Location Of Transition Research Articles

Modified Kelvin Equations for Capillary Condensation in Narrow and Wide Grooves.

We consider the location and order of capillary condensation transitions occurring in deep grooves of width L and depth D. For walls that are completely wet by liquid (contact angle θ=0) the transition is continuous and its location is not sensitive to the depth of the groove. However, for walls that are partially wet by liquid, where the transition is first order, we show that the pressure at which it occurs is determined by a modified Kelvin equation characterized by an edge contact angle θ_{E} describing the shape of the meniscus formed at the top of the groove. The dependence of θ_{E} on the groove depth D relies, in turn, on whether corner menisci are formed at the bottom of the groove in the low density gaslike phase. While for macroscopically wide grooves these are always present when θ<45° we argue that their formation is inhibited in narrow grooves. This has a number of implications including that the local pinning of the meniscus and location of the condensation transition is different depending on whether the contact angle is greater or less than a universal value θ^{*}≈31°. Our arguments are supported by detailed microscopic density functional theory calculations that show that the modified Kelvin equation remains highly accurate even when L and D are of the order of tens of molecular diameters.

Effect of plasma actuator control parameters on a transitional flow

This study uses a wall-resolved implicit large eddy simulation to investigate the effects of different surface dielectric barrier discharge actuator parameters such as the geometry of the electrodes, frequency, amplitude of actuation and thermal effect. The actuator is used as a tripping device on a zero-pressure gradient laminar boundary layer flow. It is shown that the standard linear actuator creates structures like the Tollmien–Schlichting wave transition. The circular serpentine, square serpentine and spanwise actuators have subharmonic sinuous streak breakdown and behave like oblique wave transition scenario. The spanwise and square actuators cause comparably faster transition to turbulence. The square actuator adds energy into the higher spanwise wavenumber modes resulting in a faster transition compared to the circular actuator. When the Strouhal number of actuation is varied, the transition does not occur for a value below 0.292. Higher frequencies with same amplitude of actuation lead to faster transition. Small changes (<4%) in the amplitude of actuation can have a significant impact on the transition location which suggests that an optimal combination of frequency and amplitude exists for highest control authority. The thermal bumps approximating the actuator heating only shows localized effects on the later stages of transition for temperatures up to 373 K and can be ignored for standard actuators operating in subsonic regimes.

Classifying dynamic transitions in high dimensional neural mass models: A random forest approach.

Neural mass models (NMMs) are increasingly used to uncover the large-scale mechanisms of brain rhythms in health and disease. The dynamics of these models is dependent upon the choice of parameters, and therefore it is crucial to be able to understand how dynamics change when parameters are varied. Despite being considered low dimensional in comparison to micro-scale, neuronal network models, with regards to understanding the relationship between parameters and dynamics, NMMs are still prohibitively high dimensional for classical approaches such as numerical continuation. Therefore, we need alternative methods to characterise dynamics of NMMs in high dimensional parameter spaces. Here, we introduce a statistical framework that enables the efficient exploration of the relationship between model parameters and selected features of the simulated, emergent model dynamics of NMMs. We combine the classical machine learning approaches of trees and random forests to enable studying the effect that varying multiple parameters has on the dynamics of a model. The method proceeds by using simulations to transform the mathematical model into a database. This database is then used to partition parameter space with respect to dynamic features of interest, using random forests. This allows us to rapidly explore dynamics in high dimensional parameter space, capture the approximate location of qualitative transitions in dynamics and assess the relative importance of all parameters in the model in all dimensions simultaneously. We apply this method to a commonly used NMM in the context of transitions to seizure dynamics. We find that the inhibitory sub-system is most crucial for the generation of seizure dynamics, confirm and expand previous findings regarding the ratio of excitation and inhibition, and demonstrate that previously overlooked parameters can have a significant impact on model dynamics. We advocate the use of this method in future to constrain high dimensional parameter spaces enabling more efficient, person-specific, model calibration.

Finding Transitions of Physical Condition in Jets from Observations over the Range of 103–109 Schwarzschild Radii in Radio Galaxy NGC 4261

Abstract We report new measurements of jet width and radiation profiles along jets over the range of 103–109 Schwarzschild radius (R S) in the nearby radio galaxy NGC 4261 using multifrequency Very Long Baseline Array (VLBA) and Very Large Array images. In the VLBA images, we found parabolic-to-conical transition signatures on both the approaching jet and counterjet width profiles at ∼104 R S from the central engine. A transition in the radiation profile along the approaching jet was also found at ∼104 R S clearly. Based on the consistency of the transition locations, we conclude that the physical conditions of the NGC 4261 jets change at this distance. Jet flows that change from accelerating to expanding regions were previously found in M87 and NGC 6251 and are presumably present in NGC 4261. Additionally, we found another transition in the radiation profile at ∼3 × 106 R S in the conical region. NGC 4261 is the first case in which a jet structural transition is suggested in both the approaching and counter jets; this implies that the active galactic nucleus jet collimation process is fundamentally characterized by the global distribution of ambient pressure rather than the local interaction between the jet and the surrounding medium. We discuss the evolution of jet conditions in terms particle acceleration, cooling, dissipation, and jet pressure balance with the surrounding hot gas.

Laminar-turbulent transition tripped by step on transonic compressor profile

The shock wave boundary layer interaction on the suction side of transonic compressor blade is one of the main objectives of TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). The experimental and numerical results for the flow structure investigations are shown for the flow conditions as the existing ones on the suction side of the compressor profile. The two cases are investigated: without and with boundary layer tripping device. In the first case, boundary layer is laminar up to the shock wave, while in the second case the boundary layer is tripped by the step. Numerical results carried out by means of Fine/Turbo Numeca with Explicit Algebraic Reynolds Stress Model including transition modeling are compared with schlieren, Temperature Sensitive Paint and wake measurements. Boundary layer transition location is detected by Temperature Sensitive Paint.

Responsive behavior of a branched-chain polymer network: a molecular dynamics study.

Smart polymer hydrogels, which can undergo structural and volume phase transitions in response to external stimuli, have gained much attention for their widespread technological applications. Compared to linear polymers, branched chains offer more extensive opportunities to rationally design functional materials, since they permit more extensive structural tunability-for instance by adjusting the balance between hydrophobic and hydrophilic units, the grafting fraction of backbone monomers, or the side chain length, topology, and solubility. Here we conduct coarse-grained molecular dynamics simulations to assess how well generic physical principles capture this complex interplay of tuning parameters, specifically when building networks from complex branched chains with a hydrophobic backbone. Swollen chains collapse upon reducing side chain solubility, length, and grafting density, but neither the sharpness of this transition nor its dynamic range, if measured via chain extension, depends monotonically on these parameters. Networks comprising such chains are more swollen and exhibit even sharper transitions, but their higher responsiveness goes along with a swelling ratio that falls behind that of single chains.

Swept-tone stimulus-frequency otoacoustic emissions: Normative data and methodological considerations.

Stimulus-frequency otoacoustic emissions (SFOAEs) are reflection-source emissions, and are the least familiar and perhaps most underutilized otoacoustic emission. Here, normative SFOAE data are presented from a large group of 48 young adults at probe levels from 20 to 60 dB sound pressure level (SPL) across a four-octave frequency range to characterize the typical SFOAE and describe recent methodological advances that have made its measurement more efficient. In young-adult ears, SFOAE levels peaked in the low-to-mid frequencies at mean levels of ∼6-7 dB SPL while signal-to-noise ranged from 23 to 34 dB SPL and test-retest reliability was ±4 dB for 90% of the SFOAE data. On average, females had ∼2.5 dB higher SFOAE levels than males. SFOAE input/output functions showed near linear growth at low levels and a compression threshold averaging 35 dB SPL across frequency. SFOAE phase accumulated ∼32-36 cycles across four octaves on average, and showed level effects when converted to group delay: low-level probes produced longer SFOAE delays. A "break" in the normalized SFOAE delay was observed at 1.1 kHz on average, elucidating the location of the putative apical-basal transition. Technical innovations such as the concurrent sweeping of multiple frequency segments, post hoc suppressor decontamination, and a post hoc artifact-rejection technique were tested.

Regional thermo-rheological field related to granite emplacement in the upper crust: implications for the Larderello area (Tuscany, Italy)

ABSTRACTWe modelled thermo-rheological perturbations, related to the emplacement of a magmatic body in the upper crust. This approach was considered relevant for the areas characterized by elevated surface heat flow and chiefly for the geothermal fields. The numerical conductive thermal model applied to the Larderello geothermal area in Tuscany, allowed to constrain size, depth and timing of emplacement of the pluton. We inferred that the emplacement of a magmatic body, at a minimum depth of 3 km, having a horizontal extension of 14 km and a maximum thickness of 8 km, can reasonably reproduce the observed regional surface heat flow anomaly of the Larderello area, when 300 (± 100) kyr are elapsed from the magma emplacement. Even assuming an incremental growth, the first magma injection should not be older than 1 ± 0.3 Ma.Results of the thermal model were used to set up a rheological model and to simulate the drifting of the brittle-ductile transition during the cooling of the pluton. A comparison with the K-horizon profile, a prominent seismic reflector in the Larderello area, was then performed. It was found that the K-horizon approximately corresponds with the pluton roof and with the current location of the brittle-ductile transition.

Flows of Supersonic Underexpanded Jets on the Range of Moderate Reynolds Numbers

The results of an experimental investigation of the gasdynamic structure of supersonic underexpanded air jets flowing out of a sonic nozzle into a low-pressure medium are presented. This setting of the experimentmakes it possible to achieve high values of the nozzle-to-ambient pressure ratio at moderate outflow Reynolds numbers characteristic of underexpanded jets issuing from micronozzles. The data on the supersonic core length, the laminar-turbulent transition location, and the jet flow characteristics are obtained. The results are compared with those obtained in microjets flowing out of sonic nozzles. Emphasis is placed on the earlier discovered effect of inverse transition of a turbulent jet into the laminar flow regime with increase in the Reynolds number.

Smart Rotors: Dynamic-Stall Load Control by Means of an Actuated Flap

This study focuses on an active strategy for unsteady-load control by means of a trailing-edge flap. Experiments on a 2D pitching and heaving NACA 0018 airfoil with an actuated trailing-edge flap are performed at a reduced frequency in a free-stream flow with . The model is equipped with 24 differential pressure transducers to provide with the time-resolved distribution of the pressure difference between pressure and suction sides. Results show that an actuated flap significantly decreases the magnitude of unsteady loads. A reduced order model of the flap effect on the loads is proposed. The loads are estimated by adding the contribution of the clean wing with the flap one. This model can be applied to unsteady loads for both attached flow and dynamic stall conditions, constituting an effective control strategy for dynamic loads, if the airfoil transition location is properly controlled.

Natural laminar flow airfoil shape design at transonic regimes with multi-objective evolutionary algorithms

The natural laminar flow airfoil shape design at transonic regime is solved using multi-objective evolutionary algorithms in this paper. A shock wave control bump is used to reduce wave drag of natural laminar flow airfoil in transonic flow, and the eN transition prediction method based on the linear stability theory is used to predict the transition location. The multi-island parallel multi-objective evolutionary algorithms is implemented to optimize the airfoil shape equipped with shock wave control bump for obtaining a larger laminar flow region and a weaker wave drag simultaneously. Optimization experiment shows that it is easy to capture the Pareto front of wave drag minimization and laminar flow region maximization. Results demonstrate that both wave drag and friction drag performance of several chosen Pareto members are significantly improved via the optimal airfoil shape and shock wave control bump device compared to that of the baseline shape.

How active forces influence nonequilibrium glass transitions

Dense assemblies of self-propelled particles undergo a nonequilibrium form of glassy dynamics. Physical intuition suggests that increasing departure from equilibrium due to active forces fluidifies a glassy system. We falsify this belief by devising a model of self-propelled particles where increasing departure from equilibrium can both enhance or depress glassy dynamics, depending on the chosen state point. We analyze a number of static and dynamic observables and suggest that the location of the nonequilibrium glass transition is primarily controlled by the evolution of two-point static density correlations due to active forces. The dependence of the density correlations on the active forces varies non-trivially with the details of the system, and is difficult to predict theoretically. Our results emphasize the need to develop an accurate liquid state theory for nonequilibrium systems.

Examining the Pedestrian Itineraries in the Built Environment Around the Quito’s BRT ( poster )

Pedestrian accessibility is a key factor in the integration of the built environment and the transport system. This study proposes an analysis of spatial configuration in relation to service coverage and the pedestrian attraction of important traffic zones of Quito, Ecuador. The analysis aims to evaluate the spatial configuration of the build environment around the stops of the bus rapid transit covered by this study. With the support of geographic information systems is established the coverage of the service with a maximum distance of 500 meters. Within this area, the capacity to service is analyzed according to the location of the stop and the variable of resident and non-resident population. In relation to the analysis of pedestrian attraction, the itineraries were classified according to the level of service and in them were measured the criteria related to comfort, such as, presence of barriers, material and condition of the sidewalk. Moreover, in this analysis considers safety attributes, such as, signaling, ramps, crossing aids, and public illumination. These variables are analyzed on each street segment. The results show that the location of bus rapid transit stops in the city has an important role and can be optimized with the evaluation of the spatial configuration. In addition, this analysis allows to know the streets which could be intervened at the design level to facilitate pedestrian access to stops.

Measuring Spatial Accessibility of Healthcare Services in Calgary ( poster )

Access to healthcare is one of the deterministic factors in an individual’s quality of life. Ideally, access to healthcare facilities should be optimized for walkability and/or public transit, for all people, regardless of (dis)ability. However, spatial accessibility of health services in Calgary is often difficult to measure since there could be more than one walking or transit route from the neighborhood to the healthcare facility. The focus of this research is to map the spatial accessibility of healthcare facilities within Calgary census tracts, with a focus on vulnerable groups, including elderly, children, visually impaired pedestrians, and persons with disabilities. The spatial accessibility of healthcare facilities is measured by various proxies for accessible walkability, including sidewalks, public transit, and accessible pedestrian signal locations. Geographic Information Systems (GIS) are used to measure spatial accessibility to delineate spatial patterns and trends in the accessibility of health services in Calgary. The data sources for this study include Calgary’s 2016 census, health facilities data from the Alberta Health Services data portal, transit and walkability routes from the City of Calgary Open Data Catalogue, and the accessible pedestrian signal locations data. Specifically, the two-step floating catchment area approach is used to analyze the interactions between the built environment and the accessibility to healthcare. The results of this research developed an accessibility index as a proxy for spatial access to healthcare services. The cartographic outputs effectively illustrate the ease of access to the healthcare facility, including the interaction of transit, walkable routes, and the accessible pedestrian signal locations in Calgary. From the results obtained through this study, specific improvements can be made to the built environment to enhance the healthcare accessibility, by car-free means, for all residents inclusively. The ultimate aim of this research is to disseminate our results to empower stakeholders like Alberta Health Services, to direct their respective services towards inclusively enhancing Calgary’s spatial accessibility to healthcare.

Universality laws for randomized dimension reduction, with applications

AbstractDimension reduction is the process of embedding high-dimensional data into a lower dimensional space to facilitate its analysis. In the Euclidean setting, one fundamental technique for dimension reduction is to apply a random linear map to the data. This dimension reduction procedure succeeds when it preserves certain geometric features of the set. The question is how large the embedding dimension must be to ensure that randomized dimension reduction succeeds with high probability. This article studies a natural family of randomized dimension reduction maps and a large class of data sets. It proves that there is a phase transition in the success probability of the dimension reduction map as the embedding dimension increases. For a given data set, the location of the phase transition is the same for all maps in this family. Furthermore, each map has the same stability properties, as quantified through the minimum RSV. These results can be viewed as new universality laws in high-dimensional stochastic geometry. Universality laws for randomized dimension reduction have many applications in applied mathematics, signal processing and statistics. They yield design principles for numerical linear algebra algorithms, for compressed sensing measurement ensembles and for random linear codes. Furthermore, these results have implications for the performance of statistical estimation methods under a large class of random experimental designs.

Influence of polymorphism and the new trigonal modification on the mechanical response of isotactic poly(propylene-co-1-pentene-co-1-hexene) terpolymers

The mechanical response and crystalline structure have been analyzed in several propylene-co-1-pentene-co-1-hexene terpolymers. Different polymorphs are developed in these terpolymers depending on global comonomer content, 1-pentene:1-hexene ratio and thermal history. The trigonal δ crystal modification is observed in addition to monoclinic and orthorhombic crystallites and mesomorphic entities. For the terpolymers with higher comonomers contents, the mesophase and even the totally amorphous samples can be readily obtained at easily accessible cooling rates. Intensity and location of relaxation processes, values for storage and indentation modulus and hardness as well are found to be related to the type of crystallites and to the crystallinity. The variation of crystallinity upon the comonomer content is rather unusual when trigonal lattice is able to be developed if compared with that exhibited by other copolymers/terpolymers based on propylene. Because of the important effect of this variable on mechanical response and mobility within amorphous regions, relationships found in other mechanical parameters and in the relaxation associated with glass transition (location and intensity) are also uncommon. The presence of trigonal polymorph exerts a key role in those atypical dependences.

Internal Fit and Marginal Gap Evaluation of Zirconia Copings Using Microcomputed Tomography: An In Vitro Analysis.

The purpose of this in vitro study was to measure the marginal and internal fit of single-unit all-ceramic zirconia copings (ZCs) fabricated through three different computer-aided design/computer-assisted manufacture (CAD/CAM) systems using microcomputed tomography (microCT). A total of 10 ZCs were produced for each experimental group. Scanning of the stainless steel (SS) model with its respective copings was conducted with a SkyScan machine. DataViewer software was used to acquire cross-sectional images. Locations of cross-sections for all specimens were standardized to reduce errors. Seven different cross-section locations were selected: four transverse and three sagittal. Adobe Photoshop CS3 was used for the measurements. One-way analysis of variance and Tukey post hoc test were used for the statistical analysis for each group. In addition, t test (α = .05) was used to compare values at each measurement location for the different groups. The results of this study show significant differences in the precision of fit of the experimental groups at the axio-occlusal transition (AOT) location, with a significant gap present in the DeguDent CAD/CAM System compared to the other two systems. Tukey test results indicate a significant difference in the marginal gap between the DeguDent CAD/CAM System and KaVo Everest Dental CAD/CAM System (P = .004). In addition, there is a significant difference in gap size values in the sagittal sections distal to the midline between the DeguDent CAD/CAM System and the Lava Ultimate CAD/CAM System (P = .002). The different CAD/CAM systems showed a clinically acceptable internal fit and marginal adaptation. Different levels of fit were found between the experimental groups. Marginal adaptation was the best in all experimental groups. The gap at the AOT area varied among the three groups, with the DeguDent CAD/CAM System showing the greatest value.

Machine learning of frustrated classical spin models. I. Principal component analysis

This work aims at the goal whether the artificial intelligence can recognize phase transition without the prior human knowledge. If this becomes successful, it can be applied to, for instance, analyze data from quantum simulation of unsolved physical models. Toward this goal, we first need to apply the machine learning algorithm to well-understood models and see whether the outputs are consistent with our prior knowledge, which serves as the benchmark of this approach. In this work, we feed the compute with data generated by the classical Monte Carlo simulation for the XY model in frustrated triangular and union jack lattices, which has two order parameters and exhibits two phase transitions. We show that the outputs of the principle component analysis agree very well with our understanding of different orders in different phases, and the temperature dependences of the major components detect the nature and the locations of the phase transitions. Our work offers promise for using machine learning techniques to study sophisticated statistical models, and our results can be further improved by using principle component analysis with kernel tricks and the neural network method.

Multidisciplinary optimization of an NLF forward swept wing in combination with aeroelastic tailoring using CFRP

This article introduces a process chain for commercial aircraft wing multidisciplinary optimization (MDO) based on high fidelity simulation methods. The architecture of this process chain enables two of the most promising future technologies in commercial aircraft design in the context of MDO. These technologies are natural laminar flow (NLF) and aeroelastic tailoring using carbon fiber reinforced plastics (CFRP). With this new approach the application of MDO to a NLF forward swept composite wing will be possible. The main feature of the process chain is the hierarchical decomposition of the optimization problem into two levels. On the highest level the wing planform including twist and airfoil thickness distributions as well as the orthotropy direction of the composite structure will be optimized. The lower optimization level includes the wing box sizing for essential load cases considering the static aeroelastic deformations. Additionally, the airfoil shape adaptation based on sectional pressure distribution optimization and inverse design follows for the design point. Thereby, the objective function of the sectional pressure distribution optimization is the minimization of drag to find the best trade-off between profile drag considering NLF and transonic wave drag. First optimization results of the multidisciplinary process chain are presented for a forward swept wing aircraft configuration. At this stage, airfoil shape optimization has not been included yet. Instead, natural laminar flow is considered by prescribing laminar-turbulent transition locations.

Signature of inverse Compton emission from blazars

Blazars are classified into high, intermediate and low energy peaked sources based on the location of their synchrotron peak. This lies in infra-red/optical to ultra-violet bands for low and intermediate peaked blazars. The transition from synchrotron to inverse Compton emission falls in the X-ray bands for such sources. We present the spectral and timing analysis of 14 low and intermediate energy peaked blazars ob- served with XMMNewton spanning 31 epochs. Parametric fits to X-ray spectra helps constrain the possible location of transition from the high energy end of the syn- chrotron to the low energy end of the inverse Compton emission. In seven sources in our sample, we infer such a transition and constrain the break energy in the range 0.6 10 keV. The Lomb-Scargle periodogram is used to estimate the power spectral density (PSD) shape. It is well described by a power law in a majority of light curves, the index being flatter compared to general expectation from AGN, ranging here between 0.01 and 1.12, possibly due to short observation durations resulting in an absence of long term trends. A toy model involving synchrotron self-Compton (SSC) and exter- nal Compton (EC; disk, broad line region, torus) mechanisms are used to estimate magnetic field strength 6 0.03 - 0.88 G in sources displaying the energy break and infer a prominent EC contribution. The timescale for variability being shorter than synchrotron cooling implies steeper PSD slopes which are inferred in these sources.