Contributions in Merlin

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Core-collapse supernovae (CCSNe) are among the most energetic explosions in the universe, liberating the prodigious amount of ~ 1053 erg, the binding energy of their compact remnants, neutron stars or stellar mass black holes. While 99% of this energy is emitted in neutrinos, 1% goes into the internal and asymptotic kinetic energy of the ejecta, and it is reasonable to assume that a tiny fraction is radiated in gravitational waves (GWs). Ever since the first experimental efforts to detect GWs, CCSNe have been considered prime sources of gravitational waves for interferometric detectors. Besides neutrinos, which have already been observed in the context of stellar core collapse of SN1987A, GWs could provide us access to the electromagnetically hidden compact inner core of some such cataclysmic events, supplying us for example with valuable information about the angular momentum distribution and the baryonic equation of state, both of which are uncertain. Furthermore, they might even help to constrain theoretically predicted SN mechanisms. However, GW astronomy strongly depends on the extensive data processing of the detector output on the basis of reliable GW estimates, which only recently have become feasible with the emerging power of supercomputers. The work presented in this thesis is concerned with numerical CCSN models and their imprints in GWs. I performed an extensive series of more than 30 three-dimensional magnetohydrodynamical (MHD) core-collapse simulations. My models are based on a 15M [...] progenitor stemming from stellar evolution calculations, an effective general relativistic potential and either the Lattimer-Swesty (with three possible compressibilities) or the Shen equation of state (EoS) for hot, dense matter. Furthermore, the neutrino transport is tracked by computationally efficient algorithms for the radiative transfer of massless fermions. I systematically investigated the effects of the microphysical finite-temperature nuclear EoS, the initial rotation rate, both the toroidal and the poloidal magnetic fields, and multidimensional gravitational potentials on the GW signature. Based on the results of these calculations, I obtained the largest – and also one of the most realistic – catalogue of GW signatures from 3D MHD stellar core collapse simulations at present. I stress the importance of including postbounce neutrino physics, since it quantitatively alters the GW signature. Non- and slowly-rotating models show GW emission caused by prompt and protoneutron star (PNS) convection. Moreover, the signal stemming from prompt convection allows for the distinction between the two different nuclear EoS indirectly by different properties of the fluid instabilities. For simulations with moderate or even fast rotation rates, I only find the axisymmetric type I wave signature at core bounce. In line with recent results, I could confirm that the maximum GW amplitude scales roughly linearly with the ratio of rotational to gravitational energy (T/|W|) at core bounce below a threshold value of about 10%. Furthermore, I point out that PNS can become dynamically unstable to rotational instabilities at T/|W| values as low as ~ 2% at core bounce. Apart from these two points, I show that it is generally very difficult to discern the effects of the individual features of the input physics in a GW signal from a rotating CCSN that can be attributed unambiguously to a specific model. Weak magnetic fields do not notably influence the dynamical evolution of the core and thus the GW emission. However, for strong initial poloidal magnetic fields ≥ 1012G, the combined action of flux-freezing and field winding leads to conditions where the ratio of magnetic field pressure to matter pressure reaches about unity which leads to the onset of a jet-like supernova explosion. The collimated bipolar out-stream of matter is then reflected in the emission of a type IV GW signal. In contradiction to axisymmetric simulations, I find evidence that nonaxisymmetric fluid modes can counteract or even suppress jet formation for models with strong initial toroidal magnetic fields. I emphasize the importance of including multidimensional gravitational potentials in rapidly rotating 3D CCSN simulations: taking them into account can alter the resulting GW amplitudes up to a factor of 2 compared to simulations which encounter gravity only by a monopolar approximation. Moreover, I show that the postbounce dynamics occuring in the outer layers (at radii R ≥ 200km) of models run with 3D gravity deviates vastly from the ones run with a 1D or 2D gravitational potential. The latter finding implies that both spherically symmetric and axisymmetric treatments of gravity are too restrictive for a quantitative description of the overall postbounce evolution of rapidly rotating CCSN models. The results of models with continued neutrino emission show that including deleptonization during the postbounce phase is an indispensable issue for the quantitative prediction of GWs from core-collapse supernovae, because it can alter the GW amplitude up to a factor of 10 compared to a pure hydrodynamical treatment. My collapse simulations indicate that corresponding events in our Galaxy would be detectable either by LIGO, if the source is rotating, or at least by the advanced LIGO detector, if it is not or only slowly rotating.

We describe a sparse-grid collocation method to compute recursive solutions of dynamic economies with a sizable number of state variables. We show how powerful this method can be in applications by computing the non-linear recursive solution of an international real business cycle model with a substantial number of countries, complete insurance markets and frictions that impede frictionless international capital flows. In this economy, the aggregate state vector includes the distribution of world capital across different countries as well as the exogenous country-specific technology shocks. We use the algorithm to efficiently solve models with up to 10 countries (i.e., up to 20 continuous-valued state variables).

Research evaluation is praised as the symbol of modern quality management. We claim firstly, performance evaluations in research have higher costs than normally assumed, because the evaluated persons and institutions systematically change their behavior and develop counter strategies. Moreover, intrinsic work motivation is crowded out and undesired lock-in effects take place. Secondly, the benefits of performance evaluations are questionable. Evaluations provide too little information relevant for decision-making. In addition, they lose importance due to new forms of scientific cooperation on the internet. Thirdly, there exist superior alternatives. They consist in careful selection and supportive process coaching – and then leave individuals and research institutions to direct themselves.

We present a model of (re)elections in which an incumbency advantage arises because the incumbent can manipulate issue salience by choosing inefficient policies in the policy dimension in which he is the stronger candidate. The voters are uncertain about the state of the world and the incumbent’s choice of policy. Under complete information they would reelect the incumbent if and only if the state is sufficiently high. Undesirable policy outcomes may be due to either a bad state or the incumbent’s choice of inefficient policies. The incumbent uses inefficient policies in intermediate states, whereby he creates uncertainty about the true state in such a way that voters are better off in expectation reelecting him. Hence the equilibrium exhibits an incumbency advantage that stems from asymmetric information and the use of inefficient policies.

We investigate debt restructurings in Germany for a sample of 116 financially distressed companies. About half of the firms succeed in restructuring their debt in a workout while the others file for bankruptcy. Our evidence suggests that firms which have higher leverage, owe more debt to banks, and exhibit higher going concern values are more likely to conduct a workout. Bankruptcy is more likely for firms with deficient lender coordination and a high fraction of collateralized debt. An analysis of stock returns suggests that the market uses similar information to predict workouts. 84% of the bankrupt firms were ultimately liquidated.

In this paper, we address the issue of spurious correlation in the production of health in a systematic way. Spurious correlation entails the risk of linking health status to medical (and nonmedical) inputs when no links exist. This note first presents the bounds testing procedure as a method to detect and avoid spurious correlation. It then applies it to a recent contribution by Lichtenberg (2004), which relates longevity in the United States to pharmaceutical innovation and public health care expenditure. The results of the bounds testing procedure show longevity to be related to these two factors. Therefore, the estimates reported by Lichtenberg (2004) cannot be said to be result of spurious correlation, to the contrary, they very likely reflect an effective relationship, at least for the United States.

Companies in the software business often distribute requirements engineering responsibilities over several roles. Product management has overall product responsibility and performs early-phase market-driven requirements engineering. Product development implements the product and performs late-phase solution-oriented requirements engineering. Such shared responsibility provides advantages in the utilization of specific knowledge, skills, and resources, but leads to problems of mutual understanding and coordination. Earlier research proposed a negotiation process, handshaking with implementation proposals, that allows product management and development to achieve agreed requirements understanding. The process found acceptance in industry, but the relative advantages compared with traditional requirements hand-off and analysis had not been understood yet. This paper fills this gap by describing a case of measuring requirements and design volatility and an architect's requirements understanding during requirements hand-off, analysis, and negotiation.