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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A Soft-Matter Biomolecular Memristor Synapse for Neuromorphic Systems

The goal of neuromorphic computing is to recreate the computational power and efficiency of the human brain with circuitry. The ability of the brain to solve complex real time tasks, while consuming 20 W of power on average, is made possible through its connection density, adaptability, and parallel processing. Recreating these features using traditional electronics circuit elements is incredibly difficult, and therefore, soft-matter memristors made of biomolecules similar to those found in biological synapses and capable of emulating various synaptic features can be used as neuromorphic hardware. In this work, we introduce and experimentally demonstrate an electronic neuron circuit capable of interacting with ionic, soft-matter memristors. These memristors are proven to exhibit short-term plasticity, especially paired-pulse facilitation and depression found in presynaptic terminals - features that are not found in state-of-the-art solid-state memristors. We make use of these features for applications in online learning by developing a synapse-neuron circuit which implements spike-rate-dependent plasticity (SRDP) as a learning function.

Weiss, Ryan↗
DOE OSTI2016

A large-scale study of soft-errors on GPUs in the field

Parallelism provided by the GPU architecture has enabled domain scientists to simulate physical phenomena at a much faster rate and finer granularity than what was previously possible by CPU-based large-scale clusters. Architecture researchers have been investigating reliability characteristics of GPUs and innovating techniques to increase the reliability of these emerging computing devices. Such efforts are often guided by technology projections and simplistic scientific kernels, and performed using architectural simulators and modeling tools. Lack of large-scale field data impedes the effectiveness of such efforts. This study attempts to bridge this gap by presenting a large-scale field data analysis of GPU reliability. We characterize and quantify different kinds of soft-errors on the Titan supercomputer's GPU nodes. Our study uncovers several interesting and previously unknown insights about the characteristics and impact of soft-errors.

Nie, Bin↗
DOE OSTI2016

Load-Dependent Soft-Switching Method of Half-Bridge Current Doubler for High-Voltage Point-of-Load Converter in Data Center Power Supplies

With the increased cloud computing and digital information storage, the energy requirement of data centers keeps increasing. A high-voltage point of load (HV POL) with an input series output parallel structure is proposed to convert 400 to 1 VDC within a single stage to increase the power conversion efficiency. The symmetrical controlled half-bridge current doubler is selected as the converter topology in the HV POL. A load-dependent soft-switching method has been proposed with an auxiliary circuit that includes inductor, diode, and MOSFETs so that the hard-switching issue of typical symmetrical controlled half-bridge converters is resolved. The operation principles of the proposed soft-switching half-bridge current doubler have been analyzed in detail. Then, the necessity of adjusting the timing with the loading in the proposed method is analyzed based on losses, and a controller is designed to realize the load-dependent operation. A lossless RCD current sensing method is used to sense the output inductor current value in the proposed load-dependent operation. In conclusion, experimental efficiency of a hardware prototype is provided to show that the proposed method can increase the converter's efficiency in both heavy- and light-load conditions.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2019

A Hybrid Modulation Method for Single-Stage Soft-Switching Inverter Based on Series Resonant Converter

Pseudo-dc-link inverters are promising due to the single-stage configuration. The inverters can be isolated by high-frequency transformers, which also provide the freedom of step-up/down through winding turns ratio. Conventionally, a pseudo-dc-link inverter is based upon a pulsewidth modulation converter like flyback converter, but the accompanying switching losses can degrade efficiency and overall system performance. Alternatively, resonant converters (e.g., series resonant converter) seem to fit the need as they typically display soft-switching characteristics. However, the relevant research results are scarce because of two main reasons: high resonant current and limited soft-switching range. To overcome the difficulties, a hybrid modulation method is proposed in this article for a pseudo-dc-link inverter based on series resonant converter. In high-line region, the inverter operates with variable-frequency modulation, which leads to zero-voltage switching and relatively low-resonant current. In low-line region, the inverter operates with a short-pulse density modulation so that switching losses are greatly curtailed without excessive resonant current. The merits in both regions together contribute toward the high efficiency of the inverter. This article presents the operational principle of the proposed modulation as well as a comparison with other modulation methods. In addition, a 400 V-230 Vac, 2-kW prototype was built to verify the proposed modulation and the peak efficiency reaches 98.0%.

42 ENGINEERING↗
DOE OSTI2020

Performance simulation of the soft gamma-ray concentrator

The soft gamma-ray concentrator is a telescope mission concept utilizing a suitable arrangement of bent multilayer structures of alternating low- and high-density materials. This lens is able to channel gamma-ray photons via total external reflection and concentrate the incident radiation to a point. The channeling technique offers the potential for concentrating gamma rays with focal lengths <10 m and energies >100 keV, beyond the reach of current grazing-incidence hard x-ray mirrors. For the performance estimation of such an instrument, we have developed a flexible set of computer modeling tools to compute the optical properties of multilayer structures, predict the channeling efficiency for a given multilayer configuration, and aid in the optimization of potential gamma-ray concentrator-based telescope designs. This modeling includes the multilayer optical properties calculated by the IMD software, the ray tracing using an IDL code, and the focal plane detector simulation by MEGAlib. We illustrate the potential of this approach by presenting simulated astronomical observations from a balloon-borne platform. The final result, including simulated effective area, instrument sensitivity, and polarization performance, shows that the gamma-ray concentrator will provide greatly increased sensitivity for next-generation soft gamma-ray missions with modest cost and complexity.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

BlackCAT CubeSat: a soft x-ray sky monitor, transient finder, and burst detector for high-energy and multimessenger astophysics

Here we present the conceptual design of a wide field imager onboard a 6U class CubeSat platform for the study of GRB prompt and afterglow emission and detection of electromagnetic counterparts of gravitational waves in soft X-rays. The planned instrument configuration consists of an array of X-ray Hybrid CMOS detectors (HCD), chosen for their soft-X-ray response, flexible and rapid readout rate, and low power, which makes these detectors well suited for detecting bright transients on a CubeSat platform. The wide field imager is realized by a 2D coded mask. This paper will give an overview of the instrument design and the scientific requirements of the proposed mission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Telerobotic system concept for real-time soft-tissue imaging during radiotherapy beam delivery

Purpose: The curative potential of external beam radiation therapy is critically dependent on having the ability to accurately aim radiation beams at intended targets while avoiding surrounding healthy tissues. However, existing technologies are incapable of real-time, volumetric, soft-tissue imaging during radiation beam delivery, when accurate target tracking is most critical. The authors address this challenge in the development and evaluation of a novel, minimally interfering, telerobotic ultrasound (U.S.) imaging system that can be integrated with existing medical linear accelerators (LINACs) for therapy guidance. Methods: A customized human-safe robotic manipulator was designed and built to control the pressure and pitch of an abdominal U.S. transducer while avoiding LINAC gantry collisions. A haptic device was integrated to remotely control the robotic manipulator motion and U.S. image acquisition outside the LINAC room. The ability of the system to continuously maintain high quality prostate images was evaluated in volunteers over extended time periods. Treatment feasibility was assessed by comparing a clinically deployed prostate treatment plan to an alternative plan in which beam directions were restricted to sectors that did not interfere with the transabdominal U.S. transducer. To demonstrate imaging capability concurrent with delivery, robot performance and U.S. target tracking in a phantom were tested with a 15 MV radiation beam active. Results: Remote image acquisition and maintenance of image quality with the haptic interface was successfully demonstrated over 10 min periods in representative treatment setups of volunteers. Furthermore, the robot's ability to maintain a constant probe force and desired pitch angle was unaffected by the LINAC beam. For a representative prostate patient, the dose-volume histogram (DVH) for a plan with restricted sectors remained virtually identical to the DVH of a clinically deployed plan. With reduced margins, as would be enabled by real-time imaging, gross tumor volume coverage was identical while notable reductions of bladder and rectal volumes exposed to large doses were possible. The quality of U.S. images obtained during beam operation was not appreciably degraded by radiofrequency interference and 2D tracking of a phantom object in U.S. images obtained with the beam on/off yielded no significant differences. Conclusions: Remotely controlled robotic U.S. imaging is feasible in the radiotherapy environment and for the first time may offer real-time volumetric soft-tissue guidance concurrent with radiotherapy delivery.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2013

Real-time soft tissue motion estimation for lung tumors during radiotherapy delivery

Purpose: To provide real-time lung tumor motion estimation during radiotherapy treatment delivery without the need for implanted fiducial markers or additional imaging dose to the patient.Methods: 2D radiographs from the therapy beam's-eye-view (BEV) perspective are captured at a frame rate of 12.8 Hz with a frame grabber allowing direct RAM access to the image buffer. An in-house developed real-time soft tissue localization algorithm is utilized to calculate soft tissue displacement from these images in real-time. The system is tested with a Varian TX linear accelerator and an AS-1000 amorphous silicon electronic portal imaging device operating at a resolution of 512 × 384 pixels. The accuracy of the motion estimation is verified with a dynamic motion phantom. Clinical accuracy was tested on lung SBRT images acquired at 2 fps.Results: Real-time lung tumor motion estimation from BEV images without fiducial markers is successfully demonstrated. For the phantom study, a mean tracking error <1.0 mm [root mean square (rms) error of 0.3 mm] was observed. The tracking rms accuracy on BEV images from a lung SBRT patient (≈20 mm tumor motion range) is 1.0 mm.Conclusions: The authors demonstrate for the first time real-time markerless lung tumor motion estimation from BEV images alone. The described system can operate at a frame rate of 12.8 Hz and does not require prior knowledge to establish traceable landmarks for tracking on the fly. The authors show that the geometric accuracy is similar to (or better than) previously published markerless algorithms not operating in real-time.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Computerized detection of noncalcified plaques in coronary CT angiography: Evaluation of topological soft gradient prescreening method and luminal analysis

Purpose: The buildup of noncalcified plaques (NCPs) that are vulnerable to rupture in coronary arteries is a risk for myocardial infarction. Interpretation of coronary CT angiography (cCTA) to search for NCP is a challenging task for radiologists due to the low CT number of NCP, the large number of coronary arteries, and multiple phase CT acquisition. The authors conducted a preliminary study to develop machine learning method for automated detection of NCPs in cCTA. Methods: With IRB approval, a data set of 83 ECG-gated contrast enhanced cCTA scans with 120 NCPs was collected retrospectively from patient files. A multiscale coronary artery response and rolling balloon region growing (MSCAR-RBG) method was applied to each cCTA volume to extract the coronary arterial trees. Each extracted vessel was reformatted to a straightened volume composed of cCTA slices perpendicular to the vessel centerline. A topological soft-gradient (TSG) detection method was developed to prescreen for NCP candidates by analyzing the 2D topological features of the radial gradient field surface along the vessel wall. The NCP candidates were then characterized by a luminal analysis that used 3D geometric features to quantify the shape information and gray-level features to evaluate the density of the NCP candidates. With machine learning techniques, useful features were identified and combined into an NCP score to differentiate true NCPs from false positives (FPs). To evaluate the effectiveness of the image analysis methods, the authors performed tenfold cross-validation with the available data set. Receiver operating characteristic (ROC) analysis was used to assess the classification performance of individual features and the NCP score. The overall detection performance was estimated by free response ROC (FROC) analysis. Results: With our TSG prescreening method, a prescreening sensitivity of 92.5% (111/120) was achieved with a total of 1181 FPs (14.2 FPs/scan). On average, six features were selected during the tenfold cross-validation training. The average area under the ROC curve (AUC) value for training was 0.87 ± 0.01 and the AUC value for validation was 0.85 ± 0.01. Using the NCP score, FROC analysis of the validation set showed that the FP rates were reduced to 3.16, 1.90, and 1.39 FPs/scan at sensitivities of 90%, 80%, and 70%, respectively. Conclusions: The topological soft-gradient prescreening method in combination with the luminal analysis for FP reduction was effective for detection of NCPs in cCTA, including NCPs causing positive or negative vessel remodeling. The accuracy of vessel segmentation, tracking, and centerline identification has a strong impact on NCP detection. Studies are underway to further improve these techniques and reduce the FPs of the CADe system.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

SU-E-J-269: Assessing the Precision of Dose Delivery in CBCT-Guided Stereotactic Body Radiation Therapy for Lung and Soft Tissue Metastatic Lesions

Purpose: Ensuring reproducibility of target localization is critical to accurate stereotactic body radiation treatment (SBRT) for lung and soft tissue metastatic lesions. To characterize interfraction variability in set-up and evaluate PTV margins utilized for SBRT, daily CBCTs were used to calculate delivered target and OAR doses compared to those expected from planning. Methods: CBCT images obtained prior to each fraction of SBRT for a lung and thyroid metastatic lesion were evaluated. The target CTV/ITV and OARs on each of 8 CBCT data sets were contoured. Using MIM fusion software and Pinnacle{sup 3} RTP system, delivered dose distribution was reconstructed on each CBCT, utilizing translational shifts performed prior to treatment. Actual delivered vs. expected doses received by target CTV/ITV and adjacent critical structures were compared to characterize accuracy of pre-treatment translational shifts and PTV margins. Results: The planned CTV/ITV D95% and V100% were 4595cGy and 91.47% for the lung lesion, and 3010cGy and 96.34% for the thyroid lesion. Based on CBCT analysis, actual mean D95% and V100% for lung ITV were 4542±344.4cGy and 91.54±3.45%; actual mean D95% and V100% for thyroid metastasis CTV were 3005±25.98cGy and 95.20±2.522%. For the lung lesion, ipsilateral lung V20, heart V32 (cc) and spinal cord (.03 cc) max were 110.15cc, 3.33cc, and 1680cGy vs. 110.27±14.79cc, 6.74±3.76cc, and 1711±46.56cGy for planned vs. delivered doses, respectively. For the thyroid metastatic lesion, esophagus V18, trachea (.03 cc) max, and spinal cord (.03 cc) max were 0.35cc, 2555cGy, and 850cGy vs. 0.16±0.13cc, 2147±367cGy, and 838±45cGy for planned vs. delivered treatments, respectively. Conclusion: Minimal variability in SBRT target lesion dose delivered based on pre-treatment CBCT-based translational shifts suggests tighter PTV margins may be considered to further decrease dose to surrounding critical structures. Guidelines for optimal target alignment during CBCT-guidance for lung and soft tissue metastatic lesions treated with SBRT are being established.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

A model for complex flows of soft glassy materials with application to flows through fixed fiber beds

The soft glassy rheology (SGR) model has successfully described the time dependent simple shear rheology of a broad class of complex fluids including foams, concentrated emulsions, colloidal glasses, and solvent-free nanoparticle-organic hybrid materials (NOHMs). The model considers a distribution of mesoscopic fluid elements that hop from trap to trap at a rate which is enhanced by the work done to strain the fluid element. While an SGR fluid has a broad exponential distribution of trap energies, the rheology of NOHMs is better described by a narrower energy distribution and we consider both types of trap energy distributions in this study. We introduce a tensorial version of these models with a hopping rate that depends on the orientation of the element relative to the mean stress field, allowing a range of relative strengths of the extensional and simple shear responses of the fluid. As an application of these models we consider the flow of a soft glassy material through a dilute fixed bed of fibers. The dilute fixed bed exhibits a range of local linear flows which alternate in a chaotic manner with time in a Lagrangian reference frame. It is amenable to an analytical treatment and has been used to characterize the strong flow response of many complex fluids including fiber suspensions, dilute polymer solutions and emulsions. We show that the accumulated strain in the fluid elements has an abrupt nonlinear growth at a Deborah number of order one in a manner similar to that observed for polymer solutions. The exponential dependence of the hopping rate on strain leads to a fluid element deformation that grows logarithmically with Deborah number at high Deborah numbers. SGR fluids having a broad range of trap energies flowing through fixed beds can exhibit a range of rheological behaviors at small Deborah numbers ranging from a yield stress, to a power law response and finally to Newtonian behavior.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Necklace-structured high-harmonic generation for low-divergence, soft x-ray harmonic combs with tunable line spacing

The extreme nonlinear optical process of high-harmonic generation (HHG) makes it possible to map the properties of a laser beam onto a radiating electron wave function and, in turn, onto the emitted x-ray light. Bright HHG beams typically emerge from a longitudinal phased distribution of atomic-scale quantum antennae. Here, we form a transverse necklace-shaped phased array of linearly polarized HHG emitters, where orbital angular momentum conservation allows us to tune the line spacing and divergence properties of extreme ultraviolet and soft x-ray high-harmonic combs. The on-axis HHG emission has extremely low divergence, well below that obtained when using Gaussian driving beams, which further decreases with harmonic order. This work provides a new degree of freedom for the design of harmonic combs—particularly in the soft x-ray regime, where very limited options are available. Such harmonic beams can enable more sensitive probes of the fastest correlated charge and spin dynamics in molecules, nanoparticles, and materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Autonomous alignment and healing in multilayer soft electronics using immiscible dynamic polymers

Self-healing soft electronic and robotic devices can, like human skin, recover autonomously from damage. While current devices use a single type of dynamic polymer for all functional layers to ensure strong interlayer adhesion, this approach requires manual layer alignment. In this study, we used two dynamic polymers, which have immiscible backbones but identical dynamic bonds, to maintain interlayer adhesion while enabling autonomous realignment during healing. These dynamic polymers exhibit a weakly interpenetrating and adhesive interface, whose width is tunable. When multilayered polymer films are misaligned after damage, these structures autonomously realign during healing to minimize interfacial free energy. Finally, we fabricated devices with conductive, dielectric, and magnetic particles that functionally heal after damage, enabling thin-film pressure sensors, magnetically assembled soft robots, and underwater circuit assembly.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Quark degrees of freedom in the production of soft pion jets

Experimental results obtained by studying the properties of soft jets in the 4-velocity space at √s ∼ 2 to 20 GeV are presented. The changes in the mean distance from the jet axis to the jet particles, the mean kinetic energy of these particles, and the cluster dimension in response to the growth of the collision energy are consistent with the assumption that quark degrees of freedom manifest themselves in processes of pion-jet production at intermediate energies. The energy at which quark degrees of freedom begin to manifest themselves experimentally in the production of soft pion jets is estimated for the first time. The estimated value of this energy is 2.8 ± 0.6 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Nitrogen soft and hard X-ray emissions using different shapes of anodes in a 4-kJ plasma focus device

The effect of different anode tip geometries on the intensity of soft and hard X-rays emitted from a 4-kJ plasma focus device is investigated using five different anode tips. The shapes of the uppermost region of these anodes (tips) have been cylindrical-flat, cylindrical-hollow, spherical-convex, cone-flat, and cone-hollow. For time-resolved measurement of the emitted X-rays, several BPX-65 pin diodes covered by different filters and a fast plastic scintillator are used. Experimental results have shown that, the highest intensity of the both soft and hard X-ray is recorded in cone-flat, spherical-convex, and cone-hollow tips, respectively. The use of cone-flat anode tip has augmented the emitted X-ray three times.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Reducing Soft-error Vulnerability of Caches using Data Compression

With ongoing chip miniaturization and voltage scaling, particle strike-induced soft errors present increasingly severe threat to the reliability of on-chip caches. In this paper, we present a technique to reduce the vulnerability of caches to soft-errors. Our technique uses data compression to reduce the number of vulnerable data bits in the cache and performs selective duplication of more critical data-bits to provide extra protection to them. Microarchitectural simulations have shown that our technique is effective in reducing architectural vulnerability factor (AVF) of the cache and outperforms another technique. For single and dual-core system configuration, the average reduction in AVF is 5.59X and 8.44X, respectively. Also, the implementation and performance overheads of our technique are minimal and it is useful for a broad range of workloads.

Mittal, Sparsh↗
DOE OSTI2012

Development and calibration of mirrors and gratings for the Soft X-ray materials science beamline at the Linac Coherent Light Source free-electron laser

This article discusses the development and calibration of the x-ray reflective and diffractive elements for the Soft X-ray Materials Science (SXR) beamline of the Linac Coherent Light Source (LCLS) free-electron laser (FEL), designed for operation in the 500 – 2000 eV region. The surface topography of three Si mirror substrates and two Si diffraction grating substrates was examined by atomic force microscopy (AFM) and optical profilometry. The figure of the mirror substrates was also verified via surface slope measurements with a long trace profiler. A boron carbide (B 4 C) coating especially optimized for the LCLS FEL conditions was deposited on all SXR mirrors and gratings. Coating thickness uniformity of 0.14 nm root mean square (rms) across clear apertures extending to 205 mm length was demonstrated for all elements, as required to preserve the coherent wavefront of the LCLS source. The reflective performance of the mirrors and the diffraction efficiency of the gratings were calibrated at beamline 6.3.2 at the Advanced Light Source synchrotron. To verify the integrity of the nanometer-scale grating structure, the grating topography was examined by AFM before and after coating. This is to our knowledge the first time B 4 C-coated diffraction gratings are demonstrated for operation in the soft x-ray region.

36 MATERIALS SCIENCE↗