Journal articles: 'THz quasi time domain'

1

Gente, Ralf, Arno Rehn, Thorsten Probst, Eva-Maria Stübling, Enrique Castro Camus, Alejandra A. Covarrubias, Jan C. Balzer, and Martin Koch. "Outdoor Measurements of Leaf Water Content Using THz Quasi Time-Domain Spectroscopy." Journal of Infrared, Millimeter, and Terahertz Waves 39, no. 10 (July 17, 2018): 943–48. http://dx.doi.org/10.1007/s10762-018-0520-4.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Demsar, J. "Non-equilibrium Phenomena in Superconductors Probed by Femtosecond Time-Domain Spectroscopy." Journal of Low Temperature Physics 201, no. 5-6 (April 29, 2020): 676–709. http://dx.doi.org/10.1007/s10909-020-02461-y.

Full text

Abstract:

AbstractDevelopment of ultrafast lasers and nonlinear optical techniques over the last two decades provides tools to access real-time dynamics of low energy excitations in superconductors. For example, time-resolved THz spectroscopy and time- and angular-resolved photoemission spectroscopy provide access to the real-time dynamics of the superconducting gap amplitude. Such studies enable determination of microscopic parameters like quasi-particle recombination rates, pair-breaking rates and electron–boson coupling constants. Recently, intense THz pulses have been used to probe the nonlinear dynamics, including observation of collective modes. Moreover, using low-frequency electromagnetic pulses, there are several reports of amplification of superconductivity in both conventional and unconventional superconductors. Starting with a brief historical overview of the pioneering work, where non-equilibrium phenomena in superconductors were investigated using quasi-continuous excitation, we review some of the insights that are provided by using real-time approaches. We focus on conventional BCS superconductors, whose ground state is reasonably well understood, and address similarities and open questions related to the corresponding studies in high-$${T}_{c}$$ T c superconductors.

APA, Harvard, Vancouver, ISO, and other styles

3

Bergen, Mark H., and Jonathan F. Holzman. "Terahertz Time-Domain Spectroscopy for Ultrafast and Quasi-Static Characterizations of Germanium." IEEE Transactions on Terahertz Science and Technology 11, no. 1 (January 2021): 54–61. http://dx.doi.org/10.1109/tthz.2020.3013101.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Singh, Khushboo, Aparajita Bandyopadhyay, and Amartya Sengupta. "Physics of effective media in plastic polymer-composites using THz Time-Domain Spectroscopy." Journal of Physics D: Applied Physics 55, no. 9 (November 19, 2021): 095303. http://dx.doi.org/10.1088/1361-6463/ac3700.

Full text

Abstract:

Abstract Polymer composites have been an integral part of our lives for centuries and their applicability has increased substantially with recent technological advancements. However, with the vast range of available fillers and polymer materials, it is crucial to have a priori knowledge of the physical and chemical properties of the materials for various applications. Hence, material characterization at different stages of production is one of the most important parts of product development and quality control. In this article, we have probed the optical behavior of a few polymer composites, with absorptive and dispersive guests, using THz time-domain spectroscopy. Subsequently, we used quasi-static effective medium theory to investigate the impact of absorptive and dispersive filler materials on the optical properties of the composites. This enables us to address the significance of filler properties on the detection limits of real-life composite compounds.

APA, Harvard, Vancouver, ISO, and other styles

5

Rehn, Arno, Mikhail Mikerov, Sascha Preu, Martin Koch, and Jan C. Balzer. "Enhancing the performance of THz quasi time-domain spectroscopy systems by low duty cycle laser operation." Optics Express 26, no. 25 (November 29, 2018): 32758. http://dx.doi.org/10.1364/oe.26.032758.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Nakagawa, Hiroshi, and Naoki Yamamoto. "Incoherent Neutron Scattering and Terahertz Time-Domain Spectroscopy on Protein and Hydration Water." Life 13, no. 2 (January 23, 2023): 318. http://dx.doi.org/10.3390/life13020318.

Full text

Abstract:

Incoherent inelastic and quasi-elastic neutron scattering (INS) and terahertz time-domain spectroscopy (THz-TDS) are spectroscopy methods that directly detect molecular dynamics, with an overlap in the measured energy regions of each method. Due to the different characteristics of their probes (i.e., neutron and light), the information obtained and the sample conditions suitable for each method differ. In this review, we introduce the differences in the quantum beam properties of the two methods and their associated advantages and disadvantages in molecular spectroscopy. Neutrons are scattered via interaction with nuclei; one characteristic of neutron scattering is a large incoherent scattering cross-section of a hydrogen atom. INS records the auto-correlation functions of atomic positions. By using the difference in neutron scattering cross-sections of isotopes in multi-component systems, some molecules can be selectively observed. In contrast, THz-TDS observes the cross-correlation function of dipole moments. In water-containing biomolecular samples, the absorption of water molecules is particularly large. While INS requires large-scale experimental facilities, such as accelerators and nuclear reactors, THz-TDS can be performed at the laboratory level. In the analysis of water molecule dynamics, INS is primarily sensitive to translational diffusion motion, while THz-TDS observes rotational motion in the spectrum. The two techniques are complementary in many respects, and a combination of the two is very useful in analyzing the dynamics of biomolecules and hydration water.

APA, Harvard, Vancouver, ISO, and other styles

7

Liu, Xiankuan, Jiadong Zhang, Zeyu Zhang, Xian Lin, Yang Yu, Xiao Xing, Zuanming Jin, Zhenxiang Cheng, and Guohong Ma. "Thermodynamics of quasi-2D electron gas at BFO/Si interface probed with THz time-domain spectroscopy." Applied Physics Letters 111, no. 15 (October 9, 2017): 152906. http://dx.doi.org/10.1063/1.4989667.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Bron, Walter E., Arnold Guerra, and Carlos Suárez. "Quasi-electron and phonon interactions in the femtosecond time domain." Journal of Luminescence 76-77 (February 1998): 518–25. http://dx.doi.org/10.1016/s0022-2313(97)00162-2.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Tehrani, Ali Moradi, Evert Slob, and Wim Mulder. "Quasi-analytical method for frequency-to-time conversion in CSEM applications." GEOPHYSICS 77, no. 5 (September 1, 2012): E357—E363. http://dx.doi.org/10.1190/geo2011-0432.1.

Full text

Abstract:

Frequency-to-time transformations are of interest to controlled-source electromagnetic methods when time-domain data are inverted for a subsurface resistivity model by numerical frequency-domain modeling at a selected, small number of frequencies whereas the data misfit is determined in the time domain. We propose an efficient, Prony-type method using frequency-domain diffusive-field basis functions for which the time-domain equivalents are known. Diffusive fields are characterized by an exponential part whose argument is proportional to the square root of frequency and a part that is polynomial in integer powers of the square root of frequency. Data at a limited number of frequencies suffice for the transformation back to the time. In the exponential part, several diffusion-time values must be chosen. Once a suitable range of diffusion-time values are found, the method is quite robust in the number of values used. The highest power in the polynomial part can be determined from the source and receiver type. When the frequency-domain data are accurately approximated by the basis functions, the time-domain result is also accurate. This method is accurate over a wider time range than other methods and has the correct late-time asymptotic behavior. The method works well for data computed for layered and 3D subsurface models.

APA, Harvard, Vancouver, ISO, and other styles

10

Krug, F., S. Braun, and P. Russer. "A novel quasi-peak-detector for time-domain EMI-measurements." Advances in Radio Science 2 (May 27, 2005): 27–32. http://dx.doi.org/10.5194/ars-2-27-2004.

Full text

Abstract:

Abstract. In this paper, an advanced ultra-fast, broadband time domain EMI measurement system is described. Measurements were performed in the 30–1000MHz range. The digital signal processing of EMI measurements allows to emulate in real-time the modes of conventional analogous equipment, e.g. Peak-, Average-, RMS- and Quasi-Peak- Detector. With the presented time domain measurement system the measurement time can be reduced by a factor of 10. A novel signal recording routine for time-domain EMI (TDEMI) measurements and Quasi-Peak-Detection is described. Measurement results obtained from the investigation of a drillmachine, monitor and laptop obtained with the timedomain electromagnetic interference (TDEMI) measurement system are discussed. The results obtained with the described system have been compared with measurements performed with a conventional EMI receiver.

APA, Harvard, Vancouver, ISO, and other styles

11

Jaehoon Jeong, Ic-Pyo Hong, and R. Nevels. "The Time Domain Propagator Method for Lossless Multiconductor Quasi-TEM Lines." IEEE Transactions on Advanced Packaging 32, no. 3 (August 2009): 619–26. http://dx.doi.org/10.1109/tadvp.2009.2022016.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Bai, Peng, Giulio Vignoli, Andrea Viezzoli, Jouni Nevalainen, and Giuseppina Vacca. "(Quasi-)Real-Time Inversion of Airborne Time-Domain Electromagnetic Data via Artificial Neural Network." Remote Sensing 12, no. 20 (October 20, 2020): 3440. http://dx.doi.org/10.3390/rs12203440.

Full text

Abstract:

The possibility to have results very quickly after, or even during, the collection of electromagnetic data would be important, not only for quality check purposes, but also for adjusting the location of the proposed flight lines during an airborne time-domain acquisition. This kind of readiness could have a large impact in terms of optimization of the Value of Information of the measurements to be acquired. In addition, the importance of having fast tools for retrieving resistivity models from airborne time-domain data is demonstrated by the fact that Conductivity-Depth Imaging methodologies are still the standard in mineral exploration. In fact, they are extremely computationally efficient, and, at the same time, they preserve a very high lateral resolution. For these reasons, they are often preferred to inversion strategies even if the latter approaches are generally more accurate in terms of proper reconstruction of the depth of the targets and of reliable retrieval of true resistivity values of the subsurface. In this research, we discuss a novel approach, based on neural network techniques, capable of retrieving resistivity models with a quality comparable with the inversion strategy, but in a fraction of the time. We demonstrate the advantages of the proposed novel approach on synthetic and field datasets.

APA, Harvard, Vancouver, ISO, and other styles

13

Bonnefoy, Florent, Maxime Bernier, Etienne Perret, Nicolas Barbot, Romain Siragusa, David Hely, Eiji Kato, and Frederic Garet. "Video-Rate Identification of High-Capacity Low-Cost Tags in the Terahertz Domain." Sensors 21, no. 11 (May 26, 2021): 3692. http://dx.doi.org/10.3390/s21113692.

Full text

Abstract:

In this article, we report on video-rate identification of very low-cost tags in the terahertz (THz) domain. Contrary to barcodes, Radio Frequency Identification (RFID) tags, or even chipless RFID tags, operate in the Ultra-Wide Band (UWB). These THz labels are not based on a planar surface pattern but are instead embedded, thus hidden, in the volume of the product to identify. The tag is entirely made of dielectric materials and is based on a 1D photonic bandgap structure, made of a quasi-periodic stack of two different polyethylene-based materials presenting different refractive indices. The thickness of each layer is of the order of the THz wavelength, leading to an overall tag thickness in the millimetre range. More particularly, we show in this article that the binary information coded within these tags can be rapidly and reliably identified using a commercial terahertz Time Domain Spectroscopy (THz-TDS) system as a reader. More precisely, a bit error rate smaller than 1% is experimentally reached for a reading duration as short as a few tens of milliseconds on an 8 bits (~40 bits/cm2) THID tag. The performance limits of such a tag structure are explored in terms of both dielectric material properties (losses) and angular acceptance. Finally, realistic coding capacities of about 60 bits (~300 bits/cm2) can be envisaged with such tags.

APA, Harvard, Vancouver, ISO, and other styles

14

Senba, Takasi, and Takasi Suzuki. "A quasi-linear parabolic system of chemotaxis." Abstract and Applied Analysis 2006 (2006): 1–21. http://dx.doi.org/10.1155/aaa/2006/23061.

Full text

Abstract:

We consider a quasi-linear parabolic system with respect to unknown functionsuandvon a bounded domain ofn-dimensional Euclidean space. We assume that the diffusion coefficient ofuis a positive smooth functionA(u), and that the diffusion coefficient ofvis a positive constant. IfA(u)is a positive constant, the system is referred to as so-called Keller-Segel system. In the case where the domain is a bounded domain of two-dimensional Euclidean space, it is shown that some solutions to Keller-Segel system blow up in finite time. In three and more dimensional cases, it is shown that solutions to so-called Nagai system blow up in finite time. Nagai system is introduced by Nagai. The diffusion coefficients of Nagai system are positive constants. In this paper, we describe that solutions to the quasi-linear parabolic system exist globally in time, if the positive functionA(u)rapidly increases with respect tou.

APA, Harvard, Vancouver, ISO, and other styles

15

El Bouajaji, M., B. Thierry, X. Antoine, and C. Geuzaine. "A quasi-optimal domain decomposition algorithm for the time-harmonic Maxwell's equations." Journal of Computational Physics 294 (August 2015): 38–57. http://dx.doi.org/10.1016/j.jcp.2015.03.041.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Golitsyna, Olga M., and Sergey N. Drozhdin. "Formation of a quasi-equilibrium domain structure of crystals of the TGS group near TC." Kondensirovannye sredy i mezhfaznye granitsy = Condensed Matter and Interphases 23, no. 4 (November 24, 2021): 507–17. http://dx.doi.org/10.17308/kcmf.2021.23/3669.

Full text

Abstract:

In the temperature range ΔT ≈ 321 K ÷ 322 K, the kinetics of the nonequilibrium domain structure of triglycine sulphate crystals, both pure and with specially introduced defects, has been studied by means of piezoresponse force microscopy technique. The temporal change in the domain structure as a set of regions with a scalar order parameter of P (r, t) = +1 and −1 for oppositely polarized domains was analysed by the behaviour of the space-time correlation function C(r,t) = ·Р(r,t)Р(0,t)Ò. At different distances from the Curie point Tc, the characteristic length Lc, as a scale measure of the average domain size, increases with time according to the power law Lc(t)~(t−t0)a. A decrease of the exponent a with distance from Tc can be a consequence of the transition of the domain structure of TGS crystals from a non-conservative state to aconservative one.

APA, Harvard, Vancouver, ISO, and other styles

17

Huang, Sheng Bo, Yu Cang Wen, Wen Ye, and Tong Liang Fan. "A Simplified Time-Domain Channel Estimation Approach for OFDM System." Applied Mechanics and Materials 738-739 (March 2015): 1111–14. http://dx.doi.org/10.4028/www.scientific.net/amm.738-739.1111.

Full text

Abstract:

OFDM usually incorporates pilot tones in the frequency domain (FD) or training symbols in the time-domain (TD) to facilitate channel estimation algorithms. TD channel estimation becomes more attractive in quasi-static channels because channel estimation scheme will optimize the spectral efficiency by re-using the training symbols designated for FD channel estimation. A channel estimation method based on time domain averaging algorithm is proposed. Due to the principle of centralized energy in time domain, the effective channel impulse response length can be detected by setting of threshold for the estimated channel impulse response length. Computer simulation demonstrates the performance of the proposed algorithms in terms of bit error rate performance.

APA, Harvard, Vancouver, ISO, and other styles

18

Ozakin, Mehmet Burak, and Serkan Aksoy. "Application of Magneto-Quasi-Static Approximation in the Finite Difference Time Domain Method." IEEE Transactions on Magnetics 52, no. 8 (August 2016): 1–9. http://dx.doi.org/10.1109/tmag.2016.2535415.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

De Moerloose, Jan, Trevor W. Dawson, and Maria A. Stuchly. "Application of the finite difference time domain algorithm to quasi-static field analysis." Radio Science 32, no. 2 (March 1997): 329–41. http://dx.doi.org/10.1029/96rs03690.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Steib, Imola, Sándor Nagy, and János Polonyi. "Renormalization in Minkowski space–time." International Journal of Modern Physics A 36, no. 05 (February 20, 2021): 2150031. http://dx.doi.org/10.1142/s0217751x21500317.

Full text

Abstract:

The multiplicative and the functional renormalization group methods are applied for the four-dimensional scalar theory in Minkowski space–time. It is argued that the appropriate choice of the subtraction point is more important in Minkowski than in Euclidean space–time. The parameters of the cutoff theory, defined by a subtraction point in the quasi-particle domain, are complex due to the mass-shell contributions and the renormalization group flow becomes much more involved than its Euclidean counterpart.

APA, Harvard, Vancouver, ISO, and other styles

21

Boccotti, Paolo. "Field verification of quasi-determinism theory for wind waves in the space–time domain." Ocean Engineering 38, no. 13 (September 2011): 1503–7. http://dx.doi.org/10.1016/j.oceaneng.2011.07.015.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Gimperlein, Heiko, Ceyhun Özdemir, David Stark, and Ernst P. Stephan. "hp-version time domain boundary elements for the wave equation on quasi-uniform meshes." Computer Methods in Applied Mechanics and Engineering 356 (November 2019): 145–74. http://dx.doi.org/10.1016/j.cma.2019.07.018.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

VANHILLE, CHRISTIAN, and CLEOFÉ CAMPOS-POZUELO. "THREE TIME-DOMAIN COMPUTATIONAL MODELS FOR QUASI-STANDING NONLINEAR ACOUSTIC WAVES, INCLUDING HEAT PRODUCTION." Journal of Computational Acoustics 14, no. 02 (June 2006): 143–56. http://dx.doi.org/10.1142/s0218396x06002986.

Full text

Abstract:

Applications of high-amplitude acoustic or ultrasonic waves in industrial processing require a good knowledge of the nonlinear pressure field, as well as the heat produced by the wave. In this article a new time-domain algorithm solving a second-order nonlinear wave equation written in Lagrangian coordinates and valid for any fluid is presented. The new model is compared with two others which were previously developed, corresponding to the two other possible physical approaches. This paper discusses the limits of application of every approach and the suitability of every one to model nonlinear acoustic waves in resonators. Conclusions about the applicability of the physical models are given. The time-domain character of the models allows the development of a new algorithm to calculate the temperature evolution inside a resonator due to acoustic losses. This algorithm is presented here and applied to strongly nonlinear waves for which the nonlinear attenuation is dominant. Several kinds of time functions for excitation can be considered in the models. The strongly nonlinear resonator response to a short pulsed signal is analyzed to show the efficiency of the time-domain numerical model.

APA, Harvard, Vancouver, ISO, and other styles

24

PUYESKY, I., and I. FRANKEL. "The motion of a dipolar spherical particle in homogeneous shear and time-periodic fields." Journal of Fluid Mechanics 369 (August 25, 1998): 191–216. http://dx.doi.org/10.1017/s0022112098001724.

Full text

Abstract:

The effects of the intensity and frequency of a time-periodic external field on the rotary motion of a dipolar spherical particle suspended in homogeneous shear are studied with the goal of providing insight into problems concerning the motion of swimming microorganisms and the macroscopic behaviour of ferrofluids. The analysis reveals two modes of motion: convergence of the particle to a global time-periodic attractor, and quasi-periodic motion. The former mode of particle rotation generally appears for sufficiently strong fields. However, asymptotic analysis clarifies that it may occur even for very weak fields as a cumulative result of appropriate resonance interactions.A sufficient condition for the occurrence of a global time-periodic attractor is established for an external field acting in the plane of shear. Asymptotic results together with numerical evidence indicate that this condition is in fact a necessary condition as well. Making use of this condition we obtain the division of the plane of parameters into domains respectively corresponding to quasi-periodic motion and global time-periodic attractors. The latter domain has the structure of non-intersecting Arnold's tongues. Throughout each, the average frequency of dipole rotation about the vorticity vector is a constant (integral) multiple of the forcing frequency (frequency locking). In the case of quasi-periodic motion, there simultaneously coexist separate domains in orientation space where the rotary motion is locally characterized by different constant rotation numbers. These may assume both rational and irrational values. Potential implications of the distinction between these modes of rotary motion on the characterization of effective (macroscale) ferrofluid properties are briefly discussed.

APA, Harvard, Vancouver, ISO, and other styles

25

Qian, TianTian, and ShiHong Miao. "Discrete-Time Nonlinear Control of VSC-HVDC System." Mathematical Problems in Engineering 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/929467.

Full text

Abstract:

Because VSC-HVDC is a kind of strong nonlinear, coupling, and multi-input multioutput (MIMO) system, its control problem is always attracting much attention from scholars. And a lot of papers have done research on its control strategy in the continuous-time domain. But the control system is implemented through the computer discrete sampling in practical engineering. It is necessary to study the mathematical model and control algorithm in the discrete-time domain. The discrete mathematical model based on output feedback linearization and discrete sliding mode control algorithm is proposed in this paper. And to ensure the effectiveness of the control system in the quasi sliding mode state, the fast output sampling method is used in the output feedback. The results from simulation experiment in MATLAB/SIMULINK prove that the proposed discrete control algorithm can make the VSC-HVDC system have good static, dynamic, and robust characteristics in discrete-time domain.

APA, Harvard, Vancouver, ISO, and other styles

26

Han, Feiyan, Juan Wei, Bin Feng, and Wu Zhang. "A High-Efficiency Impeller Channel Quasi-Triangular Tool Path Planning Method Based on Template Trajectory Mapping." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 36, no. 6 (December 2018): 1216–23. http://dx.doi.org/10.1051/jnwpu/20183661216.

Full text

Abstract:

The manufacturing technology of an integral impeller is an important indicator for measuring the manufacturing capability of a country. Its manufacturing process involves complex free-form surface machining, a time consuming and error-prone process, and the tool path planning is considered as a critical issue of free-form surface machining but still lacks a systematic solution. In this paper, aiming at the tool path planning of the impeller channel, a quasi-triangular tool path planning method based on parametric domain template trajectory mapping is proposed. The main idea is to map the template trajectory to physical domain by using the mapping model of parametric domain to the physical domain to obtain the actual machining path. Firstly, the trajectory mapping model of parametric domain to physical domain is established using the morphing technique, and the template trajectory mapping method in the parametric domain is given. Secondly, the clean-up boundary of the impeller channel is determined in the parametric domain, and the quasi-triangular template trajectory of the impeller channel is defined. Finally, taking a certain type of impeller as an example, the quasi-triangular tool path of the impeller channel is calculated, and the tool path calculation time of this method is compared with that of the traditional isometric offset method. The result shows that the computational efficiency is improved by 45% with this method, which provides a new method for the rapid acquisition of NC machining tool path for impeller channels. In addition, the simulation and actual machining are carried out, the results show that the shape of actual cutting traces on the surface of the impeller channel is quasi-triangular, showing that this method is effective and feasible.

APA, Harvard, Vancouver, ISO, and other styles

27

Kim, Minhyuk, and SangWook Park. "Modified Finite-Difference Time-Domain Method for Hertzian Dipole Source under Low-Frequency Band." Electronics 10, no. 22 (November 9, 2021): 2733. http://dx.doi.org/10.3390/electronics10222733.

Full text

Abstract:

In this paper, a modified finite-difference time-domain (FDTD) method is proposed for the rapid analysis of a Hertzian dipole source in the low-frequency band. The FDTD technique is one of the most widely used methods for interpreting high-resolution problems such as those associated with the human body. However, this method has been difficult to use in the low-frequency band as the required number of iterations has increased significantly in such cases. To avoid this problem, FDTD techniques using quasi-static assumptions in low-frequency bands were used. However, this method was applied only to plane wave excitation, making it difficult to apply to near-field problems. Therefore, a modified approach is proposed, involving the application of the FDTD technique with a quasi-static approximation to an electric and magnetic dipole problem. The results when using the proposed method are in good agreement with those from a theoretical solution. An example of comparison with the standard FDTD method is shown for illustrating the proposed method’s performance.

APA, Harvard, Vancouver, ISO, and other styles

28

REZAI-RAD, GHOLAMALI, and AHMAD CHELDAVI. "DISCRETE TIME-DOMAIN ANALYSIS OF NONUNIFORM LOSSLESS COUPLED TRANSMISSION LINES." Journal of Circuits, Systems and Computers 14, no. 05 (October 2005): 973–86. http://dx.doi.org/10.1142/s0218126605002763.

Full text

Abstract:

In this paper, a discrete time-domain method to analyze multiple coupled nonuniform lossless transmission lines has been presented. The solution is based on the steplines approximation of the nonuniform transmission lines and quasi-TEM assumptions. Using steplines approximation, the system of coupled nonuniform transmission lines is decomposed into a large number of coupled steplines with different characteristics. Then, using modal decomposition method, the system of coupled partial differential equations for each step is decomposed to a set of uncoupled ordinary wave equation. Using time-domain approach and invoking the boundary condition at the discontinuities of the adjacent steps, each step is modeled as continuous time linear filter characterized by a time-domain transfer matrix. Finally, this continuous time linear filter (for band limited input signal), is modeled as a discrete time-domain linear filter with constant matrix coefficients using sampling theorem. The method proposed here can be implemented using general purpose software packages like MATLAB.

APA, Harvard, Vancouver, ISO, and other styles

29

Qu, Yingming, Jianping Huang, Zhenchun Li, Zhe Guan, and Jinli Li. "Attenuation compensation in anisotropic least-squares reverse time migration." GEOPHYSICS 82, no. 6 (November 1, 2017): S411—S423. http://dx.doi.org/10.1190/geo2016-0677.1.

Full text

Abstract:

Anisotropic and attenuating properties of subsurface media cause amplitude loss and waveform distortion in seismic wave propagation, resulting in negative influence on seismic imaging. To correct the anisotropy effect and compensate amplitude attenuation, a compensated-amplitude vertical transverse isotropic (VTI) least-squares reverse time migration (LSRTM) method is adopted. In this method, the attenuation term of an attenuated acoustic wave equation is extended to a VTI quasi-differential wave equation, which takes care of effects from anisotropy and attenuation. The finite-difference method is used to solve the equation, in which attenuation terms are solved in the wavenumber domain, and other terms are solved in the space or wavenumber domain. Stable regularization operators are derived and introduced to the equations to eliminate severe numerical noise in high-frequency components during backward propagation. Meanwhile, a demigration operator, migration operator, and gradient formula for attenuated VTI media are derived to implement the amplitude-compensated VTI LSRTM. Test of a homogeneous model proves the accuracy of the attenuated VTI quasi-differential equations and the effectiveness of the regularization operators. A numerical example for a modified Marmousi model verifies the accuracy and superiority to the amplitude-compensated VTI LSRTM. Our results show that the sensitivity to anisotropic parameters is much higher than that to the [Formula: see text] parameters.

APA, Harvard, Vancouver, ISO, and other styles

30

GARCIANO, L. O., K. SAKAI, and R. TORISU. "EXPERIMENTALLY OBTAINED BIFURCATION PHENOMENON IN CHAOTIC TRACTOR VIBRATING IN TIME AND FREQUENCY DOMAIN." International Journal of Bifurcation and Chaos 15, no. 01 (January 2005): 225–31. http://dx.doi.org/10.1142/s0218127405012120.

Full text

Abstract:

This paper investigates through experimental methods the dynamic characteristics of a farm tractor by changing the forward velocity from 0.63 m/s to 4.50 m/s. Nonlinear time series, frequency spectrum and continuous wavelet transform were used in the analysis. From the nonlinear time series analysis, a nonlinear resonance of the tractor vibration occurred at forward velocity of 2.15 m/s. The existence of a subharmonic frequency at 4.32 m/s indicated chaotic dynamics that was confirmed by the trend of the Lyapunov exponent analysis with a positive exponent indicating chaos. Continuous wavelet transform analysis results, presented graphically, called coefficient plots showed patterns composed of large and fine feature distribution in both time and scale. Quasi-periodic velocities of 1.95 m/s and 2.15 m/s were estimated by these coefficient plots. At forward velocity of 2.88 m/s, the coefficient plots showed dominant features that varied periodically and were estimated to be a period-doubling vibration. The coefficient plots during chaotic vibration at 3.52 m/s, 4.02 m/s and 4.32 m/s showed various feature distributions. At forward velocities of 0.95 m/s and 1.42 m/s, the existence of features with scale values of almost equal and half of the dominant feature was due to the influence of the gravel road surface and not to the artificial test track profile. Experimentally obtained bifurcation was observed clearly from the coefficient plots that showed three different patterns from quasi-periodic vibration at 2.15 m/s, period-doubling at 2.88 m/s and chaos at 3.52 m/s.

APA, Harvard, Vancouver, ISO, and other styles

31

Ri, Kwangchol, Junhyok Jang, Cholil Yun, Choljun Pak, and Kwangchol Kim. "Analysis of subharmonic and quasi-periodic vibrations of a Jeffcott rotor supported on a squeeze-film damper by the IHB method." AIP Advances 12, no. 5 (May 1, 2022): 055328. http://dx.doi.org/10.1063/5.0088334.

Full text

Abstract:

In rotors supported on a squeeze-film damper (SFD) with static eccentricity, subharmonic and quasi-periodic vibrations are generated by rotor unbalance. In this paper, subharmonic and quasi-periodic vibrations in a Jeffcott rotor supported on an SFD are analyzed using the modified incremental harmonic balance (IHB) method. Oil film forces in the damper are calculated using π film theory and short bearing approximation. These forces are first calculated in the time domain and then transformed into the frequency domain by Fourier transformation. The oil film forces in the frequency domain are multiplied by a transformation matrix to match the matrices used in the classical IHB method. To apply the continuation technique, the Jacobian matrix of residuals is calculated analytically. The stability analysis of the calculated solutions is analyzed using Floquet theory. Using this theory, saddle-node, symmetry breaking, period-doubling, and secondary Hopf bifurcations are detected. The phase plane, Poincaré sections, and time history at these bifurcation points are calculated using the Runge–Kutta method.

APA, Harvard, Vancouver, ISO, and other styles

32

Bourreau, Daniel, Alain Peden, and Sandrick Le Maguer. "A Quasi-Optical Free-Space Measurement Setup Without Time-Domain Gating for Material Characterization in the $W$-Band." IEEE Transactions on Instrumentation and Measurement 55, no. 6 (December 2006): 2022–28. http://dx.doi.org/10.1109/tim.2006.884283.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Sun, Enchang, Kechu Yi, Bin Tian, and Dongying Zhang. "Quasi-Orthogonal Time Division Multiplexing and Its Performances in Rayleigh Fading Channels." ISRN Communications and Networking 2012 (March 27, 2012): 1–5. http://dx.doi.org/10.5402/2012/295424.

Full text

Abstract:

This paper proposes an efficient transmission scheme, Quasi-Orthogonal Time Division Multiplexing (QOTDM), which employs the shift orthogonal property of the pulse function with raised-cosine spectral shape, and the signal waveforms are quasi-orthogonal in time domain. Comparing to orthogonal frequency division multiplexing (OFDM), QOTDM is less sensitive to carrier frequency offset and power amplifier nonlinearities while keeping a similar spectral efficiency with OFDM due to single-carrier characteristics. QOTDM is a suitable consideration for the downlink transmission such as in satellite communications. An upper bound of sample error probability (SER) is derived to evaluate the performance of QOTDM. Comparisons of QOTDM and OFDM in Rayleigh fading channels show that the proposed QOTDM system is better than that of OFDM system in terms of bit error rate (BER) in high Eb/No regions.

APA, Harvard, Vancouver, ISO, and other styles

34

Kwon, Young W., and Joshua H. Gordis. "Frequency Domain Structural Synthesis Applied to Quasi-Static Crack Growth Modeling." Shock and Vibration 16, no. 6 (2009): 637–46. http://dx.doi.org/10.1155/2009/978437.

Full text

Abstract:

Quasi-static crack growth in a composite beam was modeled using the structural synthesis technique along with a finite element model. The considered crack was an interface crack in the shear mode (i.e. mode II), which occurs frequently in the scarf joint of composite structures. The analysis model was a composite beam with an edge crack at the midplane of the beam subjected to a three-point bending load. In the finite element model, beam finite elements with translational degrees of freedom only were used to model the crack conveniently. Then, frequency domain structural synthesis (substructure coupling) was applied to reduce the computational time associated with a repeated finite element calculation with crack growth. The quasi-static interface crack growth in a composite beam was predicted using the developed computational technique, and its result was compared to experimental data. The computational and experimental results agree well. In addition, the substructure-based synthesis technique showed the significantly improved computational efficiency when compared to the conventional full analysis.

APA, Harvard, Vancouver, ISO, and other styles

35

Lozovskiy, Alexander, Maxim A. Olshanskii, and Yuri V. Vassilevski. "A quasi-Lagrangian finite element method for the Navier–Stokes equations in a time-dependent domain." Computer Methods in Applied Mechanics and Engineering 333 (May 2018): 55–73. http://dx.doi.org/10.1016/j.cma.2018.01.024.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Wang, Jianlin, and Bjorn Birgisson. "A time domain boundary element method for modeling the quasi-static viscoelastic behavior of asphalt pavements." Engineering Analysis with Boundary Elements 31, no. 3 (March 2007): 226–40. http://dx.doi.org/10.1016/j.enganabound.2006.09.007.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Depalo, Francesco, Shan Wang, Sheng Xu, and C. Guedes Soares. "Design and Analysis of a Mooring System for a Wave Energy Converter." Journal of Marine Science and Engineering 9, no. 7 (July 19, 2021): 782. http://dx.doi.org/10.3390/jmse9070782.

Full text

Abstract:

The objective of this work is to develop an efficient method to carry out the preliminary design of the mooring system for a wave energy converter. A practical mooring design procedure is applied to a specific case of study, and it can be replicated for other cases. Firstly, the static analysis is performed for a configuration with three mooring cables with different pre-tensions on fairlead, diameters of the cables, and materials. Based on these configurations from the static analysis, a quasi-static analysis is carried out in the frequency domain and a preliminary design is conducted according to DNV rules. Then, a 3-h dynamic analysis in the time domain is performed on several selected configurations, considering the same environmental conditions in the quasi-static analysis using the finite element method. Extreme dynamic responses of the system, such as extreme surge motion and mooring tensions, are estimated by the global maximum method, which is performed by fitting 20 individual maximum observations by Gumbel distribution. The quasi-static method is validated by comparing the results of extreme tension and displacement with the coupled time domain analysis. In addition, the influence of pre-tensions and cable diameters on the static and dynamic responses of the mooring system are discussed.

APA, Harvard, Vancouver, ISO, and other styles

38

Persson, Magnus, and Ronny Berndtsson. "Transect Scale Solute Transport Measured by Time Domain Reflectometry." Hydrology Research 33, no. 2-3 (April 1, 2002): 145–64. http://dx.doi.org/10.2166/nh.2002.0020.

Full text

Abstract:

Two quasi steady-state solute transport experiments were carried out in a loamy sand under field conditions. The flux was 40 mm/d in experiment 1 and 18.7 mm/d in experiment 2. Both water content (θ) and resident concentration (Cr) measurements were taken using 64 time domain reflectometry probes at depths ranging from 0.05 to 0.90 m. The Cr measurement was calibrated in situ for each probe location in the field. The convective dispersive equation (CDE) and convective lognormal transfer function (CLT) models were fitted to the breakthrough curves (BTCs). The results indicated fingered flow, which has been shown to exist in previous studies of this soil. The finger width was larger in experiment 1 leading to smaller horizontal heterogeneity and a relatively smaller solute transport velocity. The location of the fingers was consistent between the two experiments resulting in a high correlation between the velocity and mass balance fields. Mass balance calculations showed that the solute mass integrated over depth one day after the solute application was larger than the mass balance for the entire experiment (integrated over time). The probable reason being that solutes were transported out of the measurement volume by horizontal flow across the Ap/E horizon boundary. The investigation of the transport parameters revealed that both the CDE and CLT models could be successfully used to predict most individual BTCs. Horizontally averaged global CDE and CLT models were also fitted to the data. Global solute transport was better modeled with the CDE model in experiment 1, while in experiment 2, the CLT model was better. This study clearly shows the applicability of using TDR with the in situ calibration technique in field experiments with varying water content.

APA, Harvard, Vancouver, ISO, and other styles

39

LE, KIM NGAN, WILLIAM MCLEAN, and BISHNU LAMICHHANE. "FINITE ELEMENT APPROXIMATION OF A TIME-FRACTIONAL DIFFUSION PROBLEM FOR A DOMAIN WITH A RE-ENTRANT CORNER." ANZIAM Journal 59, no. 1 (April 5, 2017): 61–82. http://dx.doi.org/10.1017/s1446181116000365.

Full text

Abstract:

An initial-boundary value problem for a time-fractional diffusion equation is discretized in space, using continuous piecewise-linear finite elements on a domain with a re-entrant corner. Known error bounds for the case of a convex domain break down, because the associated Poisson equation is no longer $H^{2}$-regular. In particular, the method is no longer second-order accurate if quasi-uniform triangulations are used. We prove that a suitable local mesh refinement about the re-entrant corner restores second-order convergence. In this way, we generalize known results for the classical heat equation.

APA, Harvard, Vancouver, ISO, and other styles

40

Globus, Tatiana, Igor Sizov, and Boris Gelmont. "Sub-THz specific relaxation times of hydrogen bond oscillations in E.coli thioredoxin. Molecular dynamics and statistical analysis." Faraday Discuss. 171 (2014): 179–93. http://dx.doi.org/10.1039/c4fd00029c.

Full text

Abstract:

Hydrogen bonds (H-bonds) in biological macromolecules are important for the molecular structure and functions. Since interactions via hydrogen bonds are weaker than covalent bonds, it can be expected that atomic movements involving H-bonds have low frequency vibrational modes. Sub-Terahertz (sub-THz) vibrational spectroscopy that combines measurements with molecular dynamics (MD) computational prediction has been demonstrated as a promising approach for biological molecule characterization. Multiple resonance absorption lines have been reported. The knowledge of relaxation times of atomic oscillations is critical for the successful application of THz spectroscopy for hydrogen bond characterization. The purpose of this work is to use atomic oscillations in the 0.35–0.7 THz range, found from molecular dynamic (MD) simulations of E.coli thioredoxin (2TRX), to study relaxation dynamics of two intra-molecular H-bonds, O⋯H–N and O⋯H–C. Two different complimentary techniques are used in this study, one is the analysis of the statistical distribution of relaxation time and dissipation factor values relevant to low frequency oscillations, and the second is the analysis of the autocorrelation function of low frequency quasi-periodic movements. By studying hydrogen bond atomic displacements, it was found that the atoms are involved in a number of collective oscillations, which are characterized by different relaxation time scales ranging from 2–3 ps to more than 150 ps. The existence of long lasting relaxation processes opens the possibility to directly observe and study H-bond vibrational modes in sub-THz absorption spectra of bio-molecules if measured with an appropriate spectral resolution. The results of measurements using a recently developed frequency domain spectroscopic sensor with a spectral resolution of 1 GHz confirm the MD analysis.

APA, Harvard, Vancouver, ISO, and other styles

41

Zhang, Qingchen, Hui Zhou, Qingqing Li, Hanming Chen, and Jie Wang. "Robust source-independent elastic full-waveform inversion in the time domain." GEOPHYSICS 81, no. 2 (March 1, 2016): R29—R44. http://dx.doi.org/10.1190/geo2015-0073.1.

Full text

Abstract:

Accurate estimation of source wavelet is crucial in a successful full-waveform inversion (FWI); however, it cannot be guaranteed in the case of real seismic data. We have developed time-domain source-independent elastic FWI using the convolution-based objective function that was originally developed for acoustic FWI. We have applied a new time window on the reference traces in the objective function to suppress the noises induced by the convolution and crosscorrelation operations. Also, we have adopted [Formula: see text]-, Huber-, and hybrid-norm objective functions to improve the antinoise ability of our algorithm. We implemented a multiscale inversion strategy to conduct the tests with a quasi-Newton limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) method to reduce the sensitivity to initial models and to improve the quality of inversion results. Synthetic tests verified that the new added time window can not only improve the inversion results, but also accelerate the convergence rate. Our method can be implemented successfully without a priori knowledge or accurate estimation of the source wavelet and can be more robust to Gaussian and spike noises, even for a Dirac wavelet. Finally, we applied our method to real seismic data. The similarity between the observed and modeled seismic data, the higher resolution of the migration image, and flatter common image gathers corresponding to the inverted models proved the relevance of our algorithm.

APA, Harvard, Vancouver, ISO, and other styles

42

Kusanovic, Danilo S., Elnaz Seylabi, and Domniki Asimaki. "Optimization of frequency domain impedances for time-domain response analyses of building structures with rigid shallow foundations." Earthquake Spectra 37, no. 3 (January 19, 2021): 1955–79. http://dx.doi.org/10.1177/8755293020981994.

Full text

Abstract:

The effects of dynamic soil–structure interaction (SSI) have been extensively studied in the last few decades, and proper analysis for the linear elastic case in frequency domain has been established successfully. However, SSI is rarely considered in the design of building structures, and instead, buildings are frequently analyzed using a rigid base assumption and quasi-static loading conditions that ignore SSI and its dynamic nature. Acknowledging these shortcomings, the National Institute of Standards and Technology (NIST) published in 2012 a set of recommendations on time-domain analyses of SSI for building structures compatible with standard finite element packages for consideration in engineering design. The so-called NIST GCR 12-917-21 report introduced a major simplification to enable frequency domain tools to be implemented in time domain analyses. That is, replacing the frequency-dependent soil impedance functions by a single-valued functions read at the flexible-base structure frequency; This work seeks to quantify the accuracy of this simplification considering fully coupled two-dimensional (2D) finite element models (FEM) as the reference. Using a Bayesian approach based on ensemble Kalman inversion (EnKI) and a range of numerical simulations of soil–foundation–building interaction, we estimate the optimal frequency that can be used to estimate soil impedance for time domain analyses; and we evaluate the improvement that the corresponding impedance offers relative to the full FEM results when compared to time domain analyses performed in accordance to the NIST recommendations outlined above.

APA, Harvard, Vancouver, ISO, and other styles

43

Dombovari, Zoltan, and Gabor Stepan. "On the bistable zone of milling processes." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2051 (September 28, 2015): 20140409. http://dx.doi.org/10.1098/rsta.2014.0409.

Full text

Abstract:

A modal-based model of milling machine tools subjected to time-periodic nonlinear cutting forces is introduced. The model describes the phenomenon of bistability for certain cutting parameters. In engineering, these parameter domains are referred to as unsafe zones, where steady-state milling may switch to chatter for certain perturbations. In mathematical terms, these are the parameter domains where the periodic solution of the corresponding nonlinear, time-periodic delay differential equation is linearly stable, but its domain of attraction is limited due to the existence of an unstable quasi-periodic solution emerging from a secondary Hopf bifurcation. A semi-numerical method is presented to identify the borders of these bistable zones by tracking the motion of the milling tool edges as they might leave the surface of the workpiece during the cutting operation. This requires the tracking of unstable quasi-periodic solutions and the checking of their grazing to a time-periodic switching surface in the infinite-dimensional phase space. As the parameters of the linear structural behaviour of the tool/machine tool system can be obtained by means of standard modal testing, the developed numerical algorithm provides efficient support for the design of milling processes with quick estimates of those parameter domains where chatter can still appear in spite of setting the parameters into linearly stable domains.

APA, Harvard, Vancouver, ISO, and other styles

44

Bonning, Erin Wells. "Variability in Active Galactic Nuclei." Proceedings of the International Astronomical Union 7, S285 (September 2011): 109–10. http://dx.doi.org/10.1017/s1743921312000385.

Full text

Abstract:

AbstractThis talk explored variability in active galactic nuclei (AGN) for a variety of scales across the time domain. From billion-year-scale intermittency to a quasi-periodic oscillation signal with a period of one hour, time-varying signals offer insights into a myriad of complex processes driven by the AGN central engine. Athough the era of time-domain observations of AGN across the spectrum has but just begun, already observations reveal the rich detail of phenomena associated with actively accreting black holes which challenge theoretical models.

APA, Harvard, Vancouver, ISO, and other styles

45

Cummings, A., and I. J. Chang. "High Amplitude Sound Propagation at Low Frequencies in a Flow Duct Lined With Resonators: A Time Domain Solution." Journal of Vibration and Acoustics 110, no. 4 (October 1, 1988): 545–51. http://dx.doi.org/10.1115/1.3269564.

Full text

Abstract:

A quasi one-dimensional analysis of sound transmission in a flow duct lined with an array of nonlinear resonators is described. The solution to the equations describing the sound field and the hydrodynamic flow in the neighborhood of the resonator orifices is performed numerically in the time domain, with the object of properly accounting for the nonlinear interaction between the acoustic field and the resonators. Experimental data are compared to numerical computations in the time domain and generally very good agreement is noted. The method described here may readily be extended for use in the design of exhaust mufflers for internal combustion engines.

APA, Harvard, Vancouver, ISO, and other styles

46

Margrave, Gary F. "Theory of nonstationary linear filtering in the Fourier domain with application to time‐variant filtering." GEOPHYSICS 63, no. 1 (January 1998): 244–59. http://dx.doi.org/10.1190/1.1444318.

Full text

Abstract:

A general linear theory describes the extension of the convolutional method to nonstationary processes. This theory can apply any linear, nonstationary filter, with arbitrary time and frequency variation, in the time, Fourier, or mixed domains. The filter application equations and the expressions to move the filter between domains are all ordinary Fourier transforms or generalized convolutional integrals. Nonstationary transforms such as the wavelet transform are not required. There are many possible applications of this theory including: the one‐way propagation of waves through complex media, time migration, normal moveout removal, time‐variant filtering, and forward and inverse Q filtering. Two complementary nonstationary filters are developed by generalizing the stationary convolution integral. The first, called nonstationary convolution, corresponds to the linear superposition of scaled impulse responses of a nonstationary filter. The second, called nonstationary combination, does not correspond to such a superposition but is shown to be a linear process capable of achieving arbitrarily abrupt temporal variations in the output frequency spectrum. Both extensions have stationary convolution as a limiting form and, in the discrete case, can be formulated as matrix operations. Fourier transformation shows that both filter types are nonstationary filter integrals in the Fourier domain as well. This result is a generalization of the convolution theorem for stationary signals because, as the filter becomes stationary in one domain, the integral in the other domain collapses to a scalar multiplication. For discrete signals, stationary filters are a matrix multiplication of the input signal spectrum by a diagonal spectral matrix, while nonstationary filters require off‐diagonal terms. For quasi‐stationary filters, a computational advantage is obtained by computing only the significant terms near the diagonal. Unlike stationary theory, a mixed domain of time and frequency is also possible. In this context, the nonstationary filter is applied simultaneously with the transform from time to frequency or the reverse. Nonstationary convolution becomes a generalized forward Fourier integral and nonstationary combination is a generalized inverse Fourier integral.

APA, Harvard, Vancouver, ISO, and other styles

47

CHAKRABORTY, DEBANANDA, JAE-HUN JUNG, and GAURAV KHANNA. "A MULTI-DOMAIN HYBRID METHOD FOR HEAD-ON COLLISION OF BLACK HOLES IN PARTICLE LIMIT." International Journal of Modern Physics C 22, no. 05 (May 2011): 517–41. http://dx.doi.org/10.1142/s0129183111016415.

Full text

Abstract:

A hybrid method is developed based on the spectral and finite-difference methods for solving the inhomogeneous Zerilli equation in time-domain. The developed hybrid method decomposes the domain into the spectral and finite-difference domains. The singular source term is located in the spectral domain while the solution in the region without the singular term is approximated by the higher-order finite-difference method. The spectral domain is also split into multi-domains and the finite-difference domain is placed as the boundary domain. Due to the global nature of the spectral method, a multi-domain method composed of the spectral domain only does not yield the proper power-law decay unless the range of the computational domain is large. The finite-difference domain helps reduce boundary effects due to the truncation of the computational domain. The multi-domain approach with the finite-difference boundary domain method reduces the computational cost significantly and also yields the proper power-law decay. Stable and accurate interface conditions between the finite-difference and spectral domains and the spectral and spectral domains are derived. For the singular source term, we use both the Gaussian model with various values of full width at half-maximum and a localized discrete δ-function. The discrete δ-function was generalized to adopt the Gauss–Lobatto collocation points of the spectral domain. The gravitational waveforms are measured. Numerical results show that the developed hybrid method accurately yields the quasi-normal modes and the power-law decay profile. The numerical results also show that the power-law decay profile is less sensitive to the shape of the regularized δ-function for the Gaussian model than expected. The Gaussian model also yields better results than the localized discrete δ-function.

APA, Harvard, Vancouver, ISO, and other styles

48

Kumar, Udaya, Rosy B. Raysaha, and K. P. Dileep Kumar. "Time Domain Modelling of First Return Stroke of Lightning." Open Atmospheric Science Journal 2, no. 1 (December 29, 2008): 261–70. http://dx.doi.org/10.2174/1874282300802010261.

Full text

Abstract:

The four most important factors that govern the return stroke evolution can be identified as: (i) electric field due to charge distributed along the channel, (ii) transient enhancement of conductance by several orders at the bridging regime (iii) the non-linear increase in channel conductance at the propagating current front and (iv) the associated dynamic electromagnetic field which support the evolution of current along the channel. For a more realistic modelling of the lightning return stroke, the present work attempts to consider these aspects in suitable manner. The charge simulation method is employed for evaluating the quasi-static field due to (i). For the dynamic field, the problem involves conduction along a thin structure with open boundary on one side. Further, in order to efficiently represent a vertically extended grounded strike object, as well as, channel of quite arbitrary geometry, boundary based approach is believed to be the ideal choice. Considering these, a time-dependent electric field integral equation (TD-EFIE) along with a sub-sectional collocation form of the method of moments (MoM) is chosen for the numerical field evaluation. The dynamic variation of conductance in the channel other than the bridging zone is modelled by a first order arc equation. For the bridging zone, arc equation which explicitly portray in some sense, accumulation of energy is considered. Accordingly, formulations given by Barannik, Popovic and Toepler were scrutinized for their suitability. After some preliminary simulation studies, a self contained model for the first return stoke of a lightning flash is presented. The stability of the model is verified by running the program for longer durations with different cloud base potentials and cloud base heights. Simulation results are in agreement with the field data on current and velocity decay rate for the first one kilometer height. Also, the relation between the charge density at channel tip and the return stroke current peak favorably compares with the literature.

APA, Harvard, Vancouver, ISO, and other styles

49

Winterstein, S. R., R. Torhaug, and S. Kumar. "Design Seastates for Extreme Response of Jackup Structures." Journal of Offshore Mechanics and Arctic Engineering 120, no. 2 (May 1, 1998): 103–8. http://dx.doi.org/10.1115/1.2829523.

Full text

Abstract:

The extreme response of a jackup structure is studied. We consider how design seastate histories can be introduced to reduce the cost of time-domain response analysis. We first identify critical wave characteristics for extreme response prediction. In quasi-static cases, the maximum wave crest height, ηmax, is shown to best explain extreme deck sway. For more flexible structures we introduce a new wave characteristic, SD, based on response spectral concepts from earthquake engineering. Finally, we show how accurate response estimates can require fewer time-domain analyses, provided design seastates are pre-selected to ensure that ηmax or SD is near its average value. With respect to standard Monte-Carlo simulation, these design seastates achieve at least a 50-percent reduction in response variability, and hence at least a fourfold savings in needed simulation cost. These results may lend insight, not only into time-domain simulation, but also into more fundamental questions of jackup behavior. They also suggest that, at least in quasi-static cases, still simpler design wave methods based on ηmax may suffice. We illustrate and evaluate some such design wave methods here (e.g., the “new wave” model and others based on Slepian theory).

APA, Harvard, Vancouver, ISO, and other styles

50

Zhang, Shi Kai, and Jian Li Jin. "Asymmetric Binary Frequency Shift Keying and its Frequency Attribute." Advanced Materials Research 765-767 (September 2013): 1236–39. http://dx.doi.org/10.4028/www.scientific.net/amr.765-767.1236.

Full text

Abstract:

An innovative asymmetric binary frequency shift keying (ABFSK) modulation format is presented and studied both in the time domain and frequency domain. First, the modulation function is demonstrated, it shows a quasi-continuous phase attribute and an ability of high speed data modulation. Second, the domain attribute is studied; it has a high degree of energy centralization. Thus, a narrow occupied bandwidth can be achieved after a proper filtering. Then, the finite spectrum can be conserved to improve spectrum efficiency.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'THz quasi time domain'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles