SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
With in situ ESEM and GIWAXS we saw that the perovskite degradation passes through hexagonal polytypes and is dependent on the composition.
Synchrotron X-ray scattering reveals that atomic-scale defect control manipulated by chemical substitution optimizes nanomagnetism and enables hyperthermia heating in core-shell iron-oxide nanocrystals.
The electron- and hole-transport properties in cadmium zinc telluride selenide (CZTS) crystals are studied using a laser-induced transient-current technique with pulsed and dc bias. The internal electric field profile and velocity of surface recombination are determined by Monte Carlo simulations of electron and hole transient currents combined with a numerical solution of the drift-diffusion equation coupled with Poisson’s equation. Electron and hole drift mobilities of μe = 830 cm 2 /Vs and μh = 40 cm 2 /Vs, respectively, are determined. We also develop a simple technique for evaluating surface recombination directly from measured current waveforms without the need for numerical simulation. The good quality of the prepared detector at pulsed bias, with electron- and hole-mobility-lifetime products of (μτ)e = 1.9 × 10 -3 cm 2 /V and (μτ)h = 1.4 × 10 -4 cm 2 /V, respectively, are observed. The formation of a positive space charge, originating from hole injection combined with a recombination level, is found. We observe a significant position dependence of the lifetime of electrons and holes in dc bias due to hole injection. The experiment is successfully fitted by a simple model dominated by a single deep recombination level with an energy of E t =E C -0.73eV; concentration of 7.3 × 10 11 cm -3 ; and electron- and hole-capture cross sections of 3.5 × 10 -14 cm 2 and 6.5 × 10 -14 cm 2 , respectively.
Here, the entropic signatures of magnetic phase transitions in the skyrmion lattice host compounds MnSi 0.962 Al 0.038 and Fe 0.7 Co 0.3 Si were investigated through low field magnetization and ac susceptibility measurements. These data indicate that the conical to skyrmion transition that occurs with the application of magnetic field in MnSi 0.962 Al 0.038 is characterized by clear discontinuity in the magnetic entropy as expected for first order topological phase transition. These same magnetoentropic features are negligibly small in isostructural Fe 0.7 Co 0.3 Si due to the level of chemical substitution related disorder and differences in the spin dynamics (range and timescales). Despite the obvious similarities in the magnetic structures of these two compounds, the transitions between these phases is substantially different indicating a surprising nonuniversality to the magnetic phase transitions in this class of materials.
Herein, thermoelectric materials hold tremendous promise for advances in fundamental science and practical ap- plications, particularly for robust electricity generation in extreme and remote environments. Despite this, for most materials the energy conversion efficiency is limited by the proportionality between the electrical and thermal conductivities and small values of the Seebeck coefficient for metals. It was previously reported that the heavy-fermion compound $\text{YbIr}_2$ $\text{Zn}_{20}$ exhibits large Seebeck coefficient and thermoelectric figure of merit $ZT$ at 35 K. This behavior is primarily associated with strong hybridization between the $f$- and conduction electron states. Here, we seek to improve the thermoelectric properties through chemical substitution on the Yb site using Ce and Sm. By surveying different levels of substitution, we find that the thermoelectric properties vary strongly with the $f$-element ratio. This confirms that electronic hybridization dominates the thermoelectric properties and clarifies directions for optimizing these materials for applications. We also investigate the impact of the disorder on the thermal conductivity, where we find only weak variation with lanthanide content.
Explore the source record for details and available documents.
Operator solutions for complex valued second order differential equation
A differential equation proposed by H. Lashinsky to describe the nonlinear solution of aperiodic instabilities is investigated. Oscillatory and nonoscillatory solutions are discussed and a numerical integration is presented.
A new double graded band-gap (DGBG) Al sub x Ga sub l-x As-Al sub z Ga sub l-z As solar cell has potential for providing high efficiency performance throughout the entire life of a solar cell in a space environment. A preliminary theoretical analysis indicates that short circuit current available from an optimized DGBG cell is slightly larger than that of a previously reported single graded band-gap cell. However, the DGBG cell potentially offers a substantial improvement in radiation resistance of the base region.
The paper reports on the first demonstration of pseudomorphic InGaAs single quantum well surface-emitting lasers (SELs), with etched vertical mirrors and integrated 45-deg beam deflectors fabricated by ion beam etching. 100-micron-wide broad-area SELs exhibited a threshold current of 320 mA, a total power of 126 mW, and a total external differential quantum efficiency of 0.09 W/A for a 500-micron-long cavity. The perpendicular far-field pattern of broad-area SELs showed a full width at half maximum of about 20 deg. Lasers with various types of cavities fabricated from the same wafer were compared. Broad-area edge-emitting lasers had a threshold current of 200 mA, a total power of 700 mW, and a total external differential quantum efficiency of 0.52 W/A.
Thermoelectric materials based on the skutterudite crystal structure have demonstrated enhanced performance (ZT greater than 1), along with good thermal stability and favorable mechanical properties. Binary skutterudites, with single and multiple fillers, have been intensively studied in recent years. Compared to binary skutterudites, the ternary systems have received less attention, e.g. Ni4Sb8Sn4. Ternary skutterudites are isoelectronic variants of binary skutterudites; cation substitutions appear to be isostructural to their binary analogues. In general, ternary skutterudites exhibit lower thermal conductivity. Ternary systems of Ni4Bi8Ge4, Ni4Sb8Ge4, and Ni4Sb8Sn4 were investigated using combined solidification and sintering steps. Skutterudite formation was not achieved in the Ni4Bi8Ge4 and Ni4Sb8Ge4 systems; skutterudite formation occurred in Ni4Sb8Sn4 system. P-type material was achieved by Co substitution for Ni. Thermoelectric properties were measured from 298 K to 673 K for Ni4Sb8Sn4, Ni4 Sb7Sn5 and Co2Ni2Sb7Sn5. N-type Ni4Sb8Sn4 exhibit the highest figure of merit of 0.1 at 523 K.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The Jefferson Lab eta Factory (JEF) began acquiring data in early 2025. The experiment aims to give insight into the connection between Dark Matter physics models and the Standard Model by investigating rare decay processes of n and n' mesons. Several other physics motivations are also a key factor in the experiment, such as probing C and/or P violation and aspects of chiral perturbation theory. For these purposes, the forward calorimeter of the GlueX experiment in Jefferson Lab was upgraded so that it provides greater positional and energy resolution. Understanding physics-motivated cuts and background removal methods is of great importance to achieving JEF goals. Several methods have been implemented to obtain invariant mass plots for the “golden” channel of interest ¿ ¿ p0¿¿, while channels such as ¿ ¿ p+p-e+e- open a promising window into CP-violating physics. This thesis work shows a sig nificant background reduction in rare decay channels of interest, asymmetry factors comparable to recent experimental measurements, an evaluation on which analysis cuts to use after data acquisition and the likelihood of probing specific rare ¿ decays. Despite background rejection from obstructing decay channels, much remains to do to extract the p0¿¿ final-state. The asymmetry between the pion and lepton planes looks promising for p+p-e+e-; simulations show that the asymmetry is consistent with zero (no instrumental asymmetry), and the next step should include generators that model the physics of the asymmetry. This thesis work may help in the effort of probing CP-violating physics or solving the mysteries between “beyond-Standard Model” and our current understanding of physics.
Y is alpha Samarium structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are six inequivalent Y sites. In the first Y site, Y is bonded to twelve Y atoms to form a mixture of face, edge, and corner-sharing YY12 cuboctahedra. There are six shorter (3.57 Å) and six longer (3.60 Å) Y–Y bond lengths. In the second Y site, Y is bonded to twelve Y atoms to form a mixture of face, edge, and corner-sharing YY12 cuboctahedra. There are three shorter (3.54 Å) and six longer (3.60 Å) Y–Y bond lengths. In the third Y site, Y is bonded to twelve Y atoms to form a mixture of face, edge, and corner-sharing YY12 cuboctahedra. There are a spread of Y–Y bond distances ranging from 3.54–3.60 Å. In the fourth Y site, Y is bonded to twelve Y atoms to form a mixture of face, edge, and corner-sharing YY12 cuboctahedra. There are three shorter (3.57 Å) and six longer (3.60 Å) Y–Y bond lengths. In the fifth Y site, Y is bonded to twelve Y atoms to form a mixture of face, edge, and corner-sharing YY12 cuboctahedra. There are three shorter (3.54 Å) and six longer (3.60 Å) Y–Y bond lengths. In the sixth Y site, Y is bonded to twelve Y atoms to form a mixture of face, edge, and corner-sharing YY12 cuboctahedra. There are three shorter (3.57 Å) and six longer (3.60 Å) Y–Y bond lengths.
Y(ReAl5)2 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent Y sites. In the first Y site, Y is bonded in a 10-coordinate geometry to four Re and sixteen Al atoms. There are two shorter (3.40 Å) and two longer (3.52 Å) Y–Re bond lengths. There are a spread of Y–Al bond distances ranging from 3.06–3.50 Å. In the second Y site, Y is bonded in a 4-coordinate geometry to fourteen Al atoms. There are a spread of Y–Al bond distances ranging from 3.07–3.28 Å. There are two inequivalent Re sites. In the first Re site, Re is bonded in a 10-coordinate geometry to one Y and ten Al atoms. There are a spread of Re–Al bond distances ranging from 2.55–2.79 Å. In the second Re site, Re is bonded in a 10-coordinate geometry to two equivalent Y and ten Al atoms. There are a spread of Re–Al bond distances ranging from 2.57–2.74 Å. There are twelve inequivalent Al sites. In the first Al site, Al is bonded in a 2-coordinate geometry to two equivalent Y, two equivalent Re, and four Al atoms. There are two shorter (2.74 Å) and two longer (3.07 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 12-coordinate geometry to one Y, two equivalent Re, and nine Al atoms. There are a spread of Al–Al bond distances ranging from 2.66–3.14 Å. In the third Al site, Al is bonded in a 2-coordinate geometry to two equivalent Y, two equivalent Re, and eight Al atoms. There are a spread of Al–Al bond distances ranging from 2.67–3.05 Å. In the fourth Al site, Al is bonded in a 2-coordinate geometry to one Y, two equivalent Re, and nine Al atoms. There are a spread of Al–Al bond distances ranging from 2.80–3.10 Å. In the fifth Al site, Al is bonded in a 12-coordinate geometry to two Y, two equivalent Re, and eight Al atoms. There are a spread of Al–Al bond distances ranging from 2.62–3.00 Å. In the sixth Al site, Al is bonded in a 2-coordinate geometry to two Y, two equivalent Re, and six Al atoms. There are a spread of Al–Al bond distances ranging from 2.66–2.96 Å. In the seventh Al site, Al is bonded in a 2-coordinate geometry to one Y, two equivalent Re, and eight Al atoms. There are two shorter (2.77 Å) and two longer (3.04 Å) Al–Al bond lengths. In the eighth Al site, Al is bonded in a 12-coordinate geometry to one Y, two equivalent Re, and nine Al atoms. There are a spread of Al–Al bond distances ranging from 2.67–2.89 Å. In the ninth Al site, Al is bonded in a 12-coordinate geometry to two Y, two equivalent Re, and eight Al atoms. The Al–Al bond length is 2.70 Å. In the tenth Al site, Al is bonded in a 11-coordinate geometry to one Y, two equivalent Re, and eight Al atoms. Both Al–Al bond lengths are 2.97 Å. In the eleventh Al site, Al is bonded in a distorted linear geometry to two equivalent Y, two Re, and four Al atoms. In the twelfth Al site, Al is bonded in a 2-coordinate geometry to one Y, two Re, and four Al atoms.
YFe6Sn6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are two inequivalent Y sites. In the first Y site, Y is bonded to twelve Fe and eight Sn atoms to form distorted YFe12Sn8 hexagonal bipyramids that share faces with eight FeY2Fe4Sn6 cuboctahedra and faces with six YFe12Sn8 hexagonal bipyramids. There are four shorter (3.49 Å) and eight longer (3.51 Å) Y–Fe bond lengths. There are a spread of Y–Sn bond distances ranging from 3.02–3.17 Å. In the second Y site, Y is bonded to twelve Fe and eight Sn atoms to form distorted YFe12Sn8 hexagonal bipyramids that share corners with four equivalent YFe12Sn8 hexagonal bipyramids, faces with sixteen FeY2Fe4Sn6 cuboctahedra, and faces with four YFe12Sn8 hexagonal bipyramids. There are a spread of Y–Fe bond distances ranging from 3.49–3.53 Å. There are a spread of Y–Sn bond distances ranging from 3.03–3.17 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent Y, four equivalent Fe, and six Sn atoms to form distorted FeY2Fe4Sn6 cuboctahedra that share corners with six FeY2Fe4Sn6 cuboctahedra, edges with three equivalent FeY2Fe4Sn6 cuboctahedra, a faceface with one FeY2Fe4Sn6 cuboctahedra, and faces with four YFe12Sn8 hexagonal bipyramids. All Fe–Fe bond lengths are 2.72 Å. There are a spread of Fe–Sn bond distances ranging from 2.72–2.82 Å. In the second Fe site, Fe is bonded to two equivalent Y, four Fe, and six Sn atoms to form distorted FeY2Fe4Sn6 cuboctahedra that share corners with eight FeY2Fe4Sn6 cuboctahedra, edges with four FeY2Fe4Sn6 cuboctahedra, faces with eight FeY2Fe4Sn6 cuboctahedra, and faces with four equivalent YFe12Sn8 hexagonal bipyramids. There are two shorter (2.70 Å) and two longer (2.72 Å) Fe–Fe bond lengths. There are a spread of Fe–Sn bond distances ranging from 2.73–2.83 Å. In the third Fe site, Fe is bonded to two equivalent Y, four Fe, and six Sn atoms to form distorted FeY2Fe4Sn6 cuboctahedra that share corners with ten FeY2Fe4Sn6 cuboctahedra, edges with five FeY2Fe4Sn6 cuboctahedra, faces with five FeY2Fe4Sn6 cuboctahedra, and faces with four YFe12Sn8 hexagonal bipyramids. Both Fe–Fe bond lengths are 2.70 Å. There are a spread of Fe–Sn bond distances ranging from 2.71–2.82 Å. In the fourth Fe site, Fe is bonded in a 12-coordinate geometry to two Y, four Fe, and six Sn atoms. There are one shorter (2.70 Å) and one longer (2.71 Å) Fe–Fe bond lengths. There are a spread of Fe–Sn bond distances ranging from 2.71–2.83 Å. There are nine inequivalent Sn sites. In the first Sn site, Sn is bonded in a 8-coordinate geometry to one Y, six Fe, and one Sn atom. Both Sn–Fe bond lengths are 2.82 Å. The Sn–Sn bond length is 2.95 Å. In the second Sn site, Sn is bonded in a 6-coordinate geometry to six Fe atoms. In the third Sn site, Sn is bonded in a 12-coordinate geometry to three Y and six Fe atoms. In the fourth Sn site, Sn is bonded in a 8-coordinate geometry to two equivalent Y and six Fe atoms. In the fifth Sn site, Sn is bonded in a 12-coordinate geometry to three Y and six Fe atoms. In the sixth Sn site, Sn is bonded in a 6-coordinate geometry to six Fe atoms. In the seventh Sn site, Sn is bonded in a 7-coordinate geometry to one Y and six Fe atoms. In the eighth Sn site, Sn is bonded in a 8-coordinate geometry to one Y, six Fe, and one Sn atom. The Sn–Sn bond length is 2.94 Å. In the ninth Sn site, Sn is bonded in a 8-coordinate geometry to one Y, six Fe, and one Sn atom. The Sn–Y bond length is 3.02 Å. All Sn–Fe bond lengths are 2.83 Å. The Sn–Sn bond length is 2.95 Å.