IPM and ISM Coherence and Polarization Effects on Observations With Low-Frequency Space Arrays

1996 ◽  
Vol 111 ◽  
pp. 2465 ◽  
Author(s):  
R. P. Linfield
Keyword(s):  
Low Frequency ◽  
Polarization Effects ◽  
Frequency Space

The Low Frequency Space Array (LFSA)

1988 ◽  
pp. 459-460 ◽  
Author(s):  
K. W. Weiler ◽  
B. K. Dennisonz ◽  
K. J. Johnston ◽  
R. S. Simon ◽  
J. H. Spencer ◽  
...  
Keyword(s):  
Low Frequency ◽  
Frequency Space

Low frequency conductivity in monolayer graphene model with partial unfolding of Dirac bands

2016 ◽  
Vol 30 (13) ◽  
pp. 1642009
Author(s):  
H. V. Grushevskaya ◽  
G. G. Krylov
Keyword(s):  
Gauge Theory ◽  
Low Frequency ◽  
Charge Carriers ◽  
Monolayer Graphene ◽  
Dirac Cone ◽  
Polarization Effects ◽  
Graphene Doping ◽  
Partial Unfolding ◽  
Quantized Field

A secondary quantized field gauge theory with a number of flavors [Formula: see text] has been proposed to describe monolayer graphene. Charge carriers in this graphene model are Majorana pseudo-fermions. Partial unfolding of Dirac bands proceeds from coupling between anti-ordered pseudo-spins and valley currents. Splitting of Dirac cone replicas on Weyl-like node and anti-node leads to polarization effects analogous to graphene doping.

Analysis of turbulence power spectra and velocity correlations in a pipeline with obstructions

2017 ◽  
Vol 28 (02) ◽  
pp. 1750019 ◽  
Author(s):  
A. T. da Cunha Lima ◽  
I. C. da Cunha Lima ◽  
M. P. de Almeida
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Cross Sections ◽  
Power Spectra ◽  
Low Frequency ◽  
Frequency Range ◽  
Frequency Space ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Low Frequency Power

We calculate the power spectral density and velocity correlations for a turbulent flow of a fluid inside a duct. Turbulence is induced by obstructions placed near the entrance of the flow. The power spectral density is obtained for several points at cross-sections along the duct axis, and an analysis is made on the way the spectra changes according to the distance to the obstruction. We show that the differences on the power spectral density are important in the lower frequency range, while in the higher frequency range, the spectra are very similar to each other. Our results suggest the use of the changes on the low frequency power spectral density to identify the occurrence of obstructions in pipelines. Our results show some frequency regions where the power spectral density behaves according to the Kolmogorov hypothesis. At the same time, the calculation of the power spectral densities at increasing distances from the obstructions indicates an energy cascade where the spectra evolves in frequency space by spreading the frequency amplitude.

scholarly journals NUMERICAL WAVE FIELDS QUASISTATIC MODELING IN FLUID-FILLED POROELASTIC MEDIA

2021 ◽  
Vol 2 (2) ◽  
pp. 298-311
Author(s):  
Sergey A. Solovyev ◽  
Vadim V. Lisitsa
Keyword(s):  
Temporal Frequency ◽  
Low Frequency ◽  
Wide Frequency Range ◽  
Algebraic Equations ◽  
Static State ◽  
Frequency Space ◽  
Poroelastic Media ◽  
Poroelastic Materials ◽  
Linear Algebraic Equations ◽  
Dependent Strain

This paper presents a numerical algorithm to simulate low-frequency loading of fluid-filled poroelastic materials and estimate the effective frequency-dependent strain-stress relations for such media. The algorithm solves Biot equation in quasi-static state in the frequency space. As a result a system of linear algebraic equations have to be solved for each temporal frequency. We use the direct solver, based on the $LU$ decomposition to resolve the SLAE. According to the presented numerical examples the suggested algorithm allows reconstructing the stiffness tensor within a wide Frequency range.

scholarly journals Removing low-frequency artefacts from Datawell DWR-G4 wave buoy measurements

2015 ◽  
Vol 5 (2) ◽  
pp. 363-383
Author(s):  
J.-V. Björkqvist ◽  
H. Pettersson ◽  
L. Laakso ◽  
K. K. Kahma ◽  
H. Jokinen ◽  
...  
Keyword(s):  
Time Series ◽  
Power Law ◽  
Low Frequency ◽  
Vertical Displacement ◽  
Correction Method ◽  
Wave Spectra ◽  
Maximum Frequency ◽  
Simple Method ◽  
Frequency Space ◽  
Buoy Measurements

Abstract. In this study we describe a previously unreported error in the vertical displacement time series made with GPS-based Datawell DWR-G4 wave buoys and introduce a simple method to correct the resulting wave spectra. The artefact in the time series is found to resemble a sawtooth wave, which produces an erroneous trend following an f−2 power law in frequency space. The correction method quantifies the amount of erroneous trend below a certain maximum frequency and removes the spurious energy from all frequencies assuming the above mentioned f−2 power law. The presented correction method is validated against an experimental field test and its impact on the measured significant wave height is quantified. The method's sensitivity to the choice of the maximum frequency is also briefly discussed.

scholarly journals On the Effectiveness of Low Frequency Perturbations

2019 ◽  
Author(s):  
Yash Sharma ◽  
Gavin Weiguang Ding ◽  
Marcus A. Brubaker
Keyword(s):  
High Frequency ◽  
State Of The Art ◽  
Low Frequency ◽  
Human Perception ◽  
Search Space ◽  
Frequency Space ◽  
Performance Improvements ◽  
Frequency Regime ◽  
Frequency Components ◽  
Norm Constraint

Carefully crafted, often imperceptible, adversarial perturbations have been shown to cause state-of-the-art models to yield extremely inaccurate outputs, rendering them unsuitable for safety-critical application domains. In addition, recent work has shown that constraining the attack space to a low frequency regime is particularly effective. Yet, it remains unclear whether this is due to generally constraining the attack search space or specifically removing high frequency components from consideration. By systematically controlling the frequency components of the perturbation, evaluating against the top-placing defense submissions in the NeurIPS 2017 competition, we empirically show that performance improvements in both the white-box and black-box transfer settings are yielded only when low frequency components are preserved. In fact, the defended models based on adversarial training are roughly as vulnerable to low frequency perturbations as undefended models, suggesting that the purported robustness of state-of-the-art ImageNet defenses is reliant upon adversarial perturbations being high frequency in nature. We do find that under L-inf-norm constraint 16/255, the competition distortion bound, low frequency perturbations are indeed perceptible. This questions the use of the L-inf-norm, in particular, as a distortion metric, and, in turn, suggests that explicitly considering the frequency space is promising for learning robust models which better align with human perception.

Very large antenna for low frequency space-borne SAR

2012 ◽  
Author(s):  
S. Khureim Castiglioni ◽  
J. Lorenzo ◽  
E. Labiole ◽  
S. Pouyez ◽  
Y. Baudasse ◽  
...  
Keyword(s):  
Low Frequency ◽  
Frequency Space
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