Minimal Separation Research Articles

Enhanced Mechanical Properties by Ionomeric Complexation in Interpenetrating Network Hydrogels of Hydrolyzed Poly (N-vinyl Formamide) and Polyacrylamide.

Tough hydrogels were made by hydrolysis of a neutral interpenetrating network (IPN) of poly (N-vinyl formamide) PNVF and polyacrylamide (PAAm) networks to form an IPN of polyvinylamine (PVAm) and poly (acrylic acid) (PAAc) capable of intermolecular ionic complexation. Single network (SN) PAAm and SN PNVF have similar chemical structures, parameters and physical properties. The hypothesis was that starting with neutral IPN networks of isomeric monomers that hydrolyze to comparable extents under similar conditions would lead to formation of networks with minimal phase separation and maximize potential for charge–charge interactions of the networks. Sequential IPNs of both PNVF/PAAm and PAAm/PNVF were synthesized and were optically transparent, an indication of homogeneity at submicron length scales. Both IPNs were hydrolyzed in base to form PVAm/PAAc and PAAc/PVAm IPNs. These underwent ~5-fold or greater decrease in swelling at intermediate pH values (3–6), consistent with the hypothesis of intermolecular charge complexation, and as hypothesized, the globally neutral, charge-complexed gel states showed substantial increases in failure properties upon compression, including an order of magnitude increases in toughness when compared to their unhydrolyzed states or the swollen states at high or low pH values. There was no loss of mechanical performance upon repeated compression over 95% strain.

(Theta, triangle)‐free and (even hole, K4)‐free graphs. Part 2: Bounds on treewidth

AbstractA theta is a graph made of three internally vertex‐disjoint chordless paths , of length at least 2 and such that no edges exist between the paths except the three edges incident to and the three edges incident to . A pyramid is a graph made of three chordless paths , of length at least 1, two of which have length at least 2, vertex‐disjoint except at , and such that is a triangle and no edges exist between the paths except those of the triangles and the three edges incident to . An even hole is a chordless cycle of even length. For three nonnegative integers , let be the tree with a vertex , from which start three paths with , and edges, respectively. We denote by the complete graph on vertices. We prove that for all nonnegative integers , the class of graphs that contain no theta, no , and no as induced subgraphs have bounded treewidth. We prove that for all nonnegative integers , the class of graphs that contain no even hole, no pyramid, no , and no as induced subgraphs have bounded treewidth. To bound the treewidth, we prove that every graph of large treewidth must contain a large clique or a minimal separator of large cardinality.

Finding a maximum minimal separator: Graph classes and fixed-parameter tractability

We study the problem of finding a maximum cardinality minimal separator of a graph. This problem is known to be NP-hard even for bipartite graphs. In this paper, we strengthen this hardness by showing that for planar bipartite graphs, the problem remains NP-hard. Moreover, for co-bipartite graphs and for line graphs, the problem also remains NP-hard. On the positive side, we give an algorithm deciding whether an input graph has a minimal separator of size at least k that runs in time 2O(k)nO(1). We further show that there is no 2o(n)nO(1)-time algorithm unless the Exponential Time Hypothesis (ETH) fails. Finally, we discuss a lower bound for polynomial kernelizations of this problem.

Polynomially Bounding the Number of Minimal Separators in Graphs: Reductions, Sufficient Conditions, and a Dichotomy Theorem

A graph class is said to be tame if graphs in the class have a polynomially bounded number of minimal separators. Tame graph classes have good algorithmic properties, which follow, for example, from an algorithmic metatheorem of Fomin, Todinca, and Villanger from 2015. We show that a hereditary graph class $\mathcal{G}$ is tame if and only if the subclass consisting of graphs in $\mathcal{G}$ without clique cutsets is tame. This result and Ramsey's theorem lead to several types of sufficient conditions for a graph class to be tame. In particular, we show that any hereditary class of graphs of bounded clique cover number that excludes some complete prism is tame, where a complete prism is the Cartesian product of a complete graph with a $K_2$. We apply these results, combined with constructions of graphs with exponentially many minimal separators, to develop a dichotomy theorem separating tame from non-tame graph classes within the family of graph classes defined by sets of forbidden induced subgraphs with at most four vertices.

Covering Minimal Separators and Potential Maximal Cliques in $P_t$-Free Graphs

A graph is called $P_t$-free if it does not contain a $t$-vertex path as an induced subgraph. While $P_4$-free graphs are exactly cographs, the structure of $P_t$-free graphs for $t \geqslant 5$ remains little understood. On one hand, classic computational problems such as Maximum Weight Independent Set (MWIS) and $3$-Coloring are not known to be NP-hard on $P_t$-free graphs for any fixed $t$. On the other hand, despite significant effort, polynomial-time algorithms for MWIS in $P_6$-free graphs~[SODA 2019] and $3$-Coloring in $P_7$-free graphs~[Combinatorica 2018] have been found only recently. In both cases, the algorithms rely on deep structural insights into the considered graph classes.
 One of the main tools in the algorithms for MWIS in $P_5$-free graphs~[SODA 2014] and in $P_6$-free graphs~[SODA 2019] is the so-called Separator Covering Lemma that asserts that every minimal separator in the graph can be covered by the union of neighborhoods of a constant number of vertices. In this note we show that such a statement generalizes to $P_7$-free graphs and is false in $P_8$-free graphs. We also discuss analogues of such a statement for covering potential maximal cliques with unions of neighborhoods.

Single Microhole per Pixel in CMOS Image Sensors With Enhanced Optical Sensitivity in Near-Infrared

Silicon photodiode-based CMOS sensors with backside-illumination for 300-1100 nm wavelength range were studied. We showed that a single hole in the photodiode increases the optical efficiency of the pixel. In near-infrared wavelengths, the enhancement allows 70% absorption in a 3 μm thick Si. It is 4× better than that for the flat pixel. We compared different shapes and sizes of single hole and hole arrays. We have shown that a certain size and shape in single hole-based pixels contribute to stronger enhancement of optical efficiencies. The crosstalk was successfully reduced by employing trenches between pixels. We optimized the dimensions of the trenches to achieve minimal pixel separation for 1.12 μm pixels.

Simulations of Intracycle Angular Velocity Control for a Crossflow Turbine

Straight-bladed crossflow turbines are computationally explored for harvesting energy in wind and water currents. One challenge for crossflow turbines is the transient occurrence of high apparent angles of attack on the blades that reduces efficiency due to flow separation. This paper explores kinematic manipulation of the apparent angle of attack through intracycle control of the angular velocity. Using an unsteady Reynolds-averaged Navier–Stokes model at moderate Reynolds numbers, the kinematics and associated flow physics are explored for confined and unconfined configurations. The computations demonstrate an increase in turbine efficiency up to 54%, very closely matching the benefits shown by previous intracycle control experiments. Simulations display the time evolution of angle of attack and flow velocity relative to the blade, which are modified with sinusoidal angular velocity such that the peak torque generation aligns with the peak angular velocity. With optimal kinematics in a confined flow there is minimal flow separation during peak power generation; however, there is a large trailing edge vortex shed as the torque decreases. The unconfined configuration has more prominent flow separation and is more susceptible to Reynolds number, resulting in a 41% increase in power generation under the same kinematic conditions as the confined flow.

Discrimination and estimation of incoherent sources under misalignment

Spatially resolving two incoherent point sources whose separation is well below the diffraction limit dictated by classical optics has recently been shown possible using techniques that decompose the incoming radiation into orthogonal transverse modes. Such a demultiplexing procedure, however, must be perfectly calibrated to the transverse profile of the incoming light as any misalignment of the modes effectively restores the diffraction limit for small source separations. We study by how much can one mitigate such an effect at the level of measurement which, after being imperfectly demultiplexed due to inevitable misalignment, may still be partially corrected by linearly transforming the relevant dominating transverse modes. We consider two complementary tasks: the estimation of the separation between the two sources and the discrimination between one and two incoherent point sources. We show that, although one cannot fully restore super-resolving powers even when the value of the misalignment is perfectly known its negative impact on the ultimate sensitivity can be significantly reduced. In the case of estimation we analytically determine the exact relation between the minimal resolvable separation as a function of misalignment whereas for discrimination we analytically determine the relation between misalignment and the probability of error, as well as numerically determine how the latter scales in the limit of long interrogation times.

Null hypersurface caustics, closed null curves, and super entropy

Recently it was discovered that null hypersurfaces can develop caustics outside the event horizon of super-entropic Kerr-AdS black holes, in contrast to the usual Kerr-AdS case. In this work we explore a few more examples of black hole spacetimes in which such exterior caustics can develop. If a closed null curve is present, e.g., in the case of Taub-NUT and the "transunital" Kerr-AdS spacetimes, then it coincides with a null hypersurface caustic (NHC) of a minimal separation parameter. Thus a spacetime on the verge of forming closed timelike curves could develop a caustic. Known examples of super-entropic black holes also have exterior NHC, although such spacetimes are free of closed null/timelike curves. Nevertheless the relationship between closed causal curves, NHC, and super-entropy is not straightforward. This is best illustrated with the BTZ black string, which for some choices of the warp factor in the extra dimension and the value of the charge, can be super-entropic. However, even those that are not super-entropic can admit NHC outside the horizon.

ANÁLISIS TÉRMICO ÓPTIMO DE LA TRANSMISIÓN DEL CORONAVIRUS (COVID-19) DURANTE DÍAS DE CUARENTENA EN PERÚ

En esta investigación se analiza la transmisión de COVID-19 por equilibrio termodinámico y energético entre áreas geográficas y su correlación con la posible transmisión de COVID-19 entre al menos 2 personas. Con el fin de lograr parámetros para los médicos, como por ejemplo la distancia mínima entre dos personas infectadas que tienen este virus, se diseñaron modelos matemáticos basados en datos estadísticos para obtener información sobre la propagación de COVID-19 como la dependencia de la temperatura de áreas geográficas, además, el efecto térmico de la distancia mínima entre dos personas evitando la infección por COVID-19. Con este trabajo, se buscan respuestas a las preguntas: ¿Si fuera posible encontrar una relación entre la temperatura y la transmisión del virus? ¿O si fuera posible obtener una variable de correlación entre variables térmicas con una separación mínima de distancia (se describió anteriormente) para dos personas? Por lo tanto, se esperan respuestas a estas preguntas debido al apoyo de los médicos, que están tratando de encontrar una solución contra la propagación de COVID-19. Vale la pena mencionar que esta investigación puede extenderse a áreas más complejas como mercados y ferias abiertas al aire libre o mercados cerrados, donde se venden productos y servicios, además, no todas las áreas tienen un sistema de aire acondicionado en Perú. Sin embargo, en esta investigación se logra la técnica, cómo resolver esta tarea: obtener parámetros de ventilación apropiados como la dependencia de la distancia mínima que las personas necesitan para separarse, para evitar la transmisión del virus entre sí. Además, se sugieren algunas características geométricas / materiales para los filtros de aire y la desinfección mediante ultravioleta (UV) en la entrada del conducto de aire principal.

High-resolution manometry findings with hiatus hernia

: The esophagogastric junction (EGJ) is comprised of both the intrinsic lower esophageal sphincter (LES) and extrinsic crural diaphragm (CD) such that intraluminal pressure represents a composite of the two. With type I hiatal hernias there is weakening of the pharyngoesophageal ligament attaching the esophagus to the CD such that the distal esophagus, including the LES, becomes displaced cephalad. High-resolution manometry (HRM), can accurately detect an axial hiatal hernia as confirmed by studies comparing HRM to barium esophagram, upper endoscopy, or intraoperative findings. In HRM studies, hiatus hernia becomes evident by a spatial separation between the pressure signature of the LES and that of the CD; the operative confirmation of hiatus hernia correlates with this separation exceeding 1 cm. With LES-CD separation of <2 cm the HRM pressure signatures of the two overlap, but as the LES-CD separation increases beyond that the two become completely separate. The other progression noted in HRM studies is in the location of the respiratory inversion point (RIP), the axial location at which the inspiratory change in pressure transitions from an inspiratory increase, characteristic of intra-abdominal recordings to an inspiratory decrease, characteristic of intrathoracic recordings. In the normal state and with small hiatal hernias, the location of the RIP correlates with where the CD impinges on the esophagus at inspiration. However, with larger hernias the RIP can localize with either the CD or the LES reflective of whether or not the CD has become incompetent, presumably a result of hiatal dilatation. Consequently, there are three distinct EGJ pressure morphologies in HRM: (I) normal with minimal LES-CD separation, (II) hiatus hernia with LES-CD separation >1 cm and the RIP localized at the CD, and (III) hiatus hernia with LES-CD separation >1 cm and the RIP localized at the LES.

The utility of minimal access and separation surgery in the management of metastatic spine disease

The utility of minimal access and separation surgery in the management of metastatic spine disease

Theoretical and Experimental Evaluation of a Compact Aerosol Wind-tunnel and its Application for Performance Investigation of Particulate Matter Instruments

In this study, we developed a compact low-speed wind tunnel. First, we computationally analysed the flow quality of different wall shapes for the contraction section, the most critical part of a wind tunnel, and selected the design exhibiting minimal boundary layer separation at simulated flow velocities of 2 and 8 km h−1. Then, after constructing the wind tunnel, we experimentally evaluated its overall performance based on different parameters per the United States Environmental Protection Agency (U.S. EPA) guidelines (40 CFR 53.62). The air velocity and turbulence profiles were uniform, displaying ≤ 10% variation in the section we tested. Additionally, we measured the mass concentrations and size distributions of polydisperse dust particles, which were generated by a custom-made rotary dust feeder to ensure the homogeneity of the aerosol, inside the wind tunnel at air velocities of 2 and 8 km h−1 and found ≤ 10% deviation for the mean values across the test section relative to those for the central sampling point. We also assessed the effectiveness of the Well Impactor Ninety-Six (WINS) and Very Sharp Cut Cyclone (VSCC) in the wind tunnel at an air velocity of 8 km h−1 by determining the D50 cutoffs, which, being 2.44 ± 0.05 µm and 2.54 ± 0.05 µm, respectively, fulfilled U.S. EPA’s criteria. Furthermore, we compared the performance of a low-cost sensor against that of a reference instrument in measuring PM2.5 concentrations, and our results agreed with those from previous studies.

Turbulent flow characteristics over forward-facing obstacle

The local flow field and wake region over a forward-facing obstacle were experimentally investigated, when the water surface above the obstacle was dipped compared to flow further upstream and further downstream. The obstacle was modelled resembling the shape of an airfoil with a flat top having stoss-side slope and downstream lee-side slope designed for minimal flow separation. The submerged obstacle showed an evolutionary change in the flow field with a dipped water surface shape over the crest; and consequently three distinct flow regions were observed: upstream region, crest region and the downstream. The velocity data were recorded using a three-dimensional micro-acoustic Doppler velocimeter along the flume centreline for three flow Reynolds numbers and different localised Froude numbers. The paper highlights the flow and turbulence prime parameters: second-order statistics, turbulence kinetic energy, eddy viscosity, turbulence production, probability-density functions and the contributions of stress fraction into four quadrants to the total shear stress along the flow. The spectral analysis was performed to examine the energy distributions, vortex-shedding frequencies with corresponding Strouhal numbers. Variations of turbulence integral length scale along the flow passing over the obstacle were investigated to examine the eddy turnover scales. The turbulent features were fairly inspiring since it led to a pronounced acceleration on the crest location like a jet with a potential core region, and elongated deflection in the downside slope. The results provide a basic turbulence in natural environment for various phases of ebb and tide over a submerged smooth obstacle or mountain hills in river/ocean.

Low-power transimpedance amplifier for cryogenic integration with quantum devices

The development of quantum electronic devices operating below a few Kelvin degrees is raising the demand for cryogenic complementary metal-oxide-semiconductor electronics (CMOS) to be used as in situ classical control/readout circuitry. Having a minimal spatial separation between quantum and classical hardware is necessary to limit the electrical wiring to room temperature and the associated heat load and parasitic capacitances. Here, we report prototypical demonstrations of hybrid circuits combining silicon quantum dot devices and a classical transimpedance amplifier, which is characterized and then used to measure the current through the quantum dots. The two devices are positioned next to each other at 4.2 K to assess the use of the cryogenic transimpedance amplifier with respect to a room-temperature transimpedance amplifier. A quantum device built on the same substrate as the transimpedance amplifier is characterized down to 10 mK. The transimpedance amplifier is based on commercial 28 nm fully depleted Silicon-on-insulator (FDSOI) CMOS. It consists of a two-stage Miller-compensated operational amplifier with a 10 MΩ polysilicon feedback resistor, yielding a gain of 1.1×107 V/A. We show that the transimpedance amplifier operates at 10 mK with only 1 μW of power consumption, low enough to prevent heating. It exhibits linear response up to ±40 nA and a measurement bandwidth of 2.6 kHz, which could be extended to about 200 kHz by design optimization. The realization of custom-made electronics in FDSOI technology for cryogenic operation at any temperature will improve measurement speed and quality inside cryostats with higher bandwidth, lower noise, and higher signal-to-noise ratio.

Electro-responsive surfaces with controllable wrinkling patterns for switchable light reflection–diffusion–grating devices

Dynamic microscale surface topographies are desired in smart optics, controlling surface wettability and preventing marine biofouling. Voltage-controlled reversible responses have demonstrated potential for reliable reproducibility and stability, fast response, and for actuating thin films fixed over large solid surfaces. To obtain reversible deformation with regular geometric patterns, however, electrical methods have had to be coupled with mechanical stretching/bending and other ways to induce anisotropy. There is a great need and potential for on-demand electrical generation of programmable complex responsive surface patterns. Here we demonstrate a responsive polymer coating over an underlying pattern of counter electrodes which can be activated selectively. We present a patternable electrode printing method to achieve localized and structured wrinkling deformation without mechanical pre-force deformation. We discover that below a minimal separation distance, electrodes below the polymer act as a single electrode. We establish parameters that govern the alignment of wrinkles and quantify the regularity and direction of the new patterns between electrodes separated by larger than this distance. We analyze and quantify the regularity of the formed wrinkling patterns by four disorder metrics: box-counting fractal dimension, tortuosity, angle distribution, and branch number. We demonstrate the application of such electrode/wrinkles-on-demand patterning with a working multi-state light reflection–diffusion–grating device.

Utilization of high-pressure homogenization of potato protein isolate for the production of dairy-free yogurt-like fermented product

The demand for alternatives to milk-based yogurts with high acceptance and functionality has been increasing in recent years. Yet, many plant-based proteins suffer from limited techno-functional properties such as poor solubility, color, and other sensory properties. The utilization of high-pressure homogenization (HPH) has been suggested as a tool for attenuating some of these technological limitations. This work aims to study the combination of an alternative plant protein source, potato protein isolate (PPI), with the utilization of HPH for the formation of a yogurt-like fermented product without the addition of stabilizers. The utilization of HPH 200 MPa, Tin = 15 °C as a pre-processing step reduced downstream PPI sedimentation. The formation of a stable (against separation) PPI and canola oil emulsions by HPH allowed lactic acid fermentation with minimal creaming. The results show that increasing the homogenization pressure reduced the particle size, and allowed the formation of finer and whiter emulsion with improved physical stability against separation. The yogurt-like substitutes were obtained in the same time frame as milk-based yogurt and presented a gel-like behavior. The stability against phase separation of the yogurt alternative increased with increasing homogenization pressure, and the minimal phase separation was observed for the 200 MPa system. Also, the lightness value and water holding capacity of the yogurt-like substitutes obtained were similar to values reported for commercial plant-based yogurts alternatives containing stabilizers.

AMP Chain Graphs: Minimal Separators and Structure Learning Algorithms

This paper deals with chain graphs (CGs) under the Andersson–Madigan–Perlman (AMP) interpretation. We address the problem of finding a minimal separator in an AMP CG, namely, finding a set Z of nodes that separates a given non-adjacent pair of nodes such that no proper subset of Z separates that pair. We analyze several versions of this problem and offer polynomial time algorithms for each. These include finding a minimal separator from a restricted set of nodes, finding a minimal separator for two given disjoint sets, and testing whether a given separator is minimal. To address the problem of learning the structure of AMP CGs from data, we show that the PC-like algorithm is order dependent, in the sense that the output can depend on the order in which the variables are given. We propose several modifications of the PC-like algorithm that remove part or all of this order-dependence. We also extend the decomposition-based approach for learning Bayesian networks (BNs) to learn AMP CGs, which include BNs as a special case, under the faithfulness assumption. We prove the correctness of our extension using the minimal separator results. Using standard benchmarks and synthetically generated models and data in our experiments demonstrate the competitive performance of our decomposition-based method, called LCD-AMP, in comparison with the (modified versions of) PC-like algorithm. The LCD-AMP algorithm usually outperforms the PC-like algorithm, and our modifications of the PC-like algorithm learn structures that are more similar to the underlying ground truth graphs than the original PC-like algorithm, especially in high-dimensional settings. In particular, we empirically show that the results of both algorithms are more accurate and stabler when the sample size is reasonably large and the underlying graph is sparse

A sensitivity study of the primary correlators used to characterize chiral-magnetically-driven charge separation

A Multi-Phase Transport (AMPT) model is used to study the detection sensitivity of two of the primary correlators – Δγ and RΨ2 – employed to characterize charge separation induced by the Chiral Magnetic Effect (CME). The study, performed relative to several event planes for different input “CME signals”, indicates a detection threshold for the fraction fCME=ΔγCME/Δγ, which renders the Δγ-correlator insensitive to values of the Fourier dipole coefficient a1≲2.5%, that is larger than the purported signal (signal difference) for ion-ion(isobaric) collisions. By contrast, the RΨ2 correlator indicates concave-shaped distributions with inverse widths (σRΨ2−1) that are linearly proportional to a1, and independent of the character of the event plane used for their extraction. The sensitivity of the RΨ2 correlator to minimal CME-driven charge separation in the presence of realistic backgrounds, could aid better characterization of the CME in heavy-ion collisions.

Assessing the Effect of Tandem Phase Sentinel-3 OLCI Sensor Uncertainty on the Estimation of Potential Ocean Chlorophyll-a Trends

The Sentinel-3 tandem project represents the first time that two ocean colour satellites have been flown in the same orbit with minimal temporal separation (~30 s), thus allowing them to have virtually identical views of the ocean. This offers an opportunity for understanding how differences in individual sensor uncertainty can affect conclusions drawn from the data. Here, we specifically focus on trend estimation. Observational chlorophyll-a uncertainty is assessed from the Sentinel-3A Ocean and Land Colour Imager (OLCI-A) and Sentinel-3B OLCI (OLCI-B) sensors using a bootstrapping approach. Realistic trends are then imposed on a synthetic chlorophyll-a time series to understand how sensor uncertainty could affect potential long-term trends in Sentinel-3 OLCI data. We find that OLCI-A and OLCI-B both show very similar trends, with the OLCI-B trend estimates tending to have a slightly wider distribution, although not statistically different from the OLCI-A distribution. The spatial pattern of trend estimates is also assessed, showing that the probability distributions of trend estimates in OLCI-A and OLCI-B are most similar in open ocean regions, and least similar in coastal regions and at high northern latitudes. This analysis shows that the two sensors should provide consistent trends between the two satellites, provided future ageing is well quantified and mitigated. The Sentinel-3 programme offers a strong baseline for estimating long-term chlorophyll-a trends by offering a series of satellites (starting with Sentinel-3A and Sentinel-3B) that use the same sensor design, reducing potential issues with cross-calibration between sensors. This analysis contributes an important understanding of the reliability of the two current Sentinel-3 OLCI sensors for future studies of climate change driven chlorophyll-a trends.