Distinct Patches Research Articles

Upper Ocean Response to Two Sequential Tropical Cyclones over the Northwestern Pacific Ocean

The upper ocean thermodynamic and biological responses to two sequential tropical cyclones (TCs) over the Northwestern Pacific Ocean were investigated using multi-satellite datasets, in situ observations and numerical model outputs. During Kalmaegi and Fung-Wong, three distinct cold patches were observed at sea surface. The locations of these cold patches are highly correlated with relatively shallower depth of the 26 °C isotherm and mixed layer depth (MLD) and lower upper ocean heat content. The enhancement of surface chlorophyll a (chl-a) concentration was detected in these three regions as well, mainly due to the TC-induced mixing and upwelling as well as the terrestrial runoff. Moreover, the pre-existing ocean cyclonic eddy (CE) has been found to significantly modulate the magnitude of surface cooling and chl-a increase. With the deepening of the MLD on the right side of TCs, the temperature of the mixed layer decreased and the salinity increased. The sequential TCs had superimposed effects on the upper ocean response. The possible causes of sudden track change in sequential TCs scenario were also explored. Both atmospheric and oceanic conditions play noticeable roles in abrupt northward turning of the subsequent TC Fung-Wong.

Universal optimal geometry of minimal phoretic pumps

Unlike pressure-driven flows, surface-mediated phoretic flows provide efficient means to drive fluid motion on very small scales. Colloidal particles covered with chemically-active patches with nonzero phoretic mobility (e.g. Janus particles) swim using self-generated gradients, and similar physics can be exploited to create phoretic pumps. Here we analyse in detail the design principles of phoretic pumps and show that for a minimal phoretic pump, consisting of 3 distinct chemical patches, the optimal arrangement of the patches maximizing the flow rate is universal and independent of chemistry.

A failure mechanics and strength optimization study for patched laminates

Fiber patch placement (FPP) is a manufacturing technique for variable-stiffness composites structures. Using FPP, a component is assembled from a multitude of discrete fiber patches. Thus, FPP allows tailoring a composite layup to local load states. However, complex stress distributions occur due to discontinuous fibers at patch edges. This paper investigates the failure of unidirectional patched laminates and assesses the influence of governing design parameters on their strength by nonlinear FE analyses. It is found that, depending on their configuration, fiber breakage, yield-slip, or interface fracture are the leading causes of failure. Moreover, the study reveals that the outer layers of patched laminates are much more susceptible to failure than the inner layers. Based on these findings, three distinct patch overlapping patterns are derived, with each of them having their benefits at different locations in the design space. Lastly, strength optimization measures are investigated, aiming at a load reduction of the outer layers. Patched laminate configurations are found which, for intermediate patch length and thickness, feature up to 70% tensile strength retention compared to continuous laminates from the same material. The findings of this work give valuable guidance for the design and analysis of patched laminates.

Structural basis of tubulin detyrosination by the vasohibin-SVBP enzyme complex.

Vasohibins are tubulin tyrosine carboxypeptidases that are important in neuron physiology. We examined the crystal structures of human vasohibin 1 and 2 in complex with small vasohibin-binding protein (SVBP) in the absence and presence of different inhibitors and a C-terminal α-tubulin peptide. In combination with functional data, we propose that SVBP acts as an activator of vasohibins. An extended groove and a distinctive surface residue patch of vasohibins define the specific determinants for recognizing and cleaving the C-terminal tyrosine of α-tubulin and for binding microtubules, respectively. The vasohibin-SVBP interaction and the ability of the enzyme complex to associate with microtubules regulate axon specification of neurons. Our results define the structural basis of tubulin detyrosination by vasohibins and show the relevance of this process for neuronal development. Our findings offer a unique platform for developing drugs against human conditions with abnormal tubulin tyrosination levels, such as cancer, heart defects and possibly brain disorders.

Bifunctional Janus Spheres with Chemically Orthogonal Patches.

Bifunctional Janus particles with patches carrying orthogonal surface functionalities that can be independently modified are widely seen as promising building blocks for the bottom-up assembly of functional materials due to their full compositional and geometrical programmability. However, synthesis of these colloids remains an elusive task as current scalable procedures are generally limited to monofunctional particles only. Herein, a scalable bulk wet-chemical synthetic method for fabricating bifunctional Janus particles following a two-step dispersion polymerization is developed. Patch formation on these colloids is driven by the spontaneous phase separation between a brominated outer shell and poly(propargyl acrylate) (p(PA)), formed after the seed particles were swollen with the corresponding monomer. The size ratio between the two patches is readily tunable by controlling the volumetric ratio between the feeding monomers. The distinct patches of these Janus particles carry chemical handles facilitating independent and orthogonal surface modification using Atom Transfer Radical Polymerization (ATRP) and thiol-yne Click chemistry for the brominated and alkyne-containing patches, respectively. The presented route toward bifunctional patchy spheres provides a versatile starting point for the development of bifunctional colloidal particles with tailored directional properties.

Effect of two distinct patches of Myriophyllum species on downstream turbulence in a natural river

Velocity profiles upstream and downstream of two aquatic plant species that are similar in morphology but differ in patch structures were measured in a natural river. Turbulence statistics were analyzed after thorough data filtering. In the wake of the M. alterniflorum, which was a slender, 0.3 m wide and 1.2 m long patch of aspect ratio 1:4, there were distinctive peaks in both, turbulence intensity and turbulent kinetic energy, which indicated increased lateral mixing. In contrast to the M. alterniflorum, turbulence statistics in the wake of the M. spicatum, which was the larger, 2 m wide and 2.4 m long patch of aspect ratio 1:1.5, indicated increased lateral shear of a greater magnitude. The turbulent kinetic energy was diminished in the closest layer to the bed downstream the both plants, although, in the case of M. alterniflorum, the observed values were similar to those upstream. The occurrence of the mixing layer below the height of M. spicatum was visible in the power spectral density plot. In both cases, ejections in the wake diminished in favor of other coherent structures. The shape and configuration of a patch are decisive factors governing the occurrence of flow instabilities downstream of the patch.

Kinematics of the 2012 Ahar–Varzaghan complex earthquake doublet (Mw6.5 and Mw6.3)

On 2012 August 11, an earthquake doublet (Mw6.5 and Mw6.3), separated in time by 11 min, occur in the northwest of Iran. The hypocentres of these earthquakes are close (∼6 km) and located near the cities of Ahar and Varzaghan. The rupture process of both main shocks is retrieved by inverting the near-field strong motions data and using the elliptical subfault approximation method. Our calculations show that the two earthquakes are occurring on two distinct fault planes: the first main shock (M1) has nucleated at a depth of ∼8.5 km, and is located ∼4 km east of the eastern termination of the E-W trending surface rupture. The slip reaches the ground surface west of the hypocentre on an E-W striking fault (N88°E) that dips almost vertically (80°S). This earthquake exhibits a right-lateral strike-slip mechanism. The entire slip is imaged on a single patch that ruptures with an average speed of 2.4 km s−1. The rupture duration is ∼5.6 s and the earthquake releases a seismic moment of ∼8.41E + 18 N·m. The slip reaches the surface with a right-lateral dislocation value of ∼1 m, which is consistent with the observed surface rupture. About 11 min later, the second main shock (M2) nucleates ∼5 km to the west and 4 km to the north with respect to the hypocentre of the M1, and at a depth of ∼16.5 km. The M2 rupture evolves toward shallower depths and to the west on an ENE-WSW oriented fault plane (strike ∼256°) with a dip of ∼60° northward. The slip is essentially distributed on two distinct patches with strike-slip and reverse mechanisms, respectively. The first patch has a pure right-lateral strike-slip mechanism, and ruptures at a relatively fast speed of over 2.8 km s−1, and last for about 2.6 s until it reaches the second patch. The latter has a reverse mechanism (rake∼112°) and extends the rupture toward shallow depths, and to the west at a speed of ∼2.5 km s−1, and its rupture lasts for ∼2.5 s. The top of the slip distribution of M2 stops at a depth of ∼8 km. We observe that aftershocks surround the M1 and most of the M2 slip models. They are not distributed in the region of high slip (∼3.1 m) of M1. We show that the rupture of M2 is controlled by the static Coulomb stress changes caused by M1, with the maximum slip of M2 located in the positive Coulomb stress caused by M1. The M2 rupture stops where it reaches the area of high negative Coulomb stress change (over −10 bars). The cumulative Coulomb stress fields of both main shocks show a transfer of positive static Coulomb stress change of >0.1 bars on the eastern segment of the North Tabriz Fault. This segment did not rupture since the 1721 M∼7.6–7.7 event that has destroyed the city of Tabriz, and that currently hosts 2 million people. The occurrence of this earthquake doublet with different mechanisms reveals the slip partitioning of the oblique convergence regime of NW Iran on the Ahar–Varzaghan complex fault system.

A mutagenesis analysis of Tim50, the major receptor of the TIM23 complex, identifies regions that affect its interaction with Tim23

Maintenance of the mitochondrial proteome depends on import of newly made proteins from the cytosol. More than half of mitochondrial proteins are made as precursor proteins with N-terminal extensions called presequences and use the TIM23 complex for translocation into the matrix, the inner mitochondrial membrane and the intermembrane space (IMS). Tim50 is the central receptor of the complex that recognizes precursor proteins in the IMS. Additionally, Tim50 interacts with the IMS domain of the channel forming subunit, Tim23, an interaction that is essential for protein import across the mitochondrial inner membrane. In order to gain deeper insight into the molecular function of Tim50, we used random mutagenesis to determine residues that are important for its function. The temperature-sensitive mutants isolated were defective in import of TIM23-dependent precursor proteins. The residues mutated map to two distinct patches on the surface of Tim50. Notably, mutations in both patches impaired the interaction of Tim50 with Tim23. We propose that two regions of Tim50 play a role in its interaction with Tim23 and thereby affect the import function of the complex.

DFP-ALC: Automatic video summarization using Distinct Frame Patch index and Appearance based Linear Clustering

Video summarization aims to create a succinct representation of videos for efficient browsing and retrieval. We propose an innovative method for the task. It includes two main steps: (i) the first step proposes a Distinct Frame Patch (DFP) index for selecting a set of good candidate frames, and (ii) the second step proposes a novel Appearance based Linear Clustering (ALC) to refine them for distinct ones. While the first step measures the content of frames, the second step considers to what extent one frame is different from another in both the spatial and temporal spaces. The experiments are performed over two publicly accessible datasets. The results show the effectiveness and efficiency of the proposed method when compared with other state-of-the-art techniques.

Dynamic Multicontext Segmentation of Remote Sensing Images Based on Convolutional Networks

Semantic segmentation requires methods capable of learning high-level features while dealing with large volume of data. Towards such goal, Convolutional Networks can learn specific and adaptable features based on the data. However, these networks are not capable of processing a whole remote sensing image, given its huge size. To overcome such limitation, the image is processed using fixed size patches. The definition of the input patch size is usually performed empirically (evaluating several sizes) or imposed (by network constraint). Both strategies suffer from drawbacks and could not lead to the best patch size. To alleviate this problem, several works exploited multi-context information by combining networks or layers. This process increases the number of parameters resulting in a more difficult model to train. In this work, we propose a novel technique to perform semantic segmentation of remote sensing images that exploits a multi-context paradigm without increasing the number of parameters while defining, in training time, the best patch size. The main idea is to train a dilated network with distinct patch sizes, allowing it to capture multi-context characteristics from heterogeneous contexts. While processing these varying patches, the network provides a score for each patch size, helping in the definition of the best size for the current scenario. A systematic evaluation of the proposed algorithm is conducted using four high-resolution remote sensing datasets with very distinct properties. Our results show that the proposed algorithm provides improvements in pixelwise classification accuracy when compared to state-of-the-art methods.

Symptomology and yield impact of pea necrotic yellow dwarf virus (PNYDV) in faba bean (Vicia faba L. minor)

We surveyed 33 symptomatic faba bean sites in central Germany towards the end of the growing season 2016 to analyse the suspected virus spectrum. All sites displayed plants with characteristic symptoms and had distinct funnel-shaped patches with a severely affected centre. The central core consisted of stunted, prematurely senescent plants. Symptomatic foci were scattered at random over a largely symptomless field. At two exemplary investigation sites we combined ground based yield assessments with remote sensing techniques to describe disease-loss relationships. Based on low altitude true-colour aerial imaging data, symptomatic patches were categorised into: (i) severely affected blackish core region, (ii) yellowish symptomatic periphery, and (iii) a corresponding non-symptomatic reference patch. Serological tests revealed PNYDV (Pea necrotic yellow dwarf virus) together with PEMV (Pea enation mosaic virus) as dominant and equally abundant viruses. However, because PNYDV was significantly more restricted to the focal core than PEMV, we perceived PNYDV to be the causal agent for this apparently new symptom pattern in faba bean. As both viruses are vectored persistently by leguminous aphids, the observed symptom gradient within individual foci mirrored the epidemiological development over time, starting from an initial infection point and expanding towards the periphery via secondary virus spread to successively maturing and less susceptible plants. For each investigation site the segmented symptomatic surface of category (i) was 0.8 and 0.4%, for (ii) 20.5 and 6.4%, respectively. Combining the relative yield level for each symptom category with its respective surface, the overall yield gap at the field scale was extrapolated to 4.1 and 9.2% for grain yield and for 3.9 and 1.2% for crude protein. In the symptomatic core category, TKWs (thousand kernel weights) were halved due to enhanced proportions of shriveled grain. Because PNYDV-related yield decline was determined by the number, relative surface and disease intensity of individual foci, remote sensing techniques can offer valuable options for monitoring, loss assessment and agricultural decision-making.

Dispersal of open-habitat butterflies in managed forest landscapes: are colonisers special?

Forests managed by clear-cutting, rich in open spaces, provide alternative habitat for many grassland butterfly species in boreal and temperate environments. We have recently shown that local butterfly assemblages in forest openings are shaped by environmental filtering rather than dispersal limitation. However, at the level of individual movements, forest is known to form dispersal barrier for open-habitat butterflies—routine movements associated with resource exploitation do not result in dispersal in such landscapes. Typically, clear-cuts are varyingly surrounded by forest, meaning that movements between them and colonisation of newly created clear-cuts often require crossing hard boundaries between open habitat and matrix. Butterflies making such dispersal decisions may not be a random sample of individuals from the population. We used this semi-experimental landscape configuration with distinct habitat patches and matrix to examine if dispersal decisions are associated with special morphological phenotypes. Contrary to expectations, we found no significant associations between flight morphology and realised dispersal decisions—colonisers of isolated clear-cuts (fully surrounded by forest) did not differ from individuals of surrounding non-isolated habitats in any of measured wing traits. The differences in flight morphology between contrasting sites were negligible in all species and there were no consistent differences between males and females. As a possible interpretation, we link our findings to frequent, deterministic events of habitat loss and formation in forests managed by clear-cutting which may imply that virtually all phenotypes in such landscapes represent “dispersal phenotypes”.

Spatial heterogeneity and affecting factors of litter organic carbon and total nitrogen over natural spruce-fir mixed forests in northeastern China

Litter, as the basic carrier of nutrients, is a link between plants and soil in nutrient cycling and plays a major role in maintaining soil fertility and promoting material cycling and nutrient balance in forest ecosystems. The present study used geostatistics to investigate the spatial heterogeneity of organic carbon (OC) and total nitrogen (TN) in litter and their influencing factors, over four representative 1-ha natural spruce-fir mixed stands in Jilin Province, China. Our results showed that forest litter OC and TN varied in the four stands with an average OC concentration ranging from 378 to 453 g·kg−1 and average TN concentration ranging from 16.4 to 21.8 g·kg−1. The nugget-to-sill values were <25%, revealing that litter OC and TN had a strong spatial autocorrelation. Spatial distributions were estimated using ordinary kriging and showed a distinct strip and patch as the gradient changed. The fractal dimension of litter OC concentration was higher than that of litter TN. This indicated that litter OC had a more complex spatial pattern, whereas litter TN exhibited a better structure and stronger spatial dependence. Stand characteristics (i.e., species number, stem number, biodiversity indices, proportion of conifer species and stems), together with litter properties (i.e., litterfall, litter moisture content and total phosphorous concentration), affected the spatial variation in litter TN concentration, but they had no significant effects on litter OC. Therefore, this study demonstrated the feasibility of using geostatistics to predict litter nutrient concentrations at small scales and provided a theoretical basis for large-scale monitoring of biogeochemical cycles and disturbances in forest ecosystems.

A new signal of marine tropicalization in the Macaronesia region: First record of the mesophotic macroalga Avrainvillea canariensis A. Gepp & E.S. Gepp in the Madeira archipelago

Mesophotic green algal meadows of Avrainvillea canariensis are firstly reported for Madeira island. This represents a northern expansion of the species by nearly 500 km turning the species a Macaronesian endemism. The meadows of A. canariensis were found in a sandy bottom in the South coast of the island of Madeira, inside the Marine Park of Cabo Girão, covering an estimated area of 50 m2 at a depth range 25–30 m. The collected specimens reached about 12 cm in height and were found clustered, forming distinct patches. Since this type of subtidal surveys in soft bottoms are scant in Madeira, we cannot evaluate whether this is a recent colonization. Yet, this new record can be another clear sign of climate change effects in the madeiran benthic communities, a process previously documented in the Macaronesia region with the arrival and subsequent settlement of other warm water marine species.

Two pKM101-encoded proteins, the pilus-tip protein TraC and Pep, assemble on the Escherichia coli cell surface as adhesins required for efficient conjugative DNA transfer.

Mobile genetic elements (MGEs) encode type IV secretion systems (T4SSs) known as conjugation machines for their transmission between bacterial cells. Conjugation machines are composed of an envelope-spanning translocation channel, and those functioning in Gram-negative species additionally elaborate an extracellular pilus to initiate donor-recipient cell contacts. We report that pKM101, a self-transmissible MGE functioning in the Enterobacteriaceae, has evolved a second target cell attachment mechanism. Two pKM101-encoded proteins, the pilus-tip adhesin TraC and a protein termed Pep, are exported to the cell surface where they interact and also form higher order complexes appearing as distinct foci or patches around the cell envelope. Surface-displayed TraC and Pep are required for an efficient conjugative transfer, 'extracellular complementation' potentially involving intercellular protein transfer, and activation of a Pseudomonas aeruginosa type VI secretion system. Both proteins are also required for bacteriophage PRD1 infection. TraC and Pep are exported across the outer membrane by a mechanism potentially involving the β-barrel assembly machinery. The pKM101 T4SS, thus, deploys alternative routing pathways for the delivery of TraC to the pilus tip or both TraC and Pep to the cell surface. We propose that T4SS-encoded, pilus-independent attachment mechanisms maximize the probability of MGE propagation and might be widespread among this translocation superfamily.

Pseudo Rabies Virus Protein UL34 Interacted with UL31 to Disrupt the Human Lamin A

Pseudo rabies virus (PRV) egresses from the nucleus by budding from the inner nuclear membrane (INM). The nuclear lamina forms a rigid meshwork of intermediate filaments underlying the INM. It remains unknown whether PRV infection induces the disruption of lamina. In this paper, it can be observed that nuclear Lamin A became fractured during PRV infection. UL34 was localized at the nuclear rim, but UL31 was accumulated in the nucleus as distinct patches. Interestingly, a part of UL31 was localized at the INM in the presence of UL34. Immunoprecipitation (IP) assay confirmed that PRV UL31 and UL34 interacted in the transfected cells. Importantly, the co-expression of UL31 and UL34 directly disrupted Lamin A, resembling that observed during PRV infection. In conclusion, PRV infection induces the disruption of Lamin A, and UL34 and UL31 play a critical role in the disruption of Lamin A.

Structural Characterization of Competence-Stimulating Peptide Analogues Reveals Key Features for ComD1 and ComD2 Receptor Binding in Streptococcus pneumoniae.

Streptococcus pneumoniae is an important pathogen that utilizes quorum sensing (QS) to regulate genetic transformation, virulence, and biofilm formation. The competence-stimulating peptide (CSP) is a 17-amino acid signal peptide that is used by S. pneumoniae to trigger QS. S. pneumoniae strains can be divided into two main specificity groups based on the CSP signal they produce (CSP1 or CSP2) and their compatible receptors (ComD1 or ComD2, respectively). Modulation of QS in S. pneumoniae can be achieved by targeting the CSP:ComD interaction using synthetic CSP analogues. However, to rationally design CSP-based QS modulators with enhanced activities, an in-depth understanding of the structural features that are required for receptor binding is needed. Herein, we report a comprehensive in-solution three-dimensional structural characterization of eight CSP1 and CSP2 analogues with varied biological activities using nuclear magnetic resonance spectroscopy. Analysis of these structures revealed two distinct hydrophobic patches required for effective ComD1 and ComD2 binding.

Rusty blackbird patch use during winter in suburban landscapes

ABSTRACTThe rusty blackbird (Euphagus carolinus) is a species of conservation concern throughout its range because of rapid population decline. During winter, relatively large flocks are in suburban landscapes within the Georgia and South Carolina Piedmont Plateau of the southeastern United States. We studied radio‐tagged blackbirds within flocks that moved daily among 3 distinct patch types: pecan (Carya illinoinensis) and small‐seeded oak (Quercus spp.) groves, shallowly flooded forested wetlands, and residential areas landscaped with turf grass. The patch types used for foraging have varying availability of invertebrate and mast food. We investigated the relationship between daily observations of blackbird flocks and previous, current, and oncoming short‐term weather. Suburban landscapes with the appropriate configuration of shallow wetland, residential lawns, and mast grove patches within a 153–415‐ha area, the size of patch aggregations in this study, likely constitute high quality wintering areas for this species. Blackbird flocks were 1.6–1.8 times more likely to be observed foraging in wetlands with each 10°C increase in current temperature, 1.5 times more likely in wetlands for every 5 days with no previous precipitation, and 3.2 times more likely in wetlands with every 10 extra hours of oncoming cold weather. Blackbirds were 4.1–4.5 times less likely to be observed foraging in forested wetlands with every 5‐mm increase in current precipitation. Blackbirds were 2.2 times more likely to be observed in mast groves with every 5‐mm of oncoming precipitation. Radio‐tagged blackbirds used pecan groves for foraging in 2011 but not 2012, which was an overall warmer winter. Pecan groves may be a sporadically used component of a combination of foraging patches that are rarely near flooded forested wetlands or residential areas. Our results can be used to identify and conserve patch components used by rusty blackbird flocks during winter in suburban nature parks and greenways. © 2018 The Wildlife Society.

A positive-charged patch and stabilized hydrophobic core are essential for avirulence function of AvrPib in the rice blast fungus.

Fungal avirulence effectors, a key weapon utilized by pathogens to promote their infection, are recognized by immune receptors to boost host R gene-mediated resistance. Many avirulence effectors share sparse sequence homology to proteins with known functions, and their molecular and biochemical functions together with the evolutionary relationship among different members remain largely unknown. Here, the crystal structure of AvrPib, an avirulence effector from Magnaporthe oryzae, was determined and showed a high degree of similarity to the M.oryzae Avrs and ToxB (MAX) effectors. Compared with other MAX effectors, AvrPib has a distinct positive-charge patch formed by five positive-charged residues (K29, K30, R50, K52 and K70) on the surface. These five key residues were essential to avirulence function of AvrPib and affected its nuclear localization into host cells. Moreover, residues V39 and V58, which locate in the hydrophobic core of the structure, cause loss of function of AvrPib by single-point mutation in natural isolates. In comparison with the wild-type AvrPib, the V39A or V58A mutations resulted in a partial or entire loss of secondary structure elements. Taken together, our results suggest that differences in the surface charge distribution of avirulence proteins could be one of the major bases for the variation in effector-receptor specificity, and that destabilization of the hydrophobic core is one of the major mechanisms employed by AvrPib for the fungus to evade recognition by resistance factors in the host cell.

A spatial and statistical analysis of the impact of transformation of raster cost surfaces on the variation of least-cost paths

ABSTRACTPlanners who are involved in locational decision-making often use raster-based geographic information systems to quantify the value of land in terms of suitability or cost for a certain use. From a computational point of view, this process can be seen as a transformation of one or more sets of values associated with a grid of cells into another set of such values through a function reflecting one or more criteria. While it is generally anticipated that different transformations lead to different ‘best’ locations, little has been known on how such differences arise (or do not arise). The paper attempts to answer this question in the context of path planning through a series of computational experiments using a number of random landscape grids with a variety of spatial and nonspatial structures. In the experiments, we generated least-cost paths on a number of cost grids transformed from the landscape grids using a variety of transformation parameters and analyzed the locations and (weighted) lengths of those paths. Results show that the same pair of terminal cells may well be connected by different least-cost paths on different cost grids though derived from the same landscape grid and that the variation among those paths is affected by how given values are distributed in the landscape grid as well as by how derived values are distributed in the cost grids. Most significantly, the variation tends to be smaller when the landscape grid contains more distinct patches of cells potentially attracting or distracting cost-saving passage or when the cost grid contains a smaller number of low-cost cells.