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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

A compact in situ polarized 3He neutron spin filter for the diffractometer VULCAN at the Spallation Neutron Source

We have built and commissioned a compact in situ 3He polarizer based on spin-exchange optical pumping for the engineering materials diffractometer, named VULCAN, at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. The system achieved 78% 3He polarization with a short pump-up time constant of 2.2 h. Its first deployment in an in situ half-polarized neutron diffraction experiment on a magnetic shape memory alloy, Ni–Mn–Ga, revealed changes in magnetization coupled to deformation twinning under compression. With this new capability, VULCAN has become the first diffractometer at SNS capable of performing polarized neutron experiments, opening new opportunities to study a wider range of magnetism-related material behaviors under varied thermal, mechanical, electrical, and/or magnetic fields.

Fu, Sichao [ORNL] (ORCID:0009000846771640)↗
DOE OSTI2014

A highly efficient, compact Yb:KYW laser for mobile precision systems

We have developed a promising scheme of a multimodediode-pumped ytterbium laser. The Yb:KYW laser in the cw regime demonstrates record-high differential (40%) and total optical (35%) efficiencies. Mode locking is realised, which allows the scheme to be used for the development of compact laser systems, such as mobile femtosecond precision synthesisers. The peculiarities of the laser operation and ways of further improving its efficiency are discussed. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Development of a prototype compact fibre frequency synthesiser for mobile femtosecond optical clocks

A prototype compact fibre frequency synthesiser based on a femtosecond erbium fibre laser and an original hybrid highly nonlinear fibre is developed and preliminarily studied. This synthesiser will ensure an extremely low relative instability of synthesised frequencies (down to 10{sup -17}) with the use of a corresponding optical standard and will be used in mobile optical clocks. The realised frequency stabilisation principle makes the synthesiser universal and allows it to transfer the frequency stability of various types of optical standards to the synthesised radio- and optical frequencies. (extreme light fields and their applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

High-power compact laser with segmented longitudinal pumping of coupled laser channels

The characteristics of a compact Nd:YAG/Cr:YAG laser with segmented end pumping using a bundle of seven optical fibres are presented. In the regime of optical coupling of thus formed seven laser channels, 3-ns pulses with an energy up to 20 mJ, as well as their trains, are obtained. The used method makes it possible to scale the energy and power of lasers of this type with controlled spatial beam profile. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Analysis of the possibility of designing more compact DF lasers driven by combustion of preheated fuels

We report a theoretical calculation of the processes proceeding in the combustor of combustion-driven cw DF/HF chemical lasers with different mixtures of fuels preheated to high temperatures. Calculation results demonstrate a great effect of the preheating temperature on the yield of F atoms and strongest deactivator, on the primary dilution ratio Ψp and on the estimated specific power. When fuels are preheated to about 1300 K, the specific power is improved by about 74.2 %, and the total mass of the fuel is reduced by about 43 %, which makes it possible to realise a more compact and efficient design of combustion-driven cw DF/HF chemical lasers at elevated combustor pressures. Fuel preheating can facilitate the development of chemical lasers and high-power lasers based not only on airborne and space-borne platforms, but also on mobile ground-based platforms. (active media)

42 ENGINEERING↗
DOE OSTI2016

Compact transversely diode-pumped Nd :YAG laser with a self-pumped phase-conjugate multiloop cavity

A compact high-power repetitively pulsed Nd :YAG laser with transverse diode pumping and a multiloop self-pumped phase-conjugate cavity is presented. The obtained pulse trains have an energy of 2.55 J with beam quality M{sup 2}⩽1.2, a divergence of 0.35 mrad, and a spatial brightness of 7×10{sup 14} W cm{sup −2} sr{sup −1}. The peak power of single-frequency pulses exceeds 21 MW at a pulse energy of 230 mJ. The laser bandwidth is 300 MHz. (lasers)

42 ENGINEERING↗
DOE OSTI2017

Versatile and compact wide-range VUV spectrometer for quantitative measurements

Main parameters of a new scheme of a compact VUV grazing incidence spectrometer based on a plane amplitude diffraction grating are considered. The spectrometer will allow simultaneous detection of spectra at the +1st order diffraction edge with a sufficiently high ( λ/δ λ ∼ 150) spectral resolution and in the –1st order with a moderate resolution ( λ/δ λ ∼ 15 – 30), but in a very wide (5 – 200 nm) spectral range. The use of such a spectrometer is promising for measuring the absolute radiation yield in these spectral regions, which is necessary for the diagnostics and control of plasma radiation sources, including those intended for projection EUV nanolithography. (vuv spectroscopy)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Compact Q-switched Yb : Er laser with a pulse repetition rate of 10 Hz

A compact acousto-optically Q-switched Yb : Er laser emitting 20-ns pulses at λ = 1.5 μm with an energy of 8 mJ and a repetition rate of 10 Hz is developed. The laser radiation divergence at the exit of an optical forming system is 1 mrad. The experimental sample can stably operate in a wide temperature range with unchanged output parameters. The developed laser is 110 × 30 × 30 mm in size taking into account the dimensions of the optical forming system. Life tests demonstrated stable continuous operation of the sample for 50000 pulses. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Compact laser diode array based on epitaxially integrated AlGaAs/GaAs heterostructures

The main results of the development of compact laser diode mini-arrays operating under 875-nm pulsed pumping are presented and the instrumental characteristics of these arrays are studied. Specific features of these sources, in addition to a high output power (∼1.5 kW), are a narrow directional pattern (angular divergence 21° × 8°) and a small emitting area (less than 1 mm{sup 2}). The use of serially integrated AlGaAs/GaAs MOCVD heterostructures with three emitting regions to develop laser diode arrays allowed us to improve their working parameters. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Vertical-cavity surface-emitting lasers with intracavity contacts and a rhomboidal current aperture for compact atomic clocks

Single-mode vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts, composite distributed Bragg reflectors, and a rhomboidal selectively-oxidised current aperture are studied. It is shown that the use of a rhomboidal current aperture allows the light output polarisation to be fixed without using a special surface relief and leads to efficient narrowing of the emission line with retaining a high slope efficiency. The developed VCSELs have a high output power (exceeding 1 mW), a threshold current below 1 mA, an effective modulation frequency exceeding 5 GHz, and a linewidth smaller than 60 MHz at increased (65 – 75 °C) temperatures and are promising for application in compact Cs vapour cell atomic clocks. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Several versions of the compensated compactness principle

The convergence of the product of a solenoidal vector w{sub {epsilon}} and a gradient {nabla}u{sub {epsilon}} in L{sup 1}({Omega}) (where {Omega} is a region in R{sup d}) is investigated in the case when the factors converge weakly in the spaces L{sup {gamma}({Omega})}{sup d} and L{sup {alpha}({Omega})}{sup d}, respectively, with 1/{gamma}+1/{alpha}>1, which means that the main assumption of the classical div-curl lemma fails. Nevertheless, the same convergence (in the sense of distributions in {Omega}) as in the framework of the div-curl lemma, survives under certain additional assumptions. The new versions of the compensated compactness principle proved in the paper can be used in homogenization and in the theory of G-convergence of monotone operators with non-standard coercivity and growth properties, for instance, some degenerate operators. Bibliography: 20 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Criteria for compactness in L{sup p}-spaces, p {>=} 0

The paper puts forward new compactness criteria for spaces of summable and measurable functions on a metric space with measure satisfying the doubling condition. These criteria are formulated in terms of either local smoothness inequalities or maximal operators that measure local smoothness. Bibliography: 28 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Ergodic decomposition for measures quasi-invariant under a Borel action of an inductively compact group

The aim of this paper is to prove ergodic decomposition theorems for probability measures which are quasi-invariant under Borel actions of inductively compact groups as well as for σ-finite invariant measures. For infinite measures the ergodic decomposition is not unique, but the measure class of the decomposing measure on the space of projective measures is uniquely defined by the initial invariant measure. Bibliography: 21 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Extension of transformation groups of compact solvmanifolds

We indicate a way to extend connected simply connected soluble Lie groups acting transitively and locally effectively on a given compact solvmanifold. In 1973, Auslander posed the problem of describing all groups of this kind. The results obtained here lead to the conclusion that it is unlikely that this problem has an exhaustive solution. Bibliography: 10 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Compact noncontraction semigroups of affine operators

We analyze compact multiplicative semigroups of affine operators acting in a finite-dimensional space. The main result states that every such semigroup is either contracting, that is, contains elements of arbitrarily small operator norm, or all its operators share a common invariant affine subspace on which this semigroup is contracting. The proof uses functional difference equations with contraction of the argument. We look at applications to self-affine partitions of convex sets, the investigation of finite affine semigroups and the proof of a criterion of primitivity for nonnegative matrix families. Bibliography: 32 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

A novel compact end-loaded piston cylinder cell for high pressure neutron scattering up to 5 GPa

Here, a miniature sized end-loaded piston cylinder cell with radial side windows for neutron scattering experiments is described. The principle of the bicone-shaped cylinders used was first presented by McWhan in 1974. The present cell is of compact portable design yet significantly enlarges the scattering angles. Its small size allows neutron scattering experiments at low temperatures. The bicone-shaped cylinders are made from various ceramics or a highly neutron-transmissive Ni-free Cr–Mo–V steel. Successful neutron scattering experiments up to 5 GPa have been demonstrated on the CORELLI single-crystal diffractometer and the VISION vibrational spectrometer of the Spallation Neutron Source at the Oak Ridge National Laboratory.

Neutrons↗
DOE OSTI2011

VII Zw 403: H I STRUCTURE IN A BLUE COMPACT DWARF GALAXY

We present optical (UBVJ), ultraviolet (FUV, NUV), and high-resolution atomic hydrogen (H I) observations of the nearby blue compact dwarf (BCD), VII Zw 403. We find that VII Zw 403 has a relatively high H I mass-to-light ratio for a BCD. The rotation velocity is nominally 10-15 km s{sup -1}, but rises to {approx}20 km s{sup -1} after correction for the {approx}8-10 km s{sup -1} random motions present in the gas. The velocity field is complex, including a variation in the position angle of the major axis going from the northeast to the southwest parts of the galaxy. Our high-resolution H I maps reveal structure in the central gas, including a large, low-density H I depression or hole between the southern and northern halves of the galaxy, coincident with an unresolved X-ray source. Although interactions have been proposed as the triggering mechanism for the vigorous star formation occurring in BCDs, VII Zw 403 does not seem to have been tidally triggered by an external interaction, as we have found no nearby possible perturbers. It also does not appear to fall in the set of galaxies that exhibit a strong central mass density concentration, as its optical scale length is large in comparison to similar systems. However, there are some features that are compatible with an accretion event: optical/H I axis misalignment, a change in position angle of the kinematic axis, and a complex velocity field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE RELATIONSHIPS AMONG COMPACT STELLAR SYSTEMS: A FRESH VIEW OF ULTRACOMPACT DWARFS

We use a combined imaging and spectroscopic survey of the nearby central cluster galaxy, M87, to assemble a sample of 34 confirmed ultracompact dwarfs (UCDs) with half-light radii of {approx}>10 pc measured from Hubble Space Telescope images. This doubles the existing sample in M87, making it the largest such sample for any galaxy, while extending the detection of UCDs to unprecedentedly low luminosities (M{sub V} = -9). With this expanded sample, we find no correlation between size and luminosity, in contrast to previous suggestions, and no general correlation between size and galactocentric distance. We explore the relationships between UCDs, less luminous extended clusters (including faint fuzzies), globular clusters (GCs), as well as early-type galaxies and their nuclei, assembling an extensive new catalog of sizes and luminosities for stellar systems. Most of the M87 UCDs follow a tight color-magnitude relation, offset from the metal-poor GCs. This, along with kinematical differences, demonstrates that most UCDs are a distinct population from normal GCs, and not simply a continuation to larger sizes and higher luminosities. The UCD color-magnitude trend couples closely with that for Virgo dwarf elliptical nuclei. We conclude that the M87 UCDs are predominantly stripped nuclei. The brightest and reddest UCDs may be the remnant nuclei of more massive galaxies while a subset of the faintest UCDs may be tidally limited and related to more compact star clusters. In the broader context of galaxy assembly, blue UCDs may trace halo build-up by accretion of low-mass satellites, while red UCDs may be markers of metal-rich bulge formation in larger galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗