Minimum Volume Criterion Research Articles

Detecting Changes by Learning No Changes: Data-Enclosing-Ball Minimizing Autoencoders for One-Class Change Detection in Multispectral Imagery

Change detection is a long-standing and challenging problem in remote sensing. Very often, features about changes are difficult to model beforehand, thus making the collection of changed samples a challenging task. In comparison, it is much easier to collect numerous no-change samples. It is possible to define a change detection approach by using only easily available annotated no-change samples, which we henceforth call one-class change detection. Autoencoder networks being trained on no-change data are natural candidates for addressing this task due to their superior performance as compared to other one-class classification models. However, the autoencoders usually suffer from the problem of overgeneralization, i.e., they tend to generalize too well, thus risking properly reconstructing changed samples. In this paper, we propose a novel data-enclosing-ball minimizing autoencoder (DebM-AE) that is trained with dual objectives—a reconstruction error criterion and a minimum volume criterion. The network learns a compact latent space, where encodings of no-change samples have low intra-class variance, which as counter part has the identification of changed instances. We conducted extensive experiments on three real-world data sets. Results demonstrate advantages of the proposed method over other competitors. We make our data and code publicly available¹.

Smallest Ellipsoid Containing $p$-Sum of Ellipsoids With Application to Reachability Analysis

In this article the problem of ellipsoidal bounding of convex set-valued data, where the convex set is obtained by the p-sum of finitely many ellipsoids, for any real p ≥ 1 is studied. The notion of p-sum appears in the Brunn-Minkowski-Firey theory in convex analysis, and generalizes several well-known set-valued operations, such as the Minkowski sum of the summand convex sets (here, ellipsoids). We derive an outer ellipsoidal parameterization for the p-sum of a given set of ellipsoids, and compute the tightest such parameterization for two optimality criteria: minimum trace and minimum volume. For such optimal parameterizations, several known results in the system-control literature are recovered as special cases of our general formula. For the minimum volume criterion, our analysis leads to a fixed point recursion over a scalar that parameterizes the shape matrix of the outer ellipsoid. This recursion is proved to be contractive, and found to converge fast in practice. We apply these results to compute the forward reach sets for a linear control system subject to different convex set-valued uncertainty models for the initial condition and control, generated by varying p ∈ [1,∞]. Our numerical results show that the proposed fixed point algorithm offers more than two orders of magnitude speed-up in computational time for p=1, compared to the existing semidefinite programming approach without significant effect on the numerical accuracy. For p > 1, the reach set computation results reported here are novel. Our results are expected to be useful in real-time safety critical applications, such as decision making, for collision avoidance of autonomous vehicles, where the computational time scale for reach set calculation needs to be much smaller than the vehicular dynamics time scale.

Abstract TMP83: Association Between Hospital Procedural Volumes and Clinical Outcomes For Patients With Non-Traumatic Subarachnoid Hemorrhage

Introduction: Previous studies of patients with non-traumatic subarachnoid hemorrhage (SAH) suggest better outcomes at hospitals with higher case and procedural volumes, but the shape of the volume-outcome curve has not been defined. We sought to establish minimum volume criteria for SAH and aneurysm obliteration procedures that could be used for comprehensive stroke centers (CSC) certification. Methods: The 8,512 SAH discharges in the National Inpatient Sample (NIS) from 2010-11 were analyzed. Logistic regression models were used to evaluate the association between clinical outcomes (in-hospital mortality and the NIS-SAH Outcome Measure (NIS-SOM)) and 3 measures of hospital annual case volume (ACV) (nontraumatic SAH discharges, coiling, and clipping procedures). Sensitivity and specificity analyses for the association of desirable clinical outcomes with different volume thresholds were performed. Results: 28.7% of cases underwent clipping and 20.1% underwent coiling with rates of 21.2%for in-hospital mortality and 38.6% for poor outcome on the NIS-SOM. The mean (range) of SAH ACV, coiling ACV, and clipping ACV were 30.9 (1-195), 8.7 (0-94), and 6.1 (0-69). Logistic regression demonstrated improved outcomes with increasing ACVs of SAH discharges and procedures for aneurysm obliteration, with attenuation of the benefit beyond 35 SAH cases/yr. Sensitivity and specificity analyses with different ACV thresholds confirmed the results. Analysis of previously proposed ACV thresholds, including those used as minimum standards for CSC certification, showed that hospitals with more than 35 SAH cases annually had better outcomes compared to hospitals with fewer cases, but some hospitals below this threshold had similar outcomes to those with more cases. The adjusted odds ratio favoring better outcomes with SAH ACV ≥ 35 compared to SAH 20 to 34 was 0.82 for the NIS-SOM (p=0.0054) and 0.80 (p=0.0055) for in-hospital mortality. Conclusions: Outcomes for SAH patients improve with increasing hospital case volumes and procedure volumes, with consistently better outcomes for hospitals with more than 35 SAH cases per year.

Effective recursive parallelotopic bounding for robust output-feedback control

In this paper an approach is studied to guaranteed (set-membership) state estimation for robust output-feedback model predictive control (MPC) with hard input and state constraints. Uncertainties are assumed to arise in a dynamic system from unknown initial conditions of state variables and due to unknown-but-bounded measurement noise. The uncertainty in the state variables is represented as a parallelotopic set. The employed state-estimation algorithm recursively outbounds the feasible set that is given by an intersection of model predictions with obtained measurement information. Along with the well-known minimum-volume criterion for parallelotopic outbounding, three alternative criteria are proposed and studied. The aim is to identify the best outbounding approach for improving performance of the robust MPC.

Institutional experience and outcomes of transcatheter aortic valve replacement: Results from an international multicentre registry

BackgroundDespite rapidly increasing use of TAVR across institutions, limited data is available for the effect of procedural experience on TAVR outcomes. We investigate the relationship between institutional experience and TAVR outcomes. Methods1953 patients undergoing TAVR at 8 international sites were grouped into chronological quantiles (Q) to assess temporal changes on procedural and clinical outcomes and multivariate logistic regression performed to determine predictors of device success, early safety and all-cause mortality. ResultsThe mean age of patients was 81±7years and 991 (51%) were female. The quantiles comprised of first 62 cases for Q1, 63–133 for Q2, 134 to 242 for Q3 and 243 to 476 for Q4. Device success increased from Q1 to Q4 (78% vs 89%, p<0.001) with significant improvement in the early safety endpoint (19% vs 10%, p<0.001). All cause mortality reduced by half in Q4 compared to Q1 (8% vs 4%, p=0.01) and rates of major vascular complications, major bleeding and valve embolization decreased with increasing experience. The multivariate analysis identified TAVR in Q3 and Q4 to be independently associated with higher device success and lower risk of complications. TAVR in Q4 was independently associated with lower mortality (OR 0.36 95% CI 0.19–0.70, p=0.002). ConclusionsGreater institutional experience with TAVR procedures improves device success and clinical outcomes. An experience of >242 cases is independently associated with lower mortality. These findings have important implications for defining minimum volume criteria for institutions and training standards for TAVR procedure.

Reply to the Comments on “Near-Infrared Hyperspectral Unmixing Based on a Minimum Volume Criterion for Fast and Accurate Chemometric Characterization of Counterfeit Tablets”

Reply to the Comments on “Near-Infrared Hyperspectral Unmixing Based on a Minimum Volume Criterion for Fast and Accurate Chemometric Characterization of Counterfeit Tablets”

Measurements of magnetic field induced by screening currents in YBCO solenoidcoils

Coated conductors are promising candidates for the construction of high-field magnets. Insolenoid magnets built with coated conductors, large screening currents are induced in thesuperconducting layer by the radial component of the magnetic field. The screeningcurrents generate a screening field that reduces the central magnetic field and affects theaxial uniformity and temporal stability of the magnetic field. The effects of the screeningfield on the central magnetic field have been measured in one short coil (minimum volumecriterion) and in one long coil (geometry similar to NMR coils). Depending on theoperating current, the reduction of the central field due to the screening fieldreached 14% in the short coil and 8% in the NMR-type coil. In the NMR-type coil,the temporal stability of the magnetic field was also measured: a drift of about10 ppm h − 1 after a holding time of 3 h was observed.

Comments on “Near-Infrared Hyperspectral Unmixing Based on a Minimum Volume Criterion for Fast and Accurate Chemometric Characterization of Counterfeit Tablets”

Comments on “Near-Infrared Hyperspectral Unmixing Based on a Minimum Volume Criterion for Fast and Accurate Chemometric Characterization of Counterfeit Tablets”

Near-Infrared Hyperspectral Unmixing Based on a Minimum Volume Criterion for Fast and Accurate Chemometric Characterization of Counterfeit Tablets

A rapid detection of the nonauthenticity of suspect tablets is a key first step in the fight against pharmaceutical counterfeiting. The chemical characterization of these tablets is the logical next step to evaluate their impact on patient health and help authorities in tracking their source. Hyperspectral unmixing of near-infrared (NIR) image data is an emerging effective technology to infer the number of compounds, their spectral signatures, and the mixing fractions in a given tablet, with a resolution of a few tens of micrometers. In a linear mixing scenario, hyperspectral vectors belong to a simplex whose vertices correspond to the spectra of the compounds present in the sample. SISAL (simplex identification via split augmented Lagrangian), MVSA (minimum volume simplex analysis), and MVES (minimum-volume enclosing simplex) are recent algorithms designed to identify the vertices of the minimum volume simplex containing the spectral vectors and the mixing fractions at each pixel (vector). This work demonstrates the usefulness of these techniques, based on minimum volume criteria, for unmixing NIR hyperspectral data of tablets. The experiments herein reported show that SISAL/MVSA and MVES largely outperform MCR-ALS (multivariate curve resolution-alternating least-squares), which is considered the state-of-the-art in spectral unmixing for analytical chemistry. These experiments are based on synthetic data (studying the effect of noise and the presence/absence of pure pixels) and on a real data set composed of NIR images of counterfeit tablets.

Sequential experimental design for estimation and analysis of thermal parameters in a fixed bed

AbstractThe analysis of the effective radial thermal conductivity and the film heat transfer coefficient were carried out in a fixed bed. The temperature profiles were described by two‐dimensional pseudo‐homogeneous model. The thermal parameters were estimated using a sequential experimental design technique. The minimum volume criterion was used to design the next point for temperature measurement in the bed. The utilization of T = T0 (constant) as the boundary condition at the bed inlet resulted in an axial variation of thermal parameters, which was the factor responsible for the inadequacy of the model in fitting experimental data of different bed heights simultaneously. Using T = T(r) as the boundary condition makes the thermal parameters independent of the axial position and the model statiscally adequate to describe the axial and radial temperature profiles throughout the bed.

Design, manufacturing and cold test of a superconducting coil and its cryostat for SMES applications

This paper describes the design and manufacturing of a 25 kJ superconducting coil as well as its cryostat and magnet support, including current leads and cryogenic services, for an SMES. The coil design is based on a minimum volume criteria. The cryostat is designed for 60 l of liquid helium, and the magnet support with current leads optimised for 150 A. Using numerical modelling, the total heat transfer into the liquid is calculated and minimised. The manufacturing of both components is also presented, as well as the complete system operation. Finally the paper presents the power converter topology that is controlled in optimal PWM mode with a low switching frequency. In order to compensate different power oscillations, the power converter quickly interchanges adjustable and uncoupled levels of real and reactive power.

Reconstruction of volume boundary from layers by triangulation

Abstract Volume boundary reconstruction from a stack of layers is necessary for process planning tasks such as determination of the optimal part orientation and nesting if a model is represented by layer contours. This paper presents a new algorithm for this purpose. The algorithm is able to construct a valid solid boundary satisfying the manifold solid condition while maintaining the capability of creating a smooth boundary. The reconstruction problem is reduced to that of reconstructing a boundary between two adjacent layers. Thus, first are calculated the intersection points of contours of two layers on the layer plane. Then the minimum volume criterion is introduced and yields two kinds of sets of planar straight-line graphs (PSLGs) from the Boolean difference operation between layer contours. These sets of PSLGs are separately triangulated in 2-D. The solid boundary finally results from inserting additional triangles into the triangulation by analyzing the connectivity of the triangulation in 3-D. Unlike most previous approaches, the algorithm does not distinguish between single and multiple contours and does not need any special treatments such as the introduction of intuitive bridges between contours or simplifying contours with holes for handling complex geometric situations. The robustness of the algorithm has been demonstrated by many practical examples from medical imaging, rapid prototyping, and reverse engineering applications.

Controlled clinical comparison of Isolator and BACTEC 9240 Aerobic/F resin bottle for detection of bloodstream infections

A controlled clinical comparison was carried out with the BACTEC 9240 Aerobic/F resin bottle and the Isolator system with adult patients suspected of having bloodstream infections. A total of 10,500 paired specimens were collected, of which 1,122 from 520 patients were positive. There were 68 false-positive BACTEC bottles; 259 positive cultures that were excluded from analysis because the bottle, the Isolator, or both failed to meet the minimum volume criterion of 8 ml of blood; and 207 positive cultures that were excluded because the isolates were found to be clinically insignificant or of indeterminate clinical significance on the basis of patient assessment. A total of 656 positive cultures from 258 patients formed the basis of the analysis. Significantly more Staphylococcus aureus isolates (P = 0.03), Staphylococcus epidermidis isolates (P = 0.03), members of the family Enterobacteriaceae (P = 0.03), and Pseudomonas aeruginosa isolates (P = 0.04) were recovered from the resin bottle, and there was no category of organism that was recovered significantly more frequently from the Isolator system. With patients receiving antibiotics at the time of blood culture, S. aureus, S. epidermidis, and gram-negative bacilli were recovered significantly more frequently from the resin bottle. No significant differences between systems were found with cultures from patients not receiving antibiotics at the time of blood culture. Only 12 clinically significant organisms were recovered from the bottle on terminal subcultures, and only 1 of these had not been previously isolated from another blood culture set (10 of the 12) or from the companion Isolator (1 of 12). The Aerobic/F resin bottle continuously monitored in the BACTEC 9240 instrument proved to be superior to the Isolator in overall yield of organisms causing bloodstream infection in adults and required less technician time for specimen processing and examination than the Isolator system.

A Note on Evershed's Minimum Volume Criterion: A third method for finding the maximum value of the (–H)B product

A Note on Evershed's Minimum Volume Criterion: A third method for finding the maximum value of the (–H)^B product