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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

General Anesthesia Versus Conscious Sedation in Acute Stroke Treatment: The Importance of Head Immobilization

PurposeWhile today mechanical thrombectomy is an established treatment option for main branch occlusions in anterior circulation stroke, there is still an ongoing debate on the kind of anesthesia to be preferred. Introducing a simple method for head stabilization, we analyzed safety and duration of endovascular recanalization procedures under general anesthesia (GA) and conscious sedation (CS).MethodsWe retrospectively identified 84 consecutive patients who underwent mechanical thrombectomy owing to acute anterior circulation stroke. Fifty-three were treated under GA and 31 under CS equipped with a standard cervical collar to reduce head movement. We evaluated recanalization results, in-house time to start recanalization, procedure times, technical and clinical complication rates, and conversion rates from CS to GA.ResultsRecanalization of mTICI ≥2b was achieved in 80 % under CS and in 81 % under GA. Median in-house time to start recanalization for CS was 60 min (IQR 28; 44–72) and 77 min (IQR 23; 68–91) for GA (P = 0.001). Median procedure time under CS was 35 min (IQR 43; 69–25) and 41 min (IQR 43; 66–23) for GA (P = 0.9). No major complications such as ICH occurred in either group, and no conversions from CS to GA were necessary.ConclusionMechanical thrombectomy can be performed faster and safely under CS in combination with simple head immobilization using a standard cervical collar.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Predicting Treatment Response of Colorectal Cancer Liver Metastases to Conventional Lipiodol-Based Transarterial Chemoembolization Using Diffusion-Weighted MR Imaging: Value of Pretreatment Apparent Diffusion Coefficients (ADC) and ADC Changes Under Therapy

PurposeTo use absolute pretreatment apparent diffusion coefficients (ADC) derived from diffusion-weighted MR imaging (DWI) to predict response to repetitive cTACE for unresectable liver metastases of colorectal carcinoma (CRLM) at 1 and 3 months after start of treatment.Materials and MethodsFifty-five metastases in 34 patients were examined with DWI prior to treatment and 1 month after initial cTACE. Treatment was performed in 4-week intervals. Response was evaluated at 1 and 3 months after start of therapy. Metastases showing a decrease of ≥30% in axial diameter were classified as responding lesions.ResultsOne month after initial cTACE, seven lesions showed early response. There was no significant difference in absolute pretreatment ADC values between responding and non-responding lesions (p = 0.94). Three months after initial cTACE, 17 metastases showed response. There was a significant difference (p = 0.021) between absolute pretreatment ADC values of lesions showing response (median 1.08 × 10{sup −3} mm{sup 2}/s) and no response (median 1.30 × 10{sup −3} mm{sup 2}/s). Pretreatment ADC showed fair diagnostic value to predict response (AUC 0.7). Lesions showing response at 3 months also revealed a significant increase in ADC between measurements before treatment and at one month after initial cTACE (p < 0.001). Applying an increase in ADC of 12.17%, response at 3 months after initial cTACE could be predicted with a sensitivity and specificity of 77 and 74%, respectively (AUC 0.817). Furthermore, there was a strong and significant correlation (r = 0.651, p < 0.001) between percentage change in size after third cTACE and percentage change in ADC.ConclusionIn patients with CRLM, ADC measurements are potential biomarkers for assessing response to cTACE.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Percutaneous Mechanical Thromboembolectomy in Acute Lower Limb Ischemia

Purpose: To analyze the immediate outcome of percutaneous mechanical thromboembolectomy in acute infrainguinal leg ischemia in a consecutive cohort of patients with acute lower limb ischemia. Material and Method: We retrospectively analyzed the data of 156 acute infrainguinal ischemic events in 148 patients. Patients presented with acute limb ischemia Rutherford category I in 68 cases (44%), Rutherford category II A in 64 instances (41%) and Rutherford II B in 24 instances (15%). In 62 cases (39.7%), the occlusion site started below the knee joint level, in 94 (60.3%) cases above. As a basic technique, an intervention was started by manual aspiration but if aspiration failed, an additional device was added. Most frequently, a rotational thrombectomy device (Rotarex, Straub Medical, Wangs, Switzerland) was used. An antegrade access to the femoral artery was the preferred access to the limb (154/156). Results: In 145 of 156 incidents, a technical success was achieved (93%). Aspiration was used in 153 cases (98%). Rotational thrombectomy by use of the Rotarex catheter was added in 60 cases (38%). Directional atherectomy was applied in a total of five patients. As main technical complications, a downward embolization occurred (n = 11). There were four surgical groin revisions. Five patients died during the early follow-up with four not related to the intervention. Clinically, 135 patients (86.5%) showed an improvement in their clinical situation. Conclusion: Acute lower limb ischemia can be successfully treated by mechanical thromboembolectomy only by combining aspiration embolectomy with rotational thrombectomy in most cases but manual aspiration alone will frequently fail especially above the knee joint level.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Tuning working potential of silicon-phosphorus anode via microstructure control for high-energy lithium-ion batteries

The primary research on anode materials of lithium-ion batteries have been focused on increasing the specific capacity, while the working potential that is also closely related to the practical energy density of batteries has been paid much less attention. In this paper, starting from micrometer-sized silicon and black phosphorus, we have reported a high-energy silicon-phosphorus/carbon anode (denoted as mSPC) via a high-energy ball milling process, which demonstrates an average discharge working potential of 0.3 volts versus lithium, together with a high reversible capacity of > 2000 mAh/g, high initial coulombic efficiency of 84%, excellent cycle stability, and superior rate capability up to 15 A/g. Furthermore, in situ focused-ion-beam scanning electron microscopy reveals that the volume change of the mSPC anode during repeated (de) lithiation is effectively alleviated. In contrast, starting from nanometer-sized silicon, the resulted anode (denoted as nSPC) not only presents a lower reversible capacity (~1200 mAh/g), but also exhibits a higher charge/discharge working potential, leading to reduced energy density. Our results indicate the importance of composition/structure control in tailoring the working potential and specific capacity of alloying-type anodes towards high-energy lithium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2017

Core Conversion of VVR-K Research Reactors

The conversion of the VVR-K research reactor to low-enrichment uranium fuel includes switching to a compact core with low-enrichment uranium and gradually transitioning from a light-water side reflector to a beryllium reflector with restoration of the working reactivity margin without makeup with fresh fuel. In 2015, the reactor was stopped in order to modernize the main elements of the core, the control and protection system for the channels of the working rods, and the emergency electric power source. First criticality of VVR-K with low-enrichment fuel followed by first start of the reactor occurred in spring 2016. The VVR-KN type FA specially developed for VVR-K make it possible to not only preserve but also improve the neutronphysical characteristics of the core. The design-basis reactivity margin of the working core load ~7%Δk/k is adequate for reactor operation for three 20-day cycles with ~10% average burnup reached in the central FA. The beryllium reflector is built up in stages starting at the fourth cycle. The beryllium reflector will make it possible to preserve the radial dimensions of the core and increase the neutron flux density in the central and peripheral irradiation channels.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

Processing and consolidation of copper/tungsten

Here, we developed a copper/tungsten (Cu/W) composite for mesoscale Materials Science applications using the novel High-Energy Diffraction Microscopy (HEDM) technique. Argon-atomized copper powder was selected as the starting raw powder and screened to remove the extremely large particle fraction. Tungsten particles were collected by milling and screening the -325 mesh tungsten powder between 500 and 635 mesh sieves. Hot pressing of screened Cu powder was performed at 900 °C in Ar/4 %H 2 atmosphere. XRD and ICP results show that the hot-pressed Cu sample consists of about 5 vol% Cu 2 O, which is caused by the presence of oxygen on the surface of the starting Cu powder. Hot pressing the copper powder in a pure hydrogen atmosphere was successful in removing most of the surface oxygen. Our process was also implemented for hot pressing the Cu/W composite. The density of the Cu/W composites hot pressed at 950 °C in pure hydrogen was about 94 % of the theoretical density (TD). The hot-pressed Cu/W composites were further hot isostatic pressed at 1050 °C in argon atmosphere, which results in 99.6 % of the TD with the designed Cu grain size and W particle distribution. Tensile specimens with D-notch were machined using the wire EDM method. Furthermore, the processing and consolidation of these materials will be discussed in detail. The HEDM images are also showed and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Synthesis of Poly(dichlorophosphazene) by the Melt Phase Polymerization of P-Trichloro-N-(dichlorophosphoryl)monophosphazene

A major barrier to commercialization of any of the many exciting applications of the poly(phosphazenes) has been the cost and ease of preparation of the most widely utilized starting polymer, poly(dichlorophosphazene) (Cl2PN)n (1). One attractive route is the thermal polycondensation reaction of P-trichloro-N-(dichlorophosphoryl)monophosphazene, Cl3P=N–P(O)Cl2 (2). We are reporting a modified bulk polymerization of 2 which represents a convenient route to laboratory scale amounts of (NPCl2)n with moderate molecular weights and polydispersity. GPC characterization data were obtained on the corresponding phenoxy derivatives, [(PhO)2PN]n. We also have developed a one pot synthesis of 1 from ammonium sulfate and phosphorus pentachloride which are the starting materials for the synthesis of 2 and examined the major variables, time and temperature, for this process. The resulting poly(phosphazene) exhibits more branching than the product of bulk polymerization of 1.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2017

Pairing and Short-Range Correlations in Nuclear Systems

The structure and density dependence of the pairing gap in infinite matter is relevant for astrophysical phenomena and provides a starting point for the discussion of pairing properties in nuclear structure. Short-range correlations can significantly deplete the available single-particle strength around the Fermi surface and thus provide a reduction mechanism of the pairing gap. Here, we study this effect in the singlet and triplet channels of both neutron matter and symmetric nuclear matter. Our calculations use phase-shift equivalent interactions and chiral two-body and three-body interactions as a starting point. We find an unambiguous reduction of the gap in all channels with very small dependence on the NN force in the singlet neutron matter and the triplet nuclear matter channel. In the latter channel, SRC alone provide a 50% reduction of the pairing gap.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Zero-Temperature Dynamics in the Dilute Curie–Weiss Model

We consider the Ising model on a dense Erdős–Rényi random graph, G(N,p), with p>0 fixed—equivalently, a disordered Curie–Weiss Ising model with Ber(p) couplings—at zero temperature. The disorder may induce local energy minima in addition to the two uniform ground states. In this paper we prove that, starting from a typical initial configuration, the zero-temperature dynamics avoids all such local minima and absorbs into a predetermined one of the two uniform ground states. We relate this to the local MINCUT problem on dense random graphs; namely with high probability, the greedy search for a local MINCUT of G(N,p) with p>0 fixed, started from a uniform random partition, fails to find a non-trivial cut. In contrast, in the disordered Curie–Weiss model with heavy-tailed couplings, we demonstrate that zero-temperature dynamics has positive probability of absorbing in a random local minimum different from the two homogenous ground states.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Uncovering Uranium Isotopic Heterogeneity of Fuel Pellets from the Fifth Collaborative Materials Exercise of the Nuclear Forensics International Technical Working Group

In 2017, the Nuclear Forensics International Technical Working Group (ITWG) organized their fifth 37 Collaborative Materials Exercise (CMX-5). The exercise samples were two uranium dioxide fuel pellets 38 manufactured from the same starting materials by different processes to have similar bulk isotopic 39 composition, but different spatial uranium isotopic distributions. Sets of identical materials were sent to 40 all participating laboratories, who then utilized their existing nuclear forensic capabilities to 41 independently analyse fuel pellets and identify similarities and differences of the materials’ 42 characteristics. The analytical methods used to probe the fuel pellets included ex situ, such as sectioning 43 or breaking up the pellets and analyzing dissolved pieces using inductively coupled plasma mass 44 spectrometry (ICP-MS), analyzing particles collected from intact or fragmented pellets by secondary ion 45 mass spectrometry (SIMS), as well as in situ methods, such as laser ablation coupled with ICP-MS, 46 autoradiography and nanoSIMS. In this paper we present the results of these independent analyses and 47 compare the capabilities of those nuclear forensic analytical methods to uncover details of the isotopic 48 heterogeneity of uranium fuel pellets.

Nuclear Forensic Analysis of Uranium Fuel Pellets,↗
DOE OSTI2015

Cyclic Corrosion and Chlorination of an FeCrAl Alloy in the Presence of KCl

The KCl-induced corrosion of the FeCrAl alloy Kanthal® APMT in an O 2 + N 2 + H 2 O environment was studied at 600 °C. The samples were pre-oxidized prior to exposure in order to investigate the protective nature of alumina scales in the present environment. The microstructure and composition of the corroded surface was investigated in detail. Corrosion started at flaws in the pre-formed α-alumina scales, i.e. α-alumina was protective in itself. Consequently, KCl-induced corrosion started locally and, subsequently, spread laterally. An electrochemical mechanism is proposed here by which a transition metal chloride forms in the alloy and K 2 CrO 4 forms at the scale/gas interface. Scale de-cohesion is attributed to the formation of a sub-scale transition metal chloride.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Mechanism of the unusual substituent exchange in the reactions of alkylene oxides with organic compounds bearing β-hydroxyalkyl groups at heteroatoms S, Se, N, and P

The review summarizes the data on the study of the unusual exchange reaction between alkylene oxides and organic compounds of groups 15 and 16 of the Periodic Table bearing β-hydroxyalkyl substituents at the S, Se, N, and P heteroatoms. Despite the apparent identity of one of the starting reagents and the reaction product (retention of the three-membered ring), the structures of the formed alkylene oxide and organic compound with β-hydroxyalkyl group at the heteroatom differ from the structures of the starting materials. Using β-hydroxyalkyl sulfides as a model, the plausible mechanisms of the exchange reactions were discussed taking into account the change in the reaction order in β-hydroxyalkyl sulfide with its concentration increase. Irrespectively of the mechanism, the first stage of the reaction is the formation of an intermediate H-complex due to the H-bond formation between the OH sulfide group and the alkylene oxide oxygen atom and subsequent (for the dilute solutions) monomolecular intracomplex transformation of this H-complex. The mechanism was confirmed by semi-empirical quantum chemical calculations. In the case of concentrated solutions of β-hydroxyalkyl sulfides, possibility of the formation of intermediate sulfonium salt was discussed. Each pathway proceeds via its unique intermediates and transition states but the final stage results in the same intermediate bipolar ion with an intramolecular H-bond thus leading to the same nature and compositions of the reaction products for all reaction pathways.

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

Imaging of Formaldehyde Adsorption and Diffusion on TiO2(110)

Surface reactions of formaldehyde with reduced TiO2(110) surfaces have been studied using variable-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). STM results show that formaldehyde preferably adsorbs on the bridging bonded oxygen (Ob) vacancy (VO) defect site. Bias-dependent STM images show that both the Ti-bound CH2O and the VO-bound CH2O are positioned between the Ob row and the Ti row. The VO-bound formaldehyde rotates at 95 K. It starts to diffuse along the Ob row as –CH2– at ~170 K and starts to diffuse along the Ti row as a molecule at ~215 K. However, the stabilities and the configurations of the Ti-bound and the VO-bound formaldehyde calculated using DFT are not in line with the experimental results. The values of diffusion barriers determined experimentally and theoretically are also different. The discrepancy between the experiment and theory indicates the presence of a complex charge distribution related to the defects.

defects↗
DOE OSTI2024

Multistart algorithm for identifying all optima of nonconvex stochastic functions

Here, we propose a multistart algorithm to identify all local minima of a constrained, nonconvex stochastic optimization problem. The algorithm uniformly samples points in the domain and then starts a local stochastic optimization run from any point that is the "probabilistically best" point in its neighborhood. Under certain conditions, our algorithm is shown to asymptotically identify all local optima with high probability; this holds even though our algorithm is shown to almost surely start only finitely many local stochastic optimization runs. We demonstrate the performance of an implementation of our algorithm on nonconvex stochastic optimization problems, including identifying optimal variational parameters for the quantum approximate optimization algorithm.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Cyclic-loading Induced Lattice-Strain Asymmetry in Loading and Transverse Directions

Cyclic-loading effects on a nickel-based superalloy are investigated with in-situ neutron-diffraction measurements. The thermoelastic-temperature evolution subjected to cyclic loading is estimated based on the lattice-strain evolution. The atomic thermoelastic responses are compared with the measured bulk temperature evolution. Two transitions in the temperature-evolution are observed. The first transition, observed with the neutron-measurement results, is associated with the cyclic hardening/softening-structural transformation. The second transition is observed at larger number of fatigue cycles. It has a distinct origin and is related to the start of irreversible structural transformations during fatigue. A lattice-strain asymmetry behavior is observed. The lattice-strain asymmetry is quantified as a grain-orientation-dependent transverse/loading parameter (P-ratio). The P-ratio parameter evolution reveals the irreversible plastic deformation subjected to the fatigue. The irreversible fatigue phenomena might relate to the formation of the microcracks. At elevated temperatures the cyclic hardening/softening transition starts at lower fatigue cycles as compared to room temperature. A comparison between the room-temperature and the elevated-temperature fatigue experiments is performed. The P-ratio parameters show the same irreversible trends at both the room and the elevated temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Temperature-Dependent Thermal and Mechanical Properties of a Wire Arc Additively Manufactured Low Transformation Temperature Steel

Recent research has studied the use of low transformation temperature (LTT) martensite steel as feedstock for wire arc additive manufacturing (WAAM) and low tensile residual stresses or compressive residual stresses were detected in the printed walls. These residual stress states help to improve printed product properties such as fatigue strength and corrosion resistance. However, the thermal and mechanical properties of WAAM printed LTT martensite steel walls are largely unknown. In this work, a printed LTT martensite steel was characterized for its thermal, metallurgical, and mechanical behavior at room and elevated temperatures. The temperature-dependent specific heat capacity, thermal expansion, atomic lattice spacing, and tensile properties were measured during both heating and cooling and related to observed microstructural features and computational thermodynamics predictions. These results revealed a large hysteresis in the martensitic transformation, with a martensite start temperature of 240 °C and austenite start temperature of 680 °C. Additional thermal cycles and specimen orientation did not affect the printed specimen austenite and martensite transformations. However, it was observed that the printed metal may exhibit tempering embrittlement at about 350 °C but further studies are needed to confirm that. Further, these results suggest that a temperature control of 250 °C to 350 °C during WAAM is needed to maximize the stress reduction potential of the LTT250 martensite steel. Opportunities for future implementation of LTT martensite steels and optimization of additive manufacturing process conditions are identified.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Analysis of Hot- and Cold-Rolled Loads in Medium-Mn TRIP Steels

The purpose of this work is to investigate the hot- and cold-rolling requirements to produce third-generation advanced high-strength steels (AHSS). Therefore, five medium-Mn (10 to 14 wt pct Mn) alloys that exhibit transformation-induced plasticity (TRIP) were compared to a commercially produced grade of AISI 1018 using hot- and cold-rolling experiments. Experimental data collected from a STANAT instrumented rolling mill was utilized to measure force and torque during hot- and cold-rolling. Experimental data were processed by a 1D analytical model, based on Orowan model, to determine rolling pressure. It was determined that pressures required to hot-roll TRIP alloys are 1.4 to 1.8 times greater than pressures for rolling AISI 1018 steel. Cold rolling of the medium-Mn TRIP steels was found to be 1.5 to 2.8 times greater than the AISI 1018 steel. Mechanical and microstructural characterization was also performed and the variation in rolling pressure was related to the starting microstructural constituents, and alloys containing greater starting quantities of ε-martensite in the microstructure had higher flow stresses at equivalent rolling strains during cold rolling.

36 MATERIALS SCIENCE↗