89 research outputs found
Development of Spectroscopic Methods for Dynamic Cellular Level Study of Biochemical Kinetics and Disease Progression
One of the current fundamental objectives in biomedical research is understanding molecular and cellular mechanisms of disease progression. Recent work in genetics support the stochastic nature of disease progression on the single cell level. For example, recent work has demonstrated that cancer as a disease state is reached after the accumulation of damages that result in genetic errors. Other diseases like Huntingtons, Parkinsons, Alzheimers, cardiovascular disease are developed over time and their cellular mechanisms of disease transition are largely unknown. Modern techniques of disease characterization are perturbative, invasive and fully destructive to biological samples. Many methods need a probe or enhancement to take data which alters the biochemistry of the cells and may not be a true representations of cellular mechanisms. Current methods of characterizing disease progression cannot measure dynamics of a process but rely on an average state of a system at a fixed endpoint. They track cellular changes at a population level that rely on static ensemble averages that compare the same population at different time points or populations exposed to different stimuli. Ensemble averaging obscures spatiotemporal and dynamic molecular and cellular mechanism information by only measuring changes before and after disease transitions which neglects mechanistic information. This type of snap shot measurement contains no information regarding the transition into a disease state. The use of an ensemble averages ignores single cell level changes by assuming cells in a population are similar. In reality individual cell-to-cell variability in the same cell population can cause one cell to transition to disease state while another cell does not. Fluctuations are indicators of disease and if cellular processes are not studied spatiotemporally then key molecular changes are undetected. If the path to disease progression is known on an individual cell level, then treatments can be modified to alleviate or prevent disease through early detection. The aim of this thesis is to quantitatively and dynamically measure a biomedical sample on the single cell level without destroying or manipulating it significantly to characterize cellular mechanisms. The technique developed uses microRaman Spectroscopy to analyze molecular signatures of single cells and compare differences between signatures of cells in different populations
How selection and weighting of astrometric observations influence the impact probability. Asteroid (99942) Apophis case
The aim is to show that in case of low probability of asteroid collision with
Earth, the appropriate selection and weighing of the data are crucial for the
impact investigation, and to analyze the impact possibilities using extensive
numerical simulations. By means of the Monte Carlo special method a large
number of ``clone'' orbits have been generated. A full range of orbital
elements in the 6-dimensional parameter space, e.g. in the entire confidence
region allowed by the observational material has been examined. On the basis of
1000 astrometric observations of (99942) Apophis, the best solution for the
geocentric encounter distance of 6.065\pm 0.081 R_{Earth} were derived for the
close encounter with the Earth on April 13, 2029. The present uncertainties
allow for the special configurations (``keyholes'') during these encounter
which may lead to the very close encounters in the future approaches of
Apophis. Two groups of keyholes are connected with the close encounter with the
Earth in 2036 (within the minimal distance of 5.7736-5.7763 R_{Earth} on April
13, 2029) and 2037 (within the minimal distance of 6.3359-6.3488 R_{Earth}).
The nominal orbits for our most accurate models run almost exactly in the
middle between these two impact keyhole groups. A very small keyhole for the
impact in 2076 has been found between these groups at the minimal distance of
5.97347 R_{Earth} (close to the nominal orbit)
The Keplerian orbit of G2
We give an update of the observations and analysis of G2 - the gaseous red
emission-line object that is on a very eccentric orbit around the Galaxy's
central black hole and predicted to come within 2400 Rs in early 2014. During
2013, the laser guide star adaptive optics systems on the W. M. Keck I and II
telescopes were used to obtain three epochs of spectroscopy and imaging at the
highest spatial resolution currently possible in the near-IR. The updated
orbital solution derived from radial velocities in addition to Br-Gamma line
astrometry is consistent with our earlier estimates. Strikingly, even ~6 months
before pericenter passage there is no perceptible deviation from a Keplerian
orbit. We furthermore show that a proposed "tail" of G2 is likely not
associated with it but is rather an independent gas structure. We also show
that G2 does not seem to be unique, since several red emission-line objects can
be found in the central arcsecond. Taken together, it seems more likely that G2
is ultimately stellar in nature, although there is clearly gas associated with
it.Comment: Proceedings of IAU Symposium #303, "The Galactic Center: Feeding and
Feedback in a Normal Galactic Nucleus"; 2013 September 30 - October 4, Santa
Fe New Mexico (USA
Constraining the Variability and Binary Fraction of Galactic Center Young Stars
We present constraints on the variability and binarity of young stars in the
central 10 arcseconds (~0.4 pc) of the Milky Way Galactic Center (GC) using
Keck Adaptive Optics data over a 12 year baseline. Given our experiment's
photometric uncertainties, at least 36% of our sample's known early-type stars
are variable. We identified eclipsing binary systems by searching for periodic
variability. In our sample of spectroscopically confirmed and likely early-type
stars, we detected the two previously discovered GC eclipsing binary systems.
We derived the likely binary fraction of main sequence, early-type stars at the
GC via Monte Carlo simulations of eclipsing binary systems, and find that it is
at least 32% with 90% confidence.Comment: Accepted for publication in Proceedings of IAU Symposium 322: The
Multi-Messenger Astrophysics of the Galactic Centre, 2 pages, 1 figur
An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis
We present new, more precise measurements of the mass and distance of our
Galaxy's central supermassive black hole, Sgr A*. These results stem from a new
analysis that more than doubles the time baseline for astrometry of faint stars
orbiting Sgr A*, combining two decades of speckle imaging and adaptive optics
data. Specifically, we improve our analysis of the speckle images by using
information about a star's orbit from the deep adaptive optics data (2005 -
2013) to inform the search for the star in the speckle years (1995 - 2005).
When this new analysis technique is combined with the first complete
re-reduction of Keck Galactic Center speckle images using speckle holography,
we are able to track the short-period star S0-38 (K-band magnitude = 17,
orbital period = 19 years) through the speckle years. We use the kinematic
measurements from speckle holography and adaptive optics to estimate the orbits
of S0-38 and S0-2 and thereby improve our constraints of the mass ()
and distance () of Sgr A*: and kpc. The
uncertainties in and as determined by the combined orbital fit
of S0-2 and S0-38 are improved by a factor of 2 and 2.5, respectively, compared
to an orbital fit of S0-2 alone and a factor of 2.5 compared to previous
results from stellar orbits. This analysis also limits the extended dark mass
within 0.01 pc to less than at 99.7% confidence, a
factor of 3 lower compared to prior work.Comment: 56 pages, 14 figures, accepted to Ap
Keck Adaptive Optics Observations of the Protostellar Disk around Radio Source I in the Orion Kleinmann-Low Nebula
We have made the first detection of a near-infrared counterpart associated
with the disk around Radio Source "I," a massive protostar in the Kleinmann-Low
Nebula in Orion using imaging with laser guide star adaptive optics on the Keck
II telescope. The infrared emission is evident in images acquired using L' (3.8
microns) and Ms (4.7 microns) filters and is not detectable at K' (2.1
microns). The observed morphology strongly suggests that we are seeing some
combination of scattered and thermal light emanating from the disk. The disk is
also manifest in the L'/Ms flux ratio image. We interpret the near-infrared
emission as the illuminated surface of a nearly edge-on disk, oriented so that
only the northern face is visible; the opposite surface remains hidden by the
disk. We do not see infrared radiation associated directly with the star
proposed to be associated with Source "I." The data also suggest that there is
a cavity above and below the disk that is oriented perpendicular to the disk,
and is sculpted by the known, strong outflow from the inner disk of Source I.
We compare our data to models of a protostar with a surrounding disk, envelope,
and wind-blown cavity in order to elucidate the nature of the disk around Radio
Source I.Comment: 22 pages, 7 figures. Accepted for publication to Ap
Modeling instrumental field-dependent aberrations in the NIRC2 instrument on the Keck II telescope
We present a model of field-dependent aberrations arising in the NIRC2 instrument on the W. M. Keck II telescope. We use high signal-to-noise phase diversity data employing a source in the Nasmyth focal plane to construct a model of the optical path difference as a function of field position and wavelength. With a differential wavefront error of up to 190 nm, this effect is one of the main sources of astrometric and photometric measurement uncertainties. Our tests of temporal stability show sufficient reliability for our measurements over a 20-month period at the field extrema. Additionally, while chromaticity exists, applying a correction for field-dependent aberrations provides overall improvement compared to the existing aberrations present across the field of view
The Post-periapsis Evolution of Galactic Center Source G1: The Second Case of a Resolved Tidal Interaction with a Supermassive Black Hole
We present new adaptive optics (AO) imaging and spectroscopic measurements of Galactic center source G1 from W. M. Keck Observatory. Our goal is to understand its nature and relationship to G2, which is the first example of a spatially resolved object interacting with a supermassive black hole (SMBH). Both objects have been monitored with AO for the past decade (2003–2014) and are comparatively close to the black hole (ɑ_(min) ~ 200–300 au) on very eccentric orbits (ℯ_(G1) ~ 0.99; ℯ_(G2) ~ 0.96). While G2 has been tracked before and during periapsis passage (T_0 ~ 2014.2), G1 has been followed since soon after emerging from periapsis (T_0 ~ 2001.3). Our observations of G1 double the previously reported observational time baseline, which improves its orbital parameter determinations. G1's orbital trajectory appears to be in the same plane as that of G2 but with a significantly different argument of periapsis (Δω = 21° ± 4°). This suggests that G1 is an independent object and not part of a gas stream containing G2, as has been proposed. Furthermore, we show for the first time that (1) G1 is extended in the epochs closest to periapsis along the direction of orbital motion, and (2) it becomes significantly smaller over time (450 au in 2004 to less than 170 au in 2009). Based on these observations, G1 appears to be the second example of an object tidally interacting with an SMBH. G1's existence 14 yr after periapsis, along with its compactness in epochs further from the time of periapsis, suggest that this source is stellar in nature
- …