These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Effect of substituents on the /sup 35/Cl NQR frequencies of atoms in conditions of hyperconjugation  

SciTech Connect

The authors studied the mechanisms of the change in the NOR spectra in a series of alpha-chloro-substituted dialkyl ethers, organonitrogen compounds, and benzyl and benzylidene chlorides. The NQR spectra were made on a pulsed IS-3 spectrometer at a temperature of 77 degrees K. There are n-o and ..pi..-o interactions which decrease the Cl 35 and Br 79 NQR frequencies in the series of alpha-chloro ethers, alpha-chloroalkylamides, and benzyl halides. The introduction of a geminal halogen atom (dichloromethyl ethers, benzylidene halides) decreases the effect of hyperconjugation.

Arbuzov, B.A.; Andreeva, A.I.; Bredikhin, A.A.; Safin, I.A.; Vereshchagin, A.N.

1985-12-10

2

Correlation between proton transfer and (35)Cl NQR frequency as well as molecular geometry of chloranilic acid in co-crystals with some organic bases.  

PubMed

Proton transfer in hydrogen-bonded organic co-crystals of chloranilic acid with some organic bases was investigated by nuclear quadrupole resonance (NQR) spectroscopy. The (35)Cl NQR frequencies of chloranilic acid molecule as well as (14)N NQR frequencies of the organic base molecule were measured with the conventional pulse methods as well as double-resonance methods, respectively. The extent of proton transfer in the O...H...N hydrogen bond was estimated from Townes-Dailey analysis of the (14)N NQR parameters. The (35)Cl NQR frequency and molecular geometry of chloranilic acid are correlated to the extent of proton transfer in the protonation process of the organic base molecule. It is shown that the hydrogen bond affects the pi-electron system of chloranilic acid. Geometry dependence of the O...H...N hydrogen bond, i.e. the H-N valence bond order versus the hydrogen-bond geometry correlation is also discussed. PMID:20535777

Asaji, Tetsuo; Seliger, Janez; Zagar, Veselko; Ishida, Hiroyuki

2010-07-01

3

35 Cl, 79 Br, and 127 I NQR spectra of some halogen-containing organoselenium compounds  

Microsoft Academic Search

1.The35Cl,79Br, and127I NQR spectra of a number of halogen-containing organoselenium compounds were obtained.2.The35Cl NQR frequencies of compounds of type R1R2R3SeCl (Ri=Me, Ph, Cl) are linearly related to the induction constants of the substituentssi.

V. V. Saatsazov; T. L. Khotsyanova; N. N. Magdesieva; S. I. Kuznetsov; I. M. Alymov; R. A. Kyandzhetsian; E. V. Bryukhova

1974-01-01

4

The incommensurate phase of 4,4'-dichlorobiphenyl sulphone reinvestigated by 35Cl NQR  

Microsoft Academic Search

In order to acquire new information about the normal-incommensurate (IC) phase transition and to check the existence of a lock-in transition in 4,4'-dichlorobiphenyl sulphone (4,4'-DCBS), a comprehensive 35Cl nuclear quadrupole resonance (NQR) study is reported. Detailed NQR measurements of frequency, line width and spin relaxation time (Tl) were obtained in the temperature range 80-270 K. The results show that the

J. Schneider; A. Wolfenson; A. Brunetti

1994-01-01

5

35Cl NQR of an organic ferroelectric phenazine chloranilic acid co-crystal  

NASA Astrophysics Data System (ADS)

A ferroelectric transition of phenazine (Phz) chloranilic acid (H 2ca) co-crystal was studied by 35Cl nuclear quadrupole resonance (NQR). The single NQR line observed at 36.689 MHz at 295 K, split into a doublet below the ferroelectric transition temperature Tc=253 K in accord with the inversion-symmetry breaking at the H 2ca molecular center in the crystal. The continuous variation of the splitting-width through Tc suggests a second-order nature of this phase transition. The NQR frequency is consistent with the crystal structure in which the two acid hydrogen atoms of H 2ca remain as attached to the quinone molecules. The spin-lattice relaxation time T1 showed a decrease with decreasing temperature in the ferroelectric phase. This suggests the existence of a fast motion of nearby atomic group, which is a cause of electric field gradient fluctuation.

Asaji, Tetsuo; Gotoh, Kazuma; Watanabe, Jun

2006-06-01

6

Partial disorder and molecular motion of 4-chlorobiphenyl studied by 35Cl NQR and Raman spectroscopy  

Microsoft Academic Search

Pulsed 35Cl nuclear quadrupole resonance (NQR) and Raman spectroscopy studies were performed to get information about the structural and dynamic thermal behavior of the 4-chlorobiphenyl. NQR measurements of the line shape and the spin-lattice relaxation time (T1) were obtained in the temperature range 80-320 K. An inhomogeneously broadened NQR line shape was observed, suggesting a disordered structure in all the

J. Schneider; A. Wolfenson; C. Schürrer; A. Brunetti; L. A. de O. Nunes

1996-01-01

7

Thermal hysteresis in 4,4' dichlorobenzophenone studied by 35Cl NQR  

Microsoft Academic Search

A pulsed NQR study of 4,4' dichlorobenzophenone has been performed to get information about dynamic features in its three crystalline phases. The authors found in phases I (T>190 K) and III (T<180 K) a normal thermal behaviour of the NQR frequency and spin-lattice relaxation time. In the intermediate phase II (180 KNQR parameters could

J. F. Schneider; A. E. Wolfenson; A. H. Brunetti

1992-01-01

8

Studies of the electronic structure and biological activity of chosen 1,4-benzodiazepines by 35Cl NQR spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

Selected derivatives of 1,4-benzodiazepine: lorazepam, lormetazepam, oxazepam and temazepam, used as active substances in anxiolytic drugs, have been studied by 35Cl NQR method in order to find the correlation between electronic structure and biological activity. The 35Cl NQR resonance frequencies ( ?Q) measured at 77 K have been correlated with the following parameters characterising their biological activity: biological half-life period ( t0.5), affinity to benzodiazepine receptor (IC 50) and mean dose equivalent. The results of experimental study of some benzodiazepine derivatives by nuclear quadrupole resonance of 35Cl nuclei are compared with theoretical results based on DFT calculations which were carried out by means of Gaussian'98 W software.

Bronisz, K.; Ostafin, M.; Poleshchuk, O. Kh.; Mielcarek, J.; Nogaj, B.

2006-11-01

9

35 Cl, 79 Br, and 127 I NQR spectra of several polyhalophenols and their phenylmercury derivatives  

Microsoft Academic Search

1.The intramolecular contribution to the splitting of the NQR frequencies in the 2,6-dihalo-4-X-derivatives of phenol has been separated out. The strength of the intramolecular hydrogen bond is substantially dependent on the nature of the substituants in position 4. The splittings in the NQR spectra are reduced upon passing from electron-accepting substituents to electron-donating substituents.2.The intramolecular coordination interactions of mercury atoms

G. Ko Semin; E. V. Bryukhova; D. N. Kravtsov; L. S. Golovchenko

1982-01-01

10

35 Cl, 79 Br, and 127 I NQR spectra and crystallographic parameters of some halomethylated phosphine oxides  

Microsoft Academic Search

1.The35Cl,79Br, and127I NQR spectra and the crystallographic parameters of a number of halomethylated phosphine oxides were measured.2.A structural nonequivalence of the bromine atoms was detected in (CH2Br)3PO.3.Phase transitions, with a change in the multipleticity of the NQR spectra, were recorded in (CH2Cl)3PO and (CH2I)3PO in the range 77–296°K.

V. V. Saatsazov; T. L. Khotsyanova; S. I. Kuznetsov

1975-01-01

11

Hydrogen transfer in hydrogen-bonded chloranilic acid studied by 35Cl NQR I - a 1:2 complex with 1,4-diazine  

NASA Astrophysics Data System (ADS)

35Cl NQR frequencies and spin-lattice relaxation time ( T1Q) and 1H NMR relaxation times ( T1H) in a H-bonded three molecular system, chloranilic acid-1,4-diazine (1:2) were measured to reveal H-motions in a symmetric two H-bonds in solid. A single 35Cl NQR frequency observed implies that the time-averaged structure of chloranilic acid is roughly monovalent in accordance with p Ka values in both acid and base. T1H temperature dependence was explained by a single relaxation mechanism due to the correlated H-transfer in two H-bonds, while that of T1Q yielded two relaxation processes. One of these undetected by 1H NMR was explained by the uncorrelated H-transfer.

Nihei, Taka-aki; Ishimaru, Shin'ichi; Ishida, Hiroyuki; Ishihara, Hideta; Ikeda, Ryuichi

2000-10-01

12

Conformational isomerism of methyl dichloroacetate. An infrared, Raman and 35Cl NQR study  

NASA Astrophysics Data System (ADS)

The IR and Raman spectra of methyl dichloroacetate (M-DCA) have been recorded on the liquid, glassy and crystalline states. The vibrational assignment for M-DCA is proposed on the basis of the spectral comparisons between CCl nH 3? n COOCH 3 and CCl nH 5? n CONHCH 5 ( n = 0-3) in the solid state. The observed spectral data indicate that M-DCA exists as a conformational equilibrium in the liquid and in the glassy state and that the conformation in the crystalline state is entirely different from those in the liquid and glassy states. The 35Cl NQR spectrum suggests that the conformation of M-DCA in the crystalline state is the cis form in which one of the two chlorine atoms is located in the cis position with respect to the carbonyl group. Examination of vibrational spectra also leads to the same conclusion.

Mido, Yoshiyuki; Hashimoto, Masao

1985-10-01

13

35 Cl, 79 Br, 81 Br, and 127 I NQR spectra of organomercury halides  

Microsoft Academic Search

A study of the NQR spectra of some halides disclosed that in the crystals of organomercury halides the behavior of the quadrupole constants is determined to a greater degree by the effect of the nature of the substituants on the intermolecular coordination reactions of Hg... Hal than by the usual transfer of the influence of the electronic effects along the

E. V. Bryukhova; A. K. Prokof'ev; T. Ya. Mel'nikova; O. Yu. Okhlobystia; G. K. Semin

1974-01-01

14

Detection of {sup 14}N and {sup 35}Cl in cocaine base and hydrochloride using NQR, NMR, and SQUID techniques  

SciTech Connect

Results from {sup 14}N pure NQR of cocaine in the free base form (cocaine base) yield a nuclear quadrupole coupling constant (NQCC) e{sup 2}Qq/h of 5.0229 ({+-}0.0001) MHz and an asymmetry parameter {eta} of 0.0395 ({+-}0.0001) at 295 K, with corresponding values of 5.0460 ({+-}0.0013) MHz and 0.0353 ({+-}0.0008) at 77 K. Both pure NQR (at 295-77 K) and a superconducting quantum interference device (SQUID) detector (at 4.2 K) were used to measure the very low (<1 MHz) {sup 14}N transition frequencies in cocaine hydrochloride; at 295 K the NQCC is 1.1780 ({+-}0.0014) MHz and the asymmetry parameter is 0.2632 ({+-}0.0034). Stepping the carrier frequency enables one to obtain a powder pattern without the severe intensity distortions that otherwise arise from finite pulse power. A powder pattern simulation using an NQCC value of 5.027 MHz and an asymmetry parameter {eta} of 0.2 agrees reasonably well with the experimental stepped-frequency spectrum. The use of pure NQR for providing nondestructive, quantitative, and highly specific detection of crystalline compounds is discussed, as are experimental strategies. 31 refs., 8 figs., 1 tab.

Yesinowski, J.P.; Buess, M.L.; Garroway, A.N. [Naval Research Lab., Washington, DC (United States); Ziegeweid, M.; Pines, A. [Univ. of California, Berkeley, CA (United States)]|[Lawrence Berkeley Lab., CA (United States)

1995-07-01

15

35Cl NQR study of lattice dynamic and magnetic property of a crystalline coordination polymer {CuCA(phz)(H 2O) 2} n  

NASA Astrophysics Data System (ADS)

Copper(II) compounds {CuCA(phz)(H 2O) 2} n (H 2CA = chloranilic acid, phz = phenazine) having a layer structure of -CuCA(H 2O) 2- polymer chains and phenazine were studied by 35Cl nuclear quadrupole resonance (NQR). The single NQR line observed at 35.635 MHz at 261.5 K increased to 35.918 MHz at 4.2 K. The degree of reduction of electric field gradient due to lattice vibrations was similar to that of chloranilic acid crystal. Temperature dependence of spin-lattice relaxation time, T1, of the 35Cl NQR signal below 20 K, between 20 and 210 K, and above 210 K, was explained by (1) a decrease of effective electron-spin density caused by antiferromagnetic interaction, (2) a magnetic interaction between Cl nuclear-spin and electron-spins on paramagnetic Cu(II) ions, and (3) an increasing contribution from reorientation of ligand molecules, respectively. The electron spin-exchange parameter ? J? between the neighboring Cu(II) electrons was estimated to be 0.33 cm -1 from the T1 value of the range 20-210 K. Comparing this value with that of J = -1.84 cm -1 estimated from the magnetic susceptibility, it is suggested that the magnetic dipolar coupling with the electron spins on Cu(II) ions must be the principal mechanism for the 35Cl NQR spin-lattice relaxation of {CuCA(phz)(H 2O) 2} n but a delocalization of electron spin over the chloranilate ligand has to be taken into account.

Gotoh, Kazuma; Terao, Takeshi; Asaji, Tetsuo

2007-01-01

16

Frequency selective detection of nuclear quadrupole resonance (NQR) spin echoes  

NASA Astrophysics Data System (ADS)

Nuclear Quadrupole Resonance (NQR) is a radio frequency (RF) technique that can be used to detect the presence of quadrupolar nuclei, such as the 14N nucleus prevalent in many explosives and narcotics. The technique has been hampered by low signal-to-noise ratios and is further aggravated by the presence of RF interference (RFI). To ensure accurate detection, proposed detectors should exploit the rich form of the NQR signal. Furthermore, the detectors should also be robust to any remaining residual interference, left after suitable RFI mitigation has been employed. In this paper, we propose a new NQR data model, particularly for the realistic case where multiple pulse sequences are used to generate trains of spin echoes. Furthermore, we refine two recently proposed approximative maximum likelihood (AML) detectors, enabling the algorithm to optimally exploit the data model of the entire echo train and also incorporate knowledge of the temperature dependent spin-echo decay time. The AML-based detectors ensure accurate detection and robustness against residual RFI, even when the temperature of the sample is not precisely known, by exploiting the dependencies of the NQR resonant lines on temperature. Further robustness against residual interference is gained as the proposed detector is frequency selective; exploiting only those regions of the spectrum where the NQR signal is expected. Extensive numerical evaluations based on both simulated and measured NQR data indicate that the proposed Frequency selective Echo Train AML (FETAML) detector offers a significant improvement as compared to other existing detectors.

Somasundaram, Samuel D.; Jakobsson, Andreas; Smith, John A. S.; Althoefer, Kaspar A.

2006-05-01

17

Hyperfine-resolved transition frequency list of fundamental vibration bands of H35Cl and H37Cl  

NASA Astrophysics Data System (ADS)

Sub-Doppler resolution spectroscopy of the fundamental vibration bands of H35Cl and H37Cl has been carried out from 87.1 to 89.9 THz. We have determined the absolute transition frequencies of the hyperfine-resolved R(0) to R(4) transitions with a typical uncertainty of 10 kHz. We have also yielded six molecular constants for each isotopomer in the vibrational excited state, which reproduce the determined frequencies with a standard deviation of about 10 kHz.

Iwakuni, Kana; Sera, Hideyuki; Abe, Masashi; Sasada, Hiroyuki

2014-12-01

18

Nuclear quadrupole resonance of 35Cl nuclei in glassy solution of chlorobenzene in pyridine  

Microsoft Academic Search

Pulsed nuclear quadrupole resonance (NQR) measurements of 35Cl nuclei were performed on 43.5 mol % chlorobenzene solution in pyridine (a) in glassy state (Tg=131 K) after quenching in liquid nitrogen and (b) in crystalline precipitate under slow cooling starting from liquid phase. In both cases the NQR line shape, obtained by the fast Fourier transform (FFT) method, consisted of a

A. E. Wolfenson; A. H. Brunetti; D. J. Pusiol; W. M. Pontuschka

1990-01-01

19

Temperature dependence of one-dimensional hydrogen bonding in morpholinium hydrogen chloranilate studied by 35Cl nuclear quadrupole resonance and multi-temperature X-ray diffraction.  

PubMed

The temperature dependence of (35)Cl NQR frequencies and the spin-lattice relaxation times T(1) has been measured in the wide temperature range of 4.2-420 K for morpholinium hydrogen chloranilate in which a one-dimensional O-HO hydrogen-bonded molecular chain of hydrogen chloranilate ions is formed. An anomalous temperature dependence of the NQR frequencies was analyzed to deduce a drastic temperature variation of the electronic state of the hydrogen-bonded molecular chain. The hydrogen atom distribution in the OHO hydrogen bond is discussed from the results of NQR as well as multi-temperature X-ray diffraction. Above ca. 330 K, the T(1) showed a steep decrease with an activation energy of ca. 70 kJ mol(-1) and with an isotope ratio (37)Cl T(1)/(35)Cl T(1) = 0.97 ± 0.2. The orientational change of the z axis of electric field gradient tensor in conjunction with the hydrogen transfer between adjacent hydrogen chloranilate ions is suggested as a possible relaxation mechanism. PMID:22872006

Tobu, Yasuhiro; Ikeda, Ryuichi; Nihei, Taka-aki; Gotoh, Kazuma; Ishida, Hiroyuki; Asaji, Tetsuo

2012-09-21

20

Low-frequency NMR and NQR with a dc SQUID amplifier  

SciTech Connect

A sensitive Fourier-transform spectrometer based on a dc SQUID (Superconducting QUantum Interference Device) has been developed for the direct detection of nuclear magnetic resonance (NMR) in zero applied magnetic field and pure nuclear quadrupole resonance (NQR) at low frequencies. The motivation to detect zero field NMR and NQR is to provide a new high resolution spectroscopy technique at frequencies below 200 kHz to study ultra-weak interactions in chemicals and materials. By comparing the sensitivity of a SQUID amplifier with that of a conventional semiconductor amplifier, it is shown that a SQUID amplifier is essential for the direct detection of low frequency resonant signals. The spectrometer has a frequency response extending from about 10 to 200 kHz, and a recovery time (after the magnetic pulse is removed) of about 50 {mu}s. The spectrometer is used to detect NMR spectra from Pt and Cu metal powders in a magnetic field of 6 mtesla, and NQR spectra from {sup 2}D in a tunneling methyl group and {sup 14}N in NH{sub 4}ClO{sub 4}. Finally, the zero field NMR spectrum from a quantum tunneling methyl group is calculated. 25 refs., 34 figs., 2 tabs.

Fan, Nong-Qiang.

1990-11-01

21

Molecular structure and nuclear quadrupole coupling tensors of 14N and 35Cl in 1-chloro-2,4-dinitrobenzene. Phase I  

Microsoft Academic Search

The crystal structure of the orthorhombic, stable phase of 1-chloro-2,4-dinitrobenzene was studied at T=295 K by x-ray diffraction; space group D102h=Pccn; a=893.0(1) pm, b=1104.5(2) pm, c=1567.6(2) pm, Z=8, &rgr;calc=1.740 Mg m?3, all atoms in position 8(e). The Zeeman split single crystal 35Cl NQR gives e2&Fgr;zzQh?1(35Cl)=74.287(4) MHz, &eegr;(35Cl)=0.1636(18) at T=295 K. At 110 K the values are: e2&Fgr;zzQh?1(35Cl)=75.183(4) MHz, &eegr;(35Cl)=0.1572(20). &Fgr;zz(35Cl)

Surendra Sharma; Norbert Weiden; Alarich Weiss

1989-01-01

22

Electron density distribution in cladribine (2-chloro-2?-deoxyadenosine) - A drug against leukemia and multiple sclerosis - Studied by multinuclear NQR spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

2-Chloro-2'-deoxyadenosine (Cladribine) chemotherapeutic drug has been studied experimentally in solid state by 35Cl NQR and NMR-NQR double resonance and theoretically by the Density Functional Theory. Fifteen resonance frequencies on 14N have been detected and assigned to particular nitrogen sites in the 2-CdA molecule. The effects of tautomerism, regioisomerism, conformations and molecular aggregations, related to intermolecular hydrogen bond formation, on the NQR parameters have been analysed within the DFT and AIM ( Atoms in Molecules) formalism. The properties of the whole molecule, the so-called global reactivity descriptors, have been calculated for a comparison of both syn and anti conformations of 2-CdA molecule to check the effect of crystal packing on molecular conformation.

Latosi?ska, J. N.; Latosi?ska, M.; Seliger, J.; Žagar, V.; Kazimierczuk, Z.

2009-07-01

23

I: Low Frequency NMR and NQR Using a dc SQUID. II: Variable-temperature 13C CP\\/MAS of Organometallics  

Microsoft Academic Search

NMR and NQR at low frequencies are difficult prospects due to small nuclear spin polarization. Furthermore, the sensitivity'of the inductive pickup circuitry of standard spectrometers is reduced as the frequency is lowered. I have used a cw-SQUID (Superconducting QUantum Interference Device) spectrometer, which has no such frequency dependence, to study the local atomic environment of ¹N via the quadrupolar interaction.

Ziegeweid

1995-01-01

24

35Cl nuclear quadrupole resonance study in 4,4'-dichlorobiphenyl sulphone: A possible incommensurate system  

Microsoft Academic Search

Pulsed nuclear quadrupole resonance (NQR) has been used to get information about the nature of the molecular dynamics in two crystalline phases of 4,4'-dichlorobiphenyl sulphone. This work includes detailed experimental measurements of the NQR frequency, spin-lattice relaxation time, and line intensity temperature behavior in the range of temperature where a possible normal-to-incommensurate phase transition occurs. The experimental results show the

D. J. Pusiol; A. E. Wolfenson; A. H. Brunetti

1989-01-01

25

Explosives detection by nuclear quadrupole resonance (NQR)  

NASA Astrophysics Data System (ADS)

Pure nuclear quadrupole resonance (NQR) of 14N nuclei is quite promising as a method for detecting explosives such as RDX and contraband narcotics such as cocaine and heroin in quantities of interest. Pure NQR is conducted without an external applied magnetic field, so potential concerns about damage to magnetically encoded data or exposure of personnel to large magnetic fields are not relevant. Because NQR frequencies of different compounds are quite distinct, we do not encounter false alarms from the NQR signals of other benign materials. We have constructed a laboratory prototype NQR explosives detector which interrogates a volume of 300 liters (10 ft3). This paper presents abbreviated results from a demonstration of the laboratory prototype NQR explosives detector conducted at the Federal Aviation Administration Technical Center in May 1994 on RDX-based explosives.

Garroway, Allen N.; Buess, Michael L.; Yesinowski, James P.; Miller, Joel B.; Krauss, Ronald A.

1994-10-01

26

Oxygen isotope effect of the plane-copper NQR frequency in YBa2Cu4O8  

NASA Astrophysics Data System (ADS)

We report high-precision measurements of the temperature dependence of the plane-63Cu NQR line frequency ?Q(Cu2) and the linewidth in normal and superconducting 16O and 18O-exchanged YBa2Cu4O8. Whereas ?Q(Cu2) passes Tc very smoothly without a discontinuity either in value or slope, the linewidth increases in the normal conducting phase down to Tc and starts to decrease sharply in the superconducting phase to finally resume its high-temperature value of the normal phase. There is a well discernible oxygen isotope effect on the ?Q(Cu2) temperature dependencies. The temperature dependence of ?Q(Cu2) is described by an empirical expression consisting of two parts, one related to the thermal expansion of the lattice and the other due to charge redistribution during the formation of new electronic structures in the CuO2 planes. From the fit to the experimental data we determine for the conjectured formation of new electronic structures an energy scale ?(16O)=188.0(1.6) K and ?(18O)=180.0(1.6) K. This results in a partial oxygen isotope effect coefficient ??Q=0.42(11) which is larger than both the spin pseudogap coefficient ?PG=0.061(8) and the Tc coefficient ?Tc=0.056(12) [F. Raffa, T. Ohno, M. Mali, J. Roos, D. Brinkmann, K. Conder, and M. Eremin, Phys. Rev. Lett. 81, 5912 (1998)].

Mali, M.; Roos, J.; Keller, H.; Karpinski, J.; Conder, K.

2002-05-01

27

A miniaturized NQR spectrometer for a multi-channel NQR-based detection device.  

PubMed

A low frequency (0.5-5 MHz) battery operated sensitive pulsed NQR spectrometer with a transmitter power up to 5 W and a total mass of about 3 kg aimed at detecting (14)N NQR signals, predominantly of illicit materials, was designed and assembled. This spectrometer uses a standard software defined radio (SDR) platform for the data acquisition unit. Signal processing is done with the LabView Virtual instrument on a personal computer. We successfully tested the spectrometer by measuring (14)N NQR signals from aminotetrazole monohydrate (ATMH), potassium nitrate (PN), paracetamol (PCM) and trinitrotoluene (TNT). Such a spectrometer is a feasible component of a portable single or multichannel (14)N NQR based detection device. PMID:25233110

Beguš, Samo; Jazbinšek, Vojko; Pirnat, Janez; Trontelj, Zvonko

2014-10-01

28

I: Low Frequency NMR and NQR Using a dc SQUID. II: Variable-temperature 13C CP/MAS of Organometallics  

SciTech Connect

NMR and NQR at low frequencies are difficult prospects due to small nuclear spin polarization. Furthermore, the sensitivity'of the inductive pickup circuitry of standard spectrometers is reduced as the frequency is lowered. I have used a cw-SQUID (Superconducting QUantum Interference Device) spectrometer, which has no such frequency dependence, to study the local atomic environment of {sup 14}N via the quadrupolar interaction. Because {sup 14}N has spin I = 1 and a 0-6 MHz frequency range, it is not possible to obtain well-resolved spectra in high magnetic fields. I have used a technique to observe {sup 14}N NQR resonances via their effect on neighboring protons mediated by the heteronuclear dipolar interaction to study peptides and narcotics. The sensitivity of the SQUID is not enough to measure low-frequency surface (or other low spin density) systems. The application of spin-polarized xenon has been previously used to enhance polarization in conventional NMR experiments. Because xenon only polarizes spins with which it is in contact, it is surface selective. While differences in chemical shifts between surface and bulk spins are not large, it is expected that the differences in quadrupole coupling constant should be very large due to the drastic change of the electric field gradient surrounding spins at the surface. With this in mind, I have taken preliminary steps to measure SQUID detected polarization transfer from Xe to another spin species at 4.2 K and in small magnetic fields (<50 G). In this regime, the spin-lattice relaxation of xenon is dependent on the applied magnetic field. The results of our efforts to characterize the relaxation of xenon are presented. The final section describes the solid-state variable-temperature (VT) one- and two-dimensional {sup 13}C cross polarization (CP)/magic angle spinning (MAS) NMR of Hf({eta}{sup 5}-C{sub 5}H{sub 5}){sub 2}({eta}{sup 1}-C{sub 5}H{sub 5}){sub 2}, Zr({eta}{sup 5}-C{sub 5}H{sub 5}){sub 3}({eta}{sup 1}-C{sub 5}H{sub 5}) and Sn({eta}{sup 1}-C{sub 5}H{sub 5}){sub 4}. This work was undertaken in the hope of gaining insight into the intramolecuhrr dynamics, specifically which fluxional processes exist in the solid state, by what mechanism rearrangements are occurring, and the activation energies by which these processes are governed.

Ziegeweid, M.A.

1995-11-29

29

Intensity of NQR lines for integer spins  

NASA Astrophysics Data System (ADS)

Because of the publication of contradictory information demonstrating an incorrect approach to the modeling of NQR-NMR frequency-intensity spectra of integral-spin isotopes (for example, boron-10), we study the NQR-NMR double resonance with level crossing (DRLC) in10B-1H,11B-1H,59K-1H and23Na-1H in crystal hydrates of sodium tetraborate (Na2B4O7·10H2O) and potassium tetraborate (K2B4O7·4H2O) and the results of the measurements are compared with theoretical calculations. The fact that for a system including three elements-quadrupole (NQR), Zeeman (NMR), and dipole-dipole, which establishes the interaction of the first two- the intensities of the lines in double resonance spectra are determined both by the equations of balance of the populations of the levels of the quadrupole and Zeeman reservoirs and by the probabilities of transitions within each reservoir is taken into account in the calculations. The distortion of the energy levels of the NQR subsystem by the magnetic field in the process of level crossing with the NMR subsystem is taken into account.

Anferov, V. P.; Beloglazov, G. S.; Grechishkin, V. S.

1986-12-01

30

79 Br and 127 I nqr spectra in series of acetylene derivatives  

Microsoft Academic Search

The complete79Br and127I NQR spectra of a number of bromo and iodo derivatives of acetylene were studied for the first time, and the field constants of the NQR frequencies were determined. It was found that the asymmetry parameters in them are low. Changes in the field constants are determined by the competing conjugation of the iodine atom and the corresponding

G. K. Semin; S. A. Petukhov; S. I. Gushchin; I. R. Gol'ding; E. V. Bryukhova; A. M. Sladkov

1983-01-01

31

Two-dimensional NQR using ultra-broadband electronics.  

PubMed

We have recently developed an ultra-broadband instrument that can effectively excite and detect NMR and NQR signals over a wide frequency range. Our current system operates between 100 kHz and 3.2 MHz using an un-tuned sample coil. The major benefits of this instrument compared to conventional NQR/NMR systems include increased robustness, ease of use (in particular for multi-frequency experiments), and elimination of the need for tuning adjustments in the hardware. Here we describe its use for performing two-dimensional (2D) scans, which allow improved interpretation of complex NQR spectra by detecting the connected resonances. Our method relies on population transfers between the three energy levels of spin-1 nuclei (such as (14)N) by using multi-frequency excitation and a single RF coil. Experimental results on pure samples and mixtures are also presented. PMID:24495675

Mandal, S; Song, Y-Q

2014-03-01

32

Field constants of 79 Br and 127 I NQR of halogen derivatives of carbon  

Microsoft Academic Search

A study has been made of the NQR frequency field constants for the chlorine, bromine, and iodine atoms. It has been shown that the degree to which the field constants are characteristic decreases in the series Cl-Br-I.

S. A. Petukhov; E. V. Bryukhova; G. K. Semin; A. A. Boguslavskii

1984-01-01

33

Ultra-Low Temperature Thermometry Using Zeeman Perturbed NQR  

Microsoft Academic Search

We report the results of measurements of the magnetic field perturbed nuclear quadrupole resonance (NQR) lines of powdered Sb immersed in liquid3He at low temperatures. The magnetic field was used to separate the frequencies of the allowed transitions between the \\u000a

E. B. Genio; G. G. Ihas; N. S. Sullivan

1998-01-01

34

35Cl nuclear quadrupolar resonance study of 4,4'-dichlorobiphenyl sulphone  

Microsoft Academic Search

Pulsed NQR spectroscopy was used to search for a structural phase transition from a normal to an incommensurate phase and others in 4,4'-dichlorobiphenyl sulphone. The experimental results show the existence of a structural phase transition to an incommensurate phase at 150 K and another transition to a possible commensurate phase at 110 K.

J. M. Corberó; A. E. Wolfenson; D. J. Pusiol; A. H. Brunetti

1986-01-01

35

SQUID detected NMR and NQR  

Microsoft Academic Search

The dc Superconducting QUantum Interference Device (SQUID) is a sensitive detector of magnetic flux, with a typical flux noise of the order 1 ??0 Hz?1\\/2 at liquid helium temperatures. Here ?0=?\\/2e is the flux quantum. In our NMR or NQR spectrometer, a niobium wire coil wrapped around the sample is coupled to a thin film superconducting coil deposited on the

Matthew P. Augustine; Dinh M. TonThat; John Clarke

1998-01-01

36

DTA and NQR studies of polymorphism in p-chlorofluorobenzene  

Microsoft Academic Search

Differential thermal analysis, and the 35Cl Nuclear Quadrupole Resonance frequency (?Q) and spin-lattice relaxation time (T1) were measured as a function of temperature in p-chlorofluorobenzene. Three different phases were found according to the thermal history of the sample and only one was stable up to the melting point. In one of the phases, the presence of molecular reorientations can be

L. Cerioni; S. Perez; A. Wolfenson

2004-01-01

37

(35)Cl solid-state NMR of halide ionic liquids at ultrahigh fields.  

PubMed

This Letter describes recent work investigating the solid-state NMR spectra of (35)Cl nuclei in an assortment of ionic liquids under static and MAS conditions at field strengths of 9.4 and 21.1 T. At high field it was possible to resolve and extract information from multiple unique crystallographic sites and to resolve otherwise complex spectra that were analyzed to extract information regarding the electric field gradient (EFG) and chemical shift tensors, including their relative orientation. The NMR parameters were found to be typical of organic salts in general. PMID:19007195

Gordon, Peter G; Brouwer, Darren H; Ripmeester, John A

2008-12-11

38

Isotope ratio of Cl NQR spin-lattice relaxation times in 1D hydrogen-bonding system of tetramethylpyrazine-chloranilic acid at high temperatures  

NASA Astrophysics Data System (ADS)

The temperature dependences of spin-lattice relaxation time T 1 of 35Cl and 37Cl NQR were studied for the co-crystal of tetramethylpyrazine (TMP) with chloranilic acid (H2ca), TMP-H2ca, in which one-dimensional hydrogen bonding is formed by alternate arrangement of TMP and H2ca. The isotope ratio 37Cl T 1 / 35Cl T 1 was determined to be 1.0 ± 0.1 above ca. 290 K where a steep decrease of spin-lattice relaxation time T 1 with increasing temperature was observed. In this temperature range it is suggested that the relaxation is originated from the slow fluctuation of electric field gradient (EFG). Beside EFG fluctuation due to the external-charge-density fluctuation, the small angle reorientation of the quantization axis triggered by a proton transfer motion between N...H-O and N-H...O hydrogen bonding states is proposed.

Asaji, Tetsuo

2013-05-01

39

Copper valence, structural separation and lattice dynamics in tennantite (fahlore): NMR, NQR and SQUID studies  

NASA Astrophysics Data System (ADS)

Electronic and magnetic properties of tennantite subfamily of tetrahedrite-group minerals have been studied by copper nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR) and SQUID magnetometry methods. The temperature dependences of copper NQR frequencies and line-width, nuclear spin-lattice relaxation rate T {1/-1} and nuclear spin-echo decay rate T {2/-1} in tennantite samples in the temperature range 4.2-210 K is evidence of the presence of field fluctuations caused by electronic spins hopping between copper CuS3 positions via S2 bridging atom. The analysis of copper NQR data at low temperatures points to the magnetic phase transition near 65 K. The magnetic susceptibility in the range 2-300 K shows a Curie-Weiss behavior, which is mainly determined by Fe2+ paramagnetic substituting ions.

Gainov, R. R.; Dooglav, A. V.; Pen'kov, I. N.; Mukhamedshin, I. R.; Savinkov, A. V.; Mozgova, N. N.

2008-01-01

40

NQR and Raman spectroscopy study of ?-dichlorobiphenyl  

Microsoft Academic Search

Pulsed 0953-8984\\/8\\/21\\/016\\/img9 nuclear quadrupole resonance (NQR) and Raman spectroscopy studies were performed to get information about the structural and dynamic thermal behaviour of the 0953-8984\\/8\\/21\\/016\\/img10 dichlorobiphenyl. NQR measurements of the line-shape and the spin - lattice relaxation time 0953-8984\\/8\\/21\\/016\\/img11 were obtained in the temperature range 80 K - 320 K. Raman spectra from powder samples were recorded for temperatures between

J. Schneider; A. Wolfenson; A. Brunetti; L. A. de O. Nunes

1996-01-01

41

Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds.  

PubMed

Two hexanuclear niobium halide cluster compounds with a [Nb6X12](2+) (X=Cl, Br) diamagnetic cluster core, have been studied by a combination of experimental solid-state NMR/NQR techniques and PAW/GIPAW calculations. For niobium sites the NMR parameters were determined by using variable Bo field static broadband NMR measurements and additional NQR measurements. It was found that they possess large positive chemical shifts, contrary to majority of niobium compounds studied so far by solid-state NMR, but in accordance with chemical shifts of (95)Mo nuclei in structurally related compounds containing [Mo6Br8](4+) cluster cores. Experimentally determined ?iso((93)Nb) values are in the range from 2,400 to 3,000 ppm. A detailed analysis of geometrical relations between computed electric field gradient (EFG) and chemical shift (CS) tensors with respect to structural features of cluster units was carried out. These tensors on niobium sites are almost axially symmetric with parallel orientation of the largest EFG and the smallest CS principal axes (Vzz and ?33) coinciding with the molecular four-fold axis of the [Nb6X12](2+) unit. Bridging halogen sites are characterized by large asymmetry of EFG and CS tensors, the largest EFG principal axis (Vzz) is perpendicular to the X-Nb bonds, while intermediate EFG principal axis (Vyy) and the largest CS principal axis (?11) are oriented in the radial direction with respect to the center of the cluster unit. For more symmetrical bromide compound the PAW predictions for EFG parameters are in better correspondence with the NMR/NQR measurements than in the less symmetrical chlorine compound. Theoretically predicted NMR parameters of bridging halogen sites were checked by (79/81)Br NQR and (35)Cl solid-state NMR measurements. PMID:24581866

Peri?, Berislav; Gautier, Régis; Pickard, Chris J; Bosio?i?, Marko; Grbi?, Mihael S; Požek, Miroslav

2014-01-01

42

A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on 35Cl, 113Cd, and 139La  

E-print Network

An apparatus for measuring parity-violating asymmetries in gamma-ray emission following polarized cold neutron capture was constructed as a 1/10th scale test of the design for the forthcoming n+p->d+gamma experiment at LANSCE. The elements of the polarized neutron beam, including a polarized 3He neutron spin filter and a radio frequency neutron spin rotator, are described. Using CsI(Tl) detectors and photodiode current mode readout, measurements were made of asymmetries in gamma-ray emission following neutron capture on 35Cl, 113Cd, and 139La targets. Upper limits on the parity-allowed asymmetry $s_n \\cdot (k_{\\gamma} \\times k_n)$ were set at the level of 7 x 10^-6 for all three targets. Parity-violating asymmetries $s_n \\cdot k_{\\gamma}$ were observed in 35Cl, A_gamma = (-29.1 +- 6.7) x 10^-6, and 139La, A_gamma = (-15.5 +- 7.1) x 10^-6, values consistent with previous measurements.

G. S. Mitchell; C. S. Blessinger; J. D. Bowman; T. E. Chupp; K. P. Coulter; M. T. W. Gericke; G. L. Jones; M. B. Leuschner; H. Nann; S. A. Page; S. I. Penttila; T. B. Smith; W. M. Snow; W. S. Wilburn

2004-01-08

43

Improving the sensitivity of a high-Tc SQUID at MHz frequency using a normal metal transformer  

Microsoft Academic Search

Superconducting quantum interference devices (SQUIDs) can be used to detect the signals of nuclear quadrupole resonance (NQR). The NQR frequencies of some interesting materials are in the order of MHz. However, the sensitivity of a high-Tc SQUID is normally not enough to detect the weak NQR signals. To improve the sensitivity of a high-Tc SQUID at MHz frequency, we used

D. F. He; H. Itozaki; M. Tachiki

2006-01-01

44

Methyl quantum tunneling and nitrogen-14 NQR NMR studies using a SQUID magnetic resonance spectrometer  

SciTech Connect

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) techniques have been very successful in obtaining molecular conformation and dynamics information. Unfortunately, standard NMR and NQR spectrometers are unable to adequately detect resonances below a few megahertz due to the frequency dependent sensitivity of their Faraday coil detectors. For this reason a new spectrometer with a dc SQUID (Superconducting Quantum Interference Device) detector, which has no such frequency dependence, has been developed. Previously, this spectrometer was used to observe {sup 11}B and {sup 27}Al NQR resonances. The scope of this study was increased to include {sup 23}Na, {sup 51}V, and {sup 55}Mn NQR transitions. Also, a technique was presented to observe {sup 14}N NQR resonances through cross relaxation of the nitrogen polarization to adjacent proton spins. When the proton Zeeman splitting matches one nitrogen quadrupoler transition the remaining two {sup 14}N transitions can be detected by sweeping a saturating rf field through resonance. Additionally, simultaneous excitation of two nitrogen resonances provides signal enhancement which helps to connect transitions from the same site. In this way, nitrogen-14 resonances were observed in several amino acids and polypeptides. This spectrometer has also been useful in the direct detection of methyl quantum tunneling splittings at 4.2 K. Tunneling, frequencies of a homologous series of carboxylic acids were measured and for solids with equivalent crystal structures, an exponential correlation between the tunneling frequency and the enthalpy of fusion is observed. This correlation provides information about the contribution of intermolecular interactions to the energy barrier for methyl rotation.

Black, B.E. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (United States)

1993-07-01

45

75As, 63Cu NMR and NQR characterization of selected arsenic minerals.  

PubMed

The direct measurement and identification of solid state arsenic phases using (75)As NMR is made difficult by the simultaneous conditions of large quadrupole moment and low coordination symmetry in many compounds. However, specific arsenic minerals can efficiently be detected and discriminated via nuclear quadrupolar resonance (NQR). We report on the first NMR and NQR measurements in the natural minerals enargite (Cu3AsS4), niccolite (NiAs), arsenopyrite (FeAsS) and loellingite (FeAs2). The NQR frequencies have been determined from both high-field NMR powder patterns and via zero-field frequency sweeps. Density functional theory (DFT) based ab initio calculations support the experimental results. The compounds studied here are common in terms of the known set of As-containing minerals. They are sometimes encountered in the context of base metal or gold mining. The study represents a significant addition to the list of arsenic minerals that can now be detected with NQR techniques. PMID:23706610

Lehmann-Horn, J A; Miljak, D G; Bastow, T J

2013-01-01

46

NQR investigation and characterization of cocrystals and crystal polymorphs  

NASA Astrophysics Data System (ADS)

The application of 14N NQR to the study of cocrystals and crystal polymorphs is reviewed. In ferroelectric and antiferroelectric organic cocrystals 14N NQR is used to determine proton position in an N-H...O hydrogen bond and proton displacement below TC. In cocrystal isonicitinamide - oxalic acid (2:1) 14N NQR is used to distinguish between two polymorphs and to determine the type of the hydrogen bond (N-...H-O). The difference in the 14N NQR spectra of cocrystal formers and cocrystal is investigated in case of carbamazepine, saccharin and carbamazepine - saccharin (1:1). The experimental resolution allows an unambiguous distinction between the 14N NQR spectrum of the cocrystal and the 14N NQR spectra of the cocrystal formers. The possibility of application of NQR and double resonance for the determination of the inhomogeneity of the sample and for the study of the life time of an unstable polymorph is discussed.

Seliger, Janez; Žagar, Veselko; Asaji, Tetsuo

2013-05-01

47

Band 3 structure and function: sup 35 Cl NMR and topographical investigations  

SciTech Connect

Band 3 is the anion exchange protein in red blood cells. Physiologically, it transports Cl{sup {minus}} into or out of the red blood cells and then transports HCO{sub 3}{sup {minus}} in the opposite direction so that electroneutrality is maintained on both sides of the membrane. The anion exchange mechanism of band 3 is unique among the ion transport proteins. It transports anions by a ping-pong mechanism, meaning it is a gated protein which effects the one-for-one exchange of anions across the membrane. It is also unusual because it transports a wide variety of anions in a very efficient manner (up to 200 sec{sup {minus}1}). An arginine has been implicated in the binding and transport of chloride across the red blood cell membrane. The primary goal of this work was to determine the location of that arginine. A second goal was to investigate divalent anion binding to the active site. {sup 35}Cl NMR was used to investigate the competition of chloride with divalent anions at the chloride binding site of band 3. These studies were performed to determine if divalent anions compete with chloride for binding at the active site. pH profiles of chloride competition with divalent anions were also obtained. The goal of the biochemical studies was to determine the location of the band 3 arginine anion binding site. In order to insure that an arginine preferentially labeled by {sup 14}C-phenylglyoxal was indeed at a transmembrane peptide and to verify the model, many of the transmembrane sequences have been isolated. This was accomplished by modification of a technique developed to separate hydrophobic synthetic peptides. Of a probable total of 14 transmembrane helices, the N-termini and/or C-termini have been determined for 6 of them.

Kanes, K.J.

1989-01-01

48

Effect of the oxygen protonation on the electronic structure of urea in the solid state: A 14N NQR study  

NASA Astrophysics Data System (ADS)

The 14N NQR frequencies of urea complexes with H2O2 (1:1), NH4Cl (1:1), oxalic (2:1), phosphoric (1:1), and nitric acid (1:1) at 77 °K are reported. The analysis of the NQR data indicates that the population of the N nonbonding orbital decreases and that the population of the s N-H and N-C bonds increases as the degree of protonation of the O atom of urea increases. These changes are consistent with a larger weight of structures like C = N+H2 as the protonation increases. The NQR results are in agreement with those obtained from a CNDO/2 calculation for the uronioum ion [Yu. A. Panteleev and A. A. Lipovskii, Zhu. Struk. Khim. 17, 2 (1976)].

Murgich, Juan; Santana R., Magaly

1981-04-01

49

Effects of nonsinusoidal character of atomic modulation on NQR spin-lattice relaxation time of incommensurate phases  

Microsoft Academic Search

The present work is an extention of the theoretical calculation developed by Blinc to explain the temperature and frequency dependence of the spin-lattice relaxation time in incommensurate phases. We have evaluated the influence of the nonsinusoidal character of the atomic modulation, in the linear approximation, over the NQR spectra and over the spin-lattice relaxation due to direct and Raman processes.

Silvina C. Pérez; Clemar Schurrer; Alberto Wolfenson

2001-01-01

50

Copper NQR and NMR in the superconductor YBa2Cu4O8+x  

Microsoft Academic Search

The frequencies nuQ, the linewidth and the spin-lattice and spin-spin relaxation times T1 and T2, respectively, of the 63Cu nuclear quadrupole resonance (NQR) signals for chain and planar copper sites in YBa2Cu4O8 were measured between 6 and 750 K; in addition nuclear magnetic resonance (NMR) spectra were taken at 150 and 300 K. The results are compared with data known

H. Zimmermann; M. Mali; D. Brinkmann; J. Karpinski; E. Kaldis; S. Rusiecki

1989-01-01

51

Some features of double-resonance detection of 17O NQR in ice  

NASA Astrophysics Data System (ADS)

Proton oxygen-17 double resonance was used to detect the NQR signals of 17O in natural abundance and isotope-enriched ice. When a nonmodulated rf irradiation was applied to a search for the NQR signals, absorptions due to the "solid state effect" which were shifted toward higher frequencies from resonance were detected only in enriched samples. In such circumtances, a saturation phenomenon was observed; at a given frequency (in the vicinity of a resonance) and 17O concentration, the scaling-down factor of the proton signal reaches a characteristic minimum value. The dependence of this value on the 17O concentration indicates that the two spin systems evolve toward a common final spin temperature in the rotating frame, limiting the signal detection to enriched ice. When the NQR irradiation was modulated at a frequency comparable to the dipole-dipole interaction energy between the two nuclear spin systems and applied at resonance, the proton spin temperature evolved to infinity, thus allowing signal detection even at very low concentrations such as the natural abundance of 17O. Distinct signals were detected at 1615 ± 5, 1710 ± 5, and 3320 ± 10 kHz, which yield the quadrupolar parameters e2qQ = 6.42 MHz and ? = 0.924, consistent with a recent report by Brosnon and Edmonds.

Margalit, Yair; Shporer, Mordechai

52

Crystallization and preliminary analysis of the NqrA and NqrC subunits of the Na+-translocating NADH:ubiquinone oxidoreductase from Vibrio cholerae.  

PubMed

The Na+-translocating NADH:ubiquinone oxidoreductase (Na+-NQR) from Vibrio cholerae is a membrane protein complex consisting of six different subunits NqrA-NqrF. The major domains of the NqrA and NqrC subunits were heterologously expressed in Escherichia coli and crystallized. The structure of NqrA1-377 was solved in space groups C222? and P2? by SAD phasing and molecular replacement at 1.9 and 2.1?Å resolution, respectively. NqrC devoid of the transmembrane helix was co-expressed with ApbE to insert the flavin mononucleotide group covalently attached to Thr225. The structure was determined by molecular replacement using apo-NqrC of Parabacteroides distasonis as search model at 1.8?Å resolution. PMID:25005105

Vohl, Georg; Nedielkov, Ruslan; Claussen, Björn; Casutt, Marco S; Vorburger, Thomas; Diederichs, Kay; Möller, Heiko M; Steuber, Julia; Fritz, Günter

2014-07-01

53

NQR Characteristics of an RDX Plastic Explosives Simulant.  

PubMed

For reliable detection of explosives, a combination of methods integrated within a single measurement platform may increase detection performance. However, the efficient field testing of such measurement platforms requires the use of inexplosive simulants that are detectable by a wide range of methods. Physical parameters such as simulant density, elemental composition and crystalline structure must closely match those of the target explosive. The highly discriminating bulk detection characteristics of nuclear quadrupole resonance (NQR) especially constrain simulant design. This paper describes the development of an inexplosive RDX simulant suited to a wide range of measurement methods, including NQR. Measurements are presented that confirm an RDX NQR response from the simulant. The potential use of the simulant for field testing a prototype handheld NQR-based RDX detector is analyzed. Only modest changes in prototype operation during field testing would be required to account for the use of simulant rather than real explosive. PMID:23204647

Turecek, J; Schwitter, B; Miljak, D; Stancl, M

2012-12-01

54

Site-directed mutagenesis of conserved cysteine residues in NqrD and NqrE subunits of Na+-translocating NADH:quinone oxidoreductase.  

PubMed

Each of two hydrophobic subunits of Na+-translocating NADH:quinone oxidoreductase (NQR), NqrD and NqrE, contain a pair of strictly conserved cysteine residues within their transmembrane alpha-helices. Site-directed mutagenesis showed that substitutions of these residues in NQR of Vibrio harveyi blocked the Na+-dependent and 2-n-heptyl-4-hydroxyquinoline N-oxide-sensitive quinone reductase activity of the enzyme. However, these mutations did not affect the interaction of NQR with NADH and menadione. It was demonstrated that these conserved cysteine residues are necessary for the correct folding and/or the stability of the NQR complex. Mass and EPR spectroscopy showed that NQR from V. harveyi bears only a 2Fe-2S cluster as a metal-containing prosthetic group. PMID:18298367

Fadeeva, M S; Bertsova, Y V; Verkhovsky, M I; Bogachev, A V

2008-02-01

55

Effects of nonsinusoidal character of atomic modulation on NQR spin-lattice relaxation time of incommensurate phases  

SciTech Connect

The present work is an extention of the theoretical calculation developed by Blinc to explain the temperature and frequency dependence of the spin-lattice relaxation time in incommensurate phases. We have evaluated the influence of the nonsinusoidal character of the atomic modulation, in the linear approximation, over the NQR spectra and over the spin-lattice relaxation due to direct and Raman processes. It is shown that the peak with lower intensity in the NQR spectra always has a larger T{sub 1} and viceversa. The results have been applied to bis(4-chlorophenyl)sulfone T{sub 1} and line-shape data. The temperature and frequency dependence of T{sub 1} are well reproduced if Raman processes are considered.

Perez, Silvina C.; Schurrer, Clemar; Wolfenson, Alberto

2001-06-01

56

Behavior and structure of the band 3 anion transport site: a /sup 35/Cl and /sup 37/Cl NMR study  

SciTech Connect

The present thesis focuses on band 3, the most heavily used ion transport protein in typical vertebrate systems. The strategy employed involves /sup 35/Cl NMR, which is shown to be a sensitive probe of (1) Cl/sup -/ migration from solution to a binding site, (2) Cl/sup -/ binding to the site, and (3) the sidedness of a membrane-bound site. Both low-affinity (K/sub D >> 0.5 M) and high-affinity (K/sub D/ = 80 +/- 20 mM) sites are observed on both surfaces of isolated red cell membranes. The latter sites are identified as band 3 transport sites by their affinity for a variety of anions. The transport sites on both sides on both sides of the membrane together behave like a homogeneous population under varying (pCl/sup -/), (Br/sup -/), or pH. These results support the ping-pong model for the transport cycle. The rates of Cl/sup -/ binding and dissociation at the inward- and outward-facing sites are shown by /sup 35/Cl and /sup 37/Cl NMR to exceed 10/sup 5/ events sec/sup -1/ site/sup -1/. Three classes of inhibitors are found: (1) niflumic acid has no effect on Cl/sup -/ migration or binding to the transport site - this inhibitor slows the translocation of bound Cl/sup -/ during both influx and efflux; (2) 1.2-cyclohexanedione (CHD) slows the migration of Cl/sup -/ between the transport site and solution; and (3) phenylglyoxal (PG) modifies an essential transport site arginine. The transport site remains intact following a variety of stripping and proteolytic treatments. Together these results indicate that the transport site is buried in the membrane, where access to solution is provided by a channel that can be blocked by CHD. All essential transport site and channel residues lie on the papain-generated fragments. A model involving a sliding hydrophobic barrier is presented for the ion translocation event.

Falke, J.J.

1985-01-01

57

101Ru NQR study in CeRu 2  

NASA Astrophysics Data System (ADS)

We present measurements of the NQR spectrum and the nuclear spin lattice relaxation rate, 1/ T1, of 101Ru in superconducting CeRu 2 from 1.9 K to 10 K. From the NQR spectrum, the electric quadrupole interaction parameters were determined to be ?Q = 13.2 MHz and ? = 0.1/ T1 varies in proportion to temperature in the normal state, has the Hebel-Slichter coherence peak just below the superconducting transition temperature, TC, of 6.2 K, and decreases exponentially at low temperatures with the energy gap of 2 ? = 4.0 kBTC. 101Ru NQR study indicates that CeRu 2 is an s-wave and strong-coupling superconductor.

Matsuda, K.; Kohori, Y.; Kohara, T.

1996-02-01

58

Rapid detection of arsenic minerals using portable broadband NQR  

NASA Astrophysics Data System (ADS)

remote real-time detection of specific arsenic species would significantly benefit in minerals processing to mitigate the release of arsenic into aquatic environments and aid in selective mining. At present, there are no technologies available to detect arsenic minerals in bulk volumes outside of laboratories. Here we report on the first room-temperature broadband 75As nuclear quadrupole resonance (NQR) detection of common and abundant arsenic ores in the Earth crust using a large sample (0.78 L) volume prototype sensor. Broadband excitation aids in detection of natural minerals with low crystallinity. We briefly discuss how the proposed NQR detector could be employed in mining operations.

Lehmann-Horn, J. A.; Miljak, D. G.; O'Dell, L. A.; Yong, R.; Bastow, T. J.

2014-10-01

59

Possibility of valence-fluctuatsion-mediated superconductivity in Cd-doped CeIrIn(5) probed by In NQR.  

PubMed

We report on a pressure-induced evolution of exotic superconductivity and spin correlations in CeIr(In(1-x)Cd(x))(5) by means of in-nuclear-quadrupole-resonance (NQR) studies. Measurements of an NQR spectrum and nuclear-spin-lattice-relaxation rate 1/T(1) have revealed that antiferromagnetism induced by Cd doping emerges locally around Cd dopants, but superconductivity is suddenly induced at T(c)=0.7 and 0.9 K at 2.34 and 2.75 GPa, respectively. The unique superconducting characteristics with a large fraction of the residual density of state at the Fermi level which increases with T(c) differ from those for anisotropic superconductivity mediated by antiferromagnetic correlations. By incorporating the pressure dependence of the NQR frequency pointing to the valence change of Ce, we suggest that unconventional superconductivity in the CeIr(In(1-x)Cd(x))(5) system may be mediated by valence fluctuations. PMID:23005666

Yashima, M; Tagami, N; Taniguchi, S; Unemori, T; Uematsu, K; Mukuda, H; Kitaoka, Y; Ota, Y; Honda, F; Settai, R; Onuki, Y

2012-09-14

60

The Vibration-Rotation Bands of the Hydrogen Halides HF, H35Cl, H37Cl, H79Br, H81Br and H127I  

Microsoft Academic Search

The 2-0, 3-0 and 4-0 bands of 1H19F, the 4-0 and 5-0 bands of 1H35Cl and 1H37Cl, the 4-0 band of 1H79Br and 1H81Br, and the 4-0 band of 1H127I were photographed under great dispersion in the infra-red. The molecular constants have been calculated and are summarized in a table.

S. M. Naudé; H. Verleger

1950-01-01

61

14N NQR and relaxation in ammonium nitrate  

NASA Astrophysics Data System (ADS)

The complete 14N nuclear quadrupole resonance (NQR) spectrum of ammonium nitrate is presented recorded using two double resonance techniques - double contact cross relaxation and zero field NQR. The spectra gave the quadrupole coupling constant (Qcc) and asymmetry parameter (?) values for the nitro of 611 kHz, 0.229 and that for the ammonium nitrogen of 242 kHz, 0.835. The three relaxation transition probabilities have been determined for both the nitro and ammonium nitrogen atoms. The bi-exponential relaxation times (T 1) were measured at 295 K. The values for nitro are 16.9 s and 10.5 s and that of the ammonium are 23.0 s and 16.4 s.

Stephenson, David

2014-11-01

62

Gapless superconductivity in overdoped Hg System; Cu-NQR study  

Microsoft Academic Search

The nuclear quadrupole resonance (NQR) investigation of Cu in the overdoped compounds HgBa2CuOy (Hg1201) with y=4. 06 (Tc=92K) and 4.11 (64K) and HgBa2CaCu2Oy (Hg1212) with y=6.13 (Tc=125K) and 6.21 (117K) was carried out in zero field. From the temperature (T) dependence of the nuclear spin-lattice relaxation time, T1, of63Cu, we discuss a cause of the Tc suppression with decreasing the

Shigeki Ohsugi; Tetsuo Tsuchiya; Tadashi Koyama; Kazuo Fueki

1996-01-01

63

NMR and NQR investigations of local symmetry in the hidden order phase of URu2Si2  

NASA Astrophysics Data System (ADS)

In order to study local symmetries at the 4e(Si)- and 4d(Ru)-sites above and below hidden order transition temperature TO = 17.5 K in URu2Si2, we have investigated the nuclear quadrupole interaction by 73Ge-nuclear magnetic resonance (NMR) measurement on a 10% 73Ge-substituted sample URu2(Si0.9Ge0.1)2, and by 101Ru-nuclear quadrupole resonance (NQR) measurement on a pure single crystal sample. The present 73Ge-NMR measurements do not give any evidence for change in the local symmetry at 4e-site within experimental accuracy. On the other hand, the precise measurement of 101Ru-NQR frequency has detected an anomaly just below TO as sensitively as the thermal expansion measurement dose. Its temperature dependence shows a linear relation with that of the in-plane lattice parameter, which may be a clue to clarify a modification in microscopic charge distribution at TO.

Mito, T.; Hattori, M.; Motoyama, G.; Sakai, Y.; Koyama, T.; Ueda, K.; Kohara, T.; Yokoyama, M.; Amitsuka, H.

2012-12-01

64

1H NMR and 14N NQR study of the ferroelectric phase transition in (CH3)2NH2H2PO4  

NASA Astrophysics Data System (ADS)

The ferroelectric phase transition in (CH3)2NH2H2PO4 has been studied by 14N nuclear-quadrupole resonance (NQR) and 1H spin-lattice relaxation. Both above and below TC, the 14N quadrupole coupling constant is approximately 1.2 MHz and the asymmetry parameter ? is close to 1. Two nonequivalent nitrogen positions in the unit cell are observed below TC whereas, above TC, all nitrogen crystallographic positions are equivalent. Proton spin-lattice relaxation times T1 and T1D show the presence of two molecular motions. Both below and above TC, proton T1 as measured at ?L=32 MHz is dominated by a motion that slows down on the NMR frequency scale below -100 °C. This motion is most probably the 180° reorientation of a dimethylammonium ion around its twofold axis. In the paraelectric phase we observed a slow motion dominating T1D and T1 at low Larmor frequencies. This motion seems to be an up-down reorientation of a dimethylammonium ion along its twofold axis. The NMR and NQR data are interpreted in a model assuming close similarities between the crystal structures of KH2PO4 and (CH3)2NH2H2PO4.

Seliger, J.; Žagar, V.

1998-04-01

65

NMR/NQR and disorder effects in URu2Si2  

NASA Astrophysics Data System (ADS)

NMR experiments at ambient pressure in URu2Si2 demonstrate a linewidth enhancement effect at the hidden order transition temperature (T0). We find that larger amounts of sample disorder appear to induce larger linewidth enhancement at T0. We will present recent NMR and NQR experiments in oriented powder and single crystal samples of URu2Si2 and discuss the measurements with emphasis on a possible connection between linewidth/disorder effects and hidden order. Both NQR and NMR spectra as functions of temperature and NMR for different magnetic field strengths and orientations will be reported.

Bernal, O. O.; Ishida, K.; Reyes, A. P.; Maclaughlin, D. E.; Lukefarh, H. G.; Mydosh, J. A.; Gortenmulder, T. J.; Amitsuka, H.

2005-03-01

66

Subfemtotesla radio-frequency atomic magnetometer for detection of nuclear quadrupole resonance  

E-print Network

Subfemtotesla radio-frequency atomic magnetometer for detection of nuclear quadrupole resonance S 20 November 2006 A radio-frequency tunable atomic magnetometer is developed for detection of nuclearHz 14 N NQR frequency of ammonium nitrate. A potential application of the magnetometer is detection

Romalis, Mike

67

Charge-carrier density and interplane coupling in Y2Ba4Cu7O15: A Cu NMR-NQR study  

NASA Astrophysics Data System (ADS)

We report an observation of the 63,65Cu nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) in Y2Ba4Cu7O15. We have measured the temperature dependence of the Cu NQR frequency and spin-lattice relaxation at all four chemically inequivalent Cu sites, and of the Cu magnetic shift at two inequivalent plane Cu sites (for the magnetic field parallel and perpendicular to the c axis). The Y2Ba4Cu7O15 compound turns out to be a structure containing two inequivalent CuO2 planes of differing doping levels, a multilattice in which YBa2Cu4O8 blocks and YBa2Cu3O7 blocks alternate. In the normal conducting state both the static and the dynamic electron spin susceptibilities of the individual planes of a double plane are governed by the same temperature dependence, which shows a behavior typical for an underdoped high-Tc compound. The same temperature dependence means strong coupling between these planes, with the lower limit of the coupling constant not much less than 30 meV. Although the planes are strongly coupled, their spin susceptibilities retain a distinct q dependence. The temperature variation of relaxation rate and Knight shift is described in terms of spin-gap formation or, alternatively, of frustrated phase separation. Below Tc, the common temperature dependence is lost, which could arise from the opening of two superconducting gaps that differ in the individual planes.

Stern, R.; Mali, M.; Mangelschots, I.; Roos, J.; Brinkmann, D.; Genoud, J.-Y.; Graf, T.; Muller, J.

1994-07-01

68

IMPLEMENTATION OF A -NQR SYSTEM AT THE NSCL FOR GROUND STATE QUADRUPOLE MOMENT  

E-print Network

The nuclear electric quadrupole moment, Q, is a direct measure of the nuclear charge distribution, and provides an important test of nuclear structure models. The detected nuclear quadrupole resonance (-NQR, my family, all my teachers and friends iii #12;ACKNOWLEDGMENTS I am very grateful to my advisor

Mantica, Paul F.

69

The conformational changes induced by ubiquinone binding in the Na+-pumping NADH:ubiquinone oxidoreductase (Na+-NQR) are kinetically controlled by conserved glycines 140 and 141 of the NqrB subunit.  

PubMed

Na(+)-pumping NADH:ubiquinone oxidoreductase (Na(+)-NQR) is responsible for maintaining a sodium gradient across the inner bacterial membrane. This respiratory enzyme, which couples sodium pumping to the electron transfer between NADH and ubiquinone, is not present in eukaryotes and as such could be a target for antibiotics. In this paper it is shown that the site of ubiquinone reduction is conformationally coupled to the NqrB subunit, which also hosts the final cofactor in the electron transport chain, riboflavin. Previous work showed that mutations in conserved NqrB glycine residues 140 and 141 affect ubiquinone reduction and the proper functioning of the sodium pump. Surprisingly, these mutants did not affect the dissociation constant of ubiquinone or its analog HQNO (2-n-heptyl-4-hydroxyquinoline N-oxide) from Na(+)-NQR, which indicates that these residues do not participate directly in the ubiquinone binding site but probably control its accessibility. Indeed, redox-induced difference spectroscopy showed that these mutations prevented the conformational change involved in ubiquinone binding but did not modify the signals corresponding to bound ubiquinone. Moreover, data are presented that demonstrate the NqrA subunit is able to bind ubiquinone but with a low non-catalytically relevant affinity. It is also suggested that Na(+)-NQR contains a single catalytic ubiquinone binding site and a second site that can bind ubiquinone but is not active. PMID:25006248

Strickland, Madeleine; Juárez, Oscar; Neehaul, Yashvin; Cook, Darcie A; Barquera, Blanca; Hellwig, Petra

2014-08-22

70

Improving the sensitivity of a high-Tc SQUID at MHz frequency using a normal metal transformer  

NASA Astrophysics Data System (ADS)

Superconducting quantum interference devices (SQUIDs) can be used to detect the signals of nuclear quadrupole resonance (NQR). The NQR frequencies of some interesting materials are in the order of MHz. However, the sensitivity of a high-Tc SQUID is normally not enough to detect the weak NQR signals. To improve the sensitivity of a high-Tc SQUID at MHz frequency, we used a transformer made of normal copper wire. The transformer was composed of a pickup coil, an input coil and a capacitor. The pickup coil was used to detect the magnetic field; the input coil was used to couple the field to the SQUID; and the capacitor was used to create a resonant frequency. By using the normal metal transformer, the magnetic field resolution of the high-Tc dc SQUID was improved by about 38.8 times (from 220 to 5.67 fT Hz-1/2) at 954 kHz.

He, D. F.; Itozaki, H.; Tachiki, M.

2006-05-01

71

NMR and NQR studies of quadrupolar effects in glasses and polycrystals with half-integer spins  

NASA Astrophysics Data System (ADS)

NMR and NQR techniques have been used in the present study to investigate glasses and polycrystalline compounds containing nuclei with half-integer spins such as: sp{11}B, sp{23}Na, sp{45}Sc, and sp{93}Nb. The low field ({˜}1.2{-}1.5 Tesla) continuous wave (CW) NMR experiments were performed using the Non-Adiabatic Superfast Passage (NASP) or the slow passage methods. A BRUKER MSL 300 pulsed NMR spectrometer was used for the high field (7.1 Tesla) studies. The CW NQR experiments at room and liquid nitrogen temperature were carried out on a home built Robinson-type spectrometer. Using pulsed NMR the sp{45}Sc response from the glass system CaO-Bsb2Osb3-Scsb2Osb3, yielded a first-order quadrupolar interaction with eta=0 and Qsb{cc}?617 kHz. A new Sc site with Qsb{cc}=23.44 MHz and eta=0 was found in polycrystalline Scsb2Osb3 and it was confirmed by NQR. Employing the NASP method it was found that the fraction of four-coordinated (Nsb4) boron atoms in the alkali thioborate (Nasb2S-Bsb2Ssb3) glass system follows a 3x/(1 - x) relationship for x?0.15, where x is the molar fraction of Nasb2S in the glass. For the NQR spectra the 10% Nasb2S content glass exhibited a broader NQR resonance than the NQR resonance for pure v-Bsb2Ssb3. The additional width was attributed to responses of BSsb3 units whose Qsb{cc} values differ somewhat from the BSsb3 units in the pure vitreous Bsb2Ssb3. The CW NASP method was used to study the sp{23}Na response in the Nasb2O*2SiOsb2 glass, heat treated in three ways: annealed, slow cooled and splat quenched. Subjecting the glass to rapid cooling will produce an increased range of values for the components of the electric field gradient (EFG), and, hence an increased range of values for Qsb{cc} and eta. This was observed for the slow cooled sample when compared with the annealed glass. The effect should be seen also from the slow cooled to the splat quenched sample, but this was not observed. Crystalline sodium disilicate was examined by both NMR and NQR and yielded Qsb{cc} = 1.89 MHz for sp{23}Na and eta=0.9. Furthermore the response from sp{23}Na in the polycrystalline forms of sodium molybdate, sodium tungstate, sodium stanate and albite was examined by means of NASP, pulsed NMR, and NQR. The sp{23}Na spectra for these compounds yielded values of Qsb{cc}, in the range 2.56 MHz to 2.80 MHz. A computer simulation program was used to simulate the spectra of sp{93}Nb-containing compounds. The survey of the niobium response in various polycrystalline compounds using the pulse-echo technique revealed first-order and second-order quadrupolar effects. The sp{93}Nb responses from five glasses in the Nbsb2Osb5-Nasb2O-SiOsb2 ternary glass system produced a second-order quadrupole pattern, but the response might contain more than one Nb site.

Orengo-Aviles, Moises

72

127 I and 79 Br NQR spectra of halo-substituted phenols and phenylmercury phenoxides  

Microsoft Academic Search

The full127I NQR spectra of a series of iodo-substituted phenols and phenylmercury phenoxides have been studied. The quadrupole coupling constants and asymmetry parameters have been determined. The character of the OH...Hal hydrogen bond has been found to depend on the nature of substituents in the ring. Correlation dependences of the asymmetry parameters on the sum of the substituents resonance constants

G. K. Semin; S. I. Gushchin; S. B. Karpov; E. V. Bryukhova; L. S. Golovchenko; D. N. Kramov

1996-01-01

73

Calculation of 14N and 35Cl quadrupole coupling constants on optimized molecular structures of pyrimidine, 2-X- and 5-X-pyrimidine, with X=F, Cl, Br, and CN  

NASA Astrophysics Data System (ADS)

14N(1,3) quadrupole coupling constants (nqcc's) were calculated on B3P86/6-31G(3d,3p) optimized molecular structures of pyrimidine (PRM), 2-X-PRM, and 5-X-PRM, with X=F, Cl, Br, and CN. For PRM, the root mean square difference between calculated and experimental nqcc's is 6 kHz (0.3%). For 2-F-PRM, the calculated value of -5.254 MHz for ( ?bb- ?cc) lies within the rather large uncertainty (?1%) in the experimental value. Hyperfine structure due to ?aa was unresolved - its calculated value is -0.062 MHz. In the remaining molecules, for which no experimental data are available, nitrogen nqcc's are predicted. In the Cl-PRMs, 35Cl nqcc's are predicted. In the halogen substituted PRMs, differences in nqcc's correlate with differences in carbon-halogen bond lengths.

Bailey, W. C.

2001-07-01

74

Inhibition of the sodium-translocating NADH-ubiquinone oxidoreductase [Na+-NQR] decreases cholera toxin production in Vibrio cholerae O1 at the late exponential growth phase.  

PubMed

Two virulence factors produced by Vibrio cholerae, cholera toxin (CT) and toxin-corregulated pilus (TCP), are indispensable for cholera infection. ToxT is the central regulatory protein involved in activation of CT and TCP expression. We previously reported that lack of a respiration-linked sodium-translocating NADH-ubiquinone oxidoreductase (Na(+)-NQR) significantly increases toxT transcription. In this study, we further characterized this link and found that Na(+)-NQR affects toxT expression only at the early-log growth phase, whereas lack of Na(+)-NQR decreases CT production after the mid-log growth phase. Such decreased CT production was independent of toxT and ctxB transcription. Supplementing a respiratory substrate, l-lactate, into the growth media restored CT production in the nqrA-F mutant, suggesting that decreased CT production in the Na(+)-NQR mutant is dependent on electron transport chain (ETC) activity. This notion was supported by the observations that two chemical inhibitors, a Na(+)-NQR specific inhibitor 2-n-Heptyl-4-hydroxyquinoline N-oxide (HQNO) and a succinate dehydrogenase (SDH) inhibitor, thenoyltrifluoroacetone (TTFA), strongly inhibited CT production in both classical and El Tor biotype strains of V. cholerae. Accordingly, we propose the main respiratory enzyme of V. cholerae, as a potential drug target to treat cholera because human mitochondria do not contain Na(+)-NQR orthologs. PMID:24361395

Minato, Yusuke; Fassio, Sara R; Reddekopp, Rylan L; Häse, Claudia C

2014-01-01

75

Selective excitation of single and multiple quantum transitions for spin 7/2 in NQR  

NASA Astrophysics Data System (ADS)

The dynamics of spin 7/2 in pure NQR is considered. The orientation of the applied RF field is assumed arbitrary and ? ? 0. For this situation various selective pulses are considered and analytical results obtained. Shaped pulses are also treated. A key feature of this work is to construct the interaction representation from which an analytical calculation, using the computer program 'Maple', can be obtained in a tractable form. The results presented are general for all half integer spins of magnitude higher than 1/2.

Ageev, S. Z.; Sanctuary, B. C.

76

Roles of the Sodium-Translocating NADH:Quinone Oxidoreductase (Na+-NQR) on Vibrio cholerae Metabolism, Motility and Osmotic Stress Resistance  

PubMed Central

The Na+ translocating NADH:quinone oxidoreductase (Na+-NQR) is a unique respiratory enzyme catalyzing the electron transfer from NADH to quinone coupled with the translocation of sodium ions across the membrane. Typically, Vibrio spp., including Vibrio cholerae, have this enzyme but lack the proton-pumping NADH:ubiquinone oxidoreductase (Complex I). Thus, Na+-NQR should significantly contribute to multiple aspects of V. cholerae physiology; however, no detailed characterization of this aspect has been reported so far. In this study, we broadly investigated the effects of loss of Na+-NQR on V. cholerae physiology by using Phenotype Microarray (Biolog), transcriptome and metabolomics analyses. We found that the V. cholerae ?nqrA-F mutant showed multiple defects in metabolism detected by Phenotype Microarray. Transcriptome analysis revealed that the V. cholerae ?nqrA-F mutant up-regulates 31 genes and down-regulates 55 genes in both early and mid-growth phases. The most up-regulated genes included the cadA and cadB genes, encoding a lysine decarboxylase and a lysine/cadaverine antiporter, respectively. Increased CadAB activity was further suggested by the metabolomics analysis. The down-regulated genes include sialic acid catabolism genes. Metabolomic analysis also suggested increased reductive pathway of TCA cycle and decreased purine metabolism in the V. cholerae ?nqrA-F mutant. Lack of Na+-NQR did not affect any of the Na+ pumping-related phenotypes of V. cholerae suggesting that other secondary Na+ pump(s) can compensate for Na+ pumping activity of Na+-NQR. Overall, our study provides important insights into the contribution of Na+-NQR to V. cholerae physiology. PMID:24811312

Minato, Yusuke; Halang, Petra; Quinn, Matthew J.; Faulkner, Wyatt J.; Aagesen, Alisha M.; Steuber, Julia; Stevens, Jan F.; Häse, Claudia C.

2014-01-01

77

Roles of the sodium-translocating NADH:quinone oxidoreductase (Na+-NQR) on vibrio cholerae metabolism, motility and osmotic stress resistance.  

PubMed

The Na+ translocating NADH:quinone oxidoreductase (Na+-NQR) is a unique respiratory enzyme catalyzing the electron transfer from NADH to quinone coupled with the translocation of sodium ions across the membrane. Typically, Vibrio spp., including Vibrio cholerae, have this enzyme but lack the proton-pumping NADH:ubiquinone oxidoreductase (Complex I). Thus, Na+-NQR should significantly contribute to multiple aspects of V. cholerae physiology; however, no detailed characterization of this aspect has been reported so far. In this study, we broadly investigated the effects of loss of Na+-NQR on V. cholerae physiology by using Phenotype Microarray (Biolog), transcriptome and metabolomics analyses. We found that the V. cholerae ?nqrA-F mutant showed multiple defects in metabolism detected by Phenotype Microarray. Transcriptome analysis revealed that the V. cholerae ?nqrA-F mutant up-regulates 31 genes and down-regulates 55 genes in both early and mid-growth phases. The most up-regulated genes included the cadA and cadB genes, encoding a lysine decarboxylase and a lysine/cadaverine antiporter, respectively. Increased CadAB activity was further suggested by the metabolomics analysis. The down-regulated genes include sialic acid catabolism genes. Metabolomic analysis also suggested increased reductive pathway of TCA cycle and decreased purine metabolism in the V. cholerae ?nqrA-F mutant. Lack of Na+-NQR did not affect any of the Na+ pumping-related phenotypes of V. cholerae suggesting that other secondary Na+ pump(s) can compensate for Na+ pumping activity of Na+-NQR. Overall, our study provides important insights into the contribution of Na+-NQR to V. cholerae physiology. PMID:24811312

Minato, Yusuke; Fassio, Sara R; Kirkwood, Jay S; Halang, Petra; Quinn, Matthew J; Faulkner, Wyatt J; Aagesen, Alisha M; Steuber, Julia; Stevens, Jan F; Häse, Claudia C

2014-01-01

78

Ru-NQR Study for Novel Phase Transition in CeRu2Al10  

NASA Astrophysics Data System (ADS)

We have performed Ru-NQR measurements on CeRu2Al10 exhibiting novel phase transition at an abnormally high temperature T0 = 27.3 K and on NdRu2Al10 with a magnetic transition temperature Tm = 2.4 K as a reference RKKY system. The splitting of the NQR line due to internal fields below T0 shows a mean-field-like monotonic increase, indicating no change in the magnetic structure below T0. The internal field strength is one order larger than those at Al sites in CeRu2Al10, and is comparable to that at the Ru site in NdRu2Al10 despite the sevenfold smaller magnitude of the 4f moment, being indicative of an enhanced conduction electron polarization at the Ru site. One of the causes of the high T0 might be the enhanced exchange coupling through the Ce–Ru–Ce path mediated by the enhanced conduction electron polarization. Being similar to that in the Al site, the nuclear spin–lattice relaxation rate 1/T1 shows a gap-like decrease below T0 without enhancement owing to a critical slowing down at T0, in contrast to the mean field 2nd-order transition.

Matsumura, Masahiro; Tomita, Naoya; Matsuoka, Junichirou; Kishimoto, Yasuki; Kato, Harukazu; Kitagawa, Kentaro; Nishioka, Takashi; Tanida, Hiroshi; Sera, Masafumi

2014-10-01

79

Measurement of in-situ stress in salt and rock using NQR techniques  

SciTech Connect

A discussion of how stress and strain affect the quantities which can be measured in an NQR experiment shows that, for stresses of the magnitude to be expected at depths up to about 10,000 feet, quadrupole coupling constants will fall in the range of 1 to 10 kHz for both the sodium and chloride ions in NaCl. The most promising system involves pulsed nuclear double resonance detection; and alterative is to observe the quadrupolar splitting of the NMR signal. Choices to be made in the measurement and mapping techniques are discussed. The well-known perturbation of the homogenous stress field in the neighborhood of a borehole is shown to be advantageous from the point of view of obtaining directional information on the stress. Construction and operation of a borehole stress sensor are considered. The NQR technique seems feasible for measuring the magnitude and direction of underground stress with a resolution of about 25 psi, or 2.5% at 1000 psi. Downhole instrumentation suitable for in-situ determinations of stress appears within the state of the art. Additional tasks required on the project are identified.

Schempp, E.; Hirschfeld, T.; Klainer, S.

1980-12-01

80

A Mutation in Na(+)-NQR Uncouples Electron Flow from Na(+) Translocation in the Presence of K(+).  

PubMed

The sodium-pumping NADH:ubiquinone oxidoreductase (Na(+)-NQR) is a bacterial respiratory enzyme that obtains energy from the redox reaction between NADH and ubiquinone and uses this energy to create an electrochemical Na(+) gradient across the cell membrane. A number of acidic residues in transmembrane helices have been shown to be important for Na(+) translocation. One of these, Asp-397 in the NqrB subunit, is a key residue for Na(+) uptake and binding. In this study, we show that when this residue is replaced with asparagine, the enzyme acquires a new sensitivity to K(+); in the mutant, K(+) both activates the redox reaction and uncouples it from the ion translocation reaction. In the wild-type enzyme, Na(+) (or Li(+)) accelerates turnover while K(+) alone does not activate. In the NqrB-D397N mutant, K(+) accelerates the same internal electron transfer step (2Fe-2S ? FMNC) that is accelerated by Na(+). This is the same step that is inhibited in mutants in which Na(+) uptake is blocked. NqrB-D397N is able to translocate Na(+) and Li(+), but when K(+) is introduced, no ion translocation is observed, regardless of whether Na(+) or Li(+) is present. Thus, this mutant, when it turns over in the presence of K(+), is the first, and currently the only, example of an uncoupled Na(+)-NQR. The fact the redox reaction and ion pumping become decoupled from each other only in the presence of K(+) provides a switch that promises to be a useful experimental tool. PMID:25486106

Shea, Michael E; Mezic, Katherine G; Juárez, Oscar; Barquera, Blanca

2015-01-20

81

Mass and charge distributions in chlorine-induced nuclear reactions. [[sup 35]Cl at E/A = 15 MeV, [sup 37]Cl at E/A = 7. 3 MeV  

SciTech Connect

Projectile-like fragments were detected and characterized in terms of A, Z, and energy for the reactions [sup 37]Cl on [sup 40]Ca and [sup 209]Bi at E/A = 7.3 MeV, and [sup 35]Cl, on [sup 209]Bi at E/A = 15 MeV, at angles close to the grazing angle. Mass and charge distributions were generated in the N-Z plane as a function of energy loss, and have been parameterized in terms of their centroids, variances, and coefficients of correlation. Due to experimental problems, the mass resolution corresponding to the [sup 31]Cl on [sup 209]Bi reaction was very poor. This prompted the study and application of a deconvolution technique for peak enhancement. The drifts of the charge and mass centroids for the system [sup 37]Cl on [sup 40]Ca are consistent with a process of mass and charge equilibration mediated by nucleon exchange between the two partners, followed by evaporation. The asymmetric systems show a strong drift towards larger asymmetry, with the production of neutron-rich nuclei. It was concluded that this is indicative of a net transfer of protons from the light to the heavy partner, and a net flow of neutrons in the opposite direction. The variances for all systems increase with energy loss, as it would be expected from a nucleon exchange mechanism; however, the variances for the reaction [sup 37]Cl on [sup 40]Ca are higher than those expected from that mechanism. The coefficients of correlation indicate that the transfer of nucleons between projectile and target is correlated. The results were compared to the predictions of two current models based on a stochastic nucleon exchange mechanism. In general, the comparisons between experimental and predicted variances support this mechanism; however, the need for more realistic driving forces in the model calculations is indicated by the disagreement between predicted and experimental centroids.

Marchetti, A.A.

1991-01-01

82

115In-NQR study of CeRh1-xIrxIn5 under pressure  

NASA Astrophysics Data System (ADS)

We report on pressure-induced evolutions of antiferromagnetic spin fluctuations (AFM-SFs) and unconventional superconductivity on the x=0.6 sample in a series of compounds CeRh1-xIrxIn5 via the 115In nuclear-quadrupole-resonance (NQR) experiment. The In-NQR 1/T1 measurements have revealed that the slight application of pressure makes Tc=0.9 K at P=0 increase up to Tc=1.06 K at P=0.47 GPa. Concomitantly, the character of AFM-SF evolves from an isotropic regime to an anisotropic one as P increases. These results suggest that AFM-SFs play vital role in mediating the strong-coupling superconductivity in CeRh1-xIrxIn5.

Mugino, Y.; Kawasaki, S.; Yashima, M.; Mukuda, H.; Kitaoka, Y.; Shishido, H.; ?nuki, Y.

2007-03-01

83

A study of hydrogen bond of imidazole and its 4-nitro derivative by ab initio and DFT calculated NQR parameters  

NASA Astrophysics Data System (ADS)

Nuclear quadrupole resonance (NQR) parameters of 14N, 2H of N 2H groups are calculated for imidazole and 4-nitroimidazole using HF and B3LYP methods. These computations are performed on the basis of X-ray and neutron diffraction structural data which are collected at 100, 103, 123 and 293 K temperatures. In order to take into account intermolecular hydrogen bonds and the van der Waals effects, two different sizes of clusters have been considered. Results of calculation have been compared with that of a single molecule in each case. Calculations illustrate that for imidazole and 4-nitroimidazole octameric and trimeric clusters, respectively, suffice to generate results which are compatible with experimental data. Our calculated NQR parameters and X-ray data show no significant structural change for 4-nitroimidazole at 293 and 100 K.

Amini, S. K.; Hadipour, N. L.; Elmi, F.

2004-06-01

84

NQR Spin--Echo Double Resonance (SEDOR) Study of Interplane Coupling in Y_2Ba_4Cu_7O_15  

NASA Astrophysics Data System (ADS)

We report a detailed spin--echo double resonance study(R. Stern, M. Mali, J. Roos, and D. Brinkmann, Phys. Rev. B 52), (in press). of the planar Cu sites in Y_2Ba_4Cu_7O_15 above Tc employing nuclear quadrupole resonance (NQR). Due to the alternation of YBa_2Cu_3O7 and YBa_2Cu_4O8 blocks in its structure the individual planes of a CuO2 double plane in Y_2Ba_4Cu_7O_15 are inequivalent and hence can separately be monitored by NMR/NQR methods.(R. Stern et al.), Phys. Rev. B 50, 426 (1994), ibid. 51, 15478 (1995). The experiments directly reveal the coupling between the inequivalent single planes of a double CuO2 plane. The ratio of particular NQR relaxation rates is a measure for the strength of this interplane coupling with respect to the intraplane coupling. This ratio increases with decreasing temperature. Using recent calculations by Millis and Monien,(A. J. Millis and H. Monien, cond-mat # 9506088.) an interplane coupling constant of about 5 meV is deduced.

Stern, Raivo

1996-03-01

85

Studies of Ga NMR and NQR in SrGa4  

NASA Astrophysics Data System (ADS)

In order to microscopically investigate the properties in SrGa4, the Ga NMR measurements of a powder sample were carried out. The Ga NMR spectra corresponding to Ga(I) and Ga(II) sites are obtained. The NMR spectra of 69&71Ga (a nuclear spin I = 3/2) in the powder sample of SrGa4 do not take a typical powder pattern caused by the NQR interaction, but take the spectra consisting of three well resolved resonance-lines, which indicates that the nonuniform distribution of crystal orientation in the powder sample occurs because of the magnetic anisotropy. From the analysis of the Ga NMR spectrum, it is found that the ab-plane of the crystal is parallel to the external magnetic field, which would be attributed to the anisotropy of the magnetic susceptibility with the easy axis parallel to the ab-plane. This result is also confirmed by the 69Ga NQR in SrGa4. The Knight shifts of the 69Ga(I) and 69Ga(II) shift slightly to the negative side with decreasing temperature due to the core polarization of the d-electrons. The values of the Knight shift of the 69Ga(I) and 69Ga(II) are 0.01 and -0.11 % at 4.2 K, and 0.09 and -0.08 % at 300 K, respectively. The values of the 1/ T 1 T of the NMR of both 69Ga(I) and 69Ga(II) are almost constant between 4.2 and 100 K, whose values are 1.5 s -1 K -1 at 69Ga(I) and 0.12 s -1 K -1 at 69Ga(II), while the 1/ T 1 T slightly increase above 100K with increasing temperature. The value of T 1 of 69Ga(I) is one order of magnitude less than that of 69Ga(II).

Niki, H.; Higa, N.; Nakamura, S.; Kuroshima, H.; Toji, T.; Yogi, M.; Nakamura, A.; Hedo, M.; Nakama, T.; ?nuki, Y.; Harima, H.

2014-11-01

86

The 14N NQR spectrum and the crystal structure of Ba[Fe(CN) 5NO] · 3H 2O at room temperature  

NASA Astrophysics Data System (ADS)

The previously reported 14N NQR spectrum of the CN groups of Ba [Fe (CN) 5NO] · 3H 2O (BNP) was shown to also contain lines of Na 2 [Fe (CN) 5NO] · 2H 2O used in the preparation of BNP. The number of NQR lines and their relative intensities in BNP confirmed that it has a Pbcm instead of a Pca2 1 space group at 293 K as previously assumed. The three CN sites found in BNP at room temperature are increased to five below 233 K and to eight below 131 K as a result of phase transitions. The effect on the NQR lines of the axial CN group of the disorder of some water molecules in BNP is also discussed.

Murgich, Juan; Bonalde, Ismardo

1990-07-01

87

Detection of ¹⁴N and ³⁵Cl in cocaine base and hydrochloride using NQR, NMR, and SQUID techniques  

Microsoft Academic Search

Results from ¹⁴N pure NQR of cocaine in the free base form (cocaine base) yield a nuclear quadrupole coupling constant (NQCC) e²Qq\\/h of 5.0229 ({+-}0.0001) MHz and an asymmetry parameter η of 0.0395 ({+-}0.0001) at 295 K, with corresponding values of 5.0460 ({+-}0.0013) MHz and 0.0353 ({+-}0.0008) at 77 K. Both pure NQR (at 295-77 K) and a superconducting quantum

James P. Yesinowski; Michael L. Buess; Allen N. Garroway; Marcia. Ziegeweid; Alexander. Pines

1995-01-01

88

Interplane coupling in the superconductor Y2Ba4Cu7O15 as revealed by NQR spin-echo double resonance  

NASA Astrophysics Data System (ADS)

We report a detailed spin-echo double-resonance study of the planar Cu sites in Y2Ba4Cu7O15 above Tc employing nuclear quadrupole resonance (NQR). The experiments directly reveal the coupling between the inequivalent single planes of a double CuO2 plane. The ratio of particular NQR relaxation rates is a measure for the strength of this interplane coupling with respect to the intraplane coupling. This ratio increases with decreasing temperature. Using recent calculations by Millis and Monien, an interplane coupling constant of about 5 meV is deduced.

Stern, R.; Mali, M.; Roos, J.; Brinkmann, D.

1995-12-01

89

NQR Spin--Echo Double Resonance (SEDOR) Study of Interplane Coupling in Y_2Ba_4Cu_7O_15  

Microsoft Academic Search

We report a detailed spin--echo double resonance study(R. Stern, M. Mali, J. Roos, and D. Brinkmann, Phys. Rev. B 52), (in press). of the planar Cu sites in Y_2Ba_4Cu_7O_15 above Tc employing nuclear quadrupole resonance (NQR). Due to the alternation of YBa_2Cu_3O7 and YBa_2Cu_4O8 blocks in its structure the individual planes of a CuO2 double plane in Y_2Ba_4Cu_7O_15 are inequivalent

Raivo Stern

1996-01-01

90

Central role of the Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) in sodium bioenergetics of Vibrio cholerae.  

PubMed

Abstract Vibrio cholerae is a Gram-negative bacterium that lives in brackish or sea water environments. Strains of V. cholerae carrying the pathogenicity islands infect the human gut and cause the fatal disease cholera. Vibrio cholerae maintains a Na+ gradient at its cytoplasmic membrane that drives substrate uptake, motility, and efflux of antibiotics. Here, we summarize the major Na+-dependent transport processes and describe the central role of the Na+-translocating NADH:quinone oxidoreductase (Na+-NQR), a primary Na+ pump, in maintaining a Na+-motive force. The Na+-NQR is a membrane protein complex with a mass of about 220 kDa that couples the exergonic oxidation of NADH to the transport of Na+ across the cytoplasmic membrane. We describe the molecular architecture of this respiratory complex and summarize the findings how electron transport might be coupled to Na+-translocation. Moreover, recent advances in the determination of the three-dimensional structure of this complex are reported. PMID:25205724

Steuber, Julia; Halang, Petra; Vorburger, Thomas; Steffen, Wojtek; Vohl, Georg; Fritz, Günter

2014-12-01

91

High Pressure NQR Measurement in CeCu2Si2 up to Sudden Disappearance of Superconductivity  

NASA Astrophysics Data System (ADS)

We report the results of 63Cu nuclear quadrupole resonance (NQR) measurements on CeCu2Si2 under high pressures up to 4.8 GPa. Enhanced spin fluctuations due to quantum criticality at ambient pressure are drastically suppressed with increasing pressure, whereas Tc increases from 0.7 K at ambient pressure to 1.64 K at 4.2 GPa. We have found that bulk superconductivity suddenly disappears at 4.8 GPa accompanied with a rapid decrease in the density of states at the Fermi level. The nuclear spin-lattice relaxation rate 1/T1 at 4.2 GPa reveals that anisotropic superconductivity in the strong-coupling regime is realized even under high pressure far from the antiferromagnetic critical point. Superconductivity under high pressure is unconventional in origin, but the spin fluctuation scenario is not likely to be applicable.

Fujiwara, Kenji; Hata, Yoshiki; Kobayashi, Keigo; Miyoshi, Kiyotaka; Takeuchi, Jun; Shimaoka, Yoshiyuki; Kotegawa, Hisashi; Kobayashi, Tatsuo C.; Geibel, Christoph; Steglich, Frank

2008-12-01

92

Magnetic correlations in La(2-x)Sr(x)CuO4 from NQR relaxation and specific heat  

NASA Technical Reports Server (NTRS)

La-139 and Cu-63 Nuclear Quadrupole Resonance (NQR) relaxation measurements in La(2-x)Sr(x)CuO4 for x ranging from 0 up to 0.3, with particular emphasis on the effect of doping on the Cu(2+) magnetic correlations and dynamics, are reviewed. In the low doping limit, x less than or equal to 0.05, the results can be interpreted consistently in terms of a simple phenomenological 'two-fluids' model whereby the effect of thermally-activated mobile O(2p) holes is the one of disrupting locally the Cu(2+) spin correlations. For x greater than or equal to 0.1, the results indicate the onset, as T approaches T(sub c)(+), of a strong coupling between Cu(2+) spins and the Fermi liquid of O(2p) holes leading to the apparent disappearance of localized Cu(2+) moment in connection with the opening of a superconducting gap.

Borsa, F.; Rigamonti, A.

1991-01-01

93

1H NMR and 14N NQR study of the ferroelectric phase transition in (CH3)2NH2H2PO4  

Microsoft Academic Search

The ferroelectric phase transition in (CH3)2NH2H2PO4 has been studied by 14N nuclear-quadrupole resonance (NQR) and 1H spin-lattice relaxation. Both above and below TC, the 14N quadrupole coupling constant is approximately 1.2 MHz and the asymmetry parameter eta is close to 1. Two nonequivalent nitrogen positions in the unit cell are observed below TC whereas, above TC, all nitrogen crystallographic positions

J. Seliger; V. Zagar

1998-01-01

94

Infrared spectroscopic evidence of a redox-dependent conformational change involving ion binding residue NqrB-D397 in the Na(+)-pumping NADH:quinone oxidoreductase from Vibrio cholerae.  

PubMed

The Na(+)-pumping NADH:quinone oxidoreductase (Na(+)-NQR) is a unique respiratory enzyme that conserves energy by translocating Na(+) through the plasma membrane. Found only in prokaryotes, the enzyme serves as the point of entry of electrons into the respiratory chain in many pathogens, including Vibrio cholerae and Yersinia pestis. In this study, a combined electrochemical and Fourier transform infrared (FTIR) spectroscopic approach revealed that Na(+)-NQR undergoes significant conformational changes upon oxidoreduction, depending on the monovalent cation present (Na(+), Li(+), K(+), or Rb(+)). In the presence of the inhibitor Rb(+), additional conformational changes are evident, indicating a changed accessibility of the sodium binding sites. In electrochemically induced FTIR difference spectra, the involvement of deprotonated acid residues in the binding of cations, together with the spectral features, that point toward a monodentate binding mode for these acid residues in the oxidized form of the enzyme and bidentate binding in the reduced form could be identified. The measurements confirmed that NqrB-D397 is one of the acid residues involved in Na(+) and Li(+) binding. In the NqrB-D397E mutant, the spectral features characteristic of COO(-) groups are shifted, and a weakening of the hydrogen binding of the ion binding cluster is revealed. Finally, H-D exchange kinetics of amide protons confirmed that Na(+)-NQR adopts different conformations, with different accessibilities to the aqueous environment, depending on the cation present, which contributes to the selectivity mechanism of ion translocation. PMID:23566241

Neehaul, Yashvin; Juárez, Oscar; Barquera, Blanca; Hellwig, Petra

2013-05-01

95

Electronic properties of Y-Ba-Cu-O superconductors as seen by Cu and O NMR/NQR  

SciTech Connect

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) allow the investigation of electronic properties at the atomic level. The authors will report on such studies of typical members of the the Y-Ba-Cu-O family such as YBa2Cu30(6 + x) (1-2-3-(6 + x)), YBa2Cu4O8 (1-2-4) and Y2Ba4Cu7015 (2-4-7) with many examples of recent work performed in their laboratory. In particular, they will deal with Knight shift and relaxation studies of copper and oxygen. They will discuss important issues of current studies such as: (1) Existence of a common electronic spin-susceptibility in the planes (and perhaps in the chains) of 1-2-4; (2) Strong evidence for the existence of a pseudo spin-gap of the antiferromagnetic fluctuations in 1-2-4 and 2-4-7; (3) Evidence for d-wave pairing in 1-2-4; (4) Strong coupling of inequivalent Cu-O planes in 2-4-7 and possible origin for the high Tc value of this compound; and (5) The possibility to describe NMR data in the framework of a charge-excitation picture.

Brinkmann, D.

1995-04-01

96

Electronic properties of Y-Ba-Cu-O superconductors as seen by Cu and O NMR/NQR  

NASA Astrophysics Data System (ADS)

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) allow the investigation of electronic properties at the atomic level. We will report on such studies of typical members of the the Y-Ba-Cu-O family such as YBa2Cu30(6 + x) (1-2-3-(6 + x)), YBa2Cu4O8 (1-2-4) and Y2Ba4Cu7015 (2-4-7) with many examples of recent work performed in our laboratory. In particular, we will deal with Knight shift and relaxation studies of copper and oxygen. We will discuss important issues of current studies such as: (1) Existence of a common electronic spin-susceptibility in the planes (and perhaps in the chains) of 1-2-4; (2) Strong evidence for the existence of a pseudo spin-gap of the antiferromagnetic fluctuations in 1-2-4 and 2-4-7; (3) Evidence for d-wave pairing in 1-2-4; (4) Strong coupling of inequivalent Cu-O planes in 2-4-7 and possible origin for the high Tc value of this compound; and (5) The possibility to describe NMR data in the framework of a charge-excitation picture.

Brinkmann, D.

1995-04-01

97

Electronic properties of Y-Ba-Cu-O superconductors as seen by Cu and O NMR/NQR  

NASA Technical Reports Server (NTRS)

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) allow the investigation of electronic properties at the atomic level. We will report on such studies of typical members of the the Y-Ba-Cu-O family such as YBa2Cu30(6 + x) (1-2-3-(6 + x)), YBa2Cu4O8 (1-2-4) and Y2Ba4Cu7015 (2-4-7) with many examples of recent work performed in our laboratory. In particular, we will deal with Knight shift and relaxation studies of copper and oxygen. We will discuss important issues of current studies such as: (1) Existence of a common electronic spin-susceptibility in the planes (and perhaps in the chains) of 1-2-4; (2) Strong evidence for the existence of a pseudo spin-gap of the antiferromagnetic fluctuations in 1-2-4 and 2-4-7; (3) Evidence for d-wave pairing in 1-2-4; (4) Strong coupling of inequivalent Cu-O planes in 2-4-7 and possible origin for the high Tc value of this compound; and (5) The possibility to describe NMR data in the framework of a charge-excitation picture.

Brinkmann, D.

1995-01-01

98

Field-tuned critical fluctuations in YFe2Al10: Evidence from magnetization, 27Al NMR, and NQR investigations  

NASA Astrophysics Data System (ADS)

We report magnetization, specific heat, and NMR investigations on YFe2Al10 over a wide range of temperature and magnetic field and zero field (NQR) measurements. Magnetic susceptibility, specific heat, and spin-lattice relaxation rate divided by T(1/T1T) follow a weak power law (˜T-0.4) temperature dependence, which is a signature of the critical fluctuations of Fe moments. The value of the Sommerfeld-Wilson ratio and the linear relation between 1/T1T and ? suggest the existence of ferromagnetic correlations in this system. No magnetic ordering down to 50 mK in Cp(T)/T and the unusual T and H scaling of the bulk and NMR data are associated with a magnetic instability which drives the system to quantum criticality. The magnetic properties of the system are tuned by field wherein ferromagnetic fluctuations are suppressed and a crossover from quantum critical to Fermi-liquid behavior is observed with increasing magnetic field.

Khuntia, P.; Strydom, A. M.; Wu, L. S.; Aronson, M. C.; Steglich, F.; Baenitz, M.

2012-12-01

99

Magnetic correlations in La(2-x)Sr(x)CuO4 from NQR relaxation and specific heat  

NASA Technical Reports Server (NTRS)

La-139 and Cu-63 Nuclear Quadrupole Resonance (NQR) relaxation measurements in La(2-x)Sr(x)CuO4 for O = to or less than 0.3 and in the temperature range 1.6 + 450 K are analyzed in terms of Cu(++) magnetic correlations and dynamics. It is described how the magnetic correlations that would result from Cu-Cu exchange are reduced by mobile charge defects related to x-doping. A comprehensive picture is given which explains satisfactorily the x and T dependence of the correlation time, of the correlation length and of the Neel temperature T(sub n)(x) as well as being consistent with known electrical resistivity and magnetic susceptibility measurements. It is discussed how, in the superconducting samples, the mobile defects also cause the decrease, for T yields T(sub c)(+) of the hyperfine Cu electron-nucleus effective interaction, leading to the coexistence of quasi-localized, reduced magnetic moments from 3d Cu electrons and mobile oxygen p-hole carriers. The temperature dependence of the effective hyperfine field around the superconducting transition yields an activation energy which could be related to the pairing energy. New specific heat measurements are also presented and discussed in terms of the above picture.

Borsa, F.; Rigamonti, A.

1990-01-01

100

Measurement of the 14N nuclear quadrupole resonance frequencies by the solid effect  

NASA Astrophysics Data System (ADS)

1H- 14N nuclear quadrupole double resonance using magnetic field cycling between high and low magnetic field and solid effect in the low magnetic field is analyzed in details. The transition probabilities per unit time for the solid-effect transitions are calculated. The double resonance spectra are calculated in the limiting cases of fast and slow nitrogen spin-lattice relaxation. The double resonance spectra are measured in histamine and quinolinic acid. The experimental spectra are analyzed and the 14N NQR frequencies are determined.

Seliger, J.; Žagar, V.

2008-07-01

101

Low frequency magnetic resonance with a dc SQUID (Superconducting QUantum Interference Device)  

SciTech Connect

Conventional NMR and NQR spectrometers use transistor-based detectors, which are responsive only to voltage. This forces the experimenter to convert the sample magnetization to a voltage, a process that is less efficient at low frequencies when the Faraday induction effect is used. However, the SQUID directly measures the magnetization, so there is no frequency dependent sensitivity to the sample magnetization. Of course, many other devices also measure magnetic field directly, but none has the low frequency sensitivity of the SQUID. Chapter 2 presents the theory required to extend conventional magnetic resonance to z-axis magnetic resonance, a form most efficient for the SQUID. The operating principles of the SQUID, as well as the techniques used to convert the SQUID response into a useful output voltage, are outlined in Chapter 3. The SQUID spectrometer constructed for these experiments is described in Chapter 4. Also in this chapter are a discussion of the design considerations for a SQUID spectrometer, and indications of the overall performance of our instrument. Experimental results on NQR and low frequency NMR are found in Chapters 5 and 6, respectively. 96 refs., 38 figs., 5 tabs.

Connor, C.

1989-10-01

102

NMR and NQR Studies on Non-centrosymmetric Superconductors Re7B3, LaBiPt, and BiPd  

NASA Astrophysics Data System (ADS)

We report the nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements for non-centrosymmetric superconductors Re7B3, LaBiPt, and BiPd containing heavy elements. For all three compounds, the spin--lattice relaxation rate 1/T1 shows a coherence peak just below Tc and decreases exponentially at low temperatures, which indicates that an isotropic superconducting gap is dominant in these compounds. In BiPd, the height of the coherence peak just below Tc is much suppressed, which suggests that there exists a substantial component of gap with nodes in this compound. Our results indicate that heavy element is not the only factor, but the extent of inversion symmetry breaking is also important to induce a large spin--orbit coupling and an unconventional superconducting state.

Matano, Kazuaki; Maeda, Satoki; Sawaoka, Hiroki; Muro, Yuji; Takabatake, Toshiro; Joshi, Bhanu; Ramakrishnan, Srinivasan; Kawashima, Kenji; Akimitsu, Jun; Zheng, Guo-qing

2013-08-01

103

New aspects on URu2Si2 and CeT In5 (T=Rh, Ir, Co) observed by high pressure NMR and NQR  

NASA Astrophysics Data System (ADS)

NMR and NQR studies on two interesting systems (URu2Si2, CeTIn5) were performed under high pressure. (1) URu2Si2: In the pressure range 3.0 to 8.3 kbar, we have observed new 29Si NMR signals arising from the antiferromagnetic (AF) region besides the previously observed 29Si NMR signals which come from the paramagnetic (PM) region in the sample. This gives definite evidence for spatially-inhomogeneous development of AF ordering below T0 of 17.5 K. The volume fraction is enhanced by applied pressure, whereas the value of internal field (~ 91 mT) remains constant up to 8.3 kbar. In the AF region, the ordered moment is about one order of magnitude larger than 0.03 mB. (2) CeTIn5: The pressure and temperature (T) dependences of nuclear spin-lattice relaxation rate 1/T1 of 115In in CeTIn5 have shown that the superconductivity (SC) occurs close to an AF instability. From the T dependences of 1/T1and Knight shift below Tc, CeTIn5 has been found to exhibit non-s wave (probable d wave) SC with even parity and line nodes in the SC energy gap.

Kohara, T.

2002-05-01

104

Stark effect of 75As NQR and asymmetric 1H-75As level crossing in paraelectric potassium dihydrogen arsenate  

Microsoft Academic Search

The nuclear quadrupole coupling constant of 75As in paraelectric KH2AsO4 (KDA) increases when an electric field is applied along the c-axis. The very large shift ?(e2Qq\\/2h)\\/?E of 75As is 9.1 kHz\\/kV cm-1 at T = 106°K = Tc + 10°. At room temperature, when the proton NMR frequency exceeds the alpha' frequency of 75As by Deltanu, the proton relaxation rate

D. Gill

1968-01-01

105

High-temperature protonic motion and low-temperature lattice deformation in one-dimensional hydrogen-bonded molecular chain in tetramethylpyrazine-chloranilic acid (1?1)  

NASA Astrophysics Data System (ADS)

The phase transition of tetramethylpyrazine-chloranilic acid (1?1) was studied by 35Cl NQR measurements. The frequency splits into a doublet below T c=83.0 ± 0.5 K. The averaged frequency of 36.98 MHz at 77 K suggests an electrically neutral electronic state of the chloranilic acid molecule, that is, no proton transfer between the acid and base molecules. An enhancement of the relaxation rate was observed at T c: it is presumably due to critical slowing down of a hydrogen motion in the one-dimensional hydrogen bond network. The excitation of a high-temperature hydrogen motion at T > 250 K is also suggested by the steep decrease of T 1 observed above 250 K. From the slope of the Arrhenius plots, an activation energy of 35 kJ mol- is calculated for the motion.

Asaji, Tetsuo; Yoshimura, Yusuke; Amino, Daiki

106

High-temperature protonic motion and low-temperature lattice deformation in one-dimensional hydrogen-bonded molecular chain in tetramethylpyrazine chloranilic acid (1:1)  

NASA Astrophysics Data System (ADS)

The phase transition of tetramethylpyrazine chloranilic acid (1:1) was studied by 35Cl NQR measurements. The frequency splits into a doublet below T c = 83.0 ± 0.5 K. The averaged frequency of 36.98 MHz at 77 K suggests an electrically neutral electronic state of the chloranilic acid molecule, that is, no proton transfer between the acid and base molecules. An enhancement of the relaxation rate was observed at T c: it is presumably due to critical slowing down of a hydrogen motion in the one-dimensional hydrogen bond network. The excitation of a high-temperature hydrogen motion at T > 250 K is also suggested by the steep decrease of T 1 observed above 250 K. From the slope of the Arrhenius plots, an activation energy of 35 kJ mol - 1 is calculated for the motion.

Asaji, Tetsuo; Yoshimura, Yusuke; Amino, Daiki

2007-09-01

107

Local magnetic and structural properties of the low-temperature orthorhombic to low-temperature tetragonal transition: A {sup 139}La NQR study in lightly hole-doped La{sub 1.8{minus}x}Eu{sub 0.2}Sr{sub x}CuO{sub 4}  

SciTech Connect

{sup 139}La nuclear quadrupole resistance (NQR) and relaxation measurements in lightly hole-doped La{sub 1.8{minus}x}Eu{sub 0.2}Sr{sub x}CuO{sub 4} have been used to investigate the microscopic properties of the low-temperature orthorhombic to low-temperature tetragonal transition. The transition is characterized by a sharp peak in {sup 139}La NQR relaxation rate, indicating phonon softening. We find that the structural phase transition is accompanied by a modification of the spin state. The data for the spin freezing and the recovery of sublattice magnetization at low T are presented and discussed in relation to the studies of La{sub 2{minus}x}Sr{sub x}CuO{sub 4} and La{sub 2}Cu{sub 1{minus}x}Li{sub x}O{sub 4}. {copyright} {ital 1999} {ital The American Physical Society}

Suh, B.J.; Hammel, P.C. [Condensed Matter and Thermal Physics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Condensed Matter and Thermal Physics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Huecker, M.; Buechner, B. [II. Physikalisches Institut, Universitaet zu Koeln, D-50937 Koeln (Germany)] [II. Physikalisches Institut, Universitaet zu Koeln, D-50937 Koeln (Germany)

1999-02-01

108

Local magnetic and structural properties of the low-temperature orthorhombic to low-temperature tetragonal transition: A 139La NQR study in lightly hole-doped La1.8-xEu0.2SrxCuO4  

NASA Astrophysics Data System (ADS)

139La nuclear quadrupole resistance (NQR) and relaxation measurements in lightly hole-doped La1.8-xEu0.2SrxCuO4 have been used to investigate the microscopic properties of the low-temperature orthorhombic to low-temperature tetragonal transition. The transition is characterized by a sharp peak in 139La NQR relaxation rate, indicating phonon softening. We find that the structural phase transition is accompanied by a modification of the spin state. The data for the spin freezing and the recovery of sublattice magnetization at low T are presented and discussed in relation to the studies of La2-xSrxCuO4 and La2Cu1-xLixO4.

Suh, B. J.; Hammel, P. C.; Hücker, M.; Büchner, B.

1999-02-01

109

Zero field NMR and NQR  

Microsoft Academic Search

Methods are described and demonstrated for detecting the coherent evolution of nuclear spin observables in zero magnetic field with the full sensitivity of high field NMR. The principle motivation is to provide a means of obtaining solid state spectra of the magnetic dipole and electric quadrupole interactions of disordered systems without the line broadening associated with random orientation with respect

D. B. Zax; A. Bielecki; K. W. Zilm; A. Pines; D. P. Weitekamp

1985-01-01

110

Sb-NQR probe for superconducting properties in the Pr-based filled-skutterudite compound PrRu4Sb12  

Microsoft Academic Search

We report the electronic and superconducting properties in the Pr-based filled-skutterudite superconductor PrRu4Sb12 with Tc=1.3 K via the measurements of nuclear-quadrupole-resonance frequency nuQ and nuclear-spin-lattice-relaxation time T1 of Sb nuclei. The temperature dependence of nuQ has revealed the energy scheme of Pr3+ crystal electric field that is consistent with an energy separation DeltaCEF˜70 K between the ground state and the

M. Yogi; H. Kotegawa; Y. Imamura; G.-Q. Zheng; Y. Kitaoka; H. Sugawara; H. Sato

2003-01-01

111

Sb-NQR probe for superconducting properties in the Pr-based filled-skutterudite compound PrRu4Sb12  

NASA Astrophysics Data System (ADS)

We report the electronic and superconducting properties in the Pr-based filled-skutterudite superconductor PrRu4Sb12 with Tc=1.3 K via the measurements of nuclear-quadrupole-resonance frequency ?Q and nuclear-spin-lattice-relaxation time T1 of Sb nuclei. The temperature dependence of ?Q has revealed the energy scheme of Pr3+ crystal electric field that is consistent with an energy separation ?CEF˜70 K between the ground state and the first-excited state. In the normal state, the Korringa relation of (1/T1T)Pr=const is valid, with [(1/T1T)Pr/(1/T1T)La]1/2˜1.44, where (1/T1T)La is for LaRu4Sb12. These results are understood in terms of a conventional Fermi-liquid picture in which the Pr-4f2 state derives neither magnetic nor quadrupolar degrees of freedom at low temperatures. In the superconducting state, 1/T1 shows a distinct coherence peak just below Tc, followed by an exponential decrease with a value of 2?/kBTc=3.1. These results demonstrate that PrRu4Sb12 is a typical weak-coupling s-wave superconductor, in strong contrast with the heavy-fermion superconductor PrOs4Sb12 that is in an unconventional strong coupling regime. The present study on PrRu4Sb12 highlights that the Pr-4f2-derived nonmagnetic doublet plays a key role in the unconventional electronic and superconducting properties in PrOs4Sb12.

Yogi, M.; Kotegawa, H.; Imamura, Y.; Zheng, G.-Q.; Kitaoka, Y.; Sugawara, H.; Sato, H.

2003-05-01

112

Converting Frequency Responses to Daily Frequency  

Cancer.gov

Frequency information on the DSQ in NHANES 2009-2010 was collected using a rate and time unit (e.g., 3 times per week). A different response format consisting of a set number of frequency categories is used in the self-administered paper questionnaire (link to questionnaire) ,. In both cases, the frequency responses are converted to a common unit of time, i.e. times per day.

113

Vibrational relaxation dynamics of I35Cl(B, v') induced by low-temperature collisions with He atoms.  

PubMed

Using laser-induced fluorescence and two-laser, pump-probe spectroscopy, collision-induced vibrational relaxation is observed to compete with the dissociation of electronically excited ICl in a helium carrier gas expansion. By thoroughly characterizing the expansion properties, we observe that collisions of ICl(B, v'= 3) molecules with He atoms in the expansion induce vibrational relaxation of the initially prepared dihalogen down to rotor states in the next lower ICl(B,v'= 2) level on timescales that compete with the rate for non-adiabatic transfer from the B state to the Z1 state. The resulting ICl(B,v'= 2,j') product rotational distribution, along with the analogous ICl(B,v'= 1,j') distribution formed by collisional relaxation of molecules in the long-lived ICl(B,v'= 2) level are compared to ICl(B,v'= 2,j') products formed by vibrational predissociation of He...ICl complexes prepared in different intermolecular vibrational levels within the He + ICl(B,v'= 3) potential. No evidence is observed for resonance-enhanced collisional cross sections, even at the low temperatures achieved, T < 1.0 K. PMID:16240047

Darr, Joshua P; Loomis, Richard A

2005-09-21

114

Characterization of solid phases and study of transformation kinetics in m-chlorofluorobenzene by 35Cl nuclear quadrupole resonance.  

PubMed

Polymorphism is of widespread occurrence in the world of molecular crystals. In this work we present experimental results showing the existence of four solid phases in m-chlorofluorobenzene. A glass structure is achieved by quenching the liquid phase at 77 K. This glassy state crystallizes in a disordered phase at T~143 K, which in turn transforms to the high-temperature stable phase (phase I) at T~153 K. Depending on the thermal history of the sample, a different ordered phase (phase III) can be obtained. The disorder is attributed to a molecular orientational disorder. There is no evidence of molecular reorientation in any phase. A study of the disorder-order phase transformation kinetics, using nuclear quadrupole resonance, is presented. The results are analyzed following Cahn's theory. Nucleation seems to take place at grain boundaries. Growth rates for different temperatures have been determined. PMID:22209621

Pérez, Silvina; Wolfenson, Alberto

2012-02-01

115

Physical Activity Frequency & Health  

MedlinePLUS Videos and Cool Tools

... hand corner of the player. Physical Activity Frequency & Health HealthDay February 20, 2015 Related MedlinePlus Pages Exercise ... in a study on physical activity frequency and health. They reported their level of activity at the ...

116

Radio frequency pressure transducer  

Microsoft Academic Search

A novel system is reported here for the pressure measurement at microwave and millimetre-wave frequencies. This method consists in using a radio frequency transducer based on RF resonator. Accurate determination of the pressure is expected.

M. M. Jatlaoui; P. Pons; H. Aubert

2007-01-01

117

Frequency comb swept lasers  

E-print Network

We demonstrate a frequency comb (FC) swept laser and a frequency comb Fourier domain mode locked (FC-FDML) laser for applications in optical coherence tomography (OCT). The fiber-based FC swept lasers operate at a sweep ...

Tsai, Tsung-Han

118

Analysis of nuclear-quadrupole-resonance spectrum of incommensurate phases: The case of bis(4-chlorophenyl) sulfone  

Microsoft Academic Search

In this work, previous experimental studies of the 35Cl nuclear-quadrupole-resonance (NQR) line shape in the incommensurate phase of bis(4-chlorophenyl) sulfone were extended. The broad spectra in the incommensurate phase (IC) were measured using the Fourier transform of the nuclear signal to avoid systematic errors committed in some studies of this compound. The results were interpreted within the framework of the

J. Schneider; C. Schürrer; A. Wolfenson; A. Brunetti

1998-01-01

119

Frequency reference in VSAT  

NASA Astrophysics Data System (ADS)

A low cost technique of frequency reference distribution within a VSAT network is discussed. This technique allows the use of a modestly frequency stable oscillator as the master frequency reference in the hub of a star-connected VSAT network. The need for extremely frequency stable OCXOs in VSATs is completely avoided. This technique was successfully incorporated in the early commercial VSAT networks. It contributes partially to the low cost nature of some of the VSAT networks available today.

Cheah, Jonathon Y. C.

1994-02-01

120

Frequency diverse array radars  

Microsoft Academic Search

This paper presents a generalized structure for a frequency diverse array radar. In its simplest form, the frequency diverse array applies a linear phase progression across the aperture. This linear phase progression induces an electronic beam scan, as in a conventional phased array. When an additional linear frequency shift is applied across the elements, a new term is generated which

Paul Antonik; Michael C. Wicks; Hugh D. Griffiths; Christopher J. Baker

2006-01-01

121

Frequency selective infrared sensors  

DOEpatents

A frequency selective infrared (IR) photodetector having a predetermined frequency band. The exemplary frequency selective photodetector includes: a dielectric IR absorber having a first surface and a second surface substantially parallel to the first surface; an electrode electrically coupled to the first surface of the dielectric IR absorber; and a frequency selective surface plasmonic (FSSP) structure formed on the second surface of the dielectric IR absorber. The FSSP structure is designed to selectively transmit radiation in the predetermined frequency band that is incident on the FSSP structure substantially independent of the angle of incidence of the incident radiation on the FSSP structure.

Davids, Paul; Peters, David W

2013-05-28

122

Frequency selective infrared sensors  

DOEpatents

A frequency selective infrared (IR) photodetector having a predetermined frequency band. The exemplary frequency selective photodetector includes: a dielectric IR absorber having a first surface and a second surface substantially parallel to the first surface; an electrode electrically coupled to the first surface of the dielectric IR absorber; and a frequency selective surface plasmonic (FSSP) structure formed on the second surface of the dielectric IR absorber. The FSSP structure is designed to selectively transmit radiation in the predetermined frequency band that is incident on the FSSP structure substantially independent of the angle of incidence of the incident radiation on the FSSP structure.

Davids, Paul; Peters, David W

2014-11-25

123

Radio frequency detection assembly and method for detecting radio frequencies  

DOEpatents

A radio frequency detection assembly is described and which includes a radio frequency detector which detects a radio frequency emission produced by a radio frequency emitter from a given location which is remote relative to the radio frequency detector; a location assembly electrically coupled with the radio frequency detector and which is operable to estimate the location of the radio frequency emitter from the radio frequency emission which has been received; and a radio frequency transmitter electrically coupled with the radio frequency detector and the location assembly, and which transmits a radio frequency signal which reports the presence of the radio frequency emitter.

Cown, Steven H. (Rigby, ID); Derr, Kurt Warren (Idaho Falls, ID)

2010-03-16

124

Frequency conversion system  

NASA Technical Reports Server (NTRS)

A frequency conversion system comprises first and second gain sources providing first and second frequency radiation outputs where the second gain source receives as input the output of the first gain source and, further, the second gain source comprises a Raman or Brillouin gain fiber for wave shifting a portion of the radiation of the first frequency output into second frequency radiation output to provided a combined output of first and second frequencies. Powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Raman/Brillouin amplifier or oscillator between the high power source and the NFM device. Further, polarization conversion using Raman or Brillouin wavelength shifting is provided to optimize frequency conversion efficiency in the NFM device.

Sanders, Steven (Inventor); Waarts, Robert G. (Inventor)

2001-01-01

125

Stabilized radio frequency quadrupole  

DOEpatents

Disclosed is a long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator. 5 figs.

Lancaster, H.D.; Fugitt, J.A.; Howard, D.R.

1984-12-25

126

Ultrastable automatic frequency control  

NASA Technical Reports Server (NTRS)

Center frequency of wideband AFC circuit drifts only hundredths of percent per day. Since circuit responds only to slow frequency drifts and modulation signal has high-pass characteristics, AFC does not interfere with normal FM operation. Stable oscillator, reset circuit, and pulse generator constitute time-averaging discriminator; digital counter in pulse generator replaces usual monostable multivibrator.

Sabourin, D. J.; Furiga, A.

1981-01-01

127

FREQUENCY ASSIGNMENT PROBLEMS  

Microsoft Academic Search

The ever growing number of wireless communications systems deployed around the globe have made the optimal assignment of a limited radio frequency spectrum a problem of primary importance. At issue are planning models for permanent spectrum al- location, licensing, regulation, and network design. Furt her at issue are on-line algorithms for dynamically assigning frequencies to users within an es tablished

ROBERT A. MURPHEY; PANOS M. PARDALOS; MAURICIO G. C. RESE

128

Wavelet frequency decomposition method  

NASA Astrophysics Data System (ADS)

A wavelet variation of the frequency decomposition multigrid method of Hackbusch is presented. The perfect reconstruction property of the wavelet system enable us to perform the convergence analysis of the frequency decomposition method. Some applications of this method are also presented.

Rieder, Andreas; Wells, Raymond O., Jr.; Zhou, Xiaodong

1994-03-01

129

Optical frequency metrology  

Microsoft Academic Search

Extremely narrow optical resonances in cold atoms or single trapped ions can be measured with high resolution. A laser locked to such a narrow optical resonance could serve as a highly stable oscillator for an all-optical atomic clock. However, until recently there was no reliable clockwork mechanism that could count optical frequencies of hundreds of terahertz. Techniques using femtosecond-laser frequency

Th. Udem; R. Holzwarth; T. W. Hänsch

2002-01-01

130

Stabilized radio frequency quadrupole  

DOEpatents

A long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator.

Lancaster, Henry D. (Orinda, CA); Fugitt, Jock A. (Berkeley, CA); Howard, Donald R. (Danville, CA)

1984-01-01

131

Frequency Distributions August 2009  

E-print Network

=Level of Academic Challenge ACL=Active and Collaborative Learning Interpreting the Frequency Distributions Report The Frequency Distributions report is based on information from all randomly selected students for both your the count numbers. For more information about weighting, please visit the NSSE Web site at www

132

Microfabricated ion frequency standard  

DOEpatents

A microfabricated ion frequency standard (i.e. an ion clock) is disclosed with a permanently-sealed vacuum package containing a source of ytterbium (Yb) ions and an octupole ion trap. The source of Yb ions is a micro-hotplate which generates Yb atoms which are then ionized by a ultraviolet light-emitting diode or a field-emission electron source. The octupole ion trap, which confines the Yb ions, is formed from suspended electrodes on a number of stacked-up substrates. A microwave source excites a ground-state transition frequency of the Yb ions, with a frequency-doubled vertical-external-cavity laser (VECSEL) then exciting the Yb ions up to an excited state to produce fluorescent light which is used to tune the microwave source to the ground-state transition frequency, with the microwave source providing a precise frequency output for the ion clock.

Schwindt, Peter (Albuquerque, NM); Biedermann, Grant (Albuquerque, NM); Blain, Matthew G. (Albuquerque, NM); Stick, Daniel L. (Albuquerque, NM); Serkland, Darwin K. (Albuquerque, NM); Olsson, III, Roy H. (Albuquerque, NM)

2010-12-28

133

Precision frequency synthesizing sources with excellent time/frequency performances  

NASA Technical Reports Server (NTRS)

Precision frequency synthesizing sources are needed in the time / frequency measuring system, atomic frequency standards, telemetry, communication, and radar systems. This kind of frequency synthesizing source possesses high frequency accuracy and excellent long term and short term frequency stability. Several precision frequency synthesizing sources developed by Beijing Institute of Radio Metrology and Measurement (BIRMM) which have been successfully applied to the time / frequency measuring system, atomic frequency standards system, and radar system are described. In addition, the working principle, implementation approach, and the main technical specifications of the frequency synthesizing sources are also given.

Zhou, Liren; Lin, Hai

1994-01-01

134

Roll Out the Frequency  

NSDL National Science Digital Library

In this activity, students use marks on a 1.4 m strip of paper to simulate light wave frequencies and measure the time it takes for different frequencies to pass through the "viewer" made from a manila folder. Students learn that different colors of light have different wave frequencies. The resource is part of the teacher's guide accompanying the video, NASA Why Files: The Case of the Mysterious Red Light. Lesson objectives supported by the video, additional resources, teaching tips and an answer sheet are included in the teacher's guide.

135

Graphene Frequency Multipliers  

E-print Network

In this letter, the ambipolar transport properties of graphene flakes have been used to fabricate full-wave signal rectifiers and frequency-doubling devices. By correctly biasing an ambipolar graphene field-effect transistor ...

Wang, Han

136

Acoustic emission frequency discrimination  

NASA Technical Reports Server (NTRS)

In acoustic emission nondestructive testing, broadband frequency noise is distinguished from narrow banded acoustic emission signals, since the latter are valid events indicative of structural flaws in the material being examined. This is accomplished by separating out those signals which contain frequency components both within and beyond (either above or below) the range of valid acoustic emission events. Application to acoustic emission monitoring during nondestructive bond verification and proof loading of undensified tiles on the Space Shuttle Orbiter is considered.

Sugg, Frank E. (inventor); Graham, Lloyd J. (inventor)

1988-01-01

137

Frequency domain measurement systems  

NASA Technical Reports Server (NTRS)

Stable frequency sources and signal processing blocks were characterized by their noise spectra, both discrete and random, in the frequency domain. Conventional measures are outlined, and systems for performing the measurements are described. Broad coverage of system configurations which were found useful is given. Their functioning and areas of application are discussed briefly. Particular attention is given to some of the potential error sources in the measurement procedures, system configurations, double-balanced-mixer-phase-detectors, and application of measuring instruments.

Eischer, M. C.

1978-01-01

138

A digital frequency synthesizer  

Microsoft Academic Search

A digital frequency synthesizer has been designed and constructed based on generating digital samples ofexp [j(2^{pi}nk\\/N)]at timenT. The real and imaginary parts of this exponential form samples of quadrature sinusoids where the frequency indexkis allowed to vary(-N\\/4) leq K < (N\\/4). The digital samples drive digital to analog converters followed by low-pass interpolating filters to produce analog sinusoids. The method

JOSEPH TIERNEY; CHARLES M. RADER; B. Gold

1971-01-01

139

High frequency breakdown voltage  

SciTech Connect

This report contains information about the effect of frequency on the breakdown voltage of an air gap at standard pressure and temperature, 76 mm Hg and O{degrees}C, respectively. The frequencies of interest are 47 MHz and 60 MHz. Additionally, the breakdown in vacuum is briefly considered. The breakdown mechanism is explained on the basis of collision and ionization. The presence of the positive ions produced by ionization enhances the field in the gap, and thus determines the breakdown. When a low-frequency voltage is applied across the gap, the breakdown mechanism is the same as that caused by the DC or static voltage. However, when the frequency exceeds the first critical value f{sub c}, the positive ions are trapped in the gap, increasing the field considerably. This makes the breakdown occur earlier; in other words, the breakdown voltage is lowered. As the frequency increases two decades or more, the second critical frequency, f{sub ce}, is reached. This time the electrons start being trapped in the gap. Those electrons that travel multiple times across the gap before reaching the positive electrode result in an enormous number of electrons and positive ions being present in the gap. The result is a further decrease of the breakdown voltage. However, increasing the frequency does not decrease the breakdown voltage correspondingly. In fact, the associated breakdown field intensity is almost constant (about 29 kV/cm).The reason is that the recombination rate increases and counterbalances the production rate, thus reducing the effect of the positive ions` concentration in the gap. The theory of collision and ionization does not apply to the breakdown in vacuum. It seems that the breakdown in vacuum is primarily determined by the irregularities on the surfaces of the electrodes. Therefore, the effect of frequency on the breakdown, if any, is of secondary importance.

Chu, Thanh Duy

1992-03-01

140

Frequency Standards and Metrology  

NASA Astrophysics Data System (ADS)

Preface / Lute Maleki -- Symposium history / Jacques Vanier -- Symposium photos -- pt. I. Fundamental physics. Variation of fundamental constants from the big bang to atomic clocks: theory and observations (Invited) / V. V. Flambaum and J. C. Berengut. Alpha-dot or not: comparison of two single atom optical clocks (Invited) / T. Rosenband ... [et al.]. Variation of the fine-structure constant and laser cooling of atomic dysprosium (Invited) / N. A. Leefer ... [et al.]. Measurement of short range forces using cold atoms (Invited) / F. Pereira Dos Santos ... [et al.]. Atom interferometry experiments in fundamental physics (Invited) / S. W. Chiow ... [et al.]. Space science applications of frequency standards and metrology (Invited) / M. Tinto -- pt. II. Frequency & metrology. Quantum metrology with lattice-confined ultracold Sr atoms (Invited) / A. D. Ludlow ... [et al.]. LNE-SYRTE clock ensemble: new [symbol]Rb hyperfine frequency measurement - spectroscopy of [symbol]Hg optical clock transition (Invited) / M. Petersen ... [et al.]. Precise measurements of S-wave scattering phase shifts with a juggling atomic clock (Invited) / S. Gensemer ... [et al.]. Absolute frequency measurement of the [symbol] clock transition (Invited) / M. Chwalla ... [et al.]. The semiclassical stochastic-field/atom interaction problem (Invited) / J. Camparo. Phase and frequency noise metrology (Invited) / E. Rubiola ... [et al.]. Optical spectroscopy of atomic hydrogen for an improved determination of the Rydberg constant / J. L. Flowers ... [et al.] -- pt. III. Clock applications in space. Recent progress on the ACES mission (Invited) / L. Cacciapuoti and C. Salomon. The SAGAS mission (Invited) / P. Wolf. Small mercury microwave ion clock for navigation and radioScience (Invited) / J. D. Prestage ... [et al.]. Astro-comb: revolutionizing precision spectroscopy in astrophysics (Invited) / C. E. Kramer ... [et al.]. High frequency very long baseline interferometry: frequency standards and imaging an event horizon (Invited) / S. Doeleman. Optically-pumped space cesium clock for Galileo: results of the breadboard / R. Ruffieux ... [et al.] -- pt. IV. Optical clocks I: lattice clocks. Optical lattice clock: seven years of progress and next steps (Invited) / H. Katori, M. Takamoto and T. Akatsuka. The Yb optical lattice clock (Invited) / N. D. Demke ... [et al.]. Optical Lattice clock with Sr atoms (Invited) / P. G. Westergaard ... [et al.]. Development of an optical clock based on neutral strontium atoms held in a lattice trap / E. A. Curtis ... [et al.]. Decoherence and losses by collisions in a [symbol]Sr lattice clock / J. S. R. Vellore Winfred ... [et al.]. Lattice Yb optical clock and cryogenic Cs fountain at INRIM / F. Levi ... [et al.] -- pt. V. Optical clocks II: ion clocks. [Symbol]Yb+ single-ion optical frequency standards (Invited) / Chr. Tamm ... [et al.]. An optical clock based on a single trapped [symbol]Sr+ ion (Invited) / H. S. Margolis ... [et al.]. A trapped [symbol]Yb+ ion optical frequency standard based on the [symbol] transition (Invited) / P. Gill ... [et al.]. Overview of highly accurate RF and optical frequency standards at the National Research Council of Canada (Invited) / A. A. Madej ... [et al.] -- pt. VI. Optical frequency combs. Extreme ultraviolet frequency combs for spectroscopy (Invited) / A. Ozawa ... [et al.]. Development of an optical clockwork for the single trapped strontium ion standard at 445 THz / J. E. Bernard ... [et al.]. A phase-coherent link between the visible and infrared spectral ranges using a combination of CW OPO and femtosecond laser frequency comb / E. V. Kovalchuk and A. Peters. Improvements to the robustness of a TI: sapphire-based femtosecond comb at NPL / V. Tsatourian ... [et al.] -- pt. VII. Atomic microwave standards. NIST FI and F2 (Invited) / T. P. Heavner ... [et al.]. Atomic fountains for the USNO master clock (Invited) / C. Ekstrom ... [et al.]. The transportable cesium fountain clock NIM5: its construction and performance (Invited) / T. Li ... [et al.].Compensated multi-pole merc

Maleki, Lute

2009-04-01

141

Monolithic THz Frequency Multipliers  

NASA Technical Reports Server (NTRS)

Frequency multipliers are required as local oscillator sources for frequencies up to 2.7 THz for FIRST and airborne applications. Multipliers at these frequencies have not previously been demonstrated, and the object of this work was to show whether such circuits are really practical. A practical circuit is one which not only performs as well as is required, but also can be replicated in a time that is feasible. As the frequency of circuits is increased, the difficulties in fabrication and assembly increase rapidly. Building all of the circuit on GaAs as a monolithic circuit is highly desirable to minimize the complexity of assembly, but at the highest frequencies, even a complete monolithic circuit is extremely small, and presents serious handling difficulty. This is compounded by the requirement for a very thin substrate. Assembly can become very difficult because of handling problems and critical placement. It is very desirable to make the chip big enough to that it can be seen without magnification, and strong enough that it may be picked up with tweezers. Machined blocks to house the chips present an additional challenge. Blocks with complex features are very expensive, and these also imply very critical assembly of the parts. It would be much better if the features in the block were as simple as possible and non-critical to the function of the chip. In particular, grounding and other electrical interfaces should be done in a manner that is highly reproducible.

Erickson, N. R.; Narayanan, G.; Grosslein, R. M.; Martin, S.; Mehdi, I.; Smith, P.; Coulomb, M.; DeMartinez, G.

2001-01-01

142

Frequency conversion system  

NASA Technical Reports Server (NTRS)

Laser diode pumped mid-IR wavelength sources include at least one high power, near-IR wavelength, injection and/or sources wherein one or both of such sources may be tunable providing a pump wave output beam to a quasi-phase matched (QPM) nonlinear frequency mixing (NFM) device. The NFM device may be a difference frequency mixing (DFM) device or an optical parametric oscillation (OPO) device. Wavelength tuning of at least one of the sources advantageously provides the ability for optimizing pump or injection wavelengths to match the QPM properties of the NFM device enabling a broad range of mid-IR wavelength selectivity. Also, pump powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Raman/Brillouin amplifier or oscillator between the high power source and the NFM device. Further, polarization conversion using Raman or Brillouin wavelength shifting is provided to optimize frequency conversion efficiency in the NFM device.

Sanders, Steven (Inventor); Lang, Robert J. (Inventor)

2001-01-01

143

High frequency energy measurements  

SciTech Connect

High-frequency (> 100 MHz) energy measurements present special problems to the experimenter. Environment or available electronics often limit the applicability of a given detector type. The physical properties of many detectors are frequency dependent and in some cases, the physical effect employed can be frequency dependent. State-of-the-art measurements generally involve a detection scheme in association with high-speed electronics and a method of data recording. Events can be single or repetitive shot requiring real time, sampling, or digitizing data recording. Potential modification of the pulse by the detector and the associated electronics should not be overlooked. This presentation will review typical applications, methods of choosing a detector, and high-speed detectors. Special considerations and limitations of some applications and devices will be described.

Stotlar, S.C.

1981-01-01

144

Name That Frequency  

NSDL National Science Digital Library

This activity was designed for blind learners, but all types of learners can model how vibrating particles, such as in a sound wave, bump into other particles causing them to vibrate, and that the vibrations travel. The chain reaction of sound waves will be demonstrated using old video cassettes (in a way similar to a dominoes game). Learners with visual impairments as well as sighted learners will have the chance to create tactile diagrams of varying wave frequencies. The activity includes setting up the row of tapes at various âfrequencies,â closer together for higher frequency, farther apart for lower.

Blind, Perkins S.

2012-06-26

145

Rotating Phasors- Negative Frequencies  

NSDL National Science Digital Library

This interactive phasor page allows you to control the values of a rotating phasor and see a visualization of each change that is done. You can control: one, pos/neg, two, beats, delta, sawtooth, square, triangle, time, zoom, plus you can put into five different values: Frequency (rel, HZ, mHZ), Amplitude (raw, rel), and Phases (Deg, Rad, unitrad).

146

improving maser frequency stability  

NASA Technical Reports Server (NTRS)

Hydrogen maser frequency standard is more stable by addition of parallel pyrex capillary tube array collimator. With collimator, maser line width has been made as narrow as 0.24 hertz representing fivefold improvement over maser without collimator. Fluorocarbon coating in tubes virtually eliminates energy loss in collimator.

Crampton, S. B.

1980-01-01

147

Dual frequency optical cavity  

DOEpatents

Method and apparatus for generating two distinct laser frequencies in an optical cavity, using a "T" configuration laser cavity and means for intermittently increasing or decreasing the index of refraction n of an associated transmission medium in one arm of the optical cavity to enhance laser action in one arm or the second arm of the cavity.

George, E. Victor (Livermore, CA); Schipper, John F. (Palo Alto, CA)

1985-01-01

148

Radio frequency identification (RFID)  

Microsoft Academic Search

First conceived in 1948, Radio Frequency Identification (RFID) has taken many years for the technology to mature to the point where it is sufficiently affordable and reliable for widespread use. From Electronic Article Surveillance (EAS) for article (mainly clothing) security to more sophisticated uses, RFID is seen by some as the inevitable replacement for bar codes. With increasing use comes

C. M. Roberts

2006-01-01

149

Fast frequency hopping PLL synthesizer  

Microsoft Academic Search

An account is given of a fast frequency-hopping phase-locked loop (PLL) synthesizer for TDMA equipment which allows changes to the carrier frequency within the guard time of burst signals. The use of phase and frequency preset (PFP) PLL circuits allows the proposed synthesizer to achieve fast, stable frequency setting in intervals shorter than the burst signal duration. Experimental results indicate

Kazuhiko Seki; Masahiro Umehira

1990-01-01

150

Image restoration using fast Fourier and wavelet transforms  

NASA Astrophysics Data System (ADS)

Pure nuclear quadrupole resonance (NQR) of 14N nuclei is quite promising as a method for detecting explosives such as RDX and contraband narcotics such as cocaine and heroin in quantities of interest. Pure NQR is conducted without an external applied magnetic field, so potential concerns about damage to magnetically encoded data or exposure of personnel to large magnetic fields are not relevant. Because NQR frequencies of different compounds are quite distinct, we do not encounter false alarms from the NQR signals of other benign materials. We have constructed a proof-of-concept NQR explosives detector which interrogates a volume of 300 liters (10 ft3). With minimal modification to the existing explosives detector, we can detect operationally relevant quantities of (free base) cocaine within the 300-liter inspection volume in 6 seconds. We are presently extending this approach to the detection of heroin base and also examining 14N and 35,37Cl pure NQR for detection of the hydrochloride forms of both materials. An adaptation of this NQR approach may be suitable for scanning personnel for externally carried contraband and explosives. We first outline the basics of the NQR approach, highlighting strengths and weaknesses, and then present representative results for RDX and cocaine detection. We also present a partial compendium of relevant NQR parameters measured for some materials of interest.

Harrod, William J.; Nagy, James G.; Plemmons, Robert J.

1994-02-01

151

Narcotics and explosives detection by 14N pure nuclear quadrupole resonance  

NASA Astrophysics Data System (ADS)

Pure nuclear quadrupole resonance (NQR) of 14N nuclei is quite promising as a method for detecting explosives such as RDX and contraband narcotics such as cocaine and heroin in quantities of interest. Pure NQR is conducted without an external applied magnetic field, so potential concerns about damage to magnetically encoded data or exposure of personnel to large magnetic fields are not relevant. Because NQR frequencies of different compounds are quite distinct, we do not encounter false alarms from the NQR signals of other benign materials. We have constructed a proof-of-concept NQR explosives detector which interrogates a volume of 300 liters (10 ft3). With minimal modification to the existing explosives detector, we can detect operationally relevant quantities of (free base) cocaine within the 300-liter inspection volume in 6 seconds. We are presently extending this approach to the detection of heroin base and also examining 14N and 35,37Cl pure NQR for detection of the hydrochloride forms of both materials. An adaptation of this NQR approach may be suitable for scanning personnel for externally carried contraband and explosives. We first outline the basics of the NQR approach, highlighting strengths and weaknesses, and then present representative results for RDX and cocaine detection. We also present a partial compendium of relevant NQR parameters measured for some materials of interest.

Garroway, Allen N.; Buess, Michael L.; Yesinowski, James P.; Miller, Joel B.

1994-03-01

152

Investigation of the electronic effects in a series of halo derivatives of organosilicon compounds by the method of nuclear quadrupole resonance of 79 Br, 81 Br, and 127 I  

Microsoft Academic Search

1.The NQR spectra of certain bromo and iodo derivatives of organosilicon compounds were investigated.2.The correlation of the NQR frequencies and the quadrupole coupling constants with the induction and conjugation constants of the substituents at the silicon atom was constructed.

G. K. Semin; E. V. Bryukhova; M. A. Kadina; G. V. Frolova

1971-01-01

153

Fiber optic frequency transfer link  

NASA Technical Reports Server (NTRS)

A reference frequency distribution system is disclosed for transmitting a reference frequency from a reference unit to a remote unit while keeping the reference frequency at the reference unit and the remote unit in phase. A fiber optic cable connects the reference unit to the remote unit. A frequency source at the reference unit produces a reference frequency having an adjustable phase. A fiber optic transmitter at the reference unit modulates a light beam with the reference frequency and transmits the light beam into the fiber optic cable. A 50/50 reflector at the remote unit reflects a first portion of the light beam from the reference unit back into the fiber optic cable to the reference unit. A first fiber optic receiver disposed at the remote unit receives a second portion of the light beam and demodulates the reference frequency to be used at the remote unit. A second fiber optic receiver disposed at the reference unit receives the first portion of the light beam and demodulates a reference frequency component. A phase conjugator is connected to the frequency source for comparing the phase of the reference frequency component to the phase of the reference frequency modulating the light beam being transmitted from the reference unit to maintain a conjugate (anti-symmetric) relationship between the reference frequency component and the reference frequency modulating the light beam where virtually no phase difference exists between the phase of the reference frequency component and the phase of the reference frequency modulating the light beam.

Primas, Lori E. (inventor); Sydnor, Richard L. (inventor); Lutes, George F. (inventor)

1991-01-01

154

High frequency reference electrode  

DOEpatents

A high frequency reference electrode for electrochemical experiments comprises a mercury-calomel or silver-silver chloride reference electrode with a layer of platinum around it and a layer of a chemically and electrically resistant material such as TEFLON around the platinum covering all but a small ring or halo' at the tip of the reference electrode, adjacent to the active portion of the reference electrode. The voltage output of the platinum layer, which serves as a redox electrode, and that of the reference electrode are coupled by a capacitor or a set of capacitors and the coupled output transmitted to a standard laboratory potentiostat. The platinum may be applied by thermal decomposition to the surface of the reference electrode. The electrode provides superior high-frequency response over conventional electrodes. 4 figs.

Kronberg, J.W.

1994-05-31

155

High frequency reference electrode  

DOEpatents

A high frequency reference electrode for electrochemical experiments comprises a mercury-calomel or silver-silver chloride reference electrode with a layer of platinum around it and a layer of a chemically and electrically resistant material such as TEFLON around the platinum covering all but a small ring or "halo" at the tip of the reference electrode, adjacent to the active portion of the reference electrode. The voltage output of the platinum layer, which serves as a redox electrode, and that of the reference electrode are coupled by a capacitor or a set of capacitors and the coupled output transmitted to a standard laboratory potentiostat. The platinum may be applied by thermal decomposition to the surface of the reference electrode. The electrode provides superior high-frequency response over conventional electrodes.

Kronberg, James W. (Aiken, SC)

1994-01-01

156

Micro ion frequency standard  

NASA Astrophysics Data System (ADS)

We are developing a highly miniaturized trapped ion clock to probe the 12.6 GHz hyperfine transition in the 171Yb+ ion. The clock development is being funded by the Integrated Micro Primary Atomic Clock Technology (IMPACT) program from DARPA where the stated goals are to develop a clock that consumes 50 mW of power, has a size of 5 cm3, and has a long-term frequency stability of 10-14 at one month. One of the significant challenges will be to develop miniature single-frequency lasers at 369 nm and 935 nm and the optical systems to deliver light to the ions and to collect ion fluorescence on a detector.

Schwindt, Peter D. D.; Jau, Yuan-Yu; Partner, Heather; Serkland, Darwin K.; Boye, Robert; Fang, Lu; Casias, Adrian; Manginell, Ronald P.; Moorman, Matthew; Prestage, John; Yu, Nan

2011-06-01

157

Flood Frequency Analysis  

NSDL National Science Digital Library

The Flood Frequency Analysis module offers an introduction to the use of flood frequency analysis for flood prediction and planning. Through use of rich illustrations, animations, and interactions, this module explains the basic concepts, underlying issues, and methods for analyzing flood data. Common concepts such as the 100-year flood and return periods as well as issues affecting the statistical representation of floods are discussed. Common flood data analysis methods as well as an overview of design events are also covered. As a foundation topic for the Basic Hydrologic Science course, this module may be taken on its own, but it will also be available as a supporting topic providing factual scientific information to support students in completion of the case-based forecasting modules.

Comet

2006-10-10

158

Microwave Frequency Polarizers  

NASA Technical Reports Server (NTRS)

This article describes the fabrication and analysis of microwave frequency polarizing grids. The grids are designed to measure polarization from the cosmic microwave background. It is effective in the range of 500 to 1500 micron wavelength. It is cryogenic compatible and highly robust to high load impacts. Each grid is fabricated using an array of different assembly processes which vary in the types of tension mechanisms to the shape and size of the grids. We provide a comprehensive study on the analysis of the grids' wire heights, diameters, and spacing.

Ha, Vien The; Mirel, Paul; Kogut, Alan J.

2013-01-01

159

Hurricane Frequency and Intensity  

NSDL National Science Digital Library

In recent years more and more attention has been paid to the Earth's climate and how it is evolving. When studying hurricanes it is important to understand that, for a hurricane to grow, warm water is an absolute necessity. So if the Earth continues to warm, what does that mean for hurricanes and their intensity? In this lesson, the student will look at past hurricane data by researching the intensity and frequency of hurricanes using the Live Access Server and several Internet sites found in the Lesson Links section.

160

Frequency Dependent Attenuation Revisited  

E-print Network

The work is inspired by thermo-and photoacoustic imaging, where recent efforts are devoted to take into account attenuation and varying wave speed parameters. In this paper we study causal equations describing propagation of attenuated pressure waves. We review standard models like frequency power laws and and the thermo-viscous equation. The lack of causality of standard models in the parameter range relevant for photoacoustic imaging requires to derive novel equations. The main ingredients for deriving causal equations are the Kramers-Kronig relation and the mathematical concept of linear system theory. The theoretical results of this work are underpined by numerical experiments.

Richard, Kowar; Xavier, Bonnefond

2009-01-01

161

SECURING RADIO FREQUENCY IDENTIFICATION (RFID)  

E-print Network

May 2007 SECURING RADIO FREQUENCY IDENTIFICATION (RFID) SYSTEMS SECURING RADIO FREQUENCY IDENTIFICATION (RFID) SYSTEMS Karen Scarfone, EditorKaren Scarfone, Editor Computer Security Division of Standards and Technology National Institute of Standards and Technology RFID is a form of automatic

162

High-frequency ECG  

NASA Technical Reports Server (NTRS)

The standard ECG is by convention limited to 0.05-150 Hz, but higher frequencies are also present in the ECG signal. With high-resolution technology, it is possible to record and analyze these higher frequencies. The highest amplitudes of the high-frequency components are found within the QRS complex. In past years, the term "high frequency", "high fidelity", and "wideband electrocardiography" have been used by several investigators to refer to the process of recording ECGs with an extended bandwidth of up to 1000 Hz. Several investigators have tried to analyze HF-QRS with the hope that additional features seen in the QRS complex would provide information enhancing the diagnostic value of the ECG. The development of computerized ECG-recording devices that made it possible to record ECG signals with high resolution in both time and amplitude, as well as better possibilities to store and process the signals digitally, offered new methods for analysis. Different techniques to extract the HF-QRS have been described. Several bandwidths and filter types have been applied for the extraction as well as different signal-averaging techniques for noise reduction. There is no standard method for acquiring and quantifying HF-QRS. The physiological mechanisms underlying HF-QRS are still not fully understood. One theory is that HF-QRS are related to the conduction velocity and the fragmentation of the depolarization wave in the myocardium. In a three-dimensional model of the ventricles with a fractal conduction system it was shown that high numbers of splitting branches are associated with HF-QRS. In this experiment, it was also shown that the changes seen in HF-QRS in patients with myocardial ischemia might be due to the slowing of the conduction velocity in the region of ischemia. This mechanism has been tested by Watanabe et al by infusing sodium channel blockers into the left anterior descending artery in dogs. In their study, 60 unipolar ECGs were recorded from the entire ventricular surface and were signal-averaged and filtered in the 30-250 Hz frequency range. The results showed that the decrease noted in the HF-QRS correlated linearly with the local conduction delay. The results suggest that HF-QRS is a potent indicator of disturbed local conduction. An alternative theory is that HF-QRS reflect the shape of the original electrocardiographic signal. Bennhagen et al showed that root mean square (RMS) voltage values of the depolarization signal correlate poorly with the signal amplitude but highly with the first and second derivatives, i.e. the velocity and the acceleration of the signal. It has also been suggested that the autonomic nervous system affects HF-QRS. For example, sitting up causes significant changes in HF-QRS in some leads compared to the supine position [Douglas et al., 2006]. Unpublished results indicate that familial dysautonomic patients (both vagal and sympathetic degeneration) have very little Reduced Amplitude Zones (RAZ) formation . Athletic individuals, especially elite athletes, who have vagally-mediated changes on the conventional ECG (i.e. early repolarization, bradycardia) have increased RAZ formation. Further electrophysiological studies are needed, however, to better understand the underlying mechanisms of HF-QRS. Several investigators have studied HF-QRS in different cardiac conditions, including acute myocardial ischemia and myocardial infarction (MI). However, in order for clinicians to confidently use HF-QRS as an adjunct to standard ECG, more knowledge about the characteristics of HF-QRS is needed.

Tragardh, Elin; Schlegel, Todd T.

2006-01-01

163

Low frequency sinusoidal pressure generator  

NASA Technical Reports Server (NTRS)

Low frequency pressure generator is built to provide sinusoidal driving function in frequency range from 0.05 to 50 Hz for frequency response testing of pressure transducers used in liquid-filled systems. Generator consists of piston-in-cylinder, scotch-yoke mechanism machined into piston, and adjustable eccentric.

Curreri, J. S.

1972-01-01

164

Flying radio frequency undulator  

NASA Astrophysics Data System (ADS)

A concept for the room-temperature rf undulator, designed to produce coherent X-ray radiation by means of a relatively low-energy electron beam and pulsed mm-wavelength radiation, is proposed. The "flying" undulator is a high-power short rf pulse co-propagating together with a relativistic electron bunch in a helically corrugated waveguide. The electrons wiggle in the rf field of the -1st spatial harmonic with the phase velocity directed in the opposite direction in respect to the bunch velocity, so that particles can irradiate high-frequency Compton's photons. A high group velocity (close to the speed of light) ensures long cooperative motion of the particles and the co-propagating rf pulse.

Kuzikov, S. V.; Savilov, A. V.; Vikharev, A. A.

2014-07-01

165

Instantaneous Frequency Attribute Comparison  

NASA Astrophysics Data System (ADS)

The instantaneous seismic data attribute provides a different means of seismic interpretation, for all types of seismic data. It first came to the fore in exploration seismology in the classic paper of Taner et al (1979), entitled " Complex seismic trace analysis". Subsequently a vast literature has been accumulated on the subject, which has been given an excellent review by Barnes (1992). In this research we will compare two different methods of computation of the instantaneous frequency. The first method is based on the original idea of Taner et al (1979) and utilizes the derivative of the instantaneous phase of the analytic signal. The second method is based on the computation of the power centroid of the time-frequency spectrum, obtained using either the Gabor Transform as computed by Margrave et al (2011) or the Stockwell Transform as described by Stockwell et al (1996). We will apply both methods to exploration seismic data and the DPRK events recorded in 2006 and 2013. In applying the classical analytic signal technique, which is known to be unstable, due to the division of the square of the envelope, we will incorporate the stabilization and smoothing method proposed in the two paper of Fomel (2007). This method employs linear inverse theory regularization coupled with the application of an appropriate data smoother. The centroid method application is straightforward and is based on the very complete theoretical analysis provided in elegant fashion by Cohen (1995). While the results of the two methods are very similar, noticeable differences are seen at the data edges. This is most likely due to the edge effects of the smoothing operator in the Fomel method, which is more computationally intensive, when an optimal search of the regularization parameter is done. An advantage of the centroid method is the intrinsic smoothing of the data, which is inherent in the sliding window application used in all Short-Time Fourier Transform methods. The Fomel technique has a larger CPU run-time, resulting from the necessary matrix inversion. Barnes, Arthur E. "The calculation of instantaneous frequency and instantaneous bandwidth.", Geophysics, 57.11 (1992): 1520-1524. Fomel, Sergey. "Local seismic attributes.", Geophysics, 72.3 (2007): A29-A33. Fomel, Sergey. "Shaping regularization in geophysical-estimation problems." , Geophysics, 72.2 (2007): R29-R36. Stockwell, Robert Glenn, Lalu Mansinha, and R. P. Lowe. "Localization of the complex spectrum: the S transform."Signal Processing, IEEE Transactions on, 44.4 (1996): 998-1001. Taner, M. Turhan, Fulton Koehler, and R. E. Sheriff. "Complex seismic trace analysis." Geophysics, 44.6 (1979): 1041-1063. Cohen, Leon. "Time frequency analysis theory and applications."USA: Prentice Hall, (1995). Margrave, Gary F., Michael P. Lamoureux, and David C. Henley. "Gabor deconvolution: Estimating reflectivity by nonstationary deconvolution of seismic data." Geophysics, 76.3 (2011): W15-W30.

Yedlin, M. J.; Margrave, G. F.; Ben Horin, Y.

2013-12-01

166

High frequency nanotube oscillator  

DOEpatents

A tunable nanostructure such as a nanotube is used to make an electromechanical oscillator. The mechanically oscillating nanotube can be provided with inertial clamps in the form of metal beads. The metal beads serve to clamp the nanotube so that the fundamental resonance frequency is in the microwave range, i.e., greater than at least 1 GHz, and up to 4 GHz and beyond. An electric current can be run through the nanotube to cause the metal beads to move along the nanotube and changing the length of the intervening nanotube segments. The oscillator can operate at ambient temperature and in air without significant loss of resonance quality. The nanotube is can be fabricated in a semiconductor style process and the device can be provided with source, drain, and gate electrodes, which may be connected to appropriate circuitry for driving and measuring the oscillation. Novel driving and measuring circuits are also disclosed.

Peng, Haibing (Houston, TX); Zettl, Alexander K. (Kensington, TX)

2012-02-21

167

Radio frequency coaxial feedthrough  

DOEpatents

An improved radio frequency coaxial transmission line vacuum feed-through provided based on the use of a half-wavelength annular dielectric pressure barrier disk, or multiple disks comprising an effective half wavelength structure to eliminate reflections from the barrier surfaces. Gas-tight seals are formed about the outer and inner diameter surfaces of the barrier disk using a sealing technique which generates radial forces sufficient to form seals by forcing the conductor walls against the surfaces of the barrier disks in a manner which does not deform the radii of the inner and outer conductors, thereby preventing enhancement of the electric field at the barrier faces which limits voltage and power handling capabilities of a feedthrough.

Owens, Thomas L. (Kingston, TN)

1989-01-17

168

An assessment of derived flood frequency distributions  

E-print Network

Flood Frequency Curve - Turtle Creek. . . FIG. 9. Statistical Flood Frequency Curve - Halls Bayou . . . . . . 51 . . . 51 FIG. 10. Derived Flood Frequency Curves ? South Rocky Creek. . . . . . 53 FIG. 11. Derived Flood Frequency Curves - Briar Creek... . . FIG. 12, Derived Flood Frequency Curves - Turtle Creek. . . FIG. 13. Derived Flood Frequency Curves - Halls Bayou. . . . . . . . . . . . . . FIG. 14. Simulation Flood Frequency Curve ? South Rocky Creek. . . . . . 54 . . . 56 FIG. 15. Simulation...

Raines, Timothy Howard

1991-01-01

169

Frequency error estimation for frequency comb multiple access demodulation  

NASA Astrophysics Data System (ADS)

Frequency comb multiple access (FCMA) has been suggested as an efficient means of multiple access for satellite communication networks. The authors suggest a new algorithm for rapid FCMA frequency error estimation with excellent performance at low E(sub b)/N(sub o) and heavy interchannel interference. This frequency correction must be achieved before acquisition of timing and phase. The performance of the algorithm is also given.

Reisenfeld, S.; Kumar, A.

1994-04-01

170

Radio Frequency Identification  

NSDL National Science Digital Library

A wealth of information about RFID is available at this site (1), ranging from background material to case studies. A discussion highlighting the myriad of uses for RFID is included. Transponder News (2) offers several articles that explore the technology in greater detail. Two in particular look at current and future trends, while others are editorial essays and technical notes. Pacific Northwest National Laboratory (3) is involved in the development of advanced tags for RFID systems. The project's homepage outlines current research efforts for three different types of radio frequency tags, which are being designed for varying degrees of sophistication and functionality. While RFID technology can be very useful, the fact that information about items is collected remotely raises concerns about privacy and security. This issue is addressed in a research paper from the Massachusetts Institute of Technology (4). The authors review current RFID systems and their operation, and then propose a number of security mechanisms that could reduce the risk associated with their use. A paper presented at the 2002 European Wireless Conference (5) compares the performance of RFID systems that use ultra-high frequency (UHF) communications to those that use microwave communications. It is argued that although microwave-based devices, such as Bluetooth, are suitable for worldwide operation, systems that communicate in the UHF range have greater range and less interference. The introduction of RFID smart tags in goods is discussed in this article (6). Now that these tags are cheap enough to be attached to thousands of items, stores will be able to track goods as they are transferred from storehouses to retail shelves, thereby minimizing the possibility of loss or theft. RFID technology has found another use in the war with Iraq. An article from May 20, 2003 (7) describes wristbands embedded with an RFID chip. The status and position of a wounded soldier who is wearing such a wristband can be monitored while he or she is recovering at a medical facility. For additional updates on the development of RFID technology, RFID News (8) maintains current news about emerging standards, innovative applications, and general issues.

Leske, Cavin.

171

Understanding of nuclear quadrupole interactions of 35 Cl, 79 Br and 129 I and binding energies of solid halogens at first-principles level  

Microsoft Academic Search

This paper deals with the understanding at a first-principles level of the nuclear quadrupole interaction (NQI) parameters\\u000a of solid chlorine, bromine and iodine as well as the intermolecular binding of these molecules in the solid. The electronic\\u000a structure investigations that we have carried out to study these properties of the solid halogens are based on the Hartree–Fock\\u000a Cluster approach using

M. M. Aryal; D. R. Mishra; D. D. Paudyal; S. Byahut; N. B. Maharjan; N. P. Adhikari; R. H. Scheicher; Junho Jeong; S. R. Badu; R. H. Pink; Lee Chow; T. P. Das

2007-01-01

172

Towards VECSEL frequency combs  

NASA Astrophysics Data System (ADS)

Significant progress has been made over the last year towards generating frequency combs using VECSELs. Here, I will discuss recent progress made generating < 4kW peak power femtosecond pulse VECSELs, where we have achieved 3.3 W average power with 400 fs pulse duration at 1.7 GHz repetition rate. This has been achieved by exploiting the rapid power scaling progress made in the field of CW VECSELs [1]. The gain structure used here is grown and processed by the University of Marburg, and the window layer is etched for anti-resonance to increase the gain bandwidth and reduce the dispersion [2]. We have used this to generate supercontinuum, achieving 45 % throughput in a 2.2 micron core photonic crystal fiber when the VECSEL produced 1 W average output power. A continuum with a width of 175 nm is generated. At higher average powers heating of the fiber tip reduces coupling efficiency which limits the supercontinuum bandwidth and we will discuss measures to avoid this. Finally, I will outline approaches to further reduce the pulse length, whilst maintaining the average power, to a point where generating coherent octave spanning supercontinuum, suitable for F-2F stabilization should become a reality.

Wilcox, Keith G.

2013-02-01

173

High frequency ultrasound torturer.  

PubMed

The discernible aim of torture as everyone believes--and rightly so--is to destroy the personality of an individual in a way that would render his compliance in future. But to destroy a personality is easier said than done. It requires long sessions of detention and torture. The torturers risk themselves getting exposed. The Human Rights groups are active all around the world. Ultimately the personality may not be destroyed much to the chagrin of the torturers, and an unexpected resilient rebounding may take place. Therefore, with the repertoire of modern knowledge, the strategy may well change in the 21st century. Discreet methods may be employed to selectively destroy areas in brain by high dosage and high frequency ultrasound. It is completely a non-invasive technique that does not leave its fingerprint for painful, later denials of subornation. Nevertheless the personality will change--from rightful aggression to slavish submission. The aim of this article is to put forward the theoretical perspective and cofounded projection of the darker and menacing side of ultrasound technology so that future generation could be saved from sin of omission. PMID:20509473

Husain, Munawwar; Rizvi, Shameem Jahan; Usmani, Javed Ahmad

2009-12-01

174

Flood frequency in Alaska  

USGS Publications Warehouse

Records of peak discharge at 183 sites were used to study flood frequency in Alaska. The vast size of Alaska, its great ranges of physiography, and the lack of data for much of the State precluded a comprehensive analysis of all flood determinants. Peak stream discharges, where gaging-station records were available, were analyzed for 2-year, 5-year, 10-year, 25-year, and 50-year average-recurrence intervals. A regional analysis of the flood characteristics by multiple-regression methods gave a set of equations that can be used to estimate floods of selected recurrence intervals up to 50 years for any site on any stream in Alaska. The equations relate floods to drainage-basin characteristics. The study indicates that in Alaska the 50-year flood can be estimated from 10-year gaging- station records with a standard error of 22 percent whereas the 50-year flood can be estimated from the regression equation with a standard error of 53 percent. Also, maximum known floods at more than 500 gaging stations and miscellaneous sites in Alaska were related to drainage-area size. An envelope curve of 500 cubic feet per second per square mile covered all but 2 floods in the State.

Childers, J.M.

1970-01-01

175

Frequency-Shift Hearing Aid  

NASA Technical Reports Server (NTRS)

Proposed hearing aid maps spectrum of speech into band of lower frequencies at which ear remains sensitive. By redirecting normal speech frequencies into frequency band from 100 to 1,500 Hz, hearing aid allows people to understand normal conversation, including telephone calls. Principle operation of hearing aid adapted to other uses such as, clearing up noisy telephone or radio communication. In addition, loud-speakers more easily understood in presence of high background noise.

Weinstein, Leonard M.

1994-01-01

176

Effective switching frequency multiplier inverter  

DOEpatents

A switching frequency multiplier inverter for low inductance machines that uses parallel connection of switches and each switch is independently controlled according to a pulse width modulation scheme. The effective switching frequency is multiplied by the number of switches connected in parallel while each individual switch operates within its limit of switching frequency. This technique can also be used for other power converters such as DC/DC, AC/DC converters.

Su, Gui-Jia (Oak Ridge, TN); Peng, Fang Z. (Okemos, MI)

2007-08-07

177

Flood Frequency Analysis: International Edition  

NSDL National Science Digital Library

Flood frequency analysis uses historical flow records to both estimate the frequency with which floods of a certain magnitude may occur and predict the possible flood magnitude over a certain time period. This module offers a thorough introduction to appropriately constructing the necessary historical data series, calculating the flooding probabilities, and gauging the reliability of the resulting probability values. Methods for assessing flood frequency in basins with limited data are also discussed.

Comet

2010-08-31

178

Statistics of atomic frequency standards  

Microsoft Academic Search

Abstract-A theoretical development,is presented,which,results in a relationship,between,the,expectation,value,of the standard deviation,of the frequency,fluctuations,for any finite number,of data samples and the infinite time average value of the standard deviation, which,provides,an invariant,measure,of an important,quality factor of a frequency,standard. A practical and,straightforward,method,of determining,the power,spectral density of the frequency,fluctuations from the variance of the frequency fluctuations, the sampling time, the number of samples taken, and

W. Allan

1996-01-01

179

Fast frequency hopping PLL synthesizer  

NASA Astrophysics Data System (ADS)

An account is given of a fast frequency-hopping phase-locked loop (PLL) synthesizer for TDMA equipment which allows changes to the carrier frequency within the guard time of burst signals. The use of phase and frequency preset (PFP) PLL circuits allows the proposed synthesizer to achieve fast, stable frequency setting in intervals shorter than the burst signal duration. Experimental results indicate that PFP PLL circuit setting time is less than 500 microsec; the spurious level of the reference signal is less than -90 dBc.

Seki, Kazuhiko; Umehira, Masahiro

180

Research on the Automatic Frequency Modulation of Rubidium Frequency Standard  

Microsoft Academic Search

The present status of rubidium atom frequency standard is introduced. The temperature coefficient of traditional Rb clock was mainly made from pump system and variode phase modulation circuit. After filling absorb cell with buffer gas of positive temperature coefficient and adjusting pumping light intensity properly, the temperature coefficient from pump system may be extremely less than that of rubidium frequency

Yutai Wang; Feng Liu; Jie Sun

2007-01-01

181

Atomic frequency standards for ultra-high-frequency stability  

NASA Technical Reports Server (NTRS)

The general features of the Hg-199(+) trapped-ion frequency standard are outlined and compared to other atomic frequency standards, especially the hydrogen maser. The points discussed are those which make the trapped Hg-199(+) standard attractive: high line Q, reduced sensitivity to external magnetic fields, and simplicity of state selection, among others.

Maleki, L.; Prestage, J. D.; Dick, G. J.

1987-01-01

182

Stabilized radio-frequency quadrupole  

DOEpatents

A long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator.

Lancaster, H.D.; Fugitt, J.A.; Howard, D.R.

1982-09-29

183

Statistics of atomic frequency standards  

Microsoft Academic Search

A theoretical development is presented which results in a relationship between the expectation value of the standard deviation of the frequency fluctuations for any finite number of data samples and the infinite time average value of the standard deviation, which provides an invariant measure of an important quality factor of a frequency standard. A practical and straightforward method of determining

DAVID W. ALLAN

1966-01-01

184

Finite frequency negative imaginary systems  

Microsoft Academic Search

This paper is concerned with finite frequency negative imaginary (FFNI) systems. The paper introduces the concept of FFNI transfer function matrices, and the relationship between the FFNI property and the finite frequency positive real (FFPR) property of transfer function matrices is established. The paper also establishes an FFNI lemma which gives a necessary and sufficient condition on the matrices appearing

Junlin Xiong; Ian R. Petersen; Alexander Lanzon

2010-01-01

185

Constrained Load-frequency Control  

Microsoft Academic Search

Load-frequency control (LFC) is one of the major problems when dealing with the design and\\/or operation of electric power systems. Moreover, due to practical and physical considerations, bounds are often imposed on the level of control signals as well as the maximum frequency deviation. Control strategies that satisfy systems constraints, and, at the same time, guarantee optimal systems performance, are

M. F. Hassan; A. A. Abouelsoud; H. M. Soliman

2008-01-01

186

Blackbody Radiation: Frequency and Wavelength  

NSDL National Science Digital Library

The Blackbody Radiation: Frequency and Wavelength model simulates the blackbody radiation curves of Planck both as a function of frequency and as a function of wavelength to allow for comparison of the two functions. The Planck radiation law can be derived both as a function of frequency and as a function of wavelength. In doing so, one gets two slightly different expressions for the energy density per frequency (wavelength) as a function of frequency (wavelength. Shown in the main window is a schematic of a blackbody cavity showing (on the right) the color of the radiation emitted. The graph plots the energy density per frequency (wavelength) as a function of frequency (wavelength and shows the visible spectrum. One can switch between the two functions by using the radio buttons provided. A slider alows the twmperature to be set or changed. The Blackbody Radiation: Frequency and Wavelength model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_qm_blackbody_fw.jar file will run the program if Java is installed.

Palop, Jose I.

2010-12-12

187

IIigh Frequency Electronic Packaging Technology  

Microsoft Academic Search

Commercial and government communication, radar, and information systems face the challenge of cost and mass reduction via the application of advanced packaging technology. A majority of both government and industry support has been focused on low frequency digital electronics. However higher operating frequencies for both digital and analog circuits will be required for future systems. By 1997, the projected domestic

Martin IIermrnn; Lynn Lowry; Karen Lee; Elizribeth Kolawa; Ann Tulintseff; Kurt Shalkhauser; John Whitaker; Melinda Piket-May

188

Frequency Combs 250 Special Topics  

E-print Network

Frequency Combs 250 Special Topics Jennie Guzman 1 #12;Frequency Comb http://www.nist crystal 3 #12;Kerr Effect ·Index of refraction is proportional to intensity ·Kerr medium acts like a lens:sapphire laser Output Coupler Pump Ti: sapphire crystal 6 #12;Dispersion ·Spectral dispersion due to variation

Budker, Dmitry

189

Frequency diversity in multistatic radars  

Microsoft Academic Search

This paper presents the model and analysis of a frequency-diverse radar system. Multistatic radar systems provide an inherent spatial diversity by processing signals from different platforms which view a potential target from different aspect angles. By using different frequencies at each platform, an additional diversity gain can be obtained on top of the advantages of spatial diversity. Here, since platforms

Byung Wook Jung; R aviraj S. Adve; Joohwan Chun

2008-01-01

190

Gaming Frequency and Academic Performance  

ERIC Educational Resources Information Center

There are numerous claims that playing computer and video games may be educationally beneficial, but there has been little formal investigation into whether or not the frequency of exposure to such games actually affects academic performance. This paper explores the issue by analysing the relationships between gaming frequency--measured as the…

Ip, Barry; Jacobs, Gabriel; Watkins, Alan

2008-01-01

191

Laser Spectroscopy and Frequency Combs  

NASA Astrophysics Data System (ADS)

The spectrum of a frequency comb, commonly generated by a mode-locked femtosecond laser consists of several hundred thousand precisely evenly spaced spectral lines. Such laser frequency combs have revolutionized the art measuring the frequency of light, and they provide the long-missing clockwork for optical atomic clocks. The invention of the frequency comb technique has been motivated by precision laser spectroscopy of the simple hydrogen atom. The availability of commercial instruments is facilitating the evolution of new applications far beyond the original purpose. Laser combs are becoming powerful instruments for broadband molecular spectroscopy by dramatically improving the resolution and recording speed of Fourier spectrometers and by creating new opportunities for highly multiplexed nonlinear spectroscopy, such as two-photon spectroscopy or coherent Raman spectroscopy. Other emerging applications of frequency combs range from fundamental research in astronomy, chemistry, or attosecond science to telecommunications and satellite navigation.

Hänsch, Theodor W.; Picqué, Nathalie

2013-12-01

192

Proton dynamics in one-dimensional hydrogen-bonding system in molecular co-crystals TMP-D2ca and DMP-H2ca  

NASA Astrophysics Data System (ADS)

The proton dynamics in one-dimensional hydrogen-bonding system in molecular co-crystals of tetramethylpyrazine (TMP) with chloranilic acid (H2ca), as well as 2,6-dimethylpyrazine (DMP) with H2ca is studied by 35Cl NQR and 2H NMR spin-lattice relaxation measurements. No transfer motion of proton between the acid and base molecules is observed in DMP-H2ca, while the motion of the acid proton is excited in TMP-H2ca and the activation energy for the motion increases from 35 kJ mol - 1 to 50 kJ mol - 1 by the deuteration.

Asaji, T.; Amino, D.; Tago, N.; Mizuno, M.

2010-04-01

193

Medium-Frequency Pseudonoise Georadar  

NASA Technical Reports Server (NTRS)

Ground-probing radar systems featuring medium-frequency carrier signals phase-modulated by binary pseudonoise codes have been proposed. These systems would be used to locate and detect movements of subterranean surfaces; the primary intended application is in warning of the movement of underground water toward oil-well intake ports in time to shut down those ports to avoid pumping of water. Other potential applications include oil-well logging and monitoring of underground reservoirs. A typical prior georadar system operates at a carrier frequency of at least 50 MHz in order to provide useable range resolution. This frequency is too high for adequate penetration of many underground layers of interest. On the other hand, if the carrier frequency were to be reduced greatly to increase penetration, then bandwidth and thus range resolution would also have to be reduced, thereby rendering the system less useful. The proposed medium-frequency pseudonoise georadar systems would offer the advantage of greater penetration at lower carrier frequencies, but without the loss of resolution that would be incurred by operating typical prior georadar systems at lower frequencies.

Arendt, G. Dickey; Carl, J. R.; Byerly, Kent A.; Amini, B. Jon

2005-01-01

194

AUTO ID FUTURE - FREQUENCY AGNOSTIC  

E-print Network

Identification of information is one key to the development of intelligent decision systems of the future. Frequency agnostic automatic identification is only one step in the physical world to make physical objects identify ...

DATTA, SHOUMEN

195

Instantaneous Frequency Stock Market Model  

NSDL National Science Digital Library

The Instantaneous Frequency Stock Model estimates a stock's cyclical fluctuations over a three-day period to determine how fast the market is moving. The instantaneous frequency of an input signal is calculated by modeling an input function's most recent data points as a sin wave and performing a Fourier transform to derive the function's frequency. This model implements different velocity indicators on daily closing prices of a few common companies, and allows the user to compare values of the indicators at different times. The Instantaneous Frequency model was developed by Matt Mohorn using the Easy Java Simulations (EJS) modeling tool.  You can examine and modify the physical model for this simulation if you have Ejs installed by right-clicking within the plot and selecting "Open Ejs Model" from the pop-up menu. 

Mohorn, Matthew

2013-05-17

196

High Frequency Electronic Packaging Technology  

NASA Technical Reports Server (NTRS)

Commercial and government communication, radar, and information systems face the challenge of cost and mass reduction via the application of advanced packaging technology. A majority of both government and industry support has been focused on low frequency digital electronics.

Herman, M.; Lowry, L.; Lee, K.; Kolawa, E.; Tulintseff, A.; Shalkhauser, K.; Whitaker, J.; Piket-May, M.

1994-01-01

197

Frequency regulator for synchronous generators  

DOEpatents

The present invention is directed to a novel frequency regulator which controls a generator output frequency for variations in both the input power to the generator and the power supplied to an uncontrolled external load. The present invention further includes over current and current balance protection devices which are relatively inexpensive to manufacture, which may be encapsulated to provide protection from the operating environment and which respond more quickly than previously known electromechanical devices. 11 figs.

Karlicek, R.F.

1982-08-10

198

Prospects for atomic frequency standards  

NASA Technical Reports Server (NTRS)

The potentialities of different atomic frequency standards which are not yet into field operation, for most of them, but for which preliminary data, obtained in laboratory experiments, give confidence that they may improve greatly the present state of the art are described. The review will mainly cover the following devices: (1) cesium beam frequency standards with optical pumping and detection; (2) optically pumped rubidium cells; (3) magnesium beam; (4) cold hydrogen masers; and (5) traps with stored and cooled ions.

Audoin, C.

1984-01-01

199

Frequency regulator for synchronous generators  

DOEpatents

The present invention is directed to a novel frequency regulator which controls a generator output frequency for variations in both the input power to the generator and the power supplied to an uncontrolled external load. The present invention further includes over current and current balance protection devices which are relatively inexpensive to manufacture, which may be encapsulated to provide protection from the operating environment and which respond more quickly than previously known electromechanical devices.

Karlicek, Robert F. (1920 Camino Centroloma, Fullerton, CA 92633)

1982-01-01

200

ECRIS Operation With Multiple Frequencies  

NASA Astrophysics Data System (ADS)

The usefulness of two-frequency heating for the production of high-charge state high-intensity beams from an ECRIS has been well established. Factors of 2?5 increase in beam currents have been observed accompanied by a shift to higher charge states. The ECRIS at Argonne National Laboratory has been routinely operated utilizing a 14 GHz klystron and a tunable 11-13 GHz traveling wave tube amplifier (TWTA) and the operating characteristics of the source are well known. However, the characteristics of the multi-frequency heated plasma are less well known. Investigations regarding the changes in the source production have been taking place at Argonne National Laboratory. Parameters such as the charge state distribution (CSD), production times and plasma potential have been measured for a multi-frequency heated plasma with emphasis being given to the effect of the frequency gap between the two RF waves. It has been found that the production times decrease in multi-frequency mode with a corresponding increase in the CSD and the overall beam output. At the same time, the plasma potential appears to not change significantly. It has also been found that a larger frequency gap (14.0 and 10.84 GHz), while producing higher charge-state ions, produces less overall beam of the material of interest but reaches equilibrium more quickly when compared to a smaller gap (14,0 and 12.31 GHz). Possible mechanisms for the observed behavior will be discussed.

Vondrasek, R.; Scott, R.; Pardo, R.; Koivisto, H.; Tarvainen, O.; Suominen, P.; Edgell, D. H.

2005-03-01

201

Stepped frequency ground penetrating radar  

DOEpatents

A stepped frequency ground penetrating radar system is described comprising an RF signal generating section capable of producing stepped frequency signals in spaced and equal increments of time and frequency over a preselected bandwidth which serves as a common RF signal source for both a transmit portion and a receive portion of the system. In the transmit portion of the system the signal is processed into in-phase and quadrature signals which are then amplified and then transmitted toward a target. The reflected signals from the target are then received by a receive antenna and mixed with a reference signal from the common RF signal source in a mixer whose output is then fed through a low pass filter. The DC output, after amplification and demodulation, is digitized and converted into a frequency domain signal by a Fast Fourier Transform. A plot of the frequency domain signals from all of the stepped frequencies broadcast toward and received from the target yields information concerning the range (distance) and cross section (size) of the target.

Vadnais, Kenneth G. (Ojai, CA); Bashforth, Michael B. (Buellton, CA); Lewallen, Tricia S. (Ventura, CA); Nammath, Sharyn R. (Santa Barbara, CA)

1994-01-01

202

Frequency stability of a femtosecond optical parametric oscillator frequency comb.  

PubMed

Carrier-envelope-offset (CEO) and pulse-repetition frequencies of a Ti:sapphire-pumped femtosecond optical parametric oscillator were locked to uncertainties of 0.09 Hz and 0.16 mHz respectively, with the CEO beat signal linewidth being stabilized to 15 Hz (instrument limited). In-loop phase-noise power spectral density measurements showed a contribution of our servo electronics to the comb-line frequency uncertainty of up to 110 Hz. Complementary time-series data implied an in-loop comb instability of 2 x 10(-11) (1-s gate time), matching the Rb-stabilized reference used and verifying that dual servo-control of the CEO and repetition frequencies was effective in stabilizing the comb to at least this precision. PMID:22109442

Ferreiro, Teresa I; Sun, Jinghua; Reid, Derryck T

2011-11-21

203

Spatial frequencies and emotional perception.  

PubMed

It has been suggested that, during evolution, specific mechanisms developed in order to optimize the detection of threats and opportunities even in perceptually degraded conditions. A naturalistic example of perceptual degradation can be found in blurry images, which contain the coarsest elements of a scene (low spatial frequencies) but lack the fine-grained details (high spatial frequencies). In the past decade, several studies have examined the relation between spatial frequencies and emotions, using a variety of methods, stimuli, and rationales. Here, we conduct a literature survey on the studies that have examined the relation between emotion and spatial frequencies. Some studies have suggested that the low spatial frequencies of emotional stimuli may be processed by a subcortical neural pathway, eventually eliciting emotional responses. However, the evidence provided by the reviewed studies does not support this possibility, for conceptual and methodological reasons (e.g., mistaking the processing of a fuzzy stimulus for subcortical processing). Here, the conceptual and methodological problems present in the reviewed studies are analyzed and discussed, along with suggestions for future research. PMID:23183741

De Cesarei, Andrea; Codispoti, Maurizio

2013-01-01

204

47 CFR 87.449 - Frequencies.  

Code of Federal Regulations, 2013 CFR

...Frequencies. The following frequencies in the 72-76 MHz band are assignable to operational fixed stations using vertical polarization, if no harmful interference is caused to TV reception on Channels 4 and 5. These frequencies are shared with the...

2013-10-01

205

47 CFR 87.449 - Frequencies.  

Code of Federal Regulations, 2011 CFR

...Frequencies. The following frequencies in the 72-76 MHz band are assignable to operational fixed stations using vertical polarization, if no harmful interference is caused to TV reception on Channels 4 and 5. These frequencies are shared with the...

2011-10-01

206

47 CFR 87.449 - Frequencies.  

Code of Federal Regulations, 2010 CFR

...Frequencies. The following frequencies in the 72-76 MHz band are assignable to operational fixed stations using vertical polarization, if no harmful interference is caused to TV reception on Channels 4 and 5. These frequencies are shared with the...

2010-10-01

207

47 CFR 87.449 - Frequencies.  

Code of Federal Regulations, 2012 CFR

...Frequencies. The following frequencies in the 72-76 MHz band are assignable to operational fixed stations using vertical polarization, if no harmful interference is caused to TV reception on Channels 4 and 5. These frequencies are shared with the...

2012-10-01

208

47 CFR 24.235 - Frequency stability.  

Code of Federal Regulations, 2014 CFR

...2014-10-01 2014-10-01 false Frequency stability. 24.235 Section 24.235 Telecommunication...SERVICES Broadband PCS § 24.235 Frequency stability. The frequency stability shall be sufficient to ensure that the...

2014-10-01

209

47 CFR 22.863 - Frequency stability.  

Code of Federal Regulations, 2014 CFR

...2014-10-01 2014-10-01 false Frequency stability. 22.863 Section 22.863 Telecommunication...Air-Ground Systems § 22.863 Frequency stability. The frequency stability of equipment used under this subpart...

2014-10-01

210

47 CFR 24.135 - Frequency stability.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Frequency stability. 24.135 Section 24.135 Telecommunication...SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained...

2011-10-01

211

47 CFR 27.54 - Frequency stability.  

Code of Federal Regulations, 2014 CFR

...2014-10-01 2014-10-01 false Frequency stability. 27.54 Section 27.54 Telecommunication... Technical Standards § 27.54 Frequency stability. The frequency stability shall be sufficient to ensure that the...

2014-10-01

212

47 CFR 24.135 - Frequency stability.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Frequency stability. 24.135 Section 24.135 Telecommunication...SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained...

2012-10-01

213

47 CFR 24.235 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Frequency stability. 24.235 Section 24.235 Telecommunication...SERVICES Broadband PCS § 24.235 Frequency stability. The frequency stability shall be sufficient to ensure that the...

2013-10-01

214

47 CFR 24.135 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Frequency stability. 24.135 Section 24.135 Telecommunication...SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained...

2013-10-01

215

47 CFR 24.135 - Frequency stability.  

Code of Federal Regulations, 2014 CFR

...2014-10-01 2014-10-01 false Frequency stability. 24.135 Section 24.135 Telecommunication...SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained...

2014-10-01

216

47 CFR 24.135 - Frequency stability.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 2010-10-01 false Frequency stability. 24.135 Section 24.135 Telecommunication...SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained...

2010-10-01

217

Intermediate-Frequency-to-Video-Band Converter  

NASA Technical Reports Server (NTRS)

Analog and digital circuits combined to frequency-convert from intermediate frequencies directly to video-band frequencies to meet stringent requirements. IF-to-video-band converter operates on principle of signal-band cancellation in phase-quadrature circuits. Downconverts intermediate frequencies directly to video-band frequencies to near-zero frequency with good image-band rejection and low phase variation within passband.

Ham, N. C.; Chavez, V. M.; Chen, V. S.; Sato, T.

1986-01-01

218

Swept Frequency Laser Metrology System  

NASA Technical Reports Server (NTRS)

A swept frequency laser ranging system having sub-micron accuracy that employs multiple common-path heterodyne interferometers, one coupled to a calibrated delay-line for use as an absolute reference for the ranging system. An exemplary embodiment uses two laser heterodyne interferometers to create two laser beams at two different frequencies to measure distance and motions of target(s). Heterodyne fringes generated from reflections off a reference fiducial X(sub R) and measurement (or target) fiducial X(sub M) are reflected back and are then detected by photodiodes. The measured phase changes Delta phi(sub R) and Delta phi (sub m) resulting from the laser frequency swept gives target position. The reference delay-line is the only absolute reference needed in the metrology system and this provides an ultra-stable reference and simple/economical system.

Zhao, Feng (Inventor)

2010-01-01

219

Variable frequency microwave heating apparatus  

DOEpatents

A variable frequency microwave heating apparatus (10) designed to allow modulation of the frequency of the microwaves introduced into a multi-mode microwave cavity (34) for testing or other selected applications. The variable frequency microwave heating apparatus (10) includes a microwave signal generator (12) and a high-power microwave amplifier (20) or a high-power microwave oscillator (14). A power supply (22) is provided for operation of the high-power microwave oscillator (14) or microwave amplifier (20). A directional coupler (24) is provided for detecting the direction and amplitude of signals incident upon and reflected from the microwave cavity (34). A first power meter (30) is provided for measuring the power delivered to the microwave furnace (32). A second power meter (26) detects the magnitude of reflected power. Reflected power is dissipated in the reflected power load (28).

Bible, Don W. (Clinton, TN); Lauf, Robert J. (Oak Ridge, TN); Johnson, Arvid C. (Lake in the Hills, IL); Thigpen, Larry T. (Angier, NC)

1999-01-01

220

Variable frequency microprocessor clock generator  

SciTech Connect

A microprocessor-based system is described comprising: a digital central microprocessor provided with a clock input and having a rate of operation determined by the frequency of a clock signal input thereto; memory means operably coupled to the central microprocessor for storing programs respectively including a plurality of instructions and addressable by the central microprocessor; peripheral device operably connected to the central microprocessor, the first peripheral device being addressable by the central microprocessor for control thereby; a system clock generator for generating a digital reference clock signal having a reference frequency rate; and frequency rate reduction circuit means connected between the clock generator and the clock input of the central microprocessor for selectively dividing the reference clock signal to generate a microprocessor clock signal as an input to the central microprocessor for clocking the central microprocessor.

Branson, C.N.

1989-04-04

221

Frequency-chirped subwavelength nanoantennas.  

PubMed

Herein we propose, theoretically investigate, and numerically demonstrate the first use to our knowledge of frequency chirping to achieve broadband, efficient subwavelength vertical emission from a dielectric waveguide. We demonstrate this unique and effective approach in the telecom C band in a nanophotonic frequency-chirped dipole antenna. The structure utilizes a plasmonic antenna placed above an Si3N4 waveguide and a ground plane to enhance emission efficiency. Three-dimensional finite-difference time-domain simulations reveal up to 55% vertical emission efficiency, and a bandwidth of 500 nm is possible in a structure less than half a wavelength long. The design methodology and theoretical underpinnings of frequency-chirped nanophotonic antennas coupled to dielectric waveguides are presented. PMID:23202110

Yaacobi, Ami; Watts, Michael R

2012-12-01

222

Power enhanced frequency conversion system  

NASA Technical Reports Server (NTRS)

A frequency conversion system includes at least one source providing a first near-IR wavelength output including a gain medium for providing high power amplification, such as double clad fiber amplifier, a double clad fiber laser or a semiconductor tapered amplifier to enhance the power output level of the near-IR wavelength output. The NFM device may be a difference frequency mixing (DFM) device or an optical parametric oscillation (OPO) device. Pump powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Ra-man/Brillouin amplifier or oscillator between the high power source and the NFM device.

Sanders, Steven (Inventor); Lang, Robert J. (Inventor); Waarts, Robert G. (Inventor)

2001-01-01

223

Frequency Separation Locking and Synchronization for FDM Optical Sources Using Widely Frequency Tunable Laser Diodes  

Microsoft Academic Search

A laser diode (LD) frequency separation locking method (called the reference pulse method) is proposed. This method has advantageous features for frequency division multiplexing (FDM) networks from the viewpoint of frequency separation stability with a strict frequency separation standard, modulation format independence, controllability over a large number of LDs, and frequency synchronization capability. Frequency locking experiments, using four and ten

Naoki Shimosaka; Kazuhisa Kaede; Masahiko Fujiwara; Shuntaro Yamazaki; Shigeru Murata; Makoto Nishio

1990-01-01

224

Detecting body cavity bombs with nuclear quadrupole resonance  

NASA Astrophysics Data System (ADS)

Nuclear Quadrupole Resonance (NQR) is a technology with great potential for detecting hidden explosives. Past NQR research has studied the detection of land mines and bombs concealed within luggage and packages. This thesis focuses on an NQR application that has received less attention and little or no publicly available research: detecting body cavity bombs (BCBs). BCBs include explosives that have been ingested, inserted into orifices, or surgically implanted. BCBs present a threat to aviation and secure facilities. They are extremely difficult to detect with the technology currently employed at security checkpoints. To evaluate whether or not NQR can be used to detect BCBs, a computational model is developed to assess how the dielectric properties of biological tissue affect the radio frequency magnetic field employed in NQR (0.5-5MHz). The relative permittivity of some biological tissue is very high (over 1,000 at 1MHz), making it conceivable that there is a significant effect on the electromagnetic field. To study this effect, the low-frequency approximation known as the Darwin model is employed. First, the electromagnetic field of a coil is calculated in free space. Second, a dielectric object or set of objects is introduced, and the free-space electric field is modified to accommodate the dielectric object ensuring that the relevant boundary conditions are obeyed. Finally, the magnetic field associated with the corrected electric field is calculated. This corrected magnetic field is evaluated with an NQR simulation to estimate the impact of dielectric tissue on NQR measurements. The effect of dielectric tissue is shown to be small, thus obviating a potential barrier to BCB detection. The NQR model presented may assist those designing excitation and detection coils for NQR. Some general coil design considerations and strategies are discussed.

Collins, Michael London

225

Isomorphism and disorder in o-chlorohalobenzenes studied by NQR.  

PubMed

In this work we present experimental results that allow to characterize different solid modifications found in o-chlorohalobenzenes. Three disordered phases have been found in o-chlorobromobenzene. The stable phase at high temperature (phase I) is also obtained by quenching the sample at 77 K. Slow cooling allow to obtain the low temperature phase III which, on heating, transforms to phase II at 183 K and this, in turns, transforms to phase I at T~210 K. The disorder evidenced through the Nuclear Quadrupole Resonance spectra, is attributed to a random occupation of chlorine and bromine sites. In all phases there is evidence of molecular reorientations out of the benzene ring plane around the pseudo-symmetry axis between the atoms of Cl and Br. In o-chlorofluorobenzene two phases have been found depending on the cooling rate. One phase is disordered due to the random exchange of the occupation of Cl and F sites. In this case, there is also evidence of molecular reorientations out of the benzene ring plane, but in this case the reorientation is around the pseudo-symmetry axis that pass through the C-Cl bonds. Comparisons with the behavior of o-dichlorobenzene are also made. PMID:24440588

Pérez, Silvina C; Wolfenson, Alberto; Zuriaga, Mariano

2014-01-01

226

Sparse time-frequency representations  

PubMed Central

Auditory neurons preserve exquisite temporal information about sound features, but we do not know how the brain uses this information to process the rapidly changing sounds of the natural world. Simple arguments for effective use of temporal information led us to consider the reassignment class of time-frequency representations as a model of auditory processing. Reassigned time-frequency representations can track isolated simple signals with accuracy unlimited by the time-frequency uncertainty principle, but lack of a general theory has hampered their application to complex sounds. We describe the reassigned representations for white noise and show that even spectrally dense signals produce sparse reassignments: the representation collapses onto a thin set of lines arranged in a froth-like pattern. Preserving phase information allows reconstruction of the original signal. We define a notion of “consensus,” based on stability of reassignment to time-scale changes, which produces sharp spectral estimates for a wide class of complex mixed signals. As the only currently known class of time-frequency representations that is always “in focus” this methodology has general utility in signal analysis. It may also help explain the remarkable acuity of auditory perception. Many details of complex sounds that are virtually undetectable in standard sonograms are readily perceptible and visible in reassignment. PMID:16601097

Gardner, Timothy J.; Magnasco, Marcelo O.

2006-01-01

227

Frequency diversity and its applications  

Microsoft Academic Search

Adaptive shared resource methods may be the only available effective countermeasures to rain-induced attenuation in satellite communication systems above 20 GHz. Two of these methods, frequency diversity (FDV) and burst length control (BLC) are examined and compared by using a unified approach. The fundamental statistical relationships between unassisted and assisted conditions are derived, and optimum values are identified. It is

F. Carassa; G. Tartara; E. Matricciani

1988-01-01

228

Frequency agile optical parametric oscillator  

DOEpatents

The frequency agile OPO device converts a fixed wavelength pump laser beam to arbitrary wavelengths within a specified range with pulse to pulse agility, at a rate limited only by the repetition rate of the pump laser. Uses of this invention include Laser radar, LIDAR, active remote sensing of effluents/pollutants, environmental monitoring, antisensor lasers, and spectroscopy. 14 figs.

Velsko, S.P.

1998-11-24

229

Frequency agile optical parametric oscillator  

DOEpatents

The frequency agile OPO device converts a fixed wavelength pump laser beam to arbitrary wavelengths within a specified range with pulse to pulse agility, at a rate limited only by the repetition rate of the pump laser. Uses of this invention include Laser radar, LIDAR, active remote sensing of effluents/pollutants, environmental monitoring, antisensor lasers, and spectroscopy.

Velsko, Stephan P. (Livermore, CA)

1998-01-01

230

Original article Frequency and evolution  

E-print Network

Original article Frequency and evolution of Melampsora larici-populina Klebahn races in north Champenoux, France (Received 11 February 1991; accepted 7 September 1991) Summary — Race populations in M larici-populina were studied for 4 years (nearly 7 000 identifica- tions). Race E1 is ubiquitous

Boyer, Edmond

231

Frequency Allocation; The Radio Spectrum.  

ERIC Educational Resources Information Center

The Federal Communications Commission (FCC) assigns segments of the radio spectrum to categories of users, and specific frequencies within each segment to individual users. Since demand for channel space exceeds supply, the process is complex. The radio spectrum can be compared to a long ruler: the portion from 10-540 kiloHertz has been set aside…

Federal Communications Commission, Washington, DC.

232

NRL Low-Frequency Antenna Development  

E-print Network

using cross-polarized LF antenna design. #12;NRL Low Frequency Antenna Development Genuine TasmanianNRL Low-Frequency Antenna Development Brian Hicks W. Erickson, K. Stewart #12;NRL Low Frequency Antenna Development Our goal has been to research and develop wide- bandwidth low-frequency antennas

Ellingson, Steven W.

233

47 CFR 90.539 - Frequency stability.  

Code of Federal Regulations, 2012 CFR

... 2012-10-01 false Frequency stability. 90.539 Section 90.539 Telecommunication...793-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate...frequency bands must meet the frequency stability requirements in this section....

2012-10-01

234

47 CFR 90.539 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

... 2013-10-01 false Frequency stability. 90.539 Section 90.539 Telecommunication...788-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate...frequency bands must meet the frequency stability requirements in this section....

2013-10-01

235

47 CFR 90.539 - Frequency stability.  

Code of Federal Regulations, 2010 CFR

... 2010-10-01 false Frequency stability. 90.539 Section 90.539 Telecommunication...793-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate...frequency bands must meet the frequency stability requirements in this section....

2010-10-01

236

47 CFR 90.539 - Frequency stability.  

Code of Federal Regulations, 2011 CFR

... 2011-10-01 false Frequency stability. 90.539 Section 90.539 Telecommunication...793-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate...frequency bands must meet the frequency stability requirements in this section....

2011-10-01

237

47 CFR 80.1077 - Frequencies.  

Code of Federal Regulations, 2010 CFR

...one other 156-174 MHz frequency 9 GHz radar transponders 9200-9500 MHz. 1 Frequency 156.525 MHz can be...ships equipped with MF/HF equipment, there is a...5 kHz, and one other frequency. 3 Frequency...

2010-10-01

238

Radars. Volume 6 - Frequency agility and diversity  

Microsoft Academic Search

Radar frequency diversity techniques, which reduce measurement errors caused by target glint, amplitude modulation and multipath, are discussed. Attention is given to frequency diversity attained through use of two or more parallel transmitting and receiving channels, or through the sequential use of many frequencies. Topics of the papers include a sequential detection logic to improve signal detectability in frequency-agile search

D. K. Barton

1977-01-01

239

Lossless equalization of frequency combs.  

PubMed

Frequency combs obtained by sinusoidal phase modulation of narrowband cw lasers are widely used in the field of optical communications. However, the resulting spectral envelope of the comb is not flat. We propose a general and efficient approach to achieve flat frequency combs with tunable bandwidth. The idea is based on a two-step process. First, efficient generation of a train with a temporal flat-top-pulse profile is required. Second, we use large parabolic phase modulation in every train period to map the temporal intensity shape into the spectral domain. In this way the resulting spectral envelope is flat, and the size is tunable with the chirping rate. Two different schemes are proposed and verified through numerical simulations. PMID:18709099

Torres-Company, Víctor; Lancis, Jesús; Andrés, Pedro

2008-08-15

240

Frequency response of electrochemical cells  

NASA Technical Reports Server (NTRS)

The main objective was to examine the feasibility of using frequency response techniques (1) as a tool in destructive physical analysis of batteries, particularly for estimating electrode structural parameters such as specific area, porosity, and tortuosity and (2) as a non-destructive testing technique for obtaining information such as state of charge and acceptability for space flight. The phenomena that contribute to the frequency response of an electrode include: (1) double layer capacitance; (2) Faradaic reaction resistance; (3) mass transfer of Warburg impedance; and (4) ohmic solution resistance. Nickel cadmium cells were investigated in solutions of KOH. A significant amount of data was acquired. Quantitative data analysis, using the developed software, is planned for the future.

Thomas, Daniel L.

1990-01-01

241

Frequency response of electrochemical cells  

NASA Technical Reports Server (NTRS)

Impedance concepts can be applied to the analysis of battery electrodes, yielding information about the structure of the electrode and the processes occurring in the electrode. Structural parameters such as the specific area (surface area per gram of electrode) can be estimated. Electrode variables such as surface overpotential, ohmic losses, and diffusion limitations may be studied. Nickel and cadmium electrodes were studied by measuring the ac impedance as a function of frequency, and the specific areas that were determined were well within the range of specific areas determined from BET measurements. Impedance spectra were measured for the nickel and cadmium electrodes, and for a 20 A-hr NiCd battery as functions of the state of charge. More work is needed to determine the feasibility of using frequency response as a nondestructive testing technique for batteries.

Thomas, Daniel L.

1989-01-01

242

Natural frequency of regular basins  

NASA Astrophysics Data System (ADS)

Similar to the vibration of a guitar string or an elastic membrane, water waves in an enclosed basin undergo standing oscillatory waves, also known as seiches. The resonant (eigen) periods of seiches are determined by water depth and geometry of the basin. For regular basins, explicit formulas are available. Resonance occurs when the dominant frequency of external force matches the eigen frequency of the basin. In this paper, we implement the conservative finite volume scheme to 2D shallow water equation to simulate resonance in closed basins. Further, we would like to use this scheme and utilizing energy spectra of the recorded signal to extract resonant periods of arbitrary basins. But here we first test the procedure for getting resonant periods of a square closed basin. The numerical resonant periods that we obtain are comparable with those from analytical formulas.

Tjandra, Sugih S.; Pudjaprasetya, S. R.

2014-03-01

243

Radio frequency coaxial feedthrough device  

DOEpatents

A radio frequency coaxial vacuum feedthrough is provided which utilizes a cylindrical ceramic vacuum break formed of an alumina ceramic. The cylinder is coaxially disposed and brazed between tapered coaxial conductors to form a vacuum sealed connection between a pressurized upstream coaxial transmission line and a utilization device located within a vacuum container. The feedthrough provides 50 ohm matched impedance RF feedthrough up to about 500 MHz at power levels in the multimegawatt range.

Owens, Thomas L. (Kingston, TN); Baity, Frederick W. (Oak Ridge, TN); Hoffman, Daniel J. (Oak Ridge, TN); Whealton, John H. (Oak Ridge, TN)

1987-01-01

244

Low Frequency Radio Experiment (LORE)  

NASA Astrophysics Data System (ADS)

High temporal and frequency resolution observations of solar generated disturbances below 15 MHz in the near-Sun region and at Sun-Earth distances in conjunction with optical and high energy observations of Sun are essential to understand the structure and evolution of eruptions, such as, flares, coronal mass ejections (CMEs), and their associated solar wind disturbances at heights above the photosphere and their consequences in the interplanetary medium. This talk presents a case study of Low Frequency Radio Experiment (LORE) payload to probe the corona and the solar disturbances at solar offsets greater than 2 solar radii below 30 MHz. The LORE, although not part of Aditya-L1 mission, can be complimentary to planned Aditya-L1 coronagraph and its other on-board payloads as well as synergistic to ground based observations, which are routinely carried out by Ooty Radio Telescope. We discuss the baseline design and technical details of the proposed LORE and it is particularly suitable for providing data on the detailed time and frequency structure of fast drifting Type-III and slow drifting Type-II radio bursts with unprecedented time and frequency resolution as well as goniopolarimetry, made possible with better designed antennas and state-of-art electronics, employing FPGAs and an intelligent data management system. This would enable wide ranging studies such as studies of nonlinear plasma processes, CME in-situ radio emission, CME driven phenomena, interplanetary CME driven shocks, ICMEs driven by decelerating IP shocks and space weather effects of Solar Wind interaction regions. The talk will highlight the science objectives as well as the proposed technical design features.

Manoharan, Periasamy K.; Joshi, Bhal Chandra; Naidu, Arun Kumar

245

Hyperbolic times: frequency versus integrability  

Microsoft Academic Search

We consider dynamical systems on compact manifolds, which are local\\u000adiffeomorphisms outside an exceptional set (a compact submanifold). We are\\u000ainterested in analyzing the relation between the integrability (with respect to\\u000aLebesgue measure) of the first hyperbolic time map and the existence of\\u000apositive frequency of hyperbolic times. We show that some (strong)\\u000aintegrability of the first hyperbolic time map

Jose F Alves; VTOR ARAJO

2004-01-01

246

Superconducting Radio-Frequency Cavities  

NASA Astrophysics Data System (ADS)

Superconducting cavities have been operating routinely in a variety of accelerators with a range of demanding applications. With the success of completed projects, niobium cavities have become an enabling technology, offering upgrade paths for existing facilities and pushing frontier accelerators for nuclear physics, high-energy physics, materials science, and the life sciences. With continued progress in basic understanding of radio-frequency superconductivity, the performance of cavities has steadily improved to approach theoretical capabilities.

Padamsee, Hasan S.

2014-10-01

247

HELIOS dual swept frequency radiometer  

NASA Technical Reports Server (NTRS)

The HELIOS dual swept frequency radiometer, used in conjunction with a dipole antenna, was designed to measure electromagnetic radiation in space. An engineering prototype was fabricated and tested on the HELIOS spacecraft. Two prototypes and two flight units were fabricated and three of the four units were integrated into the HELIOS spacecraft. Two sets of ground support equipment were provided for checkout of the radiometer.

White, J. R.

1975-01-01

248

Oscillation frequencies of solar models  

SciTech Connect

Two solar models have been constructed, one with no diffusion of the atomic nuclei, and another including diffusive element separation. The opacity at the bottom of the convection zone was increased 15--20 percent (within its theoretical uncertainty) to obtain a few microhertz agreement with observed p-mode frequencies. Original helium mass fractions were 0.291 and 0.289 for the no-diffusion and diffusion models, respectively. The diffusion model evolved to a surface Y = 0.256 at the solar age, and the original Z value of 0.0200 decreased to 0.0179. Agreement of l = 0 and 2 p-mode frequency separations with those observed is good. The g-mode nonadiabatic solutions do not have equal period spacing until high radial order. The lowest order modes are more visible if they all have the same kinetic energy. High central temperatures, produce over 9 SNUs from the B and 1.5 SNUs from the Be reactions. Models with iron condensed-out below the convection zone, and with WIMPs cooling the central regions to reduce the SNUs, agree less well with p-mode frequency separations. 53 refs., 6 figs., 4 tabs.

Cox, A.N.; Guzik, J.A.; Kidman, R.B.

1988-01-01

249

Variable frequency microwave furnace system  

DOEpatents

A variable frequency microwave furnace system designed to allow modulation of the frequency of the microwaves introduced into a furnace cavity for testing or other selected applications. The variable frequency microwave furnace system includes a microwave signal generator or microwave voltage-controlled oscillator for generating a low-power microwave signal for input to the microwave furnace. A first amplifier may be provided to amplify the magnitude of the signal output from the microwave signal generator or the microwave voltage-controlled oscillator. A second amplifier is provided for processing the signal output by the first amplifier. The second amplifier outputs the microwave signal input to the furnace cavity. In the preferred embodiment, the second amplifier is a traveling-wave tube (TWT). A power supply is provided for operation of the second amplifier. A directional coupler is provided for detecting the direction of a signal and further directing the signal depending on the detected direction. A first power meter is provided for measuring the power delivered to the microwave furnace. A second power meter detects the magnitude of reflected power. Reflected power is dissipated in the reflected power load. 5 figs.

Bible, D.W.; Lauf, R.J.

1994-06-14

250

LOFAR, the low frequency array  

NASA Astrophysics Data System (ADS)

LOFAR, the Low Frequency Array, is a next-generation radio telescope designed by ASTRON, with antenna stations concentrated in the north of the Netherlands and currently spread into Germany, France, Sweden and the United Kingdom; plans for more LOFAR stations exist in several other countries. Utilizing a novel, phased-array design, LOFAR is optimized for the largely unexplored low frequency range between 30 and 240 MHz. Digital beam-forming techniques make the LOFAR system agile and allow for rapid re-pointing of the telescopes as well as the potential for multiple simultaneous observations. Processing (e.g. cross-correlation) takes place in the LOFAR BlueGene/P supercomputer, and associated post-processing facilities. With its dense core (inner few km) array and long (more than 1000 km) interferometric baselines, LOFAR reaches unparalleled sensitivity and resolution in the low frequency radio regime. The International LOFAR Telescope (ILT) is now issuing its first call for observing projects that will be peer reviewed and selected for observing starting in December. Part of the allocations will be made on the basis of a fully Open Skies policy; there are also reserved fractions assigned by national consortia in return for contributions from their country to the ILT. In this invited talk, the gradually expanding complement of operationally verified observing modes and capabilities are reviewed, and some of the exciting first astronomical results are presented.

Vermeulen, R. C.

2012-09-01

251

Variable frequency microwave furnace system  

DOEpatents

A variable frequency microwave furnace system (10) designed to allow modulation of the frequency of the microwaves introduced into a furnace cavity (34) for testing or other selected applications. The variable frequency microwave furnace system (10) includes a microwave signal generator (12) or microwave voltage-controlled oscillator (14) for generating a low-power microwave signal for input to the microwave furnace. A first amplifier (18) may be provided to amplify the magnitude of the signal output from the microwave signal generator (12) or the microwave voltage-controlled oscillator (14). A second amplifier (20) is provided for processing the signal output by the first amplifier (18). The second amplifier (20) outputs the microwave signal input to the furnace cavity (34). In the preferred embodiment, the second amplifier (20) is a traveling-wave tube (TWT). A power supply (22) is provided for operation of the second amplifier (20). A directional coupler (24) is provided for detecting the direction of a signal and further directing the signal depending on the detected direction. A first power meter (30) is provided for measuring the power delivered to the microwave furnace (32). A second power meter (26) detects the magnitude of reflected power. Reflected power is dissipated in the reflected power load (28).

Bible, Don W. (Clinton, TN); Lauf, Robert J. (Oak Ridge, TN)

1994-01-01

252

Optical beat-note frequency stabilization between two lasers using a radio frequency interferometer in the gigahertz frequency band  

NASA Astrophysics Data System (ADS)

A beat-note frequency stabilization system using a distributed-feedback laser and external cavity laser diode has become a very important technique for laser spectroscopy, where highly stabilized high-frequency beat notes are required. We have developed a simple and versatile system capable of stabilizing the high-frequency beat notes (3 to 11 GHz) of two lasers using a delayed radio frequency self-heterodyne interferometer and have confirmed its basic operation. The frequency stability of the obtained beat notes is higher than 1 MHz in the 3- to 11-GHz frequency range with an average time of 20 s.

Uehara, Tomoyuki; Tsuji, Kenichiro; Hagiwara, Kohei; Onodera, Noriaki

2014-12-01

253

Nuclear quadrupole resonance of Cl 35 , Br 79 , Br 81 , and I 127 of halogen-containing organomercury compounds  

Microsoft Academic Search

1.The NQR spectra of halogens in a number of organomercury compounds of the RHgHal and p-ClC6 H4HgX types were investigated.2.In crystals of the compounds studied, coordination interactions arise between the mercury atoms and the halogens. However, when the type of coordination is preserved within a narrow series of compounds, the changes in the NQR frequencies may be determined by the

A. N. Nesmeyanov; O. Yu. Okhlobystin; E. V. Bryukhova; V. I. Bregadze; D. N. Kravtsov; B. A. Faingor; L. S. Golovchenko; G. K. Semin

1969-01-01

254

Optical Frequency Synthesis with Ultrashort Pulses  

NASA Astrophysics Data System (ADS)

Femtosecond laser frequency comb techniques are vastly simplifying the art of measuring the frequency of light. A single mode-locked femtosecond laser is now sufficient to synthesize hundreds of thousands of evenly spaced spectral lines, spanning much of the visible and near infrared region. The mode frequencies are absolutely known in terms of the pulse repetition rate and the carrier-envelope phase slippage rate, which are both accessible to radio frequency counters. Such a universal optical frequency comb synthesizer can serve as a clockwork in atomic clocks, based on atoms, ions or molecules oscillating at optical frequencies.

Udem, Th.; Holzwarth, R.; Zimmermann, M.; Hänsch, T. W.

2002-04-01

255

Precision Optical Frequency Metrology Using Pulsed Lasers  

NASA Astrophysics Data System (ADS)

Femtosecond laser frequency comb techniques are vastly simplifying the art of measuring the frequency of light. A single mode-locked femtosecond laser is now sufficient to synthesize hundreds of thousands of evenly spaced spectral lines, spanning much of the visible and near infrared region. The mode frequencies are absolutely known in terms of the pulse repetition rate and the carrier-envelope phase slippage rate, which are both accessible to radio frequency counters. Such a universal optical frequency comb synthesizer can serve as a clockwork in atomic clocks, based on atoms, ions or molecules oscillating at optical frequencies.

Udem, Th.; Holzwarth, R.; Zimmermann, M.; Hänsch, T. W.

2002-10-01

256

Frequency dependence and frequency control of microbubble streaming flows  

NASA Astrophysics Data System (ADS)

Steady streaming from oscillating microbubbles is a powerful actuating mechanism in microfluidics, enjoying increased use due to its simplicity of manufacture, ease of integration, low heat generation, and unprecedented control over the flow field and particle transport. As the streaming flow patterns are caused by oscillations of microbubbles in contact with walls of the set-up, an understanding of the bubble dynamics is crucial. Here we experimentally characterize the oscillation modes and the frequency response spectrum of such cylindrical bubbles, driven by a pressure variation resulting from ultrasound in the range of 1 kHz raisebox {-.9ex{stackrel{textstyle <}{˜ }} }f raisebox {-.9ex{stackrel{textstyle <}{˜ }} } 100 kHz. We find that (i) the appearance of 2D streaming flow patterns is governed by the relative amplitudes of bubble azimuthal surface modes (normalized by the volume response), (ii) distinct, robust resonance patterns occur independent of details of the set-up, and (iii) the position and width of the resonance peaks can be understood using an asymptotic theory approach. This theory describes, for the first time, the shape oscillations of a pinned cylindrical bubble at a wall and gives insight into necessary mode couplings that shape the response spectrum. Having thus correlated relative mode strengths and observed flow patterns, we demonstrate that the performance of a bubble micromixer can be optimized by making use of such flow variations when modulating the driving frequency.

Wang, Cheng; Rallabandi, Bhargav; Hilgenfeldt, Sascha

2013-02-01

257

Low Radio Frequency Picosatellite Missions  

NASA Astrophysics Data System (ADS)

The dramatic advances in cubesat and other picosatellite capabilities are opening the door for scientifically important observations at low radio frequencies. Because simple antennas are effective at low frequencies, and receiver technology allows low mass and low power instruments, these observations are an ideal match for very small spacecraft. A workshop on cubesat missions for low frequency radio astronomy was held at the Kiss Institute for Space Sciences, Caltech, to explore mission concepts involving one up to hundreds of picosatellites. One result from this workshop was that there are opportunities for viable missions throughout this large range. For example, the sky-integrated spectral signature of highly redshifted neutral hydrogen from the dark ages and cosmic dawn epochs can be measured by a single antenna on a single spacecraft. There are challenging issues of calibration, foreground removal, and RF interference that need to be solved, but the basic concept is appealingly simple. At the other extreme, imaging of angular structure in the high-redshift hydrogen signal will require an interferometer array with a very large number of antennas. In this case the primary requirement is a sufficiently low individual spacecraft mass that hundreds can be launched affordably. The technical challenges for large arrays are long-term relative station keeping and high downlink data rates. Missions using several to a few tens of picosatellites can image and track bright sources such as solar and planetary radio bursts, and will provide essential validation of technologies needed for much larger arrays.This work has been carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Jones, Dayton L.

2014-06-01

258

A low power prescaler, phase frequency detector, and charge pump for a 12 ghz frequency synthesizer  

E-print Network

A low power implementation of a CMOS frequency synthesizer at 12 GHz is an important step to improve the efficiency of a wireless transceiver in this frequency band. Since synthesizers are often employed as reference frequency sources such as local...

Eschenko, Evan Lee

2009-05-15

259

47 CFR 5.85 - Frequencies and policy governing frequency assignment.  

Code of Federal Regulations, 2013 CFR

...experimental stations may not use any frequency or frequency band exclusively allocated to the passive services (including the radio astronomy service). Stations authorized under subparts E and F are subject to additional restrictions. (b) Frequency or...

2013-10-01

260

47 CFR 5.85 - Frequencies and policy governing frequency assignment.  

Code of Federal Regulations, 2014 CFR

...experimental stations may not use any frequency or frequency band exclusively allocated to the passive services (including the radio astronomy service). Stations authorized under subparts E and F are subject to additional restrictions. (b) Frequency or...

2014-10-01

261

Planet frequency from microlensing observations  

NASA Astrophysics Data System (ADS)

Galactic gravitational microlensing is a very efficient technique to detect brown dwarfs and extrasolar planets at large orbital distances from their stars, and down to Earth-mass planets. More than 50 planets have been discovered so far, with 31 already published. Recent statistical results on the frequency of exoplanets based on several years of microlensing observations find that planets should be the rule rather than the exception, and confirm that super-Earth are much more frequent that giant planets in the Galaxy.

Cassan, A.; Ranc, C.

2014-12-01

262

TUTORIAL: Frequency metrology and clocks  

NASA Astrophysics Data System (ADS)

Transitions between discrete energy levels in well-isolated atomic systems are highly reproducible and therefore make ideal references for highly accurate frequency standards or clocks. In particular, a single laser-cooled ion confined in a radiofrequency ion trap closely approximates the spectroscopic ideal of a particle at rest in a perturbation-free environment. Narrow optical transitions in such systems are therefore very promising for the realization of optical clocks with accuracy around 2 orders of magnitude higher than current microwave primary standards. In this paper the fundamental aspects, current performance and applications of trapped ion optical clocks are reviewed and the potential for future improvements is considered.

Margolis, H. S.

2009-08-01

263

Multiple frequency printed slot and dipole antennas  

E-print Network

Multiple frequency antennas are becoming more and more important as the technology advances. Printed circuit antennas can be designed to achieve multiple frequency operation. The advantages like low cost, conformal and planar, and a possible...

Kolsrud, Arild

2012-06-07

264

47 CFR 101.505 - Frequencies.  

Code of Federal Regulations, 2010 CFR

...101.505 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES 24 GHz Service and Digital Electronic Message Service § 101.505 Frequencies. Frequencies, and...

2010-10-01

265

Substructure coupling in the frequency domain  

NASA Technical Reports Server (NTRS)

Frequency domain analysis was found to be a suitable method for determining the transient response of systems subjected to a wide variety of loads. However, since a large number of calculations are performed within the discrete frequency loop, the method loses it computational efficiency if the loads must be represented by a large number of discrete frequencies. It was also discovered that substructure coupling in the frequency domain work particularly well for analyzing structural system with a small number of interface and loaded degrees of freedom. It was discovered that substructure coupling in the frequency domain can lead to an efficient method of obtaining natural frequencies of undamped structures. It was also found that the damped natural frequencies of a system may be determined using frequency domain techniques.

1985-01-01

266

High frequency testing of rubber mounts.  

PubMed

Rubber and fluid-filled rubber engine mounts are commonly used in automotive and aerospace applications to provide reduced cabin noise and vibration, and/or motion accommodations. In certain applications, the rubber mount may operate at frequencies as high as 5000 Hz. Therefore, dynamic stiffness of the mount needs to be known in this frequency range. Commercial high frequency test machines are practically nonexistent, and the best high frequency test machine on the market is only capable of frequencies as high as 1000 Hz. In this paper, a high frequency test machine is described that allows test engineers to study the high frequency performance of rubber mounts at frequencies up to 5000 Hz. PMID:12071247

Vahdati, Nader; Saunders, L Ken Lauderbaugh

2002-04-01

267

Environmental Tests Of Cesium Frequency Standards  

NASA Technical Reports Server (NTRS)

Report describes environmental tests of cesium-beam frequency standards of United States Naval Observatory. Purpose of tests to determine effects of atmospheric temperature, relative humidity, and pressure on frequencies.

Sydnor, Richard L.; Tucker, Thomas K.; Greenhall, Charles A.; Diener, William A.; Maleki, Lutfollah

1992-01-01

268

Low frequency AC waveform generator  

DOEpatents

Low frequency sine, cosine, triangle and square waves are synthesized in circuitry which allows variation in the waveform amplitude and frequency while exhibiting good stability and without requiring significant stabilization time. A triangle waveform is formed by a ramped integration process controlled by a saturation amplifier circuit which produces the necessary hysteresis for the triangle waveform. The output of the saturation circuit is tapped to produce the square waveform. The sine waveform is synthesized by taking the absolute value of the triangular waveform, raising this absolute value to a predetermined power, multiplying the raised absolute value of the triangle wave with the triangle wave itself and properly scaling the resultant waveform and subtracting it from the triangular waveform itself. The cosine is synthesized by squaring the triangular waveform, raising the triangular waveform to a predetermined power and adding the squared waveform raised to the predetermined power with a DC reference and subtracting the squared waveform therefrom, with all waveforms properly scaled. The resultant waveform is then multiplied with a square wave in order to correct the polarity and produce the resultant cosine waveform.

Bilharz, Oscar W. (Scotia, NY)

1986-01-01

269

Low frequency ac waveform generator  

DOEpatents

Low frequency sine, cosine, triangle and square waves are synthesized in circuitry which allows variation in the waveform amplitude and frequency while exhibiting good stability and without requiring significant stablization time. A triangle waveform is formed by a ramped integration process controlled by a saturation amplifier circuit which produces the necessary hysteresis for the triangle waveform. The output of the saturation circuit is tapped to produce the square waveform. The sine waveform is synthesized by taking the absolute value of the triangular waveform, raising this absolute value to a predetermined power, multiplying the raised absolute value of the triangle wave with the triangle wave itself and properly scaling the resultant waveform and subtracting it from the triangular waveform to a predetermined power and adding the squared waveform raised to the predetermined power with a DC reference and subtracting the squared waveform therefrom, with all waveforms properly scaled. The resultant waveform is then multiplied with a square wave in order to correct the polarity and produce the resultant cosine waveform.

Bilharz, O.W.

1983-11-22

270

Neural analysis of sound frequency in insects  

E-print Network

Neural analysis of sound frequency in insects Gerald S. Pollack* and Kazuo Imaizumi Summary Insects appropriately. One parameter of sound that carries information is its frequency content. Insects analyze sound and prey. We review how frequency is analyzed in the insect nervous system, focusing on two taxa in which

Pollack, Gerald

271

47 CFR 5.403 - Frequencies.  

Code of Federal Regulations, 2013 CFR

...including those above 38.6 GHz, except for frequency bands exclusively allocated to the passive services (including the radio astronomy service). In addition, licensees may not use any frequency or frequency band below 38.6 GHz that is listed in §...

2013-10-01

272

47 CFR 5.403 - Frequencies.  

Code of Federal Regulations, 2014 CFR

...including those above 38.6 GHz, except for frequency bands exclusively allocated to the passive services (including the radio astronomy service). In addition, licensees may not use any frequency or frequency band below 38.6 GHz that is listed in §...

2014-10-01

273

Heterodyne laser instantaneous frequency measurement system  

DOEpatents

A heterodyne laser instantaneous frequency measurement system is disclosed. The system utilizes heterodyning of a pulsed laser beam with a continuous wave laser beam to form a beat signal. The beat signal is processed by a controller or computer which determines both the average frequency of the laser pulse and any changes or chirp of th frequency during the pulse.

Wyeth, Richard W. (Livermore, CA); Johnson, Michael A. (Pleasanton, CA); Globig, Michael A. (Livermore, CA)

1989-01-01

274

Heterodyne laser instantaneous frequency measurement system  

DOEpatents

A heterodyne laser instantaneous frequency measurement system is disclosed. The system utilizes heterodyning of a pulsed laser beam with a continuous wave laser beam to form a beat signal. The beat signal is processed by a controller or computer which determines both the average frequency of the laser pulse and any changes or chirp of the frequency during the pulse.

Wyeth, Richard W. (Livermore, CA); Johnson, Michael A. (Pleasanton, CA); Globig, Michael A. (Livermore, CA)

1990-01-01

275

Self-organizing photorefractive frequency demultiplexer  

Microsoft Academic Search

We demonstrate a self-organizing photorefractive circuit that demultiplexes a beam that has two signals im- posed on separate optical carrier frequencies into two beams, each containing one of the signals on its carrier. Unlike conventional demultiplexing techniques, this method requires little a priori knowledge about the carrier frequencies. The signal channels must be spatially uncorrelated, and their frequency separation must

Mark Saffman; Claus Benkert; Dana Z. Anderson

1991-01-01

276

High frequency-heated air turbojet  

NASA Technical Reports Server (NTRS)

A description is given of a method to heat air coming from a turbojet compressor to a temperature necessary to produce required expansion without requiring fuel. This is done by high frequency heating, which heats the walls corresponding to the combustion chamber in existing jets, by mounting high frequency coils in them. The current transformer and high frequency generator to be used are discussed.

Miron, J. H. D.

1986-01-01

277

Least-Squares Frequency-Acquisition Algorithm  

NASA Technical Reports Server (NTRS)

Algorithm finds frequency and phase of sinudoidal signal in presence of noise. Algorithm is special case of more-general, adaptive-paramenter-estimation techniques. Computational requirements of algorithm comparable to corresponding fast-Fourier-transform (FFT) algorithm. Algorithm works directly in time domain, whereas FFT algorithm transforms data into frequency domain for estimation and detection and requires secondary algorithm to interpolate between frequencies.

Kumar, Rajendra

1988-01-01

278

47 CFR 101.507 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Frequency stability. 101.507 Section 101.507 Telecommunication...Electronic Message Service § 101.507 Frequency stability. The frequency stability in the 10,550-10,680 MHz band must...

2013-10-01

279

47 CFR 101.507 - Frequency stability.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Frequency stability. 101.507 Section 101.507 Telecommunication...Electronic Message Service § 101.507 Frequency stability. The frequency stability in the 10,550-10,680 MHz band must...

2012-10-01

280

47 CFR 101.507 - Frequency stability.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 2010-10-01 false Frequency stability. 101.507 Section 101.507 Telecommunication...Electronic Message Service § 101.507 Frequency stability. The frequency stability in the 10,550-10,680 MHz band must...

2010-10-01

281

47 CFR 101.507 - Frequency stability.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Frequency stability. 101.507 Section 101.507 Telecommunication...Electronic Message Service § 101.507 Frequency stability. The frequency stability in the 10,550-10,680 MHz band must...

2011-10-01

282

Frequency domain least-mean-square algorithm  

Microsoft Academic Search

Frequency domain adaptive filtering can be performed by Fourier transforming the input-signal vector and weighting the contents of each frequency bin. By reducing the eigenvalue spread of the data autocorrelation matrix, frequency domain filtering promises great improvements in convergence rate over the conventional time-domain adaptive filtering.

S. S. Narayan; A. M. Peterson

1981-01-01

283

Low Frequency Rada Sounding Through Martian Ionosphere  

NASA Technical Reports Server (NTRS)

In remote radar sounding, it is highly desirable to operate at low frequencies to improve depth of penetration. For spaceborne sounders, the lowest operating frequency is limited by the effect of the ionosphere due to significant dispersion of the radar waves at near plasma frequency.

Safaeinili, A.; Jordan, R.

2000-01-01

284

Judging the Frequency of English Words  

ERIC Educational Resources Information Center

Given the lack of empirical corpus-based frequency counts in many languages, it would be useful and of theoretical interest if judgements of relative frequency of words in a language by proficient speakers of that language could substitute objective frequency counts for the purposes of devising language teaching materials, tests, and research…

Alderson, J. Charles

2007-01-01

285

47 CFR 95.655 - Frequency capability.  

Code of Federal Regulations, 2011 CFR

... 2011-10-01 false Frequency capability. 95.655 Section 95.655 Telecommunication...Requirements § 95.655 Frequency capability. (a) No transmitter will be certificated...service if it is equipped with a frequency capability not listed in § 95.625, and...

2011-10-01

286

47 CFR 95.655 - Frequency capability.  

Code of Federal Regulations, 2010 CFR

... 2010-10-01 false Frequency capability. 95.655 Section 95.655 Telecommunication...Requirements § 95.655 Frequency capability. (a) No transmitter will be certificated...service if it is equipped with a frequency capability not listed in § 95.625, and...

2010-10-01

287

High Frequency Dynamic Nuclear Polarization  

PubMed Central

Conspectus During the three decades 1980–2010, magic angle spinning (MAS) NMR developed into the method of choice to examine many chemical, physical and biological problems. In particular, a variety of dipolar recoupling methods to measure distances and torsion angles can now constrain molecular structures to high resolution. However, applications are often limited by the low sensitivity of the experiments, due in large part to the necessity of observing spectra of low-? nuclei such as the I = ½ species 13C or 15N. The difficulty is still greater when quadrupolar nuclei, like 17O or 27Al, are involved. This problem has stimulated efforts to increase the sensitivity of MAS experiments. A particularly powerful approach is dynamic nuclear polarization (DNP) which takes advantage of the higher equilibrium polarization of electrons (which conventionally manifests in the great sensitivity advantage of EPR over NMR). In DNP, the sample is doped with a stable paramagnetic polarizing agent and irradiated with microwaves to transfer the high polarization in the electron spin reservoir to the nuclei of interest. The idea was first explored by Overhauser and Slichter in 1953. However, these experiments were carried out on static samples, at magnetic fields that are low by current standards. To be implemented in contemporary MAS NMR experiments, DNP requires microwave sources operating in the subterahertz regime — roughly 150–660 GHz — and cryogenic MAS probes. In addition, improvements were required in the polarizing agents, because the high concentrations of conventional radicals that are required to produce significant enhancements compromise spectral resolution. In the last two decades scientific and technical advances have addressed these problems and brought DNP to the point where it is achieving wide applicability. These advances include the development of high frequency gyrotron microwave sources operating in the subterahertz frequency range. In addition, low temperature MAS probes were developed that permit in-situ microwave irradiation of the samples. And, finally, biradical polarizing agents were developed that increased the efficiency of DNP experiments by factors of ~4 at considerably lower paramagnet concentrations. Collectively these developments have made it possible to apply DNP on a routine basis to a number of different scientific endeavors, most prominently in the biological and material sciences. This Account reviews these developments, including the primary mechanisms used to transfer polarization in high frequency DNP, and the current choice of microwave sources and biradical polarizing agents. In addition, we illustrate the utility of the technique with a description of applications to membrane and amyloid proteins that emphasizes the unique structural information that is available in these two cases. PMID:23597038

Ni, Qing Zhe; Daviso, Eugenio; Can, Thach V.; Markhasin, Evgeny; Jawla, Sudheer K.; Swager, Timothy M.; Temkin, Richard J.; Herzfeld, Judith; Griffin, Robert G.

2013-01-01

288

Temperature and baric dependence of nuclear quadruple resonance spectra in indium and gallium monoselenides  

NASA Astrophysics Data System (ADS)

Pulsed radiospectroscopy method has been used to study nuclear quadruple resonance (NQR) spectra of 69Ga and 115In isotopes in the layered semiconductors GaSe and InSe. It has been found that in GaSe and InSe there is a considerable temperature dependence of NQR frequency which in the temperature range of 250 to 390 K is practically linear with conversion slope 1.54 kHz/degree for 69Ga and 2.35 kHz/degree for 115In. In the same crystals the effect of uniaxial pressure on NQR spectra applied along the optical axis ? up to the values of 500 kg/?m2 has been studied. A strong attenuation of NQR spectra intensity with increase in pressure on layered crystal package has been established. The unvaried multiplicity of resonance spectra indicates the absence of structural transformations in these layered crystals over the investigated range of temperatures and pressures.

Khandozhko, Victor; Raranskii, Nikolai; Balazjuk, Vitaly; Samila, Andriy; Kovalyuk, Zahar

2013-12-01

289

Frequency domain laser velocimeter signal processor  

NASA Technical Reports Server (NTRS)

A laser velocimeter frequency domain signal processor is described which utilizes smart instrumentation to configure itself to maximize measurement accuracy based on the determined characteristics of the input signals. The stystem provides the same measurement capabilities as the high-speed burst counter in instantaneous measurements of signal frequency, the same automatic gain control and automatic frequency control as the frequency tracker, and the same immunity to signal-to-noise derived errors as the photon correlator. Simulation results demonstrate measurement accuracies of better than 0.2 percent for signal frequencies up to 100 MHz.

Meyers, J. F.; Stoughton, J. W.

1986-01-01

290

Multiple frequency method for operating electrochemical sensors  

DOEpatents

A multiple frequency method for the operation of a sensor to measure a parameter of interest using calibration information including the steps of exciting the sensor at a first frequency providing a first sensor response, exciting the sensor at a second frequency providing a second sensor response, using the second sensor response at the second frequency and the calibration information to produce a calculated concentration of the interfering parameters, using the first sensor response at the first frequency, the calculated concentration of the interfering parameters, and the calibration information to measure the parameter of interest.

Martin, Louis P. (San Ramon, CA)

2012-05-15

291

Preferred frequencies for three unconsolidated earth materials  

SciTech Connect

Exploring near-surface mechanical wave propagation through cohesive and noncohesive soils is important for detecting buried objects (i.e., landmines and unexploded ordnance). Here, we determine that certain preferred frequencies travel through specific soils more efficiently. A controlled-frequency acoustic seismic source was developed to modulate the applied frequency and amplitude. Surface response due to continuous waves traveling through soils was recorded both instantaneously and after a finite load time. Preferred frequencies for sand, clay loam, and silt loam were measured to be 300-330, 100-140, and 140-260 Hz, respectively. Observed frequency shifts were dependent upon applied amplitude and load time.

Gilcrist, Laura E.; Baker, Gregory S.; Sen, Surajit [Department of Geology, State University of New York at Buffalo, Buffalo, New York 14260 (United States); Department of Earth and Planetary Science, University of Tennessee, Knoxville, Tennessee 37996 (United States); Department of Physics, State University of New York at Buffalo, Buffalo, New York 14260 (United States)

2007-12-17

292

A radio frequency coaxial feedthrough  

DOEpatents

An improved radio frequency coaxial transmission line vacuum feedthrough is provided based on the use of a half-wavelength annular dielectric pressure barrier disk, or multiple disks comprising an effective half wavelength structure to eliminate reflection from the barrier surfaces. Gas-tight seals are formed about the outer and inner diameter surfaces of the barrier disk using a sealing technique which generates radial forces sufficient to form seals by forcing the conductor walls against the surfaces of the barrier disks in a manner which does not deform the radii of the inner and outer conductors, thereby preventing enhancement of the electric field at the barrier faces which limits the voltage and power handling capabilities of a feedthrough.

Owens, T.L.

1987-12-07

293

Magnetic nanocomposites at microwave frequencies  

E-print Network

Most conventional magnetic materials used in the electronic devices are ferrites, which are composed of micrometer-size grains. But ferrites have small saturation magnetization, therefore the performance at GHz frequencies is rather poor. That is why functionalized nanocomposites comprising magnetic nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm, and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have a significant potential for the electronics industry. When the size of the nanoparticles is smaller than the critical size for multidomain formation, these nanocomposites can be regarded as an ensemble of particles in single-domain states and the losses (due for example to eddy currents) are expected to be relatively small. Here we review the theory of magnetism in such materials, and we present a novel measurement method used for the characterization of the electromagnetic properties of composites with nanomagnetic insertions. We also present a few experimenta...

Timonen, J V I; Ikkala, O; Oksanen, M; Seppala, E; Chalapat, K; Li, J; Paraoanu, G S; 10.1007/978-3-642-12070-1\\_11

2011-01-01

294

Frequency domain optical parametric amplification  

PubMed Central

Today’s ultrafast lasers operate at the physical limits of optical materials to reach extreme performances. Amplification of single-cycle laser pulses with their corresponding octave-spanning spectra still remains a formidable challenge since the universal dilemma of gain narrowing sets limits for both real level pumped amplifiers as well as parametric amplifiers. We demonstrate that employing parametric amplification in the frequency domain rather than in time domain opens up new design opportunities for ultrafast laser science, with the potential to generate single-cycle multi-terawatt pulses. Fundamental restrictions arising from phase mismatch and damage threshold of nonlinear laser crystals are not only circumvented but also exploited to produce a synergy between increased seed spectrum and increased pump energy. This concept was successfully demonstrated by generating carrier envelope phase stable, 1.43?mJ two-cycle pulses at 1.8??m wavelength. PMID:24805968

Schmidt, Bruno E.; Thiré, Nicolas; Boivin, Maxime; Laramée, Antoine; Poitras, François; Lebrun, Guy; Ozaki, Tsuneyuki; Ibrahim, Heide; Légaré, François

2014-01-01

295

Lightweight, high-frequency transformers  

NASA Technical Reports Server (NTRS)

The 25-kVA space transformer was developed under contract by Thermal Technology Laboratory, Buffalo, N. Y. The NASA Lewis transformer technology program attempted to develop the baseline technology. For the 25-kVA transformer the input voltage was chosen as 200 V, the output voltage as 1500 V, the input voltage waveform as square wave, the duty cycle as continuous, the frequency range (within certain constraints) as 10 to 40 kHz, the operating temperatures as 85 deg. and 130 C, the baseplate temperature as 50 C, the equivalent leakage inductance as less than 10 micro-h, the operating environment as space, and the life expectancy as 10 years. Such a transformer can also be used for aircraft, ship and terrestrial applications.

Schwarze, G. E.

1983-01-01

296

Optical-frequency balanced mixer.  

PubMed

Optical signal processing devices based on quasi-phase-matched three-wave mixing and cascaded three-wave mixing in guided-wave geometries have been demonstrated to operate efficiently at practical pump-power levels. We describe operation of such devices in a balanced mode that allows mixing without wavelength offset and separation of mixed output from pump and signal input without wavelength-selective filters. We present a design for an optical-frequency balanced mixer using quasi-phase-matched, cascaded second-order nonlinear processes. Using this design, we fabricated a balanced mixer in periodically poled lithium niobate waveguides that has the expected linear and nonlinear optical performance. PMID:18049587

Kurz, J R; Parameswaran, K R; Roussev, R V; Fejer, M M

2001-08-15

297

Frequency stabilization of algaas lasers  

SciTech Connect

Performances of semiconductor lasers have been remarkably improved by the demand of the optical communications industry. Recently, a single longitudinal mode, CW oscillation at room temperature has been realized. The price of each laser has been reduced as low as $250. These lasers are mostly oscillated in the near-infrared, and the coherent lights of 0.83 micrometers and 1.3-1.6 micrometers in wavelengths are obtained by AlGaAs lasers and InGaAsP lasers, respectively. Since few number of other kind of lasers oscillates in these wavelength regions, these semiconductor lasers could be conveniently used not only in optical communications but in many fields of application, e.g., laser spectroscopy, optical pumping, frequency and length standards, laser radar, air-borne gyroscope, etc.

Ohtsu, M.; Tsuchida, H.; Tako, T.

1982-01-01

298

High frequency RF discharge laser  

SciTech Connect

This patent describes a high frequency high power stabilized RF discharge laser comprising in combination; a ground plane; a stripline waveguide electrode having first and second ends located in a plane substantially parallel to the ground plane; an RF source connected to the first end of the stripline waveguide electrode by a means for preventing a high voltage pulse from damaging the RF source; a discharge tube located between the ground plane and the stripline waveguide electrode; preionization pulse means including a high voltage source applying a high voltage pulse to the second end of the stripline waveguide electrode. It also includes a means placed between the high voltage pulse source and the stripline waveguide electrode for preventing the RF from damaging the high voltage source; and a waveguide region formed by the ground plane and the stripline waveguide electrode wherein the discharge tube lies within the waveguide region.

Christensen, C.P.

1986-12-23

299

Magnetic Earth Ionosphere Resonant Frequencies  

NASA Technical Reports Server (NTRS)

The Community College Division is pleased to report progress of NASA funded research at West Virginia State College. During this reporting period, the project research group has continued with activities to develop instrumentation capability designed to monitor resonant cavity frequencies in the atmospheric region between the Earth's surface and the ionosphere. In addition, the project's principal investigator, Dr. Craig Spaniol, and NASA technical officer, Dr. John Sutton, have written and published technical papers intended to expand the scientific and technical framework needed for project research. This research continues to provide an excellent example of government and education working together to provide significant research in the college environment. This cooperative effort has provided many students with technical project work which compliments their education.

Spaniol, Craig

1994-01-01

300

LOFAR- The Low Frequency Array  

NASA Astrophysics Data System (ADS)

LOFAR is an innovative radio telescope in the frequency range of 10-240 MHz, realized as a phased array. It will become the largest radio telescope in the world in the time frame 2006-2010, located in Northern Europe. LOFAR is being implemented as a Wide Area Sensor Network which connects thousands of cheap sensors spread throughout the country to a central super computer using an ultra-broadband, synchronized data network. As the central processor IBM has provided its Blue Gene/L supercomputer. It will process streaming data with about 0.5 Terabit per second. Many simple radio antennas connected to the network turn it into a huge radio telescope for cosmological studies. In addition, geophones will turn LOFAR into an earthquake monitoring system and infrasound and meteorology sensors will turn LOFAR into a real-time weather monitoring array for agricultural applications. LOFAR is the first radio telescopes that can listen to radio signals from the entire sky overhead, on all time scales, at a large range of frequencies, and even look back in time for a couple of seconds. The main strength of LOFAR are surveys. One goal is to detect the first generation of black holes and galaxies in the universe during the epoch of reionization and study hydrogen formed after the big bang. LOFAR is also an ideal system to discover transient and sporadic radio signals. Likely transient sources to be discovered with LOFAR are bursting stars and Jupiter-like planets, gamma-ray bursts, radio outbursts from black holes, but also lightning on Earth and even radio flashes from ultra-high energy cosmic particles hitting the Earth atmosphere. Some LOFAR prototypes have recently been built. They have produced the first instantaneous all-sky maps and discovered the radio emission from cosmic particle air showers.

Falcke, H. D. E.

2006-08-01

301

Electron pumping at gigahertz frequencies  

NASA Astrophysics Data System (ADS)

Recently, we have overcome the upper frequency limit measured for earlier pumps, by removing the reliance on quantum mechanical tunnelling through barriers on either side of a quantum dot [1]. The ease of operation, high frequency and simplicity of the waveform driving the pump were unexpected findings, contrary to previous predictions. The high speed (GHz), accurate pumping of electrons at the nano-Amp current level allows for easy integration in a wide range of applications from the development of the current standard in the field of metrology to single photon production and quantum based computing, making these new findings of value to many scientific disciplines. The inclusion of a perpendicular magnetic field [2] has shown a marked improvement in the accuracy of the pumped current and allows the study of the interactions of controlled dynamic electrons with a magnet field. Recent work combining two electron pumps in parallel [3] has demonstrated an increase in current output without the increase in error associated with a higher output current from a single pump. With the control and manipulation of a selected number of electrons there is the possibility of the creation of a two-particle entangled state. An interference-type experiment with the inclusion of a beam splitter could be used to probe this state. [4pt] [1] M. D. Blumenthal, B. Kaestner, L. Li, S. Giblin, T. J. B. M. Janssen, M. Pepper, D. Anderson, G. Jones, and D. A. Ritchie, Nature Physics 3, 343 (2007). [0pt] [2] S. J. Wright, M. D. Blumenthal, Godfrey Gumbs, A. L. Thorn, M. Pepper, T. J. B. M. Janssen, S. N. Holmes, D. Anderson, G. A. C. Jones, C. A. Nicoll, and D. A. Ritchie, Phys Rev B. 78, 233311 (2008). [0pt] [3] S. J. Wright, M. D. Blumenthal, M. Pepper, D. Anderson, G. A. C. Jones, C. A. Nicoll, and D. A. Ritchie, Phys Rev B. 80, 113303 (2009).

Ritchie, David

2010-03-01

302

A frequency-controlled beam-steering array with mixing frequency compensation for multichannel applications  

Microsoft Academic Search

A frequency-controlled beam-steering planar array with mixing frequency compensation is presented for cost-effective multichannel phased array applications. The new feed networks for frequency compensation not only operate in wide band but also ensure radio-frequency (RF) amplitude imbalance cancellation and progressive phase distribution. The parallel equal power dividers installed in both LO and intermediate-frequency (IF) feed networks provide uniform amplitude and

Takahide Nishio; Yuanxun Wang; Tatsuo Itoh

2004-01-01

303

High Frequency Chandler Wobble Excitation  

NASA Astrophysics Data System (ADS)

Variations of Earth rotation on sub-daily to secular timescales are caused by mass redistributions in the Earth system as a consequence of geophysical processes and gravitational influences. Forced oscillations of polar motion are superposed by free oscillations of the Earth, i.e. the Chandler wobble and the free core nutation. In order to study the interactions between externally induced polar motion and the Earth's free oscillations, a non-linear gyroscopic model has been developed. In most of the former investigations on polar motion, the Chandler wobble is introduced as a damped oscillation with predetermined frequency and amplitude. However, as the effect of rotational deformation is a backcoupling mechanism of polar motion on the Earth's rotational dynamics, both period and amplitude of the Chandler wobble are time-dependent when regarding additional excitations from, e.g., atmospheric or oceanic mass redistributions. The gyroscopic model is free of any explicit information concerning amplitude, phase, and period of free oscillations. The characteristics of the Earth's free oscillation is reproduced by the model from rheological and geometrical parameters and rotational deformation is taken into account. This enables to study the time variable Chandler oscillation when the gyro is forced with atmospheric and oceanic angular momentum from the global atmospheric ECHAM3-T21 general circulation model together with the ocean model for circulation and tides OMCT driven by ECHAM including surface pressure. Besides, mass redistributions in the Earth's body due to gravitational and loading deformations are regarded and external torques exerted by Moon and Sun are considered. The numerical results of the gyro are significantly related with the geodetically observed time series of polar motion published by the IERS. It is shown that the consistent excitation is capable to counteract the damping and thus to maintain the Chandler amplitude. Spectral analyses of the ECHAM and OMCT forcing fields give no hint for increased excitation power in the Chandler band. Thus it is assumed, that continuous high frequency excitation due to stochastic weather phenomena is responsible for the perpetuation of the Chandler wobble.

Seitz, F.; Stuck, J.; Thomas, M.

2003-04-01

304

Dual-frequency capacitively coupled chlorine discharge  

NASA Astrophysics Data System (ADS)

The effect of the control parameters of both high and low frequency sources on a dual-frequency capacitively coupled chlorine discharge is systematically investigated using a hybrid approach, which consists of a particle-in-cell/Monte Carlo simulation and a volume-averaged global model. The high frequency current density is varied from 20 to 80 A m?2, the driving high frequency is varied from 27.12 to 100 MHz, and the driving low frequency is varied from 1 to 13.56 MHz, while the low frequency current density is kept at 1 A m?2. The discharge pressure is maintained at 10 mTorr. Key plasma parameters (including the electron heating rate, the electron energy probability function, the ion flux, the ion energy, and angular distributions) are explored and their variations with the control parameters are analyzed and compared with other discharge chemistries. As the high frequency current increases, the electron heating is enhanced in the sheath region and is diminished in the bulk region, showing a transition of the electron heating from the drift-ambipolar mode to the ? mode. The fluxes of Cl_2+ ions and high-energy Cl2 molecules reaching the surface decrease with an increase in the driving high frequency, and the average sheath potential is approximately inversely proportional to the driving high frequency. The electron heating rate, the fluxes of Cl_2+ and Cl+ ions reaching the surface, and the average sheath potential show little dependence on the driving low frequency, while the profile of the ion energy distribution evolves from a broad bimodal profile to a narrow single-peak profile as the driving low frequency increases, which corresponds to the transition of the discharge from the intermediate frequency regime to the high frequency regime.

Huang, Shuo; Gudmundsson, J. T.

2015-02-01

305

The driving frequency effects on the atmospheric pressure corona jet plasmas from low frequency to radio frequency  

SciTech Connect

Lately, the atmospheric pressure jet type corona plasma, which has been typically driven by dc to low frequency (LF: several tens of kHz), is often generated by using radio frequency of 13.56 MHz. Yet, the relationship between the plasma and its driving frequency has seldom been investigated. Hence, in this study, dependence of the atmospheric pressure corona plasma characteristics on the driving frequency was explored experimentally from LF to rf (5 kHz-13.56 MHz). The plasmas generated by the driving frequency under 2 MHz were cylindrical shape of several tens of millimeters long while the 13.56 MHz plasma is spherical and a few millimeters long. As the driving frequency was increased, the plasma length became shortened. At the lower driving frequencies (below 2 MHz), the plasmas existed as positive streamer and negative glow for each half period of the applied voltage, but the discharge was more continuous in time for the 13.56 MHz plasma. It was inferred from the measured I-V curves that the higher driving frequency induced higher discharge currents, and the gas temperature was increased as the driving frequency was increased.

Kim, Dan Bee [Division of Physical Metrology, Korea Research Institute of Standards and Science, 209 Gajeongno, Yuseong-gu, Daejeon 305-340 (Korea, Republic of); Jung, H.; Gweon, B.; Rhee, J. K.; Choe, W. [Department of Physics, Korea Advanced Institute of Science and Technology, 335 Gwahangno, Yuseong-gu, Daejeon 305-701 (Korea, Republic of); Moon, S. Y. [LG Electronics Advanced Research Institute, 16 Woomyeon-Dong, Seocho-Gu, Seoul 137-724 (Korea, Republic of)

2011-04-15

306

[Low-Frequency Flow Oscillation  

NASA Technical Reports Server (NTRS)

The results of the research conducted under this grant are presented in detail in three Master theses, by Heinrich, Balow, and Broeren. Additional analysis of the experimental data can be found in two AIAA Journal articles and two conference papers. Citations for all of the studies' publications can be found in the bibliography which is attached. The objective of Heinrich's study was to document the low-frequency flow oscillation on the LRN-1007 airfoil, which had been previously observed at low Reynolds number, to determine its origin, and explore the phenomenon at higher Reynolds number. Heinrich performed detailed flow visualization on the airfoil using surface fluorescent oil and laser-sheet off-body visualization. A large leading-edge separation bubble and trailing-edge separation was identified on the airfoil just prior to the onset of the unsteady stall flow oscillation. From the laser-sheet data, the unsteady flow appeared as a massive boundary-layer separation followed by flow reattachment. Hot-wire data were taken in the wake to identify the presence of the flow oscillation and the dominant frequency. The oscillation was found in the flow from a Reynolds number of 0.3 to 1.3 x 10 exp 6. The Strouhal number based on airfoil projected height was nominally 0.02 and increased slightly with increasing Reynolds number and significantly with increasing airfoil angle of attack. Balow focused his research on the leading-edge separation bubble which was hypothesized to be the origin of the low-frequency oscillation. Initially, experimental measurements in the bubble at the onset of the low-frequency oscillation were attempted to study the characteristics of the bubble and explain possible relationships to the shear-layer-flapping phenomena. Unfortunately, the bubble proved to be extremely sensitive to the probe interference and it drastically reduced the size of the bubble. These detailed measurements were then abandoned by Balow. However, this led to a series of tests where the leading-edge bubble and trailing-edge separation were altered and the affect on the flow-oscillation studied. Balow found that by tripping the airfoil boundary-layer with "zigzag" tape ahead of bubble separation, the bubble was effectively eliminated mid the oscillation suppressed. Wake survey drag measurements showed a drastic reduction in airfoil drag when the bubble and oscillation were eliminated. Using the "zigzag" tape, the trailing-edge separation was moved downstream approximately 5 percent chord. This was found to reduce the amplitude of the oscillation, particularly in the onset stage at low angle of attack (around 14 degrees). Through detailed analysis of the wake behind the airfoil during the unsteady flow oscillation, Balow provided a better understanding of the wake flowfield. Broeren studied the oscillating flowfield in detail at Reynolds number equal 3 x 10 exp 5 and an angle of attack of 15 degrees using laser Doppler velocimetry (LDV). Two-dimensional LDV data were acquired at 687 grid points above the model upper surface while hot-wire data were taken simultaneously in the wake. Using the hot-wire signal, the LDV data were phase averaged into 24 bins to represent a single ensemble average of one oscillation cycle. The velocity data showed a flowfield oscillation that could be divided into three flow regimes. In the first regime, the flow over the airfoil was completely separated initially, the flowfield reattached from the leading edge and the reattachment point moved downstream with increasing time or phase. Broeren referred to this as the reattachment regime. The bubble development regime followed, where a leading-edge separation bubble formed at the leading edge and grew with increasing time. During the initial part of this regime the trailing-edge separation continued to move downstream. However, during the last 30 degrees of phase the trailing-edge separation moved rapidly forward and appeared to merge with the leading-edge bubble. During the third regime, the separation regime, the flow was segmented f

Bragg, Michael B.

1997-01-01

307

Integrally formed radio frequency quadrupole  

DOEpatents

An improved radio frequency quadrupole (10) is provided having an elongate housing (11) with an elongate central axis (12) and top, bottom and two side walls (13a-d) symmetrically disposed about the axis, and vanes (14a-d) formed integrally with the walls (13a-d), the vanes (14a-d) each having a cross-section at right angles to the central axis (12) which tapers inwardly toward the axis to form electrode tips (15a-d) spaced from each other by predetermined distances. Each of the four walls (13a-d), and the vanes (14a-d) integral therewith, is a separate structural element having a central lengthwise plane (16) passing through the tip of the vane, the walls (13a-d) having flat mounting surfaces (17, 18) at right angles to and parallel to the control plane (16), respectively, which are butted together to position the walls and vane tips relative to each other.

Abbott, Steven R. (Concord, CA)

1989-01-01

308

Nonlinear cloaking at microwave frequencies  

NASA Astrophysics Data System (ADS)

The ideas of employing the unique properties of metamaterials for cloaking and invisibility applications has been recently suggested and investigated by several groups, because they may find numerous applications in physics and technology. While many of the recent designs of the cloaking structures are based on the transformation optics and exact formulas, the original concept suggested by Tretyakov employed the periodical set of parallel-plate waveguides with the height smoothly varying from H to h in order to reduce drastically the total scattering cross-section of a given object and to obtain broadband cloaking effect. Our paper is devoted to improvement of this design to make tunability and nonlinear effect. The Tretyakov's design was scaled for Ku-band frequencies and the cloak was placed into rectangular waveguide. The broad transmission band ("invisibility region") was obtained. The tunability of transmission band was realized by addition the capacitors into the cloak, between metallic plates. The cloaking system was simulated numerically by CST Microwave Studio. The possibility of invisibility switching on/off was shown by changing of capacity of varactor diodes from 0.4 to 3.4 pF by incident power. The nonlinear cloak behavior was shown at microwaves.

Gurvitz, E. A.; Sedykh, E. A.; Khodzitskiy, M. K.

309

Cluster analysis of word frequency dynamics  

NASA Astrophysics Data System (ADS)

This paper describes the analysis and modelling of word usage frequency time series. During one of previous studies, an assumption was put forward that all word usage frequencies have uniform dynamics approaching the shape of a Gaussian function. This assumption can be checked using the frequency dictionaries of the Google Books Ngram database. This database includes 5.2 million books published between 1500 and 2008. The corpus contains over 500 billion words in American English, British English, French, German, Spanish, Russian, Hebrew, and Chinese. We clustered time series of word usage frequencies using a Kohonen neural network. The similarity between input vectors was estimated using several algorithms. As a result of the neural network training procedure, more than ten different forms of time series were found. They describe the dynamics of word usage frequencies from birth to death of individual words. Different groups of word forms were found to have different dynamics of word usage frequency variations.

Maslennikova, Yu S.; Bochkarev, V. V.; Belashova, I. A.

2015-01-01

310

Wide band stepped frequency ground penetrating radar  

DOEpatents

A wide band ground penetrating radar system is described embodying a method wherein a series of radio frequency signals is produced by a single radio frequency source and provided to a transmit antenna for transmission to a target and reflection therefrom to a receive antenna. A phase modulator modulates those portions of the radio frequency signals to be transmitted and the reflected modulated signal is combined in a mixer with the original radio frequency signal to produce a resultant signal which is demodulated to produce a series of direct current voltage signals, the envelope of which forms a cosine wave shaped plot which is processed by a Fast Fourier Transform Unit 44 into frequency domain data wherein the position of a preponderant frequency is indicative of distance to the target and magnitude is indicative of the signature of the target. 6 figs.

Bashforth, M.B.; Gardner, D.; Patrick, D.; Lewallen, T.A.; Nammath, S.R.; Painter, K.D.; Vadnais, K.G.

1996-03-12

311

Wide band stepped frequency ground penetrating radar  

DOEpatents

A wide band ground penetrating radar system (10) embodying a method wherein a series of radio frequency signals (60) is produced by a single radio frequency source (16) and provided to a transmit antenna (26) for transmission to a target (54) and reflection therefrom to a receive antenna (28). A phase modulator (18) modulates those portion of the radio frequency signals (62) to be transmitted and the reflected modulated signal (62) is combined in a mixer (34) with the original radio frequency signal (60) to produce a resultant signal (53) which is demodulated to produce a series of direct current voltage signals (66) the envelope of which forms a cosine wave shaped plot (68) which is processed by a Fast Fourier Transform unit 44 into frequency domain data (70) wherein the position of a preponderant frequency is indicative of distance to the target (54) and magnitude is indicative of the signature of the target (54).

Bashforth, Michael B. (Buellton, CA); Gardner, Duane (Santa Maria, CA); Patrick, Douglas (Santa Maria, CA); Lewallen, Tricia A. (Ventura, CA); Nammath, Sharyn R. (Santa Barbara, CA); Painter, Kelly D. (Goleta, CA); Vadnais, Kenneth G. (Alexandria, VA)

1996-01-01

312

Explaining the gender difference in nightmare frequency.  

PubMed

A recent meta-analysis showed a robust gender difference in nightmare frequency of medium effect size in adolescents and young adults: Women tend to report nightmares more frequently than men. The present study, carried out in an unselected student sample, indicates that 2 factors mediate the gender difference in nightmare frequency: neuroticism and overall dream recall frequency. The effect of neuroticism on the gender difference and the finding that the gender difference in nightmare frequency emerges at an age of about 10 years suggest that gender-specific socialization processes may play an important role in explaining the gender differences in nightmare frequency in adolescents and young to middle-aged adults. This idea is supported by the previous finding that nightmare frequency is related to sex role orientation. However, longitudinal studies are necessary to validate these hypotheses. PMID:24934011

Schredl, Michael

2014-01-01

313

On frequency dependence of pulsar linear polarization  

E-print Network

Frequency dependence of pulsar linear polarization is investigated by simulations of emission and propagation processes. Linearly polarized waves are generated through curvature radiation by relativistic particles streaming along curved magnetic field lines, which have ordinary mode (O-mode) and extra-ordinary mode (X-mode) components. As emitted waves propagate outwards, two mode components are separated due to re- fraction of the O mode, and their polarization states are also modified. According to the radius to frequency mapping, low frequency emission is generated from higher magnetosphere, where significant rotation effect leads the X and O modes to be sepa- rated. Hence, the low frequency radiation has a large fraction of linear polarization. As the frequency increases, emission is generated from lower heights, where the rotation effect becomes weaker and the distribution regions of two modes are more overlapped. Hence, more significant depolarization appears for emission at higher frequencies. In addit...

Wang, P F; Han, J L

2015-01-01

314

Frequency modulation drive for a piezoelectric motor  

DOEpatents

A piezoelectric motor has peak performance at a specific frequency f.sub.1 that may vary over a range of frequencies. A drive system is disclosed for operating such a motor at peak performance without feedback. The drive system consists of the motor and an ac source connected to power the motor, the ac source repeatedly generating a frequency over a range from f.sub.1 -.DELTA.x to f.sub.1 +.DELTA.y.

Mittas, Anthony (Albuquerque, NM)

2001-01-01

315

Widely tunable extreme UV frequency comb generation.  

PubMed

Extreme UV (XUV) frequency comb generation in the wavelength range of 51 to 85 nm is reported based on high-order harmonic generation of two consecutive IR frequency comb pulses that were amplified in an optical parametric chirped pulse amplifier. The versatility of the system is demonstrated by recording direct XUV frequency comb excitation signals in He, Ne, and Ar with visibilities of up to 61%. PMID:21633437

Pinkert, T J; Kandula, D Z; Gohle, C; Barmes, I; Morgenweg, J; Eikema, K S E

2011-06-01

316

Ultra-High-Frequency Capacitive Displacement Sensor  

NASA Technical Reports Server (NTRS)

Improved class of compact, high-resolution capacitive displacement sensors operates at excitation frequency of 915 MHz and measures about 7.5 by 4 by 2 centimeters. Contains commercially available 915-MHz oscillator and transmission-line resonator. Resonator contains stripline inductor in addition to variable capacitor. Ultrahigh excitation frequency offers advantages of resolution and frequency response. Not deleteriously affected by mechanical overdriving, or contact between electrodes.

Vanzandt, Thomas R.; Kenny, Thomas W.; Kaiser, William J.

1994-01-01

317

Frequency-offset insensitive digital modem techniques  

NASA Technical Reports Server (NTRS)

Conventional DPSK systems are adversely affected by transmitter/receiver frequency offsets due to frequency reference errors and Doppler shifts. Two DPSK modem concepts are presented which avoid the long frequency acquisition process of conventional DPSK. One technique involves a modified demodulator for conventional DPSK signals, while the other involves making minor changes to both the modulator and demodulator. Simulation results are provided showing performance relative to conventional DPSK.

Dutta, S.; Nicholas, D. C.

1990-01-01

318

Operation of Graphene Transistors at Gigahertz Frequencies  

Microsoft Academic Search

Top-gated graphene transistors operating at high frequencies (GHz) have been fabricated and their characteristics analyzed. The measured intrinsic current gain shows an ideal 1\\/f frequency dependence, indicating an FET-like behavior for graphene transistors. The cutoff frequency fT is found to be proportional to the dc transconductance gm of the device. The peak fT increases with a reduced gate length, and

Yu-Ming Lin; Keith A. Jenkins; Alberto Valdes-Garcia; Joshua P. Small; Damon B. Farmer; Phaedon Avouris

2009-01-01

319

Precision frequency measurements with interferometric weak values  

E-print Network

We demonstrate an experiment which utilizes a Sagnac interferometer to measure a change in optical frequency of 129 kHz per root Hz with only 2 mW of continuous wave, single mode input power. We describe the measurement of a weak value and show how even higher frequency sensitivities may be obtained over a bandwidth of several nanometers. This technique has many possible applications, such as precision relative frequency measurements and laser locking without the use of atomic lines.

David J. Starling; P. Ben Dixon; Andrew N. Jordan; John C. Howell

2011-01-07

320

Laser frequency stabilization using Zeeman effect  

Microsoft Academic Search

We describe a new and easy to handle method to stabilize the laser frequency on an atomic transition. This method, based on Zeeman effect, involves the circular dichroism of an atomic vapour submitted to a magnetic field. It is applied to the frequency stabilization of a single frequency LNA laser on (2 (2 ^3S1-2 ^3P0) helium transition. Nous décrivons une

B. Chéron; H. Gilles; J. Hamel; O. Moreau; H. Sorel

1994-01-01

321

Apparatus for measuring high frequency currents  

NASA Technical Reports Server (NTRS)

An apparatus for measuring high frequency currents includes a non-ferrous core current probe that is coupled to a wide-band transimpedance amplifier. The current probe has a secondary winding with a winding resistance that is substantially smaller than the reactance of the winding. The sensitivity of the current probe is substantially flat over a wide band of frequencies. The apparatus is particularly useful for measuring exposure of humans to radio frequency currents.

Hagmann, Mark J. (Inventor); Sutton, John F. (Inventor)

2003-01-01

322

A high frequency silicon pressure sensor  

NASA Technical Reports Server (NTRS)

Theoretical and design considerations as well as fabrication and experimental work involved in the development of high-frequency silicon pressure sensors with an ultra-small diaphragm are discussed. A sensor is presented with a rectangular diaphragm of 0.0127 cm x 0.0254 cm x 1.06 micron; the sensor has a natural frequency of 625 kHz and a sensitivity of 0.82 mv/v-psi. High-frequency results from shock tube testing and low-frequency (less than 50 kHz) comparison with microphones are given.

Kahng, S. K.; Gross, C.

1980-01-01

323

47 CFR 87.195 - Frequencies.  

Code of Federal Regulations, 2011 CFR

... Section 87.195 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AVIATION SERVICES Aircraft Stations Emergency Locator Transmitters § 87.195 Frequencies. (a)...

2011-10-01

324

47 CFR 87.195 - Frequencies.  

Code of Federal Regulations, 2013 CFR

... Section 87.195 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AVIATION SERVICES Aircraft Stations Emergency Locator Transmitters § 87.195 Frequencies. (a)...

2013-10-01

325

47 CFR 87.195 - Frequencies.  

Code of Federal Regulations, 2012 CFR

... Section 87.195 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AVIATION SERVICES Aircraft Stations Emergency Locator Transmitters § 87.195 Frequencies. (a)...

2012-10-01

326

47 CFR 87.195 - Frequencies.  

Code of Federal Regulations, 2010 CFR

... Section 87.195 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AVIATION SERVICES Aircraft Stations Emergency Locator Transmitters § 87.195 Frequencies. (a)...

2010-10-01

327

Psychophysical tuning curves at very high frequencies  

NASA Astrophysics Data System (ADS)

For most normal-hearing listeners, absolute thresholds increase rapidly above about 16 kHz. One hypothesis is that the high-frequency limit of the hearing-threshold curve is imposed by the transmission characteristics of the middle ear, which attenuates the sound input [Masterton et al., J. Acoust. Soc. Am. 45, 966-985 (1969)]. An alternative hypothesis is that the high-frequency limit of hearing is imposed by the tonotopicity of the cochlea [Ruggero and Temchin, Proc. Nat. Acad. Sci. U.S.A. 99, 13206-13210 (2002)]. The aim of this study was to test these hypotheses. Forward-masked psychophysical tuning curves (PTCs) were derived for signal frequencies of 12-17.5 kHz. For the highest signal frequencies, the high-frequency slopes of some PTCs were steeper than the slope of the hearing-threshold curve. The results also show that the human auditory system displays frequency selectivity for characteristic frequencies (CFs) as high as 17 kHz, above the frequency at which absolute thresholds begin to increase rapidly. The findings suggest that, for CFs up to 17 kHz, the high-frequency limitation in humans is imposed in part by the middle-ear attenuation, and not by the tonotopicity of the cochlea.

Yasin, Ifat; Plack, Christopher J.

2005-10-01

328

Optimum Detection of Frequency-Hopped Signals  

NASA Technical Reports Server (NTRS)

This paper derives and analyzes optimum and near-optimum structures for detecting frequency-hopped (FH) signals with arbitrary modulation in additive white Gaussian noise. The principalmodulation formats considered are M-ary frequency-shift-keying (MFSK) with fast frequency hopping(FFH) wherein a single tone is transmitted per hop, and slow frequency hopping (SFH) with multipleMFSK tones (data symbols) per hop. The SFH detection category has not previously been addressedin the open literature and its analysis is generally more complex than FFH.

Cheng, Unjeng; Levitt, Barry; Polydoros, Andreas; Simon, Marvin K.

1992-01-01

329

Frequency doubled, cavity dumped feedback laser  

NASA Technical Reports Server (NTRS)

Higher efficiency in cavity dumping and frequency doubling in a laser used to produce modulated output beam pulses is achieved by deflecting light out of the resonant cavity to a third mirror through a frequency doubler using an electro-optic modulator and a polarizing beamsplitter in the resonant cavity, or using just an acousto-optic modulator to deflect light out of the laser cavity in response to a control signal (electric or acoustic). The frequency doubler in front of the third mirror rotates the frequency doubled light so that it will pass out of the laser cavity through the polarizing beamsplitter, while undoubled frequency light is reflected by the polarizing beamsplitter back into the gain medium of the laser. In the case of using a type-II frequency doubler, a dichroic beamsplitter deflects out the frequency doubled light and passes the undoubled frequency light to the polarizing beamsplitter for return to the laser gain medium. If an acousto-optic modulator is used, it deflects light out of the primary laser cavity, so a polarizing beamsplitter is not needed, and only a dichroic beamsplitter is needed to separate frequency doubled light out of the path from the third mirror.

Sipes, Jr., Donald L. (Inventor); Robinson, Deborah L. (Inventor)

1989-01-01

330

The resonant step frequency in human running.  

PubMed

At running speeds less than about 13 km h-1 the freely chosen step frequency (ffree) is lower than the frequency at which the mechanical power is minimized (fmin). This dissociation between ffree and fmin was investigated by measuring mechanical power, metabolic energy expenditure and apparent natural frequency of the body's bouncing system (fsist) during running at three given speeds with different step frequencies. The ffree requires a mechanical power greater than that at fmin mainly due to a larger vertical oscillation of the body at each step. Energy expenditure is minimal and the mechanical efficiency is maximal at ffree. At a given speed, an increase in step frequency above ffree results in an increase in energy expenditure despite a decrease in mechanical power. On the other hand, a decrease in step frequency below ffree results in a larger increase in energy expenditure associated with an increase in mechanical power. When the step frequency is forced to values above or below ffree, fsist is forced to change similarly by adjusting the stiffness of the bouncing system. However the best match between fsist and step frequency takes place only in proximity of ffree (2. 6-2.8 Hz). It is concluded that during running at speeds less than 13 km h-1 energy is saved by tuning step frequency to fsist, even if this requires a mechanical power larger than necessary. PMID:9305998

Cavagna, G A; Mantovani, M; Willems, P A; Musch, G

1997-11-01

331

Frequency multiplying behavior in a magnetoelectric unimorph  

NASA Astrophysics Data System (ADS)

We observe frequency multiplying behavior in a magnetoelectric (ME) unimorph: such a frequency-multiplied signal is generated when the input frequency (fin) of an alternating current magnetic field (Hac) is around 1/n (n denotes integer) of the mechanical resonance frequency (fr) of the device. We observe both odd and even harmonic signals when a direct current magnetic field (Hdc) is applied, whereas only even harmonic signals arise for Hdc = 0. This behavior results from the combined effect of the nonlinear character of the Metglas magnetostriction and a mechanical resonance phenomenon in the magnetoelectric unimorph.

Zhang, Wenhui; Yin, Ge; Cao, Jiangwei; Bai, Jianmin; Wei, Fulin

2012-01-01

332

Gradual adaptation to auditory frequency mismatch.  

PubMed

What is the best way to help humans adapt to a distorted sensory input? Interest in this question is more than academic. The answer may help facilitate auditory learning by people who became deaf after learning language and later received a cochlear implant (a neural prosthesis that restores hearing through direct electrical stimulation of the auditory nerve). There is evidence that some cochlear implants (which provide information that is spectrally degraded to begin with) stimulate neurons with higher characteristic frequency than the acoustic frequency of the original stimulus. In other words, the stimulus is shifted in frequency with respect to what the listener expects to hear. This frequency misalignment may have a negative influence on speech perception by CI users. However, a perfect frequency-place alignment may result in the loss of important low frequency speech information. A trade-off may involve a gradual approach: start with correct frequency-place alignment to allow listeners to adapt to the spectrally degraded signal first, and then gradually increase the frequency shift to allow them to adapt to it over time. We used an acoustic model of a cochlear implant to measure adaptation to a frequency-shifted signal, using either the gradual approach or the "standard" approach (sudden imposition of the frequency shift). Listeners in both groups showed substantial auditory learning, as measured by increases in speech perception scores over the course of fifteen one-hour training sessions. However, the learning process was faster for listeners who were exposed to the gradual approach. These results suggest that gradual rather than sudden exposure may facilitate perceptual learning in the face of a spectrally degraded, frequency-shifted input. This article is part of a Special Issue entitled . PMID:25445816

Svirsky, Mario A; Talavage, Thomas M; Sinha, Shivank; Neuburger, Heidi; Azadpour, Mahan

2014-11-01

333

A precision millimeter-wave measurement of the Rydberg frequency  

E-print Network

The Rydberg frequency, cR[infinity], sets the frequency scale for the spectrum of hydrogen atoms. From a frequency measurement of one transition in hydrogen, cR[infinity] can be extracted and the frequency of any other ...

De Vries, Joel Christopher, 1971-

2001-01-01

334

47 CFR 80.377 - Frequencies for ship earth stations.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Frequencies for ship earth stations. 80.377 Section 80.377 ...THE MARITIME SERVICES Frequencies Ship Earth Stations § 80.377 Frequencies for ship earth stations. The frequency band...

2010-10-01

335

47 CFR 80.377 - Frequencies for ship earth stations.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Frequencies for ship earth stations. 80.377 Section 80.377 ...THE MARITIME SERVICES Frequencies Ship Earth Stations § 80.377 Frequencies for ship earth stations. The frequency band...

2011-10-01

336

47 CFR 80.377 - Frequencies for ship earth stations.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Frequencies for ship earth stations. 80.377 Section 80.377 ...THE MARITIME SERVICES Frequencies Ship Earth Stations § 80.377 Frequencies for ship earth stations. The frequency band...

2012-10-01

337

47 CFR 80.377 - Frequencies for ship earth stations.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 false Frequencies for ship earth stations. 80.377 Section 80.377 ...THE MARITIME SERVICES Frequencies Ship Earth Stations § 80.377 Frequencies for ship earth stations. The frequency band...

2013-10-01

338

2014 Amplifier -1 FREQUENCY RESPONSE OF  

E-print Network

2014 Amplifier - 1 FREQUENCY RESPONSE OF AN AUDIO AMPLIFIER The objectives of this experiment are amplifier · To thoroughly bore you APPARATUS: Audio Amplifier (Circuit Chip), Computer with FFTScope software, Speaker, Power supply, Interconnecting Cables good high fidelity amplifier will have frequency

Glashausser, Charles

339

Exploring the limits of frequency lowering  

PubMed Central

Objective This study examined how frequency lowering affected sentence intelligibility and quality, for adults with postlingually acquired, mild-to-moderate hearing loss. Method Listeners included adults aged 60–92 years with sloping sensorineural loss and a control group of similarly-aged adults with normal hearing. Sentences were presented in quiet and babble at a range of signal-to-noise ratios. Intelligibility and quality were measured with varying amounts of frequency lowering, implemented using a form of frequency compression. Results Moderate amounts of compression, particularly with high cutoff frequencies, had minimal effects on intelligibility. Listeners with the greatest high-frequency hearing loss showed the greatest benefit. Sentence intelligibility decreased with more compression. Listeners were more affected by a given set of parameters in noise. In quiet, any amount of compression resulted in lower speech quality for most listeners, with the greatest degradation for listeners with better high-frequency hearing. Quality ratings were lower with background noise, and in noise the effect of changing compression parameters was small. Conclusions The benefits of frequency lowering in adults were affected by the compression parameters as well as individual hearing thresholds. Data are consistent with the idea that frequency lowering can be viewed in terms of an improved audibility vs increased distortion tradeoff. PMID:23785188

Souza, Pamela E.; Arehart, Kathryn H.; Kates, James M.; Croghan, Naomi B.H.; Gehani, Namita

2013-01-01

340

Amplitude Frequency Response Measurement: A Simple Technique  

ERIC Educational Resources Information Center

A simple method is described to combine a modern function generator and a digital oscilloscope to configure a setup that can directly measure the amplitude frequency response of a system. This is achieved by synchronously triggering both instruments, with the function generator operated in the "Linear-Sweep" frequency mode, while the oscilloscope…

Satish, L.; Vora, S. C.

2010-01-01

341

Interference diversity gain in frequency hopping GSM  

Microsoft Academic Search

Wideband random frequency hopping is one of the key properties of GSM in an evolution towards PCS (personal communication services). Random frequency hopping introduces diversity on the transmission link, which improves the performance. In this paper, the impact of interference diversity in GSM is analyzed by means of bit level simulations of the GSM full rate speech channel. The analysis

H. Olofsson; J. Naslund; J. Skold

1995-01-01

342

Hydrogen masers with cavity frequency switching servos  

NASA Technical Reports Server (NTRS)

The stability of the free-running hydrogen maser is limited by pulling of the unperturbed hydrogen transition frequency due to instability of the cavity resonance frequency. While automatic spin-exchange tuning is in principle the more basic and accurate method, the required beam intensity switching and the long servo time constant result in reduced stability for measuring intervals up to 10(exp 6) seconds. More importantly, the spin-exchange tuning method requires a second stable frequency source as a reference, ideally a second hydrogen maser, to get the best results. The cavity frequency switching servo, on the other hand, has very little effect on the maser short term stability, and is fast enough to correct for cavity drift while maintaining the cavity at the spin-exchange tuned offset required to minimize instability due to beam intensity fluctuations. Not only does the cavity frequency switching servo not require a second stable frequency source, but the frequency reference is the atomic hydrogen radiated beam signal, so that no extra RF connections need be made to the cavity, and externally generated signals that would perturb the hydrogen atom need not be transmitted through the cavity. The operation of the cavity frequency switching stabilization method is discussed and the transient response of the servo and certain other aspects of the technique that have potential for achieving improved basic accuracy are illustrated.

Peters, Harry E.; Owings, H. B.; Koppang, Paul A.

1990-01-01

343

The frequencies of conversion reaction symptoms  

Microsoft Academic Search

Compared the frequencies with which 69 conversion symptoms are described in 18 abnormal psychology and psychiatry textbooks with the frequencies with which they appeared in a sample of 40 male hysterics and a group of female conversion reactions depicted in an earlier study. The correlations were small. Results suggest that textbook descriptions do not focus on the more common conversion

Charles G. Watson; Cheryl Buranen

1979-01-01

344

Multi-Frequency Band Pyroelectric Sensors  

PubMed Central

A methodology is proposed for designing a multi-frequency band pyroelectric sensor which can detect subjects with various frequencies or velocities. A structure with dual pyroelectric layers, consisting of a thinner sputtered ZnO layer and a thicker aerosol ZnO layer, proved helpful in the development of the proposed sensor. The thinner sputtered ZnO layer with a small thermal capacity and a rapid response accomplishes a high-frequency sensing task, while the thicker aerosol ZnO layer with a large thermal capacity and a tardy response is responsible for low-frequency sensing tasks. A multi-frequency band pyroelectric sensor is successfully designed, analyzed and fabricated in the present study. The range of the multi-frequency sensing can be estimated by means of the proposed design and analysis to match the thicknesses of the sputtered and the aerosol ZnO layers. The fabricated multi-frequency band pyroelectric sensor with a 1 ?m thick sputtered ZnO layer and a 20 ?m thick aerosol ZnO layer can sense a frequency band from 4000 to 40,000 Hz without tardy response and low voltage responsivity. PMID:25429406

Hsiao, Chun-Ching; Liu, Sheng-Yi

2014-01-01

345

Detection and frequency tracking of chirping signals  

SciTech Connect

This paper discusses several methods to detect the presence of and track the frequency of a chirping signal in broadband noise. The dynamic behavior of each of the methods is described and tracking error bounds are investigated in terms of the chirp rate. Frequency tracking and behavior in the presence of varying levels of noise are illustrated in examples. 11 refs., 29 figs.

Elliott, G.R.; Stearns, S.D.

1990-08-01

346

High Frequency Microphone Measurements for Transition Detection  

E-print Network

! High Frequency Microphone Measurements for Transition Detection on Airfoils Mads Døssing Risø Døssing Risø­R­1645(EN) Title: High Frequency Microphone Measurements for Transition Detection on Airfoils of airfoils un- dergoing wind tunnel tests in the LM Windtunnel, owned by 'LM Glasfiber', Denmark. The present

347

ENGLISH WORDS OF VERY HIGH FREQUENCY.  

ERIC Educational Resources Information Center

THE BIAS OF THE FREQUENCY OF THE 122 MOST COMMONLY USED ENGLISH WORDS WAS STUDIED. THE METHOD USED TO ASSEMBLE THESE DATA IS DESCRIBED FULLY. THE MOST FREQUENTLY USED WORDS WERE TAKEN FROM A DISSERTATION BY GEORGE K. MONROE, "PHONEMIC TRANSCRIPTION OF GRAPHIC POSTBASE AFFIXES IN ENGLISH," GODFREY DEWEY, "RELATIVE FREQUENCY OF ENGLISH SPEECH…

CARD, WILLIAM; MCDAVID, VIRGINIA

348

On Resonant Heating Below the Cyclotron Frequency  

SciTech Connect

Resonant heating of particles by an electrostatic wave propagating perpendicular to a confining uniform magnetic field is examined. It is shown that, with a sufficiently large wave amplitude, significant perpendicular stochastic heating can be obtained with wave frequency at a fraction of the cyclotron frequency.

Liu Chen; Zhihong Lin; White, R.

2001-02-02

349

Electronic power generators for ultrasonic frequencies  

NASA Technical Reports Server (NTRS)

The design and construction of an ultrasonic frequency electronic power generator are discussed. The principle design elements of the generator are illustrated. The generator provides an inductive load with an output power of two kilowatts and a variable output frequency in the fifteen to thirty KiloHertz range. The method of conducting the tests and the results obtained with selected materials are analyzed.

Ciovica, D.

1974-01-01

350

Robust frequency and timing synchronization for OFDM  

Microsoft Academic Search

A rapid synchronization method is presented for an orthogonal frequency-division multiplexing (OFDM) system using either a continuous transmission or a burst operation over a frequency-selective channel. The presence of a signal can be detected upon the receipt of just one training sequence of two symbols. The start of the frame and the beginning of the symbol can be found, and

Timothy M. Schmidl; Donald C. Cox

1997-01-01

351

47 CFR 101.803 - Frequencies.  

Code of Federal Regulations, 2013 CFR

...frequency band is shared with stations in the earth-exploration satellite service. ...is shared with space stations (space to earth) in the fixed-satellite service...5) This frequency band is shared with earth stations (earth to space) in the...

2013-10-01

352

47 CFR 101.803 - Frequencies.  

Code of Federal Regulations, 2012 CFR

...frequency band is shared with stations in the earth-exploration satellite service. ...is shared with space stations (space to earth) in the fixed-satellite service...5) This frequency band is shared with earth stations (earth to space) in the...

2012-10-01

353

47 CFR 101.803 - Frequencies.  

Code of Federal Regulations, 2010 CFR

...frequency band is shared with stations in the earth-exploration satellite service. ...is shared with space stations (space to earth) in the fixed-satellite service...5) This frequency band is shared with earth stations (earth to space) in the...

2010-10-01

354

47 CFR 101.803 - Frequencies.  

Code of Federal Regulations, 2011 CFR

...frequency band is shared with stations in the earth-exploration satellite service. ...is shared with space stations (space to earth) in the fixed-satellite service...5) This frequency band is shared with earth stations (earth to space) in the...

2011-10-01

355

Fundamental Frequency Estimation in the SMS Analysis  

Microsoft Academic Search

This paper deals with the fundamental frequency estimation for monophonic sounds in the SMS analysis environment. The importance of the fundamental frequency as well as some uses in SMS is commented. The particular method of F0 estimation based on a two-way mismatched measure is described as well as some modifications. Finally we explain how pitch -unpitched decision is performed.

Pedro Cano

1998-01-01

356

Mel Frequency Cepstral Coefficients for Music Modeling  

Microsoft Academic Search

We examine in some detail Mel Frequency Cepstral Coefficients (MFCCs) - the dominant features used for speech recognition - and investigate their applicability to modeling music. In particular, we examine two of the main assumptions of the process of forming MFCCs: the use of the Mel frequency scale to model the spectra; and the use of the Discrete Cosine Transform

Beth Logan

2000-01-01

357

Encoding frequency contrast in primate auditory cortex.  

PubMed

Changes in amplitude and frequency jointly determine much of the communicative significance of complex acoustic signals, including human speech. We have previously described responses of neurons in the core auditory cortex of awake rhesus macaques to sinusoidal amplitude modulation (SAM) signals. Here we report a complementary study of sinusoidal frequency modulation (SFM) in the same neurons. Responses to SFM were analogous to SAM responses in that changes in multiple parameters defining SFM stimuli (e.g., modulation frequency, modulation depth, carrier frequency) were robustly encoded in the temporal dynamics of the spike trains. For example, changes in the carrier frequency produced highly reproducible changes in shapes of the modulation period histogram, consistent with the notion that the instantaneous probability of discharge mirrors the moment-by-moment spectrum at low modulation rates. The upper limit for phase locking was similar across SAM and SFM within neurons, suggesting shared biophysical constraints on temporal processing. Using spike train classification methods, we found that neural thresholds for modulation depth discrimination are typically far lower than would be predicted from frequency tuning to static tones. This "dynamic hyperacuity" suggests a substantial central enhancement of the neural representation of frequency changes relative to the auditory periphery. Spike timing information was superior to average rate information when discriminating among SFM signals, and even when discriminating among static tones varying in frequency. This finding held even when differences in total spike count across stimuli were normalized, indicating both the primacy and generality of temporal response dynamics in cortical auditory processing. PMID:24598525

Malone, Brian J; Scott, Brian H; Semple, Malcolm N

2014-06-01

358

Operating Frequencies for Educational Satellite Services.  

ERIC Educational Resources Information Center

Part of a continuing study of application of communication satellites for helping to meet educational needs, this memorandum discusses operating frequencies for educational satellite services. Each of the factors affecting choice of transmission frequencies is identified and discussed in a separate section. Included among these factors are…

Singh, Jai P.

359

DQPSK Receiver tolerance to transmitter frequency stability  

Microsoft Academic Search

In case of Differential Quadrature Phase Shift Keying transmission, the diode laser frequency instability affects the quality of the received signal. Free-running transmitters are employed to experimentally evaluate the tolerance of the interferometric DQPSK receiver to this instability. Heterodyne measure of the frequency offset is discussed for different transmitters. Experimental data are related both with BER performance and power penalty.

Lucia Marazzi; Paola Parolari; Pierpaolo Boffi; Rocco Siano; Matteo Feroldi; M. Martinelli

2006-01-01

360

Prospects for stored ion frequency standards  

NASA Technical Reports Server (NTRS)

Fundamental limitations of possible frequency standards based on stored ions are examined. Practical limitations are also addressed but without regard to size, power consumption, and cost. With these guidelines, one can anticipate that a stored ion frequency standard with accuracy and stability better than 10 to the -15th power is now possible.

Wineland, D. J.

1982-01-01

361

Frequency characteristics of the saccadic eye movement.  

PubMed

Using a piecewise linear approach, individual saccadic eye movements have been Fourier decomposed in an attempt to determine the effect of saccadic amplitude on frequency characteristics. These characteristics were plotted in the traditional Bode plot form, showing gain and phase as a function of frequency for various eye movement amplitudes. Up to about one octave beyond the -3 db gain frequency, the limiting system dynamics represented by the saccadic trajectory of a given amplitude may be considered linear and second order. The -3 db gain frequency was used as a measure of bandwidth, and the -90 degrees phase crossover frequency was used as a measure of undamped natural frequency. These two quantities were used to calculate the damping factor. Both bandwidth and undamped natural frequency decrease with increasing saccadic eye movement amplitude. The damping factor shows no trend with amplitude and indicates approximate critical damping. When compared with the normal variation of characteristics for a given movement, the frequency characteristics of fixed-amplitude saccades showed no generalized trends with changes in direction or DC operating level of movement. PMID:5696212

Zuber, B L; Semmlow, J L; Stark, L

1968-11-01

362

Frequency Selective Volumes for Optical Spatial Filters  

SciTech Connect

A new model is proposed for modeling metallic losses at optical frequencies and is used in the analysis of Frequency Selective Surfaces (FSSs) and Volumes (FSVs). Conventional methods for simulating metallic losses are also outlined and a comparison with those models is given for a patch FSS. Measured data for a slot-ring FSS are also given for model validation.

E Topsakal; JL Volakis

2004-04-15

363

LOFAR, a new low frequency radio telescope  

Microsoft Academic Search

LOFAR, the Low Frequency Array, is a large radio telescope consisting of approximately 100 soccer-field sized antenna stations spread over a region of 400 km in diameter. It will operate at frequencies from ?10 to 240 MHz, with a resolution at 240 MHz of better than an arcsecond. Its superb sensitivity will allow for studies of a broad range of

Huub Röttgering

2003-01-01

364

Multi-dimensional ultra-high frequency passive radio frequency identification tag antenna designs  

E-print Network

In this thesis, we present the design, simulation, and empirical evaluation of two novel multi-dimensional ultra-high frequency (UHF) passive radio frequency identification (RFID) tag antennas, the Albano-Dipole antenna ...

Delichatsios, Stefanie Alkistis

2006-01-01

365

1 Pitch, Frequency, Musical Scales 1 1.1 Pitch and Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1  

E-print Network

Contents ix 1 Pitch, Frequency, Musical Scales 1 1.1 Pitch and Frequency.2 Overtones, Pitch Equivalence, and Musical Scales . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2.2 Musical Scales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3 The 12

Walker, James S.

366

Frequency correlations in reflection from random media  

E-print Network

We present a theoretical study of frequency correlations of light backscattered from a random scattering medium. This statistical quantity provides insight into the dynamics of multiple scattering processes accessible both, in theoretical and experimental investigations. For frequency correlations between field amplitudes, we derive a simple expression in terms of the path length distribution of the underlying backscattering processes. In a second step, we apply this relation to describe frequency correlations between intensities in the regime of weak disorder. Since, with increasing disorder strength, an unexplained breakdown of the angular structure of the frequency correlation function has recently been reported in experimental studies, we explore extensions of our model to the regime of stronger disorder. In particular, we show that closed scattering trajectories tend to suppress the angular dependence of the frequency correlation function.

Knothe, Angelika

2015-01-01

367

Frequency resolving power measured by rippled noise.  

PubMed

Frequency resolving power (FRP) was measured in normal humans using rippled noise with a phase-reversal test. The principle of the test was to find the highest ripple density at which an interchange of mutual peak and trough position (the phase reversal) in the rippled spectrum is detectable. In the frequency range below 0.5 kHz FRP was found to be about 21 ripples per kHz when tested by both broad-band and narrow-band rippled noise. In the frequency range above 2 kHz, FRP measured by the narrow-band rippled noise was 22 to 23 relative units (relation of the noise central frequency to the ripple frequency spacing). PMID:7961175

Supin AYa; Popov, V V; Milekhina, O N; Tarakanov, M B

1994-07-01

368

Waveform Selectivity at the Same Frequency  

E-print Network

Electromagnetic properties depend on the composition of materials, i.e. either angstrom scales of molecules or, for metamaterials, subwavelength periodic structures. Each material behaves differently in accordance with the frequency of an incoming electromagnetic wave due to the frequency dispersion or the resonance of the periodic structures. This indicates that if the frequency is fixed, the material always responds in the same manner unless it has nonlinearity. However, such nonlinearity is controlled by the magnitude of the incoming wave or other bias. Therefore, it is difficult to distinguish different incoming waves at the same frequency. Here we present a new concept of circuit-based metasurfaces to selectively absorb or transmit specific types of waveforms even at the same frequency. The metasurfaces, integrated with schottky diodes as well as either capacitors or inductors, selectively absorb short or long pulses, respectively. The two types of the circuit elements are then combined to absorb or tran...

Wakatsuchi, Hiroki; Rushton, Jeremiah J; Gao, Fei; Kim, Sanghoon; Sievenpiper, Daniel F

2014-01-01

369

Reference frequency transmission over optical fiber  

NASA Technical Reports Server (NTRS)

A 100-MHz reference frequency from a hydrogen maser frequency standard has been transmitted via optical fiber over a 14-km distance with a measured stability of 1.5 X 10 to the-15 power for 1000 seconds averaging time. This capability was demonstrated in a frequency distribution experiment performed in April, 1986. The reference frequency was transmitted over a single-mode fiber-optic link from Deep Space Station (DSS) 13 to DSS 12 and back. The background leading up to the experiment and the significance of stable reference frequency distribution in the Deep Space Network (DSN) is discussed. Also described are the experiment, including the fiber-optic link, the measurement method and equipment, and finally the results of the experiment.

Lutes, G.; Kirk, A.

1986-01-01

370

Wideband digital low-frequency radio receiver  

NASA Astrophysics Data System (ADS)

A wideband digital low-frequency radio receiver for scientific applications is described. The portable battery-powered instrument has the capability to record electric field strengths in the frequency range from ~4 Hz to ~400 kHz with a sampling frequency of 1 MHz, an amplitude resolution of ~35 µV and a timing accuracy of ~12 ns whilst performing continuous digital waveform recordings for several days. The instrument strictly follows a modular design such that it can be extended to higher frequencies and timing accuracy when the corresponding digital technology becomes available. The low-cost radio receiver can be developed into an interferometric network by synchronizing individual radio receivers to map the low-frequency radio sky. The first measurements of atmospheric electric fields are carried out at Exmoor National Park in Southwest England to illustrate the capabilities of the novel instrument.

Füllekrug, M.

2010-01-01

371

High frequency characterization of graphene nanoribbon interconnects  

NASA Astrophysics Data System (ADS)

Interconnects and nanoscale transmission lines are critical components in the design of nanoelectronic systems. In this letter, we study the high frequency characteristics of chemical vapor deposition (CVD) graphene nanoribbon (GNR) interconnects and radio frequency propagation in GNRs embedded in a coplanar waveguide structure up to 20 GHz. An equivalent transmission line model is proposed to characterize the GNRs in high frequency regime. The strong agreement between fitting circuit parameters and measured data suggests that our model can be used in the design of nanoscale circuits in which GNRs are used to interconnect elements in the circuits. The fabricated GNRs show fairly constant characteristic impedance at high frequencies which could be useful for radio frequency interconnect applications. Our study provides an insight into microwave behavior of GNRs for developing high speed graphene devices.

Nguyen, Phuong Duc; Cong Nguyen, Thanh; Trong Huynh, Anh; Skafidas, Efstratios

2014-09-01

372

A New Frequency Partitioning and Allocation of Subcarriers for Fractional Frequency Reuse in Mobile Communication Systems  

NASA Astrophysics Data System (ADS)

Some OFDMA-based wireless commuication systems, e. g., Wireless Broadband Internet (WiBro) or Worldwide interoperability for Microwave Access (WiMAX), support frequency reuse of 1 to maximize spectral efficiency. One of the efficient methods to reduce co-channel interference (CCI) caused by frequency reuse is fractional frequency reuse (FFR). In this paper, we propose and validate a novel frequency partitioning method and subcarrier assignment mechanism to improve system and individual capacity of mobile systems using FFR.

Han, Seung Su; Park, Jongho; Lee, Tae-Jin; Ahn, Hyun Gi; Jang, Kyunghun

373

A variable-frequency local oscillator for the frequency-hopping technique  

NASA Technical Reports Server (NTRS)

The frequency hopping technique described elsewhere requires the use of a local oscillator whose output frequency may be rapidly and accurately changed by a fixed frequency increment. Such a device, capable of producing 16 different frequencies separated by 50 kHz over the range of 35.02 to 35.77 MHz, has been built for the Urbana MST (mesosphere stratosphere troposphere) radar facility. The design and construction of that device is described and illustrated.

Stitt, G. R.; Johnson, L. J.

1986-01-01

374

Coordination of Voltage and Frequency Feedback in Load-Frequency Control Capability of Wind Turbine  

E-print Network

role and the importance of the rotor angle stability as a key criterion in power system stability/reactive power balance and subsequently participation in frequency/voltage regulation is assigned to VSWTs [2 energy stored in spinning rotor proportional to grid frequency gradient for primary frequency control

Silva, Filipe Faria Da

375

Estimating minimum allele frequencies for DNA profile frequency estimates for PCR-based loci  

Microsoft Academic Search

In order that there can be confidence that DNA profile frequency estimates will not place undue bias against a defendant, 2 methods are described for estimating minimum allele frequency bounds for PCR-based loci. One approach estimates minimum allele frequencies for VNTR and STR loci using sample size and the observed heterozygosity at a locus, while the second approach, appropriate for

B. Budowle; K. L. Monson; R. Chakraborty

1996-01-01

376

78 FR 70567 - Nationwide Use of High Frequency and Ultra High Frequency Active SONAR Technology; Final...  

Federal Register 2010, 2011, 2012, 2013, 2014

The Coast Guard (USCG) announces the availability of the Final Programmatic Environmental Assessment (PEA) for the Nationwide Use of High Frequency (HF) and Ultra High Frequency (UHF) Sound Navigation and Ranging (SONAR) Technology and Finding of No Significant Impact (FONSI). The USCG is proposing the nationwide use of active SONAR technologies that operate at frequencies of 50 kiloHertz (kHz)......

2013-11-26

377

Phase-stabilized 167 MHz Repetition Frequency Carbon Nanotube Fiber Laser Frequency Comb  

E-print Network

Phase-stabilized 167 MHz Repetition Frequency Carbon Nanotube Fiber Laser Frequency Comb Jinkang [2, 3]. Mode-locked fiber lasers using single-walled carbon nanotubes as a saturable absorber have-referenced frequency comb from a fiber laser passively modelocked by single walled carbon nanotubes. The carbon

Washburn, Brian

378

Beyond Phonotactic Frequency: Presentation Frequency Effects Word Productions in Specific Language Impairment  

ERIC Educational Resources Information Center

Phonotactic frequency effects on word production are thought to reflect accumulated experience with a language. Here we demonstrate that frequency effects can also be obtained through short-term manipulations of the input to children. We presented children with nonwords in an experiment that systematically manipulated English phonotactic frequency…

Plante, Elena; Bahl, Megha; Vance, Rebecca; Gerken, LouAnn

2011-01-01

379

164-GHz MMIC HEMT Frequency Doubler  

NASA Technical Reports Server (NTRS)

A monolithic microwave integrated circuit (MMIC) that includes a high-electron-mobility transistor (HEMT) has been developed as a prototype of improved frequency doublers for generating signals at frequencies greater than 100 GHz. Signal sources that operate in this frequency range are needed for a variety of applications, notably including general radiometry and, more specifically, radiometric remote sensing of the atmosphere. Heretofore, it has been common practice to use passive (diode-based) frequency multipliers to obtain frequencies greater than 100 GHz. Unfortunately, diode-based frequency multipliers are plagued by high DC power consumption and low conversion efficiency. Moreover, multiplier diodes are not easily integrated with such other multiplier-circuit components as amplifiers and oscillators. The goals of developing the present MMIC HEMT frequency doubler were (1) to utilize the HEMT as an amplifier to increase conversion efficiency (more precisely, to reduce conversion loss), thereby increasing the output power for a given DC power consumption or, equivalently, reducing the DC power consumption for a given output power; and (2) to provide for the integration of amplifier and oscillator components on the same chip. The MMIC frequency doubler (see Figure 1) contains an AlInAs/GaInAs/InP HEMT biased at pinch-off to make it function as a class-B amplifier (meaning that it conducts in half-cycle pulses). Grounded coplanar waveguides (GCPWs) are used as impedance-matching transmission lines. Air bridges are placed at discontinuities to suppress undesired slot electromagnetic modes. Another combination of GCPWs also serves both as a low-pass filter to suppress undesired oscillations at frequencies below 60 GHz and as a DC blocker. Large decoupling capacitors and epitaxial resistors are added in the drain and gate lines to suppress bias oscillations. At the output terminal, the fundamental frequency is suppressed by a quarter-wave open stub, which presents a short circuit at the fundamental frequency and an open circuit at the second harmonic. At an input power of 7 mW, the output power and conversion loss at an output frequency of 164 GHz were found to be 5 dBm (approximately equal to 3.2 mW) and 2 dB, respectively, with a 3-dB output-power bandwidth of 14 GHz. This is the best performance reported to date for an MMIC HEMT frequency doubler above 100 GHz.

Samoska, Lorene; Radisic, Vesna; Micovic, Miro; Hu, Ming; Janke, Paul; Ngo, Catherine; Nguyen, Loi; Morgan, Matthew

2003-01-01

380

A novel frequency method for quantitative analysis of fluorescence dye concentration by using series photodetector frequency circuit system  

Microsoft Academic Search

This study reported the frequency characteristics of series photodetector frequency circuit system for detection of fluorescence dye concentration. In the condition of the same fluorescence intensity, the series photodetector frequency circuit system with higher responsivity of photodetector had higher frequency shift. The 100MHz series photodetector frequency circuit system was applied to determine the fluorescence dye concentration of HEX by frequency

Yuh Ming Hsu; Chung Cheng Chang

2009-01-01

381

Interplay between morphology and frequency in lexical access: The case of the base frequency effect  

PubMed Central

A major issue in lexical processing concerns storage and access of lexical items. Here we make use of the base frequency effect to examine this. Specifically, reaction time to morphologically complex words (words made up of base and suffix, e.g., agree+able) typically reflects frequency of the base element (i.e., total frequency of all words in which agree appears) rather than surface word frequency (i.e., frequency of agreeable itself). We term these complex words decomposable. However, a class of words termed whole-word do not show such sensitivity to base frequency (e.g., serenity). Using an event-related MRI design, we exploited the fact that processing low-frequency words increases BOLD activity relative to high frequency ones, and examined effects of base frequency on brain activity for decomposable and whole-word items. Morphologically complex words, half high and half low base frequency, were compared to matched high and low frequency simple monomorphemic words using a lexical decision task. Morphologically complex words increased activation in left inferior frontal and left superior temporal cortices versus simple words. The only area to mirror the behavioral distinction between decomposable and whole-word types was the thalamus. Surprisingly, most frequency-sensitive areas failed to show base frequency effects. This variety of responses to frequency and word type across brain areas supports an integrative view of multiple variables during lexical access, rather than a dichotomy between memory-based access and on-line computation. Lexical access appears best captured as interplay of several neural processes with different sensitivities to various linguistic factors including frequency and morphological complexity. PMID:21167136

Vannest, Jennifer; Newport, Elissa L.; Newman, Aaron J.; Bavelier, Daphne

2011-01-01

382

Interplay between morphology and frequency in lexical access: the case of the base frequency effect.  

PubMed

A major issue in lexical processing concerns storage and access of lexical items. Here we make use of the base frequency effect to examine this. Specifically, reaction time to morphologically complex words (words made up of base and suffix, e.g., agree+able) typically reflects frequency of the base element (i.e., total frequency of all words in which agree appears) rather than surface word frequency (i.e., frequency of agreeable itself). We term these complex words decomposable. However, a class of words termed whole-word do not show such sensitivity to base frequency (e.g., serenity). Using an event-related MRI design, we exploited the fact that processing low-frequency words increases BOLD activity relative to high frequency ones, and examined effects of base frequency on brain activity for decomposable and whole-word items. Morphologically complex words, half high and half low base frequency, were compared to match high and low frequency simple monomorphemic words using a lexical decision task. Morphologically complex words increased activation in the left inferior frontal and left superior temporal cortices versus simple words. The only area to mirror the behavioral distinction between the decomposable and the whole-word types was the thalamus. Surprisingly, most frequency-sensitive areas failed to show base frequency effects. This variety of responses to frequency and word type across brain areas supports an integrative view of multiple variables during lexical access, rather than a dichotomy between memory-based access and on-line computation. Lexical access appears best captured as interplay of several neural processes with different sensitivities to various linguistic factors including frequency and morphological complexity. PMID:21167136

Vannest, Jennifer; Newport, Elissa L; Newman, Aaron J; Bavelier, Daphne

2011-02-10

383

On zero frequency magnetic fluctuations in plasmas  

SciTech Connect

A plasma sustains fluctuations of electromagnetic fields and particle density even in a thermal equilibrium and such fluctuations have a large zero frequency peak. The level of fluctuations in the plasma for a given wavelength and frequency of electromagnetic fields is calculated through the fluctuation-dissipation theorem. The frequency spectrum shows that the energy contained in this peak is complementary to the energy lost'' by the plasma cutoff effect. The level of the zero (or nearly zero) frequency magnetic is computed as {l angle}B{sup 2}{r angle}{sup 0}/ 8{pi} = 1/2{pi}{sup 3}T({omega}{sub p}/c){sup 3}, where T and {omega}{sub p} are the temperature and plasma frequency. The relation between the nonradiative and radiative fluctuations is elucidated. Both a simple collision model and a kinetic theoretic treatment are presented with essentially the same results. The size of the fluctuations is {lambda} {approximately} (c/{omega}{sub p})({eta}/{omega}){sup {1/2}}, where {eta} and {omega} are the collision frequency and the (nearly zero) frequency of magnetic fields oscillations. Perhaps the most dramatic application of the present theory, however, is to the cosmological plasma of early epoch. Implications of these magnetic fields in the early Universe are discussed. Quantum mechanical calculations are also carried out for degenerate plasmas.

Tajima, T.; Cable, S. (Texas Univ., Austin, TX (United States). Inst. for Fusion Studies); Kulsrud, R.M. (Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences)

1992-01-01

384

On zero frequency magnetic fluctuations in plasmas  

SciTech Connect

A plasma sustains fluctuations of electromagnetic fields and particle density even in a thermal equilibrium and such fluctuations have a large zero frequency peak. The level of fluctuations in the plasma for a given wavelength and frequency of electromagnetic fields is calculated through the fluctuation-dissipation theorem. The frequency spectrum shows that the energy contained in this peak is complementary to the energy ``lost`` by the plasma cutoff effect. The level of the zero (or nearly zero) frequency magnetic is computed as {l_angle}B{sup 2}{r_angle}{sup 0}/ 8{pi} = 1/2{pi}{sup 3}T({omega}{sub p}/c){sup 3}, where T and {omega}{sub p} are the temperature and plasma frequency. The relation between the nonradiative and radiative fluctuations is elucidated. Both a simple collision model and a kinetic theoretic treatment are presented with essentially the same results. The size of the fluctuations is {lambda} {approximately} (c/{omega}{sub p})({eta}/{omega}){sup {1/2}}, where {eta} and {omega} are the collision frequency and the (nearly zero) frequency of magnetic fields oscillations. Perhaps the most dramatic application of the present theory, however, is to the cosmological plasma of early epoch. Implications of these magnetic fields in the early Universe are discussed. Quantum mechanical calculations are also carried out for degenerate plasmas.

Tajima, T.; Cable, S. [Texas Univ., Austin, TX (United States). Inst. for Fusion Studies; Kulsrud, R.M. [Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences

1992-01-01

385

Frequency division using a micromechanical resonance cascade  

NASA Astrophysics Data System (ADS)

A coupled micromechanical resonator array demonstrates a mechanical realization of multi-stage frequency division. The mechanical structure consists of a set of N sequentially perpendicular microbeams that are connected by relatively weak elastic elements such that the system vibration modes are localized to individual microbeams and have natural frequencies with ratios close to 1:2:⋯:2N. Conservative (passive) nonlinear inter-modal coupling provides the required energy transfer between modes and is achieved by finite deformation kinematics. When the highest frequency beam is excited, this arrangement promotes a cascade of subharmonic resonances that achieve frequency division of 2j at microbeam j for j = 1, …, N. Results are shown for a capacitively driven three-stage divider in which an input signal of 824 kHz is passively divided through three modal stages, producing signals at 412 kHz, 206 kHz, and 103 kHz. The system modes are characterized and used to delineate the range of AC input voltages and frequencies over which the cascade occurs. This narrow band frequency divider has simple design rules that are scalable to higher frequencies and can be extended to a larger number of modal stages.

Qalandar, K. R.; Strachan, B. S.; Gibson, B.; Sharma, M.; Ma, A.; Shaw, S. W.; Turner, K. L.

2014-12-01

386

Frequency resolving power of the human's hearing.  

PubMed

Frequency resolving power (FRP) of the human's hearing was measured using the rippled noise as a probe. To examine the ripple discrimination, a phase-reversal test was used: the rippled noise was replaced by that with the opposite peak and through positions. This switch can be detected only when rippled structure of the noise spectrum is discriminated. The highest ripple density when the switch was detectable was taken as a FRP measure. Narrow-band rippled spectra were used to measure the FRP within a frequency range of 0.175 to 11 kHz. The highest resolvable ripple density in absolute measure (ripples number per kHz) was about 21/kHz at frequencies below 0.5 kHz and fell down at higher frequencies. Resolvable ripple density in relative measure (central frequency divided by ripple spacing) was about 22 relative units at frequencies above 2.8 kHz and fell down at lower frequencies. PMID:8015725

Supin AYa; Popov, V V; Milekhina, O N

1994-01-01

387

Low-Frequency Oscillations in Rotating Stars  

NASA Astrophysics Data System (ADS)

We review the properties of low-frequency oscillations in uniformly rotating stars. Rotation not only yields a new class of modes, like inertial modes and r-modes, but also significantly modifies the properties of low-frequency g-modes. For slow rotation rates where |?/?|?1, we can treat the rotation frequency ? as a small parameter for perturbation analysis, but for |\\varOmega/?|not?1, we have to properly solve the oscillation equation given as a set of partial differential equations, taking account of the effects of the Coriolis force and the centrifugal force, where ? stands for the oscillation frequency observed in the corotating frame of the star. The Coriolis force couples modes having different spherical harmonic degrees l, and the centrifugal force deforms the equilibrium structure. Rapid rotation affects the stability and the frequency of low-frequency modes. We discuss perturbation theory, the traditional approximation, linear mode coupling, series expansion methods, and weakly nonlinear calculations, which are applied to low-frequency modes in rotating stars.

Lee, Umin

388

Frequency analysis with coupled nonlinear oscillators  

NASA Astrophysics Data System (ADS)

We present a method to obtain the frequency spectrum of a signal with a nonlinear dynamical system. The dynamical system is composed of a pool of adaptive frequency oscillators with negative mean-field coupling. For the frequency analysis, the synchronization and adaptation properties of the component oscillators are exploited. The frequency spectrum of the signal is reflected in the statistics of the intrinsic frequencies of the oscillators. The frequency analysis is completely embedded in the dynamics of the system. Thus, no pre-processing or additional parameters, such as time windows, are needed. Representative results of the numerical integration of the system are presented. It is shown, that the oscillators tune to the correct frequencies for both discrete and continuous spectra. Due to its dynamic nature the system is also capable to track non-stationary spectra. Further, we show that the system can be modeled in a probabilistic manner by means of a nonlinear Fokker-Planck equation. The probabilistic treatment is in good agreement with the numerical results, and provides a useful tool to understand the underlying mechanisms leading to convergence.

Buchli, Jonas; Righetti, Ludovic; Ijspeert, Auke Jan

2008-08-01

389

Effect of laser frequency noise on fiber-optic frequency reference distribution  

NASA Technical Reports Server (NTRS)

The effect of the linewidth of a single longitude-mode laser on the frequency stability of a frequency reference transmitted over a single-mode optical fiber is analyzed. The interaction of the random laser frequency deviations with the dispersion of the optical fiber is considered to determine theoretically the effect on the Allan deviation (square root of the Allan variance) of the transmitted frequency reference. It is shown that the magnitude of this effect may determine the limit of the ultimate stability possible for frequency reference transmission on optical fiber, but is not a serious limitation to present system performance.

Logan, R. T., Jr.; Lutes, G. F.; Maleki, L.

1989-01-01

390

When does word frequency influence written production?  

PubMed Central

The aim of the present study was to explore the central (e.g., lexical processing) and peripheral processes (motor preparation and execution) underlying word production during typewriting. To do so, we tested non-professional typers in a picture typing task while continuously recording EEG. Participants were instructed to write (by means of a standard keyboard) the corresponding name for a given picture. The lexical frequency of the words was manipulated: half of the picture names were of high-frequency while the remaining were of low-frequency. Different measures were obtained: (1) first keystroke latency and (2) keystroke latency of the subsequent letters and duration of the word. Moreover, ERPs locked to the onset of the picture presentation were analyzed to explore the temporal course of word frequency in typewriting. The results showed an effect of word frequency for the first keystroke latency but not for the duration of the word or the speed to which letter were typed (interstroke intervals). The electrophysiological results showed the expected ERP frequency effect at posterior sites: amplitudes for low-frequency words were more positive than those for high-frequency words. However, relative to previous evidence in the spoken modality, the frequency effect appeared in a later time-window. These results demonstrate two marked differences in the processing dynamics underpinning typing compared to speaking: First, central processing dynamics between speaking and typing differ already in the manner that words are accessed; second, central processing differences in typing, unlike speaking, do not cascade to peripheral processes involved in response execution. PMID:24399980

Baus, Cristina; Strijkers, Kristof; Costa, Albert

2013-01-01

391

Scaling of Yb-Fiber Frequency Combs  

NASA Astrophysics Data System (ADS)

Immediately after their introduction in 1999, femtosecond laser frequency combs revolutionized the field of precision optical frequency metrology and are key elements in many experiments. Frequency combs based on femtosecond Er-fiber lasers based were demonstrated in 2005, allowing additionally rugged, compact set-ups and reliable unattended long-term operation. The introduction of Yb-fiber technology led to an dramatic improvement in fiber-comb performance in various aspects. Low-noise Yb-fiber femtosecond oscillators enabled a reduction of relative comb tooth linewidth to the sub-Hz level as well as scaling of the fundamental comb spacings up to 1 GHz. This is beneficial for any frequency-domain comb application due to the higher power per comb-mode. Many spectroscopic applications require, however, frequency combs way beyond the wavelength range accessible with broad band laser materials, so nonlinear conversion and hence higher peak intensity is required. We demonstrated power scaling of Yb-fiber frequency combs up to 80 W average power in a strictly linear chirped-pulse amplification schemes compatible with low-noise phase control. These high-power Yb-fiber-frequency combs facilitated not only the extension to the mid-IR spectral region. When coupled to a passive enhancement cavity, the average power can be further scaled to the kW-level opening new capabilities for XUV frequency combs via high-harmonic generation. All these advances of fiber-based frequency combs will trigger many novel applications both in fundamental and applied sciences. Schibli et al., Nature Photonics 2 355 (2008). Hartl et al., MF9 in Advanced Solid-State Photonics. 2009, Optical Society of America. Ruehl et al., AWC7 in Advanced Solid-State Photonics. 2010, Optical Society of America. Adler et al., Optics Letters 34 1330 (2009). Yost et al., Nature Physics 5 815 (2009).

Ruehl, Axel; Marcinkevicius, Andrius; Fermann, Martin E.; Hartl, Ingmar

2010-06-01

392

Frequency response in short thermocouple wires  

NASA Astrophysics Data System (ADS)

Theoretical expressions are derived for the steady state frequency response of a thermocouple wire. In particular, the effects of axial heat conduction are demonstrated for a nonuniform wire with unequal material properties and wire diameters across the junction. The amplitude ratio at low frequency omega approaches 0 agrees with the results of Scadron and Warshawsky (1952) for a steady state temperature distribution. Moreover, the frequency response for a nonuniform wire in the limit of infinite length l approaches infinity is shown to reduce to a simple expression that is analogous to the classic first order solution for a thermocouple wire with uniform properties. Theoretical expressions are also derived for the steady state frequency response of a supported thermocouple wire. In particular, the effects of axial heat conduction are demonstrated for both a supported one material wire and a two material wire with unequal material properties across the junction. For the case of a one material supported wire, an exact solution is derived which compares favorably with an approximate expression that only matches temperatures at the support junction. Moreover, for the case of a two material supported wire, an analytical expression is derived that closely correlates numerical results. Experimental measurements are made for the steady state frequency response of a supported thermocouple wire. In particular, the effects of axial heat conduction are demonstrated for both a supported one material wire (type K) and a two material wire (type T) with unequal material properties across the junction. The data for the amplitude ratio and phase angle are correlated to within 10 pct. with the theoretical predictions of Forney and Fralick (1991). This is accomplished by choosing a natural frequency omega sub n for the wire data to correlate the first order response at large gas temperature frequencies. It is found that a large bead size, however, will increase the amplitude ratio at low frequencies but decrease the natural frequency of the wire. The phase angle data are also distorted for imperfect junctions.

Forney, L. J.; Meeks, E. L.; Ma, J.; Fralick, G. C.

1992-10-01

393

Hearing at low and infrasonic frequencies.  

PubMed

The human perception of sound at frequencies below 200 Hz is reviewed. Knowledge about our perception of this frequency range is important, since much of the sound we are exposed to in our everyday environment contains significant energy in this range. Sound at 20-200 Hz is called low-frequency sound, while for sound below 20 Hz the term infrasound is used. The hearing becomes gradually less sensitive for decreasing frequency, but despite the general understanding that infrasound is inaudible, humans can perceive infrasound, if the level is sufficiently high. The ear is the primary organ for sensing infrasound, but at levels somewhat above the hearing threshold it is possible to feel vibrations in various parts of the body. The threshold of hearing is standardized for frequencies down to 20 Hz, but there is a reasonably good agreement between investigations below this frequency. It is not only the sensitivity but also the perceived character of a sound that changes with decreasing frequency. Pure tones become gradually less continuous, the tonal sensation ceases around 20 Hz, and below 10 Hz it is possible to perceive the single cycles of the sound. A sensation of pressure at the eardrums also occurs. The dynamic range of the auditory system decreases with decreasing frequency. This compression can be seen in the equal-loudness-level contours, and it implies that a slight increase in level can change the perceived loudness from barely audible to loud. Combined with the natural spread in thresholds, it may have the effect that a sound, which is inaudible to some people, may be loud to others. Some investigations give evidence of persons with an extraordinary sensitivity in the low and infrasonic frequency range, but further research is needed in order to confirm and explain this phenomenon. PMID:15273023

Møller, H; Pedersen, C S

2004-01-01

394

High frequency dynamic pressure calibration technique  

NASA Astrophysics Data System (ADS)

A high frequency dynamic calibration technique for pressure transducers has been developed using a siren pressure generator (SPG). The SPG is an inlet-area-modulated device generating oscillating waveforms with dynamic pressure amplitudes up to 58.6 kPa (8.5 psi) in a frequency range of 1 to 10 kHz. A description of the generator, its operating characteristics and instrumentation used for pressure amplitude and frequency measurements is given. Waveform oscillographs and spectral analysis of the pressure transducers' output signals are presented.

Davis, P. A.; Zasimowich, R. F.

395

Gauribidanur Low-Frequency Solar Spectrograph  

NASA Astrophysics Data System (ADS)

A new radio spectrograph, dedicated to observe the Sun, has been recently commissioned by the Indian Institute of Astrophysics (IIA) at the Gauribidanur Radio Observatory, about 100 km North of Bangalore. The instrument, called the Gauribidanur Low-frequency Solar Spectrograph (GLOSS), operates in the frequency range?40 - 440 MHz. Radio emission in this frequency range originates close to the Sun, typically in the radial distance range r?1.1 - 2.0 R?. This article describes the characteristics of the GLOSS and the first results.

Kishore, P.; Kathiravan, C.; Ramesh, R.; Rajalingam, M.; Barve, Indrajit V.

2014-10-01

396

Time-frequency analysis of chaotic systems  

E-print Network

We describe a method for analyzing the phase space structures of Hamiltonian systems. This method is based on a time-frequency decomposition of a trajectory using wavelets. The ridges of the time-frequency landscape of a trajectory, also called instantaneous frequencies, enable us to analyze the phase space structures. In particular, this method detects resonance trappings and transitions and allows a characterization of the notion of weak and strong chaos. We illustrate the method with the trajectories of the standard map and the hydrogen atom in crossed magnetic and elliptically polarized microwave fields.

C. Chandre; S. Wiggins; T. Uzer

2002-09-06

397

Multi-mode radio frequency device  

DOEpatents

A transponder device having multiple modes of operation, such as an active mode and a passive mode, wherein the modes of operation are selected in response to the strength of a received radio frequency signal. A communication system is also provided having a transceiver configured to transmit a radio frequency signal and to receive a responsive signal, and a transponder configured to operate in a plurality of modes and to activate modes of operation in response to the radio frequency signal. Ideally, each mode of operation is activated and deactivated independent of the other modes, although two or more modes may be concurrently operational.

Gilbert, Ronald W. (Morgan Hill, CA); Carrender, Curtis Lee (Morgan Hill, CA); Anderson, Gordon A. (Benton City, WA); Steele, Kerry D. (Kennewick, WA)

2007-02-13

398

High power radio frequency attenuation device  

DOEpatents

A resistor device for attenuating radio frequency power includes a radio frequency conductor connected to a series of fins formed of high relative magnetic permeability material. The fins are dimensional to accommodate the skin depth of the current conduction therethrough, as well as an inner heat conducting portion where current does not travel. Thermal connections for air or water cooling are provided for the inner heat conducting portions of each fin. Also disclosed is a resistor device to selectively alternate unwanted radio frequency energy in a resonant cavity.

Kerns, Quentin A. (Bloomingdale, IL); Miller, Harold W. (Winfield, IL)

1984-01-01

399

Finite frequency tomography: the checkerboard test revisited  

NASA Astrophysics Data System (ADS)

We address some consequences of the application of finite frequency theory for seismic tomography by revisiting the classical checkerboard test. We use a simple borehole-to-borehole experiment set-up in order to have complete control of the situation and to avoid complicating factors such as crustal corrections that still hamper global tomography. We are particularly interested in the feasibility of using ray-based finite frequency kernels in the inversion of travel time perturbations measured by crosscorrelation, in the cross-dependence between S wave velocity perturbations and the measured P travel times, and in the benefits of using finite-frequency theory on one or multiple frequency bands. We have done a 3D checkerboard test to assess the influence of these issues. Full-waveform synthetic seismograms are calculated using the spectral elements method up to 2 kHz maximum frequency. The computational domain extends 200 m x 120 m x 120 m and the target velocity model is a checkerboard with 12 m x 12 m x 12 m blocks of velocities 5% slower and faster than the background (homogeneous, Vp=6 km/s) model. First, we make a comparison between finite-frequency kernels calculated by ray theory with those based on the spectral elements method (adjoint technique), in terms of resolution, accuracy, but also computational cost. From synthetic seismograms calculated for the 3D checkerboard model as well as for the homogeneous model, we measure crosscorrelation travel times at different frequency bands and invert them with classical ray theory as well as with finite frequency theory. Several interesting features are highlighted in our multi-band data set, such as the wavefront healing effect. For instance, we observe that the delay times, in absolute value, are usually larger at short (0.5 ms) than long (4 ms) periods. This can be explained by the presence of the "doughnut hole" along the geometrical ray path in the sensitivity kernels, whose diameter is proportional to the period. Thus, as the period increases, the anomalies are able to "hide" inside the growing "doughnut hole". When a single frequency band is interpreted using ray theory (infinite frequency approximation), the fact that wavefront healing is not taken into account has a disastrous effect, in particular on the imaging of blocks that are somewhat smaller than the Fresnel zone. When interpreting the same data set with finite-frequency theory we do much better, especially in the center of the model where Fresnel zones are widest. Adding a range of frequencies in the inversion (i.e. taking body wave dispersion into account) significantly increases resolution.

Mercerat, E. D.; Zaroli, C.; Nolet, G.

2011-12-01

400

Frequency Response of Pressure Sensitive Paints  

NASA Technical Reports Server (NTRS)

An experimental method for measuring the frequency response of Pressure Sensitive Paints (PSP) is presented. These results lead to the development of a dynamic correction technique for PSP measurements which is of great importance to the advancement of PSP as a measurement technique. The ability to design such a dynamic corrector is most easily formed from the frequency response of the given system. An example of this correction technique is shown. In addition to the experimental data, an analytical model for the frequency response is developed from the one dimensional mass diffusion equation.

Winslow, Neal A.; Carroll, Bruce F.; Setzer, Fred M.

1996-01-01

401

Microwave Frequency Discriminator With Sapphire Resonator  

NASA Technical Reports Server (NTRS)

Cooled sapphire resonator provides ultralow phase noise. Apparatus comprises microwave oscillator operating at nominal frequency of about 8.1 GHz, plus frequency-discriminator circuit measuring phase fluctuations of oscillator output. One outstanding feature of frequency discriminator is sapphire resonator serving as phase reference. Sapphire resonator is dielectric ring resonator operating in "whispering-gallery" mode. Functions at room temperature, but for better performance, typically cooled to operating temperature of about 80 K. Similar resonator described in "Sapphire Ring Resonator for Microwave Oscillator" (NPO-18082).

Santiago, David G.; Dick, G. John

1994-01-01

402

Investigation of Wavelet-Based Enhancements to Nuclear Quadrupole Resonance Explosives Detectors  

SciTech Connect

Nuclear Quadrupole Resonance (NQR) is effective for the detection and identification of certain types of explosives such as RDX, PETN and TNT. In explosive detection, the NQR response of certain 14N nuclei present in the crystalline material is probed. The 14N nuclei possess a nuclear quadrupole moment which in the presence of an electric field gradient produces an energy level splitting which may be excited by radio-frequency magnetic fields. Pulsing on the sample with a radio signal of the appropriate frequency produces a transient NQR response which may then be detected. Since the resonant frequency is dependent upon both the quadrupole moment of the 14N nucleus and the nature of the local electric field gradients, it is very compound specific. Under DARPA sponsorship, the authors are using multiresolution methods to investigate the enhancement of operation of NQR explosives detectors used for land mine detection. For this application, NQR processing time must be reduced to less than one second. False alarm responses due to acoustic and piezoelectric ringing must be suppressed. Also, as TNT is the most prevalent explosive found in land mines, NQR detection of TNT must be made practical despite unfavorable relaxation tunes. All three issues require improvement in signal-to-noise ratio, and all would benefit from improved feature extraction. This paper reports some of the insights provided by multiresolution methods that can be used to obtain these improvements. It includes results of multiresolution analysis of experimentally observed NQR signatures for RDX responses and various false alarm signatures in the absence of explosive compounds.

Kercel, Stephen W.; Dress, William B.; Hibbs, Andrew D.; Barrall, Geoffrey A.

1998-06-01

403

Tidal frequency estimation for closed basins  

NASA Technical Reports Server (NTRS)

A method was developed for determining the fundamental tidal frequencies for closed basins of water, by means of an eigenvalue analysis. The mathematical model employed, was the Laplace tidal equations.

Eades, J. B., Jr.

1978-01-01

404

Low Frequency Noise in Nano-Devices  

E-print Network

frequency noise limits the sensitivity of sensors and up-converts to the phase noise of microwave as ballistic conductors, field effect transistors, non-volatile memories, and chemical and pressure sensors

405

Terahertz Optical Subcarrier Radio Frequency Generation  

NASA Astrophysics Data System (ADS)

There is interest to develop optically generated radio frequency signals for systems such as radar, microwave-over-fiber, and high-frequency wireless communication. Because such systems have the potential for multi-channel broadband communication. We demonstrate the generation of terahertz optical subcarrier radio frequencies in a semiconductor optical amplifier. The circuit arrangement consists of a 1550 nm pigtailed laser diode driven below its lasing threshold to generate a spectrum of spontaneous emission. The spontaneous emissions signalsare passed through a semiconductor amplifier driveninto saturation. A fraction of the output signal emerging from theamplifier is fed back into the input of the amplifier. By appropriately arranging the phases of the input and the feedback signals, optical subcarrier frequencies of up to 3.75 terahertzwere generated and measured.

Sanchez, Sonia; Donkor, Eric

2000-11-01

406

Casimir energy of frequency dependent interactions  

NASA Astrophysics Data System (ADS)

Vacuum polarization (or Casimir) energies can be straightforwardly computed from scattering data for static field configurations whose interactions with the fluctuating field are frequency independent. In effective theories, however, such interactions are typically frequency dependent. As a consequence, the relationship between scattering data and the Green's function is modified, which may or may not induce additional contributions to the vacuum polarization energy. We discuss several examples that naturally include frequency dependent interactions: (i) scalar electrodynamics with a static background potential, (ii) an effective theory that emerges from integrating out a heavy degree of freedom, and (iii) quantum electrodynamics coupled to a frequency dependent dielectric material. In the latter case, we argue that introducing dissipation as required by the Kramers-Kronig relations requires the consideration of the Casimir energy within a statistical mechanics formalism, while in the absence of dissipation, we can work entirely within field theory, using an alternative formulation of the energy density.

Graham, N.; Quandt, M.; Weigel, H.

2014-10-01

407

Developing high-frequency equities trading models  

E-print Network

The purpose of this paper is to show evidence that there are opportunities to generate alpha in the high frequency environment of the US equity market, using Principal Component Analysis (PCA hereafter) as a basis for short ...

Infantino, Leandro Rafael

2010-01-01

408

computational inverse medium scattering at fixed frequency  

E-print Network

FIXED FREQUENCY. Gang Bao? and Peijun Li† .... Using the special form of the incident wave and the test function, we then get. ?. D ..... 447–452. [13] F. Natterer, The Mathematics of Computerized Tomography, Stuttgart: Teubner, 1986. 10.

2005-12-08

409

47 CFR 87.133 - Frequency stability.  

Code of Federal Regulations, 2011 CFR

...20 Hz. 9 Where specific frequencies are not assigned to radar stations, the bandwidth occupied by the emissions of such...10 Hz. (2) All aircraft stations—20 Hz. (d) For radar transmitters, except non-pulse signal radio...

2011-10-01

410

47 CFR 87.133 - Frequency stability.  

Code of Federal Regulations, 2012 CFR

...20 Hz. 9 Where specific frequencies are not assigned to radar stations, the bandwidth occupied by the emissions of such...10 Hz. (2) All aircraft stations—20 Hz. (d) For radar transmitters, except non-pulse signal radio...

2012-10-01

411

47 CFR 87.133 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...20 Hz. 9 Where specific frequencies are not assigned to radar stations, the bandwidth occupied by the emissions of such...10 Hz. (2) All aircraft stations—20 Hz. (d) For radar transmitters, except non-pulse signal radio...

2013-10-01

412

47 CFR 101.101 - Frequency availability.  

Code of Federal Regulations, 2013 CFR

...SERVICES FIXED MICROWAVE SERVICES Technical Standards § 101.101 Frequency availability...21, 22, 24, 25, 74, 78 & 100) Notes 928-929 MAS MAS PRS 932...Fixed Satellite Service—(Part 25) Notes: F—Fixed M—Mobile...

2013-10-01

413

IHgi OPTICAL FREQUENCY STANDARD: RZCENT PROGRESS*  

E-print Network

Broadway, Boulder, CO 80303, USA E-mail: byoungC?boulder.nist.gov We report progress toward an optical*P, deuterated ammonium dihydrogen phosphate crystal for frequency doubling; AOM, acousto-optic modulator; 3

414

Frequency requirements for active earth observation sensors  

NASA Technical Reports Server (NTRS)

The foundation and rationale for the selection of microwave frequencies for active remote sensing usage and for subsequent use in determination of sharing criteria and allocation strategies for the WARC-79 are presented.

1977-01-01

415

Frequency-Dependent Electro-osmosis  

E-print Network

Electro-osmosis, the movement of a fluid with respect to solid wall when an electric field is applied tangentially to the solid wall, has been studied for many years[superscript 1]. Frequency-dependent electro-osmosis ...

Reppert, Phillip M.

2002-01-01

416

Operating frequencies for educational satellite services  

NASA Technical Reports Server (NTRS)

The factors affecting the choice of transmission frequencies are identified. These include international radio regulations, natural environment, man-made environment, hardware considerations, and interconnection and spectrum space considerations. An analysis is presented of international radio regulations with emphasis on 1963 EARC and 1971 WARC frequency allocations, powerflux density restrictions, and resolutions concerning introduction of broadcasting-satellite systems. Natural-environmental effects were divided into two categories: (1) those due to transionospheric propagation, and (2) those that can be credited to the earth's atmosphere and its constituents. The frequency dependence of the signal attenuation, signal distortion, and contributions to system noise temperature due to environmental effects are discussed, and comparisons were made for frequencies of interest. Man-made environmental effects were examined in terms of various sharing limitations as well as the indigenous noise contribution to the overall system noise.

Singh, J. P.

1971-01-01

417

Component external leakage and rupture frequency estimates  

SciTech Connect

In order to perform detailed internal flooding risk analyses of nuclear power plants, external leakage and rupture frequencies are needed for various types of components - piping, valves, pumps, flanges, and others. However, there appears to be no up-to-date, comprehensive source for such frequency estimates. This report attempts to fill that void. Based on a comprehensive search of Licensee Event Reports (LERs) contained in Nuclear Power Experience (NPE), and estimates of component populations and exposure times, component external leakage and rupture frequencies were generated. The remainder of this report covers the specifies of the NPE search for external leakage and rupture events, analysis of the data, a comparison with frequency estimates from other sources, and a discussion of the results.

Eide, S.A.; Khericha, S.T.; Calley, M.B.; Johnson, D.A.; Marteeny, M.L.

1991-11-01

418

Graphene mechanical oscillators with tunable frequency.  

PubMed

Oscillators, which produce continuous periodic signals from direct current power, are central to modern communications systems, with versatile applications including timing references and frequency modulators. However, conventional oscillators typically consist of macroscopic mechanical resonators such as quartz crystals, which require excessive off-chip space. Here, we report oscillators built on micrometre-size, atomically thin graphene nanomechanical resonators, whose frequencies can be electrostatically tuned by as much as 14%. Self-sustaining mechanical motion is generated and transduced at room temperature in these oscillators using simple electrical circuitry. The prototype graphene voltage-controlled oscillators exhibit frequency stability and a modulation bandwidth sufficient for the modulation of radiofrequency carrier signals. As a demonstration, we use a graphene oscillator as the active element for frequency-modulated signal generation and achieve efficient audio signal transmission. PMID:24240431

Chen, Changyao; Lee, Sunwoo; Deshpande, Vikram V; Lee, Gwan-Hyoung; Lekas, Michael; Shepard, Kenneth; Hone, James

2013-12-01

419

Graphene mechanical oscillators with tunable frequency  

NASA Astrophysics Data System (ADS)

Oscillators, which produce continuous periodic signals from direct current power, are central to modern communications systems, with versatile applications including timing references and frequency modulators. However, conventional oscillators typically consist of macroscopic mechanical resonators such as quartz crystals, which require excessive off-chip space. Here, we report oscillators built on micrometre-size, atomically thin graphene nanomechanical resonators, whose frequencies can be electrostatically tuned by as much as 14%. Self-sustaining mechanical motion is generated and transduced at room temperature in these oscillators using simple electrical circuitry. The prototype graphene voltage-controlled oscillators exhibit frequency stability and a modulation bandwidth sufficient for the modulation of radiofrequency carrier signals. As a demonstration, we use a graphene oscillator as the active element for frequency-modulated signal generation and achieve efficient audio signal transmission.

Chen, Changyao; Lee, Sunwoo; Deshpande, Vikram V.; Lee, Gwan-Hyoung; Lekas, Michael; Shepard, Kenneth; Hone, James

2013-12-01

420

Real-time, high frequency QRS electrocardiograph  

NASA Technical Reports Server (NTRS)

Real time cardiac electrical data are received from a patient, manipulated to determine various useful aspects of the ECG signal, and displayed in real time in a useful form on a computer screen or monitor. The monitor displays the high frequency data from the QRS complex in units of microvolts, juxtaposed with a display of conventional ECG data in units of millivolts or microvolts. The high frequency data are analyzed for their root mean square (RMS) voltage values and the discrete RMS values and related parameters are displayed in real time. The high frequency data from the QRS complex are analyzed with imbedded algorithms to determine the presence or absence of reduced amplitude zones, referred to herein as RAZs. RAZs are displayed as go, no-go signals on the computer monitor. The RMS and related values of the high frequency components are displayed as time varying signals, and the presence or absence of RAZs may be similarly displayed over time.

Schlegel, Todd T. (Inventor); DePalma, Jude L. (Inventor); Moradi, Saeed (Inventor)

2006-01-01

421

47 CFR 74.802 - Frequency assignment.  

Code of Federal Regulations, 2010 CFR

...Operations in the bands allocated for TV broadcasting, listed below, are limited to...removed from existing co-channel TV broadcast stations by not less...within the bands allocated for TV broadcasting. (1) The frequency...

2010-10-01

422

Perceptually motivated time-frequency analysis.  

PubMed

This paper describes the design of a bilinear time-frequency distribution which is a joint model of temporal and spectral masking. The distribution is used to generate temporally evolving excitation patterns of nonstationary signals and systems and is conceived as a tool for acousticians and engineers for perceptual time-frequency analysis. Distribution time and frequency resolutions are controlled by a separable kernel consisting of a set of low-pass time and frequency smoothing windows. These windows are designed by adapting existing psychoacoustic models of auditory resolution, rather than using mathematical window functions. Cross-term interference and windowing clutter are highly suppressed for the distribution, ensuring resolution accuracy over a dynamic range sufficient to encompass that of the auditory system (in excess of 100 dB). Application to the analysis of a synthetic and two real signals are included to demonstrate the approach. PMID:15704418

O'Donovan, Jonathan J; Furlong, Dermot J

2005-01-01

423

Tracing buried pipelines using multi frequency electromagnetic  

NASA Astrophysics Data System (ADS)

In this paper the application of multi frequency electromagnetic techniques to locate buried pipelines is described. The survey site has two pipelines of SUMED, one of the world chokepoints. At desert or arid areas, regular geophysical surveys usually are difficult to carry out. EM techniques could be the best among geophysical techniques to be used for this target at these conditions. The EM survey was performed using a GEM-300 multi-frequency electromagnetic profiler. It is of handheld electromagnetic induction-type that measures in-phase and quadrature terrain conductivity without electrodes or direct soil contact. An area of 60 × 15 m was surveyed, that supposed SUMED pipeline existed. Six different frequencies, typically 2025, 2875, 4125, 5875, 8425, 12,025 Hz, have been used simultaneously. The slice maps for in-phase and conductivity distribution at each frequency could help to trace the extension of the pipeline. Two pipelines were traced successfully with 20 m spacing of each others.

El-Qady, Gad; Metwaly, Mohamed; Khozaym, Ashraf

2014-06-01

424

Very-High-Frequency Resonant Boost Converters  

E-print Network

This paper presents a resonant boost topology suitable for very-high-frequency (VHF, 30-300 MHz) DC-DC power conversion. The proposed design features low device voltage stress, high efficiency over a wide load range, and ...

Perreault, David J.

425

47 CFR 101.101 - Frequency availability.  

Code of Federal Regulations, 2011 CFR

... SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES Technical...Frequency availability. Link to an amendment published...Frequencyband (MHz) Radio service Commoncarrier...Fixed Point-to-Point Microwave Service—(Part...

2011-10-01

426

47 CFR 101.107 - Frequency tolerance.  

Code of Federal Regulations, 2011 CFR

... SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES Technical...Frequency tolerance. Link to an amendment published...authorizations for new radio equipment...fixed point-to-point microwave and stations...

2011-10-01

427

Detecting deception via eyeblink frequency modulation  

PubMed Central

To assess the efficacy of using eyeblink frequency modulation to detect deception about a third party, 32 participants were sent on a mission to deliver a package to an interviewer. 17 of the participants lied to the interviewer about the details of their mock mission and 15 responded truthfully. During the interview, eyeblink frequency data were collected via electromyography and recorded video. Liars displayed eyeblink frequency suppression while lying, while truth tellers exhibited an increase in eyeblink frequency during the mission relevant questioning period. The compensatory flurry of eyeblinks following deception observed in previous studies was absent in the present study. A discriminant function using eyeblink suppression to predict lying correctly classified 81.3% of cases, with a sensitivity of 88.2% and a specificity of 73.3%. This technique, yielding a reasonable sensitivity, shows promise for future testing as, unlike polygraph, it is compatible with distance technology. PMID:24688844

2014-01-01

428

Audio classification from time-frequency texture  

E-print Network

Time-frequency representations of audio signals often resemble texture images. This paper derives a simple audio classification algorithm based on treating sound spectrograms as texture images. The algorithm is inspired ...

Slotine, Jean-Jacques E.

429

47 CFR 5.303 - Frequencies.  

Code of Federal Regulations, 2013 CFR

...COMMUNICATIONS COMMISSION GENERAL EXPERIMENTAL RADIO SERVICE Program Experimental Radio Licenses § 5.303 Frequencies. Licensees...this chapter with the additional exception that program licensees are permitted to operate in...

2013-10-01

430

Frequency comb generation in quadratic nonlinear media  

E-print Network

Optical frequency combs are nowadays routinely used tools in a wide range of scientific and technological applications. Different techniques have been developed for generating optical frequency combs, like mode-locking in lasers and third-order interactions in microresonators, or to extend their spectral capabilities, using frequency conversion processes in nonlinear materials. Here, we experimentally demonstrate and theoretically explain the onset of optical frequency combs in a simple cavity-enhanced second-harmonic-generation system, exploiting second-order nonlinear interactions. We develop an elemental model which provides a deep physical insight into the observed dynamics. Moreover, despite the different underlying physical mechanism, the proposed model is remarkably similar to the description of third-order effects in microresonators, revealing a potential variety of new effects to be explored. Finally, exploiting a nonlinearity intrinsically stronger than the third-order one, our work lays the groundw...

Ricciardi, Iolanda; Parisi, Maria; Maddaloni, Pasquale; Santamaria, Luigi; De Natale, Paolo; De Rosa, Maurizio

2014-01-01

431

Magnetic field corrections to solar oscillation frequencies  

NASA Technical Reports Server (NTRS)

It is argued that the frequencies of both the solar p- and g-modes of oscillation are modified by a magnetic field. In particular, the decrease in p-mode frequencies is attributed to a magnetic field within the solar interior evolving over the solar cycle. Field strengths at the base of the convection zone of at least 500,000 G are required.

Roberts, B.; Campbell, W. R.

1986-01-01

432

Satellite time and frequency transfer (STIFT)  

NASA Technical Reports Server (NTRS)

The concept of placing a hydrogen maser high stability clock in Earth orbit to provide accurate time and frequency comparisons worldwide to major timing centers and to a large number of radio observatory antenna sites involved in VLBI measurements was studied. The proposal was chiefly directed toward studies and initial hardware designs for time comparisons between hydrogen maser frequency standards and to modifications of the hydrogen maser for long-term use in space.

Vessot, R. F. C.

1983-01-01

433

Parametric frequency conversion in layered nonlinear media  

Microsoft Academic Search

Frequency-angular distributions of signal wave intensity are calculated for spontaneous parametric down-conversion and parametric\\u000a frequency conversion in spatially nonuniform nonlinear media. Wave reflection from interfaces is taken into account, and both\\u000a regular and irregular nonuniform distributions of second-order nonlinear susceptibility are considered. A unified approach\\u000a using a scattering matrix and a generalized Kirchhoff law is applied in calculations of spontaneous

G. Kh. Kitaeva; A. N. Penin

2004-01-01

434

Low-frequency noise in polymer transistors  

Microsoft Academic Search

The low-frequency noise (LFN) properties of field-effect transistors (FETs) using polymers as the semiconducting substrate material are investigated and explained in terms of the nonstationary mobility ? in the semiconducting polymer. In the frequency (f) range f<1 kHz it was found that 1\\/f noise prevails over other types of LFN in these polymer FETs (PFETs). The spectral density SI of

M. Jamal Deen; Ognian Marinov; S. Holdcroft; W. Woods

2001-01-01

435

Perceived time is spatial frequency dependent  

Microsoft Academic Search

We investigated whether changes in low-level image characteristics, in this case spatial frequency, were capable of generating a well-known expansion in the perceived duration of an infrequent “oddball” stimulus relative to a repeatedly-presented “standard” stimulus. Our standard and oddball stimuli were Gabor patches that differed from each other in spatial frequency by two octaves. All stimuli were equated for visibility.

C. Aaen-Stockdale; J. Hotchkiss; J. Heron; D. Whitaker

2011-01-01

436

Time and frequency technology at NIST  

NASA Technical Reports Server (NTRS)

The state of development of advanced timing systems at NIST is described. The work on cesium and rubidium frequency standards, stored-ion frequency standards, diode lasers used to pump such standards, time transfer, and methods for characterizing clocks, oscillators, and time distribution systems is presented. The emphasis is on NIST-developed technology rather than the general state of the art in this field.

Sullivan, D. B.

1994-01-01

437

Frequency-Reconfigurable Antenna Using Metasurface  

Microsoft Academic Search

A frequency-reconfigurable antenna designed using metasurface (MS) to operate at around 5 GHz is proposed and studied. The frequency-reconfigurable metasurfaced (FRMS) an- tennaiscomposedofasimplecircularpatchantennaandacircular MS with the same diameter of 40 mm (0.67 ) and implemented using planar technology. The MS is placed directly atop the patch antenna, making the FRMS antenna very compact and low pro- file with a thickness

H. L. Zhu; X. H. Liu; S. W. Cheung; T. I. Yuk

2014-01-01

438

Low Frequency Characterization of PWM Converters  

Microsoft Academic Search

Low frequency components of states or outputs in pulse-width modulation (PWM) dc and ac converters can be characterized by differential equations called describing state-space equations. These equations are derived by inspection of converter topology and use of switching functions and duty ratios. Their steady-state and small-signal dynamic solutions show how energy-storage elements in a converter\\/load system shape the frequency response

Khai D. T. Ngo

1986-01-01

439

Alewives Avoid High-Frequency Sound  

Microsoft Academic Search

We studied the response of the alewife Alosa pseudoharengus to high-frequency sound to develop an acoustic system for preventing fish from entering power plant intakes. Four groups of alewives were subjected to different frequencies of sounds ranging from 110 to 150 kHz at sound pressure levels (SPLs, given in decibels [dB] in reference to 1 ?Pa) ranging from 125 to

Dennis J. Dunning; Quentin E. Ross; Paul Geoghegan; James J. Reichle; John K. Menezes; John K. Watson

1992-01-01

440

Spectroscopy by frequency-entangled photon pairs  

SciTech Connect

Quantum spectroscopy was performed using the frequency-entangled broadband photon pairs generated by spontaneous parametric down-conversion. An absorptive sample was placed in front of the idler photon detector, and the frequency of signal photons was resolved by a diffraction grating. The absorption spectrum of the sample was measured by counting the coincidences, and the result is in agreement with the one measured by a conventional spectrophotometer with a classical light source.

Yabushita, Atsushi; Kobayashi, Takayoshi [Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST) and Department of Physics, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 (Japan)

2004-01-01

441

The calculation of molecular Eigen-frequencies  

NASA Technical Reports Server (NTRS)

A method of determining molecular eigen-frequencies based on the function of Einstein expressing the variation of the atomic heat of various elements is proposed. It is shown that the same equation can be utilized to calculate both atomic heat and optically identifiably eigen-frequencies - at least to an order of magnitude - suggesting that in both cases the same oscillating structure is responsible.

Lindemann, F. A.

1984-01-01

442

Improved Linear-Ion-Trap Frequency Standard  

NASA Technical Reports Server (NTRS)

Improved design concept for linear-ion-trap (LIT) frequency-standard apparatus proposed. Apparatus contains lengthened linear ion trap, and ions processed alternately in two regions: ions prepared in upper region of trap, then transported to lower region for exposure to microwave radiation, then returned to upper region for optical interrogation. Improved design intended to increase long-term frequency stability of apparatus while reducing size, mass, and cost.

Prestage, John D.

1995-01-01

443

Different frequencies should be prescribed for different high frequency chest compression machines.  

PubMed

High frequency chest compression (HFCC) is used for treatment and prevention of the lung diseases characterized by impaired mucus clearance and/or cough, where patients are at risk for acquiring acute bronchitis or pneumonia. The HFCC treatment frequencies may be prescribed according to the manufacturers' generic guidelines or may be determined for each individual patient by a "tuning" method that measures, at the mouth, the air volume displacement and the associated airflows produced at each frequency. Tuning is performed while the patient is breathing normally during the HFCC system operation. After measurements for several breaths at one frequency have been collected, the program randomly selects and measures another frequency until the entire frequency range of the machine being tuned has been sampled. Frequencies range from 6 to 21 Hz for the sine waveform machines and from 6 to 25 Hz for the square waveform machines. Each group of flow signals is digitized and analyzed by the program. For each frequency, the HFCC flow velocities and volumes are computed and averaged. These average flows and volumes are rank ordered; the three frequencies with the highest flows and the three frequencies producing the largest volumes are selected for prescription. If the same frequency is selected as one of the three best frequencies for both flow and volume, the next ranked frequency is selected randomly for flow or volume. Significant differences exist between patients and HFCC machines. In a series of 100 cystic fibrosis (CF) patients with varying degrees of lung disease, we found that the best-ranked frequencies varied from patient to patient and did not correlate with patients' age, gender, height, weight, or spirometry parameters. With the sine waveform, the highest HFCC airflows were between 13 and 20 Hz 82% of the time and the largest HFCC volumes were between 6 and 10 Hz 83% of the time. With the square waveform, both the highest average HFCC flow rates and the largest volume average HFCC displacements were between 6 and 14 Hz. Nevertheless, in this sample of 100 consecutive tunings, every frequency from 6 and 20 Hz was a best frequency for at least one patient. These findings provide the basis for recommending a tuning protocol to be used for prescribing frequencies with the various HFCC machines, because they are different from one another. If a patient's tuning cannot be done, it may be useful to prescribe the best frequencies based on the waveform machine he or she uses. PMID:16941931

Milla, Carlos E; Hansen, Leland G; Warwick, Warren J

2006-01-01

444

Black phosphorus radio-frequency transistors.  

PubMed

Few-layer and thin film forms of layered black phosphorus (BP) have recently emerged as a promising material for applications in high performance nanoelectronics and infrared optoelectronics. Layered BP thin films offer a moderate bandgap of around 0.3 eV and high carrier mobility, which lead to transistors with decent on-off ratios and high on-state current densities. Here, we demonstrate the gigahertz frequency operation of BP field-effect transistors for the first time. The BP transistors demonstrated here show respectable current saturation with an on-off ratio that exceeds 2 × 10(3). We achieved a current density in excess of 270 mA/mm and DC transconductance above 180 mS/mm for hole conduction. Using standard high frequency characterization techniques, we measured a short-circuit current-gain cutoff frequency fT of 12 GHz and a maximum oscillation frequency fmax of 20 GHz in 300 nm channel length devices. BP devices may offer advantages over graphene transistors for high frequency electronics in terms of voltage and power gain due to the good current saturation properties arising from their finite bandgap, thus can be considered as a promising candidate for the future high performance thin film electronics technology for operation in the multi-GHz frequency range and beyond. PMID:25347787

Wang, Han; Wang, Xiaomu; Xia, Fengnian; Wang, Luhao; Jiang, Hao; Xia, Qiangfei; Chin, Matthew L; Dubey, Madan; Han, Shu-jen

2014-11-12

445

Extremely high frequency RF effects on electronics.  

SciTech Connect

The objective of this work was to understand the fundamental physics of extremely high frequency RF effects on electronics. To accomplish this objective, we produced models, conducted simulations, and performed measurements to identify the mechanisms of effects as frequency increases into the millimeter-wave regime. Our purpose was to answer the questions, 'What are the tradeoffs between coupling, transmission losses, and device responses as frequency increases?', and, 'How high in frequency do effects on electronic systems continue to occur?' Using full wave electromagnetics codes and a transmission-line/circuit code, we investigated how extremely high-frequency RF propagates on wires and printed circuit board traces. We investigated both field-to-wire coupling and direct illumination of printed circuit boards to determine the significant mechanisms for inducing currents at device terminals. We measured coupling to wires and attenuation along wires for comparison to the simulations, looking at plane-wave coupling as it launches modes onto single and multiconductor structures. We simulated the response of discrete and integrated circuit semiconductor devices to those high-frequency currents and voltages, using SGFramework, the open-source General-purpose Semiconductor Simulator (gss), and Sandia's Charon semiconductor device physics codes. This report documents our findings.

Loubriel, Guillermo Manuel; Vigliano, David; Coleman, Phillip Dale; Williams, Jeffery Thomas; Wouters, Gregg A.; Bacon, Larry Donald; Mar, Alan

2012-01-01

446

Voluntary attention increases perceived spatial frequency  

PubMed Central

Voluntary covert attention selects relevant sensory information for prioritized processing. The behavioral and neural consequences of such selection have been extensively documented, but its phenomenology has received little empirical investigation. Involuntary attention increases perceived spatial frequency (Gobell & Carrasco, 2005), but involuntary attention can differ from voluntary attention in its effects on performance in tasks mediated by spatial resolution (Yeshurun, Montagna, & Carrasco, 2008). Therefore, we ask whether voluntary attention affects the subjective appearance of spatial frequency—a fundamental dimension of visual perception underlying spatial resolution. We used a demanding rapid serial visual presentation task to direct voluntary attention and measured perceived spatial frequency at the attended and unattended locations. Attention increased the perceived spatial frequency of suprathreshold stimuli and also improved performance on a concurrent orientation discrimination task. In the control experiment, we ruled out response bias as an alternative account by using a lengthened interstimulus interval, which allows observers to disengage attention from the cued location. In contrast to the main experiment, the observers showed neither increased perceived spatial frequency nor improved orientation discrimination at the attended location. Thus, this study establishes that voluntary attention increases perceived spatial frequency. This phenomenological consequence links behavioral and neurophysiological studies on the effects of attention. PMID:20675797

Abrams, Jared; Barbot, Antoine; Carrasco, Marisa

2010-01-01

447

Stabilizing Microwave Frequency of a Photonic Oscillator  

NASA Technical Reports Server (NTRS)

A scheme for stabilizing the frequency of a microwave signal is proposed that exploits the operational characteristics of a coupled optoelectronic oscillator (COEO) and related optoelectronic equipment. An essential element in the scheme is a fiber mode-locked laser (MLL), the optical frequency of which is locked to an atomic transition. In this scheme, the optical frequency stability of the mode-locked laser is transferred to that of the microwave in the same device. Relative to prior schemes for using wideband optical frequency comb to stabilize microwave signals, this scheme is simpler and lends itself more readily to implementation in relatively compact, rugged equipment. The anticipated development of small, low-power, lightweight, highly stable microwave oscillators based on this scheme would afford great benefits in communication, navigation, metrology, and fundamental sciences. COEOs of various designs, at various stages of development, in some cases called by different names, have been described in a number of prior NASA Tech Briefs articles. A COEO is an optoelectronic apparatus that generates both short (picosecond) optical pulses and a steady microwave signal having an ultrahigh degree of spectral purity. The term "coupled optoelectronic" in the full name of such an apparatus signifies that its optical and electronic oscillations are coupled to each other in a single device. The present frequency-stabilization scheme is best described indirectly by describing the laboratory apparatus used to demonstrate it. The apparatus (see figure) includes a COEO that generates a comb-like optical spectrum, the various frequency components of which interfere, producing short optical pulses. This spectrum is centered at a nominal wavelength of 1,560 nm. The spectrum separation of this comb is about 10 GHz, as determined primarily by the length of an optical loop and the bandpass filter in the microwave feedback loop. The optical loop serves as microwave resonator having a very high value of the resonance quality factor (Q). The optical frequency of MLL is then stabilized by locking it to an atomic transition as described below. The COEO contains a tunable 1-nm band-pass optical filter and a piezoelectric-transducer (PZT) drum over which a stretch of fiber is wound. The 1-nm-wide pass band of the filter provides coarse tuning to overlap the frequency comb with the atomic transition frequency. Controlled stretching of the fiber by means of the PZT drum can be used in conjunction with temperature control for locking the laser frequency. To reference to an atomic resonance at 780 nm in this demonstration setup, the optical output of the COEO at 1,560 nm is fed through an erbium-doped-fiber amplifier (EDFA) to a frequency doubler in the form of a periodically poled lithium niobate (PPLN) crystal. The frequency-doubled output is combined with the output of a separate frequency-stabilized diode laser at a photodetector. As described thus far, the two 780-nm laser subsystems are nominally independent of each other and can, therefore, operate at different frequencies. Hence, at the photodetector, the two laser beams interfere, so that the output of the photodetector includes a beat note (a component at the difference between the two laser frequencies).

Maleki, Lute; Yu, Nan; Tu, Meirong

2006-01-01

448

Long term comparison of two fiber based frequency comb systems  

NASA Astrophysics Data System (ADS)

Mode-locked erbium-doped fiber lasers are ideal comb generators for optical frequency metrology. We compare two fiber frequency combs by measuring an optical frequency independently with both combs and comparing their results. The two frequency measurements agree within 6×10-16. This is to our knowledge the first direct comparison between two fiber based frequency combs.

Kubina, Philipp; Adel, Peter; Adler, Florian; Grosche, Gesine; Hänsch, Theodor W.; Holzwarth, Ronald; Leitenstorfer, Alfred; Lipphardt, Burghard; Schnatz, Harald

2005-02-01

449

The VLA Low Frequency Sky Survey  

NASA Astrophysics Data System (ADS)

We present an overview of the ongoing VLA Low-frequency Sky Survey (VLSS, formerly known as 4MASS). The VLSS will map an area of 9.1 sr covering the entire sky above a declination of -30 degrees (or 75% of the full sky), at a frequency of 74 MHz (4 meter wavelength) with an unprecedented combination of sensitivity and resolution at this low frequency. The observational challenges at this wavelength include radio frequency interference (RFI), ionospheric phase distortions and a large field of view filled with sources. These challenges have been surmounted by a variety of new algorithms. The principle data products from the survey will be a set of publicly available images along with a source catalog of approximately 80,000 objects. Thus we will create an online virtual observatory at this previously unexplored frequency which will complement other major surveys at higher frequencies such as the NVSS. From these data, statistically useful samples of extragalactic and Galactic objects, such as high redshift radio galaxies, galaxy clusters, supernova remnants and pulsars can be assembled for further study. In addition, this survey will provide a crucial calibration grid for use with next generation of large low frequency telescopes such as LWA and LOFAR. The observations are now roughly 50% complete, and we expect to observe the majority of the remaining fields by spring 2005. Current data products and more information are available on our website (URL:http://lwa.nrl.navy.mil/VLSS). Basic research in radio astronomy at the Naval Research Laboratory is supported by the office of Naval Research.

Cohen, A. S.; Lane, W. M.; Kassim, N. E.; Lazio, T. J. W.; Cotton, W. D.; Condon, J. J.; Perley, R. A.; Erickson, W. C.

2005-12-01

450

Dual-frequency ADCPs measuring turbidity  

NASA Astrophysics Data System (ADS)

A pair of self-contained acoustic Doppler current profilers (SC-ADCPs) operating with different frequencies were moored on a muddy sea bottom at about 20 m depth in the Bay of Vilaine off the French Atlantic coast. With their acoustic beams oriented upwards, the SC-ADCPs ensonified most of the water column. The results of several months of in situ recorded echo intensity data spanning 2 years (2003 to 2004) from the dual-frequency ADCPs are presented in this paper. The aim was to estimate suspended particle mass concentration and mean size. A concentration index CI is proposed for the estimation of particle concentration. Based on theory the CI—unlike the volume backscatter strength—does not depend on particle size. Compared with in situ optical data, the CI shows reasonable precision but not increased with respect to that of the highest-frequency backscatter strength. Concerning the mean particle size, despite a lack of quantitative validation with optical particle-size measurements, the method yielded a qualitative discrimination of mineral (small) and organic (large) particles. This supports the potential of dual-frequency ADCPs to quantitatively determine particle size. A cross-calibration of the transducers of each ADCP shows that a specific component of the precision of the backscatter strength measured by ADCP depends on the acoustic frequency, the cell thickness and the ensemble integration time. Based on these results, the use of two ADCPs operating with distinctly different frequencies (two octaves apart) or a single dual-frequency ADCP is recommended.

Jourdin, Frédéric; Tessier, Caroline; Le Hir, Pierre; Verney, Romaric; Lunven, Michel; Loyer, Sophie; Lusven, André; Filipot, Jean-François; Lepesqueur, Jérémy

2014-08-01

451

Frequency response of lift control in Drosophila.  

PubMed

The flight control responses of the fruitfly represent a powerful model system to explore neuromotor control mechanisms, whose system level control properties can be suitably characterized with a frequency response analysis. We characterized the lift response dynamics of tethered flying Drosophila in presence of vertically oscillating visual patterns, whose oscillation frequency we varied between 0.1 and 13 Hz. We justified these measurements by showing that the amplitude gain and phase response is invariant to the pattern oscillation amplitude and spatial frequency within a broad dynamic range. We also showed that lift responses are largely linear and time invariant (LTI), a necessary condition for a meaningful analysis of frequency responses and a remarkable characteristic given its nonlinear constituents. The flies responded to increasing oscillation frequencies with a roughly linear decrease in response gain, which dropped to background noise levels at about 6 Hz. The phase lag decreased linearly, consistent with a constant reaction delay of 75 ms. Next, we estimated the free-flight response of the fly to generate a Bode diagram of the lift response. The limitation of lift control to frequencies below 6 Hz is explained with inertial body damping, which becomes dominant at higher frequencies. Our work provides the detailed background and techniques that allow optomotor lift responses of Drosophila to be measured with comparatively simple, affordable and commercially available techniques. The identification of an LTI, pattern velocity dependent, lift control strategy is relevant to the underlying motion computation mechanisms and serves a broader understanding of insects' flight control strategies. The relevance and potential pitfalls of applying system identification techniques in tethered preparations is discussed. PMID:20462877

Graetzel, Chauncey F; Nelson, Bradley J; Fry, Steven N

2010-11-01

452

Analysis and suppression of nonlinear frequency modulation in an optical frequency-domain reflectometer.  

PubMed

A new method for monitoring the nonlinearities perturbing the optical frequency sweep in high speed tunable laser sources is presented. The swept-frequency monitoring system comprises a Mach-Zehnder interferometer and simple signal processing steps. It has been implemented in a coherent optical frequency domain reflectometer which allowed to drastically reduce the effects of nonlinear sweep, resulting to a spatial resolution enhancement of 30 times. PMID:19333353

Yuksel, Kivilcim; Wuilpart, Marc; Mégret, Patrice

2009-03-30

453

Blade frequency program for nonuniform helicopter rotors, with automated frequency search  

NASA Technical Reports Server (NTRS)

A computer program for determining the natural frequencies and normal modes of a lumped parameter model of a rotating, twisted beam, with nonuniform mass and elastic properties was developed. The program is used to solve the conditions existing in a helicopter rotor where the outboard end of the rotor has zero forces and moments. Three frequency search methods have been implemented. Including an automatic search technique, which allows the program to find up to the fifteen lowest natural frequencies without the necessity for input estimates of these frequencies.

Sadler, S. G.

1972-01-01

454

A sensitivity analysis of frequency selective surface based metamaterial at THz frequency  

NASA Astrophysics Data System (ADS)

This work presents a sensitivity analysis for the resonance frequency and bandwidth of dielectric supported Split Ring Resonator (SRR) metmaterial in THz frequency. The different designed parameters have been considered and their parametric sensitivities on resonance frequency and on bandwidth have been analyzed. The finite integral technique is used to simulate the structure and the numerical techniques are used to obtain the resonance frequency and bandwidth sensitivities as a function of the designed parameters. The analysis for sensitivity of the scattering parameters of metamaterial is especially very important in THz frequency range. The resonance frequency and the bandwidth are the main characteristics of a resonator Frequency Selective Surface (FSS). The development of FSS in mm-wave frequency range can be simplified by the knowledge of the sensitivity of their main characteristics as a function of the considered physical parameters. The FSS structure considered in this section is the square split ring resonator with copper strip lines backed by Roger 4003 C dielectric substrate. The FSS structure is simulated by using CST Microwave Studio transient solver. The resonance frequency and the bandwidth sensitivities as function structural parameters of FSS are obtained by using the simulation data. In this analysis, normal incident TE modes are considered.

Islam, S.; Stiens, J.; Vounckx, R.

2010-04-01

455

Time-frequency analysis of Transitory/Permanent frequency decrease in civil engineering structures during earthquakes  

E-print Network

The analysis of strong motion recordings in structures is crucial to understand the damaging process during earthquakes. A very precise time-frequency representation, the reassigned smoothed pseudo-Wigner-Ville method, allowed us to follow the variation of the Millikan Library (California) and the Grenoble City Hall building (France) resonance frequencies during earthquakes. Under strong motions, a quick frequency drop, attributed to damage of the soil-structure system, followed by a slower increase is found. However, in the case of weak earthquakes, we show that frequency variations come from the ground motion spectrum and cannot be interpreted in terms of change of the soil-structure system.

Michel, Clotaire

2008-01-01

456

Supersonic Free-jet Quantum Cascade Laser Measurements of v4 for CF3(35)Cl and CF3(37)Cl and FTS Measurements from 400 to 1260 cm-1  

SciTech Connect

A supersonic free-jet spectrum of the ?4 band of CF3Cl has been measured using a quantum cascade laser system. Those measurements were combined with a low temperature (-67 C) FTS spectrum of the region 1060 to 1260 cm-1 and with room temperature FTS measurements down to 400 cm-1 to give improved values for the rovibrational constants for the v1, v2, v3, 2v3, 2v5, v4, and v5 states of CF335Cl and CF337Cl. The principal perturbation found by earlier investigators in the v1 band is treated as a very weak Coriolis interaction at several avoided crossings of the rotational levels of the v1 state and the 2v5 state with kl < 0. None of the other vibrational states showed any signs of perturbations. With these new measurements we now have high resolution data on all of the fundamental vibrational states except v6.

Kelly, James F.; Maki, Arthur; Blake, Thomas A.; Sams, Robert L.

2008-11-01

457

High frequency inductive lamp and power oscillator  

DOEpatents

A high frequency inductively coupled electrodeless lamp includes an excitation coil with an effective electrical length which is less than one half wavelength of a driving frequency applied thereto, preferably much less. The driving frequency may be greater than 100 MHz and is preferably as high as 915 MHz. Preferably, the excitation coil is configured as a non-helical, semi-cylindrical conductive surface having less than one turn, in the general shape of a wedding ring. At high frequencies, the current in the coil forms two loops which are spaced apart and parallel to each other. Configured appropriately, the coil approximates a Helmholtz configuration. The lamp preferably utilizes an bulb encased in a reflective ceramic cup with a pre-formed aperture defined therethrough. The ceramic cup may include structural features to aid in alignment and/or a flanged face to aid in thermal management. The lamp head is preferably an integrated lamp head comprising a metal matrix composite surrounding an insulating ceramic with the excitation integrally formed on the ceramic. A novel solid-state oscillator preferably provides RF power to the lamp. The oscillator is a single active element device capable of providing over 70 watts of power at over 70% efficiency. Various control circuits may be employed to match the driving frequency of the oscillator to a plurality of tuning states of the lamp.

MacLennan, Donald A. (Gaithersburg, MD); Turner, Brian P. (Damascus, MD); Dolan, James T. (Frederick, MD); Kirkpatrick, Douglas A. (Great Falls, VA); Leng, Yongzhang (Damascus, MD)

2000-01-01

458

High frequency inductive lamp and power oscillator  

DOEpatents

A high frequency inductively coupled electrodeless lamp includes an excitation coil with an effective electrical length which is less than one half wavelength of a driving frequency applied thereto, preferably much less. The driving frequency may be greater than 100 MHz and is preferably as high as 915 MHz. Preferably, the excitation coil is configured as a non-helical, semi-cylindrical conductive surface having less than one turn, in the general shape of a wedding ring. At high frequencies, the current in the coil forms two loops which are spaced apart and parallel to each other. Configured appropriately, the coil approximates a Helmholtz configuration. The lamp preferably utilizes an bulb encased in a reflective ceramic cup with a pre-formed aperture defined therethrough. The ceramic cup may include structural features to aid in alignment and I or a flanged face to aid in thermal management. The lamp head is preferably an integrated lamp head comprising a metal matrix composite surrounding an insulating ceramic with the excitation integrally formed on the ceramic. A novel solid-state oscillator preferably provides RF power to the lamp. The oscillator is a single active element device capable of providing over 70 watts of power at over 70% efficiency. Various control circuits may be employed to adjust the driving frequency of the oscillator.

MacLennan, Donald A. (Gaithersburg, MD); Dymond, Jr., Lauren E. (North Potomac, MD); Gitsevich, Aleksandr (Montgomery Village, MD); Grimm, William G. (Silver Spring, MD); Kipling, Kent (Gaithersburg, MD); Kirkpatrick, Douglas A. (Great Falls, VA); Ola, Samuel A. (Silver Spring, MD); Simpson, James E. (Gaithersburg, MD); Trimble, William C. (Columbia, MD); Tsai, Peter (Olney, MD); Turner, Brian P. (Damascus, MD)

2001-01-01

459

Orbital and epicyclic frequencies of Maclaurin spheroids  

NASA Astrophysics Data System (ADS)

We present analytical formulae for the orbital and epicyclic frequencies in orbits around Maclaurin spheroids in Newtonian gravity. The Laplace equation for the gravitational potential implies that the orbital frequency squared is the arithmetic mean of the squares of the epicyclic frequencies, ? _r^2 + ? _z^2 = 2? _o^2. The radial epicyclic frequency has a maximum at radius r=?{2}ae for spheroid ellipticities e>1/?{2}, while for e = 0.834 583 18 it vanishes at the stellar equator (at r = a). For still larger ellipticities the innermost stable circular orbit (ISCO) is separated from the surface of the spheroid by a gap and has radius rms = 1.198 203 ae. The vertical epicyclic frequency is always larger than the orbital one, and always by a factor of ?{2} in the marginally stable orbit. The presence of periastron motion, nodal precession (whose sense is the same as in retrograde orbits in the Kerr metric) and of the ISCO makes the properties of orbital motion around Maclaurin spheroids analogous to those in the Kerr metric. We find that the condition for the existence of circular orbits in test-particle motion is ? _r^2 + ? _z^2 >0, equally for the Maclaurin spheroid and for the Kerr metric.

Klu?niak, W.; Rosi?ska, D.

2013-10-01

460

Wave Dissipation Formulations in Frequency Domain Models  

NASA Astrophysics Data System (ADS)

Incorporation of wave dissipation due to breaking in both time-domain and frequency domain models have long been a subject of study. Until recently, the formulation of wave breaking in frequency domain models have been based on lumped-parameter dissipation models based on a Rayleigh distribution function for the wave heights in the surf zone (Battjes and Janssen, 1978; Thornton and Guza, 1983). Modifications to improve the dissipation model include allowing for nonlinear energy transfer (Mase and Kirby, 1992), which leads to improvements in predictions of the skewness and asymmetry. Bredmose (2004) show how time- domain wave breaking models can be included in a frequency domain version of the Boussinesq model using a time-domain inversion of the roller model. However, frequency domain versions of the Boussinesq model tend to perform poorly until the waves are close to breaking. In this study, we will show how time-domain wave breaking models can be included in frequency domain models that are based on the mild-slope formulation. We will then compare the results of using such a breaking model to the empirical bulk-dissipation formulation. Comparisons will include wave height distributions, skewness, and asymmetry. We will also discuss implications of using different breaking models on sediment transport.

Veeramony, J.; Kaihatu, J. M.

2008-12-01

461

Multi-frequency axial transmission bone ultrasonometer.  

PubMed

The last decade has seen a surge in the development of axial transmission QUS (Quantitative UltraSound) technologies for the assessment of long bones using various modes of acoustic waves. The condition of cortical bones and the development of osteoporosis are determined by numerous mechanical, micro-structural, and geometrical or macro-structural bone properties like hardness, porosity and cortical thickness. Such complex manifestations of osteoporosis require the evaluation of multiple parameters with different sensitivities to the various properties of bone that are affected by the disease. This objective may be achieved by using a multi-frequency ultrasonic examination The ratio of the acoustic wavelength to the cortical thickness can be changed by varying the frequency of the ultrasonic pulse propagating through the long bone that results in the change in composition of the induced wave comprised of a set of numerous modes of guided, longitudinal, and surface acoustic waves. The multi-frequency axial transmission QUS method developed at Artann Laboratories (Trenton, NJ) is implemented in the Bone Ultrasonic Scanner (BUSS). In the current version of the BUSS, a train of ultrasonic pulses with 60, 100, 400, 800, and 1200 kHz frequencies is used. The developed technology was tested on a variety of bone phantoms simulating normal, osteopenic, and osteoporotic bones. The results of this study confirm the feasibility of the multi-frequency approach for the assessment of the processes leading to osteoporosis. PMID:24206675

Tatarinov, Alexey; Egorov, Vladimir; Sarvazyan, Noune; Sarvazyan, Armen

2014-07-01

462

The development of spatial frequency discrimination.  

PubMed

We compared thresholds for discriminating spatial frequency for children aged 5, 7, and 9 years, and adults at two baseline spatial frequencies (1 and 3 cpd). In Experiment 1, the minimum change from baseline necessary to detect a change in spatial frequency from either baseline decreased with age from 34% in 5-year-olds to 11% in 7-year-olds, 8% in 9-year-olds, and 6% in adults. The data were best fit by an exponential function reflecting the rapid improvement in thresholds between 5 and 7 years of age and more gradual improvement thereafter (r(2) = 0.50, p < 0.0001). In Experiment 2, 5-year-olds' thresholds were higher than those of adults, even when memory demands were eliminated by presenting the two spatial frequencies side by side for an unlimited time. The pattern of development for sensitivity to spatial frequency (this study) resembles those for the development of sensitivity to orientation (T. L. Lewis, S. E. Chong, & D. Maurer, 2009) and contrast (D. Ellemberg, T. L. Lewis, C. H. Lui, & D. Maurer, 1999). The similar patterns are consistent with theories of common underlying mechanisms in primary visual cortex (A. Vincent & D. Regan, 1995; W. Zhu, M. Shelley, & R. Shapley, 2008) and suggest that those mechanisms continue to develop throughout childhood. PMID:21196509

Patel, Ashna; Maurer, Daphne; Lewis, Terri L

2010-01-01

463

Frequency-agile wireless sensor networks  

NASA Astrophysics Data System (ADS)

Our goal was to demonstrate a wireless communications system capable of simultaneous, high speed data communications from a variety of sensors. We have previously reported on the design and application of 2 KHz data logging transceiver nodes, however, only one node may stream data at a time, since all nodes on the network use the same communications frequency. To overcome these limitations, second generation data logging transceivers were developed with software programmable radio frequency (RF) communications. Each node contains on-board memory (2 Mbytes), sensor excitation, instrumentation amplifiers with programmable gains & offsets, multiplexer, 16 bit A/D converter, microcontroller, and frequency agile, bi-directional, frequency shift keyed (FSK) RF serial data link. These systems are capable of continuous data transmission from 26 distinct nodes (902-928 MHz band, 75 kbaud). The system was demonstrated in a compelling structural monitoring application. The National Parks Service requested a means for continual monitoring and recording of sensor data from the Liberty Bell during a move to a new location (Philadelphia, October 2003). Three distinct, frequency agile, wireless sensing nodes were used to detect visible crack shear/opening micromotions, triaxial accelerations, and hairline crack tip strains. The wireless sensors proved to be useful in protecting the Liberty Bell.

Arms, Steven W.; Townsend, Christopher P.; Churchill, David L.; Hamel, Michael J.; Galbreath, Jacob H.; Mundell, Steven W.

2004-07-01

464

Clinical Usefulness of ECG Frequency Spectrum Analysis  

PubMed Central

The QRS portion of the electrocardiogram of the complexes of patients were sampled at the rate of 1024 samples per second. The power spectral densities were calculated using the fast Fourier transform on a quarter of a second portion of an FM recorded ECG, centered on the peak of the R wave. It was discovered that in a typical QRS complex of normal duration, virtually all of the power is contained in frequencies below 30 Hz with peak power occurring in the range of 4 to 12 Hz. It should be noted that the frequency corresponding to the location of the peak is the heart rate of the patient. Furthermore, most noticeably, premature ventricular contractions typically contain less high frequency power than normal beats, with virtually all the power contained in frequencies below 12 Hz with peak power located at about 4 Hz. Finally, notches in some QRS complexes was associated with a broadened distribution of power in the power spectral density even though the tail from 30-100 Hz contained relatively less power than that contained in the frequency band below 30 Hz.

Murthy, Vrudhula K.; Grove, Thomas M.; Harvey, George A.; Haywood, L. Julian

1978-01-01

465

Low Frequency Interstellar Scattering and Pulsar Observations  

NASA Technical Reports Server (NTRS)

Radio astronomy at frequencies from 2 to 30 MHz challenges time tested methods for extracting usable information from observations. One fundamental reason for this is that propagation effects due to the magnetoionic ionosphere, interplanetary medium, and interstellar matter (ISM) increase strongly with wavelength. The problems associated with interstellar scattering off of small scale irregularities in the electron density are addressed. What is known about interstellar scattering is summarized on the basis of high frequency observations, including scintillation and temporal broadening of pulsars and angular broadening of various galactic and extragalactic radio sources. Then those high frequency phenomena are addressed that are important or detectable at low frequencies. The radio sky becomes much simpler at low frequencies, most pulsars will not be seen as time varying sources, intensity variations will be quenched or will occur on time scales much longer than a human lifetime, and many sources will be angularly broadened and/or absorbed into the noise. Angular broadening measurements will help delineate the galactic distribution and power spectrum of small scale electron density irregularities.

Cordes, James M.

1992-01-01

466

The frequency distribution of mechanically stable packings  

NASA Astrophysics Data System (ADS)

We generate mechanically stable packings of soft particles in 2D using an algorithm in which we successively grow or shrink purely repulsive grains and minimize the total energy at each step until particles are just at contact and at rest. We focus on small systems of up to 20 particles, and thus we are able to enumerate nearly all of the possible mechanically stable packings. Complete enumeration allows us to factorize the probability distribution, P(?), for obtaining a mechanically stable state at packing fraction ? into algorithm-dependent and independent contributions, ?(?) and ?(?). ?(?) is the probability density to obtain a distinct mechanically stable packing at ?, while ?(?) is the frequency with which each distinct state occurs. We found several remarkable features of the frequency distribution. For example, the frequency averaged over bins of width d? grows exponentially with increasing packing fraction. In addition, distinct mechanically stable packings within d? can occur with frequencies that differ by orders of magnitude. We also add thermal fluctuations to these stable configurations to understand the relationship between the frequency and shape of the potential landscape near the stable configurations.

Gao, Guo-Jie; Blawzdziewicz, Jerzy; O'Hern, Corey

2006-03-01

467

Reconfigurable Ring Filter with Controllable Frequency Response  

PubMed Central

Reconfigurable ring filter based on single-side-access ring topology is presented. Using capacitive tuning elements, the electrical length of the ring can be manipulated to shift the nominal center frequency to a desired position. A synthesis is developed to determine the values of the capacitive elements. To show the advantage of the synthesis, it is applied to the reconfigurable filter design using RF lumped capacitors. The concept is further explored by introducing varactor-diodes to continuously tune the center frequency of the ring filter. For demonstration, two prototypes of reconfigurable ring filters are realized using microstrip technology, simulated, and measured to validate the proposed concept. The reconfigured filter using lumped elements is successfully reconfigured from 2?GHz to 984.4?MHz and miniaturized by 71% compared to the filter directly designed at the same reconfigured frequency, while, for the filter using varactor-diodes, the frequency is chosen from 1.10?GHz to 1.38?GHz spreading over 280?MHz frequency range. Both designs are found to be compact with acceptable insertion loss and high selectivity. PMID:25121132

Ismail Khan, Zuhani; Abd Rashid, Nur Emileen

2014-01-01

468

47 CFR 2.815 - External radio frequency power amplifiers.  

Code of Federal Regulations, 2011 CFR

... External radio frequency power amplifiers. 2.815 Section 2.815 ...External radio frequency power amplifiers. (a) As used in this part, an external radio frequency power amplifier is any device which,...

2011-10-01

469

47 CFR 2.815 - External radio frequency power amplifiers.  

Code of Federal Regulations, 2012 CFR

... External radio frequency power amplifiers. 2.815 Section 2.815 ...External radio frequency power amplifiers. (a) As used in this part, an external radio frequency power amplifier is any device which,...

2012-10-01

470

47 CFR 2.815 - External radio frequency power amplifiers.  

Code of Federal Regulations, 2013 CFR

... External radio frequency power amplifiers. 2.815 Section 2.815 ...External radio frequency power amplifiers. (a) As used in this part, an external radio frequency power amplifier is any device which,...

2013-10-01

471

47 CFR 90.214 - Transient frequency behavior.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Transient frequency behavior. 90.214 Section 90.214 Telecommunication...Standards § 90.214 Transient frequency behavior. Transmitters designed to operate... 421 to 512 MHz Transient Frequency Behavior for Equipment Designed to Operate...

2011-10-01

472

47 CFR 90.214 - Transient frequency behavior.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Transient frequency behavior. 90.214 Section 90.214 Telecommunication...Standards § 90.214 Transient frequency behavior. Transmitters designed to operate... 421 to 512 MHz Transient Frequency Behavior for Equipment Designed to Operate...

2010-10-01

473

47 CFR 80.391 - Frequencies for developmental stations.  

Code of Federal Regulations, 2010 CFR

...false Frequencies for developmental stations. 80.391 Section 80.391 Telecommunication... SAFETY AND SPECIAL RADIO SERVICES STATIONS IN THE MARITIME SERVICES Frequencies Developmental Stations § 80.391 Frequencies for...

2010-10-01

474

47 CFR 2.815 - External radio frequency power amplifiers.  

Code of Federal Regulations, 2014 CFR

... External radio frequency power amplifiers. 2.815 Section 2.815 ...External radio frequency power amplifiers. (a) As used in this part, an external radio frequency power amplifier is any device which,...

2014-10-01

475

Nonresonant and Resonant Frequency-Selectable Induction-Heating Targets  

E-print Network

This paper examines a scheme for developing frequency-selectable induction-heating targets for stimulating temperature-sensitive polymer gels. The phrase “frequency selectable” implies that each target has a frequency at ...

Rodriguez, John I.

476

47 CFR 80.363 - Frequencies for facsimile.  

Code of Federal Regulations, 2010 CFR

...facsimile. Assignable Ship Frequencies for Facsimile (kHz) 2070...2076.5 (2) Coast station frequencies. The following table describes the exclusive maritime mobile HF frequency bands that are available...

2010-10-01

477

47 CFR 95.627 - FRS unit channel frequencies.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false FRS unit channel frequencies. 95.627 Section 95.627...Technical Standards § 95.627 FRS unit channel frequencies. (a) The FRS unit channel frequencies are: Channel No....

2011-10-01

478

47 CFR 95.626 - FRS unit channel frequencies.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false FRS unit channel frequencies. 95.626 Section 95.626...Technical Standards § 95.626 FRS unit channel frequencies. (a) The FRS unit channel frequencies are: Channel No....

2013-10-01

479

47 CFR 95.626 - FRS unit channel frequencies.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false FRS unit channel frequencies. 95.626 Section 95.626...Technical Standards § 95.626 FRS unit channel frequencies. (a) The FRS unit channel frequencies are: Channel No....

2012-10-01

480

47 CFR 95.625 - CB transmitter channel frequencies.  

Code of Federal Regulations, 2010 CFR

... 2010-10-01 false CB transmitter channel frequencies. 95.625 Section 95.625...Technical Standards § 95.625 CB transmitter channel frequencies. (a) The CB transmitter channel frequencies are: Channel No....

2010-10-01

481

47 CFR 95.625 - CB transmitter channel frequencies.  

Code of Federal Regulations, 2011 CFR

... 2011-10-01 false CB transmitter channel frequencies. 95.625 Section 95.625...Technical Standards § 95.625 CB transmitter channel frequencies. (a) The CB transmitter channel frequencies are: Channel No....

2011-10-01

482

47 CFR 95.625 - CB transmitter channel frequencies.  

Code of Federal Regulations, 2012 CFR

... 2012-10-01 false CB transmitter channel frequencies. 95.625 Section 95.625...Technical Standards § 95.625 CB transmitter channel frequencies. (a) The CB transmitter channel frequencies are: Channel No....

2012-10-01

483

47 CFR 95.627 - FRS unit channel frequencies.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 2010-10-01 false FRS unit channel frequencies. 95.627 Section 95.627...Technical Standards § 95.627 FRS unit channel frequencies. (a) The FRS unit channel frequencies are: Channel No....

2010-10-01

484

47 CFR 95.625 - CB transmitter channel frequencies.  

Code of Federal Regulations, 2013 CFR

... 2013-10-01 false CB transmitter channel frequencies. 95.625 Section 95.625...Technical Standards § 95.625 CB transmitter channel frequencies. (a) The CB transmitter channel frequencies are: Channel No....

2013-10-01

485

47 CFR 2.815 - External radio frequency power amplifiers.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 2010-10-01 false External radio frequency power amplifiers. 2.815...COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Marketing of Radio-frequency Devices § 2.815...

2010-10-01

486

47 CFR 90.723 - Selection and assignment of frequencies.  

Code of Federal Regulations, 2011 CFR

...assignment of frequencies. (a) Phase II applications for frequencies...aid use, or emergency medical use. Phase II applicants for frequencies for...assigned by the Commission. (b) Phase II channels will be assigned...

2011-10-01

487

47 CFR 90.723 - Selection and assignment of frequencies.  

Code of Federal Regulations, 2010 CFR

...assignment of frequencies. (a) Phase II applications for frequencies...aid use, or emergency medical use. Phase II applicants for frequencies for...assigned by the Commission. (b) Phase II channels will be assigned...

2010-10-01

488

47 CFR 90.723 - Selection and assignment of frequencies.  

Code of Federal Regulations, 2013 CFR

...assignment of frequencies. (a) Phase II applications for frequencies...aid use, or emergency medical use. Phase II applicants for frequencies for...assigned by the Commission. (b) Phase II channels will be assigned...

2013-10-01

489

47 CFR 90.723 - Selection and assignment of frequencies.  

Code of Federal Regulations, 2012 CFR

...assignment of frequencies. (a) Phase II applications for frequencies...aid use, or emergency medical use. Phase II applicants for frequencies for...assigned by the Commission. (b) Phase II channels will be assigned...

2012-10-01

490

Detecting DNS Tunnels Using Character Frequency Analysis  

E-print Network

High-bandwidth covert channels pose significant risks to sensitive and proprietary information inside company networks. Domain Name System (DNS) tunnels provide a means to covertly infiltrate and exfiltrate large amounts of information passed network boundaries. This paper explores the possibility of detecting DNS tunnels by analyzing the unigram, bigram, and trigram character frequencies of domains in DNS queries and responses. It is empirically shown how domains follow Zipf's law in a similar pattern to natural languages, whereas tunneled traffic has more evenly distributed character frequencies. This approach allows tunnels to be detected across multiple domains, whereas previous methods typically concentrate on monitoring point to point systems. Anomalies are quickly discovered when tunneled traffic is compared to the character frequency fingerprint of legitimate domain traffic.

Born, Kenton

2010-01-01

491

Anechoic chamber qualification at ultrasonic frequencies  

NASA Astrophysics Data System (ADS)

Qualifying an anechoic chamber for frequencies that extend into the ultrasonic range is necessary for research work involving airborne ultrasonic sound. For example, an anechoic chamber allows for measurements of the direct sound radiated by an object without reflections from walls. The ANSI S12.55/ISO 3745 standard which covers anechoic chamber qualification does not extend into the ultrasonic frequency range, nor have others discussed this frequency range in the literature. An increasing number of technologies are employing ultrasound; hence the need to develop facilities to conduct basic research studies on airborne ultrasound. This presentation will discuss the challenges associated with chamber qualification and present the results for qualification of a chamber at Brigham Young University. [This work has been funded by the Los Alamos National Laboratory

Jenny, Trevor; Anderson, Brian

2010-10-01

492

Low-frequency radio navigation system  

NASA Technical Reports Server (NTRS)

A method of continuous wave navigation using four transmitters operating at sufficiently low frequencies to assure essentially pure groundwave operation is described. The transmitters are keyed to transmit constant bursts (1/4 sec) in a time-multiplexed pattern with phase modulation of at least one transmitter for identification of the transmitters and with the ability to identify the absolute phase of the modulated transmitter and the ability to modulate low rate data for transmission. The transmitters are optimally positioned to provide groundwave coverage over a service region of about 50 by 50 km for the frequencies selected in the range of 200 to 500 kHz, but their locations are not critical because of the beneficial effect of overdetermination of position of a receiver made possible by the fourth transmitter. Four frequencies are used, at least two of which are selected to provide optimal resolution. All transmitters are synchronized to an average phase as received by a monitor receiver.

Wallis, D. E. (inventor)

1983-01-01

493

Frequency dependence of the Chiral Vortical Effect  

E-print Network

We study the frequency dependence of all the chiral vortical and magnetic conductivities for a relativistic gas of free chiral fermions and for a strongly coupled conformal field theory with holographic dual in four dimensions. Both systems have gauge and gravitational anomalies, and we compute their contribution to the conductivities. The chiral vortical conductivities and the chiral magnetic conductivity in the energy current show a frequency dependence in the form of a delta centered at zero frequency. This highly discontinuous behavior is a natural consequence of the Ward identities that include the energy momentum tensor. We discuss the physical interpretation of this result and its possible implications for the quark gluon plasma as created in heavy ion collisions. In the Appendix we discuss why the chiral magnetic effect seems to vanish in the consistent current for a particular implementation of the axial chemical potential.

Karl Landsteiner; Eugenio Megias; Francisco Peña Benítez

2013-12-04