2,118 research outputs found
Optical sorting and detection of sub-micron objects in a motional standing wave
An extended interference pattern close to surface may result in both a
transmissive or evanescent surface fields for large area manipulation of
trapped particles. The affinity of differing particle sizes to a moving
standing wave light pattern allows us to hold and deliver them in a
bi-directional manner and importantly demonstrate experimentally particle
sorting in the sub-micron region. This is performed without the need of fluid
flow (static sorting). Theoretical calculations experimentally confirm that
certain sizes of colloidal particles thermally hop more easily between
neighboring traps. A new generic method is also presented for particle position
detection in an extended periodic light pattern and applied to characterization
of optical traps and particle behaviorComment: 5 pages, 6 figures, Optical Trapping pape
Pattern Matching with Variables: Fast Algorithms and New Hardness Results
A pattern (i. e., a string of variables and terminals) maps to a word, if this is obtained by uniformly replacing the variables by terminal words; deciding this is NP-complete. We present efficient
algorithmsfootnote{The computational model we use is the standard unit-cost RAM with logarithmic word size. Also, all logarithms appearing in our time complexity evaluations are in base 2.} that solve this problem for restricted classes of patterns. Furthermore, we show that it is NP-complete to decide, for a given number k and a word w, whether w can be factorised into k distinct factors; this shows that the injective version (i.e., different variables are replaced by different words) of the above matching problem is NP-complete even for very restricted cases
Probing molecular free energy landscapes by periodic loading
Single molecule pulling experiments provide information about interactions in
biomolecules that cannot be obtained by any other method. However, the
reconstruction of the molecule's free energy profile from the experimental data
is still a challenge, in particular for the unstable barrier regions. We
propose a new method for obtaining the full profile by introducing a periodic
ramp and using Jarzynski's identity for obtaining equilibrium quantities from
non-equilibrium data. Our simulated experiments show that this method delivers
significant more accurate data than previous methods, under the constraint of
equal experimental effort.Comment: 4 pages, 3 figure
Long-Life, Lightweight, Multi-Roller Traction Drives for Planetary Vehicle Surface Exploration
NASA s initiative for Lunar and Martian exploration will require long lived, robust drive systems for manned vehicles that must operate in hostile environments. The operation of these mechanical drives will pose a problem because of the existing extreme operating conditions. Some of these extreme conditions include operating at a very high or very cold temperature, operating over a wide range of temperatures, operating in very dusty environments, operating in a very high radiation environment, and operating in possibly corrosive environments. Current drive systems use gears with various configurations of teeth. These gears must be lubricated with oil (or grease) and must have some sort of a lubricant resupply system. For drive systems, oil poses problems such as evaporation, becoming too viscous and eventually freezing at cold temperatures, being too thin to lubricate at high temperatures, being degraded by the radiation environment, being contaminated by the regolith (soil), and if vaporized (and not sealed), it will contaminate the regolith. Thus, it may not be advisable or even possible to use oil because of these limitations. An oil-less, compact traction vehicle drive is a drive designed for use in hostile environments like those that will be encountered on planetary surfaces. Initially, traction roller tests in vacuum were conducted to obtain traction and endurance data needed for designing the drives. From that data, a traction drive was designed that would fit into a prototype lunar rover vehicle, and this design data was used to construct several traction drives. These drives were then tested in air to determine their performance characteristics, and if any final corrections to the designs were necessary. A limitation with current speed reducer systems such as planetary gears and harmonic drives is the high-contact stresses that occur at tooth engagement and in the harmonic drive wave generator interface. These high stresses induce high wear of solid lubricant coatings, thus necessitating the use of liquid lubricants for long life
Extraction of Airways with Probabilistic State-space Models and Bayesian Smoothing
Segmenting tree structures is common in several image processing
applications. In medical image analysis, reliable segmentations of airways,
vessels, neurons and other tree structures can enable important clinical
applications. We present a framework for tracking tree structures comprising of
elongated branches using probabilistic state-space models and Bayesian
smoothing. Unlike most existing methods that proceed with sequential tracking
of branches, we present an exploratory method, that is less sensitive to local
anomalies in the data due to acquisition noise and/or interfering structures.
The evolution of individual branches is modelled using a process model and the
observed data is incorporated into the update step of the Bayesian smoother
using a measurement model that is based on a multi-scale blob detector.
Bayesian smoothing is performed using the RTS (Rauch-Tung-Striebel) smoother,
which provides Gaussian density estimates of branch states at each tracking
step. We select likely branch seed points automatically based on the response
of the blob detection and track from all such seed points using the RTS
smoother. We use covariance of the marginal posterior density estimated for
each branch to discriminate false positive and true positive branches. The
method is evaluated on 3D chest CT scans to track airways. We show that the
presented method results in additional branches compared to a baseline method
based on region growing on probability images.Comment: 10 pages. Pre-print of the paper accepted at Workshop on Graphs in
Biomedical Image Analysis. MICCAI 2017. Quebec Cit
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