Surface sum-frequency vibrational spectroscopy of nonpolar media

DOE PAGES

Sun, Shumei; Tian, Chuanshan; Shen, Y. Ron

2015-04-27

Sum-frequency generation spectroscopy is surface specific only if the bulk contribution to the signal is negligible. Negligible bulk contribution is, however, not necessarily true, even for media with inversion symmetry. The inevitable challenge is to find the surface spectrum in the presence of bulk contribution, part of which has been believed to be inseparable from the surface contribution. Here, we show that, for nonpolar media, it is possible to separately deduce surface and bulk spectra from combined phase-sensitive sum-frequency vibrational spectroscopic measurements in reflection and transmission. Finally, the study of benzene interfaces is presented as an example.

Observation of sum-frequency-generation-induced cascaded four-wave mixing using two crossing femtosecond laser pulses in a 0.1 mm beta-barium-borate crystal.

PubMed

Liu, Weimin; Zhu, Liangdong; Fang, Chong

2012-09-15

We demonstrate the simultaneous generation of multicolor femtosecond laser pulses spanning the wavelength range from UV to near IR in a 0.1 mm Type I beta-barium borate crystal from 800 nm fundamental and weak IR super-continuum white light (SCWL) pulses. The multicolor broadband laser pulses observed are attributed to two concomitant cascaded four-wave mixing (CFWM) processes as corroborated by calculation: (1) directly from the two incident laser pulses; (2) by the sum-frequency generation (SFG) induced CFWM process (SFGFWM). The latter signal arises from the interaction between the frequency-doubled fundamental pulse (400 nm) and the SFG pulse generated in between the fundamental and IR-SCWL pulses. The versatility and simplicity of this spatially dispersed multicolor self-compressed laser pulse generation offer compact and attractive methods to conduct femtosecond stimulated Raman spectroscopy and time-resolved multicolor spectroscopy.

Photon wave function formalism for analysis of Mach–Zehnder interferometer and sum-frequency generation

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

Ritboon, Atirach, E-mail: atirach.3.14@gmail.com; Department of Physics, Faculty of Science, Prince of Songkla University, Hat Yai 90112; Daengngam, Chalongrat, E-mail: chalongrat.d@psu.ac.th

2016-08-15

Biakynicki-Birula introduced a photon wave function similar to the matter wave function that satisfies the Schrödinger equation. Its second quantization form can be applied to investigate nonlinear optics at nearly full quantum level. In this paper, we applied the photon wave function formalism to analyze both linear optical processes in the well-known Mach–Zehnder interferometer and nonlinear optical processes for sum-frequency generation in dispersive and lossless medium. Results by photon wave function formalism agree with the well-established Maxwell treatments and existing experimental verifications.

Cross-Propagation Sum-Frequency Generation Vibrational Spectroscopy

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

Fu, Li; Chen, Shun-li; Gan, Wei

2016-02-27

Here we report the theory formulation and the experiment realization of sum-frequency generation vibrational spectroscopy (SFG-VS) in the cross-propagation (XP) geometry or configuration. In the XP geometry, the visible and the infrared (IR) beams in the SFG experiment are delivered to the same location on the surface from visible and IR incident planes perpendicular to each other, avoiding the requirement to have windows or optics to be transparent to both the visible and IR frequencies. Therefore, the XP geometry is applicable to study surfaces in the enclosed vacuum or high pressure chambers with far infrared (FIR) frequencies that can directlymore » access the metal oxide and other lower frequency surface modes, with much broader selection of visible and IR transparent window materials.« less

Second order harmonic guided wave mutual interactions in plate: Vector analysis, numerical simulation, and experimental results

NASA Astrophysics Data System (ADS)

Hasanian, Mostafa; Lissenden, Cliff J.

2017-08-01

The extraordinary sensitivity of nonlinear ultrasonic waves to the early stages of material degradation makes them excellent candidates for nondestructive material characterization. However, distinguishing weak material nonlinearity from instrumentation nonlinearity remains problematic for second harmonic generation approaches. A solution to this problem is to mix waves having different frequencies and to let their mutual interaction generate sum and difference harmonics at frequencies far from those of the instrumentation. Mixing of bulk waves and surface waves has been researched for some time, but mixing of guided waves has not yet been investigated in depth. A unique aspect of guided waves is their dispersive nature, which means we need to assure that a wave can propagate at the sum or difference frequency. A wave vector analysis is conducted that enables selection of primary waves traveling in any direction that generate phase matched secondary waves. We have tabulated many sets of primary waves and phase matched sum and difference harmonics. An example wave mode triplet of two counter-propagating collinear shear horizontal waves that interact to generate a symmetric Lamb wave at the sum frequency is simulated using finite element analysis and then laboratory experiments are conducted. The finite element simulation eliminates issues associated with instrumentation nonlinearities and signal-to-noise ratio. A straightforward subtraction method is used in the experiments to identify the material nonlinearity induced mutual interaction and show that the generated Lamb wave propagates on its own and is large enough to measure. Since the Lamb wave has different polarity than the shear horizontal waves the material nonlinearity is clearly identifiable. Thus, the mutual interactions of shear horizontal waves in plates could enable volumetric characterization of material in remote regions from transducers mounted on just one side of the plate.

Flattop wideband wavelength converters based on cascaded sum and difference-frequency generation using step-chirped gratings

NASA Astrophysics Data System (ADS)

Tehranchi, Amirhossein; Kashyap, Raman

2011-03-01

We investigate the role of step-chirped gratings (SCG) for flattening of conversion efficiency response and enhancing the pump bandwidth in cascaded sum and difference frequency generation (SFG + DFG) with a large pump wavelength difference. To obtain a flat response with maximum efficiency, using SCG instead of uniform grating with the same length, the appropriate critical period shifts are presented for the reasonable number of sections and chirp steps feasible for fabrication. Furthermore, it is shown that adding the section numbers for SCG structure increases the pump bandwidth.

Continuous-wave sodium D2 resonance radiation generated in single-pass sum-frequency generation with periodically poled lithium niobate.

PubMed

Yue, J; She, C-Y; Williams, B P; Vance, J D; Acott, P E; Kawahara, T D

2009-04-01

With two cw single-mode Nd:YAG lasers at 1064 and 1319 nm and a periodically poled lithium niobate crystal, 11 mW of 2 kHz/100 ms bandwidth single-mode tunable 589 nm cw radiation has been detected using single-pass sum-frequency generation. The demonstrated conversion efficiency is approximately 3.2%[W(-1) cm(-1)]. This compact solid-state light source has been used in a solid-state-dye laser hybrid sodium fluorescence lidar transmitter to measure temperatures and winds in the upper atmosphere (80-105 km); it is being implemented into the transmitter of a mobile all-solid-state sodium temperature and wind lidar under construction.

Vibrationally resonant sum-frequency generation microscopy with a solid immersion lens

PubMed Central

Lee, Eun Seong; Lee, Sang-Won; Hsu, Julie; Potma, Eric O.

2014-01-01

We use a hemispheric sapphire lens in combination with an off-axis parabolic mirror to demonstrate high-resolution vibrationally resonant sum-frequency generation (VR-SFG) microscopy in the mid-infrared range. With the sapphire lens as an immersed solid medium, the numerical aperture (NA) of the parabolic mirror objective is enhanced by a factor of 1.72, from 0.42 to 0.72, close to the theoretical value of 1.76 ( = nsapphire). The measured lateral resolution is as high as 0.64 μm. We show the practical utility of the sapphire immersion lens by imaging collagen-rich tissues with and without the solid immersion lens. PMID:25071953

Intensity enhancement of vibrational sum frequency generation by gap-mode plasmon resonance

NASA Astrophysics Data System (ADS)

Okuno, Masanari; Tokimoto, Taichi; Eguchi, Miharu; Kano, Hideaki; Ishibashi, Taka-aki

2015-10-01

A metal sphere-plane structure consisting of gold nanoparticles, p-methylbenzenethiol and a gold substrate was measured by vibrational sum frequency generation spectroscopy with four excitation wavelengths, 630, 680, 720, and 780 nm. The enhancement factors of Raman signals were estimated to be 250 and 104 for the 532 and 647 nm excitation. Contrastingly, we found that the enhancements of VSFG signals were much smaller, a factor of 5 at maximum. We speculate that the small enhancement factor of VSFG signals is due to the coherent nature of the VSFG process or the extinction of the infrared laser by the gold nanoparticles.

Quantum frequency up-conversion of continuous variable entangled states

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

Liu, Wenyuan; Wang, Ning; Li, Zongyang

We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pumpmore » field, making it a practical building block for quantum information processing and communication networks.« less

Unified treatment and measurement of the spectral resolution and temporal effects in frequency-resolved sum-frequency generation vibrational spectroscopy (SFG-VS).

PubMed

Velarde, Luis; Wang, Hong-Fei

2013-12-14

The lack of understanding of the temporal effects and the restricted ability to control experimental conditions in order to obtain intrinsic spectral lineshapes in surface sum-frequency generation vibrational spectroscopy (SFG-VS) have limited its applications in surface and interfacial studies. The emergence of high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) with sub-wavenumber resolution [Velarde et al., J. Chem. Phys., 2011, 135, 241102] offers new opportunities for obtaining and understanding the spectral lineshapes and temporal effects in SFG-VS. Particularly, the high accuracy of the HR-BB-SFG-VS experimental lineshape provides detailed information on the complex coherent vibrational dynamics through direct spectral measurements. Here we present a unified formalism for the theoretical and experimental routes for obtaining an accurate lineshape of the SFG response. Then, we present a detailed analysis of a cholesterol monolayer at the air/water interface with higher and lower resolution SFG spectra along with their temporal response. With higher spectral resolution and accurate vibrational spectral lineshapes, it is shown that the parameters of the experimental SFG spectra can be used both to understand and to quantitatively reproduce the temporal effects in lower resolution SFG measurements. This perspective provides not only a unified picture but also a novel experimental approach to measuring and understanding the frequency-domain and time-domain SFG response of a complex molecular interface.

Salt Effects on Surface Structures of Polyelectrolyte Multilayers (PEMs) Investigated by Vibrational Sum Frequency Generation (SFG) Spectroscopy.

PubMed

Ge, Aimin; Matsusaki, Michiya; Qiao, Lin; Akashi, Mitsuru; Ye, Shen

2016-04-26

Sum frequency generation (SFG) vibrational spectroscopy was employed to investigate the surface structures of polyelectrolyte multilayers (PEMs) constructed by sequentially alternating adsorption of poly(diallyldimethylammonium chloride) (PDDA) and poly(styrenesulfonate) (PSS). It was found that the surface structures and surface charge density of the as-deposited PEMs of PDDA/PSS significantly depend on the concentration of sodium chloride (NaCl) present in the polyelectrolyte solutions. Furthermore, it was found that the surface structure of the as-deposited PEMs is in a metastable state and will reach the equilibrium state by diffusion of the polyelectrolyte chain after an aging process, resulting in a polyelectrolyte mixture on the PEM surfaces.

Self-assembled organic and fullerene monolayers characterisation by two-colour SFG spectroscopy: a pathway to meet doubly resonant SFG process

NASA Astrophysics Data System (ADS)

Humbert, C.; Caudano, Y.; Dreesen, L.; Sartenaer, Y.; Mani, A. A.; Silien, C.; Lemaire, J.-J.; Thiry, P. A.; Peremans, A.

2004-10-01

Two-colour sum-frequency generation (two-colour SFG) spectroscopy was used to probe both vibrational and electronic properties of 1-dodecanethiol/Ag(1 1 1), Au(1 1 1), and Pt(1 1 1), of 5-[ p-(6-mercaptohexoxy)-phenyl]-10,15,20-triphenylporphin/Pt(1 1 1), and of C 60/Ag(1 1 1). The role of the various physical parameters determining the sum-frequency generation (SFG) intensity equation is highlighted. The enhancement of the non-linear second order susceptibility in the aforementioned interfaces is explained in terms of metal interband transition, molecular electronic transition and of electron-phonon coupling, respectively.

First-Principles Framework to Compute Sum-Frequency Generation Vibrational Spectra of Semiconductors and Insulators.

PubMed

Wan, Quan; Galli, Giulia

2015-12-11

We present a first-principles framework to compute sum-frequency generation (SFG) vibrational spectra of semiconductors and insulators. The method is based on density functional theory and the use of maximally localized Wannier functions to compute the response to electric fields, and it includes the effect of electric field gradients at surfaces. In addition, it includes quadrupole contributions to SFG spectra, thus enabling the verification of the dipole approximation, whose validity determines the surface specificity of SFG spectroscopy. We compute the SFG spectra of ice I_{h} basal surfaces and identify which spectra components are affected by bulk contributions. Our results are in good agreement with experiments at low temperature.

Wetting effect on optical sum frequency generation (SFG) spectra of D-glucose, D-fructose, and sucrose

NASA Astrophysics Data System (ADS)

Hieu, Hoang Chi; Li, Hongyan; Miyauchi, Yoshihiro; Mizutani, Goro; Fujita, Naoko; Nakamura, Yasunori

2015-03-01

We report a sum frequency generation (SFG) spectroscopy study of D-glucose, D-fructose and sucrose in the Csbnd H stretching vibration regime. Wetting effect on the SFG spectra was investigated. The SFG spectrum of D-glucose changed from that of α-D-glucose into those of α-D-glucose monohydrate by wetting. The SFG spectra showed evidence of a small change of β-D-fructopyranose into other anomers by wetting. SFG spectra of sucrose did not change by wetting. Assignments of the vibrational peaks in the SFG spectra of the three sugars in the dry and wet states were performed in the Csbnd H stretching vibration region near 3000 cm-1.

Wetting effect on optical sum frequency generation (SFG) spectra of d-glucose, d-fructose, and sucrose.

PubMed

Hieu, Hoang Chi; Li, Hongyan; Miyauchi, Yoshihiro; Mizutani, Goro; Fujita, Naoko; Nakamura, Yasunori

2015-03-05

We report a sum frequency generation (SFG) spectroscopy study of d-glucose, d-fructose and sucrose in the CH stretching vibration regime. Wetting effect on the SFG spectra was investigated. The SFG spectrum of d-glucose changed from that of α-d-glucose into those of α-d-glucose monohydrate by wetting. The SFG spectra showed evidence of a small change of β-d-fructopyranose into other anomers by wetting. SFG spectra of sucrose did not change by wetting. Assignments of the vibrational peaks in the SFG spectra of the three sugars in the dry and wet states were performed in the CH stretching vibration region near 3000cm(-1). Copyright © 2014 Elsevier B.V. All rights reserved.

Generation of energetic femtosecond green pulses based on an OPCPA-SFG scheme.

PubMed

Mero, M; Sipos, A; Kurdi, G; Osvay, K

2011-05-09

Femtosecond green pulses were generated from broadband pulses centered at 800 nm and quasi-monochromatic pulses centered at 532 nm using noncollinear optical parametric chirped pulse amplification (NOPCPA) followed by sum frequency mixing. In addition to amplifying the 800-nm pulses, the NOPCPA stage pumped by a Q-switched, injection seeded Nd:YAG laser also provided broadband idler pulses at 1590 nm. The signal and idler pulses were sum frequency mixed using achromatic and chirp assisted phase matching yielding pulses near 530 nm with a bandwidth of 12 nm and an energy in excess of 200 μJ. The generated pulses were recompressed with a grating compressor to a duration of 150 fs. The technique is scalable to high energies, broader bandwidths, and shorter pulse durations with compensation for higher order chirps and dedicated engineering of the interacting beams. © 2011 Optical Society of America

Combined IR-Raman vs vibrational sum-frequency heterospectral correlation spectroscopy

NASA Astrophysics Data System (ADS)

Roy, Sandra; Beutier, Clémentine; Hore, Dennis K.

2018-06-01

Vibrational sum-frequency generation spectroscopy is a valuable probe of surface structure, particularly when the same molecules are present in one of the adjacent bulk solid or solution phases. As a result of the non-centrosymmetric requirement of SFG, the signal generated is a marker of the extent to which the molecules are ordered in an arrangement that breaks the up-down symmetry at the surface. In cases where the accompanying changes in the bulk are of interest in understanding and interpreting the surface structure, simultaneous analysis of the bulk IR absorption or bulk Raman scattering is helpful, and may be used in heterospectral surface-bulk two-dimensional correlation. We demonstrate that, in such cases, generating a new type of bulk spectrum that combines the IR and Raman amplitudes is a better candidate than the individual IR and Raman spectra for the purpose of correlation with the SFG signal.

Photon entanglement signatures in difference-frequency-generation

PubMed Central

Roslyak, Oleksiy; Mukamel, Shaul

2010-01-01

In response to quantum optical fields, pairs of molecules generate coherent nonlinear spectroscopy signals. Homodyne signals are given by sums over terms each being a product of Liouville space pathways of the pair of molecules times the corresponding optical field correlation function. For classical fields all field correlation functions may be factorized and become identical products of field amplitudes. The signal is then given by the absolute square of a susceptibility which in turn is a sum over pathways of a single molecule. The molecular pathways of different molecules in the pair are uncorrelated in this case (each path of a given molecule can be accompanied by any path of the other). However, entangled photons create an entanglement between the molecular pathways. We use the superoperator nonequlibrium Green’s functions formalism to demonstrate the signatures of this pathway-entanglement in the difference frequency generation signal. Comparison is made with an analogous incoherent two-photon fluorescence signal. PMID:19158927

Broadband sum-frequency generation using d₃₃ in periodically poled LiNbO₃ thin film in the telecommunications band.

PubMed

Li, Guangzhen; Chen, Yuping; Jiang, Haowei; Chen, Xianfeng

2017-03-01

We demonstrate the first, to the best of our knowledge, type-0 broadband sum-frequency generation (SFG) based on single-crystal periodically poled LiNbO₃ (PPLN) thin film. The broad bandwidth property was largely tuned from mid-infrared region to the telecommunications band by engineering the thickness of PPLN from bulk crystal to nanoscale. It provides SFG a solution with both broadband and high efficiency by using the highest nonlinear coefficient d₃₃ instead of d₃₁ in type-I broadband SFG or second-harmonic generation. The measured 3 dB upconversion bandwidth is about 15.5 nm for a 4 cm long single crystal at 1530 nm wavelength. It can find applications in chip-scale spectroscopy, quantum information processing, LiNbO₃-thin-film-based microresonator and optical nonreciprocity devices, etc.

Driving an Active Vibration Balancer to Minimize Vibrations at the Fundamental and Harmonic Frequencies

NASA Technical Reports Server (NTRS)

Holliday, Ezekiel S. (Inventor)

2014-01-01

Vibrations of a principal machine are reduced at the fundamental and harmonic frequencies by driving the drive motor of an active balancer with balancing signals at the fundamental and selected harmonics. Vibrations are sensed to provide a signal representing the mechanical vibrations. A balancing signal generator for the fundamental and for each selected harmonic processes the sensed vibration signal with adaptive filter algorithms of adaptive filters for each frequency to generate a balancing signal for each frequency. Reference inputs for each frequency are applied to the adaptive filter algorithms of each balancing signal generator at the frequency assigned to the generator. The harmonic balancing signals for all of the frequencies are summed and applied to drive the drive motor. The harmonic balancing signals drive the drive motor with a drive voltage component in opposition to the vibration at each frequency.

Guided wave methods and apparatus for nonlinear frequency generation

DOEpatents

Durfee, III, Charles G.; Rundquist, Andrew; Kapteyn, Henry C.; Murnane, Margaret M.

2000-01-01

Methods and apparatus are disclosed for the nonlinear generation of sum and difference frequencies of electromagnetic radiation propagating in a nonlinear material. A waveguide having a waveguide cavity contains the nonlinear material. Phase matching of the nonlinear generation is obtained by adjusting a waveguide propagation constant, the refractive index of the nonlinear material, or the waveguide mode in which the radiation propagates. Phase matching can be achieved even in isotropic nonlinear materials. A short-wavelength radiation source uses phase-matched nonlinear generation in a waveguide to produce high harmonics of a pulsed laser.

Flexible approach to vibrational sum-frequency generation using shaped near-infrared light

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

Chowdhury, Azhad U.; Liu, Fangjie; Watson, Brianna R.

We describe a new approach that expands the utility of vibrational sum-frequency generation (vSFG) spectroscopy using shaped near-infrared (NIR) laser pulses. Here, we demonstrate that arbitrary pulse shapes can be specified to match experimental requirements without the need for changes to the optical alignment. In this way, narrowband NIR pulses as long as 5.75 ps are readily generated, with a spectral resolution of about 2.5 cm -1, an improvement of approximately a factor of 3 compared to a typical vSFG system. Moreover, the utility of having complete control over the NIR pulse characteristics is demonstrated through nonresonant background suppression frommore » a metallic substrate by generating an etalon waveform in the pulse shaper. The flexibility afforded by switching between arbitrary NIR waveforms at the sample position with the same instrument geometry expands the type of samples that can be studied without extensive modifications to existing apparatuses or large investments in specialty optics.« less

Flexible approach to vibrational sum-frequency generation using shaped near-infrared light

DOE PAGES

Chowdhury, Azhad U.; Liu, Fangjie; Watson, Brianna R.; ...

2018-04-23

We describe a new approach that expands the utility of vibrational sum-frequency generation (vSFG) spectroscopy using shaped near-infrared (NIR) laser pulses. Here, we demonstrate that arbitrary pulse shapes can be specified to match experimental requirements without the need for changes to the optical alignment. In this way, narrowband NIR pulses as long as 5.75 ps are readily generated, with a spectral resolution of about 2.5 cm -1, an improvement of approximately a factor of 3 compared to a typical vSFG system. Moreover, the utility of having complete control over the NIR pulse characteristics is demonstrated through nonresonant background suppression frommore » a metallic substrate by generating an etalon waveform in the pulse shaper. The flexibility afforded by switching between arbitrary NIR waveforms at the sample position with the same instrument geometry expands the type of samples that can be studied without extensive modifications to existing apparatuses or large investments in specialty optics.« less

Experimental demonstration of wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) in LiNbO3 waveguides

NASA Astrophysics Data System (ADS)

Wang, Jian; Sun, Junqiang; Lou, Chuanhong; Sun, Qizhen

2005-09-01

All-optical wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) is proposed and experimentally demonstrated in periodically poled LiNbO3 (PPLN) waveguides. The signal pulse with 40-GHz repetition rate and 1.57- ps pulse width is adopted. The converted idler wavelength can be tuned from 1527.4 to 1540.5nm as the signal wavelength is varied from 1561.9 to 1548.4nm. No obvious changes of the pulse shape and width, also no chirp are observed in the converted idler pulse. The results imply that single-to-multiple channel wavelength conversions can be achieved by appropriately tuning the two pump wavelengths.

Experimental demonstration of wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) in LiNbO3 waveguides.

PubMed

Wang, Jian; Sun, Junqiang; Lou, Chuanhong; Sun, Qizhen

2005-09-19

All-optical wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) is proposed and experimentally demonstrated in periodically poled LiNbO3 (PPLN) waveguides. The signal pulse with 40-GHz repetition rate and 1.57- ps pulse width is adopted. The converted idler wavelength can be tuned from 1527.4 to 1540.5nm as the signal wavelength is varied from 1561.9 to 1548.4nm. No obvious changes of the pulse shape and width, also no chirp are observed in the converted idler pulse. The results imply that single-to-multiple channel wavelength conversions can be achieved by appropriately tuning the two pump wavelengths.

Orientations of nonlocal vibrational modes from combined experimental and theoretical sum frequency spectroscopy

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

Chase, Hilary M.; Chen, Shunli; Fu, Li

2017-09-01

Inferring molecular orientations from vibrational sum frequency generation (SFG) spectra is challenging in polarization combinations that result in low signal intensities, or when the local point group symmetry approximation fails. While combining experiments with density functional theory (DFT) could overcome this problem, the scope of the combined method has yet to be established. Here, we assess its feasibility of determining the distributions of molecular orientations for one monobasic ester, two epoxides and three alcohols at the vapor/fused silica interface. We find that molecular orientations of nonlocal vibrational modes cannot be determined using polarization-resolved SFG measurements alone.

Simultaneous passively Q-switched dual-wavelength solid-state laser working at 1065 and 1066 nm.

PubMed

Pallas, Florent; Herault, Emilie; Roux, Jean-Francois; Kevorkian, Antoine; Coutaz, Jean-Louis; Vitrant, Guy

2012-07-15

A passively Q-switched dual-wavelength solid-state laser is presented. The two wavelengths are emitted by two different crystals in order to avoid gain competition, and the synchronization between the pulses is obtained by external triggering of the saturable absorber. Sum frequency mixing is demonstrated, proving the interest of this source for terahertz generation in the 0.3-0.4 THz range through difference frequency generation.

NOLM-based all-optical 40 Gbit/s format conversion through sum-frequency generation (SFG) in a PPLN waveguide

NASA Astrophysics Data System (ADS)

Wang, Jian; Sun, Junqiang

2005-11-01

A novel all-optical format conversion scheme from NRZ to RZ based on sum-frequency generation (SFG) in a periodically poled LiNbO 3 (PPLN) waveguide is proposed, using a nonlinear optical loop mirror (NOLM). The conversion mechanism relies on the combination of attenuation and nonlinear phase shift induced on the clockwise signal field during the SFG process. The SFG between pump, and co- and counter- propagating signals in the PPLN waveguide are numerically studied, showing that counter-propagating SFG can be ignored when quasi-phase matching (QPM) for SFG during co-propagating interaction. The nonlinear phase shift induced on the clockwise signal field is analyzed in detail, showing that it is more effective to yield large values for nonlinear phase shift when appropriately phase mismatched for the SFG process. Two tuning schemes are proposed depend on whether the sum-frequency wavelength is variable or fixed. It is found that the latter has a rather wide 3dB signal conversion bandwidth approximately 154nm. Finally, the influence of reversible process of SFG is discussed and the optimum arrangement of pump and signal peak powers is theoretically demonstrated. The result shows that proper power arrangement, pump width, and waveguide length are necessary for achieving a good conversion effect.

Quantitative Surface Chirality Detection with Sum Frequency Generation Vibrational Spectroscopy: Twin Polarization Angle Approach

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

Wei, Feng; Xu, Yanyan; Guo, Yuan

2009-12-27

Here we report a novel twin polarization angle (TPA) approach in the quantitative chirality detection with the surface sum-frequency generation vibrational spectroscopy (SFG-VS). Generally, the achiral contribution dominates the surface SFG-VS signal, and the pure chiral signal is usually two or three orders of magnitude smaller. Therefore, it has been difficult to make quantitative detection and analysis of the chiral contributions to the surface SFG- VS signal. In the TPA method, by varying together the polarization angles of the incoming visible light and the sum frequency signal at fixed s or p polarization of the incoming infrared beam, the polarizationmore » dependent SFG signal can give not only direct signature of the chiral contribution in the total SFG-VS signal, but also the accurate measurement of the chiral and achiral components in the surface SFG signal. The general description of the TPA method is presented and the experiment test of the TPA approach is also presented for the SFG-VS from the S- and R-limonene chiral liquid surfaces. The most accurate degree of chiral excess values thus obtained for the 2878 cm⁻¹ spectral peak of the S- and R-limonene liquid surfaces are (23.7±0.4)% and ({25.4±1.3)%, respectively.« less

Harmonic generation with a dual frequency pulse.

PubMed

Keravnou, Christina P; Averkiou, Michalakis A

2014-05-01

Nonlinear imaging was implemented in commercial ultrasound systems over the last 15 years offering major advantages in many clinical applications. In this work, pulsing schemes coupled with a dual frequency pulse are presented. The pulsing schemes considered were pulse inversion, power modulation, and power modulated pulse inversion. The pulse contains a fundamental frequency f and a specified amount of its second harmonic 2f. The advantages and limitations of this method were evaluated with both acoustic measurements of harmonic generation and theoretical simulations based on the KZK equation. The use of two frequencies in a pulse results in the generation of the sum and difference frequency components in addition to the other harmonic components. While with single frequency pulses, only power modulation and power modulated pulse inversion contained odd harmonic components, with the dual frequency pulse, pulse inversion now also contains odd harmonic components.

Selective detection of crystalline cellulose in plant cell walls with sum-frequency-generation (SFG) vibration spectroscopy.

PubMed

Barnette, Anna L; Bradley, Laura C; Veres, Brandon D; Schreiner, Edward P; Park, Yong Bum; Park, Junyeong; Park, Sunkyu; Kim, Seong H

2011-07-11

The selective detection of crystalline cellulose in biomass was demonstrated with sum-frequency-generation (SFG) vibration spectroscopy. SFG is a second-order nonlinear optical response from a system where the optical centrosymmetry is broken. In secondary plant cell walls that contain mostly cellulose, hemicellulose, and lignin with varying concentrations, only certain vibration modes in the crystalline cellulose structure can meet the noninversion symmetry requirements. Thus, SFG can be used to detect and analyze crystalline cellulose selectively in lignocellulosic biomass without extraction of noncellulosic species from biomass or deconvolution of amorphous spectra. The selective detection of crystalline cellulose in lignocellulosic biomass is not readily achievable with other techniques such as XRD, solid-state NMR, IR, and Raman analyses. Therefore, the SFG analysis presents a unique opportunity to reveal the cellulose crystalline structure in lignocellulosic biomass.

Novel SiO2-deposited CaF2 substrate for vibrational sum-frequency generation (SFG) measurements of chemisorbed monolayers in an aqueous environment.

PubMed

Padermshoke, Adchara; Konishi, Shouta; Ara, Masato; Tada, Hirokazu; Ishibashi, Taka-Aki

2012-06-01

A novel SiO(2)-deposited CaF(2) (SiO(2)/CaF(2)) substrate for measuring vibrational sum-frequency generation (SFG) spectra of silane-based chemisorbed monolayers in aqueous media has been developed. The substrate is suitable for silanization and transparent over a broad range of the infrared (IR) probe. The present work demonstrates the practical application of the SiO(2)/CaF(2) substrate and, to our knowledge, the first SFG spectrum at the solid/water interface of a silanized monolayer observed over the IR fingerprint region (1780-1400 cm(-1)) using a back-side probing geometry. This new substrate can be very useful for SFG studies of various chemisorbed organic molecules, particularly biological compounds, in aqueous environments.

A tunable dual-wavelength pump source based on simulated polariton scattering for terahertz-wave generation

NASA Astrophysics Data System (ADS)

Sun, Bo; Liu, Jinsong; Yao, Jianquan; Li, Enbang

2013-11-01

We propose a dual-wavelength pump source by utilizing stimulated polariton scattering in a LiNbO3 crystal. The residual pump and the generated tunable Stokes waves can be combined to generate THz-wave generation via difference frequency generation (DFG). With a pump energy of 49 mJ, Stokes waves with a tuning range from 1067.8 to 1074 nm have been generated, and an output energy of up to 14.9 mJ at 1070 nm has been achieved with a conversion efficiency of 21.7%. A sum frequency generation experiment was carried out to demonstrate the feasibility of the proposed scheme for THz-wave DFG.

Device and method for generating a beam of acoustic energy from a borehole, and applications thereof

DOEpatents

Vu, Cung Khac; Sinha, Dipen N; Pantea, Cristian; Nihei, Kurt T; Schmitt, Denis P; Skelt, Christopher

2013-10-01

In some aspects of the invention, a method of generating a beam of acoustic energy in a borehole is disclosed. The method includes generating a first broad-band acoustic pulse at a first broad-band frequency range having a first central frequency and a first bandwidth spread; generating a second broad-band acoustic pulse at a second broad-band frequency range different than the first frequency range having a second central frequency and a second bandwidth spread, wherein the first acoustic pulse and second acoustic pulse are generated by at least one transducer arranged on a tool located within the borehole; and transmitting the first and the second broad-band acoustic pulses into an acoustically non-linear medium, wherein the composition of the non-linear medium produces a collimated pulse by a non-linear mixing of the first and second acoustic pulses, wherein the collimated pulse has a frequency equal to the difference in frequencies between the first central frequency and the second central frequency and a bandwidth spread equal to the sum of the first bandwidth spread and the second bandwidth spread.

Quantum Mechanical Calculations of Vibrational Sum-Frequency-Generation (SFG) Spectra of Cellulose: Dependence of the CH and OH Peak Intensity on the Polarity of Cellulose Chains within the SFG Coherence Domain.

PubMed

Lee, Christopher M; Chen, Xing; Weiss, Philip A; Jensen, Lasse; Kim, Seong H

2017-01-05

Vibrational sum-frequency-generation (SFG) spectroscopy is capable of selectively detecting crystalline biopolymers interspersed in amorphous polymer matrices. However, the spectral interpretation is difficult due to the lack of knowledge on how spatial arrangements of crystalline segments influence SFG spectra features. Here we report time-dependent density functional theory (TD-DFT) calculations of cellulose crystallites in intimate contact with two different polarities: parallel versus antiparallel. TD-DFT calculations reveal that the CH/OH intensity ratio is very sensitive to the polarity of the crystallite packing. Theoretical calculations of hyperpolarizability tensors (β abc ) clearly show the dependence of SFG intensities on the polarity of crystallite packing within the SFG coherence length, which provides the basis for interpretation of the empirically observed SFG features of native cellulose in biological systems.

In situ sum-frequency generation spectroscopy of ethylene-glycol and poly-N-isopropylacrylamide films

NASA Astrophysics Data System (ADS)

Kurz, Volker; Koelsch, Patrick

2009-03-01

Ethylene-glycol(EG)-based self-assembled monolayers (SAMs) are often used as a model systems for thin liquid films. Temperature series in heavy water were measured using a unique sample cell developed for in situ sum-frequency generation (SFG) spectroscopy experiments. Results obtained from model EG-SAMs with different lengths and terminating groups in various ionic solutions showed temperature-dependent changes in the molecular order. Films of poly-N-isopropylacrylamide(pNIPAM) were also characterized by in situ SFG spectroscopy in the CH, OH, OD and amide spectral regions under different polarization combinations. These systems have many applications as thermo-responsive polymers due to their ability to change solubility in water at the biologically relevant temperature of 32 C. This so-called lower critical solution temperature (LCST) phase transition was characterized in depth, allowing for the identification of the molecular groups involved in this process.

What is limiting low-temperature atomic layer deposition of Al{sub 2}O{sub 3}? A vibrational sum-frequency generation study

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

Vandalon, V., E-mail: v.vandalon@tue.nl, E-mail: w.m.m.kessels@tue.nl; Kessels, W. M. M., E-mail: v.vandalon@tue.nl, E-mail: w.m.m.kessels@tue.nl

2016-01-04

The surface reactions during atomic layer deposition (ALD) of Al{sub 2}O{sub 3} from Al(CH{sub 3}){sub 3} and H{sub 2}O have been studied with broadband sum-frequency generation to reveal what is limiting the growth at low temperatures. The –CH{sub 3} surface coverage was measured for temperatures between 100 and 300 °C and the absolute reaction cross sections, describing the reaction kinetics, were determined for both half-cycles. It was found that –CH{sub 3} groups persisted on the surface after saturation of the H{sub 2}O half-cycle. From a direct correlation with the growth per cycle, it was established that the reduced reactivity of H{submore » 2}O towards –CH{sub 3} is the dominant factor limiting the ALD process at low temperatures.« less

Investigation of the summation of copper-vapour laser frequencies

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

Karpukhin, Vyacheslav T; Konev, Yu B; Malikov, Mikhail M

1998-09-30

An investigation was made of the conversion of the copper-vapour laser radiation ( {lambda}{sub 1} = 0.51 {mu}m and {lambda}{sub 2} = 0.578 {mu}m) into UV radiation at the sum frequency ({lambda}{sub 3} = 0.271 {mu}m) in a DKDP crystal. The operation of this frequency converter was compared for two magnifications of the laser cavity: M = 5 and 200. The best results were obtained for M = 200 (average UV radiation power 0.75 W, conversion efficiency 12%). A study was made of the characteristics of the formation of radiation pulses representing the two lines in the laser beam asmore » a whole and in its weakly diverging core. In a low-divergence beam the yellow- and green-line pulses were emitted practically simultaneously with approximately the same peak power, which facilitated the sum-frequency generation. (nonlinear optical phenomena)« less

Nonlinear scattering of acoustic waves by natural and artificially generated subsurface bubble layers in sea.

PubMed

Ostrovsky, Lev A; Sutin, Alexander M; Soustova, Irina A; Matveyev, Alexander L; Potapov, Andrey I; Kluzek, Zigmund

2003-02-01

The paper describes nonlinear effects due to a biharmonic acoustic signal scattering from air bubbles in the sea. The results of field experiments in a shallow sea are presented. Two waves radiated at frequencies 30 and 31-37 kHz generated backscattered signals at sum and difference frequencies in a bubble layer. A motorboat propeller was used to generate bubbles with different concentrations at different times, up to the return to the natural subsurface layer. Theoretical consideration is given for these effects. The experimental data are in a reasonably good agreement with theoretical predictions.

Simultaneous Teleportation of the Spectral and Polarization States of a Photon

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

Humble, Travis S; Bennink, Ryan S; Grice, Warren P

2008-01-01

We describe how spectrally multimode, polarization-entangled photons simultaneously teleport quantum information encoded into the spectral and polarization degrees of freedom of a single photon using sum frequency generation to implement a Bell-state measurement.

Comparison of scattering and reflection SFG: a question of phase-matching.

PubMed

de Aguiar, Hilton B; Scheu, Rüdiger; Jena, Kailash C; de Beer, Alex G F; Roke, Sylvie

2012-05-21

We present a comparison between sum frequency scattering (SFS) and reflection mode sum frequency generation (R-SFG). We have used scattering theory to describe both scattering experiments as well as reflection mode experiments. The interfacial vibrational spectrum of nanoscopic oil droplets dispersed in water was probed with SFS as well as with R-SFG. Spectra recorded in phase-matched R-SFG mode and spectra recorded with SFS from the same sample are different, which shows that different interfaces are measured. Scattering spectra at different scattering angles agree with nonlinear light scattering theory. We further present experiments with polymer films aimed at quantifying the comparative strength of R-SFG and SFS experiments.

Phase Acrobatics: The Influence of Excitonic Resonance and Gold Nonresonant Background on Heterodyne-Detected Vibrational Sum Frequency Generation Emission.

PubMed

Rich, Christopher C; Lindberg, Kathryn A; Krummel, Amber T

2017-04-06

We show how heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy can discriminate between the excitonic and monomeric properties of a helical, nanotube molecular aggregate by monitoring the phase of the VSFG emission associated with different polarization configurations. By keeping track of the "phase acrobatics" associated with the added phase of the nonresonant SFG emission of gold as well as that of the double-resonance conditions achieved when the SF frequency is resonant with an electronic exciton transition, we discover that for aggregates of tetra(sulfonatophenyl)porphyrin (TSPP) the PPP-polarized spectra exhibit double-resonance conditions while SSP-polarized spectra exhibit resonance only with the ground-state vibration. Along with observed shifts in the vibrational frequency, intensity differences, and sign flips in the imaginary second-order susceptibility, χ s,Im (2) , we conclude that PPP-polarized HD-VSFG spectra reflect the delocalized, excitonic nature of the molecular aggregate, while the SSP-polarized HD-VSFG spectra measure the localized, monomeric nature of the molecular subunits. It is implied from this study that HD-VSFG spectroscopy can be uniquely utilized to measure the excitonic and monomeric properties associated with molecular assemblies for a single sample.

Tunable, continuous-wave, ultraviolet source based on intracavity sum-frequency-generation in an optical parametric oscillator using BiB₃O₆.

PubMed

Devi, Kavita; Kumar, S Chaitanya; Ebrahim-Zadeh, M

2013-10-21

We report a continuous-wave (cw) source of tunable radiation across 333-345 nm in the ultraviolet (UV) using bismuth triborate, BiB₃O₆ (BIBO) as the nonlinear gain material. The source is based on internal sum-frequency-generation (SFG) in a cw singly-resonant optical parametric oscillator (OPO) pumped at 532 nm. The compact tunable source employs a 30-mm-long MgO:sPPLT crystal as the OPO gain medium and a 5-mm-long BIBO crystal for intracavity SFG of the signal and pump, providing up to 21.6 mW of UV power at 339.7 nm, with >15 mW over 64% of the SFG tuning range. The cw OPO is also tunable across 1158-1312 nm in the idler, delivering as much as 1.7 W at 1247 nm, with >1W over 65% of the tuning range. The UV output at maximum power exhibits passive power stability better than 3.4% rms and frequency stability of 193 GHz over more than one minute.

Automated Shirt Collar Manufacturing. Volume 3. Sewing Head Control for High Speed Stitch Contour Tracking.

DTIC Science & Technology

1993-06-23

mal control scheme sums the cost function for all data points from time zero to infinity; however, the preview case sums only through the preview step...shaft speed that is generated by the monitor port on the servo amplifiers. Therefore, the zero frequency gain shown in the figure contains the gain...Delivery Order 0014 SAOORESS (City, State, and ZIP Code ) 10. SOURCE OF FUNDING NUMBERS Rom415CmrnSainPROGRAM IPROJECT TASK WORK UNITAlexandriaR VA 22304-6100

Theoretical Sum Frequency Generation Spectroscopy of Peptides

PubMed Central

2015-01-01

Vibrational sum frequency generation (SFG) has become a very promising technique for the study of proteins at interfaces, and it has been applied to important systems such as anti-microbial peptides, ion channel proteins, and human islet amyloid polypeptide. Moreover, so-called “chiral” SFG techniques, which rely on polarization combinations that generate strong signals primarily for chiral molecules, have proven to be particularly discriminatory of protein secondary structure. In this work, we present a theoretical strategy for calculating protein amide I SFG spectra by combining line-shape theory with molecular dynamics simulations. We then apply this method to three model peptides, demonstrating the existence of a significant chiral SFG signal for peptides with chiral centers, and providing a framework for interpreting the results on the basis of the dependence of the SFG signal on the peptide orientation. We also examine the importance of dynamical and coupling effects. Finally, we suggest a simple method for determining a chromophore’s orientation relative to the surface using ratios of experimental heterodyne-detected signals with different polarizations, and test this method using theoretical spectra. PMID:25203677

Sensitive Infrared Signal Detection by Upconversion Technique

NASA Technical Reports Server (NTRS)

Wong, Teh-Hwa; Yu, Jirong; Bai, Yingxin; Johnson, William; Chen, Songsheng; Petros, Mulugeta; Singh, Upendra N.

2014-01-01

We demonstrated upconversion assisted detection of a 2.05-micron signal by sum frequency generation to generate a 700-nm light using a bulk periodically poled lithium niobate crystal. The achieved 94% intrinsic upconversion efficiency and 22.58% overall detection efficiency at a pW level of 2.05 micron pave the path to detect extremely weak infrared (IR) signals for remote sensing applications.

Generation and tunable enhancement of a sum-frequency signal in lithium niobate nanowires

NASA Astrophysics Data System (ADS)

Sergeyev, Anton; Reig Escalé, Marc; Grange, Rachel

2017-02-01

Recent developments in the fabrication of lithium niobate (LiNbO3) structures down to the nanoscale opens up novel applications of this versatile material in nonlinear optics. Current nonlinear optical studies in sub-micron waveguides are mainly restricted to the generation of second and third harmonics. In this work, we demonstrate the generation and waveguiding of the sum-frequency generation (SFG) signal in a single LiNbO3 nanowire with a cross-section of 517 nm  ×  654 nm. Furthermore, we enhance the guided SFG signal 17.9 times by means of modal phase matching. We also display tuning of the phase-matched wavelength by varying the nanowire cross-section and changing the polarization of the incident laser. The results prove that LiNbO3 nanowires can be successfully used for nonlinear wave-mixing applications and assisting the miniaturization of optical devices. , which features invited work from the best early-career researchers working within the scope of J Phys D. This project is part of the Journal of Physics series’ 50th anniversary celebrations in 2017. Rachel Grange was selected by the Editorial Board of J Phys D as an Emerging Leader.

Homogeneous and inhomogeneous broadenings and the Voigt line shapes in the phase-resolved and intensity sum-frequency generation vibrational spectroscopy.

PubMed

Chen, Shun-Li; Fu, Li; Gan, Wei; Wang, Hong-Fei

2016-01-21

In this report, we show that the ability to measure the sub-1 cm(-1) resolution phase-resolved and intensity high-resolution broadband sum frequency generation vibrational spectra of the -CN stretch vibration of the Langmuir-Blodgett (LB) monolayer of the 4-n-octyl-4'-cyanobiphenyl (8CB) on the z-cut α-quartz surface allows the direct comparison and understanding of the homogeneous and inhomogeneous broadenings in the imaginary and intensity SFG vibrational spectral line shapes in detail. The difference of the full width at half maximum (FWHM) of the imaginary and intensity sum-frequency generation vibrational spectroscopy spectra of the same vibrational mode is the signature of the Voigt line shape and it measures the relative contribution to the overall line shape from the homogeneous and inhomogeneous broadenings in SFG vibrational spectra. From the phase-resolved and intensity spectra, we found that the FWHM of the 2238.00 ± 0.02 cm(-1) peak in the phase-resolved imaginary and intensity spectra is 19.2 ± 0.2 cm(-1) and 21.6 ± 0.4 cm(-1), respectively, for the -CN group of the 8CB LB monolayer on the z-cut α-quartz crystal surface. The FWHM width difference of 2.4 cm(-1) agrees quantitatively with a Voigt line shape with a homogeneous broadening half width of Γ = 5.29 ± 0.08 cm(-1) and an inhomogeneous standard derivation width Δω = 5.42 ± 0.07 cm(-1). These results shed new lights on the understanding and interpretation of the line shapes of both the phase-resolved and the intensity SFG vibrational spectra, as well as other incoherent and coherent spectroscopic techniques in general.

Quantification of crystalline cellulose in lignocellulosic biomass using sum frequency generation (SFG) vibration spectroscopy and comparison with other analytical methods.

PubMed

Barnette, Anna L; Lee, Christopher; Bradley, Laura C; Schreiner, Edward P; Park, Yong Bum; Shin, Heenae; Cosgrove, Daniel J; Park, Sunkyu; Kim, Seong H

2012-07-01

The non-centrosymmetry requirement of sum frequency generation (SFG) vibration spectroscopy allows the detection and quantification of crystalline cellulose in lignocellulose biomass without spectral interferences from hemicelluloses and lignin. This paper shows a correlation between the amount of crystalline cellulose in biomass and the SFG signal intensity. Model biomass samples were prepared by mixing commercially available cellulose, xylan, and lignin to defined concentrations. The SFG signal intensity was found sensitive to a wide range of crystallinity, but varied non-linearly with the mass fraction of cellulose in the samples. This might be due to the matrix effects such as light scattering and absorption by xylan and lignin, as well as the non-linear density dependence of the SFG process itself. Comparison with other techniques such as XRD, FT-Raman, FT-IR and NMR demonstrate that SFG can be a complementary and sensitive tool to assess crystalline cellulose in biomass. Copyright © 2012 Elsevier Ltd. All rights reserved.

Sum frequency generation vibrational spectroscopy (SFG-VS) for complex molecular surfaces and interfaces: Spectral lineshape measurement and analysis plus some controversial issues

NASA Astrophysics Data System (ADS)

Wang, Hong-Fei

2016-12-01

Sum-frequency generation vibrational spectroscopy (SFG-VS) was first developed in the 1980s and it has been proven a uniquely sensitive and surface/interface selective spectroscopic probe for characterization of the structure, conformation and dynamics of molecular surfaces and interfaces. In recent years, there have been many progresses in the development of methodology and instrumentation in the SFG-VS toolbox that have significantly broadened the application to complex molecular surfaces and interfaces. In this review, after presenting a unified view on the theory and methodology focusing on the SFG-VS spectral lineshape, as well as the new opportunities in SFG-VS applications with such developments, some of the controversial issues that have been puzzling the community are discussed. The aim of this review is to present to the researchers and students interested in molecular surfaces and interfacial sciences up-to-date perspectives complementary to the existing textbooks and reviews on SFG-VS.

Alkyl chain interaction at the surface of room temperature ionic liquids: systematic variation of alkyl chain length (R = C(1)-C(4), C(8)) in both cation and anion of [RMIM][R-OSO(3)] by sum frequency generation and surface tension.

PubMed

Santos, Cherry S; Baldelli, Steven

2009-01-29

The gas-liquid interface of halide-free 1,3-dialkylimidazolium alkyl sulfates [RMIM][R-OSO(3)] with R chain length from C(1)-C(4) and C(8) has been studied systematically using the surface-specific sum frequency generation (SFG) vibrational spectroscopy and surface tension measurements. From the SFG spectra, vibrational modes from the methyl group of both cation and anion are observed for all ionic liquid samples considered in the present study. These results suggest the presence of both ions at the gas-liquid interface, which is further supported by surface tension measurements. Surface tension data show a decreasing trend as the alkyl chain in the imidazolium cation is varied from methyl to butyl chain, with a specific anion. A similar trend is observed when the alkyl chain of the anion is modified and the cation is fixed.

Interferometric 2D Sum Frequency Generation Spectroscopy Reveals Structural Heterogeneity of Catalytic Monolayers on Transparent Materials.

PubMed

Vanselous, Heather; Stingel, Ashley M; Petersen, Poul B

2017-02-16

Molecular monolayers exhibit structural and dynamical properties that are different from their bulk counterparts due to their interaction with the substrate. Extracting these distinct properties is crucial for a better understanding of processes such as heterogeneous catalysis and interfacial charge transfer. Ultrafast nonlinear spectroscopic techniques such as 2D infrared (2D IR) spectroscopy are powerful tools for understanding molecular dynamics in complex bulk systems. Here, we build on technical advancements in 2D IR and heterodyne-detected sum frequency generation (SFG) spectroscopy to study a CO 2 reduction catalyst on nanostructured TiO 2 with interferometric 2D SFG spectroscopy. Our method combines phase-stable heterodyne detection employing an external local oscillator with a broad-band pump pulse pair to provide the first high spectral and temporal resolution 2D SFG spectra of a transparent material. We determine the overall molecular orientation of the catalyst and find that there is a static structural heterogeneity reflective of different local environments at the surface.

Extracting the Density of States of Copper Phthalocyanine at the SiO2 Interface with Electronic Sum Frequency Generation.

PubMed

Pandey, Ravindra; Moon, Aaron P; Bender, Jon A; Roberts, Sean T

2016-03-17

Organic semiconductors (OSCs) constitute an attractive platform for optoelectronics design due to the ease of their processability and chemically tunable properties. Incorporating OSCs into electrical circuits requires forming junctions between them and other materials, yet the change in dielectric properties about these junctions can strongly perturb the electronic structure of the OSC. Here we adapt an interface-selective optical technique, electronic sum frequency generation (ESFG), to the study of a model OSC thin-film system, copper phthalocyanine (CuPc) deposited on SiO2. We find that by modeling the thickness dependence of our measured spectra, we can identify changes in CuPc's electronic density of states at both its buried interface with SiO2 and air-exposed surface. Our work demonstrates that ESFG can be used to noninvasively probe the interfacial electronic structure of optically thick OSC films, indicating that it can be used for the study of OSC-based optoelectronics in situ.

Development of Mesospheric Sodium Laser Beacon for Atmospheric Adaptive Optics

NASA Technical Reports Server (NTRS)

Jeys, T. H.

1992-01-01

A solid-state source of long pulse length, sodium-resonance radiation was developed for the purpose of generating an artificial star in the earth's mesospheric sodium layer. This radiation is generated by sum-frequency mixing the output of a 1.064 micron Nd:YAG laser with the output of a 1.319-micron Nd:YAG laser. By operating these lasers at wavelengths very close to the peak of their tuning curves, it is possible to match the wavelength of the sum-frequency radiation to that of the sodium D2 adsorption wavelength. Two pulsed laser systems were constructed, one producing as much as 0.6 J of sodium resonance radiation at a 10-Hz repetition rate and another producing as much as 24 mJ at a 840-Hz repetition rate. In both laser systems, the 1.06-micron and 1.32-micron Nd:YAG lasers are configured as mode-locked master oscillators followed by power amplifiers. Other aspects of this project are presented.

Sum frequency generation vibrational spectroscopy (SFG-VS) for complex molecular surfaces and interfaces: Spectral lineshape measurement and analysis plus some controversial issues

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

Wang, Hong-Fei

Sum-frequency generation vibrational spectroscopy (SFG-VS) was first developed in the 1980s and it has been proven a uniquely sensitive and surface/interface selective spectroscopic probe for characterization of the structure, conformation and dynamics of molecular surfaces and interfaces. In recent years, there has been significant progress in the development of methodology and instrumentation in the SFG-VS toolbox that has significantly broadened the application to complex molecular surfaces and interfaces. In this review, after presenting a unified view on the theory and methodology focusing on the SFG-VS spectral lineshape, as well as the new opportunities in SFG-VS applications with such developments, somemore » of the controversial issues that have been puzzling the community are to be discussed. The aim of this review is to present to the researchers and students interested in molecular surfaces and interfacial sciences up-to-date perspectives complementary to the existing textbooks and reviews on SFG-VS.« less

Spectrally- and Time-Resolved Sum Frequency Generation (STiR-SFG): a new tool for ultrafast hydrogen bond dynamics at interfaces.

NASA Astrophysics Data System (ADS)

Benderskii, Alexander; Bordenyuk, Andrey; Weeraman, Champika

2006-03-01

The recently developed spectrally- and time-resolved Sum Frequency Generation (STiR-SFG) is a surface-selective 3-wave mixing (IR+visible) spectroscopic technique capable of measuring ultrafast spectral evolution of vibrational coherences. A detailed description of this measurement will be presented, and a noniterative method or deconvolving the laser pulses will be introduced to obtain the molecular response function. STiR-SFG, combined with the frequency-domain SFG spectroscopy, was applied to study hydrogen bonding dynamics at aqueous interfaces (D2O/CaF2). Spectral dynamics of the OD-stretch on the 50-150 fs time scale provides real-time observation of ultrafast H-bond rearrangement. Tuning the IR wavelength to the blue or red side of the OD-stretch transition, we selectively monitor the dynamics of different sub-ensembles in the distribution of the H-bond structures. The blue-side excitation (weaker H-bonding) shows monotonic red-shift of the OD-frequency. In contrast, the red-side excitation (stronger H-bonding structures) produces a blue-shift and a recursion, which may indicate the presence of an underdamped intermolecular mode of interfacial water. Effect of electrolyte concentration on the H-bond dynamics will be discussed.

Tomography and Purification of the Temporal-Mode Structure of Quantum Light

NASA Astrophysics Data System (ADS)

Ansari, Vahid; Donohue, John M.; Allgaier, Markus; Sansoni, Linda; Brecht, Benjamin; Roslund, Jonathan; Treps, Nicolas; Harder, Georg; Silberhorn, Christine

2018-05-01

High-dimensional quantum information processing promises capabilities beyond the current state of the art, but addressing individual information-carrying modes presents a significant experimental challenge. Here we demonstrate effective high-dimensional operations in the time-frequency domain of nonclassical light. We generate heralded photons with tailored temporal-mode structures through the pulse shaping of a broadband parametric down-conversion pump. We then implement a quantum pulse gate, enabled by dispersion-engineered sum-frequency generation, to project onto programmable temporal modes, reconstructing the quantum state in seven dimensions. We also manipulate the time-frequency structure by selectively removing temporal modes, explicitly demonstrating the effectiveness of engineered nonlinear processes for the mode-selective manipulation of quantum states.

Excitation of low-frequency residual currents at combination frequencies of an ionising two-colour laser pulse

NASA Astrophysics Data System (ADS)

Vvedenskii, N. V.; Kostin, V. A.; Laryushin, I. D.; Silaev, A. A.

2016-05-01

We have studied the processes of excitation of low-frequency residual currents in a plasma produced through ionisation of gases by two-colour laser pulses in laser-plasma schemes for THz generation. We have developed an analytical approach that allows one to find residual currents in the case when one of the components of a two-colour pulse is weak enough. The derived analytical expressions show that the effective generation of the residual current (and hence the effective THz generation) is possible if the ratio of the frequencies in the two-colour laser pulse is close to a rational fraction with a not very big odd sum of the numerator and denominator. The results of numerical calculations (including those based on the solution of the three-dimensional time-dependent Schrödinger equation) agree well with the analytical results.

Vibrational spectral signatures of crystalline cellulose using high resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS)

DOE PAGES

Zhang, Libing; Lu, Zhou; Velarde, Luis; ...

2015-03-03

Both the C–H and O–H region spectra of crystalline cellulose were studied using the sub-wavenumber high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS) for the first time. The resolution of HR-BB-SFG-VS is about 10-times better than conventional scanning SFG-VS and has the capability of measuring the intrinsic spectral lineshape and revealing many more spectral details. With HR-BB-SFG-VS, we found that in cellulose samples from different sources, including Avicel and cellulose crystals isolated from algae Valonia (Iα) and tunicates (Iβ), the spectral signatures in the O–H region were unique for the two allomorphs, i.e. Iα and Iβ, while the spectral signaturesmore » in the C–H regions varied in all samples examined. Even though the origin of the different spectral signatures of the crystalline cellulose in the O–H and C–H vibrational frequency regions are yet to be correlated to the structure of cellulose, these results lead to new spectroscopic methods and opportunities to classify and to understand the basic crystalline structures, as well as variations in polymorphism of the crystalline cellulose.« less

Vibrational spectral signatures of crystalline cellulose using high resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS)

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

Zhang, Libing; Lu, Zhou; Velarde, Luis

Both the C–H and O–H region spectra of crystalline cellulose were studied using the sub-wavenumber high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS) for the first time. The resolution of HR-BB-SFG-VS is about 10-times better than conventional scanning SFG-VS and has the capability of measuring the intrinsic spectral lineshape and revealing many more spectral details. With HR-BB-SFG-VS, we found that in cellulose samples from different sources, including Avicel and cellulose crystals isolated from algae Valonia (Iα) and tunicates (Iβ), the spectral signatures in the O–H region were unique for the two allomorphs, i.e. Iα and Iβ, while the spectral signaturesmore » in the C–H regions varied in all samples examined. Even though the origin of the different spectral signatures of the crystalline cellulose in the O–H and C–H vibrational frequency regions are yet to be correlated to the structure of cellulose, these results lead to new spectroscopic methods and opportunities to classify and to understand the basic crystalline structures, as well as variations in polymorphism of the crystalline cellulose.« less

The spatiotemporal MEG covariance matrix modeled as a sum of Kronecker products.

PubMed

Bijma, Fetsje; de Munck, Jan C; Heethaar, Rob M

2005-08-15

The single Kronecker product (KP) model for the spatiotemporal covariance of MEG residuals is extended to a sum of Kronecker products. This sum of KP is estimated such that it approximates the spatiotemporal sample covariance best in matrix norm. Contrary to the single KP, this extension allows for describing multiple, independent phenomena in the ongoing background activity. Whereas the single KP model can be interpreted by assuming that background activity is generated by randomly distributed dipoles with certain spatial and temporal characteristics, the sum model can be physiologically interpreted by assuming a composite of such processes. Taking enough terms into account, the spatiotemporal sample covariance matrix can be described exactly by this extended model. In the estimation of the sum of KP model, it appears that the sum of the first 2 KP describes between 67% and 93%. Moreover, these first two terms describe two physiological processes in the background activity: focal, frequency-specific alpha activity, and more widespread non-frequency-specific activity. Furthermore, temporal nonstationarities due to trial-to-trial variations are not clearly visible in the first two terms, and, hence, play only a minor role in the sample covariance matrix in terms of matrix power. Considering the dipole localization, the single KP model appears to describe around 80% of the noise and seems therefore adequate. The emphasis of further improvement of localization accuracy should be on improving the source model rather than the covariance model.

Spectral filtering of gradient for l2-norm frequency-domain elastic waveform inversion

NASA Astrophysics Data System (ADS)

Oh, Ju-Won; Min, Dong-Joo

2013-05-01

To enhance the robustness of the l2-norm elastic full-waveform inversion (FWI), we propose a denoise function that is incorporated into single-frequency gradients. Because field data are noisy and modelled data are noise-free, the denoise function is designed based on the ratio of modelled data to field data summed over shots and receivers. We first take the sums of the modelled data and field data over shots, then take the sums of the absolute values of the resultant modelled data and field data over the receivers. Due to the monochromatic property of wavefields at each frequency, signals in both modelled and field data tend to be cancelled out or maintained, whereas certain types of noise, particularly random noise, can be amplified in field data. As a result, the spectral distribution of the denoise function is inversely proportional to the ratio of noise to signal at each frequency, which helps prevent the noise-dominant gradients from contributing to model parameter updates. Numerical examples show that the spectral distribution of the denoise function resembles a frequency filter that is determined by the spectrum of the signal-to-noise (S/N) ratio during the inversion process, with little human intervention. The denoise function is applied to the elastic FWI of synthetic data, with three types of random noise generated by the modified version of the Marmousi-2 model: white, low-frequency and high-frequency random noises. Based on the spectrum of S/N ratios at each frequency, the denoise function mainly suppresses noise-dominant single-frequency gradients, which improves the inversion results at the cost of spatial resolution.

Frequency comb SFG: a new approach to multiplex detection.

PubMed

Kearns, Patrick M; Sohrabpour, Zahra; Massari, Aaron M

2016-08-22

Determination of molecular orientation at interfaces by vibrational sum frequency generation spectroscopy (VSFG) requires measurements using at least two different polarization combinations of the incoming visible, IR, and generated SFG beams. We present a new method for the simultaneous collection of different VSFG polarization outputs by use of a modified 4f pulseshaper to create a simple frequency comb. Via the frequency comb, two visible pulses are separated spectrally but aligned in space and time to interact at the sample with mixed polarization IR light. This produces two different VSFG outputs that are separated by their frequencies at the monochromator rather than their polarizations. Spectra were collected from organic thin films with different polarization combinations to show the reliability of the method. The results show that the optical arrangement is immune to fluctuations in laser power, beam pointing, and IR spectral shape.

IR visible sum-frequency vibrational spectroscopy of Biphenyl-3 methylene thiol monolayer on gold and silver: effect of the visible wavelength on the SFG spectrum

NASA Astrophysics Data System (ADS)

Humbert, C.; Dreesen, L.; Mani, A. A.; Caudano, Y.; Lemaire, J.-J.; Thiry, P. A.; Peremans, A.

2002-04-01

We measured IR-visible sum-frequency generation spectra of CH 3-(C 6H 4) 2-(CH 2) 3-S-H (Biphenyl-3) self-assembled monolayers on a silver and a gold substrate. For the latter substrate, we observed different interference patterns between the resonant signal of the CH vibration and the non-resonant contribution of the substrate as a function of the visible beam wavelength. The non-linear response of the gold substrate is enhanced around 480 nm corresponding to the s-d interband transition. Such effect is not observed for the silver substrate the interband transition of which is located out of the investigated visible spectral range of 450-700 nm.

Rectenna for high-voltage applications

NASA Technical Reports Server (NTRS)

Epp, Larry W. (Inventor); Khan, Abdur R. (Inventor)

2002-01-01

An energy transfer system is disclosed. The system includes patch elements, shielding layers, and energy rectifying circuits. The patch elements receive and couple radio frequency energy. The shielding layer includes at least one opening that allows radio frequency energy to pass through. The openings are formed and positioned to receive the radio frequency energy and to minimize any re-radiating back toward the source of energy. The energy rectifying circuit includes a circuit for rectifying the radio frequency energy into dc energy. A plurality of energy rectifying circuits is arranged in an array to provide a sum of dc energy generated by the energy rectifying circuit.

Chemical imaging of structured SAMs with a novel SFG microscope

NASA Astrophysics Data System (ADS)

Hoffmann, Dominik M. P.; Kuhnke, Klaus; Kern, Klaus

2002-11-01

We present a newly developed microscope for sum frequency generation (SFG) imaging of opaque and reflecting interfaces. The sample is viewed at an angle of 60° with respect to the surface normal in order to increase the collected SFG intensity. Our setup is designed to keep the whole field of view (FOV) in focus and to compensate for the distortion usually related to oblique imaging by means of a blazed grating. The separation of the SFG intensity and the reflected visible beam is accomplished by a suitable combination of spectral filters. The sum frequency microscope (SFM) is capable of in-situ chemically selective imaging by tuning the IR-beam to vibrational transitions of the respective molecules. The SFM is applied to imaging of structured self-assembled monolayers (SAM) of thiol molecules on a gold surface.

Back-surface gold mirrors for vibrationally resonant sum-frequency (VR-SFG) spectroscopy using 3-mercaptopropyltrimethoxysilane as an adhesion promoter.

PubMed

Quast, Arthur D; Zhang, Feng; Linford, Matthew R; Patterson, James E

2011-06-01

Back-surface mirrors are needed as reference materials for vibrationally resonant sum-frequency generation (VR-SFG) probing of liquid-solid interfaces. Conventional noble metal mirrors are not suitable for back-surface applications due to the presence of a metal adhesion layer (chromium or titanium) between the window substrate and the reflective metal surface. Using vapor deposited 3-mercaptopropyltrimethoxysilane (MPTMS) as a bi-functional adhesion promoter, gold mirrors were fabricated on fused silica substrates. These mirrors exhibit excellent gold adhesion as determined by the Scotch(®) tape test. They also produce minimal spectroscopic interference in the C-H stretching region (2800-3000 cm(-1)), as characterized by VR-SFG. These mirrors are thus robust and can be used as back-surface mirrors for a variety of applications, including reference mirrors for VR-SFG.

Sum frequency generation (SFG) vibrational spectroscopy of planar phosphatidylethanolamine hybrid bilayer membranes under water.

PubMed

Kett, Peter J N; Casford, Michael T L; Davies, Paul B

2010-06-15

Sum frequency generation (SFG) spectroscopy has been used to study the structure of phosphatidylethanolamine hybrid bilayer membranes (HBMs) under water at ambient temperatures. The HBMs were formed using a modified Langmuir-Schaefer technique and consisted of a layer of dipalmitoyl phosphatidylethanolamine (DPPE) physisorbed onto an octadecanethiol (ODT) self-assembled monolayer (SAM) at a series of surface pressures from 1 to 40 mN m(-1). The DPPE and ODT were selectively deuterated so that the contributions to the SFG spectra from the two layers could be determined separately. SFG spectra in both the C-H and C-D stretching regions confirmed that a monolayer of DPPE had been adsorbed to the ODT SAM and that there were gauche defects within the alkyl chains of the phospholipid. On adsorption of a layer of DPPE, methylene modes from the ODT SAM were detected, indicating that the phospholipid had partially disordered the alkanethiol monolayer. SFG spectra recorded in air indicated that removal of water from the surface of the HBM resulted in disruption of the DPPE layer and the formation of phospholipid bilayers.

Vibrational Dynamics of Interfacial Water by Free Induction Decay Sum Frequency Generation (FID-SFG) at the Al2O3(1120)/H2O Interface.

PubMed

Boulesbaa, Abdelaziz; Borguet, Eric

2014-02-06

The dephasing dynamics of a vibrational coherence may reveal the interactions of chemical functional groups with their environment. To investigate this process at a surface, we employ free induction decay sum frequency generation (FID-SFG) to measure the time that it takes for free OH stretch oscillators at the charged (pH ≈ 13, KOH) interface of alumina/water (Al2O3/H2O) to lose their collective coherence. By employing noncollinear optical parametric amplification (NOPA) technology and nonlinear vibrational spectroscopy, we showed that the single free OH peak actually corresponds to two distinct oscillators oriented opposite to each other and measured the total dephasing time, T2, of the free OH stretch modes at the Al2O3/H2O interface with a sub-40 fs temporal resolution. Our results suggested that the free OH oscillators associated with interfacial water dephase on the time scale of 89.4 ± 6.9 fs, whereas the homogeneous dephasing of interfacial alumina hydroxyls is an order of magnitude slower.

Substrate dependent structure of adsorbed aryl isocyanides studied by sum frequency generation (SFG) spectroscopy.

PubMed

Ito, Mikio; Noguchi, Hidenori; Ikeda, Katsuyoshi; Uosaki, Kohei

2010-04-07

Effects of metal substrate on the bonding nature of isocyanide group of two aryl isocyanides, 1,4-phenylene diisocyanide (PDI) and 4-methylphenyl isocyanide (MPI), and tilt angle of MPI were examined by measuring sum frequency generation (SFG) spectra of the self-assembled monolayers (SAMs) of these molecules on Au, Pt, Ag, and Pd surfaces. The SFG peaks due to "metal bonded" and "free"-NC groups were resolved by comparing the SFG spectra of PDI with IR spectra obtained by DFT calculations and previous results of vibrational spectroscopy. Based on the peak positions of the "metal bonded"-NC, it is clarified that while PDI and MPI were adsorbed at top sites on Au, Ag, and Pt surfaces, they adsorbed at bridge sites on the Pd surface. The tilt angles of MPI were determined from the intensity ratio between the SFG peaks of C-H symmetric and asymmetric stretching vibrational modes of the CH(3) group. The tilt angles of the MPI SAMs were in the order of Pt < Pd < Ag < Au, reflecting the bonding nature between the -NC group and the substrate atoms.

Environmental chemistry at vapor/water interfaces: insights from vibrational sum frequency generation spectroscopy.

PubMed

Jubb, Aaron M; Hua, Wei; Allen, Heather C

2012-01-01

The chemistry that occurs at surfaces has been an intense area of study for many years owing to its complexity and importance in describing a wide range of physical phenomena. The vapor/water interface is particularly interesting from an environmental chemistry perspective as this surface plays host to a wide range of chemistries that influence atmospheric and geochemical interactions. The application of vibrational sum frequency generation (VSFG), an inherently surface-specific, even-order nonlinear optical spectroscopy, enables the direct interrogation of various vapor/aqueous interfaces to elucidate the behavior and reaction of chemical species within the surface regime. In this review we discuss the application of VSFG to the study of a variety of atmospherically important systems at the vapor/aqueous interface. Chemical systems presented include inorganic ionic solutions prevalent in aqueous marine aerosols, small molecular solutes, and long-chain fatty acids relevant to fat-coated aerosols. The ability of VSFG to probe both the organization and reactions that may occur for these systems is highlighted. A future perspective toward the application of VSFG to the study of environmental interfaces is also provided.

Sum Frequency Generation Spectroscopy and Molecular Dynamics Simulations Reveal a Rotationally Fluid Adsorption State of α-Pinene on Silica

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

Ho, Junming; Psciuk, Brian T.; Chase, Hilary M.

2016-06-16

A rotationally fluid state of α-pinene at fused silica/vapor interfaces is revealed by computational and experimental vibrational sum frequency generation (SFG) studies. We report the first assignment of the vibrational modes in the notoriously congested C-H stretching region of α-pinene and identify its bridge methylene group on the four-membered ring ("βCH2") as the origin of its dominant spectral feature. We find that the spectra are perfused with Fermi resonances that need to be accounted for explicitly in the computation of vibrational spectra of strained hydrocarbons such α-pinene. The preferred orientations of α-pinene are consistent with optimization of van der Waalsmore » contacts with the silica surface that results in a bimodal distribution of highly fluxional orientations in which the βCH2 group points "towards" or "away from” the surface. The reported findings are particularly relevant to the exposure of α-pinene to primary oxidants in heterogeneous catalytic pathways that exploit α-pinene as a sustainable feedstock for fine chemicals and polymers.« less

Inhomogeneity of Cellulose Microfibril Assembly in Plant Cell Walls Revealed with Sum Frequency Generation Microscopy.

PubMed

Huang, Shixin; Makarem, Mohamadamin; Kiemle, Sarah N; Hamedi, Hossein; Sau, Moujhuri; Cosgrove, Daniel J; Kim, Seong H

2018-05-17

Sum frequency generation (SFG) vibrational spectroscopy can selectively detect and analyze noncentrosymmetric components interspersed in amorphous matrices; this principle has been used for studies of nanoscale structure and mesoscale assembly of cellulose in plant cell walls. However, the spectral information averaged over a large area or volume cannot provide regiospecific or tissue-specific information of different cells in plants. This study demonstrates spatially resolved SFG analysis and imaging by combining a broad-band SFG spectroscopy system with an optical microscope. The system was designed to irradiate both narrow-band 800 nm and broad-band tunable IR beams through a single reflective objective lens, but from opposite sides of the surface normal direction of the sample. The developed technique was used to reveal inhomogeneous distributions of cellulose microfibrils within single cell walls, such as cotton fibers and onion epidermis as well as among different tissues in Arabidopsis inflorescence stems and bamboo culms. SFG microscopy can be used for vibrational spectroscopic imaging of other biological systems in complement to conventional Fourier transform infrared spectroscopy and confocal Raman microscopy.

Vibrational sum-frequency generation spectroscopy of ionic liquid 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate at the air-water interface

NASA Astrophysics Data System (ADS)

Saha, Ankur; SenGupta, Sumana; Kumar, Awadhesh; Choudhury, Sipra; Naik, Prakash D.

2016-08-01

The structure and orientation of room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [PF3(C2F5)3], commonly known as [bmim][fap], have been investigated at the air-[bmim][fap] and air-water interfaces, employing vibrational sum-frequency generation (VSFG) spectroscopy. The VSFG spectra in the CH stretch region suggest presence of the [bmim] cation at the interfaces. Studies reveal that the butyl chain protrudes out into air, and the imidazolium ring lies almost planar to the interface. The CH stretch intensities get enhanced at the air-water interface, mainly because of polar orientation of imidazolium cation induced by interfacial water molecules. The OH stretch intensities are also enhanced at the air-water interface due to polar orientation of interfacial water molecules induced by [bmim][fap]. The Brewster angle microscopy suggests self aggregation of [bmim][fap] in the presence of water, and the aggregation becomes extensive showing dense surface domains with time. However, the surface pressure is almost unaffected due to aggregation.

Method for determining surface properties of microparticles

DOEpatents

Eisenthal, Kenneth B.

2000-01-01

Second harmonic generation (SHG), sum frequency generation (SFG) and difference frequency generation (DFG) can be used for surface analysis or characterization of microparticles having a non-metallic surface feature. The microparticles can be centrosymmetric or such that non-metallic molecules of interest are centrosymmetrically distributed inside and outside the microparticles but not at the surface of the microparticles where the asymmetry aligns the molecules. The signal is quadratic in incident laser intensity or proportional to the product of two incident laser intensities for SFG, it is sharply peaked at the second harmonic wavelength, quadratic in the density of molecules adsorbed onto the microparticle surface, and linear in microparticles density. In medical or pharmacological applications, molecules of interest may be of drugs or toxins, for example.

Orbital angular momentum light frequency conversion and interference with quasi-phase matching crystals.

PubMed

Zhou, Zhi-Yuan; Ding, Dong-Sheng; Jiang, Yun-Kun; Li, Yan; Shi, Shuai; Wang, Xi-Shi; Shi, Bao-Sen

2014-08-25

Light with helical phase structures, carrying quantized orbital angular momentum (OAM), has many applications in both classical and quantum optics, such as high-capacity optical communications and quantum information processing. Frequency conversion is a basic technique to expand the frequency range of the fundamental light. The frequency conversion of OAM-carrying light gives rise to new physics and applications such as up-conversion detection of images and generation of high dimensional OAM entanglements. Quasi-phase matching (QPM) nonlinear crystals are good candidates for frequency conversion, particularly due to their high-valued effective nonlinear coefficients and no walk-off effect. Here we report the first experimental second-harmonic generation (SHG) of an OAM-carried light with a QPM crystal, where a UV light with OAM of 100 ℏ is generated. OAM conservation is verified using a specially designed interferometer. With a pump beam carrying an OAM superposition of opposite sign, we observe interesting interference phenomena in the SHG light; specifically, a photonics gear-like structure is obtained that gives direct evidence of OAM conservation, which will be very useful for ultra-sensitive angular measurements. Besides, we also develop a theory to reveal the underlying physics of the phenomena. The methods and theoretical analysis shown here are also applicable to other frequency conversion processes, such as sum frequency generation and difference-frequency generation, and may also be generalized to the quantum regime for single photons.

Two-dimensional sum-frequency generation (2D SFG) reveals structure and dynamics of a surface-bound peptide

PubMed Central

Laaser, Jennifer E.; Skoff, David R.; Ho, Jia-Jung; Joo, Yongho; Serrano, Arnaldo L.; Steinkruger, Jay D.; Gopalan, Padma; Gellman, Samuel H.; Zanni, Martin T.

2014-01-01

Surface-bound polypeptides and proteins are increasingly used to functionalize inorganic interfaces such as electrodes, but their structural characterization is exceedingly difficult with standard technologies. In this paper, we report the first two-dimensional sum-frequency generation (2D SFG) spectra of a peptide monolayer, which is collected by adding a mid-IR pulse shaper to a standard femtosecond SFG spectrometer. On a gold surface, standard FTIR spectroscopy is inconclusive about the peptide structure because of solvation-induced frequency shifts, but the 2D lineshapes, anharmonic shifts, and lifetimes obtained from 2D SFG reveal that the peptide is largely α-helical and upright. Random coil residues are also observed, which do not themselves appear in SFG spectra due to their isotropic structural distribution, but which still absorb infrared light and so can be detected by cross-peaks in 2D SFG spectra. We discuss these results in the context of peptide design. Because of the similar way in which the spectra are collected, these 2D SFG spectra can be directly compared to 2D IR spectra, thereby enabling structural interpretations of surface-bound peptides and biomolecules based on the well-studied structure/2D IR spectra relationships established from soluble proteins. PMID:24372101

Adding a dimension to the infrared spectra of interfaces using heterodyne detected 2D sum-frequency generation (HD 2D SFG) spectroscopy

PubMed Central

Xiong, Wei; Laaser, Jennifer E.; Mehlenbacher, Randy D.; Zanni, Martin T.

2011-01-01

In the last ten years, two-dimensional infrared spectroscopy has become an important technique for studying molecular structures and dynamics. We report the implementation of heterodyne detected two-dimensional sum-frequency generation (HD 2D SFG) spectroscopy, which is the analog of 2D infrared (2D IR) spectroscopy, but is selective to noncentrosymmetric systems such as interfaces. We implement the technique using mid-IR pulse shaping, which enables rapid scanning, phase cycling, and automatic phasing. Absorptive spectra are obtained, that have the highest frequency resolution possible, from which we extract the rephasing and nonrephasing signals that are sometimes preferred. Using this technique, we measure the vibrational mode of CO adsorbed on a polycrystalline Pt surface. The 2D spectrum reveals a significant inhomogenous contribution to the spectral line shape, which is quantified by simulations. This observation indicates that the surface conformation and environment of CO molecules is more complicated than the simple “atop” configuration assumed in previous work. Our method can be straightforwardly incorporated into many existing SFG spectrometers. The technique enables one to quantify inhomogeneity, vibrational couplings, spectral diffusion, chemical exchange, and many other properties analogous to 2D IR spectroscopy, but specifically for interfaces. PMID:22143772

Adding a dimension to the infrared spectra of interfaces using heterodyne detected 2D sum-frequency generation (HD 2D SFG) spectroscopy.

PubMed

Xiong, Wei; Laaser, Jennifer E; Mehlenbacher, Randy D; Zanni, Martin T

2011-12-27

In the last ten years, two-dimensional infrared spectroscopy has become an important technique for studying molecular structures and dynamics. We report the implementation of heterodyne detected two-dimensional sum-frequency generation (HD 2D SFG) spectroscopy, which is the analog of 2D infrared (2D IR) spectroscopy, but is selective to noncentrosymmetric systems such as interfaces. We implement the technique using mid-IR pulse shaping, which enables rapid scanning, phase cycling, and automatic phasing. Absorptive spectra are obtained, that have the highest frequency resolution possible, from which we extract the rephasing and nonrephasing signals that are sometimes preferred. Using this technique, we measure the vibrational mode of CO adsorbed on a polycrystalline Pt surface. The 2D spectrum reveals a significant inhomogenous contribution to the spectral line shape, which is quantified by simulations. This observation indicates that the surface conformation and environment of CO molecules is more complicated than the simple "atop" configuration assumed in previous work. Our method can be straightforwardly incorporated into many existing SFG spectrometers. The technique enables one to quantify inhomogeneity, vibrational couplings, spectral diffusion, chemical exchange, and many other properties analogous to 2D IR spectroscopy, but specifically for interfaces.

Spectral assignment and orientational analysis in a vibrational sum frequency generation study of DPPC monolayers at the air/water interface

NASA Astrophysics Data System (ADS)

Feng, Rong-Juan; Li, Xia; Zhang, Zhen; Lu, Zhou; Guo, Yuan

2016-12-01

The interfacial behavior of the benchmark zwitterionic phospholipid molecule dipalmitoylphosphatidylcholine (DPPC) has been extensively investigated by surface-selective vibrational sum frequency generation spectroscopy (VSFG). However, there is still a lack of agreement between various orientational measurements of phospholipid monolayers at the air/water interface, mainly because of the difficulty in assigning congested VSFG features. In this study, polarization-dependent VSFG measurements reveal a frequency shift between the in-plane and out-of-plane antisymmetric stretching modes of the terminal methyl groups in the DPPC alkyl tails, favoring the model of Cs local symmetry rather than the previously assumed C3v symmetry. Further VSFG experiments of isotopically labeled DPPC successfully capture the vibrational signatures of the glycerol backbone. With the newly derived VSFG polarization selection rules for Cs symmetry and the refreshed spectral assignments, the average tilt angles of the alkyl tail groups, choline headgroup, and glycerol backbone of DPPC molecules can all be determined, showing the powerful capability of VSFG spectroscopy in revealing the structural details at interfaces. The VSFG polarization dependence rules and the orientational analysis procedures developed for Cs symmetry in this work are applicable to other bulky molecules in which the methyl group cannot freely rotate, and they therefore have general applications in future VSFG studies.

Hyperspectral imaging with laser-scanning sum-frequency generation microscopy

PubMed Central

Hanninen, Adam; Shu, Ming Wai; Potma, Eric O.

2017-01-01

Vibrationally sensitive sum-frequency generation (SFG) microscopy is a chemically selective imaging technique sensitive to non-centrosymmetric molecular arrangements in biological samples. The routine use of SFG microscopy has been hampered by the difficulty of integrating the required mid-infrared excitation light into a conventional, laser-scanning nonlinear optical (NLO) microscope. In this work, we describe minor modifications to a regular laser-scanning microscope to accommodate SFG microscopy as an imaging modality. We achieve vibrationally sensitive SFG imaging of biological samples with sub-μm resolution at image acquisition rates of 1 frame/s, almost two orders of magnitude faster than attained with previous point-scanning SFG microscopes. Using the fast scanning capability, we demonstrate hyperspectral SFG imaging in the CH-stretching vibrational range and point out its use in the study of molecular orientation and arrangement in biologically relevant samples. We also show multimodal imaging by combining SFG microscopy with second-harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) on the same imaging platfrom. This development underlines that SFG microscopy is a unique modality with a spatial resolution and image acquisition time comparable to that of other NLO imaging techniques, making point-scanning SFG microscopy a valuable member of the NLO imaging family. PMID:28966861

Experimental implementation of optical clockwork without carrier-envelope phase control.

PubMed

Mücke, O D; Kuzucu, O; Wong, F N C; Ippen, E P; Kärtner, F X; Foreman, S M; Jones, D J; Ma, L S; Hall, J L; Ye, J

2004-12-01

We demonstrate optical clockwork without the need for carrier-envelope phase control by use of sum-frequency generation between a continuous-wave optical parametric oscillator at 3.39 microm and a femtosecond mode-locked Ti:sapphire laser with two strong spectral peaks at 834 and 670 nm, a spectral difference matched by the 3.39-microm radiation.

Usefulness of parametric renal clearance images in the assessment of basic risk factors for renalnal clearance images in the assessment of basic risk factors for renal scarring in children with recurrent urinary tract infections.

PubMed

Pietrzak-Stelasiak, Ewa; Bieńkiewicz, Małgorzata; Woźnicki, Wojciech; Bubińska, Krystyna; Kowalewska-Pietrzak, Magdalena; Płachcińska, Anna; Kuśmierek, Jacek

2017-01-01

Clinically confirmed incidents of acute pyelonephritis (APN) following recurrent infections of urinary tract (UTI) form basic risk factors for renal scarring in children. Vesico-uretheral reflux (VUR) of higher grade is additional risk factor for this scarring. Opinions on diagnostic value of summed sequential images of renal uptake phase (SUM) of dynamic renal scintigraphy in detection of renal scars are diverse. However, several publications point to higher diagnostic efficacy of clearance parametric images (PAR) generated from this study. To establish a clinical value of parametric renal clearance images in detection of renal scarring. A prospective study was performed in a group of 91 children at the age of 4 to 18 years with recurrent UTI. Clinically documented incidents of APN were noted in 32 children: in 8 cases - one and in the remaining 24 - 2 to 5 (mean 3) incidents. In the remaining 59 patients only infections of the lower part of urinary tract were diagnosed. Static renal 99mTc-DMSA SPECT study and after 2-4 days dynamic renal studies (99mTc-EC) were performed in every patient not earlier than 6 months after the last documented incident of UTI. PAR images generated from a dynamic study by in-house developed software and SUM images were compared with a gold standard SPECT study. Percentages of children with detected renal scar(s) with SPECT and PAR methods amounted to 55% and 54%, respectively and were statistically significantly higher (p < 0.0001) than with SUM method - 31%. Scars in children with history of APN detected with SPECT and PAR methods were significantly more frequent than with infections of only lower part of urinary tract (72% vs. 46%; p = 0.017 and 69% vs. 46%; p = 0.036, respectively). A SUM method did not reveal statistically significant differences between frequencies of detection of scars in groups specified above - 38% vs. 27% (p = 0.31). Both SPECT and PAR methods showed also that frequencies of occurrence of renal scars in children with higher grades of VUR were higher than without or with lower grades of VUR: 79% vs. 50% (p = 0.048) and 79% vs. 49% (p = 0.04). A SUM method did not reveal higher frequency of renal scars in children with high VUR grades: 36% vs. 30% (p = 0.44). Results obtained with PAR and SPECT methods were similar. An advantage of PAR over SUM images obtained from a dynamic renal scintigraphy in detection of renal scars in children with UTI was confirmed.

X-Ray Sum Frequency Diffraction for Direct Imaging of Ultrafast Electron Dynamics

NASA Astrophysics Data System (ADS)

Rouxel, Jérémy R.; Kowalewski, Markus; Bennett, Kochise; Mukamel, Shaul

2018-06-01

X-ray diffraction from molecules in the ground state produces an image of their charge density, and time-resolved x-ray diffraction can thus monitor the motion of the nuclei. However, the density change of excited valence electrons upon optical excitation can barely be monitored with regular diffraction techniques due to the overwhelming background contribution of the core electrons. We present a nonlinear x-ray technique made possible by novel free electron laser sources, which provides a spatial electron density image of valence electron excitations. The technique, sum frequency generation carried out with a visible pump and a broadband x-ray diffraction pulse, yields snapshots of the transition charge densities, which represent the electron density variations upon optical excitation. The technique is illustrated by ab initio simulations of transition charge density imaging for the optically induced electronic dynamics in a donor or acceptor substituted stilbene.

Capturing inhomogeneous broadening of the -CN stretch vibration in a Langmuir monolayer with high-resolution spectra and ultrafast vibrational dynamics in sum-frequency generation vibrational spectroscopy (SFG-VS)

NASA Astrophysics Data System (ADS)

Velarde, Luis; Wang, Hong-fei

2013-08-01

While in principle the frequency-domain and time-domain spectroscopic measurements should generate identical information for a given molecular system, the inhomogeneous character of surface vibrations in sum-frequency generation vibrational spectroscopy (SFG-VS) studies has only been studied with time-domain SFG-VS by mapping the decay of the vibrational polarization using ultrafast lasers, this due to the lack of SFG vibrational spectra with high enough spectral resolution and accurate enough lineshape. Here, with the recently developed high-resolution broadband SFG-VS (HR-BB-SFG-VS) technique, we show that the inhomogeneous lineshape can be obtained in the frequency-domain for the anchoring CN stretch of the 4-n-octyl-4'-cyanobiphenyl (8CB) Langmuir monolayer at the air-water interface, and that an excellent agreement with the time-domain SFG free-induction-decay can be established. We found that the 8CB CN stretch spectrum consists of a single peak centered at 2234.00 ± 0.01 cm-1 with a total linewidth of 10.9 ± 0.3 cm-1 at half maximum. The Lorentzian contribution accounts only for 4.7 ± 0.4 cm-1 to this width and the Gaussian (inhomogeneous) broadening for as much as 8.1 ± 0.2 cm-1. Polarization analysis of the -CN spectra showed that the -CN group is tilted 57° ± 2° from the surface normal. The large heterogeneity in the -CN spectrum is tentatively attributed to the -CN group interactions with the interfacial water molecules penetrated/accommodated into the 8CB monolayer, a unique phenomenon for the nCB Langmuir monolayers reported previously.

Capturing inhomogeneous broadening of the -CN stretch vibration in a Langmuir monolayer with high-resolution spectra and ultrafast vibrational dynamics in sum-frequency generation vibrational spectroscopy (SFG-VS).

PubMed

Velarde, Luis; Wang, Hong-fei

2013-08-28

While in principle the frequency-domain and time-domain spectroscopic measurements should generate identical information for a given molecular system, the inhomogeneous character of surface vibrations in sum-frequency generation vibrational spectroscopy (SFG-VS) studies has only been studied with time-domain SFG-VS by mapping the decay of the vibrational polarization using ultrafast lasers, this due to the lack of SFG vibrational spectra with high enough spectral resolution and accurate enough lineshape. Here, with the recently developed high-resolution broadband SFG-VS (HR-BB-SFG-VS) technique, we show that the inhomogeneous lineshape can be obtained in the frequency-domain for the anchoring CN stretch of the 4-n-octyl-4'-cyanobiphenyl (8CB) Langmuir monolayer at the air-water interface, and that an excellent agreement with the time-domain SFG free-induction-decay can be established. We found that the 8CB CN stretch spectrum consists of a single peak centered at 2234.00 ± 0.01 cm(-1) with a total linewidth of 10.9 ± 0.3 cm(-1) at half maximum. The Lorentzian contribution accounts only for 4.7 ± 0.4 cm(-1) to this width and the Gaussian (inhomogeneous) broadening for as much as 8.1 ± 0.2 cm(-1). Polarization analysis of the -CN spectra showed that the -CN group is tilted 57° ± 2° from the surface normal. The large heterogeneity in the -CN spectrum is tentatively attributed to the -CN group interactions with the interfacial water molecules penetrated/accommodated into the 8CB monolayer, a unique phenomenon for the nCB Langmuir monolayers reported previously.

Capturing inhomogeneous broadening of the -CN stretch vibration in a Langmuir monolayer with high-resolution spectra and ultrafast vibrational dynamics in sum-frequency generation vibrational spectroscopy (SFG-VS)

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

Velarde Ruiz Esparza, Luis A.; Wang, Hongfei

2013-08-28

Even though in principle the frequency-domain and time-domain spectroscopic measurement should generate identical information for a given molecular system, inhomogeneous character of surface vibrations in the sum-frequency generation vibrational spectroscopy (SFG-VS) studies has only been studied with the time-domain SFGVS by mapping the decay of the vibrational polarization using ultrafast lasers, due to the lack of SFG vibrational spectra with high enough spectral resolution and accurate enough line shape. Here with recently developed high-resolution broadband SFG-VS (HR-BB-SFG-VS) we show that the inhomogeneous line shape can be obtained in the frequency-domain, for the anchoring CN stretch of the 4-n-octyl-4'-cyanobiphenyl (8CB) Langmuirmore » monolayer at the air-water interface, and that an excellent agreement with the time-domain SFG free-induction-decay (FID) results can be established. We found that the 8CB CN stretch spectrum consists of a single peak centered at 2234.00 + * 0.01 cm-1 with a total line width of 10.9 + - 0.3 cm-1 at half maximum. The Lorentzian contribution accounts only for 4:7 + -0:4 cm-1 to this width and the Gaussian (inhomogeneous) broadening for as much as 8:1+*0:2 cm-1. Polarization analysis of the -CN spectra showed that the -CN group is tilted 57 + - 2 degrees from the surface normal. The large heterogeneity in the -CN spectrum is tentatively attributed to the -CN group interactions with the interfacial water molecules penetrated/accomodated into the 8CB monolayer, a unique phenomenon for the nCB Langmuir monolayers reported previously.« less

Investigation of Second- and Third-Harmonic Generation in Few-Layer Gallium Selenide by Multiphoton Microscopy

PubMed Central

Karvonen, Lasse; Säynätjoki, Antti; Mehravar, Soroush; Rodriguez, Raul D.; Hartmann, Susanne; Zahn, Dietrich R. T.; Honkanen, Seppo; Norwood, Robert A.; Peyghambarian, N.; Kieu, Khanh; Lipsanen, Harri; Riikonen, Juha

2015-01-01

Gallium selenide (GaSe) is a layered semiconductor and a well-known nonlinear optical crystal. The discovery of graphene has created a new vast research field focusing on two-dimensional materials. We report on the nonlinear optical properties of few-layer GaSe using multiphoton microscopy. Both second- and third-harmonic generation from few-layer GaSe flakes were observed. Unexpectedly, even the peak at the wavelength of 390 nm, corresponding to the fourth-harmonic generation or the sum frequency generation from third-harmonic generation and pump light, was detected during the spectral measurements in thin GaSe flakes. PMID:25989113

Robust, frequency-stable and accurate mid-IR laser spectrometer based on frequency comb metrology of quantum cascade lasers up-converted in orientation-patterned GaAs.

PubMed

Hansen, Michael G; Ernsting, Ingo; Vasilyev, Sergey V; Grisard, Arnaud; Lallier, Eric; Gérard, Bruno; Schiller, Stephan

2013-11-04

We demonstrate a robust and simple method for measurement, stabilization and tuning of the frequency of cw mid-infrared (MIR) lasers, in particular of quantum cascade lasers. The proof of principle is performed with a quantum cascade laser at 5.4 µm, which is upconverted to 1.2 µm by sum-frequency generation in orientation-patterned GaAs with the output of a standard high-power cw 1.5 µm fiber laser. Both the 1.2 µm and the 1.5 µm waves are measured by a standard Er:fiber frequency comb. Frequency measurement at the 100 kHz-level, stabilization to sub-10 kHz level, controlled frequency tuning and long-term stability are demonstrated.

The use of impedance matching capillaries for reducing resonance in rosette infrasonic spatial filters.

PubMed

Hedlin, Michael A H; Alcoverro, Benoit

2005-04-01

Rosette spatial filters are used at International Monitoring System infrasound array sites to reduce noise due to atmospheric turbulence. A rosette filter consists of several clusters, or rosettes, of low-impedance inlets. Acoustic energy entering each rosette of inlets is summed, acoustically, at a secondary summing manifold. Acoustic energy from the secondary manifolds are summed acoustically at a primary summing manifold before entering the microbarometer. Although rosette filters have been found to be effective at reducing infrasonic noise across a broad frequency band, resonance inside the filters reduces the effectiveness of the filters at high frequencies. This paper presents theoretical and observational evidence that the resonance inside these filters that is seen below 10 Hz is due to reflections occuring at impedance discontinuities at the primary and secondary summing manifolds. Resonance involving reflections at the inlets amplifies noise levels at frequencies above 10 Hz. This paper further reports results from theoretical and observational tests of impedance matching capillaries for removing the resonance problem. Almost total removal of resonant energy below 5 Hz was found by placing impedance matching capillaries adjacent to the secondary summing manifolds in the pipes leading to the primary summing manifold and the microbarometer. Theory and recorded data indicate that capillaries with resistance equal to the characteristic impedance of the pipe connecting the secondary and primary summing manifolds suppresses resonance but does not degrade the reception of acoustic signals. Capillaries at the inlets can be used to remove resonant energy at higher frequencies but are found to be less effective due to the high frequency of this energy outside the frequency band of interest.

Frequency characteristics of vibration generated by dual acoustic radiation force for estimating viscoelastic properties of biological tissues

NASA Astrophysics Data System (ADS)

Watanabe, Ryoichi; Arakawa, Mototaka; Kanai, Hiroshi

2018-07-01

We proposed a new method for estimating the viscoelastic property of the local region of a sample. The viscoelastic parameters of the phantoms simulating the biological tissues were quantitatively estimated by analyzing the frequency characteristics of displacement generated by acoustic excitation. The samples were locally strained by irradiating them with the ultrasound simultaneously generated from two point-focusing transducers by applying the sum of two signals with slightly different frequencies of approximately 1 MHz. The surface of a phantom was excited in the frequency range of 20–2,000 Hz, and its displacement was measured. The frequency dependence of the acceleration provided by the acoustic radiation force was also measured. From these results, we determined the frequency characteristics of the transfer function from the stress to the strain and estimated the ratio of the elastic modulus to the viscosity modulus (K/η) by fitting the data to the Maxwell model. Moreover, the elastic modulus K was separately estimated from the measured sound velocity and density of the phantom, and the viscosity modulus η was evaluated by substituting the estimated elastic modulus into the obtained K/η ratio.

Front end for GPS receivers

NASA Technical Reports Server (NTRS)

Thomas, Jr., Jess Brooks (Inventor)

1999-01-01

The front end in GPS receivers has the functions of amplifying, down-converting, filtering and sampling the received signals. In the preferred embodiment, only two operations, A/D conversion and a sum, bring the signal from RF to filtered quadrature baseband samples. After amplification and filtering at RF, the L1 and L2 signals are each sampled at RF at a high selected subharmonic rate. The subharmonic sample rates are approximately 900 MHz for L1 and 982 MHz for L2. With the selected subharmonic sampling, the A/D conversion effectively down-converts the signal from RF to quadrature components at baseband. The resulting sample streams for L1 and L2 are each reduced to a lower rate with a digital filter, which becomes a straight sum in the simplest embodiment. The frequency subsystem can be very simple, only requiring the generation of a single reference frequency (e.g. 20.46 MHz minus a small offset) and the simple multiplication of this reference up to the subharmonic sample rates for L1 and L2. The small offset in the reference frequency serves the dual purpose of providing an advantageous offset in the down-converted carrier frequency and in the final baseband sample rate.

Simultaneous parametric generation and up-conversion of entangled optical images

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

Saygin, M. Yu., E-mail: mihasyu@gmail.com; Chirkin, A. S., E-mail: aschirkin@rambler.r

A quantum theory of parametric amplification and frequency conversion of an optical image in coupled nonlinear optical processes that include one parametric amplification process at high-frequency pumping and two up-conversion processes in the same pump field is developed. The field momentum operator that takes into account the diffraction and group velocities of the waves is used to derive the quantum equations related to the spatial dynamics of the images during the interaction. An optical scheme for the amplification and conversion of a close image is considered. The mean photon number density and signal-to-noise ratio are calculated in the fixed-pump-field approximationmore » for images at various frequencies. It has been established that the signal-to-noise ratio decreases with increasing interaction length in the amplified image and increases in the images at the generated frequencies, tending to asymptotic values for all interacting waves. The variance of the difference of the numbers of photons is calculated for various pairs of frequencies. The quantum entanglement of the optical images formed in a high-frequency pump field is shown to be converted to higher frequencies during the generation of sum frequencies. Thus, two pairs of entangled optical images are produced in the process considered.« less

The Dual Wavelength UV Transmitter Development for Space Based Ozone DIAL Measurements

NASA Technical Reports Server (NTRS)

Prasad, Narasimha S.

2008-01-01

The objective of this research is to develop efficient 1-micron to UV wavelength conversion technology to generate tunable, single mode, pulsed UV wavelengths of 320 nm and 308 nm. The 532 nm wavelength radiation is generated by a 1064 nm Nd:YAG laser through second harmonic generation. The 532 nm pumps an optical parametric oscillator (OPO) to generate 803 nm. The 320 nm is generated by sum frequency generation (SFG) of 532 nm and 803 nm wavelengths The hardware consists of a conductively cooled, 1 J/pulse, single mode Nd:YAG pump laser coupled to an efficient RISTRA OPO and SFG assembly-Both intra and extra-cavity approaches are examined for efficiency.

Vibrational sum-frequency generation spectroscopy of lipid bilayers at repetition rates up to 100 kHz

NASA Astrophysics Data System (ADS)

Yesudas, Freeda; Mero, Mark; Kneipp, Janina; Heiner, Zsuzsanna

2018-03-01

Broadband vibrational sum-frequency generation (BB-VSFG) spectroscopy has become a well-established surface analytical tool capable of identifying the orientation and structure of molecular layers. A straightforward way to boost the sensitivity of the technique could be to increase the laser repetition rate beyond that of standard BB-VSFG spectrometers, which rely on Ti:sapphire lasers operating at repetition rates of 1-5 kHz. Nevertheless, possible thermally induced artifacts in the vibrational spectra due to higher laser average powers are unexplored. Here, we discuss laser power induced temperature accumulation effects that distort the BB-VSFG spectra of 1,2-diacyl-sn-glycero-3-phosphocholine at an interface between two transparent phases at repetition rates of 5, 10, 50, and 100 kHz at constant pulse energy. No heat-induced distortions were found in the spectra, suggesting that the increase in the laser repetition rate provides a feasible route to an improved signal-to-noise ratio or shorter data acquisition times in BB-VSFG spectroscopy for thin films on transparent substrates. The results have implications for future BB-VSFG spectrometers pushing the detection limit for molecular layers with low surface coverage.

Elucidation of Compression-Induced Surface Crystallization in Amorphous Tablets Using Sum Frequency Generation (SFG) Microscopy.

PubMed

Mah, Pei T; Novakovic, Dunja; Saarinen, Jukka; Van Landeghem, Stijn; Peltonen, Leena; Laaksonen, Timo; Isomäki, Antti; Strachan, Clare J

2017-05-01

To investigate the effect of compression on the crystallization behavior in amorphous tablets using sum frequency generation (SFG) microscopy imaging and more established analytical methods. Tablets containing neat amorphous griseofulvin with/without excipients (silica, hydroxypropyl methylcellulose acetate succinate (HPMCAS), microcrystalline cellulose (MCC) and polyethylene glycol (PEG)) were prepared. They were analyzed upon preparation and storage using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM) and SFG microscopy. Compression-induced crystallization occurred predominantly on the surface of the neat amorphous griseofulvin tablets, with minimal crystallinity being detected in the core of the tablets. The presence of various types of excipients was not able to mitigate the compression-induced surface crystallization of the amorphous griseofulvin tablets. However, the excipients affected the crystallization rate of amorphous griseofulvin in the core of the tablet upon compression and storage. SFG microscopy can be used in combination with ATR-FTIR spectroscopy and SEM to understand the crystallization behaviour of amorphous tablets upon compression and storage. When selecting excipients for amorphous formulations, it is important to consider the effect of the excipients on the physical stability of the amorphous formulations.

Investigating buried polymer interfaces using sum frequency generation vibrational spectroscopy

PubMed Central

Chen, Zhan

2010-01-01

This paper reviews recent progress in the studies of buried polymer interfaces using sum frequency generation (SFG) vibrational spectroscopy. Both buried solid/liquid and solid/solid interfaces involving polymeric materials are discussed. SFG studies of polymer/water interfaces show that different polymers exhibit varied surface restructuring behavior in water, indicating the importance of probing polymer/water interfaces in situ. SFG has also been applied to the investigation of interfaces between polymers and other liquids. It has been found that molecular interactions at such polymer/liquid interfaces dictate interfacial polymer structures. The molecular structures of silane molecules, which are widely used as adhesion promoters, have been investigated using SFG at buried polymer/silane and polymer/polymer interfaces, providing molecular-level understanding of polymer adhesion promotion. The molecular structures of polymer/solid interfaces have been examined using SFG with several different experimental geometries. These results have provided molecular-level information about polymer friction, adhesion, interfacial chemical reactions, interfacial electronic properties, and the structure of layer-by-layer deposited polymers. Such research has demonstrated that SFG is a powerful tool to probe buried interfaces involving polymeric materials, which are difficult to study by conventional surface sensitive analytical techniques. PMID:21113334

Retrieval of complex χ(2) parts for quantitative analysis of sum-frequency generation intensity spectra

PubMed Central

Hofmann, Matthias J.; Koelsch, Patrick

2015-01-01

Vibrational sum-frequency generation (SFG) spectroscopy has become an established technique for in situ surface analysis. While spectral recording procedures and hardware have been optimized, unique data analysis routines have yet to be established. The SFG intensity is related to probing geometries and properties of the system under investigation such as the absolute square of the second-order susceptibility χ(2)2. A conventional SFG intensity measurement does not grant access to the complex parts of χ(2) unless further assumptions have been made. It is therefore difficult, sometimes impossible, to establish a unique fitting solution for SFG intensity spectra. Recently, interferometric phase-sensitive SFG or heterodyne detection methods have been introduced to measure real and imaginary parts of χ(2) experimentally. Here, we demonstrate that iterative phase-matching between complex spectra retrieved from maximum entropy method analysis and fitting of intensity SFG spectra (iMEMfit) leads to a unique solution for the complex parts of χ(2) and enables quantitative analysis of SFG intensity spectra. A comparison between complex parts retrieved by iMEMfit applied to intensity spectra and phase sensitive experimental data shows excellent agreement between the two methods. PMID:26450297

Theoretical vibrational sum-frequency generation spectroscopy of water near lipid and surfactant monolayer interfaces. II. Two-dimensional spectra.

PubMed

Roy, S; Gruenbaum, S M; Skinner, J L

2014-12-14

The structural stability and function of biomolecules is strongly influenced by the dynamics and hydrogen bonding of interfacial water. Understanding and characterizing the dynamics of these water molecules require a surface-sensitive technique such as two-dimensional vibrational sum-frequency generation (2DSFG) spectroscopy. We have combined theoretical 2DSFG calculations with molecular dynamics simulations in order to investigate the dynamics of water near different lipid and surfactant monolayer surfaces. We show that 2DSFG can distinguish the dynamics of interfacial water as a function of the lipid charge and headgroup chemistry. The dynamics of water is slow compared to the bulk near water-zwitterionic and water-anionic interfaces due to conformational constraints on interfacial water imposed by strong phosphate-water hydrogen bonding. The dynamics of water is somewhat faster near water-cationic lipid interfaces as no such constraint is present. Using hydrogen bonding and rotational correlation functions, we characterize the dynamics of water as a function of the distance from the interface between water and zwitterionic lipids. We find that there is a transition from bulk-like to interface-like dynamics approximately 7 Å away from a zwitterionic phosphatidylcholine monolayer surface.

Small Molecules and Sum Frequency Generation Probes of Nanoparticulate TiO2

NASA Astrophysics Data System (ADS)

Shultz, Mary Jane

2006-03-01

Anatase TiO2 is known to photo catalytically mineralize a wide variety of pollutants and pathogens, both airborne and in aqueous solution. One of the major benefits of basing water treatment systems on TiO2 is that it is environmentally benign and so non toxic that it is used as a colorant in creamy salad dressing. The primary impediment to wide spread implementation of a TiO2 based system for water decontamination is that the quantum efficiency in contact with condense phase water is less than 5%. Since the quantum efficiency for destruction of airborne materials is greater than 80%, the potential for increased efficiency is very real. To convert the potential to practice, the oxidation mechanism needs to be more fully understood. We will report on the results of using a nonlinear optical spectroscopy, sum frequency generation (SFG) as an in situ probe of interactions at the TiO2 surface. Results suggest that the dominant oxidation mechanism converts from a direct to an indirect mechanism as the water content (vapor pressure) increases. This presentation will discuss the probe technique as well as the results.

Coherent detection of THz laser signals in optical fiber systems.

PubMed

Folland, Thomas G; Marshall, Owen P; Beere, Harvey E; Ritchie, David A; Chakraborty, Subhasish

2017-10-16

Terahertz (THz) coherent detectors are crucial for the stabilization and measurement of the properties of quantum cascade lasers (QCLs). This paper describes the exploitation of intra-cavity sum frequency generation to up-convert the emission of a THz QCL to the near infrared for detection with fiber optic coupled components alone. Specifically, a low cost infrared photodiode is used to detect a radio frequency (RF) signal with a signal-to-noise ratio of approximately 20dB, generated by beating the up-converted THz wave and a near infrared local oscillator. This RF beat note allows direct analysis of the THz QCL emission in time and frequency domains. The application of this technique for QCL characterization is demonstrated by analyzing the continuous tuning of the RF signal over 2 GHz, which arises from mode tuning across the QCL's operational current range.

Understanding fifth-harmonic generation in CLBO

NASA Astrophysics Data System (ADS)

Patankar, S.; Yang, S. T.; Moody, J. D.; Bayramian, A. J.; Swadling, G. F.; Barker, D.; Datte, P.; Mennerat, G.; Norton, M.; Carr, C. W.; Begishev, I. A.; Bromage, J.; Ross, J. S.

2018-02-01

We report on results of fifth harmonic generation in Cesium Lithium Borate (CLBO) using a three-crystal cascaded frequency conversion scheme designed to study the energy balance of the final sum frequency generation stage. The experimental setup independently combines the first and fourth harmonic of a Nd:Glass laser in a 5mm thick CLBO crystal. Energy balance between the incoming and output energy is close to unity when the CLBO is out of phase matching and approximately 80% when the crystal is in phase matching. A detailed analysis of the residual fundamental and fourth harmonic energy indicates 5th harmonic light is being generated but only 26% is unaccounted for. We attribute the missing light to linear transmission loss in the CLBO oven. The ratio of the output to input energy is unity when the missing 5th harmonic is incorporated into the calculations. Two-dimensional plane wave mixing simulations show agreement with the results at lower intensities.

Single-photon frequency conversion via cascaded quadratic nonlinear processes

NASA Astrophysics Data System (ADS)

Xiang, Tong; Sun, Qi-Chao; Li, Yuanhua; Zheng, Yuanlin; Chen, Xianfeng

2018-06-01

Frequency conversion of single photons is an important technology for quantum interface and quantum communication networks. Here, single-photon frequency conversion in the telecommunication band is experimentally demonstrated via cascaded quadratic nonlinear processes. Using cascaded quasi-phase-matched sum and difference frequency generation in a periodically poled lithium niobate waveguide, the signal photon of a photon pair from spontaneous down-conversion is precisely shifted to identically match its counterpart, i.e., the idler photon, in frequency to manifest a clear nonclassical dip in the Hong-Ou-Mandel interference. Moreover, quantum entanglement between the photon pair is maintained after the frequency conversion, as is proved in time-energy entanglement measurement. The scheme is used to switch single photons between dense wavelength-division multiplexing channels, which holds great promise in applications in realistic quantum networks.

Effect of spectral sampling on the temporal coherence analysis of a broadband source in a SFG interferometer.

PubMed

Darré, Pascaline; Szemendera, Ludovic; Grossard, Ludovic; Delage, Laurent; Reynaud, François

2015-10-05

In the frame of sum frequency generation of a broadband infrared source, we aim to enlarge the converted bandwidth by using a pump frequency comb while keeping a high conversion efficiency. The nonlinear effects are simultaneously induced in the same nonlinear medium. In this paper, we investigate the spectral filtering effect on the temporal coherence behavior with a Mach-Zehnder interferometer using two pump lines. We show that joined effects of quasi-phase matching and spectral sampling lead to an original coherence behavior.

Stimulated Raman scattering in an optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO3.

PubMed

My, T-H; Robin, O; Mhibik, O; Drag, C; Bretenaker, F

2009-03-30

The evolution of the spectrum of a singly resonant optical parametric oscillator based on an MgO-doped periodically poled stoichiometric lithium tantalate crystal is observed when the pump power is varied. The onset of cascade Raman lasing due to stimulated Raman scattering in the nonlinear crystal is analyzed. Spurious frequency doubling and sum-frequency generation phenomena are observed and understood. A strong reduction of the intracavity Raman scattering is obtained by a careful adjustment of the cavity losses.

Compact high-power red-green-blue laser light source generation from a single lithium tantalate with cascaded domain modulation.

PubMed

Xu, P; Zhao, L N; Lv, X J; Lu, J; Yuan, Y; Zhao, G; Zhu, S N

2009-06-08

1W quasi-white-light source has been generated from a single lithium tantalate with cascaded domain modulation. The quasi-white-light is combined by proper proportion of the red, green and blue laser light. The red and the blue result from a compact self-sum frequency optical parametric oscillation when pumped by a single green laser. The efficiency of quasi-white-light from the green pump reaches 27%. This compact design can be employed not only as a stable and powerful RGB light source but also an effective blue laser generator.

Raman Microscopy: A Noninvasive Method to Visualize the Localizations of Biomolecules in the Cornea.

PubMed

Kaji, Yuichi; Akiyama, Toshihiro; Segawa, Hiroki; Oshika, Tetsuro; Kano, Hideaki

2017-11-01

In vivo and in situ visualization of biomolecules without pretreatment will be important for diagnosis and treatment of ocular disorders in the future. Recently, multiphoton microscopy, based on the nonlinear interactions between molecules and photons, has been applied to reveal the localizations of various molecules in tissues. We aimed to use multimodal multiphoton microscopy to visualize the localizations of specific biomolecules in rat corneas. Multiphoton images of the corneas were obtained from nonlinear signals of coherent anti-Stokes Raman scattering, third-order sum frequency generation, and second-harmonic generation. The localizations of the adhesion complex-containing basement membrane and Bowman layer were clearly visible in the third-order sum frequency generation images. The fine structure of type I collagen was observed in the corneal stroma in the second-harmonic generation images. The localizations of lipids, proteins, and nucleic acids (DNA/RNA) was obtained in the coherent anti-Stokes Raman scattering images. Imaging technologies have progressed significantly and been applied in medical fields. Optical coherence tomography and confocal microscopy are widely used but do not provide information on the molecular structure of the cornea. By contrast, multiphoton microscopy provides information on the molecular structure of living tissues. Using this technique, we successfully visualized the localizations of various biomolecules including lipids, proteins, and nucleic acids in the cornea. We speculate that multiphoton microscopy will provide essential information on the physiological and pathological conditions of the cornea, as well as molecular localizations in tissues without pretreatment.

Mechanism and computational model for Lyman-α-radiation generation by high-intensity-laser four-wave mixing in Kr-Ar gas

NASA Astrophysics Data System (ADS)

Louchev, Oleg A.; Bakule, Pavel; Saito, Norihito; Wada, Satoshi; Yokoyama, Koji; Ishida, Katsuhiko; Iwasaki, Masahiko

2011-09-01

We present a theoretical model combined with a computational study of a laser four-wave mixing process under optical discharge in which the non-steady-state four-wave amplitude equations are integrated with the kinetic equations of initial optical discharge and electron avalanche ionization in Kr-Ar gas. The model is validated by earlier experimental data showing strong inhibition of the generation of pulsed, tunable Lyman-α (Ly-α) radiation when using sum-difference frequency mixing of 212.6 nm and tunable infrared radiation (820-850 nm). The rigorous computational approach to the problem reveals the possibility and mechanism of strong auto-oscillations in sum-difference resonant Ly-α generation due to the combined effect of (i) 212.6-nm (2+1)-photon ionization producing initial electrons, followed by (ii) the electron avalanche dominated by 843-nm radiation, and (iii) the final breakdown of the phase matching condition. The model shows that the final efficiency of Ly-α radiation generation can achieve a value of ˜5×10-4 which is restricted by the total combined absorption of the fundamental and generated radiation.

Unambiguous demonstration of soliton evolution in slow-light silicon photonic crystal waveguides with SFG-XFROG.

PubMed

Li, Xiujian; Liao, Jiali; Nie, Yongming; Marko, Matthew; Jia, Hui; Liu, Ju; Wang, Xiaochun; Wong, Chee Wei

2015-04-20

We demonstrate the temporal and spectral evolution of picosecond soliton in the slow light silicon photonic crystal waveguides (PhCWs) by sum frequency generation cross-correlation frequency resolved optical grating (SFG-XFROG) and nonlinear Schrödinger equation (NLSE) modeling. The reference pulses for the SFG-XFROG measurements are unambiguously pre-characterized by the second harmonic generation frequency resolved optical gating (SHG-FROG) assisted with the combination of NLSE simulations and optical spectrum analyzer (OSA) measurements. Regardless of the inevitable nonlinear two photon absorption, high order soliton compressions have been observed remarkably owing to the slow light enhanced nonlinear effects in the silicon PhCWs. Both the measurements and the further numerical analyses of the pulse dynamics indicate that, the free carrier dispersion (FCD) enhanced by the slow light effects is mainly responsible for the compression, the acceleration, and the spectral blue shift of the soliton.

Detection of amide I signals of interfacial proteins in situ using SFG.

PubMed

Wang, Jie; Even, Mark A; Chen, Xiaoyun; Schmaier, Alvin H; Waite, J Herbert; Chen, Zhan

2003-08-20

In this Communication, we demonstrate the novel observation that it is feasible to collect amide signals from polymer/protein solution interfaces in situ using sum frequency generation (SFG) vibrational spectroscopy. Such SFG amide signals allow for acquisition of more detailed molecular level information of entire interfacial protein structures. Proteins investigated include bovine serum albumin, mussel protein mefp-2, factor XIIa, and ubiquitin. Our studies indicate that different proteins generate different SFG amide signals at the polystyrene/protein solution interface, showing that they have different interfacial coverage, secondary structure, or orientation.

Phase-matching directions, refined Sellmeier equations, and second-order nonlinear coefficient of the infrared Langatate crystal La₃Ga(5.5)Ta(0.5)O₁₄.

PubMed

Boursier, Elodie; Segonds, Patricia; Boulanger, Benoit; Félix, Corinne; Debray, Jérôme; Jegouso, David; Ménaert, Bertrand; Roshchupkin, Dmitry; Shoji, Ichiro

2014-07-01

We directly measured phase-matching directions of second harmonic, sum, and difference frequency generations in the Langatate La₃Ga(5.5)Ta(0.5)O₁₄ (LGT) uniaxial crystal. The simultaneous fit of the data enabled us to refine the Sellmeier equations of the ordinary and extraordinary principal refractive indices over the entire transparency range of the crystal, and to calculate the phase-matching curves and efficiencies of LGT for infrared optical parametric generation.

Intrinsic chirality and prochirality at Air/R-(+)- and S-(-)-limonene interfaces: spectral signatures with interference chiral sum-frequency generation vibrational spectroscopy.

PubMed

Fu, Li; Zhang, Yun; Wei, Zhe-Hao; Wang, Hong-Fei

2014-09-01

We report in this work detailed measurements of the chiral and achiral sum-frequency vibrational spectra in the C-H stretching vibration region (2800-3050 cm(-1)) of the air/liquid interfaces of R-(+)-limonene and S-(-)-limonene, using the recently developed high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS). The achiral SFG spectra of R-limonene and S-limonene, as well as the RS racemic mixture (50/50 equal amount mixture), show that the corresponding molecular groups of the R and S enantiomers are with the same interfacial orientations. The interference chiral SFG spectra of the limonene enantiomers exhibit a spectral signature from the chiral response of the Cα-H stretching mode, and a spectral signature from the prochiral response of the CH(2) asymmetric stretching mode, respectively. The chiral spectral feature of the Cα-H stretching mode changes sign from R-(+)-limonene to S-(-)-limonene surfaces, and disappears for the RS racemic mixture surface. While the prochiral spectral feature of the CH(2) asymmetric stretching mode is the same for R-(+)-limonene and S-(-)-limonene surfaces, and also surprisingly remains the same for the RS racemic mixture surface. Therefore, the structures of the R-(+)-limonene and the S-(-)-limonene at the liquid interfaces are nevertheless not mirror images to each other, even though the corresponding groups have the same tilt angle from the interfacial normal, i.e., the R-(+)-limonene and the S-(-)-limonene at the surface are diastereomeric instead of enantiomeric. These results provide detailed information in understanding the structure and chirality of molecular interfaces and demonstrate the sensitivity and potential of SFG-VS as a unique spectroscopic tool for chirality characterization and chiral recognition at the molecular interface. © 2014 Wiley Periodicals, Inc.

Biologically Inspired Model for Inference of 3D Shape from Texture

PubMed Central

Gomez, Olman; Neumann, Heiko

2016-01-01

A biologically inspired model architecture for inferring 3D shape from texture is proposed. The model is hierarchically organized into modules roughly corresponding to visual cortical areas in the ventral stream. Initial orientation selective filtering decomposes the input into low-level orientation and spatial frequency representations. Grouping of spatially anisotropic orientation responses builds sketch-like representations of surface shape. Gradients in orientation fields and subsequent integration infers local surface geometry and globally consistent 3D depth. From the distributions in orientation responses summed in frequency, an estimate of the tilt and slant of the local surface can be obtained. The model suggests how 3D shape can be inferred from texture patterns and their image appearance in a hierarchically organized processing cascade along the cortical ventral stream. The proposed model integrates oriented texture gradient information that is encoded in distributed maps of orientation-frequency representations. The texture energy gradient information is defined by changes in the grouped summed normalized orientation-frequency response activity extracted from the textured object image. This activity is integrated by directed fields to generate a 3D shape representation of a complex object with depth ordering proportional to the fields output, with higher activity denoting larger distance in relative depth away from the viewer. PMID:27649387

Temporal Interactions between Cortical Rhythms

PubMed Central

Roopun, Anita K.; Kramer, Mark A.; Carracedo, Lucy M.; Kaiser, Marcus; Davies, Ceri H.; Traub, Roger D.; Kopell, Nancy J.; Whittington, Miles A.

2008-01-01

Multiple local neuronal circuits support different, discrete frequencies of network rhythm in neocortex. Relationships between different frequencies correspond to mechanisms designed to minimise interference, couple activity via stable phase interactions, and control the amplitude of one frequency relative to the phase of another. These mechanisms are proposed to form a framework for spectral information processing. Individual local circuits can also transform their frequency through changes in intrinsic neuronal properties and interactions with other oscillating microcircuits. Here we discuss a frequency transformation in which activity in two co-active local circuits may combine sequentially to generate a third frequency whose period is the concatenation sum of the original two. With such an interaction, the intrinsic periodicity in each component local circuit is preserved – alternate, single periods of each original rhythm form one period of a new frequency – suggesting a robust mechanism for combining information processed on multiple concurrent spatiotemporal scales. PMID:19225587

Electro-optically Q-switched dual-wavelength Nd:YLF laser emitting at 1047 nm and 1053 nm

NASA Astrophysics Data System (ADS)

Men, Shaojie; Liu, Zhaojun; Cong, Zhenhua; Li, Yongfu; Zhang, Xingyu

2015-05-01

A flash-lamp pumped electro-optically Q-switched dual-wavelength Nd:YLF laser is demonstrated. Two Nd:YLF crystals placed in two cavities are employed to generate orthogonally polarized 1047 nm and 1053 nm radiations, respectively. The two cavities are jointed together by a polarizer and share the same electro-optical Q-switch. Two narrow-band pass filters are used to block unexpected oscillations at the hold-off state of the electro-optical Q-switch. In this case, electro-optical Q-switching is able to operate successfully. With pulse synchronization realized, the maximum output energy of 66.2 mJ and 83.9 mJ are obtained for 1047 nm and 1053 nm lasers, respectively. Correspondingly, the minimum pulse width is both 17 ns for 1047 nm and 1053 nm lasers. Sum frequency generation is realized. This demonstrates the potential of this laser in difference-frequency generations to obtain terahertz wave.

Tunable ultraviolet and blue light generation from Nd:YAB random laser bolstered by second-order nonlinear processes

NASA Astrophysics Data System (ADS)

Moura, André L.; Carreño, Sandra J. M.; Pincheira, Pablo I. R.; Fabris, Zanine V.; Maia, Lauro J. Q.; Gomes, Anderson S. L.; de Araújo, Cid B.

2016-06-01

Ultraviolet and blue light were obtained by nonlinear frequency conversion in a random laser (RL) based on Nd0.10Y0.90Al3(BO3)4 nanocrystalline powder. RL operation at 1062 nm, due to the 4F3/2 → 4I11/2 transition of neodymium ions (Nd3+), was achieved by exciting the Nd3+ with a tunable beam from 680 to 920 nm covering the ground state absorption transitions to the 4F9/2, (4F7/2,4S3/2), (4F5/2,2H9/2), and 4F3/2 states. Light from 340 to 460 nm was obtained via the second-harmonic generation of the excitation beam while tunable blue light, from 417 to 486 nm, was generated by self-sum-frequency mixing between the excitation beam and the RL emission.

Agile multicasting based on cascaded χ(2) nonlinearities in a step-chirped periodically poled lithium niobate.

PubMed

Ahlawat, Meenu; Bostani, Ameneh; Tehranchi, Amirhossein; Kashyap, Raman

2013-08-01

We experimentally demonstrate the possibility of agile multicasting for wavelength division multiplexing (WDM) networks, of a single-channel to two and seven channels over the C band, also extendable to S and L bands. This is based on cascaded χ(2) nonlinear mixing processes, namely, second-harmonic generation (SHG)-sum-frequency generation (SFG) and difference-frequency generation (DFG) in a 20-mm-long step-chirped periodically poled lithium niobate crystal, specially designed and fabricated for a 28-nm-wide SH-SF bandwidth centered at around 1.55 μm. The multiple idlers are simultaneously tuned by detuning the pump wavelengths within the broad SH-SF bandwidth. By selectively tuning the pump wavelengths over less than 10 and 6 nm, respectively, multicasting into two and seven idlers is successfully achieved across ~70 WDM channels within the 50 GHz International Telecommunication Union grid spacing.

Communication: atomic force detection of single-molecule nonlinear optical vibrational spectroscopy.

PubMed

Saurabh, Prasoon; Mukamel, Shaul

2014-04-28

Atomic Force Microscopy (AFM) allows for a highly sensitive detection of spectroscopic signals. This has been first demonstrated for NMR of a single molecule and recently extended to stimulated Raman in the optical regime. We theoretically investigate the use of optical forces to detect time and frequency domain nonlinear optical signals. We show that, with proper phase matching, the AFM-detected signals closely resemble coherent heterodyne-detected signals. Applications are made to AFM-detected and heterodyne-detected vibrational resonances in Coherent Anti-Stokes Raman Spectroscopy (χ((3))) and sum or difference frequency generation (χ((2))).

Extending the Local Mode Hamiltonian Into the Condensed Phase: Using Vibrational Sum Frequency Generation to Study the Benzene-Air Interface

NASA Astrophysics Data System (ADS)

Johnson, Britta; Sibert, Edwin

2017-06-01

Surfaces and interfaces play an important role in understanding many chemical process; they also contain molecular configurations and vibrations that are unique compared to those seen in the bulk and gas phases. Sum frequency generated (SFG) vibrational spectroscopy provides an incredibly detailed picture of these interfaces. In particular, the CH stretch region of the spectrum contains an extensive degree of information about the molecular vibrations and arrangements at the surface or interface. The presence of a strong bandwidth SFG signal for the benzene/air interface has generated controversy since it was discovered; since benzene is centrosymmetric, no SFG signal is expected. It has been hypothesized that this signal is primarily a result of bulk contributions that results from electric quadrupole transitions. Our work focuses on testing this conclusion by calculating a theoretical VSF spectrum from pure surface contributions using a mixed quantum/classical local mode Hamiltonian. We take as a starting point our local mode CH/OH stretch Hamiltonian, that was previously used to study alkylbenzenes, benzene-(H_2O)_n, and DPOE-water clusters, and extend it to the condensed phase by including shifts in the intensities and frequencies as a function of the environment. This environment is modeled using a SAPT-based force-field that accurately reproduces the quadrupole for the benzene dimer. A series of independent time-dependent trajectories are used to obtain an ensemble of surface configurations and calculate the appropriate correlation functions. These correlations functions allow us to determine the origins of the VSF signal. Our talk will focus on the challenges of extending our local mode Hamiltonian into the condensed phase.

Radio-Frequency and Wideband Modulation Arraying

NASA Technical Reports Server (NTRS)

Brockman, M. H.

1984-01-01

Summing network receives coherent signals from all receivers in array. Method sums narrow-band radio-frequency (RF) carrier powers and wide-band spectrum powers of array of separate antenna/receiver systems designed for phase-locked-loop or suppressed-carrier operation.

Applications of Second Harmonic and Sum Frequency Generation to Graphite and Silica Type Interfaces.

DTIC Science & Technology

1994-08-01

investigated. The ultrafast barrierless isomerization of an organic dye, Malachite Green, has also been probed with femtosecond time resolution, enabling the... Malachite Green, has also been probed with femtosecond time resolution, enabling the structure of water at various aqueous interfaces to be probed. In...6G at air/aqueous interface ....................................... 7 6. Time-resolved SHG of Malachite Green at air and silica/aqueous interfaces

Probing crystal structure and mesoscale assembly of cellulose microfibrils in plant cell walls, tunicate tests, and bacterial films using vibrational sum frequency generation (SFG) spectroscopy.

PubMed

Lee, Christopher M; Kafle, Kabindra; Park, Yong Bum; Kim, Seong H

2014-06-14

This study reports that the noncentrosymmetry and phase synchronization requirements of the sum frequency generation (SFG) process can be used to distinguish the three-dimensional organization of crystalline cellulose distributed in amorphous matrices. Crystalline cellulose is produced as microfibrils with a few nanometer diameters by plants, tunicates, and bacteria. Crystalline cellulose microfibrils are embedded in wall matrix polymers and assembled into hierarchical structures that are precisely designed for specific biological and mechanical functions. The cellulose microfibril assemblies inside cell walls are extremely difficult to probe. The comparison of vibrational SFG spectra of uniaxially-aligned and disordered films of cellulose Iβ nanocrystals revealed that the spectral features cannot be fully explained with the crystallographic unit structure of cellulose. The overall SFG intensity, the alkyl peak shape, and the alkyl/hydroxyl intensity ratio are sensitive to the lateral packing and net directionality of the cellulose microfibrils within the SFG coherence length scale. It was also found that the OH SFG stretch peaks could be deconvoluted to find the polymorphic crystal structures of cellulose (Iα and Iβ). These findings were used to investigate the cellulose crystal structure and mesoscale cellulose microfibril packing in intact plant cell walls, tunicate tests, and bacterial films.

Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM).

PubMed

Wu, Heng-Liang; Tong, Yujin; Peng, Qiling; Li, Na; Ye, Shen

2016-01-21

The phase transition behaviors of a supported bilayer of dipalmitoylphosphatidyl-choline (DPPC) have been systematically evaluated by in situ sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM). By using an asymmetric bilayer composed of per-deuterated and per-protonated monolayers, i.e., DPPC-d75/DPPC and a symmetric bilayer of DPPC/DPPC, we were able to probe the molecular structural changes during the phase transition process of the lipid bilayer by SFG spectroscopy. It was found that the DPPC bilayer is sequentially melted from the top (adjacent to the solution) to bottom leaflet (adjacent to the substrate) over a wide temperature range. The conformational ordering of the supported bilayer does not decrease (even slightly increases) during the phase transition process. The conformational defects in the bilayer can be removed after the complete melting process. The phase transition enthalpy for the bottom leaflet was found to be approximately three times greater than that for the top leaflet, indicating a strong interaction of the lipids with the substrate. The present SFG and AFM observations revealed similar temperature dependent profiles. Based on these results, the temperature-induced structural changes in the supported lipid bilayer during its phase transition process are discussed in comparison with previous studies.

Sum-frequency generation analyses of the structure of water at amphoteric SAM-liquid water interfaces.

PubMed

Nomura, Kouji; Nakaji-Hirabayashi, Tadashi; Gemmei-Ide, Makoto; Kitano, Hiromi; Noguchi, Hidenori; Uosaki, Kohei

2014-09-01

Surfaces of both a cover glass and the flat plane of a semi-cylindrical quartz prism were modified with a mixture of positively and negatively charged silane coupling reagents (3-aminopropyltriethoxysilane (APTES) and 3-(trihydroxysilyl)propylmethylphosphonate (THPMP), respectively). The glass surface modified with a self-assembled monolayer (SAM) prepared at a mixing ratio of APTES:THPMP=4:6 was electrically almost neutral and was resistant to non-specific adsorption of proteins, whereas fibroblasts gradually adhered to an amphoteric (mixed) SAM surface probably due to its stiffness, though the number of adhered cells was relatively small. Sum frequency generation (SFG) spectra indicated that total intensity of the OH stretching region (3000-3600cm(-1)) for the amphoteric SAM-modified quartz immersed in liquid water was smaller than those for the positively and negatively charged SAM-modified quartz prisms and a bare quartz prism in contact with liquid water. These results suggested that water molecules at the interface of water and an amphoteric SAM-modified quartz prism are not strongly oriented in comparison with those at the interface of a lopsidedly charged SAM-modified quartz prism and bare quartz. The importance of charge neutralization for the anti-biofouling properties of solid materials was strongly suggested. Copyright © 2014 Elsevier B.V. All rights reserved.

Experimental evidence for an optical interference model for vibrational sum frequency generation on multilayer organic thin film systems. I. Electric dipole approximation.

PubMed

O'Brien, Daniel B; Massari, Aaron M

2015-01-14

In the field of vibrational sum frequency generation spectroscopy (VSFG) applied to organic thin film systems, a significant challenge to data analysis is in the accurate description of optical interference effects. Herein, we provide experimental evidence that a model recently developed in our lab provides an accurate description of this phenomenon. We studied the organic small molecule N,N'-dioctyl-3,4,9,10-perylenedicarboximide vapor deposited as a thickness gradient on silicon wafer substrates with two oxide thicknesses and two surface preps. VSFG data were obtained using the ssp and the sps polarization combinations in the imide carbonyl stretching region as a function of organic thickness. In this first of two reports, the data are modeled and interpreted within the ubiquitous electric dipole approximation for VSFG. The intrinsic sample responses are parameterized during the fitting routines while optical interference effects are simply calculated from the model using known refractive indices, thin film thicknesses, and beam angles. The results indicate that the thin film model provides a good description of optical interferences, indicating that interfacial terms are significant. Inconsistencies between the fitting results within the bounds of the electric dipole response motivate deliberation for additional effects to be considered in the second report.

Characterization of starch polymorphic structures using vibrational sum frequency generation spectroscopy.

PubMed

Kong, Lingyan; Lee, Christopher; Kim, Seong H; Ziegler, Gregory R

2014-02-20

The polymorphic structures of starch were characterized with vibrational sum frequency generation (SFG) spectroscopy. The noncentrosymmetry requirement of SFG spectroscopy allows for the detection of the ordered domains without spectral interferences from the amorphous phase and also the distinction of the symmetric elements among crystalline polymorphs. The V-type amylose was SFG-inactive due to the antiparallel packing of single helices in crystal unit cells, whereas the A- and B-type starches showed strong SFG peaks at 2904 cm(-1) and 2952-2968 cm(-1), which were assigned to CH stretching of the axial methine group in the ring and CH2 stretching of the exocyclic CH2OH side group, respectively. The CH2/CH intensity ratios of the A- and B-type starches are significantly different, indicating that the conformation of hydroxymethyl groups in these two polymorphs may be different. Cyclodextrin inclusion complexes were also analyzed as a comparison to the V-type amylose and showed that the head-to-tail and head-to-head stacking patterns of cyclodextrin molecules govern their SFG signals and peak positions. Although the molecular packing is different between V-type amylose and cyclodextrin inclusion complexes, both crystals show the annihilation of SFG signals when the functional group dipoles are arranged pointing in opposite directions.

New Insights from Sum Frequency Generation Vibrational Spectroscopy into the Interactions of Islet Amyloid Polypeptides with Lipid Membranes

PubMed Central

Wang, Zhuguang; Batista, Victor S.; Yan, Elsa C. Y.

2016-01-01

Studies of amyloid polypeptides on membrane surfaces have gained increasing attention in recent years. Several studies have revealed that membranes can catalyze protein aggregation and that the early products of amyloid aggregation can disrupt membrane integrity, increasing water permeability and inducing ion cytotoxicity. Nonetheless, probing aggregation of amyloid proteins on membrane surfaces is challenging. Surface-specific methods are required to discriminate contributions of aggregates at the membrane interface from those in the bulk phase and to characterize protein secondary structures in situ and in real time without the use of perturbing spectroscopic labels. Here, we review the most recent applications of sum frequency generation (SFG) vibrational spectroscopy applied in conjunction with computational modeling techniques, a joint experimental and computational methodology that has provided valuable insights into the aggregation of islet amyloid polypeptide (IAPP) on membrane surfaces. These applications show that SFG can provide detailed information about structures, kinetics, and orientation of IAPP during interfacial aggregation, relevant to the molecular mechanisms of type II diabetes. These recent advances demonstrate the promise of SFG as a new approach for studying amyloid diseases at the molecular level and for the rational drug design targeting early aggregation products on membrane surfaces. PMID:26697504

Sum frequency generation spectroscopy study of hydrogenated stepped Si(111) surfaces made by molecular hydrogen exposure

NASA Astrophysics Data System (ADS)

Hien, K. T. T.; Sattar, M. A.; Miyauchi, Y.; Mizutani, G.; Rutt, H. N.

2017-09-01

Hydrogen adsorption on stepped Si(111) surfaces 9.5° miscut in the [ 1 ̅ 1 ̅ 2 ] direction has been investigated in situ in a UHV chamber with a base pressure of 10-8 Pa. The H-Si(111)1×1 surface was prepared by exposing the wafer to ultra-pure hydrogen gas at a pressure of 470 Pa. Termination of hydrogen on terraces and steps was observed by sum frequency generation (SFG) with several polarization combinations such as ppp, ssp, pps, spp, psp, sps, pss and sss. Here the 1st, 2nd and 3rd symbols indicate SFG, visible and IR polarizations, respectively. ppp and ssp-SFG clearly showed only two modes: the Si-H stretching vibration terrace mode at 2082 cm-1 (A) and the vertical step dihydride vibration mode at 2094 cm-1 (C1). Interesting points are the appearance of the C1 mode in contrast to the previous SFG spectrum of the H-Si(111)1×1 surface with the same miscut surface angle prepared by wet chemical etching. We suggest that the formation of step dihydride and its orientation on the Si(111) stepped surfaces depend strongly on the preparation method.

Freezing and melting of salt hydrates next to solid surfaces probed by infrared-visible sum frequency generation spectroscopy.

PubMed

Anim-Danso, Emmanuel; Zhang, Yu; Dhinojwala, Ali

2013-06-12

Understanding the freezing of salt solutions near solid surfaces is important in many scientific fields. Here we use sum frequency generation (SFG) spectroscopy to study the freezing of a NaCl solution next to a sapphire substrate. During cooling we observe two transitions. The first corresponds to segregation of concentrated brine next to the sapphire surface as we cool the system down to the region where ice and brine phases coexist. At this transition, the intensity of the ice-like peak decreases, suggesting the disruption of hydrogen-bonding by sodium ions. The second transition corresponds to the formation of NaCl hydrates with abrupt changes in both the SFG intensity and the sharpness of spectral peaks. The similarity in the position of the SFG peaks with those observed using IR and Raman spectroscopy indicates the formation of NaCl·2H2O crystals next to the sapphire substrate. The melting temperatures of the hydrates are very similar to those reported for bulk NaCl·2H2O. This study enhances our understanding of nucleation and freezing of salt solutions on solid surfaces and the effects of salt ions on the structure of interfacial ice.

Sum Frequency Generation of Interfacial Lipid Monolayers Shows Polarization Dependence on Experimental Geometries.

PubMed

Li, Bolin; Li, Xu; Ma, Yong-Hao; Han, Xiaofeng; Wu, Fu-Gen; Guo, Zhirui; Chen, Zhan; Lu, Xiaolin

2016-07-19

Sum frequency generation (SFG) vibrational spectroscopy has been widely employed to investigate molecular structures of biological surfaces and interfaces including model cell membranes. A variety of lipid monolayers or bilayers serving as model cell membranes and their interactions with many different molecules have been extensively studied using SFG. Here, we conducted an in-depth investigation on polarization-dependent SFG signals collected from interfacial lipid monolayers using different experimental geometries, i.e., the prism geometry (total internal reflection) and the window geometry (external reflection). The different SFG spectral features of interfacial lipid monolayers detected using different experimental geometries are due to the interplay between the varied Fresnel coefficients and second-order nonlinear susceptibility tensor terms of different vibrational modes (i.e., ss and as modes of methyl groups), which were analyzed in detail in this study. Therefore, understanding the interplay between the interfacial Fresnel coefficients and χ((2)) tensors is a prerequisite for correctly understanding the SFG spectral features with respect to different experimental geometries. More importantly, the derived information in this paper should not be limited to the methyl groups with a C3v symmetry; valid extension to interfacial functional groups with different molecular symmetries and even chiral interfaces could be expected.

Fast time-domain measurements on telecom single photons

NASA Astrophysics Data System (ADS)

Allgaier, Markus; Vigh, Gesche; Ansari, Vahid; Eigner, Christof; Quiring, Viktor; Ricken, Raimund; Brecht, Benjamin; Silberhorn, Christine

2017-09-01

Direct measurements on the temporal envelope of quantum light are a challenging task and not many examples are known because most classical pulse characterisation methods do not work on the single-photon level. Knowledge of both spectrum and timing can, however, give insights on properties that cannot be determined by the spectral intensity alone. While temporal measurements on single photons on timescales of tens of picoseconds are possible with superconducting photon detectors, and picosecond measurements have been performed using streak cameras, there are no commercial single-photon sensitive devices with femtosecond resolution available. While time-domain sampling using sum-frequency generation has already been exploited for such a measurement, inefficient conversion has necessitated long integration times to build the temporal profile. We demonstrate a highly efficient waveguided sum-frequency generation process in Lithium Niobate to measure the temporal envelope of single photons with femtosecond resolution with short enough acquisition time to provide a live-view of the measurement. We demonstrate the measurement technique and combine it with spectral measurements using a dispersive-fibre time-of-flight spectrometer to determine upper and lower bounds for the spectral purity of heralded single photons. The approach complements the joint spectral intensity measurements as a measure on the purity can be given without knowledge of the spectral phase.

Theoretical vibrational sum-frequency generation spectroscopy of water near lipid and surfactant monolayer interfaces.

PubMed

Roy, S; Gruenbaum, S M; Skinner, J L

2014-11-14

Understanding the structure of water near cell membranes is crucial for characterizing water-mediated events such as molecular transport. To obtain structural information of water near a membrane, it is useful to have a surface-selective technique that can probe only interfacial water molecules. One such technique is vibrational sum-frequency generation (VSFG) spectroscopy. As model systems for studying membrane headgroup/water interactions, in this paper we consider lipid and surfactant monolayers on water. We adopt a theoretical approach combining molecular dynamics simulations and phase-sensitive VSFG to investigate water structure near these interfaces. Our simulated spectra are in qualitative agreement with experiments and reveal orientational ordering of interfacial water molecules near cationic, anionic, and zwitterionic interfaces. OH bonds of water molecules point toward an anionic interface leading to a positive VSFG peak, whereas the water hydrogen atoms point away from a cationic interface leading to a negative VSFG peak. Coexistence of these two interfacial water species is observed near interfaces between water and mixtures of cationic and anionic lipids, as indicated by the presence of both negative and positive peaks in their VSFG spectra. In the case of a zwitterionic interface, OH orientation is toward the interface on the average, resulting in a positive VSFG peak.

Local cochlear damage reduces local nonlinearity and decreases generator-type cochlear emissions while increasing reflector-type emissions.

PubMed

Dong, Wei; Olson, Elizabeth S

2010-03-01

Distortion product otoacoustic emissions (DPOAEs) originate in cochlear nonlinearity and emerge into the ear canal as an apparent sum of emission types, one of which (generator) travels directly out and the other (reflector) travels out following linear reflection. The present study explores intracochlear sources of DPOAEs via simultaneous ear canal and intracochlear pressure measurements in gerbils. A locally damaged cochlea was produced with reduced local intracochlear nonlinearity and significant elevation of the compound action potential thresholds at frequencies represented within the damaged region. In the DPOAE the comparison of healthy to locally damaged cochleae showed the following: (1) In the broad frequency region corresponding to the locally damaged best frequency, DPOAEs evoked by wider f(2)/f(1) stimuli decreased, consistent with the reduction in local nonlinearity. (2) DPOAEs evoked by narrow f(2)/f(1) stimuli often had a bimodal change, decreasing in a lower frequency band and increasing in a band just adjacent and higher, and the DPOAE phase-vs-frequency slope steepened. These changes confirm the complex nature of the DPOAE.

Digital second-order phase-locked loop

NASA Technical Reports Server (NTRS)

Holes, J. K.; Carl, C.; Tegnelia, C. R. (Inventor)

1973-01-01

A digital second-order phase-locked loop is disclosed in which a counter driven by a stable clock pulse source is used to generate a reference waveform of the same frequency as an incoming waveform, and to sample the incoming waveform at zero-crossover points. The samples are converted to digital form and accumulated over M cycles, reversing the sign of every second sample. After every M cycles, the accumulated value of samples is hard limited to a value SGN = + or - 1 and multiplied by a value delta sub 1 equal to a number of n sub 1 of fractions of a cycle. An error signal is used to advance or retard the counter according to the sign of the sum by an amount equal to the sum.

Mid-IR femtosecond frequency conversion by soliton-probe collision in phase-mismatched quadratic nonlinear crystals.

PubMed

Liu, Xing; Zhou, Binbin; Guo, Hairun; Bache, Morten

2015-08-15

We show numerically that ultrashort self-defocusing temporal solitons colliding with a weak pulsed probe in the near-IR can convert the probe to the mid-IR. A near-perfect conversion efficiency is possible for a high effective soliton order. The near-IR self-defocusing soliton can form in a quadratic nonlinear crystal (beta-barium borate) in the normal dispersion regime due to cascaded (phase-mismatched) second-harmonic generation, and the mid-IR converted wave is formed in the anomalous dispersion regime between λ=2.2-2.4  μm as a resonant dispersive wave. This process relies on nondegenerate four-wave mixing mediated by an effective negative cross-phase modulation term caused by cascaded soliton-probe sum-frequency generation.

The frequency-difference and frequency-sum acoustic-field autoproducts.

PubMed

Worthmann, Brian M; Dowling, David R

2017-06-01

The frequency-difference and frequency-sum autoproducts are quadratic products of solutions of the Helmholtz equation at two different frequencies (ω + and ω - ), and may be constructed from the Fourier transform of any time-domain acoustic field. Interestingly, the autoproducts may carry wave-field information at the difference (ω + - ω - ) and sum (ω + + ω - ) frequencies even though these frequencies may not be present in the original acoustic field. This paper provides analytical and simulation results that justify and illustrate this possibility, and indicate its limitations. The analysis is based on the inhomogeneous Helmholtz equation and its solutions while the simulations are for a point source in a homogeneous half-space bounded by a perfectly reflecting surface. The analysis suggests that the autoproducts have a spatial phase structure similar to that of a true acoustic field at the difference and sum frequencies if the in-band acoustic field is a plane or spherical wave. For multi-ray-path environments, this phase structure similarity persists in portions of the autoproduct fields that are not suppressed by bandwidth averaging. Discrepancies between the bandwidth-averaged autoproducts and true out-of-band acoustic fields (with potentially modified boundary conditions) scale inversely with the product of the bandwidth and ray-path arrival time differences.

Development of ultrasound transducer diffractive field theory for nonlinear propagation-based imaging

NASA Astrophysics Data System (ADS)

Kharin, Nikolay A.

2000-04-01

In nonlinear ultrasound imaging the images are formed using the second harmonic energy generated due to the nonlinear nature of finite amplitude propagation. This propagation can be modeled using the KZK wave equation. This paper presents further development of nonlinear diffractive field theory based on the KZK equation and its solution by means of the slowly changing profile method for moderate nonlinearity. The analytical expression for amplitudes and phases of sum frequency wave are obtained in addition to the second harmonic wave. Also, the analytical expression for the relative curvature of the wave fronts of fundamental and second harmonic signals are derived. The media with different nonlinear properties and absorption coefficients were investigated to characterize the diffractive field of the transducer at medical frequencies. All expressions demonstrate good agreement with experimental results. The expressions are novel and provide an easy way for prediction of amplitude and phase structure of nonlinearly distorted field of a transducer. The sum frequency signal technique could be implemented as well as second harmonic technique to improve the quality of biomedical images. The results obtained are of importance for medical diagnostic ultrasound equipment design.

Non-collinear interaction of guided elastic waves in an isotropic plate

NASA Astrophysics Data System (ADS)

Ishii, Yosuke; Biwa, Shiro; Adachi, Tadaharu

2018-04-01

The nonlinear wave propagation in a homogeneous and isotropic elastic plate is analyzed theoretically to investigate the non-collinear interaction of plate wave modes. In the presence of two primary plate waves (Rayleigh-Lamb or shear horizontal modes) propagating in arbitrary directions, an explicit expression for the modal amplitude of nonlinearly generated wave fields with the sum or difference frequency of the primary modes is derived by using the perturbation analysis. The modal amplitude is shown to grow in proportion with the propagation distance when the resonance condition is satisfied, i.e., when the wavevector of secondary wave coincides with the sum or difference of those of primary modes. Furthermore, the non-collinear interaction of two symmetric or two antisymmetric modes is shown to produce the secondary wave fields consisting only of the symmetric modes, while a pair of symmetric and antisymmetric primary modes is shown to produce only the antisymmetric modes. The influence of the intersection angle, the primary frequencies, and the mode combinations on the modal amplitude of secondary wave is examined for a low-frequency range where the lowest-order symmetric and antisymmetric Rayleigh-Lamb waves and the lowest-order symmetric shear horizontal wave are the only propagating modes.

[Research on Time-frequency Characteristics of Magneto-acoustic Signal of Different Thickness Medium Based on Wave Summing Method].

PubMed

Zhang, Shunqi; Yin, Tao; Ma, Ren; Liu, Zhipeng

2015-08-01

Functional imaging method of biological electrical characteristics based on magneto-acoustic effect gives valuable information of tissue in early tumor diagnosis, therein time and frequency characteristics analysis of magneto-acoustic signal is important in image reconstruction. This paper proposes wave summing method based on Green function solution for acoustic source of magneto-acoustic effect. Simulations and analysis under quasi 1D transmission condition are carried out to time and frequency characteristics of magneto-acoustic signal of models with different thickness. Simulation results of magneto-acoustic signal were verified through experiments. Results of the simulation with different thickness showed that time-frequency characteristics of magneto-acoustic signal reflected thickness of sample. Thin sample, which is less than one wavelength of pulse, and thick sample, which is larger than one wavelength, showed different summed waveform and frequency characteristics, due to difference of summing thickness. Experimental results verified theoretical analysis and simulation results. This research has laid a foundation for acoustic source and conductivity reconstruction to the medium with different thickness in magneto-acoustic imaging.

2D heterodyne-detected sum frequency generation study on the ultrafast vibrational dynamics of H{sub 2}O and HOD water at charged interfaces

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

Inoue, Ken-ichi; Singh, Prashant C.; Nihonyanagi, Satoshi

2015-06-07

Two-dimensional heterodyne-detected vibrational sum-frequency generation (2D HD-VSFG) spectroscopy is applied to study the ultrafast vibrational dynamics of water at positively charged aqueous interfaces, and 2D HD-VSFG spectra of cetyltrimethylammonium bromide (CTAB)/water interfaces in the whole hydrogen-bonded OH stretch region (3000 cm{sup −1} ≤ ω{sub pump} ≤ 3600 cm{sup −1}) are measured. 2D HD-VSFG spectrum of the CTAB/isotopically diluted water (HOD-D{sub 2}O) interface exhibits a diagonally elongated bleaching lobe immediately after excitation, which becomes round with a time constant of ∼0.3 ps due to spectral diffusion. In contrast, 2D HD-VSFG spectrum of the CTAB/H{sub 2}O interface at 0.0 ps clearly showsmore » two diagonal peaks and their cross peaks in the bleaching region, corresponding to the double peaks observed at 3230 cm{sup −1} and 3420 cm{sup −1} in the steady-state HD-VSFG spectrum. Horizontal slices of the 2D spectrum show that the relative intensity of the two peaks of the bleaching at the CTAB/H{sub 2}O interface gradually change with the change of the pump frequency. We simulate the pump-frequency dependence of the bleaching feature using a model that takes account of the Fermi resonance and inhomogeneity of the OH stretch vibration, and the simulated spectra reproduce the essential features of the 2D HD-VSFG spectra of the CTAB/H{sub 2}O interface. The present study demonstrates that heterodyne detection of the time-resolved VSFG is critically important for studying the ultrafast dynamics of water interfaces and for unveiling the underlying mechanism.« less

Laser Research and Development Studies for Laser Guide Star Systems

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

Pennington, D.; Beach, R.; Ebbers, C.

2000-02-23

In this paper we consider two CW solid state laser approaches to a 589 nm LGS system. Both are based on the technique of sum-frequency generation, but differ in the cavity architecture. Both technologies are very promising and are worth of further consideration. This preliminary proposal is intended to encompass both designs. A down select shall be performed early in the project execution to focus on the most promising option. The two design options consist of: (1) A dual-frequency resonator with intra-cavity doubling in LB0 offers the promise of a simple architecture and may scale more easily to high power.more » This design has been shown to be highly reliable, efficient and high power when used in frequency-doubled Nd:YAG lasers for programs at LLNL and in commercial products. The challenge in this design is the demonstration of a high power13 18 nm oscillator with adequate suppression of the 1064 nm line. (2) A MOPA based design uses commercial low power oscillators to produce both wavelengths, then amplifies the wavelengths before doubling. This design requires the demonstration of a 1318 nm amplifier, though the design is scaled from a kW CW amplifier already delivered to a customer at a different wavelength. The design must also demonstrate high power scaling of sum-frequency generation in the relatively new nonlinear material, PPLN. The first step in the process would be to further evaluate the two conceptual options for technical feasibility, cost and constructability. Then a down selection to one design would be conducted. Finally, R&D on that design would then proceed. Minimal testing should be required for this selection. The majority of the funding received would be allocated to development of the design selected.« less

Novel Cavities in Vertical External Cavity Surface Emitting Lasers for Emission in Broad Spectral Region by Means of Nonlinear Frequency Conversion

NASA Astrophysics Data System (ADS)

Lukowski, Michal L.

Optically pumped semiconductor vertical external cavity surface emitting lasers (VECSEL) were first demonstrated in the mid 1990's. Due to the unique design properties of extended cavity lasers VECSELs have been able to provide tunable, high-output powers while maintaining excellent beam quality. These features offer a wide range of possible applications in areas such as medicine, spectroscopy, defense, imaging, communications and entertainment. Nowadays, newly developed VECSELs, cover the spectral regions from red (600 nm) to around 5 microm. By taking the advantage of the open cavity design, the emission can be further expanded to UV or THz regions by the means of intracavity nonlinear frequency generation. The objective of this dissertation is to investigate and extend the capabilities of high-power VECSELs by utilizing novel nonlinear conversion techniques. Optically pumped VECSELs based on GaAs semiconductor heterostructures have been demonstrated to provide exceptionally high output powers covering the 900 to 1200 nm spectral region with diffraction limited beam quality. The free space cavity design allows for access to the high intracavity circulating powers where high efficiency nonlinear frequency conversions and wavelength tuning can be obtained. As an introduction, this dissertation consists of a brief history of the development of VECSELs as well as wafer design, chip fabrication and resonator cavity design for optimal frequency conversion. Specifically, the different types of laser cavities such as: linear cavity, V-shaped cavity and patented T-shaped cavity are described, since their optimization is crucial for transverse mode quality, stability, tunability and efficient frequency conversion. All types of nonlinear conversions such as second harmonic, sum frequency and difference frequency generation are discussed in extensive detail. The theoretical simulation and the development of the high-power, tunable blue and green VECSEL by the means of type I second harmonic generation in a V- cavity is presented. Tens of watts of output power for both blue and green wavelengths prove the viability for VECSELs to replace the other types of lasers currently used for applications in laser light shows, for Ti:Sapphire pumping, and for medical applications such as laser skin resurfacing. The novel, recently patented, two-chip T-cavity configuration allowing for spatial overlap of two, separate VECSEL cavities is described in detail. This type of setup is further used to demonstrate type II sum frequency generation to green with multi-watt output, and the full potential of the T-cavity is utilized by achieving type II difference frequency generation to the mid-IR spectral region. The tunable output around 5.4 microm with over 10 mW power is showcased. In the same manner the first attempts to generate THz radiation are discussed. Finally, a slightly modified T-cavity VECSEL is used to reach the UV spectral regions thanks to type I fourth harmonic generation. Over 100 mW at around 265 nm is obtained in a setup which utilizes no stabilization techniques. The dissertation demonstrates the flexibility of the VECSEL in achieving broad spectral coverage and thus its potential for a wide range of applications.

Wind noise under a pine tree canopy.

PubMed

Raspet, Richard; Webster, Jeremy

2015-02-01

It is well known that infrasonic wind noise levels are lower for arrays placed in forests and under vegetation than for those in open areas. In this research, the wind noise levels, turbulence spectra, and wind velocity profiles are measured in a pine forest. A prediction of the wind noise spectra from the measured meteorological parameters is developed based on recent research on wind noise above a flat plane. The resulting wind noise spectrum is the sum of the low frequency wind noise generated by the turbulence-shear interaction near and above the tops of the trees and higher frequency wind noise generated by the turbulence-turbulence interaction near the ground within the tree layer. The convection velocity of the low frequency wind noise corresponds to the wind speed above the trees while the measurements showed that the wind noise generated by the turbulence-turbulence interaction is near stationary and is generated by the slow moving turbulence adjacent to the ground. Comparison of the predicted wind noise spectrum with the measured wind noise spectrum shows good agreement for four measurement sets. The prediction can be applied to meteorological estimates to predict the wind noise under other pine forests.

An innovative Yb-based ultrafast deep ultraviolet source for time-resolved photoemission experiments

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

Boschini, F.; Hedayat, H.; Dallera, C.

2014-12-15

Time- and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amplification and sum-frequency generation, ultrashort pump (hν = 1.82 eV) and ultraviolet probe (hν = 6.05 eV) pulses are generated. Overall temporal and instrumental energy resolutions of, respectively, 85 fs and 50 meV are obtained. Time- and angle-resolved measurements on BiTeI semiconductor are presented to show the capabilities of the setup.

Phase-matching properties of LiGaSe2 for SHG and SFG in the 1.026-10.5910 μm range.

PubMed

Miyata, Kentaro; Petrov, Valentin; Kato, Kiyoshi

2017-08-01

This paper reports on the new experimental results for second-harmonic generation and sum-frequency generation in LiGaSe 2 in the 1.026-10.5910 μm range, and the improved Sellmeier equations that provide a good reproduction of the present experimental results, as well as the published data points for a Ti:Al 2 O 3 laser (λ=0.8200  μm)-pumped optical parametric amplifier and a Nd:YAG laser-pumped optical parametric oscillator in the mid-IR.

SFG study of methanol dissociative adsorption at Pt(1 0 0), Pt(1 1 0) and Pt(1 1 1) electrodes surfaces

NASA Astrophysics Data System (ADS)

Vidal, F.; Busson, B.; Six, C.; Pluchery, O.; Tadjeddine, A.

2002-04-01

The Pt( hkl)/methanol in acidic solution interface which constitutes a model of the anodic part of a fuel cell is studied by infrared-visible sum frequency generation vibrational spectroscopy. Methanol dissociative adsorption leads to CO poisoning of the Pt electrode surfaces. The structure of the CO/Pt( hkl) interface depends strongly on the orientation of the surface electrode.

SFG spectroscopy from 10 -8 to 1000 mbar: less-ordered CO structures and coadsorption on Pd (1 1 1)

NASA Astrophysics Data System (ADS)

Morkel, Matthias; Unterhalt, Holger; Salmeron, Miquel; Rupprechter, Günther; Freund, Hans-Joachim

2003-06-01

Vibrational sum frequency generation spectroscopy was employed to study "less-ordered" phases resulting from low-temperature CO exposure on Pd(1 1 1). Such imperfect structures may also occur under catalytic reaction conditions up to 1000 mbar and originate from the superposition of ordered structures when the CO mobility and flux were insufficient. The effect of coadsorbed hydrogen and water was also examined.

Frequency-domain nonlinear regression algorithm for spectral analysis of broadband SFG spectroscopy.

PubMed

He, Yuhan; Wang, Ying; Wang, Jingjing; Guo, Wei; Wang, Zhaohui

2016-03-01

The resonant spectral bands of the broadband sum frequency generation (BB-SFG) spectra are often distorted by the nonresonant portion and the lineshapes of the laser pulses. Frequency domain nonlinear regression (FDNLR) algorithm was proposed to retrieve the first-order polarization induced by the infrared pulse and to improve the analysis of SFG spectra through simultaneous fitting of a series of time-resolved BB-SFG spectra. The principle of FDNLR was presented, and the validity and reliability were tested by the analysis of the virtual and measured SFG spectra. The relative phase, dephasing time, and lineshapes of the resonant vibrational SFG bands can be retrieved without any preset assumptions about the SFG bands and the incident laser pulses.

Time reversal of arbitrary photonic temporal modes via nonlinear optical frequency conversion

NASA Astrophysics Data System (ADS)

Raymer, Michael G.; Reddy, Dileep V.; van Enk, Steven J.; McKinstrie, Colin J.

2018-05-01

Single-photon wave packets can carry quantum information between nodes of a quantum network. An important general operation in photon-based quantum information systems is ‘blind’ reversal of a photon’s temporal wave packet envelope, that is, the ability to reverse an envelope without knowing the temporal state of the photon. We present an all-optical means for doing so, using nonlinear-optical frequency conversion driven by a short pump pulse. The process used may be sum-frequency generation or four-wave Bragg scattering. This scheme allows for quantum operations such as a temporal-mode parity sorter. We also verify that the scheme works for arbitrary states (not only single-photon ones) of an unknown wave packet.

Identification of scalp EEG circadian variation using a novel correlation sum measure

NASA Astrophysics Data System (ADS)

Shahidi Zandi, Ali; Boudreau, Philippe; Boivin, Diane B.; Dumont, Guy A.

2015-10-01

Objective. In this paper, we propose a novel method to determine the circadian variation of scalp electroencephalogram (EEG) in both individual and group levels using a correlation sum measure, quantifying self-similarity of the EEG relative energy across waking epochs. Approach. We analysed EEG recordings from central-parietal and occipito-parietal montages in nine healthy subjects undergoing a 72 h ultradian sleep-wake cycle protocol. Each waking epoch (˜1 s) of every nap opportunity was decomposed using the wavelet packet transform, and the relative energy for that epoch was calculated in the desired frequency band using the corresponding wavelet coefficients. Then, the resulting set of energy values was resampled randomly to generate different subsets with equal number of elements. The correlation sum of each subset was then calculated over a range of distance thresholds, and the average over all subsets was computed. This average value was finally scaled for each nap opportunity and considered as a new circadian measure. Main results. According to the evaluation results, a clear circadian rhythm was identified in some EEG frequency ranges, particularly in 4-8 Hz and 10-12 Hz. The correlation sum measure not only was able to disclose the circadian rhythm on the group data but also revealed significant circadian variations in most individual cases, as opposed to previous studies only reporting the circadian rhythms on a population of subjects. Compared to a naive measure based on the EEG absolute energy in the frequency band of interest, the proposed measure showed a clear superiority using both individual and group data. Results also suggested that the acrophase (i.e., the peak) of the circadian rhythm in 10-12 Hz occurs close to the core body temperature minimum. Significance. These results confirm the potential usefulness of the proposed EEG-based measure as a non-invasive circadian marker.

Ultrafast Plasmonic Control of Second Harmonic Generation

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

Davidson, Roderick B.; Yanchenko, Anna; Ziegler, Jed I.

Efficient frequency conversion techniques are crucial to the development of plasmonic metasurfaces for information processing and signal modulation. In principle, nanoscale electric-field confinement in nonlinear materials enables higher harmonic conversion efficiencies per unit volume than those attainable in bulk materials. Here we demonstrate efficient second-harmonic generation (SHG) in a serrated nanogap plasmonic geometry that generates steep electric field gradients on a dielectric metasurface. An ultrafast control pulse is used to control plasmon-induced electric fields in a thin-film material with inversion symmetry that, without plasmonic enhancement, does not exhibit an even-order nonlinear optical response. The temporal evolution of the plasmonic near-fieldmore » is characterized with ~100 as resolution using a novel nonlinear interferometric technique. The serrated nanogap is a unique platform in which to investigate optically controlled, plasmonically enhanced harmonic generation in dielectric materials on an ultrafast time scale. Lastly, this metamaterial geometry can also be readily extended to all-optical control of other nonlinear phenomena, such as four-wave mixing and sum- and difference-frequency generation, in a wide variety of dielectric materials.« less

Ultrafast Plasmonic Control of Second Harmonic Generation

DOE PAGES

Davidson, Roderick B.; Yanchenko, Anna; Ziegler, Jed I.; ...

2016-06-01

Efficient frequency conversion techniques are crucial to the development of plasmonic metasurfaces for information processing and signal modulation. In principle, nanoscale electric-field confinement in nonlinear materials enables higher harmonic conversion efficiencies per unit volume than those attainable in bulk materials. Here we demonstrate efficient second-harmonic generation (SHG) in a serrated nanogap plasmonic geometry that generates steep electric field gradients on a dielectric metasurface. An ultrafast control pulse is used to control plasmon-induced electric fields in a thin-film material with inversion symmetry that, without plasmonic enhancement, does not exhibit an even-order nonlinear optical response. The temporal evolution of the plasmonic near-fieldmore » is characterized with ~100 as resolution using a novel nonlinear interferometric technique. The serrated nanogap is a unique platform in which to investigate optically controlled, plasmonically enhanced harmonic generation in dielectric materials on an ultrafast time scale. Lastly, this metamaterial geometry can also be readily extended to all-optical control of other nonlinear phenomena, such as four-wave mixing and sum- and difference-frequency generation, in a wide variety of dielectric materials.« less

Broadband continuous-variable entanglement source using a chirped poling nonlinear crystal

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

Zhao, J. S.; Sun, L.; Yu, X. Q.

2010-01-15

Aperiodically poled nonlinear crystal can be used as a broadband continuous-variable entanglement source and has strong stability under perturbations. We study the conversion dynamics of the sum-frequency generation and the quantum correlation of the two pump fields in a chirped-structure nonlinear crystal using the quantum stochastic method. The results show that there exists a frequency window for the pumps where two optical fields can perform efficient upconversion. The two pump fields are demonstrated to be entangled in the window and the chirped-structure crystal can be used as a continuous-variable entanglement source with a broad response bandwidth.

Using surface lattice resonances to engineer nonlinear optical processes in metal nanoparticle arrays

NASA Astrophysics Data System (ADS)

Huttunen, Mikko J.; Rasekh, Payman; Boyd, Robert W.; Dolgaleva, Ksenia

2018-05-01

Collective responses of localized surface plasmon resonances, known as surface lattice resonances (SLRs) in metal nanoparticle arrays, can lead to high quality factors (˜100 ), large local-field enhancements, and strong light-matter interactions. SLRs have found many applications in linear optics, but little work of the influence of SLRs on nonlinear optics has been reported. Here we show how SLRs could be utilized to enhance nonlinear optical interactions. We devote special attention to the sum-frequency, difference-frequency, and third-harmonic generation processes because of their potential for the realization of novel sources of light. We also demonstrate how such arrays could be engineered to enhance higher-order nonlinear optical interactions through cascaded nonlinear processes. In particular, we demonstrate how the efficiency of third-harmonic generation could be engineered via cascaded second-order responses.

Thermodynamics of Radiation Modes

ERIC Educational Resources Information Center

Pina, Eduardo; de la Selva, Sara Maria Teresa

2010-01-01

We study the equilibrium thermodynamics of the electromagnetic radiation in a cavity of a given volume and temperature. We found three levels of description, the thermodynamics of one mode, the thermodynamics of the distribution of frequencies in a band by summing over the frequencies in it and the global thermodynamics by summing over all the…

Application of the Convolution Formalism to the Ocean Tide Potential: Results from the Gravity and Recovery and Climate Experiment (GRACE)

NASA Technical Reports Server (NTRS)

Desai, S. D.; Yuan, D. -N.

2006-01-01

A computationally efficient approach to reducing omission errors in ocean tide potential models is derived and evaluated using data from the Gravity Recovery and Climate Experiment (GRACE) mission. Ocean tide height models are usually explicitly available at a few frequencies, and a smooth unit response is assumed to infer the response across the tidal spectrum. The convolution formalism of Munk and Cartwright (1966) models this response function with a Fourier series. This allows the total ocean tide height, and therefore the total ocean tide potential, to be modeled as a weighted sum of past, present, and future values of the tide-generating potential. Previous applications of the convolution formalism have usually been limited to tide height models, but we extend it to ocean tide potential models. We use luni-solar ephemerides to derive the required tide-generating potential so that the complete spectrum of the ocean tide potential is efficiently represented. In contrast, the traditionally adopted harmonic model of the ocean tide potential requires the explicit sum of the contributions from individual tidal frequencies. It is therefore subject to omission errors from neglected frequencies and is computationally more intensive. Intersatellite range rate data from the GRACE mission are used to compare convolution and harmonic models of the ocean tide potential. The monthly range rate residual variance is smaller by 4-5%, and the daily residual variance is smaller by as much as 15% when using the convolution model than when using a harmonic model that is defined by twice the number of parameters.

Balancing Vibrations at Harmonic Frequencies by Injecting Harmonic Balancing Signals into the Armature of a Linear Motor/Alternator Coupled to a Stirling Machine

NASA Technical Reports Server (NTRS)

Holliday, Ezekiel S. (Inventor)

2014-01-01

Vibrations at harmonic frequencies are reduced by injecting harmonic balancing signals into the armature of a linear motor/alternator coupled to a Stirling machine. The vibrations are sensed to provide a signal representing the mechanical vibrations. A harmonic balancing signal is generated for selected harmonics of the operating frequency by processing the sensed vibration signal with adaptive filter algorithms of adaptive filters for each harmonic. Reference inputs for each harmonic are applied to the adaptive filter algorithms at the frequency of the selected harmonic. The harmonic balancing signals for all of the harmonics are summed with a principal control signal. The harmonic balancing signals modify the principal electrical drive voltage and drive the motor/alternator with a drive voltage component in opposition to the vibration at each harmonic.

Two-Way Satellite Time and Frequency Transfer (TWSTFT) Calibration Constancy From Closure Sums

DTIC Science & Technology

2008-12-01

40th Annual Precise Time and Time Interval (PTTI) Meeting 587 TWO-WAY SATELLITE TIME AND FREQUENCY TRANSFER ( TWSTFT ) CALIBRATION...Paris, France Abstract Two-way Satellite Time and Frequency Transfer ( TWSTFT ) is considered to be the most accurate means of long-distance...explanations for small, but non-zero, biases observed in the closure sums of uncalibrated data are presented. I. INTRODUCTION TWSTFT [1] has

Calculations of the first frequency moment of the structure factor in the BCS model

NASA Astrophysics Data System (ADS)

Rendell, J. M.; Carbotte, J. P.

1998-03-01

We have calculated the first frequency moment of the dynamical structure factor, S(q,ω), known as the f-sum, using the BCS model of susceptibility, \\chi(q,ω), with phenomenological models of the normal state dispersion, tilde\\varepsilon_k, and the superconducting energy gap, Δ_k(T). We have found an explicit expression for the f-sum in both the normal state and the superconducting state. Numerically, we show that the f-sum is insensitive to temperature changes in the range 0 to the order of magnitude of T_c, to the state (normal or superconducting) and to the size and type of energy gap, Δ_k(T), in the superconducting state. The f-sum does depend intimately on the normal state dispersion model, tilde\\varepsilonk and on the filling in the first Brillouin zone. In addition, we show numerically that the f-sum is nearly constant for the Random Phase Approximation (RPA) of the susceptibility up to pseudo-potentials, U <= U_c, the critical potential. Thus, a large increase in Im \\chi(q_0,ω_0) at frequency ω0 and a potential U > 0 (e.g. examining the 41 meV peak at q0 = (π,π)), is compensated by commensurate reduction in Im \\chi(q_0,ω) at other frequencies.

Inverse Design, Development and Characterization of Catalytic Adsorbates at Semiconductor/Liquid Interfaces

DTIC Science & Technology

2016-07-08

theoretical determination of orientation of Re(I) bipyridyl complexes for CO2 reduction on Au and on TiO2 . We have recently determined the binding...crystalline TiO2 (110) surfaces relative to (001) surfaces using vibrational sum frequency generation (SFG) spectroscopy. The SFG signal shows an...isotropic distribution with the rotation of the TiO2 (001) surface relative to the incident plane, but an anisotropic distribution with the rotation

Understanding Protein-Interface Interactions of a Fusion Protein at Silicone Oil-Water Interface Probed by Sum Frequency Generation Vibrational Spectroscopy.

PubMed

Li, Yaoxin; Pan, Duohai; Nashine, Vishal; Deshmukh, Smeet; Vig, Balvinder; Chen, Zhan

2018-02-01

Protein adsorbed at the silicone oil-water interface can undergo a conformational change that has the potential to induce protein aggregation on storage. Characterization of the protein structures at interface is therefore critical for understanding the protein-interface interactions. In this article, we have applied sum frequency generation (SFG) spectroscopy for studying the secondary structures of a fusion protein at interface and the surfactant effect on protein adsorption to silicone oil-water interface. SFG and chiral SFG spectra from adsorbed protein in the amide I region were analyzed. The presence of beta-sheet vibrational band at 1635 cm -1 implies the protein secondary structure was likely perturbed when protein adsorbed at silicone oil interface. The time-dependent SFG study showed a significant reduction in the SFG signal of preadsorbed protein when polysorbate 20 was introduced, suggesting surfactant has stronger interaction with the interface leading to desorption of protein from the interface. In the preadsorbed surfactant and a mixture of protein/polysorbate 20, SFG analysis confirmed that surfactant can dramatically prevent the protein adsorption to silicone oil surface. This study has demonstrated the potential of SFG for providing the detailed molecular level understanding of protein conformation at interface and assessing the influence of surfactant on protein adsorption behavior. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

In Situ Potentiodynamic Analysis of the Electrolyte/Silicon Electrodes Interface Reactions - A Sum Frequency Generation Vibrational Spectroscopy Study

DOE PAGES

Horowitz, Yonatan; Han, Hui-Ling; Ross, Philip N.; ...

2015-12-11

The key factor in long-term use of batteries is the formation of an electrically insulating solid layer that allows lithium ion transport but stops further electrolyte redox reactions on the electrode surface, hence solid electrolyte interphase (SEI). In this paper, we have studied a common electrolyte, 1.0 M LiPF 6/ethylene carbonate (EC)/diethyl carbonate (DEC), reduction products on crystalline silicon (Si) electrodes in a lithium (Li) half-cell system under reaction conditions. We employed in situ sum frequency generation vibrational spectroscopy (SFG-VS) with interface sensitivity in order to probe the molecular composition of the SEI surface species under various applied potentials wheremore » electrolyte reduction is expected. We found that, with a Si(100)-hydrogen terminated wafer, a Si-ethoxy (Si-OC 2H 5) surface intermediate forms due to DEC decomposition. Our results suggest that the SEI surface composition varies depending on the termination of Si surface, i.e., the acidity of the Si surface. We provide the evidence of specific chemical composition of the SEI on the anode surface under reaction conditions. This supports an electrochemical electrolyte reduction mechanism in which the reduction of the DEC molecule to an ethoxy moiety plays a key role. Finally, these findings shed new light on the formation mechanism of SEI on Si anodes in particular and on SEI formation in general.« less

Cooperative Effects of Zwitterionic-Ionic Surfactant Mixtures on the Interfacial Water Structure Revealed by Sum Frequency Generation Vibrational Spectroscopy.

PubMed

Pan, Xuecong; Yang, Fangyuan; Chen, Shunli; Zhu, Xuefeng; Wang, Chuanyi

2018-05-08

Cooperative effects of a series of equimolar binary zwitterionic-ionic surfactant mixtures on the interfacial water structure at the air-water interfaces have been studied by sum frequency generation vibrational spectroscopy (SFG-VS). For zwitterionic surfactant palmityl sulfobetaine (SNC 16 ), anionic surfactant sodium hexadecyl sulfate (SHS), and cationic surfactant cetyltrimethylammonium bromide (CTAB) with the same length of alkyl chain, significantly enhanced ordering of interfacial water molecules was observed for the zwitterionic-anionic surfactant mixtures SNC 16 -SHS, indicating that SNC 16 interacts more strongly with SHS than with CTAB because of the strong headgroup-headgroup electrostatic attraction for SNC 16 -SHS. Meanwhile, the SFG amplitude ratio of methyl and methylene symmetric stretching modes was used to verify the stronger interaction between SNC 16 and SHS. The conformational order indicator increased from 0.64 for SNC 16 to 7.17 for SNC 16 -SHS but only 0.94 for SNC 16 -CTAB. In addition, another anionic surfactant sodium dodecyl sulfate (SDS) was introduced to study the influence of chain-chain interaction. Decreased SFG amplitude of interfacial water molecules for SNC 16 -SDS was observed. Therefore, both the headgroup-headgroup electrostatic interaction and chain-chain van der Waals attractive interaction of the surfactants play an important role in enhancing the ordering of interfacial water molecules. The results provided experimental and theoretical bases for practical applications of the surfactants.

Efficient flattop ultra-wideband wavelength converters based on double-pass cascaded sum and difference frequency generation using engineered chirped gratings.

PubMed

Tehranchi, Amirhossein; Morandotti, Roberto; Kashyap, Raman

2011-11-07

High-efficiency ultra-broadband wavelength converters based on double-pass quasi-phase-matched cascaded sum and difference frequency generation including engineered chirped gratings in lossy lithium niobate waveguides are numerically investigated and compared to the single-pass counterparts, assuming a large twin-pump wavelength difference of 75 nm. Instead of uniform gratings, few-section chirped gratings with the same length, but with a small constant period change among sections with uniform gratings, are proposed to flatten the response and increase the mean efficiency by finding the common critical period shift and minimum number of sections for both single-pass and double-pass schemes whilst for the latter the efficiency is remarkably higher in a low-loss waveguide. It is also verified that for the same waveguide length and power, the efficiency enhancement expected due to the use of the double-pass scheme instead of the single-pass one, is finally lost if the waveguide loss increases above a certain value. For the double-pass scheme, the criteria for the design of the low-loss waveguide length, and the assignment of power in the pumps to achieve the desired efficiency, bandwidth and ripple are presented for the optimum 3-section chirped-gratings-based devices. Efficient conversions with flattop bandwidths > 84 nm for lengths < 3 cm can be obtained.

Structure and orientation of interfacial proteins determined by sum frequency generation vibrational spectroscopy: method and application.

PubMed

Ye, Shuji; Wei, Feng; Li, Hongchun; Tian, Kangzhen; Luo, Yi

2013-01-01

In situ and real-time characterization of molecular structures and orientation of proteins at interfaces is essential to understand the nature of interfacial protein interaction. Such work will undoubtedly provide important clues to control biointerface in a desired manner. Sum frequency generation vibrational spectroscopy (SFG-VS) has been demonstrated to be a powerful technique to study the interfacial structures and interactions at the molecular level. This paper first systematically introduced the methods for the calculation of the Raman polarizability tensor, infrared transition dipole moment, and SFG molecular hyperpolarizability tensor elements of proteins/peptides with the secondary structures of α-helix, 310-helix, antiparallel β-sheet, and parallel β-sheet, as well as the methodology to determine the orientation of interfacial protein secondary structures using SFG amide I spectra. After that, recent progresses on the determination of protein structure and orientation at different interfaces by SFG-VS were then reviewed, which provides a molecular-level understanding of the structures and interactions of interfacial proteins, specially understanding the nature of driving force behind such interactions. Although this review has focused on analysis of amide I spectra, it will be expected to offer a basic idea for the spectral analysis of amide III SFG signals and other complicated molecular systems such as RNA and DNA. Copyright © 2013 Elsevier Inc. All rights reserved.

Dependence of Sum Frequency Generation (SFG) Spectral Features on the Mesoscale Arrangement of SFG-Active Crystalline Domains Interspersed in SFG-Inactive Matrix: A Case Study with Cellulose in Uniaxially Aligned Control Samples and Alkali-Treated Secondary Cell Walls of Plants

DOE PAGES

Makarem, Mohamadamin; Sawada, Daisuke; O'Neill, Hugh M.; ...

2017-04-21

Vibrational sum frequency generation (SFG) spectroscopy can selectively detect not only molecules at two-dimensional (2D) interfaces but also noncentrosymmetric domains interspersed in amorphous three-dimensional (3D) matrixes. However, the SFG analysis of 3D systems is more complicated than 2D systems because more variables are involved. One such variable is the distance between SFG-active domains in SFG-inactive matrixes. In this study, we fabricated control samples in which SFG-active cellulose crystals were uniaxially aligned in an amorphous matrix. Assuming uniform separation distances between cellulose crystals, the relative intensities of alkyl (CH) and hydroxyl (OH) SFG peaks of cellulose could be related to themore » intercrystallite distance. The experimentally measured CH/OH intensity ratio as a function of the intercrystallite distance could be explained reasonably well with a model constructed using the theoretically calculated hyperpolarizabilities of cellulose and the symmetry cancellation principle of dipoles antiparallel to each other. In conclusion, this comparison revealed physical insights into the intercrystallite distance dependence of the CH/OH SFG intensity ratio of cellulose, which can be used to interpret the SFG spectral features of plant cell walls in terms of mesoscale packing of cellulose microfibrils.« less

Orientation Tuning in the Visual Cortex of 3-Month-old Human Infants

PubMed Central

Baker, Thomas J.; Norcia, Anthony M.; Candy, T. Rowan

2016-01-01

Sensitivity to orientation is critical for making a whole and complete picture of the world. We measured the orientation tuning of mechanisms inthe visual cortex of typically developing 3-month-olds and adults using a nonlinear analysis of the two-input steady-state visually evoked potential (VEP). Two gratings, one a fixed test and the other a variable orientation masker were tagged with distinct temporal frequencies and the corresponding evoked responses were measured at the harmonics of the test and masker frequencies and at a frequency equal to the sum of the two stimulus frequencies. The magnitude of the sum frequency component depended strongly on the relative orientation of the test and masker in both infants and adults. The VEP tuning bandwidths of the 3-month-olds measured at the sum frequency were similar to those of adults, suggesting that behavioral immaturities in functions such as orientation discrimination and contour integration may result from other immaturities in long-range lateral projections or feedback mechanisms. PMID:21236289

Optical Frequency Measurements Relying on a Mid-Infrared Frequency Standard

NASA Astrophysics Data System (ADS)

Rovera, G. Daniele; Acef, Ouali

Only a small number of groups are capable of measuring optical frequencies throughout the world. In this contribution we present some of the underlying philosophy of such frequency measurement systems, including some important theoretical hints. In particular, we concentrate on the approach that has been used with the BNM-LPTF frequency chain, where a separate secondary frequency standard in the mid-infrared has been used. The low-frequency section of the chain is characterized by a measurement of the phase noise spectral density Sφ at 716GHz.Most of the significant measurements performed in the last decade are briefly presented, together with a report on the actual stability and reproducibility of the CO2/ OsO4 frequency standard.Measuring the frequency of an optical frequency standard by direct comparison with the signal available at the output of a primary frequency standard (usually between 5MHz and 100MHz) requires a multiplication factor greater than 107. A number of possible configurations, using harmonic generation, sum or difference frequency generation, have been proposed and realized in the past [1,2,3,4,5,6] and in more recent times [7]. A new technique, employing a femtosecond laser, is presently giving its first impressive results [8].All of the classical frequency chains require a large amount of manpower, together with a great deal of simultaneously operating hardware. This has the consequence that only a very few systems are actually in an operating condition throughout the world.

Excited-state lifetime measurement of silicon vacancy centers in diamond by single-photon frequency upconversion

NASA Astrophysics Data System (ADS)

Rong, Youying; Ma, Jianhui; Chen, Lingxiao; Liu, Yan; Siyushev, Petr; Wu, Botao; Pan, Haifeng; Jelezko, Fedor; Wu, E.; Zeng, Heping

2018-05-01

We report a method with high time resolution to measure the excited-state lifetime of silicon vacancy centers in bulk diamond avoiding timing jitter from the single-photon detectors. Frequency upconversion of the fluorescence emitted from silicon vacancy centers was achieved from 738 nm to 436 nm via sum frequency generation with a short pump pulse. The excited-state lifetime can be obtained by measuring the intensity of upconverted light while the pump delay changes. As a probe, a pump laser with pulse duration of 11 ps provided a high temporal resolution of the measurement. The lifetime extracted from the pump–probe curve was 0.755 ns, which was comparable to the timing jitter of the single-photon detectors.

All optical wavelength broadcast based on simultaneous Type I QPM broadband SFG and SHG in MgO:PPLN.

PubMed

Gong, Mingjun; Chen, Yuping; Lu, Feng; Chen, Xianfeng

2010-08-15

We experimentally demonstrate wavelength broadcast based on simultaneous Type I quasi-phase-matched (QPM) broadband sum-frequency generation (SFG) and second-harmonic generation (SHG) in 5 mol.% MgO-doped periodically poled lithium niobate (MgO:PPLN). One signal has been synchronously converted into seven different wavelengths using two pumps at a 1.5 microm band via quadratic cascaded nonlinear wavelength conversion. By selecting different pump regions, i.e., selecting different cascaded chi((2)):chi((2)) interactions, the flexible wavelength conversions with shifting from one signal to single, double, and triple channels were also demonstrated.

Adding a dimension to the infrared spectra of interfaces: 2D SFG spectroscopy via mid-IR pulse shaping

NASA Astrophysics Data System (ADS)

Zanni, Martin

2012-02-01

Sum-frequency generation spectroscopy provides an infrared spectrum of interfaces and thus has widespread use in the materials and chemical sciences. In this presentation, I will present our recent work in developing a 2D pulse sequence to generate 2D SFG spectra of interfaces, in analogy to 2D infrared spectra used to measure bulk species. To develop this spectroscopy, we have utilized many of the tricks-of-the-trade developed in the 2D IR and 2D Vis communities in the last decade, including mid-IR pulse shaping. With mid-IR pulse shaping, the 2D pulse sequence is manipulated by computer programming in the desired frequency resolution, rotating frame, and signal pathway. We believe that 2D SFG will become an important tool in the interfacial sciences in an analogous way that 2D IR is now being used in many disciplines.

A CW green laser emission by self-sum-frequency-mixing in Nd:GdCOB crystal

NASA Astrophysics Data System (ADS)

Shao, Y.; Jin, H. J.; Lin, J.; Zhang, D.; Tao, Z. H.; Zhang, T. Y.; Li, Y. L.; Ruan, Q. R.

2011-10-01

A compact and efficient green laser light at 538 nm produced by self-sum-frequency-mixing of both fundamental infrared laser waves (1061 and 1091 nm) in Nd:GdCa4O(BO3)3 (Nd:GdCOB) crystal is demonstrated. With 18.2 W of diode pump power, a maximum output power of 1.73 W in the green spectral range at 538 nm has been achieved, corresponding to an optical-to-optical conversion efficiency of 9.5%; the output power stability over 30 min is better than 3%. To the best of our knowledge, this is first work on self-sum-frequency-mixing of a diode pumped Nd:GdCOB laser.

Ramanujan sums for signal processing of low-frequency noise.

PubMed

Planat, Michel; Rosu, Haret; Perrine, Serge

2002-11-01

An aperiodic (low-frequency) spectrum may originate from the error term in the mean value of an arithmetical function such as Möbius function or Mangoldt function, which are coding sequences for prime numbers. In the discrete Fourier transform the analyzing wave is periodic and not well suited to represent the low-frequency regime. In place we introduce a different signal processing tool based on the Ramanujan sums c(q)(n), well adapted to the analysis of arithmetical sequences with many resonances p/q. The sums are quasiperiodic versus the time n and aperiodic versus the order q of the resonance. Different results arise from the use of this Ramanujan-Fourier transform in the context of arithmetical and experimental signals.

Ramanujan sums for signal processing of low-frequency noise

NASA Astrophysics Data System (ADS)

Planat, Michel; Rosu, Haret; Perrine, Serge

2002-11-01

An aperiodic (low-frequency) spectrum may originate from the error term in the mean value of an arithmetical function such as Möbius function or Mangoldt function, which are coding sequences for prime numbers. In the discrete Fourier transform the analyzing wave is periodic and not well suited to represent the low-frequency regime. In place we introduce a different signal processing tool based on the Ramanujan sums cq(n), well adapted to the analysis of arithmetical sequences with many resonances p/q. The sums are quasiperiodic versus the time n and aperiodic versus the order q of the resonance. Different results arise from the use of this Ramanujan-Fourier transform in the context of arithmetical and experimental signals.

Statistical properties of filtered pseudorandom digital sequences formed from the sum of maximum-length sequences

NASA Technical Reports Server (NTRS)

Wallace, G. R.; Weathers, G. D.; Graf, E. R.

1973-01-01

The statistics of filtered pseudorandom digital sequences called hybrid-sum sequences, formed from the modulo-two sum of several maximum-length sequences, are analyzed. The results indicate that a relation exists between the statistics of the filtered sequence and the characteristic polynomials of the component maximum length sequences. An analysis procedure is developed for identifying a large group of sequences with good statistical properties for applications requiring the generation of analog pseudorandom noise. By use of the analysis approach, the filtering process is approximated by the convolution of the sequence with a sum of unit step functions. A parameter reflecting the overall statistical properties of filtered pseudorandom sequences is derived. This parameter is called the statistical quality factor. A computer algorithm to calculate the statistical quality factor for the filtered sequences is presented, and the results for two examples of sequence combinations are included. The analysis reveals that the statistics of the signals generated with the hybrid-sum generator are potentially superior to the statistics of signals generated with maximum-length generators. Furthermore, fewer calculations are required to evaluate the statistics of a large group of hybrid-sum generators than are required to evaluate the statistics of the same size group of approximately equivalent maximum-length sequences.

Record fifth-harmonic-generation efficiency producing 211 nm, joule-level pulses using cesium lithium borate

DOE PAGES

Begishev, I. A.; Bromage, J.; Yang, S. T.; ...

2018-05-16

The fifth harmonic of a pulsed Nd:YLF laser has been realized in a cascade of nonlinear crystals with a record efficiency of 30%. Cesium lithium borate is used in a Type-I configuration for sum-frequency mixing of 1053 nm and 266 nm, producing 211-nm pulses. Flattopped beam profiles and pulse shapes optimize efficiency. Furthermore, energies of the fifth harmonic up to 335 mJ in 2.4 ns pulses were demonstrated.

Record fifth-harmonic-generation efficiency producing 211  nm, joule-level pulses using cesium lithium borate

DOE PAGES

Begishev, I. A.; Bromage, J.; Yang, S. T.; ...

2018-01-01

The fifth harmonic of a pulsed Nd:YLF laser has been realized in a cascade of nonlinear crystals with a record efficiency of 30%. Cesium lithium borate is used in a Type-I configuration for sum-frequency mixing of 1053 nm and 266 nm, producing 211-nm pulses. Flattopped beam profiles and pulse shapes optimize efficiency. Energies of the fifth harmonic up to 335 mJ in 2.4 ns pulses were demonstrated.

Potential for Terahertz/Optical, Two Color Non-linear Sensing of Liquid Biochemical Agents

DTIC Science & Technology

2011-05-18

through the geometry and phase matching dependencies in the setup using enantiomeric and racemic limonene as a me- dium. In completely identical...around the 532 nm 18 795.2 cm−1 YAG line generated in S- limonene by 0.61 THz 20.3 cm−1. The rotation angle was 27°. At each point, 500 mixing events...In the following, signals are extracted as the integral of the total sideband line. Sum frequency sidebands for both S- limonene and a ra- cemic

Record fifth-harmonic-generation efficiency producing 211 nm, joule-level pulses using cesium lithium borate

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

Begishev, I. A.; Bromage, J.; Yang, S. T.

The fifth harmonic of a pulsed Nd:YLF laser has been realized in a cascade of nonlinear crystals with a record efficiency of 30%. Cesium lithium borate is used in a Type-I configuration for sum-frequency mixing of 1053 nm and 266 nm, producing 211-nm pulses. Flattopped beam profiles and pulse shapes optimize efficiency. Furthermore, energies of the fifth harmonic up to 335 mJ in 2.4 ns pulses were demonstrated.

Support effects in catalysis studied by in-situ sum frequency generation vibrational spectroscopy and in-situ x-ray spectroscopies

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

Kennedy, Griffin John

Here, kinetic measurements are paired with in-situ spectroscopic characterization tools to investigate colloidally based, supported Pt catalytic model systems in order to elucidate the mechanisms by which metal and support work in tandem to dictate activity and selectivity. The results demonstrate oxide support materials, while inactive in absence of Pt nanoparticles, possess unique active sites for the selective conversion of gas phase molecules when paired with an active metal catalyst.

Bi-Directional Theta Modulation between the Septo-Hippocampal System and the Mammillary Area in Free-Moving Rats

PubMed Central

Ruan, Ming; Young, Calvin K.; McNaughton, Neil

2017-01-01

Hippocampal (HPC) theta oscillations have long been linked to various functions of the brain. Many cortical and subcortical areas that also exhibit theta oscillations have been linked to functional circuits with the hippocampus on the basis of coupled activities at theta frequencies. We examine, in freely moving rats, the characteristics of diencephalic theta local field potentials (LFPs) recorded in the supramammillary/mammillary (SuM/MM) areas that are bi-directionally connected to the HPC through the septal complex. Using partial directed coherence (PDC), we find support for previous suggestions that SuM modulates HPC theta at higher frequencies. We find weak separation of SuM and MM by dominant theta frequency recorded locally. Contrary to oscillatory cell activities under anesthesia where SuM is insensitive, but MM is sensitive to medial septal (MS) inactivation, theta LFPs persisted and became indistinguishable after MS-inactivation. However, MS-inactivation attenuated SuM/MM theta power, while increasing the frequency of SuM/MM theta. MS-inactivation also reduced root mean squared power in both HPC and SuM/MM equally, but reduced theta power differentially in the time domain. We provide converging evidence that SuM is preferentially involved in coding HPC theta at higher frequencies, and that the MS-HPC circuit normally imposes a frequency-limiting modulation over the SuM/MM area as suggested by cell-based recordings in anesthetized animals. In addition, we provide evidence that the postulated SuM-MS-HPC-MM circuit is under complex bi-directional control, rather than SuM and MM having roles as unidirectional relays in the network. PMID:28955209

Determination of the optimum phase-matching directions for the self-frequency conversion of Nd:GdCOB and Nd:YCOB crystals

NASA Astrophysics Data System (ADS)

Chen, Xueyuan; Huang, Miaoliang; Luo, Zundu; Huang, Yidong

2001-09-01

We report on the nonlinear optical properties of Nd:Ca 4GdO(BO 3) 3 (Nd:GdCOB) and Nd:Ca 4YO(BO 3) 3 (Nd:YCOB) biaxial crystals by theoretical calculation. The phase-matching curves for the self-frequency conversion generation of both crystals are presented. The dependence of the effective nonlinear coefficients and walk-off angles on different phase-matching directions are discussed. The results show that the optimum type-I phase-matching directions for the self-frequency doubling and self-sum-frequency mixing lasers are not in the principal planes but are located respectively in the directions ( θ=67.1°, ϕ=132.35°) and ( θ=68.75°, ϕ=118.1°) for Nd:GdCOB, and ( θ=66.5°, ϕ=143.4°) and ( θ=65.9°, ϕ=134.1°) for Nd:YCOB.

Nonlinear dynamics of nanoscale systems

NASA Astrophysics Data System (ADS)

Hodas, Nathan Oken

This work builds theoretical tools to better understand nanoscale systems, and it ex- plores experimental techniques to probe nanoscale dynamics using nonlinear optical microscopy. In both the theory and experiment, this work harnesses nonlinearity to explore new boundaries in the ongoing attempts to understand the amazing world that is much smaller than we can see. In particular, the first part of this work proves the upper-bounds on the number and quality of oscillations when the sys- tem in question is homogeneously driven and has discrete states, a common way of describing nanoscale motors and chemical systems, although it has application to networked systems in general. The consequences of this limit are explored in the context of chemical clocks and limit cycles. This leads to the analysis of sponta- neous oscillations in GFPmut2, where we postulate that the oscillations must be due to coordinated rearrangement of the beta-barrel. Next, we utilize nonlinear optics to probe the constituent structures of zebrafish muscle. By comparing experimental observations with computational models, we show how second harmonic generation differs from fluorescence for confocal imaging. We use the wavelength dependence of the second harmonic generation conversion efficiency to extract information about the microscopic organization of muscle fibers, using the coherent nature of second ix harmonic generation as an analytical probe. Finally, existing experiments have used a related technique, sum-frequency generation, to directly probe the dynamics of free OH bonds at the water-vapor boundary. Using molecular dynamic simulations of the water surface and by designating surface-sensitive free OH bonds on the water surface, many aspects of the sum-frequency generation measurements were calcu- lated and compared with those inferred from experiment. The method utilizes results available from independent IR and Raman experiments to obtain some of the needed quantities, rather than calculating them ab initio. The results provide insight into the microscopic dynamics at the air-water interface and have useful application in the field of on-water catalysis.

Inequalities for frequency-moment sum rules of electron liquids

NASA Technical Reports Server (NTRS)

Iwamoto, N.

1986-01-01

The relations between the various frequency-moment sum rules of electron liquids, which include even-power moments, are systematically examined by using the Cauchy-Schwarz and Hoelder inequalities. A relation involving the isothermal sound velocity and the kinetic and potential energies is obtained from one of the inequalities in the long-wavelength limit, and is generalized to arbitrary spatial dimensions.

Simultaneously phase-matched second- and third-harmonic generation from 1.55 microm radiation in annealed proton-exchanged periodically poled lithium niobate waveguides.

PubMed

Marangoni, M; Lobino, M; Ramponi, R

2006-09-15

Third-harmonic generation (THG) in the cw regime from C-band radiation was achieved in annealed proton-exchanged periodically poled lithium niobate (PPLN) waveguides. By suitable design of fabrication parameters and operating conditions, quasi-phase-matching (QPM) is obtained simultaneously for the second-harmonic generation process (omega-->2omega, first-order QPM) and for the sum-frequency-generation process (omega+2omega-->3omega, third-order QPM), which provides the third harmonic of the pump field. The high overlap between the field profiles of the interacting modes--TM00 at omega and TM10 at 2omega and 3omega--results in what is believed to be the highest ever reported normalized conversion efficiency for THG from telecommunication wavelengths, equal to 0.72%W(-2) cm(-4).

Two-dimensional sum-frequency generation (2D SFG) spectroscopy: Summary of principles and its application to amyloid fiber monolayers

PubMed Central

Ghosh, Ayanjeet; Ho, Jia-Jung; Serrano, Arnaldo L.; Skoff, David R.; Zhang, Tianqi; Zanni, Martin T.

2015-01-01

By adding a mid-infrared pulse shaper to a sum-frequency generation (SFG) spectrometer, we have built a 2D SFG spectrometer capable of measuring spectra analogous to 2D IR spectra but with monolayer sensitivity and SFG selection rules. In this paper, we describe the experimental apparatus and provide an introduction to 2D SFG spectroscopy to help the reader interpret 2D SFG spectra. The main aim of this manuscript is to report 2D SFG spectra of the amyloid forming peptide FGAIL. FGAIL is a critical segment of the human islet amyloid polypeptide (hIAPP or amylin) that aggregates in people with type 2 diabetes. FGAIL is catalyzed into amyloid fibers by many types of surfaces. Here, we study the structure of FGAIL upon deposition onto a gold surface covered with a self-assembled monolayer of methyl 4-mercaptobenzoate (MMB) that produces an ester coating. FGAIL deposited on bare gold does not form ordered layers. The measured 2D SFG spectrum is consistent with amyloid fiber formation, exhibiting both the parallel (a+) and perpendicular (a−) symmetry modes associated with amyloid β-sheets. Cross peaks are observed between the ester stretches of the coating and the FGAIL peptides. Simulations are presented for two possible structures of FGAIL amyloid β-sheets that illustrates the sensitivity of the 2D SFG spectra to structure and orientation. These results provide some of the first molecular insights into surface catalyzed amyloid fiber structure. PMID:25611039

Hydration of Sulphobetaine (SB) and Tetra(ethylene glycol) (EG4)-Terminated Self-Assembled Monolayers Studied by Sum Frequency Generation (SFG) Vibrational Spectroscopy

PubMed Central

Stein, M. Jeanette; Weidner, Tobias; McCrea, Keith; Castner, David G.; Ratner, Buddy D.

2010-01-01

Sum frequency generation (SFG) vibrational spectroscopy is used to study the surface and the underlying substrate of both homogeneous and mixed self-assembled monolayers (SAMs) of 11-mercaptoundecyl-1-sulphobetainethiol (HS(CH2)11N+(CH3)2(CH2)3SO3−, SB) and 1-mercapto-11-undecyl tetra(ethylene glycol) (HS(CH2)11O(CH2CH2O)4OH, EG4) with an 11-mercapto-1-undecanol (HS(CH2)11OH, MCU) diluent. SFG results on the C–H region of the dry and hydrated SAMs gave an in situ look into the molecular orientation and suggested an approach to maximize signal-to-noise ratio on these difficult to analyze hydrophilic SAMs. Vibrational fingerprint studies in the 3000–3600 cm−1 spectral range for the SAMs exposed serially to air, water, and deuterated water revealed that a layer of tightly-bound structured water was associated with the surface of a non-fouling monolayer but was not present on a hydrophobic N-undecylmercaptan (HS(CH2)10CH3, UnD) control. The percentage of water retained upon submersion in D2O correlated well with the relative amount of protein that was previously shown to absorb onto the monolayers. These results provide evidence supporting the current theory regarding the role of a tightly-bound vicinal water layer in the protein resistance of a non-fouling group. PMID:19639981

Two-dimensional sum-frequency generation (2D SFG) spectroscopy: summary of principles and its application to amyloid fiber monolayers.

PubMed

Ghosh, Ayanjeet; Ho, Jia-Jung; Serrano, Arnaldo L; Skoff, David R; Zhang, Tianqi; Zanni, Martin T

2015-01-01

By adding a mid-infrared pulse shaper to a sum-frequency generation (SFG) spectrometer, we have built a 2D SFG spectrometer capable of measuring spectra analogous to 2D IR spectra but with monolayer sensitivity and SFG selection rules. In this paper, we describe the experimental apparatus and provide an introduction to 2D SFG spectroscopy to help the reader interpret 2D SFG spectra. The main aim of this manuscript is to report 2D SFG spectra of the amyloid forming peptide FGAIL. FGAIL is a critical segment of the human islet amyloid polypeptide (hIAPP or amylin) that aggregates in people with type 2 diabetes. FGAIL is catalyzed into amyloid fibers by many types of surfaces. Here, we study the structure of FGAIL upon deposition onto a gold surface covered with a self-assembled monolayer of methyl-4-mercaptobenzoate (MMB) that produces an ester coating. FGAIL deposited on bare gold does not form ordered layers. The measured 2D SFG spectrum is consistent with amyloid fiber formation, exhibiting both the parallel (a+) and perpendicular (a-) symmetry modes associated with amyloid β-sheets. Cross peaks are observed between the ester stretches of the coating and the FGAIL peptides. Simulations are presented for two possible structures of FGAIL amyloid β-sheets that illustrate the sensitivity of the 2D SFG spectra to structure and orientation. These results provide some of the first molecular insights into surface catalyzed amyloid fiber structure.

Multimodal Broadband Vibrational Sum Frequency Generation (MM-BB-V-SFG) Spectrometer and Microscope.

PubMed

Lee, Christopher M; Kafle, Kabindra; Huang, Shixin; Kim, Seong H

2016-01-14

A broadband sum frequency generation (BB-SFG) spectrometer with multimodal (MM) capabilities was constructed, which could be routinely reconfigured for tabletop experiments in reflection, transmission, and total internal reflection (TIR) geometries, as well as microscopic imaging. The system was constructed using a Ti:sapphire amplifier (800 nm, pulse width = 85 fs, repetition rate = 2 kHz), an optical parameter amplification (OPA) system for production of broadband IR pulses tunable between 1000 and 4000 cm(-1), and two Fabry-Pérot etalons arranged in series for production of narrowband 800 nm pulses. The key feature allowing the MM operation was the nearly collinear alignment of the visible (fixed, 800 nm) and infrared (tunable, 1000-4000 cm(-1)) pulses which were spatially separated. Physical insights discussed in this paper include the comparison of spectral bandwidth produced with 40 and 85 fs pump beams, the improvement of spectral resolution using etalons, the SFG probe volume in bulk analysis, the normalization of SFG signals, the stitching of multiple spectral segments, and the operation in different modes for air/liquid and adsorbate/solid interfaces, bulk samples, as well as spectral imaging combined with principle component analysis (PCA). The SFG spectral features obtained with the MM-BB-SFG system were compared with those obtained with picosecond-scanning-SFG system and high-resolution BB-SFG system (HR-BB-SFG) for dimethyl sulfoxide, α-pinene, and various samples containing cellulose (purified commercial products, Cladophora cell wall, cotton and flax fibers, and onion epidermis cell wall).

Vibrational Sum Frequency Generation Spectroscopy Study of Hydrous Species in Soda Lime Silica Float Glass.

PubMed

Luo, Jiawei; Banerjee, Joy; Pantano, Carlo G; Kim, Seong H

2016-06-21

It is generally accepted that the mechanical properties of soda lime silica (SLS) glass can be affected by the interaction between sodium ions and hydrous species (silanol groups and water molecules) in its surface region. While the amount of these hydrous species can be estimated from hydrogen profiles and infrared spectroscopy, their chemical environment in the glass network is still not well understood. This work employed vibrational sum frequency generation (SFG) spectroscopy to investigate the chemical environment of hydrous species in the surface region of SLS float glass. SLS float glass shows sharp peaks in the OH stretching vibration region in SFG spectra, while the OH stretch peaks of glasses that do not have leachable sodium ions and the OH peaks of water molecules in condensed phases are normally broad due to fast hydrogen bonding dynamics. The hydrous species responsible for the sharp SFG peaks for the SLS float glass were found to be thermodynamically more stable than physisorbed water molecules, did not exchange with D2O, and were associated with the sodium concentration gradient in the dealkalized subsurface region. These results suggested that the hydrous species reside in static solvation shells defined by the silicate network with relatively slow hydrogen bonding dynamics, compared to physisorbed water layers on top of the glass surface. A putative radial distribution of the hydrous species within the SLS glass network was estimated based on the OH SFG spectral features, which could be compared with theoretical distributions calculated from computational simulations.

Monitoring Meso-Scale Ordering of Cellulose in Intact Plant Cell Walls Using Sum Frequency Generation Spectroscopy1[C][W][OPEN

PubMed Central

Park, Yong Bum; Lee, Christopher M.; Koo, Bon-Wook; Park, Sunkyu; Cosgrove, Daniel J.; Kim, Seong H.

2013-01-01

Sum frequency generation (SFG) vibration spectroscopy can selectively detect crystalline cellulose without spectral interference from cell wall matrix components. Here, we show that the cellulose SFG spectrum is sensitive to cellulose microfibril alignment and packing within the cell wall. SFG intensity at 2,944 cm−1 correlated well with crystalline cellulose contents of various regions of the Arabidopsis (Arabidopsis thaliana) inflorescence, while changes in the 3,320/2,944 cm−1 intensity ratio suggest subtle changes in cellulose ordering as tissues mature. SFG analysis of two cellulose synthase mutants (irx1/cesa8 and irx3/cesa7) indicates a reduction in cellulose content without evidence of altered cellulose structure. In primary cell walls of Arabidopsis, cellulose exhibited a characteristic SFG peak at 2,920 and 3,320 cm−1, whereas in secondary cell walls, it had peaks at 2,944 and 3,320 cm−1. Starch (amylose) gave an SFG peak at 2,904 cm−1 (CH methine) whose intensity increased with light exposure prior to harvest. Selective removal of matrix polysaccharides from primary cell walls by acid hydrolysis resulted in an SFG spectrum resembling that of secondary wall cellulose. Our results show that SFG spectroscopy is sensitive to the ordering of cellulose microfibrils in plant cell walls at the meso scale (nm to μm) that is important for cell wall architecture but cannot be probed by other spectroscopic or diffraction techniques. PMID:23995148

Broad-Bandwidth Chiral Sum Frequency Generation Spectroscopy for Probing the Kinetics of Proteins at Interfaces

PubMed Central

2016-01-01

The kinetics of proteins at interfaces plays an important role in biological functions and inspires solutions to fundamental problems in biomedical sciences and engineering. Nonetheless, due to the lack of surface-specific and structural-sensitive biophysical techniques, it still remains challenging to probe protein kinetics in situ and in real time without the use of spectroscopic labels at interfaces. Broad-bandwidth chiral sum frequency generation (SFG) spectroscopy has been recently developed for protein kinetic studies at interfaces by tracking the chiral vibrational signals of proteins. In this article, we review our recent progress in kinetic studies of proteins at interfaces using broad-bandwidth chiral SFG spectroscopy. We illustrate the use of chiral SFG signals of protein side chains in the C–H stretch region to monitor self-assembly processes of proteins at interfaces. We also present the use of chiral SFG signals from the protein backbone in the N–H stretch region to probe the real-time kinetics of proton exchange between protein and water at interfaces. In addition, we demonstrate the applications of spectral features of chiral SFG that are typical of protein secondary structures in both the amide I and the N–H stretch regions for monitoring the kinetics of aggregation of amyloid proteins at membrane surfaces. These studies exhibit the power of broad-bandwidth chiral SFG to study protein kinetics at interfaces and the promise of this technique in research areas of surface science to address fundamental problems in biomedical and material sciences. PMID:26196215

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy.

PubMed

Chen, Xiaoyun; Wang, Jie; Paszti, Zoltan; Wang, Fulin; Schrauben, Joel N; Tarabara, Volodymyr V; Schmaier, Alvin H; Chen, Zhan

2007-05-01

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), zeta-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

Sum frequency generation spectroscopy of tetraalkylphosphonium ionic liquids at the air-liquid interface

NASA Astrophysics Data System (ADS)

Peñalber-Johnstone, Chariz; Adamová, Gabriela; Plechkova, Natalia V.; Bahrami, Maryam; Ghaed-Sharaf, Tahereh; Ghatee, Mohammad Hadi; Seddon, Kenneth R.; Baldelli, Steven

2018-05-01

Sum frequency generation (SFG) spectroscopy is a nonlinear vibrational spectroscopic technique used in the study of interfaces, due to its unique ability to distinguish surface molecules that have preferential ordering compared to the isotropic bulk. Here, a series of alkyltrioctylphosphonium chloride ionic liquids, systematically varied by cation structure, were characterized at the air-liquid interface by SFG. The effect on surface structure resulting from molecular variation (i.e., addition of cyano- and methoxy-functional groups) of the cation alkyl chain was investigated. SFG spectra in the C—H stretching region (2750-3100 cm-1) for [P8 8 8 n][Cl], where n = 4, 5, 8, 10, 12, or 14, showed characteristic changes as the alkyl chain length was increased. Spectral profiles for n = 4, 5, 8, or 10 appeared similar; however, when the fourth alkyl chain was sufficiently long (as in the case of n = 12 or n = 14), abrupt changes occurred in the spectra. Molecular dynamics (MD) simulation of a slab of each ionic liquid (with n = 8, 10, or 12) confirmed gauche defects, with enhancement for the long alkyl chain and an abrupt increase of gauche occurrence from n = 8 to n = 10. A comparison of the tilt angle distribution from the simulation and the SFG analysis show a broad distribution of angles. Using experimental SFG spectra in conjunction with MD simulations, a comprehensive molecular picture at the surface of this unique class of liquids is presented.

Monitoring meso-scale ordering of cellulose in intact plant cell walls using sum frequency generation spectroscopy.

PubMed

Park, Yong Bum; Lee, Christopher M; Koo, Bon-Wook; Park, Sunkyu; Cosgrove, Daniel J; Kim, Seong H

2013-10-01

Sum frequency generation (SFG) vibration spectroscopy can selectively detect crystalline cellulose without spectral interference from cell wall matrix components. Here, we show that the cellulose SFG spectrum is sensitive to cellulose microfibril alignment and packing within the cell wall. SFG intensity at 2,944 cm(-1) correlated well with crystalline cellulose contents of various regions of the Arabidopsis (Arabidopsis thaliana) inflorescence, while changes in the 3,320/2,944 cm(-1) intensity ratio suggest subtle changes in cellulose ordering as tissues mature. SFG analysis of two cellulose synthase mutants (irx1/cesa8 and irx3/cesa7) indicates a reduction in cellulose content without evidence of altered cellulose structure. In primary cell walls of Arabidopsis, cellulose exhibited a characteristic SFG peak at 2,920 and 3,320 cm(-1), whereas in secondary cell walls, it had peaks at 2,944 and 3,320 cm(-1). Starch (amylose) gave an SFG peak at 2,904 cm(-1) (CH methine) whose intensity increased with light exposure prior to harvest. Selective removal of matrix polysaccharides from primary cell walls by acid hydrolysis resulted in an SFG spectrum resembling that of secondary wall cellulose. Our results show that SFG spectroscopy is sensitive to the ordering of cellulose microfibrils in plant cell walls at the meso scale (nm to μm) that is important for cell wall architecture but cannot be probed by other spectroscopic or diffraction techniques.

Hydrogenation and dehydrogenation of cyclohexene on Pt(1 0 0): A sum frequency generation vibrational spectroscopic and kinetic study

NASA Astrophysics Data System (ADS)

Bratlie, Kaitlin M.; Flores, Lucio D.; Somorjai, Gabor A.

2005-12-01

Sum frequency generation (SFG) vibrational spectroscopy and kinetic measurements were performed during cyclohexene hydrogenation/dehydrogenation over a range of pressures (10 -8-5 Torr) and temperatures (300-500 K) on the Pt(1 0 0) surface. Upon adsorption at pressures below 1.5 Torr and at 300 K, cyclohexene dehydrogenates to form π-allyl c-C 6H 9 and hydrogenates to form cyclohexyl (C 6H 11) surface intermediates. Increasing the pressure to 1.5 Torr produces adsorbed 1,4-cyclohexadiene, π-allyl c-C 6H 9, and cyclohexyl species. These adsorbed molecules are found both in the absence and presence of excess hydrogen on the Pt(1 0 0) surface at high pressures and up to 380 K and 360 K, respectively. π-Allyl c-C 6H 9 and cyclohexyl are adsorbed on the surface up to 440 K in the absence of excess hydrogen and 460 K in the presence of excess hydrogen, at which point they are no longer detectable by SFG. Kinetic studies in the absence of excess hydrogen show that the apparent activation energy for the dehydrogenation pathway (14.3 ± 1.2 kcal/mol) is similar to that of the hydrogenation pathway (12.9 ± 0.6 kcal/mol). Different apparent activation energies are observed for the dehydrogenation pathway (22.4 ± 1.6 kcal/mol) and the hydrogenation pathway (18.8 ± 0.9 kcal/mol) in the presence of excess hydrogen.

Third-harmonic entanglement and Einstein-Podolsky-Rosen steering over a frequency range of more than an octave

NASA Astrophysics Data System (ADS)

Olsen, M. K.

2018-03-01

The development of quantum technologies which use quantum states of the light field interacting with other systems creates a demand for such states over wide frequency ranges. In this work we compare the bipartite entanglement and Einstein-Podolsky-Rosen (EPR) -steering properties of the two different parametric schemes which produce third-harmonic optical fields from an input field at the fundamental frequency. The first scheme uses second harmonic cascaded with sum-frequency generation, while the second uses triply degenerate four- wave mixing, also known as direct third-harmonic generation. We find that both schemes produce continuous-variable bipartite entanglement and EPR steering over a frequency range which has previously been unobtainable. The direct scheme produces a greater degree of EPR steering, while the cascaded scheme allows for greater flexibility in having three available bipartitions, thus allowing for greater flexibility in the tailoring of light matter interfaces. There are also parameter regimes in both for which classical mean-field analyses fail to predict the mean-field solutions. Both schemes may be very useful for applications in quantum communication and computation networks, as well as providing for quantum interfaces between a wider range of light and atomic ensembles than is presently practicable.

Enhanced Primary Production, and Altered Biogeochemical Patterns in the German Bight in Response to the Extreme June 2013 Elbe Flood

NASA Astrophysics Data System (ADS)

Voynova, Y. G.; Petersen, W.; Brix, H.

2016-02-01

Due to a number of well documented and unusual atmospheric conditions, the late-spring of 2013 in Central and Eastern Europe was colder and wetter than usual, with saturated soils and higher than average cumulative precipitation. Additional precipitation at the end of May, and beginning of June 2013, caused widespread floods within the Danube and Elbe Rivers, and billions of euros in damages. Within the Elbe watershed, the discharge generated under these conditions was the largest among all summer floods and the second largest on record over the last 140 years (based on daily discharges). The high-frequency monitoring network of the Coastal Observing System for Northern and Arctic Seas (COSYNA) captured the influence of this major freshwater influx on the German Bight. Data from an Elbe Estuary (Cuxhaven) monitoring station, and from a FerryBox aboard a ferry travelling between Büsum and Helgoland, documented the salinity changes in the German Bight, which persisted for a month after the peak river discharge. The flood generated a large influx of dissolved and particulate organic carbon, associated with the freshwater plume, while surface dissolved oxygen between Büsum and Helgoland became undersaturated (not typical for the summer). The Federal Maritime and Hydrographic Agency (BSH) also reported unusually high nutrient concentrations in the German Bight caused by the flood. These conditions subsequently generated a month-long chlorophyll bloom, prolonged dissolved oxygen supersaturation, and higher than usual surface water pH within the German Bight. In the context of predicted increase in frequency of extreme discharge events due to climate change, the June 2013 flood-related biogeochemical changes could become more ubiquitous in the future, and should be considered in management and modeling efforts.

Unique determination of the -CN group tilt angle in Langmuir monolayers using sum-frequency polarization null angle and phase

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

Velarde Ruiz Esparza, Luis A.; Wang, Hongfei

2013-10-14

The relative phase and amplitude ratio between the ssp and ppp polarization combinations of the vibrational sum-frequency generation (SFG) response can be uniquely and accurately determined by the polarization null angle (PNA) method. In this report we show that PNA measurements of the -CN vibration in the 4-n pentyl-4'-cyanoterphenyl (5CT) Langmuir monolayer at the air/water interface yields ssp and ppp response of the same phase, while those in the 4-n-octyl-4'cyanobiphenyl (8CB) Langmuir monolayer have the opposite phase. Accordingly, the -CN group in the 5CT monolayer is tilted around 25+/-2 from the interface normal, while that in the 8CB is tiltedmore » around 57+/-2, consistent with the significant differences in the phase diagrams and hydrogen bonding SFG spectra of the two Langmuir monolayers as reported in the literature. These results also demonstrate that in SFG studies the relative phase information of the different polarization combinations, especially for the ssp and ppp, is important in the unique determination of the tilt angle and conformation of a molecular group at the interface.« less

Effect of bottom slope on the nonlinear triad interactions in shallow water

NASA Astrophysics Data System (ADS)

Chen, Hongzhou; Tang, Xiaocheng; Zhang, Ri; Gao, Junliang

2018-05-01

This paper aims at investigating the effect of bottom slope to the nonlinear triad interactions for irregular waves propagating in shallow water. The physical experiments are conducted in a wave flume with respect to the transformation of waves propagating on three bottom slopes ( β = 1/15, 1/30, and 1/45). Irregular waves with different type of breaking that are mechanically generated based on JONSWAP spectra are used for the test. The obviously different variations of spectra measured on each bottom reveal a crucial role of slope effect in the energy transfer between harmonics. The wavelet-based bispectrum were used to examine the bottom slope effect on the nonlinear triad interactions. Results show that the different bottom slopes which waves are propagated on will cause a significant discrepancy of triad interactions. Then, the discussions on the summed bicoherence which denote the distribution of phase coupling on each frequency further clarify the effect of bottom slope. Furthermore, the summed of the real and imaginary parts of bispectrum which could reflect the intensity of frequency components participating in the wave skewness and asymmetry were also investigated. Results indicate that the value of these parameters will increase as the bottom slope gets steeper.

Broadband upconversion imaging around 4 μm using an all-fiber supercontinuum source

NASA Astrophysics Data System (ADS)

Huot, Laurent; Moselund, Peter M.; Leick, Lasse; Tidemand-Lichtenberg, Peter; Pedersen, Christian

2017-02-01

We present a novel mid-infrared imaging system born from the combination of an all-fiber mid-IR supercontinuum source developed at NKT with ultra-sensitive upconversion detection technology from DTU Fotonik. The source delivers 100 mW of average power and its spectrum extends up to 4.5 μm. The infrared signal is passed through a sample and then focused into a bulk AgGaS2 crystal and subsequently mixed with a synchronous mixing signal at 1550 nm extracted from the pump laser of the supercontinuum. Through sum frequency generation, an upconverted signal ranging from 1030 nm to 1155 nm is generated and acquired using an InGaAs camera.

A compact OPO/SFG laser for ultraviolet biological sensing

NASA Astrophysics Data System (ADS)

Tiihonen, Mikael; Pasiskevicius, Valdas; Laurell, Fredrik; Jonsson, Per; Lindgren, Mikael

2004-07-01

A compact parametric oscillator (OPO) with intracavity sum-frequency generation (SFG) to generate 293 nm UV laser irradiation, was developed. The OPO/SFG device was pumped by a 100 Hz Nd:YAG laser (1064 nm) of own design, including subsequent second harmonic generation (SHG) in an external periodically poled KTiOPO4 (KTP) crystal. The whole system could be used to deliver more than 30 μJ laser irradiation per pulse (100 Hz) at 293 nm. The UV laser light was introduced in an optical fiber attached to a sample compartment allowing detection of fluorescence emission using a commercial spectrometer. Aqueous samples containing biomolecules (ovalbumin) or bacteria spores (Bacillus subtilis) were excited by the UV-light at 293 nm resulting in strong fluorescence emission in the range 325 - 600 nm.

Implementation of spatial overlap modulation nonlinear optical microscopy using an electro-optic deflector

PubMed Central

Isobe, Keisuke; Kawano, Hiroyuki; Kumagai, Akiko; Miyawaki, Atsushi; Midorikawa, Katsumi

2013-01-01

A spatial overlap modulation (SPOM) technique is a nonlinear optical microscopy technique which enhances the three-dimensional spatial resolution and rejects the out-of-focus background limiting the imaging depth inside a highly scattering sample. Here, we report on the implementation of SPOM in which beam pointing modulation is achieved by an electro-optic deflector. The modulation and demodulation frequencies are enhanced to 200 kHz and 400 kHz, respectively, resulting in a 200-fold enhancement compared with the previously reported system. The resolution enhancement and suppression of the out-of-focus background are demonstrated by sum-frequency-generation imaging of pounded granulated sugar and deep imaging of fluorescent beads in a tissue-like phantom, respectively. PMID:24156055

Systems and Methods for Ejection of Ions from an Ion Trap

NASA Technical Reports Server (NTRS)

Cooks, Robert Graham (Inventor); Snyder, Dalton (Inventor)

2018-01-01

The invention generally relates to systems and methods for ejection of ions from an ion trap. In certain embodiments, systems and methods of the invention sum two different frequency signals into a single summed signal that is applied to an ion trap. In other embodiments, an amplitude of a single frequency signal is modulated as the single frequency signal is being applied to the ion trap. In other embodiments, a first alternating current (AC) signal is applied to an ion trap that varies as a function of time, while a constant radio frequency (RF) signal is applied to the ion trap.

Quantitative Interpretation of Polarization SFG Vibrational Spectra of Air/Methanol Interface

NASA Astrophysics Data System (ADS)

Wu, Hui; Zhang, Wen-kai; Gan, Wei; Cui, Zhi-feng; Wang, Hong-fei

2006-06-01

Even though in IR and Raman spectra of liquid methanol there is always an apparent feature for the asymmetric stretching mode of the CH3 group around 2970 cm-1, this feature has not been observed in the Sum Frequency Generation Vibrational Spectroscopy (SFG-VS) in any polarizations from the air/methanol interface. Here we present a treatment based on a corrected bond additivity model to quantitatively interpret the SFG-VS of the air/methanol interface from the IR and Raman spectra of liquid methanol.

Probing organic field effect transistors in situ during operation using SFG.

PubMed

Ye, Hongke; Abu-Akeel, Ashraf; Huang, Jia; Katz, Howard E; Gracias, David H

2006-05-24

In this communication, we report results obtained using surface-sensitive IR+Visible Sum Frequency Generation (SFG) nonlinear optical spectroscopy on interfaces of organic field effect transistors during operation. We observe remarkable correlations between trends in the surface vibrational spectra and electrical properties of the transistor, with changes in gate voltage (VG). These results suggest that field effects on electronic conduction in thin film organic semiconductor devices are correlated to interfacial nonlinear optical characteristics and point to the possibility of using SFG spectroscopy to monitor electronic properties of OFETs.

Frequency conversion of structured light.

PubMed

Steinlechner, Fabian; Hermosa, Nathaniel; Pruneri, Valerio; Torres, Juan P

2016-02-15

Coherent frequency conversion of structured light, i.e. the ability to manipulate the carrier frequency of a wave front without distorting its spatial phase and intensity profile, provides the opportunity for numerous novel applications in photonic technology and fundamental science. In particular, frequency conversion of spatial modes carrying orbital angular momentum can be exploited in sub-wavelength resolution nano-optics and coherent imaging at a wavelength different from that used to illuminate an object. Moreover, coherent frequency conversion will be crucial for interfacing information stored in the high-dimensional spatial structure of single and entangled photons with various constituents of quantum networks. In this work, we demonstrate frequency conversion of structured light from the near infrared (803 nm) to the visible (527 nm). The conversion scheme is based on sum-frequency generation in a periodically poled lithium niobate crystal pumped with a 1540-nm Gaussian beam. We observe frequency-converted fields that exhibit a high degree of similarity with the input field and verify the coherence of the frequency-conversion process via mode projection measurements with a phase mask and a single-mode fiber. Our results demonstrate the suitability of exploiting the technique for applications in quantum information processing and coherent imaging.

Quantum cascade lasers as metrological tools for space optics

NASA Astrophysics Data System (ADS)

Bartalini, S.; Borri, S.; Galli, I.; Mazzotti, D.; Cancio Pastor, P.; Giusfredi, G.; De Natale, P.

2017-11-01

A distributed-feedback quantum-cascade laser working in the 4.3÷4.4 mm range has been frequency stabilized to the Lamb-dip center of a CO2 ro-vibrational transition by means of first-derivative locking to the saturated absorption signal, and its absolute frequency counted with a kHz-level precision and an overall uncertainty of 75 kHz. This has been made possible by an optical link between the QCL and a near-IR Optical Frequency Comb Synthesizer, thanks to a non-linear sum-frequency generation process with a fiber-amplified Nd:YAG laser. The implementation of a new spectroscopic technique, known as polarization spectroscopy, provides an improved signal for the locking loop, and will lead to a narrower laser emission and a drastic improvement in the frequency stability, that in principle is limited only by the stability of the optical frequency comb synthesizer (few parts in 1013). These results confirm quantum cascade lasers as reliable sources not only for high-sensitivity, but also for highprecision measurements, ranking them as optimal laser sources for space applications.

High average power, widely tunable femtosecond laser source from red to mid-infrared based on an Yb-fiber-laser-pumped optical parametric oscillator.

PubMed

Gu, Chenglin; Hu, Minglie; Zhang, Limeng; Fan, Jintao; Song, Youjian; Wang, Chingyue; Reid, Derryck T

2013-06-01

We report on the highly efficient generation of widely tunable femtosecond pulses based on intracavity second harmonic generation (SHG) and sum frequency generation (SFG) in a MgO-doped periodically poled LiNbO(3) optical parametric oscillator (OPO), which is pumped by a Yb-doped large-mode-area photonics crystal fiber femtosecond laser. Red and near infrared from intracavity SHG and SFG and infrared signals were directly obtained from the OPO. A 2 mm β-BaB(2)O(4) is applied for Type I (oo → e) intracavity SHG and SFG, and then femtosecond laser pulses over 610 nm ~ 668 nm from SFG and 716 nm ~ 970 nm from SHG are obtained with high efficiency. In addition, the oscillator simultaneously generates signal and idler femtosecond pulses over 1450 nm ~ 2200 nm and 2250 nm ~ 4000 nm, respectively.

Vibrational dynamics of adsorbed molecules under conditions of photodesorption: pump-probe SFG spectra of CO/Pt(111).

PubMed

Fournier, Frédéric; Zheng, Wanquan; Carrez, Serge; Dubost, Henri; Bourguignon, Bernard

2004-09-08

Interaction of CO adsorbed on Pt(111) with electrons and phonons is studied experimentally by means of a pump-probe experiment where CO is probed by IR + visible sum frequency generation under a pump laser intensity that allows photodesorption. Vibrational spectra of CO internal stretch are obtained as a function of pump-probe delay. A two-temperature and anharmonic coupling model is used to extract from the spectra the real time variations of CO peak frequency and dephasing time. The main conclusions are the following: (i) The CO stretch is perturbed by two low-frequency modes, assigned to frustrated rotation and frustrated translation. (ii) The frustrated rotation is directly coupled to electrons photoexcited in Pt(111) by the pump laser. (iii) There is no evidence of Pt-CO stretch excitation in the spectra. The implications for the photodesorption dynamics are discussed. Copyright 2004 American Institute of Physics

Vibrational dynamics of adsorbed molecules under conditions of photodesorption: Pump-probe SFG spectra of CO/Pt(111)

NASA Astrophysics Data System (ADS)

Fournier, Frédéric; Zheng, Wanquan; Carrez, Serge; Dubost, Henri; Bourguignon, Bernard

2004-09-01

Interaction of CO adsorbed on Pt(111) with electrons and phonons is studied experimentally by means of a pump-probe experiment where CO is probed by IR+visible sum frequency generation under a pump laser intensity that allows photodesorption. Vibrational spectra of CO internal stretch are obtained as a function of pump-probe delay. A two-temperature and anharmonic coupling model is used to extract from the spectra the real time variations of CO peak frequency and dephasing time. The main conclusions are the following: (i) The CO stretch is perturbed by two low-frequency modes, assigned to frustrated rotation and frustrated translation. (ii) The frustrated rotation is directly coupled to electrons photoexcited in Pt(111) by the pump laser. (iii) There is no evidence of Pt-CO stretch excitation in the spectra. The implications for the photodesorption dynamics are discussed.

Method of detecting system function by measuring frequency response

NASA Technical Reports Server (NTRS)

Morrison, John L. (Inventor); Morrison, William H. (Inventor); Christophersen, Jon P. (Inventor)

2012-01-01

Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. The time profile of this signal has a duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time record by rectifying relative to the sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.

Method of detecting system function by measuring frequency response

DOEpatents

Morrison, John L [Butte, MT; Morrison, William H [Manchester, CT; Christophersen, Jon P [Idaho Falls, ID

2012-04-03

Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. The time profile of this signal has a duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time record by rectifying relative to the sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.

Method of detecting system function by measuring frequency response

DOEpatents

Morrison, John L.; Morrison, William H.; Christophersen, Jon P.; Motloch, Chester G.

2013-01-08

Methods of rapidly measuring an impedance spectrum of an energy storage device in-situ over a limited number of logarithmically distributed frequencies are described. An energy storage device is excited with a known input signal, and a response is measured to ascertain the impedance spectrum. An excitation signal is a limited time duration sum-of-sines consisting of a select number of frequencies. In one embodiment, magnitude and phase of each frequency of interest within the sum-of-sines is identified when the selected frequencies and sample rate are logarithmic integer steps greater than two. This technique requires a measurement with a duration of one period of the lowest frequency. In another embodiment, where selected frequencies are distributed in octave steps, the impedance spectrum can be determined using a captured time record that is reduced to a half-period of the lowest frequency.

Characterisation of the membrane affinity of an isoniazide peptide conjugate by tensiometry, atomic force microscopy and sum-frequency vibrational spectroscopy, using a phospholipid Langmuir monolayer model.

PubMed

Hill, Katalin; Pénzes, Csanád Botond; Schnöller, Donát; Horváti, Kata; Bosze, Szilvia; Hudecz, Ferenc; Keszthelyi, Tamás; Kiss, Eva

2010-10-07

Tensiometry, sum-frequency vibrational spectroscopy, and atomic force microscopy were employed to assess the cell penetration ability of a peptide conjugate of the antituberculotic agent isoniazide. Isoniazide was conjugated to peptide (91)SEFAYGSFVRTVSLPV(106), a functional T-cell epitope of the immunodominant 16 kDa protein of Mycobacterium tuberculosis. As a simple but versatile model of the cell membrane a phospholipid Langmuir monolayer at the liquid/air interface was used. Changes induced in the structure of the phospholipid monolayer by injection of the peptide conjugate into the subphase were followed by tensiometry and sum-frequency vibrational spectroscopy. The drug penetrated lipid films were transferred to a solid support by the Langmuir-Blodgett technique, and their structures were characterized by atomic force microscopy. Peptide conjugation was found to strongly enhance the cell penetration ability of isoniazide.

Enhanced detection of thiophenol adsorbed on gold nanoparticles by SFG and DFG nonlinear optical spectroscopy.

PubMed

Pluchery, Olivier; Humbert, Christophe; Valamanesh, Mehrnoush; Lacaze, Emmanuelle; Busson, Bertrand

2009-09-21

Sum frequency generation (SFG) and difference frequency generation (DFG) are applied to study vibrational resonance of the thiophenol molecule adsorbed on two different gold samples. One sample is made of 17 nm gold nanoparticles (AuNPs) fixed on a silicon substrate that has been previously functionalized with a silane monolayer (aminopropyltriethoxysilane, APTES). This sample is fully characterized through visible reflection spectroscopy and AFM. The second sample is a gold monocrystal also covered with thiophenol molecules. From their comparison, an enhancement factor of 21 is deduced for the SFG signal on AuNPs with respect to the Au(111), related to the surface plasmon resonance (SPR). From a combined analysis of the SFG and DFG spectra, we demonstrate that SFG/DFG spectroscopy is able to identify the nature of the substrate where the molecules are adsorbed. This opens new perspectives for this nonlinear spectroscopy by adding to its well-known intrinsic surface specificity, the ability to selectively probe the chemical layer capping the AuNPs.

Dipole, quadrupole, and octupole terms in the long-range hyperfine frequency shift for hydrogen in the presence of inert gases

NASA Astrophysics Data System (ADS)

Greenwood, W. G.; Tang, K. T.

1987-03-01

The R-6, R-8, and R-10 terms in the long-range expansion for the hyperfine frequency shift are calculated for hydrogen in the presence of He, Ne, Ar, Kr, and Xe. The R-6 terms are based on the dipole oscillator strength sums. For helium, the R-8 and R-10 terms are based on quadrupole and octupole oscillator strength sums. For the heavier inert gases, the results for the R-8 and R-10 terms are obtained from the sum rules and the static polarizabilities. Upper bounds are also determined for the R-8 and R-10 terms.

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

Lai, C.-M.; Chang, K.-H.; Yang, Z.-Y.

Spectrally broad frequency comb generation over 510–555 nm range was reported on chirped quasi-phase-matching (QPM) χ{sup (2)} nonlinear photonic crystals of 12 mm length with periodicity stepwise increased from 5.9 μm to 7.1 μm. When pumped with nanosecond infrared (IR) frequency comb derived from a QPM optical parametric oscillator (OPO) and spanned over 1040 nm to 1090 nm wavelength range, the 520 nm to 545 nm up-converted green spectra were shown to consist of contributions from (a) second-harmonic generation among the signal or the idler modes, and (b) sum-frequency generation (SFG) from the neighboring pairs of the signal or the idler modes. These mechanisms led the up-converted greenmore » frequency comb to have the same mode spacing of 450 GHz as that in the IR-OPO pump comb. As the pump was further detuned from the aforementioned near-degeneracy point and moved toward the signal (1020–1040 nm) and the idler (1090–1110 nm) spectral range, the above QPM parametric processes were preserved in the chirped QPM devices to support up-converted green generation in the 510–520 nm and the 545–555 nm spectral regime. Additional 530–535 nm green spectral generation was also observed due to concurrence of multi-wavelength SFG processes between the (signal, idler) mode pairs. These mechanisms facilitate the chirped QPM device to support a single-pass up-conversion efficiency ∼10% when subject to an IR-OPO pump comb with 200 mW average power operated near- or off- the degeneracy point.« less

Wind fence enclosures for infrasonic wind noise reduction.

PubMed

Abbott, JohnPaul; Raspet, Richard; Webster, Jeremy

2015-03-01

A large porous wind fence enclosure has been built and tested to optimize wind noise reduction at infrasonic frequencies between 0.01 and 10 Hz to develop a technology that is simple and cost effective and improves upon the limitations of spatial filter arrays for detecting nuclear explosions, wind turbine infrasound, and other sources of infrasound. Wind noise is reduced by minimizing the sum of the wind noise generated by the turbulence and velocity gradients inside the fence and by the area-averaging the decorrelated pressure fluctuations generated at the surface of the fence. The effects of varying the enclosure porosity, top condition, bottom gap, height, and diameter and adding a secondary windscreen were investigated. The wind fence enclosure achieved best reductions when the surface porosity was between 40% and 55% and was supplemented by a secondary windscreen. The most effective wind fence enclosure tested in this study achieved wind noise reductions of 20-27 dB over the 2-4 Hz frequency band, a minimum of 5 dB noise reduction for frequencies from 0.1 to 20 Hz, constant 3-6 dB noise reduction for frequencies with turbulence wavelengths larger than the fence, and sufficient wind noise reduction at high wind speeds (3-6 m/s) to detect microbaroms.

Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering at flame temperatures using a second-harmonic bandwidth-compressed probe.

PubMed

Kearney, Sean P; Scoglietti, Daniel J

2013-03-15

We demonstrate an approach for picosecond probe-beam generation that enables hybrid femtosecond/picosecond pure-rotational coherent anti-Stokes Raman scattering (CARS) measurements in flames. Sum-frequency generation of bandwidth-compressed picosecond radiation from femtosecond pumps with phase-conjugate chirps provides probe pulses with energies in excess of 1 mJ that are temporally locked to the femtosecond pump/Stokes preparation. This method overcomes previous limitations on hybrid femtosecond/picosecond rotational CARS techniques, which have relied upon less efficient bandwidth-reduction processes that have generally resulted in prohibitively low probe energy for flame measurements. We provide the details of the second-harmonic approach and demonstrate the technique in near-adiabatic hydrogen/air flames.

Competition between SFG and two SHGs in broadband type-I QPM

NASA Astrophysics Data System (ADS)

Dang, Weirui; Chen, Yuping; Gong, Mingjun; Chen, Xianfeng

2013-03-01

In this paper, we have studied the characteristics of second-order nonlinear interactions with band-overlapped type-I quasi-phase-matching (QPM) second harmonic generation (SHG) and sum-frequency generation (SFG), and predicted a blue-shift with a band-narrowing of their bands and a sunken response in the SFG curve, which are due to the phase-matching-dependent competition between band-overlapped SHG and SFG processes. This prediction is then verified by the experiment in an 18-mm-long bulk MgO-doped periodically poled lithium niobate crystal (MgO:PPLN) and may provide the candidate solution to output controlling for flexible broadcast wavelength conversion, channel-selective wavelength conversion and all-optical logic gates by cascaded QPM second-order nonlinear processes.

High frequency oscillations are associated with cognitive processing in human recognition memory.

PubMed

Kucewicz, Michal T; Cimbalnik, Jan; Matsumoto, Joseph Y; Brinkmann, Benjamin H; Bower, Mark R; Vasoli, Vincent; Sulc, Vlastimil; Meyer, Fred; Marsh, W R; Stead, S M; Worrell, Gregory A

2014-08-01

High frequency oscillations are associated with normal brain function, but also increasingly recognized as potential biomarkers of the epileptogenic brain. Their role in human cognition has been predominantly studied in classical gamma frequencies (30-100 Hz), which reflect neuronal network coordination involved in attention, learning and memory. Invasive brain recordings in animals and humans demonstrate that physiological oscillations extend beyond the gamma frequency range, but their function in human cognitive processing has not been fully elucidated. Here we investigate high frequency oscillations spanning the high gamma (50-125 Hz), ripple (125-250 Hz) and fast ripple (250-500 Hz) frequency bands using intracranial recordings from 12 patients (five males and seven females, age 21-63 years) during memory encoding and recall of a series of affectively charged images. Presentation of the images induced high frequency oscillations in all three studied bands within the primary visual, limbic and higher order cortical regions in a sequence consistent with the visual processing stream. These induced oscillations were detected on individual electrodes localized in the amygdala, hippocampus and specific neocortical areas, revealing discrete oscillations of characteristic frequency, duration and latency from image presentation. Memory encoding and recall significantly modulated the number of induced high gamma, ripple and fast ripple detections in the studied structures, which was greater in the primary sensory areas during the encoding (Wilcoxon rank sum test, P = 0.002) and in the higher-order cortical association areas during the recall (Wilcoxon rank sum test, P = 0.001) of memorized images. Furthermore, the induced high gamma, ripple and fast ripple responses discriminated the encoded and the affectively charged images. In summary, our results show that high frequency oscillations, spanning a wide range of frequencies, are associated with memory processing and generated along distributed cortical and limbic brain regions. These findings support an important role for fast network synchronization in human cognition and extend our understanding of normal physiological brain activity during memory processing. © The Author (2014). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Sum frequency generation and solid-state NMR study of the structure, orientation, and dynamics of polystyrene-adsorbed peptides

PubMed Central

Weidner, Tobias; Breen, Nicholas F.; Li, Kun; Drobny, Gary P.; Castner, David G.

2010-01-01

The power of combining sum frequency generation (SFG) vibrational spectroscopy and solid-state nuclear magnetic resonance (ssNMR) spectroscopy to quantify, with site specificity and atomic resolution, the orientation and dynamics of side chains in synthetic model peptides adsorbed onto polystyrene (PS) surfaces is demonstrated in this study. Although isotopic labeling has long been used in ssNMR studies to site-specifically probe the structure and dynamics of biomolecules, the potential of SFG to probe side chain orientation in isotopically labeled surface-adsorbed peptides and proteins remains largely unexplored. The 14 amino acid leucine-lysine peptide studied in this work is known to form an α-helical secondary structure at liquid-solid interfaces. Selective, individual deuteration of the isopropyl group in each leucine residue was used to probe the orientation and dynamics of each individual leucine side chain of LKα14 adsorbed onto PS. The selective isotopic labeling methods allowed SFG analysis to determine the orientations of individual side chains in adsorbed peptides. Side chain dynamics were obtained by fitting the deuterium ssNMR line shape to specific motional models. Through the combined use of SFG and ssNMR, the dynamic trends observed for individual side chains by ssNMR have been correlated with side chain orientation relative to the PS surface as determined by SFG. This combination provides a more complete and quantitative picture of the structure, orientation, and dynamics of these surface-adsorbed peptides than could be obtained if either technique were used separately. PMID:20628016

Structure of water at zwitterionic copolymer film-liquid water interfaces as examined by the sum frequency generation method.

PubMed

Kondo, Takuya; Nomura, Kouji; Gemmei-Ide, Makoto; Kitano, Hiromi; Noguchi, Hidenori; Uosaki, Kohei; Saruwatari, Yoshiyuki

2014-01-01

A copolymer film composed of zwitterionic carboxymethylbetaine (CMB) and n-butyl methacrylate (BMA), Poly(CMB-r-BMA), was cast on a flat plane of an octadecyltrichlorosilane (ODS)-modified fused quartz prism with a semi-cylindrical shape. CH stretching of the polymer film and O-H stretching of water at the surface of the film were examined using the sum frequency generation (SFG) technique. The C-H stretching band of the cast film, indicating a gauche defect of the film, was affected by the contact medium including dry nitrogen, water vapor-saturated nitrogen and liquid water. In contrast, the C-H stretching of an octadecyl group introduced onto the quartz prism for stable attachment of the cast film was not significantly changed by the contact medium. The O-H stretching band indicated that water molecules at the surface of the Poly(CMB-r-BMA) film in contact with liquid water were not greatly oriented in comparison with those at the surfaces of a bare prism, an ODS SAM-modified prism, and a prism covered with a PolyBMA film or a copolymer film of BMA and methacrylic acid or 2-(dimethylamino)ethyl methacrylate. A similar small perturbation of the structure of water was previously observed in the vicinity of water-soluble zwitterionic polymers and zwitterionic copolymer films using Raman and attenuated total reflection infrared spectroscopies, respectively. A distinct effect of charge neutralization to diminish the perturbation of the structure of interfacial water around polymer materials was suggested. Copyright © 2013 Elsevier B.V. All rights reserved.

Pyrrole Hydrogenation over Rh(111) and Pt(111) Single-Crystal Surfaces and Hydrogenation Promotion Mediated by 1-Methylpyrrole: A Kinetic and Sum-Frequency Generation Vibrational Spectroscopy Study

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

Kliewer, Christopher J.; Bieri, Marco; Somorjai, Gabor A.

Sum-frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to study the adsorption and hydrogenation of pyrrole over both Pt(111) and Rh(111) single-crystal surfaces at Torr pressures (3 Torr pyrrole, 30 Torr H{sub 2}) to form pyrrolidine and the minor product butylamine. Over Pt(111) at 298 K it was found that pyrrole adsorbs in an upright geometry cleaving the N-H bond to bind through the nitrogen evidenced by SFG data. Over Rh(111) at 298 K pyrrole adsorbs in a tilted geometry relative to the surface through the p-aromatic system. A pyrroline surface reaction intermediate,more » which was not detected in the gas phase, was seen by SFG during the hydrogenation over both surfaces. Significant enhancement of the reaction rate was achieved over both metal surfaces by adsorbing 1-methylpyrrole before reaction. SFG vibrational spectroscopic results indicate that reaction promotion is achieved by weakening the bonding between the N-containing products and the metal surface because of lateral interactions on the surface between 1-methylpyrrole and the reaction species, reducing the desorption energy of the products. It was found that the ring-opening product butylamine was a reaction poison over both surfaces, but this effect can be minimized by treating the catalyst surfaces with 1-methylpyrrole before reaction. The reaction rate was not enhanced with elevated temperatures, and SFG suggests desorption of pyrrole at elevated temperatures.« less

Atmospheric pressure reaction cell for operando sum frequency generation spectroscopy of ultrahigh vacuum grown model catalysts

NASA Astrophysics Data System (ADS)

Roiaz, Matteo; Pramhaas, Verena; Li, Xia; Rameshan, Christoph; Rupprechter, Günther

2018-04-01

A new custom-designed ultrahigh vacuum (UHV) chamber coupled to a UHV and atmospheric-pressure-compatible spectroscopic and catalytic reaction cell is described, which allows us to perform IR-vis sum frequency generation (SFG) vibrational spectroscopy during catalytic (kinetic) measurements. SFG spectroscopy is an exceptional tool to study vibrational properties of surface adsorbates under operando conditions, close to those of technical catalysis. This versatile setup allows performing surface science, SFG spectroscopy, catalysis, and electrochemical investigations on model systems, including single crystals, thin films, and deposited metal nanoparticles, under well-controlled conditions of gas composition, pressure, temperature, and potential. The UHV chamber enables us to prepare the model catalysts and to analyze their surface structure and composition by low energy electron diffraction and Auger electron spectroscopy, respectively. Thereafter, a sample transfer mechanism moves samples under UHV to the spectroscopic cell, avoiding air exposure. In the catalytic cell, SFG spectroscopy and catalytic tests (reactant/product analysis by mass spectrometry or gas chromatography) are performed simultaneously. A dedicated sample manipulation stage allows the model catalysts to be examined from LN2 temperature to 1273 K, with gaseous reactants in a pressure range from UHV to atmospheric. For post-reaction analysis, the SFG cell is rapidly evacuated and samples are transferred back to the UHV chamber. The capabilities of this new setup are demonstrated by benchmark results of CO adsorption on Pt and Pd(111) single crystal surfaces and of CO adsorption and oxidation on a ZrO2 supported Pt nanoparticle model catalyst grown by atomic layer deposition.

Mixing of two co-directional Rayleigh surface waves in a nonlinear elastic material.

PubMed

Morlock, Merlin B; Kim, Jin-Yeon; Jacobs, Laurence J; Qu, Jianmin

2015-01-01

The mixing of two co-directional, initially monochromatic Rayleigh surface waves in an isotropic, homogeneous, and nonlinear elastic solid is investigated using analytical, finite element method, and experimental approaches. The analytical investigations show that while the horizontal velocity component can form a shock wave, the vertical velocity component can form a pulse independent of the specific ratios of the fundamental frequencies and amplitudes that are mixed. This analytical model is then used to simulate the development of the fundamentals, second harmonics, and the sum and difference frequency components over the propagation distance. The analytical model is further extended to include diffraction effects in the parabolic approximation. Finally, the frequency and amplitude ratios of the fundamentals are identified which provide maximum amplitudes of the second harmonics as well as of the sum and difference frequency components, to help guide effective material characterization; this approach should make it possible to measure the acoustic nonlinearity of a solid not only with the second harmonics, but also with the sum and difference frequency components. Results of the analytical investigations are then confirmed using the finite element method and the experimental feasibility of the proposed technique is validated for an aluminum specimen.

Effects of Second-Order Sum- and Difference-Frequency Wave Forces on the Motion Response of a Tension-Leg Platform Considering the Set-down Motion

NASA Astrophysics Data System (ADS)

Wang, Bin; Tang, Yougang; Li, Yan; Cai, Runbo

2018-04-01

This paper presents a study on the motion response of a tension-leg platform (TLP) under first- and second-order wave forces, including the mean-drift force, difference and sum-frequency forces. The second-order wave force is calculated using the full-field quadratic transfer function (QTF). The coupled effect of the horizontal motions, such as surge, sway and yaw motions, and the set-down motion are taken into consideration by the nonlinear restoring matrix. The time-domain analysis with 50-yr random sea state is performed. A comparison of the results of different case studies is made to assess the influence of second-order wave force on the motions of the platform. The analysis shows that the second-order wave force has a major impact on motions of the TLP. The second-order difference-frequency wave force has an obvious influence on the low-frequency motions of surge and sway, and also will induce a large set-down motion which is an important part of heave motion. Besides, the second-order sum-frequency force will induce a set of high-frequency motions of roll and pitch. However, little influence of second-order wave force is found on the yaw motion.

Engineering quadratic nonlinear photonic crystals for frequency conversion of lasers

NASA Astrophysics Data System (ADS)

Chen, Baoqin; Hong, Lihong; Hu, Chenyang; Zhang, Chao; Liu, Rongjuan; Li, Zhiyuan

2018-03-01

Nonlinear frequency conversion offers an effective way to extend the laser wavelength range. Quadratic nonlinear photonic crystals (NPCs) are artificial materials composed of domain-inversion structures whose sign of nonlinear coefficients are modulated with desire to implement quasi-phase matching (QPM) required for nonlinear frequency conversion. These structures can offer various reciprocal lattice vectors (RLVs) to compensate the phase-mismatching during the quadratic nonlinear optical processes, including second-harmonic generation (SHG), sum-frequency generation and the cascaded third-harmonic generation (THG). The modulation pattern of the nonlinear coefficients is flexible, which can be one-dimensional or two-dimensional (2D), be periodic, quasi-periodic, aperiodic, chirped, or super-periodic. As a result, these NPCs offer very flexible QPM scheme to satisfy various nonlinear optics and laser frequency conversion problems via design of the modulation patterns and RLV spectra. In particular, we introduce the electric poling technique for fabricating QPM structures, a simple effective nonlinear coefficient model for efficiently and precisely evaluating the performance of QPM structures, the concept of super-QPM and super-periodically poled lithium niobate for finely tuning nonlinear optical interactions, the design of 2D ellipse QPM NPC structures enabling continuous tunability of SHG in a broad bandwidth by simply changing the transport direction of pump light, and chirped QPM structures that exhibit broadband RLVs and allow for simultaneous radiation of broadband SHG, THG, HHG and thus coherent white laser from a single crystal. All these technical, theoretical, and physical studies on QPM NPCs can help to gain a deeper insight on the mechanisms, approaches, and routes for flexibly controlling the interaction of lasers with various QPM NPCs for high-efficiency frequency conversion and creation of novel lasers.

Multi-wavelength emission through self-induced second-order wave-mixing processes from a Nd3+ doped crystalline powder random laser

NASA Astrophysics Data System (ADS)

Moura, André L.; Jerez, Vladimir; Maia, Lauro J. Q.; Gomes, Anderson S. L.; de Araújo, Cid B.

2015-09-01

Random lasers (RLs) based on neodymium ions (Nd3+) doped crystalline powders rely on multiple light scattering to sustain laser oscillation. Although Stokes and anti-Stokes Nd3+ RLs have been demonstrated, the optical gain obtained up to now was possibly not large enough to produce self-frequency conversion. Here we demonstrate self-frequency upconversion from Nd3+ doped YAl3(BO3)4 monocrystals excited at 806 nm, in resonance with the Nd3+ transition 4I9/2 → 4F5/2. Besides the observation of the RL emission at 1062 nm, self-converted second-harmonic at 531 nm, and self-sum-frequency generated emission at 459 nm due to the RL and the excitation laser at 806 nm, are reported. Additionally, second-harmonic of the excitation laser at 403 nm was generated. These results exemplify the first multi-wavelength source of radiation owing to nonlinear optical effect in a Nd3+ doped crystalline powder RL. Contrary to the RLs based on dyes, this multi-wavelength light source can be used in photonic devices due to the large durability of the gain medium.

Diode-pumped laser altimeter

NASA Technical Reports Server (NTRS)

Welford, D.; Isyanova, Y.

1993-01-01

TEM(sub 00)-mode output energies up to 22.5 mJ with 23 percent slope efficiencies were generated at 1.064 microns in a diode-laser pumped Nd:YAG laser using a transverse-pumping geometry. 1.32-micron performance was equally impressive at 10.2 mJ output energy with 15 percent slope efficiency. The same pumping geometry was successfully carried forward to several complex Q-switched laser resonator designs with no noticeable degradation of beam quality. Output beam profiles were consistently shown to have greater than 90 percent correlation with the ideal TEM(sub 00)-order Gaussian profile. A comparison study on pulse-reflection-mode (PRM), pulse-transmission-mode (PTM), and passive Q-switching techniques was undertaken. The PRM Q-switched laser generated 8.3 mJ pulses with durations as short as 10 ns. The PTM Q-switch laser generated 5 mJ pulses with durations as short as 5 ns. The passively Q-switched laser generated 5 mJ pulses with durations as short as 2.4 ns. Frequency doubling of both 1.064 microns and 1.32 microns with conversion efficiencies of 56 percent in lithium triborate and 10 percent in rubidium titanyl arsenate, respectively, was shown. Sum-frequency generation of the 1.064 microns and 1.32 microns radiations was demonstrated in KTP to generate 1.1 mJ of 0.589 micron output with 11.5 percent conversion efficiency.

Interpreting Vibrational Sum-frequency Spectra of Sulfur Dioxide at the Air/Water Interface: A Comprehensive Molecular Dynamics Study

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

Baer, Marcel; Mundy, Christopher J.; Chang, Tsun-Mei

We investigated the solvation and spectroscopic properties of SO2 at the air/water interface using molecular simulation techniques. Molecular interactions from both Kohn-Sham (KS) density functional theory (DFT) and classical polarizable models were utilized to understand the properties of SO2:(H2O)x complexes in the vicinity of the air/water interface. The KS-DFT was included to allow comparisons with sum-frequency generation spectroscopy through the identification of surface SO2:(H2O)x complexes. Using our simulation results, we were able to develop a much more detailed picture for the surface structure of SO2 that is consistent with the spectroscopic data obtained Richmond and coworkers (J. Am. Chem. Soc.more » 127, 16806 (2005)). We also found many similarities and differences between to the two interaction potentials, including a noticeable weakness of the classical potential model in reproducing the asymmetric hydrogen bonding of water with SO2 due to its inability to account for SO2 resonance structures. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.« less

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

Fu, Li; Zhang, Yun; Wei, Zhehao

We report in this work detailed measurements on the chiral and achiral sum-frequency vibrational spectra in the C-H stretching vibration region (2800-3050cm-1) of the air/liquid interfaces of R-limonene and S-limonene, using the recently developed high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS). The achiral SFG spectra of R-limonene and S-limonene, as well as the equal amount (50/50) racemic mixture show that the enantiomers are with the same interfacial orientations. The interference chiral SFG spectra of the limonene enantiomers exhibit spectral signature from chiral response of the Cα-H stretching mode, and spectral signature from prochiral response of the CH2 asymmetric stretching mode,more » respectively. The chiral spectral feature of the Cα-H stretching mode changes sign from R-limonene to S-limonene, and disappears for the 50/50 racemic mixture. While the prochiral spectral feature of the CH2 asymmetric stretching mode is the same for R-limonene and S-limonene, and also surprisingly remains the same for the 50/50 racemic mixture. These results provided detail information in understanding the structure and chirality of molecular interfaces, and demonstrated the sensitivity and potential of SFG-VS as unique spectroscopic tool for chirality characterization and chiral recognition at the molecular interface.« less

Potential of promotion of alleles by genome editing to improve quantitative traits in livestock breeding programs.

PubMed

Jenko, Janez; Gorjanc, Gregor; Cleveland, Matthew A; Varshney, Rajeev K; Whitelaw, C Bruce A; Woolliams, John A; Hickey, John M

2015-07-02

Genome editing (GE) is a method that enables specific nucleotides in the genome of an individual to be changed. To date, use of GE in livestock has focussed on simple traits that are controlled by a few quantitative trait nucleotides (QTN) with large effects. The aim of this study was to evaluate the potential of GE to improve quantitative traits that are controlled by many QTN, referred to here as promotion of alleles by genome editing (PAGE). Multiple scenarios were simulated to test alternative PAGE strategies for a quantitative trait. They differed in (i) the number of edits per sire (0 to 100), (ii) the number of edits per generation (0 to 500), and (iii) the extent of use of PAGE (i.e. editing all sires or only a proportion of them). The base line scenario involved selecting individuals on true breeding values (i.e., genomic selection only (GS only)-genomic selection with perfect accuracy) for several generations. Alternative scenarios complemented this base line scenario with PAGE (GS + PAGE). The effect of different PAGE strategies was quantified by comparing response to selection, changes in allele frequencies, the number of distinct QTN edited, the sum of absolute effects of the edited QTN per generation, and inbreeding. Response to selection after 20 generations was between 1.08 and 4.12 times higher with GS + PAGE than with GS only. Increases in response to selection were larger with more edits per sire and more sires edited. When the total resources for PAGE were limited, editing a few sires for many QTN resulted in greater response to selection and inbreeding compared to editing many sires for a few QTN. Between the scenarios GS only and GS + PAGE, there was little difference in the average change in QTN allele frequencies, but there was a major difference for the QTN with the largest effects. The sum of the effects of the edited QTN decreased across generations. This study showed that PAGE has great potential for application in livestock breeding programs, but inbreeding needs to be managed.

The molecular orientation of CO on Pd(1 1 1): a polarization-dependent SFG study

NASA Astrophysics Data System (ADS)

Galletto, Paolo; Unterhalt, Holger; Rupprechter, Günther

2003-01-01

The molecular orientation of carbon monoxide adsorbed on Pd(1 1 1) was examined by sum frequency generation (SFG) vibrational spectroscopy utilizing different polarization combinations of the visible and SFG light. This allows to determine the CO tilt angle with respect to the substrate, provided that a proper optical model for the interface can be defined. It is demonstrated that it is essential to invoke the βaac hyperpolarizability into the analysis and that polarization-dependent SFG of CO/Pd(1 1 1) yields information on βaac/ βccc rather than the tilt angle.

160-Gb/s all-optical phase-transparent wavelength conversion through cascaded SFG-DFG in a broadband linear-chirped PPLN waveguide.

PubMed

Lu, Guo-Wei; Shinada, Satoshi; Furukawa, Hideaki; Wada, Naoya; Miyazaki, Tetsuya; Ito, Hiromasa

2010-03-15

We experimentally demonstrated ultra-fast phase-transparent wavelength conversion using cascaded sum- and difference-frequency generation (cSFG-DFG) in linear-chirped periodically poled lithium niobate (PPLN). Error-free wavelength conversion of a 160-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) signal was successfully achieved. Thanks to the enhanced conversion bandwidth in the PPLN with linear-chirped periods, no optical equalizer was required to compensate the spectrum distortion after conversion, unlike a previous demonstration of 160-Gb/s RZ on-off keying (OOK) using fixed-period PPLN.

Upconversion-based receivers for quantum hacking-resistant quantum key distribution

NASA Astrophysics Data System (ADS)

Jain, Nitin; Kanter, Gregory S.

2016-07-01

We propose a novel upconversion (sum frequency generation)-based quantum-optical system design that can be employed as a receiver (Bob) in practical quantum key distribution systems. The pump governing the upconversion process is produced and utilized inside the physical receiver, making its access or control unrealistic for an external adversary (Eve). This pump facilitates several properties which permit Bob to define and control the modes that can participate in the quantum measurement. Furthermore, by manipulating and monitoring the characteristics of the pump pulses, Bob can detect a wide range of quantum hacking attacks launched by Eve.

Origin of Vibrational Spectroscopic Response at Ice Surface.

PubMed

Ishiyama, Tatsuya; Takahashi, Hideaki; Morita, Akihiro

2012-10-18

Since the basal plane surface of ice was first observed by sum frequency generation, an extraordinarily intense band for the hydrogen(H)-bonded OH stretching vibration has been a matter of debate. We elucidate the remarkable spectral feature of the ice surface by quantum mechanics/molecular mechanics calculations. The intense H-bonded band is originated mostly from the "bilayer-stitching" modes of a few surface bilayers, through significant intermolecular charge transfer. The mechanism of enhanced signal is sensitive to the order of the tetrahedral ice structure, as the charge transfer is coupled to the vibrational delocalization.

Determination of conformation and orientation of immobilized peptides and proteins at buried interfaces

NASA Astrophysics Data System (ADS)

Shen, Lei; Ulrich, Nathan W.; Mello, Charlene M.; Chen, Zhan

2015-01-01

Surface immobilized peptides/proteins have important applications such as antimicrobial coating and biosensing. We report a study of such peptides/proteins using sum frequency generation vibrational spectroscopy and ATR-FTIR. Immobilization on surfaces via physical adsorption and chemical coupling revealed that structures of chemically immobilized peptides are determined by immobilization sites, chemical environments, and substrate surfaces. In addition, controlling enzyme orientation by engineering the surface immobilization site demonstrated that structures can be well-correlated to measured chemical activity. This research facilitates the development of immobilized peptides/proteins with improved activities by optimizing their surface orientation and structure.

A solid state tunable laser for resonance measurements of atmospheric sodium

NASA Technical Reports Server (NTRS)

Philbrick, C. R.; Bufton, J. L.; Gardner, C. S.

1985-01-01

The measurement of wave dynamics in the upper mesosphere using a solid-state laser to excite the resonance fluorescence line of sodium is examined. Two Nd:YAG lasers are employed to produce the sodium resonance line. The method involves mixing the 1064 nm radiation with that from a second Nd:YAG operating at 1319 nm in a nonlinear infrared crystal to directly produce 589 nm radiation by sum frequency generation. The use of the transmitter to measure the sodium layer from the Space Shuttle Platform is proposed. A diagram of the laser transmitter is presented.

Total teleportation of a single-photon state

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

Humble, Travis S; Bennink, Ryan S; Grice, Warren P

2008-01-01

Recent demonstrations of teleportation have transferred quantum information encoded into either polarization or field-quadrature degrees of freedom (DOFs), but an outstanding question is how to simultaneously teleport quantum information encoded into multiple DOFs. We describe how the transverse-spatial, spectral and polarization states of a single photon can be simultaneously teleported using a pair of multimode, polarization-entangled photons derived from spontaneous parametric down-conversion. Furthermore, when the initial photon pair is maximally entangled in the spatial, spectral, and polarization DOFs then the photon s full quantum state can be reliably teleported using a Bell-state measurement based on sum-frequency generation.

Detection of elemental mercury by multimode diode laser correlation spectroscopy.

PubMed

Lou, Xiutao; Somesfalean, Gabriel; Svanberg, Sune; Zhang, Zhiguo; Wu, Shaohua

2012-02-27

We demonstrate a method for elemental mercury detection based on correlation spectroscopy employing UV laser radiation generated by sum-frequency mixing of two visible multimode diode lasers. Resonance matching of the multimode UV laser is achieved in a wide wavelength range and with good tolerance for various operating conditions. Large mode-hops provide an off-resonance baseline, eliminating interferences from other gas species with broadband absorption. A sensitivity of 1 μg/m3 is obtained for a 1-m path length and 30-s integration time. The performance of the system shows promise for mercury monitoring in industrial applications.

300 mW of coherent light at 488 nm using a generic approach

NASA Astrophysics Data System (ADS)

Karamehmedović, Emir; Pedersen, Christian; Andersen, Martin T.; Tidemand-Lichtenberg, Peter

2008-02-01

We present a generic approach for efficient generation of CW light with a predetermined wavelength within the visible or UV spectrum. Based on sum-frequency generation (SFG), the circulating intra-cavity field of a high-finesse diode pumped CW solid-state laser (DPSSL) and the output from a tapered, single-frequency external cavity diode laser (ECDL) are mixed inside a 10 mm periodically poled KTP crstal (pp-KTP). The pp-KTP is situated inside the DPSSL cavity to enhance conversion efficiency of the nonlinear mixing process. This approach combines different solid state technologies; the tuneability of ECDLs, the high intra-cavity filed of DPSSLs and flexible quasi phase matching in pp-tapered ECDL with a center wavelength of 766 nm in combination with a high finesse Nd:YVo4 laser at 1342 nm. Up to 308 mW of light at 488nm was measured in our experiments. The conversion of te ECDL beam was up to 47% after it was transmitted through a PM fiber, and up to 32% without fiber coupling. Replacing the seed laser and the nonlinear crystal makes it possible to generate light at virtually any desired wavelength withing the visible spectrum.

Single-mode, All-Solid-State Nd:YAG Laser Pumped UV Converter

NASA Technical Reports Server (NTRS)

Prasad, Narasimha S.; Armstrong, Darrell, J.; Edwards, William C.; Singh, Upendra N.

2008-01-01

In this paper, the status of a high-energy, all solid-state Nd:YAG laser pumped nonlinear optics based UV converter development is discussed. The high-energy UV transmitter technology is being developed for ozone sensing applications from space based platforms using differential lidar technique. The goal is to generate greater than 200 mJ/pulse with 10-50 Hz PRF at wavelengths of 308 nm and 320 nm. A diode-pumped, all-solid-state and single longitudinal mode Nd:YAG laser designed to provide conductively cooled operation at 1064 nm has been built and tested. Currently, this pump laser provides an output pulse energy of >1 J/pulse at 50 Hz PRF and a pulsewidth of 22 ns with an electrical-to-optical system efficiency of greater than 7% and a M(sup 2) value of <2. The single frequency UV converter arrangement basically consists of an IR Optical Parametric Oscillator (OPO) and a Sum Frequency Generator (SFG) setups that are pumped by 532 nm wavelength obtained via Second Harmonic Generation (SHG). In this paper, the operation of an inter cavity SFG with CW laser seeding scheme generating 320 nm wavelength is presented. Efforts are underway to improve conversion efficiency of this mJ class UV converter by modifying the spatial beam profile of the pump laser.

Auditory alert systems with enhanced detectability

NASA Technical Reports Server (NTRS)

Begault, Durand R. (Inventor)

2008-01-01

Methods and systems for distinguishing an auditory alert signal from a background of one or more non-alert signals. In a first embodiment, a prefix signal, associated with an existing alert signal, is provided that has a signal component in each of three or more selected frequency ranges, with each signal component in each of three or more selected level at least 3-10 dB above an estimated background (non-alert) level in that frequency range. The alert signal may be chirped within one or more frequency bands. In another embodiment, an alert signal moves, continuously or discontinuously, from one location to another over a short time interval, introducing a perceived spatial modulation or jitter. In another embodiment, a weighted sum of background signals adjacent to each ear is formed, and the weighted sum is delivered to each ear as a uniform background; a distinguishable alert signal is presented on top of this weighted sum signal at one ear, or distinguishable first and second alert signals are presented at two ears of a subject.

SFG characterization of a cationic ONLO dye in biological thin films

NASA Astrophysics Data System (ADS)

Johnson, Lewis E.; Casford, Michael T.; Elder, Delwin L.; Davies, Paul B.; Johal, Malkiat S.

2013-10-01

Biopolymer-based thin films, such as those composed of CTMA-DNA, can be used as a host material for NLOactive dyes for applications such as electro-optic (EO) switching and second harmonic generation. Previous work by Heckman et al. (Proc. SPIE 6401, 640108-2) has demonstrated functioning DNA-based EO modulators. Improved performance requires optimization of both the first hyperpolarizabilities (β) and degree of acentric ordering exhibited by the chromophores. The cationic dye DANPY-1 (Proc. SPIE 8464, 846409-D) has a high affinity for DNA and a substantial hyperpolarizability; however, its macroscopic ordering has not been previously characterized. We have characterized the acentric ordering of the dye using sum-frequency generation (SFG) vibrational spectroscopy in surface-immobilized DNA and on planar metal and dielectric surfaces.

Method, system and computer-readable media for measuring impedance of an energy storage device

DOEpatents

Morrison, John L.; Morrison, William H.; Christophersen, Jon P.; Motloch, Chester G.

2016-01-26

Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. A time profile of this sampled signal has a duration that is a few periods of the lowest frequency. A voltage response of the battery, average deleted, is an impedance of the battery in a time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time profile by rectifying relative to sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.

Homogeneous and inhomogeneous broadenings and the Voigt line shapes in the phase-resolved and intensity sum-frequency generation vibrational spectroscopy

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

Chen, Shunli; Fu, Li; Gan, Wei

2016-01-21

In this report we show that the ability to measure the sub-1 cm -1 resolution phase-resolved and intensity high-resolution broadband sum frequency generation vibrational spectra (HR-BB-SFG-VS) of the –CN stretch vibration of the Langmuir-Blodgett (LB) monolayer of the 4-n-octyl-4’-cyanobiphenyl (8CB) on the z-cut α-quartz surface allows for the first time the direct comparison and understanding of the homogeneous and inhomogeneous broadenings in the imaginary and intensity SFG vibrational spectral lineshapes in detail. The difference of the full width at half maxima (FWHM) of the imaginary and intensity SFG-VS spectra of the same vibrational mode is the signature of the Voigtmore » lineshape and it measures the relative contribution to the overall lineshape from the homogeneous and inhomogeneous broadenings in SFG vibrational spectra. From the phase-resolved and intensity spectra, we found that the FWHM of the 2238.00 ±0.02 cm -1 peak in the phase-resolved imaginary and intensity spectra is 19.2 ± 0.2 cm -1 and 21.6 ± 0.4 cm -1, respectively, for the –CN group of the 8CB LB monolayer on the z-cut α-quartz crystal surface. The FWHM width difference of 2.4 cm -1 agrees quantitatively with a Voigt lineshape with a homogeneous broadening half width of Γ = 5.29 ± 0.08 cm -1 and a inhomogeneous standard derivation width Δω = 5.42 ± 0.07 cm -1. These results shed new lights on the understanding and interpretation of the lineshapes of both the phase-resolved and the intensity SFG vibrational spectra, as well as other incoherent and coherent spectroscopic techniques in general.« less

Reorientation of the ‘free OH’ group in the top-most layer of air/water interface of sodium fluoride aqueous solution probed with sum-frequency generation vibrational spectroscopy

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

Feng, Ran-Ran; Guo, Yuan; Wang, Hongfei

2014-09-17

Many experimental and theoretical studies have established the specific anion, as well as cation effects on the hydrogen-bond structures at the air/water interface of electrolyte solutions. However, the ion effects on the top-most layer of the air/water interface, which is signified by the non-hydrogen-bonded so-called ‘free O-H’ group, has not been discussed or studied. In this report, we present the measurement of changes of the orientational angle of the ‘free O-H’ group at the air/water interface of the sodium fluoride (NaF) solutions at different concentrations using the interface selective sum-frequency generation vibrational spectroscopy (SFG-VS) in the ssp and ppp polarizations.more » The polarization dependent SFG-VS results show that the average tilt angle of the ‘free O-H’ changes from about 35.3 degrees ± 0.5 degrees to 43.4 degrees ± 2.1degrees as the NaF concentration increase from 0 to 0.94M (nearly saturated). Such tilt angle change is around the axis of the other O-H group of the same water molecule at the top-most layer at the air/water interface that is hydrogen-bonded to the water molecules below the top-most layer. These results provide quantitative molecular details of the ion effects of the NaF salt on the structure of the water molecules at the top-most layer of the air/water interfacial, even though both the Na+ cation and the F- anion are believed to be among the most excluded ions from the air/water interface.« less

Interactions of Organic Solvents at Graphene/α-Al 2 O 3 and Graphene Oxide/α-Al 2 O 3 Interfaces Studied by Sum Frequency Generation

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

Achtyl, Jennifer L.; Vlassiouk, Ivan V.; Dai, Sheng

2014-07-17

The adsorption of 1-hexanol from cyclohexane-d12 at single-layer graphene/α-Al2O3 interfaces was probed at mole percent values as low as 0.05 in the C–H stretching region using vibrational sum frequency generation (SFG). The SFG spectra are indiscernible from those obtained in the absence of graphene, and from those obtained in the presence of graphene oxide films prepared via oxygen plasma treatment of pristine single-layer graphene. A Langmuir adsorption model yields observed free adsorption energies of -19.9(5) to -20.9(3) kJ/mol for the three interfaces. The results indicate that the molecular structure of the hexanol alkyl chain is subject to the same orientationmore » distribution when graphene, oxidized or not, is present or absent at the α-Al2O3/cyclohexane-d12 interface. Moreover, it appears that the adsorption of 1-hexanol in this binary mixture is driven by hexanol interactions with the underlying oxide support, and that a single layer of graphene does not influence the extent of this interaction, even when defects are introduced to it. Finally, our structural and quantitative thermodynamic data provide important benchmarks for theoretical calculations and atomistic simulations of liquid/graphene interfaces. We hypothesize that defects emerging in graphene during operation of any device application that relies on layered solvent/graphene/oxide interfaces have little impact on the interfacial structure or thermodynamics, at least for the binary mixture and over the range of defect densities probed in our studies.« less

Toward ab initio molecular dynamics modeling for sum-frequency generation spectra; an efficient algorithm based on surface-specific velocity-velocity correlation function.

PubMed

Ohto, Tatsuhiko; Usui, Kota; Hasegawa, Taisuke; Bonn, Mischa; Nagata, Yuki

2015-09-28

Interfacial water structures have been studied intensively by probing the O-H stretch mode of water molecules using sum-frequency generation (SFG) spectroscopy. This surface-specific technique is finding increasingly widespread use, and accordingly, computational approaches to calculate SFG spectra using molecular dynamics (MD) trajectories of interfacial water molecules have been developed and employed to correlate specific spectral signatures with distinct interfacial water structures. Such simulations typically require relatively long (several nanoseconds) MD trajectories to allow reliable calculation of the SFG response functions through the dipole moment-polarizability time correlation function. These long trajectories limit the use of computationally expensive MD techniques such as ab initio MD and centroid MD simulations. Here, we present an efficient algorithm determining the SFG response from the surface-specific velocity-velocity correlation function (ssVVCF). This ssVVCF formalism allows us to calculate SFG spectra using a MD trajectory of only ∼100 ps, resulting in the substantial reduction of the computational costs, by almost an order of magnitude. We demonstrate that the O-H stretch SFG spectra at the water-air interface calculated by using the ssVVCF formalism well reproduce those calculated by using the dipole moment-polarizability time correlation function. Furthermore, we applied this ssVVCF technique for computing the SFG spectra from the ab initio MD trajectories with various density functionals. We report that the SFG responses computed from both ab initio MD simulations and MD simulations with an ab initio based force field model do not show a positive feature in its imaginary component at 3100 cm(-1).

Surface and buried interfacial structures of epoxy resins used as underfills studied by sum frequency generation vibrational spectroscopy.

PubMed

Vázquez, Anne V; Holden, Brad; Kristalyn, Cornelius; Fuller, Mike; Wilkerson, Brett; Chen, Zhan

2011-05-01

Flip chip technology has greatly improved the performance of semiconductor devices, but relies heavily on the performance of epoxy underfill adhesives. Because epoxy underfills are cured in situ in flip chip semiconductor devices, understanding their surface and interfacial structures is critical for understanding their adhesion to various substrates. Here, sum frequency generation (SFG) vibrational spectroscopy was used to study surface and buried interfacial structures of two model epoxy resins used as underfills in flip chip devices, bisphenol A digylcidyl ether (BADGE) and 1,4-butanediol diglycidyl ether (BDDGE). The surface structures of these epoxies were compared before and after cure, and the orientations of their surface functional groups were deduced to understand how surface structural changes during cure may affect adhesion properties. Further, the effect of moisture exposure, a known cause of adhesion failure, on surface structures was studied. It was found that the BADGE surface significantly restructured upon moisture exposure while the BDDGE surface did not, showing that BADGE adhesives may be more prone to moisture-induced delamination. Lastly, although surface structure can give some insight into adhesion, buried interfacial structures more directly correspond to adhesion properties of polymers. SFG was used to study buried interfaces between deuterated polystyrene (d-PS) and the epoxies before and after moisture exposure. It was shown that moisture exposure acted to disorder the buried interfaces, most likely due to swelling. These results correlated with lap shear adhesion testing showing a decrease in adhesion strength after moisture exposure. The presented work showed that surface and interfacial structures can be correlated to adhesive strength and may be helpful in understanding and designing optimized epoxy underfill adhesives.

Adsorption of 1- and 2-butylimidazoles at the copper/air and steel/air interfaces studied by sum frequency generation vibrational spectroscopy.

PubMed

Casford, Michael T L; Davies, Paul B

2012-07-24

The structure of thin films of 1- and 2-butylimidazoles adsorbed on copper and steel surfaces under air was examined using sum frequency generation (SFG) vibrational spectroscopy in the ppp and ssp polarizations. Additionally, the SFG spectra of both isomers were recorded at 55 °C at the liquid imidazole/air interface for reference. Complementary bulk infrared, reflection-absorption infrared spectroscopy (RAIRS), and Raman spectra of both imidazoles were recorded for assignment purposes. The SFG spectra in the C-H stretching region at the liquid/air interface are dominated by resonances from the methyl end group of the butyl side chain of the imidazoles, indicating that they are aligned parallel or closely parallel to the surface normal. These are also the most prominent features in the SFG spectra on copper and steel. In addition, both the ppp and ssp spectra on copper show resonances from the C-H stretching modes of the imidazole ring for both isomers. The ring C-H resonances are completely absent from the spectra on steel and at the liquid/air interface. The relative intensities of the SFG spectra can be interpreted as showing that, on copper, under air, both butylimidazoles are adsorbed with their butyl side chains perpendicular to the interface and with the ring significantly inclined away from the surface plane and toward the surface normal. The SFG spectra of both imidazoles on steel indicate an orientation where the imidazole rings are parallel or nearly parallel to the surface. The weak C-H resonances from the ring at the liquid/air interface suggest that the tilt angle of the ring from the surface normal at this interface is significantly greater than it is on copper.

Theory of Talbot lasers

NASA Astrophysics Data System (ADS)

Guillet de Chatellus, H.; Lacot, E.; Glastre, W.; Jacquin, O.; Hugon, O.

2013-09-01

We provide a theoretical study of frequency-shifted feedback (FSF) lasers, i.e., lasers with an internal frequency shifter, seeded with a monochromatic wave. The resulting spectrum consists in a set of equidistant modes, labeled by n, whose phases vary quadratically with n. We prove the emergence of a temporal fractional Talbot effect, leading to generation of Fourier-transform-limited pulses at a repetition rate tunable by the parameters of the FSF cavity (cavity length and frequency shift per round trip), and limited by the spectral bandwidth of the laser. We characterize in detail the output field of this so-called “Talbot laser” and emphasize its specific intensity fluctuations. We evidence connections with some aspects of number theory by the appearance of Gauss sums and theta series in the expression of the laser field. Our predictions are in full agreement with the experimental results published in Guillet de Chatellus [Opt. ExpressOPEXFF1094-408710.1364/OE.21.015065 21, 15065 (2013)]. Practical applications and limitations are discussed.

Structure from Dynamics: Vibrational Dynamics of Interfacial Water as a Probe of Aqueous Heterogeneity

PubMed Central

2018-01-01

The structural heterogeneity of water at various interfaces can be revealed by time-resolved sum-frequency generation spectroscopy. The vibrational dynamics of the O–H stretch vibration of interfacial water can reflect structural variations. Specifically, the vibrational lifetime is typically found to increase with increasing frequency of the O–H stretch vibration, which can report on the hydrogen-bonding heterogeneity of water. We compare and contrast vibrational dynamics of water in contact with various surfaces, including vapor, biomolecules, and solid interfaces. The results reveal that variations in the vibrational lifetime with vibrational frequency are very typical, and can frequently be accounted for by the bulk-like heterogeneous response of interfacial water. Specific interfaces exist, however, for which the behavior is less straightforward. These insights into the heterogeneity of interfacial water thus obtained contribute to a better understanding of complex phenomena taking place at aqueous interfaces, such as photocatalytic reactions and protein folding. PMID:29490138

Development of a solid-state sodium Doppler lidar using an all-fiber-coupled injection seeding unit for simultaneous temperature and wind measurements in the mesopause region.

PubMed

Xia, Yuan; Du, LiFang; Cheng, XueWu; Li, FaQuan; Wang, JiHong; Wang, ZeLong; Yang, Yong; Lin, Xin; Xun, YuChang; Gong, ShunSheng; Yang, GuoTao

2017-03-06

A solid-state sodium (Na) Doppler lidar developed at YanQing Station, Beijing, China (40°N, 116°E) aiming to simultaneous wind and temperature measurement of mesopause region was reported. The 589 nm pulse laser was produced by two injection seeded 1064 nm and 1319 nm Nd:YAG pulse lasers using the sum-frequency generation (SFG) technique. A fiber amplifier is implemented to boost the seed power at 1064 nm, enabling a robust, all-fiber-coupled design for seeding laser unit, absolute laser frequency locking, and cyclic three-frequency switching necessary for simultaneous temperature and wind measurements. The all-fiber-coupled injection seeding configuration together with the solid-state Nd:YAG lasers make the Na Doppler lidar more compact and greatly reduce the system maintenance, which is conducive to transportable and unattended operation. A preliminary observational result obtained with this solid-state sodium Doppler lidar was also reported in this paper.

Magnetic force microscopy with frequency-modulated capacitive tip-sample distance control

NASA Astrophysics Data System (ADS)

Zhao, X.; Schwenk, J.; Mandru, A. O.; Penedo, M.; Baćani, M.; Marioni, M. A.; Hug, H. J.

2018-01-01

In a step towards routinely achieving 10 nm spatial resolution with magnetic force microscopy, we have developed a robust method for active tip-sample distance control based on frequency modulation of the cantilever oscillation. It allows us to keep a well-defined tip-sample distance of the order of 10 nm within better than +/- 0.4 nm precision throughout the measurement even in the presence of energy dissipative processes, and is adequate for single-passage non-contact operation in vacuum. The cantilever is excited mechanically in a phase-locked loop to oscillate at constant amplitude on its first flexural resonance mode. This frequency is modulated by an electrostatic force gradient generated by tip-sample bias oscillating from a few hundred Hz up to a few kHz. The sum of the side bands’ amplitudes is a proxy for the tip-sample distance and can be used for tip-sample distance control. This method can also be extended to other scanning probe microscopy techniques.

Study of the Imidazolium-Based Ionic Liquid - ag Electrified Interface on the CO_{2} Electroreduction by Sum Frequency Spectroscopy.

NASA Astrophysics Data System (ADS)

Garcia Rey, Natalia; Dlott, Dana

2017-06-01

Imidazolium based ionic liquids (ILs) have been used as a promising system to improve the CO_{2} electroreduction at lower overpotential than other organic or aqueous electrolytes^{1}. Although the detailed mechanism of the CO_{2} electroreduction on Ag has not been elucidated yet, we have developed a methodology to study the electrified interface during the CO_{2} electroreduction using sum frequency generation (SFG) spectroscopy in combination with cyclic voltammetry^{2}. In this work, we tuned the composition of imidazolium-based ILs by exchanging the anion or the functional groups of the imidazolium. We use the nonresonant SFG (NR-SFG) to study the IL-Ag interface and resonant SFG (RES-SFG) to identify the CO adsorbed on the electrode and monitor the Stark shift as a function of cell potential. In previous studies on CO_{2} electroreduction in the IL: 1-ethyl-3-methylimidazolium tetrafluorborate (EMIM-BF_{4}) on Ag, we showed three events occurred at the same potential (-1.33 V vs. Ag/AgCl): the current associated with CO_{2} electroreduction increased, the Stark shift of the adsorbed atop CO doubled in magnitude and the EMIM-BF_{4} underwent a structural transition^{3}. In addition, we also observed how the structural transition of the EMIM-BF_{4} electrolyte shift to lower potentials when the IL is mixed with water. It is known that water enhances the CO_{2} electroreduction producing more CO^{4}. Moreover, the CO is adsorbed in multi-bonded and in atop sites when more water is present in the electrolyte. ^{1}Lau, G. P. S.; Schreier, M.; Vasilyev, D.; Scopelliti, R.; Grätzel, M.; Dyson, P. J., New Insights into the Role of Imidazolium-Based Promoters for the Electroreduction of CO_{2} on a Silver Electrode. J. Am. Chem. Soc. 2016, 138, 7820-7823. ^{2}Garcia Rey, N.; Dlott, D. D., Studies of Electrochemical Interfaces by Broadband Sum Frequency Generation. J. Electroanal. Chem. 2016. DOI:10.1016/j.jelechem.2016.12.023. ^{3}Garcia Rey, N.; Dlott, D. D., Structural Transition in an Ionic Liquid Controls CO_{2} Electrochemical Reduction. J. Phys. Chem. C 2015, 119, 20892-20899. ^{4}Rosen, B. A.; Zhu, W.; Kaul, G.; Salehi-Khojin, A.; Masel, R. I., Water Enhancement of CO_{2} Conversion on Silver in 1-Ethyl-3-Methylimidazolium Tetrafluoroborate. J. Electrochem. Soc. 2013, 160, H138-H141.

Dipole polarizability, sum rules, mean excitation energies, and long-range dispersion coefficients for buckminsterfullerene C 60

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Thakkar, Ajit J.

2011-11-01

Experimental photoabsorption cross-sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule and the high-energy behavior of the dipole-oscillator-strength density are used to construct dipole oscillator strength distributions for buckminsterfullerene (C60). The distributions are used to predict dipole sum rules Sk, mean excitation energies Ik, the frequency dependent polarizability, and C6 coefficients for the long-range dipole-dipole interactions of C60 with a variety of atoms and molecules.

Impact of the phase-mismatch in the SHG crystal and consequential self-action of the fundamental wave by cascaded second-order effects on the THG efficiency of a Q-switched 1342 nm Nd:YVO₄ laser.

PubMed

Koch, Peter; Bartschke, Juergen; L'huillier, Johannes A

2015-05-18

We report on the influence of self-focusing and self-defocusing in the phase-mismatched frequency doubling crystal on the third harmonic generation (THG) efficiency in a two crystal frequency tripling scheme. By detuning the temperature of the doubling crystal, the impact of a phase-mismatch in second harmonic generation (SHG) on the subsequent sum frequency mixing process was investigated. It was found that adjusting the temperature not only affected the power ratio of the second harmonic to the fundamental but also the beam diameter of the fundamental beam in the THG crystal, which was caused by self-focusing and self-defocusing of the fundamental beam, respectively. This self-action was induced by a cascaded χ(2) : χ(2) process in the phase-mismatched SHG crystal. Self-defocusing was observable for positive detuning and self-focusing for negative detuning of the phase-matching temperature. Hence, the THG efficiency was not symmetric with respect to the point of optimum phase-matching. Optimum THG was obtained for positive detuning and the resulting self-defocusing in combination with the focusing lens in front of the THG stage was also beneficial for the beam quality of the third harmonic.

Efficient wavelength converters with flattop responses based on counterpropagating cascaded SFG and DFG in low-loss QPM LiNbO3 waveguides.

PubMed

Tehranchi, Amirhossein; Kashyap, Raman

2009-10-12

A wavelength converter based on counterpropagating quasi-phase matched cascaded sum and difference frequency generation in lossy lithium niobate waveguide is numerically evaluated and compared to a single-pass scheme assuming a large pump wavelength difference of 75 nm. A double-pass device is proposed to improve the conversion efficiency while the response flattening is accomplished by increasing the wavelength tuning of one pump. The criteria for the design of the low-loss waveguide length, and the assignment of power in the pumps to achieve the desired efficiency, ripple and bandwidth are presented.

Time-resolved study of formate on Ni( 1 1 1 ) by picosecond SFG spectroscopy

NASA Astrophysics Data System (ADS)

Kusafuka, K.; Noguchi, H.; Onda, K.; Kubota, J.; Domen, K.; Hirose, C.; Wada, A.

2002-04-01

Time-resolved vibrational measurements were carried out on formate (HCOO) adsorbed on Ni(1 1 1) surface by combining the sum-frequency generation method and picosecond laser system (time resolution of 6 ps). Rapid intensity decrease (within the time resolution) followed by intensity recovery (time constant of several tens of ps) of CH stretching signal was observed when picosecond 800 nm pulse was irradiated on the sample surface. From the results of temperature and pump fluence dependences of temporal behaviour of signal intensity, we concluded that the observed intensity change was induced by non-thermal process. Mechanism of the temporal intensity change was discussed.

1/f Noise from nonlinear stochastic differential equations.

PubMed

Ruseckas, J; Kaulakys, B

2010-03-01

We consider a class of nonlinear stochastic differential equations, giving the power-law behavior of the power spectral density in any desirably wide range of frequency. Such equations were obtained starting from the point process models of 1/fbeta noise. In this article the power-law behavior of spectrum is derived directly from the stochastic differential equations, without using the point process models. The analysis reveals that the power spectrum may be represented as a sum of the Lorentzian spectra. Such a derivation provides additional justification of equations, expands the class of equations generating 1/fbeta noise, and provides further insights into the origin of 1/fbeta noise.

U.S. Navy Hindcast Spectral Ocean Wave Model Climatic Atlas: Mediterranean Sea

DTIC Science & Technology

1990-01-01

8217 (total) were obtained by summing the percent frequencies across each row. Rounding may cause minor differences between printed totals and total cell counts...34c9 3 N6 l7 4, i 5E F TI + e "t1- 4TI 3- ’$69"- -’ - + el4 𔄃 t 14 t , + t. -. ----- + 13,, 6 6 , 4- +0 2 4 9,: o . ;.. .;,+ + 5 ., 𔃿 6.--’ r’ ---- ’p...The SOWM generates ’en-.!rgy ’ariaLLcb’ cell within the 180 element matrix f The output from a SOWM hindcast includes a wind fields. There is a

The VERRUN and VERNAL software systems for steady-state visual evoked response experimentation

NASA Technical Reports Server (NTRS)

Levison, W. H.; Zacharias, G. L.

1984-01-01

Two digital computer programs were developed for use in experiments involving steady-state visual evoked response (VER): VERRUN, whose primary functions are to generate a sum-of-sines (SOS) stimulus and to digitize and store electro-cortical response; and VERNAL, which provides both time- and frequency-domain metrics of the evoked response. These programs were coded in FORTRAN for operation on the PDP-11/34, using the RSX-11 Operating System, and the PDP-11/23, using the RT-11 Operating System. Users' and programmers' guides to these programs are provided, and guidelines for model analysis of VER data are suggested.

Analytic descriptions of cylindrical electromagnetic waves in a nonlinear medium

PubMed Central

Xiong, Hao; Si, Liu-Gang; Yang, Xiaoxue; Wu, Ying

2015-01-01

A simple but highly efficient approach for dealing with the problem of cylindrical electromagnetic waves propagation in a nonlinear medium is proposed based on an exact solution proposed recently. We derive an analytical explicit formula, which exhibiting rich interesting nonlinear effects, to describe the propagation of any amount of cylindrical electromagnetic waves in a nonlinear medium. The results obtained by using the present method are accurately concordant with the results of using traditional coupled-wave equations. As an example of application, we discuss how a third wave affects the sum- and difference-frequency generation of two waves propagation in the nonlinear medium. PMID:26073066

Diverse wave-particle interactions for energetic ions that traverse Alfvén eigenmodes on their first full orbit [Diverse nonlinear wave-particle interactions for energetic ions that traverse Alfvén eigenmodes on their first full orbit

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

Heidbrink, W. W.; Persico, E. A. D.; Austin, M. E.

2016-02-09

Here, neutral-beam ions that are deflected onto loss orbits by Alfvén eigenmodes (AE) on their first bounce orbit and are detected by a fast-ion loss detector (FILD) satisfy the “local resonance” condition. This theory qualitatively explains FILD observations for a wide variety of AE-particle interactions. When coherent losses are measured for multiple AE, oscillations at the sum and difference frequencies of the independent modes are often observed. The amplitudes of the sum and difference peaks correlate with the amplitudes of the fundamental loss-signal amplitudes but do not correlate with the measured mode amplitudes. In contrast to a simple uniform-plasma theorymore » of the interaction, the loss-signal amplitude at the sum frequency is often larger than the loss-signal amplitude at the difference frequency, indicating a more detailed computation of the orbital trajectories through the mode eigenfunctions is needed.« less

Diverse wave-particle interactions for energetic ions that traverse Alfvén eigenmodes on their first full orbit

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

Heidbrink, W. W.; Persico, E. A. D.; Austin, M. E.

2016-02-15

Neutral-beam ions that are deflected onto loss orbits by Alfvén eigenmodes (AE) on their first bounce orbit and are detected by a fast-ion loss detector (FILD) satisfy the “local resonance” condition proposed by Zhang et al. [Nucl. Fusion 55, 22002 (2015)]. This theory qualitatively explains FILD observations for a wide variety of AE-particle interactions. When coherent losses are measured for multiple AE, oscillations at the sum and difference frequencies of the independent modes are often observed in the loss signal. The amplitudes of the sum and difference peaks correlate weakly with the amplitudes of the fundamental loss-signal amplitudes but domore » not correlate with the measured mode amplitudes. In contrast to a simple uniform-plasma theory of the interaction [Chen et al., Nucl. Fusion 54, 083005 (2014)], the loss-signal amplitude at the sum frequency is often larger than the loss-signal amplitude at the difference frequency, indicating a more detailed computation of the orbital trajectories through the mode eigenfunctions is needed.« less

High-Resolution Dual-Comb Spectroscopy with Ultra-Low Noise Frequency Combs

NASA Astrophysics Data System (ADS)

Hänsel, Wolfgang; Giunta, Michele; Beha, Katja; Perry, Adam J.; Holzwarth, R.

2017-06-01

Dual-comb spectroscopy is a powerful tool for fast broad-band spectroscopy due to the parallel interrogation of thousands of spectral lines. Here we report on the spectroscopic analysis of acetylene vapor in a pressurized gas cell using two ultra-low noise frequency combs with a repetition rate around 250 MHz. Optical referencing to a high-finesse cavity yields a sub-Hertz stability of all individual comb lines (including the virtual comb lines between 0 Hz and the carrier) and permits one to pick a small difference of repetition rate for the two frequency combs on the order of 300 Hz, thus representing an optical spectrum of 100 THz (˜3300 \\wn) within half the free spectral range (125 MHz). The transmission signal is derived straight from a photodetector and recorded with a high-resolution spectrum analyzer or digitized with a computer-controlled AD converter. The figure to the right shows a schematic of the experimental setup which is all fiber-coupled with polarization-maintaining fiber except for the spectroscopic cell. The graph on the lower right reveals a portion of the recorded radio-frequency spectrum which has been scaled to the optical domain. The location of the measured absorption coincides well with data taken from the HITRAN data base. Due to the intrinsic linewidth of all contributing comb lines, each sampling point in the transmission graph corresponds to the probing at an optical frequency with sub-Hertz resolution. This resolution is maintained in coherent wavelength conversion processes such as difference-frequency generation (DFG), sum-frequency generation (SFG) or non-linear broadening (self-phase modulation), and is therefore easily transferred to a wide spectral range from the mid infrared up to the visible spectrum.

Histotripsy Lesion Formation Using an Ultrasound Imaging Probe Enabled by a Low-Frequency Pump Transducer.

PubMed

Lin, Kuang-Wei; Hall, Timothy L; Xu, Zhen; Cain, Charles A

2015-08-01

When histotripsy pulses shorter than 2 cycles are applied, the formation of a dense bubble cloud relies only on the applied peak negative pressure (p-) exceeding the "intrinsic threshold" of the medium (absolute value of 26-30 MPa in most soft tissues). It has been found that a sub-threshold high-frequency probe pulse (3 MHz) can be enabled by a sub-threshold low-frequency pump pulse (500 kHz) where the sum exceeds the intrinsic threshold, thus generating lesion-producing dense bubble clouds ("dual-beam histotripsy"). Here, the feasibility of using an imaging transducer to provide the high-frequency probe pulse in the dual-beam histotripsy approach is investigated. More specifically, an ATL L7-4 imaging transducer (Philips Healthcare, Andover, MA, USA), pulsed by a V-1 Data Acquisition System (Verasonics, Redmond, WA, USA), was used to generate the high-frequency probe pulses. The low-frequency pump pulses were generated by a 20-element 345-kHz array transducer, driven by a custom high-voltage pulser. These dual-beam histotripsy pulses were applied to red blood cell tissue-mimicking phantoms at a pulse repetition frequency of 1 Hz, and optical imaging was used to visualize bubble clouds and lesions generated in the red blood cell phantoms. The results indicated that dense bubble clouds (and resulting lesions) were generated when the p- of the sub-threshold pump and probe pulses combined constructively to exceed the intrinsic threshold. The average size of the smallest reproducible lesions using the imaging probe pulse enabled by the sub-threshold pump pulse was 0.7 × 1.7 mm, whereas that using the supra-threshold pump pulse alone was 1.4 × 3.7 mm. When the imaging transducer was steered laterally, bubble clouds and lesions were steered correspondingly until the combined p- no longer exceeded the intrinsic threshold. These results were also validated with ex vivo porcine liver experiments. Using an imaging transducer for dual-beam histotripsy can have two advantages: (i) lesion steering can be achieved using the steering of the imaging transducer (implemented with the beamformer of the accompanying programmable ultrasound system), and (ii) treatment can be simultaneously monitored when the imaging transducer is used in conjunction with an ultrasound imaging system. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Histotripsy Lesion Formation using an Ultrasound Imaging Probe Enabled by a Low-Frequency Pump Transducer

PubMed Central

Lin, Kuang-Wei; Hall, Timothy L.; Xu, Zhen; Cain, Charles A.

2015-01-01

When applying histotripsy pulses shorter than 2 cycles, the formation of a dense bubble cloud only relies on the applied peak negative pressure (p-) exceeding the “intrinsic threshold” of the medium (absolute value of 26 – 30 MPa in most soft tissue). A previous study conducted by our research group showed that a sub-threshold high-frequency probe pulse (3 MHz) can be enabled by a sub-threshold low-frequency pump pulse (500 kHz) where the sum exceeds the intrinsic threshold, thus generating lesion-producing dense bubble clouds (“dual-beam histotripsy”). This paper investigates the feasibility of using an imaging transducer to provide the high-frequency probe pulse in the dual-beam histotripsy approach. More specifically, an ATL L7–4 imaging transducer, pulsed by a Verasonics V-1 Data Acquisition System, was used to generate the high-frequency probe pulses. The low-frequency pump pulses were generated by a 20-element 345 kHz array transducer, driven by a custom high voltage pulser. These dual-beam histotripsy pulses were applied to red-blood-cell (RBC) tissue-mimicking phantoms at a pulse repetition frequency of 1 Hz, and optical imaging was used to visualize bubble clouds and lesions generated in the RBC phantoms. The results showed that dense bubble clouds (and resulting lesions) were generated when the p- of the sub-threshold pump and probe pulses combined constructively to exceed the intrinsic threshold. The average size of the smallest reproducible lesions using the imaging probe pulse enabled by the sub-threshold pump pulse was 0.7 × 1.7 mm while that using the supra-threshold pump pulse alone was 1.4 × 3.7 mm. When the imaging transducer was steered laterally, bubble clouds and lesions were steered correspondingly until the combined p- no longer exceeded the intrinsic threshold. These results were also validated with ex vivo porcine liver experiments. Using an imaging transducer for dual-beam histotripsy can have two advantages, 1) lesion steering can be achieved using the steering of the imaging transducer (implemented with the beamformer of the accompanying programmable ultrasound system) and 2) treatment can be simultaneously monitored when the imaging transducer is used in conjunction with an ultrasound imaging system. PMID:25929995

High-frequency sum rules for the quasi-one-dimensional quantum plasma dielectric tensor

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

Genga, R.O.

A high-frequency sum-rule expansion is derived for all elements of the spinless quasi-one-dimensional quantum plasma response tensor at T = 0 K. As in the magnetized classical plasmas, we find that Omega/sub 4//sup 13/ is the only coefficient of omega/sup -4/ that has no correlational term. Further, we find that the correlations either enhance or reduce the negative quantum dispersion, depending on the direction of propagation. It is also noted that the quantum effect does not exist for the ordinary and the extraordinary modes for perpendicular and parallel propagation, respectively.

Effects of cations and cholesterol with sphingomyelin membranes investigated by high-resolution broadband sum frequency vibrational spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Zhen; Feng, Rong-juan; Li, Yi-yi; Liu, Ming-hua; Guo, Yuan

2017-08-01

Sphingomyelin(SM) is specifically enriched in the plasma membrane of mammalian cells. Its molecular structure is compose by N-acyl-Derythro-sphingosylphosphorylcholine. The function of the SM related to membrane signaling and protein trafficking are relied on the interactions of the SM, cations, cholesterol and proteins. In this report, the interaction of three different nature SMs, cations and cholesterol at air/aqueous interfaces studied by high-resolution broadband sum frequency vibrational spectroscopy, respectively. Our results shed lights on understanding the relationship between SMs monolayer, cholesterol and Cations.

All-Optical Stern-Gerlach Effect

NASA Astrophysics Data System (ADS)

Karnieli, Aviv; Arie, Ady

2018-01-01

We introduce a novel formalism in which the paraxial coupled wave equations of the nonlinear optical sum-frequency generation process are shown to be equivalent to the Pauli equation describing the dynamics of a spin-1 /2 particle in a spatially varying magnetic field. This interpretation gives rise to a new classical state of paraxial light, described by a mutual beam comprising of two frequencies. As a straightforward application, we propose the existence of an all-optical Stern-Gerlach effect, where an idler beam is deflected by a gradient in the nonlinear coupling, into two mutual beams of the idler and signal waves (equivalent to oppositely oriented spinors), propagating in two discrete directions. The Stern-Gerlach deflection angle and the intensity pattern in the far field are then obtained analytically, in terms of the parameters of the original optical system, laying the grounds for future experimental realizations.

Alcohol Oxidation at Platinum–Gas and Platinum–Liquid Interfaces: The Effect of Platinum Nanoparticle Size, Water Coadsorption, and Alcohol Concentration

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

Tatsumi, Hironori; Liu, Fudong; Han, Hui-Ling

Platinum nanoparticles size range from 1 to 8 nm deposited on mesoporous silica MCF-17 catalyzed alcohol oxidations were studied in the gas and liquid phases. Among methanol, ethanol, 2- propanol and 2-butanol reactions, the turnover frequency increased with Pt nanoparticle size for all the alcohols utilized. The activation energies for the oxidations were almost same among all alcohol species, but higher in the gas phase than those in the liquid phase. Water coadsorption poisoned the reaction in the gas phase, while it increased the reaction turnover rates in the liquid phase. Sum frequency generation (SFG) vibrational spectroscopy studies and DFTmore » calculations revealed that the alcohol molecules pack horizontally on the metal surface in low concentrations and stand up in high concentrations, which affect the dissociation of β-hydrogen of the alcohols as the critical step in alcohol oxidations.« less

Alcohol Oxidation at Platinum–Gas and Platinum–Liquid Interfaces: The Effect of Platinum Nanoparticle Size, Water Coadsorption, and Alcohol Concentration

DOE PAGES

Tatsumi, Hironori; Liu, Fudong; Han, Hui-Ling; ...

2017-03-21

Platinum nanoparticles size range from 1 to 8 nm deposited on mesoporous silica MCF-17 catalyzed alcohol oxidations were studied in the gas and liquid phases. Among methanol, ethanol, 2- propanol and 2-butanol reactions, the turnover frequency increased with Pt nanoparticle size for all the alcohols utilized. The activation energies for the oxidations were almost same among all alcohol species, but higher in the gas phase than those in the liquid phase. Water coadsorption poisoned the reaction in the gas phase, while it increased the reaction turnover rates in the liquid phase. Sum frequency generation (SFG) vibrational spectroscopy studies and DFTmore » calculations revealed that the alcohol molecules pack horizontally on the metal surface in low concentrations and stand up in high concentrations, which affect the dissociation of β-hydrogen of the alcohols as the critical step in alcohol oxidations.« less

A comprehensive prediction and evaluation method of pilot workload

PubMed Central

Feng, Chuanyan; Wanyan, Xiaoru; Yang, Kun; Zhuang, Damin; Wu, Xu

2018-01-01

BACKGROUND: The prediction and evaluation of pilot workload is a key problem in human factor airworthiness of cockpit. OBJECTIVE: A pilot traffic pattern task was designed in a flight simulation environment in order to carry out the pilot workload prediction and improve the evaluation method. METHODS: The prediction of typical flight subtasks and dynamic workloads (cruise, approach, and landing) were built up based on multiple resource theory, and a favorable validity was achieved by the correlation analysis verification between sensitive physiological data and the predicted value. RESULTS: Statistical analysis indicated that eye movement indices (fixation frequency, mean fixation time, saccade frequency, mean saccade time, and mean pupil diameter), Electrocardiogram indices (mean normal-to-normal interval and the ratio between low frequency and sum of low frequency and high frequency), and Electrodermal Activity indices (mean tonic and mean phasic) were all sensitive to typical workloads of subjects. CONCLUSION: A multinominal logistic regression model based on combination of physiological indices (fixation frequency, mean normal-to-normal interval, the ratio between low frequency and sum of low frequency and high frequency, and mean tonic) was constructed, and the discriminate accuracy was comparatively ideal with a rate of 84.85%. PMID:29710742

A comprehensive prediction and evaluation method of pilot workload.

PubMed

Feng, Chuanyan; Wanyan, Xiaoru; Yang, Kun; Zhuang, Damin; Wu, Xu

2018-01-01

The prediction and evaluation of pilot workload is a key problem in human factor airworthiness of cockpit. A pilot traffic pattern task was designed in a flight simulation environment in order to carry out the pilot workload prediction and improve the evaluation method. The prediction of typical flight subtasks and dynamic workloads (cruise, approach, and landing) were built up based on multiple resource theory, and a favorable validity was achieved by the correlation analysis verification between sensitive physiological data and the predicted value. Statistical analysis indicated that eye movement indices (fixation frequency, mean fixation time, saccade frequency, mean saccade time, and mean pupil diameter), Electrocardiogram indices (mean normal-to-normal interval and the ratio between low frequency and sum of low frequency and high frequency), and Electrodermal Activity indices (mean tonic and mean phasic) were all sensitive to typical workloads of subjects. A multinominal logistic regression model based on combination of physiological indices (fixation frequency, mean normal-to-normal interval, the ratio between low frequency and sum of low frequency and high frequency, and mean tonic) was constructed, and the discriminate accuracy was comparatively ideal with a rate of 84.85%.

Terahertz Sum-Frequency Excitation of a Raman-Active Phonon.

PubMed

Maehrlein, Sebastian; Paarmann, Alexander; Wolf, Martin; Kampfrath, Tobias

2017-09-22

In stimulated Raman scattering, two incident optical waves induce a force oscillating at the difference of the two light frequencies. This process has enabled important applications such as the excitation and coherent control of phonons and magnons by femtosecond laser pulses. Here, we experimentally and theoretically demonstrate the so far neglected up-conversion counterpart of this process: THz sum-frequency excitation of a Raman-active phonon mode, which is tantamount to two-photon absorption by an optical transition between two adjacent vibrational levels. Coherent control of an optical lattice vibration of diamond is achieved by an intense terahertz pulse whose spectrum is centered at half the phonon frequency of 40 THz. Remarkably, the carrier-envelope phase of the THz pulse is directly transferred into the phase of the lattice vibration. New prospects in general infrared spectroscopy, action spectroscopy, and lattice trajectory control in the electronic ground state emerge.

Generalization of the Lord-Wingersky Algorithm to Computing the Distribution of Summed Test Scores Based on Real-Number Item Scores

ERIC Educational Resources Information Center

Kim, Seonghoon

2013-01-01

With known item response theory (IRT) item parameters, Lord and Wingersky provided a recursive algorithm for computing the conditional frequency distribution of number-correct test scores, given proficiency. This article presents a generalized algorithm for computing the conditional distribution of summed test scores involving real-number item…

Fine Structure Analysis of 4702 oA Band of the Molecule

NASA Astrophysics Data System (ADS)

Sureshkumar, M. B.; Srikant, S. R.

1998-01-01

The emission spectrum of the cobalt monochloride molecule has been excited in a high frequency discharge tube source and the (0,0) band of H-system at 4702 Å was photo-graphed at an inverse dispersion of 0.973 Å/mm in the 5th order of a two meter plane grating spectrograph (Carl-Zeiss). The fine structure analysis of the band has been carried out and the molecular constants are reported for the first time. Rotational isotopic shift due to 37Cl support the analysis. The electronic transition involved is of the type 0---- 0- of case (c) which is equivalent of 3sum+---3sum+ or 5sum+---5sum+.

Development of a system for measurement and analysis of tremor using a three-axis accelerometer.

PubMed

Mamorita, N; Iizuka, T; Takeuchi, A; Shirataka, M; Ikeda, N

2009-01-01

The aim of the study was to develop a low-cost and compact system for analysis of tremor using a three-axis accelerometer (the Wii Remote (Nintendo)). To analyze tremor, we hypothesized that the influence of gravitational acceleration should be separated from that of movement. This hypothesis was tested experimentally and we also attempted to record and analyze tremor using our system in a clinical ward. A system for tremor measurement and analysis was developed using the three-axis accelerometer built into the Wii Remote. The frequency and amplitude of mechanical oscillation were calculated using methods for frequency analysis of the axis of largest variance and an estimation of tremor amplitude. The system consists of a program for measurement and analysis of Wii Remote acceleration (Tremor Analyzer), a Wii Remote, a Bluetooth USB adapter and a Web camera. The Tremor Analyzer has a GUI (graphical user interface) that is divided into five seg- ments. The sampling period of the analyzer is 30 msec. To confirm the hypothesis, mechanical oscillations were fed to the Wii Remote. The peak frequency of the power spectrum and the frequency of the oscillation generator were in good agreement, except at 1 Hz (0.01 G) and 2 Hz (0.02 G). With a change in the sum of squares of the three axes from 1.0 to 1.8 (G), the estimated and generated amplitude (0.3 cm) were in close agreement. This system using a Wii Remote is capable of analyzing frequency and estimated amplitude of tremor between 3 Hz and 15 Hz.

High-frequency sum rules for classical one-component plasma in a magnetic field

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

Genga, R.O.

A high-frequency sum-rule expansion is derived for all elements of a classical plasma dielectric tensor in the presence of an external magnetic field. Omega/sub 4//sup 13/ is found to be the only coefficient of omega/sup -4/ that has no correlational and finite-radiation-temperature contributions. The finite-radiation-temperature effect results in an upward renormalization of the frequencies of the modes; it also leads to either reduction of the negative correlational effect on the positive thermal dispersion or, together with correlation, enhancement of the positive thermal dispersion for finite k, depending on the direction of propagation. Further, for the extraordinary mode, the finite-radiation-temperature effectmore » increases the positive refractive dispersion for finite k.« less

FIA BioSum: a tool to evaluate financial costs, opportunities and effectiveness of fuel treatments.

Treesearch

Jeremy Fried; Glenn Christensen

2004-01-01

FIA BioSum, a tool developed by the USDA Forest Services Forest Inventory and Analysis (FIA) Program, generates reliable cost estimates, identifies opportunities and evaluates the effectiveness of fuel treatments in forested landscapes. BioSum is an analytic framework that integrates a suite of widely used computer models with a foundation of attribute-rich,...

Coupled-cluster sum-frequency generation nonlinear susceptibilities of methyl (CH3) and methylene (CH2) groups.

PubMed

Tetsassi Feugmo, Conrard Giresse; Liégeois, Vincent; Champagne, Benoît

2017-11-15

The first vibrational sum frequency generation (SFG) spectra based on molecular properties calculated at the coupled cluster singles and doubles (CCSD) level of approximation have been simulated for interfacial model alkyl chains, providing benchmark data for comparisons with approximate methods, including density functional theory (DFT). The approach proceeds in three steps. In the first two steps, the molecular spectral properties are determined: the vibrational normal modes and frequencies and then the derivatives of the dipole moment and of the polarizability with respect to the normal coordinates. These derivatives are evaluated with a numerical differentiation approach, of which the accuracy was monitored using Romberg's procedure. Then, in the last step, a three-layer model is employed to evaluate the macroscopic second-order nonlinear optical responses and thereby the simulated SFG spectra of the alkyl interface. Results emphasize the following facts: (i) the dipole and polarizability derivatives calculated at the DFT level with the B3LYP exchange-correlation functional can differ, with respect to CCSD, by as much as ±10 to 20% and ±20 to 50% for the CH 3 and CH 2 vibrations, respectively; (ii) these differences are enhanced when considering the SFG intensities as well as their variations as a function of the experimental configuration (ppp versus ssp) and as a function of the tilt and rotation angles, defining the orientation of the alkyl chain at the interface; (iii) these differences originate from both the vibrational normal coordinates and the Cartesian derivatives of the dipole moment and polarizability; (iv) freezing the successive fragments of the alkyl chain strongly modifies the SFG spectrum and enables highlighting the delocalization effects between the terminal CH 3 group and its neighboring CH 2 units; and finally (v) going from the free chain to the free methyl model, and further to C 3v constraints on leads to large variations of two ratios that are frequently used to probe the molecular orientation at the interface, the (r + r)/r + ratio for both antisymmetric and symmetric CH 3 vibrations and the I ppp /I ssp ratio.

Studies on the dynamic stability of an axially moving nanobeam based on the nonlocal strain gradient theory

NASA Astrophysics Data System (ADS)

Wang, Jing; Shen, Huoming; Zhang, Bo; Liu, Juan

2018-06-01

In this paper, we studied the parametric resonance issue of an axially moving viscoelastic nanobeam with varying velocity. Based on the nonlocal strain gradient theory, we established the transversal vibration equation of the axially moving nanobeam and the corresponding boundary condition. By applying the average method, we obtained a set of self-governing ordinary differential equations when the excitation frequency of the moving parameters is twice the intrinsic frequency or near the sum of certain second-order intrinsic frequencies. On the plane of parametric excitation frequency and excitation amplitude, we can obtain the instability region generated by the resonance, and through numerical simulation, we analyze the influence of the scale effect and system parameters on the instability region. The results indicate that the viscoelastic damping decreases the resonance instability region, and the average velocity and stiffness make the instability region move to the left- and right-hand sides. Meanwhile, the scale effect of the system is obvious. The nonlocal parameter exhibits not only the stiffness softening effect but also the damping weakening effect, while the material characteristic length parameter exhibits the stiffness hardening effect and damping reinforcement effect.

Narrow-line, cw orange light generation in a diode-pumped Nd:YVO4 laser using volume Bragg gratings.

PubMed

Chen, Y L; Chen, W W; Du, C E; Chang, W K; Wang, J L; Chung, T Y; Chen, Y H

2009-12-07

We report on the demonstration of a narrow-line, cw orange 593-nm laser achieved via intracavity sum-frequency generation (SFG) of a diode-pumped dual-wavelength (1064 and 1342 nm) Nd:YVO(4) laser using two volume Bragg grating (VBG) reflectors. At diode pump power of up to 3.6 W, the 593-nm intracavity SFG laser radiates at the single longitudinal mode of spectral linewidth as narrow as approximately 15 MHz. More than 23-mW single-longitudinal-mode or 40-mW, <8.5-GHz (10-pm) linewidth (at 4.2-W diode pump power) 593-nm orange lights can be obtained from this compact laser system. Spectral tuning of the orange light was performed via the temperature tuning of the two VBGs in this system, achieving an effective tuning rate of ~5 pm/degrees C.

Compact, passively Q-switched, all-solid-state master oscillator-power amplifier-optical parametric oscillator (MOPA-OPO) system pumped by a fiber-coupled diode laser generating high-brightness, tunable, ultraviolet radiation.

PubMed

Peuser, Peter; Platz, Willi; Fix, Andreas; Ehret, Gerhard; Meister, Alexander; Haag, Matthias; Zolichowski, Paul

2009-07-01

We report on a compact, tunable ultraviolet laser system that consists of an optical parametric oscillator (OPO) and a longitudinally diode-pumped Nd:YAG master oscillator-power amplifier (MOPA). The pump energy for the whole laser system is supplied via a single delivery fiber. Nanosecond pulses are produced by an oscillator that is passively Q-switched by a Cr(4+):YAG crystal. The OPO is pumped by the second harmonic of the Nd:YAG MOPA. Continuously tunable radiation is generated by an intracavity sum-frequency mixing process within the OPO in the range of 245-260 nm with high beam quality. Maximum pulse energies of 1.2 mJ were achieved, which correspond to an optical efficiency of 3.75%, relating to the pulse energy of the MOPA at 1064 nm.

Stable, high power, high efficiency picosecond ultraviolet generation at 355 nm in K3B6O10 Br crystal

NASA Astrophysics Data System (ADS)

Hou, Z. Y.; Wang, L. R.; Xia, M. J.; Yan, D. X.; Zhang, Q. L.; Zhang, L.; Liu, L. J.; Xu, D. G.; Zhang, D. X.; Wang, X. Y.; Li, R. K.; Chen, C. T.

2018-06-01

We demonstrate a high efficiency and high power picosecond ultraviolet source at 355 nm with stable output by sum frequency generation from a Nd:YAG laser using a type-I critically phase matched K3B6O10 Br crystal as nonlinear optical material. Conversion efficiency as high as 30.8% was achieved using a 25 ps laser at 1064 nm operated at 10 Hz. Similar work is done by using a 35 W 10 ps laser at 1064 nm as the pump source with a repetition rate of 80 MHz, and the highest average output power obtained was up to 5.3 W. In addition, the power stability of the 355 nm output power measurement shows that the standard deviation fluctuations of the average power are ±0.69% and ±0.91% at 3.0 W and 3.5 W, respectively.

Control of the coherence behavior in a SFG interferometer through the multipump phases command.

PubMed

Darré, P; Lehmann, L; Grossard, L; Delage, L; Reynaud, F

2018-03-19

In this paper, we report on a novel method to control the coherence behavior in a sum frequency generation interferometer powered by two independent pump lines. At the output of the interferometer, the two incoherent fringe patterns must be superimposed to maximize the contrast. The first step consists in canceling the differential group delay. The second one uses the phase control on one pump to synchronize the fringe patterns. This innovative method is experimentally demonstrated with a setup involving a 1544 nm signal and two pump lines around 1064 nm leading to a converted signal around 630 nm. It can be easily extended to a greater number of pump lines.

Probing alpha-helical and beta-sheet structures of peptides at solid/liquid interfaces with SFG.

PubMed

Chen, Xiaoyun; Wang, Jie; Sniadecki, Jason J; Even, Mark A; Chen, Zhan

2005-03-29

We demonstrated that sum frequency generation (SFG) vibrational spectroscopy can distinguish different secondary structures of proteins or peptides adsorbed at solid/liquid interfaces. The SFG spectrum for tachyplesin I at the polystyrene (PS)/solution interface has a fingerprint peak corresponding to the B1/B3 mode of the antiparallel beta-sheet. This peak disappeared upon the addition of dithiothreitol, which can disrupt the beta-sheet structure. The SFG spectrum indicative of the MSI594 alpha-helical structure was observed at the PS/MSI594 solution interface. This research validates SFG as a powerful technique for revealing detailed secondary structures of interfacial proteins and peptides.

Interfacial structure of soft matter probed by SFG spectroscopy.

PubMed

Ye, Shen; Tong, Yujin; Ge, Aimin; Qiao, Lin; Davies, Paul B

2014-10-01

Sum frequency generation (SFG) vibrational spectroscopy, an interface-specific technique in contrast to, for example, attenuated total reflectance spectroscopy, which is only interface sensitive, has been employed to investigate the surface and interface structure of soft matter on a molecular scale. The experimental arrangement required to carry out SFG spectroscopy, with particular reference to soft matter, and the analytical methods developed to interpret the spectra are described. The elucidation of the interfacial structure of soft matter systems is an essential prerequisite in order to understand and eventually control the surface properties of these important functional materials. Copyright © 2014 The Chemical Society of Japan and Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vibrational Studies of Saccharide-Induced Lipid Film Reorganization at Aqueous/Air Interfaces

DOE PAGES

Link, Katie A.; Hsieh, Chia -Yun; Tuladhar, Aashish; ...

2018-02-09

Vibrational sum frequency generation (VSFG) and surface tension experiments were used to examine the effects of aqueous phase soluble saccharides on the structure and organization of insoluble lipid monolayers adsorbed to aqueous-air interfaces. Changes in dipalmitoylphosphocholine (DPPC) chain structure as a function of aqueous phase saccharide concentration and pH are reported. Complementary differential scanning calorimetry (DSC) measurements performed on solutions containing soluble saccharides and DPPC vesicles measured the effects of the saccharides on the lipid membrane phase behavior. Here, data show that the saccharides glucosamine and glucuronic acid induce a higher degree of organization in compressed DPPC monolayers regardless ofmore » the saccharide’s charge.« less

Nanocylindrical confinement imparts highest structural order in molecular self-assembly of organophosphonates on aluminum oxide.

PubMed

Pathak, Anshuma; Bora, Achyut; Braunschweig, Björn; Meltzer, Christian; Yan, Hongdan; Lemmens, Peter; Daum, Winfried; Schwartz, Jeffrey; Tornow, Marc

2017-05-18

We report the impact of geometrical constraint on intramolecular interactions in self-assembled monolayers (SAMs) of alkylphosphonates grown on anodically oxidized aluminum (AAO). Molecular order in these films was determined by sum frequency generation (SFG) spectroscopy, a more sensitive measure of order than infrared absorption spectroscopy. Using SFG we show that films grown on AAO are, within detection limits, nearly perfectly ordered in an all-trans alkyl chain configuration. In marked contrast, films formed on planar, plasma-oxidized aluminum oxide or α-Al 2 O 3 (0001) are replete with gauche defects. We attribute these differences to the nanocylindrical structure of AAO, which enforces molecular confinement.

Quantum Nonlinear Optics without real Photons

NASA Astrophysics Data System (ADS)

Macrí, Vincenzo; Frisk Kockum, Anton; Stassi, Roberto; di Stefano, Omar; Savasta, Salvatore; Nori, Franco

We propose a physical process analogous to spontaneous parametric down-conversion, where one excited atom directly transfers its excitation to a couple of spatially-separated atoms with probability approaching one. The interaction is mediated by the exchange of virtual, rather than real, photons. This nonlinear optical process is coherent and reversible, so that the two excited atoms can transfer back the excitation to the first one: the atomic analogue of sum-frequency generation. The parameters used here correspond to experimentally-demonstrated values in circuit QED. This approach can be extended to consider other nonlinear interatomic processes, e.g. four-qubit mixing, and is an attractive architecture for the realization of quantum devices on a chip. Univ. of Michigan, USA.

Quantum Nonlinear Optics without Photons

NASA Astrophysics Data System (ADS)

Macrı, Vincenzo

Here we propose a physical process analogous to spontaneous parametric down-conversion, where one excited atom directly transfers its excitation to a couple of spatially separated atoms with probability approaching one. The interaction is mediated by the exchange of virtual rather than real photons. This nonlinear optical process is coherent and reversible, so that the couple of excited atoms can transfer back the excitation to the first one: the analogous for atoms of sum-frequency generation. The parameters used here correspond to experimentally-demonstrated values in circuit QED. This approach can be expanded to consider other nonlinear inter-atomic processes as the four-qubit mixing and is an attractive architecture for the realization of quantum devices on a chip.

A diode-pumped Nd:YAlO3 dual-wavelength yellow light source

NASA Astrophysics Data System (ADS)

Zhang, Jing; Fu, Xihong; Zhai, Pei; Xia, Jing; Li, Shutao

2013-11-01

We present what is, to the best of our knowledge, the first diode-pumped Nd:YAlO3 (Nd:YAP) continuous-wave (cw) dual-wavelength yellow laser at 593 nm and 598 nm, based on sum-frequency generation between 1064 and 1339 nm in a-axis polarization using LBO crystal and between 1079 and 1341 nm in c-axis polarization using PPKTP crystal, respectively. At an incident pump power of 17.3 W, the maximum output power obtained at 593 nm and 598 nm is 0.18 W and 1.86 W, respectively. The laser experiment shows that Nd:YAP crystal can be used for an efficient diode-pumped dual-wavelength yellow laser system.

Vibrational Studies of Saccharide-Induced Lipid Film Reorganization at Aqueous/Air Interfaces

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

Link, Katie A.; Hsieh, Chia -Yun; Tuladhar, Aashish

Vibrational sum frequency generation (VSFG) and surface tension experiments were used to examine the effects of aqueous phase soluble saccharides on the structure and organization of insoluble lipid monolayers adsorbed to aqueous-air interfaces. Changes in dipalmitoylphosphocholine (DPPC) chain structure as a function of aqueous phase saccharide concentration and pH are reported. Complementary differential scanning calorimetry (DSC) measurements performed on solutions containing soluble saccharides and DPPC vesicles measured the effects of the saccharides on the lipid membrane phase behavior. Here, data show that the saccharides glucosamine and glucuronic acid induce a higher degree of organization in compressed DPPC monolayers regardless ofmore » the saccharide’s charge.« less

Assembly and relaxation behaviours of phosphatidylethanolamine monolayers investigated by polarization and frequency resolved SFG-VS.

PubMed

Wei, Feng; Xiong, Wei; Li, Wenhui; Lu, Wangting; Allen, Heather C; Zheng, Wanquan

2015-10-14

The assembly conformation and kinetics of phosphatidylethanolamine (PE) lipids are the key to their membrane curvatures and activities, such as exocytosis, endocytosis and Golgi membrane fusion. In the current study, a polarization and frequency resolved (bandwidth ≈ 1 cm(-1)) picosecond sum frequency generation (SFG) system was developed to characterize phosphatidylethanolamine monolayers. In addition to obtaining π-A isotherms and Brewster angle microscopy (BAM) images, the conformational changes and assembly behaviors of phosphatidylethanolamine molecules are investigated by analyzing the SFG spectra collected at various surface pressures (SPs). The compression kinetics and relaxation kinetics of phosphatidylethanolamine monolayers are also reported. The conformational changes of PE molecules during the monolayer compression are separated into several stages: reorientation of the head group PO2(-) in the beginning of the liquid-expanded (LE) phase, conformational changes of head group alkyl chains in the LE phase, and conformational changes of tail group alkyl chains in the LE-liquid condensed (LE-LC) phase. Such an understanding may help researchers to effectively control the lipid molecular conformation and membrane curvatures during the exocytosis/endocytosis processes.

On synchronization in power-grids modelled as networks of second-order Kuramoto oscillators

NASA Astrophysics Data System (ADS)

Grzybowski, J. M. V.; Macau, E. E. N.; Yoneyama, T.

2016-11-01

This work concerns analytical results on the role of coupling strength in the phenomenon of onset of complete frequency locking in power-grids modelled as a network of second-order Kuramoto oscillators. Those results allow estimation of the coupling strength for the onset of complete frequency locking and to assess the features of network and oscillators that favor synchronization. The analytical results are evaluated using an order parameter defined as the normalized sum of absolute values of phase deviations of the oscillators over time. The investigation of the frequency synchronization within the subsets of the parameter space involved in the synchronization problem is also carried out. It is shown that the analytical results are in good agreement with those observed in the numerical simulations. In order to illustrate the methodology, a case study is presented, involving the Brazilian high-voltage transmission system under a load peak condition to study the effect of load on the syncronizability of the grid. The results show that both the load and the centralized generation might have concurred to the 2014 blackout.

Development of a solid-state sodium Doppler lidar using an all-fiber-coupled injection seeding unit for simultaneous temperature and wind measurements in the mesopause region

NASA Astrophysics Data System (ADS)

Yang, Guotao; Xia, Yuan; Cheng, Xuewu; Du, Lifang; Wang, Jihong; Xun, Yuchang

2017-04-01

We present a solid-state sodium (Na) Doppler lidar developed at YanQing Station, Beijing, China (40°N, 116°E) to achieve simultaneous wind and temperature measurements of mesopause region. The 589nm pulse laser is produced by two injection seeded 1064nm and 1319nm Nd:YAG pulse lasers using the sum-frequency generation (SFG) technique. An all-fiber-coupled seeding laser unit was designed to enable absolute laser frequency locking and cycling the measurements among three different operating frequencies. Experimental observations were carried out using this Na lidar system and the preliminary results were described and compared with the temperature of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and the horizontal wind of the meteor Radar, demonstrating the reliability and good performance of this lidar system. The all-fiber-coupled injection seeding configuration together with the solid-state Nd:YAG lasers make the Na Doppler lidar more compact and greatly reduce the system maintenance, which is conducive to transportable and unattended operation.

Lunar and Solar Torques on the Oceanic Tides

NASA Technical Reports Server (NTRS)

Ray, Richard D.; Bills, Bruce G.; Chao, Benjamin F.

1998-01-01

Brosche and Seiler recently suggested that direct lunar and solar tidal torques on the oceanic tides play a significant role in the earth's short-period angular momentum balance ("short-period" here meaning daily and sub-daily). We reexamine that suggestion here, concentrating on axial torques and hence on variations in rotation rate. Only those spherical harmonic components of the ocean tide having the same degree and order as the tidal potential induce nonzero torques. Prograde components (those moving in the same direction as the tide-generating body) produce the familiar secular braking of the earth's rotation. Retrograde components, however, produce rapid variations in UTI at twice the tidal frequency. There also exist interaction torques between tidal constituents, e.g. solar torques on lunar tides. They generate UTI variations at frequencies equal to the sums and differences of the original tidal frequencies. We give estimates of the torques and angular momentum variations for each of the important regimes, secular to quarter-diurnal. For the M(sub 2) potential acting on the M(sub 2) ocean tide, we find an associated angular momentum variation of amplitude 3 x 10(exp 19) N m. This is 5 to 6 orders of magnitude smaller than the angular momentum variations associated with tidal currents. We conclude that these torques do not play a significant role in the short-period angular momentum balance.

Which colors would extraterrestrial civilizations use to transmit signals?: The ;magic wavelengths; for optical SETI

NASA Astrophysics Data System (ADS)

Narusawa, Shin-ya; Aota, Tatusya; Kishimoto, Ryo

2018-04-01

In the case of radio SETI, there are predicted frequencies which extraterrestrial beings select to send messages to other civilizations. Those are called ;magic frequencies. Considering the optical region, terrestrial technologies can not transmit arbitrary wavelengths of high-power optical lasers, easily. In this article, we discuss communications among civilizations with the same level of technology as us to enhance the persuasive power. It might be possible to make a reasonable assumption about the laser wavelengths transmitted by extraterrestrial intelligences to benefit optical SETI (OSETI) methods. Therefore, we propose some ;magic wavelengths; for spectroscopic OSETI observations in this article. From the senders point of view, we argue that the most favorable wavelength used for interstellar communication would be the one of YAG lasers, at 1.064 μm or its Second Harmonic Generation (532.1 nm). On the contrary, there are basic absorption lines in the optical spectra, which are frequently observed by astrophysicists on Earth. It is possible that the extraterrestrials used lasers, which wavelengths are tuned to such absorption lines for sending messages. In that case, there is a possibility that SHG and/or Sum Frequency Generation of YAG and YLF lasers are used. We propose three lines at, 393.8 nm (near the Ca K line), 656.5 nm (near the Hα line) and 589.1 nm (Na D2 line) as the magic wavelengths.

Time-domain SFG spectroscopy using mid-IR pulse shaping: practical and intrinsic advantages.

PubMed

Laaser, Jennifer E; Xiong, Wei; Zanni, Martin T

2011-03-24

Sum-frequency generation (SFG) spectroscopy is a ubiquitous tool in the surface sciences. It provides infrared transition frequencies and line shapes that probe the structure and environment of molecules at interfaces. In this article, we apply techniques learned from the multidimensional spectroscopy community to SFG spectroscopy. We implement balanced heterodyne detection to remove scatter and the local oscillator background. Heterodyning also separates the resonant and nonresonant signals by acquiring both the real and imaginary parts of the spectrum. We utilize mid-IR pulse shaping to control the phase and delay of the mid-IR pump pulse. Pulse shaping allows phase cycling for data collection in the rotating frame and additional background subtraction. We also demonstrate time-domain data collection, which is a Fourier transform technique, and has many advantages in signal throughput, frequency resolution, and line shape accuracy over existing frequency domain methods. To demonstrate time-domain SFG spectroscopy, we study an aryl isocyanide on gold, and find that the system has an inhomogeneous structural distribution, in agreement with computational results, but which was not resolved by previous frequency-domain SFG studies. The ability to rapidly and actively manipulate the mid-IR pulse in an SFG pules sequence makes possible new experiments and more accurate spectra. © 2011 American Chemical Society

Design and status of the RF-digitizer integrated circuit

NASA Technical Reports Server (NTRS)

Rayhrer, B.; Lam, B.; Young, L. E.; Srinivasan, J. M.; Thomas, J. B.

1991-01-01

An integrated circuit currently under development samples a bandpass-limited signal at a radio frequency in quadrature and then performs a simple sum-and-dump operation in order to filter and lower the rate of the samples. Downconversion to baseband is carried out by the sampling step itself through the aliasing effect of an appropriately selected subharmonic sampling frequency. Two complete RF digitizer circuits with these functions will be implemented with analog and digital elements on one GaAs substrate. An input signal, with a carrier frequency as high as 8 GHz, can be sampled at a rate as high as 600 Msamples/sec for each quadrature component. The initial version of the chip will sign-sample (1-bit) the input RF signal. The chip will contain a synthesizer to generate a sample frequency that is a selectable integer multiple of an input reference frequency. In addition to the usual advantages of compactness and reliability associated with integrated circuits, the single chip will replace several steps required by standard analog downconversion. Furthermore, when a very high initial sample rate is selected, the presampling analog filters can be given very large bandwidths, thereby greatly reducing phase and delay instabilities typically introduced by such filters, as well as phase and delay variation due to Doppler changes.

The Effect of Pulse Length and Ejector Radius on Unsteady Ejector Performance

NASA Technical Reports Server (NTRS)

Wilson, Jack

2005-01-01

The thrust augmentation of a set of ejectors driven by a shrouded Hartmann-Sprenger tube has been measured at four different frequencies. Each frequency corresponded to a different length to diameter ratio of the pulse of air leaving the driver shroud. Two of the frequencies had length to diameter ratios below the formation number, and two above. The formation number is the value of length to diameter ratio below which the pulse converts to a vortex ring only, and above which the pulse becomes a vortex ring plus a trailing jet. A three level, three parameter Box-Behnken statistical design of experiment scheme was performed at each frequency, measuring the thrust augmentation generated by the appropriate ejectors from the set. The three parameters were ejector length, radius, and inlet radius. The results showed that there is an optimum ejector radius and length at each frequency. Using a polynomial fit to the data, the results were interpolated to different ejector radii and pulse length to diameter ratios. This showed that a peak in thrust augmentation occurs when the pulse length to diameter ratio equals the formation number, and that the optimum ejector radius is 0.87 times the sum of the vortex ring radius and the core radius.

Steel characteristics measurement system using Barkhausen jump sum rate and magnetic field intensity and method of using same

DOEpatents

Kohn, Gabriel; Hicho, George; Swartzendruber, Lydon

1997-01-01

A steel hardness measurement system and method of using same are provided for measuring at least one mechanical or magnetic characteristic of a ferromagnetic sample as a function of at least one magnetic characteristic of the sample. A magnetic field generator subjects the sample to a variable external magnetic field. The magnetic field intensity of the magnetic field generated by the magnetic field generating means is measured and a signal sensor is provided for measuring Barkhausen signals from the sample when the sample is subjected to the external magnetic field. A signal processing unit calculates a jump sum rate first moment as a function of the Barkhausen signals measured by the signal sensor and the magnetic field intensity, and for determining the at least one mechanical or magnetic characteristic as a function of the jump sum rate first moment.

Steel characteristics measurement system using Barkhausen jump sum rate and magnetic field intensity and method of using same

DOEpatents

Kohn, G.; Hicho, G.; Swartzendruber, L.

1997-04-08

A steel hardness measurement system and method of using same are provided for measuring at least one mechanical or magnetic characteristic of a ferromagnetic sample as a function of at least one magnetic characteristic of the sample. A magnetic field generator subjects the sample to a variable external magnetic field. The magnetic field intensity of the magnetic field generated by the magnetic field generating means is measured and a signal sensor is provided for measuring Barkhausen signals from the sample when the sample is subjected to the external magnetic field. A signal processing unit calculates a jump sum rate first moment as a function of the Barkhausen signals measured by the signal sensor and the magnetic field intensity, and for determining the at least one mechanical or magnetic characteristic as a function of the jump sum rate first moment. 7 figs.

Integration of auditory and vibrotactile stimuli: Effects of frequency

PubMed Central

Wilson, E. Courtenay; Reed, Charlotte M.; Braida, Louis D.

2010-01-01

Perceptual integration of vibrotactile and auditory sinusoidal tone pulses was studied in detection experiments as a function of stimulation frequency. Vibrotactile stimuli were delivered through a single channel vibrator to the left middle fingertip. Auditory stimuli were presented diotically through headphones in a background of 50 dB sound pressure level broadband noise. Detection performance for combined auditory-tactile presentations was measured using stimulus levels that yielded 63% to 77% correct unimodal performance. In Experiment 1, the vibrotactile stimulus was 250 Hz and the auditory stimulus varied between 125 and 2000 Hz. In Experiment 2, the auditory stimulus was 250 Hz and the tactile stimulus varied between 50 and 400 Hz. In Experiment 3, the auditory and tactile stimuli were always equal in frequency and ranged from 50 to 400 Hz. The highest rates of detection for the combined-modality stimulus were obtained when stimulating frequencies in the two modalities were equal or closely spaced (and within the Pacinian range). Combined-modality detection for closely spaced frequencies was generally consistent with an algebraic sum model of perceptual integration; wider-frequency spacings were generally better fit by a Pythagorean sum model. Thus, perceptual integration of auditory and tactile stimuli at near-threshold levels appears to depend both on absolute frequency and relative frequency of stimulation within each modality. PMID:21117754

Coverage vs Frequency : Is Spatial Coverage or Temporal Frequency More Impactful on Transit Ridership?

DOT National Transportation Integrated Search

2017-08-01

Transit ridership has long been studied, and the findings are concisely elucidated by Taylor & Fink (2003) when they say To sum, transit ridership is largely, though not completely, a product of factors outside the control of transit managers. ...

Nonlinear evolution of Mack modes in a hypersonic boundary layer

NASA Astrophysics Data System (ADS)

Chokani, Ndaona

2005-01-01

In hypersonic boundary layer flows the nonlinear disturbance evolution occurs relatively slowly over a very long length scale and has a profound effect on boundary layer transition. In the case of low-level freestream disturbances and negligible surface roughness, the transition is due to the modal growth of exponentially growing Mack modes that are destabilized by wall cooling. Cross-bicoherence measurements, derived from hot-wire data acquired in a quiet hypersonic tunnel, are used to identify and quantify phase-locked, quadratic sum and difference interactions involving the Mack modes. In the early stages of the nonlinear disturbance evolution, cross-bicoherence measurements indicate that the energy exchange between the Mack mode and the mean flow first occurs to broaden the sidebands; this is immediately followed by a sum interaction of the Mack mode to generate the first harmonic. In the next stages of the nonlinear disturbance evolution, there is a difference interaction of the first harmonic, which is also thought to contribute to the mean flow distortion. This difference interaction, in the latter stages, is also accompanied by a difference interaction between Mack mode and first harmonic, and a sum interaction, which forces the second harmonic. Analysis using the digital complex demodulation technique, shows that the low-frequency, phase-locked interaction that is identified in the cross bicoherence when the Mack mode and first harmonic have large amplitudes, arises due to the amplitude modulation of Mack mode and first harmonic.

Interference effects in the sum frequency generation spectra of thin organic films. II: Applications to different thin-film systems.

PubMed

Tong, Yujin; Zhao, Yanbao; Li, Na; Ma, Yunsheng; Osawa, Masatoshi; Davies, Paul B; Ye, Shen

2010-07-21

In this paper, the results of the modeling calculations carried out for predicting the interference effects expected in the sum frequency generation (SFG) spectra of a specific thin-layer system, described in the accompanying paper, are tested by comparing them with the experimental spectra obtained for a real thin-layer film comprising an organic monolayer/variable thickness dielectric layer/gold substrate. In this system, two contributions to the SFG spectra arise, a resonant contribution from the organic film and a nonresonant contribution from the gold substrate. The modeling calculations are in excellent agreement with the experimental spectra over a wide range of thicknesses and for different polarization combinations. The introduction of another resonant monolayer adjacent to the gold substrate and with the molecules having a reverse orientation has a significant affect on the spectral shapes which is predicted. If a dielectric substrate such as CaF(2) is used instead of a gold substrate, only the spectral intensities vary with the film thickness but not the spectral shapes. The counterpropagating beam geometry will change both the thickness dependent spectral shapes and the intensity of different vibrational modes in comparison with a copropagating geometry. The influences of these experimental factors, i.e., the molecular orientational structure in the thin film, the nature of the substrate, and the selected incident beam geometry, on the experimental SFG spectra are quantitatively predicted by the calculations. The thickness effects on the signals from a SFG active monolayer contained in a thin liquid-layer cell of the type frequently used for in situ electrochemical measurements is also discussed. The modeling calculation is also valid for application to other thin-film systems comprising more than two resonant SFG active interfaces by appropriate choice of optical geometries and relevant optical properties.

Validation of Spectra and Phase in Sub-1 cm-1 Resolution Sum-Frequency Generation Vibrational Spectroscopy through Internal Heterodyne Phase-Resolved Measurement

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

Fu, Li; Chen, Shunli; Wang, Hongfei

2016-03-03

Reliably determination of the spectral features and their phases in sum-frequency generation vibrational spectroscopy (SFG-VS) for surfaces with closely overlapping peaks has been a standing issue. Here we present two approaches towards resolving such issue. The first utilizes the high resolution and accurate lineshape from the recently developed sub-wavenumber high resolution broadband SFG-VS (HR-BB-SFG-VS), from which the detail spectral parameters, including relative spectral phases, of overlapping peaks can be determined through reliable spectral fitting. These results are further validated by using the second method that utilizes the azimuthal angle phase dependence of the z-cut α-quartz crystal, a common phase standard,more » through the spectral interference between the SFG fields of the quartz surface, as the internal phase reference, and the adsorbed molecular layer. Even though this approach is limited to molecular layers that can be transferred or deposited onto the quartz surface, it is simple and straightforward, as it requires only an internal phase standard with a single measurement that is free of phase drifts. More importantly, it provides unambiguous SFG spectral phase information of such surfaces. Using this method, the absolute phase of the molecular susceptibility tensors of the CH3, CH2 and chiral C-H groups in different Langmuir-Blodgett (LB) molecular monolayers and drop-cast peptide films are determined. These two approaches are fully consistent with and complement to each other, making both easily applicable tools in SFG-VS studies. More importantly, as the HR-BB-SFG-VS technique can be easily applied to various surfaces and interfaces, such validation of the spectral and phase information from HR-BB-SFG-VS measurement demonstrates it as one most promising tool for interrogating the detailed structure and interactions of complex molecular interfaces.« less

Surface characterization of imidazolium-based ionic liquids with cyano-functionalized anions at the gas-liquid interface using sum frequency generation spectroscopy.

PubMed

Peñalber, Chariz Y; Grenoble, Zlata; Baker, Gary A; Baldelli, Steven

2012-04-21

Advancement in the field of ionic liquid technology requires a comprehensive understanding of their surface properties, as a wide range of chemical reactions occur mainly at interfaces. As essential media currently used in several technological applications, their accurate molecular level description at the gas-liquid interface is of utmost importance. Due to the high degree of chemical information provided in the vibrational spectrum, vibrational spectroscopy gives the most detailed model for molecular structure. The inherently surface-sensitive technique, sum frequency generation (SFG) spectroscopy, in combination with bulk-sensitive vibrational spectroscopic techniques such as FTIR and Raman, has been used in this report to characterize the surface of cyano-containing ionic liquids, such as [BMIM][SCN], [BMIM][DCA], [BMIM][TCM] and [EMIM][TCB] at the gas-liquid interface. By structural variation of the anion while keeping the cation constant, emphasis on the molecular arrangement of the anion at the gas-liquid interface is reported, and its subsequent role (if any) in determining the surface molecular orientation of the cation. Vibrational modes seen in the C-H stretching region revealed the presence of the cation at the gas-liquid interface. The cation orientation is independent of the type of cyano-containing anion, however, a similar arrangement at the surface as reported in previous studies was found, with the imidazolium ring lying flat at the surface, and the alkyl chains pointing towards the gas phase. SFG results show that all three anions of varying symmetry, namely, [DCA](-) (C(2v)), [TCM](-)(D(3h)) and [TCB](-) (T(d)) in ionic liquids [BMIM]DCA], [BMIM][TCM] and [EMIM][TCB] are significantly tilted from the surface plane, while the linear [SCN](-) in [BMIM][SCN] exhibited poor ordering, as seen in the absence of its C-N stretching mode in the SFG vibrational spectra. This journal is © the Owner Societies 2012

Surface Spectroscopic Signatures of Mechanical Deformation in HDPE.

PubMed

Averett, Shawn C; Stanley, Steven K; Hanson, Joshua J; Smith, Stacey J; Patterson, James E

2018-01-01

High-density polyethylene (HDPE) has been extensively studied, both as a model for semi-crystalline polymers and because of its own industrial utility. During cold drawing, crystalline regions of HDPE are known to break up and align with the direction of tensile load. Structural changes due to deformation should also manifest at the surface of the polymer, but until now, a detailed molecular understanding of how the surface responds to mechanical deformation has been lacking. This work establishes a precedent for using vibrational sum-frequency generation (VSFG) spectroscopy to investigate changes in the molecular-level structure of the surface of HDPE after cold drawing. X-ray diffraction (XRD) was used to confirm that the observed surface behavior corresponds to the expected bulk response. Before tensile loading, the VSFG spectra indicate that there is significant variability in the surface structure and tilt of the methylene groups away from the surface normal. After deformation, the VSFG spectroscopic signatures are notably different. These changes suggest that hydrocarbon chains at the surface of visibly necked HDPE are aligned with the direction of loading, while the associated methylene groups are oriented with the local C 2 v symmetry axis roughly parallel to the surface normal. Small amounts of unaltered material are also found at the surface of necked HDPE, with the relative amount of unaltered material decreasing as the amount of deformation increases. Aspects of the nonresonant SFG response in the transition zone between necked and undeformed polymer provide additional insight into the deformation process and may provide the first indication of mechanical deformation. Nonlinear surface spectroscopy can thus be used as a noninvasive and nondestructive tool to probe the stress history of a HPDE sample in situations where X-ray techniques are not available or not applicable. Vibrational sum-frequency generation thus has great potential as a platform for material state awareness (MSA) and should be considered as part of a broader suite of tools for such applications.

Method for extracting long-equivalent wavelength interferometric information

NASA Technical Reports Server (NTRS)

Hochberg, Eric B. (Inventor)

1991-01-01

A process for extracting long-equivalent wavelength interferometric information from a two-wavelength polychromatic or achromatic interferometer. The process comprises the steps of simultaneously recording a non-linear sum of two different frequency visible light interferograms on a high resolution film and then placing the developed film in an optical train for Fourier transformation, low pass spatial filtering and inverse transformation of the film image to produce low spatial frequency fringes corresponding to a long-equivalent wavelength interferogram. The recorded non-linear sum irradiance derived from the two-wavelength interferometer is obtained by controlling the exposure so that the average interferogram irradiance is set at either the noise level threshold or the saturation level threshold of the film.

Frequency tripling of convergent beam employing crystals tiling in large-aperture high-energy laser facilities

NASA Astrophysics Data System (ADS)

Wang, Junhua; Li, Dazhen; Wang, Bo; Yang, Jing; Yang, Houwen; Wang, Xiaoqian; Cheng, Wenyong

2017-11-01

In inertial confinement fusion, ultraviolet laser damage of the fused silica lens is an important limiting factor for load capability of the laser driver. To solve this problem, a new configuration of frequency tripling is proposed in this paper. The frequency tripling crystal is placed on downstream of the focusing lens, thus sum frequency generation of fundamental frequency light and doubling frequency light occurs in the beam convergence path. The focusing lens is only irradiated by fundamental light and doubling frequency lights. Thus, its damage threshold will increase. LiB3O5 (LBO) crystals are employed as frequency tripling crystals for its larger acceptance angle and higher damage threshold than KDP/DKDP crystals'. With the limitation of acceptance angle and crystal growth size are taken into account, the tiling scheme of LBO crystals is proposed and designed optimally to adopt to the total convergence angle of 36.0 mrad. Theoretical results indicate that 3 LBO crystals titling with different cutting angles in θ direction can meet the phase matching condition. Compared with frequency tripling of parallel beam using one LBO crystal, 83.8% (93.1% with 5 LBO crystals tiling) of the frequency tripling conversion efficiency can be obtained employing this new configuration. The results of a principle experiment also support this scheme. By employing this new design, not only the load capacity of a laser driver will be significantly improved, but also the fused silica lens can be changed to K9 glass lens which has the mature technology and low cost.

Time and Frequency Activities at the U.S. Naval Observatory

DTIC Science & Technology

2009-11-01

Massachusetts, USA (Institute of Navigation, Alexandria, Virginia). [22] D. Kirchner, 1999, “Two Way Satellite Time and Frequency Transfer ( TWSTFT ...Piester, D., and Z. Jiang, 2009, “Two-Way Satellite Time and Frequency ( TWSTFT ) Transfer Calibration Constancy from Closure Sums,” in Proceedings of...Shäfer, and A. Pawlitzki, 2005, “Development of Carrier- Phase-Based Two-Way Satellite Time and Frequency Transfer ( TWSTFT ),” in Proceedings of the 36 th

Neurocognitive functions and brain atrophy after proven neuroborreliosis: a case-control study.

PubMed

Schmidt, Holger; Djukic, Marija; Jung, Klaus; Holzgraefe, Manfred; Dechent, Peter; von Steinbüchel, Nicole; Blocher, Joachim; Eiffert, Helmut; Schmidt-Samoa, Carsten

2015-08-19

Patients often report neurocognitive difficulties after neuroborreliosis (NB). The frequency and extent of cognitive problems in European patients have been studied incompletely. Sixty patients received a neurological and neuropsychological work-up 6 months or longer after treatment for proven NB. Quality of life, psychiatric symptom load, and brain atrophy were measured. All results were compared with a group of 30 healthy control persons adapted for age, gender and education being serologically negative for Borrelia burgdorferi senso latu. A cognitive sum score and a global sum score including cognitive, psychological results and quality of life data was calculated for both groups. Patients after NB showed a lower (i.e. more impaired) score on the Scripps Neurological rating scale (SNRS), but the observed neurological deficits were generally mild (mean ± SD: 97.1 ± 4.7 vs. 99.1 ± 2.4, p = 0.02). The mean neuropsychological domain results of the NB group were all within the normal range. However, a lower performance was found for the frontal executive function z-values (mean ± SD -0.29 ± 0.60 vs. 0.09 ± 0.60; p = 0.0059) of NB patients. Comparing the global sum score (mean ± SD 11.3 ± 4.2 NB vs. 14.3 ± 2.9 control , p = 0.001) and the cognitive sum score of the NB group with those of the control group (mean ± SD -0.15 ± 0.42 NB vs. 0.08 ± 0.31 control , p = 0.0079), both differences were statistically different. The frequencies of impaired global sum scores and those of the pathological cognitive sum scores (p = 0.07) did not differ statistically. No significant differences were found for health-related quality of life (hrQoL), sleep, psychiatric symptom load, or brain atrophy. The mean cognitive functions of patients after proven NB were in the normal range. However, we were able to demonstrate a lower performance for the domain of frontal executive functions, for the mean cognitive sum score and the global sum score as a sign of subtle but measurable sequelae of neuroborreliosis. Brain atrophy is not a common consequence of neuroborreliosis.

Acoustic waves in gases with strong pressure gradients

NASA Technical Reports Server (NTRS)

Zorumski, William E.

1989-01-01

The effect of strong pressure gradients on the acoustic modes (standing waves) of a rectangular cavity is investigated analytically. When the cavity response is represented by a sum of modes, each mode is found to have two resonant frequencies. The lower frequency is near the Viaesaela-Brundt frequency, which characterizes the buoyant effect, and the higher frequency is above the ordinary acoustic resonance frequency. This finding shows that the propagation velocity of the acoustic waves is increased due to the pressure gradient effect.

High-performance graphdiyne-based electrochemical actuators.

PubMed

Lu, Chao; Yang, Ying; Wang, Jian; Fu, Ruoping; Zhao, Xinxin; Zhao, Lei; Ming, Yue; Hu, Ying; Lin, Hongzhen; Tao, Xiaoming; Li, Yuliang; Chen, Wei

2018-02-21

Electrochemical actuators directly converting electrical energy to mechanical energy are critically important for artificial intelligence. However, their energy transduction efficiency is always lower than 1.0% because electrode materials lack active units in microstructure, and their assembly systems can hardly express the intrinsic properties. Here, we report a molecular-scale active graphdiyne-based electrochemical actuator with a high electro-mechanical transduction efficiency of up to 6.03%, exceeding that of the best-known piezoelectric ceramic, shape memory alloy and electroactive polymer reported before, and its energy density (11.5 kJ m -3 ) is comparable to that of mammalian skeletal muscle (~8 kJ m -3 ). Meanwhile, the actuator remains responsive at frequencies from 0.1 to 30 Hz with excellent cycling stability over 100,000 cycles. Furthermore, we verify the alkene-alkyne complex transition effect responsible for the high performance through in situ sum frequency generation spectroscopy. This discovery sheds light on our understanding of actuation mechanisms and will accelerate development of smart actuators.

Adaptive phase extraction: incorporating the Gabor transform in the matching pursuit algorithm.

PubMed

Wacker, Matthias; Witte, Herbert

2011-10-01

Short-time Fourier transform (STFT), Gabor transform (GT), wavelet transform (WT), and the Wigner-Ville distribution (WVD) are just some examples of time-frequency analysis methods which are frequently applied in biomedical signal analysis. However, all of these methods have their individual drawbacks. The STFT, GT, and WT have a time-frequency resolution that is determined by algorithm parameters and the WVD is contaminated by cross terms. In 1993, Mallat and Zhang introduced the matching pursuit (MP) algorithm that decomposes a signal into a sum of atoms and uses a cross-term free pseudo-WVD to generate a data-adaptive power distribution in the time-frequency space. Thus, it solved some of the problems of the GT and WT but lacks phase information that is crucial e.g., for synchronization analysis. We introduce a new time-frequency analysis method that combines the MP with a pseudo-GT. Therefore, the signal is decomposed into a set of Gabor atoms. Afterward, each atom is analyzed with a Gabor analysis, where the time-domain gaussian window of the analysis matches that of the specific atom envelope. A superposition of the single time-frequency planes gives the final result. This is the first time that a complete analysis of the complex time-frequency plane can be performed in a fully data-adaptive and frequency-selective manner. We demonstrate the capabilities of our approach on a simulation and on real-life magnetoencephalogram data.

FigSum: automatically generating structured text summaries for figures in biomedical literature.

PubMed

Agarwal, Shashank; Yu, Hong

2009-11-14

Figures are frequently used in biomedical articles to support research findings; however, they are often difficult to comprehend based on their legends alone and information from the full-text articles is required to fully understand them. Previously, we found that the information associated with a single figure is distributed throughout the full-text article the figure appears in. Here, we develop and evaluate a figure summarization system - FigSum, which aggregates this scattered information to improve figure comprehension. For each figure in an article, FigSum generates a structured text summary comprising one sentence from each of the four rhetorical categories - Introduction, Methods, Results and Discussion (IMRaD). The IMRaD category of sentences is predicted by an automated machine learning classifier. Our evaluation shows that FigSum captures 53% of the sentences in the gold standard summaries annotated by biomedical scientists and achieves an average ROUGE-1 score of 0.70, which is higher than a baseline system.

FigSum: Automatically Generating Structured Text Summaries for Figures in Biomedical Literature

PubMed Central

Agarwal, Shashank; Yu, Hong

2009-01-01

Figures are frequently used in biomedical articles to support research findings; however, they are often difficult to comprehend based on their legends alone and information from the full-text articles is required to fully understand them. Previously, we found that the information associated with a single figure is distributed throughout the full-text article the figure appears in. Here, we develop and evaluate a figure summarization system – FigSum, which aggregates this scattered information to improve figure comprehension. For each figure in an article, FigSum generates a structured text summary comprising one sentence from each of the four rhetorical categories – Introduction, Methods, Results and Discussion (IMRaD). The IMRaD category of sentences is predicted by an automated machine learning classifier. Our evaluation shows that FigSum captures 53% of the sentences in the gold standard summaries annotated by biomedical scientists and achieves an average ROUGE-1 score of 0.70, which is higher than a baseline system. PMID:20351812

Femtosecond noncollinear SFG dynamics in autocorrelator setup at low level of photons

NASA Astrophysics Data System (ADS)

Tenishev, Vladimir P.; Persson, A.; Larsson, J.

2004-06-01

We report here the characteristics of noncollinear sum frequency generation in nonlinear KDP crystals by ultrashort (80 fsec) IR pulses irradiated by the intense Ti:Sapphire laser and their behavior in single shot auto-crosscorrelator (ACC) configuration. In particular we study the case where one of the beams is very weak. Our aim is to develop a procedure to provide delay time signal between light pulses for time resolved pump probe experiments based on the extraction of the phase-matched SHG spatial distribution by means of pulse shape analysis technique. We intend to apply these results to synchronize a weak short-pulse source and an intense Ti:Sapphire laser and to measure the pulse time jitter between them.

Deducing 2D crystal structure at the liquid/solid interface with atomic resolution: a combined STM and SFG study.

PubMed

McClelland, Arthur A; Ahn, Seokhoon; Matzger, Adam J; Chen, Zhan

2009-11-17

Sum frequency generation vibrational spectroscopy (SFG) has been applied to study two-dimensional (2D) crystals formed by an isophthalic acid diester on the surface of highly oriented pyrolytic graphite, providing complementary measurements to scanning tunneling microscopy (STM) and computational modeling. SFG results indicate that both aromatic and C=O groups in the 2D crystal tilt from the surface. This study demonstrates that a combination of SFG and STM techniques can be used to gain a more complete picture of 2D crystal structure, and it is necessary to consider solvent-2D crystal interactions and dynamics in the computer models to achieve an accurate representation of interfacial structure.

2 W quasi-white-light based on idler-resonant optical parametric oscillation cascading sum-frequency generation with PPSLT

NASA Astrophysics Data System (ADS)

Zhao, L. N.; Liu, J.; Yuan, Y.; Hu, X. P.; Zhao, G.; Gao, Z. D.; Zhu, S. N.

2012-03-01

We present a high power red-green-blue (RGB) laser light source based on cascaded quasi-phasematched wavelength conversions in a single stoichiometric lithium tantalate. The superiority of the experimental setup is: the facula of the incident beam is elliptical to increase interaction volume, and the cavity was an idler resonant configuration for realizing more efficient red and blue light output. An average power of 2 W of quasi-white-light was obtained by proper combination of the RGB three colors. The conversion efficiency for the power of the quasi-white-light over pump power reached 36%. This efficiency and powerful RGB laser light source has potential applications in laser-based projection display et al.

Retrieval of all effective susceptibilities in nonlinear metamaterials

NASA Astrophysics Data System (ADS)

Larouche, Stéphane; Radisic, Vesna

2018-04-01

Electromagnetic metamaterials offer a great avenue to engineer and amplify the nonlinear response of materials. Their electric, magnetic, and magnetoelectric linear and nonlinear response are related to their structure, providing unprecedented liberty to control those properties. Both the linear and the nonlinear properties of metamaterials are typically anisotropic. While the methods to retrieve the effective linear properties are well established, existing nonlinear retrieval methods have serious limitations. In this work, we generalize a nonlinear transfer matrix approach to account for all nonlinear susceptibility terms and show how to use this approach to retrieve all effective nonlinear susceptibilities of metamaterial elements. The approach is demonstrated using sum frequency generation, but can be applied to other second-order or higher-order processes.

Three-dimensional scanning confocal laser microscope

DOEpatents

Anderson, R. Rox; Webb, Robert H.; Rajadhyaksha, Milind

1999-01-01

A confocal microscope for generating an image of a sample includes a first scanning element for scanning a light beam along a first axis, and a second scanning element for scanning the light beam at a predetermined amplitude along a second axis perpendicular to the first axis. A third scanning element scans the light beam at a predetermined amplitude along a third axis perpendicular to an imaging plane defined by the first and second axes. The second and third scanning element are synchronized to scan at the same frequency. The second and third predetermined amplitudes are percentages of their maximum amplitudes. A selector determines the second and third predetermined amplitudes such that the sum of the percentages is equal to one-hundred percent.

Diode-pumped quasi-three-level Nd:GdV O4-Nd:YAG sum-frequency laser at 464 nm

NASA Astrophysics Data System (ADS)

Lu, Jie

2014-04-01

We report a laser architecture to obtain continuous-wave (cw) blue radiation at 464 nm. A 808 nm diode pumped a Nd:GdV O4 crystal emitting at 912 nm. A part of the pump power was then absorbed by the Nd:GdV O4 crystal. The remainder was used to pump a Nd:YAG crystal emitting at 946 nm. Intracavity sum-frequency mixing at 912 and 946 nm was then realized in a LiB3O5 (LBO) crystal to produce blue radiation. We obtained a cw output power of 1.52 W at 464 nm with a pump laser diode emitting 18.4 W at 808 nm.

Double-frequency microwave ionization of Na

NASA Astrophysics Data System (ADS)

Ruff, G. A.; Dietrick, K. M.; Gallagher, T. F.

1990-11-01

We report the ionization of Na atoms by the simultaneous application of microwave fields of two different frequencies. We conclude that the salient features of double-frequency ionization can be readily understood. Both the hydrogenlike ||m||=2 states and the nonhydrogenic ||m||=0 and 1 states ionize when the sum of the field amplitudes, the peak field, reaches the field required for ionization by a single microwave frequency, E=1/9n4 and E=1/3n5, respectively.

Nonlinear optical effects in a three-nanolayer metal sandwich assembly

NASA Astrophysics Data System (ADS)

Khmelinskii, Igor; Makarov, Vladimir I.

2018-04-01

We report spectral properties and frequency summing that induce superemission (SE) in sandwich structures built of Co nanolayers. We found that separate Co films with a layer thickness of 8.1, 9.2, and 11.3 nm have discrete absorption spectra, originating in transverse quantum confinement in such thin metal films. The surface plasmon resonance in this system should appear at energies over 50 000 cm-1, with its longer-wavelength tail easily observable. All of the nanolayers studied also presented discrete emission spectra, with the emission bands strongly overlapping due to large bandwidths (1500-2300 cm-1). The emission decay is described by a single-exponential function with the lifetime of 103±5 ns. Similarly, the sandwich assembly with three Co nanolayers separated by two BN nanolayers also has discrete lines in its absorption spectrum. The spectrum of the assembly is a superposition of the respective spectra of the individual Co layers. We report that the assembly can sum the pumping radiation photons, producing photons with a higher energy. This excitation summing/exciton joining effect, discovered in sandwich film systems, is reported for the first time. Exiting the two outside Co nanolayers at specific frequencies, the Co nanolayer in the middle produces the sum frequency. We identified this emission as SE, with a bandwidth of only 179±5 cm-1. This superemission band appeared with the rise time of 36±3 ns and disappeared with 73±5 ns decay time, with the estimated SE quantum yield of 0.063. We analyzed the energy transfer by the exchange mechanism in detail, although a contribution of the electric dipole-dipole mechanism could not be excluded.

Sugar snack consumption in Ugandan schoolchildren: Validity and reliability of a food frequency questionnaire.

PubMed

Kiwanuka, S N; Astrøm, A N; Trovik, T A

2006-10-01

This study assessed the reproducibility and relative validity of an eight-item self-administered food frequency questionnaire (FFQ) on intake of sugared snacks in Ugandan schoolchildren. A 5-day precoded food behaviour checklist (FBC) was used as validation criteria. Sociodemographic correlates of a sum frequency sugar score were explored. The study was conducted in Kampala, Uganda, in 2004. Six hundred and fourteen schoolchildren (mean age 12.4 years) completed the FFQ on cakes/biscuits, chocolate, ice sticks, soft drinks, coffee, tea, sugared desserts and sweets/candies at school. They were examined clinically for dental caries. Forty students completed the FFQ twice, 1 week apart and 325 students completed the 5 day FBC at school. The mean decayed, missing and filled tooth index score was 0.98 (SD 1.6, range 0-15). Reproducibility scores (Cohen's kappa) for the sugar items ranged from 0.17 (ice sticks) to 0.55 (biscuits). No differences were seen between the average intakes at test and retest. Higher intake was reported in FFQ than in FBC across all sugar items. Crude agreement between students reporting intake at least 3-5 times a week/less than three times a week ranged from 50% to 55% (e.g. biscuits, chocolate) to 87% (tea). Spearman's correlation coefficients ranged from 0.14 (desserts) to 0.27 (sweets). anova revealed significant increase (P = 0.001) in the mean FBC sum scores by increasing quartiles of the FFQ sum scores. The average sum FFQ sugar scores were higher in girls than in boys and higher in older than in younger students. Fair reproducibility was established for the FFQ sugar items. The FFQ was acceptable in classifying individuals into broad categories of low and high sugar consumption.

Fluorinated End-Groups in Electrolytes Induce Ordered Electrolyte/Anode Interface Even at Open-Circuit Potential as Revealed by Sum Frequency Generation Vibrational Spectroscopy

DOE PAGES

Horowitz, Yonatan; Han, Hui-Ling; Ralston, Walter T.; ...

2017-05-12

Fluorine-based additives have a tremendously beneficial effect on the performance of lithium-ion batteries, yet the origin of this phenomenon is unclear. This study shows that the formation of a solid-electrolyte interphase (SEI) on the anode surface in the first five charge/discharge cycles is affected by the stereochemistry of the electrolyte molecules on the anode surface starting at open-circuit potential (OCP). This study shows an anode-specific model system, the reduction of 1,2-diethoxy ethane with lithium bis(trifluoromethane)sulfonimide, as a salt on an amorphous silicon anode, and compares the electrochemical response and SEI formation to its fluorinated version, bis(2,2,2-trifluoroethoxy) ethane (BTFEOE), by summore » frequency generation (SFG) vibrational spectroscopy under reaction conditions. The SFG results suggest that the —CF 3 end-groups of the linear ether BTFEOE change their adsorption orientation on the a-Si surface at OCP, leading to a better protective layer. Finally, supporting evidence from ex situ scanning electron microscopy and X-ray photoelectron spectroscopy depth profiling measurements shows that the fluorinated ether, BTFEOE, yields a smooth SEI on the a-Si surface and enables lithium ions to intercalate deeper into the a-Si bulk.« less

Fluorinated End-Groups in Electrolytes Induce Ordered Electrolyte/Anode Interface Even at Open-Circuit Potential as Revealed by Sum Frequency Generation Vibrational Spectroscopy

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

Horowitz, Yonatan; Han, Hui-Ling; Ralston, Walter T.

Fluorine-based additives have a tremendously beneficial effect on the performance of lithium-ion batteries, yet the origin of this phenomenon is unclear. This study shows that the formation of a solid-electrolyte interphase (SEI) on the anode surface in the first five charge/discharge cycles is affected by the stereochemistry of the electrolyte molecules on the anode surface starting at open-circuit potential (OCP). This study shows an anode-specific model system, the reduction of 1,2-diethoxy ethane with lithium bis(trifluoromethane)sulfonimide, as a salt on an amorphous silicon anode, and compares the electrochemical response and SEI formation to its fluorinated version, bis(2,2,2-trifluoroethoxy) ethane (BTFEOE), by summore » frequency generation (SFG) vibrational spectroscopy under reaction conditions. The SFG results suggest that the —CF 3 end-groups of the linear ether BTFEOE change their adsorption orientation on the a-Si surface at OCP, leading to a better protective layer. Finally, supporting evidence from ex situ scanning electron microscopy and X-ray photoelectron spectroscopy depth profiling measurements shows that the fluorinated ether, BTFEOE, yields a smooth SEI on the a-Si surface and enables lithium ions to intercalate deeper into the a-Si bulk.« less

Systematics-insensitive Periodic Signal Search with K2

NASA Astrophysics Data System (ADS)

Angus, Ruth; Foreman-Mackey, Daniel; Johnson, John A.

2016-02-01

From pulsating stars to transiting exoplanets, the search for periodic signals in K2 data, Kepler’s two-wheeled extension, is relevant to a long list of scientific goals. Systematics affecting K2 light curves due to the decreased spacecraft pointing precision inhibit the easy extraction of periodic signals from the data. We here develop a method for producing periodograms of K2 light curves that are insensitive to pointing-induced systematics; the Systematics-insensitive Periodogram (SIP). Traditional sine-fitting periodograms use a generative model to find the frequency of a sinusoid that best describes the data. We extend this principle by including systematic trends, based on a set of “eigen light curves,” following Foreman-Mackey et al., in our generative model as well as a sum of sine and cosine functions over a grid of frequencies. Using this method we are able to produce periodograms with vastly reduced systematic features. The quality of the resulting periodograms are such that we can recover acoustic oscillations in giant stars and measure stellar rotation periods without the need for any detrending. The algorithm is also applicable to the detection of other periodic phenomena such as variable stars, eclipsing binaries and short-period exoplanet candidates. The SIP code is available at https://github.com/RuthAngus/SIPK2.

Coherent state amplification using frequency conversion and a single photon source

NASA Astrophysics Data System (ADS)

Kasture, Sachin

2017-11-01

Quantum state discrimination lies at the heart of quantum communication and quantum cryptography protocols. Quantum Key Distribution (QKD) using coherent states and homodyne detection has been shown to be a feasible method for quantum communication over long distances. However, this method is still limited because of optical losses. Noiseless coherent state amplification has been proposed as a way to overcome this. Photon addition using stimulated Spontaneous Parametric Down-conversion followed by photon subtraction has been used as a way to implement amplification. However, this process occurs with very low probability which makes it very difficult to implement cascaded stages of amplification due to dark count probability in the single photon detectors used to herald the addition and subtraction of single photons. We discuss a scheme using the χ (2) and χ (3) optical non-linearity and frequency conversion (sum and difference frequency generation) along with a single photon source to implement photon addition. Unlike the photon addition scheme using SPDC, this scheme allows us to tune the success probability at the cost of reduced amplification. The photon statistics of the converted field can be controlled using the power of the pump field and the interaction time.

Sum of the m-th Powers of n Successive Terms of an Arithmetic Sequence: b[superscript m] + (a + b)[superscript m] + (2a + b)[superscript m] ... + ((n - 1)a + b)[superscript m

ERIC Educational Resources Information Center

Gauthier, N.

2006-01-01

This note describes a method for evaluating the sums of the m -th powers of n consecutive terms of a general arithmetic sequence: { S[subscript m] = 0, 1, 2,...}. The method is based on the use of a differential operator that is repeatedly applied to a generating function. A known linear recurrence is then obtained and the m-th sum, S[subscript…

Some Applications of Fourier's Great Discovery for Beginners

ERIC Educational Resources Information Center

Kraftmakher, Yaakov

2012-01-01

Nearly two centuries ago, Fourier discovered that any periodic function of period T can be presented as a sum of sine waveforms of frequencies equal to an integer times the fundamental frequency [omega] = 2[pi]/T (Fourier's series). It is impossible to overestimate the importance of Fourier's discovery, and all physics or engineering students…

High and low frequency unfolded partial least squares regression based on empirical mode decomposition for quantitative analysis of fuel oil samples.

PubMed

Bian, Xihui; Li, Shujuan; Lin, Ligang; Tan, Xiaoyao; Fan, Qingjie; Li, Ming

2016-06-21

Accurate prediction of the model is fundamental to the successful analysis of complex samples. To utilize abundant information embedded over frequency and time domains, a novel regression model is presented for quantitative analysis of hydrocarbon contents in the fuel oil samples. The proposed method named as high and low frequency unfolded PLSR (HLUPLSR), which integrates empirical mode decomposition (EMD) and unfolded strategy with partial least squares regression (PLSR). In the proposed method, the original signals are firstly decomposed into a finite number of intrinsic mode functions (IMFs) and a residue by EMD. Secondly, the former high frequency IMFs are summed as a high frequency matrix and the latter IMFs and residue are summed as a low frequency matrix. Finally, the two matrices are unfolded to an extended matrix in variable dimension, and then the PLSR model is built between the extended matrix and the target values. Coupled with Ultraviolet (UV) spectroscopy, HLUPLSR has been applied to determine hydrocarbon contents of light gas oil and diesel fuels samples. Comparing with single PLSR and other signal processing techniques, the proposed method shows superiority in prediction ability and better model interpretation. Therefore, HLUPLSR method provides a promising tool for quantitative analysis of complex samples. Copyright © 2016 Elsevier B.V. All rights reserved.

Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples.

PubMed

Hong, Hyobong; Lim, Eul-Gyoon; Jeong, Jae-Chan; Chang, Jiho; Shin, Sung-Woong; Krause, Hans-Joachim

2016-06-09

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. It consists of two magnetic measurement heads on both sides of the sample mounted on the legs of a u-shaped support. The sample is locally exposed to a magnetic excitation field consisting of two distinct frequencies, a stronger component at about 77 kHz and a weaker field at 61 Hz. The nonlinear magnetization characteristics of superparamagnetic particles give rise to the generation of intermodulation products. A selected sum-frequency component of the high and low frequency magnetic field incident on the magnetically nonlinear particles is recorded by a demodulation electronics. In contrast to a conventional MPI scanner, p-FMMD does not require the application of a strong magnetic field to the whole sample because mixing of the two frequencies occurs locally. Thus, the lateral dimensions of the sample are just limited by the scanning range and the supports. However, the sample height determines the spatial resolution. In the current setup it is limited to 2 mm. As examples, we present two 20 mm × 25 mm p-FMMD images acquired from samples with 1 µm diameter maghemite particles in silanol matrix and with 50 nm magnetite particles in aminosilane matrix. The results show that the novel MPI scanner can be applied for analysis of thin biological samples and for medical diagnostic purposes.

Polynomials with Restricted Coefficients and Their Applications

DTIC Science & Technology

1987-01-01

sums of exponentials of quadratics, he reduced such ýzums to exponentials of linears (geometric sums!) by simplg multiplying by their conjugates...n, the same algebraic manipulations as before lead to rn V`-~ v ie ? --8-- el4V’ .fk ts with 𔄃 = a+(2r+l)t, A = a+(2r+2m+l)t. To estimate the right...coefficients. These random polynomials represent the deviation in frequency response of a linear , equispaced antenna array cauised by coefficient

Dual-wavelength green laser with a 4.5 THz frequency difference based on self-frequency- doubling in Nd3+ -doped aperiodically poled lithium niobate.

PubMed

Maestre, H; Torregrosa, A J; Fernández-Pousa, C R; Rico, M L; Capmany, J

2008-05-01

We report a dual-wavelength continuous-wave laser at 542.4 and 546.8 nm based on an Nd(3+)-doped aperiodically poled lithium niobate crystal. Two fundamental infrared (IR) wavelengths at 1084.8 and 1093.6 nm are simultaneously oscillated and self-frequency-doubled to green. The aperiodic domain distribution patterned in the crystal allows for quasi-phase matched self-frequency-doubling of both IR fundamentals while avoiding their sum-frequency mixing.

Beat frequency ultrasonic microsphere contrast agent detection system

NASA Technical Reports Server (NTRS)

Pretlow, Robert A., III (Inventor); Yost, William T. (Inventor); Cantrell, John H., Jr. (Inventor)

1995-01-01

A system for and method of detecting and measuring concentrations of an ultrasonically-reflective microsphere contrast agent involving detecting non-linear sum and difference beat frequencies produced by the microspheres when two impinging signals with non-identical frequencies are combined by mixing. These beat frequencies can be used for a variety of applications such as detecting the presence of and measuring the flow rates of biological fluids and industrial liquids, including determining the concentration level of microspheres in the myocardium.

Beat frequency ultrasonic microsphere contrast agent detection system

NASA Technical Reports Server (NTRS)

Pretlow, III, Robert A. (Inventor); Yost, William T. (Inventor); Cantrell, Jr., John H. (Inventor)

1997-01-01

A system for and method of detecting and measuring concentrations of an ultrasonically-reflective microsphere contrast agent involving detecting non-linear sum and difference beat frequencies produced by the microspheres when two impinging signals with non-identical frequencies are combined by mixing. These beat frequencies can be used for a variety of applications such as detecting the presence of and measuring the flow rates of biological fluids and industrial liquids, including determining the concentration level of microspheres in the myocardium.

Least square regularized regression in sum space.

PubMed

Xu, Yong-Li; Chen, Di-Rong; Li, Han-Xiong; Liu, Lu

2013-04-01

This paper proposes a least square regularized regression algorithm in sum space of reproducing kernel Hilbert spaces (RKHSs) for nonflat function approximation, and obtains the solution of the algorithm by solving a system of linear equations. This algorithm can approximate the low- and high-frequency component of the target function with large and small scale kernels, respectively. The convergence and learning rate are analyzed. We measure the complexity of the sum space by its covering number and demonstrate that the covering number can be bounded by the product of the covering numbers of basic RKHSs. For sum space of RKHSs with Gaussian kernels, by choosing appropriate parameters, we tradeoff the sample error and regularization error, and obtain a polynomial learning rate, which is better than that in any single RKHS. The utility of this method is illustrated with two simulated data sets and five real-life databases.

Physiologically-Relevant Modes of Membrane Interactions by the Human Antimicrobial Peptide, LL-37, Revealed by SFG Experiments

PubMed Central

Ding, Bei; Soblosky, Lauren; Nguyen, Khoi; Geng, Junqing; Yu, Xinglong; Ramamoorthy, Ayyalusamy; Chen, Zhan

2013-01-01

Antimicrobial peptides (AMPs) could become the next generation antibiotic compounds which can overcome bacterial resistance by disrupting cell membranes and it is essential to determine the factors underlying its mechanism of action. Although high-resolution NMR and other biological studies have provided valuable insights, it has been a major challenge to follow the AMP-membrane interactions at physiologically-relevant low peptide concentrations. In this study, we demonstrate a novel approach to overcome this major limitation by performing Sum Frequency Generation (SFG) vibrational spectroscopic experiments on lipid bilayers containing an AMP, LL-37. Our results demonstrate the power of SFG to study non-linear helical peptides and also infer that lipid-peptide interaction and the peptide orientation depend on the lipid membrane composition. The observed SFG signal changes capture the aggregating process of LL-37 on membrane. In addition, our SFG results on cholesterol-containing lipid bilayers indicate the inhibition effect of cholesterol on peptide-induced membrane permeation process. PMID:23676762

Wavelength tunable CW red laser generated based on an intracavity-SFG composite cavity

NASA Astrophysics Data System (ADS)

Zhang, Z. N.; Bai, Y.; Lei, G. Z.; Bai, B.; Sun, Y. X.; Hu, M. X.; Wang, C.; Bai, J. T.

2016-12-01

We report a wavelength-tunable watt-level continuous wave (CW) red laser that uses a composite cavity based on an intracavity sum-frequency generation (SFG). The composite cavity is composed of a LD side-pumped Nd: GdVO4 p-polarized 1062.9 nm resonant cavity and a resonant optical parametric oscillator (SRO) of s-polarized signal light using a periodically poled crystal MgO: PPLN. Based on the temperature tuning from 30 °C to 200 °C, the CW red laser beams are obtained in a tunable waveband from 634.4 nm to 649.1 nm, corresponding to a tunable output waveband from 3278.0 nm to 2940.2 nm of the mid-infrared idler lights. The maximum CW output power of the red laser at 634.4 nm and the idler light at 3278.0 nm reach 3.03 W and 4.13 W under 30 °C, respectively.

Molecular orientation of organic thin films on dielectric solid substrates: a phase-sensitive vibrational SFG study.

PubMed

Ge, Aimin; Peng, Qiling; Qiao, Lin; Yepuri, Nageshwar R; Darwish, Tamim A; Matsusaki, Michiya; Akashi, Mitsuru; Ye, Shen

2015-07-21

Broadband phase-sensitive vibrational sum frequency generation (SFG) spectroscopy was utilized to study the molecular orientation of molecules adsorbed on dielectric solid substrates. A gold thin film was employed to generate a SFG signal as a local oscillator (LO). To simplify the phase measurement, a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) was used as a standard sample for phase correction of the phase-sensitive SFG measurements on the solid/air interface. It was demonstrated that the absolute orientation of molecules in the LB films on a fused quartz surface can be clearly distinguished by phase-sensitive SFG measurement. In addition, the observation on the SAM of d35-OTS reveals that the two C-H stretching modes for α-CH2 group are in opposite phase. Furthermore, by using the present phase-sensitive SFG setup, the orientation flipping of water molecules on positively and negatively charged solid/liquid interface can be distinguished.

Physiologically-Relevant Modes of Membrane Interactions by the Human Antimicrobial Peptide, LL-37, Revealed by SFG Experiments

NASA Astrophysics Data System (ADS)

Ding, Bei; Soblosky, Lauren; Nguyen, Khoi; Geng, Junqing; Yu, Xinglong; Ramamoorthy, Ayyalusamy; Chen, Zhan

2013-05-01

Antimicrobial peptides (AMPs) could become the next generation antibiotic compounds which can overcome bacterial resistance by disrupting cell membranes and it is essential to determine the factors underlying its mechanism of action. Although high-resolution NMR and other biological studies have provided valuable insights, it has been a major challenge to follow the AMP-membrane interactions at physiologically-relevant low peptide concentrations. In this study, we demonstrate a novel approach to overcome this major limitation by performing Sum Frequency Generation (SFG) vibrational spectroscopic experiments on lipid bilayers containing an AMP, LL-37. Our results demonstrate the power of SFG to study non-linear helical peptides and also infer that lipid-peptide interaction and the peptide orientation depend on the lipid membrane composition. The observed SFG signal changes capture the aggregating process of LL-37 on membrane. In addition, our SFG results on cholesterol-containing lipid bilayers indicate the inhibition effect of cholesterol on peptide-induced membrane permeation process.

Physiologically-relevant modes of membrane interactions by the human antimicrobial peptide, LL-37, revealed by SFG experiments.

PubMed

Ding, Bei; Soblosky, Lauren; Nguyen, Khoi; Geng, Junqing; Yu, Xinglong; Ramamoorthy, Ayyalusamy; Chen, Zhan

2013-01-01

Antimicrobial peptides (AMPs) could become the next generation antibiotic compounds which can overcome bacterial resistance by disrupting cell membranes and it is essential to determine the factors underlying its mechanism of action. Although high-resolution NMR and other biological studies have provided valuable insights, it has been a major challenge to follow the AMP-membrane interactions at physiologically-relevant low peptide concentrations. In this study, we demonstrate a novel approach to overcome this major limitation by performing Sum Frequency Generation (SFG) vibrational spectroscopic experiments on lipid bilayers containing an AMP, LL-37. Our results demonstrate the power of SFG to study non-linear helical peptides and also infer that lipid-peptide interaction and the peptide orientation depend on the lipid membrane composition. The observed SFG signal changes capture the aggregating process of LL-37 on membrane. In addition, our SFG results on cholesterol-containing lipid bilayers indicate the inhibition effect of cholesterol on peptide-induced membrane permeation process.

Nonlinear plasmonic behavior of nanohole arrays in thin gold films for imaging lipids

NASA Astrophysics Data System (ADS)

Subramaniyam, Nagarajan; Shah, Ali; Dreser, Christoph; Isomäki, Antti; Fleischer, Monika; Sopanen, Markku

2018-06-01

We demonstrate linear and nonlinear plasmonic behaviors of periodic nanohole arrays in thin gold (Au) films with varying periodicities. As expected, the linear optical transmission spectra of the nanohole arrays show a red-shift of the resonance wavelength and Wood's anomaly with increasing hole spacing. The optical transmission and electric near-field intensity distribution of the nanohole arrays are simulated using the finite element method. The nonlinear plasmonic behavior of the nanohole arrays is studied by using picosecond pulsed excitation at near-infrared wavelengths. The characteristic nonlinear signals indicating two-photon excited luminescence (TPEL), sum frequency generation, second harmonic generation, and four-wave mixing (FWM) are observed. A maximum FWM/TPEL signal intensity ratio is achieved for nanohole arrays with a periodicity of 500 nm. Furthermore, the significant FWM signal intensity and contrast compared to the background were harnessed to demonstrate the ability of surface-enhanced coherent anti-Stokes Raman scattering to visualize low concentrations of lipids deposited on the nanohole array with a periodicity of 500 nm.

Efficient high-performance ultrasound beamforming using oversampling

NASA Astrophysics Data System (ADS)

Freeman, Steven R.; Quick, Marshall K.; Morin, Marc A.; Anderson, R. C.; Desilets, Charles S.; Linnenbrink, Thomas E.; O'Donnell, Matthew

1998-05-01

High-performance and efficient beamforming circuitry is very important in large channel count clinical ultrasound systems. Current state-of-the-art digital systems using multi-bit analog to digital converters (A/Ds) have matured to provide exquisite image quality with moderate levels of integration. A simplified oversampling beamforming architecture has been proposed that may a low integration of delta-sigma A/Ds onto the same chip as digital delay and processing circuitry to form a monolithic ultrasound beamformer. Such a beamformer may enable low-power handheld scanners for high-end systems with very large channel count arrays. This paper presents an oversampling beamformer architecture that generates high-quality images using very simple; digitization, delay, and summing circuits. Additional performance may be obtained with this oversampled system for narrow bandwidth excitations by mixing the RF signal down in frequency to a range where the electronic signal to nose ratio of the delta-sigma A/D is optimized. An oversampled transmit beamformer uses the same delay circuits as receive and eliminates the need for separate transmit function generators.

On the origin of the extracellular field potential in the nucleus laminaris of the barn owl (Tyto alba).

PubMed

Kuokkanen, Paula T; Wagner, Hermann; Ashida, Go; Carr, Catherine E; Kempter, Richard

2010-10-01

The neurophonic is a sound-evoked, frequency-following potential that can be recorded extracellularly in nucleus laminaris of the barn owl. The origin of the neurophonic, and thus the mechanisms that give rise to its exceptional temporal precision, has not yet been identified. Putative generators of the neurophonic are the activity of afferent axons, synaptic activation of laminaris neurons, or action potentials in laminaris neurons. To identify the generators, we analyzed the neurophonic in the high-frequency (>2.5 kHz) region of nucleus laminaris in response to monaural pure-tone stimulation. The amplitude of the neurophonic is typically in the millivolt range. The signal-to-noise ratio reaches values beyond 30 dB. To assess which generators could give rise to these large, synchronous extracellular potentials, we developed a computational model. Spike trains were produced by an inhomogeneous Poisson process and convolved with a spike waveform. The model explained the dependence of the simulated neurophonic on parameters such as the mean rate, the vector strength of phase locking, the number of statistically independent sources, and why the signal-to-noise ratio is independent of the spike waveform and subsequent filtering of the signal. We found that several hundred sources are needed to reach the observed signal-to-noise ratio. The summed coherent signal from the densely packed afferent axons and activation of their synapses on laminaris neurons are alone sufficient to explain the measured properties of the neurophonic.

Photonic generation of FCC-compliant UWB pulses based on modified Gaussian quadruplet and incoherent wavelength-to-time conversion

NASA Astrophysics Data System (ADS)

Mu, Hongqian; Wang, Muguang; Tang, Yu; Zhang, Jing; Jian, Shuisheng

2018-03-01

A novel scheme for the generation of FCC-compliant UWB pulse is proposed based on modified Gaussian quadruplet and incoherent wavelength-to-time conversion. The modified Gaussian quadruplet is synthesized based on linear sum of a broad Gaussian pulse and two narrow Gaussian pulses with the same pulse-width and amplitude peak. Within specific parameter range, FCC-compliant UWB with spectral power efficiency of higher than 39.9% can be achieved. In order to realize the designed waveform, a UWB generator based on spectral shaping and incoherent wavelength-to-time mapping is proposed. The spectral shaper is composed of a Gaussian filter and a programmable filter. Single-mode fiber functions as both dispersion device and transmission medium. Balanced photodetection is employed to combine linearly the broad Gaussian pulse and two narrow Gaussian pulses, and at same time to suppress pulse pedestals that result in low-frequency components. The proposed UWB generator can be reconfigured for UWB doublet by operating the programmable filter as a single-band Gaussian filter. The feasibility of proposed UWB generator is demonstrated experimentally. Measured UWB pulses match well with simulation results. FCC-compliant quadruplet with 10-dB bandwidth of 6.88-GHz, fractional bandwidth of 106.8% and power efficiency of 51% is achieved.

Vibrational Stark Effect to Probe the Electric-Double Layer of the Ionic Liquid-Metal Electrodes

NASA Astrophysics Data System (ADS)

Garcia Rey, Natalia; Moore, Alexander Knight; Toyouchi, Shuichi; Dlott, Dana

2017-06-01

Vibrational sum frequency generation (VSFG) spectroscopy is used to study the effect of room temperature ionic liquids (RTILs) in situ at the electrical double layer (EDL). RTILs have been recognized as electrolytes without solvent for applications in batteries, supercapacitors and electrodeposition^{1}. The molecular response of the RTIL in the EDL affects the performance of these devices. We use the vibrational Stark effect on CO as a probe to detect the changes in the electric field affected by the RTIL across the EDL on metal electrodes. The Stark effect is a shift in the frequency in response to an externally applied electric field and also influenced by the surrounding electrolyte and electrode^{2}. The CO Stark shift is monitored by the CO-VSFG spectra on Pt or Ag in a range of different imidazolium-based RTILs electrolytes, where their composition is tuned by exchanging the anion, the cation or the imidazolium functional group. We study the free induction decay (FID)^{3} of the CO to monitor how the RTIL structure and composition affect the vibrational relaxation of the CO. Combining the CO vibrational Stark effect and the FID allow us to understand how the RTIL electrochemical response, molecular orientation response and collective relaxation affect the potential drop of the electric field across the EDL, and, in turn, how determines the electrical capacitance or reactivity of the electrolyte/electrode interface. ^{1}Fedorov, M. V.; Kornyshev, A. A., Ionic Liquids at Electrified Interfaces. Chem. Rev. 2014, 114, 2978-3036. ^{2} (a) Lambert, D. K., Vibrational Stark Effect of Adsorbates at Electrochemical Interfaces. Electrochim. Acta 1996, 41, 623-630. (b) Oklejas, V.; Sjostrom, C.; Harris, J. M., SERS Detection of the Vibrational Stark Effect from Nitrile-Terminated SAMs to Probe Electric Fields in the Diffuse Double-Layer. J. Am. Chem. Soc. 2002, 124, 2408-2409. ^{3}Symonds, J. P. R.; Arnolds, H.; Zhang, V. L.; Fukutani, K.; King, D. A.,Broadband Femtosecond Sum-Frequency Spectroscopy of CO on Ru{1010} in the Frequency and Time Domains. J. Chem. Phys. 2004, 120, 7158-7164.

Theoretical study of sum-frequency vibrational spectroscopy on limonene surface

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

Zheng, Ren-Hui, E-mail: zrh@iccas.ac.cn; Liu, Hao; Jing, Yuan-Yuan

2014-03-14

By combining molecule dynamics (MD) simulation and quantum chemistry computation, we calculate the surface sum-frequency vibrational spectroscopy (SFVS) of R-limonene molecules at the gas-liquid interface for SSP, PPP, and SPS polarization combinations. The distributions of the Euler angles are obtained using MD simulation, the ψ-distribution is between isotropic and Gaussian. Instead of the MD distributions, different analytical distributions such as the δ-function, Gaussian and isotropic distributions are applied to simulate surface SFVS. We find that different distributions significantly affect the absolute SFVS intensity and also influence on relative SFVS intensity, and the δ-function distribution should be used with caution whenmore » the orientation distribution is broad. Furthermore, the reason that the SPS signal is weak in reflected arrangement is discussed.« less

An efficient continuous-wave 591 nm light source based on sum-frequency mixing of a diode pumped Nd:GdVO4-Nd:CNGG laser

NASA Astrophysics Data System (ADS)

Zhao, Y. D.; Liu, J. H.

2013-08-01

We report a laser architecture to obtain continuous-wave (CW) yellow-orange light sources at the 591 nm wavelength. An 808 nm diode pumped a Nd:GdVO4 crystal emitting at 1063 nm. A part of the pump power was then absorbed by the Nd:CNGG crystal. The remaining pump power was used to pump a Nd:CNGG crystal emitting at 1329 nm. Intracavity sum-frequency mixing at 1063 and 1329 nm was then realized in a LiB3O5 (LBO) crystal to reach the yellow-orange radiation. We obtained a CW output power of 494 mW at 591 nm with a pump laser diode emitting 17.8 W at 808 nm.

The evolution of high summit metabolism and cold tolerance in birds and its impact on present-day distributions.

PubMed

Swanson, David L; Garland, Theodore

2009-01-01

Summit metabolic rate (M(sum), maximum cold-induced metabolic rate) is positively correlated with cold tolerance in birds, suggesting that high M(sum) is important for residency in cold climates. However, the phylogenetic distribution of high M(sum) among birds and the impact of its evolution on current distributions are not well understood. Two potential adaptive hypotheses might explain the phylogenetic distribution of high M(sum) among birds. The cold adaptation hypothesis contends that species wintering in cold climates should have higher M(sum) than species wintering in warmer climates. The flight adaptation hypothesis suggests that volant birds might be capable of generating high M(sum) as a byproduct of their muscular capacity for flight; thus, variation in M(sum) should be associated with capacity for sustained flight, one indicator of which is migration. We collected M(sum) data from the literature for 44 bird species and conducted both conventional and phylogenetically informed statistical analyses to examine the predictors of M(sum) variation. Significant phylogenetic signal was present for log body mass, log mass-adjusted M(sum), and average temperature in the winter range. In multiple regression models, log body mass, winter temperature, and clade were significant predictors of log M(sum). These results are consistent with a role for climate in determining M(sum) in birds, but also indicate that phylogenetic signal remains even after accounting for associations indicative of adaptation to winter temperature. Migratory strategy was never a significant predictor of log M(sum) in multiple regressions, a result that is not consistent with the flight adaptation hypothesis.

Nonlinear frequency conversion of radiation from a copper-vapor laser

NASA Astrophysics Data System (ADS)

Polunin, Iu. P.; Troitskii, V. O.

1987-11-01

The nonlinear frequency conversion of copper-vapor laser radiation in a KDP crystal was studied experimentally. Output powers of 600 mW and 120 mW were obtained at wavelengths of 271 nm (the sum frequency) and 289 nm (the second harmonic of the yellow line), respectively. The conversion efficiency in both cases was about 3 percent; when selector losses were taken into accounted, the efficiency amounted to 5 percent.

Josephson A/D Converter Development.

DTIC Science & Technology

1981-10-01

by Zappe and A Landman [20]. They conclude that the simple model of the Josephson effect is applicable up to frequencies at least as high (a) as 300...GHz. B. Time-Domain Experiments 4ooF so The early high - frequency experiments with Josephson devices I .O suggested their use as very fast logic switches...exactly as for the phenomenological model . The tunneling pacitive current paths dominate the circuit at high frequencies . current is the sum of two

Advanced ACTPol Low-Frequency Array: Readout and Characterization of Prototype 27 and 39 GHz Transition Edge Sensors

NASA Astrophysics Data System (ADS)

Koopman, B. J.; Cothard, N. F.; Choi, S. K.; Crowley, K. T.; Duff, S. M.; Henderson, S. W.; Ho, S. P.; Hubmayr, J.; Gallardo, P. A.; Nati, F.; Niemack, M. D.; Simon, S. M.; Staggs, S. T.; Stevens, J. R.; Vavagiakis, E. M.; Wollack, E. J.

2018-05-01

Advanced ACTPol (AdvACT) is a third-generation polarization upgrade to the Atacama Cosmology Telescope, designed to observe the cosmic microwave background (CMB). AdvACT expands on the 90 and 150 GHz transition edge sensor (TES) bolometer arrays of the ACT Polarimeter (ACTPol), adding both high-frequency (HF, 150/230 GHz) and low-frequency (LF, 27/39 GHz) multichroic arrays. The addition of the high- and low-frequency detectors allows for the characterization of synchrotron and spinning dust emission at the low frequencies and foreground emission from galactic dust and dusty star-forming galaxies at the high frequencies. The increased spectral coverage of AdvACT will enable a wide range of CMB science, such as improving constraints on dark energy, the sum of the neutrino masses, and the existence of primordial gravitational waves. The LF array will be the final AdvACT array, replacing one of the MF arrays for a single season. Prior to the fabrication of the final LF detector array, we designed and characterized prototype TES bolometers. Detector geometries in these prototypes are varied in order to inform and optimize the bolometer designs for the LF array, which requires significantly lower noise levels and saturation powers (as low as {˜ } 1 pW) than the higher-frequency detectors. Here we present results from tests of the first LF prototype TES detectors for AdvACT, including measurements of the saturation power, critical temperature, thermal conductance, and time constants. We also describe the modifications to the time-division SQUID readout architecture compared to the MF and HF arrays.

Probing electronic and vibrational properties at the electrochemical interface using SFG spectroscopy: Methanol electro-oxidation on Pt(1 1 0)

NASA Astrophysics Data System (ADS)

Vidal, F.; Busson, B.; Tadjeddine, A.

2005-02-01

We report the study of methanol electro-oxidation on Pt(1 1 0) using infrared-visible sum-frequency generation (SFG) vibrational spectroscopy. The use of this technique enables to probe the vibrational and electronic properties of the interface simultaneously in situ. We have investigated the vibrational properties of the interface in the CO ads internal stretch spectral region (1700-2150 cm -1) over a wide range of potentials. The analysis of the evolution of the C-O stretch line shape, which is related to the interference between the vibrational and electronic parts of the non-linear response, with the potential allows us to show that the onset of bulk methanol oxidation corresponds to the transition from a negatively to a positively charged surface.

Stent-induced coronary artery stenosis characterized by multimodal nonlinear optical microscopy

NASA Astrophysics Data System (ADS)

Wang, Han-Wei; Simianu, Vlad; Locker, Mattew J.; Cheng, Ji-Xin; Sturek, Michael

2011-02-01

We demonstrate for the first time the applicability of multimodal nonlinear optical (NLO) microscopy to the interrogation of stented coronary arteries under different diet and stent deployment conditions. Bare metal stents and Taxus drug-eluting stents (DES) were placed in coronary arteries of Ossabaw pigs of control and atherogenic diet groups. Multimodal NLO imaging was performed to inspect changes in arterial structures and compositions after stenting. Sum frequency generation, one of the multimodalities, was used for the quantitative analysis of collagen content in the peristent and in-stent artery segments of both pig groups. Atherogenic diet increased lipid and collagen in peristent segments. In-stent segments showed decreased collagen expression in neointima compared to media. Deployment of DES in atheromatous arteries inhibited collagen expression in the arterial media.

OCEANFILMS-2: Representing coadsorption of saccharides in marine films and potential impacts on modeled marine aerosol chemistry

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

Burrows, Susannah M.; Gobrogge, Eric; Fu, Li

Here we show that the addition of chemical interactions of soluble polysaccharides with a surfactant monolayer improves agreement of modeled sea spray chemistry with observed marine aerosol chemistry. In particular, the fraction of hydroxyl functional groups in modeled sea spray organic matter is increased, improving agreement with FTIR observations of marine aerosol composition. The overall organic fraction of submicron sea spray also increases, allowing organic mass fractions in the range 0.5 – 0.7 for submicron sea spray particles over highly active phytoplankton blooms. We show results from Sum Frequency Generation (SFG) experiments that support the modeling approach, by demonstrating thatmore » soluble polysaccharides can strongly adsorb to a lipid monolayer via columbic interactions under appropriate conditions.« less

A Novel Noncircular MUSIC Algorithm Based on the Concept of the Difference and Sum Coarray.

PubMed

Chen, Zhenhong; Ding, Yingtao; Ren, Shiwei; Chen, Zhiming

2018-01-25

In this paper, we propose a vectorized noncircular MUSIC (VNCM) algorithm based on the concept of the coarray, which can construct the difference and sum (diff-sum) coarray, for direction finding of the noncircular (NC) quasi-stationary sources. Utilizing both the NC property and the concept of the Khatri-Rao product, the proposed method can be applied to not only the ULA but also sparse arrays. In addition, we utilize the quasi-stationary characteristic instead of the spatial smoothing method to solve the coherent issue generated by the Khatri-Rao product operation so that the available degree of freedom (DOF) of the constructed virtual array will not be reduced by half. Compared with the traditional NC virtual array obtained in the NC MUSIC method, the diff-sum coarray achieves a higher number of DOFs as it comprises both the difference set and the sum set. Due to the complementarity between the difference set and the sum set for the coprime array, we choose the coprime array with multiperiod subarrays (CAMpS) as the array model and summarize the properties of the corresponding diff-sum coarray. Furthermore, we develop a diff-sum coprime array with multiperiod subarrays (DsCAMpS) whose diff-sum coarray has a higher DOF. Simulation results validate the effectiveness of the proposed method and the high DOF of the diff-sum coarray.

A Novel Noncircular MUSIC Algorithm Based on the Concept of the Difference and Sum Coarray

PubMed Central

Chen, Zhenhong; Ding, Yingtao; Chen, Zhiming

2018-01-01

In this paper, we propose a vectorized noncircular MUSIC (VNCM) algorithm based on the concept of the coarray, which can construct the difference and sum (diff–sum) coarray, for direction finding of the noncircular (NC) quasi-stationary sources. Utilizing both the NC property and the concept of the Khatri–Rao product, the proposed method can be applied to not only the ULA but also sparse arrays. In addition, we utilize the quasi-stationary characteristic instead of the spatial smoothing method to solve the coherent issue generated by the Khatri–Rao product operation so that the available degree of freedom (DOF) of the constructed virtual array will not be reduced by half. Compared with the traditional NC virtual array obtained in the NC MUSIC method, the diff–sum coarray achieves a higher number of DOFs as it comprises both the difference set and the sum set. Due to the complementarity between the difference set and the sum set for the coprime array, we choose the coprime array with multiperiod subarrays (CAMpS) as the array model and summarize the properties of the corresponding diff–sum coarray. Furthermore, we develop a diff–sum coprime array with multiperiod subarrays (DsCAMpS) whose diff–sum coarray has a higher DOF. Simulation results validate the effectiveness of the proposed method and the high DOF of the diff–sum coarray. PMID:29370138

Diagrams for the Free Energy and Density Weight Factors of the Ising Models.

DTIC Science & Technology

1983-01-01

sum to zero . The associated R. A. Farrell, T. Morita, and P. H. E. Meijer, "Cluster Expan- also, "_ ratum: New Generating Functions and Results for the...given for the cubic lattices. We employ a theorem that states that a certain sum of diagrams is zero in order to obtain the density-dependent weight...these diagrams are given for the cubic lattices. We employ a theorem that states that a certain sum of diagrams is zero in order to obtain the density

A fast summation method for oscillatory lattice sums

NASA Astrophysics Data System (ADS)

Denlinger, Ryan; Gimbutas, Zydrunas; Greengard, Leslie; Rokhlin, Vladimir

2017-02-01

We present a fast summation method for lattice sums of the type which arise when solving wave scattering problems with periodic boundary conditions. While there are a variety of effective algorithms in the literature for such calculations, the approach presented here is new and leads to a rigorous analysis of Wood's anomalies. These arise when illuminating a grating at specific combinations of the angle of incidence and the frequency of the wave, for which the lattice sums diverge. They were discovered by Wood in 1902 as singularities in the spectral response. The primary tools in our approach are the Euler-Maclaurin formula and a steepest descent argument. The resulting algorithm has super-algebraic convergence and requires only milliseconds of CPU time.

The sumLINK statistic for genetic linkage analysis in the presence of heterogeneity.

PubMed

Christensen, G B; Knight, S; Camp, N J

2009-11-01

We present the "sumLINK" statistic--the sum of multipoint LOD scores for the subset of pedigrees with nominally significant linkage evidence at a given locus--as an alternative to common methods to identify susceptibility loci in the presence of heterogeneity. We also suggest the "sumLOD" statistic (the sum of positive multipoint LOD scores) as a companion to the sumLINK. sumLINK analysis identifies genetic regions of extreme consistency across pedigrees without regard to negative evidence from unlinked or uninformative pedigrees. Significance is determined by an innovative permutation procedure based on genome shuffling that randomizes linkage information across pedigrees. This procedure for generating the empirical null distribution may be useful for other linkage-based statistics as well. Using 500 genome-wide analyses of simulated null data, we show that the genome shuffling procedure results in the correct type 1 error rates for both the sumLINK and sumLOD. The power of the statistics was tested using 100 sets of simulated genome-wide data from the alternative hypothesis from GAW13. Finally, we illustrate the statistics in an analysis of 190 aggressive prostate cancer pedigrees from the International Consortium for Prostate Cancer Genetics, where we identified a new susceptibility locus. We propose that the sumLINK and sumLOD are ideal for collaborative projects and meta-analyses, as they do not require any sharing of identifiable data between contributing institutions. Further, loci identified with the sumLINK have good potential for gene localization via statistical recombinant mapping, as, by definition, several linked pedigrees contribute to each peak.

Use of a genetic algorithm for the analysis of eye movements from the linear vestibulo-ocular reflex

NASA Technical Reports Server (NTRS)

Shelhamer, M.

2001-01-01

It is common in vestibular and oculomotor testing to use a single-frequency (sine) or combination of frequencies [sum-of-sines (SOS)] stimulus for head or target motion. The resulting eye movements typically contain a smooth tracking component, which follows the stimulus, in which are interspersed rapid eye movements (saccades or fast phases). The parameters of the smooth tracking--the amplitude and phase of each component frequency--are of interest; many methods have been devised that attempt to identify and remove the fast eye movements from the smooth. We describe a new approach to this problem, tailored to both single-frequency and sum-of-sines stimulation of the human linear vestibulo-ocular reflex. An approximate derivative is used to identify fast movements, which are then omitted from further analysis. The remaining points form a series of smooth tracking segments. A genetic algorithm is used to fit these segments together to form a smooth (but disconnected) wave form, by iteratively removing biases due to the missing fast phases. A genetic algorithm is an iterative optimization procedure; it provides a basis for extending this approach to more complex stimulus-response situations. In the SOS case, the genetic algorithm estimates the amplitude and phase values of the component frequencies as well as removing biases.

Finite-frequency tomography using adjoint methods-Methodology and examples using membrane surface waves

NASA Astrophysics Data System (ADS)

Tape, Carl; Liu, Qinya; Tromp, Jeroen

2007-03-01

We employ adjoint methods in a series of synthetic seismic tomography experiments to recover surface wave phase-speed models of southern California. Our approach involves computing the Fréchet derivative for tomographic inversions via the interaction between a forward wavefield, propagating from the source to the receivers, and an `adjoint' wavefield, propagating from the receivers back to the source. The forward wavefield is computed using a 2-D spectral-element method (SEM) and a phase-speed model for southern California. A `target' phase-speed model is used to generate the `data' at the receivers. We specify an objective or misfit function that defines a measure of misfit between data and synthetics. For a given receiver, the remaining differences between data and synthetics are time-reversed and used as the source of the adjoint wavefield. For each earthquake, the interaction between the regular and adjoint wavefields is used to construct finite-frequency sensitivity kernels, which we call event kernels. An event kernel may be thought of as a weighted sum of phase-specific (e.g. P) banana-doughnut kernels, with weights determined by the measurements. The overall sensitivity is simply the sum of event kernels, which defines the misfit kernel. The misfit kernel is multiplied by convenient orthonormal basis functions that are embedded in the SEM code, resulting in the gradient of the misfit function, that is, the Fréchet derivative. A non-linear conjugate gradient algorithm is used to iteratively improve the model while reducing the misfit function. We illustrate the construction of the gradient and the minimization algorithm, and consider various tomographic experiments, including source inversions, structural inversions and joint source-structure inversions. Finally, we draw connections between classical Hessian-based tomography and gradient-based adjoint tomography.

Fluoroethylene Carbonate as a Directing Agent in Amorphous Silicon Anodes: Electrolyte Interface Structure Probed by Sum Frequency Vibrational Spectroscopy and Ab Initio Molecular Dynamics.

PubMed

Horowitz, Yonatan; Han, Hui-Ling; Soto, Fernando A; Ralston, Walter T; Balbuena, Perla B; Somorjai, Gabor A

2018-02-14

Fluorinated compounds are added to carbonate-based electrolyte solutions in an effort to create a stable solid electrolyte interphase (SEI). The SEI mitigates detrimental electrolyte redox reactions taking place on the anode's surface upon applying a potential in order to charge (discharge) the lithium (Li) ion battery. The need for a stable SEI is dire when the anode material is silicon as silicon cracks due to its expansion and contraction upon lithiation and delithiation (charge-discharge) cycles, consequently limiting the cyclability of a silicon-based battery. Here we show the molecular structures for ethylene carbonate (EC): fluoroethylene carbonate (FEC) solutions on silicon surfaces by sum frequency generation (SFG) vibrational spectroscopy, which yields vibrational spectra of molecules at interfaces and by ab initio molecular dynamics (AIMD) simulations at open circuit potential. Our AIMD simulations and SFG spectra indicate that both EC and FEC adsorb to the amorphous silicon (a-Si) through their carbonyl group (C═O) oxygen atom with no further desorption. We show that FEC additives induce the reorientation of EC molecules to create an ordered, up-right orientation of the electrolytes on the Si surface. We suggest that this might be helpful for Li diffusion under applied potential. Furthermore, FEC becomes the dominant species at the a-Si surface as the FEC concentration increases above 20 wt %. Our finding at open circuit potential can now initiate additive design to not only act as a sacrificial compound but also to produce a better suited SEI for the use of silicon anodes in the Li-ion vehicular industry.

Doubly resonant three-wave-mixing spectroscopy of a chiral coupled-chromophore system in solution: coherent two-dimensional optical activity spectroscopy.

PubMed

Cheon, Sangheon; Lee, Hochan; Choi, Jun-Ho; Cho, Minhaeng

2007-02-07

Theoretical descriptions of doubly resonant two-dimensional (2D) sum-frequency-generation (SFG) and difference-frequency-generation (DFG) spectroscopies of coupled-chromophore systems are presented. Despite that each electronic or vibrational chromophore is achiral, the interaction-induced chirality of a coupled multichromophore system in solution can be measured by using the doubly resonant 2D three-wave-mixing (3WM) spectroscopic method. An electronically coupled dimer, where each monomer is modeled as a simple two-level system, can have nonvanishing SFG (or DFG) properties, e.g., susceptibility in frequency domain or nonlinear response function in time domain, if the induced dipole vector of the dimer is not orthogonal to the vector product of the two monomer electronic transition dipole vectors. In order to demonstrate that these 2D 3WM spectroscopic methods can be used to determine the solution structure of a polypeptide, the authors carried out quantum chemistry calculations for an alanine dipeptide and obtained first- and second-order dipole derivatives associated with the amide I vibrational transitions of the dipeptide. It is shown that the numerically simulated 2D IR-IR SFG spectrum is highly sensitive to the dipeptide secondary structure and provides rich information on the one- and two-exciton states. It is believed that the theoretically proposed doubly resonant 2D 3WM spectroscopy, which can be considered to be an optical activity spectroscopy, will be of use in studying both structural and dynamical aspects of coupled multichromophore systems, such as proteins, nucleic acids, nanoparticle aggregates etc.

Accounting for genotype uncertainty in the estimation of allele frequencies in autopolyploids.

PubMed

Blischak, Paul D; Kubatko, Laura S; Wolfe, Andrea D

2016-05-01

Despite the increasing opportunity to collect large-scale data sets for population genomic analyses, the use of high-throughput sequencing to study populations of polyploids has seen little application. This is due in large part to problems associated with determining allele copy number in the genotypes of polyploid individuals (allelic dosage uncertainty-ADU), which complicates the calculation of important quantities such as allele frequencies. Here, we describe a statistical model to estimate biallelic SNP frequencies in a population of autopolyploids using high-throughput sequencing data in the form of read counts. We bridge the gap from data collection (using restriction enzyme based techniques [e.g. GBS, RADseq]) to allele frequency estimation in a unified inferential framework using a hierarchical Bayesian model to sum over genotype uncertainty. Simulated data sets were generated under various conditions for tetraploid, hexaploid and octoploid populations to evaluate the model's performance and to help guide the collection of empirical data. We also provide an implementation of our model in the R package polyfreqs and demonstrate its use with two example analyses that investigate (i) levels of expected and observed heterozygosity and (ii) model adequacy. Our simulations show that the number of individuals sampled from a population has a greater impact on estimation error than sequencing coverage. The example analyses also show that our model and software can be used to make inferences beyond the estimation of allele frequencies for autopolyploids by providing assessments of model adequacy and estimates of heterozygosity. © 2015 John Wiley & Sons Ltd.

Tachometer

NASA Technical Reports Server (NTRS)

Nola, F. J. (Inventor)

1977-01-01

A tachometer in which sine and cosine signals responsive to the angular position of a shaft as it rotates are each multiplied by like, sine or cosine, functions of a carrier signal, the products summed, and the resulting frequency signal converted to fixed height, fixed width pulses of a like frequency. These pulses are then integrated, and the resulting dc output is an indication of shaft speed.

Low-Speed Wind Tunnel Flow Quality Determination

DTIC Science & Technology

2011-09-01

Traverse Motor The traverse motor for the BiSlide is a NEMA Type 34D, Slo-Syn® stepper motor, allowing the operator to position items in the test... norm (w1)^2/sum(w1)^2,’k’); %% plot on log-log scale ylabel(‘RMS Power/Frequency (V^2)’) xlabel(‘Frequency (Hz)’) title(‘Power Spectrum’) end

An analog integrated circuit beamformer for high-frequency medical ultrasound imaging.

PubMed

Gurun, Gokce; Zahorian, Jaime S; Sisman, Alper; Karaman, Mustafa; Hasler, Paul E; Degertekin, F Levent

2012-10-01

We designed and fabricated a dynamic receive beamformer integrated circuit (IC) in 0.35-μm CMOS technology. This beamformer IC is suitable for integration with an annular array transducer for high-frequency (30-50 MHz) intravascular ultrasound (IVUS) imaging. The beamformer IC consists of receive preamplifiers, an analog dynamic delay-and-sum beamformer, and buffers for 8 receive channels. To form an analog dynamic delay line we designed an analog delay cell based on the current-mode first-order all-pass filter topology, as the basic building block. To increase the bandwidth of the delay cell, we explored an enhancement technique on the current mirrors. This technique improved the overall bandwidth of the delay line by a factor of 6. Each delay cell consumes 2.1-mW of power and is capable of generating a tunable time delay between 1.75 ns to 2.5 ns. We successfully integrated the fabricated beamformer IC with an 8-element annular array. Experimental test results demonstrated the desired buffering, preamplification and delaying capabilities of the beamformer.

High harmonic emission from a superposition of multiple unrelated frequency fields.

PubMed

Siegel, T; Torres, R; Hoffmann, D J; Brugnera, L; Procino, I; Zaïr, A; Underwood, Jonathan G; Springate, E; Turcu, I C E; Chipperfield, L E; Marangos, J P

2010-03-29

We report observations and analysis of high harmonic generation driven by a superposition of fields at 1290 nm and 780 nm. These fields are not commensurate in frequency and the superposition leads to an increase in the yield of the mid-plateau harmonics of more than two orders of magnitude compared to using the 1290 nm field alone. Significant extension of the cut-off photon energy is seen even by adding only a small amount of the 780 nm field. These observations are explained by calculations performed in the strong field approximation. Most importantly we find that enhancement is found to arise as a consequence of both increased ionization in the sum-field and modification of the electron trajectories leading to an earlier return time. The enhanced yield even when using modest intensity fields of 5 x 10(13) Wcm(-2) is extended to the 80 eV range and is a promising route to provide a greater photon number for applications in XUV imaging and time-resolved experiments at a high repetition rate.

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

Zhang, Libing; Lu, Zhou; Velarde Ruiz Esparza, Luis A.

Here we reported the first sub-wavenumber high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS) study on both the C-H and O-H region spectra of crystalline cellulose. HR-BB-SFG-VS has about 10 times better resolution than the conventional scanning SFG-VS and is known to be able to measure the intrinsic spectral lineshape and to resolve much more spectral details. With HR-BB-SFG-VS, we found that in cellulose from different sources, including Avicel and cellulose crystals isolated from algae Valonia (Iα) and tunicates (Iβ), the spectral signatures in the OH regions were unique for different allomorphs, i.e. Iα and Iβ, while the spectral signaturesmore » in the C-H regions varied in all samples examined. Even though the origin of the different behaviors of the crystalline cellulose in the O-H and C-H vibrational frequency regions is yet to be correlated to the structure of cellulose, these results provided new spectroscopic methods and opportunities to classify and understand the basic crystalline structure, as well as variations, in polymorphism of the crystalline cellulose structure.« less

A theoretical description of the polarization dependence of the sum frequency generation spectroscopy of the water/vapor interface

NASA Astrophysics Data System (ADS)

Perry, Angela; Neipert, Christine; Kasprzyk, Christina Ridley; Green, Tony; Space, Brian; Moore, Preston B.

2005-10-01

An improved time correlation function (TCF) description of sum frequency generation (SFG) spectroscopy was developed and applied to theoretically describing the spectroscopy of the ambient water/vapor interface. A more general TCF expression than was published previously is presented—it is valid over the entire vibrational spectrum for both the real and imaginary parts of the signal. Computationally, earlier time correlation function approaches were limited to short correlation times that made signal processing challenging. Here, this limitation is overcome, and well-averaged spectra are presented for the three independent polarization conditions that are possible for electronically nonresonant SFG. The theoretical spectra compare quite favorably in shape and relative magnitude to extant experimental results in the O H stretching region of water for all polarization geometries. The methodological improvements also allow the calculation of intermolecular SFG spectra. While the intermolecular spectrum of bulk water shows relatively little structure, the interfacial spectra (for polarizations that are sensitive to dipole derivatives normal to the interface—SSP and PPP) show a well-defined intermolecular mode at 875cm-1 that is comparable in intensity to the rest of the intermolecular structure, and has an intensity that is approximately one-sixth of the magnitude of the intense free OH stretching peak. Using instantaneous normal mode methods, the resonance is shown to be due to a wagging mode localized on a single water molecule, almost parallel to the interface, with two hydrogens displaced normal to the interface, and the oxygen anchored in the interface. We have also uncovered the origin of another intermolecular mode at 95cm-1 for the SSP and PPP spectra, and at 220cm-1 for the SPS spectra. These resonances are due to hindered translations perpendicular to the interface for the SSP and PPP spectra, and translations parallel to the interface for the SPS spectra. Further, by examining the real and imaginary parts of the SFG signal, several resonances are shown to be due to a single spectroscopic species while the "donor" OH region is shown to consist of three distinct species—consistent with an earlier experimental analysis.

Density functional theory-based simulations of sum frequency generation spectra involving methyl stretching vibrations: effect of the molecular model on the deduced molecular orientation and comparison with an analytical approach.

PubMed

Cecchet, F; Lis, D; Caudano, Y; Mani, A A; Peremans, A; Champagne, B; Guthmuller, J

2012-03-28

The knowledge of the first hyperpolarizability tensor elements of molecular groups is crucial for a quantitative interpretation of the sum frequency generation (SFG) activity of thin organic films at interfaces. Here, the SFG response of the terminal methyl group of a dodecanethiol (DDT) monolayer has been interpreted on the basis of calculations performed at the density functional theory (DFT) level of approximation. In particular, DFT calculations have been carried out on three classes of models for the aliphatic chains. The first class of models consists of aliphatic chains, containing from 3 to 12 carbon atoms, in which only one methyl group can freely vibrate, while the rest of the chain is frozen by a strong overweight of its C and H atoms. This enables us to localize the probed vibrational modes on the methyl group. In the second class, only one methyl group is frozen, while the entire remaining chain is allowed to vibrate. This enables us to analyse the influence of the aliphatic chain on the methyl stretching vibrations. Finally, the dodecanethiol (DDT) molecule is considered, for which the effects of two dielectrics, i.e. n-hexane and n-dodecane, are investigated. Moreover, DDT calculations are also carried out by using different exchange-correlation (XC) functionals in order to assess the DFT approximations. Using the DFT IR vectors and Raman tensors, the SFG spectrum of DDT has been simulated and the orientation of the methyl group has then been deduced and compared with that obtained using an analytical approach based on a bond additivity model. This analysis shows that when using DFT molecular properties, the predicted orientation of the terminal methyl group tends to converge as a function of the alkyl chain length and that the effects of the chain as well as of the dielectric environment are small. Instead, a more significant difference is observed when comparing the DFT-based results with those obtained from the analytical approach, thus indicating the importance of a quantum chemical description of the hyperpolarizability tensor elements of the methyl group. © 2012 IOP Publishing Ltd

Simple data-smoothing and noise-suppression technique

NASA Technical Reports Server (NTRS)

Duty, R. L.

1970-01-01

Algorithm, based on the Borel method of summing divergent sequences, is used for smoothing noisy data where knowledge of frequency content is not required. Technique's effectiveness is demonstrated by a series of graphs.

Adaptive ground implemented phase array

NASA Technical Reports Server (NTRS)

Spearing, R. E.

1973-01-01

The simulation of an adaptive ground implemented phased array of five antenna elements is reported for a very high frequency system design that is tolerant to the radio frequency interference environment encountered by a tracking data relay satellite. Signals originating from satellites are received by the VHF ring array and both horizontal and vertical polarizations from each of the five elements are multiplexed and transmitted down to ground station. A panel on the transmitting end of the simulation chamber contains up to 10 S-band RFI sources along with the desired signal to simulate the dynamic relationship between user and TDRS. The 10 input channels are summed, and desired and interference signals are separated and corrected until the resultant sum signal-to-interference ratio is maximized. Testing performed with this simulation equipment demonstrates good correlation between predicted and actual results.

Real-Time Fourier Synthesis of Ensembles with Timbral Interpolation

NASA Astrophysics Data System (ADS)

Haken, Lippold

1990-01-01

In Fourier synthesis, natural musical sounds are produced by summing time-varying sinusoids. Sounds are analyzed to find the amplitude and frequency characteristics for their sinusoids; interpolation between the characteristics of several sounds is used to produce intermediate timbres. An ensemble can be synthesized by summing all the sinusoids for several sounds, but in practice it is difficult to perform such computations in real time. To solve this problem on inexpensive hardware, it is useful to take advantage of the masking effects of the auditory system. By avoiding the computations for perceptually unimportant sinusoids, and by employing other computation reduction techniques, a large ensemble may be synthesized in real time on the Platypus signal processor. Unlike existing computation reduction techniques, the techniques described in this thesis do not sacrifice independent fine control over the amplitude and frequency characteristics of each sinusoid.

Energy storage cell impedance measuring apparatus, methods and related systems

DOEpatents

Morrison, John L.; Morrison, William H.; Christophersen, Jon P.

2017-12-26

Energy storage cell impedance testing devices, circuits, and related methods are disclosed. An energy storage cell impedance measuring device includes a sum of sinusoids (SOS) current excitation circuit including differential current sources configured to isolate a ground terminal of the differential current sources from a positive terminal and a negative terminal of an energy storage cell. A method includes applying an SOS signal comprising a sum of sinusoidal current signals to the energy storage cell with the SOS current excitation circuit, each of the sinusoidal current signals oscillating at a different one of a plurality of different frequencies. The method also includes measuring an electrical signal at a positive terminal and a negative terminal of the energy storage cell, and computing an impedance of the energy storage cell at each of the plurality of different frequencies using the measured electrical signal.

Energy-Based Tetrahedron Sensor for High-Temperature, High-Pressure Environments

NASA Technical Reports Server (NTRS)

Gee, Kent L.; Sommerfeldt, Scott D.; Blotter, Jonathan D.

2012-01-01

An acoustic energy-based probe has been developed that incorporates multiple acoustic sensing elements in order to obtain the acoustic pressure and three-dimensional acoustic particle velocity. With these quantities, the user can obtain various energy-based quantities, including acoustic energy density, acoustic intensity, and acoustic impedance. In this specific development, the probe has been designed to operate in an environment characterized by high temperatures and high pressures as is found in the close vicinity of rocket plumes. Given these capabilities, the probe is designed to be used to investigate the acoustic conditions within the plume of a rocket engine or jet engine to facilitate greater understanding of the noise generation mechanisms in those plumes. The probe features sensors mounted inside a solid sphere. The associated electronics for the probe are contained within the sphere and the associated handle for the probe. More importantly, the design of the probe has desirable properties that reduce the bias errors associated with determining the acoustic pressure and velocity using finite sum and difference techniques. The diameter of the probe dictates the lower and upper operating frequencies for the probe, where accurate measurements can be acquired. The current probe design implements a sphere diameter of 1 in. (2.5 cm), which limits the upper operating frequency to about 4.5 kHz. The sensors are operational up to much higher frequencies, and could be used to acquire pressure data at higher frequencies, but the energy-based measurements are limited to that upper frequency. Larger or smaller spherical probes could be designed to go to lower or higher frequency range

The Role of Electrode-Catalyst Interactions in Enabling Efficient CO2 Reduction with Mo(bpy)(CO)4 As Revealed by Vibrational Sum-Frequency Generation Spectroscopy.

PubMed

Neri, Gaia; Donaldson, Paul M; Cowan, Alexander J

2017-10-04

Group 6 metal carbonyl complexes ([M(bpy)(CO) 4 ], M = Cr, Mo, W) are potentially promising CO 2 reduction electrocatalysts. However, catalytic activity onsets at prohibitively negative potentials and is highly dependent on the nature of the working electrode. Here we report in situ vibrational SFG (VSFG) measurements of the electrocatalyst [Mo(bpy)(CO) 4 ] at platinum and gold electrodes. The greatly improved onset potential for electrocatalytic CO 2 reduction at gold electrodes is due to the formation of the catalytically active species [Mo(bpy)(CO) 3 ] 2- via a second pathway at more positive potentials, likely avoiding the need for the generation of [Mo(bpy)(CO) 4 ] 2- . VSFG studies demonstrate that the strength of the interaction between initially generated [Mo(bpy)(CO) 4 ] •- and the electrode is critical in enabling the formation of the active catalyst via the low energy pathway. By careful control of electrode material, solvent and electrolyte salt, it should therefore be possible to attain levels of activity with group 6 complexes equivalent to their much more widely studied group 7 analogues.

Aeroacoustic Analysis of Turbofan Noise Generation

NASA Technical Reports Server (NTRS)

Meyer, Harold D.; Envia, Edmane

1996-01-01

This report provides an updated version of analytical documentation for the V072 Rotor Wake/Stator Interaction Code. It presents the theoretical derivation of the equations used in the code and, where necessary, it documents the enhancements and changes made to the original code since its first release. V072 is a package of FORTRAN computer programs which calculate the in-duct acoustic modes excited by a fan/stator stage operating in a subsonic mean flow. Sound is generated by the stator vanes interacting with the mean wakes of the rotor blades. In this updated version, only the tonal noise produced at the blade passing frequency and its harmonics, is described. The broadband noise component analysis, which was part of the original report, is not included here. The code provides outputs of modal pressure and power amplitudes generated by the rotor-wake/stator interaction. The rotor/stator stage is modeled as an ensemble of blades and vanes of zero camber and thickness enclosed within an infinite hard-walled annular duct. The amplitude of each propagating mode is computed and summed to obtain the harmonics of sound power flux within the duct for both upstream and downstream propagating modes.

Algorithms to evaluate multiple sums for loop computations

NASA Astrophysics Data System (ADS)

Anzai, C.; Sumino, Y.

2013-03-01

We present algorithms to evaluate two types of multiple sums, which appear in higher-order loop computations. We consider expansions of a generalized hyper-geometric-type sums, sum _{n_1,\\cdots,n_N} Γ ({a}_1\\cdot {n}+c_1) Γ ({a}_2\\cdot {n}+c_2) \\cdots Γ ({a}_P\\cdot {n}+c_P) / Γ ({b_1\\cdot {n}+d_1) Γ ({b}_2\\cdot {n}+d_2) \\cdots Γ ({b}_Q\\cdot {n}+d_Q) } x_1^{n_1}\\cdots x_N^{n_N} with {a}_i \\cdot {n} = sum _{j=1}^N a_{ij}n_j, etc., in a small parameter ɛ around rational values of ci,di's. Type I sum corresponds to the case where, in the limit ɛ → 0, the summand reduces to a rational function of nj's times x_1^{n_1}\\cdots x_N^{n_N}; ci,di's can depend on an external integer index. Type II sum is a double sum (N = 2), where ci, di's are half-integers or integers as ɛ → 0 and xi = 1; we consider some specific cases where at most six Γ functions remain in the limit ɛ → 0. The algorithms enable evaluations of arbitrary expansion coefficients in ɛ in terms of Z-sums and multiple polylogarithms (generalized multiple zeta values). We also present applications of these algorithms. In particular, Type I sums can be used to generate a new class of relations among generalized multiple zeta values. We provide a Mathematica package, in which these algorithms are implemented.

Apparatus and method for detecting and measuring changes in linear relationships between a number of high frequency signals

DOEpatents

Bittner, J.W.; Biscardi, R.W.

1991-03-19

An electronic measurement circuit is disclosed for high speed comparison of the relative amplitudes of a predetermined number of electrical input signals independent of variations in the magnitude of the sum of the signals. The circuit includes a high speed electronic switch that is operably connected to receive on its respective input terminals one of said electrical input signals and to have its common terminal serve as an input for a variable-gain amplifier-detector circuit that is operably connected to feed its output to a common terminal of a second high speed electronic switch. The respective terminals of the second high speed electronic switch are operably connected to a plurality of integrating sample and hold circuits, which in turn have their outputs connected to a summing logic circuit that is operable to develop first, second and third output voltages, the first output voltage being proportional to a predetermined ratio of sums and differences between the compared input signals, the second output voltage being proportional to a second summed ratio of predetermined sums and differences between said input signals, and the third output voltage being proportional to the sum of signals to the summing logic circuit. A servo system that is operably connected to receive said third output signal and compare it with a reference voltage to develop a slowly varying feedback voltage to control the variable-gain amplifier in said common amplifier-detector circuit in order to make said first and second output signals independent of variations in the magnitude of the sum of said input signals. 2 figures.

Apparatus and method for detecting and measuring changes in linear relationships between a number of high frequency signals

DOEpatents

Bittner, John W.; Biscardi, Richard W.

1991-01-01

An electronic measurement circuit for high speed comparison of the relative amplitudes of a predetermined number of electrical input signals independent of variations in the magnitude of the sum of the signals. The circuit includes a high speed electronic switch that is operably connected to receive on its respective input terminals one of said electrical input signals and to have its common terminal serve as an input for a variable-gain amplifier-detector circuit that is operably connected to feed its output to a common terminal of a second high speed electronic switch. The respective terminals of the second high speed electronic switch are operably connected to a plurality of integrating sample and hold circuits, which in turn have their outputs connected to a summing logic circuit that is operable to develop first, second and third output voltages, the first output voltage being proportional to a predetermined ratio of sums and differences between the compared input signals, the second output voltage being proportional to a second summed ratio of predetermined sums and differences between said input signals, and the third output voltage being proportional to the sum of signals to the summing logic circuit. A servo system that is operably connected to receive said third output signal and compare it with a reference voltage to develop a slowly varying feedback voltage to control the variable-gain amplifier in said common amplifier-detector circuit in order to make said first and second output signals independent of variations in the magnitude of the sum of said input signals.

Superalgebraically convergent smoothly windowed lattice sums for doubly periodic Green functions in three-dimensional space

PubMed Central

Bruno, Oscar P.; Turc, Catalin; Venakides, Stephanos

2016-01-01

This work, part I in a two-part series, presents: (i) a simple and highly efficient algorithm for evaluation of quasi-periodic Green functions, as well as (ii) an associated boundary-integral equation method for the numerical solution of problems of scattering of waves by doubly periodic arrays of scatterers in three-dimensional space. Except for certain ‘Wood frequencies’ at which the quasi-periodic Green function ceases to exist, the proposed approach, which is based on smooth windowing functions, gives rise to tapered lattice sums which converge superalgebraically fast to the Green function—that is, faster than any power of the number of terms used. This is in sharp contrast to the extremely slow convergence exhibited by the lattice sums in the absence of smooth windowing. (The Wood-frequency problem is treated in part II.) This paper establishes rigorously the superalgebraic convergence of the windowed lattice sums. A variety of numerical results demonstrate the practical efficiency of the proposed approach. PMID:27493573

Cytotoxicity of diesel engine exhaust among the Chinese occupational population: a complement of cytokinesis-block micronucleus cytome.

PubMed

Zhang, Xiao; Xiao, Xinhua; Duan, Huawei; Gao, Feng; Li, Yuanyuan; Niu, Yong; Gao, Weimin; Wang, Haisheng; Yu, Shanfa; Zheng, Yuxin

2016-01-01

Diesel engine exhaust (DEE), a ubiquitous environmental pollutant, has been associated with adverse health effects. Revelation of cellular and molecular changes is critical for understanding environmental exposure-related diseases. Although the molecular-level effects of DEE exposure have been investigated, whether it is associated with aberrant changes at cellular level is largely unknown at the population level. In the present study, we measured urinary concentrations of 6 mono-hydroxylated PAHs (OH-PAHs) and cytotoxicity-related endpoints including apoptosis and necrosis frequencies, and nuclear division cytotoxicity index (NDCI) in peripheral blood lymphocytes (PBLs) of 79 DEE-exposed workers and 59 non-DEE-exposed workers. We found that DEE-exposed workers had significantly higher necrosis frequency and lower NDCI than did non-DEE-exposed workers (both p < 0.001). In all study subjects and nonsmoking workers, urinary summed OH-PAHs was associated with increased necrosis frequency and reduced NDCI. In nonsmoking workers, an interquartile range increase in urinary summed OH-PAHs was associated with 105.03% increase in necrosis frequency and 8.70% decrease in NDCI. Taking advantage of the previous measure of micronucleus frequency, we observed that micronucleus frequency was positively correlated with apoptosis and necrosis frequencies (r = 0.277, p = 0.047 and r = 0.452, p = 0.001, respectively) and negatively correlated with NDCI (r = -0.477, p < 0.001). In conclusion, our results suggested that DEE exposure was associated with increased necrosis frequency and further with reduced NDCI in PBLs, providing evidence of DEE exposure-induced cytotoxicity in humans.

EMR Gage Would Measure Coal Thickness Accurately

NASA Technical Reports Server (NTRS)

King, J. D.; Rollwitz, W. L.

1982-01-01

Laboratory tests indicate electron magnetic resonance (EMR) would be effective in measuring thickness of coal overlying rock substrate. In prototype dual-frequency EMR system, Sample is irradiated by two radio frequencies. Signals are mixed, producing sum and difference output frequencies that are detected by receiver. Magnetic field is varied to scan resonant spot through sample. In system designed for field use, electromagnet is U-shaped, so that sample can be adjacent to, rather than inside the probe. Same coil is used for transmitting and receiving.

A Survey of Scattering, Attenuation, and Size Spectra Studies of Bubble Layers and Plumes Beneath the Air-Sea Interface.

DTIC Science & Technology

1991-08-30

authors exploit the spatial resolution benefits of nonlinear bubble response (at the sum frequency) to the double frequency excitation by two...interaction method is the computational require- ment. Although exact runtimes for MIM are not given, and it apparently does have speed advantages over...Frequencies," J. Acoust. Soc. Am. 75(5), 1473-1477 (1984). (136] T.D.K. Ngoc, E.R. Franchi , and B.B. Adams, "Modeling of Ocean Surface Spectrum and

Rapid Transient Pressure Field Computations in the Nearfield of Circular Transducers using Frequency Domain Time-Space Decomposition

PubMed Central

Alles, E. J.; Zhu, Y.; van Dongen, K. W. A.; McGough, R. J.

2013-01-01

The fast nearfield method, when combined with time-space decomposition, is a rapid and accurate approach for calculating transient nearfield pressures generated by ultrasound transducers. However, the standard time-space decomposition approach is only applicable to certain analytical representations of the temporal transducer surface velocity that, when applied to the fast nearfield method, are expressed as a finite sum of products of separate temporal and spatial terms. To extend time-space decomposition such that accelerated transient field simulations are enabled in the nearfield for an arbitrary transducer surface velocity, a new transient simulation method, frequency domain time-space decomposition (FDTSD), is derived. With this method, the temporal transducer surface velocity is transformed into the frequency domain, and then each complex-valued term is processed separately. Further improvements are achieved by spectral clipping, which reduces the number of terms and the computation time. Trade-offs between speed and accuracy are established for FDTSD calculations, and pressure fields obtained with the FDTSD method for a circular transducer are compared to those obtained with Field II and the impulse response method. The FDTSD approach, when combined with the fast nearfield method and spectral clipping, consistently achieves smaller errors in less time and requires less memory than Field II or the impulse response method. PMID:23160476

Line Tunable Ultraviolet Laser

NASA Technical Reports Server (NTRS)

Walsh, Brian M.; Barnes, Norman P.

2004-01-01

An ultraviolet laser is demonstrated using a dual wavelength Nd:YAG oscillator, sum frequency and second harmonic process. Synchronous pulses at 1.052 and 1.319 micrometers are amplified, mixed and subsequently doubled, producing pulses at 0.293 micrometers.

Efficient use of bit planes in the generation of motion stimuli

NASA Technical Reports Server (NTRS)

Mulligan, Jeffrey B.; Stone, Leland S.

1988-01-01

The production of animated motion sequences on computer-controlled display systems presents a technical problem because large images cannot be transferred from disk storage to image memory at conventional frame rates. A technique is described in which a single base image can be used to generate a broad class of motion stimuli without the need for such memory transfers. This technique was applied to the generation of drifting sine-wave gratings (and by extension, sine wave plaids). For each drifting grating, sine and cosine spatial phase components are first reduced to 1 bit/pixel using a digital halftoning technique. The resulting pairs of 1-bit images are then loaded into pairs of bit planes of the display memory. To animate the patterns, the display hardware's color lookup table is modified on a frame-by-frame basis; for each frame the lookup table is set to display a weighted sum of the spatial sine and cosine phase components. Because the contrasts and temporal frequencies of the various components are mutually independent in each frame, the sine and cosine components can be counterphase modulated in temporal quadrature, yielding a single drifting grating. Using additional bit planes, multiple drifting gratings can be combined to form sine-wave plaid patterns. A large number of resultant plaid motions can be produced from a single image file because the temporal frequencies of all the components can be varied independently. For a graphics device having 8 bits/pixel, up to four drifting gratings may be combined, each having independently variable contrast and speed.

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

Engel, Edgar A., E-mail: eae32@cam.ac.uk; Needs, Richard J.; Monserrat, Bartomeu

Surface energies of hexagonal and cubic water ice are calculated using first-principles quantum mechanical methods, including an accurate description of anharmonic nuclear vibrations. We consider two proton-orderings of the hexagonal and cubic ice basal surfaces and three proton-orderings of hexagonal ice prism surfaces, finding that vibrations reduce the surface energies by more than 10%. We compare our vibrational densities of states to recent sum frequency generation absorption measurements and identify surface proton-orderings of experimental ice samples and the origins of characteristic absorption peaks. We also calculate zero point quantum vibrational corrections to the surface electronic band gaps, which range frommore » −1.2 eV for the cubic ice basal surface up to −1.4 eV for the hexagonal ice prism surface. The vibrational corrections to the surface band gaps are up to 12% smaller than for bulk ice.« less

Sodium temperature/wind lidar based on laser-diode-pumped Nd:YAG lasers deployed at Tromsø, Norway (69.6°N, 19.2°E).

PubMed

Kawahara, T D; Nozawa, S; Saito, N; Kawabata, T; Tsuda, T T; Wada, S

2017-06-12

An Nd:YAG laser-based sodium temperature/wind lidar was developed for the measurement of the northern polar mesosphere and lower thermosphere at Tromsø (69.6N, 19.2E), Norway. Coherent light at 589 nm is produced by sum frequency generation of 1064 nm and 1319 nm from two diode laser end-pumped pulsed Nd:YAG lasers. The output power is as high as 4W, with 4 mJ/pulse at 1000 Hz repetition rate. Five tilting Cassegrain telescopes enable us to make five-direction (zenith, north, south, east, west) observation for temperature and wind simultaneously. This highly stable laser system is first of its kind to operate virtually maintenance-free during the observation season (from late September to March) since 2010.

Hybrid finite element/waveguide mode analysis of passive RF devices

NASA Astrophysics Data System (ADS)

McGrath, Daniel T.

1993-07-01

A numerical solution for time-harmonic electromagnetic fields in two-port passive radio frequency (RF) devices has been developed, implemented in a computer code, and validated. Vector finite elements are used to represent the fields in the device interior, and field continuity across waveguide apertures is enforced by matching the interior solution to a sum of waveguide modes. Consequently, the mesh may end at the aperture instead of extending into the waveguide. The report discusses the variational formulation and its reduction to a linear system using Galerkin's method. It describes the computer code, including its interface to commercial CAD software used for geometry generation. It presents validation results for waveguide discontinuities, coaxial transitions, and microstrip circuits. They demonstrate that the method is an effective and versatile tool for predicting the performance of passive RF devices.

Unexpected series of regular frequency spacing of δ Scuti stars in the non-asymptotic regime - I. The methodology

DOE PAGES

Paparo, M.; Benko, J. M.; Hareter, M.; ...

2016-05-11

In this study, a sequence search method was developed to search the regular frequency spacing in δ Scuti stars through visual inspection and an algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 δ Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 δ Scuti stars (from one to eight sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequencesmore » (echelle ridges) were found in the 5–21 d –1 region where the pairs of the sequences are shifted (between 0.5 and 0.59 d –1) by twice the value of the estimated rotational splitting frequency (0.269 d –1). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT (Fourier transform of the frequencies), and the statistics of the shifts are also compared. In many stars more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to formulate the possible explanation that one spacing is the large separation while the other is the sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d –1) are in better agreement with the sum of a possible 1.710 d –1 large separation and two or one times, respectively, the value of the rotational frequency.« less

Unexpected series of regular frequency spacing of δ Scuti stars in the non-asymptotic regime - I. The methodology

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

Paparo, M.; Benko, J. M.; Hareter, M.

In this study, a sequence search method was developed to search the regular frequency spacing in δ Scuti stars through visual inspection and an algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 δ Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 δ Scuti stars (from one to eight sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequencesmore » (echelle ridges) were found in the 5–21 d –1 region where the pairs of the sequences are shifted (between 0.5 and 0.59 d –1) by twice the value of the estimated rotational splitting frequency (0.269 d –1). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT (Fourier transform of the frequencies), and the statistics of the shifts are also compared. In many stars more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to formulate the possible explanation that one spacing is the large separation while the other is the sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d –1) are in better agreement with the sum of a possible 1.710 d –1 large separation and two or one times, respectively, the value of the rotational frequency.« less

Modulator for tone and binary signals. [phase of modulation of tone and binary signals on carrier waves in communication systems

NASA Technical Reports Server (NTRS)

Mcchesney, J. R.; Lerner, T.; Fitch, E. J. (Inventor)

1975-01-01

Tones and binary information are transmitted as phase variations on a carrier wave of constant amplitude and frequency. The carrier and tones are applied to a balanced modulator for deriving an output signal including a pair of sidebands relative to the carrier. The carrier is phase modulated by a digital signal so that it is + or - 90 deg out of phase with the predetermined phase of the carrier. The carrier is combined in an algebraic summing device with the phase modulated signal and the balanced modulator output signal. The output of the algebraic summing device is hard limited to derive a constant amplitude and frequency signal having very narrow bandwidth requirements. At a receiver, the tones and binary data are detected with a phase locked loop having a voltage controlled oscillator driving a pair of orthogonal detection channels.

Combining total internal reflection sum frequency spectroscopy spectral imaging and confocal fluorescence microscopy.

PubMed

Allgeyer, Edward S; Sterling, Sarah M; Gunewardene, Mudalige S; Hess, Samuel T; Neivandt, David J; Mason, Michael D

2015-01-27

Understanding surface and interfacial lateral organization in material and biological systems is critical in nearly every field of science. The continued development of tools and techniques viable for elucidation of interfacial and surface information is therefore necessary to address new questions and further current investigations. Sum frequency spectroscopy (SFS) is a label-free, nonlinear optical technique with inherent surface specificity that can yield critical organizational information on interfacial species. Unfortunately, SFS provides no spatial information on a surface; small scale heterogeneities that may exist are averaged over the large areas typically probed. Over the past decade, this has begun to be addressed with the advent of SFS microscopy. Here we detail the construction and function of a total internal reflection (TIR) SFS spectral and confocal fluorescence imaging microscope directly amenable to surface investigations. This instrument combines, for the first time, sample scanning TIR-SFS imaging with confocal fluorescence microscopy.

Amine Chemistry at Aqueous Interfaces: The Study of Organic Amines in Neutralizing Acidic Gases at an Air/Water Surface Using Vibrational Sum Frequency Spectroscopy

NASA Astrophysics Data System (ADS)

McWilliams, L.; Wren, S. N.; Valley, N. A.; Richmond, G.

2014-12-01

Small organic bases have been measured in atmospheric samples, with their sources ranging from industrial processing to animal husbandry. These small organic amines are often highly soluble, being found in atmospheric condensed phases such as fogwater and rainwater. Additionally, they display acid-neutralization ability often greater than ammonia, yet little is known regarding their kinetic and thermodynamic properties. This presentation will describe the molecular level details of a model amine system at the vapor/liquid interface in the presence of acidic gas. We find that this amine system shows very unique properties in terms of its bonding, structure, and orientation at aqueous surfaces. The results of our studies using a combination of computation, vibrational sum frequency spectroscopy, and surface tension will report the properties inherent to these atmospherically relevant species at aqueous surfaces.

A Census of Southern Pulsars at 185 MHz

NASA Astrophysics Data System (ADS)

Xue, Mengyao; Bhat, N. D. R.; Tremblay, S. E.; Ord, S. M.; Sobey, C.; Swainston, N. A.; Kaplan, D. L.; Johnston, Simon; Meyers, B. W.; McSweeney, S. J.

2017-12-01

The Murchison Widefield Array, and its recently developed Voltage Capture System, facilitates extending the low-frequency range of pulsar observations at high-time and -frequency resolution in the Southern Hemisphere, providing further information about pulsars and the ISM. We present the results of an initial time-resolved census of known pulsars using the Murchison Widefield Array. To significantly reduce the processing load, we incoherently sum the detected powers from the 128 Murchison Widefield Array tiles, which yields 10% of the attainable sensitivity of the coherent sum. This preserves the large field-of-view ( 450 deg2 at 185 MHz), allowing multiple pulsars to be observed simultaneously. We developed a WIde-field Pulsar Pipeline that processes the data from each observation and automatically folds every known pulsar located within the beam. We have detected 50 pulsars to date, 6 of which are millisecond pulsars. This is consistent with our expectation, given the telescope sensitivity and the sky coverage of the processed data ( 17 000 deg2). For 10 pulsars, we present the lowest frequency detections published. For a subset of the pulsars, we present multi-frequency pulse profiles by combining our data with published profiles from other telescopes. Since the Murchison Widefield Array is a low-frequency precursor to the Square Kilometre Array, we use our census results to forecast that a survey using the low-frequency component of the Square Kilometre Array Phase 1 can potentially detect around 9 400 pulsars.

Enabling the detection of UV signal in multimodal nonlinear microscopy with catalogue lens components.

PubMed

Vogel, Martin; Wingert, Axel; Fink, Rainer H A; Hagl, Christian; Ganikhanov, Feruz; Pfeffer, Christian P

2015-10-01

Using an optical system made from fused silica catalogue optical components, third-order nonlinear microscopy has been enabled on conventional Ti:sapphire laser-based multiphoton microscopy setups. The optical system is designed using two lens groups with straightforward adaptation to other microscope stands when one of the lens groups is exchanged. Within the theoretical design, the optical system collects and transmits light with wavelengths between the near ultraviolet and the near infrared from an object field of at least 1 mm in diameter within a resulting numerical aperture of up to 0.56. The numerical aperture can be controlled with a variable aperture stop between the two lens groups of the condenser. We demonstrate this new detection capability in third harmonic generation imaging experiments at the harmonic wavelength of ∼300 nm and in multimodal nonlinear optical imaging experiments using third-order sum frequency generation and coherent anti-Stokes Raman scattering microscopy so that the wavelengths of the detected signals range from ∼300 nm to ∼660 nm. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Program Predicts Performance of Optical Parametric Oscillators

NASA Technical Reports Server (NTRS)

Cross, Patricia L.; Bowers, Mark

2006-01-01

A computer program predicts the performances of solid-state lasers that operate at wavelengths from ultraviolet through mid-infrared and that comprise various combinations of stable and unstable resonators, optical parametric oscillators (OPOs), and sum-frequency generators (SFGs), including second-harmonic generators (SHGs). The input to the program describes the signal, idler, and pump beams; the SFG and OPO crystals; and the laser geometry. The program calculates the electric fields of the idler, pump, and output beams at three locations (inside the laser resonator, just outside the input mirror, and just outside the output mirror) as functions of time for the duration of the pump beam. For each beam, the electric field is used to calculate the fluence at the output mirror, plus summary parameters that include the centroid location, the radius of curvature of the wavefront leaving through the output mirror, the location and size of the beam waist, and a quantity known, variously, as a propagation constant or beam-quality factor. The program provides a typical Windows interface for entering data and selecting files. The program can include as many as six plot windows, each containing four graphs.

Upconversion of the mid-IR pulses to the near-IR in LiGaS2

NASA Astrophysics Data System (ADS)

Kato, Kiyoshi; Umemura, Nobuhiro; Okamoto, Takuya; Petrov, Valentin

2018-02-01

This paper reports on the phase-matching properties of LiGaS2 for upconverting a Nd:YAG laser-pumped KTP and AgGaS2 optical parametric oscillator (OPO) at mid-IR to the near-IR by mixing with its pump source together with the new Sellmeier equations that provide a good reproduction of the present experimental results as well as the published data points of second-harmonic generation (SHG) and sum-frequency generation (SFG) of a CO2 laser, a Ti:Al2O3 laser-pumped optical parametric amplifier (OPA), and a Nd:YAG laser-pumped OPO in the mid-IR. This index formula gives the important information that group velocity mismatch (GVM) (Δsp = 1/υs - 1/υp) of LiGaS2 in the 4 - 11 μm range is 12 27 fs/mm lower than that of the widely used LiInS2, which makes it ideal for the upconversion of the mid-IR femtosecond pulses having large spectral bandwidths to the near-IR.

Explicit symplectic algorithms based on generating functions for charged particle dynamics.

PubMed

Zhang, Ruili; Qin, Hong; Tang, Yifa; Liu, Jian; He, Yang; Xiao, Jianyuan

2016-07-01

Dynamics of a charged particle in the canonical coordinates is a Hamiltonian system, and the well-known symplectic algorithm has been regarded as the de facto method for numerical integration of Hamiltonian systems due to its long-term accuracy and fidelity. For long-term simulations with high efficiency, explicit symplectic algorithms are desirable. However, it is generally believed that explicit symplectic algorithms are only available for sum-separable Hamiltonians, and this restriction limits the application of explicit symplectic algorithms to charged particle dynamics. To overcome this difficulty, we combine the familiar sum-split method and a generating function method to construct second- and third-order explicit symplectic algorithms for dynamics of charged particle. The generating function method is designed to generate explicit symplectic algorithms for product-separable Hamiltonian with form of H(x,p)=p_{i}f(x) or H(x,p)=x_{i}g(p). Applied to the simulations of charged particle dynamics, the explicit symplectic algorithms based on generating functions demonstrate superiorities in conservation and efficiency.

Explicit symplectic algorithms based on generating functions for charged particle dynamics

NASA Astrophysics Data System (ADS)

Zhang, Ruili; Qin, Hong; Tang, Yifa; Liu, Jian; He, Yang; Xiao, Jianyuan

2016-07-01

Dynamics of a charged particle in the canonical coordinates is a Hamiltonian system, and the well-known symplectic algorithm has been regarded as the de facto method for numerical integration of Hamiltonian systems due to its long-term accuracy and fidelity. For long-term simulations with high efficiency, explicit symplectic algorithms are desirable. However, it is generally believed that explicit symplectic algorithms are only available for sum-separable Hamiltonians, and this restriction limits the application of explicit symplectic algorithms to charged particle dynamics. To overcome this difficulty, we combine the familiar sum-split method and a generating function method to construct second- and third-order explicit symplectic algorithms for dynamics of charged particle. The generating function method is designed to generate explicit symplectic algorithms for product-separable Hamiltonian with form of H (x ,p ) =pif (x ) or H (x ,p ) =xig (p ) . Applied to the simulations of charged particle dynamics, the explicit symplectic algorithms based on generating functions demonstrate superiorities in conservation and efficiency.

Two-dimensional, phase modulated lattice sums with application to the Helmholtz Green’s function

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

Linton, C. M., E-mail: C.M.Linton@lboro.ac.uk

2015-01-15

A class of two-dimensional phase modulated lattice sums in which the denominator is an indefinite quadratic polynomial Q is expressed in terms of a single, exponentially convergent series of elementary functions. This expression provides an extremely efficient method for the computation of the quasi-periodic Green’s function for the Helmholtz equation that arises in a number of physical contexts when studying wave propagation through a doubly periodic medium. For a class of sums in which Q is positive definite, our new result can be used to generate representations in terms of θ-functions which are significant generalisations of known results.

Coherence analysis of a class of weighted networks

NASA Astrophysics Data System (ADS)

Dai, Meifeng; He, Jiaojiao; Zong, Yue; Ju, Tingting; Sun, Yu; Su, Weiyi

2018-04-01

This paper investigates consensus dynamics in a dynamical system with additive stochastic disturbances that is characterized as network coherence by using the Laplacian spectrum. We introduce a class of weighted networks based on a complete graph and investigate the first- and second-order network coherence quantifying as the sum and square sum of reciprocals of all nonzero Laplacian eigenvalues. First, the recursive relationship of its eigenvalues at two successive generations of Laplacian matrix is deduced. Then, we compute the sum and square sum of reciprocal of all nonzero Laplacian eigenvalues. The obtained results show that the scalings of first- and second-order coherence with network size obey four and five laws, respectively, along with the range of the weight factor. Finally, it indicates that the scalings of our studied networks are smaller than other studied networks when 1/√{d }

Color image encryption based on gyrator transform and Arnold transform

NASA Astrophysics Data System (ADS)

Sui, Liansheng; Gao, Bo

2013-06-01

A color image encryption scheme using gyrator transform and Arnold transform is proposed, which has two security levels. In the first level, the color image is separated into three components: red, green and blue, which are normalized and scrambled using the Arnold transform. The green component is combined with the first random phase mask and transformed to an interim using the gyrator transform. The first random phase mask is generated with the sum of the blue component and a logistic map. Similarly, the red component is combined with the second random phase mask and transformed to three-channel-related data. The second random phase mask is generated with the sum of the phase of the interim and an asymmetrical tent map. In the second level, the three-channel-related data are scrambled again and combined with the third random phase mask generated with the sum of the previous chaotic maps, and then encrypted into a gray scale ciphertext. The encryption result has stationary white noise distribution and camouflage property to some extent. In the process of encryption and decryption, the rotation angle of gyrator transform, the iterative numbers of Arnold transform, the parameters of the chaotic map and generated accompanied phase function serve as encryption keys, and hence enhance the security of the system. Simulation results and security analysis are presented to confirm the security, validity and feasibility of the proposed scheme.

A Novel Genome-Information Content-Based Statistic for Genome-Wide Association Analysis Designed for Next-Generation Sequencing Data

PubMed Central

Luo, Li; Zhu, Yun

2012-01-01

Abstract The genome-wide association studies (GWAS) designed for next-generation sequencing data involve testing association of genomic variants, including common, low frequency, and rare variants. The current strategies for association studies are well developed for identifying association of common variants with the common diseases, but may be ill-suited when large amounts of allelic heterogeneity are present in sequence data. Recently, group tests that analyze their collective frequency differences between cases and controls shift the current variant-by-variant analysis paradigm for GWAS of common variants to the collective test of multiple variants in the association analysis of rare variants. However, group tests ignore differences in genetic effects among SNPs at different genomic locations. As an alternative to group tests, we developed a novel genome-information content-based statistics for testing association of the entire allele frequency spectrum of genomic variation with the diseases. To evaluate the performance of the proposed statistics, we use large-scale simulations based on whole genome low coverage pilot data in the 1000 Genomes Project to calculate the type 1 error rates and power of seven alternative statistics: a genome-information content-based statistic, the generalized T2, collapsing method, multivariate and collapsing (CMC) method, individual χ2 test, weighted-sum statistic, and variable threshold statistic. Finally, we apply the seven statistics to published resequencing dataset from ANGPTL3, ANGPTL4, ANGPTL5, and ANGPTL6 genes in the Dallas Heart Study. We report that the genome-information content-based statistic has significantly improved type 1 error rates and higher power than the other six statistics in both simulated and empirical datasets. PMID:22651812

A novel genome-information content-based statistic for genome-wide association analysis designed for next-generation sequencing data.

PubMed

Luo, Li; Zhu, Yun; Xiong, Momiao

2012-06-01

The genome-wide association studies (GWAS) designed for next-generation sequencing data involve testing association of genomic variants, including common, low frequency, and rare variants. The current strategies for association studies are well developed for identifying association of common variants with the common diseases, but may be ill-suited when large amounts of allelic heterogeneity are present in sequence data. Recently, group tests that analyze their collective frequency differences between cases and controls shift the current variant-by-variant analysis paradigm for GWAS of common variants to the collective test of multiple variants in the association analysis of rare variants. However, group tests ignore differences in genetic effects among SNPs at different genomic locations. As an alternative to group tests, we developed a novel genome-information content-based statistics for testing association of the entire allele frequency spectrum of genomic variation with the diseases. To evaluate the performance of the proposed statistics, we use large-scale simulations based on whole genome low coverage pilot data in the 1000 Genomes Project to calculate the type 1 error rates and power of seven alternative statistics: a genome-information content-based statistic, the generalized T(2), collapsing method, multivariate and collapsing (CMC) method, individual χ(2) test, weighted-sum statistic, and variable threshold statistic. Finally, we apply the seven statistics to published resequencing dataset from ANGPTL3, ANGPTL4, ANGPTL5, and ANGPTL6 genes in the Dallas Heart Study. We report that the genome-information content-based statistic has significantly improved type 1 error rates and higher power than the other six statistics in both simulated and empirical datasets.

A data-driven method to enhance vibration signal decomposition for rolling bearing fault analysis

NASA Astrophysics Data System (ADS)

Grasso, M.; Chatterton, S.; Pennacchi, P.; Colosimo, B. M.

2016-12-01

Health condition analysis and diagnostics of rotating machinery requires the capability of properly characterizing the information content of sensor signals in order to detect and identify possible fault features. Time-frequency analysis plays a fundamental role, as it allows determining both the existence and the causes of a fault. The separation of components belonging to different time-frequency scales, either associated to healthy or faulty conditions, represents a challenge that motivates the development of effective methodologies for multi-scale signal decomposition. In this framework, the Empirical Mode Decomposition (EMD) is a flexible tool, thanks to its data-driven and adaptive nature. However, the EMD usually yields an over-decomposition of the original signals into a large number of intrinsic mode functions (IMFs). The selection of most relevant IMFs is a challenging task, and the reference literature lacks automated methods to achieve a synthetic decomposition into few physically meaningful modes by avoiding the generation of spurious or meaningless modes. The paper proposes a novel automated approach aimed at generating a decomposition into a minimal number of relevant modes, called Combined Mode Functions (CMFs), each consisting in a sum of adjacent IMFs that share similar properties. The final number of CMFs is selected in a fully data driven way, leading to an enhanced characterization of the signal content without any information loss. A novel criterion to assess the dissimilarity between adjacent CMFs is proposed, based on probability density functions of frequency spectra. The method is suitable to analyze vibration signals that may be periodically acquired within the operating life of rotating machineries. A rolling element bearing fault analysis based on experimental data is presented to demonstrate the performances of the method and the provided benefits.

Primary and secondary parasitoids (Hymenoptera) of aphids (Hemiptera: Aphididae) on blueberry and other Vaccinium in the Pacific Northwest.

PubMed

Raworth, D A; Pike, K S; Tanigoshi, L K; Mathur, S; Graf, G

2008-04-01

Blueberry scorch virus, a commercially important Carlavirus in highbush blueberry, Vaccinium corymbosum L., is vectored by aphids (Hemiptera: Aphididae). We surveyed the aphids, primary parasitoids (Hymenoptera: Aphelinidae, Braconidae), and associated secondary parasitoids (Hymenoptera: Charipidae, Megaspilidae, Pteromalidae) on highbush blueberry and other Vaccinium in the Pacific Northwest from 1995 to 2006, with samples concentrated in 2005 and 2006, to lay the groundwork for augmentative biological control. Ericaphis fimbriata (Richards) was the principal aphid. The dominant parasitoid species were Praon unicum Smith, Aphidius n. sp., A. sp., and Aphidius ervi Haliday. Their frequency in relation to the other primary parasitoids varied significantly with geographical area; P. unicum dominated the frequency distribution in southwestern British Columbia, A. n. sp., west of the Cascades, and A. sp. and A. ervi east of the Cascades. Among the secondary parasitoids, pteromalids dominated, and their frequency in relation to the other secondary parasitoids was lowest in southwestern British Columbia. The parasitization rate for P. unicum and A. n. sp. in southwestern British Columbia increased from May or June to a maximum of 0.080 +/- 0.024 and 0.090 +/- 0.084 (SD), respectively, in late July or early August. P. unicum emerged in the spring 4 wk before A. n. sp. The parasitization rate for P. unicum was lower in conventional than organic fields. Whereas aphid density increased monotonically, P. unicum had two spring peaks. A simulation model showed that these peaks could reflect discrete generations. Releases of insectary-reared P. unicum at 150 or 450 DD above 5.6 degrees C, summing from 1 January, may effectively augment the natural spring populations by creating overlapping generations.

The nature of tremor circuits in parkinsonian and essential tremor

PubMed Central

Cagnan, Hayriye; Little, Simon; Foltynie, Thomas; Limousin, Patricia; Zrinzo, Ludvic; Hariz, Marwan; Cheeran, Binith; Fitzgerald, James; Green, Alexander L.; Aziz, Tipu

2014-01-01

Tremor is a cardinal feature of Parkinson’s disease and essential tremor, the two most common movement disorders. Yet, the mechanisms underlying tremor generation remain largely unknown. We hypothesized that driving deep brain stimulation electrodes at a frequency closely matching the patient’s own tremor frequency should interact with neural activity responsible for tremor, and that the effect of stimulation on tremor should reveal the role of different deep brain stimulation targets in tremor generation. Moreover, tremor responses to stimulation might reveal pathophysiological differences between parkinsonian and essential tremor circuits. Accordingly, we stimulated 15 patients with Parkinson’s disease with either thalamic or subthalamic electrodes (13 male and two female patients, age: 50–77 years) and 10 patients with essential tremor with thalamic electrodes (nine male and one female patients, age: 34–74 years). Stimulation at near-to tremor frequency entrained tremor in all three patient groups (ventrolateral thalamic stimulation in Parkinson’s disease, P = 0.0078, subthalamic stimulation in Parkinson’s disease, P = 0.0312; ventrolateral thalamic stimulation in essential tremor, P = 0.0137; two-tailed paired Wilcoxon signed-rank tests). However, only ventrolateral thalamic stimulation in essential tremor modulated postural tremor amplitude according to the timing of stimulation pulses with respect to the tremor cycle (e.g. P = 0.0002 for tremor amplification, two-tailed Wilcoxon rank sum test). Parkinsonian rest and essential postural tremor severity (i.e. tremor amplitude) differed in their relative tolerance to spontaneous changes in tremor frequency when stimulation was not applied. Specifically, the amplitude of parkinsonian rest tremor remained unchanged despite spontaneous changes in tremor frequency, whereas that of essential postural tremor reduced when tremor frequency departed from median values. Based on these results we conclude that parkinsonian rest tremor is driven by a neural network, which includes the subthalamic nucleus and ventrolateral thalamus and has broad frequency-amplitude tolerance. We propose that it is this tolerance to changes in tremor frequency that dictates that parkinsonian rest tremor may be significantly entrained by low frequency stimulation without stimulation timing-dependent amplitude modulation. In contrast, the circuit influenced by low frequency thalamic stimulation in essential tremor has a narrower frequency-amplitude tolerance so that tremor entrainment through extrinsic driving is necessarily accompanied by amplitude modulation. Such differences in parkinsonian rest and essential tremor will be important in selecting future strategies for closed loop deep brain stimulation for tremor control. PMID:25200741

SFG experiment and ab initio study of the chemisorption of CN - on low-index platinum surfaces

NASA Astrophysics Data System (ADS)

Tadjeddine, M.; Flament, J.-P.; Le Rille, A.; Tadjeddine, A.

2006-05-01

A dual analysis is proposed in order to have a better understanding of the adsorption of the cyanide ions on a platinum electrode. The SFG (Sum Frequency Generation) spectroscopy allows the in situ vibrational study and the SFG spectra of the CN - species adsorbed on single crystal Pt electrode allow a systematic study of the low-index platinum surfaces. This experimental work is supported by ab initio calculations using density functional theory and cluster models. For each surface orientation and each geometry, a cluster model of 20-30 Pt atoms has been built in order to interpret the chemisorption of the CN - ions through four kinds of adsorption geometry: on-top or bridge site, bonding via C or N atoms. Geometries have been optimized and adsorption energies, electronic properties and vibrational frequencies have been computed. From the electronic properties, we can propose an analysis of the bonding mechanism for each studied kind of adsorption. The SFG spectra of the CN -/Pt(1 1 1) system present an unique resonance owing to the top C adsorption. It is mainly the same for the CN -/Pt(1 0 0) system. It is also the case for the SFG spectra of the CN -/Pt(1 1 0) system recorded at negative electrochemical voltage; at more positive voltage, a second resonance appears at a lower frequency, owing to the top N adsorption. Experimental and theoretical values of the C-N stretching frequencies are in excellent agreement.

CLEARPOND: Cross-Linguistic Easy-Access Resource for Phonological and Orthographic Neighborhood Densities

PubMed Central

Marian, Viorica; Bartolotti, James; Chabal, Sarah; Shook, Anthony

2012-01-01

Past research has demonstrated cross-linguistic, cross-modal, and task-dependent differences in neighborhood density effects, indicating a need to control for neighborhood variables when developing and interpreting research on language processing. The goals of the present paper are two-fold: (1) to introduce CLEARPOND (Cross-Linguistic Easy-Access Resource for Phonological and Orthographic Neighborhood Densities), a centralized database of phonological and orthographic neighborhood information, both within and between languages, for five commonly-studied languages: Dutch, English, French, German, and Spanish; and (2) to show how CLEARPOND can be used to compare general properties of phonological and orthographic neighborhoods across languages. CLEARPOND allows researchers to input a word or list of words and obtain phonological and orthographic neighbors, neighborhood densities, mean neighborhood frequencies, word lengths by number of phonemes and graphemes, and spoken-word frequencies. Neighbors can be defined by substitution, deletion, and/or addition, and the database can be queried separately along each metric or summed across all three. Neighborhood values can be obtained both within and across languages, and outputs can optionally be restricted to neighbors of higher frequency. To enable researchers to more quickly and easily develop stimuli, CLEARPOND can also be searched by features, generating lists of words that meet precise criteria, such as a specific range of neighborhood sizes, lexical frequencies, and/or word lengths. CLEARPOND is freely-available to researchers and the public as a searchable, online database and for download at http://clearpond.northwestern.edu. PMID:22916227

The in vivo Pig-a gene mutation assay, a potential tool for regulatory safety assessment.

PubMed

Dobrovolsky, Vasily N; Miura, Daishiro; Heflich, Robert H; Dertinger, Stephen D

2010-01-01

The Pig-a (phosphatidylinositol glycan, Class A) gene codes for a catalytic subunit of the N-acetylglucosamine transferase complex involved in an early step of glycosylphosphatidyl inositol (GPI) cell surface anchor synthesis. Pig-a is the only gene involved in GPI anchor synthesis that is on the X-chromosome, and research into the origins of an acquired genetic disease involving GPI anchor deficiency (paroxysmal nocturnal hemoglobinuria) indicates that cells lacking GPI anchors, or GPI-anchored cell surface proteins, almost always have mutations in the Pig-a gene. These properties of the Pig-a gene and the GPI anchor system have been exploited in a series of assays for measuring in vivo gene mutation in blood cells from humans, rats, mice, and monkeys. In rats, flow cytometric measurement of Pig-a mutation in red blood cells requires microliter volumes of blood and data can be generated in hours. Spontaneous mutant frequencies are relatively low (<5 × 10(-6)) and rats treated with multiple doses of the potent mutagen, N-ethyl-N-nitrosourea, display Pig-a mutant frequencies that are close to the sum of the frequencies produced by the individual exposures. A general observation is that induced mutant frequencies are manifested earlier in reticulocytes (about 2 weeks after treatment) than in total red blood cells (about 2 months after exposure). Based on data from a limited number of test agents, the assay shows promise for regulatory applications, including integration of gene mutation measurement into repeat-dose toxicology studies.

Analog simulation of flux-summing servo-model, phases 1 and 2

NASA Technical Reports Server (NTRS)

Hriber, E. J.

1984-01-01

The analog simulation was developed for a closed-loop system having an electrohydraulic flux-summing servo valve and actuator with associated inertial load. One-fourth of the system's total forward gain is carried by each of four channels. The present study successfully applied failure mode management techniques to the problem of channel failure. Digital logic circuitry was developed to maintain the overall forward gain of the system at a constant value, in the presence of channel failure. Finally, the stability of the system was verified, and performance characteristics were determined through the use of frequency response methods.

PAH mutation spectrum and correlation with PKU manifestation in north Jiangsu province population.

PubMed

Wang, Zhen-Wen; Jiang, Shi-Wen; Zhou, Bao-Cheng

2018-02-01

Phenylketonuria (PKU) is a common autosomal recessive disorder of phenylalanine metabolism and mainly results a deficiency of phenylalanine hydroxylase gene (PAH). The incidence of various PAH mutations have race and ethnicity differences. We report a spectrum of PAH mutations complied from 35 PKU children who are all Chinese Han population from north Jiangsu in this study. All 13 exons and their flanking intron sequences of PAH were determined by Ion Torrent PGM™ sequencing. The relationship of genotype and phenotype was analyzed based on the sum of the arbitrary value (AV) values of the two alleles. We identified 61 mutations, with a frequency of 87.14%, among 70 alleles of 35 patients. The most prevalent mutations were R243Q (26.23%), R241C (9.84%) and V399V (8.20%). Furthermore, the consistency between prediction of the biochemical phenotype and the observed phenotype was 81.25%, with the highest consistency observed in classic PKU (87.50%). A significant correlation was found between pretreatment levels of phenylalanine and AV sum (r = -0.87, P < 0.05). Finally, our study constructs PAH mutation spectrum by next generation sequencing (NGS), and reveals that the PAH genotypes and biochemical phenotypes were significantly correlated. These offers facilitate the provision of appropriate genetic counseling for PKU patients. Copyright © 2017. Published by Elsevier Taiwan.

Sum Rules, Classical and Quantum - A Pedagogical Approach

NASA Astrophysics Data System (ADS)

Karstens, William; Smith, David Y.

2014-03-01

Sum rules in the form of integrals over the response of a system to an external probe provide general analytical tools for both experiment and theory. For example, the celebrated f-sum rule gives a system's plasma frequency as an integral over the optical-dipole absorption spectrum regardless of the specific spectral distribution. Moreover, this rule underlies Smakula's equation for the number density of absorbers in a sample in terms of the area under their absorption bands. Commonly such rules are derived from quantum-mechanical commutation relations, but many are fundamentally classical (independent of ℏ) and so can be derived from more transparent mechanical models. We have exploited this to illustrate the fundamental role of inertia in the case of optical sum rules. Similar considerations apply to sum rules in many other branches of physics. Thus, the ``attenuation integral theorems'' of ac circuit theory reflect the ``inertial'' effect of Lenz's Law in inductors or the potential energy ``storage'' in capacitors. These considerations are closely related to the fact that the real and imaginary parts of a response function cannot be specified independently, a result that is encapsulated in the Kramers-Kronig relations. Supported in part by the US Department of Energy, Office of Nuclear Physics under contract DE-AC02-06CH11357.

A New Proof of the Expected Frequency Spectrum under the Standard Neutral Model.

PubMed

Hudson, Richard R

2015-01-01

The sample frequency spectrum is an informative and frequently employed approach for summarizing DNA variation data. Under the standard neutral model the expectation of the sample frequency spectrum has been derived by at least two distinct approaches. One relies on using results from diffusion approximations to the Wright-Fisher Model. The other is based on Pólya urn models that correspond to the standard coalescent model. A new proof of the expected frequency spectrum is presented here. It is a proof by induction and does not require diffusion results and does not require the somewhat complex sums and combinatorics of the derivations based on urn models.

Behavioral, Psychological, and Demographic Predictors of Physical Fitness.

DTIC Science & Technology

1987-12-14

calisthenics ) were assessed: (a) frequency (i.e., times per week or month an exercise was done), and (b) duration (i.e., time spent exercising during a... workout period). An exercise activity scale was computed as the sum of the frequency-by-duration cross-product for each exercise. Substance consumption... street ") (alpha =- .79). Items used in these scales were taken from health behavior questionnaires developed by Vickers and He-vig (cf. Vickers & Hervig

Time-resolved SFG study of formate on a Ni( 1 1 1 ) surface under irradiation of picosecond laser pulses

NASA Astrophysics Data System (ADS)

Noguchi, H.; Okada, T.; Onda, K.; Kano, S. S.; Wada, A.; Domen, K.

2003-03-01

Time-resolved sum-frequency generation spectroscopy was carried out on a deuterated formate (DCOO) adsorbed on Ni(1 1 1) surface to investigate the surface reaction dynamics under instantaneous surface temperature jump induced by the irradiation by picosecond laser pulses. The irradiation of pump pulse (800 nm) caused the rapid intensity decrease of both CD and OCO stretching modes of bridged formate on Ni(1 1 1). Different temporal behaviors of intensity recovery between these two vibrational modes were observed, i.e., CD stretching mode recovered faster than OCO. This is the first result to show that the dynamics of adsorbates on metals strongly depends on the observed vibrational mode. From the results of temperature and pump fluence dependence, we concluded that the observed intensity change was not due to the decomposition or desorption, but was induced by a non-thermal process.

Coherent optical effect on time-resolved vibrational SFG spectrum of adsorbates

NASA Astrophysics Data System (ADS)

Ueba, H.; Sawabu, T.; Mii, T.

2002-04-01

We present a theory to study the influence of the coherent mixing between pump-infrared and probe-visible pulse on a time-resolved sum-frequency generation (TR-SFG) spectrum for vibrations at surfaces. The general formula of the time-dependent and its Fourier transform of the SFG polarization and its Fourier transform allows us to calculate the time-resolved vibrational SFG spectrum and the transient characteristics of the SFG intensity as a function of the delay time td between the pump-infrared and probe-visible pulse. It is found the coherent optical effect manifests itself in the broadening and narrowing of the SFG spectrum with the intrinsic width of T2 at negative and positive td, respectively, being in qualitative agreement with recent experimental results. The influence of the coherent mixing on the transient behavior of the SFG intensity is also discussed in conjunction to the T2 determination.

Atomic Origins of the Self-Healing Function in Cement–Polymer Composites

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

Nguyen, Manh-Thuong; Wang, Zheming; Rod, Kenton A.

Motivated by recent advances in self-healing cement and epoxy polymer composites, we present a combined ab initio molecular dynamics and sum frequency generation (SFG) spectroscopy study of a calcium-silicate-hydrate/polymer interface. On stable, low-defect surfaces, the polymer only weakly adheres through coordination and hydrogen bonding interactions and can be easily mobilized towards defected surfaces. Conversely, on fractured surfaces, the polymer strongly anchors through ionic Ca-O bonds resulting from the deprotonation of polymer hydroxyl groups. In addition, polymer S-S groups are turned away from the cement/polymer interface, allowing for the self-healing function within the polymer. The overall elasticity and healing properties ofmore » these composites stem from a flexible hydrogen bonding network that can readily adapt to surface morphology. The theoretical vibrational signals associated with the proposed cement-polymer interfacial chemistry were confirmed experimentally by SFG spectroscopy.« less

Subsite mapping of enzymes. Depolymerase computer modelling.

PubMed Central

Allen, J D; Thoma, J A

1976-01-01

We have developed a depolymerase computer model that uses a minimization routine. The model is designed so that, given experimental bond-cleavage frequencies for oligomeric substrates and experimental Michaelis parameters as a function of substrate chain length, the optimum subsite map is generated. The minimized sum of the weighted-squared residuals of the experimental and calculated data is used as a criterion of the goodness-of-fit for the optimized subsite map. The application of the minimization procedure to subsite mapping is explored through the use of simulated data. A procedure is developed whereby the minimization model can be used to determine the number of subsites in the enzymic binding region and to locate the position of the catalytic amino acids among these subsites. The degree of propagation of experimental variance into the subsite-binding energies is estimated. The question of whether hydrolytic rate coefficients are constant or a function of the number of filled subsites is examined. PMID:999629

Molecular catalysis science: Perspective on unifying the fields of catalysis.

PubMed

Ye, Rong; Hurlburt, Tyler J; Sabyrov, Kairat; Alayoglu, Selim; Somorjai, Gabor A

2016-05-10

Colloidal chemistry is used to control the size, shape, morphology, and composition of metal nanoparticles. Model catalysts as such are applied to catalytic transformations in the three types of catalysts: heterogeneous, homogeneous, and enzymatic. Real-time dynamics of oxidation state, coordination, and bonding of nanoparticle catalysts are put under the microscope using surface techniques such as sum-frequency generation vibrational spectroscopy and ambient pressure X-ray photoelectron spectroscopy under catalytically relevant conditions. It was demonstrated that catalytic behavior and trends are strongly tied to oxidation state, the coordination number and crystallographic orientation of metal sites, and bonding and orientation of surface adsorbates. It was also found that catalytic performance can be tuned by carefully designing and fabricating catalysts from the bottom up. Homogeneous and heterogeneous catalysts, and likely enzymes, behave similarly at the molecular level. Unifying the fields of catalysis is the key to achieving the goal of 100% selectivity in catalysis.

Molecular catalysis science: Perspective on unifying the fields of catalysis

PubMed Central

Ye, Rong; Hurlburt, Tyler J.; Sabyrov, Kairat; Alayoglu, Selim; Somorjai, Gabor A.

2016-01-01

Colloidal chemistry is used to control the size, shape, morphology, and composition of metal nanoparticles. Model catalysts as such are applied to catalytic transformations in the three types of catalysts: heterogeneous, homogeneous, and enzymatic. Real-time dynamics of oxidation state, coordination, and bonding of nanoparticle catalysts are put under the microscope using surface techniques such as sum-frequency generation vibrational spectroscopy and ambient pressure X-ray photoelectron spectroscopy under catalytically relevant conditions. It was demonstrated that catalytic behavior and trends are strongly tied to oxidation state, the coordination number and crystallographic orientation of metal sites, and bonding and orientation of surface adsorbates. It was also found that catalytic performance can be tuned by carefully designing and fabricating catalysts from the bottom up. Homogeneous and heterogeneous catalysts, and likely enzymes, behave similarly at the molecular level. Unifying the fields of catalysis is the key to achieving the goal of 100% selectivity in catalysis. PMID:27114536

Strong cooperative effect of oppositely charged surfactant mixtures on their adsorption and packing at the air-water interface and interfacial water structure.

PubMed

Nguyen, Khoi T; Nguyen, Tuan D; Nguyen, Anh V

2014-06-24

Remarkable adsorption enhancement and packing of dilute mixtures of water-soluble oppositely-charged surfactants, sodium dodecyl sulfate (SDS) and dodecyl amine hydrochloride (DAH), at the air-water interface were observed by using sum frequency generation spectroscopy and tensiometry. The interfacial water structure was also observed to be significantly influenced by the SDS-DAH mixtures, differently from the synergy of the single surfactants. Most strikingly, the obtained spectroscopic evidence suggests that the interfacial hydrophobic alkyl chains of the binary mixtures assemble differently from those of single surfactants. This study highlights the significance of the cooperative interaction between the headgroups of oppositely charged binary surfactant systems and subsequently provides some insightful observations about the molecular structure of the air-aqueous interfacial water molecules and, more importantly, about the packing nature of the surfactant hydrophobic chains of dilute SDS-DAH mixtures of concentration below 1% of the CMC.

Atomic Origins of the Self-Healing Function in Cement-Polymer Composites.

PubMed

Nguyen, Manh-Thuong; Wang, Zheming; Rod, Kenton A; Childers, M Ian; Fernandez, Carlos; Koech, Phillip K; Bennett, Wendy D; Rousseau, Roger; Glezakou, Vassiliki-Alexandra

2018-01-24

Motivated by recent advances in self-healing cement and epoxy polymer composites, we present a combined ab initio molecular dynamics and sum frequency generation (SFG) vibrational spectroscopy study of a calcium-silicate-hydrate/polymer interface. On stable, low-defect surfaces, the polymer only weakly adheres through coordination and hydrogen bonding interactions and can be easily mobilized toward defected surfaces. Conversely, on fractured surfaces, the polymer strongly anchors through ionic Ca-O bonds resulting from the deprotonation of polymer hydroxyl groups. In addition, polymer S-S groups are turned away from the cement-polymer interface, allowing for the self-healing function within the polymer. The overall elasticity and healing properties of these composites stem from a flexible hydrogen bonding network that can readily adapt to surface morphology. The theoretical vibrational signals associated with the proposed cement-polymer interfacial chemistry were confirmed experimentally by SFG vibrational spectroscopy.

Unraveling the Molecular Weight Dependence of Interfacial Interactions in Poly(2-vinylpyridine)/Silica Nanocomposites

DOE PAGES

Voylov, Dmitry N.; Holt, Adam P.; Doughty, Benjamin; ...

2017-01-10

In this paper, the structure and polymer–nanoparticle interactions among physically adsorbed poly(2-vinylpyridine) chains on the surface of silica nanoparticles (NPs) were systematically studied as a function of molecular weight (MW) by sum frequency generation (SFG) and X-ray photoelectron (XPS) spectroscopies. Analysis of XPS data identified hydrogen bonds between the polymer and NPs, while SFG evaluated the change in the number of free OH sites on the NP’s surface. Our data revealed that the hydrogen bonds and amount of the free ¯OH sites have a significant dependence on the polymer’s MW. Finally, these results provide clear experimental evidence that the interactionmore » of physically adsorbed chains with nanoparticles is strongly MW dependent and aids in unraveling the microscopic mechanism responsible for the strong MW dependence of dynamics of the interfacial layer in polymer nanocomposites.« less

Cytocompatibility evaluation of gum Arabic-coated ultra-pure boron nitride nanotubes on human cells.

PubMed

Ciofani, Gianni; Del Turco, Serena; Rocca, Antonella; de Vito, Giuseppe; Cappello, Valentina; Yamaguchi, Maho; Li, Xia; Mazzolai, Barbara; Basta, Giuseppina; Gemmi, Mauro; Piazza, Vincenzo; Golberg, Dmitri; Mattoli, Virgilio

2014-05-01

Boron nitride nanotubes (BNNTs) are tubular nanoparticles with a structure analogous to that of carbon nanotubes, but with B and N atoms that completely replace the C atoms. Many favorable results indicate BNNTs as safe nanomaterials; however, important concerns have recently been raised about ultra-pure, long (~10 µm) BNNTs tested on several cell types. Here, we propose additional experiments with the same BNNTs, but shortened (~1.5 µm) with a homogenization/sonication treatment that allows for their dispersion in gum Arabic aqueous solutions. Obtained BNNTs are tested on human endothelial and neuron-like cells with several independent biocompatibility assays. Moreover, for the first time, their strong sum-frequency generation signal is exploited to assess the cellular uptake. Our data demonstrate no toxic effects up to concentrations of 20 µg/ml, once more confirming biosafety of BNNTs, and again highlighting that nanoparticle aspect ratio plays a key role in the biocompatibility evaluation.

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

Pandey, Ravindra; Usui, Kota; Livingstone, Ruth A.

Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as Pseudomonas syringae attack plants through frost damage using specialized ice-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering onmore » the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation. Finally, the freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved SFG spectroscopy.« less

Femtowatt incoherent image conversion from mid-infrared light to near-infrared light

NASA Astrophysics Data System (ADS)

Huang, Nan; Liu, Hongjun; Wang, Zhaolu; Han, Jing; Zhang, Shuan

2017-03-01

We report on the experimental conversion imaging of an incoherent continuous-wave dim source from mid-infrared light to near-infrared light with a lowest input power of 31 femtowatt (fW). Incoherent mid-infrared images of light emission from a heat lamp bulb with an adjustable power supply at window wavelengths ranging from 2.9 µm to 3.5 µm are used for upconversion. The sum-frequency generation is realized in a laser cavity with the resonant wavelength of 1064 nm pumped by an LD at 806 nm built around a periodically poled lithium niobate (PPLN) crystal. The converted infrared image in the wavelength range ~785 nm with a resolution of about 120  ×  70 is low-noise detected using a silicon-based camera. By optimizing the system parameters, the upconversion quantum efficiency is predicted to be 28% for correctly polarized, on-axis and phase-matching light.

Entanglement-enhanced Neyman-Pearson target detection using quantum illumination

NASA Astrophysics Data System (ADS)

Zhuang, Quntao; Zhang, Zheshen; Shapiro, Jeffrey H.

2017-08-01

Quantum illumination (QI) provides entanglement-based target detection---in an entanglement-breaking environment---whose performance is significantly better than that of optimum classical-illumination target detection. QI's performance advantage was established in a Bayesian setting with the target presumed equally likely to be absent or present and error probability employed as the performance metric. Radar theory, however, eschews that Bayesian approach, preferring the Neyman-Pearson performance criterion to avoid the difficulties of accurately assigning prior probabilities to target absence and presence and appropriate costs to false-alarm and miss errors. We have recently reported an architecture---based on sum-frequency generation (SFG) and feedforward (FF) processing---for minimum error-probability QI target detection with arbitrary prior probabilities for target absence and presence. In this paper, we use our results for FF-SFG reception to determine the receiver operating characteristic---detection probability versus false-alarm probability---for optimum QI target detection under the Neyman-Pearson criterion.

Biomolecular Imaging with Coherent Nonlinear Vibrational Microscopy

PubMed Central

Chung, Chao-Yu; Boik, John; Potma, Eric O.

2014-01-01

Optical imaging with spectroscopic vibrational contrast is a label-free solution for visualizing, identifying, and quantifying a wide range of biomolecular compounds in biological materials. Both linear and nonlinear vibrational microscopy techniques derive their imaging contrast from infrared active or Raman allowed molecular transitions, which provide a rich palette for interrogating chemical and structural details of the sample. Yet nonlinear optical methods, which include both second-order sum-frequency generation (SFG) and third-order coherent Raman scattering (CRS) techniques, offer several improved imaging capabilities over their linear precursors. Nonlinear vibrational microscopy features unprecedented vibrational imaging speeds, provides strategies for higher spatial resolution, and gives access to additional molecular parameters. These advances have turned vibrational microscopy into a premier tool for chemically dissecting live cells and tissues. This review discusses the molecular contrast of SFG and CRS microscopy and highlights several of the advanced imaging capabilities that have impacted biological and biomedical research. PMID:23245525

Unraveling the Molecular Weight Dependence of Interfacial Interactions in Poly(2-vinylpyridine)/Silica Nanocomposites

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

Voylov, Dmitry N.; Holt, Adam P.; Doughty, Benjamin

In this paper, the structure and polymer–nanoparticle interactions among physically adsorbed poly(2-vinylpyridine) chains on the surface of silica nanoparticles (NPs) were systematically studied as a function of molecular weight (MW) by sum frequency generation (SFG) and X-ray photoelectron (XPS) spectroscopies. Analysis of XPS data identified hydrogen bonds between the polymer and NPs, while SFG evaluated the change in the number of free OH sites on the NP’s surface. Our data revealed that the hydrogen bonds and amount of the free ¯OH sites have a significant dependence on the polymer’s MW. Finally, these results provide clear experimental evidence that the interactionmore » of physically adsorbed chains with nanoparticles is strongly MW dependent and aids in unraveling the microscopic mechanism responsible for the strong MW dependence of dynamics of the interfacial layer in polymer nanocomposites.« less

A longitudinal study of low back pain and daily vibration exposure in professional drivers.

PubMed

Bovenzi, Massimo

2010-01-01

The aim of this study was to investigate the relation between low back pain (LBP) outcomes and measures of daily exposure to whole-body vibration (WBV) in professional drivers. In a study population of 202 male drivers, who were not affected with LBP at the initial survey, LBP in terms of duration, intensity, and disability was investigated over a two-year follow-up period. Vibration measurements were made on representative samples of machines and vehicles. The following measures of daily WBV exposure were obtained: (i) 8-h energy-equivalent frequency-weighted acceleration (highest axis), A(8)(max) in ms(-2) r.m.s.; (ii) A(8)(sum) (root-sum-of-squares) in ms(-2) r.m.s.; (iii) Vibration Dose Value (highest axis), VDV(max) in ms(-1.75); (iv) VDV(sum) (root-sum-of-quads) in ms(-1.75). The cumulative incidence of LBP over the follow-up period was 38.6%. The incidence of high pain intensity and severe disability was 16.8 and 14.4%, respectively. After adjustment for several confounders, VDV(max) or VDV(sum) gave better predictions of LBP outcomes over time than A(8)(max) or A(8)(sum), respectively. Poor predictions were obtained with A(8)(max), which is the currently preferred measure of daily WBV exposure in European countries. In multivariate data analysis, physical work load was a significant predictor of LBP outcomes over the follow-up period. Perceived psychosocial work environment was not associated with LBP.

A Generalization of the Doubling Construction for Sums of Squares Identities

NASA Astrophysics Data System (ADS)

Zhang, Chi; Huang, Hua-Lin

2017-08-01

The doubling construction is a fast and important way to generate new solutions to the Hurwitz problem on sums of squares identities from any known ones. In this short note, we generalize the doubling construction and obtain from any given admissible triple [r,s,n] a series of new ones [r+ρ(2^{m-1}),2^ms,2^mn] for all positive integer m, where ρ is the Hurwitz-Radon function.

AFRL Advanced Electric Lasers Branch - Construction and Upgrade of a 50-watt Facility-Class Sodium Guidestar Pump Laser

NASA Astrophysics Data System (ADS)

Bronder, T.; Miller, H.; Stohs, J.; Lu, C.; Baker, J.; Lucero, A.

The development of a reliable and effective laser source for pumping mesospheric sodium to generate an artificial guidestar has been well documented. From the early achievements with 589nm high-power dye lasers at the Keck and Lick observatories to the ground-breaking 50W CW FASOR (Frequency Addition Source of Optical Radiation) Guidestar at the Air Forces Starfire Optical Range (SOR), there has been intense interest in this technology from both the academic and military communities. Beginning in the fall of 2008, the Air Force Research Laboratorys Advanced Electric Lasers Branch began a project to build, test, verify and deliver an upgraded version of the SOR FASOR for use at the AF Maui Optical Station (AMOS) in the summer of 2010. This FASOR will be similar in design to the existing SOR device and produce 50W of diffraction limited, linearly polarized narrow linewidth 589nm light by combining the output of two injection-locked Nd:YAG ring lasers (operating at 1064nm and 1319nm) using resonant sum-frequency generation in a lithium triborate crystal (LBO). The upgraded features will include modularized sub-components, embedded control electronics, and a simplified cooling system. The first portion of this upgrade project is to reconstruct the current SOR FASOR components and include improved methods of regulating the gain modules of the two injection lasers. In parallel with this effort, the technical plans for the modularization and re-packaging of the FASOR will be finalized and coordinated with the staff at Maui. This presentation will summarize the result of these efforts to date and provide updates on the AMOS FASOR status. Additionally, plans for "next-generation" FASOR upgrades for both SOR and AMOS will also be discussed.

Femtosecond time-resolved vibrational SFG spectroscopy of CO/Ru( 0 0 1 )

NASA Astrophysics Data System (ADS)

Hess, Ch.; Wolf, M.; Roke, S.; Bonn, M.

2002-04-01

Vibrational sum-frequency generation (SFG) employing femtosecond infrared (IR) laser pulses is used to study the dynamics of the C-O stretch vibration on Ru(0 0 1). Time-resolved measurements of the free induction decay (FID) of the IR-polarization for 0.33 ML CO/Ru(0 0 1) exhibit single exponential decays over three decades corresponding to dephasing times of T2=1.94 ps at 95 K and T2=1.16 ps at 340 K. This is consistent with pure homogeneous broadening due to anharmonic coupling with the thermally activated low-frequency dephasing mode together with a contribution from saturation of the IR transition. In pump-probe SFG experiments using a strong visible (VIS) pump pulse the perturbation of the FID leads to transient line shifts even at negative delay times, i.e. when the IR-VIS SFG probe pair precedes the pump pulse. Based on an analysis of the time-dependent polarization we discuss the influence of the perturbed FID on time-resolved SFG spectra. We investigate how coherent effects affect the SFG spectra and we examine the time resolution in these experiments, in particular in dependence of the dephasing time.

Tuning into Scorpius X-1: adapting a continuous gravitational-wave search for a known binary system

NASA Astrophysics Data System (ADS)

Meadors, Grant David; Goetz, Evan; Riles, Keith

2016-05-01

We describe how the TwoSpect data analysis method for continuous gravitational waves (GWs) has been tuned for directed sources such as the low-mass X-ray binary (LMXB), Scorpius X-1 (Sco X-1). A comparison of five search algorithms generated simulations of the orbital and GW parameters of Sco X-1. Whereas that comparison focused on relative performance, here the simulations help quantify the sensitivity enhancement and parameter estimation abilities of this directed method, derived from an all-sky search for unknown sources, using doubly Fourier-transformed data. Sensitivity is shown to be enhanced when the source sky location and period are known, because we can run a fully templated search, bypassing the all-sky hierarchical stage using an incoherent harmonic sum. The GW strain and frequency, as well as the projected semi-major axis of the binary system, are recovered and uncertainty estimated, for simulated signals that are detected. Upper limits for GW strain are set for undetected signals. Applications to future GW observatory data are discussed. Robust against spin-wandering and computationally tractable despite an unknown frequency, this directed search is an important new tool for finding gravitational signals from LMXBs.

[Costs of maternal-infant care in an institutionalized health care system].

PubMed

Villarreal Ríos, E; Salinas Martínez, A M; Guzmán Padilla, J E; Garza Elizondo, M E; Tovar Castillo, N H; García Cornejo, M L

1998-01-01

Partial and total maternal and child health care costs were estimated. The study was developed in a Primary Care Health Clinic (PCHC) and a General Hospital (GH) of a social security health care system. Maternal and child health care services, type of activity and frequency utilization during 1995, were defined; cost examination was done separately for the PCHC and the GH. Estimation of fixed cost included departmentalization, determination of inputs, costs, basic services disbursements, and weighing. These data were related to depreciation, labor period and productivity. Estimation of variable costs required the participation of field experts; costs corresponded to those registered in billing records. The fixed cost plus the variable cost determined the unit cost, which multiplied by the of frequency of utilization generated the prenatal care, labor and delivery care, and postnatal care cost. The sum of these three equaled the maternal and child health care cost. The prenatal care cost was $1,205.33, the labor and delivery care cost was $3,313.98, and the postnatal care was $559.91. The total cost of the maternal and child health care corresponded to $5,079.22. Cost information is valuable for the health care personnel for health care planning activities.

An efficient sampling technique for sums of bandpass functions

NASA Technical Reports Server (NTRS)

Lawton, W. M.

1982-01-01

A well known sampling theorem states that a bandlimited function can be completely determined by its values at a uniformly placed set of points whose density is at least twice the highest frequency component of the function (Nyquist rate). A less familiar but important sampling theorem states that a bandlimited narrowband function can be completely determined by its values at a properly chosen, nonuniformly placed set of points whose density is at least twice the passband width. This allows for efficient digital demodulation of narrowband signals, which are common in sonar, radar and radio interferometry, without the side effect of signal group delay from an analog demodulator. This theorem was extended by developing a technique which allows a finite sum of bandlimited narrowband functions to be determined by its values at a properly chosen, nonuniformly placed set of points whose density can be made arbitrarily close to the sum of the passband widths.

Method and system of doppler correction for mobile communications systems

NASA Technical Reports Server (NTRS)

Georghiades, Costas N. (Inventor); Spasojevic, Predrag (Inventor)

1999-01-01

Doppler correction system and method comprising receiving a Doppler effected signal comprising a preamble signal (32). A delayed preamble signal (48) may be generated based on the preamble signal (32). The preamble signal (32) may be multiplied by the delayed preamble signal (48) to generate an in-phase preamble signal (60). The in-phase preamble signal (60) may be filtered to generate a substantially constant in-phase preamble signal (62). A plurality of samples of the substantially constant in-phase preamble signal (62) may be accumulated. A phase-shifted signal (76) may also be generated based on the preamble signal (32). The phase-shifted signal (76) may be multiplied by the delayed preamble signal (48) to generate an out-of-phase preamble signal (80). The out-of-phase preamble signal (80) may be filtered to generate a substantially constant out-of-phase preamble signal (82). A plurality of samples of the substantially constant out-of-phase signal (82) may be accumulated. A sum of the in-phase preamble samples and a sum of the out-of-phase preamble samples may be normalized relative to each other to generate an in-phase Doppler estimator (92) and an out-of-phase Doppler estimator (94).

Effects of a community-based nutrition promotion programme on child feeding and hygiene practices among caregivers in rural Eastern Ethiopia.

PubMed

Kang, Yunhee; Suh, Youn Kyoung; Debele, Lemma; Juon, Hee-Soon; Christian, Parul

2017-06-01

To evaluate the effectiveness of a community-based participatory nutrition promotion (CPNP) programme involving a 2-week group nutrition session in improving child feeding and hygiene practices among caregivers. Cluster randomized trial. In the intervention area (six clusters), the CPNP programme was added to the context of government nutrition programmes; the control area (six clusters) received the government programme only. Child feeding practices were assessed every 3 months using a 24 h dietary recall questionnaire, and hand washing with soap was assessed every 6 months, over a period of 12 months. Feeding and hygiene measures at each visit were scored and the scores summed up for the entire follow-up period. Habro and Melka Bello districts, Ethiopia. Randomly selected mothers with a child aged 6-12 months (n 1790). A total of 1199 mothers, 629 in the control and 570 in the intervention areas, were assessed at all visits and included in the analysis. Mothers in the intervention area showed higher scores than those in the control area regarding meal frequency (difference: 1·04, 95 % CI 0·35, 1·73), composite feeding score_1 (difference: 1·25, 95 % CI 0·37, 2·13; a summing score of currently breast-feeding, meal frequency and dietary diversity) and composite feeding score_2 (difference: 1·40, 95 % CI 0·49, 2·32; a summing score of meal frequency and dietary diversity). However, there were no differences in the scores of breast-feeding, dietary diversity and hand washing between the two areas (all P>0·05). The CPNP programme was effective in improving some child feeding behaviours in rural Eastern Ethiopia.

Analytic Confusion Matrix Bounds for Fault Detection and Isolation Using a Sum-of-Squared- Residuals Approach

NASA Technical Reports Server (NTRS)

Simon, Dan; Simon, Donald L.

2009-01-01

Given a system which can fail in 1 or n different ways, a fault detection and isolation (FDI) algorithm uses sensor data in order to determine which fault is the most likely to have occurred. The effectiveness of an FDI algorithm can be quantified by a confusion matrix, which i ndicates the probability that each fault is isolated given that each fault has occurred. Confusion matrices are often generated with simulation data, particularly for complex systems. In this paper we perform FDI using sums of squares of sensor residuals (SSRs). We assume that the sensor residuals are Gaussian, which gives the SSRs a chi-squared distribution. We then generate analytic lower and upper bounds on the confusion matrix elements. This allows for the generation of optimal sensor sets without numerical simulations. The confusion matrix bound s are verified with simulated aircraft engine data.

The human oculomotor response to simultaneous visual and physical movements at two different frequencies

NASA Technical Reports Server (NTRS)

Wall, C.; Assad, A.; Aharon, G.; Dimitri, P. S.; Harris, L. R.

2001-01-01

In order to investigate interactions in the visual and vestibular systems' oculomotor response to linear movement, we developed a two-frequency stimulation technique. Thirteen subjects lay on their backs and were oscillated sinusoidally along their z-axes at between 0.31 and 0.81 Hz. During the oscillation subjects viewed a large, high-contrast, visual pattern oscillating in the same direction as the physical motion but at a different, non-harmonically related frequency. The evoked eye movements were measured by video-oculography and spectrally analysed. We found significant signal level at the sum and difference frequencies as well as at other frequencies not present in either stimulus. The emergence of new frequencies indicates non-linear processing consistent with an agreement-detector system that have previously proposed.

Two-wavelength laser-diode heterodyne interferometry with one phasemeter

NASA Astrophysics Data System (ADS)

Onodera, Ribun; Ishii, Yukihiro

1995-12-01

A two-wavelength laser-diode interferometer that is based on heterodyne detection with one phasemeter has been constructed. Two laser diodes are frequency modulated by mutually inverted sawtooth currents on an unbalanced interferometer. One can measure the tested phase at a synthetic wavelength from the sum of the interference beat signals by synchronizing them with the modulation frequency. The experimental result presented shows a phase-measurement range with a 4.7- mu m synthetic wavelength.

Magneto-optical polarization rotation in a ladder-type atomic system for tunable offset locking

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

Parniak, Michał, E-mail: michal.parniak@fuw.edu.pl; Leszczyński, Adam; Wasilewski, Wojciech

2016-04-18

We demonstrate an easily tunable locking scheme for stabilizing frequency-sum of two lasers on a two-photon ladder transition based on polarization rotation in warm rubidium vapors induced by magnetic field and circularly polarized drive field. Unprecedented tunability of the two-photon offset frequency is due to strong splitting and shifting of magnetic states in external field. In our experimental setup, we achieve two-photon detuning of up to 700 MHz.

Note: Demodulation of spectral signal modulated by optical chopper with unstable modulation frequency.

PubMed

Zhang, Shengzhao; Li, Gang; Wang, Jiexi; Wang, Donggen; Han, Ying; Cao, Hui; Lin, Ling; Diao, Chunhong

2017-10-01

When an optical chopper is used to modulate the light source, the rotating speed of the wheel may vary with time and subsequently cause jitter of the modulation frequency. The amplitude calculated from the modulated signal would be distorted when the frequency fluctuations occur. To precisely calculate the amplitude of the modulated light flux, we proposed a method to estimate the range of the frequency fluctuation in the measurement of the spectrum and then extract the amplitude based on the sum of power of the signal in the selected frequency range. Experiments were designed to test the feasibility of the proposed method and the results showed lower root means square error than the conventional way.

Computation of diverging sums based on a finite number of terms

NASA Astrophysics Data System (ADS)

Lv, Q. Z.; Norris, S.; Pelphrey, R.; Su, Q.; Grobe, R.

2017-10-01

We propose a numerical method that permits us to compute the sum of a diverging series from only the first N terms by generalizing the traditional Borel technique. The method is rather robust and can be used to recover the ground state energy from the diverging perturbation theory for quantum field theoretical systems that are spatially constrained. Surprisingly, even the corresponding eigenvectors can be generated despite the intrinsic non-perturbative nature of bound state problems.

A Chronic Fatigue Syndrome (CFS) severity score based on case designation criteria.

PubMed

Baraniuk, James N; Adewuyi, Oluwatoyin; Merck, Samantha Jean; Ali, Mushtaq; Ravindran, Murugan K; Timbol, Christian R; Rayhan, Rakib; Zheng, Yin; Le, Uyenphuong; Esteitie, Rania; Petrie, Kristina N

2013-01-01

Chronic Fatigue Syndrome case designation criteria are scored as physicians' subjective, nominal interpretations of patient fatigue, pain (headaches, myalgia, arthralgia, sore throat and lymph nodes), cognitive dysfunction, sleep and exertional exhaustion. Subjects self-reported symptoms using an anchored ordinal scale of 0 (no symptom), 1 (trivial complaints), 2 (mild), 3 (moderate), and 4 (severe). Fatigue of 3 or 4 distinguished "Fatigued" from "Not Fatigued" subjects. The sum of the 8(Sum8) ancillary criteria was tested as a proxy for fatigue. All subjects had history and physical examinations to exclude medical fatigue, and ensure categorization as healthy or CFS subjects. Fatigued subjects were divided into CFS with ≥4 symptoms or Chronic Idiopathic Fatigue (CIF) with ≤3 symptoms. ROC of Sum8 for CFS and Not Fatigued subjects generated a threshold of 14 (specificity=0.934; sensitivity=0.928). CFS (n=256) and CIF (n=55) criteria were refined to include Sum8≥14 and ≤13, respectively. Not Fatigued subjects had highly skewed Sum8 responses. Healthy Controls (HC; n=269) were defined by fatigue≤2 and Sum8≤13. Those with Sum8≥14 were defined as CFS-Like With Insufficient Fatigue Syndrome (CFSLWIFS; n=20). Sum8 and Fatigue were highly correlated (R(2)=0.977; Cronbach's alpha=0.924) indicating an intimate relationship between symptom constructs. Cluster analysis suggested 4 clades each in CFS and HC. Translational utility was inferred from the clustering of proteomics from cerebrospinal fluid. Plotting Fatigue severity versus Sum8 produced an internally consistent classifying system. This is a necessary step for translating symptom profiles into fatigue phenotypes and their pathophysiological mechanisms.

A Chronic Fatigue Syndrome (CFS) severity score based on case designation criteria

PubMed Central

Baraniuk, James N; Adewuyi, Oluwatoyin; Merck, Samantha Jean; Ali, Mushtaq; Ravindran, Murugan K; Timbol, Christian R; Rayhan, Rakib; Zheng, Yin; Le, Uyenphuong; Esteitie, Rania; Petrie, Kristina N

2013-01-01

Background: Chronic Fatigue Syndrome case designation criteria are scored as physicians’ subjective, nominal interpretations of patient fatigue, pain (headaches, myalgia, arthralgia, sore throat and lymph nodes), cognitive dysfunction, sleep and exertional exhaustion. Methods: Subjects self-reported symptoms using an anchored ordinal scale of 0 (no symptom), 1 (trivial complaints), 2 (mild), 3 (moderate), and 4 (severe). Fatigue of 3 or 4 distinguished “Fatigued” from “Not Fatigued” subjects. The sum of the 8(Sum8) ancillary criteria was tested as a proxy for fatigue. All subjects had history and physical examinations to exclude medical fatigue, and ensure categorization as healthy or CFS subjects. Results: Fatigued subjects were divided into CFS with ≥4 symptoms or Chronic Idiopathic Fatigue (CIF) with ≤3 symptoms. ROC of Sum8 for CFS and Not Fatigued subjects generated a threshold of 14 (specificity=0.934; sensitivity=0.928). CFS (n=256) and CIF (n=55) criteria were refined to include Sum8≥14 and ≤13, respectively. Not Fatigued subjects had highly skewed Sum8 responses. Healthy Controls (HC; n=269) were defined by fatigue≤2 and Sum8≤13. Those with Sum8≥14 were defined as CFS–Like With Insufficient Fatigue Syndrome (CFSLWIFS; n=20). Sum8 and Fatigue were highly correlated (R2=0.977; Cronbach’s alpha=0.924) indicating an intimate relationship between symptom constructs. Cluster analysis suggested 4 clades each in CFS and HC. Translational utility was inferred from the clustering of proteomics from cerebrospinal fluid. Conclusions: Plotting Fatigue severity versus Sum8 produced an internally consistent classifying system. This is a necessary step for translating symptom profiles into fatigue phenotypes and their pathophysiological mechanisms. PMID:23390566

Matching methods evaluation framework for stereoscopic breast x-ray images.

PubMed

Rousson, Johanna; Naudin, Mathieu; Marchessoux, Cédric

2016-01-01

Three-dimensional (3-D) imaging has been intensively studied in the past few decades. Depth information is an important added value of 3-D systems over two-dimensional systems. Special focuses were devoted to the development of stereo matching methods for the generation of disparity maps (i.e., depth information within a 3-D scene). Dedicated frameworks were designed to evaluate and rank the performance of different stereo matching methods but never considering x-ray medical images. Yet, 3-D x-ray acquisition systems and 3-D medical displays have already been introduced into the diagnostic market. To access the depth information within x-ray stereoscopic images, computing accurate disparity maps is essential. We aimed at developing a framework dedicated to x-ray stereoscopic breast images used to evaluate and rank several stereo matching methods. A multiresolution pyramid optimization approach was integrated to the framework to increase the accuracy and the efficiency of the stereo matching techniques. Finally, a metric was designed to score the results of the stereo matching compared with the ground truth. Eight methods were evaluated and four of them [locally scaled sum of absolute differences (LSAD), zero mean sum of absolute differences, zero mean sum of squared differences, and locally scaled mean sum of squared differences] appeared to perform equally good with an average error score of 0.04 (0 is the perfect matching). LSAD was selected for generating the disparity maps.

Rayleigh-enhanced attosecond sum-frequency polarization beats via twin color-locking noisy lights

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

Zhang Yanpeng; Li Long; Ma Ruiqiong

2005-07-15

Based on color-locking noisy field correlation, a time-delayed method is proposed to suppress the thermal effect, and the ultrafast longitudinal relaxation time can be measured even in an absorbing medium. One interesting feature in field-correlation effects is that Rayleigh-enhanced four-wave mixing (RFWM) with color-locking noisy light exhibits spectral symmetry and temporal asymmetry with no coherence spike at {tau}=0. Due to the interference between the Rayleigh-resonant signal and the nonresonant background, RFWM exhibits hybrid radiation-matter detuning with terahertz damping oscillations. The subtle Markovian high-order correlation effects have been investigated in the homodyne- or heterodyne-detected Rayleigh-enhanced attosecond sum-frequency polarization beats (RASPBs). Analyticmore » closed forms of fourth-order Markovian stochastic correlations are characterized for homodyne (quadratic) and heterodyne (linear) detection, respectively. Based on the polarization interference between two four-wave mixing processes, the phase-sensitive detection of RASPBs has also been used to obtain the real and imaginary parts of the Rayleigh resonance.« less

The structure of oleamide films at the aluminum/oil interface and aluminum/air interface studied by Sum Frequency Generation (SFG) vibrational spectroscopy and Reflection Absorption Infrared Spectroscopy (RAIRS).

PubMed

Casford, Michael T L; Davies, Paul B

2009-08-01

The structure of oleamide (cis-9-octadecenamide) films on aluminum has been investigated by sum frequency generation vibrational spectroscopy (SFG) and reflection absorption infrared spectroscopy (RAIRS). Three different film deposition strategies were investigated: (i) films formed by equilibrium adsorption from oleamide solutions in oil, (ii) Langmuir-Blodgett films cast at 1 and 25 mN m(-1), (iii) thick spin-cast films. Both L-B and spin-cast films were examined in air and under oil. The adsorbate formed in the 1 mN m(-1) film in air showed little orientational order. For this film, the spectroscopic results and the ellipsometric thickness point to a relatively conformationally disordered monolayer that is oriented principally in the plane of the interface. Direct adsorption to the metal interface from oil results in SFG spectra of oleamide that are comparable to those observed for the 1 mN m(-1) L-B film in air. In contrast, SFG and RAIRS results for the 25 mN m(-1) film in air and SFG spectra of the spin-cast film in air both show strong conformational ordering and orientational alignment normal to the interface. The 25 mN m(-1) film has an ellipsometric thickness almost twice that of the 1 mN m(-1) L-B film. Taken in combination with the spectroscopic results, this is indicative of a well packed monolayer in air in which the hydrocarbon chain is in an essentially defect-free extended conformation with the methyl terminus oriented away from the surface. A similar structure is also deduced for the surface of the spin-cast film in air. Upon immersion of the 25 mN m(-1) L-B film in oil the SFG spectra show that this film rapidly adopts a relatively disordered structure similar to that seen for the 1 mN m(-1) L-B film in air. Immersion of the spin-cast film in oil results in the gradual disordering of the amide film over a period of several days until the observed spectra become essentially identical to those observed for direct adsorption of oleamide from oil.

Sum Frequency Generation Vibrational Spectroscopy Studies on ModelPeptide Adsorption at the Hydrophobic Solid-Water and HydrophilicSolid-Water Interfaces

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

York, Roger L.

2007-01-01

Sum frequency generation (SFG) vibrational spectroscopy has been used to study the interfacial structure of several polypeptides and amino acids adsorbed to hydrophobic and hydrophilic surfaces under a variety of experimental conditions. Peptide sequence, peptide chain length, peptide hydrophobicity, peptide side-chain type, surface hydrophobicity, and solution ionic strength all affect an adsorbed peptide's interfacial structure. Herein, it is demonstrated that with the choice of simple, model peptides and amino acids, surface specific SFG vibrational spectroscopy can be a powerful tool to elucidate the interfacial structure of these adsorbates. Herein, four experiments are described. In one, a series of isosequential amphiphilicmore » peptides are synthesized and studied when adsorbed to both hydrophobic and hydrophilic surfaces. On hydrophobic surfaces of deuterated polystyrene, it was determined that the hydrophobic part of the peptide is ordered at the solid-liquid interface, while the hydrophilic part of the peptide appears to have a random orientation at this interface. On a hydrophilic surface of silica, it was determined that an ordered peptide was only observed if a peptide had stable secondary structure in solution. In another experiment, the interfacial structure of a model amphiphilic peptide was studied as a function of the ionic strength of the solution, a parameter that could change the peptide's secondary structure in solution. It was determined that on a hydrophobic surface, the peptide's interfacial structure was independent of its structure in solution. This was in contrast to the adsorbed structure on a hydrophilic surface, where the peptide's interfacial structure showed a strong dependence on its solution secondary structure. In a third experiment, the SFG spectra of lysine and proline amino acids on both hydrophobic and hydrophilic surfaces were obtained by using a different experimental geometry that increases the SFG signal. Upon comparison of these spectra to the SFG spectra of interfacial polylysine and polyproline it was determined that the interfacial structure of a peptide is strongly dependent on its chain length. Lastly, SFG spectroscopy has been extended to the Amide I vibrational mode of a peptide (which is sensitive to peptide secondary structure) by building a new optical parametric amplifier based on lithium thioindate. Evidence is presented that suggests that the interfacial secondary structure of a peptide can be perturbed by a surface.« less

High-Pressure Catalytic Reactions of C6 Hydrocarbons on PlatinumSingle-Crystals and nanoparticles: A Sum Frequency Generation VibrationalSpectroscopic and Kinetic Study

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

Bratlie, Kaitlin

Catalytic reactions of cyclohexene, benzene, n-hexane, 2-methylpentane, 3-methylpentane, and 1-hexene on platinum catalysts were monitored in situ via sum frequency generation (SFG) vibrational spectroscopy and gas chromatography (GC). SFG is a surface specific vibrational spectroscopic tool capable of monitoring submonolayer coverages under reaction conditions without gas-phase interference. SFG was used to identify the surface intermediates present during catalytic processes on Pt(111) and Pt(100) single-crystals and on cubic and cuboctahedra Pt nanoparticles in the Torr pressure regime and at high temperatures (300K-450K). At low pressures (<10 -6 Torr), cyclohexene hydrogenated and dehydrogenates to form cyclohexyl (C 6H 11) and π-allyl Cmore » 6H 9, respectively, on Pt(100). Increasing pressures to 1.5 Torr form cyclohexyl, π-allyl C 6H 9, and 1,4-cyclohexadiene, illustrating the necessity to investigate catalytic reactions at high-pressures. Simultaneously, GC was used to acquire turnover rates that were correlated to reactive intermediates observed spectroscopically. Benzene hydrogenation on Pt(111) and Pt(100) illustrated structure sensitivity via both vibrational spectroscopy and kinetics. Both cyclohexane and cyclohexene were produced on Pt(111), while only cyclohexane was formed on Pt(100). Additionally, π-allyl c-C 6H 9 was found only on Pt(100), indicating that cyclohexene rapidly dehydrogenates on the (100) surface. The structure insensitive production of cyclohexane was found to exhibit a compensation effect and was analyzed using the selective energy transfer (SET) model. The SET model suggests that the Pt-H system donates energy to the E 2u mode of free benzene, which leads to catalysis. Linear C 6 (n-hexane, 2-methylpentane, 3-methylpentane, and 1-hexene) hydrocarbons were also investigated in the presence and absence of excess hydrogen on Pt(100). Based on spectroscopic signatures, mechanisms for catalytic isomerization and dehydrocyclization of n-hexane were identified. The structure sensitivity of benzene hydrogenation on shape controlled platinum nanoparticles was also studied. The nanoparticles showed similar selectivities to those found for Pt(111) and Pt(100) single-crystals. Additionally, the nanoparticles have lower activation energies than their single-crystal counterparts.« less

Probing the Orientation of Surface-Immobilized Protein G B1 Using ToF-SIMS Sum Frequency Generation and NEXAFS Spectroscopy

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

L Baugh; T Weidner; J Baio

2011-12-31

The ability to orient active proteins on surfaces is a critical aspect of many medical technologies. An important related challenge is characterizing protein orientation in these surface films. This study uses a combination of time-of-flight secondary ion mass spectrometry (ToF-SIMS), sum frequency generation (SFG) vibrational spectroscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to characterize the orientation of surface-immobilized Protein G B1, a rigid 6 kDa domain that binds the Fc fragment of IgG. Two Protein G B1 variants with a single cysteine introduced at either end were immobilized via the cysteine thiol onto maleimide-oligo(ethylene glycol)-functionalized gold and baremore » gold substrates. X-ray photoelectron spectroscopy was used to measure the amount of immobilized protein, and ToF-SIMS was used to measure the amino acid composition of the exposed surface of the protein films and to confirm covalent attachment of protein thiol to the substrate maleimide groups. SFG and NEXAFS were used to characterize the ordering and orientation of peptide or side chain bonds. On both substrates and for both cysteine positions, ToF-SIMS data showed enrichment of mass peaks from amino acids located at the end of the protein opposite to the cysteine surface position as compared with nonspecifically immobilized protein, indicating end-on protein orientations. Orientation on the maleimide substrate was enhanced by increasing pH (7.0-9.5) and salt concentration (0-1.5 M NaCl). SFG spectral peaks characteristic of ordered {alpha}-helix and {beta}-sheet elements were observed for both variants but not for cysteine-free wild type protein on the maleimide surface. The phase of the {alpha}-helix and {beta}-sheet peaks indicated a predominantly upright orientation for both variants, consistent with an end-on protein binding configuration. Polarization dependence of the NEXAFS signal from the N 1s to {pi}* transition of {beta}-sheet peptide bonds also indicated protein ordering, with an estimated tilt angle of inner {beta}-strands of 40-50{sup o} for both variants (one variant more tilted than the other), consistent with SFG results. The combined results demonstrate the power of using complementary techniques to probe protein orientation on surfaces.« less

UNEXPECTED SERIES OF REGULAR FREQUENCY SPACING OF δ SCUTI STARS IN THE NON-ASYMPTOTIC REGIME. I. THE METHODOLOGY

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

Paparó, M.; Benkő, J. M.; Hareter, M.

A sequence search method was developed to search the regular frequency spacing in δ Scuti stars through visual inspection and an algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 δ Scuti stars observed by CoRoT . We found an unexpectedly large number of independent series of regular frequency spacing in 77 δ Scuti stars (from one to eight sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequences (echelle ridges)more » were found in the 5–21 d{sup −1} region where the pairs of the sequences are shifted (between 0.5 and 0.59 d{sup −1}) by twice the value of the estimated rotational splitting frequency (0.269 d{sup −1}). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT (Fourier transform of the frequencies), and the statistics of the shifts are also compared. In many stars more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to formulate the possible explanation that one spacing is the large separation while the other is the sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d{sup −1}) are in better agreement with the sum of a possible 1.710 d{sup −1} large separation and two or one times, respectively, the value of the rotational frequency.« less

Precision digital pulse phase generator

DOEpatents

McEwan, T.E.

1996-10-08

A timing generator comprises a crystal oscillator connected to provide an output reference pulse. A resistor-capacitor combination is connected to provide a variable-delay output pulse from an input connected to the crystal oscillator. A phase monitor is connected to provide duty-cycle representations of the reference and variable-delay output pulse phase. An operational amplifier drives a control voltage to the resistor-capacitor combination according to currents integrated from the phase monitor and injected into summing junctions. A digital-to-analog converter injects a control current into the summing junctions according to an input digital control code. A servo equilibrium results that provides a phase delay of the variable-delay output pulse to the output reference pulse that linearly depends on the input digital control code. 2 figs.

Precision digital pulse phase generator

DOEpatents

McEwan, Thomas E.

1996-01-01

A timing generator comprises a crystal oscillator connected to provide an output reference pulse. A resistor-capacitor combination is connected to provide a variable-delay output pulse from an input connected to the crystal oscillator. A phase monitor is connected to provide duty-cycle representations of the reference and variable-delay output pulse phase. An operational amplifier drives a control voltage to the resistor-capacitor combination according to currents integrated from the phase monitor and injected into summing junctions. A digital-to-analog converter injects a control current into the summing junctions according to an input digital control code. A servo equilibrium results that provides a phase delay of the variable-delay output pulse to the output reference pulse that linearly depends on the input digital control code.

L(p) approximation capabilities of sum-of-product and sigma-pi-sigma neural networks.

PubMed

Long, Jinling; Wu, Wei; Nan, Dong

2007-10-01

This paper studies the L(p) approximation capabilities of sum-of-product (SOPNN) and sigma-pi-sigma (SPSNN) neural networks. It is proved that the set of functions that are generated by the SOPNN with its activation function in $L_{loc};p(\\mathcal{R})$ is dense in $L;p(\\mathcal{K})$ for any compact set $\\mathcal{K}\\subset \\mathcal{R};N$, if and only if the activation function is not a polynomial almost everywhere. It is also shown that if the activation function of the SPSNN is in ${L_{loc};\\infty(\\mathcal{R})}$, then the functions generated by the SPSNN are dense in $L;p(\\mathcal{K})$ if and only if the activation function is not a constant (a.e.).

Dual-frequency ultrasound for detecting and sizing bubbles.

PubMed

Buckey, Jay C; Knaus, Darin A; Alvarenga, Donna L; Kenton, Marc A; Magari, Patrick J

2005-01-01

ISS construction and Mars exploration require extensive extravehicular activity (EVA), exposing crewmembers to increased decompression sickness risk. Improved bubble detection technologies could help increase EVA efficiency and safety. Creare Inc. has developed a bubble detection and sizing instrument using dual-frequency ultrasound. The device emits "pump" and "image" signals at two frequencies. The low-frequency pump signal causes an appropriately-sized bubble to resonate. When the image frequency hits a resonating bubble, mixing signals are returned at the sum and difference of the two frequencies. To test the feasibility of transcutaneous intravascular detection, intravascular bubbles in anesthetized swine were produced using agitated saline and decompression stress. Ultrasonic transducers on the chest provided the two frequencies. Mixing signals were detected transthoracically in the right atrium using both methods. A histogram of estimated bubble sizes could be constructed. Bubbles can be detected and sized transthoracically in the right atrium using dual-frequency ultrasound. c2005 Elsevier Ltd. All rights reserved.

Design and Implementation of a CMOS Chip for a Prolog

DTIC Science & Technology

1988-03-01

generation scheme . We use the P -circuit [9] with pre-conditioning and post- conditioning 12,3] circuits to generate the carry. The implementation of...system generates vertical microcode for a general purpose processor, the NCR 9300 sys- S tem, from W- code [7]. Three significant pieces of software are...calculation block generating the pro- pagate ( P ) and generate (G) signals needed for carry calculation, and a sum block supplying the final result. The top

An efficient and accurate technique to compute the absorption, emission, and transmission of radiation by the Martian atmosphere

NASA Technical Reports Server (NTRS)

Lindner, Bernhard Lee; Ackerman, Thomas P.; Pollack, James B.

1990-01-01

CO2 comprises 95 pct. of the composition of the Martian atmosphere. However, the Martian atmosphere also has a high aerosol content. Dust particles vary from less than 0.2 to greater than 3.0. CO2 is an active absorber and emitter in near IR and IR wavelengths; the near IR absorption bands of CO2 provide significant heating of the atmosphere, and the 15 micron band provides rapid cooling. Including both CO2 and aerosol radiative transfer simultaneously in a model is difficult. Aerosol radiative transfer requires a multiple scattering code, while CO2 radiative transfer must deal with complex wavelength structure. As an alternative to the pure atmosphere treatment in most models which causes inaccuracies, a treatment was developed called the exponential sum or k distribution approximation. The chief advantage of the exponential sum approach is that the integration over k space of f(k) can be computed more quickly than the integration of k sub upsilon over frequency. The exponential sum approach is superior to the photon path distribution and emissivity techniques for dusty conditions. This study was the first application of the exponential sum approach to Martian conditions.

Seasonally adjusted birth frequencies follow the Poisson distribution.

PubMed

Barra, Mathias; Lindstrøm, Jonas C; Adams, Samantha S; Augestad, Liv A

2015-12-15

Variations in birth frequencies have an impact on activity planning in maternity wards. Previous studies of this phenomenon have commonly included elective births. A Danish study of spontaneous births found that birth frequencies were well modelled by a Poisson process. Somewhat unexpectedly, there were also weekly variations in the frequency of spontaneous births. Another study claimed that birth frequencies follow the Benford distribution. Our objective was to test these results. We analysed 50,017 spontaneous births at Akershus University Hospital in the period 1999-2014. To investigate the Poisson distribution of these births, we plotted their variance over a sliding average. We specified various Poisson regression models, with the number of births on a given day as the outcome variable. The explanatory variables included various combinations of years, months, days of the week and the digit sum of the date. The relationship between the variance and the average fits well with an underlying Poisson process. A Benford distribution was disproved by a goodness-of-fit test (p < 0.01). The fundamental model with year and month as explanatory variables is significantly improved (p < 0.001) by adding day of the week as an explanatory variable. Altogether 7.5% more children are born on Tuesdays than on Sundays. The digit sum of the date is non-significant as an explanatory variable (p = 0.23), nor does it increase the explained variance. INERPRETATION: Spontaneous births are well modelled by a time-dependent Poisson process when monthly and day-of-the-week variation is included. The frequency is highest in summer towards June and July, Friday and Tuesday stand out as particularly busy days, and the activity level is at its lowest during weekends.

Generation and Amplification of Coherent Radiation with Optical Orbital Angular Momentum in a Free-Electron Laser

NASA Astrophysics Data System (ADS)

Hemsing, Erik Willard

The object of this work is to examine how coherent light that carries orbital angular momentum (OAM) can be generated and amplified in a single pass, high-gain free-electron laser (FEL) at the fundamental operating frequency. This concept unites two rapidly expanding, but at present largely non-overlapping fields of study: high-order OAM light modes, which interact in new ways with matter, and FELs, in which a relativistically energetic electron beam emits coherent, ultra high-brightness, highly frequency-tunable light. The ability to generate OAM light in an FEL enables new regimes of laser interaction physics to be explored at wavelengths down to hard x-rays. The theoretical portion of this dissertation attempts to provide a new predictive mathematical framework. It builds on existing work, and describes the three-dimensional electromagnetic field of the high-gain FEL as a sum of OAM modes such that the amplification properties of individual modes can be characterized. The effects of uncorrelated energy spread, longitudinal space charge, energy detuning, and transverse emittance in the electron beam are included, as is the diffraction of the laser light. Theoretical predictions are corroborated by detailed numerical Genesis 1.3 simulations. When the theory is extended to frequency harmonics, a novel interaction is uncovered that generates a helical electron beam density distribution. These predictions are also supported by numerical Tredi simulations. This type of highly correlated structure is shown to naturally emit OAM light, and forms the basis of a new high-gain, high-mode generation (HGHMG) scheme proposed in its entirety here. The experimental section examines the helical microbunching concept in a proof-of-principle experiment dubbed HELIX, performed at the UCLA Neptune laboratory. We present detailed measurement of the coherent transition radiation emitted by the 12.5 MeV electron beam that is microbunched in a second harmonic interaction with an input laser and helical undulator. The predicted dependence of the CTR signal on the input laser polarization is observed, and is consistent with microbunching that has a periodicity near the 10.6 mum wavelength of the 30 MW CO2 laser pulse. Scans of the interaction energy bandwidth are consistent with predictions that indicate a dominant azimuthal density mode with a bunching factor of 10%, and thus provide indication of the first experimental evidence of helical microbunching. This result offers support for future successful realization of the proposed HGHMG scheme to generate OAM modes in high-gain FELs.

Measuring Radiofrequency and Microwave Radiation from Varying Signal Strengths

NASA Technical Reports Server (NTRS)

Davis, Bette; Gaul, W. C.

2007-01-01

This viewgraph presentation discusses the process of measuring radiofrequency and microwave radiation from various signal strengths. The topics include: 1) Limits and Guidelines; 2) Typical Variable Standard (IEEE) Frequency Dependent; 3) FCC Standard 47 CFR 1.1310; 4) Compliance Follows Unity Rule; 5) Multiple Sources Contribute; 6) Types of RF Signals; 7) Interfering Radiations; 8) Different Frequencies Different Powers; 9) Power Summing - Peak Power; 10) Contribution from Various Single Sources; 11) Total Power from Multiple Sources; 12) Are You Out of Compliance?; and 13) In Compliance.

An Approach to Co-Channel Talker Interference Suppression Using a Sinusoidal Model for Speech

DTIC Science & Technology

1988-02-05

Massachusetts Institute of Technologp, with the ’Apport of the Department of the Air Force under Contract F19628-85-C-0002. ŕir re-port tniay be...Extracted from Summed Vocalic Waveforms 28 5-1 Failure of the Least Squares Solution with Closely-Spaced Frequencies. (a) Crossing Frequency Tracks, (b... Crossing Pitch Contours. 31 5-2 Multi-Frame Interpolation 33 5-3 Different Forms of Multi-Frame Interpolation 33 5-4 Recovery of Missing Lobe with Multi

A Broadband Infrared Laser Source (2.5-17 μm) for Plasma Diagnostics

NASA Astrophysics Data System (ADS)

Ionin, A. A.; Kinyaevskii, I. O.; Klimachev, Yu. M.; Kozlov, A. Yu.; Kotkov, A. A.

2017-12-01

This paper presents the results of studies aimed at the creation of a hybrid laser system which is composed of a gas lasers and a nonlinear crystal and appreciably broadens and enriches the radiation spectrum of these lasers. A highly efficient conversion (37%) is attained when generating the second harmonic in a ZnGeP2 crystal owing to an increase in the peak power of CO laser radiation in the mode locking regime. The two-cascade conversion (generation of both sum and difference frequencies) of radiation of a broadband CO laser in the single sample of such nonlinear crystals as ZnGeP2 and AgGaSe2 is demonstrated. In this case, the radiation spectrum is broadened by nearly a factor of two, and the number of detected spectral lines grows by a factor of four. The use of a comparatively simple laser system of gas-discharge CO and CO2 lasers to conversion in AgGaSe2 results in laser radiation tunable over a set of narrow spectral lines within a range from 2.5 to 16.6 μm (more than two and a half octaves).