scholarly journals Wave modes in a cold pair plasma: the complete phase and group diagram point of view

2019 ◽  
Vol 85 (1) ◽  
Author(s):  
Rony Keppens ◽  
Hans Goedbloed
Keyword(s):  
Dispersion Relation ◽  
Point Of View ◽  
Complete Analysis ◽  
Fixed Frequency ◽  
Pair Plasma ◽  
Standard Textbook ◽  
Propagating Waves ◽  
General Dispersion ◽  
Avoided Crossings ◽  
Wave Modes

We present a complete analysis of all wave modes in a cold pair plasma, significantly extending standard textbook treatments. Instead of identifying the maximal number of two propagating waves at fixed frequency $\unicode[STIX]{x1D714}$, we introduce a unique labelling of all 5 mode pairs described by the general dispersion relation $\unicode[STIX]{x1D714}(k)$, starting from their natural ordering at small wavenumber $k$. There, the 5 pairs start off as Alfvén (A), fast magnetosonic (F), modified electrostatic (M) and electromagnetic O and X branches, and each $\unicode[STIX]{x1D714}(k)$ branch smoothly connects to large wavenumber resonances or limits. For cold pair plasmas, these 5 branches show avoided crossings, which become true crossings at exactly parallel or perpendicular orientation. Only for those orientations, we find a changed connectivity between small and large wavenumber behaviour. Analysing phase and group diagrams for all 5 wave modes, distinctly different from the Clemmow–Mullaly–Allis representation, reveals the true anisotropy of the A, M and O branches.

Dosimetry and optimization in digital radiography based on the contrast-detail resolution

2018 ◽  
Vol 6 (3) ◽  
Author(s):  
Wilson Otto Gomes Batista ◽  
Alexandre Gomes De Carvalho
Keyword(s):  
Image Quality ◽  
Inverse Image ◽  
Point Of View ◽  
Complete Analysis ◽  
Portable Devices ◽  
Evaluation Tool ◽  
Air Kerma ◽  
Direct Radiography ◽  
Definition Of ◽  
Entrance Surface Air Kerma

Contrast-detail (C-D) curves are useful in evaluating the radiographic image quality in a global way. The objective of the present study was to obtain the C-D curves and the inverse image quality figure. Both of these parameters were used as an evaluation tool for abdominal and chest imaging protocols. The C-D curves were obtained with the phantom CDRAD 2.0 in computerized radiography and the direct radiography systems (including portable devices). The protocols were 90 and 102 kV in the range of 2 to 20 mAs for the chest and 80 kV in the range of 10 to 80 mAs for the abdomen. The incident air kerma values were evaluated with a solid state sensor. The analysis of these C-D curves help to identify which technique would allow a lower value of the entrance surface air kerma, Ke, while maintaining the image quality from the point of view of C-D detectability. The results showed that the inverse image quality figure, IQFinv, varied little throughout the range of mAs, while the value of Ke varied linearly directly with the mAs values. Also, the complete analysis of the curves indicated that there was an increase in the definition of the details with increasing mAs. It can be concluded that, in the transition phase for the use of the new receptors, it is necessary to evaluate and adjust the practised protocols to ensure, at a minimum, the same levels of the image quality, taking into account the aspects of the radiation protection of the patient.

scholarly journals “Fuzzy Band Gaps”: A Physically Motivated Indicator of Bloch Wave Evanescence in Phononic Systems

Crystals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 66
Author(s):  
Connor D. Pierce ◽  
Kathryn H. Matlack
Keyword(s):  
Wave Propagation ◽  
Dispersion Relation ◽  
Quantitative Measure ◽  
Bloch Wave ◽  
Phononic Crystals ◽  
Wave Transmission ◽  
Band Gaps ◽  
Dissipative Systems ◽  
Frequency Range ◽  
Wave Modes

Phononic crystals (PCs) have been widely reported to exhibit band gaps, which for non-dissipative systems are well defined from the dispersion relation as a frequency range in which no propagating (i.e., non-decaying) wave modes exist. However, the notion of a band gap is less clear in dissipative systems, as all wave modes exhibit attenuation. Various measures have been proposed to quantify the “evanescence” of frequency ranges and/or wave propagation directions, but these measures are not based on measurable physical quantities. Furthermore, in finite systems created by truncating a PC, wave propagation is strongly attenuated but not completely forbidden, and a quantitative measure that predicts wave transmission in a finite PC from the infinite dispersion relation is elusive. In this paper, we propose an “evanescence indicator” for PCs with 1D periodicity that relates the decay component of the Bloch wavevector to the transmitted wave amplitude through a finite PC. When plotted over a frequency range of interest, this indicator reveals frequency regions of strongly attenuated wave propagation, which are dubbed “fuzzy band gaps” due to the smooth (rather than abrupt) transition between evanescent and propagating wave characteristics. The indicator is capable of identifying polarized fuzzy band gaps, including fuzzy band gaps which exists with respect to “hybrid” polarizations which consist of multiple simultaneous polarizations. We validate the indicator using simulations and experiments of wave transmission through highly viscoelastic and finite phononic crystals.

Magnetic Superlattice: Localized Magnetostatic Waves and Magnetic Polaritons

2003 ◽  
Vol 17 (15) ◽  
pp. 829-839
Author(s):  
R. T. Tagiyeva ◽  
M. Saglam
Keyword(s):  
Magnetic Material ◽  
Electromagnetic Wave ◽  
Dispersion Relation ◽  
Wave Theory ◽  
Frequency Region ◽  
Long Wavelength ◽  
Magnetostatic Waves ◽  
General Dispersion ◽  
Magnetic Polaritons ◽  
Magnetic Superlattice

Localized magnetostatic waves and magnetic polaritons at the junction of the magnetic material and magnetic superlattice composed of the alternating ferromagnetic or ferromagnetic and nonmagnetic layers are investigated in the framework of the electromagnetic wave theory in Voigt geometry. The general dispersion relation for localized magnetic polaritons and magnetostatic waves (MW) are derived in the long-wavelength limit. The dispersion curves and frequency region of the exsistence of the localized MW and magnetic polaritons are calculated numerically.

scholarly journals The general dispersion relation of induced streaming instabilities in quantum outflow systems

AIP Advances ◽  
2015 ◽  
Vol 5 (11) ◽  
pp. 117236 ◽  
Author(s):  
H. Mehdian ◽  
K. Hajisharifi ◽  
A. Hasanbeigi
Keyword(s):  
Dispersion Relation ◽  
General Dispersion

scholarly journals Complexes for continuous monitoring of drilling fluid parameters during drilling

2021 ◽  
Vol 6 (3) ◽  
pp. 144-151
Author(s):  
Sergey V. Lakhtionov ◽  
Ivan S. Chumakov ◽  
Sergey G. Filinkov ◽  
Dmitry M. Chukin ◽  
Evgeny N. Ishmetyev
Keyword(s):  
Continuous Monitoring ◽  
Drilling Fluid ◽  
Point Of View ◽  
Complete Analysis ◽  
Drilling Fluids ◽  
Automatic Mode ◽  
Design Values ◽  
Drilling Rigs ◽  
Almost All ◽  
Fluid Parameters

Background. The article provides an overview of existing complexes (units) for continuous monitoring of drilling fluid parameters in automatic mode. Aim. To justify the need to develop a complex (module) that will allow combining existing technologies and making a step forward in the field of process automation in terms of monitoring the parameters of drilling fluids. Materials and methods. In the current realities of well construction, the control of drilling fluid parameters on almost all drilling rigs operating on the territory of Russia (possibly with the exception of a few off shore projects) is carried out by the work of a solution engineer, usually a representative of a service company. The analysis of the parameters, depending on the number of personnel, the speed of penetration, the complexity or importance of the well, can be carried out from 2 to 6 times a day [1, 2]. This means a complete analysis, rather than monitoring the density and conditional viscosity, which can be measured by a representative of the drilling crew, for rapid response, and with greater frequency. Due to such a low measurement discreteness, there is a high probability of a significant deviation of the drilling fluid parameters from the design values. As a result, the probability of various complications, both geological and technological, increase significantly. Results. During the analysis of information from open sources, the most promising complexes (modules) from the point of view of application in the current conditions were identified, their positive and negative sides were evaluated. As a result of the conducted review of open sources, the most promising complexes (modules) in terms of application in the current conditions are identified, the positive and negative sides of the systems under consideration are displayed, and the need to develop a complex (module) that will combine all the best that is available today and make a qualitative step forward in the field of “peopleless” technologies used during drilling wells in terms of monitoring the parameters of drilling fluids is justified. Conclusions. The necessity of developing a complex (module) for automating processes in terms of monitoring the parameters of drilling fluids is justified.

Discovery of Sustainable Transport Modes Underlying TripAdvisor Reviews With Sentiment Analysis

2021 ◽  
pp. 180-199
Author(s):  
Ainhoa Serna ◽  
Jon Kepa Gerrikagoitia
Keyword(s):  
Social Media ◽  
Sentiment Analysis ◽  
Language Processing ◽  
Predictive Analytics ◽  
Data Gathering ◽  
Point Of View ◽  
Training Data ◽  
Complete Analysis ◽  
Sustainable Transport ◽  
Transport Modes

In recent years, digital technology and research methods have developed natural language processing for better understanding consumers and what they share in social media. There are hardly any studies in transportation analysis with TripAdvisor, and moreover, there is not a complete analysis from the point of view of sentiment analysis. The aim of study is to investigate and discover the presence of sustainable transport modes underlying in non-categorized TripAdvisor texts, such as walking mobility in order to impact positively in public services and businesses. The methodology follows a quantitative and qualitative approach based on knowledge discovery techniques. Thus, data gathering, normalization, classification, polarity analysis, and labelling tasks have been carried out to obtain sentiment labelled training data set in the transport domain as a valuable contribution for predictive analytics. This research has allowed the authors to discover sustainable transport modes underlying the texts, focused on walking mobility but extensible to other means of transport and social media sources.

Elasto-plastic analysis of a rotating model conical turbine disc

1975 ◽  
Vol 10 (3) ◽  
pp. 167-171 ◽  
Author(s):  
F Ginesu ◽  
B Picasso ◽  
P Priolo
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Limit Analysis ◽  
Point Of View ◽  
Complete Analysis ◽  
The Finite Element Method ◽  
Computational Simplicity ◽  
Rotating Shell ◽  
Good Agreement ◽  
Element Method

Results on the plastic collapse behaviour of an axisymmetric rotating shell, obtained by Limit Analysis and the Finite Element Method, are in good agreement with experimental data. The Finite Element Method, though computationally rather costly, permits, however, a more complete analysis of elasto-plastic behaviour. For the present case, the Limit Analysis has the advantage of greater computational simplicity and leads to a quite satisfactory forecast of collapse speed from the engineering point of view.

Advantages of Spectrally Analyzed Data: Stochastic Models for Automotive Measured Parameters

2014 ◽  
Vol 1036 ◽  
pp. 493-498 ◽  
Author(s):  
Radu Vilău ◽  
Marin Marinescu ◽  
Octavian Alexa ◽  
Florin Oloeriu ◽  
Marian Truta
Keyword(s):  
Dynamic Models ◽  
Real Life ◽  
Stochastic Approach ◽  
Angular Speed ◽  
Point Of View ◽  
Mechanical Parameter ◽  
Complete Analysis ◽  
Measured Parameter ◽  
Useful Signal ◽  
Non Linear

The paper deals with a new approach in data analysis of a measured mechanical parameter. The classic approach is mainly based on the deterministic statistics that cant cover the whole field of a complete analysis. The stochastic approach, to be used in this paper, offers far more information about the mechanical parameter and can take into account the non-linearity of the signal, eventually, the mechanical parameter itself. Starting from the point of view that, in real life, there is no steady evolution of any parameter, we decide to take into account the importance of the non-linear components of any signal. After e thorough investigation, we hope we could make the difference between the noise, as non-linear components of the measured parameter, and the useful non-linear components (e.g. important shocks, typically met within a vehicles transmission). Using the stochastic modeling procedures, we aimed at issuing comprehensive, accurate and valuable dynamic models of the phenomenon. These models cam be used in a large variety of situations, from describing the process, to evaluating the health of a mechanical system and to controlling a real-time process based on the pre-set models (previously drawing a map of the systems normal behavior and permanently assessing the deviation from it and acting accordingly). The data were measured within the transmission system of a military vehicle. Specifically, we have gathered information about torque and angular speed of different shafts of the driveline. As everybody knows, the power flows within any vehicles transmission in transient modes mainly and it is accompanied by plenty of noise. It is rather challenging to separate (filter) the useful signal form the noise but, on the other hand, it is the only way to achieve useful data. Therefore, a spectral analysis is a must, but not the conventional one, which has its drawbacks, but a multi-spectral one, which is able to insulate the noise. Moreover, starting from the analysis developed with this method, mathematical models, both in discrete and continuos time can be achieved. It is easy to notice that the models that we have achieved are featured by a very good accuracy. We could push the data processing even further, getting generalized models that provide the needs we have mentioned before, with respect to the mapping of a normal (averaged) behavior of a system, to be used in controlling procedures.

scholarly journals Evaluation of Delamination in Concrete by IE Testing Using Multi-Channel Elastic Wave Data

Sensors ◽  
2019 ◽  
Vol 20 (1) ◽  
pp. 201 ◽  
Author(s):  
Seong-Hoon Kee ◽  
Jin-Wook Lee ◽  
Ma. Doreen Candelaria
Keyword(s):  
Data Processing ◽  
Elastic Wave ◽  
Single Channel ◽  
Experimental Studies ◽  
Test Method ◽  
Wave Data ◽  
Wave Measurements ◽  
Propagating Waves ◽  
The Impact ◽  
Wave Modes

The main objectives of this study are to develop a non-destructive test method for evaluating delamination defects in concrete by the Impact-echo test using multi-channel elastic wave data and to verify the validity of the proposed method by experimental studies in the laboratory. First, prototype equipment using an eight-channel linear sensor array was developed to perform elastic wave measurements on the surface of the concrete. In this study, three concrete slab specimens (1500 mm (width) by 1500 mm (length) by 300 mm (thickness)), with simulated delamination defects of various lateral dimensions and depth, were designed and constructed in the laboratory. Multi-channel elastic wave signals measured on the three concrete specimens were converted to the frequency-phase velocity image by using the phase-shift method. A data processing method was proposed to extract the dominant propagating waves and non-propagating waves from the dispersion images. The dominant wave modes were used to evaluate delamination defects in concrete. It was demonstrated that the surface wave velocity values were useful for characterizing the shallow delamination defects in concrete. In addition, the peak frequency of non-propagating wave modes extracted from the dispersion images gives information on the lateral dimensions and depths of the delamination defects. This study also discussed the feasibility of combined use of the results from propagating and non-propagating wave modes to better understand the information on delamination defects in concrete. As will be discussed, the multi-channel elastic wave measurements enable more accurate, consistent, and rapid measurements and data processing for evaluation of delamination defects in concrete than the single-channel sensing method.

INVERSE DISPERSION RELATION OF BZ-WAVES IN NONSTATIONARY GELS

1999 ◽  
Vol 09 (10) ◽  
pp. 2099-2104 ◽  
Author(s):  
W. HANKE
Keyword(s):  
Dispersion Relation ◽  
Point Of View ◽  
Excitable Media ◽  
Experimental Investigations ◽  
Theoretical Point ◽  
Bz Reaction ◽  
Inverse Dispersion ◽  
Sustained Activity ◽  
System A ◽  
Theoretical Considerations

The behavior of wave propagation, as well that of isolated waves as that of self-sustained activity, in excitable media is characterized by the dispersion relation of the system. For the Belousov–Zhabotinsky (BZ)-reaction as by far the best described system, a number of theoretical considerations and experimental investigations do exist. From the theoretical point of view the dispersion relation of the BZ-reaction has two branches, an upper "fast" or stable branch typified by singular solutions and a lower "slow" branch whose solutions are regular, with a connection between the two branches, defining the smallest possible period and the absolute refractory period of the system. Experimental data are usually located on the upper branch giving higher propagation velocity at increasing period. Only one set of results was published in the early 1970s with velocity being an increasing function of frequency. This set of data was stated to be "difficult to believe" in later papers. We now present here a more detailed study of a BZ-system with a dispersion relation with an increasing velocity at decreasing period, verifying the existence of an "inverse" dispersion relation at least in the nonstationary gels we have used.

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