scholarly journals A new era for low frequency Galactic center transient monitoring

2013 ◽  
Vol 9 (S303) ◽  
pp. 458-460
Author(s):  
N. E. Kassim ◽  
S. D. Hyman ◽  
H. Intema ◽  
T. J. W. Lazio
Keyword(s):  
Radio Astronomy ◽  
Galactic Center ◽  
Monitoring Program ◽  
Low Frequency ◽  
Frequency Range ◽  
New Era ◽  
The Impact ◽  
New System

AbstractAn upgrade of the low frequency observing system of the VLA developed by NRL and NRAO, called low band (LB), will open a new era of Galactic center (GC) transient monitoring. Our previous searches using the VLA and GMRT have revealed a modest number of radio-selected transients, but have been severely sensitivity and observing time limited. The new LB system, currently accessing the 236--492 MHz frequency range, promises ≥5 × improved sensitivity over the legacy VLA system. The new system is emerging from commissioning in time to catch any enhanced sub-GHz emission from the G2 cloud event, and we review existing limits based on recent observations. We also describe a proposed 24/7 commensal system, called the LOw Band Observatory (LOBO). LOBO offers over 100 VLA GC monitoring hours per year, possibly revealing new transients and helping validate ASTRO2010's anticipation of a new era of transient radio astronomy. A funded LOBO pathfinder called the VLA Low Frequency Ionosphere and Transient Experiment (VLITE) is under development. Finally, we consider the impact of LB and LOBO on our GC monitoring program.

Low-frequency impact sound of timber floors: A finite element–based study of conceptual designs

2020 ◽  
pp. 1351010X2091787
Author(s):  
Jörgen Olsson ◽  
Andreas Linderholt
Keyword(s):  
Finite Element ◽  
Low Frequency ◽  
Sound Transmission ◽  
Human Perception ◽  
Finite Element Simulations ◽  
Building Industry ◽  
Frequency Range ◽  
Floor Surfaces ◽  
The Impact ◽  
Selection Of

Traditionally, product development concerning acoustics in the building industry is measurement oriented. For lightweight floors, frequencies that are lower than the frequency range for heavy concrete floors are an issue. The frequency range of from 50 Hz down to 20 Hz influences the human perception of impact sound in multi-story apartment buildings with lightweight floor constructions, such as timber floors, for example. It is well known that a lower frequency range of interest makes finite element simulations more feasible. Strategies for reducing impact sound tend to be less straightforward for timber floors because they have a larger variation of designs when compared to concrete floors. This implies that reliable finite element simulations of impact sound can save time and money for the building industry. This study researches the impact sound transmission of lightweight timber floors. Frequency response functions, from forces on excitation points to sound pressure in the receiving cavity below, are calculated. By using fluid elements connected to reflection-free boundary elements under the floors in the models, the transmission and insulation can be studied without involving reverberation. A floor model with a hard screed surface will have a larger impact force than a softer floor, although this issue seems less pronounced at the lowest frequencies. To characterize floor surfaces, the point mobilities of the impact points are also calculated and presented. The vibration and sound transmission levels are dependent on the selection of the excitation points.

scholarly journals A survey of spatially and temporally resolved radio frequency interference in the FM band at the Murchison Radio-astronomy Observatory

2020 ◽  
Vol 37 ◽  
Author(s):  
S. J. Tingay ◽  
M. Sokolowski ◽  
R. Wayth ◽  
D. Ung
Keyword(s):  
Radio Frequency ◽  
Radio Astronomy ◽  
Angular Resolution ◽  
Low Frequency ◽  
Earth Orbit ◽  
Radio Frequency Interference ◽  
Astronomy Observatory ◽  
Frequency Range ◽  
Radio Astronomy Observatory ◽  
Imaging Mode

Abstract We present the first survey of radio frequency interference (RFI) at the future site of the low frequency Square Kilometre Array (SKA), the Murchison Radio-astronomy Observatory (MRO), that both temporally and spatially resolves the RFI. The survey is conducted in a 1 MHz frequency range within the FM band, designed to encompass the closest and strongest FM transmitters to the MRO (located in Geraldton, approximately 300 km distant). Conducted over approximately three days using the second iteration of the Engineering Development Array in an all-sky imaging mode, we find a range of RFI signals. We are able to categorise the signals into: those received directly from the transmitters, from their horizon locations; reflections from aircraft (occupying approximately 13% of the observation duration); reflections from objects in Earth orbit; and reflections from meteor ionisation trails. In total, we analyse 33 994 images at 7.92 s time resolution in both polarisations with angular resolution of approximately 3.5 $^{\circ}$ , detecting approximately forty thousand RFI events. This detailed breakdown of RFI in the MRO environment will enable future detailed analyses of the likely impacts of RFI on key science at low radio frequencies with the SKA.

scholarly journals Low-frequency range magnetic fields at workplaces: hygiene regulation criteria

2021 ◽  
Vol 100 (5) ◽  
pp. 436-443
Author(s):  
Yury P. Paltsev ◽  
Larisa V. Pokhodzey ◽  
Yury V. Kurilenko ◽  
Elena A. Rudneva
Keyword(s):  
Magnetic Fields ◽  
Russian Federation ◽  
Low Frequency ◽  
Frequency Range ◽  
Limit Values ◽  
Frequency Bands ◽  
Target Values ◽  
Scientific Substantiation ◽  
The Russian Federation ◽  
The Impact

Introduction. Until now, in the Russian Federation, unlike Western countries, hygienic regulations have not been developed for magnetic fields (MF) of low-frequency ranges. The aim of the study is a scientific substantiation of the threshold limit values (TLV) of magnetic fields in the range of 3 Hz - 30 kHz at workplaces. Materials and methods. A comparative analysis of domestic and foreign hygienic normative-methodical documentation regulating the TLV of magnetic fields of low-frequency ranges at workplaces is carried out. When substantiating TLV in the frequency range of 3 Hz - 30 kHz, the method of calculating the corrected value of the RMS MF strength in decadal frequency bands is used, taking into account its target values for different exposure times. Results. MF sources in the frequency range 3 Hz - 30 kHz were shown to be widely used in various areas of activity. The analysis of current domestic and foreign documents regulating the impact of MF in low-frequency bands showed the possibility of harmonizing hygienic regulations. The TLV MP in decadal frequency bands and the criteria for their hygienic assessment are scientifically substantiated. Conclusion. The studies made it possible for the first time in the Russian Federation to develop MF hygienic standards in the frequency range of 3Hz - 30 kHz at workplaces, the introduction of which into the practice of sanitary and epidemiological supervision will ensure adequate control over the electromagnetic environment and preservation of workers’ health.

Autonomic cardiovascular control in conscious mice

2000 ◽  
Vol 279 (6) ◽  
pp. R2214-R2221 ◽  
Author(s):  
Armin Just ◽  
Jörg Faulhaber ◽  
Heimo Ehmke
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Cardiovascular Control ◽  
Adrenergic Blockade ◽  
Frequency Range ◽  
Autonomic Tone ◽  
Very Low Frequency ◽  
Autonomic Blockade ◽  
Autonomic Cardiovascular Control ◽  
The Impact

Autonomic cardiovascular control was characterized in conscious, chronically catheterized mice by spectral analysis of arterial pressure (AP) and heart rate (HR) during autonomic blockade or baroreflex modulation of autonomic tone. Both spectra were similar to those obtained in humans, but at ∼10× higher frequencies. The 1/ f relation of the AP spectrum changed to a more shallow slope below 0.1–0.2 Hz. Coherence between AP and HR reached 0.5 or higher below 0.3–0.4 Hz and also above 2.5 Hz. Muscarinic blockade (atropine) or β-adrenergic blockade (atenolol) did not significantly affect the AP spectrum. Atropine reduced HR variability at all frequencies, but this effect waned above 1 Hz. β-Adrenergic blockade (atenolol) slightly enhanced the HR variability only above 1 Hz. α-Adrenergic blockade (prazosin) reduced AP variability between 0.05 and 3 Hz, most prominently at 0.15–0.7 Hz. A shift of the autonomic nervous tone by a hypertensive stimulus (phenylephrine) enhanced, whereas a hypotensive stimulus (nitroprusside) depressed AP variability at 1–3 Hz; other frequency ranges of the AP spectrum were not affected except for a reduction below 0.4 Hz after nitroprusside. Variability of HR was enhanced after phenylephrine at all frequencies and reduced after nitroprusside. As with atropine, the reduction with nitroprusside waned above 1 Hz. In conclusion, in mice HR variability is dominated by parasympathetic tone at all frequencies, during both blockade and physiological modulation of autonomic tone. There is a limitation for further reduction but not for augmentation of HR variability from the resting state above 1 Hz. The impact of HR on AP variability in mice is confined to frequencies higher than 1 Hz. Limits between frequency ranges are proposed as 0.15 Hz between VLF (very low frequency range) and LF (low frequency range) and 1.5 Hz between LF and HF (high frequency range).

Effect of Pore Morphology on the Electrochemical Properties of Electric Double Layer Carbon Cryogel Supercapacitors

2007 ◽  
Vol 1056 ◽  
Author(s):  
Betzaida Batalla Garcia ◽  
Aaron M. Feaver ◽  
Richard Champion ◽  
Qifeng Zhang ◽  
Tim T. Fister ◽  
...  
Keyword(s):  
Electrochemical Properties ◽  
Electrochemical Impedance ◽  
Porous Electrode ◽  
Low Frequency ◽  
Frequency Range ◽  
Low Frequencies ◽  
Diffusion Dynamics ◽  
Pore Size Distributions ◽  
Complex Capacitance ◽  
The Impact

ABSTRACTIn this study a group of resorcinol-formaldehyde carbon cryogels (CC) have been processed chemically, via catalysis and activation, to obtain varied nanostructures and pore size distributions. To understand the relation between structure and electrochemical properties the capacitor can be studied as a dielectric system composed of a porous electrode and the electrolyte (Tetraethylammonium tetrafluoroborate in propylene carbonate). Using Electrochemical impedance spectroscopy (EIS) the complex capacitance and power are used to study the behavior of the system below the relaxation frequency fo (φ = −45°). Therefore, the relaxation of the capacitor system at the low frequency range, f < fo, may be used as a measure of pore/electrolyte interaction. The approach here proposed also allows for a direct experimental characterization of the capacitance and power at low frequencies where small pores are likely to affect the diffusion dynamics of the electrolyte molecules. The results suggest a correlation between the occurrence of small micropores and that of high power losses that are related to the resistive element produced at the low frequency range. Moreover, the impact of the micropore structure upon the supercapacitor's performance is apparent in its capacitance and energy as well. In addition to the complex power and capacitance other measurements including BET Nitrogen sorption, cyclic voltammetry, galvanic cycling and X-Ray Raman Scattering were used to characterize the samples and support these results.

Adjustment of the Southern Ocean to Wind Forcing on Synoptic Time Scales

2005 ◽  
Vol 35 (11) ◽  
pp. 2076-2089 ◽  
Author(s):  
Wilbert Weijer ◽  
Sarah T. Gille
Keyword(s):  
Southern Ocean ◽  
Time Scales ◽  
Wind Stress ◽  
High Frequency ◽  
Low Frequency ◽  
Wind Forcing ◽  
Minor Role ◽  
Frequency Range ◽  
Free Mode ◽  
The Impact

Abstract This study addresses the response of the Southern Ocean to high-frequency wind forcing, focusing on the impact of several barotropic modes on the circumpolar transport. A suite of experiments is performed with an unstratified model of the Southern Ocean, forced with a stochastic wind stress that contains a large range of frequencies with synoptic time scales. The Southern Ocean adjustment displays a different character for frequencies below and above 0.2 cpd. The low-frequency range is dominated by an “almost-free-mode” response in the region where contours of f /H are obstructed by only a few bathymetric features; the truly free mode only plays a minor role. Topographic form stress, rather than friction, is the dominant decay mechanism of the Southern Mode. It leads to a spindown time scale on the order of 3 days. For the high-frequency range, the circumpolar transport is dominated by the resonant excitation of oscillatory modes. The “active” response of the ocean leads to strong changes and even discontinuities in the phase relation between transport and wind stress.

The Llanherne Low Frequency Radio Telescope

1972 ◽  
Vol 2 (3) ◽  
pp. 135-137 ◽  
Author(s):  
G. R. A. Ellis
Keyword(s):  
Lower Limit ◽  
Radio Telescope ◽  
Radio Astronomy ◽  
Angular Resolution ◽  
Low Frequency ◽  
Earth Satellite ◽  
The Sun ◽  
Frequency Range ◽  
Interstellar Absorption ◽  
The Galaxy

A large proportion of the easily accessible radio astronomy spectrum lies between 50 MHz and a lower limit of about 1 MHz set by interstellar absorption. The features of the spectrum in this frequency range, from sources such as the galaxy, extragalactic sources, pulsars, the Sun and Jupiter, remain only partially explored mainly owing to the large sizes of telescopes necessary to obtain adequate angular resolution and sensitivity. In addition, below 20 MHz, interference from man-made radiation and from the ionosphere severely hinders observations. At the lowest frequencies, the effects of the ionosphere can be overcome by using earth satellite telescopes at the expense of greatly increased difficulty in attaining sufficient telescope aperture.

Measurement of CIELAB spatio-chromatic contrast sensitivity in different spatial and chromatic directions

2019 ◽  
Vol 2019 (1) ◽  
pp. 326-330
Author(s):  
Vlado Kitanovski ◽  
Alastair Reed ◽  
Kristyn Falkenstern ◽  
Marius Pedersen
Keyword(s):  
Contrast Sensitivity ◽  
Low Frequency ◽  
Published Data ◽  
Psychophysical Experiment ◽  
Frequency Range ◽  
Chromatic Contrast ◽  
Vertical Orientation ◽  
Spatial Frequencies ◽  
The Impact ◽  
Chromatic Contrast Sensitivity

This paper presents data on CIELAB chromatic contrast sensitivity collected in a psychophysical experiment. To complement previously published data in the low-frequency range, we selected five spatial frequencies in the range from 2.4 to 19.1 cycles per degree (cpd). A Gabor stimulus was modulated along six chromatic directions in the a*-b* plane. We also investigated the impact on contrast sensitivity from spatial orientations – both vertically and diagonally oriented stimuli were used. The analysis of the collected data showed lowest contrast sensitivity in the chromatic direction of around 120° from the positive a*-axis. The contrast sensitivity in the diagonal spatial orientation is slightly lower when compared to the vertical orientation.

scholarly journals CREATION AND APPROBATION OF A LOW-FREQUENCY RADIO ASTRONOMY ANTENNA FOR STUDIES OF OBJECTS OF THE UNIVERSE FROM THE MOON'S FARSIDE

2021 ◽  
Vol 26 (3) ◽  
pp. 197-210
Author(s):  
I. N. Bubnov ◽  
◽  
O. O. Konovalenko ◽  
P. L. Tokarsky ◽  
O. M. Korolev ◽  
...  
Keyword(s):  
Radio Astronomy ◽  
Environmental Conditions ◽  
Low Frequency ◽  
Low Noise ◽  
Low Noise Amplifier ◽  
Experimental Measurements ◽  
Active Antenna ◽  
Frequency Range ◽  
The Earth ◽  
Noise Amplifier

Purpose: Theoretical and experimental studies of the active antenna – an element of the low-frequency radio telescope antenna array for the future observatory on the farside of the Moon. Design/methodology/approach: To study the active antenna, consisting of a complex-shaped dipole and a low-noise amplifier, we used its mathematical model in the form of a two-port network, whose electrical parameters are set by the scattering matrix, the noise parameters being set by the covariance matrix of the spectral densities of noise waves. This model allows ma[1]king the correct analysis of the signal-to-noise ratio at the active antenna output with account for the external and internal noise sources. The modelling results were compared with those of experimental measurements of antenna characteristics. A series of radio astronomy observations were made with the developed antenna under the Earth environmental conditions. Findings: A numerical analysis of the radio telescope active antenna parameters has been made in a wide frequency range of 4–40 MHz. Two versions of the low-noise amplifier were developed to operate in the active antenna under the space and Earth environmental conditions. Under the Earth conditions, it has been experimentally proven that the range of problems, which such radio telescopes can effectively solve at low frequencies, is quite wide – from the solar research to the search for cosmological effects. Conclusions: The results of numerical simulations and experimental measurements obtained in this work have shown a satisfactory agreement between them for the most of the frequency range. The results of this work can be useful in the research and development of active antennas designed for operation at the decameter and hectometer wavelength ranges, particularly those intended for using under the space environmental conditions. Keywords: active antenna, Moon, radio astronomy observations, sensitivity

scholarly journals Vibration Isolation of a Rubber-Concrete Alternating Superposition In-Filled Trench for Train-Induced Environmental Vibration Based on 2.5D Indirect Boundary Element Method

2021 ◽  
Vol 9 ◽  
Author(s):  
Liguo Jin ◽  
Jingya Wang ◽  
Xujin Liu ◽  
Qiangqiang Li ◽  
Zhenghua Zhou
Keyword(s):  
Elastic Waves ◽  
High Speed ◽  
Vibration Isolation ◽  
Soft Soil ◽  
Low Frequency ◽  
Isolation Effect ◽  
High Speed Train ◽  
Frequency Range ◽  
The Impact ◽  
Rubber Concrete

A new train-induced vibration isolation measure of rubber-concrete alternating superposition in-filled trench is presented in this paper. For analyzing the vibration isolation effect of the new measure, this paper establishes a 2.5D train-track-layered foundation-filled trench model to analyze the dynamics of track and layered foundation with the in-filled trench. The correctness of the model is verified by using the measured data of the Sweden X-2000 high-speed train. The vibration isolation effect of the rubber-concrete alternating superposition in-filled trench is calculated by using the actual soft soil foundation parameters of the X-2000 high-speed train, and the vibration isolation effect is also compared with that of the empty trench, rubber in-filled trench, and concrete in-filled trench. The results show that the vibration isolation effect of the rubber-concrete alternating superposition in-filled trench proposed in this paper is better than that of the C30 concrete in-filled trench, especially the impact on displacement. Compared with low-frequency vibrations generated by the lower train speed, the rubber-concrete alternating superposition in-filled trench has a better vibration isolation effect on high-frequency vibrations caused by higher-speed trains. The rubber-concrete alternately superposition in-filled trench has the frequency band characteristics of elastic waves. Elastic waves in the passband frequency range can propagate without attenuation, while the elastic waves in the forbidden frequency range will be filtered out.

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