Spatial Flow Patterns Research Articles

In vivo voltage-sensitive dye imaging of mouse cortical activity with mesoscopic optical tomography.

.Significance: Cellular layering is a hallmark of the mammalian neocortex with layer and cell type-specific connections within the cortical mantle and subcortical connections. A key challenge in studying circuit function within the neocortex is to understand the spatial and temporal patterns of information flow between different columns and layers.Aim: We aimed to investigate the three-dimensional (3D) layer- and area-specific interactions in mouse cortex in vivo.Approach: We applied a new promising neuroimaging method—fluorescence laminar optical tomography in combination with voltage-sensitive dye imaging (VSDi). VSDi is a powerful technique for interrogating membrane potential dynamics in assemblies of cortical neurons, but it is traditionally used for two-dimensional (2D) imaging. Our mesoscopic technique allows visualization of neuronal activity in a 3D manner with high temporal resolution.Results: We first demonstrated the depth-resolved capability of 3D mesoscopic imaging technology in Thy1-ChR2-YFP transgenic mice. Next, we recorded the long-range functional projections between sensory cortex (S1) and motor cortex (M1) in mice, in vivo, following single whisker deflection.Conclusions: The results show that mesoscopic imaging technique has the potential to investigate the layer-specific neural connectivity in the mouse cortex in vivo. Combination of mesoscopic imaging technique with optogenetic control strategy is a promising platform for determining depth-resolved interactions between cortical circuit elements.

Modeling the spatial pattern of sediment flow in lower Hugli estuary, West Bengal, India by quantifying suspended sediment concentration (SSC) and depth conditions using geoinformatics

Suspended sediment concentration (SSC) information on the coastal waters is necessary for understanding and management of the estuarine environment. It serves as an indicator of coastal erosion and deposition. It is challenging for a macro-tidal estuary like the Hugli with a complex hydrodynamic condition and depth variations to estimate suspended sediment concentration by field observations only. In the present study, we estimated suspended sediment concentration at different depths of the lower Hugli estuary in the post-monsoon season by using Sentinel-2 satellite data. Since SSC is highest in the monsoon months, the image of October 22, 2019 was selected, which was the earliest available cloud-free data. Furthermore, about forty water samples were collected from different depths on the same date and time of the satellite pass for ground truth verification and data calibration. An empirical multivariate regression algorithm was used to demarcate the SSC zones in the image and correlate them with depth variations. MIKE-21 hydrodynamic model was also used to assess the spatial pattern of sediment flow in the Hugli river estuary. Remote sensing and GIS have proved to be a useful framework to estimate the SSC of any water column’s surface layer to overcome the limitation posed by the field measurements alone.

Discovering spatial patterns of tourist flow with multi-layer transport networks

Transport is an integral part of the tourism industry. The tourist traveling patterns are highly dependent on the transport infrastructure in a tourism destinations. Based on the Social Network Theory, four centrality indicators and the transition possibility are adopted to explore the tourism flow network related to different modes of transportation and tourist transition capabilities in tourism destinations. A complex tourist itinerary visualization model uncovers the spatial structure of multi-layer tourist flows. Dunhuang, a rapidly growing tourist destination in Northwest China, reveals this patterning. Results show that: (1) The spatial structure and flow rate of the tourism flow network is significantly different when different transport modes are observed. (2) The tourists transition capability for different transport modes in the same region varies according to the geographic location and infrastructure level. (3) Tourists manifest different movement patterns among the available transport networks within a destination area.

Comparative Analysis of Calculated and Experimental Data on an Oscillating Flow Induced by the Gasdynamic Interaction of a Particle with a Shock Layer

A supersonic flow around a cylinder with a flat end is studied for the case in which a single particle is launched from the end surface towards the incident flow. Numerical modeling is carried out with allowance for the gas-dynamic interaction of the particle with the shock layer. High-resolution, adaptive, rectangular grids are used to obtain detailed spatial and temporal flow patterns. The calculation results are compared with experimental data. It is shown that a single, large particle moving along the axis of symmetry against the incident flow and crossing the bow shock wave causes a significant restructuring of the flow and the formation of complex shock-wave and vortex structures. An important role in the formation of the flow structure is played by the formation of a toroidal vortex, which leads to an “inviscid” separation of the incident flow from the axis of symmetry. A distinctive feature of the flow around a cylinder with a flat end is the oscillatory flow regime caused by alternating stages of growth and decay of a toroidal vortex. The patterns of the oscillating flow and the oscillation frequency obtained via numerical simulation are in good agreement with the experimental data.

Fine-scale landscape genetics unveiling contemporary asymmetric movement of red panda (Ailurus fulgens) in Kangchenjunga landscape, India

Wildlife management in rapid changing landscapes requires critical planning through cross cutting networks, and understanding of landscape features, often affected by the anthropogenic activities. The present study demonstrates fine-scale spatial patterns of genetic variation and contemporary gene flow of red panda (Ailurus fulgens) populations with respect to landscape connectivity in Kangchenjunga Landscape (KL), India. The study found about 1,309.54 km2 area suitable for red panda in KL—India, of which 62.21% area fell under the Protected Area network. We identified 24 unique individuals from 234 feces collected at nine microsatellite loci. The spatially explicit and non-explicit Bayesian clustering algorithms evident to exhibit population structuring and supported red panda populations to exist in meta-population frame work. In concurrence to the habitat suitability and landscape connectivity models, gene flow results supported a contemporary asymmetric movement of red panda by connecting KL—India in a crescent arc. We demonstrate the structural-operational connectivity of corridors in KL—India that facilitated red panda movement in the past. We also seek for cooperation in Nepal, Bhutan and China to aid in preparing for a comprehensive monitoring plan for the long-term conservation and management of red panda in trans-boundary landscapes.

Discriminative pattern of reduced cerebral blood flow in Parkinson\u2019s disease and Parkinsonism-Plus syndrome: an ASL-MRI study

BackgroundAccurate identification of Parkinson’s disease (PD) and Parkinsonism-Plus syndrome (PPS), especially in the early stage of the disease, is very important. The purpose of this study was to investigate the discriminative spatial pattern of cerebral blood flow (CBF) between patients with PD and PPS.MethodsArterial spin labeling (ASL) perfusion-weighted imaging was performed in 20 patients with PD (mean age 56.35 ± 7.56 years), 16 patients with PPS (mean age 59.62 ± 6.89 years), and 17 healthy controls (HCs, mean age 54.17 ± 6.58 years). Voxel-wise comparison of the CBF was performed among PD, PPS, and HC groups. The receiver operating characteristic (ROC) curve was used to evaluate the performance of CBF in discriminating between PD and PPS. The relationship between CBF and non-motor neuropsychological scores was assessed by correlation analysis.ResultsPD group showed a significantly decreased CBF in the right cerebelum_crus2, the left middle frontal gyrus (MFG), the triangle inferior frontal gyrus (IFG_Tri), the left frontal medial orbital gyrus (FG_Med_Orb) and the left caudate nucleus (CN) compared with the HC group (P < 0.05). Besides the above regions, the left supplementary motor area (SMA), the right thalamus had decreased CBF in the PPS group compared with the HC group (P < 0.05). PPS group had lower CBF value in the left MFG, the left IFG_Tri, the left CN, the left SMA, and the right thalamus compared with the PD group (P < 0.05). CBFs in left IFG_Tri, the left CN, the left SMA, and the right thalamus had moderate to high capacity in discriminating between PD and PPS patients (AUC 0.719–0.831). The CBF was positively correlated with the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) scores in PD patients, while positively correlated with the MMSE, Hamilton Anxiety Scale (HAMA), Hamilton Depression Scale (HAMD) scores in PPS patients (P < 0.05).ConclusionPD and PPS patients have certain discriminative patterns of reduced CBFs, which can be used as a surrogate marker for differential diagnosis.

How the completeness of spatial knowledge influences the evacuation behavior of passengers in metro stations: A VR-based experimental study

Emergency evacuation in metro stations could be highly challenging due to complex underground environments, dynamic hazards and high-density crowds. There are different types of metro passengers, such as first-time visitors and daily commuters, who may possess different levels of prior spatial knowledge about the metro station. While spatial knowledge is known as an influential factor on people's indoor wayfinding behavior, it has largely remained unknown whether and how the level of completeness of prior spatial knowledge would affect people's wayfinding behavior during emergency evacuation in underground environments such as metro stations. Motivated by this gap, this study aimed to examine the effect of completeness of spatial knowledge on the evacuation behavior of passengers in metro stations, as they observed different patterns of crowd flow. An evacuation experiment was conducted in an immersive virtual environment, which was a virtual representation of a real metro station in Beijing. Participants were divided into six groups according to a 3 × 2 between-participants design. Participants could possess none, partial or complete spatial knowledge of the metro station, acquired from a spatial exploration task, prior to evacuation. Meanwhile, they could observe two patterns of crowd flow, modeled by having virtual avatars evacuating from the metro station evenly or unevenly split at every decision point (DP) along the evacuation routes. Five wayfinding performance measures, as well as the emotional responses, sense of direction, wayfinding anxiety, simulator sickness and sense of presence of all participants were collected and analyzed. The results showed that the completeness of spatial knowledge significantly impacted all measures of participants' evacuation performance, and that the pattern of crowd flow significantly impacted participants' evacuation speed, route choice, and directional choices at two DPs. Significant interaction effect between completeness of spatial knowledge and pattern of crowd flow was observed, which negatively impacted participants' evacuation time, distance and speed. The behavioral explanations underlying these findings, their practical implications and future work are also discussed in the paper.

The Impact of Virtual Water on Sustainable Development in Gansu Province

The concept of virtual water, as a new approach for addressing water shortage and safety issues, can be applied to support sustainable development in water-scarce regions. Using the input-output method, the direct and the complete water use coefficients of industries categorized as primary, secondary, or tertiary, and the spatial flow patterns of the inter-provincial trade in the Gansu province region of China, were explored. The results show that in 2007, 2010, and 2012 the direct and complete water use coefficients of the primary industries were the greatest among the three industry categories, with direct water use coefficients of 1545.58, 882.28, and 762.16, respectively, and complete water use coefficients of 1692.22, 1005.38, and 873.44, respectively; whereas, the direct and complete water use coefficient values of the tertiary industry category were the lowest, with direct water use coefficients of 16.65, 7.74, and 66.89 for 2007, 2010, and 2012, respectively, and complete water use coefficients of 65.46, 66.89, and 72.81 for 2007, 2010, and 2012, respectively. In addition, study results suggest that the volume of virtual water supplied to Gasnu province’s local industries has decreased annually, while virtual water exports from the province have increased annually, with the primary industry accounting for 95% of virtual water output. Overall, the virtual water of Gansu province in 2010 showed a net output trend, with a total output of 0.506 billion m3, while in 2007 and 2012 it showed a net input trend with a total input of 0.104 and 1.235 billion m3, respectively. Beijing, Shanghai, Guangdong, Ningxia and other water-scarce areas were the main input, or import source for Gansu’s virtual water; during the years studied, these provinces imported more than 50 million m3 individually. Based on these results, it is clear that under the current structure, virtual water is mainly exported to the well-developed coastal areas and their adjacent provinces or other water-abundant regions. Therefore, Gansu province should (1) adjust the industrial structure and develop water-saving and high-tech industries; (2) adjust the current trade pattern to reduce virtual water output while increasing its input to achieve balanced economic development and water resource security.

Spatial flow pattern and optimization of Sinopec's first distribution of refined oil of Jiangsu province

Spatial flow pattern and optimization of Sinopec's first distribution of refined oil of Jiangsu province

Exploring Spatial and Temporal Connection Patterns among the Districts in Chongqing Based on Highway Passenger Flow

Investigating regional connections and their influencing factors from the perspective of “flow” space is one of the foundations of promoting regional development. In this article, the data we used includes actual highway passenger flow data, National Polar-orbiting Partnership/Visible Infrared Imaging Radiometer Suite (NPP/VIIRS) nighttime light remote sensing data, and socioeconomic data. We analyzed the spatial distribution pattern, connection intensity and spatial autocorrelation of highway passenger flow in Chongqing during the working day, weekend and May Day and revealed the influencing factors by means of a geographic detector. Three key conclusions resulted from this research. First, highway passenger flow in Chongqing districts exhibits spatial agglomeration that is clearly higher in western Chongqing than in eastern Chongqing and forms an obviously dual-core “star” structure, with the main urban area and Wanzhou serving as the core. Second, a factor detector notes that the nighttime light area index (0.9251, 0.9512, 0.9541) has the strongest explanatory power for the spatial differentiation of passenger traffic in Chongqing districts, which is the key factor. Third, interaction detection shows that the interaction between the two factors displays an enhancement effect at different times. The nighttime light area index shows the strongest explanatory power under the synergy of tourist attractions, which are 0.9850, 0.9903 and 0.9908. But the per capita GDP and highway mileage have the most obvious enhancement effect after interaction (0.9544, 0.9661, 0.9652). Therefore, in future planning and development, we should pay attention to cooperation and exchanges between districts and use the nighttime light area index as an important reference factor to provide a scientific basis for the construction of public transport and economic construction in Chongqing.

Disrupted Information Flow in Resting-State in Adolescents With Sports Related Concussion.

Children and youths are at a greater risk of concussions than adults, and once injured, take longer to recover. A key feature of concussion is an increase in functional connectivity, yet it remains unclear how changes in functional connectivity relate to the patterns of information flow within resting state networks following concussion and how these relate to brain function. We applied a data-driven measure of directed effective brain connectivity to compare the patterns of information flow in healthy adolescents and adolescents with subacute concussion during the resting state condition. Data from 32 healthy adolescents (mean age =16 years) and 21 concussed adolescents (mean age = 15 years) within 1 week of injury were included in the study. Five minutes of resting state data EEG were collected while participants sat quietly with their eyes closed. We applied the information flow rate to measure the transfer of information between the EEG time series of each individual at different source locations, and therefore between different brain regions. Based on the ensemble means of the magnitude of normalized information flow rate, our analysis shows that the dominant nexus of information flow in healthy adolescents is primarily left lateralized and anterior-centric, characterized by strong bidirectional information exchange between the frontal regions, and between the frontal and the central/temporal regions. In contrast, adolescents with concussion show distinct differences in information flow marked by a more left-right symmetrical, albeit still primarily anterior-centric, pattern of connections, diminished activity along the central-parietal midline axis, and the emergence of inter-hemispheric connections between the left and right frontal and the left and right temporal regions of the brain. We also find that the statistical distribution of the normalized information flow rates in each group (control and concussed) is significantly different. This paper is the first to describe the characteristics of the source space information flow and the effective connectivity patterns between brain regions in healthy adolescents in juxtaposition with the altered spatial pattern of information flow in adolescents with concussion, statistically quantifying the differences in the distribution of the information flow rate between the two populations. We hypothesize that the observed changes in information flow in the concussed group indicate functional reorganization of resting state networks in response to brain injury.

Cross-Verification of 1D and 3D Models for a VVER-1000 Reactor’s Pressure Chamber Simulated by the KORSAR/CFD Computation Code in the Modes with Asymmetric Loop Operation

The KORSAR/CFD code results from the development of the KORSAR/GP system code certified in 2009 by the Rostekhnadzor (Federal Service for Ecological, Technological, and Nuclear Supervision) as applied to the calculated justification of the safety for VVER reactors. One of the important aspects of the development consists in the introduction of the CFD-module code into functional content for the simulation of spatial turbulent flows in the mixing chambers of reactors using a nested boundary method in the RANS-approximation. The CFD module is combined with a 1D model according to a semi-implicit scheme as a standard code element. Based on the calculations performed for three modes with an asymmetrical equipment operation in the heat-transfer loops of the VVER-1000 reactor, cross-verification has been performed for a 3D model in the CFD approximation, and a quasi-3D-multichannel model of the KORSAR/CFD computation code for the reactor pressure chamber. For cross-verification, the following modes have been chosen: breaking steam pipeline in a steam generator, connecting the main circulation pump while initially operating three pumps at the reactor power of 71% with respect to the nominal value, connecting a pump while initially operating two opposite pumps at the reactor power of 52% with respect to the nominal value. The scenario of the chosen modes is characterized by a decrease in the heat-carrier temperature at the entry into the pressure chamber from a single loop, which leads to an asymmetric increase in the reactor power with respect to the fuel assemblies owing to a negative reactivity effect. It is shown that, because of the artificial increase in the resistance to the downward heat-carrier flow along the channels that represent a pressure chamber in the multichannel calculation scheme, the reproduction of a spatial in-chamber flow pattern obtained using the 3D model of the chamber and its effect exerted on temperature change in the course of the heat-carrier stirring have been gained. The results of calculation using this scheme are in good agreement with data obtained by means of the 3D simulation of the pressure chamber in the CFD approximation in all the considered modes. A sensitivity of the calculation results with respect to changes in the calculation scheme under using the quasi-3D multichannel model of the reactor chamber is demonstrated.

Multiple incursion pathways for Helicoverpa armigera in Brazil show its genetic diversity spreading in a connected world

The Old World cotton bollworm Helicoverpa armigera was first detected in Brazil with subsequent reports from Paraguay, Argentina, Bolivia, and Uruguay. This pattern suggests that the H. armigera spread across the South American continent following incursions into northern/central Brazil, however, this hypothesis has not been tested. Here we compare northern and central Brazilian H. armigera mtDNA COI haplotypes with those from southern Brazil, Uruguay, Argentina, and Paraguay. We infer spatial genetic and gene flow patterns of this dispersive pest in the agricultural landscape of South America. We show that the spatial distribution of H. armigera mtDNA haplotypes and its inferred gene flow patterns in the southwestern region of South America exhibited signatures inconsistent with a single incursion hypothesis. Simulations on spatial distribution patterns show that the detection of rare and/or the absence of dominant mtDNA haplotypes in southern H. armigera populations are inconsistent with genetic signatures observed in northern and central Brazil. Incursions of H. armigera into the New World are therefore likely to have involved independent events in northern/central Brazil, and southern Brazil/Uruguay-Argentina-Paraguay. This study demonstrates the significant biosecurity challenges facing the South American continent, and highlights alternate pathways for introductions of alien species into the New World.

Hydrodynamics and heat exchange of crystal pulling from melts. Part I: Experimental studies of free convection mode

This work is a brief overview of experimental study results for hydrodynamics and convective heat exchange in thermal gravity capillary convection modes for the classic Czochralski technique setup obtained at the Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences. The experiments have been carried out at test benches which simulated the physics of the Czochralski technique for 80 and 295 mm diameter crucibles. Melt simulating fluids with Prandtl numbers Pr = 0.05, 16, 45.6 and 2700 have been used. Experiments with transparent fluids have been used for comparing the evolution of flow structure from laminar mode to well-developed turbulent mode. Advanced visualization and measurement methods have been used. The regularities of local and integral convective heat exchange in the crucible/melt/crystal system have been studied. The experiments have shown that there are threshold Grashof and Marangoni numbers at which the structure of the thermal gravity capillary flow undergoes qualitative changes and hence the regularities of heat exchange in the melt change. The effect of melt hydrodynamics on the crystallization front shape has been studied for Pr = 45.6. Crystallization front shapes have been determined for the 1 × 105 to 1.9 × 105 range of Grashof numbers. We show that the crystallization front shape depends largely on the spatial flow pattern and the temperature distribution in the melt.

Hydrodynamics and heat exchange of crystal pulling from melts. Part I: Experimental studies of free convection mode

This work is a brief overview of experimental study results for hydrodynamics and convective heat exchange in thermal gravity capillary convection modes for the classic Czochralski technique setup obtained at the Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences. The experiments have been carried out at test benches which simulated the physics of the Czochralski technique for 80 and 295 mm diameter crucibles. Melt simulating fluids with Prandtl numbers Pr = 0.05, 16, 45.6 and 2700 have been used. Experiments with transparent fluids have been used for comparing the evolution of flow structure from laminar mode to well-developed turbulent mode. Advanced visualization and measurement methods have been used. The regularities of local and integral convective heat exchange in the crucible/melt/crystal system have been studied. The experiments have shown that there are threshold Grashof and Marangoni numbers at which the structure of the thermal gravity capillary flow undergoes qualitative changes and hence the regularities of heat exchange in the melt change. The effect of melt hydrodynamics on the crystallization front shape has been studied for Pr = 45.6. Crystallization front shapes have been determined for the 1 × 105 to 1.9 × 105 range of Grashof numbers. We show that the crystallization front shape depends largely on the spatial flow pattern and the temperature distribution in the melt.

Blood flow kinetics of a xenogeneic collagen matrix following a vestibuloplasty procedure in the human gingiva—An explorative study

The aim of the present study was to investigate temporal and spatial blood flow patterns following vestibuloplasty procedures using a collagen matrix (CM) to get an insight into the timing and direction of neovascularization in the CM. Five patients were treated using a modified apically repositioned flap combined with a CM. Intraoral photographs and blood flow measurements by laser speckle contrast imaging were taken for 12months. Thirty regions of interest in the graft and the surrounding mucosa were evaluated. The clinical parameters were assessed after 6 and 12months. VEGF expression was analyzed in the wound fluid on days 2 and 4. At 6months, the mean width of keratinized gingiva increased, but the thickness was unchanged. Scar formation was observed in all cases. Perfusion in the graft began to increase at the lateral and coronal edges and then spread concentrically toward the center. The apical side showed a significant delay in perfusion, the highest VEGF expression, and wound fluid production as well as the most abundant scar formation. Neovascularization occurs mainly from the lateral and coronal edges, which may limit the extent of the surgical area. Abundant scar formation may be explained by increased VEGF expression induced by prolonged ischemia in this area.

Analyzing Spatial Community Pattern of Network Traffic Flow and Its Variations across Time Based on Taxi GPS Trajectories

The transport system is a critical component of the urban environment in terms of its connectivity, aggregation, and dynamic functions. The transport system can be considered a complex system due to the massive traffic flows generated by the spatial interactions between land uses. Benefiting from the recent development of location-aware sensing technologies, large volumes of traffic flow data (e.g., taxi trajectory data) have been increasingly collected in spatial databases, which provides new opportunities to interpret transport systems in cities. This paper aims to analyze network traffic flow from the perspective of the properties of spatial connectivity, spatial aggregation, and spatial dynamics. To this end, we propose a three level framework to mine intra-city vehicle trajectory data. More specifically, the first step was to construct the network traffic flow, with nodes and edges representing the partitioned regions and associated traffic flows, respectively. We then detected community structures of network traffic flow based on their structural and traffic volume properties. Finally, we analyzed the variations of those communities across time for the dynamic transport system. Through experiments in Beijing city, we found that the method is effective in interpreting the mechanisms of urban space, and can provide references for administrative divisions.

Gene flow and genetic structure in Acacia stenophylla (Fabaceae): Effects of hydrological connectivity

AbstractAimRiparian ecosystems are regarded as vulnerable to the effects of climate change. Because of their reliance on passive dispersal to migrate from areas where conditions have become unfavourable, plants are particularly susceptible. On dryland river floodplains, the species diversity of herbaceous annuals is often high while that of structurally dominant woody perennials is low. We examined gene flow genetic structure and dispersal in Acacia stenophylla, a small perennial tree widely distributed throughout river systems of inland Australia. The role of the river corridor in shaping patterns of gene flow and genetic structure is also investigated.LocationMurray‐Darling Basin, south eastern AustraliaMethodsA total of 127 individuals, from 12 subpopulations located on seven rivers were genotyped at 13 microsatellite loci. Several population and landscape genetic tools were applied to the microsatellite data to evaluate spatial patterns of gene flow and genetic structure and make inferences regarding possible modes of dispersal.ResultsHigh gene flow and weak genetic structure was identified for the 12 subpopulations of A. stenophylla sampled, a surprising result given large distances between subpopulations. Pairwise genetic distance between subpopulations was low to moderate and could largely be explained (R2 = 0.68) by two variables: distance along the river and the proportion of no flow days. structure analysis revealed two genetic clusters. Subpopulations located on the Darling and Lower Balonne rivers were dominated by cluster one while subpopulations from the Warrego and Paroo rivers showed largely mixed ancestry with individuals descending from both clusters one and two.Main ConclusionsThese results indicate that the river corridor facilitates extensive gene flow between subpopulations of A. stenophylla in this system. Hydrochory appears to be the dominant process; however, upstream movements of propagules most probably via animal movement are sufficient to negate effects expected under unidirectional dispersal.

Flow Cross K-function: a bivariate flow analytical method

ABSTRACTSpatial flow data represent meaningful interaction activities between pairs of corresponding locations, such as daily commuting, animal migration, and merchandise shipping. Despite recent advances in flow data analytics, there is a lack of literature on detecting bivariate or multivariate spatial flow patterns. In this paper we introduce a new spatial statistical method called Flow Cross K-function, which combines the Cross K-function that detects marked point patterns and the Flow K-function that detects univariate flow clustering patterns. Flow Cross K-function specifically assesses spatial dependence of two types of flow events, in other words, whether one type of flows is spatially associated with the other, and if so, whether this is according to a clustering or dispersion trend. Both a global version and a local version of Flow Cross K-function are developed. The former measures the overall bivariate flow patterns in the study area, while the latter can identify anomalies at local scales that may not follow the global trend. We test our method with carefully designed synthetic data that simulate the extreme situations. We exemplify the usefulness of this method with an empirical study that examines the distributions of taxi trip flows in New York City.

Three-dimensional CFD study of a β-type Stirling Engine

A three-dimensional beta-type Stirling Engine is simulated with the use of Computational Fluid Dynamics. Numerical modelling enables the study of gas properties spatial distribution and gas flow patterns, as well as the understanding of the effects of engine’s design. Results include the time variation of mean pressure and pressure drop, mass flow-rate and heat transfer, as well as the time variation and spatial distribution of temperature. The biggest portion of pressure drop is observed at the interfaces between adjacent engine spaces, where the flow patterns of working gas change rapidly. In addition to that, temperature is not uniform inside each engine space at a given time instance. Moreover, a time interval of about 60° of crank angle is found, during which gas is flowing towards opposite directions in two different engine spaces. The results coming from the simulation are validated against a third order one-dimensional model. The work output of the simulated engine and the indicated work of the analytical model are in good agreement. Moreover, the efficiency resulting from the simulation is close to the efficiency of a real Stirling Engine. The magnitude of the thermal losses is within the range suggested by the bibliography for a beta-type rhombic-drive Stirling Engine similar to the simulated engine.