Why does mutual fund performance not persist? The impact and interaction of fund flows and manager changes

This paper investigates the reasons for the lack of long-term persistence in the investment performance of actively managed equity mutual funds. We document that the responses of investors, fund managers, and investment management companies to past performance have an important impact on future performance. Conditioning on fund flows and manager changes allows us to predict future performance of both past outperforming (winner) and past underperforming (loser) funds. Recent winner funds, experiencing neither high inflows nor the departure of a skilled fund manager, outperform by 3.60 percentage points based on risk-adjusted returns in the following year, relative to winner funds suffering from both effects. We also find that the performance of the worst performing funds experiencing both the replacement of the fund manager (internal governance) and high outflows (external governance) enjoy a subsequent increase in performance of 2.40 percentage points in the following year, relative to loser funds not experiencing these effects. Among loser funds, in particular, both mechanisms appear to interact strongly.Mutual Funds; Performance Persistence; Fund Flows; Manager Turnover

Excitation of the precessing vortex core by active flow control to suppress thermoacoustic instabilities in swirl flames

In this study, we apply periodic flow excitation of the precessing vortex core at the centerbody of a swirl-stabilized combustor to investigate the impact of the precessing vortex core on flame shape, flame dynamics, and especially thermoacoustic instabilities. The current control scheme is based on results from linear stability theory that determine the precessing vortex core as a global hydrodynamic instability with its maximum receptivity to open-loop actuation located near the center of the combustor inlet. The control concept is first validated at isothermal conditions. This is of utmost importance for the proceeding studies that focus on the exclusive impact of the precessing vortex core on the combustion dynamics. Subsequently, the control is applied to reacting conditions considering lean premixed turbulent swirl flames. Considering thermoacoustically stable flames first, it is shown that the actuation locks onto the precessing vortex core when it is naturally present in the flame, which allows the precessing vortex core frequency to be controlled. Moreover, the control allows the precessing vortex core to be excited in conditions where it is naturally suppressed by the flame, which yields a very effective possibility to control the precessing vortex core amplitude. The control is then applied to thermoacoustically unstable conditions. Considering perfectly premixed flames first, it is shown that the precessing vortex core actuation has only a minor effect on the thermoacoustic oscillation amplitude. However, we observe a continuous increase of the thermoacoustic frequency with increasing precessing vortex core amplitude due to an upstream displacement of the mean flame and resulting reduction of the convective time delay. Considering partially premixed flames, the precessing vortex core actuation shows a dramatic reduction of the thermoacoustic oscillation amplitude. In consideration of the perfectly premixed cases, we suspect that this is caused by the precessing vortex core-enhanced mixing of equivalence ratio fluctuations at the flame root and due to a reduction of time delays due to mean flame displacement.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Interferon beta signaling and microglial activation in a murine model for age-related macular degeneration

Age-related macular degeneration (AMD) is a disease of the retina and the leading cause of vision loss among the elderly in industrial countries. It is characterized by progressive impairment of the visual perception and can be categorized into two distinct forms; wet and dry AMD. Typical hallmarks of wet AMD are chronic activation of the innate immune system in the retina and the ingrowth of blood vessels from the choroid into the retina termed as choroidal neovascularization (CNV). Microglia, the immune competent cells of the retina, play a major role in the induction and advancement of chronic inflammation and CNV development observed during AMD pathogenesis regulating the immune answer and tissue homeostasis. Therefore, strategies to dampen microgliosis present attractive therapeutic options in the treatment of AMD and other retinal degenerative disorders. Interferon beta (IFN-ß), an endogenous cytokine and signaling molecule, is responsible for essential regulatory functions of the innate immune system and is well known for its anti-angiogenic and immunomodulatory properties. Consequently, IFN-ß is used as first line treatment of multiple sclerosis, a neuroinflammatory autoimmune disease of the brain. However, it was previously unknown whether the protective effect is transferable to the retina. Hence, to fill this gap the current study endeavored to determine the effects of IFN-ß signaling on microglial activation and choroidal neovascularization using a reproducible murine laser-coagulation model of wet AMD. The results presented in this study reveal a crucial role of IFN-ß signaling in regulating microglial reactivity and pathological angiogenesis. Global as well as microglia specific interferon-?/-ß receptor (IFNAR) deletion fortified disease severity and progression as evidenced by enhanced microglia reactivity, vessel leakage and CNV development. In contrast, IFN-ß therapy resulted in a significant reduction of the clinical features associated with the murine laser-coagulation model of wet AMD. In conclusion, this work indicates a protective role of IFNAR signaling in retinal immune mechanisms and identifies IFN-ß as a promising new strategy for future therapy approaches to modulate chronic inflammation in retinal degenerative diseases. Doktorarbeit Anika Lückoff Cologne, July 201

Fund Flows, Manager Changes, and Performance Persistence

Most empirical studies suggest that mutual funds do not persistently outperform an appropriate benchmark in the long run. We analyze this lack of persistence in terms of two equilibrating mechanisms: fund flows and manager changes. Using data on actively managed US equity mutual funds, we find that if neither mechanism is operating, winner funds (top-decile ranked in previous year) continue to significantly outperform loser funds (bottom-decile ranked in previous year) by 4.08 percentage points per annum. However, the difference between previous winner and loser funds declines to zero within one year if the two mechanisms are acting together. Thus, equity mutual fund out- and underperformance are unlikely to persist in well-functioning financial markets

Why Does Mutual Fund Performance Not Persist? The impact and interaction of fund flows and manager changes

We explain the lack of long-term performance persistence by actively managed U.S. equitymutual funds in terms of two equilibrating mechanisms: fund flows and manager changes. Wefind that these mechanisms acting together affect the future performance of past outperforming(winner) funds and past underperforming (loser) funds. Fund flows in isolation have a significanteffect on performance, whereas manager changes in isolation have only a limited effect. Acombination of both fund flows and manager changes has a substantial impact on future fundperformance. If neither of these equilibrating mechanisms is operating, winner funds continue to significantly outperform loser funds by 4.08 percentage points per annum. However, the difference between winner and loser funds declines to almost zero if the two mechanisms are acting together. We also document that managers of winner funds increase risk, while managers of loser funds reduce risk, although losers who are fired took more risk than losers who keep theirjobs

Why does mutual fund performance not persist? The impact and interaction of fund flows and manager changes

This paper investigates the reasons for the lack of long-term persistence in the investment performance of actively managed equity mutual funds. We document that the responses of investors, fund managers, and investment management companies to past performance have an important impact on future performance. Conditioning on fund flows and manager changes allows us to predict future performance of both past outperforming (winner) and past underperforming (loser) funds. Recent winner funds, experiencing neither high inflows nor the departure of a skilled fund manager, outperform by 3.60 percentage points based on risk-adjusted returns in the following year, relative to winner funds suffering from both effects. We also find that the performance of the worst performing funds experiencing both the replacement of the fund manager (internal governance) and high outflows (external governance) enjoy a subsequent increase in performance of 2.40 percentage points in the following year, relative to loser funds not experiencing these effects. Among loser funds, in particular, both mechanisms appear to interact strongly

Aktive Strömungskontrolle als Werkzeug zur Erforschung der Rolle es präzidierenden Wirbelkerns in Drallflammen

The flow inside a gas turbine is typically highly turbulent when it leaves the compressor and reaches the burner inlet. Inside the burner, the flow typically passes through a swirl generator which transforms the almost parallel flow into a swirling flow. The degree of the swirl induced to the flow is su ciently high such that the swirling jet emanating from the burner outlet into the combustion chamber undergoes a phenomenon known as vortex breakdown. As a consequence of this phenomenon, a central recirculation zone forms around the jet axis which allows the flame to stabilize inside the resulting shear layers. This reacting flow configuration allows for an e cient and low-emission lean combustion, but is prone to thermoacoustic and hydrodynamic instabilities. One of the most prominent hydrodynamic instabilities in this flow configuration is the so-called precessing vortex core (PVC) which manifests as a single-helical coherent structure meandering in downstream direction along the shear layers. Although, there are already several studies about the PVC, its impact on the combustion process is not fully understood and described, yet. In this thesis, an active flow control system is developed which creates exclusive experimental conditions to further investigate the role of the PVC on the combustion process. This flow control system is integrated into the mixing section of a swirl burner. There, helical actuation, according to the zero-net-mass-flux principle, is achieved which mimics the helical motion of the PVC. The actuation is applied in the region where the response of the PVC to external periodic forcing is maximal which can be considered as the origin of the PVC. Due to the maximal response of the PVC in this region, only small actuation amplitudes are necessary to achieve a considerable control e ect without changing the flow configuration fundamentally. After a comprehensive proof of the control concept under isothermal and reacting operating conditions, the flow control system is applied to either excite a PVC via open-loop forcing or suppress it via closed-loop control depending on the flow configuration. With this tool at hand, the exclusive impact of the PVC on flame dynamics, mixing and NOx emissions is investigated. It is observed that the excitation of the PVC can damp self-excited thermoacoustic oscillations considerably. One explanation for this observation, is a possible break of the symmetry of axisymmetric equivalence ratio fluctuations by the skew-symmetric actuated PVC. Further explanations for this observation are given by two mean field coupling mechanisms which are derived from time-resolved flow field and heat release rate measurements. These mechanisms are derived in connection with measurements of the flame transfer function (FTF) which reveal that the PVC is capable of reducing the FTF gain without changing the FTF phase. According to mechanism one, the PVC reduces the growth rate of the Kelvin-Helmholtz instability which hinders axisymmetric modes to grow in the shear layers. Mechanism two refers to the PVC-induced change of the mean flame shape which becomes more compact and is shifted upstream towards the burner outlet. As a result, less heat release fluctuations reach the sensitive flame tip which leads as well to a damping of the FTF gain. Besides these findings regarding the impact of the ing cold reactants with hot products from the central recirculation zone. This large-scale mixing enhances the reaction rate and entrains radicals into the incoming flow. Consequently, the flame follows the PVC-induced vortices and the NOx emission level increases. With the developed flow control approach at hand, unique experimental conditions are generated which allow for investigating the exclusive impact of the PVC on the combustion process. Furthermore, this flow control approach can be applied to actively control the stability and e ciency of the combustion process. To apply the laboratory actuation system to a machine of industrial scale, an alternative actuation design is suggested which relies on fluidic oscillators. Moreover, the flow control approach studied in the present thesis is applicable to all types of flow with inherent global hydrodynamic modes such as the PVC.Die Strömung innerhalb einer Gasturbine ist typischerweise stark turbulent, wenn sie den Verdichter verlässt und den Brennereinlass erreicht. Im Inneren des Brenners passiert die Strömung typischerweise einen Drallgenerator, der die fast parallele Strömung in eine Drallströmung umwandelt. Der Grad des in der Strömung induzierten Dralls ist ausreichend hoch, so dass der vom Brennerauslass in die Brennkammer austretende Drallstrahl ein Phänomen erfährt, das als Wirbelaufplatzen (vortex breakdown) bezeichnet wird. Als Folge dieses Phänomens bildet sich um die Strahlachse eine zentrale Rezirkulationszone, die es der Flamme ermöglicht, sich innerhalb der entstehenden Scherschichten zu stabilisieren. Diese reaktive Strömungskonfiguration ermöglicht eine effiziente und emissionsarme magere Verbrennung, ist jedoch anfällig für thermoakustische und hydrodynamische Instabilitäten. Eine der bekanntesten hydrodynamischen Instabilitäten in dieser Strömungskonfiguration ist der so genannte precessing vortex core (PVC), der sich als eine spiralförmige, kohärente Struktur manifestiert, welche stromabgerichtet die Scherschichten entlang mäandert. Obwohl es bereits mehrere Studien über den PVC gibt, ist dessen Einfluss auf den Verbrennungsprozess noch nicht vollständig verstanden und beschrieben. In der vorliegenden Arbeit wird ein aktives Strömungskontrollsystem entwickelt, das exklusive experimentelle Bedingungen scha t, um die Rolle des PVC auf den Verbrennungsprozess weiter zu untersuchen. Dieses Strömungskontrollsystem ist in die Mischsektion eines Drallbrenners integriert. Dort wird eine helikale Aktuation, nach dem zero-netmass- flux Prinzip, realisiert, durch welche die präzedierende Bewegung des PVC nachgeahmt wird. Die Aktuation wird in jenem Bereich angewendet, in welchem die Antwort des PVC auf äußere periodische Anregung maximal ist. Dieser Bereich der höchsten Rezeptivität kann als Ursprung des PVC betrachtet werden. Aufgrund der maximalen Antwort des PVC in diesem Bereich sind nur kleine Anregungsamplituden notwendig, um eine erhebliche Kontrollwirkung zu erzielen, ohne die Strömungskonfiguration grundlegend zu verändern. Nach einem umfassenden Nachweis der Funktionalität des Regelkonzepts unter isothermen und reaktiven Betriebsbedingungen wird das Strömungskontrollsystem eingesetzt, um den PVC je nach Strömungskonfiguration anzuregen (o ener Regelkreis) oder zu unterdrücken (geschlossener Regelkreis). Mit diesem Werkzeug kann der ausschließliche Einfluss des PVC auf Flammendynamik, Mischung und NOx-Emissionen untersucht werden. Es wird beobachtet, dass die Anregung des PVC selbsterregte thermoakustische Schwingungen erheblich dämpfen kann. Eine Erklärung für diese Beobachtung ist ein möglicher Bruch der Symmetrie der achsensymmetrischen Äquivalenzverhältnisschwankungen durch den angegereten asymmetrischen PVC. Weitere Erklärungen für diese Beobachtung werden durch zwei Kopplungsmechanismen zeitlich gemittelter Felder gegeben, die aus zeitaufgelösten Strömungsfeld- und Wärmefreisetzungsratenmessungen abgeleitet werden. Diese Mechanismen werden in Verbindung mit Messungen der Flammentransferfunktion (FTF) abgeleitet, die zeigen, dass der PVC in der Lage ist, den FTF-Gain zu reduzieren, ohne die FTF-Phase zu verändern. Dem ersten Mechanismus zufolge reduziert der PVC die Wachstumsrate der Kelvin-Helmholtz-Instabilität, was das Wachstum der achsensymmetrischen Moden in den Scherschichten behindert. Mechanismus zwei bezieht sich auf die PVC-induzierte Änderung der mittleren Flammenform, die kompakter wird und sich stromaufwärts zum Brenneraustritt hin verschiebt. Dadurch erreichen weniger Wärmefreisetzungsratenschwankungen die empfindliche Flammenspitze, was ebenfalls zu einer Dämpfung des FTF-Gains führt. Neben diesen Erkenntnissen zum Einfluss des PVC auf die Flammendynamik wird gezeigt, dass der PVC eine großräumige Vermischung der einströmenden kalten Reaktanden mit den heißen Produkten in der zentralen Rezirkulationszone bewirkt. Diese großräumige Vermischung erhöht die Reaktionsgeschwindigkeit und befördert Radikale in das einströmende Fluid. Dadurch folgt die Flamme den PVC-induzierten Wirbeln und das Niveau der NOx-Emissionspegel erhöht sich. Mit dem entwickelten Strömungskontrollansatz werden einzigartige experimentelle Bedingungen gescha en, die es erlauben, den ausschließlichen Einfluss des PVC auf den Verbrennungsprozess zu untersuchen. Darüber hinaus kann dieser Strömungskontrollansatz zur aktiven Steuerung der Stabilität und E zienz des Verbrennungsprozesses eingesetzt werden. Um den Laboraufbau des Strömungskontrollsystems auf eine Maschine im industriellen Maßstab anzuwenden, wird ein alternatives Aktuationskonzept vorgeschlagen, das sich auf fluidische Oszillatoren stützt. Darüber hinaus ist der in der vorliegenden Arbeit untersuchte Strömungskontrollansatz auf alle Arten von Strömungen mit inhärenten globalen hydrodynamischen Moden, wie z.B. dem PVC, anwendbar.DFG, 247226395, Untersuchung des direkten Einflusses des Precessing Vortex Core auf die Dynamik, thermoakustische Instabilitäten und Emissionen drallstabilisierter Flammen mittels aktiver Strömungskontroll