Reverse Trajectory Research Articles

Calibration of backward-in-time model using drifting buoys in the East China Sea

Summary In the process of oil exploitation and transportation, large amounts of crude oil are often spilled, resulting in serious pollution of the marine environment. Forecasting oil spill reverse trajectories to determine the exact oil spill sources is crucial for taking proactive and effective emergency measures. In this study, the backward-in-time model (BTM) is proposed for identifying sources of oil spills in the East China Sea. The wind, current and random walk are three major factors in the simulation of oil spill sources. The wind drag coefficient varies along with the uncertainty of the wind field, and the random walk is sensitive to various traits of different regions, these factors are taken as constants in most of the state-of-the-art studies. In this paper, a self-adaptive modification mechanism for drift factors is proposed, which depends on a data set derived from the drifter buoys deployed over the East China Sea shelf. It can be well adapted to the regional characteristics of different sea areas. The correlation factor between predicted positions and actual locations of the drifters is used to estimate optimal coefficients of the BTM. A comparison between the BTM and the traditional method is also made in this study. The results presented in this paper indicate that our method can be used to predict the actual specific spillage locations.

SME growth trajectories, transitions and board role portfolios: A critical review and integrative model

This article presents a novel framework integrating a dynamic states approach to firm growth and a portfolio perspective of board roles. In our framework, we highlight four typical firm growth states aligned with primary board roles to guide firms effectively through the transitions associated with each state to reach a new equilibrium. The particular contribution of our framework is that it takes small and medium firm (SME) heterogeneity into account while capturing the dynamic nature of these states which are reached along non-linear, non-sequential and non-deterministic transitional pathways, as well as incorporating reverse and counterintuitive trajectories between states.

Multi-Channel Optical Isolator Based on Nonlinear Triangular Parity Time Symmetric Lattice

We report the design procedure for a broadband multi-channel cavity-less optical isolator composed of a triangular perturbed nonlinear parity time (PT) symmetric lattice. The interplay between the nonlinearity and the PT-symmetric lattice that results in nonreciprocal transmission enables us to design the isolator outputs and inputs positions as desired. In the transmitting regime, a number of solitons that are simultaneously launched into individual inputs positioned appropriately, on the waveguides’ gain sides in the periodic lattice, swing along the waveguide until they are self-trapped along the respective waveguides axes, where the isolator outputs are located. In the isolating regime, however, the solitons that are launched into the inputs—i.e., the outputs of the transmitting regime—propagate along the waveguides axes, until they exit from the new outputs. Simulations show that the neighboring soliton trajectories in each regime are completely isolated and so are the forward and reverse trajectories in each waveguide cell. Moreover, operation of this cavity-less PT-symmetric isolator that is designed on an inhomogeneous slab waveguide does not suffer from the narrow frequency band limitation, unlike their cavity-based counterparts.

Active microrheology of hydrodynamically interacting colloids: Normal stresses and entropic energy density

A single Brownian “probe” particle is driven by an external force through a colloidal suspension and its motion studied to elucidate the relative impacts of external, Brownian, and interparticle forces on the suspension stress. As the probe moves through the suspension, distortions to and relaxation of the particle arrangement give rise to nonequilibrium stress. The shape of the distorted microstructure is set by the strength of the external force, F0, relative to the entropic restoring force, kT/ath, of the suspension, and by the balance of microscopic forces between the constituent particles. The former is given by the Péclet number, Pe≡F0/(2kT/ath), where kT is the thermal energy and ath is the thermodynamic size of the particles. The latter comprise external, Brownian, and interparticle forces, and the sensitivity of each to flow strength Pe is set by the dimensionless repulsion range, κ≡(ath−a)/a, where a is the hydrodynamic size of the particles. The total stress comprises hydrodynamic and entropic contributions which manifest as Brownian, interparticle, and external force-induced stress. To analyze the influence of these forces on structure and suspension stress as they evolve with flow strength, we formulate and solve a Smoluchowski equation analytically in the dual limits of weak and strong external force and hydrodynamic interactions, and numerically for arbitrary values of Pe and κ. Nonequilibrium statistical mechanics are then utilized to compute elements of the stress tensor. Owing to the axisymmetric geometry of the microstructure about the line of the external force, only the diagonal elements are nonzero. When hydrodynamic interactions are negligibly weak, only the hard-sphere interparticle force matters regardless of the flow strength, and the results of Zia and Brady [J. Rheol. 56(5), 1175–1208 (2012)] are recovered whereby normal stresses scale as Pe2 and Pe in the limits of weak and strong forcing, respectively. That is, entropic forces dominate suspension stress regardless of the value of Pe when hydrodynamic interactions are weak. As the repulsion range κ shrinks, hydrodynamic interactions begin to play a role: When forcing is weak, Brownian disturbance flows provide the dominant contribution to suspension stress, but as Pe increases, the external force-induced stress takes over to dominate the total stress. Interestingly, the total suspension stress decreases as the strength of hydrodynamic interactions increases, regardless of the value of Pe. That is, hydrodynamic interactions suppress suspension stress. Owing to the dependence of hydrodynamic interactions on particle configuration, this stress suppression varies with flow strength: At low Pe, the stress scales as Pe2 and the suppression is quantitative, whereas at high Pe, the stress scales as Peδ, where 1 ≥ δ ≥ 0.799 for hydrodynamic interactions spanning from weak to strong. We identify the origin of such suppression via an analysis of pair trajectories: While entropic forces—interparticle repulsion and Brownian motion—destroy reversible trajectories, hydrodynamic interactions suppress structural asymmetry and this underlies the suppression of the nonequilibrium stress. We relate the stress to the energy density: Hydrodynamic interactions shield particles from direct collisions and promote fore-aft and structural symmetry, resulting in reduced entropic energy storage.

Extended fluctuation theorems for repeated measurements and feedback within Hamiltonian framework

We derive the extended fluctuation theorems in presence of multiple measurements and feedback, when the system is governed by Hamiltonian dynamics. We use only the forward phase space trajectories in the derivation. However, to obtain an expression for the efficacy parameter, we must necessarily use the notion of reverse trajectory. Our results show that the correction term appearing in the exponent of the extended fluctuation theorems is non-unique, whereas the physical meaning of the efficacy parameter is unique.

A pivot mutation impedes reverse evolution across an adaptive landscape for drug resistance in Plasmodium vivax.

BackgroundThe study of reverse evolution from resistant to susceptible phenotypes can reveal constraints on biological evolution, a topic for which evolutionary theory has relatively few general principles. The public health catastrophe of antimicrobial resistance in malaria has brought these constraints on evolution into a practical realm, with one proposed solution: withdrawing anti-malarial medication use in high resistance settings, built on the assumption that reverse evolution occurs readily enough that populations of pathogens may revert to their susceptible states. While past studies have suggested limits to reverse evolution, there have been few attempts to properly dissect its mechanistic constraints.MethodsGrowth rates were determined from empirical data on the growth and resistance from a set of combinatorially complete set of mutants of a resistance protein (dihydrofolate reductase) in Plasmodium vivax, to construct reverse evolution trajectories. The fitness effects of individual mutations were calculated as a function of drug environment, revealing the magnitude of epistatic interactions between mutations and genetic backgrounds. Evolution across the landscape was simulated in two settings: starting from the population fixed for the quadruple mutant, and from a polymorphic population evenly distributed between double mutants.ResultsA single mutation of large effect (S117N) serves as a pivot point for evolution to high resistance regions of the landscape. Through epistatic interactions with other mutations, this pivot creates an epistatic ratchet against reverse evolution towards the wild type ancestor, even in environments where the wild type is the most fit of all genotypes. This pivot mutation underlies the directional bias in evolution across the landscape, where evolution towards the ancestor is precluded across all examined drug concentrations from various starting points in the landscape.ConclusionsThe presence of pivot mutations can dictate dynamics of evolution across adaptive landscape through epistatic interactions within a protein, leaving a population trapped on local fitness peaks in an adaptive landscape, unable to locate ancestral genotypes. This irreversibility suggests that the structure of an adaptive landscape for a resistance protein should be understood before considering resistance management strategies. This proposed mechanism for constraints on reverse evolution corroborates evidence from the field indicating that phenotypic reversal often occurs via compensatory mutation at sites independent of those associated with the forward evolution of resistance. Because of this, molecular methods that identify resistance patterns via single SNPs in resistance-associated markers might be missing signals for resistance and compensatory mutation throughout the genome. In these settings, whole genome sequencing efforts should be used to identify resistance patterns, and will likely reveal a more complicated genomic signature for resistance and susceptibility, especially in settings where anti-malarial medications have been used intermittently. Lastly, the findings suggest that, given their role in dictating the dynamics of evolution across the landscape, pivot mutations might serve as future targets for therapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1090-3) contains supplementary material, which is available to authorized users.

Genomics: From sea to sea.

The genome sequence of the marine flowering plant eelgrass (Zostera marina) sheds light on how marine algae evolved into land plants before moving back to the sea. See Letter p.331 The seagrass Zostera marina, or eelgrass, is widely distributed throughout the Northern Hemisphere. It is therefore of considerable ecological importance but — as with other seagrasses — its coastal habitats are among the world's most threatened ecosystems. Jeanine Olsen and colleagues report the whole-genome sequence of Zostera. Their analyses provide insights into the evolutionary changes associated with the 'back to the sea' reverse evolutionary trajectory that has occurred in this angiosperm lineage, including the loss of the entire repertoire of stomatal genes, and the presence of sulfated cell-wall polysaccharides that are more macro-algal-like than plant-like.

Prostate diffusion imaging with distortion correction

PurposeDiffusion imaging in the prostate is susceptible to distortion from B0 inhomogeneity. Distortion correction in prostate imaging is not routinely performed, resulting in diffusion images without accurate localization of tumors. We performed and evaluated distortion correction for diffusion imaging in the prostate. Materials and methods28 patients underwent pre-operative MRI (T2, Gadolinium perfusion, diffusion at b=800s/mm2). The restriction spectrum protocol parameters included b-values of 0, 800, 1500, and 4000s/mm2 in 30 directions for each nonzero b-value. To correct for distortion, forward and reverse trajectories were collected at b=0s/mm2. Distortion maps were generated to reflect the offset of the collected data versus the corrected data. Whole-mount histology was available for correlation. ResultsAcross the 27 patients evaluated (excluding one patient due to data collection error), the average root mean square distortion distance of the prostate was 3.1mm (standard deviation, 2.2mm; and maximum distortion, 12mm). ConclusionImproved localization of prostate cancer by MRI will allow better surgical planning, targeted biopsies and image-guided treatment therapies. Distortion distances of up to 12mm due to standard diffusion imaging may grossly misdirect treatment decisions. Distortion correction for diffusion imaging in the prostate improves tumor localization.

Principal component analysis of electron beams generated in K-shell aluminum X-pinch plasma produced by a compact LC-generator

Principal component analysis (PCA) method is applied and compared with the line ratios of H-like and He-like transitions, in order to investigate the effects of electron beam on the K-shell Aluminum synthetic spectra. It is also used as a diagnostics to estimate the plasma parameters of K-shell Al X-pinch plasma spectrum. This spectrum is produced by the explosion of two 25-μm Al wires on a compact LC (40 kV, 200 kA) generator. The database for the principal component extraction is created over a previously developed, non-LTE, collisional radiative K-shell Aluminum model. As a result, PCA shows an agreement with the line ratios which are sensitive to plasma electron temperatures, densities and beam fractions. Principal component analysis also illustrates that the addition to the non-LTE model of a fraction f of electrons in an energetic beam, generates the clusters in a three dimensional vector space which are translations of each other and follows reverse v-shaped cascade trajectories, except for the f = 0.0 case. Modeling of a typical shot by PCA gives the plasma electron temperature of Te = 100 eV, density of Ne = 1 × 1020 cm−3 and hot electron fraction of f = 0.2 (with a beam energy centered at 10 keV).

Qianwei (‘avant-garde’) art in reform-era China: Divergence, reversal and the persistence of (subjective) realism

Abstract In this article attention will be drawn to ways in which so-called ‘qianwei’ (literally, ‘avant-garde’) Chinese art of the 1980s and early 1990s can be understood to diverge from and/or reverse positions, trajectories and intentions conventionally associated with the work of the European and North American politicized avant-gardes. It shall also be argued that those divergences and reversals are informed in part by the persistence of subjective realist approaches to artistic representation within the People’s Republic of China that not only differ in intent from the western avant-garde’s signature anti-aesthetic and anti-realist use of collage-montage, but also related postmodernist framings of contemporary art as a focus for the critical deconstruction of supposedly authoritative meanings.

Ontogenetic changes of the water status and accumulated soluble compounds in developing and ripening mume (Prunus mume) fruit measured by 1H-NMR analysis

The physiological changes of intact mume (Prunus mume Sieb. et Zucc. cv. Rinshu) fruit tissues were examined by measuring the physical states of cell-associated water in the fruit tissues with developing and ripening using 1H-NMR spectroscopy. We found that the water molecules in mume fruit tissues existed in several different compartments with different mobilities. Additionally, spectral recovery in the water proton indicated reverse relationships between the pericarps and seeds at the immature and mature stages. In the pericarp tissues, the longest T1 and longer T2 markedly increased, while those in the seeds decreased. From these results, the change in the water status with growth stage had reverse trajectories in the pericarp and seed of the fruit. In the pericarp tissues, both water uptake and dry weight prominently increased with ripening. The epidermis and inner parenchymal cells of the pericarp tissues remarkably enlarged as a sigmoidal growth curve. Membrane permeability, indicating a loss of membrane integrity, increased in the pericarp tissues. The elongation in the fully vacuolated cells and changes in the membrane permeability in the pericarp tissues with ripening correlated to the longest T1. In contrast, the high mobility of water in the seeds began to decrease with maturation, while oil began to accumulate. Thus, the mobility of water, as analyzed in this study, is considered to reflect the results of physiological changes such as cellular heterogeneity and spatial arrangements both in the pericarp and in seed tissues for mume fruit with development and ripening.

Análisis de la Controlabilidad de Estado de Sistemas Irreversibles Mediante Teoría de Conjuntos

The irreversible systems have been little studied within the control theory framework, although one of their relevant cases is the batch process control problem. Therefore, in this work a method for analysing state controllability of irreversible systems is proposed. The method uses set theory and its extension to batch processes. Definitions for Reversible Set and Controllable Trajectories Set, both for nonlinear systems, are given in order to analyze state controllability for irreversible systems. Additionally, an algorithm for calculating mentioned sets from the dynamic process knowledge is proposed. The proposal is applied to a batch process benchmark. Obtained simulation results demonstrate the advantages of that proposal to analyze the state controllability of irreversible systems.

Axially extended-volume C-arm CT using a reverse helical trajectory in the interventional room.

C-arm computed tomography (CT) is an innovative technique that enables a C-arm system to generate 3-D images from a set of 2-D X-ray projections. This technique can reduce treatment-related complications and may improve interventional efficacy and safety. However, state-of-the-art C-arm systems rely on a circular short scan for data acquisition, which limits coverage in the axial direction. This limitation was reported as a problem in hepatic vascular interventions. To solve this problem, as well as to further extend the value of C-arm CT, axially extended-volume C-arm CT is needed. For example, such an extension would enable imaging the full aorta, the peripheral arteries or the spine in the interventional room, which is currently not feasible. In this paper, we demonstrate that performing long object imaging using a reverse helix is feasible in the interventional room. This demonstration involved developing a novel calibration method, assessing geometric repeatability, implementing a reconstruction method that applies to real reverse helical data, and quantitatively evaluating image quality. Our results show that: 1) the reverse helical trajectory can be implemented and reliably repeated on a multiaxis C-arm system; and 2) a long volume can be reconstructed with satisfactory image quality using reverse helical data.

Oil spill hazard assessment using a reverse trajectory method for the Egadi marine protected area (Central Mediterranean Sea)

The Egadi Marine Protected Area (MPA) on the western side of the Sicily Channel (Central Mediterranean) is exposed to a high risk of oil pollution from the tanker routes connecting the eastern and western basins of the Mediterranean Sea. Areas where an oil spill would do most damage, and thus where surveillance should be concentrated, are identified in this study by Lagrangian tracers tracked backwards in time from points along the MPA perimeter using data spanning six years from 2006 to 2011. Results indicate that the areas where oil surveillance would be most beneficial are segments of the tanker routes south of Sicily (highly frequented) and north of Sicily (scarcely frequented), both extending about 150 miles from November to March and 100 miles in the other months. The third route, close to the Tunisian shore, is the most frequented by oil tankers but the threat period is limited to November and December.

Magnetically driven quantum heat engine.

We studied the efficiency of two different schemes for a magnetically driven quantum heat engine, by considering as the "working substance" a single nonrelativistic particle trapped in a cylindrical potential well, in the presence of an external magnetic field. The first scheme is a cycle, composed of two adiabatic and two isoenergetic reversible trajectories in configuration space. The trajectories are driven by a quasistatic modulation of the external magnetic-field intensity. The second scheme is a variant of the former, where the isoenergetic trajectories are replaced by isothermal ones, along which the system is in contact with macroscopic thermostats. This second scheme constitutes a quantum analog of the classical Carnot cycle.

Forced oscillations of an unbalanced rotor in nonisotropic bearings

The influence of anisotropy of elastic bearings on forced oscillations of a rotor with the static and moment unbalance is studied for the cases of its fastening on a rigid shaft and on a flexible one. The rotor with four degrees of freedom is considered. It is suggested that the shaft is fixed in linear elastic nonisotropic bearings. The differential equations of rotation of the rotor are written in complex variables, and an exact solution to the equation system is found that corresponds to the elliptical synchronous precession. The exact solution is a sum of two vectors, one of which parameterizes a forward precession, while another parameterizes a reverse precession. Amplitude-frequency characteristics of forward and reverse precessions and elliptical trajectories of the rotor axis ends are constructed. It is shown that, in case of nonisotropic bearings, both the forward and reverse precession, as well as the axis motion of nonsimple type (when its one end is moving forward, while another is moving in the reverse direction), can take place. The influence of anisotropy of elastic bearings also manifests itself by change in critical frequencies towards their reduction and by arising of additional critical frequencies in the bottom part of the spectrum, which significantly complicates dynamics of the high-speed rotor at the moment when it reaches the working angular speed.

Variabilidad espacial de los cambios de cauce en una rambla mediterránea en las seis últimas décadas (1946-2006)

An analysis of morphological changes during the last six decades is presented for the Rambla de Cervera, a Mediterranean ephemeral stream located in the eastern sector of the Iberian Mountain Range. The studied channel (16.5 km) has two contrasted sectors: a horst confined sector (5.5 km) and a graben sector (11 km). Channel changes were analysed through the analysis of aerial photographs, with geographical information systems (GIS) and comparison of topographic surveys made with a GPS-RTK. Between 1946 and 2006 the Rambla de Cervera, underwent channel adjustments comparable to those observed in other Mediterranean rivers. The gravel channel markedly narrowed, losing width (68.5%) and channel surface area (45.7%), and incision processes occurred along the entire study reach at an average depth of 3.5 m. The progressive reduction of discharge and sediment supply due to land use changes, gravel mining and hydroclimatic variability has been considered responsible for these changes. However, these morphological changes exhibit an interesting temporal variability, with a maximum decrease of the gravel channel in the period 1946-1956 and another clear narrowing stage between 1977 and 1991, whereas incision mainly progressed after 1977. In addition, a contrasted behavior between the graben and horst sectors has been observed and analyzed. The horst sector underwent a constant and continuous trend, whereas the graben sector had more intense changes and two stages with significant reverse trajectories. The differential behavior of the graben and horst sectors was caused by the different responses generated by the overlapping of the lack of sediment supply, the timing and intensity of flood events and the particular hydraulic conditions of both sectors. The hydraulic geometry of the different river sections conditioned the effectiveness of flood events, influencing on the existence or absence of floodplain destructive trajectories and on the stability of fluvial forms.

A Method of Estimating the Domain of Attraction for Nonlinear Discrete-Time Systems

This paper investigates the problem of estimating an asymptotic stability region of nonlinear polynomial discrete-time systems. To achieve an appropriate estimation of subsets of attraction regions for asymptotically stable equilibrium points, the reverse trajectory formalism is applied through the formulation of iterative algorithms. The developed methods enable us to obtain enlarged circular domains of attraction that are comparable with the ones obtained by delicate computational procedures. The main advantage of the synthesized algorithms is that they disregard the problem of constructing Lyapunov function to achieve the control target for nonlinear systems. An instructive example of a power electrical system is used as an illustration of the results of the synthesized approaches.

Reducing magnocellular processing of various motion trajectories tests single process theories of visual position perception

Spatial projection and temporal integration are two prominent theories of visual localization for moving stimuli which gain most of their explanatory power from a single process. Spatial projection theories posit that a moving stimulus' perceived position is projected forwards in order to compensate for processing delays (Eagleman & Sejnowski, 2007; Nijhawan, 2008). Temporal integration theories (Krekelberg & Lappe, 2000) suggest that an averaging over positions occupied by the moving stimulus for a period of time is the dominant process underlying perception of position. We found that when magnocellular (M) pathway processing was reduced, there were opposite effects on localization judgments when a smooth, continuous trajectory was used, compared to when the moving object suddenly appeared, or suddenly reversed direction. The flash-lag illusion was decreased for the continuous trajectory, but increased for the onset and reversal trajectories. This cross-over interaction necessitates processes additional to those proposed by either the spatial projection or temporal integration theories in order to explain the perception of the position of moving stimuli across all our conditions. Differentiating our onset trajectory conditions from a Fröhlich illusion, in a second experiment, we found a null Fröhlich illusion under normal luminance-defined conditions, significantly smaller than the corresponding flash-lag illusion, but significantly increased when M processing was reduced. Our data are most readily accounted for by Kirschfeld and Kammer's (1999) backward-inhibition and focal attention theory.

Suppression and Emergence of Granular Segregation under Cyclic Shear

While convective flows are implicated in many granular segregation processes, the associated particle-scale rearrangements are not well understood. A three-dimensional bidisperse mixture segregates under steady shear, but the cyclically driven system either remains mixed or segregates slowly. Individual grain motion shows no signs of particle-scale segregation dynamics that precede bulk segregation. Instead, we find that the transition from nonsegregating to segregating flow is accompanied by significantly less reversible particle trajectories and the emergence of a convective flow field.