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1

Isotope effect on the temperature dependence of the 35Cl NQR frequency in (NH4)2RuCl6  

NASA Astrophysics Data System (ADS)

The 35Cl nuclear quadrupole resonance frequencies and spin-lattice relaxation times for (NH4)2RuCl6, (ND4)2RuCl6, (NH4)2SnCl6, and (ND4)2SnCl6 were measured in the temperature range 4.2-300 K. In these four compounds, it was confirmed that no phase transition occurs in the observed temperature range. At 4.2 K, discrepancies of the NQR frequency between non-deuterated and deuterated compounds, which are attributed to the difference in the spatial distributions of hydrogen (deuterium) atoms in the ground states of the rotational motion of ammonium ion, reached to 24 kHz and 23 kHz for the ruthenate compounds and the stannate compounds, respectively. The separation between the ground and the first excited states of the rotational motion of the ammonium ion was estimated to be 466 J mol-1 and 840 J mol-1 for (ND4)2RuCl6 and (NH4)2RuCl6, respectively, by least-square fitting calculations of temperature dependence of the NQR frequency. For (ND4)2SnCl6 and (NH4)2SnCl6, these quantities were estimated to be 501 J mol-1 and 1544 J mol-1, respectively. It was clarified that the T1 minimum, which has been observed for the stannate compounds at around 60 K as a feature of the temperature dependence, was dependent on a method of sample preparation. It is concluded that the minimum is not an essential character of the ammonium hexachlorostannate(IV) since the crystals prepared in strong acid condition to prevent a partial substitution of chlorine atoms by hydroxyl groups, did not show such T1 minimum.

Kume, Yoshio; Amino, Daiki; Asaji, Tetsuo

2013-07-01

2

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

3

Sodium and potassium salts of dichloroisocyanuric acid and their hydrates as antimicrobials agents studied by 35Cl-NQR spectroscopy and DFT calculations  

Microsoft Academic Search

The electronic structure of dichloroisocyanuric acid derivatives was analysed by 35Cl-NQR spectroscopy and DFT calculations. Here we concentrate our attention on three different factors: type of metallic substituent (sodium and potassium), temperature of the sample (liquid nitrogen and room) and degree of hydration (an amount of water molecules attached to analysed compounds). In particular, all the variations in 35Cl-NQR frequencies

A. Walczak; B. Brycki; M. Kaczmarek; O. Kh. Poleshchuk; M. Ostafin; B. Nogaj

2006-01-01

4

Sodium and potassium salts of dichloroisocyanuric acid and their hydrates as antimicrobials agents studied by 35Cl-NQR spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

The electronic structure of dichloroisocyanuric acid derivatives was analysed by 35Cl-NQR spectroscopy and DFT calculations. Here we concentrate our attention on three different factors: type of metallic substituent (sodium and potassium), temperature of the sample (liquid nitrogen and room) and degree of hydration (an amount of water molecules attached to analysed compounds). In particular, all the variations in 35Cl-NQR frequencies upon hydration of salts containing sodium and potassium ions are explained as a consequence of H-bonds formation and accompanied effects of charge redistribution. Our studies can be useful in searching for the derivatives of dichloroisocyanuric acid revealing higher antimicrobial activity.

Walczak, A.; Brycki, B.; Kaczmarek, M.; Poleshchuk, O. Kh.; Ostafin, M.; Nogaj, B.

2006-06-01

5

Neutral-Ionic Phase Transition in DMTTF-QCl4 Investigated by 35Cl NQR  

NASA Astrophysics Data System (ADS)

We report a 35Cl NQR investigation into the neutral-ionic (NI) phase transition in DMTTF-QCl4 (4,4'-dimethyltetrathiafulvalene- p-chloranil), the end material of the family containing an NI quantum transition system. Four distinct lines with comparable intensities were observed well below Tc=65 K; this observation is consistent with the antiferroelectric nature of the ionic phase. The temperature dependences of the spectral shift and splitting below Tc are moderate in contrast with the case of TTF-QCl4. Low-energy charge-lattice fluctuations are observed around Tc as a drastic increase of 1/T1, allowing the observation of the quantum fluctuations in a chemically substituted complex. An analysis of the NQR spectra yields detailed temperature variations in the charge transfer and the concomitant lattice distortion around the NI transition.

Iwase, Fumitatsu; Miyagawa, Kazuya; Fujiyama, Shigeki; Kanoda, Kazushi; Horiuchi, Sachio; Tokura, Yoshinori

2007-07-01

6

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

7

Stereoelectronic structure and 35Cl NQR parameters of 4-(trichlorgermyl)butan-2-one using ab initio calculations  

NASA Astrophysics Data System (ADS)

The results of ab initio calculations at the RHF/6-31G(d) and MP2/6-31G(d) levels of two stable structures of the 4-(trichlorgermyl)butan-2-one molecule with total optimization of their geometry have been represented. The structure with pentacoordinated Ge atom is energetically more advantageous as compared with that with tetracoordinated one. Using these results, the 35Cl nuclear quadrupole resonance (NQR) frequencies and asymmetry parameters of the electric field gradient (EFG) at the 35Cl nuclei in molecule with pentacoordinated Ge atom have been assessed, the frequencies satisfactorily agreeing with experimental data. Calculations at the RHF/6-31G(d) level have been performed also at various Ge⋯O distances. It has been demonstrated that convergence of the Ge and O coordination centers leads to the increase of positive charge at the Ge coordination center and of negative charge at the O coordination center, at that, electron density from the Ge atom shifts mainly to the axial Cl atom and from the C atom of carbonyl group - to its O atom. The electron density transfer from the O to Ge atom does not occur.

Feshin, V. P.; Feshina, E. V.

2012-03-01

8

Stability and molecular dynamics of chloroxylenol (API of antiseptics and drugs) in solid state studied by 35Cl-NQR spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

Thermal stability of 4-chloro-3,5-dimethyl-phenol (chloroxylenol) in solid state has been studied by 35Cl-NQR spectroscopy. Two NQR resonance lines at the frequencies 34.348 and 34.415 MHz at 77 K have been assigned to chlorine atoms from two crystallographically inequivalent molecules on the basis of the B3LYP/6-311++G ?? results. The temperature dependence of the resonance frequency and full width at half maximum suggest the occurrence of small-angle torsional oscillations of the mean activation energy of 3.83 kJ/mol and rotation of both methyl groups around their symmetry axis C3 with the activation energies 12.49 and 11.27 kJ/mol for CH 3 in molecule A and B, respectively. B3LYP/6-311++G ?? method reproduced very well the activation energies of both motions.

Latosi?ska, J. N.; Tomczak, M. A.; Kasprzak, J.

2009-02-01

9

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

10

Conformations and intermolecular interactions pattern in solid chloroxylenol and triclosan (API of anti-infective agents and drugs). A (35) Cl NQR, (1) H-(14) ?N NQDR, X-ray and DFT/QTAIM study.  

PubMed

Two antibacterial and antifungal agents, chloroxylenol (4-chloro-3,5-dimethyl-phenol) and triclosan (5-chloro-2-(2',4'-dichlorophenoxy)-phenol), were studied experimentally in solid state with an X-ray, (35) Cl-nuclear quadrupole resonance (NQR) and (17) O-nuclear quadrupole double resonance (NQDR) spectroscopies and, theoretically, with the density functional theory/quantum theory of atoms in molecules (DFT/QTAIM). The crystallographic structure of triclosan, which crystallises in space group P3(1) with one molecule in the asymmetric unit [a?=?12.64100(10), b?=?12.64100(10), c = 6.71630(10) Å], was solved with an X-ray and refined to a final R-factor of 2.81% at room temperature. The NQR frequencies of (35) Cl and (17) O were detected with the help of the density functional theory (DFT) assigned to particular chlorine and oxygen sites in the molecules of both compounds. The NQR frequencies at (35) Cl sites in chloroxylenol and triclosan were found to be more differentiated than frequencies at the (17) O site. The former better describes the substituent withdrawing effects connected to ?-electron delocalization within the benzene rings and the influence of temperature; whereas, those at the (17) O site provide more information on O-H bond and intermolecular interactions pattern. The conformation adopted by diphenyl ether of triclosan in solid state was found to be typical of diphenyl ethers, but the opposite to those adopted when it was bound to different inhibitors. According to an X-ray study, temperature had no effect on the conformation of the diphenyl ring of triclosan, which was the same at 90?K and at room temperature (RT). The scattering of NQR frequencies reproduced by the DFT under assumption of the X-ray data at 90?K and RT is found to be a good indicator of the quality of resolution of the crystallographic structure. Copyright © 2012 John Wiley & Sons, Ltd. PMID:22354770

Latosi?ska, J N; Latosi?ska, M; Tomczak, M A; Seliger, J; Zagar, V; Maurin, J K

2012-02-21

11

Structure and phase transition in bis(pyrrolidinium) hexachlorometallates, (C 4H 8NH 2) 2MCl 6 (M=Sn, Te and Pt), studied by X-ray diffraction, 35Cl NQR and DSC  

NASA Astrophysics Data System (ADS)

Single crystal X-ray diffraction, 35Cl nuclear quadrupole resonance (NQR) and differential scanning calorimetry (DSC) measurements were taken for bis(pyrrolidinium) hexachlorometallates, (C 4H 8NH 2) 2MCl 6 (M=Sn, Te and Pt). A solid-solid phase transition was observed at 150(1), 159(1) and 134(1) K for stannate, tellurate and platinate, respectively. 35Cl NQR signals were observed in stannate and platinate, both of which showed a two-line spectrum in the high-temperature phase and a three-line spectrum in the low-temperature phase. The high-temperature phases of the three complexes were found to be isostructural with each other belonging to the space group C2/ m (#12). The C 4H 8NH 2+ and MCl 62- ions are connected by N-H⋯Cl hydrogen bonds forming parallel sheets in the crystals. Disorder of the cation ring appears in these high-temperature phases. Semi-empirical MO calculations were performed to estimate the stable structure of the pyrrolidinium ion.

Ishida, H.; Furukawa, Y.; Sato, S.; Kashino, S.

2000-06-01

12

35Cl-NQR and DFT study of electronic structure of amlodipine and felodipine vascular-selective drugs from the dihydropyridine Ca ++ antagonists group  

NASA Astrophysics Data System (ADS)

Amlodipine (AM) and felodipine (FL) have been studied in solid state by the nuclear quadrupole resonance (NQR) and density functional theory (DFT). The results have shown that NQR data do not permit a differentiation between R and S enantiomers, which is a consequence of the symmetry of the 4-aryl ring, whereas they permit a differentiation between free bases and salts. The HOMO-LUMO gap is smaller for AM than for FL, which suggests smaller energy of excitation for AM. The absolute hardness, chemical potential and electrophilicity of both AM enantiomers are lower than the corresponding values for FL enantiomers, suggesting that AM should be more reactive than FL in unimolecular reactions.

Latosi?ska, J. N.; Latosi?ska, M.; Kasprzak, J.

2008-09-01

13

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.

2006-06-01

14

INDO Investigation of the halogen N.Q.R. frequencies and 14 N nuclear quadrupole coupling constants of halothiophenes and halopyridines  

Microsoft Academic Search

The 35Cl, 79Br, and 127I N.Q.R. frequencies of a number of halothiophenes and halopyridines and the 14N nuclear quadrupole coupling constants of halopyridines have been determined in terms of the Kaplansky-Whitehead theory with the INDO MO approximations using a consistent set of atomic parameters derived from SCF Hartree-Fock calculations. The theoretical spectral properties are in satisfactory overall agreement with experiment.

V. Galasso

1974-01-01

15

Muon capture on 35Cl  

NASA Astrophysics Data System (ADS)

We report measurements of ?-ray spectra from muon capture on 35Cl. For the allowed Gamow-Teller transitions to the 35S(2939,3/2+) state and the 35S(3421,5/2+) state we obtained their capture rates, hyperfine dependences, and ?-? correlation coefficients. The capture rates and hyperfine dependences were compared to shell model calculations using the complete 1s-0d space and the universal SD interaction. With gp/ga=6.7 and ga=-1.00 (or ga=-1.26) we found agreement of the model and the data at the 1-2 ? level. However, we caution that the transitions are sensitive to l=2 forbidden matrix elements.

Arole, S.; Armstrong, D. S.; Gorringe, T. P.; Hasinoff, M. D.; Kovash, M. A.; Kuzmin, V.; Moftah, B. A.; Sedlar, R.; Stocki, T. J.; Tetereva, T.

2002-12-01

16

Multi-Frequency Resonances in Pure Multiple-Pulse NQR  

NASA Astrophysics Data System (ADS)

We have observed multi-frequency resonances in a system with a spin 3/2 irradiated simultaneously by a multiple-pulse radiofrequency sequence and a low frequency field swept in the range 0 ÷ 80 kHz. The theoretical description of the effect is presented using both the rotating frame approximation and the Floquet theory. Both approaches give indentical results at the calculation of the resonance frequencies, transition probabilities and shifts of resonance frequency. The calculated magnetization vs. the frequency of the low-frequency field agrees with the obtained experimental data.

Furman, G. B.; Kibrik, G. E.; Polyakov, A. Yu.

2004-12-01

17

Radio-frequency tunable atomic magnetometer for detection of solid-state NQR  

NASA Astrophysics Data System (ADS)

We constructed a potassium atomic magnetometer which resonantly detects rf magnetic fields with subfemtotesla sensitivity. The resonance frequency is set by the Zeeman resonance of the potassium atoms in a static magnetic field applied to the magnetometer cell. Strong optical pumping of the potassium atoms into a stretched state reduces spin-exchange broadening of the Zeeman resonance, resulting in relatively small linewidth of about 200 Hz (half-width at half-maximum). The magnetometer was used to detect ^14N NQR signal from powdered ammonium nitrate at 423 kHz, with sensitivity an order of magnitude higher than with a conventional room temperature pickup coil with comparable geometry. The demonstrated sensitivity of 0.24 fT/Hz^1/2 can be improved by several means, including use of higher power lasers for pumping and probing. Our technique can potentially be used to develop a mobile, open-access NQR spectrometer for detection of nitrogen-containing solids of interest in security applications.

Lee, S.-K.; Sauer, K. L.; Seltzer, S. J.; Alem, O.; Romalis, M. V.

2007-06-01

18

35-Cl nuclear quadrupole resonance spectra in diazepam and its 1:1 complex with chloral hydrate  

NASA Astrophysics Data System (ADS)

The 35-Cl NQR spectra of diazepam and some of its related compounds are reported; they yield information about the hydrogen bonded complex that diazepam forms with chloral hydrate. The results reflect large changes in electron distribution at the CCl 3 group while the diazepam chlorine at the 7 position remains almost unaffected.

Brisson, Colette; Durand, Marcel; Jugie, Gérard; Pasdeloup, Maurice

1980-11-01

19

Application of the spherical tensor method for Two-Frequency pure NQR of spin I =1 nuclei  

Microsoft Academic Search

The results of a theoretical investigation of two-frequency excitation in pure nuclear quadrupole resonance (NQR) for a spinI=1 nucleus with a nonaxial elecric field gradient are presented. The multipole tensor operator technique is used for the treatment\\u000a of the one- and two-frequency pulse excitations. The results are applied to the characterization of the two-frequency signal\\u000a of nitrogen14N nuclei. The experiments

G. V. Mozjoukhine

2002-01-01

20

Pressure and temperature dependence of the chlorine NQR in caesium and sodium chlorates.  

PubMed

The (35)Cl nuclear quadrupole resonance (NQR) frequencies (nu(Q)) in caesium and sodium chlorates were measured as a function of temperature, from 77 to 300 K at different pressures up to 5.1 kbar, and the data were analysed to estimate the volume dependence of the electric field gradient (EFG), torsional frequency and also the contributions to the NQR frequency from static and dynamic effects. The variation of spin-lattice relaxation time with pressure at different temperatures was studied in the case of sodium chlorate and at room temperature in case of caesium chlorate. The pressure dependence of the spin-lattice relaxation time (T(1)) suggests that the relaxation is mainly due to the torsional motions. PMID:18324738

Ramesh, K P; Suresh, K S; Raghavendra Rao, C; Ramakrishna, J

2008-06-01

21

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, M. L.; Yesinowski, J. P.; Miller, J. B.; Krauss, Ronald A.

1994-10-01

22

Compound model-morphed potentials contrasting OC-79Br35Cl with the halogen bonded OC-35Cl2 and hydrogen-bonded OC-HX (X = 19F, 35Cl, 79Br)  

NASA Astrophysics Data System (ADS)

A five-dimensional compound-model morphed (CMM) potential has been generated for the halogen bonded intermolecular interaction 16O12C-79Br35Cl based on a fit to the currently generated infrared and previously available microwave spectroscopic data. The experimentally determined blue frequency shift of the 16O12C stretching frequency on complexation with 79Br35Cl is found to be ?? = 12.89643(28) cm-1 indicating a more strongly bound complex than in OC-35Cl2. Re center-of-mass to center-of-mass distance of 4.270(7) Å and dissociation energies De = 778(70) cm-1 and D0 = 605(70) cm-1 are predicted from the CMM potential and also compared with the corresponding values of Re = 4.742(3) Å and De = 544(5) cm-1 and D0 = 397(5) cm-1 for 16O12C-35Cl2. The molecular dynamics, binding energy and other molecular parameters of OC-BrCl are also compared with the hydrogen bonded dimers OC-HX (X = F, Cl, Br) giving further insight into the characteristics of the complex.

Rivera-Rivera, Luis A.; Scott, Kevin W.; McElmurry, Blake A.; Lucchese, Robert R.; Bevan, John W.

2013-11-01

23

14N NQR in the tetrazole family  

NASA Astrophysics Data System (ADS)

14N NQR frequencies and spin-lattice relaxation times were measured in technologically important 5-aminotetrazole and 5-aminotetrazole monohydrate at different temperatures between 77 K and 300 K. Five NQR triplets ?+, ?- and ?0 were found for the five inequivalent nitrogen atoms in each compound between 0.7 MHz and 4 MHz. Carr-Purcell based multipulse sequences were used to accumulate quadrupole echo signals before the FFT analysis. Assignment of the frequencies to atomic positions was made and the results are analysed in relation to the molecular chemical bonds and possible H-bonds in the crystal structures. The new NQR frequencies are reasonably related to the previously published NQR spectrum of the third family member, 1H-tetrazole.

Pirnat, Janez; Lužnik, Janko; Jazbinšek, Vojko; Žagar, Veselko; Seliger, Janez; Klapötke, Thomas M.; Trontelj, Zvonko

2009-10-01

24

FPGA based pulsed NQR spectrometer  

NASA Astrophysics Data System (ADS)

An NQR spectrometer for the frequency range of 1 MHz to 5 MHZ has been designed constructed and tested using an FPGA module. Consisting of four modules viz. Transmitter, Probe, Receiver and computer controlled (FPGA & Software) module containing frequency synthesizer, pulse programmer, mixer, detection and display, the instrument is capable of exciting nuclei with a power of 200W and can detect signal of a few microvolts in strength. 14N signal from NaNO2 has been observed with the expected signal strength.

Hemnani, Preeti; Rajarajan, A. K.; Joshi, Gopal; Motiwala, Paresh D.; Ravindranath, S. V. G.

2014-04-01

25

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

26

Preparation of highly polarized nuclei: Observation and control of time-dependent polarization transfer from H{sup 35}Cl molecular rotation to {sup 35}Cl nuclear spin  

SciTech Connect

We demonstrate time-dependent polarization transfer from molecular rotation to nuclear spin. The H{sup 35}Cl (v=2,J=1,M=1) state is excited with a 1.7 {mu}m laser pulse, and then dissociated with a delayed 235 nm laser pulse to produce {sup 35}Cl atoms. Time-dependent polarizations of both H{sup 35}Cl (v=2,J=1) molecules and {sup 35}Cl({sup 2}P{sub 3/2}) atoms, which vary due to hyperfine quantum beating, are measured. The {sup 35}Cl nuclear spin is highly polarized ({approx_equal}1.1) at a pump-probe delay of 145 ns. Densities surpassing 10{sup 14} cm{sup -3} are achieved. The technique is applicable to many atoms not amenable to optical pumping.

Sofikitis, Dimitris; Rakitzis, T. Peter [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, 71110 Heraklion-Crete (Greece); Department of Physics, University of Crete, P.O. 2208, 71003 Voutes-Heraklion (Greece); Rubio-Lago, Luis [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, 71110 Heraklion-Crete (Greece); Martin, Marion R.; Brown, Davida J. Ankeny; Bartlett, Nathaniel C.-M.; Zare, Richard N. [Department of Chemistry, Stanford University, Stanford, California 94305-5080 (United States)

2007-07-15

27

Peak Determination of ^35 Cl(n,?) Lines  

NASA Astrophysics Data System (ADS)

To achieve our goal of performing a stringent test of the Isobaric Multiplet Mass Equation (IMME) for the lowest T = 2 quintuplet, an accurate measurement of the mass of ^32 S in its lowest T = 2 state is needed, as the other masses of the members of the quintuplet are well known [1]. To achieve the desired precision, several calibration reactions are required including ^35 Cl(n,?). A proton beam of 1.912 MeV is incident upon a Li 2 O target to create neutrons via ^7Li(p,n). The neutrons are then moderated and absorbed by a volume of NaCl. The resulting radiation is measured with a Ge(Li) detector. Due to differences in the position of the source during calibration versus data runs, a source of mis-calibration may result from detector orientation to and distance from the source [2]. We are currently measuring the centroid shifts with respect to detector angle to see its influence upon our data collection. [1] K. Blaum, G. Audi et. al, Phys. Rev. Lett., 91, 260801, (2003) [2] R. G. Helmer, R. J. Gehrke, R. C. Greenwood, Nucl. Instr. and Meth., 123 (1975) p. 51-59.

Young, Patrick

2004-10-01

28

35Cl profiling using centric scan SPRITE with variable flip angle excitation  

NASA Astrophysics Data System (ADS)

An efficient MRI technique for quantitative density profiling of samples with fast spin-lattice relaxation ( T1 < 5 ms) is introduced. The pulse scheme is based on the 1D centric scan SPRITE technique. Strong excitation of the sample at the k-space origin improves the sensitivity with respect to the original centric scan SPRITE technique. Radio frequency pulse durations are defined so as to provide uniform excitation of the sample at every k-space point. For a particular k-space point the pulse duration is required to be less than the inverse sample bandwidth. Simulations permit one to examine distortions from ideal profile geometry due to flip angle and spin-lattice relaxation effects. The proposed technique is especially suitable for the observation of low sensitivity samples, in particular, low-? nuclei like 35Cl. In some cases, this strategy permits one to reduce the number of scans, i.e. the experiment time, by a factor of 100, depending on hardware, sample length and tolerable resolution loss. The designed pulse scheme is tested on cylindrical agar gel and type 1 Portland cement paste phantoms prepared to provide 1H and 35Cl signals, respectively.

Romanenko, Konstantin V.; Cano-Barrita, P. F. de J.; Balcom, Bruce J.

2009-05-01

29

Mid-Infrared Diode Laser Spectroscopy of X˜1A' HC 35Cl  

NASA Astrophysics Data System (ADS)

The observation of the C-Cl stretching fundamental of HC 35Cl in its ground X˜1A' state is reported. HCCl was formed in a continuous flow system by the excimer laser photolysis of CHBr 2Cl at 193 nm and the transient absorption recorded by infrared diode laser spectroscopy. The band has a-type character and the fundamental vibrational frequency is found to be 811.5963 cm -1. No evidence was found for perturbations in either the ground or vibrationally excited states, implying that the excited triplet ã3A? states lies above the C-Cl stretching level in HCCl. The observed rotation-vibration transitions were well fit by a standard asymmetric rotor Hamiltonian. There is a decrease in the Arotational constant on vibrational excitation, suggesting that some bend-C-Cl stretch coupling is present.

Chang, Bor-Chen; Fei, Ruian; Sears, Trevor J.

1997-06-01

30

Mid-Infrared Diode Laser Spectroscopy of X ; 1 A ' HC35 Cl  

PubMed

The observation of the C-Cl stretching fundamental of HC35 Cl in its ground X ; 1 A ' state is reported. HCCl was formed in a continuous flow system by the excimer laser photolysis of CHBr2 Cl at 193 nm and the transient absorption recorded by infrared diode laser spectroscopy. The band has a -type character and the fundamental vibrational frequency is found to be 811.5963 cm-1 . No evidence was found for perturbations in either the ground or vibrationally excited states, implying that the excited triplet a 3 A " states lies above the C-Cl stretching level in HCCl. The observed rotation-vibration transitions were well fit by a standard asymmetric rotor Hamiltonian. There is a decrease in the A rotational constant on vibrational excitation, suggesting that some bend-C-Cl stretch coupling is present. PMID:9252304

Chang; Fei; Sears

1997-06-01

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

In Vivo (35)Cl MR Imaging in Humans: A Feasibility Study.  

PubMed

Purpose To implement chlorine 35 ((35)Cl) magnetic resonance (MR) at a 7-T whole-body MR system and evaluate its feasibility for imaging humans. Materials and Methods All examinations were performed with ethical review board approval; written informed consent was obtained from all volunteers. Seven examinations each of brain and muscle in healthy volunteers and four examinations of patients were performed. Two patients with histologically confirmed glioblastoma multiforme underwent brain imaging. (35)Cl MR and (35)Cl inversion-recovery (IR) MR were performed. Two patients with genetically confirmed hypokalemic periodic paralysis underwent calf muscle imaging. Seven multiecho sequences (acquisition time, 5 minutes; voxel dimension, 11 mm(3)) were applied to determine transverse relaxation time as affected by magnetic field heterogeneity (T2*) and chlorine concentration. (35)Cl and sodium 23 ((23)Na) MR were conducted with a 7-T whole-body MR system. (35)Cl longitudinal relaxation time (T1) and T2* of healthy human brain and muscle were determined with a three-dimensional density-adapted-projection reconstruction technique to achieve short echo times and high signal-to-noise ratio (SNR) efficiency. A nonlinear least squares routine and mono- (T1) and biexponential (T2*) models were used for curve fitting. Results Phantom imaging revealed 15-fold lower SNR and much shorter relaxation times for (35)Cl than (23)Na. In vivo T2* was biexponential and extremely short. Monoexponential fits of T1 revealed 9.2 and 4.0 milliseconds ± 0.7 (standard deviation) for brain and muscle, respectively. In glioblastoma tissue, increased Cl(-) concentrations and increased Cl(-) IR signal intensities were detected. Voxel dimension and acquisition time, respectively, were 6 mm(3) and 9 minutes 45 seconds ((35)Cl MR) and 10 mm(3) and 10 minutes ((35)Cl IR MR). In patients with hypokalemic periodic paralysis versus healthy volunteers, Cl(-) and Na(+) concentrations were increased. Cl(-) concentration of muscle could be determined (voxel size, 11 mm(3); total acquisition time, 35 minutes). Conclusion MR at 7 T enables in vivo imaging of (35)Cl in human brain and muscle in clinically feasible acquisition times (10-35 minutes) and voxel volumes (0.2-1.3 cm(3)). Pathophysiological changes of Cl(-) homeostasis due to cancer or muscular ion channel disease can be visualized. © RSNA, 2014 Online supplemental material is available for this article. PMID:24495267

Nagel, Armin M; Lehmann-Horn, Frank; Weber, Marc-André; Jurkat-Rott, Karin; Wolf, Maya B; Radbruch, Alexander; Umathum, Reiner; Semmler, Wolfhard

2014-05-01

33

[sup 81]Br and [sup 35]Cl NMR investigation of sodium, silver, halo-sodalite semiconductor supralattices  

Microsoft Academic Search

[sup 81]Br and [sup 35]Cl NMR yields, respectively, bromide and chloride site-specific information pertinent to the structural and electronic properties of Na[sub 8-n-p]Ag[sub n]X[sub 2-p]-sodalite, semiconductor cluster supralattices, where X = Br, Cl; 0 [le] n [le] 8; 0 [le] p [le] 2. The [sup 81]Br and [sup 35]Cl MAS chemical shifts and line shapes observed for encapsulated Na[sub 4]X

R. Jelinek; A. Stein; G. A. Ozin

1993-01-01

34

The 35Cl/37Cl isotopic ratio in dense molecular clouds: HIFI observations of hydrogen chloride towards W3 A  

NASA Astrophysics Data System (ADS)

We report on the detection with the HIFI instrument on board the Herschel satellite of the two hydrogen chloride isotopologues, H35Cl and H37Cl, towards the massive star-forming region W3 A. The J = 1-0 line of both species was observed with receiver 1b of the HIFI instrument at ~625.9 and ~624.9 GHz. The different hyperfine components were resolved. The observations were modeled with a non-local, non-LTE radiative transfer model that includes hyperfine line overlap and radiative pumping by dust. Both effects are found to play an important role in the emerging intensity from the different hyperfine components. The inferred H35Cl column density (a few times ~1014 cm-2), and fractional abundance relative to H nuclei (~7.5 × 10-10), supports an upper limit to the gas phase chlorine depletion of ?200. Our best-fit model estimate of the H35Cl/H37Cl abundance ratio is ? 2.1 ± 0.5, slightly lower, but still compatible with the solar isotopic abundance ratio (?3.1). Since both species were observed simultaneously, this is the first accurate estimation of the [35Cl] /[37Cl] isotopic ratio in molecular clouds. Our models indicate that even for large line opacities and possible hyperfine intensity anomalies, the H35Cl and H37Cl J = 1-0 integrated line-intensity ratio provides a good estimate of the 35Cl/37Cl isotopic abundance ratio. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important particiation from NASA.

Cernicharo, J.; Goicoechea, J. R.; Daniel, F.; Agúndez, M.; Caux, E.; de Graauw, T.; de Jonge, A.; Kester, D.; Leduc, H. G.; Steinmetz, E.; Stutzki, J.; Ward, J. S.

2010-07-01

35

Cu-NQR of CeCu2Si2 under high pressure  

NASA Astrophysics Data System (ADS)

We have measured 63Cu-NQR spectral lines and nuclear spin-lattice relaxation time T1 under pressure up to 5.4 GPa. Daphne oil 7474 is used as the pressure-transmitting medium to obtain good hydrostaticity. NQR frequency 63?q above 4 GPa suddenly decreases from the linear pressure dependence in the low pressure range (P <= 3.5 GPa). The observed sudden downward deviation of 63?q is associated with an increase of Ce valence. Above 4.5 GPa, the linear pressure dependence of 63?q is observed again, most likely related to the sharp crossover to the high valence state.

Fujiwara, K.; Iwata, M.; Okazaki, Y.; Ikeda, Y.; Araki, S.; Kobayashi, T. C.; Murata, K.; Geibel, C.; Steglich, F.

2012-12-01

36

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

37

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 2400 to 3000ppm. 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

38

Pulsed Spin Locking in Spin-1 NQR: Broadening Mechanisms  

NASA Astrophysics Data System (ADS)

Nuclear Quadrupole Resonance (NQR) is a branch of magnetic resonance physics that allows for the detection of spin I > 1/2 nuclei in crystalline and semi-crystalline materials. Through the application of a resonant radio frequency (rf) pulse, the nuclei's response is to create an oscillating magnetic moment at a frequency unique to the target substance. This creates the NQR signal, which is typically weak and rapidly decaying. The decay is due to the various line broadening mechanisms, the relative strengths of which are functions of the specific material, in addition to thermal relaxation processes. Through the application of a series of rf pulses the broadening mechanisms can be refocused, narrowing the linewidth and extending the signal in time. Three line broadening mechanisms are investigated to explain the NQR signal's linewidth and behavior. The first, electric field gradient (EFG) inhomogeneity, is due to variations in the local electric environment among the target nuclei, for instance from crystal imperfections. While EFG inhomogeneity can vary between samples of the same chemical composition and structure, the other broadening mechanisms of homonuclear and heteronuclear dipolar coupling are specific to this composition and structure. Simple analytical models are developed that explain the NQR signal response to pulse sequences by accounting for the behavior of each broadening mechanism. After a general theoretical introduction, a model of pairs of spin-1 nuclei is investigated, and the refocusing behaviors of EFG and homonuclear dipolar coupling are analyzed. This reveals the conditions where EFG is refocused but homonuclear dipolar coupling is not. In this case the resulting signal shows a rapid decay, the rate of which becomes a measure of interatomic distances. This occurs even in the more complex case of a powder sample with its many randomly oriented crystallites, under particular pulsing conditions. Many target NQR compounds are rich in hydrogen, and therefore might have a significant heteronuclear dipolar coupling component. To incorporate this, a second model is developed composed of two different nuclear species, one spin 1 the other spin 1/2, although the work can be extended to additional spin species. This model reveals that heteronuclear dipolar coupling for this system behaves just like EFG broadening under spin locking, and that the strong homonuclear response is still observable. The experimental results closely match theoretical predictions, and the conclusions greatly expand the number of target substances that are suitable for this measurement technique of homonuclear dipolar coupling. The combined results explain why certain pulse sequences perform better than others for substance detection: it is because of the relative strengths of the line broadening mechanisms. Therefore the ability to measure homonuclear dipolar coupling's contribution to the linewidth is useful not only for material characterization, but also for substance detection. By explaining the conditions that reveal homonuclear coupling, we make it possible to measure the relative broadening strengths, increasing the efficiency of NQR in these roles.

Malone, Michael W.

39

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

40

Millimeter and Submillimeter Spectroscopy of NO35Cl: J Dependence of N2 and O2 Broadenings  

Microsoft Academic Search

Measurements on broadening by nitrogen and oxygen of lines of the type J + 10,J+1 <-- J0,J of NO35Cl have been carried out in the region 88-700 GHz with J ranging from 7 to 64. The observed decrease of the pressure-broadening coefficients for J > 10 is reproduced by theoretical calculations on N2 broadening performed by employing an ATC impact

L. Dore; G. Cazzoli; M. E. Charro; C. D. Esposti; G. Buffa; O. Tarrini

1993-01-01

41

37Cl/ 35Cl isotope effects on the carbon and proton shielding in CH 3Cl: measurement and theory  

NASA Astrophysics Data System (ADS)

A model is proposed to explain the small isotope shifts in the 1H resonance (? 0.2 ppb) and in the 13C resonance (? 6 ppb) of CH 3Cl when 35Cl is replaced by 37Cl. These shifts are related to the slight changes in the C?Cl and C?H bond lengths and the HCCl interbond angles brought about by the isotopic substitution and to the derivatives of the shielding with respect to these parameters. The changes in geometry calculated from a quadratic and cubic force field are ? r(C?Cl) = -0.000041 Å, ? r(C?H) = 0.000001 Å and ??(HCCl) = 0.00063° at 300 K when 37Cl replaces 35Cl. The derivatives are obtained from a large basis set calculation at the SCF level. Excellent agreement between calculated and experimental results is obtained. In the case of the 13C isotope effect, changes in the C?Cl bond length and the mean square of the C?Cl bond lengths are sufficient to account for the shift. For the proton shift the contributions from the slight changes in the C?H bond length and HCCl angles, though they tend to cancel, are individually larger than experimental error and cannot be neglected even though the changes in the C?Cl bond length are again dominant.

Raynes, William T.; Grayson, Martin; Sergeyev, Nickolai M.; Sergeyeva, Natalia D.

1994-08-01

42

[sup 81]Br and [sup 35]Cl NMR investigation of sodium, silver, halo-sodalite semiconductor supralattices  

SciTech Connect

[sup 81]Br and [sup 35]Cl NMR yields, respectively, bromide and chloride site-specific information pertinent to the structural and electronic properties of Na[sub 8-n-p]Ag[sub n]X[sub 2-p]-sodalite, semiconductor cluster supralattices, where X = Br, Cl; 0 [le] n [le] 8; 0 [le] p [le] 2. The [sup 81]Br and [sup 35]Cl MAS chemical shifts and line shapes observed for encapsulated Na[sub 4]X and Ag[sub 4]X clusters within the sodalite cavities provide insight into the nature of the intracluster bonding (ionic-covalent character) and the extent of intercavity coupling. Substantial nuclear shielding is observed for encapsulated Ag[sub 4]X clusters in sodalite materials with high loading of Ag[sub 4]Br clusters, whereas no NMR signal is detected from silver-bromide clusters isolated within sodalite lattices. Spin-lattice and spin-spin relaxation measurements yield information on intracavity coupling and motion within the sodalite cages. The results enable one to explore the transition from isolated clusters to an expanded Ag[sub 4]X supralattice, through the compositional and temperature dependence of the NMR spectra of the sodalite halide anions. 22 refs., 10 figs.

Jelinek, R. (Lawrence Berkeley Lab., CA (United States)); Stein, A.; Ozin, G.A. (Univ. of Toronto, Ontario (Canada))

1993-03-24

43

A general numerical analysis of time-domain NQR experiments.  

PubMed

We introduce a general numerical approach for solving the Liouville equation of an isolated quadrupolar nuclide that can be used to analyze the unitary dynamics of time-domain NQR experiments. A numerical treatment is necessitated by the dimensionality of the Liouville space, which precludes analytical, closed form solutions for I > 3/2. Accurate simulations of experimental nutation curves, forbidden transition intensities, powder and single crystal spectra, and off-resonance irradiation dynamics can be computed with this method. We also examine the validity of perturbative approximations where the signal intensity of a transition is proportional to the transition moment between the eigenstates of the system, thus providing a simple basis for determining selection rules. Our method allows us to calculate spectra for all values of the asymmetry parameter, eta, and sample orientations relative to the coil axis. We conclude by demonstrating the methodology for calculating the response of the quadrupole system to amplitude- and frequency-modulated pulses. PMID:16996760

Harel, Elad; Cho, Herman

2006-12-01

44

Hyperfine structure of the J=1?0 transition of H 35Cl and H 37Cl: improved ground state parameters  

Microsoft Academic Search

The pure rotational J=1?0 transitions of H35Cl and H37Cl have been observed in the millimeter-wave region using the Lamb-dip technique to resolve the hyperfine structure due to 35Cl or 37Cl and H. The present observations allow to provide not only very accurate hyperfine constants but also, joint together with previous data, the most accurate ground state rotational parameters known up

Gabriele Cazzoli; Cristina Puzzarini

2004-01-01

45

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 C2221 and P21 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

46

Decay studies of 59Cu* formed in the 35Cl + 24Mg reaction using the dynamical cluster-decay model  

NASA Astrophysics Data System (ADS)

The reformulated dynamical cluster-decay model (DCM) is applied to study the decay of odd-A and non-? structured 59Cu* formed in the 35Cl+24Mg reaction at Elab=275 MeV. Here, the temperature (T)-dependent binding energies due to Krappe are used. The roles of Wigner and pairing energies in the fragmentation potential are explicitly shown in this work. For the temperature T=4.1898 MeV corresponding to Elab=275 MeV, the contribution of pairing vanishes and the resulting structure of the fragmentation potential due to Wigner term is shown. In addition to this, we have studied the role of factor ? appearing in the inertia part of the equation of motion dictating the mass-transfer process. It is shown that this factor has significant effect in the structure of preformation probability values and hence in turn we see significant changes in the cross sections. We compare the cross sections of the measured charge distributions of the fission fragments for two limiting values of the parameter ? with the experimental data. In order to fit the total cross-section values, a linear relation is obtained between the free parameter of the model ?R and the factor ? appearing in the hydrodynamical mass.

Karthikraj, C.; Balasubramaniam, M.

2013-02-01

47

Isospin symmetry breaking at high spin in the mirror nuclei {sup 35}Ar and {sup 35}Cl  

SciTech Connect

High-spin states in {sup 35}Ar and {sup 35}Cl have been populated in the {sup 24}Mg({sup 16}O, {alpha}n) and {sup 24}Mg({sup 16}O, {alpha}p) reactions, respectively, at a beam energy of 70 MeV. The comparison between the level schemes of these mirror nuclei shows a striking asymmetry in the population yield of high-spin analog states of positive parity, which indicates different intensities of E1 transitions connecting positive- and negative-parity structures in both nuclei. Large energy differences are observed between analog states of negative parity with configurations of dominant pure single-particle character. This results from the comparison with large-scale shell-model calculations in the s{sub 1/2}d{sub 3/2}f{sub 7/2}p{sub 3/2} valence space. It is shown that important contributions to the energy differences arise from the multipole Coulomb and the relativistic electromagnetic spin-orbit interactions.

Della Vedova, F. [Dipartimento di Fisica dell Universita and INFN, Padova (Italy); INFN, Laboratori Nazionali di Legnaro, Legnaro (Italy); Lenzi, S. M.; Bazzacco, D.; Brandolini, F.; Farnea, E.; Lunardi, S.; Menegazzo, R.; Nespolo, M.; Pavan, P.; Alvarez, C. Rossi; Venturelli, R. [Dipartimento di Fisica dell Universita and INFN, Padova (Italy); Ionescu-Bujor, M.; Bucurescu, D.; Iordachescu, A. [Horia Hulubei National Institute for Physics and Nuclear Engineering, Bucharest (Romania); Marginean, N. [INFN, Laboratori Nazionali di Legnaro, Legnaro (Italy); Horia Hulubei National Institute for Physics and Nuclear Engineering, Bucharest (Romania); Axiotis, M.; Martinez, T.; Napoli, D. R. [INFN, Laboratori Nazionali di Legnaro, Legnaro (Italy); Bizzeti-Sona, A. M.; Bizzeti, P. G. [Dipartimento di Fisica dell Universita and INFN, Florence (Italy)] (and others)

2007-03-15

48

High-Resolution Infrared Studies of ? 1, 2? 1, and 2? 4 Bands of CH 35Cl 3  

NASA Astrophysics Data System (ADS)

The C-H stretching fundamental band ? 1 (3033 cm -1) of chloroform CH 35Cl 3 has been investigated together with the first overtone 2? 1 (5941 cm -1) in order to determine the rotation vibration parameters. From the ? 1 band ? 1C=-0.025 46(41)×10 -3 cm -1 and ? 1B=-0.010 688(44)×10 -3 cm -1 were obtained. The hot bands connected to the low lying fundamentals ? 3 and ? 6 have been analyzed and anharmonicity constants have been derived. Both the parallel and the perpendicular component band of the C-H bending overtone 2? 4 have also been studied. In the parallel band (2410 cm -1) more than 900 lines were included in the fit. In the perpendicular band (2443 cm -1) 2615 lines were fitted using a model with one resonance. Among other things the results C0- Cv=0.025 262 (20)×10 -3 cm -1, B0- Bv=0.134 883 (25)×10 -3 cm -1, and ( C?) v=-0.111 867 56 (30) cm -1 were obtained.

Pietilä, J.; Alanko, S.; Horneman, V.-M.; Anttila, R.

2002-12-01

49

Fragmentation Cross Sections of Medium-Energy 35Cl, 40Ar, and 48TiBeams on Elemental Targets  

SciTech Connect

Charge-changing and fragment production cross sections at 0degrees have been obtained for interactions of 290, 400, and 650MeV/nucleon 40Ar beams, 650 and 1000 MeV/nucleon 35Cl beams, and a 1000MeV/nucleon 48Ti beam. Targets of C, CH2, Al, Cu, Sn, and Pb were used.Using standard analysis methods, we obtain fragment cross sections forcharges as low as 8 for Cl and Ar beams, and as low as 10 for the Tibeam. Using data obtained with small-acceptance detectors, we reportfragment production cross sections for charges as low as 5, corrected foracceptance using a simple model of fragment angular distributions. Withthe lower-charged fragment cross sections, we cancompare the data topredictions from several models (including NUCFRG2, EPAX2, and PHITS) ina region largely unexplored in earlier work. As found in earlier workwith other beams, NUCFRG2 and PHITS predictions agree reasonably wellwith the data for charge-changing cross sections, but do not accuratelypredict the fragment production cross sections. The cross sections forthe lightest fragments demonstrate the inadequacy of several models inwhich the cross sections fall monotonically with the charge of thefragment. PHITS, despite not agreeing particularly well with the fragmentproduction cross sections on average, nonetheless qualitativelyreproduces somesignificant features of the data that are missing from theother models.

Zeitlin, C.; Guetersloh, S.; Heilbronn, L.; Miller, J.; Fukumura,A.; Iwata, Y.; Murakami, T.; Sihver, L.; Mancusi, D.

2007-12-08

50

Numerical simulation of NQR/NMR: Applications in quantum computing.  

PubMed

A numerical simulation program able to simulate nuclear quadrupole resonance (NQR) as well as nuclear magnetic resonance (NMR) experiments is presented, written using the Mathematica package, aiming especially applications in quantum computing. The program makes use of the interaction picture to compute the effect of the relevant nuclear spin interactions, without any assumption about the relative size of each interaction. This makes the program flexible and versatile, being useful in a wide range of experimental situations, going from NQR (at zero or under small applied magnetic field) to high-field NMR experiments. Some conditions specifically required for quantum computing applications are implemented in the program, such as the possibility of use of elliptically polarized radiofrequency and the inclusion of first- and second-order terms in the average Hamiltonian expansion. A number of examples dealing with simple NQR and quadrupole-perturbed NMR experiments are presented, along with the proposal of experiments to create quantum pseudopure states and logic gates using NQR. The program and the various application examples are freely available through the link http://www.profanderson.net/files/nmr_nqr.php. PMID:21324720

Possa, Denimar; Gaudio, Anderson C; Freitas, Jair C C

2011-04-01

51

Probing midrapidity source characteristics with charged particles and neutrons in the 35Cl+natTa reaction at 43 MeV\\/nucleon  

Microsoft Academic Search

The characteristics of the midrapidity and target sources (apparent temperatures, velocities, and neutron multiplicities) extracted from the neutron energy spectra, have been measured for various quasiprojectile (QP) excitation energies, reconstructed from charged particles of well defined peripheral events in the 35Cl+natTa reaction at 43 MeV\\/nucleon. The reconstructed excitation energy of the QP is always smaller than the excitation energy calculated

Y. Larochelle; C. St-Pierre; L. Beaulieu; N. Colonna; L. Gingras; G. C. Ball; D. R. Bowman; M. Colonna; G. D'erasmo; E. Fiore; D. Fox; A. Galindo-Uribarri; E. Hagberg; D. Horn; R. Laforest; A. Pantaleo; R. Roy; G. Tagliente

1999-01-01

52

NQR spin-echo methods at very low temperatures  

Microsoft Academic Search

Pulsed methods may be successfully used in very low temperature NMR or NQR experiments provided good thermal anchoring of the sample is achieved. In order to reduce heating effects, it is advantageous to use rf pulses that are shorter than the standard magnetization tipping pulses used at higher temperatures. The present work describes the use of short nonstandard rf pulses

I. P. Goudemond; J. M. Keartland; M. J. R. Hoch

1991-01-01

53

The two-frequency nuclear quadrupole resonance for explosives detection  

Microsoft Academic Search

The two-frequency nuclear quadrupole resonance (NQR) of14N nuclei is described for purposes of explosives detection. Two applications are known: two-frequency NQR for increasing the\\u000a signal intensity, two-frequency NQR for improved reliability of explosives detection. The two-frequency experiments were carried\\u000a out in hexahydro-1,3,5-trinitro-s-triazine C3H6N6O6 and sodium nitrite NaNO2 as a substitute for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocycine C4H8N8O8. The two-frequency sequences for NQR are proposed

G. V. Mozjoukhine

2000-01-01

54

27Al-NQR\\/NMR Study of Kondo Semiconductor CeFe2Al10  

Microsoft Academic Search

27Al-NQR\\/NMR measurements have been performed on CeFe2Al10 in relevance to the novel phase below T0=27 K of isostructural CeRu2Al10. NQR peaks are assigned to five crystallographically inequivalent Al sites. No splitting of the NQR spectra down to 1.5 K confirms the lack of phase transition in this compound. The gaplike decrease in the spin-lattice relaxation rate 1\\/T1 above about 20

Yukihiro Kawamura; Shingo Edamoto; Tomoaki Takesaka; Takashi Nishioka; Harukazu Kato; Masahiro Matsumura; Yo Tokunaga; Shinsaku Kambe; Hiroshi Yasuoka

2010-01-01

55

The single NqrB and NqrC subunits in the Na(+)-translocating NADH: quinone oxidoreductase (Na(+)-NQR) from Vibrio cholerae each carry one covalently attached FMN.  

PubMed

The Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) is the prototype of a novel class of flavoproteins carrying a riboflavin phosphate bound to serine or threonine by a phosphodiester bond to the ribityl side chain. This membrane-bound, respiratory complex also contains one non-covalently bound FAD, one non-covalently bound riboflavin, ubiquinone-8 and a [2Fe-2S] cluster. Here, we report the quantitative analysis of the full set of flavin cofactors in the Na(+)-NQR and characterize the mode of linkage of the riboflavin phosphate to the membrane-bound NqrB and NqrC subunits. Release of the flavin by ?-elimination and analysis of the cofactor demonstrates that the phosphate group is attached at the 5'-position of the ribityl as in authentic FMN and that the Na(+)-NQR contains approximately 1.7mol covalently bound FMN per mol non-covalently bound FAD. Therefore, each of the single NqrB and NqrC subunits in the Na(+)-NQR carries a single FMN. Elimination of the phosphodiester bond yields a dehydro-2-aminobutyrate residue, which is modified with ?-mercaptoethanol by Michael addition. Proteolytic digestion followed by mass determination of peptide fragments reveals exclusive modification of threonine residues, which carry FMN in the native enzyme. The described reactions allow quantification and localization of the covalently attached FMNs in the Na(+)-NQR and in related proteins belonging to the Rhodobacter nitrogen fixation (RNF) family of enzymes. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012). PMID:22366169

Casutt, Marco S; Schlosser, Andreas; Buckel, Wolfgang; Steuber, Julia

2012-10-01

56

Detection of chloronium and measurement of the 35Cl/37Cl isotopic ratio at z = 0.89 toward PKS 1830-211  

NASA Astrophysics Data System (ADS)

We report the first extragalactic detection of chloronium (H2Cl+) in the z = 0.89 absorber in front of the lensed blazar PKS 1830-211. The ion is detected through its 111-000 line along two independent lines of sight toward the North-East and South-West images of the blazar. The relative abundance of H2Cl+ is significantly higher (by a factor ~7) in the NE line of sight, which has a lower H2/H fraction, indicating that H2Cl+ preferably traces the diffuse gas component. From the ratio of the H235Cl+ and H237Cl+ absorptions toward the SW image, we measure a 35Cl/37Cl isotopic ratio of 3.1-0.2+0.3 at z = 0.89, similar to that observed in the Galaxy and the solar system.

Muller, S.; Black, J. H.; Guélin, M.; Henkel, C.; Combes, F.; Gérin, M.; Aalto, S.; Beelen, A.; Darling, J.; Horellou, C.; Martín, S.; Menten, K. M.; V-Trung, Dinh; Zwaan, M. A.

2014-06-01

57

Relative intensities of prompt ?-rays from the 35Cl(n,?)36Cl reaction with thermal neutrons as secondary ?-ray intensity standards.  

PubMed

The relative intensities of 16 prompt ?-rays from the (35)Cl(n,?)(36)Cl reaction with a thermal neutron were precisely determined as secondary ?-ray intensity standards with HPGe detectors. The detection efficiencies were calibrated from 0.2 to 10.8 MeV using the standard sources (152)Eu and (56)Co and the (14)N(n,?)(15)N reaction. We performed appropriate analyses for the evaluation of doublet peaks, subtraction of mixing with escape ?-rays and other corrections; consequently, the values were determined within 1% accuracy. Relative intensities in the range of 0.7 to 8.6 MeV are proposed as reliable secondary standards for 16 ?-rays. PMID:23287705

Shibata, Michihiro; Tojo, Akinori; Miyazaki, Itaru; Furuta, Masataka; Hayashi, Hiroaki; Kojima, Yasuaki; Shima, Yosuke; Taniguchi, Akihiro

2013-03-01

58

Possible stripe fluctuations in La2 - x - yNdySrxCuO4 at room temperature observed by 63Cu NQR spectroscopy  

NASA Astrophysics Data System (ADS)

63Cu nuclear quadrupole resonance (NQR) studies at room temperature were reported on six Nd-doped La2 - xSrxCuO4 samples. The NQR spectrum for La1.48Nd0.4Sr0.12CuO4 has a different line shape compared with those from the other samples, which is similar to the case of the insulating La2CuO4. This may suggest that the stripe fluctuations at such a special Nd and Sr doping fall into the frequency window of 63Cu NQR. The spectra of the other five samples were analysed by pairs of 63Cu and 65Cu Gaussians at A and B sites. The full width of half-maxim (FWHM) for 63Cu at B sites is anomalously large for La1.45Nd0.4Sr0.15CuO4, which was considered to be related to the stripe fluctuations.

Zhang, Q.-M.; Ying, X. N.; Gu, M.; Wang, Y. N.

2005-04-01

59

^63Cu NQR relaxation in the p-type transparent conductor CuScO_2:Mg  

NASA Astrophysics Data System (ADS)

Transparent conducting oxides with p-type conductivity are of interest as electronic complements to the more familiar n-type transparent conductors. This paper reports the first results of a study of carrier spin dynamics in p-type CuScO_2:Mg using ^63Cu nuclear spin-lattice relaxation measurements. Relaxation rates 1/T1 have been measured by nuclear quadrupole resonance (NQR) over the range 280 K to 400 K. The ^63Cu NQR frequency is found to be 28,135 ± 5 kHz at 300 K and to decrease linearly with temperature over the experimental range. The value of 1/T1 at 300 K is 130 ± 10 s-1. The rate is weakly dependent on temperature and increases by only about 15 % up to 400 K. This behavior contrasts sharply with results obtained previously(1. A. Rajabzadeh, J. Tate and W. Warren, Bull. Am. Phys. Soc. 48, 1009 (2003).) for the related material CuYO_2:Ca. In that material, relaxation rates for ^63Cu and ^65Cu were strongly temperature dependent, being approximately thermally-activated with activation energy 152 ± 10 meV. The nuclear relaxation properties of CuScO_2:Mg are suggestive of more conventional metallic transport in CuScO_2:Mg compared with CuYO_2:Ca.

Rossi, Vincent; Tate, Janet; Warren, William; Li, Jun; Sleight, Arthur

2003-05-01

60

Investigation of Structural Information for Boron - Solids and Aluminates via NMR and Nqr Studies.  

NASA Astrophysics Data System (ADS)

Nuclear Magnetic Resonance (NMR) has been prevailed in investigating local structures for a variety of materials: various oxide glasses, zeolites, superconductors, etc. Since glasses have short range ordered structures instead of long range ordered ones in crystals, NMR is usually more useful in determining the local structures for many glasses than any other detection methods do. Along with NMR, Nuclear Quadrupole Resonance (NQR) has become important recently for obtaining structural information from such glasses. The NQR studies prove in this thesis that they provide more accurate structural information than the NMR studies have done. This study presents boron and aluminum NMR, and NQR studies for some borate glasses and compounds, icosahedral boron-rich solids, some crystalline aluminosilicates. Various borates were employed to acquire structural information as well as to determine the quadrupole parameters (the quadrupole coupling constant Q_{cc } and the asymmetry parameter eta ) using NQR under a guidance of NMR or vice versa. By NQR a previously unknown boron site was observed for vitreous Li_2OcdotB _2O_3. The boron site had an intermediate Q_{cc } value in-between the reported value ranges of Q_{cc} for BO _3 and BO_4 sites, and was concluded to be a previously unknown BO _4 site. The NMR and NQR studies were performed on some icosachedral boron-rich solids: alpha -rhombohedral boron (B_{12}), beta-boron (B_{105 }) and boron carbide (B_{12 }C_3). Strong NQR responses were obtained from boron atoms in the C-B-C chains along with several other NQR responses from boron atoms in the icosahedral. These NQR results were consistent with the NMR studies by Silver and Bray, and those by Hynes and Alexander. Also, for the icosahedral boron-rich solids, the ^{11}B NMR studies revealed the possibility of chemical shifts due to two distinct boron sites in the icosahedra. A very interesting phenomenon was found from an isotopic change of boron nuclei (substitution of ^{10}B for ^{11}B) in boron carbide: in ^{11}B high field (7.05 Tesla) NMR spectra, two distinct peaks separated by some chemical shifts for unenriched boron carbide (B _{12}C_3) became a single peak for ^{10} B enriched boron carbide (90.61 at.% of ^{10}B). Three different forms of crystalline aluminosilicate (Al_2SiO_5) were studied by NQR. The NQR study yielded more accurate values of the quadrupole parameters for ^ {27}Al than the previous NMR single crystal study did.

Lee, Donghoon

61

Stark effect of 14N NQR in single crystals of ferroelectric NaNO2  

Microsoft Academic Search

The effects of the external electric field on 14N nuclear quadrupole resonance (NQR) have been investigated in the ferroelectric phase of sodium nitrite (NaNO2) single crystals with either the single domain or the multidomain structure. NQR measurements of two resonance lines of n and n were made at 77 K under the external electric field up to 25 kV\\/cm. The

S. H. Choh; Y. J. Park; H. K. Kim; Y. M. Chang

1989-01-01

62

Nuclear Quadrupole Tensors for (35)Cl and (37)Cl in cis-1-chloro-2-fluoroethylene Obtained by Detection of Perturbation-Allowed DeltaJ = 2 and DeltaJ = 3 Transitions.  

PubMed

The nuclear quadrupole hyperfine structure in rotational transitions of cis-1-chloro-2-fluoroethylene was measured for both (35)Cl and (37)Cl containing isotopomers in the millimeter-wave region. Near degeneracies of the 9(3,7) and 10(2,9) levels of (35)ClHC&dbond;CFH and of the 19(9,10/11) and 17(10,7/8) levels of (37)ClHC&dbond;CFH cause strong perturbations of the hyperfine patterns and give rise to perturbation-allowed DeltaJ = 2 and DeltaJ = 3 transitions. Lamb-dip measurements of such perturbed hyperfine patterns and of forbidden DeltaJ = +2 and perturbation-enhanced DeltaJ = 0 transitions of (35)ClHC&dbond;CFH provided an accurate determination of chi(ab), the off-diagonal element of the inertial nuclear quadrupole tensor. For (37)ClHC&dbond;CFH, chi(ab) was determined for the first time thanks to the observation of perturbed hyperfine patterns and of forbidden DeltaJ = +3 and DeltaJ = -2 transitions. Additional measurements of hyperfine structures led to improved values for the diagonal elements of the chi tensor of both (35)Cl and (37)Cl. Moreover, the complete inertial nuclear quadrupole tensor was evaluated from the field gradient at the chlorine nucleus computed by using the Multi-Configuration Self-Consistent Field (MCSCF) approach and employing basis sets of triple-zeta quality: very good agreement with the experiment was obtained. Copyright 2000 Academic Press. PMID:11148094

Dore; Puzzarini; Cazzoli; Gambi

2000-12-01

63

Experimental study of the structure of chalcogenide glassy semiconductors in three-component systems of Ge-As-Se and As-Sb-Se by means of NQR and EPR spectroscopy  

NASA Astrophysics Data System (ADS)

The structure of chalcogenide glassy semiconductors in three-component systems of Ge-As-Se and As-Sb-Se has been studied by means of both NQR (nuclear quadrupole resonance) and EPR (electron paramagnetic resonance) spectroscopy. It is investigated that in the glasses of both systems the value of the electric field gradient at the resonating nuclei grows with increasing concentration of the clusters As2Se3 and Sb2Se3, thereby increasing the NQR resonance frequencies. It appears that for the Ge-As-Se system the structural transition from a two-dimensional to three-dimensional structure occurs at average coordination number = 2.45. The EPR spectral parameters of glasses depend on the composition, the average coordination number and the temperature, and these are discussed. The effect of "ageing" for CGS (chalcogenide glassy semiconductors) of As-Sb-Se system due to partial crystallization of the sample is observed from the EPR spectra.

Bolebrukh, Olga N.; Sinyavsky, Nikolay Ya.; Korneva, Irina P.; Dobosz, Bernadeta; Ostafin, Michal; Nogaj, Boleslaw; Krzyminiewski, Ryszard

2013-12-01

64

Copper Nqr and NMR Study of Metal-Substituted Yttrium BARIUM(2) COPPER(3) OXYGEN(7) and Yttrium BARIUM(2) COPPER(4) OXYGEN(8)  

NASA Astrophysics Data System (ADS)

Pulsed nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) have been used to investigate the effect of metal-substitution for copper in YBa_2Cu_3O_7 (YBCO123) and YBa_2Cu_4O_8 (YBCO124). Among many metal substitutions, Zn has an especially dramatic effect in suppressing the superconducting temperature T_{c}, and hence superconductivity. More interesting is that Zn and Fe have the same T_{c} suppression effect in YBCO124. This study focuses on the Zn substitutions in YBCO123 and Zn, Fe, and Co substitutions in YBCO124. In Zn doped YBCO123, Cu(2), plane site, NQR spectra and the frequency dependence of the spin-lattice relaxation rates have been measured over a temperature range from 77 K to 300 K to study the correlation of the suppression of the relaxation rate with the distance between the probe Cu nuclei and the impurity. It is found that the relaxation rate is insensitive to the variation of the NQR resonance frequency. However, by comparing the results of the Zn doped YBCO124 with those of YBCO123, it can be concluded that the suppression of the relaxation rate for both YBCO compounds in the normal state is caused by destruction of short-range antiferromagnetic correlation with substitution of nonmagnetic ion Zn on the Cu(2) sites. NQR and NMR measurements were carried out on both Cu(2), plane, and Cu(1), chain sites, for various concentrations of Zn, Fe, and Co dopants in YBCO124 over a temperature range from 77 K to 300 K. A strong correlation of the enhancement of Cu(2) spin lattice relaxation rate and suppression of superconductivity by impurities was found. The temperature dependence of the Cu(2) NMR linewidth exhibits a strong RKKY type exchange interaction below 225 K for Zn and Fe doped samples, which indicates the formation of the local magnetic moment. The enhancement of the relaxation rate is caused by the local magnetic moment Fe^ {+3} ion and the moments on Cu(2) neighbors when Zn^{+2} is substituted on Cu(2). This study gives us a clear picture of the spin pseudogap behavior in the high temperature superconductor cuprates. It also suggests that the magnetic moment on the CuO_2 plane may relate to the suppression of T_{c} in metal-substituted YBCO124.

Cheng, Show-Jye

65

27Al-NQR Study on Novel Phase Transition in CeOs2Al10  

NASA Astrophysics Data System (ADS)

We have performed 27Al-NQR measurements in CeOs2Al10 which exhibits a novel phase transition at T0=29 K The NQR parameters determined for all the Al sites in ambient pressure were compared with those in CeRu2Al10 with T0=27 K and CeFe2Al10 with no phase transition. The distinct NQR splitting just below T0=32.5 K under pressure 0.66 GPa ensures an enhancement of T0 and a homogeneous transition. Despite the increase of T0, the nuclear spin-lattice relaxation rate 1/Tl is suppressed over whole range of temperature than in ambient pressure. The characteristic features of no critical slowing down at T0 and of the remarkable decrease of 1/T1T starting at T > T0 become prominent under pressure, suggesting an approach to Kondo semiconductor in a valence fluctuation regime.

Matsumura, M.; Inagaki, T.; Kato, H.; Nishioka, T.; Tanida, H.; Sera, M.

2012-12-01

66

NQR1 controls lifespan by regulating the promotion of respiratory metabolism in yeast  

PubMed Central

Summary The activity and expression of plasma membrane NADH coenzyme Q reductase is increased by calorie restriction (CR) in rodents. Although this effect is well established and is necessary for CR's ability to delay aging, the mechanism is unknown. Here we show that the Saccharomyces cerevisiae homolog, NQR1, resides at the plasma membrane and when overexpressed extends both replicative and chronological lifespan. We show that NQR1 extends replicative lifespan in a SIR2-dependent manner by shifting cells towards respiratory metabolism. Chronological lifespan extension, in contrast, occurs via a SIR2-independent decrease in ethanol production. We conclude that NQR1 is a key mediator of lifespan extension by CR through its effects on yeast metabolism and discuss how these findings could suggest a function for this protein in lifespan extension in mammals.

Jimenez-Hidalgo, Maria; Santos-Ocana, Carlos; Padilla, Sergio; Villalba, Jose M.; Lopez-Lluch, Guillermo; Martin-Montalvo, Alejandro; Minor, Robin K.; Sinclair, David A.; de Cabo, Rafael; Navas, Placido

2009-01-01

67

Optimised NQR pulse technique for the effective detection of Heroin Base.  

PubMed

The nuclear quadrupole resonance (NQR) method has been applied to Heroin Base (HB) to find an optimised multi-pulse technique for effective detection of HB. Experimental results of applying the proposed spin-locking multi-pulse (SLMP) technique to nitrogen-14 NQR in this sample are presented and convincingly demonstrate as a path towards efficient detection. A detection using a sequence of this character could be achieved over real-world scan volumes for screening of goods. All experiments were carried out at room temperature. PMID:18342493

Rudakov, T N; Hayes, P A; Flexman, J H

2008-03-01

68

35Cl/37Cl isotope effects in 103Rh NMR of [RhCl(n)(H2O)(6-n)](3-n) complex anions in hydrochloric acid solution as a unique 'NMR finger-print' for unambiguous speciation.  

PubMed

A detailed analysis of the (35)Cl/(37)Cl isotope effects observed in the 19.11 MHz (103)Rh NMR resonances of [RhCl(n)(H(2)O)(6-n)](3-n) complexes (n=3-6) in acidic solution at 292.1K, shows that the 'fine structure' of each (103)Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These (35)Cl/(37)Cl isotope effects in the (103)Rh NMR resonance of the [Rh(35/37)Cl(6)](3-) species manifest only as a result of the statistically expected (35)Cl/(37)Cl isotopologues, whereas for the aquated species such as for example [Rh(35/37)Cl(5)(H(2)O)](2-), cis-[Rh(35/37)Cl(4)(H(2)O)(2)](-) as well as the mer-[Rh(35/37)Cl(3)(H(2)O)(3)] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-[RhCl(4)(H(2)O)(2)](-), trans-[RhCl(4)(H(2)O)(2)](-), fac-[RhCl(3)(H(2)O)(3)] and mer-[RhCl(3)(H(2)O)(3)] based on the (103)Rh NMR line shape, other than on the basis of their very similar ?((103)Rh) chemical shift. The (103)Rh NMR resonance structure thus serves as a novel and unique 'NMR-fingerprint' leading to the unambiguous assignment of [RhCl(n)(H(2)O)(6-n)](3-n) complexes (n=3-6), without reliance on accurate ?((103)Rh) chemical shifts. PMID:22632050

Geswindt, Theodor E; Gerber, Wilhelmus J; Brand, D Jacobus; Koch, Klaus R

2012-06-12

69

NQR investigation of pressure-induced charge transfer in oxygen-deficient YBa sub 2 Cu sub 3 O sub 7-. delta. (. delta. = 0. 38)  

SciTech Connect

Measurements of the pressure dependence of {sup 63}Cu nuclear quadrupole frequency in YBa{sub 2}Cu{sub 3}O{sub 6.62} from ambient pressure up to 1.5 GPa at 4k have been performed. {Tc} was found to increase with pressure: d{Tc}/dp {approximately} 5 K/GPa. All observed NQR lines are linear in pressure: dln{nu}{sub Q}/dp=z. We found positive z for the empty chain sites, consistent with ionic (Cu{sup 1+}) configuration in which the atom simply feels a squeezing lattice. Planar coppers close to the empty chains have positive z, while those that are close to full chains have z {approximately} 0. We present an analysis of the NQR result on the basis of the charge transfer model in which the mobile charges migrate from the chain to the plane sites. We deduced that a transfer of 0.021 holes to the O(2,3) sites would explain the result in YBa{sub 2}Cu{sub 3}O{sub 6.62}, whereas only 0.007 holes transfer in fully oxygenated YBa{sub 2}Cu{sub 3}O{sub 7}.

Reyes, A.P.; Ahrens, E.T.; Hammel, P.C.; Heffner, R.H. (Los Alamos National Lab., NM (United States)); Takigawa, M. (International Business Machines Corp., Yorktown Heights, NY (United States). Thomas J. Watson Research Center)

1992-01-01

70

Spectroscopic Constants for HCFC22 from Rotational and High-Resolution Vibration–Rotation Spectra: CHF 2 37Cl and 13CHF 2 35Cl Isotopomers  

Microsoft Academic Search

The rotational spectrum of CHF2Cl in natural abundance has been measured over the frequency region 8–705 GHz and accurate sextic level constants in the rotational Hamiltonian have been determined for the ground states of the CHF237Cl and the13CHF235Cl isotopic species. In addition, the rotational spectrum in the two lowest excited vibrational states,v9= 1 andv6= 1, of the CHF237Cl isotopomer and

Z. Kisiel; J. L. Alonso; S. Blanco; G. Cazzoli; J. M. Colmont; G. Cotti; G. Graner; J. C. López; I. Merke

1997-01-01

71

Measurement of the spin-lattice relaxation time in the NQR of light nuclei  

SciTech Connect

This work proposed a method for increasing the signal/noise ratio in NQR by preliminary magnetization of the sample in a constant magnetic field B/sub 0/ and it subsequent adiabatic demagnetization. The proposed method for the measurement of spin-lattice relaxation times is verified experimentally with a number of compounds. The results agree well with published data.

Anferov, V.P.; Anferova, S.V.; Grechishkin, V.S.; Sinyavskii, N.Ya.

1988-01-01

72

Cooperative Phenomenon of Ferromagnetism and Unconventional Superconductivity in UGe2: A 73Ge-NQR Study under Pressure  

Microsoft Academic Search

We report on a cooperative phenomenon of ferromagnetism and unconventional superconductivity (SC) in UGe2 through the measurements of 73Ge nuclear-quadrupole-resonance (NQR) under pressure (P). The NQR spectra evidenced phase separation into ferromagnetic and paramagnetic phases in the vicinity of Pc˜ 1.5 GPa, pointing to a first-order transition. The measurements of nuclear-spin-lattice-relaxation-rate 1\\/T1 revealed that SC emerges under the background of

Atsushi Harada; Shinji Kawasaki; Hisashi Kotegawa; Yoshio Kitaoka; Yoshinori Haga; Etsuji Yamamoto; Yoshichika Onuki; K. M. Itoh; Eugene Haller; Hisatomo Harima

2005-01-01

73

Novel phase diagram of superconductivity and ferromagnetism in UGe2: a 73Ge-NQR study under high pressure  

Microsoft Academic Search

We report on the pressure-induced novel phases of ferromagnetism (FM) and superconductivity (SC) in the itinerant ferromagnet UGe2 through 73Ge-NQR measurements under pressure (P). The P dependence of the NQR spectrum points to a first-order transition from strongly to weakly polarized ferromagnetic phases (SP and WP) around a critical pressure of P_{\\\\mathrm {c}}^*\\\\sim 1.2 GPa. Furthermore, it shows the phase

Y. Kitaoka; H. Kotegawa; A. Harada; S. Kawasaki; Y. Kawasaki; Y. Haga; E. Yamamoto; Y. Onuki; K. M. Itoh; E. E. Haller; H. Harima

2005-01-01

74

Evidence for the microscopic coexistence of superconductivity and ferromagnetism in UGe2:Ge-NMR\\/NQR study  

Microsoft Academic Search

We report on the pressure-induced novel phases of ferromagnetism and superconductivity (SC) in the itinerant ferromagnet UGe2 via the 73Ge-NQR measurements under pressure (P). The NQR spectrum has revealed that the ferromagnetic phases are separated into weakly and strongly polarized phases around a critical value of Pc*˜1.2GPa, pointing to a first-order transition around Pc*. Here we present further evidence for

A. Harada; H. Kotegawa; Y. Kawasaki; G.-Q. Zheng; Y. Kitaoka; E. Yamamoto; Y. Haga; Y. Onuki; K. Itoh; E. E. Haller

2005-01-01

75

Evidence for Uniform Coexistence of Ferromagnetism and Unconventional Superconductivity in UGe2: A 73Ge-NQR Study under Pressure  

Microsoft Academic Search

We report on the itinerant ferromagnetic superconductor UGe2 through 73Ge-NQR measurements under pressure (P). The P dependence of the NQR spectrum signals a first-order transition from the low-temperature (T) and low-P ferromagnetic phase (FM2) to high-T and high-P one (FM1) around a critical pressure of Px ˜ 1.2 GPa. The superconductivity exhibiting a maximum value of Tsc=0.7 K at Px

H. Kotegawa; A. Harada; S. Kawasaki; Y. Kawasaki; Y. Kitaoka; Y. Haga; E. Yamamoto; Y. Onuki; K. M. Itoh; E. E. Haller; H. Harima

2005-01-01

76

Cooperative Phenomenon of Ferromagnetism and Unconventional Superconductivity in UGe2: A 73Ge-NQR Study under Pressure  

NASA Astrophysics Data System (ADS)

We report on a cooperative phenomenon of ferromagnetism and unconventional superconductivity (SC) in UGe2 through the measurements of 73Ge nuclear-quadrupole-resonance (NQR) under pressure (P). The NQR spectra evidenced phase separation into ferromagnetic and paramagnetic phases in the vicinity of Pc˜ 1.5 GPa, pointing to a first-order transition. The measurements of nuclear-spin-lattice-relaxation-rate 1/T1 revealed that SC emerges under the background of ferromagnetism, but not of the paramagnetic phase.

Harada, A.; Kawasaki, S.; Kotegawa, H.; Kitaoka, Y.; Haga, Y.; Yamamoto, E.; ?nuki, Y.; Itoh, K. M.; Haller, E. E.; Harima, H.

2005-10-01

77

Low-frequency nuclear quadrupole resonance with a dc SQUID  

SciTech Connect

Conventional pure nuclear quadrupole resonance (NQR) is a technique well suited for the study of very large quadrupolar interactions. Numerous nuclear magnetic resonance (NMR) techniques have been developed for the study of smaller quadrupolar interactions. However, there are many nuclei which have quadrupolar interactions of intermediate strength. Quadrupolar interactions in this region have traditionally been difficult or unfeasible to detect. This work describes the development and application of a SQUID NQR technique which is capable of measuring intermediate strength quadrupolar interactions, in the range of a few hundred kilohertz to several megahertz. In this technique, a dc SQUID (Superconducting QUantum Interference Device) is used to monitor the longitudinal sample magnetization, as opposed to the transverse magnetization, as a rf field is swept in frequency. This allows the detection of low-frequency nuclear quadrupole resonances over a very wide frequency range with high sensitivity. The theory of this NQR technique is discussed and a description of the dc SQUID system is given. In the following chapters, the spectrometer is discussed along with its application to the study of samples containing half-odd-integer spin quadrupolar nuclei, in particular boron-11 and aluminum-27. The feasibility of applying this NQR technique in the study of samples containing integer spin nuclei is discussed in the last chapter. 140 refs., 46 figs., 6 tabs.

Chang, J.W.

1991-07-01

78

Ru NQR Probe of Superconducting Property in Impurity-Doped CeRu 2  

Microsoft Academic Search

Superconducting characteristics of CeRu2 have been investigated by systematic measurements of the nuclear-spin lattice relaxation rate, 1\\/T1 of 101Ru on pure and impurity-substituted CeRu2, employing an NQR technique in zero magnetic field. (1\\/T1) for CeRu2 shows a broad coherence plateau just below T c followed by an exponential decrease well below T c. By contrast, a distinct coherence peak of

Hidekazu Mukuda; Kenji Ishida; Yoshio Kitaoka; Kunisuke Asayama

1998-01-01

79

Addition compounds of antimony trichloride and tribromide. Crystal structure and charge transfer from NQR data  

NASA Astrophysics Data System (ADS)

The correlation analysis of the quadrupcle coupling constants(QCC) for the antimony nuclei in the intermolecular compounds of SbCl 3 and SbBr 3 with aromatic hydrocarbons is carried out. The results confirm a supposition about the general similarity of the crystal structures of these complexes. The correlative dependence between the antimony QCC values and also the results of the chlorine and bromine NQR spectra Investigation permit the evaluation of the relative acceptor strength of the antimony trihalide molecules.

Kjuntsel, I. A.; Gordeev, A. D.

80

27Al-NQR/NMR Study of Kondo Semiconductor CeFe2Al10  

NASA Astrophysics Data System (ADS)

27Al-NQR/NMR measurements have been performed on CeFe2Al10 in relevance to the novel phase below T0=27 K of isostructural CeRu2Al10. NQR peaks are assigned to five crystallographically inequivalent Al sites. No splitting of the NQR spectra down to 1.5 K confirms the lack of phase transition in this compound. The gaplike decrease in the spin-lattice relaxation rate 1/T1 above about 20 K, following the Korringa law (T1T = const.) below 20 K, indicates a pseudogap opening near the Fermi level. The gap magnitude of 70 K with a mid-gap state of 42% is estimated based on a rectangular density of states. The gap magnitude is much larger than the gap of 15 K evaluated previously from the electrical resistivity, which suggests CeFe2Al10 to be a Kondo semiconductor with a Kondo temperature much higher than 300 K.

Kawamura, Yukihiro; Edamoto, Shingo; Takesaka, Tomoaki; Nishioka, Takashi; Kato, Harukazu; Matsumura, Masahiro; Tokunaga, Yo; Kambe, Shinsaku; Yasuoka, Hiroshi

2010-10-01

81

NQR Line Broadening Due to Crystal Lattice Imperfections and Its Relationship to Shock Sensitivity  

NASA Astrophysics Data System (ADS)

The hydrodynamic hot spot model is used to explain the difference between shock sensitive and shock insensitive explosives. Among the major factors that influence the shock sensitivity of energetic compounds are the quality and particle size of the energetic crystals used to formulate the cast plastic bonded explosive. As do all energetic compounds, RDX and HMX exhibit internal crystal defects the magnitude and type of which depend on the manufacturing process used to synthesize and re-crystallize the energetic compound. Nuclear Quadrupole Resonance (NQR) spectroscopy was used to determine the crystal quality of RDX, HMX and CL-20 obtained from various manufacturers. The NQR experimental results are discussed. Cast plastic bonded explosives were made using the RDX and HMX obtained from the various manufacturers and subsequently subjected to the NOL large-scale gap test (LSGT). The results of the LSGT are discussed and correlated with the NQR results. A relationship between the crystal defect density and shock initiation pressure of the plastic bonded explosive is developed and discussed.

Caulder, S. M.; Buess, M. L.; Garroway, A. N.; Miller, P. J.

2004-07-01

82

Multiple-pulse NQR dynamics of spin systems with strong heteronuclear coupling  

NASA Astrophysics Data System (ADS)

The results are presented of a theoretical consideration of the nuclear quadrupole resonance (NQR) and spin—spin relaxation for a paramagnetic body containing nuclei of two different sorts coupled by the strong homonuclear and heteronuclear dipole—dipole interactions and influenced by an external multiple-pulse radiofrequency magnetic field acting only on nuclei of one sort. Kinetic equations were obtained giving the possibility of finding the time dependence of the magnetization of the body and the kinetic coefficients calculated as a function of the multiple-pulse field parameters. The possibilities of using the results in question for molecular structure and molecular dynamics investigations are briefly surveyed.

Furman, G. B.; Shaposhnikov, I. G.

1994-05-01

83

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

84

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.

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

2014-01-01

85

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

86

NQR investigation of pressure-induced charge transfer in oxygen-deficient YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} ({delta} = 0.38)  

SciTech Connect

Measurements of the pressure dependence of {sup 63}Cu nuclear quadrupole frequency in YBa{sub 2}Cu{sub 3}O{sub 6.62} from ambient pressure up to 1.5 GPa at 4k have been performed. {Tc} was found to increase with pressure: d{Tc}/dp {approximately} 5 K/GPa. All observed NQR lines are linear in pressure: dln{nu}{sub Q}/dp=z. We found positive z for the empty chain sites, consistent with ionic (Cu{sup 1+}) configuration in which the atom simply feels a squeezing lattice. Planar coppers close to the empty chains have positive z, while those that are close to full chains have z {approximately} 0. We present an analysis of the NQR result on the basis of the charge transfer model in which the mobile charges migrate from the chain to the plane sites. We deduced that a transfer of 0.021 holes to the O(2,3) sites would explain the result in YBa{sub 2}Cu{sub 3}O{sub 6.62}, whereas only 0.007 holes transfer in fully oxygenated YBa{sub 2}Cu{sub 3}O{sub 7}.

Reyes, A.P.; Ahrens, E.T.; Hammel, P.C.; Heffner, R.H. [Los Alamos National Lab., NM (United States); Takigawa, M. [International Business Machines Corp., Yorktown Heights, NY (United States). Thomas J. Watson Research Center

1992-03-01

87

Relaxation Anomalies of 69/71Ga NQR in the Paramagnetic State of the Itinerant Antiferromagnet UGa3: Possible Evidence for a Crossover to Localized Spin Fluctuations and Development of Orbital Fluctuations of 5f-electrons at High Temperatures  

NASA Astrophysics Data System (ADS)

The microscopic magnetic properties of the itinerant 5f-electron antiferromagnet UGa3 (TN=67 K) have been investigated in the paramagnetic state by means of Ga NQR studies of the two naturally abundant isotopes 69Ga and 71Ga. A striking and unusual increase of the nuclear longitudinal relaxation rate 1/T1 has been observed above 230 K, which includes a strong component of nuclear quadrupolar relaxation. Both the magnetic and quadrupolar relaxation rates have been found to increase simultaneously above 230 K. Correspondingly, the NQR frequencies also show a clear deviation from lower-T T3/2-dependence above 230 K. These results are discussed in terms of a crossover from lower-T itinerant to higher-T more localized spin fluctuations and associated orbital fluctuations on the part of the U 5f electrons. A mechanism of transferred quadrupole interaction is presented, through which the fluctuations among the U 5f orbitals involve those among the counter-anion Ga 4p orbitals and thereby cause quadrupolar relaxation of the Ga nuclear spins.

Takagi, Shigeru; Muraoka, Hideaki; Matsuda, Tatsuma D.; Haga, Yoshinori; Kambe, Shinsaku; Walstedt, Russell E.; Yamamoto, Etsuji; ?nuki, Yoshichika

2004-02-01

88

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

89

Frequencies of nuclear resonances for copper and electronic wave function of antiferromagnetic La2CuO4  

Microsoft Academic Search

Calculated values of the frequencies of nuclear magnetic and quadrupole resonances (for65Cuv(NMR) = 107 MHz, v(NQR) = 32 MHz) are close to the experimental values (100 MHz and 29.5 MHz). This coincidence is a reliable test of the obtained electronic wave function.

V. V. Flambaum; O. P. Sushkov

1990-01-01

90

First-principles study of (75)As NQR in arsenic-chalcogenide compounds.  

PubMed

We present a theoretical study of the nuclear quadrupole interaction, ?(Q), of (75)As in crystalline and amorphous materials containing sulfur and selenium, and compare them with experiment. We studied a combination of hydrogen-terminated molecular clusters and periodic cells at various levels of quantum chemical theory. The results show clearly that the standard density functional theory (DFT) approximations, LDA and GGA, underestimate the nuclear quadrupole (NQR) interaction systematically, while Hartree-Fock theory overestimates it to an even greater degree. However, various levels of configuration interaction and the B3LYP hybrid exchange-correlation functional, which includes some exact exchange, give very good quantitative agreement for As bonded only to the chalcogen species. As-As bonds require highly converged basis sets. We have performed a systematic study of the effect of local distortions around an arsenic atom on ?(Q) and ?. Using a simple, semiclassical model, we have combined our total energy results with our NQR calculations to predict ?(Q) lineshapes for bond angle and bond length distortions. Our predictions for lineshape, including first and second moments, are in excellent agreement with the results of Su et al for a-As(2)S(3), a-As(2)Se(3) and a-AsSe. We offer new insight into the distortions that led to this inhomogeneous broadening. Our results show clearly that, for trivalent arsenic atoms with zero or one arsenic nearest neighbor, symmetric bond stretching is the predominant contributor to the ?(Q) linewidth. However, in the presence of two arsenic nearest neighbors, distortions of the As-As-As apex angle dominates and, in fact, leads to a much larger second moment, in agreement with experiment. PMID:21406910

Edwards, Arthur H; Taylor, P C; Campbell, Kristy A; Pineda, Andrew C

2011-02-01

91

First-principles study of 75As NQR in arsenic-chalcogenide compounds  

NASA Astrophysics Data System (ADS)

We present a theoretical study of the nuclear quadrupole interaction, ?Q, of 75As in crystalline and amorphous materials containing sulfur and selenium, and compare them with experiment. We studied a combination of hydrogen-terminated molecular clusters and periodic cells at various levels of quantum chemical theory. The results show clearly that the standard density functional theory (DFT) approximations, LDA and GGA, underestimate the nuclear quadrupole (NQR) interaction systematically, while Hartree-Fock theory overestimates it to an even greater degree. However, various levels of configuration interaction and the B3LYP hybrid exchange-correlation functional, which includes some exact exchange, give very good quantitative agreement for As bonded only to the chalcogen species. As-As bonds require highly converged basis sets. We have performed a systematic study of the effect of local distortions around an arsenic atom on ?Q and ?. Using a simple, semiclassical model, we have combined our total energy results with our NQR calculations to predict ?Q lineshapes for bond angle and bond length distortions. Our predictions for lineshape, including first and second moments, are in excellent agreement with the results of Su et al for a-As2S3, a-As2Se3 and a-AsSe. We offer new insight into the distortions that led to this inhomogeneous broadening. Our results show clearly that, for trivalent arsenic atoms with zero or one arsenic nearest neighbor, symmetric bond stretching is the predominant contributor to the ?Q linewidth. However, in the presence of two arsenic nearest neighbors, distortions of the As-As-As apex angle dominates and, in fact, leads to a much larger second moment, in agreement with experiment.

Edwards, Arthur H.; Taylor, P. C.; Campbell, Kristy A.; Pineda, Andrew C.

2011-02-01

92

Pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3 : An In115 -NQR study under pressure  

NASA Astrophysics Data System (ADS)

We report on pressure-induced unconventional superconductivity (SC) in the heavy-fermion (HF) antiferromagnet CeIn3 by means of nuclear-quadrupole-resonance (NQR) studies conducted under a high pressure. The temperature (T) and pressure (P) dependences of the In-NQR spectra have revealed a first-order quantum-phase transition (QPT) from antiferromagnetism (AFM) to paramagnetism (PM) at a critical pressure Pc=2.46GPa at which AFM disappears with a minimum value of TN(Pc)=1.2K . High-energy x-ray scattering measurements under P show a progressive decrease in the lattice density without any change in the crystal structure, whereas an increase in the NQR frequency (?Q) indicates an increase in the hybridization between 4f electrons and conduction electrons, which stabilizes the HF-PM state. This competition between the AFM phase where TN is reduced and the formation of the HF-PM phase triggers the first-order QPT at Pc=2.46GPa . Despite the lack of an AFM quantum critical point in the P-T phase diagram, we highlight the fact that unconventional SC occurs in both phases of AFM and PM. The measurements of the nuclear spin-lattice relaxation rate 1/T1 in the AFM phase have provided evidence for the uniformly coexisting AFM+SC phase. Remarkably, the significant increase in 1/T1 upon cooling in the AFM phase has revealed the development of low-lying magnetic excitations down to Tc in the AFM phase; it is indeed relevant to the onset of the uniformly coexisting AFM+SC phase. In the HF-PM phase where AFM fluctuations are not developed, 1/T1 decreases without the coherence peak just below Tc , followed by a power-law-like T dependence that indicates an unconventional SC with a line-node gap. Remarkably, Tc has a peak around Pc in the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists with a maximum value of Tc=230mK around Pc , indicating that the origin of the pressure-induced HF SC in CeIn3 is not relevant to AFM spin fluctuations but to the emergence of the first-order QPT in CeIn3 . These phenomena observed in CeIn3 should be understood in terms of the first-order QPT because these new phases of matter are induced by applying P . When the AFM critical temperature is suppressed at the termination point of the first-order QPT, Pc=2.46GPa , the diverging AFM spin-density fluctuations emerge at the critical point from AFM to PM. The results with CeIn3 leading to a new type of quantum criticality deserve further theoretical investigations.

Kawasaki, S.; Yashima, M.; Kitaoka, Y.; Takeda, K.; Shimizu, K.; Oishi, Y.; Takata, M.; Kobayashi, T. C.; Harima, H.; Araki, S.; Shishido, H.; Settai, R.; ?nuki, Y.

2008-02-01

93

Evidence for the microscopic coexistence of superconductivity and ferromagnetism in UGe2:73Ge-NMR/NQR study  

NASA Astrophysics Data System (ADS)

We report on the pressure-induced novel phases of ferromagnetism and superconductivity (SC) in the itinerant ferromagnet UGe2 via the 73Ge-NQR measurements under pressure ( P). The NQR spectrum has revealed that the ferromagnetic phases are separated into weakly and strongly polarized phases around a critical value of Pc*?1.2 GPa, pointing to a first-order transition around Pc*. Here we present further evidence for the phase separation into ferromagnetic and paramagnetic phases around a critical pressure Pc?1.6 GPa. The measurements of nuclear spin-lattice relaxation rate 1/T1 have probed that SC sets only in the ferromagnetic phase at Tsc?0.2 K, but it does not in the paramagnetic phase.

Harada, A.; Kotegawa, H.; Kawasaki, Y.; Zheng, G.-q.; Kitaoka, Y.; Yamamoto, E.; Haga, Y.; ?nuki, Y.; Itoh, K.; Haller, E. E.

2005-04-01

94

Room-Temperature Sulfur Chloride Ionic Liquids in Processes for the Isolation of Noble and other Metals  

Microsoft Academic Search

\\u000a A correlation of interatomic distances (d\\/Å), chalcogen-chlorine bond stretching frequencies (v\\/cm?1) and 35Cl NQR frequencies (MHz) has been performed for crystals of chalcogen chloride complexes of gold(III) and osmium(IV). A conclusion\\u000a has been drawn as to the functional peculiarities of chalcogen chloride molecules being part of complexes. The state of the\\u000a complexes under investigation in nonaqueous polar solvents has been

V. I. Pekhnyo; S. V. Volkov; N. G. Alexandrova

95

Unconventional Pairing States in Heavy-Fermion Superconductors Studied by the NQR/NMR Experiments  

NASA Astrophysics Data System (ADS)

We review the studies on the unconventional superconducting pairing states and their relevance with magnetism in the f-electron derived heavy-fermion (HF) systems by means of nuclear-magnetic-resonance (NMR) and nuclear-quadrupole-resonance (NQR). These studies have unraveled a rich variety of the phenomena in the ground state of HF systems. In this article, we address an intimate relationship between the onset of strong-coupling superconductivity (SC) and critical magnetic fluctuations emerging in the vicinity of quantum critical point (QCP). Furthermore, we focus on the novel phase diagram of the HF antiferromagnet CeRhIn5 under pressure which is characterized by the tetracritical point separating the pure antiferromagnetism (AFM) phase, the AFM+SC uniformly coexisting phase, and the paramagnetic SC phase. A comparison is also presented on the AFM+SC uniformly coexisting phase in high-temperature superconductors as the function of carrier doping. As a consequence, we raise a question; Do we need a bosonic glue to pair electrons in these superconductors? Finally, we address a possible origin of the novel SC in the itinerant ferromagnet UGe2, which is mediated by ferromagnetic spin-density fluctuations relevant with the first-order transition inside the ferromagnetic states.

Kitaoka, Yoshio; Mukuda, Hidekazu; Yashima, Mitsuharu; Harada, Atsushi

2007-05-01

96

Nuclear quadrupole resonance. Electronic structure and sterochemistry of halogenonaphthalenones  

SciTech Connect

The /sup 35/Cl NQR spectra of 2-chloro-, 2, 3-dihydro-2-bromo-2,3-dichloro-, and 2,2,3-trichloro-4-diphenyl-methylene-1(4H)-napthalenones (I-III) were studied. The experimental data are compared with the results from quantum-chemical calculations for the conformers of the molecules of (I-III) by the CNDO/2 method. The adequacy of the conformation description of systems (I-III) by the method using the /sup 35/Cl NQR frequencies was established by study of 1,2-dichloroacenaphthene and 2-chlorotetrahydropyran. It was established that compound (II) in the crystal exists in the form of the conformer with the bromine atom in the axial position. The possibilities of using an electrostatic model for the discussion of the conformations of the 2,3-dyhydro derivatives (II) and (III) with separate allowance for the geminal and vicinal environments of the chlorine probe atom are examined.

Romanenko, E.A.; Nesterenko, A.M.; Novikov, V.P.; Kolesnikov, V.T.

1987-11-01

97

Evidence for Uniform Coexistence of Ferromagnetism and Unconventional Superconductivity in UGe2: A 73Ge-NQR Study under Pressure  

NASA Astrophysics Data System (ADS)

We report on the itinerant ferromagnetic superconductor UGe2 through 73Ge-NQR measurements under pressure (P). The P dependence of the NQR spectrum signals a first-order transition from the low-temperature (T) and low-P ferromagnetic phase (FM2) to high-T and high-P one (FM1) around a critical pressure of Px ˜ 1.2 GPa. The superconductivity exhibiting a maximum value of Tsc=0.7 K at Px ˜ 1.2 GPa, was found to take place in connection with the P-induced first-order transition. The nuclear spin-lattice relaxation rate 1/T1 has probed the ferromagnetic transition, exhibiting a peak at the Curie temperature as well as a decrease without the coherence peak below~Tsc. These results reveal the uniformly coexistent phase of ferromagnetism and unconventional superconductivity with a line--node gap. We remark on an intimate interplay between the onset of superconductivity and the underlying electronic state for the ferromagnetic phases.

Kotegawa, H.; Harada, A.; Kawasaki, S.; Kawasaki, Y.; Kitaoka, Y.; Haga, Y.; Yamamoto, E.; ?nuki, Y.; Itoh, K. M.; Haller, E. E.; Harima, H.

2005-02-01

98

N.Q.R measurements of low energy Chiral structures in powdered glassy As2Se3  

NASA Astrophysics Data System (ADS)

Experimental and theoretical work on the As-chalcogen glasses have shown that in the glassy state the local cylindrical symmetry associated with the elemental pyramidal unit is preserved. Here we introduce a local paracrystalline model of glassy As2Se3. This model is based on a tight binding calculation of the electric field gradient (EFG) at the core of an As atom located at the apex of the pyramidal structure. This EFG is shown to be hyper sensitive to the bond angles and bond lengths the As atom forms with the chalcogen nearest neighbors, as well as the hybrid angle formed with second neighbor As atoms. A continuous variation of the bonding parameters produces a unique set of these pyramidal units which are shown to fit the NQR data for powdered glassy samples. The best fit to the NQR data indicates that the pyramidal units organize themselves into Chiral structures in the glass. A plot of the electronic energy per molecular site shows that the chiral structures have on average a lower electronic energy than a random configuration.

Nelson, Chris

2012-02-01

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 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

100

NMR and NQR parameters of the SiC-doped on the (4,4) armchair single-walled BPNT: a computational study.  

PubMed

The structural properties, NMR and NQR parameters in the pristine and silicon carbide (SiC) doped boron phosphide nanotubes (BPNTs) were calculated using DFT methods (BLYP, B3LYP/6-31G) in order to evaluate the influence of SiC-doped on the (4,4) armchair BPNTs. Nuclear magnetic resonance (NMR) parameters including isotropic (CS(I)) and anisotropic (CS(A)) chemical shielding parameters for the sites of various (13)C, (29)Si, (11)B, and (31)P atoms and quadrupole coupling constant (C ( Q )), and asymmetry parameter (? ( Q )) at the sites of various (11)B nuclei were calculated in pristine and SiC- doped (4,4) armchair boron phosphide nanotubes models. The calculations indicated that doping of (11)B and (31)P atoms by C and Si atoms had a more significant influence on the calculated NMR and NQR parameters than did doping of the B and P atoms by Si and C atoms. In comparison with the pristine model, the SiC- doping in Si(P)C(B) model of the (4,4) armchair BPNTs reduces the energy gaps of the nanotubes and increases their electrical conductance. The NMR results showed that the B and P atoms which are directly bonded to the C atoms in the SiC-doped BPNTs have significant changes in the NMR parameters with respect to the B and P atoms which are directly bonded to the Si atoms in the SiC-doped BPNTs. The NQR results showed that in BPNTs, the B atoms at the edges of nanotubes play dominant roles in determining the electronic behaviors of BPNTs. Also, the NMR and NQR results detect that the Fig. 1b (Si(P)C(B)) model is a more reactive material than the pristine and the Fig. 1a (Si(B)C(p)) models of the (4,4) armchair BPNTs. PMID:21625895

Baei, Mohammad T; Sayyad-Alangi, S Zahra; Moradi, Ali Varasteh; Torabi, Parviz

2012-03-01

101

Recent results of measurements of the {sup 14}N(n,p){sup 14}C, {sup 35}Cl(n,p){sup 35}S, {sup 36}Cl(n,p){sup 36}S, and {sup 36}Cl(n,{alpha}){sup 33}P reaction cross sections  

SciTech Connect

Experiments are reported for measuring the cross section of the {sup 14}N(n,p){sup 14}C reaction over the neutron energy range from thermal energy to 150 keV at the IBR-30 pulsed booster at JNR, Dubna and the WWR-M reactor at INR, Kiev. The reaction cross section values were found for the thermal energy and for the neutron energies of 24 keV, 54 keV, 144 keV. The {sup 36}Cl(n,p){sup 36}S cross section was measured for the neutron energies from thermal energy to approximately 800 keV at the neutron source of LANSCE, Los Alamos. The contributions of the {sup 36}Cl(n,p){sup 36}S and {sup 36}Cl(n,{alpha}){sup 33}P reactions to resonances at 0.9 keV and 1.3 keV were identified. Also, at the WWR-M reactor of PINR, Gatchina, preliminary measurements of the {sup 36}Cl(n,p){sup 36}S cross section at the thermal neutron energy were conducted. The {sup 35}Cl(n,p){sup 35}S reaction cross section was measured at the IBR-30 pulsed booster. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Gledenov, Y.M.; Salatski, V.I.; Sedyshev, P.V.; Sedysheva, M.V. [Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Koehler, P.E. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Vesna, V.A.; Okunev, I.S. [Petersburg Nuclear Physics Institute, 188350 Gatchina (Russian Federation)

1995-02-05

102

An ultra-broadband low-frequency magnetic resonance system  

NASA Astrophysics Data System (ADS)

MR probes commonly employ resonant circuits for efficient RF transmission and low-noise reception. These circuits are narrow-band analog devices that are inflexible for broadband and multi-frequency operation at low Larmor frequencies. We have addressed this issue by developing an ultra-broadband MR probe that operates in the 0.1-3 MHz frequency range without using conventional resonant circuits for either transmission or reception. This “non-resonant” approach significantly simplifies the probe circuit and allows robust operation without probe tuning while retaining efficient power transmission and low-noise reception. We also demonstrate the utility of the technique through a variety of NMR and NQR experiments in this frequency range.

Mandal, S.; Utsuzawa, S.; Cory, D. G.; Hürlimann, M.; Poitzsch, M.; Song, Y.-Q.

2014-05-01

103

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

NASA Astrophysics Data System (ADS)

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.

1990-04-01

104

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

105

NMR and NQR study of the electronic and structural properties of Al-Cu-Fe and Al-Cu-Ru quasicrystals  

SciTech Connect

[sup 27]Al and [sup 63,65]Cu NMR is reported for powdered stable Al-Cu-Fe and Al-Cu-Ru icosahedral quasicrystals and crystalline approximants, and for an Al-Pd-Mn single-grain quasicrystal. [sup 27]Al NQR spectra at 4.2 K were observed in Al-Cu-Fe and Al-Cu-Ru samples. From quadrupole-perturbed NMR spectra at different magnetic fields, and from zero-field NQR spectra, a wide distribution of local electric-field gradient (EFG) tensor components and principal-axis-system orientations was found at the Al site. A model EFG calculation based on a 1/1 Al-Cu-Fe approximant successfully explained the observed NQR spectra. The average local gradient is largely determined by the [ital p]-electron wave function at the Al site, while the width of the distribution is due to EFG lattice contribution. Comparison of [sup 63]Cu and [sup 27]Al NMR shows the EFG distribution at the two sites is similar, but the electronic contribution to the EFG is considerably smaller at the Cu site, in agreement with a more [ital s]-type wave function of the conduction electrons. Overall spread of EFG values is well reproduced by calculation based on the approximant. However, the experimental spectra indicate a much larger number of nonequivalent sites when compared with the simulated NQR spectra based on the 1/1 approximant. The short-range, local chemical order is well represented by the approximant, but differences in coordination must be included at intermediate range in the quasicrystal. Measured [sup 27]Al Knight shift, magnetic susceptibility, and nuclear spin-lattice relaxation time as a function of temperature indicate reduced density of states at the Fermi level by a factor of 7 or 8 from the value in Al metal, consistent with the notion of a pseudogap for these quasicrystals. No differences in measured parameters were detected as a function of composition of the quasicrystalline alloys.

Shastri, A.; Borsa, F.; Torgeson, D.R.; Shield, J.E.; Goldman, A.I. (Ames Laboratory, U.S. Department of Energy and Department of Physics Astronomy, Iowa State University, Ames, Iowa 50011 (United States))

1994-12-01

106

Novel Phase Transition in CeRu2Al10 Probed by 27Al-NQR/NMR —No Evidence of Magnetic Ordering—  

NASA Astrophysics Data System (ADS)

The 27Al-NQR/NMR measurements of CeRu2Al10 were carried out to clarify the unusual phase transition at T0=27 K. Distinct NQR peaks associated with five nonequivalent Al sites have been observed at T > T0, and each peak is successfully assigned to their respective Al sites. Below the transition temperature T < T0, each peak simply splits into two peaks except for one site. This indicates that the phase transition is not accompanied by magnetic order, but is presumably associated with the onset of structural transition with lowering symmetry. The nuclear spin-lattice relaxation rate 1/T1 suggests a local moment picture above T*˜ 60 K, and the development of Kondo coherence toward T0. Below T0, 1/T1 shows a gaplike decrease with a gap magnitude of 106 K, being consistent with the macroscopic measurements. The Korringa term below 10 K after the gaplike decrease suggests a gap opening over a portion of the Fermi surface.

Matsumura, Masahiro; Kawamura, Yukihiro; Edamoto, Shingo; Takesaka, Tomoaki; Kato, Harukazu; Nishioka, Takashi; Tokunaga, Yo; Kambe, Shinsaku; Yasuoka, Hiroshi

2009-12-01

107

NMR and NQR study of Si-doped (6,0) zigzag single-walled aluminum nitride nanotube as n or P-semiconductors.  

PubMed

Density functional theory (DFT) calculations were performed to investigate the electronic structure properties of pristine and Si-doped aluminum nitride nanotubes as n or P-semiconductors at the B3LYP/6-31G* level of theory in order to evaluate the influence of Si-doped in the (6,0) zigzag AlNNTs. We extended the DFT calculation to predict the electronic structure properties of Si-doped aluminum nitride nanotubes, which are very important for production of solid-state devices and other applications. To this aim, pristine and Si-doped AlNNT structures in two models (Si(N) and Si(Al)) were optimized, and then the electronic properties, the isotropic (CS(I)) and anisotropic (CS(A)) chemical shielding parameters for the sites of various (27)Al and (14)N atoms, NQR parameters for the sites of various of (27)Al and (14)N atoms, and quantum molecular descriptors were calculated in the optimized structures. The optimized structures, the electronic properties, NMR and NQR parameters, and quantum molecular descriptors for the Si(N) and Si(Al) models show that the Si(N) model is a more reactive material than the pristine or Si(Al) model. PMID:22588584

Baei, Mohammad T; Peyghan, Ali Ahmadi; Tavakoli, Khadijeh; Babaheydari, Ali Kazemi; Moghimi, Masoumeh

2012-09-01

108

Ferromagnetic Quantum Critical Fluctuations and Anomalous Coexistence of Ferromagnetism and Superconductivity in UCoGe Revealed by Co-NMR and NQR Studies  

NASA Astrophysics Data System (ADS)

Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies were carried out for the recently discovered UCoGe, in which the ferromagnetic and superconducting (SC) transitions are reported to occur at TCurie˜ 3 K and TS˜ 0.8 K [Huy et al.: Phys. Rev. Lett. 99 (2007) 067006], in order to investigate the coexistence of ferromagnetism and superconductivity as well as the normal-state and SC properties from a microscopic point of view. From the nuclear spin-lattice relaxation rate 1/T1 and Knight-shift measurements, we confirm that ferromagnetic fluctuations that possess a quantum critical character are present above TCurie and also the occurrence of a ferromagnetic transition at 2.5 K in our polycrystalline sample. The magnetic fluctuations in the normal state show that UCoGe is an itinerant ferromagnet similar to ZrZn2 and YCo2. The onset SC transition is identified at TS˜ 0.7 K, below which 1/T1 arising from 30% of the volume fraction starts to decrease due to the opening of the SC gap. This component of 1/T1, which follows a T3 dependence in the temperature range 0.3-0.1 K, coexists with the magnetic components of 1/T1 showing a \\sqrt{T} dependence below TS. From the NQR measurements in the SC state, we suggest that the self-induced vortex state is realized in UCoGe.

Ohta, Tetsuya; Nakai, Yusuke; Ihara, Yoshihiko; Ishida, Kenji; Deguchi, Kazuhiko; Sato, Noriaki K.; Satoh, Isamu

2008-02-01

109

Density functional calculations of 14N and 11B NQR parameters in the H-capped (6,0) and (4,4) single-walled BN nanotubes  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) calculations were performed to calculate nitrogen-14 and boron-11 nuclear quadrupole resonance (NQR) spectroscopy parameters in the representative considered models of zigzag and armchair boron nitride nanotubes (BNNTs) for the first time. The considered models consisting of 1 nm length of H-capped (6,0) and (4,4) single-walled BNNT were first allowed to fully relax and then the NQR calculations were performed on the geometrically optimized models. The evaluated nuclear quadrupole coupling constants and asymmetry parameters for the mentioned nuclei reveal that the considered models can be divided into four layers of nuclei with an equivalent electrostatic environment where those nuclei at the ends of tubes have a very strong electrostatic environment compared to the other nuclei along the length of tubes. Those nuclei at the center of the tube length also have an equivalent electrostatic environment. The calculations were performed based on the B3LYP DFT method and 6-311G** and 6-311++G** standard basis sets using the Gaussian 98 package of program.

Mirzaei, Mahmoud; Hadipour, Nasser L.

2008-02-01

110

Bonding and molecular motions in the 1:1 molecular complexes of 1,4-diazabicyclo[2.2.2]octane with tetrahalomethane as studied by means of NQR  

NASA Astrophysics Data System (ADS)

NQR spectra were observed in the complexes of 1,4-diazabicyclo[2.2.2]octane (DABCO) with tetrachloromethane and tetrabromomethane at various temperatures. A phase transition was found at 319 K for DABCO·CBr 4. From spin-lattice relaxation times of nitrogen-14 in DABCO·CBr 4, the activation energy of the reorientation of DABCO about the N?N axis was calculated to be 18.3 kJ/mol which agrees with the value obtained from the second moment of proton NMR spectra. The bond nature is discussed using the Townes-Dailey treatment.

Okuda, T.; Suzuki, T.; Negita, H.

1983-12-01

111

Supramolecular synthon pattern in solid clioquinol and cloxiquine (APIs of antibacterial, antifungal, antiaging and antituberculosis drugs) studied by ³?Cl NQR, ¹H-¹?O and ¹H-¹?N NQDR and DFT/QTAIM.  

PubMed

The quinolinol derivatives clioquinol (5-chloro-7-iodo-8-quinolinol, Quinoform) and cloxiquine (5-chloro-8-quinolinol) were studied experimentally in the solid state via ³?Cl NQR, ¹H-¹?O and ¹H-¹?N NQDR spectroscopies, and theoretically by density functional theory (DFT). The supramolecular synthon pattern of O-H···N hydrogen bonds linking dimers and ?-? stacking interactions were described within the QTAIM (quantum theory of atoms in molecules) /DFT (density functional theory) formalism. Both proton donor and acceptor sites in O-H···N bonds were characterized using ¹H-¹?O and ¹H-¹?N NQDR spectroscopies and QTAIM. The possibility of the existence of O-H···H-O dihydrogen bonds was excluded. The weak intermolecular interactions in the crystals of clioquinol and cloxiquine were detected and examined. The results obtained in this work suggest that considerable differences in the NQR parameters for the planar and twisted supramolecular synthons permit differentiation between specific polymorphic forms, and indicate that the more planar supramolecular synthons are accompanied by a greater number of weaker hydrogen bonds linking them and stronger ?···? stacking interactions. PMID:21080020

Latosi?ska, Jolanta Natalia; Latosi?ska, Magdalena; Tomczak, Marzena Agnieszka; Seliger, Janez; Zagar, Veselko

2011-07-01

112

An infrared spectrum of the molecular dication (doubly positively charged molecule), D35Cl2+  

NASA Astrophysics Data System (ADS)

We have observed an infrared spectrum within the X 3?- state of DCl2+ using a fast-ion-beam/laser-beam spectrometer. A preliminary analysis shows good agreement with the rotational constants and tunneling lifetimes calculated by Bennett and McNab for the ?=1-2 vibrational band, although the calculated band origin appear to be in error by 21.1 cm-1.

Abusen, Ramadan; Bennett, Frederick R.; McNab, Iain R.; Sharp, David N.; Shiell, Ralph C.; Woodward, Clare A.

1998-02-01

113

Frequency Generating Source: Frequency Synthesizers.  

National Technical Information Service (NTIS)

A mode of fractional frequency harmonic generation obtained by the modulation of a square wave reference signal is considered. The produced spectrum exhibits a particular structure. The longer the fractional part of the frequency of the modulating wave is...

N. Yahyabey S. Hassani

1992-01-01

114

Orbital electronegativities and the determination of s and d hybridization in various halides from nuclear quadrupole resonance frequencies  

Microsoft Academic Search

The use of Orbital Electronegativities in the interpretation of NQR results for various halides is discussed, and an attempt to determine the amount of d hybridization in s and p bonding is made. The ionic characters are assessed.

M. A. Whitehead; H. H. Jaffé

1963-01-01

115

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

116

Frequency Agility Technique for Frequency Scanned Antenna.  

National Technical Information Service (NTIS)

In a serpentine feed structure for a frequency scanned antenna a switching network is provided which allows the serpentine to be fed from either end on alternate or random scans. This variable transmission system significantly increases the frequency band...

R. R. Boothe

1980-01-01

117

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.

118

Frequency doubling in ultralow frequency wave signals  

NASA Astrophysics Data System (ADS)

We report a new theory to explain the long-observed frequency-doubling phenomenon detected in the compressional component of ``high-m'' ultralow-frequency signals seen in the Earth's magnetosphere. We show that the effect is a nonlinear response directly associated with resonant particles. The phase relationship observed between the linear signal and the nonlinear frequency-doubled signal is predicted by the theory. Our explanation and the fit with observation mean that the occurrence of frequency doubling provides critical evidence of the fact that ring current particles drive high-m waves.

Southwood, David J.; Kivelson, Margaret G.

1997-12-01

119

Correlation of far-infrared and nuclear quadrupole resonance studies in 1,3,5-tribromobenzene  

NASA Astrophysics Data System (ADS)

The torsional modes that contribute to the change in nuclear quadrupole resonance (NQR) frequencies with temperatures in 1,3,5-tribromobenzene are indentified by correlating the observed variation of 79Br NQR frequencies with temperature with the theoretical expectations using the low frequency vibrational modes obtained from the far-infrared (FIR) spectrum.

Venkatacharyulu, P.; Krishnamurthy, V.

1991-02-01

120

Precision Frequency Synthesizing Sources with Excellent Time/Frequency Performances.  

National Technical Information Service (NTIS)

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 excelle...

L. Zhou H. Lin

1994-01-01

121

Anharmonic Frequency Analysis.  

National Technical Information Service (NTIS)

A new numerical method of frequency analysis is described, designed mainly to search for discrete frequencies in a time series. An integral transform is applied twice to the data for different reference times. A complex amplitude within a selected narrow ...

A. K. Paul

1971-01-01

122

High Frequency Via.  

National Technical Information Service (NTIS)

Techniques that enable the transitioning of high frequency signals on a printed wiring board processed in accordance with industry standards (such as the IPC specifications) are disclosed. One embodiment provides a high frequency via structure for a print...

J. S. Greeley

2004-01-01

123

Quantum frequency conversion  

Microsoft Academic Search

An experimental scheme is proposed by which the quantum states of two light beams of different frequencies can be interchanged. With this scheme it is possible to generate frequency-tunable squeezed light for spectroscopic applications.

Prem Kumar

1990-01-01

124

Limit of Frequency Estimation.  

National Technical Information Service (NTIS)

In phase and frequency measurements, the measured phase and frequency are not the true phase and frequency but the ones which are disturbed by noises, due to the effects of the noise processes. In this paper, we discussed the effects of three noise proces...

W. Guo

1992-01-01

125

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

126

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

127

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

128

63Cu-NMR/NQR studies on apical-F bi-layered cuprates Ba2CaCu2O4F2 and Ba2CaCu2O4(F1.6O0.4)  

NASA Astrophysics Data System (ADS)

We report 63Cu-NMR/NQR on the bi-layered high- Tc copper oxide Ba2CaCu2O4F2, which is expected to be a Mott insulator in an ideal case of a nominal content of fluorine, and less fluorinated Ba2CaCu2O4(F1.6O0.4) to clear the doping mechanism in apical-fluorine multilayered system Ba2CaCunO2nF2, where n is the number of the layers in a unit cell. In the case of n=3 and, especially, n=4, the origin of carrier doping has been attributed to a self-doping mechanism based on the nominal stoichiometry; electrons are transferred between the inner CuO2 plane (IP) and the outer one (OP), keeping Cu+2 on average. It is revealed that Ba2CaCu2O4F2 is an underdoped superconductor with hole carriers, doped by an inevitable deviation from the nominal content of apical fluorines. This result suggests that hole carriers are doped in the same manner for the case of n=3 and 4, and that we should reconsider the self-doping mechanism as the carrier source in the apical-fluorine system.

Shimizu, S.; Sakaguchi, T.; Mukuda, H.; Kitaoka, Y.; Iyo, A.; Shirage, P. M.; Kito, H.; Kodama, Y.

2009-10-01

129

Estimating frequency of change  

Microsoft Academic Search

Many online data sources are updated autonomously and independently. In this article, we make the case for estimating the change frequency of data to improve Web crawlers, Web caches and to help data mining. We first identify various scenarios, where different applications have different requirements on the accuracy of the estimated frequency. Then we develop several \\

Junghoo Cho; Hector Garcia-Molina

2003-01-01

130

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

131

Dialysis dose and frequency  

Microsoft Academic Search

Background. From the beginning of the dialysis era, the issue of optimal dialysis dose and frequency has been a central topic in the delivery of dialysis treatment. Methods. We undertook a discussion to achieve a consensus on key points relating to dialysis dose and frequency, focusing on the relationships with clinical and patient outcomes. Results. Traditionally, dialysis adequacy has been

Francesco Locatelli; Umberto Buoncristiani; Bernard Canaud; Hans Kohler; Thierry Petitclerc; Pietro Zucchelli; Ospedale A. Manzoni; CHU Montpellier; Schwerpunkt Nephrologie

2004-01-01

132

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

133

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

134

Laser Frequency Stabilization  

NASA Technical Reports Server (NTRS)

Laser ranging and interferometry are essential technologies allowing for many astounding new spacebased missions such as the Laser Interferometer Space Antenna (LISA) to measure gravitational radiation emitted from distant super massive black hole mergers or distributed aperture telescopes with unprecedented angular resolution in the NIR or visible regime. The requirements on laser frequency noise depend on the residual motion and the distances between the spacecraft forming the interferometer. The intrinsic frequency stability of commercial lasers is several orders of magnitude above these requirements. Therefore, it is necessary for lasers to be stabilized to an ultrastable frequency reference so that they can be used to sense and control distances between spacecraft. Various optical frequency references and frequency stabilization schemes are considered and investigated for the applicability and usefulness for space-based interferometry missions.

Donelan, Darsa; Mueller, Guido; Thorpe, James; Livas, Jeffrey

2011-01-01

135

Frequency comb swept lasers  

PubMed Central

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 rate of 1kHz and 120kHz, respectively over a 135nm tuning range centered at 1310nm with average output powers of 50mW. A 25GHz free spectral range frequency comb filter in the swept lasers causes the lasers to generate a series of well defined frequency steps. The narrow bandwidth (0.015nm) of the frequency comb filter enables a ~?1.2dB sensitivity roll off over ~3mm range, compared to conventional swept source and FDML lasers which have ?10dB and ?5dB roll offs, respectively. Measurements at very long ranges are possible with minimal sensitivity loss, however reflections from outside the principal measurement range of 0–3mm appear aliased back into the principal range. In addition, the frequency comb output from the lasers are equally spaced in frequency (linear in k-space). The filtered laser output can be used to self-clock the OCT interference signal sampling, enabling direct fast Fourier transformation of the fringe signals, without the need for fringe recalibration procedures. The design and operation principles of FC swept lasers are discussed and designs for short cavity lasers for OCT and interferometric measurement applications are proposed.

Tsai, Tsung-Han; Zhou, Chao; Adler, Desmond C.; Fujimoto, James G.

2010-01-01

136

A beat frequency buncher  

SciTech Connect

A superconducting high energy buncher operating at 13/12 times the linac frequency has been built and installed, to combine with the low energy buncher operating at 1/12 the linac frequency. The system is synchronized so the linac and high energy buncher beat frequency remains in phase with the low energy buncher. On linac cycles not corresponding to a primary bunch, the high energy buncher bunches residual beam away from the linac longitudinal acceptance rather than into it. The resonator for the new high energy buncher was constructed by shortening an existing low-{beta} resonator.

Storm, D.W.; Corcoran, D.T.; Harper, G.C.

1995-09-01

137

Radio frequency strain monitor  

NASA Technical Reports Server (NTRS)

A radio frequency strain monitor includes a voltage controlled oscillator for generating an oscillating signal that is input into a propagation path. The propagation path is preferably bonded to the surface of a structure to be monitored and produces a propagated signal. A phase difference between the oscillating and propagated signals is detected and maintained at a substantially constant value which is preferably a multiple of 90.degree. by changing the frequency of the oscillating signal. Any change in frequency of the oscillating signal provides an indication of strain in the structure to which the propagation path is bonded.

Heyman, Joseph S. (Inventor); Rogowski, Robert S. (Inventor); Holben, Jr., Milford S. (Inventor)

1989-01-01

138

Low Frequency Blocking Oscillator.  

National Technical Information Service (NTIS)

The patent describes a low frequency astable blocking oscillator composed of a transistor with a first transformer winding in the collector circuit and a second transformer winding in the base circuit to provide regenerative feedback between the collector...

C. H. Johnson

1972-01-01

139

Low Frequency Vibration Absorber.  

National Technical Information Service (NTIS)

This patent application discloses a mounting assembly for absorbing low frequency vibrational energy as produced by a source and isolating a base member therefrom. The mounting assembly includes a central metallic ring, non-metallic foam rings located on ...

N. J. Dubois B. G. Gauthier

1990-01-01

140

Frequency Independent Antennas.  

National Technical Information Service (NTIS)

The basic principles of frequency independent operation are reviewed. The connection between the self-complementary condition for planar structures and the dipole arrays with switched connections is an interesting point. The vital importance of radiation ...

V. H. Rumsey

1965-01-01

141

Histograms and Frequency Density.  

ERIC Educational Resources Information Center

Introduces exercises on histograms and frequency density. Guides pupils to Discovering Important Statistical Concepts Using Spreadsheets (DISCUSS), created at the University of Coventry. Includes curriculum points, teaching tips, activities, and internet address (http://www.coventry.ac.uk/discuss/). (KHR)

Micromath, 2003

2003-01-01

142

Frequency Domain Identification Toolbox.  

National Technical Information Service (NTIS)

This report documents software written in MATLAB programming language for performing identification of systems from frequency response functions. MATLAB is a commercial software environment which allows easy manipulation of data matrices and provides othe...

L. G. Horta J. N. Juang C. W. Chen

1996-01-01

143

Frequency Domain Simulated Annealing  

NASA Astrophysics Data System (ADS)

This dissertation presents the feasible extension of simulated annealing into the frequency domain. A mathematical development of the algorithm, proof of the asymptotic convergence, and proof of polynomial-bound execution times substantiate frequency domain annealing as a combinatorial optimization technique. Results obtained from experimental implementation of the algorithm in an adaptive spatial filter application demonstrate the stability and reliability of the algorithm. Additional studies of parameter interdependence and effects facilitate the usage of this technique. Frequency domain annealing overcomes some of the inadequacies of its spatial domain predecessor for large, complex applications such as image processing with multiple grey levels. Adaptive spatial filters using frequency annealing are shown to yield global mean-squared error reduction without the loss of fine details or excessive computation.

Reddick, Wilburn Eugene

144

VHF frequency multiplier  

NASA Technical Reports Server (NTRS)

Low-power step-recovery-diode frequency multiplier generates 361-MHz signal. Diode conducts when ac waveform is positive at its upper terminal. When voltage is negative, diode continues to conduct stored charge in its junction.

Cusack, J. A.

1979-01-01

145

Electromechanical Frequency Filters  

NASA Astrophysics Data System (ADS)

Frequency filters select signals with a frequency inside a definite frequency range or band from signals outside this band, traditionally afforded by a combination of L-C-resonators. The fundamental principle of all modern frequency filters is the constructive interference of travelling waves. If a filter is set up of coupled resonators, this interference occurs as a result of the successive wave reflection at the resonators' ends. In this case, the center frequency f c of a filter, e.g., set up of symmetrical ?/2-resonators of length 1, is given by f_c = f_r = v_{ph}/? = v_{ph}/2l , where v ph is the phase velocity of the wave. This clearly shows the big advantage of acoustic waves for filter applications in comparison to electro-magnetic waves. Because v ph of acoustic waves in solids is about 104-105 smaller than that of electro-magnetic waves, much smaller filters can be realised. Today, piezoelectric materials and processing technologies exist that electromechanical resonators and filters can be produced in the frequency range from 1 kHz up to 10 GHz. Further requirements for frequency filters such as low losses (high resonator Q) and low temperature coefficients of frequency constants can also be fulfilled with these filters. Important examples are quartz-crystal resonators and filters (1 kHz-200 MHz) as discussed in Chap. 2, electromechanical channel filters (50 kHz and 130 kHz) for long-haul communication systems as discussed in this section, surface acoustic wave (SAW) filters (20 MHz-5 GHz), as discussed in Chap. 14, and thin film bulk acoustic resonators (FBAR) and filters (500 MHz-10 GHz), as discussed in Chap. 15.

Wersing, W.; Lubitz, K.

146

Radio Link Frequency Assignment  

Microsoft Academic Search

Abstract: The problem of radio frequency assignment is to provide communication channelsfrom limited spectral resources whilst keeping to a minimum the interference suered by thosewhishing to communicate in a given radio communication network. This problem is a combinatorial(NP-hard) optimization problem. In 1993, the CELAR (the French \\\\Centre d'Electronique del'Armement") built a suite of simplied versions of Radio Link Frequency Assignment

Bertrand Cabon; Simon De Givry; Lionel Lobjois; Thomas Schiex; Joost P. Warners

1999-01-01

147

Twirling Rope Frequency  

NSDL National Science Digital Library

In this activity (page 1 of the PDF), learners will stand twelve feet apart swinging a rope at the slowest tempo possible while someone uses a stopwatch to record the number of twirls per minute. Based on this frequency, learners will predict whether the tempo will speed up or slow down when the twirlers move closer to each other. Use this activity to introduce the terms frequency and period. Relates to the linked video, DragonflyTV: Double Dutch.

Twin Cities Public Television, Inc.

2006-01-01

148

Characterization of Frequency Stability  

Microsoft Academic Search

Consider a signal generator whose instantaneous output voltage V(t) may be written as V(t) = [V0 + ??(t)] sin [2??v0t + s(t)] where V0 and v0 are the nominal amplitude and frequency, respectively, of the output. Provided that ??(t) and ??(t) = (d??\\/(dt) are sufficiently small for all time t, one may define the fractional instantaneous frequency deviation from nominal

James A. Barnes; Andrew R. Chi; Leonard S. Cutler; Daniel J. Healey; David B. Leeson; Thomas E. McGunigal; James A. Mullen; Warren L. Smith; Richard L. Sydnor; Robert F. C. Vessot; Gernot M. R. Winkler

1971-01-01

149

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

150

High frequency betatrons  

Microsoft Academic Search

The scaling of the betatron technique with the use of high-frequency, low-loss magnetic materials (ferrites, Metglas, etc.) is discussed. Because of synchrotron radiation, the maximum betatron energy Emax(GeV) scales as ~0.013 f(Hz)\\/Bs 2(T), where Bs is the maximum magnetic field on the orbit and f is the full-wave acceleration frequency. Eddy current losses in laminated iron limit f to ~120

David R. Winn

1991-01-01

151

Speech reconstruction from mel frequency cepstral coefficients and pitch frequency  

Microsoft Academic Search

This paper presents a novel low complexity, frequency domain algorithm for reconstruction of speech from the mel-frequency cepstral coefficients (MFCC), commonly used by speech recognition systems, and the pitch frequency values. The reconstruction technique is based on the sinusoidal speech representation. A set of sine-wave frequencies is derived using the pitch frequency and voicing decisions, and synthetic phases are then

Dan Chazan; Ron Hoory; Gilad Cohen; Meir Zibulski

2000-01-01

152

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

153

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, M. L.; Yesinowski, J. P.; Miller, J. B.

1994-03-01

154

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

155

Absolute wavenumber measurements of 1-0, 2-0, HF and 2-0, H35Cl, H37Cl absorption bands  

Microsoft Academic Search

Fourier absorption spectra of HCl and HF at room temperature permitted to measure 87 absolute wavenumbers. The absolute observed position of the P(6) line of the 1-0 band of HF is not in agreement with a recent heterodyne determination [3]. It is found equal to 110 725 739 +\\/- 7.5 MHz.

G. Guelachvili

1976-01-01

156

Direct Measurement of Dissipation in the {sup {bold 35}}Cl{bold +}{sup {bold 12}}C Reaction at 43 MeV\\/nucleon  

Microsoft Academic Search

Characteristics of ³⁵Cl+¹²C collisions at 43 MeV\\/nucleon have been studied for events with total charge detected ({ital Z}=23). It is shown that while single-source events are present in the data, the binary nature of the collision is dominant. For binary events, the emitting sources (projectile-like and target-like) were reconstructed independently allowing a direct measurement of the total dissipated energy. It

L. Beaulieu; Y. Larochelle; L. Gingras; G. C. Ball; D. R. Bowman; B. Djerroud; D. Dore; A. Galindo-Uribarri; D. Guinet; E. Hagberg; D. Horn; R. Laforest; P. Lautesse; R. Roy; M. Samri; C. St-Pierre

1996-01-01

157

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

158

Single frequency multitransmitter telemetry  

NASA Technical Reports Server (NTRS)

The invention relates to a single frequency multitransmitter telemetry system that will deliver a substantial amount of data at low cost. The invention consists essentially of a plurality of sensor transmitter units at different locations, with individual signal conditioning and logic, which send sampled data signals to a single receiver. The transmitters operate independently on the same frequency in a frequency shift keying modulation system and are not synchronized to the receiver. The problem of reception of data from more than one transmitter simultaneously is solved by discarding the data - when there is overlap of data from two or more transmitters, the data is discarded and when there is no overlap the data is retained. The invention utilizes a unique overlap detection technique to determine if data should be retained or discarded. When data is received from a transmitter, it goes into a shift register.

Carreno, Victor A. (inventor)

1986-01-01

159

Ultra Stable Frequency Distribution System.  

National Technical Information Service (NTIS)

The frequency distribution system of the present invention can be utilized for distributing a frequency standard to remotely located land based or satellite stations. A signal is synchronized at a remotely located slave station with the phase and frequenc...

R. L. Sydnor J. W. Macconnell

1976-01-01

160

Effective Frequency Technique  

NASA Technical Reports Server (NTRS)

An effective monochromatic frequency technique is described to represent the effects of finite spectral bandwidth for active and passive measurements centered on an absorption line, a trough region, or a slowly varying spectral feature. For Gaussian and rectangular laser line shapes, the effective frequency is shown to have a simple form which depends only on the instrumental line shape and bandwidth and not on the absorption line profile. The technique yields accuracies better than 0.1% for bandwidths less than 0.2 times the atmospheric line width.

Kirk, C. Laurence; Weng, Chi Y.

2002-01-01

161

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

162

High frequency pupillometry  

NASA Astrophysics Data System (ADS)

We report pupillometry results corresponding to three studies. A first study aims at measuring 2D pupil geometry with high precision (below 2 microns) at high frequency (more than 450Hz). The two other studies aim at measuring 3D pupil movements, with and without a chin rest. Results of measurements over 42 subjects are presented.

Meimon, Serge; Jarosz, Jessica; Chenegros, Guillaume; Petit, Cyril; Conan, Jean-Marc; Sorrente, Béatrice; Paques, Michel

2014-02-01

163

Low Frequency Hydrophone.  

National Technical Information Service (NTIS)

The pressure-balanced hydrophone has a low cut-off frequency which includes a pair of piezo-ceramic tubes, wired in series, and having one end of each tube secured to a metal block in the center. the second end of one of the ceramic tubes is covered by me...

H. J. Cini T. J. Meyers

1978-01-01

164

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

165

Flood Frequency Analysis  

NSDL National Science Digital Library

This assignment asks students to do a flood frequency analysis to determine the size and stage of various floods and determine if the town of Crawford, OH is likely to be flooded or not. Outcomes: learn to work with quantitative data, learn to use Excel, be able to use USGS data.

Roberts, Sheila

166

Children's Association Frequency Tables  

Microsoft Academic Search

The primary object of the present investigation is to make a comparative study of the mental associations of children and adults. It is a study in group psychology, one group being that of children and the other that of adults. The study is made by means of association frequency tables. We have compiled such tables from the responses of one

Herbert Woodrow; Frances Lowell

1916-01-01

167

Adaptive fuzzy frequency hopper  

Microsoft Academic Search

An adaptive fuzzy system generates the frequency hopping sequence for a spread spectrum communications system. The system learns rules from data and acts as a pseudorandom number generator. The IMSL uniform random number generator gives training samples. An adaptive scheme learns associations between previous samples and the current sample and encodes these as fuzzy rules. The output fuzzy set for

Peter J. Pacini; Bart Kosko

1995-01-01

168

Radar Frequency Radiation.  

National Technical Information Service (NTIS)

A method is presented for the determination of radar frequency radiation power densities that the PAVE PAWS radar system could produce in its air and ground environment. The effort was prompted by the concern of the people in the vicinity of OTIS AFB MA a...

E. Malowicki

1981-01-01

169

The Frequency Spectrum Radio.  

ERIC Educational Resources Information Center

This journal issue focuses on the frequency spectrum used in radio communication and on the World Administrative Radio Conference, sponsored by the International Telecommunication Union, held in Geneva, Switzerland, in the fall of 1979. Articles describe the World Administrative Radio Conference as the most important radio communication conference…

Howkins, John, Ed.

1979-01-01

170

Quadrature frequency conversion  

Microsoft Academic Search

A technique for frequency conversion of high-power lasers is described which uses two crystals for each conversion step rather than one. The two crystals are oriented so that the waves generated in them are orthogonally polarized. The conversion efficiency of these quadrature arrangements is much less sensitive to laser pulse nonuniformities than that in single-crystal methods. Consequently, very high conversion

David Eimerl

1987-01-01

171

Application of instantaneous frequency estimation for fundamental frequency detection  

Microsoft Academic Search

Speech signals are nonstationary processes in nature. To represent the nonstationarity, time-frequency analysis techniques are suitable tools since they represent signals simultaneously in both time and frequency. In this paper, the instantaneous frequency (IF) technique is used for fundamental frequency estimation. Since a speech signal is a multicomponent signal, the wavelet transform (WT) which functions as a special bandpass filter,

Haiyun Yang; Lunji Qui; Soo-Ngee Koh

1994-01-01

172

Endless frequency shifting of optical frequency comb lines.  

PubMed

The functional principle of a novel technique for frequency shifting lines of an optical frequency comb is demonstrated. The underlying principle is to shift the carrier frequency by changing the carrier phase within the time span between subsequent pulses of a mode-locked laser used as comb generator. This universal frequency shifter does not require intrusion into the comb generator and provides high agility for arbitrary temporal frequency evolutions. PMID:23482149

Benkler, Erik; Rohde, Felix; Telle, Harald R

2013-03-11

173

Judged frequency of lethal events  

Microsoft Academic Search

A series of 5 experiments with 660 adult Ss studied how people judge the frequency of death from various causes. The judgments exhibited a highly consistent but systematically biased subjective scale of frequency. Two kinds of bias were identified: (a) a tendency to overestimate small frequencies and underestimate larger ones; and (b) a tendency to exaggerate the frequency of some

Sarah Lichtenstein; Baruch Fischhoff; Mark Layman; Barbara Combs

1978-01-01

174

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

175

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.

Spangler, Tim

2006-10-10

176

Extended frequency turbofan model  

NASA Technical Reports Server (NTRS)

The fan model was developed using two dimensional modeling techniques to add dynamic radial coupling between the core stream and the bypass stream of the fan. When incorporated into a complete TF-30 engine simulation, the fan model greatly improved compression system frequency response to planar inlet pressure disturbances up to 100 Hz. The improved simulation also matched engine stability limits at 15 Hz, whereas the one dimensional fan model required twice the inlet pressure amplitude to stall the simulation. With verification of the two dimensional fan model, this program formulated a high frequency F-100(3) engine simulation using row by row compression system characteristics. In addition to the F-100(3) remote splitter fan, the program modified the model fan characteristics to simulate a proximate splitter version of the F-100(3) engine.

Mason, J. R.; Park, J. W.; Jaekel, R. F.

1980-01-01

177

Frequency domain lifetime characterization  

Microsoft Academic Search

Time-based measurements are commonly used for lifetime characterization of semiconductors. We have developed the theory, verified by experiment, of frequency-based lifetime characterization as an alternative to time-based measurements for MOS devices biased in inversion. One consideration during lifetime\\/diffusion length measurements, is whether the near-surface space-charge region or the bulk or quasineutral region is characterized. To characterize the near-surface space-charge region

Dieter K. Schroder; Jae-Eun Park; Suat-Eng Tan; Byoung D. Choi; Seigo Kishino; Haruhiko Yoshida

2000-01-01

178

Frequency steerable acoustic transducers  

NASA Astrophysics Data System (ADS)

Structural health monitoring (SHM) is an active research area devoted to the assessment of the structural integrity of critical components of aerospace, civil and mechanical systems. Guided wave methods have been proposed for SHM of plate-like structures using permanently attached piezoelectric transducers, which generate and sense waves to evaluate the presence of damage. Effective interrogation of structural health is often facilitated by sensors and actuators with the ability to perform electronic, i.e. phased array, scanning. The objective of this research is to design an innovative directional piezoelectric transducer to be employed for the localization of broadband acoustic events, or for the generation of Lamb waves for active interrogation of structural health. The proposed Frequency Steerable Acoustic Transducers (FSATs) are characterized by a spatial arrangement of active material which leads to directional characteristics varying with frequency. Thus FSATs can be employed both for directional sensing and generation of guided waves without relying on phasing and control of a large number of channels. The analytical expression of the shape of the FSATs is obtained through a theoretical formulation for continuously distributed active material as part of a shaped piezoelectric device. The FSAT configurations analyzed in this work are a quadrilateral array and a geometry which corresponds to a spiral in the wavenumber domain. The quadrilateral array is experimentally validated, confirming the concept of frequency-dependent directionality. Its limited directivity is improved by the Wavenumber Spiral FSAT (WS-FSAT), which, instead, is characterized by a continuous frequency dependent directionality. Preliminary validations of the WS-FSAT, using a laser doppler vibrometer, are followed by the implementation of the WS-FSAT as a properly shaped piezo transducer. The prototype is first used for localization of acoustic broadband sources. Signal processing algorithms and related imaging techniques for damage location are also presented. Finally, the WS-FSAT has also been experimentally validated in generation.

Senesi, Matteo

179

Multiwire thermocouples: Frequency response  

NASA Technical Reports Server (NTRS)

Experimental measurements are made with a novel two wire thermocouple. Signals from two wires of unequal diameters are recorded from the thermocouple suspended in constant flow with a periodic temperature fluctuation. It is demonstrated that the reconstructed signal from the two wire thermocouple requires no compensation for omega less than or equal to 2 omega(sub 1) where omega is the natural frequency of the smaller wire. A compensation factor is recommended for larger frequencies omega greater than 2 omega(sub 1). Theory and experimental measurements are compared with a novel three wire thermocouple. Signals from three wires of unequal diameters are recorded from the thermocouple suspended in constant flow with a periodic temperature fluctuation. It is demonstrated that the reconstructed signal from the three wire thermocouple requires no compensation for omega less than or equal to 5 omega(sub 1) where omega (sub 1) is the natural frequency of the smaller wire. The latter result represents a significant improvement compared to previous work with two wire thermocouples. A correction factor has also been derived to account for wires of arbitrary diameter. Measurements are recorded for multiwire thermocouples consisting of either two or three wires of unequal diameters. Signals from the multiwire probe are recorded for a reversing gas flow with a periodic temperature fluctuation. It is demonstrated that the reconstructed signal from the multiwire thermocouple requires no compensation provided omega/omega(sub 1) is less than 2.3 for two wires or omega/omega(sub 1) is less than 3.6 for three wires where omega(sub 1) is the natural frequency of the smaller wire based on the maximum gas velocity. The latter results were possible provided Fourier transformed data were used and knowledge of the gas velocity is available.

Forney, L. J.; Fralick, G. C.

1994-01-01

180

Low frequency cavitation erosion  

NASA Astrophysics Data System (ADS)

Damage of diesel engine piston sleeve liners due to cavitation of the coolant fluid can be severe. Coolant fluid additives are used to inhibit cavitation damage, and are evaluated by industry suppliers using ASTM G32-98 Standard Test Method for Cavitation Erosion Using Vibratory Apparatus. The ASTM G32-98 test procedure uses an ultrasonic horn at 20 kHz to vibrate a test button in the coolant. The test button mass loss and surface appearance are studied to sort the performance of new coolant additives. Mismatch between good lab performers and actual engine test runs has raised concerns over the current lab test. The frequency range of the current test has been targeted for investigation. A low frequency, less than 2000 Hz, test rig was built to explore the cavitation damage. The test system did produce cavitation on the surface of the test button for a period of 36 h, with minimal mass loss. The test rig experienced cyclic fatigue when test times were extended. The work is now focusing on designing a better test rig for long duration tests and on developing numerical models in order to explore the effects of cavitation excitation frequency on surface erosion.

Pardue, Sally J.; Chandekar, Gautam

2002-11-01

181

Rapid frequency scan EPR.  

PubMed

In rapid frequency scan EPR with triangular scans, sufficient time must be allowed to insure that the magnetization in the x, y plane decays to baseline at the end of the scan, which typically is about 5T(2) after the spins are excited. To permit relaxation of signals excited toward the extremes of the scan the total scan time required may be much longer than 5T(2). However, with periodic, saw-tooth excitation, the slow-scan EPR spectrum can be recovered by Fourier deconvolution of data recorded with a total scan period of 5T(2), even if some spins are excited later in the scan. This scan time is similar to polyphase excitation methods. The peak power required for either polyphase excitation or rapid frequency scans is substantially smaller than for pulsed EPR. The use of an arbitrary waveform generator (AWG) and cross loop resonator facilitated implementation of the rapid frequency scan experiments reported here. The use of constant continuous low B(1), periodic excitation waveform, and constant external magnetic field is similar to polyphase excitation, but could be implemented without the AWG that is required for polyphase excitation. PMID:21664848

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

2011-08-01

182

Rapid Frequency Scan EPR  

PubMed Central

In rapid frequency scan EPR with triangular scans, sufficient time must be allowed to insure that the magnetization in the x,y plane decays to baseline at the end of the scan, which typically is about 5 T2 after the spins are excited. To permit relaxation of signals excited toward the extremes of the scan the total scan time required may be much longer than 5 T2. However, with periodic, saw-tooth excitation, the slow-scan EPR spectrum can be recovered by Fourier deconvolution of data recorded with a total scan period of 5 T2, even if some spins are excited later in the scan. This scan time is similar to polyphase excitation methods. The peak power required for either polyphase excitation or rapid frequency scans is substantially smaller than for pulsed EPR. The use of an arbitrary waveform generator (AWG) and cross loop resonator facilitated implementation of the rapid frequency scan experiments reported here. The use of constant continuous low B1, periodic excitation waveform, and constant external magnetic field is similar to polyphase excitation, but could be implemented without the AWG that is required for polyphase excitation.

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

2011-01-01

183

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

184

Local oscillator limited frequency stability for passive atomic frequency standards using square wave frequency modulation  

Microsoft Academic Search

Atomic frequency standards using square wave frequency modulation effectively interrogate the atomic line by switching back and forth between two frequencies with equal atomic absorption values. For a symmetric absorption line, the slope of the responses will also be equal. In the quasistatic limit, this would seem to be an ideal interrogation process: the sign reversal of frequency slope can

Charles A. Greenhall; G. John Dick

2000-01-01

185

Effective Collision Frequency and Radio Frequency Conductivity in the Magnetosphere.  

National Technical Information Service (NTIS)

The electron density and electron temperature profiles have been chosen, and with help of these data the effective electron collision frequency along various geomagnetic lines of force have been calculated. The effective electron collision frequency in th...

K. D. Misra P. K. Shukla R. N. Singh

1970-01-01

186

Radar frequency radiation  

NASA Astrophysics Data System (ADS)

A method is presented for the determination of radar frequency radiation power densities that the PAVE PAWS radar system could produce in its air and ground environment. The effort was prompted by the concern of the people in the vicinity of OTIS AFB MA and BEALE AFB CA about the possible radar frequency radiation hazard of the PAVE PAWS radar. The method is based on the following main assumptions that: (a) the total field can be computed as the vector summation of the individual fields due to each antenna element; (b) the individual field can be calculated using distances for which the field point is in the far field of the antenna element. An RFR computer program was coded for the RADC HE 6180 digital computer and exercised to calculate the radiation levels in the air and ground space for the present baseline and the possible Six DB and 10 DB growth systems of the PAVE PAWS radar system at OTIS AFB MA. The average radiation levels due to the surveillance fence were computed for three regions: in the air space in front of the radar, at the radar hazard fence at OTIS AFB MA and at representative ground points in the OTIS AFB vicinity. It was concluded that the radar frequency radiation of PAVE PAWS does not present a hazard to personnel provided there is no entry to the air hazard zone or to the area within the hazard fence. The method developed offers a cost effective way to determine radiation levels from a phased array radar especially in the near field and transition regions.

Malowicki, E.

1981-11-01

187

High frequency electromagnetic tomography  

SciTech Connect

An experiment was conducted in G Tunnel at the Nevada Test Site to evaluate high frequency electromagnetic tomography as a candidate for in situ monitoring of hydrology in the near field of a heater placed in densely welded tuff. Tomographs of 200 MHz electromagnetic permittivity were made for several planes between boreholes. Data were taken before the heater was turned on, during heating and during cooldown of the rockmass. This data is interpreted to yield maps of changes in water content of the rockmass as a function of time. This interpretation is based on laboratory measurement of electromagnetic permittivity as a function of water content for densely welded tuff. 8 refs., 6 figs.

Daily, W.; Ramirez, A.; Ueng, T.; Latorre, R.

1989-09-01

188

Frequency doubling crystals  

SciTech Connect

A systematic approach to the production of frequency conversion crystals is described in which a chiral molecule has attached to it a harmonic generating unit which contributes to the noncentrosymmetry of the molecule. Certain preferred embodiments of such harmonic generating units include carboxylate, guanadyly and imidazolyl units. Certain preferred crystals include L- arginine fluoride, deuterated L-arginine fluoride, L-arginine chloride monohydrate, L-arginine acetate, dithallium tartrate, ammonium N-acetyl valine, N-acetyl tyrosine and N-acetyl hydroxyproline. Chemical modifications of the chiral molecule, such as deuteration, halogenation and controlled counterion substitution are available to adapt the dispersive properties of a crystal in a particular wavelength region.

Wang, F.; Velsko, S.P.

1989-10-24

189

Frequency Domain Identification Toolbox  

NASA Technical Reports Server (NTRS)

This report documents software written in MATLAB programming language for performing identification of systems from frequency response functions. MATLAB is a commercial software environment which allows easy manipulation of data matrices and provides other intrinsic matrix functions capabilities. Algorithms programmed in this collection of subroutines have been documented elsewhere but all references are provided in this document. A main feature of this software is the use of matrix fraction descriptions and system realization theory to identify state space models directly from test data. All subroutines have templates for the user to use as guidelines.

Horta, Lucas G.; Juang, Jer-Nan; Chen, Chung-Wen

1996-01-01

190

Radio frequency pulse compression  

SciTech Connect

High gradients require peak powers. One possible way to generate high peak powers is to generate a relatively long pulse at a relatively low power and compress it into a shorter pulse with higher peak power. It is possible to compress before dc to rf conversion as is done for the relativistic klystron or after dc to rf conversion as is done with SLED. In this note only radio frequency pulse compression (RFPC) is considered. Three methods of RFPC will be discussed: SLED, BEC, and REC. 3 refs., 8 figs., 1 tab.

Farkas, Z.D.

1988-12-01

191

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

192

Frequency shifts of high frequency p-modes  

NASA Technical Reports Server (NTRS)

Frequency shifts of high frequency p-modes during the solar cycle are calculated for a non-magnetic polytrope convection zone model. An isothermal chromospheric atmosphere threaded by a uniform horizontal magnetic field is correlated to this model. The relevant observations of such frequency changes are discussed. The calculated simultaneous changes in the field strength and chromospheric temperature result in the frequency shifts that are similar to those of the observations.

Jain, Rekha

1995-01-01

193

Optical frequency comb generation for terahertz difference-frequency measurements  

Microsoft Academic Search

We describe the operation of an optical frequency comb generator and its utility in measuring optical frequency differences in the terahertz range. The comb generator is a high-frequency resonant electro-optic modulator capable of generating hundreds of sidebands with a sideband spacing of 17 GHz and a span of at ;east 3 THz. The span is currently limited by the dispersion

L. R. Brothers; Ngai C. Wong

1995-01-01

194

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

195

Firewater system inadvertent actuation frequencies  

SciTech Connect

This paper presents some recommended generic values for fire protection system inadvertent actuation frequencies. The frequencies are based on actual data from Department of Energy and commercial reactor plant facilities.

Schroeder, J.A. (EG and G Idaho, Inc., Idaho Falls, ID (United States)); Eide, S.A. (Los Alamos Technical Associates, Inc., Albuquerque, NM (United States))

1993-01-01

196

Firewater system inadvertent actuation frequencies  

SciTech Connect

This paper presents some recommended generic values for fire protection system inadvertent actuation frequencies. The frequencies are based on actual data from Department of Energy and commercial reactor plant facilities.

Schroeder, J.A. [EG and G Idaho, Inc., Idaho Falls, ID (United States); Eide, S.A. [Los Alamos Technical Associates, Inc., Albuquerque, NM (United States)

1993-04-01

197

Low Noise Frequency Changing Circuit.  

National Technical Information Service (NTIS)

The low noise frequency changing circuit is utilized in radio and radar systems. An improvement is shown in a conventional twin triode frequency changer or mixer circuit. The improved circuit includes an anode load resistor and a capacitor. Transistors ar...

D. J. Healey

1965-01-01

198

Frequency coupling in dual frequency capacitively coupled radio-frequency plasmas  

NASA Astrophysics Data System (ADS)

An industrial, confined, dual frequency, capacitively coupled, radio-frequency plasma etch reactor (Exelan®, Lam Research) has been modified for spatially resolved optical measurements. Space and phase resolved optical emission spectroscopy yields insight into the dynamics of the discharge. A strong coupling of the two frequencies is observed in the emission profiles. Consequently, the ionization dynamics, probed through excitation, is determined by both frequencies. The control of plasma density by the high frequency is, therefore, also influenced by the low frequency. Hence, separate control of plasma density and ion energy is rather complex.

Gans, T.; Schulze, J.; O'Connell, D.; Czarnetzki, U.; Faulkner, R.; Ellingboe, A. R.; Turner, M. M.

2006-12-01

199

Frequency Estimation in Intradyne Reception  

Microsoft Academic Search

We report on an optical intradyne receiver experiment with frequency estimation. Frequency estimation allows, if performed prior to block phase estimation or other phase recovery techniques, for a much higher frequency difference between transmit laser and local oscillator laser. We demonstrate the feasibility of our approach in a 20-Gb\\/s quadrature phase-shift keying experiment

Andreas Leven; Noriaki Kaneda; Ut-Va Koc; Young-Kai Chen

2007-01-01

200

Minicomputer-controlled frequency generator  

NASA Technical Reports Server (NTRS)

Extremely-accurate and low-phase-noise frequency generator varies oscillator frequency as predetermined function of time. System could be used: (a) to automatically vary transmission frequencies in accordance with seasonal and diurnal changes in ionospheric conditions, (b) as automatic tuner for heterodyne receivers, or (c) as control element for phase-locked telemetry receivers.

Winkelstein, R. A.

1974-01-01

201

Fiber Optic Frequency Transfer Link.  

National Technical Information Service (NTIS)

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...

L. Primas R. Sydnor G. Lutes

1989-01-01

202

Frequency detectors for CPM signals  

Microsoft Academic Search

Frequency tracking loops are used in digital links to control the carrier frequency of the received signals. A basic component in such loops is the frequency difference detector (FDD). This paper concentrates on a class of FDDs for use with binary continuous-phase modulation (CPM). Their derivation is based on two ideas: the maximum-likelihood principle for parameter estimation and Laurent's (1986)

A. N. D'Andrea; A. Ginesi; U. Mengali

1995-01-01

203

Word Frequencies in Toddlers' Lexicons.  

ERIC Educational Resources Information Center

Two studies examined word frequencies in toddlers' lexicons using the Language Development Survey (LDS). In Study 1, a high degree of consistency in LDS word frequencies was found in the lexicons of 758 24-month-olds. In Study 2, LDS word frequencies in 40 late talkers found both lexicon size and age of subject influenced the degree of consistency…

Rescorla, Leslie; Alley, Amie; Christine, Joanne Book

2001-01-01

204

Pulsed optically pumped frequency standard  

Microsoft Academic Search

We reconsider the idea of a pulsed optically pumped frequency standard conceived in the early 1960s to eliminate the light-shift effect. The development of semiconductor lasers and of pulsed electronic techniques for atomic fountains and new theoretical findings allow an implementation of this idea which may lead to a frequency standard whose frequency stability is limited only by the thermal

Aldo Godone; Salvatore Micalizio; Filippo Levi

2004-01-01

205

Observation of quantum frequency conversion  

Microsoft Academic Search

Quantum frequency conversion, a process with which an input beam of light can be converted into an output beam of a different frequency while preserving the quantum state, is experimentally demonstrated for the first time. Nonclassical intensity correlation (about 3 dB) between two beams at 1064 nm is used as the input quantum property. When the frequency of one of

Jianming Huang; Prem Kumar

1992-01-01

206

Mixed Frequency AC Signals  

NSDL National Science Digital Library

All About Circuits is a website that âÂÂprovides a series of online textbooks covering electricity and electronics.â Written by Tony R. Kuphaldt, the textbooks available here are wonderful resources for students, teachers, and anyone who is interested in learning more about electronics. This specific section, Mixed Frequency AC Signals, is the seventh chapter in Volume II âÂÂAlternating Current (AC). A few of the topics covered in this chapter include: Square wave signals, spectrum analysis, circuit effects, and other waveshapes. Diagrams and detailed descriptions of concepts are included throughout the chapter to provide users with a comprehensive lesson. Visitors to the site are also encouraged to discuss concepts and topics using the All About Circuits discussion forums (registration with the site is required to post materials).

Kuphaldt, Tony R.

2008-07-02

207

Radio frequency picosecond phototube  

SciTech Connect

We propose a photon detector for recording low-level and ultra-fast optical signals, based on radio frequency (RF) analysis of low-energy photoelectrons (PEs). By using currently developed 500 MHz RF deflector, it is possible to scan circularly and detect single PEs, amplified in multi-channel plates (MCPs). The operation of the tube is investigated by means of thermionic electron source. It is demonstrated that the signals generated in the MCP can be processed event by event; by using available nanosecond electronics and that time resolution better than 20 ps can be achieved. Timing characteristics of the Cherenkov detector with RF phototube in a ''head-on'' geometry is investigated by means of Monte Carlo simulation.

A. Margaryan; R. Carlini; R. Ent; N. Grigoryan; K. Gyunashyan; O. Hashimoto; K. Hovater; M. Ispiryan; S. Knyazyan; B. Kross; S. Majewski; G. Marikyan; M. Mkrtchyan; L. Parlakyan; V. Popov; L. Tang; H. Vardanyan; C. Yan; S. Zhamkochyan; C. Zorn

2006-10-01

208

Frequency doubling crystals  

SciTech Connect

A systematic approach to the production of frequency conversion crystals is described in which a chiral molecule has attached to it a "harmonic generating unit" which contributes to the noncentrosymmetry of the molecule. Certain preferred embodiments of such harmonic generating units include carboxylate, guanadyly and imidazolyl units. Certain preferred crystals include L-arginine fluoride, deuterated L-arginine fluoride, L-arginine chloride monohydrate, L-arginine acetate, dithallium tartrate, ammonium N-acetyl valine, N-acetyl tyrosine and N-acetyl hydroxyproline. Chemical modifications of the chiral molecule, such as deuteration, halogenation and controlled counterion substitution are available to adapt the dispersive properties of a crystal in a particular wavelength region.

Wang, Francis (Danville, CA); Velsko, Stephan P. (Livermore, CA)

1989-01-01

209

Frequency doubling crystals  

SciTech Connect

A systematic approach to the production of frequency conversion crystals is described in which a chiral molecule has attached to it a harmonic generating unit'' which contributes to the noncentrosymmetry of the molecule. Certain preferred embodiments of such harmonic generating units include carboxylate, guanadyly and imidazolyl units. Certain preferred crystals include L-arginine fluoride, deuterated L-arginine fluoride, L-arginine chloride monohydrate, L-arginine acetate, dithallium tartrate, ammonium N-acetyl valine, N-acetyl tyrosine and N-acetyle hydroxyyproline. Chemical modifications of the chiral molecule, such as deuteration, halogenation and controlled counterion substitution are available to adapt the dispersive properties of a crystal in a particular wavelength region.

Wang, F.; Velsko, S.P.

1988-08-15

210

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

211

Terahertz laser frequency combs  

NASA Astrophysics Data System (ADS)

Terahertz light can be used to identify numerous complex molecules, but has traditionally remained unexploited due to the lack of powerful broadband sources. Pulsed lasers can be used to generate broadband radiation, but such sources are bulky and produce only microwatts of average power. Conversely, although terahertz quantum cascade lasers are compact semiconductor sources of high-power terahertz radiation, their narrowband emission makes them unsuitable for complex spectroscopy. In this work, we demonstrate frequency combs based on terahertz quantum cascade lasers, which combine the high power of lasers with the broadband capabilities of pulsed sources. By fully exploiting the quantum-mechanically broadened gain spectrum available to these lasers, we can generate 5 mW of terahertz power spread across 70 laser lines. This radiation is sufficiently powerful to be detected by Schottky-diode mixers, and will lead to compact terahertz spectrometers.

Burghoff, David; Kao, Tsung-Yu; Han, Ningren; Chan, Chun Wang Ivan; Cai, Xiaowei; Yang, Yang; Hayton, Darren J.; Gao, Jian-Rong; Reno, John L.; Hu, Qing

2014-06-01

212

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

213

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

214

Spatial Frequency Discrimination in Schizophrenia  

PubMed Central

Pathways within the visual system can be distinguished on the basis of selectivity for low or high spatial frequencies. Spatial frequency discrimination was evaluated in 17 medicated male patients with schizophrenia and 19 male control subjects. Subjects were required to discriminate whether pairs of high contrast, sinusoidally modulated gratings were the same or different in spatial frequency. Accuracy performance was compared at high, medium, and low spatial frequencies on tasks matched for control performance. Patients showed a greater performance decrement of 12% on low as compared with 4% on high spatial frequencies. These findings suggest a disturbance of right hemisphere mechanisms involved in spatial perception and attention in schizophrenia.

O'Donnell, Brian F.; Potts, Geoffrey F.; Nestor, Paul G.; Stylianopoulos, Kiriaki C.; Shenton, Martha E.; McCarley, Robert W.

2010-01-01

215

Frequency-bin entangled photons  

SciTech Connect

A monochromatic laser pumping a parametric down-conversion crystal generates frequency-entangled photon pairs. We study this experimentally by addressing such frequency-entangled photons at telecommunication wavelengths (around 1550 nm) with fiber-optics components such as electro-optic phase modulators and narrow-band frequency filters. The theory underlying our approach uses the notion of frequency-bin entanglement. Our results show that the phase modulators address coherently up to eleven frequency bins, leading to an interference pattern which can violate by more than five standard deviations a Bell inequality adapted to our setup.

Olislager, L.; Emplit, P. [Service OPERA-Photonique, CP 194/5, Universite Libre de Bruxelles, Avenue F.D. Roosevelt 50, B-1050 Brussels (Belgium); Cussey, J. [SmartQuantum SA, Espace Phoenix, Route du Radome, FR-22560 Pleumeur-Bodou (France); Nguyen, A. T. [Service de Physique et Electricite, Institut Meurice, Haute Ecole Lucia de Brouckere, Avenue Emile Gryzon 1, B-1070 Brussels (Belgium); Massar, S. [Laboratoire d'Information Quantique, CP 225, Universite Libre de Bruxelles, Boulevard du Triomphe, B-1050 Brussels (Belgium); Merolla, J.-M.; Huy, K. Phan [Departement d'Optique P. M. Duffieux, Institut Franche-Comte Electronique Mecanique Thermique et Optique-Sciences et Technologies, Centre National de la Recherche Scientifique, Unite Mixte de Recherche 6174, Universite de Franche-Comte, FR-25030 Besancon (France)

2010-07-15

216

Mid-infrared frequency combs  

NASA Astrophysics Data System (ADS)

Laser frequency combs are coherent light sources that emit a broad spectrum of discrete, evenly spaced narrow lines whose absolute frequency can be measured to within the accuracy of an atomic clock. Their development in the near-infrared and visible domains has revolutionized frequency metrology while also providing numerous unexpected opportunities in other fields such as astronomy and attosecond science. Researchers are now exploring how to extend frequency comb techniques to the mid-infrared spectral region. Versatile mid-infrared frequency comb generators based on novel laser gain media, nonlinear frequency conversion or microresonators promise to significantly expand the applications of frequency combs. In particular, novel approaches to molecular spectroscopy in the 'fingerprint region', with dramatically improved precision, sensitivity, recording time and/or spectral bandwidth may lead to new discoveries in the various fields relevant to molecular science.

Schliesser, Albert; Picqué, Nathalie; Hänsch, Theodor W.

2012-07-01

217

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.

218

A technique for orthogonal frequency division multiplexing frequency offset correction  

Microsoft Academic Search

This paper discusses the effects of frequency offset on the performance of orthogonal frequency division multiplexing (OFDM) digital communications. The main problem with frequency offset is that it introduces interference among the multiplicity of carriers in the OFDM signal. It is shown, and confirmed by simulation, that to maintain signal-to-interference ratios of 20 dB or greater for the OFDM carriers,

P. H. Moose

1994-01-01

219

Robust Flood Frequency Models  

NASA Astrophysics Data System (ADS)

The concept of a robust model is briefly explored. In the context of flood frequency analysis, two necessary properties of a robust model are advanced, namely, resistance and efficiency. Strategies for seeking more robust models are discussed. Because of its versatility, the five-parameter Wakeby distribution can credibly be considered a parent flood distribution. Four regionalized Wakeby parents are employed in simulation studies to search for robust models. These parents were shown by Houghton to be representative of U.S. flood experience in the sense that certain raw flood data characteristics could be reproduced. A limited range of sampling experiments were undertaken. The results suggest that of the site-specific estimators considered, the two-parameter log normal maximum likelihood estimator is most resistant, with Gumbel estimators employing either maximum likelihood or probability-weighted moments displaying comparable resistance. Several estimators which utilize regional flood information were compared. Included were empirical Bayes estimators which are structurally similar to James-Stein rules and regionalized estimators based on the flood index method. These estimators exhibited substantial improvements in aggregate risk performance over their site-specific counterparts, particularly for short record lengths. Regionalized estimators appear to be preferable for short record lengths, while estimators which combine both site and regional flood information are preferable for longer record lengths. When such estimation procedures are considered, other distributional models such as log Pearson type III and Wakeby become practical alternatives to the two-parameter log normal model.

Kuczera, George

1982-04-01

220

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

221

Operational frequency stability of rubidium and cesium frequency standards  

NASA Technical Reports Server (NTRS)

The frequency stabilities under operational conditions of several commercially available rubidium and cesium frequency standards were determined from experimental data for frequency averaging times from 10 to the 7th power s and are presented in table and graph form. For frequency averaging times between 10 to the 5th power and 10 to the 7th power s, the rubidium standards tested have a stability of between 10 to the minus 12th power and 5 x 10 to the minus 12th power, while the cesium standards have a stability of between 2 x 10 to the minus 13th power and 5 x 10 to the minus 13th power.

Lavery, J. E.

1973-01-01

222

Frequency synchronization of a frequency-hopped MFSK communication system  

NASA Technical Reports Server (NTRS)

This paper presents the performance of fine-frequency synchronization. The performance degradation due to imperfect frequency synchronization is found in terms of the effect on bit error probability as a function of full-band or partial-band noise jamming levels and of the number of frequency hops used in the estimator. The effect of imperfect fine-time synchronization is also included in the calculation of fine-frequency synchronization performance to obtain the overall performance degradation due to synchronization errors.

Huth, G. K.; Polydoros, A.; Simon, M. K.

1981-01-01

223

Light beam frequency comb generator  

DOEpatents

A light beam frequency comb generator uses an acousto-optic modulator to generate a plurality of light beams with frequencies which are uniformly separated and possess common noise and drift characteristics. A well collimated monochromatic input light beam is passed through this modulator to produce a set of both frequency shifted and unshifted optical beams. An optical system directs one or more frequency shifted beams along a path which is parallel to the path of the input light beam such that the frequency shifted beams are made incident on the modulator proximate to but separated from the point of incidence of the input light beam. After the beam is thus returned to and passed through the modulator repeatedly, a plurality of mutually parallel beams are generated which are frequency-shifted different numbers of times and possess common noise and drift characteristics.

Priatko, Gordon J. (Cupertino, CA); Kaskey, Jeffrey A. (Livermore, CA)

1992-01-01

224

Light beam frequency comb generator  

DOEpatents

A light beam frequency comb generator uses an acousto-optic modulator to generate a plurality of light beams with frequencies which are uniformly separated and possess common noise and drift characteristics. A well collimated monochromatic input light beam is passed through this modulator to produce a set of both frequency shifted and unshifted optical beams. An optical system directs one or more frequency shifted beams along a path which is parallel to the path of the input light beam such that the frequency shifted beams are made incident on the modulator proximate to but separated from the point of incidence of the input light beam. After the beam is thus returned to and passed through the modulator repeatedly, a plurality of mutually parallel beams are generated which are frequency-shifted different numbers of times and possess common noise and drift characteristics. 2 figs.

Priatko, G.J.; Kaskey, J.A.

1992-11-24

225

The limit of frequency estimation  

NASA Technical Reports Server (NTRS)

In phase and frequency measurements, the measured phase and frequency are not the true phase and frequency but the ones which are disturbed by noises, due to the effects of the noise processes. The effects of three noise processes, i.e., White PM, White FM, and Random Walk FM, on the estimations of phase and frequency is discussed. It is indicated that the properties of these two estimations are very different. In phase estimation, the error can be reduced by properly selecting suitable smoothing length NT and smaple interval T. But in frequency estimation, the error cannot be reduced arbitrarily by means of improving estimator or measurement equipment. The precision of frequency is limited by the intrinsic noises in the clock.

Guo, Wei

1993-01-01

226

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

227

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

228

A contactless rotary frequency changer  

NASA Astrophysics Data System (ADS)

The design and the principle of operation of a contactless rotary frequency changer for converting commercial-frequency alternating current to stabilized three-phase current with a higher frequency (400 Hz or more) are presented. The frequency changer consists of a synchronous motor with a rotating rectifier and two asynchronous electric machines with phase rotors, one of which has an adjustable magnetic shunt in the stator. It is shown that the use of an adjustable magnetic shunt makes it possible to obtain a stable output voltage, while the use of toroidal three-phase windings reduces the amount of the winding wire as well as the dimensions and weight of the unit.

Krasnoshapka, M. M.; Kovalenko, G. A.; Krasnoshapka, D. M.

1984-10-01

229

Automatic oscillator frequency control system  

NASA Technical Reports Server (NTRS)

A frequency control system makes an initial correction of the frequency of its own timing circuit after comparison against a frequency of known accuracy and then sequentially checks and corrects the frequencies of several voltage controlled local oscillator circuits. The timing circuit initiates the machine cycles of a central processing unit which applies a frequency index to an input register in a modulo-sum frequency divider stage and enables a multiplexer to clock an accumulator register in the divider stage with a cyclical signal derived from the oscillator circuit being checked. Upon expiration of the interval, the processing unit compares the remainder held as the contents of the accumulator against a stored zero error constant and applies an appropriate correction word to a correction stage to shift the frequency of the oscillator being checked. A signal from the accumulator register may be used to drive a phase plane ROM and, with periodic shifts in the applied frequency index, to provide frequency shift keying of the resultant output signal. Interposition of a phase adder between the accumulator register and phase plane ROM permits phase shift keying of the output signal by periodic variation in the value of a phase index applied to one input of the phase adder.

Smith, S. F. (inventor)

1985-01-01

230

ECRIS operation with multiple frequencies  

NASA Astrophysics Data System (ADS)

The 10.5 GHz electron cyclotron resonance ion source (ECRIS) at Argonne National Laboratory has been utilizing a 10.5 GHz klystron and an 11-13 GHz traveling wave tube amplifier (TWTA) for beam production in two-frequency heating mode. The beam intensities obtained from the source with two-frequency heating have shown a factor of 2 improvement over single-frequency heating for the higher charge states. Following a simple logic that an increased number of resonance zones leads to enhanced source performance, a 14 GHz klystron was added to the source configuration enabling the plasma to be simultaneously excited with three discrete frequencies. In studies with three-frequency heating when compared to two-frequency heating, the beam intensity for O7+ increased from 70.4 to 84.2 e?A, Kr23+ (mass 86, 99.9% enriched) increased from 3.5 to 7.2 e?A, and Xe28+ (mass 136, 60% enriched) increased from 7.9 to 12.2 e?A. A rf power combiner was added to the TWTA so that it could be driven simultaneously with two frequencies. With the TWTA operating at 10.85 and 12.66 GHz, the intensities of O6+ increased 80% and O7+ doubled compared to single-frequency operation, further demonstrating the multiple frequency heating effect except in this instance with a single transmitter.

Vondrasek, R. C.; Scott, R.; Pardo, R. C.

2006-03-01

231

Simultaneous Frequency and Direction Finding Technique using Frequency Scanning Antenna  

Microsoft Academic Search

A frequency and phase scannring antenna array svstem having the capability of finding simultaneously the frequency and the direction of arrival of the incident wave by using simple amplitude measurements is described. Microstrip wide slot is used as the antenna array element due to its broad bandwidth. The incident RF wave received by the antenna array is fed to a

Ibrahim Tekin; Altunkan Hizal

1992-01-01

232

Miniaturization of dual frequency RFID antenna with high frequency ratio  

Microsoft Academic Search

We have presented a novel design for dual frequency RFID antenna with high frequency ratio. This antenna works well in both the HF and UHF bands for RFID operation with a single feed. Comparisons between the new design and the previous design are made and the new design is shown to be less than half of the size of the

Kin Seong Leong; Mun Leng Ng; Peter H. Cole

2007-01-01

233

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

234

47 CFR 22.863 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...Frequency stability. The frequency stability of equipment used...after accounting for Doppler frequency shifts, the occupied bandwidth of the fundamental emissions remains within the authorized frequency bands of operation....

2013-10-01

235

Reconfigurable infrared frequency selective surfaces  

Microsoft Academic Search

In this paper, a new reconfigurable frequency selective surface (RFSS) design concept is introduced. A grid of simple metallic patches interconnected by a matrix of switches is proposed as the unit cell of an RFSS. The switches are independently addressable and provide significant transmission and reflection flexibility over a large range of frequencies. This flexibility is exploited by optimizing the

J. A. Bossard; D. H. Werner; T. S. Mayer; R. P. Drupp

2004-01-01

236

Frequency effects in phoneme processing  

NASA Astrophysics Data System (ADS)

This study tested the hypothesis that phonological segments are activated during word recognition in proportion to their frequency of use, analogous to frequency effects in whole word recognition. Preliminary evidence for the hypothesis was given by Moates, Bond, and Stockmal [LabPhon 7 (2002)] using a word reconstruction task. The present study used a gating task in which progressively longer fragments of a word are presented to listeners who must identify the word after as few gates as possible. High- and low-frequency segments were contrasted by presenting them in word pairs that differed in two segments, e.g., collision-collusion, where /I/ is more frequent than /u/. We constructed 15 words pairs contrasting vowels and 16 pairs contrasting consonants (e.g., relief-release, where /s/ is more frequent than /f/). Identification judgments were gathered from 125 participants. An ANOVA showed high-frequency consonants to be identified at significantly earlier gates than their matched low-frequency consonants with both subjects and items as random factors. No such effect appeared for vowels. Also, whole words containing the high-frequency segments were not identified significantly earlier than those containing low-frequency segments. If the phoneme frequency effect is reliable, then spoken word recognition models should address it.

Moates, Danny; Stockmal, Verna; Bond, Zinny

2001-05-01

237

STABILIZING AND MEASURING OPTICAL FREQUENCIES  

Microsoft Academic Search

Many factors are coming together to make this an exciting time in the development of optical frequency standards. These include improved strategies for interrogation of the resonant quantum reference sample, improved accuracy and control of the modulation process, demonstration of an external modulation-removal strategy, and a rich field of new possibilities for frequency measurement, particularly the arrival of broad optical

JOHN L. HALL; MATTHEW S. TAUBMAN; SCOTT A. DIDDAMS; BRUCE TIEMANN; JUN YE; LONG-SHENG MA; DAVID JONES; STEVEN CUNDIFF

2007-01-01

238

Frequency Hopping With Analog Messages.  

National Technical Information Service (NTIS)

Frequency hopping (FH) is used by the military as an electronic counter-counter-measure (ECCM) technique. The carrier frequency is caused to vary from one value to another over a range of values in usually a random or pseudo-random manner. The message is ...

S. Kardisan

1988-01-01

239

High Frequency Hearing Following Meningitis.  

National Technical Information Service (NTIS)

The high frequency hearing of 26 military persons, diagnosed as having had meningitis was examined and compared to the high frequency hearing of a control population of the same age. Those persons who had been categorized as seriously ill differed signifi...

J. L. Fletcher A. B. Cairns F. G. Collins J. Endicott

1966-01-01

240

High Frequency Power Distribution System.  

National Technical Information Service (NTIS)

The objective of this project was to provide the technology of high frequency, high power transmission lines to the 100 kW power range at 20 kHz frequency. In addition to the necessary design studies, a 150 m long, 600 V, 60 A transmission line was built,...

M. R. Patel

1986-01-01

241

Frequency management for ESA's missions  

NASA Astrophysics Data System (ADS)

Frequency management is a discipline in which international regulations, technical discussions and negotiations play a key role. The radio-frequency spectrum is becoming an increasingly scarce resource and more and more users of all kinds are competing with each other for their share.

Marelli, Edoardo; Vassallo, Enrico

2005-02-01

242

Frequency Modulation in Microwave Spectroscopy  

Microsoft Academic Search

The absorption coefficient of a gas is related to the density matrix of that gas. The density matrix is obtained formally from its equation of motion, which takes into account a possible time-dependence of the resonant frequency of the molecule and of the frequency of the exciting radiation. The shape of the absorption line is calculated explicitly in a variety

Robert Karplus

1948-01-01

243

Lexical Frequency in Sign Languages  

ERIC Educational Resources Information Center

Measures of lexical frequency presuppose the existence of corpora, but true machine-readable corpora of sign languages (SLs) are only now being created. Lexical frequency ratings for SLs are needed because there has been a heavy reliance on the interpretation of results of psycholinguistic and neurolinguistic experiments in the SL research…

Johnston, Trevor

2012-01-01

244

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

245

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

246

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

247

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

248

The Low Frequency Space Array  

NASA Technical Reports Server (NTRS)

The Low Frequency Space Array (LFSA) is a conceptual mission to survey the entire sky and to image individual sources at frequencies between 1.5 and 26 MHz, a frequency range over which the earth's ionosphere transmits poorly or not at all. With high resolution, high sensitivity observations, a new window will be opened in the electromagnetic spectrum for astronomical investigation. Also, extending observations down to such low frequencies will bring astronomy to the fundamental limit below which the galaxy becomes optically thick due to free-free absorption. A number of major scientific goals can be pursued with such a mission, including mapping galactic emission and absorption, studies of individual source spectra in a frequency range where a number of important processes may play a role, high resolution imaging of extended sources, localization of the impulsive emission from Jupiter, and a search for coherent emission processes.

Dennison, Brian; Weiler, K. W.; Johnston, K. J.; Simon, R. S.; Spencer, J. H.; Hammarstrom, L. M.; Wilhelm, P. G.; Kaiser, M. L.; Desch, M. D.; Fainberg, J.

1987-01-01

249

Controlled frequency high power laser  

SciTech Connect

A system is described for frequency locking the output of one or many laser amplifiers to a reference laser oscillator beam without injection of the reference beam into the amplifier medium. This avoids the necessity of exciting at the frequency of the desired output and of beam splitting from the oscillator to inject a portion of the oscillator radiation into each of several controlled amplifiers. The amplifier includes a lasing medium confined within a cavity and having a portion of the radiation in the medium directed onto a closed loop. A frequency selecting element is supplied within the closed loop and controlled electronicaly to maintain a predetermined frequency relationship to the laser beam of the reference laser oscillator. Radiation in the closed loop is thus controlled in frequency and a portion of it within the amplifier medium is diverted for repeated medium traversals in an unstable cavity configuration to achieve a desired amplification and pulse elongation.

McAllister, G.L.

1980-01-01

250

Optical frequency/wavelength references  

NASA Astrophysics Data System (ADS)

For more than 100 years, optical atomic/molecular frequency references have played important roles in science and technology, and provide standards enabling precision measurements. Frequency-stable optical sources have been central to experimental tests of Einstein's relativity, and also serve to realize our base unit of length. The technology has evolved from atomic discharge lamps and interferometry, to narrow atomic resonances in laser-cooled atoms that are probed by frequency-stabilized cw lasers that in turn control optical frequency synthesizers (combs) based on ultra-fast mode-locked lasers. Recent technological advances have improved the performance of optical frequency references by almost four orders of magnitude in the last eight years. This has stimulated new enthusiasm for the development of optical atomic clocks, and allows new probes into nature, such as searches for time variation of fundamental constants and precision spectroscopy.

Hollberg, L.; Oates, C. W.; Wilpers, G.; Hoyt, C. W.; Barber, Z. W.; Diddams, S. A.; Oskay, W. H.; Bergquist, J. C.

2005-05-01

251

Pitch perception: dissociating frequency from fundamental-frequency discrimination.  

PubMed

High-frequency pure tones (>6 kHz), which alone do not produce salient melodic pitch information, provide melodic pitch information when they form part of a harmonic complex tone with a lower fundamental frequency (F0). We explored this phenomenon in normal-hearing listeners by measuring F0 difference limens (F0DLs) for harmonic complex tones and pure-tone frequency difference limens (FDLs) for each of the tones within the harmonic complexes. Two spectral regions were tested. The low- and high-frequency band-pass regions comprised harmonics 6-11 of a 280- or 1,400-Hz F0, respectively; thus, for the high-frequency region, audible frequencies present were all above 7 kHz. Frequency discrimination of inharmonic log-spaced tone complexes was also tested in control conditions. All tones were presented in a background of noise to limit the detection of distortion products. As found in previous studies, F0DLs in the low region were typically no better than the FDL for each of the constituent pure tones. In contrast, F0DLs for the high-region complex were considerably better than the FDLs found for most of the constituent (high-frequency) pure tones. The data were compared with models of optimal spectral integration of information, to assess the relative influence of peripheral and more central noise in limiting performance. The results demonstrate a dissociation in the way pitch information is integrated at low and high frequencies and provide new challenges and constraints in the search for the underlying neural mechanisms of pitch. PMID:23716218

Oxenham, Andrew J; Micheyl, Christophe

2013-01-01

252

Laser frequency stabilization for LISA  

NASA Technical Reports Server (NTRS)

The requirement on laser frequency noise in the Laser Interferometer Space Antenna (LISA) depends on the velocity and our knowledge of the position of each spacecraft of the interferometer. Currently it is assumed that the lasers must have a pre-stabilized frequency stability of 30Hz/square root of Hz over LISA'S most sensitive frequency band (3 mHz - 30 mHz). The intrinsic frequency stability of even the most stable com- mercial lasers is several orders of magnitude above this level. Therefore it is necessary to stabilize the laser frequency to an ultra-stable frequency reference which meets the LISA requirements. The baseline frequency reference for the LISA lasers are high finesse optical cavities based on ULE spacers. We measured the stability of two ULE spacer cavities with respect to each other. Our current best results show a noise floor at, or below, 30 Hz/square root of Hz above 3 mHz. In this report we describe the experimental layout of the entire experiment and discuss the limiting noise sources.

Mueller, Guido; McNamara, Paul; Thorpe, Ira; Camp, Jordan

2005-01-01

253

Frequency Multipliers for Local Oscillators at THz Frequencies  

Microsoft Academic Search

Sources at THz frequencies have been the subject of intense research for several decades. From backward-wave oscillators (BWOs) to photo-mixers, a variety of sources have been developed for applications ranging from spectroscopy and radio-astronomy to skin- cancer detection. Among them, sources based on a solid-state millimeter-wave oscillator followed by power amplifiers and a cascade of frequency multipliers can produce several

Alain Maestrini

254

ECRIS operation with multiple frequencies  

SciTech Connect

The 10.5 GHz electron cyclotron resonance ion source (ECRIS) at Argonne National Laboratory has been utilizing a 10.5 GHz klystron and an 11-13 GHz traveling wave tube amplifier (TWTA) for beam production in two-frequency heating mode. The beam intensities obtained from the source with two-frequency heating have shown a factor of 2 improvement over single-frequency heating for the higher charge states. Following a simple logic that an increased number of resonance zones leads to enhanced source performance, a 14 GHz klystron was added to the source configuration enabling the plasma to be simultaneously excited with three discrete frequencies. In studies with three-frequency heating when compared to two-frequency heating, the beam intensity for O{sup 7+} increased from 70.4 to 84.2 e{mu}A, Kr{sup 23+} (mass 86, 99.9% enriched) increased from 3.5 to 7.2 e{mu}A, and Xe{sup 28+} (mass 136, 60% enriched) increased from 7.9 to 12.2 e{mu}A. A rf power combiner was added to the TWTA so that it could be driven simultaneously with two frequencies. With the TWTA operating at 10.85 and 12.66 GHz, the intensities of O{sup 6+} increased 80% and O{sup 7+} doubled compared to single-frequency operation, further demonstrating the multiple frequency heating effect except in this instance with a single transmitter.

Vondrasek, R.C.; Scott, R.; Pardo, R.C. [Argonne National Laboratory, Physics Division, Argonne, Illinois 60439 (United States)

2006-03-15

255

Booster synchrotron frequency below transition  

SciTech Connect

The dipole mode synchrotron frequency is a basic beam parameter; it and a few similarly basic quantities measured at small time intervals serve to characterize the longitudinal beam dynamics throughout the acceleration cycle. The effective accelerating voltage, in conjunction with the amount of rf voltage required for the acceleration, is important for the estimate of the beam energy loss per turn. The dipole mode frequency can be used to obtain the effective accelerating rf voltage, providing that it can be measured precisely. The synchrotron frequency measured from the synchrotron phase detector signal (SPD) generally agrees well with calculation, and it can be applied for such purposes as inferring the effective rf voltage.

Xi Yang et al.

2004-04-21

256

Spectrally resolved frequency comb interferometry  

NASA Astrophysics Data System (ADS)

In this contribution a novel method for interferometric distance measurement is presented, that is based on unraveling the spectrum of a femtosecond frequency comb. The light of a frequency comb is sent into a Michelson interferometer. The output of the interferometer is analyzed by a high-resolution spectrometer, resolving the individual comb modes. The path-length difference between the two arms is determined on the level of tens of nm, by utilizing the wealth of information present in the unraveled spectrum, showing homodyne interference for each individual frequency comb mode. The measurement method allows for high-accuracy measurements in combination with a large range of non-ambiguity.

van den Berg, S.

2014-04-01

257

Nuclear quadrupole resonance of boron in borate glasses  

NASA Astrophysics Data System (ADS)

A continuous wave nuclear quadrupole resonance spectrometer that has a high sensitivity even at low frequencies has been built. Boron and aluminum NQR has been detected in the region 200 kHz to 1.4 MHz. For the first time, boron NQR has been detected in a glass. The NQR spectrum of pure B 20 3 glass is consistent with 85 ± 2% of the boron atoms belonging to boroxol rings. In sodium borate glasses, the number of borons in boroxol rings decreases with increasing sodium content, until when sodium oxide comprises 20 mol% of the glass less than 2% of the borons are in boroxol rings.

Gravina, Samuel J.; Bray, Phillip J.

258

The vibrational frequencies of ozone  

NASA Technical Reports Server (NTRS)

The singles and doubles coupled-cluster (CCSD) method is used, together with the recently proposed CCSD(T) and CCSDT-1 methods, to determine the equilibrium structure and harmonic frequencies of ozone at various levels, on the basis of large one-particle basis sets. It is demonstrated that f-type functions are required in order to obtain quantitative accuracy for the equilibrium structure and harmonic frequencies. The CCSD(T) level of theory, in conjunction with a (4s 3p 2d 1f) atomic natural orbital set, yields an equilibrium geometry and harmonic frequencies that are in excellent agreement with experimental results; an effort has accordingly been made to determine the cubic and quartic force constants, and evaluate the anharmonic corrections to the fundamental vibrational frequencies.

Lee, Timothy J.; Scuseria, Gustavo E.

1990-01-01

259

Multiband Infrared Frequency Selective Surfaces.  

National Technical Information Service (NTIS)

This paper describes the design and fabrication of multiband infrared frequency selective surfaces (FSSs) that consist of selfsimilar fractal cross dipole metallic elements patterned on flexible dielectric substrates. Two transmission stopbands centered a...

R. Drupp J. Bossard D. H. Werner T. S. Mayer Y. Ye

2003-01-01

260

Frequency coded sensors incorporating tapers  

NASA Technical Reports Server (NTRS)

A surface acoustic wave device includes a piezoelectric substrate on which is formed a transducer that generates acoustic waves on the surface of the substrate from electrical waves received by the transducer. The waves are carried along an acoustic track to either a second transducer or a reflector. The transducers or transducer and reflector are formed of subsections that are constructed to operate at mutually different frequencies. The subsections of at least one of the transducers or transducer and reflector are out of alignment with respect to one another relative to the transverse of the propagation direction. The out of aligned subsections provide not only a frequency component but also a time to the signal output signal. Frequency response characteristics are improved. An alternative embodiment provides that the transducers and/or reflectors are continuously tapered instead of having discrete frequency subsections.

Hines, Jacqueline H. (Inventor); Solie, Leland P. (Inventor)

2010-01-01

261

Stepped Frequency Imaging Radar Simulation.  

National Technical Information Service (NTIS)

In this thesis, a technique involving Stepped Frequency and Inverse Synthetic Aperture Radar (ISAR) processing have been employed to develop two- dimensional radar images of an aircraft target. Radar returns from prominent scatterers of various parts of t...

K. L. Mun

2000-01-01

262

Electron-Optical Frequency Multiplier.  

National Technical Information Service (NTIS)

Recent developments in electron optics in the area of optically modulated frequency multiplication are discussed. The multipliers discussed employ modulators built around gallium arsenide and gallium phosphide diodes and KDP and ADP dihydrophosphates crys...

A. G. Zharov N. V. Kravtsov L. E. Chirkov

1969-01-01

263

Dual-frequency microwave antenna  

NASA Technical Reports Server (NTRS)

Single antenna using two feed horns (one for receiving and radiation X-band signals, and one for S-band signals), in conjunction with ellipsoid reflector and dichronic plate, can accommodate two different frequencies simultaneously.

Bathker, D. A.; Brunstein, S. A.; Ludwig, A. C.; Potter, P. D.

1980-01-01

264

Economic Areawise Load Frequency Control.  

National Technical Information Service (NTIS)

The report describes a proposed solution for the generation control problem which unifies economic dispatch, load frequency control and statistical load forecasting. This solution retains the decentralized character of the Area Control Principle but updat...

J. Zaborszky T. Ying Chiang

1975-01-01

265

Frequency Correlation in Tropospheric Propagation.  

National Technical Information Service (NTIS)

The theoretical correlation of signals with varying frequency spacing for propagation through the troposphere is considered. It seems that certain conclusions on the signal propagation paths can be drawn from the correlation characteristics. The report th...

L. Jonasson

1971-01-01

266

Acoustic Propagation at Microwave Frequencies.  

National Technical Information Service (NTIS)

Techniques for the generation, propagation and detection of sound at microwave frequencies have been investigated. Transmission and reflection experiments with quartz crystals are discussed with the design of a microwave delay line as the final product. V...

W. F. Gavin J. R. Miller

1964-01-01

267

Chemically Polished High Frequency Resonators.  

National Technical Information Service (NTIS)

The upper frequency limit of quartz resonators is determined by the physical properties of quartz and restrictions imposed by processing techniques. More often than not, the processing limitations are reached long before the physical limitations. Mechanic...

W. P. Hanson

1983-01-01

268

Miniature Low Frequency Acoustic Transmitter.  

National Technical Information Service (NTIS)

A miniature lightweight transmitter that mechanically generates low- frequency acoustic energy is described, wherein one or more miniature balloons filled with air are positioned at the center of a pressure vessel filled with water and tethered in place. ...

A. A. Ruffa

2006-01-01

269

Booster Synchrotron Frequency Below Transition.  

National Technical Information Service (NTIS)

The dipole mode synchrotron frequency is a basic beam parameter; it and a few similarly basic quantities measured at small time intervals serve to characterize the longitudinal beam dynamics throughout the acceleration cycle. The effective accelerating vo...

X. Yang J. MacLachlan R. Padilla C. Ankenbrandt

2004-01-01

270

NMR and NQR fluctuation effects in layered superconductors  

Microsoft Academic Search

We study the effect of thermal fluctuations of the s-wave order parameter of a quasi-two-dimensional superconductor on the nuclear spin relaxation rate near the transition temperature TC. We consider both the effects of the amplitude fluctuations and the Berezinskii-Kosterlitz-Thouless (BKT) phase fluctuations in weakly coupled layered superconductors. In the treatment of the amplitude fluctuations we employ the Gaussian approximation and

D. Fay; J. Appel; C. Timm; A. Zabel

2001-01-01

271

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

272

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

273

Frequency converter energetic performances analysis  

Microsoft Academic Search

The issue of non-conventional energy sources now is correlated with energy efficiency and clean energy. An application researched by the authors is vibration stress relieving, which consist in vibration of stress reliving piece with electromagnetic or electro-dynamic vibrator to determine frequencies of resonance. Technology is energy efficient and involves a single-phase inverter with variable frequencies, which generate a load current

Horia Balan; Mircea Chindris; l. Vadan; Aurel Botezan; Victor Proca

2007-01-01

274

Frequency chirping in external modulators  

Microsoft Academic Search

A general formula is given that expresses frequency chirping in some types of external intensity modulators, such as the loss modulator, directional-coupler-type modulator, Mach-Zehnder interferometry-type modulator, and total-internal-reflection-type modulator. The chirping phenomenon treated is caused by the phase modulation due to an accompanied refractive index change. It is uniquely expressed in terms of an ?-parameter that contributes to frequency chirping

Fumio Koyama; KENICHI IGA

1988-01-01

275

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

276

Photoconductive frequency-resolved spectrometer  

Microsoft Academic Search

The study of recombination lifetimes and kinetics is an essential part of the analysis of recombination mechanisms in semiconductors. The fundamental differences between the experimental techniques, which are used for, frequency- resolved and for time-resolved spectroscopy are present in this paper. A photoconductive frequency-resolved spectrometer (PCFRS) for carrier lifetime determination in semiconductor is described. The PCFRS uses a super-bright light

Ioan Burda; Simion Simon; Gheorghe Cristea; Georgeta Cerbanic; Lavinia Cociu; Mihai Todica

2000-01-01

277

Digital Channelizing Radio Frequency Receiver  

Microsoft Academic Search

HYPRES is developing a class of digital receivers featuring direct digitization at radio frequency (RF). Such a receiver consists of a wideband analog-to-digital converter (ADC) modulator and multiple digital channelizer units to extract different frequency bands-of-interest within the broad digitized spectrum. The single-bit oversampled data, from either a lowpass delta or bandpass delta-sigma modulator, are applied to one or more

Deepnarayan Gupta; Timur V. Filippov; Alexander F. Kirichenko; Dmitri E. Kirichenko; Igor V. Vernik; Anubhav Sahu; Saad Sarwana; Pavel Shevchenko; Andrei Talalaevskii; Oleg A. Mukhanov

2007-01-01

278

Low-Frequency Radioastronomy Basics  

NASA Astrophysics Data System (ADS)

With the many large instruments in construction or in project, the present epoch corresponds to a renewal of low-frequency radioastronomy. The field will attract new researchers and students not expert of the radioastronomy techniques. With this audience in mind, we present here a very brief introduction to radioastronomy basics, including propagation and polarization of low-frequency radio waves as well as instrumental aspects. Basic formulas are given. The references and internet links will allow the interested reader to go further.

Zarka, P.

2011-04-01

279

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

280

Stepped frequency ground penetrating radar  

SciTech Connect

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 receiver 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. 12 figures.

Vadnais, K.G.; Bashforth, M.B.; Lewallen, T.S.; Nammath, S.R.

1994-06-28

281

ECRIS Operation With Multiple Frequencies  

SciTech Connect

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{yields}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. [Argonne National Laboratory, Argonne (United States); Koivisto, H.; Tarvainen, O.; Suominen, P. [Department of Physics, Accelerator laboratory, University of Jyvaeskylae, FIN-40351, Jyvaeskylae (Finland); Edgell, D.H. [Laboratory for Laser Energetics, University of Rochester, Rochester, NY 14623-1299 (United States)

2005-03-15

282

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

283

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

284

Frequency response of ice streams  

PubMed Central

Changes at the grounding line of ice streams have consequences for inland ice dynamics and hence sea level. Despite substantial evidence documenting upstream propagation of frontal change, the mechanisms by which these changes are transmitted inland are not well understood. In this vein, the frequency response of an idealized ice stream to periodic forcing in the downstream strain rate is examined for basally and laterally resisted ice streams using a one-dimensional, linearized membrane stress approximation. This reveals two distinct behavioural branches, which we find to correspond to different mechanisms of upstream velocity and thickness propagation, depending on the forcing frequency. At low frequencies (centennial to millennial periods), slope and thickness covary hundreds of kilometres inland, and the shallow-ice approximation is sufficient to explain upstream propagation, which occurs through changes in grounding-line flow and geometry. At high frequencies (decadal to sub-decadal periods), penetration distances are tens of kilometres; while velocity adjusts rapidly to such forcing, thickness varies little and upstream propagation occurs through the direct transmission of membrane stresses. Propagation properties vary significantly between 29 Antarctic ice streams considered. A square-wave function in frontal stress is explored by summing frequency solutions, simulating some aspects of the dynamical response to sudden ice-shelf change.

Williams, C. Rosie; Hindmarsh, Richard C. A.; Arthern, Robert J.

2012-01-01

285

Skewed Frequency Selective Surface Absorber  

NASA Astrophysics Data System (ADS)

In this paper, a skewed Frequency Selective Surface (FSS) absorber based on cross-dipole elements is presented. The proposed FSS design provides good frequency stability for oblique incidences. It provides better absorption rate for 5-GHz WLAN frequency band and allow other communication bands to pass through it. Also, the absorption in the stop-band reduces multipath fading of additional WLAN signals which occurred due to the placement of conducting/reflecting FSS. The FSS design consists of two layers; first layer consists of conducting cross-dipole and second layer consists of resistive cross-dipole placed in-front of the first layer. The periodicity of both elements is same. Asymmetric property is applied to FSS elements by taking a reference of central element. This technique leads to achieve a maximum stability in the stop-band. Simulated results demonstrated that the proposed FSS design has a stable frequency response for 5-GHz frequency band for both horizontal (TE) and vertical (TM) polarizations when the incident wave angle varied from 0 0 to 45 0.

Rafique, Umair; Khan, M. Arif; Afzal, M. Tausif; Malik, Fahad; Qasim, Shahzaib

2012-12-01

286

Optimal filtering in multipulse sequences for nuclear quadrupole resonance detection  

NASA Astrophysics Data System (ADS)

The application of the multipulse sequences in nuclear quadrupole resonance (NQR) detection of explosive and narcotic substances has been studied. Various approaches to increase the signal to noise ratio (SNR) of signal detection are considered. We discussed two modifications of the phase-alternated multiple-pulse sequence (PAMS): the 180° pulse sequence with a preparatory pulse and the 90° pulse sequence. The advantages of optimal filtering to detect NQR in the case of the coherent steady-state precession have been analyzed. It has been shown that this technique is effective in filtering high-frequency and low-frequency noise and increasing the reliability of NQR detection. Our analysis also shows the PAMS with 180° pulses is more effective than PSL sequence from point of view of the application of optimal filtering procedure to the steady-state NQR signal.

Osokin, D. Ya.; Khusnutdinov, R. R.; Mozzhukhin, G. V.; Rameev, B. Z.

2014-05-01

287

Ultra stable frequency distribution system  

NASA Technical Reports Server (NTRS)

A system is presented for synchronizing a signal at a remotely located slave station with the phase and frequency of a signal generated at a master station. The signal transmitted at the master station and received by the slave station provides compensation for the phase shift caused by the transmission path delays between the master and slave station. The slave station transmits a signal to the master station at a frequency that is different from the frequency of the signal being transmitted by the master station. The signal transmitted by the slave station is received by the master station while the master station transmitter is off. The signal transmitted by the master station is received by the slave station while the slave station transmitter is off.

Sydnor, R. L.; Macconnell, J. W. (inventors)

1977-01-01

288

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

289

Low-frequency electrical properties.  

USGS Publications Warehouse

In the interpretation of induced polarization data, it is commonly assumed that metallic mineral polarization dominantly or solely causes the observed response. However, at low frequencies, there is a variety of active chemical processes which involve the movement or transfer of electrical charge. Measurements of electrical properties at low frequencies (such as induced polarization) observe such movement of charge and thus monitor many geochemical processes at a distance. Examples in which this has been done include oxidation-reduction of metallic minerals such as sulfides, cation exchange on clays, and a variety of clay-organic reactions relevant to problems in toxic waste disposal and petroleum exploration. By using both the frequency dependence and nonlinear character of the complex resistivity spectrum, these reactions may be distinguished from each other and from barren or reactionless materials.-Author

Olhoeft, G. R.

1985-01-01

290

Variable frequency microwave heating apparatus  

SciTech Connect

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, D.W.; Lauf, R.J.; Johnson, A.C.; Thigpen, L.T.

1999-10-05

291

Frequency Synthesizer For Tracking Filter  

NASA Technical Reports Server (NTRS)

Digital frequency-synthesizing subsystem generates trains of pulses, free of jitter, for use as frequency-control signals in tracking filters. Part of assembly of electronic equipment used to measure vibrations in bearings in rotating machinery. Designed to meet requirements for tracking narrow-band cage-rotation and ball-pass components of vibrations, as discussed in "Frequency-Tracking Error Detector" (MFS-29538) and "Ball-Pass Cage-Modulation Detector" (MFS-29539). Synthesizer includes preset counter, output of which controls signal for ball-pass filter. Input to this preset counter updated every 2 microseconds: responds almost immediately, effectively eliminating relatively long response time (lock-in time) and phase jitter.

Randall, Richard L.

1990-01-01

292

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

293

47 CFR 87.305 - Frequency coordination.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Frequency coordination. 87.305 Section... Flight Test Stations § 87.305 Frequency coordination. (a)(1) Each...existing license concerning flight test frequencies, except as provided in...

2013-10-01

294

47 CFR 87.303 - Frequencies.  

Code of Federal Regulations, 2013 CFR

... 2013-10-01 2013-10-01 false Frequencies. 87.303 Section 87.303 Telecommunication...SERVICES Flight Test Stations § 87.303 Frequencies. (a) These frequencies are available for assignment to flight...

2013-10-01

295

47 CFR 87.41 - Frequencies.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Frequencies. 87.41 Section 87.41...Applications and Licenses § 87.41 Frequencies. (a) Applicant responsibilities. The applicant must propose frequencies to be used by the station...

2013-10-01

296

47 CFR 101.107 - Frequency tolerance.  

Code of Federal Regulations, 2013 CFR

... 2013-10-01 2013-10-01 false Frequency tolerance. 101.107 Section 101.107...SERVICES Technical Standards § 101.107 Frequency tolerance. (a) The carrier frequency of each transmitter authorized in...

2013-10-01

297

Time and Frequency: Theory and Fundamentals.  

National Technical Information Service (NTIS)

The document is a tutorial Monograph describing various aspects of time and frequency (T/F). Included are chapters relating to elemental concepts of precise time and frequency; basic principles of quartz oscillators and atomic frequency standards; histori...

B. E. Blair

1974-01-01

298

33 CFR 401.61 - Assigned frequencies.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 false Assigned frequencies. 401.61 Section...AND RULES Regulations Radio Communications § 401.61 Assigned frequencies. The Seaway stations...following assigned VHF frequencies: 156.8...

2013-07-01

299

47 CFR 95.655 - Frequency capability.  

Code of Federal Regulations, 2013 CFR

...for use in another radio service for which the frequency is authorized and...Transmitters with frequency capability for the Amateur Radio Services and Military Affiliate Radio System will not... (b) All frequency...

2013-10-01

300

47 CFR 27.5 - Frequencies.  

Code of Federal Regulations, 2013 CFR

...MHz (2) Post transition frequency assignments. The frequencies available in the Broadband...section in accordance with the frequency allocations table of § 2.106 of this chapter. (i) Lower Band Segment (LBS): The...

2013-10-01

301

47 CFR 87.133 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...section, the carrier frequency of each station must...these tolerances: Frequency band (lower limit exclusive, upper...within the authorized frequency band and must not be...MHz to the upper and lower limits of the...

2013-10-01

302

47 CFR 74.503 - Frequency selection.  

Code of Federal Regulations, 2013 CFR

...Broadcast Auxiliary Stations § 74.503 Frequency selection. (a) Each application for...existing station shall be specific with regard to frequency. In general, the lowest suitable frequency will be assigned which, on an...

2013-10-01

303

47 CFR 74.802 - Frequency assignment.  

Code of Federal Regulations, 2013 CFR

... (1) Any low power auxiliary...that operates at frequencies in the 700... (2) Any low power auxiliary...that operates at frequencies in the 700...on specified frequencies in the market in which the low power...

2013-10-01

304

47 CFR 87.351 - Frequency changes.  

Code of Federal Regulations, 2010 CFR

...Telecommunication 5 2010-10-01 2010-10-01 false Frequency changes. 87.351...CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AVIATION SERVICES Aeronautical...351 Frequency changes. When the...frequency within 10 days from...

2010-10-01

305

Estimating high frequency ocean bottom pressure variability  

Microsoft Academic Search

Current ocean model estimates of high frequency OBP have significant errorsNeed to improve high frequency OBP estimates to minimise satellite aliasingNeed to improve knowledge of high frequency OBP errors

Katherine J. Quinn; Rui M. Ponte

2011-01-01

306

Frequency-coded monopulse MTI  

NASA Astrophysics Data System (ADS)

A pulse-compression, MTI, doppler-radar system for determining target velocity information from a single, frequency-coded uncompressed target-return pulse includes a coded modulator, two pulse compressors, and a phase-comparison processor. The coded modulator generates for transmission an uncompressed pulse with the first and second halves of the pulse coded with the even and odd harmonic sidebands of a pulse repetition frequency, respectively. The first and second halves of the pulse returning from the target are pulse compressed simultaneously by the two pulse compressors. The phase comparison processor then determines the phase difference between the compressed pulses to obtain the target velocity information.

Lewis, Bernard L.; Cantrell, Ben H.

1994-09-01

307

DSS 13 frequency stability tests  

NASA Technical Reports Server (NTRS)

In a previous article, the results of frequency stability tests at DSS 13 were presented in table form for tau = 1000 s for the test period May 1985 through March 1986. This article is a continuation of that initial report and presents specially selected Allan sigma (square root of variance) plots of each of the subsystem test previously reported. An additional result obtained from tests performed during July 1986 was included for completeness. The Allan sigma plots are useful in that frequency stability information is not only given for tau = 1000 s, but for tau values in the regions of 1, 100, 500, and 2000 s as well.

Otoshi, T. Y.; Franco, M. M.

1987-01-01

308

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

309

The vibrational frequencies of difluoroethyne  

NASA Technical Reports Server (NTRS)

Ab initio coupled-cluster calculations with single and double excitations and with a perturbational treatment of connected triple excitations are reported for difluoroethyne using large basis sets. The results for the transbending mode nu-4 are extremely sensitive to electron correlation and basis set effects. The best theoretical and experimental estimates for the fundamental vibrational frequencies are in excellent agreement.

Breidung, Juergen; Schneider, Winfried; Thiel, Walter; Lee, Timothy J.

1992-01-01

310

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

311

High Frequency (HF) Radiowave Propagation.  

National Technical Information Service (NTIS)

This report serves to introduce the basics of high frequency radiowave propagation in the earth's ionosphere. It is intended for people who are not fully acquainted with the physics of the problem but have had some experience working with or will have to ...

G. S. Sales

1992-01-01

312

Frequency based oscilloscope triggering scheme  

Microsoft Academic Search

This paper presents a novel frequency based oscilloscope triggering technique for measurements involving complex waveforms that are challenging even today. Proposed technique is capable of providing stable triggering even in the case of complex periodic waveforms category where commonly used level triggering scheme fail to perform adequately and may be used in problem of estimating many typical signal processing situations,

S. A. Khan; A. Nigam; A. K. Agarwala; M. S. Thomas

2010-01-01

313

Frequency Effects, Noticing, and Creativity  

ERIC Educational Resources Information Center

Ellis's target article suggests that language processing is based on frequency and probabilistic knowledge and that language learning is implicit. These findings are consistent with those of SLA researchers working within a variationist framework (e.g., Tarone, 1985; Bayley & Preston, 1996). This paper provides a brief overview of this research…

Tarone, Elaine

2002-01-01

314

OPTIMUM FREQUENCY OF CALIBRATION MONITORING  

EPA Science Inventory

The paper develops an algorithm by which to compute the optimal frequency of calibration monitoring to minimize the total cost of analyzing a set of samples and the required calibration standards. Optimum calibration monitoring is needed because of the high cost and calibration d...

315

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.

316

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.

Gardner, Timothy J.; Magnasco, Marcelo O.

2006-01-01

317

Medium frequency propagation: A survey  

Microsoft Academic Search

At medium frequencies, ground waves and sky waves are both of equal importance. Ground waves provide stable signals during the day, when sky waves are weak. At night sky waves propagate to considerable distances with very little attenuation but are more variable. Published ground-wave propagation curves apply to land which is smooth and of uniform conductivity, but this condition is

P. Knight

1983-01-01

318

Frequency stabilization in semiconductor lasers  

Microsoft Academic Search

Three promising methods of improving temporal coherence in semiconductor lasers are reviewed. They are the development of novel laser devices, a technique of optical feedback and a technique of electrical feedback. The main discussion in this paper is focused on the technique of electrical feedback. The theoretical limit of frequency stability and recent experimental results are presented with respect to

Motoichi Ohtsu

1988-01-01

319

Primary Frequency Standards at NIST.  

National Technical Information Service (NTIS)

NIST has a more than 50-year history of developing ever more accurate atomic frequency standards. For most of that time, the technology was based on thermal atomic beams of cesium atoms, and the accuracy improvement was approximately a factor of 10 every ...

R. Drullinger

2001-01-01

320

Frequency analysis of digital holography  

Microsoft Academic Search

A coherent optical imaging system consisting of recording a digital hologram by a CCD array and numerical reconstruction of the complex wave field in a computer is subjected to a frequency analysis. This analysis recognizes Fresnel and lensless Fourier transform holography; collimated and divergent reference waves; as well as the real image, the virtual image, and the dc term. The

Thomas M. Kreis

2002-01-01

321

Frequency-Domain Optical Mammograph.  

National Technical Information Service (NTIS)

This research project involves the analysis of a clinical data set of frequency-domain optical mammograms ((caret)150 patients) to assess the performance of this approach to breast cancer detection. The analysis of the breast images is complemented by the...

S. Fantini

2000-01-01

322

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

323

Frequency space environment map rendering  

Microsoft Academic Search

We present a new method for real-time rendering of objects with complex isotropic BRDFs under distant natural illumination, as specified by an environment map. Our approach is based on spherical frequency space analysis and includes three main contributions. Firstly, we are able to theoretically analyze required sampling rates and resolutions, which have traditionally been determined in an ad-hoc manner. We

Ravi Ramamoorthi; Pat Hanrahan

2002-01-01

324

Low Frequency Nonresonant Acoustic Projector.  

National Technical Information Service (NTIS)

A nonresonant acoustic projector especially suited to the creation of low frequency (0-100 Hz, approximately) acoustic signals is provided, this projector including a housing and a rocker arm which is mounted within the housing on a pivotal transverse axi...

H. A. Wilcox

1981-01-01

325

A globally convergent frequency estimator  

Microsoft Academic Search

Online estimation of the frequency of a sinusoidal signal is a classical problem in systems theory that has many practical applications. In this paper the authors provide a solution to the problem of ensuring a globally convergent estimation. More specifically, they propose a new adaptive notch filter whose dynamic equations exhibit the following remarkable features: 1) all signals are globally

Liu Hsu; Romeo Ortega; G. Damm

1999-01-01

326

Modeling of EEG Signal Sound Frequency Characteristic Using Time Frequency Analysis  

Microsoft Academic Search

This paper presents the study of sound frequency characteristic based on Electroencephalography (EEG) signals. The study includes feature extraction of the EEG signals with respect to different sound frequencies, covering low frequency (40 Hz), mid-range frequency (5000 Hz), and high frequency (15000 Hz). Human brain activities are expected to be different when exposed to different sound frequencies, and can be

R. Sudirman; A. K. Chee; W. B. Daud

2010-01-01

327

Radio-Frequency Plasma Probes  

NASA Astrophysics Data System (ADS)

The utility of radio-frequency probes for diagnosing low-temperature plasmas has recently been extended through the use of a network analyzer to measure the small-signal, complex probe impedance Zac as a function of applied frequency and dc bias. To interpret the results, account must be taken of the gas pressure, the plasma density, the applied frequency, and the applied magnetic field if any. In this talk four different models are presented for use in different regimes. At high gas pressure, Re(Zac) is shown to give ne0/?, where ne0 is the ambient electron density and ? is the electron-neutral collision frequency. At low pressure Re(Zac) gives not only ne0 but also ne(r) within the sheath immediately outside the probe, the plasma potential, and the electron energy distribution and temperature. Magnetized plasmas can be treated by adding an external inductance in series with the probe and operating above the upper hybrid frequency; alternatively, rf voltage can be applied between two closely-spaced planar electrodes oriented either parallel or perpendicular to the field. As will be shown, rf probes not only provide more information than Langmuir probes, but the data is easier to analyze and generally less affected by noise. Additional advantages include the following: decreased sensitivity to secondary electron emission, ions, plasma flow, and high-energy beams; clear and unequivocal determination of ne0, even in magnetized plasmas; direct utility at high pressure; multiple checks on the results; and the ability to operate in reactive and depositing gases.

Fernsler, Richard

2011-11-01

328

Fine Frequency Measurement by Coincidence Detection.  

National Technical Information Service (NTIS)

A method of measuring a desired frequency by comparing it with a standard frequency is reported. The zero crossings of both frequencies are detected. A command pulse is generated at each coincidence and is used to start and stop a pair of frequency counte...

E. Nossen E. R. Starner

1974-01-01

329

Measuring fundamental frequencies in local field potentials  

Microsoft Academic Search

Neural processes display rhythmic oscillations in local field potentials; identification of their characteristic frequencies is complicated due to their highly non-stationary nature. A simple technique, combining Fourier transforms and correlation coefficients yields unambiguous determinations of the frequencies without a priori filtering. This procedure also provides quantitative information concerning interactions between frequencies. Fundamental frequencies in local field potential data acquired from

B. Masimore; J. Kakalios; A. D. Redish

2004-01-01

330

47 CFR 78.18 - Frequency assignments.  

Code of Federal Regulations, 2013 CFR

...shall be 1.25 MHz above the lower channel-edge frequency. The center frequency...transmission, the assigned carrier frequency for each channel listed...shall be 6.25 MHz above the lower boundary frequency for each channel, and...

2013-10-01

331

Designing A Beam Waveguide For Multiple Frequencies  

NASA Technical Reports Server (NTRS)

Paper addresses defocusing and diffraction effects important in design of beam waveguide. Phase center of beam waveguide at lower frequency differs from focal point of geometric optics. If antenna system optimized for higher frequency, shift in phase center causes defocusing, with loss of signal at lower frequency. Defocusing caused by diffraction at lower frequencies reduced by shaping input pattern.

Galindo, Victor; Imbriale, William A.; Rengarajan, Sembiam R.

1992-01-01

332

The dual-frequency scatterometer reexamined  

NASA Technical Reports Server (NTRS)

The utility of dual frequency scatterometers in measuring ocean wave directional spectra can be increased by adding third frequency to the system. The background which effectively limits signal detectability in dual frequency operation can be made a part of the signal through the addition of this third frequency. Signal detectability is limited only by system thermal noise and space based operation becomes more feasible.

Plant, W. J.; Reeves, A. B.

1984-01-01

333

TIME AND FREQUENCY ACTIVITIES AT IEN  

Microsoft Academic Search

The Time and Frequency Department of the Istituto Elettrotecnico Nazionale ((EN), as national laboratory for time and frequency metrology in Italy, is charged of the realization and dissemination of the national time and frequency standards and the development of new frequency standards and synchronization techniques. The present status of these activities and their future developments are reported in the paper.

F. Cordara; G. Brida; A. Godone; F. Levi; L. Lorini; M. Mascarello; S. Micalizio; V. Pettiti; P. Tavella; G. Vizio

334

Frequency of dipeptides and antidipeptides  

PubMed Central

Although it is reasonable to expect that the frequency of a generic dipeptide XY in proteins is the same of its counterpart YX, on the basis of an accurate statistical analysis of a large number of protein sequences, it appears that some dipeptides XY are considerably more frequent than their mirror images YX, referred to as antidipeptides. Given that it has been verified that this unexpected anisotropic frequency of occurrence is unbiased by the type of protein sequences that are analyzed, it is possible to conclude that this is a genuine phenomenon. Nevertheless, it was impossible to find the mechanism underlying this unexpected phenomenon, which does not seem to be related to diverse conformational propensities, to the different conformational flexibility of the peptide/antidipeptide pair, to dissimilar accessibility to the solvent or to gene random mutations.

Carugo, Oliviero

2013-01-01

335

High frequency power distribution system  

NASA Technical Reports Server (NTRS)

The objective of this project was to provide the technology of high frequency, high power transmission lines to the 100 kW power range at 20 kHz frequency. In addition to the necessary design studies, a 150 m long, 600 V, 60 A transmission line was built, tested and delivered for full vacuum tests. The configuration analysis on five alternative configurations resulted in the final selection of the three parallel Litz straps configuration, which gave a virtually concentric design in the electromagnetic sense. Low inductance, low EMI and flexibility in handling are the key features of this configuration. The final design was made after a parametric study to minimize the losses, weight and inductance. The construction of the cable was completed with no major difficulties. The R,L,C parameters measured on the cable agreed well with the calculated values. The corona tests on insulation samples showed a safety factor of 3.

Patel, Mikund R.

1986-01-01

336

Monochromatic radio frequency accelerating cavity  

DOEpatents

A radio frequency resonant cavity having a fundamental resonant frequency and characterized by being free of spurious modes. A plurality of spaced electrically conductive bars are arranged in a generally cylindrical array within the cavity to define a chamber between the bars and an outer solid cylindrically shaped wall of the cavity. A first and second plurality of mode perturbing rods are mounted in two groups at determined random locations to extend radially and axially into the cavity thereby to perturb spurious modes and cause their fields to extend through passageways between the bars and into the chamber. At least one body of lossy material is disposed within the chamber to damp all spurious modes that do extend into the chamber thereby enabling the cavity to operate free of undesired spurious modes.

Giordano, S.

1984-02-09

337

Monochromatic radio frequency accelerating cavity  

DOEpatents

A radio frequency resonant cavity having a fundamental resonant frequency and characterized by being free of spurious modes. A plurality of spaced electrically conductive bars are arranged in a generally cylindrical array within the cavity to define a chamber between the bars and an outer solid cylindrically shaped wall of the cavity. A first and second plurality of mode perturbing rods are mounted in two groups at determined random locations to extend radially and axially into the cavity thereby to perturb spurious modes and cause their fields to extend through passageways between the bars and into the chamber. At least one body of lossy material is disposed within the chamber to damp all spurious modes that do extend into the chamber thereby enabling the cavity to operate free of undesired spurious modes.

Giordano, Salvatore (Port Jefferson, NY)

1985-01-01

338

FAST low frequency pulsar survey  

NASA Astrophysics Data System (ADS)

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is under construction and will be commissioned in September 2016. A low frequency 7-beam receiver working around 400 MHz is proposed for FAST early science. It will be optimized for a whole FAST sky drift-scan pulsar survey. Simulations show that about 1500 new normal pulsars will be discovered, as while as about 200 millisecond pulsars.

Yue, Youling; Li, Di; Nan, Rendong

2013-03-01

339

High-Frequency EPR Instrumentation  

Microsoft Academic Search

An overview of the most recent developments in high-frequency high-field electron paramagnetic resonance (EPR) instrumentation\\u000a is given. In particular, the practical choices concerning sources, detectors, resonators, propagation systems as well as magnet\\u000a technology are discussed in the light of various possible applications. Examples of particular homodyne and heterodyne quasi-optic\\u000a EPR systems illustrate the potential for future developments in EPR technology.

Edward J. Reijerse

2010-01-01

340

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

341

Magnetic Nanocomposites at Microwave Frequencies  

Microsoft Academic Search

\\u000a Most conventional magnetic materials used in the electronic devices are ferrites, which are composed of micrometer-size grains.\\u000a But ferrites have small saturation magnetization, therefore the performance at GHz frequencies is rather poor. That is why\\u000a functionalized nanocomposites comprising magnetic nanoparticles (e.g. composed of Fe, Co) with dimensions ranging from a few\\u000a nm to 100 nm, and embedded in dielectric matrices (e.g.

Jaakko V. I. Timonen; Robin H. A. Ras; Olli Ikkala; Markku Oksanen; Eira Seppälä; Khattiya Chalapat; Jian Li; Gheorghe Sorin Poraoanu

2011-01-01

342

Dynamic optical frequency domain reflectometry.  

PubMed

We describe a dynamic Optical Frequency Domain Reflectometry (OFDR) system which enables real time, long range, acoustic sensing at high sampling rate. The system is based on a fast scanning laser and coherent detection scheme. Distributed sensing is obtained by probing the Rayleigh backscattered light. The system was tested by interrogation of a 10km communication type single mode fiber and successfully detected localized impulse and sinusoidal excitations. PMID:24787772

Arbel, Dror; Eyal, Avishay

2014-04-21

343

Frequency stabilization of gas lasers  

Microsoft Academic Search

Methods of frequency and wavelength stabilization of gas lasers are reviewed with emphasis on principles of operation and results of stability measurements rather than experimental details or apparatus design. Most of the stabilization work has been done with the He-Ne laser. The best long-term stability is about 1 part in 109. Various wavelength measurements of stabilized He-Ne lasers by interferometric

GEORGE BIRNBAUM

1967-01-01

344

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

345

Frequency Conversion with Semiconductor Heterostructures  

Microsoft Academic Search

\\u000a In this lecture different aspects of frequency conversion in semiconductor heterostructures are reviewed. Thanks to the very\\u000a high degree of control of growth and technology of thin layers of semiconductors, both electronic wavefunction and optical\\u000a mode properties can be tailored, through band gap engineering and refractive index engineering. These two aspects lead to\\u000a the possibility of optimization of nonlinear susceptibilities

V. Berger

346

Automatic frequency control for FM transmitter  

NASA Technical Reports Server (NTRS)

An automatic frequency control circuit for an FM television transmitter is described. The frequency of the transmitter is sampled during what is termed the back porch portion of the horizontal synchronizing pulse which occurs during the retrace interval, the frequency sample compared with the frequency of a reference oscillator, and a correction applied to the frequency of the transmitter during this portion of the retrace interval.

Honnell, M. A. (inventor)

1974-01-01

347

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

348

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

349

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

350

A tunable dual frequency dye laser - dual frequency oscillator design  

NASA Technical Reports Server (NTRS)

The pulsed dye laser offers a tunable oscillator, followed by three amplifiers. It is pumped by a dual frequency Nd:YAG laser. Tuning and spectral width are controlled by a holographic network connected to a high power telescope. The modified two wavelength dye laser allows for absorption lidar techniques for remote sensing of the atmosphere. Line switching is achieved by electrooptical commutation. A feasibility experiment was performed with the original oscillator. A model was then built, and tested with different dyes. After a few modifications were made to improve the conversion efficiency, this oscillator was inserted in the laser to check whether the amplifier stages were correctly adjusted.

Abury, Y.

1983-01-01

351

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 <~f<~ 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

352

Extending the frequency matching in linear FMCW radar exploiting extreme frequencies  

Microsoft Academic Search

Frequency matching is an essential block of the signal processing chain in LFMCW (linear frequency modulated continuous wave) radar. Its task is to associate frequency detections obtained in multiple measurements. Under certain conditions, this association may fail and frequency detections from multiple real targets may be combined to a mismatch. The classification of a frequency association as match (real target)

Marcus Reiher; Bin Yang

2009-01-01

353

Spectral line shape analysis and systematic frequency shifts of laser frequency standards  

Microsoft Academic Search

A practical realization of the unit of length often relies on values of the frequency of optical frequency standards in the form of frequency stabilized lasers. A technique of frequency stabilization commonly used for He-Ne lasers at 633 nm stabilized in frequency to hyperfine spectral components in the saturated absorption spectrum of molecular iodine is that based on phase-sensitive detection

Leslie R. Pendrill; Ulf Karn

1993-01-01

354

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

355

Robust laser frequency stabilization by serrodyne modulation.  

PubMed

We report the relative frequency stabilization of a distributed feedback erbium-doped fiber laser on an optical cavity by serrodyne frequency shifting. A correction bandwidth of 2.3 MHz and a dynamic range of 220 MHz are achieved, which leads to a strong robustness against large disturbances up to high frequencies. We demonstrate that serrodyne frequency shifting reaches a higher correction bandwidth and lower relative frequency noise level compared to a standard acousto-optical modulator based scheme. Our results allow us to consider promising applications in the absolute frequency stabilization of lasers on optical cavities. PMID:22446205

Kohlhaas, Ralf; Vanderbruggen, Thomas; Bernon, Simon; Bertoldi, Andrea; Landragin, Arnaud; Bouyer, Philippe

2012-03-15

356

Perceptual frames in frequency estimation.  

PubMed

This study is an introductory investigation of cognitive frames, focused on perceptual frames divided into information and formal perceptual frames, which were studied based on sub-additivity of frequency estimations. It was postulated that different presentations of a response scale would result in different percentage estimates of time spent watching TV or using the Internet. The results supported the existence of perceptual frames that influence the perception process and indicated that information perceptual frames had a stronger effect than formal frames. The measures made possible the exploration of the operation of perceptual frames and also outlined the relations between heuristics and cognitive frames. PMID:24765715

Zy?owska, Aleksandra; Kossek, Marcin; Wawrzyniak, Ma?gorzata

2014-02-01

357

Radio-Frequency Strain Monitor  

NASA Technical Reports Server (NTRS)

Radio-frequency (RF) strain monitor developed to measure lengths of objects. RF waveguide or cable bonded to structure monitored. Propagation of RF signal along waveguide results in phase shift proportional to length of path traveled. Impedance mismatches placed in RF cable at nodes of structure. Records mismatches and detects overall length of line and lengths of intervals between nodes. Used to detect changes in elements of large structure with single cable. Monitor has potential for many applications, including monitoring stability of such large structures as aircraft, bridges, and buildings in Earthquake zones.

Heyman, Joseph S.; Rogowski, Robert S.; Holben, Milford S., Jr.

1988-01-01

358

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

359

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

360

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) [Scotia, NY

1986-01-01

361

Luminescent radio frequency radiation dosimetry.  

PubMed

Thermoluminescent dosimetry has been the industry standard for ionizing radiation dosimetry because it is inexpensive, sensitive, and accurate. No such system exists for radio frequency radiation. This paper describes the state of the art of efforts toward developing such a system. Thermochemiluminescent (TCL) dosimetry, first reported in 1991, is a first step toward achieving this goal. However, it has had problems in the production of TCL materials and in conversion of the luminescent signal into specific absorption rate (SAR). The former problem has been solved by the development of a genetically engineered Escherichia coli bacterium (JM 109/plC20RNR1.1), described herein, that produces the TCL material in a fermentation process. The latter problem stems from the difficulty in determining the structure of the currently best TCL material diazoluminomelanin. A theoretical approach for the solution of this problem has been achieved by combining equations for delayed fluorescence, temperature determination by TCL, and the free energy equation for equilibrium reactions. It has led to an explanation for the stable display of steady-state energy disposition, illustrated by TCL, in phantoms without the expected disruption by thermal conduction or convection, at frequencies ranging from 2.06 GHz to 35 GHz. PMID:10334714

Kiel, J L; Alls, J L; Mason, P A; Erwin, D N

1999-01-01

362

47 CFR 5.303 - Frequencies.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Frequencies. 5.303 Section 5.303 Telecommunication...COMMISSION GENERAL EXPERIMENTAL RADIO SERVICE Program Experimental Radio Licenses § 5.303 Frequencies. Licensees may operate in any...

2013-10-01

363

47 CFR 5.101 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...COMMISSION GENERAL EXPERIMENTAL RADIO SERVICE Technical Standards...Requirements § 5.101 Frequency stability. Experimental Radio Service licensees shall ensure...remain within the authorized frequency band under normal...

2013-10-01

364

Multi-Band Frequency Selective Surfaces: Analysis.  

National Technical Information Service (NTIS)

Present trends in antenna development go toward the integration on the same antenna aperture of more functions operating in separate frequency bands. In view of this, the necessity to look at new Frequency Selective Surface (FSS) concepts becomes evident....

A. Francavilla A. Neto D. Beckers G. Gerini S. Monni

2008-01-01

365

Performance Analysis of a Frequency Hopping Modem.  

National Technical Information Service (NTIS)

The report summarizes an analysis of a wide band modem in the presence of Gaussian noise or CW interference. The modem incorporates time division as the multiple access technique, multiple frequency keying as the modulation technique, frequency hopping as...

A. L. Covitt

1972-01-01

366

47 CFR 74.762 - Frequency measurements.  

Code of Federal Regulations, 2013 CFR

...DISTRIBUTIONAL SERVICES Low Power TV, TV Translator...Booster Stations § 74.762 Frequency measurements. (a) The licensee of a low power TV station, a TV translator...station must measure the carrier frequencies of its output channel...

2013-10-01

367

47 CFR 74.602 - Frequency assignment.  

Code of Federal Regulations, 2013 CFR

...Service (Part 101) may be assigned frequencies available to television broadcast...TV auxiliary stations licensed to low power TV stations and translator...having primary use of TV auxiliary frequencies. (g) The following...

2013-10-01

368

Velocity Compensation in Stepped Frequency Radar.  

National Technical Information Service (NTIS)

As compared to the commonly used constant frequency radar waveforms, the stepped-frequency waveform can achieve high range resolution while still retaining the advantages of lower instantaneous receiver bandwidth and lower analog-to-digital sampling rate....

Y. B. Ma

1995-01-01

369

47 CFR 90.539 - Frequency stability.  

Code of Federal Regulations, 2010 CFR

...stability requirements in this section. (a) Mobile, portable and control transmitters must normally use automatic frequency control (AFC) to lock on to the base station signal. (b) The frequency stability of base transmitters operating...

2010-10-01

370

Laser frequency modulation with electron plasma  

NASA Technical Reports Server (NTRS)

When laser beam passes through electron plasma its frequency shifts by amount proportional to plasma density. This density varies with modulating signal resulting in corresponding modulation of laser beam frequency. Necessary apparatus is relatively inexpensive since crystals are not required.

Burgess, T. J.; Latorre, V. R.

1972-01-01

371

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

372

High Frequency Solid-State Power Rectification.  

National Technical Information Service (NTIS)

This report covers the progress made on high frequency power rectification from September 1966 to September 1967. The requirements for a high frequency rectifying diode are reviewed. The germanium-gallium arsenide p-n heterojunction diode is presented and...

K. E. Mortenson P. E. Bakeman W. C. Taft

1967-01-01

373

Fifty Years of Atomic Frequency Standards  

Microsoft Academic Search

This brief review of the history of atomic frequency standards includes: atomic beam magnetic resonance, microwave absorption and optical pumping, atomic masers, lasers, laser cooling and laser cooled atoms and ions at optical frequencies.

Norman F. Ramsey

2002-01-01

374

47 CFR 101.107 - Frequency tolerance.  

Code of Federal Regulations, 2010 CFR

...from the frequency tolerance requirement noted...restrictive frequency tolerance (up to .01 percent...must provide all calculations and indicate the desired tolerance over each path...assigned channel at a level greater than...

2010-10-01

375

47 CFR 101.107 - Frequency tolerance.  

Code of Federal Regulations, 2010 CFR

...from the frequency tolerance requirement noted...restrictive frequency tolerance (up to .01 percent...must provide all calculations and indicate the desired tolerance over each path...assigned channel at a level greater than...

2009-10-01

376

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

377

47 CFR 18.301 - Operating frequencies.  

Code of Federal Regulations, 2013 CFR

...frequencies. 18.301 Section 18.301 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL INDUSTRIAL, SCIENTIFIC, AND MEDICAL EQUIPMENT Technical Standards § 18.301 Operating frequencies. ISM equipment may be operated...

2013-10-01

378

Quantum Theory of Parametric Frequency Conversion.  

National Technical Information Service (NTIS)

The frequency conversion of electromagnetic fields is treated quantum mechanically through an analysis of a simple theoretical model. Two modes of the field are considered to be coupled by a parameter which oscillates at the difference frequency. The fiel...

J. Tucker D. F. Walls

1968-01-01

379

Reduction of frequency noise and frequency shift by phase shifting elements in frequency modulation atomic force microscopy  

SciTech Connect

We recently reported the analysis of the frequency noise in the frequency modulation atomic force microscopy (FM-AFM) both in high-Q and low-Q environments [Rev. Sci. Instrum. 80, 043708 (2009)]. We showed in the paper that the oscillator noise, the frequency fluctuation of the oscillator, becomes prominent in the modulation frequency lower than f{sub 0}/2Q, where f{sub 0} and Q are the resonance frequency and Q-factor. The magnitude of the oscillator noise is determined by the slope of the phase versus frequency curve of the cantilever at f{sub 0}. However, in actual FM-AFM in liquids, the phase versus frequency curve may not be always ideal because of the existence of various phase shifting elements (PSEs). For example, the spurious resonance peaks caused by the acoustic excitation and a band-pass filter in the self-oscillation loop increase the slope of the phase versus frequency curve. Due to those PSEs, the effective Q-factor is often increased from the intrinsic Q-factor of the cantilever. In this article, the frequency noise in the FM-AFM system with the PSEs in the self-oscillation loop is analyzed to show that the oscillator noise is reduced by the increase of the effective Q-factor. It is also shown that the oscillation frequency deviates from the resonance frequency due to the increase of the effective Q-factor, thereby causing the reduction in the frequency shift signal with the same factor. Therefore the increase of the effective Q-factor does not affect the signal-to-noise ratio in the frequency shift measurement, but it does affect the quantitativeness of the measured force in the FM-AFM. Furthermore, the reduction of the frequency noise and frequency shift by the increase of the effective Q-factor were confirmed by the experiments.

Kobayashi, Kei [Office of Society-Academia Collaboration for Innovation, Kyoto University, Katsura, Nishikyo, Kyoto 615-8520 (Japan); Yamada, Hirofumi; Matsushige, Kazumi [Department of Electronic Science and Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510 (Japan)

2011-03-15

380

An Improved Audio-Frequency Generator  

Microsoft Academic Search

This paper describes in detail the construction of an audio-frequency generator, for use in making radio-frequency measurments. The variable audio-frequency output is the beat note between two sources of radio frequency; the one a piezo oscillator, and the other a variable oscillator. The output is continuously variable from 50 to 1500 cycles per second. The entire unit is assembled very

E. G. Lapham

1932-01-01

381

UWB Spatial-Frequency Channel Characterization  

Microsoft Academic Search

This paper investigates the spatial-frequency chan- nel characterization of Ultra-wideband (UWB) wireless commu- nication systems. Firstly, a novel frequency dependent UWB channel model is constructed based on the theory of electro- magnetic diffraction mechanism, which causes the field strength to vary with the frequency in each multipath. Secondly, we build a space-frequency model, which includes spatial characteristics such as angular

Wen Zhang; Thushara D. Abhayapala; Jian Zhang

382

Frequency-Comb Mid-Infrared Spectroscopy  

Microsoft Academic Search

A new class of IR coherent sources and IR frequency combs, that combine optical frequency-comb synthesizers (OFCSs) and optical parametric up\\/down-conversions, is already available and still progressing at a very fast pace. Peculiar features for IR radiation produced by difference-frequency-generation (DFG) set-ups or quantum-cascade lasers (QCLs) can he achieved when they are phase and frequency controlled by the OFCS. Indeed,

P. de Natale; D. Mazzotti; G. Giusfredi; S. Bartalini; P. Cancio; P. Maddaloni; P. Malara; G. Gagliardi; I. Galli; S. Borri

2008-01-01

383

High frequency dynamic nuclear polarization.  

PubMed

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 = 1/2 species (13)C or (15)N. The difficulty is still greater when quadrupolar nuclei, such as (17)O or (27)Al, 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

2013-09-17

384

47 CFR 90.539 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Frequency stability. 90.539 Section 90...Regulations Governing the Licensing and Use of Frequencies in the 758-775 and 788-805 MHz Bands § 90.539 Frequency stability. Transmitters...

2013-10-01

385

47 CFR 90.613 - Frequencies available.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01false Frequencies available.90.613 Section 90...Regulations Governing Licensing and Use of Frequencies in the 806-824, 851-869, 896-901...Applications and the Selection and Assignment of Frequencies for Use in the 806-824 Mhz,...

2013-10-01

386

47 CFR 74.502 - Frequency assignment.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Frequency assignment. 74.502 Section 74...Broadcast Auxiliary Stations § 74.502 Frequency assignment. (a) Except as provided...the band in accordance with the Table of Frequency Allocations. These stations will...

2013-10-01

387

Time and frequency in fundamental metrology  

Microsoft Academic Search

The author shows that because time and frequency are the most accurately measured physical quantities, it is desirable to tie other physical quantities to time and frequency measurements. A review of the progress that has been made in this direction along with speculation on possibilities for the future are given. The role of time and frequency in a wide range

BRIAN W. PETLEY

1991-01-01

388

Analysis of Fundamental Frequency Pattern in Speech.  

National Technical Information Service (NTIS)

The fundamental frequency pattern is varied in speech. For example, when we speak angrily, the fundamental frequency is high, and the intonation comes to be deep. Is there a rule about the pattern and speech. The way to analyze the fundamental frequency p...

T. Okudera Y. Takasawa

1993-01-01

389

Lasers with internal frequency-shifted feedback  

SciTech Connect

Properties of lasers with frequency-shifted feedback are discussed. The analysis concentrates on the passive characteristics of the cavity. Particular emphasis is given to the case in which the frequency shift is small compared to the free spectral range of a normal Fabry-Perot cavity with no frequency shift.

Kowalski, F.V. (Colorado School of Mines, Golden, CO (United States). Dept. of Physics); Balle, S.; Littler, I.C.M.; Bergmann, K. (Fachbereich Physik der Univ., Kaiserslautern (Germany))

1994-04-01

390

Frequency Selective Surface Subreflector Development Rept.  

National Technical Information Service (NTIS)

The need, in microwave tracking and radar systems for antennas with a dual-frequency capability, has necessitated the development of multi-frequency, multipurpose antennas. It is the purpose of the report to describe one type of dual-frequency antenna tha...

G. H. Schennum

1970-01-01

391

Magnetic MEMS reconfigurable frequency-selective surfaces  

Microsoft Academic Search

A reconfigurable frequency-selective electromagnetic filter implemented by integrating hard magnetic materials with microelectromechanical systems (MEMS) provides a new variation of reconfigurable frequency-selective surfaces (FSS). By incorporating magnetically actuated dipole elements that are capable of being tilted away from the supporting surface, we can tune the FSSs operating frequency without having to physically alter the dimensions of the dipole elements. The

Joe M. Zendejas; John P. Gianvittorio; Yahya Rahmat-Samii; Jack W. Judy

2006-01-01

392

Concerning Optimum Frequencies for Space Vehicle Communication  

Microsoft Academic Search

Optimum frequencies for the varied needs of space vehicle communication can best be determined from the estimated system performance. Each of the contributing equipment and propagation factors over the range of the radio frequency spectrum affects the minimum tolerable signal-to-noise power ratio at the receiver. Over the range of the radio frequency spectrum, the behavior of the individual building blocks,

S. Perlman; L. Kelley; W. Russell; W. Stuart

1959-01-01

393

Heterodyne laser instantaneous frequency measurement system  

SciTech Connect

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, R.W.; Johnson, M.A.; Globig, M.A.

1989-12-17

394

47 CFR 90.213 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...channel bandwidth must have a frequency stability of 1.0 ppm...designed to operate on a frequency specifically designated...itinerant use or designed for low-power operation of two watts or less, must have a frequency stability of 5.0...

2013-10-01

395

47 CFR 90.715 - Frequencies available.  

Code of Federal Regulations, 2013 CFR

...in pairs, with base station frequencies taken from the 220-221 MHz...mobile and control station frequencies being 1 MHz higher and taken...221-222 MHz band. Only the lower half of the frequency pair(s) is listed in...

2013-10-01

396

47 CFR 87.475 - Frequencies.  

Code of Federal Regulations, 2013 CFR

...available for differential GPS stations. Frequencies in the 112-118 MHz band may...differential GPS data links. (1) The frequencies available are on 25 kHz centers with the lowest assignable frequency being centered at 112.000 MHz...

2013-10-01

397

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

398

Gated stepped-frequency ground penetrating radar  

Microsoft Academic Search

This paper describes a newly developed stepped-frequency ground penetrating radar (SFGPR) prototype operating across the 10–620 MHz frequency band. The SFGPR system has been developed to improve the maximum penetration depth capability of ground penetrating radar (GPR) applications without degradation of resolving power. The radar has the unique capability to employ a short gate at each frequency step that can

G. F. Stickley; D. A. Noon; M. Cherniakov; I. D. Longstaff

2000-01-01

399

MSW frequency selective limiters at UHF  

Microsoft Academic Search

Frequency selective limiters (FSLs) have potential application in maintaining the dynamic range of RF receivers in the presence of interference. Stripline FSLs, fabricated using thick YIG films, have been described previously and are suitable for broadband, microwave applications. Here a magnetostatic wave (MSW) FSL operating in the 400 MHz to 800 MHz frequency range is described with frequency selectivity and

J. D. Adam; Steven N. Stitzer

2004-01-01

400

Low frequencies in Kepler ? Scuti stars  

NASA Astrophysics Data System (ADS)

We use Kepler photometry to examine the properties of low-frequency oscillations in A stars. We find that multiple peaks in the range 0-5 d-1 are found in nearly all ? Scuti stars, even those well outside the blue edge of the ? Doradus instability strip. All ? Sct stars are essentially ? Sct/? Dor hybrids. The reason why this fact was not recognized from ground-based observations is due to the fact that the low frequencies reach maximum amplitude close to the blue edge of the ? Dor instability strip. Stars which do not have high frequencies characteristic of ? Sct pulsations also do not have low frequencies. The amplitudes of the low frequencies correlate with the amplitudes of the ? Sct pulsations. The low frequencies have long lifetimes similar to those of the ? Sct modes. They are therefore not excited by a stochastic mechanism. We show that the low frequencies cannot be explained as non-linear combinations of ? Sct modes. By comparing the observed distribution of frequencies with those from ? Sct models, we show that low-frequency peaks cannot be explained as a result of rotational perturbation of high-frequency ? Sct modes. We find that the number of low-frequency peaks increases with rotation, but Rossby and Kelvin modes can be ruled out as possible candidates. The presence of low frequencies in A stars would be explained if the convective blocking mechanism continues to be active even in the hottest A stars.

Balona, L. A.

2014-01-01

401

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

402

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

403

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

404

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

405

A solid-state atomic frequency standard  

Microsoft Academic Search

This paper describes a new class of frequency reference. The frequency source uses the same operating principle as a passive atomic frequency standard; however, the device is entirely solid-state, removing many cost and reliability issues associated with gas phase atomic clocks. More specifically, the \\

Christopher J. White; Ali Hajimiri

2005-01-01

406

Flight frequency and mergers in airline markets  

Microsoft Academic Search

The welfare consequences of airline mergers have been analyzed almost exclusively in terms of ticket price. However, when flight frequency decisions are endogenized in a model, we can estimate measures of the relative importance of price and flight frequency in customer decisions. Hence, in a merger analysis, we can not only predict changes in flight frequency, but also the consequences

Oliver Richard

2003-01-01

407

Statistical Frequency-Distance Curves, Initial Model.  

National Technical Information Service (NTIS)

The report describes an initial computer program that produces statistical frequency-distance curves. The computer program has been developed as a tool for use by the frequency managers' community of OTP/IRAC. The statistical frequency-distance curves est...

R. D. Jennings L. E. Vogler J. J. Stephenson

1976-01-01

408

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

409

Frequency conversion of an entangled state  

Microsoft Academic Search

The quantum characteristics of sum-frequency process in an optical cavity with an input signal optical beam, which is a half of entangled optical beams, are analyzed. The calculated results show that the quantum properties of the signal beam can be maintained after its frequency is conversed during the intracavity nonlinear optical interaction. The frequency-conversed output signal beam is still in

Aihong Tan; Xiaojun Jia; Changde Xie

2006-01-01

410

Biomechanics of Fundamental Frequency Regulation  

PubMed Central

Accurate characterization of biomechanical characteristics of the vocal fold is critical for understanding the regulation of vocal fundamental frequency (F0), which depends on the active control of the intrinsic laryngeal muscles as well as the passive biomechanical response of the vocal fold lamina propria. Specifically, the tissue stress-strain response and viscoelastic properties under cyclic tensile deformation are relevant, when the vocal folds are subjected to length and tension changes due to posturing. This paper describes a constitutive modeling approach quantifying the relationship between vocal fold stress and strain (or stretch), and establishes predictions of F0 with the string model of phonation based on the constitutive parameters. Results indicated that transient and time-dependent changes in F0, including global declinations in declarative sentences, as well as local F0 overshoots and undershoots, can be partially attributed to the time-dependent viscoplastic response of the vocal fold cover.

Chan, Roger W.; Siegmund, Thomas; Zhang, Kai

2009-01-01

411

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.

Schmidt, Bruno E.; Thire, Nicolas; Boivin, Maxime; Laramee, Antoine; Poitras, Francois; Lebrun, Guy; Ozaki, Tsuneyuki; Ibrahim, Heide; Legare, Francois

2014-01-01

412

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

413

Coded phase/frequency modulation  

NASA Astrophysics Data System (ADS)

Channel coding combined with expanded signal sets has been shown to improve error performance over uncoded modulation without expanding the bandwidth of the transmitted signals. In this paper, new coded modulation formats defined over an expanded set of signals varying both in phase and frequency are presented. The new schemes combine FSK and PSK modulation and make use of trellis coding and Viterbi decoding to improve error performance over uncoded modulation. The free Euclidean distance is calculated for several classes of codes, and upper bounds and simulation results are also presented for some simple codes. The spectral characteristics of the proposed coded modulation formats are evaluated and compared to conventional two-dimensional modulation formats. Differential encoding and various extensions of the basic scheme are also discussed.

Padovani, R.; Wolf, J. K.

1986-05-01

414

Frequency domain optical parametric amplification.  

PubMed

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

415

Frequency domain optical parametric amplification  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

416

75 FR 19277 - PLMR Licensing; Frequency Coordination and Eligibility Issues  

Federal Register 2010, 2011, 2012, 2013

...applicable frequency coordinator. Applicants for frequencies in the SMR Category must request specific frequencies by including in their...of frequencies that may be trunked. Authorizations for non-SMR stations may be granted for up to 20 trunked frequency...

2010-04-14

417

Coping with Radio Frequency Interference  

NASA Astrophysics Data System (ADS)

The radio spectrum is a finite resource, on which humanity makes many demands. And pressure on it is ever increasing with the development of new technology and ideas for radio services. After all, we all benefit from wifi and cell phones. Radio astronomers have a small percentage of the spectrum allocated to them at octave intervals in the metre-centimetre bands, and at important frequencies, such as that of the 21cm line of HI. Signals from other services, as well as from our own poorly-engineered equipment, sometimes contaminate our bands: these signals constitute RFI. These may totally obliterate the astronomical signal, or, in the case of CLOUDSAT, may be capable of completely destroying a receiver, which introduces us to the new possibility of 'destructive interference'. A geo-stationary satellite can block access to a piece of sky from one site. Good equipment design eliminates self-inflicted interference, while physical separation often provides adequate practical mitigation at many frequencies. However, new observatories end up being located in the West Australian desert or Antarctica. In future they may be on the back side of the Moon. But there is no Earth-bound protection via physical separation against satellite signals. Some mitigation can be achieved by frequent data dumps and the excision of RFI, or by real-time detection and blanking of the receiver, or by more sophisticated algoriths. Astronomers of necessity aim to achieve mitigation via coordination, at the local level, and by participating in spectrum management at the national and international levels. This involves them spending a lot of time in Geneva at the International Telegraphic Union protecting their access to spectrum, and access to clean spectrum from the L3 point and the far side of the Moon.

Lewis, B. M.

2009-01-01

418

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

419

Frequency control of cell cycle oscillators.  

PubMed

The cell cycle oscillator, based on a core negative feedback loop and modified extensively by positive feedback, cycles with a frequency that is regulated by environmental and developmental programs to encompass a wide range of cell cycle times. We discuss how positive feedback allows frequency tuning, how size and morphogenetic checkpoints regulate oscillator frequency, and how extrinsic oscillators such as the circadian clock gate cell cycle frequency. The master cell cycle regulatory oscillator in turn controls the frequency of peripheral oscillators controlling essential events. A recently proposed phase-locking model accounts for this coupling. PMID:20851595

Oikonomou, Catherine; Cross, Frederick R

2010-12-01

420

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

421

Frequency domain representations of wavelet transforms  

NASA Astrophysics Data System (ADS)

Much of the wavelet literature is focussed on wavelets with compact support in the time domain. For many geophysical applications, compact support in the frequency domain is desirable. For these applications, simple window functions can be used to construct appropriate filter banks in the frequency domain. Convolution with filter coefficients in the time domain is replaced with a Fourier transform and multiplication by window functions in the frequency domain. Given the dual nature of the Fourier transform, the time and frequency variables can be exchanged to produce a time windowing algorithm for computing wave packet transforms. Taken together, frequency-windowed and time-windowed wave packet transforms provide a comprehensive tool set for constructing new geophysical applications that take advantage of simultaneous access to time and frequency. Depending on the application, frequency windowing or time windowing may be more desirable.

Mosher, Charles C.; Foster, Douglas J.

1995-09-01

422

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  

Microsoft Academic Search

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,

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

2008-01-01

423

Supersonic free-jet quantum cascade laser measurements of ? 4 for CF 3 35Cl and CF 3 37Cl and FTS measurements from 400 to 1260 cm ?1  

Microsoft Academic Search

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 1060–1260cm?1 and with room temperature FTS measurements down to 400cm?1 to give improved values for the rovibrational constants for the ?1, ?2, ?3, 2?3, 2?5, ?4, and

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

2008-01-01

424

A hardware phase continuous frequency synthesiser for frequency hopping spread spectrum  

Microsoft Academic Search

One of the major problems when implementing frequency-hopping spread-spectrum systems is to obtain an accurate, fast, and transient free frequency synthesizer. Direct digital synthesis meets these requirements with economy and simplicity. A brief analysis of a direct digital frequency synthesizer is made, indicating the several sources of noise that contribute to signal degradation, the frequency distribution of spurious response due

FRANCISCO A B. CERCAS; M. Tomlinson; J. M. N. Pereira; A. A. Albuquerque

1989-01-01

425

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

426

Optical frequency comb comparison between optical clock mode and optical frequency synthesizer mode  

NASA Astrophysics Data System (ADS)

We report on an accuracy limit test result of the optical frequency comb technique by comparing the frequencies of two optical frequency combs that operate in two different modes. These two modes are distinguished by the reference frequency for the comb frequency stabilization; an optical frequency (in an optical clock mode) or a microwave frequency (in an optical frequency synthesizer mode). The comparison of the two combs was carried out by simultaneously measuring an absolute frequency of an acetylene-stabilized diode laser with both combs. The frequencies of the two combs agreed with each other within the uncertainty of 16 Hz at 194 THz. The uncertainty is reduced by more than an order compared with a previous report.

Kim, Eok Bong; Park, Chang Yong; Yu, Dai-Hyuk; Park, Sang Eon; Lee, Won-Kyu

2011-02-01

427

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

428

The characteristics of atmospheric radio frequency discharges with frequency increasing at a constant power density  

SciTech Connect

A computational model is used to investigate the characteristics of atmospheric radio frequency discharges by increasing frequency from 20 to 100 MHz at a constant power density. The simulation results show that increasing frequency can effectively enhance electron density before the transition frequency but after it the ignition is quenched then the electron density decreases. However this simulation also indicates the maximum time-averaged electron energy reduces monotonically with the excitation frequency increasing at a constant power density.

Zhang Yuantao; Li Qingquan; Lou Jie; Li Qingmin [School of Electrical Engineering, Shandong University, Jinan, Shandong Province 250061 (China)

2010-10-04

429

Convolutionally encoded FFH-MFSK - Demodulation and frequency tracking over frequency-varying jammed channels  

NASA Astrophysics Data System (ADS)

A technique is described for Viterbi demodulation and deconvolution of convolutionally encoded fast-frequency-hopped M-ary frequency shift keying. The Viterbi frequency-tracking technique provides fast tracking of frequency offsets with worst-case partial-band tone-jamming of 0.5 dB for 16 possible carrier-frequency positions. The procedure is relevant to the development of methods for discriminating against jamming waveforms without generating potentially disruptive waveforms.

Gibbs, J. A.; Braithwaite, S. J.

1992-08-01

430

Effects of relative frequency, absolute frequency, and phase on fundamental frequency discrimination: Data and an autocorrelation model  

Microsoft Academic Search

Fundamental frequency (F0) difference limens (DLs) were measured versus F0 for sine- and random-phase harmonic complexes bandpass-filtered into low- or high-frequency regions, with 3-dB passbands of 2.5-3.5 and 5-7 kHz, respectively. In all cases, F0 DLs decreased dramatically with increasing F0 as approximately the tenth harmonic appeared in the passband. Generally, F0 DLs were similar in both frequency regions for

Joshua Bernstein; Andrew Oxenham

2003-01-01

431

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

432

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

NASA Astrophysics Data System (ADS)

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; Jung, H.; Gweon, B.; Moon, S. Y.; Rhee, J. K.; Choe, W.

2011-04-01

433

Frequency response of a thermal diode.  

PubMed

A thermal diode that rectifies heat current is one of the basic devices for functional heat control. Frequency response is an important feature of many electric devices, such as diodes and transistors. Frequency response measures the ability of a device to process high-frequency signals. In this paper, we systematically study the frequency response of a thermal diode model that consists of two dissimilar Frenkel-Kontorova (FK) segments. The rectification ability of this thermal diode is badly affected when the input temperatures oscillate with a frequency that exceeds a critical value. The dependence of this critical frequency on various system parameters, including system size, interface coupling strength, etc., is quantitatively calculated. PMID:24580184

Wang, Lei; Wu, Junpeng

2014-01-01

434

Age differences in thalamic low frequency fluctuations  

PubMed Central

The thalamus plays a role in many different types of cognitive processes and is critical for communication between disparate cortical regions. Given its critical role in coordinating cognitive processes, it is important to understand how its function might be affected by aging. In the present study, we examined whether there are age differences in low-frequency fluctuations during rest in the thalamus. Across independent datasets, we found that the amplitude of low frequency (.01–.10 Hz) oscillations was greater in the thalamus among older than younger adults. Breaking this low frequency range down further revealed that this increase in amplitude with age in the thalamus was most pronounced at the low end of the frequency range (.010–.027 Hz), whereas in the higher low frequency range (.198–.250 Hz) younger adults showed greater amplitude than older adults. These shifts in thalamic low frequency oscillatory activity likely influence the complex dynamics of coordinated brain activity and influence cognitive performance.

Mather, Mara; Nga, Lin

2014-01-01

435

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

436

Harmonic generation with a dual frequency pulse.  

PubMed

Nonlinear imaging was implemented in commercial ultrasound systems over the last 15 years offering major advantages in many clinical applications. In this work, pulsing schemes coupled with a dual frequency pulse are presented. The pulsing schemes considered were pulse inversion, power modulation, and power modulated pulse inversion. The pulse contains a fundamental frequency f and a specified amount of its second harmonic 2f. The advantages and limitations of this method were evaluated with both acoustic measurements of harmonic generation and theoretical simulations based on the KZK equation. The use of two frequencies in a pulse results in the generation of the sum and difference frequency components in addition to the other harmonic components. While with single frequency pulses, only power modulation and power modulated pulse inversion contained odd harmonic components, with the dual frequency pulse, pulse inversion now also contains odd harmonic components. PMID:24815238

Keravnou, Christina P; Averkiou, Michalakis A

2014-05-01

437

Capture of Attention in Selective Frequency Listening  

Microsoft Academic Search

Four signal-detection experiments demonstrated robust stimulus-driven, or exogenous, attentional processes in selective frequency listening. Detection of just-above-threshold signal tones was consistently better when the signal matched the frequency of an uninformative cue tone, even with relatively long cue–signal delays (Experiment 1) or when as few as 1 in 8 signals were at the cued frequency (Experiment 2). Experiments 3 and

Tim J. Green; J. Denis McKeown

2001-01-01

438

Time-Frequency Methods for Multicomponents Signals  

Microsoft Academic Search

Instantaneous frequency (IF) is a very important parameter in a large number of applications. Generally, the IF is a non-linear function of time. For such cases the analysis of time-frequency content provides an efficient solution. This paper is a comparative study of the performances in IF estimation of the two time-frequency based methods. Limitations of the two methods are presented

Marius Salagean; I. Nafornita

2007-01-01

439

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

440

The Umbella high-frequency EPR facility  

Microsoft Academic Search

The Umbella high-frequency electron paramagnetic resonance (EPR) facility is a part of the Nijmegen High Field Magnet Laboratory\\u000a with special emphasis on multifrequency EPR for chemical and biological applications. At present the facility has various\\u000a solid-state sources available for the frequency range between 95 and 400 GHz, combined with magnetic fields up to 30 T. For\\u000a frequencies above 400 GHz

P. J. M. van Bentum; E. van der Horst; M. E. J. Boonman; A. Priem; W. R. Hagen; E. J. Reijerse; M. Gross; P. Goy; M. Martinelli; A. Colligiani

2000-01-01

441

Microelectromechanical resonators for radio frequency communication applications  

Microsoft Academic Search

Over the past few years, microelectromechanical system (MEMS) based on-chip resonators have shown significant potential for\\u000a sensing and high frequency signal processing applications. This is due to their excellent features like small size, large\\u000a frequency-quality factor product, low power consumption, low cost batch fabrication, and integrability with CMOS IC technology.\\u000a Radio frequency communication circuits like reference oscillators, filters, and mixers

Joydeep BasuTarun; Tarun Kanti Bhattacharyya

442

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

443

Dynamic response of a frequency measuring system  

Microsoft Academic Search

A frequency measurement system using a double-buffered method is designed for PC\\/AT compatible computers. The extremely wide range of measured frequencies (from 1.67 mHz to 7 MHz) is independent of a wide range of sampling periods (from 100 ?s to 300 s). The response time to an instantaneously increased frequency from 1.67 mHz to 7 MHz is less than two

Milan Prokin

1992-01-01

444

Variable frequency RFQs as cyclotron injectors  

Microsoft Academic Search

Injectors for cyclotrons must provide low emittance beams with variable energy and bunch repetition frequency. The parameters of standard RFQs, which are short duty factor and constant operating frequency are not favourable for cyclotron application. Our development of the VE-RFQ has been adopted to match the HMI-cyclotron at HMI in Berlin as a first variable frequency RFQ operating in cw-mode.

A. Schempp

2001-01-01

445

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

446

High-Frequency Transient Eddies and Blocking  

Microsoft Academic Search

In this paper we investigate the role of high-frequency transient eddies in the maintenance of the blocking high which occurred over Europe on 16-25 February 1979. Time-filtering is used to decompose the atmospheric large-scale flow into contributions from high-frequency and low-frequency fluctuations. the separation being roughly at the period of six days. The net effect on the ten-day mean flow

Eero Holopainen; Carl Fortelius

1987-01-01

447

Vibrational frequency prediction using density functional theory  

Microsoft Academic Search

A comparison of several density functional methods for calculating vibrational frequencies is reported. Methods examined include the local S-VWN (LSDA) functional, the non-local B-LYP and B-VWN functionals and the hybrid B3-LYP and B3-P86 functionals. The split-valence polarized 6-31G? basis set has been used in all methods. The computed frequencies were compared with experimental frequencies for a set of 122 molecules

Ming Wah Wong

1996-01-01

448

A novel frequency control scheme for comb-referenced sensitive difference-frequency-generation spectroscopy.  

PubMed

We present a novel scheme of frequency scan and wavelength modulation of a difference-frequency-generation source for comb-referenced sensitive spectroscopy. While the pump and signal frequencies are phase-locked to an optical frequency comb (OFC), the offset frequency between the signal wave and the nearest comb tooth is modulated to apply a wavelength-modulation technique, and the idler wave frequency is repeatedly swept for signal accumulation by changing the repetition frequency of the OFC. The spectrometer is applied to absolute frequency measurement of weak hyperfine-resolved rovibration transitions of the ?(1) band of CH(3)I, and the uncertainty in frequency determination is reduced by one order of magnitude in compared with that of the previous work published in Optics Express 20, 9178-9186 (2012). PMID:23787670

Iwakuni, Kana; Okubo, Sho; Sasada, Hiroyuki

2013-06-17

449

Power Supply for Variable Frequency Induction Heating Using MERS Soft-Switching High Frequency Inverter  

NASA Astrophysics Data System (ADS)

Variable frequency induction heating has great potential for industrial heating applications due to the possibility of achieving heating distribution control; however, large-scale induction heating with variable frequency has not yet been introduced for practical use. This paper proposes a high frequency soft-switching inverter for induction heating that can achieve variable frequency operation. One challenge of variable frequency induction heating is increasing power electronics ratings. This paper indicates that its current source type dc-link configuration and soft-switching characteristics can make it possible to build a large-scale system with variable frequency capability. A 90-kVA 150-1000Hz variable frequency experimental power supply for steel strip induction heating was developed. Experiments confirmed the feasibility of variable frequency induction heating with proposed converter and the advantages of variable frequency operation.

Isobe, Takanori; Kitahara, Tadayuki; Fukutani, Kazuhiko; Shimada, Ryuichi

450

Low-frequency cosmology from the moon  

NASA Astrophysics Data System (ADS)

From a low-frequency point of view, the moon provides excess to the virtually unexplored radio frequency domain below 30 MHz that is not accessible from Earth due to the atmospheric cutoff and interference from man-made RFI. We show that with a single low-frequency radio antenna the detection of the 21-cm Dark Ages signal is possible within integration times of months, and address the size and integration times required for a future low-frequency array to perform detailed tomography and power spectral analysis of the Dark Ages signal.

Klein Wolt, M.; Aminaei, A.; Pourshaghaghi, H.; Koopmans, L.; Falcke, H.

2013-09-01

451

Low frequency acoustic and electromagnetic scattering  

NASA Technical Reports Server (NTRS)

This paper deals with two classes of problems arising from acoustics and electromagnetics scattering in the low frequency stations. The first class of problem is solving Helmholtz equation with Dirichlet boundary conditions on an arbitrary two dimensional body while the second one is an interior-exterior interface problem with Helmholtz equation in the exterior. Low frequency analysis show that there are two intermediate problems which solve the above problems accurate to 0(k(2) log k) where k is the frequency. These solutions greatly differ from the zero frequency approximations. For the Dirichlet problem numerical examples are shown to verify the theoretical estimates.

Hariharan, S. I.; Maccamy, R. C.

1983-01-01

452

Low frequency acoustic and electromagnetic scattering  

NASA Technical Reports Server (NTRS)

This paper deals with two classes of problems arising from acoustics and electromagnetics scattering in the low frequency stations. The first class of problem is solving Helmholtz equation with Dirichlet boundary conditions on an arbitrary two dimensional body while the second one is an interior-exterior interface problem with Helmholtz equation in the exterior. Low frequency analysis show that there are two intermediate problems which solve the above problems accurate to 0(k/2/ log k) where k is the frequency. These solutions greatly differ from the zero frequency approximations. For the Dirichlet problem numerical examples are shown to verify the theoretical estimates.

Hariharan, S. I.; Maccamy, R. C.

1986-01-01

453

Electronic tunneling currents at optical frequencies  

NASA Technical Reports Server (NTRS)

Rectification characteristics of nonsuperconducting metal-barrier-metal junctions as deduced from electronic tunneling theory have been observed experimentally for optical frequency irradiation of the junction.

Faris, S. M.; Fan, B.; Gustafson, T. K.

1975-01-01

454

47 CFR 27.54 - Frequency stability.  

Code of Federal Regulations, 2013 CFR

...stability. 27.54 Section 27.54 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES Technical Standards § 27.54 Frequency...

2013-10-01

455

A Bayesian approach to frequency line tracking  

NASA Astrophysics Data System (ADS)

A computationally efficient Bayesian frequency line tracker is presented. This frequency tracker has been implemented and operationally tested in the Navy's Passive Tracking Algorithm (PTA) program. Acoustic sensors receive narrowband signature from an ocean target. Using power spectral data as input, a discrete probability density function (PDF) of the received frequency is propagated in time using a first order Markov process to model line dynamics. The minimum mean squared error estimate (i.e., the posterior mean) and its standard deviation are obtained from the a posteriori PDF for use in the PTA Doppler target tracking algorithm. The frequency tracking algorithm is derived from a mathematical model, and results are presented.

Bethel, R. E.; Gauss, J. A.

456

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

457

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

458

Variable frequency RFQs as cyclotron injectors  

NASA Astrophysics Data System (ADS)

Injectors for cyclotrons must provide low emittance beams with variable energy and bunch repetition frequency. The parameters of standard RFQs, which are short duty factor and constant operating frequency are not favourable for cyclotron application. Our development of the VE-RFQ has been adopted to match the HMI-cyclotron at HMI in Berlin as a first variable frequency RFQ operating in cw-mode. Another example ist the RFQ at RIKEN which injects into the RILAC variable frequency linac. The layout and properties of these RFQs will be described. .

Schempp, A.

2001-12-01

459

Subjective frequency ratings for 432 ASL signs.  

PubMed

Given the importance of lexical frequency for psycholinguistic research and the lack of comprehensive frequency data for sign languages, we collected subjective estimates of lexical frequency for 432 signs in American Sign Language (ASL). Our participants were 59 deaf signers who first began to acquire ASL at ages ranging from birth to 14 years old and who had a minimum of 10 years of experience. Subjective frequency estimates were made on a scale ranging from 1 = rarely see the sign to 7 = always see the sign. The mean subjective frequency ratings for individual signs did not vary in relation to age of sign language exposure (AoLE), chronological age, or length of ASL experience. Nor did AoLE show significant effects on the response times (RTs) for making the ratings. However, RTs were highly correlated with mean frequency ratings. These results suggest that the distributions of subjective lexical frequencies are consistent across signers with varying AoLEs. The implications for research practice are that subjective frequency ratings from random samples of highly experienced deaf signers can provide a reasonable measure of lexical control in sign language experiments. The Appendix gives the mean and median subjective frequency ratings and the mean and median log(RT) of the ASL signs for the entire sample; the supplemental material gives these measures for the three AoLE groups: native, early, and late. PMID:23943581

Mayberry, Rachel I; Hall, Matthew L; Zvaigzne, Meghan

2014-06-01

460

Frequency spectrum analyzer with phase-lock  

DOEpatents

A frequency-spectrum analyzer with phase-lock for analyzing the frequency and amplitude of an input signal is comprised of a voltage controlled oscillator (VCO) which is driven by a ramp generator, and a phase error detector circuit. The phase error detector circuit measures the difference in phase between the VCO and the input signal, and drives the VCO locking it in phase momentarily with the input signal. The input signal and the output of the VCO are fed into a correlator which transfers the input signal to a frequency domain, while providing an accurate absolute amplitude measurement of each frequency component of the input signal.

Boland, Thomas J. (Idaho Falls, ID)

1984-01-01

461

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

462

Conceptual test of frequency diversity lidar  

NASA Technical Reports Server (NTRS)

The present consideration of the estimation accuracy of lidar-backscattered signals in atmospheric remote sensing proposes a method that can furnish additional uncorrelated data within the atmospheric decorrelation time, with enhanced energy efficiency. This frequency-diversity method recognizes that additional uncorrelated data from a given illuminated region is obtainable by changing the frequency of the incoming radiation. The mathematical analysis of the frequency-diversity concept by Wallace (1953) confirms the physical scenario employed. A simple version of a coherent lidar system incorporating the frequency-diversity concept is included to illustrate the design principles involved.

Schotland, Richard M.; Vujkovic Cvijin, P.; Zhao, Yanzeng; Hudor, A. M.

1988-01-01

463

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

464

Excitation frequency dependent mode manipulation in radio-frequency atmospheric argon glow discharges  

NASA Astrophysics Data System (ADS)

An experimental investigation is presented to characterize the dependence of discharge operation modes (? and ? modes) and their transition on excitation frequency in radio-frequency atmospheric argon glow discharges. The current-voltage characteristics are used to distinguish the ? and ? modes at an excitation frequency range of 5-24 MHz. The operation regime of ? mode with stable and uniform discharge in large volume is found to expand at higher excitation frequency. It is shown that, when excitation frequency is below 10 MHz, the discharge evolves directly into ? mode after gas breakdown and, when excitation frequency is above 10 MHz, the discharge operates in the coexistence mode of ? and ? after mode transition.

Zhang, Jie; Ding, Ke; Wei, Kaya; Zhang, Jing; Shi, Jianjun

2009-09-01

465

Generalization of Frequency Discrimination Learning Across Frequencies and Ears: Implications for Underlying Neural Mechanisms in Humans  

PubMed Central

Frequency discrimination thresholds (FDTs) at 750, 1500, 3000, and 6000 Hz were measured in 32 normal-hearing listeners before and after each listener practiced the task for 12 h at one of the above frequencies using a single ear. Marked improvements in thresholds taking place over several hours were observed during the frequency- and ear-specific training period. Comparisons between pre- and posttraining thresholds showed large improvements at the trained frequency, but also at other frequencies. The improvements were initially slightly—but significantly—larger at the trained frequency than at untrained frequencies. However, this trained-frequency advantage disappeared rapidly during the course of the two-hour multifrequency posttraining session, suggesting rapid relearning or learning generalization across frequencies. In contrast, no significant ear specificity was found, not even at early stages of the posttraining session. These findings add to earlier results suggesting that, in humans, frequency discrimination learning is only weakly frequency-specific, and they reveal that a complete generalization across frequencies can occur rapidly with little retraining at the initially untrained frequencies. Implications regarding underlying mechanisms are discussed.

Delhommeau, Karine; Jouvent, Roland

2005-01-01

466

Generalization of frequency discrimination learning across frequencies and ears: implications for underlying neural mechanisms in humans.  

PubMed

Frequency discrimination thresholds (FDTs) at 750, 1500, 3000, and 6000 Hz were measured in 32 normal-hearing listeners before and after each listener practiced the task for 12 h at one of the above frequencies using a single ear. Marked improvements in thresholds taking place over several hours were observed during the frequency- and ear-specific training period. Comparisons between pre- and posttraining thresholds showed large improvements at the trained frequency, but also at other frequencies. The improvements were initially slightly-but significantly-larger at the trained frequency than at untrained frequencies. However, this trained-frequency advantage disappeared rapidly during the course of the two-hour multifrequency posttraining session, suggesting rapid relearning or learning generalization across frequencies. In contrast, no significant ear specificity was found, not even at early stages of the posttraining session. These findings add to earlier results suggesting that, in humans, frequency discrimination learning is only weakly frequency-specific, and they reveal that a complete generalization across frequencies can occur rapidly with little retraining at the initially untrained frequencies. Implications regarding underlying mechanisms are discussed. PMID:15834630

Delhommeau, Karine; Micheyl, Christophe; Jouvent, Roland

2005-06-01

467

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

468

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...STATIONS IN THE MARITIME SERVICES Frequencies Ship Earth Stations § 80.377 Frequencies for ship earth stations. The frequency...

2012-10-01

469

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...STATIONS IN THE MARITIME SERVICES Frequencies Ship Earth Stations § 80.377 Frequencies for ship earth stations. The frequency...

2010-10-01

470

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...STATIONS IN THE MARITIME SERVICES Frequencies Ship Earth Stations § 80.377 Frequencies for ship earth stations. The frequency...

2011-10-01

471

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

472

Frequency response corrections for eddy correlation systems  

Microsoft Academic Search

Simplified expressions describing the frequency response of eddy correlation systems due to sensor response, path-length averaging, sensor separation and signal processing are presented. A routine procedure for estimating and correcting for the frequency response loss in flux and variance measurements is discussed and illustrated by application to the Institute of Hydrology's ‘Hydra’ eddy correlation system.

C. J. Moore

1986-01-01

473

Fundamental Frequency of Oscillation in LSA Circuits.  

National Technical Information Service (NTIS)

The report traces out the development of the low frequency equivalent circuit of the diode-on-a-post type waveguide LSA oscillator and shows that circuit conditions exist for the low frequency oscillations. The input impedance presented to a diode mounted...

K. W. H. Foulds

1970-01-01

474

High frequency fundamental VCXO for SDH system  

Microsoft Academic Search

This paper describes a high frequency fundamental (HFF) crystal resonator in the frequency range from 156 MHz to nearly 1 GHz, which is fabricated by an industrial photolithographic batch manufacturing process with chemical etching. It also describes a 156 MHz voltage controlled crystal oscillator (VCXO) and a 622 MHz VCXO employing the prototype HFF crystal resonators developed for SDH (synchronous

O. Ishii; T. Shibata; T. Ohshima

1996-01-01

475

Hydrogenic systems, frequency standards and fundamental constants  

Microsoft Academic Search

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum

JL Flowers; HA Klein; HS Margolis

2004-01-01

476

A circuit for high frequency crystal oscillators  

Microsoft Academic Search

This paper describes a circuit for high frequency crystal oscillators using an AT-cut resonator in the UHF frequency range. This circuit can be built based on a conventional Colpitts oscillator circuit with a feedback capacitor between the collector terminal and the emitter terminal of a transistor. The new circuit has the characteristic features of low drive level and high negative

Jun MATSUOKA; Tomio SATO; Tsuyoshi OHSHIMA

2003-01-01

477

Radio Propagation at Frequencies above 30 Megacycles  

Microsoft Academic Search

Radio propagation is affected by many factors, including the frequency, distance, antenna heights, curvature of the earth, atmospheric conditions, and the presence of hills and buildings. The influence of each of these factors at frequencies above about 30 megacycles is discussed, with most of the quantitative data being presented in a series of nomograms. By means of three or four

K. Bullington

1947-01-01

478

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

479

Frequency Selective Structures on a Bianisotropic Slab.  

National Technical Information Service (NTIS)

In this paper a method for the analysis of a frequency selective surface (FSS) supported by a bianisotropic substrate is presented. The frequency selective structure is a thin metallic pattern-the actual FSS-on a plane supporting substrate. Integral repre...

G. Kristensson M. Akerberg S. Poulsen

2000-01-01

480

An active square loop frequency selective surface  

Microsoft Academic Search

An active frequency selective surface incorporating PIN diodes as switches is discussed. Waveguide simulation studies show that the frequency response of the surface can be electronically switched from that of a reflecting structure to a transmitting structure. A semi-empirical model based on a series-connected LC equivalent circuit approach gives agreement with measurements

T. K. Chang; R. J. Langley; E. Parker

1993-01-01