High Gradient Regions Research Articles

Dose evaluation for skin and organ in hepatocellular carcinoma during angiographic procedure.

PurposeThe purpose of this study is to evaluate the radiation dose in patients undergoing liver angiographic procedure and verify the usefulness of different dose measurements to prevent deterministic effects. Gafchromic film, MicroMOSFET data and DIAMENTOR device of the X-ray system were used to characterize the examined interventional radiology (IR) procedure.Materials and methodsA liver embolization procedure, the SIRT (Selective Internal Radiation Therapy), was investigated. The exposure parameters from the DIAMENTOR as well as patient and geometrical data were registered. Entrance skin dose map obtained using Gafchromic film (ESDGAF) in a standard phantom as well as in 12 patients were used to calculate the maximum skin dose (MSDGAF). MicroMOSFETs were used to assess ESD in relevant points/areas. Moreover, the maximum value of five MicroMOSFETs array, due to the extension of treated area and to the relative distance of 2–3 cm of two adjacent MicroMOSFETs, was useful to predict the MSD without interfering with the clinical practice. PCXMC vers.1.5 was used to calculate effective dose (E) and equivalent dose (H).ResultsThe mean dose-area product (DAPDIAMENTOR) for SIRT procedures was 166 Gycm2, although a wide range was observed. The mean MSDGAF for SIRT procedures was 1090 mGy, although a wide range was experienced. A correlation was found between the MSDGAF measured on a patient and the DAPDIAMENTOR value for liver embolizations. MOSFET and Gafchromic data were in agreement within 5% in homogeneous area and within 20% in high dose gradient regions. The mean equivalent dose in critical organs was 89.8 mSv for kidneys, 22.9 mSv for pancreas, 20.2 mSv for small intestine and 21.0 mSv for spleen. Whereas the mean E was 3.7 mSv (range: 0.5-13.7).ConclusionsGafchromic films result useful to study patient exposure and determine localization and amplitude of high dose skin areas to better predict the skin injuries. Then, DAPDIAMENTOR or MOSFET data could offer real-time methods, as on-line dose alert, to avoid any side effects during liver embolization with prolonged duration.

Finding fibres and their contacts within 3D images of disordered fibrous media

Abstract Modelling physical and mechanical properties of fibrous materials requires a relevant description of their microstructures, e.g. the descriptors of fibres and fibre–fibre contacts. In this work, a method is proposed to identify fibres with complex cross sections and their contacts from 3D images of disordered fibrous media, obtained from X-ray microtomography. The image analysis procedure first consists in obtaining a map of the local fibre orientation. Fibres are then detected by deleting regions of high local orientation gradients. Therewith, dilatation operations using slender orientated structuring elements are performed to retrieve deleted fibre parts. The procedure thus provides 3D images with labelled fibres and fibre–fibre contacts. Its relevance is assessed by analysing the microstructures of three typical fibrous media used in short fibre reinforced polymer composites or as paper materials: mats of (i) mono-disperse copper fibres with circular cross sections, (ii) glass fibres bundles, (iii) wood fibres.

A comparison of the gamma index analysis in various commercial IMRT/VMAT QA systems

PurposeTo investigate the variability of the global gamma index (γ) analysis in various commercial IMRT/VMAT QA systems and to assess the impact of measurement with low resolution detector arrays on γ. MaterialsFive commercial QA systems (PTW 2D-Array, Scandidos Delta4, SunNuclear ArcCHECK, Varian EPID, and Gafchromic EBT2 film) were investigated. The response of γ analysis to deliberately introduced errors in pelvis and head & neck IMRT and RapidArc™ plans was evaluated in each system. A theoretical γ was calculated in each commercial QA system software (PTW Verisoft, Delta4 software, SNC Patient, Varian Portal Dosimetry and IBA OmniPro, respectively), using treatment planning system resolution virtual measurements and compared to an independent calculation. Error-induced plans were measured on a linear accelerator and were evaluated against the error-free dose distribution calculated using Varian Eclipse™ in the relevant phantom CT scan. In all cases, global γ was used with a 20% threshold relative to a point selected in a high dose and low gradient region. The γ based on measurement was compared against the theoretical to evaluate the response of each system. ResultsThere was statistically good agreement between the predicted γ based on the virtual measurements from each software (concordance correlation coefficient, ρc>0.92) relative to the independent prediction in all cases. For the actual measured data, the agreement with the predicted γ reduces with tightening passing criteria and the variability between the different systems increases. This indicates that the detector array configuration and resolution have greater impact on the experimental calculation of γ due to under-sampling of the dose distribution, blurring effects, noise, or a combination. ConclusionsIt is important to understand the response and limitations of the gamma index analysis combined with the equipment in use. For the same pass-rate criteria, different devices and software combinations exhibit varying levels of agreement with the predicted γ analysis.

Modular Turbulence Modeling Applied to an Engine Intake

The one equation Spalart–Allmaras (SA) turbulence model in an extended modular form is presented. It is employed for the prediction of crosswind flow around the lip of a 90 deg sector of an intake with and without surface roughness. The flow features around the lip are complex. There exists a region of high streamline curvature. For this, the Richardson number would suggest complete degeneration to laminar flow. Also, there are regions of high favorable pressure gradient (FPG) sufficient to laminarize a turbulent boundary layer (BL). This is all terminated by a shock and followed by a laminar separation. Under these severe conditions, the SA model is insensitive to capturing the effects of laminarization and the reenergization of eddy viscosity. The latter promotes the momentum transfer and correct reattachment prior to the fan face. Through distinct modules, the SA model has been modified to account for the effect of laminarization and separation induced transition. The modules have been implemented in the Rolls-Royce HYDRA computational fluid dynamic (CFD) solver. They have been validated over a number of experimental test cases involving laminarization and also surface roughness. The validated modules are finally applied in unsteady Reynolds-averaged Navier–Stokes (URANS) mode to flow around an engine intake and comparisons made with measurements. Encouraging agreement is found and hence advances made towards a more reliable intake design framework.

Postoperative Metabolic Abnormality in Craniopharyngioma Patients Before Proton Therapy

Purpose/Objective(s): To assess postoperative changes of cerebral glucose metabolism in craniopharyngioma patients receiving proton therapy. Materials/Methods: From 2011 to 2012, 17 patients enrolled in a prospective proton therapy trial for craniopharyngioma and received longitudinal PET and MR imaging for tumor and normal tissue response. Sixteen of them underwent craniotomies before baseline FDG PET studies followed by proton therapy of 54 CGEs. One did not require surgical intervention before radiation. Patient FDG PET images were nonlinearly warped to a 3D reference template in Talairach coordinates created from images of normal subjects. Left-right asymmetry of the count per voxel in each of 63 anatomical regions and region-based statistics of activity were computed. Regional asymmetry was considered significant when its Z score exceeded two standard deviations of normal population. To exclude any potential bias in PET acquisition, 12 control children with extracranial diseases but normal cerebral PET scans were also analyzed. Results: Median age of craniopharyngioma patients at diagnosis was 13 years (range, 4-18 years). Median time from craniotomies to baseline PET studies and from PET to proton therapy was 136 days (range, 7-226 days) and 32 days (range, 20-52 days). Significantly decreased glucose uptake was most prominent in right frontal lobe, striatum, and thalamus. It occurred in 7 of 10 patients who underwent transcranial craniotomies and in 2 of 3 patients receiving endoscopic craniostomy for cyst drainage, but in none of the 4 patients who received transphenoidal surgery or no surgery. Significant asymmetry in superior frontal gyrus is related to the surgical approach (89% occurrence in right frontal, bifrontal, and interhemispheric approaches vs 0% in other approaches). Significant asymmetry in caudate nucleus, putamen, and thalamus likely resulted from mass effect, venous occlusion, and surgical damage. A large, but not significant, uptake asymmetry (averaged 9%) in the inferior occipital gyrus was observed in both craniopharyngioma and control patients. This asymmetry is possibly due to the left occipital petalia commonly seen in right handers. None of the uptake asymmetry in superior frontal lobe, striatum, and thalamus was significant in control subjects. Conclusions: Postoperative metabolic abnormalities in the right superior frontal gyrus, striatum, and thalamus were noted in craniopharyngioma patients before proton therapy. The latter two are of particular interest since they subsequently receive the tumoricidal dose or are in high dose gradient regions and play an important role in regulation of motor control, sensory function, memory, sleep, and consciousness. The association with observed clinical deficits before and after proton therapy in this population will be reported. Author Disclosure: C. Hua: None. H.M. Conklin: None. M.A. Madey: None. D.J. Indelicato: None. B.L. Shulkin: None. T.E. Merchant: None.

Factors Impacting Long-term Local Control in Nonmetastatic Medulloblastoma

Purpose/Objective(s): To assess postoperative changes of cerebral glucose metabolism in craniopharyngioma patients receiving proton therapy. Materials/Methods: From 2011 to 2012, 17 patients enrolled in a prospective proton therapy trial for craniopharyngioma and received longitudinal PET and MR imaging for tumor and normal tissue response. Sixteen of them underwent craniotomies before baseline FDG PET studies followed by proton therapy of 54 CGEs. One did not require surgical intervention before radiation. Patient FDG PET images were nonlinearly warped to a 3D reference template in Talairach coordinates created from images of normal subjects. Left-right asymmetry of the count per voxel in each of 63 anatomical regions and region-based statistics of activity were computed. Regional asymmetry was considered significant when its Z score exceeded two standard deviations of normal population. To exclude any potential bias in PET acquisition, 12 control children with extracranial diseases but normal cerebral PET scans were also analyzed. Results: Median age of craniopharyngioma patients at diagnosis was 13 years (range, 4-18 years). Median time from craniotomies to baseline PET studies and from PET to proton therapy was 136 days (range, 7-226 days) and 32 days (range, 20-52 days). Significantly decreased glucose uptake was most prominent in right frontal lobe, striatum, and thalamus. It occurred in 7 of 10 patients who underwent transcranial craniotomies and in 2 of 3 patients receiving endoscopic craniostomy for cyst drainage, but in none of the 4 patients who received transphenoidal surgery or no surgery. Significant asymmetry in superior frontal gyrus is related to the surgical approach (89% occurrence in right frontal, bifrontal, and interhemispheric approaches vs 0% in other approaches). Significant asymmetry in caudate nucleus, putamen, and thalamus likely resulted from mass effect, venous occlusion, and surgical damage. A large, but not significant, uptake asymmetry (averaged 9%) in the inferior occipital gyrus was observed in both craniopharyngioma and control patients. This asymmetry is possibly due to the left occipital petalia commonly seen in right handers. None of the uptake asymmetry in superior frontal lobe, striatum, and thalamus was significant in control subjects. Conclusions: Postoperative metabolic abnormalities in the right superior frontal gyrus, striatum, and thalamus were noted in craniopharyngioma patients before proton therapy. The latter two are of particular interest since they subsequently receive the tumoricidal dose or are in high dose gradient regions and play an important role in regulation of motor control, sensory function, memory, sleep, and consciousness. The association with observed clinical deficits before and after proton therapy in this population will be reported. Author Disclosure: C. Hua: None. H.M. Conklin: None. M.A. Madey: None. D.J. Indelicato: None. B.L. Shulkin: None. T.E. Merchant: None.

A synthetic diamond diode in volumetric modulated arc therapy dosimetry

The aim of this work is to investigate the behavior of a single crystal diamond diode (SCDD) for volumetric modulated arc therapy (VMAT) dose verifications. This delivery technique is one of the most severe test of a dosimeter performance due to the modulation of the dose rate achieved by simultaneously changing the velocity of the gantry and the position of the collimator leaves. The performed measurements with VMAT photon beams can therefore contribute to an overall global validation of the device to be used in dose distribution verifications. The SCDD response to 6 MVRX has been tested and compared with reference ionization chambers and treatment planning system (TPS) calculations in different experiments: (a) measurements of output factors for small field sizes (square fields of side ranging between 8 mm and 104 mm) by SCDD and A1SL ionization chamber; (b) angular dependence evaluation of the entire experimental set-up by SCDD, A1SL, and Farmer ionization chambers; and (c) acquisition of dose profiles for a VMAT treatment of a pulmonary disease in latero-lateral and gantry-target directions by SCDD and A1SL ionization chamber. The output factors measured by SCDD favorably compare with the ones obtained by A1SL, whose response is affected by the lack of charged particle equilibrium and by averaging effect when small fields are involved. From the experiment on angular dependence, a good agreement is observed among the diamond diode, the ion chambers, and the TPS. In VMAT profiles, the absorbed doses measured by SCDD and A1SL compare well with the TPS calculated ones. An overall better agreement is observed in the case of the diamond dosimeter, which is also showing a better accuracy in terms of distance to agreement in the high gradient regions. Synthetic diamond diodes, whose performance were previously studied for conformal and IMRT radiotherapy techniques, were found to be suitable detectors also for dosimetric measurements in volumetric arc therapy treatments.

TRUS image segmentation with non-parametric kernel density estimation shape prior

Due to noises, speckles, etc., automatic prostate segmentation is rather challenging, and using only low-level information such as intensity gradient is insufficient and unable to tackle the problem. In this paper, we propose an automatic prostate segmentation method combining intrinsic properties of TRUS images with the high-level shape prior information. First, intrinsic properties of TRUS images, such as the intensity transition near the prostate boundary as well as the speckle induced texture features obtained by Gabor filter banks, are integrated to deform the model to the target contour. These properties make our method insensitive to high gradient regions introduced by noises and speckles. Then, the preliminary segmentation is fine-tuned by the non-parametric shape prior, which is optimally distilled by non-parametric kernel density estimation as it can approximate arbitrary distributions. The refinement is along the direction of mean shift vector, and considerably strengthens the robustness of the method. The performance of our method is validated by experimental results. Compared with the state of the art, the accuracy and robustness of the method is quite promising, and the mean absolute distance is only 1.21±0.85mm.

High strain gradient measurements using modified automated grid technique

The automated grid technique, which was constantly used to measure strain field mapping, is a full field optical technique with the character of high efficiency, good adaptability and simple applicability. Due to the limitation of the spot pattern preparation, it was restricted for the measurement of strain distribution in regions of high strain gradient. In this paper, an modified automated grid technique, in which the grid spots were made by using the lithography technique, was applied for the measurement of the high strain gradient. To validate the modified automated grid technique, aluminum specimens with circular holes were employed as the test specimens and the deformation behaviors in the regions of stress concentration were investigated. The testing results agreed well with the analytical and numerical analysis. In comparison with the traditional automated grid technique, the modified method is more accurate. All the results indicate that the high strain gradient test method based on the modified automated grid technique is reliable and appropriate.

Bifurcation Study of Three-Dimensional Solutions of the Curved Square-Duct Flow

Steady, periodic and traveling-wave solutions of the flow through a curved square duct are obtained numerically, and their linear stability to two- and three-dimensional disturbances is investigated. It is found that a steady traveling-wave (STW) solution bifurcates from the symmetric steady solution branch and is linearly stable in the intermediate range between low and high pressure gradient regions. Two stable periodic traveling-wave (PTW) solutions are also found, which have oscillating components with different symmetry. One keeps the same symmetry as the STW solution and the other breaks it. They seem to bifurcate from the STW solution branch via Hopf bifurcation although their solution branches are not obtained exactly. It is strongly suggested that a two-dimensional time-periodic (2DP) solution is created via heteroclinic bifurcation, not from local bifurcation. 2DP solution is always linearly unstable against three-dimensional disturbances though it has linearly stable region to two-dimensional disturbances.

Rupture propagation in strong earthquake sources and tectonic stress field

Abstract Problems of physical basis of earthquake source mechanics are discussed. Results of stress state reconstruction based on the cataclastic analysis of discontinuous dislocations in some seismotectonic active earth crust domains are presented. Common features of the stress state in areas of preparation of strong earthquake in this century are revealed. It is demonstrated that the distribution of the effective isotropic pressure and of the maximal shear stress in areas of earthquake source preparation is characterized by essential heterogeneity. The main part of the source is always associated to crust domain under low effective confining pressure. Specific role of crust domains characterized by high stress gradients is recognized. The nucleation point of the earthquake is usually associated to such domains. Based on some strong earthquake case studies it is demonstrated that usually the rupture propagates from the region of high gradients of stresses toward the crust domains characterized by low effective compression.

SU-E-T-382: Investigation of the Characteristics of the OCTAVIUS Detector 1000 SRS for Verification of the Small Field Size IMRT and SRS Beams

Purpose: The aim for the study was to investigate characteristics of the OCTAVIUS Detector 1000 SRS for verification of the small field size IMRT and SRS beams. Methods: Several different treatments sites have been chosen. High modulation steep gradient small field size beams were delivered in two different setup settings. In the first setup virtual water phantom has been placed on the detector and irradiated. In the same setup EDR film has been irradiated. Measured data has been analyzed. In the second setup detector has been placed in the PTW Octavius phantom and irradiated. In the same setup EDR film and PTW 729 have been irradiated. Measured data has been analyzed. Results: In the first setup detector has been irradiated with virtual water phantom and measured Result showed excellent agreement with the film measurements. Along the compared profiles, absolute dose measured was in ±1 % of the film measurements in the high dose region and ±3 % in low dose region. Measured results showed also very good agreement in region of high gradients. Second set of measurements showed excellent agreement with the film measurements in high dose region with absolute dose difference within ±1% and ±3% in low dose region. Agreement with PTW 729 was in ±3 % in high and low dose region along the compared profiles. Region of high gradient showed better agreement with the film than with PTW 729 due to the inferior detector resolution. Conclusion: Broad range of measurements performed in the investigation showed that OCTAVIUS Detector 1000 SRS is a dosimetrically accurate and sensitive device and it can be used for clinical verification of the highly modulated small field size beams used in the IMRT and SRS treatments.

A comparison of numerical methods for charge transport simulation in insulating materials

Bipolar charge transport (BCT) model has been widely used to simulate time/space evolution of space charges in insulating materials. The BCT simulations are performed to investigate the relationships between space charge accumulation and conduction, electroluminescence (EL), charge packet formation, electrical breakdown, and surface potential decay (SPD) properties. Accordingly, the charge advection-reaction equation that contains shocks or high gradient regions should be solved by highly accurate and stable numerical methods to obtain high resolution. We use Runge-Kutta discontinuous Galerkin (RKDG) method and finite differential weighted essentially non-oscillatory (WENO) method to resolve the charge advection-reaction equation. Then, we calculate the SPD properties and space charge profiles of corona charged low-density polyethylene (LDPE) at various initial surface potentials. The simulated results of the two schemes are compared with analytical SPD results, and also compared with each other. It is found that the simulated SPD curves of RKDG and WENO in the case of single carrier injection are both consistent with the analytical results. Moreover, in the case of both single carrier injection and bipolar carrier injection, WENO scheme is more accurate than RKDG scheme at a given spatial discretization.

TU‐E‐108‐05: In‐House IMRT QA Versus External Phantom Audit Results

Purpose: The Radiological Physics Center (RPC) credentials institutions for clinical trials involving advanced radiotherapy techniques with anthropomorphic phantoms. This study compared phantom results with in‐house IMRT QA results. Methods: We examined RPC head phantom irradiations for which institutions had submitted their own in‐house IMRT QA results for the same plan. The RPC phantom includes 6 TLD‐based point dose measurements, and film for evaluating distance to agreement (DTA) between the target and a neighbouring critical structure. Treatments failed the RPC phantom if any TLD‐measured dose was outside 7% or the DTA in the high gradient region between the target and critical structure was more than 4mm from the institution's TPS‐calculation. Institutions' IMRT QA on the same plan was per their protocol. The institution failed IMRT QA if a) they declared that their results did not meet their internal criteria, or, b) if their point doses agreed outside 3% or planar analysis agreed with less than 90% of pixels passing a 3%/3mm (or less stringent) gamma criteria. 189 plans were examined. Results: 23 plans failed RPC phantom irradiation, while 18 failed in‐house IMRT QA. However, consistency was not observed between the two systems. Plans that failed the RPC phantom irradiation were only 22% likely to be noted as failing in‐house IMRT QA (i.e., sensitivity = 0.22). Plans that passed the RPC phantom tended to pass IMRT QA; the specificity was 92%. No correlation was found between the agreement of in‐house point dose and TPS versus RPC point dose and TPS. Conclusion: Sensitivity, the most important quality of a QA process, was found to be very low overall for in‐house IMRT QA as compared to the RPC phantom. These results challenge the merit of IMRT QA to detect problems in an end‐to‐end treatment delivery. This work was supported by Public Health Service Grants CA10953 and CA081647 awarded by the National Cancer Institute, United States Department of Health and Human Services.

SU‐E‐T‐579: Effect of Dose Calculation Grid Size On Proton Dose Calculation

Purpose: The effect of dose calculation grid size for highly conformal proton planning is evaluated for the first time. Our goal is to find the optimal dose calculation grid size for different cases to increase the treatment planning efficiency while maintaining the dose calculation accuracy within clinical tolerance. Methods: Four clinical head& neck, prostate, lung and CSI cases are studied and calculated at three different calculation grid sizes (1 mm, 3 mm, 5 mm). To further understand the dose accuracy, a phantom simulating lung treatment with small fields and large fields is measured with EBT films. The measured results are compared with the calculated results in the form of point dose and dose profiles in regions of low and high dose gradients, dosimetric parameters, DVHs, and gamma analysis. The calculation time difference is investigated against the grid resolution as well. Results: There is no significant difference in pass rate of gamma analysis with 3 mm/3% acceptance criteria. The grid size effect is observed more clearly for small field size in inhomogeneous media. When comparing varying calculation grid sizes and measurements, the variation of the dose difference histogram is insignificant, but a local effect is observed in the dose difference map and point dose comparisons. Conclusion: The effect of calculation grid size on proton dose calculation can be clinically significant, depending on the disease sites, patient anatomy and treatment target volume and organ at risk. Small grid sizes (1 or 2mm) are necessary for small structures in and near inhomogeneous geometries such as in the head and neck regions.

Adaptive concurrent multi-level model for multi-scale analysis of ductile fracture in heterogeneous aluminum alloys

This paper creates a novel adaptive multi-level modeling framework for rate-dependent ductile fracture of heterogeneous aluminum alloys with non-uniform microstructures. The microstructure of aluminum alloys is characterized by a dispersion of brittle heterogeneities such as silicon and intermetallics in a ductile aluminum matrix. These microstructural heterogeneities affect their failure properties like ductility in an adverse manner. The multi-level model invokes two-way coupling, viz. homogenization for upscaled constitutive modeling, and top-down scale-transition in regions of localization and damage. Adaptivity is necessary for incorporating continuous changes in the computational model as a consequence of evolving microstructural deformation and damage. The macroscopic finite element analysis in regions of homogeneity incorporates homogenization-based continuum rate-dependent plasticity-damage (HCPD) models. Transcending scales is required in regions of high macroscopic gradients caused by underlying localized plasticity and damage. Complete microscopic analysis using the LE-VCFEM is conducted in these regions, which follow the growth of microscopic voids and cracking to cause local ductile fracture. The macroscopic and microscopic simulations are done concurrently in a coupled manner. Physics-based level change criteria are developed to improve the accuracy and efficiency of the model. Numerical simulations are conducted for validations and ductile fracture in a real microstructure is demonstrated.

SU‐E‐T‐433: Evaluation of the ArcCheck Device for Patient‐Specific Quality Assurance in Step‐And‐Shoot IMRT for Single‐Fraction Spinal SBRT

Purpose: Current standard for patient specific spine SBRT IMRT QA in our institution is a combination of a point dose measurement in solid water under delivery of the beams at actual treatment angles, and 2D planar verification using an ion chamber (IC) array with all beams delivered at standard gantry angle of zero. The very small active area of ArcChecks diodes (∼0.6mm2) has the potential to improve measurement accuracy in high dose gradient regions present in spinal SBRT. Given high clinical workload we seek to improve ease of workflow and decrease time necessary for patient‐specific QA, by obtaining 2D verification and point dose measurement at actual treatment angles in one single measurement. Methods: The results of 10 patient specific QA measurements, as performed with single‐point and 2D IC array were compared to results obtained with ArcCheck. ArcCheck and 2D IC array pass rates are evaluated for 3%/3mm gamma criteria, single‐point measurement based on percent deviation from QA plan dose. The constancy of the device was assessed by re‐measuring the same treatment plan over the course of three weeks, and evaluating pass rate variationResults: The gamma pass rates are generally higher for ArcCheck (average 99.3%) than for Matrixx (average 93.1%). Average absolute deviation for the single‐point IC measurement was 3.4%. Maximum variation in pass rate between any two ArcCheck measurements within the three‐week evaluation period was 0.5%. Since ArcCheck allows for the use of an insert with an ion chamber in place, simultaneous redundant point measurement is possible with no time addedConclusion: Based on our results patient‐specific QA for spine SBRT treatments will be performed using ArcCheck with pass/fail criteria 98%. High sensitivity towards geometrical shifts necessitates careful initial alignment of the device.

Optical velocity measurements of electrolytic boundary layer flows influenced by magnetic fields

Magnetic fields are applied to electrically conducting fluids in order to influence electrochemical processes through the magnetohydrodynamic effect. Various phenomena, e.g. on electrodeposited metal layers, which can be attributed to forced convections were observed. To provide information about acting forces, the laser Doppler velocity profile sensor was applied to measure the transition layer of a Lorentz force influenced flow over a backward-facing step and the velocity boundary layer during copper deposition. With this sensor, the electrolyte convection within < 500 μm of the front of an electrode is measured with a spatial resolution down to 15 μm. The interaction of buoyancy, Lorentz and magnetic field gradient forces is studied by measuring the velocities down to 10 μm in front of the cathode. Inside the concentration boundary layer, complex electrolyte convection is induced, which varies not only in time but also in its structure, depending on the forces present and their influence over time. In inhomogeneous magnetic field configurations, the magnetic field gradient force dominates the velocity boundary layer at steady state and transports electrolyte toward regions of high magnetic gradients, where maximum deposit thicknesses are found. In this way, the measurements confirm the predicted influence of the magnetic field gradient force on the structuring of copper deposits.

Structured electrodeposition in magnetic gradient fields

Electrodeposition in superimposed magnetic gradient fields is a new and promising method of structuring metal deposits while avoiding masking techniques. The magnetic properties of the ions involved, their concentrations, the electrochemical deposition parameters, and the amplitude of the applied magnetic gradient field determine the structure generated. This structure can be thicker in regions of high magnetic field gradients. It can also be free-standing or inversely structured. The complex mechanism of structured electrodeposition of metallic layers in superimposed magnetic gradient fields was studied by different experimental methods, by analytical methods and by numerical simulation and will be discussed comprehensively.

S055011 矩形断面曲がり管内流の分岐解析([S055-01]内部流れ(1))

Steady, periodic and traveling-wave solutions of the flow through a curved square duct are obtained numerically, and their linear stability to two- and three-dimensional disturbances is investigated. It is found that a steady traveling-wave (STW) solution bifurcates from the symmetric steady solution branch and is linearly stable in the intermediate range between low and high pressure gradient regions. Two stable periodic traveling-wave (PTW) solutions are also found, which have oscillating components with different symmetry. One keeps the same symmetry as the STW solution and the other breaks it. It is strongly suggested that a two-dimensional time-periodic (2DP) solution is created via heteroclinic bifurcation, not from local bifurcation. 2DP solution is always linearly unstable against three-dimensional disturbances though it has linearly stable region to two-dimensional disturbances.