Far infrared spectra and vibrational assignments of substituted benzenes

1967 ◽  
Vol 298 (1452) ◽  
pp. 51-63 ◽  
Keyword(s):  
Low Temperature ◽  
Low Frequency ◽  
Far Infrared ◽  
Marked Variation ◽  
Frequency Range ◽  
Substituted Benzenes ◽  
Low Frequencies ◽  
Vibrational Assignments ◽  
Bending Mode ◽  
Far Infrared Spectra

The vibrational absorption spectra of some substituted benzenes have been measured in the range 50 to 450 cm -1 . The compounds were measured as liquids, in solutions, as crystalline solidsat low temperature, and in polyethylene matrices. The extension of the infrared spectrum to very low frequencies has made it possible to determine new values for many fundamental vibrations. An assignment of all the vibrational frequencies in the low-frequency range has been made, from the infrared and Raman data, for p -dihalogeno-benzenes, p -halogenotoluenes, p -halogeno-nitrobenzenes, and for some mono-substituted benzenes. Some measurements have been made on the marked variation of intensity of the lowest frequency bending mode of p -dihalogeno-benzenes.

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 854-859 ◽  
Author(s):  
Xiao Ming Tang
Keyword(s):  
Elastic Wave ◽  
Wave Attenuation ◽  
Waveform Inversion ◽  
Finite Size ◽  
Low Frequency ◽  
Frequency Range ◽  
Multiple Reflections ◽  
Low Frequencies ◽  
The Time Domain ◽  
Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

Optimally Sensitive and Efficient Compact Loudspeakers for Low Audio Frequencies

2007 ◽  
Vol 38 (7) ◽  
pp. 11-17
Author(s):  
Ronald M. Aarts
Keyword(s):  
Optimality Criterion ◽  
Low Frequency ◽  
Audio Signal ◽  
Design Procedure ◽  
Frequency Range ◽  
Force Factor ◽  
Low Frequencies ◽  
Limited Frequency ◽  
The Cost ◽  
Higher Sensitivity

Conventionally, the ultimate goal in loudspeaker design has been to obtain a flat frequency response over a specified frequency range. This can be achieved by carefully selecting the main loudspeaker parameters such as the enclosure volume, the cone diameter, the moving mass and the very crucial “force factor”. For loudspeakers in small cabinets the results of this design procedure appear to be quite inefficient, especially at low frequencies. This paper describes a new solution to this problem. It consists of the combination of a highly non-linear preprocessing of the audio signal and the use of a so called low-force-factor loudspeaker. This combination yields a strongly increased efficiency, at least over a limited frequency range, at the cost of a somewhat altered sound quality. An analytically tractable optimality criterion has been defined and has been verified by the design of an experimental loudspeaker. This has a much higher efficiency and a higher sensitivity than current low-frequency loudspeakers, while its cabinet can be much smaller.

Low-frequency single-crystal Raman, far-infrared, and inelastic neutron scattering studies of acetanilide at low temperature

1991 ◽  
Vol 95 (13) ◽  
pp. 5281-5286 ◽  
Author(s):  
Clifford T. Johnston ◽  
Stephen F. Agnew ◽  
Juergen Eckert ◽  
Llewellyn H. Jones ◽  
Basil I. Swanson ◽  
...  
Keyword(s):  
Low Temperature ◽  
Neutron Scattering ◽  
Single Crystal ◽  
Inelastic Neutron Scattering ◽  
Low Frequency ◽  
Far Infrared ◽  
Inelastic Neutron

scholarly journals A census of the pulsar population observed with the international LOFAR station FR606 at low frequencies (25–80 MHz)

2020 ◽  
Vol 635 ◽  
pp. A76 ◽  
Author(s):  
L. Bondonneau ◽  
J.-M. Grießmeier ◽  
G. Theureau ◽  
A. V. Bilous ◽  
V. I. Kondratiev ◽  
...  
Keyword(s):  
Low Frequency ◽  
Frequency Range ◽  
Radio Pulsars ◽  
Low Frequencies ◽  
Radio Observatory ◽  
Future Studies ◽  
New Information ◽  
Upper Limits ◽  
Widespread Phenomenon ◽  
First Time

Context. To date, only 69 pulsars have been identified with a detected pulsed radio emission below 100 MHz. A LOFAR-core LBA census and a dedicated campaign with the Nançay LOFAR station in stand-alone mode were carried out in the years 2014–2017 in order to extend the known population in this frequency range. Aims. In this paper, we aim to extend the sample of known radio pulsars at low frequencies and to produce a catalogue in the frequency range of 25–80 MHz. This will allow future studies to probe the local Galactic pulsar population, in addition to helping explain their emission mechanism, better characterising the low-frequency turnover in their spectra, and obtaining new information about the interstellar medium through the study of dispersion, scattering, and scintillation. Methods. We observed 102 pulsars that are known to emit radio pulses below 200 MHz and with declination above −30°. We used the Low Band Antennas (LBA) of the LOw Frequency ARray (LOFAR) international station FR606 at the Nançay Radio Observatory in stand-alone mode, recording data between 25 and 80 MHz. Results. Out of our sample of 102 pulsars, we detected 64. We confirmed the existence of ten pulsars detected below 100 MHz by the LOFAR LBA census for the first time (Bilous et al. 2020, A&A, 635, A75) and we added two more pulsars that had never before been detected in this frequency range. We provided average pulse profiles, DM values, and mean flux densities (or upper limits in the case of non-detections). The comparison with previously published results allows us to identify a hitherto unknown spectral turnover for five pulsars, confirming the expectation that spectral turnovers are a widespread phenomenon.

An infrared and Raman spectroscopic study of some Group 1B halide complexes containing an M4X4 core

1978 ◽  
Vol 31 (10) ◽  
pp. 2137 ◽  
Author(s):  
GA Bowmaker ◽  
RJ Knappstein ◽  
SF Tham
Keyword(s):  
Raman Spectra ◽  
Broad Band ◽  
Low Frequency ◽  
Far Infrared ◽  
Infrared And Raman Spectra ◽  
Intense Band ◽  
Raman Spectroscopic ◽  
Raman Spectroscopic Study ◽  
Halide Complexes ◽  
Far Infrared Spectra

The infrared and Raman spectra of [Et3PcuI]4 and [Et3AsCuI]4 have been measured, and bands have been assigned to vibrations of the ligand and of the Td Cu4I4 core. The far-infrared spectra show two strong T2 v(CuI) bands at about 90 and 140 cm-1, the higher frequency member of which has a Raman counterpart which shows possible longitudinal-transverse splitting. The Raman spectra also show an intense band at about 50 cm-1. Similar features have been observed in the low-frequency vibrational spectra of [Et2S]3 [CuI]4, [C5H5NcuI]4, [C5H11NAgI]4, [Et3PAgBr]4 and [Et3PagCl]4, although the last two compounds gave only a single broad band in the v(MX) region.

Low Frequency Absorption of Additively Manufactured Cylinders

2019 ◽  
Author(s):  
Sophie R. Kaye ◽  
Ethan D. Casavant ◽  
Paul E. Slaboch
Keyword(s):  
Low Frequency ◽  
Normal Incidence ◽  
Frequency Noise ◽  
Outer Diameter ◽  
Acoustic Absorption ◽  
Frequency Range ◽  
Large Space ◽  
Low Frequencies ◽  
Cylinder Length ◽  
Hollow Cylinders

Abstract Attenuating low frequencies is often problematic, due to the large space required for common absorptive materials to mitigate such noise. However, natural hollow reeds are known to effectively attenuate low frequencies while occupying relatively little space compared to traditional absorptive materials. This paper discusses the effect of varied outer diameter, and outer spacing on the 200–1600 Hz acoustic absorption of additively manufactured arrays of hollow cylinders. Samples were tested in a 10 cm diameter normal incidence impedance tube such that cylinder length was oriented perpendicular to the incoming plane wave. By varying only one geometric element of each array, the absorption due to any particular parameter can be assessed individually. The tests confirmed the hypothesis that minimizing cylinder spacing and maximizing cylinder diameter resulted in increased overall absorption and produced more focused absorption peaks at specific low frequencies. Wider cylinder spacing produced a broader absorptive frequency range, despite shifting upward in frequency. Thus, manipulating these variables can specifically target absorption for low frequency noise that would otherwise disturb listeners.

The far-infrared spectra of arsenic chalcogenides

1971 ◽  
Vol 24 (4) ◽  
pp. 697 ◽  
Author(s):  
HJ Whitfield
Keyword(s):  
Infrared Spectra ◽  
Far Infrared ◽  
Symmetry Class ◽  
Strong Band ◽  
Bending Mode ◽  
Bending Modes ◽  
Far Infrared Spectra ◽  
Class E

The far-infrared spectra of AsS, As2S3, As4Se3, and As2Se3 are reported for the range 15-400 cm-1. For As4S3 molecules, of symmetry C3v, strong bands at 370 cm-1 and 340 cm-1 arise from symmetric As-S stretching frequencies of symmetry class A1 and a strong band at 176 cm-1 arises from a S-4s-S bending mode of degenerate class E. For As2Se3, bands in the region 90-130 cm-1 are identified as Se-As-Se bending modes and bands between 200 and 280 cm-1 are due to As-Se stretching modes.

Sign in / Sign up

Export Citation Format

Share Document