Low Gradient Regions Research Articles

Collection of serum albumin aggregate nanoparticles from human plasma by dielectrophoresis.

Dielectrophoresis (DEP) is a fast and reliable nanoparticle recovery method that utilizes nonuniform electric fields to manipulate particles based on their material composition and size, enabling recovery of biologically-derived nanoparticles from plasma for diagnostic applications. When applying DEP to undiluted human plasma, collection of endogenous albumin proteins was observed at electric field gradients much lower than predicted by theory to collect molecular proteins. To understand this collection, nanoparticle tracking analysis of bovine serum albumin (BSA) dissolved in 0.5× phosphate-buffered saline was performed and showed that albumin spontaneously formed aggregate nanoparticles with a mean diameter of 237nm. These aggregates experienceda dielectrophoretic force as a function of aggregate radius rather than the diameter of individual protein molecules which contributed to their collection. In high conductance buffer (6.8mS/cm), DEP was able to move these aggregates into regions of high electric field gradient, and in lower conductance buffer (0.68mS/cm), these aggregates could be moved into high or low gradient regions depending on the applied frequency. Disruption of BSA aggregates using a nonionic detergent significantly decreased the particle diameter, resulting in decreased dielectrophoretic collection of albumin which increased the collection consistency of particles of interest. These results provide techniques to manipulate albumin aggregates via DEP, which impacts collection of diagnostic biomarkers.

Patient-specific quality assurance of dynamically-collimated proton therapy treatment plans.

The dynamic collimation system (DCS) provides energy layer-specific collimation for pencil beam scanning (PBS) proton therapy using two pairs of orthogonal nickel trimmer blades. While excellent measurement-to-calculation agreement has been demonstrated for simple cube-shaped DCS-trimmed dose distributions, no comparison of measurement and dose calculation has been made for patient-specific treatment plans. To validate a patient-specific quality assurance (PSQA) process for DCS-trimmed PBS treatment plans and evaluate the agreement between measured and calculated dose distributions. Three intracranial patient cases were considered. Standard uncollimated PBS and DCS-collimated treatment plans were generated for each patient using the Astroid treatment planning system (TPS). Plans were recalculated in a water phantom and delivered at the Miami Cancer Institute (MCI) using an Ion Beam Applications (IBA) dedicated nozzle system and prototype DCS. Planar dose measurements were acquired at two depths within low-gradient regions of the target volume using an IBA MatriXX ion chamber array. Measured and calculated dose distributions were compared using 2D gamma analysis with 3%/3mm criteria and low dose threshold of 10% of the maximum dose. Median gamma pass rates across all plans and measurement depths were 99.0% (PBS) and 98.3% (DCS), with a minimum gamma pass rate of 88.5% (PBS) and 91.2% (DCS). The PSQA process has been validated and experimentally verified for DCS-collimated PBS. Dosimetric agreement between the measured and calculated doses was demonstrated to be similar for DCS-collimated PBS to that achievable with noncollimated PBS.

Route-Based Energy Analysis of Hybrid Rail Consists

Abstract Adding battery locomotives to traditional diesel locomotives to form a hybrid consist has the potential to reduce fuel consumption and emissions in freight rail operations. This paper provides route-based estimates of diesel (hpd/ton) and battery (hpb/ton) power requirements and diesel (gal/ton) and battery (hpbhr/ton) energy requirements for hybrid consists. Given a route-specific power profile, the power split between the battery pack and the diesel engine is optimized to minimize fuel consumption by running the diesel engine at maximum efficiency during the entire route. Simulations for 200-mile round trips between Chicago and Harrisburg show that the diesel power is maximum in low-gradient regions at 1.05 (hpd/ton) and battery power is maximum in hilly regions at 2 (hpb/ton) for discharge and 6.5 (hpb/ton) for charge. Maximum fuel efficiency gains of approximately 60% are seen in the mountains, where 2.09 (hpbhr/ton) of battery energy is needed. Minimum fuel economy gains are observed in flat regions, with 20% fuel consumption reduction. With battery current and voltage limits, the battery pack size increases, and fuel savings decrease.

Effects of Edge Heating and Strain Gradient on Stretch Flange Deformation Limit of Steel Sheet

To improve the stretch flange deformation limit of ultrahigh-strength steels, a partial edge heating method was investigated. The effect of the strain gradient on the stretch flange deformation limit when a partial edge heating method was applied was investigated by the hole expansion test and FEM analysis. The stretch flange formability was improved by application of a partial edge heating method because of the recovery of the shearing microstructure and the reduction of the hardness difference of microstructure. It was found that the improvement of the deformation limit strain for the strain gradient with edge heating depends on the strain gradient region. In the low strain gradient region, the improvement margin of the deformation limit strain with edge heating was small. On the other hand, in the high strain gradient region, the deformation limit strain was markedly improved compared with that without heating. It was confirmed that the strain gradient in the direction perpendicular to the maximum principal strain could be used for the prediction of the deformation limit and also the determination of the stretch flange fracture by the FEM analysis of actual parts even under edge heating conditions.

The effect of dose gradients on gamma comparison insensitivity in patient specific QA comparisons.

While many have speculated on the reasons for gamma comparison insensitivity for patient-specific quality assurance analysis, the true reasons for insensitivity have not yet been elucidated. Failing to understand the reasons for this technique's insensitivity limits our ability to either improve the gamma metric to increase sensitivity of the comparison or the capacity to develop new comparison techniques that circumvent the limitations of the gamma comparison. To understand the underlying cause(s) for gamma comparison insensitivity and determine if simple plan characteristics can quantitatively predict for gamma comparison sensitivity. Known MLC and MU errors of varying magnitudes were induced on simple test fields to preliminarily investigate where gamma failures first begin to appear as error magnitude is increased. Gamma value maps between error-induced plan calculations and error-free plan calculations were created for 20 IMRT and 20 VMAT cases, each on three different detector geometries-ArcCHECK, MapCHECK, and Delta4. Gamma value maps were qualitatively compared to dose-gradient maps, and quantitative comparisons were performed between various plan descriptors and the computed gamma sensitivity for five different classes of induced errors were utilized to determine if any plan descriptor could predict the gamma sensitivity on a case-by-case basis. All comparisons were performed in a calculation-only scenario to remove uncertainties introduced by comparisons made with real patient specific QA measurements. Gamma value maps with increasing induced error magnitude illustrated that gamma comparisons fail first in high-dose, low-gradient regions of the field. Conversely, in areas of high gradient, gamma values typically remain low, even in the presence of large errors, regardless of detector geometry and gamma normalization setting. Thus, the complex, and often overlapping, high dose gradients in plans appear to be a limiting factor in gamma comparison sensitivity as the number of points along these gradients may often outnumber the points available for failing the comparison in lower gradient regions of the field. None of the simple plan descriptors studied were able to quantitively predict gamma comparison sensitivity, suggesting that quantitatively predicting the sensitivity of gamma comparisons on a case-by-case basis may require a combination of multiple factors or metrics not studied here. Simple plan descriptors and the number of points in high-dose, low-gradient regions of the field did not quantitively predict for gamma comparison sensitivity. However, it is clear from gradient and gamma value maps that gamma comparisons fail first in high-dose, low-gradient regions of the field in the presence of known induced errors, which we have shown to be independent of detector geometry and gamma comparison normalization setting. Gamma comparison sensitivity is thus limited by the ever-increasing complexity of plans and is particularly important to consider as treatment volumes become smaller and the complexity of overlapping plan gradients increases. This suggests that new methods for patient-specific QA comparisons are required to circumvent this limitation.

Gas kinematics around filamentary structures in the Orion B cloud

Context. Understanding the initial properties of star-forming material and how they affect the star formation process is key. From an observational point of view, the feedback from young high-mass stars on future star formation properties is still poorly constrained. Aims. In the framework of the IRAM 30m ORION-B large program, we obtained observations of the translucent (2 ≤ AV < 6 mag) and moderately dense gas (6 ≤ AV < 15 mag), which we used to analyze the kinematics over a field of 5 deg2 around the filamentary structures. Methods. We used the Regularized Optimization for Hyper-Spectral Analysis (ROHSA) algorithm to decompose and de-noise the C18O(1–0) and 13CO(1–0) signals by taking the spatial coherence of the emission into account. We produced gas column density and mean velocity maps to estimate the relative orientation of their spatial gradients. Results. We identified three cloud velocity layers at different systemic velocities and extracted the filaments in each velocity layer. The filaments are preferentially located in regions of low centroid velocity gradients. By comparing the relative orientation between the column density and velocity gradients of each layer from the ORION-B observations and synthetic observations from 3D kinematic toy models, we distinguish two types of behavior in the dynamics around filaments: (i) radial flows perpendicular to the filament axis that can be either inflows (increasing the filament mass) or outflows and (ii) longitudinal flows along the filament axis. The former case is seen in the Orion B data, while the latter is not identified. We have also identified asymmetrical flow patterns, usually associated with filaments located at the edge of an H II region. Conclusions. This is the first observational study to highlight feedback from H II regions on filament formation and, thus, on star formation in the Orion B cloud. This simple statistical method can be used for any molecular cloud to obtain coherent information on the kinematics.

Turbulent wakes in a non-uniformly stratified environment

This study explores the behavior of turbulent wakes generated by a sphere propagating with constant speed in a non-uniformly stratified fluid. The investigation is based on a series of high-resolution direct numerical simulations in which the background stratification is systematically varied. We consider one linear and three nonlinear density profiles and discover that even modest, spatially localized non-uniformities of stratification can profoundly influence the wake dynamics, structure, and evolution. The analysis of microstructure signatures shows that wakes in non-uniformly stratified fluids tend to be more spread horizontally, and internal waves are much stronger than in linear stratification. Simulations performed with Gaussian perturbations are characterized by a vertically asymmetric energy distribution, which is attributed to internal wave reflections from low-gradient regions. Using microstructure decay rates, we estimate the effective persistence period of wakes, showing that it substantially increases with the increasing Froude number. We also find that wakes persist much longer in high-gradient profiles, whereas weak local gradients can substantially reduce the wake longevity.

Hydraulic performance of mole drains and validation of steady-state drainage spacing equations for Mollisols

Central Santa Fe (Argentina) is a low-gradient region with impaired natural drainage. Extreme rainfall events are increasingly common and cause significant economic losses to agriculture. There is a growing interest in the use of mole drainage as a cost-effective strategy to mitigate such impacts. However, there is no information available that assists with mole drainage design, installation and maintenance, or the field assessment of a system’s hydraulic performance. This work was conducted with the dual objective of evaluating the hydraulic performance of an existing mole drains system and validating Hooghoudt’s steady-state drainage spacing equation for Mollisols. Three treatments representing different hydrologic conditions were tested; namely: (T1) rainfall of 360-min duration and intensity of 23 mm h-1, (T2) surface water ponding achieved through rainfall intensity of 50 mm h-1 and water depths between 50 and 100 mm, and (T3) similar surface water ponding conditions to treatment T2, but achieved through a rainfall intensity of 65 mm h-1 and either one (T3A) or two (T3B) sequential rainfall events. Following application of water, drainage commenced at 270 and 21 min for T1 and T2, and at 40 and 30 min for T3A and T3B, respectively. Mean drained depths were 1 and 3 mm for T1 and T2, respectively. For T3A, the mean drained depth was about one-third that measured for T3B (2.5 vs. 8.5 mm). Under a dry antecedent soil moisture condition, and rainfall intensity of 23 mm h-1, downward water movement was better described by piston flow. As surface water depth and soil water content increased, water flowed preferentially through the fissures and leg slots created by the mole plough implement at installation. Soil fissuring increased field hydraulic conductivity by factors between approximately three and ten. A 4 m mole drains spacing system was considered to be appropriate for managing excess water in the studied soil type. If the contribution of soil fissures to the field hydraulic conductivity can be accounted for, the Hooghoudt’s equation applied to two-layered soils may be used with confidence to help optimise the design of mole drainage systems for Mollisols. Application of this numerical approach, however, will require that the resultant spacing between mole drains be increased by about 30–40 %. Such an allowance will reduce installation costs and will not compromise the hydraulic efficiency of the drainage system.

Dosimetric validation of Acuros® XB algorithm for RapidArc™ treatment technique: A post software upgrade analysis.

To validate the Acuros® XB (AXB) algorithm in Eclipse treatment planning system (TPS) for RapidArc™ (RA) technique following the software upgrades. A Clinac-iX (2300CD) linear accelerator and Eclipse TPS (Varian Medical System, Inc., Palo Alto, USA) was used for commissioning of AXB algorithm using a 6 megavolts photon beam. Percentage depth dose (PDD) and profiles for field size 2 cm × 2 cm, 4 cm × 4 cm, 6 cm × 6 cm, 10 cm × 10 cm, 20 cm × 20 cm, 30 cm × 30 cm to 40 cm × 40 cm were taken. AXB calculated PDDs and profiles were evaluated against the measured and analytical anisotropic algorithm (AAA)-calculated PDDs and profiles. Test sites recommended by American Association of Physicists in Medicine task group (AAPM TG)-119 recommendation were used for RA planning and delivery verification using AXB algorithm. AXB shows excellent agreement with measurements and AAA calculated data. The CLs were consistent with the baseline values published by TG-119. AXB algorithm has the potential to perform photon dose calculation with comparable fast calculation speed without negotiating the accuracy. AAPM TG-119 was successfully implemented to access the proper configuration of AXB algorithm following the TPS upgrade.

Impact of High Thermal Setting and Fluid Activities on Sandstone Compaction: A Case Study of the Baiyun Sag in the Pearl River Mouth Basin (Northern South China Sea)

Compaction is regarded as central to the reduction of reservoir physical properties. The thermal compaction process controlled by a basin’s heat flow and the static compaction caused by overload on rocks are both important factors controlling the compaction strength. However, porosity loss resulting from thermal and static compaction has not been distinguished. The Baiyun Sag in the Pearl River Mouth Basin in the northern part of the South China Sea with high heat flows and a variable geothermal gradient is an ideal setting for studying the characteristics and mechanisms of the thermal compaction process. The characteristics of compaction and the effect of thermal fluid activities on reservoir physical properties are carried out, based on the observation and identification of sandstone thin sections under a microscope, the measurement and simulation of the temperatures and trapping pressures of fluid inclusions, and the calculation of the compaction porosity loss as well. The result shows that the compaction mode of sandstone reservoirs in the Zhuhai Formation is dominated by static compaction in the LGR (the low geothermal gradient region), whereas the diagenetic process of the Zhuhai Formation in the MGR (the moderate geothermal gradient region) and HGR (the high geothermal gradient region) is affected not only by the static compaction effect but also by the thermal compaction effect caused by abnormal formation temperature and pressure conditions. The porosity loss caused by the thermal compaction ranges from 5.5% to 11.2% with an average of 7.9% and from 4.6% to 16.6% with an average of 10.2% in the MGR and HGR, respectively. The porosity loss caused by the static compaction ranges from 15.9% to 20.8% with an average of 19.4% and from 8.4% to 15.8% with an average of 12.8% in the MGR and HGR, respectively.

A generalized quality assessment method for natural and screen content images

A generalized objective quality assessment method is proposed for natural images andscreen content images. Since natural images and screen content images have different sta-tistical properties, the modelling of a generalized quality assessment method that worksfor both types of images is complicated because some properties of natural imag es andscreen content images are conflicting to one another. The proposed method assesses theperceptual quality of an image based on edge magnitude and direction. In this method, animage is first separated into regions with high and low gradients. Gradient is used due tothe small perceptual span of the human visual system for textual content. For high gradientregions, small kernel size of Prewitt operators is used to obtain the gradient magnitude anddirection. Correspondingly, bigger kernel size of Prewitt operators is utilized for low gra-dient regions. Visual quality indices are computed from both regions and pooled to obtainthe final quality index. From the performance comparison, it is shown that the proposedmethod could assess the perceived quality of natural images and screen content imageswith high accuracy.

Analysis of central axis and build up region dose calculated by different dose calculation algorithms used for radiation treatment planning

Introduction: Computerized Treatment planning system (TPS) is an integral part of radiation treatment procedure. The main part of treatment planning system is a calculation algorithm incorporated in the Treatment Planning System. Various algorithms used in the TPS have capabilities and limitation on specific situations. Objective: The objective of the work is to analyse the depth dose distribution generated by different dose calculation algorithms used in TPS in regions of low and high dose gradient. Materials and Methods: Four different dose calculation algorithms used for treatment planning such as Modified Clarkson, Sector integration, Fast Fourier Transform, Convolution- Superposition algorithm were used to generate the percentage depth dose distribution in a water phantom up to 25 cm depth. The values are compared with experimental results using Radiation Field Analyser. The PDD values also generated at build up region and the values were compared with experimental results using a Parallel plate ionization chamber. Results: The results show that the dose calculated by different algorithms shows difference at build up region and at larger depths.

Enhanced Interferometric Phase Noise Filtering of the Refined InSAR Filter

The effectiveness of refined interferometric synthetic aperture radar (InSAR) filter (refined filter) was validated using both simulated and real interferometric data. However, the threshold as a key parameter in the refined filter is determined by repeated attempts, and the deterministic method has some disadvantages, such as strong subjectivity, long time consuming, and bad adaptation. This letter makes full use of the robustness of inverse distance weighting (IDW) to simplify the refined filter. In the proposed filter, using an $11 \times 11$ window and an improved IDW, the computational burden of $| {\langle {e^{j\psi _{z}}} \rangle } |$ for 16 windows per pixel is avoided, and the need for setting the threshold is eliminated. From the beginning, the initial window angle is determined using four preprocessing windows. The filtering direction of the center pixel is affected by the initial window angle of each pixel, the degree of homogeneity of each pixel, and the distance of the pixel from the center pixel in the $11\times 11$ window. The improved weighting method is then used to further refine the window angle of the center pixel. Numerical experiments by simulated and real InSAR data were used to validate the proposed approach. By comparison, the proposed filter greatly improves the efficiency of the refined filter and exhibits the superiority in filtering performance compared to commonly used filters, particularly for regions of low coherence, high-coherence-gradient, and high-phase gradient.

Improved global surface currents from the merging of altimetry and Sea Surface Temperature data

Six years of surface velocities have been calculated over the global ocean by combining altimeter derived geostrophic velocities and Sea Surface Temperature (SST) data. The method is based on the inversion for the velocity of the heat conservation equation using the altimeter velocities as background. By accurately prescribing the error both on the background velocities and on the forcing term (heat fluxes), the altimeter background velocities are successfully improved in areas characterized by strong SST gradients and remain unchanged in low SST gradient regions, where by construction no additional information may be brought by the SST field. This allows us to provide for the first time a global field of surface velocities from the merging of altimetry and SST. Both the spatial and temporal resolution of the altimeter derived velocities is enhanced by the SST information. Validation is performed through comparison to in-situ drifting buoy velocities. Major improvements (10–20% globally, up to 35% locally) are obtained on the meridional component of the velocity and in the equatorial band. Due to the large uncertainty on the heat fluxes and the spatio-temporal resolution of the input datasets, the high frequency ageostrophic components of the circulation is hardly resolved by the method and, outside the equatorial band, improvements are mainly on the geostrophic component. It is shown that the level of accuracy obtained by combining altimeter velocities based on a two satellite configuration and microwave SST data is equivalent or higher to the one from a four altimeter constellation in western boundary currents. This opens the perspective for a systematic use of the method to improve the altimeter derived surface velocities over the 1993–2001 period, for which only 2 altimeters have been flying simultaneously. Finally, over the recent years, the use of higher resolution SST products based on both microwave and infrared measurements leads to further enhancement of the accuracy of the altimeter velocities on both the zonal and the meridional component in strong SST gradients areas.

Kinetic electromagnetic instabilities in an ITB plasma with weak magnetic shear

Kinetic Alfvén and pressure gradient driven instabilities are very common in magnetized plasmas, both in space and the laboratory. These instabilities will be easily excited by energetic particles (EPs) and/or pressure gradients in present-day fusion and future burning plasmas. This will not only cause the loss and redistribution of the EPs, but also affect plasma confinement and transport. Alfvénic ion temperature gradient (AITG) instabilities with the frequency and the toroidal mode numbers are found to be unstable in NBI internal transport barrier plasmas with weak shear and low pressure gradients, where and are the frequencies of the beta- and toroidicity-induced Alfvén eigenmodes, respectively. The measured results are consistent with the general fishbone-like dispersion relation and kinetic ballooning mode equation, and the modes become more unstable the smaller the magnetic shear is in low pressure gradient regions. The interaction between AITG activity and EPs also needs to be investigated with greater attention in fusion plasmas, such as ITER (Tomabechi and The ITER Team 1991 Nucl. Fusion 31 1135), since these fluctuations can be enhanced by weak magnetic shear and EPs.

Flow induced crystallisation of penetrable particles

For a system of Brownian particles interacting via a soft exponential potential we investigate the interaction between equilibrium crystallisation and spatially varying shear flow. For thermodynamic state points within the liquid part of the phase diagram, but close to the crystallisation phase boundary, we observe that imposing a Poiseuille flow can induce nonequilibrium crystalline ordering in regions of low shear gradient. The physical mechanism responsible for this phenomenon is shear-induced particle migration, which causes particles to drift preferentially towards the center of the flow channel, thus increasing the local density in the channel center. The method employed is classical dynamical density functional theory.

Characteristics Analysis of Land Use Spatial Distribution on Terrain Gradient in Henan Province

Terrain is the most basic natural geographical elements, restricting the redistribution of surface material and energy, affecting the soil and vegetation formation and development process. Land use structure is the inevitable result of the interaction between nature and mankind. Based on the digital elevation model and land use classification grid data, the paper utilizes geostatistical analysis method to quantitatively analyze the spatial distribution characteristics of terrain gradient, and the spatial relations between land use structure and terrain gradient in Henan province. The results show that: In Henan province, the terrain gradient is dominated by low value, with the increase of terrain gradient, the area of unit gradient decreases gradually; With the increase of the longitude, the terrain gradient decreases gradually, showing the spatial pattern of the west high east low, the variety on the same latitude belt is significantly larger than that on the corresponding longitude belt. Farmland, water area, construction land and unused land are mainly distributed in the low gradient regions, and the grassland distributes in the middle gradient regions, and the gradient of forest land distribution is relatively high. The total area of construction land is increasing over time, occupying lots of farmland and forest land, the growth rate in middle low gradient region is higher than that in the low gradient region, and there is a trend of expanding to higher gradient region at the same time. The total area of farmland is decreasing over time, it tries to expand to higher gradient region to make up for the lost area, the area of middle gradient in its advantage region decreases mostly. In order to make up for the occupied area, the forest grassland is expanding toward higher gradient region. The area of water land has been increasing continuously, but the area of agricultural water in low gradient region is decreasing, and the advantage position is reducing.

Shear Banding in Telechelic Associative Polymers by Molecular Dynamics.

Results on the shear flow of telechelic associative polymers using nonequilibrium molecular dynamics (NEMD) are presented. The particle stream velocities can be calculated from the peculiar velocities and the imposed velocity profile using a novel approach. The constitutive relationship stress-shear rate becomes nonmonotonic when the interaction force between hydrophobic sites is increased. This condition induces a steady banding flow, which arises under transient conditions as a local instability originated from the breakage of micellar aggregates, thus promoting the migration of these aggregates to regions of low velocity gradients. Here, for the first time, NEMD simulations predict the banding flow of associative polymers.

Alfvénic ion temperature gradient activities in a weak magnetic shear plasma

We report the first experimental evidence of Alfvénic ion temperature gradient (AITG) modes in HL-2A Ohmic plasmas. A group of oscillations with and is detected by various diagnostics in high-density Ohmic regimes. They appear in the plasmas with peaked density profiles and weak magnetic shear, which indicates that corresponding instabilities are excited by pressure gradients. The time trace of the fluctuation spectrogram can be either a frequency staircase, with different modes excited at different times or multiple modes may simultaneously coexist. Theoretical analyses by the extended generalized fishbone-like dispersion relation (GFLDR-E) reveal that mode frequencies scale with ion diamagnetic drift frequency and , and they lie in KBM-AITG-BAE frequency ranges. AITG modes are most unstable when the magnetic shear is small in low pressure gradient regions. Numerical solutions of the AITG/KBM equation also shed light on why AITG modes can be unstable for weak shear and low pressure gradients. It is worth emphasizing that these instabilities may be linked to the internal transport barrier (ITB) and H-mode pedestal physics for weak magnetic shear.

Dynamic Programming Using Polar Variance for Image Segmentation.

When using polar dynamic programming (PDP) for image segmentation, the object size is one of the main features used. This is because if size is left unconstrained the final segmentation may include high-gradient regions that are not associated with the object. In this paper, we propose a new feature, polar variance, which allows the algorithm to segment the objects of different sizes without the need for training data. The polar variance is the variance in a polar region between a user-selected origin and a pixel we want to analyze. We also incorporate a new technique that allows PDP to segment complex shapes by finding low-gradient regions and growing them. The experimental analysis consisted on comparing our technique with different active contour segmentation techniques on a series of tests. The tests consisted on robustness to additive Gaussian noise, segmentation accuracy with different grayscale images and finally robustness to algorithm-specific parameters. Experimental results show that our technique performs favorably when compared with other segmentation techniques.