Amplitude and phase controlled adaptive optics system

NASA Astrophysics Data System (ADS)

Pham, Ich; Ma, Sam

2006-06-01

An adaptive optics (AO) system is used to control the deformable mirror (DM) actuators for compensating the optical effects introduced by the turbulence in the Earth's atmosphere and distortions produced by the optical elements between the distant object and its local sensor. The typical AO system commands the DM actuators while minimizing the measured wave front (WF) phase error. This is known as the phase conjugator system, which does not work well in the strong scintillation condition because both amplitude and phase are corrupted along the propagation path. In order to compensate for the wave front amplitude, a dual DM field conjugator system may be used. The first and second DM compensate for the amplitude and the phase respectively. The amplitude controller requires the mapping from DM1 actuator command to DM2 intensity. This can be obtained from either a calibration routine or an intensity transport equation, which relates the phase to the intensity. Instead of a dual-DM, a single Spatial Light Modulator (SLM) may control the amplitude and phase independently. The technique uses the spatial carrier frequency and the resulting intensity is related to the carrier modulation, while the phase is the average carrier phase. The dynamical AO performance using the carrier modulation is limited by the actuator frequency response and not by the computational load of the controller algorithm. Simulation of the proposed field conjugator systems show significant improvement for the on-axis performance compared to the phase conjugator system.

Spatial-heterodyne interferometry for transmission (SHIFT) measurements

DOEpatents

Bingham, Philip R.; Hanson, Gregory R.; Tobin, Ken W.

2006-10-10

Systems and methods are described for spatial-heterodyne interferometry for transmission (SHIFT) measurements. A method includes digitally recording a spatially-heterodyned hologram including spatial heterodyne fringes for Fourier analysis using a reference beam, and an object beam that is transmitted through an object that is at least partially translucent; Fourier analyzing the digitally recorded spatially-heterodyned hologram, by shifting an original origin of the digitally recorded spatially-heterodyned hologram to sit on top of a spatial-heterodyne carrier frequency defined by an angle between the reference beam and the object beam, to define an analyzed image; digitally filtering the analyzed image to cut off signals around the original origin to define a result; and performing an inverse Fourier transform on the result.

Evaluation of local free carrier concentrations in individual heavily-doped GaN:Si micro-rods by micro-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Mohajerani, M. S.; Khachadorian, S.; Schimpke, T.; Nenstiel, C.; Hartmann, J.; Ledig, J.; Avramescu, A.; Strassburg, M.; Hoffmann, A.; Waag, A.

2016-02-01

Three-dimensional III-nitride micro-structures are being developed as a promising candidate for the future opto-electrical devices. In this study, we demonstrate a quick and straight-forward method to locally evaluate free-carrier concentrations and a crystalline quality in individual GaN:Si micro-rods. By employing micro-Raman mapping and analyzing lower frequency branch of A1(LO)- and E1(LO)-phonon-plasmon-coupled modes (LPP-), the free carrier concentrations are determined in axial and planar configurations, respectively. Due to a gradual doping profile along the micro-rods, a highly spatially resolved mapping on the sidewall is exploited to reconstruct free carrier concentration profile along the GaN:Si micro-rods. Despite remarkably high free carrier concentrations above 1 × 1020 cm-3, the micro-rods reveal an excellent crystalline quality, without a doping-induced stress.

Hearing and spatial behavior in Gryllotalpa major Saussure (Orthoptera: Gryllotalpidae).

PubMed

Howard, Daniel R; Mason, Andrew C; Hill, Peggy S M

2008-11-01

The prairie mole cricket (Gryllotalpa major Saussure) is a rare orthopteran insect of the tallgrass prairie ecosystem of the south central USA. Populations are known to currently occupy fragmented prairie sites in Oklahoma, Arkansas, Kansas and Missouri, including The Nature Conservancy's Tallgrass Prairie Preserve in north central Oklahoma. Prairie mole cricket populations were surveyed at this site and at another site in Craig County, OK during the spring of 2005 and 2006, using the male cricket's acoustic call to locate advertising aggregations of males. Five males from one large aggregation were removed in a study to describe (1) the hearing thresholds across the call's range of frequencies, (2) the distances over which the higher harmonic components of the male's calls are potentially detectable, (3) the species' sensitivity to ultrasound and (4) the spatio-auditory dynamics of the prairie mole cricket lek. Results indicate that G. major has a bimodal pattern of frequency tuning, with hearing sensitivities greatest at the 2 kHz carrier frequency (41 dB SPL) and declining through the call's frequency range (84 dB at 10 kHz). A second sensitivity peak is evident in the ultrasound range at 25 kHz (62 dB SPL). Spatial analysis of G. major lek sites indicates that approximately 73% of males within the lek are spaced in such a way as to allow acoustic interaction at the species' carrier frequency, while any information in higher harmonic overtones in the call appears to be available only to nearest neighbors.

Photo-Carrier Multi-Dynamical Imaging at the Nanometer Scale in Organic and Inorganic Solar Cells.

PubMed

Fernández Garrillo, Pablo A; Borowik, Łukasz; Caffy, Florent; Demadrille, Renaud; Grévin, Benjamin

2016-11-16

Investigating the photocarrier dynamics in nanostructured and heterogeneous energy materials is of crucial importance from both fundamental and technological points of view. Here, we demonstrate how noncontact atomic force microscopy combined with Kelvin probe force microscopy under frequency-modulated illumination can be used to simultaneously image the surface photopotential dynamics at different time scales with a sub-10 nm lateral resolution. The basic principle of the method consists in the acquisition of spectroscopic curves of the surface potential as a function of the illumination frequency modulation on a two-dimensional grid. We show how this frequency-spectroscopy can be used to probe simultaneously the charging rate and several decay processes involving short-lived and long-lived carriers. With this approach, dynamical images of the trap-filling, trap-delayed recombination and nongeminate recombination processes have been acquired in nanophase segregated organic donor-acceptor bulk heterojunction thin films. Furthermore, the spatial variation of the minority carrier lifetime has been imaged in polycrystalline silicon thin films. These results establish two-dimensional multidynamical photovoltage imaging as a universal tool for local investigations of the photocarrier dynamics in photoactive materials and devices.

Development of Michelson interferometer based spatial phase-shift digital shearography

NASA Astrophysics Data System (ADS)

Xie, Xin

Digital shearography is a non-contact, full field, optical measurement method, which has the capability of directly measuring the gradient of deformation. For high measurement sensitivity, phase evaluation method has to be introduced into digital shearography by phase-shift technique. Catalog by phase-shift method, digital phase-shift shearography can be divided into Temporal Phase-Shift Digital Shearography (TPS-DS) and Spatial Phase-Shift Digital Shearography (SPS-DS). TPS-DS is the most widely used phase-shift shearography system, due to its simple algorithm, easy operation and good phase-map quality. However, the application of TPS-DS is only limited in static/step-by-step loading measurement situation, due to its multi-step shifting process. In order to measure the strain under dynamic/continuous loading situation, a SPS-DS system has to be developed. This dissertation aims to develop a series of Michelson Interferometer based SPS-DS measurement methods to achieve the strain measurement by using only a single pair of speckle pattern images. The Michelson Interferometer based SPS-DS systems utilize special designed optical setup to introduce extra carrier frequency into the laser wavefront. The phase information corresponds to the strain field can be separated on the Fourier domain using a Fourier Transform and can further be evaluated with a Windowed Inverse Fourier Transform. With different optical setups and carrier frequency arrangements, the Michelson Interferometer based SPS-DS method is capable to achieve a variety of measurement tasks using only single pair of speckle pattern images. Catalog by the aimed measurand, these capable measurement tasks can be divided into five categories: 1) measurement of out-of-plane strain field with small shearing amount; 2) measurement of relative out-of-plane deformation field with big shearing amount; 3) simultaneous measurement of relative out-of-plane deformation field and deformation gradient field by using multiple carrier frequencies; 4) simultaneous measurement of two directional strain field using dual measurement channels 5) measurement of pure in-plane strain and pure out-of-plane strain with multiple carrier frequencies. The basic theory, optical path analysis, preliminary studies, results analysis and research plan are shown in detail in this dissertation.

The Effects of Spatial Diversity and Imperfect Channel Estimation on Wideband MC-DS-CDMA and MC-CDMA

DTIC Science & Technology

2009-10-01

In our previous work, we compared the theoretical bit error rates of multi-carrier direct sequence code division multiple access (MC- DS - CDMA ) and...consider only those cases where MC- CDMA has higher frequency diversity than MC- DS - CDMA . Since increases in diversity yield diminishing gains, we conclude

Nonuniform carrier density in Cd 3 As 2 evidenced by optical spectroscopy

DOE PAGES

Crassee, I.; Martino, E.; Homes, C. C.; ...

2018-03-22

In this paper, we report the detailed optical properties of Cd 3As 2 crystals in a wide parameter space: temperature, magnetic field, carrier concentration, and crystal orientation. We investigate high-quality crystals synthesized by three different techniques. In all the studied samples, independently of how they were prepared and how they were treated before the optical experiments, our data indicate conspicuous fluctuations in the carrier density (up to 30%). These charge puddles have a characteristic scale of 100 μm, they become more pronounced at low temperatures, and possibly, they become enhanced by the presence of crystal twinning. The Drude response ismore » characterized by very small scattering rates (~1 meV) for as-grown samples. Mechanical treatment, such as cutting or polishing, influences the optical properties of single crystals, by increasing the Drude scattering rate and also modifying the high-frequency optical response. Finally, magnetoreflectivity and Kerr rotation are consistent with electronlike charge carriers and a spatially nonuniform carrier density.« less

Nonuniform carrier density in Cd3As2 evidenced by optical spectroscopy

NASA Astrophysics Data System (ADS)

Crassee, I.; Martino, E.; Homes, C. C.; Caha, O.; Novák, J.; Tückmantel, P.; Hakl, M.; Nateprov, A.; Arushanov, E.; Gibson, Q. D.; Cava, R. J.; Koohpayeh, S. M.; Arpino, K. E.; McQueen, T. M.; Orlita, M.; Akrap, Ana

2018-03-01

We report the detailed optical properties of Cd3As2 crystals in a wide parameter space: temperature, magnetic field, carrier concentration, and crystal orientation. We investigate high-quality crystals synthesized by three different techniques. In all the studied samples, independently of how they were prepared and how they were treated before the optical experiments, our data indicate conspicuous fluctuations in the carrier density (up to 30%). These charge puddles have a characteristic scale of 100 μ m , they become more pronounced at low temperatures, and possibly, they become enhanced by the presence of crystal twinning. The Drude response is characterized by very small scattering rates (˜1 meV) for as-grown samples. Mechanical treatment, such as cutting or polishing, influences the optical properties of single crystals, by increasing the Drude scattering rate and also modifying the high-frequency optical response. Magnetoreflectivity and Kerr rotation are consistent with electronlike charge carriers and a spatially nonuniform carrier density.

Nonuniform carrier density in Cd 3 As 2 evidenced by optical spectroscopy

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

Crassee, I.; Martino, E.; Homes, C. C.

In this paper, we report the detailed optical properties of Cd 3As 2 crystals in a wide parameter space: temperature, magnetic field, carrier concentration, and crystal orientation. We investigate high-quality crystals synthesized by three different techniques. In all the studied samples, independently of how they were prepared and how they were treated before the optical experiments, our data indicate conspicuous fluctuations in the carrier density (up to 30%). These charge puddles have a characteristic scale of 100 μm, they become more pronounced at low temperatures, and possibly, they become enhanced by the presence of crystal twinning. The Drude response ismore » characterized by very small scattering rates (~1 meV) for as-grown samples. Mechanical treatment, such as cutting or polishing, influences the optical properties of single crystals, by increasing the Drude scattering rate and also modifying the high-frequency optical response. Finally, magnetoreflectivity and Kerr rotation are consistent with electronlike charge carriers and a spatially nonuniform carrier density.« less

Acoustic manipulation of active spherical carriers: Generation of negative radiation force

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

Rajabi, Majid, E-mail: majid_rajabi@iust.ac.ir; Mojahed, Alireza

2016-09-15

This paper examines theoretically a novel mechanism of generating negative (pulling) radiation force for acoustic manipulation of spherical carriers equipped with piezoelectric actuators in its inner surface. In this mechanism, the spherical particle is handled by common plane progressive monochromatic acoustic waves instead of zero-/higher- order Bessel beams or standing waves field. The handling strategy is based on applying a spatially uniform harmonic electrical voltage at the piezoelectric actuator with the same frequency of handling acoustic waves, in order to change the radiation force effect from repulsive (away from source) to attractive (toward source). This study may be considered asmore » a start point for development of contact-free precise handling and entrapment technology of active carriers which are essential in many engineering and medicine applications.« less

47 CFR 73.1540 - Carrier frequency measurements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 73.1540 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES... measurements. (a) The carrier frequency of each AM and FM station and the visual carrier frequency and the difference between the visual carrier and the aural carrier or center frequency of each TV and Class A TV...

Monitoring method and apparatus using high-frequency carrier

DOEpatents

Haynes, Howard D.

1996-01-01

A method and apparatus for monitoring an electrical-motor-driven device by injecting a high frequency carrier signal onto the power line current. The method is accomplished by injecting a high frequency carrier signal onto an AC power line current. The AC power line current supplies the electrical-motor-driven device with electrical energy. As a result, electrical and mechanical characteristics of the electrical-motor-driven device modulate the high frequency carrier signal and the AC power line current. The high frequency carrier signal is then monitored, conditioned and demodulated. Finally, the modulated high frequency carrier signal is analyzed to ascertain the operating condition of the electrical-motor-driven device.

47 CFR 73.1545 - Carrier frequency departure tolerances.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 4 2010-10-01 2010-10-01 false Carrier frequency departure tolerances. 73.1545... departure tolerances. (a) AM stations. The departure of the carrier frequency for monophonic transmissions.... The departure of the carrier frequency of Class A TV stations may not exceed the values specified in...

Monitoring method and apparatus using high-frequency carrier

DOEpatents

Haynes, H.D.

1996-04-30

A method and apparatus for monitoring an electrical-motor-driven device by injecting a high frequency carrier signal onto the power line current. The method is accomplished by injecting a high frequency carrier signal onto an AC power line current. The AC power line current supplies the electrical-motor-driven device with electrical energy. As a result, electrical and mechanical characteristics of the electrical-motor-driven device modulate the high frequency carrier signal and the AC power line current. The high frequency carrier signal is then monitored, conditioned and demodulated. Finally, the modulated high frequency carrier signal is analyzed to ascertain the operating condition of the electrical-motor-driven device. 6 figs.

On interaction of P-waves with one-dimensional photonic crystal consisting of weak conducting matter and transparent dielectric layers

NASA Astrophysics Data System (ADS)

Yushkanov, A. A.; Zverev, N. V.

2018-03-01

An influence of quantum and spatial dispersion properties of the non-degenerate electron plasma on the interaction of electromagnetic P-waves with one-dimensional photonic crystal consisting of conductor with low carrier electron density and transparent dielectric matter, is studied numerically. It is shown that at the frequencies of order of the plasma frequency and at small widths of the conducting and dielectric layers of the photonic crystal, optical coefficients in the quantum non-degenerate plasma approach differ from the coefficients in the classical electron gas approach. And also, at these frequencies one observes a temperature dependence of the optical coefficients.

Intelligent Data Transfer for Multiple Sensor Networks over a Broad Temperature Range

NASA Technical Reports Server (NTRS)

Krasowski, Michael (Inventor)

2018-01-01

A sensor network may be configured to operate in extreme temperature environments. A sensor may be configured to generate a frequency carrier, and transmit the frequency carrier to a node. The node may be configured to amplitude modulate the frequency carrier, and transmit the amplitude modulated frequency carrier to a receiver.

Physiological and content considerations for a second low frequency channel for bass management, subwoofers, and low frequency enhancement (LFE)

NASA Astrophysics Data System (ADS)

Miller, Robert E. (Robin)

2005-04-01

Perception of very low frequencies (VLF) below 125 Hz reproduced by large woofers and subwoofers (SW), encompassing 3 octaves of the 10 regarded as audible, has physiological and content aspects. Large room acoustics and vibrato add VLF fluctuations, modulating audible carrier frequencies to >1 Hz. By convention, sounds below 90 Hz produce no interaural cues useful for spatial perception or localization, therefore bass management redirects the VLF range from main channels to a single (monaural) subwoofer channel, even if to more than one subwoofer. Yet subjects claim they hear a difference between a single subwoofer channel and two (stereo bass). If recordings contain spatial VLF content, is it possible physiologically to perceive interaural time/phase difference (ITD/IPD) between 16 and 125 Hz? To what extent does this perception have a lifelike quality; to what extent is it localization? If a first approximation of localization, would binaural SWs allow a higher crossover frequency (smaller satellite speakers)? Reported research supports the Jeffress model of ITD determination in brain structures, and extending the accepted lower frequency limit of IPD. Meanwhile, uncorrelated very low frequencies exist in all tested multi-channel music and movie content. The audibility, recording, and reproduction of uncorrelated VLF are explored in theory and experiments.

A Dual Frequency Carrier Phase Error Difference Checking Algorithm for the GNSS Compass.

PubMed

Liu, Shuo; Zhang, Lei; Li, Jian

2016-11-24

The performance of the Global Navigation Satellite System (GNSS) compass is related to the quality of carrier phase measurement. How to process the carrier phase error properly is important to improve the GNSS compass accuracy. In this work, we propose a dual frequency carrier phase error difference checking algorithm for the GNSS compass. The algorithm aims at eliminating large carrier phase error in dual frequency double differenced carrier phase measurement according to the error difference between two frequencies. The advantage of the proposed algorithm is that it does not need additional environment information and has a good performance on multiple large errors compared with previous research. The core of the proposed algorithm is removing the geographical distance from the dual frequency carrier phase measurement, then the carrier phase error is separated and detectable. We generate the Double Differenced Geometry-Free (DDGF) measurement according to the characteristic that the different frequency carrier phase measurements contain the same geometrical distance. Then, we propose the DDGF detection to detect the large carrier phase error difference between two frequencies. The theoretical performance of the proposed DDGF detection is analyzed. An open sky test, a manmade multipath test and an urban vehicle test were carried out to evaluate the performance of the proposed algorithm. The result shows that the proposed DDGF detection is able to detect large error in dual frequency carrier phase measurement by checking the error difference between two frequencies. After the DDGF detection, the accuracy of the baseline vector is improved in the GNSS compass.

Healthy versus Entorhinal Cortical Atrophy Identification in Asymptomatic APOE4 Carriers at Risk for Alzheimer’s Disease

PubMed Central

Konishi, Kyoko; Joober, Ridha; Poirier, Judes; MacDonald, Kathleen; Chakravarty, Mallar; Patel, Raihaan; Breitner, John; Bohbot, Véronique D.

2018-01-01

Early detection of Alzheimer’s disease (AD) has been challenging as current biomarkers are invasive and costly. Strong predictors of future AD diagnosis include lower volume of the hippocampus and entorhinal cortex, as well as the ɛ4 allele of the Apolipoprotein E gene (APOE) gene. Therefore, studying functions that are critically mediated by the hippocampus and entorhinal cortex, such as spatial memory, in APOE ɛ4 allele carriers, may be key to the identification of individuals at risk of AD, prior to the manifestation of cognitive impairments. Using a virtual navigation task developed in-house, specifically designed to assess spatial versus non-spatial strategies, the current study is the first to differentiate functional and structural differences within APOE ɛ4 allele carriers. APOE ɛ4 allele carriers that predominantly use non-spatial strategies have decreased fMRI activity in the hippocampus and increased atrophy in the hippocampus, entorhinal cortex, and fimbria compared to APOE ɛ4 allele carriers who use spatial strategies. In contrast, APOE ɛ4 allele carriers who use spatial strategies have grey matter levels comparable to non-APOE ɛ4 allele carriers. Furthermore, in a leave-one-out analysis, grey matter in the entorhinal cortex could predict navigational strategy with 92% accuracy. PMID:29278888

Healthy versus Entorhinal Cortical Atrophy Identification in Asymptomatic APOE4 Carriers at Risk for Alzheimer's Disease.

PubMed

Konishi, Kyoko; Joober, Ridha; Poirier, Judes; MacDonald, Kathleen; Chakravarty, Mallar; Patel, Raihaan; Breitner, John; Bohbot, Véronique D

2018-01-01

Early detection of Alzheimer's disease (AD) has been challenging as current biomarkers are invasive and costly. Strong predictors of future AD diagnosis include lower volume of the hippocampus and entorhinal cortex, as well as the ɛ4 allele of the Apolipoprotein E gene (APOE) gene. Therefore, studying functions that are critically mediated by the hippocampus and entorhinal cortex, such as spatial memory, in APOE ɛ4 allele carriers, may be key to the identification of individuals at risk of AD, prior to the manifestation of cognitive impairments. Using a virtual navigation task developed in-house, specifically designed to assess spatial versus non-spatial strategies, the current study is the first to differentiate functional and structural differences within APOE ɛ4 allele carriers. APOE ɛ4 allele carriers that predominantly use non-spatial strategies have decreased fMRI activity in the hippocampus and increased atrophy in the hippocampus, entorhinal cortex, and fimbria compared to APOE ɛ4 allele carriers who use spatial strategies. In contrast, APOE ɛ4 allele carriers who use spatial strategies have grey matter levels comparable to non-APOE ɛ4 allele carriers. Furthermore, in a leave-one-out analysis, grey matter in the entorhinal cortex could predict navigational strategy with 92% accuracy.

Cyclic additional optical true time delay for microwave beam steering with spectral filtering.

PubMed

Cao, Z; Lu, R; Wang, Q; Tessema, N; Jiao, Y; van den Boom, H P A; Tangdiongga, E; Koonen, A M J

2014-06-15

Optical true time delay (OTTD) is an attractive way to realize microwave beam steering (MBS) due to its inherent features of broadband, low-loss, and compactness. In this Letter, we propose a novel OTTD approach named cyclic additional optical true time delay (CAO-TTD). It applies additional integer delays of the microwave carrier frequency to achieve spectral filtering but without disturbing the spatial filtering (beam steering). Based on such concept, a broadband MBS scheme for high-capacity wireless communication is proposed, which allows the tuning of both spectral filtering and spatial filtering. The experimental results match well with the theoretical analysis.

Photon energy lifter.

PubMed

Gaburro, Zeno; Ghulinyan, Mher; Riboli, Francesco; Pavesi, Lorenzo; Recati, Alessio; Carusotto, Iacopo

2006-08-07

We propose a time-dependent, spatially periodic photonic structure which is able to shift the carrier frequency of an optical pulse which propagates through it. Taking advantage of the slow group velocity of light in periodic photonic structures, the wavelength conversion process can be performed with an efficiency close to 1 and without affecting the shape and the coherence of the pulse. Quantitative Finite Difference Time Domain simulations are performed for realistic systems with optical parameters of conventional silicon technology.

Off-axis illumination direct-to-digital holography

DOEpatents

Thomas, Clarence E.; Price, Jeffery R.; Voelkl, Edgar; Hanson, Gregory R.

2004-06-08

Systems and methods are described for off-axis illumination direct-to-digital holography. A method of recording an off-axis illuminated spatially heterodyne hologram including spatially heterodyne fringes for Fourier analysis, includes: reflecting a reference beam from a reference mirror at a non-normal angle; reflecting an object beam from an object at an angle with respect to an optical axis defined by a focusing lens; focusing the reference beam and the object beam at a focal plane of a digital recorder to form the off-axis illuminated spatially heterodyne hologram including spatially heterodyne fringes for Fourier analysis; digitally recording the off-axis illuminated spatially heterodyne hologram including spatially heterodyne fringes for Fourier analysis; Fourier analyzing the recorded off-axis illuminated spatially heterodyne hologram including spatially heterodyne fringes by transforming axes of the recorded off-axis illuminated spatially heterodyne hologram including spatially heterodyne fringes in Fourier space to sit on top of a heterodyne carrier frequency defined as an angle between the reference beam and the object beam; applying a digital filter to cut off signals around an original origin; and then performing an inverse Fourier transform.

140 GHz pulsed Fourier transform microwave spectrometer

DOEpatents

Kolbe, W.F.; Leskovar, B.

1985-07-29

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer, including means for generating a high frequency carrier signal, and means for generating a low frequency modulating signal. The carrier signal is continuously fed to a modulator and the modulating signal is fed through a pulse switch to the modulator. When the pulse switch is on, the modulator will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device is tuned to one of the sideband signals and sway from the carrier frequency so that the high frequency energization of the frequency-responsive device is controlled by the pulse switch.

140 GHz pulsed Fourier transform microwave spectrometer

DOEpatents

Kolbe, W.F.; Leskovar, B.

1987-10-27

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer, including means for generating a high frequency carrier signal, and means for generating a low frequency modulating signal is disclosed. The carrier signal is continuously fed to a modulator and the modulating signal is fed through a pulse switch to the modulator. When the pulse switch is on, the modulator will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device is tuned to one of the sideband signals and away from the carrier frequency so that the high frequency energization of the frequency-responsive device is controlled by the pulse switch. 5 figs.

Spontaneous generation of frequency combs in QD lasers

NASA Astrophysics Data System (ADS)

Columbo, Lorenzo Luigi; Bardella, Paolo; Gioannini, Mariangela

2018-02-01

We report a systematic analysis of the phenomenon of self-generation of optical frequency combs in single section Fabry-Perot Quantum Dot lasers using a Time Domain Travelling Wave model. We show that the carriers grating due to the standing wave pattern (spatial hole burning) peculiar of Quantum Dots laser and the Four Wave Mixing are the key ingredients to explain spontaneous Optical Frequency Combs in these devices. Our results well agree with recent experimental evidences reported in semiconductor lasers based on Quantum Dots and Quantum Dashes active material and pave the way to the development of a simulation tool for the design of these comb laser sources for innovative applications in the field of high-data rate optical communications.

140 GHz pulsed fourier transform microwave spectrometer

DOEpatents

Kolbe, William F.; Leskovar, Branko

1987-01-01

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer (10), including means (11, 19) for generating a high frequency carrier signal, and means (12) for generating a low frequency modulating signal. The carrier signal is continuously fed to a modulator (20) and the modulating signal is fed through a pulse switch (23) to the modulator. When the pulse switch (23) is on, the modulator (20) will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device (31) is tuned to one of the sideband signals and away from the carrier frequency so that the high frequency energization of the frequency-responsive device (31) is controlled by the pulse switch (23).

Acoustic manipulation: Bessel beams and active carriers

NASA Astrophysics Data System (ADS)

Rajabi, Majid; Mojahed, Alireza

2017-10-01

In this paper, we address the interaction of zero-order acoustic Bessel beams as an acoustic manipulation tool, with an active spherical shell, as a carrier in drug, agent, or material delivery systems, in order to investigate the controllability of exerted acoustic radiation force as the driver. The active body is comprised of a spherical elastic shell stimulated in its monopole mode of vibrations with the same frequency as the incident wave field via an internally bonded and spatially uniformly excited piezoelectric actuator. The main aim of this work is to examine the performance of a nondiffracting and self-reconstructing zero-order Bessel beam to obtain the full manipulability condition of active carriers in comparison with the case of a plane wave field. The results unveil some unique potentials of the Bessel beams in the company of active carriers, with emphasis on the consumed power of the actuation system. This paper will widen the path toward the single-beam robust acoustic manipulation techniques and may lead to the prospect of combined tweezers and fields, with applications in delivery systems, microswimmers, and trapper designs.

Performance Analysis of Control Signal Transmission Technique for Cognitive Radios in Dynamic Spectrum Access Networks

NASA Astrophysics Data System (ADS)

Sakata, Ren; Tomioka, Tazuko; Kobayashi, Takahiro

When cognitive radio (CR) systems dynamically use the frequency band, a control signal is necessary to indicate which carrier frequencies are currently available in the network. In order to keep efficient spectrum utilization, this control signal also should be transmitted based on the channel conditions. If transmitters dynamically select carrier frequencies, receivers have to receive control signals without knowledge of their carrier frequencies. To enable such transmission and reception, this paper proposes a novel scheme called DCPT (Differential Code Parallel Transmission). With DCPT, receivers can receive low-rate information with no knowledge of the carrier frequencies. The transmitter transmits two signals whose carrier frequencies are spaced by a predefined value. The absolute values of the carrier frequencies can be varied. When the receiver acquires the DCPT signal, it multiplies the signal by a frequency-shifted version of the signal; this yields a DC component that represents the data signal which is then demodulated. The performance was evaluated by means of numerical analysis and computer simulation. We confirmed that DCPT operates successfully even under severe interference if its parameters are appropriately configured.

A review of recent advances in the spherical harmonics expansion method for semiconductor device simulation.

PubMed

Rupp, K; Jungemann, C; Hong, S-M; Bina, M; Grasser, T; Jüngel, A

The Boltzmann transport equation is commonly considered to be the best semi-classical description of carrier transport in semiconductors, providing precise information about the distribution of carriers with respect to time (one dimension), location (three dimensions), and momentum (three dimensions). However, numerical solutions for the seven-dimensional carrier distribution functions are very demanding. The most common solution approach is the stochastic Monte Carlo method, because the gigabytes of memory requirements of deterministic direct solution approaches has not been available until recently. As a remedy, the higher accuracy provided by solutions of the Boltzmann transport equation is often exchanged for lower computational expense by using simpler models based on macroscopic quantities such as carrier density and mean carrier velocity. Recent developments for the deterministic spherical harmonics expansion method have reduced the computational cost for solving the Boltzmann transport equation, enabling the computation of carrier distribution functions even for spatially three-dimensional device simulations within minutes to hours. We summarize recent progress for the spherical harmonics expansion method and show that small currents, reasonable execution times, and rare events such as low-frequency noise, which are all hard or even impossible to simulate with the established Monte Carlo method, can be handled in a straight-forward manner. The applicability of the method for important practical applications is demonstrated for noise simulation, small-signal analysis, hot-carrier degradation, and avalanche breakdown.

Transverse Mode Dynamics of VCSELs Undergoing Current Modulation

NASA Technical Reports Server (NTRS)

Goorjian, Peter M.; Ning, C. Z.; Agrawal, Govind

2000-01-01

Transverse mode dynamics of a 20-micron-diameter vertical-cavity surface-emitting laser (VCSEL) undergoing gain switching by deep current modulation is studied numerically. The direct current (dc) level is set slightly below threshold and is modulated by a large alternating current (ac). The resulting optical pulse train and transverse-mode patterns are obtained numerically. The ac frequency is varied from 2.5 GHz to 10 GHz, and the ac amplitude is varied from one-half to four times that of the dc level. At high modulation frequencies, a regular pulse train is not generated unless the ac amplitude is large enough. At all modulation frequencies, the transverse spatial profile switches from single-mode to multiple-mode pattern as the ac pumping level is increased. Optical pulse widths vary in the range 5-30 ps. with the pulse width decreasing when either the frequency is increased or the ac amplitude is decreased. The numerical modeling uses an approximation form of the semiconductor Maxwell-Bloch equations. Temporal evolution of the spatial profiles of the laser (and of carrier density) is determined without any assumptions about the type or number of modes. Keywords: VCSELs, current modulation, gain switching, transverse mode dynamics, computational modeling

Extended-area nanostructuring of TiO2 with femtosecond laser pulses at 400 nm using a line focus.

PubMed

Das, Susanta Kumar; Dasari, Kiran; Rosenfeld, Arkadi; Grunwald, Ruediger

2010-04-16

An efficient way to generate nanoscale laser-induced periodic surface structures (LIPSS) in rutile-type TiO(2) with frequency-converted femtosecond laser pulses at wavelengths around 400 nm is reported. Extended-area structuring on fixed and moving substrates was obtained by exploiting the line focus of a cylindrical lens. Under defined conditions with respect to pulse number, pulse energy and scanning velocity, two types of ripple-like LIPSS with high and low spatial frequencies (HSFL, LSFL) with periods in the range of 90 nm and 340 nm, respectively, were formed. In particular, lower numbers of high energetic pulses favour the generation of LSFL whereas higher numbers of lower energetic pulses enable the preferential creation of HSFL. Theoretical calculations on the basis of the Drude model support the assumption that refractive index changes by photo-excited carriers are a major mechanism responsible for LSFL. Furthermore, the appearance of random substructures as small as 30 nm superimposing low spatial frequency ripples is demonstrated and their possible origin is discussed.

Multipactor susceptibility on a dielectric with two carrier frequencies

NASA Astrophysics Data System (ADS)

Iqbal, Asif; Verboncoeur, John; Zhang, Peng

2018-04-01

This work investigates multipactor discharge on a single dielectric surface with two carrier frequencies of an rf electric field. We use Monte Carlo simulations and analytical calculations to obtain susceptibility diagrams in terms of the rf electric field and normal electric field due to the residual charge on the dielectric. It is found that in contrast to the single frequency case, in general, the presence of a second carrier frequency of the rf electric field increases the threshold of the magnitude of the rf electric field to initiate multipactor. The effects of the relative strength and phase, and the frequency separation of the two carrier frequencies are examined. The conditions to minimize mulitpactor are derived.

Carrier-frequency synchronization system for improved amplitude modulation and television broadcast reception

DOEpatents

Smith, Stephen F.; Moore, James A.

2003-05-13

Systems and methods are described for carrier-frequency synchronization for improved AM and TV broadcast reception. A method includes synchronizing a carrier frequency of a broadcast signal with a remote reference frequency. An apparatus includes a reference signal receiver; a phase comparator coupled to the reference signal receiver; a voltage controlled oscillator coupled to the phase comparator; and a radio frequency output coupled to the voltage controlled oscillator.

47 CFR 78.111 - Frequency tolerance.

Code of Federal Regulations, 2010 CFR

2010-10-01

... Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES CABLE TELEVISION RELAY... shall maintain their operating frequency within 0.0005% the visual carrier, and the aural carrier shall be 4.5 MHz ±1 kHz above the visual carrier frequency. [52 FR 7145, Mar. 9, 1987, as amended at 68 FR...

Digital EPR with an arbitrary waveform generator and direct detection at the carrier frequency

PubMed Central

Tseitlin, Mark; Quine, Richard W.; Rinard, George A.; Eaton, Sandra S.; Eaton, Gareth R.

2011-01-01

A digital EPR spectrometer was constructed by replacing the traditional bridge with an arbitrary waveform generator (AWG) to produce excitation patterns and a high-speed digitizer for direct detection of the spin system response at the carrier frequency. Digital down-conversion produced baseband signals in quadrature with very precise orthogonality. Real-time resonator tuning was performed by monitoring the Fourier transforms of signals reflected from the resonator during frequency sweeps generated by the AWG. The capabilities of the system were demonstrated by rapid magnetic field scans at 256 MHz carrier frequency, and FID and spin echo experiments at 1 and 10 GHz carrier frequencies. For the rapid scan experiments the leakage through a cross-loop resonator was compensated by adjusting the amplitude and phase of a sinusoid at the carrier frequency that was generated with another AWG channel. PMID:21968420

Artifactual responses when recording auditory steady-state responses.

PubMed

Small, Susan A; Stapells, David R

2004-12-01

The goal of this study was to investigate, in hearing-impaired participants who could not hear the stimuli, the possibility of artifactual auditory steady-state responses (ASSRs) when stimuli are presented at high intensities. ASSRs to single (60 dB HL) and multiple (20 to 50 dB HL; 500 to 4000 Hz) bone-conduction stimuli as well as single 114 to 120 dB HL air-conduction stimuli, were obtained using the Rotman MASTER system, using analog-to-digital (A/D) conversion rates of 500, 1000, and 1250 Hz. Responses (p < 0.05) were considered artifactual when their numbers exceeded that expected by chance. In some conditions, we also obtained ASSRs to "alternated" stimuli (stimuli inverted and ASSRs to the two polarities averaged). A total of 17 subjects were tested. Bone conduction results: 500 Hz A/D rate: Large-amplitude (43 to 1558 nV) artifactual ASSRs were seen at 40 and 50 dB HL for the 500 Hz carrier frequency. Smaller responses (28 to 53 nV) were also recorded at 20 dB HL for the 500 Hz carrier frequency. Artifactual ASSRs (17 to 62 nV) were seen at 40 dB HL and above for the 1000 Hz carrier frequency and at 50 dB HL for the 2000 Hz carrier frequency. Alternating the stimulus polarity decreased the amplitude and occurrence of these artifactual responses but did not eliminate responses for the 500 Hz carrier frequency at 40 dB HL and above. No artifactual responses were recorded for 4000 Hz stimuli for any condition. 1000 Hz A/D rate: Artifactual ASSRs (15 to 523 nV) were seen at 50 dB HL and above for the 500 Hz carrier frequency and 40 dB HL and above for the 1000 Hz carrier frequency. Artifactual responses were also obtained at 50 dB HL for a 2000 Hz carrier frequency but not at lower levels. Artifactual responses were not seen for the 4000 Hz carrier frequency. Alternating the stimulus polarity removed the responses for the 1000 and 2000 Hz carrier frequencies but did not change the results for the 500 Hz carrier frequency. 1250 Hz A/D rate: Artifactual ASSRs (16 to 220 nV) were seen at 50 dB HL and above for the 500 Hz carrier frequency and 60 dB HL and above for the 1000 Hz carrier frequency. Alternating the stimulus polarity removed the responses for the 1000 Hz carrier frequency but did not change the results for the 500 Hz carrier frequency. There were no artifactual responses at 2000 and 4000 Hz. Air conduction results: 500 Hz A/D rate: Artifactual ASSRs (49 to 153 nV) were seen for 114 to 120 dB HL stimuli for 500 and 1000 Hz carrier frequencies. Alternating the stimulus polarity removed these responses. There were no artifactual responses at 2000 and 4000 Hz. 1000 and 1250 Hz A/D rates: Artifactual ASSRs (19 to 55 nV) were seen for a 120 dB HL stimulus for a 1000 Hz carrier. Alternating the stimulus polarity removed these responses. High-intensity air- or bone-conduction stimuli can produce spurious ASSRs, especially for 500 and 1000 Hz carrier frequencies. High-amplitude stimulus artifact can result in energy that is aliased to exactly the modulation frequency. Choice of signal conditioning (electroencephalogram filter slope and low-pass cutoff) and processing (A/D rate) can avoid spurious responses due to aliasing. However, artifactual responses due to other causes may still occur for bone-conduction stimuli 50 dB HL and higher (and possibly for high-level air conduction). Because the phases of these spurious responses do not invert with inversion of stimulus, the possibility of nonauditory physiologic responses cannot be ruled out. The clinical implications of these results are that artifactual responses may occur for any patient for bone-conduction stimuli at levels greater than 40 dB HL and for high-intensity air-conduction stimuli used to assess patients with profound hearing loss.

Experience with Carrier Screening and Prenatal Diagnosis for Sixteen Ashkenazi Jewish Genetic Diseases

PubMed Central

Scott, Stuart A.; Edelmann, Lisa; Liu, Liu; Luo, Minjie; Desnick, Robert J.; Kornreich, Ruth

2010-01-01

The success of prenatal carrier screening as a disease prevention strategy in the Ashkenazi Jewish (AJ) population has driven the expansion of screening panels as disease-causing founder mutations have been identified. However, the carrier frequencies of many of these mutations have not been reported in large AJ cohorts. We determined the carrier frequencies of over 100 mutations for 16 recessive disorders in the New York metropolitan area AJ population. Among the 100% AJ-descended individuals, screening for 16 disorders resulted in ~1 in 3.3 being a carrier for one disease and ~1 in 24 for two diseases. The carrier frequencies ranged from 0.066 (1 in 15.2; Gaucher disease) to 0.006 (1 in 168; nemaline myopathy), which averaged ~15% higher than those for all screenees. Importantly, over 95% of screenees chose to be screened for all possible AJ diseases, including disorders with lower carrier frequencies and/or detectability. Carrier screening also identified rare individuals homozygous for disease-causing mutations who had previously unrecognized clinical manifestations. Additionally, prenatal testing results and experience for all 16 disorders (n = 574) are reported. Together, these data indicate the general acceptance, carrier frequencies, and prenatal testing results for an expanded panel of 16 diseases in the AJ population. PMID:20672374

Range Sidelobe Suppression Using Complementary Sets in Distributed Multistatic Radar Networks

PubMed Central

Wang, Xuezhi; Song, Yongping; Huang, Xiaotao; Moran, Bill

2017-01-01

We propose an alternative waveform scheme built on mutually-orthogonal complementary sets for a distributed multistatic radar. Our analysis and simulation show a reduced frequency band requirement for signal separation between antennas with centralized signal processing using the same carrier frequency. While the scheme can tolerate fluctuations of carrier frequencies and phases, range sidelobes arise when carrier frequencies between antennas are significantly different. PMID:29295566

Bichromatic Sisyphus Cooling

NASA Astrophysics Data System (ADS)

Cashen, M.; Yatsenko, L.; Metcalf, H.

2001-05-01

Sisyphus cooling arises when the conservative dipole force of a monochromatic optical standing wave (SW) is modified by optical pumping among multiple ground state sublevels at low intensity(J. Dalibard and C. Cohen-Tannoudji, J. Opt. Soc. B6), 2023 (1989)., or among dressed state manifolds at high intensity(A. Aspect et al., Phys. Rev. Lett. 57), 1688 (1986). As part of our ongoing exploration of optical forces in non-monochromatic light, we have discovered a new type of Sisyphus cooling in a two-level atom where the optical pumping is driven by a second SW produced as a sideband from weak frequency modulation. Each beam of the carrier's SW has a Rabi frequency Ωc ~ 20 γ and is tuned below atomic resonance by δc ~ -38 γ. Thus the light shift at the antinodes is ω_c^ls ~ 8.6 γ. For the sideband, Ωs ~ 1.4 γ and δs ~ +1 γ so ω_s^ls ~ 1 γ. The resulting forces satisfy Fc > 8 F_s. By contrast, the excitation rate γ_s^p > 2 γ_c^p. We choose the relative spatial phase of the SW's to be π, so moving atoms are most likely to be excited at the red-tuned carrier nodes, and thus they climb more hills than they descend. We observe transverse cooling of a beam of He metastables when δc < 0 and heating otherwise, in contrast to Ref. 3 because here the excitation is at the nodes of the high intensity carrier SW. We also observe channeling of the slow atoms in the carrier's SW.

Estimation of free carrier concentrations in high-quality heavily doped GaN:Si micro-rods by photoluminescence and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Mohajerani, M. S.; Khachadorian, S.; Nenstiel, C.; Schimpke, T.; Avramescu, A.; Strassburg, M.; Hoffmann, A.; Waag, A.

2016-03-01

The controlled growth of highly n-doped GaN micro rods is one of the major challenges in the fabrication of recently developed three-dimensional (3D) core-shell light emitting diodes (LEDs). In such structures with a large active area, higher electrical conductivity is needed to achieve higher current density. In this contribution, we introduce high quality heavily-doped GaN:Si micro-rods which are key elements of the newly developed 3D core-shell LEDs. These structures were grown by metal-organic vapor phase epitaxy (MOVPE) using selective area growth (SAG). We employed spatially resolved micro-Raman and micro-photoluminescence (PL) in order to directly determine a free-carrier concentration profile in individual GaN micro-rods. By Raman spectroscopy, we analyze the low-frequency branch of the longitudinal optical (LO)-phonon-plasmon coupled modes and estimate free carrier concentrations from ≍ 2.4 × 1019 cm-3 up to ≍ 1.5 × 1020 cm-3. Furthermore, free carrier concentrations are determined by estimating Fermi energy level from the near band edge emission measured by low-temperature PL. The results from both methods reveal a good consistency.

An experimental distribution of analog and digital information in a hybrid wireless visible light communication system based on acousto-optic modulation and sinusoidal gratings

NASA Astrophysics Data System (ADS)

Gómez Colín, R.; García Juárez, A.; Zaldívar Huerta, I. E.; Marquina, A. Vera; García Delgado, L. A.; Leal Cruz, A. L.; Gómez Fuentes, R.

2016-03-01

In this paper we propose a photonic architecture as an alternative tool to distribute point to multipoint analog and digital information over a hybrid wireless visible optical communication system. The experimental set-up is composed of a red laser pointer, an acousto-optic modulator, a sinusoidal grating and a photo-detector array. By using a simple and variable interferometric system, diffraction gratings with different spatial frequencies are generated and recorded on a photoemulsion which is composed of vanilla with dichromate gelatin. Analog video and digital information are first transmitted and recovered over a wireless communication system using a microwave carrier at 4.52 GHz which is generated by distributed feedback lasers operating in the low laser threshold current region. Separately, the recovered video information and digital data are combined with a radio frequency signal of 80 MHz, obtaining a subcarrier of information that is imposed on the optical carrier of the pointer laser using an acousto-optic modulator which is operated with an angle of incident light that satisfies the Bragg condition. The modulated optical carrier is sent to a sinusoidal grating, the diffraction pattern is photo-detected using an array of PIN photo-detectors. The use of sinusoidal gratings with acousto-optic modulators allows that number of channels to be increased when both components are placed in cascade.

Method and apparatus for generating motor current spectra to enhance motor system fault detection

DOEpatents

Linehan, Daniel J.; Bunch, Stanley L.; Lyster, Carl T.

1995-01-01

A method and circuitry for sampling periodic amplitude modulations in a nonstationary periodic carrier wave to determine frequencies in the amplitude modulations. The method and circuit are described in terms of an improved motor current signature analysis. The method insures that the sampled data set contains an exact whole number of carrier wave cycles by defining the rate at which samples of motor current data are collected. The circuitry insures that a sampled data set containing stationary carrier waves is recreated from the analog motor current signal containing nonstationary carrier waves by conditioning the actual sampling rate to adjust with the frequency variations in the carrier wave. After the sampled data is transformed to the frequency domain via the Discrete Fourier Transform, the frequency distribution in the discrete spectra of those components due to the carrier wave and its harmonics will be minimized so that signals of interest are more easily analyzed.

Ultrasonic speech translator and communications system

DOEpatents

Akerman, M.A.; Ayers, C.W.; Haynes, H.D.

1996-07-23

A wireless communication system undetectable by radio frequency methods for converting audio signals, including human voice, to electronic signals in the ultrasonic frequency range, transmitting the ultrasonic signal by way of acoustical pressure waves across a carrier medium, including gases, liquids, or solids, and reconverting the ultrasonic acoustical pressure waves back to the original audio signal. The ultrasonic speech translator and communication system includes an ultrasonic transmitting device and an ultrasonic receiving device. The ultrasonic transmitting device accepts as input an audio signal such as human voice input from a microphone or tape deck. The ultrasonic transmitting device frequency modulates an ultrasonic carrier signal with the audio signal producing a frequency modulated ultrasonic carrier signal, which is transmitted via acoustical pressure waves across a carrier medium such as gases, liquids or solids. The ultrasonic receiving device converts the frequency modulated ultrasonic acoustical pressure waves to a frequency modulated electronic signal, demodulates the audio signal from the ultrasonic carrier signal, and conditions the demodulated audio signal to reproduce the original audio signal at its output. 7 figs.

Photonic engineering for biological study

NASA Astrophysics Data System (ADS)

Wu, Fei

My dissertation focuses on designing and developing prototypes of optical tools in the laboratory that can facilitate practical medical therapies. More specifically, this dissertation examines two novel biophotonic techniques: (1) a frequency multiplexed confocal microscope with the potential to provide rational therapy of congestive heart failure (CHF), and (2) the "optical comb" with the potential to improve results of retina reattachment surgery and accelerate post surgical recovery. Next, I will discuss the background, design and initial experimental results of each study individually. Part I: The Frequency Multiplexed Confocal Microscope. To overcome the limitations of existing confocal microscope technology, this dissertation proposes a non-scanning, real-time, high resolution technique (a multi-point frequency multiplexed confocal microscope) to measure 3-D intracellular calcium ion concentration in a living cardiac myocyte. This method can be also applied to measure the intracellular sodium ion concentration, or other ions in which high quantum-yield fluorescent probes are available. The novelty of the proposed research lies in the introduction of carrier frequency multiplexing techniques which can differentiate fluorescence emitted at different spatial locations in cardiac myocyte by their modulated frequency. It therefore opens the possibility to visualize the transient dynamics of intracellular dynamics at multiple locations in cells simultaneously, which will shine a new light on our understanding of CHF. The procedure for frequency multiplexing proposed is described below. Multiple incident laser beams are focused onto different locations in an isolated rat cardiac myocyte with each beam modulated at a different carrier frequency. The fluorescence emission at each location therefore bears the same modulated frequency as the stimulation laser beam. Each fluorescence signal is sent to the photo multiplier tube (PMT) after being spatially filtered by a single mode fiber (functioning as a pinhole). Since each signal has a different carrier frequency, only one signal detector is required to collect multiple signal streams which eliminates the errors introduced by difference of multiple detectors. After taking the Fourier Transform of the collected data, multiple peaks can be found in the frequency domain. Each peak refers to a corresponding location in the sample. The temporal information of the fluorescence signal variation at each location can be obtained by demodulating the low frequency information from the carrier frequency, followed by an inverse Fourier transform. Part II: The "Optical Comb". Retinal detachment refers to separation of the inner layers of the retina from the underlying retinal pigment epithelium. It can cause degeneration of the retina and may lead to permanent vision loss if not promptly treated and hence is considered an ocular emergency. Currently, the only treatment available for retinal detachment is surgical reattachment. The idea of an "optical comb" is developed from the general working principle of the well known "optical tweezers" in the optical literature, which can pull micro-objects through the trapping force produced by a focused laser beam. If we can manage to incident the focused laser beam onto the misaligned photoreceptors and further scan it back and forth, trapping forces that produced may be able to "comb" the photoreceptors to be aligned, and thereby help with post surgery recovery. A series of experiments have been carried out to demonstrate the plausibility of this idea. First, several micro glass rods with size similar to human's photoreceptors (6 microns in diameter and 30 microns in length) were used. We observed that when the laser beam is focused close to one end of the micro rod originally laid on a glass coverslip, the rod is pulled to stand upright successfully, and we can manipulate the direction it faces by controlling its relative position to the laser beam. We are now experimenting with this combing technique with detached bovine retina samples to further verify its feasibility over live animal cells. (Abstract shortened by UMI.)

Electrical power inverter having a phase modulated, twin-inverter, high frequency link and an energy storage module

DOEpatents

Pitel, Ira J.

1987-02-03

The present invention provides an electrical power inverter method and apparatus, which includes a high frequency link, for converting DC power into AC power. Generally stated, the apparatus includes a first high frequency module which produces an AC voltage at a first output frequency, and a second high frequency inverter module which produces an AC voltage at a second output frequency that is substantially the same as the first output frequency. The second AC voltage is out of phase with the first AC voltage by a selected angular phase displacement. A mixer mixes the first and second output voltages to produce a high frequency carrier which has a selected base frequency impressed on the sidebands thereof. A rectifier rectifies the carrier, and a filter filters the rectified carrier. An output inverter inverts the filtered carrier to produce an AC line voltage at the selected base frequency. A phase modulator adjusts the relative angular phase displacement between the outputs of the first and second high frequency modules to control the base frequency and magnitude of the AC line voltage.

Electrical power inverter having a phase modulated, twin-inverter, high frequency link and an energy storage module

DOEpatents

Pitel, I.J.

1987-02-03

The present invention provides an electrical power inverter method and apparatus, which includes a high frequency link, for converting DC power into AC power. Generally stated, the apparatus includes a first high frequency module which produces an AC voltage at a first output frequency, and a second high frequency inverter module which produces an AC voltage at a second output frequency that is substantially the same as the first output frequency. The second AC voltage is out of phase with the first AC voltage by a selected angular phase displacement. A mixer mixes the first and second output voltages to produce a high frequency carrier which has a selected base frequency impressed on the sidebands thereof. A rectifier rectifies the carrier, and a filter filters the rectified carrier. An output inverter inverts the filtered carrier to produce an AC line voltage at the selected base frequency. A phase modulator adjusts the relative angular phase displacement between the outputs of the first and second high frequency modules to control the base frequency and magnitude of the AC line voltage. 19 figs.

Amplitude modulation detection with concurrent frequency modulation.

PubMed

Nagaraj, Naveen K

2016-09-01

Human speech consists of concomitant temporal modulations in amplitude and frequency that are crucial for speech perception. In this study, amplitude modulation (AM) detection thresholds were measured for 550 and 5000 Hz carriers with and without concurrent frequency modulation (FM), at AM rates crucial for speech perception. Results indicate that adding 40 Hz FM interferes with AM detection, more so for 5000 Hz carrier and for frequency deviations exceeding the critical bandwidth of the carrier frequency. These findings suggest that future cochlear implant processors, encoding speech fine-structures may consider limiting the FM to narrow bandwidth and to low frequencies.

Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis

PubMed

Jones; Diddams; Ranka; Stentz; Windeler; Hall; Cundiff

2000-04-28

We stabilized the carrier-envelope phase of the pulses emitted by a femtosecond mode-locked laser by using the powerful tools of frequency-domain laser stabilization. We confirmed control of the pulse-to-pulse carrier-envelope phase using temporal cross correlation. This phase stabilization locks the absolute frequencies emitted by the laser, which we used to perform absolute optical frequency measurements that were directly referenced to a stable microwave clock.

Spatial variation in carrier dynamics along a single CdSSe nanowire

NASA Astrophysics Data System (ADS)

Blake, Jolie C.; Eldridge, Peter S.; Gundlach, Lars

2014-10-01

Ultrafast charge carrier dynamics along individual CdSxSe1-x nanowires has been measured. The use of an improved ultrafast Kerr-gated microscope allows for spatially resolved luminescence measurements along a single nanowire. Amplified spontaneous emission (ASE) was observed at high excitation fluences. Position dependent variations of ultrafast ASE dynamics were observed. SEM and colorimetric measurements showed that the difference in dynamics can be attributed to variations in non-radiative recombination rates along the wire. The dominant Shockley-Read recombination rate can be extracted from ASE dynamics and can be directly related to charge carrier mobility and defect density. Employing ASE as a probe for defect densities provides a new sub-micron spatially resolved, contactless method for measurements of charge carrier mobility.

Measurement of the carrier envelope offset frequency of a femtosecond frequency comb using a Fabry-Perot interferometer

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

Basnak, D V; Bikmukhametov, K A; Dmitrieva, N I

2010-10-15

A method for measuring the carrier envelope offset (CEO) frequency of the femtosecond frequency comb with a bandwidth of less than one octave by using a Fabry-Perot interferometer is proposed and experimentally demonstrated. (laser components)

Notched-noise precursors improve detection of low-frequency amplitude modulationa)

PubMed Central

Almishaal, Ali; Bidelman, Gavin M.; Jennings, Skyler G.

2017-01-01

Amplitude modulation (AM) detection was measured with a short (50 ms), high-frequency carrier as a function of carrier level (Experiment I) and modulation frequency (Experiment II) for conditions with or without a notched-noise precursor. A longer carrier (500 ms) was also included in Experiment I. When the carrier was preceded by silence (no precursor condition) AM detection thresholds worsened for moderate-level carriers compared to lower- or higher-level carriers, resulting in a “mid-level hump.” AM detection thresholds with a precursor were better than those without a precursor, primarily for moderate-to-high level carriers, thus eliminating the mid-level hump in AM detection. When the carrier was 500 ms, AM thresholds improved by a constant (across all levels) relative to AM thresholds with a precursor, consistent with the longer carrier providing more “looks” to detect the AM signal. Experiment II revealed that improved AM detection with compared to without a precursor is limited to low-modulation frequencies (<60 Hz). These results are consistent with (1) a reduction in cochlear gain over the course of the precursor perhaps via the medial olivocochlear reflex or (2) a form of perceptual enhancement which may be mediated by adaptation of inhibition. PMID:28147582

Ultrasonic speech translator and communications system

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

Akerman, M.A.; Ayers, C.W.; Haynes, H.D.

1996-07-23

A wireless communication system undetectable by radio frequency methods for converting audio signals, including human voice, to electronic signals in the ultrasonic frequency range, transmitting the ultrasonic signal by way of acoustical pressure waves across a carrier medium, including gases, liquids, or solids, and reconverting the ultrasonic acoustical pressure waves back to the original audio signal. The ultrasonic speech translator and communication system includes an ultrasonic transmitting device and an ultrasonic receiving device. The ultrasonic transmitting device accepts as input an audio signal such as human voice input from a microphone or tape deck. The ultrasonic transmitting device frequency modulatesmore » an ultrasonic carrier signal with the audio signal producing a frequency modulated ultrasonic carrier signal, which is transmitted via acoustical pressure waves across a carrier medium such as gases, liquids or solids. The ultrasonic receiving device converts the frequency modulated ultrasonic acoustical pressure waves to a frequency modulated electronic signal, demodulates the audio signal from the ultrasonic carrier signal, and conditions the demodulated audio signal to reproduce the original audio signal at its output. 7 figs.« less

Ultrasonic speech translator and communications system

DOEpatents

Akerman, M. Alfred; Ayers, Curtis W.; Haynes, Howard D.

1996-01-01

A wireless communication system undetectable by radio frequency methods for converting audio signals, including human voice, to electronic signals in the ultrasonic frequency range, transmitting the ultrasonic signal by way of acoustical pressure waves across a carrier medium, including gases, liquids, or solids, and reconverting the ultrasonic acoustical pressure waves back to the original audio signal. The ultrasonic speech translator and communication system (20) includes an ultrasonic transmitting device (100) and an ultrasonic receiving device (200). The ultrasonic transmitting device (100) accepts as input (115) an audio signal such as human voice input from a microphone (114) or tape deck. The ultrasonic transmitting device (100) frequency modulates an ultrasonic carrier signal with the audio signal producing a frequency modulated ultrasonic carrier signal, which is transmitted via acoustical pressure waves across a carrier medium such as gases, liquids or solids. The ultrasonic receiving device (200) converts the frequency modulated ultrasonic acoustical pressure waves to a frequency modulated electronic signal, demodulates the audio signal from the ultrasonic carrier signal, and conditions the demodulated audio signal to reproduce the original audio signal at its output (250).

Method and apparatus for generating motor current spectra to enhance motor system fault detection

DOEpatents

Linehan, D.J.; Bunch, S.L.; Lyster, C.T.

1995-10-24

A method and circuitry are disclosed for sampling periodic amplitude modulations in a nonstationary periodic carrier wave to determine frequencies in the amplitude modulations. The method and circuit are described in terms of an improved motor current signature analysis. The method insures that the sampled data set contains an exact whole number of carrier wave cycles by defining the rate at which samples of motor current data are collected. The circuitry insures that a sampled data set containing stationary carrier waves is recreated from the analog motor current signal containing nonstationary carrier waves by conditioning the actual sampling rate to adjust with the frequency variations in the carrier wave. After the sampled data is transformed to the frequency domain via the Discrete Fourier Transform, the frequency distribution in the discrete spectra of those components due to the carrier wave and its harmonics will be minimized so that signals of interest are more easily analyzed. 29 figs.

47 CFR 76.1804 - Aeronautical frequencies: leakage monitoring (CLI).

Code of Federal Regulations, 2010 CFR

2010-10-01

... through 76.616 and § 76.1803; (d) Carrier frequency, tolerance, and type of modulation of all carriers in... 47 Telecommunication 4 2010-10-01 2010-10-01 false Aeronautical frequencies: leakage monitoring... Aeronautical frequencies: leakage monitoring (CLI). An MVPD shall notify the Commission before transmitting any...

Time domain multiplexed spatial division multiplexing receiver.

PubMed

van Uden, Roy G H; Okonkwo, Chigo M; Chen, Haoshuo; de Waardt, Hugo; Koonen, Antonius M J

2014-05-19

A novel time domain multiplexed (TDM) spatial division multiplexing (SDM) receiver which allows for the reception of >1 dual polarization mode with a single coherent receiver, and corresponding 4-port oscilloscope, is experimentally demonstrated. Received by two coherent receivers and respective 4-port oscilloscopes, a 3 mode transmission of 28GBaud QPSK, 8, 16, and 32QAM over 41.7km of few-mode fiber demonstrates the performance of the TDM-SDM receiver with respect to back-to-back. In addition, by using carrier phase estimation employing one digital phase locked loop per output, the frequency offset between the transmitter laser and local oscillator is shown to perform similar to previous work which employs 3 coherent receivers and 4-port oscilloscopes which are dedicated to the reception of each the three modes.

47 CFR 1.10014 - What happens after officially filing my application?

Code of Federal Regulations, 2010 CFR

2010-10-01

... ARC-xxxxx Foreign Carrier Affiliation Notification FCN-xxxxx International High Frequency IHF-xxxxx... PN released International High Frequency IHF-xxxxx International Public Fixed IPF-xxxxx Recognized... Foreign Carrier Affiliation Notification. International High Frequency: Construction Permits,Licenses...

47 CFR 1.10014 - What happens after officially filing my application?

Code of Federal Regulations, 2011 CFR

2011-10-01

... ARC-xxxxx Foreign Carrier Affiliation Notification FCN-xxxxx International High Frequency IHF-xxxxx... PN released International High Frequency IHF-xxxxx International Public Fixed IPF-xxxxx Recognized... Foreign Carrier Affiliation Notification. International High Frequency: Construction Permits,Licenses...

Carrier-interleaved orthogonal multi-electrode multi-carrier resistivity-measurement tool

NASA Astrophysics Data System (ADS)

Cai, Yu; Sha, Shuang

2016-09-01

This paper proposes a new carrier-interleaved orthogonal multi-electrode multi-carrier resistivity-measurement tool used in a cylindrical borehole environment during oil-based mud drilling processes. The new tool is an orthogonal frequency division multiplexing access-based contactless multi-measurand detection tool. The tool can measure formation resistivity in different azimuthal angles and elevational depths. It can measure many more measurands simultaneously in a specified bandwidth than the legacy frequency division multiplexing multi-measurand tool without a channel-select filter while avoiding inter-carrier interference. The paper also shows that formation resistivity is not sensitive to frequency in certain frequency bands. The average resistivity collected from N subcarriers can increase the measurement of the signal-to-noise ratio (SNR) by N times given no amplitude clipping in the current-injection electrode. If the clipping limit is taken into account, with the phase rotation of each single carrier, the amplitude peak-to-average ratio can be reduced by 3 times, and the SNR can achieve a 9/N times gain over the single-carrier system. The carrier-interleaving technique is also introduced to counter the carrier frequency offset (CFO) effect, where the CFO will cause inter-pad interference. A qualitative analysis and simulations demonstrate that block-interleaving performs better than tone-interleaving when coping with a large CFO. The theoretical analysis also suggests that increasing the subcarrier number can increase the measurement speed or enhance elevational resolution without sacrificing receiver performance. The complex orthogonal multi-pad multi-carrier resistivity logging tool, in which all subcarriers are complex signals, can provide a larger available subcarrier pool than other types of transceivers.

Precise frequency calibration using television video carriers

NASA Technical Reports Server (NTRS)

Burkhardt, Edward E.

1990-01-01

The availability of inexpensive and quick precise frequency calibration methods is limited. VLF and GPS do offer precise calibration. However, antenna placement, cost of equipment, and calibration time place many restrictions on the user. The USNO maintained line-10 television Time of Coincidence (TOC) of station WTTG, channel 5, Washington, DC requires a frequency stable video carrier. This video carrier, 77.24 MHz is controlled by the same cesium beam standard controlling the TOC of line-10. Excellent frequency comparisons against this video carrier have been accomplished at 95 miles (153 km). With stable propagation and a three foot wire antenna, a part in 10(exp 9) can be determined in a few minutes. Inexpensive field equipment with a synthesized 1 kHz offset from the video carrier offers parts in 10(exp 11) calibrations in a few minutes using an oscilloscope as a phase comparator.

Precise frequency calibration using television video carriers

NASA Astrophysics Data System (ADS)

Burkhardt, Edward E.

1990-05-01

The availability of inexpensive and quick precise frequency calibration methods is limited. VLF and GPS do offer precise calibration. However, antenna placement, cost of equipment, and calibration time place many restrictions on the user. The USNO maintained line-10 television Time of Coincidence (TOC) of station WTTG, channel 5, Washington, DC requires a frequency stable video carrier. This video carrier, 77.24 MHz is controlled by the same cesium beam standard controlling the TOC of line-10. Excellent frequency comparisons against this video carrier have been accomplished at 95 miles (153 km). With stable propagation and a three foot wire antenna, a part in 10(exp 9) can be determined in a few minutes. Inexpensive field equipment with a synthesized 1 kHz offset from the video carrier offers parts in 10(exp 11) calibrations in a few minutes using an oscilloscope as a phase comparator.

OFDM Coupled Compressive Sensing Algorithm for Stepped-Frequency Ground Penetrating Radar

DTIC Science & Technology

2014-10-01

These frequencies are combined in such a way to achieve orthogonality between the carrier frequencies, while mitigating any interference between...in such a way to achieve orthogonality between the carrier frequencies, while mitigating any interference between said frequencies. In CS, a signal...frequency tones is mitigated . Orthogonality requires that the sub-bands are spaced at = is the OFDM symbol period, and k is any

Sensitive frequency dependence of the carrier-envelope phase effect on bound-bound transitions: An interference perspective

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

Peng Dian; Fu Panming; Wang Bingbing

2010-11-15

We investigate numerically with Hylleraas coordinates the frequency dependence of the carrier-envelope phase (CEP) effect on bound-bound transitions of helium induced by an ultrashort laser pulse of a few cycles. We find that the CEP effect is very sensitive to the carrier frequency of the laser pulse, occurring regularly even at far-off-resonance frequencies. By analyzing a two-level model, we find that the CEP effect can be attributed to the quantum interference between neighboring multiphoton transition pathways, which is made possible by the broadened spectrum of the ultrashort laser pulse. A general picture is developed along this line to understand themore » sensitivity of the CEP effect to the laser's carrier frequency. Multilevel influence on the CEP effect is also discussed.« less

Carrier-phase control among subharmonic pulses in a femtosecond optical parametric oscillator.

PubMed

Kobayashi, Y; Torizuka, K

2001-08-15

We have generated femtosecond subharmonic pulses by using an optical parametric oscillator. The optical frequencies of the idler and the signal are one third and two thirds, respectively, of the optical frequency of the pump pulse. The carrier phase of the signal pulse relative to that of the pump pulse was locked by electronic feedback. The carrier-envelope phase slip frequency of the signal pulse relative to that of the pump was locked to F/6 , where F is defined as the repetition frequency.

Transient GaAs plasmonic metasurfaces at terahertz frequencies

DOE PAGES

Yang, Yuanmu; Kamaraju, N.; Campione, Salvatore; ...

2016-12-09

Here we demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation of spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on of the transient plasmon mode, governed by the GaAs effective electron mass and electron–phonon interactions, is revealed by structured-optical pump THz probe spectroscopy, on a time scale of 500 fs. By modulating the carrier density using different pump fluences, we observe a wide tuning of the electric dipole resonance of the transient GaAs metasurface from 0.5 THz to 1.7 THz. Furthermore, we numerically demonstrate that the metasurface presented here can be generalized to moremore » complex architectures for realizing functionalities such as perfect absorption, leading to a 30 dB modulation depth. In conclusion, the platform also provides a pathway to achieve ultrafast manipulation of infrared beams in the linear and, potentially, nonlinear regime.« less

47 CFR 15.107 - Conducted limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

... not apply to carrier current systems operating as unintentional radiators on frequencies below 30 MHz... carrier current systems containing their fundamental emission within the frequency band 535-1705 kHz and... 50 μH/50 ohms LISN. (3) Carrier current systems operating below 30 MHz are also subject to the...

A model of anuran auditory periphery reveals frequency-dependent adaptation to be a contributing mechanism for two-tone suppression and amplitude modulation coding.

PubMed

Wotton, J M; Ferragamo, M J

2011-10-01

Anuran auditory nerve fibers (ANF) tuned to low frequencies display unusual frequency-dependent adaptation which results in a more phasic response to signals above best frequency (BF) and a more tonic response to signals below. A network model of the first two layers of the anuran auditory system was used to test the contribution of this dynamic peripheral adaptation on two-tone suppression and amplitude modulation (AM) tuning. The model included a peripheral sandwich component, leaky-integrate-and-fire cells and adaptation was implemented by means of a non-linear increase in threshold weighted by the signal frequency. The results of simulations showed that frequency-dependent adaptation was both necessary and sufficient to produce high-frequency-side two-tone suppression for the ANF and cells of the dorsal medullary nucleus (DMN). It seems likely that both suppression and this dynamic adaptation share a common mechanism. The response of ANFs to AM signals was influenced by adaptation and carrier frequency. Vector strength synchronization to an AM signal improved with increased adaptation. The spike rate response to a carrier at BF was the expected flat function with AM rate. However, for non-BF carrier frequencies the response showed a weak band-pass pattern due to the influence of signal sidebands and adaptation. The DMN received inputs from three ANFs and when the frequency tuning of inputs was near the carrier, then the rate response was a low-pass or all-pass shape. When most of the inputs were biased above or below the carrier, then band-pass responses were observed. Frequency-dependent adaptation enhanced the band-pass tuning for AM rate, particularly when the response of the inputs was predominantly phasic for a given carrier. Different combinations of inputs can therefore bias a DMN cell to be especially well suited to detect specific ranges of AM rates for a particular carrier frequency. Such selection of inputs would clearly be advantageous to the frog in recognizing distinct spectral and temporal parameters in communication calls. Copyright © 2011 Elsevier B.V. All rights reserved.

Wide-band analog frequency modulation of optic signals using indirect techniques

NASA Technical Reports Server (NTRS)

Fitzmartin, D. J.; Balboni, E. J.; Gels, R. G.

1991-01-01

The wideband frequency modulation (FM) of an optical carrier by a radio frequency (RF) or microwave signal can be accomplished independent of laser type when indirect modulation is employed. Indirect modulators exploit the integral relation of phase to frequency so that phase modulators can be used to impress frequency modulation on an optical carrier. The use of integrated optics phase modulators, which are highly linear, enables the generation of optical wideband FM signals with very low intermodulation distortion. This modulator can be used as part of an optical wideband FM link for RF and microwave signals. Experimental results from the test of an indirect frequency modulator for an optical carrier are discussed.

Frequency-Diversity Reception for Phase Modulation

NASA Technical Reports Server (NTRS)

Brockman, M. H.

1984-01-01

Signal-to-noise ratio improved. System receives phase modulation transmitted simultaneously on different carrier frequencies. Used for carriers received through different antennas or through same antenna.

Cystic fibrosis carrier screening in a North American population.

PubMed

Zvereff, Val V; Faruki, Hawazin; Edwards, Marcia; Friedman, Kenneth J

2014-07-01

The aim of this study was to compare the mutation frequency distribution for a 32-mutation panel and a 69-mutation panel used for cystic fibrosis carrier screening. Further aims of the study were to examine the race-specific detection rates provided by both panels and to assess the performance of extended panels in large-scale, population-based cystic fibrosis carrier screening. Although genetic screening for the most common CFTR mutations allows detection of nearly 90% of cystic fibrosis carriers, the large number of other mutations, and their distribution within different ethnic groups, limits the utility of general population screening. Patients referred for cystic fibrosis screening from January 2005 through December 2010 were tested using either a 32-mutation panel (n = 1,601,308 individuals) or a 69-mutation panel (n = 109,830). The carrier frequencies observed for the 69-mutation panel study population (1/36) and Caucasian (1/27) and African-American individuals (1/79) agree well with published cystic fibrosis carrier frequencies; however, a higher carrier frequency was observed for Hispanic-American individuals (1/48) using the 69-mutation panel as compared with the 32-mutation panel (1/69). The 69-mutation panel detected ~20% more mutations than the 32-mutation panel for both African-American and Hispanic-American individuals. Expanded panels using race-specific variants can improve cystic fibrosis carrier detection rates within specific populations. However, it is important that the pathogenicity and the relative frequency of these variants are confirmed.

Carrier-envelope phase dynamics and noise analysis in octave-spanning Ti:sapphire lasers.

PubMed

Matos, Lia; Mücke, Oliver D; Chen, Jian; Kärtner, Franz X

2006-03-20

We investigate the carrier-envelope phase dynamics of octave-spanning Ti:sapphire lasers and perform a complete noise analysis of the carrier-envelope phase stabilization. We model the effect of the laser dynamics on the residual carrier-envelope phase noise by deriving a transfer function representation of the octave-spanning frequency comb. The modelled phase noise and the experimental results show excellent agreement. This greatly enhances our capability of predicting the dependence of the residual carrier-envelope phase noise on the feedback loop filter, the carrier-envelope frequency control mechanism and the pump laser used.

Blind identification of the number of sub-carriers for orthogonal frequency division multiplexing-based elastic optical networking

NASA Astrophysics Data System (ADS)

Zhao, Lei; Xu, Hengying; Bai, Chenglin

2018-03-01

In orthogonal frequency division multiplexing (OFDM)-based elastic optical networking (EON), it is imperative to identify unknown parameters of OFDM-based EON signals quickly, intelligently and robustly. Because the number of sub-carriers determines the size of the sub-carriers spacing and then affects the symbol period of the OFDM and the anti-dispersion capability of the system, the identification of the number of sub-carriers has a profound effect on the identification of other key parameters of the system. In this paper, we proposed a method of number identification for sub-carriers of OFDM-based EON signals with help of high-order cyclic cumulant. The specific fourth-order cyclic cumulant exists only at the location of its sub-carriers frequencies. So the identification of the number of sub-carriers can be implemented by detecting the cyclic-frequencies. The proposed scheme in our study can be divided into three sub-stages, i.e. estimating the spectral range, calculating the high-order cyclic cumulant and identifying the number of sub-carriers. When the optical signal-to-noise ratios (OSNR) varied from 16dB to 22dB, the number of sub-carriers (64-512) was successfully identified in the experiment, and from the statistical point of view, the average identification absolute accuracy (IAAs) exceeded 94%.

Discriminator aided phase lock acquisition for suppressed carrier signals

NASA Technical Reports Server (NTRS)

Carson, L. M.; Krasin, F. E. (Inventor)

1982-01-01

A discriminator aided technique for acquisition of phase lock to a suppressed carrier signal utilizes a Costas loop which is initially operated open loop and control voltage for its VCXO is derived from a phase detector that compares the VCXO to a reference frequency thus establishing coarse frequency resolution with the received signal. Then the Costas loop is closed with the low-pass filter of the channel having a bandwidth much greater (by a factor of about 10) than in the I channel so that a frequency discriminator effect results to aid carrier resolution. Finally, after carrier acquisition, the Q-channel filter of the Costas loop is switched to a bandwidth substantially equal to that of the I-channel for carrier tracking.

Dual frequency optical carrier technique for transmission of reference frequencies in dispersive media

NASA Technical Reports Server (NTRS)

Maleki, Lutfollah (Inventor)

1993-01-01

Two different carrier frequencies modulated by a reference frequency are transmitted to each receiver to be synchronized therewith. Each receiver responds to local phase differences between the two received signals to correct the phase of one of them so as to maintain the corrected signal as a reliable synchronization reference.

47 CFR 15.303 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-10-01

... Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL RADIO FREQUENCY DEVICES Unlicensed Personal..., one below the carrier center frequency and one above the carrier center frequency, that are 26 dB down... transmission burst of the device under all conditions of modulation. Usually this parameter is measured as a...

Nonlinear effects in the radiation force generated by amplitude-modulated focused beams

NASA Astrophysics Data System (ADS)

González, Nuria; Jiménez, Noé; Redondo, Javier; Roig, Bernardino; Picó, Rubén; Sánchez-Morcillo, Víctor; Konofagou, Elisa E.; Camarena, Francisco

2012-10-01

Harmonic Motion Imaging (HMI) uses an amplitude-modulated (AM) beam to induce an oscillatory radiation force before, during and after ablation. In this paper, the findings from a numerical analysis of the effects related with the nonlinear propagation of AM focused ultrasonic beams in water on the radiation force and the location of its maxima will be presented. The numerical modeling is performed using the KZK nonlinear parabolic equation. The radiation force is generated by a focused transducer with a gain of 18, a carrier frequency of 1 MHz and a modulation frequency of 25 kHz. The modulated excitation generates a spatially-invariant force proportional to the intensity. Regarding the nonlinear wave propagation, the force is no longer proportional to the intensity, reaching a factor of eight between the nonlinear and linear estimations. Also, a 9 mm shift in the on-axis force peak occurs when the initial pressure increased from 1 to 300 kPa. This spatial shift, due to the nonlinear effects, becomes dynamic in AM focused beams, as the different signal periods have different amplitudes. This study shows that both the value and the spatial position of the force peak are affected by the nonlinear propagation of the ultrasonic waves.

A joint tracking method for NSCC based on WLS algorithm

NASA Astrophysics Data System (ADS)

Luo, Ruidan; Xu, Ying; Yuan, Hong

2017-12-01

Navigation signal based on compound carrier (NSCC), has the flexible multi-carrier scheme and various scheme parameters configuration, which enables it to possess significant efficiency of navigation augmentation in terms of spectral efficiency, tracking accuracy, multipath mitigation capability and anti-jamming reduction compared with legacy navigation signals. Meanwhile, the typical scheme characteristics can provide auxiliary information for signal synchronism algorithm design. This paper, based on the characteristics of NSCC, proposed a kind of joint tracking method utilizing Weighted Least Square (WLS) algorithm. In this method, the LS algorithm is employed to jointly estimate each sub-carrier frequency shift with the frequency-Doppler linear relationship, by utilizing the known sub-carrier frequency. Besides, the weighting matrix is set adaptively according to the sub-carrier power to ensure the estimation accuracy. Both the theory analysis and simulation results illustrate that the tracking accuracy and sensitivity of this method outperforms the single-carrier algorithm with lower SNR.

Sensitivity to Envelope Interaural Time Differences at High Modulation Rates

PubMed Central

Bleeck, Stefan; McAlpine, David

2015-01-01

Sensitivity to interaural time differences (ITDs) conveyed in the temporal fine structure of low-frequency tones and the modulated envelopes of high-frequency sounds are considered comparable, particularly for envelopes shaped to transmit similar fidelity of temporal information normally present for low-frequency sounds. Nevertheless, discrimination performance for envelope modulation rates above a few hundred Hertz is reported to be poor—to the point of discrimination thresholds being unattainable—compared with the much higher (>1,000 Hz) limit for low-frequency ITD sensitivity, suggesting the presence of a low-pass filter in the envelope domain. Further, performance for identical modulation rates appears to decline with increasing carrier frequency, supporting the view that the low-pass characteristics observed for envelope ITD processing is carrier-frequency dependent. Here, we assessed listeners’ sensitivity to ITDs conveyed in pure tones and in the modulated envelopes of high-frequency tones. ITD discrimination for the modulated high-frequency tones was measured as a function of both modulation rate and carrier frequency. Some well-trained listeners appear able to discriminate ITDs extremely well, even at modulation rates well beyond 500 Hz, for 4-kHz carriers. For one listener, thresholds were even obtained for a modulation rate of 800 Hz. The highest modulation rate for which thresholds could be obtained declined with increasing carrier frequency for all listeners. At 10 kHz, the highest modulation rate at which thresholds could be obtained was 600 Hz. The upper limit of sensitivity to ITDs conveyed in the envelope of high-frequency modulated sounds appears to be higher than previously considered. PMID:26721926

Modes of elastic plates and shells in water driven by modulated radiation pressure of focused ultrasound

NASA Astrophysics Data System (ADS)

Marston, Philip L.; Daniel, Timothy D.; Abawi, Ahmad T.; Kirsteins, Ivars

2015-11-01

The modulated radiation pressure (MRP) of ultrasound has been used for decades to selectively excite low frequency modes associated with surface tension of fluid objects in water. Much less is known about the excitation of low frequency modes of less compliant metallic objects. Here we use MRP of focused ultrasound to excite resonant flexural vibrations of a circular metal plate in water. The source transducer was driven with a double-sideband suppressed carrier voltage as in. The response of the target (detected with a hydrophone) was at twice the modulation frequency and proportional to the square of the drive voltage. Since the radiation pressure of focused beams is spatially localized, mode shapes could be identified by scanning the source along the target while measuring the target's response. Additional measurements were done with an open-ended water-filled copper circular cylindrical shell in which resonant frequencies and mode shapes were also identified. These experiments show how focused ultrasound can be used to identify low-frequency modes of elastic objects without direct contact. Supported by ONR.

Open-loop frequency acquisition for suppressed-carrier biphase signals using one-pole arm filters

NASA Technical Reports Server (NTRS)

Shah, B.; Holmes, J. K.

1991-01-01

Open loop frequency acquisition performance is discussed for suppressed carrier binary phase shift keyed signals in terms of the probability of detecting the carrier frequency offset when the arms of the Costas loop detector have one pole filters. The approach, which does not require symbol timing, uses fast Fourier transforms (FFTs) to detect the carrier frequency offset. The detection probability, which depends on both the 3 dB arm filter bandwidth and the received symbol signal to noise ratio, is derived and is shown to be independent of symbol timing. It is shown that the performance of this technique is slightly better that other open loop acquisition techniques which use integrators in the arms and whose detection performance varies with symbol timing.

Filamentation of a surface plasma wave over a semiconductor-free space interface

NASA Astrophysics Data System (ADS)

Kumar, Gagan; Tripathi, V. K.

2007-12-01

A large amplitude surface plasma wave (SPW), propagating over a semiconductor-free space interface, is susceptible to filamentation instability. A small perturbation in the amplitude of the SPW across the direction of propagation exerts a ponderomotive force on free electrons and holes, causing spatial modulation in free carrier density and hence the effective permittivity ɛeff of the semiconductor. The regions with higher ɛeff attract more power from the nieghborhood, leading to the growth of the perturbation. The growth rate increases with the intensity of the surface wave. It decreases with the frequency of the SPW.

Two AFC Loops For Low CNR And High Dynamics

NASA Technical Reports Server (NTRS)

Hinedi, Sami M.; Aguirre, Sergio

1992-01-01

Two alternative digital automatic-frequency-control (AFC) loops proposed to acquire (or reacquire) and track frequency of received carrier radio signal. Intended for use where carrier-to-noise ratios (CNR's) low and carrier frequency characterized by high Doppler shift and Doppler rate because of high relative speed and acceleration, respectively, between transmitter and receiver. Either AFC loops used in place of phase-locked loop. New loop concepts integrate ideas from classical spectrum-estimation, digital-phase-locked-loop, and Kalman-Filter theories.

Carrier phase synchronization system for improved amplitude modulation and television broadcast reception

DOEpatents

Smith, Stephen F [Loudon, TN; Moore, James A [Powell, TN

2011-02-01

Systems and methods are described for carrier phase synchronization for improved AM and TV broadcast reception. A method includes synchronizing the phase of a carrier frequency of a broadcast signal with the phase of a remote reference frequency. An apparatus includes a receiver to detect the phase of a reference signal; a phase comparator coupled to the reference signal-phase receiver; a voltage controlled oscillator coupled to the phase comparator; and a phase-controlled radio frequency output coupled to the voltage controlled oscillator.

Multidimensional signal modulation and/or demodulation for data communications

DOEpatents

Smith, Stephen F [London, TN; Dress, William B [Camas, WA

2008-03-04

Systems and methods are described for multidimensional signal modulation and/or demodulation for data communications. A method includes modulating a carrier signal in a first domain selected from the group consisting of phase, frequency, amplitude, polarization and spread; modulating the carrier signal in a second domain selected from the group consisting of phase, frequency, amplitude, polarization and spread; and modulating the carrier signal in a third domain selected from the group consisting of phase, frequency, amplitude, polarization and spread.

Hot carrier-assisted intrinsic photoresponse in graphene.

PubMed

Gabor, Nathaniel M; Song, Justin C W; Ma, Qiong; Nair, Nityan L; Taychatanapat, Thiti; Watanabe, Kenji; Taniguchi, Takashi; Levitov, Leonid S; Jarillo-Herrero, Pablo

2011-11-04

We report on the intrinsic optoelectronic response of high-quality dual-gated monolayer and bilayer graphene p-n junction devices. Local laser excitation (of wavelength 850 nanometers) at the p-n interface leads to striking six-fold photovoltage patterns as a function of bottom- and top-gate voltages. These patterns, together with the measured spatial and density dependence of the photoresponse, provide strong evidence that nonlocal hot carrier transport, rather than the photovoltaic effect, dominates the intrinsic photoresponse in graphene. This regime, which features a long-lived and spatially distributed hot carrier population, may offer a path to hot carrier-assisted thermoelectric technologies for efficient solar energy harvesting.

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

Smith, Stephen F; Moore, James A

Systems and methods are described for carrier-frequency synchronization for improved AM and TV broadcast reception. A method includes synchronizing a carrier frequency of a broadcast signal with a remote reference frequency. An apparatus includes a reference signal receiver; a phase comparator coupled to the reference signal receiver; a voltage controlled oscillator coupled to the phase comparator; and a radio frequency output coupled to the voltage controlled oscillator.

Orthogonal Multi-Carrier DS-CDMA with Frequency-Domain Equalization

NASA Astrophysics Data System (ADS)

Tanaka, Ken; Tomeba, Hiromichi; Adachi, Fumiyuki

Orthogonal multi-carrier direct sequence code division multiple access (orthogonal MC DS-CDMA) is a combination of orthogonal frequency division multiplexing (OFDM) and time-domain spreading, while multi-carrier code division multiple access (MC-CDMA) is a combination of OFDM and frequency-domain spreading. In MC-CDMA, a good bit error rate (BER) performance can be achieved by using frequency-domain equalization (FDE), since the frequency diversity gain is obtained. On the other hand, the conventional orthogonal MC DS-CDMA fails to achieve any frequency diversity gain. In this paper, we propose a new orthogonal MC DS-CDMA that can obtain the frequency diversity gain by applying FDE. The conditional BER analysis is presented. The theoretical average BER performance in a frequency-selective Rayleigh fading channel is evaluated by the Monte-Carlo numerical computation method using the derived conditional BER and is confirmed by computer simulation of the orthogonal MC DS-CDMA signal transmission.

Demonstration of an optical frequency synthesizer with zero carrier-envelope-offset frequency stabilized by the direct locking method.

PubMed

Kim, Eok Bong; Lee, Jae-hwan; Trung, Luu Tran; Lee, Wong-Kyu; Yu, Dai-Hyuk; Ryu, Han Young; Nam, Chang Hee; Park, Chang Yong

2009-11-09

We developed an optical frequency synthesizer (OFS) with the carrier-envelope-offset frequency locked to 0 Hz achieved using the "direct locking method." This method differs from a conventional phaselock method in that the interference signal from a self-referencing f-2f interferometer is directly fed back to the carrier-envelope-phase control of a femtosecond laser in the time domain. A comparison of the optical frequency of the new OFS to that of a conventional OFS stabilized by a phase-lock method showed that the frequency comb of the new OFS was not different to that of the conventional OFS within an uncertainty of 5.68x10(-16). As a practical application of this OFS, we measured the absolute frequency of an acetylene-stabilized diode laser serving as an optical frequency standard in optical communications.

Flip-Flop Digital Modulator

NASA Technical Reports Server (NTRS)

Eno, R. F.

1984-01-01

Clock switched on and off in response to data signal. Flip-flop modulator generates square-wave carrier frequency that is half clock frequency and turns carrier on and off. Final demodulator output logical inverse of data input.

Carrier-Envelope Phase Effect on Atomic Excitation by Few-Cycle rf Pulses

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

Li Hebin; Welch, George R.; Sautenkov, Vladimir A.

2010-03-12

We present an experimental and theoretical study of the carrier-envelope phase effects on population transfer between two bound atomic states interacting with intense ultrashort pulses. Radio frequency pulses are used to transfer population among the ground state hyperfine levels in rubidium atoms. These pulses are only a few cycles in duration and have Rabi frequencies of the order of the carrier frequency. The phase difference between the carrier and the envelope of the pulses has a significant effect on the excitation of atomic coherence and population transfer. We provide a theoretical description of this phenomenon using density matrix equations. Wemore » discuss the implications and possible applications of our results.« less

Features of anti-inflammatory effects of modulated extremely high-frequency electromagnetic radiation.

PubMed

Gapeyev, Andrew B; Mikhailik, Elena N; Chemeris, Nikolay K

2009-09-01

Using a model of acute zymosan-induced paw edema in NMRI mice, we test the hypothesis that anti-inflammatory effects of extremely high-frequency electromagnetic radiation (EHF EMR) can be essentially modified by application of pulse modulation with certain frequencies. It has been revealed that a single exposure of animals to continuous EHF EMR for 20 min reduced the exudative edema of inflamed paw on average by 19% at intensities of 0.1-0.7 mW/cm(2) and frequencies from the range of 42.2-42.6 GHz. At fixed effective carrier frequency of 42.2 GHz, the anti-inflammatory effect of EHF EMR did not depend on modulation frequencies, that is, application of different modulation frequencies from the range of 0.03-100 Hz did not lead to considerable changes in the effect level. On the contrary, at "ineffective" carrier frequencies of 43.0 and 61.22 GHz, the use of modulation frequencies of 0.07-0.1 and 20-30 Hz has allowed us to restore the effect up to a maximal level. The results obtained show the critical dependence of anti-inflammatory action of low-intensity EHF EMR on carrier and modulation frequencies. Within the framework of this study, the possibility of changing the level of expected biological effect of modulated EMR by a special selection of combination of carrier and modulation frequencies is confirmed.

Quantifying charge carrier concentration in ZnO thin films by Scanning Kelvin Probe Microscopy

PubMed Central

Maragliano, C.; Lilliu, S.; Dahlem, M. S.; Chiesa, M.; Souier, T.; Stefancich, M.

2014-01-01

In the last years there has been a renewed interest for zinc oxide semiconductor, mainly triggered by its prospects in optoelectronic applications. In particular, zinc oxide thin films are being widely used for photovoltaic applications, in which the determination of the electrical conductivity is of great importance. Being an intrinsically doped material, the quantification of its doping concentration has always been challenging. Here we show how to probe the charge carrier density of zinc oxide thin films by Scanning Kelvin Probe Microscopy, a technique that allows measuring the contact potential difference between the tip and the sample surface with high spatial resolution. A simple electronic energy model is used for correlating the contact potential difference with the doping concentration in the material. Limitations of this technique are discussed in details and some experimental solutions are proposed. Two-dimensional doping concentration images acquired on radio frequency-sputtered intrinsic zinc oxide thin films with different thickness and deposited under different conditions are reported. We show that results inferred with this technique are in accordance with carrier concentration expected for zinc oxide thin films deposited under different conditions and obtained from resistivity and mobility measurements. PMID:24569599

Evaluation of a GPS Receiver for Code and Carrier-Phase Time and Frequency Transfer

DTIC Science & Technology

2010-11-01

2], and carrier-phase [3]. NIST also employs GPS time transfer as the backup link to Two Way Satellite Time and Frequency Transfer ( TWSTFT ) [4...4] D. Kirchner, 1999, “Two-Way Satellite Time and Frequency Transfer ( TWSTFT ): Principle, Implementation, and Current Performance,” Review of

Unpowered wireless ultrasound tomography system

NASA Astrophysics Data System (ADS)

Zahedi, Farshad; Huang, Haiying

2016-04-01

In this paper, an unpowered wireless ultrasound tomography system is presented. The system consists of two subsystems; the wireless interrogation unit (WIU) and three wireless nodes installed on the structure. Each node is designed to work in generation and sensing modes, but operates at a specific microwave frequency. Wireless transmission of the ultrasound signals between the WIU and the wireless nodes is achieved by converting ultrasound signals to microwave signals and vice versa, using a microwave carrier signal. In the generation mode, both a carrier signal and an ultrasound modulated microwave signal are transmitted to the sensor nodes. Only the node whose operating frequency matches the carrier signal will receive these signals and demodulate them to recover the original ultrasound signal. In the sensing mode, a microwave carrier signal with two different frequency components matching the operating frequencies of the sensor nodes is broadcasted by the WIU. The sensor nodes, in turn, receive the corresponding carrier signals, modulate it with the ultrasound sensing signal, and wirelessly transmit the modulated signal back to the WIU. The demodulation of the sensing signals is performed in the WIU using a digital signal processing. Implementing a software receiver significantly reduces the complexity and the cost of the WIU. A wireless ultrasound tomography system is realized by interchanging the carrier frequencies so that the wireless transducers can take turn to serve as the actuator and sensors.

Parametric array technique for microbubble excitation.

PubMed

Vos, Hendrik J; Goertz, David E; van der Steen, Antonius F W; de Jong, Nico

2011-05-01

This study investigates the use of an acoustic parametric array as a means for microbubble excitation. The excitation wave is generated during propagation in a nonlinear medium of two high-frequency carrier waves, whereby the frequency of the excitation wave is the difference frequency of the carrier waves. Carrier waves of around 10 and 25 MHz are used to generate low-frequency waves between 0.5 and 3.5 MHz at amplitudes in the range of 25 to 80 kPa in water. We demonstrate with high-speed camera observations that it is possible to induce microbubble oscillations with the low frequency signal arising from the nonlinear propagation process. As an application, we determined the resonance frequency of Definity contrast agent microbubbles with radius ranging from 1.5 to 5 μm by sweeping the difference frequency in the range from 0.5 to 3.5 MHz.

Methods and apparatuses using filter banks for multi-carrier spread-spectrum signals

DOEpatents

Moradi, Hussein; Farhang, Behrouz; Kutsche, Carl A

2014-10-14

A transmitter includes a synthesis filter bank to spread a data symbol to a plurality of frequencies by encoding the data symbol on each frequency, apply a common pulse-shaping filter, and apply gains to the frequencies such that a power level of each frequency is less than a noise level of other communication signals within the spectrum. Each frequency is modulated onto a different evenly spaced subcarrier. A demodulator in a receiver converts a radio frequency input to a spread-spectrum signal in a baseband. A matched filter filters the spread-spectrum signal with a common filter having characteristics matched to the synthesis filter bank in the transmitter by filtering each frequency to generate a sequence of narrow pulses. A carrier recovery unit generates control signals responsive to the sequence of narrow pulses suitable for generating a phase-locked loop between the demodulator, the matched filter, and the carrier recovery unit.

Methods and apparatuses using filter banks for multi-carrier spread-spectrum signals

DOEpatents

Moradi, Hussein; Farhang, Behrouz; Kutsche, Carl A

2014-05-20

A transmitter includes a synthesis filter bank to spread a data symbol to a plurality of frequencies by encoding the data symbol on each frequency, apply a common pulse-shaping filter, and apply gains to the frequencies such that a power level of each frequency is less than a noise level of other communication signals within the spectrum. Each frequency is modulated onto a different evenly spaced subcarrier. A demodulator in a receiver converts a radio frequency input to a spread-spectrum signal in a baseband. A matched filter filters the spread-spectrum signal with a common filter having characteristics matched to the synthesis filter bank in the transmitter by filtering each frequency to generate a sequence of narrow pulses. A carrier recovery unit generates control signals responsive to the sequence of narrow pulses suitable for generating a phase-locked loop between the demodulator, the matched filter, and the carrier recovery unit.

Estimate of air carrier and air taxi crash frequencies from high altitude en route flight operations

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

Sanzo, D.; Kimura, C.Y.; Prassinos, P.G.

1996-06-03

In estimating the frequency of an aircraft crashing into a facility, it has been found convenient to break the problem down into two broad categories. One category estimates the aircraft crash frequency due to air traffic from nearby airports, the so-called near-airport environment. The other category estimates the aircraft crash frequency onto facilities due to air traffic from airways, jet routes, and other traffic flying outside the near-airport environment The total aircraft crash frequency is the summation of the crash frequencies from each airport near the facility under evaluation and from all airways, jet routes, and other traffic near themore » facility of interest. This paper will examine the problems associated with the determining the aircraft crash frequencies onto facilities outside the near-airport environment. This paper will further concentrate on the estimating the risk of aircraft crashes to ground facilities due to high altitude air carrier and air taxi traffic. High altitude air carrier and air taxi traffic will be defined as all air carrier and air taxi flights above 18,000 feet Mean Sea Level (MSL).« less

Influence of rate of change of frequency on the overall pitch of frequency-modulated tones.

PubMed

Gockel, H; Moore, B C; Carlyon, R P

2001-02-01

The mechanism(s) determining pitch may assign less weight to portions of a sound where the frequency is changing rapidly. The present experiments explored the possible effect of this on the overall pitch of frequency-modulated sounds. Pitch matches were obtained between an adjustable unmodulated sinusoid and a sinusoidal carrier that was frequency modulated using a highly asymmetric function with the form of a repeating U or inverted U shaped function. The amplitude was constant during the 400-ms presentation time of each stimulus, except for 10-ms raised-cosine onset and offset ramps. In experiment 1, the carrier level was 50 dB SPL and the geometric mean of the instantaneous frequency of the modulated carrier, fc, was either 0.5, 1, 2, or 8 kHz. The modulation rate (fm) was 5, 10, or 20 Hz. The overall depth (maximum to minimum) of the FM was 8% of fc. For all carrier frequencies, the matched frequency was shifted away from the mean carrier frequency, downwards for the U shaped function stimuli and upwards for the repeated inverted U shaped function stimuli. The shift was typically slightly greater than 1% of fc, and did not vary markedly with fc. The effect of fm was small, but there was a trend for the shifts to decrease with increasing fm for fc = 0.5 kHz and to increase with increasing fm for fc = 2 kHz. In experiment 2, the carrier level was reduced to 20 dB SL and matches were obtained only for fc = 2 kHz. Shifts in matched frequency of about 1% were still observed, but the trend for the shifts to increase with increasing fm no longer occurred. In experiment 3, matches were obtained for a 4-kHz carrier at 50 dB SPL. Shifts of about 1% again occurred, which did not vary markedly with fm. The shifts in matched frequency observed in all three experiments are not predicted by models based on the amplitude- or intensity-weighted average of instantaneous frequency (EWAIF or IWAIF). The shifts (and the pitch shifts observed earlier for two-tone complexes and for stimuli with simultaneous AM and FM) are consistent with a model based on the assumption that the overall pitch of a frequency-modulated sound is determined from a weighted average of period estimates, with the weight attached to a given estimate being inversely related to the short-term rate of change of period and directly related to a compressive function of the amplitude.

Wireless multi-level terahertz amplitude modulator using active metamaterial-based spatial light modulation.

PubMed

Rout, Saroj; Sonkusale, Sameer

2016-06-27

The ever increasing demand for bandwidth in wireless communication systems will inevitably lead to the extension of operating frequencies toward the terahertz (THz) band known as the 'THz gap'. Towards closing this gap, we present a multi-level amplitude shift keying (ASK) terahertz wireless communication system using terahertz spatial light modulators (SLM) instead of traditional voltage mode modulation, achieving higher spectral efficiency for high speed communication. The fundamental principle behind this higher efficiency is the conversion of a noisy voltage domain signal to a noise-free binary spatial pattern for effective amplitude modulation of a free-space THz carrier wave. Spatial modulation is achieved using an an active metamaterial array embedded with pseudomorphic high-electron mobility (pHEMT) designed in a consumer-grade galium-arsenide (GaAs) integrated circuit process which enables electronic control of its THz transmissivity. Each array is assembled as individually controllable tiles for transmissive terahertz spatial modulation. Using the experimental data from our metamaterial based modulator, we show that a four-level ASK digital communication system has two orders of magnitude improvement in symbol error rate (SER) for a degradation of 20 dB in transmit signal-to-noise ratio (SNR) using spatial light modulation compared to voltage controlled modulation.

Theoretical study of low-frequency noise and amplitude – frequency characteristics of a semiconductor laser with a fiber Bragg grating

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

Kurnosov, V D; Kurnosov, K V

2013-09-30

Using the rate equations for the density of photons and charge carriers, we have studied the amplitude low-frequency noise of a fibre Bragg grating semiconductor laser. The calculations rely on two versions of the rate equation for the carriers, characterised by the presence of the optical confinement coefficient for the term, which takes into account the rate of stimulated recombination. It is shown that the relative noise intensity, which is calculated by using the rate equation for the carriers without optical confinement, agrees better with the experimental results. The calculation of the amplitude – frequency characteristics (AFCs) has shown thatmore » it is impossible to give preference to any one of these systems, since the AFCs for the two versions of the rate equations for the carriers coincide. (lasers)« less

Statistical analysis of dispersion relations in turbulent solar wind fluctuations using Cluster data

NASA Astrophysics Data System (ADS)

Perschke, C.; Narita, Y.

2012-12-01

Multi-spacecraft measurements enable us to resolve three-dimensional spatial structures without assuming Taylor's frozen-in-flow hypothesis. This is very useful to study frequency-wave vector diagram in solar wind turbulence through direct determination of three-dimensional wave vectors. The existence and evolution of dispersion relation and its role in fully-developed plasma turbulence have been drawing attention of physicists, in particular, if solar wind turbulence represents kinetic Alfvén or whistler mode as the carrier of spectral energy among different scales through wave-wave interactions. We investigate solar wind intervals of Cluster data for various flow velocities with a high-resolution wave vector analysis method, Multi-point Signal Resonator technique, at the tetrahedral separation about 100 km. Magnetic field data and ion data are used to determine the frequency- wave vector diagrams in the co-moving frame of the solar wind. We find primarily perpendicular wave vectors in solar wind turbulence which justify the earlier discussions about kinetic Alfvén or whistler wave. The frequency- wave vector diagrams confirm (a) wave vector anisotropy and (b) scattering in frequencies.

Interaural time discrimination of envelopes carried on high-frequency tones as a function of level and interaural carrier mismatch

PubMed Central

Blanks, Deidra A.; Buss, Emily; Grose, John H.; Fitzpatrick, Douglas C.; Hall, Joseph W.

2009-01-01

Objectives The present study investigated interaural time discrimination for binaurally mismatched carrier frequencies in listeners with normal hearing. One goal of the investigation was to gain insights into binaural hearing in patients with bilateral cochlear implants, where the coding of interaural time differences may be limited by mismatches in the neural populations receiving stimulation on each side. Design Temporal envelopes were manipulated to present low frequency timing cues to high frequency auditory channels. Carrier frequencies near 4 kHz were amplitude modulated at 128 Hz via multiplication with a half-wave rectified sinusoid, and that modulation was either in-phase across ears or delayed to one ear. Detection thresholds for non-zero interaural time differences were measured for a range of stimulus levels and a range of carrier frequency mismatches. Data were also collected under conditions designed to limit cues based on stimulus spectral spread, including masking and truncation of sidebands associated with modulation. Results Listeners with normal hearing can detect interaural time differences in the face of substantial mismatches in carrier frequency across ears. Conclusions The processing of interaural time differences in listeners with normal hearing is likely based on spread of excitation into binaurally matched auditory channels. Sensitivity to interaural time differences in listeners with cochlear implants may depend upon spread of current that results in the stimulation of neural populations that share common tonotopic space bilaterally. PMID:18596646

Methods and devices based on brillouin selective sideband amplification

NASA Technical Reports Server (NTRS)

Yao, X. Steve (Inventor)

2003-01-01

Opto-electronic devices and techniques using Brillouin scattering to select a sideband in a modulated optical carrier signal for amplification. Two lasers respectively provide a carrier signal beam and a Brillouin pump beam which are fed into an Brillouin optical medium in opposite directions. The relative frequency separation between the lasers is adjusted to align the frequency of the backscattered Brillouin signal with a desired sideband in the carrier signal to effect a Brillouin gain on the sideband. This effect can be used to implement photonic RF signal mixing and conversion with gain, conversion from phase modulation to amplitude modulation, photonic RF frequency multiplication, optical and RF pulse generation and manipulation, and frequency-locking of lasers.

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.

An assessment of envelope-based demodulation in case of proximity of carrier and modulation frequencies

NASA Astrophysics Data System (ADS)

Shahriar, Md Rifat; Borghesani, Pietro; Randall, R. B.; Tan, Andy C. C.

2017-11-01

Demodulation is a necessary step in the field of diagnostics to reveal faults whose signatures appear as an amplitude and/or frequency modulation. The Hilbert transform has conventionally been used for the calculation of the analytic signal required in the demodulation process. However, the carrier and modulation frequencies must meet the conditions set by the Bedrosian identity for the Hilbert transform to be applicable for demodulation. This condition, basically requiring the carrier frequency to be sufficiently higher than the frequency of the modulation harmonics, is usually satisfied in many traditional diagnostic applications (e.g. vibration analysis of gear and bearing faults) due to the order-of-magnitude ratio between the carrier and modulation frequency. However, the diversification of the diagnostic approaches and applications shows cases (e.g. electrical signature analysis-based diagnostics) where the carrier frequency is in close proximity to the modulation frequency, thus challenging the applicability of the Bedrosian theorem. This work presents an analytic study to quantify the error introduced by the Hilbert transform-based demodulation when the Bedrosian identity is not satisfied and proposes a mitigation strategy to combat the error. An experimental study is also carried out to verify the analytical results. The outcome of the error analysis sets a confidence limit on the estimated modulation (both shape and magnitude) achieved through the Hilbert transform-based demodulation in case of violated Bedrosian theorem. However, the proposed mitigation strategy is found effective in combating the demodulation error aroused in this scenario, thus extending applicability of the Hilbert transform-based demodulation.

Self-similar gravity wave spectra resulting from the modulation of bound waves

NASA Astrophysics Data System (ADS)

Michel, Guillaume; Semin, Benoît; Cazaubiel, Annette; Haudin, Florence; Humbert, Thomas; Lepot, Simon; Bonnefoy, Félicien; Berhanu, Michaël; Falcon, Éric

2018-05-01

We experimentally study the properties of nonlinear surface gravity waves in a large-scale basin. We consider two different configurations: a one-dimensional (1D) monochromatic wave forcing, and a two-dimensional (2D) forcing with bichromatic waves satisfying resonant-wave interaction conditions. For the 1D forcing, we find a discrete wave-energy spectrum dominated at high frequencies by bound waves whose amplitudes decrease as a power law of the frequency. Bound waves (e.g., to the carrier) are harmonics superimposed on the carrier wave propagating with the same phase velocity as the one of the carrier. When a narrow frequency random modulation is applied to this carrier, the high-frequency part of the wave-energy spectrum becomes continuous with the same frequency-power law. Similar results are found for the 2D forcing when a random modulation is also applied to both carrier waves. Our results thus show that all these nonlinear gravity wave spectra are dominated at high frequencies by the presence of bound waves, even in the configuration where resonant interactions occur. Moreover, in all these configurations, the power-law exponent of the spectrum is found to depend on the forcing amplitude with the same trend as the one found in previous gravity wave turbulence experiments. Such a set of bound waves may thus explain this dependence that was previously poorly understood.

Increased Anatomical Specificity of Neuromodulation via Modulated Focused Ultrasound

PubMed Central

Mehić, Edin; Xu, Julia M.; Caler, Connor J.; Coulson, Nathaniel K.; Moritz, Chet T.; Mourad, Pierre D.

2014-01-01

Transcranial ultrasound can alter brain function transiently and nondestructively, offering a new tool to study brain function now and inform future therapies. Previous research on neuromodulation implemented pulsed low-frequency (250–700 kHz) ultrasound with spatial peak temporal average intensities (ISPTA) of 0.1–10 W/cm2. That work used transducers that either insonified relatively large volumes of mouse brain (several mL) with relatively low-frequency ultrasound and produced bilateral motor responses, or relatively small volumes of brain (on the order of 0.06 mL) with relatively high-frequency ultrasound that produced unilateral motor responses. This study seeks to increase anatomical specificity to neuromodulation with modulated focused ultrasound (mFU). Here, ‘modulated’ means modifying a focused 2-MHz carrier signal dynamically with a 500-kHz signal as in vibro-acoustography, thereby creating a low-frequency but small volume (approximately 0.015 mL) source of neuromodulation. Application of transcranial mFU to lightly anesthetized mice produced various motor movements with high spatial selectivity (on the order of 1 mm) that scaled with the temporal average ultrasound intensity. Alone, mFU and focused ultrasound (FUS) each induced motor activity, including unilateral motions, though anatomical location and type of motion varied. Future work should include larger animal models to determine the relative efficacy of mFU versus FUS. Other studies should determine the biophysical processes through which they act. Also of interest is exploration of the potential research and clinical applications for targeted, transcranial neuromodulation created by modulated focused ultrasound, especially mFU’s ability to produce compact sources of ultrasound at the very low frequencies (10–100s of Hertz) that are commensurate with the natural frequencies of the brain. PMID:24504255

Nonlinear Y-Like Receptive Fields in the Early Visual Cortex: An Intermediate Stage for Building Cue-Invariant Receptive Fields from Subcortical Y Cells.

PubMed

Gharat, Amol; Baker, Curtis L

2017-01-25

Many of the neurons in early visual cortex are selective for the orientation of boundaries defined by first-order cues (luminance) as well as second-order cues (contrast, texture). The neural circuit mechanism underlying this selectivity is still unclear, but some studies have proposed that it emerges from spatial nonlinearities of subcortical Y cells. To understand how inputs from the Y-cell pathway might be pooled to generate cue-invariant receptive fields, we recorded visual responses from single neurons in cat Area 18 using linear multielectrode arrays. We measured responses to drifting and contrast-reversing luminance gratings as well as contrast modulation gratings. We found that a large fraction of these neurons have nonoriented responses to gratings, similar to those of subcortical Y cells: they respond at the second harmonic (F2) to high-spatial frequency contrast-reversing gratings and at the first harmonic (F1) to low-spatial frequency drifting gratings ("Y-cell signature"). For a given neuron, spatial frequency tuning for linear (F1) and nonlinear (F2) responses is quite distinct, similar to orientation-selective cue-invariant neurons. Also, these neurons respond to contrast modulation gratings with selectivity for the carrier (texture) spatial frequency and, in some cases, orientation. Their receptive field properties suggest that they could serve as building blocks for orientation-selective cue-invariant neurons. We propose a circuit model that combines ON- and OFF-center cortical Y-like cells in an unbalanced push-pull manner to generate orientation-selective, cue-invariant receptive fields. A significant fraction of neurons in early visual cortex have specialized receptive fields that allow them to selectively respond to the orientation of boundaries that are invariant to the cue (luminance, contrast, texture, motion) that defines them. However, the neural mechanism to construct such versatile receptive fields remains unclear. Using multielectrode recording, we found a large fraction of neurons in early visual cortex with receptive fields not selective for orientation that have spatial nonlinearities like those of subcortical Y cells. These are strong candidates for building cue-invariant orientation-selective neurons; we present a neural circuit model that pools such neurons in an imbalanced "push-pull" manner, to generate orientation-selective cue-invariant receptive fields. Copyright © 2017 the authors 0270-6474/17/370998-16$15.00/0.

Frequency Dependent Harmonic Powers in a Modified Uni-Traveling Carrier (MUTC) Photodetector

DTIC Science & Technology

2017-01-27

Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/5651--17-9712 Frequency Dependent Harmonic Powers in a Modified Uni- Traveling Carrier...burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing...Modified Uni- Traveling Carrier (MUTC) Photodetector Yue Hu,* Meredith N. Hutchinson, and Curtis R. Menyuk* Naval Research Laboratory 4555 Overlook

Highly noise-tolerant hybrid algorithm for phase retrieval from a single-shot spatial carrier fringe pattern

NASA Astrophysics Data System (ADS)

Dong, Zhichao; Cheng, Haobo

2018-01-01

A highly noise-tolerant hybrid algorithm (NTHA) is proposed in this study for phase retrieval from a single-shot spatial carrier fringe pattern (SCFP), which effectively combines the merits of spatial carrier phase shift method and two dimensional continuous wavelet transform (2D-CWT). NTHA firstly extracts three phase-shifted fringe patterns from the SCFP with one pixel malposition; then calculates phase gradients by subtracting the reference phase from the other two target phases, which are retrieved respectively from three phase-shifted fringe patterns by 2D-CWT; finally, reconstructs the phase map by a least square gradient integration method. Its typical characters include but not limited to: (1) doesn't require the spatial carrier to be constant; (2) the subtraction mitigates edge errors of 2D-CWT; (3) highly noise-tolerant, because not only 2D-CWT is noise-insensitive, but also the noise in the fringe pattern doesn't directly take part in the phase reconstruction as in previous hybrid algorithm. Its feasibility and performances are validated extensively by simulations and contrastive experiments to temporal phase shift method, Fourier transform and 2D-CWT methods.

A new approach to harmonic elimination based on a real-time comparison method

NASA Astrophysics Data System (ADS)

Gourisetti, Sri Nikhil Gupta

Undesired harmonics are responsible for noise in a transmission channel, power loss in power electronics and in motor control. Selective Harmonic Elimination (SHE) is a well-known method used to eliminate or suppress the unwanted harmonics between the fundamental and the carrier frequency harmonic/component. But SHE bears the disadvantage of its incapability to use in real-time applications. A novel reference-carrier comparative method has been developed which can be used to generate an SPWM signal to apply in real-time systems. A modified carrier signal is designed and tested for different carrier frequencies based on the generated SPWM FFT. The carrier signal may change for different fundamental to carrier ratio that leads to solving the equations each time. An analysis to find all possible solutions for a particular carrier frequency and fundamental amplitude is performed and found. This proves that there is no one global maxima instead several local maximas exists for a particular condition set that makes this method less sensitive. Additionally, an attempt to find a universal solution that is valid for any carrier signal with predefined fundamental amplitude is performed. A uniform distribution Monte-Carlo sensitivity analysis is performed to measure the window i.e., best and worst possible solutions. The simulations are performed using MATLAB and are justified with experimental results.

A review of ionospheric effects on Earth-space propagation

NASA Technical Reports Server (NTRS)

Klobuchar, J. A.

1984-01-01

A short description is given of each ionospheric total electron content (TEC) effect upon radio waves, along with a representative value of the magnitude of each of these effects under normal ionospheric conditions. A discussion is given of the important characteristics of average ionospheric TEC behavior and the temporal and spatial variability of TEC. Radio waves undergo several effects when they pass through the Earth's ionosphere. One of the most important of these effects is a retardation, or group delay, on the modulation or information carried on the radio wave that is due to its encounter with the free, thermal electrons in the Earth's ionosphere. Other effects the ionosphere has on radio waves include: radio frequency (RF) carrier phase advance; Doppler shift of the RF carrier of the radio wave; Faraday rotation of the plane of polarization of linearly polarized waves; angular refraction or bending of the radio wave path as it travels through the ionosphere; and amplitude and phase scintillations.

Three-dimensional Fourier transform evaluation of sequences of spatially and temporally modulated speckle interferograms.

PubMed

Trillo, C; Doval, A F; López-Vázquez, J C

2010-07-05

Phase evaluation methods based on the 2D spatial Fourier transform of a speckle interferogram with spatial carrier usually assume that the Fourier spectrum of the interferogram has a trimodal distribution, i. e. that the side lobes corresponding to the interferential terms do not overlap the other two spectral terms, which are related to the intensity of the object and reference beams, respectively. Otherwise, part of the spectrum of the object beam is inside the inverse-transform window of the selected interference lobe and induces an error in the resultant phase map. We present a technique for the acquisition and processing of speckle interferogram sequences that separates the interference lobes from the other spectral terms when the aforementioned assumption does not apply and regardless of the temporal bandwidth of the phase signal. It requires the recording of a sequence of interferograms with spatial and temporal carriers, and their processing with a 3D Fourier transform. In the resultant 3D spectrum, the spatial and temporal carriers separate the conjugate interferential terms from each other and from the term related to the object beam. Experimental corroboration is provided through the measurement of the amplitude of surface acoustic waves in plates with a double-pulsed TV holography setup. The results obtained with the proposed method are compared to those obtained with the processing of individual interferograms with the regular spatial-carrier 2D Fourier transform method.

Femtosecond diffraction dynamics of laser-induced periodic surface structures on fused silica

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

Hoehm, S.; Rosenfeld, A.; Krueger, J.

2013-02-04

The formation of laser-induced periodic surface structures (LIPSS) on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration, 800 nm center wavelength) is studied experimentally using a transillumination femtosecond time-resolved (0.1 ps-1 ns) pump-probe diffraction approach. This allows to reveal the generation dynamics of near-wavelength-sized LIPSS showing a transient diffraction at specific spatial frequencies even before a corresponding permanent surface relief was observed. The results confirm that the ultrafast energy deposition to the materials surface plays a key role and triggers subsequent physical mechanisms such as carrier scattering into self-trapped excitons.

Optical frequency upconversion technique for transmission of wireless MIMO-type signals over optical fiber.

PubMed

Shaddad, R Q; Mohammad, A B; Al-Gailani, S A; Al-Hetar, A M

2014-01-01

The optical fiber is well adapted to pass multiple wireless signals having different carrier frequencies by using radio-over-fiber (ROF) technique. However, multiple wireless signals which have the same carrier frequency cannot propagate over a single optical fiber, such as wireless multi-input multi-output (MIMO) signals feeding multiple antennas in the fiber wireless (FiWi) system. A novel optical frequency upconversion (OFU) technique is proposed to solve this problem. In this paper, the novel OFU approach is used to transmit three wireless MIMO signals over a 20 km standard single mode fiber (SMF). The OFU technique exploits one optical source to produce multiple wavelengths by delivering it to a LiNbO3 external optical modulator. The wireless MIMO signals are then modulated by LiNbO3 optical intensity modulators separately using the generated optical carriers from the OFU process. These modulators use the optical single-sideband with carrier (OSSB+C) modulation scheme to optimize the system performance against the fiber dispersion effect. Each wireless MIMO signal is with a 2.4 GHz or 5 GHz carrier frequency, 1 Gb/s data rate, and 16-quadrature amplitude modulation (QAM). The crosstalk between the wireless MIMO signals is highly suppressed, since each wireless MIMO signal is carried on a specific optical wavelength.

Spectrotemporal modulation sensitivity for hearing-impaired listeners: dependence on carrier center frequency and the relationship to speech intelligibility.

PubMed

Mehraei, Golbarg; Gallun, Frederick J; Leek, Marjorie R; Bernstein, Joshua G W

2014-07-01

Poor speech understanding in noise by hearing-impaired (HI) listeners is only partly explained by elevated audiometric thresholds. Suprathreshold-processing impairments such as reduced temporal or spectral resolution or temporal fine-structure (TFS) processing ability might also contribute. Although speech contains dynamic combinations of temporal and spectral modulation and TFS content, these capabilities are often treated separately. Modulation-depth detection thresholds for spectrotemporal modulation (STM) applied to octave-band noise were measured for normal-hearing and HI listeners as a function of temporal modulation rate (4-32 Hz), spectral ripple density [0.5-4 cycles/octave (c/o)] and carrier center frequency (500-4000 Hz). STM sensitivity was worse than normal for HI listeners only for a low-frequency carrier (1000 Hz) at low temporal modulation rates (4-12 Hz) and a spectral ripple density of 2 c/o, and for a high-frequency carrier (4000 Hz) at a high spectral ripple density (4 c/o). STM sensitivity for the 4-Hz, 4-c/o condition for a 4000-Hz carrier and for the 4-Hz, 2-c/o condition for a 1000-Hz carrier were correlated with speech-recognition performance in noise after partialling out the audiogram-based speech-intelligibility index. Poor speech-reception and STM-detection performance for HI listeners may be related to a combination of reduced frequency selectivity and a TFS-processing deficit limiting the ability to track spectral-peak movements.

Microresonator-based solitons for massively parallel coherent optical communications

NASA Astrophysics Data System (ADS)

Marin-Palomo, Pablo; Kemal, Juned N.; Karpov, Maxim; Kordts, Arne; Pfeifle, Joerg; Pfeiffer, Martin H. P.; Trocha, Philipp; Wolf, Stefan; Brasch, Victor; Anderson, Miles H.; Rosenberger, Ralf; Vijayan, Kovendhan; Freude, Wolfgang; Kippenberg, Tobias J.; Koos, Christian

2017-06-01

Solitons are waveforms that preserve their shape while propagating, as a result of a balance of dispersion and nonlinearity. Soliton-based data transmission schemes were investigated in the 1980s and showed promise as a way of overcoming the limitations imposed by dispersion of optical fibres. However, these approaches were later abandoned in favour of wavelength-division multiplexing schemes, which are easier to implement and offer improved scalability to higher data rates. Here we show that solitons could make a comeback in optical communications, not as a competitor but as a key element of massively parallel wavelength-division multiplexing. Instead of encoding data on the soliton pulse train itself, we use continuous-wave tones of the associated frequency comb as carriers for communication. Dissipative Kerr solitons (DKSs) (solitons that rely on a double balance of parametric gain and cavity loss, as well as dispersion and nonlinearity) are generated as continuously circulating pulses in an integrated silicon nitride microresonator via four-photon interactions mediated by the Kerr nonlinearity, leading to low-noise, spectrally smooth, broadband optical frequency combs. We use two interleaved DKS frequency combs to transmit a data stream of more than 50 terabits per second on 179 individual optical carriers that span the entire telecommunication C and L bands (centred around infrared telecommunication wavelengths of 1.55 micrometres). We also demonstrate coherent detection of a wavelength-division multiplexing data stream by using a pair of DKS frequency combs—one as a multi-wavelength light source at the transmitter and the other as the corresponding local oscillator at the receiver. This approach exploits the scalability of microresonator-based DKS frequency comb sources for massively parallel optical communications at both the transmitter and the receiver. Our results demonstrate the potential of these sources to replace the arrays of continuous-wave lasers that are currently used in high-speed communications. In combination with advanced spatial multiplexing schemes and highly integrated silicon photonic circuits, DKS frequency combs could bring chip-scale petabit-per-second transceivers into reach.

Usage Autocorrelation Function in the Capacity of Indicator Shape of the Signal in Acoustic Emission Testing of Intricate Castings

NASA Astrophysics Data System (ADS)

Popkov, Artem

2016-01-01

The article contains information about acoustic emission signals analysing using autocorrelation function. Operation factors were analysed, such as shape of signal, the origins time and carrier frequency. The purpose of work is estimating the validity of correlations methods analysing signals. Acoustic emission signal consist of different types of waves, which propagate on different trajectories in object of control. Acoustic emission signal is amplitude-, phase- and frequency-modeling signal. It was described by carrier frequency at a given point of time. Period of signal make up 12.5 microseconds and carrier frequency make up 80 kHz for analysing signal. Usage autocorrelation function like indicator the origin time of acoustic emission signal raises validity localization of emitters.

Carrier-phase-based two-way satellite time and frequency transfer.

PubMed

Fujieda, Miho; Gotoh, Tadahiro; Nakagawa, Fumimaru; Tabuchi, Ryo; Aida, Masanori; Amagai, Jun

2012-12-01

We performed measurements of carrier-phase-based two-way satellite time and frequency transfer (TWST-FT) with an A/D sampler and conventional TWSTFT system. We found that an instability resulting from a local signal at the satellite transponder was negligible. The short-term stability of 4 × 10(-13) at 1 s was achieved in a short-baseline measurement. The results showed good agreement with the GPS carrier phase.

Photonics-based microwave frequency measurement using a double-sideband suppressed-carrier modulation and an InP integrated ring-assisted Mach-Zehnder interferometer filter.

PubMed

Fandiño, Javier S; Muñoz, Pascual

2013-11-01

A photonic system capable of estimating the unknown frequency of a CW microwave tone is presented. The core of the system is a complementary optical filter monolithically integrated in InP, consisting of a ring-assisted Mach-Zehnder interferometer with a second-order elliptic response. By simultaneously measuring the different optical powers produced by a double-sideband suppressed-carrier modulation at the outputs of the photonic integrated circuit, an amplitude comparison function that depends on the input tone frequency is obtained. Using this technique, a frequency measurement range of 10 GHz (5-15 GHz) with a root mean square value of frequency error lower than 200 MHz is experimentally demonstrated. Moreover, simulations showing the impact of a residual optical carrier on system performance are also provided.

ACSS2 gene variant associated with cleft lip and palate in two independent Hispanic populations.

PubMed

Dodhia, Sonam; Celis, Katrina; Aylward, Alana; Cai, Yi; Fontana, Maria E; Trespalacios, Alberto; Hoffman, David C; Alfonso, Henry Ostos; Eisig, Sidney B; Su, Gloria H; Chung, Wendy K; Haddad, Joseph

2017-10-01

A candidate variant (p.Val496Ala) of the ACSS2 gene (T > C missense, rs59088485 variant at chr20: bp37 33509608) was previously found to consistently segregate with nonsyndromic cleft lip and/or palate (NSCLP) in three Honduran families. Objectives of this study were 1) to investigate the frequency of this ACSS2 variant in Honduran unrelated NSCLP patients and unrelated unaffected controls and 2) to investigate the frequency of this variant in Colombian unrelated affected NSCLP patients and unrelated unaffected controls. Case-control studies. Sanger sequencing of 99 unrelated Honduran NSCLP patients and 215 unrelated unaffected controls for the p.Val496Ala ACSS2 variant was used to determine the carrier frequency in NSCLP patients and controls. Sanger sequencing of 230 unrelated Colombian NSCLP patients and 146 unrelated unaffected controls for the p.Val496Ala ACSS2 variant was used to determine the carrier frequency in NSCLP patients and controls. In the Honduran population, the odds ratio of having NSCLP among carriers of the p.Val496Ala ACSS2 variant was 4.0 (P = .03), with a carrier frequency of seven of 99 (7.1%) in unrelated affected and four of 215 (1.9%) in unrelated unaffected individuals. In the Colombian population, the odds ratio of having NSCLP among carriers of the p.Val496Ala ACSS2 variant was 2.6 (P = .04), with a carrier frequency of 23 of 230 (10.0%) in unrelated affected and six of 146 (4.1%) in unrelated unaffected individuals. These findings support the role of ACSS2 in NSCLP in two independent Hispanic populations from Honduras and Colombia. NA Laryngoscope, 127:E336-E339, 2017. © 2017 The American Laryngological, Rhinological and Otological Society, Inc.

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.

Methods and apparatuses using filter banks for multi-carrier spread spectrum signals

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

Moradi, Hussein; Farhang, Behrouz; Kutsche, Carl A

2017-01-31

A transmitter includes a synthesis filter bank to spread a data symbol to a plurality of frequencies by encoding the data symbol on each frequency, apply a common pulse-shaping filter, and apply gains to the frequencies such that a power level of each frequency is less than a noise level of other communication signals within the spectrum. Each frequency is modulated onto a different evenly spaced subcarrier. A demodulator in a receiver converts a radio frequency input to a spread-spectrum signal in a baseband. A matched filter filters the spread-spectrum signal with a common filter having characteristics matched to themore » synthesis filter bank in the transmitter by filtering each frequency to generate a sequence of narrow pulses. A carrier recovery unit generates control signals responsive to the sequence of narrow pulses suitable for generating a phase-locked loop between the demodulator, the matched filter, and the carrier recovery unit.« less

Methods and apparatuses using filter banks for multi-carrier spread spectrum signals

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

Moradi, Hussein; Farhang, Behrouz; Kutsche, Carl A.

2016-06-14

A transmitter includes a synthesis filter bank to spread a data symbol to a plurality of frequencies by encoding the data symbol on each frequency, apply a common pulse-shaping filter, and apply gains to the frequencies such that a power level of each frequency is less than a noise level of other communication signals within the spectrum. Each frequency is modulated onto a different evenly spaced subcarrier. A demodulator in a receiver converts a radio frequency input to a spread-spectrum signal in a baseband. A matched filter filters the spread-spectrum signal with a common filter having characteristics matched to themore » synthesis filter bank in the transmitter by filtering each frequency to generate a sequence of narrow pulses. A carrier recovery unit generates control signals responsive to the sequence of narrow pulses suitable for generating a phase-locked loop between the demodulator, the matched filter, and the carrier recovery unit.« less

Phase retrieval of singular scalar light fields using a two-dimensional directional wavelet transform and a spatial carrier.

PubMed

Federico, Alejandro; Kaufmann, Guillermo H

2008-10-01

We evaluate a method based on the two-dimensional directional wavelet transform and the introduction of a spatial carrier to retrieve optical phase distributions in singular scalar light fields. The performance of the proposed phase-retrieval method is compared with an approach based on Fourier transform. The advantages and limitations of the proposed method are discussed.

Code-Phase Clock Bias and Frequency Offset in PPP Clock Solutions.

PubMed

Defraigne, Pascale; Sleewaegen, Jean-Marie

2016-07-01

Precise point positioning (PPP) is a zero-difference single-station technique that has proved to be very effective for time and frequency transfer, enabling the comparison of atomic clocks with a precision of a hundred picoseconds and a one-day stability below the 1e-15 level. It was, however, noted that for some receivers, a frequency difference is observed between the clock solution based on the code measurements and the clock solution based on the carrier-phase measurements. These observations reveal some inconsistency either between the code and carrier phases measured by the receiver or between the data analysis strategy of codes and carrier phases. One explanation for this discrepancy is the time offset that can exist for some receivers between the code and the carrier-phase latching. This paper explains how a code-phase bias in the receiver hardware can induce a frequency difference between the code and the carrier-phase clock solutions. The impact on PPP is then quantified. Finally, the possibility to determine this code-phase bias in the PPP modeling is investigated, and the first results are shown to be inappropriate due to the high level of code noise.

Multicarrier orthogonal spread-spectrum (MOSS) data communications

DOEpatents

Smith, Stephen F [London, TN; Dress, William B [Camas, WA

2008-01-01

Systems and methods are described for multicarrier orthogonal spread-spectrum (MOSS) data communication. A method includes individually spread-spectrum modulating at least two of a set of orthogonal frequency division multiplexed carriers, wherein the resulting individually spread-spectrum modulated at least two of a set of orthogonal frequency division multiplexed carriers are substantially mutually orthogonal with respect to both frequency division multiplexing and spread-spectrum modulation.

Parallel PWMs Based Fully Digital Transmitter with Wide Carrier Frequency Range

PubMed Central

Zhou, Bo; Zhang, Kun; Zhou, Wenbiao; Zhang, Yanjun; Liu, Dake

2013-01-01

The carrier-frequency (CF) and intermediate-frequency (IF) pulse-width modulators (PWMs) based on delay lines are proposed, where baseband signals are conveyed by both positions and pulse widths or densities of the carrier clock. By combining IF-PWM and precorrected CF-PWM, a fully digital transmitter with unit-delay autocalibration is implemented in 180 nm CMOS for high reconfiguration. The proposed architecture achieves wide CF range of 2 M–1 GHz, high power efficiency of 70%, and low error vector magnitude (EVM) of 3%, with spectrum purity of 20 dB optimized in comparison to the existing designs. PMID:24223503

Reconfigurable optical-to-optical frequency conversion method and apparatus

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

Zortman, William A.; Lentine, Anthony L.

A photonic device is provided for impressing a modulation pattern on an optical carrier. The device includes a unit in which a photodetector and an optical microresonator are monolithically integrated. The device further includes an optical waveguide evanescently coupled to the optical microresonator and having at least an upstream portion configured to carry at least one optical carrier toward the microresonator. The optical microresonator is tunable so as to resonate with the optical carrier frequency. The optical microresonator and the photodetector are mutually coupled such that in operation, charge carriers photogenerated in the photodetector are injected into the microresonator, wheremore » the photocurrent changes the resonant conditions. In some embodiments the device is operable as an optical-to-optical frequency converter. In other embodiments the device is operable as an oscillator.« less

Apparatus and methods of measuring minority carrier lifetime using a liquid probe

DOEpatents

Li, Jian

2016-04-12

Methods and apparatus for measuring minority carrier lifetimes using liquid probes are provided. In one embodiment, a method of measuring the minority carrier lifetime of a semiconductor material comprises: providing a semiconductor material having a surface; forming a rectifying junction at a first location on the surface by temporarily contacting the surface with a conductive liquid probe; electrically coupling a second junction to the semiconductor material at a second location, wherein the first location and the second location are physically separated; applying a forward bias to the rectifying junction causing minority carrier injection in the semiconductor material; measuring a total capacitance as a function of frequency between the rectifying junction and the second junction; determining an inflection frequency of the total capacitance; and determining a minority lifetime of the semiconductor material from the inflection frequency.

Carrier-envelope phase effects for a dipolar molecule interacting with two-color pump-probe laser pulses

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

Cheng Taiwang; Brown, Alex

2004-12-01

The interaction of a two-level dipolar molecule with two laser pulses, where one laser's frequency is tuned to the energy level separation (pump laser) while the second laser's frequency is extremely small (probe laser), is investigated. A dipolar molecule is one with a nonzero difference between the permanent dipole moments of the molecular states. As shown previously [A. Brown, Phys. Rev. A 66, 053404 (2002)], the final population transfer between the two levels exhibits a dependence on the carrier-envelope phase of the probe laser. Based on the rotating-wave approximation (RWA), an effective Hamiltonian is derived to account for the basicmore » characteristics of the carrier-envelope phase dependence effect. By analysis of the effective Hamiltonian, scaling properties of the system are found with regard to field strengths, pulse durations, and frequencies. According to these scaling properties, the final-state population transfer can be controlled by varying the carrier-envelope phase of the probe laser field using lasers with weak field strengths (low intensities) and relatively long pulse durations. In order to examine the possible roles of background states, the investigation is extended to a three-level model. It is demonstrated that the carrier-envelope phase effect still persists in a well-defined manner even when neighboring energy levels are present. These results illustrate the potential of utilizing excitation in dipolar molecules as a means of measuring the carrier-envelope phase of a laser pulse or if one can manipulate the carrier envelope phase, as a method of controlling population transfer in dipolar molecules. The results also suggest that the carrier-envelope phases must be taken into account properly when performing calculations involving pump-probe excitation schemes with laser frequencies which differ widely in magnitude.« less

47 CFR 73.322 - FM stereophonic sound transmission standards.

Code of Federal Regulations, 2010 CFR

2010-10-01

... frequency in a transmission system meeting the following parameters: (1) The modulating signal for the main... frequency modulate the main carrier between the limits of 8 and 10 percent. (3) One stereophonic subcarrier... stereophomic subcarriers are not precluded. (4) Double sideband, suppressed-carrier, amplitude modulation of...

47 CFR 15.207 - Conducted limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

... apply to carrier current systems operating as intentional radiators on frequencies below 30 MHz. In lieu... current system containing their fundamental emission within the frequency band 535-1705 kHz and intended.../50 ohms LISN. (3) Carrier current systems operating below 30 MHz are also subject to the radiated...

Spectrotemporal modulation sensitivity for hearing-impaired listeners: Dependence on carrier center frequency and the relationship to speech intelligibility

PubMed Central

Mehraei, Golbarg; Gallun, Frederick J.; Leek, Marjorie R.; Bernstein, Joshua G. W.

2014-01-01

Poor speech understanding in noise by hearing-impaired (HI) listeners is only partly explained by elevated audiometric thresholds. Suprathreshold-processing impairments such as reduced temporal or spectral resolution or temporal fine-structure (TFS) processing ability might also contribute. Although speech contains dynamic combinations of temporal and spectral modulation and TFS content, these capabilities are often treated separately. Modulation-depth detection thresholds for spectrotemporal modulation (STM) applied to octave-band noise were measured for normal-hearing and HI listeners as a function of temporal modulation rate (4–32 Hz), spectral ripple density [0.5–4 cycles/octave (c/o)] and carrier center frequency (500–4000 Hz). STM sensitivity was worse than normal for HI listeners only for a low-frequency carrier (1000 Hz) at low temporal modulation rates (4–12 Hz) and a spectral ripple density of 2 c/o, and for a high-frequency carrier (4000 Hz) at a high spectral ripple density (4 c/o). STM sensitivity for the 4-Hz, 4-c/o condition for a 4000-Hz carrier and for the 4-Hz, 2-c/o condition for a 1000-Hz carrier were correlated with speech-recognition performance in noise after partialling out the audiogram-based speech-intelligibility index. Poor speech-reception and STM-detection performance for HI listeners may be related to a combination of reduced frequency selectivity and a TFS-processing deficit limiting the ability to track spectral-peak movements. PMID:24993215

Both hemophilia health care providers and hemophilia a carriers report that carriers have excessive bleeding.

PubMed

Paroskie, Allison; Oso, Olatunde; Almassi, Benjamin; DeBaun, Michael R; Sidonio, Robert F

2014-05-01

Hemophilia A, the result of reduced factor VIII activity, is an X-linked recessive bleeding disorder. Previous reports of hemophilia A carriers suggest an increased bleeding tendency. Our objective was to determine the attitudes and understanding of the hemophilia A carrier bleeding phenotype, and opinions regarding timing of carrier testing from the perspective of both medical providers and affected patients. Data from this survey were used as preliminary data for an ongoing prospective study. An electronic survey was distributed to physicians and nurses employed at Hemophilia Treatment Centers, and hemophilia A carriers who were members of Hemophilia Federation of America. The questions focused on the clinical understanding of bleeding symptoms and management of hemophilia A carriers, and the timing and intensity of carrier testing. Our survey indicates that 51% (36/51) of providers compared with 78% (36/46) of carriers believe that hemophilia A carriers with normal factor VIII activity have an increased bleeding tendency (P<0.001); 72% (33/36) of hemophilia A carriers report a high frequency of bleeding symptoms. Regarding carrier testing, 72% (50/69) of medical providers recommend testing after 14 years of age, conversely 65% (29/45) of hemophilia A carriers prefer testing to be done before this age (P<0.001). Hemophilia A carriers self-report a higher frequency of bleeding than previously acknowledged, and have a preference for earlier testing to confirm carrier status.

Optical Frequency Upconversion Technique for Transmission of Wireless MIMO-Type Signals over Optical Fiber

PubMed Central

Shaddad, R. Q.; Mohammad, A. B.; Al-Gailani, S. A.; Al-Hetar, A. M.

2014-01-01

The optical fiber is well adapted to pass multiple wireless signals having different carrier frequencies by using radio-over-fiber (ROF) technique. However, multiple wireless signals which have the same carrier frequency cannot propagate over a single optical fiber, such as wireless multi-input multi-output (MIMO) signals feeding multiple antennas in the fiber wireless (FiWi) system. A novel optical frequency upconversion (OFU) technique is proposed to solve this problem. In this paper, the novel OFU approach is used to transmit three wireless MIMO signals over a 20 km standard single mode fiber (SMF). The OFU technique exploits one optical source to produce multiple wavelengths by delivering it to a LiNbO3 external optical modulator. The wireless MIMO signals are then modulated by LiNbO3 optical intensity modulators separately using the generated optical carriers from the OFU process. These modulators use the optical single-sideband with carrier (OSSB+C) modulation scheme to optimize the system performance against the fiber dispersion effect. Each wireless MIMO signal is with a 2.4 GHz or 5 GHz carrier frequency, 1 Gb/s data rate, and 16-quadrature amplitude modulation (QAM). The crosstalk between the wireless MIMO signals is highly suppressed, since each wireless MIMO signal is carried on a specific optical wavelength. PMID:24772009

Analysis of OFDMA receiver with carrier frequency offset and common carrier frequency offset (CCFO)

NASA Astrophysics Data System (ADS)

Gauni, Sabitha; Kumar, R.

2013-01-01

The technique of Orthogonal frequency multiplexing (OFDM) is used to mitigate the multipath effects and to achieve better data rate. When these systems are extended to enable multiple access wireless multimedia communications they are more beneficial. The performance of the OFDM systems degrades with frequency offset and phase offset. The OFDM multiple access (OFDMA) technology allots groups of the OFDM subcarriers allocated to different users for transmission. In this paper we study the interference effects of the individual subcarriers with the neighbouring subcarriers which also plays a role in the system degradation is termed as Multiuser Interference (MUI). The effect of Carrier frequency offset (CFO) on these systems is also taken in account. There are conventional CFO compensation methods for OFDMA systems the CFOs are usually compensated by directly eliminating the intercarrier interference (ICI) caused by the residual CFOs for individual users.

EQUALIZING THE ELECTRIC FIELD INTENSITY WITHIN CHICK BRAIN IMMERSED IN BUFFER SOLUTION AT DIFFERENT CARRIER FREQUENCIES

EPA Science Inventory

Presented here are the numerical relationships between incident power densities that produce the same average electric field intensity within a chick brain half immersed in buffered saline solution and exposed to a uniform electromagnetic field at carrier frequencies of 50, 147, ...

BIOLOGICAL INFLUENCES OF LOW-FREQUENCY SINUSOIDAL ELECTROMAGNETIC SIGNALS ALONE AND SUPERIMPOSED ON RF CARRIER WAVES

EPA Science Inventory

The report describes in a historical context the experiments that have been performed to examine the biological responses caused by exposure to low frequency electromagnetic radiation directly or as modulation of RF carrier waves. A detailed review is provided of the independentl...

System Design Plan for a DCS (Defense Communications System) Data Transmission Network.

DTIC Science & Technology

1981-07-01

modems , FDO group modems , and Voice Frequency Carrier Telegraph (VFCT) networks. The DTN will be a synchronous network and its implementation must coincide...Frequency (VF) modems and Voice Frequency Carrier Telegraph (VFCT) networks. Further, data circuits can be extended over present analog FDM facilities using...VF or group data modems . In addition to the availability of terrestrial and satellite digital transmission facilities, the implementation of the DTN

A Precision, Low-Cost GPS-Based Transmitter Synchronization Scheme for Improved AM Reception

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

Smith, Stephen Fulton; Moore, Anthony

2009-01-01

This paper describes a highly accurate carrier-frequency synchronization scheme for actively, automatically locking multiple, remotely located AM broadcast transmitters to a common frequency/timing reference source such as GPS. The extremely tight frequency lock (to {approx}1 part in 10{sup 9} or better) permits the effective elimination of audible and even sub-audible beats between the local (desired) station's carrier signal and the distant stations carriers, usually received via skywave propagation during the evening and nighttime hours. These carrier-beat components cause annoying modulations of the desired station's audio at the receiver and concurrent distortion of the audio modulation from the distant station(s) andmore » often cause listeners to ldquotune outrdquo due to the low reception quality. Significant reduction or elimination of the beats and related effects will greatly enlarge the effective (interference-limited) listening area of the desired station (from 4 to 10 times as indicated in our tests) and simultaneously reduce the corresponding interference of the local transmitter to the distant stations as well. In addition, AM stereo (CQUAM) reception will be particularly improved by minimizing the phase shifts induced by co-channel interfering signals; hybrid digital (HD) signals will also benefit via reduction in beats from analog signals. The automatic frequency-control hardware described is inexpensive ($1000-$2000), requires no periodic recalibration, has essentially zero long-term drift, and could employ alternate wide-area frequency references of suitable accuracy, including broadcasts from WWVB, LORAN-C, and equivalent sources. The basic configuration of the GPS-disciplined oscillator which solves this problem is extremely simple. The main oscillator is a conventional high-stability quartz-crystal type. To counter long- term drifts, the oscillator is slightly adjusted to track a high-precision source of standard frequency obtained from a specialized GPS receiver (or other source), usually at 10.000 MHz. This very stable local reference frequency is then used as a clock for a standard digitally implemented frequency synthesizer, which is programmed to generate the specific carrier frequency desired. The stability of the disciplining source, typically {approx}1 part in 10{sup 9} to 10{sup 11}, is thus transferred to the final AM transmitter carrier output frequency.« less

Moving target detection for frequency agility radar by sparse reconstruction

NASA Astrophysics Data System (ADS)

Quan, Yinghui; Li, YaChao; Wu, Yaojun; Ran, Lei; Xing, Mengdao; Liu, Mengqi

2016-09-01

Frequency agility radar, with randomly varied carrier frequency from pulse to pulse, exhibits superior performance compared to the conventional fixed carrier frequency pulse-Doppler radar against the electromagnetic interference. A novel moving target detection (MTD) method is proposed for the estimation of the target's velocity of frequency agility radar based on pulses within a coherent processing interval by using sparse reconstruction. Hardware implementation of orthogonal matching pursuit algorithm is executed on Xilinx Virtex-7 Field Programmable Gata Array (FPGA) to perform sparse optimization. Finally, a series of experiments are performed to evaluate the performance of proposed MTD method for frequency agility radar systems.

Moving target detection for frequency agility radar by sparse reconstruction.

PubMed

Quan, Yinghui; Li, YaChao; Wu, Yaojun; Ran, Lei; Xing, Mengdao; Liu, Mengqi

2016-09-01

Frequency agility radar, with randomly varied carrier frequency from pulse to pulse, exhibits superior performance compared to the conventional fixed carrier frequency pulse-Doppler radar against the electromagnetic interference. A novel moving target detection (MTD) method is proposed for the estimation of the target's velocity of frequency agility radar based on pulses within a coherent processing interval by using sparse reconstruction. Hardware implementation of orthogonal matching pursuit algorithm is executed on Xilinx Virtex-7 Field Programmable Gata Array (FPGA) to perform sparse optimization. Finally, a series of experiments are performed to evaluate the performance of proposed MTD method for frequency agility radar systems.

Modeling space-charge-limited current transport in spatially disordered organic semiconductors

NASA Astrophysics Data System (ADS)

Zubair, M.; Ang, Y. S.; Ang, L. K.

Charge transport properties in organic semiconductors are determined by two kinds of microscopic disorder, namely energetic disorder and the spatial disorder. It is demonstrated that the thickness dependence of space-charge limited current (SCLC) can be related to spatial disorder within the framework of fractional-dimensional space. We present a modified Mott-Gurney (MG) law in different regimes to model the varying thickness dependence in such spatially disordered materials. We analyze multiple experimental results from literature where thickness dependence of SCLC shows that the classical MG law might lead to less accurate extraction of mobility parameter, whereas the modified MG law would be a better choice in such devices. Experimental SCLC measurement in a PPV-based structure was previously modeled using a carrier-density dependent model which contradicts with a recent experiment that confirms a carrier-density independent mobility originating from the disordered morphology of the polymer. Here, this is reconciled by the modified MG law which intrinsically takes into account the effect of spatial disorder without the need of using a carrier-density dependent model. This work is supported by Singapore Temasek Laboratories (TL) Seed Grant (IGDS S16 02 05 1).

Controlling the high frequency response of H2 by ultra-short tailored laser pulses: A time-dependent configuration interaction study

NASA Astrophysics Data System (ADS)

Schönborn, Jan Boyke; Saalfrank, Peter; Klamroth, Tillmann

2016-01-01

We combine the stochastic pulse optimization (SPO) scheme with the time-dependent configuration interaction singles method in order to control the high frequency response of a simple molecular model system to a tailored femtosecond laser pulse. For this purpose, we use H2 treated in the fixed nuclei approximation. The SPO scheme, as similar genetic algorithms, is especially suited to control highly non-linear processes, which we consider here in the context of high harmonic generation. Here, we will demonstrate that SPO can be used to realize a "non-harmonic" response of H2 to a laser pulse. Specifically, we will show how adding low intensity side frequencies to the dominant carrier frequency of the laser pulse and stochastically optimizing their contribution can create a high-frequency spectral signal of significant intensity, not harmonic to the carrier frequency. At the same time, it is possible to suppress the harmonic signals in the same spectral region, although the carrier frequency is kept dominant during the optimization.

Controlling the high frequency response of H{sub 2} by ultra-short tailored laser pulses: A time-dependent configuration interaction study

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

Schönborn, Jan Boyke; Saalfrank, Peter; Klamroth, Tillmann, E-mail: klamroth@uni-potsdam.de

2016-01-28

We combine the stochastic pulse optimization (SPO) scheme with the time-dependent configuration interaction singles method in order to control the high frequency response of a simple molecular model system to a tailored femtosecond laser pulse. For this purpose, we use H{sub 2} treated in the fixed nuclei approximation. The SPO scheme, as similar genetic algorithms, is especially suited to control highly non-linear processes, which we consider here in the context of high harmonic generation. Here, we will demonstrate that SPO can be used to realize a “non-harmonic” response of H{sub 2} to a laser pulse. Specifically, we will show howmore » adding low intensity side frequencies to the dominant carrier frequency of the laser pulse and stochastically optimizing their contribution can create a high-frequency spectral signal of significant intensity, not harmonic to the carrier frequency. At the same time, it is possible to suppress the harmonic signals in the same spectral region, although the carrier frequency is kept dominant during the optimization.« less

Improved MIMO radar GMTI via cyclic-shift transmission of orthogonal frequency division signals

NASA Astrophysics Data System (ADS)

Li, Fuyou; He, Feng; Dong, Zhen; Wu, Manqing

2018-05-01

Minimum detectable velocity (MDV) and maximum detectable velocity are both important in ground moving target indication (GMTI) systems. Smaller MDV can be achieved by longer baseline via multiple-input multiple-output (MIMO) radar. Maximum detectable velocity is decided by blind velocities associated with carrier frequencies, and blind velocities can be mitigated by orthogonal frequency division signals. However, the scattering echoes from different carrier frequencies are independent, which is not good for improving MDV performance. An improved cyclic-shift transmission is applied in MIMO GMTI system in this paper. MDV performance is improved due to the longer baseline, and maximum detectable velocity performance is improved due to the mitigation of blind velocities via multiple carrier frequencies. The signal model for this mode is established, the principle of mitigating blind velocities with orthogonal frequency division signals is presented; the performance of different MIMO GMTI waveforms is analysed; and the performance of different array configurations is analysed. Simulation results by space-time-frequency adaptive processing proves that our proposed method is a valid way to improve GMTI performance.

Spatial carrier color digital speckle pattern interferometry for absolute three-dimensional deformation measurement

NASA Astrophysics Data System (ADS)

Gao, Xinya; Wang, Yonghong; Li, Junrui; Dan, Xizuo; Wu, Sijin; Yang, Lianxiang

2017-06-01

It is difficult to measure absolute three-dimensional deformation using traditional digital speckle pattern interferometry (DSPI) when the boundary condition of an object being tested is not exactly given. In practical applications, the boundary condition cannot always be specifically provided, limiting the use of DSPI in real-world applications. To tackle this problem, a DSPI system that is integrated by the spatial carrier method and a color camera has been established. Four phase maps are obtained simultaneously by spatial carrier color-digital speckle pattern interferometry using four speckle interferometers with different illumination directions. One out-of-plane and two in-plane absolute deformations can be acquired simultaneously without knowing the boundary conditions using the absolute deformation extraction algorithm based on four phase maps. Finally, the system is proved by experimental results through measurement of the deformation of a flat aluminum plate with a groove.

Tracking Architecture Based on Dual-Filter with State Feedback and Its Application in Ultra-Tight GPS/INS Integration

PubMed Central

Zhang, Xi; Miao, Lingjuan; Shao, Haijun

2016-01-01

If a Kalman Filter (KF) is applied to Global Positioning System (GPS) baseband signal preprocessing, the estimates of signal phase and frequency can have low variance, even in highly dynamic situations. This paper presents a novel preprocessing scheme based on a dual-filter structure. Compared with the traditional model utilizing a single KF, this structure avoids carrier tracking being subjected to code tracking errors. Meanwhile, as the loop filters are completely removed, state feedback values are adopted to generate local carrier and code. Although local carrier frequency has a wide fluctuation, the accuracy of Doppler shift estimation is improved. In the ultra-tight GPS/Inertial Navigation System (INS) integration, the carrier frequency derived from the external navigation information is not viewed as the local carrier frequency directly. That facilitates retaining the design principle of state feedback. However, under harsh conditions, the GPS outputs may still bear large errors which can destroy the estimation of INS errors. Thus, an innovative integrated navigation filter is constructed by modeling the non-negligible errors in the estimated Doppler shifts, to ensure INS is properly calibrated. Finally, field test and semi-physical simulation based on telemetered missile trajectory validate the effectiveness of methods proposed in this paper. PMID:27144570

Tracking Architecture Based on Dual-Filter with State Feedback and Its Application in Ultra-Tight GPS/INS Integration.

PubMed

Zhang, Xi; Miao, Lingjuan; Shao, Haijun

2016-05-02

If a Kalman Filter (KF) is applied to Global Positioning System (GPS) baseband signal preprocessing, the estimates of signal phase and frequency can have low variance, even in highly dynamic situations. This paper presents a novel preprocessing scheme based on a dual-filter structure. Compared with the traditional model utilizing a single KF, this structure avoids carrier tracking being subjected to code tracking errors. Meanwhile, as the loop filters are completely removed, state feedback values are adopted to generate local carrier and code. Although local carrier frequency has a wide fluctuation, the accuracy of Doppler shift estimation is improved. In the ultra-tight GPS/Inertial Navigation System (INS) integration, the carrier frequency derived from the external navigation information is not viewed as the local carrier frequency directly. That facilitates retaining the design principle of state feedback. However, under harsh conditions, the GPS outputs may still bear large errors which can destroy the estimation of INS errors. Thus, an innovative integrated navigation filter is constructed by modeling the non-negligible errors in the estimated Doppler shifts, to ensure INS is properly calibrated. Finally, field test and semi-physical simulation based on telemetered missile trajectory validate the effectiveness of methods proposed in this paper.

System for transmitting low frequency analog signals over AC power lines

DOEpatents

Baker, Steven P.; Durall, Robert L.; Haynes, Howard D.

1989-01-01

A system for transmitting low frequency analog signals over AC power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an AC power line. The modulation signal frequency range in selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the AC power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal.

System for transmitting low frequency analog signals over AC power lines

DOEpatents

Baker, Steven P.; Durall, Robert L.; Haynes, Howard D.

1989-09-05

A system for transmitting low frequency analog signals over AC power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an AC power line. The modulation signal frequency range in selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the AC power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal.

A system for tranmitting low frequency analog signals over ac power lines

DOEpatents

Baker, S.P.; Durall, R.L.; Haynes, H.D.

1987-07-30

A system for transmitting low frequency analog signals over ac power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an ac power line. The modulation signal frequency range is selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the ac power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal. 4 figs.

Effect of confinement potential on exciton diamagnetism in the perspective of constituent carriers in a Quantum Well

NASA Astrophysics Data System (ADS)

Vignesh, G.; Nithiananthi, P.

2018-03-01

Diamagnetic susceptibility of excitons is investigated in the perspective of the electron and hole separation along the lateral (ρ) and normal direction (z) of a GaAs/AlxGa1-xAs quantum well. Using a variational technique, the spatial extensions of these carriers has been observed. The coulomb interaction of the carriers is investigated by subjecting the carriers to three confinement potentials, Square (SQW), Parabolic (PQW) and Triangular Quantum Wells (TQW). The stability of the exciton has been estimated by observing the diamagnetic susceptibility. The hole is very sensitive to confinement potential and has tremendous variations in spatial extension. Among the three confinements, TQW offers more localization and high stability to excitons. The anisotropy of band parameters and the dielectric constants of the well and barrier materials are taken into consideration.

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

Smith, Stephen F; Moore, James A

Systems and methods are described for carrier phase synchronization for improved AM and TV broadcast reception. A method includes synchronizing the phase of a carrier frequency of a broadcast signal with the phase of a remote reference frequency. An apparatus includes a receiver to detect the phase of a reference signal; a phase comparator coupled to the reference signal-phase receiver; a voltage controlled oscillator coupled to the phase comparator; and a phase-controlled radio frequency output coupled to the voltage controlled oscillator.

Plasmonic hot electron transport drives nano-localized chemistry

PubMed Central

Cortés, Emiliano; Xie, Wei; Cambiasso, Javier; Jermyn, Adam S.; Sundararaman, Ravishankar; Narang, Prineha; Schlücker, Sebastian; Maier, Stefan A.

2017-01-01

Nanoscale localization of electromagnetic fields near metallic nanostructures underpins the fundamentals and applications of plasmonics. The unavoidable energy loss from plasmon decay, initially seen as a detriment, has now expanded the scope of plasmonic applications to exploit the generated hot carriers. However, quantitative understanding of the spatial localization of these hot carriers, akin to electromagnetic near-field maps, has been elusive. Here we spatially map hot-electron-driven reduction chemistry with 15 nm resolution as a function of time and electromagnetic field polarization for different plasmonic nanostructures. We combine experiments employing a six-electron photo-recycling process that modify the terminal group of a self-assembled monolayer on plasmonic silver nanoantennas, with theoretical predictions from first-principles calculations of non-equilibrium hot-carrier transport in these systems. The resulting localization of reactive regions, determined by hot-carrier transport from high-field regions, paves the way for improving efficiency in hot-carrier extraction science and nanoscale regio-selective surface chemistry. PMID:28348402

Super-diffusion of excited carriers in semiconductors

PubMed Central

Najafi, Ebrahim; Ivanov, Vsevolod; Zewail, Ahmed; Bernardi, Marco

2017-01-01

The ultrafast spatial and temporal dynamics of excited carriers are important to understanding the response of materials to laser pulses. Here we use scanning ultrafast electron microscopy to image the dynamics of electrons and holes in silicon after excitation with a short laser pulse. We find that the carriers exhibit a diffusive dynamics at times shorter than 200 ps, with a transient diffusivity up to 1,000 times higher than the room temperature value, D0≈30 cm2s−1. The diffusivity then decreases rapidly, reaching a value of D0 roughly 500 ps after the excitation pulse. We attribute the transient super-diffusive behaviour to the rapid expansion of the excited carrier gas, which equilibrates with the environment in 100−150 ps. Numerical solution of the diffusion equation, as well as ab initio calculations, support our interpretation. Our findings provide new insight into the ultrafast spatial dynamics of excited carriers in materials. PMID:28492283

Both Hemophilia Health Care Providers and Hemophilia A Carriers Report that Carriers have Excessive Bleeding

PubMed Central

Paroskie, Allison; Oso, Olatunde; DeBaun, Michael R.; Sidonio, Robert F

2014-01-01

Introduction Hemophilia A, the result of reduced factor VIII (FVIII) activity, is an X-linked recessive bleeding disorder. Previous reports of Hemophilia A carriers suggest an increased bleeding tendency. Our objective was to determine the attitudes and understanding of the Hemophilia A carrier bleeding phenotype, and opinions regarding timing of carrier testing from the perspective of both medical providers and affected patients. Data from this survey was used as preliminary data for an ongoing prospective study. Material and Methods An electronic survey was distributed to physicians and nurses employed at Hemophilia Treatment Centers (HTC), and Hemophilia A carriers who were members of Hemophilia Federation of America. Questions focused on the clinical understanding of bleeding symptoms and management of Hemophilia A carriers, and the timing and intensity of carrier testing. Results Our survey indicates that 51% (36/51) of providers compared to 78% (36/46) of carriers believe that Hemophilia A carriers with normal FVIII activity have an increased bleeding tendency (p<0.001); 72% (33/36) of Hemophilia A carriers report a high frequency of bleeding symptoms. Regarding carrier testing, 72% (50/69) of medical providers recommend testing after 14 years of age, conversely 65% (29/45) of Hemophilia A carriers prefer testing to be done prior to this age (p<0.001). Discussion Hemophilia A carriers self-report a higher frequency of bleeding than previously acknowledged, and have a preference for earlier testing to confirm carrier status. PMID:24309601

47 CFR 101.705 - Special showing for renewal of common carrier station facilities using frequency diversity.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Special showing for renewal of common carrier... COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES Common Carrier Fixed Point-to-Point Microwave Service § 101.705 Special showing for renewal of common carrier station...

POWER DENSITY, FIELD INTENSITY, AND CARRIER FREQUENCY DETERMINANTS OF RF-ENERGY-INDUCED CALCIUM-ION EFFLUX FROM BRAIN TISSUE

EPA Science Inventory

To explain a carrier frequency dependence reported for radiofrequency (RF)-induced calcium-ion efflux from brain tissue, a chick-brain hemisphere bathed in buffer solution is modeled as a sphere within the uniform field of the incident electromagnetic wave. Calculations on a sphe...

47 CFR 95.639 - Maximum transmitter power.

Code of Federal Regulations, 2010 CFR

2010-10-01

...) No GMRS transmitter, under any condition of modulation, shall exceed: (1) 50 W Carrier power (average... transmitter, under any condition of modulation, shall exceed a carrier power or peak envelope TP (single-sideband only) of: (1) 4 W in the 26-27 MHz frequency band, except on channel frequency 27.255 MHz; (2) 25...

47 CFR 101.705 - Special showing for renewal of common carrier station facilities using frequency diversity.

Code of Federal Regulations, 2014 CFR

2014-10-01

... COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES Common Carrier Fixed Point-to-Point Microwave Service § 101.705 Special showing for renewal of common carrier station...

47 CFR 101.705 - Special showing for renewal of common carrier station facilities using frequency diversity.

Code of Federal Regulations, 2013 CFR

2013-10-01

... COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES Common Carrier Fixed Point-to-Point Microwave Service § 101.705 Special showing for renewal of common carrier station...

47 CFR 101.705 - Special showing for renewal of common carrier station facilities using frequency diversity.

Code of Federal Regulations, 2012 CFR

2012-10-01

... COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES Common Carrier Fixed Point-to-Point Microwave Service § 101.705 Special showing for renewal of common carrier station...

47 CFR 101.705 - Special showing for renewal of common carrier station facilities using frequency diversity.

Code of Federal Regulations, 2011 CFR

2011-10-01

... COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES Common Carrier Fixed Point-to-Point Microwave Service § 101.705 Special showing for renewal of common carrier station...

A model for phase noise generation in amplifiers.

PubMed

Tomlin, T D; Fynn, K; Cantoni, A

2001-11-01

In this paper, a model is presented for predicting the phase modulation (PM) and amplitude modulation (AM) noise in bipolar junction transistor (BJT) amplifiers. The model correctly predicts the dependence of phase noise on the signal frequency (at a particular carrier offset frequency), explains the noise shaping of the phase noise about the signal frequency, and shows the functional dependence on the transistor parameters and the circuit parameters. Experimental studies on common emitter (CE) amplifiers have been used to validate the PM noise model at carrier frequencies between 10 and 100 MHz.

Self Consistent Ambipolar Transport and High Frequency Oscillatory Transient in Graphene Electronics

DTIC Science & Technology

2015-08-17

study showed that in the presence of an ac field, THz oscillations exhibit soft resonances at a frequency roughly equal to half of the inverse of the ...exhibit soft resonances at a frequency roughly equal to half of the inverse of the carrier transit time to the LO phonon energy. It also showed that in...carriers in graphene undergo an anomalous parametric resonance. Such resonance occurs at about half the frequency ωF = 2πeF/~ωOP , where 2π/ωF is the time

Ultrafast spintronics roadmap: from femtosecond spin current pulses to terahertz non-uniform spin dynamics via nano-confined spin transfer torques (Conference Presentation)

NASA Astrophysics Data System (ADS)

Melnikov, Alexey; Razdolski, Ilya; Alekhin, Alexandr; Ilin, Nikita; Meyburg, Jan; Diesing, Detlef; Roddatis, Vladimir; Rungger, Ivan; Stamenova, Maria; Sanvito, Stefano; Bovensiepen, Uwe

2016-10-01

Further development of spintronics requires miniaturization and reduction of characteristic timescales of spin dynamics combining the nanometer spatial and femtosecond temporal ranges. These demands shift the focus of interest towards the fundamental open question of the interaction of femtosecond spin current (SC) pulses with a ferromagnet (FM). The spatio-temporal properties of the spin transfer torque (STT) exerted by ultrashort SC pulses on the FM open the time domain for studying STT fingerprint on spatially non-uniform magnetization dynamics. Using the sensitivity of magneto-induced second harmonic generation to SC, we develop technique for SC monitoring. With 20 fs resolution, we demonstrate the generation of 250 fs-long SC pulses in Fe/Au/Fe/MgO(001) structures. Their temporal profile indicates (i) nearly-ballistic hot electron transport in Au and (ii) that the pulse duration is primarily determined by the thermalization time of laser-excited hot carriers in Fe. Together with strongly spin-dependent Fe/Au interface transmission calculated for these carriers, this suggests the non-thermal spin-dependent Seebeck effect dominating the generation of ultrashort SC pulses. The analysis of SC transmission/reflection at the Au/Fe interface shows that hot electron spins orthogonal to the Fe magnetization rotate gaining huge parallel (anti-parallel) projection in transmitted (reflected) SC. This is accompanied by a STT-induced perturbation of the magnetization localized at the interface, which excites the inhomogeneous high-frequency spin dynamics in the FM. Time-resolved magneto-optical studies reveal the excitation of several standing spin wave modes in the Fe film with their spectrum extending up to 0.6 THz and indicating the STT spatial confinement to 2 nm.

Spectral context affects temporal processing in awake auditory cortex

PubMed Central

Beitel, Ralph E.; Vollmer, Maike; Heiser, Marc A; Schreiner, Christoph E.

2013-01-01

Amplitude modulation encoding is critical for human speech perception and complex sound processing in general. The modulation transfer function (MTF) is a staple of auditory psychophysics, and has been shown to predict speech intelligibility performance in a range of adverse listening conditions and hearing impairments, including cochlear implant-supported hearing. Although both tonal and broadband carriers have been employed in psychophysical studies of modulation detection and discrimination, relatively little is known about differences in the cortical representation of such signals. We obtained MTFs in response to sinusoidal amplitude modulation (SAM) for both narrowband tonal carriers and 2-octave bandwidth noise carriers in the auditory core of awake squirrel monkeys. MTFs spanning modulation frequencies from 4 to 512 Hz were obtained using 16 channel linear recording arrays sampling across all cortical laminae. Carrier frequency for tonal SAM and center frequency for noise SAM was set at the estimated best frequency for each penetration. Changes in carrier type affected both rate and temporal MTFs in many neurons. Using spike discrimination techniques, we found that discrimination of modulation frequency was significantly better for tonal SAM than for noise SAM, though the differences were modest at the population level. Moreover, spike trains elicited by tonal and noise SAM could be readily discriminated in most cases. Collectively, our results reveal remarkable sensitivity to the spectral content of modulated signals, and indicate substantial interdependence between temporal and spectral processing in neurons of the core auditory cortex. PMID:23719811

Development of Scanning Ultrafast Electron Microscope Capability.

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

Collins, Kimberlee Chiyoko; Talin, Albert Alec; Chandler, David W.

Modern semiconductor devices rely on the transport of minority charge carriers. Direct examination of minority carrier lifetimes in real devices with nanometer-scale features requires a measurement method with simultaneously high spatial and temporal resolutions. Achieving nanometer spatial resolutions at sub-nanosecond temporal resolution is possible with pump-probe methods that utilize electrons as probes. Recently, a stroboscopic scanning electron microscope was developed at Caltech, and used to study carrier transport across a Si p-n junction [ 1 , 2 , 3 ] . In this report, we detail our development of a prototype scanning ultrafast electron microscope system at Sandia National Laboratoriesmore » based on the original Caltech design. This effort represents Sandia's first exploration into ultrafast electron microscopy.« less

Gas separation using ultrasound and light absorption

DOEpatents

Sinha, Dipen N [Los Alamos, NM

2012-07-31

An apparatus and method for separating a chosen gas from a mixture of gases having no moving parts and utilizing no chemical processing is described. The separation of particulates from fluid carriers thereof has been observed using ultrasound. In a similar manner, molecular species may be separated from carrier species. It is also known that light-induced drift may separate light-absorbing species from carrier species. Therefore, the combination of temporally pulsed absorption of light with ultrasonic concentration is expected to significantly increase the efficiency of separation by ultrasonic concentration alone. Additionally, breaking the spatial symmetry of a cylindrical acoustic concentrator decreases the spatial distribution of the concentrated particles, and increases the concentration efficiency.

PWM Switching Frequency Effects on Eddy Current Sensors for Magnetically Suspended Flywheel Systems

NASA Technical Reports Server (NTRS)

Jansen, Ralph; Lebron, Ramon; Dever, Timothy P.; Birchenough, Arthur G.

2003-01-01

A flywheel magnetic bearing (MB) pulse width modulated power amplifier (PWM) configuration is selected to minimize noise generated by the PWMs in the flywheel position sensor system. Two types of noise are addressed: beat frequency noise caused by variations in PWM switching frequencies, and demodulation noise caused by demodulation of high order harmonics of the switching voltage into the MB control band. Beat frequency noise is eliminated by synchronizing the PWM switch frequencies, and demodulation noise is minimized by selection of a switching frequency which does not have harmonics at the carrier frequency of the sensor. The recommended MB PWM system has five synchronized PWMs switching at a non-integer harmonic of the sensor carrier.

Exploring the Role of Spatial Frequency Information during Neural Emotion Processing in Human Infants.

PubMed

Jessen, Sarah; Grossmann, Tobias

2017-01-01

Enhanced attention to fear expressions in adults is primarily driven by information from low as opposed to high spatial frequencies contained in faces. However, little is known about the role of spatial frequency information in emotion processing during infancy. In the present study, we examined the role of low compared to high spatial frequencies in the processing of happy and fearful facial expressions by using filtered face stimuli and measuring event-related brain potentials (ERPs) in 7-month-old infants ( N = 26). Our results revealed that infants' brains discriminated between emotional facial expressions containing high but not between expressions containing low spatial frequencies. Specifically, happy faces containing high spatial frequencies elicited a smaller Nc amplitude than fearful faces containing high spatial frequencies and happy and fearful faces containing low spatial frequencies. Our results demonstrate that already in infancy spatial frequency content influences the processing of facial emotions. Furthermore, we observed that fearful facial expressions elicited a comparable Nc response for high and low spatial frequencies, suggesting a robust detection of fearful faces irrespective of spatial frequency content, whereas the detection of happy facial expressions was contingent upon frequency content. In summary, these data provide new insights into the neural processing of facial emotions in early development by highlighting the differential role played by spatial frequencies in the detection of fear and happiness.

Potential of dynamic spectrum allocation in LTE macro networks

NASA Astrophysics Data System (ADS)

Hoffmann, H.; Ramachandra, P.; Kovács, I. Z.; Jorguseski, L.; Gunnarsson, F.; Kürner, T.

2015-11-01

In recent years Mobile Network Operators (MNOs) worldwide are extensively deploying LTE networks in different spectrum bands and utilising different bandwidth configurations. Initially, the deployment is coverage oriented with macro cells using the lower LTE spectrum bands. As the offered traffic (i.e. the requested traffic from the users) increases the LTE deployment evolves with macro cells expanded with additional capacity boosting LTE carriers in higher frequency bands complemented with micro or small cells in traffic hotspot areas. For MNOs it is crucial to use the LTE spectrum assets, as well as the installed network infrastructure, in the most cost efficient way. The dynamic spectrum allocation (DSA) aims at (de)activating the available LTE frequency carriers according to the temporal and spatial traffic variations in order to increase the overall LTE system performance in terms of total network capacity by reducing the interference. This paper evaluates the DSA potential of achieving the envisaged performance improvement and identifying in which system and traffic conditions the DSA should be deployed. A self-optimised network (SON) DSA algorithm is also proposed and evaluated. The evaluations have been carried out in a hexagonal and a realistic site-specific urban macro layout assuming a central traffic hotspot area surrounded with an area of lower traffic with a total size of approximately 8 × 8 km2. The results show that up to 47 % and up to 40 % possible DSA gains are achievable with regards to the carried system load (i.e. used resources) for homogenous traffic distribution with hexagonal layout and for realistic site-specific urban macro layout, respectively. The SON DSA algorithm evaluation in a realistic site-specific urban macro cell deployment scenario including realistic non-uniform spatial traffic distribution shows insignificant cell throughput (i.e. served traffic) performance gains. Nevertheless, in the SON DSA investigations, a gain of up to 25 % has been observed when analysing the resource utilisation in the non-hotspot cells.

Carrier Decay and Diffusion Dynamics in Single-Crystalline CdTe as seen via Microphotoluminescence

NASA Astrophysics Data System (ADS)

Mascarenhas, Angelo; Fluegel, Brian; Alberi, Kirstin; Zhang, Yong-Hang

2015-03-01

The ability to spatially resolve the degree to which extended defects impact carrier diffusion lengths and lifetimes is important for determining upper limits for defect densities in semiconductor devices. We show that a new spatially and temporally resolved photoluminescence (PL) imaging technique can be used to accurately extract carrier lifetimes in the immediate vicinity of dark-line defects in CdTe/MgCdTe double heterostructures. A series of PL images captured during the decay process show that extended defects with a density of 1.4x10-5 cm-2 deplete photogenerated charge carriers from the surrounding semiconductor material on a nanosecond time scale. The technique makes it possible to elucidate the interplay between nonradiative carrier recombination and carrier diffusion and reveals that they both combine to degrade the PL intensity over a fractional area that is much larger than the physical size of the defects. Carrier lifetimes are correctly determined from numerical simulations of the decay behavior by taking these two effects into account. Our study demonstrates that it is crucial to measure and account for the influence of local defects in the measurement of carrier lifetime and diffusion, which are key transport parameters for the design and modeling of advanced solar-cell and light-emitting devices. We acknowledge the financial support of the Department of Energy Office of Science under Grant No. DE-AC36-08GO28308.

Increased cancer risk of heterozygotes with NBS1 germline mutations in Poland.

PubMed

Steffen, Jan; Varon, Raymonda; Mosor, Maria; Maneva, Galina; Maurer, Martin; Stumm, Markus; Nowakowska, Dorota; Rubach, Maryna; Kosakowska, Ewa; Ruka, Włodzimierz; Nowecki, Zbigniew; Rutkowski, Piotr; Demkow, Tomasz; Sadowska, Małgorzata; Bidziński, Mariusz; Gawrychowski, Krzysztof; Sperling, Karl

2004-08-10

It has been suggested based on familial data that Nijmegen breakage syndrome (NBS) heterozygotes have an increased risk of malignant tumors. We found 15 carriers of the 657del5 mutation and 8 carriers of the R215W molecular variant of the NBS1 gene among 1,289 consecutive patients from Central Poland with various cancers and only 10 and 4 such carriers, respectively, in 1,620 controls from this region. Most of the 657del5 mutation carriers were found among patients with melanoma (4/105), non-Hodgkin lymphoma (2/42) and breast cancer (4/224) and of the 234 patients with colorectal carcinoma 3 carried the 657del5 mutation and 3 others the R215W molecular variant. The frequencies of 657del5 mutation carriers among patients with melanoma and non-Hodgkin lymphoma and of R215W carriers in patients with colorectal cancer were significantly higher than in controls (p < 0.01, < 0.05 and < 0.05 respectively). The pooled frequencies of 657del5 and R215W mutations in all cancer patients were also significantly higher than in controls (p < 0.05). Two carriers of the 657del5 mutation had second primary tumors. Malignant tumors among parents and siblings of 657del5 mutation carriers (14/77) were twice more frequent than in population controls. Three carriers of this mutation (2 probands with melanoma) reported melanoma in relatives. These results suggest strongly that NBS1 heterozygosity may be associated with elevated risk of some cancers. Larger studies are needed to evaluate the impact of the high frequency of germline NBS1 mutations on the cancer burden in the Slav populations. Copyright 2004 Wiley-Liss, Inc.

Long distance measurement with a femtosecond laser based frequency comb

NASA Astrophysics Data System (ADS)

Bhattacharya, N.; Cui, M.; Zeitouny, M. G.; Urbach, H. P.; van den Berg, S. A.

2017-11-01

Recent advances in the field of ultra-short pulse lasers have led to the development of reliable sources of carrier envelope phase stabilized femtosecond pulses. The pulse train generated by such a source has a frequency spectrum that consists of discrete, regularly spaced lines known as a frequency comb. In this case both the frequency repetition and the carrier-envelope-offset frequency are referenced to a frequency standard, like an atomic clock. As a result the accuracy of the frequency standard is transferred to the optical domain, with the frequency comb as transfer oscillator. These unique properties allow the frequency comb to be applied as a versatile tool, not only for time and frequency metrology, but also in fundamental physics, high-precision spectroscopy, and laser noise characterization. The pulse-to-pulse phase relationship of the light emitted by the frequency comb has opened up new directions for long range highly accurate distance measurement.

Associated Clinical Disorders Diagnosed by Medical Specialists in 188 FMR1 Premutation Carriers Found in the Last 25 Years in the Spanish Basque Country: A Retrospective Study

PubMed Central

Merino, Sonia; Ibarluzea, Nekane; Maortua, Hiart; Prieto, Begoña; Rouco, Idoia; López-Aríztegui, Maria-Asunción; Tejada, Maria-Isabel

2016-01-01

Fragile X-associated tremor/ataxia syndrome (FXTAS) and fragile X-associated primary ovarian insufficiency (FXPOI) are definitely related to the fragile X mental retardation 1 (FMR1) premutation (PM). Additional medical problems have also been associated with the PM, such as fibromyalgia, endocrine, and psychiatric disorders. To improve our understanding in the field, we reviewed all PM carriers and their reasons for any medical referrals from 104 fragile X families molecularly diagnosed in our laboratory and living in the Spanish Basque Country. After signing the written informed consent, we studied their electronic medical records in order to identify the disorders associated with the PM and their frequencies. We obtained clinical data in 188 PM carriers (147 women and 41 men). In women, the frequency of FXPOI (22.61%) was similar to that previously reported in PM carriers. In men, the frequency of definite FXTAS (28.57%) was lower than reported elsewhere. Furthermore, thyroid pathology was associated with the PM, the frequency of hypothyroidism being much higher in the studied region than in the general population (8.84% vs. 0.93%). Finally, we found no association with fibromyalgia or psychiatric problems. These findings represent another population contribution in this field and may be useful for the clinical management of PM carriers. PMID:27775646

Multiplexing of Radio-Frequency Single Electron Transistors

NASA Technical Reports Server (NTRS)

Stevenson, Thomas R.; Pellerano, F. A.; Stahle, C. M.; Aidala, K.; Schoelkopf, R. J.; Krebs, Carolyn (Technical Monitor)

2001-01-01

We present results on wavelength division multiplexing of radio-frequency single electron transistors. We use a network of resonant impedance matching circuits to direct applied rf carrier waves to different transistors depending on carrier frequency. A two-channel demonstration of this concept using discrete components successfully reconstructed input signals with small levels of cross coupling. A lithographic version of the rf circuits had measured parameters in agreement with electromagnetic modeling, with reduced cross capacitance and inductance, and should allow 20 to 50 channels to be multiplexed.

Polaron formation in normal state optical conductivity of iron-based superconductor

NASA Astrophysics Data System (ADS)

Choudhary, K. K.; Lodhi, Pavitra Devi; Kaurav, Netram

2018-05-01

Normal state Optical conductivity σ(ω) of Iron-Based superconductor LaFeAsO have been investigated using polaron formation mechanism. The coherent Drude free carrier excitations as well as the incoherent motion of carriers leading to a polaron formation, originated from inter and intra layer transitions of charge carriers are incorporated in the present model. Coherent motion of Drude carriers obtained from an effective interaction potential leads to a peak at zero frequency regime which is an indication of metallic conduction in superconducting materials and also produces a long tail at higher frequencies infrared region. Whereas, the incoherent motion i.e. hopping of carriers from Fe to Fe in the FeAs layer and from FeAs layer to LaO layer produces two different peaks at around 100 cm-1 and 430 cm-1 respectively. Two contributions, Drude and hopping carriers successfully explain the anomalies observed in the optical conductivity of metallic state of the iron-based superconductors.

Suppression of Rayleigh backscattering noise using cascaded-SOA and microwave photonic filter for 10 Gb/s loop-back WDM-PON.

PubMed

Feng, Hanlin; Ge, Jia; Xiao, Shilin; Fok, Mable P

2014-05-19

In this paper, we present a novel Rayleigh backscattering (RB) noise mitigation scheme based on central carrier suppression for 10 Gb/s loop-back wavelength division multiplexing passive optical network (WDM-PON). Microwave modulated multi-subcarrier optical signal is used as downstream seeding light, while cascaded semiconductor optical amplifier (SOA) are used in the optical network unit (ONU) for suppressing the central carrier of the multi-subcarrier upstream signal. With central carrier suppression, interference generated by carrier RB noise at low frequency region is eliminated successfully. Transmission performance over 45 km single mode fiber (SMF) is studied experimentally, and the optical-signal-to-Rayleigh-noise-ratio (OSRNR) can be reduced to 15 dB with central carrier suppression ratio (CCSR) of 21 dB. Receiver sensitivity is further improved by 6 dB with the use of microwave photonic filter (MPF) for suppressing residual upstream microwave signal and residual carrier RB at high frequency region.

A universal array-based multiplexed test for cystic fibrosis carrier screening.

PubMed

Amos, Jean A; Bridge-Cook, Philippa; Ponek, Victor; Jarvis, Michael R

2006-01-01

Cystic fibrosis is a multisystem autosomal recessive disorder with high carrier frequencies in caucasians and significant, but lower, carrier frequencies in other ethnicities. Based on technology that allows high detection of mutations in caucasians and significant detection in other ethnic groups, the American College of Medical Genetics (ACMG) and American College of Obstetricians and Gynecologists (ACOG) have recommended pan-ethnic cystic fibrosis carrier screening for all reproductive couples. This paper discusses carrier screening using the Tag-It multiplex mutation platform and the Cystic Fibrosis Mutation Detection Kit. The Tag-It cystic fibrosis assay is a multiplexed genotyping assay that detects a panel of 40 cystic fibrosis transmembrane conductance regulator mutations including the 23 mutations recommended by the ACMG and ACOG for population screening. A total of 16 additional mutations detected by the Tag-It cystic fibrosis assay may also be common. The assay method is described in detail, and its performance in a genetics reference laboratory performing high-volume cystic fibrosis carrier screening is assessed.

Carrier-phase two-way satellite frequency transfer over a very long baseline

NASA Astrophysics Data System (ADS)

Fujieda, M.; Piester, D.; Gotoh, T.; Becker, J.; Aida, M.; Bauch, A.

2014-06-01

In this paper we report that carrier-phase two-way satellite time and frequency transfer (TWSTFT) was successfully demonstrated over a very long baseline of 9000 km, established between the National Institute of Information and Communications Technology (NICT) and the Physikalisch-Technische Bundesanstalt (PTB). We verified that the carrier-phase TWSTFT (TWCP) result agreed with those obtained by conventional TWSTFT and GPS carrier-phase (GPSCP) techniques. Moreover, a much improved short-term instability for frequency transfer of 2 × 10-13 at 1 s was achieved, which is at the same level as previously confirmed over a shorter baseline within Japan. The precision achieved was so high that the effects of ionospheric delay became significant; they are ignored in conventional TWSTFT even over a long link. We compensated for these effects using ionospheric delays computed from regional vertical total electron content maps. The agreement between the TWCP and GPSCP results was improved because of this compensation.

Joint Entropy for Space and Spatial Frequency Domains Estimated from Psychometric Functions of Achromatic Discrimination

PubMed Central

Silveira, Vladímir de Aquino; Souza, Givago da Silva; Gomes, Bruno Duarte; Rodrigues, Anderson Raiol; Silveira, Luiz Carlos de Lima

2014-01-01

We used psychometric functions to estimate the joint entropy for space discrimination and spatial frequency discrimination. Space discrimination was taken as discrimination of spatial extent. Seven subjects were tested. Gábor functions comprising unidimensionalsinusoidal gratings (0.4, 2, and 10 cpd) and bidimensionalGaussian envelopes (1°) were used as reference stimuli. The experiment comprised the comparison between reference and test stimulithat differed in grating's spatial frequency or envelope's standard deviation. We tested 21 different envelope's standard deviations around the reference standard deviation to study spatial extent discrimination and 19 different grating's spatial frequencies around the reference spatial frequency to study spatial frequency discrimination. Two series of psychometric functions were obtained for 2%, 5%, 10%, and 100% stimulus contrast. The psychometric function data points for spatial extent discrimination or spatial frequency discrimination were fitted with Gaussian functions using the least square method, and the spatial extent and spatial frequency entropies were estimated from the standard deviation of these Gaussian functions. Then, joint entropy was obtained by multiplying the square root of space extent entropy times the spatial frequency entropy. We compared our results to the theoretical minimum for unidimensional Gábor functions, 1/4π or 0.0796. At low and intermediate spatial frequencies and high contrasts, joint entropy reached levels below the theoretical minimum, suggesting non-linear interactions between two or more visual mechanisms. We concluded that non-linear interactions of visual pathways, such as the M and P pathways, could explain joint entropy values below the theoretical minimum at low and intermediate spatial frequencies and high contrasts. These non-linear interactions might be at work at intermediate and high contrasts at all spatial frequencies once there was a substantial decrease in joint entropy for these stimulus conditions when contrast was raised. PMID:24466158

Joint entropy for space and spatial frequency domains estimated from psychometric functions of achromatic discrimination.

PubMed

Silveira, Vladímir de Aquino; Souza, Givago da Silva; Gomes, Bruno Duarte; Rodrigues, Anderson Raiol; Silveira, Luiz Carlos de Lima

2014-01-01

We used psychometric functions to estimate the joint entropy for space discrimination and spatial frequency discrimination. Space discrimination was taken as discrimination of spatial extent. Seven subjects were tested. Gábor functions comprising unidimensionalsinusoidal gratings (0.4, 2, and 10 cpd) and bidimensionalGaussian envelopes (1°) were used as reference stimuli. The experiment comprised the comparison between reference and test stimulithat differed in grating's spatial frequency or envelope's standard deviation. We tested 21 different envelope's standard deviations around the reference standard deviation to study spatial extent discrimination and 19 different grating's spatial frequencies around the reference spatial frequency to study spatial frequency discrimination. Two series of psychometric functions were obtained for 2%, 5%, 10%, and 100% stimulus contrast. The psychometric function data points for spatial extent discrimination or spatial frequency discrimination were fitted with Gaussian functions using the least square method, and the spatial extent and spatial frequency entropies were estimated from the standard deviation of these Gaussian functions. Then, joint entropy was obtained by multiplying the square root of space extent entropy times the spatial frequency entropy. We compared our results to the theoretical minimum for unidimensional Gábor functions, 1/4π or 0.0796. At low and intermediate spatial frequencies and high contrasts, joint entropy reached levels below the theoretical minimum, suggesting non-linear interactions between two or more visual mechanisms. We concluded that non-linear interactions of visual pathways, such as the M and P pathways, could explain joint entropy values below the theoretical minimum at low and intermediate spatial frequencies and high contrasts. These non-linear interactions might be at work at intermediate and high contrasts at all spatial frequencies once there was a substantial decrease in joint entropy for these stimulus conditions when contrast was raised.

The Realization and Analysis of Capacitance Self Tracing (CST) Method for Wide Band Response Measurement of Carrier Type Dynamic Strain Amplifier

NASA Astrophysics Data System (ADS)

Kubodera, Shinji; Tanzawa, Tsutomu; Morisawa, Masayuki; Kiyohiro, Noriaki

Carrier type dynamic strain amplifiers are frequently used for stress measurement with strain gages. That is because the carrier type dynamic strain amplifier can conduct high precision measurement since it is highly resistant against hum noise from the power supply frequency in principle and is free from the thermoelectomotive force even if a metal contact is used in wiring to a Wheatstone bridge for measuring. A problem of the carrier type dynamic strain amplifier is generation of Capacitive component (hereinafter referred to as the C component) in an input cable connecting from the amplifier to the input sensor (Wheatstone bridge for measuring). The C component varies with cable length, cable materials, or ambient temperature change. The aforementioned changing adversely affects the stability of the amplifier. In this paper, we realize and analyze the method that increases the stability of amplifier by detecting, eliminating and self tracking the above C component constantly. Used carrier frequency at 12kHz and 28kHz. We made amplifiers with noise resistant and wide band frequency of measurement range and verified the theory of the Capacitance Self Tracing with the above amplifiers.

Amplitude modulation detection by human listeners in reverberant sound fields: Carrier bandwidth effects and binaural versus monaural comparison.

PubMed

Zahorik, Pavel; Kim, Duck O; Kuwada, Shigeyuki; Anderson, Paul W; Brandewie, Eugene; Collecchia, Regina; Srinivasan, Nirmal

2012-06-01

Previous work [Zahorik et al., POMA, 12, 050005 (2011)] has reported that for a broadband noise carrier signal in a simulated reverberant sound field, human sensitivity to amplitude modulation (AM) is higher than would be predicted based on the broadband acoustical modulation transfer function (MTF) of the listening environment. Interpretation of this result was complicated by the fact that acoustical MTFs of rooms are often quite different for different carrier frequency regions, and listeners may have selectively responded to advantageous carrier frequency regions where the effective acoustic modulation loss due to the room was less than indicated by a broadband acoustic MTF analysis. Here, AM sensitivity testing and acoustic MTF analyses were expanded to include narrowband noise carriers (1-octave and 1/3-octave bands centered at 4 kHz), as well as monaural and binaural listening conditions. Narrowband results were found to be consistent with broadband results: In a reverberant sound field, human AM sensitivity is higher than indicated by the acoustical MTFs. The effect was greatest for modulation frequencies above 32 Hz and was present whether the stimulation was monaural or binaural. These results are suggestive of mechanisms that functionally enhance modulation in reverberant listening.

Optical injection locking-based amplification in phase-coherent transfer of optical frequencies.

PubMed

Kim, Joonyoung; Schnatz, Harald; Wu, David S; Marra, Giuseppe; Richardson, David J; Slavík, Radan

2015-09-15

We demonstrate the use of an optical injection phase locked loop (OIPLL) as a regenerative amplifier for optical frequency transfer applications. The optical injection locking provides high gain within a narrow bandwidth (<100  MHz) and is capable of preserving the fractional frequency stability of the incoming carrier to better than 10(-18) at 1000 s. The OIPLL was tested in the field as a mid-span amplifier for the transfer of an ultrastable optical carrier, stabilized to an optical frequency standard, over a 292 km long installed dark fiber link. The transferred frequency at the remote end reached a fractional frequency instability of less than 1×10(-19) at averaging time of 3200 s.

Time resolved photo-luminescent decay characterization of mercury cadmium telluride focal plane arrays

DOE PAGES

Soehnel, Grant

2015-01-20

The minority carrier lifetime is a measurable material property that is an indication of infrared detector device performance. To study the utility of measuring the carrier lifetime, an experiment has been constructed that can time resolve the photo-luminescent decay of a detector or wafer sample housed inside a liquid nitrogen cooled Dewar. Motorized stages allow the measurement to be scanned over the sample surface, and spatial resolutions as low as 50µm have been demonstrated. A carrier recombination simulation was developed to analyze the experimental data. Results from measurements performed on 4 mercury cadmium telluride focal plane arrays show strong correlationmore » between spatial maps of the lifetime, dark current, and relative response.« less

Design and implementation of a CMOS light pulse receiver cell array for spatial optical communications.

PubMed

Sarker, Md Shakowat Zaman; Itoh, Shinya; Hamai, Moeta; Takai, Isamu; Andoh, Michinori; Yasutomi, Keita; Kawahito, Shoji

2011-01-01

A CMOS light pulse receiver (LPR) cell for spatial optical communications is designed and evaluated by device simulations and a prototype chip implementation. The LPR cell consists of a pinned photodiode and four transistors. It works under sub-threshold region of a MOS transistor and the source terminal voltage which responds to the logarithm of the photo current are read out with a source follower circuit. For finding the position of the light spot on the focal plane, an image pixel array is embedded on the same plane of the LPR cell array. A prototype chip with 640 × 240 image pixels and 640 × 240 LPR cells is implemented with 0.18 μm CMOS technology. A proposed model of the transient response of the LPR cell agrees with the result of the device simulations and measurements. Both imaging at 60 fps and optical communication at the carrier frequency of 1 MHz are successfully performed. The measured signal amplitude and the calculation results of photocurrents show that the spatial optical communication up to 100 m is feasible using a 10 × 10 LED array.

Comparison of CYP2C9, CYP2C19, CYP2D6, ABCB1, and SLCO1B1 gene-polymorphism frequency in Russian and Nanai populations

PubMed Central

Sychev, Dmitrij Alekseevitch; Shuev, Grigorij Nikolaevich; Suleymanov, Salavat Shejhovich; Ryzhikova, Kristina Anatol’evna; Mirzaev, Karin Badavievich; Grishina, Elena Anatol’evna; Snalina, Natalia Evgenievna; Sozaeva, Zhannet Alimovna; Grabuzdov, Anton Mikhailovich; Matsneva, Irina Andreevna

2017-01-01

Background The efficiency and safety of drug therapy depends on the peculiarities of functioning of the P450 cytochrome group and transporting proteins. There are significant differences for single-nucleotide polymorphism (SNP) frequency. Materials and methods We studied the peculiarities of P450 cytochrome polymorphisms, SLCO1B1 transporting protein, and P-glycoprotein carriage in healthy volunteers in the Nanai ethnic group living in Russia, and compared them to the carriage of SNPs in the Russian population according to literature data. Results After performing the real-time polymerase chain reactions on the samples from 70 healthy volunteers from the Nanai group, for the CYP2C9*2C430T polymorphism we determined 70 CC-genotype carriers. As for the CYP2C9*3A1075C polymorphism, we found 62 AA-genotype carriers and eight AC-genotype carriers. For the CYP2C19*2G681A polymorphism, we determined 39 GG-genotype carriers and 28 GA-genotype carriers, for the CYP2C19*3G636A polymorphism 58 GG-genotype carriers and 12 GA-genotype carriers, and for the CYP2C19*17C806T polymorphism 67 CC-genotype carriers and three CT-genotype carriers. For the CYP2D6*4G1846A polymorphism, the GG genotype had 68 carriers, and the GA genotype two carriers. For the ABCB1*6C3435T polymorphism, there were 19 CC-genotype carriers and 39 CT-genotype carriers. For the SLCO1B1*5T521C polymorphism, the TT genotype had 41 carriers and the CT genotype 25 carriers. The distribution of genotypes fitted the Hardy–Weinberg equilibrium for all the polymorphisms, except those of CYP2C9*2. There were also significant differences in allele frequencies for some polymorphisms between the Nanais and the Russians. Conclusion In the Nanai population, there are polymorphisms connected with the decrease in safety and efficiency of drug therapy. Studying the ethnic differences might influence the determination of priority in the introduction of pharmacogenetic tests in clinical practice in different regions of Russia. PMID:28435307

Cross-sectional transport imaging in a multijunction solar cell

DOE PAGES

Haegel, Nancy M.; Ke, Chi -Wen; Taha, Hesham; ...

2016-12-01

Here, we combine a highly localized electron-beam point source excitation to generate excess free carriers with the spatial resolution of optical near-field imaging to map recombination in a cross-sectioned multijunction (Ga 0.5In 0.5P/GaIn 0.01As/Ge) solar cell. By mapping the spatial variations in emission of light for fixed generation (as opposed to traditional cathodoluminescence (CL), which maps integrated emission as a function of position of generation), it is possible to directly monitor the motion of carriers and photons. We observe carrier diffusion throughout the full width of the middle (GaInAs) cell, as well as luminescent coupling from point source excitation inmore » the top cell GaInP to the middle cell. Supporting CL and near-field photoluminescence (PL) measurements demonstrate the excitation-dependent Fermi level splitting effects that influence cross-sectioned spectroscopy results, as well as transport limitations on the spatial resolution of conventional cross-sectional far-field measurements.« less

Carrier-envelope offset frequency stabilization of an ultrafast semiconductor laser

NASA Astrophysics Data System (ADS)

Jornod, Nayara; Gürel, Kutan; Wittwer, Valentin J.; Brochard, Pierre; Hakobyan, Sargis; Schilt, Stéphane; Waldburger, Dominik; Keller, Ursula; Südmeyer, Thomas

2018-02-01

We present the self-referenced stabilization of the carrier-envelope offset (CEO) frequency of a semiconductor disk laser. The laser is a SESAM-modelocked VECSEL emitting at a wavelength of 1034 nm with a repetition frequency of 1.8 GHz. The 270-fs pulses are amplified to 3 W and compressed to 120 fs for the generation of a coherent octavespanning supercontinuum spectrum. A quasi-common-path f-to-2f interferometer enables the detection of the CEO beat with a signal-to-noise ratio of 30 dB sufficient for its frequency stabilization. The CEO frequency is phase-locked to an external reference with a feedback signal applied to the pump current.

A Novel Photonic Clock and Carrier Recovery Device

NASA Technical Reports Server (NTRS)

Yao, X. Steve; Lutes, George; Maleki, Lute

1996-01-01

As data communication rates climb toward ten Gb/s, clock recovery and synchronization become more difficult, if not impossible, using conventional electronic circuits. We present in this article experimental results of a high speed clock and carrier recovery using a novel device called a photonic oscillator that we recently developed in our laboratory. This device is capable of recovering clock signals up to 70 GHz. To recover the clock, the incoming data is injected into the photonic oscillator either through the optical injection port or the electrical injection port. The free running photonic oscillator is tuned to oscillate at a nominal frequency equal to the clock frequency of the incoming data. With the injection of the data, the photonic oscillator will be quickly locked to clock frequency of the data stream while rejecting other frequency components associated with the data. Consequently, the output of the locked photonic oscillator is a continuous periodical wave synchronized with the incoming data or simply the recovered clock. We have demonstrated a clock to spur ratio of more than 60 dB of the recovered clock using this technique. Similar to the clock recovery, the photonic oscillator can be used to recover a high frequency carrier degraded by noise and an improvement of about 50 dB in signal-to-noise ratio was demonstrated. The photonic oscillator has both electrical and optical inputs and outputs and can be directly interfaced with a photonic system without signal conversion. In addition to clock and carrier recovery, the photonic oscillator can also be used for (1) stable high frequency clock signal generation, (2) frequency multiplication, (3) square wave and comb frequency generation, and (4) photonic phase locked loop.

Formation of periodic surface structures on dielectrics after irradiation with laser beams of spatially variant polarisation: a comparative study

NASA Astrophysics Data System (ADS)

Papadopoulos, Antonis; Skoulas, Evangelos; Tsibidis, George D.; Stratakis, Emmanuel

2018-02-01

A comparative study is performed to explore the periodic structure formation upon intense femtosecond-pulsed irradiation of dielectrics with radially and azimuthally polarised beams. Laser conditions have been selected appropriately to produce excited carriers with densities below the optical breakdown threshold in order to highlight the role of phase transitions in surface modification mechanisms. The frequency of the laser-induced structures is calculated based on a theoretical model that comprises estimation of electron density excitation, heat transfer, relaxation processes, and hydrodynamics-related mass transport. The influence of the laser wavelength in the periodicity of the structures is also unveiled. The decreased energy absorption for azimuthally polarised beams yields periodic structures with smaller frequencies which are more pronounced as the number of laser pulses applied to the irradiation spot increases. Similar results are obtained for laser pulses of larger photon energy and higher fluences. All induced periodic structures are oriented parallel to the laser beam polarisation.

Carrier Estimation Using Classic Spectral Estimation Techniques for the Proposed Demand Assignment Multiple Access Service

NASA Technical Reports Server (NTRS)

Scaife, Bradley James

1999-01-01

In any satellite communication, the Doppler shift associated with the satellite's position and velocity must be calculated in order to determine the carrier frequency. If the satellite state vector is unknown then some estimate must be formed of the Doppler-shifted carrier frequency. One elementary technique is to examine the signal spectrum and base the estimate on the dominant spectral component. If, however, the carrier is spread (as in most satellite communications) this technique may fail unless the chip rate-to-data rate ratio (processing gain) associated with the carrier is small. In this case, there may be enough spectral energy to allow peak detection against a noise background. In this thesis, we present a method to estimate the frequency (without knowledge of the Doppler shift) of a spread-spectrum carrier assuming a small processing gain and binary-phase shift keying (BPSK) modulation. Our method relies on an averaged discrete Fourier transform along with peak detection on spectral match filtered data. We provide theory and simulation results indicating the accuracy of this method. In addition, we will describe an all-digital hardware design based around a Motorola DSP56303 and high-speed A/D which implements this technique in real-time. The hardware design is to be used in NMSU's implementation of NASA's demand assignment, multiple access (DAMA) service.

Incidence and Carrier Frequency of CFTR Gene Mutations in Pregnancies With Echogenic Bowel in Nova Scotia and Prince Edward Island.

PubMed

Miller, Michelle E; Allen, Victoria M; Brock, Jo-Ann K

2018-03-01

Fetal echogenic bowel (echogenic bowel) is associated with cystic fibrosis (CF), with a reported incidence ranging from 1% to 13%. Prenatal testing for CF in the setting of echogenic bowel can be done by screening parental or fetal samples for pathogenic CFTR variants. If only one pathogenic variant is identified, sequencing of the CFTR gene can be undertaken, to identify a second pathogenic variant not covered in the standard screening panel. Full gene sequencing, however, also introduces the potential to identify variants of uncertain significance (VUSs) that can create counselling challenges and cause parental anxiety. To provide accurate counselling for families in the study population, the incidence of CF associated with echogenic bowel and the carrier frequency of CFTR variants were investigated. All pregnancies for which CF testing was undertaken for the indication of echogenic bowel (from Nova Scotia and Prince Edward Island) were identified (January 2007-July 2017). The CFTR screening and sequencing results were reviewed, and fetal outcomes related to CF were assessed. A total of 463 pregnancies with echogenic bowel were tested. Four were confirmed to be affected with CF, giving an incidence of 0.9% in this cohort. The carrier frequency of CF among all parents in the cohort was 5.0% (1 in 20); however, when excluding parents of affected fetuses, the carrier frequency for the population was estimated at 4.1% (1 in 25). CFTR gene sequencing identified an additional VUS in two samples. The incidence of CF in pregnancies with echogenic bowel in Nova Scotia and Prince Edward Island is 0.9%, with an estimated population carrier frequency of 4.1%. These results provide the basis for improved counselling to assess the risk of CF in the pregnancy, after parental carrier screening, using Bayesian probability. Counselling regarding VUSs should be undertaken before gene sequencing. Copyright © 2017 Society of Obstetricians and Gynaecologists of Canada. Published by Elsevier Inc. All rights reserved.

5 Gbps wireless transmission link with an optically pumped uni-traveling carrier photodiode mixer at the receiver.

PubMed

Mohammad, Ahmad W; Shams, Haymen; Balakier, Katarzyna; Graham, Chris; Natrella, Michele; Seeds, Alwyn J; Renaud, Cyril C

2018-02-05

We report the first demonstration of a uni-traveling carrier photodiode (UTC-PD) used as a 5 Gbps wireless receiver. In this experiment, a 35.1 GHz carrier was electrically modulated with 5 Gbps non-return with zero on-off keying (NRZ-OOK) data and transmitted wirelessly over a distance of 1.3 m. At the receiver, a UTC-PD was used as an optically pumped mixer (OPM) to down-convert the received radio frequency (RF) signal to an intermediate frequency (IF) of 11.7 GHz, before it was down-converted to the baseband using an electronic mixer. The recovered data show a clear eye diagram, and a bit error rate (BER) of less than 10 -8 was measured. The conversion loss of the UTC-PD optoelectronic mixer has been measured at 22 dB. The frequency of the local oscillator (LO) used for the UTC-PD is defined by the frequency spacing between the two optical tones, which can be broadly tuneable offering the frequency agility of this photodiode-based receiver.

A Precision, Low-Cost GPS-Based Synchronization Scheme for Improved AM Reception.

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

Smith, Stephen Fulton; Moore, Anthony

2009-01-01

This paper describes a highly accurate carrier-frequency synchronization scheme for actively, automatically locking multiple, remotely located AM broadcast transmitters to a common frequency/timing reference source such as GPS. The extremely tight frequency lock (to ~1 part in 109 or better) permits the effective elimination of audible and even sub-audible beats between the local (desired) station s carrier signal and the distant stations carriers, usually received via skywave propagation during the evening and nighttime hours. These carrier-beat components cause annoying modulations of the desired station s audio at the receiver and concurrent distortion of the audio modulation from the distant station(s)more » and often cause listeners to tune out due to the poor reception quality. Significant reduction or elimination of the beats and related effects will greatly enlarge the effective (interference-limited) listening area of the desired station (from 4 to 10 times as indicated in our tests) and simultaneously reduce the corresponding interference of the local transmitter to the distant stations as well. In addition, AM stereo (CQUAM) reception will be particularly improved by minimizing the phase shifts induced by co-channel interfering signals; HD will also benefit via reduction in beats from analog signals. The automatic frequency-control hardware described is inexpensive ($1-2K), requires no periodic recalibration, has essentially zero long-term drift, and could employ alternate wide-area frequency references of suitable accuracy, including broadcasts from WWVB, LORAN-C, and equivalent sources. The basic configuration of the GPS-disciplined oscillator which solves this problem is extremely simple. The main oscillator is a conventional high-stability quartz-crystal type. To counter long-term drifts, the oscillator is slightly adjusted to track a high-precision source of standard frequency obtained from a specialized GPS receiver (or other source), usually at 10.000 MHz. This very stable local reference frequency is then used as a clock for a standard digitally implemented frequency synthesizer, which is programmed to generate the specific (AM broadcast) transmitter carrier frequency desired. The stability of the disciplining source, typically ~ 1 part in 109 to 1011, is thus transferred to the final AM transmitter carrier output frequency. Generally, an AM radio listener during the evening and nighttime hours, and to a lesser extent in the early morning, receives undesired skywave signals from several distant stations as well as the desired local (groundwave) signal. If all of these signals are within about 0.01-0.001 Hz of each other, any resulting carrier beats will be of such long periods that the beats will be effectively suppressed by the action of the receiver s AGC circuitry and thus be unnoticeable to the listener. Many modern, synthesizer-based transmitters can directly lock to the precision disciplined 10-MHz source, while older units usually require references at either1 e, 2 e, or 4 e the final frequency. In these latter cases, the existing transmitter crystal can usually be satisfactorily pulled via injection locking. The effectiveness of the synchronization concept to reduce interference effects was demonstrated in a laboratory test setup. Many hours of careful subjective listening were conducted, with the two interfering units both precisely on-frequency with the main unit (synchronous operation) and with the two interferers at various frequency offsets, from below 1 Hz to above 10 Hz.« less

A code-aided carrier synchronization algorithm based on improved nonbinary low-density parity-check codes

NASA Astrophysics Data System (ADS)

Bai, Cheng-lin; Cheng, Zhi-hui

2016-09-01

In order to further improve the carrier synchronization estimation range and accuracy at low signal-to-noise ratio ( SNR), this paper proposes a code-aided carrier synchronization algorithm based on improved nonbinary low-density parity-check (NB-LDPC) codes to study the polarization-division-multiplexing coherent optical orthogonal frequency division multiplexing (PDM-CO-OFDM) system performance in the cases of quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (16-QAM) modes. The simulation results indicate that this algorithm can enlarge frequency and phase offset estimation ranges and enhance accuracy of the system greatly, and the bit error rate ( BER) performance of the system is improved effectively compared with that of the system employing traditional NB-LDPC code-aided carrier synchronization algorithm.

Prevalence and mutations of β-thalassemia trait and abnormal hemoglobins in premarital screening in Çanakkale province, Turkey

PubMed Central

Uludağ, A; Uludağ, A; Ertekin, YH; Tekin, M; Kütük, B; Silan, F; Özdemir, Ö

2016-01-01

Abstract The prevalence of β-thalassemia (β-thal) carriers in Turkey varies according to region but in general it is 2.0%. Çanakkale is a city in the Aegean region of Turkey but no study about β-thal frequency in Çanakkale has been published to date. In this study, we aimed to investigate the frequency of β-thal mutations in this province. A total of 4452 couples (8904 individuals) applied for premarital thalassemia scans at the Çanakkale State Health Directorate Laboratory between January 2008 and June 2012 and scanning was done with high performance liquid chromatography (HPLC). Of 125 β-thal carriers seen at the Medical Genetics Clinic, Çanakkale Onsekiz Mart University, Çanakkale, Turkey, for genetic counseling, 46 participated in the study. The remaining 79 patients could not be reached. The prevalence for β-thal carriers in Çanakkale was identified as 1.4% (125/8904). One couple were both β-thal carriers. β-Globin gene analysis of 46 carriers found the total frequency of the three most common mutations was 45.6%. These mutations were found to be HBB: c.93-21G>A [IVS-I-110 (G>A)], 26.08% (12/46); HBB: c.17_ 18delCT [codon 5 (‒CT)], 10.85% (5/46); HBB: c.20delA [codon 6 (‒A)] 8.69% (4/46). This is the first report on the frequency and mutation profiles of β-thal for Çanakkale. The incidence of β-thal carriers in Çanakkale is below the average for Turkey. The most frequently observed mutation profile and rate of β-thal in our region is different from the other regions of Turkey. PMID:27785405

The frequency spectrum crisis - Issues and answers

NASA Astrophysics Data System (ADS)

Armes, G. L.

The frequency spectrum represents a unique resource which can be overtaxed. In the present investigation, it is attempted to evalute the demand for satellite and microwave services. Dimensions of increased demand are discussed, taking into account developments related to the introduction of the personal computer, the activities of the computer and communications industries in preparation for the office of the future, and electronic publishing. Attention is given to common carrier spectrum congestion, common carrier microwave, satellite communications, teleports, international implications, satellite frequency bands, satellite spectrum implications, alternatives regarding the utilization of microwave frequency bands, U.S. Government spectrum utilization, and the impact at C-band.

Ultrafast carrier capture and Auger recombination in single GaN/InGaN multiple quantum well nanowires

DOE PAGES

Boubanga-Tombet, Stephane; Wright, Jeremy B.; Lu, Ping; ...

2016-11-04

Ultrafast optical microscopy is an important tool for examining fundamental phenomena in semiconductor nanowires with high temporal and spatial resolution. In this paper, we used this technique to study carrier dynamics in single GaN/InGaN core–shell nonpolar multiple quantum well nanowires. We find that intraband carrier–carrier scattering is the main channel governing carrier capture, while subsequent carrier relaxation is dominated by three-carrier Auger recombination at higher densities and bimolecular recombination at lower densities. Finally, the Auger constants in these nanowires are approximately 2 orders of magnitude lower than in planar InGaN multiple quantum wells, highlighting their potential for future light-emitting devices.

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

Lim, Eunju, E-mail: elim@dankook.ac.kr, E-mail: taguchi.d.aa@m.titech.ac.jp, E-mail: iwamoto@pe.titech.ac.jp; Taguchi, Dai, E-mail: elim@dankook.ac.kr, E-mail: taguchi.d.aa@m.titech.ac.jp, E-mail: iwamoto@pe.titech.ac.jp; Iwamoto, Mitsumasa, E-mail: elim@dankook.ac.kr, E-mail: taguchi.d.aa@m.titech.ac.jp, E-mail: iwamoto@pe.titech.ac.jp

We studied the carrier transport and carrier trapping in indium tin oxide/polyimide (PI)/6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/Au diodes by using charge modulation spectroscopy (CMS) and time-resolved electric field induced optical second harmonic generation (TR-EFISHG) measurements. TR-EFISHG directly probes the spatial carrier behaviors in the diodes, and CMS is useful in explaining the carrier motion with respect to energy. The results clearly indicate that the injected carriers move across TIPS-pentacene thorough the molecular energy states of TIPS-pentacene and accumulate at the PI/TIPS-pentacene interface. However, some carriers are trapped in the PI layers. These findings take into account the capacitance-voltage and current-voltage characteristics of themore » diodes.« less

[The parallelisms in of sound signal of domestic sheep and Northern fur seals].

PubMed

Nikol'skiĭ, A A; Lisitsina, T Iu

2011-01-01

The parallelisms in communicative behavior of domestic sheep and Northern fur seals within a herd are accompanied by parallelisms in parameters of sound signal, the calling scream. This signal ensures ties between babies and their mothers at a long distance. The basis of parallelisms is formed by amplitude modulation at two levels: the one being a direct amplitude modulation of the carrier frequency and the other--modulation of the carrier frequency oscillation. Parallelisms in the signal oscillatory process result in corresponding parallelisms in the structure of its frequency spectrum.

Wavelength Division Multiplexing Scheme for Radio-Frequency Single Electron Transistors

NASA Technical Reports Server (NTRS)

Stevenson, Thomas R.; Pellerano, F. A.; Stahle, C. M.; Aidala, K.; Schoelkopf, R. J.; Krebs, Carolyn (Technical Monitor)

2001-01-01

We describe work on a wavelength division multiplexing scheme for radio-frequency single electron transistors. We use a network of resonant impedance matching circuits to direct applied rf carrier waves to different transistors depending on carrier frequency. Using discrete components, we made a two-channel demonstration of this concept and successfully reconstructed input signals with small levels of cross coupling. A lithographic version of the rf circuits had measured parameters in agreement with electromagnetic modeling, with reduced cross capacitance and inductance, and should allow 20 to 50 channels to be multiplexed.

Collinear interferometer with variable delay for carrier-envelope offset frequency measurement

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

Pawlowska, Monika; Ozimek, Filip; Fita, Piotr

2009-08-15

We demonstrate a novel scheme for measuring the carrier-envelope offset frequency in a femtosecond optical frequency comb. Our method is based on a common-path interferometer with a calcite Babinet-Soleil compensator employed to control the delay between the two interfering beams of pulses. The large delay range (up to 8 ps) of our device is sufficient for systems that rely on spectral broadening in microstructured fibers. We show an experimental proof that the stability of a common-path arrangement is superior to that of the standard interferometers.

Collinear interferometer with variable delay for carrier-envelope offset frequency measurement

NASA Astrophysics Data System (ADS)

Pawłowska, Monika; Ozimek, Filip; Fita, Piotr; Radzewicz, Czesław

2009-08-01

We demonstrate a novel scheme for measuring the carrier-envelope offset frequency in a femtosecond optical frequency comb. Our method is based on a common-path interferometer with a calcite Babinet-Soleil compensator employed to control the delay between the two interfering beams of pulses. The large delay range (up to 8 ps) of our device is sufficient for systems that rely on spectral broadening in microstructured fibers. We show an experimental proof that the stability of a common-path arrangement is superior to that of the standard interferometers.

A Spatial and Temporal Frequency Based Figure-Ground Processor

NASA Astrophysics Data System (ADS)

Weisstein, Namoi; Wong, Eva

1990-03-01

Recent findings in visual psychophysics have shown that figure-ground perception can be specified by the spatial and temporal response characteristics of the visual system. Higher spatial frequency regions of the visual field are perceived as figure and lower spatial frequency regions are perceived as background/ (Klymenko and Weisstein, 1986, Wong and Weisstein, 1989). Higher temporal frequency regions are seen as background and lower temporal frequency regions are seen as figure (Wong and Weisstein, 1987, Klymenko, Weisstein, Topolski, and Hsieh, 1988). Thus, high spatial and low temporal frequencies appear to be associated with figure and low spatial and high temporal frequencies appear to be associated with background.

Stabilization of a self-referenced, prism-based, Cr:forsterite laser frequency comb using an intracavity prism

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

Tillman, Karl A.; Thapa, Rajesh; Knabe, Kevin

2009-12-20

The frequency comb from a prism-based Cr:forsterite laser has been frequency stabilized using intracavity prism insertion and pump power modulation. Absolute frequency measurements of a CW fiber laser stabilized to the P(13) transition of acetylene demonstrate a fractional instability of {approx}2x10{sup -11} at a 1 s gate time, limited by a commercial Global Positioning System (GPS)-disciplined rubidium oscillator. Additionally, absolute frequency measurements made simultaneously using a second frequency comb indicate relative instabilities of 3x10{sup -12} for both combs for a 1 s gate time. Estimations of the carrier-envelope offset frequency linewidth based on relative intensity noise and the response dynamicsmore » of the carrier-envelope offset to pump power changes confirm the observed linewidths.« less

Pilot-Assisted Channel Estimation for Orthogonal Multi-Carrier DS-CDMA with Frequency-Domain Equalization

NASA Astrophysics Data System (ADS)

Shima, Tomoyuki; Tomeba, Hiromichi; Adachi, Fumiyuki

Orthogonal multi-carrier direct sequence code division multiple access (orthogonal MC DS-CDMA) is a combination of time-domain spreading and orthogonal frequency division multiplexing (OFDM). In orthogonal MC DS-CDMA, the frequency diversity gain can be obtained by applying frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion to a block of OFDM symbols and can improve the bit error rate (BER) performance in a severe frequency-selective fading channel. FDE requires an accurate estimate of the channel gain. The channel gain can be estimated by removing the pilot modulation in the frequency domain. In this paper, we propose a pilot-assisted channel estimation suitable for orthogonal MC DS-CDMA with FDE and evaluate, by computer simulation, the BER performance in a frequency-selective Rayleigh fading channel.

Spatial emission distribution of InGaN/GaN light-emitting diodes depending on the pattern structures

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

Lee, Kwanjae; Lee, Hyunjung; Lee, Cheul-Ro

2014-10-15

Highlights: • We study carrier lifetimes of InGaN/GaN LEDs fabricated on different PSS. • Spatial EL distribution was investigated depending on the pattern structure. • The carrier lifetime of the LEDs was compared with the spatial EL distribution. - Abstract: We investigated the emission characteristics of InGaN/GaN light-emitting diodes (LEDs) fabricated on lens-shaped (LS) patterned-sapphire substrates (PSS) by using time-resolved photoluminescence (TRPL) and confocal-scanning-electroluminescence microscopy (CSEM). The carrier lifetimes evaluated from the TRPL spectra for the LEDs on the LS-PSS (LS-LEDs) at 10 K were relatively shorter than those of the LEDs on a conventional planar substrate (C-LED). However, themore » carrier lifetimes for the LS-LEDs were relatively long compared to that of the C-LED at room temperature. In the CSEM images of the LS-LEDs, the emission beam around the center region of the LS pattern was relatively weaker than that of the edge region. In addition, the beam profile for the LS-LEDs showed different shapes according to the pattern structures. The emission beam around the boundary region of the LS pattern showed periodic fluctuation with the peak-to-peak distance of 814 nm.« less

A Hybrid Solution for Simultaneous Transfer of Ultrastable Optical Frequency, RF Frequency, and UTC Time-Tags Over Optical Fiber.

PubMed

Krehlik, Przemyslaw; Schnatz, Harald; Sliwczynski, Lukasz

2017-12-01

We describe a fiber-optic solution for simultaneous distribution of all signals generated at today's most advanced time and frequency laboratories, i.e., an ultrastable optical reference frequency derived from an optical atomic clock, a radio frequency precisely linked to a realization of the SI-Second, and a realization of an atomic timescale, being the local representation of the virtual, global UTC timescale. In our solution both the phase of the optical carrier and the delay of electrical signals (10-MHz frequency reference and one-pulse-per-second time tags) are stabilized against environmental perturbations influencing the fiber link instability and accuracy. We experimentally demonstrate optical transfer stabilities of and for 100 s averaging period, for optical carrier and 10-MHz signals, respectively.

Using individual differences to test the role of temporal and place cues in coding frequency modulation

PubMed Central

Whiteford, Kelly L.; Oxenham, Andrew J.

2015-01-01

The question of how frequency is coded in the peripheral auditory system remains unresolved. Previous research has suggested that slow rates of frequency modulation (FM) of a low carrier frequency may be coded via phase-locked temporal information in the auditory nerve, whereas FM at higher rates and/or high carrier frequencies may be coded via a rate-place (tonotopic) code. This hypothesis was tested in a cohort of 100 young normal-hearing listeners by comparing individual sensitivity to slow-rate (1-Hz) and fast-rate (20-Hz) FM at a carrier frequency of 500 Hz with independent measures of phase-locking (using dynamic interaural time difference, ITD, discrimination), level coding (using amplitude modulation, AM, detection), and frequency selectivity (using forward-masking patterns). All FM and AM thresholds were highly correlated with each other. However, no evidence was obtained for stronger correlations between measures thought to reflect phase-locking (e.g., slow-rate FM and ITD sensitivity), or between measures thought to reflect tonotopic coding (fast-rate FM and forward-masking patterns). The results suggest that either psychoacoustic performance in young normal-hearing listeners is not limited by peripheral coding, or that similar peripheral mechanisms limit both high- and low-rate FM coding. PMID:26627783

Using individual differences to test the role of temporal and place cues in coding frequency modulation.

PubMed

Whiteford, Kelly L; Oxenham, Andrew J

2015-11-01

The question of how frequency is coded in the peripheral auditory system remains unresolved. Previous research has suggested that slow rates of frequency modulation (FM) of a low carrier frequency may be coded via phase-locked temporal information in the auditory nerve, whereas FM at higher rates and/or high carrier frequencies may be coded via a rate-place (tonotopic) code. This hypothesis was tested in a cohort of 100 young normal-hearing listeners by comparing individual sensitivity to slow-rate (1-Hz) and fast-rate (20-Hz) FM at a carrier frequency of 500 Hz with independent measures of phase-locking (using dynamic interaural time difference, ITD, discrimination), level coding (using amplitude modulation, AM, detection), and frequency selectivity (using forward-masking patterns). All FM and AM thresholds were highly correlated with each other. However, no evidence was obtained for stronger correlations between measures thought to reflect phase-locking (e.g., slow-rate FM and ITD sensitivity), or between measures thought to reflect tonotopic coding (fast-rate FM and forward-masking patterns). The results suggest that either psychoacoustic performance in young normal-hearing listeners is not limited by peripheral coding, or that similar peripheral mechanisms limit both high- and low-rate FM coding.

A Computer Model of a Phase Lock Loop

NASA Technical Reports Server (NTRS)

Shelton, Ralph Paul

1973-01-01

A computer model is reported of a PLL (phase-lock loop), preceded by a bandpass filter, which is valid when the bandwidth of the bandpass filter is of the same order of magnitude as the natural frequency of the PLL. New results for the PLL natural frequency equal to the bandpass filter bandwidth are presented for a second order PLL operating with carrier plus noise as the input. However, it is shown that extensions to higher order loops, and to the case of a modulated carrier are straightforward. The new results presented give the cycle skipping rate of the PLL as a function of the input carrier to noise ratio when the PLL natural frequency is equal to the bandpass filter bandwidth. Preliminary results showing the variation of the output noise power and cycle skipping rates of the PLL as a function of the loop damping ratio for the PLL natural frequency equal to the bandpass filter bandwidth are also included.

Robust frequency stabilization of multiple spectroscopy lasers with large and tunable offset frequencies.

PubMed

Nevsky, A; Alighanbari, S; Chen, Q-F; Ernsting, I; Vasilyev, S; Schiller, S; Barwood, G; Gill, P; Poli, N; Tino, G M

2013-11-15

We have demonstrated a compact, robust device for simultaneous absolute frequency stabilization of three diode lasers whose carrier frequencies can be chosen freely relative to the reference. A rigid ULE multicavity block is employed, and, for each laser, the sideband locking technique is applied. A small lock error, computer control of frequency offset, wide range of frequency offset, simple construction, and robust operation are the useful features of the system. One concrete application is as a stabilization unit for the cooling and trapping lasers of a neutral-atom lattice clock. The device significantly supports and improves the clock's operation. The laser with the most stringent requirements imposed by this application is stabilized to a line width of 70 Hz, and a residual frequency drift less than 0.5 Hz/s. The carrier optical frequency can be tuned over 350 MHz while in lock.

Nystagmus as an early ocular alteration in Machado-Joseph disease (MJD/SCA3)

PubMed Central

2014-01-01

Background Machado-Joseph disease (MJD), also named spinocerebellar ataxia type 3 (SCA3) is the most common autosomal dominant ataxia worldwide. Although nystagmus is one of the most frequently reported ocular alterations in MJD patients its behaviour during the course of the disease, namely in its early stages, has only recently started to be investigated. The main goal of this work was to characterize the frequency of nystagmus in symptomatic and presymptomatic carriers of the MJD mutation, and investigate its usefulness as an early indicator of the disease. Methods We conducted an observational study of Azorean MJD family members, comprising a total of 158 subjects which underwent neurological evaluation. Sixty eight were clinically and molecularly diagnosed with MJD, 48 were confirmed asymptomatic carriers and 42 were confirmed non-carriers of the MJD mutation. The frequency of nystagmus was calculated for the 3 groups. Results Nystagmus was present in 88% of the MJD patients. Seventeen percent of the at-risk subjects with a carrier result in the molecular test and none of the 42 individuals who received a non-carrier test result displayed nystagmus (p < 0.006). Although not reaching statistical significance, symptomatic subjects showing nystagmus had a tendency for a higher length of the CAG tract in the expanded allele, when compared to individuals who did not have nystagmus. Conclusions The frequency of nystagmus in asymptomatic carriers and its absence in non-carriers of the mutation, suggests that nystagmus may appear before gait disturbance and can thus be considered an early sign of MJD. PMID:24450306

Tay-Sachs disease preconception screening in Australia: self-knowledge of being an Ashkenazi Jew predicts carrier state better than does ancestral origin, although there is an increased risk for c.1421 + 1G > C mutation in individuals with South African heritage.

PubMed

Lew, Raelia; Burnett, Leslie; Proos, Anné

2011-12-01

The Australasian Community Genetics Program provided a preconception screening for Tay-Sachs disease (TSD) to 4,105 Jewish high school students in Sydney and Melbourne over the 12-year period 1995-2007. By correlating the frequencies of mutant HEXA, MIM *606869 (gene map locus 15q23-q24) alleles with subjects' nominated ethnicity (Ashkenazi/Sephardi/Mixed) and grandparental birthplaces, we established that Ashkenazi ethnicity is a better predictor of TSD carrier status than grandparental ancestral origins. Screening self-identified Ashkenazi subjects detected 95% of TSD carriers (carrier frequency 1:25). Having mixed Ashkenazi and non-Ashkenazi heritage reduced the carrier frequency (1:97). South African heritage conveyed a fourfold risk of c.1421 + 1G > C mutation compared with other AJ subjects (odds ratio (OR), 4.19; 95% confidence interval (CI), 1.83-9.62, p = 0.001), but this was the only specific case of ancestral origin improving diagnostic sensitivity over that based on determining Ashkenazi ethnicity. Carriers of c.1278insTATC mutations were more likely to have heritage from Western Europe (OR, 1.65 (95% CI, 1.04-2.60), p = 0.032) and South Eastern Europe (OR, 1.77 (95% CI, 1.14-2.73), p = 0.010). However, heritage from specific European countries investigated did not significantly alter the overall odds of TSD carrier status.

Spread-Spectrum Carrier Estimation With Unknown Doppler Shift

NASA Technical Reports Server (NTRS)

DeLeon, Phillip L.; Scaife, Bradley J.

1998-01-01

We present a method for the frequency estimation of a BPSK modulated, spread-spectrum carrier with unknown Doppler shift. The approach relies on a classic periodogram in conjunction with a spectral matched filter. Simulation results indicate accurate carrier estimation with processing gains near 40. A DSP-based prototype has been implemented for real-time carrier estimation for use in New Mexico State University's proposal for NASA's Demand Assignment Multiple Access service.

Nasal microenvironments and interspecific interactions influence nasal microbiota complexity and S. aureus carriage

PubMed Central

Yan, Miling; Pamp, Sünje J.; Fukuyama, Julia; Hwang, Peter H.; Cho, Do-Yeon; Holmes, Susan; Relman, David A.

2013-01-01

Summary The indigenous microbiota of the nasal cavity plays important roles in human health and disease. Patterns of spatial variation in microbiota composition may help explain Staphylococcus aureus colonization, and reveal interspecies and species-host interactions. To assess the biogeography of the nasal microbiota, we sampled healthy subjects, representing both S. aureus carriers and non-carriers, at 3 nasal sites (anterior naris, middle meatus, and sphenoethmoidal recess). Phylogenetic compositional and sparse linear discriminant analyses revealed communities that differed according to site epithelium type and S. aureus culture-based carriage status. Corynebacterium accolens and C. pseudodiphtheriticum were identified as the most important microbial community determinants of S. aureus carriage, with competitive interactions evident only at sites with ciliated pseudostratified columnar epithelium. In vitro co-cultivation experiments provided supporting evidence of interactions among these species. These results highlight spatial variation in nasal microbial communities and differences in community composition between S. aureus carriers and non-carriers. PMID:24331461

47 CFR 15.113 - Power line carrier systems.

Code of Federal Regulations, 2012 CFR

2012-10-01

...-interference basis in accordance with § 15.5 of this part. If harmful interference occurs, the electric power... frequencies. (e) Power line carrier system apparatus shall conform to such engineering standards as may be... 47 Telecommunication 1 2012-10-01 2012-10-01 false Power line carrier systems. 15.113 Section 15...

77 FR 59244 - Agency Information Collection Activities; Extension of Currently-Approved Information Collection...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-09-26

...: Class I Motor Carriers of Passengers. Estimated Number of Respondents: 2 (per year). Estimated Time per Response: 18 minutes per response. Expiration Date: September 30, 2012. Frequency of Response: Annually and..., passenger carriers are classified into two groups: (1) Class I carriers are those having average annual...

An OKQPSK modem incorporating numerically controlled carrier synthesis

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

Oetken, R.E.

1988-04-04

The feasibility of incorporating numerically controlled oscillators (NCO) in communication related applications is evaluated. NCO generation of sinusoids may prove useful in systems requiring precise frequency control, tuning linearity, and orthogonality versus frequency. An OKQPSK modem operating at a data rate of 200 kb/s was fabricated. The modem operates in a back to back hardwired channel and thus does not incorporate carrier or symbol timing recovery. Spectra of the NCO generated sinusoids are presented along with waveforms from the modulation and demodulation process. Generation of sinusoids in the digital domain is a viable alternative to analog oscillators. Implementation of anmore » NCO should be considered when frequency allocation, tuning bandwidth, or frequency hopped transmission requires precise frequency synthesis. 24 figs.« less

Optical communications beyond orbital angular momentum

NASA Astrophysics Data System (ADS)

Rosales-Guzmán, Carmelo; Trichili, Abderrahmen; Dudley, Angela; Ndagano, Bienvenu; Ben Salem, Amine; Zghal, Mourad; Forbes, Andrew

2016-09-01

Current optical communication technologies are predicted to face a bandwidth capacity limit in the near future. The nature of the limitation is fundamental rather than technological and is set by nonlinearities in optical fibers. One solution, suggested over 30 years ago, comprises the use of spatial modes of light as information carriers. Along this direction, light beams endowed with orbital angular momentum (OAM) have been demonstrated as potential information carriers in both, free space and fibres. However, recent studies suggest that purely OAM modes does not increase the bandwidth of optical communication systems. In fact, in all work to date, only the azimuthal component of transverse spatial modes has been used. Crucially, all transverse spatial modes require two degrees of freedom to be described; in the context of Laguerre-Gaussian (LGp`) beams these are azimuthal (l) and radial (p), the former responsible for OAM. Here, we demonstrate a technique where both degrees of freedom of LG modes are used as information carrier over free space. We transfer images encoded using 100 spatial modes in three wavelengths as our basis, and employ a spatial demultiplexing scheme that detects all 100 modes simultaneously. Our scheme is a hybrid of MIMO and SMM, and serves as a proof-of-principle demonstration. The cross-talk between the modes is small and independent of whether OAM modes are used or not.

Gigahertz frequency comb from a diode-pumped solid-state laser.

PubMed

Klenner, Alexander; Schilt, Stéphane; Südmeyer, Thomas; Keller, Ursula

2014-12-15

We present the first stabilization of the frequency comb offset from a diode-pumped gigahertz solid-state laser oscillator. No additional external amplification and/or compression of the output pulses is required. The laser is reliably modelocked using a SESAM and is based on a diode-pumped Yb:CALGO gain crystal. It generates 1.7-W average output power and pulse durations as short as 64 fs at a pulse repetition rate of 1 GHz. We generate an octave-spanning supercontinuum in a highly nonlinear fiber and use the standard f-to-2f carrier-envelope offset (CEO) frequency f_CEO detection method. As a pump source, we use a reliable and cost-efficient commercial diode laser. Its multi-spatial-mode beam profile leads to a relatively broad frequency comb offset beat signal, which nevertheless can be phase-locked by feedback to its current. Using improved electronics, we reached a feedback-loop-bandwidth of up to 300 kHz. A combination of digital and analog electronics is used to achieve a tight phase-lock of f_CEO to an external microwave reference with a low in-loop residual integrated phase-noise of 744 mrad in an integration bandwidth of [1 Hz, 5 MHz]. An analysis of the laser noise and response functions is presented which gives detailed insights into the CEO stabilization of this frequency comb.

Analysis of carrier transport and carrier trapping in organic diodes with polyimide-6,13-Bis(triisopropylsilylethynyl)pentacene double-layer by charge modulation spectroscopy and optical second harmonic generation measurement

NASA Astrophysics Data System (ADS)

Lim, Eunju; Taguchi, Dai; Iwamoto, Mitsumasa

2014-08-01

We studied the carrier transport and carrier trapping in indium tin oxide/polyimide (PI)/6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/Au diodes by using charge modulation spectroscopy (CMS) and time-resolved electric field induced optical second harmonic generation (TR-EFISHG) measurements. TR-EFISHG directly probes the spatial carrier behaviors in the diodes, and CMS is useful in explaining the carrier motion with respect to energy. The results clearly indicate that the injected carriers move across TIPS-pentacene thorough the molecular energy states of TIPS-pentacene and accumulate at the PI/TIPS-pentacene interface. However, some carriers are trapped in the PI layers. These findings take into account the capacitance-voltage and current-voltage characteristics of the diodes.

Few-cycle carrier envelope phase-dependent stereo detection of electrons.

PubMed

Verhoef, Aart J; Fernández, Alma; Lezius, Matthias; O'Keeffe, Kevin; Uiberacker, Matthias; Krausz, Ferenc

2006-12-01

The spatial distribution of electrons emitted from atoms by few-cycle optical fields is known to be dependent on the carrier envelope phase, i.e., the phase of the field with respect to the pulse envelope. With respect to Paulus et al. [Phys. Rev. Lett.91, 253004 (2003)] we propose a greatly simplified device to measure and control the carrier envelope phase of few-cycle pulses with an accuracy of better than pi/10 based on this principle. We compared different schemes to control the carrier envelope phase of our pulses.

A Simplified Baseband Prefilter Model with Adaptive Kalman Filter for Ultra-Tight COMPASS/INS Integration

PubMed Central

Luo, Yong; Wu, Wenqi; Babu, Ravindra; Tang, Kanghua; Luo, Bing

2012-01-01

COMPASS is an indigenously developed Chinese global navigation satellite system and will share many features in common with GPS (Global Positioning System). Since the ultra-tight GPS/INS (Inertial Navigation System) integration shows its advantage over independent GPS receivers in many scenarios, the federated ultra-tight COMPASS/INS integration has been investigated in this paper, particularly, by proposing a simplified prefilter model. Compared with a traditional prefilter model, the state space of this simplified system contains only carrier phase, carrier frequency and carrier frequency rate tracking errors. A two-quadrant arctangent discriminator output is used as a measurement. Since the code tracking error related parameters were excluded from the state space of traditional prefilter models, the code/carrier divergence would destroy the carrier tracking process, and therefore an adaptive Kalman filter algorithm tuning process noise covariance matrix based on state correction sequence was incorporated to compensate for the divergence. The federated ultra-tight COMPASS/INS integration was implemented with a hardware COMPASS intermediate frequency (IF), and INS's accelerometers and gyroscopes signal sampling system. Field and simulation test results showed almost similar tracking and navigation performances for both the traditional prefilter model and the proposed system; however, the latter largely decreased the computational load. PMID:23012564

Frequency-division multiplexer and demultiplexer for terahertz wireless links.

PubMed

Ma, Jianjun; Karl, Nicholas J; Bretin, Sara; Ducournau, Guillaume; Mittleman, Daniel M

2017-09-28

The development of components for terahertz wireless communications networks has become an active and growing research field. However, in most cases these components have been studied using a continuous or broadband-pulsed terahertz source, not using a modulated data stream. This limitation may mask important aspects of the performance of the device in a realistic system configuration. We report the characterization of one such device, a frequency multiplexer, using modulated data at rates up to 10 gigabits per second. We also demonstrate simultaneous error-free transmission of two signals at different carrier frequencies, with an aggregate data rate of 50 gigabits per second. We observe that the far-field spatial variation of the bit error rate is different from that of the emitted power, due to a small nonuniformity in the angular detection sensitivity. This is likely to be a common feature of any terahertz communication system in which signals propagate as diffracting beams not omnidirectional broadcasts.There is growing interest in the development of components to facilitate wireless communications in the terahertz but the characterization of these systems involve an unmodulated input. Here the authors demonstrate multiplexing and demultiplexing of data streams in the terahertz range using a real data link.

47 CFR 27.54 - Frequency stability.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Frequency stability. 27.54 Section 27.54 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES Technical Standards § 27.54 Frequency stability. The frequency stability shall be...

47 CFR 27.54 - Frequency stability.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 2 2011-10-01 2011-10-01 false Frequency stability. 27.54 Section 27.54 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES Technical Standards § 27.54 Frequency stability. The frequency stability shall be...

Spatially continuous distributed fiber optic sensing using optical carrier based microwave interferometry.

PubMed

Huang, Jie; Lan, Xinwei; Luo, Ming; Xiao, Hai

2014-07-28

This paper reports a spatially continuous distributed fiber optic sensing technique using optical carrier based microwave interferometry (OCMI), in which many optical interferometers with the same or different optical path differences are interrogated in the microwave domain and their locations can be unambiguously determined. The concept is demonstrated using cascaded weak optical reflectors along a single optical fiber, where any two arbitrary reflectors are paired to define a low-finesse Fabry-Perot interferometer. While spatially continuous (i.e., no dark zone), fully distributed strain measurement was used as an example to demonstrate the capability, the proposed concept may also be implemented on other types of waveguide or free-space interferometers and used for distributed measurement of various physical, chemical and biological quantities.

Interplay between plasmon and single-particle excitations in a metal nanocluster

DOE PAGES

Ma, Jie; Wang, Zhi; Wang, Lin-Wang

2015-12-17

Plasmon-generated hot carriers are used in photovoltaic or photochemical applications. However, the interplays between the plasmon and single-particle excitations in nanosystems have not been theoretically addressed using ab initio methods. Here we show such interplays in a Ag 55 nanocluster using real-time time-dependent density functional theory simulations. We find that the disappearance of the zero-frequency peak in the Fourier transform of the band-to-band transition coefficient is a hallmark of the plasmon. We show the importance of the d-states for hot-carrier generations. If the single-particle d-to-s excitations are resonant to the plasmon frequency, the majority of the plasmon energy will bemore » converted into hot carriers, and the overall hot-carrier generation is enhanced by the plasmon; if such resonance does not exist, we observe an intriguing Rabi oscillation between the plasmon and hot carriers. Phonons play a minor role in plasmonic dynamics in such small systems. Ultimately, this study provides guidance on improving plasmonic applications.« less

Measurement of Relaxation Time of Excess Carriers in Si and CIGS Solar Cells by Modulated Electroluminescence Technique

DOE PAGES

Khatavkar, Sanchit; Muniappan, Kulasekaran; Kannan, Chinna V.; ...

2017-11-10

Excess carrier lifetime plays a crucial role in determining the efficiency of solar cells. In this paper, we use the frequency dependence of inphase and quadrature components of modulated electroluminescence (MEL) to measure the relaxation time (decay) of excess carriers. The advantage of the MEL technique is that the relaxation time is obtained directly from the angular frequency at which the quadrature component peaks. It does not need knowledge of the material parameters like mobility, etc., and can be used for any finished solar cells which have detectable light emission. The experiment is easy to perform with standard electrical equipment.more » For silicon solar cells, the relaxation time is dominated by recombination and hence, the relaxation time is indeed the excess carrier lifetime. In contrast, for the CIGS solar cells investigated here, the relaxation time is dominated by trapping and emission from shallow minority carrier traps.« less

Measurement of Relaxation Time of Excess Carriers in Si and CIGS Solar Cells by Modulated Electroluminescence Technique

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

Khatavkar, Sanchit; Muniappan, Kulasekaran; Kannan, Chinna V.

Excess carrier lifetime plays a crucial role in determining the efficiency of solar cells. In this paper, we use the frequency dependence of inphase and quadrature components of modulated electroluminescence (MEL) to measure the relaxation time (decay) of excess carriers. The advantage of the MEL technique is that the relaxation time is obtained directly from the angular frequency at which the quadrature component peaks. It does not need knowledge of the material parameters like mobility, etc., and can be used for any finished solar cells which have detectable light emission. The experiment is easy to perform with standard electrical equipment.more » For silicon solar cells, the relaxation time is dominated by recombination and hence, the relaxation time is indeed the excess carrier lifetime. In contrast, for the CIGS solar cells investigated here, the relaxation time is dominated by trapping and emission from shallow minority carrier traps.« less

Interplay between plasmon and single-particle excitations in a metal nanocluster

PubMed Central

Ma, Jie; Wang, Zhi; Wang, Lin-Wang

2015-01-01

Plasmon-generated hot carriers are used in photovoltaic or photochemical applications. However, the interplays between the plasmon and single-particle excitations in nanosystems have not been theoretically addressed using ab initio methods. Here we show such interplays in a Ag55 nanocluster using real-time time-dependent density functional theory simulations. We find that the disappearance of the zero-frequency peak in the Fourier transform of the band-to-band transition coefficient is a hallmark of the plasmon. We show the importance of the d-states for hot-carrier generations. If the single-particle d-to-s excitations are resonant to the plasmon frequency, the majority of the plasmon energy will be converted into hot carriers, and the overall hot-carrier generation is enhanced by the plasmon; if such resonance does not exist, we observe an intriguing Rabi oscillation between the plasmon and hot carriers. Phonons play a minor role in plasmonic dynamics in such small systems. This study provides guidance on improving plasmonic applications. PMID:26673449

Effect of soil temperature on optical frequency transfer through unidirectional dense-wavelength-division-multiplexing fiber-optic links.

PubMed

Pinkert, T J; Böll, O; Willmann, L; Jansen, G S M; Dijck, E A; Groeneveld, B G H M; Smets, R; Bosveld, F C; Ubachs, W; Jungmann, K; Eikema, K S E; Koelemeij, J C J

2015-02-01

Results of optical frequency transfer over a carrier-grade dense-wavelength-division-multiplexing (DWDM) optical fiber network are presented. The relation between soil temperature changes on a buried optical fiber and frequency changes of an optical carrier through the fiber is modeled. Soil temperatures, measured at various depths by the Royal Netherlands Meteorology Institute (KNMI) are compared with observed frequency variations through this model. A comparison of a nine-day record of optical frequency measurements through the 2×298  km fiber link with soil temperature data shows qualitative agreement. A soil temperature model is used to predict the link stability over longer periods (days-months-years). We show that optical frequency dissemination is sufficiently stable to distribute and compare, e.g., rubidium frequency standards over standard DWDM optical fiber networks using unidirectional fibers.

47 CFR Appendix 1 to Subpart E of... - Glossary of Terms

Code of Federal Regulations, 2012 CFR

2012-10-01

... Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO... frequencies. Reference frequencies from which the carrier frequency, suppressed or otherwise, may not deviate by more than the specified frequency tolerance. Crystal. Quartz piezo-electric element. Crystal...

Time-Resolved Photoluminescence Spectroscopy Of The Carrier Dynamics In GaAs/AlxGa1-xAs Quantum Wells

NASA Astrophysics Data System (ADS)

Polland, Hans J.; Kuhl, Jurgen; Gobel, Ernst O.

1988-08-01

Picosecond photoluminescence experiments at low temperature (6K) have been employed to study the trapping dynamics of photoexcited carriers in GaAs/AlGaAs single quantum wells for different shapes of the AlxGai_xAs confinement layers. We have obtained the following results by analyzing the spectral and temporal distribution of the photoluminescence after picosecond pulse excitation: Trapping efficiency is ==, 40% for a standard ungraded cladding layer (A10.3G1.7As with constant band gap and 5nm thick wells) but increases to ,-, 60% and 100% for samp es with a spatially parabolic or linear band gap profile of the confinement layers, respectively. Trapping times are appreciably shorter than the luminescence risetime which is between 60ps to 100ps. Thus carrier trapping does not impose severe limitations on the modulation speed of single quantum well devices up to frequencies in the order of 10GHz. Similar results are obtained for a well with a width of 1.2nm. Inhomogeneities in the carrier trapping mechanism due to well width fluctuations are not observed in our samples. In the second part we describe the photoluminescence properties of GaAs/A1,Gai_x As quantum wells (x=0.3) under the influence of electric fields perpendicular to the layers. We observe a drastic red shift and a concomitant strong increase of the electron-hole recombination lifetime for well widths > lOnm due to the quantum-confined Stark effect. At high fields (50-100kV/cm) field ionization due to tunneling leads to a decrease of both the photoluminescence yield and decay time, in accordance with a simple WKB theory

Modelling the dependence of contrast sensitivity on grating area and spatial frequency.

PubMed

Rovamo, J; Luntinen, O; Näsänen, R

1993-12-01

We modelled the human foveal visual system in a detection task as a simple image processor comprising (i) low-pass filtering due to the optical transfer function of the eye, (ii) high-pass filtering of neural origin, (iii) addition of internal neural noise, and (iv) detection by a local matched filter. Its detection efficiency for gratings was constant up to a critical area but then decreased with increasing area. To test the model we measured Michelson contrast sensitivity as a function of grating area at spatial frequencies of 0.125-32 c/deg for simple vertical and circular cosine gratings. In circular gratings luminance was sinusoidally modulated as a function of the radius of the grating field. In agreement with the model, contrast sensitivity at all spatial frequencies increased in proportion to the square-root of grating area at small areas. When grating area exceeded critical area, the increase saturated and contrast sensitivity became independent of area at large grating areas. Spatial integration thus obeyed Piper's law at small grating areas. The critical area of spatial integration, marking the cessation of Piper's law, was constant in solid degrees at low spatial frequencies but inversely proportional to spatial frequency squared at medium and high spatial frequencies. At low spatial frequencies the maximum contrast sensitivity obtainable by spatial integration increased in proportion to spatial frequency but at high spatial frequencies it decreased in proportion to the cube of the increasing spatial frequency. The increase was due to high-pass filtering of neural origin (lateral inhibition) and the decrease was mainly due to the optical transfer function of the eye. Our model explained 95% of the total variance of the contrast sensitivity data.

CFTR mutation distribution among U.S. Hispanic and African American individuals: evaluation in cystic fibrosis patient and carrier screening populations.

PubMed

Sugarman, Elaine A; Rohlfs, Elizabeth M; Silverman, Lawrence M; Allitto, Bernice A

2004-01-01

We reviewed CFTR mutation distribution among Hispanic and African American individuals referred for CF carrier screening and compared mutation frequencies to those derived from CF patient samples. Results from CFTR mutation analyses received from January 2001 through September 2003, were analyzed for four populations: Hispanic individuals with a CF diagnosis (n = 159) or carrier screening indication (n = 15,333) and African American individuals with a CF diagnosis (n = 108) or carrier screening indication (n = 8,973). All samples were tested for the same 87 mutation panel. In the Hispanic population, 42 mutations were identified: 30 in the patient population (77.5% detection rate) and 33 among carrier screening referrals. Five mutations not included in the ACMG/ACOG carrier screening panel (3876delA, W1089X, R1066C, S549N, 1949del84) accounted for 7.55% detection in patients and 5.58% among carriers. Among African American referrals, 33 different mutations were identified: 21 in the patient population (74.4% detection) and 23 in the carrier screening population. Together, A559T and 711+5G>A were observed at a detection rate of 3.71% in CF patients and 6.38% in carriers. The mutation distribution seen in both the carrier screening populations reflected an increased frequency of mutations with variable expression such as D1152H, R117H, and L206W. A detailed analysis of CFTR mutation distribution in the Hispanic and African American patient and carrier screening populations demonstrates that a diverse group of mutations is most appropriate for diagnostic and carrier screening in these populations. To best serve the increasingly diverse U.S. population, ethnic-specific mutations should be included in mutation panels.

47 CFR 15.247 - Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz.

Code of Federal Regulations, 2011 CFR

2011-10-01

... channel carrier frequencies separated by a minimum of 25 kHz or the 20 dB bandwidth of the hopping channel... have hopping channel carrier frequencies that are separated by 25 kHz or two-thirds of the 20 dB...: if the 20 dB bandwidth of the hopping channel is less than 250 kHz, the system shall use at least 50...

47 CFR 15.247 - Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz.

Code of Federal Regulations, 2014 CFR

2014-10-01

... channel carrier frequencies separated by a minimum of 25 kHz or the 20 dB bandwidth of the hopping channel... have hopping channel carrier frequencies that are separated by 25 kHz or two-thirds of the 20 dB...: if the 20 dB bandwidth of the hopping channel is less than 250 kHz, the system shall use at least 50...

47 CFR 15.247 - Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz.

Code of Federal Regulations, 2010 CFR

2010-10-01

... channel carrier frequencies separated by a minimum of 25 kHz or the 20 dB bandwidth of the hopping channel... have hopping channel carrier frequencies that are separated by 25 kHz or two-thirds of the 20 dB...: if the 20 dB bandwidth of the hopping channel is less than 250 kHz, the system shall use at least 50...

47 CFR 15.247 - Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz.

Code of Federal Regulations, 2013 CFR

2013-10-01

... channel carrier frequencies separated by a minimum of 25 kHz or the 20 dB bandwidth of the hopping channel... have hopping channel carrier frequencies that are separated by 25 kHz or two-thirds of the 20 dB...: if the 20 dB bandwidth of the hopping channel is less than 250 kHz, the system shall use at least 50...

47 CFR 15.247 - Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz.

Code of Federal Regulations, 2012 CFR

2012-10-01

... channel carrier frequencies separated by a minimum of 25 kHz or the 20 dB bandwidth of the hopping channel... have hopping channel carrier frequencies that are separated by 25 kHz or two-thirds of the 20 dB...: if the 20 dB bandwidth of the hopping channel is less than 250 kHz, the system shall use at least 50...

Quantum and Carbon Nanomaterials | Chemistry and Nanoscience Research |

Science.gov Websites

acceptors in composites with thiophene-based conjugated polymers, ultimately determining that the free interface to efficiently dissociate excitons and spatially separate long-lived free carriers, but pointed toward a dependence of the free-carrier yield on the energetic driving force at the interface. By tuning

Power allocation and range performance considerations for a dual-frequency EBPSK/MPPSK system

NASA Astrophysics Data System (ADS)

Yao, Yu; Wu, Lenan; Zhao, Junhui

2017-12-01

Extended binary phase shift keying/M-ary position phase shift keying (EBPSK/MPPSK)-MODEM provides radar and communication functions on a single hardware platform with a single waveform. However, its range estimation accuracy is worse than continuous-wave (CW) radar because of the imbalance of power in two carrier frequencies. In this article, the power allocation method for dual-frequency EBPSK/MPPSK modulated systems is presented. The power of two signal transmitters is adequately allocated to ensure that the power in two carrier frequencies is equal. The power allocation ratios for two types of modulation systems are obtained. Moreover, considerations regarding the range of operation of the dual-frequency system are analysed. In addition to theoretical considerations, computer simulations are provided to illustrate the performance.

Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields.

PubMed

Noe, G Timothy; Katayama, Ikufumi; Katsutani, Fumiya; Allred, James J; Horowitz, Jeffrey A; Sullivan, David M; Zhang, Qi; Sekiguchi, Fumiya; Woods, Gary L; Hoffmann, Matthias C; Nojiri, Hiroyuki; Takeda, Jun; Kono, Junichiro

2016-12-26

We have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers in the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.

Dynamics of a multimode semiconductor laser with optical feedback

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

Koryukin, I. V.

A new model of a multi-longitudinal-mode semiconductor laser with weak optical feedback is proposed. This model generalizes the well-known Tang-Statz-deMars equations, which are derived from the first principles and adequately describe solid-state lasers to a semiconductor active medium. Steady states of the model and the spectrum of relaxation oscillations are found, and the laser dynamics in the chaotic regime of low-frequency fluctuations of intensity is investigated. It is established that the dynamic properties of the proposed model depend mainly on the carrier diffusion, which controls mode-mode coupling in the active medium via spread of gratings of spatial inversion. The resultsmore » obtained are compared with the predictions of previous semiphenomenological models and the scope of applicability of these models is determined.« less

47 CFR Appendix 1 to Subpart E of... - Glossary of Terms

Code of Federal Regulations, 2013 CFR

2013-10-01

... typically includes a frequency monitoring system that initiates a MedRadio communications session. MedRadio... Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO... station authorized in the CB. Channel frequencies. Reference frequencies from which the carrier frequency...

47 CFR Appendix 1 to Subpart E of... - Glossary of Terms

Code of Federal Regulations, 2010 CFR

2010-10-01

... which also typically includes a frequency monitoring system that initiates a MedRadio communications... Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO... station authorized in the CB. Channel frequencies. Reference frequencies from which the carrier frequency...

47 CFR Appendix 1 to Subpart E of... - Glossary of Terms

Code of Federal Regulations, 2011 CFR

2011-10-01

... which also typically includes a frequency monitoring system that initiates a MedRadio communications... Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO... station authorized in the CB. Channel frequencies. Reference frequencies from which the carrier frequency...

47 CFR Appendix 1 to Subpart E of... - Glossary of Terms

Code of Federal Regulations, 2014 CFR

2014-10-01

... typically includes a frequency monitoring system that initiates a MedRadio communications session. MedRadio... Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO... station authorized in the CB. Channel frequencies. Reference frequencies from which the carrier frequency...

47 CFR 74.761 - Frequency tolerance.

Code of Federal Regulations, 2013 CFR

2013-10-01

... Booster Stations § 74.761 Frequency tolerance. The licensee of a low power TV, TV translator, or TV booster station shall maintain the transmitter output frequencies as set forth below. The frequency... channel carrier frequency if the low power TV, TV translator, or TV booster station is authorized with a...

47 CFR 74.761 - Frequency tolerance.

Code of Federal Regulations, 2014 CFR

2014-10-01

... Booster Stations § 74.761 Frequency tolerance. The licensee of a low power TV, TV translator, or TV booster station shall maintain the transmitter output frequencies as set forth below. The frequency... channel carrier frequency if the low power TV, TV translator, or TV booster station is authorized with a...

47 CFR 74.761 - Frequency tolerance.

Code of Federal Regulations, 2011 CFR

2011-10-01

... Booster Stations § 74.761 Frequency tolerance. The licensee of a low power TV, TV translator, or TV booster station shall maintain the transmitter output frequencies as set forth below. The frequency... channel carrier frequency if the low power TV, TV translator, or TV booster station is authorized with a...

47 CFR 74.761 - Frequency tolerance.

Code of Federal Regulations, 2012 CFR

2012-10-01

... Booster Stations § 74.761 Frequency tolerance. The licensee of a low power TV, TV translator, or TV booster station shall maintain the transmitter output frequencies as set forth below. The frequency... channel carrier frequency if the low power TV, TV translator, or TV booster station is authorized with a...

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

Yamashita, G.; Nagai, M., E-mail: mnagai@mp.es.osaka-u.ac.jp, E-mail: ashida@mp.es.osaka-u.ac.jp; Ashida, M., E-mail: mnagai@mp.es.osaka-u.ac.jp, E-mail: ashida@mp.es.osaka-u.ac.jp

We estimated the carrier multiplication efficiency in the most common solar-cell material, Si, by using optical-pump/terahertz-probe spectroscopy. Through close analysis of time-resolved data, we extracted the exact number of photoexcited carriers from the sheet carrier density 10 ps after photoexcitation, excluding the influences of spatial diffusion and surface recombination in the time domain. For incident photon energies greater than 4.0 eV, we observed enhanced internal quantum efficiency due to carrier multiplication. The evaluated value of internal quantum efficiency agrees well with the results of photocurrent measurements. This optical method allows us to estimate the carrier multiplication and surface recombination of carriersmore » quantitatively, which are crucial for the design of the solar cells.« less

Characterization of Local Carrier Dynamics in AlN and AlGaN Films using High Spatial- and Time-resolution Cathodoluminescence Spectroscopy

DTIC Science & Technology

2012-10-12

21/2012 Abstract: In order to assess the impacts of structural and point defects on the local carrier (exciton) recombination dynamics in...quantitatively understood as functions of structural / point defect and impurity concentrations (crystal imperfections). However, only few papers [5...NOTES 14. ABSTRACT In order to assess the impacts of structural and point defects on the local carrier (exciton) recombination dynamics in wide bandgap

Characterization of Carrier Concentration and Mobility in n-type SiC Wafers Using Infrared Reflectance Spectroscopy

NASA Astrophysics Data System (ADS)

Narita, Katsutoshi; Hijikata, Yasuto; Yaguchi, Hiroyuki; Yoshida, Sadafumi; Nakashima, Shinichi

2004-08-01

We have estimated the free-carrier concentration and drift mobility in n-type 6H-SiC wafers in the carrier concentration range of 1017-1019 cm-3 from far- and mid-infrared (30-2000 cm-1) reflectance spectra obtained at room temperature. A modified classical dielectric function model was employed for the analysis. We found good agreement between the electrical properties derived from infrared reflectance spectroscopy and those derived from Hall effect measurements. We have demonstrated the spatial mapping of carrier concentration and mobility for commercially produced 2 inch SiC wafers.

Multiple differences in calling songs and other traits between solitary and gregarious Mormon crickets from allopatric mtDNA clades

PubMed Central

Bailey, Nathan W; Gwynne, Darryl T; Bailey, William V; Ritchie, Michael G

2007-01-01

Background In acoustic species, traits such as male calling song are likely to diverge quickly between allopatric populations due to sexual selection, and divergence in parameters such as carrier frequency, chirp structure, and other important song characters can influence sexual isolation. Here we make use of two forms of Mormon crickets to examine differences in a broad suite of traits that have the potential to influence speciation via sexual isolation. Mormon crickets in "gregarious" populations aggregate into dense migratory bands, and females are the sexually competitive sex (sex-role reversal). There is also a non-outbreak "solitary" form. These two forms are largely but not perfectly correlated with a significant mtDNA subdivision within the species that is thought to have arisen in allopatry. Combined information about multiple, independently evolving traits, such as morphology and structural and behavioural differences in calling song, provides greater resolution of the overall differences between these allopatric populations, and allows us to assess their stage of divergence. We test two predictions, first that the forms differ in song and second that gregarious males are more reluctant to sing than solitary males due to sex role reversal. We also tested for a difference in the relationship between the size of the forewing resonator, the mirror, and carrier frequency, as most models of sound production in crickets indicate that mirror size should predict carrier frequency. Results Multivariate analyses showed that solitary and gregarious individuals from different populations representing the two mtDNA clades had almost non-overlapping distributions based on multiple song and morphological measurements. Carrier frequency differed between the two, and gregarious males were more reluctant to sing overall. Mirror size predicted carrier frequency; however, the relationship between mirror size and surface area varied between solitary and gregarious forms, suggesting that factors above and beyond mirror size contribute to carrier frequency. Conclusion The two clades of Mormon crickets differ in a broad suite of independent traits that probably justify subspecies status (the two can successfully mate so may not be reproductively isolated). However, our results emphasize the importance of carefully distinguishing the ultimate causation of differences between traits used to delineate species or subspecies boundaries. PMID:17241474

Incidence of bovine leukocyte adhesion deficiency, complex vertebral malformation, and deficiency of uridine-5-monophosphate synthase carriers in Brazilian Girolando cattle.

PubMed

Paiva, D S; Fonseca, I; Pinto, I S B; Ianella, P; Campos, T A; Caetano, A R; Paiva, S R; Silva, M V G B; Martins, M F

2013-08-29

Among the various hereditary diseases that have been widely studied in dairy cattle, bovine leukocyte adhesion deficiency (BLAD), deficiency of uridine-5-monophosphate synthase (DUMPS), and complex vertebral malformation (CVM) are noteworthy because of their high impact on overall herd productivity as a consequence of increased calf mortality. The aim of this study was to verify the frequency of carriers of BLAD, CVM, and DUMPS mutant alleles in cows and bulls from the National Girolando Progeny Test carried out in Brazil by using polymerase chain reaction (PCR)-restriction fragment length polymorphism and allele-specific PCR assays. A total of 777 animals were genotyped for BLAD, 783 for CVM, and 122 for DUMPS. The frequencies of carriers for BLAD and CVM were 0.77 and 1.53%, respectively, whereas no carriers of DUMPS were observed.

Terahertz-infrared electrodynamics of single-wall carbon nanotube films

NASA Astrophysics Data System (ADS)

Zhukova, E. S.; Grebenko, A. K.; Bubis, A. V.; Prokhorov, A. S.; Belyanchikov, M. A.; Tsapenko, A. P.; Gilshteyn, E. P.; Kopylova, D. S.; Gladush, Yu G.; Anisimov, A. S.; Anzin, V. B.; Nasibulin, A. G.; Gorshunov, B. P.

2017-11-01

Broad-band (4-20 000 cm-1) spectra of real and imaginary conductance of a set of high-quality pristine and AuCl3-doped single-walled carbon nanotube (SWCNT) films with different transparency are systematically measured. It is shown that while the high-energy (≥1 eV) response is determined by well-known interband transitions, the lower-energy electrodynamic properties of the films are fully dominated by unbound charge carriers. Their main spectral effect is seen as the free-carrier Drude-type contribution. Partial localization of these carriers leads to a weak plasmon resonance around 100 cm-1. At the lowest frequencies, below 10 cm-1, a gap-like feature is detected whose origin is associated with the energy barrier experienced by the carriers at the intersections between SWCNTs. It is assumed that these three mechanisms are universal and determine the low-frequency terahertz-infrared electrodynamics of SWCNT wafer-scale films.

Rate equation modeling of the frequency noise and the intrinsic spectral linewidth in quantum cascade lasers.

PubMed

Wang, Xing-Guang; Grillot, Frédéric; Wang, Cheng

2018-02-05

This work theoretically investigates the frequency noise (FN) characteristics of quantum cascade lasers (QCLs) through a three-level rate equation model, which takes into account both the carrier noise and the spontaneous emission noise through the Langevin approach. It is found that the power spectral density of the FN exhibits a broad peak due to the carrier noise induced carrier variation in the upper laser level, which is enhanced by the stimulated emission process. The peak amplitude is strongly dependent on the gain stage number and the linewidth broadening factor. In addition, an analytical formula of the intrinsic spectral linewidth of QCLs is derived based on the FN analysis. It is demonstrated that the laser linewidth can be narrowed by reducing the gain coefficient and/or accelerating the carrier scattering rates of the upper and the lower laser levels.

Optical conductivity of three and two dimensional topological nodal-line semimetals

NASA Astrophysics Data System (ADS)

Barati, Shahin; Abedinpour, Saeed H.

2017-10-01

The peculiar shape of the Fermi surface of topological nodal-line semimetals at low carrier concentrations results in their unusual optical and transport properties. We analytically investigate the linear optical responses of three- and two-dimensional nodal-line semimetals using the Kubo formula. The optical conductivity of a three-dimensional nodal-line semimetal is anisotropic. Along the axial direction (i.e., the direction perpendicular to the nodal-ring plane), the Drude weight has a linear dependence on the chemical potential at both low and high carrier dopings. For the radial direction (i.e., the direction parallel to the nodal-ring plane), this dependence changes from linear into quadratic in the transition from low into high carrier concentration. The interband contribution into optical conductivity is also anisotropic. In particular, at large frequencies, it saturates to a constant value for the axial direction and linearly increases with frequency along the radial direction. In two-dimensional nodal-line semimetals, no interband optical transition could be induced and the only contribution to the optical conductivity arises from the intraband excitations. The corresponding Drude weight is independent of the carrier density at low carrier concentrations and linearly increases with chemical potential at high carrier doping.

Background-free millimeter-wave ultra-wideband signal generation based on a dual-parallel Mach-Zehnder modulator.

PubMed

Zhang, Fangzheng; Pan, Shilong

2013-11-04

A novel scheme for photonic generation of a millimeter-wave ultra-wideband (MMW-UWB) signal is proposed and experimentally demonstrated based on a dual-parallel Mach-Zehnder modulator (DPMZM). In the proposed scheme, a single-frequency radio frequency (RF) signal is applied to one sub-MZM of the DPMZM to achieve optical suppressed-carrier modulation, and an electrical control pulse train is applied to the other sub-MZM biased at the minimum transmission point, to get an on/off switchable optical carrier. By filtering out the optical carrier with one of the first-order sidebands, and properly setting the amplitude of the control pulse, an MMW-UWB pulse train without the residual local oscillation is generated after photo-detection. The generated MMW-UWB signal is background-free, because the low-frequency components in the electrical spectrum are effectively suppressed. In the experiment, an MMW-UWB pulse train centered at 25 GHz with a 10-dB bandwidth of 5.5 GHz is successfully generated. The low frequency components are suppressed by 22 dB.

Carrier Envelope Phase Effect of a Long Duration Pulse in the Low Frequency Region

NASA Astrophysics Data System (ADS)

Zhao, Xi; Yang, Yu-Jun; Liu, Xue-Shen; Wang, Bing-Bing

2014-04-01

Using the characteristic of small energy difference between two high Rydberg states, we theoretically investigate the carrier envelope phase (CEP) effect in a bound-bound transition of an atom in a low-frequency long laser pulse with tens of optical cycles. Particularly, we first prepare a Rydberg state of a hydrogen-like atom by a laser field with the resonant frequency between this state and the ground state. Then by using a low-frequency long laser pulse interacting with this Rydberg atom, we calculate the population of another Rydberg state nearby this Rydberg state at the end of the laser pulse and find that the population changes dramatically with the CEP of the low-frequency pulse. This CEP effect is attributed to the interference between the positive-frequency and negative-frequency components in one-photon transition. These results may provide a method to measure the CEP value of a long laser pulse with low frequency.

Offset frequency dynamics and phase noise properties of a self-referenced 10 GHz Ti:sapphire frequency comb.

PubMed

Heinecke, Dirk C; Bartels, Albrecht; Diddams, Scott A

2011-09-12

This paper shows the experimental details of the stabilization scheme that allows full control of the repetition rate and the carrier-envelope offset frequency of a 10 GHz frequency comb based on a femtosecond Ti:sapphire laser. Octave-spanning spectra are produced in nonlinear microstructured optical fiber, in spite of the reduced peak power associated with the 10 GHz repetition rate. Improved stability of the broadened spectrum is obtained by temperature-stabilization of the nonlinear optical fiber. The carrier-envelope offset frequency and the repetition rate are simultaneously frequency stabilized, and their short- and long-term stabilities are characterized. We also measure the transfer of amplitude noise of the pump source to phase noise on the offset frequency and verify an increased sensitivity of the offset frequency to pump power modulation compared to systems with lower repetition rate. Finally, we discuss merits of this 10 GHz system for the generation of low-phase-noise microwaves from the photodetected pulse train.

Coarse-to-Fine Encoding of Spatial Frequency Information into Visual Short-Term Memory for Faces but Impartial Decay

ERIC Educational Resources Information Center

Gao, Zaifeng; Bentin, Shlomo

2011-01-01

Face perception studies investigated how spatial frequencies (SF) are extracted from retinal display while forming a perceptual representation, or their selective use during task-imposed categorization. Here we focused on the order of encoding low-spatial frequencies (LSF) and high-spatial frequencies (HSF) from perceptual representations into…

An adaptive narrow band frequency modulation voice communication system

NASA Technical Reports Server (NTRS)

Wishna, S.

1972-01-01

A narrow band frequency modulation communication system is described which provides for the reception of good quality voice at low carrier-to-noise ratios. The high level of performance is obtained by designing a limiter and phase lock loop combination as a demodulator, so that the bandwidth of the phase lock loop decreases as the carrier level decreases. The system was built for the position location and aircraft communication equipment experiment of the ATS 6 program.

Modal Analysis of Space-rocket Equipment Components

NASA Astrophysics Data System (ADS)

Igolkin, A. A.; Safin, A. I.; Prokofiev, A. B.

2018-01-01

In order to prevent vibration damage an analysis of natural frequencies and mode shapes of elements of rocket and space technology should be developed. This paper discusses technique of modal analysis on the example of the carrier platform. Modal analysis was performed by using mathematical modeling and laser vibrometer. Experimental data was clarified by using Test.Lab software. As a result of modal analysis amplitude-frequency response of carrier platform was obtained and the parameters of the elasticity was clarified.

Doping-induced change of optical properties in underdoped cuprate superconductors

NASA Astrophysics Data System (ADS)

Liu, H. L.; Quijada, M. A.; Zibold, A. M.; Yoon, Y.-D.; Tanner, D. B.; Cao, G.; Crow, J. E.; Berger, H.; Margaritondo, G.; Forró, L.; O, Beom-Hoan; Markert, J. T.; Kelly, R. J.; Onellion, M.

1999-01-01

We report on the ab-plane optical reflectance measurements of single crystals of Y-doped 0953-8984/11/1/020/img15 and Pr-doped 0953-8984/11/1/020/img16 over a wide frequency range from 80 to 0953-8984/11/1/020/img17 (10 meV-5 eV) and at temperatures between 20 and 300 K. Y and Pr doping both decrease the hole concentration in the 0953-8984/11/1/020/img18 planes. This has allowed us to investigate the evolution of ab-plane charge dynamics at doping levels ranging from heavily underdoped to nearly optimally doped. Our results of the low-frequency optical conductivity and spectral weight do not show any features associated with the normal-state pseudogap. Instead, one-component analysis for the optical conductivity shows the low-frequency depression in the scattering rate at 0953-8984/11/1/020/img19, signalling entry into the pseudogap state. Alternatively, no clear indications of the normal-state pseudogap are detected in the temperature-dependent zero-frequency free-carrier scattering rate by using two-component analysis. In the superconducting state, there is also no convincing evidence of superconducting gap absorption in all spectra. We find that there is a `universal correlation' between the numbers of carriers and the transition temperature. This correlation holds whether one considers the number of carriers in the superfluid or the total number of carriers.

Frequency and spectrum of hemoglobinopathy mutations in a Uruguayan pediatric population

PubMed Central

Luz, Julio Da; Ávila, Amalia; Icasuriaga, Sandra; Gongóra, María; Castillo, Luis; Serrón, Alejandra; Kimura, Elza Miyuki; Costa, Fernando Ferreira; Sans, Mónica; Sonati, Maria de Fátima

2013-01-01

Hemoglobinopathies are the most common recessive diseases worldwide but their prevalence in Uruguay has not been investigated. In this study, 397 unrelated outpatient children from the Pereira Rosell Hospital Center (CHPR), as well as 31 selected patients with microcytic anemia and 28 β-thalassemia carriers were analyzed for hemoglobinopathies by using biochemical and molecular biology methods. Parametric and non-parametric methods were used to compare the hematological indices between groups of genotypes. Of the 397 patients in the first group, approximately 1% (0.76% HbS and 0.25% β-thalassemia) had a mutation in the HBB gene and 3.3% had β-thalassemia. These mutations had a heterogeneous distribution that varied according to individual ancestry. HbS was found exclusively in individuals with declared African ancestry and had a carrier frequency of 2.2%. The frequency of α-thalassemia carriers in outpatients of European and African ancestry was 1.2% and 6.5%, respectively. In contrast, the frequency of α-thalassemia carriers in patients with microcytic anemia was 25.8%, significantly higher (p < 0.01) than that observed in the sample as a whole and in Afro-descendants and Euro-descendants. Significant differences were observed in the hematological parameters between individuals with thalassemia genotypes and those with a normal genotype. These results indicate that hemoglobinopathies are a relevant health problem in Uruguay. PMID:24130436

Theoretical predictions for spatially-focused heating of magnetic nanoparticles guided by magnetic particle imaging field gradients

NASA Astrophysics Data System (ADS)

Dhavalikar, Rohan; Rinaldi, Carlos

2016-12-01

Magnetic nanoparticles in alternating magnetic fields (AMFs) transfer some of the field's energy to their surroundings in the form of heat, a property that has attracted significant attention for use in cancer treatment through hyperthermia and in developing magnetic drug carriers that can be actuated to release their cargo externally using magnetic fields. To date, most work in this field has focused on the use of AMFs that actuate heat release by nanoparticles over large regions, without the ability to select specific nanoparticle-loaded regions for heating while leaving other nanoparticle-loaded regions unaffected. In parallel, magnetic particle imaging (MPI) has emerged as a promising approach to image the distribution of magnetic nanoparticle tracers in vivo, with sub-millimeter spatial resolution. The underlying principle in MPI is the application of a selection magnetic field gradient, which defines a small region of low bias field, superimposed with an AMF (of lower frequency and amplitude than those normally used to actuate heating by the nanoparticles) to obtain a signal which is proportional to the concentration of particles in the region of low bias field. Here we extend previous models for estimating the energy dissipation rates of magnetic nanoparticles in uniform AMFs to provide theoretical predictions of how the selection magnetic field gradient used in MPI can be used to selectively actuate heating by magnetic nanoparticles in the low bias field region of the selection magnetic field gradient. Theoretical predictions are given for the spatial decay in energy dissipation rate under magnetic field gradients representative of those that can be achieved with current MPI technology. These results underscore the potential of combining MPI and higher amplitude/frequency actuation AMFs to achieve selective magnetic fluid hyperthermia (MFH) guided by MPI.

A stabilized optical frequency comb based on an Er-doped fiber femtosecond laser

NASA Astrophysics Data System (ADS)

Xia, Chuanqing; Wu, Tengfei; Zhao, Chunbo; Xing, Shuai

2018-03-01

An optical frequency comb based on a 250 MHz home-made Er-doped fiber femtosecond laser is presented in this paper. The Er-doped fiber laser has a ring cavity and operates mode-locked in femtosecond regime with the technique of nonlinear polarization rotation. The pulse duration is 118 fs and the spectral width is 30 nm. A part of the femtosecond laser is amplified in Er-doped fiber amplifier before propagating through a piece of highly nonlinear fiber for expanding the spectrum. The carrier-envelope offset frequency of the comb which has a signal-to-noise ratio more than 35 dB is extracted by means of f-2f beating. It demonstrates that both carrier-envelope offset frequency and repetition frequency keep phase locked to a Rubidium atomic clock simultaneously for 2 hours. The frequency stabilized fiber combs will be increasingly applied in optical metrology, attosecond pulse generation, and absolute distance measurement.

Design and test of a regenerative satellite transmultiplexer

NASA Astrophysics Data System (ADS)

Hung, Kenny King-Ming

1993-05-01

In a multiple access scheme for regenerative satellite communications, the bulk frequency division multiple access (FDMA) uplink signal is demodulated on board the satellite and then remodulated for time division multiplexing (TDM) downlink transmission. Conversion from frequency to time division multiplex format requires that the uplink signal be frequency demultiplexed and each individual carrier be subsequently demodulated. For thin-route application which consists of a large number of channels with fixed data rate, multicarrier demodulation can be accomplished efficiently by a digital transmultiplexer (TMUX) using a fast Fourier transform processor followed by a bank of per-channel processors. A time domain description of the TMUX algorithm is derived which elucidates how the TMUX functions. The per-channel processor performs timing and carrier recovery for optimum and coherent data detection. Timing recovery is necessarily achieved asynchronously by a filter coefficient interpolation. Carrier recovery is performed using an all-digital phase-locked loop. The combination of both timing and carrier loops is investigated for a multi-user system. The performance of the overall system is assessed over a multi-user, additive white Gaussian noise channel for a bit energy to noise power spectral density ratio down to zero dB.

Ka-Band Transponder for Deep-Space Radio Science

NASA Technical Reports Server (NTRS)

Dennis, Matthew S.; Mysoor, Narayan R.; Folkner, William M.; Mendoza, Ricardo; Venkatesan, Jaikrishna

2008-01-01

A one-page document describes a Ka-band transponder being developed for use in deep-space radio science. The transponder receives in the Deep Space Network (DSN) uplink frequency band of 34.2 to 34.7 GHz, transmits in the 31.8- to 32.3 GHz DSN downlink band, and performs regenerative ranging on a DSN standard 4-MHz ranging tone subcarrier phase-modulated onto the uplink carrier signal. A primary consideration in this development is reduction in size, relative to other such transponders. The transponder design is all-analog, chosen to minimize not only the size but also the number of parts and the design time and, thus, the cost. The receiver features two stages of frequency down-conversion. The receiver locks onto the uplink carrier signal. The exciter signal for the transmitter is derived from the same source as that used to generate the first-stage local-oscillator signal. The ranging-tone subcarrier is down-converted along with the carrier to the second intermediate frequency, where the 4-MHz tone is demodulated from the composite signal and fed into a ranging-tone-tracking loop, which regenerates the tone. The regenerated tone is linearly phase-modulated onto the downlink carrier.

A comprehensive screening program for β-thalassemia and other hemoglobinopathies in the Hooghly District of West Bengal, India, dealing with 21 137 cases.

PubMed

Bhattacharyya, Kallol Kumar; Chatterjee, Tridip; Mondal, Ujjalendu Bikash

2016-11-01

We here present a report of population screening programs (January 2012-December 2015) conducted by the Thalassemia Control Unit, Imambara Sadar Hospital, Chinsurah, Hooghly in the Hooghly District of West Bengal, India for prevention of thalassemia. We screened β-thalassemia (β-thal) heterozygotes and homozygotes, and Hb E (HBB: c.79G > A)-β-thal compound heterozygotes. Among 21 137 cases, we found 1968 heterozygotes and 192 homozygotes or compound heterozygotes. Results were evaluated with standard hematological analyses including red cell indices, hemoglobin (Hb) typing and quantification. The participants of the screening program were divided into six groups (children, pre-marriage cases, post-marital cases, family members of affected individuals, family members of carriers and pregnant women). While considering the average frequency of carriers, many reports recorded both related individuals (family members of trait and affected individuals) as well as unrelated individuals such as school children and pregnant women. These would have to be considered separately and only the unrelated individuals taken to estimate carrier frequencies in this article that would give more realistic data on carrier frequency of unrelated individuals.

Grain Boundaries Act as Solid Walls for Charge Carrier Diffusion in Large Crystal MAPI Thin Films.

PubMed

Ciesielski, Richard; Schäfer, Frank; Hartmann, Nicolai F; Giesbrecht, Nadja; Bein, Thomas; Docampo, Pablo; Hartschuh, Achim

2018-03-07

Micro- and nanocrystalline methylammonium lead iodide (MAPI)-based thin-film solar cells today reach power conversion efficiencies of over 20%. We investigate the impact of grain boundaries on charge carrier transport in large crystal MAPI thin films using time-resolved photoluminescence (PL) microscopy and numerical model calculations. Crystal sizes in the range of several tens of micrometers allow for the spatially and time resolved study of boundary effects. Whereas long-ranged diffusive charge carrier transport is observed within single crystals, no detectable diffusive transport occurs across grain boundaries. The observed PL transients are found to crucially depend on the microscopic geometry of the crystal and the point of observation. In particular, spatially restricted diffusion of charge carriers leads to slower PL decay near crystal edges as compared to the crystal center. In contrast to many reports in the literature, our experimental results show no quenching or additional loss channels due to grain boundaries for the studied material, which thus do not negatively affect the performance of the derived thin-film devices.

Enhancement of carrier lifetimes in type-II quantum dot/quantum well hybrid structures

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

Couto, O. D. D., E-mail: odilon@ifi.unicamp.br; Almeida, P. T. de; Santos, G. E. dos

We investigate optical transitions and carrier dynamics in hybrid structures containing type-I GaAs/AlGaAs quantum wells (QWs) and type-II GaSb/AlGaAs quantum dots (QDs). We show that the optical recombination of photocreated electrons confined in the QWs with holes in the QDs and wetting layer can be modified according to the QW/QD spatial separation. In particular, for low spacer thicknesses, the QW optical emission can be suppressed due to the transference of holes from the QW to the GaSb layer, favoring the optical recombination of spatially separated carriers, which can be useful for optical memory and solar cell applications. Time-resolved photoluminescence (PL)more » measurements reveal non-exponential recombination dynamics. We demonstrate that the PL transients can only be quantitatively described by considering both linear and quadratic terms of the carrier density in the bimolecular recombination approximation for type-II semiconductor nanostructures. We extract long exciton lifetimes from 700 ns to 5 μs for QDs depending on the spacer layer thickness.« less

Influence of spatial frequency and emotion expression on face processing in patients with panic disorder.

PubMed

Shim, Miseon; Kim, Do-Won; Yoon, Sunkyung; Park, Gewnhi; Im, Chang-Hwan; Lee, Seung-Hwan

2016-06-01

Deficits in facial emotion processing is a major characteristic of patients with panic disorder. It is known that visual stimuli with different spatial frequencies take distinct neural pathways. This study investigated facial emotion processing involving stimuli presented at broad, high, and low spatial frequencies in patients with panic disorder. Eighteen patients with panic disorder and 19 healthy controls were recruited. Seven event-related potential (ERP) components: (P100, N170, early posterior negativity (EPN); vertex positive potential (VPP), N250, P300; and late positive potential (LPP)) were evaluated while the participants looked at fearful and neutral facial stimuli presented at three spatial frequencies. When a fearful face was presented, panic disorder patients showed a significantly increased P100 amplitude in response to low spatial frequency compared to high spatial frequency; whereas healthy controls demonstrated significant broad spatial frequency dependent processing in P100 amplitude. Vertex positive potential amplitude was significantly increased in high and broad spatial frequency, compared to low spatial frequency in panic disorder. Early posterior negativity amplitude was significantly different between HSF and BSF, and between LSF and BSF processing in both groups, regardless of facial expression. The possibly confounding effects of medication could not be controlled. During early visual processing, patients with panic disorder prefer global to detailed information. However, in later processing, panic disorder patients overuse detailed information for the perception of facial expressions. These findings suggest that unique spatial frequency-dependent facial processing could shed light on the neural pathology associated with panic disorder. Copyright © 2016 Elsevier B.V. All rights reserved.

Air Carrier Financial Statistics : third quarter : [2009

DOT National Transportation Integrated Search

2009-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2006

DOT National Transportation Integrated Search

2006-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : second quarter : [2013

DOT National Transportation Integrated Search

2013-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : first quarter : [2009

DOT National Transportation Integrated Search

2009-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2004

DOT National Transportation Integrated Search

2004-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : second quarter : [2008

DOT National Transportation Integrated Search

2008-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : second quarter : [2012

DOT National Transportation Integrated Search

2012-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : first quarter : [2008

DOT National Transportation Integrated Search

2008-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2003

DOT National Transportation Integrated Search

2003-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : second quarter : [2011

DOT National Transportation Integrated Search

2011-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2013

DOT National Transportation Integrated Search

2013-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2002

DOT National Transportation Integrated Search

2002-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2005

DOT National Transportation Integrated Search

2005-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : second quarter : [2012

DOT National Transportation Integrated Search

2010-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : second quarter : [2010

DOT National Transportation Integrated Search

2010-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : second quarter : [2009

DOT National Transportation Integrated Search

2009-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : first quarter : [2012

DOT National Transportation Integrated Search

2012-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2010

DOT National Transportation Integrated Search

2010-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2012

DOT National Transportation Integrated Search

2012-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : third quarter : [2011

DOT National Transportation Integrated Search

2011-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2011

DOT National Transportation Integrated Search

2011-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2007

DOT National Transportation Integrated Search

2007-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : third quarter : [2013

DOT National Transportation Integrated Search

2013-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : first quarter : [2011

DOT National Transportation Integrated Search

2011-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : first quarter : [2014

DOT National Transportation Integrated Search

2014-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : first quarter : [2013

DOT National Transportation Integrated Search

2013-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : third quarter : [2012

DOT National Transportation Integrated Search

2012-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : third quarter : [2008

DOT National Transportation Integrated Search

2008-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : first quarter : [2010

DOT National Transportation Integrated Search

2010-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2009

DOT National Transportation Integrated Search

2009-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

Air Carrier Financial Statistics : fourth quarter : [2008

DOT National Transportation Integrated Search

2008-01-01

This report presents airline financial statistics obtained from carrier reports to DOT on BTS Form 41 financial schedules. Effective with a rule (ER-1297) adopted July 1982, the filing frequency for income statement and balance sheet data was changed...

1998 NASA Review: Center for Space Telemetering and Telecommunication Systems

NASA Technical Reports Server (NTRS)

Cunningham, Garry

1998-01-01

The following topics are included in the conference proceedings following the program overview: (1) Coding and Carrier Recovery Techniques; (2) Carrier Frequency Estimation Under Unknown Doppler Shifts; (3) Small Satellite Experiments; (4) Bandwidth Efficient Modulation/Equalization Techniques.

The neural bases of spatial frequency processing during scene perception

PubMed Central

Kauffmann, Louise; Ramanoël, Stephen; Peyrin, Carole

2014-01-01

Theories on visual perception agree that scenes are processed in terms of spatial frequencies. Low spatial frequencies (LSF) carry coarse information whereas high spatial frequencies (HSF) carry fine details of the scene. However, how and where spatial frequencies are processed within the brain remain unresolved questions. The present review addresses these issues and aims to identify the cerebral regions differentially involved in low and high spatial frequency processing, and to clarify their attributes during scene perception. Results from a number of behavioral and neuroimaging studies suggest that spatial frequency processing is lateralized in both hemispheres, with the right and left hemispheres predominantly involved in the categorization of LSF and HSF scenes, respectively. There is also evidence that spatial frequency processing is retinotopically mapped in the visual cortex. HSF scenes (as opposed to LSF) activate occipital areas in relation to foveal representations, while categorization of LSF scenes (as opposed to HSF) activates occipital areas in relation to more peripheral representations. Concomitantly, a number of studies have demonstrated that LSF information may reach high-order areas rapidly, allowing an initial coarse parsing of the visual scene, which could then be sent back through feedback into the occipito-temporal cortex to guide finer HSF-based analysis. Finally, the review addresses spatial frequency processing within scene-selective regions areas of the occipito-temporal cortex. PMID:24847226

Envelope contributions to the representation of interaural time difference in the forebrain of barn owls.

PubMed

Tellers, Philipp; Lehmann, Jessica; Führ, Hartmut; Wagner, Hermann

2017-09-01

Birds and mammals use the interaural time difference (ITD) for azimuthal sound localization. While barn owls can use the ITD of the stimulus carrier frequency over nearly their entire hearing range, mammals have to utilize the ITD of the stimulus envelope to extend the upper frequency limit of ITD-based sound localization. ITD is computed and processed in a dedicated neural circuit that consists of two pathways. In the barn owl, ITD representation is more complex in the forebrain than in the midbrain pathway because of the combination of two inputs that represent different ITDs. We speculated that one of the two inputs includes an envelope contribution. To estimate the envelope contribution, we recorded ITD response functions for correlated and anticorrelated noise stimuli in the barn owl's auditory arcopallium. Our findings indicate that barn owls, like mammals, represent both carrier and envelope ITDs of overlapping frequency ranges, supporting the hypothesis that carrier and envelope ITD-based localization are complementary beyond a mere extension of the upper frequency limit. NEW & NOTEWORTHY The results presented in this study show for the first time that the barn owl is able to extract and represent the interaural time difference (ITD) information conveyed by the envelope of a broadband acoustic signal. Like mammals, the barn owl extracts the ITD of the envelope and the carrier of a signal from the same frequency range. These results are of general interest, since they reinforce a trend found in neural signal processing across different species. Copyright © 2017 the American Physiological Society.

Spatial-frequency dependent binocular imbalance in amblyopia

PubMed Central

Kwon, MiYoung; Wiecek, Emily; Dakin, Steven C.; Bex, Peter J.

2015-01-01

While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance. Here we examined binocular imbalance as a function of spatial frequency in amblyopia using a novel computer-based method. Binocular imbalance at four spatial frequencies was measured with a novel dichoptic letter chart in individuals with amblyopia, or normal vision. Our dichoptic letter chart was composed of band-pass filtered letters arranged in a layout similar to the ETDRS acuity chart. A different chart was presented to each eye of the observer via stereo-shutter glasses. The relative contrast of the corresponding letter in each eye was adjusted by a computer staircase to determine a binocular Balance Point at which the observer reports the letter presented to either eye with equal probability. Amblyopes showed pronounced binocular imbalance across all spatial frequencies, with greater imbalance at high compared to low spatial frequencies (an average increase of 19%, p < 0.01). Good test-retest reliability of the method was demonstrated by the Bland-Altman plot. Our findings suggest that spatial-frequency dependent binocular imbalance may be useful for diagnosing amblyopia and as an outcome measure for recovery of binocular vision following therapy. PMID:26603125

Spatial-frequency dependent binocular imbalance in amblyopia.

PubMed

Kwon, MiYoung; Wiecek, Emily; Dakin, Steven C; Bex, Peter J

2015-11-25

While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance. Here we examined binocular imbalance as a function of spatial frequency in amblyopia using a novel computer-based method. Binocular imbalance at four spatial frequencies was measured with a novel dichoptic letter chart in individuals with amblyopia, or normal vision. Our dichoptic letter chart was composed of band-pass filtered letters arranged in a layout similar to the ETDRS acuity chart. A different chart was presented to each eye of the observer via stereo-shutter glasses. The relative contrast of the corresponding letter in each eye was adjusted by a computer staircase to determine a binocular Balance Point at which the observer reports the letter presented to either eye with equal probability. Amblyopes showed pronounced binocular imbalance across all spatial frequencies, with greater imbalance at high compared to low spatial frequencies (an average increase of 19%, p < 0.01). Good test-retest reliability of the method was demonstrated by the Bland-Altman plot. Our findings suggest that spatial-frequency dependent binocular imbalance may be useful for diagnosing amblyopia and as an outcome measure for recovery of binocular vision following therapy.

A low-frequency noise model with carrier generation-recombination process for pentacene organic thin-film transistor

NASA Astrophysics Data System (ADS)

Han, C. Y.; Qian, L. X.; Leung, C. H.; Che, C. M.; Lai, P. T.

2013-07-01

By including the generation-recombination process of charge carriers in conduction channel, a model for low-frequency noise in pentacene organic thin-film transistors (OTFTs) is proposed. In this model, the slope and magnitude of power spectral density for low-frequency noise are related to the traps in the gate dielectric and accumulation layer of the OTFT for the first time. The model can well fit the measured low-frequency noise data of pentacene OTFTs with HfO2 or HfLaO gate dielectric, which validates this model, thus providing an estimate on the densities of traps in the gate dielectric and accumulation layer. It is revealed that the traps in the accumulation layer are much more than those in the gate dielectric, and so dominate the low-frequency noise of pentacene OTFTs.

Coherent optical modulation for antenna remoting

NASA Technical Reports Server (NTRS)

Fitzmartin, D. J.; Gels, R. G.; Balboni, E. J.

1991-01-01

A coherent fiber optic link employing wideband frequency modulation (FM) of the optical carrier is used to transfer radio frequency (RF) or microwave signals. This system is used to link a remotely located antenna to a conveniently located electronics processing site. The advantages of coherent analog fiber optic systems over non-coherent intensity modulated fiber optic analog transmission systems are described. An optical FM link employing an indirect transmitter to frequency modulate the optical carrier and a microwave delay line discriminator receiver is described. Measured performance data for a video signal centered at 60 MHz is presented showing the use of wideband FM in the link.

High-Frequency Subband Compressed Sensing MRI Using Quadruplet Sampling

PubMed Central

Sung, Kyunghyun; Hargreaves, Brian A

2013-01-01

Purpose To presents and validates a new method that formalizes a direct link between k-space and wavelet domains to apply separate undersampling and reconstruction for high- and low-spatial-frequency k-space data. Theory and Methods High- and low-spatial-frequency regions are defined in k-space based on the separation of wavelet subbands, and the conventional compressed sensing (CS) problem is transformed into one of localized k-space estimation. To better exploit wavelet-domain sparsity, CS can be used for high-spatial-frequency regions while parallel imaging can be used for low-spatial-frequency regions. Fourier undersampling is also customized to better accommodate each reconstruction method: random undersampling for CS and regular undersampling for parallel imaging. Results Examples using the proposed method demonstrate successful reconstruction of both low-spatial-frequency content and fine structures in high-resolution 3D breast imaging with a net acceleration of 11 to 12. Conclusion The proposed method improves the reconstruction accuracy of high-spatial-frequency signal content and avoids incoherent artifacts in low-spatial-frequency regions. This new formulation also reduces the reconstruction time due to the smaller problem size. PMID:23280540

The incidence of adult T-cell leukemia/lymphoma among human T-lymphotropic virus type 1 carriers in Japan.

PubMed

Satake, Masahiro; Yamada, Yasuaki; Atogami, Sunao; Yamaguchi, Kazunari

2015-06-01

Human T-lymphotropic virus type 1 (HTLV-1) is highly endemic in the Kyushu/Okinawa region of Japan. A nationwide investigation verified the frequency of HTLV-1 carriers among first-time blood donors and the occurrence of newly diagnosed adult T-cell leukemia/lymphoma (ATL) cases from 2007 through 2008. After adjusting for differences in capture rate between areas, the age-, sex- and area-specific incidence of ATL among carriers was determined. Annual ATL incidence among 10 000 carriers was 7.7 and 8.7 for the Kyushu and non-Kyushu/Okinawa regions, respectively. The incidence increased sharply for men from their 40s to their 70s, but the rate in females remained unchanged through their 40s to 70s. ATL incidence in middle-aged females was still low, even if female carrier frequency was assumed to be identical to that of males. Patients with ATL in their 60s and 70s will comprise two-thirds of all patients with ATL for the next 15 years in Japan.

Infrared countermeasure flare performance measurements using a gas gun

NASA Astrophysics Data System (ADS)

Krishnamoorthy, Lakshmanan; Stringer, Michael; Taylor, Mark R. G.; Kollias, S.

2004-12-01

A unique and cost effective measurement facility called the Reusable Aerodynamic Flare Ejection Capability (RAFEC) has been developed at the Defence Science and Technology Organisation (DSTO), Australia. The RAFEC system involves the use of a reusable, carrier projectile that is launched from a 10 inch, nitrogen driven gas gun. The IRCM flare is loaded in the carrier projectile and the gas gun launches the carrier projectile with a known velocity of between approximately 350 to 650 knots. At a pre-determined time after firing and in the field of view of the measuring instrumentation, the flare is ejected from the carrier projectile for performance measurements to be undertaken. The temporal, spatial and spectral quantities were accomplished with the instruments fielded around the gas gun line of fire and the trajectory is derived from the spatial measurements. The data will be used for hardware in the loop simulations and modelling. Further improvements such as; (1) multiple (maximum of three) flare ejection, (2) 1"x1"x8" format flares made to the carrier projectile, and (3) design and manufacture of the puston, a new item of firing hardware to obtain lower muzzle velocities have enhanced the RAFEC capability. Thus the RAFEC system provides a more realistic IRCM performance measurement capability as it incorporates the deceleration effects experienced by the flare on deployment.

Estimation of the center frequency of the highest modulation filter.

PubMed

Moore, Brian C J; Füllgrabe, Christian; Sek, Aleksander

2009-02-01

For high-frequency sinusoidal carriers, the threshold for detecting sinusoidal amplitude modulation increases when the signal modulation frequency increases above about 120 Hz. Using the concept of a modulation filter bank, this effect might be explained by (1) a decreasing sensitivity or greater internal noise for modulation filters with center frequencies above 120 Hz; and (2) a limited span of center frequencies of the modulation filters, the top filter being tuned to about 120 Hz. The second possibility was tested by measuring modulation masking in forward masking using an 8 kHz sinusoidal carrier. The signal modulation frequency was 80, 120, or 180 Hz and the masker modulation frequencies covered a range above and below each signal frequency. Four highly trained listeners were tested. For the 80-Hz signal, the signal threshold was usually maximal when the masker frequency equaled the signal frequency. For the 180-Hz signal, the signal threshold was maximal when the masker frequency was below the signal frequency. For the 120-Hz signal, two listeners showed the former pattern, and two showed the latter pattern. The results support the idea that the highest modulation filter has a center frequency in the range 100-120 Hz.

Spatial frequency discrimination learning in normal and developmentally impaired human vision

PubMed Central

Astle, Andrew T.; Webb, Ben S.; McGraw, Paul V.

2010-01-01

Perceptual learning effects demonstrate that the adult visual system retains neural plasticity. If perceptual learning holds any value as a treatment tool for amblyopia, trained improvements in performance must generalise. Here we investigate whether spatial frequency discrimination learning generalises within task to other spatial frequencies, and across task to contrast sensitivity. Before and after training, we measured contrast sensitivity and spatial frequency discrimination (at a range of reference frequencies 1, 2, 4, 8, 16 c/deg). During training, normal and amblyopic observers were divided into three groups. Each group trained on a spatial frequency discrimination task at one reference frequency (2, 4, or 8 c/deg). Normal and amblyopic observers who trained at lower frequencies showed a greater rate of within task learning (at their reference frequency) compared to those trained at higher frequencies. Compared to normals, amblyopic observers showed greater within task learning, at the trained reference frequency. Normal and amblyopic observers showed asymmetrical transfer of learning from high to low spatial frequencies. Both normal and amblyopic subjects showed transfer to contrast sensitivity. The direction of transfer for contrast sensitivity measurements was from the trained spatial frequency to higher frequencies, with the bandwidth and magnitude of transfer greater in the amblyopic observers compared to normals. The findings provide further support for the therapeutic efficacy of this approach and establish general principles that may help develop more effective protocols for the treatment of developmental visual deficits. PMID:20832416

Quantitative holographic interferometry applied to combustion and compressible flow research

NASA Astrophysics Data System (ADS)

Bryanston-Cross, Peter J.; Towers, D. P.

1993-03-01

The application of holographic interferometry to phase object analysis is described. Emphasis has been given to a method of extracting quantitative information automatically from the interferometric fringe data. To achieve this a carrier frequency has been added to the holographic data. This has made it possible, firstly to form a phase map using a fast Fourier transform (FFT) algorithm. Then to `solve,' or unwrap, this image to give a contiguous density map using a minimum weight spanning tree (MST) noise immune algorithm, known as fringe analysis (FRAN). Applications of this work to a burner flame and a compressible flow are presented. In both cases the spatial frequency of the fringes exceed the resolvable limit of conventional digital framestores. Therefore, a flatbed scanner with a resolution of 3200 X 2400 pixels has been used to produce very high resolution digital images from photographs. This approach has allowed the processing of data despite the presence of caustics, generated by strong thermal gradients at the edge of the combustion field. A similar example is presented from the analysis of a compressible transonic flow in the shock wave and trailing edge regions.

Linear and nonlinear transparencies in binocular vision.

PubMed Central

Langley, K; Fleet, D J; Hibbard, P B

1998-01-01

When the product of a vertical square-wave grating (contrast envelope) and a horizontal sinusoidal grating (carrier) are viewed binocularly with different disparity cues they can be perceived transparently at different depths. We found, however, that the transparency was asymmetric; it only occurred when the envelope was perceived to be the overlaying surface. When the same two signals were added, the percept of transparency was symmetrical; either signal could be seen in front of or behind the other at different depths. Differences between these multiplicative and additive signal combinations were examined in two experiments. In one, we measured disparity thresholds for transparency as a function of the spatial frequency of the envelope. In the other, we measured disparity discrimination thresholds. In both experiments the thresholds for the multiplicative condition, unlike the additive condition, showed distinct minima at low envelope frequencies. The different sensitivity curves found for multiplicative and additive signal combinations suggest that different processes mediated the disparity signal. The data are consistent with a two-channel model of binocular matching, with multiple depth cues represented at single retinal locations. PMID:9802240

A Hydrodynamic Theory for Spatially Inhomogeneous Semiconductor Lasers. 2; Numerical Results

NASA Technical Reports Server (NTRS)

Li, Jianzhong; Ning, C. Z.; Biegel, Bryan A. (Technical Monitor)

2001-01-01

We present numerical results of the diffusion coefficients (DCs) in the coupled diffusion model derived in the preceding paper for a semiconductor quantum well. These include self and mutual DCs in the general two-component case, as well as density- and temperature-related DCs under the single-component approximation. The results are analyzed from the viewpoint of free Fermi gas theory with many-body effects incorporated. We discuss in detail the dependence of these DCs on densities and temperatures in order to identify different roles played by the free carrier contributions including carrier statistics and carrier-LO phonon scattering, and many-body corrections including bandgap renormalization and electron-hole (e-h) scattering. In the general two-component case, it is found that the self- and mutual- diffusion coefficients are determined mainly by the free carrier contributions, but with significant many-body corrections near the critical density. Carrier-LO phonon scattering is dominant at low density, but e-h scattering becomes important in determining their density dependence above the critical electron density. In the single-component case, it is found that many-body effects suppress the density coefficients but enhance the temperature coefficients. The modification is of the order of 10% and reaches a maximum of over 20% for the density coefficients. Overall, temperature elevation enhances the diffusive capability or DCs of carriers linearly, and such an enhancement grows with density. Finally, the complete dataset of various DCs as functions of carrier densities and temperatures provides necessary ingredients for future applications of the model to various spatially inhomogeneous optoelectronic devices.

Arrays of Individually Controlled Ions Suitable for Two-Dimensional Quantum Simulations (Open Access, Publisher’s Version)

DTIC Science & Technology

2016-06-13

motional ground state, the ratio of Rabi frequencies of carrier and sideband couplings is given by the Lamb-Dicke parameter48, which is for u1 and Dkx...carrier Rabi - frequencies determine Lamb-Dicke parameters and allow for finding the orientation of modes. We use a single ion near T0 to determine the...and find corresponding coefficient settings where we obtain a maximal Rabi rate of the detection transition and/or minimal Rabi rates of micromotion

Controlling the carrier-envelope phase of Raman-generated periodic waveforms.

PubMed

Hsieh, Zhi-Ming; Lai, Chien-Jen; Chan, Han-Sung; Wu, Sih-Ying; Lee, Chao-Kuei; Chen, Wei-Jan; Pan, Ci-Ling; Yee, Fu-Goul; Kung, A H

2009-05-29

We demonstrate control of the carrier-envelope phase of ultrashort periodic waveforms that are synthesized from a Raman-generated optical frequency comb. We generated the comb by adiabatically driving a molecular vibrational coherence with a beam at a fundamental frequency plus its second harmonic. Heterodyne measurements show that full interpulse phase locking of the comb components is realized. The results set the stage for the synthesis of periodic arbitrary waveforms in the femtosecond and subfemtosecond regimes with full control.

Direct carrier-envelope phase control of an amplified laser system.

PubMed

Balčiūnas, Tadas; Flöry, Tobias; Baltuška, Andrius; Stanislauskas, Tomas; Antipenkov, Roman; Varanavičius, Arūnas; Steinmeyer, Günter

2014-03-15

Direct carrier-envelope phase stabilization of an Yb:KGW MOPA laser system is demonstrated with a residual phase jitter reduced to below 100 mrad, which compares favorably with previous stabilization reports, both of amplified laser systems as well as of ytterbium-based oscillators. This novel stabilization scheme relies on a frequency synthesis scheme and a feed-forward approach. The direct stabilization of a sub-MHz frequency comb from a CPA amplifier not only reduces the phase noise but also greatly simplifies the stabilization setup.

47 CFR 80.383 - Vessel Traffic Services (VTS) system frequencies.

Code of Federal Regulations, 2012 CFR

2012-10-01

... protection areas provided there is no interference to VTS communications within the VTS areas. [51 FR 31213... geographic radio protected areas. (a) Assigned frequencies: Vessel Traffic Control Frequencies Carrier frequencies (MHz) Geographic areas 156.250 Seattle. 156.550 New York, New Orleans, 2 Houston, Prince William...

47 CFR 80.383 - Vessel Traffic Services (VTS) system frequencies.

Code of Federal Regulations, 2010 CFR

2010-10-01

... protection areas provided there is no interference to VTS communications within the VTS areas. [51 FR 31213... geographic radio protected areas. (a) Assigned frequencies: Vessel Traffic Control Frequencies Carrier frequencies (MHz) Geographic areas 156.250 Seattle. 156.550 New York, New Orleans, 2 Houston, Prince William...

47 CFR 80.383 - Vessel Traffic Services (VTS) system frequencies.

Code of Federal Regulations, 2013 CFR

2013-10-01

... protection areas provided there is no interference to VTS communications within the VTS areas. [51 FR 31213... geographic radio protected areas. (a) Assigned frequencies: Vessel Traffic Control Frequencies Carrier frequencies (MHz) Geographic areas 156.250 Seattle. 156.550 New York, New Orleans, 2 Houston, Prince William...

47 CFR 80.383 - Vessel Traffic Services (VTS) system frequencies.

Code of Federal Regulations, 2014 CFR

2014-10-01

... protection areas provided there is no interference to VTS communications within the VTS areas. [51 FR 31213... geographic radio protected areas. (a) Assigned frequencies: Vessel Traffic Control Frequencies Carrier frequencies (MHz) Geographic areas 156.250 Seattle. 156.550 New York, New Orleans, 2 Houston, Prince William...

47 CFR 80.383 - Vessel Traffic Services (VTS) system frequencies.

Code of Federal Regulations, 2011 CFR

2011-10-01

... protection areas provided there is no interference to VTS communications within the VTS areas. [51 FR 31213... geographic radio protected areas. (a) Assigned frequencies: Vessel Traffic Control Frequencies Carrier frequencies (MHz) Geographic areas 156.250 Seattle. 156.550 New York, New Orleans, 2 Houston, Prince William...

Optimum Detection Of Slow-Frequency-Hopping Signals

NASA Technical Reports Server (NTRS)

Levitt, Barry K.; Cheng, Unjeng

1994-01-01

Two papers present theoretical analyses of various schemes for coherent and noncoherent detection of M-ary-frequency-shift-keyed (MFSK) signals with slow frequency hopping. Special attention focused on continuous-phase-modulation (CPM) subset of SFH/MFSK signals, for which frequency modulation such carrier phase remains continuous (albeit unknown) during each hop.

47 CFR 22.863 - Frequency stability.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Frequency stability. 22.863 Section 22.863 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.863 Frequency stability. The...

47 CFR 1.10014 - What happens after officially filing my application?

Code of Federal Regulations, 2013 CFR

2013-10-01

... Frequency IHF-xxxxx. Recognized Operating Agency ROA-xxxxx. Satellite Space Station SAT-xxxxx. Satellite... PN released. International High Frequency IHF-xxxxx. Recognized Operating Agency No action taken PN... Carrier Affiliation Notification. International High Frequency: Construction Permits, Licenses...

47 CFR 1.10014 - What happens after officially filing my application?

Code of Federal Regulations, 2014 CFR

2014-10-01

... Frequency IHF-xxxxx. Recognized Operating Agency ROA-xxxxx. Satellite Space Station SAT-xxxxx. Satellite... PN released. International High Frequency IHF-xxxxx. Recognized Operating Agency No action taken PN... Carrier Affiliation Notification. International High Frequency: Construction Permits, Licenses...

47 CFR 1.10014 - What happens after officially filing my application?

Code of Federal Regulations, 2012 CFR

2012-10-01

... Frequency IHF-xxxxx. Recognized Operating Agency ROA-xxxxx. Satellite Space Station SAT-xxxxx. Satellite... PN released. International High Frequency IHF-xxxxx. Recognized Operating Agency No action taken PN... Carrier Affiliation Notification. International High Frequency: Construction Permits, Licenses...

47 CFR 80.375 - Radiodetermination frequencies.

Code of Federal Regulations, 2013 CFR

2013-10-01

... SERVICES STATIONS IN THE MARITIME SERVICES Frequencies Radiodetermination § 80.375 Radiodetermination... direction finding radar stations will be authorized on land. (a) Direction finding frequencies. The carrier... usage must comply with the following requirements: (1) They are not permitted within the territorial...

47 CFR 80.375 - Radiodetermination frequencies.

Code of Federal Regulations, 2014 CFR

2014-10-01

... SERVICES STATIONS IN THE MARITIME SERVICES Frequencies Radiodetermination § 80.375 Radiodetermination... direction finding radar stations will be authorized on land. (a) Direction finding frequencies. The carrier... usage must comply with the following requirements: (1) They are not permitted within the territorial...

47 CFR 80.375 - Radiodetermination frequencies.

Code of Federal Regulations, 2012 CFR

2012-10-01

... SERVICES STATIONS IN THE MARITIME SERVICES Frequencies Radiodetermination § 80.375 Radiodetermination... direction finding radar stations will be authorized on land. (a) Direction finding frequencies. The carrier... usage must comply with the following requirements: (1) They are not permitted within the territorial...

Cross-Sectional Transport Imaging in a Multijunction Solar Cell

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

Haegel, Nancy M.; Ke, Chi-Wen; Taha, Hesham

2015-06-14

Combining highly localized electron-beam excitation at a point with the spatial resolution capability of optical near-field imaging, we have imaged carrier transport in a cross-sectioned multijunction (GaInP/GaInAs/Ge) solar cell. We image energy transport associated with carrier diffusion throughout the full width of the middle (GaInAs) cell and luminescent coupling from point excitation in the top cell GaInP to the middle cell. Supporting cathodoluminescence and near-field photoluminescence measurements demonstrate excitation-dependent Fermi level splitting effects that influence cross-sectioned spectroscopy results as well as transport limitations on the spatial resolution of cross-sectional measurements.

Carrier-phase multipath corrections for GPS-based satellite attitude determination

NASA Technical Reports Server (NTRS)

Axelrad, A.; Reichert, P.

2001-01-01

This paper demonstrates the high degree of spatial repeatability of these errors for a spacecraft environment and describes a correction technique, termed the sky map method, which exploits the spatial correlation to correct measurements and improve the accuracy of GPS-based attitude solutions.

Spatial localization of excitons and charge carriers in hybrid perovskite thin films

DOE PAGES

Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin; ...

2015-07-21

The fundamental photophysics underlying the remarkably high power conversion efficiency of organic-inorganic hybrid perovskite-based solar cells has been increasingly studied using complementary spectroscopic techniques. The spatially heterogeneous polycrystalline morphology of the photoactive layers owing to the presence of distinct crystalline grains has been generally neglected in optical measurements and therefore the reported results are typically averaged over hundreds or even thousands of such grains. Here, we apply femtosecond transient absorption microscopy to spatially and temporally probe ultrafast electronic excited-state dynamics in pristine methylammonium lead tri-iodide (CH 3NH 3PbI 3) thin films and composite structures. We found that the electronic excited-statemore » relaxation kinetics are extremely sensitive to the sample location probed, which was manifested by position-dependent decay timescales and transient signals. As a result, analysis of transient absorption kinetics acquired at distinct spatial positions enabled us to identify contributions of excitons and free charge carriers.« less

Sharpening coarse-to-fine stereo vision by perceptual learning: asymmetric transfer across the spatial frequency spectrum

PubMed Central

Tran, Truyet T.; Craven, Ashley P.; Leung, Tsz-Wing; Chat, Sandy W.; Levi, Dennis M.

2016-01-01

Neurons in the early visual cortex are finely tuned to different low-level visual features, forming a multi-channel system analysing the visual image formed on the retina in a parallel manner. However, little is known about the potential ‘cross-talk’ among these channels. Here, we systematically investigated whether stereoacuity, over a large range of target spatial frequencies, can be enhanced by perceptual learning. Using narrow-band visual stimuli, we found that practice with coarse (low spatial frequency) targets substantially improves performance, and that the improvement spreads from coarse to fine (high spatial frequency) three-dimensional perception, generalizing broadly across untrained spatial frequencies and orientations. Notably, we observed an asymmetric transfer of learning across the spatial frequency spectrum. The bandwidth of transfer was broader when training was at a high spatial frequency than at a low spatial frequency. Stereoacuity training is most beneficial when trained with fine targets. This broad transfer of stereoacuity learning contrasts with the highly specific learning reported for other basic visual functions. We also revealed strategies to boost learning outcomes ‘beyond-the-plateau’. Our investigations contribute to understanding the functional properties of the network subserving stereovision. The ability to generalize may provide a key principle for restoring impaired binocular vision in clinical situations. PMID:26909178

Sequential soil transport and its influence on the spatial organisation of collective digging in leaf-cutting ants.

PubMed

Pielström, Steffen; Roces, Flavio

2013-01-01

The Chaco leaf-cutting ant Atta vollenweideri (Forel) inhabits large and deep subterranean nests composed of a large number of fungus and refuse chambers. The ants dispose of the excavated soil by forming small pellets that are carried to the surface. For ants in general, the organisation of underground soil transport during nest building remains completely unknown. In the laboratory, we investigated how soil pellets are formed and transported, and whether their occurrence influences the spatial organisation of collective digging. Similar to leaf transport, we discovered size matching between soil pellet mass and carrier mass. Workers observed while digging excavated pellets at a rate of 26 per hour. Each excavator deposited its pellets in an individual cluster, independently of the preferred deposition sites of other excavators. Soil pellets were transported sequentially over 2 m, and the transport involved up to 12 workers belonging to three functionally distinct groups: excavators, several short-distance carriers that dropped the collected pellets after a few centimetres, and long-distance, last carriers that reached the final deposition site. When initiating a new excavation, the proportion of long-distance carriers increased from 18% to 45% within the first five hours, and remained unchanged over more than 20 hours. Accumulated, freshly-excavated pellets significantly influenced the workers' decision where to start digging in a choice experiment. Thus, pellets temporarily accumulated as a result of their sequential transport provide cues that spatially organise collective nest excavation.

Technical Note: Detective quantum efficiency simulation of a-Se imaging detectors using ARTEMIS.

PubMed

Fang, Yuan; Ito, Takaaki; Nariyuki, Fumito; Kuwabara, Takao; Badano, Aldo; Karim, Karim S

2017-08-01

This work studies the detective quantum efficiency (DQE) of a-Se-based solid state x-ray detectors for medical imaging applications using ARTEMIS, a Monte Carlo simulation tool for modeling x-ray photon, electron and charged carrier transport in semiconductors with the presence of applied electric field. ARTEMIS is used to model the signal formation process in a-Se. The simulation model includes x-ray photon and high-energy electron interactions, and detailed electron-hole pair transport with applied detector bias taking into account drift, diffusion, Coulomb interactions, recombination and trapping. For experimental validation, the DQE performance of prototype a-Se detectors is measured following IEC Testing Standard 62220-1-3. Comparison of simulated and experimental DQE results show reasonable agreement for RQA beam qualities. Experimental validation demonstrated within 5% percentage difference between simulation and experimental DQE results for spatial frequency above 0.25 cycles/mm using uniform applied electric field for RQA beam qualities (RQA5, RQA7 and RQA9). Results include two different prototype detectors with thicknesses of 240 μm and 1 mm. ARTEMIS can be used to model the DQE of a-Se detectors as a function of x-ray energy, detector thickness, and spatial frequency. The ARTEMIS model can be used to improve understanding of the physics of x-ray interactions in a-Se and in optimization studies for the development of novel medical imaging applications. © 2017 American Association of Physicists in Medicine.

Spatial Resolution Versus Data Acquisition Efficiency in Mapping an Inhomogeneous System with Species Diffusion

DOE PAGES

Chen, Fengxiang; Zhang, Yong; Gfroerer, T. H.; ...

2015-06-02

Traditionally, spatially-resolved photoluminescence (PL) has been performed using a point-by-point scan mode with both excitation and detection occurring at the same spatial location. But with the availability of high quality detector arrays like CCDs, an imaging mode has become popular for performing spatially-resolved PL. By illuminating the entire area of interest and collecting the data simultaneously from all spatial locations, the measurement efficiency can be greatly improved. However, this new approach has proceeded under the implicit assumption of comparable spatial resolution. We show here that when carrier diffusion is present, the spatial resolution can actually differ substantially between the twomore » modes, with the less efficient scan mode being far superior. We apply both techniques in investigation of defects in a GaAs epilayer – where isolated singlet and doublet dislocations can be identified. A superposition principle is developed for solving the diffusion equation to extract the intrinsic carrier diffusion length, which can be applied to a system with arbitrarily distributed defects. The understanding derived from this work is significant for a broad range of problems in physics and beyond (for instance biology) – whenever the dynamics of generation, diffusion, and annihilation of species can be probed with either measurement mode.« less

Light tuning DC and AC electrical properties of ZnO-rGO based hybrid nanocomposite film

NASA Astrophysics Data System (ADS)

Nath, Debarati; Mandal, S. K.; Deb, Debajit; Rakshit, J. K.; Dey, P.; Roy, J. N.

2018-03-01

We have investigated the electrical and optoelectrical properties of a zinc oxide (ZnO):reduced graphene oxide (rGO) nanocomposite film prepared through the sol gel process on a glass substrate under dark and illumination conditions of light. The bandgap of the composite film is decreased from the pure ZnO nanofilm due to the formation of a Zn-O-C bond in the composite film. The linear behavior in the Current-Voltage curve is attributed to Ohmic contact between ZnO and rGO grains. The photocurrent of the composite film is found to increase with an increase in light intensity having two different slopes, indicating an enhancement of the mobility of carriers and dissociation rate of excitons. The observed decrement of the impedance value with the intensity of light may be due to the flow of charge carriers and the presence of the light dependent relaxation process in the system. Nyquist plots have been fitted using a parallel combination of grain boundary resistances and grain boundary capacitance at different intensities of light. The relaxation frequency is observed to shift towards the high frequency regime. Carrier transit time has been calculated from relaxation frequency showing opposite behavior with the intensity of light. These results indicate the higher generations of photogenerated carriers at the interface between rGO and ZnO grains and an enhancement of the charge transport process due to the increment of the mobility of charge carriers in the system.

Spatial relationship between Taenia solium tapeworm carriers and necropsy cyst burden in pigs

PubMed Central

Ayvar, Viterbo; Gamboa, Ricardo; Muro, Claudio; Moyano, Luz M.; Benavides, Victor; Flecker, Robert H.; Garcia, Hector H.; O’Neal, Seth E.

2017-01-01

Background Taenia solium, a parasite that affects humans and pigs, is the leading cause of preventable epilepsy in the developing world. Geographic hotspots of pigs testing positive for serologic markers of T. solium exposure have been observed surrounding the locations of human tapeworm carriers. This clustered pattern of seropositivity in endemic areas formed the basis for geographically targeted control interventions, which have been effective at reducing transmission. In this study, we further explore the spatial relationship between human tapeworm carriers and infected pigs using necroscopic examination as a quantitative gold-standard diagnostic to detect viable T. solium cyst infection in pigs. Methodology/Principal findings We performed necroscopic examinations on pigs from 7 villages in northern Peru to determine the number of viable T. solium cysts in each pig. Participating humans in the study villages were tested for T. solium tapeworm infection (i.e., taeniasis) with an ELISA coproantigen assay, and the distances from each pig to its nearest human tapeworm carrier were calculated. We assessed the relationship between proximity to a tapeworm carrier and the prevalence of light, moderate, and heavy cyst burden in pigs. The prevalence of pig infection was greatest within 50 meters of a tapeworm carrier and decreased monotonically as distance increased. Pigs living less than 50 meters from a human tapeworm carrier were 4.6 times more likely to be infected with at least one cyst than more distant pigs. Heavier cyst burdens, however, were not more strongly associated with proximity to tapeworm carriers than light cyst burdens. Conclusion/Significance Our study shows that human tapeworm carriers and pigs with viable T. solium cyst infection are geographically correlated in endemic areas. This finding supports control strategies that treat humans and pigs based on their proximity to other infected individuals. We did not, however, find sufficient evidence that heavier cyst burdens in pigs would serve as improved targets for geographically focused control interventions. PMID:28406898

Spatial relationship between Taenia solium tapeworm carriers and necropsy cyst burden in pigs.

PubMed

Pray, Ian W; Ayvar, Viterbo; Gamboa, Ricardo; Muro, Claudio; Moyano, Luz M; Benavides, Victor; Flecker, Robert H; Garcia, Hector H; O'Neal, Seth E

2017-04-01

Taenia solium, a parasite that affects humans and pigs, is the leading cause of preventable epilepsy in the developing world. Geographic hotspots of pigs testing positive for serologic markers of T. solium exposure have been observed surrounding the locations of human tapeworm carriers. This clustered pattern of seropositivity in endemic areas formed the basis for geographically targeted control interventions, which have been effective at reducing transmission. In this study, we further explore the spatial relationship between human tapeworm carriers and infected pigs using necroscopic examination as a quantitative gold-standard diagnostic to detect viable T. solium cyst infection in pigs. We performed necroscopic examinations on pigs from 7 villages in northern Peru to determine the number of viable T. solium cysts in each pig. Participating humans in the study villages were tested for T. solium tapeworm infection (i.e., taeniasis) with an ELISA coproantigen assay, and the distances from each pig to its nearest human tapeworm carrier were calculated. We assessed the relationship between proximity to a tapeworm carrier and the prevalence of light, moderate, and heavy cyst burden in pigs. The prevalence of pig infection was greatest within 50 meters of a tapeworm carrier and decreased monotonically as distance increased. Pigs living less than 50 meters from a human tapeworm carrier were 4.6 times more likely to be infected with at least one cyst than more distant pigs. Heavier cyst burdens, however, were not more strongly associated with proximity to tapeworm carriers than light cyst burdens. Our study shows that human tapeworm carriers and pigs with viable T. solium cyst infection are geographically correlated in endemic areas. This finding supports control strategies that treat humans and pigs based on their proximity to other infected individuals. We did not, however, find sufficient evidence that heavier cyst burdens in pigs would serve as improved targets for geographically focused control interventions.

Decision feedback loop for tracking a polyphase modulated carrier

NASA Technical Reports Server (NTRS)

Simon, M. K. (Inventor)

1974-01-01

A multiple phase modulated carrier tracking loop for use in a frequency shift keying system is described in which carrier tracking efficiency is improved by making use of the decision signals made on the data phase transmitted in each T-second interval. The decision signal is used to produce a pair of decision-feedback quadrature signals for enhancing the loop's performance in developing a loop phase error signal.

Carrier-envelope phase control by a composite plate.

PubMed

Ell, Richard; Birge, Jonathan R; Araghchini, Mohammad; Kärtner, Franz X

2006-06-12

We demonstrate a new concept to vary the carrier-envelope phase of a mode-locked laser by a composite plate while keeping all other pulse parameters practically unaltered. The effect is verified externally in an interferometric autocorrelator, as well as inside the cavity of an octave-spanning femtosecond oscillator. The carrier-envelope frequency can be shifted by half the repetition rate with negligible impact on pulse spectrum and energy.

Temperature feedback control for long-term carrier-envelope phase locking.

PubMed

Yun, Chenxia; Chen, Shouyuan; Wang, He; Chini, Michael; Chang, Zenghu

2009-09-20

We report a double feedback loop for the improvement of the carrier-envelope phase stabilization of a chirped mirror based femtosecond laser oscillator. By combining the control of the Ti:sapphire crystal temperature and the modulation of the pump power, the carrier envelope offset frequency, fCEO, was locked for close to 20 h, which is much longer than the typical phase stabilization time with only pump power modulation.

Frequency and Clinicopathological Characteristics of Presenilin 1 Gly206Ala Mutation in Puerto Rican Hispanics with Dementia

PubMed Central

Arnold, Steven E.; Vega, Irving E.; Karlawish, Jason H.; WoIk, David A.; Nunez, Jessica; Negron, Mirna; Xie, Sharon X.; Wang, Li-San; Dubroff, Jacob G.; McCarty-Wood, Elisabeth; Trojanowski, John Q.; Van Deerlin, Vivianna

2012-01-01

The frequency and clinical and pathological characteristics associated with the Gly206Ala presenilin 1 (PSEN1) mutation in Puerto Rican and non-Puerto Rican Hispanics were evaluated at the University of Pennsylvania’s Alzheimer’s Disease Center. DNAs from all cohort subjects were genotyped for the Gly206Ala PSEN1 mutation. Carriers and non-carriers with neurodegenerative disease dementias were compared for demographic, clinical, psychometric, and biomarker variables. Nineteen (12.6%) of 151 unrelated subjects with dementia were discovered to carry the PSEN1 Gly 206Ala mutation. Microsatellite marker genotyping determined a common ancestral haplotype for all carriers. Carriers were all of Puerto Rican heritage with significantly younger age of onset, but otherwise were clinically and neuropsychologically comparable to those of non-carriers with AD. Three subjects had extensive topographic and biochemical biomarker assessments that were also typical of non-carriers with AD. Neuropathological examination in one subject revealed severe, widespread plaque and tangle pathology without other meaningful disease lesions. The PSEN1 Gly206Ala mutation is notably frequent in unrelated Puerto Rican immigrants with dementia in Philadelphia. Considered together with the increased prevalence and mortality of AD reported in Puerto Rico, these high rates may reflect hereditary risk concentrated in the island which warrants further study. PMID:23114514

Cortical feedback signals generalise across different spatial frequencies of feedforward inputs.

PubMed

Revina, Yulia; Petro, Lucy S; Muckli, Lars

2017-09-22

Visual processing in cortex relies on feedback projections contextualising feedforward information flow. Primary visual cortex (V1) has small receptive fields and processes feedforward information at a fine-grained spatial scale, whereas higher visual areas have larger, spatially invariant receptive fields. Therefore, feedback could provide coarse information about the global scene structure or alternatively recover fine-grained structure by targeting small receptive fields in V1. We tested if feedback signals generalise across different spatial frequencies of feedforward inputs, or if they are tuned to the spatial scale of the visual scene. Using a partial occlusion paradigm, functional magnetic resonance imaging (fMRI) and multivoxel pattern analysis (MVPA) we investigated whether feedback to V1 contains coarse or fine-grained information by manipulating the spatial frequency of the scene surround outside an occluded image portion. We show that feedback transmits both coarse and fine-grained information as it carries information about both low (LSF) and high spatial frequencies (HSF). Further, feedback signals containing LSF information are similar to feedback signals containing HSF information, even without a large overlap in spatial frequency bands of the HSF and LSF scenes. Lastly, we found that feedback carries similar information about the spatial frequency band across different scenes. We conclude that cortical feedback signals contain information which generalises across different spatial frequencies of feedforward inputs. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Fringe pattern demodulation with a two-frame digital phase-locked loop algorithm.

PubMed

Gdeisat, Munther A; Burton, David R; Lalor, Michael J

2002-09-10

A novel technique called a two-frame digital phase-locked loop for fringe pattern demodulation is presented. In this scheme, two fringe patterns with different spatial carrier frequencies are grabbed for an object. A digital phase-locked loop algorithm tracks and demodulates the phase difference between both fringe patterns by employing the wrapped phase components of one of the fringe patterns as a reference to demodulate the second fringe pattern. The desired phase information can be extracted from the demodulated phase difference. We tested the algorithm experimentally using real fringe patterns. The technique is shown to be suitable for noncontact measurement of objects with rapid surface variations, and it outperforms the Fourier fringe analysis technique in this aspect. Phase maps produced withthis algorithm are noisy in comparison with phase maps generated with the Fourier fringe analysis technique.

Polariton excitation in epsilon-near-zero slabs: Transient trapping of slow light

NASA Astrophysics Data System (ADS)

Ciattoni, Alessandro; Marini, Andrea; Rizza, Carlo; Scalora, Michael; Biancalana, Fabio

2013-05-01

We numerically investigate the propagation of a spatially localized and quasimonochromatic electromagnetic pulse through a slab with a Lorentz dielectric response in the epsilon-near-zero regime, where the real part of the permittivity vanishes at the pulse carrier frequency. We show that the pulse is able to excite a set of virtual polariton modes supported by the slab, with the excitation undergoing a generally slow damping due to absorption and radiation leakage. Our numerical and analytical approaches indicate that in its transient dynamics the electromagnetic field displays the very same enhancement of the field component perpendicular to the slab, as in the monochromatic regime. The transient trapping is inherently accompanied by a significantly reduced group velocity ensuing from the small dielectric permittivity, thus providing an alternative platform for achieving control and manipulation of slow light.

Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields

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

Noe, II, G. Timothy; Katayama, Ikufumi; Katsutani, Fumiya

Here, we have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers inmore » the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.« less

Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields

DOE PAGES

Noe, II, G. Timothy; Katayama, Ikufumi; Katsutani, Fumiya; ...

2016-12-22

Here, we have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers inmore » the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.« less

Giant Faraday Rotation of High-Order Plasmonic Modes in Graphene-Covered Nanowires.

PubMed

Kuzmin, Dmitry A; Bychkov, Igor V; Shavrov, Vladimir G; Temnov, Vasily V

2016-07-13

Plasmonic Faraday rotation in nanowires manifests itself in the rotation of the spatial intensity distribution of high-order surface plasmon polariton (SPP) modes around the nanowire axis. Here we predict theoretically the giant Faraday rotation for SPPs propagating on graphene-coated magneto-optically active nanowires. Upon the reversal of the external magnetic field pointing along the nanowire axis some high-order plasmonic modes may be rotated by up to ∼100° on the length scale of about 500 nm at mid-infrared frequencies. Tuning the carrier concentration in graphene by chemical doping or gate voltage allows for controlling SPP-properties and notably the rotation angle of high-order azimuthal modes. Our results open the door to novel plasmonic applications ranging from nanowire-based Faraday isolators to the magnetic control in quantum-optical applications.

Auger heating of carriers in {GaAs}/{AlAs} heterostructures

NASA Astrophysics Data System (ADS)

Borri, P.; Ceccherini, S.; Gurioli, M.; Bogani, F.

1997-07-01

The photoluminescence of {GaAs}/{AlAs} multiple quantum wells structures under optical ps excitation is investigated for carrier densities in the range 10 18-4 × 10 19 cm -3 with frequency and time-resolved spectroscopic techniques. The measurements give a direct evidence of the occurrence in the sample of carrier heating. This energy up-conversion gives rise to photoluminescence from the states near the Fermi level whose intensity and time evolution depend on the carrier density in a strongly non-linear way. The observed behaviour can be explained introducing in the carrier dynamics an up-conversion mechanism due to Auger-like processes.

Pulse width modulation inverter with battery charger

DOEpatents

Slicker, James M.

1985-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Pulse width modulation inverter with battery charger

NASA Technical Reports Server (NTRS)

Slicker, James M. (Inventor)

1985-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.

Effects of trap density on drain current LFN and its model development for E-mode GaN MOS-HEMT

NASA Astrophysics Data System (ADS)

Panda, D. K.; Lenka, T. R.

2017-12-01

In this paper the drain current low-frequency noise (LFN) of E-mode GaN MOS-HEMT is investigated for different gate insulators such as SiO2, Al2O3/Ga2O3/GdO3, HfO2/SiO2, La2O3/SiO2 and HfO2 with different trap densities by IFM based TCAD simulation. In order to analyze this an analytical model of drain current low frequency noise is developed. The model is developed by considering 2DEG carrier fluctuations, mobility fluctuations and the effects of 2DEG charge carrier fluctuations on the mobility. In the study of different gate insulators it is observed that carrier fluctuation is the dominant low frequency noise source and the non-uniform exponential distribution is critical to explain LFN behavior, so the analytical model is developed by considering uniform distribution of trap density. The model is validated with available experimental data from literature. The effect of total number of traps and gate length scaling on this low frequency noise due to different gate dielectrics is also investigated.

A protective effect of the BDNF Met/Met genotype in obesity in healthy Caucasian subjects but not in patients with coronary heart disease.

PubMed

Sustar, A; Nikolac Perkovic, M; Nedic Erjavec, G; Svob Strac, D; Pivac, N

2016-08-01

Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor with an important role in the regulation of body weight, body mass index (BMI) and obesity. Increased BMI that leads to obesity is a substantial risk factor for coronary heart disease (CHD). The functional BDNF Val66Met polymorphism (rs6265) has been associated with CHD, obesity and BMI. The aim of the study was to determine the association between BDNF rs6265 polymorphism and CHD and/or BMI in patients with CHD and healthy control subjects. The study included 704 Caucasian subjects: 206 subjects with CHD and 498 healthy control subjects. The BDNF rs6265 genotype frequency was similar in male and female subjects, and there were no differences in the frequency of the BDNF rs6265 genotypes in 206 patients with CHD and in 498 healthy subjects. When study participants were subdivided according to the BMI categories into normal weight, overweight and obese subjects, significantly different BDNF rs6265 genotype frequency was found within healthy subjects, but not within patients with CHD. Healthy subjects, but not patients with CHD, subdivided into carriers of the Met/Met, Met/Val and Val/Val genotype, had different BMI scores. The BDNF rs6265 genotype frequency was similar in male and female subjects, and there were no differences in the frequency of the BDNF rs6265 genotypes in 206 patients with CHD and in 498 healthy subjects. When study participants were subdivided according to the BMI categories into normal weight, overweight and obese subjects, significantly different BDNF rs6265 genotype frequency was found within healthy subjects, but not within patients with CHD. Healthy subjects, but not patients with CHD, subdivided into carriers of the Met/Met, Met/Val and Val/Val genotype, had different BMI scores. BDNF rs6265 polymorphism was not associated with a diagnosis of CHD or with BMI categories among patients with CHD. In contrast, healthy Caucasians, carriers of the BDNF Met/Met genotype, had more frequently normal weight compared to carriers of other BDNF genotypesBDNF rs6265 polymorphism was not associated with a diagnosis of CHD or with BMI categories among patients with CHD. In contrast, healthy Caucasians, carriers of the BDNF Met/Met genotype, had more frequently normal weight compared to carriers of other BDNF genotypes. BDNF rs6265 polymorphism is associated with BMI categories, and the BDNF Met/Met genotype has a protective role in obesity in healthy subjects, while this effect was not present in patients with CHD.

Time delay and distance measurement

NASA Technical Reports Server (NTRS)

Abshire, James B. (Inventor); Sun, Xiaoli (Inventor)

2011-01-01

A method for measuring time delay and distance may include providing an electromagnetic radiation carrier frequency and modulating one or more of amplitude, phase, frequency, polarization, and pointing angle of the carrier frequency with a return to zero (RZ) pseudo random noise (PN) code. The RZ PN code may have a constant bit period and a pulse duration that is less than the bit period. A receiver may detect the electromagnetic radiation and calculate the scattering profile versus time (or range) by computing a cross correlation function between the recorded received signal and a three-state RZ PN code kernel in the receiver. The method also may be used for pulse delay time (i.e., PPM) communications.

A proposed technique for the Venus balloon telemetry and Doppler frequency recovery

NASA Technical Reports Server (NTRS)

Jurgens, R. F.; Divsalar, D.

1985-01-01

A technique is proposed to accurately estimate the Doppler frequency and demodulate the digitally encoded telemetry signal that contains the measurements from balloon instruments. Since the data are prerecorded, one can take advantage of noncausal estimators that are both simpler and more computationally efficient than the usual closed-loop or real-time estimators for signal detection and carrier tracking. Algorithms for carrier frequency estimation subcarrier demodulation, bit and frame synchronization are described. A Viterbi decoder algorithm using a branch indexing technique has been devised to decode constraint length 6, rate 1/2 convolutional code that is being used by the balloon transmitter. These algorithms are memory efficient and can be implemented on microcomputer systems.

Generation of tunable, high repetition rate optical frequency combs using on-chip silicon modulators

NASA Astrophysics Data System (ADS)

Nagarjun, K. P.; Jeyaselvan, Vadivukarassi; Selvaraja, Shankar Kumar; Supradeepa, V. R.

2018-04-01

We experimentally demonstrate tunable, highly-stable frequency combs with high repetition-rates using a single, charge injection based silicon PN modulator. In this work, we demonstrate combs in the C-band with over 8 lines in a 20-dB bandwidth. We demonstrate continuous tuning of the center frequency in the C-band and tuning of the repetition-rate from 7.5GHz to 12.5GHz. We also demonstrate through simulations the potential for bandwidth scaling using an optimized silicon PIN modulator. We find that, the time varying free carrier absorption due to carrier injection, an undesirable effect in data modulators, assists here in enhancing flatness in the generated combs.

Re-entry of the Soyuz MS-08 carrier rocket 25 March 2018

NASA Astrophysics Data System (ADS)

Stomeo, Enrico

2018-03-01

The re-entry of the Soyuz MS-08 carrier rocket on 2018 March 25 could be observed from a large part of the central Mediterranean Sea. The radio station of the Planetarium in Venice was able to record the return into the atmosphere. The radio signal was perceived in Venice from 01h23m52,5s UTC with a frequency of 1431,363 Hz until 01h24m02,0s with a frequency of 805,487 Hz. Considering the recorded frequency variations due to the Doppler effect, it can be deduced that the object was drastically decelerating in those last moments by about 1.3 km/s.

Experimental observation of carrier-envelope-phase effects by multicycle pulses

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

Jha, Pankaj K.; Scully, Marlan O.; Mechanical and Aerospace Engineering and the Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544

2011-03-15

We present an experimental and theoretical study of carrier-envelope-phase (CEP) effects on the population transfer between two bound atomic states interacting with pulses consisting of many cycles. Using intense radio-frequency pulse with Rabi frequency of the order of the atomic transition frequency, we investigate the influence of the CEP on the control of phase-dependent multiphoton transitions between the Zeeman sublevels of the ground state of {sup 87}Rb. Our scheme has no limitation on the duration of the pulses. Extending the CEP control to longer pulses creates interesting possibilities to generate pulses with accuracy that is better than the period ofmore » optical oscillations.« less

Effects of surface nanostructuring and impurity doping on ultrafast carrier dynamics of silicon photovoltaic cells: a pump-probe study

NASA Astrophysics Data System (ADS)

Chen, Tianyu; Nam, Yoon-Ho; Wang, Xinke; Han, Peng; Sun, Wenfeng; Feng, Shengfei; Ye, Jiasheng; Song, Jae-Won; Lee, Jung-Ho; Zhang, Chao; Zhang, Yan

2018-01-01

We present femtosecond optical pump-terahertz probe studies on the ultrafast dynamical processes of photo-generated charge carriers in silicon photovoltaic cells with various nanostructured surfaces and doping densities. The pump-probe measurements provide direct insight on the lifetime of photo-generated carriers, frequency-dependent complex dielectric response along with photoconductivity of silicon photovoltaic cells excited by optical pump pulses. A lifetime of photo-generated carriers of tens of nanosecond is identified from the time-dependent pump-induced attenuation of the terahertz transmission. In addition, we find a large value of the imaginary part of the dielectric function and of the real part of the photoconductivity in silicon photovoltaic cells with micron length nanowires. We attribute these findings to the result of defect-enhanced electron-photon interactions. Moreover, doping densities of phosphorous impurities in silicon photovoltaic cells are also quantified using the Drude-Smith model with our measured frequency-dependent complex photoconductivities.

Efficient algorithms for solution of interference cancellation and channel estimation for mobile OFDM system

NASA Astrophysics Data System (ADS)

Fan, Tong-liang; Wen, Yu-cang; Kadri, Chaibou

Orthogonal frequency-division multiplexing (OFDM) is robust against frequency selective fading because of the increase of the symbol duration. However, the time-varying nature of the channel causes inter-carrier interference (ICI) which destroys the orthogonal of sub-carriers and degrades the system performance severely. To alleviate the detrimental effect of ICI, there is a need for ICI mitigation within one OFDM symbol. We propose an iterative Inter-Carrier Interference (ICI) estimation and cancellation technique for OFDM systems based on regularized constrained total least squares. In the proposed scheme, ICI aren't treated as additional additive white Gaussian noise (AWGN). The effect of Inter-Carrier Interference (ICI) and inter-symbol interference (ISI) on channel estimation is regarded as perturbation of channel. We propose a novel algorithm for channel estimation o based on regularized constrained total least squares. Computer simulations show that significant improvement can be obtained by the proposed scheme in fast fading channels.

Carrier screening of RTEL1 mutations in the Ashkenazi Jewish population.

PubMed

Fedick, A M; Shi, L; Jalas, C; Treff, N R; Ekstein, J; Kornreich, R; Edelmann, L; Mehta, L; Savage, S A

2015-08-01

Hoyeraal-Hreidarsson syndrome (HH) is a clinically severe variant of dyskeratosis congenita (DC), characterized by cerebellar hypoplasia, microcephaly, intrauterine growth retardation, and severe immunodeficiency in addition to features of DC. Germline mutations in the RTEL1 gene have recently been identified as causative of HH. In this study, the carrier frequency for five RTEL1 mutations that occurred in individuals of Ashkenazi Jewish descent was investigated in order to advise on including them in existing clinical mutation panels for this population. Our screening showed that the carrier frequency for c.3791G>A (p.R1264H) was higher than expected, 1% in the Ashkenazi Orthodox and 0.45% in the general Ashkenazi Jewish population. Haplotype analyses suggested the presence of a common founder. We recommend that the c.3791G>A RTEL1 mutation be considered for inclusion in carrier screening panels in the Ashkenazi population. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Thickness-dependent carrier mobility of ambipolar MoTe2: Interplay between interface trap and Coulomb scattering

NASA Astrophysics Data System (ADS)

Ji, Hyunjin; Lee, Gwanmu; Joo, Min-Kyu; Yun, Yoojoo; Yi, Hojoon; Park, Ji-Hoon; Suh, Dongseok; Lim, Seong Chu

2017-05-01

The correlation between the channel thickness and the carrier mobility is investigated by conducting static and low frequency (LF) noise characterization for ambipolar carriers in multilayer MoTe2 transistors. For channel thicknesses in the range of 5-15 nm, both the low-field carrier mobility and the Coulomb-scattering-limited carrier mobility (μC) are maximal at a thickness of ˜10 nm. For LF noise, the interplay of interface trap density (NST), which was minimal at ˜10 nm, and the interfacial Coulomb scattering parameter (αSC), which decreased up to 10 nm and saturated above 10 nm, explained the mobility (μC) peaked near 10 nm by the carrier fluctuation and charge distribution.

Ground Isolation Circuit for Isolating a Transmission Line from Ground Interference

NASA Technical Reports Server (NTRS)

Davidson, Craig A. (Inventor)

1996-01-01

This invention relates generally to a system for isolating ground interference from a transmission line, e.g., a ground isolation circuit for isolating a wideband transmission signal (such as a video signal) from ground by modulating the base signal on a carrier signal to permit the transmission signal to be isolated. In one embodiment, the circuit includes a pair of matched mixer circuits, each of which receives a carrier signal from the same oscillator circuit. The first mixer circuit also receives the baseband signal input, after appropriate conditioning, and modulates the baseband signal onto the carrier signal. In a preferred embodiment the carrier signal has a predetermined frequency which is at least two times the frequency of the baseband signal. The modulated signal (which can comprise an rf signal) is transmitted via an rf transmission line to the second mixer, which demodulates the rf signal to recover the baseband signal. Each port of the mixer connects to an isolation transformer to ensure isolation from ground interference. The circuit is considered to be of commercial value in that it can provide isolation between transmitting and receiving circuits, e.g., ground isolation for television circuits or high frequency transmitters, without the need for video transformers or optical isolators, thereby reducing the complexity, power consumption, and weight of the system.

Expansion of epicyclic gear dynamic analysis program

NASA Technical Reports Server (NTRS)

Boyd, Linda Smith; Pike, James A.

1987-01-01

The multiple mesh/single stage dynamics program is a gear tooth analysis program which determines detailed geometry, dynamic loads, stresses, and surface damage factors. The program can analyze a variety of both epicyclic and single mesh systems with spur or helical gear teeth including internal, external, and buttress tooth forms. The modifications refine the options for the flexible carrier and flexible ring gear rim and adds three options: a floating Sun gear option; a natural frequency option; and a finite element compliance formulation for helical gear teeth. The option for a floating Sun incorporates two additional degrees of freedom at the Sun center. The natural frequency option evaluates the frequencies of planetary, star, or differential systems as well as the effect of additional springs at the Sun center and those due to a flexible carrier and/or ring gear rim. The helical tooth pair finite element calculated compliance is obtained from an automated element breakup of the helical teeth and then is used with the basic gear dynamic solution and stress postprocessing routines. The flexible carrier or ring gear rim option for planetary and star spur gear systems allows the output torque per carrier and ring gear rim segment to vary based on the dynamic response of the entire system, while the total output torque remains constant.

47 CFR 73.682 - TV transmission standards.

Code of Federal Regulations, 2012 CFR

2012-10-01

....682 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO... frequency shall be nominally 1.25 MHz above the lower boundary of the channel. (3) The aural center frequency shall be 4.5 MHz higher than the visual carrier frequency. (4) The visual transmission amplitude...

47 CFR 73.682 - TV transmission standards.

Code of Federal Regulations, 2011 CFR

2011-10-01

....682 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO... frequency shall be nominally 1.25 MHz above the lower boundary of the channel. (3) The aural center frequency shall be 4.5 MHz higher than the visual carrier frequency. (4) The visual transmission amplitude...

47 CFR 73.682 - TV transmission standards.

Code of Federal Regulations, 2013 CFR

2013-10-01

....682 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO... frequency shall be nominally 1.25 MHz above the lower boundary of the channel. (3) The aural center frequency shall be 4.5 MHz higher than the visual carrier frequency. (4) The visual transmission amplitude...

47 CFR 73.682 - TV transmission standards.

Code of Federal Regulations, 2014 CFR

2014-10-01

....682 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO... frequency shall be nominally 1.25 MHz above the lower boundary of the channel. (3) The aural center frequency shall be 4.5 MHz higher than the visual carrier frequency. (4) The visual transmission amplitude...

47 CFR 73.682 - TV transmission standards.

Code of Federal Regulations, 2010 CFR

2010-10-01

....682 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO... frequency shall be nominally 1.25 MHz above the lower boundary of the channel. (3) The aural center frequency shall be 4.5 MHz higher than the visual carrier frequency. (4) The visual transmission amplitude...

Ultra-wideband microwave photonic frequency downconverter based on carrier-suppressed single-sideband modulation

NASA Astrophysics Data System (ADS)

Wang, Yunxin; Li, Jingnan; Wang, Dayong; Zhou, Tao; Xu, Jiahao; Zhong, Xin; Yang, Dengcai; Rong, Lu

2018-03-01

An ultra-wideband microwave photonic frequency downconverter is proposed based on carrier-suppressed single-sideband (CS-SSB) modulation. A radio frequency (RF) signal and a local oscillator (LO) signal are combined to drive a dual-parallel Mach-Zehnder modulator (DPMZM) through the electrical 90°hybrid coupler. To break through the bandwidth limit, an optical bandpass filter (OBPF) is applied simultaneously. Then a photodetector (PD) after OBPF is used to obtain intermediate frequency (IF) signal. Experimental results demonstrate that the proposed frequency downconverter can generate the CS-SSB modulation signal from 2 to 40 GHz in optical spectrum. All the mixing spurs are completely suppressed under the noise floor in electrical spectrum, and the output IF signal possesses high purity with a suppression ratio of the undesired signals (≥40 dB). Furthermore, the multi-octave downconversion can also be implemented to satisfy the bandwidth requirement of multi-channel communication. The proposed frequency downconverter supplies an ultra-wideband and high-purity alternative for the signal processing in microwave photonic applications.

Tunneling-assisted transport of carriers through heterojunctions.

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

Wampler, William R.; Myers, Samuel M.; Modine, Normand A.

The formulation of carrier transport through heterojunctions by tunneling and thermionic emission is derived from first principles. The treatment of tunneling is discussed at three levels of approximation: numerical solution of the one-band envelope equation for an arbitrarily specified potential profile; the WKB approximation for an arbitrary potential; and, an analytic formulation assuming constant internal field. The effects of spatially varying carrier chemical potentials over tunneling distances are included. Illustrative computational results are presented. The described approach is used in exploratory physics models of irradiated heterojunction bipolar transistors within Sandia's QASPR program.

Is attention based on spatial contextual memory preferentially guided by low spatial frequency signals?

PubMed

Patai, Eva Zita; Buckley, Alice; Nobre, Anna Christina

2013-01-01

A popular model of visual perception states that coarse information (carried by low spatial frequencies) along the dorsal stream is rapidly transmitted to prefrontal and medial temporal areas, activating contextual information from memory, which can in turn constrain detailed input carried by high spatial frequencies arriving at a slower rate along the ventral visual stream, thus facilitating the processing of ambiguous visual stimuli. We were interested in testing whether this model contributes to memory-guided orienting of attention. In particular, we asked whether global, low-spatial frequency (LSF) inputs play a dominant role in triggering contextual memories in order to facilitate the processing of the upcoming target stimulus. We explored this question over four experiments. The first experiment replicated the LSF advantage reported in perceptual discrimination tasks by showing that participants were faster and more accurate at matching a low spatial frequency version of a scene, compared to a high spatial frequency version, to its original counterpart in a forced-choice task. The subsequent three experiments tested the relative contributions of low versus high spatial frequencies during memory-guided covert spatial attention orienting tasks. Replicating the effects of memory-guided attention, pre-exposure to scenes associated with specific spatial memories for target locations (memory cues) led to higher perceptual discrimination and faster response times to identify targets embedded in the scenes. However, either high or low spatial frequency cues were equally effective; LSF signals did not selectively or preferentially contribute to the memory-driven attention benefits to performance. Our results challenge a generalized model that LSFs activate contextual memories, which in turn bias attention and facilitate perception.

Is Attention Based on Spatial Contextual Memory Preferentially Guided by Low Spatial Frequency Signals?

PubMed Central

Patai, Eva Zita; Buckley, Alice; Nobre, Anna Christina

2013-01-01

A popular model of visual perception states that coarse information (carried by low spatial frequencies) along the dorsal stream is rapidly transmitted to prefrontal and medial temporal areas, activating contextual information from memory, which can in turn constrain detailed input carried by high spatial frequencies arriving at a slower rate along the ventral visual stream, thus facilitating the processing of ambiguous visual stimuli. We were interested in testing whether this model contributes to memory-guided orienting of attention. In particular, we asked whether global, low-spatial frequency (LSF) inputs play a dominant role in triggering contextual memories in order to facilitate the processing of the upcoming target stimulus. We explored this question over four experiments. The first experiment replicated the LSF advantage reported in perceptual discrimination tasks by showing that participants were faster and more accurate at matching a low spatial frequency version of a scene, compared to a high spatial frequency version, to its original counterpart in a forced-choice task. The subsequent three experiments tested the relative contributions of low versus high spatial frequencies during memory-guided covert spatial attention orienting tasks. Replicating the effects of memory-guided attention, pre-exposure to scenes associated with specific spatial memories for target locations (memory cues) led to higher perceptual discrimination and faster response times to identify targets embedded in the scenes. However, either high or low spatial frequency cues were equally effective; LSF signals did not selectively or preferentially contribute to the memory-driven attention benefits to performance. Our results challenge a generalized model that LSFs activate contextual memories, which in turn bias attention and facilitate perception. PMID:23776509

Bombarding Cancer: Biolistic Delivery of therapeutics using Porous Si Carriers

PubMed Central

Zilony, Neta; Tzur-Balter, Adi; Segal, Ester; Shefi, Orit

2013-01-01

A new paradigm for an effective delivery of therapeutics into cancer cells is presented. Degradable porous silicon carriers, which are tailored to carry and release a model anti-cancer drug, are biolistically bombarded into in-vitro cancerous targets. We demonstrate the ability to launch these highly porous microparticles by a pneumatic capillary gene gun, which is conventionally used to deliver cargos by heavy metal carriers. By optimizing the gun parameters e.g., the accelerating gas pressure, we have successfully delivered the porous carriers, to reach deep targets and to cross a skin barrier in a highly spatial resolution. Our study reveals significant cytotoxicity towards the target human breast carcinoma cells following the delivery of drug-loaded carriers, while administrating empty particles results in no effect on cell viability. The unique combination of biolistics with the temporal control of payload release from porous carriers presents a powerful and non-conventional platform for designing new therapeutic strategies. PMID:23975675

Circular carrier squeezing interferometry: Suppressing phase shift error in simultaneous phase-shifting point-diffraction interferometer

NASA Astrophysics Data System (ADS)

Zheng, Donghui; Chen, Lei; Li, Jinpeng; Sun, Qinyuan; Zhu, Wenhua; Anderson, James; Zhao, Jian; Schülzgen, Axel

2018-03-01

Circular carrier squeezing interferometry (CCSI) is proposed and applied to suppress phase shift error in simultaneous phase-shifting point-diffraction interferometer (SPSPDI). By introducing a defocus, four phase-shifting point-diffraction interferograms with circular carrier are acquired, and then converted into linear carrier interferograms by a coordinate transform. Rearranging the transformed interferograms into a spatial-temporal fringe (STF), so the error lobe will be separated from the phase lobe in the Fourier spectrum of the STF, and filtering the phase lobe to calculate the extended phase, when combined with the corresponding inverse coordinate transform, exactly retrieves the initial phase. Both simulations and experiments validate the ability of CCSI to suppress the ripple error generated by the phase shift error. Compared with carrier squeezing interferometry (CSI), CCSI is effective on some occasions in which a linear carrier is difficult to introduce, and with the added benefit of eliminating retrace error.

Electric properties and carrier multiplication in breakdown sites in multi-crystalline silicon solar cells

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

Schneemann, Matthias; Carius, Reinhard; Rau, Uwe

2015-05-28

This paper studies the effective electrical size and carrier multiplication of breakdown sites in multi-crystalline silicon solar cells. The local series resistance limits the current of each breakdown site and is thereby linearizing the current-voltage characteristic. This fact allows the estimation of the effective electrical diameters to be as low as 100 nm. Using a laser beam induced current (LBIC) measurement with a high spatial resolution, we find carrier multiplication factors on the order of 30 (Zener-type breakdown) and 100 (avalanche breakdown) as new lower limits. Hence, we prove that also the so-called Zener-type breakdown is followed by avalanche multiplication. Wemore » explain that previous measurements of the carrier multiplication using thermography yield results higher than unity, only if the spatial defect density is high enough, and the illumination intensity is lower than what was used for the LBIC method. The individual series resistances of the breakdown sites limit the current through these breakdown sites. Therefore, the measured multiplication factors depend on the applied voltage as well as on the injected photocurrent. Both dependencies are successfully simulated using a series-resistance-limited diode model.« less

Channel Equalization for Single Carrier MIMO Underwater Acoustic Communications

DTIC Science & Technology

2010-01-01

II Tx 1 Tx 2 Symbol mapping s1 s2 x1 x2 sa Figure 2: Signalling at the transmitter in Makai05 experiment. fc = 32 kHz and the symbol interval was...frequency was fc = 37.5 kHz and the symbol interval was 0.05ms. The occupied channel bandwidth was fb = 25 kHz due to a pulse shaping filter with roll...water. QPSK modulation was used with a symbol rate of 4 ksps. The carrier frequency was fc = 17 kHz. The structure of the transmission packet is

Flexible, polymer gated, AC-driven organic electroluminescence devices

NASA Astrophysics Data System (ADS)

Xu, Junwei; Carroll, David L.

2017-08-01

Comparing rigid inorganic layer, polymeric semiconducting gate layer exhibits superior flexibility as well as efficient carrier manipulation in high frequency AC cycles. Mechanism of the carrier manipulation at the gate in forward and reversed bias of AC cycle is studied. The flexible PET-based AC-OEL device with poly[(9,9-bis(3'-((N,N-dimethyl)-Nethylammonium)- propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN-Br) gate shows a stable electroluminescent performance in frequency sweep with a color rendering index (CRI) over 81 at 2800K color temperature.

Comparison of FDMA and CDMA for second generation land-mobile satellite communications

NASA Technical Reports Server (NTRS)

Yongacoglu, A.; Lyons, R. G.; Mazur, B. A.

1990-01-01

Code Division Multiple Access (CDMA) and Frequency Division Multiple Access (FDMA) (both analog and digital) systems capacities are compared on the basis of identical link availabilities and physical propagation models. Parameters are optimized for a bandwidth limited, multibeam environment. For CDMA, the benefits of voice activated carriers, antenna discrimination, polarization reuse, return link power control and multipath suppression are included in the analysis. For FDMA, the advantages of bandwidth efficient modulation/coding combinations, voice activated carriers, polarization reuse, beam placement, and frequency staggering were taken into account.

Terahertz Oscillations of Hot Electrons in Graphene

DTIC Science & Technology

2015-01-01

half the frequency ?F = 2?eF/~?OP , where 2?/?F is the time taken for carriers to accelerate ballistically to the optic phonon...resonance. Such resonance occurs at about half the frequency ωF = 2πeF/~ωOP , where 2π/ωF is the time taken for carriers to accelerate ballistically to the ... The current density on the plane is given by, Jx(t) = −4evF ∑ ~k f(~k, t) cos(φ), (2.16) where φ is the angle between ~k and the kx axis. Figure

Prevalence of combinatorial CYP2C9 and VKORC1 genotypes in Puerto Ricans: implications for warfarin management in Hispanics.

PubMed

Duconge, Jorge; Cadilla, Carmen L; Windemuth, Andreas; Kocherla, Mohan; Gorowski, Krystyna; Seip, Richard L; Bogaard, Kali; Renta, Jessica Y; Piovanetti, Paola; D'Agostino, Darrin; Santiago-Borrero, Pedro J; Ruaño, Gualberto

2009-01-01

Polymorphisms in the cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) genes significantly alter the effective warfarin dose. We determined the frequencies of alleles, single carriers, and double carriers of single nucleotide polymorphisms (SNPs) in the CYP2C9 and VKORC1 genes in a Puerto Rican cohort and gauged the impact of these polymorphisms on warfarin dosage using a published algorithm. A total of 92 DNA samples were genotyped using Luminex x-MAP technology. The polymorphism frequencies were 6.52%, 5.43% and 28.8% for CYP2C9 *2, *3 and VKORC1-1639 C>A polymorphisms, respectively. The prevalence of combinatorial genotypes was 16% for carriers of both the CYP2C9 and VKORC1 polymorphisms, 9% for carriers of CYP2C9 polymorphisms, 35% for carriers of the VKORC1 polymorphism, and the remaining 40% were non-carriers for either gene. Based on a published warfarin dosing algorithm, single, double and triple carriers of functionally deficient polymorphisms predict reductions of 1.0-1.6, 2.0-2.9, and 2.9-3.7 mg/day, respectively, in warfarin dose. Overall, 60% of the population carried at least a single polymorphism predicting deficient warfarin metabolism or responsiveness and 13% were double carriers with polymorphisms in both genes studied. Combinatorial genotyping of CYP2C9 and VKORC1 can allow for individualized dosing of warfarin among patients with gene polymorphisms, potentially reducing the risk of stroke or bleeding.

Acoustic radiation force control: Pulsating spherical carriers.

PubMed

Rajabi, Majid; Mojahed, Alireza

2018-02-01

The interaction between harmonic plane progressive acoustic beams and a pulsating spherical radiator is studied. The acoustic radiation force function exerted on the spherical body is derived as a function of the incident wave pressure and the monopole vibration characteristics (i.e., amplitude and phase) of the body. Two distinct strategies are presented in order to alter the radiation force effects (i.e., pushing and pulling states) by changing its magnitude and direction. In the first strategy, an incident wave field with known amplitude and phase is considered. It is analytically shown that the zero- radiation force state (i.e., radiation force function cancellation) is achievable for specific pulsation characteristics belong to a frequency-dependent straight line equation in the plane of real-imaginary components (i.e., Nyquist Plane) of prescribed surface displacement. It is illustrated that these characteristic lines divide the mentioned displacement plane into two regions of positive (i.e., pushing) and negative (i.e., pulling) radiation forces. In the second strategy, the zero, negative and positive states of radiation force are obtained through adjusting the incident wave field characteristics (i.e., amplitude and phase) which insonifies the radiator with prescribed pulsation characteristics. It is proved that zero radiation force state occurs for incident wave pressure characteristics belong to specific frequency-dependent circles in Nyquist plane of incident wave pressure. These characteristic circles divide the Nyquist plane into two distinct regions corresponding to positive (out of circles) and negative (in the circles) values of radiation force function. It is analytically shown that the maximum amplitude of negative radiation force is exactly equal to the amplitude of the (positive) radiation force exerted upon the sphere in the passive state, by the same incident field. The developed concepts are much more deepened by considering the required power supply for distinct cases of zero, negative and positive radiation force states along with the frequency dependent asymmetry index. In addition, considering the effect of phase difference between the incident wave field and the pulsating object, and its possible variation with respect to spatial position of object, some practical points about the spatial average of generated radiation force, the optimal state of operation, the stability of zero radiation force states and the possibly of precise motion control are discussed. This work would extend the novel concept of smart carriers to and may be helpful for robust single-beam acoustic handling techniques. Furthermore, the shown capability of precise motion control may be considered as a new way toward smart acoustic driven micro-mechanisms and micro-machines. Copyright © 2017 Elsevier B.V. All rights reserved.

Model of human visual-motion sensing

NASA Technical Reports Server (NTRS)

Watson, A. B.; Ahumada, A. J., Jr.

1985-01-01

A model of how humans sense the velocity of moving images is proposed. The model exploits constraints provided by human psychophysics, notably that motion-sensing elements appear tuned for two-dimensional spatial frequency, and by the frequency spectrum of a moving image, namely, that its support lies in the plane in which the temporal frequency equals the dot product of the spatial frequency and the image velocity. The first stage of the model is a set of spatial-frequency-tuned, direction-selective linear sensors. The temporal frequency of the response of each sensor is shown to encode the component of the image velocity in the sensor direction. At the second stage, these components are resolved in order to measure the velocity of image motion at each of a number of spatial locations and spatial frequencies. The model has been applied to several illustrative examples, including apparent motion, coherent gratings, and natural image sequences. The model agrees qualitatively with human perception.

47 CFR 90.207 - Types of emissions.

Code of Federal Regulations, 2010 CFR

2010-10-01

... under this part, see § 2.201 of this chapter. (1) The first symbol indicates the type of modulation on the transmitter carrier. A—Amplitude modulation, double sideband with identical information on each sideband. F—Frequency modulation. G—Phase modulation. J—Single sideband with suppressed carrier. P...

Real time quantitative imaging for semiconductor crystal growth, control and characterization

NASA Technical Reports Server (NTRS)

Wargo, Michael J.

1991-01-01

A quantitative real time image processing system has been developed which can be software-reconfigured for semiconductor processing and characterization tasks. In thermal imager mode, 2D temperature distributions of semiconductor melt surfaces (900-1600 C) can be obtained with temperature and spatial resolutions better than 0.5 C and 0.5 mm, respectively, as demonstrated by analysis of melt surface thermal distributions. Temporal and spatial image processing techniques and multitasking computational capabilities convert such thermal imaging into a multimode sensor for crystal growth control. A second configuration of the image processing engine in conjunction with bright and dark field transmission optics is used to nonintrusively determine the microdistribution of free charge carriers and submicron sized crystalline defects in semiconductors. The IR absorption characteristics of wafers are determined with 10-micron spatial resolution and, after calibration, are converted into charge carrier density.

A recovery principle provides insight into auxin pattern control in the Arabidopsis root

PubMed Central

Moore, Simon; Liu, Junli; Zhang, Xiaoxian; Lindsey, Keith

2017-01-01

Regulated auxin patterning provides a key mechanism for controlling root growth and development. We have developed a data-driven mechanistic model using realistic root geometry and formulated a principle to theoretically investigate quantitative auxin pattern recovery following auxin transport perturbation. This principle reveals that auxin patterning is potentially controlled by multiple combinations of interlinked levels and localisation of influx and efflux carriers. We demonstrate that (1) when efflux carriers maintain polarity but change levels, maintaining the same auxin pattern requires non-uniform and polar distribution of influx carriers; (2) the emergence of the same auxin pattern, from different levels of influx carriers with the same nonpolar localisation, requires simultaneous modulation of efflux carrier level and polarity; and (3) multiple patterns of influx and efflux carriers for maintaining an auxin pattern do not have spatially proportional correlation. This reveals that auxin pattern formation requires coordination between influx and efflux carriers. We further show that the model makes various predictions that can be experimentally validated. PMID:28220889

Generation of narrowband, high-intensity, carrier-envelope phase-stable pulses tunable between 4 and 18  THz.

PubMed

Liu, B; Bromberger, H; Cartella, A; Gebert, T; Först, M; Cavalleri, A

2017-01-01

We report on the generation of high-energy (1.9 μJ) far-infrared pulses tunable between 4 and 18 THz frequency. Emphasis is placed on tunability and on minimizing the bandwidth of these pulses to less than 1 THz, as achieved by difference-frequency mixing of two linearly chirped near-infrared pulses in the organic nonlinear crystal DSTMS. As the two near-infrared pulses are derived from amplification of the same white light continuum, their carrier envelope phase fluctuations are mutually correlated, and hence the difference-frequency THz field exhibits absolute phase stability. This source opens up new possibilities for the control of condensed matter and chemical systems by selective excitation of low-energy modes in a frequency range that has, to date, been difficult to access.

Kilohertz and Low-Frequency Electrical Stimulation With the Same Pulse Duration Have Similar Efficiency for Inducing Isometric Knee Extension Torque and Discomfort.

PubMed

Medeiros, Flávia Vanessa; Bottaro, Martim; Vieira, Amilton; Lucas, Tiago Pires; Modesto, Karenina Arrais; Bo, Antonio Padilha L; Cipriano, Gerson; Babault, Nicolas; Durigan, João Luiz Quagliotti

2017-06-01

To test the hypotheses that, as compared with pulsed current with the same pulse duration, kilohertz frequency alternating current would not differ in terms of evoked-torque production and perceived discomfort, and as a result, it would show the same current efficiency. A repeated-measures design with 4 stimuli presented in random order was used to test 25 women: (1) 500-microsecond pulse duration, (2) 250-microsecond pulse duration, (3) 500-microsecond pulse duration and low carrier frequency (1 kHz), (4) 250-microsecond pulse duration and high carrier frequency (4 kHz). Isometric peak torque of quadriceps muscle was measured using an isokinetic dynamometer. Discomfort was measured using a visual analog scale. Currents with long pulse durations induced approximately 21% higher evoked torque than short pulse durations. In addition, currents with 500 microseconds delivered greater amounts of charge than stimulation patterns using 250-microsecond pulse durations (P < 0.05). All currents presented similar discomfort. There was no difference on stimulation efficiency with the same pulse duration. Both kilohertz frequency alternating current and pulsed current, with the same pulse duration, have similar efficiency for inducing isometric knee extension torque and discomfort. However, neuromuscular electrical stimulation (NMES) with longer pulse duration induces higher NMES-evoked torque, regardless of the carrier frequency. Pulse duration is an important variable that should receive more attention for an optimal application of NMES in clinical settings.

47 CFR 51.319 - Specific unbundling requirements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... Triennial Review Order, the high frequency portion of a copper loop shall no longer be required to be... the requesting telecommunications carrier using the high frequency portion of the loop. The high... the demarcation point at the end-user customer premises, and includes the high frequency portion of...

47 CFR 51.319 - Specific unbundling requirements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... Triennial Review Order, the high frequency portion of a copper loop shall no longer be required to be... the requesting telecommunications carrier using the high frequency portion of the loop. The high... the demarcation point at the end-user customer premises, and includes the high frequency portion of...

47 CFR 51.319 - Specific unbundling requirements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... Triennial Review Order, the high frequency portion of a copper loop shall no longer be required to be... the requesting telecommunications carrier using the high frequency portion of the loop. The high... the demarcation point at the end-user customer premises, and includes the high frequency portion of...

47 CFR 2.1515 - Spectral measurements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... applicable, change the type of modulation of the EPIRB and record the shift in carrier frequency as observed... Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL... radiated signal from the EPIRB. A signal generator and frequency counter capable of operating at 121.5 and...

47 CFR 74.401 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-10-01

... controlled carrier) during one radio frequency cycle under conditions of no modulation. Mean power. The power... long compared with the period of the lowest frequency encountered in the modulation. A time of 1/10... bandwidth. Occupied bandwidth. The frequency bandwidth such that, below its lower and above its upper...

Spatial Release From Masking in Simulated Cochlear Implant Users With and Without Access to Low-Frequency Acoustic Hearing

PubMed Central

Dietz, Mathias; Hohmann, Volker; Jürgens, Tim

2015-01-01

For normal-hearing listeners, speech intelligibility improves if speech and noise are spatially separated. While this spatial release from masking has already been quantified in normal-hearing listeners in many studies, it is less clear how spatial release from masking changes in cochlear implant listeners with and without access to low-frequency acoustic hearing. Spatial release from masking depends on differences in access to speech cues due to hearing status and hearing device. To investigate the influence of these factors on speech intelligibility, the present study measured speech reception thresholds in spatially separated speech and noise for 10 different listener types. A vocoder was used to simulate cochlear implant processing and low-frequency filtering was used to simulate residual low-frequency hearing. These forms of processing were combined to simulate cochlear implant listening, listening based on low-frequency residual hearing, and combinations thereof. Simulated cochlear implant users with additional low-frequency acoustic hearing showed better speech intelligibility in noise than simulated cochlear implant users without acoustic hearing and had access to more spatial speech cues (e.g., higher binaural squelch). Cochlear implant listener types showed higher spatial release from masking with bilateral access to low-frequency acoustic hearing than without. A binaural speech intelligibility model with normal binaural processing showed overall good agreement with measured speech reception thresholds, spatial release from masking, and spatial speech cues. This indicates that differences in speech cues available to listener types are sufficient to explain the changes of spatial release from masking across these simulated listener types. PMID:26721918

Remote beating of parallel or orthogonally polarized dual-wavelength optical carriers for 5G millimeter-wave radio-over-fiber link.

PubMed

Wang, Huai-Yung; Chi, Yu-Chieh; Lin, Gong-Ru

2016-08-08

A novel millimeter-wave radio over fiber (MMW-RoF) link at carrier frequency of 35-GHz is proposed with the use of remotely beating MMW generation from reference master and injected slave colorless laser diode (LD) carriers at orthogonally polarized dual-wavelength injection-locking. The slave colorless LD supports lasing one of the dual-wavelength master modes with orthogonal polarizations, which facilitates the single-mode direct modulation of the quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data. Such an injected single-carrier encoding and coupled dual-carrier transmission with orthogonal polarization effectively suppresses the cross-heterodyne mode-beating intensity noise, the nonlinear modulation (NLM) and four-wave mixing (FWM) sidemodes during injection locking and fiber transmission. In 25-km single-mode fiber (SMF) based wireline system, the dual-carrier under single-mode encoding provides baseband 24-Gbit/s 64-QAM OFDM transmission with an error vector magnitude (EVM) of 8.8%, a bit error rate (BER) of 3.7 × 10^-3, a power penalty of <1.5 dB. After remotely self-beating for wireless transmission, the beat MMW carrier at 35 GHz can deliver the passband 16-QAM OFDM at 4 Gbit/s to show corresponding EVM and BER of 15.5% and 1.4 × 10^-3, respectively, after 25-km SMF and 1.6-m free-space transmission.

Trinary Encoder, Decoder, Multiplexer and Demultiplexer Using Savart Plate and Spatial Light Modulator

NASA Astrophysics Data System (ADS)

Ghosh, Amal K.; Singha Roy, Souradip; Mandal, Sudipta; Basuray, Amitabha

Optoelectronic processors have already been developed with the strong potentiality of optics in information and data processing. Encoder, Decoder, Multiplexers and Demultiplexers are the most important components in modern system designs and in communications. We have implemented the same using trinary logic gates with signed magnitude defined as Modified Trinary Number (MTN). The Spatial Light Modulator (SLM) based optoelectronic circuit is suitable for high speed data processing and communications using photon as carrier. We also presented here a possible method of implementing the same using light with photon as carrier of information. The importance of the method is that all the basic gates needed may be fabricated based on basic building block.

Ultrafast Microscopy of Energy and Charge Transport

NASA Astrophysics Data System (ADS)

Huang, Libai

The frontier in solar energy research now lies in learning how to integrate functional entities across multiple length scales to create optimal devices. Advancing the field requires transformative experimental tools that probe energy transfer processes from the nano to the meso lengthscales. To address this challenge, we aim to understand multi-scale energy transport across both multiple length and time scales, coupling simultaneous high spatial, structural, and temporal resolution. In my talk, I will focus on our recent progress on visualization of exciton and charge transport in solar energy harvesting materials from the nano to mesoscale employing ultrafast optical nanoscopy. With approaches that combine spatial and temporal resolutions, we have recently revealed a new singlet-mediated triplet transport mechanism in certain singlet fission materials. This work demonstrates a new triplet exciton transport mechanism leading to favorable long-range triplet exciton diffusion on the picosecond and nanosecond timescales for solar cell applications. We have also performed a direct measurement of carrier transport in space and in time by mapping carrier density with simultaneous ultrafast time resolution and 50 nm spatial precision in perovskite thin films using transient absorption microscopy. These results directly visualize long-range carrier transport of 220nm in 2 ns for solution-processed polycrystalline CH3NH3PbI3 thin films. The spatially and temporally resolved measurements reported here underscore the importance of the local morphology and establish an important first step towards discerning the underlying transport properties of perovskite materials.

‘Energy landscapes’: Meeting energy demands and human aspirations

PubMed Central

Blaschke, Thomas; Biberacher, Markus; Gadocha, Sabine; Schardinger, Ingrid

2013-01-01

Renewable energy will play a crucial role in the future society of the 21st century. The various renewable energy sources need to be balanced and their use carefully planned since they are characterized by high temporal and spatial variability that will pose challenges to maintaining a well balanced supply and to the stability of the grid. This article examines the ways that future ‘energy landscapes’ can be modelled in time and space. Biomass needs a great deal of space per unit of energy produced but it is an energy carrier that may be strategically useful in circumstances where other renewable energy carriers are likely to deliver less. A critical question considered in this article is whether a massive expansion in the use of biomass will allow us to construct future scenarios while repositioning the ‘energy landscape’ as an object of study. A second important issue is the utilization of heat from biomass energy plants. Biomass energy also has a larger spatial footprint than other carriers such as, for example, solar energy. This article seeks to provide a bridge between energy modelling and spatial planning while integrating research and techniques in energy modelling with Geographic Information Science. This encompasses GIS, remote sensing, spatial disaggregation techniques and geovisualization. Several case studies in Austria and Germany demonstrate a top-down methodology and some results while stepwise calculating potentials from theoretical to technically feasible potentials and setting the scene for the definition of economic potentials based on scenarios and assumptions. PMID:26109751

Lexical frequency and acoustic reduction in spoken Dutch

NASA Astrophysics Data System (ADS)

Pluymaekers, Mark; Ernestus, Mirjam; Baayen, R. Harald

2005-10-01

This study investigates the effects of lexical frequency on the durational reduction of morphologically complex words in spoken Dutch. The hypothesis that high-frequency words are more reduced than low-frequency words was tested by comparing the durations of affixes occurring in different carrier words. Four Dutch affixes were investigated, each occurring in a large number of words with different frequencies. The materials came from a large database of face-to-face conversations. For each word containing a target affix, one token was randomly selected for acoustic analysis. Measurements were made of the duration of the affix as a whole and the durations of the individual segments in the affix. For three of the four affixes, a higher frequency of the carrier word led to shorter realizations of the affix as a whole, individual segments in the affix, or both. Other relevant factors were the sex and age of the speaker, segmental context, and speech rate. To accommodate for these findings, models of speech production should allow word frequency to affect the acoustic realizations of lower-level units, such as individual speech sounds occurring in affixes.

Influence of spherical aberration, stimulus spatial frequency, and pupil apodisation on subjective refractions

PubMed Central

Bradley, Arthur; Xu, Renfeng; Thibos, Larry; Marin, Gildas; Hernandez, Martha

2014-01-01

Purpose To test competing hypotheses (Stiles Crawford pupil apodising or superior imaging of high spatial frequencies by the central pupil) for the pupil size independence of subjective refractions in the presence of primary spherical aberration. Methods Subjective refractions were obtained with a variety of test stimuli (high contrast letters, urban cityscape, high and low spatial frequency gratings) while modulating pupil diameter, levels of primary spherical aberration and pupil apodisation. Subjective refractions were also obtained with low-pass and high-pass stimuli and using “darker” and “sharper” subjective criteria. Results Subjective refractions for stimuli containing high spatial frequencies focus a near paraxial region of the pupil and are affected only slightly by level of Seidel spherical aberration, degree of pupil apodisation and pupil diameter, and generally focused a radius of about 1 to 1.5 mm from the pupil centre. Low spatial frequency refractions focus a marginal region of the pupil, and are significantly affected by level of spherical aberration, amount of pupil apodisation, and pupil size. Clinical refractions that employ the “darker” or “sharper” subjective criteria bias the patient to use lower or higher spatial frequencies respectively. Conclusions In the presence of significant levels of spherical aberration, the pupil size independence of subjective refractions occurs with or without Stiles Crawford apodisation for refractions that optimise high spatial frequency content in the image. If low spatial frequencies are optimised by a subjective refraction, spherical refractive error varies with spherical aberration, pupil size, and level of apodisation. As light levels drop from photopic to scotopic, therefore, we expect a shift from pupil size independent to pupil size dependent subjective refractions. Emphasising a “sharper” criterion during subjective refractions will improve image quality for high spatial frequencies and generate pupil size independent refractions. PMID:24397356

Transport limited interfacial carrier relaxation in a double-layer device investigated by time-resolved second harmonic generation and impedance spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Le; Taguchi, Dai; Li, Jun; Manaka, Takaaki; Iwamoto, Mitsumasa

2011-02-01

The interfacial carrier relaxation in an indium tin oxide/polyimide/pentacene/Au double-layer device was studied in both time and frequency domains by using time-resolved second harmonic generation (TR-SHG) and impedance spectroscopy (IS), respectively. Although both hole and electron injection into the pentacene layer and their accumulation at the pentacene/polyimide interface were revealed in TR-SHG, it was only observed in IS under the hole injection condition. The "contradiction" between the two methods for the same carrier relaxation process was explained on the basis of a model, transport limited interfacial carrier relaxation, in which the quasistatic state governs the one-directional carrier transport.

Carrier-phase time transfer.

PubMed

Larson, K M; Levine, J

1999-01-01

We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code, as is done in current GPS-based time-transfer systems. Atomic clocks were connected to geodetic GPS receivers; we then used the GPS carrier-phase observations to estimate relative clock behavior at 6-minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common view time transfer and agrees, within the experimental uncertainty, with two-way satellite time-transfer measurements for a 2400 km baseline. GPS carrier-phase time transfer has a stability of 100 ps, which translates into a frequency uncertainty of about two parts in 10(-15) for an average time of 1 day.

Self-consistent modeling of electrochemical strain microscopy of solid electrolytes

DOE PAGES

Tselev, Alexander; Morozovska, Anna N.; Udod, Alexei; ...

2014-10-10

Electrochemical strain microscopy (ESM) employs a strong electromechanical coupling in solid ionic conductors to map ionic transport and electrochemical processes with nanometer-scale spatial resolution. To elucidate the mechanisms of the ESM image formation, we performed self-consistent numerical modeling of the electromechanical response in solid electrolytes under the probe tip in a linear, small-signal regime using the Boltzmann–Planck–Nernst–Einstein theory and Vegard's law while taking account of the electromigration and diffusion. We identified the characteristic time scales involved in the formation of the ESM response and found that the dynamics of the charge carriers in the tip-electrolyte system with blocking interfaces canmore » be described as charging of the diffuse layer at the tip-electrolyte interface through the tip contact spreading resistance. At the high frequencies used in the detection regime, the distribution of the charge carriers under the tip is governed by evanescent concentration waves generated at the tip-electrolyte interface. The ion drift length in the electric field produced by the tip determines the ESM response at high frequencies, which follows a 1/f asymptotic law. The electronic conductivity, as well as the electron transport through the electrode-electrolyte interface, do not have a significant effect on the ESM signal in the detection regime. The results indicate, however, that for typical solid electrolytes at room temperature, the ESM response originates at and contains information about the very surface layer of a sample, and the properties of the one-unit-cell-thick surface layer may significantly contribute to the ESM response, implying a high surface sensitivity and a high lateral resolution of the technique. On the other hand, it follows that a rigorous analysis of the ESM signals requires techniques that account for the discrete nature of a solid.« less

Nanoscale Characterization of Carrier Dynamic and Surface Passivation in InGaN/GaN Multiple Quantum Wells on GaN Nanorods.

PubMed

Chen, Weijian; Wen, Xiaoming; Latzel, Michael; Heilmann, Martin; Yang, Jianfeng; Dai, Xi; Huang, Shujuan; Shrestha, Santosh; Patterson, Robert; Christiansen, Silke; Conibeer, Gavin

2016-11-23

Using advanced two-photon excitation confocal microscopy, associated with time-resolved spectroscopy, we characterize InGaN/GaN multiple quantum wells on nanorod heterostructures and demonstrate the passivation effect of a KOH treatment. High-quality InGaN/GaN nanorods were fabricated using nanosphere lithography as a candidate material for light-emitting diode devices. The depth- and time-resolved characterization at the nanoscale provides detailed carrier dynamic analysis helpful for understanding the optical properties. The nanoscale spatially resolved images of InGaN quantum well and defects were acquired simultaneously. We demonstrate that nanorod etching improves light extraction efficiency, and a proper KOH treatment has been found to reduce the surface defects efficiently and enhance the luminescence. The optical characterization techniques provide depth-resolved and time-resolved carrier dynamics with nanoscale spatially resolved mapping, which is crucial for a comprehensive and thorough understanding of nanostructured materials and provides novel insight into the improvement of materials fabrication and applications.

OAM-labeled free-space optical flow routing.

PubMed

Gao, Shecheng; Lei, Ting; Li, Yangjin; Yuan, Yangsheng; Xie, Zhenwei; Li, Zhaohui; Yuan, Xiaocong

2016-09-19

Space-division multiplexing allows unprecedented scaling of bandwidth density for optical communication. Routing spatial channels among transmission ports is critical for future scalable optical network, however, there is still no characteristic parameter to label the overlapped optical carriers. Here we propose a free-space optical flow routing (OFR) scheme by using optical orbital angular moment (OAM) states to label optical flows and simultaneously steer each flow according to their OAM states. With an OAM multiplexer and a reconfigurable OAM demultiplexer, massive individual optical flows can be routed to the demanded optical ports. In the routing process, the OAM beams act as data carriers at the same time their topological charges act as each carrier's labels. Using this scheme, we experimentally demonstrate switching, multicasting and filtering network functions by simultaneously steer 10 input optical flows on demand to 10 output ports. The demonstration of data-carrying OFR with nonreturn-to-zero signals shows that this process enables synchronous processing of massive spatial channels and flexible optical network.

Experimental evidence of zone-center optical phonon softening by accumulating holes in thin Ge

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

Kabuyanagi, Shoichi; Nishimura, Tomonori; Yajima, Takeaki

2016-01-15

We discuss the impact of free carriers on the zone-center optical phonon frequency in germanium (Ge). By taking advantage of the Ge-on-insulator structure, we measured the Raman spectroscopy by applying back-gate bias. Phonon softening by accumulating holes in Ge film was clearly observed. This fact strongly suggests that the phonon softening in heavily-doped Ge is mainly attributed to the free carrier effect rather than the dopant atom counterpart. Furthermore, we propose that the free carrier effect on phonon softening is simply understandable from the viewpoint of covalent bonding modification by free carriers.

Pattern masking: the importance of remote spatial frequencies and their phase alignment.

PubMed

Huang, Pi-Chun; Maehara, Goro; May, Keith A; Hess, Robert F

2012-02-16

To assess the effects of spatial frequency and phase alignment of mask components in pattern masking, target threshold vs. mask contrast (TvC) functions for a sine-wave grating (S) target were measured for five types of mask: a sine-wave grating (S), a square-wave grating (Q), a missing fundamental square-wave grating (M), harmonic complexes consisting of phase-scrambled harmonics of a square wave (Qp), and harmonic complexes consisting of phase-scrambled harmonics of a missing fundamental square wave (Mp). Target and masks had the same fundamental frequency (0.46 cpd) and the target was added in phase with the fundamental frequency component of the mask. Under monocular viewing conditions, the strength of masking depends on phase relationships among mask spatial frequencies far removed from that of the target, at least 3 times the target frequency, only when there are common target and mask spatial frequencies. Under dichoptic viewing conditions, S and Q masks produced similar masking to each other and the phase-scrambled masks (Qp and Mp) produced less masking. The results suggest that pattern masking is spatial frequency broadband in nature and sensitive to the phase alignments of spatial components.

Influence of 4,4’-azobis (4-cyanopentanoic acid) in Transmission and Reflection Gratings Stored in a PVA/AA Photopolymer

PubMed Central

Fernandez, Elena; Fuentes, Rosa; Belendez, Augusto; Pascual, Inmaculada

2016-01-01

Holographic transmission gratings with a spatial frequency of 2658 lines/mm and reflection gratings with a spatial frequency of 4553 lines/mm were stored in a polyvinyl alcohol (PVA)/acrylamide (AA) based photopolymer. This material can reach diffraction efficiencies close to 100% for spatial frequencies about 1000 lines/mm. However, for higher spatial frequencies, the diffraction efficiency decreases considerably as the spatial frequency increases. To enhance the material response at high spatial frequencies, a chain transfer agent, the 4,4’-azobis (4-cyanopentanoic acid), ACPA, is added to the composition of the material. Different concentrations of ACPA are incorporated into the main composition of the photopolymer to find the concentration value that provides the highest diffraction efficiency. Moreover, the refractive index modulation and the optical thickness of the transmission and reflection gratings were obtained, evaluated and compared to procure more information about the influence of the ACPA on them. PMID:28773322

The role of spatial frequency information for ERP components sensitive to faces and emotional facial expression.

PubMed

Holmes, Amanda; Winston, Joel S; Eimer, Martin

2005-10-01

To investigate the impact of spatial frequency on emotional facial expression analysis, ERPs were recorded in response to low spatial frequency (LSF), high spatial frequency (HSF), and unfiltered broad spatial frequency (BSF) faces with fearful or neutral expressions, houses, and chairs. In line with previous findings, BSF fearful facial expressions elicited a greater frontal positivity than BSF neutral facial expressions, starting at about 150 ms after stimulus onset. In contrast, this emotional expression effect was absent for HSF and LSF faces. Given that some brain regions involved in emotion processing, such as amygdala and connected structures, are selectively tuned to LSF visual inputs, these data suggest that ERP effects of emotional facial expression do not directly reflect activity in these regions. It is argued that higher order neocortical brain systems are involved in the generation of emotion-specific waveform modulations. The face-sensitive N170 component was neither affected by emotional facial expression nor by spatial frequency information.

Frequency of a FAS ligand gene variant associated with inherited feline autoimmune lymphoproliferative syndrome in British shorthair cats in New Zealand.

PubMed

Aberdein, D; Munday, J S; Dittmer, K E; Heathcott, R W; Lyons, L A

2017-11-01

AIMS To determine the frequency of the FAS-ligand gene (FASLG) variant associated with feline autoimmune lymphoproliferative syndrome (FALPS) and the proportion of carriers of the variant in three British shorthair (BSH) breeding catteries in New Zealand. METHODS Buccal swabs were collected from all cats in two BSH breeding catteries from the South Island and one from the North Island of New Zealand. DNA was extracted and was tested for the presence of the FASLG variant using PCR. Cats with the FASLG variant were identified and the frequency of the FASLG variant allele calculated. Pedigree analysis was performed and inbreeding coefficients were calculated for cats with the FASLG variant. RESULTS Of 32 BSH cats successfully tested for the presence of the FASLG variant, one kitten (3%) was homozygous (FALPS-affected), and seven (22%) cats were heterozygous (carriers) for the FASLG variant allele, and 24 (75%) cats were homozygous for the wild type allele. The overall frequency of the FASLG variant allele in these 32 cats was 0.14. Cats carrying the FASLG variant were from all three breeding catteries sampled, including two catteries that had not previously reported cases of FALPS. Pedigree analysis revealed common ancestry of FALPS-affected and carrier cats within six generations, as well as frequent inbreeding, with inbreeding coefficients >0.12 for five cats with the FASLG variant. CONCLUSIONS AND CLINICAL RELEVANCE There was a high frequency of the FASLG variant allele (0.14) in this small sample of BSH cats, with 22% of healthy cats identified as carriers of the FASLG variant. For an inherited disease, lethal at a young age, in a small population in which inbreeding is common, these results are significant. To prevent future cases of disease and stop further spread of the FASLG variant allele within the BSH population in New Zealand, it is recommended that all BSH and BSH-cross cats be tested for the presence of the FASLG variant before mating. Cats identified as carriers of the variant allele should be desexed and not used for breeding. Results support the need for further investigations of the true frequency of the FASLG variant allele and occurrence of FALPS in the wider population of BSH cats in New Zealand.

47 CFR 25.144 - Licensing provisions for the 2.3 GHz satellite digital audio radio service.

Code of Federal Regulations, 2012 CFR

2012-10-01

... (CONTINUED) COMMON CARRIER SERVICES SATELLITE COMMUNICATIONS Applications and Licenses Space Stations § 25... frequencies and emission designators of such communications, and the frequencies and emission designators used... repeaters will communicate, the frequencies and emission designators of such communications, and the...

47 CFR 25.144 - Licensing provisions for the 2.3 GHz satellite digital audio radio service.

Code of Federal Regulations, 2014 CFR

2014-10-01

... (CONTINUED) COMMON CARRIER SERVICES SATELLITE COMMUNICATIONS Applications and Licenses Space Stations § 25... of such communications, and the frequencies and emission designators used by the repeaters to re..., the frequencies and emission designators of such communications, and the frequencies and emission...

47 CFR 25.144 - Licensing provisions for the 2.3 GHz satellite digital audio radio service.

Code of Federal Regulations, 2010 CFR

2010-10-01

... (CONTINUED) COMMON CARRIER SERVICES SATELLITE COMMUNICATIONS Applications and Licenses Space Stations § 25... frequencies and emission designators of such communications, and the frequencies and emission designators used... repeaters will communicate, the frequencies and emission designators of such communications, and the...

47 CFR 25.144 - Licensing provisions for the 2.3 GHz satellite digital audio radio service.

Code of Federal Regulations, 2011 CFR

2011-10-01

... (CONTINUED) COMMON CARRIER SERVICES SATELLITE COMMUNICATIONS Applications and Licenses Space Stations § 25... frequencies and emission designators of such communications, and the frequencies and emission designators used... repeaters will communicate, the frequencies and emission designators of such communications, and the...

47 CFR 25.144 - Licensing provisions for the 2.3 GHz satellite digital audio radio service.

Code of Federal Regulations, 2013 CFR

2013-10-01

... (CONTINUED) COMMON CARRIER SERVICES SATELLITE COMMUNICATIONS Applications and Licenses Space Stations § 25... frequencies and emission designators of such communications, and the frequencies and emission designators used... repeaters will communicate, the frequencies and emission designators of such communications, and the...

Time and Frequency Activities at the U.S. Naval Observatory

DTIC Science & Technology

2005-01-01

Naval Observatory, Washington, D.C.), pp. 325-332. [15] D. Kirchner, 1999, “Two Way Satellite Time and Frequency Transfer ( TWSTFT ),” Review of...of Carrier- Phase-Based Two-Way Satellite Time and Frequency Transfer ( TWSTFT ),” in Proceedings of the 36th Annual Precise Time and Time Interval

47 CFR 74.761 - Frequency tolerance.

Code of Federal Regulations, 2010 CFR

2010-10-01

..., AUXILIARY, SPECIAL BROADCAST AND OTHER PROGRAM DISTRIBUTIONAL SERVICES Low Power TV, TV Translator, and TV Booster Stations § 74.761 Frequency tolerance. The licensee of a low power TV, TV translator, or TV... channel carrier frequency if the low power TV, TV translator, or TV booster station is authorized with a...

Separate channels for the analysis of the shape and the movement of moving visual stimulus.

PubMed

Tolhurst, D J

1973-06-01

1. The effects of temporal modulation on the properties of spatial frequency channels have been investigated using adaptation.2. Adapting to drifting sinusoidal gratings caused threshold elevation that was both spatial frequency and direction specific. Little systematic difference was found between the band widths of the elevation curves for drifting and stationary gratings.3. It was confirmed that adaptation fails to reveal channels at low spatial frequencies when stationary gratings are used. However, channels were revealed at frequencies at least as low as 0.66 c/deg when the test gratings were made to move. These channels are adapted only a little by stationary gratings, confirming their dependence on movement.4. The existence of movement-sensitive channels at low spatial frequencies explains the well known observation that temporal modulation greatly increases the sensitivity of the visual system to low spatial frequencies.5. Temporal modulation was effective at revealing these channels only when the flicker or movement of the test patterns was apparent to the observer; only at low spatial frequencies did patterns, modulated at low rates, actually appear to be temporarily modulated at threshold. At higher spatial frequencies, they were indistinguishable from stationary patterns until the contrast was some way above the detection threshold.6. It is suggested, therefore, that the movement-sensitive channels are responsible for signalling the occurrence of movement; the channels at higher spatial frequencies give no information about temporal changes. These two systems of channels are compared to the Y- and X-cells respectively of the cat.

An automatic frequency control loop using overlapping DFTs (Discrete Fourier Transforms)

NASA Technical Reports Server (NTRS)

Aguirre, S.

1988-01-01

An automatic frequency control (AFC) loop is introduced and analyzed in detail. The new scheme is a generalization of the well known Cross Product AFC loop that uses running overlapping discrete Fourier transforms (DFTs) to create a discriminator curve. Linear analysis is included and supported with computer simulations. The algorithm is tested in a low carrier to noise ratio (CNR) dynamic environment, and the probability of loss of lock is estimated via computer simulations. The algorithm discussed is a suboptimum tracking scheme with a larger frequency error variance compared to an optimum strategy, but offers simplicity of implementation and a very low operating threshold CNR. This technique can be applied during the carrier acquisition and re-acquisition process in the Advanced Receiver.

Efficient carrier-envelope offset frequency stabilization through gain modulation via stimulated emission.

PubMed

Karlen, Lauriane; Buchs, Gilles; Portuondo-Campa, Erwin; Lecomte, Steve

2016-01-15

A novel scheme for intracavity control of the carrier-envelope offset (CEO) frequency of a 100 MHz mode-locked Er:Yb:glass diode-pumped solid-state laser (DPSSL) based on the modulation of the laser gain via stimulated emission of the excited Er(3+) ions is demonstrated. This method allows us to bypass the ytterbium system few-kHz low-pass filter in the f(CEO) stabilization loop and thus to push the phase lock bandwidth up to a limit close to the relaxation oscillations frequency of the erbium system. A phase lock bandwidth above 70 kHz has been achieved with the fully stabilized laser, leading to an integrated phase noise [1 Hz-1 MHz] of 120 mrad.

A straightforward frequency-estimation technique for GPS carrier-phase time transfer.

PubMed

Hackman, Christine; Levine, Judah; Parker, Thomas E; Piester, Dirk; Becker, Jürgen

2006-09-01

Although Global Positioning System (GPS) carrier-phase time transfer (GPSCPTT) offers frequency stability approaching 10-15 at averaging times of 1 d, a discontinuity occurs in the time-transfer estimates between the end of one processing batch (1-3 d in length) and the beginning of the next. The average frequency over a multiday analysis period often has been computed by first estimating and removing these discontinuities, i.e., through concatenation. We present a new frequency-estimation technique in which frequencies are computed from the individual batches then averaged to obtain the mean frequency for a multiday period. This allows the frequency to be computed without the uncertainty associated with the removal of the discontinuities and requires fewer computational resources. The new technique was tested by comparing the fractional frequency-difference values it yields to those obtained using a GPSCPTT concatenation method and those obtained using two-way satellite time-and-frequency transfer (TWSTFT). The clocks studied were located in Braunschweig, Germany, and in Boulder, CO. The frequencies obtained from the GPSCPTT measurements using either method agreed with those obtained from TWSTFT at several parts in 1016. The frequency values obtained from the GPSCPTT data by use of the new method agreed with those obtained using the concatenation technique at 1-4 x 10(-16).

Photo-conductive detection of continuous THz waves via manipulated ultrafast process in nanostructures

NASA Astrophysics Data System (ADS)

Moon, Kiwon; Lee, Eui Su; Lee, Il-Min; Park, Dong Woo; Park, Kyung Hyun

2018-01-01

Time-domain and frequency-domain terahertz (THz) spectroscopy systems often use materials fabricated with exotic and expensive methods that intentionally introduce defects to meet short carrier lifetime requirements. In this study, we demonstrate the development of a nano-photomixer that meets response speed requirements without using defect-incorporated, low-temperature-grown (LTG) semiconductors. Instead, we utilized a thin InGaAs layer grown on a semi-insulating InP substrate by metal-organic chemical vapor deposition (MOCVD) combined with nano-electrodes to manipulate local ultrafast photo-carrier dynamics via a carefully designed field-enhancement and plasmon effect. The developed nano-structured photomixer can detect continuous-wave THz radiation up to a frequency of 2 THz with a peak carrier collection efficiency of 5%, which is approximately 10 times better than the reference efficiency of 0.4%. The better efficiency results from the high carrier mobility of the MOCVD-grown InGaAs thin layer with the coincidence of near-field and plasmon-field distributions in the nano-structure. Our result not only provides a generally applicable methodology for manipulating ultrafast carrier dynamics by means of nano-photonic techniques to break the trade-off relation between the carrier lifetime and mobility in typical LTG semiconductors but also contributes to mass-producible photo-conductive THz detectors to facilitate the widespread application of THz technology.

The dependence of graphene Raman D-band on carrier density.

PubMed

Liu, Junku; Li, Qunqing; Zou, Yuan; Qian, Qingkai; Jin, Yuanhao; Li, Guanhong; Jiang, Kaili; Fan, Shoushan

2013-01-01

Raman spectroscopy has been an integral part of graphene research and can provide information about graphene structure, electronic characteristics, and electron-phonon interactions. In this study, the characteristics of the graphene Raman D-band, which vary with carrier density, are studied in detail, including the frequency, full width half-maximum, and intensity. We find the Raman D-band frequency increases for hole doping and decreases for electron doping. The Raman D-band intensity increases when the Fermi level approaches half of the excitation energy and is higher in the case of electron doping than that of hole doping. These variations can be explained by electron-phonon interaction theory and quantum interference between different Raman pathways in graphene. The intensity ratio of Raman D- and G-band, which is important for defects characterization in graphene, shows a strong dependence on carrier density.

High-amplitude VLF transmitter signals and associated sidebands observed near the magnetic equatorial plane on the ISEE 1 satellite

NASA Technical Reports Server (NTRS)

Bell, T. F.

1985-01-01

New high-altitude ISEE 1 satellite observations of high-amplitude nonducted signals from the Omega navigation transmitter in North Dakota are reported. The amplitude of the signal was approximately 16-26 dB higher than that of similar signals observed at comparable locations on other days. Over the range L = 3.3-3.7, the transmitter pulses at 13.1 and 13.6 kHz were associated with sideband signals spaced in frequency roughly symmetrically about the carrier and generally reduced in amplitude by about 5 dB with respect to the carrier. The strongest sidebands were generally offset in frequency from the carrier by about + or - 55 Hz. Reasons are discussed for believing that the unusually high amplitude of the signals was due to wave amplification through the whistler-mode instability.

Contralateral Bias of High Spatial Frequency Tuning and Cardinal Direction Selectivity in Mouse Visual Cortex

PubMed Central

Zeitoun, Jack H.; Kim, Hyungtae

2017-01-01

Binocular mechanisms for visual processing are thought to enhance spatial acuity by combining matched input from the two eyes. Studies in the primary visual cortex of carnivores and primates have confirmed that eye-specific neuronal response properties are largely matched. In recent years, the mouse has emerged as a prominent model for binocular visual processing, yet little is known about the spatial frequency tuning of binocular responses in mouse visual cortex. Using calcium imaging in awake mice of both sexes, we show that the spatial frequency preference of cortical responses to the contralateral eye is ∼35% higher than responses to the ipsilateral eye. Furthermore, we find that neurons in binocular visual cortex that respond only to the contralateral eye are tuned to higher spatial frequencies. Binocular neurons that are well matched in spatial frequency preference are also matched in orientation preference. In contrast, we observe that binocularly mismatched cells are more mismatched in orientation tuning. Furthermore, we find that contralateral responses are more direction-selective than ipsilateral responses and are strongly biased to the cardinal directions. The contralateral bias of high spatial frequency tuning was found in both awake and anesthetized recordings. The distinct properties of contralateral cortical responses may reflect the functional segregation of direction-selective, high spatial frequency-preferring neurons in earlier stages of the central visual pathway. Moreover, these results suggest that the development of binocularity and visual acuity may engage distinct circuits in the mouse visual system. SIGNIFICANCE STATEMENT Seeing through two eyes is thought to improve visual acuity by enhancing sensitivity to fine edges. Using calcium imaging of cellular responses in awake mice, we find surprising asymmetries in the spatial processing of eye-specific visual input in binocular primary visual cortex. The contralateral visual pathway is tuned to higher spatial frequencies than the ipsilateral pathway. At the highest spatial frequencies, the contralateral pathway strongly prefers to respond to visual stimuli along the cardinal (horizontal and vertical) axes. These results suggest that monocular, and not binocular, mechanisms set the limit of spatial acuity in mice. Furthermore, they suggest that the development of visual acuity and binocularity in mice involves different circuits. PMID:28924011

Discriminative spatial-frequency-temporal feature extraction and classification of motor imagery EEG: An sparse regression and Weighted Naïve Bayesian Classifier-based approach.

PubMed

Miao, Minmin; Zeng, Hong; Wang, Aimin; Zhao, Changsen; Liu, Feixiang

2017-02-15

Common spatial pattern (CSP) is most widely used in motor imagery based brain-computer interface (BCI) systems. In conventional CSP algorithm, pairs of the eigenvectors corresponding to both extreme eigenvalues are selected to construct the optimal spatial filter. In addition, an appropriate selection of subject-specific time segments and frequency bands plays an important role in its successful application. This study proposes to optimize spatial-frequency-temporal patterns for discriminative feature extraction. Spatial optimization is implemented by channel selection and finding discriminative spatial filters adaptively on each time-frequency segment. A novel Discernibility of Feature Sets (DFS) criteria is designed for spatial filter optimization. Besides, discriminative features located in multiple time-frequency segments are selected automatically by the proposed sparse time-frequency segment common spatial pattern (STFSCSP) method which exploits sparse regression for significant features selection. Finally, a weight determined by the sparse coefficient is assigned for each selected CSP feature and we propose a Weighted Naïve Bayesian Classifier (WNBC) for classification. Experimental results on two public EEG datasets demonstrate that optimizing spatial-frequency-temporal patterns in a data-driven manner for discriminative feature extraction greatly improves the classification performance. The proposed method gives significantly better classification accuracies in comparison with several competing methods in the literature. The proposed approach is a promising candidate for future BCI systems. Copyright © 2016 Elsevier B.V. All rights reserved.

Hyperspectral interferometry: Sizing microscale surface features in the pine bark beetle.

PubMed

Beach, James M; Uertz, James L; Eckhardt, Lori G

2015-10-01

A new method of interferometry employing a Fabry-Perot etalon model was used to locate and size microscale features on the surface of the pine bark beetle. Oscillations in the reflected light spectrum, caused by self-interference of light reflecting from surfaces of foreleg setae and spores on the elytrum, were recorded using white light hyperspectral microscopy. By making the assumption that pairs of reflecting surfaces produce an etalon effect, the distance between surfaces could be determined from the oscillation frequency. Low frequencies of less than 0.08 nm(-1) were observed in the spectrum below 700 nm while higher frequencies generally occupied wavelengths from 600 to 850 nm. In many cases, two frequencies appeared separately or in combination across the spectrum. The etalon model gave a mean spore size of 3.04 ± 1.27 μm and a seta diameter of 5.44 ± 2.88 μm. The tapering near the setae tip was detected as a lowering of frequency. Spatial fringes were observed together with spectral oscillations from surfaces on the exoskeleton at higher magnification. These signals were consistent with embedded multi-layer reflecting surfaces. Possible applications for hyperspectral interferometry include medical imaging, detection of spore loads in insects and other fungal carriers, wafer surface and subsurface inspection, nanoscale materials, biological surface analysis, and spectroscopy calibration. This is, to our knowledge, the first report of oscillations directly observed by microscopy in the reflected light spectra from Coleoptera, and the first demonstration of broadband hyperspectral interferometry using microscopy that does not employ an internal interferometer. © 2015 Wiley Periodicals, Inc.

VEP contrast sensitivity responses reveal reduced functional segregation of mid and high filters of visual channels in autism.

PubMed

Jemel, Boutheina; Mimeault, Daniel; Saint-Amour, Dave; Hosein, Anthony; Mottron, Laurent

2010-06-01

Despite the vast amount of behavioral data showing a pronounced tendency in individuals with autism spectrum disorder (ASD) to process fine visual details, much less is known about the neurophysiological characteristics of spatial vision in ASD. Here, we address this issue by assessing the contrast sensitivity response properties of the early visual-evoked potentials (VEPs) to sine-wave gratings of low, medium and high spatial frequencies in adults with ASD and in an age- and IQ-matched control group. Our results show that while VEP contrast responses to low and high spatial frequency gratings did not differ between ASD and controls, early VEPs to mid spatial frequency gratings exhibited similar response characteristics as those to high spatial frequency gratings in ASD. Our findings show evidence for an altered functional segregation of early visual channels, especially those responsible for processing mid- and high-frequency spatial scales.

A new unequal-weighted triple-frequency first order ionosphere correction algorithm and its application in COMPASS

NASA Astrophysics Data System (ADS)

Liu, WenXiang; Mou, WeiHua; Wang, FeiXue

2012-03-01

As the introduction of triple-frequency signals in GNSS, the multi-frequency ionosphere correction technology has been fast developing. References indicate that the triple-frequency second order ionosphere correction is worse than the dual-frequency first order ionosphere correction because of the larger noise amplification factor. On the assumption that the variances of three frequency pseudoranges were equal, other references presented the triple-frequency first order ionosphere correction, which proved worse or better than the dual-frequency first order correction in different situations. In practice, the PN code rate, carrier-to-noise ratio, parameters of DLL and multipath effect of each frequency are not the same, so three frequency pseudorange variances are unequal. Under this consideration, a new unequal-weighted triple-frequency first order ionosphere correction algorithm, which minimizes the variance of the pseudorange ionosphere-free combination, is proposed in this paper. It is found that conventional dual-frequency first-order correction algorithms and the equal-weighted triple-frequency first order correction algorithm are special cases of the new algorithm. A new pseudorange variance estimation method based on the three carrier combination is also introduced. Theoretical analysis shows that the new algorithm is optimal. The experiment with COMPASS G3 satellite observations demonstrates that the ionosphere-free pseudorange combination variance of the new algorithm is smaller than traditional multi-frequency correction algorithms.

Controlling Energy Radiations of Electromagnetic Waves via Frequency Coding Metamaterials.

PubMed

Wu, Haotian; Liu, Shuo; Wan, Xiang; Zhang, Lei; Wang, Dan; Li, Lianlin; Cui, Tie Jun

2017-09-01

Metamaterials are artificial structures composed of subwavelength unit cells to control electromagnetic (EM) waves. The spatial coding representation of metamaterial has the ability to describe the material in a digital way. The spatial coding metamaterials are typically constructed by unit cells that have similar shapes with fixed functionality. Here, the concept of frequency coding metamaterial is proposed, which achieves different controls of EM energy radiations with a fixed spatial coding pattern when the frequency changes. In this case, not only different phase responses of the unit cells are considered, but also different phase sensitivities are also required. Due to different frequency sensitivities of unit cells, two units with the same phase response at the initial frequency may have different phase responses at higher frequency. To describe the frequency coding property of unit cell, digitalized frequency sensitivity is proposed, in which the units are encoded with digits "0" and "1" to represent the low and high phase sensitivities, respectively. By this merit, two degrees of freedom, spatial coding and frequency coding, are obtained to control the EM energy radiations by a new class of frequency-spatial coding metamaterials. The above concepts and physical phenomena are confirmed by numerical simulations and experiments.

Spatial-frequency spectrum of patterns changes the visibility of spatial-phase differences

NASA Technical Reports Server (NTRS)

Lawton, T. B.

1985-01-01

It is shown that spatial-frequency components over a 4-octave range affected the visibility of spatial-phase differences. Contrast thresholds were measured for discrimination between two (+45- and -45-deg) spatial phases of a sinusoidal test grating added to a background grating. The background could contain one or several sinusoidal components, all in 0-deg phase. Phase differences between the test and the background were visible at lower contrasts when test and background frequencies were harmonically related than when they were not, when test and background frequencies were within 1 octave than when they were farther apart, when the fundamental frequency of the background was low than when it was high, and for some discriminations more than for others, after practice. The visibility of phase differences was not affected by additional components in the background if the fundamental and difference frequencies of the background remained unchanged. Observers' reports of their strategies gave information about the types of attentive processing that were used to discriminate phase differences. Attentive processing facilitated phase discrimination for multifrequency gratings spanning a much wider range of spatial frequencies than would be possible by using only local preattentive processing. These results were consistent with the visibility of phase differences being processed by some combination of even- and odd-symmetric simple cells tuned to a wide range of different spatial frequencies.

Broadband interferometric characterization of divergence and spatial chirp.

PubMed

Meier, Amanda K; Iliev, Marin; Squier, Jeff A; Durfee, Charles G

2015-09-01

We demonstrate a spectral interferometric method to characterize lateral and angular spatial chirp to optimize intensity localization in spatio-temporally focused ultrafast beams. Interference between two spatially sheared beams in an interferometer will lead to straight fringes if the wavefronts are curved. To produce reference fringes, we delay one arm relative to another in order to measure fringe rotation in the spatially resolved spectral interferogram. With Fourier analysis, we can obtain frequency-resolved divergence. In another arrangement, we spatially flip one beam relative to the other, which allows the frequency-dependent beamlet direction (angular spatial chirp) to be measured. Blocking one beam shows the spatial variation of the beamlet position with frequency (i.e., the lateral spatial chirp).

A Theory of the Visual System Biology Underlying Development of Spatial Frequency Lateralization

ERIC Educational Resources Information Center

Howard, Mary F.; Reggia, James A.

2007-01-01

The spatial frequency hypothesis contends that performance differences between the hemispheres on various visuospatial tasks are attributable to lateralized processing of the spatial frequency content of visual stimuli. Hellige has proposed that such lateralization could arise during infant development from the earlier maturation of the right…

Spatiotemporal frequency tuning of BOLD and gamma band MEG responses compared in primary visual cortex.

PubMed

Muthukumaraswamy, Suresh D; Singh, Krish D

2008-05-01

In this study, the spatial and temporal frequency tuning characteristics of the MEG gamma (40-60 Hz) rhythm and the BOLD response in primary visual cortex were measured and compared. In an identical MEG/fMRI paradigm, 10 participants viewed reversing square wave gratings at 2 spatial frequencies [0.5 and 3 cycles per degree (cpd)] reversing at 5 temporal frequencies (0, 1 6, 10, 15 Hz). Three-dimensional images of MEG source power were generated with synthetic aperture magnetometry (SAM) and showed a high degree of spatial correspondence with BOLD responses in primary visual cortex with a mean spatial separation of 6.5 mm, but the two modalities showed different tuning characteristics. The gamma rhythm showed a clear increase in induced power for the high spatial frequency stimulus while BOLD showed no difference in activity for the two spatial frequencies used. Both imaging modalities showed a general increase of activity with temporal frequency, however, BOLD plateaued around 6-10 Hz while the MEG generally increased with a dip exhibited at 6 Hz. These results demonstrate that the two modalities may show activation in similar spatial locations but that the functional pattern of these activations may differ in a complex manner, suggesting that they may be tuned to different aspects of neuronal activity.

Method and apparatus for pulse width modulation control of an AC induction motor

DOEpatents

Geppert, Steven; Slicker, James M.

1984-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a micro-processor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .THETA., where .THETA. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands of electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Charge carrier dynamics in PMMA-LiClO4 based polymer electrolytes plasticized with different plasticizers

NASA Astrophysics Data System (ADS)

Pal, P.; Ghosh, A.

2017-07-01

We have studied the charge carrier dynamics in poly(methylmethacrylate)-LiClO4 polymer electrolytes plasticized with different plasticizers such as ethylene carbonate (EC), propylene carbonate (PC), polyethylene glycol (PEG), and dimethyl carbonate (DMC). We have measured the broadband complex conductivity spectra of these electrolytes in the frequency range of 0.01 Hz-3 GHz and in the temperature range of 203 K-363 K and analyzed the conductivity spectra in the framework of the random barrier model by taking into account the contribution of the electrode polarization observed at low frequencies and/or at high temperatures. It is observed that the temperature dependences of the ionic conductivity and relaxation time follow the Vogel-Tammann-Fulcher relation for all plasticized electrolytes. We have also performed the scaling of the conductivity spectra, which indicates that the charge carrier dynamics is almost independent of temperature and plasticizers in a limited frequency range. The existence of nearly constant loss in these electrolytes has been observed at low temperatures and/or high frequencies. We have studied the dielectric relaxation in these electrolytes using electric modulus formalism and obtained the stretched exponent and the decay function. We have observed less cooperative ion dynamics in electrolytes plasticized with DMC compared to electrolytes plasticized with EC, PC, and PEG.

Temporal modulation transfer functions in cochlear implantees using a method that limits overall loudness cues

PubMed Central

Fraser, Matthew; McKay, Colette M.

2012-01-01

Temporal modulation transfer functions (TMTFs) were measured for six users of cochlear implants, using different carrier rates and levels. Unlike most previous studies investigating modulation detection, the experimental design limited potential effects of overall loudness cues. Psychometric functions (percent correct discrimination of modulated from unmodulated stimuli versus modulation depth) were obtained. For each modulation depth, each modulated stimulus was loudness balanced to the unmodulated reference stimulus, and level jitter was applied in the discrimination task. The loudness-balance data showed that the modulated stimuli were louder than the unmodulated reference stimuli with the same average current, thus confirming the need to limit loudness cues when measuring modulation detection. TMTFs measured in this way had a low-pass characteristic, with a cut-off frequency (at comfortably loud levels) similar to that for normal-hearing listeners. A reduction in level caused degradation in modulation detection efficiency and a lower-cut-off frequency (i.e. poorer temporal resolution). An increase in carrier rate also led to a degradation in modulation detection efficiency, but only at lower levels or higher modulation frequencies. When detection thresholds were expressed as a proportion of dynamic range, there was no effect of carrier rate for the lowest modulation frequency (50 Hz) at either level. PMID:22146425

Method and apparatus for pulse width modulation control of an AC induction motor

NASA Technical Reports Server (NTRS)

Geppert, Steven (Inventor); Slicker, James M. (Inventor)

1984-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a micro-processor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .THETA., where .THETA. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands of electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.

PREVALENCE OF COMBINATORIAL CYP2C9 AND VKORC1 GENOTYPES IN PUERTO RICANS: IMPLICATIONS FOR WARFARIN MANAGEMENT IN HISPANICS

PubMed Central

Duconge, Jorge; Cadilla, Carmen L.; Windemuth, Andreas; Kocherla, Mohan; Gorowski, Krystyna; Seip, Richard L.; Bogaard, Kali; Renta, Jessica Y.; Piovanetti, Paola; D’Agostino, Darrin; Santiago-Borrero, Pedro J.; Ruaño, Gualberto

2010-01-01

Polymorphisms in the cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) genes significantly alter the effective warfarin dose. We determined the frequencies of alleles, single carriers, and double carriers of single nucleotide polymorphisms (SNPs) in the CYP2C9 and VKORC1 genes in a Puerto Rican cohort and gauged the impact of these polymorphisms on warfarin dosage using a published algorithm. A total of 92 DNA samples were genotyped using Luminex® x-MAP technology. The polymorphism frequencies were 6.52%, 5.43% and 28.8% for CYP2C9 *2, *3 and VKORC1-1639 G>A polymorphisms, respectively. The prevalence of combinatorial genotypes was 16% for carriers of both the CYP2C9 and VKORC1 polymorphisms, 9% for carriers of CYP2C9 polymorphisms, 35% for carriers of the VKORC1 polymorphism, and the remaining 40% were non-carriers for either gene. Based on a published warfarin dosing algorithm, single, double and triple carriers of functionally deficient polymorphisms predict reductions of 1.0–1.6, 2.0–2.9, and 2.9–3.7 mg/day, respectively, in warfarin dose. Overall, 60% of the population carried at least a single polymorphism predicting deficient warfarin metabolism or responsiveness and 13% were double carriers with polymorphisms in both genes studied. Combinatorial genotyping of CYP2C9 and VKORC1 can allow for individualized dosing of warfarin among patients with gene polymorphisms, potentially reducing the risk of stroke or bleeding. PMID:20073138

Real-Time Point Positioning Performance Evaluation of Single-Frequency Receivers Using NASA's Global Differential GPS System

NASA Technical Reports Server (NTRS)

Muellerschoen, Ronald J.; Iijima, Byron; Meyer, Robert; Bar-Sever, Yoaz; Accad, Elie

2004-01-01

This paper evaluates the performance of a single-frequency receiver using the 1-Hz differential corrections as provided by NASA's global differential GPS system. While the dual-frequency user has the ability to eliminate the ionosphere error by taking a linear combination of observables, the single-frequency user must remove or calibrate this error by other means. To remove the ionosphere error we take advantage of the fact that the magnitude of the group delay in range observable and the carrier phase advance have the same magnitude but are opposite in sign. A way to calibrate this error is to use a real-time database of grid points computed by JPL's RTI (Real-Time Ionosphere) software. In both cases we evaluate the positional accuracy of a kinematic carrier phase based point positioning method on a global extent.

High-frequency self-aligned graphene transistors with transferred gate stacks.

PubMed

Cheng, Rui; Bai, Jingwei; Liao, Lei; Zhou, Hailong; Chen, Yu; Liu, Lixin; Lin, Yung-Chen; Jiang, Shan; Huang, Yu; Duan, Xiangfeng

2012-07-17

Graphene has attracted enormous attention for radio-frequency transistor applications because of its exceptional high carrier mobility, high carrier saturation velocity, and large critical current density. Herein we report a new approach for the scalable fabrication of high-performance graphene transistors with transferred gate stacks. Specifically, arrays of gate stacks are first patterned on a sacrificial substrate, and then transferred onto arbitrary substrates with graphene on top. A self-aligned process, enabled by the unique structure of the transferred gate stacks, is then used to position precisely the source and drain electrodes with minimized access resistance or parasitic capacitance. This process has therefore enabled scalable fabrication of self-aligned graphene transistors with unprecedented performance including a record-high cutoff frequency up to 427 GHz. Our study defines a unique pathway to large-scale fabrication of high-performance graphene transistors, and holds significant potential for future application of graphene-based devices in ultra-high-frequency circuits.

Application of Excitation from Multiple Locations on a Simplified High-Lift System

NASA Technical Reports Server (NTRS)

Melton, LaTunia Pack; Yao, Chung-Sheng; Seifert, Avi

2004-01-01

A series of active flow control experiments were recently conducted on a simplified high-lift system. The purpose of the experiments was to explore the prospects of eliminating all but simply hinged leading and trailing edge flaps, while controlling separation on the supercritical airfoil using multiple periodic excitation slots. Excitation was provided by three. independently controlled, self-contained, piezoelectric actuators. Low frequency excitation was generated through amplitude modulation of the high frequency carrier wave, the actuators' resonant frequencies. It was demonstrated, for the first time, that pulsed modulated signal from two neighboring slots interact favorably to increase lift. Phase sensitivity at the low frequency was measured, even though the excitation was synthesized from the high-frequency carrier wave. The measurements were performed at low Reynolds numbers and included mean and unsteady surface pressures, surface hot-films, wake pressures and particle image velocimetry. A modest (6%) increase in maximum lift (compared to the optimal baseline) was obtained due t o the activation of two of the three actuators.

Analysis of Recombination in CdTe Heterostructures With Time-Resolved Two-Photon Excitation Microscopy

DOE PAGES

Kuciauskas, Darius; Wernsing, Keith; Jensen, Soren Alkaersig; ...

2016-11-01

Here, we used time-resolved photoluminescence microscopy to analyze charge carrier transport and recombination in CdTe double heterostructures fabricated by molecular beam epitaxy (MBE). This allowed us to determine the charge carrier mobility in this system, which was found to be 500-625 cm 2/(V s). Charge carrier lifetimes in the 15-100 ns range are limited by the interface recombination, and the data indicate higher interface recombination velocity near extended defects. This study describes a new method to analyze the spatial distribution of the interface recombination velocity and the interface defects in semiconductor heterostructures.

Analysis of Recombination in CdTe Heterostructures With Time-Resolved Two-Photon Excitation Microscopy

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

Kuciauskas, Darius; Wernsing, Keith; Jensen, Soren Alkaersig

Here, we used time-resolved photoluminescence microscopy to analyze charge carrier transport and recombination in CdTe double heterostructures fabricated by molecular beam epitaxy (MBE). This allowed us to determine the charge carrier mobility in this system, which was found to be 500-625 cm 2/(V s). Charge carrier lifetimes in the 15-100 ns range are limited by the interface recombination, and the data indicate higher interface recombination velocity near extended defects. This study describes a new method to analyze the spatial distribution of the interface recombination velocity and the interface defects in semiconductor heterostructures.

Electrical and optical characterizations of InAs/GaAs quantum dot solar cells

NASA Astrophysics Data System (ADS)

Han, Im Sik; Kim, Seung Hyun; Kim, Jong Su; Noh, Sam Kyu; Lee, Sang Jun; Kim, Honggyun; Kim, Deok-Kee; Leem, Jae-Young

2018-03-01

The electrical and optical characterizations of InAs/GaAs quantum dot solar cells (QDSCs) were investigated by frequency dependent capacitance-voltage ( C- V) measurements and photoreflectance (PR) spectroscopy. The C- V results confirmed that the frequency dependent junction capacitance ( C j) of QDSC is sensitive to the carrier exhaustion process through trapping and recapturing in the strain-induced defects and QD states caused by the interface strain between InAs and GaAs materials. As a result, at a low frequency (≤ 200 kHz), the C j of the QDSCs decreased with increasing InAs deposition thickness ( θ), leading to the decrease in carrier concentration ( N d) of the n-GaAs absorber layer due to the carrier losses processes caused by the trapping and re-capturing in the defects and the relatively large QDs. At θ ≤ 2.0 ML, the p-n junction electric field strength ( F pn) of the QDSCs which was evaluated by PR spectra decreased with increasing excitation photon intensity ( I ex) due to the typical field screening effect in the SC structure. On the other hand, the F pn of QDSCs with θ ≥ 2.5 ML approached a constant value with a relatively high I ex, which suggests that the decrease in photo-generated carriers in the QDSC was caused by the re-capturing and trapping process.

Theoretical study of high-order harmonic generation from the hydrogen molecular ion with a dichromatic spatially inhomogeneous field

NASA Astrophysics Data System (ADS)

Xu, Xiao-Hu; Wang, Yan-Jun; Miao, Xiang-Yang

2018-05-01

We theoretically investigate the enhancement of high-order harmonic generation by numerically solving the non-Born-Oppenheimer time-dependent Schrödinger equation from the hydrogen molecular ion in a dichromatic inhomogeneous laser field. An ultrabroad supercontinuum up to 300 orders spectral width is generated. It is found that not only the inhomogeneity, but also the dichromatic field contributes to the significant extension of the harmonic cutoff compared with a monochromatic inhomogeneous laser field. Meanwhile, the long quantum paths can be suppressed and short ones can be enhanced by selecting optimized inhomogeneous parameter β, intensity and carrier envelope phase of the dichromatic inhomogeneous laser field. Furthermore, by superposing a properly selected range of the harmonic spectrum in the continuum region, an isolated 29-as pulse is generated. Both the classical theory and quantum time-frequency analysis are adopted to explain the physical mechanism.

Silicon etching of difluoromethane atmospheric pressure plasma jet combined with its spectroscopic analysis

NASA Astrophysics Data System (ADS)

Sung, Yu-Ching; Wei, Ta-Chin; Liu, You-Chia; Huang, Chun

2018-06-01

A capacitivly coupled radio-frequency double-pipe atmospheric-pressure plasma jet is used for etching. An argon carrier gas is supplied to the plasma discharge jet; and CH2F2 etch gas is inserted into the plasma discharge jet, near the silicon substrate. Silicon etchings rate can be efficiently-controlled by adjusting the feeding etching gas composition and plasma jet operating parameters. The features of silicon etched by the plasma discharge jet are discussed in order to spatially spreading plasma species. Electronic excitation temperature and electron density are detected by increasing plasma power. The etched silicon profile exhibited an anisotropic shape and the etching rate was maximum at the total gas flow rate of 4500 sccm and CH2F2 concentration of 11.1%. An etching rate of 17 µm/min was obtained at a plasma power of 100 W.

Optical Signal Processing: Poisson Image Restoration and Shearing Interferometry

NASA Technical Reports Server (NTRS)

Hong, Yie-Ming

1973-01-01

Optical signal processing can be performed in either digital or analog systems. Digital computers and coherent optical systems are discussed as they are used in optical signal processing. Topics include: image restoration; phase-object visualization; image contrast reversal; optical computation; image multiplexing; and fabrication of spatial filters. Digital optical data processing deals with restoration of images degraded by signal-dependent noise. When the input data of an image restoration system are the numbers of photoelectrons received from various areas of a photosensitive surface, the data are Poisson distributed with mean values proportional to the illuminance of the incoherently radiating object and background light. Optical signal processing using coherent optical systems is also discussed. Following a brief review of the pertinent details of Ronchi's diffraction grating interferometer, moire effect, carrier-frequency photography, and achromatic holography, two new shearing interferometers based on them are presented. Both interferometers can produce variable shear.

Sustained delivery of biomolecules from gelatin carriers for applications in bone regeneration.

PubMed

Song, Jiankang; Leeuwenburgh, Sander Cg

2014-08-01

Local delivery of therapeutic biomolecules to stimulate bone regeneration has matured considerably during the past decades, but control over the release of these biomolecules still remains a major challenge. To this end, suitable carriers that allow for tunable spatial and temporal delivery of biomolecules need to be developed. Gelatin is one of the most widely used natural polymers for the controlled and sustained delivery of biomolecules because of its biodegradability, biocompatibility, biosafety and cost-effectiveness. The current study reviews the applications of gelatin as carriers in form of bulk hydrogels, microspheres, nanospheres, colloidal gels and composites for the programmed delivery of commonly used biomolecules for applications in bone regeneration with a specific focus on the relationship between carrier properties and delivery characteristics.

Multivariate spatial models of excess crash frequency at area level: case of Costa Rica.

PubMed

Aguero-Valverde, Jonathan

2013-10-01

Recently, areal models of crash frequency have being used in the analysis of various area-wide factors affecting road crashes. On the other hand, disease mapping methods are commonly used in epidemiology to assess the relative risk of the population at different spatial units. A natural next step is to combine these two approaches to estimate the excess crash frequency at area level as a measure of absolute crash risk. Furthermore, multivariate spatial models of crash severity are explored in order to account for both frequency and severity of crashes and control for the spatial correlation frequently found in crash data. This paper aims to extent the concept of safety performance functions to be used in areal models of crash frequency. A multivariate spatial model is used for that purpose and compared to its univariate counterpart. Full Bayes hierarchical approach is used to estimate the models of crash frequency at canton level for Costa Rica. An intrinsic multivariate conditional autoregressive model is used for modeling spatial random effects. The results show that the multivariate spatial model performs better than its univariate counterpart in terms of the penalized goodness-of-fit measure Deviance Information Criteria. Additionally, the effects of the spatial smoothing due to the multivariate spatial random effects are evident in the estimation of excess equivalent property damage only crashes. Copyright © 2013 Elsevier Ltd. All rights reserved.

Role of the mouse retinal photoreceptor ribbon synapse in visual motion processing for optokinetic responses.

PubMed

Sugita, Yuko; Araki, Fumiyuki; Chaya, Taro; Kawano, Kenji; Furukawa, Takahisa; Miura, Kenichiro

2015-01-01

The ribbon synapse is a specialized synaptic structure in the retinal outer plexiform layer where visual signals are transmitted from photoreceptors to the bipolar and horizontal cells. This structure is considered important in high-efficiency signal transmission; however, its role in visual signal processing is unclear. In order to understand its role in visual processing, the present study utilized Pikachurin-null mutant mice that show improper formation of the photoreceptor ribbon synapse. We examined the initial and late phases of the optokinetic responses (OKRs). The initial phase was examined by measuring the open-loop eye velocity of the OKRs to sinusoidal grating patterns of various spatial frequencies moving at various temporal frequencies for 0.5 s. The mutant mice showed significant initial OKRs with a spatiotemporal frequency tuning (spatial frequency, 0.09 ± 0.01 cycles/°; temporal frequency, 1.87 ± 0.12 Hz) that was slightly different from the wild-type mice (spatial frequency, 0.11 ± 0.01 cycles/°; temporal frequency, 1.66 ± 0.12 Hz). The late phase of the OKRs was examined by measuring the slow phase eye velocity of the optokinetic nystagmus induced by the sinusoidal gratings of various spatiotemporal frequencies moving for 30 s. We found that the optimal spatial and temporal frequencies of the mutant mice (spatial frequency, 0.11 ± 0.02 cycles/°; temporal frequency, 0.81 ± 0.24 Hz) were both lower than those in the wild-type mice (spatial frequency, 0.15 ± 0.02 cycles/°; temporal frequency, 1.93 ± 0.62 Hz). These results suggest that the ribbon synapse modulates the spatiotemporal frequency tuning of visual processing along the ON pathway by which the late phase of OKRs is mediated.

Role of the Mouse Retinal Photoreceptor Ribbon Synapse in Visual Motion Processing for Optokinetic Responses

PubMed Central

Sugita, Yuko; Araki, Fumiyuki; Chaya, Taro; Kawano, Kenji; Furukawa, Takahisa; Miura, Kenichiro

2015-01-01

The ribbon synapse is a specialized synaptic structure in the retinal outer plexiform layer where visual signals are transmitted from photoreceptors to the bipolar and horizontal cells. This structure is considered important in high-efficiency signal transmission; however, its role in visual signal processing is unclear. In order to understand its role in visual processing, the present study utilized Pikachurin-null mutant mice that show improper formation of the photoreceptor ribbon synapse. We examined the initial and late phases of the optokinetic responses (OKRs). The initial phase was examined by measuring the open-loop eye velocity of the OKRs to sinusoidal grating patterns of various spatial frequencies moving at various temporal frequencies for 0.5 s. The mutant mice showed significant initial OKRs with a spatiotemporal frequency tuning (spatial frequency, 0.09 ± 0.01 cycles/°; temporal frequency, 1.87 ± 0.12 Hz) that was slightly different from the wild-type mice (spatial frequency, 0.11 ± 0.01 cycles/°; temporal frequency, 1.66 ± 0.12 Hz). The late phase of the OKRs was examined by measuring the slow phase eye velocity of the optokinetic nystagmus induced by the sinusoidal gratings of various spatiotemporal frequencies moving for 30 s. We found that the optimal spatial and temporal frequencies of the mutant mice (spatial frequency, 0.11 ± 0.02 cycles/°; temporal frequency, 0.81 ± 0.24 Hz) were both lower than those in the wild-type mice (spatial frequency, 0.15 ± 0.02 cycles/°; temporal frequency, 1.93 ± 0.62 Hz). These results suggest that the ribbon synapse modulates the spatiotemporal frequency tuning of visual processing along the ON pathway by which the late phase of OKRs is mediated. PMID:25955222

Comparison of CDMA and FDMA for the MobileStar(sm) system

NASA Technical Reports Server (NTRS)

Jacobs, I. M.; Gilhousen, K. S.; Weaver, L. A.; Renshaw, K.; Murphy, T.

1988-01-01

Spread-spectrum code division multiple access (CDMA) and single channel per carrier frequency division multiple access (FDMA) systems are compared for spectrum efficiency. CDMA is shown to have greater maximum throughput than FDMA for the MobileStar(sm) system which uses digital voice activated carriers and directive circularly polarized satellite antennas.

Phase-locked Optical Signal Recovery

DTIC Science & Technology

2009-01-01

detection . However, implementing an optical phase lock loop ( OPLL ) to generate the synchronised carrier for the homodyne technique requires... Loop (OIPLL) in which a narrow bandwidth optical phase lock loop ( OPLL ) is used to control the free -running frequency of an optically injection...receiver uses an Optical Injection Phase Lock Loop (OIPLL) for carrier recovery,

Phase-locked Optical Signal Recovery

DTIC Science & Technology

2009-01-01

detection . However, implementing an optical phase lock loop ( OPLL ) to generate the synchronised carrier for the homodyne technique requires... Loop (OIPLL) in which a narrow bandwidth optical phase lock loop ( OPLL ) is used to control the free -running frequency of an optically injection...The receiver uses an Optical Injection Phase Lock Loop (OIPLL) for carrier

47 CFR Figure 4 to Subpart N of... - Example of EPIRB Carrier Component

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 1 2011-10-01 2011-10-01 false Example of EPIRB Carrier Component 4 Figure 4 to Subpart N of Part 2 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY... Emergency Position Indicating Radiobeacons (EPIRBs) Pt. 2, Subpt. N, Fig. 4 Figure 4 to Subpart N of Part 2...

47 CFR Figure 4 to Subpart N of... - Example of EPIRB Carrier Component

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 1 2010-10-01 2010-10-01 false Example of EPIRB Carrier Component 4 Figure 4 to Subpart N of Part 2 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY... Emergency Position Indicating Radiobeacons (EPIRBs) Pt. 2, Subpt. N, Fig. 4 Figure 4 to Subpart N of Part 2...

Demodulator for carrier transducers

NASA Technical Reports Server (NTRS)

Roller, R. F. (Inventor)

1974-01-01

A carrier type transducer is supplied with a carrier wave via an audio amplifier, a filter, a frequency divider, and an oscillator. The carrier is modulated in accordance with the parameter being measured by the transducer and is fed to the input of a digital data system which may include a voltmeter. The output of the oscillator and the output of each stage of the divider are fed to an AND or a NAND gate and suitable variable and fixed delay circuits to the command input of the digital data system. With this arrangement, the digital data system is commanded to sample at the proper time so that the average voltage of the modulated carrier is measured. It may be utilized with ancillary circuitry for control of the parameter

Motion mechanisms with different spatiotemporal characteristics identified by an MAE technique with superimposed gratings.

PubMed

Shioiri, Satoshi; Matsumiya, Kazumichi

2009-05-29

We investigated spatiotemporal characteristics of motion mechanisms using a new type of motion aftereffect (MAE) we found. Our stimulus comprised two superimposed sinusoidal gratings with different spatial frequencies. After exposure to the moving stimulus, observers perceived the MAE in the static test in the direction opposite to that of the high spatial frequency grating even when low spatial frequency motion was perceived during adaptation. In contrast, in the flicker test, the MAE was perceived in the direction opposite to that of the low spatial frequency grating. These MAEs indicate that two different motion systems contribute to motion perception and can be isolated by using different test stimuli. Using a psychophysical technique based on the MAE, we investigated the differences between the two motion mechanisms. The results showed that the static MAE is the aftereffect of the motion system with a high spatial and low temporal frequency tuning (slow motion detector) and the flicker MAE is the aftereffect of the motion system with a low spatial and high temporal frequency tuning (fast motion detector). We also revealed that the two motion detectors differ in orientation tuning, temporal frequency tuning, and sensitivity to relative motion.

47 CFR 74.762 - Frequency measurements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... Booster Stations § 74.762 Frequency measurements. (a) The licensee of a low power TV station, a TV translator, or a TV booster station must measure the carrier frequencies of its output channel as often as... intervals not exceeding 14 months. (b) In the event that a low power TV, TV translator, or TV booster...