4,288 research outputs found
Supersonic Jet Noise Reduction by Coaxial Jets with Coplanar and Staggered Exits
Far-field noise radiated from coaxial cold underexpanded
jet flows issuing from convergent two-nozzle
configurations with coplanar and staggered-exits
is investigated experimentally. The coaxial
jets are operated in the "inverted" mode, i.e., the
outer (annular) jet flow Mach number is higher than
that of the inner (round) jet. Keeping all other
geometrical and operating conditions the same, the
exit-stagger of the inner (round) and the outer
(annular) nozzles was varied. It is shown that the
extent of the exit-stagger affects both the flows
and the radiated noise from such coaxial underexpanded
jet flows and that comparatively, the lowest
noise levels are achieved when the coaxial nozzle-exits
are coplanar. Moreover, the effectiveness
of the co-flowing inner jet flow in reducing the
noise radiated from either the annular or the coaxial
underexpanded jet flows decreases noticeably
as the exit-stagger is increased
Smoothness without Smoothing: Why Gaussian Naive Bayes is Not Naive for Multi-Subject Searchlight Studies
Spatial smoothness is helpful when averaging fMRI signals across multiple subjects, as it allows different subjects\u27 corresponding brain areas to be pooled together even if they are slightly misaligned. However, smoothing is usually not applied when performing multivoxel pattern-based analyses (MVPA), as it runs the risk of blurring away the information that fine-grained spatial patterns contain. It would therefore be desirable, if possible, to carry out pattern-based analyses which take unsmoothed data as their input but which produce smooth images as output. We show here that the Gaussian Naive Bayes (GNB) classifier does precisely this, when it is used in âsearchlightâ pattern-based analyses. We explain why this occurs, and illustrate the effect in real fMRI data. Moreover, we show that analyses using GNBs produce results at the multi-subject level which are statistically robust, neurally plausible, and which replicate across two independent data sets. By contrast, SVM classifiers applied to the same data do not generate a replication, even if the SVM-derived searchlight maps have smoothing applied to them. An additional advantage of GNB classifiers for searchlight analyses is that they are orders of magnitude faster to compute than more complex alternatives such as SVMs. Collectively, these results suggest that Gaussian Naive Bayes classifiers may be a highly non-naive choice for multi-subject pattern-based fMRI studies
Feshbach resonances in a quasi-2D atomic gas
Strongly confining an ultracold atomic gas in one direction to create a
quasi-2D system alters the scattering properties of this gas. We investigate
the effects of confinement on Feshbach scattering resonances and show that
strong confinement results in a shift in the position of the Feshbach resonance
as a function of the magnetic field. This shift, as well as the change of the
width of the resonance, are computed. We find that the resonance is strongly
damped in the thermal gas, but in the condensate the resonance remains sharp
due to many-body effects. We introduce a 2D model system, suited for the study
of resonant superfluidity, and having the same scattering properties as the
tightly confined real system near a Feshbach resonance. Exact relations are
derived between measurable quantities and the model parameters.Comment: 8 pages, 2 figure
A Fast and Accurate Diagnostic Test for Severe Sepsis Using Kernel Classifiers
Severe sepsis occurs frequently in the intensive care unit (ICU) and is a leading cause of admission, mortality, and cost. Treatment guidelines recommend early intervention, however gold standard blood culture test results may return in up to 48 hours. Insulin sensitivity (SI) is known to decrease with worsening condition and inflammatory response, and could thus be used to aid clinical treatment decisions. Some glycemic control protocols are able to accurately identify SI in real-time.
A biomarker for severe sepsis was developed from retrospective SI and concurrent temperature, heart rate, respiratory rate, blood pressure, and SIRS score from 36 adult patients with sepsis. Patients were identified as having sepsis based on a clinically validated sepsis score (ss) of 2 or higher (ss = 0â4 for increasing severity). Kernel density estimates were used for the development of joint probability density profiles for ss = 2 and ss < 2 data hours (213 and 5858 respectively of 6071 total hours) and for classification. From the receiver operator characteristic (ROC) curve, the optimal probability cutoff values for classification were determined for in-sample and out-of-sample estimates.
A biomarker including concurrent insulin sensitivity and clinical data for the diagnosis of severe sepsis (ss = 2) achieves 69â94% sensitivity, 75â94% specificity, 0.78â0.99 AUC, 3â17 LHR+, 0.06â0.4 LHR-, 9â38% PPV, 99â100% NPV, and a diagnostic odds ratio of 7â260 for optimal probability cutoff values of 0.32 and 0.27 for in-sample and out-of-sample data, respectively. The overall result lies between these minimum and maximum error bounds. Thus, the clinical biomarker shows good to high accuracy and may provide useful information as a real-time diagnostic test for severe sepsis
Micro Membrane Filters for Passive Plasma Extraction From Whole Human Blood Using Silicon Nitride-based Microfilters and Plama Collection Using Agarose Gels
AbstractThe novelty of this study resides in the fabrication of a passive, operating on capillary force, penetration-flow microfluidic device for plasma separation, based on both silicon nitride combination (SiN-SiO-SiN)-based microfilters and agarose gels, and its characterization for plasma separation from whole human blood. The fabrication processes are compatible with IC process protocols, with merits of mass productions and precise size control. The fabrication process for silicon nitride membrane was reported at Lab Chip [1], and quantification its applications to affinity-based protein separation on the silicon nitride was reported at MicroTASâ07 [2]. Our method differs from that of group Yobas [3] in the specific separation method and materials, and of group Pizziconi [4] in the geometry of the filter, and fluidic components with the structure
Practical Multiple Scattering for Rough Surfaces
Microfacet theory concisely models light transport over rough surfaces. Specular reflection is the result of single mirror reflections on each facet, while exact computation of multiple scattering is either neglected, or modeled using costly importance sampling techniques. Practical but accurate simulation of multiple scattering in microfacet theory thus remains an open challenge. In this work, we revisit the traditional V-groove cavity model and derive an analytical, cost-effective solution for multiple scattering in rough surfaces. Our kaleidoscopic model is made up of both real and virtual V-grooves, and allows us to calculate higher-order scattering in the microfacets in an analytical fashion. We then extend our model to include nonsymmetric grooves, allowing for additional degrees of freedom on the surface geometry, improving multiple reflections at grazing angles with backward compatibility to traditional normal distribution functions. We validate the accuracy of our model against ground-truth Monte Carlo simulations, and demonstrate its flexibility on anisotropic and textured materials. Our model is analytical, does not introduce significant cost and variance, can be seamless integrated in any rendering engine, preserves reciprocity and energy conservation, and is suitable for bidirectional methods
Active transonic aerofoil design optimization using robust multiobjective evolutionary algorithms
The use of adaptive wing/aerofoil designs is being considered, as they are promising techniques in aeronautic/ aerospace since they can reduce aircraft emissions and improve aerodynamic performance of manned or unmanned aircraft. This paper investigates the robust design and optimization for one type of adaptive techniques: active flow control bump at transonic flow conditions on a natural laminar flow aerofoil. The concept of using shock control bump is to control supersonic flow on the suction/pressure side of natural laminar flow aerofoil that leads to delaying shock occurrence (weakening its strength) or boundary-layer separation. Such an active flow control technique reduces total drag at transonic speeds due to reduction of wave drag. The location of boundary-layer transition can influence the position and structure of the supersonic shock on the suction/pressure side of aerofoil. The boundarylayer transition position is considered as an uncertainty design parameter in aerodynamic design due to the many factors, such as surface contamination or surface erosion. This paper studies the shock-control-bump shape design optimization using robust evolutionary algorithms with uncertainty in boundary-layer transition locations. The optimization method is based on a canonical evolution strategy and incorporates the concepts of hierarchical topology, parallel computing, and asynchronous evaluation. Two test cases are conducted: the first test assumes the boundary-layer transition position is at 45% of chord from the leading edge, and the second test considers robust design optimization for the shock control bump at the variability of boundary-layer transition positions. The numerical result shows that the optimization method coupled to uncertainty design techniques produces Pareto optimal shock-control-bump shapes, which have low sensitivity and high aerodynamic performance while having significant total drag reduction
The Anderson-Mott Transition as a Random-Field Problem
The Anderson-Mott transition of disordered interacting electrons is shown to
share many physical and technical features with classical random-field systems.
A renormalization group study of an order parameter field theory for the
Anderson-Mott transition shows that random-field terms appear at one-loop
order. They lead to an upper critical dimension for this model.
For the critical behavior is mean-field like. For an
-expansion yields exponents that coincide with those for the
random-field Ising model. Implications of these results are discussed.Comment: 8pp, REVTeX, db/94/
Comment on "Role of heavy meson exchange in near threshold N N --> d pi"
In a recent paper by C. J. Horowitz (Phys. Rev. C {\bf 48}, 2920 (1993)) a
heavy meson exchange is incorporated into threshold NN --> d pi to enhance the
grossly underestimated cross section. However, that calculation uses an
unjustified assumption on the initial and final momenta, which causes an
overestimate of this effect by a factor of 3--4. I point out that the inclusion
of the Delta(1232) isobar increases the cross section significantly even at
threshold.Comment: 7 pages, figures by fax or mail from [email protected]
A general T-matrix approach applied to two-body and three-body problems in cold atomic gases
We propose a systematic T-matrix approach to solve few-body problems with
s-wave contact interactions in ultracold atomic gases. The problem is generally
reduced to a matrix equation expanded by a set of orthogonal molecular states,
describing external center-of-mass motions of pairs of interacting particles;
while each matrix element is guaranteed to be finite by a proper
renormalization for internal relative motions. This approach is able to
incorporate various scattering problems and the calculations of related
physical quantities in a single framework, and also provides a physically
transparent way to understand the mechanism of resonance scattering. For
applications, we study two-body effective scattering in 2D-3D mixed dimensions,
where the resonance position and width are determined with high precision from
only a few number of matrix elements. We also study three fermions in a
(rotating) harmonic trap, where exotic scattering properties in terms of mass
ratios and angular momenta are uniquely identified in the framework of
T-matrix.Comment: 14 pages, 4 figure
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