Assoc. Prof. Murat Ak&#231;ay

Yıldırım U., Akçay M., Çoksevim M.

MEDICINA-LITHUANIA , vol.60, no.8, 2024 (SCI-Expanded)

Evaluation of Atrial Electromechanical Delay and Left Atrial Phasic Function in Individuals with Electrocardiographic Early Repolarization Pattern

Akçay M., Yıldırım U.

ACTA CARDIOLOGICA SINICA , vol.38, no.6, pp.714-722, 2022 (SCI-Expanded)

Massive Coronary Stent Thrombosis Treated with Ultra-Slow Thrombolytic Therapy in a Patient with Coronavirus Disease 2019

ACTA CARDIOLOGICA SINICA , vol.38, no.4, pp.536-538, 2022 (SCI-Expanded)

Low-Dose Slow Infusion Tissue Plasminogen Activator (tPA) in Treatment of Thrombotic Coronary Artery Occlusions: Case Series and Literature Review

Akçay M., Çoksevim M., Yıldırım U., Gedikli Ö., Gülel O., Yüksel S., et al.

ANATOLIAN JOURNAL OF CARDIOLOGY , vol.26, no.4, pp.249-257, 2022 (SCI-Expanded)

Comparison of left atrial deformation parameters between renal transplant and hemodialysis patients

Yıldırım U., Akçay M., Çoksevim M., Türkmen E., Gülel O.

CARDIOVASCULAR ULTRASOUND , vol.20, no.1, 2022 (SCI-Expanded)

Effect of supraphysiological estrogen levels on arterial stiffness and hemodynamic parameters

Akçay M., Özdemir A. Z.

ANATOLIAN JOURNAL OF CARDIOLOGY , vol.25, no.5, pp.346-351, 2021 (SCI-Expanded)

Multimodality imaging of asymptomatic huge floating thrombus in the thoracic aorta

Akçay M., Çamlıdağ İ.

ANATOLIAN JOURNAL OF CARDIOLOGY , vol.24, no.1, 2020 (SCI-Expanded)

Noninvasive cardiac output measurement based optimization in nonresponders of cardiac resynchronization therapy

Yenercag M., Yüksel S., Çoksevim M., Akçay M., Arslan U.

PACE-PACING AND CLINICAL ELECTROPHYSIOLOGY , vol.43, no.4, pp.394-401, 2020 (SCI-Expanded)

Is there an association between the parameters of arterial stifness and tinnitus?

Gedikli Ö., Kemal Ö., Yildirim U., Cecen A. B., Karabulut H., Akçay M., et al.

ACTA OTO-LARYNGOLOGICA , vol.140, no.2, pp.128-132, 2020 (SCI-Expanded)

Association of Epicardial Adipose Tissue Thickness with Extent and Complexity of Coronary Artery Disease in Patients with Acute Coronary Syndrome

Akçay M., Şahin M.

ACTA CARDIOLOGICA SINICA , vol.35, no.5, pp.459-467, 2019 (SCI-Expanded)

Effect of routine postdilatation on final coronary blood flow in primary percutaneous coronary intervention patients without angiographic stent expansion problems

Soylu K., Atas A. E., Yenercag M., Akçay M., Seker O., Aksan G., et al.

JOURNAL OF INVESTIGATIVE MEDICINE , vol.66, no.8, pp.1096-1101, 2018 (SCI-Expanded)

The effect of moderate altitude on Tp-e interval, Tp-e/QT, QT, cQT and P-wave dispersion

JOURNAL OF ELECTROCARDIOLOGY , vol.51, no.6, pp.929-933, 2018 (SCI-Expanded) Sustainable Development

Percutaneous intervention of left main coronary artery chronic total occlusion: A case report

Çoksevim M., Akçay M., Soylu K., Goktekin O.

ANATOLIAN JOURNAL OF CARDIOLOGY , vol.19, no.6, pp.419-421, 2018 (SCI-Expanded)

Ibuprofen-induced Kounis syndrome with diffuse ST segment depression and atrial fibrillation

ANATOLIAN JOURNAL OF CARDIOLOGY , vol.18, no.5, pp.380-381, 2017 (SCI-Expanded)

Successful management of complications after inappropriate positioning of a hemodialysis catheter

Akçay M., Deser S. B., Gedikli Ö., Yüksel S., Gülel O.

ANATOLIAN JOURNAL OF CARDIOLOGY , vol.18, no.4, 2017 (SCI-Expanded)

An unusual side effect of weight loss pills in a young man; acute myocardial infarction due to cayenne pepper pills

Akçay M., Gedikli Ö., Yüksel S.

ANATOLIAN JOURNAL OF CARDIOLOGY , vol.18, no.4, pp.310-311, 2017 (SCI-Expanded)

Percutaneous closure of isolated ostium secundum-type atrial septal defect in a patient with Mayer-Rokitansky-Kuster-Hauser syndrome

Akcay M., Gülel O., Soylu K., Meriç M., Elmalı M.

REVISTA PORTUGUESA DE CARDIOLOGIA , vol.35, no.12, 2016 (SCI-Expanded)

Acute thrombotic left main coronary artery; treatment with low dose slow infusion tPA

Akçay M., Soylu K., Yanik A.

INTERNATIONAL JOURNAL OF CARDIOLOGY , vol.224, pp.265-266, 2016 (SCI-Expanded)

Left Ventricular Myocardial Deformation Parameters Are Affected by Coronary Slow Flow Phenomenon: A Study of Speckle Tracking Echocardiography

Gülel O., Akcay M., Soylu K., Aksan G., Yüksel S., Zengin H., et al.

ECHOCARDIOGRAPHY-A JOURNAL OF CARDIOVASCULAR ULTRASOUND AND ALLIED TECHNIQUES , vol.33, no.5, pp.714-723, 2016 (SCI-Expanded)

Double giant thrombi in the left atrium in a patient with rheumatic mitral valve stenosis and atrial fibrillation

Akçay M., Gülel O., Bahcivan M., Yüksel S.

EUROPEAN JOURNAL OF CARDIO-THORACIC SURGERY , vol.44, no.6, pp.1150, 2013 (SCI-Expanded)

A Forgotten Guidewire Causing Intracardiac Multiple Thrombi With Paradoxical and Pulmonary Embolism

Gülel O., Soylu K., Yüksel S., Keçeligil H. T., Akçay M.

CANADIAN JOURNAL OF CARDIOLOGY , vol.29, no.6, 2013 (SCI-Expanded)

Evaluation of the Relationship Between Arterial Blood Pressure, Aortic Stiffness and Serum Endothelin-1 Levels in Patients with Essential Hypertension

Nar G., Soylu K., Akçay M., Gülel O., Yüksel S., Meriç M., et al.

CLINICAL AND EXPERIMENTAL HYPERTENSION , vol.35, no.8, pp.589-594, 2013 (SCI-Expanded)

Articles Published in Other Journals

Causation or coincidence? A case of methanol intoxication presenting with acute myocardial infarction and visual impairment

Boyaci F., Akçay M., Şahin M. K., Erzincan M., Ucar M.

Journal of Experimental and Clinical Medicine (Turkey) , vol.41, no.2, pp.436-439, 2024 (Scopus)

ST-segment Yükselmeli Miyokart Enfarktüsünde Kronik Total Oklüzyonu Öngörmede Nötrofil/Lenfosit ve Trombosit/Lenfosit Oranı

Boyacı F., AKÇAY M., Gökdeniz T.

Harran Universitesi Tip Fakultesi Dergisi , vol.19, no.2, pp.277-283, 2022 (Peer-Reviewed Journal)

Dasatinib: A rare cause of recurrent cardiac tamponade

Akçay M., Çoksevim M.

Journal of Experimental and Clinical Medicine (Turkey) , vol.39, no.2, pp.584-586, 2022 (Scopus)

Effect of ranolazine on Tp-e interval, Tp-e/QTc, and P-wave dispersion in patients with stable coronary artery disease

Akçay M., Çoksevim M., Yenercag M.

JOURNAL OF ARRHYTHMIA , vol.37, no.4, pp.1015-1022, 2021 (ESCI)

Assessment of Arterial Stiffness with Cardio-Ankle Vascular Index in Patients with Mitral Annular Calcification

Boyaci F., Akçay M., Hatem E., Yanik A., Gokdeniz T.

EURASIAN JOURNAL OF MEDICINE , vol.53, no.2, pp.90-95, 2021 (ESCI)

Does Arterial Stiffness Increase in Patients with Surgical Early Menopause?

Akçay M., ÇOKSEVİM M., GEDİKLİ Ö., ULUBAŞOĞLU H., YILMAZ Ö.

Harran Üniversitesi Tıp Fakültesi Dergisi , vol.18, no.2, pp.290-296, 2021 (Peer-Reviewed Journal)

Effect of dialysis and transplantation on myocardial repolarization parameters and P-wave dispersion in chronic kidney disease

Akçay M., Yıldırım U.

JOURNAL OF ARRHYTHMIA , vol.37, no.2, pp.348-355, 2021 (ESCI)

Chronic heavy alcohol consumption and asymptomatic cardiovascular effects: An observational study

Aydin E., Akçay M.

ANNALS OF CLINICAL AND ANALYTICAL MEDICINE , vol.11, no.5, pp.492-497, 2020 (ESCI)

Resuscitated sudden cardiac death due to severe hypokalemia caused by teff grain herbal tea: A case report

TURK KARDIYOLOJI DERNEGI ARSIVI-ARCHIVES OF THE TURKISH SOCIETY OF CARDIOLOGY , vol.48, no.6, pp.623-626, 2020 (ESCI) Sustainable Development

The effect of cardiac resynchronization therapy on arterial stiffness and central hemodynamic parameters

Çoksevim M., Akçay M., Yüksel S., Yenercag M., Cerik B., Gedikli Ö., et al.

JOURNAL OF ARRHYTHMIA , vol.36, no.3, pp.498-507, 2020 (ESCI)

Sakubitril/Valsartan Kalp yetersizliği olgularında yaşam beklentisini ne kadar uzatır?

Updates in Cardiology , vol.3, no.2, pp.17-19, 2020 (Peer-Reviewed Journal)

Successful treatment of a huge thrombotic saphenous vein graft occlusion with aspiration thrombectomy: A case report

Akcay M.

Journal of Tehran University Heart Center , vol.15, no.2, pp.69-72, 2020 (Scopus)

Purulent pericarditis with cardiac tamponade secondary to candida albicans after total parenteral nutrition: A case report

Kertmen Ö., Gök G., Akçay M.

Journal of Tehran University Heart Center , vol.15, no.3, pp.128-130, 2020 (Scopus)

Determining the Cost of Reuse of Disposable Devices in Cardiology

Akcay A., Akçay M.

KLIMIK JOURNAL , vol.32, no.2, pp.136-145, 2019 (ESCI)

Isotretinoin-associated possible Kounis syndrome: A case report and a review of other cardiovascular side effects reported in the literature

TURK KARDIYOLOJI DERNEGI ARSIVI-ARCHIVES OF THE TURKISH SOCIETY OF CARDIOLOGY , vol.47, no.4, pp.324-328, 2019 (ESCI)

The relationship between visible thrombus aspiration material with no-reflow and in-hospital mortality ratio in patients with acute anterior ST-elevation myocardial infarction

Akçay M., Çamlıdağ İ., Gülel O.

TURK KARDIYOLOJI DERNEGI ARSIVI-ARCHIVES OF THE TURKISH SOCIETY OF CARDIOLOGY , vol.47, no.4, pp.333-334, 2019 (ESCI) Sustainable Development

Huge hiatal hernia mimicking a mass with compressive effects on the left atrium causing paroxysmal atrial fibrillation

Akçay M., Çamlıdağ İ.

Journal of Tehran University Heart Center , vol.14, no.2, pp.90-91, 2019 (Scopus)

Evaluation of left atrial electromechanical delay and left atrial phasic functions in surgical early menopause patients

Akcay M., Coksevim M., Ulubaşoğlu H., Gedikli O., Yılmaz Ö.

Journal of Cardiovascular Imaging , vol.27, no.2, pp.137-146, 2019 (Scopus)

An unusual thrombosis of an ostial left internal mammary artery graft causing acute coronary syndrome five years after coronary bypass surgery

Akçay M., Gedikli Ö., Soylu K.

TURK KARDIYOLOJI DERNEGI ARSIVI-ARCHIVES OF THE TURKISH SOCIETY OF CARDIOLOGY , vol.47, no.2, pp.137-139, 2019 (ESCI)

Percutaneous coronary intervention for coronary arteries with origin and course anomalies: Case reports and literature review

Journal of Tehran University Heart Center , vol.14, no.3, pp.141-145, 2019 (Scopus)

Successful percutaneous intervention of the woven coronary artery anomaly: A case report

AKÇAY M., ÇERİK İ. B., SOYLU K.

IHJ Cardiovascular Case Reports (CVCR) , vol.3, no.1, pp.51-53, 2019 (Peer-Reviewed Journal)

Unusual compression of the left internal mammary artery associated with left arm hyperabduction

Journal of Tehran University Heart Center , vol.14, no.1, pp.40-41, 2019 (Scopus)

Pericardial tamponade as the initial sign of systemic lupus erythematosus within Myasthenia Gravis patient

Journal of Experimental and Clinical Medicine (Turkey) , vol.35, no.4, pp.111-113, 2018 (Scopus)

Acute anterior myocardial infarction in the 36th week of pregnancy: A successful stepwise treatment approach

Akçay M., Meriç M., Gedikli Ö., Yüksel S., Şahin M.

TURK KARDIYOLOJI DERNEGI ARSIVI-ARCHIVES OF THE TURKISH SOCIETY OF CARDIOLOGY , vol.46, no.8, pp.702-705, 2018 (ESCI)

Transient ST-segment elevation due to intracranial hemorrhage in a patient presenting with acute anterior myocardial infarction

Akçay M., Coksevim M.

Journal of Experimental and Clinical Medicine (Turkey) , vol.35, no.4, pp.115-117, 2018 (Scopus)

The Relationship Between Fragmented QRS and DiastolicParameters in Coronary Artery Disease Patients withNoncritical Lesions

SEZER F., MERİÇ M., YÜKSEL S., AKÇAY M., GÜLEL O.

Eurasian Journal of Medical Investigation , vol.2, no.4, pp.213-219, 2018 (Peer-Reviewed Journal)

An unusual etiology of ischemic stroke: Woven coronary artery anomaly

Akçay M., Soylu K.

JOURNAL OF THE SAUDI HEART ASSOCIATION , vol.30, no.4, pp.316-318, 2018 (ESCI)

An unusual clinical presentation of isolated tricuspid valve endocarditis: Acute leukosis

Akcay M., Gülel O., Deser S. B., Gedikli Ö.

Journal of Experimental and Clinical Medicine (Turkey) , vol.35, no.3, pp.85-87, 2018 (Scopus)

Evaluation of thrombotic left main coronary artery occlusions; old problem, different treatment approaches

Akçay M., Tanrıvermiş Sayıt A., Gülel O., Celenk C.

INDIAN HEART JOURNAL , vol.70, no.4, pp.573-574, 2018 (ESCI)

Multimodality imaging of a rare type of coronary cameral fistula

JOURNAL OF THE SAUDI HEART ASSOCIATION , vol.30, no.3, pp.276-278, 2018 (ESCI)

Conservative treatment of localized periatrial hematoma associated with functional mitral stenosis, a complication of percutaneous coronary intervention

Akçay M., Soylu K., Yenercag M.

TURK KARDIYOLOJI DERNEGI ARSIVI-ARCHIVES OF THE TURKISH SOCIETY OF CARDIOLOGY , vol.45, no.6, pp.575, 2017 (ESCI)

Smoking and cardiovascular diseases

JOURNAL OF EXPERIMENTAL AND CLINICAL MEDICINE , vol.34, no.1, pp.21-25, 2017 (Scopus)

Giant Coronary Artery Aneurysm Causing Acute Anterior Myocardial Infarction

YANIK A., ARSLAN U., AKÇAY M., MENEKŞE S., YAZGAN U. G.

CASE REPORTS IN MEDICINE , vol.2016, pp.1-2, 2016 (Scopus)

Papers Presented at Peer-Reviewed Scientific Conferences

Progressif Atrial Lead Kopması

Uluslararası Katılımlı Aritmi Toplantısı 2021, Antalya, Turkey, 17 - 19 December 2021, (Summary Text)

Percutaneous extraction of transvenous permanent pacemaker/defibrillator leads; A single center experience

YÜKSEL S., AKÇAY M.

37. Uluslararası Katılımlı Kardiyoloji Kongresi, Antalya, Turkey, 18 - 21 November 2021, (Summary Text)

Dasatinib: A Rare Cause of Recurrent Cardiac Tamponade.

ÇOKSEVİM M., AKÇAY M., UYANIK M.

Uluslararası katılımlı 36.Türk Kardiyoloji Kongresi. TKD2020DİGİTAL, Turkey, 3 - 06 December 2020, vol.24, pp.1-139, (Summary Text)

The effect of diﬀerent therapies on myocardial repolarization parameters and P-wave dispersion in chronic kidney disease

AKÇAY M., yıldırım u.

TKD2020DİJİTAL” 36. Uluslararası Katılımlı Türk Kardiyoloji Kongres, Turkey, 3 - 06 December 2020, vol.24, pp.1-144, (Summary Text)

An alternative solution for the uncrossable microcatheter problem in retrograde CTO case is to cross the lesion directly with RG3

yıldırım u., SOYLU K., AKÇAY M.

27. Ulusal Uygulamalı Girişimsel Kardiyoloji Toplantısı, Turkey, 12 November 2020, vol.24, pp.1-36, (Summary Text)

The Effect of Ranolazine on P-wave dispersion in patients with stable coronary artery disease

AKÇAY M., AKSOY İ.

16. Ulusal Acil Tip Kongresi, Turkey, 12 - 15 November 2020, (Summary Text)

EVALUATION OF MIYOCARDIAL REPOLARIZATION PARAMETERS AND INDEX OF CARDIAC ELECTROPHYSIOLOGICAL BALANCE (ICEB) IN PATIENTS WITH SURGICAL EARLY MENOPAUSE

AKÇAY M., GEDİKLİ Ö.

16. Uluslararası Kardiyoloji ve Kardiyovasküler Cerrahide yenilikler kongresi, 30 October 2020, (Summary Text)

The Effect of Moderate Altitude on Index of Cardiac Electrophysiological Balance (iCEB)

AKÇAY M., YENERÇAĞ M.

Cardiovascular Academy Congress, Digital2020, Turkey, 16 - 20 September 2020, (Summary Text)

The effect of cardiac resynchronization therapy on arterial stiffness and central hemodynamic parameters

ÇOKSEVİM M., AKÇAY M., YÜKSEL S., YENERÇAĞ M., ÇERİK İ. B., GEDİKLİ Ö., et al.

35th International Participation in Turkish Cardiology Congress, Antalya, Turkey, 3 - 06 October 2019, vol.22, pp.13-14, (Full Text)

Trauma-induced acute myocardial infarction treated with low dose slow infusion tPA A Case Report

AKÇAY M., yıldırım u., GEDİKLİ Ö., ÇOKSEVİM M., YÜKSEL S.

35th International Participation in Turkish Cardiology Congress, 3 - 06 October 2019, (Full Text)

Takipsiz Katekolaminerjik Polimorfik Taşikardi Olgusu ve Komplikasyonlar Zinciri

Uluslararası Katılımlı Aritmi Toplantısı, 5 - 07 April 2019, vol.47, pp.33, (Full Text)

Koroner arter stentleme sırasında serbest anjiyoplasti balon kateterinin çıkartılması

AKÇAY M.

34. Uluslararası Katılımlı Kardiyoloji Kongresi, Antalya, Turkey, 20 - 23 October 2018, (Summary Text)

Evaluation of left atrial electromechanical delay and left atrialphasic functions in surgical early menopause patients

AKÇAY M., ÇOKSEVİM M., GEDİKLİ Ö., ULUBAŞOĞLU H., YILMAZ Ö.

34. Uluslararası Katılımlı Türk Kardiyoloji Kongresi, Antalya, Turkey, 20 - 23 October 2018, vol.20, pp.100-101, (Full Text)

An Unusual Compression of the Left Internal Mammary Artery (LIMA) Associated with Left Arm Hyperabduction

AKÇAY M.

34. Uluslararası Katılımlı Kardiyoloji Kongresi, 20 - 23 October 2018, (Summary Text)

An Unusual Clinical Presentation of Isolated Tricuspid Valve Endocarditis: Acute Leukosis

AKÇAY M., GÜLEL O., DEŞER S. B., GEDİKLİ Ö.

34. Uluslararası Katılımlı Kardiyoloji Kongresi, Antalya, Turkey, 20 - 23 October 2018, (Summary Text)

‘‘Cepte hap’’ Tedavisine Bağlı Yeni Gelişen Sol Dal Bloğu ve Hipotansiyon

AKÇAY M., ŞEKER O. O., VURAL Ö., GÖK G., KERTMEN Ö., GEDİKLİ Ö., et al.

34. Uluslararası Katılımlı Kardiyoloji Kongresi, Antalya, Turkey, 20 - 23 October 2018, (Summary Text)

Fenilefrinli göz damlasıyla tetiklenen akut koroner sendrom olgusu

AKÇAY M., GEDİKLİ Ö., ÇERİK İ. B., KERTMEN Ö., yıldırım u., ÇOKSEVİM M., et al.

33.Uluslararası katılımlı Türk Kardiyoloji Kongresi, Antalya, Turkey, 5 - 08 October 2017, (Summary Text)

Nadir Bir Yan Etki: Dabigatran Sonrası Gelişen Derin Hiponatremi

ÇOKSEVİM M., AKÇAY M., DAĞAŞAN G., YENERÇAĞ M., GEDİKLİ Ö., ÇERİK İ. B., et al.

33. Uluslararası Katılımlı Kardiyoloji Kongresi, Antalya, Turkey, 5 - 08 October 2017, (Summary Text)

Gebe komplike aort kapak trombozu

GEDİKLİ Ö., AKÇAY M., GÜLEL O., ŞAHİN M.

33. Uluslararası Katılımlı Kardiyoloji Kongresi, Antalya, Turkey, 5 - 08 October 2017, (Summary Text)

An unusual thrombosis of the ostial left internal mammary artery graft causing acute coronary syndrome five years after coronary bypass surgery

AKÇAY M., GEDİKLİ Ö., SOYLU K.

33. Uluslararası Katılımlı Kardiyoloji Kongresi, 5 - 08 October 2017, (Summary Text)

Brugada phenocopy in a 31 year-old male patient with pectus excavatum

AKÇAY M., YÜKSEL S., ŞAHİN M.

33. Uluslarası Katılımlı Türk Kardiyoloji Kongresi, Antalya, Turkey, 5 - 08 October 2017, (Summary Text)

Atriyoventriküler tam blok ile kardiyak manifestasyonu olan Behçet hastalığı olgusu

AKÇAY M., GEDİKLİ Ö., YÜKSEL S.

33. Uluslarası Katılımlı Türk Kardiyoloji Kongresi, Antalya, Turkey, 5 - 08 October 2017, (Summary Text)

Perikardiyal tamponad ve plevral efüzyonla kliniğe presente olan akut lenfoblastik T-hücreli lenfoma olgusu

AKÇAY M., ÇOKSEVİM M., GEDİKLİ Ö., SOYLU K., yıldırım u., YILMAZ Ö.

33. Uluslararası Katılımlı Kardiyoloji Kongresi, 5 - 08 October 2017, (Summary Text)

Akut inferior myokard infarktüsüne yol açan floppy wire ile düzelen nitrata dirençli koroner vazospazm olgusu

AKÇAY M., YÜKSEL S., YENERÇAĞ M., ÇOKSEVİM M., Yanık A., Dağaşan G., et al.

33. Uluslarası Katılımlı Türk Kardiyoloji Kongresi, Turkey, 5 - 08 October 2017, (Summary Text)

Parenteral Diklofenak sodyum kullanımını takiben gelişen akut koroner sendrom olgusu: Kounis Sendromu

YENERÇAĞ M., ÇOKSEVİM M., YÜKSEL S., Ateş A. H., Yontar O. C., AKÇAY M., et al.

33. Uluslarası Katılımlı Türk Kardiyoloji Kongresi, Antalya, Turkey, 5 - 08 October 2017, (Summary Text)

Successful management of complications after inappropriate positioning of a hemodialysis catheter

AKÇAY M., DEŞER S. B., GEDİKLİ Ö., YÜKSEL S., GÜLEL O., KERTMEN Ö., et al.

33. Uluslarası Katılımlı Türk Kardiyoloji Kongresi, Antalya, Turkey, 5 - 08 October 2017, (Summary Text)

CRT-ICD Batarya Replasmanı Esnasında Bataryadan Ayrılamayıp Kırılan Leadlerin Traksiyon Yöntemiyle Başarılı Ekstraksiyonu ve Yeni CRT-ICD İmplantasyonu