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Search Results: 1 - 10 of 467482 matches for " Oleg A. Tretyakov;Mehmet Kaya "
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Time-Domain Real-Valued TM-Modal Waves in Lossy Waveguides
Oleg A. Tretyakov;Mehmet Kaya
PIER , 2013, DOI: 10.2528/PIER13030206
Abstract: The waveguide has a perfectly conducting surface. Its cross section domain is bounded by a singly-connected contour of a rather arbitrary but enough smooth form. Possible waveguide losses are modeled by a homogeneous conductive medium in the waveguide. The boundary-value problem for the system of Maxwell's equations with time derivative is solved in the time domain. The real-valued solutions are obtained in Hilbert space L in a form of transverse-longitudinal decompositions. Every field component is a product of the vector element of the modal basis dependent on transverse coordinates, and the modal amplitudes dependent on time and the axial coordinate. Three examples are included. The dynamic properties of the modal waves and concomitant energetic waves are studied and their dependence on time illustrated graphically.
The Real-Valued Time-Domain TE-Modes in Lossy Waveguides
Oleg A. Tretyakov;Mehmet Kaya
PIER , 2012, DOI: 10.2528/PIER12031402
Abstract: The time-domain studies of the modal fields in a lossy waveguide are executed. The waveguide has a perfectly conducting surface. Its cross section domain is bounded by a singly-connected contour of rather arbitrary but enough smooth form. Possible waveguide losses are modeled by a conductive medium which fills the waveguide volume. Standard formulation of the boundary-value problem for the system of Maxwell's equations with time derivative is given and rearranged to the transverse-longitudinal decompositions. Hilbert space of the real-valued functions of coordinates and time is chosen as a space of solutions. Complete set of the -time-domain modal waves is established and studied in detail. A continuity equation for the conserved energetic quantities for the time-domain modal waves propagating in the lossy waveguide is established. Instant velocity of transportation of the modal flux energy is found out as a function of time for any waveguide cross section. Fundamental solution to the problem is obtained in accordance with the causality principle. Exact explicit solutions are obtained and illustrated by graphical examples.
Derivation of Klein-Gordon Equation from Maxwell's Equations and Study of Relativistic Time-Domain Waveguide Modes
Oleg A. Tretyakov;Ozlem Akgun
PIER , 2010, DOI: 10.2528/PIER10042702
Abstract: A initial-boundary value problem for the system of Maxwell's equations with time derivative is formulated and solved rigorously for transient modes in a hollow waveguide. It is supposed that the latter has perfectly conducting surface. Cross section, , is bounded by a closed singly-connected contour of arbitrary but smooth enough shape. Hence, the and modes are under study. Every modal field is a product of a vector function of transverse coordinates and a scalar amplitude dependent on time, , and axial coordinate, . It has been established that the study comes down to, eventually, solving two autonomous problems. . Final result of this step is de nition of complete (in Hilbert space, ) set of functions dependent on transverse coordinates which originates a basis. . The amplitudes are generated by the solutions to Klein-Gordon equation (), derived from Maxwell's equations directly, with and as independent variables. The solutions to are invariant under relativistic Lorentz transforms and subjected to the causality principle. Special attention is paid to various ways that lead to analytical solutions to . As an example, one case (among eleven others) is considered in detail. The modal amplitudes are found out explicitly and expressed via products of Airy functions with arguments dependent on and .
Temporal Cavity Oscillations Caused by a Wide-Band Waveform
Oleg A. Tretyakov;Fatih Erden
PIER B , 2008, DOI: 10.2528/PIERB08031222
Abstract: Excitation of the electromagnetic fields by a wide-band current surge, which has a beginning in time, is studied in a cavity bounded by a closed perfectly conducting surface. The cavity is filled with Debye or Lorentz dispersive medium. The fields are presented as the modal expansion in terms of the solenoidal and irrotational cavity modes with the time-dependent modal amplitudes, which should be found. Completeness of this form of solution has been proved earlier. The systems of ordinary differential equations with time derivative for the modal amplitudes are derived and solved under the initial conditions and in compliance with the causality principle. The solutions are obtained in the form of simple convolution (with respect to time variable) integrals. Numerical examples are exhibited as well.
Electromagnetic Fields in a Cavity Filled with Some Nonstationary Media
Mariya S. Antyufeyeva;Oleg A. Tretyakov
PIER B , 2010, DOI: 10.2528/PIERB09112402
Abstract: The paper presents an analytical approach to treat the problem of transient oscillations in a cavity uniformly filled with nonstationary medium, which is characterized by time-varying permittivity and conductivity. Closed-form solutions are found for some transient excitations and medium parameters.
Transient Electromagnetic Fields in a Cavity with Dispersive Double Negative Medium
Mariya S. Antyufeyeva;Alexander Yu. Butrym;Oleg A. Tretyakov
PIER M , 2009, DOI: 10.2528/PIERM09062307
Abstract: Electromagnetic fields in a cavity filled with double negative dispersive medium and bounded by a closed perfectly conducting surface is studied in the Time Domain. The sought electromagnetic fields are found in a closed form by using decomposition over cavity modes and solving in TD the differential equations for the time varying mode amplitudes. Some features of frequency response of such an electromagnetic system are presented. Waveforms of electromagnetic fields excited by a wideband pulse are considered.
Theranostic Oxygen Delivery Using Ultrasound and Microbubbles
James J. Kwan, Mehmet Kaya, Mark A. Borden, Paul A. Dayton
Theranostics , 2012,
Abstract: Means to overcome tumor hypoxia have been the subject of clinical investigations since the 1960's; however these studies have yet to find a treatment which is widely accepted. It has been known for nearly a century that hypoxic cells are more resistant to radiotherapy than aerobic cells, and tumor hypoxia is a major factor leading to the resistance of tumors to radiation treatment as well as several cytotoxic agents. In this manuscript, the application of ultrasound combined with oxygen-carrier microbubbles is demonstrated as a method to locally increase dissolved oxygen. Microbubbles can also be imaged by ultrasound, thus providing the opportunity for image-guided oxygen delivery. Simulations of gas diffusion and microbubble gas exchange show that small amounts (down to 5 vol%) of a low-solubility osmotic gas can substantially increase microbubble persistence and therefore production rates and stability of oxygen-carrier microbubbles. Simulations also indicate that the lipid shell can be engineered with long-chain lipids to increase oxygen payload during in vivo transit. Experimental results demonstrate that the application of ultrasound to destroy the microbubbles significantly enhances the local oxygen release. We propose this technology as an application for ultrasound image-guided release of oxygen directly to hypoxic tissue, such as tumor sites to enhance radiotherapy.
The prevalance, epidemiology and risk factors for onychomycosis in hemodialysis patients
Güven Kuvandik, Meryem ?etin, Gultekin Genctoy, Mehmet Horoz, Mehmet Duru, Cenk Akcali, Salim Satar, Ahmet A Kiykim, Hasan Kaya
BMC Infectious Diseases , 2007, DOI: 10.1186/1471-2334-7-102
Abstract: One hundred and nine hemodialysis patients were enrolled. Fifty-seven of hemodialysis patients had the diagnosis of diabetes mellitus. Nail scrapings were obtained from 76 patients who had dystrophic nail changes. Samples were examined with 20% potassium hydroxide solution and all of the samples were inoculated on Saboraud's dextrose agar, potateus dextrose agar and mycobiotic agar. Diagnosis of onychomycosis was based on the presence of both positive clinical signs and positive potassium hydroxide test.Onychomycosis was diagnosed in 26.6% of hemodialysis patients. Diabetes mellitus was present in 68.9% of patients with onychomycosis. Toenail scraping cultures were reported to be positive in 19.7% of patients with dystrophic nail changes. Logistic regression analysis revealed that the presence of diabetes mellitus and the mean duration of hemodialysis were the significant predictors associated with the development of onychomycosis.The prevalence of dystrophic nail changes and onychomycosis is increased among hemodialysis patients. The dialysis duration and the presence of diabetes mellitus are the independent risk factors associated with the development of onychomycosis in uraemic patients.In general population, the prevalence of onychomycosis (OM) ranged between 2 to 11.1% [1-4]. Risk factors associated with the development of OM include increasing age, immunosupression, the presence of diabetes mellitus, family history, peripheral vascular disease, and disorders related to the skin such as hyperhidrosis, psoriasis, onychogriposis and nail trauma [1,5-8].Among diabetic patients, the reported prevalence of OM ranges between 1.2–26% [9-11]. In a multicentre study, the risk odds ratio for diabetic subjects to have toenail onychomycosis has been reported as 2.77 times compared with normal individuals [9]. Patients with chronic renal failure may exhibit various cutaneous abnormalities including pruritus, xerosis cutis, alterations in cutaneous pigmentation, actinic elas
A case of acute disseminated encephalomyelitis presented with transvers myelitis - Case Report
Avni Kaya,Mustafa ?zkan,M. Sel?uk Bekta?,Mehmet A??kg?z
Turk Pediatri Ar?ivi , 2010,
Abstract: Acute disseminated encephalomyelitis is an inflammatory and demyelinating disorder of central nervous system. A 9-year-old male was admitted with unable to walk, non-sensation of legs, urinary incontinence and encopresis for 2 days. On physical examination, muscle strength was 5/5 on upper extremities and 1/5 on lower extremities. Loss of pain, temperature and touch sensation was present on both lower extremities, reaches to T8 level. On spinal magnetic resonance imaging, diffuse hyperintensity from C3 to conus medullaris was detected. While electromyography was consistent with polyradiculoneuritis, magnetic resonance imaging findings were concordant with acute disseminated encephalomyelitis. On account of this case, we would like to emphasize that acute disseminated encephalomyelitis should be considered in patients presented with transverse myelitis; therefore, in addition to spinal magnetic resonance imaging, cranial magnetic resonance imaging should be examined in these patients. (Turk Arch Ped 2010; 45: 299-302)
Mehmet Fatih KAYA
Turkish Studies , 2011,
Abstract: In this study, focused on problems on this topic and how geography teachers develops the visual literacy skills on students at the highschools.This research is action research of the qualitative research methods. The study group of research, consists of twenty-geography teacher who serve in Gaziantep. The datas collected through the interview evaluated by descriptive analysis method.All of teachers according to datas where gets end of the research; are agrees that visual are given in many tectbooks and requirement of visual literacy. Most of teachers consider inadequate textbooks on prometing visual leteracy skills. Being different form the experince and knowledge of teachers that prometing visual skills leads to a different application to submit on geography lessons. In this research, tried to obtain problems on development of visual literacy skills Bu al mada, liselerde co rafya retmenlerinin rencilerde g rsel okuryazarl k becerilerini nas l geli tirdiklerini ve bu konuda kar la t klar sorunlar üzerinde durulmu tur.Bu ara t rma nitel ara t rma y ntemlerinden eylem ara t rmas desenindedir. Ara t rman n al ma grubu Gaziantep’te g rev yapan yirmi co rafya retmeninden olu maktad r. G rü me yoluyla elde edilen veriler betimsel analiz y ntemiyle de erlendirilmi tir. Ara t rma sonucunda elde edilen bulgulara g re retmenlerin tamam ; g rsel okuryazarl n gereklili i ve ders kitaplar n n ok say da g rsele yer verdi i konusunda hemfikirlerdir. retmenlerin büyük b lümü g rsel okuryazarl k becerisi kazand rmada ders kitaplar n yetersiz g rmektedir. retmenlerin deneyim ve bilgi birikimlerinin farkl olu u co rafya derslerinde g rsellerle ilgili beceri kazand rmada farkl uygulamalara yer vermelerine neden olmaktad r. Ara t rmada g rsel okuryazarl k becerisinin geli tirilmesinde kar la lan sorunlara ula lmaya al lm t r.
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