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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Controlling Rheology of Fluid Interfaces through Microblock Length of Sequence-Controlled Amphiphilic Copolymers

Previous studies have demonstrated that films of sequence-controlled amphiphilic copolymers display contact angles that depend on microblock size. This suggests that microblock length may provide a means of tuning surface and interfacial properties. In this work, the interfacial rheology of a series of sequence-controlled copolymers, prepared through the addition of bicyclo[4.2.0]oct-1(8)-ene-8-carboxamide (monomer A) and cyclohexene (monomer B) to generate sequences up to 24 monomeric units composed of (A m B n ) i microblocks, where m, n, and i range from 1 to 6. Interfacial rheometry is used to measure the mechanical properties of an air–water interface with these copolymers. As the microblock size increases, the interfacial storage modulus, G', increases, which may be due to an increase in the size of interfacial hydrophobic domains. Small-angle X-ray scattering shows that the copolymers have a similar conformation in solution, suggesting that any variations in the mechanics of the interface are due to assembly at the interface, and not on solution association or bulk rheological properties. This is the first study demonstrating that microblock size can be used to control interfacial rheology of amphiphilic copolymers. Here, the results provide a new strategy for controlling the dynamics of fluid interfaces through precision sequence-controlled polymers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A micromorphic filter for determining stress and deformation measures from direct numerical simulations of lower length scale behavior

A micromorphic filter is presented for the extraction of stress and deformation measures from underlying direct numerical simulation (DNS) of microstructural mechanical response. The filter is consistent with the micromorphic continuum theory of Eringen and Suhubi (1964), and allows the interrogation of a DNS to generate higher order constitutive models. The filter adopts aspects of the overlap coupling techniques for atomistic-continuum scale-bridging in order to update the nodal degrees of freedom of the finite-element-based filter. Here, two methods for the extraction of quantities of interest from the underlying DNS are presented. The first is a least squares fitting technique which is appropriate for finite-element-style macro-scale domains, and the second is a variationally based approach which generalizes the method to any macro-scale domain which has a variational form. No restrictions on the form of the micro-scale simulation are inherent to the approach, provided that the required quantities (stress, position, etc.) can be provided. The filter is applied to a simple homogeneous medium undergoing homogeneous deformation to demonstrate the recovery of a classical continuum response, what we call the null case. We then apply the framework to the same homogeneous medium with a central and edge penny-shaped crack to show micromorphic effects. We demonstrate that varying the size of the filter causes the micromorphic behaviors to arise and then dissipate as the filter becomes smaller than the crack's length scale. Additionally we show the effect of filter size on a chiral element network along with a plate perforated with evenly spaced and perturbed holes through the thickness. The micromorphic effects are shown to be present for the chiral elements under any loading but become most pronounced when a single element is located within each averaging domain. Micromorphic effects become pronounced for the plate upon the onset of localization.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Effect of additive length and chemistry on the morphology of blends of conjugated thiophenes and fullerene derivative acceptor molecules

ABSTRACT Small molecule additives have been shown to increase the device efficiency of conjugated polymer (donor) and fullerene derivative (acceptor) based organic solar cells by modifying the morphology of the device active layer. In this paper we conduct a systematic study of how additives affect the donor‐acceptor morphology using molecular dynamics simulations of blends of thiophene‐based oligomers, mimicking poly(3‐dodecylthiophene) (P3DDT) or poly(2,2′:5′,2”‐3,3”‐didocyl‐terthiophene) (PTTT), and fullerene derivatives with additives of varying length and chemical functionalization, mimicking experimentally used additives like methyl ester additives, diiodooctane, and alkanedithiols. We find that functionalization of additives with end groups that are attracted to acceptor molecules are necessary to induce increased donor‐acceptor macrophase separation. In blends where acceptors intercalate between oligomer alkyl side chains, functionalized additives decrease acceptor intercalation. Functionalized additives with shorter alkyl segments increase acceptor macrophase separation more than additives with same chemical functionalization but longer alkyl segments. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53 , 1046–1057

Marsh, Hilary S.↗
DOE OSTI2018

Side chain length affects backbone dynamics in poly(3-alkylthiophene)s

Charge transport in conjugated polymers may be governed not only by the static microstructure but also fluctuations of backbone segments. Using molecular dynamics simulations, we predict the role of side chains in the backbone dynamics for regiorandom poly(3-alkylthiophene-2,5-diyl)s (P3ATs). Here, we show that the backbone of poly(3-dodecylthiophene-2-5-diyl) (P3DDT) moves faster than that of poly(3-hexylthiophene-2,5-diyl) (P3HT) as a result of the faster motion of the longer side chains. To verify our predictions, we investigated the structures and dynamics of regiorandom P3ATs with neutron scattering and solid state NMR. Measurements of spin-lattice relaxations (T1) using NMR support our prediction of faster motion for side chain atoms that are farther away from the backbone. Using small-angle neutron scattering (SANS), we confirmed that regiorandom P3ATs are amorphous at about 300K, although microphase separation between the side chains and backbones is apparent. Furthermore, Quasi-elastic neutron scattering (QENS) reveals that thiophene backbone motion is enhanced as the side chain length increases from hexyl to dodecyl. The faster motion of longer side chains leads to faster backbone dynamics, which in turn may affect charge transport for conjugated polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Radiative Efficiency and Charge-Carrier Lifetimes and Diffusion Length in Polycrystalline CdSeTe Heterostructures

CdTe-based photovoltaics is a rapidly developing energy technology with one of the lowest levelized costs of electricity. But nonradiative Shockley-Read-Hall (SRH) recombination limits the efficiency of CdTe solar cells. Partial mitigation of bulk and grain-boundary SRH recombination was achieved by alloying CdTe with Se, and CdSe x Te 1-x absorbers are used in high-efficiency solar cells. Recently, interface recombination was significantly reduced with alumina passivation, but other properties of Al 2 O 3 /CdSe x Te 1-x /Al 2 O 3 heterostructures have not yet been investigated. Herein, further progress in understanding and developing polycrystalline heterostructures with x = 0.2 is reported. It is shown that external photoluminescence quantum yield is increased to 0.2%, quasi-Fermi-level splitting to 950 mV, minority carrier lifetimes to 750 ns, and mobility to 100 cm 2 Vs -1 . Such polycrystalline CdSe x Te 1-x electronic characteristics match or exceed CdTe single-crystal properties. The resulting charge-carrier diffusion length of ≈14 $\mu$m is several times greater than the absorber thickness in test structures and in typical CdTe solar cells. Herein, with passivation and absorbers, polycrystalline CdSeTe solar cell open-circuit voltage is increased from the current 76% of the Shockley-Queisser limit to 82%, or close to 1 V is reported.

14 SOLAR ENERGY↗
DOE OSTI2023

Generalized filtered lifting line theory for arbitrary chord lengths and application to wind turbine blades

Abstract The filtered lifting line theory is an analytical approach used to solve the equations of flow subjected to body forces with a Gaussian distribution, such as used in the actuator line model. In the original formulation, the changes in chord length along the blade were assumed to be small. This assumption can lead to errors in the induced velocities predicted by the theory compared to full solutions of the equations. In this work, we revisit the original derivation and provide a more general formulation that can account for significant changes in chord along the blade. The revised formulation can be applied to wings with significant changes in chord along the span, such as wind turbine blades.

17 WIND ENERGY↗
DOE OSTI2015

An Evaluation of OpenSHMEM Interfaces for the Variable-Length Alltoallv() Collective Operation, In: OpenSHMEM and Related Technologies. Experiences, Implementations, and Technologies

Alltoallv() is a collective operation which allows all processes to exchange variable amounts of data with all other processes in the communication group. This means that Alltoallv() requires not only O(N2) communications, but typically also additional exchanges of the data lengths that will be transmitted in the eventual Alltoallv() call. This pre-exchange is used to calculate the proper offsets for the receiving buffers on the target processes. However, we propose two new candidate interfaces for Alltoallv() that would mitigate the need for the user to set up this extra exchange of information at the possible cost of memory efficiency. We explain the new interface variants and show how a single call can be used in place of the traditional Alltoall()/ Alltoallv() pair. We then discuss the performance tradeoffs for overall communication and memory costs, as well as both software and hardware-based optimizations and their applicability to the various proposed interfaces.

Computer Science↗
DOE OSTI2015

Decreasing transmembrane segment length greatly decreases perfringolysin O pore size

Perfringolysin O (PFO) is a transmembrane (TM) β-barrel protein that inserts into mammalian cell membranes. Once inserted into membranes, PFO assembles into pore-forming oligomers containing 30–50 PFO monomers. These form a pore of up to 300 Å, far exceeding the size of most other proteinaceous pores. In this study, we found that altering PFO TM segment length can alter the size of PFO pores. A PFO mutant with lengthened TM segments oligomerized to a similar extent as wild-type PFO, and exhibited pore-forming activity and a pore size very similar to wild-type PFO as measured by electron microscopy and a leakage assay. In contrast, PFO with shortened TM segments exhibited a large reduction in pore-forming activity and pore size. This suggests that the interaction between TM segments can greatly affect the size of pores formed by TM β-barrel proteins. PFO may be a promising candidate for engineering pore size for various applications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Reconstruction of the springtime East Asian Subtropical Jet and Western Pacific pattern from a millennial-length Taiwanese tree-ring chronology

The East Asian subtropical jet (EAJ) and the closely related Western Pacific pattern (WP) are among the most important features in global atmospheric dynamics, but little is known about their long-term variability. This study presents reconstructions of the Spring EAJ index (EAJI) and the Spring WP index (WPI) based on significant relationships identified between mean values for these features and a millennial length tree-ring width chronology of Chamaecyparis obtusa var. formosana, a high-mountain cloud forest species from northeastern Taiwan. Tree-ring based reconstructions of high pass filtered versions of the EAJI and WPI (EAJI 5YR and WPI 5YR) presented herein explain 42 and 31 % of the WPI 5YR and EAJI 5YR, respectively, and display acceptable reliability back to A.D. 1237. A significant trend present in the long-term variance of the reconstructed EAJI and WPI after A.D. 1860 suggests long-term increasing variability in the spring mean latitudinal placement and/or the strength/breadth of the EAJ core region near Taiwan and Japan and in the trajectory of the EAJ over the North Pacific. Related features affected by changes in the EAJ include the North Pacific storm track and Asian Dust transport.

Meteorology & Atmospheric Sciences↗
DOE OSTI2015

Review of the synergies between computational modeling and experimental characterization of materials across length scales

With the increasing interplay between experimental and computational approaches at multiple length scales, new research directions are emerging in materials science and computational mechanics. Such cooperative interactions find many applications in the development, characterization and design of complex material systems. This manuscript provides a broad and comprehensive overview of recent trends in which predictive modeling capabilities are developed in conjunction with experiments and advanced characterization to gain a greater insight into structure–property relationships and study various physical phenomena and mechanisms. The focus of this review is on the intersections of multiscale materials experiments and modeling relevant to the materials mechanics community. After a general discussion on the perspective from various communities, the article focuses on the latest experimental and theoretical opportunities. Emphasis is given to the role of experiments in multiscale models, including insights into how computations can be used as discovery tools for materials engineering, rather than to “simply” support experimental work. This is illustrated by examples from several application areas on structural materials. In conclusion this manuscript ends with a discussion on some problems and open scientific questions that are being explored in order to advance this relatively new field of research.

3-D microstructure characterization↗
DOE OSTI2018

Shear localization and size-dependent strength of YCd 6 quasicrystal approximant at the micrometer length scale

Mechanical properties of materials are strongly dependent of their atomic arrangement as well as the sample dimension, particularly at the micrometer length scale. Here in this study, we investigated the small-scale mechanical properties of single-crystalline YCd 6 , which is a rational approximant of the icosahedral Y-Cd quasicrystal. In situ microcompression tests revealed that shear localization always occurs on {101} planes, but the shear direction is not constrained to any particular crystallographic directions. Furthermore, the yield strengths show the size dependence with a power law exponent of 0.4. Shear localization on {101} planes and size-dependent yield strength are explained in terms of a large interplanar spacing between {101} planes and the energetics of shear localization process, respectively. The mechanical behavior of the icosahedral Y-Cd quasicrystal is also compared to understand the influence of translational symmetry on the shear localization process in both YCd 6 and Y-Cd quasicrystal micropillars. Finally, the results of this study will provide an important insight in a fundamental understanding of shear localization process in novel complex intermetallic compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Molecular Structure and Crystallization Dynamics of Poly(3-hydroxyl alkanoate) with Medium-Chain Length Biosynthesized from Pseudomonas putida

The molecular structure of poly(3-hydroxyalkanoate) (P3HA) with medium-chain length, biosynthesized from Psuedomonas putida (P. putida), was investigated by thermal analysis, X-ray diffraction, and infrared spectrum. Cultivation in a medium of nonanoic acid and a mixed substrate of nonanoic acid and glycerin as carbon sources provided P3HA with monomer units of 7 and 9 carbons (P3HA{sub n}) and 5, 6, 7, 8, 9, and 10 carbons (P3HA{sub mix}). Since these P3HA has comparatively long side chains, the crystallinity was as low as about 10%. It was suggested that the hydrogen bonding plays an important role in constructing the crystal. The lamellar thickness was 1.20 nm, estimated from the melting temperature depression. This lamellar thickness corresponds to two repeating units. Crystallinity depending on time was observed by the CO stretching mode in the infrared spectrum, and then Avrami’s theory was applied to analyze the crystallization mechanism. The crystallization rate of P3HA{sub n} was very low, on the order of a few hours. An Avrami exponent of 1.45 was estimated from the slope of the Avrami plot. This shows that the conformational arrangement is presumably promoted along the chain axis. The slow crystallization is attributed to the long side chain, which prevents aggregation of the polymer chains.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Constant-Length Random Substitutions and Gibbs Measures

This work is devoted to the study of processes generated by random substitutions over a finite alphabet. We prove, under mild conditions on the substitution’s rule, the existence of a unique process which remains invariant under the substitution, and which exhibits a polynomial decay of correlations. For constant-length substitutions, we go further by proving that the invariant state is precisely a Gibbs measure which can be obtained as the projective limit of its natural Markovian approximations. We end up the paper by studying a class of substitutions whose invariant state is the unique Gibbs measure for a hierarchical two-body interaction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Estimating the Contribution of the Nickel to Protium Loading of Full-Length Getters

The full-length getter (FLG) is a critical component of the tritium producing burnable absorber rod (TPBAR), designed to capture tritium produced within the lithium aluminate pellets. However, due to the chemical similarity between protium (¹H) and tritium (³H), the FLG readily absorbs protium, reducing its capacity to absorb tritium and increasing the risk of tritium permeation into the reactor coolant. This study evaluates protium produced from neutron irradiation of nickel plating on the FLG through 5?Ni(n,p) reactions, quantifies its contribution to the total protium observed, and informs models of tritium and hydrogen transport within TPBARs. During irradiation, neutron capture by 58Ni results in the formation of 5?Ni, which undergoes neutron bombardment to produce 4He via 5?Ni(n,a) reactions and protium via 5?Ni(n,p) reactions. The measured helium content post-irradiation provides insight into the neutron capture processes within the getter. The 4He measured within the getter may be useful in determining hydrogen produced by the nickel plating on FLG because 59Ni also produces protium in a 59Ni(n, p) reaction. The contribution of 1H from the nickel in FLG contributed less than 1% of the measured H2 gas in PIE, ranging from 0.005% to 0.614%. These findings refine current knowledge of the protium-tritium interplay in TPBARs and support the development of improved transport models for tritium and hydrogen, ultimately aiding in the optimization of TPBAR design and reactor operations.

Arbova, Dana L.↗
DOE OSTI2020

Heterogeneities at multiple length scales in 2D layered materials: From localized defects and dopants to mesoscopic heterostructures

Two-dimensional (2D) materials hold great promise for applications in optoelectronics, quantum information science, and energy conversion due to their remarkable properties imbued by their physical characteristics. Although heterogeneities in their intrinsic structure are the major challenges limiting their synthesis and predictable properties, they also provide a pathway to controllably tune the properties and broaden the potential of 2D materials. Heterogeneities that can be tailored, including defects, dopants, strain, edges, and layer stackings offer transformative opportunities in heterogeneous 2D materials through the introduction of novel properties for technological applications. This article provides a review of recent progress in studying heterogeneities in 2D materials. The review uses examples from our work to develop a strategy to understand the heterogeneities across multiple length scales to link the effect of heterogeneity at the nanoscale with the macroscale properties of 2D materials. We describe specific types of heterogeneities and explore novel synthesis and processing methods for their controlled production with example of the potential impact and applications enabled by their intriguing properties. Finally, we provide a perspective on how to extend the range of tunable properties through further engineering the heterogeneities in 2D materials.

2D materials↗
DOE OSTI2020

Competing Interactions between Mesoscale Length-Scales, Order-Disorder, and Martensitic Transformation in Ferromagnetic Shape Memory Alloys

In the present study, the effects of composition and heat treatments and the resulting microstructural changes on the martensitic transformation and ferromagnetic transition have been investigated in NiCoMnIn metamagnetic shape memory alloys. In this shape memory alloy system, it is observed that upon heat treatments at a wide temperature range, the onset temperature of the martensitic transformation follows a non-monotonic behavior with respect to heat treatment time, and the nature of the non-monotonic behavior is also a function of composition. This behavior cannot be attributed to well-known factors such as precipitation, change in local composition due to the precipitation and/or global degree of order. In this work, a systematic investigation through synthesis, thermal processing and characterization via thermo-physical measurements, transmission electron microscopy and in-situ synchrotron x-ray diffraction experiments has been used to correlate the non-monotonic dependence of the martensitic transformation and ferromagnetic transition temperatures to the evolution of L2 1 domains arising from a order/disorder phase transition. A thermodynamic model for the magneto-structural transition is combined with classical nucleation theory to further ascertain the role of microstructural length-scales on the onset of the martensitic transformation. This work thus provides understanding of the thermodynamic and kinetic factors that can be controlled to tune the coupled magneto-structural transformations in NiCoMnIn metamagnetic shape memory alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tailoring mechanical properties of a multi-principal element alloy through a multi-length-scale approach

In this study, a multi-length-scale strengthening approach was used to tailor the microstructure and the mechanical properties of a NiCoCr-based multi-principal element alloy (MPEA). Grain size refinement, severe lattice distortion, and stacking fault energy (SFE) reduction with Mo addition (up to 10 at.%) enhance yield strength by 85% with only 10% reduction in ductility in as-annealed MPEAs. A pronounced increase in the strain hardening rate was observed with the addition of Mo, which is ascribed to the promotion of complex stacking fault (SF) interaction and intersection, accompanied by Lomer-Cottrell (L-C) and Hirth locks inhibiting dislocation motion and substantial increase in the accumulation of back stress. To push the limit of the yield strength further, the Suzuki segregation phenomenon was manipulated by a careful control of SF density by pre-straining and a subsequent 500 °C heat treatment. The stress-strain responses of the pre-strained and heat treated MPEAs showed an obvious SF density and Mo concentration dependence. Furthermore, the yield strength of the pre-strained Mo-added MPEAs with subsequent heat treatment was increased up to true stress of 2.3 GPa with a corresponding fracture elongation of 12% true strain. SFs formed during pre-straining served as Cr segregation sites during subsequent heat treatment, which substantially varies the local SFE within the SF, presenting a roughened landscape and frustrating the dislocation dynamics.

mechanical properties↗
DOE OSTI2014

The internal structure of a vortex in a two-dimensional superfluid with long healing length and its implications

We analyze the motion of quantum vortices in a two-dimensional spinless superfluid within Popov’s hydrodynamic description. In the long healing length limit (where a large number of particles are inside the vortex core) the superfluid dynamics is determined by saddle points of Popov’s action, which, in particular, allows for weak solutions of the Gross–Pitaevskii equation. We solve the resulting equations of motion for a vortex moving with respect to the superfluid and find the reconstruction of the vortex core to be a non-analytic function of the force applied on the vortex. This response produces an anomalously large dipole moment of the vortex and, as a result, the spectrum associated with the vortex motion exhibits narrow resonances lying within the phonon part of the spectrum, contrary to traditional view.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗