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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Multiple species beam production on laser ion source for electron beam ion source in Brookhaven National Laboratory

Extracted ion beams from the test laser ion source (LIS) were transported through a test beam transport line which is almost identical to the actual primary beam transport in the current electron beam ion source apparatus. The tested species were C, Al, Si, Cr, Fe, Cu, Ag, Ta, and Au. The all measured beam currents fulfilled the requirements. However, in the case of light mass ions, the recorded emittance shapes have larger aberrations and the RMS values are higher than 0.06 π mm mrad, which is the design goal. Since we have margin to enhance the beam current, if we then allow some beam losses at the injection point, the number of the single charged ions within the acceptance can be supplied. For heaver ions like Ag, Ta, and Au, the LIS showed very good performance.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Precision control of multiple quantum cascade lasers for calibration systems

We present a precision, 1-A, digitally interfaced current controller for quantum cascade lasers, with demonstrated temperature coefficients for continuous and 40-kHz full-depth square-wave modulated operation, of 1–2 ppm/ °C and 15 ppm/ °C, respectively. High precision digital to analog converters (DACs) together with an ultra-precision voltage reference produce highly stable, precision voltages, which are selected by a multiplexer (MUX) chip to set output currents via a linear current regulator. The controller is operated in conjunction with a power multiplexing unit, allowing one of three lasers to be driven by the controller, while ensuring protection of controller and all lasers during operation, standby, and switching. Simple ASCII commands sent over a USB connection to a microprocessor located in the current controller operate both the controller (via the DACs and MUX chip) and the power multiplexer.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Communication: Active space decomposition with multiple sites: Density matrix renormalization group algorithm

We extend the active space decomposition method, recently developed by us, to more than two active sites using the density matrix renormalization group algorithm. The fragment wave functions are described by complete or restricted active-space wave functions. Numerical results are shown on a benzene pentamer and a perylene diimide trimer. It is found that the truncation errors in our method decrease almost exponentially with respect to the number of renormalization states M, allowing for numerically exact calculations (to a few μE{sub h} or less) with M = 128 in both cases. This rapid convergence is because the renormalization steps are used only for the interfragment electron correlation.

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

Electron transport in unipolar InGaN/GaN multiple quantum well structures grown by NH{sub 3} molecular beam epitaxy

Unipolar-light emitting diode like structures were grown by NH{sub 3} molecular beam epitaxy on c plane (0001) GaN on sapphire templates. Studies were performed to experimentally examine the effect of random alloy fluctuations on electron transport through quantum well active regions. These unipolar structures served as a test vehicle to test our 2D model of the effect of compositional fluctuations on polarization-induced barriers. Variables that were systematically studied included varying quantum well number from 0 to 5, well thickness of 1.5 nm, 3 nm, and 4.5 nm, and well compositions of In{sub 0.14}Ga{sub 0.86}N and In{sub 0.19}Ga{sub 0.81}N. Diode-like current voltage behavior was clearly observed due to the polarization-induced conduction band barrier in the quantum well region. Increasing quantum well width and number were shown to have a significant impact on increasing the turn-on voltage of each device. Temperature dependent IV measurements clearly revealed the dominant effect of thermionic behavior for temperatures from room temperature and above. Atom probe tomography was used to directly analyze parameters of the alloy fluctuations in the quantum wells including amplitude and length scale of compositional variation. A drift diffusion Schrödinger Poisson method accounting for two dimensional indium fluctuations (both in the growth direction and within the wells) was used to correctly model the turn-on voltages of the devices as compared to traditional 1D simulation models.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Using multiple secondary fusion products to evaluate fuel ρR, electron temperature, and mix in deuterium-filled implosions at the NIF

In deuterium-filled inertial confinement fusion implosions, the secondary fusion processes D( 3 He,p) 4 He and D(T,n) 4 He occur, as the primary fusion products 3 He and T react in flight with thermal deuterons. In implosions with moderate fuel areal density (~ 5–100 mg/cm 2 ), the secondary D- 3 He reaction saturates, while the D-T reaction does not, and the combined information from these secondary products is used to constrain both the areal density and either the plasma electron temperature or changes in the composition due to mix of shell material into the fuel. The underlying theory of this technique is developed and applied to three classes of implosions on the National Ignition Facility: direct-drive exploding pushers, indirect-drive 1-shock and 2-shock implosions,and polar direct-drive implosions. In the 1- and 2-shock implosions, the electron temperature is inferred to be 0.65 x and 0.33 x the burn-averaged ion temperature, respectively. The inferred mixed mass in the polar direct-drive implosions is in agreement with measurements using alternative techniques.

42 ENGINEERING↗
DOE OSTI2014

Energetic neutral atoms measured by the interstellar boundary explorer (IBEX): Evidence for multiple heliosheath populations

Energetic neutral atoms (ENAs) observed by the Interstellar Boundary Explorer (IBEX) provide powerful diagnostics about the origin of the progenitor ion populations and the physical mechanisms responsible for their production. In this paper, we extend the work of Desai et al. and Fuselier et al. and combine and compare ENA spectra from the first 3 yr of observations by the IBEX-Hi and -Lo ENA imagers along the lines-of-sight (LOSs) from the inner heliosphere through to the locations of Voyager 1 and 2 with results from an updated physics-based model of the three-dimensional heliosphere and its constituent ion populations. Our results show that (1) IBEX ENA fluxes and spectra above ∼0.7 keV measured along the LOSs of the Voyagers are consistent with several models in which the parent pickup ion (PUI) populations originate in the inner heliosheath, and (2) a significant fraction of lower energy ENAs between ∼0.1-0.5 keV may originate from interstellar neutral gas charge-exchanging with a non-thermalized (hot) population of PUIs in the outer heliosheath beyond the heliopause. We discuss the implications of ENAs observed by IBEX originating from distinct parent populations as well as from two distinct locations in the heliospheric interface. These results indicate that ENA spectral measurements at various energies can be used to remotely probe distinct physical processes operating in vastly different regions of the distant heliosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Multiple highly expressed phospho enol pyruvate carboxylase genes have divergent enzyme kinetic properties in two C4 grasses

Abstract Background and Aims Phosphoenolpyruvate (PEP) carboxylase (PEPC) catalyses the irreversible carboxylation of PEP with bicarbonate to produce oxaloacetate. This reaction powers the carbon-concentrating mechanism (CCM) in plants that perform C4 photosynthesis. This CCM is generally driven by a single PEPC gene product that is highly expressed in the cytosol of mesophyll cells. We found two C4 grasses, Panicum miliaceum and Echinochloa colona, that each have two highly expressed PEPC genes. We characterized the kinetic properties of the two most abundant PEPCs in E. colona and P. miliaceum to better understand how the enzyme’s amino acid structure influences its function. Methods Coding sequences of the two most abundant PEPC proteins in E. colona and P. miliaceum were synthesized by GenScript and were inserted into bacteria expression plasmids. Point mutations resulting in substitutions at conserved amino acid residues (e.g. N-terminal serine and residue 890) were created via site-directed PCR mutagenesis. The kinetic properties of semi-purified plant PEPCs from Escherichia coli were analysed using membrane-inlet mass spectrometry and a spectrophotometric enzyme-coupled reaction. Key Results The two most abundant P. miliaceum PEPCs (PmPPC1 and PmPPC2) have similar sequence identities (>95 %), and as a result had similar kinetic properties. The two most abundant E. colona PEPCs (EcPPC1 and EcPPC2) had identities of ~78 % and had significantly different kinetic properties. The PmPPCs and EcPPCs had different responses to allosteric inhibitors and activators, and substitutions at the conserved N-terminal serine and residue 890 resulted in significantly altered responses to allosteric regulators. Conclusions The two, significantly expressed C4Ppc genes in P. miliaceum were probably the result of genomes combining from two closely related C4Panicum species. We found natural variation in PEPC’s sensitivity to allosteric inhibition that seems to bypass the conserved 890 residue, suggesting alternative evolutionary pathways for increased malate tolerance and other kinetic properties.

DiMario, Robert J. (ORCID:0000000250566868)↗
DOE OSTI2017

Multiple superconducting states induced by pressure in Mo 3 Sb 7

Tuning competing ordering mechanisms with hydrostatic pressure in the 4 d intermetallic compound Mo 3 Sb 7 reveals an intricate interplay of structure, magnetism, and superconductivity. Synchrotron x-ray diffraction and magnetic susceptibility measurements, both employing diamond anvil cell technologies, link a first-order structural phase transition to a doubling of the superconducting transition temperature. In contrast to the spin-dimer picture for Mo 3 Sb 7 , we deduce from x-ray absorption near-edge structure and dc magnetization measurements at ambient pressure that Mo 3 Sb 7 should possess only very small, itinerant magnetic moments. As a result, the pressure evolution of the superconducting transition temperature strongly suggests its enhancement is due to a difference in the phonon density-of-states with changed crystal symmetry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗