27 research outputs found
Design of a smart system for rapid bacterial test
In this article, we present our initial findings to support the design of an advanced field test to detect bacterial contamination in water samples. The system combines the use of image processing and neural networks to detect an early presence of bacterial activity. We present here a proof of concept with some tests results. Our initial findings are very promising and indicate detection of viable bacterial cells within a period of 2 h. To the authors' knowledge this is the first attempt to quantify viable bacterial cells in a water sample using cell splitting. We also present a detailed design of the complete system that uses the time lapse images from a microscope to complete the design of a neural network based smart system
A kinetic approach to studying low-frequency molecular fluctuations in a one-dimensional shock
Low-frequency molecular fluctuations in the translational nonequilibrium zone
of one-dimensional strong shock waves are characterised for the first time in a
kinetic collisional framework in the Mach number range . Our
analysis draws upon the well-known bimodal nature of the probability density
function (PDF) of gas particles in the shock, as opposed to their Maxwellian
distribution in the freestream, the latter exhibiting an order of magnitude
higher dominant frequencies than the former. Inside the (finite-thickness)
shock region, the strong correlation between perturbations in the bimodal PDF
and fluctuations in the normal stress suggests introducing a novel two-bin
model to describe the reduced-order dynamics of a large number of collision
interactions of gas particles. Our model correctly predicts the
order-of-magnitude difference in fluctuation frequencies in the shock versus
those in the freestream and is consistent with the small-amplitude fluctuations
obtained from the highly resolved Direct Simulation Monte Carlo (DSMC)
computations of the same configuration. The variation of low-frequency
fluctuations with changes in the conditions upstream of the shock revealed that
these fluctuations can be described by a Strouhal number, based on the bulk
velocity upstream of the shock and the shock-thickness based on the maximum
density-gradient inside the shock, that remains practically independent of Mach
number in the range examined. Our results are expected to have far-reaching
implications for boundary conditions employed in the vicinity of shocks in the
framework of flow instability and laminar-turbulent transition studies of flows
containing both unsteady and nominally stationary shocks.Comment: 31 pages, 14 figures, and 2 supplementary movie
Analytical prediction of low-frequency fluctuations inside a one-dimensional shock
Linear instability of high-speed boundary layers is routinely examined
assuming quiescent edge conditions, without reference to the internal structure
of shocks or to instabilities potentially generated in them. Our recent work
has shown that the kinetically modeled internal nonequilibrium zone of straight
shocks away from solid boundaries exhibits low-frequency molecular
fluctuations. The presence of the dominant low frequencies observed using the
Direct Simulation Monte Carlo (DSMC) method has been explained as a consequence
of the well-known bimodal probability density function (PDF) of the energy of
particles inside a shock. Here, PDFs of particle energies are derived in the
upstream and downstream equilibrium regions, as well as inside shocks, and it
is shown for the first time that they have the form of the non-central
chi-squared (NCCS) distributions. A linear correlation is proposed to relate
the change in the shape of the analytical PDFs as a function of Mach number,
within the range , with the DSMC-derived average characteristic
low-frequency of shocks, as computed in our earlier work. At a given Mach
number , varying the input translational temperature in the range , it is shown that the variation in DSMC-derived
low-frequencies is correlated with the change in most-probable-speed inside
shocks at the location of maximum bulk velocity gradient. Using the proposed
linear functions, average low-frequencies are estimated within the examined
ranges of Mach number and input temperature and a semi-empirical relationship
is derived to predict low-frequency oscillations in shocks. Our model can be
used to provide realistic physics-based boundary conditions in receptivity and
linear stability analysis studies of laminar-turbulent transition in high-speed
flows.Comment: 22 pages, 6 figure
Linear Instability of Shock-Dominated Laminar Hypersonic Separated Flows
The self-excited spanwise homogeneous perturbations arising in
shock-wave/boundary-layer interaction (SWBLI) system formed in a hypersonic
flow of molecular nitrogen over a double wedge are investigated using the
kinetic Direct Simulation Monte Carlo (DSMC) method. The flow has transitional
Knudsen and unit Reynolds numbers of 3.4 x 10 and 5.2 x 10 m,
respectively. Strong thermal nonequilibrium exists downstream of the Mach 7
detached (bow) shock generated due to the upper wedge surface. A linear
instability mechanism is expected to make the pre-computed 2-D base flow
potentially unstable under spanwise perturbations. The specific intent is to
assess the growth rates of unstable modes, the wavelength, location, and origin
of spanwise periodic flow structures, and the characteristic frequencies
present in this interaction.Comment: 10 pages, 6 figures. To appear in the proceedings of the IUTAM
Transition 201
Linear stability analysis of hypersonic boundary layers computed by a kinetic approach: a semi-infinite flat plate at 4.5 <= M-infinity <= 9
Linear stability analysis is performed using a combination of two-dimensional
Direct Simulation Monte Carlo (DSMC) method for the computation of the basic
state and solution of the pertinent eigenvalue problem, as applied to the
canonical boundary layer on a semi-infinite flat plate. Three different gases
are monitored, namely nitrogen, argon and air, the latter as a mixture of 79\%
Nitrogen and 21\% Oxygen at a range of free-stream Mach numbers corresponding
to flight at an altitude of 55km. A neural network has been utilised to predict
and smooth the raw DSMC data; the steady laminar profiles obtained are in very
good agreement with those computed by (self-similar) boundary layer theory,
under isothermal or adiabatic wall conditions, subject to the appropriate slip
corrections computed in the DSMC method.
The leading eigenmode results pertaining to the unsmoothed DSMC profiles are
compared against those of the classic boundary layer theory. Small
quantitative, but no significant qualitative differences between the results of
the two classes of steady base flows have been found at all parameters
examined. The frequencies of the leading eigenmodes at all conditions examined
are practically identical, while perturbations corresponding to the DSMC
profiles are found to be systematically more damped than their counterparts
arising in the boundary layer at the conditions examined, when the correct
velocity slip and temperature jump boundary conditions are imposed in the base
flow profiles; by contrast, when the classic no-slip boundary conditions are
used, less damped/more unstable profiles are obtained, which would lead the
flow to earlier transition. On the other hand, the DSMC profiles smoothed by
the neural network are marginally more stable than their unsmoothed
counterparts
Multimodal microscopy for automated histologic analysis of prostate cancer
<p>Abstract</p> <p>Background</p> <p>Prostate cancer is the single most prevalent cancer in US men whose gold standard of diagnosis is histologic assessment of biopsies. Manual assessment of stained tissue of all biopsies limits speed and accuracy in clinical practice and research of prostate cancer diagnosis. We sought to develop a fully-automated multimodal microscopy method to distinguish cancerous from non-cancerous tissue samples.</p> <p>Methods</p> <p>We recorded chemical data from an unstained tissue microarray (TMA) using Fourier transform infrared (FT-IR) spectroscopic imaging. Using pattern recognition, we identified epithelial cells without user input. We fused the cell type information with the corresponding stained images commonly used in clinical practice. Extracted morphological features, optimized by two-stage feature selection method using a minimum-redundancy-maximal-relevance (mRMR) criterion and sequential floating forward selection (SFFS), were applied to classify tissue samples as cancer or non-cancer.</p> <p>Results</p> <p>We achieved high accuracy (area under ROC curve (AUC) >0.97) in cross-validations on each of two data sets that were stained under different conditions. When the classifier was trained on one data set and tested on the other data set, an AUC value of ~0.95 was observed. In the absence of IR data, the performance of the same classification system dropped for both data sets and between data sets.</p> <p>Conclusions</p> <p>We were able to achieve very effective fusion of the information from two different images that provide very different types of data with different characteristics. The method is entirely transparent to a user and does not involve any adjustment or decision-making based on spectral data. By combining the IR and optical data, we achieved high accurate classification.</p
Non-Standard Errors
In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty: Non-standard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for better reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants
On the synchronisation of three-dimensional shock layer and laminar separation bubble instabilities in hypersonic flow over a double wedge
Linear global instability of the three-dimensional (3-D), spanwise-homogeneous laminar separation bubble (LSB) induced by shock-wave/boundary-layer interaction (SBLI) in a Mach 7 flow of nitrogen over a double wedge is studied. At these conditions corresponding to a freestream unit Reynolds number, m, the flow exhibits rarefaction effects and comparable shock-thicknesses to the size of the boundary-layer at separation. This, in turn, requires the use of the high-fidelity Direct Simulation Monte Carlo (DSMC) method to accurately resolve unsteady flow features. We show for the first time that the LSB sustains self-excited, small-amplitude, 3-D perturbations that lead to spanwise-periodic flow structures not only in and downstream of the separated region, as seen in a multitude of experiments and numerical simulations, but also in the internal structure of the separation and detached shock layers. The spanwise-periodicity length and growth rate of the structures in the two zones are found to be identical. It is shown that the linear global instability leads to low-frequency unsteadiness of the triple point formed by the intersection of separation and detached shocks, corresponding to a Strouhal number of . Linear superposition of the spanwise-homogeneous base flow and the leading 3-D flow eigenmode provides further evidence of the strong coupling between linear instability in the LSB and the shock layer