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Öğe Akut koroner sendrom ile prezente olan ailesel Akdeniz Ateşi (FMF) olgusu(2009) Ordu, Serkan; Kaya, Ahmet; Aydın, Mesut; Dindar, Gökhan; Özhan, Hakan; Yazıcı, MehmetAilesel Akdeniz Ateşi (FMF), klinik olarak tekrarlayan peritonit, plevrit ve artrit gibi seröz zar tutulumuyla karakterize, histolojik ve laboratuar bulgularıyla lokalize veya sistemik inflamasyon kanıtları olan, otozomal resesif geçiş gösteren genetik bir hastalıktır. Sistemik inflamasyon, ateroskleroz başlangıcı ve gelişimi açısından önemli bir faktördür. Biz burada uzun süredir FMF tanısıyla tedavi alan bir hastanın, febril atakları esnasında akut koroner sendrom gelişerek semptom verebileceğini gösterdik.Öğe AV tam blokla gelen subklinik hipotiroidi olgusu(2008) Yazıcı, Mehmet; Koca, Emel Acar; Kaya, Ahmet; Özhan, Hakan; Balaban, YakupSubklinik hipotiroidi serum serbest tiroksin seviyesi normal sınırlarda iken serum tiroid stimülan hormon konsantrasyonunun referans aralığının üstünde tespit edilmesi olarak tanımlanmaktadır. Ateroskleroz riskinde artış, iskemik kalp hastalığı, sistolik ve diastolik disfonksiyon gibi çeşitli kardiyak bozukluklarla subklinik hipotiroidi arasındaki ilişki bilinmektedir. Burada AV tam blokla gelen ve levotiroksin tedavisi ile normal sinüs ritmine döndürülen subklinik hipotiroidili bir olgu sunulmaktadır.Öğe A case of infective endocarditis presented with a giant free wall vegetation [Serbest duvarda büyük hareketli vejetasyon ile kendisini belli eden infektif endokardit olgusu](2010) Sözen, Serhat Bahadır; Kaya, Ahmet; Cinemre, Hakan; Albayrak, Enver Sinan; Özhan, Hakan; Yazıcı, Mehmet[No abstract available]Öğe A case successfully treated giant ventricular septal rupture after acute myocardial infarction(Springer, 2007) Kaya, Ahmet; Kaya, Yasemin; Ordu, Serkan; Özkökeli, Mehmet; Özhan, Hakan; Dağlar, Bahadır; Mehmet, Yazıcı…Öğe A closed interatrial septal aneurysm mimicking a tumor in the left atrium(Texas Heart Inst, 2006) Akdemir, Ramazan; Duran, Sadık; Bulur, Serkan; Kaya, Ahmet; Sözen, Serhat Bahadır; Bilir, Cemil; Uyan, Cihangir…Öğe A comparative electric and dielectric properties of Al/p-Si structures with undoped and Co-doped interfacial PVA layer(Elsevier Sci Ltd, 2014) Kaya, Ahmet; Yücedağ, İbrahim; Tecimer, Hüseyin; Altındal, ŞemsettinIn this study, Al/p-Si structures with undoped and Co-doped PVA interfacial layer called S-1 and S-2 were fabricated and their both electrical and dielectric properties were compared by using 300 kHz capacitance voltage (C-V) and conductance voltage (G/omega-V) measurements at room temperature. Experimental results show that both C and G or dielectric constant (epsilon'), dielectric loss (epsilon '') values were found as strongly function of applied bias voltage especially at inverse and accumulation bias regions. It was found that the value of R-5 considerably decreases with doping Co metal contrary to conductivity especially in the forward bias region. Such behavior can be attributed to the lack of free charges in pure PVA. The imaginary parr of dielectric modulus (M '') gives Two peaks for S-1 corresponding To enough reverse and forward biases and passes from a minimum at about zero bias. Also, it is clear That the minimum of The M '' for S-2 coincides with The maximum of The for S-1 at zero bias. As a result, Co-doped PVA considerable improved The performance of structure. In addition, loss Tangent. (tan delta), ac conductivity (sigma(ac)) and real part. of The electric modulus (M') were obtained and compared each other. (C) 2014 Elsevier Ltd. All rights reserved,Öğe Effect of olmesartan medoxomil on cystatin C level, left ventricular hypertrophy and diastolic function(Taylor & Francis Ltd, 2009) Albayrak, Sinan; Ordu, Serkan; Özhan, Hakan; Yazıcı, Mehmet; Aydın, Mesut; Alemdar, Recai; Kaya, AhmetSerum cystatin C concentration is an alternative measure of kidney function that is less affected by age, sex or muscle mass, and is a more sensitive indicator of early renal dysfunction than creatinine-based estimations of glomerular filtration rate. Cardiovascular sequela increases progressively with the increase in left ventricular mass. Our goal was to evaluate the effect of olmesartan medoxomil on cystatin C levels and left ventricular hypertrophy (LVH) in patients with hypertension. Forty-four newly diagnosed hypertensive patients (27 women and 17 men) were recruited in the study. Olmesartan medoxomil (20 mg/day) was started and the patients were followed up for 6 months. Baseline echocardiographic findings (i.e. left ventricular mass index), serum creatinine, urine albumin/creatinine ratio (ACR) and serum cystatin C levels were compared with the levels of these variables measured at the end of 6-month follow-up period. After 6 months of treatment with olmesartan medoxomil, there was a significant reduction in systolic and diastolic blood pressure (p < 0.001) and in urine ACR (p = 0.04). Mean serum cystatin C levels decreased from 1.61 +/- 0.24 mg/l to 1.31 +/- 0.29 mg/l (p < 0.001). Olmesartan medoxomil treatment also reduced left ventricular mass index (p < 0.001) and LVH (p < 0.001). Our findings indicate that olmesartan medoxomil decreases serum cystatin C levels, urine ACR and reduces LVH in patients with hypertension. To our knowledge, this study is the first to show that olmesartan medoxomil decreases serum cystatin C levels, indicating that in patients with essential hypertension it may counteract end organ damage.Öğe Electrical and dielectric properties and intersection behavior of G/omega-V plots for Al/Co-PVA/p-Si (MPS) structures at temperatures below room temperature(Korean Physical Soc, 2014) Yücedağ, İbrahim; Kaya, Ahmet; Altındal, Şemsettin; Uslu, İbrahimBoth the electrical and the dielectric properties of the Al/Co-doped polyvinyl alcohol/p-Si metal-polymer-semiconductor (MPS) structure have been studied using temperature-dependent admittance-voltage (C/G-V) measurements at temperatures below room temperature at 300 kHz. The C-V plot indicates two peaks for each temperature corresponding to inversion and accumulation regions, respectively. The first peak was attributed to a particular distribution of interface traps (D (it) ), and the second was attributed to the series resistance (R (s) ) and interfacial polymer layer. G/omega-V plots show almost U-shape behavior for all temperatures and a crossing at almost 3 V. Such behavior of the G/omega-V plots may be attributed to the lack of free charge at low temperatures. After this intersection point, while the value of the capacitance (C) starts decreasing, the G/omega continues to increase. The temperature-dependent real and imaginary parts of the dielectric constant (epsilon', epsilon aEuro(3)) and of the electric modulus (M', MaEuro(3)), as well as the ac electrical conductivity (sigma (ac) ), of structure were obtained using C and G data before and after the intersection point (at 2 and 6 V), respectively. Experimental results show that the epsilon', epsilon aEuro(3), loss tangent (tan delta), sigma (ac) , M', and MaEuro(3) values were strong functions of the temperature and the applied bias voltage. In addition, G/omega-T and epsilon aEuro(3)-T plots show two different behaviors, one before and the other after the intersection point.Öğe Frequency and voltage-dependent electrical and dielectric properties of Al/Co-doped PVA/p-Si structures at room temperature(Iop Publishing Ltd, 2014) Yücedağ, İbrahim; Kaya, Ahmet; Altındal, Şemsettin; Uslu, İbrahimIn order to investigate of cobalt-doped interfacial polyvinyl alcohol (PVA) layer and interface trap (D-it) effects, Al/pSi Schottky barrier diodes (SBDs) are fabricated, and their electrical and dielectric properties are investigated at room temperature. The forward and reverse admittance measurements are carried out in the frequency and voltage ranges of 30 kHz-300 kHz and -5 V-6 V, respectively. C-V or epsilon '-V plots exhibit two distinct peaks corresponding to inversion and accumulation regions. The first peak is attributed to the existence of Dit, the other to the series resistance (R-s), and interfacial layer. Both the real and imaginary parts of dielectric constant (epsilon ' and epsilon '') and electric modulus (M ' and M ''), loss tangent (tan delta), and AC electrical conductivity (sigma(ac)) are investigated, each as a function of frequency and applied bias voltage. Each of the M ' versus V and M '' versus V plots shows a peak and the magnitude of peak increases with the increasing of frequency. Especially due to the Dit and interfacial PVA layer, both capacitance (C) and conductance (G/w) values are strongly affected, which consequently contributes to deviation from both the electrical and dielectric properties of Al/Co-doped PVA/p-Si (MPS) type SBD. In addition, the voltage-dependent profile of Dit is obtained from the low-high frequency capacitance (CLF-CHF) method.Öğe Impact of Body Mass Index on Left Ventricular Diastolic Dysfunction(Wiley, 2012) Çil, Habib; Bulur, Serkan; Türker, Yasin; Kaya, Ahmet; Alemdar, Recai; Karabacak, Ahmet; Özhan, HakanBackground: The prevalence of obesity is increasing in the developed and developing world. It is an independent risk factor for heart failure. Left ventricular (LV) diastolic dysfunction has been demonstrated to be a strong predictor of heart failure. In the present study we aimed to assess the impact of body weight on LV diastolic function. Methods: The study was conducted on 2,228 participants (1,424 women, 804 men with a mean age of 49). Traditional and tissue Doppler echocardiographic examination were performed in all of the participants. The demographic and echocardiographic data were compared. Multivariate logistic regression analysis was used to assess the independent predictors of association of LV diastolic function. The study sample was divided into four groups: group 1 (body mass index [BMI] < 25.0 kg/m2), group 2 (BMI 25.029.9 kg/m2), group 3 (BMI = 3039.9 kg/m2), and group 4 (BMI = 40 kg/m2). Results: Septal E was significantly lower in groups 2 and 3 compared to group 1 (P = 0.003). Septal A and septal A were significantly higher whereas septal E and lateral E were significantly lower in the groups 2, 3, and 4 compared to the normal weight group (P < 0.001). Lateral A, deceleration time, and ejection time were significantly higher in obese when compared to the normal weight (P = 0.025, P < 0.001, and P = 0.009, respectively). The E/E ratio was significantly higher in groups 2, 3, and 4 compared to the group 1 (P < 0.001). Logistic regression analysis revealed that age, BMI (OR = 1.060 [95% CI = 1.040 and 1.080]; P < 0.001), hypertension, and diabetes mellitus were independent predictors of LV diastolic dysfunction. Conclusion: BMI is an independent predictor of LV diastolic dysfunction along with age, hypertension, and diabetes mellitus. (Echocardiography 2012;29:647-651)Öğe An incidental case of myxoma presented with the symptoms of critical aortic stenosis in a patient with coronary artery disease: Case report(2011) Ordu, Serkan; Albayrak, Enver Sinan; Satılmışoğlu, Muhammet Hulusi; Yıldırım, Ümran; Kaya, Ahmet; Özhan, Hakan; Yazıcı, MehmetMyxomas are the most common primary cardiac tumors in adult. Clinical presentation of cardiac myxomas is very different. The most common symptoms include dyspnea, atypical chest pain, and obstructive and embolic phenomena. A prevalence of coronary artery disease between 0 and 11% was reported in different series of myxoma. Definitive treatment involves surgical excision of the mass as soon as possible. Because, cases of sudden death have been described, probably related to embolization of the myxoma material into the coronary circulation. A myxoma accompanying with coronary artery disease and severe valvular heart disease is extremely rare. We report here a case of myxoma prolapsing into the left ventricle with concomittant severe aortic stenosis. Copyright © 2011 by Türkiye Klinikleri.Öğe Koroner anjiyoplasti yapılan hastalarda Brain Natriüretik Peptid'in restenoz ve kardiyovasküler olayları öngördürücü değeri(Düzce Üniversitesi, 2009) Kaya, Ahmet; Özhan, Hakan; Albayrak, E. SinanGiriş: BNP, kalp yetmezliğinin gelişimini öngörmede olduğu kadar, iskemik kalp hastalıklarında da kardiyovasküler olayları öngörmede de faydalıdır. Perkütan koroner girişim ile koroner revaskülarizasyon geçiren hastaların önemli kısmında tekrar daralma ve koroner olay gelişmektedir. Bu hastaların uzun dönem takiplerinin ve tedavilerinin daha etkin yapılabilmesi için kolay bakılabilen ve tahmin ettirici değeri olan bir parametreye ihtiyaç duyulmaktadır. Bu çalışmada, BNP'nin uzun dönem restenoz ve kardiyovasküler olaylardaki öngördürücülüğünün araştırılması amaçlandı.Materyal-Metod: Bu çalışmaya, 2006-2008 yılları arasında göğüs ağrısı şikayeti ile ardışık olarak, Düzce Üniversitesi Tıp fakültesi Kardiyoloji ve Acil polikliniklerine başvuran, klinik veya non-invaziv testlerle yüksek riskli olduğu tespit edilen stabil koroner arter hastalığı veya akut koroner sendrom tanısı konup koroner anjiyoplasti uygulanan 73 hasta dahil edildi. Tüm hastaların koroner girişimden hemen önce ve hemen sonra alınan kan örneklerinden bekletilmeden BNP çalışıldı. Altıncı ayda hastalar kardiyovasküler olay ve restenoz yönünden değerlendirilmek üzere arandıBulgular: Bu çalışmada koroner anjiyoplasti yapılan hastalarda, takipte meydana gelişebilecek ölüm ve re-infarktüsün öngörülmesinde BNP'nin faydalı olduğu bulunmuştur. BNP değerleri ?150 pg/ml olarak alındığında, altı ay takip sonrasında ölümü %100 sensitivite ve %79 spesifite ile re-infarktüsü ise %80 sensitivite ve %79 spesifite ile öngördürmekte olduğu bulundu. Koroner işlem öncesi veya işlem sonrası bakılan BNP'nin uzun dönem takipte gelişebilecek restenozun öngörülmesinde faydalı olmadığı bulundu.(p= 0.5, p= 0.4)Sonuçlar: Bu çalışmada koroner anjiyoplasti yapılan hastalarda, uzun dönem takipte meydana gelişebilecek ölüm ve re-infarktüsün öngörülmesinde BNP'nin faydalı olduğu, fakat restenozun tahmininde yeterli olmadığı bulunmuştur. Bunun için de daha ileri klinik çalışmalara ihtiyaç olduğunu düşünmekteyiz.Öğe Koroner arter hastalığı için aile öyküsü pozitif olan bireylerde asimetrik dimetilarjinin düzeylerinin geleneksel risk puanlama yöntemleri ile ilişkisi(Turkish Soc Cardiology, 2011) Satılmışoğlu, Muhammet Hulusi; Özhan, Hakan; Albayrak, Sinan; Kaya, Ahmet; Erden, İsmail; Yazıcı, MehmetAmaç: Koroner arter hastalığı (KAH) Dünyada ve Türkiye’de en sık ölüm nedenidir. Asimetrik dimetilarjinin insanda nitrik oksit biyosentezinin majör inhibitörüdür. Yapılan çalışmalarda plazma asimetrik dimetilarjinin (ADMA) düzeylerindeki artışın endotel disfonksiyonu ve artmış aterogenez ile ilişkili olduğu gösterilmiştir. Bu çalışmada asimetrik dimetilarjinin düzeylerinin koroner arter hastalığı aile öyküsü olan sağlıklı bireylerde mevcut risk belirleme yöntemleri ile ilişkisi araştırılmıştır. Yöntemler: Enine-kesitli gözlemsel olarak tasarlanan bu çalışmaya birinci derece yakınları erken yaşta miyokart enfarktüsü geçiren, yaşları 20-40 arasında olan 52 birey ile kontrol grubu olarak benzer yaş grubunda 26 sağlıklı birey alınmıştır. Çalışmaya alınan deneklerin sigara, diyabet, hiperlipidemi gibi klasik, homosistein ve C-reaktif protein (CRP) gibi biyokimyasal risk faktörleri; Framingham ve TEKHARF risk skorları ve serum asimetrik dimetilarjinin seviyeleri arasındaki ilişki kategorik değişkenler için Ki-kare, sürekli değişkenler için Mann-Whitney U testi ile karşılaştırıldı. Bulgular: Yapılan değerlendirme sonunda KAH açısından riskli bireylerin ortalama açlık kan şekeri, trigliserit, yüksek-dansiteli lipoprotein, diyastolik kan basıncı, bel çevresi, TEKHARF risk skoru kontrol grubundan yüksekti. Total kolesterol, düşük-dansiteli lipoprotein, CRP, homosistein, kreatinin, Framingham risk skoru değerleri gruplar arasında benzer bulundu. Asimetrik dimetilarjinin değerleri risk grubunda ortalama 0.1 μmol/L daha yüksek bulunsa da, bu fark istatistiksel olarak anlamlılığa ulaşmadı (0.7±0.1 μmol/l’e karşılık 0.8±0.1 μmol/l; p=0.061). Sonuç: Asimetrik dimetilarjinin düzeyinin aile öyküsü pozitif olan bireylerde mevcut risk belirleme yöntemlerine ek fayda sağladığı gösterilememiştir. Bu konuda değişik risk gruplarına ait daha fazla sayıda olgu ile yapılacak çalışmalara ihtiyaç vardır. (Anadolu Kardiyol Derg 2011; 2: 114-8)Öğe Koroner arter hastalığı için aile öyküsü pozitif olan bireylerde asimetrik dimetilarjinin düzeylerinin geleneksel risk puanlama yöntemleri ile ilişkisi(2011) Satılmışoğlu, Muhammet Hulusi; Özhan, Hakan; Albayrak, Sinan; Kaya, Ahmet; Erden, İsmail; Yazıcı, MehmetAmaç: Koroner arter hastalığı (KAH) Dünyada ve Türkiye’de en sık ölüm nedenidir. Asimetrik dimetilarjinin insanda nitrik oksit biyosentezinin majör inhibitörüdür. Yapılan çalışmalarda plazma asimetrik dimetilarjinin (ADMA) düzeylerindeki artışın endotel disfonksiyonu ve artmış aterogenez ile ilişkili olduğu gösterilmiştir. Bu çalışmada asimetrik dimetilarjinin düzeylerinin koroner arter hastalığı aile öyküsü olan sağlıklı bireylerde mevcut risk belirleme yöntemleri ile ilişkisi araştırılmıştır. Yöntemler: Enine-kesitli gözlemsel olarak tasarlanan bu çalışmaya birinci derece yakınları erken yaşta miyokart enfarktüsü geçiren, yaşları 20-40 arasında olan 52 birey ile kontrol grubu olarak benzer yaş grubunda 26 sağlıklı birey alınmıştır. Çalışmaya alınan deneklerin sigara, diyabet, hiperlipidemi gibi klasik, homosistein ve C-reaktif protein (CRP) gibi biyokimyasal risk faktörleri; Framingham ve TEKHARF risk skorları ve serum asimetrik dimetilarjinin seviyeleri arasındaki ilişki kategorik değişkenler için Ki-kare, sürekli değişkenler için Mann-Whitney U testi ile karşılaştırıldı. Bulgular: Yapılan değerlendirme sonunda KAH açısından riskli bireylerin ortalama açlık kan şekeri, trigliserit, yüksek-dansiteli lipoprotein, diyastolik kan basıncı, bel çevresi, TEKHARF risk skoru kontrol grubundan yüksekti. Total kolesterol, düşük-dansiteli lipoprotein, CRP, homosistein, kreatinin, Framingham risk skoru değerleri gruplar arasında benzer bulundu. Asimetrik dimetilarjinin değerleri risk grubunda ortalama 0.1 µmol/L daha yüksek bulunsa da, bu fark istatistiksel olarak anlamlılığa ulaşmadı (0.70.1 µmol/l’e karşılık 0.80.1 µmol/l; p0.061). Sonuç: Asimetrik dimetilarjinin düzeyinin aile öyküsü pozitif olan bireylerde mevcut risk belirleme yöntemlerine ek fayda sağladığı gösterilememiştir. Bu konuda değişik risk gruplarına ait daha fazla sayıda olgu ile yapılacak çalışmalara ihtiyaç vardır.Öğe Lifestyle modification decreases the mean platelet volume in prehypertensive patients(Taylor & Francis Inc, 2009) Yazıcı, Mehmet; Kaya, Ahmet; Kaya, Yasemin; Albayrak, Sinan; Cinemre, Hakan; Özhan, HakanMean platelet volume (MPV) is an indicator of platelet activation. The present study was designed to investigate platelet function by measuring MPV, platelet count (PLC) and platelet mass (PLM) in prehypertensive (PHT) subjects. Additionally, we also evaluated the effects of lifestyle modification on platelet functions by measuring MPV, PLC and PLM. We selected 36 newly diagnosed PHT patients and 21 control subjects (BP 120/80 mmHg) matched for age and sex. Lifestyle modifications (weight loss, reduced sodium intake, increased physical activity, limited alcohol consumption and the Dietary Approaches to Stop Hypertension (DASH) diet) were recommended to PHT individuals for 20 weeks. At entry into the study, although PLM and PLC values were similar between study groups, MPV values were significantly higher in the PHT group than in the control group (respectively, 10.41 0.93 fl vs. 9.56 1.04 fl, p 0.01). Additionally, MPV was positively correlated with the systolic blood pressure (BP), body mass index (BMI) and insulin resistance (IR) in the PHT group (r: 0.41; p 0.02, r: 0.37; p 0.04, r: 0.35; p 0.05, respectively). Only age and PHT were found to be independent predictors of MPV after regression analysis. The program substantially lowered BP (net reductions in systolic and diastolic BPs of 16.2 and 8.7 mmHg, p 0.001, p 0.001, respectively). In addition, BMI, waist circumference (WC) and IR were significantly reduced in the PHT group (p 0.01, p 0.01, p 0.05, respectively). At the end of study, although PLM, PLC values were reduced in the PHT group, only the decrease in MPV reached statistical significance (respectively, 10.41 0.93 fl vs. 9.67 1.2 fl, p 0.01). In closing, to our best notice, our study is the first to display a significant increase in MPV in PHT subjects and to show a decrease in MPV by lifestyle modification after 20 weeks. As a result, we consider that decreased platelet activation with multi-aspect effects of lifestyle modification therapy might play an important role in reducing thrombotic risk in PHT patients.Öğe Lingual hematoma due to streptokinase in a patient with acute myocardial infarction(W.B. Saunders, 2010) Kaya, Ahmet; Ordu, Serkan; Albayrak, Enver Sinan; Aydın, Mesut; Erden, İsmail; Özhan, HakanThrombolysis with streptokinase is routinely used for the treatment of acute myocardial infarction. Hematoma of the tongue, vocal cord, uvula, and pharyngeal hemorrhage after streptokinase treatment is a very rare condition. Herein, we describe a case of lingual hematoma after thrombolysis with streptokinase in a patient with acute myocardial infarction. © 2010 Elsevier Inc.Öğe Lithium intoxication related multiple temporary ecg changes: A case report(BioMed Central Ltd., 2008) Canan, Fatih; Kaya, Ahmet; Bulur, Serkan; Albayrak, Enver Sinan; Ordu, Serkan; Ataoğlu, AhmetLithium is a widely used mood stabilizer, which may cause cardiac side effects. In this article, we present the case of a 39-year-old woman who had presented with pre-syncope and developed multiple ECG abnormalities that are caused by lithium intoxication and are disappeared after hemodialysis. © 2008 Canan et al; licensee BioMed Central Ltd.Öğe On the Anomalous Peak in the Forward Bias Capacitance and Dielectric Properties of the Al/Co-Doped (PVC plus TCNQ)/p-Si structures as Function of Temperature(Amer Scientific Publishers, 2015) Yücedağ, İbrahim; Kaya, Ahmet; Altındal, ŞemsettinThe temperature and voltage dependence of electric and dielectric characteristics and ac electrical conductivity (sigma(ac)) of Al/Co-doped (PVC + TCNQ)/p-Si structure in the temperature range of 200-360 K and voltage range of (-4 V)-(9 V) have been investigated in detail by using experimental C-V and G/omega -V measurements at 500 kHz. The value of dielectric constant (epsilon'), dielectric loss (epsilon ''), dielectric loss tangent (tan delta), the real and imaginary parts of electric modulus (M' and M ''), and the sigma(ac) were strongly dependent applied bias voltage and temperature, especially in the depletion and accumulation regions. Such a behavior in these parameters can be explained on restructuring and reordering of charges at interface traps/states. The forward C-V plots exhibit an anomalous peak for each temperature and the peak position shift towards lower voltages with increasing temperature due to the particular density distribution of interface traps (D-it) and series resistance (Rs) of structure. Therefore the plots of dielectric properties and also sigma(ac) indicate two different behaviors before and after intersection point. Before this intersection point, while the values of the epsilon', epsilon '', and sigma(ac) increase, the tan delta decreases, after this intersection point, while the value of the epsilon', epsilon '', and sigma(ac) decrease, the tan delta increases. The ln (sigma(ac))-q/kT plot shows two linear regions both for the 2 V and 9 V which are corresponding to below room temperature (200-300 K) and above room temperature (320-360 K) and the corresponding activation energy (E-a) values were called as Ea((I)) and Ea((II)), respectively. Thus the E-a values were obtained from the slope of these Arrhenius plot as 182 meV and 4.7 meV for 2 V and 22 meV and 0.6 meV for 9 V, respectively.Öğe On the frequency dependent negative dielectric constant behavior in Al/Co-doped (PVC plus TCNQ)/p-Si structures(World Scientific Publ Co Pte Ltd, 2014) Yücedağ, İbrahim; Kaya, Ahmet; Altındal, ŞemsettinThe dielectric properties, electric modulus and ac electrical conductivity (sigma(ac)) of Al/Co-doped (PVC + TCNQ)/p-Si structures have been investigated in the wide frequency and voltage range of 0.5 kHz-3 MHz and (-4 V)-( 9 V), respectively, using the capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements at room temperature. The real and imaginary parts of dielectric constant (epsilon ', epsilon ''), loss tangent (tan delta), sigma(ac) and the real and imaginary parts of electric modulus (M ', M '') were found strongly function of frequency and applied voltage especially at low frequencies. The epsilon '-V plot shows an anomalous peak in the forward bias region due to the series resistance (R-s), surface states (N-ss) and interfacial layer (PVC + TCNQ) effects for each frequency and then it goes to negative values known as negative dielectric constant (NDC) at low frequencies (f <= 70 kHz). Such observation of NDC is important result because it implies that an increment of bias voltage produces a decrease in the charge on the electrodes. The amount of negativity epsilon ' value increases with decreasing frequency and this decrement in the NDC corresponds to the increment in the epsilon ''.Öğe Performance of Bioelectrical Impedance Analysis in the Diagnosis of Metabolic Syndrome(Lippincott Williams & Wilkins, 2012) Özhan, Hakan; Alemdar, Recai; Çağlar, Onur; Ordu, Serkan; Kaya, Ahmet; Albayrak, Sinan; Bulur, SerkanObjective: Central obesity is a prerequisite for the diagnosis of metabolic syndrome (MetS). Precise measurement of visceral fat by bioelectrical impedance analysis (BIA) has been validated. The aim of this study was to investigate the diagnostic performance of BIA in MetS and validate the best cutoff in a large adult cohort. Materials and Methods: The study was performed on the MELEN Study cohort-a prospectively designed survey on the prevalence of cardiometabolic risk factors in Turkish adults. The final cohort consisted of 2219 participants. Weight and visceral body composition were measured without shoes in light indoor clothes using a bioimpedance analyzer (Omron BF 510; Omron Corp, Kyoto, Japan). Plasma concentrations of cholesterol, insulin, fasting triglycerides, high-density lipoprotein cholesterol, glucose, and other biochemical variables were measured. The diagnostic performance of visceral fat measurement by BIA in patients with MetS was assessed. Results: Metabolic syndrome was detected in 751 participants (520 women and 231 men with a mean age of 55 [12] years; 34% of the whole study population). Total body fat and visceral fat levels were higher in subjects with MetS. Correlation analyses showed that there were significant correlations between anthropometric and BIA measurements. Receiver operating curve characteristics of visceral adiposity revealed the best cutoff values as greater than 12% for men and greater than 9% for women. The diagnostic performance was good in both sexes (the sensitivity/specificity and area-under-the-curve values were 76%/75% and 0.83 for men and 83%/67% and 0.81 for women, respectively). Conclusions: Visceral fat measured with BIA is an easily applicable and useful method for identifying people with MetS. The best cutoff values were higher than 12% for men and higher than 9% for women.
