Graphene-based waveguide resonators for submillimeter-wave applications

Utilization of graphene covered waveguide inserts to form tunable waveguide resonators is theoretically explained and rigorously investigated by means of full-wave numerical electromagnetic simulations. Instead of using graphene-based switching elements, the concept we propose incorporates graphene sheets as parts of a resonator. Electrostatic tuning of the graphene surface conductivity leads to changes in the electromagnetic field boundary conditions at the resonator edges and surfaces, thus producing an effect similar to varying the electrical length of a resonator. The presented outline of the theoretical background serves to give phenomenological insight into the resonator behavior, but it can also be used to develop customized software tools for design and optimization of graphene-based resonators and filters. Due to the linear dependence of the imaginary part of the graphene surface impedance on frequency, the proposed concept was expected to become effective for frequencies above 100 GHz, which is confirmed by the numerical simulations. A frequency range from 100 GHz up to 1100 GHz, where the rectangular waveguides are used, is considered. Simple, all-graphene-based resonators are analyzed first, to assess the achievable tunability and to check the performance throughout the considered frequency range. Graphene–metal combined waveguide resonators are proposed in order to preserve the excellent quality factors typical for the type of waveguide discontinuities used. Dependence of resonator properties on key design parameters is studied in detail. Dependence of resonator properties throughout the frequency range of interest is studied using eight different waveguide sections appropriate for different frequency intervals. Proposed resonators are aimed at applications in the submillimeter-wave spectral region, serving as the compact tunable components for the design of bandpass filters and other devices

Structural Characterization of Toxoplasma gondii Brain Cysts in a Model of Reactivated Toxoplasmosis Using Computational Image Analysis

Toxoplasma gondii is an obligate intracellular parasite existing in three infectious life stages—tachyzoites, bradyzoites, and sporozoites. Rupture of tissue cysts and re-conversion of bradyzoites to tachyzoites leads to reactivated toxoplasmosis (RT) in an immunocompromised host. The aim of this study was to apply ImageJ software for analysis of T. gondii brain cysts obtained from a newly established in vivo model of RT. Mice chronically infected with T. gondii (BGD1 and BGD26 strains) were treated with cyclophosphamide and hydrocortisone (experimental group—EG) or left untreated as infection controls (ICs). RT in mice was confirmed by qPCR (PCR+); mice remaining chronically infected were PCR−. A total of 90 images of cysts were analyzed for fractal dimension (FD), lacunarity (L), diameter (D), circularity (C), and packing density (PD). Circularity was significantly higher in PCR+ compared to IC mice (p < 0.05 for BGD1, p < 0.001 for the BGD26 strain). A significant negative correlation between D and PD was observed only in IC for the BGD1 strain (ρ = −0.384, p = 0.048), while fractal parameters were stable. Significantly higher D, C, and PD and lower lacunarity, L, were noticed in the BGD1 compared to the more aggressive BGD26 strain. In conclusion, these results demonstrate the complexity of structural alterations of T. gondii cysts in an immunocompromised host and emphasize the application potential of ImageJ in the experimental models of toxoplasmosis

Burnout Among Students of Technical Faculties in Serbia – A Case Study

Even though university students are not employees of the faculties, their academic duties (attending classes, taking exams, writing term papers and essays, and so on) can be considered as forms of work, whereby they engage socially with their teachers and other students, which is why student burnout has come into increased focus of numerous studies. The aim of this paper is to examine the relationship between gender, tuition fee status, and year of study and burnout among the students of basic academic studies at one of the public faculties in southern Serbia (N=194) using the School Burnout Inventory (SBI-U 9). The obtained results indicate that moderate exhaustion, cynicism, and the feeling of inadequacy are related to moderate burnout of the majority of the students. It has been determined that gender influences one burnout dimension – exhaustion, while the students’ tuition fee status is related to cynicism and inadequacy, as is their year of study. This study also found that high degree of burn-out increases with the years of study

Very-High-Order CEM Modeling

This paper reviews very-highorder techniques for analysis of electromagnetic problems developed in our group over the past ten years and presents some recent advances. 2. CEM Techniques Used The method of moments (MoM) technique based on the volume-integral-equation (VIE) formulation empoloys very-high-order divergence-conforming hierarchical polynomial vector basis functions defined in trilinear hexahedral elements (distorted bricks) [1]. In the recent version of the MoM technique based on the surface-integral-equation (SIE) formulation [2], the elements used for the approximation of metallic and dielectric surfaces are generalized curvilinear quadrilaterals of arbitrary geometrical orders. The basis functions used for the approximation of electric and magnetic surface currents are the surface version of those used in the VIE technique. The hybrid MoM-PO technique introduces divergence-conforming interpolatory Chebyshev-type polynomial basis functions in the physical-optics (PO) part of the structure [3]. The finite element method (FEM) for discretizing partial differential equations in frequency domain employs volumetric hierarchical curl-conforming vector basis functions of high polynomial orders defined in generalized curved hexahedra of high geometrical orders [4

JOURNAL OF AUTOMATIC CONTROL, UNIVERSITY OF BELGRADE, VOL. 16:5-8, 2006© Preliminary Results of the Ion Trajectory Tracking in the Acceleration Region of the Vincy

Abstract—In an accelerating region of a cyclotron an ion makes a large number of turns; thus its tracking requires fast as well as highly accurate computation. Computer code, based on the adaptive time step fourth order Runge Kutta method, has been developed. Accuracy requirement is set simultaneously on the position and momentum calculation. Magnetic fields, used as input, have been evaluated in terms of the radial fluctuations of the orbital frequency, i.e. their isochronism. Ion trajectory tracking has been performed for the four test beams: H – , H2 +, 4 He +, and 40 Ar 6+. Index Terms—Cyclotron, ion beam, trajectory tracking, adaptive time step, magnetic fields, isochronism. I I

Planar printed electrodes for electroporation with high EM field homogeneity

Up to date, several designs of planar electroporation (EP) electrodes have been reported. We propose a novel planar general array-type electrode design, which can be optimized for a desired area of exposure, electric field magnitude and high field homogeneity (uniformity). Unlike other designs that mostly use interdigitated electrodes with alternating potentials, in this design the same polarity electric potentials are used on all elements of the electrode array, with a circular ground electrode surrounding the electrode array. Thereby, an exposure area can be increased and the electric field depth is increased, as well. We describe the procedures used for the design optimization, applicable in general to this type of arrays. Following the initial theoretical assessment, we use full-wave numerical simulations for the design optimization. The electric field measurements on printed circuit board prototypes are included to validate the numerical calculations. Two designs (type A/type B) are presented. Field homogeneity with less than 10% variation in the majority of points of interest is observed, for the designed area of exposure sufficient to place a standard Petri dish bottom (35 mm diameter), and field levels comparable with those obtained in cuvettes. We perform EP experiments in order to confirm the expected EP efficiency. Results confirm high EP efficiency as well as possible easy adaptation of this electrode type for various design specifications. The proposed electrode design is low-cost, scalable, it allows flexible adjustment of the exposure area by adding additional array elements, and both in vivo and in vitro utilization is envisioned with somewhat different applicator mountings

Distinct fatty acid redistribution and textural changes in the brain tissue upon the static magnetic field exposure

We observed different outcomes upon the subacute exposure to the 128 mT highly homogeneous static magnetic field (SMF) when its orientation was (i) aligned with the vertical component of the geomagnetic field; (ii) in the opposite direction. We employed the fatty acids (FA) composition and digital image analyses (DIA) to provide insights into the underlying processes and examine the possible weak SMF effects. Swiss-Webster male mice were whole-body exposed for 1 h/day over five days. Brain tissue’s thin liquid chromatography resulted in brain FA composition, indicating a possible sequence of changes due to the SMF exposure. Quantitative DIA accurately assessed different image parameters. Delicate textural changes were revealed in the group where pathohistological or biochemical alterations have not been detected. DIA-based biological markers seem to be very promising for studying delicate tissue changes, which results from the high sensitivity and wide availability of DIA