26 research outputs found
Contact Pathway Function During Human Whole Blood Clotting on Procoagulant Surfaces
Microfluidic thrombosis assays allow the control of anticoagulation, hemodynamics, pharmacology, and procoagulant surfaces containing collagen ± tissue factor (TF). With corn trypsin inhibitor (CTI) ranging from low (1â4 ÎŒg/mL) to high levels (40â60 ÎŒg/mL), the function of Factor XIIa (FXIIa) can be modulated in the presence of low or high surface TF. With high CTI and no collagen/TF in the assay, no thrombin is generated during 15-min microfluidic perfusion. At low CTI (no TF), the generation of FXIa leads to fibrin polymerization at ~300 s after the initiation of flow over collagen, an onset time shortened at zero CTI and prolonged at high CTI. The engagement of FXIa was difficult to observe for clotting on high TF surfaces due to the dominance of the extrinsic pathway. Low TF surfaces allowed observable crosstalk between extrinsic pathway generation of thrombin and thrombin-mediated activation of FXIa, a feedback detected at >5 min and attenuated with polyphosphate inhibitor. From thrombin-antithrombin immunoassay of the effluent of blood flowing over collagen/TF, the majority of thrombin was found captured on intrathrombus fibrin. Additionally, extreme shear rates (>10,000 sâ1) can generate massive von Willebrand Factor fibers that capture FXIIa and FXIa to drive fibrin generation, an event that facilitates VWF fiber dissolution under fibrinolytic conditions. Finally, we found that occlusive sterile thrombi subjected to pressure drops >70 mm-Hg/mm-clots have interstitial stresses sufficient to drive NETosis. These microfluidic studies highlight the interaction of contact pathway factors with the extrinsic pathway, platelet polyphosphate, VWF fibers, and potentially shear-induced NETs
Rosen-Zener model in cold molecule formation
The Rosen-Zener model for association of atoms in a Bose-Einstein condensate
is studied. Using a nonlinear Volterra integral equation, we obtain an analytic
formula for final probability of the transition to the molecular state for weak
interaction limit. Considering the strong coupling limit of high field
intensities, we show that the system reveals two different time-evolution
pictures depending on the detuning of the frequency of the associating field.
For both limit cases we derive highly accurate formulas for the molecular state
probability valid for the whole range of variation of time. Using these
formulas, we show that at large detuning regime the molecule formation process
occurs almost non-oscillatory in time and a Rosen-Zener pulse is not able to
associate more than one third of atoms at any time point. The system returns to
its initial all-atomic state at the end of the process and the maximal
transition probability is achieved when the field intensity reaches its peak.
In contrast, at small detuning the evolution of the system displays
large-amplitude oscillations between atomic and molecular populations. We find
that the shape of the oscillations in the first approximation is defined by the
field detuning only. Finally, a hidden singularity of the Rosen-Zener model due
to the specific time-variation of the field amplitude at the beginning of the
interaction is indicated. It is this singularity that stands for many of the
qualitative and quantitative properties of the model. The singularity may be
viewed as an effective resonance-touching
Grain growth in the inner regions of Herbig Ae/Be star disks
We present new mid-infrared spectroscopy of
the emission from warm circumstellar dust grains
in Herbig Ae/Be stars. Our survey significantly
extends the sample that was studied by Bouwman et
al. (2001). We find a correlation between the
strength of the silicate feature and its shape.
We interpret this as evidence for the removal of
small (0.1 mu m) grains from the disk surface
while large (1-2 mu m) grains persist. If the
evolution of the grain size distribution is
dominated by gravitational settling, large grains
are expected to disappear first, on a timescale
which is much shorter than the typical age of our
programme stars. Our observations thus suggest a
continuous replenishment of micron sized grains
at the disk surface. If the grain replenishment
is due to the dredge-up of dust from the disk
interior, the mineralogy we observe is
representative of the bulk composition of dust in
these stars. Based on observations obtained at
the European Southern Observatory (ESO), La
Silla, and on observations with ISO, an ESA
project with instruments funded by ESA Member
States (especially the PI countries: France,
Germany, The Netherlands and the UK) and with the
participation of ISAS and NASA
PTF10nvg: An Outbursting Class I Protostar in the Pelican/North American Nebula
During a synoptic survey of the North American Nebula region, the Palomar
Transient Factory (PTF) detected an optical outburst (dubbed PTF10nvg)
associated with the previously unstudied flat or rising spectrum infrared
source IRAS 20496+4354. The PTF R-band light curve reveals that PTF10nvg
brightened by more than 5 mag during the current outburst, rising to a peak
magnitude of R~13.5 in 2010 Sep. Follow-up observations indicate PTF10nvg has
undergone a similar ~5 mag brightening in the K band, and possesses a rich
emission-line spectrum, including numerous lines commonly assumed to trace mass
accretion and outflows. Many of these lines are blueshifted by ~175 km/s from
the North American Nebula's rest velocity, suggesting that PTF10nvg is driving
an outflow. Optical spectra of PTF10nvg show several TiO/VO bandheads fully in
emission, indicating the presence of an unusual amount of dense (> 10^10
cm^-3), warm (1500-4000 K) circumstellar material. Near-infrared spectra of
PTF10nvg appear quite similar to a spectrum of McNeil's Nebula/V1647 Ori, a
young star which has undergone several brightenings in recent decades, and
06297+1021W, a Class I protostar with a similarly rich near--infrared emission
line spectrum. While further monitoring is required to fully understand this
event, we conclude that the brightening of PTF10nvg is indicative of enhanced
accretion and outflow in this Class-I-type protostellar object, similar to the
behavior of V1647 Ori in 2004-2005.Comment: Accepted to the Astronomical Journal; 21 pages, 11 figures, 6 tables
in emulateapj format; v2 fixes typo in abstract; v3 updates status to
accepted, adjusts affiliations, adds acknowledgmen
Production of a chromium Bose-Einstein condensate
The recent achievement of Bose-Einstein condensation of chromium atoms [1]
has opened longed-for experimental access to a degenerate quantum gas with
long-range and anisotropic interaction. Due to the large magnetic moment of
chromium atoms of 6 {}B, in contrast to other Bose- Einstein condensates
(BECs), magnetic dipole-dipole interaction plays an important role in a
chromium BEC. Many new physical properties of degenerate gases arising from
these magnetic forces have been predicted in the past and can now be studied
experimentally. Besides these phenomena, the large dipole moment leads to a
breakdown of standard methods for the creation of a chromium BEC. Cooling and
trapping methods had to be adapted to the special electronic structure of
chromium to reach the regime of quantum degeneracy. Some of them apply
generally to gases with large dipolar forces. We present here a detailed
discussion of the experimental techniques which are used to create a chromium
BEC and alow us to produce pure condensates with up to {} atoms in an
optical dipole trap. We also describe the methods used to determine the
trapping parameters.Comment: 17 pages, 9 figure
The Behavior of Novae Light Curves Before Eruption
In 1975, E. R. Robinson conducted the hallmark study of the behavior of
classical nova light curves before eruption, and this work has now become part
of the standard knowledge of novae. He made three points; that 5 out of 11
novae showed pre-eruption rises in the years before eruption, that one nova
(V446 Her) showed drastic changes in the variability across eruptions, and that
all but one of the novae (excepting BT Mon) have the same quiescent magnitudes
before and after the outburst. This work has not been tested since it came out.
We have now tested these results by going back to the original archival
photographic plates and measuring large numbers of pre-eruption magnitudes for
many novae using comparison stars on a modern magnitude scale. We find in
particular that four out of five claimed pre-eruption rises are due to simple
mistakes in the old literature, that V446 Her has the same amplitude of
variations across its 1960 eruption, and that BT Mon has essentially unchanged
brightness across its 1939 eruption. Out of 22 nova eruptions, we find two
confirmed cases of significant pre-eruption rises (for V533 Her and V1500 Cyg),
while T CrB has a deep pre-eruption dip. These events are a challenge to
theorists. We find no significant cases of changes in variability across 27
nova eruptions beyond what is expected due to the usual fluctuations seen in
novae away from eruptions. For 30 classical novae plus 19 eruptions from 6
recurrent novae, we find that the average change in magnitude from before the
eruption to long after the eruption is 0.0 mag. However, we do find five novae
(V723 Cas, V1500 Cyg, V1974 Cyg, V4633 Sgr, and RW UMi) that have significantly
large changes, in that the post-eruption quiescent brightness level is over ten
times brighter than the pre-eruption level.Comment: 91 pages (preprint), AJ accepte
The QMAP and MAT/TOCO Experiments for Measuring Anisotropy in the Cosmic Microwave Background
We describe two related experiments that measured the anisotropy in the
cosmic microwave background (CMB). QMAP was a balloon-borne telescope that flew
twice in 1996, collecting data on degree angular scales with an array of six
high electron mobility transistor-based amplifiers (HEMTs). QMAP was the first
experiment to use an interlocking scan strategy to directly produce high
signal-to-noise CMB maps. The QMAP gondola was then refit for ground based work
as the MAT/TOCO experiment. Observations were made from 5200 m on Cerro Toco in
Northern Chile in 1997 and 1998 using time-domain beam synthesis. MAT/TOCO was
the first experiment to see both the rise and fall of the CMB angular spectrum,
thereby localizing the position of the first peak to l_{peak}=216 +/- 14. In
addition to describing the instruments, we discuss the data selection methods,
checks for systematic errors, and we compare the MAT/TOCO results to those from
recent experiments. We also correct the data to account for an updated
calibration and a small contribution from foreground emission. We find the
amplitude of the first peak for l between 160 and 240 to be T_{peak}=80.9 +/-
3.4 +/- 5.1 uK, where the first error is statistical and the second is from
calibration.Comment: 31 pages, 11 figures, Submitted to Ap
Collisions of Ultracold Trapped Cesium Feshbach Molecules
We study collisions in an optically trapped, pure sample of ultracold Cs
molecules in various internal states. The molecular gas is created by Feshbach
association from a near-degenerate atomic gas, with adjustable temperatures in
the nanokelvin range. We identify several narrow loss resonances, which point
to the coupling to more complex molecular states and may be interpreted as
Feshbach resonances in dimer-dimer interactions. Moreover, in some molecular
states we observe a surprising temperature dependence in collisional loss. This
shows that the situation cannot be understood in terms of the usual simple
threshold behavior for inelastic two-body collisions. We interpret this
observation as further evidence for a more complex molecular structure beyond
the well-understood dimer physics.Comment: To appear in Laser Physics, special issue in memoriam Prof. Vladilen
S. Letokho
A 10 micron spectroscopic survey of Herbig Ae star disks: grain growth and crystallization
We present spectroscopic observations of a large sample of Herbig Ae stars in
the 10 micrometer spectral region. We perform compositional fits of the spectra
based on properties of homogeneous as well as inhomogeneous spherical
particles, and derive the mineralogy and typical grain sizes of the dust
responsible for the 10 m emission. Several trends are reported that can
constrain theoretical models of dust processing in these systems: i) none of
the sources consists of fully pristine dust comparable to that found in the
interstellar medium, ii) all sources with a high fraction of crystalline
silicates are dominated by large grains, iii) the disks around more massive
stars (M >~ 2.5 M_sun, L >~ 60 L_sun) have a higher fraction of crystalline
silicates than those around lower mass stars, iv) in the subset of lower mass
stars (M <~ 2.5 M_sun) there is no correlation between stellar parameters and
the derived crystallinity of the dust. The correlation between the shape and
strength of the 10 micron silicate feature reported by van Boekel et al. (2003)
is reconfirmed with this larger sample. The evidence presented in this paper is
combined with that of other studies to present a likely scenario of dust
processing in Herbig Ae systems. We conclude that the present data favour a
scenario in which the crystalline silicates are produced in the innermost
regions of the disk, close to the star, and transported outward to the regions
where they can be detected by means of 10 micron spectroscopy. Additionally, we
conclude that the final crystallinity of these disks is reached very soon after
active accretion has stopped.Comment: 22 pages, 14 figures, accepted for publication in A&A. Note: this
submission was replaced on 26.04.2005: we used incorrect terminology in
figure 6 and the discussion of this figure. The vertical axis label of figure
6 has been corrected and now reads "Normalized 11.3/9.8 Flux Ratio", in the
discussion of this figure (section 4.2) "continuum subtracted" has been
replaced by "normalized