Optical Absorbance Enhancement in PbS QD/Cinnamate Ligand Complexes.

PubMed

Kroupa, Daniel M; Vörös, Márton; Brawand, Nicholas P; Bronstein, Noah; McNichols, Brett W; Castaneda, Chloe V; Nozik, Arthur J; Sellinger, Alan; Galli, Giulia; Beard, Matthew C

2018-06-08

We studied the optical absorption enhancement in colloidal suspensions of PbS quantum dots (QD) upon ligand exchange from oleate to a series of cinnamate ligands. By combining experiments and ab initio simulations, we elucidate physical parameters that govern the optical absorption enhancement. We find that, within the cinnamate/PbS QD system, the optical absorption enhancement scales linearly with the electronic gap of the ligand, indicating that the ligand/QD coupling occurs equally efficient between the QD and ligand HOMO and their respective LUMO levels. Disruption of the conjugation that connects the aromatic ring and its substituents to the QD core causes a reduction of the electronic coupling. Our results further support the notion that the ligand/QD complex should be considered as a distinct chemical system with emergent behavior rather than a QD core with ligands whose sole purpose is to passivate surface dangling bonds and prevent agglomeration.

VARIATION IN THE PRE-TRANSIT BALMER LINE SIGNAL AROUND THE HOT JUPITER HD 189733B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cauley, P. Wilson; Redfield, Seth; Jensen, Adam G.

As followup to our recent detection of a pre-transit signal around HD 189733 b, we obtained full pre-transit phase coverage of a single planetary transit. The pre-transit signal is again detected in the Balmer lines but with variable strength and timing, suggesting that the bow shock geometry reported in our previous work does not describe the signal from the latest transit. We also demonstrate the use of the Ca ii H and K residual core flux as a proxy for the stellar activity level throughout the transit. A moderate trend is found between the pre-transit absorption signal in the 2013more » data and the Ca ii H flux. This suggests that some of the 2013 pre-transit hydrogen absorption can be attributed to varying stellar activity levels. A very weak correlation is found between the Ca ii H core flux and the Balmer line absorption in the 2015 transit, hinting at a smaller contribution from stellar activity compared to the 2013 transit. We simulate how varying stellar activity levels can produce changes in the Balmer line transmission spectra. These simulations show that the strength of the 2013 and 2015 pre-transit signals can be reproduced by stellar variability. If the pre-transit signature is attributed to circumplanetary material, its evolution in time can be described by accretion clumps spiraling toward the star, although this interpretation has serious limitations. Further high-cadence monitoring at H α is necessary to distinguish between true absorption by transiting material and short-term variations in the stellar activity level.« less

Impact of material absorption on supercontinuum generation in liquid core photonic crystal fiber

NASA Astrophysics Data System (ADS)

Nithyanandan, K.; Raja, Vasantha Jayakantha; Uthayakumar, T.; Porsezian, K.

2013-06-01

The impact of material absorption on supercontinuum generation (SCG) in liquid core photonic crystal fiber (LCPCF) is presented. While PCFs with cores made from different glasses are well studied in previous works with saturable nonlinear response (SNL), in this paper, it is planned to investigate the dynamics of nonlinear processes of supercontinuum generation in high-index fiber with material absorption to understand the physical phenomena of pulse propagation.

Evidence for Abnormal H α Variability During Near-transit Observations of HD 189733 b

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cauley, P. Wilson; Redfield, Seth; Jensen, Adam G., E-mail: pcauley@wesleyan.edu

2017-04-01

Changes in levels of stellar activity can mimic absorption signatures in transmission spectra from circumplanetary material. Thus, it is critical to understand the frequency and magnitude of these changes in order to attribute any particular signal to the circumplanetary environment. We present short-cadence, high-resolution out-of-transit H α spectra for the hot Jupiter host HD 189733 in order to establish the frequency and magnitude of intrinsic stellar variations in the H α line core. We find that changes in the line core strength similar to those observed immediately pre- and post-transit in two independent data sets are uncommon. This suggests thatmore » the observed near-transit signatures are either due to absorption of circumplanetary material or they occur preferentially in time, very near planetary transits. In either case, the evidence for abnormal H α variability is strengthened, though the short-cadence out-of-transit data do not argue for circumplanetary absorption versus stellar activity caused by a star–planet interaction. Further out-of-transit monitoring at higher signal-to-noise would be useful to more strictly constrain the frequency of the near-transit changes in the H α line core.« less

Polypyrrole coated phase-change contrast agents for sono-photoacoustic imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Li, David S.; Yoon, Soon Joon; Matula, Thomas J.; O'Donnell, Matthew; Pozzo, Lilo D.

2017-03-01

A new light and sound sensitive nanoemulsion contrast agent is presented. The agents feature a low boiling point liquid perfluorocarbon core and a broad light spectrum absorbing polypyrrole (PPy) polymer shell. The PPy coated nanoemulsions can reversibly convert from liquid to gas phase upon cavitation of the liquid perfluorocarbon core. Cavitation can be initiated using a sufficiently high intensity acoustic pulse or from heat generation due to light absorption from a laser pulse. The emulsions can be made between 150 and 350 nm in diameter and PPy has a broad optical absorption covering both the visible spectrum and extending into the near-infrared spectrum (peak absorption 1053 nm). The size, structure, and optical absorption properties of the PPy coated nanoemulsions were characterized and compared to PPy nanoparticles (no liquid core) using dynamic light scattering, ultraviolet-visible spectrophotometry, transmission electron microscopy, and small angle X-ray scattering. The cavitation threshold and signal intensity were measured as a function of both acoustic pressure and laser fluence. Overlapping simultaneous transmission of an acoustic and laser pulse can significantly reduce the activation energy of the contrast agents to levels lower than optical or acoustic activation alone. We also demonstrate that simultaneous light and sound cavitation of the agents can be used in a new sono-photoacoustic imaging method, which enables greater sensitivity than traditional photoacoustic imaging.

The shell spectrum of HD 94509

NASA Astrophysics Data System (ADS)

Cowley, Charles R.; Przybilla, Norbert; Hubrig, Swetlana

2015-01-01

HD 94509 is a 9th magnitude Be star with an unusually rich metallic-lined shell. The absorption spectrum is rich, comparable to that of an A or F supergiant, but Mg II (4481A), and the Si II (4128 and 4130A), are weak, indicating a dilute radiation field, as described by Otto Struve. The H-alpha emission is double with components of equal intensity and an absorption core that dips well below the stellar continuum. H-beta is weaker, but with a similar structure. H-gamma through H-epsilon have virtually black cores, indicating that the shell covers the stellar disk. The stronger metallic absorption lines are wide near the continuum, but taper to very narrow cores. This line shape is unexplained. However, the total absorption can be modeled to reveal an overall particle densities of 10^{10}-10^{12} cm^{-3}. An electron density log(n_e) = 11.2 is obtained from the Paschen-line convergence and the Inglis-Tellar relation. Column densities are obtained with the help of curves of growth by assuming uniform conditions in the cloud. These indicate a nearly solar composition. The CLOUDY code (Ferland, et al. Rev. Mex. Astron. Astroph. 49, 137, 213) is used to produce a model that predicts matching column densities of the dominant ions, the n = 3 level of hydrogen, the H-alpha strength, and the electron density (± 0.5 dex).

Double core-hole emissivity of transient aluminum plasmas produced in the interaction with ultra-intense x-ray laser pulse

NASA Astrophysics Data System (ADS)

Gao, Cheng; Zeng, Jiaolong; Yuan, Jianmin

2015-11-01

Emissivity of single core-hole (SCH) and double core-hole (DCH) states of aluminum plasmas produced in the interaction with ultra-intense x-ray laser pulse interaction are investigated systematically by solving the time-dependent rate equation implemented in the detailed level accounting approximation. We first demonstrated the plasma density effects on level populations and charge state distribution. Compared with recent experiments, it is shown that the plasma density effects play important roles in the evolution dynamics. Then we systematically investigated the emissivity of the transient aluminum plasmas produced by the x-ray laser pulses with a few photon energies above the threshold photon energy to create DCH states. For the laser photon energy where there are resonant absorptions (RA), 1s-np transitions with both full 1s and SCH 1s states play important roles in time evolution of the population and DCH emission spectroscopy. The significant RA effects are illustrated in detail for x-ray pulses, which creates the 1s-2p resonant absorption from the SCH states of Al VII. With the increase of the photon energy, the emissions from lower charge states become larger.

Consequences of realistic embedding for the L 2,3 edge XAS of α-Fe 2 O 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bagus, Paul S.; Nelin, Connie J.; Sassi, Michel

Cluster models of condensed systems are often used to simulate the core-level spectra obtained with X-ray Photoelectron Spectroscopy, XPS, or with X-ray Absorption Spectroscopy, XAS, especially for near edge features.

Excited state X-ray absorption spectroscopy: Probing both electronic and structural dynamics

NASA Astrophysics Data System (ADS)

Neville, Simon P.; Averbukh, Vitali; Ruberti, Marco; Yun, Renjie; Patchkovskii, Serguei; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

2016-10-01

We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L 2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. We anticipate that the method presented here can be combined with ab initio molecular dynamics calculations to simulate the time-resolved X-ray spectroscopy of excited state molecular wavepacket dynamics.

Composite Sandwich Structures for Shock Mitigation and Energy Absorption

DTIC Science & Technology

2016-06-28

analysis of the blast performance of foam -core, composite sandwich panels was that on a per unit areal weight density basis, lighter and more crushable... foam cores offered greater blast resistance and energy absorption than the heavier and stronger foam cores. This was found to be the case even on an...absolute weight basis for cuNed sandwich panels and panels subjected to underwater blast. 15. SUBJECT TERMS composite; foam -core sandwich; blast

Intraparticle reduction of arsenite (As(III)) by nanoscale zerovalent iron (nZVI) investigated with In Situ X-ray absorption spectroscopy.

PubMed

Yan, Weile; Vasic, Relja; Frenkel, Anatoly I; Koel, Bruce E

2012-07-03

While a high efficiency of contaminant removal by nanoscale zerovalent iron (nZVI) has often been reported for several contaminants of great concern, including aqueous arsenic species, the transformations and translocation of contaminants at and within the nanoparticles are not clearly understood. By analysis using in situ time-dependent X-ray absorption spectroscopy (XAS) of the arsenic core level for nZVI in anoxic As(III) solutions, we have observed that As(III) species underwent two stages of transformation upon adsorption at the nZVI surface. The first stage corresponds to breaking of As-O bonds at the particle surface, and the second stage involves further reduction and diffusion of arsenic across the thin oxide layer enclosing the nanoparticles, which results in arsenic forming an intermetallic phase with the Fe(0) core. Extended X-ray absorption fine-structure (EXAFS) data from experiments conducted at different iron/arsenic ratios indicate that the reduced arsenic species tend to be enriched at the surface of the Fe(0) core region and had limited mobility into the interior of the metal core within the experimental time frame (up to 22 h). Therefore, there was an accumulation of partially reduced arsenic at the Fe(0)/oxide interface when a relatively large arsenic content was present in the solid phase. These results illuminate the role of intraparticle diffusion and reduction in affecting the chemical state and spatial distribution of arsenic in nZVI materials.

Experimental Evaluation of Tuned Chamber Core Panels for Payload Fairing Noise Control

NASA Technical Reports Server (NTRS)

Schiller, Noah H.; Allen, Albert R.; Herlan, Jonathan W.; Rosenthal, Bruce N.

2015-01-01

Analytical models have been developed to predict the sound absorption and sound transmission loss of tuned chamber core panels. The panels are constructed of two facesheets sandwiching a corrugated core. When ports are introduced through one facesheet, the long chambers within the core can be used as an array of low-frequency acoustic resonators. To evaluate the accuracy of the analytical models, absorption and sound transmission loss tests were performed on flat panels. Measurements show that the acoustic resonators embedded in the panels improve both the absorption and transmission loss of the sandwich structure at frequencies near the natural frequency of the resonators. Analytical predictions for absorption closely match measured data. However, transmission loss predictions miss important features observed in the measurements. This suggests that higher-fidelity analytical or numerical models will be needed to supplement transmission loss predictions in the future.

Near Edge X-Ray Absorption and X-Ray Photoelectron Diffraction Studies of the Structural Environment of Ge-Si Systems

NASA Astrophysics Data System (ADS)

Castrucci, P.; Gunnella, R.; Pinto, N.; Bernardini, R.; de Crescenzi, M.; Sacchi, M.

Near edge X-ray absorption spectroscopy (XAS), X-ray photoelectron diffraction (XPD) and Auger electron diffraction (AED) are powerful techniques for the qualitative study of the structural and electronic properties of several systems. The recent development of a multiple scattering approach to simulating experimental spectra opened a friendly way to the study of structural environments of solids and surfaces. This article reviews recent X-ray absorption experiments using synchrotron radiation which were performed at Ge L edges and core level electron diffraction measurements obtained using a traditional X-ray source from Ge core levels for ultrathin Ge films deposited on silicon substrates. Thermodynamics and surface reconstruction have been found to play a crucial role in the first stages of Ge growth on Si(001) and Si(111) surfaces. Both techniques show the occurrence of intermixing processes even for room-temperature-grown Ge/Si(001) samples and give a straightforward measurement of the overlayer tetragonal distortion. The effects of Sb as a surfactant on the Ge/Si(001) interface have also been investigated. In this case, evidence of layer-by-layer growth of the fully strained Ge overlayer with a reduced intermixing is obtained when one monolayer of Sb is predeposited on the surface.

Single and double core-hole ion emission spectroscopy of transient neon plasmas produced by ultraintense x-ray laser pulses

NASA Astrophysics Data System (ADS)

Gao, Cheng; Zeng, Jiaolong; Yuan, Jianmin

2016-05-01

Single core-hole (SCH) and double core-hole (DCH) spectroscopy is investigated systematically for neon gas in the interaction with ultraintense x-ray pulses with photon energy from 937 eV to 2000 eV. A time-dependent rate equation, implemented in the detailed level accounting approximation, is utilized to study the dynamical evolution of the level population and emission properties of the laser-produced highly transient plasmas. The plasma density effects on level populations are demonstrated with an x-ray photon energy of 2000 eV. For laser photon energy in the range of 937 - 1360 eV, resonant absorptions (RA) of 1s-np (n> = 2) transitions play important roles in time evolution of the population and DCH emission spectroscopy. For x-ray photon energy larger than 1360 eV, no RA exist and transient plasmas show different features in the DCH spectroscopy.

Carrier-Specific Femtosecond XUV Transient Absorption of PbI 2 Reveals Ultrafast Nonradiative Recombination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Ming-Fu; Verkamp, Max A.; Leveillee, Joshua

Femtosecond carrier recombination in PbI 2 is measured using tabletop high-harmonic extreme ultraviolet (XUV) transient absorption spectroscopy and ultrafast electron diffraction. XUV absorption from 45 eV to 62 eV measures transitions from the iodine 4d core level to the conduction band density of states. Photoexcitation at 400 nm creates separate and distinct transient absorption signals for holes and electrons, separated in energy by the 2.4 eV band gap of the semiconductor. The shape of the conduction band and therefore the XUV absorption spectrum is temperature dependent, and nonradiative recombination converts the initial electronic excitation to thermal excitation within picoseconds. Ultrafastmore » electron diffraction (UED) is used to measure the lattice temperature and confirm the recombination mechanism. Lastly, the XUV and UED results support a 2nd-order recombination model with a rate constant of 2.5x10 -9 cm 3/s.« less

Carrier-Specific Femtosecond XUV Transient Absorption of PbI 2 Reveals Ultrafast Nonradiative Recombination

DOE PAGES

Lin, Ming-Fu; Verkamp, Max A.; Leveillee, Joshua; ...

2017-11-30

Femtosecond carrier recombination in PbI 2 is measured using tabletop high-harmonic extreme ultraviolet (XUV) transient absorption spectroscopy and ultrafast electron diffraction. XUV absorption from 45 eV to 62 eV measures transitions from the iodine 4d core level to the conduction band density of states. Photoexcitation at 400 nm creates separate and distinct transient absorption signals for holes and electrons, separated in energy by the 2.4 eV band gap of the semiconductor. The shape of the conduction band and therefore the XUV absorption spectrum is temperature dependent, and nonradiative recombination converts the initial electronic excitation to thermal excitation within picoseconds. Ultrafastmore » electron diffraction (UED) is used to measure the lattice temperature and confirm the recombination mechanism. Lastly, the XUV and UED results support a 2nd-order recombination model with a rate constant of 2.5x10 -9 cm 3/s.« less

Transmission Loss and Absorption of Corrugated Core Sandwich Panels With Embedded Resonators

NASA Technical Reports Server (NTRS)

Allen, Albert R.; Schiller, Noah H.; Zalewski, Bart F.; Rosenthal, Bruce N.

2014-01-01

The effect of embedded resonators on the diffuse field sound transmission loss and absorption of composite corrugated core sandwich panels has been evaluated experimentally. Two 1.219 m × 2.438 m panels with embedded resonator arrangements targeting frequencies near 100 Hz were evaluated using non-standard processing of ASTM E90-09 acoustic transmission loss and ASTM C423-09a room absorption test measurements. Each panel is comprised of two composite face sheets sandwiching a corrugated core with a trapezoidal cross section. When inlet openings are introduced in one face sheet, the chambers within the core can be used as embedded acoustic resonators. Changes to the inlet and chamber partition locations allow this type of structure to be tuned for targeted spectrum passive noise control. Because the core chambers are aligned with the plane of the panel, the resonators can be tuned for low frequencies without compromising the sandwich panel construction, which is typically sized to meet static load requirements. Absorption and transmission loss performance improvements attributed to opening the inlets were apparent for some configurations and inconclusive for others.

Development of Spiro[cyclopenta[1,2-b:5,4-b']dithiophene-4,9'-fluorene]-Based A-π-D-π-A Small Molecules with Different Acceptor Units for Efficient Organic Solar Cells.

PubMed

Wang, Wengong; Shen, Ping; Dong, Xinning; Weng, Chao; Wang, Guo; Bin, Haijun; Zhang, Jing; Zhang, Zhi-Guo; Li, Yongfang

2017-02-08

Three acceptor-π-donor-π-acceptor (A-π-D-π-A) small molecules (STFYT, STFRDN, and STFRCN) with spiro[cyclopenta[1,2-b:5,4-b']dithiophene-4,9'-fluorene] (STF) as the central donor unit, terthiophene as the π-conjugated bridge, indenedione, 3-ethylrhodanine, or 2-(1,1-dicyanomethylene)rhodanine as the acceptor unit are designed, synthesized, and characterized as electron donor materials in solution-processing organic solar cells (OSCs). The effects of the spiro STF-based central core and different acceptors on the molecular configuration, absorption properties, electronic energy levels, carrier transport properties, the morphology of active layers, and photovoltaic properties are investigated in detail. The three molecules exhibit desirable physicochemical features: wide absorption bands (300-850 nm) and high molar absorption coefficients (4.82 × 10 4 to 7.56 × 10 4 M -1 cm -1 ) and relatively low HOMO levels (-5.15 to -5.38 eV). Density functional theory calculations reveal that the spiro STF central core benefits to reduce the steric hindrance effect between the central donor block and terthiophene bridge and suppress excessive intermolecular aggregations. The optimized OSCs based on these molecules deliver power conversion efficiencies (PCEs) of 6.68%, 3.30%, and 4.33% for STFYT, STFRDN, and STFRCN, respectively. The higher PCE of STFYT-based OSCs should be ascribed to its better absorption ability, higher and balanced hole and electron mobilities, and superior active layer morphology as compared to the other two compounds. So far, this is the first example of developing the A-π-D-π-A type small molecules with a spiro central donor core for high-performance OSC applications. Meanwhile, these results demonstrate that using spiro central block to construct A-π-D-π-A molecule is an alternative and effective strategy for achieving high-performance small molecule donor materials.

The origin of anisotropy and high density of states in the electronic structure of Cr2GeC by means of polarized soft x-ray spectroscopy and ab initio calculations

NASA Astrophysics Data System (ADS)

Magnuson, Martin; Mattesini, Maurizio; Bugnet, Matthieu; Eklund, Per

2015-10-01

The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr2GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal differences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr2GeC. The Cr L 2, 3, C K, and Ge M 1, M 2, 3 emission spectra are interpreted with first-principles density-functional theory (DFT) including core-to-valence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should affect the thermal expansion coefficient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.

The origin of anisotropy and high density of states in the electronic structure of Cr2GeC by means of polarized soft x-ray spectroscopy and ab initio calculations.

PubMed

Magnuson, Martin; Mattesini, Maurizio; Bugnet, Matthieu; Eklund, Per

2015-10-21

The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr2GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal differences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr2GeC. The Cr L(2, 3), C K, and Ge M1, M(2, 3) emission spectra are interpreted with first-principles density-functional theory (DFT) including core-to-valence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should affect the thermal expansion coefficient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.

Rational Construction of Uniform CoNi-Based Core-Shell Microspheres with Tunable Electromagnetic Wave Absorption Properties.

PubMed

Chen, Na; Jiang, Jian-Tang; Xu, Cheng-Yan; Yan, Shao-Jiu; Zhen, Liang

2018-02-16

Core-shell particles with integration of ferromagnetic core and dielectric shell are attracting extensive attention for promising microwave absorption applications. In this work, CoNi microspheres with conical bulges were synthesized by a simple and scalable liquid-phase reduction method. Subsequent coating of dielectric materials was conducted to acquire core-shell structured CoNi@TiO 2 composite particles, in which the thickness of TiO 2 is about 40 nm. The coating of TiO 2 enables the absorption band of CoNi to effectively shift from K u to S band, and endows CoNi@TiO 2 microspheres with outstanding electromagnetic wave absorption performance along with a maximum reflection loss of 76.6 dB at 3.3 GHz, much better than that of bare CoNi microspheres (54.4 dB at 17.8 GHz). The enhanced EMA performance is attributed to the unique core-shell structures, which can induce dipole polarization and interfacial polarization, and tune the dielectric properties to achieve good impedance matching. Impressively, TiO 2 coating endows the composites with better microwave absorption capability than CoNi@SiO 2 microspheres. Compared with SiO 2 , TiO 2 dielectric shells could protect CoNi microspheres from merger and agglomeration during annealed. These results indicate that CoNi@TiO 2 core-shell microspheres can serve as high-performance absorbers for electromagnetic wave absorbing application.

Eigenvalue equation and core-mode cutoff of weakly guiding tapered fiber as three layer optical waveguide and used as biochemical sensor.

PubMed

Linslal, C L; Mohan, P M S; Halder, A; Gangopadhyay, T K

2012-06-01

The core-mode cutoff plays a major role in evanescent field absorption based sensors. A method has been proposed to calculate the core-mode cutoff by solving the eigenvalue equations of a weakly guiding three layer optical waveguide graphically. The variation of normalized waveguide parameter (V) is also calculated with different wavelengths at core-mode cutoff. At the first step, theoretical analysis of tapered fiber parameters has been performed for core-mode cutoff. The taper angle of an adiabatic tapered fiber is also analyzed using the length-scale criterion. Secondly, single-mode tapered fiber has been developed to make a precision sensor element suitable for chemical detection. Finally, the sensor element has been used to detect absorption peak of ethylenediamine. Results are presented in which an absorption peak at 1540 nm is observed.

Pulsed photothermal interferometry for spectroscopic gas detection with hollow-core optical fibre

PubMed Central

Lin, Yuechuan; Jin, Wei; Yang, Fan; Ma, Jun; Wang, Chao; Ho, Hoi Lut; Liu, Yang

2016-01-01

Gas detection with hollow-core photonic bandgap fibre (HC-PBF) and pulsed photothermal (PT) interferometry spectroscopy are studied theoretically and experimentally. A theoretical model is developed and used to compute the gas-absorption-induced temperature and phase modulation in a HC-PBF filled with low-concentration of C2H2 in nitrogen. The PT phase modulation dynamics for different pulse duration, peak power and energy of pump beam are numerically modelled, which are supported by the experimental results obtained around the P(9) absorption line of C2H2 at 1530.371 nm. Thermal conduction is identified as the main process responsible for the phase modulation dynamics. For a constant peak pump power level, the phase modulation is found to increase with pulse duration up to ~1.2 μs, while it increases with decreasing pulse duration for a constant pulse energy. It is theoretically possible to achieve ppb level detection of C2H2 with ~1 m length HC-PBF and a pump beam with ~10 ns pulse duration and ~100 nJ pulse energy. PMID:28009011

Pulsed photothermal interferometry for spectroscopic gas detection with hollow-core optical fibre.

PubMed

Lin, Yuechuan; Jin, Wei; Yang, Fan; Ma, Jun; Wang, Chao; Ho, Hoi Lut; Liu, Yang

2016-12-23

Gas detection with hollow-core photonic bandgap fibre (HC-PBF) and pulsed photothermal (PT) interferometry spectroscopy are studied theoretically and experimentally. A theoretical model is developed and used to compute the gas-absorption-induced temperature and phase modulation in a HC-PBF filled with low-concentration of C 2 H 2 in nitrogen. The PT phase modulation dynamics for different pulse duration, peak power and energy of pump beam are numerically modelled, which are supported by the experimental results obtained around the P(9) absorption line of C 2 H 2 at 1530.371 nm. Thermal conduction is identified as the main process responsible for the phase modulation dynamics. For a constant peak pump power level, the phase modulation is found to increase with pulse duration up to ~1.2 μs, while it increases with decreasing pulse duration for a constant pulse energy. It is theoretically possible to achieve ppb level detection of C 2 H 2 with ~1 m length HC-PBF and a pump beam with ~10 ns pulse duration and ~100 nJ pulse energy.

Comprehensive Experimental and Computational Spectroscopic Study of Hexacyanoferrate Complexes in Water: From Infrared to X-ray Wavelengths.

PubMed

Ross, Matthew; Andersen, Amity; Fox, Zachary W; Zhang, Yu; Hong, Kiryong; Lee, Jae-Hyuk; Cordones, Amy; March, Anne Marie; Doumy, Gilles; Southworth, Stephen H; Marcus, Matthew A; Schoenlein, Robert W; Mukamel, Shaul; Govind, Niranjan; Khalil, Munira

2018-05-17

We present a joint experimental and computational study of the hexacyanoferrate aqueous complexes at equilibrium in the 250 meV to 7.15 keV regime. The experiments and the computations include the vibrational spectroscopy of the cyanide ligands, the valence electronic absorption spectra, and Fe 1s core hole spectra using element-specific-resonant X-ray absorption and emission techniques. Density functional theory-based quantum mechanics/molecular mechanics molecular dynamics simulations are performed to generate explicit solute-solvent configurations, which serve as inputs for the spectroscopy calculations of the experiments spanning the IR to X-ray wavelengths. The spectroscopy simulations are performed at the same level of theory across this large energy window, which allows for a systematic comparison of the effects of explicit solute-solvent interactions in the vibrational, valence electronic, and core-level spectra of hexacyanoferrate complexes in water. Although the spectroscopy of hexacyanoferrate complexes in solution has been the subject of several studies, most of the previous works have focused on a narrow energy window and have not accounted for explicit solute-solvent interactions in their spectroscopy simulations. In this work, we focus our analysis on identifying how the local solvation environment around the hexacyanoferrate complexes influences the intensity and line shape of specific spectroscopic features in the UV/vis, X-ray absorption, and valence-to-core X-ray emission spectra. The identification of these features and their relationship to solute-solvent interactions is important because hexacyanoferrate complexes serve as model systems for understanding the photochemistry and photophysics of a large class of Fe(II) and Fe(III) complexes in solution.

Relativistic many-body XMCD theory including core degenerate effects

NASA Astrophysics Data System (ADS)

Fujikawa, Takashi

2009-11-01

A many-body relativistic theory to analyze X-ray Magnetic Circular Dichroism (XMCD) spectra has been developed on the basis of relativistic quantum electrodynamic (QED) Keldysh Green's function approach. This theoretical framework enables us to handle relativistic many-body effects in terms of correlated nonrelativistic Green's function and relativistic correction operator Q, which naturally incorporates radiation field screening and other optical field effects in addition to electron-electron interactions. The former can describe the intensity ratio of L2/L3 which deviates from the statistical weight (branching ratio) 1/2. In addition to these effects, we consider the degenerate or nearly degenerate effects of core levels from which photoelectrons are excited. In XPS spectra, for example in Rh 3d sub level excitations, their peak shapes are quite different: This interesting behavior is explained by core-hole moving after the core excitation. We discuss similar problems in X-ray absorption spectra in particular excitation from deep 2p sub levels which are degenerate in each sub levels and nearly degenerate to each other in light elements: The hole left behind is not frozen there. We derive practical multiple scattering formulas which incorporate all those effects.

Development of Lightweight, Compact, Structurally-Integrated Acoustic Liners for Broadband Low-Frequency Noise Mitigation

NASA Astrophysics Data System (ADS)

Chambers, Andrew T.

Airborne noise with a low dominant frequency content (< 500 Hz) has detrimental effects in many applications, but is as yet beyond the scope of conventional acoustic noise mitigation techniques using liners, foams or claddings owing to mass and volume considerations. Its low evanescence contributes significantly to environmental noise pollution, and unwanted structural vibrations causing diminished efficiency, comfort, payload integrity and mission capabilities. An alternative approach using liner configurations with realistic mass and volume constraints having innovative 'folded' core geometries is investigated to ascertain its low-frequency noise absorption characteristics. In contrast to mass-driven approaches, the folded core approach relies on tailoring interactions between acoustic resonances to tune the liner's impedance to suit the dominant low-frequency content of the source. This allows to keep non-structural mass-addition to a minimum, while retaining an overall thickness comparable to conventional liners for these low-frequency liner designs. The relative acoustic performance of various candidate folded core designs is evaluated by means of a new composite metric termed the Low-Frequency Performance (LFP) factor, which is educed from the absorption coefficient spectrum obtained using Zwikker-Kosten Transmission Line (ZKTL) theory-based numerical studies. An LFP-based software tool is developed to determine optimal 3D cavity packing for a prescribed liner volume and target frequency range. ZKTL-based parametric studies on core dimensions and face sheet porosity are utilized for detailed design of test articles. Experimental verification of absorption coefficient spectra conducted using 3D printed test articles in a normal incidence acoustic impedance tube yield good correlation with simulations. More than 100 Hz of continuous bandwidth with an absorption coefficient greater than 0.6 is shown to be possible in the 300 to 400 Hz range with a 38.1-mm (1.5-inch) thick liner. Further, the influence of face sheet type, Mach number, and sound pressure level on the attenuation across folded core liners is evaluated using grazing flow impedance tube tests. Up to 20 dB of attenuation is observed in the targeted frequency range in these tests indicating potential for performance retention in an operational scenario. With current additive and hybrid manufacturing techniques attaining critical commercial maturity, lightweight and compact acoustic liners employing folded cores could provide a promising practical solution to mitigate low-frequency airborne noise, especially in aerospace applications.

X-ray absorption in insulators with non-Hermitian real-time time-dependent density functional theory.

PubMed

Fernando, Ranelka G; Balhoff, Mary C; Lopata, Kenneth

2015-02-10

Non-Hermitian real-time time-dependent density functional theory was used to compute the Si L-edge X-ray absorption spectrum of α-quartz using an embedded finite cluster model and atom-centered basis sets. Using tuned range-separated functionals and molecular orbital-based imaginary absorbing potentials, the excited states spanning the pre-edge to ∼20 eV above the ionization edge were obtained in good agreement with experimental data. This approach is generalizable to TDDFT studies of core-level spectroscopy and dynamics in a wide range of materials.

Mode-locked Er-doped fiber laser based on PbS/CdS core/shell quantum dots as saturable absorber.

PubMed

Ming, Na; Tao, Shina; Yang, Wenqing; Chen, Qingyun; Sun, Ruyi; Wang, Chang; Wang, Shuyun; Man, Baoyuan; Zhang, Huanian

2018-04-02

Previously, PbS/CdS core/shell quantum dots with excellent optical properties have been widely used as light-harvesting materials in solar cell and biomarkers in bio-medicine. However, the nonlinear absorption characteristics of PbS/CdS core/shell quantum dots have been rarely investigated. In this work, PbS/CdS core/shell quantum dots were successfully employed as nonlinear saturable absorber (SA) for demonstrating a mode-locked Er-doped fiber laser. Based on a film-type SA, which was prepared by incorporating the quantum dots with the polyvinyl alcohol (PVA), mode-locked Er-doped operation with a pulse width of 54 ps and a maximum average output power of 2.71 mW at the repetition rate of 3.302 MHz was obtained. Our long-time stable results indicate that the CdS shell can effectively protect the PbS core from the effect of photo-oxidation and PbS/CdS core/shell quantum dots were efficient SA candidates for demonstrating pulse fiber lasers due to its tunable absorption peak and excellent saturable absorption properties.

The influence of reaction times on structural, optical and luminescence properties of cadmium telluride nanoparticles prepared by wet-chemical process

NASA Astrophysics Data System (ADS)

Kiprotich, Sharon; Dejene, Francis B.; Ungula, Jatani; Onani, Martin O.

2016-01-01

This paper explains one pot synthesis of type II water soluble L-cysteine capped cadmium telluride (CdTe) core shell quantum dots using cadmium acetate, potassium tellurite and L-cysteine as the starting materials. The reaction was carried out in a single three necked flask without nitrogen under reflux at 100 °C. Results from PL show a sharp absorption excitonic band edge of the CdTe core with respect to the core shell which loses its shoulder during the growth of the shell on the core. The PL spectra indicate a drastic shift in emission window of the core which is simultaneously accompanied by an increase in emission intensity. X-ray diffraction pattern confirms the formation of hexagonal phase for all samples. Some difference in absorption edges were observed due to varying synthesis time of CdTe NPs. The position of the absorption band is observed to shift towards the lower wavelength side for shorter durations of synthesis.

Ultrafast light matter interaction in CdSe/ZnS core-shell quantum dots

NASA Astrophysics Data System (ADS)

Yadav, Rajesh Kumar; Sharma, Rituraj; Mondal, Anirban; Adarsh, K. V.

2018-04-01

Core-shell quantum dot are imperative for carrier (electron and holes) confinement in core/shell, which provides a stage to explore the linear and nonlinear optical phenomena at the nanoscalelimit. Here we present a comprehensive study of ultrafast excitation dynamics and nonlinear optical absorption of CdSe/ZnS core shell quantum dot with the help of ultrafast spectroscopy. Pump-probe and time-resolved measurements revealed the drop of trapping at CdSe surface due to the presence of the ZnS shell, which makes more efficient photoluminescence. We have carried out femtosecond transient absorption studies of the CdSe/ZnS core-shell quantum dot by irradiation with 400 nm laser light, monitoring the transients in the visible region. The optical nonlinearity of the core-shell quantum dot studied by using the Z-scan technique with 120 fs pulses at the wavelengths of 800 nm. The value of two photon absorption coefficients (β) of core-shell QDs extracted as80cm/GW, and it shows excellent benchmark for the optical limiting onset of 2.5GW/cm2 with the low limiting differential transmittance of 0.10, that is an order of magnitude better than graphene based materials.

Multioctave infrared supercontinuum generation in large-core As₂S₃ fibers.

PubMed

Théberge, Francis; Thiré, Nicolas; Daigle, Jean-François; Mathieu, Pierre; Schmidt, Bruno E; Messaddeq, Younès; Vallée, Réal; Légaré, François

2014-11-15

We report on infrared supercontinuum (SC) generation through laser filamentation and subsequent nonlinear propagation in a step-index As2S3 fiber. The 100 μm core and high-purity As2S3 fiber used exhibit zero-dispersion wavelength around 4.5 μm, a mid-infrared background loss of 0.2  dB/m, and a maximum loss of only 0.55  dB/m at the S-H absorption peak around 4.05 μm. When pumping with ultrashort laser pulses slightly above the S-H absorption band, broadband infrared supercontinua were generated with a 20 dB spectral flatness spanning from 1.5 up to 7 μm. The efficiency and spectral shape of the SC produced by ultrashort pulses in large-core As2S3 fiber are mainly determined by its dispersion, the S-H contaminant absorption, and the mid-infrared nonlinear absorption.

Towards better light harvesting capability for DSSC (dye sensitized solar cells) through addition of Au@SiO2 core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Fadhilah, Nur; Alhadi, Emha Riyadhul Jinan; Risanti, Doty Dewi

2018-04-01

The Au nanoparticles as core can increase the light harvesting due to the strong near-field effect LSPR (Localized Surface Plasmon Resonance), effectively minimized the electron recombination process and also can improve the optical absorption of the dye sensitized. Au@SiO2 core-shell nanoparticles were prepared using SiO2 extracted from Sidoarjo mud volcano. In this work investigated the influence of pH solution and silica shell volume fraction in Au@SiO2 nanoparticles core-shell structure on DSSC loaded with Ru-based dye. From XRD characterization it was found that core-shell contains SiO2, Au, γAl2O3 and traces NaCl. UV-Vis absorption spectra of core-shell showed the position of the surface plasmon AuNP band in the range of 500-600 nm. The Au@SiO2 core-shell with volume fraction of 30ml silica has the highest peak absorbance. The enhanced light absorption is primarily attributed to the LSPR effect of the Au core. Our results on incident photon-to-current conversion efficiency indicates that the presence of SiO2 depending on its volume fraction tends to shift to longer wavelength.

Core–shell interaction and its impact on the optical absorption of pure and doped core-shell CdSe/ZnSe nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xinqin; Cui, Yingqi; Zeng, Qun

The structural, electronic, and optical properties of core-shell nanoclusters, (CdSe){sub x}@(CdSe){sub y} and their Zn-substituted complexes of x = 2–4 and y = 16–28, were studied with density functional theory calculations. The substitution was applied in the cores, the shells, and/or the whole clusters. All these clusters are characterized by their core-shell structures in which the core-shell interaction was found different from those in core or in shell, as reflected by their bondlengths, volumes, and binding energies. Moreover, the core and shell combine together to compose a new cluster with electronic and optical properties different from those of separated individuals,more » as reflected by their HOMO-LUMO gaps and optical absorptions. With the substitution of Cd by Zn, the structural, electronic, and optical properties of clusters change regularly. The binding energy increases with Zn content, attributed to the strong Zn–Se bonding. For the same core/shell, the structure with a CdSe shell/core has a narrower gap than that with a ZnSe shell/core. The optical absorption spectra also change accordingly with Zn substitution. The peaks blueshift with increasing Zn concentration, accompanying with shape variations in case large number of Cd atoms are substituted. Our calculations reveal the core-shell interaction and its influence on the electronic and optical properties of the core-shell clusters, suggesting a composition–structure–property relationship for the design of core-shell CdSe and ZnSe nanoclusters.« less

Ingestion of insoluble dietary fibre increased zinc and iron absorption and restored growth rate and zinc absorption suppressed by dietary phytate in rats.

PubMed

Hayashi, K; Hara, H; Asvarujanon, P; Aoyama, Y; Luangpituksa, P

2001-10-01

We examined the effects of ingestion of five types of insoluble fibre on growth and Zn absorption in rats fed a marginally Zn-deficient diet (6.75 mg (0.103 mmol) Zn/kg diet) with or without added sodium phytate (12.6 mmol/kg diet). The types of insoluble fibre tested were corn husks, watermelon skin, yam-bean root (Pachyrhizus erosus) and pineapple core, and cellulose was used as a control (100 g/kg diet). Body-weight gain in the cellulose groups was suppressed by 57 % by feeding phytate. Body-weight gain in phytate-fed rats was 80 % greater in the watermelon skin fibre and yam-bean root fibre group than that in the cellulose group. Zn absorption ratio in the cellulose groups was lowered by 46 and 70 % in the first (days 7-10) and second (days 16-19) measurement periods with feeding phytate. In the rats fed the phytate-containing diets, Zn absorption ratio in the watermelon skin, yam-bean root and pineapple core fibre groups was 140, 80 and 54 % higher respectively than that in the cellulose group, in the second period. Fe absorption was not suppressed by phytate, however, feeding of these three types of fibre promoted Fe absorption in rats fed phytate-free diets. The concentration of soluble Zn in the caecal contents in the watermelon skin fibre or yam-bean root fibre groups was identical to that in the control group in spite of a higher short-chain fatty acid concentration and lower pH in the caecum. These findings indicate that ingestion of these types of insoluble fibre recovered the growth and Zn absorption suppressed by feeding a high level of phytate, and factors other than caecal fermentation may also be involved in this effect of insoluble fibre.

Luminescence and photoinduced absorption in ytterbium-doped optical fibres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rybaltovsky, A A; Aleshkina, S S; Likhachev, M E

2011-12-31

Photochemical reactions induced in the glass network of an ytterbium-doped fibre core by IR laser pumping and UV irradiation have been investigated by analysing absorption and luminescence spectra. We have performed comparative studies of the photoinduced absorption and luminescence spectra of fibre preforms differing in core glass composition: Al{sub 2}O{sub 3} : SiO{sub 2}, Al{sub 2}O{sub 3} : Yb{sub 2}O{sub 3} : SiO{sub 2}, and P{sub 2}O{sub 5} : Yb{sub 2}O{sub 3} : SiO{sub 2}. The UV absorption spectra of unirradiated preform core samples show strong bands peaking at 5.1 and 6.5 eV, whose excitation plays a key role inmore » photoinduced colour centre generation in the glass network. 'Direct' UV excitation of the 5.1- and 6.5-eV absorption bands at 244 and 193 nm leads to the reduction of some of the Yb{sup 3+} ions to Yb{sup 2+}. The photodarkening of ytterbium-doped fibres by IR pumping is shown to result from oxygen hole centre generation. A phenomenological model is proposed for the IR-pumping-induced photodarkening of ytterbium-doped fibres. The model predicts that colour centre generation in the core glass network and the associated absorption in the visible range result from a cooperative effect involving simultaneous excitation of a cluster composed of several closely spaced Yb{sup 3+} ions.« less

Theoretical study of the crystal-field energy levels and two-photon absorption intensities of Tb3+ in cubic host lattices.

PubMed

Duan, Chang-Kui; Tanner, Peter A

2011-03-17

Published two photon excitation (TPE) intensities for the cubic elpasolite systems Cs(2)NaTbX(6) (X = Cl, F) have been simulated by a calculation of two photon absorption (TPA) intensities which takes into account electric dipole transitions involving the detailed crystal-field structure of 4f(7)5d intermediate states, as well as the interactions of the 4f(7) core with the d-electron. The intensity calculation employed parameters from an energy level calculation which not only presented an accurate fit, but also yielded parameters consistent with those from other lanthanide ions. The calculated intensities were used to confirm or adjust the previous assignments of energy levels, resulting in some minor revisions. Generally, the TPA intensity simulations were in better agreement with experimental data for the fluoride, rather than the chloride, system and possible reasons for this are given.

Enhancing the microwave absorption properties of amorphous CoO nanosheet-coated Co (hexagonal and cubic phases) through interfacial polarizations.

PubMed

Deng, Jiushuai; Li, Shimei; Zhou, Yuanyuan; Liang, Luyang; Zhao, Biao; Zhang, Xi; Zhang, Rui

2018-01-01

Core-shell flower-like composites were successfully prepared by a simple polyol method. These composites were formed by coating dual-phased (face-centered cubic [fcc] and hexagonal close-packed [hcp]) Co with amorphous CoO nanosheets. The microwave absorption properties of the flower-like Co@CoO paraffin composites with various Co@CoO amounts were then investigated. Results showed that the paraffin-based composite containing 70wt% flower-like Co@CoO displayed excellent microwave absorption properties (R E =24.74dB·GHz/mm). The minimum reflection loss of -30.4dB was obtained at 16.1GHz with a small thickness of 1.5mm, and 1.5mm bandwidth reached 4.6GHz (13.4-18GHz) below -10dB (90% microwave absorption). The excellent microwave absorption properties of flower-like Co@CoO are attributed to the synergetic effect between magnetic loss and dielectric loss, and the magnetic loss makes a main contribution to absorption. The core-shell flower-like structures with dual Co phases also contributed to microwave absorption. The amorphous CoO nanosheets were able to generate multiple reflections and exhibit scattering. In addition, the novel absorption mechanism that enhanced interfacial polarization was proposed. This enhancement resulted from the presence of interfaces between the hcp and fcc phases and between the core-shell Co@CoO composites. Copyright © 2017 Elsevier Inc. All rights reserved.

Electrokinetic detection for X-ray spectra of weakly interacting liquids: n-decane and n-nonane.

PubMed

Lam, Royce K; Shih, Orion; Smith, Jacob W; Sheardy, Alex T; Rizzuto, Anthony M; Prendergast, David; Saykally, Richard J

2014-06-21

The introduction of liquid microjets into soft X-ray absorption spectroscopy enabled the windowless study of liquids by this powerful atom-selective high vacuum methodology. However, weakly interacting liquids produce large vapor backgrounds that strongly perturb the liquid signal. Consequently, solvents (e.g., hydrocarbons, ethers, ketones, etc.) and solutions of central importance in chemistry and biology have been inaccessible by this technology. Here we describe a new detection method, upstream detection, which greatly reduces the vapor phase contribution to the X-ray absorption signal while retaining important advantages of liquid microjet sample introduction (e.g., minimal radiation damage). The effectiveness of the upstream detection method is demonstrated in this first study of room temperature liquid hydrocarbons: n-nonane and n-decane. Good agreement with first principles' calculations indicates that the eXcited electron and Core Hole theory adequately describes the subtle interactions in these liquids that perturb the electronic structure of the unoccupied states probed in core-level experiments.

Wave Function Engineering in CdSe/PbS Core/Shell Quantum Dots.

PubMed

Wieliczka, Brian M; Kaledin, Alexey L; Buhro, William E; Loomis, Richard A

2018-05-25

The synthesis of epitaxial CdSe/PbS core/shell quantum dots (QDs) is reported. The PbS shell grows in a rock salt structure on the zinc blende CdSe core, thereby creating a crystal structure mismatch through additive growth. Absorption and photoluminescence (PL) band edge features shift to lower energies with increasing shell thickness, but remain above the CdSe bulk band gap. Nevertheless, the profiles of the absorption spectra vary with shell growth, indicating that the overlap of the electron and hole wave functions is changing significantly. This leads to over an order of magnitude reduction of absorption near the band gap and a large, tunable energy shift, of up to 550 meV, between the onset of strong absorption and the band edge PL. While the bulk valence and conduction bands adopt an inverse type-I alignment, the observed spectroscopic behavior is consistent with a transition between quasi-type-I and quasi-type-II behavior depending on shell thickness. Three effective mass approximation models support this hypothesis and suggest that the large difference in effective masses between the core and shell results in hole localization in the CdSe core and a delocalization of the electron across the entire QD. These results show the tuning of wave functions and transition energies in CdSe/PbS nanoheterostructures with prospects for use in optoelectronic devices for luminescent solar concentration or multiexciton generation.

Grazing incidence modeling of a metamaterial-inspired dual-resonance acoustic liner

NASA Astrophysics Data System (ADS)

Beck, Benjamin S.

2014-03-01

To reduce the noise emitted by commercial aircraft turbofan engines, the inlet and aft nacelle ducts are lined with acoustic absorbing structures called acoustic liners. Traditionally, these structures consist of a perforated facesheet bonded on top of a honeycomb core. These traditional perforate over honeycomb core (POHC) liners create an absorption spectra where the maximum absorption occurs at a frequency that is dictated by the depth of the honeycomb core; which acts as a quarter-wave resonator. Recent advances in turbofan engine design have increased the need for thin acoustic liners that are effective at low frequencies. One design that has been developed uses an acoustic metamaterial architecture to improve the low frequency absorption. Specifically, the liner consists of an array of Helmholtz resonators separated by quarter-wave volumes to create a dual-resonance acoustic liner. While previous work investigated the acoustic behavior under normal incidence, this paper outlines the modeling and predicted transmission loss and absorption of a dual-resonance acoustic metamaterial when subjected to grazing incidence sound.

Pump absorption in coiled and twisted double-clad hexagonal fiber: effect of launching conditions and core location

NASA Astrophysics Data System (ADS)

Dalidet, Romain; Peterka, Pavel; Doya, Valérie; Aubrecht, Jan; Koška, Pavel

2018-02-01

Ever extending applications of fiber lasers require energy efficient, high-power, small footprint and reliable fiber lasers and laser wavelength versatility. To meet these demands, next generation of active fibers for high-power fiber lasers is coming out that will eventually offer tailored spectroscopic properties, high robustness and reduced cooling requirements and improved efficiency through tailored pump absorption. We report on numerical modelling of the efficiency of the pump absorption in double clad active fibers with hexagonal shape of the inner cladding cross section and rare-earth-doped core. We analyze both the effect of different radii of the spool on which the fiber is coiled and different fiber twisting rates. Two different launching conditions were investigated: the Gaussian input pump beam and a speckle pattern that mimics the output of the pump laser diode pigtail. We have found that by asymmetric position of the rare-earth-doped core we can significantly improve the pump absorption.

Extreme absorption enhancement in ZnTe:O/ZnO intermediate band core-shell nanowires by interplay of dielectric resonance and plasmonic bowtie nanoantennas.

PubMed

Nie, Kui-Ying; Li, Jing; Chen, Xuanhu; Xu, Yang; Tu, Xuecou; Ren, Fang-Fang; Du, Qingguo; Fu, Lan; Kang, Lin; Tang, Kun; Gu, Shulin; Zhang, Rong; Wu, Peiheng; Zheng, Youdou; Tan, Hark Hoe; Jagadish, Chennupati; Ye, Jiandong

2017-08-08

Intermediate band solar cells (IBSCs) are conceptual and promising for next generation high efficiency photovoltaic devices, whereas, IB impact on the cell performance is still marginal due to the weak absorption of IB states. Here a rational design of a hybrid structure composed of ZnTe:O/ZnO core-shell nanowires (NWs) with Al bowtie nanoantennas is demonstrated to exhibit strong ability in tuning and enhancing broadband light response. The optimized nanowire dimensions enable absorption enhancement by engineering leaky-mode dielectric resonances. It maximizes the overlap of the absorption spectrum and the optical transitions in ZnTe:O intermediate-band (IB) photovoltaic materials, as verified by the enhanced photoresponse especially for IB states in an individual nanowire device. Furthermore, by integrating Al bowtie antennas, the enhanced exciton-plasmon coupling enables the notable improvement in the absorption of ZnTe:O/ZnO core-shell single NW, which was demonstrated by the profound enhancement of photoluminescence and resonant Raman scattering. The marriage of dielectric and metallic resonance effects in subwavelength-scale nanowires opens up new avenues for overcoming the poor absorption of sub-gap photons by IB states in ZnTe:O to achieve high-efficiency IBSCs.

Hybrid acoustic metamaterial as super absorber for broadband low-frequency sound

PubMed Central

Tang, Yufan; Ren, Shuwei; Meng, Han; Xin, Fengxian; Huang, Lixi; Chen, Tianning; Zhang, Chuanzeng; Lu, Tian Jain

2017-01-01

A hybrid acoustic metamaterial is proposed as a new class of sound absorber, which exhibits superior broadband low-frequency sound absorption as well as excellent mechanical stiffness/strength. Based on the honeycomb-corrugation hybrid core (H-C hybrid core), we introduce perforations on both top facesheet and corrugation, forming perforated honeycomb-corrugation hybrid (PHCH) to gain super broadband low-frequency sound absorption. Applying the theory of micro-perforated panel (MPP), we establish a theoretical method to calculate the sound absorption coefficient of this new kind of metamaterial. Perfect sound absorption is found at just a few hundreds hertz with two-octave 0.5 absorption bandwidth. To verify this model, a finite element model is developed to calculate the absorption coefficient and analyze the viscous-thermal energy dissipation. It is found that viscous energy dissipation at perforation regions dominates the total energy consumed. This new kind of acoustic metamaterials show promising engineering applications, which can serve as multiple functional materials with extraordinary low-frequency sound absorption, excellent stiffness/strength and impact energy absorption. PMID:28240239

Low-Velocity Impact Behavior of Sandwich Structures with Additively Manufactured Polymer Lattice Cores

NASA Astrophysics Data System (ADS)

Turner, Andrew J.; Al Rifaie, Mohammed; Mian, Ahsan; Srinivasan, Raghavan

2018-05-01

Sandwich panel structures are widely used in aerospace, marine, and automotive applications because of their high flexural stiffness, strength-to-weight ratio, good vibration damping, and low through-thickness thermal conductivity. These structures consist of solid face sheets and low-density cellular core structures, which are traditionally based upon honeycomb folded-sheet topologies. The recent advances in additive manufacturing (AM) or 3D printing process allow lattice core configurations to be designed with improved mechanical properties. In this work, the sandwich core is comprised of lattice truss structures (LTS). Two different LTS designs are 3D-printed using acrylonitrile butadiene styrene (ABS) and are tested under low-velocity impact loads. The absorption energy and the failure mechanisms of lattice cells under such loads are investigated. The differences in energy-absorption capabilities are captured by integrating the load-displacement curve found from the impact response. It is observed that selective placement of vertical support struts in the unit-cell results in an increase in the absorption energy of the sandwich panels.

Low-Velocity Impact Behavior of Sandwich Structures with Additively Manufactured Polymer Lattice Cores

NASA Astrophysics Data System (ADS)

Turner, Andrew J.; Al Rifaie, Mohammed; Mian, Ahsan; Srinivasan, Raghavan

2018-04-01

Sandwich panel structures are widely used in aerospace, marine, and automotive applications because of their high flexural stiffness, strength-to-weight ratio, good vibration damping, and low through-thickness thermal conductivity. These structures consist of solid face sheets and low-density cellular core structures, which are traditionally based upon honeycomb folded-sheet topologies. The recent advances in additive manufacturing (AM) or 3D printing process allow lattice core configurations to be designed with improved mechanical properties. In this work, the sandwich core is comprised of lattice truss structures (LTS). Two different LTS designs are 3D-printed using acrylonitrile butadiene styrene (ABS) and are tested under low-velocity impact loads. The absorption energy and the failure mechanisms of lattice cells under such loads are investigated. The differences in energy-absorption capabilities are captured by integrating the load-displacement curve found from the impact response. It is observed that selective placement of vertical support struts in the unit-cell results in an increase in the absorption energy of the sandwich panels.

Quanty for core level spectroscopy - excitons, resonances and band excitations in time and frequency domain

NASA Astrophysics Data System (ADS)

Haverkort, Maurits W.

2016-05-01

Depending on the material and edge under consideration, core level spectra manifest themselves as local excitons with multiplets, edge singularities, resonances, or the local projected density of states. Both extremes, i.e., local excitons and non-interacting delocalized excitations are theoretically well under control. Describing the intermediate regime, where local many body interactions and band-formation are equally important is a challenge. Here we discuss how Quanty, a versatile quantum many body script language, can be used to calculate a variety of different core level spectroscopy types on solids and molecules, both in the frequency as well as the time domain. The flexible nature of Quanty allows one to choose different approximations for different edges and materials. For example, using a newly developed method merging ideas from density renormalization group and quantum chemistry [1-3], Quanty can calculate excitons, resonances and band-excitations in x-ray absorption, photoemission, x-ray emission, fluorescence yield, non-resonant inelastic x-ray scattering, resonant inelastic x-ray scattering and many more spectroscopy types. Quanty can be obtained from: http://www.quanty.org.

Open cycle gas core nuclear rockets

NASA Technical Reports Server (NTRS)

Ragsdale, Robert

1991-01-01

The open cycle gas core engine is a nuclear propulsion device. Propulsion is provided by hot hydrogen which is heated directly by thermal radiation from the nuclear fuel. Critical mass is sustained in the uranium plasma in the center. It has typically 30 to 50 kg of fuel. It is a thermal reactor in the sense that fissions are caused by absorption of thermal neutrons. The fast neutrons go out to an external moderator/reflector material and, by collision, slow down to thermal energy levels, and then come back in and cause fission. The hydrogen propellant is stored in a tank. The advantage of the concept is very high specific impulse because you can take the plasma to any temperature desired by increasing the fission level by withdrawing or turning control rods or control drums.

Continuous analysis of phosphate in a Greenland shallow ice core

NASA Astrophysics Data System (ADS)

Kjær, Helle Astrid; Svensson, Anders; Bigler, Matthias; Vallelonga, Paul; Kettner, Ernesto; Dahl-Jensen, Dorthe

2010-05-01

Phosphate is an important and sometimes limiting nutrient for primary production in the oceans. Because of deforestation and the use of phosphate as a fertilizer changes in the phosphate cycle have occurred over the last centuries. On longer time scales, sea level changes are thought to have also caused changes in the phosphate cycle. Analyzing phosphate concentrations in ice cores may help to gain important knowledge about those processes. In the present study, we attach a phosphate detection line to an existing continuous flow analysis (CFA) setup for ice core analysis at the University of Copenhagen. The CFA system is optimized for high-resolution measurements of insoluble dust particles, electrolytic melt water conductivity, and the concentrations of ammonium and sodium. For the phosphate analysis we apply a continuous and highly sensitive absorption method that has been successfully applied to determine phosphate concentrations of sea water (Zhang and Chi, 2002). A line of melt water from the CFA melt head (1.01 ml per minute) is combined with a molybdate blue reagent and an ascorbic acid buffer. An uncompleted reaction takes place in five meters of heated mixing coils before the absorption measurement at a wavelength of 710 nanometer takes place in a 2 m long liquid waveguide cell (LWCC) with an inner volume of 0.5 ml. The method has a detection limit of around 0.1 ppb and we are currently investigating a possible interference from molybdate reacting with silicates that are present in low amounts in the ice. Preliminary analysis of early Holocene samples from the NGRIP ice core show phosphate concentration values of a few ppb. In this study, we will attempt to determine past levels of phosphate in a shallow Northern Greenland firn core with an annual layer thickness of about 20 cm ice equivalent. With a melt speed of 2.5 cm ice per minute our method should allow the resolution of any seasonal variability in phosphate concentrations.

Cloaks for suppression or enhancement of scattering of diffuse photon density waves

NASA Astrophysics Data System (ADS)

Renthlei, Lalruatfela; Ramakrishna, S. Anantha; Wanare, Harshawardhan

2018-07-01

Enhancement of wave-like characteristics of heavily damped diffuse photon density waves in a random medium by amplification can induce strongly localised resonances. These resonances can be used to either suppress or enhance scattering from an inhomogeneity in the random medium by cloaking the inhomogeneous region by a shell of random medium with the correct levels of absorption or amplification. A spherical core-shell structure consisting of a shell of a random amplifying medium is shown to enhance or suppress specific resonant modes. A shell with an absorbing random medium is also shown to suppress scattering which can also be used for cloaking the core region.

Electronic structure and intersubband magnetoabsorption spectra of CdSe/CdS core-shell nanowires

NASA Astrophysics Data System (ADS)

Xiong, Wen

2016-10-01

The electronic structures of CdSe/CdS core-shell nanowires are calculated based on the effective-mass theory, and it is found that the hole states in CdSe/CdS core-shell nanowires are strongly mixed, which are very different from the hole states in CdSe or CdS nanowires. In addition, we find the three highest hole states at the Γ point are almost localized in the CdSe core and the energies of the hole states in CdSe/CdS core-shell nanowires can be enhanced greatly when the core radius Rc increases and the total radius R is fixed. The degenerate hole states are split by the magnetic field, and the split energies will increase when |Jh | increases from 1/2 to 7/2, while they are almost not influenced by the change of the core radius Rc. The absorption spectra of CdSe/CdS core-shell nanowires at the Γ point are also studied in the magnetic field when the temperature T is considered, and we find there are only two peaks will arise if the core radius Rc and the temperature T increase. The intensity of each optical absorption can be considerably enhanced by increasing the core radius Rc when the temperature T is fixed, it is due to the increase of their optical transition matrix element. Meanwhile, the intensity of each optical absorption can be decreased when the temperature T increases and the core radius Rc is fixed, and this is because the Fermi-Dirac distribution function of the corresponding hole states will increase as the increase of the temperature T.

Ultrafast Transient Absorption Spectroscopy Investigation of Photoinduced Dynamics in Novel Donor-Acceptor Core-Shell Nanostructures for Organic Photovoltaics

NASA Astrophysics Data System (ADS)

Strain, Jacob; Jamhawi, Abdelqader; Abeywickrama, Thulitha M.; Loomis, Wendy; Rathnayake, Hemali; Liu, Jinjun

2016-06-01

Novel donor-acceptor nanostructures were synthesized via covalent synthesis and/or UV cross-linking method. Their photoinduced dynamics were investigated with ultrafast transient absorption (TA) spectroscopy. These new nanostructures are made with the strategy in mind to reduce manufacturing steps in the process of fabricating an organic photovoltaic cell. By imitating the heterojunction interface within a fixed particle domain, several fabrication steps can be bypassed reducing cost and giving more applicability to other film deposition methods. Such applications include aerosol deposition and ink-jet printing. The systems that were studied by TA spectroscopy include PDIB core, PDIB-P3HT core-shell, and PDIB-PANT core-shell which range in size from 60 to 130 nm. Within the experimentally accessible spectra range there resides a region of ground state bleaching, stimulated emission, and excited-state absorption of both neutrals and anions. Control experiments have been carried out to assign these features. At high pump fluences the TA spectra of PDIB core alone also indicate an intramolecular charge separation. The TA spectroscopy results thus far suggest that the core-shells resemble the photoinduced dynamics of a standard film although the particles are dispersed in solution, which indicates the desired outcome of the work.

Low-Cost Carbothermal Reduction Preparation of Monodisperse Fe3O4/C Core-Shell Nanosheets for Improved Microwave Absorption.

PubMed

Liu, Yun; Fu, Yiwei; Liu, Lin; Li, Wei; Guan, Jianguo; Tong, Guoxiu

2018-05-16

This paper demonstrates a facile and low-cost carbothermal reduction preparation of monodisperse Fe 3 O 4 /C core-shell nanosheets (NSs) for greatly improved microwave absorption. In this protocol, the redox reaction between sheet-like hematite (α-Fe 2 O 3 ) precursors and acetone under inert atmosphere and elevated temperature generates Fe 3 O 4 /C core-shell NSs with the morphology inheriting from α-Fe 2 O 3 . Thus, Fe 3 O 4 /C core-shell NSs of different sizes ( a) and Fe 3 O 4 /C core-shell nanopolyhedrons are obtained by using different precursors. Benefited from the high crystallinity of the Fe 3 O 4 core and the thin carbon layer, the resultant NSs exhibit high specific saturation magnetization larger than 82.51 emu·g -1 . Simultaneously, the coercivity enhances with the increase of a, suggesting a strong shape anisotropy effect. Furthermore, because of the anisotropy structure and the complementary behavior between Fe 3 O 4 and C, the as-obtained Fe 3 O 4 /C core-shell NSs exhibit strong natural magnetic resonance at a high frequency, enhanced interfacial polarization, and improved impedance matching, ensuring the enhancement of the microwave absorption. The 250 nm NSs-paraffin composites exhibit reflection loss (RL) lower than -20 dB (corresponding to 99% absorption) in a large frequency ( f) range of 2.08-16.40 GHz with a minimum RL of -43.95 dB at f = 3.92 GHz when the thickness is tuned from 7.0 to 1.4 mm, indicating that the Fe 3 O 4 /C core-shell NSs are a good candidate to manufacture high-performance microwave absorbers. Moreover, the as-developed carbothermal reduction method could be applied for the fabrication of other composites based on ferrites and carbon.

Biopharmaceutical evaluation of time-controlled press-coated tablets containing polymers to adjust drug release.

PubMed

Halsas, M; Ervasti, P; Veski, P; Jürjenson, H; Marvola, M

1998-01-01

This paper deals with press-coated modified release tablets in which the drug dose is situated in the core or is divided between the core and the coat. The coat contains polymer (sodium alginate or hydroxypropylmethyl cellulose, HPMC) to control drug release. The main objective was to investigate how the pharmacokinetic profile of the model drug could be modified by altering the proportion of the drug between the core and the coat. The effect of the amount of the polymer in the coat was also studied. Bioavailability tests were carried out on healthy volunteers. In the absorption curves of the tablets containing 50%, 67% and 80% of the drug in the core and 180 mg HPMC in the coat a bimodal profile was observed. No bimodal release pattern in the in vitro dissolution studies was found. If the whole dose was incorporated in the core the absorption curve has only one clear t(max) value at about 10 h. Doubling the amount of HPMC in the coat dramatically decreased drug absorption. It was concluded that, if a slightly reduced t(max)-value was required, the viscosity grade of HPMC used should be lowered.

Electronic structure and fundamental absorption edges of KPb2Br5, K0.5Rb0.5Pb2Br5, and RbPb2Br5 single crystals

NASA Astrophysics Data System (ADS)

Tarasova, A. Yu.; Isaenko, L. I.; Kesler, V. G.; Pashkov, V. M.; Yelisseyev, A. P.; Denysyuk, N. M.; Khyzhun, O. Yu.

2012-05-01

X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated (001) surfaces of KPb2Br5, K0.5Rb0.5Pb2Br5, and RbPb2Br5 single crystals grown by the Bridgman method have been measured and fundamental absorption edges of the ternary bromides have been recorded in the polarized light at 300 K and 80 K. The present X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of (001) surfaces of KxRb1-xPb2Br5 (x=0, 0.5, and 1.0) single crystals. Substitution of potassium for rubidium in KxRb1-xPb2Br5 does not cause any changes of binding energy values and shapes of the XPS constituent element core-level spectra. Measurements of the fundamental absorption edges indicate that band gap energy, Eg, increases by about 0.14 and 0.19 eV when temperature decreases from 300 K to 80 K in KPb2Br5 and RbPb2Br5, respectively. Furthermore, there is no dependence of the Eg value for KPb2Br5 upon the light polarization, whilst the band gap energy value for RbPb2Br5 is bigger by 0.03-0.05 eV in the case of E‖c compared to those in the cases of E‖a and E‖b.

Disentangling atomic-layer-specific x-ray absorption spectra by Auger electron diffraction spectroscopy

NASA Astrophysics Data System (ADS)

Matsui, Fumihiko; Matsushita, Tomohiro; Kato, Yukako; Hashimoto, Mie; Daimon, Hiroshi

2009-11-01

In order to investigate the electronic and magnetic structures of each atomic layer at subsurface, we have proposed a new method, Auger electron diffraction spectroscopy, which is the combination of x-ray absorption spectroscopy (XAS) and Auger electron diffraction (AED) techniques. We have measured a series of Ni LMM AED patterns of the Ni film grown on Cu(001) surface for various thicknesses. Then we deduced a set of atomic-layer-specific AED patterns in a numerical way. Furthermore, we developed an algorithm to disentangle XANES spectra from different atomic layers using these atomic-layer-specific AED patterns. Surface and subsurface core level shift were determined for each atomic layer.

Measuring Moisture Levels in Graphite Epoxy Composite Sandwich Structures

NASA Technical Reports Server (NTRS)

Nurge, Mark; Youngquist, Robert; Starr, Stanley

2011-01-01

Graphite epoxy composite (GEC) materials are used in the construction of rocket fairings, nose cones, interstage adapters, and heat shields due to their high strength and light weight. However, they absorb moisture depending on the environmental conditions they are exposed to prior to launch. Too much moisture absorption can become a problem when temperature and pressure changes experienced during launch cause the water to vaporize. The rapid state change of the water can result in structural failure of the material. In addition, heat and moisture combine to weaken GEC structures. Diffusion models that predict the total accumulated moisture content based on the environmental conditions are one accepted method of determining if the material strength has been reduced to an unacceptable level. However, there currently doesn t exist any field measurement technique to estimate the actual moisture content of a composite structure. A multi-layer diffusion model was constructed with Mathematica to predict moisture absorption and desorption from the GEC sandwich structure. This model is used in conjunction with relative humidity/temperature sensors both on the inside and outside of the material to determine the moisture levels in the structure. Because the core materials have much higher diffusivity than the face sheets, a single relative humidity measurement will accurately reflect the moisture levels in the core. When combined with an external relative humidity measurement, the model can be used to determine the moisture levels in the face sheets. Since diffusion is temperaturedependent, the temperature measurements are used to determine the diffusivity of the face sheets for the model computations.

Probing Chemical Bonding in Uranium Dioxide by Means of High-Resolution X-ray Absorption Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butorin, Sergei M.; Modin, Anders; Vegelius, Johan R.

Here, a systematic X-ray absorption study at the U 3d, 4d, and 4f edges of UO 2 was performed, and the data were analyzed within framework of the Anderson impurity model. By applying the high-energy-resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS) at the U 3d 3/2 edge and conducting the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved resulting from reduced core-hole lifetime broadening. This multiedge study enabled a far more effective analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree ofmore » the 5f localization in UO 2. The results support the covalent character of UO 2 and do not agree with the suggestions of rather ionic bonding in this compound as expressed in some publications.« less

Probing Chemical Bonding in Uranium Dioxide by Means of High-Resolution X-ray Absorption Spectroscopy

DOE PAGES

Butorin, Sergei M.; Modin, Anders; Vegelius, Johan R.; ...

2016-11-30

Here, a systematic X-ray absorption study at the U 3d, 4d, and 4f edges of UO 2 was performed, and the data were analyzed within framework of the Anderson impurity model. By applying the high-energy-resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS) at the U 3d 3/2 edge and conducting the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved resulting from reduced core-hole lifetime broadening. This multiedge study enabled a far more effective analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree ofmore » the 5f localization in UO 2. The results support the covalent character of UO 2 and do not agree with the suggestions of rather ionic bonding in this compound as expressed in some publications.« less

Two-photon absorption in SiO{sub 2}- and (SiO{sub 2} + GeO{sub 2})-based fibres at a wavelength of 349 nm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chunaev, D S; Karasik, A Ya

2014-06-30

The nonlinear two-photon light absorption coefficients have been measured in an optical fibre with a quartz glass (SiO{sub 2}) core and in a fibre with a germanosilicate glass (SiO{sub 2} + GeO{sub 2}) core. The two-photon absorption coefficient β measured at a wavelength of 349 nm in the (SiO{sub 2} + GeO{sub 2})-based fibre (13.7 cm TW{sup -1}) multiply exceeds that for the pure quartz glass optical fibre (0.54 cm TW{sup -1}). (nonlinear optical phenomena)

Scrutiny of the Core of the Galactic Center by H_3^+ and Co: Gcirs 3 and Gcirs 1W

NASA Astrophysics Data System (ADS)

Goto, M.; Usuda, T.; Geballe, T. R.; Indriolo, N.; McCall, B. J.; Oka, T.

2011-06-01

Out of the over two dozen sightlines toward the Central Molecular Zone of the Galactic center so far observed by infrared spectra of H_3^+ and CO, sightlines toward GCIRS 3 and Iota stand out as exceptional since they show cloud components with clear R(2,2)^l absorption indicating that their unstable (J,K) = (2,2) levels are well populated. Those two sightlines toward the Galactic core and Sgr B, respectively, must pass through hot and dense gas. The cloud component at ˜ 60 km S-1 toward GCIRS 3 is particularly intriguing since GCIRS 1W, which is separated from it only by 5".8 (0.23 pc if the same distance to the Galactic center of 8 k pc is assumed), barely shows the R(2,2)^l absorption. The cloud must be compact and this calls for a high ionization rate. To further study this problem the sightlines toward GCIRS 3 and GCIRS 1W have been observed by VLT under high spectral resolution. The observed R(3,3)^l absorption is extraordinarily deep and the R(2,2)^l absorption is clearly observable at ˜ 60 km S-1 for GCIRS 3 indicating unusually high temperature and high density of the cloud. In contrast, toward GCIRS 1W, the R(3,3)^l absorption is of ordinary depth and the R(2,2)^l absorptions is marginal if any indicating the well known warm and diffuse gas observed toward other regions of the Central Molecular Zone. Their analysis and comparison with radio HCN emission observed in the area will be discussed. M. Goto, T. Usuda, T. Nagata, T. R. Geballe, B. J. McCall, N. Indriolo, H. Suto, Th. Henning, C. P. Morong, and T. Oka, ApJ, 688, 306 (2008). Goto, Usuda, Geballe, Indriolo, McCall, Henning, Oka, PASJ (2011) in press.

Evolution of wavelength-dependent mass absorption cross sections of carbonaceous aerosols during the 2010 DOE CARES campaign

NASA Astrophysics Data System (ADS)

Flowers, B. A.; Dubey, M. K.; Subramanian, R.; Sedlacek, A. J.; Kelley, P.; Luke, W. T.; Jobson, B. T.; Zaveri, R. A.

2011-12-01

Predictions of aerosol radiative forcing require process level optical property models that are built on precise and accurate field observations. Evolution of aerosol optical properties for urban influenced carbonaceous aerosol undergoing transport and mixing with rural air masses was a focal point of the DOE Carbonaceous Aerosol and Radiative Effects (CARES) campaign near Sacramento, CA in summer 2010. Urban aerosol was transported from Sacramento, CA (T0) to the foothills of the Sierra Nevada Mountains to a rural site located near Cool, CA (T1). Aerosol absorption and scattering coefficients were measured at the T0 and T1 sites using integrated photoacoustic acoustic/nephelometer instruments (PASS-3 and PASS-UV) at 781, 532, 405, and 375 nm. Single particle soot photometry (SP2) instrumentation was used to monitor black carbon (BC) mass at both sites. Combining data from these sensors allows estimate of the wavelength-dependent mass absorption coefficient (MAC(λ)) and partitioning of MAC(λ) into contributions from the BC core and from enhancements from coating of BC cores. MAC(λ) measured in this way is free of artifacts associated with filter-based aerosol absorption measurements and takes advantage of the single particle sensitivity of the SP2 instrument, allowing observation of MAC(λ) on 10 minute and faster time scales. Coating was observed to enhance MAC(λ) by 20 - 30 % and different wavelength dependence for MAC(λ) was observed for urban and biomass burning aerosol. Further, T0 - T1 evolution of MAC(λ) was correlated with separately measured NO/NOy ratios and CO/CO2 ratios to understand the effects of aging & transport on MAC(λ) and the implications of aerosol processing that links air quality to radiative forcing on a regional scale. Aircraft observations made from the Gulfstream-1 during CARES are also analyzed to enhance process level understanding of the optical properties of fresh and aged carbonaceous aerosol in the urban-rural interface.

Synthesis, photophysical, structural and electronic properties of novel regioisomerically pure 1,7-disubstituted perylene-3,4,9,10-tetracarboxylic monoimide dibutylester derivatives

NASA Astrophysics Data System (ADS)

Ozser, Mustafa E.; Mohiuddin, Obaidullah

2018-04-01

Three new isomerically pure 1,7-disubstituted perylene-3,4,9,10-tetracarboxylic monoimide dibutylester derivatives namely; N-[2-(diethylamino)ethyl]-1,7-dibromoperylene-3,4,9,10-tetracarboxy monoimide dibutylester (PMD-1), N-[2-(diethylamino)ethyl]-1,7-di(4-tert-butylphenoxy)perylene-3,4,9,10-tetracarboxy monoimide dibutylester (PMD-2) and N-[2-(diethylamino)ethyl]-1,7-di(pyrrolidinyl)perylene-3,4,9,10-tetracarboxy monoimide dibutylester (PMD-3), have been synthesized and their electronic absorption spectra, and steady-state fluorescence were investigated experimentally as well as by using density functional theory (DFT) calculations. All three compounds show good solubility in toluene and chloroform. Attachment of two tert-butylphenoxy groups at the 1,7-positions in PMD-2 resulted in a red shifted absorption band with an absorption maximum at 518 nm. UV/Vis absorption spectrum of PMD-3 bearing electron donating pyrrolidinyl groups at the 1,7-positions shows a broad absorption band within the visible region, extending to red region. Absorption maximum of lowest energy transition now shifts to 653 nm. In addition to the S0 → S1 absorption bands, bands belonging to S0 → S2 electronic transitions were observed at 378, 386, and 411 nm for PMD-1, PMD-2, and PMD-3 respectively. Compounds PMD-1, PMD-2 and PMD-3 display low fluorescence quantum yields of 0.027, 0.040 and 0.001, respectively in chloroform. DFT calculations revealed that the attachment of electron donating groups at 1,7-positions of perylene core, results in an increase in frontier orbitals energy levels. Observed energy increase in HOMO level is larger in each case, compared to the energy increase in LUMO levels, due to the higher contribution of side groups to HOMO. DFT calculated band gaps for PMD-1, PMD-2 and PMD-3 are 2.68, 2.63 and 2.29 eV respectively.

Natural circular dichroism in non-resonant x-ray emission

NASA Astrophysics Data System (ADS)

Vahtras, Olav; Ågren, Hans; Carravetta, Vincenzo

1997-03-01

The possibility of observing natural circular dichroism in non-resonant x-ray emission spectroscopy is investigated by means of simulations of the chiral molecules twisted ethylene, propylene oxide and trans-1, 2-dimethylcyclopropane, in a two-step model and at the SCF level, with or without relaxation of the core-hole states. We observe both a chemical and an element dependence of the phenomenon and also an effect of electron relaxation. However, the latter is much less crucial than for circular dichroism in x-ray absorption. The calculations indicate that, at least for the decay of the carbon core-hole states, the effect could be detectable with the present or soon to be available experimental equipment.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bogdanov, Nikolay A.; Bisogni, Valentina; Kraus, Roberto

In existing theoretical approaches to core-level excitations of transition-metal ions in solids relaxation and polarization effects due to the inner core hole are often ignored or described phenomenologically. Here, we set up an ab initio computational scheme that explicitly accounts for such physics in the calculation of x-ray absorption and resonant inelastic x-ray scattering spectra. Good agreement is found with experimental transition-metal L-edge data for the strongly correlated d 9 cuprate Li 2CuO 2, for which we also determine the absolute scattering intensities. The newly developed methodology opens the way for the investigation of even more complex d n electronicmore » structures of group VI B to VIII B correlated oxide compounds.« less

Efficient implementation of core-excitation Bethe-Salpeter equation calculations

NASA Astrophysics Data System (ADS)

Gilmore, K.; Vinson, John; Shirley, E. L.; Prendergast, D.; Pemmaraju, C. D.; Kas, J. J.; Vila, F. D.; Rehr, J. J.

2015-12-01

We present an efficient implementation of the Bethe-Salpeter equation (BSE) method for obtaining core-level spectra including X-ray absorption (XAS), X-ray emission (XES), and both resonant and non-resonant inelastic X-ray scattering spectra (N/RIXS). Calculations are based on density functional theory (DFT) electronic structures generated either by ABINIT or QuantumESPRESSO, both plane-wave basis, pseudopotential codes. This electronic structure is improved through the inclusion of a GW self energy. The projector augmented wave technique is used to evaluate transition matrix elements between core-level and band states. Final two-particle scattering states are obtained with the NIST core-level BSE solver (NBSE). We have previously reported this implementation, which we refer to as OCEAN (Obtaining Core Excitations from Ab initio electronic structure and NBSE) (Vinson et al., 2011). Here, we present additional efficiencies that enable us to evaluate spectra for systems ten times larger than previously possible; containing up to a few thousand electrons. These improvements include the implementation of optimal basis functions that reduce the cost of the initial DFT calculations, more complete parallelization of the screening calculation and of the action of the BSE Hamiltonian, and various memory reductions. Scaling is demonstrated on supercells of SrTiO3 and example spectra for the organic light emitting molecule Tris-(8-hydroxyquinoline)aluminum (Alq3) are presented. The ability to perform large-scale spectral calculations is particularly advantageous for investigating dilute or non-periodic systems such as doped materials, amorphous systems, or complex nano-structures.

Blast protection of infrastructure using advanced composites

NASA Astrophysics Data System (ADS)

Brodsky, Evan

This research was a systematic investigation detailing the energy absorption mechanisms of an E-glass web core composite sandwich panel subjected to an impulse loading applied orthogonal to the facesheet. Key roles of the fiberglass and polyisocyanurate foam material were identified, characterized, and analyzed. A quasi-static test fixture was used to compressively load a unit cell web core specimen machined from the sandwich panel. The web and foam both exhibited non-linear stress-strain responses during axial compressive loading. Through several analyses, the composite web situated in the web core had failed in axial compression. Optimization studies were performed on the sandwich panel unit cell in order to maximize the energy absorption capabilities of the web core. Ultimately, a sandwich panel was designed to optimize the energy dissipation subjected to through-the-thickness compressive loading.

Perforated hollow-core optical waveguides for on-chip atomic spectroscopy and gas sensing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giraud-Carrier, M., E-mail: mgeecee@byu.edu; Hill, C.; Decker, T.

2016-03-28

A hollow-core waveguide structure for on-chip atomic spectroscopy is presented. The devices are based on Anti-Resonant Reflecting Optical Waveguides and may be used for a wide variety of applications which rely on the interaction of light with gases and vapors. The designs presented here feature short delivery paths of the atomic vapor into the hollow waveguide. They also have excellent environmental stability by incorporating buried solid-core waveguides to deliver light to the hollow cores. Completed chips were packaged with an Rb source and the F = 3 ≥ F′ = 2, 3, 4 transitions of the D2 line in {sup 85}Rb were monitored formore » optical absorption. Maximum absorption peak depths of 9% were measured.« less

Linear and nonlinear magneto-optical properties of an off-center single dopant in a spherical core/shell quantum dot

NASA Astrophysics Data System (ADS)

Feddi, E.; Talbi, A.; Mora-Ramos, M. E.; El Haouari, M.; Dujardin, F.; Duque, C. A.

2017-11-01

Using the effective mass approximation and a variational procedure, we have investigated the nonlinear optical absorption coefficient and the relative refractive index changes associated to a single dopant confined in core/shell quantum dots considering the influences of the core/shell dimensions, externally applied magnetic field, and dielectric mismatch. The results show that the optical absorption coefficient and the coefficients of relative refractive index change depend strongly on the core/shell sizes and they are blue shifted when the spatial confinement increases so this effect is magnified by higher structural dimensions. Additionally, it is obtained that both studied optical properties are sensitive to the dielectric environment in such a way that their amplitudes are very affected by the local field corrections.

Comparison of experimental and modeled absorption enhancement by black carbon (BC) cored polydisperse aerosols under hygroscopic conditions.

PubMed

Shamjad, P M; Tripathi, S N; Aggarwal, S G; Mishra, S K; Joshi, Manish; Khan, Arshad; Sapra, B K; Ram, Kirpa

2012-08-07

The quantification of the radiative impacts of light absorbing ambient black carbon (BC) particles strongly depends on accurate measurements of BC mass concentration and absorption coefficient (β(abs)). In this study, an experiment has been conducted to quantify the influence of hygroscopic growth of ambient particles on light absorption. Using the hygroscopic growth factor (i.e., Zdanovskii-Stokes-Robinson (ZSR) approach), a model has been developed to predict the chemical composition of particles based on measurements, and the absorption and scattering coefficients are derived using a core-shell assumption with light extinction estimates based on Mie theory. The estimated optical properties agree within 7% for absorption coefficient and 30% for scattering coefficient with that of measured values. The enhancement of absorption is found to vary according to the thickness of the shell and BC mass, with a maximum of 2.3 for a shell thickness of 18 nm for the particles. The findings of this study underline the importance of considering aerosol-mixing states while calculating their radiative forcing.

The nature of the Fe–graphene interface at the nanometer level

DOE PAGES

Cattelan, M.; Peng, G. W.; Cavaliere, E.; ...

2014-12-22

The emerging fields of graphene-based magnetic and spintronic devices require a deep understanding of the interface between graphene and ferromagnetic metals. This paper reports a detailed investigation at the nanometer level of the Fe–graphene interface carried out by angle-resolved photoemission, high-resolution photoemission from core levels, near edge X-ray absorption fine structure, scanning tunnelling microscopy and spin polarized density functional theory calculations. Quasi-free-standing graphene was grown on Pt(111), and the iron film was either deposited atop or intercalated beneath graphene. Here, calculations and experimental results show that iron strongly modifies the graphene band structure and lifts its π band spin degeneracy.

Designing of an artificial light energy converter in the form of short-chain dyad when combined with core-shell gold/silver nanocomposites.

PubMed

Dutta Pal, Gopa; Paul, Somnath; Bardhan, Munmun; De, Asish; Ganguly, Tapan

2017-06-05

UV-vis absorption, steady state and time resolved fluorescence and absorption spectroscopic investigations demonstrate that the short chain dyad MNTMA when combined with gold-silver core-shell (Au@Ag) nanocomposite , forms elongated conformers in the excited state whereas for the dyad - Ag (spherical) system the majority of dyads remains in a folded conformation. In the dyad-core-shell nanocomposite system, energy wasting charge recombination rate slows down primarily due to elongated conformation and thus it may be anticipated that this hybrid nanocomposite system may serve as a better light energy conversion device. Copyright © 2017 Elsevier B.V. All rights reserved.

Numerical Investigation on Absorption Enhancement of Black Carbon Aerosols Partially Coated With Nonabsorbing Organics

NASA Astrophysics Data System (ADS)

Zhang, Xiaolin; Mao, Mao; Yin, Yan; Wang, Bin

2018-01-01

This study numerically evaluates the effects of aerosol microphysics, including coated volume fraction of black carbon (BC), shell/core ratio, and size distribution, on the absorption enhancement (Eab) of polydisperse BC aggregates partially coated by organics, which is calculated by the exact multiple-sphere T-matrix method. The coated volume fraction of BC plays a substantial role in determining the absorption enhancement of partially coated BC aggregates, which typically have an Eab in the range of 1.0-2.0 with a larger value for larger coated volume fraction of BC as the shell/core ratio, BC geometry, and size distribution are fixed. The shell/core ratio, BC geometry, and size distribution have little impact on the Eab of coated BC with small coated volume fraction of BC, while they become significant for large coated volume fraction of BC. The Eab of partially coated BC particles can be slightly less than 1.0 for the large BC in the accumulation mode exhibiting large shell/core ratio and small coated volume fraction of BC, indicating that the absorption shows even slight decrease relative to uncoated BC particles. For partially coated BC aggregates in the accumulation and coarse modes, the refractive index uncertainties of BC result in the Eab differences of less than 9% and 2%, respectively, while those of organics can induce larger variations with the maximum differences up to 22% and 18%, respectively. Our study indicates that accounting for particle coating microphysics, particularly the coated volume fraction of BC, can potentially help to understand the differences in observations of largely variable absorption enhancements over various regions.

Transmission Electron Microscopy and Scanning Transmission X-Ray Microscopy Studies on the Bioaccumulation and Tissue Level Absorption of TiO2 Nanoparticles in Daphnia magna.

PubMed

Kwon, Dongwook; Nho, Hyun Woo; Yoon, Tae Hyun

2015-06-01

In this study, bioaccumulation and tissue-level absorption of TiO2 nanoparticles (NPs) in freshwater invertebrates were investigated using transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM). The TiO2 NPs were used to test impacts of core sizes (i.e., 5 ± 2 nm and 23 ± 7 nm for TiO2(SYN) and TiO2(P25), respectively) and agglomerations (i.e., well dispersed vs. highly agglomerated) on the uptake of TiO2 NPs in Daphnia magna (D. magna). Highly agglomerated TiO2 NPs, regardless of their core sizes, were heavily taken up into the digestive tract of D. magna and no detectable penetration of both TiO2 NPs into the gut epithelial cells of D. magna was observed in TEM and STXM images. However, significant damages involving morphological changes in the microvilli and gut epithelial cells (e.g., irregular shaped microvilli, epithelial cell protrusion, and dilatation of cytoplasmic inclusion) were observed only with the commercial TiO2 NPs (TiO2(P25)) with larger core size and mixed crystalline phase, while the laboratory synthesized TiO2 NPs (TiO2(Syn)) with smaller core size and single crystalline phase showed slight morphological changes in the gut microvilli and epithelial cells. In the case of D. magna exposed to the well dispersed synthetic TiO2 NP ((Cit)TiO2(Syn)), only a negligible amount of TiO2 NPs were found within the digestive tract of the D. magna without any significant damages in the gut microvilli and epithelial cells and any detectable penetrations of TiO2 NPs into epithelial cells of D. magna gut. These TEM and STXM observations confirmed us that uptake of NP into D. magna are strongly dependent on their agglomeration (i.e., hydrodynamic sizes), rather than their core sizes, while direct penetration of NPs into tissues of digestive tract seems unlikely without significant morphological changes (e.g., collapse of the epithelial tissue) caused by high toxicity of NPs or released metal ions.

Core-shell nanophosphor architecture: toward efficient energy transport in inorganic/organic hybrid solar cells.

PubMed

Li, Qinghua; Yuan, Yongbiao; Chen, Zihan; Jin, Xiao; Wei, Tai-huei; Li, Yue; Qin, Yuancheng; Sun, Weifu

2014-08-13

In this work, a core-shell nanostructure of samarium phosphates encapsulated into a Eu(3+)-doped silica shell has been successfully fabricated, which has been confirmed by X-ray diffraction, transmission electron microscopy (TEM), and high-resolution TEM. Moreover, we report the energy transfer process from the Sm(3+) to emitters Eu(3+) that widens the light absorption range of the hybrid solar cells (HSCs) and the strong enhancement of the electron-transport of TiO2/poly(3-hexylthiophene) (P3HT) bulk heterojunction (BHJ) HSCs by introducing the unique core-shell nanoarchitecture. Furthermore, by applying femtosecond transient absorption spectroscopy, we successfully obtain the electron transport lifetimes of BHJ systems with or without incorporating the core-shell nanophosphors (NPs). Concrete evidence has been provided that the doping of core-shell NPs improves the efficiency of electron transfers from donor to acceptor, but the hole transport almost remains unchanged. In particular, the hot electron transfer lifetime was shortened from 30.2 to 16.7 ps, i.e., more than 44% faster than pure TiO2 acceptor. Consequently, a notable power conversion efficiency of 3.30% for SmPO4@Eu(3+):SiO2 blended TiO2/P3HT HSCs is achieved at 5 wt % as compared to 1.98% of pure TiO2/P3HT HSCs. This work indicates that the core-shell NPs can efficiently broaden the absorption region, facilitate electron-transport of BHJ, and enhance photovoltaic performance of inorganic/organic HSCs.

Core@shell@shell structured carbon-based magnetic ternary nanohybrids: Synthesis and their enhanced microwave absorption properties

NASA Astrophysics Data System (ADS)

Yang, Erqi; Qi, Xiaosi; Xie, Ren; Bai, Zhongchen; Jiang, Yang; Qin, Shuijie; Zhong, Wei; Du, Youwei

2018-05-01

High encapsulation efficiency of core@shell@shell structured carbon-based magnetic ternary nanohybrids have been synthesized in high yield by chemical vapor deposition of acetylene directly over octahedral-shaped Fe2O3 nanoparticles. By controlling the pyrolysis temperature, Fe3O4@Fe3C@carbon nanotubes (CNTs) and Fe@Fe3C@CNTs ternary nanohybrids could be selectively produced. The optimal RL values for the as-prepared ternary nanohybrids could reach up to ca. -46.7, -52.7 and -29.5 dB, respectively. The excellent microwave absorption properties of the obtaiend ternary nanohybrids were proved to ascribe to the quarter-wavelength matching model. Moreover, the as-prepared Fe@Fe3C@CNTs ternary nanohybrids displayed remarkably enhanced EM wave absorption capabilities compared to Fe3O4@Fe3C@CNTs due to their excellent dielectric loss abilities, good complementarities between the dielectric loss and the magnetic loss, and high attenuation constant. Generally, this strategy can be extended to explore other categories of core@shell or core@shell@shell structured carbon-based nanohybrids, which is very beneficial to accelerate the advancements of high performance MAMs.

Spectral and kinetic effects accompanying the assembly of core complexes of Rhodobacter sphaeroides.

PubMed

Freiberg, Arvi; Chenchiliyan, Manoop; Rätsep, Margus; Timpmann, Kõu

2016-11-01

In the present work, spectral and kinetic changes accompanying the assembly of the light-harvesting 1 (LH1) complex with the reaction center (RC) complex into monomeric RC-LH1 and dimeric RC-LH1-PufX core complexes of the photosynthetic purple bacterium Rhodobacter sphaeroides are systematically studied over the temperature range of 4.5-300K. The samples were interrogated with a combination of optical absorption, hole burning, fluorescence excitation, steady state and picosecond time resolved fluorescence spectroscopy. Fair additivity of the LH1 and RC absorption spectra suggests rather weak electronic coupling between them. A low-energy tail revealed at cryogenic temperatures in the absorption spectra of both monomeric and dimeric core complexes is proved to be due to the special pair of the RC. At selected excitation intensity and temperature, the fluorescence decay time of core complexes is shown to be a function of multiple factors, most importantly of the presence/absence of RCs, the supramolecular architecture (monomeric or dimeric) of the complexes, and whether the complexes were studied in a native membrane environment or in a detergent - purified state. Copyright © 2016 Elsevier B.V. All rights reserved.

Hollow-core photonic-crystal-fiber-based optical frequency references

NASA Astrophysics Data System (ADS)

Holá, Miroslava; Hrabina, Jan; Mikel, Břetislav; Lazar, Josef; Číp, Ondřej

2016-12-01

This research deals with preparation of an optical frequency references based on hollow-core photonic crystal fibers (HC-PCF). This fiber-based type of absorption cells represents a effiecient way how to replace classic bulky and fragile glass made tubes references with low-weight and low-volume optical fibers. This approach allows not only to increase possible interaction length between incident light and absorption media but it also carries a possibility of manufacturing of easy-operable reference which is set up just by plugging-in of optical connectors into the optical setup. We present the results of preparation, manufacturing and filling of a set of fiber-based cells intended for lasers frequency stabilization. The work deals with setting and optimalization of HC-PCF splicing processes, minimalization of optical losses between HC-PCF and SMF fiber transitions and finishing of HC-PCF spliced ends with special care for optimal closing of hollow-core structure needed for avoiding of absorption media leakage.

Exchange coupling and microwave absorption in core/shell-structured hard/soft ferrite-based CoFe2O4/NiFe2O4 nanocapsules

NASA Astrophysics Data System (ADS)

Feng, Chao; Liu, Xianguo; Or, Siu Wing; Ho, S. L.

2017-05-01

Core/shell-structured, hard/soft spinel-ferrite-based CoFe2O4/NiFe2O4 (CFO/NFO) nanocapsules with an average diameter of 17 nm are synthesized by a facile two-step hydrothermal process using CFO cores of ˜15 nm diameter as the hard magnetic phase and NFO shells of ˜1 nm thickness as the soft magnetic phase. The single-phase-like hysteresis loop with a high remnant-to-saturation magnetization ratio of 0.7, together with a small grain size of ˜16 nm, confirms the existence of exchange-coupling interaction between the CFO cores and the NFO shells. The effect of hard/soft exchange coupling on the microwave absorption properties is studied. Comparing to CFO and NFO nanoparticles, the finite-size NFO shells and the core/shell structure enable a significant reduction in electric resistivity and an enhancement in dipole and interfacial polarizations in the CFO/NFO nanocapsules, resulting in an obvious increase in dielectric permittivity and loss in the whole S-Ku bands of microwaves of 2-18 GHz, respectively. The exchange-coupling interaction empowers a more favorable response of magnetic moment to microwaves, leading to enhanced exchange resonances in magnetic permeability and loss above 10 GHz. As a result, strong absorption, as characterized by a large reflection loss (RL) of -20.1 dB at 9.7 GHz for an absorber thickness of 4.5 mm as well as a broad effective absorption bandwidth (for RL<-10 dB) of 8.4 GHz (7.8-16.2 GHz) at an absorber thickness range of 3.0-4.5 mm, is obtained.

Modeling of absorption and scattering properties of core -shell nanoparticles for application as nanoantenna in optical domain

NASA Astrophysics Data System (ADS)

Devi, Jutika; Saikia, Rashmi; Datta, Pranayee

2016-10-01

The present paper describes the study of core-shell nanoparticles for application as nanoantenna in the optical domain. To obtain the absorption and extinction efficiencies as well as the angular distribution of the far field radiation pattern and the resonance wavelengths for these metal-dielectric, dielectric-metal and metal-metal core-shell nanoparticles in optical domain, we have used Finite Element Method based COMSOL Multiphysics Software and Mie Theory. From the comparative study of the extinction efficiencies of core-shell nanoparticles of different materials, it is found that for silica - gold core - shell nanoparticles, the resonant wavelength is greater than that of the gold - silver, silver-gold and gold-silica core - shell nanoparticles and also the radiation pattern of the silica-gold core-shell nanoparticle is the most suitable one from the point of view of directivity. The dielectric functions of the core and shell material as well as of the embedded matrix are extremely important and plays a very major role to tune the directivity and resonance wavelength. Such highly controllable parameters of the dielectric - metal core - shell nanoparticles make them suitable for efficient coupling of optical radiation into nanoscale structures for a broad range of applications in the field of communications.

Production of Ti-C presolar carbide grain analogies and its infrared spectra

NASA Astrophysics Data System (ADS)

Kimura, Y.; Ikegami, A.; Tanigaki, T.; Ishikawa, M.; Sato, T.; Suzuki, H.; Kido, O.; Kaito, C.

The infrared emission of the circumstellar environment of carbon-rich stars and dense molecular cloud cores is believed to be dominated by the emissivity of carbon dust. The origins of absorption peaks will be identified on the basis of laboratory studies. Important factors in the determination of absorption features are size, shape and structure of the grain (Bohren and Huffman, 1983). Therefore, the production of presolar grain analogy is important for the identification of the observation spectra. Recently, we succeeded in the formation of Si-, Ti- and Zr-C grains of the order of 50 nm by advanced gas evaporation method. We have started to obtain characteristic data of carbide grains in laboratory experiments. The spectra from ultraviolet to infrared of samples embedded in KBr pellets are presented. In the present study, we will elucidate the correlation between the size of TiC grain or thickness of the carbon mantle layer and spectra of TiC core-carbon mantle grains. Because TiC is one of the candidates of 21 micron feature. The absorption peaks of TiC core (50 nm)-carbon mantle (2 nm) grains were found to be at 9.5 and 12.5 microns. When the thickness of the mantle layer increased to 15 nm, the peak at 12.5 microns disappeared and the peak at 9.5 microns was significantly weakened. These results are similar to the calculated result for SiC core-carbon mantle grains, i.e., increased thickness of the mantle layer weakens the spectrum intensity (Kozasa et al., 1996). The 20.1 micron absorption feature never appeared, even if the same size grains seen in meteorites were produced. Moreover, the infrared spectra were observed when the size of TiC grains was smaller than presolar grain. Carbon was deposited on the surface of Ti grains. Then, TiC nanocrystallites with the size of 2-3 nm were produced by the diffusion of Ti and/or carbon. The new absorption feature was appeared at 14 microns. The 12.5 micron absorption was hardly seen. If the samples are heated at 700circC for 1h, crystallites size of TiC was increased to about 5 nm. The absorption feature at 14 microns was weaken. It was concluded that the infrared absorption feature was depend on the crystallites size.

Microporous Co@C Nanoparticles Prepared by Dealloying CoAl@C Precursors: Achieving Strong Wideband Microwave Absorption via Controlling Carbon Shell Thickness.

PubMed

Li, Da; Liao, Haoyan; Kikuchi, Hiroaki; Liu, Tong

2017-12-27

Excellent magnetic features make Co-based materials promising candidates as high-performance microwave absorbers. However, it is still a significant challenge for Co-based absorbers to possess high-intensity and broadband absorption simultaneously, owing to the lack of dielectric loss and impedance matching. Herein, microporous Co@C nanoparticles (NPs) with carbon shell thicknesses ranging from 1.8-4.9 nm have been successfully synthesized by dealloying CoAl@C precursors. All of the samples exhibit high microwave absorption performance. The microporous Co@C sample possessing a carbon shell of 1.8 nm exhibits the highest absorption intensity among these samples with a minimum reflection loss (RL) of -141.1 dB, whose absorption bandwidth for RL ≤ -10 dB is 7.3 GHz. As the thickness of the carbon shell increases, the absorption bandwidth of the NPs becomes wider. For the sample with the carbon shell thickness of 4.9 nm, the absorption bandwidth for RL ≤ -10 dB reaches a record high of 13.2 GHz. The outstanding microwave attenuation properties are attributed to the dielectric loss of the carbon shell, the magnetic loss of the Co core, and the cooperation of the core-shell structure and microporous morphology. The strong wideband microwave absorption of the carbon-coated microporous Co NPs highlights their potential applications in microwave absorbing systems.

Foam Core Shielding for Spacecraft

NASA Technical Reports Server (NTRS)

Adams, Marc

2007-01-01

A foam core shield (FCS) system is now being developed to supplant multilayer insulation (MLI) systems heretofore installed on spacecraft for thermal management and protection against meteoroid impacts. A typical FCS system consists of a core sandwiched between a face sheet and a back sheet. The core can consist of any of a variety of low-to-medium-density polymeric or inorganic foams chosen to satisfy application-specific requirements regarding heat transfer and temperature. The face sheet serves to shock and thereby shatter incident meteoroids, and is coated on its outer surface to optimize its absorptance and emittance for regulation of temperature. The back sheet can be dimpled to minimize undesired thermal contact with the underlying spacecraft component and can be metallized on the surface facing the component to optimize its absorptance and emittance. The FCS systems can perform better than do MLI systems, at lower mass and lower cost and with greater volumetric efficiency.

Measurements and Modeling of Aerosol Absorption and Single Scattering Albedo at Ambient Relative Hum

NASA Technical Reports Server (NTRS)

Redemann, J.; Russell, P. B.; Hamill, P.

2000-01-01

Uncertainties in the aerosol single scattering albedo have been identified to be an important source of errors in current large-scale model estimates of the direct aerosol radiative forcing of climate. A number of investigators have obtained estimates of the single scattering albedo from a variety of remote sensing and in situ measurements during aerosol field experiments. During the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX, 1996) for example, estimates of the aerosol single scattering albedo were obtained (1) as a best-fit parameter in comparing radiative flux changes measured by airborne pyranometer to those computed from independently measured aerosol properties; (2) from estimates of the aerosol complex index of refraction derived using a combination of airborne sunphotometer, lidar backscatter and in situ size distribution measurements; and (3) from airborne measurements of aerosol scattering and absorption using nephelometers and absorption photometers. In this paper, we briefly compare the results of the latter two methods for two TARFOX case studies, since those techniques provide height-resolved information about the aerosol single scattering albedo. Estimates of the aerosol single scattering albedo from nephelometer and absorption photometer measurements require knowledge of the scattering and absorption humidification (i.e., the increase in these properties in response to an increase in ambient relative humidity), since both measurements are usually carried out at a relative humidity different from the ambient atmosphere. In principle, the scattering humidification factor can be measured, but there is currently no technique widely available to measure the absorption of an aerosol sample as a function of relative humidity. Frequently, for lack of better knowledge, the absorption humidification is assumed to be unity (meaning that there is no change in aerosol absorption due to an increase in ambient relative humidity). This assumption then enters the estimate of the single scattering albedo at ambient relative humidity. To investigate the validity of this assumption we have carried out modeling studies of the absorption humidification factor, assuming that the aerosols contain an insoluble soot core and a coating which determines its hygroscopic growth behavior. The aerosol optical properties are then computed on the basis of the shell/core particle morphology using a Mie-code for concentric shells. From basic physical principles, it is conceivable that aerosol absorption increases when an atmospheric aerosol particle collects a non-absorbing shell, since the soot core is then exposed to an increased (focused) electric field strength. Indeed, our preliminary modeling studies show that the absorption of an atmospheric aerosol particle composed of a soot core and an aqueous sulfuric acid shell may increase by a factor of 50% due to a change in ambient relative humidity from 30 to 95%. We will show how this increased absorption is a function of the initial particle size and soot mass fraction.

Metal-core/semiconductor-shell nanocones for broadband solar absorption enhancement.

PubMed

Zhou, Lin; Yu, Xiaoqiang; Zhu, Jia

2014-02-12

Nanostructure-based photovoltaic devices have exhibited several advantages, such as reduced reflection, extraordinary light trapping, and so forth. In particular, semiconductor nanostructures provide optical modes that have strong dependence on the size and geometry. Metallic nanostructures also attract a lot of attention because of the appealing plasmonic effect on the near-field enhancement. In this study, we propose a novel design, the metal-core/semiconductor-shell nanocones with the core radius varying in a linearly gradient style. With a thin layer of semiconductor absorber coated on a metallic cone, such a design can lead to significant and broadband absorption enhancement across the entire visible and near-infrared solar spectrum. As an example of demonstration, a layer of 16 nm thick crystalline silicon (c-Si) coated on a silver nanocone can absorb 27% of standard solar radiation across a broad spectral range of 300-1100 nm, which is equivalent to a 700 nm thick flat c-Si film. Therefore, the absorption enhancement factor approaching the Yablonovitch limit is achieved with this design. The significant absorption enhancement can be ascribed to three types of optical modes, that is, Fabry-Perot modes, plasmonic modes, and hybrid modes that combine the features of the previous two. In addition, the unique nanocone geometry enables the linearly gradient radius of the semiconductor shell, which can support multiple optical resonances, critical for the broadband absorption. Our design may find general usage as elements for the low cost, high efficiency solar conversion and water-splitting devices.

First-Principles Predictions of Near-Edge X-ray Absorption Fine Structure Spectra of Semiconducting Polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, Gregory M.; Patel, Shrayesh N.; Pemmaraju, C. D.

The electronic structure and molecular orientation of semiconducting polymers in thin films determine their ability to transport charge. Methods based on near-edge X-ray absorption fine structure (NEXAFS) spectroscopy can be used to probe both the electronic structure and microstructure of semiconducting polymers in both crystalline and amorphous films. However, it can be challenging to interpret NEXAFS spectra on the basis of experimental data alone, and accurate, predictive calculations are needed to complement experiments. Here, we show that first-principles density functional theory (DFT) can be used to model NEXAFS spectra of semiconducting polymers and to identify the nature of transitions inmore » complicated NEXAFS spectra. Core-level X-ray absorption spectra of a set of semiconducting polymers were calculated using the excited electron and core-hole (XCH) approach based on constrained-occupancy DFT. A comparison of calculations on model oligomers and periodic structures with experimental data revealed the requirements for accurate prediction of NEXAFS spectra of both conjugated homopolymers and donor–acceptor polymers. The NEXAFS spectra predicted by the XCH approach were applied to study molecular orientation in donor–acceptor polymers using experimental spectra and revealed the complexity of using carbon edge spectra in systems with large monomeric units. The XCH approach has sufficient accuracy in predicting experimental NEXAFS spectra of polymers that it should be considered for design and analysis of measurements using soft X-ray techniques, such as resonant soft X-ray scattering and scanning transmission X-ray microscopy.« less

Core–Shell to Doped Quantum Dots: Evolution of the Local Environment Using XAFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, Avijit; Chattopadhyay, Soma; Shibata, Tomohiro

2016-09-30

Internal structure study at an atomic level is a challenging task with far reaching consequences to its material properties, specifically in the field of transition metal doping in quantum dots. Diffusion of transition metal ions in and out of quantum dots forming magnetic clusters has been a major bottleneck in this class of materials. Diffusion of the magnetic ions from the core into the nonmagnetic shell in a core/shell heterostructure architecture to attain uniform doping has been recently introduced and yet to be understood. In this work, we have studied the local structure variation of Fe as a function ofmore » CdS matrix thickness and annealing time during the overcoating of Fe 3O 4 core with CdS using X-ray absorption spectroscopy. The data reveals that Fe 3O 4 core initially forms a core/shell structure with CdS followed by alloying at the interface eventually completely diffusing all the way through the CdS matrix to form homogeneously Fe-doped CdS QDs with excellent control over size and size distribution. Study of Fe K-edge shows a complete change of Fe local environment from Fe–O to FeS.« less

Toward high performance nanoscale optoelectronic devices: super solar energy harvesting in single standing core-shell nanowire.

PubMed

Zhou, Jian; Wu, Yonggang; Xia, Zihuan; Qin, Xuefei; Zhang, Zongyi

2017-11-27

Single nanowire solar cells show great promise for next-generation photovoltaics and for powering nanoscale devices. Here, we present a detailed study of light absorption in a single standing semiconductor-dielectric core-shell nanowire (CSNW). We find that the CSNW structure can not only concentrate the incident light into the structure, but also confine most of the concentrated light to the semiconductor core region, which boosts remarkably the light absorption cross-section of the semiconductor core. The CSNW can support multiple higher-order HE modes, as well as Fabry-Pérot (F-P) resonance, compared to the bare nanowire (BNW). Overlapping of the adjacent higher-order HE modes results in broadband light absorption enhancement in the solar radiation spectrum. Results based on detailed balance analysis demonstrate that the super light concentration of the single CSNW gives rise to higher short-circuit current and open-circuit voltage, and thus higher apparent power conversion efficiency (3644.2%), which goes far beyond that of the BNW and the Shockley-Queisser limit that restricts the performance of a planar counterparts. Our study shows that the single CSNW can be a promising platform for construction of high performance nanoscale photodetectors, nanoelectronic power sources, super miniature cells, and diverse integrated nanosystems.

Electronic structure of binuclear acetylacetonates of boron difluoride

NASA Astrophysics Data System (ADS)

Tikhonov, Sergey A.; Svistunova, Irina V.; Samoilov, Ilya S.; Osmushko, Ivan S.; Borisenko, Aleksandr V.; Vovna, Vitaliy I.

2018-05-01

The electronic structure of boron difluoride acetylacetonate and its three derivatives was studied using photoelectron and absorption spectroscopy, as well as the density functional theory. In a series of binuclear acetylacetonate complexes containing bridge-moieties of sulfur and selenium atoms, it was found an appreciable mixing of the π3-orbital of the chelate cycle with atomic orbitals S 3p and Se 4p resulting in destabilization of the HOMO levels by 0.4-0.6 eV, in comparison with the monomer. The positively charged fragment C(CH3)-CX-C(CH3) causes the field effect, which leads to stabilization of the LUMO levels by 0.3-0.4 eV and C 1s-levels by 0.5-1.2 eV. An analysis of the research results on the electronic structure made it possible to determine the effect of substituents in the γ position on the absorption spectra, which is mainly determined by the electron density transfer from the chalcogen atoms to the chelate cycles. It is shown that the calculated energy intervals between electron levels correlate well with the structure of the photoelectron spectra of valence and core electrons.

A Case For Free-free Absorption In The GPS Sources 1321+410 And 0026+346

NASA Astrophysics Data System (ADS)

Marr, Jonathan M.; Perry, T. M.; Read, J. W.; Taylor, G. B.

2010-05-01

We report on the results of VLBI observations of two gigahertz-peaked spectrum sources, 1321+410 and 0026+346, at five frequencies bracketing the spectral peaks. By comparing the three lower-frequency flux-density maps with extrapolations of the high frequency spectra we obtained maps of the optical depths as a function of frequency. The morphologies of the optical depth maps of 1321+410, at all frequencies, are strikingly uniform, consistent with there being a foreground screen of absorbing gas. We also find that the flux densities across the map fit free-free absorption spectra within the uncertainties. The required free-free optical depths are satisfied with reasonable gas parameters (ne 4000 cm-3, T 104 K, and L 1 pc). We conclude that the case for free-free absorption in 1321+410 is strong. In 0026+346, there is a compact feature with an inverted spectrum at the highest frequencies which we take to be the core. The optical depth maps, even excluding the possible core component, exhibit a noticeable amount of structure, but the morphology does not correlate with that in the flux-density maps, as would be expected if the absorption was due to synchrotron self-absorption. Additionally, the spectra (except at the core component) are consistent with free-free absorption, to within the uncertainties, and require column depths about one half of that in 1321+410. We conclude that free-free absorption by a relatively thin amount of gas with structure apparent on the scale of our maps in 0026+346 is likely, although the case is weaker than in 1321+410. This research was supported by an award from the Research Corporation, a NASA NY Space Grant, and by a Booth-Ferris Research Fellowship. The VLBA is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Optical Methods for Identifying Hard Clay Core Samples During Petrophysical Studies

NASA Astrophysics Data System (ADS)

Morev, A. V.; Solovyeva, A. V.; Morev, V. A.

2018-01-01

X-ray phase analysis of the general mineralogical composition of core samples from one of the West Siberian fields was performed. Electronic absorption spectra of the clay core samples with an added indicator were studied. The speed and availability of applying the two methods in petrophysical laboratories during sample preparation for standard and special studies were estimated.

Spectrally resolved opacities and Rosseland and Planck mean opacities of lowly ionized gold plasmas: a detailed level-accounting investigation.

PubMed

Zeng, Jiaolong; Yuan, Jianmin

2007-08-01

Calculation details of radiative opacity for lowly ionized gold plasmas by using our developed fully relativistic detailed level-accounting approach are presented to show the importance of accurate atomic data for a quantitative reproduction of the experimental observations. Even though a huge number of transition lines are involved in the radiative absorption of high- Z plasmas so that one believes that statistical models can often give a reasonable description of their opacities, we first show in detail that an adequate treatment of physical effects, in particular the configuration interaction (including the core-valence electron correlation), is essential to produce atomic data of bound-bound and bound-free processes for gold plasmas, which are accurate enough to correctly explain the relative intensity of two strong absorption peaks experimentally observed located near photon energy of 70 and 80 eV. A detailed study is also carried out for gold plasmas of an average ionization degree sequence of 10, for both spectrally resolved opacities and Rosseland and Planck means. For comparison, results obtained by using an average atom model are also given to show that even for a relatively higher density of matter, correlation effects are also important to predict the correct positions of absorption peaks of transition arrays.

Photoinduced electron-transfer in perylenediimide triphenylamine-based dendrimers: single photon timing and femtosecond transient absorption spectroscopy.

PubMed

Fron, Eduard; Pilot, Roberto; Schweitzer, Gerd; Qu, Jianqiang; Herrmann, Andreas; Müllen, Klaus; Hofkens, Johan; Van der Auweraer, Mark; De Schryver, Frans C

2008-05-01

The excited state dynamics of two generations perylenediimide chromophores substituted in the bay area with dendritic branches bearing triphenylamine units as well as those of the respective reference compounds are investigated. Using single photon timing and multi-pulse femtosecond transient absorption experiments a direct proof of a reversible charge transfer occurring from the peripheral triphenylamine to the electron acceptor perylenediimide core is revealed. Femtosecond pump-dump-probe experiments provide evidence for the ground state dynamics by populating excited vibronic levels. It is found by the means of both techniques that the rotational isomerization of the dendritic branches occurs on a time scale that ranges up to 1 ns. This time scale of the isomerization depends on the size of the dendritic arms and is similar both in the ground and excited state.

The electronic characterization of biphenylene—Experimental and theoretical insights from core and valence level spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lüder, Johann; Sanyal, Biplab; Eriksson, Olle

In this paper, we provide detailed insights into the electronic structure of the gas phase biphenylene molecule through core and valence spectroscopy. By comparing results of X-ray Photoelectron Spectroscopy (XPS) measurements with ΔSCF core-hole calculations in the framework of Density Functional Theory (DFT), we could decompose the characteristic contributions to the total spectra and assign them to non-equivalent carbon atoms. As a difference with similar molecules like biphenyl and naphthalene, an influence of the localized orbitals on the relative XPS shifts was found. The valence spectrum probed by photoelectron spectroscopy at a photon energy of 50 eV in conjunction withmore » hybrid DFT calculations revealed the effects of the localization on the electronic states. Using the transition potential approach to simulate the X-ray absorption spectroscopy measurements, similar contributions from the non-equivalent carbon atoms were determined from the total spectrum, for which the slightly shifted individual components can explain the observed asymmetric features.« less

The single scattering properties of soot aggregates with concentric core-shell spherical monomers

NASA Astrophysics Data System (ADS)

Wu, Yu; Cheng, Tianhai; Gu, Xingfa; Zheng, Lijuan; Chen, Hao; Xu, Hui

2014-03-01

Anthropogenic soot aerosols are shown as complex, fractal-like aggregated structures with high light absorption efficiency. In atmospheric environment, soot monomers may tend to acquire a weakly absorbing coating, such as an organic coating, which introduces further complexity to the optical properties of the aggregates. The single scattering properties of soot aggregates can be significantly influenced by the coated status of these kinds of aerosols. In this article, the monomers of fractal soot aggregates are modelled as semi-external mixtures (physical contact) with constant radius of soot core and variable sizes of the coating for specific soot volume fractions. The single scattering properties of these coated soot particles, such as phase function, the cross sections of extinction and absorption, single scattering albedo (SSA) and asymmetry parameter (ASY), are calculated using the numerically exact superposition T-matrix method. The random-orientation averaging results have shown that the single scattering properties of these coated soot aggregates are significantly different from the single volume-equivalent core-shell sphere approximation using the Mie theory and the homogeneous aggregates with uncoated monomers using the effective medium theory, such as Maxwell-Garnett and Bruggemann approximations, which overestimate backscattering of coated soot. It is found that the SSA and cross sections of extinction and absorption are increased for soot aggregates with thicker weakly absorbing coating on the monomers. Especially, the SSA values of these simulated aggregates with less soot core volume fractions are remarkably (~50% for core volume fraction of soot aggregates of 0.5, ~100% for a core volume fraction of 0.2, at 0.67 μm) larger than for uncoated soot particles without consideration of coating. Moreover, the cross sections of extinction and absorption are underestimated by the computation of equivalent homogeneous fractal aggregate approximation (within 5% for the T-matrix method and 10-25% for the Rayleigh-Debye-Gans approximation due to different soot volume fractions). Further understanding of the optical properties of these coated soot aggregates would be helpful for both environment monitoring and climate studies.

Photoenergy Harvesting Organic PV Cells Using Modified Photosynthetic Light-Harvesting Complex for Energy Harvesting Materials

DTIC Science & Technology

2008-07-03

complex is still unclear even in the crystal structure of RC-LH1 core complex from Rhodopseudomonas (Rps.) palustris [1]. In this study, we use a...complex of R. palustris . 16 The NIR absorption spectra of these core complexes on the electrode indicate that these complexes are stable when...as the LH or the core complex. For example, the core complex, isolated from the photosynthetic bacterium, Rps. palustris , was successfully

Atomic Processes for XUV Lasers: Alkali Atoms and Ions

NASA Astrophysics Data System (ADS)

Dimiduk, David Paul

The development of extreme ultraviolet (XUV) lasers is dependent upon knowledge of processes in highly excited atoms. Described here are spectroscopy experiments which have identified and characterized certain autoionizing energy levels in core-excited alkali atoms and ions. Such levels, termed quasi-metastable, have desirable characteristics as upper levels for efficient, powerful XUV lasers. Quasi -metastable levels are among the most intense emission lines in the XUV spectra of core-excited alkalis. Laser experiments utilizing these levels have proved to be useful in characterizing other core-excited levels. Three experiments to study quasi-metastable levels are reported. The first experiment is vacuum ultraviolet (VUV) absorption spectroscopy on the Cs 109 nm transitions using high-resolution laser techniques. This experiment confirms the identification of transitions to a quasi-metastable level, estimates transition oscillator strengths, and estimates the hyperfine splitting of the quasi-metastable level. The second experiment, XUV emission spectroscopy of Ca II and Sr II in a microwave-heated plasma, identifies transitions from quasi-metastable levels in these ions, and provides confirming evidence of their radiative, rather than autoionizing, character. In the third experiment, core-excited Ca II ions are produced by inner-shell photoionization of Ca with soft x-rays from a laser-produced plasma. This preliminary experiment demonstrated a method of creating large numbers of these highly-excited ions for future spectroscopic experiments. Experimental and theoretical evidence suggests the CA II 3{ rm p}^5 3d4s ^4 {rm F}^circ_{3/2 } quasi-metastable level may be directly pumped via a dipole ionization process from the Ca I ground state. The direct process is permitted by J conservation, and occurs due to configuration mixing in the final state and possibly the initial state as well. The experiments identifying and characterizing quasi-metastable levels are compared to calculations using the Hartree-Fock code RCN/RCG. Calculated parameters include energy levels, wavefunctions, and transition rates. Based on an extension of this code, earlier unexplained experiments showing strong two-electron radiative transitions from quasi-metastable levels are now understood.

Franck-Condon Simulations including Anharmonicity of the Ã(1)A''-X̃(1)A' Absorption and Single Vibronic Level Emission Spectra of HSiCl and DSiCl.

PubMed

Mok, Daniel W K; Lee, Edmond P F; Chau, Foo-Tim; Dyke, John M

2009-03-10

RCCSD(T) and/or CASSCF/MRCI calculations have been carried out on the X̃(1)A' and Ã(1)A'' states of HSiCl employing basis sets of up to the aug-cc-pV5Z quality. Contributions from core correlation and extrapolation to the complete basis set limit were included in determining the computed equilibrium geometrical parameters and relative electronic energy of these two states of HSiCl. Franck-Condon factors which include allowance for anharmonicity and Duschinsky rotation between these two states of HSiCl and DSiCl were calculated employing RCCSD(T) and CASSCF/MRCI potential energy functions, and were used to simulate the Ã(1)A'' ← X̃(1)A' absorption and Ã(1)A'' → X̃(1)A' single vibronic level (SVL) emission spectra of HSiCl and DSiCl. Simulated absorption and experimental LIF spectra, and simulated and observed Ã(1)A''(0,0,0) → X̃(1)A' SVL emission spectra, of HSiCl and DSiCl are in very good agreement. However, agreement between simulated and observed Ã(1)A''(0,1,0) → X̃(1)A' and Ã(1)A''(0,2,1) → X̃(1)A' SVL emission spectra of DSiCl is not as good. Preliminary calculations on low-lying excited states of HSiCl suggest that vibronic interaction between low-lying vibrational levels of the Ã(1)A'' state and highly excited vibrational levels of the ã(3)A'' is possible. Such vibronic interaction may change the character of the low-lying vibrational levels of the Ã(1)A'' state, which would lead to perturbation in the SVL emission spectra from these vibrational levels.

NEUTRONIC REACTOR

DOEpatents

Wigner, E.P.

1958-04-22

A nuclear reactor for isotope production is described. This reactor is designed to provide a maximum thermal neutron flux in a region adjacent to the periphery of the reactor rather than in the center of the reactor. The core of the reactor is generally centrally located with respect tn a surrounding first reflector, constructed of beryllium. The beryllium reflector is surrounded by a second reflector, constructed of graphite, which, in tune, is surrounded by a conventional thermal shield. Water is circulated through the core and the reflector and functions both as a moderator and a coolant. In order to produce a greatsr maximum thermal neutron flux adjacent to the periphery of the reactor rather than in the core, the reactor is designed so tbat the ratio of neutron scattering cross section to neutron absorption cross section averaged over all of the materials in the reflector is approximately twice the ratio of neutron scattering cross section to neutron absorption cross section averaged over all of the material of the core of the reactor.

Spin polarization and magnetic dichroism in photoemission from core and valence states in localized magnetic systems. IV. Core-hole polarization in resonant photoemission

NASA Astrophysics Data System (ADS)

van der Laan, Gerrit; Thole, B. T.

1995-12-01

A simple theory is presented for core-hole polarization probed by resonant photoemission in a two-steps approximation. After excitation from a core level to the valence shell, the core hole decays into two shallower core holes under emission of an electron. The nonspherical core hole and the final state selected cause a specific angle and spin distribution of the emitted electron. The experiment is characterized by the ground-state moments, the polarization of the light, and the spin and angular distribution of the emitted electron. The intensity is a sum over ground-state expectation values of tensor operators times the probability to create a polarized core hole using polarized light, times the probability for decay of such a core hole into the final state. We give general expressions for the angle- and spin-dependent intensities in various regimes of Coulomb and spin-orbit interaction: LS, LSJ, and jjJ coupling. The core-polarization analysis, which generalizes the use of sum rules in x-ray absorption spectroscopy where the integrated peak intensities give ground-state expectation values of the spin and orbital moment operators, makes it possible to measure different linear combinations of these operators. As an application the 2p3/23p3p decay in ferromagnetic nickel is calculated using Hartree-Fock values for the radial matrix elements and phase factors, and compared with experiment, the dichroism is smaller in the 3P final state but stronger in the 1D, 1S peak.

No Radiative Heat Transport Through Pyrolitic Lower Mantle

NASA Astrophysics Data System (ADS)

Lobanov, S.; Holtgrewe, N.; Badro, J.; Goncharov, A. F.

2017-12-01

Transport properties of the lower mantle, such as its thermal conductivity, are key parameters required to understand the nature and dynamics of the core-mantle boundary (CMB) region. Radiative thermal conductivity (krad) of the mantle is determined by its visible-infrared absorption coefficient (α) at high pressure (P) and temperature (T). The latter is highly uncertain at the CMB conditions as optical measurements at high temperature suffer from intense thermal radiation that diminishes the probe contrast. Room-temperature high-pressure studies of bridgmanite and ferropericlase absorption coefficients suggest a steady increase of mantle radiative conductivity with depth mirroring the temperature increase along the geotherm (Goncharov et al., 2008; Keppler et al., 2008). Here we reconstruct optical properties of the mantle as a function of depth by using fast time-resolved spectroscopic technology combined with laser-heated diamond anvil cells. We found a strong increase in the rock absorption coefficient upon heating to 3000 K at 40-135 GPa. Using the pressure- and temperature-dependent pyrolite absorption coefficient we establish that lower mantle radiative thermal conductivity is decreasing with depth from 0.35 W/m/K at 1000 km to 0.15 W/m/K at the CMB, making it 50 times smaller than the corresponding lattice thermal conductivity at such conditions (Ohta et al., 2017; Okuda et al., 2017). Combining our results with models of lattice thermal conductivity in pyrolitic lower mantle we obtain a CMB heat flow of 8.5 TW. This estimate implies an inner core age of 0.7-1.3 Gy and favors a low-to-moderate core thermal conductivity (< 80 W/m/K). A core with higher thermal conductivity (Ohta et al., 2016; Pozzo et al., 2012) would be thermally stratified, halting a thermally driven dynamo prior to the inner core growth, if no other mechanism is invoked, such as MgO (Badro et al., 2016) or SiO2 (Hirose et al., 2017) exsolution. On the other hand, the low iron thermal conductivity scenario (Konopkova et al., 2016) combined with our model of low thermal conductivity at the base of the mantle, suggests that core convection could have taken place prior to inner core growth whether sources of chemical buoyancy were present or not.

Shell thickness-dependent microwave absorption of core-shell Fe3O4@C composites.

PubMed

Du, Yunchen; Liu, Wenwen; Qiang, Rong; Wang, Ying; Han, Xijiang; Ma, Jun; Xu, Ping

2014-08-13

Core-shell composites, Fe3O4@C, with 500 nm Fe3O4 microspheres as cores have been successfully prepared through in situ polymerization of phenolic resin on the Fe3O4 surface and subsequent high-temperature carbonization. The thickness of carbon shell, from 20 to 70 nm, can be well controlled by modulating the weight ratio of resorcinol and Fe3O4 microspheres. Carbothermic reduction has not been triggered at present conditions, thus the crystalline phase and magnetic property of Fe3O4 micropsheres can be well preserved during the carbonization process. Although carbon shells display amorphous nature, Raman spectra reveal that the presence of Fe3O4 micropsheres can promote their graphitization degree to a certain extent. Coating Fe3O4 microspheres with carbon shells will not only increase the complex permittivity but also improve characteristic impedance, leading to multiple relaxation processes in these composites, thus the microwave absorption properties of these composites are greatly enhanced. Very interestingly, a critical thickness of carbon shells leads to an unusual dielectric behavior of the core-shell structure, which endows these composites with strong reflection loss, especially in the high frequency range. By considering good chemical homogeneity and microwave absorption, we believe the as-fabricated Fe3O4@C composites can be promising candidates as highly effective microwave absorbers.

Measurements of gas temperatures at 100 kHz within the annulus of a rotating detonation engine

NASA Astrophysics Data System (ADS)

Rein, Keith D.; Roy, Sukesh; Sanders, Scott T.; Caswell, Andrew W.; Schauer, Frederick R.; Gord, James R.

2017-03-01

Cycle-resolved measurements of H2O temperatures and number densities taken within the detonation channel of a hydrogen—air rotating detonation engine (RDE) at a 100 kHz repetition rate using laser absorption spectroscopy are presented. The laser source used is an MEMS-tunable Vertical-Cavity Surface Emitting laser which scans from 1330 to 1360 nm. Optical access into and out of the RDE is achieved using a dual-core fiber optic. Light is pitched into the RDE through a sapphire window via a single-mode core, retroreflected off the mirror-polished inner radius of the RDE annulus, and collected with the multi-mode fiber core. The resulting absorption spectra are used to determine gas temperatures as a function of time. These measurements allow characterization of the transient-temperature response of the RDE.

Ag@ZnO core-shell nanoparticles study by first principle: The structural, magnetic and optical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Hai-Xia; Wang, Xiao-Xu; Beijing Computing Center, Beijing 100094

Ag@ZnO core-shell nanoparticles of around 72 atoms have been investigated by the density functional theory, revealing proving for the first time that the core-shell structure exhibits a shrinkage phenomenon from outer shell in agreement with the other studies in literatures. Our calculations predict that the Ag@ZnO core-shell structure is a ferromagnetic spin polarized state, and the magnetism mainly stems from the spin splitting of 2p electrons of O atoms. In addition, the total and partial DOS of Ag@ZnO indicate that the nanostructure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. Furthermore, the optical properties calculations showmore » that the absorption edge of Ag@ZnO have a red shift and good photocatalysis compare to that of the bulk ZnO. These results of the Ag@ZnO core-shell structure obtain a well agreement with the experimental measurement. - Graphical abstract: Geometric structure of (a) Ag@ZnO core-shell nanostructure; (b) the core of Ag; (c) the shell of ZnO The core-shell nanoparticle Ag@ZnO contains Ag inner core of radius of 4 Å and ZnO outer shell with thickness of 2 Å. Ag@ZnO core-shell nanoparticles of around 72 atoms have been proved for the first time that the core-shell structure exhibit a shrinkage phenomenon from outer shell. Our calculations predict that the Ag@ZnO core-shell structure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. The absorption edge of Ag@ZnO have a red shift and get good photo-catalysis compare to that of the bulk ZnO.« less

Absorption band Q model for the Earth

NASA Technical Reports Server (NTRS)

Anderson, D. L.; Given, J. W.

1981-01-01

Attenuation in solids and liquids, as measured by the quality factor Q, is typically frequency dependent. In seismology, however, Q is usually assumed to be independent of frequency. Body wave, surface wave, and normal mode data are used to place constraints on the frequency dependence of Q in the mantle. Specific features of the absorption band model are: low-Q in the seismic band at both the top and the base of the mantle, low-Q for long-period body waves in the outer core, an inner core Q sub s that increases with period, and low Q sub p/Q sub s at short periods in the middle mantle.

Electron Dynamics in the Core-Excited CS2 Molecule Revealed through Resonant Inelastic X-Ray Scattering Spectroscopy

NASA Astrophysics Data System (ADS)

Marchenko, T.; Carniato, S.; Journel, L.; Guillemin, R.; Kawerk, E.; Žitnik, M.; Kavčič, M.; Bučar, K.; Bohinc, R.; Petric, M.; Vaz da Cruz, V.; Gel'mukhanov, F.; Simon, M.

2015-07-01

We present an experimental and theoretical study of resonant inelastic x-ray scattering (RIXS) in the carbon disulphide CS2 molecule near the sulfur K-absorption edge. We observe a strong evolution of the RIXS spectral profile with the excitation energy tuned below the lowest unoccupied molecular orbital (LUMO) absorption resonance. The reason for this is twofold. Reducing the photon energy in the vicinity of the LUMO absorption resonance leads to a relative suppression of the LUMO contribution with respect to the emission signal from the higher unoccupied molecular orbitals, which results in the modulation of the total RIXS profile. At even larger negative photon-energy detuning from the resonance, the excitation-energy dependence of the RIXS profile is dominated by the onset of electron dynamics triggered by a coherent excitation of multiple electronic states. Furthermore, our study demonstrates that in the hard x-ray regime, localization of the S 1s core hole occurs in CS2 during the RIXS process because of the orientational dephasing of interference between the waves scattering on the two sulfur atoms. Core-hole localization leads to violation of the symmetry selection rules for the electron transitions observed in the spectra.

Ligand-core NLO-phores: a combined experimental and theoretical approach to the two-photon absorption and two-photon excited emission properties of small-ligated silver nanoclusters.

PubMed

Russier-Antoine, Isabelle; Bertorelle, Franck; Calin, Nathalie; Sanader, Željka; Krstić, Marjan; Comby-Zerbino, Clothilde; Dugourd, Philippe; Brevet, Pierre-François; Bonačić-Koutecký, Vlasta; Antoine, Rodolphe

2017-01-19

We report a combined experimental and theoretical study of the two-photon absorption and excited emission properties of monodisperse ligand stabilized Ag 11 , Ag 15 and Ag 31 nanoclusters in aqueous solutions. The nanoclusters were synthesized using a cyclic reduction under oxidative conditions and separated by vertical gel electrophoresis. The two-photon absorption cross-sections of these protected noble metal nanoclusters measured within the biologically attractive 750-900 nm window are several orders of magnitude larger than that reported for commercially available standard organic dyes. The two-photon excited fluorescence spectra are also presented for excitation wavelengths within the same excitation spectral window. They exhibit size-tunability. Because the fundamental photophysical mechanisms underlying these multiphoton processes in ligand protected clusters with only a few metal atoms are not fully understood yet, a theoretical model is proposed to identify the key driving elements. Elements that regulate the dipole moments and the nonlinear optical properties are the nanocluster size, its structure and the charge distribution on both the metal core and the bound ligands. We coined this new class of NLO materials as "Ligand-Core" NLO-phores.

Fast Time-Dependent Density Functional Theory Calculations of the X-ray Absorption Spectroscopy of Large Systems.

PubMed

Besley, Nicholas A

2016-10-11

The computational cost of calculations of K-edge X-ray absorption spectra using time-dependent density functional (TDDFT) within the Tamm-Dancoff approximation is significantly reduced through the introduction of a severe integral screening procedure that includes only integrals that involve the core s basis function of the absorbing atom(s) coupled with a reduced quality numerical quadrature for integrals associated with the exchange and correlation functionals. The memory required for the calculations is reduced through construction of the TDDFT matrix within the absorbing core orbitals excitation space and exploiting further truncation of the virtual orbital space. The resulting method, denoted fTDDFTs, leads to much faster calculations and makes the study of large systems tractable. The capability of the method is demonstrated through calculations of the X-ray absorption spectra at the carbon K-edge of chlorophyll a, C 60 and C 70 .

Temperature dependence of the optical absorption spectra of InP/ZnS quantum dots

NASA Astrophysics Data System (ADS)

Savchenko, S. S.; Vokhmintsev, A. S.; Weinstein, I. A.

2017-03-01

The optical-absorption spectra of InP/ZnS (core/shell) quantum dots have been studied in a broad temperature range of T = 6.5-296 K. Using the second-order derivative spectrophotometry technique, the energies of optical transitions at room temperature were found to be E 1 = 2.60 ± 0.02 eV (for the first peak of excitonic absorption in the InP core) and E 2 = 4.70 ± 0.02 eV (for processes in the ZnS shell). The experimental curve of E 1( T) has been approximated for the first time in the framework of a linear model and in terms of the Fan's formula. It is established that the temperature dependence of E 1 is determined by the interaction of excitons and longitudinal acoustic phonons with hω = 15 meV.

Vibrational effects in x-ray absorption and resonant inelastic x-ray scattering using a semiclassical scheme

NASA Astrophysics Data System (ADS)

Ljungberg, Mathias P.

2017-12-01

A method is presented for describing vibrational effects in x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) using a combination of the classical Franck-Condon (FC) approximation and classical trajectories run on the core-excited state. The formulation of RIXS is an extension of the semiclassical Kramers-Heisenberg formalism of Ljungberg et al. [Phys. Rev. B 82, 245115 (2010), 10.1103/PhysRevB.82.245115] to the resonant case, retaining approximately the same computational cost. To overcome difficulties with connecting the absorption and emission processes in RIXS, the classical FC approximation is used for the absorption, which is seen to work well provided that a zero-point-energy correction is included. In the case of core-excited states with dissociative character, the method is capable of closely reproducing the main features for one-dimensional test systems, compared to the quantum-mechanical formulation. Due to the good accuracy combined with the relatively low computational cost, the method has great potential of being used for complex systems with many degrees of freedom, such as liquids and surface adsorbates.

Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

NASA Astrophysics Data System (ADS)

Wawrzynczyk, Dominika; Szeremeta, Janusz; Samoc, Marek; Nyk, Marcin

2015-11-01

Spectrally resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and two-photon fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. In principle, both techniques should provide comparable results and can be interchangeably used for determination of the nonlinear optical absorption parameters, finding maximal values of the cross sections and optimizing them. We have observed slight differences between the two-photon absorption cross sections measured by the two techniques and attributed them to the presence of non-radiative paths of absorption or relaxation. The most significant value of two-photon absorption cross section σ2 for 4.3 nm size InP@ZnS quantum dot was equal to 2200 GM, while the two-photon excitation action cross section σ2Φ was found to be 682 GM at 880 nm. The properties of these cadmium-free colloidal quantum dots can be potentially useful for nonlinear bioimaging.

Orbital breathing effects in the computation of x-ray d -ion spectra in solids by ab initio wave-function-based methods

DOE PAGES

Bogdanov, Nikolay A.; Bisogni, Valentina; Kraus, Roberto; ...

2016-11-21

In existing theoretical approaches to core-level excitations of transition-metal ions in solids relaxation and polarization effects due to the inner core hole are often ignored or described phenomenologically. Here, we set up an ab initio computational scheme that explicitly accounts for such physics in the calculation of x-ray absorption and resonant inelastic x-ray scattering spectra. Good agreement is found with experimental transition-metal L-edge data for the strongly correlated d 9 cuprate Li 2CuO 2, for which we also determine the absolute scattering intensities. The newly developed methodology opens the way for the investigation of even more complex d n electronicmore » structures of group VI B to VIII B correlated oxide compounds.« less

High ink absorption performance of inkjet printing based on SiO2@Al13 core-shell composites

NASA Astrophysics Data System (ADS)

Chen, YiFan; Jiang, Bo; Liu, Li; Du, Yunzhe; Zhang, Tong; Zhao, LiWei; Huang, YuDong

2018-04-01

The increasing growth of the inkjet market makes the inkjet printing more necessary. A composite material based on core-shell structure has been developed and applied to prepare inkjet printing layer. In this contribution, the ink printing record layers based on SiO2@Al13 core-shell composite was elaborated. The prepared core-shell composite materials were characterized by X-ray photoelectron spectroscopy (XPS), zeta potential, X-ray diffraction (XRD), scanning electron microscopy (SEM). The results proved the presence of electrostatic adsorption between SiO2 molecules and Al13 molecules with the formation of the well-dispersed system. In addition, based on the adsorption and the liquid permeability analysis, SiO2@Al13 ink printing record layer achieved a relatively high ink uptake (2.5 gmm-1) and permeability (87%), respectively. The smoothness and glossiness of SiO2@Al13 record layers were higher than SiO2 record layers. The core-shell structure facilitated the dispersion of the silica, thereby improved its ink absorption performance and made the clear printed image. Thus, the proposed procedure based on SiO2@Al13 core-shell structure of dye particles could be applied as a promising strategy for inkjet printing.

Boron difluoride dibenzoylmethane derivatives: Electronic structure and luminescence

NASA Astrophysics Data System (ADS)

Tikhonov, Sergey A.; Vovna, Vitaliy I.; Osmushko, Ivan S.; Fedorenko, Elena V.; Mirochnik, Anatoliy G.

2018-01-01

Electronic structure and optical properties of boron difluoride dibenzoylmethanate and four of its derivatives have been studied by X-ray photoelectron spectroscopy, absorption and luminescence spectroscopy and quantum chemistry (DFT, TDDFT). The relative quantum luminescence yields have been revealed to correlate with charge transfers of HOMO-LUMO transitions, energy barriers of aromatic substituents rotation and the lifetime of excited states in the investigated complexes. The bathochromic shift of intensive bands in the optical spectra has been observed to occur when the functional groups are introduced into p-positions of phenyl cycles due to destabilizing HOMO levels. Calculated energy intervals between electronic levels correlate well with XPS spectra structure of valence and core electrons.

Fabrication and investigation of effect of core size in heterostructure PbS/CdS core/shell nanoparticles

NASA Astrophysics Data System (ADS)

Das, D.; Hussain, A. M. P.

2018-04-01

PbS/CdS core/shell (CS) nanoparticles (NPs) were fabricated with three different concentrations of PbS core and CdS shell. Formation of core/shell heterostructure was confirmed from X-ray diffraction studies. The diffraction patterns exhibited formation of cubic phase and polycrystalline core/shell nanostructure. The crystalline sizes calculated from Williamson-Hall plot exhibited increase with molar concentration of precursors with decrease in strain. High resolution electron microscopy studies also confirm the formation of core/shell structure with particle size around 10 nm. A large blue-shift for PbS core compared to its bulk and small red-shift for the PbS/CdS core/shell as compared to the core is being observed in absorption spectra.

The role of ion exchange in the passivation of In(Zn)P nanocrystals with ZnS

PubMed Central

Cho, Deok-Yong; Xi, Lifei; Boothroyd, Chris; Kardynal, Beata; Lam, Yeng Ming

2016-01-01

We have investigated the chemical state of In(Zn)P/ZnS core/shell nanocrystals (NCs) for color conversion applications using hard X-ray absorption spectroscopy (XAS) and photoluminescence excitation (PLE). Analyses of the edge energies as well as the X-ray absorption fine structure (XAFS) reveal that the Zn2+ ions from ZnS remain in the shell while the S2− ions penetrate into the core at an early stage of the ZnS deposition. It is further demonstrated that for short growth times, the ZnS shell coverage on the core was incomplete, whereas the coverage improved gradually as the shell deposition time increased. Together with evidence from PLE spectra, where there is a strong indication of the presence of P vacancies, this suggests that the core-shell interface in the In(Zn)P/ZnS NCs are subject to substantial atomic exchanges and detailed models for the shell structure beyond simple layer coverage are needed. This substantial atomic exchange is very likely to be the reason for the improved photoluminescence behavior of the core-shell particles compare to In(Zn)P-only NCs as S can passivate the NCs surfaces. PMID:26972936

DETERMINATION OF CENTRAL ENGINE POSITION AND ACCRETION DISK STRUCTURE IN NGC 4261 BY CORE SHIFT MEASUREMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haga, Takafumi; Doi, Akihiro; Murata, Yasuhiro

2015-07-01

We report multifrequency phase-referenced observations of the nearby radio galaxy NGC 4261, which has prominent two-sided jets, using the Very Long Baseline Array at 1.4–43 GHz. We measured radio core positions showing observing frequency dependences (known as “core shift”) in both approaching jets and counterjets. The limit of the core position as the frequency approaches infinity, which suggests a jet base, is separated by 82 ± 16 μas upstream in projection, corresponding to (310 ± 60)R{sub s} (R{sub s}: Schwarzschild radius) as a deprojected distance, from the 43 GHz core in the approaching jet. In addition, the innermost component atmore » the counterjet side appeared to approach the same position at infinity of the frequency, indicating that cores on both sides are approaching the same position, suggesting a spatial coincidence with the central engine. Applying a phase-referencing technique, we also obtained spectral index maps, which indicate that emission from the counterjet is affected by free–free absorption (FFA). The result of the core shift profile on the counterjet also requires FFA because the core positions at 5–15 GHz cannot be explained by a simple core shift model based on synchrotron self-absorption (SSA). Our result is apparently consistent with the SSA core shift with an additional disk-like absorber over the counterjet side. Core shift and opacity profiles at the counterjet side suggest a two-component accretion: a radiatively inefficient accretion flow at the inner region and a truncated thin disk in the outer region. We proposed a possible solution about density and temperature profiles in the outer disk on the basis of the radio observation.« less

Special Features of Light Absorption by the Dimer of Bilayer Microparticles

NASA Astrophysics Data System (ADS)

Geints, Yu. É.; Panina, E. K.; Zemlyanov, A. A.

2018-05-01

Results of numerical simulation of light absorption by the dimer of bilayer spherical particles consisting of a water core and a polymer shell absorbing radiation are presented. The spatial distribution and the amplitude characteristics of the volume density of the absorbed power are investigated. It is shown that for a certain spatial dimer configuration, the maximal achievable density of the absorbed power is realized. It is also established that for closely spaced microcapsules with high shell absorption indices, the total power absorbed in the dimer volume can increase in comparison with the radiation absorption by two insulated microparticles.

Nitrogen K-edge x-ray absorption near edge structure of pyrimidine-containing nucleotides in aqueous solution

NASA Astrophysics Data System (ADS)

Shimada, Hiroyuki; Minami, Hirotake; Okuizumi, Naoto; Sakuma, Ichiro; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

2015-05-01

X-ray absorption near edge structure (XANES) was measured at energies around the N K-edge of the pyrimidine-containing nucleotides, cytidine 5'-monophosphate (CMP), 2'-deoxythymidine 5'-monophosphate (dTMP), and uridine 5'-monophosphate (UMP), in aqueous solutions and in dried films under various pH conditions. The features of resonant excitations below the N K-edge in the XANES spectra for CMP, dTMP, and UMP changed depending on the pH of the solutions. The spectral change thus observed is systematically explained by the chemical shift of the core-levels of N atoms in the nucleobase moieties caused by structural changes due to protonation or deprotonation at different proton concentrations. This interpretation is supported by the results of theoretical calculations using density functional theory for the corresponding nucleobases in the neutral and protonated or deprotonated forms.

Nitrogen K-edge x-ray absorption near edge structure of pyrimidine-containing nucleotides in aqueous solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shimada, Hiroyuki, E-mail: hshimada@cc.tuat.ac.jp; Minami, Hirotake; Okuizumi, Naoto

2015-05-07

X-ray absorption near edge structure (XANES) was measured at energies around the N K-edge of the pyrimidine-containing nucleotides, cytidine 5′-monophosphate (CMP), 2′-deoxythymidine 5′-monophosphate (dTMP), and uridine 5′-monophosphate (UMP), in aqueous solutions and in dried films under various pH conditions. The features of resonant excitations below the N K-edge in the XANES spectra for CMP, dTMP, and UMP changed depending on the pH of the solutions. The spectral change thus observed is systematically explained by the chemical shift of the core-levels of N atoms in the nucleobase moieties caused by structural changes due to protonation or deprotonation at different proton concentrations.more » This interpretation is supported by the results of theoretical calculations using density functional theory for the corresponding nucleobases in the neutral and protonated or deprotonated forms.« less

Electronic spectroscopy of HRe(CO) 5: a CASSCF/CASPT2 and TD-DFT study

NASA Astrophysics Data System (ADS)

Bossert, J.; Ben Amor, N.; Strich, A.; Daniel, C.

2001-07-01

The low-lying excited states of HRe(CO) 5 have been calculated at the CASSCF/CASPT2 and TD-DFT level of theory using relativistic effective core potentials (ECP) or ab initio model potentials (AIMP). The theoretical absorption spectrum is compared to the experimental one. Despite the similarity between the experimental absorption spectra of HMn(CO) 5 and HRe(CO) 5 in the UV/visible energy domain it is shown that the assignment differs significantly between the two molecules. The low-lying excited states of HRe(CO) 5 correspond to 5d→π *CO excitations whereas the spectrum of HMn(CO) 5 consists mainly of 3d→3d and 3d→ σ*Mn-H excitations. If the CASPT2 and TD-DFT results are quite comparable for the lowest excited states, the upper part assignment is more problematic with the TD-DFT method.

Near-Infrared Spectroscopy of Small Protonated Water Clusters

NASA Astrophysics Data System (ADS)

Wagner, J. Philipp; McDonald, David C., II; McCoy, Anne B.; Duncan, Michael A.

2017-06-01

Small protonated water clusters and their argon tagged analogues of the general formula H^{+}(H_{2}O)_{n}Ar_{m} have been generated in a pulsed electric discharge source. Clusters containing n=1-8 water molecules were mass-selected and their absorptions in the near-infrared were probed with a tunable Nd/colonYAG pumped OPA/OPA laser system in the region from 4850-7350 cm^{-1}. A doublet corresponding to overtones of the free O-H stretches of the external waters was observed around 7200 cm^{-1} that was continuously decreasing in intensity with increasing cluster size. Broad, mostly featureless absorptions were found around 5300 cm^{-1} associated with stretch/bend combinations and with the hydrogen bonded waters in the core of the clusters. Vibrational assignments were substantiated by comparison to anharmonic frequency computations via second-order vibrational perturbation theory (VPT2) at the MP2/aug-cc-pVTZ level of theory.

Kinetics of Spontaneous Bimetallization between Silver and Noble Metal Nanoparticles.

PubMed

Hirakawa, Kazutaka; Kaneko, Tetsuya; Toshima, Naoki

2018-06-05

A physical mixture of polymer-protected Ag nanoparticles and Rh, Pd, or Pt nanoparticles spontaneously forms Ag-core bimetallic nanoparticles. The formed nanoparticles were smaller than the parent Ag nanoparticles. In the initial process of this reaction, the surface plasmon absorption of Ag nanoparticles diminished and then almost ceased within one hour. Within several minutes, the decrease in Ag surface plasmon absorption could be analyzed by second-order reaction. This reaction was accelerated with an increase of temperature and the energy gap in the Fermi level between Ag and the other metals. The activation energy (E a ) of this reaction could be determined. An electron transfer reaction from Ag to other metal nanoparticles was proposed as the initial interaction between these metal nanoparticles because the Fermi level of Ag is relatively high, and the electron transfer is possible in terms of energy. The Marcus plot between the rate constant and the driving force, roughly estimated from the work function of metals, and the observed E a values reasonably explained the proposed electron transfer mechanism. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Core-shell silicon nanowire solar cells

PubMed Central

Adachi, M. M.; Anantram, M. P.; Karim, K. S.

2013-01-01

Silicon nanowires can enhance broadband optical absorption and reduce radial carrier collection distances in solar cell devices. Arrays of disordered nanowires grown by vapor-liquid-solid method are attractive because they can be grown on low-cost substrates such as glass, and are large area compatible. Here, we experimentally demonstrate that an array of disordered silicon nanowires surrounded by a thin transparent conductive oxide has both low diffuse and specular reflection with total values as low as < 4% over a broad wavelength range of 400 nm < λ < 650 nm. These anti-reflective properties together with enhanced infrared absorption in the core-shell nanowire facilitates enhancement in external quantum efficiency using two different active shell materials: amorphous silicon and nanocrystalline silicon. As a result, the core-shell nanowire device exhibits a short-circuit current enhancement of 15% with an amorphous Si shell and 26% with a nanocrystalline Si shell compared to their corresponding planar devices. PMID:23529071

Multi-domain electromagnetic absorption of triangular quantum rings

NASA Astrophysics Data System (ADS)

Sitek, Anna; Thorgilsson, Gunnar; Gudmundsson, Vidar; Manolescu, Andrei

2016-06-01

We present a theoretical study of the unielectronic energy spectra, electron localization, and optical absorption of triangular core-shell quantum rings. We show how these properties depend on geometric details of the triangle, such as side thickness or corners’ symmetry. For equilateral triangles, the lowest six energy states (including spin) are grouped in an energy shell, are localized only around corner areas, and are separated by a large energy gap from the states with higher energy which are localized on the sides of the triangle. The energy levels strongly depend on the aspect ratio of the triangle sides, i.e., thickness/length ratio, in such a way that the energy differences are not monotonous functions of this ratio. In particular, the energy gap between the group of states localized in corners and the states localized on the sides strongly decreases with increasing the side thickness, and then slightly increases for thicker samples. With increasing the thickness the low-energy shell remains distinct but the spatial distribution of these states spreads. The behavior of the energy levels and localization leads to a thickness-dependent absorption spectrum where one transition may be tuned in the THz domain and a second transition can be tuned from THz to the infrared range of electromagnetic spectrum. We show how these features may be further controlled with an external magnetic field. In this work the electron-electron Coulomb repulsion is neglected.

Multi-domain electromagnetic absorption of triangular quantum rings.

PubMed

Sitek, Anna; Thorgilsson, Gunnar; Gudmundsson, Vidar; Manolescu, Andrei

2016-06-03

We present a theoretical study of the unielectronic energy spectra, electron localization, and optical absorption of triangular core-shell quantum rings. We show how these properties depend on geometric details of the triangle, such as side thickness or corners' symmetry. For equilateral triangles, the lowest six energy states (including spin) are grouped in an energy shell, are localized only around corner areas, and are separated by a large energy gap from the states with higher energy which are localized on the sides of the triangle. The energy levels strongly depend on the aspect ratio of the triangle sides, i.e., thickness/length ratio, in such a way that the energy differences are not monotonous functions of this ratio. In particular, the energy gap between the group of states localized in corners and the states localized on the sides strongly decreases with increasing the side thickness, and then slightly increases for thicker samples. With increasing the thickness the low-energy shell remains distinct but the spatial distribution of these states spreads. The behavior of the energy levels and localization leads to a thickness-dependent absorption spectrum where one transition may be tuned in the THz domain and a second transition can be tuned from THz to the infrared range of electromagnetic spectrum. We show how these features may be further controlled with an external magnetic field. In this work the electron-electron Coulomb repulsion is neglected.

Synthesis, characterization, and nonlinear optical (NLO) properties of truxene-cored diphenylamine derivatives

NASA Astrophysics Data System (ADS)

Li, Fusheng; Zhao, Baodong; Chen, Yu; Zhang, Yufei; Wang, Tao; Xue, Song

2017-10-01

Three star-shaped compounds based on a truxene core (FS11, FS12 and FS13) were prepared. The truxene core is incorporating with asymmetric diphenylamines, including one phenyl of diphenylamine substituted by methoxy group and the other phenyl substituted by tolyl, fluorophenyl and phenylethynyl for FS11, FS12 and FS13, respectively. Their one-photon, two-photon absorption, geometric structures, electrochemical behavior and thermal properties were investigated. The absorption maxima of charge transfer band for FS11, FS12 and FS13 are 375 nm, 373 nm and 383 nm, and the corresponding molar extinction coefficients of FS11, FS12 and FS13 is 79,950 M- 1 cm- 1, 67,220 M- 1 cm- 1 and 108,780 M- 1 cm- 1. The ;pull-push; structure promotes charge transfer between asymmetric diphenylamine branches and the truxene core. Their two-photon absorbtion property is measured by two-photon induced fluorescence. The maximum two-photon cross-sections values of FS11, FS12 and FS13 are excited at 750 nm, which are 260 GM, 204GM and 367 GM, respectively.

Extreme IR absorption in group IV-SiGeSn core-shell nanowires

NASA Astrophysics Data System (ADS)

Attiaoui, Anis; Wirth, Stephan; Blanchard-Dionne, André-Pierre; Meunier, Michel; Hartmann, J. M.; Buca, Dan; Moutanabbir, Oussama

2018-06-01

Sn-containing Si and Ge (Ge1-y-xSixSny) alloys are an emerging family of semiconductors with the potential to impact group IV material-based devices. These semiconductors provide the ability to independently engineer both the lattice parameter and bandgap, which holds the premise to develop enhanced or novel photonic and electronic devices. With this perspective, we present detailed investigations of the influence of Ge1-y-xSixSny layers on the optical properties of Si and Ge based heterostructures and nanowires. We found that by adding a thin Ge1-y-xSixSny capping layer on Si or Ge greatly enhances light absorption especially in the near infrared range, leading to an increase in short-circuit current density. For the Ge1-y-xSixSny structure at thicknesses below 30 nm, a 14-fold increase in the short-circuit current is observed with respect to bare Si. This enhancement decreases by reducing the capping layer thickness. Conversely, decreasing the shell thickness was found to improve the short-circuit current in Si/Ge1-y-xSixSny and Ge/Ge1-y-xSixSny core/shell nanowires. The optical absorption becomes very important by increasing the Sn content. Moreover, by exploiting an optical antenna effect, these nanowires show extreme light absorption, reaching an enhancement factor, with respect to Si or Ge nanowires, on the order of 104 in Si/Ge0.84Si0.04Sn0.12 and 12 in Ge/Ge0.84Si0.04Sn0.12. Furthermore, we analyzed the optical response after the addition of a dielectric layer of Si3N4 to the Si/Ge1-y-xSixSny core-shell nanowire and found approximatively a 50% increase in the short-circuit current density for a dielectric layer of thickness equal to 45 nm and both a core radius and a shell thickness greater than 40 nm. The core-shell optical antenna benefits from a multiplication of enhancements contributed by leaky mode resonances in the semiconductor part and antireflection effects in the dielectric part.

Complete Au@ZnO core-shell nanoparticles with enhanced plasmonic absorption enabling significantly improved photocatalysis

NASA Astrophysics Data System (ADS)

Sun, Yiqiang; Sun, Yugang; Zhang, Tao; Chen, Guozhu; Zhang, Fengshou; Liu, Dilong; Cai, Weiping; Li, Yue; Yang, Xianfeng; Li, Cuncheng

2016-05-01

Nanostructured ZnO exhibits high chemical stability and unique optical properties, representing a promising candidate among photocatalysts in the field of environmental remediation and solar energy conversion. However, ZnO only absorbs the UV light, which accounts for less than 5% of total solar irradiation, significantly limiting its applications. In this article, we report a facile and efficient approach to overcome the poor wettability between ZnO and Au by carefully modulating the surface charge density on Au nanoparticles (NPs), enabling rapid synthesis of Au@ZnO core-shell NPs at room temperature. The resulting Au@ZnO core-shell NPs exhibit a significantly enhanced plasmonic absorption in the visible range due to the Au NP cores. They also show a significantly improved photocatalytic performance in comparison with their single-component counterparts, i.e., the Au NPs and ZnO NPs. Moreover, the high catalytic activity of the as-synthesized Au@ZnO core-shell NPs can be maintained even after many cycles of photocatalytic reaction. Our results shed light on the fact that the Au@ZnO core-shell NPs represent a promising class of candidates for applications in plasmonics, surface-enhanced spectroscopy, light harvest devices, solar energy conversion, and degradation of organic pollutants.Nanostructured ZnO exhibits high chemical stability and unique optical properties, representing a promising candidate among photocatalysts in the field of environmental remediation and solar energy conversion. However, ZnO only absorbs the UV light, which accounts for less than 5% of total solar irradiation, significantly limiting its applications. In this article, we report a facile and efficient approach to overcome the poor wettability between ZnO and Au by carefully modulating the surface charge density on Au nanoparticles (NPs), enabling rapid synthesis of Au@ZnO core-shell NPs at room temperature. The resulting Au@ZnO core-shell NPs exhibit a significantly enhanced plasmonic absorption in the visible range due to the Au NP cores. They also show a significantly improved photocatalytic performance in comparison with their single-component counterparts, i.e., the Au NPs and ZnO NPs. Moreover, the high catalytic activity of the as-synthesized Au@ZnO core-shell NPs can be maintained even after many cycles of photocatalytic reaction. Our results shed light on the fact that the Au@ZnO core-shell NPs represent a promising class of candidates for applications in plasmonics, surface-enhanced spectroscopy, light harvest devices, solar energy conversion, and degradation of organic pollutants. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00933f

Distributed gas detection system and method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Challener, William Albert; Palit, Sabarni; Karp, Jason Harris

A distributed gas detection system includes one or more hollow core fibers disposed in different locations, one or more solid core fibers optically coupled with the one or more hollow core fibers and configured to receive light of one or more wavelengths from a light source, and an interrogator device configured to receive at least some of the light propagating through the one or more solid core fibers and the one or more hollow core fibers. The interrogator device is configured to identify a location of a presence of a gas-of-interest by examining absorption of at least one of themore » wavelengths of the light at least one of the hollow core fibers.« less

Dibenzo[a,f]perylene bisimide: effects of introducing two fused rings.

PubMed

Chaolumen; Enno, Hiroki; Murata, Michihisa; Wakamiya, Atsushi; Murata, Yasujiro

2014-11-01

Perylene bisimides (PBIs) are fascinating dyes with various potential applications. To study the effects of introducing a dibenzo-fused structure to the perylene moiety, π-extended PBI derivatives with a dibenzo-fused structure at both of the a and f bonds were synthesized. The twisted structure was characterized by X-ray crystal structure analysis. In the cyclic voltammograms, the dibenzo[a,f]-fused PBI showed a reversible oxidation wave at much less positive potential, relative to a dibenzo[a,o]-fused PBI derivative. These data indicated that two ring fusions at both sides of a naphthalene moiety, which construct a tetracene core, effectively raise the HOMO level compared to fusion of one ring at each naphthalene moiety (two anthracene cores). The dibenzo[a,f]-fused PBI derivative showed an absorption band at 735 nm with a shoulder band reaching 900 nm. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Broadband absorption and enhanced photothermal conversion property of octopod-like Ag@Ag2S core@shell structures with gradually varying shell thickness.

PubMed

Jiang, Qian; Zeng, Wenxia; Zhang, Canying; Meng, Zhaoguo; Wu, Jiawei; Zhu, Qunzhi; Wu, Daxiong; Zhu, Haitao

2017-12-19

Photothermal conversion materials have promising applications in many fields and therefore they have attracted tremendous attention. However, the multi-functionalization of a single nanostructure to meet the requirements of multiple photothermal applications is still a challenge. The difficulty is that most nanostructures have specific absoprtion band and are not flexible to different demands. In the current work, we reported the synthesis and multi-band photothermal conversion of Ag@Ag 2 S core@shell structures with gradually varying shell thickness. We synthesized the core@shell structures through the sulfidation of Ag nanocubes by taking the advantage of their spatially different reactivity. The resulting core@shell structures show an octopod-like mopgorlogy with a Ag 2 S bulge sitting at each corner of the Ag nanocubes. The thickness of the Ag 2 S shell gradually increases from the central surface towards the corners of the structure. The synthesized core@shell structures show a broad band absorption spectrum from 300 to 1100 nm. Enhanced photothermal conversion effect is observed under the illuminations of 635, 808, and 1064 nm lasers. The results indicate that the octopod-like Ag@Ag 2 S core@shell structures have characteristics of multi-band photothermal conversion. The current work might provide a guidance for the design and synthesis of multifunctional photothermal conversion materials.

Fabrication and characterization of CNT-based smart tips for synchrotron assisted STM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Hui; Cummings, Marvin; Camino, Fernando

Determination of chemical composition along with imaging at the atomic level provides critical information towards fundamental understanding of the surface of materials and, hence, yields the capability to design new materials by tailoring their ultimate functionalities. Synchrotron X-ray assisted scanning tunneling microscopy (SX-STM) is a promising new technique to achieve real space chemically specific atomic mapping. Chemical sensitivity of SX-STM relies on excitation of core electrons by incident X-rays when their energy is tuned to an absorption edge of a particular element. However, along with core-level electrons, photoelectrons are also excited, which yield additional current and interfere with the tunnelingmore » current. To reduce the background photoelectron current and to improve ultimate resolution of SX-STM, we have developed and fabricated multiwalled carbon nanotubes (MWCNT) based “smart tips” using plasma enhanced chemical vapor deposition and focused ion beam milling. As a result, the newly developed CNT-based smart tips, characterized step by step by scanning electron microscopy (SEM) during the fabrication process, demonstrate good performance and provide opportunity for realizing atomic chemical mapping.« less

Effective D-A-D type chromophore of fumaronitrile-core and terminal alkylated bithiophene for solution-processed small molecule organic solar cells.

PubMed

Nazim, M; Ameen, Sadia; Seo, Hyung-Kee; Shin, Hyung Shik

2015-06-12

A new and novel organic π-conjugated chromophore (named as RCNR) based on fumaronitrile-core acceptor and terminal alkylated bithiophene was designed, synthesized and utilized as an electron-donor material for the solution-processed fabrication of bulk-heterojunction (BHJ) small molecule organic solar cells (SMOSCs). The synthesized organic chromophore exhibited a broad absorption peak near green region and strong emission peak due to the presence of strong electron-withdrawing nature of two nitrile (-CN) groups of fumaronitrile acceptor. The highest occupied molecular orbital (HOMO) energy level of -5.82 eV and the lowest unoccupied molecular orbital (LUMO) energy level of -3.54 eV were estimated for RCNR due to the strong electron-accepting tendency of -CN groups. The fabricated SMOSC devices with RCNR:PC60BM (1:3, w/w) active layer exhibited the reasonable power conversion efficiency (PCE) of ~2.69% with high short-circuit current density (JSC) of ~9.68 mA/cm(2) and open circuit voltage (VOC) of ~0.79 V.

Effective D-A-D type chromophore of fumaronitrile-core and terminal alkylated bithiophene for solution-processed small molecule organic solar cells

PubMed Central

Nazim, M.; Ameen, Sadia; Seo, Hyung-Kee; Shin, Hyung Shik

2015-01-01

A new and novel organic π-conjugated chromophore (named as RCNR) based on fumaronitrile-core acceptor and terminal alkylated bithiophene was designed, synthesized and utilized as an electron-donor material for the solution-processed fabrication of bulk-heterojunction (BHJ) small molecule organic solar cells (SMOSCs). The synthesized organic chromophore exhibited a broad absorption peak near green region and strong emission peak due to the presence of strong electron-withdrawing nature of two nitrile (–CN) groups of fumaronitrile acceptor. The highest occupied molecular orbital (HOMO) energy level of –5.82 eV and the lowest unoccupied molecular orbital (LUMO) energy level of –3.54 eV were estimated for RCNR due to the strong electron-accepting tendency of –CN groups. The fabricated SMOSC devices with RCNR:PC60BM (1:3, w/w) active layer exhibited the reasonable power conversion efficiency (PCE) of ~2.69% with high short-circuit current density (JSC) of ~9.68 mA/cm2 and open circuit voltage (VOC) of ~0.79 V. PMID:26066557

Fabrication and characterization of CNT-based smart tips for synchrotron assisted STM

DOE PAGES

Yan, Hui; Cummings, Marvin; Camino, Fernando; ...

2015-08-05

Determination of chemical composition along with imaging at the atomic level provides critical information towards fundamental understanding of the surface of materials and, hence, yields the capability to design new materials by tailoring their ultimate functionalities. Synchrotron X-ray assisted scanning tunneling microscopy (SX-STM) is a promising new technique to achieve real space chemically specific atomic mapping. Chemical sensitivity of SX-STM relies on excitation of core electrons by incident X-rays when their energy is tuned to an absorption edge of a particular element. However, along with core-level electrons, photoelectrons are also excited, which yield additional current and interfere with the tunnelingmore » current. To reduce the background photoelectron current and to improve ultimate resolution of SX-STM, we have developed and fabricated multiwalled carbon nanotubes (MWCNT) based “smart tips” using plasma enhanced chemical vapor deposition and focused ion beam milling. As a result, the newly developed CNT-based smart tips, characterized step by step by scanning electron microscopy (SEM) during the fabrication process, demonstrate good performance and provide opportunity for realizing atomic chemical mapping.« less

From core to coax: extending core RF modelling to include SOL, Antenna, and PFC

NASA Astrophysics Data System (ADS)

Shiraiwa, Syun'ichi

2017-10-01

A new technique for the calculation of RF waves in toroidal geometry enables the simultaneous incorporation of antenna geometry, plasma facing components (PFCs), the scrape off-layer (SOL), and core propagation. Traditionally, core RF wave propagation and antenna coupling has been calculated separately both using rather simplified SOL plasmas. The new approach, instead, allows capturing wave propagation in the SOL and its interactions with non-conforming PFCs permitting self-consistent calculation of core absorption and edge power loss, as well as investigating far and near field impurity generation from RF sheaths and a breakdown issue from antenna electric fields. Our approach combines the field solutions obtained from a core spectral code with a hot plasma dielectric and an edge FEM code using a cold plasma approximation via surface admittance-like matrix. Our approach was verified using the TORIC core ICRF spectral code and the commercial COMSOL FEM package, and was extended to 3D torus using open-source scalable MFEM library. The simulation result revealed that as the core wave damping gets weaker, the wave absorption in edge could become non-negligible. Three dimensional capabilities with non axisymmetric edge are being applied to study the antenna characteristic difference between the field aligned and toroidally aligned antennas on Alcator C-Mod, as well as the surface wave excitation on NSTX-U. Work supported by the U.S. DoE, OFES, using User Facility Alcator C-Mod, DE-FC02-99ER54512 and Contract No. DE-FC02-01ER54648.

Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wawrzynczyk, Dominika; Szeremeta, Janusz; Samoc, Marek

Spectrally resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and two-photon fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. In principle, both techniques should provide comparable results and can be interchangeably used for determination of the nonlinear optical absorption parameters, finding maximal values of the cross sections and optimizing them. We have observed slight differences between the two-photon absorption cross sections measured by the two techniques and attributed them to the presence of non-radiative paths of absorption or relaxation.more » The most significant value of two-photon absorption cross section σ{sub 2} for 4.3 nm size InP@ZnS quantum dot was equal to 2200 GM, while the two-photon excitation action cross section σ{sub 2}Φ was found to be 682 GM at 880 nm. The properties of these cadmium-free colloidal quantum dots can be potentially useful for nonlinear bioimaging.« less

Development of innovative oil-core self-organized nanovesicles prepared with chitosan and lecithin using a 2(3) full-factorial design.

PubMed

Haas, Sandra Elisa; de Andrade, Cristiane; Sansone, Pedro Ernesto da Silva; Guterres, Silvia; Dalla Costa, Teresa

2014-11-01

The aim of this study was to develop innovative nanosystems with isopropyl myristate as the oil core of self-assembly nanovesicles constituted of chitosan and lecithin using a 2(3) factorial design. The factors analyzed were chitosan (X1, levels 4 and 8  mg/ml), oil (X2, levels 10 and 20  mg/ml) and lecithin (X3, levels 4 and 8 mg/ml). The responses evaluated were diameter, zeta potential, pH, viscosity, and backscattering analysis. The bioavailability was evaluated after oral administration of clozapine free and nanoencapsulated in rats. The diameter ranged from 0.348 to 1.5 µm for F2 (X1, 4; X2, 10; X3, 8 mg/ml) and F7 (X1, 8; X2, 20; X3, 4  mg/ml), respectively. Laser diffractometry analysis revealed only one diameter population for all batches. Zeta potential was positive, being influenced by X1 and X2/X3 association. Viscosity values were dependent on the X1 and X2 concentrations used. A structure proposed for the nanosystem consists of chitosan forming the hydrophilic shell layer that protects the core comprised of lecithin and the hydrophobic groups of oil. The AUC0-∞ was almost 3 times higher with the clozapine nanoencapsuted in relation to free drug. It was developed a new nanosystem which is able of improving the absorption of drugs.

Interfacial charge separation and recombination in InP and quasi-type II InP/CdS core/shell quantum dot-molecular acceptor complexes.

PubMed

Wu, Kaifeng; Song, Nianhui; Liu, Zheng; Zhu, Haiming; Rodríguez-Córdoba, William; Lian, Tianquan

2013-08-15

Recent studies of group II-VI colloidal semiconductor heterostuctures, such as CdSe/CdS core/shell quantum dots (QDs) or dot-in-rod nanorods, show that type II and quasi-type II band alignment can facilitate electron transfer and slow down charge recombination in QD-molecular electron acceptor complexes. To explore the general applicability of this wave function engineering approach for controlling charge transfer properties, we investigate exciton relaxation and dissociation dynamics in InP (a group III-V semiconductor) and InP/CdS core/shell (a heterostructure beween group III-V and II-VI semiconductors) QDs by transient absorption spectroscopy. We show that InP/CdS QDs exhibit a quasi-type II band alignment with the 1S electron delocalized throughout the core and shell and the 1S hole confined in the InP core. In InP-methylviologen (MV(2+)) complexes, excitons in the QD can be dissociated by ultrafast electron transfer to MV(2+) from the 1S electron level (with an average time constant of 11.4 ps) as well as 1P and higher electron levels (with a time constant of 0.39 ps), which is followed by charge recombination to regenerate the complex in its ground state (with an average time constant of 47.1 ns). In comparison, InP/CdS-MV(2+) complexes show similar ultrafast charge separation and 5-fold slower charge recombination rates, consistent with the quasi-type II band alignment in these heterostructures. This result demonstrates that wave function engineering in nanoheterostructures of group III-V and II-VI semiconductors provides a promising approach for optimizing their light harvesting and charge separation for solar energy conversion applications.

Historical Carbon Dioxide Record from the Siple Station Ice Core (1734-1983)

DOE Data Explorer

Neftel, A. [Physics Institute, University of Bern, Bern, Switzerland; Friedli, H. [Physics Institute, University of Bern, Bern, Switzerland; Moor, E. [Physics Institute, University of Bern, Bern, Switzerland; Lotscher, H. [Physics Institute, University of Bern, Bern, Switzerland; Oeschger, H. [Physics Institute, University of Bern, Bern, Switzerland; Siegenthaler, U. [Physics Institute, University of Bern, Bern, Switzerland; Stauffer, B. [Physics Institute, University of Bern, Bern, Switzerland

1994-09-01

Determinations of ancient atmospheric CO2 concentrations for Siple Station, located in West Antarctica, were derived from measurements of air occluded in a 200-m core drilled at Siple Station in the Antarctic summer of 1983-84. The core was drilled by the Polar Ice Coring Office in Nebraska and the Physics Institute at the University of Bern. The ice could be dated with an accuracy of approximately ±2 years to a depth of 144 m (which corresponds to the year 1834) by counting seasonal variations in electrical conductivity. Below that depth, the core was dated by extrapolation (Friedli et al. 1986). The gases from ice samples were extracted by a dry-extraction system, in which bubbles were crushed mechanically to release the trapped gases, and then analyzed for CO2 by infrared laser absorption spectroscopy or by gas chromatography (Neftel et al. 1985). After the ice samples were crushed, the gas expanded over a cold trap, condensing the water vapor at -80°C in the absorption cell. The analytical system was calibrated for each ice sample measurement with a standard mixture of CO2 in nitrogen and oxygen. For further details on the experimental and dating procedures, see Neftel et al. (1985), Friedli et al. (1986), and Schwander and Stauffer (1984).

Energy-Cascaded Upconversion in an Organic Dye-Sensitized Core/Shell Fluoride Nanocrystal.

PubMed

Chen, Guanying; Damasco, Jossana; Qiu, Hailong; Shao, Wei; Ohulchanskyy, Tymish Y; Valiev, Rashid R; Wu, Xiang; Han, Gang; Wang, Yan; Yang, Chunhui; Ågren, Hans; Prasad, Paras N

2015-11-11

Lanthanide-doped upconversion nanoparticles hold promises for bioimaging, solar cells, and volumetric displays. However, their emission brightness and excitation wavelength range are limited by the weak and narrowband absorption of lanthanide ions. Here, we introduce a concept of multistep cascade energy transfer, from broadly infrared-harvesting organic dyes to sensitizer ions in the shell of an epitaxially designed core/shell inorganic nanostructure, with a sequential nonradiative energy transfer to upconverting ion pairs in the core. We show that this concept, when implemented in a core-shell architecture with suppressed surface-related luminescence quenching, yields multiphoton (three-, four-, and five-photon) upconversion quantum efficiency as high as 19% (upconversion energy conversion efficiency of 9.3%, upconversion quantum yield of 4.8%), which is about ~100 times higher than typically reported efficiency of upconversion at 800 nm in lanthanide-based nanostructures, along with a broad spectral range (over 150 nm) of infrared excitation and a large absorption cross-section of 1.47 × 10(-14) cm(2) per single nanoparticle. These features enable unprecedented three-photon upconversion (visible by naked eye as blue light) of an incoherent infrared light excitation with a power density comparable to that of solar irradiation at the Earth surface, having implications for broad applications of these organic-inorganic core/shell nanostructures with energy-cascaded upconversion.

Density functional theory studies on the structures and electronic communication of meso-ferrocenylporphyrins: long range orbital coupling via porphyrin core.

PubMed

Zhang, Lijuan; Qi, Dongdong; Zhang, Yuexing; Bian, Yongzhong; Jiang, Jianzhuang

2011-02-01

The molecular and electronic structures together with the electronic absorption spectra of a series of metal free meso-ferrocenylporphyrins, namely 5-ferrocenylporphyrin (1), 5,10-diferrocenylporphyrin (2), 5,15-diferrocenylporphyrin (3), 5,10,15-triferrocenylporphyrin (4), and 5,10,15,20-tetraferrocenylporphyrin (5) have been studied with the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. For the purpose of comparative studies, metal free porphyrin without any ferrocenyl group (0) and isolated ferrocene (6) were also calculated. The effects of the number and position of meso-attached ferrocenyl substituents on their molecular and electronic structures, atomic charges, molecular orbitals, and electronic absorption spectra of 1-5 were systematically investigated. The orbital coupling is investigated in detail, explaining well the long range coupling of ferrocenyl substituents connected via porphyrin core and the systematic change in the electronic absorption spectra of porphyrin compounds. Copyright © 2010 Elsevier Inc. All rights reserved.

Detection of water and/or hydroxyl on asteroid (16) Psyche

USGS Publications Warehouse

Takir, Driss; Reddy, Vishnu; Sanchez, Juan A.; Shepard, Michael K.; Emery, Joshua P.

2016-01-01

In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 μm spectral region using the long-wavelength cross-dispersed (LXD: 1.9–4.2 μm) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility. Our observations show that Psyche exhibits a 3 μm absorption feature, attributed to water or hydroxyl. The 3 μm absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H2O-bearing phases (phyllosilicates). The detection of a 3 μm hydration absorption band on Psyche suggests that this asteroid may not be a metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 Gyr. Our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of Psyche.

Surface plasmon resonance enhanced light absorption and wavelength tuneable in gold-coated iron oxide spherical nanoparticle

NASA Astrophysics Data System (ADS)

Dasri, Thananchai; Chingsungnoen, Artit

2018-06-01

Surface plasmon in nano-sized particles, such as gold, silver, copper and their composites, has recently attracted a great deal of attention due to its possible uses in many applications, especially in life sciences. It is desirable for application devices with a tenability of surface plasmon wavelength and optical properties enhancement. This article presents enhanced optical light absorption and tunable wavelength in gold-coated magnetite (Fe3O4@Au core-shell) nanoparticles embedded in water using the theoretical method of discrete dipole approximation (DDA). The absorption spectra in the wavelengths from 350 to 900 nm were found to be the spectra obtained from Fe3O4@Au core-shell nanoparticles, and when compared with pure Fe3O4 nanoparticles, the surface plasmon resonance can be enhanced and tuned over the entire visible spectrum (viz. 350-800 nm) of the electromagnetic spectrum by varying the Au shell thickness (2-5 nm). Similarly, the Faraday rotation spectra can also be obtained.

Detection of Water and/or Hydroxyl on Asteroid (16) Psyche

NASA Astrophysics Data System (ADS)

Takir, Driss; Reddy, Vishnu; Sanchez, Juan A.; Shepard, Michael K.; Emery, Joshua P.

2017-01-01

In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 μm spectral region using the long-wavelength cross-dispersed (LXD: 1.9-4.2 μm) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility. Our observations show that Psyche exhibits a 3 μm absorption feature, attributed to water or hydroxyl. The 3 μm absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H2O-bearing phases (phyllosilicates). The detection of a 3 μm hydration absorption band on Psyche suggests that this asteroid may not be a metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 Gyr. Our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of Psyche.

DETECTION OF WATER AND/OR HYDROXYL ON ASTEROID (16) Psyche

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takir, Driss; Reddy, Vishnu; Sanchez, Juan A.

In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 μ m spectral region using the long-wavelength cross-dispersed (LXD: 1.9–4.2 μ m) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility. Our observations show that Psyche exhibits a 3 μ m absorption feature, attributed to water or hydroxyl. The 3 μ m absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H{sub 2}O-bearing phases (phyllosilicates). The detection of a 3 μ m hydration absorption band on Psyche suggestsmore » that this asteroid may not be a metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 Gyr. Our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of Psyche.« less

The Fabrication and High-Efficiency Electromagnetic Wave Absorption Performance of CoFe/C Core-Shell Structured Nanocomposites

NASA Astrophysics Data System (ADS)

Wan, Gengping; Luo, Yongming; Wu, Lihong; Wang, Guizhen

2018-03-01

CoFe/C core-shell structured nanocomposites (CoFe@C) have been fabricated through the thermal decomposition of acetylene with CoFe2O4 as precursor. The as-prepared CoFe@C was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and thermogravimetric analysis. The results demonstrate that the carbon shell in CoFe@C has a poor crystallization with a thickness about 5-30 nm and a content approximately 48.5 wt.%. Due to a good combination between intrinsic magnetic properties and high-electrical conductivity, the CoFe@C exhibits not only excellent absorption intensity but also wide frequency bandwidth. The minimum RL value of CoFe@C can reach - 44 dB at a thickness of 4.0 mm, and RL values below - 10 dB is up to 4.3 GHz at a thickness of 2.5 mm. The present CoFe@C may be a potential candidate for microwave absorption application.

Development and modeling of multi-phase polymeric origami inspired architecture by using pre-molded geometrical features

NASA Astrophysics Data System (ADS)

Kshad, Mohamed Ali E.; Naguib, Hani E.

2017-02-01

Using Origami folded cores in sandwich structures for lightweight applications has attracted attention in different engineering applications, especially in the applications where the stiffness to weight ratio is a critical design parameter. Recently, common sandwich cores such as honey-comb and foamed cores have been replaced with origami core panels due to their way of force redistribution and energy absorption; these unique characteristics give origami cores high stiffness to weight ratio and high bending and twisting resistance. This paper presents the results of experimental investigations of the effect of base material on the mechanical properties and the impact resistance of Miura-Origami sandwich cores; then, the experimental results are compared with FEA simulation results. The materials used in the study for the origami cores were polymer blends composed of polylactic acid (PLA) and thermoplastic polyurethane (TPU). PLA/TPU blend compositions are (100/0, 80/20, 65/35, 50/50, 20/80, and 0/100) as a weight percentage. The geometrical parameters of the unit cell, base material thickness, and the panel thickness were considered to be constants in this study. The study shows the behavior of the origami cores under impact test and the energy absorbed by the origami folded cores. It was found that 20/80 PLA/TPU blend demonstrated the highest specific energy absorption efficiency both in quasi-static compression and impact tests. Fractured Origami structures were observed to fail at folded edges (creases lines), while the facets exhibit rigid body rotations. The FEM simulation showed a consistency in the impact behavior of the origami cores, and the directional deformational of origami core units which explain the ability of the structure to redistribute the applied force and absorb energy. In this work the origami folded core features were molded directly from the blended material.

Metallic nanoshells with semiconductor cores: optical characteristics modified by core medium properties.

PubMed

Bardhan, Rizia; Grady, Nathaniel K; Ali, Tamer; Halas, Naomi J

2010-10-26

It is well-known that the geometry of a nanoshell controls the resonance frequencies of its plasmon modes; however, the properties of the core material also strongly influence its optical properties. Here we report the synthesis of Au nanoshells with semiconductor cores of cuprous oxide and examine their optical characteristics. This material system allows us to systematically examine the role of core material on nanoshell optical properties, comparing Cu(2)O core nanoshells (ε(c) ∼ 7) to lower core dielectric constant SiO(2) core nanoshells (ε(c) = 2) and higher dielectric constant mixed valency iron oxide nanoshells (ε(c) = 12). Increasing the core dielectric constant increases nanoparticle absorption efficiency, reduces plasmon line width, and modifies plasmon energies. Modifying the core medium provides an additional means of tailoring both the near- and far-field optical properties in this unique nanoparticle system.

Subaru HDS transmission spectroscopy of the transiting extrasolar planet HD209458b

NASA Astrophysics Data System (ADS)

Narita, N.; Suto, Y.; Winn, J. N.; Turner, E. L.; Aoki, W.; Leigh, C. J.; Sato, B.; Tamura, M.; Yamada, T.

2006-02-01

We have searched for absorption in several common atomic species due to the atmosphere or exosphere of the transiting extrasolar planet HD 209458b, using high precision optical spectra obtained with the Subaru High Dispersion Spectrograph (HDS). Previously we reported an upper limit on Hα absorption of 0.1% (3σ) within a 5.1Å band. Using the same procedure, we now report upper limits on absorption due to the optical transitions of Na D, Li, Hα, Hβ, Hγ, Fe, and Ca. The 3σ upper limit for each transition is approximately 1% within a 0.3Å band (the core of the line), and a few tenths of a per cent within a 2Å band (the full line width). The wide-band results are close to the expected limit due to photon-counting (Poisson) statistics, although in the narrow-band case we have encountered unexplained systematic errors at a few times the Poisson level. These results are consistent with all previously reported detections (Charbonneau et al. 2002, ApJ, 568, 377) and upper limits (Bundy & Marcy 2000, PASP, 112, 1421; Moutou et al. 2001, A&A, 371, 260), but are significantly more sensitive yet achieved from ground based observations.

Determining CDOM Absorption Spectra in Diverse Aquatic Environments Using a Multiple Pathlength, Liquid Core Waveguide System

NASA Technical Reports Server (NTRS)

Miller, Richard L.; Belz, Mathias; DelCastillo, Carlos; Trzaska, Rick

2001-01-01

We evaluated the accuracy, sensitivity and precision of a multiple pathlength, liquid core waveguide (MPLCW) system for measuring colored dissolved organic matter (CDOM) absorption in the UV-visible spectral range (370-700 nm). The MPLCW has four optical paths (2.0, 9.8, 49.3, and 204 cm) coupled to a single Teflon AF sample cell. Water samples were obtained from inland, coastal and ocean waters ranging in salinity from 0 to 36 PSU. Reference solutions for the MPLCW were made having a refractive index of the sample. CDOM absorption coefficients, aCDOM, and the slope of the log-linearized absorption spectra, S, were compared with values obtained using a dual-beam spectrophotometer. Absorption of phenol red secondary standards measured by the MPLCW at 558 nm were highly correlated with spectrophotometer values and showed a linear response across all four pathlengths. Values of aCDOM measured using the MPLCW were virtually identical to spectrophotometer values over a wide range of concentrations. The dynamic range of aCDOM for MPLCW measurements was 0.002 - 231.5 m-1. At low CDOM concentrations spectrophotometric aCDOM were slightly greater than MPLCW values and showed larger fluctuations at longer wavelengths due to limitations in instrument precision. In contrast, MPLCW spectra followed an exponential to 600 nm for all samples.

High power 938 nanometer fiber laser and amplifier

DOEpatents

Dawson, Jay W [Livermore, CA; Liao, Zhi Ming [Pleasanton, CA; Beach, Raymond J [Livermore, CA; Drobshoff, Alexander D [Livermore, CA; Payne, Stephen A [Castro Valley, CA; Pennington, Deanna M [Livermore, CA; Hackenberg, Wolfgang [Munich, DE; Calia, Domenico Bonaccini [Garching, DE; Taylor, Luke [Montauban de Bretagne, FR

2006-05-02

An optical fiber amplifier includes a length of silica optical fiber having a core doped with neodymium, a first cladding and a second cladding each with succeeding lower refractive indices, where the first cladding diameter is less than 10 times the diameter of the core. The doping concentration of the neodymium is chosen so that the small signal absorption for 816 nm light traveling within the core is less than 15 dB/m above the other fiber losses. The amplifier is optically pumped with one laser into the fiber core and with another laser into the first cladding.

Determining CDOM Absorption Spectra in Diverse Coastal Environments Using a Multiple Pathlength, Liquid Core Waveguide System. Measuring the Absorption of CDOM in the Field Using a Multiple Pathlength Liquid Waveguide System

NASA Technical Reports Server (NTRS)

Miller, Richard L.; Belz, Mathias; DelCastillo, Carlos; Trzaska, Rick

2000-01-01

We evaluated the accuracy, sensitivity and precision of a multiple pathlength, liquid core waveguide (MPLCW) system for measuring colored dissolved organic matter (CDOM) absorption in the UV-visible spectral range (370-700 nm). The MPLCW has four optical paths (2.0, 9.8, 49.3, and 204 cm) coupled to a single Teflon AF sample cell. Water samples were obtained from inland, coastal and ocean waters ranging in salinity from 0 to 36 PSU. Reference solutions for the MPLCW were made having a refractive index of the sample. CDOM absorption coefficients, a(sub CDOM), and the slope of the log-linearized absorption spectra, S, were compared with values obtained using a dual-beam spectrophotometer. Absorption of phenol red secondary standards measured by the MPLCW at 558 nm were highly correlated with spectrophotometer values (r > 0.99) and showed a linear response across all four pathlengths. Values of a(sub CDOM) measured using the MPLCW were virtually identical to spectrophotometer values over a wide range of concentrations. The dynamic range of a(sub CDOM) for MPLCW measurements was 0.002 - 231.5/m. At low CDOM concentrations (a(sub 370) < 0.1/m) spectrophotometric a(sub CDOM) were slightly greater than MPLCW values and showed larger fluctuations at longer wavelengths due to limitations in instrument precision. In contrast, MPLCW spectra followed an exponential to 600 nm for all samples. The maximum deviation in replicate MPLCW spectra was less than 0.001 absorbance units. The portability, sampling, and optical characteristics of a MPLCW system provide significant enhancements for routine CDOM absorption measurements in a broad range of natural waters.

Role of oxygen hole centres in the photodarkening of ytterbium-doped phosphosilicate fibre

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rybaltovsky, A A; Bobkov, K K; Likhachev, M E

2013-11-30

We have studied the photodarkening in active fibres with an ytterbium-doped phosphosilicate glass core under IR irradiation with a pump source (920 nm) and UV irradiation (193 nm). Analysis of absorption and luminescence spectra suggests that such irradiations produce phosphorus – oxygen – hole centres (P-OHCs) in the core glass network and lead to the reduction of the ytterbium ions to a divalent state (Yb{sup 2+}). The photoinduced optical loss in the fibres in the visible range (400 – 700 nm) is mainly due to absorption by the P-OHCs. A quantum-mechanical model is proposed for P-OHC and Yb{sup 2+} formation.more » (nonlinear optical phenomena)« less

Evanescent field characteristics of eccentric core optical fiber for distributed sensing.

PubMed

Liu, Jianxia; Yuan, Libo

2014-03-01

Fundamental core-mode cutoff and evanescent field are considered for an eccentric core optical fiber (ECOF). A method has been proposed to calculate the core-mode cutoff by solving the eigenvalue equations of an ECOF. Using conformal mapping, the asymmetric geometrical structure can be transformed into a simple, easily solved axisymmetric optical fiber with three layers. The variation of the fundamental core-mode cut-off frequency (V(c)) is also calculated with different eccentric distances, wavelengths, core radii, and coating refractive indices. The fractional power of evanescent fields for ECOF is also calculated with the eccentric distances and coating refractive indices. These calculations are necessary to design the structural parameters of an ECOF for long-distance, single-mode distributed evanescent field absorption sensors.

Mid-infrared 1  W hollow-core fiber gas laser source.

PubMed

Xu, Mengrong; Yu, Fei; Knight, Jonathan

2017-10-15

We report the characteristics of a 1 W hollow-core fiber gas laser emitting CW in the mid-IR. Our system is based on an acetylene-filled hollow-core optical fiber guiding with low losses at both the pump and laser wavelengths and operating in the single-pass amplified spontaneous emission regime. Through systematic characterization of the pump absorption and output power dependence on gas pressure, fiber length, and pump intensity, we determine that the reduction of pump absorption at high pump flux and the degradation of gain performance at high gas pressure necessitate the use of increased gain fiber length for efficient lasing at higher powers. Low fiber attenuation is therefore key to efficient high-power laser operation. We demonstrate 1.1 W output power at a 3.1 μm wavelength by using a high-power erbium-doped fiber amplifier pump in a single-pass configuration, approximately 400 times higher CW output power than in the ring cavity previously reported.

Ag@Aggregation-induced emission dye core/shell nanostructures with enhanced one- and two-photon fluorescence

NASA Astrophysics Data System (ADS)

Wang, Cheng; Li, Yang; Xu, Qiujin; Luo, Liang

2017-10-01

Combining plasmonic nanostructures with two-photon fluorescence materials is a promising way to significantly enhance two-photon fluorescence. Ag@1,4-bis(2-cyano-2-phenylethenyl) benzene (BCPEB) core/shell nanostructures were fabricated by simply incubating the isolated Ag nanoparticles with BCPEB microrods in ethanol. BCPEB was chosen as the fluorescent organic molecule owing to the aggregation-induced-emission (AIE) nature which would reduce the emission loss as being practically applied in solid phase. By utilizing the match of the extinction spectrum of Ag nanoparticles and BCPEB's absorption band, the target Ag@BCPEB core/shell nanostructures showed an enhanced one-photon (12×) fluorescence, integrating with SERS signal as well. Moreover, the resultant second harmonic generation of Ag nanoparticles under two-photon excitation also well matched with the absorption band of BCPEB, and significant enhanced two-photon (17×) fluorescence was obtained. The confocal images of NIH-3T3 cells with these nanostructures under one- and two-photon excitation showed good contrast and brightness for bio-imaging.

Hexavalent chromium monitor

DOEpatents

Tao, Shiquan; Winstead, Christopher B.

2005-04-12

A monitor is provided for use in measuring the concentration of hexavalent chromium in a liquid, such as water. The monitor includes a sample cell, a light source, and a photodetector. The sample cell is in the form of a liquid-core waveguide, the sample cell defining an interior core and acting as a receiver for the liquid to be analyzed, the interior surface of the sample cell having a refractive index of less than 1.33. The light source is in communication with a first end of the sample cell for emitting radiation having a wavelength of about and between 350 to 390 nm into the interior core of the waveguide. The photodetector is in communication with a second end of the waveguide for measuring the absorption of the radiation emitted by the light source by the liquid in the sample cell. The monitor may also include a processor electronically coupled to the photodetector for receipt of an absorption signal to determine the concentration of hexavalent chromium in the liquid.

Intrinsic, Narrow N V Absorption Reveals a Clumpy Outflow in z < 0.4 Radio-Loud Quasars

NASA Astrophysics Data System (ADS)

DeMarcy, Bryan; Serra, Viktoriah; Culliton, Chris; Ganguly, Rajib; Runnoe, Jessie; Charlton, Jane; Eracleous, Michael; Misawa, Toru; Narayanan, Anand

2018-01-01

Quasar outflows are often invoked in models for galaxy evolution to inject energy and momentum into the gas in the host galaxy and influence its star formation history. Thus, the study of quasar outflows is essential for understanding galaxy evolution. N V absorption systems within the associated region (|Δv| ≤ 5000 km s-1) of the quasar are thought to be intrinsic since many show evidence for partial covering of the quasar. A recent archival study of quasar spectra taken with COS/G130M or G160M found 39/181 radio-quiet quasars show intrinsic N V absorption, while none of the 31 radio-loud quasars have N V absorption detected (Culliton et al. 2017). Further investigation of these radio-loud quasars showed a clear bias towards compact morphologies as revealed by FIRST 1.4 GHz imaging and comparatively flat radio spectra. This suggests we are viewing more face-on orientations which prevent us from seeing absorption outflows. The cause for such bias within the HST archive is still unknown; however, it could explain the lack of radio-loud intrinsic N V absorption seen by Culliton et al. (2017). Alternatively, the quasar wind structure may be fundamentally different between radio-loud and radio-quiet objects. We used COS/G130M or G160M to obtain rest-frame UV spectra (1195 Å - 1250 Å) of 14 low-redshift SDSS radio-loud quasars which show lobe-dominated FIRST morphologies to distinguish between these possibilities. Intrinsic N V absorption was detected in 6 of our 14 quasars. This suggests the lack of detections in the archival study was a result of an orientation effect/sampling bias rather than to differences in wind structure between radio-loud and radio-quiet quasars. Interestingly, we find significant overlap in radio core fractions between quasars with and without N V detection. Quasars in our sample with N V detection span a range of core fractions from < 0.01 up to 0.89 while those without detected N V range from 0.04 up to 0.93. A laminar outflow with a small opening angle would be difficult to explain given this overlap in radio core fractions. Our observations suggest a clumpy, sporadic outflow is the more likely explanation.

Core-shell solar cell fabrication using heterostructure of ZnO-nanowires arrays decorated with sputtered CdTe-nanoparticles

NASA Astrophysics Data System (ADS)

Akbarnejad, Elaheh; Dehghan Nayeri, Fatemeh; Ghoranneviss, Mahmood

2018-03-01

Core-shell heterostructures of ZnO-NWs/CdTe-NPs were fabricated through covering ZnO-NWs arrays using CdTe-NPs and the room temperature RF magnetron sputtering method. The influence of different CdTe-NPs deposition time (5, 20, 40 and 60 min) on the physical properties of core-shell heterostructures were investigated. In order to achieve the highest coverage level and a wide range of optical absorption at a visible range for a ZnO-NWs/CdTe-NPs (60 min) array, FTO/ZnO-NWs/CdTe-NPs (60 min)/Ni/Au core-shell solar cells were used. Solar cell fabrication was performed by soaking the samples in a saturated CdCl2 solution in methanol and a post-annealing treatment at 400 °C for 1 h in air which led to grain growth, the passivation of deep level defects, and the decrease of stacking faults. Short-circuit current and power conversion efficiency of the fabricated cell under illumination with visible light AM1.5 (100 mW cm-2) were 13.3 mA cm-2 and 3.41%, respectively. It was found that introducing a thin interfacial layer of CdSe to the configuration (FTO/ZnO-NWs/CdSe (10 nm)/CdTe-NPs (60 min)/Ni/Au) led to a 5.58% enhancement of photovoltaic performance of the solar cell (20.9 mA cm-2), which is 63.6% more than that of the same configuration without CdSe.

Dye-Sensitized Core/Active Shell Upconversion Nanoparticles for Optogenetics and Bioimaging Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Xiang; Zhang, Yuanwei; Takle, Kendra

2016-01-26

Near Infrared (NIR) dye-sensitized upconversion nanoparticles (UCNPs) have recently been proposed in order to broaden the absorption range and to boost upconversion efficiency. However, implementing this strategy has been limited only to bare core UCNP structures that are faintly luminescent. Herein, we report on an approach to achieve significantly enhanced upconversion luminescence in dye-sensitized core-active shell UCNPs with a broadened absorption range via the doping of ytterbium ions in the UCNP shell in order to bridge the energy transfer from the dye to the UCNP core. As a result, we have been able to synergize the two most practical upconversionmore » booster effectors (dye-sensitizing and core/shell enhancement). The absolute quantum yield of our dye-sensitized core/active shell UCNPs at 800 nm was determined to be ~6% at 2 W/cm2, about 33 times larger than the highest value reported to date for existing 800 nm excitable UCNPs. Moreover, for the first time, by using dye-sensitized core/active shell UCNP embedded poly(methyl methacrylate) polymer implantable systems, we successfully shifted the optogenetic neuron excitation window to a wavelength that is compatible with deep tissue penetrable near the infrared wavelength at 800 nm. Finally, amphiphilic triblock copolymer, Pluronic F127 coatings permit the transfer of hydrophobic UCNPs into water, resulting in water-soluble nanoparticles with well-preserved optical property in aqueous solution. We believe that this research offers a new solution to enhance upconversion efficiency for photonic and biophotonic purposes and opens up new opportunities to use UCNPs as a NIR relay for optogenetic applications.« less

Small-Molecule Acceptor Based on the Heptacyclic Benzodi(cyclopentadithiophene) Unit for Highly Efficient Nonfullerene Organic Solar Cells.

PubMed

Kan, Bin; Feng, Huanran; Wan, Xiangjian; Liu, Feng; Ke, Xin; Wang, Yanbo; Wang, Yunchuang; Zhang, Hongtao; Li, Chenxi; Hou, Jianhui; Chen, Yongsheng

2017-04-05

A new nonfullerene small molecule with acceptor-donor-acceptor (A-D-A) structure, namely, NFBDT, based on a heptacyclic benzodi(cyclopentadithiophene) (FBDT) unit using benzo[1,2-b:4,5-b']dithiophene as the core unit, was designed and synthesized. Its absorption ability, energy levels, thermal stability, as well as photovoltaic performances were fully investigated. NFBDT exhibits a low optical bandgap of 1.56 eV resulting in wide and efficient absorption that covered the range from 600 to 800 nm, and suitable energy levels as an electron acceptor. With the widely used and successful wide bandgap polymer PBDB-T selected as the electron donor material, an optimized PCE of 10.42% was obtained for the PBDB-T:NFBDT-based device with an outstanding short-circuit current density of 17.85 mA cm -2 under AM 1.5G irradiation (100 mW cm -2 ), which is so far among the highest performance of NF-OSC devices. These results demonstrate that the BDT unit could also be applied for designing NF-acceptors, and the fused-ring benzodi(cyclopentadithiophene) unit is a prospective block for designing new NF-acceptors with excellent performance.

Hydrodynamic stability and Ti-tracer distribution in low-adiabat OMEGA direct-drive implosions

NASA Astrophysics Data System (ADS)

Joshi, Tirtha R.

We discuss the hydrodynamic stability of low-adiabat OMEGA direct-drive implosions based on results obtained from simultaneous emission and absorption spectroscopy of a titanium tracer added to the target. The targets were deuterium filled, warm plastic shells of varying thicknesses and filling gas pressures with a submicron Ti-doped tracer layer initially located on the inner surface of the shell. The spectral features from the titanium tracer are observed during the deceleration and stagnation phases of the implosion, and recorded with a time integrated spectrometer (XRS1), streaked crystal spectrometer (SSCA) and three gated, multi-monochromatic X-ray imager (MMI) instruments fielded along quasi-orthogonal lines-of-sight. The time-integrated, streaked and gated data show simultaneous emission and absorption spectral features associated with titanium K-shell line transitions but only the MMI data provides spatially resolved information. The arrays of gated spectrally resolved images recorded with MMI were processed to obtain spatially resolved spectra characteristic of annular contour regions on the image. A multi-zone spectroscopic analysis of the annular spatially resolved spectra permits the extraction of plasma conditions in the core as well as the spatial distribution of tracer atoms. In turn, the titanium atom distribution provides direct evidence of tracer penetration into the core and thus of the hydrodynamic stability of the shell. The observations, timing and analysis indicate that during fuel burning the titanium atoms have migrated deep into the core and thus shell material mixing is likely to impact the rate of nuclear fusion reactions, i.e. burning rate, and the neutron yield of the implosion. We have found that the Ti atom number density decreases towards the center in early deceleration phase, but later in time the trend is just opposite, i.e., it increases towards the center of the implosion core. This is in part a consequence of the convergent effect of spherical geometry. The spatial profiles of Ti areal densities in the implosion core are extracted from space-resolved spectra and also evaluated using 1D spherical scaling. The trends are similar to the Ti number density spatial profiles. The areal densities extracted from data and 1D spherical scaling are very comparable in the outer spherical zones of the implosion core but significantly deviate in the innermost zone. We have observed that approximately 85% of the Ti atoms migrate into the hot core, while 15% of the atoms are still on the shell-fuel interface and contributing to the absorption. In addition, a method to extract the hot spot size based on the formation of the absorption feature in a sequence of annular spectra will be discussed. Results and trends are discussed as a function of target shell thickness and filling pressure, and laser pulse shape.

Study on preparation and microwave absorption property of the core-nanoshell composite materials doped with La.

PubMed

Wei, Liqiu; Che, Ruxin; Jiang, Yijun; Yu, Bing

2013-12-01

Microwave absorbing material plays a great role in electromagnetic pollution controlling, electromagnetic interference shielding and stealth technology, etc. The core-nanoshell composite materials doped with La were prepared by a solid-state reaction method, which is applied to the electromagnetic wave absorption. The core is magnetic fly-ash hollow cenosphere, and the shell is the nanosized ferrite doped with La. The thermal decomposition process of the sample was investigated by thermogravimetry and differential thermal analysis. The morphology and components of the composite materials were investigated by the X-ray diffraction analysis, the microstructure was observed by scanning electron microscope and transmission electron microscope. The results of vibrating sample magnetometer analysis indicated that the exchange-coupling interaction happens between ferrite of magnetic fly-ash hollow cenosphere and nanosized ferrite coating, which caused outstanding magnetic properties. The microwave absorbing property of the sample was measured by reflectivity far field radar cross section of radar microwave absorbing material with vector network analyzer. The results indicated that the exchange-coupling interaction enhanced magnetic loss of composite materials. Therefore, in the frequency of 5 GHz, the reflection coefficient can achieve -24 dB. It is better than single material and is consistent with requirements of the microwave absorbing material at the low-frequency absorption. Copyright © 2013 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Chemical Speciation and Bond Lengths of Organic Solutes by Core-Level Spectroscopy: pH and Solvent Influence on p-Aminobenzoic Acid.

PubMed

Stevens, Joanna S; Gainar, Adrian; Suljoti, Edlira; Xiao, Jie; Golnak, Ronny; Aziz, Emad F; Schroeder, Sven L M

2015-05-04

Through X-ray absorption and emission spectroscopies, the chemical, electronic and structural properties of organic species in solution can be observed. Near-edge X-ray absorption fine structure (NEXAFS) and resonant inelastic X-ray scattering (RIXS) measurements at the nitrogen K-edge of para-aminobenzoic acid reveal both pH- and solvent-dependent variations in the ionisation potential (IP), 1s→π* resonances and HOMO-LUMO gap. These changes unequivocally identify the chemical species (neutral, cationic or anionic) present in solution. It is shown how this incisive chemical state sensitivity is further enhanced by the possibility of quantitative bond length determination, based on the analysis of chemical shifts in IPs and σ* shape resonances in the NEXAFS spectra. This provides experimental access to detecting even minor variations in the molecular structure of solutes in solution, thereby providing an avenue to examining computational predictions of solute properties and solute-solvent interactions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemical Speciation and Bond Lengths of Organic Solutes by Core-Level Spectroscopy: pH and Solvent Influence on p -Aminobenzoic Acid

DOE PAGES

Stevens, Joanna S.; Gainar, Adrian; Suljoti, Edlira; ...

2015-03-18

Through X-ray absorption and emission spectroscopies, the chemical, electronic and structural properties of organic species in solution can be observed. Near-edge X-ray absorption fine structure (NEXAFS) and resonant inelastic X-ray scattering (RIXS) measurements at the nitrogen K-edge of para-aminobenzoic acid reveal both pH- and solvent-dependent variations in the ionisation potential (IP), 1s→π* resonances and HOMO–LUMO gap. These changes unequivocally identify the chemical species (neutral, cationic or anionic) present in solution. It is shown how this incisive chemical state sensitivity is further enhanced by the possibility of quantitative bond length determination, based on the analysis of chemical shifts in IPs andmore » σ* shape resonances in the NEXAFS spectra. Finally, this provides experimental access to detecting even minor variations in the molecular structure of solutes in solution, thereby providing an avenue to examining computational predictions of solute properties and solute–solvent interactions.« less

The influence of rotation on optical emission profiles of O stars

NASA Astrophysics Data System (ADS)

Hillier, D. John; Bouret, Jean-Claude; Lanz, Thierry; Busche, Joseph R.

2012-10-01

We study the formation of photospheric emission lines in O stars and show that the rectangular profiles, sometimes double peaked, that are observed for some stars are a direct consequence of rotation, and it is unnecessary to invoke an enhanced density structure in the equatorial regions. Emission lines, such as N IV λ4058 and the N III λλ4634-4640-4642 multiplet, exhibit non-standard 'limb-darkening' laws. The lines can be in absorption for rays striking the centre of the star and in emission for rays near the limb. Weak features in the flux spectrum do not necessarily indicate an intrinsically weak feature - instead the feature can be weak because of cancellation between absorption in 'core' rays and emission from rays near the limb. Rotation also modifies line profiles of wind diagnostics such as He II λ4686 and Hα and should not be neglected when inferring the actual stratification, level and nature of wind structures.

Photonic crystal fiber monitors for intracellular ice formation

NASA Astrophysics Data System (ADS)

Battinelli, Emily; Reimlinger, Mark; Wynne, Rosalind

2012-04-01

An all-silica steering wheel photonic crystal fiber (SW-PCF) device with real-time analysis for cellular temperature sensing is presented. Results are provided for water-filled SW-PCF fibers experiencing cooling down near -40°C. Cellular temperature sensors with fast response times are of interest particularly to the study of cryopreservation, which has been influential in applications such as tissue preservation, food quality control, genetic engineering, as well as drug discovery and in- vitro toxin testing. Results of this investigation are relevant to detection of intracellular ice formation (IIF) and better understanding cell freezing at very low temperatures. IIF detection is determined as a function of absorption occurring within the core of the SW-PCF. The SW-PCF has a 3.3μm core diameter, 125μm outer diameter and steering wheel-like air hole pattern with triangular symmetry, with a 20μm radius. One end of a 0.6m length of the SW-PCF is placed between two thermoelectric coolers, filled with ~0.1μL water. This end is butt coupled to a 0.5m length of single mode fiber (SMF), the distal end of the fiber is then inserted into an optical spectrum analyzer. A near-IR light source is guided through the fiber, such that the absorption of the material in the core can be measured. Spectral characteristics demonstrated by the optical absorption of the water sample were present near the 1300-1700nm window region with strongest peaks at 1350, 1410 and 1460nm, further shifting of the absorption peaks is possible at cryogenic temperatures making this device suitable for IIF monitoring applications.

Ferroportin mediates the intestinal absorption of iron from a nanoparticulate ferritin core mimetic in mice

PubMed Central

Aslam, Mohamad F.; Frazer, David M.; Faria, Nuno; Bruggraber, Sylvaine F. A.; Wilkins, Sarah J.; Mirciov, Cornel; Powell, Jonathan J.; Anderson, Greg J.; Pereira, Dora I. A.

2014-01-01

The ferritin core is composed of fine nanoparticulate Fe3+ oxohydroxide, and we have developed a synthetic mimetic, nanoparticulate Fe3+ polyoxohydroxide (nanoFe3+). The aim of this study was to determine how dietary iron derived in this fashion is absorbed in the duodenum. Following a 4 wk run-in on an Fe-deficient diet, mice with intestinal-specific disruption of the Fpn-1 gene (Fpn-KO), or littermate wild-type (WT) controls, were supplemented with Fe2+ sulfate (FeSO4), nanoFe3+, or no added Fe for a further 4 wk. A control group was Fe sufficient throughout. Direct intestinal absorption of nanoFe3+ was investigated using isolated duodenal loops. Our data show that FeSO4 and nanoFe3+ are equally bioavailable in WT mice, and at wk 8 the mean ± sem hemoglobin increase was 18 ± 7 g/L in the FeSO4 group and 30 ± 5 g/L in the nanoFe3+ group. Oral iron failed to be utilized by Fpn-KO mice and was retained in enterocytes, irrespective of the iron source. In summary, although nanoFe3+ is taken up directly by the duodenum its homeostasis is under the normal regulatory control of dietary iron absorption, namely via ferroportin-dependent efflux from enterocytes, and thus offers potential as a novel oral iron supplement.—Aslam, M. F., Frazer, D. M., Faria, N., Bruggraber, S. F. A., Wilkins, S. J., Mirciov, C., Powell, J. J., Anderson, G. J., Pereira, D. I. A. Ferroportin mediates the intestinal absorption of iron from a nanoparticulate ferritin core mimetic in mice. PMID:24776745

Effect of geometric parameters on the in-plane crushing behavior of honeycombs and honeycombs with facesheets

NASA Astrophysics Data System (ADS)

Atli-Veltin, Bilim

In aerospace field, use of honeycombs in energy absorbing applications is a very attractive concept since they are relatively low weight structures and their crushing behavior satisfies the requirements of ideal energy absorbing applications. This dissertation is about the utilization of honeycomb crushing in energy absorbing applications and maximizing their specific energy absorption (SEA) capacity by modifying their geometry. In-plane direction crushing of honeycombs is investigated with the help of simulations conducted with ABAQUS. Due to the nonlinearity of the problem an optimization technique could not be implemented; however, the results of the trend studies lead to geometries with improved SEA. This study has two objectives; the first is to obtain modified cell geometry for a hexagonal honeycomb cell in order to provide higher energy absorption for minimum weight relative to the regular hexagonal cell geometry which has 30° cell angle and walls at equal length. The results of the first objective show that by increasing the cell angle, increasing wall thickness and reducing vertical wall length it is possible to increase the SEA 4.8 times; where the honeycomb with modified geometry provided 3.3 kJ/kg SEA and with regular geometry 0.68 kJ/kg SEA. The second objective considers integration of the energy absorbing honeycombs into the helicopter subfloor, possibly as the web section of a keel beam. In-plane direction crushing of a honeycomb core sandwiched between two facesheets is simulated. Effects of core and facesheet geometric parameters on the energy absorption are investigated, and modified geometries are suggested. For the sandwich structure with thin facesheets increasing cell angle, increasing wall thicknesses and decreasing the cell depth increase the SEA. For the ones with thick facesheet reducing vertical wall length, increasing wall thicknesses and reducing the cell depth increase the SEA. The results show that regular honeycomb geometry with thin facesheets has SEA of 7.24 kJ/kg and with thick facesheets 13.16 kJ/kg. When the geometries are modified the SEA increases to 20.5 kJ/kg for the core with thin facesheets and 53.47 kJ/kg for the core with thick facesheets. The key finding of the dissertation is that the in-plane direction crushing of the honeycombs with facesheets has great potential to be used for the energy absorbing applications since their SEA levels are high enough to make them attractive for applications where high crash loads need to be absorbed such as helicopter crash.

Study of low-velocity impact response of sandwich panels with shear-thickening gel cores

NASA Astrophysics Data System (ADS)

Wang, Yunpeng; Gong, Xinglong; Xuan, Shouhu

2018-06-01

The low-velocity impact response of sandwich panels with shear-thickening gel cores was studied. The impact tests indicated that the sandwich panels with shear-thickening gel cores showed excellent properties of energy dissipation and stress distribution. In comparison to the similar sandwich panels with chloroprene rubber cores and ethylene-propylene-diene monomer cores, the shear-thickening gel cores led to the obviously smaller contact forces and the larger energy absorptions. Numerical modelling with finite element analysis was used to investigate the stress distribution of the sandwich panels with shear-thickening gel cores and the results agreed well with the experimental results. Because of the unique mechanical property of the shear-thickening gel, the concentrated stress on the front facesheets were distributed to larger areas on the back facesheets and the peak stresses were reduced greatly.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makarov, Nikolay S.; Lin, Qianglu; Pietryga, Jeffrey M.

One source of efficiency losses in photovoltaic cells is their transparency toward solar photons with energies below the band gap of the absorbing layer. This loss can be reduced using a process of up-conversion whereby two or more sub-band-gap photons generate a single above-gap exciton. Traditional approaches to up-conversion, such as nonlinear two-photon absorption (2PA) or triplet fusion, suffer from low efficiency at solar light intensities, a narrow absorption bandwidth, nonoptimal absorption energies, and difficulties for implementing in practical devices. We show that these deficiencies can be alleviated using the effect of Auger up-conversion in thick-shell PbSe/CdSe quantum dots. Thismore » process relies on Auger recombination whereby two low-energy, core-based excitons are converted into a single higher-energy, shell-based exciton. When compared to their monocomponent counterparts, the tailored PbSe/CdSe heterostructures feature enhanced absorption cross-sections, a higher efficiency of the “productive” Auger pathway involving re-excitation of a hole, and longer lifetimes of both core- and shell-localized excitons. These features lead to effective up-conversion cross-sections that are more than 6 orders of magnitude higher than for standard nonlinear 2PA, which allows for efficient up-conversion of continuous wave infrared light at intensities as low as a few watts per square centimeter.« less

Dependence of Aerosol Light Absorption and Single-Scattering Albedo On Ambient Relative Humidity for Sulfate Aerosols with Black Carbon Cores

NASA Technical Reports Server (NTRS)

Redemann, Jens; Russell, Philip B.; Hamill, Patrick

2001-01-01

Atmospheric aerosols frequently contain hygroscopic sulfate species and black carbon (soot) inclusions. In this paper we report results of a modeling study to determine the change in aerosol absorption due to increases in ambient relative humidity (RH), for three common sulfate species, assuming that the soot mass fraction is present as a single concentric core within each particle. Because of the lack of detailed knowledge about various input parameters to models describing internally mixed aerosol particle optics, we focus on results that were aimed at determining the maximum effect that particle humidification may have on aerosol light absorption. In the wavelength range from 450 to 750 nm, maximum absorption humidification factors (ratio of wet to 'dry=30% RH' absorption) for single aerosol particles are found to be as large as 1.75 when the RH changes from 30 to 99.5%. Upon lesser humidification from 30 to 80% RH, absorption humidification for single particles is only as much as 1.2, even for the most favorable combination of initial ('dry') soot mass fraction and particle size. Integrated over monomodal lognormal particle size distributions, maximum absorption humidification factors range between 1.07 and 1.15 for humidification from 30 to 80% and between 1.1 and 1.35 for humidification from 30 to 95% RH for all species considered. The largest humidification factors at a wavelength of 450 nm are obtained for 'dry' particle size distributions that peak at a radius of 0.05 microns, while the absorption humidification factors at 700 nm are largest for 'dry' size distributions that are dominated by particles in the radius range of 0.06 to 0.08 microns. Single-scattering albedo estimates at ambient conditions are often based on absorption measurements at low RH (approx. 30%) and the assumption that aerosol absorption does not change upon humidification (i.e., absorption humidification equal to unity). Our modeling study suggests that this assumption alone can introduce absolute errors in estimates of the midvisible single-scattering albedo of up to 0.05 for realistic dry particle size distributions. Our study also indicates that this error increases with increasing wavelength. The potential errors in aerosol single-scattering albedo derived here are comparable in magnitude and in addition to uncertainties in single-scattering albedo estimates that are based on measurements of aerosol light absorption and scattering.

A new type of artificial structure to achieve broadband omnidirectional acoustic absorption

NASA Astrophysics Data System (ADS)

Zheng, Li-Yang; Wu, Ying; Zhang, Xiao-Liu; Ni, Xu; Chen, Ze-Guo; Lu, Ming-Hui; Chen, Yan-Feng

2013-10-01

We present a design for a two-dimensional omnidirectional acoustic absorber that can achieve 98.6% absorption of acoustic waves in water, forming an effective acoustic black hole. This artificial black hole consists of an absorptive core coated with layers of periodically distributed polymer cylinders embedded in water. Effective medium theory describes the response of the coating layers to the acoustic waves. The polymer parameters can be adjusted, allowing practical fabrication of the absorber. Since the proposed structure does not rely on resonances, it is applicable to broad bandwidths. The design might be extended to a variety of applications.

Analysis on Reactor Criticality Condition and Fuel Conversion Capability Based on Different Loaded Plutonium Composition in FBR Core

NASA Astrophysics Data System (ADS)

Permana, Sidik; Saputra, Geby; Suzuki, Mitsutoshi; Saito, Masaki

2017-01-01

Reactor criticality condition and fuel conversion capability are depending on the fuel arrangement schemes, reactor core geometry and fuel burnup process as well as the effect of different fuel cycle and fuel composition. Criticality condition of reactor core and breeding ratio capability have been investigated in this present study based on fast breeder reactor (FBR) type for different loaded fuel compositions of plutonium in the fuel core regions. Loaded fuel of Plutonium compositions are based on spent nuclear fuel (SNF) of light water reactor (LWR) for different fuel burnup process and cooling time conditions of the reactors. Obtained results show that different initial fuels of plutonium gives a significant chance in criticality conditions and fuel conversion capability. Loaded plutonium based on higher burnup process gives a reduction value of criticality condition or less excess reactivity. It also obtains more fuel breeding ratio capability or more breeding gain. Some loaded plutonium based on longer cooling time of LWR gives less excess reactivity and in the same time, it gives higher breeding ratio capability of the reactors. More composition of even mass plutonium isotopes gives more absorption neutron which affects to decresing criticality or less excess reactivity in the core. Similar condition that more absorption neutron by fertile material or even mass plutonium will produce more fissile material or odd mass plutonium isotopes to increase the breeding gain of the reactor.

CS Line Profiles in Hot Cores

NASA Astrophysics Data System (ADS)

Bayet, E.; Yates, J.; Viti, S.

2011-02-01

We present a theoretical study of CS line profiles in archetypal hot cores. We provide estimates of line fluxes from the CS(1-0) to the CS(15-14) transitions and present the temporal variation of these fluxes. We find that (1) the CS(1-0) transition is a better tracer of the Envelope of the hot core whereas the higher-J CS lines trace the ultracompact core (UCC); (2) the peak temperature of the CS transitions is a good indicator of the temperature inside the hot core; (3) in the Envelope, the older the hot core the stronger the self-absorption of CS; (4) the fractional abundance of CS is highest in the innermost parts of the UCC, confirming the CS molecule as one of the best tracers of very dense gas.

Supercontinuum generation through DNA-filled hollow core fiber for broadband absorption spectroscopy

NASA Astrophysics Data System (ADS)

Cho, Youngho; Park, Byeongho; Oh, Juyeong; Seo, Min Ah; Lee, Kwanil; Kim, Chulki; Lee, Taikjin; Woo, Deok Ha; Lee, Seok; Kim, Hyung Min; Lee, Hyuk Jae; Oh, Kyunghwan; Yeom, Dong-Il; Park, Sung Ha; Kim, Jae Hun

2015-07-01

In this study, we successfully generated the large bandwidth of supercontinuum spectra through hollow fibers filled with DNA. Also, by observing that spectra bandwidth was the widest in the order of the hollow core fiber filled with DNA modified by copper ion, the hollow core fiber with only DNA, and the bulk hollow core fiber, we demonstrated that DNA material modified with copper ions can further enhance the spectral bandwidth of supercontinuum. As a result, we anticipate that the SCG as a broadband light source can be used in analytical methods to demonstrate a wide range of biological and environmental questions.

Titanium carbide particles as pre-solar grains

NASA Astrophysics Data System (ADS)

Kimura, Y.; Kaito, C.

2003-08-01

Focusing on the growth of metal carbide particles and the formation of pre-solar grains, a new attempt has been made for titanium carbide (TiC) systems. Using the noble gas evaporation method, we succeeded in producing TiC core (50-nm) carbon mantle (2-nm) grains of the same core size as pre-solar grains. The infrared spectrum has broad absorption features at 9.5 and 12.5 μm. It was also found that these absorption peaks became weaker by an increase to 15 nm of carbon mantle layer. The determination method of the contact angle of carbon on the TiC grain has been developed using a high-resolution electron microscopic technique. The contact angles between TiC and carbon were and on the (111) and (100) TiC grain surfaces, respectively.

Dynamical effects in x-ray absorption spectra of graphene and monolayered h -BN on Ni(111)

NASA Astrophysics Data System (ADS)

Rusz, J.; Preobrajenski, A. B.; Ng, May Ling; Vinogradov, N. A.; Mårtensson, N.; Wessely, O.; Sanyal, B.; Eriksson, O.

2010-02-01

We present first-principles calculations of x-ray absorption spectra of graphene and hexagonal BN monolayer on the Ni(111) substrate. Including dynamical core-hole screening effects according to the theory of Mahan-Nozières-de Dominics (MND) results in an overall good agreement with previously published experimental data and our new observations. This approach provides a unified first-principles description of the electronic structure and core excitations in the sp2 -bonded materials on metal surfaces and a better insight into the dynamics of screening effects. We demonstrate in particular that the observed spectral features of graphene and hexagonal BN can be well reproduced with the MND theory, and that they are determined by a delicate balance between initial and final-state effects.

ZnO/ZnSxSe1-x core/shell nanowire arrays as photoelectrodes with efficient visible light absorption

NASA Astrophysics Data System (ADS)

Wang, Zhenxing; Zhan, Xueying; Wang, Yajun; Safdar, Muhammad; Niu, Mutong; Zhang, Jinping; Huang, Ying; He, Jun

2012-08-01

ZnO/ZnSxSe1-x core/shell nanowires have been synthesized on n+-type silicon substrate via a two-step chemical vapor deposition method. Transmission electron microscopy reveals that ZnSxSe1-x can be deposited on the entire surface of ZnO nanowire, forming coaxial heterojunction along ZnO nanowire with very smooth shell surface and high shell thickness uniformity. The photoelectrode after deposition of the ternary alloy shell significantly improves visible light absorption efficiency. Electrochemical impedance spectroscopy results explicitly indicate that the introduction of ZnSxSe1-x shell to ZnO nanowires effectively improves the photogenerated charge separation process. Our finding opens up an efficient means for achieving high efficient energy conversion devices.

The remarkable chemical uniformity of Apollo 16 layered deep drill core section 60002

NASA Technical Reports Server (NTRS)

Nava, D. F.; Philpotts, J. A.; Lindstrom, M. M.; Schuhmann, P. J.; Lindstrom, D. J.

1976-01-01

Atomic absorption and colorimetric spectrophotometers were used to determine major- and minor-element abundances in 12 samples from layered section 60002 of the Apollo 16 deep drill core. It is suggested that gardening of a relatively thick local unit produced the layering in this section in such a manner that the proportions of materials of different compositions remained virtually unchanged.

Optical studies of CdSe/HgSe and CdSe/Ag2Se core/shell nanoparticles embedded in gelatin

NASA Astrophysics Data System (ADS)

Azhniuk, Yu M.; Dzhagan, V. M.; Raevskaya, A. E.; Stroyuk, A. L.; Kuchmiy, S. Ya; Valakh, M. Ya; Zahn, D. R. T.

2008-11-01

CdSe/HgSe and CdSe/Ag2Se core-shell nanoparticles are obtained by colloidal synthesis from aqueous solutions in the presence of gelatin. Optical absorption, luminescence, and Raman spectra of the nanoparticles obtained are measured. The variation of the optical spectra of CdSe/HgSe and CdSe/Ag2Se core-shell nanoparticles with the shell thickness is discussed. Sharp non-monotonous variation of the photoluminescence spectra at low shell coverage is observed.

Near-Edge X-ray Absorption Fine Structure within Multilevel Coupled Cluster Theory.

PubMed

Myhre, Rolf H; Coriani, Sonia; Koch, Henrik

2016-06-14

Core excited states are challenging to calculate, mainly because they are embedded in a manifold of high-energy valence-excited states. However, their locality makes their determination ideal for local correlation methods. In this paper, we demonstrate the performance of multilevel coupled cluster theory in computing core spectra both within the core-valence separated and the asymmetric Lanczos implementations of coupled cluster linear response theory. We also propose a visualization tool to analyze the excitations using the difference between the ground-state and excited-state electron densities.

Core/shell colloidal quantum dot exciplex states for the development of highly efficient quantum-dot-sensitized solar cells.

PubMed

Wang, Jin; Mora-Seró, Iván; Pan, Zhenxiao; Zhao, Ke; Zhang, Hua; Feng, Yaoyu; Yang, Guang; Zhong, Xinhua; Bisquert, Juan

2013-10-23

Searching suitable panchromatic QD sensitizers for expanding the light-harvesting range, accelerating charge separation, and retarding charge recombination is an effective way to improve power conversion efficiency (PCE) of quantum-dot-sensitized solar cells (QDSCs). One possible way to obtain a wide absorption range is to use the exciplex state of a type-II core/shell-structured QDs. In addition, this system could also provide a fast charge separation and low charge-recombination rate. Herein, we report on using a CdTe/CdSe type-II core/shell QD sensitizer with an absorption range extending into the infrared region because of its exciplex state, which is covalently linked to TiO2 mesoporous electrodes by dropping a bifunctional linker molecule mercaptopropionic acid (MPA)-capped QD aqueous solution onto the film electrode. High loading and a uniform distribution of QD sensitizer throughout the film electrode thickness have been confirmed by energy dispersive X-ray (EDX) elemental mapping. The accelerated electron injection and retarded charge-recombination pathway in the built CdTe/CdSe QD cells in comparison with reference CdSe QD-based cells have been confirmed by impedance spectroscopy, fluorescence decay, and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) analysis. With the combination of the high QD loading and intrinsically superior optoelectronic properties of type-II core/shell QD (wide absorption range, fast charge separation, and slow charge recombination), the resulting CdTe/CdSe QD-based regenerative sandwich solar cells exhibit a record PCE of 6.76% (J(sc) = 19.59 mA cm(-2), V(oc) = 0.606 V, and FF = 0.569) with a mask around the active film under a full 1 sun illumination (simulated AM 1.5), which is the highest reported to date for liquid-junction QDSCs.

Testing a laser-induced breakdown spectroscopy technique on the Arctic sediments

NASA Astrophysics Data System (ADS)

Han, D.; Nam, S. I.

2017-12-01

Physical and geochemical investigations coupled with the Laser-induced Breakdown Spectroscopy (LIBS) were performed on three surface sediment cores (ARA03B/24BOX, ARA02B/01(A)MUC, ARA02B/02MUC and ARA02B/03(A)MUC) recovered from the western Arctic Ocean (Chukchi Sea) during IBRV ARON expeditions in 2012. The LIBS technique was applied to carry out elemental chemical analysis of the Arctic sediments and compared with that measured by ITRAX X-ray fuorescence (XRF) core scanning. LIBS and XRF have shown similar elemental composition within each sediment core. In this study, mineral composition (XRD), grain size distribution and organic carbon content as well as elemental composition (LIBS) were all considered to understand paleoenvironmental changes (ocean circulation, sea-ice drift, iceberg discharge, and etc.) recorded in the Arctic Holocene sediment. Quantitative LIBS analysis shows a gradually varying distribution of the elements along the sampled core and clear separation between the cores. The cores are geochemically characterized by elevated Mn profile. The gradient of mineral composition and grain sizes among the cores shows regional distribution and variation in sedimentary condition due to geological distance between East Siberian and North America. The present study reveals that a LIBS technique can be employed for in-situ sediment analyses for the Arctic Ocean. Furthermore, LIBS does not require costly equipment, trained operators, and complicated sample pre-treatment processes compared to Atomic absorption spectroscopy (AAS) and inductively coupled plasma emission spectroscopy (ICP), and also known to show relatively high levels of sensitivity, precision, and distinction than XRF analysis, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), and electron probe X-ray microanalysis (EPMA).

Pt and Ru X-ray absorption spectroscopy of PtRu anode catalysts in operating direct methanol fuel cells.

PubMed

Stoupin, Stanislav; Chung, Eun-Hyuk; Chattopadhyay, Soma; Segre, Carlo U; Smotkin, Eugene S

2006-05-25

In situ X-ray absorption spectroscopy, ex situ X-ray fluorescence, and X-ray powder diffraction enabled detailed core analysis of phase segregated nanostructured PtRu anode catalysts in an operating direct methanol fuel cell (DMFC). No change in the core structures of the phase segregated catalyst was observed as the potential traversed the current onset potential of the DMFC. The methodology was exemplified using a Johnson Matthey unsupported PtRu (1:1) anode catalyst incorporated into a DMFC membrane electrode assembly. During DMFC operation the catalyst is essentially metallic with half of the Ru incorporated into a face-centered cubic (FCC) Pt alloy lattice and the remaining half in an amorphous phase. The extended X-ray absorption fine structure (EXAFS) analysis suggests that the FCC lattice is not fully disordered. The EXAFS indicates that the Ru-O bond lengths were significantly shorter than those reported for Ru-O of ruthenium oxides, suggesting that the phases in which the Ru resides in the catalysts are not similar to oxides.

Influences of external vs. core-shell mixing on aerosol optical properties at various relative humidities.

PubMed

Ramachandran, S; Srivastava, Rohit

2013-05-01

Aerosol optical properties of external and core-shell mixtures of aerosol species present in the atmosphere are calculated in this study for different relative humidities. Core-shell Mie calculations are performed using the values of radii, refractive indices and densities of aerosol species that act as core and shell, and the core-shell radius ratio. The single scattering albedo (SSA) is higher when the absorbing species (black carbon, BC) is the core, while for a sulfate core SSA does not vary significantly as the BC in the shell dominates the absorption. Absorption gets enhanced in core-shell mixing of absorbing and scattering aerosols when compared to their external mixture. Thus, SSA is significantly lower for a core-shell mixture than their external mixture. SSA is more sensitive to core-shell ratio than mode radius when BC is the core. The extinction coefficient, SSA and asymmetry parameter are higher for external mixing when compared to BC (core)-water soluble aerosol (shell), and water soluble aerosol (core)-BC (shell) mixtures in the relative humidity range of 0 to 90%. Spectral SSA exhibits the behaviour of the species which acts as a shell in core-shell mixing. The asymmetry parameter for an external mixture of water soluble aerosol and BC is higher than BC (core)-water soluble aerosol (shell) mixing and increases as function of relative humidity. The asymmetry parameter for the water soluble aerosol (core)-BC (shell) is independent of relative humidity as BC is hydrophobic. The asymmetry parameter of the core-shell mixture decreases when BC aerosols are involved in mixing, as the asymmetry parameter of BC is lower. Aerosol optical depth (AOD) of core-shell mixtures increases at a higher rate when the relative humidity exceeds 70% in continental clean and urban aerosol models, whereas AOD remains the same when the relative humidity exceeds 50% in maritime aerosol models. The SSA for continental aerosols varies for core-shell mixing of water soluble aerosol (core)-shell (BC) when compared to their external mixture, while the SSA for maritime aerosols does not vary significantly for different mixing scenarios because of the dominance of sea salt aerosols. Thus, these results confirm that aerosol mixing can modify the physical and optical characteristics of aerosols, which vary as a function of relative humidity. These calculations will be useful in parameterising the effect of core-shell vs. external mixing of aerosols in global climate models, and in the evaluation of aerosol radiative effects.

Study of controlled-release floating tablets of dipyridamole using the dry-coated method.

PubMed

Chen, Kai; Wen, Haoyang; Yang, Feifei; Yu, Yibin; Gai, Xiumei; Wang, Haiying; Li, Pingfei; Pan, Weisan; Yang, Xinggang

2018-01-01

Dipyridamole (DIP), having a short biological half-life, has a narrow absorption window and is primarily absorbed in the stomach. So, the purpose of this study was to prepare controlled-release floating (CRF) tablets of dipyridamole by the dry-coated method. The influence of agents with different viscosity, hydroxypropylmethylcellulose (HPMC) and polyvinylpyrollidon K30 (PVP K30) in the core tablet and low-viscosity HPMC and PVP K30 in the coating layer on drug release, were investigated. Then, a study with a three-factor, three-level orthogonal experimental design was used to optimize the formulation of the CRF tablets. After data processing, the optimized formulation was found to be: 80 mg HPMC K4M in the core tablet, 80 mg HPMC E15 in core tablet and 40 mg PVP K30 in the coating layer. Moreover, an in vitro buoyancy study showed that the optimized formulation had an excellent floating ability and could immediately float without a lag time and this lasted more than 12 h. Furthermore, an in vivo gamma scintigraphic study showed that the gastric residence time of the CRF tablet was about 8 h.

A search for interstellar CH3D: Limits to the methane abundance in Orion-KL

NASA Technical Reports Server (NTRS)

Womack, Maria; Ziurys, L. M.; Apponi, A. J.

1995-01-01

A search has been performed for interstellar CH3D via its J(K) = 1(0) - 0(0) transition at 230 GHz and its J(K) = 2(0) - l(0) and J(K) = 2(1) - 1(1) lines at 465 GHz using the NRAO 12 m and CSO 10 m telescopes towards Orion-KL. This search was done in conjunction with laboratory measurements of all three transitions of CH3D using mm/sub-mm direct absorption spectroscopy. The molecule was not detected down to a 3 sigma level of T(A) less than 0.05 K towards Orion, which suggests an upper limit to the CH3D column density of N less than 6 x 10(exp 18)/sq cm in the hot core region and a fractional abundance (with respect to H2) of less than 6 x 10(exp -6). These measurements suggest that the methane abundance in the Orion hot core is f less than 6 x 10-4, assuming D/H approximately 0.01. Such findings are in agreement with recent hot core chemical models, which suggest CH4/H2 approximately 10(exp -4).

Ce Core-Level Spectroscopy, and Magnetic and Electrical Transport Properties of Lightly Ce-Doped YCoO3

NASA Astrophysics Data System (ADS)

Kobayashi, Yoshihiko; Koike, Tsuyoshi; Okawa, Mario; Takayanagi, Ryohei; Takei, Shohei; Minohara, Makoto; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Yasui, Akira; Ikenaga, Eiji; Saitoh, Tomohiko; Asai, Kichizo

2016-11-01

We have investigated the Ce and Co core level spectroscopy, and the magnetic and electrical transport properties of lightly Ce-doped YCoO3. We have successfully synthesized single-phase Y1-xCexCoO3 for 0.0 ≤ x ≤ 0.1 by the sol-gel method. Hard X-ray photoelectron and X-ray absorption spectroscopy experiments reveal that the introduced Ce ions are tetravalent, which is considered to be the first case of electron doping into bulk trivalent Co oxides with perovskite RECoO3 (RE: rare-earth element or Y) caused by RE site substitution. The magnitude of the effective magnetic moment peff obtained from the temperature dependence of magnetic susceptibility χ(T) at higher temperatures is close to that for high-spin Co2+ introduced by the Ce doping, implying that the electrons doped into the Co site induce Co2+ with a high-spin state. For x = 0.1, ferromagnetic ordering is observed below about 7 K. Electrical transport properties such as resistivity and thermoelectric power show that negative electron-like carriers are introduced by Ce substitution.

Self-Assembled Core-Shell-Type Lipid-Polymer Hybrid Nanoparticles: Intracellular Trafficking and Relevance for Oral Absorption.

PubMed

Li, Qiuxia; Xia, Dengning; Tao, Jinsong; Shen, Aijun; He, Yuan; Gan, Yong; Wang, Chi

2017-10-01

Lipid-polymer hybrid nanoparticles (NPs) are advantageous for drug delivery. However, their intracellular trafficking mechanism and relevance for oral drug absorption are poorly understood. In this study, self-assembled core-shell lipid-polymer hybrid NPs made of poly(lactic-co-glycolic acid) (PLGA) and various lipids were developed to study their differing intracellular trafficking in intestinal epithelial cells and their relevance for oral absorption of a model drug saquinavir (SQV). Our results demonstrated that the endocytosis and exocytosis of hybrid NPs could be changed by varying the kind of lipid. A glyceride mixture (hybrid NPs-1) decreased endocytosis but increased exocytosis in Caco-2 cells, whereas the phospholipid (E200) (hybrid NPs-2) decreased endocytosis but exocytosis was unaffected as compared with PLGA nanoparticles. The transport of hybrid NPs-1 in cells involved various pathways, including caveolae/lipid raft-dependent endocytosis, and clathrin-mediated endocytosis and macropinocytosis, which was different from the other groups of NPs that involved only caveolae/lipid raft-dependent endocytosis. Compared with that of the reference formulation (nanoemulsion), the oral absorption of SQV-loaded hybrid NPs in rats was poor, probably due to the limited drug release and transcytosis of NPs across the intestinal epithelium. In conclusion, the intracellular processing of hybrid NPs in intestinal epithelia can be altered by adding lipids to the NP. However, it appears unfavorable to use PLGA-based NPs to improve oral absorption of SQV compared with nanoemulsion. Our findings will be essential in the development of polymer-based NPs for the oral delivery of drugs with the purpose of improving their oral absorption. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

FDTD analysis of human body-core temperature elevation due to RF far-field energy prescribed in the ICNIRP guidelines.

PubMed

Hirata, Akimasa; Asano, Takayuki; Fujiwara, Osamu

2007-08-21

This study investigated the relationship between the specific absorption rate and temperature elevation in an anatomically-based model named NORMAN for exposure to radio-frequency far fields in the ICNIRP guidelines (1998 Health Phys. 74 494-522). The finite-difference time-domain method is used for analyzing the electromagnetic absorption and temperature elevation in NORMAN. In order to consider the variability of human thermoregulation, parameters for sweating are derived and incorporated into a conventional sweating formula. First, we investigated the effect of blood temperature variation modeling on body-core temperature. The computational results show that the modeling of blood temperature variation was the dominant factor influencing the body-core temperature. This is because the temperature in the inner tissues is elevated via the circulation of blood whose temperature was elevated due to EM absorption. Even at different frequencies, the body-core temperature elevation at an identical whole-body average specific absorption rate (SAR) was almost the same, suggesting the effectiveness of the whole-body average SAR as a measure in the ICNIRP guidelines. Next, we discussed the effect of sweating on the temperature elevation and thermal time constant of blood. The variability of temperature elevation caused by the sweating rate was found to be 30%. The blood temperature elevation at the basic restriction in the ICNIRP guidelines of 0.4 W kg(-1) is 0.25 degrees C even for a low sweating rate. The thermal time constant of blood temperature elevation was 23 min and 52 min for a man with a lower and a higher sweating rate, respectively, which is longer than the average time of the SAR in the ICNIRP guidelines. Thus, the whole-body average SAR required for blood temperature elevation of 1 degrees C was 4.5 W kg(-1) in the model of a human with the lower sweating coefficients for 60 min exposure. From a comparison of this value with the basic restriction in the ICNIRP guidelines of 0.4 W kg(-1), the safety factor was 11.

The first TDDFT and MCD studies of free base triarylcorroles: a closer look into solvent-dependent UV-visible absorption.

PubMed

Ziegler, Christopher J; Sabin, Jared R; Geier, G Richard; Nemykin, Victor N

2012-05-16

Absorption spectra of several free base triarylcorroles were investigated by MCD spectroscopy. The MCD spectra exhibit unusual sign-reverse (positive-to-negative intensities in ascending energy) features in the Soret- and Q-type band regions, suggesting a rare ΔHOMO < ΔLUMO relationship between π and π* MOs in the corrole core. This journal is © The Royal Society of Chemistry 2012

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huml, O.

The objective of this work was to determine the neutron flux density distribution in various places of the training reactor VR-1 Sparrow. This experiment was performed on the new core design C1, composed of the new low-enriched uranium fuel cells IRT-4M (19.7 %). This fuel replaced the old high-enriched uranium fuel IRT-3M (36 %) within the framework of the RERTR Program in September 2005. The measurement used the neutron activation analysis method with gold wires. The principle of this method consists in neutron capture in a nucleus of the material forming the activation detector. This capture can change the nucleusmore » in a radioisotope, whose activity can be measured. The absorption cross-section values were evaluated by MCNP computer code. The gold wires were irradiated in seven different positions in the core C1. All irradiations were performed at reactor power level 1E8 (1 kW{sub therm}). The activity of segments of irradiated wires was measured by special automatic device called 'Drat' (Wire in English). (author)« less

Assemblies of Boron Dipyrromethene/Porphyrin, Phthalocyanine, and C60 Moieties as Artificial Models of Photosynthesis: Synthesis, Supramolecular Interactions, and Photophysical Studies.

PubMed

Chen, Xiao-Fei; El-Khouly, Mohamed E; Ohkubo, Kei; Fukuzumi, Shunichi; Ng, Dennis K P

2018-03-12

A series of light-harvesting conjugates based on a zinc(II) phthalocyanine core with either two or four boron dipyrromethene (BODIPY) or porphyrin units have been synthesized and characterized. The conjugation of BODIPY/porphyrin units can extend the absorptions of the phthalocyanine core to cover most of the visible region. Upon addition of an imidazole-substituted C 60 (C 60 Im), it can axially bind to the zinc(II) center of the phthalocyanine core through metal-ligand interactions. The resulting complexes form photosynthetic antenna-reaction center mimics in which the BODIPY/porphyrin units serve as the antennas to capture the light and transfer the energy to the phthalocyanine core by efficient excitation energy transfer. The excited phthalocyanine is then quenched by the axially bound C 60 Im moiety by electron transfer, which has been supported by computational studies. The photoinduced processes of the assemblies have been studied in detail by various steady-state and time-resolved spectroscopic methods. By femtosecond transient absorption spectroscopic studies, the lifetimes of the charge-separated state of the bis(BODIPY) and bis(porphyrin) systems have been determined to be 3.2 and 4.0 ns, respectively. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of TDLAS sensor for diagnostics of CO, H2O and soot concentrations in reactor core of pilot-scale gasifier

NASA Astrophysics Data System (ADS)

Sepman, A.; Ögren, Y.; Gullberg, M.; Wiinikka, H.

2016-02-01

This paper reports on the development of the tunable diode laser absorption spectroscopy sensor near 4350 cm-1 (2298 nm) for measurements of CO and H2O mole fractions and soot volume fraction under gasification conditions. Due to careful selection of the molecular transitions [CO ( υ″ = 0 → υ' = 2) R34-R36 and H2O at 4349.337 cm-1], a very weak (negligible) sensitivity of the measured species mole fractions to the temperature distribution inside the high-temperature zone (1000 K < T < 1900 K) of the gasification process is achieved. The selected transitions are covered by the tuning range of single diode laser. The CO and H2O concentrations measured in flat flames generally agree better than 10 % with the results of 1-D flame simulations. Calibration-free absorption measurements of studied species in the reactor core of atmospheric pilot-scale entrained-flow gasifier operated at 0.1 MW power are reported. Soot concentration is determined from the measured broadband transmittance. The estimated uncertainties in the reactor core CO and H2O measurements are 15 and 20 %, respectively. The reactor core average path CO mole fractions are in quantitative agreement with the µGC CO concentrations sampled at the gasifier output.

Direct Correlation of Excitonics with Efficiency in a Core-Shell Quantum Dot Solar Cell.

PubMed

Dana, Jayanta; Maiti, Sourav; Tripathi, Vaidehi S; Ghosh, Hirendra N

2018-02-16

Shell thickness dependent band-gap engineering of quasi type II core-shell material with higher carrier cooling time, lower interfacial defect states, and longer charge carrier recombination time can be a promising candidate for both photocatalysis and solar cell. In the present investigation, colloidal CdSe@CdS core-shells with different shell thickness (2, 4 and 6 monolayer CdS) were synthesized through hot injection method and have been characterized by high resolution transmission electron microscope (HRTEM) followed by steady state absorption and luminescence techniques. Ultrafast transient absorption (TA) studies suggest longer carrier cooling, lower interfacial surface states, and slower carrier recombination time in CdSe@CdS core-shell with increasing shell thickness. By TA spectroscopy, the role of CdS shell in power conversion efficiency (PCE) has been explained in detail. The measured PCE was found to initially increase and then decrease with increasing shell thickness. Shell thickness has been optimized to maximize the efficiency after correlating the shell controlled carrier cooling and recombination with PCE values and a maximum PCE of 3.88 % was obtained with 4 monolayers of CdS shell, which is found to be 57 % higher than compared to bare CdSe QDs. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stabilizing subnanometer Ag(0) nanoclusters by thiolate and diphosphine ligands and their crystal structures

NASA Astrophysics Data System (ADS)

Yang, Huayan; Wang, Yu; Zheng, Nanfeng

2013-03-01

The combined use of thiolate and diphosphine as surface ligands helps to stabilize subnanometer Ag(0) nanoclusters, resulting in the successful crystallization of two Ag(0)-containing nanoclusters (Ag16 and Ag32) for X-ray single crystal analysis. Both clusters have core-shell structures with Ag86+ and Ag2212+ as their cores, which are not simply either fragments of face-centered cubic metals or their five-fold twinned counterparts. The clusters display UV-Vis absorption spectra consisting of molecule-like optical transitions.The combined use of thiolate and diphosphine as surface ligands helps to stabilize subnanometer Ag(0) nanoclusters, resulting in the successful crystallization of two Ag(0)-containing nanoclusters (Ag16 and Ag32) for X-ray single crystal analysis. Both clusters have core-shell structures with Ag86+ and Ag2212+ as their cores, which are not simply either fragments of face-centered cubic metals or their five-fold twinned counterparts. The clusters display UV-Vis absorption spectra consisting of molecule-like optical transitions. Electronic supplementary information (ESI) available: Experimental details, more pictures of the structure and XPS spectra of the clusters. CCDC 916463 and 916464. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3nr34328f

Single molecule magnets with protective ligand shells on gold and titanium dioxide surfaces: In situ electrospray deposition and x-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Handrup, Karsten; Richards, Victoria J.; Weston, Matthew; Champness, Neil R.; O'Shea, James N.

2013-10-01

Two single molecule magnets based on the dodecamanganese (III, IV) cluster with either benzoate or terphenyl-4-carboxylate ligands, have been studied on the Au(111) and rutile TiO2(110) surfaces. We have used in situ electrospray deposition to produce a series of surface coverages from a fraction of a monolayer to multilayer films in both cases. X-ray absorption spectroscopy measured at the Mn L-edge (Mn 2p) has been used to study the effect of adsorption on the oxidation states of the manganese atoms in the core. In the case of the benzoate-functionalised complex reduction of the manganese metal centres is observed due to the interaction of the manganese core with the underlying surface. In the case of terphenyl-4-carboxylate, the presence of this much larger ligand prevents the magnetic core from interacting with either the gold or the titanium dioxide surfaces and the characteristic Mn3+ and Mn4+ oxidation states necessary for magnetic behaviour are preserved.

Comparison Pore Aggregate Levels After Extraction With Solvents Pertamax Plus And Gasoline

NASA Astrophysics Data System (ADS)

Anggraini, Muthia

2017-12-01

Loss of asphalt content extraction results become problems in Field Work For implementing parties. The use of solvents with high octane (pertamax plus) for the extraction, dissolving the asphalt more than gasoline. By comparing the levels of aggregate pores after using solvent extraction pertamax plus compared to gasoline could answer that pertamax plus more solvent dissolves the bitumen compared to gasoline. This study aims to obtain comparative levels of porous aggregate mix AC-WC after using solvent extraction pertamax plus compared to gasoline. This study uses the aggregate that has been extracted from the production of asphalt mixtures, when finisher and after compaction field. The method used is the assay of coarse and fine aggregate pores, extraction of bitumen content to separate the aggregate with bitumen. Results of testing the total absorption after extraction using a solvent preta max plus in the production of asphalt mixtures 0.80%, while gasoline solvent 0.67% deviation occurs 0.13%. In the finisher after the solvent extraction preta max plus 0.77%, while 0.67% gasoline solvent occurs deviation of 0.1%. At the core after extraction and solvent pertamax plus 0.71%, while gasoline solvent 0.60% 0.11% deviation occurs. The total water absorption after extraction using a solvent pertamax plus greater than gasoline. This proves that the solvent dissolves pertamax plus more asphalt than gasoline.

Interpretation of the prominence differential emissions measure for 3 geometries

NASA Technical Reports Server (NTRS)

Schmahl, E. J.; Orrall, F. Q.

1986-01-01

Researchers have used prominence extreme ultraviolet line intensities observed from Skylab to derive the differential emission measure Q(T) in the prominence-corona (PC) interface from 3 x 10,000 to 3 times 1 million K, including the effects of Lyman Continuum absorption. Using lines both shortward and longward of the Lyman limit, researchers have estimated the importance of absorption as function of temperature. The magnitude of the absorption, as well as its rate of increase as a function of temperature, place limits on the thread scales and the character of the interfilar medium. Researchers have calculated models based on three assumed geometries: (1) threads with hot sheaths and cool cores; (2) isothermal threads; and (3) threads with longitudinal temperature gradients along the magnetic field. Comparison of the absorption computed from these models with the observed absorption in prominences shows that none of the geometries is totally satisfactory.

Modeling of light absorption in tissue during infrared neural stimulation.

PubMed

Thompson, Alexander C; Wade, Scott A; Brown, William G A; Stoddart, Paul R

2012-07-01

A Monte Carlo model has been developed to simulate light transport and absorption in neural tissue during infrared neural stimulation (INS). A range of fiber core sizes and numerical apertures are compared illustrating the advantages of using simulations when designing a light delivery system. A range of wavelengths, commonly used for INS, are also compared for stimulation of nerves in the cochlea, in terms of both the energy absorbed and the change in temperature due to a laser pulse. Modeling suggests that a fiber with core diameter of 200 μm and NA=0.22 is optimal for optical stimulation in the geometry used and that temperature rises in the spiral ganglion neurons are as low as 0.1°C. The results show a need for more careful experimentation to allow different proposed mechanisms of INS to be distinguished.

Modeling of light absorption in tissue during infrared neural stimulation

NASA Astrophysics Data System (ADS)

Thompson, Alexander C.; Wade, Scott A.; Brown, William G. A.; Stoddart, Paul R.

2012-07-01

A Monte Carlo model has been developed to simulate light transport and absorption in neural tissue during infrared neural stimulation (INS). A range of fiber core sizes and numerical apertures are compared illustrating the advantages of using simulations when designing a light delivery system. A range of wavelengths, commonly used for INS, are also compared for stimulation of nerves in the cochlea, in terms of both the energy absorbed and the change in temperature due to a laser pulse. Modeling suggests that a fiber with core diameter of 200 μm and NA=0.22 is optimal for optical stimulation in the geometry used and that temperature rises in the spiral ganglion neurons are as low as 0.1°C. The results show a need for more careful experimentation to allow different proposed mechanisms of INS to be distinguished.

Thermo-responsive plasmonic nanohybrids with tunable optical properties

NASA Astrophysics Data System (ADS)

Zhang, Lingyu; Song, Gang

2017-10-01

In this paper, we study the temperature-dependent optical properties of gold-silver core-shell (Au@Ag) nanorods coated by a thermo-responsive polymer poly (N-isopropylacrylamide) (PNIPAM). The wavelength of the plasmonic resonant absorption of the nanohybrids changes with temperature due to the combination effects of the plasmon resonance of the core and the thermal response of the shell. Using effective medium theory, we find that with increase of temperature, the absorption peak red-shifts due to the competition effects from the changes of the thickness and the effective refractive index of the polymer shell. The working wavelength can be tuned by the aspect ratio of nanorods. Moreover, the temperature sensitivity of plasmon resonance increases with the increase of the aspect ratio. Our studies provide a proof-of-concept design of thermal responsive plasmonic smart material.

FDTD computation of temperature elevation in the elderly for far-field RF exposures.

PubMed

Nomura, Tomoki; Laakso, Ilkka; Hirata, Akimasa

2014-03-01

Core temperature elevation and perspiration in younger and older adults is investigated for plane-wave exposure at whole-body averaged specific absorption rate of 0.4 W kg(-1). Numeric Japanese male model is considered together with a thermoregulatory response formula proposed in the authors' previous study. The frequencies considered were at 65 MHz and 2 GHz where the total power absorption in humans becomes maximal for the allowable power density prescribed in the international guidelines. From the computational results used here, the core temperature elevation in the older adult model was larger than that in the younger one at both frequencies. The reason for this difference is attributable to the difference of sweating, which is originated from the difference in the threshold activating the sweating and the decline in sweating in the legs.

A New Window into Escaping Exoplanet Atmospheres: 10830 Å Line of Helium

NASA Astrophysics Data System (ADS)

Oklopčić, Antonija; Hirata, Christopher M.

2018-03-01

Observational evidence for escaping exoplanet atmospheres has been obtained for a few exoplanets to date. It comes from strong transit signals detected in the ultraviolet, most notably in the wings of the hydrogen Lyα (Lyα) line. However, the core of the Lyα line is often heavily affected by interstellar absorption and geocoronal emission, limiting the information about the atmosphere that can be extracted from that part of the spectrum. Transit observations in atomic lines that are (a) sensitive enough to trace the rarefied gas in the planetary wind and (b) do not suffer from significant extinction by the interstellar medium could enable more detailed observations, and thus provide better constraints on theoretical models of escaping atmospheres. The absorption line of a metastable state of helium at 10830 Å could satisfy both of these conditions for some exoplanets. We develop a simple 1D model of escaping planetary atmospheres containing hydrogen and helium. We use it to calculate the density profile of helium in the 23S metastable excited state and the expected in-transit absorption at 10830 Å for two exoplanets known to have escaping atmospheres. Our results indicate that exoplanets similar to GJ 436b and HD 209458b should exhibit enhanced transit depths at 10830 Å, with ∼8% and ∼2% excess absorption in the line core, respectively.

Core-based intrinsic fiber-optic absorption sensor for the detection of volatile organic compounds

NASA Astrophysics Data System (ADS)

Klunder, Gregory L.; Russo, Richard E.

1995-03-01

A core-based intrinsic fiber-optic absorption sensor has been developed and tested for the detection of volatile organic compounds. The distal ends of transmitting and receiving fibers are connected by a small cylindrical section of an optically clear silicone rubber. The silicone rubber acts both as a light pipe and as a selective membrane into which the analyte molecules can diffuse. The sensor has been used to detect volatile organics (trichloroethylene, 1,1-dichloroethylene, and benzene) in both aqueous solutions and in the vapor phase or headspace. Absorption spectra obtained in the near-infrared (near-IR) provide qualitative and quantitative information about the analyte. Water, which has strong broad-band absorption in the near-IR, is excluded from the spectra because of the hydrophobic properties of the silicone rubber. The rate-limiting step is shown to be the diffusion through the Nernstian boundary layer surrounding the sensor and not the diffusion through the silicone polymer. The rate of analyte diffusion into the sensor, as measured by the t(sub 90) values (the time required for the sensor to reach 90% of the equilibrium value), is 30 min for measurements in aqueous solutions and approximately 3 min for measurements made in the headspace. The limit of detection obtained with this sensor is approximately 1.1 ppm for trichloroethylene in an aqueous solution.

Auger Up-Conversion of Low-Intensity Infrared Light in Engineered Quantum Dots

DOE PAGES

Makarov, Nikolay S.; Lin, Qianglu; Pietryga, Jeffrey M.; ...

2016-11-29

One source of efficiency losses in photovoltaic cells is their transparency toward solar photons with energies below the band gap of the absorbing layer. This loss can be reduced using a process of up-conversion whereby two or more sub-band-gap photons generate a single above-gap exciton. Traditional approaches to up-conversion, such as nonlinear two-photon absorption (2PA) or triplet fusion, suffer from low efficiency at solar light intensities, a narrow absorption bandwidth, nonoptimal absorption energies, and difficulties for implementing in practical devices. We show that these deficiencies can be alleviated using the effect of Auger up-conversion in thick-shell PbSe/CdSe quantum dots. Thismore » process relies on Auger recombination whereby two low-energy, core-based excitons are converted into a single higher-energy, shell-based exciton. When compared to their monocomponent counterparts, the tailored PbSe/CdSe heterostructures feature enhanced absorption cross-sections, a higher efficiency of the “productive” Auger pathway involving re-excitation of a hole, and longer lifetimes of both core- and shell-localized excitons. These features lead to effective up-conversion cross-sections that are more than 6 orders of magnitude higher than for standard nonlinear 2PA, which allows for efficient up-conversion of continuous wave infrared light at intensities as low as a few watts per square centimeter.« less

Compressive Behaviour and Energy Absorption of Aluminium Foam Sandwich

NASA Astrophysics Data System (ADS)

Endut, N. A.; Hazza, M. H. F. Al; Sidek, A. A.; Adesta, E. T. Y.; Ibrahim, N. A.

2018-01-01

Development of materials in automotive industries plays an important role in order to retain the safety, performance and cost. Metal foams are one of the idea to evolve new material in automotive industries since it can absorb energy when it deformed and good for crash management. Recently, new technology had been introduced to replace metallic foam by using aluminium foam sandwich (AFS) due to lightweight and high energy absorption behaviour. Therefore, this paper provides reliable data that can be used to analyze the energy absorption behaviour of aluminium foam sandwich by conducting experimental work which is compression test. Six experiments of the compression test were carried out to analyze the stress-strain relationship in terms of energy absorption behavior. The effects of input variables include varying the thickness of aluminium foam core and aluminium sheets on energy absorption behavior were evaluated comprehensively. Stress-strain relationship curves was used for energy absorption of aluminium foam sandwich calculation. The result highlights that the energy absorption of aluminium foam sandwich increases from 12.74 J to 64.42 J respectively with increasing the foam and skin thickness.

Selectivity of peptide bond dissociation on excitation of a core electron: Effects of a phenyl group

NASA Astrophysics Data System (ADS)

Tsai, Cheng-Cheng; Chen, Jien-Lian; Hu, Wei-Ping; Lin, Yi-Shiue; Lin, Huei-Ru; Lee, Tsai-Yun; Lee, Yuan T.; Ni, Chi-Kung; Liu, Chen-Lin

2016-09-01

The selective dissociation of a peptide bond upon excitation of a core electron in acetanilide and N-benzylacetamide was investigated. The total-ion-yield near-edge X-ray absorption fine structure spectra were recorded and compared with the predictions from time-dependent density functional theory. The branching ratios for the dissociation of a peptide bond are observed as 16-34% which is quite significant. This study explores the core-excitation, the X-ray photodissociation pathways, and the theoretical explanation of the NEXAFS spectra of organic molecules containing both a peptide bond and a phenyl group.

NEUTRON FLUX INTENSITY DETECTION

DOEpatents

Russell, J.T.

1964-04-21

A method of measuring the instantaneous intensity of neutron flux in the core of a nuclear reactor is described. A target gas capable of being transmuted by neutron bombardment to a product having a resonance absorption line nt a particular microwave frequency is passed through the core of the reactor. Frequency-modulated microwave energy is passed through the target gas and the attenuation of the energy due to the formation of the transmuted product is measured. (AEC)

Gold core@silver semishell Janus nanoparticles prepared by interfacial etching

NASA Astrophysics Data System (ADS)

Chen, Limei; Deming, Christopher P.; Peng, Yi; Hu, Peiguang; Stofan, Jake; Chen, Shaowei

2016-07-01

Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface.Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface. Electronic supplementary information (ESI) available: Additional TEM, UV-vis, XPS, and electrochemical data. See DOI: 10.1039/c6nr03368g

Effect of metallothionein core promoter region polymorphism on cadmium, zinc and copper levels in autopsy kidney tissues from a Turkish population

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kayaalti, Zeliha, E-mail: kayaalti@medicine.ankara.edu.t; Mergen, Goerkem; Soeylemezoglu, Tuelin

2010-06-01

Metallothioneins (MTs) are metal-binding, low molecular weight proteins and are involved in pathophysiological processes like metabolism of essential metals, metal ion homeostasis and detoxification of heavy metals. Metallothionein expression is induced by various heavy metals especially cadmium, mercury and zinc; MTs suppress toxicity of heavy metals by binding themselves to these metals. The aim of this study was to investigate the association between the - 5 A/G metallothionein 2A (MT2A) single nucleotide polymorphism (SNP) and Cd, Zn and Cu levels in the renal cortex from autopsy cases. MT2A core promoter region - 5 A/G SNP was analyzed by PCR-RFLP methodmore » using 114 autopsy kidney tissues and the genotype frequencies of this polymorphism were found as 87.7% homozygote typical (AA), 11.4% heterozygote (AG) and 0.9% homozygote atypical (GG). In order to assess the Cd, Zn and Cu levels in the same autopsy kidney tissues, a dual atomic absorption spectrophotometer system was used and the average levels of Cd, Zn and Cu were measured as 95.54 {+-} 65.58 {mu}g/g, 181.20 {+-} 87.72 {mu}g/g and 17.14 {+-} 16.28 {mu}g/g, respectively. As a result, no statistical association was found between the - 5 A/G SNP in the MT2A gene and the Zn and Cu levels in the renal cortex (p > 0.05), but considerably high accumulation of Cd was monitored for individuals having AG (151.24 {+-} 60.21 {mu}g/g) and GG genotypes (153.09 {mu}g/g) compared with individuals having AA genotype (87.72 {+-} 62.98 {mu}g/g) (p < 0.05). These results show that the core promoter region polymorphism of metallothionein 2A increases the accumulation of Cd in human renal cortex.« less

Exposure time-dependent thermal effects of radiofrequency electromagnetic field exposure on the whole body of rats.

PubMed

Ohtani, Shin; Ushiyama, Akira; Maeda, Machiko; Hattori, Kenji; Kunugita, Naoki; Wang, Jianqing; Ishii, Kazuyuki

2016-01-01

We investigated the thermal effects of radiofrequency electromagnetic fields (RF-EMFs) on the variation in core temperature and gene expression of some stress markers in rats. Sprague-Dawley rats were exposed to 2.14 GHz wideband code division multiple access (W-CDMA) RF signals at a whole-body averaged specific absorption rate (WBA-SAR) of 4 W/kg, which causes behavioral disruption in laboratory animals, and 0.4 W/kg, which is the limit for the occupational exposure set by the International Commission on Non-Ionizing Radiation Protection guideline. It is important to understand the possible in vivo effects derived from RF-EMF exposures at these intensities. Because of inadequate data on real-time core temperature analyses using free-moving animal and the association between stress and thermal effects of RF-EMF exposure, we analyzed the core body temperature under nonanesthetic condition during RF-EMF exposure. The results revealed that the core temperature increased by approximately 1.5°C compared with the baseline and reached a plateau till the end of RF-EMF exposure. Furthermore, we analyzed the gene expression of heat-shock proteins (Hsp) and heat-shock transcription factors (Hsf) family after RF-EMF exposure. At WBA-SAR of 4 W/kg, some Hsp and Hsf gene expression levels were significantly upregulated in the cerebral cortex and cerebellum following exposure for 6 hr/day but were not upregulated after exposure for 3 hr/day. On the other hand, there was no significant change in the core temperature and gene expression at WBA-SAR of 0.4 W/kg. Thus, 2.14-GHz RF-EMF exposure at WBA-SAR of 4 W/kg induced increases in the core temperature and upregulation of some stress markers, particularly in the cerebellum.

Feasibility of Valence-to-Core X-ray Emission Spectroscopy for Tracking Transient Species

DOE PAGES

March, Anne Marie; Assefa, Tadesse A.; Bressler, Christian; ...

2015-02-09

X-ray spectroscopies, when combined in laser-pump, X-ray-probe measurement schemes, can be powerful tools for tracking the electronic and geometric structural changes that occur during the course of a photoinitiated chemical reaction. X-ray absorption spectroscopy (XAS) is considered an established technique for such measurements, and X-ray emission spectroscopy (XES) of the strongest core-to-core emission lines (Kα and Kβ) is now being utilized. Flux demanding valence-to-core XES promises to be an important addition to the time-resolved spectroscopic toolkit. Here In this paper we present measurements and density functional theory calculations on laser-excited, solution-phase ferrocyanide that demonstrate the feasibility of valence-to-core XES formore » time-resolved experiments. Lastly, we discuss technical improvements that will make valence-to-core XES a practical pump–probe technique.« less

Magnetically separable {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped TiO{sub 2} core-shell nanocomposites: Fabrication and visible-light-driven photocatalytic activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Minqiang, E-mail: jbmwgkc@126.com; Li, Di; Jiang, Deli

2012-08-15

Novel visible-light-induced {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped-TiO{sub 2} core-shell nanocomposite photocatalysts capable of magnetic separation have been synthesized by a facile sol-gel and after-annealing process. The as-obtained core-shell nanocomposite is composed of a central {gamma}-Fe{sub 2}O{sub 3} core with a strong response to external fields, an interlayer of SiO{sub 2}, and an outer layer of Ce-doped TiO{sub 2} nanocrystals. UV-vis spectra analysis indicates that Ce doping in the compound results in a red-shift of the absorption edge, thus offering increased visible light absorption. We show that such a {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped-TiO{sub 2} core-shell nanocomposite with appreciated Ce doping amount exhibitsmore » much higher visible-light photocatalytic activity than bare TiO{sub 2} and undoped {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-TiO{sub 2} core-shell nanocomposite toward the degradation of rhodamine B (RhB). Moreover, the {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped-TiO{sub 2} core-shell nanocomposite photocatalysts could be easily separated and reused from the treated water under application of an external magnetic field. - Graphical abstract: Novel {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped-TiO{sub 2} core/shell nanocomposite photocatalysts with enhanced photocatalytic activity and fast magnetic separability were prepared. Highlights: Black-Right-Pointing-Pointer Novel {gamma}-Fe{sub 2}O{sub 3}-SiO{sub 2}-Ce-doped TiO{sub 2} core/shell composite photocatalysts were prepared. Black-Right-Pointing-Pointer The resulting core/shell composite show high visible light photocatalytic activity. Black-Right-Pointing-Pointer The nanocomposite photocatalysts can be easily recycled with excellent durability.« less

Unexpected electronic perturbation effects of simple PEG environments on the optical properties of small cadmium chalcogenide clusters

NASA Astrophysics Data System (ADS)

Fukunaga, Naoto; Konishi, Katsuaki

2015-12-01

Poly(ethylene glycol) (PEG) has been widely used for the surface protection of inorganic nanoobjects because of its virtually `inert' nature, but little attention has been paid to its inherent electronic impacts on inorganic cores. Herein, we definitively show, through studies on optical properties of a series of PEG-modified Cd10Se4(SR)10 clusters, that the surrounding PEG environments can electronically affect the properties of the inorganic core. For the clusters with PEG units directly attached to an inorganic core (R = (CH2CH2O)nOCH3, 1-PEGn, n = 3, ~7, ~17, ~46), the absorption bands, associated with the low-energy transitions, continuously blue-shifted with the increasing PEG chain length. The chain length dependencies were also observed in the photoluminescence properties, particularly in the excitation spectral profiles. By combining the spectral features of several PEG17-modified clusters (2-Cm-PEG17 and 3) whose PEG and core units are separated by various alkyl chain-based spacers, it was demonstrated that sufficiently long PEG units, including PEG17 and PEG46, cause electronic perturbations in the cluster properties when they are arranged near the inorganic core. These unique effects of the long-PEG environments could be correlated with their large dipole moments, suggesting that the polarity of the proximal chemical environment is critical when affecting the electronic properties of the inorganic cluster core.Poly(ethylene glycol) (PEG) has been widely used for the surface protection of inorganic nanoobjects because of its virtually `inert' nature, but little attention has been paid to its inherent electronic impacts on inorganic cores. Herein, we definitively show, through studies on optical properties of a series of PEG-modified Cd10Se4(SR)10 clusters, that the surrounding PEG environments can electronically affect the properties of the inorganic core. For the clusters with PEG units directly attached to an inorganic core (R = (CH2CH2O)nOCH3, 1-PEGn, n = 3, ~7, ~17, ~46), the absorption bands, associated with the low-energy transitions, continuously blue-shifted with the increasing PEG chain length. The chain length dependencies were also observed in the photoluminescence properties, particularly in the excitation spectral profiles. By combining the spectral features of several PEG17-modified clusters (2-Cm-PEG17 and 3) whose PEG and core units are separated by various alkyl chain-based spacers, it was demonstrated that sufficiently long PEG units, including PEG17 and PEG46, cause electronic perturbations in the cluster properties when they are arranged near the inorganic core. These unique effects of the long-PEG environments could be correlated with their large dipole moments, suggesting that the polarity of the proximal chemical environment is critical when affecting the electronic properties of the inorganic cluster core. Electronic supplementary information (ESI) available: Details of synthetic procedures and characterisation data of the PEGylated thiols and clusters and additional absorption, photoluminescence emission and excitation spectral data. See DOI: 10.1039/c5nr06307h

Black TiO2 synthesized via magnesiothermic reduction for enhanced photocatalytic activity

NASA Astrophysics Data System (ADS)

Wang, Xiangdong; Fu, Rong; Yin, Qianqian; Wu, Han; Guo, Xiaoling; Xu, Ruohan; Zhong, Qianyun

2018-04-01

Utilizing solar energy for hydrogen evolution is a great challenge for its insufficient visible-light power conversion. In this paper, we report a facile magnesiothermic reduction of commercial TiO2 nanoparticles under Ar atmosphere and at 550 °C followed by acid treatment to synthesize reduced black TiO2 powders, which possesses a unique crystalline core-amorphous shell structure composed of disordered surface and oxygen vacancies and shows significantly improved optical absorption in the visible region. The unique core-shell structure and high absorption enable the reduced black TiO2 powders to exhibit enhanced photocatalytic activity, including splitting of water in the presence of Pt as a cocatalyst and degradation of methyl blue (MB) under visible light irradiation. Photocatalytic evaluations indicate that the oxygen vacancies play key roles in the catalytic process. The maximum hydrogen production rates are 16.1 and 163 μmol h-1 g-1 under the full solar wavelength range of light and visible light, respectively. This facile and versatile method could be potentially used for large scale production of colored TiO2 with remarkable enhancement in the visible light absorption and solar-driven hydrogen production.

Asymmetry between absorption and photoluminescence line shapes of TPD: spectroscopic fingerprint of the twisted biphenyl core.

PubMed

Scholz, Reinhard; Gisslén, Linus; Himcinschi, Cameliu; Vragović, Igor; Calzado, Eva M; Louis, Enrique; San Fabián Maroto, Emilio; Díaz-García, María A

2009-01-08

We analyze absorption, photoluminescence (PL), and resonant Raman spectra of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD), with the aim of providing a microscopic interpretation of a significant Stokes shift of about 0.5 eV that makes this material suitable for stimulated emission. The optical spectra were measured for TPD dissolved in toluene and chloroform, as well as for polystyrene films doped with varying amounts of TPD. In addition, we measured preresonant and resonant Raman spectra, giving direct access to the vibrational modes elongated in the relaxed excited geometry of the molecule. The experimental data are interpreted with calculations of the molecular geometry in the electronic ground state and the optically excited state using density functional theory. Several strongly elongated high-frequency modes within the carbon rings results in a vibronic progression with a calculated spacing of 158 meV, corroborated by the observation of vibrational sidebands in the PL spectra. The peculiarities of the potential energy surfaces related to a twisting around the central bond in the biphenyl core of TPD allow to quantify the asymmetry between the line shapes observed in absorption and emission.

Enhanced light absorption due to the mixing state of black carbon in fresh biomass burning emissions

NASA Astrophysics Data System (ADS)

Wang, Qiyuan; Cao, Junji; Han, Yongming; Tian, Jie; Zhang, Yue; Pongpiachan, Siwatt; Zhang, Yonggang; Li, Li; Niu, Xinyi; Shen, Zhenxing; Zhao, Zhuzi; Tipmanee, Danai; Bunsomboonsakul, Suratta; Chen, Yang; Sun, Jian

2018-05-01

A lack of information on the radiative effects of refractory black carbon (rBC) emitted from biomass burning is a significant gap in our understanding of climate change. A custom-made combustion chamber was used to simulate the open burning of crop residues and investigate the impacts of rBC size and mixing state on the particles' optical properties. Average rBC mass median diameters ranged from 141 to 162 nm for the rBC produced from different types of crop residues. The number fraction of thickly-coated rBC varied from 53 to 64%, suggesting that a majority of the freshly emitted rBC were internally mixed. By comparing the result of observed mass absorption cross-section to that calculated with Mie theory, large light absorption enhancement factors (1.7-1.9) were found for coated particles relative to uncoated cores. These effects were strongly positively correlated with the percentage of coated particles but independent of rBC core size. We suggest that rBC from open biomass burning may have strong impact on air pollution and radiative forcing immediately after their production.

Emission and absorption x-ray edges of Li

DOE Office of Scientific and Technical Information (OSTI.GOV)

Callcott, T A; Arakawa, E T; Ederer, D L

1977-01-01

Measurements of the K X-ray absorption and emission edges of Li are reported. They were made with the same spectrometer at the NBS storage ring and serve to establish a 0.1 eV separation between the edges with no possibility of instrument calibration error. These results are compared with recent theories of Almbladh and Mahan describing the effects of incomplete phonon relaxation about the core hole. It is concluded that these theories give a satisfactory explanation of the data.

Synthesis of NiAu alloy and core-shell nanoparticles in water-in-oil microemulsions

NASA Astrophysics Data System (ADS)

Chiu, Hsin-Kai; Chiang, I.-Chen; Chen, Dong-Hwang

2009-07-01

NiAu alloy nanoparticles with various Ni/Au molar ratios were synthesized by the hydrazine reduction of nickel chloride and hydrogen tetrachloroaurate in the microemulsion system. They had a face-centered cubic structure and a mean diameter of 6-13 nm, decreasing with increasing Au content. As Au nanoparticles did, they showed a characteristic absorption peak at about 520 nm but the intensity decreased with increasing Ni content. Also, they were nearly superparamagnetic, although the magnetization decreased significantly with increasing Au content. Under an external magnetic field, they could be self-organized into the parallel lines. In addition, the core-shell nanoparticles, Ni3Au1@Au, were prepared by the Au coating on the surface of Ni3Au1 alloy nanoparticles. By increasing the hydrogen tetrachloroaurate concentration for Au coating, the thickness of Au shells could be raised and led to an enhanced and red-shifted surface plasmon absorption.

Fiber optic strain measurements using an optically-active polymer

NASA Astrophysics Data System (ADS)

Buckley, Leonard J.; Neumeister, Gary C.

1992-03-01

A study encompassing the use of an optically-active polymer as the strain-sensing medium in an organic matrix composite was performed. Several compounds were synthesized for use as the inner cladding material for silica fiber-optic cores. These materials include a diacetylene containing polyamide. It is possible to dynamically modify the optical properties of these materials through changes in applied strain or temperature. By doing so the characteristic absorption in the visible is reversibly shifted to a higher energy state. The polymer-coated fiber-optic cores were initially studied in epoxy resin. Additionally, one of the polyamide/diacetylene polymers was studied in a spin-fiber form consisting of 15 micron filaments assembled in multifilament tows. The most promising configuration and materials were then investigated further by embedding in graphite/epoxy composite laminates. In each case the shift in the visible absorption peak was monitored as a function of applied mechanical strain.

Inelastic losses in X-ray absorption theory

NASA Astrophysics Data System (ADS)

Campbell, Luke Whalin

There is a surprising lack of many body effects observed in XAS (X-ray Absorption Spectroscopy) experiments. While collective excitations and other satellite effects account for between 20% and 40% of the spectral weight of the core hole and photoelectron excitation spectrum, the only commonly observed many body effect is a relatively structureless amplitude reduction to the fine structure, typically no more than a 10% effect. As a result, many particle effects are typically neglected in the XAS codes used to predict and interpret modern experiments. To compensate, the amplitude reduction factor is simply fitted to experimental data. In this work, a quasi-boson model is developed to treat the case of XAS, when the system has both a photoelectron and a core hole. We find that there is a strong interference between the extrinsic and intrinsic losses. The interference reduces the excitation amplitudes at low energies where the core hole and photo electron induced excitations tend to cancel. At high energies, the interference vanishes, and the theory reduces to the sudden approximation. The x-ray absorption spectrum including many-body excitations is represented by a convolution of the one-electron absorption spectrum with an energy dependent spectral function. The latter has an asymmetric quasiparticle peak and broad satellite structure. The net result is a phasor sum, which yields the many body amplitude reduction and phase shift of the fine structure oscillations (EXAFS), and possibly additional satellite structure. Calculations for several cases of interest are found to be in reasonable agreement with experiment. Edge singularity effects and deviations from the final state rule arising from this theory are also discussed. The ab initio XAS code FEFF has been extended for calculations of the many body amplitude reduction and phase shift in x-ray spectroscopies. A new broadened plasmon pole self energy is added. The dipole matrix elements are modified to include a projection operator to calculate deviations from the final state rule and edge singularities.

Comparison of the Manganese Cluster in Oxygen-Evolving Photosystem II with Distorted Cubane Manganese Compounds through X-ray Absorption Spectroscopy

PubMed Central

Cinco, Roehl M.; Rompel, Annette; Visser, Hendrik; Aromí, Guillem; Christou, George; Sauer, Kenneth; Klein, Melvin P.; Yachandra, Vittal K.

2014-01-01

X-ray absorption spectroscopy has been employed to assess the degree of similarity between the oxygen-evolving complex (OEC) in photosystem II (PS II) and a family of synthetic manganese complexes containing the distorted cubane [Mn4O3X] core (X = benzoate, acetate, methoxide, hydroxide, azide, fluoride, chloride, or bromide). These [Mn4(μ3-O)3(μ3-X)] cubanes possess C3v symmetry except for the X = benzoate species, which is slightly more distorted with only Cs symmetry. In addition, Mn4O3Cl complexes containing three or six terminal Cl ligands at three of the Mn were included in this study. The Mn K-edge X-ray absorption near edge structure (XANES) from the oxygen-ligated complexes begin to resemble general features of the PS II (S1 state) spectrum, although the second derivatives are distinct from those in PS II. The extended X-ray absorption fine structure (EXAFS) of these Mn compounds also displays superficial resemblance to that of PS II, but major differences emerge on closer examination of the phases and amplitudes. The most obvious distinction is the smaller magnitude of the Fourier transform (FT) of the PS II EXAFS compared to the FTs from the distorted cubanes. Curve fitting of the Mn EXAFS spectra verifies the known core structures of the Mn cubanes, and shows that the number of the crucial 2.7 and 3.3 Å Mn–Mn distances differs from that observed in the OEC. The EXAFS method detects small changes in the core structures as X is varied in this series, and serves to exclude the distorted cubane of C3v symmetry as a topological model for the Mn catalytic cluster of the OEC. Instead, the method shows that even more distortion of the cubane framework, altering the ratio of the Mn–Mn distances, is required to resemble the Mn cluster in PS II. PMID:11671305

Optical properties of core-shell and multi-shell nanorods

NASA Astrophysics Data System (ADS)

Mokkath, Junais Habeeb; Shehata, Nader

2018-05-01

We report a first-principles time dependent density functional theory study of the optical response modulations in bimetallic core-shell (Na@Al and Al@Na) and multi-shell (Al@Na@Al@Na and Na@Al@Na@Al: concentric shells of Al and Na alternate) nanorods. All of the core-shell and multi-shell configurations display highly enhanced absorption intensity with respect to the pure Al and Na nanorods, showing sensitivity to both composition and chemical ordering. Remarkably large spectral intensity enhancements were found in a couple of core-shell configurations, indicative that optical response averaging based on the individual components can not be considered as true as always in the case of bimetallic core-shell nanorods. We believe that our theoretical results would be useful in promising applications depending on Aluminum-based plasmonic materials such as solar cells and sensors.

Subwavelength core/shell cylindrical nanostructures for novel plasmonic and metamaterial devices

NASA Astrophysics Data System (ADS)

Kim, Kyoung-Ho; No, You-Shin

2017-12-01

In this review, we introduce novel plasmonic and metamaterial devices based on one-dimensional subwavelength nanostructures with cylindrical symmetry. Individual single devices with semiconductor/metal core/shell or dielectric/metal core/multi-shell structures experience strong light-matter interaction and yield unique optical properties with a variety of functions, e.g., invisibility cloaking, super-scattering/super-absorption, enhanced luminescence and nonlinear optical activities, and deep subwavelength-scale optical waveguiding. We describe the rational design of core/shell cylindrical nanostructures and the proper choice of appropriate constituent materials, which allow the efficient manipulation of electromagnetic waves and help to overcome the limitations of conventional homogeneous nanostructures. The recent developments of bottom-up synthesis combined with the top-down fabrication technologies for the practical applications and the experimental realizations of 1D subwavelength core/shell nanostructure devices are briefly discussed.

X-ray absorption spectra: Graphene, h-BN, and their alloy

NASA Astrophysics Data System (ADS)

Bhowmick, Somnath; Rusz, Jan; Eriksson, Olle

2013-04-01

Using first-principles density functional theory calculations, in conjunction with the Mahan-Nozières-de Dominicis theory, we calculate the x-ray absorption spectra of the alloys of graphene and monolayer hexagonal boron nitride on a Ni (111) substrate. The chemical neighborhood of the constituent atoms (B, C, and N) inside the alloy differs from that of the parent phases. In a systematic way, we capture the change in the K-edge spectral shape, depending on the chemical neighborhood of B, C, and N. Our work also reiterates the importance of the dynamical core-hole screening for a proper description of the x-ray absorption process in sp2-bonded layered materials.

Microwave absorption properties of Ni/(C, silicides) nanocapsules

PubMed Central

2012-01-01

The microwave absorption properties of Ni/(C, silicides) nanocapsules prepared by an arc discharge method have been studied. The composition and the microstructure of the Ni/(C, silicides) nanocapsules were determined by means of X-ray diffraction, X-ray photoelectric spectroscopy, and transmission electron microscope observations. Silicides, in the forms of SiOx and SiC, mainly exist in the shells of the nanocapsules and result in a large amount of defects at the ‘core/shell’ interfaces as well as in the shells. The complex permittivity and microwave absorption properties of the Ni/(C, silicides) nanocapsules are improved by the doped silicides. Compared with those of Ni/C nanocapsules, the positions of maximum absorption peaks of the Ni/(C, silicides) nanocapsules exhibit large red shifts. An electric dipole model is proposed to explain this red shift phenomenon. PMID:22548846

Size resolved Internally Mixed Black Carbon and the Absorption Enhancement in the Indo-Gangetic Plain due to internally mixed BC

NASA Astrophysics Data System (ADS)

Tripathi, S. N.; Thamban, N.

2017-12-01

Indo-Gangetic Plain (IGP) is one of the most populated and polluted regions in northern India. Even though IGP is a well-known "absorbing aerosol hotspot", information of BC mixing state in IGP is mostly unknown. Our calculation on size resolved mixing state in IGP shown that the mixing state of BC changes with the core diameter of BC. The majority of BC particle were thickly coated ( 80%) at lower diameter (75-125 nm) and the externally mixed BC fraction was gradually increased at higher core diameter of BC (125-250 nm). The mean fraction of "thickly coated BC" particles (fTCBC) was found to be 61.6% for a BC core diameter of 70 to 450 nm, indicating that a large fraction of BC particles was internally mixed in IGP. The fTCBC increased after sunrise with a peak at about noontime, indicating that the formation of secondary organic aerosol under active photochemistry can enhance organic coating on a core of black carbon. A positive correlation between the fTCBC and the mass absorption cross-section at 781nm (MAC781) was also observed (r=0.58). Our results identify that the observed fTCBC in IGP could amplify the MAC781 approximately by a factor of 1.8, which may catalyze the positive radiative forcing.

Optical trapping of nanoshells

NASA Astrophysics Data System (ADS)

Hester, Brooke C.; Crawford, Alice; Kishore, Rani B.; Helmerson, Kristian; Halas, Naomi J.; Levin, Carly

2007-09-01

We investigate near-resonant trapping of Rayleigh particles in optical tweezers. Although optical forces due to a near-resonant laser beam have been extensively studied for atoms, the situation for larger particles is that the laser wavelength is far from any absorption resonance. Theory predicts, however, that the trapping force exerted on a Rayleigh particle is enhanced, and may be three to fifty times larger for frequencies near resonance than for frequencies far off resonance. The ability to selectively trap only particles with a given absorption peak may have many practical applications. In order to investigate near-resonant trapping we are using nanoshells, particles with a dielectric core and metallic coating that can exhibit plasmon resonances. The resonances of the nanoshells can be tuned by adjusting the ratio of the radius of the dielectric core, r I, to the overall radius, r II, which includes the thickness of the metallic coating. Our nanoshells, fabricated at Rice University, consist of a silica core with a gold coating. Using back focal plane detection, we measure the trap stiffness of a single focus optical trap (optical tweezers), from a diode laser at 853 nm for nanoshells with several different r I/r II ratios.

Effects of morphology on the radiative properties of internally mixed light absorbing carbon aerosols with different aging status.

PubMed

Cheng, Tianhai; Wu, Yu; Chen, Hao

2014-06-30

Light absorbing carbon aerosols play a substantial role in climate change through radiative forcing, which is the dominant absorber of solar radiation. Radiative properties of light absorbing carbon aerosols are strongly dependent on the morphological factors and the mixing mechanism of black carbon with other aerosol components. This study focuses on the morphological effects on the optical properties of internally mixed light absorbing carbon aerosols using the numerically exact superposition T-matrix method. Three types aerosols with different aging status such as freshly emitted BC particles, thinly coated light absorbing carbon aerosols, heavily coated light absorbing carbon aerosols are studied. Our study showed that morphological factors change with the aging of internally mixed light absorbing carbon aerosols to result in a dramatic change in their optical properties. The absorption properties of light absorbing carbon aerosols can be enhanced approximately a factor of 2 at 0.67 um, and these enhancements depend on the morphological factors. A larger shell/core diameter ratio of volume-equivalent shell-core spheres (S/C), which indicates the degree of coating, leads to stronger absorption. The enhancement of absorption properties accompanies a greater enhancement of scattering properties, which is reflected in an increase in single scattering albedo (SSA). The enhancement of single scattering albedo due to the morphological effects can reach a factor of 3.75 at 0.67 μm. The asymmetry parameter has a similar yet smaller enhancement. Moreover, the corresponding optical properties of shell-and-core model determined by using Lorenz -Mie solutions are presented for comparison. We found that the optical properties of internally mixed light absorbing carbon aerosol can differ fundamentally from those calculated for the Mie theory shell-and-core model, particularly for thinly coated light absorbing carbon aerosols. Our studies indicate that the complex morphology of internally mixed light absorbing carbon aerosols must be explicitly considered in climate radiation balance.

X-ray Absorption and Emission Spectroscopic Studies of [L2Fe2S2]n Model Complexes: Implications for the Experimental Evaluation of Redox States in Iron–Sulfur Clusters

PubMed Central

2016-01-01

Herein, a systematic study of [L2Fe2S2]n model complexes (where L = bis(benzimidazolato) and n = 2-, 3-, 4-) has been carried out using iron and sulfur K-edge X-ray absorption (XAS) and iron Kβ and valence-to-core X-ray emission spectroscopies (XES). These data are used as a test set to evaluate the relative strengths and weaknesses of X-ray core level spectroscopies in assessing redox changes in iron–sulfur clusters. The results are correlated to density functional theory (DFT) calculations of the spectra in order to further support the quantitative information that can be extracted from the experimental data. It is demonstrated that due to canceling effects of covalency and spin state, the information that can be extracted from Fe Kβ XES mainlines is limited. However, a careful analysis of the Fe K-edge XAS data shows that localized valence vs delocalized valence species may be differentiated on the basis of the pre-edge and K-edge energies. These findings are then applied to existing literature Fe K-edge XAS data on the iron protein, P-cluster, and FeMoco sites of nitrogenase. The ability to assess the extent of delocalization in the iron protein vs the P-cluster is highlighted. In addition, possible charge states for FeMoco on the basis of Fe K-edge XAS data are discussed. This study provides an important reference for future X-ray spectroscopic studies of iron–sulfur clusters. PMID:27097289

Radiative absorption enhancement from coatings on black carbon aerosols.

PubMed

Cui, Xinjuan; Wang, Xinfeng; Yang, Lingxiao; Chen, Bing; Chen, Jianmin; Andersson, August; Gustafsson, Örjan

2016-05-01

The radiative absorption enhancement of ambient black carbon (BC), by light-refractive coatings of atmospheric aerosols, constitutes a large uncertainty in estimates of climate forcing. The direct measurements of radiative absorption enhancement require the experimentally-removing the coating materials in ambient BC-containing aerosols, which remains a challenge. Here, the absorption enhancement of the BC core by non-absorbing aerosol coatings was quantified using a two-step removal of both inorganic and organic matter coatings of ambient aerosols. The mass absorption cross-section (MAC) of decoated/pure atmospheric BC aerosols of 4.4±0.8m(2)g(-1) was enhanced to 9.6±1.8m(2)g(-1) at 678-nm wavelength for ambiently-coated BC aerosols at a rural Northern China site. The enhancement of MAC (EMAC) rises from 1.4±0.3 in fresh combustion emissions to ~3 for aged ambient China aerosols. The three-week high-intensity campaign observed an average EMAC of 2.25±0.55, and sulfates were primary drivers of the enhanced BC absorption. Copyright © 2016 Elsevier B.V. All rights reserved.

Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters

NASA Astrophysics Data System (ADS)

Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; Nobusada, Katsuyuki; Jin, Rongchao

2016-03-01

Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications. Electronic supplementary information (ESI) available: The pump dependent transient absorption spectra and the corresponding global analysis results. See DOI: 10.1039/c6nr01008c

Absorption Coefficient of Alkaline Earth Halides.

DTIC Science & Technology

1980-04-01

not observed at low energy level , are developed at high power levels . No matter how low the absorption is. the effect is objectionable at high-energy... levels . As a natural consequence, the magnitude of the absorption coefficient is the key parameter in selecting laser window materials. Over the past...Presence of impurities can complicate the exponential tail. particularly at low absorption levels . The impurities may enter 12 the lattice singly or

Synthesis and evaluation of mesoporous carbon/lipid bilayer nanocomposites for improved oral delivery of the poorly water-soluble drug, nimodipine.

PubMed

Zhang, Yanzhuo; Zhao, Qinfu; Zhu, Wufu; Zhang, Lihua; Han, Jin; Lin, Qisi; Ai, Fengwei

2015-07-01

A novel mesoporous carbon/lipid bilayer nanocomposite (MCLN) with a core-shell structure was synthesized and characterized as an oral drug delivery system for poorly water-soluble drugs. The objective of this study was to investigate the potential of MCLN-based formulation to modulate the in vitro release and in vivo absorption of a model drug, nimodipine (NIM). NIM-loaded MCLN was prepared by a procedure involving a combination of thin-film hydration and lyophilization. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area analysis, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were employed to characterize the NIM-loaded MCLN formulation. The effect of MCLN on cell viability was assessed using the MTT assay. In addition, the oral bioavailability of NIM-loaded MCLN in beagle dogs was compared with that of the immediate-release formulation, Nimotop®. Our results demonstrate that the NIM-loaded MCLN formulation exhibited a typical sustained release pattern. The NIM-loaded MCLN formulation achieved a greater degree of absorption and longer lasting plasma drug levels compared with the commercial formulation. The relative bioavailability of NIM for NIM-loaded MCLN was 214%. MCLN exhibited negligible toxicity. The data reported herein suggest that the MCLN matrix is a promising carrier for controlling the drug release rate and improving the oral absorption of poorly water-soluble drugs.

X-ray Absorption Study of Graphene Oxide and Transition Metal Oxide Nanocomposites.

PubMed

Gandhiraman, Ram P; Nordlund, Dennis; Javier, Cristina; Koehne, Jessica E; Chen, Bin; Meyyappan, M

2014-08-14

The surface properties of the electrode materials play a crucial role in determining the performance and efficiency of energy storage devices. Graphene oxide and nanostructures of 3d transition metal oxides were synthesized for construction of electrodes in supercapacitors, and the electronic structure and oxidation states were probed using near-edge X-ray absorption fine structure. Understanding the chemistry of graphene oxide would provide valuable insight into its reactivity and properties as the graphene oxide transformation to reduced-graphene oxide is a key step in the synthesis of the electrode materials. Polarized behavior of the synchrotron X-rays and the angular dependency of the near-edge X-ray absorption fine structures (NEXAFS) have been utilized to study the orientation of the σ and π bonds of the graphene oxide and graphene oxide-metal oxide nanocomposites. The core-level transitions of individual metal oxides and that of the graphene oxide nanocomposite showed that the interaction of graphene oxide with the metal oxide nanostructures has not altered the electronic structure of either of them. As the restoration of the π network is important for good electrical conductivity, the C K edge NEXAFS spectra of reduced graphene oxide nanocomposites confirms the same through increased intensity of the sp 2 -derived unoccupied states π* band. A pronounced angular dependency of the reduced sample and the formation of excitonic peaks confirmed the formation of extended conjugated network.

A theoretical study on the geometry and spectroscopic properties of ground-state and local minima isomers of (CuS)n=2-6 clusters

NASA Astrophysics Data System (ADS)

Luque-Ceballos, Jonathan C.; Posada-Borbón, Alvaro; Herrera-Urbina, Ronaldo; Aceves, R.; Juárez-Sánchez, J. Octavio; Posada-Amarillas, Alvaro

2018-03-01

Spectroscopic properties of gas-phase copper sulfide clusters (CuS)n (n = 2-6) are calculated using Density Functional Theory (DFT) and time-dependent (TD) DFT approaches. The energy landscape of the potential energy surface is explored through a basin-hopping DFT methodology. Ground-state and low-lying isomer structures are obtained. The global search was performed at the B3PW91/SDD level of theory. Normal modes are calculated to validate the existence of optimal cluster structures. Energetic properties are obtained for the ground-state and isomer clusters and their relative energies are evaluated for probing isomerization. This is a few tenths of an eV, except for (CuS)2 cluster, which presents energy differences of ∼1 eV. Notable differences in the infrared spectra exist between the ground-state and first isomer structures, even for the (CuS)5 cluster, which has in both configurations a core copper pyramid. TDDFT provides the simulated absorption spectrum, presenting a theoretical description of optical absorption bands in terms of electronic excitations in the UV and visible regions. Results exhibit a significant dependence of the calculated UV/vis spectra on clusters size and shape regarding the ground state structures. Optical absorption is strong in the UV region, and weak or forbidden in the visible region of the spectrum.

SWCNT Photocatalyst for Hydrogen Production from Water upon Photoexcitation of (8, 3) SWCNT at 680-nm Light

NASA Astrophysics Data System (ADS)

Murakami, Noritake; Tango, Yuto; Miyake, Hideaki; Tajima, Tomoyuki; Nishina, Yuta; Kurashige, Wataru; Negishi, Yuichi; Takaguchi, Yutaka

2017-03-01

Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n, m). Their application for solar energy conversion is difficult because of the large binding energy (>100 meV) of electron-hole pairs, known as excitons, produced by optical absorption. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C60 is the key for high power conversion efficiency. In contrast to thin film devices, photocatalytic reactions in a dispersion/solution system triggered by the photoexcitation of SWCNTs have never been reported due to the difficulty of the construction of a well-ordered surface on SWCNTs. Here, we show a clear-cut example of a SWCNT photocatalyst producing H2 from water. Self-organization of a fullerodendron on the SWCNT core affords water-dispersible coaxial nanowires possessing SWCNT/C60 heterojunctions, of which a dendron shell can act as support of a co-catalyst for H2 evolution. Because the band offset between the LUMO levels of (8, 3)SWCNT and C60 satisfactorily exceeds the exciton binding energy to allow efficient exciton dissociation, the (8, 3)SWCNT/fullerodendron coaxial photocatalyst shows H2-evolving activity (QY = 0.015) upon 680-nm illumination, which is E22 absorption of (8, 3) SWCNT.

Sources and physicochemical characteristics of black carbon aerosol from the southeastern Tibetan Plateau: internal mixing enhances light absorption

NASA Astrophysics Data System (ADS)

Wang, Qiyuan; Cao, Junji; Han, Yongming; Tian, Jie; Zhu, Chongshu; Zhang, Yonggang; Zhang, Ningning; Shen, Zhenxing; Ni, Haiyan; Zhao, Shuyu; Wu, Jiarui

2018-04-01

Black carbon (BC) aerosol has important effects on the climate and hydrology of the Tibetan Plateau (TP). An intensive measurement campaign was conducted at Lulang (˜ 3300 m a.s.l. - above sea level), southeastern TP, from September to October 2015, to investigate the sources and physicochemical characteristics of refractory BC (rBC) aerosol. The average rBC mass concentration was 0.31 ± 0.55 µg m-3, which is higher than most prior results for BC on the TP. A clear diurnal cycle in rBC showed high values in the morning and low values in the afternoon. A bivariate polar plot showed that rBC loadings varied with wind speed and direction, which also reflected the dominant transport direction. The estimated net surface rBC transport intensity was +0.05 ± 0.29 µg s-1 m-2, indicating stronger transport from outside the TP compared with its interior. Cluster analysis and a concentration-weighted trajectory model connected emissions from north India to the high rBC loadings, but the effects of internal TP sources should not be overlooked. The average mass median diameter (MMD) of rBC was 160 ± 23 nm, with smaller MMDs on rainy days (145 nm) compared with non-rainy days (164 nm). The average number fraction of thickly coated rBC (FrBC) was 39 ± 8 %, and it increased with the O3 mixing ratios from 10:00 to 14:00 LT, indicating that photochemical oxidation played a role in forming rBC coatings. The average rBC absorption enhancement (Eabs) was estimated to be 1.9, suggesting that light absorption by coated rBC particles was greater than for uncoated ones. The Eabs was strongly positively correlated with the FrBC, indicating an amplification of light absorption for internally mixed rBC. For rBC cores < 170 nm, Eabs was negatively correlated with MMD, but it was nearly constant for rBC cores > 170 nm. Our study provides insight into the sources and evolution of rBC aerosol on the TP, and the results should be useful for improving models of the radiative effects of carbonaceous aerosols in this area.

Effect of heat treatment on absorption and fluorescence properties of PbS-doped silica optical fibre

NASA Astrophysics Data System (ADS)

Qin, Fu; Dong, Yanhua; Wen, Jianxiang; Pang, Fufei; Luo, Yanhua; Peng, Gang-Ding; Chen, Zhenyi; Wang, Tingyun

2017-02-01

The effect of heat treatment on the optical properties of a PbS-doped silica optical fibre was investigated. The experimental results showed that the absorption peak of the fibre red shifted from 1032 to 1133 nm when the heat treatment temperatures were carried out at 900, 950, 1000, and 1100 °C for 1 h, respectively. At the same time, when the heat treatment at 900 °C was carried out for 2, 5, 10, 20, and 40 h, the absorption spectra of the fibre showed a red shift from 1074 to 1143 nm. In addition, the intensity of the absorption peak increased from 0.258 to 1.384 dB/m and the full width at half maximum (FWHM) became narrower (from 130 to 50 nm) as the heat treatment proceeded. Moreover, the photoluminescence (PL) intensity in the wavelength range of 1100-1500 nm decreased with an increase in the heat treatment temperature. The theoretical analysis, using an effective mass method, showed that the effective band gap energy and average size of the lead sulphide (PbS) quantum dots (QDs) in the silica fibre core varied from 1.199 to 1.083 eV and from 4.28 to 4.81 nm, respectively. The results indicate that the size of the PbS QDs present in the silica fibre core could be controlled by a proper heat treatment, which is of great interest in optical fibre amplifiers and other fibre optic devices.

Collision-Induced Infrared Absorption by Hydrogen-Helium gas mixtures at Thousands of Kelvin

NASA Astrophysics Data System (ADS)

Abel, Martin; Frommhold, Lothar; Li, Xiaoping; Hunt, Katharine L. C.

2010-10-01

The interaction-induced absorption by collisional pairs of H2 molecules is an important opacity source in the atmospheres of the outer planets and cool stars ^[1]. The emission spectra of cool white dwarf stars differ significantly in the infrared from the expected blackbody spectra of their cores, which is largely due to absorption by collisional H2--H2, H2--He, and H2--H complexes in the stellar atmospheres. Using quantum-chemical methods we compute the atmospheric absorption from hundreds to thousands of kelvin ^[2]. Laboratory measurements of interaction-induced absorption spectra by H2 pairs exist only at room temperature and below. We show that our results reproduce these measurements closely ^[2], so that our computational data permit reliable modeling of stellar atmosphere opacities even for the higher temperatures ^[2]. [1] L. Frommhold, Collision-Induced Absorption in Gases, Cambridge University Press, Cambridge, New York, 1993 and 2006 [2] Xiaoping Li, Katharine L. C. Hunt, Fei Wang, Martin Abel, and Lothar Frommhold, ``Collision-Induced Infrared Absorption by Molecular Hydrogen Pairs at Thousands of Kelvin'', International Journal of Spectroscopy, vol. 2010, Article ID 371201, 11 pages, 2010. doi: 10.1155/2010/371201

Multi-frequency Optical-depth Maps And The Case For Free-free Absorption In Two Compact Symmetric Objects: 1321+410 And 0026+346

NASA Astrophysics Data System (ADS)

Perry, Thomas M.; Marr, J. M.; Read, J. W.; Taylor, G. B.

2011-01-01

We obtained VLBI observations at six frequencies of two Compact Symmetric Objects, 1321+410 and 0026+346. By comparing the lower frequency maps with spectral extrapolations of the higher frequency maps, we produced maps of the optical depth as a function of frequency. The optical-depth maps of 1321+410 are strikingly uniform, consistent with a foreground screen of absorbing gas; the optical depths as a function of frequency are consistent with free-free absorption; and no net polarization was detected. We conclude that the case for free-free absorption in 1321+410 is strong. The optical-depth maps of 0026+346 exhibit structure but the morphology does not correlate with that in the intensity maps, in conflict with that expected in the case of synchrotron self-absorption. No net polarization was detected. The frequency dependence of the optical depths does not fit well to a simple free-free absorption model, but this does not take into account possible structure in the absorbing gas on smaller scales. We conclude that free-free absorption by a thin amount of gas with structure on the scale of our maps and smaller is possible in 0026+346, although no definitive conclusion can be made. A compact feature between the lobes in 0026+346 has an inverted spectrum even at the highest frequencies, suggesting that this component is synchrotron self-absorbed. We infer this to be the location of the core. We estimate an upper limit to the magnetic field in the core of 50 Gauss at a radius of 1 pc. This research was supported by an award from the Research Corporation, a NASA NY Space Grant, and a Booth-Ferris Research Fellowship. The VLBA is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Possible role of zinc in diminishing lead-related occupational stress-a zinc nutrition concern.

PubMed

Wani, Ab Latif; Ahmad, Ajaz; Shadab, G G H A; Usmani, Jawed Ahmad

2017-03-01

Lead and zinc are mostly present at the same occupational source and usually found as co-contaminants. Lead is known to associate with detrimental effects to humans. Zinc however is an essential nutrient and its deficiency causes debilitating effects on growth and development. Besides, it acts as core ion of important enzymes and proteins. The purpose of this study was to examine if zinc concentrations are associated with blood lead levels and if zinc may prevent lead-induced DNA damage. Blood samples were collected from 92 workers as participants occupationally exposed to lead or lead and zinc and 38 comparison participants having no history of such exposure. Lead and zinc levels were determined from blood by atomic absorption spectrophotometry and genetic damage was assessed by comet assay. Correlation was calculated by Spearman's rho. Lead concentrations were observed to increase among workers with increase in years of exposure. There was a significant difference (p < 0.001) in blood lead levels between workers and controls. In addition, significant difference (p < 0.001) in the genetic damage was observed among workers and controls. A clear effect of increased occupational exposure was visible among workers. Multiple regression analysis further reveals the positive effect of lead, while as the inverse effect of zinc on DNA damage. The results suggest that zinc may influence body lead absorption and may have a role in preventing the genetic damage caused by lead.

Molecules for Fluorescence Detection of Specific Chemicals

NASA Technical Reports Server (NTRS)

Fedor, Steve

2008-01-01

A family of fluorescent dye molecules has been developed for use in on-off fluorescence detection of specific chemicals. By themselves, these molecules do not fluoresce. However, when exposed to certain chemical analytes in liquid or vapor forms, they do fluoresce (see figure). These compounds are amenable to fixation on or in a variety of substrates for use in fluorescence-based detection devices: they can be chemically modified to anchor them to porous or non-porous solid supports or can be incorporated into polymer films. Potential applications for these compounds include detection of chemical warfare agents, sensing of acidity or alkalinity, and fluorescent tagging of proteins in pharmaceutical research and development. These molecules could also be exploited for use as two-photon materials for photodynamic therapy in the treatment of certain cancers and other diseases. A molecule in this family consists of a fluorescent core (such as an anthracene or pyrene) attached to two end groups that, when the dye is excited by absorption of light, transfer an electron to the core, thereby quenching the fluorescence. The end groups can be engineered so that they react chemically with certain analytes. Upon reaction, electrons on the end groups are no longer available for transfer to the core and, consequently, the fluorescence from the core is no longer quenched. The chemoselectivity of these molecules can be changed by changing the end groups. For example, aniline end groups afford a capability for sensing acids or acid halides (including those contained in chemical warfare agents). Pyridine or bipyridyl end groups would enable sensing of metal ions. Other chemicals that can be selectively detected through suitable choice of end groups include glucose and proteins. Moreover, the fluorescent cores can be changed to alter light-absorption and -emission characteristics: anthracene cores fluoresce at wavelengths around 500 nm, whereas perylene cores absorb and emit at wavelengths of about 600 nm.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukerjee, S.; Ziegelbauer, J; Arruda, T

Over the last few decades, researchers have made significant developments in producing more advanced electrocatalytic materials for power generation applications. For example, traditional fuel cell catalysts often involve high-priced precious metals such as Pt. However, in order for fuel cells to become commercially viable, there is a need to reduce or completely remove precious metal altogether. As a result, a myriad of novel, unconventional materials have been explored such as chalcogenides, porphyrins, and organic-metal-macrocycles for low/medium temperature fuel cells as well as enzymatic and microbial fuel cells. As these materials increasingly become more complex, researchers often find themselves in searchmore » of new characterization methods, especially those which are allow in situ and operando measurements with element specificity. One such method that has received much attention for analysis of electrocatalytic materials is X-ray absorption spectroscopy (XAS). XAS is an element specific, core level absorption technique which yields structural and electronic information. As a core electron method, XAS requires an extremely bright source, hence a synchrotron. The resulting intensity of synchrotron radiation allow for experiments to be conducted in situ, under electrochemically relevant conditions. Although a bulk-averaging technique requiring rigorous mathematical manipulation, XAS has the added benefit that it can probe materials which possess no long range order. This makes it ideal to characterize nano-scale electrocatalysts. XAS experiments are conducted by ramping the X-ray photon energy while measuring absorption of the incident beam the sample or by counting fluorescent photons released from a sample due to subsequent relaxation. Absorption mode XAS follows the Beer-Lambert Law, {mu}x = log(I{sub 0}/I{sub t}) (1) where {mu} is the absorption coefficient, x is the sample thickness and I{sub 0} and I{sub t} are the intensities of the incident and transmission beams respectively. When the energy of the incident X-rays exceed the electron binding energy (E{sub 0}) of the element under investigation, the electron is ejected from the core to available excited states in the form of a photoelectron with kinetic energy: E{sub k} = h? - E{sub 0} (2) with, E{sub k} being the kinetic energy of the released photoelectron and h? the energy of the incident beam. In general, the X-ray absorption spectrum is broken down into two distinct energy regions: the X-ray absorption near-edge structure or XANES (-50eV {le} E{sub 0} {le} 50eV) and the extended X-ray absorption fine-structure or EXAFS (50eV {le} E{sub 0} {le} {approx}1000eV). The XANES region is dominated by low-energy photoelectrons which undergo multiple scattering events. As such, it can reveal information about oxidation state, local symmetry, electronic structure, and the extent of oxidation of a material. Due to this complex multiple scattering, there is no simple XANES equation to describe it quantitatively. However, recent advancements in computers and the evolution of numerical methods such as the FEFF code have made possible reliable XANES simulations. Photoelectrons in the EXAFS region have high enough E{sub k} to undergo primarily single back-scattering events. These back-scattered photoelectrons interfere with the outgoing photoelectrons, causing the oscillations in the absorption spectrum. Using the previously developed EXAFS equations it is now possible to model EXAFS data to determine coordination numbers, bond distances, and mean-square disorder (commonly referred to as Debye-Waller factor). EXAFS data is often shown by Fourier Transforming KSpace into distance, r, space where the total magnitude is plotted against the radial coordinates. This allow for easy qualitative comparison of samples. Employing EXAFS on nanoscale materials has the added advantage that it can quantitatively illustrate changes in atom-atom coordination, which can be related to particle size or morphology. Overall this technique enables the measurement of both bulk and surface adsorbed species with element specificity under actual electrochemical operating conditions. Thus this represents the one of the most powerful methods to understand the exact role of the reaction center and degradation processes such as sintering and corrosion.« less

Tuned Chamber Core Panel Acoustic Test Results

NASA Technical Reports Server (NTRS)

Schiller, Noah H.; Allen, Albert R.

2016-01-01

This report documents acoustic testing of tuned chamber core panels, which can be used to supplement the low-frequency performance of conventional acoustic treatment. The tuned chamber core concept incorporates low-frequency noise control directly within the primary structure and is applicable to sandwich constructions with a directional core, including corrugated-, truss-, and fluted-core designs. These types of sandwich structures have long, hollow channels (or chambers) in the core. By adding small holes through one of the facesheets, the hollow chambers can be utilized as an array of low-frequency acoustic resonators. These resonators can then be used to attenuate low-frequency noise (below 400 Hz) inside a vehicle compartment without increasing the weight or size of the structure. The results of this test program demonstrate that the tuned chamber core concept is effective when used in isolation or combined with acoustic foam treatments. Specifically, an array of acoustic resonators integrated within the core of the panels was shown to improve both the low-frequency absorption and transmission loss of the structure in targeted one-third octave bands.

Monitoring Changes of Tropical Extreme Rainfall Events Using Differential Absorption Barometric Radar (DiBAR)

NASA Technical Reports Server (NTRS)

Lin, Bing; Harrah, Steven; Lawrence, R. Wes; Hu, Yongxiang; Min, Qilong

2015-01-01

This work studies the potential of monitoring changes in tropical extreme rainfall events such as tropical storms from space using a Differential-absorption BArometric Radar (DiBAR) operating at 50-55 gigahertz O2 absorption band to remotely measure sea surface air pressure. Air pressure is among the most important variables that affect atmospheric dynamics, and currently can only be measured by limited in-situ observations over oceans. Analyses show that with the proposed radar the errors in instantaneous (averaged) pressure estimates can be as low as approximately 5 millibars (approximately 1 millibar) under all weather conditions. With these sea level pressure measurements, the forecasts, analyses and understanding of these extreme events in both short and long time scales can be improved. Severe weathers, especially hurricanes, are listed as one of core areas that need improved observations and predictions in WCRP (World Climate Research Program) and NASA Decadal Survey (DS) and have major impacts on public safety and national security through disaster mitigation. Since the development of the DiBAR concept about a decade ago, our team has made substantial progress in advancing the concept. Our feasibility assessment clearly shows the potential of sea surface barometry using existing radar technologies. We have developed a DiBAR system design, fabricated a Prototype-DiBAR (P-DiBAR) for proof-of-concept, conducted lab, ground and airborne P-DiBAR tests. The flight test results are consistent with our instrumentation goals. Observational system simulation experiments for space DiBAR performance show substantial improvements in tropical storm predictions, not only for the hurricane track and position but also for the hurricane intensity. DiBAR measurements will lead us to an unprecedented level of the prediction and knowledge on tropical extreme rainfall weather and climate conditions.

Remote Sensing Global Surface Air Pressure Using Differential Absorption BArometric Radar (DiBAR)

NASA Technical Reports Server (NTRS)

Lin, Bing; Harrah, Steven; Lawrence, Wes; Hu, Yongxiang; Min, Qilong

2016-01-01

Tropical storms and severe weathers are listed as one of core events that need improved observations and predictions in World Meteorological Organization and NASA Decadal Survey (DS) documents and have major impacts on public safety and national security. This effort tries to observe surface air pressure, especially over open seas, from space using a Differential-absorption BArometric Radar (DiBAR) operating at the 50-55 gigahertz O2 absorption band. Air pressure is among the most important variables that affect atmospheric dynamics, and currently can only be measured by limited in-situ observations over oceans. Analyses show that with the proposed space radar the errors in instantaneous (averaged) pressure estimates can be as low as approximately 4 millibars (approximately 1 millibar under all weather conditions). With these sea level pressure measurements, the forecasts of severe weathers such as hurricanes will be significantly improved. Since the development of the DiBAR concept about a decade ago, NASA Langley DiBAR research team has made substantial progress in advancing the concept. The feasibility assessment clearly shows the potential of sea surface barometry using existing radar technologies. The team has developed a DiBAR system design, fabricated a Prototype-DiBAR (P-DiBAR) for proof-of-concept, conducted lab, ground and airborne P-DiBAR tests. The flight test results are consistent with the instrumentation goals. Observational system simulation experiments for space DiBAR performance based on the existing DiBAR technology and capability show substantial improvements in tropical storm predictions, not only for the hurricane track and position but also for the hurricane intensity. DiBAR measurements will lead us to an unprecedented level of the prediction and knowledge on global extreme weather and climate conditions.

A core-substituted naphthalene diimide fluoride sensor.

PubMed

Bhosale, Sheshanath V; Bhosale, Sidhanath V; Kalyankar, Mohan B; Langford, Steven J

2009-12-03

The synthesis and characterization of a highly fluorescent core-substituted naphthalene diimide sensor (varphi = 0.34) bearing a bis-sulfonamide group is described. The compound shows a unique selectivity and reactivity for the fluoride ion over other anions in CHCl(3) by a two-stage deprotonation process leading to a colorimetric response. In DMSO solution, the sensor is shown to be highly selective for fluoride (K(a) approximately 10(6) M(-1)) over other anions with more pronounced changes in absorption characteristics.

Control of exposure to hexavalent chromium concentration in shielded metal arc welding fumes by nano-coating of electrodes.

PubMed

Sivapirakasam, S P; Mohan, Sreejith; Santhosh Kumar, M C; Thomas Paul, Ashley; Surianarayanan, M

2017-04-01

Background Cr(VI) is a suspected human carcinogen formed as a by-product of stainless steel welding. Nano-alumina and nano-titania coating of electrodes reduced the welding fume levels. Objective To investigate the effect of nano-coating of welding electrodes on Cr(VI) formation rate (Cr(VI) FR) from a shielded metal arc welding process. Methods The core welding wires were coated with nano-alumina and nano-titania using the sol-gel dip coating technique. Bead-on plate welds were deposited on SS 316 LN plates kept inside a fume test chamber. Cr(VI) analysis was done using an atomic absorption spectrometer (AAS). Results A reduction of 40% and 76%, respectively, in the Cr(VI) FR was observed from nano-alumina and nano-titania coated electrodes. Increase in the fume level decreased the Cr(VI) FR. Discussion Increase in fume levels blocked the UV radiation responsible for the formation of ozone thereby preventing the formation of Cr(VI).

Phosphine-free synthesis and characterization of type-II ZnSe/CdS core-shell quantum dots

NASA Astrophysics Data System (ADS)

Ghasemzadeh, Roghayyeh; Armanmehr, Mohammad Hasan; Abedi, Mohammad; Fateh, Davood Sadeghi; Bahreini, Zaker

2018-01-01

A phosphine-free route for synthesis of type-II ZnSe/CdS core-shell quantum dots, using green, low cost and environmentally friendly reagents and phosphine-free solvents such as 1-octadecene (ODE) and liquid paraffin has been reported. Hot-injection technique has been used for the synthesis of ZnSe core quantum dots. The CdS shell quantum dots prepared by reaction of CdO precursor and S powder in 1-octadecene (ODE). The ZnSe/CdS core-shell quantum dots were synthesized via successive ion layer adsorption and reaction (SILAR) technique. The characterization of produced quantum dots were performed by absorption and fluorescence spectroscopy, X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The results showed the formation of type-II ZnSe/CdS core-shell quantum dots with FWHM 32 nm and uniform size distribution.

Titanium dioxide@polypyrrole core-shell nanowires for all solid-state flexible supercapacitors

NASA Astrophysics Data System (ADS)

Yu, Minghao; Zeng, Yinxiang; Zhang, Chong; Lu, Xihong; Zeng, Chenghui; Yao, Chenzhong; Yang, Yangyi; Tong, Yexiang

2013-10-01

Herein, we developed a facile two-step process to synthesize TiO2@PPy core-shell nanowires (NWs) on carbon cloth and reported their improved electrochemical performance for flexible supercapacitors (SCs). The fabricated solid-state SC device based on TiO2@PPy core-shell NWs not only has excellent flexibility, but also exhibits remarkable electrochemical performance.Herein, we developed a facile two-step process to synthesize TiO2@PPy core-shell nanowires (NWs) on carbon cloth and reported their improved electrochemical performance for flexible supercapacitors (SCs). The fabricated solid-state SC device based on TiO2@PPy core-shell NWs not only has excellent flexibility, but also exhibits remarkable electrochemical performance. Electronic supplementary information (ESI) available: Experimental details, XRD pattern, FT-IR absorption spectrum and CV curves of TiO2@PPy NWs, and SEM images of the PPy. See DOI: 10.1039/c3nr03578f

Dye-Sensitized Core/Active Shell Upconversion Nanoparticles for Optogenetics and Bioimaging Applications

DOE PAGES

Wu, Xiang; Zhang, Yuanwei; Takle, Kendra; ...

2016-01-06

A near-infrared (NIR) dye-sensitized upconversion nanoparticles (UCNPs) can broaden the absorption range and boost upconversion efficiency of UCNPs. We achieved significantly enhanced upconversion luminescence in dye-sensitized core/active shell UCNPs via the doping of ytterbium ions (Yb 3+ ) in the UCNP shell, which bridged the energy transfer from the dye to the UCNP core. As a result, we synergized the two most practical upconversion booster effectors (dye-sensitizing and core/shell enhancement) to amplify upconversion efficiency. We also demonstrated two biomedical applications using these UCNPs. By using dye-sensitized core/active shell UCNP embedded poly(methyl methacrylate) polymer implantable systems, we successfully shifted the optogeneticmore » neuron excitation window to a biocompatible and deep tissue penetrable 800 nm wavelength. Furthermore, UCNPs were water-solubilized with Pluronic F127 with high upconversion efficiency and can be imaged in a mouse model.« less

Ultra low-loss hybrid core porous fiber for broadband applications.

PubMed

Islam, Md Saiful; Sultana, Jakeya; Atai, Javid; Abbott, Derek; Rana, Sohel; Islam, Mohammad Rakibul

2017-02-01

In this paper, we present the design and analysis of a novel hybrid porous core octagonal lattice photonic crystal fiber for terahertz (THz) wave guidance. The numerical analysis is performed using a full-vector finite element method (FEM) that shows that 80% of bulk absorption material loss of cyclic olefin copolymer (COC), commercially known as TOPAS can be reduced at a core diameter of 350 μm. The obtained effective material loss (EML) is as low as 0.04  cm^-1 at an operating frequency of 1 THz with a core porosity of 81%. Moreover, the proposed photonic crystal fiber also exhibits comparatively higher core power fraction, lower confinement loss, higher effective mode area, and an ultra-flattened dispersion profile with single mode propagation. This fiber can be readily fabricated using capillary stacking and sol-gel techniques, and it can be used for broadband terahertz applications.

Optical fiber sensor having a sol-gel fiber core and a method of making

DOEpatents

Tao, Shiquan; Jindal, Rajeev; Winstead, Christopher; Singh, Jagdish P.

2006-06-06

A simple, economic wet chemical procedure is described for making sol-gel fibers. The sol-gel fibers made from this process are transparent to ultraviolet, visible and near infrared light. Light can be guided in these fibers by using an organic polymer as a fiber cladding. Alternatively, air can be used as a low refractive index medium. The sol-gel fibers have a micro pore structure which allows molecules to diffuse into the fiber core from the surrounding environment. Chemical and biochemical reagents can be doped into the fiber core. The sol-gel fiber can be used as a transducer for constructing an optical fiber sensor. The optical fiber sensor having an active sol-gel fiber core is more sensitive than conventional evanescent wave absorption based optical fiber sensors.

Core/shell structured Zn/ZnO nanoparticles synthesized by gaseous laser ablation with enhanced photocatalysis efficiency

NASA Astrophysics Data System (ADS)

Song, Lu; Wang, Yafei; Ma, Jing; Zhang, Qinghua; Shen, Zhijian

2018-06-01

Zinc oxide (ZnO) is a competitive candidate in semiconductor photocatalysts, only if the efficiency could be fully optimized especially by tailored nanostructures. Here we report a kind of core/shell structured Zn/ZnO nanoparticles with enhanced photocatalysis efficiency, which were synthesized by a highly-productive gaseous laser ablation method. The nanodroplets generated by laser ablation would be reduced to zinc in the protective atmosphere, and further be oxidized at surface to form a specific core/shell structured Zn/ZnO nanoparticles within seconds. Thanks to the formation of this Zn-ZnO Schottky junction, the photocatalysis degradation efficiency of such core/shell Zn/ZnO nanostructure is significantly improved owing to the enhanced visible light absorption and inhibited carrier recombination by introducing the metallic zinc.

Understanding the features in the ultrafast transient absorption spectra of CdSe quantum dots

NASA Astrophysics Data System (ADS)

Zhang, Cheng; Do, Thanh Nhut; Ong, Xuanwei; Chan, Yinthai; Tan, Howe-Siang

2016-12-01

We describe a model to explain the features of the ultrafast transient absorption (TA) spectra of CdSe core type quantum dots (QDs). The measured TA spectrum consists of contributions by the ground state bleach (GSB), stimulated emission (SE) and excited state absorption (ESA) processes associated with the three lowest energy transition of the QDs. We model the shapes of the GSB, SE and ESA spectral components after fits to the linear absorption. The spectral positions of the ESA components take into account the biexcitonic binding energy. In order to obtain the correct weightage of the GSB, SE and ESA components to the TA spectrum, we enumerate the set of coherence transfer pathways associated with these processes. From our fits of the experimental TA spectra of 65 Å diameter QDs, biexcitonic binding energies for the three lowest energy transitions are obtained.

Electron localization and optical absorption of polygonal quantum rings

NASA Astrophysics Data System (ADS)

Sitek, Anna; Serra, Llorenç; Gudmundsson, Vidar; Manolescu, Andrei

2015-06-01

We investigate theoretically polygonal quantum rings and focus mostly on the triangular geometry where the corner effects are maximal. Such rings can be seen as short core-shell nanowires, a generation of semiconductor heterostructures with multiple applications. We show how the geometry of the sample determines the electronic energy spectrum, and also the localization of electrons, with effects on the optical absorption. In particular, we show that irrespective of the ring shape low-energy electrons are always attracted by corners and are localized in their vicinity. The absorption spectrum in the presence of a magnetic field shows only two peaks within the corner-localized state domain, each associated with different circular polarization. This picture may be changed by an external electric field which allows previously forbidden transitions, and thus enables the number of corners to be determined. We show that polygonal quantum rings allow absorption of waves from distant ranges of the electromagnetic spectrum within one sample.

[Construction and application of an onboard absorption analyzer device for CDOM].

PubMed

Lin, Jun-Fang; Sun, Zhao-Hua; Cao, Wen-Xi; Hu, Shui-Bo; Xu, Zhan-Tang

2013-04-01

Colored dissolved organic matter (CDOM) plays an important role in marine ecosystems. In order to solve the current problems in measurement of CDOM absorption, an automated onboard analyzer based on liquid core waveguides (Teflon AF LWCC/LCW) was constructed. This analyzer has remarkable characteristics including adjusted optical pathlength, wide measurement range, and high sensitivity. The model of filtration and injection can implement the function of automated filtration, sample injection, and LWCC cleaning. The LabVIEW software platform can efficiently control the running state of the analyzer and acquire real time data including light absorption spectra, GPS data, and CTW data. By the comparison experiments and shipboard measurements, it was proved that the analyzer was reliable and robust.

Construction of Au@Pt core—satellite nanoparticles based on in-situ reduction of polymeric ionic liquid protected gold nanoparticles

NASA Astrophysics Data System (ADS)

Wu, Wenlan; Li, Junbo; Zou, Sheng; Guo, Jinwu; Zhou, Huiyun

2017-03-01

A method of in-situ reduction to prepare Au@Pt core-satellite nanoparticles (NPs) is described by using Au NPs coating poly[1-methyl 3-(2-methacryloyloxy propylimidazolium bromine)] (PMMPImB-@-Au NPs) as the template. After electrostatic complex chloroplatinic acid with PMMPImB shell, the composite NP was directly reduced with N2H4 to produce Au@Pt core-satellite NPs. The characterization of composite and core-satellite NPs under different amounts of chloroplatinic acid were studied by DLS, UV-vis absorption spectrum and TEM. The satellite Pt NPs with a small size ( 2 nm) dotted around Au core, and the resulting Au@Pt core-satellite NPs showed a red-shift surface plasmon resonance (SPR) and a good dispersion due to effectively electrostatic repulsion providing by the polymeric ionic liquid (PIL) shell. Finally, Au@Pt core-satellite NPs exhibit an enhanced catalytic activity and cycled catalytic capability for the reduction of p-nitrophenol with NaBH4.

Evolution of silver/gold triangular nanoframes from prismatic silver/gold core/shell nanostructures and their SERS properties

NASA Astrophysics Data System (ADS)

Parthiban, P.; Sakar, M.; Balakumar, S.

2013-02-01

We report the evolution of Ag/Au triangular nanoframes from nano core/shell of Ag/Au and their surface enhanced Raman scattering (SERS) properties. The Ag/Au prismatic core/shell nanostructures were synthesized using chemical reduction method. It was observed that, on the addition of excess gold chloride (HAuCl4) solution, the morphology of nano core/shell was changed to alloy like triangular nanoframes. Accordingly, a shift was found towards higher wavelengths in the UV-Visible absorption peaks of Ag/Au nanoframes compare to Ag/Au nano core/shell. Consequently, the SERS effect of these Ag/Au anisotropic nanostructures were studied on methylene blue. The Ag/Au alloy like prismatic nanoframes showed improved SERS effect than that of prismatic core/shell nanostructures. The experimental findings were revealed that the improved SERS effect could be resulted from the enhanced surface plasmon resonance (SPR) due to the alloy like construction of Ag/Au system.

`Giant' nanocrystal quantum dots (gNQDs) as FRET donors

NASA Astrophysics Data System (ADS)

Chern, Margaret; Nguyen, Thuy; Dennis, Allison

2017-02-01

High-quality core/shell CdSe/xCdS quantum dots (QDs) ranging from 3 to 20 nm in diameter were synthesized for use as Förster Resonance Energy Transfer (FRET) donors. gNQDs are carefully characterized for size, emission, absorption, QY, and brightness in both organic and aqueous solution. FRET has been verified in optimally designed systems that use short capping ligands and donor-acceptor pairs that have well-matched emission and absorption spectra. The interplay between shell thickness, donor-acceptor distance, and particle brightness is systematically analyzed to optimize our biosensor design.

An electrochemical and photophysical study of a covalently linked inorganic-organic dyad.

PubMed

Kahnt, Axel; Heiniger, Leo-Philipp; Liu, Shi-Xia; Tu, Xiaoyan; Zheng, Zhiping; Hauser, Andreas; Decurtins, Silvio; Guldi, Dirk M

2010-02-22

A molecular donor-acceptor dyad comprising a hexarhenium cluster core, [Re(6)(mu(3)-Se)(8)](2+), and a fullerene moiety which are covalently linked through a pyridine ligand was synthesized and fully characterized. The electrochemical and photophysical properties are reported. The detailed study includes cyclic voltammetry, steady-state absorption and fluorescence spectroscopy, radiation chemistry and transient absorption spectroscopy. A light-induced electron transfer between the inorganic cluster moiety and the fullerene can be excluded. However, a light-induced energy transfer from the rhenium cluster to the fullerene is proposed.

U-Shaped and Surface Functionalized Polymer Optical Fiber Probe for Glucose Detection.

PubMed

Azkune, Mikel; Ruiz-Rubio, Leire; Aldabaldetreku, Gotzon; Arrospide, Eneko; Pérez-Álvarez, Leyre; Bikandi, Iñaki; Zubia, Joseba; Vilas-Vilela, Jose Luis

2017-12-25

In this work we show an optical fiber evanescent wave absorption probe for glucose detection in different physiological media. High selectivity is achieved by functionalizing the surface of an only-core poly(methyl methacrylate) (PMMA) polymer optical fiber with phenilboronic groups, and enhanced sensitivity by using a U-shaped geometry. Employing a supercontinuum light source and a high-resolution spectrometer, absorption measurements are performed in the broadband visible light spectrum. Experimental results suggest the feasibility of such a fiber probe as a low-cost and selective glucose detector.

Determination of bacterial activity by use of an evanescent-wave fiber-optic sensor

NASA Astrophysics Data System (ADS)

John, M. Shelly; Kishen, Anil; Sing, Lim Chu; Asundi, Anand

2002-12-01

A novel technique based on fiber-optic evanescent-wave spectroscopy is proposed for the detection of bacterial activity in human saliva. The sensor determines the specific concentration of Streptococcus mutans in saliva, which is a major causative factor in dental caries. In this design, one prepares the fiber-optic bacterial sensor by replacing a portion of the cladding region of a multimode fiber with a dye-encapsulated xerogel, using the solgel technique. The exponential decay of the evanescent wave at the core-cladding interface of a multimode fiber is utilized for the determination of bacterial activity in saliva. The acidogenic profile of Streptococcus mutans is estimated by use of evanescent-wave absorption spectra at various levels of bacterial activity.

Microwave electromagnetic and absorption properties of SiO2/C core/shell composites plated with metal cobalt

NASA Astrophysics Data System (ADS)

Shen, Guozhu; Fang, Xumin; Wu, Hongyan; Wei, Hongyu; Li, Jingfa; Li, Kaipeng; Mei, Buqing; Xu, Yewen

2017-04-01

A facile method has been developed to fabricate magnetic core/shell SiO2/C/Co sub-microspheres via the pyrolysis of SiO2/PANI (polyaniline) and electroless plating method. The electromagnetic parameters of these SiO2/C and SiO2/C/Co composites were measured and the microwave reflection loss properties were evaluated in the frequency range of 2-18 GHz. The results show that the dielectric loss of SiO2/C composite increases with the increase of carbonization temperature and the magnetic loss enhances due to the deposition of cobalt on the SiO2/C sub-microspheres. The reflection loss results exhibit that the microwave absorption properties of the SiO2/C/Co composites are more excellent than those of SiO2/C composites for each thickness. The maximum effective absorption bandwidth (reflection loss ≤ -10 dB) arrives at 5.0 GHz (13.0-18 GHz) for SiO2/C/Co composite with 1.5 mm of thickness and the minimum reflection loss value is -24.0 dB at 5.0 GHz with 4.0 mm of thickness. The microwave loss mechanism of the SiO2/C/Co composites was also discussed in this paper.

Hydrogen storage and hydrolysis properties of core-shell structured Mg-MFx (M=V, Ni, La and Ce) nano-composites prepared by arc plasma method

NASA Astrophysics Data System (ADS)

Mao, Jianfeng; Zou, Jianxin; Lu, Chong; Zeng, Xiaoqin; Ding, Wenjiang

2017-10-01

In this work, core-shell structured Mg-MFx (M = V, Ni, La and Ce) nano-composites are prepared by using arc plasma method. The particle size distribution, phase components, microstructures, hydrogen sorption properties of these composites and hydrolysis properties of their corresponding hydrogenated powders are carefully investigated. It is shown that the addition of MFx through arc plasma method can improve both the hydrogen absorption kinetics of Mg and the hydrolysis properties of corresponding hydrogenated powders. Among them, the Mg-NiF2 composite shows the best hydrogen absorption properties at relatively low temperatures, which can absorb 3.26 wt% of H2 at 373 K in 2 h. Such rapid hydrogen absorption rate is mainly due to the formation of Mg2Ni and MgF2 on Mg particles during arc evaporation and condensation. In contrast, measurements also show that the hydrogenated Mg-VF3 composite has the lowest peak desorption temperature and the fastest hydrolysis rate among all the hydrogenated Mg-MFx composites. The less agglomeration tendency of Mg particles and VO2 covered on MgH2 particles account for the reduced hydrogen desorption temperature and enhanced hydrolysis rate.

In-situ Density and Thermal Expansion Measurements of Fe and Fe-S Alloying Liquids Under Planetary Core Conditions

NASA Astrophysics Data System (ADS)

Jing, Z.; Chantel, J.; Yu, T.; Sakamaki, T.; Wang, Y.

2015-12-01

Liquid iron is likely the dominant constituent in the cores of terrestrial planets and icy satellites such as Earth, Mars, Mercury, the Moon, Ganymede, and Io. Suggested by geophysical and geochemical observations, light elements such as S, C, Si, etc., are likely present in planetary cores. These light elements can significantly reduce the density and melting temperature of the Fe cores, and hence their abundances are crucial to our understanding of the structure and thermal history of planetary cores, as well as the generation of intrinsic magnetic fields. Knowledge on the density of Fe-light element alloying liquids at high pressures is critical to place constraints on the composition of planetary cores. However, density data on liquid Fe-light element alloys at core pressures are very limited in pressure and composition and are sometimes controversial. In this study, we extend the density dataset for Fe-rich liquids by measuring the density of Fe, Fe-10wt%S, Fe-20wt%S, Fe-27wt%S, and FeS liquids using the X-ray absorption technique in a DIA-type multianvil apparatus up to 7 GPa and 2173 K. An ion chamber (1D-detector) and a CCD camera (2D-detector) were used to measure intensities of transmitted monochromatic X-rays through molten samples, with the photon energy optimized at 40 keV. The densities were then determined from the Beer-Lambert law using the mass absorption coefficients, calibrated by solid standards using X-ray diffraction. At each pressure, density measurements were conducted at a range of temperatures above the liquidus of the samples, enabling the determination of thermal expansion. Combined with our previous results on the sound velocity of Fe and Fe-S liquids at high pressures (Jing et al., 2014, Earth Planet. Sci. Lett. 396, 78-87), these data provide tight constraints on the equation of state and thermodynamic properties such as the adiabatic temperature gradient for Fe-S liquids. We will discuss these results with implications to planetary cores.

Application of a radiotelemetric system to evaluate the performance of enteric coated and plain aspirin tablets.

PubMed

Lui, C Y; Oberle, R; Fleisher, D; Amidon, G L

1986-05-01

The bioavailability of enteric coated and plain aspirin tablets was studied in four beagle dogs. Blood sampling for enteric coated tablets was planned with the aid of a radiotelemetric system. The release of aspirin from its dosage form was detected by monitoring the change in intestinal pH. Aspirin and salicylic acid levels in plasma obtained from the enteric coated dosage form exhibited familiar concentration versus time absorption profiles. Variation in the plasma concentrations of these two compounds within each dog studied (four runs each) was relatively small when time zero was adjusted to the commencement of tablet dissolution. The plasma levels obtained from plain aspirin (three runs each), however, show atypical absorption. The estimated absolute bioavailability was 0.432 +/- 0.0213 and 0.527 +/- 0.0260 for enteric coated and plain aspirin, respectively. Other pharmacokinetic parameters for these two dosage forms such as the highest observed plasma concentration (Cmax) (10.9 +/- 0.535 microgram/mL versus 13.6 +/- 1.88 micrograms/mL) and the time to reach Cmax (tmax) (26.6 +/- 1.94 min versus 31.0 +/- 7.04 min) agree well. The mean values for gastric emptying time, in vivo coating dissolution time, and in vivo disintegration/dissolution time of the tablet core for enteric coated aspirin are 48.7 +/- 7.23 min, 44.3 +/- 3.80 min, and 34.7 +/- 2.04 min, respectively.

Size-dependent structural evolution of the biomineralized iron-core nanoparticles in ferritins

NASA Astrophysics Data System (ADS)

Lee, Eunsook; Kim, D. H.; Hwang, Jihoon; Lee, Kiho; Yoon, Sungwon; Suh, B. J.; Hyun Kim, Kyung; Kim, J.-Y.; Jang, Z. H.; Kim, Bongjae; Min, B. I.; Kang, J.-S.

2013-04-01

The structural identity of the biomineralized iron core nanoparticles in Helicobacter pylori ferritins (Hpf's) has been determined by employing soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism. Valence states of Fe ions are nearly trivalent in all Hpf's, indicating that the amount of magnetite (Fe3O4) is negligible. With increasing filling of Fe ions, the local configurations of Fe3+ ions change from the mixture of the tetrahedral and octahedral symmetries to the octahedral symmetry. These results demonstrate that the biomineralization of the ferritin core changes from maghemite-like (γ-Fe2O3) formation to hematite-like (α-Fe2O3) formation with increasing Fe content.

Stability of core-shell nanowires in selected model solutions

NASA Astrophysics Data System (ADS)

Kalska-Szostko, B.; Wykowska, U.; Basa, A.; Zambrzycka, E.

2015-03-01

This paper presents the studies of stability of magnetic core-shell nanowires prepared by electrochemical deposition from an acidic solution containing iron in the core and modified surface layer. The obtained nanowires were tested according to their durability in distilled water, 0.01 M citric acid, 0.9% NaCl, and commercial white wine (12% alcohol). The proposed solutions were chosen in such a way as to mimic food related environment due to a possible application of nanowires as additives to, for example, packages. After 1, 2 and 3 weeks wetting in the solutions, nanoparticles were tested by Infrared Spectroscopy, Atomic Absorption Spectroscopy, Transmission Electron Microscopy and X-ray diffraction methods.

Synthesis and optical properties of core-multi-shell CdSe/CdS/ZnS quantum dots: Surface modifications

NASA Astrophysics Data System (ADS)

Ratnesh, R. K.; Mehata, Mohan Singh

2017-02-01

We report two port synthesis of CdSe/CdS/ZnS core-multi-shell quantum dots (Q-dots) and their structural properties. The multi-shell structures of Q-dots were developed by using successive ionic layer adsorption and reaction (SILAR) technique. The obtained Q-dots show high crystallinity with the step-wise adjustment of lattice parameters in the radial direction. The size of the core and core-shell Q-dots estimated by transmission electron microscopy images and absorption spectra is about 3.4 and 5.3 nm, respectively. The water soluble Q-dots (scheme-1) were prepared by using ligand exchange method, and the effect of pH was discussed regarding the variation of quantum yield (QY). The decrease of a lifetime of core-multi-shell Q-dots with respect to core CdSe indicates that the shell growth may be tuned by the lifetimes. Thus, the study clearly demonstrates that the core-shell approach can be used to substantially improve the optical properties of Q-dots desired for various applications.

Efficient photocatalytic degradation of malachite green dye under visible irradiation by water soluble ZnS:Mn/ZnS core/shell nanoparticles

NASA Astrophysics Data System (ADS)

Khaparde, Rohini A.; Acharya, Smita A.

2018-05-01

ZnS:Mn/ ZnS core/shell nanoparticles was prepared by two step synthesis method. In first step, oleic acid - coated Mn doped ZnS core nanoparticles were prepared which were charged through ligand exchange. Shell of ZnS NPs was finally deposited upon the surface of charged Mn doped ZnS core. Scanning electron microscopy (SEM) image exhibit morphological confirmation of ZnS:Mn/ZnS core/shell. As Nano ZnS are the most suitable candidates for photocatalyst that extensively involved in degradation and complete mineralization of various toxic organic pollutants owing to its high efficiency, strong oxidizing power, non-toxicity, high photochemical and biological stability, corrosive resistance and low cost. Photodegradation of malachite green is systematically investigated by adding different molar proportional of ZnS:Mn/ZnS core/shell in the dye. The rate of de-coloration of dye is detected by UV-VIS absorption spectroscopy. Efficient detoriation in the colour of dye is attributed to the core /shell morphology of the particles.

Gold core@silver semishell Janus nanoparticles prepared by interfacial etching.

PubMed

Chen, Limei; Deming, Christopher P; Peng, Yi; Hu, Peiguang; Stofan, Jake; Chen, Shaowei

2016-08-14

Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface.

Synthesis of Ag@TiO2 core-shells using a rapid microwave irradiation and study of their nonlinear optical properties

NASA Astrophysics Data System (ADS)

Karimipour, M.; Ebrahimi, M.; Abafat, Z.; Molaei, M.

2016-07-01

Ag@TiO2 core-shells were synthesized by employing oleylamine as capping agent and using a rapid microwave method. The shell growth was optimized first based on the variation of oleylamine content in the reaction solution. Thereafter the shell thickness was varied just by varying titanium isopropoxide (TiTP) with 25, 50, 100 and 200 μl as TiO2 precursor. The prepared core-shells were characterized by means of XRD, FTIR spectroscopy, transmission electron microscopy, and UV-Vis spectroscopy. XRD analysis revealed a cubic crystal structure for Ag and Anatase phase for TiO2. TEM images clearly indicated that the size of Ag core is roughly 15 nm and with the increase of TiTP, the shell thickness increases and varies between 5 nm and 15 nm. UV-Vis spectroscopy indicated that the plasmon resonance of Ag nanoparticles shifts from 407 nm up to 454 nm with the increase of TiTP precursor. Using a low power laser diode at a 532 nm wavelength, the magnitude and the sign of the nonlinear refractive index were determined by the Z-scan technique and Sheik-Bahae model. The results show that the enhancement of nonlinear optical properties originates from the quality of TiO2 shell growth. The highest nonlinearity belongs to the sample synthesized with 100 μlit TiTP. Generally all the prepared Ag@TiO2 core-shells show both saturable and reverse saturable absorption. They exhibit also a considerable nonlinear absorption and nonlinear refractive index ranging from -4.21 × 10-7 to -3.51 × 10-6 which are comparable to the sole Ag and TiO2 nanoparticles.

Detection of Interstellar Ortho-D2H+ with SOFIA

NASA Astrophysics Data System (ADS)

Harju, Jorma; Sipilä, Olli; Brünken, Sandra; Schlemmer, Stephan; Caselli, Paola; Juvela, Mika; Menten, Karl M.; Stutzki, Jürgen; Asvany, Oskar; Kamiński, Tomasz; Okada, Yoko; Higgins, Ronan

2017-05-01

We report on the detection of the ground-state rotational line of ortho-D2H+ at 1.477 THz (203 μm) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) on board the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D2H+ line at 691.7 GHz was not detected with the APEX telescope toward this position. These D2H+ observations complement our previous detections of para-H2D+ and ortho-H2D+ using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D2H+ and para-H2D+ absorption features mainly originate in the cool (T < 18 K) outer envelope of the core. In contrast, the ortho-H2D+ emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D2H+ and H2D+ data result in an age estimate of ˜5 × 105 yr for the core, with an uncertainty of ˜2 × 105 yr. The core material has probably been pre-processed for another 5 × 105 years in conditions corresponding to those in the ambient molecular cloud. The inferred timescale is more than 10 times the age of the embedded protobinary. The D2H+ and H2D+ ions have large and nearly equal total (ortho+para) fractional abundances of ˜10-9 in the outer envelope. This confirms the central role of {{{H}}}3+ in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also {{{D}}}3+ should be abundant in these conditions.

Direct evidence of the existence of Mn3+ ions in MnTiO3

NASA Astrophysics Data System (ADS)

Maurya, R. K.; Sharma, Priyamedha; Patel, Ashutosh; Bindu, R.

2017-08-01

We investigate the room temperature electronic properties of MnTiO3 synthesised by different preparation conditions. For this purpose, we prepared MnTiO3 under two different cooling rates, one is naturally cooled while the other is quenched in liq.nitrogen. The samples were studied using optical absorbance, photoemission spectroscopy and band structure calculations. We observe significant changes in the structural parameters as a result of quenching. Interestingly, in the parent compound, our combined core level, valence band and optical absorbance studies give evidence of the Mn existence in both 2+ and 3+ states. The fraction of Mn3+ ions has been found to increase on quenching MnTiO3 suggests an increase in oxygen non-stoichiometry. The increase in the fraction of the Mn3+ ions has been manifested a) as slight enhancement in the intensity of the optical absorbance in the visible region. There occurs persistent photo-resistance when the incident light is terminated after shining; b) in the behaviour of the features (close to Fermi level) in the valence band spectra. Hence, the combined analysis of the core level, valence band and optical absorbance spectra suggests that the charge carriers are hole like which further leads to the increase in the electrical conductivity of the quenched sample. The present results provide a recipe to tune the optical absorption in the visible range for its applications in optical sensors, solar cell, etc.

Phthalocyanine Blends Improve Bulk Heterojunction Solar Cells

PubMed Central

Varotto, Alessandro; Nam, Chang-Yong; Radivojevic, Ivana; Tomé, Joao; Cavaleiro, José A.S.; Black, Charles T.; Drain, Charles Michael

2010-01-01

A core phthalocyanine platform allows engineering the solubility properties the band gap; shifting the maximum absorption toward the red. A simple method to increase the efficiency of heterojunction solar cells uses a self-organized blend of the phthalocyanine chromophores fabricated by solution processing. PMID:20136126

Enhanced photon absorption in spiral nanostructured solar cells using layered 2D materials.

PubMed

Tahersima, Mohammad H; Sorger, Volker J

2015-08-28

Recent investigations of semiconducting two-dimensional (2D) transition metal dichalcogenides have provided evidence for strong light absorption relative to its thickness attributed to high density of states. Stacking a combination of metallic, insulating, and semiconducting 2D materials enables functional devices with atomic thicknesses. While photovoltaic cells based on 2D materials have been demonstrated, the reported absorption is still just a few percent of the incident light due to their sub-wavelength thickness leading to low cell efficiencies. Here we show that taking advantage of the mechanical flexibility of 2D materials by rolling a molybdenum disulfide (MoS(2))/graphene (Gr)/hexagonal boron nitride stack to a spiral solar cell allows for optical absorption up to 90%. The optical absorption of a 1 μm long hetero-material spiral cell consisting of the aforementioned hetero stack is about 50% stronger compared to a planar MoS(2) cell of the same thickness; although the volumetric absorbing material ratio is only 6%. A core-shell structure exhibits enhanced absorption and pronounced absorption peaks with respect to a spiral structure without metallic contacts. We anticipate these results to provide guidance for photonic structures that take advantage of the unique properties of 2D materials in solar energy conversion applications.

Facile synthesis of Fe3O4/C composites for broadband microwave absorption properties

NASA Astrophysics Data System (ADS)

Liu, Xiang; Ma, Yating; Zhang, Qinfu; Zheng, Zhiming; Wang, Lai-Sen; Peng, Dong-Liang

2018-07-01

Rod-like and flower-like Fe3O4/C composites were successfully synthesized via a facile approach in aqueous phase. The morphologies, structures and static magnetic properties of as-prepared rod-like and flower-like Fe3O4/C composites were characterized thoroughly. The relative complex permittivity and permeability of Fe3O4/C/paraffin composites were recorded by a vector network analyzer (VNA) in the range of 1-18 GHz. The resonant-antiresonant electromagnetic behavior was observed simultaneously in both rod-like and flower-like Fe3O4/C composites. Moreover, the resonant-antiresonant behavior was explained using displacement current lag at the "core/shell" interface. The flower-like Fe3O4/C/paraffin composites show superior microwave absorption performance with minimum reflection loss (RL) of up to -18.73 dB at 15.37 GHz. Comparatively, the rod-like Fe3O4/C/paraffin composites have uncommon continuous trinal absorption peaks at a thickness of 2.5 mm that effectively broadens the absorption bandwidth which is from 8.0 to 13.4 GHz. Furthermore, the microwave absorption mechanism has been discussed to provide a novel design for microwave absorption materials.

Ultraviolet Spectroscopic Monitoring of a Tidal Disruption Eventd

NASA Astrophysics Data System (ADS)

Kochanek, Chris

2017-08-01

Tidal disruption events (TDE), where supermassive black holes destroy stars toproduce accretion flares, are of great current observational andtheoretical interest. Here we propose a seven epoch STIS UV spectroscopic movie'' of a UV bright TDE spread over the first 90 days after a rapid TOO trigger. The roughly 15 day cadence is comparable to the expected and observed time scales for kinematic changes in theoptical and UV emission and absorption lines. We will measurethe evolution of UV absorption and emission lines from elements(e.g., C, N, Si) and ionization states/potentials not seen in optical spectra of TDEs, which should help to illuminate theirdynamical evolution. In some cases, the debris from the stellar cores should have significantly enhanced [N/C] abundances due to the CNO cycle, so UV spectra can provide a means of differentiating debris fromthe core and the envelope of the disrupted star. Optically-selectedTDEs are energetically dominated by their UV emission, making itthe wavelength range most needed to understand these fascinatingtransients.

Permanganate-based synthesis of manganese oxide nanoparticles in ferritin

NASA Astrophysics Data System (ADS)

Olsen, Cameron R.; Smith, Trevor J.; Embley, Jacob S.; Maxfield, Jake H.; Hansen, Kameron R.; Peterson, J. Ryan; Henrichsen, Andrew M.; Erickson, Stephen D.; Buck, David C.; Colton, John S.; Watt, Richard K.

2017-05-01

This paper investigates the comproportionation reaction of MnII with {{{{MnO}}}4}- as a route for manganese oxide nanoparticle synthesis in the protein ferritin. We report that {{{{MnO}}}4}- serves as the electron acceptor and reacts with MnII in the presence of apoferritin to form manganese oxide cores inside the protein shell. Manganese loading into ferritin was studied under acidic, neutral, and basic conditions and the ratios of MnII and permanganate were varied at each pH. The manganese-containing ferritin samples were characterized by transmission electron microscopy, UV/Vis absorption, and by measuring the band gap energies for each sample. Manganese cores were deposited inside ferritin under both the acidic and basic conditions. All resulting manganese ferritin samples were found to be indirect band gap materials with band gap energies ranging from 1.01 to 1.34 eV. An increased UV/Vis absorption around 370 nm was observed for samples formed under acidic conditions, suggestive of MnO2 formation inside ferritin.

Heat exchange studies on coconut oil cells as thermal energy storage for room thermal conditioning

NASA Astrophysics Data System (ADS)

Sutjahja, I. M.; Putri, Widya A.; Fahmi, Z.; Wonorahardjo, S.; Kurnia, D.

2017-07-01

As reported by many thermal environment experts, room air conditioning might be controlled by thermal mass system. In this paper we discuss the performance of coconut oil cells as room thermal energy storage. The heat exchange mechanism of coconut oil (CO) which is one of potential organic Phase Change Material (PCM) is studied based on the results of temperature measurements in the perimeter and core parts of cells. We found that the heat exchange performance, i.e. heat absorption and heat release processes of CO cells are dominated by heat conduction in the sensible solid from the higher temperature perimeter part to the lower temperature core part and heat convection during the solid-liquid phase transition and sensible liquid phase. The capability of heat absorption as measured by the reduction of air temperature is not influenced by CO cell size. Besides that, the application of CO as the thermal mass has to be accompanied by air circulation to get the cool sensation of the room’s occupants.

Nanosized amorphous (Co‚ Fe) oxide particles decorated PANI-CNT: facile synthesis‚ characterization‚ magnetic‚ electromagnetic properties and their application

NASA Astrophysics Data System (ADS)

Heydari, Farhood; Afghahi, Seyyed Salman Seyyed; Manteghian, Mehrdad; Taghizadeh, Mohammad Javad

2017-11-01

In this research (PANI/CNT) core/shell nanocomposite were synthesized via in situ chemical oxidative seeding polymerization‚ the results of SEM indicated the structure of synthesized nanocomposite. TEM‚ FTIR‚ UV-Vis‚ XRD analyses of samples showed that this nanocomposite is decorated with (Fe‚ Co) oxide nanoparticles. The VSM test of as prepared and annealed nanocomposite exhibited the saturated magnetization of 1.1 and 3.86 emu/g, respectively; the coercivity values were also - 350 and - 110 Oe, respectively. The reflection loss characteristics of (Fe‚ Co) oxide-Pani-CNT core/shell nanocomposite were also investigated with a vector network analyzer‚ in the 8.2-12.4 GHz range (X band). The maximum absorption increases with enhancement of the dispersed nanoparticles percent in polyurethane matrix from 1 to 10%. The value of the maximum reflection loss in the absorption samples with 1 and 10% of nanoparticles is - 2.14 dB at 9.33 GHz and - 7.32 dB at 11.97 GHZ, respectively.

Finite temperature effects on the X-ray absorption spectra of energy related materials

NASA Astrophysics Data System (ADS)

Pascal, Tod; Prendergast, David

2014-03-01

We elucidate the role of room-temperature-induced instantaneous structural distortions in the Li K-edge X-ray absorption spectra (XAS) of crystalline LiF, Li2SO4, Li2O, Li3N and Li2CO3 using high resolution X-ray Raman spectroscopy (XRS) measurements and first-principles density functional theory calculations within the eXcited electron and Core Hole (XCH) approach. Based on thermodynamic sampling via ab-initio molecular dynamics (MD) simulations, we find calculated XAS in much better agreement with experiment than those computed using the rigid crystal structure alone. We show that local instantaneous distortion of the atomic lattice perturbs the symmetry of the Li 1 s core-excited-state electronic structure, broadening spectral line-shapes and, in some cases, producing additional spectral features. This work was conducted within the Batteries for Advanced Transportation Technologies (BATT) Program, supported by the U.S. Department of Energy Vehicle Technologies Program under Contract No. DE-AC02-05CH11231.

Simulation of X-ray absorption spectra with orthogonality constrained density functional theory.

PubMed

Derricotte, Wallace D; Evangelista, Francesco A

2015-06-14

Orthogonality constrained density functional theory (OCDFT) [F. A. Evangelista, P. Shushkov and J. C. Tully, J. Phys. Chem. A, 2013, 117, 7378] is a variational time-independent approach for the computation of electronic excited states. In this work we extend OCDFT to compute core-excited states and generalize the original formalism to determine multiple excited states. Benchmark computations on a set of 13 small molecules and 40 excited states show that unshifted OCDFT/B3LYP excitation energies have a mean absolute error of 1.0 eV. Contrary to time-dependent DFT, OCDFT excitation energies for first- and second-row elements are computed with near-uniform accuracy. OCDFT core excitation energies are insensitive to the choice of the functional and the amount of Hartree-Fock exchange. We show that OCDFT is a powerful tool for the assignment of X-ray absorption spectra of large molecules by simulating the gas-phase near-edge spectrum of adenine and thymine.

Light absorption and plasmon – exciton interaction in three-layer nanorods with a gold core and outer shell composed of molecular J- and H-aggregates of dyes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shapiro, B I; Tyshkunova, E S; Kondorskiy, A D

2015-12-31

Optical properties of hybrid rod-like nanoparticles, consisting of a gold core, an intermediate passive organic layer (spacer) and outer layer of ordered molecular cyanine dye aggregates, are experimentally and theoretically investigated. It is shown that these dyes can form not only ordered J-aggregates but also H-aggregates (differing by the packing angle of dye molecules in an aggregate and having other spectral characteristics) in the outer shell of the hybrid nanostructure. Absorption spectra of synthesised three-layer nanorods are recorded, and their sizes are determined. The optical properties of the composite nanostructures under study are found to differ significantly, depending on themore » type of the molecular aggregate formed in the outer shell. The experimental data are quantitatively explained based on computer simulation using the finite-difference time-domain (FDTD) method, and characteristic features of the plasmon – exciton interaction in the systems under study are revealed. (nanophotonics)« less

Black and Brown Carbon in Biogenic Settings with Different Levels of Anthropogenic Influence, and The Effect of Semivolatile Compounds on Aerosol Optical Properties

NASA Astrophysics Data System (ADS)

Tasoglou, A.; Ramachandran, S.; Khlystov, A.; Saha, P.; Grieshop, A. P.; Pandis, S. N.

2015-12-01

Secondary organic aerosol (SOA) is a major contributor to the global aerosol burden. Black carbon (BC) is a significant climate warming agent, while light-absorbing organic carbon (brown carbon, BrC), also impacts the atmospheric radiative balance. The optical properties of ambient aerosols can be affected by biogenic SOA through the lensing effect (coating of BC cores by semivolatile SOA), and by the potential formation of BrC from biogenic sources influenced by anthropogenic sources. To evaluate these effects, measurements of ambient aerosol optical properties and BC concentrations were made in rural Centreville, AL (a remote site with little anthropogenic influence) in summer 2013 and at Duke Forest in Chapel Hill, NC (a site close to high density vehicular traffic and industrial sources), during summer 2015. Photoacoustic extinctiometers (PAX, 405 nm and 532 nm) measured particulate light absorption and a single particle soot photometer (SP2) measured BC mass at both locations. A seven-wavelength Aethalometer and a three-wavelength nephelometer were also deployed at Duke Forest. A third PAX (870 nm) was deployed at Centreville. For absorption and BC measurements, the sample was cycled between a dry line and a dry/thermally-denuded line. Hourly samples were collected with a steam jet aerosol collector (SJAC) for online (2013) and offline (2015) chemical composition analysis. BC concentrations were generally higher at Duke Forest compared to the rural Centreville site. The Aethalometer readings at Duke Forest show greater absorption at the shorter wavelengths (370 nm and 470 nm) than expected from the absorption at 880 nm coupled with an inverse wavelength dependence, suggesting the presence of brown carbon. This presentation will examine the evidence for brown carbon at the two sites, as well as the effect of non-BC coatings on BC light absorption (the lensing effect.)

Efficient tungsten oxide/bismuth oxyiodide core/shell photoanode for photoelectrochemical water splitting

NASA Astrophysics Data System (ADS)

Ma, Haipeng; Zhang, Jing; Liu, Zhifeng

2017-11-01

The novel WO3 nanorods (NRs)/BiOI core/shell structure composite is used as an efficient photoanode applied in photoelectrochemical (PEC) water splitting for the first time. It is synthesized via facile hydrothermal method and, successive ionic layer adsorption and reaction (SILAR) process. This facile synthesis route can achieve uniform WO3/BiOI core/shell composite nanostructures and obtain varied BiOI morphologies simultaneously. The WO3 NRs/BiOI-20 composite exhibits enhanced PEC activity compared to pristine WO3 with a photocurrent density of 0.79 mA cm-2 measured at 0.8 V vs. RHE under AM 1.5G. This excellent performance benefits from the broader absorption spectrum and suppressed electron-hole recombination. This novel core/shell composite may provide insight in developing more efficient solar driven photoelectrodes.

Bonding properties of FCC-like Au 44 (SR) 28 clusters from X-ray absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Rui; Chevrier, Daniel M.; Zeng, Chenjie

Thiolate-protected gold clusters with precisely controlled atomic composition have recently emerged as promising candidates for a variety of applications because of their unique optical, electronic, and catalytic properties. The recent discovery of the Au44(SR)28 total structure is considered as an interesting finding in terms of the face-centered cubic (FCC)-like core structure in small gold-thiolate clusters. Herein, the unique bonding properties of Au44(SR)28 is analyzed using temperature-dependent X-ray absorption spectroscopy (XAS) measurements at the Au L3-edge and compared with other FCC-like clusters such as Au36(SR)24 and Au28(SR)20. A negative thermal expansion was detected for the Au–Au bonds of the metal coremore » (the first Au–Au shell) and was interpreted based on the unique Au core structure consisting of the Au4 units. EXAFS fitting results from Au28(SR)20, Au36(SR)24, and Au44(SR)28 show a size-dependent negative thermal expansion behavior in the first Au–Au shell, further highlighting the importance of the Au4 units in determining the Au core bonding properties and shedding light on the growth mechanism of these FCC-like Au clusters.« less

Photonic bandgap narrowing in conical hollow core Bragg fibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ozturk, Fahri Emre; Yildirim, Adem; Kanik, Mehmet

2014-08-18

We report the photonic bandgap engineering of Bragg fibers by controlling the thickness profile of the fiber during the thermal drawing. Conical hollow core Bragg fibers were produced by thermal drawing under a rapidly alternating load, which was applied by introducing steep changes to the fiber drawing speed. In conventional cylindrical Bragg fibers, light is guided by omnidirectional reflections from interior dielectric mirrors with a single quarter wave stack period. In conical fibers, the diameter reduction introduced a gradient of the quarter wave stack period along the length of the fiber. Therefore, the light guided within the fiber encountered slightlymore » smaller dielectric layer thicknesses at each reflection, resulting in a progressive blueshift of the reflectance spectrum. As the reflectance spectrum shifts, longer wavelengths of the initial bandgap cease to be omnidirectionally reflected and exit through the cladding, which narrows the photonic bandgap. A narrow transmission bandwidth is particularly desirable in hollow waveguide mid-infrared sensing schemes, where broadband light is coupled to the fiber and the analyte vapor is introduced into the hollow core to measure infrared absorption. We carried out sensing simulations using the absorption spectrum of isopropyl alcohol vapor to demonstrate the importance of narrow bandgap fibers in chemical sensing applications.« less

Uniform Fe3O4 coating on flower-like ZnO nanostructures by atomic layer deposition for electromagnetic wave absorption.

PubMed

Wan, Gengping; Wang, Guizhen; Huang, Xianqin; Zhao, Haonan; Li, Xinyue; Wang, Kan; Yu, Lei; Peng, Xiange; Qin, Yong

2015-11-21

An elegant atomic layer deposition (ALD) method has been employed for controllable preparation of a uniform Fe3O4-coated ZnO (ZnO@Fe3O4) core-shell flower-like nanostructure. The Fe3O4 coating thickness of the ZnO@Fe3O4 nanostructure can be tuned by varying the cycle number of ALD Fe2O3. When serving as additives for microwave absorption, the ZnO@Fe3O4-paraffin composites exhibit a higher absorption capacity than the ZnO-paraffin composites. For ZnO@500-Fe3O4, the effective absorption bandwidth below -10 dB can reach 5.2 GHz and the RL values below -20 dB also cover a wide frequency range of 11.6-14.2 GHz when the coating thickness is 2.3 mm, suggesting its potential application in the treatment of the electromagnetic pollution problem. On the basis of experimental observations, a mechanism has been proposed to understand the enhanced microwave absorption properties of the ZnO@Fe3O4 composites.

Resonant Absorption in GaAs-Based Nanowires by Means of Photo-Acoustic Spectroscopy

NASA Astrophysics Data System (ADS)

Petronijevic, E.; Leahu, G.; Belardini, A.; Centini, M.; Li Voti, R.; Hakkarainen, T.; Koivusalo, E.; Guina, M.; Sibilia, C.

2018-03-01

Semiconductor nanowires made of high refractive index materials can couple the incoming light to specific waveguide modes that offer resonant absorption enhancement under the bandgap wavelength, essential for light harvesting, lasing and detection applications. Moreover, the non-trivial ellipticity of such modes can offer near field interactions with chiral molecules, governed by near chiral field. These modes are therefore very important to detect. Here, we present the photo-acoustic spectroscopy as a low-cost, reliable, sensitive and scattering-free tool to measure the spectral position and absorption efficiency of these modes. The investigated samples are hexagonal nanowires with GaAs core; the fabrication by means of lithography-free molecular beam epitaxy provides controllable and uniform dimensions that allow for the excitation of the fundamental resonant mode around 800 nm. We show that the modulation frequency increase leads to the discrimination of the resonant mode absorption from the overall absorption of the substrate. As the experimental data are in great agreement with numerical simulations, the design can be optimized and followed by photo-acoustic characterization for a specific application.

A Decade of H α Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cauley, P. Wilson; Redfield, Seth; Jensen, Adam G., E-mail: pcauley@wesleyan.edu

HD 189733 b is one of the most well studied exoplanets due to its large transit depth and host star brightness. The focus on this object has produced a number of high-cadence transit observations using high-resolution optical spectrographs. Here we present an analysis of seven full H α transits of HD 189733 b using HARPS on the 3.6 meter La Silla telescope and HIRES on Keck I, taken over the course of nine years from 2006 to 2015. H α transmission signals are analyzed as a function of the stellar activity level, as measured using the normalized core flux ofmore » the Ca ii H and K lines. We find strong variations in the strength of the H α transmission spectrum from epoch to epoch. However, there is no clear trend between the Ca ii core emission and the strength of the in-transit H α signal, although the transit showing the largest absorption value also occurs when the star is the most active. We present simulations of the in-transit contrast effect and find that the planet must consistently transit active latitudes with very strong facular and plage emission regions in order to reproduce the observed line strengths. We also investigate the measured velocity centroids with models of planetary rotation and show that the small line profile velocities could be due to large velocities in the upper atmosphere of the planet. Overall, we find it more likely that the measured H α signals arise in the extended planetary atmosphere, although a better understanding of active region emission for active stars such as HD 189733 is needed.« less

Analysis of loss-of-coolant accident for a fast-spectrum lithium-cooled nuclear reactor for space-power applications

NASA Technical Reports Server (NTRS)

Turney, G. E.; Petrik, E. J.; Kieffer, A. W.

1972-01-01

A two-dimensional, transient, heat-transfer analysis was made to determine the temperature response in the core of a conceptual space-power nuclear reactor following a total loss of reactor coolant. With loss of coolant from the reactor, the controlling mode of heat transfer is thermal radiation. In one of the schemes considered for removing decay heat from the core, it was assumed that the 4 pi shield which surrounds the core acts as a constant-temperature sink (temperature, 700 K) for absorption of thermal radiation from the core. Results based on this scheme of heat removal show that melting of fuel in the core is possible only when the emissivity of the heat-radiating surfaces in the core is less than about 0.40. In another scheme for removing the afterheat, the core centerline fuel pin was replaced by a redundant, constant temperature, coolant channel. Based on an emissivity of 0.20 for all material surfaces in the core, the calculated maximum fuel temperature for this scheme of heat removal was 2840 K, or about 90 K less than the melting temperature of the UN fuel.

Direct observation of terahertz surface modes in nanometer-sized liquid water pools.

PubMed

Boyd, J E; Briskman, A; Colvin, V L; Mittleman, D M

2001-10-01

The far-infrared absorption spectrum of nanometer-sized water pools at the core of AOT micelles exhibits a pronounced resonance which is absent in bulk water. The amplitude and spectral position of this resonance are sensitive to the size of the confined water core. This resonance results from size-dependent modifications in the vibrational density of states, and thus has far-reaching implications for chemical processes which involve water sequestered within small cavities. These data represent the first study of the terahertz dielectric properties of confined liquids.

Structure Optimization of 21,23-Core-Modified Porphyrins Absorbing Long-Wavelength Light as Potential Photosensitizers Against Breast Cancer Cells

DTIC Science & Technology

2007-04-01

the core nitrogen atom(s) of natural porphyrins with heavy atoms such as S, Se, and Te provides a red -shift in their absorption spectra [4- 7]. The...shown in red , b in green and c in blue Copyright © 2007 Society of Porphyrins & Phthalocyanines J. Porphyrins Phthalocyanines 2007; 11: 1-8 Y. YOU ET AL...shown in red , b in green and c in blue Copyright © 2007 Society of Porphyrins & Phthalocyanines J. Porphyrins Phthalocyanines 2007; 11: 1-8

Helicon mode formation and radio frequency power deposition in a helicon-produced plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niemi, K.; Kraemer, M.

2008-07-15

Time- and space-resolved magnetic (B-dot) probe measurements in combination with measurements of the plasma parameters were carried out to investigate the relationship between the formation and propagation of helicon modes and the radio frequency (rf) power deposition in the core of a helicon plasma. The Poynting flux and the absorbed power density are deduced from the measured rf magnetic field distribution in amplitude and phase. Special attention is devoted to the helicon absorption under linear and nonlinear conditions. The present investigations are attached to recent observations in which the nonlinear nature of the helicon wave absorption has been demonstrated bymore » showing that the strong absorption of helicon waves is correlated with parametric excitation of electrostatic fluctuations.« less

An organoboron compound with a wide absorption spectrum for solar cell applications.

PubMed

Liu, Fangbin; Ding, Zicheng; Liu, Jun; Wang, Lixiang

2017-11-09

Organoboron compounds offer new approaches to tune the electronic structures of π-conjugated molecules. In this work, an electron acceptor (M-BNBP4P-1) is developed by endcapping an organoboron core unit with two strong electron-withdrawing groups. M-BNBP4P-1 exhibits a unique wide absorption spectrum with two strong absorption bands in the long wavelength region (λ max = 771 nm) and the short wavelength region (λ max = 502 nm), which indicate superior sunlight harvesting capability. This is due to its special electronic structure, i.e. a delocalized LUMO and a localized HOMO. Prototype solution-processed organic solar cells based on M-BNBP4P-1 show a power conversion efficiency of 7.06% and a wide photoresponse from 350 nm to 880 nm.

Complexes of DNA bases and Watson-Crick base pairs interaction with neutral silver Agn (n = 8, 10, 12) clusters: a DFT and TDDFT study.

PubMed

Srivastava, Ruby

2018-03-01

We study the binding of the neutral Ag n (n = 8, 10, 12) to the DNA base-adenine (A), guanine (G) and Watson-Crick -adenine-thymine, guanine-cytosine pairs. Geometries of complexes were optimized at the DFT level using the hybrid B3LYP functional. LANL2DZ effective core potential was used for silver and 6-31 + G ** was used for all other atoms. NBO charges were analyzed using the Natural population analysis. The absorption properties of Ag n -A,G/WC complexes were also studied using time-dependent density functional theory. The absorption spectra for these complexes show wavelength in the visible region. It was revealed that silver clusters interact more strongly with WC pairs than with isolated DNA complexes. Furthermore, it was found that the electronic charge transferred from silver to isolated DNA clusters are less than the electronic charge transferred from silver to the Ag n -WC complexes. The vertical ionization potential, vertical electron affinity, hardness, and electrophilicity index of Ag n -DNA/WC complexes have also been discussed.

Graphene quantum dots with visible light absorption of the carbon core: insights from single-particle spectroscopy and first principles based theory

NASA Astrophysics Data System (ADS)

Ghosh, Siddharth; Awasthi, Manohar; Ghosh, Moumita; Seibt, Michael; Niehaus, Thomas A.

2016-12-01

Luminescent carbon nanodots (CND) are a recent addition to the family of carbon nanostructures. Interestingly, a large group of CNDs are fluorescent in the visible spectrum and possess single dipole emitters with potential applications in super-resolution microscopy, quantum information science, and optoelectronics. There is a large diversity of CND’s size as well as a strong variability of edge topology and functional groups in real samples. This hampers a direct comparison of experimental and theoretical findings that is necessary to understand the unusual photophysics of these systems. Here, we derive atomistic models of finite sized (<2.5 nm) CNDs from high resolution transmission electron microscopy (HRTEM) which are studied using approximate time-dependent density functional theory. The atomistic models are found to be primarily two-dimensional (2D) and can hence be categorised as graphene quantum dots (GQD). The GQD model structures that are presented here show excitation energies in the visible spectrum matching previous single GQD level photoluminescence studies. We also present the effect of edge hydroxyl and carboxyl functional groups on the absorption spectrum. Overall, the study reveals the atomistic origin of CNDs photoluminescence in the visible range.

Orbital Ordering Transition in La_4Ru_2O_10 probed by O K-edge X-ray Absorption

NASA Astrophysics Data System (ADS)

Denlinger, J. D.; Rossnagel, Kai; Allen, J. W.; Khalifah, P.; Mandrus, D.; Cava, R. J.

2004-03-01

The layered ruthenate compound La_4Ru_2O_10 undergoes a first order monoclinic-to-triclinic structural phase transition at 160 K. An accompanying loss of the Ru local moment gives evidence for a full orbital ordering transition in which the Ru d_yz orbitals become completely unoccupied in the low temperature phase.(P. Khalifah et al.), Science 297, 2237 (2002). Via hybridization of Ru t_2g and O 2p orbitals this temperature-dependent Ru orbital ordering can be indirectly probed using polarized O K-edge x-ray absorption spectroscopy (XAS). O 1s core-level energy shifts allow O site-specific separation of Ru t_2g hybridizations. Identification of O sites is accomplished using polarized XAS angular dependence as well as by O 2p valence PDOS obtained from site-selective soft x-ray emission. Distinct XAS energy and intensity changes are observed upon cooling through the phase transition and are rationalized within the framework of the complete orbital ordering scenario. Supported by the U.S. NSF at U. Mich. (DMR-03-02825) and by the DOE at the Advanced Light Source (DE-AC03-76SF00098).

Effect of temperature on the spectral properties of InP/ZnS nanocrystals

NASA Astrophysics Data System (ADS)

Savchenko, S. S.; Vokhmintsev, A. S.; Weinstein, I. A.

2018-01-01

Optical absorption (OA) and photoluminescence (PL) spectra of InP/ZnS core/shell nanocrystals with 2.3 nm average size were investigated in the temperature range of 6.5-296 K. Using second derivative spectrophotometry technique energies of the OA transitions at 296 K in quantum dot (QD) solutions and films are evaluated to be E 1 = 2.37, E 2 = 4.10 and E 3 = 4.68 eV. Temperature shifts of the E 1 and E 2 levels are found to result from interaction with effective phonons of 59 and 37 meV energies, respectively. Herewith the 370 meV half-width of the first exciton absorption peak remains constant due to the dominance of inhomogeneous broadening effects caused by QD parameters distribution. Measured PL spectra have a complex structure and can be described in 6.5-296 K range by two independent Gaussian components associated with exciton and defect-related states. In addition, Stokes shift of 320 meV is observed to decrease at T > 200 K. PL thermal quenching analysis in frame of Mott mechanism points to presence of non-radiative relaxation channel with an activation energy of 74 meV.

The effect of thermal oxidation on the luminescence properties of nanostructured silicon.

PubMed

Liu, Lijia; Sham, Tsun-Kong

2012-08-06

Herein is reported a detailed study of the luminescence properties of nanostructured Si using X-ray excited optical luminescence (XEOL) in combination with X-ray absorption near-edge structures (XANES). P-type Si nanowires synthesized via electroless chemical etching from Si wafers of different doping levels and porous Si synthesized using electrochemical method are examined under X-ray excitation across the Si K-, L(3,2) -, and O K-edges. It is found that while as-prepared Si nanostructures are weak light emitters, intense visible luminescence is observed from thermally oxidized Si nanowires and porous Si. The luminescence mechanism of Si upon oxidation is investigated by oxidizing nanostructured Si at different temperatures. Interestingly, the two luminescence bands observed show different response with the variation of absorption coefficient upon Si and O core-electron excitation in elemental silicon and silicon oxide. A correlation between luminescence properties and electronic structures is thus established. The implications of the finding are discussed in terms of the behavior of the oxygen deficient center (OCD) and non-bridging oxygen hole center (NBOHC). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An evaluation of the performance of concretes containing fly ash and ground slag in bridge decks.

DOT National Transportation Integrated Search

2006-01-01

Cores from 36 bridge decks were evaluated to assess the condition and quality of the concrete by petrographic methods and direct and indirect measures of the transport properties. Transport properties were measured by a rate of absorption test (ASTM ...

Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacherjee, Aditi, E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu; Attar, Andrew R., E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu; Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720

2016-03-28

Femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy based on a high-harmonic generation source is used to study the 266 nm induced A-band photodissociation dynamics of allyl iodide (CH{sub 2} =CHCH{sub 2}I). The photolysis of the C—I bond at this wavelength produces iodine atoms both in the ground ({sup 2}P{sub 3/2}, I) and spin-orbit excited ({sup 2}P{sub 1/2}, I*) states, with the latter as the predominant channel. Using XUV absorption at the iodine N{sub 4/5} edge (45–60 eV), the experiments constitute a direct probe of not only the long-lived atomic iodine reaction products but also the fleeting transition state region ofmore » the repulsive n{sub I}σ{sup ∗}{sub C—I} excited states. Specifically, three distinct features are identified in the XUV transient absorption spectrum at 45.3 eV, 47.4 eV, and 48.4 eV (denoted transients A, B, and C, respectively), which arise from the repulsive valence-excited nσ{sup ∗} states and project onto the high-lying core-excited states of the dissociating molecule via excitation of 4d(I) core electrons. Transients A and B originate from 4d(I) → n(I) core-to-valence transitions, whereas transient C is best assigned to a 4d(I) →σ{sup ∗}(C—I) transition. The measured differential absorbance of these new features along with the I/I* branching ratios known from the literature is used to suggest a more definitive assignment, albeit provisional, of the transients to specific dissociative states within the A-band manifold. The transients are found to peak around 55 fs–65 fs and decay completely by 145 fs–185 fs, demonstrating the ability of XUV spectroscopy to map the evolution of reactants into products in real time. The similarity in the energies of transients A and B with analogous features observed in methyl iodide [Attar et al. J. Phys. Chem. Lett. 6, 5072, (2015)] together with the new observation of transient C in the present work provides a more complete picture of the valence electronic structure in the transition state region. The results provide a benchmark for theoretical calculations on the nature of core-excited states in halogenated hydrocarbons, especially in the transition state region along the C—I reaction coordinate.« less

The biodistribution of gold nanoparticles designed for renal clearance

NASA Astrophysics Data System (ADS)

Alric, Christophe; Miladi, Imen; Kryza, David; Taleb, Jacqueline; Lux, François; Bazzi, Rana; Billotey, Claire; Janier, Marc; Perriat, Pascal; Roux, Stéphane; Tillement, Olivier

2013-06-01

Owing to their tunable optical properties and their high absorption cross-section of X- and γ-ray, gold nanostructures appear as promising agents for remotely controlled therapy. Since the efficiency of cancer therapy is not limited to the eradication of the tumour but rests also on the sparing of healthy tissue, a biodistribution study is required in order to determine whether the behaviour of the nanoparticles after intravenous injection is safe (no accumulation in healthy tissue, no uptake by phagocytic cell-rich organs (liver, spleen) and renal clearance). The biodistribution of Au@DTDTPA nanoparticles which are composed of a gold core and a DTDTPA (dithiolated polyaminocarboxylate) shell can be established by X-ray imaging (owing to the X-ray absorption of the gold core) and by magnetic resonance imaging (MRI) since the DTDTPA shell was designed for the immobilization of paramagnetic gadolinium ions. However scintigraphy appears better suited for a biodistribution study owing to a great sensitivity. The successful immobilization of radioelements (99mTc, 111In) in the DTDTPA shell, instead of gadolinium ions, renders possible the follow up of Au@DTDTPA by scintigraphy which showed that Au@DTDTPA nanoparticles exhibit a safe behaviour after intravenous injection to healthy rats.Owing to their tunable optical properties and their high absorption cross-section of X- and γ-ray, gold nanostructures appear as promising agents for remotely controlled therapy. Since the efficiency of cancer therapy is not limited to the eradication of the tumour but rests also on the sparing of healthy tissue, a biodistribution study is required in order to determine whether the behaviour of the nanoparticles after intravenous injection is safe (no accumulation in healthy tissue, no uptake by phagocytic cell-rich organs (liver, spleen) and renal clearance). The biodistribution of Au@DTDTPA nanoparticles which are composed of a gold core and a DTDTPA (dithiolated polyaminocarboxylate) shell can be established by X-ray imaging (owing to the X-ray absorption of the gold core) and by magnetic resonance imaging (MRI) since the DTDTPA shell was designed for the immobilization of paramagnetic gadolinium ions. However scintigraphy appears better suited for a biodistribution study owing to a great sensitivity. The successful immobilization of radioelements (99mTc, 111In) in the DTDTPA shell, instead of gadolinium ions, renders possible the follow up of Au@DTDTPA by scintigraphy which showed that Au@DTDTPA nanoparticles exhibit a safe behaviour after intravenous injection to healthy rats. Electronic supplementary information (ESI) available: Planar scintigraphy image. See DOI: 10.1039/c3nr00012e

A binding energy study of the Atomic Mass Evaluation 2012 and an updated beta-decay study of neutron-rich 74Cu

NASA Astrophysics Data System (ADS)

Tracy, James L., Jr.

A study of ground state binding energy values listed in the Atomic Mass Evaluation 2012 (AME2012) using an interpretive approach, as opposed to the exploratory methods of previous models, is presented. This model is based on a postulate requiring all protons to pair with available neutrons to form bound alpha clusters as the ground state for an N = Z core upon which excess neutrons are added. For each core, the trend of the binding energy as a function of excess neutrons in the isotopic chain can be fit with a three-term quadratic function. The quadratic parameter reveals a smooth decaying exponential function. By re-envisioning the determination of mass excess, the constant-term fit parameters, representing N = Z nuclei, reveal a near-symmetry around Z = 50. The linear fit parameters exhibit trends which are linear functions of core size. A neutron drip-line prediction is compared against current models. By considering the possibility of an alpha-cluster core, a new ground-state structure grouping scheme is presented; nucleon-nucleon pairing is shown to have a greater role in level filling. This model, referred to as the Alpha-Deuteron-Neutron Model, yields promising first results when considering root-mean-square variances from the AME2012. The beta-decay of the neutron-rich isotope 74Cu has been studied using three high-purity Germanium clover detectors at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. A high-resolution mass separator greatly improved the purity of the 74Cu beam by removing isobaric contaminants, thus allowing decay through its isobar chain to the stable 74Ge at the center of the LeRIBSS detector array without any decay chain member dominating. Using coincidence gating techniques, 121 gamma-rays associated with 74Cu were isolated from the collective singles spectrum. Eighty-seven of these were placed in an expanded level scheme, and updated beta-feeding level intensities and log( ft) values are presented based on multiple newly-placed excited states up to 6.8 MeV. The progression of simulated Total Absorption gamma-ray Spectroscopy (TAGS) based on known levels and beta feeding values from previous measurements to this evaluation are presented and demonstrate the need for a TAGS measurement of this isotope to gain a more complete understanding of its decay scheme.

Metal-passivated PbS nanoparticles: fabrication and characterization.

PubMed

Tchaplyguine, M; Mikkelä, M-H; Mårsell, E; Polley, C; Mikkelsen, A; Zhang, W; Yartsev, A; Hetherington, C J D; Wallenberg, L R; Björneholm, O

2017-03-08

Organic-shell-free PbS nanoparticles have been produced in the size range relevant for quantum-dot solar cells (QDSCs) by a vapor aggregation method involving magnetron reactive sputtering. This method creates a beam of free 5-10 nm particles in a vacuum. The dimensions of the particles were estimated after their deposition on a substrate by imaging them using ex situ SEM and HRTEM electron microscopy. The particle structure and chemical composition could be deduced "on the fly", prior to deposition, using X-ray photoelectron spectroscopy (XPS) with tunable synchrotron radiation. Our XPS results suggest that under certain conditions it is possible to fabricate particles with a semiconductor core and 1 to 2 monolayer shells of metallic lead. For this case the absolute energy of the highest occupied molecular orbital (HOMO) in PbS has been determined to be (5.0 ± 0.5) eV below the vacuum level. For such particles deposited on a substrate HRTEM has confirmed the XPS-based conclusions on the crystalline PbS structure of the semiconductor core. Absorption spectroscopy on the deposited film has given a value of ∼1 eV for the lowest exciton. Together with the valence XPS results this has allowed us to reconstruct the energy level scheme of the particles. The results obtained are discussed in the context of the properties of PbS QDSCs.

Chemoselectivity-induced multiple interfaces in MWCNT/Fe3O4@ZnO heterotrimers for whole X-band microwave absorption.

PubMed

Wang, Zhijiang; Wu, Lina; Zhou, Jigang; Jiang, Zhaohua; Shen, Baozhong

2014-11-07

A chemoselective route to induce Fe3O4@ZnO core-shell nanoparticles decorating carbon nanotubes to form MWCNT/Fe3O4@ZnO heterotrimers has been developed. Charges are redistributed in the heterotrimers through C-O-Zn, C-O-Fe and Fe-O-Zn bondings, giving rise to multiple electronic phases. The generated significant interfacial polarization and synergetic interaction between dielectric and magnetic absorbers result in the MWCNT/Fe3O4@ZnO heterotrimers with high-performance microwave absorption in an entire X band.

The nature of C-class asteroids from 3-micron spectrophotometry

NASA Technical Reports Server (NTRS)

Feierberg, M. A.; Lebofsky, L. A.; Tholen, D. J.

1985-01-01

Narrowband spectrophotometry between 2.3 and 3.5 micrometers is presented for 14 main-belt C asteroids greater than 100 km in diameter. Absorption features at 3 micrometers due to water of hydration are present in the spectra of nine of the asteroids, with intensities ranging from 6 to 23 percent. The other five asteroids have no such absorption greater than 2 percent in intensity. The present C-asteroid population may be fragments of larger parent bodies with anhydrous C3-like cores and hydrated C1I- or C2M-like mantles.

Cascading electron and hole transfer dynamics in a CdS/CdTe core-shell sensitized with bromo-pyrogallol red (Br-PGR): slow charge recombination in type II regime.

PubMed

Maity, Partha; Debnath, Tushar; Chopra, Uday; Ghosh, Hirendra Nath

2015-02-14

Ultrafast cascading hole and electron transfer dynamics have been demonstrated in a CdS/CdTe type II core-shell sensitized with Br-PGR using transient absorption spectroscopy and the charge recombination dynamics have been compared with those of CdS/Br-PGR composite materials. Steady state optical absorption studies suggest that Br-PGR forms strong charge transfer (CT) complexes with both the CdS QD and CdS/CdTe core-shell. Hole transfer from the photo-excited QD and QD core-shell to Br-PGR was confirmed by both steady state and time-resolved emission spectroscopy. Charge separation was also confirmed by detecting electrons in the conduction band of the QD and the cation radical of Br-PGR as measured from femtosecond transient absorption spectroscopy. Charge separation in the CdS/Br-PGR composite materials was found to take place in three different pathways, by transferring the photo-excited hole of CdS to Br-PGR, electron injection from the photo-excited Br-PGR to the CdS QD, and direct electron transfer from the HOMO of Br-PGR to the conduction band of the CdS QD. However, in the CdS/CdTe/Br-PGR system hole transfer from the photo-excited CdS to Br-PGR and electron injection from the photo-excited Br-PGR to CdS take place after cascading through the CdTe shell QD. Charge separation also takes place via direct electron transfer from the Br-PGR HOMO to the conduction band of CdS/CdTe. Charge recombination (CR) dynamics between the electron in the conduction band of the CdS QD and the Br-PGR cation radical were determined by monitoring the bleach recovery kinetics. The CR dynamics were found to be much slower in the CdS/CdTe/Br-PGR system than in the CdS/Br-PGR system. The formation of the strong CT complex and the separation of charges cascading through the CdTe shell help to slow down charge recombination in the type II regime.

Absorbing Gas around the WASP-12 Planetary System

NASA Astrophysics Data System (ADS)

Fossati, L.; Ayres, T. R.; Haswell, C. A.; Bohlender, D.; Kochukhov, O.; Flöer, L.

2013-04-01

Near-UV observations of the planet host star WASP-12 uncovered the apparent absence of the normally conspicuous core emission of the Mg II h and k resonance lines. This anomaly could be due either to (1) a lack of stellar activity, which would be unprecedented for a solar-like star of the imputed age of WASP-12 or (2) extrinsic absorption, from the intervening interstellar medium (ISM) or from material within the WASP-12 system itself, presumably ablated from the extreme hot Jupiter WASP-12 b. HIRES archival spectra of the Ca II H and K lines of WASP-12 show broad depressions in the line cores, deeper than those of other inactive and similarly distant stars and similar to WASP-12's Mg II h and k line profiles. We took high-resolution ESPaDOnS and FIES spectra of three early-type stars within 20' of WASP-12 and at similar distances, which show the ISM column is insufficient to produce the broad Ca II depression observed in WASP-12. The EBHIS H I column density map supports and strengthens this conclusion. Extrinsic absorption by material local to the WASP-12 system is therefore the most likely cause of the line core anomalies. Gas escaping from the heavily irradiated planet could form a stable and thick circumstellar disk/cloud. The anomalously low stellar activity index (log R^{{\\prime }}_{HK}) of WASP-12 is evidently a direct consequence of the extra core absorption, so similar HK index deficiencies might signal the presence of translucent circumstellar gas around other stars hosting evaporating planets. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Rechereche Scientifique of France, and the University of Hawaii. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

The Small-Scale Structure of High-Velocity Na I Absorption Toward M81

NASA Astrophysics Data System (ADS)

Roth, K. C.; Meyer, D. M.; Lauroesch, J. T.

2000-12-01

We present high-resolution (R=20,000) integral field spectra of the Na I absorption toward the nucleus of the nearby spiral galaxy M81 (NGC 3031) obtained in April 2000 with the WIYN 3.5-m telescope and the DensePak fiber optic bundle. Our DensePak map covers the central 27 x 43 arcsec of M81 at a spatial resolution of 4 arcsec which corresponds to a projected length scale of 63 pc at the distance of the galaxy (3.25 Mpc). These data were intended to explore the spatial extent of high-velocity (v = 110-130 km/s) gas seen in Na I, Mg I and Mg II absorption toward SN 1993J by Bowen et al. (1994), which they proposed is due to tidal material associated with interactions between M81 and nearby M82 (Yun, Ho & Lo 1993). No H I gas at these velocities has been detected in 21 cm interferometry maps near the position of SN 1993J (2.6 arcmin SW of the M81 nucleus). Our Na I map of the M81 core shows no evidence of the strong absorption seen at v = 110-130 km/s toward SN 1993J. However, our map does reveal a strong Na I component at v = 220 km/s in several fibers that appears to trace a filamentary structure running from the SW to the NE across the M81 nuclear region. The origin and distance of this filament are unknown. No H I gas at v = 220 km/s has previously been detected in 21 cm studies of the core. At the location of SN 1993J, Bowen et al. measured weak Mg II absorption at this velocity but found no evidence of corresponding Na I absorption. The only known H I gas that corresponds to this velocity in the M81 group are the H I streamers found around M82 by Yun, Ho, & Lo that they interpreted as tidally disrupted M82 disk material.

Single- and double-core-hole ion emission spectroscopy of transient neon plasmas produced by ultraintense x-ray laser pulses

NASA Astrophysics Data System (ADS)

Gao, Cheng; Zeng, Jiaolong; Yuan, Jianmin

2016-02-01

Single-core-hole (SCH) and double-core-hole (DCH) spectroscopy is investigated systematically for neon gas in the interaction with ultraintense x-ray pulses with photon energy from 937 eV to 2000 eV. A time-dependent rate equation, implemented in detailed level accounting approximation, is utilized to study the dynamical evolution of the level population and emission properties of the laser-produced highly transient plasmas. The plasma-density effects on level populations and charge-state distribution are demonstrated with an x-ray photon energy of 2000 eV. It is shown that atomic number density of relevant experiment is about 1 × 1018 cm-3, which is comparable to a recent experiment. At this density, we systematically investigate the emissivity of the transient neon plasmas. For laser photon energy in the range 937-1360 eV, resonant absorptions (RA) of 1s\\to {np} (n≥slant 2) transitions play important roles in time evolution of the population and DCH emission spectroscopy. The RA effects are illustrated in detail for an x-ray pulse of 944 eV photon energy, which creates the 1s\\to 2p RA from the SCH states (1s2{s}22{p}4, 1s2s2p5, and 1s2p6) of Ne3+. After averaging over the space and time distribution of x-ray pulse, DCH emission spectroscopy is studied at x-ray photon energies of 937, 944, 955, 968, 980, and 990 eV, where there exist 1s\\to 2p resonances from SCH states of Ne2+-Ne7+. The processes with producing DCH states are discussed. For x-ray photon energy larger than 1360 eV, no RA exist and transient plasmas show different features in the DCH spectroscopy.

Novel applications of X-ray photoelectron spectroscopy on unsupported nanoparticles

NASA Astrophysics Data System (ADS)

Kostko, Oleg; Xu, Bo; Jacobs, Michael I.; Ahmed, Musahid

X-ray photoelectron spectroscopy (XPS) is a powerful technique for chemical analysis of surfaces. We will present novel results of XPS on unsupported, gas-phase nanoparticles using a velocity-map imaging (VMI) spectrometer. This technique allows for probes of both the surfaces of nanoparticles via XPS as well as their interiors via near edge X-ray absorption fine structure (NEXAFS) spectroscopy. A recent application of this technique has confirmed that arginine's guanidinium group exists in a protonated state even in strongly basic solution. Moreover, the core-level photoelectron spectroscopy can provide information on the effective attenuation length (EAL) of low kinetic energy electrons. This contradictory value is important for determining the probing depth of XPS and in photolithography. A new method for determining EALs will be presented.

Absorption spectra of localized surface plasmon resonance observed in an inline/picoliter spectrometer cell fabricated by a near ultraviolet femtosecond laser

NASA Astrophysics Data System (ADS)

Shiraishi, Masahiko; Nishiyama, Michiko; Watanabe, Kazuhiro; Kubodera, Shoichi

2018-03-01

Absorption spectra based on localized surface plasmon resonance (LSPR) were obtained with an inline/picoliter spectrometer cell. The spectrometer cell was fabricated into an optical glass fiber by focusing a near UV (NUV) femtosecond laser pulses at a wavelength of 400 nm with an energy of 30 μJ. The laser beam was focused from two directions opposite to each other to fabricate a through-hole spectrometer cell. A diameter of the cell was approximately 3 μm, and the length was approximately 62.5 μm, which was nearly equal to the core diameter of the optical fiber. Liquid solution of gold nanoparticles (GNPs) with a diameter of 5-10 nm was injected into the spectrometer cell with its volume of 0.4 pL. The absorption peak centered at 518 nm was observed. An increase of absorption associated with the increase of the number of nanoparticles was in agreement with the numerical calculation based on the Lambert-Beer law.

Increasing the applicability of density functional theory. V. X-ray absorption spectra with ionization potential corrected exchange and correlation potentials.

PubMed

Verma, Prakash; Bartlett, Rodney J

2016-07-21

Core excitation energies are computed with time-dependent density functional theory (TD-DFT) using the ionization energy corrected exchange and correlation potential QTP(0,0). QTP(0,0) provides C, N, and O K-edge spectra to about an electron volt. A mean absolute error (MAE) of 0.77 and a maximum error of 2.6 eV is observed for QTP(0,0) for many small molecules. TD-DFT based on QTP (0,0) is then used to describe the core-excitation spectra of the 22 amino acids. TD-DFT with conventional functionals greatly underestimates core excitation energies, largely due to the significant error in the Kohn-Sham occupied eigenvalues. To the contrary, the ionization energy corrected potential, QTP(0,0), provides excellent approximations (MAE of 0.53 eV) for core ionization energies as eigenvalues of the Kohn-Sham equations. As a consequence, core excitation energies are accurately described with QTP(0,0), as are the core ionization energies important in X-ray photoionization spectra or electron spectroscopy for chemical analysis.

Size-Independent Exciton Localization Efficiency in Colloidal CdSe/CdS Core/Crown Nanosheet Type-I Heterostructures.

PubMed

Li, Qiuyang; Wu, Kaifeng; Chen, Jinquan; Chen, Zheyuan; McBride, James R; Lian, Tianquan

2016-03-22

CdSe/CdS core/crown nanoplatelet type I heterostructures are a class of two-dimensional materials with atomically precise thickness and many potential optoelectronic applications. It remains unclear how the precise thickness and lack of energy disorder affect the properties of exciton transport in these materials. By steady-state photoluminescence excitation spectroscopy and ultrafast transient absorption spectroscopy, we show that in five CdSe/CdS core/crown structures with the same core and increasing crown size (with thickness of ∼1.8 nm, width of ∼11 nm, and length from 20 to 40 nm), the crown-to-core exciton localization efficiency is independent of crown size and increases with photon energy above the band edge (from 70% at 400 nm to ∼100% at 370 nm), while the localization time increases with the crown size. These observations can be understood by a model that accounts for the competition of in-plane exciton diffusion and selective hole trapping at the core/crown interface. Our findings suggest that the exciton localization efficiency can be further improved by reducing interfacial defects.

Agricultural Science Lab Activities. Instructor Guide. Volume 27, Number 2.

ERIC Educational Resources Information Center

Thompson, Gregory W.; And Others

This instructor guide contains 20 laboratory activities for grades 9-10 Agricultural Science I-II classes. The activities are cross-referenced to Missouri Core Competencies and Key Skills. The activities are organized into the following areas: introductory (microscope use); animal nutrition (absorption of nutrients, bacteria and disease, enzyme…

Plasma endotoxin core antibody concentration and linear growth are unrelated in rural Malawian children aged 2-5 years

USDA-ARS?s Scientific Manuscript database

Environmental enteropathy is subclinical inflammation of the upper gastrointestinal tract associated with reduced linear growth in developing countries. Usually investigators have used biopsy or a dual sugar absorption test to assess environmental enteropathy. Such tests are time and resource intens...

Failure Analysis of Alumina Reinforced Aluminum Microtruss and Tube Composites

NASA Astrophysics Data System (ADS)

Chien, Hsueh Fen (Karen)

The energy absorption capacity of cellular materials can be dramatically increased by applying a structural coating. This thesis examined the failure mechanisms of alumina reinforced 3003 aluminum alloy microtrusses and tubes. Alumina coatings were produced by hard anodizing and by plasma electrolytic oxidation (PEO). The relatively thin and discontinuous oxide coating at the hinge acted as a localized weak spot which triggered a chain reaction of failure, including oxide fracture, oxide spallation, oxide penetration to the aluminum core and severe local plastic deformation of the core. For the PEO microtrusses, delamination occurred within the oxide coating resulting in a global strut buckling failure mode. A new failure mode for the anodized tubes was observed: (i) axisymmetric folding of the aluminum core, (ii) longitudinal fracture, and (iii) alumina pulverization. Overall, the alumina coating enhanced the buckling resistance of the composites, while the aluminum core supported the oxide during the damage propagation.

One-pot synthesis of monodisperse CoFe2O4@Ag core-shell nanoparticles and their characterization.

PubMed

Hara, Shuta; Aisu, Jumpei; Kato, Masahiro; Aono, Takashige; Sugawa, Kosuke; Takase, Kouichi; Otsuki, Joe; Shimizu, Shigeru; Ikake, Hiroki

2018-06-08

In recent years, monodispersed magnetic nanoparticles with a core/shell structure are expected for their wide applications including magnetic fluid, recoverable catalysts, and biological analysis. However, their synthesis method needs numerous processes such as solvent substitution, exchange of protective agents, and centrifugation. A simple and rapid method for the synthesis of monodispersed core-shell nanoparticles makes it possible to accelerate their further applications. This paper describes a simple and rapid one-pot synthesis of core (CoFe 2 O 4 )-shell (Ag) nanoparticles with high monodispersity. The synthesized nanoparticles showed plasmonic light absorption owing to the Ag shell. Moreover, the magnetic property of the nanoparticles had a soft magnetic behavior at room temperature and a hard magnetic behavior at 5 K. In addition, the nanoparticles showed high monodispersity with a low polydispersity index (PDI) value of 0.083 in hexane.

Preparation of microcapsules with self-microemulsifying core by a vibrating nozzle method.

PubMed

Homar, Miha; Suligoj, Dasa; Gasperlin, Mirjana

2007-02-01

Incorporation of drugs in self-microemulsifying systems (SMES) offers several advantages for their delivery, the main one being faster drug dissolution and absorption. Formulation of SMES in solid dosage forms can be difficult and, to date, most SMES are applied in liquid dosage form or soft gelatin capsules. This study has explored the incorporation of SMES in microcapsules, which could then be used for formulation of solid dosage forms. An Inotech IE-50 R encapsulator equipped with a concentric nozzle was used to produce alginate microcapsules with a self-microemulsifying core. Retention of the core phase was improved by optimization of encapsulator parameters and modification of the shell forming phase and hardening solution. The mean encapsulation efficiency of final batches was more than 87%, which resulted in 0.07% drug loading. It was demonstrated that production of microcapsules with a self-microemulsifying core is possible and that the process is stable and reproducible.

Temperature Sensitivity of Water-Soluble CdTe and CdSe/ZnS Quantum Dots Incorporated into Biopolymer Submicron Particles

NASA Astrophysics Data System (ADS)

Slyusarenko, N. V.; Gerasimova, M. A.; Slabko, V. V.; Slyusareva, E. A.

2017-07-01

Polymer particles with sizes 0.3-0.4 μm are synthesized based on chitosan and chondroitin sulfate with incorporated CdTe (core) and CdSe/ZnS (core-shell) quantum dots. Their morphological and spectral properties are investigated by the methods of dynamic scattering, electron microscopy, and absorption and luminescence spectroscopy at temperatures from 10 to 80°C. Spectral effects associated with a change in temperature (a red shift and a decrease in the amplitude of the photoluminescence spectrum) can be explained by the temperature expansion of the quantum dots and activation of surface traps. It is shown that the temperature sensitivity of spectra of the quantum dots incorporated into the biopolymer particles is not less than in water. To develop an optical temperature sensor, the core quantum dots are more preferable than the core-shell quantum dots.

New core-pyrene π structure organophotocatalysts usable as highly efficient photoinitiators

PubMed Central

Telitel, Sofia; Dumur, Frédéric; Faury, Thomas; Graff, Bernadette; Tehfe, Mohamad-Ali; Fouassier, Jean-Pierre

2013-01-01

Summary Eleven di- and trifunctional compounds based on a core-pyrene π structure (Co_Py) were synthesized and investigated for the formation of free radicals. The application of two- and three-component photoinitiating systems (different Co_Pys with the addition of iodonium or sulfonium salts, alkyl halide or amine) was investigated in detail for cationic and radical photopolymerization reactions under near-UV–vis light. The proposed compounds can behave as new photocatalysts. Successful results in terms of rates of polymerization and final conversions were obtained. The strong MO coupling between the six different cores and the pyrene moiety was studied by DFT calculations. The different chemical intermediates are characterized by ESR and laser flash photolysis experiments. The mechanisms involved in the initiation step are discussed, and relationships between the core structure, the Co_Py absorption property, and the polymerization ability are tentatively proposed. PMID:23766803

One-pot synthesis of monodisperse CoFe2O4@Ag core-shell nanoparticles and their characterization

NASA Astrophysics Data System (ADS)

Hara, Shuta; Aisu, Jumpei; Kato, Masahiro; Aono, Takashige; Sugawa, Kosuke; Takase, Kouichi; Otsuki, Joe; Shimizu, Shigeru; Ikake, Hiroki

2018-06-01

In recent years, monodispersed magnetic nanoparticles with a core/shell structure are expected for their wide applications including magnetic fluid, recoverable catalysts, and biological analysis. However, their synthesis method needs numerous processes such as solvent substitution, exchange of protective agents, and centrifugation. A simple and rapid method for the synthesis of monodispersed core-shell nanoparticles makes it possible to accelerate their further applications. This paper describes a simple and rapid one-pot synthesis of core (CoFe2O4)-shell (Ag) nanoparticles with high monodispersity. The synthesized nanoparticles showed plasmonic light absorption owing to the Ag shell. Moreover, the magnetic property of the nanoparticles had a soft magnetic behavior at room temperature and a hard magnetic behavior at 5 K. In addition, the nanoparticles showed high monodispersity with a low polydispersity index (PDI) value of 0.083 in hexane.

Effects of surface and interface traps on exciton and multi-exciton dynamics in core/shell quantum dots

NASA Astrophysics Data System (ADS)

Bozio, Renato; Righetto, Marcello; Minotto, Alessandro

2017-08-01

Exciton interactions and dynamics are the most important factors determining the exceptional photophysical properties of semiconductor quantum dots (QDs). In particular, best performances have been obtained for ingeniously engineered core/shell QDs. We have studied two factors entering in the exciton decay dynamics with adverse effects for the luminescence efficiency: exciton trapping at surface and interface traps, and non-radiative Auger recombination in QDs carrying either net charges or multiple excitons. In this work, we present a detailed study into the optical absorption, fluorescence dynamics and quantum yield, as well as ultrafast transient absorption properties of CdSe/CdS, CdSe/Cd0.5Zn0.5S, and CdSe/ZnS QDs as a function of shell thickness. It turns out that de-trapping processes play a pivotal role in determining steady state emission properties. By studying the excitation dependent photoluminescence quantum yields (PLQY) in different CdSe/CdxZn1-xS (x = 0, 0.5, 1) QDs, we demonstrate the different role played by hot and cold carrier trapping rates in determining fluorescence quantum yields. Finally, the use of global analysis allows us untangling the complex ultrafast transient absorption signals. Smoothing of interface potential, together with effective surface passivation, appear to be crucial factors in slowing down both Auger-based and exciton trapping recombination processes.

Single-exciton optical gain in semiconductor nanocrystals.

PubMed

Klimov, Victor I; Ivanov, Sergei A; Nanda, Jagjit; Achermann, Marc; Bezel, Ilya; McGuire, John A; Piryatinski, Andrei

2007-05-24

Nanocrystal quantum dots have favourable light-emitting properties. They show photoluminescence with high quantum yields, and their emission colours depend on the nanocrystal size--owing to the quantum-confinement effect--and are therefore tunable. However, nanocrystals are difficult to use in optical amplification and lasing. Because of an almost exact balance between absorption and stimulated emission in nanoparticles excited with single electron-hole pairs (excitons), optical gain can only occur in nanocrystals that contain at least two excitons. A complication associated with this multiexcitonic nature of light amplification is fast optical-gain decay induced by non-radiative Auger recombination, a process in which one exciton recombines by transferring its energy to another. Here we demonstrate a practical approach for obtaining optical gain in the single-exciton regime that eliminates the problem of Auger decay. Specifically, we develop core/shell hetero-nanocrystals engineered in such a way as to spatially separate electrons and holes between the core and the shell (type-II heterostructures). The resulting imbalance between negative and positive charges produces a strong local electric field, which induces a giant ( approximately 100 meV or greater) transient Stark shift of the absorption spectrum with respect to the luminescence line of singly excited nanocrystals. This effect breaks the exact balance between absorption and stimulated emission, and allows us to demonstrate optical amplification due to single excitons.

A colorimetric assay for measuring iodide using Au@Ag core-shell nanoparticles coupled with Cu(2+).

PubMed

Zeng, Jingbin; Cao, Yingying; Lu, Chun-Hua; Wang, Xu-Dong; Wang, Qianru; Wen, Cong-Ying; Qu, Jian-Bo; Yuan, Cunguang; Yan, Zi-Feng; Chen, Xi

2015-09-03

Au@Ag core-shell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu(2+)) for the colorimetric sensing of iodide ion (I(-)). This assay relies on the fact that the absorption spectra and the color of metallic core-shell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I(-) was added to the Au@Ag core-shell NPs-Cu(2+) system/solution, Cu(2+) can oxidize I(-) into iodine (I2), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core-shell NPs led to color changes from yellow to purple, which was utilized for the colorimetric sensing of I(-). The assay only took 10 min with a lowest detectable concentration of 0.5 μM, and it exhibited excellent selectivity for I(-) over other common anions tested. Furthermore, Au@Ag core-shell NPs-Cu(2+) was embedded into agarose gels as inexpensive and portable "test strips", which were successfully used for the semi-quantitation of I(-) in dried kelps. Copyright © 2015 Elsevier B.V. All rights reserved.

Sound-proof Sandwich Panel Design via Metamaterial Concept

NASA Astrophysics Data System (ADS)

Sui, Ni

Sandwich panels consisting of hollow core cells and two face-sheets bonded on both sides have been widely used as lightweight and strong structures in practical engineering applications, but with poor acoustic performance especially at low frequency regime. Basic sound-proof methods for the sandwich panel design are spontaneously categorized as sound insulation and sound absorption. Motivated by metamaterial concept, this dissertation presents two sandwich panel designs without sacrificing weight or size penalty: A lightweight yet sound-proof honeycomb acoustic metamateiral can be used as core material for honeycomb sandwich panels to block sound and break the mass law to realize minimum sound transmission; the other sandwich panel design is based on coupled Helmholtz resonators and can achieve perfect sound absorption without sound reflection. Based on the honeycomb sandwich panel, the mechanical properties of the honeycomb core structure were studied first. By incorporating a thin membrane on top of each honeycomb core, the traditional honeycomb core turns into honeycomb acoustic metamaterial. The basic theory for such kind of membrane-type acoustic metamaterial is demonstrated by a lumped model with infinite periodic oscillator system, and the negative dynamic effective mass density for clamped membrane is analyzed under the membrane resonance condition. Evanescent wave mode caused by negative dynamic effective mass density and impedance methods are utilized to interpret the physical phenomenon of honeycomb acoustic metamaterials at resonance. The honeycomb metamaterials can extraordinarily improve low-frequency sound transmission loss below the first resonant frequency of the membrane. The property of the membrane, the tension of the membrane and the numbers of attached membranes can impact the sound transmission loss, which are observed by numerical simulations and validated by experiments. The sandwich panel which incorporates the honeycomb metamateiral as the core material maintains the mechanical property and yields a sound transmission loss that is consistently greater than 50 dB at low frequencies. Furthermore, the absorption property of the proposed honeycomb sandwich panel was experimentally studied. The honeycomb sandwich panel shows an excellent sound absorbing performance at high frequencies by using reinforced glass fiber without adding too much mass. The effect of the panel size and the stiffness of the grid-like frame effect of the honeycomb sandwich structures on sound transmission are discussed lastly. For the second sound-proof sandwich panel design, each unit cell of the sandwich panel is replaced by a Helmholtz resonator by perforating a small hole on the top face sheet. A perfect sound absorber sandwich panel with coupled Helmholtz resonators is proposed by two types: single identical Helmholtz resonator in each unit cell and dual Helmholtz resonators with different orifices, arranged in each cell arranged periodically. The soundproof sandwich panel is modelled as a panel embedded in rigid panel and assumed as a semiinfinite space with hard boundary condition. The net/mutual impedance model is first proposed and derived by solving Kirchhoff-Helmholtz integral by using the Green's function. The thermal-viscous energy dissipation at the thermal boundary layer dominates the total energy consumed. Two types of perfect sound absorber sandwich panel are designed in the last part. Two theoretical methods: the average energy and the equivalent surface impedance method are used to predict sound absorption performance. The geometry for perfect sound absorber sandwich panel at a target frequency can be obtained when the all the Helmholtz resonators are at resonance and the surface impedance of the sandwich panel matches the air impedance. The bandwidth for the identical sandwich panel mainly depends on the neck radius. The absorptive property of the dual Helmholtz resonators type of sandwich panel is studied by investigating the coupling effects between HRs. The theoretical results can be verified by numerical simulations through finite element method. The absorption bandwidth can be tuned by incorporating more HRs in each unit cell. Both sound-proof sandwich panel designs possess extraordinary acoustic performance for noise reduction at low frequency range with sub-wavelength structures. The sound absorber panel design can also achieve broadband sound attenuation at low frequencies.

A novel core-shell lipid nanoparticle for improving oral administration of water soluble chemotherapeutic agents: inhibited intestinal hydrolysis and enhanced lymphatic absorption.

PubMed

Wang, Tao; Shen, Liao; Zhang, Zhen; Li, Haiyan; Huang, Ri; Zhang, Yadan; Quan, Dongqin

2017-11-01

The oral administration of water-soluble chemotherapeutical agents is limited by their serious gastrointestinal side effects, instability at intestinal pH, and poor absorption. Aiming to solve these problems, we chose topotecan (TPT) as a model drug and developed a novel lipid formulation containing core-shell lipid nanoparticle (CLN) that makes the water-soluble drug to 'dissolve' in oil. TPT molecules can be encapsulated into nanoparticles surrounded by oil barrier while avoiding the direct contact with intestinal environment, thus easing the intestinal hydrolytic degradation and gastrointestinal (GI) irritation. Microstructure and mean particle size of TPT-CLN were characterized by Transmission Electron Microscope (TEM) and Dynamic Light Scattering (DLS), respectively. The average size of nanoparticles was approximately 60 nm with a homogeneous distribution in shapes of spheres or ellipsoid. According to in vitro stability studies, more initial form of TPT was observed in presence of lipid nanoparticle compared with free topotecan solution in artificial intestinal juice (pH 6.5). After oral administration of TPT-CLN in rats, AUC and C max of TPT were all increased compared with free TPT, indicating significant enhancement of oral absorption. Intestinal lymphatic transport was confirmed as the major way for CLN to enhance oral absorption of TPT by the treatment of blocking chylomicron flow. Lower GI irritation of TPT-CLN was observed in the gastrointestinal damage studies. The in vivo antitumor activity of TPT-CLN showed an improved antitumor efficacy by oral treatment of TPT-CLN compared to free TPT. From the obtained data, the systems appear an attractive progress in oral administration of topotecan.

Raman gain and nonlinear optical absorption measurements in a low-loss silicon waveguide

NASA Astrophysics Data System (ADS)

Rong, Haisheng; Liu, Ansheng; Nicolaescu, Remus; Paniccia, Mario; Cohen, Oded; Hak, Dani

2004-09-01

We fabricated a low-loss (˜0.22dB/cm) rib waveguide (WG) in silicon-on-insulator with a small effective core area of ˜1.57μm2 and measured the stimulated Raman scattering gain in the WG. We obtained 2.3dB Raman gain in a 4.8-cm-long S-shaped WG using a 1455nm pump laser with a cw power of 0.9W measured before the WG. In addition, we observed nonlinear dependence of Raman gain and optical propagation loss as a function of the pump power. Our study shows that this mainly is due to two-photon absorption (TPA) induced free carrier absorption in the silicon WG. We experimentally determined the TPA induced free carrier lifetime of 25ns, which agrees well with our modeling.

Observation of Reverse Saturable Absorption of an X-ray Laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, B. I.; Cho, M. S.; Kim, M.

A nonlinear absorber in which the excited state absorption is larger than the ground state can undergo a process called reverse saturable absorption. It is a well-known phenomenon in laser physics in the optical regime, but is more difficult to generate in the x-ray regime, where fast nonradiative core electron transitions typically dominate the population kinetics during light matter interactions. Here, we report the first observation of decreasing x-ray transmission in a solid target pumped by intense x-ray free electron laser pulses. The measurement has been made below the K-absorption edge of aluminum, and the x-ray intensity ranges are 10more » 16 –10 17 W=cm 2. It has been confirmed by collisional radiative population kinetic calculations, underscoring the fast spectral modulation of the x-ray pulses and charge states relevant to the absorption and transmission of x-ray photons. The processes shown through detailed simulations are consistent with reverse saturable absorption, which would be the first observation of this phenomena in the x-ray regime. These light matter interactions provide a unique opportunity to investigate optical transport properties in the extreme state of matters, as well as affording the potential to regulate ultrafast x-ray freeelectron laser pulses.« less

Observation of Reverse Saturable Absorption of an X-ray Laser

DOE PAGES

Cho, B. I.; Cho, M. S.; Kim, M.; ...

2017-08-16

A nonlinear absorber in which the excited state absorption is larger than the ground state can undergo a process called reverse saturable absorption. It is a well-known phenomenon in laser physics in the optical regime, but is more difficult to generate in the x-ray regime, where fast nonradiative core electron transitions typically dominate the population kinetics during light matter interactions. Here, we report the first observation of decreasing x-ray transmission in a solid target pumped by intense x-ray free electron laser pulses. The measurement has been made below the K-absorption edge of aluminum, and the x-ray intensity ranges are 10more » 16 –10 17 W=cm 2. It has been confirmed by collisional radiative population kinetic calculations, underscoring the fast spectral modulation of the x-ray pulses and charge states relevant to the absorption and transmission of x-ray photons. The processes shown through detailed simulations are consistent with reverse saturable absorption, which would be the first observation of this phenomena in the x-ray regime. These light matter interactions provide a unique opportunity to investigate optical transport properties in the extreme state of matters, as well as affording the potential to regulate ultrafast x-ray freeelectron laser pulses.« less

Collision-Induced Infrared Absorption by Collisional Complexes in Dense Hydrogen-Helium Gas Mixtures at Thousands of Kelvin

NASA Astrophysics Data System (ADS)

Abel, Martin; Frommhold, Lothar; Li, Xiaoping; Hunt, Katharine L. C.

2011-06-01

The interaction-induced absorption by collisional pairs of H{_2} molecules is an important opacity source in the atmospheres of the outer planets and cool stars. The emission spectra of cool white dwarf stars differ significantly in the infrared from the expected blackbody spectra of their cores, which is largely due to absorption by collisional H{_2}-H{_2}, H{_2}-He, and H{_2}-H complexes in the stellar atmospheres. Using quantum-chemical methods we compute the atmospheric absorption from hundreds to thousands of kelvin. Laboratory measurements of interaction-induced absorption spectra by H{_2} pairs exist only at room temperature and below. We show that our results reproduce these measurements closely, so that our computational data permit reliable modeling of stellar atmosphere opacities even for the higher temperatures. L. Frommhold, Collision-Induced Absorption in Gases, Cambridge University Press, Cambridge, New York, 1993 and 2006 Xiaoping Li, Katharine L. C. Hunt, Fei Wang, Martin Abel, and Lothar Frommhold, "Collision-Induced Infrared Absorption by Molecular Hydrogen Pairs at Thousands of Kelvin", International Journal of Spectroscopy, vol. 2010, Article ID 371201, 11 pages, 2010. doi: 10.1155/2010/371201 M. Abel, L. Frommhold, X. Li, and K. L. C. Hunt, "Collision-induced absorption by H{_2} pairs: From hundreds to thousands of Kelvin," J. Phys. Chem. A, published online, DOI: 10.1021/jp109441f L. Frommhold, M. Abel, F. Wang, M. Gustafsson, X. Li, and K. L. C. Hunt, "Infrared atmospheric emission and absorption by simple molecular complexes, from first principles", Mol. Phys. 108, 2265, 2010

Composite fluorescent nanoparticles for biomedical imaging.

PubMed

Pansare, Vikram J; Bruzek, Matthew J; Adamson, Douglas H; Anthony, John; Prud'homme, Robert K

2014-04-01

In the rapidly expanding field of biomedical imaging, there is a need for nontoxic, photostable, and nonquenching fluorophores for fluorescent imaging. We have successfully encapsulated a new, extremely hydrophobic, pentacene-based fluorescent dye within polymeric nanoparticles (NPs) or nanocarriers (NCs) via the Flash NanoPrecipitation (FNP) process. Nanoparticles and dye-loaded micelles were formulated by FNP and characterized by dynamic light scattering, fluorescence spectroscopy, UV-VIS absorbance spectroscopy, and confocal microscopy. These fluorescent particles were loaded from less than 1% to 78% by weight core loading and the fluorescence maximum was found to be at 2.3 wt.%. The particles were also stably formed at 2.3% core loading from 20 up to 250 nm in diameter with per-particle fluorescence scaling linearly with the NC core volume. The major absorption peaks are at 458, 575, and 625 nm, and the major emission peaks at 635 and 695 nm. In solution, the Et-TP5 dye displays a strong concentration-dependent ratio of the emission intensities of the first two emission peaks, whereas in the nanoparticle core the spectrum is independent of concentration over the entire concentration range. A model of the fluorescence quenching was consistent with Förster resonant energy transfer as the cause of the quenching observed for Et-TP5. The Förster radius calculated from the absorption and emission spectra of Et-TP5 is 4.1 nm, whereas the average dye spacing in the particles at the maximum fluorescence is 3.9 nm. We have successfully encapsulated Et-TP5, a pentacene derivative dye previously only used in light-emitting diode applications, within NCs via the FNP process. The extreme hydrophobicity of the dye keeps it encapsulated in the NC core, its extended pentacene structure gives it relatively long wavelength emission at 695 nm, and the pentacene structure, without oxygen or nitrogen atoms in its core, makes it highly resistant to photobleaching. Its bulky side groups minimize self-quenching and localization within the nanoparticle core prevents interaction of the dye with biological surfaces, or molecules in diagnostic assays. Loading of dye in the NP core allows 25 times more dye to be delivered than if it were conjugated onto the nanocarrier surface. The utility of the dye for quantifying nanoparticle binding is demonstrated. Studies to extend the wavelength range of these pentacene dyes into the near infra-red are underway.

Controlled formation of intense hot spots in Pd@Ag core-shell nanooctapods for efficient photothermal conversion

NASA Astrophysics Data System (ADS)

Liu, Maochang; Yang, Yang; Li, Naixu; Du, Yuanchang; Song, Dongxing; Ma, Lijing; Wang, Yi; Zheng, Yiqun; Jing, Dengwei

2017-08-01

Plasmonic Ag nanostructures have been of great interest for such applications in cancer therapy and catalysis, etc. However, the relatively week Ag-Ag interaction and spontaneous atom diffusion make it very difficult to generate concaved or branched structures in Ag nanocrystals with sizes less than 100 nm, which has been considered very favorable for plasmonic effects. Herein, by employing a cubic Pd seed and a specific reducing agent to restrict the surface diffusion of Ag atoms, Pd@Ag core-shell nanooctapod structures where Ag atoms can be selectively deposited onto the corner sites of the Pd cubes were obtained. Such selective decoration enables us to precisely control the locations for the hot spot formation during light irradiation. We find that the branched nanooctapod structure shows strong absorption in the visible-light region and generates intense hot spots around the octapod arms of Ag. As such, the photothermal conversion efficiency could be significantly improved by more than 50% with a colloid solution containing only ppm-level nanooctapods compared with pure water. The reported nanostructure is expected to find extensive applications due to its controlled formation of light-induced hot spots at certain points on the crystal surface.

Core-level spectra and molecular deformation in adsorption: V-shaped pentacene on Al(001)

PubMed Central

Lin, He; Brivio, Gian Paolo; Floreano, Luca; Fratesi, Guido

2015-01-01

Summary By first-principle simulations we study the effects of molecular deformation on the electronic and spectroscopic properties as it occurs for pentacene adsorbed on the most stable site of Al(001). The rationale for the particular V-shaped deformed structure is discussed and understood. The molecule–surface bond is made evident by mapping the charge redistribution. Upon X-ray photoelectron spectroscopy (XPS) from the molecule, the bond with the surface is destabilized by the electron density rearrangement to screen the core hole. This destabilization depends on the ionized carbon atom, inducing a narrowing of the XPS spectrum with respect to the molecules adsorbed hypothetically undistorted, in full agreement to experiments. When looking instead at the near-edge X-ray absorption fine structure (NEXAFS) spectra, individual contributions from the non-equivalent C atoms provide evidence of the molecular orbital filling, hybridization, and interchange induced by distortion. The alteration of the C–C bond lengths due to the V-shaped bending decreases by a factor of two the azimuthal dichroism of NEXAFS spectra, i.e., the energy splitting of the sigma resonances measured along the two in-plane molecular axes. PMID:26734516

Controlled growth of ZnO/Zn₁-xPbxSe core-shell nanowires and their interfacial electronic energy alignment.

PubMed

Chen, Z H; Yeung, S Y; Li, H; Qian, J C; Zhang, W J; Li, Y Y; Bello, I

2012-05-21

ZnO/Zn(1-x)Pb(x)Se core-shell nanowires (NWs) have been synthesized by a solution based surface ion transfer method at various temperatures. The energy dispersive spectroscopic (EDS) mapping of single NWs suggests that the Zn, Pb and Se atoms are uniformly distributed in their shell layers. The ternary Zn(1-x)Pb(x)Se layers with tunable bandgaps extend the band-edge of optical absorption from 450 nm to 700 nm contrasting with the binary ZnSe layers. The ultraviolet photoelectron spectroscopic (UPS) analysis reveals a transition from the type I to type II band alignment when the x fraction decreases from 0.66 to the value of 0.36 in the nanoshell layers. This quantitative investigation of electronic energy levels at ZnO and Zn(1-x)Pb(x)Se interfaces indicates that the proper type II band alignment is well suited for photovoltaic energy conversion. The photovoltaic cells comprising a ZnO/Zn(1-x)Pb(x)Se nano-heterojunction with the optimized Pb content are expected to be more efficient than the devices sensitized by binary ZnSe or PbSe.

Determination of total tin in silicate rocks by graphite furnace atomic absorption spectrometry

USGS Publications Warehouse

Elsheimer, H.N.; Fries, T.L.

1990-01-01

A method is described for the determination of total tin in silicate rocks utilizing a graphite furnace atomic absorption spectrometer with a stabilized-temperature platform furnace and Zeeman-effect background correction. The sample is decomposed by lithium metaborate fusion (3 + 1) in graphite crucibles with the melt being dissolved in 7.5% hydrochloric acid. Tin extractions (4 + 1 or 8 + 1) are executed on portions of the acid solutions using a 4% solution of tricotylphosphine oxide in methyl isobutyl ketone (MIBK). Ascorbic acid is added as a reducing agent prior to extraction. A solution of diammonium hydrogenphosphate and magnesium nitrate is used as a matrix modifier in the graphite furnace determination. The limit of detection is > 10 pg, equivalent to > 1 ??g l-1 of tin in the MIBK solution or 0.2-0.3 ??g g-61 in the rock. The concentration range is linear between 2.5 and 500 ??g l-1 tin in solution. The precision, measured as relative standard deviation, is < 20% at the 2.5 ??g l-1 level and < 7% at the 10-30 ??g l-1 level of tin. Excellent agreement with recommended literature values was found when the method was applied to the international silicate rock standards BCR-1, PCC-1, GSP-1, AGV-1, STM-1, JGb-1 and Mica-Fe. Application was made to the determination of tin in geological core samples with total tin concentrations of the order of 1 ??g g-1 or less.

Electronic structure at transition metal phthalocyanine-transition metal oxide interfaces: Cobalt phthalocyanine on epitaxial MnO films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glaser, Mathias; Peisert, Heiko, E-mail: heiko.peisert@uni-tuebingen.de; Adler, Hilmar

2015-03-14

The electronic structure of the interface between cobalt phthalocyanine (CoPc) and epitaxially grown manganese oxide (MnO) thin films is studied by means of photoemission (PES) and X-ray absorption spectroscopy (XAS). Our results reveal a flat-lying adsorption geometry of the molecules on the oxide surface which allows a maximal interaction between the π-system and the substrate. A charge transfer from MnO, in particular, to the central metal atom of CoPc is observed by both PES and XAS. The change of the shape of N-K XAS spectra at the interface points, however, to the involvement of the Pc macrocycle in the chargemore » transfer process. As a consequence of the charge transfer, energetic shifts of MnO related core levels were observed, which are discussed in terms of a Fermi level shift in the semiconducting MnO films due to interface charge redistribution.« less

Color reflectance spectroscopy of profundal lake sediments: a novel moisture-balance proxy for tropical East Africa

NASA Astrophysics Data System (ADS)

Meyer, Inka; Van Daele, Maarten; Fiers, Geraldine; Verleyen, Eli; De Batist, Marc; Verschuren, Dirk

2016-04-01

Investigations of the continuous sediment record from Lake Challa, a deep freshwater crater lake on the eastern slope of Mt. Kilimanjaro, are expanding our knowledge about past climate and environmental changes in equatorial East Africa. During a field campaign in 2005 a 20.65-m long composite sediment sequence was retrieved from the center of the lake, covering the past 25,000 years. Unlike many other East African lakes, Lake Challa never dried out during this period and therefore provides one of the few continuous and high-resolution regional climate-proxy records since before the LGM. Continuously taken digital line-scan images (GeoTek MSCL core logger) revealed systematic colour variation from greenish to yellow-brownish sediments throughout the core sequence. To characterize the origin of these colour variations, high-resolution colour reflectance spectrometry was carried out. The relative absorption band depth (RABD) at different wavelengths was calculated to distinguish between sediment components with distinct absorption/ reflection characteristics. RABD660/670 can be used as a proxy for chlorophyll and its derivates, and RABD610 as a proxy for carotenoids and their derivates. Comparison of RABD660/670 with independent reconstructions of rainfall (the Branched and Isoprenoid Tetraether (BIT) index of bacterial lipids) and seismic lake level reconstructions showed a positive correlation between these proxies. During times of wetter climate and higher lake level, e.g. the early Holocene, the RABD660/670 value is higher than during times of inferred dry conditions and low lake level, e.g. the early late-Glacial period (during which no chlorophyll or its derivates were detected). We attribute this positive correlation to reduced preservation of chlorophyll contained in the settling remains of dead phytoplankton during lowstands, when bottom waters may have been better oxygenated. This data is supported by the variation in fossil pigment concentration and composition analyzed by high performance liquid chromatography (HPLC). During humid/highstand episodes, chlorophyll and carotenoids are more diverse and abundant than during dry/lowstand episodes. Our data confirm the utility of reflectance spectroscopy as a tool for rapid, non-destructive and cost-effective analysis of long sequences of lithological change at high temporal resolution. They also support the previously published BIT-index record of Lake Challa as proxy for regional moisture-balance history.

Electronic and Optical Properties of Core/Shell Pb16X16/Cd52X52 (X =S, Se, Te) Quantum Dots

NASA Astrophysics Data System (ADS)

Tamukong, Patrick; Mayo, Michael; Kilina, Svetlana

2015-03-01

The electronic and optoelectronic properties of semiconductor quantum dots (QDs) are mediated by surface defects due to the presence of dangling bonds producing trap states within the HOMO-LUMO energy gap, and contributing to fluorescence quenching. Surface capping ligands are generally used to alleviate this problem and increase the quantum yields of QDs. An alternative way is to synthesize core-shell QD structures; i.e., a QD core with a shell of another semiconductor material. We have investigated the effects of Cd52X52 shells on the photoexcited dynamics of Pb16X16 (X =S, Se, Te) QDs. The thin (~ 0.50 nm) shells were found to result largely in type I core/shell structures and a blue shift of the absorption spectra. Our studies revealed fairly strong core-shell hybridization in the electronic states close to the conduction band (CB) edge for Pb16S16andPb16Se16 cores, whereas for the Pb16Te16 core, such CB states were largely shell-like in nature. Nonadiabatic DFT-based dynamics, coupled with the surface hopping method, was used to study the effects of the core and shell compositions on energy relaxation rates in these systems.

In-vivo imaging of nanoshell extravasation from solid tumor vasculature by photoacoustic microscopy

NASA Astrophysics Data System (ADS)

Li, Meng-Lin; Schwartz, Jon A.; Wang, James; Stoica, George; Wang, Lihong V.

2007-02-01

In this study, high resolution reflection-mode (backward-mode) photoacoustic microscopy (PAM) is used to noninvasively image progressive extravasation and accumulation of nanoshells within a solid tumor in vivo. This study takes advantage of the strong near-infrared absorption of nanoshells, a novel type of optically tunable gold nanoparticles that tend to extravasate from leaky tumor vasculatures (i.e., passive targeting) via the "enhanced permeability and retention" effect due to their nanoscale size. Tumors were grown in immunocompetent BALB/c mice by subcutaneous inoculation of CT26.wt murine colon carcinoma cells. PEGylated nanoshells with a peak optical absorption at ~800 nm were intravenously administered. Pre-scans prior to nanoshell injection were taken using a 584-nm laser source to highlight blood content and an 800-nm laser source to mark the background limit for nanoshell accumulation. After injection, the three-dimensional nanoshell distribution inside the tumor was monitored by PAM for 7 hours. Experimental results show that nanoshell accumulation is heterogeneous in tumors: more concentrated within the tumor cortex and largely absent from the tumor core. This correlates with others' observation that drug delivery within tumor cores is ineffective because of both high interstitial pressure and tendency to necrosis of tumor cores. Since nanoshells have been recently applied to thermal therapy for subcutaneous tumors, we anticipate that PAM will be important to this therapeutic technique.

Nanowire Optoelectronics

NASA Astrophysics Data System (ADS)

Wang, Zhihuan; Nabet, Bahram

2015-12-01

Semiconductor nanowires have been used in a variety of passive and active optoelectronic devices including waveguides, photodetectors, solar cells, light-emitting diodes (LEDs), lasers, sensors, and optical antennas. We review the optical properties of these nanowires in terms of absorption, guiding, and radiation of light, which may be termed light management. Analysis of the interaction of light with long cylindrical/hexagonal structures with subwavelength diameters identifies radial resonant modes, such as Leaky Mode Resonances, or Whispering Gallery modes. The two-dimensional treatment should incorporate axial variations in "volumetric modes,"which have so far been presented in terms of Fabry-Perot (FP), and helical resonance modes. We report on finite-difference timedomain (FDTD) simulations with the aim of identifying the dependence of these modes on geometry (length, width), tapering, shape (cylindrical, hexagonal), core-shell versus core-only, and dielectric cores with semiconductor shells. This demonstrates how nanowires (NWs) form excellent optical cavities without the need for top and bottommirrors. However, optically equivalent structures such as hexagonal and cylindrical wires can have very different optoelectronic properties meaning that light management alone does not sufficiently describe the observed enhancement in upward (absorption) and downward transitions (emission) of light inNWs; rather, the electronic transition rates should be considered. We discuss this "rate management" scheme showing its strong dimensional dependence, making a case for photonic integrated circuits (PICs) that can take advantage of the confluence of the desirable optical and electronic properties of these nanostructures.

Predicting Near Edge X-ray Absorption Spectra with the Spin-Free Exact-Two-Component Hamiltonian and Orthogonality Constrained Density Functional Theory.

PubMed

Verma, Prakash; Derricotte, Wallace D; Evangelista, Francesco A

2016-01-12

Orthogonality constrained density functional theory (OCDFT) provides near-edge X-ray absorption (NEXAS) spectra of first-row elements within one electronvolt from experimental values. However, with increasing atomic number, scalar relativistic effects become the dominant source of error in a nonrelativistic OCDFT treatment of core-valence excitations. In this work we report a novel implementation of the spin-free exact-two-component (X2C) one-electron treatment of scalar relativistic effects and its combination with a recently developed OCDFT approach to compute a manifold of core-valence excited states. The inclusion of scalar relativistic effects in OCDFT reduces the mean absolute error of second-row elements core-valence excitations from 10.3 to 2.3 eV. For all the excitations considered, the results from X2C calculations are also found to be in excellent agreement with those from low-order spin-free Douglas-Kroll-Hess relativistic Hamiltonians. The X2C-OCDFT NEXAS spectra of three organotitanium complexes (TiCl4, TiCpCl3, TiCp2Cl2) are in very good agreement with unshifted experimental results and show a maximum absolute error of 5-6 eV. In addition, a decomposition of the total transition dipole moment into partial atomic contributions is proposed and applied to analyze the nature of the Ti pre-edge transitions in the three organotitanium complexes.

Hard-X-Ray-Induced Multistep Ultrafast Dissociation

NASA Astrophysics Data System (ADS)

Travnikova, Oksana; Marchenko, Tatiana; Goldsztejn, Gildas; Jänkälä, Kari; Sisourat, Nicolas; Carniato, Stéphane; Guillemin, Renaud; Journel, Loïc; Céolin, Denis; Püttner, Ralph; Iwayama, Hiroshi; Shigemasa, Eiji; Piancastelli, Maria Novella; Simon, Marc

2016-05-01

Creation of deep core holes with very short (τ ≤1 fs ) lifetimes triggers a chain of relaxation events leading to extensive nuclear dynamics on a few-femtosecond time scale. Here we demonstrate a general multistep ultrafast dissociation on an example of HCl following Cl 1 s →σ* excitation. Intermediate states with one or multiple holes in the shallower core electron shells are generated in the course of the decay cascades. The repulsive character and large gradients of the potential energy surfaces of these intermediates enable ultrafast fragmentation after the absorption of a hard x-ray photon.

Electromagnetic absorption behaviour of ferrite loaded three phase carbon fabric composites

NASA Astrophysics Data System (ADS)

Jagatheesan, Krishnasamy; Ramasamy, Alagirusamy; Das, Apurba; Basu, Ananjan

2018-02-01

This article investigates the electromagnetic absorption behaviours of carbon helical yarn fabric reinforced composites and manganese-zinc (Mn-Zn) ferrite particles loaded 3 phase fabric composites. A carbon helical yarn having stainless steel core was prepared and made into single jersey knitted fabric. The composite was prepared by sandwiching a fabric with polypropylene films and thermal pressed. The absorption values of helical yarn fabric composite was observed to be less in the C band region (4-8 GHz). For improving the absorption coefficients of composite, Mn-Zn ferrite particles were dispersed in the polypropylene (PP) composite. The ferrite loaded PP composites exhibited better permittivity and permeability values, hence the absorption loss of the composite was improved. The helical yarn fabric reinforced with Mn-Zn ferrite/PP composite showed larger absorption coefficients than virgin PP/fabric composite. The change in thermal stability and particle size distribution in the Mn-Zn ferrite/PP composite was also analyzed. At higher ferrite concentration, bimodal particle distribution was observed which increased the conductivity and shielding effectiveness (SE) of the composite. In addition, complex permittivity value was also increased for higher incident frequency (4-8 GHz). As the ferrite content increases, the dielectric loss and magnetic permeability of PP/ferrite increases due to increased magnetic loss. Hence, ferrite loaded PP composite showed the total SE of -14.2 dB with the absorption coefficients of 0.717. The S1C7 fabric composite having ferrite dispersion showed the better absorption loss and lower reflection coefficient of 14.2 dB and 0.345 respectively compared to virgin PP/helical yarn fabric composite. The increasing ferrite content (45 wt%) improved the absorption loss and total SE. Though, ferrite based fabric composite exhibits moderate absorptive shielding, it can be used as shielding panels in the electronic industries.

H i Absorption in the Steep-Spectrum Superluminal Quasar 3C 216.

PubMed

Pihlström; Vermeulen; Taylor; Conway

1999-11-01

The search for H i absorption in strong compact steep-spectrum sources is a natural way to probe the neutral gas contents in young radio sources. In turn, this may provide information about the evolution of powerful radio sources. The recently improved capabilities of the Westerbork Synthesis Radio Telescope have made it possible to detect a 0.31% (19 mJy) deep neutral atomic hydrogen absorption line associated with the steep-spectrum superluminal quasar 3C 216. The redshift (z=0.67) of the source shifts the frequency of the 21 cm line down to the ultra-high-frequency (UHF) band (850 MHz). The exact location of the H i-absorbing gas remains to be determined by spectral line VLBI observations at 850 MHz. We cannot exclude that the gas might be extended on galactic scales, but we think it is more likely to be located in the central kiloparsec. Constraints from the lack of X-ray absorption probably rule out obscuration of the core region, and we argue that the most plausible site for the H i absorption is in the jet-cloud interaction observed in this source.

How temperature determines formation of maghemite nanoparticles

NASA Astrophysics Data System (ADS)

Girod, Matthias; Vogel, Stefanie; Szczerba, Wojciech; Thünemann, Andreas F.

2015-04-01

We report on the formation of polymer-stabilized superparamagnetic single-core and multi-core maghemite nanoparticles. The particle formation was carried out by coprecipitation of Fe(II) and Fe(III) sulfate in a continuous aqueous process using a micromixer system. Aggregates containing 50 primary particles with sizes of 2 nm were formed at a reaction temperature of 30 °C. These particles aggregated further with time and were not stable. In contrast, stable single-core particles with a diameter of 7 nm were formed at 80 °C as revealed by small-angle X-ray scattering (SAXS) coupled in-line with the micromixer for particle characterization. X-ray diffraction and TEM confirmed the SAXS results. X-ray absorption near-edge structure spectroscopy (XANES) identified the iron oxide phase as maghemite.

Theoretical investigation of geometries, stabilities, electronic and optical properties for advanced Ag{sub n}@(ZnO){sub 42} (n=6-18) hetero-nanostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Hai-Xia; Department of Physics, National University of Singapore, 117542; Wang, Xiao-Xu

The structural properties of Ag{sub n}@(ZnO){sub 42} (n=6-18) core-shell nanoparticles have been investigated by the first principles calculations, and the core-shell nanostructure with n=13 is proved to be the most stable one for the first time. Ag{sub 13}@(ZnO){sub 42} core-shell nanostructure possesses higher chemistry activity and shows a red shift phenomenon in the light of the absorption spectrum compare to the (ZnO){sub 48}, this can be confirmed by the calculated electron structure. The visible-light could be absorbed by Ag{sub 13}@(ZnO){sub 42} to improve the photo-catalysis of (ZnO){sub 48} nanostructure. Our results show good agreement with experiments.

A theoretical and experimental benchmark study of core-excited states in nitrogen

NASA Astrophysics Data System (ADS)

Myhre, Rolf H.; Wolf, Thomas J. A.; Cheng, Lan; Nandi, Saikat; Coriani, Sonia; Gühr, Markus; Koch, Henrik

2018-02-01

The high resolution near edge X-ray absorption fine structure spectrum of nitrogen displays the vibrational structure of the core-excited states. This makes nitrogen well suited for assessing the accuracy of different electronic structure methods for core excitations. We report high resolution experimental measurements performed at the SOLEIL synchrotron facility. These are compared with theoretical spectra calculated using coupled cluster theory and algebraic diagrammatic construction theory. The coupled cluster singles and doubles with perturbative triples model known as CC3 is shown to accurately reproduce the experimental excitation energies as well as the spacing of the vibrational transitions. The computational results are also shown to be systematically improved within the coupled cluster hierarchy, with the coupled cluster singles, doubles, triples, and quadruples method faithfully reproducing the experimental vibrational structure.

Luminescence and efficiency optimization of InGaN/GaN core-shell nanowire LEDs by numerical modelling

NASA Astrophysics Data System (ADS)

Römer, Friedhard; Deppner, Marcus; Andreev, Zhelio; Kölper, Christopher; Sabathil, Matthias; Strassburg, Martin; Ledig, Johannes; Li, Shunfeng; Waag, Andreas; Witzigmann, Bernd

2012-02-01

We present a computational study on the anisotropic luminescence and the efficiency of a core-shell type nanowire LED based on GaN with InGaN active quantum wells. The physical simulator used for analyzing this device integrates a multidimensional drift-diffusion transport solver and a k . p Schrödinger problem solver for quantization effects and luminescence. The solution of both problems is coupled to achieve self-consistency. Using this solver we investigate the effect of dimensions, design of quantum wells, and current injection on the efficiency and luminescence of the core-shell nanowire LED. The anisotropy of the luminescence and re-absorption is analyzed with respect to the external efficiency of the LED. From the results we derive strategies for design optimization.

Nuclear fuel element

DOEpatents

Armijo, Joseph S.; Coffin, Jr., Louis F.

1980-04-29

A nuclear fuel element for use in the core of a nuclear reactor is disclosed and has an improved composite cladding comprised of a moderate purity metal barrier of zirconium metallurgically bonded on the inside surface of a zirconium alloy tube. The metal barrier forms a shield between the alloy tube and a core of nuclear fuel material enclosed in the composite cladding. There is a gap between the cladding and the core. The metal barrier forms about 1 to about 30 percent of the thickness of the composite cladding and has low neutron absorption characteristics. The metal barrier serves as a preferential reaction site for gaseous impurities and fission products and protects the alloy tube from contact and reaction with such impurities and fission products. Methods of manufacturing the composite cladding are also disclosed.

β-Octakis(methylthio)porphycenes: synthesis, characterisation and third order nonlinear optical studies.

PubMed

Rana, Anup; Lee, Sangsu; Kim, Dongho; Panda, Pradeepta K

2015-05-04

A novel electron deficient β-octakis(methylthio)porphycene, along with its Zn(ii) and Ni(ii) derivatives, was synthesized for the first time. The macrocyclic structure exhibits core ruffling with a largely red shifted absorption band (∼750 nm) and also a large enhancement in the third order nonlinear optical response.

Direct Spectroscopy in Hollow Optical with Fiber-Based Optical Frequency Combs

DTIC Science & Technology

2015-07-09

scheme is that the generation of carrier-envelope offset frequency f0 can be avoided, which reduces the system complexity . However, a high performance RF...Peterson, "Saturated absorption in acetylene and hydrogen cyanide in hollow-core photonic bandgap fibers," Opt. Express 13, 10475-10482 (2005). 56. C

Microwave absorption properties of the core/shell-type iron and nickel nanoparticles

NASA Astrophysics Data System (ADS)

Lu, B.; Dong, X. L.; Huang, H.; Zhang, X. F.; Zhu, X. G.; Lei, J. P.; Sun, J. P.

Iron (Fe) and nickel (Ni) nanoparticles were prepared by the DC arc-discharge method in a mixture of hydrogen and argon gases, using bulk metals as the raw materials. The microstructure of core/shell (metal/metal oxide) in nanoparticle formed after in situ passivation process. The complex electromagnetic parameters (permittivity ɛ=ɛr'+iɛr″ and permeability μ=μr'+iμr″) of the paraffin-mixed nanocomposite samples (paraffin:nanoparticles=1:1 in mass ratio) were measured in the frequency range of 2-18 GHz. The polarization mechanisms of the space charge and dipole coexist in both the Fe and Ni nanoparticles. The orientational polarization is a particular polarization for Fe nanoparticles and brings a relatively higher dielectric loss. Natural resonance is the main reason for magnetic loss and the corresponding frequencies are 11.6 and 5.2 GHz for the Fe and Ni nanoparticles, respectively. The paraffin composite with Fe nanoparticles provided excellent microwave absorption properties (reflection loss <-20 dB) in the range 6.8-16.6 GHz over the absorber thickness of 1.1-2.3 mm.

Production of three-dimensional quantum dot lattice of Ge/Si core-shell quantum dots and Si/Ge layers in an alumina glass matrix.

PubMed

Buljan, M; Radić, N; Sancho-Paramon, J; Janicki, V; Grenzer, J; Bogdanović-Radović, I; Siketić, Z; Ivanda, M; Utrobičić, A; Hübner, R; Weidauer, R; Valeš, V; Endres, J; Car, T; Jerčinović, M; Roško, J; Bernstorff, S; Holy, V

2015-02-13

We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al2O3/Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells.

Broadband absorption enhancement in plasmonic nanoshells-based ultrathin microcrystalline-Si solar cells

NASA Astrophysics Data System (ADS)

Raja, Waseem; Bozzola, Angelo; Zilio, Pierfrancesco; Miele, Ermanno; Panaro, Simone; Wang, Hai; Toma, Andrea; Alabastri, Alessandro; de Angelis, Francesco; Zaccaria, Remo Proietti

2016-04-01

With the objective to conceive a plasmonic solar cell with enhanced photocurrent, we investigate the role of plasmonic nanoshells, embedded within a ultrathin microcrystalline silicon solar cell, in enhancing broadband light trapping capability of the cell and, at the same time, to reduce the parasitic loss. The thickness of the considered microcrystalline silicon (μc-Si) layer is only ~1/6 of conventional μc-Si based solar cells while the plasmonic nanoshells are formed by a combination of silica and gold, respectively core and shell. We analyze the cell optical response by varying both the geometrical and optical parameters of the overall device. In particular, the nanoshells core radius and metal thickness, the periodicity, the incident angle of the solar radiation and its wavelength are varied in the widest meaningful ranges. We further explain the reason for the absorption enhancement by calculating the electric field distribution associated to resonances of the device. We argue that both Fabry-Pérot-like and localized plasmon modes play an important role in this regard.

A Very Large Array Survey of Polar BAL Quasar Candidates

NASA Astrophysics Data System (ADS)

Olson, Kianna Alexandra; Brotherton, Michael S.; DiPompeo, Michael; Maithil, Jaya

2018-06-01

Polar broad absorption line quasars posses flat radio spectra and jets seen at small angles to the line of sight. Using the VLA we observed twelve polar broad absorption line quasar candidates at L (1.5GHz), C (4.5-5.5GHz), and X (8.5-9.5GHz) bands, and found that their cores display flat spectra. Compared to previous observations in the NVSS and First surveys, the peak flux densities all show significant variation σvar > 3, and brightness temperatures TB ≥ 1012K. Based on these findings, our quasars have the properties expected for objects that posses jets seen nearly pole on.

Analysis and design of a calcium-based sulfur sorbent for applications in integrated gasification combined cycle energy systems

NASA Astrophysics Data System (ADS)

Hasler, David Johann Ludwig

The reactivity of various Ca-based sorbent materials in pelletized form with H2S or CO2 was investigated at high temperatures (750--880°C). An extensive study was conducted to compare the performance of sorbent pellets derived from plaster of Paris and limestone. Multicycle absorption and regeneration tests showed that plaster-based pellets out performed the limestone-based pellets primarily due to a higher surface area and mesoporosity. The effect of pore-modifiers on the reactivity of limestone with H 2S was investigated by incorporating additives such as cornstarch, graphite and polyvinylalcohol (PVA) in the sorbent. Multicycle sulfidation and regeneration tests of the modified sorbent showed that starch did not improve the reactivity of the limestone, graphite reduced the reactivity, while PVA improved it. The effect of the chemical additives MgO and SrO on the performance of CaO-based sorbent pellets was investigated. The effect of MgO was tested by starting with materials that contained MgCO3 in a natural form, such as dolomite. The effect of SrO was tested by starting with SrCO 3 either co-precipitated with CaCO3 or by wet-mixing SrCO 3 with limestone in slurry form. The MgO was found to improve the thermal stability of the CaO-based sorbent but lowered the overall absorption capacity of the material when reacted with CO2 or H2S, while SrO decreased the thermal stability of the sorbent when it was reacted with CO2; no absorption tests were run with H2S. A study of the performance of pelletized CaO-based cores coated with a refractory material such as alumina and limestone or alumina and kaolin was conducted. The reactivity of the core and shell pellets with H2S was determined. The strength and durability of the pellets were determined by using crushing strength analysis and abrasion resistance tests. Pellets coated with either alumina and limestone or alumina and kaolin proved to be strong and adequate for use in industrial reactors. A semi-empirical mathematical model was developed to represent the reaction of H2S with a sorbent pellet. The model was based on the well-known shrinking core model and it was applied successfully for the analysis of both pellet cores and core and shell pellets reacting with H2S.

First X-Ray absorption spectroscopy results on Aeolian dust archived in Antarctica and Alpine firn cores

NASA Astrophysics Data System (ADS)

Marcelli, A.; Maggi, V.; Cibin, G.; Sala, M.; Marino, F.; Delmonte, B.

2006-12-01

We present the first x-ray absorption spectroscopy (XAS) data at the Fe K-edge collected on insoluble mineral dust from Talos Dome firn core (TDC, 159°04'E, 72°46'S, 2316 m a.s.l., mean accumulation rate 8 g cm-2 yr- 1), drilled in the framework of the International Trans Antarctic Scientific Expedition (ITASE), and from a Colle del Lys 2003 firn core (CDL03, 45°92'N, 7°86'E, 4248m a.s.l., mean accumulation rate 134 g cm-2 yr-1, Lys Glacier, Mt. Rosa, Italy). The low concentration of mineral particles, obtained by filtering each firn core melted samples on Nuclepore membranes in a 1000 class clean room, required a specific procedure to prepare the samples necessary to the successful collection of the XAS data. The firn samples were decontaminated in clean room under laminar flow bench by means of a ceramic knife and discarding the external part of the cores. Analyses of the insoluble particle content were performed by particle counter Beckman CounterãMultisizer III in order to defined concentration and size distribution of particles in each samples. A dedicated HV experimental chamber, devoted to the realization of XAS experiments on very low absorber concentration samples, was developed and realized in the framework of the CryoAlp collaboration at IMONT, the Italian National Institute for Mountains. The original experimental setup, thanks to the presence of an in-vacuum sample micromanipulator and special sample alignment and docking system installed for these experiments at the Stanford Synchrotron Radiation Laboratory at the beamline 6-2, allows both normal-incidence X-ray Fluorescence detection using a Ketek SDD detector having an energy resolution of about 150 eV and extremely low energy detection limit, and Total X-ray Reflection Fluorescence and Absorption Spectroscopy measurements. The high quality of the XANES experiments performed, using both normal incidence and Total Reflection XAS measurements, allowed recognizing iron-inclusion mineral fractions. Samples for Total Reflection XAS measurements were prepared just for this kind of measurements by depositing the insoluble mineral dust on clean Si wafer substrates. In addition, the XANES spectra show clear differences, corresponding to different samples mineral iron hosts, demonstrating that with this fully non-distructive technique, new information about the dust mineralogy at very low concentration can be performed. The analysis is then complementary to other well established techniques like XRD and PIXE.

Photophysical Properties of II-VI Semiconductor Nanocrystals

NASA Astrophysics Data System (ADS)

Gong, Ke

As it is well known, semiconductor nanocrystals (also called quantum dots, QDs) are being actively pursued for use in many different types of luminescent optical materials. These materials include the active media for luminescence downconversion in artificial lighting, lasers, luminescent solar concentrators and many other applications. Chapter 1 gives general introduction of QDs, which describe the basic physical properties and optical properties. Based on the experimental spectroscopic study, a semiquantitative method-effective mass model is employed to give theoretical prediction and guide. The following chapters will talks about several topics respectively. A predictive understanding of the radiative lifetimes is therefore a starting point for the understanding of the use of QDs for these applications. Absorption intensities and radiative lifetimes are fundamental properties of any luminescent material. Meantime, achievement of high efficiency with high working temperature and heterostructure fabrication with manipulation of lattice strain are not easy and need systematic investigation. To make accurate connections between extinction coefficients and radiative recombination rates, chapter 2 will consider three closely related aspects of the size dependent spectroscopy of II-VI QDs. First, it will consider the existing literature on cadmium selenide (CdSe) QD absorption spectra and extinction coefficients. From these results and fine structure considerations Boltzmann weighted radiative lifetimes are calculated. These lifetimes are compared to values measured on very high quality CdSe and CdSe coated with zinc selenide (ZnSe) shells. Second, analogous literature data are analyzed for cadmium telluride (CdTe) nanocrystals and compared to lifetimes measured for very high quality QDs. Furthermore, studies of the absorption and excitation spectra and measured radiative lifetimes for CdTe/CdSe Type-II core/shell QDs are reported. These results are also analyzed in terms of a Boltzmann population of exciton sublevels and calculated electron and hole wave functions. Much of the absorption data and fine structure calculations are already in the literature. These results are combined with new measurements of radiative lifetimes and electron-hole overlap calculations to produce an integrated picture of the II-VI QD spectroscopic fundamentals. Finally, we adopt recent synthetic advances to make very monodisperse zincblende CdSe/CdS quantum dots having near-unity photoluminescence quantum yields (PLQYs). Due the absence of nonradiative decay pathways, accurate values of the radiative lifetimes can be obtained from time resolved PL measurements. Radiative lifetimes can also be obtained from the Einstein relations, using the static absorption spectra and the relative thermal populations in the angular momentum sublevels. One of the inputs into these calculations is the shell thickness, and it is useful to be able to determine shell thickness from spectroscopic measurements. We use an empirically corrected effective mass model to produce a "map" of exciton wavelength as a function of core size and shell thickness. These calculations use an elastic continuum model and the known lattice and elastic constants to include the effect of lattice strain on the band gap energy. Radiative lifetimes calculated both experimentally and theoretically are checked and the size dependence is compared to previous studied Type-I, II and single component particles. However, it is not enough to just understanding these basic photophysics of absorption and emission. The emission intensities (related to QYs) also change with changes of the temperature. The temperature dependent PLs of II-VI QDs is extensively studied, but most of this work is at low temperatures. Temperatures well above ambient are of interest to lighting applications and in this regime both the reversible and irreversible loss of quantum yield (thermal quenching) are serious impediments to the implementation of QDs in commercial devices. Chapter 3 will elucidate the mechanism of static thermal quenching, in which the reduction of QYs does not affect the PL decay kinetics, on CdSe, CdTe and CdSe/ZnSe QDs as a function of particle sizes/shapes, surface composition and surface ligands. Through systematic experiments, this part of the dissertation discusses several possible mechanisms (e.g. structural, activated excited state, and electronic charging) and examines which the dominant cause for loss of QY at high temperature is. The more practical step is to develop the synthetic method of highly luminescent and stable core/shell QDs with minimum thermal quenching, which greatly enhance the energy efficiency of light emitting and photovoltaic devices. As the nonradiative Auger processed are induced by surface charging described in chapter 3, static and time-resolved fluorescence and high and low power transient absorption results on CdSe/CdS and CdSe/ZnSe core/shell particles are presented in chapter 4. Two CdS shell thicknesses were examined and all of the particles had either octadecylamine (ODA) and tributylphosphine (TBP) or just ODA ligands. The results can be understood in terms of a mechanism in which there is a thermal equilibrium between electrons being in the valence band or in chalcogenide localized surface states. Thermal promotion of a valence band electron to a surface state leaves the particle core positively charged. Photon absorption when the particle is in this state results in a positive trion, which undergoes a fast Auger recombination, making the particle nonluminescent. A lack of TBP ligands results in more empty surface orbitals and therefore shifts the equilibrium toward surface trapped electrons and hence trion formation. Low- and high-power transient absorption measurements give the trion and biexciton lifetimes and the ratio of the trion to biexciton Auger lifetimes are examined and compared to the degeneracies of Auger pathways. We also study the shell thickness and composition dependence of Auger times, which is compared to the scaling factors of effective volume and electron-hole overlap considerations. Core/shell QDs often exhibit much higher luminescence quantum yields (QYs), more stability, and are depicted as having a nearly spherical core and a shell of very nearly uniform thickness, which results in a very simple picture of surface passivation. The uniformity of the shell is crucial in obtaining QDs with well passivated surfaces. However, transmission electron microscope (TEM) images disprove the ideal situation. Defects and thickness inhomogeneity in shell materials are treated qualitatively as an analog to film thickness inhomogeneity in epitaxially grown thin films. More quantitatively, the extent to which the shell thickness of core/shell particles is constant can be determined by time-resolved PL studies that measure the dynamics of hole tunneling to acceptors that are adsorbed on the shell surface due that tunneling rates varies strongly with core-acceptor separation. Careful analysis of the hole transfer kinetics reveals the extent of shell thickness inhomogeneity, however, it may be complicated by the distribution of numbers of adsorbed acceptors. All the considerations can be incorporated into a model we establish in Chapter 5for the distribution of measured hole tunneling rates. From this analysis the distribution of shell thicknesses can be extracted from the luminescence kinetic results. This approach is therefore a sensitive measure of the distribution of tunneling distances. Thus, any defects or structural irregularities that allow the hole acceptors to adsorb closer to the particle core increases the hole tunneling rate and can be detected and quantified. A quantitative treatment of the lattice strain energy in determining the shell morphology of CdSe/CdS core/shell nanoparticles is presented in chapter 5. We use the inhomogeneity in hole tunneling rates through the shell to adsorbed hole acceptors to quantify the extent of shell thickness inhomogeneity. The results can be understood in terms of a model based on elastic continuum calculations, which indicate that the lattice strain energy depends on both core size and shell thickness. This model assumes thermodynamic equilibrium, i.e., that the shell morphology corresponds to a minimum total (lattice strain plus surface) energy. Comparison with the experimental results indicates that CdSe/CdS nanoparticles undergo an abrupt transition from smooth to rough shells when the total lattice strain energy exceeds about 27eV or the strain energy density exceeds 0.59 eV/nm2. The predictions of this model are not followed for CdSe/CdS nanoparticles when the shell is deposited at very low temperature and therefore equilibrium is not established. The effects of lattice strain on the spectroscopy and photoluminescence quantum yields of zincblende CdSe/CdS core/shell quantum dots are examined. The quantum yields are measured as a function of core size and shell thickness. High quantum yields are achieved as long as the lattice strain energy density is below ~0.85 eV/nm2, which is considerably greater than the limiting value of 0.59 eV/nm2 for thermodynamicstability of a smooth, defect free shell, as previously reported in chapter 5. Thus, core/shell quantum dots having strain energy densities between 0.59 and 0.85 eV/nm2 can have very high PL QYs, but are metastable with respect to surface defect formation. Such metastable core/shell QDs can be produced by shell deposition at comparatively low temperatures (< 140 °C). Annealing of these particles causes partial loss of core pressure, and a red shift of the spectrum.

Stratified NH and ND emission in the prestellar core 16293E in L1689N

NASA Astrophysics Data System (ADS)

Bacmann, A.; Daniel, F.; Caselli, P.; Ceccarelli, C.; Lis, D.; Vastel, C.; Dumouchel, F.; Lique, F.; Caux, E.

2016-03-01

Context. High degrees of deuterium fractionation are commonly found in cold prestellar cores and in the envelopes around young protostars. As it brings strong constraints to chemical models, deuterium chemistry is often used to infer core history or molecule formation pathways. Whereas a large number of observations are available regarding interstellar deuterated stable molecules, relatively little is known about the deuteration of hydride radicals, as their fundamental rotational transitions are at high frequencies where the atmosphere is mostly opaque. Aims: Nitrogen hydride radicals are important species in nitrogen chemistry, as they are thought to be related to ammonia formation. Observations have shown that ammonia is strongly deuterated, with [NH2D]/[NH3] ~ 10%. Models predict similarly high [ND]/[NH] ratios, but so far only one observational determination of this ratio is available, towards the envelope of the protostar IRAS16293-2422. To test model predictions, we aim here to determine [ND]/[NH] in a dense, starless core. Methods: We observed NH and ND in 16293E with the HIFI spectrometer on board the Herschel Space Observatory as part of the CHESS guaranteed time key programme, and derived the abundances of these two species using a non local thermodynamic equilibrium radiative transfer model. Results: Both NH and ND are detected in the source, with ND in emission and NH in absorption against the continuum that arises from the cold dust emission. Our model shows, however, that the ND emission and the NH absorption originate from different layers in the cloud, as further evidenced by their different velocities. In the central region of the core, we can set a lower limit to the [ND]/[NH] ratio of ≳2%. This estimate is consistent with recent pure gas-phase models of nitrogen chemistry. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

The microstructure and photoluminescence of ZnO-MoS2 core shell nano-materials

NASA Astrophysics Data System (ADS)

Yu, H.; Liu, C. M.; Huang, X. Y.; Lei, M. Y.

2017-01-01

In this paper, ZnO-MoS2-FT (FT is the fabrication temperature of MoS2) core shell nano-material samples (with ZnO as a core and MoS2 as a shell material) were fabricated on ITO substrate using hydrothermal method. The crystal structure, morphology, optical absorption and photoluminescence (PL) of samples were investigated. Compared with that of pure ZnO nanorods, ZnO-MoS2-FT samples show an enhanced light absorption. In addition, ultraviolet (UV) and visible (Vis) PL intensity of ZnO-MoS2-FT samples excited by 325 nm laser are greatly weakened. The UV PL peak position is not changed obviously. However, the Vis PL peak position is changed visibly. The Vis PL of ZnO-MoS2-FT samples under UV excitation indicates that the ratio of oxygen interstitial to oxygen vacancy is decreased. The suppression of UV PL of ZnO-MoS2-FT samples may be related to the weakening of crystal quality of ZnO, easier separation of electron-hole pairs, enhancement of light absorption, and newly introduced defects in the interface between ZnO and MoS2. Under 514 nm laser excitation, the PL peak position of ZnO-MoS2-FT samples has a red shift with FT being increased from 80 to 160 °C. The influence of excitation power (EP) on the PL of ZnO-MoS2-FT samples was also investigated. The PL of ZnO-MoS2-FT samples have a red shift with EP being increased. This may be due to the sample temperature is increased with EP, resulting an enhancement of electron-phonon interaction. A schematic diagram of charge generation and transfer is presented to understand the mechanism of PL of ZnO-MoS2 under UV and Vis excitation.

Modeling and Observations of Massive Binaries with the B[e] Phenomenon

NASA Astrophysics Data System (ADS)

Lobel, A.; Martayan, C.; Mehner, A.; Groh, J. H.

2017-02-01

We report a long-term high-resolution spectroscopic monitoring program of LBVs and candidate LBVs with Mercator-HERMES. Based on 7 years of data, we recently showed that supergiant MWC 314 is a (Galactic) semi-detached eccentric binary with stationary permitted and forbidden emission lines in the optical and near-IR region. MWC 314 is a luminous and massive probable LBV star showing a strongly orbitally-modulated wind variability. We observe discrete absorption components in P Cyg He I lines signaling large-scale wind structures. In 2014 XMM observed X-rays indicating strong wind-wind collision in the close binary system (a ≃1 AU). A VLT-NACO imaging survey recently revealed that MWC 314 is a triple hierarchical system. We present a 3-D non-LTE radiative transfer model of the extended asymmetric wind structure around the primary B0 supergiant for modeling the orbital variability of P Cyg absorption (v∞˜1200 km s-1) in He I lines. An analysis of the HERMES monitoring spectra of the Galactic LBV star MWC 930 however does not show clear indications of a spectroscopic binary. The detailed long-term spectroscopic variability of this massive B[e] star is very similar to the spectroscopic variability of the prototypical blue hypergiant S Dor in the LMC. We observe prominent P Cyg line shapes in MWC 930 that temporarily transform into split absorption line cores during variability phases of its S Dor cycle over the past decade with a brightening in V of ˜ 1.2 mag. The line splitting phenomenon is very similar to the split metal line cores observed in pulsating Yellow Hypergiants ρ Cas (F-K Ia+) and HR 8752 (A-K Ia+) with [Ca II] and [N II] emission lines. We propose the line core splitting in MWC 930 is due to optically thick central line emission produced in the inner ionized wind region becoming mechanically shock-excited with the increase of R* and decrease of Teff of the LBV.

Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star.

PubMed

Arcavi, Iair; Howell, D Andrew; Kasen, Daniel; Bildsten, Lars; Hosseinzadeh, Griffin; McCully, Curtis; Wong, Zheng Chuen; Katz, Sarah Rebekah; Gal-Yam, Avishay; Sollerman, Jesper; Taddia, Francesco; Leloudas, Giorgos; Fremling, Christoffer; Nugent, Peter E; Horesh, Assaf; Mooley, Kunal; Rumsey, Clare; Cenko, S Bradley; Graham, Melissa L; Perley, Daniel A; Nakar, Ehud; Shaviv, Nir J; Bromberg, Omer; Shen, Ken J; Ofek, Eran O; Cao, Yi; Wang, Xiaofeng; Huang, Fang; Rui, Liming; Zhang, Tianmeng; Li, Wenxiong; Li, Zhitong; Zhang, Jujia; Valenti, Stefano; Guevel, David; Shappee, Benjamin; Kochanek, Christopher S; Holoien, Thomas W-S; Filippenko, Alexei V; Fender, Rob; Nyholm, Anders; Yaron, Ofer; Kasliwal, Mansi M; Sullivan, Mark; Blagorodnova, Nadja; Walters, Richard S; Lunnan, Ragnhild; Khazov, Danny; Andreoni, Igor; Laher, Russ R; Konidaris, Nick; Wozniak, Przemek; Bue, Brian

2017-11-08

Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.

Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arcavi, Iair; Howell, D. Andrew; Kasen, Daniel

Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae.more » The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.« less

Structural and Optical Properties of Core-Shell TiO2/CdS Prepared by Chemical Bath Deposition

NASA Astrophysics Data System (ADS)

Al-Jawad, Selma M. H.

2017-10-01

Titanium dioxide (TiO2) nanorod arrays (NRAs) sensitized with cadmium sulfide (CdS) nanoparticles (NPs) were deposited by chemical bath deposition (CBD). TiO2 NRAs were also obtained by using the same method on glass substrates coated with fluorine-doped tin oxide (FTO). The structure of the FTO/TiO2/CdS core-shell was characterized by x-ray diffraction (XRD), atomic force microscopy, scanning electron microscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy, photoluminescence, and photoelectrocatalysis of FTO/TiO2 and FTO/TiO2/CdS. The FTO/TiO2 conformed to anatase and rutile phase structures for different pH values and also with annealing. XRD patterns of the FTO/TiO2/CdS sample exhibited two peaks corresponding to hexagonal (100) and (101) for CdS. Scanning electron micrographs showed nanorod structures for the TiO2 thin films deposited at a pH value equal 0.7. Optical results showed the CdS deposited on nanorod TiO2 exhibited increased absorption ability in the visible light, indicating an increased photocatalytic activity for TiO2/CdS core-shell nanorods in the visible light. When illuminated with a UV-Vis light source, the TiO2/CdS core-shell films displayed high responses. A composite exists between the TiO2 nanostructure and CdS NPs because the film absorbs the incident light located in both the visible and UV-Vis regions. A higher response to UV-Vis light was attained with the use of TiO2 NRAs/CdS NPs films prepared by CBD. This approach offers a technique for fabricating photoelectrodes.

Clad-pumped Er-nanoparticle-doped fiber laser (Conference Presentation)

NASA Astrophysics Data System (ADS)

Baker, Colin C.; Friebele, E. Joseph; Rhonehouse, Daniel L.; Marcheschi, Barbara A.; Peele, John R.; Kim, Woohong; Sanghera, Jasbinder S.; Zhang, Jun; Chen, Youming; Pattnaik, Radha K.; Dubinskii, Mark

2017-03-01

Erbium-doped fiber lasers are attractive for directed energy weapons applications because they operate in a wavelength region that is both eye-safer and a window of high atmospheric transmission. For these applications a clad-pumped design is desirable, but the Er absorption must be high because of the areal dilution of the doped core vs. the pump cladding. High Er concentrations typically lead to Er ion clustering, resulting in quenching and upconversion. Nanoparticle (NP) doping of the core overcomes these problems by physically surrounding the Er ions with a cage of Al and O in the NP, which keeps them separated to minimize excited state energy transfer. A significant issue is obtaining high Er concentrations without the NP agglomeration that degrades the optical properties of the fiber core. We have developed the process for synthesizing stable Er-NP suspension which have been used to fabricate EDFs with Er concentrations >90 dB/m at 1532 nm. Matched clad fibers have been evaluated in a core-pumped MOPA with pump and signal wavelengths of 1475 and 1560 nm, respectively, and efficiencies of 72% with respect to absorbed pump have been obtained. We have fabricated both NP- and solution-doped double clad fibers, which have been measured in a clad-pumped laser testbed using a 1532 nm pump. The 1595 nm laser efficiency of the NP-doped fiber was 47.7%, which is high enough for what is believed to be the first laser experiment with the cladding pumped, NP-doped fiber. Further improvements are likely with a shaped cladding and new low-index polymer coatings with lower absorption in the 1500 - 1600 nm range.

Synthesis of Photoresponsive Dual NIR Two-Photon Absorptive [60]Fullerene Triads and Tetrads

PubMed Central

Jeon, Seaho; Wang, Min; Tan, Loon-Seng; Cooper, Thomas; Hamblin, Michael R.; Chiang, Long Y.

2013-01-01

Broadband nonlinear optical (NLO) organic nanostructures exhibiting both ultrafast photoresponse and a large cross-section of two-photon absorption throughout a wide NIR spectrum may make them suitable for use as nonlinear biophotonic materials. We report here the synthesis and characterization of two C60-(antenna)x analogous compounds as branched triad C60(>DPAF-C18)(>CPAF-C2M) and tetrad C60(>DPAF-C18)(>CPAF-C2M)2 nanostructures. These compounds showed approximately equal extinction coefficients of optical absorption over 400–550 nm that corresponds to near-IR two-photon based excitation wavelengths at 780–1,100 nm. Accordingly, they may be utilized as potential precursor candidates to the active-core structures of photosensitizing nanodrugs for 2γ-PDT in the biological optical window of 800–1,050 nm. PMID:23941881

Adjustable 3-D structure with enhanced interfaces and junctions towards microwave response using FeCo/C core-shell nanocomposites.

PubMed

Li, Daoran; Liang, Xiaohui; Liu, Wei; Ma, Jianna; Zhang, Yanan; Ji, Guangbin; Meng, Wei

2017-12-01

In this work, the 3-D honeycomb-like FeCo/C nanocomposites were synthesized through the carbon thermal reduction under an inert atmosphere. The enhanced microwave absorption properties of the composites were mainly attributed to the unique three dimensional structure of the FeCo/C nanocomposites, abundant interfaces and junctions, and the appropriate impedance matching. The Cole-Cole semicircles proved the sufficient dielectric relaxation process. The sample calcinated at 600°C for 4h showed the best microwave absorption properties. A maximum reflection loss of -54.6dB was achieved at 10.8GHz with a thickness of 2.3mm and the frequency bandwidth was as large as 5.3GHz. The results showed that the as-prepared FeCo/C nanocomposite could be a potential candidate for microwave absorption. Copyright © 2017 Elsevier Inc. All rights reserved.

Dynamical core-hole screening in the x-ray absorption spectra of hydrogenated carbon nanotubes and graphene

NASA Astrophysics Data System (ADS)

Wessely, O.; Katsnelson, M. I.; Nilsson, A.; Nikitin, A.; Ogasawara, H.; Odelius, M.; Sanyal, B.; Eriksson, O.

2007-10-01

We have calculated the electronic structure and the x-ray absorption (XA) spectrum of a hydrogenated single graphite plane, in order to simulate recent experimental results on hydrogenated single wall carbon nanotubes (SWCNT) as well as hydrogenated graphene. We find that the presence of H induces a substantial component of sp3 bonding and as a result the π and π* components to the electronic structure vanish. We have calculated a theoretical x-ray absorption spectrum using a multiband version of the Mahan-Nozières-De Dominicis theory. By making a fitting of the XA signal of C atoms that have H attached to them and C atoms without H in the vicinity we obtain a good representation of the experimental data and we can draw the conclusion that in the experiments [A. Nikitin , Phys. Rev. Lett. 95, 225507 (2005)] some 35-50 % H have been absorbed in the SWCNT.

Rational Improvement of Molar Absorptivity Guided by Oscillator Strength: A Case Study with Furoindolizine-Based Core Skeleton.

PubMed

Lee, Youngjun; Jo, Ala; Park, Seung Bum

2015-12-21

The rational improvement of photophysical properties can be highly valuable for the discovery of novel organic fluorophores. Using our new design strategy guided by the oscillator strength, we developed a series of full-color-tunable furoindolizine analogs with improved molar absorptivity through the fusion of a furan ring into the indolizine-based Seoul fluorophore. The excellent correlation between the computable values (oscillator strength and theoretical S0 -S1 energy gap) and photophysical properties (molar absorptivity and emission wavelength) confirmed the effectualness of our design strategy. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution Non-Commercial NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Investigation of third-order nonlinear and optical power limiting properties of terphenyl derivatives

NASA Astrophysics Data System (ADS)

Kamath, Laxminarayana; Manjunatha, K. B.; Shettigar, Seetharam; Umesh, G.; Narayana, B.; Samshuddin, S.; Sarojini, B. K.

2014-03-01

A series of new chalcones containing terphenyl as a core and with different functional groups has been successfully synthesized by Claisen-Schmidt condensation method in search of new nonlinear optical (NLO) materials. Molecular structural characterization for the compounds was achieved by FTIR and single crystal X-ray diffraction. The third-order NLO absorption and refraction coefficients were simultaneously determined by Z-scan technique. The measurements were performed at 532 nm with 7 ns laser pulses using a Nd:YAG laser in solution form. The Z-scan experiments reveal that the compounds exhibit strong nonlinear refraction coefficient of the order 10-11 esu and the molecular two photon absorption cross section is 10-46 cm4 s/photon. The results also show that the structures of the compounds have great impact on NLO properties. The compounds show optical power limiting behavior due to two-photon absorption (TPA).

Single and multi-layered core-shell structures based on ZnO nanorods obtained by aerosol assisted chemical vapor deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sáenz-Trevizo, A.; Amézaga-Madrid, P.; Pizá-Ruiz, P.

2015-07-15

Core–shell nanorod structures were prepared by a sequential synthesis using an aerosol assisted chemical vapor deposition technique. Several samples consisting of ZnO nanorods were initially grown over TiO{sub 2} film-coated borosilicate glass substrates, following the synthesis conditions reported elsewhere. Later on, a uniform layer consisting of individual Al, Ni, Ti or Fe oxides was grown onto ZnO nanorod samples forming the so-called single MO{sub x}/ZnO nanorod core–shell structures, where MO{sub x} was the metal oxide shell. Additionally, a three-layer core–shell sample was developed by growing Fe, Ti and Fe oxides alternately, onto the ZnO nanorods. The microstructure of the core–shellmore » materials was characterized by grazing incidence X-ray diffraction, scanning and transmission electron microscopy. Energy dispersive X-ray spectroscopy was employed to corroborate the formation of different metal oxides. X-ray diffraction outcomes for single core–shell structures showed solely the presence of ZnO as wurtzite and TiO{sub 2} as anatase. For the multi-layered shell sample, the existence of Fe{sub 2}O{sub 3} as hematite was also detected. Morphological observations suggested the existence of an outer material grown onto the nanorods and further microstructural analysis by HR-STEM confirmed the development of core–shell structures in all cases. These studies also showed that the individual Al, Fe, Ni and Ti oxide layers are amorphous; an observation that matched with X-ray diffraction analysis where no apparent extra oxides were detected. For the multi-layered sample, the development of a shell consisting of three different oxide layers onto the nanorods was found. Overall results showed that no alteration in the primary ZnO core was produced during the growth of the shells, indicating that the deposition technique used herein was and it is suitable for the synthesis of homogeneous and complex nanomaterials high in quality and purity. In addition, materials absorptance determined from the total transmittance and reflectance spectra revealed a broader absorption interval including visible light, indicating potential uses of these nanostructures on solar energy appliances. - Graphical abstract: Display Omitted - Highlights: • Uniform ZnO nanorods (core)–metal oxide (shell) were obtained sequentially by AACVD. • Shells were structured of homogeneous single or multi-layered non-mixed metal oxides. • ZnO nanorod core was preserved during the shell synthesis. • Optical absorptance revealed visible interval absorption for FeO{sub x} shell samples. • Materials can be suitable for photocatalytic or photovoltaic applications.« less

The Dye Sensitized Photoelectrosynthesis Cell (DSPEC) for Solar Water Splitting and CO2 Reduction

NASA Astrophysics Data System (ADS)

Meyer, Thomas; Alibabaei, Leila; Sherman, Benjamin; Sheridan, Matthew; Ashford, Dennis; Lapides, Alex; Brennaman, Kyle; Nayak, Animesh; Roy, Subhangi; Wee, Kyung-Ryang; Gish, Melissa; Meyer, Jerry; Papanikolas, John

The dye-sensitized photoelectrosynthesis cell (DSPEC) integrates molecular level light absorption and catalysis with the bandgap properties of stable oxide materials such as TiO2 and NiO. Excitation of surface-bound chromophores leads to excited state formation and rapid electron or hole injection into the conduction or valence bands of n or p-type oxides. Addition of thin layers of TiO2 or NiO on the surfaces of mesoscopic, nanoparticle films of semiconductor or transparent conducting oxides to give core/shell structures provides a basis for accumulating multiple redox equivalents at catalysts for water oxidation or CO2 reduction. UNC EFRC Center for Solar Fuels, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001011.

The role of interfacial metal silicates on the magnetism in FeCo/SiO 2 and Fe 49% Co 49% V 2% /SiO 2 core/shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desautels, R. D.; Freeland, J. W.; Rowe, M. P.

2015-05-07

We have investigated the role of spontaneously formed interfacial metal silicates on the magnetism of FeCo/SiO2 and Fe49%Co49%V2%/SiO2 core/shell nanoparticles. Element specific x-ray absorption and photoelectron spectroscopy experiments have identified the characteristic spectral features of metallic iron and cobalt from within the nanoparticle core. In addition, metal silicates of iron, cobalt, and vanadium were found to have formed spontaneously at the interface between the nanoparticle core and silica shell. X-ray magnetic circular dichroism experiments indicated that the elemental magnetism was a result of metallic iron and cobalt with small components from the iron, cobalt, and vanadium silicates. Magnetometry experiments havemore » shown that there was no exchange bias loop shift in the FeCo nanoparticles; however, exchange bias from antiferromagnetic vanadium oxide was measured in the V-doped nanoparticles. These results showed clearly that the interfacial metal silicates played a significant role in the magnetism of these core/shell nanoparticles, and that the vanadium percolated from the FeCo-cores into the SiO2-based interfacial shell.« less

Photogenerated carriers transport behaviors in L-cysteine capped ZnSe core-shell quantum dots

NASA Astrophysics Data System (ADS)

Shan, Qingsong; Li, Kuiying; Xue, Zhenjie; Lin, Yingying; Yin, Hua; Zhu, Ruiping

2016-02-01

The photoexcited carrier transport behavior of zinc selenide (ZnSe) quantum dots (QDs) with core-shell structure is studied because of their unique photoelectronic characteristics. The surface photovoltaic (SPV) properties of self-assembled ZnSe/ZnS/L-Cys core-shell QDs were probed via electric field induced surface photovoltage and transient photovoltage (TPV) measurements supplemented by Fourier transform infrared, laser Raman, absorption, and photoluminescence spectroscopies. The ZnSe QDs displayed p-type SPV characteristics with a broader stronger SPV response over the whole ultraviolet-to-near-infrared range compared with those of other core-shell QDs in the same group. The relationship between the SPV phase value of the QDs and external bias was revealed in their SPV phase spectrum. The wide transient photovoltage response region from 3.3 × 10-8 to 2 × 10-3 s was closely related to the long diffusion distance of photoexcited free charge carriers in the interfacial space-charge region of the QDs. The strong SPV response corresponding to the ZnSe core mainly originated from an obvious quantum tunneling effect in the QDs.

Comparison of antibacterial activities of Ag@TiO2 and Ag@SiO2 core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Dhanalekshmi, K. I.; Meena, K. S.

2014-07-01

Core-shell type Ag@TiO2 nanoparticles were prepared by one pot simultaneous reduction of AgNO3 and hydrolysis of Ti (IV) isopropoxide and Ag@SiO2 core-shell nanoparticles were prepared by Stober's method. They were characterized by absorption, XRD, and HR-TEM techniques. XRD patterns show the presence of anatase form of TiO2 and amorphous form of SiO2 and the noble metal (Ag). High resolution transmission electron microscopy measurements revealed that their size is below 50 nm. The antibacterial properties of Ag@TiO2 and Ag@SiO2 core-shell nanoparticles against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were examined by the agar diffusion method. As a result E. coli and S. aureus were shown to be substantially inhibited by Ag@TiO2 and Ag@SiO2 core-shell nanoparticles. These results demonstrated that TiO2 and SiO2 supported on the surface of Ag NPs without aggregation was proved to have enhanced antibacterial activity.

Comparison of antibacterial activities of Ag@TiO2 and Ag@SiO2 core-shell nanoparticles.

PubMed

Dhanalekshmi, K I; Meena, K S

2014-07-15

Core-shell type Ag@TiO2 nanoparticles were prepared by one pot simultaneous reduction of AgNO3 and hydrolysis of Ti (IV) isopropoxide and Ag@SiO2 core-shell nanoparticles were prepared by Stober's method. They were characterized by absorption, XRD, and HR-TEM techniques. XRD patterns show the presence of anatase form of TiO2 and amorphous form of SiO2 and the noble metal (Ag). High resolution transmission electron microscopy measurements revealed that their size is below 50 nm. The antibacterial properties of Ag@TiO2 and Ag@SiO2 core-shell nanoparticles against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were examined by the agar diffusion method. As a result E. coli and S. aureus were shown to be substantially inhibited by Ag@TiO2 and Ag@SiO2 core-shell nanoparticles. These results demonstrated that TiO2 and SiO2 supported on the surface of Ag NPs without aggregation was proved to have enhanced antibacterial activity. Copyright © 2014 Elsevier B.V. All rights reserved.

Role of relaxation and time-dependent formation of x-ray spectra

NASA Astrophysics Data System (ADS)

Privalov, Timofei; Gel'mukhanov, Faris; Ågren, Hans

2001-10-01

A fundamental problem of x-ray spectroscopy is the role of relaxation of the electronic subsystem in the field of the transient core hole. The main intention of the present study is to explore the dynamics due to core-hole relaxation in the whole time domain, and to find out how it is manifested in finite molecular systems in comparison with solids. A technique is developed based on a reduction of the Noziéres-De Dominicis equation to a set of linear algebraic equations. The developed time-dependent formalism is applied to a numerical investigation of a one-dimensional tight-binding model. The formation of the x-ray profiles is explored on the real time scale, and the role of interaction with the core hole, band filling, and the final-state rule are investigated for systems of different size. The formation of spectra of the infinite translational invariant system is studied by extensions of the finite systems. We found that the dynamics of finite systems, like molecules, differs qualitatively from solids: Contrary to the latter the time lapse of the Noziéres-De Dominicis domain for finite systems is squeezed between the inverse bandwidth and the revival time, which is proportional to the system size. For small molecules this means that there is no time for a ``Mahan-Noziéres-De Dominicis singularity'' to develop. Comparison with the strict solution of the Noziéres-De Dominicis equation shows that the adiabatic approximation describes x-ray absorption and emission considerably better than the fast approximation. This explains the suppression of the relaxation effects in x-ray emission of, e.g., gas phase and surface adsorbed molecules, but also that these effects are essential for the absorption case. There is still a quantitative distinction between the adiabatic approximation and the strict approach, which becomes more important for larger systems. Adopting the so-called finite state rule by von Barth and Grossman also for molecules, an almost complete numerical agreement between this rule and the strict x-ray-absorption and emission profiles for systems of different sizes is obtained. The simulations indicate that the final-state rule correction is important mainly near the absorption edge and at the top of the emission band.

Photocatalytic activity of Ag/ZnO core-shell nanoparticles with shell thickness as controlling parameter under green environment

NASA Astrophysics Data System (ADS)

Rajbongshi, Himanshu; Bhattacharjee, Suparna; Datta, Pranayee

2017-02-01

Plasmonic Ag/ZnO core-shell nanoparticles have been synthesized via a simple two-step wet chemical method for application in Photocatalysis. The morphology, size, crystal structure, composition and optical properties of the nanoparticles are investigated by x-ray diffraction, transmission electron microscopy (TEM), FTIR spectroscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy and photoluminescence (PL) spectroscopy. The shell thicknesses are varied by varying the concentration of zinc nitrate hexa-hydrate and triethanolamine. The ZnO shell coating over Ag core enhances the charge separation, whereas the larger shell thickness and increased refractive index of surrounding medium cause red shifts of surface Plasmon resonance (SPR) peak of Ag core. The photoluminescence (PL) spectra of Ag/ZnO core-shell show that the larger shell thickness quenches the near band edge UV emission of ZnO. The electrochemical impedance spectra (EIS) i.e. Nyquist plots also confirm the higher charge transfer efficiency of the Ag/ZnO core-shell nanoparticles. The Photocatalytic activities of Ag/ZnO core-shell nanoparticles are investigated by the degradation of methylene blue (MB) dye under direct sunlight irradiation. Compared to pure ZnO nanoparticles (NPs), Ag/ZnO core-shell NPs display efficient sunlight plasmonic photocatalytic activity because of the influence of SPR of Ag core and the electron sink effect. The photocatalytic activity of Ag/ZnO core-shell NPs is found to be enhanced with increase in shell thickness.

Controlled release of cyclosporine A self-nanoemulsifying systems from osmotic pump tablets: near zero-order release and pharmacokinetics in dogs.

PubMed

Zhang, Xi; Yi, Yueneng; Qi, Jianping; Lu, Yi; Tian, Zhiqiang; Xie, Yunchang; Yuan, Hailong; Wu, Wei

2013-08-16

It is very important to enhance the absorption simultaneously while designing controlled release delivery systems for poorly water-soluble and poorly permeable drugs (BCS IV). In this study, controlled release of cyclosporine (CyA) was achieved by the osmotic release strategy taking advantage of the absorption-enhancing capacity of self-nanoemulsifying drug delivery systems (SNEDDSs). The liquid SNEDDS consisting of Labrafil M 1944CS, Transcutol P and Cremophor EL was absorbed by the osmotic tablet core excipients (sucrose, lactose monohydrate, polyethylene oxide, and partly pregelatinized starch) and then transformed into osmotic tablets. Near zero-order release could be achieved for CyA-loaded nanoemulsions reconstituted from the SNEDDS. In general, the influencing factor study indicated that the release rate increased with increase of inner osmotic pressure, ratio of osmotic agent to suspending agent, content of pore-forming agent, and size of release orifice, whereas the thickness of the membrane impeded the release of CyA nanoemulsion. Pharmacokinetic study showed steady blood CyA profiles with prolonged Tmax and MRT, and significantly reduced Cmax for self-nanoemulsifying osmotic pump tablet (SNEOPT) in comparison with highly fluctuating profiles of the core tablet and Sandimmune Neoral(®). However, similar oral bioavailability was observed for either controlled release or non-controlled release formulations. It was concluded that simultaneous controlling on CyA release and absorption-enhancing had been achieved by a combination of osmotic tablet and SNEDDS. Copyright © 2013 Elsevier B.V. All rights reserved.

Dynamics of the formation and loss of boron atoms in a H2/B2H6 microwave plasma

NASA Astrophysics Data System (ADS)

Duluard, C. Y.; Aubert, X.; Sadeghi, N.; Gicquel, A.

2016-09-01

For further improvements in doped-diamond deposition technology, an understanding of the complex chemistry in H2/CH4/B2H6 plasmas is of general importance. In this context, a H2/B2H6 plasma ignited by microwave power in a near resonant cavity at high pressure (100-200 mbar) is studied to measure the B-atom density in the ground state. The discharge is ignited in the gas mixture (0-135 ppm B2H6 in H2) by a 2.45 GHz microwave generator, leading to the formation of a hemispheric plasma core, surrounded by a faint discharge halo filling the remaining reactor volume. Measurements with both laser induced fluorescence and resonant absoption with a boron hollow cathode lamp indicate that the B-atom density is higher in the halo than in the plasma core. When the absorption line-of-sight is positioned in the halo, the absorption is so strong that the upper detection limit is reached. To understand the mechanisms of creation and loss of boron atoms, time-resolved absorption measurements have been carried out in a pulsed plasma regime (10 Hz, duty cycle 50%). The study focuses on the influence of the total pressure, the partial pressure of B2H6, as well as the source power, on the growth and decay rates of boron atoms when the plasma is turned off.

SAXS analysis of single- and multi-core iron oxide magnetic nanoparticles

PubMed Central

Szczerba, Wojciech; Costo, Rocio; Morales, Maria del Puerto; Thünemann, Andreas F.

2017-01-01

This article reports on the characterization of four superparamagnetic iron oxide nanoparticles stabilized with dimercaptosuccinic acid, which are suitable candidates for reference materials for magnetic properties. Particles p1 and p2 are single-core particles, while p3 and p4 are multi-core particles. Small-angle X-ray scattering analysis reveals a lognormal type of size distribution for the iron oxide cores of the particles. Their mean radii are 6.9 nm (p1), 10.6 nm (p2), 5.5 nm (p3) and 4.1 nm (p4), with narrow relative distribution widths of 0.08, 0.13, 0.08 and 0.12. The cores are arranged as a clustered network in the form of dense mass fractals with a fractal dimension of 2.9 in the multi-core particles p3 and p4, but the cores are well separated from each other by a protecting organic shell. The radii of gyration of the mass fractals are 48 and 44 nm, and each network contains 117 and 186 primary particles, respectively. The radius distributions of the primary particle were confirmed with transmission electron microscopy. All particles contain purely maghemite, as shown by X-ray absorption fine structure spectroscopy. PMID:28381973

Control of optical bandgap energy and optical absorption coefficient by geometric parameters in sub-10 nm silicon-nanodisc array structure

NASA Astrophysics Data System (ADS)

Fairuz Budiman, Mohd; Hu, Weiguo; Igarashi, Makoto; Tsukamoto, Rikako; Isoda, Taiga; Itoh, Kohei M.; Yamashita, Ichiro; Murayama, Akihiro; Okada, Yoshitaka; Samukawa, Seiji

2012-02-01

A sub-10 nm, high-density, periodic silicon-nanodisc (Si-ND) array has been fabricated using a new top-down process, which involves a 2D array bio-template etching mask made of Listeria-Dps with a 4.5 nm diameter iron oxide core and damage-free neutral-beam etching (Si-ND diameter: 6.4 nm). An Si-ND array with an SiO2 matrix demonstrated more controllable optical bandgap energy due to the fine tunability of the Si-ND thickness and diameter. Unlike the case of shrinking Si-ND thickness, the case of shrinking Si-ND diameter simultaneously increased the optical absorption coefficient and the optical bandgap energy. The optical absorption coefficient became higher due to the decrease in the center-to-center distance of NDs to enhance wavefunction coupling. This means that our 6 nm diameter Si-ND structure can satisfy the strict requirements of optical bandgap energy control and high absorption coefficient for achieving realistic Si quantum dot solar cells.

PNNL Report on the Development of Bench-scale CFD Simulations for Gas Absorption across a Wetted Wall Column

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Chao; Xu, Zhijie; Lai, Canhai

This report is prepared for the demonstration of hierarchical prediction of carbon capture efficiency of a solvent-based absorption column. A computational fluid dynamics (CFD) model is first developed to simulate the core phenomena of solvent-based carbon capture, i.e., the CO2 physical absorption and chemical reaction, on a simplified geometry of wetted wall column (WWC) at bench scale. Aqueous solutions of ethanolamine (MEA) are commonly selected as a CO2 stream scrubbing liquid. CO2 is captured by both physical and chemical absorption using highly CO2 soluble and reactive solvent, MEA, during the scrubbing process. In order to provide confidence bound on themore » computational predictions of this complex engineering system, a hierarchical calibration and validation framework is proposed. The overall goal of this effort is to provide a mechanism-based predictive framework with confidence bound for overall mass transfer coefficient of the wetted wall column (WWC) with statistical analyses of the corresponding WWC experiments with increasing physical complexity.« less

Alternative difference analysis scheme combining R -space EXAFS fit with global optimization XANES fit for X-ray transient absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhan, Fei; Tao, Ye; Zhao, Haifeng

Time-resolved X-ray absorption spectroscopy (TR-XAS), based on the laser-pump/X-ray-probe method, is powerful in capturing the change of the geometrical and electronic structure of the absorbing atom upon excitation. TR-XAS data analysis is generally performed on the laser-on minus laser-off difference spectrum. Here, a new analysis scheme is presented for the TR-XAS difference fitting in both the extended X-ray absorption fine-structure (EXAFS) and the X-ray absorption near-edge structure (XANES) regions.R-space EXAFS difference fitting could quickly provide the main quantitative structure change of the first shell. The XANES fitting part introduces a global non-derivative optimization algorithm and optimizes the local structure changemore » in a flexible way where both the core XAS calculation package and the search method in the fitting shell are changeable. The scheme was applied to the TR-XAS difference analysis of Fe(phen) 3spin crossover complex and yielded reliable distance change and excitation population.« less

Simulation of X-ray transient absorption for following vibrations in coherently ionized F2 molecules

NASA Astrophysics Data System (ADS)

Dutoi, Anthony D.; Leone, Stephen R.

2017-01-01

Femtosecond and attosecond X-ray transient absorption experiments are becoming increasingly sophisticated tools for probing nuclear dynamics. In this work, we explore and develop theoretical tools needed for interpretation of such spectra,in order to characterize the vibrational coherences that result from ionizing a molecule in a strong IR field. Ab initio data for F2 is combined with simulations of nuclear dynamics, in order to simulate time-resolved X-ray absorption spectra for vibrational wavepackets after coherent ionization at 0 K and at finite temperature. Dihalogens pose rather difficult electronic structure problems, and the issues encountered in this work will be reflective of those encountered with any core-valence excitation simulation when a bond is breaking. The simulations reveal a strong dependence of the X-ray absorption maximum on the locations of the vibrational wave packets. A Fourier transform of the simulated signal shows features at the overtone frequencies of both the neutral and the cation, which reflect spatial interferences of the vibrational eigenstates. This provides a direct path for implementing ultrafast X-ray spectroscopic methods to visualize coherent nuclear dynamics.

Transition metal atomic multiplets in the ligand K-edge x-ray absorption spectra and multiple oxidation states in the L2,3 emission of strongly correlated compounds

NASA Astrophysics Data System (ADS)

Jiménez-Mier, J.; Olalde-Velasco, P.; Yang, W.-L.; Denlinger, J.

2014-07-01

We present results that show that atomic multiplet ligand field calculations are in very good agreement with experimental x-ray absorption spectra at the L2,3 edge of transition metal (TM) di-fluorides (MF2, MCrCu). For chromium more than one TM oxidation state is needed to achieve such an agreement. We also show that signature of the TM atomic multiplet can be found at the pre-edge of the fluorine K-edge x-ray absorption spectra. TM atomic multiplet ligand field calculations with a structureless core hole show good agreement with the observed pre-edges in the experimental fluorine absorption spectra. Preliminary results for the comparison between calculated and experimental resonant x-ray emission spectra for nominal CrF2 with more than one oxidation state indicate the presence of three chromium oxidation states in the bulk.

Simultaneous sensing of temperature, CO, and CO2 in a scramjet combustor using quantum cascade laser absorption spectroscopy

NASA Astrophysics Data System (ADS)

Spearrin, R. M.; Goldenstein, C. S.; Schultz, I. A.; Jeffries, J. B.; Hanson, R. K.

2014-07-01

A mid-infrared laser absorption sensor was developed for gas temperature and carbon oxide (CO, CO2) concentrations in high-enthalpy, hydrocarbon combustion flows. This diagnostic enables non-intrusive, in situ measurements in harsh environments produced by hypersonic propulsion ground test facilities. The sensing system utilizes tunable quantum cascade lasers capable of probing the fundamental mid-infrared absorption bands of CO and CO2 in the 4-5 µm wavelength domain. A scanned-wavelength direct absorption technique was employed with two lasers, one dedicated to each species, free-space fiber-coupled using a bifurcated hollow-core fiber for remote light delivery on a single line of sight. Scanned-wavelength modulation spectroscopy with second-harmonic detection was utilized to extend the dynamic range of the CO measurement. The diagnostic was field-tested on a direct-connect scramjet combustor for ethylene-air combustion. Simultaneous, laser-based measurements of carbon monoxide and carbon dioxide provide a basis for evaluating combustion completion or efficiency with temporal and spatial resolution in practical hydrocarbon-fueled engines.

Alternative difference analysis scheme combining R-space EXAFS fit with global optimization XANES fit for X-ray transient absorption spectroscopy.

PubMed

Zhan, Fei; Tao, Ye; Zhao, Haifeng

2017-07-01

Time-resolved X-ray absorption spectroscopy (TR-XAS), based on the laser-pump/X-ray-probe method, is powerful in capturing the change of the geometrical and electronic structure of the absorbing atom upon excitation. TR-XAS data analysis is generally performed on the laser-on minus laser-off difference spectrum. Here, a new analysis scheme is presented for the TR-XAS difference fitting in both the extended X-ray absorption fine-structure (EXAFS) and the X-ray absorption near-edge structure (XANES) regions. R-space EXAFS difference fitting could quickly provide the main quantitative structure change of the first shell. The XANES fitting part introduces a global non-derivative optimization algorithm and optimizes the local structure change in a flexible way where both the core XAS calculation package and the search method in the fitting shell are changeable. The scheme was applied to the TR-XAS difference analysis of Fe(phen) 3 spin crossover complex and yielded reliable distance change and excitation population.

VLBI survey of compact broad absorption line quasars with balnicity index BI = 0

NASA Astrophysics Data System (ADS)

Cegłowski, M.; Kunert-Bajraszewska, M.; Roskowiński, C.

2015-06-01

We present high-resolution observations, using both the European VLBI Network (EVN) at 1.7 GHz and the Very Long Baseline Array (VLBA) at 5 and 8.4 GHz, to image radio structures of 14 compact sources classified as broad absorption line (BAL) quasars based on the absorption index (AI). All sources but one were resolved, with the majority showing core-jet morphology typical for radio-loud quasars. We discuss in detail the most interesting cases. The high radio luminosities and small linear sizes of the observed objects indicate they are strong young active galactic nuclei. Nevertheless, the distribution of the radio-loudness parameter, log RI, of a larger sample of AI quasars shows that the objects observed by us constitute the most luminous, small subgroup of the AI population. Additionally, we report that for the radio-loudness parameter, the distribution of AI quasars and that for those selected using the traditional balnicity index differ significantly. Strong absorption is connected with lower log RI and thus probably larger viewing angles. Since the AI quasars have on average larger log RI, the orientation can mean that we see them less absorbed. However, we suggest that the orientation is not the only parameter that affects the detected absorption. That the strong absorption is associated with the weak radio emission is equally important and worth exploring.

In situ aerosol optics in Reno, NV, USA during and after the summer 2008 California wildfires and the influence of absorbing and non-absorbing organic coatings on spectral light absorption

NASA Astrophysics Data System (ADS)

Gyawali, M.; Arnott, W. P.; Lewis, K.; Moosmüller, H.

2009-10-01

Hundreds of wildfires in Northern California were sparked by lightning during the summer of 2008, resulting in downwind smoke for the months of June and July. Comparisons are reported for aerosol optics measurements in Reno, Nevada made during the very smoky month of July and the relatively clean month of August. Photoacoustic instruments equipped with integrating nephelometers were used to measure aerosol light scattering and absorption coefficients at wavelengths of 405 nm and 870 nm, revealing a strong variation of aerosol light absorption with wavelength. Insight on fuels burned is gleaned from comparison of Ångström exponents of absorption (AEA) versus single scattering albedo (SSA) of the ambient measurements with laboratory biomass smoke measurements for many fuels. Measurements during the month of August, which were largely unaffected by fire smoke, exhibit surprisingly low AEA for aerosol light absorption when the SSA is highest, again likely as a consequence of the underappreciated wavelength dependence of aerosol light absorption by particles coated with non-absorbing organic and inorganic matter. Coated sphere calculations were used to show that AEA as large as 1.6 are possible for wood smoke even with non-absorbing organic coatings on black carbon cores, suggesting care be exercised when diagnosing AEA.

Time-resolved photoluminescence study of CdSe/CdMnS/CdS core/multi-shell nanoplatelets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, J. R.; Department of Physics, State University of New York, University at Buffalo, Buffalo, New York 14260; Delikanli, S.

2016-06-13

We used photoluminescence spectroscopy to resolve two emission features in CdSe/CdMnS/CdS and CdSe/CdS core/multi-shell nanoplatelet heterostructures. The photoluminescence from the magnetic sample has a positive circular polarization with a maximum centered at the position of the lower energy feature. The higher energy feature has a corresponding signature in the absorption spectrum; this is not the case for the low-energy feature. We have also studied the temporal evolution of these features using a pulsed-excitation/time-resolved photoluminescence technique to investigate their corresponding recombination channels. A model was used to analyze the temporal dynamics of the photoluminescence which yielded two distinct timescales associated withmore » these recombination channels. The above results indicate that the low-energy feature is associated with recombination of electrons with holes localized at the core/shell interfaces; the high-energy feature, on the other hand, is excitonic in nature with the holes confined within the CdSe cores.« less

The molecular core in G34.3 + 0.2 - Millimeter interferometric observations of HCO(+), H(C-13)N, H(C-15)N, and SO

NASA Technical Reports Server (NTRS)

Carral, Patricia; Welch, William J.

1992-01-01

This study presents high-resolution observations of the molecular core in the star-forming region G34.3 + 0.2. Maps at 6-arcsec resolution of emission and absorption of the J = 1 - 0 transitions of HCO(+), H (C-13)N, H(C-15)N, and of the 2(2) - 1(1) transition of SO were obtained in addition to a map of the 3.4-mm continuum emission from the compact H II component. The HCL(+) emission toward G34.3 + 0.2 traces a warm molecular core about 0.9 pc in size. Emission from H (C-13)N is detected over about 0.3 pc. The cometary H II region lies near the edge of the molecular core. The blueshift of the radio recombination lines with respect to the molecular emission suggests that gas from the H II region is accelerated in a champagne flow caused by a steep gradient in the ambient gas density.

Radiative conductivity and abundance of post-perovskite in the lowermost mantle

NASA Astrophysics Data System (ADS)

Lobanov, Sergey S.; Holtgrewe, Nicholas; Lin, Jung-Fu; Goncharov, Alexander F.

2017-12-01

Thermal conductivity of the lowermost mantle governs the heat flow out of the core energizing planetary-scale geological processes. Yet, there are no direct experimental measurements of thermal conductivity at relevant pressure-temperature conditions of Earth's core-mantle boundary. Here we determine the radiative conductivity of post-perovskite at near core-mantle boundary conditions by optical absorption measurements in a laser-heated diamond anvil cell. Our results show that the radiative conductivity of Mg0.9Fe0.1SiO3 post-perovskite (∼1.1 W/m/K) is almost two times smaller than that of bridgmanite (∼2.0 W/m/K) at the base of the mantle. By combining this result with the present-day core-mantle heat flow and available estimations on the lattice thermal conductivity we conclude that post-perovskite is at least as abundant as bridgmanite in the lowermost mantle which has profound implications for the dynamics of the deep Earth.

Glycerol capped PbS/CdS core/shell nanoparticles at different molar ratio and its application in biosensors: An optical properties study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, D., E-mail: ddasphy014@gmail.com; Hussain, A. M. P.

2016-05-06

Glycerol capped PbS/CdS core/shell type nanoparticles fabricated with two different molar ratios are characterized for study of structural and optical properties. The X-ray diffraction (XRD) pattern exhibits cubic phased polycrystalline nanocrystals. The calculated grain sizes from Williamson-Hall plot were found to be around 6 nm with increased strain. HRTEM investigation confirms the formation of core/shell nanostructures and the sizes of the particles were found to be around 7 nm which is in good agreement with the results of the W-H plot. An increase of band gap with the decrease in precursor concentration is confirmed from the blue shift in the absorption spectramore » and also from Tauc plot. A clear blue shifted intense emission is observed in the photoluminescence spectra with decrease in particle size. Intense luminescence from the core/shell nanostructure may be applied in bio labelling and biosensors.« less

The effects of staggered bandgap in the InP/CdSe and CdSe/InP core/shell quantum dots.

PubMed

Kim, Sunghoon; Park, Jaehyun; Kim, Sungwoo; Jung, Won; Sung, Jaeyoung; Kim, Sang-Wook

2010-06-15

New type-II structures of CdSe/InP and InP/CdSe core-shell nanocrystals which have staggered bandgap alignment were fabricated. Using a simple model for the wave function for electrons and holes in InP/CdSe and CdSe/InP core/shell nanocrystals showed the wave function of the electron and hole spread into the shell, respectively. The probability density of the InP/CdSe and CdSe/InP core/shell QDs also showed a similar tendency. As a result, the structure exhibits increased delocalization of electrons and holes, leading to a red-shift in absorption and emission. Quantum yield increased in the InP/CdSe, however decreased in the CdSe/InP. The reason may be due to the surface trap and high activation barrier for de-trapping in the InP shell. 2010 Elsevier Inc. All rights reserved.

Effect of Zinc Incorporation on the Performance of Red Light Emitting InP Core Nanocrystals.

PubMed

Xi, Lifei; Cho, Deok-Yong; Besmehn, Astrid; Duchamp, Martial; Grützmacher, Detlev; Lam, Yeng Ming; Kardynał, Beata E

2016-09-06

This report presents a systematic study on the effect of zinc (Zn) carboxylate precursor on the structural and optical properties of red light emitting InP nanocrystals (NCs). NC cores were assessed using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), energy-dispersive X-ray spectroscopy (EDX), and high-resolution transmission electron microscopy (HRTEM). When moderate Zn:In ratios in the reaction pot were used, the incorporation of Zn in InP was insufficient to change the crystal structure or band gap of the NCs, but photoluminescence quantum yield (PLQY) increased dramatically compared with pure InP NCs. Zn was found to incorporate mostly in the phosphate layer on the NCs. PL, PLQY, and time-resolved PL (TRPL) show that Zn carboxylates added to the precursors during NC cores facilitate the synthesis of high-quality InP NCs by suppressing nonradiative and sub-band-gap recombination, and the effect is visible also after a ZnS shell is grown on the cores.

FDTD analysis of body-core temperature elevation in children and adults for whole-body exposure.

PubMed

Hirata, Akimasa; Asano, Takayuki; Fujiwara, Osamu

2008-09-21

The temperature elevations in anatomically based human phantoms of an adult and a 3-year-old child were calculated for radio-frequency whole-body exposure. Thermoregulation in children, however, has not yet been clarified. In the present study, we developed a computational thermal model of a child that is reasonable for simulating body-core temperature elevation. Comparison of measured and simulated temperatures revealed thermoregulation in children to be similar to that of adults. Based on this finding, we calculated the body-core temperature elevation in a 3-year-old child and an adult for plane-wave exposure at the basic restriction in the international guidelines. The body-core temperature elevation in the 3-year-old child phantom was 0.03 degrees C at a whole-body-averaged specific absorption rate of 0.08 W kg(-1), which was 35% smaller than in the adult female. This difference is attributed to the child's higher body surface area-to-mass ratio.

A theoretical and experimental benchmark study of core-excited states in nitrogen

DOE PAGES

Myhre, Rolf H.; Wolf, Thomas J. A.; Cheng, Lan; ...

2018-02-14

The high resolution near edge X-ray absorption fine structure spectrum of nitrogen displays the vibrational structure of the core-excited states. This makes nitrogen well suited for assessing the accuracy of different electronic structure methods for core excitations. We report high resolution experimental measurements performed at the SOLEIL synchrotron facility. These are compared with theoretical spectra calculated using coupled cluster theory and algebraic diagrammatic construction theory. The coupled cluster singles and doubles with perturbative triples model known as CC3 is shown to accurately reproduce the experimental excitation energies as well as the spacing of the vibrational transitions. In conclusion, the computationalmore » results are also shown to be systematically improved within the coupled cluster hierarchy, with the coupled cluster singles, doubles, triples, and quadruples method faithfully reproducing the experimental vibrational structure.« less

Exploring the effects of photon correlations from thermal sources on bacterial photosynthesis

NASA Astrophysics Data System (ADS)

Manrique, Pedro D.; Caycedo-Soler, Felipe; De Mendoza, Adriana; Rodríguez, Ferney; Quiroga, Luis; Johnson, Neil F.

Thermal light sources can produce photons with strong spatial correlations. We study the role that these correlations might potentially play in bacterial photosynthesis. Our findings show a relationship between the transversal distance between consecutive absorptions and the efficiency of the photosynthetic process. Furthermore, membranes where the clustering of core complexes (so-called RC-LH1) is high, display a range where the organism profits maximally from the spatial correlation of the incoming light. By contrast, no maximum is found for membranes with low core-core clustering. We employ a detailed membrane model with state-of-the-art empirical inputs. Our results suggest that the organization of the membrane's antenna complexes may be well-suited to the spatial correlations present in an natural light source. Future experiments will be needed to test this prediction.

A theoretical and experimental benchmark study of core-excited states in nitrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Myhre, Rolf H.; Wolf, Thomas J. A.; Cheng, Lan

The high resolution near edge X-ray absorption fine structure spectrum of nitrogen displays the vibrational structure of the core-excited states. This makes nitrogen well suited for assessing the accuracy of different electronic structure methods for core excitations. We report high resolution experimental measurements performed at the SOLEIL synchrotron facility. These are compared with theoretical spectra calculated using coupled cluster theory and algebraic diagrammatic construction theory. The coupled cluster singles and doubles with perturbative triples model known as CC3 is shown to accurately reproduce the experimental excitation energies as well as the spacing of the vibrational transitions. In conclusion, the computationalmore » results are also shown to be systematically improved within the coupled cluster hierarchy, with the coupled cluster singles, doubles, triples, and quadruples method faithfully reproducing the experimental vibrational structure.« less

Gadolinium chelate coated gold nanoparticles as contrast agents for both X-ray computed tomography and magnetic resonance imaging.

PubMed

Alric, Christophe; Taleb, Jacqueline; Le Duc, Géraldine; Mandon, Céline; Billotey, Claire; Le Meur-Herland, Alice; Brochard, Thierry; Vocanson, Francis; Janier, Marc; Perriat, Pascal; Roux, Stéphane; Tillement, Olivier

2008-05-07

Functionalized gold nanoparticles were applied as contrast agents for both in vivo X-ray and magnetic resonance imaging. These particles were obtained by encapsulating gold cores within a multilayered organic shell which is composed of gadolinium chelates bound to each other through disulfide bonds. The contrast enhancement in MRI stems from the presence of gadolinium ions which are entrapped in the organic shell, whereas the gold core provides a strong X-ray absorption. This study revealed that these particles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in the lungs, spleen, and liver.

Application of Ni-Oxide@TiO₂ Core-Shell Structures to Photocatalytic Mixed Dye Degradation, CO Oxidation, and Supercapacitors.

PubMed

Lee, Seungwon; Lee, Jisuk; Nam, Kyusuk; Shin, Weon Gyu; Sohn, Youngku

2016-12-20

Performing diverse application tests on synthesized metal oxides is critical for identifying suitable application areas based on the material performances. In the present study, Ni-oxide@TiO₂ core-shell materials were synthesized and applied to photocatalytic mixed dye (methyl orange + rhodamine + methylene blue) degradation under ultraviolet (UV) and visible lights, CO oxidation, and supercapacitors. Their physicochemical properties were examined by field-emission scanning electron microscopy, X-ray diffraction analysis, Fourier-transform infrared spectroscopy, and UV-visible absorption spectroscopy. It was shown that their performances were highly dependent on the morphology, thermal treatment procedure, and TiO₂ overlayer coating.

Refined potentials for rare gas atom adsorption on rare gas and alkali-halide surfaces

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Heinbockel, J. H.; Outlaw, R. A.

1985-01-01

The utilization of models of interatomic potential for physical interaction to estimate the long range attractive potential for rare gases and ions is discussed. The long range attractive force is calculated in terms of the atomic dispersion properties. A data base of atomic dispersion parameters for rare gas atoms, alkali ion, and halogen ions is applied to the study of the repulsive core; the procedure for evaluating the repulsive core of ion interactions is described. The interaction of rare gas atoms on ideal rare gas solid and alkali-halide surfaces is analyzed; zero coverage absorption potentials are derived.

Direct observation of ring-opening dynamics in strong-field ionized selenophene using femtosecond inner-shell absorption spectroscopy

DOE PAGES

Lackner, Florian; Chatterley, Adam S.; Pemmaraju, C. D.; ...

2016-12-21

Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (C 4H 4Se). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (~58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field inducedmore » ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se + ions within an overall time scale of approximately 170 fs. In this study, we propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ 1 = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se + and ring-open cations within an additional τ 2 = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. In conclusion, the findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural rearrangements.« less

Synthesis and cytotoxicity study of magnesium ferrite-gold core-shell nanoparticles.

PubMed

Nonkumwong, Jeeranan; Pakawanit, Phakkhananan; Wipatanawin, Angkana; Jantaratana, Pongsakorn; Ananta, Supon; Srisombat, Laongnuan

2016-04-01

In this work, the core-magnesium ferrite (MgFe2O4) nanoparticles were prepared by hydrothermal technique. Completed gold (Au) shell coating on the surfaces of MgFe2O4 nanoparticles was obtained by varying core/shell ratios via a reduction method. Phase identification, morphological evolution, optical properties, magnetic properties and cytotoxicity to mammalian cells of these MgFe2O4 core coated with Au nanoparticles were examined by using a combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, UV-visible spectroscopy (UV-vis), vibrating sample magnetometry and resazurin microplate assay techniques. In general, TEM images revealed different sizes of the core-shell nanoparticles generated from various core/shell ratios and confirmed the completed Au shell coating on MgFe2O4 core nanoparticles via suitable core/shell ratio with particle size less than 100 nm. The core-shell nanoparticle size and the quality of coating influence the optical properties of the products. The UV-vis spectra of complete coated MgFe2O4-Au core-shell nanoparticles exhibit the absorption bands in the near-Infrared (NIR) region indicating high potential for therapeutic applications. Based on the magnetic property measurement, it was found that the obtained MgFe2O4-Au core-shell nanoparticles still exhibit superparamagnetism with lower saturation magnetization value, compared with MgFe2O4 core. Both of MgFe2O4 and MgFe2O4-Au core-shell also showed in vitro non-cytotoxicity to mouse areola fibroblast (L-929) cell line. Copyright © 2015 Elsevier B.V. All rights reserved.

UV Absorption Spectroscopy in Water-Filled Antiresonant Hollow Core Fibers for Pharmaceutical Detection.

PubMed

Nissen, Mona; Doherty, Brenda; Hamperl, Jonas; Kobelke, Jens; Weber, Karina; Henkel, Thomas; Schmidt, Markus A

2018-02-06

Due to a worldwide increased use of pharmaceuticals and, in particular, antibiotics, a growing number of these substance residues now contaminate natural water resources and drinking supplies. This triggers a considerable demand for low-cost, high-sensitivity methods for monitoring water quality. Since many biological substances exhibit strong and characteristic absorption features at wavelengths shorter than 300 nm, UV spectroscopy presents a suitable approach for the quantitative identification of such water-contaminating species. However, current UV spectroscopic devices often show limited light-matter interaction lengths, demand sophisticated and bulky experimental infrastructure which is not compatible with microfluidics, and leave large fractions of the sample analyte unused. Here, we introduce the concept of UV spectroscopy in liquid-filled anti-resonant hollow core fibers, with large core diameters and lengths of approximately 1 m, as a means to overcome such limitations. This extended light-matter interaction length principally improves the concentration detection limit by two orders of magnitude while using almost the entire sample volume-that is three orders of magnitude smaller compared to cuvette based approaches. By integrating the fibers into an optofluidic chip environment and operating within the lowest experimentally feasible transmission band, concentrations of the application-relevant pharmaceutical substances, sulfamethoxazole (SMX) and sodium salicylate (SS), were detectable down to 0.1 µM (26 ppb) and 0.4 µM (64 ppb), respectively, with the potential to reach significantly lower detection limits for further device integration.

Enhanced intersystem crossing in core-twisted aromatics.

PubMed

Nagarajan, Kalaivanan; Mallia, Ajith R; Muraleedharan, Keerthi; Hariharan, Mahesh

2017-03-01

We describe the design, bottom-up synthesis and X-ray single crystal structure of systematically twisted aromatics 1c and 2d for efficient intersystem crossing. Steric congestion at the cove region creates a nonplanar geometry that induces a significant yield of triplet excited states in the electron-poor core-twisted aromatics 1c and 2d . A systematic increase in the number of twisted regions in 1c and 2d results in a concomitant enhancement in the rate and yield of intersystem crossing, monitored using femtosecond and nanosecond transient absorption spectroscopy. Time-resolved absorption spectroscopic measurements display enhanced triplet quantum yields ( Φ T = 10 ± 1% for 1c and Φ T = 30 ± 2% for 2d ) in the twisted aromatics when compared to a negligible Φ T (<1%) in the planar analog 3c . Twist-induced spin-orbit coupling via activated out-of-plane C-H/C 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 C vibrations can facilitate the formation of triplet excited states in twisted aromatics 1c and 2d , in contrast to the negligible intersystem crossing in the planar analog 3c . The ease of synthesis, high solubility, access to triplet excited states and strong electron affinity make such imide functionalized core-twisted aromatics desirable materials for organic electronics such as solar cells.

UV Absorption Spectroscopy in Water-Filled Antiresonant Hollow Core Fibers for Pharmaceutical Detection

PubMed Central

Nissen, Mona; Doherty, Brenda; Hamperl, Jonas; Kobelke, Jens; Weber, Karina; Henkel, Thomas; Schmidt, Markus A.

2018-01-01

Due to a worldwide increased use of pharmaceuticals and, in particular, antibiotics, a growing number of these substance residues now contaminate natural water resources and drinking supplies. This triggers a considerable demand for low-cost, high-sensitivity methods for monitoring water quality. Since many biological substances exhibit strong and characteristic absorption features at wavelengths shorter than 300 nm, UV spectroscopy presents a suitable approach for the quantitative identification of such water-contaminating species. However, current UV spectroscopic devices often show limited light-matter interaction lengths, demand sophisticated and bulky experimental infrastructure which is not compatible with microfluidics, and leave large fractions of the sample analyte unused. Here, we introduce the concept of UV spectroscopy in liquid-filled anti-resonant hollow core fibers, with large core diameters and lengths of approximately 1 m, as a means to overcome such limitations. This extended light-matter interaction length principally improves the concentration detection limit by two orders of magnitude while using almost the entire sample volume—that is three orders of magnitude smaller compared to cuvette based approaches. By integrating the fibers into an optofluidic chip environment and operating within the lowest experimentally feasible transmission band, concentrations of the application-relevant pharmaceutical substances, sulfamethoxazole (SMX) and sodium salicylate (SS), were detectable down to 0.1 µM (26 ppb) and 0.4 µM (64 ppb), respectively, with the potential to reach significantly lower detection limits for further device integration. PMID:29415468

Optical switching property of electromagnetically induced transparency in a Λ system

NASA Astrophysics Data System (ADS)

Zhang, Lianshui; Wang, Jian; Feng, Xiaomin; Yang, Lijun; Li, Xiaoli; Zhao, Min

2008-12-01

In this paper we study the coherent transient property of a Λ-three-level system (Ωd = 0) and a quasi- Λ -four-level system (Ωd>0). Optical switching of the probe field can be achieved by applying a pulsed coupling field or rf field. In Λ -shaped three-level system, when the coupling field was switched on, there is a almost total transparency of the probe field and the time required for the absorption changing from 90% to 10% of the maximum absorption is 2.9Γ0 (Γ0 is spontaneous emission lifetime). When the coupling field was switched off, there is an initial increase of the probe field absorption and then gradually evolves to the maximum of absorption of the two-level absorption, the time required for the absorption of the system changing from 10% to 90% is 4.2Γ0. In four-level system, where rf driving field is used as switching field, to achieve the same depth of the optical switching, the time of the optical switching is 2.5Γ0 and 6.1Γ0, respectively. The results show that with the same depth of the optical switching, the switch-on time of the four-level system is shorter than that of the three-level system, while the switch-off time of the four-level system is longer. The depth of the optical switching of the four-level system was much larger than that of the three-level system, where the depth of the optical switching of the latter is merely 14.8% of that of the former. The speed of optical switching of the two systems can be increased by the increase of Rabi frequency of coupling field or rf field.

Broad absorption-line time variability in the QSO CSO 203

NASA Technical Reports Server (NTRS)

Barlow, Thomas A.; Junkkarinen, Vesa T.; Burbidge, E. M.; Weymann, Ray J.; Morris, Simon L.; Korista, Kirk T.

1992-01-01

We present spectroscopy of the BALQSO CSO 203 during four epochs over a 17-month time span. These data show three distinct levels in the broad absorption lines (BALs) of Si IV 1397A and C IV 1549A. We also note possible variations in the N V 1240A and Al III 1857A absorption troughs. A broad-band monitoring effort during this period shows that the continuum level remained constant to within 10 percent. We argue that the triggering mechanism for the absorption-line changes is most likely synchronous with the continuum source photons; however, no correlation with the central source has yet been found. The observed variations are consistent with changes in the ionization level in the broad absorption-line region (BALR). We discuss possible mechanisms for these changes and the implications for the structure of the BALR.

Quantum Monte Carlo for the x-ray absorption spectrum of pyrrole at the nitrogen K-edge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zubarev, Dmitry Yu.; Austin, Brian M.; Lester, William A. Jr.

Fixed-node diffusion Monte Carlo (FNDMC) is used to simulate the x-ray absorption spectrum of a gas-phase pyrrole molecule at the nitrogen K-edge. Trial wave functions for core-excited states are constructed from ground-state Kohn-Sham determinants substituted with singly occupied natural orbitals from configuration interaction with single excitations calculations of the five lowest valence-excited triplet states. The FNDMC ionization potential (IP) is found to lie within 0.3 eV of the experimental value of 406.1 {+-} 0.1 eV. The transition energies to anti-bonding virtual orbitals match the experimental spectrum after alignment of IP values and agree with the existing assignments.

Preparation and laser properties of Yb3+-doped microstructure fiber based on hydrolysis-melting technique

NASA Astrophysics Data System (ADS)

Wang, Chao

2017-01-01

The Yb3+-doped silica glass was prepared by the SiCl4 hydrolysis doping and powder melting technology based on high frequency plasma. The absorption and emission characteristics of the Yb3+-doped silica glass are studied at room temperature. The integrated absorption cross section, stimulated emission cross section and fluorescence lifetime are calculated to be 8.56×104 pm3, 1.39 pm2 and 0.56 ms, respectively. The Yb3+-doped microstructure fiber (MSF) was also fabricated by using the Yb3+-doped silica glass as fiber core. What's more, the laser properties of the Yb3+-doped MSF are studied.

The vertical structure of Arctic haze as determined from airborne net-flux radiometer measurements

NASA Technical Reports Server (NTRS)

Ackerman, T. P.; Valero, F. P. J.

1984-01-01

From net-flux radiometer measurements and model results, the vertical layer structure is deduced of the Arctic haze encountered during two of the AGASP flights. The total value of the absorption optical depth is found to be on the order of 0.065 for both flights, with the majority of the absorbing aerosol concentrated in the lowest 1.6 km of the atmosphere. A comparison of these results with measurements of the carbon concentration leads to a value of the specific absorption of carbon of 24 sq m g. While higher than expected, this value is shown to be consistent with an internally-mixed aerosol of carbon cores and sulfate shells.

The potential effect of metallothionein 2A - 5 A/G single nucleotide polymorphism on blood cadmium, lead, zinc and copper levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kayaalti, Zeliha, E-mail: kayaalti@ankara.edu.tr; Aliyev, Vugar; Soeylemezoglu, Tuelin

2011-10-01

Metallothioneins (MTs) are low molecular weight, cysteine-rich, metal-binding proteins. Because of their rich thiol groups, MTs bind to the biologically essential metals and perform these metals' homeostatic regulations; absorb the heavy metals and assist with their transportation and extraction. The aim of this study was to investigate the association between the metallothionein 2A (MT2A) core promoter region - 5 A/G single nucleotide polymorphism (SNP) and Cd, Pb, Zn and Cu levels in the blood samples. MT2A polymorphism was determined by the standard polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique using the 616 blood samples and the genotype frequencies weremore » found as 86.6% homozygote typical (AA), 12.8% heterozygote (AG) and 0.6% homozygote atypical (GG). Metal levels were analyzed by dual atomic absorption spectrophotometer system and the average levels of Cd, Pb, Zn and Cu in the blood samples were 1.69 {+-} 1.57 ppb, 30.62 {+-} 14.13 ppb, 0.98 {+-} 0.49 ppm and 1.04 {+-} 0.45 ppm, respectively. As a result; highly statistically significant associations were detected between the - 5 A/G core promoter region SNP in the MT2A gene and Cd, Pb and Zn levels (p = 0.004, p = 0.012 and p = 0.002, respectively), but no association was found with Cu level (p = 0.595). Individuals with the GG genotype had statistically lower Zn level and higher Cd and Pb levels in the blood samples than individuals with AA and AG genotypes. This study suggests that having the GG genotype individuals may be more sensitive for the metal toxicity and they should be more careful about protecting their health against the toxic effects of the heavy metals. - Highlights: > MT2A -5A/G SNP has strong effect on the Cd, Pb and Zn levels in the blood. > MT2A GG individuals should be more careful for their health against metal toxicity. > This SNP might be considered as a biomarker for risk of disease related to metals.« less

Does core mobility of lumbar total disc arthroplasty influence sagittal and frontal intervertebral displacement? Radiologic comparison with fixed-core prosthesis

PubMed Central

Delécrin, Joël; Allain, Jérôme; Beaurain, Jacques; Steib, Jean-Paul; Chataigner, Hervé; Aubourg, Lucie; Huppert, Jean; Ameil, Marc; Nguyen, Jean-Michel

2009-01-01

Background An artificial disc prosthesis is thought to restore segmental motion in the lumbar spine. However, it is reported that disc prosthesis can increase the intervertebral translation (VT). The concept of the mobile-core prosthesis is to mimic the kinematic effects of the migration of the natural nucleus and therefore core mobility should minimize the VT. This study explored the hypothesis that core translation should influence VT and that a mobile core prosthesis may facilitate physiological motion. Methods Vertebral translation (measured with a new method presented here), core translation, range of motion (ROM), and distribution of flexion-extension were measured on flexion-extension, neutral standing, and lateral bending films in 89 patients (63 mobile-core [M]; 33 fixed-core [F]). Results At L4-5 levels the VT with M was lower than with F and similar to the VT of untreated levels. At L5-S1 levels the VT with M was lower than with F but was significantly different compared to untreated levels. At M levels a strong correlation was found between VT and core translation; the VT decreases as the core translation increases. At F levels the VT increases as the ROM increases. No significant difference was found between the ROM of untreated levels and levels implanted with either M or F. Regarding the mobility distribution with M and F we observed a deficit in extension at L5-S1 levels and a similar distribution at L4-5 levels compared to untreated levels. Conclusion The intervertebral mobility was different between M and F. The M at L4-5 levels succeeded to replicate mobility similar to L4-5 untreated levels. The M at L5-S1 succeeded in ROM, but failed regarding VT and mobility distribution. Nevertheless M minimized VT at L5-S1 levels. The F increased VT at both L4-5 and L5-S1. Clinical Relevance This study validates the concept that the core translation of an artificial lumbar disc prosthesis minimizes the VT. PMID:25802632

In situ aerosol optics in Reno, NV, USA during and after the summer 2008 California wildfires and the influence of aerosol coatings

NASA Astrophysics Data System (ADS)

Gyawali, M.; Arnott, W. P.; Lewis, K.; Moosmüller, H.

2009-06-01

Hundreds of wildfires in Northern California were sparked by lightning during the summer of 2008, resulting in downwind smoke for the months of June and July. Comparisons are reported for aerosol optics measurements in Reno Nevada made during the very smoky summer month of July and the relatively clean month of August. Photoacoustic instruments equipped with integrating nephelometers were used to measure aerosol light scattering and absorption at wavelengths of 405 nm and 870 nm, revealing a strong variation of the aerosol light absorption with wavelength. Coated sphere calculations were used to show that Ångström exponents of absorption (AEA) as large as 1.6 are possible even with non-absorbing organic coatings on black carbon cores, suggesting care be exercised when diagnosing AEA. Insight on fuels burned is gleaned from comparison of AEA versus single scattering albedo (SSA) of the ambient measurements with laboratory biomass smoke measurements for many fuels. Measurements during the month of August, which were largely unaffected by fire smoke, exhibit surprisingly low AEA for aerosol light absorption when the SSA is highest, again likely as a consequence of the underappreciated wavelength dependence of aerosol light absorption by particles coated with non absorbing organic and inorganic matter.

Vehicle effects on human stratum corneum absorption and skin penetration.

PubMed

Zhang, Alissa; Jung, Eui-Chang; Zhu, Hanjiang; Zou, Ying; Hui, Xiaoying; Maibach, Howard

2017-05-01

This study evaluated the effects of three vehicles-ethanol (EtOH), isopropyl alcohol (IPA), and isopropyl myristate (IPM)-on stratum corneum (SC) absorption and diffusion of the [ 14 C]-model compounds benzoic acid and butenafine hydrochloride to better understand the transport pathways of chemicals passing through and resident in SC. Following application of topical formulations to human dermatomed skin for 30 min, penetration flux was observed for 24 h post dosing, using an in vitro flow-through skin diffusion system. Skin absorption and penetration was compared to the chemical-SC (intact, delipidized, or SC lipid film) binding levels. A significant vehicle effect was observed for chemical skin penetration and SC absorption. IPA resulted in the greatest levels of intact SC/SC lipid absorption, skin penetration, and total skin absorption/penetration of benzoic acid, followed by IPM and EtOH, respectively. For intact SC absorption and total skin absorption/penetration of butenafine, the vehicle that demonstrated the highest level of sorption/penetration was EtOH, followed by IPA and IPM, respectively. The percent doses of butenafine that were absorbed in SC lipid film and penetrated through skin in 24 h were greatest for IPA, followed by EtOH and IPM, respectively. The vehicle effect was consistent between intact SC absorption and total chemical skin absorption and penetration, as well as SC lipid absorption and chemical penetration through skin, suggesting intercellular transport as a main pathway of skin penetration for model chemicals. These results suggest the potential to predict vehicle effects on skin permeability with simple SC absorption assays. As decontamination was applied 30 min after chemical exposure, significant vehicle effects on chemical SC partitioning and percutaneous penetration also suggest that skin decontamination efficiency is vehicle dependent, and an effective decontamination method should act on chemical solutes in the lipid domain.

Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.

PubMed

Zhang, Kunhao; Zhao, Ziyan; Wu, Zhonghua; Zhou, Ying

2015-01-01

In this paper, the Co@SiO2 core-shell nanoparticles were prepared by the sol-gel method. The oxidization of Co core nanoparticles was studied by the synchrotron radiation-based techniques including in situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) up to 800°C in air and N2 protection conditions, respectively. It was found that the oxidization of Co cores is undergoing three steps regardless of being in air or in N2 protection condition. In the first step ranging from room temperature to 200°C, the Co cores were dominated by Co(0) state as well as small amount of Co(2+) ions. When temperature was above 300°C, the interface between Co cores and SiO2 shells was gradually oxidized into Co(2+), and the CoO layer was observed. As the temperature increasing to 800°C, the Co cores were oxidized to Co3O4 or Co3O4/CoO. Nevertheless, the oxidization kinetics of Co cores is different for the Co@SiO2 in air and N2 gas conditions. Generally, the O2 in the air could get through the SiO2 shells easily onto the Co core surface and induce the oxidization of the Co cores due to the mesoporous nature of the SiO2 shells. However, in N2 gas condition, the O atoms can only be from the SiO2 shells, so the diffusion effect of O atoms in the interface between Co core and SiO2 shell plays a key role.

Modelling, Design, Growth and Characterization of Strain Balanced Quantum Cascade Lasers (3-11mum), grown by Gas Source Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Bandyopadhyay, Neelanjan

Quantum Cascade Laser (QCL) is a compact room temperature (RT) source of mid-infrared radiation, which can be used for spectroscopic detection of trace amount of chemicals. The mid-infrared spectral range between (3-11 microm), has a dense array of absorption lines of numerous molecules, due to the presence of fundamental vibrational modes. The goal of this thesis can be subdivided into two parts. Firstly, short wavelength QCLs, emitting below 4microm, perform poorly at RT, due to inter-valley Gamma --- L carrier scattering, carrier escape to the continuum, heat removal from the core region at high power density corresponding to short wavelength operation, and large interface scattering due to highly strained materials. Secondly, it is desirable to have a single QCL based source emitting between 6-10microm, which be used to detect multiple molecules having their peak absorptions far apart, inside this spectral range. However, gain bandwidth of a single core QCL is relatively small, so laser emission cannot be tuned over a wide spectral range. This thesis describes the working principle of a QCL based on superlattice transport, rate equations, scattering mechanism, and waveguide design. The choice of the material system for this work and the fundamentals of band structure engineering has been derived. Gas source molecular beam epitaxy - growth optimization and characterization is one of the most important features of this work, especially for short wavelength QCLs, and has been explained in depth. Different strategies for design of active region design of short wavelength QCL and heterogeneous broadband QCL has been explored. The major milestones, of this research was the world's first watt level continuous wave (CW), RT demonstration at 3.76 microm, which was followed by another milestone of the first CW, RT demonstration at 3.39microm and 3.55microm, and finally the elusive result of QCL emitting at CW, RT at a wavelength as short as lambda ~3microm, a record. In the longer wavelength side a novel approach to design of strain balanced QCLs based on the same material composition was demonstrated. Finally a gapless heterogeneous broadband QCL, incorporating multiple QCL cores in a single active region, with record tunability between 6.1-10.2 microm, was demonstrated.

Comparison of International Guidelines of Dermal Absorption Tests Used in Pesticides Exposure Assessment for Operators

PubMed Central

So, Jaehwan; Ahn, Junyoung; Lee, Tae-Hee; Park, Kyung-Hun; Paik, Min-Kyoung; Jeong, Mihye; Cho, Myung-Haing

2014-01-01

The number of farmers who have suffered from non-fatal acute pesticide poisoning has been reported to vary from 5.7% to 86.7% in South Korea since 1975. Absorption through the skin is the main route of exposure to pesticides for farmers who operate with them. Several in vitro tests using the skins of humans or animal and in vivo tests using laboratory animals are introduced for the assessment of human dermal absorption level of pesticides. The objective of this study is to evaluate and compare international guidelines and strategies of dermal absorption assessments and to propose unique approaches for applications into pesticide registration process in our situation. Until present in our situation, pesticide exposure level to operator is determined just using default value of 10 as for skin absorption ratio because of data shortage. Dermal absorption tests are requested to get exposure level of pesticides and to ultimately know the safety of pesticides for operators through the comparison with the value of AOEL. When the exposure level is higher than AOEL, the pesticide cannot be approved. We reviewed the skin absorption test guidelines recommended by OECD, EFSA and EPA. The EPA recommends assessment of skin absorption of pesticides for humans through the TPA which includes all the results of in vitro human and animal and animal in vivo skin absorption studies. OECD and EFSA, employ a tiered approach, which the requirement of further study depends on the results of the former stage study. OECD guidelines accept the analysis of pesticide level absorbed through skin without radioisotope when the recovery using the non-labeled method is within 80~120%. Various factors are reviewed in this study, including the origin of skin (gender, animal species and sites of skin), thickness, temperature and, etc., which can influence the integrity of results. PMID:25584144

S2p core level spectroscopy of short chain oligothiophenes

NASA Astrophysics Data System (ADS)

Baseggio, O.; Toffoli, D.; Stener, M.; Fronzoni, G.; de Simone, M.; Grazioli, C.; Coreno, M.; Guarnaccio, A.; Santagata, A.; D'Auria, M.

2017-12-01

The Near-Edge X-ray-Absorption Fine-Structure (NEXAFS) and X-ray Photoemission Spectroscopy (XPS) of short-chain oligothiophenes (thiophene, 2,2'-bithiophene, and 2,2':5',2″-terthiophene) in the gas phase have been measured in the sulfur L2,3-edge region. The assignment of the spectral features is based on the relativistic two-component zeroth-order regular approximation time dependent density functional theory approach. The calculations allow us to estimate both the contribution of the spin-orbit splitting and of the molecular-field splitting to the sulfur binding energies and give results in good agreement with the experimental measurements. The deconvolution of the calculated S2p NEXAFS spectra into the two manifolds of excited states converging to the LIII and LII edges facilitates the attribution of the spectral structures. The main S2p NEXAFS features are preserved along the series both as concerns the energy positions and the nature of the transitions. This behaviour suggests that the electronic and geometrical environment of the sulfur atom in the three oligomers is relatively unaffected by the increasing chain length. This trend is also observed in the XPS spectra. The relatively simple structure of S2p NEXAFS spectra along the series reflects the localized nature of the virtual states involved in the core excitation process.

Core Knowledge Employee Creativity and Firm Performance: The Moderating Role of Riskiness Orientation, Firm Size, and Realized Absorptive Capacity

ERIC Educational Resources Information Center

Gong, Yaping; Zhou, Jing; Chang, Song

2013-01-01

In this study, we examine when creativity is positively or negatively related to firm performance. Building on the creation-implementation tension theorized in the literature and the attention capacity perspective, we argue that the relationship between creativity and firm performance is contingent on riskiness orientation, firm size, and realized…

A nano-disperse ferritin-core mimetic that efficiently corrects anemia without luminal iron redox activity

PubMed Central

Powell, Jonathan J.; Bruggraber, Sylvaine F.A.; Faria, Nuno; Poots, Lynsey K.; Hondow, Nicole; Pennycook, Timothy J.; Latunde-Dada, Gladys O.; Simpson, Robert J.; Brown, Andy P.; Pereira, Dora I.A.

2014-01-01

The 2-5 nm Fe(III) oxo-hydroxide core of ferritin is less ordered and readily bioavailable compared to its pure synthetic analogue, ferrihydrite. We report the facile synthesis of tartrate-modified, nano-disperse ferrihydrite of small primary particle size, but with enlarged or strained lattice structure (~ 2.7 Å for the main Bragg peak versus 2.6 Å for synthetic ferrihydrite). Analysis indicated that co-precipitation conditions can be achieved for tartrate inclusion into the developing ferrihydrite particles, retarding both growth and crystallization and favoring stabilization of the cross-linked polymeric structure. In murine models, gastrointestinal uptake was independent of luminal Fe(III) reduction to Fe(II) and, yet, absorption was equivalent to that of ferrous sulphate, efficiently correcting the induced anemia. This process may model dietary Fe(III) absorption and potentially provide a side effect-free form of cheap supplemental iron. From the Clinical Editor Small size tartrate-modified, nano-disperse ferrihydrite was used for efficient gastrointestinal delivery of soluble Fe(III) without the risk for free radical generation in murine models. This method may provide a potentially side effect-free form iron supplementation. PMID:24394211

Optically Active CdSe-Dot/CdS-Rod Nanocrystals with Induced Chirality and Circularly Polarized Luminescence.

PubMed

Cheng, Jiaji; Hao, Junjie; Liu, Haochen; Li, Jiagen; Li, Junzi; Zhu, Xi; Lin, Xiaodong; Wang, Kai; He, Tingchao

2018-05-30

Ligand-induced chirality in semiconductor nanocrystals (NCs) has attracted attention because of the tunable optical properties of the NCs. Induced circular dichroism (CD) has been observed in CdX (X = S, Se, Te) NCs and their hybrids, but circularly polarized luminescence (CPL) in these fluorescent nanomaterials has been seldom reported. Herein, we describe the successful preparation of l- and d-cysteine-capped CdSe-dot/CdS-rods (DRs) with tunable CD and CPL behaviors and a maximum anisotropic factor ( g lum ) of 4.66 × 10 -4 . The observed CD and CPL activities are sensitive to the relative absorption ratio of the CdS shell to the CdSe core, suggesting that the anisotropic g-factors in both CD and CPL increase to some extent for a smaller shell-to-core absorption ratio. In addition, the molar ratio of chiral cysteine to the DRs is investigated. Instead of enhancing the chiral interactions between the chiral molecules and DRs, an excess of cysteine molecules in aqueous solution inhibits both the CD and CPL activities. Such chiral and emissive NCs provide an ideal platform for the rational design of semiconductor nanomaterials with chiroptical properties.

Analysis of specific absorption rate and internal electric field in human biological tissues surrounding an air-core coil-type transcutaneous energy transmission transformer.

PubMed

Shiba, Kenji; Zulkifli, Nur Elina Binti; Ishioka, Yuji

2017-06-01

In this study, we analyzed the internal electric field E and specific absorption rate (SAR) of human biological tissues surrounding an air-core coil transcutaneous energy transmission transformer. Using an electromagnetic simulator, we created a model of human biological tissues consisting of a dry skin, wet skin, fat, muscle, and cortical bone. A primary coil was placed on the surface of the skin, and a secondary coil was located subcutaneously inside the body. The E and SAR values for the model representing a 34-year-old male subject were analyzed using electrical frequencies of 0.3-1.5 MHz. The transmitting power was 15 W, and the load resistance was 38.4 Ω. The results showed that the E values were below the International Commission on Non-ionizing Radiation Protection (ICNIRP) limit for the general public exposure between the frequencies of 0.9 and 1.5 MHz, and SAR values were well below the limit prescribed by the ICNIRP for the general public exposure between the frequencies of 0.3 and 1.2 MHz.

Long-Duration Gamma-Ray Burst Host Galaxies in Emission and Absorption

NASA Astrophysics Data System (ADS)

Perley, Daniel A.; Niino, Yuu; Tanvir, Nial R.; Vergani, Susanna D.; Fynbo, Johan P. U.

2016-12-01

The galaxy population hosting long-duration GRBs provides a means to constrain the progenitor and an opportunity to use these violent explosions to characterize the nature of the high-redshift universe. Studies of GRB host galaxies in emission reveal a population of star-forming galaxies with great diversity, spanning a wide range of masses, metallicities, and redshifts. However, as a population GRB hosts are significantly less massive and poorer in metals than the hosts of other core-collapse transients, suggesting that GRB production is only efficient at metallicities significantly below Solar. GRBs may also prefer compact galaxies, and dense and/or central regions of galaxies, more than other types of core-collapse explosion. Meanwhile, studies of hosts in absorption against the luminous GRB optical afterglow provide a unique means of unveiling properties of the ISM in even the faintest and most distant galaxies; these observations are helping to constrain the chemical evolution of galaxies and the properties of interstellar dust out to very high redshifts. New ground- and space-based instrumentation, and the accumulation of larger and more carefully-selected samples, are continually enhancing our view of the GRB host population.

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

NASA Astrophysics Data System (ADS)

Hansen, S. B.; Harding, E. C.; Knapp, P. F.; Gomez, M. R.; Nagayama, T.; Bailey, J. E.

2018-05-01

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. We show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 1024 e/cm3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.

Zethrene biradicals: How pro-aromaticity is expressed in the ground electronic state and in the lowest energy singlet, triplet, and ionic states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zafra, José Luis; González Cano, Rafael C.; Ruiz Delgado, M. Carmen

A analysis of the electronic and molecular structures of new molecular materials based on zethrene is presented with particular attention to those systems having a central benzo-quinoidal core able to generate Kekulé biradicals whose stability is provided by the aromaticity recovery in this central unit. These Kekulé biradicals display singlet ground electronic states thanks to double spin polarization and have low-energy lying triplet excited states also featured by the aromaticity gain. Pro-aromatization is also the driving force for the stabilization of the ionized species. Moreover, the low energy lying singlet excited states also display a profound biradical fingerprint allowing tomore » singlet exciton fission. These properties are discussed in the context of the size of the zethrene core and of its substitution. The work encompasses all known long zethrenes and makes use of a variety of experimental techniques, such as Raman, UV-Vis-NIR absorption, transient absorption, in situ spectroelectrochemistry and quantum chemical calculations. This study reveals how the insertion of suitable molecular modules (i.e., quinoidal) opens the door to new intriguing molecular properties exploitable in organic electronics.« less

The effect of intermediate-scale motions on line formation. [sawtooth and sine motions in solar atmosphere

NASA Technical Reports Server (NTRS)

Shine, R. A.

1975-01-01

The problem of LTE and non-LTE line formation in the presence of nonthermal velocity fields with geometric scales between the microscopic and macroscopic limits is investigated in the cases of periodic sinusoidal and sawtooth waves. For a fixed source function (the LTE case), it is shown that time-averaged line profiles progress smoothly from the microscopic to the macroscopic limits as the geometric scale of the motions increases, that the sinusoidal motions produce symmetric time-averaged profiles, and that the sawtooth motions cause a redshift. In several idealized non-LTE cases, it is found that intermediate-scale velocity fields can significantly increase the surface source functions and line-core intensities. Calculations are made for a two-level atom in an isothermal atmosphere for a range of velocity scales and non-LTE coupling parameters and also for a two-level atom and a four-level representation of Na I line formation in the Harvard-Smithsonian Reference Atmosphere (1971) solar model. It is found that intermediate-scale velocity fields in the solar atmosphere could explain the central intensities of the Na I D lines and other strong absorption lines without invoking previously suggested high electron densities.

A survey of lead contamination in soil along Interstate 880, Alameda County, California.

PubMed

Teichman, J; Coltrin, D; Prouty, K; Bir, W A

1993-09-01

This study was undertaken to determine the levels of lead in soils taken from yards of homes in close proximity to a major freeway. Soils were collected from the yards of homes in communities adjacent to the freeway and within a 1-mile radius. Samples were analyzed using U.S. Environmental Protection Agency (EPA) methods and atomic absorption instrumentation. Ten percent of the samples were split and sent to a second laboratory for quality control. The possibility of lead-based paint contributing to the contamination was eliminated by sampling more than 20 feet from the homes. The soils closest to the highway showed lead levels exceeding California's and EPA's criteria for hazardous waste. A stratified sample of the depth of contamination in soils was also undertaken. Previously identified "hot spots" (soils with lead levels exceeding 500 ppm in the top 0.75 inch) were core sampled. Results indicated 90% of the subsurface samples contained lead exceeding the surface contaminations. This may be attributed to decades of urban lead-laden dust deposition. As the use of leaded gasolines have diminished in the past decade, the uppermost layers of soil/dust contained lower amounts of lead.

BODIPY-Based Donor-Acceptor Pi-Conjugated Alternating Copolymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popere, Bhooshan C.; Della Pelle, Andrea M.; Thayumanavan, S.

2011-06-28

Four novel π-conjugated copolymers incorporating 4,4-difluoro-4-borata-3a-azonia-4a-aza-s-indacene (BODIPY) core as the “donor” and quinoxaline (Qx), 2,1,3-benzothiadiazole (BzT), N,N'-di(2'-ethyl)hexyl-3,4,7,8-naphthalenetetracarboxylic diimide (NDI), and N,N'-di(2'-ethyl)hexyl-3,4,9,10-perylene tetracarboxylic diimide (PDI) as acceptors were designed and synthesized via Sonogashira polymerization. The polymers were characterized by ¹H NMR spectroscopy, gel permeation chromatography (GPC), UV–vis absorption spectroscopy, and cyclic voltammetry. Density functional theory (DFT) calculations were performed on polymer repeat units, and the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels were estimated from the optimized geometry using B3LYP functional and 6-311g(d,p) basis set. Copolymers with Qx and BzT possessed HOMO and LUMOmore » energy levels comparable to those of BODIPY homopolymer, while PDI stabilized both HOMO and LUMO levels. Semiconductor behavior of these polymers was estimated in organic thin-film transistors (OTFT). While the homopolymer, Qx, and BzT-based copolymers showed only p-type semiconductor behavior, copolymers with PDI and NDI showed only n-type behavior.« less

Negative optical absorption and up-energy conversion in dendrites of nanostructured silver grafted with α/β-poly(vinylidene fluoride) in small hierarchical structures

NASA Astrophysics Data System (ADS)

Phule, A. D.; Ram, S.; Shinde, S. K.; Choi, J. H.; Tyagi, A. K.

2018-04-01

We report that a negative optical absorption arises in a sharp band at 325 nm (energy hν2) in a nanostructured silver (n-Ag) doped poly(vinylidene fluoride) (PVF2) in a hybrid nanocomposite of films (∼100 μm thickness). Two polymorphs α- and β-PVF2 are co-stretched through the n-Ag crystallites in dendrites of hierarchical structures. A critical 0.5 wt% n-Ag dosage promotes this band of extinction coefficient to be enhanced by as much as 2.009 × 103, i.e. a 30% value in the Ag-surface plasmon band 350-650 nm (hν1). An electron donor Ag (4d105s1) bonds to an electron accepter moiety CF2 of PVF2, it tunes a dielectric field and sets up an up-energy conversion of the plasmon band. The FESEM and HRTEM images reveal fcc-Ag dendrites entangled with in-built PVF2 surface layers (2-3 nm thickness). The IR phonon bands show how a α → β-PVF2 transformation propagates onto a nascent n-Ag surface and how it is raised-up in small steps of 0.1 wt% and up to 5.0 wt%. In a model scheme, we illustrate how a rigid core-shell of a capsule conducts a new transfer mechanism of the energy to a cold surface plasmon (core) in a coherent collision, so as to balance a net value hν2 = h(ν3 - ν1). It absorbs light in a weak band at 210 nm (hν3) in a π → π* electron transition in the Cdbnd C bonds of the PVF2 (shell), and results in a negative absorption in a coherent excitation of the energy-carriers. A light-emitter on absorption over a wide range of wavelengths (200-650 nm) offers a unique type of energy-converter.

Naphtho[1,2-b:5,6-b']dithiophene-Based Conjugated Polymers for Fullerene-Free Inverted Polymer Solar Cells.

PubMed

Jiang, Zhaoyan; Li, Huan; Wang, Zhen; Zhang, Jianqi; Zhang, Yajie; Lu, Kun; Wei, Zhixiang

2018-03-23

Three novel copolymers based on zigzag naphthodithiophene (zNDT) with different aromatic rings as π bridges and different core side substitutions are designed and synthesized (PzNDT-T-1,3-bis(4-(2-ethylhexyl)-thiophen-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']-dithiophene-4,8-dione (BDD), PzNDT-TT-BDD, and PzNDTP-T-BDD, respectively). The 2D conjugation structure and molecular planarity of the polymers can be effectively altered through the modification of conjugated side chains and π-bridges. These alterations contribute to the variation in energy levels, light absorption capacity, and morphology compatibility of the polymers. When blended with the nonfullerene acceptor (2,2'-[(4,4,9,9-tetrahexyl-4,9-dihydro-sindaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis[methylidyne(3-oxo-1H-indene-2,1(3H)-diylidene)

Intrinsic electronic defects and multiple-atom processes in the oxidic semiconductor Ga2O3

NASA Astrophysics Data System (ADS)

Schmeißer, Dieter; Henkel, Karsten

2018-04-01

We report on the electronic structure of gallium oxide (Ga2O3) single crystals as studied by resonant photoelectron spectroscopy (resPES). We identify intrinsic electronic defects that are formed by mixed-atomic valence states. We differentiate three coexisting defect states that differ in their electronic correlation energy and their spatial localization lengths. Their relative abundance is described by a fractional ionicity with covalent and ionic bonding contributions. For Ga2O3, our analyses of the resPES data enable us to derive two main aspects: first, experimental access is given to determine the ionicity based on the original concepts of Pauling and Phillips. Second, we report on multi-atomic energy loss processes in the Ga2p core level and X-ray absorption data. The two experimental findings can be explained consistently in the same context of mixed-atomic valence states and intrinsic electronic defects.

Part-per-trillion level SF6 detection using a quartz enhanced photoacoustic spectroscopy-based sensor with single-mode fiber-coupled quantum cascade laser excitation.

PubMed

Spagnolo, Vincenzo; Patimisco, Pietro; Borri, Simone; Scamarcio, Gaetano; Bernacki, Bruce E; Kriesel, Jason

2012-11-01

A sensitive spectroscopic sensor based on a hollow-core fiber-coupled quantum cascade laser (QCL) emitting at 10.54 μm and quartz enhanced photoacoustic spectroscopy (QEPAS) technique is reported. The design and realization of mid-IR fiber and coupler optics has ensured single-mode QCL beam delivery to the QEPAS sensor. The collimation optics was designed to produce a laser beam of significantly reduced beam size and waist so as to prevent illumination of the quartz tuning fork and microresonator tubes. SF(6) was selected as the target gas. A minimum detection sensitivity of 50 parts per trillion in 1 s was achieved with a QCL power of 18 mW, corresponding to a normalized noise-equivalent absorption of 2.7×10(-10) W·cm(-1)/Hz(1/2).

Part-Per-Trillion Level SF6 Detection Using a Quartz Enhanced Photoacoustic Spectroscopy-Based Sensor with Single-Mode Fiber-Coupled Quantum Cascade Laser Excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spagnolo, V.; Patimisco, P.; Borri, Simone

2012-10-23

A sensitive spectroscopic sensor based on a hollow-core fiber-coupled quantum cascade laser (QCL) emitting at 10.54 µm and quartz enhanced photoacoustic spectroscopy (QEPAS) technique is reported. The design and realization of mid-infrared fiber and coupler optics has ensured single-mode QCL beam delivery to the QEPAS sensor . The collimation optics was designed to produce a laser beam of significantly reduced beam size and waist so as to prevent illumination of the quartz tuning fork and micro-resonator tubes. SF6 was selected as the target gas. A minimum detection sensitivity of 50 parts per trillion in 1 s was achieved with amore » QCL power of 18 mW, corresponding to a normalized noise-equivalent absorption of 2.7x10-10 W•cm-1/Hz1/2.« less

Facile transformation of FeO/Fe3O4 core-shell nanocubes to Fe3O4 via magnetic stimulation

NASA Astrophysics Data System (ADS)

Lak, Aidin; Niculaes, Dina; Anyfantis, George C.; Bertoni, Giovanni; Barthel, Markus J.; Marras, Sergio; Cassani, Marco; Nitti, Simone; Athanassiou, Athanassia; Giannini, Cinzia; Pellegrino, Teresa

2016-09-01

Here, we propose the use of magnetic hyperthermia as a means to trigger the oxidation of Fe1-xO/Fe3-δO4 core-shell nanocubes to Fe3-δO4 phase. As a first relevant consequence, the specific absorption rate (SAR) of the initial core-shell nanocubes doubles after exposure to 25 cycles of alternating magnetic field stimulation. The improved SAR value was attributed to a gradual transformation of the Fe1-xO core to Fe3-δO4, as evidenced by structural analysis including high resolution electron microscopy and Rietveld analysis of X-ray diffraction patterns. The magnetically oxidized nanocubes, having large and coherent Fe3-δO4 domains, reveal high saturation magnetization and behave superparamagnetically at room temperature. In comparison, the treatment of the same starting core-shell nanocubes by commonly used thermal annealing process renders a transformation to γ-Fe2O3. In contrast to other thermal annealing processes, the method here presented has the advantage of promoting the oxidation at a macroscopic temperature below 37 °C. Using this soft oxidation process, we demonstrate that biotin-functionalized core-shell nanocubes can undergo a mild self-oxidation transformation without losing their functional molecular binding activity.

Mineral and Lithology Mapping of Drill Core Pulps Using Visible and Infrared Spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, G. R., E-mail: G.Taylor@unsw.edu.au

2000-12-15

A novel approach for using field spectrometry for determining both the mineralogy and the lithology of drill core pulps (powders) is developed and evaluated. The methodology is developed using material from a single drillhole through a mineralized sequence of rocks from central New South Wales. Mineral library spectra are used in linear unmixing routines to determine the mineral abundances in drill core pulps that represent between 1 m and 3 m of core. Comparison with X-Ray Diffraction (XRD) analyses shows that for most major constituents, spectrometry provides an estimate of quantitative mineralogy that is as reliable as that provided bymore » XRD. Confusion between the absorption features of calcite and those of chlorite causes the calcite contents determined by spectrometry to be unreliable. Convex geometry is used to recognize the spectra of those samples that are extreme and are representative of unique lithologies. Linear unmixing is used to determine the abundance of these lithologies in each drillhole sample and these abundances are used to interpret the geology of the drillhole. The interpreted geology agrees well with conventional drillhole logs of the visible geology and photographs of the split core. The methods developed provide a quick and cost-effective way of determining the lithology and alteration mineralogy of drill core pulps.« less

The role of interfacial metal silicates on the magnetism in FeCo/SiO{sub 2} and Fe{sub 49%}Co{sub 49%}V{sub 2%}/SiO{sub 2} core/shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desautels, R. D., E-mail: rddesautels@physics.umanitoba.ca; Toyota Research Institute of North America, Ann Arbor, Michigan 48169; Freeland, J. W.

2015-05-07

We have investigated the role of spontaneously formed interfacial metal silicates on the magnetism of FeCo/SiO{sub 2} and Fe{sub 49%}Co{sub 49%}V{sub 2%}/SiO{sub 2} core/shell nanoparticles. Element specific x-ray absorption and photoelectron spectroscopy experiments have identified the characteristic spectral features of metallic iron and cobalt from within the nanoparticle core. In addition, metal silicates of iron, cobalt, and vanadium were found to have formed spontaneously at the interface between the nanoparticle core and silica shell. X-ray magnetic circular dichroism experiments indicated that the elemental magnetism was a result of metallic iron and cobalt with small components from the iron, cobalt, andmore » vanadium silicates. Magnetometry experiments have shown that there was no exchange bias loop shift in the FeCo nanoparticles; however, exchange bias from antiferromagnetic vanadium oxide was measured in the V-doped nanoparticles. These results showed clearly that the interfacial metal silicates played a significant role in the magnetism of these core/shell nanoparticles, and that the vanadium percolated from the FeCo-cores into the SiO{sub 2}-based interfacial shell.« less

Application of two different kinds of sera against the Proteus penneri lipopolysaccharide core region in search of epitopes determining cross-reactions with antibodies.

PubMed

Palusiak, Agata; Dzieciatkowska, Monika; Sidorczyk, Zygmunt

2008-01-01

Proteus penneri lipopolysaccharide (LPS) core regions are characterized by a greater structural variability than that observed in other Enterobacteriaceae. This fact and the small amount of published data concerning the serological activity of this part of P. penneri LPS prompted an examination of which fragment might determine cross-reactions with antibodies. To date, such epitopes have been found in the LPS core regions of P. mirabilis and P. vulgaris strains. Proteus sp. LPSs were tested with unabsorbed rabbit antisera by enzyme-linked immunosorbent assay (ELISA), sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot, and once again by ELISA or passive immunohemolysis after the absorption of these antisera with selected LPSs. The serological studies of P. penneri 8 LPS demonstrated antibodies in the tested antisera recognizing a common epitope located in the core regions of six of the LPSs, i.e. P. penneri 8, 34, 133, 7, 14, and 15. Additionally, another type of antibody directed against some fragment of P. penneri 13 and the core regions of other LPSs investigated was observed in one antiserum. A distal, trisaccharide fragment of the P. penneri 8 LPS core region is suggested to determine the cross-reactions of the tested antisera with the six P. penneri LPSs.

Tracking the Magnetization Evolution in γ-Fe2O3 / Metallic Fe Core-Shell Nanoparticle Variants

NASA Astrophysics Data System (ADS)

Kons, C.; Nemati, Z.; Srikanth, H.; Phan, M.-H.; Krycka, K.; Borchers, J.; Keavney, D.; Arena, D. A.

Iron-core magnetic nanoparticles (MNPs) with oxide shells exhibit varying magnetic properties due to the different ordering temperatures of the core and shell spins, as well as the coupling across the metal/oxide interface. While spin coupling across two dimensional interfaces has been well explored, less is known about three dimensional interfaces such as those presented in the MNPs. In this work, MNPs were synthesized with a bcc Fe core and γ-Fe2O3 shell and placed in an oxygen rich environment to encourage the transition from cores shell (CS) to core void shell (CVS) to hollow (H) structures. Static magnetic measurements (MvT) and AC magnetometry were performed to explore the magnetic behavior of the various synthesized structures. To further understand the nature of the spin coupling in the MNPs, TEM and conventional magnetometry as well as variable-temperature small angle neutron scattering (SANS), x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy were performed. Modeling of the x-ray spectra and SANS data will enable us to develop a cohesive picture of spin coupling, freezing and frustration along the three-dimensional metal / oxide interface. Supported by Department of Energy award #DE-FG02-07ER46438; NSF Award #DMR-1508249.

Quantum plasmonics: optical properties of a nanomatryushka.

PubMed

Kulkarni, Vikram; Prodan, Emil; Nordlander, Peter

2013-01-01

Quantum mechanical effects can significantly reduce the plasmon-induced field enhancements around nanoparticles. Here we present a quantum mechanical investigation of the plasmon resonances in a nanomatryushka, which is a concentric core-shell nanoparticle consisting of a solid metallic core encapsulated in a thin metallic shell. We compute the optical response using the time-dependent density functional theory and compare the results with predictions based on the classical electromagnetic theory. We find strong quantum mechanical effects for core-shell spacings below 5 Å, a regime where both the absorption cross section and the local field enhancements differ significantly from the classical predictions. We also show that the workfunction of the metal is a crucial parameter determining the onset and magnitude of quantum effects. For metals with lower workfunctions such as aluminum, the quantum effects are found to be significantly more pronounced than for a noble metal such as gold.

Green Synthesis of Ag-Cu Nanoalloys Using Opuntia ficus- indica

NASA Astrophysics Data System (ADS)

Rocha-Rocha, O.; Cortez-Valadez, M.; Hernández-Martínez, A. R.; Gámez-Corrales, R.; Alvarez, Ramón A. B.; Britto-Hurtado, R.; Delgado-Beleño, Y.; Martinez-Nuñez, C. E.; Pérez-Rodríguez, A.; Arizpe-Chávez, H.; Flores-Acosta, M.

2017-02-01

Bimetallic Ag/Cu nanoparticles have been obtained by green synthesis using Opuntia ficus- indica plant extract. Two synthesis methods were applied to obtain nanoparticles with core-shell and Janus morphologies by reversing the order of precursors. Transmission electronic microscopy revealed size of 10 nm and 20 nm for the core-shell and Janus nanoparticles, respectively. Other small particles with size of up to 2 nm were also observed. Absorption bands attributed to surface plasmon resonance were detected at 440 nm and 500 nm for the core-shell and Janus nanoparticles, respectively. Density functional theory predicted a breathing mode type (BMT) located at low wavenumber due to small, low-energy clusters of (AgCu) n with n = 2 to 9, showing a certain correlation with the experimental one (at 220 cm-1). The dependence of the BMT on the number of atoms constituting the cluster is also studied.

Raman scattering in the atmospheres of the major planets

NASA Technical Reports Server (NTRS)

Cochran, W. D.; Trafton, L. M.

1978-01-01

A technique is developed to calculate the detailed effects of Raman scattering in an inhomogeneous anisotropically scattering atmosphere. The technique is applied to evaluations of Raman scattering by H2 in the atmosphere of the major planets. It is noted that Raman scattering produces an insufficient decrease in the blue and ultraviolet regions to explain the albedos of all planets investigated. For all major planets, the filling-in of solar line cores and the generation of the Raman-shifted ghosts of the Fraunhofer spectrum are observed. With regard to Uranus and Neptune, Raman scattering is seen to exert a major influence on the formation and profile of strong red and near infrared CH4 bands, and Raman scattering by H2 explains the residual intensity in the cores of these bands. Raman scattering by H2 must also be taken into account in the scattering of photons into the cores of saturated absorption bands.

Molybdenum Valence in Basaltic Silicate Melts: Effects of Temperature and Pressure

NASA Technical Reports Server (NTRS)

Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Choi, Y.; Pando, K.

2011-01-01

The metal-silicate partitioning behavior of molybdenum has been used as a test for equilibrium core formation hypotheses [for example, 1-6]. However, current models that apply experimental data to equilibrium core-mantle differentiation infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Molybdenum, a multi-valent element with a valence transition near the fO2 of interest for core formation (approx.IW-2) will be sensitive to changes in fO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo(6+) can be either octahedrally or tetrahedrally coordinated. Here we present X-ray absorption near edge structure (XANES) measurements of Mo valence in basaltic run products at a range of P, T, and fO2 and further quantify the valence transition of Mo.

Full-spectrum volumetric solar thermal conversion via photonic nanofluids.

PubMed

Liu, Xianglei; Xuan, Yimin

2017-10-12

Volumetric solar thermal conversion is an emerging technique for a plethora of applications such as solar thermal power generation, desalination, and solar water splitting. However, achieving broadband solar thermal absorption via dilute nanofluids is still a daunting challenge. In this work, full-spectrum volumetric solar thermal conversion is demonstrated over a thin layer of the proposed 'photonic nanofluids'. The underlying mechanism is found to be the photonic superposition of core resonances, shell plasmons, and core-shell resonances at different wavelengths, whose coexistence is enabled by the broken symmetry of specially designed composite nanoparticles, i.e., Janus nanoparticles. The solar thermal conversion efficiency can be improved by 10.8% compared with core-shell nanofluids. The extinction coefficient of Janus dimers with various configurations is also investigated to unveil the effects of particle couplings. This work provides the possibility to achieve full-spectrum volumetric solar thermal conversion, and may have potential applications in efficient solar energy harvesting and utilization.

Simulating Valence-to-Core X-ray Emission Spectroscopy of Transition Metal Complexes with Time-Dependent Density Functional Theory.

PubMed

Zhang, Yu; Mukamel, Shaul; Khalil, Munira; Govind, Niranjan

2015-12-08

Valence-to-core (VtC) X-ray emission spectroscopy (XES) has emerged as a powerful technique for the structural characterization of complex organometallic compounds in realistic environments. Since the spectrum represents electronic transitions from the ligand molecular orbitals to the core holes of the metal centers, the approach is more chemically sensitive to the metal-ligand bonding character compared with conventional X-ray absorption techniques. In this paper we study how linear-response time-dependent density functional theory (LR-TDDFT) can be harnessed to simulate K-edge VtC X-ray emission spectra reliably. LR-TDDFT allows one to go beyond the single-particle picture that has been extensively used to simulate VtC-XES. We consider seven low- and high-spin model complexes involving chromium, manganese, and iron transition metal centers. Our results are in good agreement with experiment.

Starless Cores as Fundamental Physics Labs

NASA Astrophysics Data System (ADS)

Mignano, Arturo; Molaro, Paolo; Levshakov, Sergei; Centurión, Miriam; Maccaferri, Giuseppe; Lapinov, Alexander

We present high resolution observations in the starless dense molecular core L1512 performed with the Medicina 32m radio telescope. The resolved hfs components of HC3N and NH3 show no kinematic sub-structure and consist of an apparently symmetric peak profile without broadened line wings or self-absorption features suggesting that they sample the same material. The velocity dispersion is 101( ± 1) m s - 1for NH3 and 85( ± 2) m s - 1 for HC3N. The kinetic temperature of the cloud is estimated at 9.2 ( ± 1.2) K and the turbulence is of 76 m s - 1in a subsonic regime. This places L1512 among the most quiescent dark cores and makes it an ideal laboratory to study variations of the electron-to-proton mass ratio, μ = {m}e/{m}p by means of observations of inversion lines of NH3 combined with rotational lines of other molecular species.

A comparative theoretical study on core-hole excitation spectra of azafullerene and its derivatives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Yunfeng; Department of Physics, Guizhou University, Guiyang 550025; Gao, Bin, E-mail: bin.gao@uit.no

2014-03-28

The core-hole excitation spectra—near-edge x-ray absorption spectroscopy (NEXAFS), x-ray emission spectroscopy (XES), and x-ray photoelectron spectroscopy (XPS) shake-up satellites have been simulated at the level of density functional theory for the azafullerene C{sub 59}N and its derivatives (C{sub 59}N){sup +}, C{sub 59}HN, (C{sub 59}N){sub 2}, and C{sub 59}N–C{sub 60}, in which the XPS shake-up satellites were simulated using our developed equivalent core hole Kohn-Sham (ECH-KS) density functional theory approach [B. Gao, Z. Wu, and Y. Luo, J. Chem. Phys. 128, 234704 (2008)] which aims for the study of XPS shake-up satellites of large-scale molecules. Our calculated spectra are generally inmore » good agreement with available experimental results that validates the use of the ECH-KS method in the present work. The nitrogen K-edge NEXAFS, XES, and XPS shake-up satellites spectra in general can be used as fingerprints to distinguish the azafullerene C{sub 59}N and its different derivatives. Meanwhile, different carbon K-edge spectra could also provide detailed information of (local) electronic structures of different molecules. In particular, a peak (at around 284.5 eV) in the carbon K-edge NEXAFS spectrum of the heterodimer C{sub 59}N–C{sub 60} is confirmed to be related to the electron transfer from the C{sub 59}N part to the C{sub 60} part in this charge-transfer complex.« less

On the growth and photocatalytic activity of the vertically aligned ZnO nanorods grafted by CdS shells

NASA Astrophysics Data System (ADS)

Zirak, M.; Moradlou, O.; Bayati, M. R.; Nien, Y. T.; Moshfegh, A. Z.

2013-05-01

We have studied systematically photocatalytic properties of the vertically aligned ZnO@CdS core-shell nanorods where the features were grown through a multistep procedure including sol-gel for the formation of ZnO seed layer, hydrothermal process to grow ZnO nanorods, and successive ion layer adsorption and reaction (SILAR) process to deposit CdS nanoshells onto the ZnO nanorods. Formation of the ZnO seed layer and vertically aligned ZnO nanorods (d ∼ 40 nm) with a hexagonal cross-section was confirmed by AFM and SEM imaging. Successful capping of ZnO nanorods with homogeneous CdS nanocrystallites (∼5 nm) was ascertained by HRTEM diffraction and imaging. Optical properties of the samples were also studied using UV-vis spectrophotometry. It was found that the absorption edge of the CdS shell has a red shift when its thickness increases. Photocatalytic activity of the samples was examined by photodecomposition of methylene blue under UV and visible lights where the maximum reaction rate constant was found to be 0.012 min-1 under UV illumination and 0.007 min-1 under visible light. The difference in catalytic activities of the ZnO@CdS core-shell nanorods under UV and visible irradiations was explained based upon the electronic structure as well as the arrangement of the energy levels in the ZnO@CdS core-shells. It is shown that the structure and photocatalytic efficiency of the samples can be tuned by manipulating the SILAR variables.

The synergistic effects of carbon coating and micropore structure on the microwave absorption properties of Co/CoO nanoparticles.

PubMed

Xie, Xiubo; Pang, Yu; Kikuchi, Hiroaki; Liu, Tong

2016-11-09

25 nm carbon-coated microporous Co/CoO nanoparticles (NPs) were synthesized by integrating chemical de-alloying and chemical vapor deposition (CVD) methods. The NPs possess micropores of 0.8-1.5 nm and display a homogeneous carbon shell of about 4 nm in thickness with a low graphitization degree. The saturation magnetization (M S ) and coercivity (H C ) of the NPs were 70.3 emu g -1 and 398.4 Oe, respectively. The microporous Co/CoO/C NPs exhibited enhanced microwave absorption performance with a minimum reflection coefficient (RC) of -78.4 dB and a wide absorption bandwidth of 8.1 GHz (RC ≤ -10 dB), larger than those of the nonporous counterparts of -68.3 dB and 5.8 GHz. The minimum RC values of the microporous Co/CoO/C NPs at different thicknesses were much smaller than the nonporous counterparts. The high microwave absorption mechanism of the microporous Co/CoO/C nanocomposite can be interpreted in terms of the interfacial polarization relaxation of the core/shell and micropore structures, the effective permittivity modification of the air in the micropores and the polarization relaxation of the defects in the low-graphitization carbon shell and the porous Co NPs. Our study demonstrates that the microporous Co/CoO/C nanocomposite is an efficient microwave absorber with high absorption intensity and wide absorption bandwidth.

Surface-plasmon-enhanced photoluminescence of quantum dots based on open-ring nanostructure array

NASA Astrophysics Data System (ADS)

Kannegulla, Akash; Liu, Ye; Cheng, Li-Jing

2016-03-01

Enhanced photoluminescence (PL) of quantum dots (QD) in visible range using plasmonic nanostructures has potential to advance several photonic applications. The enhancement effect is, however, limited by the light coupling efficiency to the nanostructures. Here we demonstrate experimentally a new open-ring nanostructure (ORN) array 100 nm engraved into a 200 nm thick silver thin film to maximize light absorption and, hence, PL enhancement at a broadband spectral range. The structure is different from the traditional isolated or through-hole split-ring structures. Theoretical calculations based on FDTD method show that the absorption peak wavelength can be adjusted by their period and dimension. A broadband absorption of about 60% was measured at the peak wavelength of 550 nm. The emission spectrum of CdSe/ZnS core-shell quantum dots was chosen to match the absorption band of the ORN array to enhance its PL. The engraved silver ORN array was fabricated on a silver thin film deposited on a silicon substrate using focus ion beam (FIB) patterning. The device was characterized by using a thin layer of QD water dispersion formed between the ORN substrate and a cover glass. The experimental results show the enhanced PL for the QD with emission spectrum overlapping the absorption band of ORN substrate and quantum efficiency increases from 50% to 70%. The ORN silver substrate with high absorption over a broadband spectrum enables the PL enhancement and will benefit applications in biosensing, wavelength tunable filters, and imaging.

Deconvolving instrumental and intrinsic broadening in core-shell x-ray spectroscopies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fister, T. T.; Seidler, G. T.; Rehr, J. J.

2007-05-01

Intrinsic and experimental mechanisms frequently lead to broadening of spectral features in core-shell spectroscopies. For example, intrinsic broadening occurs in x-ray absorption spectroscopy (XAS) measurements of heavy elements where the core-hole lifetime is very short. On the other hand, nonresonant x-ray Raman scattering (XRS) and other energy loss measurements are more limited by instrumental resolution. Here, we demonstrate that the Richardson-Lucy (RL) iterative algorithm provides a robust method for deconvolving instrumental and intrinsic resolutions from typical XAS and XRS data. For the K-edge XAS of Ag, we find nearly complete removal of {approx}9.3 eV full width at half maximum broadeningmore » from the combined effects of the short core-hole lifetime and instrumental resolution. We are also able to remove nearly all instrumental broadening in an XRS measurement of diamond, with the resulting improved spectrum comparing favorably with prior soft x-ray XAS measurements. We present a practical methodology for implementing the RL algorithm in these problems, emphasizing the importance of testing for stability of the deconvolution process against noise amplification, perturbations in the initial spectra, and uncertainties in the core-hole lifetime.« less

Facile synthesis of mercaptosuccinic acid-capped CdTe/CdS/ZnS core/double shell quantum dots with improved cell viability on different cancer cells and normal cells

NASA Astrophysics Data System (ADS)

Parani, Sundararajan; Bupesh, Giridharan; Manikandan, Elayaperumal; Pandian, Kannaiyan; Oluwafemi, Oluwatobi Samuel

2016-11-01

Water-soluble, mercaptosuccinic acid (MSA)-capped CdTe/CdS/ZnS core/double shell quantum dots (QDs) were prepared by successive growth of CdS and ZnS shells on the as-synthesized CdTe/CdSthin core/shell quantum dots. The formation of core/double shell structured QDs was investigated by ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectroscopy, PL decay studies, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The core/double shell QDs exhibited good photoluminescence quantum yield (PLQY) which is 70% higher than that of the parent core/shell QDs, and they are stable for months. The average particle size of the core/double shell QDs was ˜3 nm as calculated from the transmission electron microscope (TEM) images. The cytotoxicity of the QDs was evaluated on a variety of cancer cells such as HeLa, MCF-7, A549, and normal Vero cells by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell viability assay. The results showed that core/double shell QDs were less toxic to the cells when compared to the parent core/shell QDs. MCF-7 cells showed proliferation on incubation with QDs, and this is attributed to the metalloestrogenic activity of cadmium ions released from QDs. The core/double shell CdTe/CdS/ZnS (CSS) QDs were conjugated with transferrin and successfully employed for the biolabeling and fluorescent imaging of HeLa cells. These core/double shell QDs are highly promising fluorescent probe for cancer cell labeling and imaging applications.

Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction

NASA Astrophysics Data System (ADS)

Ahmadi, Sareh; Shariati, M. Nina; Yu, Shun; Göthelid, Mats

2012-08-01

We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the π-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; π-system and the central atom.

Velocities and rotational excitation of interstellar H2 toward Pi Scorpii

NASA Technical Reports Server (NTRS)

Jenkins, Edward B.; Lees, Joanna F.; Van Dishoeck, Ewine F.; Wilcots, Eric M.

1989-01-01

A spectrum of Pi Sco showing numerous atomic lines and 70 absorption features from the Lyman and Werner transitions of interstellar H2 in rotational level J from zero to five is presented. Their shapes of the composite column density profiles are very nearly Gaussian with a one-dimensional rms velocity dispersion of 3 km/s. The behavior of shifts in the inferred N(H2) as a function of velocity are consistent with the overall profiles being composed of nearly symmetrical, tightly paced assemblies of about seven unresolved components. The relative overall column densities in the higher J levels of H2 are consistent with a model where these states are populated by optical pumping through the Lyman and Werner transitions, powered by UV radiation from nearby stars. The slight narrowing of the high-J profiles may be due to small clumps of H2 at radial velocities some 5-8 km/s from the core of the profile are exposed to a pumping flux about 10 times lower than that for the material near the profile's center.

Charge Carrier Dynamics of Quantum Confined Semiconductor Nanoparticles Analyzed via Transient Absorption Spectroscopy

NASA Astrophysics Data System (ADS)

Thibert, Arthur Joseph, III

Semiconductor nanoparticles are tiny crystalline structures (typically range from 1 - 100 nm) whose shape in many cases can be dictated through tailored chemical synthesis with atomic scale precision. The small size of these nanoparticles often results in quantum confinement (spatial confinement of wave functions), which imparts the ability to manipulate band-gap energies thus allowing them to be optimally engineered for different applications (i.e., photovoltaics, photocatalysis, imaging). However, charge carriers excited within these nanoparticles are often involved in many different processes: trapping, trap migration, Auger recombination, non-radiative relaxation, radiative relaxation, oxidation / reduction, or multiple exciton generation. Broadband ultrafast transient absorption laser spectroscopy is used to spectrally resolve the fate of excited charge carriers in both wavelength and time, providing insight as to what synthetic developments or operating conditions will be necessary to optimize their efficiency for certain applications. This thesis outlines the effort of resolving the dynamics of excited charge carriers for several Cd and Si based nanoparticle systems using this experimental technique. The thesis is organized into five chapters and two appendices as indicated below. Chapter 1 provides a brief introduction to the photophysics of semiconductor nanoparticles. It begins by defining what nanoparticles, semiconductors, charge carriers, and quantum confinement are. From there it details how the study of charge carrier dynamics within nanoparticles can lead to increased efficiency in applications such as photocatalysis. Finally, the experimental methodology associated with ultrafast transient absorption spectroscopy is introduced and its power in mapping charge carrier dynamics is established. Chapter 2 (JPCC, 19647, 2011) introduces the first of the studied samples: water-solubilized 2D CdSe nanoribbons (NRs), which were synthesized in the Osterloh laboratory (UCD). The measured signals were decomposed into the constituent dynamics of three transient populations: hot tightly bound excitons, relaxed tightly bound excitons, and separated trapped carriers (holes and electrons). The influenes of three external factors affecting the observed dynamics were explored: (1) excitation wavelength, (2) excitation fluence, and (3) presence of the hole scavenger HS -. Both higher-energy excitation photons and higher-intensity excitation induce slower relaxation of charge carriers to the band edge due to the need to dissipate excess excitation energy. Nonlinear decay kinetics of the relaxed exciton population is observed and demonstrated to arise from bimolecular trapping of excitons with low-density trap sites located at CdSe NR surface sites instead of the commonly resolved multiparticle Auger recombination mechanism. This is supported by the observed linear excitation-fluence dependence of the trapped-carrier population that is n umerically simulated and found to deviate from the excitation fluence dependence expected of Auger recombination kinetics. Introducing hole scavenging HS- has a negligible effect on the exciton kinetics, including migration and dissociation, and instead passivates surface trap states to induce the rapid elimination of holes after exciton dissociation. This increases the lifetime of the reactive electron population and increases measured photocatalytic H2 generation activity. A broad (200 nm) and persistent (20 ps) stimulated emission observed in the tightly bound excitons suggests their potential use as broadband microlasers. In chapter 3 (JPCL, 2688, 2011), the photocatalytic H2O splitting activities of CdSe and CdSe/CdS core/shell quantum dots, which were also synthesized in the Osterloh laboratory (UCD) are contrasted. CdSe/CdS core/shell quantum dots constructed from 4.0 nm CdSe quantum dots are shown to be strongly active for visible-light-driven photocatalytic H2 evolution in 0.1M Na 2S/Na2SO3 solution with a turnover number of 9.94 after 5 h at 103.9 μmol/h. CdSe quantum dots themselves are only marginally active in 0.1 M Na2S/Na2SO3 solution with a turnover number of 1.10 after 5 h at 11.53 μmol/h, while CdSe quantum dots in pure H2O are found to be completely inactive. Broad-band transient absorption spectroscopy is used to elucidate the mechanisms that facilitate the enhancement in the CdSe core/shell quantum dots, which is attributed to passivation of surface-deep trap states with energies lying below the reduction potential necessary for H2O reduction. Thus, it is shown that surface trapping dynamics and energetics can be manipulated to dictate the photocatalytic activities of novel CdSe quantum dot based photocatalytic materials. Chapter 4 builds upon this work examining the differences in dynamics that occur upon passivation of water soluble CdZnS alloy cores with ZnS shells, which were produced in the Snee laboratory (UI Chicago), via 400 nm pump broadband probe ultrafast transient absorption spectroscopy, and global analysis modeling. We also examine the perturbation invoked on charge carrier dynamics caused by growing Pd nanoparticles on the CdZnS/ZnS shell surface in-situ and note the cyclical charge carrier transfer that takes place. Both the CdZnS core and CdZnS/ZnS core/shell quantum dots exhibit unusually long lived excited states (much > 8 ns) while the CdZnS/ZnS.Pd tandem core/shell quantum dots recover much quicker (~3 ns). Additionally, ultrafast excitation fluence dependencies are used to characterize Auger recombination and the presence of two different trap state populations observable in the visible spectrum. In chapter 5 (JACS, 20664, 2011), we switch from examining direct band-gap chalcogenide based quantum dots to Si quantum dots synthesized in the Kauzlarich laboratory (UCD), which exhibit an indirect band-gap. Here a microwave-assisted reaction to produce hydrogen-terminated silicon quantum dots is discussed. The Si quantum dots were passivated for water solubility via two different methods: hydrosilylation produced 3-aminopropenyl-terminated Si quantum dots, and a modified Stöber process produced silica-encapsulated Si quantum dots. Both methods produce water-soluble quantum dots with maximum emission at 414 nm, and after purification, the quantum dots exhibit intrinsic fluorescence quantum yield efficiencies of 15 and 23%, respectively. Even though the quantum dots have different surfaces, they exhibit nearly identical absorption and fluorescence spectra. Femtosecond transient absorption spectroscopy was used for temporal resolution of the photoexcited carrier dynamics between the quantum dots and ligand. The transient dynamics of the 3-aminopropenyl-terminated Si quantum dots is interpreted as a formation and decay of a charge-transfer excited state between the delocalized π electrons of the carbon linker and the Si core excitons. This charge transfer state is stable for ~4 ns before reverting back to a more stable, long-living species. The silica-encapsulated Si QDs show a simpler spectrum without charge transfer dynamics. Appendix I (Chem. Mat., 1220, 2010), addresses the long-time (μs) transient kinetics associated with TiO2 and layered titanates (TBA2 2Ti4O9), which were synthesized in the Osterloh laboratory (UCD). Transient absorption data reveal that photogenerated electrons become trapped in mid band-gap states, from which they decay exponentially with a time-constant of 43.67 + 0.28 ms in titanates, which is much slower than the 68 + 1 ns observed for TiO2 nanocrystals. The slower kinetics observed for the TBA 2Ti4O9 nanosheets originates either from the presence of deeper trap sites on the sheets vs. the nanoparticles, more trap sites, or from more effective electron-hole separation because of the micrometer dimensions of the 2D lattice. Appendix II, depicts the visible solar spectrum at sea level detailing the percentage of photons and energy that exist within certain wavelength ranges.

Improving sound absorption property of polyurethane foams doped with natural fiber

NASA Astrophysics Data System (ADS)

Azahari, M. Shafiq M.; Rus, Anika Zafiah M.; Taufiq Zaliran, M.; Kormin, Shaharuddin

2017-08-01

This study investigates the acoustics behavior of wood fibre filler of Red Meranti - filled polyurethane foam as a sound absorbing material. Three different thicknesses have been selected which is 10 mm, 20 mm and 30 mm. By choosing percentage loading of Red Meranti (RM) wood fibre of 5%, 10%, 15% and 20% added with polymer foam is namely as polymer foam (PF) composites of PF5%, PF10%, PF15% and PF20%. The sound absorption coefficient (α) and pore structure of the foam samples have been examined by using Impedance Tube test and Scanning Electron Microscopy (SEM). The results revealed that the highest thickness of highest filler loading (PF20%) gives higher sound absorption coefficient (α). The absorption frequency level is observed at 0.9922 and 0.99889 which contributed from low and high frequency absorption level respectively. The smallest pores size structure was observed with highest filler loading of PF. The higher the thickness and the higher the percentage loading of wood filler gives smaller pore structure, consequently, increased the sound absorption coefficient level.

Comparison of predicted engine core noise with current and proposed aircraft noise certification requirements

NASA Technical Reports Server (NTRS)

Vonglahn, U. H.; Groesbeck, D. E.

1981-01-01

Predicted engine core noise levels are compared with measured total aircraft noise levels and with current and proposed federal noise certification requirements. Comparisons are made at the FAR-36 measuring stations and include consideration of both full- and cutback-power operation at takeoff. In general, core noise provides a barrier to achieving proposed EPA stage 5 noise levels for all types of aircraft. More specifically, core noise levels will limit further reductions in aircraft noise levels for current widebody commercial aircraft.

[Effects of aluminum on neurobehavioral function and metabolism of monoamine neurotransmitter].

PubMed

Yang, H; Zheng, Y; Liang, Y

1998-03-01

To evaluate the effects of occupational exposure to aluminum on neurobahavioral function and metabolism of monoamine neurotransmitter. Thirty-three workers exposed to aluminum and 40 controls were studied. Air aluminum concentrations in workplace environment were detected with an atomic absorption spectrophotometer, homovanillic acid (HVA) and vanilylmandellic acid (VMA) in urine and aluminum in serum and urine were detected with high perfolmance liquid chromatography. Neurobehavioral function was tested with Neurobehavioral Core Test Battery recommended by WHO. Geometric time-weighted average of aluminum in workplace environment was 0.95 mg/m3, ranging from 0.31 to 4.12 mg/m3, and urine aluminum levels in workers exposed to aluminum averaged 12.25 micrograms/L, significantly higher than that in controls (5.78 micrograms/L). There was no significant difference in serum aluminum between the exposed and controls. Both urine VMA and HVA levels were higher in the workers exposed to aluminum, and urine VMA level in the exposed was significantly higher than that in controls. There was significant difference in neurobehavioral test, including Santa Ana, digit symbol and Benton tests between the exposed and control workers. It suggests that occupational exposure to low level of aluminum can affect the neurobehavioral function and metabolism of monoamine neurotransmitter.

Application of Ni-Oxide@TiO2 Core-Shell Structures to Photocatalytic Mixed Dye Degradation, CO Oxidation, and Supercapacitors

PubMed Central

Lee, Seungwon; Lee, Jisuk; Nam, Kyusuk; Shin, Weon Gyu; Sohn, Youngku

2016-01-01

Performing diverse application tests on synthesized metal oxides is critical for identifying suitable application areas based on the material performances. In the present study, Ni-oxide@TiO2 core-shell materials were synthesized and applied to photocatalytic mixed dye (methyl orange + rhodamine + methylene blue) degradation under ultraviolet (UV) and visible lights, CO oxidation, and supercapacitors. Their physicochemical properties were examined by field-emission scanning electron microscopy, X-ray diffraction analysis, Fourier-transform infrared spectroscopy, and UV-visible absorption spectroscopy. It was shown that their performances were highly dependent on the morphology, thermal treatment procedure, and TiO2 overlayer coating. PMID:28774145

Laser Frequency Stabilization for Coherent Lidar Applications using Novel All-Fiber Gas Reference Cell Fabrication Technique

NASA Technical Reports Server (NTRS)

Meras, Patrick, Jr.; Poberezhskiy, Ilya Y.; Chang, Daniel H.; Levin, Jason; Spiers, Gary D.

2008-01-01

Compact hollow-core photonic crystal fiber (HC-PCF)gas frequency reference cell was constructed using a novel packaging technique that relies on torch-sealing a quartz filling tube connected to a mechanical splice between regular and hollow-core fibers. The use of this gas cell for laser frequency stabilization was demonstrated by locking a tunable diode laser to the center of the P9 line from the (nu)1+(nu)3 band of acetylene with RMS frequency error of 2.06 MHz over 2 hours. This effort was performed in support of a task to miniaturize the laser frequency stabilization subsystem of JPL/LMCT Laser Absorption Spectrometer (LAS) instrument.

Black GE based on crystalline/amorphous core/shell nanoneedle arrays

DOEpatents

Javey, Ali; Chueh, Yu-Lun; Fan, Zhiyong

2014-03-04

Direct growth of black Ge on low-temperature substrates, including plastics and rubber is reported. The material is based on highly dense, crystalline/amorphous core/shell Ge nanoneedle arrays with ultrasharp tips (.about.4 nm) enabled by the Ni catalyzed vapor-solid-solid growth process. Ge nanoneedle arrays exhibit remarkable optical properties. Specifically, minimal optical reflectance (<1%) is observed, even for high angles of incidence (.about.75.degree.) and for relatively short nanoneedle lengths (.about.1 .mu.m). Furthermore, the material exhibits high optical absorption efficiency with an effective band gap of .about.1 eV. The reported black Ge can have important practical implications for efficient photovoltaic and photodetector applications on nonconventional substrates.

New technique for the direct measurement of core noise from aircraft engines

NASA Technical Reports Server (NTRS)

Krejsa, E. A.

1981-01-01

A new technique is presented for directly measuring the core noise levels from gas turbine aircraft engines. The technique requires that fluctuating pressures be measured in the far-field and at two locations within the engine core. The cross-spectra of these measurements are used to determine the levels of the far-field noise that propagated from the engine core. The technique makes it possible to measure core noise levels even when other noise sources dominate. The technique was applied to signals measured from an AVCO Lycoming YF102 turbofan engine. Core noise levels as a function of frequency and radiation angle were measured and are presented over a range of power settings.

Application of spatially modulated near-infrared structured light to study changes in optical properties of mouse brain tissue during heatstress.

PubMed

Shaul, Oren; Fanrazi-Kahana, Michal; Meitav, Omri; Pinhasi, Gad A; Abookasis, David

2017-11-10

Heat stress (HS) is a medical emergency defined by abnormally elevated body temperature that causes biochemical, physiological, and hematological changes. The goal of the present research was to detect variations in optical properties (absorption, reduced scattering, and refractive index coefficients) of mouse brain tissue during HS by using near-infrared (NIR) spatial light modulation. NIR spatial patterns with different spatial phases were used to differentiate the effects of tissue scattering from those of absorption. Decoupling optical scattering from absorption enabled the quantification of a tissue's chemical constituents (related to light absorption) and structural properties (related to light scattering). Technically, structured light patterns at low and high spatial frequencies of six wavelengths ranging between 690 and 970 nm were projected onto the mouse scalp surface while diffuse reflected light was recorded by a CCD camera positioned perpendicular to the mouse scalp. Concurrently to pattern projection, brain temperature was measured with a thermal camera positioned slightly off angle from the mouse head while core body temperature was monitored by thermocouple probe. Data analysis demonstrated variations from baseline measurements in a battery of intrinsic brain properties following HS.

Ultraviolet absorption by highly ionized atoms in the Orion Nebula

NASA Technical Reports Server (NTRS)

Franco, J.; Savage, B. D.

1982-01-01

The International Ultraviolet Explorer was used to obtain high-resolution, far-UV spectra of theta 1 A, theta 1 C, theta 1 D, and theta 2 A Orionis. The interstellar absorption lines in these spectra are discussed with an emphasis on the high-ionization lines of C IV and Si IV. Theta 2 A Ori has interstellar C IV and Si IV absorption of moderate strength at the velocity found for normal H II region ions. Theta 1 C Ori has very strong interstellar C IV and Si IV absorption at velocities blueshifted by about 25 km/s from that found for the normal H II region ions. The possible origin of the high-ionization lines by three processes is considered: X-ray ionization, collisional ionization, and UV photoionization. It is concluded that the C IV and Si IV ions toward theta 2 A and theta 1 C Ori are likely produced by UV photoionization of surrounding nebular gas. In the case of theta 1 C Ori, the velocity shift of the high-ionization lines may be produced through the acceleration of high-density globules in the core of the nebula by the stellar wind of theta 1 C Ori.

Comparison of the Optical Properties of Graphene and Alkyl-terminated Si and Ge Quantum Dots.

PubMed

de Weerd, Chris; Shin, Yonghun; Marino, Emanuele; Kim, Joosung; Lee, Hyoyoung; Saeed, Saba; Gregorkiewicz, Tom

2017-10-31

Semiconductor quantum dots are widely investigated due to their size dependent energy structure. In particular, colloidal quantum dots represent a promising nanomaterial for optoelectronic devices, such as photodetectors and solar cells, but also luminescent markers for biotechnology, among other applications. Ideal materials for these applications should feature efficient radiative recombination and absorption transitions, altogether with spectral tunability over a wide range. Group IV semiconductor quantum dots can fulfill these requirements and serve as an alternative to the commonly used direct bandgap materials containing toxic and/or rare elements. Here, we present optical properties of butyl-terminated Si and Ge quantum dots and compare them to those of graphene quantum dots, finding them remarkably similar. We investigate their time-resolved photoluminescence emission as well as the photoluminescence excitation and linear absorption spectra. We contemplate that their emission characteristics indicate a (semi-) resonant activation of the emitting channel; the photoluminescence excitation shows characteristics similar to those of a molecule. The optical density is consistent with band-to-band absorption processes originating from core-related states. Hence, these observations strongly indicate a different microscopic origin for absorption and radiative recombination in the three investigated quantum dot systems.

Design of dual-diameter nanoholes for efficient solar-light harvesting

PubMed Central

2014-01-01

A dual-diameter nanohole (DNH) photovoltaic system is proposed, where a top (bottom) layer with large (small) nanoholes is used to improve the absorption for the short-wavelength (long-wavelength) solar incidence, leading to a broadband light absorption enhancement. Through three-dimensional finite-element simulation, the core device parameters, including the lattice constant, nanohole diameters, and nanohole depths, are engineered in order to realize the best light-matter coupling between nanostructured silicon and solar spectrum. The designed bare DNH system exhibits an outstanding absorption capability with a photocurrent density (under perfect internal quantum process) predicted to be 27.93 mA/cm2, which is 17.39%, 26.17%, and over 100% higher than the best single-nanohole (SNH) system, SNH system with an identical Si volume, and equivalent planar configuration, respectively. Considering the fabrication feasibility, a modified DNH system with an anti-reflection coating and back silver reflector is examined by simulating both optical absorption and carrier transport in a coupled way in frequency and three-dimensional spatial domains, achieving a light-conversion efficiency of 13.72%. PACS 85.60.-q; Optoelectronic device; 84.60.Jt; Photovoltaic conversion PMID:25258605

Light Absorption Enhancement of Black Carbon Aerosol Constrained by Particle Morphology.

PubMed

Wu, Yu; Cheng, Tianhai; Liu, Dantong; Allan, James D; Zheng, Lijuan; Chen, Hao

2018-06-19

The radiative forcing of black carbon aerosol (BC) is one of the largest sources of uncertainty in climate change assessments. Contrasting results of BC absorption enhancement ( E abs ) after aging are estimated by field measurements and modeling studies, causing ambiguous parametrizations of BC solar absorption in climate models. Here we quantify E abs using a theoretical model parametrized by the complex particle morphology of BC in different aging scales. We show that E abs continuously increases with aging and stabilizes with a maximum of ∼3.5, suggesting that previous seemingly contrast results of E abs can be explicitly described by BC aging with corresponding particle morphology. We also report that current climate models using Mie Core-Shell model may overestimate E abs at a certain aging stage with a rapid rise of E abs , which is commonly observed in the ambient. A correction coefficient for this overestimation is suggested to improve model predictions of BC climate impact.

Dynamical Core-Hole Screening in the X-Ray Absorption Spectra of Hydrogenated Carbon Nanotubes And Graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wessely, O.; /Uppsala U. /Imperial Coll., London; Katsnelson, M.I.

2009-04-30

We have calculated the electronic structure and the x-ray absorption (XA) spectrum of a hydrogenated single graphite plane, in order to simulate recent experimental results on hydrogenated single wall carbon nanotubes (SWCNT) as well as hydrogenated graphene. We find that the presence of H induces a substantial component of sp{sup 3} bonding and as a result the {pi} and {pi}* components to the electronic structure vanish. We have calculated a theoretical x-ray absorption spectrum using a multiband version of the Mahan-Nozieres-De Dominicis theory. By making a fitting of the XA signal of C atoms that have H attached to themmore » and C atoms without H in the vicinity we obtain a good representation of the experimental data and we can draw the conclusion that in the experiments [A. Nikitin et al., Phys. Rev. Lett. 95, 225507 (2005)] some 35-50 % H have been absorbed in the SWCNT.« less

Jet-resolved vibronic structure in the higher excited states of N2O - Ultraviolet three-photon absorption spectroscopy from 80,000 to 90,000/cm

NASA Technical Reports Server (NTRS)

Patsilinakou, E.; Wiedmann, R. T.; Fotakis, C.; Grant, E. R.

1989-01-01

Ionization-detected UV multiphoton absorption spectroscopy of the excited states of N2O is presented, showing Rydberg structure within 20,000/cm of the first ionization threshold. Despite evidence for strong Rydberg-continuum coupling in the form of broadened bands and Fano line-shapes, the Rydberg structure persists, with atomic-like quantum defects and vibration structure well-matched with that of the ion. In the most clearly resolved spectrum, corresponding to the 3p(delta)1Pi state, Renner-Teller and Herzberg-Teller coupling of electronic and vibrational angular momentum are revealed. It is suggested that these mixings are properties of the N2O(+)Pi ion core.