Intensive studies have been done in the area of high frequency measurement of the complex permittivity of dielectric materials. The basic principles of operation include transmission line and cavity resonance [19, 20]. Transmission techniques are attractive for measurements over a very wide swept of frequencies. On the other hand cavity resonant techniques are limited to only one or a few frequencies, deﬁned by the cavity dimensions. Furthermore, these techniques are destructive. The solutions to nondestructive dielectric measurements of material at high frequency are thus limited to transmission techniques using open-endedcoaxial (OEC) probe [21– 24], open-ended rectangular waveguide [25–28] and free-space method . The latter two present frequency limitations that aﬀect the size of the MUT to be used. Hence the most widely used technique in dielectric spectroscopy is using the OEC probe due to its simplicity and accuracy in broadband nondestructive measurements. However the OEC probe is recommended for measuring liquids and semi-solids [23, 30–32].
In Fig. 3, room temperature dielectric data obtained with the OEC on 1-octanol, 2-propanol, ethanol, and methanol are plotted. Data taken with different analyzers are in excellent mutual agreement. The solid lines represent the theoretical curves according to the values listed in Table I. An example of a measurement on a solid material is shown in Fig. 4. The real part of the dielectric permittivity ⑀ ⬘ and the alternating- current 共 ac 兲 conductivity ⬘ ⫽ ⑀ 0 ⑀ ⬙ of an agglomeration of dielectric spheres coated with a conducting layer was mea- sured over a broad frequency range. 6 The data taken with the OEC 共 black dots 兲 interpolate well with the results of standard impedance measurements in a sandwich configuration ( f ⬍ 10 MHz) and data obtained from measurements in a rect- angular waveguide 共 40 GHz 兲 and quasioptical measurements 共 100–500 GHz 兲 on the same sample. The same is true for the OEC measurements on a carbon-black/polymer composite in the range 4–300 K, see Fig. 5 and paper II. Using open, short, and quartz calibration standards accurate dielectric measurements at GHz frequencies can be performed down to the lowest temperatures.
Several recent developments in non-destructive evaluation and testing of material illustrate the usefulness of microwaves sensors in applications such as, material characterization, defect monitoring, bone mineral density analysis and food quality monitoring. Compared to other nondestructive testing methods such as radiography and ultrasonics, microwaves based sensors oﬀer increased penetration, increased resolution and low cost [1–4]. The most commonly used waveguide sensors for noninvasive evaluation of materials are openendedcoaxial line (OECL) and openended rectangular waveguide (OERW). OERW based probes have more structural robustness than OECL, and OERW also oﬀers more coupling than OECL due to large aperture size . On the other hand, openended circular waveguide (OECW) oﬀers an extra orthogonal ﬁeld component, compared to OERW, thereby, providing more interaction of ﬁelds on inhomogeneous materials without the expense of structural robustness . However, analysis of OECW is more challenging than both OECL and OERW.
Having demonstrated the feasibility of the open-endedcoaxial probe using methyl alcohol and NaCl solution control samples, the system was next used to determine the unknown permittivity of WAS obtained from our local WWTF in Kelowna, British Columbia, Canada. WAS is comprised of different groups of microorganisms, organic and inorganic matter agglomerated together in a polymeric network formed by microbial extracellular polymeric substances (EPS) and cations . Here, we present the experimental data to highlight the capabilities of the measurement technique, but refer readers to a previous publication for a detailed discussion of the results . Two concentrations of WAS are common at WWTFs. One, referred to as thickened WAS (TWAS), contains 4.5% solids by weight. Before final disposal, TWAS is routinely dewatered using a centrifuge resulting in a material called “sludge cake” that is 18% solid by weight. Figure 10 shows the real and imaginary components of ε r −jσ dc /ωε 0 for both the 4.5% and 18%
nanofocus displayed in the xy plane of the wedge. The frequencies of the individual rays in a packet are indicated by color as coded by the bar at the top. (b-d) Spatiotemporal modulation of the excitation pulses at the thick edge of the wedge required for nanofocusing. The temporal dependencies (waveforms) of the electric field for the phase-modulated pulses for three points at the thick edge boundary: two extreme points and one at the center, as indicated, aligned with the corresponding x points at panel (a). (e) The three excitation pulses of panels (b-d) (as shown by their colors), superimposed to elucidate the phase shifts, delays, and shape changes between these pulses. The resulting ultrashort pulse at the nanofocus is shown by the black line. The scale of the electric fields is arbitrary but consistent throughout the figure. ........................................................................ 32 Figure 3.1. (color) (a) Schematic of the waveguide. The width of the dielectric gap a and the skin
Abstract. This paper examines the radiation characteristics of a contact emitter conceived for application in hyperther- mia and microwave reflex therapy. It is important to analyse the distribution of power density in the near field area, as the radiator’s therapeutic sphere of activity is localized here. The contact emitter is a coaxial radiator with an eccentric course of the inner conductor. According to Huygens principle, a theoretical view of the near field radiation characteristics is made by determining the equivalent current densities in the emitter aperture. It is shown that by an eccentric shift of the inner conductor, an almost isotropic near field radiation pat- tern and power density can be achieved. For this, the electro- magnetic field in the emitter aperture is determined by using a Bipolar coordinate system. This calculation considers only the fundamental TEM mode of the contact emitter. Besides the theoretical results near and far fields are simulated using the programme system Ansoft HFSS.
Coaxial probes are widely used as feeding structures for microstrip patch antennas as well as other applications. Many authors have found a transverse electromagnetic (TEM) field distribution across the probe aperture is a reasonable approximation for simulations of coaxial probes [1–7]. Therefore, a coaxial probe feeding a patch antenna can be viewed as a mode-converter which converts the TEM mode across the probe aperture into the parallel plate modes. While the higher-order parallel plate modes are usually evanescent waves localized near the probe, the zero-order parallel plate mode can propagate away, excite curtain resonant mode of the entire patch antenna, and thus radiate into surrounding environments. It is much more difficult for numerical
study the effect of analyte size on sensor response. The sensor response time is the time required to reach an equilibrium state wherein the average surface concen- tration of analytes immobilized on the sensor does not change as represented by a saturation of the wavelength shift. The attachment of 3-APTES involves a silaniza- tion process, while protein adsorption is charge-based. Our simulation results in Fig. 5 suggested that due to mass transport limitations, the response time of the porous sensor is dominated by analyte diffusivity and is only weakly dependent on adsorption rate constants. Therefore, the sensor response for adsorption of 3- APTES and proteins is primarily determined by their different sizes (i.e., diffusivities) rather than adsorption mechanisms. The adsorption of 3-APTES and HRP quickly reached saturation in approximately 10 and 20 min, re- spectively, while the adsorption of the large CAT protein was slow. This trend corresponds well to the simulation results presented in Fig. 5 that show for larger molecules that diffuse more slowly, the closed-ended PSi sensor takes longer to reach equilibrium. For the CAT protein, approxi- mately 1.5-nm wavelength shift was measured using the closed-ended pore microcavity after 120 min of continuous analyte injection. The slow response of this PSi microcavity to CAT adsorption is attributed to the corresponding relatively low diffusivity of CAT and the relatively large size of this protein molecule compared to the nanoscale pore diameters. As the CAT molecules have a hydro- dynamic diameter of approximately 10.2 nm, the pore diameters in the low porosity layers of the PSi sample become substantially reduced in half from 20 ± 5 nm to about 10 ± 5 nm upon capturing one CAT molecule. Electrostatic repulsion between protein molecules and steric hindrance in the pore entrance significantly re- duce the probability of CAT protein molecules continu- ing to enter the pores.
The use of the Lorentz lemma on reciprocity to the waveguide propagation of Maxwell optical radiation leads to the factorization of (2) into the sum of two terms involving the transverse electro- magnetic ﬁeld distributions and the exponential factor respectively. In the case of real ε and μ , the second contribution to the Lorentz lemma vanishes identically, while if Im ε Re ε , it is negligibly small. The remaining ﬁrst part of the sum, renamed as “conservation law”, can be called “truncated Lorentz lemma” for the waveguide propagation of the electromagnetic radiation.
The HCA which is to be used to drive the FEM, is based on a magnetically insulated explosive emission carbon cathode able to produce a thin annular electron beam. In Fig. 6a, the photograph of the experiment is presented and the following components are indicated: (a) pulsed wiggler and capacitor bank power supply; (b) table containing ten 250 mF, 20 kV capacitors used to generate up to 0.8 T from a large diameter (30 cm) pulsed solenoid of length 2.5 m; (c) X-ray shielded enclosure; (d) coaxial cavity, electron beam diag- nostics and guide solenoid; (e) ignitron switches with solid-state trigger units; (f) diode tank containing electron gun and transmission line output spark gap. In Fig. 6b, a schematic diagram of the HCA shows: (I) the Marxpulsed power
The propagation of electromagnetic waves in the annular region of oil wells was studied. The present study aims to analyse the propagation attenuation along the well, as well as the input impedance determined by a source placed near the wellhead. A coaxialwaveguide model was adopted with heterogeneous dielectrics and losses. First, a wave equation solution for the waveguide is presented, assuming a homogeneous medium with losses, by solving the equation in cy- lindrical coordinates using the vector potential technique. An uncertainty analysis model is then developed to model the heterogeneous characteristics of the medium. Monte Carlo simulations were performed with the created model using data gathered from the literature. The results of the simulations indicate that propagation in the transverse electromag- netic mode has the smallest attenuation and that for depths of up to 4000 m, there is an attenuation of less than 52 dB. Furthermore, the input impedance ranges from 10 Ω to 10 kΩ because of the uncertainties involved in the problem in question.
Asking students good questions is a critical tool for developing their skills. In particular, openended questions are believed to be useful for developing students’ cognitive skills, as these ques- tions encourage them to express and elaborate upon their thinking, and provide rationales for their thoughts (Lee, Kinzie, & Whittaker, 2012). Openended questions are likely to engage children in higher-order thinking (Roth, 1996) and usually involve reasoning and judgment (Har- greaves, 1984). Within this context, this study is an attempt to explore how a training program on openended questions encourages teachers to improve their classroom practices. In particular, this cross-sectional study focuses on Turkish teachers’ questioning strategies, and aims to explore how Turkish teachers benefit from openended questions in their classes, depending on their ex- perience, gender and the grade of their classes, and to what extent their use of openended ques- tions differentiate after a training program. At the start of the study, teachers who were teaching Turkish to different grades at different schools were video-recorded in their classes with their students. After the recordings, a teacher training program on the roles and types of question was given to teachers in order to develop their awareness about openended questions that they use in their classrooms. Following the training, teachers were recorded in their classes in the same way again. Finally, after the discourse transcription, the teachers’ questions were classified as open or closed ended, and a comparison of the data recorded before and after the training was designed to determine whether the training course had positive effects on teachers’ use of openended ques- tions. The results of this study indicate that the training encouraged teachers to adopt a more sys- tematic and reflective pedagogical practice. After training, the teachers asked more openended questions which resulted in more student participation, thus there was more dialogue in the class- rooms.
the problem of open-ended and closed-ended questions is very important for surveys in many different branches. for example, in branch of agricultural economy Kealy, m.J. and turner, r.W. (1993) tested whether open-ended and closed-ended contingent valuation mechanisms lead to significantly different results. their test was based on joint estimation of willingness to pay responses to open- and closed-ended questions asked of the same sample of individuals. in a public good example, individuals do respond differently depending on question format. possible explanations include different incentives for strategic behavior and respondents’ lack of familiarity with the open-ended question type. no differences in willingness to pay were found in a private good example. in hospitality management lockyer, t. (2005) investigated lockyer, t. (2005) investigated the factors that influence the selection of hotel accommodation by guests. much of the previous research into this topic used a variety of closed and open question surveys. as another example can be used survey in social gerontology. Krause, n. (2002) describes strategy that can be used to improve the quality of closed-ended survey items that assess a wide range of topics in social gerontology.
This paper describes the burgeoning interest in quality of life studies and suggests that as well as expert definitions, we need to consider people’s own perceptions of what matters. Using open-ended questions from the 1997 and 2002 waves of the British Household Panel Survey we analyse both quantitatively and qualitatively how perceptions of quality of life differ for men and women across the life course. Qualitative analysis reveals that key domains such as health, family and finances often refer, not to self, but to others. Longitudinal analysis demonstrates that people’s perceptions of quality of life change over time, particularly before and after important life transitions. Thus our findings challenge overly individualistic and static conceptions of quality of life and reveal quality of life as a process, not a fixed state.
Abstract—In this paper, a center-fed substrate integrated waveguide (SIW) inclined slot array antenna is designed for a one-dimensional active phased array. A novel coaxial-to-SIW transition is employed to realize the central feed for enhancing bandwidth. The antenna prototype printed onto a single-layer Rogers 5870 is composed of 32 × 16 inclined slots working at Ku-band. As shown in measured result, the bandwidth with return loss < − 10 dB is from 16.6 to 17.1 GHz, and the sidelobe levels of arrays are below − 24 . 8 dB at 16.8 GHz in H planes. The measured gain is 31.8 dB at 16.8 GHz with the aperture eﬃciency of 65%. The active phased array is assembled by an antenna and 32 Tx/Rx modules, and the measured results show that the main lobe can obtain a wide-angle scanning from − 45 to 45 degrees in E planes. The antenna array is suitable for low proﬁle small active phased array radars and communication systems that require spatial wide-angle scanning.
We should especially highlight the difference between the commonly known in FD surface waves and the pulse surface waves we met here. In FD there may exist surface waves at lossy dielectric boundary (so called “surface plasmons”) that decay exponentially both down and up the dielectric surface and propagates along the surface at slow speed with relatively small decay . In a lossless dielectric waveguide there exist guided waves that are localized inside the rod and also decay exponentially off the surface (see Figure 2), these waves propagate without losses at slow speed. As it was discussed above in TD we can observe a different phenomenon: a surface wave that propagates with the speed of light in free space and decay with propagation due to leakage into the dielectric. A similar effect was considered by Annan in 1973 : a horizontal dipole on dielectric surface excites a spherical wave front in the air, which creates a flat front in the dielectric halfspace by its footprint on the surface. In contrast to Annan we placed the sources inside the dielectric medium, so the spherical front in the air is partitioned due to total internal reflection effect into a radiating part (RW in Figure 5) and a surface wave with a gap between them.
In this paper, we use a Monte Carlo code to perform the simulations of multipactor in the coaxial lines using the traditional single eﬀective electron model [13, 14]. The initial particles (N e ) are randomly distributed in the computation space and consequently driven by an electromagnetic force. Consider the Coulomb repulsion among free electrons by means of a single electron sheet. This electronic sheet structure is cylindrically shaped. Considering that the entire structure is divided into two parts, we assume that there are two electronic clouds. One of them is between the outer conductor and the ceramic window, and the other is between the ceramic window and inner conductor. Correspondingly, the radius of the electronic sheet is r s 1 = (b + r ce 1 )/2 and r s 2 = (r ce 2 + a)/2 the center of the coaxial
C++, Lua and Python were the finalists of this search. C++ was discarded as sometimes is a little bit cumbersome to prototype things fast, for the syntax itself and for the fact that it is a compiled language. Lua and Python have a quite similar syntax, both being a high-level and scripting programming language with a fast learning curve and fast for prototyping. At the beginning, all the open-sourced projects that we found that had something to do with VQA where written in Lua using a deep learning framework called Torch 1 . This seemed a good reason to choose Lua over Python but then, having a look into where the community was going to, we found out that frameworks like Theano or TensorFlow were having great success and the developers and research community was moving towards them. Both frameworks are for Python, which made us choose Python as a programming language for the project. Then, we were recommended to use Keras, a library able to work upon Theano or TensorFlow to expedite the prototyping process.
The key of network begins after the need for sharing files. Sharing in local networks was later extended as Internet. In recent years, number of Internet users increased rapidly. As this count increases, the network traffic also becomes serious and a need arises to create new network topologies and to calculate corresponding reliability. The aim of this paper is to study and compare the reliability of openended networks using Wiener index. The calculation of the overall reliability of the networks becomes an important problem. This paper presents the Topology invariant which calculates the reliability of the newly constructed openended networks by introducing new nodes. The simulated experimentation of the proposed Topology invariant for the new openended networks have been done and compared with existing openended networks.