 {\deg}A image data on 3 August 2010. The jet rises obliquely above the
solar limb and then retraces its propagation path to fall back. Aims. We
numerically model this observed solar jet by implementing a realistic (VAL-C)
model of solar temperature. Methods. We solve two-dimensional ideal
magnetohydrodynamic equations numerically to simulate the observed solar jet.
We consider a localized velocity pulse that is essentially parallel to the
background magnetic field lines and initially launched at the top of the solar
photosphere. The pulse steepens into a shock at higher altitudes, which
triggers plasma perturbations that exhibit the observed features of the jet.
The typical direction of the pulse also clearly exhibits the leading front of
the moving jet. Results. Our numerical simulations reveal that a large
amplitude initial velocity pulse launched at the top of the solar photosphere
produces in general the observed properties of the jet, e.g., upward and
backward average velocities, height, width, life-time, and ballistic nature.
Conclusions. The close matching between the jet observations and numerical
simulations provides first strong evidence for the formation of this jet by a
single velocity pulse. The strong velocity pulse is most likely generated by
the low- atmospheric reconnection in the polar region which results in
triggering of the jet. The downflowing material of the jet most likely vanishes
in the next upcoming velocity pulses from lower solar atmosphere, and therefore
distinctly launched a single jet upward in the solar atmosphere is observed.Comment: 8 pages, 4 figures, A&
Modeling UV and X-Ray Emission in a Post-CME Current Sheet
A post-CME current sheet (CS) is a common feature developed behind an
erupting flux rope in CME models. Observationally, white light observations
have recorded many occurrences of a thin ray appearing behind a CME eruption
that closely resembles a post-CME CS in its spatial correspondence and
morphology. UV and X-ray observations further strengthen this interpretation by
the observations of high temperature emission at locations consistent with
model predictions. The next question then becomes whether the properties inside
a post-CME CS predicted by a model agree with observed properties. In this
work, we assume that the post-CME CS is a consequence of Petschek-like
reconnection and that the observed ray-like structure is bounded by a pair of
slow mode shocks developed from the reconnection site. We perform
time-dependent ionization calculations and model the UV line emission. We find
that such a model is consistent with SOHO/UVCS observations of the post-CME CS.
The change of Fe XVIII emission in one event implies an inflow speed of ~10
km/s and a corresponding reconnection rate of M_A ~ 0.01. We calculate the
expected X-ray emission for comparison with X-ray observations by Hinode/XRT,
as well as the ionic charge states as would be measured in-situ at 1 AU. We
find that the predicted count rate for Hinode/XRT agree with what was observed
in a post-CME CS on April 9, 2008, and the predicted ionic charge states are
consistent with high ionization states commonly measured in the interplanetary
CMEs. The model results depend strongly on the physical parameters in the
ambient corona, namely the coronal magnetic field, the electron density and
temperature during the CME event. It is crucial to obtain these ambient coronal
parameters and as many facets of the CS properties as possible by observational
means so that the post-CME current sheet models can be scrutinized more
effectively
Nonlinear Parker Instability with the Effect of Cosmic-Ray Diffusion
We present the results of linear analysis and two-dimensional local
magnetohydrodynamic (MHD) simulations of the Parker instability, including the
effects of cosmic rays (CRs), in magnetized gas disks (galactic disks). As an
unperturbed state for both the linear analysis and the MHD simulations, we
adopted an equilibrium model of a magnetized two-temperature layered disk with
constant gravitational acceleration parallel to the normal of the disk. The
disk comprises a thermal gas, cosmic rays and a magnetic field perpendicular to
the gravitational accelerartion. Cosmic ray diffusion along the magnetic field
is considered; cross field-line diffusion is supposed to be small and is
ignored. We investigated two cases in our simulations. In the mechanical
perturbation case we add a velocity perturbation parallel to the magnetic field
lines, while in the explosional perturbation case we add cosmic ray energy into
a sphere where the cosmic rays are injected. Linear analysis shows that the
growth rate of the Parker instability becomes smaller if the coupling between
the CR and the gas is stronger (i.e., the CR diffusion coefficient is smaller).
Our MHD simulations of the mechanical perturbation confirm this result. We show
that the falling matter is impeded by the CR pressure gradient, this causes a
decrease in the growth rate. In the explosional perturbation case, the growth
of the magnetic loop is faster when the coupling is stronger in the early
stage. However, in the later stage the behavior of the growth rate becomes
similar to the mechanical perturbation case.Comment: 18 pages, 11 figures, accepted in Ap
Coronal hole boundaries at small scales: III. EIS and SUMER views
We report on the plasma properties of small-scale transient events identified
in the quiet Sun, coronal holes and their boundaries.
We use spectroscopic co-observations from SUMER/SoHO and EIS/Hinode combined
with high cadence imaging data from XRT/Hinode. We measure Doppler shifts using
single and multiple Gauss fits of transition region and coronal lines as well
as electron densities and temperatures. We combine co-temporal imaging and
spectroscopy to separate brightening expansions from plasma flows. The
transient brightening events in coronal holes and their boundaries were found
to be very dynamical producing high density outflows at large speeds. Most of
these events represent X-ray jets from pre-existing or newly emerging coronal
bright points at X-ray temperatures. The average electron density of the jets
is logNe ~ 8.76 cm^-3 while in the flaring site it is logNe ~ 9.51 cm^-3. The
jet temperatures reach a maximum of 2.5 MK but in the majority of the cases the
temperatures do not exceed 1.6 MK. The footpoints of jets have temperatures of
a maximum of 2.5 MK though in a single event scanned a minute after the flaring
the measured temperature was 12 MK. The jets are produced by multiple
microflaring in the transition region and corona. Chromospheric emission was
only detected in their footpoints and was only associated with downflows. The
Doppler shift measurements in the quiet Sun transient brightenings confirmed
that these events do not produce jet-like phenomena. The plasma flows in these
phenomena remain trapped in closed loops.Comment: 16 pages, accepted for publication in A&
Particle kinetic analysis of a polar jet from SECCHI COR data
Aims. We analyze coronagraph observations of a polar jet observed by the Sun
Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument
suite onboard the Solar TErrestrial RElations Observatory (STEREO) spacecraft.
Methods. In our analysis we compare the brightness distribution of the jet in
white-light coronagraph images with a dedicated kinetic particle model. We
obtain a consistent estimate of the time that the jet was launched from the
solar surface and an approximate initial velocity distribution in the jet
source. The method also allows us to check the consistency of the kinetic
model. In this first application, we consider only gravity as the dominant
force on the jet particles along the magnetic field. Results. We find that the
kinetic model explains the observed brightness evolution well. The derived
initiation time is consistent with the jet observations by the EUVI telescope
at various wavelengths. The initial particle velocity distribution is fitted by
Maxwellian distributions and we find deviations of the high energy tail from
the Maxwellian distributions. We estimate the jet's total electron content to
have a mass between 3.2 \times 1014 and 1.8 \times 1015 g. Mapping the
integrated particle number along the jet trajectory to its source region and
assuming a typical source region size, we obtain an initial electron density
between 8 \times 109 and 5 \times 1010 cm-3 that is characteristic for the
lower corona or the upper chromosphere. The total kinetic energy of all
particles in the jet source region amounts from 2.1 \times 1028 to 2.4 \times
1029 erg.Comment: A&A, in pres
Establishment of embryonic stem cells secreting human factor VIII for cell-based treatment of hemophilia A
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72012/1/j.1538-7836.2008.03022.x.pd
Diffusion of transcription factors can drastically enhance the noise in gene expression
We study by simulation the effect of the diffusive motion of repressor
molecules on the noise in mRNA and protein levels in the case of a repressed
gene. We find that spatial fluctuations due to diffusion can drastically
enhance the noise in gene expression. For a fixed repressor strength, the noise
due to diffusion can be minimized by increasing the number of repressors or by
decreasing the rate of the open complex formation. We also show that the effect
of spatial fluctuations can be well described by a two-step kinetic scheme,
where formation of an encounter complex by diffusion and the subsequent
association reaction are treated separately. Our results also emphasize that
power spectra are a highly useful tool for studying the propagation of noise
through the different stages of gene expression.Comment: 15 pages, 6 figures, REVTeX
- …