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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Current Source Inverter Based Large Constant Power Speed Ratio SPM Machine Drive for Traction Applications

A high-performance surface permanent magnet (SPM) machine drive with an extended constant power speed ratio is proposed using a current source inverter (CSI) for a traction application. The constant-power operation regions of an SPM machine can be extended in an appealing fashion by taking advantage of the output voltage boost capability of the CSI. The CSI is naturally a boost-type converter, in contrast to the voltage source inverter (VSI) which has buck-type characteristics. To investigate the value of the CSI voltage boost feature, a new traction motor with higher rated voltage and lower rated current has been designed and compared to the motor that would be used with a VSI. The lower CSI current makes it possible to reduce the mass of the inverter and output power cable, benefiting power density and cost reduction. The SPM machine is modeled in the synchronous reference frame including the effect of the ac filter capacitors at the CSI output terminals. The capability of extending the speed range of the proposed motor is verified via closed-form analysis and FEA simulation, and its performance characteristics are compared with those of a VSI-based SPM motor of the same type.

42 ENGINEERING↗
DOE OSTI2014

SU-E-T-371: Validation of Organ Doses Delivered During Craniospinal Irradiation with Helical Tomotherapy

Purpose: New techniques have been developed to deliver more conformal treatments to the craniospinal axis. One concern, however, is the widespread low dose delivered and implications for possible late effects. The purpose of this work is for the first time to validate the organ doses calculated by the treatment planning system (TPS), including out-of-field doses for a pediatric craniospinal treatment (CSI). Methods: A CSI plan prescribed to 23.4 Gy and a posterior fossa boost plan to 30.6 Gy (total dose 54.0 Gy) was developed for a pediatric anthropomorphic phantom representing a 13 yearold- child. For the CSI plan, the planning target volumes (PTV) consisted of the brain and spinal cord with 2 mm and 5 mm expansions, respectively. Organs at risk (OAR) were contoured and included in the plan optimization. The plans were delivered on a helical tomotherapy unit. Thermoluminescent dosimeters (TLDs) were used to measure the dose at 54 positions within the PTV and OARs. Results: For the CSI treatment, the mean percent difference between TPS dose calculations and measurements was 5% for the PTV and 10% for the OARs. For the boost, the average was 3% for the PTV. The percent difference for the OARs, which lie outside the field and received a small fraction of the prescription dose, varied from 15% to 200%. However in terms of absolute dose, the average difference between measurement and TPS per treatment Gy was 2 cGy/Gy and 3 mGy/Gy for the CSI and boost plans, respectively. Conclusion: There was good agreement between doses calculated by the TPS and measurements for the CSI treatment. Higher percent differences were observed for out-of-field doses in the boost plan, but absolute dose differences were very small compared to the prescription dose. These findings can help in the estimation of late effects after radiotherapy for pediatric patients.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-446: Improving Craniospinal Irradiation Technique Using Volumetric Modulated Arc Therapy (VMAT) Planning and Its Dosimetric Verification

Purpose: The purpose of this study is to investigate a volumetric modulated arc therapy (VMAT) treatment planning technique for supine craniospinal irradiation (CSI). Evaluate the suitability of VMAT for CSI with dosimetric measurements and compare it to 3D conformal planning using specific plan metrics such as dose conformity, homogeneity, and dose of organs at risk (OAR). Methods: Ten CSI patients treated with conventional 3D technique were re-planned with VMAT. The PTV was contoured to include the whole contents of the brain and spinal canal with a uniform margin of 5 mm. VMAT plans were generated with two partial arcs covering the brain, two partial arcs for the superior portion of the spinal cord and two partial arcs covering the remaining inferior portion of the spinal cord. Conformity index (CI), heterogeneity indexes (HI) and max and mean doses of OAR were compared to 3D plans. VMAT plans were delivered onto an anthropomorphic phantom loaded with Gafchromic films and OSLDs placed at specific positions to evaluate the plan dose at the junctions and as well as the plan dose distributions. Results: This VMAT technique was validated with a clinical study of 10 patients. The average CI was 1.03±0.02 for VMAT plans and 1.96±0.32 for conformal plans. And the average HI was 1.15±0.01 for VMAT plans and 1.51±0.21 for conformal plans. The mean and max doses to the all OARs for VMAT plans were significantly lower than conformal plans. The measured dose in phantom for VAMT plans was comparable to the calculated dose in Eclipse and the doses at junctions were verified. Conclusion: VMAT CSI was able to achieve better dose conformity and heterogeneity as well as significantly reducing the dose to Heart, esophagus and larynx. VMAT CSI appears to be a dosimterically advantageous, faster delivery, has better reproducibility CSI treatment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Application of the Chloride Susceptibility Index to Study the Effects of Ni, Cr, Mn and Mo on the Repassivation of Stainless Steels

The effects of Ni, Cr, Mn and Mo on the very earliest stages of repassivation of stainless steels are quantified using the Chloride Susceptibility Index (CSI), which is an ab initio-based index for the evaluation of repassivation tendency. The quinary system of Fe-Ni-Cr-Mn-Mo is studied with density functional theory analysis and an electrochemisorption model developed previously by the authors, which are required to determine the CSI. The adsorption energies of O and Cl to different surface configurations are calculated, and then surface coverage maps of different species on the surface are obtained from the adsorption energies based on the Langmuir isotherm. Finally, CSI is calculated for different compositions of stainless steels. It is found that the effect of alloying elements on promoting repassivation of Fe alloys is in the order of Mn > ≈Ni > Cr > Mo when solute composition is less than 28 wt.%. A strong synergy is found between Cr and Mo such that a combination of these two elements at a certain ratio can give an optimal (low) CSI. Here, the usage of CSI for evaluating repassivation tendency of CRAs is validated by experimental measured repassivation potential, which shows a strong monotonic negative relation with CSI.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Bifocal Intracranial Germinoma: A Retrospective Analysis of Treatment Outcomes in 20 Patients and Review of the Literature

Purpose: Bifocal germinoma (BFG) is a rare intracranial neoplasm for which the choice of radiation therapy (RT) field is controversial. Some believe that BFG represents disseminated disease requiring craniospinal irradiation (CSI), whereas others believe that BFG represents localized disease and advocate for more limited fields. Methods and Materials: We analyzed 20 BFG patients at our institutions with classic bifocal lesions (pineal gland and suprasellar region). In addition, we identified 60 BFG patients from the literature. The RT fields, use of chemotherapy and extent of disease were recorded and analyzed for each patient. Results: There were 55 patients with bifocal lesions only (Group I), and 25 with bifocal lesions plus ventricular and/or CSF positive disease (Group II). The 5-year progression-free survival was 95% for Group I and 80% for Group II. In Group I, there were no failures in patients receiving CSI (n = 11), two spinal failures in those treated with more limited RT fields without chemotherapy (n = 17), and one spinal failure with chemotherapy (n = 23). In Group II, there were no failures in patients receiving CSI (n = 11), but four spinal failures were observed in patients receiving more limited RT fields with chemotherapy (n = 13); 1 patient who received whole-brain RT without chemotherapy experienced failure in the spine and brain. Conclusions: CSI is associated with excellent PFS in BFG. In Group I BFG patients, omission of spinal irradiation appears to be a reasonable approach, especially when chemotherapy is used. Patients with Group II BFG are best treated with CSI.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

Salvage Treatment for Recurrent Intracranial Germinoma After Reduced-Volume Radiotherapy: A Single-Institution Experience and Review of the Literature

Purpose: Intracranial germinomas (IGs) are highly curable with radiotherapy (RT). However, recurrence still occurs, especially when limited-field RT is applied, and the optimal salvage therapy remains controversial. Methods and Materials: Between January 1989 and December 2010, 14 patients with clinically or pathologically diagnosed recurrent IGs after RT were reviewed at our institution. Of these, 11 received focal-field RT, and the other 3 received whole-brain irradiation, whole-ventricle irradiation, and Gamma Knife radiosurgery as the respective first course of RT. In addition, we identified from the literature 88 patients with recurrent IGs after reduced-volume RT, in whom the details of salvage therapy were recorded. Results: The median time to recurrence was 30.3 months (range, 3.8-134.9 months). One patient did not receive further treatment and was lost during follow-up. Of the patients, 7 underwent salvage with craniospinal irradiation (CSI) plus chemotherapy (CT), 4 with CSI alone, 1 with whole-brain irradiation plus CT, and 1 with Gamma Knife radiosurgery. The median follow-up time was 105.1 months (range, 24.2-180.9 months). Three patients died without evidence of disease progression: two from second malignancies and one from unknown cause. The others remained disease free. The 3-year survival rate after recurrence was 83.3%. A total of 102 patients from our study and the literature review were analyzed to determine the factors affecting prognosis and outcomes. After recurrence, the 5-year survival rates were 71% and 92.9% for all patients and for those receiving salvage CSI, respectively. Univariate analysis showed that initial RT volume, initial RT dose, initial CT, and salvage RT type were significant prognostic predictors of survival. On multivariable analysis, salvage CSI was the most significant factor (p = 0.03). Conclusions: Protracted follow-up is recommended because late recurrence is not uncommon. CSI with or without CT is an effective salvage treatment for recurrence after reduced-volume RT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

Necrosis After Craniospinal Irradiation: Results From a Prospective Series of Children With Central Nervous System Embryonal Tumors

Purpose: Necrosis of the central nervous system (CNS) is a known complication of craniospinal irradiation (CSI) in children with medulloblastoma and similar tumors. We reviewed the incidence of necrosis in our prospective treatment series. Patients and Methods: Between 1996 and 2009, 236 children with medulloblastoma (n = 185) or other CNS embryonal tumors (n = 51) received postoperative CSI followed by dose-intense cyclophosphamide, vincristine, and cisplatin. Average risk cases (n = 148) received 23.4 Gy CSI, 36 Gy to the posterior fossa, and 55.8 Gy to the primary; after 2003, the treatment was 23.4 Gy CSI and 55.8 Gy to the primary. All high-risk cases (n = 88) received 36-39.6 Gy CSI and 55.8 Gy primary. The primary site clinical target volume margin was 2 cm (pre-2003) or 1 cm (post-2003). With competing risk of death by any cause, we determined the cumulative incidence of necrosis. Results: With a median follow-up of 52 months (range, 4-163 months), eight cases of necrosis were documented. One death was attributed. The median time to the imaging evidence was 4.8 months and to symptoms 6.0 months. The cumulative incidence at 5 years was 3.7% {+-} 1.3% (n = 236) for the entire cohort and 4.4% {+-} 1.5% (n = 196) for infratentorial tumor location. The mean relative volume of infratentorial brain receiving high-dose irradiation was significantly greater for patients with necrosis than for those without: {>=}50 Gy (92.12% {+-} 4.58% vs 72.89% {+-} 1.96%; P=.0337), {>=}52 Gy (88.95% {+-} 5.50% vs 69.16% {+-} 1.97%; P=.0275), and {>=}54 Gy (82.28% {+-} 7.06% vs 63.37% {+-} 1.96%; P=.0488), respectively. Conclusions: Necrosis in patients with CNS embryonal tumors is uncommon. When competing risks are considered, the incidence is 3.7% at 5 years. The volume of infratentorial brain receiving greater than 50, 52, and 54 Gy, respectively, is predictive for necrosis.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Variation in Proton Craniospinal Irradiation Practice Patterns in the United States: A Pediatric Proton Consortium Registry (PPCR) Study

Craniospinal irradiation (CSI) is commonly used for pediatric brain tumors with a propensity for spread in craniospinal fluid, principally medulloblastoma. Evolving technology has led to the use of highly conformal radiation therapy (RT) techniques for CSI, including proton therapy. Target delineation and plan coverage are critical for CSI, but there is ongoing controversy and variability in these realms, with little available data on practice patterns. We sought to characterize proton CSI practice patterns in the United States by examining CSI plans in the Pediatric Proton/Photon Consortium Registry (PPCR).

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

SU-E-T-255: Optimized Supine Craniospinal Irradiation with Image-Guided and Field Matched Beams

Purpose: Conventional craniospinal irradiation (CSI) challenges include dose inhomogeneity at field junctions and position uncertainty due to the field divergence, particular for the two spinal fields. Here we outline a new supine CSI technique to address these difficulties. Methods: Patient was simulated in supine position. The cranial fields had isocenter at C2/C3 vertebral and were matched with 1st spinal field. Their inferior border was chosen to avoid the shoulder, as well as chin from the 1st spine field. Their collimator angles were dependent on asymmetry jaw setting of the 1st spinal field. With couch rotation, the spinal field gantry angles were adjusted to ensure, the inferior border of 1st and superior border of 2nd spinal fields were perpendicular to the table top. The radio-opaque wire position for the spinal junction was located initially by the light field from an anterior setup beam, and was finalized by the portal imaging of the 1st spinal field. With reference to the spinal junction wire, the fields were matched by positioning the isocenter of the 2nd spinal field. A formula was derived to optimize supine CSI treatment planning, by utilizing the relationship among the Yjaw setting, the spinal field gantry angles, cranial field collimator angles, and the spinal field isocenters location. The plan was delivered with portal imaging alignment for the both cranial and spinal junctions. Results: Utilizing this technique with matching beams, and conventional technique such as feathering and forwarding planning, a homogenous dose distribution was achieved throughout the entire CSI treatment volume including the spinal junction. Placing the spinal junction wire visualized in both spinal portals, allows for precise determination and verification of the appropriate match line of the spine fields. Conclusion: This technique of optimization supine CSI achieved a homogenous dose distributions and patient localization accuracy with image-guided and matched beams.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

First-Principles Modeling of the Repassivation of Corrosion Resistant Alloys: Part II. Surface Adsorption Isotherms for Alloys and the Chloride Susceptibility Index

Quantitatively predicting the corrosion resistance of alloys is vital to the design and application of the next generation of superior corrosion resistant alloys (CRAs). Here, the Chloride Susceptibility Index (CSI), a scientifically based quantitative descriptor for repassivation tendency of CRAs, is proposed as a metric constructed through combining atomistically resolved information regarding adsorption and alloy surface composition with environmental conditions such as applied potential, temperature, pH, and Cl – concentration. Using this method, the response of CRAs to relevant environments can be predicted. CSI is determined by: (1) estimation of thermoequilibrium surface coverages of O and Cl by a Langmuir isotherm model using adsorption energies of different species (O, Cl, OH, H 2 O) obtained from DFT. (2) determination of CSI by integrating Cl surface coverage over a realistic window of applied potentials, thereby incorporating the effect of Cl surface coverage and electrochemical environment simultaneously. A series of Ni-Cr-X alloys was used as an example to develop and validate the method through studying the effect of different alloy solutes X on chloride resistance. Here, the trends and relations predicted by CSI are in qualitative agreements with experimental observations. Moreover, a quantitative correlation is found between CSI and the repassivation potential.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Integrated Motor and Drive (IMD) for Traction Applications Project (Final Technical Report)

This paper proposes the concept of the topological equivalence between the commutation cells of a voltage source inverter (VSI) and a current source inverter (CSI) using duality and equivalent circuit transformation techniques. A switching resonance of CSI is analyzed and an effective three-phase RC damper is derived from the dc-link RC damper of VSIs based on the topological equivalence of the VSI and CSI commutation cells. Furthermore, a new three-phase RC damper design framework utilizing the topological equivalence is proposed. Experimental results verify that the proposed three-phase RC damper design for CSI significantly reduces the switching resonance and improves the CSI’s output waveform total harmonics distortions (THDs).

42 ENGINEERING↗
NASA NTRS1973

Characteristics of cesium iodide for use as a particle discriminator for high energy cosmic rays

The possible use of CsI to discriminate between high energy cosmic ray electrons and interacting protons has been investigated. The pulse-shape properties as a function of ionization density, temperature, and spectral response are presented for thallium-activated CsI and as a function of ionization density for sodium-activated CsI. The results are based on previously published data and on corroborative measurements from the present work. Experimental results on the response of CsI to electron-induced electromagnetic cascades and to interacting hadrons are described. Bibliographies of publications dealing with the properties of CsI and with pulse-shape discrimination techniques are presented.

Crannell, C. J.↗
NASA NTRS1989

Control/structure interaction design methodology

The Control Structure Interaction Program is a technology development program for spacecraft that exhibit interactions between the control system and structural dynamics. The program objectives include development and verification of new design concepts (such as active structure) and new tools (such as a combined structure and control optimization algorithm) and their verification in ground and possibly flight test. The new CSI design methodology is centered around interdisciplinary engineers using new tools that closely integrate structures and controls. Verification is an important CSI theme and analysts will be closely integrated to the CSI Test Bed laboratory. Components, concepts, tools and algorithms will be developed and tested in the lab and in future Shuttle-based flight experiments. The design methodology is summarized in block diagrams depicting the evolution of a spacecraft design and descriptions of analytical capabilities used in the process. The multiyear JPL CSI implementation plan is described along with the essentials of several new tools. A distributed network of computation servers and workstations was designed that will provide a state-of-the-art development base for the CSI technologies.

Briggs, Hugh C.↗
NASA NTRS1990

The NASA controls-structures interaction technology program

The interaction between a flexible spacecraft structure and its control system is commonly referred to as controls-structures interaction (CSI). The CSI technology program is developing the capability and confidence to integrate the structure and control system, so as to avoid interactions that cause problems and to exploit interactions to increase spacecraft capability. A NASA program has been initiated to advance CSI technology to a point where it can be used in spacecraft design for future missions. The CSI technology program is a multicenter program utilizing the resources of the NASA Langley Research Center (LaRC), the NASA Marshall Space Flight Center (MSFC), and the NASA Jet Propulsion Laboratory (JPL). The purpose is to describe the current activities, results to date, and future activities of the NASA CSI technology program.

Newsom, Jerry R.↗
NASA NTRS1990

The NASA controls-structures interaction technology program

The interaction between a flexible spacecraft structure and its control system is commonly referred to as controls-structures interaction (CSI). The CSI technology program is developing the capability and confidence to integrate the structure and control system, so as to avoid interactions that cause problems and to exploit interactions to increase spacecraft capability. A NASA program has been initiated to advance CSI technology to a point where it can be used in spacecraft design for future missions. The CSI technology program is a multicenter program utilizing the resources of the NASA Langley Research Center, the NASA Marshall Space Flight Center, and the NASA Jet Propulsion Laboratory. The purpose of this paper is to describe the current activities, results to date, and future activities of the NASA CSI technology program.

Newsom, Jerry R.↗
NASA NTRS1993

Micro-precision control/structure interaction technology for large optical space systems

The CSI program at JPL is chartered to develop the structures and control technology needed for sub-micron level stabilization of future optical space systems. The extreme dimensional stability required for such systems derives from the need to maintain the alignment and figure of critical optical elements to a small fraction (typically 1/20th to 1/50th) of the wavelength of detected radiation. The wavelength is about 0.5 micron for visible light and 0.1 micron for ultra-violet light. This lambda/50 requirement is common to a broad class of optical systems including filled aperture telescopes (with monolithic or segmented primary mirrors), sparse aperture telescopes, and optical interferometers. The challenge for CSI arises when such systems become large, with spatially distributed optical elements mounted on a lightweight, flexible structure. In order to better understand the requirements for micro-precision CSI technology, a representative future optical system was identified and developed as an analytical testbed for CSI concepts and approaches. An optical interferometer was selected as a stressing example of the relevant mission class. The system that emerged was termed the Focus Mission Interferometer (FMI). This paper will describe the multi-layer control architecture used to address the FMI's nanometer level stabilization requirements. In addition the paper will discuss on-going and planned experimental work aimed at demonstrating that multi-layer CSI can work in practice in the relevant performance regime.

Sirlin, Samuel W.↗
NASA NTRS1993

Effect of aerobic capacity on Lower Body Negative Pressure (LBNP) tolerance in females

This investigation determined whether a relationship exists in females between: (1) aerobic capacity and Lower Body Negative Pressure (LBNP); and (2) aerobic capacity and change in LBNP tolerance induced by bed rest. Nine females, age 27-47 (34.6 plus or minus 6.0 (Mean plus or minus SD)), completed a treadmill-graded exercise test to establish aerobic capacity. A presyncopal-limited LBNP test was performed prior to and after 13 days of bed rest at a 6 deg head-down tilt. LBNP tolerance was quantified as: (1) the absolute level of negative pressure (NP) tolerated for greater than or equal to 60 sec; and (2) Luft's Cumulative Stress Index (CSI). Aerobic capacity was 33.3 plus or minus 5.0 mL/kg/min and ranged from 25.7 to 38.7. Bed rest was associated with a decrease in NP tolerance (-9.04 1.6 kPa(-67.8 plus or minus 12.0 mmHg) versus -7.7 1.1 kPa(-57.8 plus or minus 8.33 mmHg); p = 0.028) and in CSI (99.4 27.4 kPa min(745.7 plus or minus 205.4 mmHg min) versus 77.0 16.9 kPa min (577.3 plus or minus mmHg min); p = 0.008). The correlation between aerobic capacity and absolute NP or CSI pre-bed rest did not differ significantly from zero (r = -0.56, p = 0.11 for NP; and r = -0.52, p = 0.16 for CSI). Also, no significant correlation was observed between aerobic and pre- to post-rest change for absolute NP tolerance (r = -0.35, p = 0.35) or CSI (r = -0.32, p = 0.40). Therefore, a significant relationship does not exist between aerobic capacity and orthostatic function or change in orthostatic function induced by bed rest.

Moore, Alan D., Jr.↗
NASA NTRS1992

X-ray spectroscopy with silicon pin and avalanche photo diodes

Results of an evaluation of silicon P-Intrinsic-N (PIN) photodiodes and Avalanche Photodiodes (APD) for the direct detection of soft x rays from 1 to 20 keV and for the detection of scintillation light output from CsI(TI) for higher x ray energies (30 to 1000 keV) are presented. About one keV resolution was achieved at room temperature for both the PIN and APD detectors for soft x rays (1 to 20 keV). Commercially available, low power (18 mV), low noise, hybrid preamplifiers, were used. These photodiodes were also coupled to CsI(TI) scintillator and obtained about 6 resolution at 662 keV. The photodiode frequency response matches well with the emission spectrum of the CsI(TI) scintillator providing good spectral resolution and a higher signal than NaI(TI) when viewed by conventional photomultipliers. A PIN-CsI(TI) combination provides a low energy threshold of around 60 keV while for the APD-CsI(TI) it is 15 keV.

Desai, U. D.↗