1,591 research outputs found
Volumetric microvascular imaging of human retina using optical coherence tomography with a novel motion contrast technique
Phase variance-based motion contrast imaging is demonstrated using a spectral domain optical coherence tomography system for the in vivo human retina. This contrast technique spatially identifies locations of motion within the retina primarily associated with vasculature. Histogram-based noise analysis of the motion contrast images was used to reduce the motion noise created by transverse eye motion. En face summation images created from the 3D motion contrast data are presented with segmentation of selected retinal layers to provide non-invasive vascular visualization comparable to currently used invasive angiographic imaging. This motion contrast technique has demonstrated the ability to visualize resolution-limited vasculature independent of vessel orientation and flow velocity
UV and IR behaviour in QFT and LCQFT with fields as Operator Valued Distributions:Epstein and Glaser revisited
Following Epstein-Glaser's work we show how a QFT formulation based on
operator valued distributions (OPVD) with adequate test functions treats
original singularities of propagators on the diagonal in a mathematically
rigourous way.Thereby UV and/or IR divergences are avoided at any stage, only a
finite renormalization finally occurs at a point related to the arbitrary scale
present in the test functions.Some well known UV cases are examplified.The
power of the IR treatment is shown for the free massive scalar field theory
developed in the (conventionally hopeless) mass perturbation expansion.It is
argued that the approach should prove most useful for non pertubative methods
where the usual determination of counterterms is elusiveComment: 6 pages 2 columns per pag
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Visualization of human retinal micro-capillaries with phase contrast high-speed optical coherence tomography
We present high-speed Fourier-domain optical coherence tomography (Fd-OCT) with the phase variance based motion contrast method for visualizing retinal micro-circulation in vivo. This technique allows non-invasive visualization of a two-dimensional retinal perfusion map and concurrent volumetric morphology of retinal microvasculature with high sensitivity. The high-speed acquisition rate at 125kHz A-scans enables reduction of motion artifacts with increased scanning area if compared to previously reported results. Several scanning schemes with different sampling densities and scanning areas are evaluated to find optimal parameters for in vivo imaging. In order to evaluate this technique, we compare OCT micro-capillary imaging using the phase variance technique with fundus fluorescein angiography (FA). Additionally, volumetric visualization of blood flow for a normal subject is presented
Protostars and Outflows in the NGC7538 - IRS9 Cloud Core
New high resolution observations of HCO+ J=1-0, H13CN J=1-0, SO 2,2 - 1,1,
and continuum with BIMA at 3.4 mm show that the NGC7538 - IRS9 cloud core is a
site of active ongoing star formation. Our observations reveal at least three
young bipolar molecular outflows, all ~ 10,000 -- 20,000 years old. IRS9 drives
a bipolar, extreme high velocity outflow observed nearly pole on. South of IRS9
we find a cold, protostellar condensation with a size of ~ 14" x 6" with a mass
> 250 Msun. This is the center of one of the outflows and shows deep,
red-shifted self absorption in HCO+, suggesting that there is a protostar
embedded in the core, still in a phase of active accretion. This source is not
detected in the far infrared, suggesting that the luminosity < 10^4 Lsun; yet
the mass of the outflow is ~ 60 Msun. The red-shifted HCO+ self-absorption
profiles observed toward the southern protostar and IRS9 predict accretion
rates of a few times 10^-4 to 10^-3 Msun/yr. Deep VLA continuum observations at
3.6 cm show that IRS9 coincides with a faint thermal VLA source, but no other
young star in the IRS9 region has any detectable free-free emission at a level
of ~ 60 microJy at 3.6 cm. The HCO+ abundance is significantly enhanced in the
hot IRS9 outflow. A direct comparison of mass estimates from HCO+ and CO for
the well-characterized red-shifted IRS9 outflow predicts an HCO+ enhancement of
more than a factor of 30, or [HCO+/H2] >= 6 10^-8.Comment: 40 pages, 3 tables and 10 figures included; to appear in Ap
The heats of formation of the haloacetylenes XCCY [X, Y = H, F, Cl]: basis set limit ab initio results and thermochemical analysis
The heats of formation of haloacetylenes are evaluated using the recent W1
and W2 ab initio computational thermochemistry methods. These calculations
involve CCSD and CCSD(T) coupled cluster methods, basis sets of up to spdfgh
quality, extrapolations to the one-particle basis set limit, and contributions
of inner-shell correlation, scalar relativistic effects, and (where relevant)
first-order spin-orbit coupling. The heats of formation determined using W2
theory are: \hof(HCCH) = 54.48 kcal/mol, \hof(HCCF) = 25.15 kcal/mol,
\hof(FCCF) = 1.38 kcal/mol, \hof(HCCCl) = 54.83 kcal/mol, \hof(ClCCCl) = 56.21
kcal/mol, and \hof(FCCCl) = 28.47 kcal/mol. Enthalpies of hydrogenation and
destabilization energies relative to acetylene were obtained at the W1 level of
theory. So doing we find the following destabilization order for acetylenes:
FCCF ClCCF HCCF ClCCCl HCCCl HCCH. By a combination of W1
theory and isodesmic reactions, we show that the generally accepted heat of
formation of 1,2-dichloroethane should be revised to -31.80.6 kcal/mol, in
excellent agreement with a very recent critically evaluated review. The
performance of compound thermochemistry schemes such as G2, G3, G3X and CBS-QB3
theories has been analyzed.Comment: Mol. Phys., in press (E. R. Davidson issue
Optical imaging of the chorioretinal vasculature in the living human eye
Detailed visualization of microvascular changes in the human retina is clinically limited by the capabilities of angiography imaging, a 2D fundus photograph that requires an intravenous injection of fluorescent dye. Whereas current angiography methods enable visualization of some retinal capillary detail, they do not adequately reveal the choriocapillaris or other microvascular features beneath the retina. We have developed a noninvasive microvascular imaging technique called phase-variance optical coherence tomography (pvOCT), which identifies vasculature three dimensionally through analysis of data acquired with OCT systems. The pvOCT imaging method is not only capable of generating capillary perfusion maps for the retina, but it can also use the 3D capabilities to segment the data in depth to isolate vasculature in different layers of the retina and choroid. This paper demonstrates some of the capabilities of pvOCT imaging of the anterior layers of choroidal vasculature of a healthy normal eye as well as of eyes with geographic atrophy (GA) secondary to age-related macular degeneration. The pvOCT data presented permit digital segmentation to produce 2D depth-resolved images of the retinal vasculature, the choriocapillaris, and the vessels in Sattlerâs and Hallerâs layers. Comparisons are presented between en face projections of pvOCT data within the superficial choroid and clinical angiography images for regions of GA. Abnormalities and vascular dropout observed within the choriocapillaris for pvOCT are compared with regional GA progression. The capability of pvOCT imaging of the microvasculature of the choriocapillaris and the anterior choroidal vasculature has the potential to become a unique tool to evaluate therapies and understand the underlying mechanisms of age-related macular degeneration progression
The NASA/IPAC Teacher Archive Research Program (NITARP)
NITARP, the NASA/IPAC Teacher Archive Research Program, partners small groups of largely high school educators with research astronomers for a year-long research project. This paper presents a summary of how NITARP works. Because NITARP has been running since 2009, and its predecessor ran from 2005-2008, there have been many lessons learned over the last 13 years, some of which are also discussed here. The most important of these include the following. Scientists must see their work with the educators on their team as a partnership of equals. Educators must be reminded often that they will not have command of all the information needed during their NITARP year, and that it is ok to ask lots of questions. NITARP teams need to be about 5 people: a mentor astronomer, a mentor teacher (who has been through the program before), and 3 new educators; larger or smaller teams just donât work as well. Teams need to communicate regularly and frequently through their year
Earthquake Size Distribution: Power-Law with Exponent Beta = 1/2?
We propose that the widely observed and universal Gutenberg-Richter relation
is a mathematical consequence of the critical branching nature of earthquake
process in a brittle fracture environment. These arguments, though preliminary,
are confirmed by recent investigations of the seismic moment distribution in
global earthquake catalogs and by the results on the distribution in crystals
of dislocation avalanche sizes. We consider possible systematic and random
errors in determining earthquake size, especially its seismic moment. These
effects increase the estimate of the parameter beta of the power-law
distribution of earthquake sizes. In particular, we find that estimated
beta-values may be inflated by 1-3% because relative moment uncertainties
decrease with increasing earthquake size. Moreover, earthquake clustering
greatly influences the beta-parameter. If clusters (aftershock sequences) are
taken as the entity to be studied, then the exponent value for their size
distribution would decrease by 5-10%. The complexity of any earthquake source
also inflates the estimated beta-value by at least 3-7%. The centroid depth
distribution also should influence the beta-value, an approximate calculation
suggests that the exponent value may be increased by 2-6%. Taking all these
effects into account, we propose that the recently obtained beta-value of 0.63
could be reduced to about 0.52--0.56: near the universal constant value (1/2)
predicted by theoretical arguments. We also consider possible consequences of
the universal beta-value and its relevance for theoretical and practical
understanding of earthquake occurrence in various tectonic and Earth structure
environments. Using comparative crystal deformation results may help us
understand the generation of seismic tremors and slow earthquakes and
illuminate the transition from brittle fracture to plastic flow.Comment: 46 pages, 2 tables, 11 figures 53 pages, 2 tables, 12 figure
The NASA/IPAC Teacher Archive Research Program (NITARP)
NITARP, the NASA/IPAC Teacher Archive Research Program, partners small groups
of predominantly high school educators with research astronomers for a
year-long research project. This paper presents a summary of how NITARP works
and the lessons learned over the last 13 years. The program lasts a calendar
year, January to January, and involves three ~week-long trips: to the American
Astronomical Society (AAS) winter meeting, to Caltech in the summer (with
students), and back to a winter AAS meeting (with students) to present their
results. Because NITARP has been running since 2009, and its predecessor ran
from 2005-2008, there have been many lessons learned over the last 13 years
that have informed the development of the program. The most critical is that
scientists must see their work with the educators on their team as a
partnership of equals who have specialized in different professions. NITARP
teams appear to function most efficiently with approximately 5 people: a mentor
astronomer, a mentor teacher (who has been through the program before), and 3
new educators. Educators are asked to step into the role of learner and develop
their question-asking skills as they work to develop an understanding of a
subject in which they will not have command of all the information and
processes needed. Critical to the success of each team is the development of
communication skills and fluid plan of action to keep the lines of
communication open. This program has allowed more than 100 educators to present
more than 60 total science posters at the AAS.Comment: Accepted by refereed conference proceedings for RTSRE 201
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