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At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

A Photometric Technique for Determining Fluid Concentration using Consumer-Grade Hardware

In support of a separate study to produce an exponential concentration gradient in a magnetic fluid, a noninvasive technique for determining, species concentration from off-the-shelf hardware has been developed. The approach uses a backlighted fluid test cell photographed with a commercial digital camcorder. Because the light extinction coefficient is wavelength dependent, tests were conducted to determine the best filter color to use, although some guidance was also provided using an absorption spectrophotometer. With the appropriate filter in place, the provide attenuation of the light passing, through the test cell was captured by the camcorder. The digital image was analyzed for intensity using, software from Scion Image Corp. downloaded from the Internet. The analysis provides a two-dimensional array of concentration with an average error of 0.0095 ml/ml. This technique is superior to invasive techniques, which require extraction of a sample that disturbs the concentration distribution in the test cell. Refinements of this technique using a true monochromatic laser light Source are also discussed.

Leslie, F.↗
NASA NTRS2004

Vertical Profiles of Aerosol Volume from High Spectral Resolution Infrared Transmission Measurements: Results

The high-resolution infrared absorption spectra of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment are utilized to derive vertical profiles of sulfate aerosol volume density and extinction coefficient. Following the eruption of Mt. Pinatubo in June 1991, the ATMOS spectra obtained on three Space Shuttle missions (1992, 1993, and 1994) provide a unique opportunity to study the global stratospheric sulfate aerosol layer shortly after a major volcanic eruption and periodically during the decay phase. Synthetic sulfate aerosol spectra are fit to the observed spectra, and a global fitting inversion routine is used to derive vertical profiles of sulfate aerosol volume density. Vertical profiles of sulfate aerosol volume density for the three missions over portions of the globe are presented, with the peak in aerosol volume density occurring from as low as 10 km (polar latitudes) to as high as 20 km (subtropical latitudes). Derived aerosol volume density is as high as 2-3.5 (mu)m(exp 3) per cubic centimeter +/-10% in 1992, decreasing to 0.2-0.5 (mu)m(exp 3) per cubic centimeter +/-20% in 1994, in agreement with other experiments. Vertical extinction profiles derived from ATMOS are compared with profiles from Improved Stratospheric And Mesospheric Sounder (ISAMS) and Cryogenic Limb Array Etalon Spectrometer (CLAES) that coincide in space and time and show good general agreement. The uncertainty of the ATMOS vertical profiles is similar to CLAES and consistently smaller than ISAMS at similar altitudes.

stratospheric aerosol↗
NASA NTRS1991

The fundamental quadrupole band of (N-14)2 - Line positions from high-resolution stratospheric solar absorption spectra

Accurate measurements of the positions of O- and S-branch lines of the (1-0) vibration-rotation quadrupole band of molecular nitrogen (N-14)2 are reported. Improved Dunham coefficients were derived from a simultaneous least squares analysis of these measurements and selected infrared and far infrared data. The new measurements were performed using stratospheric solar occultation spectra recorded with Fourier transform spectrometer instruments, operated at unapodized spectral resolutions of 0.002 and 0.01/cm.

Rinsland, C. P.↗
DOE OSTI2017

Two-photon-absorption line strengths for nitric oxide: Comparison of theory and sub-Doppler, laser-induced fluorescence measurements

In this paper, we discuss the results of high-resolution, sub-Doppler two-photon-absorption laser-induced fluorescence (TPALIF) spectroscopy of nitric oxide at low pressure and room temperature. The measurements were performed using the single-longitudinal mode output of a diode-laser-seeded optical parametric generator (OPG) system with a measured frequency bandwidth of 220 MHz. The measurements were performed using a counter-propagating pump beam geometry, resulting in sub-Doppler TPALIF spectra of NO for various rotational transitions in the (0,0) vibrational band of the A 2 Σ + - X 2 Π electronic transition. The experimental results are compared with the results of a perturbative treatment of the rotational line strengths for the 20 different rotational branches of the X 2 Π(v" = 0) → A 2 Σ + (v' = 0) two-photon absorption band. In the derivation of the expressions for the two-photon transition absorption strength, the closure relation is used for rotational states in the intermediate levels of the two-photon transition in analogy with the Placzek treatment of Raman transitions. The theoretical treatment of the effect of angular momentum coupling on the two-photon rotational line strengths features the use of irreducible spherical tensors and 3j symbols. The final results are expressed in terms of the Hund’s case (a) coupling coefficients aJ and bJ for the X 2 Π(v" = 0) rotational level wavefunctions, which are intermediate between Hund’s case (a) and case (b). Considerable physical insight is provided by this final form of the equations for the rotational line strengths. Corrections to the two-photon absorption rotational line strength for higher order effects such as centrifugal stretching can be included in a straightforward fashion in the analysis by incorporating higher order terms in these coupling coefficients a J and b J , although these corrections are essentially negligible for J < 50. The theoretical calculations of relative line intensities are in good agreement both with our experiment and with published experimental results. Furthermore, the calculated line shapes and relative intensities for closely spaced main branch and satellite transitions are in excellent agreement with our experimental measurements

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

Compositional dependence of optical band gap and refractive index in lead and bismuth borate glasses

Highlights: • Refractive indices increase with increasing PbO/Bi{sub 2}O{sub 3} content. • Optical band gap arises due to direct forbidden transition. • Optical band gaps decrease with increasing PbO/Bi{sub 2}O{sub 3} content. • New empirical relation between the optical band gap and the refractive index. - Abstract: We prepared a series of lead and bismuth borate glasses by varying PbO/Bi{sub 2}O{sub 3} content and studied refractive index and optical band gap as a function of glass composition. Refractive indices were measured very accurately using a Brewster’s angle set up while the optical band gaps were determined by analyzing the optical absorption edge using the Mott–Davis model. Using the Lorentz–Lorentz method and the effective medium theory, we calculated the refractive indices and then compared them with the measured values. Bismuth borate glasses show better agreement between the calculated values of the refractive index and experimental values. We used a differential method based on Mott–Davis model to obtain the type of transition and optical band gap (E{sub opt}) which in turn was compared with the value of E{sub opt} obtained using the extinction coefficient. Our analysis shows that in both lead and bismuth borate glasses, the optical band gap arises due to direct forbidden transition. With increasing PbO/Bi{sub 2}O{sub 3} content, the absorption edge shifts toward longer wavelengths and the optical band gap decreases. This behavior can be explained in terms of changes to the Pb−O/Bi−O chemical bonds with glass composition. We obtained a new empirical relation between the optical band gap and the refractive index which can be used to accurately determine the electronic oxide polarizability in lead and bismuth oxide glasses.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Residual stress induced crystalline to amorphous phase transformation in Nb{sub 2}O{sub 5} quantum dots

Nb{sub 2}O{sub 5} quantum dots (QDs) were grown using a simple technique of vacuum thermal evaporation. QDs were found to be crystalline in nature by selected area electron diffraction (SAED) in TEM. Samples with thickness up to 20 nm did not show any significant residual strain. Residual stress effect on band gap of crystalline Nb{sub 2}O{sub 5} was studied for films thicker than 20 nm. Residual strain was determined using SAED of the films with reference to powder X-ray diffraction (XRD). Films thicker than 45 nm become amorphous as analyzed by both SAED and XRD. The optical absorption of films in the range 25–60 nm indicates significantly varying optical band gap of films. The varying band gap with film thickness scales linearly very well with the variation of residual stress with film thickness. The residual stress dependence of band gap of crystalline films yields stress free band gap as 3.37 eV with pressure coefficient of band gap (∂E{sub g}/∂P){sub T} = −29.3 meV/GPa. From this study, the crystalline to amorphous transformation in tetragonal form of M-Nb{sub 2}O{sub 5} has been determined to be at about 14 GPa. Both pressure coefficient of band gap and crystalline to amorphous transition for tetragonal M-Nb{sub 2}O{sub 5} have been determined for the first time in the literature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2002

Investigation of N2O Production from 266 and 532 nm Laser Flash Photolysis of O3/N2/O2 Mixtures

Tunable diode laser absorption spectroscopy has been employed to measure the amount of N2O produced from laser flash photolysis of O3/N2/O2 mixtures at 266 and 532 nm. In the 532 nm photolysis experiments very little N2O is observed, thus allowing an upper limit yield of 7 x 10(exp -8) to be established for the process O3 + N2 yield N2O + O2, where O3 is nascent O3 that is newly formed via O(3P(sub J)) + O2 recombination (with vibrational excitation near the dissociation energy of O3). The measured upper limit yield is a factor of approx. 600 smaller than a previous literature value and is approximately a factor of 10 below the threshold for atmospheric importance. In the 266 nm photolysis experiments, significant N2O production is observed and the N2O quantum yield is found to increase linearly with pressure over the range 100 - 900 Torr in air bath gas. The source of N2O in the 266 nm photolysis experiments is believed to be the addition reaction O(1D(sub 2)) + N2 + M yields (k(sub sigma)) N2O + M, although reaction of (very short-lived) electronically excited O3 with N2 cannot be ruled out by the available data. Assuming that all observed N2O comes from the O(1D(sub 2)) + N2 + M reaction, the following expression describes the temperature dependence of k(sub sigma) (in its third-order low-pressure limit) that is consistent with the N2O yield data: k(sub sigma) = (2.8 +/- 0.1) x 10(exp -36)(T/300)(sup -(0-88+0.36)) cm(sup 6) molecule(sup -2)/s, where the uncertainties are 2(sigma) and represent precision only. The accuracy of the reported rate coefficients at the 95% confidence level is estimated to be 30 - 40% depending on the temperature. Model calculations suggest that gas phase processes initiated by ozone absorption of a UV photon represent about 1.4% of the currently estimated global source strength of atmospheric N2O. However, these processes could account for a significant fraction of the oxygen mass-independent enrichment observed in atmospheric N2O, and they appear to be the first suggested photochemical mechanism that is capable of explaining the altitude dependence of the observed mass -independent isotopic signature.

Estupinan, E. G.↗
DOE OSTI2018

Numerical Solution of the Inverse Scattering Problem for the Acoustic Equation in an Absorptive Layered Medium

We consider a nonlinear ordinary differential equation associated with a number of inverse scattering problems in acoustic and seismic sounding in which acoustic impedance and an impedance-dependent unknown damping coefficient are the unknown function. We prove that the Cauchy problem is uniquely solvable when the derivative is treated as a generalized function. It is established that the inverse scattering problem in a layered dissipative medium simultaneously determines the acoustic impedance and the damping coefficient. A regularized numerical algorithm is proposed and numerical results are reported.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Investigation of free charge carrier dynamics in single-crystalline CVD diamond by two-photon absorption

By using the methods of transient gratings (TGs) and induced absorption, we have studied the kinetics of plasma of free charge carriers (FCCs) created by the action of a picosecond laser pulse in two high-purity diamond single crystals synthesised from the gas phase. The gratings with different spatial periods have been excited at the wavelengths of 266 or 213 nm (above and below the fundamental absorption edge in diamond) and probed with continuous-wave radiation in the visible region. At the moderate FCC concentrations (∼7 × 10{sup 17} cm{sup -3}), the coefficient of ambipolar diffusion and the carrier recombination time of two crystals are 20.3 and 18.9 cm{sup 2} s{sup -1} and 30 and 190 ns, respectively. The increase in the carrier concentration up to 5 × 10{sup 19} cm{sup -3} reduces the TG lifetime. We have determined the conditions under which the relaxation of the grating of carriers leads to the formation of a thermal grating, with the amplitude sufficient for its experimental observation. (interaction of laser radiation with matter. laser plasma)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Optical characterization of nanostructured Ge{sub 1 − x}Sn{sub x}Se{sub 2.5} (x = 0, 0.3, 0.5) films

The paper reports the optical properties of thin films of nanostructured Ge{sub 1 − x}Sn{sub x}Se{sub 2.5} (x = 0, 0.3, 0.5) glassy alloys. The glassy alloys of Ge{sub 1 − x}Sn{sub x}Se{sub 2.5} (x = 0, 0.3, 0.5) were prepared using melt quenching method. Thin films of nanostructured Ge{sub 1 − x}Sn{sub x}Se{sub 2.5} (x = 0, 0.3, 0.5) glassy alloys were prepared using physical vapor deposition method. The films were characterized using XRD, EDX and TEM, which confirmed the amorphous nature, composition and formation of nanorods in the samples. Absorption and transmission spectra of thin films were recorded in the spectral range 400–2500 nm to obtain energy band gap, refractive index, extinction coefficient, dielectric constant etc. Results show that refractive index increases while band gap decreases on increase of Sn content in the Ge–Se system. This is due to the increase in density of defect states within band gap. The values of Urbach energy support the obtained results.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Potential transfer of neurotoxic amino acid β-N-methylamino-alanine (BMAA) from mother to infant during breast-feeding: Predictions from human cell lines

β-N-methylamino-alanine (BMAA) is a non-protein amino acid produced by cyanobacteria, diatoms and dinoflagellates. BMAA has potential to biomagnify in a terrestrial food chain, and to bioaccumulate in fish and shellfish. We have reported that administration of [{sup 14}C]L-BMAA to lactating mice and rats results in a mother to off-spring transfer via the milk. A preferential enantiomer-specific uptake of [{sup 14}C]L-BMAA has also been demonstrated in differentiated murine mammary epithelium HC11 cells. These findings, together with neurotoxic effects of BMAA demonstrated both in vitro and in vivo, highlight the need to determine whether such transfer could also occur in humans. Here, we used four cell lines of human origin to examine and compare the transport of the two BMAA enantiomers in vitro. The uptake patterns of [{sup 14}C]L- and [{sup 14}C]D-BMAA in the human mammary MCF7 cell line were in agreement with the results in murine HC11 cells, suggesting a potential secretion of BMAA into human breast milk. The permeability coefficients for both [{sup 14}C]L- and [{sup 14}C]D-BMAA over monolayers of human intestinal Caco2 cells supported an efficient absorption from the human intestine. As a final step, transport experiments confirmed that [{sup 14}C]L-and [{sup 14}C]D-BMAA can be taken up by human SHSY5Y neuroblastoma cells and even more efficiently by human U343 glioblastoma cells. In competition experiments with various amino acids, the ASCT2 specific inhibitor benzylserine was the most effective inhibitor of [{sup 14}C]L-BMAA uptake tested here. Altogether, our results suggest that BMAA can be transferred from an exposed mother, via the milk, to the brain of the nursed infant. - Highlights: • Transport of BMAA in human intestinal, mammary and CNS cell lines was examined. • The transport of L-BMAA over intestinal cell monolayers was unidirectional. • Enantiomer-selective uptake of L-BMAA in breast, neuron and glia cells was evident. • Competition experiments indicate that L-BMAA uptake involved several transporters. • A potential for mother to infant transfer of BMAA is proposed.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Alternative material study for heat assisted magnetic recording transducer application

In heat assisted magnetic recording (HAMR), optical near field transducer (NFT) is a key component. Au is currently used as NFT material because of its strong surface plasmon effect. Due to the soft property of Au material, reliability of Au NFT becomes a key issue for realizing HAMR production. In this paper, the possibility of alternative materials, including transition metal nitrides (TMNs) and transparent conducting oxides (TCOs) to replace Au is studied. The results show that all of the listed TMN and TCO materials can meet the mechanical requirements at room temperature in terms of hardness and thermal expansion. An optical model, which includes optical waveguide, NFT and FePt media, is used to simulate NFT performances. The results indicate that the resonant wavelengths for NFT with TCO materials are longer than 1500 nm, which is not suitable for HAMR application. TMN materials are suitable for NFT application at wavelength band of around 800 nm. But the NFT efficiency is very low. ZrN is the best material among TMN materials and the efficiency of ZrN NFT is only 13% of the Au NFT's efficiency. Reducing refractive index (n) and increasing extinction coefficient (k) will both lead to efficiency increase. Increasing k contributes more in the efficiency increase, while reducing n has a relatively low NFT absorption. For materials with the same figure of merit, the NFT with larger k material has higher efficiency. Doping materials to increase the material conduction electron density and growing film with larger size grain may be the way to increase k and reduce n.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Silicon nanoparticles as contrast agents in the methods of optical biomedical diagnostics

The efficiency of light scattering by nanoparticles formed using the method of picosecond laser ablation of silicon in water and by nanoparticles of mechanically grinded mesoporous silicon is compared. The ensembles of particles of both types possess the scattering coefficients sufficient to use them as contrast agents in optical coherence tomography (OCT), particularly in the range of wavelengths 700 – 1000 nm, where the absorption of both silicon and most biological and mimicking tissues is small. According to the Mie theory the main contribution to the scattering in this case is made by the particles having a relatively large size (150 – 300 nm). In the experiments on visualising the agar phantom surface by means of OCT, the contrast of the medium boundary, provided by nanoparticles amounted to 14 dB and 30 dB for the ablated particles and the porous silicon powder, respectively. The numerical simulation of OCT images of skin in the presence of nanoparticles, confirmed the efficiency of using them as a contrast agent. (nanoparticles)

62 RADIOLOGY AND NUCLEAR MEDICINE↗
NASA NTRS1979

Reciprocity principle in duct acoustics

Various reciprocity relations in duct acoustics have been derived on the basis of the spatial reciprocity principle implied in Green's functions for linear waves. The derivation includes the reciprocity relations between mode conversion coefficients for reflection and transmission in nonuniform ducts, and the relation between the radiation of a mode from an arbitrarily terminated duct and the absorption of an externally incident plane wave by the duct. Such relations are well defined as long as the systems remain linear, regardless of acoustic properties of duct nonuniformities which cause the mode conversions.

Cho, Y. C.↗
NASA NTRS1980

The physics of heterodyne detection in the far-infrared: Transition from electric-field to photon-absorption detection in a simple system

The history of heterodyne detection is reviewed from the radiowave to the optical regions of the electromagnetic spectrum with emphasion the submillimeter/far infrared. The transition from electric field to photon absorption detection in a simple system is investigated. The response of an isolated two level detector to a coherent source of incident radiation is calculated for both heterodyne and video detection. When the processes of photon absorption and photon emission cannot be distinguished, the relative detected power at double- and sum-frequencies is found to be multiplied by a coefficient, which is less than or equal to unity, and which depends on the incident photon energy and on the effective temperature of the system.

Teich, M. C.↗
NASA NTRS1979

Reciprocity principle in duct acoustics

Various reciprocity relations in duct acoustics have been derived on the basis of the spatial reciprocity principle implied in Green's functions for linear waves. The derivation includes the reciprocity relations between mode conversion coefficients for reflection and transmission in nonuniform ducts, and the relation between the radiation of a mode from an arbitrarily terminated duct and the absorption of an externally incident plane wave by the duct. Such relations are well defined as long as the systems remain linear, regardless of acoustic properties of duct nonuniformities which cause the mode conversions.

Cho, Y.-C.↗
NASA NTRS1997

Kinetics of the Reactions of F((sup 2)P) and Cl((sup 2)P) with HNO3

The kinetics of the reactions of HNO3 with fluorine (k(sub 1)) and Chlorine (k(sub 2)) atoms have been studied by using a time-resolved long-path laser absorption technique to monitor the appearance of product NO3 radicals following 351-nm pulsed laser photolysis of X2/HNO3/He mixtures (X = F,Cl). Absolute rate coefficients for the F((sup 2)P) + HNO reaction have been determined over the temperature range 260-373 K. Between 260 and 320 K, the data are adequately represented by the Arrhenius expression k(sub 1)(T) = (6.0 +/- 2.6) x 10(exp -12) exp[(40 +/- 120)/T]cu cm/(molecule.s). Between 335 and 373 K, the rate coefficient is found to be (2.0 +/- 0.3) x 10(exp -11)cu cm/(molecule.s) independent of temperature. The observed temperature dependence suggests that reaction proceeds via competing direct abstraction and complex pathways. No NO3 production was observed in the experiments with X equals Cl, thus establishing that k(sub 2)(298 K) is less than 2 x 10(exp -16) cu cm/(molecule.s). The Cl((sup 2)P) + HNO reaction was also investigated by using a pulsed laser photolysis-resonance fluorescence technique to monitor the decay of Cl((sup 2)P). Upper limit values for k(sub 2) obtained from these experiments, in units of 10(exp -16)cu cm/(molecule.s), are 13 at 298 K and 10 at 400 K.

Wine, P. H.↗
NASA NTRS2012

Characterizing the Vertical Profile of Aerosol Particle Extinction and Linear Depolarization over Southeast Asia and the Maritime Continent: The 2007-2009 View from CALIOP

Vertical profiles of 0.532 μm aerosol particle extinction coefficient and linear volume depolarization ratio are described for Southeast Asia and the Maritime Continent. Quality-screened and cloud-cleared Version 3.01 Level 2 NASA Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) 5-km Aerosol Profile datasets are analyzed from 2007 to 2009. Numerical simulations from the U.S. Naval Aerosol Analysis and Predictive System (NAAPS), featuring two-dimensional variational assimilation of NASA Moderate Resolution Imaging Spectroradiometer and Multi-angle Imaging Spectro- Radiometer quality-assured datasets, combined with regional ground-based lidar measurements, are considered for assessing CALIOP retrieval performance, identifying bias, and evaluating regional representativeness. CALIOP retrievals of aerosol particle extinction coefficient and aerosol optical depth (AOD) are high over land and low over open waters relative to NAAPS (0.412/0.312 over land for all data points inclusive, 0.310/0.235 when the per bin average is used and each is treated as single data points; 0.102/0.151 and 0.086/0.124, respectively, over ocean). Regional means, however, are very similar (0.180/0.193 for all data points and 0.155/0.159 when averaged per normalized bin), as the two factors offset one another. The land/ocean offset is investigated, and discrepancies attributed to interpretation of particle composition and a-priori assignment of the extinction-to-backscatter ratio ("lidar ratio") necessary for retrieving the extinction coefficient from CALIOP signals. Over land, NAAPS indicates more dust present than CALIOP algorithms are identifying, indicating a likely assignment of a higher lidar ratio representative of more absorptive particles. NAAPS resolvesmore smoke overwater than identified with CALIOP, indicating likely usage of a lidar ratio characteristic of less absorptive particles to be applied that biases low AOD there. Over open waters except within the Bay of Bengal, aerosol particle scattering is largely capped below 1.5 km MSL, though ground-based lidar measurements at Singapore differ slightly from this finding. Significant aerosol particle presence over land is similarly capped near 3.0 km MSL over most regions. Particle presence at low levels regionally, except over India, is dominated by relatively non-depolarizing particles. Industrial haze, sea salt droplets and fresh smoke are thus most likely present.

linear volume depolarization ratio↗