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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Experimental study of neutron-rich nuclei near the N = 82 closed shell using the {sub 40}{sup 96}Zr+{sub 50}{sup 124}Sn reaction with GASP and PRISMA-CLARA arrays

In this contribution an experimental study of the deep-inelastic reaction {sub 40}{sup 96}Zr+{sub 50}{sup 124}Sn at 530 MeV, using the GASP and PRISMA-CLARA arrays, is presented. The experiments populate a wealth of projectile-like and target-like binary fragments, in a large neutron-rich region around N ≥ 50 and Z ≈ 40. Preliminary results on the study of the yrast and near-yrast states for {sup 95}Nb will be shown, along with a comparison of the experimental yields obtained in the experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Experimental and theoretical identification of a high-pressure polymorph of Ga{sub 2}S{sub 3} with α-Bi{sub 2}Te{sub 3}-type structure

Since the discovery of α-phase Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3}, and Bi{sub 2}Se{sub 3} as 3D topological insulators, many experimental and theoretical studies of A{sub 2}B{sub 3}-type chalcogenides have been performed to search for new materials with interesting elastic and electric properties at ambient and extreme conditions. In this study, high-pressure properties of Ga{sub 2}S{sub 3} have been characterized by in situ synchrotron X-ray diffraction (XRD), X-ray absorption near edge structure measurements, and Density-functional theory (DFT) calculations. At ∼16.0 GPa, a phase transition of α′-Ga{sub 2}S{sub 3} (Cc and Z = 4) is observed experimentally to a new polymorph, which is indentified to be the tetradymite-type or α-Bi{sub 2}Te{sub 3}-type crystal structure (R3{sup ¯}m and Z = 3) by laser-annealing XRD experiments and DFT calculations. The isothermal pressure-volume relationship of Ga{sub 2}S{sub 3} is well described by the second-order Birch-Murnaghan equation of state with K{sub 0} = 59(2) GPa and K{sub 0}{sup ′} = 4 (fixed) for the α′-Ga{sub 2}S{sub 3}, and K{sub 0} = 91(3) GPa, and K{sub 0}{sup ′} = 4 (fixed) for the tetradymite-type phase. In addition, band gap of α′-Ga{sub 2}S{sub 3} decreases on compression and the tetradymite-type Ga{sub 2}S{sub 3} exhibits metallization based on DFT calculations. The pressure-induced phase transition accompanying by changes of elastic and electrical properties may give some implications to other chalcogenides under high pressure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Experimental verification of a bridge-shaped, nonlinear vibration energy harvester

This paper reports a comprehensive modeling and experimental characterization of a bridge shaped nonlinear energy harvester. A doubly clamped beam at large deflection requires stretching strain in addition to the bending strain to be geometrically compatible, which stiffens the beam as the beam deflects and transforms the dynamics to a nonlinear regime. The Duffing mode non-linear resonance widens the frequency bandwidth significantly at higher frequencies than the linear resonant frequency. The modeling includes a nonlinear measure of strain coupled with piezoelectric constitutive equations which end up in nonlinear coupling terms in the equations of motion. The main result supports that the power generation is bounded by the mechanical damping for both linear and nonlinear harvesters. Modeling also shows the power generation is over a wider bandwidth in the nonlinear case. A prototype is manufactured and tested to measure the power generation at different load resistances and acceleration amplitudes. The prototype shows a nonlinear behavior with well-matched experimental data to the modeling.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Experimental characterization of edge force on the Crookes radiometer

The contribution of edge force on the Crookes radiometer is experimentally investigated with three vane geometries. This work examines increasing the force per unit weight of a radiometer vane for applications such as near-space propulsion by increasing the vane’s perimeter while decreasing the total surface area of the vane by means of machined holes in the vanes. Experimental results are given for three vane geometries. These results indicate that although force to vane weight ratios can be improved, the maximum force is achieved by a vane geometry that contains no hole features.

42 ENGINEERING↗
DOE OSTI2014

Experimental measurements and modeling of convective heat transfer in the transitional rarefied regime

We present experimental measurements and numerical simulations of convective heat transfer performance in the transitional rarefied regime for an isolated rectangular beam geometry. Experiments were performed using single crystalline silicon beam elements having width-to-thickness aspect ratios of 8.5 and 17.4. Devices were enclosed in a vacuum chamber and heated resistively using a DC power supply. A range of pressures corresponding to Knudsen numbers between 0.096 and 43.2 in terms of device thickness were swept, adjusting applied power to maintain a constant temperature of 50 K above the ambient temperature. Both parasitic electrical resistance associated with the hardware and radiative exchange with the environment were removed from measured data, allowing purely convective heat flux to be extracted. Numerical simulations were carried out deterministically through solution of the Ellipsoidal Statistical Bhatnagar-Gross-Krook collision model of the Boltzmann equation. Results agree with experimental data, revealing a strong coupling between dissipated heat flux and thermal stresses within the flowfield as well as a nonlinear transition between the free-molecule and continuum regimes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Experimental and numerical study of gas dynamic window for electron beam transport into the space with increased pressure

The paper is devoted to experimental and numerical study of the gas jet technical device for obtaining axisymmetric flow with low pressure in its near axis region. The studied geometry of the device is typical of that used in the plasma generator consisting of an electron gun with a hollow (plasma) cathode and a double supersonic ring nozzle. The geometry of the nozzles as well as the relation between the gas flow rates through the nozzles providing the electron beam extraction into the region with increased pressure are tested both experimentally and numerically. The maximum external pressure of about 0.25 bar that does not disturb the electron beam is achieved.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Experimental evidence of high-frequency complete elastic bandgap in pillar-based phononic slabs

We present strong experimental evidence for the existence of a complete phononic bandgap, for Lamb waves, in the high frequency regime (i.e., 800 MHz) for a pillar-based phononic crystal (PnC) membrane with a triangular lattice of gold pillars on top. The membrane is composed of an aluminum nitride film stacked on thin molybdenum and silicon layers. Experimental characterization shows a large attenuation of at least 20 dB in the three major crystallographic directions of the PnC lattice in the frequency range of 760 MHz–820 MHz, which is in agreement with our finite element simulations of the PnC bandgap. The results of experiments are analyzed and the physics behind the attenuation in different spectral windows is explained methodically by assessing the type of Bloch modes and the in-plane symmetry of the displacement profile.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

An orbital angular momentum radio communication system optimized by intensity controlled masks effectively: Theoretical design and experimental verification

A system of generating and receiving orbital angular momentum (OAM) radio beams, which are collectively formed by two circular array antennas (CAAs) and effectively optimized by two intensity controlled masks, is proposed and experimentally investigated. The scheme is effective in blocking of the unwanted OAM modes and enhancing the power of received radio signals, which results in the capacity gain of system and extended transmission distance of the OAM radio beams. The operation principle of the intensity controlled masks, which can be regarded as both collimator and filter, is feasible and simple to realize. Numerical simulations of intensity and phase distributions at each key cross-sectional plane of the radio beams demonstrate the collimated results. The experimental results match well with the theoretical analysis and the receive distance of the OAM radio beam at radio frequency (RF) 20 GHz is extended up to 200 times of the wavelength of the RF signals, the measured distance is 5 times of the original measured distance. The presented proof-of-concept experiment demonstrates the feasibility of the system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Single photon simultaneous K-shell ionization and K-shell excitation. I. Theoretical model applied to the interpretation of experimental results on H{sub 2}O

We present in detail a theoretical model that provides absolute cross sections for simultaneous core-ionization core-excitation (K{sup −2}V ) and compare its predictions with experimental results obtained on the water molecule after photoionization by synchrotron radiation. Two resonances of different symmetries are assigned in the main K{sup −2}V peak and comparable contributions from monopolar (direct shake-up) and dipolar (conjugate shake-up) core-valence excitations are identified. The main peak is observed with a much greater width than the total experimental resolution. This broadening is the signature of nuclear dynamics.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Experimental investigation of radiative thermal rectifier using vanadium dioxide

Vanadium dioxide (VO{sub 2}) exhibits a phase-change behavior from the insulating state to the metallic state around 340 K. By using this effect, we experimentally demonstrate a radiative thermal rectifier in the far-field regime with a thin film VO{sub 2} deposited on the silicon wafer. A rectification contrast ratio as large as two is accurately obtained by utilizing a one-dimensional steady-state heat flux measurement system. We develop a theoretical model of the thermal rectifier with optical responses of the materials retrieved from the measured mid-infrared reflection spectra, which is cross-checked with experimentally measured heat flux. Furthermore, we tune the operating temperatures by doping the VO{sub 2} film with tungsten (W). These results open up prospects in the fields of thermal management and thermal information processing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Experimental evidence of excited electron number density and temperature effects on electron-phonon coupling in gold films

The electronic transport properties of metals with weak electron-phonon coupling can be influenced by non-thermal electrons. Relaxation processes involving non-thermal electrons competing with the thermalized electron system have led to inconsistencies in the understanding of how electrons scatter and relax with the less energetic lattice. Recent theoretical and computational works have shown that the rate of energy relaxation with the metallic lattice will change depending on the thermalization state of the electrons. Even though 20 years of experimental works have focused on understanding and isolating these electronic relaxation mechanisms with short pulsed irradiation, discrepancies between these existing works have not clearly answered the fundamental question of the competing effects between non-thermal and thermal electrons losing energy to the lattice. In this work, we demonstrate the ability to measure the electron relaxation for varying degrees of both electron-electron and electron-phonon thermalization. This series of measurements of electronic relaxation over a predicted effective electron temperature range up to ∼3500 K and minimum lattice temperatures of 77 K validate recent computational and theoretical works that theorize how a nonequilibrium distribution of electrons transfers energy to the lattice. Utilizing this wide temperature range during pump-probe measurements of electron-phonon relaxation, we explain discrepancies in the past two decades of literature of electronic relaxation rates. We experimentally demonstrate that the electron-phonon coupling factor in gold increases with increasing lattice temperature and laser fluences. Specifically, we show that at low laser fluences corresponding to small electron perturbations, energy relaxation between electrons and phonons is mainly governed by non-thermal electrons, while at higher laser fluences, non-thermal electron scattering with the lattice is less influential on the energy relaxation mechanisms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A flexible experimental setup for femtosecond time-resolved broad-band ellipsometry and magneto-optics

A versatile experimental setup for femtosecond time-resolved ellipsometry and magneto-optical Kerr effect measurements in the visible light range is described. The apparatus is based on the pump-probe technique and combines a broad-band probing beam with an intense near-infrared pump. According to Fresnel scattering matrix formalism, the analysis of the reflected beam at different polarization states of the incident probe light allows one to determine the diagonal and the off-diagonal elements of the dielectric tensor in the investigated sample. Moreover, the pump-probe method permits to study the dynamics of the dielectric response after a short and intense optical excitation. The performance of the experimental apparatus is tested on CrO{sub 2} single crystals as a benchmark.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Experimental and theoretical investigation of the first-order hyperpolarizability of a class of triarylamine derivatives

This paper reports on the static and dynamic first-order hyperpolarizabilities of a class of push-pull octupolar triarylamine derivatives dissolved in toluene. We have combined hyper-Rayleigh scattering experiment and the coupled perturbed Hartree-Fock method implemented at the Density Functional Theory (DFT) level of theory to determine the static and dynamic (at 1064 nm) first-order hyperpolarizability (β{sub HRS}) of nine triarylamine derivatives with distinct electron-withdrawing groups. In four of these derivatives, an azoaromatic unit is inserted and a pronounceable increase of the first-order hyperpolarizability is reported. Based on the theoretical results, the dipolar/octupolar character of the derivatives is determined. By using a polarizable continuum model in combination with the DFT calculations, it was found that although solvated in an aprotic and low dielectric constant solvent, due to solvent-induced polarization and the frequency dispersion effect, the environment substantially affects the first-order hyperpolarizability of all derivatives investigated. This statement is supported due to the solvent effects to be essential for the better agreement between theoretical results and experimental data concerning the dynamic first-order hyperpolarizability of the derivatives. The first-order hyperpolarizability of the derivatives was also modeled using the two- and three-level models, where the relationship between static and dynamic first hyperpolarizabilities is given by a frequency dispersion model. Using this approach, it was verified that the dynamic first hyperpolarizability of the derivatives is satisfactorily reproduced by the two-level model and that, in the case of the derivatives with an azoaromatic unit, the use of a damped few-level model is essential for, considering also the molecular size of such derivatives, a good quantitative agreement between theoretical results and experimental data to be observed.

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

Experimental realization of extraordinary acoustic transmission using Helmholtz resonators

The phenomenon of extraordinary acoustic transmission through a solid barrier with an embedded Helmholtz resonator (HR) is demonstrated. The Helmholtz resonator consists of an embedded cavity and two necks that protrude, one on each side of the barrier. Extraordinary transmission occurs for a narrow spectral range encompassing the resonant frequency of the Helmholtz resonator. We show that an amplitude transmission of 97.5% is achieved through a resonator whose neck creates an open area of 6.25% of the total barrier area. In addition to the enhanced transmission, we show that there is a smooth, continuous phase transition in the transmitted sound as a function of frequency. The frequency dependent phase transition is used to experimentally realize slow wave propagation for a narrow-band Gaussian wave packet centered at the maximum transmission frequency. The use of parallel pairs of Helmholtz resonators tuned to different resonant frequencies is experimentally explored as a means of increasing the transmission bandwidth. These experiments show that because of the phase transition, there is always a frequency between the two Helmholtz resonant frequencies at which destructive interference occurs whether the resonances are close or far apart. Finally, we explain how the phase transition associated with Helmholtz-resonator-mediated extraordinary acoustic transmission can be exploited to produce diffractive acoustic components including sub-wavelength thickness acoustic lenses.

36 MATERIALS SCIENCE↗
DOE OSTI2015

β-delayed α decay of {sup 16}N and the {sup 12}C(α,γ){sup 16}O cross section at astrophysical energies: A new experimental approach

The {sup 12}C(α,γ){sup 16}O reaction at energies corresponding to the quiescent helium burning in massive stars is regarded as one of the most important processes in nuclear astrophysics. Although this process has being studied for over four decades, our knowledge of its cross section at the energies of interest for astrophysics is still widely unsatisfactory. Indeed, no experimental data are available around 300 keV and in the energy region of astrophysical interest extrapolations are performed using some theoretical approaches, usually R-matrix calculations. Consequently, the published astrophysical factors range from 1 to 288 keVb for S{sub E1}(300) and 7 to 120 keVb for S{sub E2}(300), especially because of the unknown contribution coming from subthreshold resonances. To improve the reliability of these extrapolations, data from complementary experiments, such as elastic and quasi- elastic α scattering on {sup 12}C, α-transfer reactions to {sup 16}O, and {sup 16}N decay are usually included in the analysis. Here the β-delayed α decay of {sup 16}N is used to infer information on the {sup 12}C(α,γ){sup 16}O reaction and a new experimental technique is suggested.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Experimental approaches for the development of gamma spectroscopy well logging system

This article discusses experimental approaches for the development of gamma spectroscopy well logging system. Considering the size of borehole sonde, we customize 2 x 2 inches inorganic scintillators and the system including high voltage, preamplifier, amplifier and multichannel analyzer (MCA). The calibration chart is made by test using standard radioactive sources so that the measured count rates are expressed by energy spectrum. Optimum high-voltage supplies and the measurement parameters of each detector are set up by experimental investigation. Also, the responses of scintillation detectors have been examined by analysis according to the distance between source and detector. Because gamma spectroscopy well logging needs broad spectrum, high sensitivity and resolution, the energy resolution and sensitivity as a function of gamma ray energy are investigated by analyzing the gamma ray activities of the radioactive sources.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

The shallow water equations as a hybrid flow model for the numerical and experimental analysis of hydro power stations

The numerical analysis of hydro power stations is an important method of the hydraulic design and is used for the development and optimisation of hydro power stations in addition to the experiments with the physical submodel of a full model in the hydraulic laboratory. For the numerical analysis, 2D and 3D models are appropriate and commonly used.The 2D models refer mainly to the shallow water equations (SWE), since for this flow model a large experience on a wide field of applications for the flow analysis of numerous problems in hydraulic engineering already exists. Often, the flow model is verified by in situ measurements. In order to consider 3D flow phenomena close to singularities like weirs, hydro power stations etc. the development of a hybrid fluid model is advantageous to improve the quality and significance of the global model. Here, an extended hybrid flow model based on the principle of the SWE is presented. The hybrid flow model directly links the numerical model with the experimental data, which may originate from physical full models, physical submodels and in-situ measurements. Hence a wide field of application of the hybrid model emerges including the improvement of numerical models and the strong coupling of numerical and experimental analysis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for liquid mixtures

Kirkwood-Buff or Fluctuation Solution Theory can be used to provide experimental pair fluctuations, and/or integrals over the pair distribution functions, from experimental thermodynamic data on liquid mixtures. Here, this type of approach is used to provide triplet and quadruplet fluctuations, and the corresponding integrals over the triplet and quadruplet distribution functions, in a purely thermodynamic manner that avoids the use of structure factors. The approach is then applied to binary mixtures of water + methanol and benzene + methanol over the full composition range under ambient conditions. The observed correlations between the different species vary significantly with composition. The magnitude of the fluctuations and integrals appears to increase as the number of the most polar molecule involved in the fluctuation or integral also increases. A simple physical picture of the fluctuations is provided to help rationalize some of these variations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗