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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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

High temperature creep model development using in-situ 3-D DIC techniques during a simulated LOCA transient

In-situ strain measurements of fuel cladding can enable high-throughput data collection and validation to support accelerated qualification of cladding materials. Here, in this work, 3D digital image correlation was used to map strain for both Zircaloy-4 (Zry-4) and Cr-coated Zry-4 during two types of cladding rupture experiments: isobaric temperature ramp tests at 5 °C/s and isothermal pressure jump tests at 600 °C. Zry-4 strain data initially showed a temperature dependence expected for creep deformation, yet a shift to a new plastic deformation mechanism not reported in literature dominated during the finals seconds prior to rupture. Cr-coated Zry-4 did not show the change in deformation mechanism at the end of life and showed a delay in measurable creep deformation. Stress dependences were similar for Zry-4 and Cr/Zry-4 during pressure jump tests. Cr-coatings were found to decrease the strain rate during both testing scenarios. Creep parameters were calculated to support modelling efforts regarding design basis accidents.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Ovate family protein1 interaction with BLH3 regulates transition timing from vegetative to reproductive phase in Arabidopsis

We study the Three-Amino-acid-Loop-Extension(TALE) homeodomain transcription factor BLH3 that regulates timing of transition from vegetative to reproductive phase. Previous preliminary results obtained using large-scale yeast two-hybrids indicate that BLH3 protein possibly interact with Ovate Family Proteins(OFPs) transcription co-regulators. Nevertheless, it is uncertain whether OFP1–BLH3 complex is involved in regulation of timing of transition from vegetative to reproductive phase in Arabidopsis. The interaction between BLH3 and OFP1 was re-tested and verified by a yeast two-hybrid system. We found that the BLH3–OFP1 interaction was mainly mediated through the BLH3 homeodomain. Meanwhile, this interaction was further confirmed by bimolecular fluorescence complementation (BiFC) in vivo . In addition, by establishing protoplast transient expression, we discovered that BLH3 acts as a transcriptional activator, whereas OFP1 functioned as a repressor. The interactions between OFP1 and BLH3 can reduce BLH3 transcriptional activity. The ofp1 mutant lines and blh3 mutant lines, OFP1 overexpress lines and BLH3 overexpress lines can both influence timing of transition from vegetative to reproductive phase. Furthermore, 35s:OFP1/blh3 plants exhibited flowering and leaf quantity similar to that of the wild-type controls. 35s:BLH3/ofp1 plants flowered earlier and had less leaves than wild-type controls, indicating that OFP1 protein might depend partially on BLH3 in its function to regulate the timing of transition from vegetative to reproductive phase. In conclusion, these results support our assumption that, by interacting with OFP1, BLH3 forms a functional protein complex that controls timing of progression from vegetative to reproductive phase, and OFP1 might negatively regulate BLH3 or the BLH-KNOX complex, an important interaction for sustaining the normal transition from vegetative to reproductive phase.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Transient terahertz photoconductivity measurements of minority-carrier lifetime in tin sulfide thin films: Advanced metrology for an early stage photovoltaic material

Materials research with a focus on enhancing the minority-carrier lifetime of the light-absorbing semiconductor is crucial to advancing solar energy technology for both early stage and mature material platforms alike. Tin sulfide (SnS) is an absorber material with several clear advantages for manufacturing and deployment, but the record power conversion efficiency remains below 5%. We report measurements of bulk and interface minority-carrier recombination rates in SnS thin films using optical-pump, terahertz-probe transient photoconductivity (TPC) measurements. Post-growth thermal annealing in H 2 S gas increases the minority-carrier lifetime, and oxidation of the surface reduces the surface recombination velocity. However, the minority-carrier lifetime remains below 100 ps for all tested combinations of growth technique and post-growth processing. Vast improvement in SnS solar cell performance will hinge on finding and mitigating as-yet-unknown recombination-active defects. We describe in detail our methodology for TPC experiments, and we share our data analysis routines in the form freely available software.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Hot wire needle probe for in-reactor thermal conductivity measurement

Thermal conductivity is a key property that must be known for proper design, test, and application of new fuels and structural materials in nuclear reactors. Thermal conductivity is highly dependent on the physical structure, chemical composition, and the state of the material. Typically, thermal conductivity changes that occur during irradiation are measured out-of-pile by Post Irradiated Examination (PIE) using a “cook and look” approach in hot-cells. Repeatedly removing samples from a test reactor to make out-of-pile measurements is expensive, has the potential to disturb phenomena of interest, and only provides understanding of the sample's end state at the time each measurement is made. There are also limited thermophysical property data for advanced fuels. Such data are needed for simulation design codes, the development of next generation reactors, and advanced fuels for existing nuclear plants. Being able to quickly characterize fuel thermal conductivity during irradiation can improve the fidelity of data, reduce costs of post-irradiation examinations, increase understanding of how fuels behave under irradiation, and confirm or improve existing thermal conductivity measurement techniques. This paper discusses recent efforts to develop and evaluate an in-pile thermal conductivity sensor based on a hot wire needle probe. Testing has been performed on samples with thermal conductivities ranging from 0.2 W/m-K to 22 W-m-K in temperatures ranging from 20 °C to 600 °C. Thermal conductivity values measured using the needle probe match data found in the literature to within 5% for samples tested at room temperature, 5.67% for low thermal conductivity samples tested at high temperatures, and 10% for high thermal conductivity samples tested at high temperatures. Experimental results also show that this sensor is capable of operating in various test conditions and of surviving long duration irradiations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Device-Level Thermal Management of Gallium Oxide Field-Effect Transistors

The ultra-wide bandgap (~4.8 eV) and melt-grown substrate availability of β-Ga 2 O 3 gives promise to the development of next generation power electronic devices with dramatically improved size, weight, power, and efficiency over current state-of-the-art wide bandgap devices based on 4H-SiC and GaN. Also, with recent advancements made in GHz frequency RF applications, the potential for monolithic or heterogenous integration of RF and power switches has attracted researchers’ attention. Yet, it is expected that Ga 2 O 3 devices will suffer from self-heating due to the poor thermal conductivity of the material. Thermoreflectance thermal imaging and infrared thermography were used to understand the thermal characteristics of a MOSFET fabricated via homo-epitaxy. A 3D coupled electro-thermal model was constructed based on the electrical and thermal characterization results. The device model shows that a homo-epitaxial device suffers from an unacceptable junction temperature rise of ~1500°C under a targeted power density of 10 W/mm indicating the importance of employing device level thermal managements to individual Ga 2 O 3 transistors. The effectiveness of various active and passive cooling solutions was tested to achieve a goal of reducing the device operating temperature below 200°C at a power density of 10 W/mm. Results show that flip-chip hetero-integration is a viable option to enhance both the steady-state and transient thermal characteristics of Ga 2 O 3 devices without sacrificing the intrinsic advantage of high-quality native substrates. Also, it is not an active thermal management solution that entails peripherals requiring additional size and cost implications.

42 ENGINEERING↗
DOE OSTI2023

Laboratory Experiments Examining the Effect of Thermal and Mechanical Processes on Hydraulic Transmissivity Evolution

Using laboratory slide-hold-slide experiments, at temperatures from 22 to 200 degrees C, to examine effects of fracture reactivation and quasi-static loading on the evolution of fluid transport properties of simulated fractures in Westerly granite. At all temperatures, the in-plane hydraulic transmissivity consistently decays during hold periods resulting in an overall reduction in transmissivity. During the first three to fifteen hours of an experiment, transmissivity decreases rapidly due to the generation of wear products, development of a sliding surface, and compaction of the resulting gouge. Once the sliding surface has developed, the long-term transmissivity decay rate at 22 and 100 degrees C is significantly lower than the transmissivity decay rate during the initial 3-15 hours of the experiment. However, at 200 degrees C, the decay of hydraulic transmissivity remains high throughout the experiment. The long-term decay of hydraulic transmissivity can be fitted with a power law model with more rapid reduction of hydraulic transmissivity at higher temperature. Periods of sliding on the fracture surface result in transient increases in the transmissivity, due to shear dilation, as is expected for Coulomb materials. These transients are superimposed on the long-term decay. When sliding ceases and a new hold period commences, there is a rapid reduction in transmissivity and return to the long-term rate of transmissivity decay. The rate of decay of the transmissivity transients is inversely correlated with temperature, in contrast to the long-term decay and the expected behavior for processes like subcritical crack growth and indentation creep. The higher decay rates that are observed during the initial 3-15 hours of the tests and following sliding, are associated with times that the porosity of the gouge is expected to be high. The difference in decay rates suggests that when the gouge is driven far from equilibrium by active shearing, densification may be dominated by a different mechanism from long-term compaction.

15 GEOTHERMAL ENERGY↗
DOE OSTI2012

Reactor Engineering: Experimental Investigation of Alpha Convection

This report summarizes the progress on DE-FG07-07ID14806 project funded by the US Department of Energy under Nuclear Engineering Education Research (NEER) program. During the project a test apparatus was designed and manufactured for experimental investigation of Alpha Convection. Benchmark testing of the new apparatus without the neutron radiation was performed and numerical simulations were conducted to validate the experimental results on natural convection. These results were reported in a journal publication. Subsequently, we conducted the experiment at Missouri S&T research reactor in the beam port to investigate the phenomenon of Alpha Convection. Unfortunately, these experiments were inconclusive. No observable effect of neutron beam was noticed. Insufficient neutron flux as it passes through the borated water is responsible for the unsuccessful experiments. A number of new experiments are designed and manufactured to investigate the phenomenon. A new experiment using shadowgraphy is designed and manufactured to investigate and visualize the natural convection and the impact of neutron on the phenomenon. Moreover, to continue with the original and newly designed experiments a neutron generator was needed to supply a vertical beam of neutrons. This new source of neutron is acquired using DOE NEUP General Scientific Infrastructure number DE-FOA-0000321. The new facility is installed and tested but is yet to be licensed by NRC for regular use and continuation of the experiments.

Conduction convection transition.↗
DOE OSTI2018

Fast Ion Heating in Transient Collisionless Magnetic Reconnection via an Intrinsic Stochastic Mechanism

Stochastic heating has typically been known to be a powerful ion heating mechanism in the solar wind, atmosphere, and flares. Here, we show that stochastic ion heating is inherent to transient collisionless magnetic reconnection. The explanation exploits the connected nature of electron canonical vorticity to show analytically that the in-plane electric and magnetic fields in a typical reconnection geometry satisfy the condition for stochastic heating of ions. Electron fluid simulations, test ion simulations, and comparisons to experiments all support the existence of this mechanism.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THERMAL IMAGING OF ACTIVE MAGNETIC REGERNERATOR MCE MATERIALS DURING OPERATION

An active magnetic regenerator (AMR) prototype was constructed that incorporates a Gd sheet into the regenerator wall to enable visualization of the system s thermal transients. In this experiment, the thermal conditions inside the AMR are observed under a variety of operating conditions. An infrared (IR) camera is employed to visualize the thermal transients within the AMR. The IR camera is used to visually and quantitatively evaluate the temperature difference and thus giving means to calculate the performance of the system under the various operating conditions. Thermal imaging results are presented for two differing experimental test runs. Real time imaging of the thermal state of the AMR has been conducted while operating the system over a range of conditions. A 1 Tesla twin-coil electromagnet (situated on a C frame base) is used for this experiment such that all components are stationary during testing. A modular, linear reciprocating system has been realized in which the effects of regenerator porosity and utilization factor can be investigated. To evaluate the performance variation in porosity and utilization factor the AMR housing was constructed such that the plate spacing of the Gd sheets may be varied. Each Gd sheet has dimensions of 38 mm wide and 66 mm long with a thickness of 1 mm and the regenerator can hold a maximum of 29 plates with a spacing of 0.25 mm. Quantitative and thermal imaging results are presented for several regenerator configurations.

Shassere, Benjamin↗
DOE OSTI2018

Bison Fuel Performance Modeling on RIA in a PWR

This report is prepared to fulfill a Level 2 milestone for CASL on “deliver and document RIA fuel performance modeling using Bison fuel performance code.” The work performed is focused on modeling the full length commercial fuel rod response under a design basis Reactivity Initiated Accident (RIA), in particular, a hypothetical Control Rod Ejection Accident (CREA) in a Pressurized Water Reactor (PWR). Fuel rods with different burnups, 0 (fresh fuel), 20, 40, and 60 GWd/tU have been modeled with a reactivity worth insertion of $1.24 at Hot Zero Power (HZP) condition. Bison failure modeling method, and a brief summary of validations on selected RIA cases from CABRI and NSRR testing facilities are also described. The work performed has demonstrated the successful application of Bison code in the modeling of thermal and mechanical responses in RIAs for PWRs. In particular, Bison code has a more mature capability in the modeling of the frictional contact between pellet and cladding of the high burnup fuels, which is critical for modeling the Pellet Clad Mechanical Interaction (PCMI). The modeling of RIA using Bison code shows fuels in PWR environment could have different responses than in the simulated RIA tests, and results indicate that a transition from PCMI to Departure from Nucleate Boiling (DNB) could happen at relatively lower enthalpies: a better heat transfer from the fuel to coolant could increase cladding temperature and ductility, but at the same time also reduces the margin to DNB, which could cause high temperature oxidation and ballooning type of failures. The precise determination of the transition into DNB may rely on a more accurate input of the power histories in the simulated RIAs from VERA, the core simulator of CASL. The limiting conditions in PWRs could be quite different than those tests with non-typical testing conditions, and the improvement of the modeling of thermal responses, such as, clad coolant heat transfer, gap heat transfer, clad thermal inertia, and radial power profiles could be important considerations of the RIAs. In modeling the fuel responses in a fast transient, a number of variables could affect the initial burnup states, and some material models, e.g., fuel mechanical models, fission gas release, and corrosion models, and parameters can affect modeling results as well. Those uncertainties and advanced modeling capabilities need to be investigated in the future study of RIAs.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Dynamic System Scaling Applied to Zr-4 Cladding under RIA Conditions

The research and development lifecycle for new fuel designs currently has an ideal 20-25 year timeline. Efforts are currrently underway to accelerate fuel design and development using high performance fuel modeling codes and reduced scale experiments with new instrumentation techniques. However current tools available require a full scale prototype to be designed and tested for fuel qualification. The thermal-hydraulics community has leveraged scaling methodologies to use reduced scale integral effect test facilities (Westinghouse AP600/1000, NuScale Power Module) in lieu of building full scale prototypes for reactor design certification. Dynamic System Scaling (DSS) is a recent development to scaling methodologies that enable the tracking and quantification of dynamic scaling distortions experienced throughout a transient. Recent TREAT experiments performed reactivity initiated accident (RIA) pulses on UO2 fuel rodlets in Zr-4 cladding and were accompanied by BISON predictions for the cladding temperature. DSS is applied to pyrometer data of outer cladding temperatures and two BISON predictions after peak cladding temperature has been reached. One BISON case uses a constant gap conductance value between the fuel and cladding and the other using a conventional gap conductance model. Results from the DSS analysis show that there is good agreement between both BISON predictions and the experimental data and that there is not a significant distortion seen between using either gap conductance model.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

High-Fidelity Numerical Wave Tank Verification & Validation Study: Wave Generation Through Paddle Motion: Preprint

This paper presents a numerical benchmark study of wave propagation due to a paddle motion using different high-fidelity numerical models, which are capable of replicating the nearly actual physical wave tank testing. A full time series of the measured wave generation paddle motion which was used to generate wave propagation in the physical wave tank will be utilized in each of the models contributed by IEA OES Task 10's participants, which includes both computational fluid dynamics (CFD) and smooth hydrodynamic particle (SPH). The high-fidelity simulations of the physical wave testcase will allow for the evaluation of the initial transient effects from wave ramp-up and its evolution in the wave tank over time for two representative regular waves with varying levels of nonlinearity. A couple of interesting metrics like the predicted wave surface elevation at select wave probes, wave period, and phase-shift in time will be assessed to evaluate the relative accuracy of numerical models versus experimental data within specified time intervals. These models will serve as a guide for modelers in the wave energy community and provide a base case to allow further and more detailed numerical modeling of the fixed Kramer Sphere Cases under wave excitation force wave tank testing.

HYDRO ENERGY,TIDAL AND WAVE POWER↗
DOE OSTI2019

Comparison of steady and transient flow boiling critical heat flux for FeCrAl accident tolerant fuel cladding alloy, Zircaloy, and Inconel

Steady and transient (with a heating rate of 685?/s) internal-flow CHF (Critical Heat Flux) experiments were conducted under atmospheric pressure at a fixed inlet temperature (40? or 60?) and mass flow (300kg/m 2 s) on Fe-13Cr-6Al alloy, Inconel 600 and Zircaloy-4 tube samples. Multiple experiments were repeated on the same specimen to investigate the effect of surface characteristic changes (i.e., roughness, wettability, and oxide scale morphology) on the occurrence of CHF. Despite notable changes of wettability, roughness, and oxide layer characteristics on samples that had already been subjected to CHF, measured flow CHF remained unchanged throughout repeated experiments for tested materials. This demonstrates that the surface effects on flow CHF are limited in the test conditions. In the steady-state flow boiling condition, Fe-13Cr-6Al alloy demonstrated a 22% and 14% increase in CHF compared to Zircaloy-4 and Inconel 600, respectively. Compared to the 2006 Groeneveld CHF lookup table, Fe-13Cr-6Al alloy gives a 13% increase in the tested flow boiling condition. Material properties are considered primarily responsible for the observed CHF differences among the tested materials. The surface thermal economy parameter $\frac{(pc_p)^{3/2}}{\sqrt{k}}$ is proposed as an explanation for the observed CHF differences; this parameter is related to material’s ability to avoid an irreversible dry spot formation. The apparent disagreement of Zircaloy-4 CHF with both the look up table predictions and Inconel 600 shows the limitation of departure of nuclate boiling (DNB) evaluations that do not consider cladding materials. The transient Fe-13Cr-6Al CHF is 39% and 23% higher than the lookup table prediction and the steady-state condition experimental result, respectively.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Root carbon interation with soil minerals is dynamic, leaving a legacy of microbially derived residues

Minerals preserve the oldest most persistent soil carbon, and mineral characteristics appear to play a critical role in the formation of soil organic matter (SOM) associations. To test the hypothesis that carbon source and soil microorganisms also influence mineral-SOM associations, we incubated permeable minerals bags in soil microcosms with and without plants, in a 13CO2 labelling chamber. Mineral bags contained quartz, ferrihydrite, kaolinite, or native soil minerals isolated via density separation. Using 13C-NMR, FTICR-MS, and lipidomics, we traced plant-derived carbon onto minerals harvested from microcosms at three plant growth stages, characterizing total carbon, 13C enrichment, and SOM chemistry. While C accumulation was rapid and mineral-dependent, the accumulated amount was not significantly affected by the presence of plant roots. However, the rhizosphere did shape the chemistry of mineral-associated SOM. Minerals incubated in the rhizosphere were associated with a more diverse array of compounds with different C functional groups (carbonyl, aromatics, carbohydrates, lipids) than minerals incubated in a bulk soil control. These diverse rhizosphere-derived compounds may represent a “transient fraction” of mineral SOM, rapidly exchanging with mineral surfaces. Our results also suggest that many of the lipids which persist on minerals are microbially-derived with a large fraction of fungal lipids.

Rhizosphere, soil organic matter, grassland, 13C-N↗
DOE OSTI2020

Cloud-based implementation of white-box model predictive control for a GEOTABS office building: A field test demonstration

Model predictive control (MPC) has been proven in simulations and pilot case studies to be a superior control strategy for large buildings. MPC can utilize the weather and occupancy schedule forecasts, together with the system model, to predict the future thermal behavior of the building and minimize the overall energy use and maximize thermal comfort. However, these advantages come with the cost of increased modeling effort, computational demands, communication infrastructure, and commissioning efforts. Thus a typical approach is to, often rapidly, simplify the building modeling and MPC optimization problem while paying a price of not reaching the full performance potential. It has been shown that by employing accurate physics-based models, MPC performance can be notably increased closer to its theoretical performance bound. However, implementation of such high-fidelity MPC in real buildings remains a challenge, resulting in a lack of successful field test studies. This work presents the methodology and field test demonstration of a computationally efficient implementation of the white-box MPC in an office building in Belgium. The detailed model of the building is based on first-principle physical equations. The deployment and supervision of MPC operation in a practical setting are supported by an automated cloud-based communication infrastructure. The motivating factor behind the cloud-based architecture is its compatibility with a commercially appealing control as a service concept. The building is equipped with a ground source heat pump (GSHP) and thermally activated building structures (TABS), where the combination of both is also known as GEOTABS. From a control perspective, GEOTABS buildings are particularly challenging systems due to large scale, complex heating, ventilation and air conditioning (HVAC) system, and slow dynamics with time delays. On the other hand, there is an increased potential for energy savings due to the high thermal mass, which acts as thermal storage. The MPC operation is demonstrated during the challenging transient seasons (switching between heating and cooling), and its performance is compared to a traditional rule-based controller (RBC). We provide a proof of concept of real MPC operation for the most difficult seasons with notable GSHP energy use savings equal to 53.5% and thermal comfort improvement by 36.9%. Other MPC applications found in the literature describe tests for only cooling or only heating, and up to now only for a black-box or a grey-box approach.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2013

Distributed Dynamic State Estimator, Generator Parameter Estimation and Stability Monitoring Demonstration

This is the final report for this project that was performed in the period: October1, 2009 to June 30, 2013. In this project, a fully distributed high-fidelity dynamic state estimator (DSE) that continuously tracks the real time dynamic model of a wide area system with update rates better than 60 times per second is achieved. The proposed technology is based on GPS-synchronized measurements but also utilizes data from all available Intelligent Electronic Devices in the system (numerical relays, digital fault recorders, digital meters, etc.). The distributed state estimator provides the real time model of the system not only the voltage phasors. The proposed system provides the infrastructure for a variety of applications and two very important applications (a) a high fidelity generating unit parameters estimation and (b) an energy function based transient stability monitoring of a wide area electric power system with predictive capability. Also the dynamic distributed state estimation results are stored (the storage scheme includes data and coincidental model) enabling an automatic reconstruction and “play back” of a system wide disturbance. This approach enables complete play back capability with fidelity equal to that of real time with the advantage of “playing back” at a user selected speed. The proposed technologies were developed and tested in the lab during the first 18 months of the project and then demonstrated on two actual systems, the USVI Water and Power Administration system and the New York Power Authority’s Blenheim-Gilboa pumped hydro plant in the last 18 months of the project. The four main thrusts of this project, mentioned above, are extremely important to the industry. The DSE with the achieved update rates (more than 60 times per second) provides a superior solution to the “grid visibility” question. The generator parameter identification method fills an important and practical need of the industry. The “energy function” based transient stability monitoring opens up new ways to protect the power grid, better manage disturbances, confine their impact and in general improve the reliability and security of the system. Finally, as a by-product of the proposed research project, the developed system is able to “play back” disturbances by a click of a mouse. The importance of this by-product is evident by considering the tremendous effort exerted after the August 2003 blackout to piece together all the disturbance recordings, align them and recreate the sequence of events. This project has moved the state of art from fault recording by individual devices to system wide disturbance recording with “play back” capability.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2013

Characterization of a nuclear localization signal in the foot-and-mouth disease virus polymerase

We have experimentally tested whether the MRKTKLAPT sequence in FMDV 3D protein (residues 16 to 24) can act as a nuclear localization signal (NLS). Mutants with substitutions in two basic residues within this sequence, K18E and K20E, were generated. A decreased nuclear localization was observed in transiently expressed 3D and its precursor 3CD, suggesting a role of K18 and K20 in nuclear targeting. Fusion of MRKTKLAPT to the green fluorescence protein (GFP) increased the nuclear localization of GFP, which was not observed when GFP was fused to the 3D mutated sequences. These results indicate that the sequence MRKTKLAPT can be functionally considered as a NLS. When introduced in a FMDV full length RNA replacements K18E and K20E led to production of revertant viruses that replaced the acidic residues introduced (E) by K, suggesting that the presence of lysins at positions 18 and 20 of 3D is essential for virus multiplication. - Highlights: • The FMDV 3D polymerase contains a nuclear localization signal. • Replacements K18E and K20E decrease nuclear localization of 3D and its precursor 3CD. • Fusion of the MRKTKLAPT 3D motif to GFP increases the nuclear localization of GFP. • Replacements K18E and K20E abolish the ability of MRKTKLAPT to relocate GFP. • RNAs harboring replacements K18E and K20E lead to recovery of revertant FMDVs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Temperature dependence of resistivity of carbon micro/nanostructures: Microscale spatial distribution with mixed metallic and semiconductive behaviors

The temperature coefficient of resistivity (θ T ) of carbon-based materials is a critical property that directly determines their electrical response upon thermal impulses. It could have metal- (positive) or semiconductor-like (negative) behavior, depending on the combined temperature dependence of electron density and electron scattering. Its distribution in space is very difficult to measure and is rarely studied. Here, for the first time, we report that carbon-based micro/nanoscale structures have a strong non-uniform spatial distribution of θ T . This distribution is probed by measuring the transient electro-thermal response of the material under extremely localized step laser heating and scanning, which magnifies the local θ T effect in the measured transient voltage evolution. For carbon microfibers (CMFs), after electrical current annealing, θ T varies from negative to positive from the sample end to the center with a magnitude change of >130% over <1 mm. This θ T sign change is confirmed by directly testing smaller segments from different regions of an annealed CMF. For micro-thick carbon nanotube bundles, θ T is found to have a relative change of >125% within a length of ~2 mm, uncovering strong metallic to semiconductive behavior change in space. In conclusion, our θ T scanning technique can be readily extended to nm-thick samples with μm scanning resolution to explore the distribution of θ T and provide a deep insight into the local electron conduction.

36 MATERIALS SCIENCE↗