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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Separation and Transition on a Cone-Cylinder-Flare: Computational Investigations

Base flow computation and stability analysis were conducted for hypersonic flow over a cone-cylinder-flare (CCF) geometry for conditions that correspond to the experimental runs carried out in three wind tunnels. Owing to the presence of an attached boundary layer, a separation bubble induced by a shock-boundary layer interaction, and a reattachment region, the chosen flow configuration is physically rich. The complexity of this flowfield encompasses a combination of convective instabilities developing on the cone, global instabilities in the separation bubble, and shear-layer modes and streaks in the reattachment region. Thus, the selected CCF configuration provides the opportunity for a comprehensive comparison of the currently available methodologies for analyzing boundary layer instabilities. Various tools are used for the analysis, including global stability codes as well as convective instability analyses based on a local theory, a weakly non-parallel analysis, and tools that are applicable to strongly non-parallel flows. The paper presents a comparison of the convective instability characteristics based on different methodologies, such as linear stability theory (LST), the harmonic form of linearized Navier-Stokes equations (HLNSE), and resolvent analysis. The CCF configuration provided an effective framework for conducting a detailed cross-validation of this type, which had not yet been addressed in existing literature. This document is accompanied by a companion paper that is focused on the experimental aspects of the CCF configuration. Both papers are being presented in a dedicated session that highlights the research activities of the NATO STO Research Task Group AVT-346.

Boundary Layer Transition↗
NASA NTRSDate not supplied

High Energy Hydroforming Friction Stir Welded 2050 Al-Li Blanks for Aerospace Domes and Cones

Friction stir welded (FSW) aluminum blanks offer larger preform sizes than available from the mill in single width plates. Large blanks made from aerospace-grade aluminum alloys are essential for making large domes and cones for launch vehicles and crew vehicles. Previous research efforts have demonstrated >5m FSW blanks can be formed into large domes or cones using spin forming, but the subsequent solution heat treatment consistently led to abnormal grain growth (AGG). The AGG phenomenon occurs because the FSW blanks must be spin formed in the -O annealed temper to withstand the high strain process without cracking. Subsequently, the solution heat treatment process leads to the onset of AGG, whereby a small number of grains grow much larger than the surrounding matrix. Ultimately, the large grains and bimodal grain-size distribution leads to unacceptable ductility in the short-transverse direction of the part. Alternatively, explosive hydroforming is a nascent process that can be applied to large and thick aerospace-grade aluminum alloy blanks in the -T3 temper and only require a post-forming artificial aging process to a -T8. Avoiding the solution heat treatment (SHT) process mitigates AGG, and also eliminates the need for very rare drop-furnace quench baths that can accommodate a part size larger than 5m in diameter. This presentation summarizes a Lockheed Martin-led effort that demonstrated explosive hydroforming of a 1.9m diameter, 39mm thick 2050 aluminum lithium FSW blank. Details will be provided on the process flow, mechanical properties, and metallographic analyses. This work was performed in partnership with NASA Langley Research Center (LaRC) under a NASA Announcement of Collaboration Opportunities program.

Friction stir welded blank↗
DOE OSTI2015

Cone penetrometer shear strength measurements of Hanford site sludge waste - 15314

In response to research examining the effect of gas production on the storage capacity of artificial sludge depots [1], a new mechanism was proposed for a spontaneous deep sludge gas release event (DSGRE) that had not been described in the Hanford Site Tank Farm safety basis [2]. Implementation of a new safety basis for Hanford Site sludge waste to address the DSGRE concern required showing that the waste maintains low gas fractions as settled solids depth is increased, which is directly related to the shear strength of the waste. Therefore, safety basis development involved determining the in situ shear strength of the sludge waste in C-Farm sludge accumulation Tanks 241-AN-101 (AN-101) and 241-AN-106 (AN-106). In situ measurements were taken in the sludge waste using a cone penetrometer with a 3-inch (76-mm) diameter ball attachment. Full-flow cone penetrometer measurements were taken in Tank AN-101 sludge waste in January 2014 and in Tank AN-106 in November 2013. Measurements in both AN-101 and AN-106 sludge demonstrated roughly uniform increasing undrained shear strength with increased depth, which was expected based on similar testing performed in soft, normally consolidated clays at test sites globally [3]. Comparison of in situ data to other soft-clay sites investigated with full-flow penetrometers suggests AN-101 and AN-106 sludge wastes do not behave differently in this regard than other normally consolidated clay or soil deposits, which supported revision of the safety basis to allow continuation of retrieval from C-Farm tanks. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Novel utilization of 3D technology and the hybrid operating theatre: Peri-operative assessment of posterior sterno-clavicular dislocation using cone beam CT

A patient with a medial and posterior dislocation of the right sterno-clavicular (SC) joint and displacement of the trachea and brachiocephalic artery by the medial head of the clavicle underwent general anaesthetic in the operating theatre for an open reduction procedure. The surgeon initially attempted a closed reduction, but this required imaging to check SC alignment. The patient was transferred to an adjacent hybrid operating theatre for imaging. Cone beam computed tomography (CBCT) was performed, which successfully demonstrated a significant reduction in the dislocation of the SC joint. The trachea and brachiocephalic artery were no longer compressed or displaced. This case study demonstrates an alternative to the patient being transferred to the medical imaging department for multi-slice CT. It also describes a novel use of the hybrid operating theatre and its CBCT capabilities.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Feasibility Study of Needle Placement in Percutaneous Vertebroplasty: Cone-Beam Computed Tomography Guidance Versus Conventional Fluoroscopy

ObjectiveTo investigate the accuracy, procedure time, fluoroscopy time, and dose area product (DAP) of needle placement during percutaneous vertebroplasty (PVP) using cone-beam computed tomography (CBCT) guidance versus fluoroscopy.Materials and MethodsOn 4 spine phantoms with 11 vertebrae (Th7-L5), 4 interventional radiologists (2 experienced with CBCT guidance and two inexperienced) punctured all vertebrae in a bipedicular fashion. Each side was randomization to either CBCT guidance or fluoroscopy. CBCT guidance is a sophisticated needle guidance technique using CBCT, navigation software, and real-time fluoroscopy. The placement of the needle had to be to a specific target point. After the procedure, CBCT was performed to determine the accuracy, procedure time, fluoroscopy time, and DAP. Analysis of the difference between methods and experience level was performed.ResultsMean accuracy using CBCT guidance (2.61 mm) was significantly better compared with fluoroscopy (5.86 mm) (p < 0.0001). Procedure time was in favor of fluoroscopy (7.39 vs. 10.13 min; p = 0.001). Fluoroscopy time during CBCT guidance was lower, but this difference is not significant (71.3 vs. 95.8 s; p = 0.056). DAP values for CBCT guidance and fluoroscopy were 514 and 174 mGy cm{sup 2}, respectively (p < 0.0001). There was a significant difference in favor of experienced CBCT guidance users regarding accuracy for both methods, procedure time of CBCT guidance, and added DAP values for fluoroscopy.ConclusionCBCT guidance allows users to perform PVP more accurately at the cost of higher patient dose and longer procedure time. Because procedural complications (e.g., cement leakage) are related to the accuracy of the needle placement, improvements in accuracy are clinically relevant. Training in CBCT guidance is essential to achieve greater accuracy and decrease procedure time/dose values.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Percutaneous Bone Biopsies: Comparison between Flat-Panel Cone-Beam CT and CT-Scan Guidance

PurposeThis study was designed to compare the accuracy of targeting and the radiation dose of bone biopsies performed either under fluoroscopic guidance using a cone-beam CT with real-time 3D image fusion software (FP-CBCT-guidance) or under conventional computed tomography guidance (CT-guidance).MethodsSixty-eight consecutive patients with a bone lesion were prospectively included. The bone biopsies were scheduled under FP-CBCT-guidance or under CT-guidance according to operating room availability. Thirty-four patients underwent a bone biopsy under FP-CBCT and 34 under CT-guidance. We prospectively compared the two guidance modalities for their technical success, accuracy, puncture time, and pathological success rate. Patient and physician radiation doses also were compared.ResultsAll biopsies were technically successful, with both guidance modalities. Accuracy was significantly better using FP-CBCT-guidance (3 and 5 mm respectively: p = 0.003). There was no significant difference in puncture time (32 and 31 min respectively, p = 0.51) nor in pathological results (88 and 88 % of pathological success respectively, p = 1). Patient radiation doses were significantly lower with FP-CBCT (45 vs. 136 mSv, p < 0.0001). The percentage of operators who received a dose higher than 0.001 mSv (dosimeter detection dose threshold) was lower with FP-CBCT than CT-guidance (27 vs. 59 %, p = 0.01).ConclusionsFP-CBCT-guidance for bone biopsy is accurate and reduces patient and operator radiation doses compared with CT-guidance.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Improved Visibility of Metastatic Disease in the Liver During Intra-Arterial Therapy Using Delayed Arterial Phase Cone-Beam CT

PurposeTo compare the visibility of liver metastases on dual-phase cone-beam CT (DP-CBCT) and digital subtraction angiography (DSA), with reference to preinterventional contrast-enhanced magnetic resonance imaging (CE-MRI) of the liver.MethodsThis IRB-approved, retrospective study included 28 patients with neuroendocrine (NELM), colorectal (CRCLM), or sarcoma (SLM) liver metastases who underwent DP-CBCT during intra-arterial therapy (IAT) between 01/2010 and 10/2014. DP-CBCT was acquired after a single contrast agent injection in the tumor-feeding arteries at early and delayed arterial phases (EAP and DAP). The visibility of each lesion was graded by two radiologists in consensus on a three-rank scale (complete, partial, none) on DP-CBCT and DSA images using CE-MRI as reference.Results47 NELM, 43 CRCLM, and 16 SLM were included. On DSA 85.1, 44.1, and 37.5 % of NELM, CRCLM, and SLM, were at least partially depicted, respectively. EAP-CBCT yielded significantly higher sensitivities of 88.3 and 87.5 % for CRCLM and SLM, respectively (p < 0.01), but not for NELM (89.4 %; p = 1.0). On DAP-CBCT all NELM, CRCLM, and SLM were visible (p < 0.001). Complete depiction was achieved on DSA for 59.6, 16.3, and 18.8 % of NELM, CRCLM, and SLM, respectively. The complete depiction rate on EAP-CBCT was significantly higher for CRCLM (46.5 %; p < 0.001), lower for NELM (40.4 %; p = 0.592), and similar for SLM (25 %, p = 0.399). On DAP-CBCT however, the highest rates of complete depiction were found—NELM (97.8 %; p = 0.008), CRCLM (95.3 %; p = 0.008), and SLM (100 %; p < 0.001).ConclusionDAP-CBCT substantially improved the visibility of liver metastases during IAT. Future studies need to evaluate the clinical impact.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Hepatic Arterial Embolization Using Cone Beam CT with Tumor Feeding Vessel Detection Software: Impact on Hepatocellular Carcinoma Response

PurposeDedicated tumor feeding vessel detection software (TFVDS) using cone beam CT has shown a higher sensitivity to detect tumor feeding vessels during hepatic arterial embolization (HAE) of hepatocellular carcinoma (HCC) compared to 2D imaging. Our primary hypothesis was that HCC tumors treated with HAE guided by a TFVDS would show more complete response (CR) than when treated with 2D imaging alone. Secondary analysis of the impact on X-ray exposure was performed.Materials and MethodsNineteen males and 8 females (median age: 69 year, 46–85) with 44 tumors (median size: 38 mm, 6–100) treated with selective HAE between January 2013 and December 2014 were included. Exclusion criteria were: extra-hepatic supply, >4 tumors, tumor size >10 cm, and adjunctive local therapy. Baseline patient and procedure characteristics were reviewed. Differences in CR per modified Response Evaluation Criteria in Solid Tumors were assessed by univariate and multivariate analyses for tumor size, number, location, particles size, and use of TFVDS.ResultsMedian imaging follow-up was 20.1 months (2–33). Use of TFVDS (13 patients, 19 tumors) was the only factor predictive of CR (OR = 3.85 [CI95%: 1.09, 13.67], p = 0.04) on univariate analysis but not on multivariate analysis (OR = 3.26 [0.87, 12.23], p = 0.08). A higher rate of CR was observed for HAE using TFVDS guidance versus 2D imaging alone (68.4%, 13–19, vs. 36%, 9–25, p = 0.03). Median dose area product was lower when TFVDS was used (149.7 Gy.cm{sup 2}, 38–365, vs. 227.8 Gy.cm{sup 2}, 85.3–468.6, p = 0.05).ConclusionsHCC embolized with TFVDS may result in improved local tumor response without increasing the dose exposure.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

C-Arm Cone Beam CT for Intraprocedural Image Fusion and 3D Guidance in Portal Vein Embolization (PVE)

PurposePortal vein embolization (PVE) is applied in patients with extended oncologic liver disease to induce hyperplasia of the future liver remnant and make resection feasible. Ultrasound (US) guidance is the gold standard for percutaneous portal vein access. This study evaluated feasibility and safety of C-arm cone beam computed tomography (CBCT) for needle guidance.Materials and MethodsIn 10 patients, puncture was performed under 3D needle guidance in a CBCT data set. Contrast-enhanced (CE) CBCT was generated (n = 7), or native CBCT was registered to pre-examination CE-CT via image fusion (n = 3). Technical success, number of punctures, puncture time (time between CBCT acquisition and successful portal vein access), dose parameters and safety were evaluated. For comparison, 10 patients with PVE under US guidance were analyzed retrospectively. Study and control group were matched for age, BMI, INR, platelets, portal vein anatomy.ResultsAll interventions were technically successful without intervention-related complications. In the study group, the mean number of puncture attempts was 3.1 ± 2.5. Mean puncture time was 12 min (±10). Mean total dose area product (DAP) was 288 Gy cm{sup 2} (±154). The mean relative share of CBCT-related radiation exposure was 6% (±3). Intervention times and DAP were slightly higher compared to the control group without reaching significance.ConclusionCBCT-guided PVE is feasible and safe. The relative dose of CBCT is low compared to the overall dose of the intervention. This technique may be a promising approach for difficult anatomic situations that limit the use of US for needle guidance.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Arms Down Cone Beam CT Hepatic Angiography Performance Assessment: Vascular Imaging Quality and Imaging Artifacts

IntroductionThe practice of positioning patients’ arms above the head during catheter-injected hepatic arterial phase cone beam CT (A-CBCT) imaging has been inherited from standard CT imaging due to image quality concerns, but interrupts workflow and extends procedure time. We sought to assess A-CBCT image quality and artifacts with arms extended above the head versus down by the side.MethodsWe performed an IRB approved retrospective evaluation of reformatted and 3D-volume rendered images from 91 consecutive A-CBCTs (43 arms up, 48 arms down) acquired during hepatic tumor arterial embolization procedures. Two interventional radiologists reviewed all A-CBCT imaging and assigned vessel visualization scores (VVS) from 1 to 5, ranging from non-diagnostic to optimal visualization. Streak artifacts across axial images were rated from 1 to 3 based on resulting image quality (none to significant). Presence of respiratory or cardiac motion during acquisition, body mass index and radiation dose area product (DAP) were also recorded and analyzed. Univariate and multivariate analyses were used to assess the impact of arm position on VVS and imaging artifacts.ResultsVVS were not significantly associated with arm position during A-CBCT imaging. One reader reported more streak artifacts across axial images in the arms down group (p = 0.005). DAP was not statistically different between the groups (23.9 Gy cm{sup 2} [6.1–73.4] arms up, 26.1 Gy cm{sup 2} [4.2–102.6] arms down, p = 0.54).ConclusionA-CBCT angiography performed with the arms above the head is not superior for clinically relevant hepatic vascular visualization compared to imaging performed with the arms by the patient’s side.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Numerical study of a smoothing algorithm for the complementarity system over the second-order cone

This paper deals with the complementarity system over the second-order cone (denoted by CSSOC) which contains a wide class of problems. We extend a class of regularized Chen–Harker–Kanzow–Smale smoothing functions studied by Huang and Sun (Appl Math Optim 52:237–262, 2005) for the linear complementarity problem to the CSSOC. Based on this class of functions, we propose a smoothing algorithm for solving the CSSOC. Under weak assumptions, we prove that the proposed algorithm has global and local quadratic convergence. The proposed algorithm is different from existing smoothing algorithms for solving the CSSOC because it adopts a new nonmonotone line search rule. In addition, our algorithm solves a new equation reformulation of the CSSOC. Numerical experiments indicate that the proposed algorithm is quite effective.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Manipulation of Dirac cones in intercalated epitaxial graphene

Graphene is an intriguing material in view of its unique Dirac quasi-particles, and the manipulation of its electronic structure is important in material design and applications. Here, we theoretically investigate the electronic band structure of epitaxial graphene on SiC with intercalation of rare earth metal ions (e.g., Yb and Dy) using first-principles calculations. We can use the intercalation to control the coupling of the constituent components (buffer layer, graphene, and substrate), resulting in strong modification of the graphene band structure. We also demonstrate that the metal-intercalated epitaxial graphene has tunable band structures by controlling the energies of Dirac cones as well as the linear and quadratic band dispersion depending on the intercalation layer and density. Thus, the metal intercalation is a viable method to manipulate the electronic band structure of the epitaxial graphene, which can enhance the functional utility and controllability of the material.

36 MATERIALS SCIENCE↗
DOE OSTI2016

First Clinical Investigation of Cone Beam Computed Tomography and Deformable Registration for Adaptive Proton Therapy for Lung Cancer

Purpose: An adaptive proton therapy workflow using cone beam computed tomography (CBCT) is proposed. It consists of an online evaluation of a fast range-corrected dose distribution based on a virtual CT (vCT) scan. This can be followed by more accurate offline dose recalculation on the vCT scan, which can trigger a rescan CT (rCT) for replanning. Methods and Materials: The workflow was tested retrospectively for 20 consecutive lung cancer patients. A diffeomorphic Morphon algorithm was used to generate the lung vCT by deforming the average planning CT onto the CBCT scan. An additional correction step was applied to account for anatomic modifications that cannot be modeled by deformation alone. A set of clinical indicators for replanning were generated according to the water equivalent thickness (WET) and dose statistics and compared with those obtained on the rCT scan. The fast dose approximation consisted of warping the initial planned dose onto the vCT scan according to the changes in WET. The potential under- and over-ranges were assessed as a variation in WET at the target's distal surface. Results: The range-corrected dose from the vCT scan reproduced clinical indicators similar to those of the rCT scan. The workflow performed well under different clinical scenarios, including atelectasis, lung reinflation, and different types of tumor response. Between the vCT and rCT scans, we found a difference in the measured 95% percentile of the over-range distribution of 3.4 ± 2.7 mm. The limitations of the technique consisted of inherent uncertainties in deformable registration and the drawbacks of CBCT imaging. The correction step was adequate when gross errors occurred but could not recover subtle anatomic or density changes in tumors with complex topology. Conclusions: A proton therapy workflow based on CBCT provided clinical indicators similar to those using rCT for patients with lung cancer with considerable anatomic changes.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2011

Coherent Cone-Beam X-ray Microscopy

A novel full-field imaging method using the (111) Bragg diffraction of a sub-micron gold crystal as the divergent cone-beam for sample illumination is reported. The divergence of the illumination allows for very high magnification, limited only by the achievable ratio of the crystal-to-sample and sample-to-detector distances. In this case an x-ray magnification of approximately 115 was achieved.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Light Cone Dynamics and EMC Effects in the Extraction of F{sub 2n} at Large Bjorken x

We discuss theoretical issues related to the extraction of deep inelastic (DIS) structure function of neutron from inclusive DIS scattering off the deuteron at large Bjorken x. Theoretical justification is given to the consideration of only pn component of the deuteron wave function and consistency with both the baryonic number and light-cone momentum conservation sum rules. Next we discuss the EMC type effects and argue that in all cases relevant to the nuclear DIS reactions at large x the main issue is the medium modification of the properties of bound nucleon rather than the non-nucleonic components like pions. We give brief description of the color screening model of EMC and within this model we estimate uncertainties in the extraction of the neutron DIS structure function at large x. We emphasize also that these uncertainties are rather ''model independent'' since any theoretical framework accounting for the medium modification is proportional to the magnitude of the virtuality of bound nucleon which increases with an increase of x.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Pion-photon transition form factor in light-cone sum rules

We extract constraints on the pion distribution amplitude from available data on the pionphoton transition form factor in the framework of light-cone sum rules. A pronounced discrepancy (2.7 - 3){sigma} between the Gegenbauer expansion coefficients extracted from the CELLO, CLEO, and Belle experimental data relative to those from BaBar is found. Predictions for the pion-photon transition form factor are presented by employing a pion distribution amplitude obtained long ago from QCD sum rules with nonlocal condensates. These predictions comply with the Belle data but disagree with those of BaBar beyond 9 GeV{sup 2}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Strain-induced gap transition and anisotropic Dirac-like cones in monolayer and bilayer phosphorene

The electronic properties of two-dimensional monolayer and bilayer phosphorene subjected to uniaxial and biaxial strains have been investigated using first-principles calculations based on density functional theory. Strain engineering has obvious influence on the electronic properties of monolayer and bilayer phosphorene. By comparison, we find that biaxial strain is more effective in tuning the band gap than uniaxial strain. Interestingly, we observe the emergence of Dirac-like cones by the application of zigzag tensile strain in the monolayer and bilayer systems. For bilayer phosphorene, we induce the anisotropic Dirac-like dispersion by the application of appropriate armchair or biaxial compressive strain. Our results present very interesting possibilities for engineering the electronic properties of phosphorene and pave a way for tuning the band gap of future electronic and optoelectronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗