Essays on Macroeconomics

This thesis consists of three chapters that explore different macroeconomic issues. In the first chapter, I introduce deep habit formation into an otherwise standard two-country sticky price model with local currency pricing and examine the model's ability to account for the dynamics of the real exchange rate present in the data. I show that if consumption is subject to deep habit formation, the model can match the volatility of the real exchange rate observed in the data, but falls short in generating enough persistence in line with the empirical evidence. In the second chapter, I use data from US Treasury auctions to collect information on the bid-to-cover ratio, a maturity specific proxy for the degree of excess demand in the market for US Treasury bonds. I show that the financial crisis of 2008-09 generated a significant increase in bid-to-cover for short and medium duration debt. Excess demand from private investors has thus likely imposed considerable downward pressure on these yields separate from monetary policy. Further, the notably larger observed increase in bid-to-cover for short-term debt may have contributed to short-term rates hitting the zero lower bound and point to the existence of a convenience yield within the market for US Treasuries. In addition, I find that the US Treasury issued more bonds with medium duration (2,3 and 5 years) in response to the Federal Reserve's first and third quantitative easing programs. Thus, the US Treasury may have reduced the effectiveness of these unconventional policies in lowering yields for medium duration bonds. In the third chapter (joint with Marco Airaudo), we show that the asset market segmentation model built by Chen et al. (2012) to study the effects of quantitative easing contains a unit root. The unit root introduces error in the model's linear approximation, its convergence dynamics and its determinacy properties casting uncertainty on its usefulness for policy analysis. We eliminate the unit root by assuming that agents derive utility services from government bonds. When we simulate the model, we show that it is broadly consistent with conventional theory on the transmission mechanism of quantitative easing. However, our mechanism also highlights a new channel: a negative wealth effect which may counteract some of the stimulus induced by the central bank's purchases of long-term debt.Ph.D., Economics -- Drexel University, 201

Interactive Image-space Point Cloud Rendering with Transparency and Shadows

Point-based rendering methods have proven to be effective for the display of large point cloud surface models. For a realistic visualization of the models, transparency and shadows are essential features. We propose a method for point cloud rendering with transparency and shadows at interactive rates. Our approach does not require any global or local surface reconstruction method, but operates directly on the point cloud. All passes are executed in image space and no pre-computation steps are required. The underlying technique for our approach is a depth peeling method for point cloud surface representations. Having detected a sorted sequence of surface layers, they can be blended front to back with given opacity values to obtain renderings with transparency. These computation steps achieve interactive frame rates. For renderings with shadows, we determine a point cloud shadow texture that stores for each point of a point cloud whether it is lit by a given light source. The extraction of the layer of lit points is obtained using the depth peeling technique, again. For the shadow texture computation, we also apply a Monte-Carlo integration method to approximate light from an area light source, leading to soft shadows. Shadow computations for point light sources are executed at interactive frame rates. Shadow computations for area light sources are performed at interactive or near-interactive frame rates depending on the approximation quality

Interventional treatment of pulmonary embolism - where do we currently stand?

Острата белодробна тромбоемболия е третата най-честа причина за сърдечно-съдова смъртност в света. Внезапното тенсионно обременяване на дясната камера, предизвикано от тромботичните маси в пулмоналната артерия, може бързо да прогресира до клинична картина на тежък кардиогенен шок. Това може да доведе до смъртност над 50%, при пациенти с масивна форма на белодробна тромбоемболия. В такива случаи е мотивирано провеждането на системна фибринолиза, което води до бързо подобрение в деснокамерната функция и стабилизиране на хемодинамиката. Тромболитичният ефект на системната фибринолиза, за съжаление, e съпроводен от петкратно повишен риск от кървене, особено вътречерепно. Следователно в повечето случаи хемодинамично стабилните пациенти биват третирани само с антикоагулантна терапия. Интервенционалното лечение на острата белодробна емболия включва употребата на устройства, използващи ниска доза фибринолитик или такива за перкутанна тромбаспирация. Целта е да се постигне бързо отстраняване на тромботичните маси от пулмоналната артерия, като едновременно се сведе до минимум хеморагичният риск. Този обзор ще се опита да предостави кратък преглед на най-често използваните и налични на пазара устройства, както и клиничните данни, подкрепящи тяхната употреба. Също така, ще бъдат разгледани перспективите в развитието на ендоваскуларното лечение на острата белодробна тромбоемболия. Acute pulmonary embolism is the third most common cause of cardiovascular mortality in the world. The sudden pressure overload of the right ventricle, caused by the thrombotic masses in the pulmonary artery, may quickly progress to profound cardiogenic shock. That results in a mortality rate of more than 50% in patients with a massive form of pulmonary embolism. In such cases, systemic fibrinolysis is warranted, which leads to rapid improvement of the right ventricular function and hemodynamic stabilization. The thrombolytic effect of systemic fibrinolysis is, unfortunately, accompanied by an almost 5 times increased risk of bleeding, especially intracranial one. Therefore, in most cases, for patients with uncompromised hemodynamics, only anticoagulation treatment is offered. Interventional treatment of acute pulmonary embolism consists of the usage of very low-dose fibrinolytic devices or percutaneous thrombus aspiration devices. The goal is to provide rapid removal of the thrombotic masses from the pulmonary artery circulation while keeping the hemorrhagic risk at a minimum. This paper will try to provide a concise review of the most widely used and available devices, together with the latest clinical data, supporting their use. Also, the future perspectives in the field of endovascular treatment of acute pulmonary embolism will be presented

Balloon aortic valvuloplasty in degenerative aortic stenosis

Балонната валвулопластика на аортна клапа (BAV) при аортна стеноза се практикува от над 35 години. Първоначалния ентусиазъм, породен от отличния непосредствен хемодинамичен ефект от процедурата, изчезва поради бързата рестеноза на аортната клапа след интервенция. Резултатите от съвременните методи за дефинитивно лечение на аортната клапна стеноза – sAVR и TAVI, са отлични, благодарение на което са здраво залегнали в ръководствата за лечение. Въпреки това BAV има своите индикации при симптомни пациенти, които не са подходящи за дефинитивните интервенции. Настоящата публикация разглежда съвременните индикации за BAV, основните етапи от процедурата, възможните усложнения, както и резултатите от лечението. Balloon valvuloplasty of the aortic valve (BAV) in aortic stenosis has been practiced for over 35 years. The initial enthusiasm caused by the excellent immediate hemodynamic effect of the procedure disappears due to the rapid restenosis of the aortic valve after intervention. The results of modern methods for defi nitive treatment of aortic valve stenosis – AVR and TAVI are excellent, thanks to which they are fi rmly rooted in treatment guidelines. However, BAV has its indications in symptomatic patients who are not suitable for defi nitive interventions. This publication discusses current indications for BAV, the main stages of the procedure, possible complications, and treatment outcomes

Percutaneous coronary artery intervention after transcatheter aortic valve implantation

Transcatheter implantation of the aortic valve is an increasingly used method for the treatment of aortic stenosis, with a steady trend worldwide to increase the number of TAVI procedures and reduce the age of patients. In Europe, over 180,000 TAVI procedures are currently implemented annually. This review aims to evaluate the patient’s prognosis for the different approaches, the technical diffi culties during the procedure, and to offer useful tips for overcoming them. We publish our experience in transcatheter treatment of ischemic heart disease after TAVI implantation