Set mapping reflection

In this note we will discuss a new reflection principle which follows from the Proper Forcing Axiom. The immediate purpose will be to prove that the bounded form of the Proper Forcing Axiom implies both that 2^omega = omega_2 and that L(P(omega_1)) satisfies the Axiom of Choice. It will also be demonstrated that this reflection principle implies that combinatorial principle Square(kappa) fails for all regular kappa > omega_1.Comment: 11 page

Are There Any Class Size Effects on Early Career Earnings in West Germany?

The paper analyses the effect of class size, which stands proxy for school quality, on early career earnings. Using confidential district level information from the German Socio-Economic Panel (GSOEP), it is demonstrated that class size has no discernible effect on early career earnings. This finding is robust to changes in specification and the choice of sub-samples. The economic literature focused so far mainly on the US and the UK. This paper confirms this literature and adds new evidence to the growing empirical literature on this issue from Germany.School quality; Class size; Labour market outcomes

Andreev bound states probed in three-terminal quantum dots

We demonstrate several new electron transport phenomena mediated by Andreev bound states (ABSs) that form on three-terminal carbon nanotube (CNT) QDs, with one superconducting (S) contact in the center and two adjacent normal metal (N) contacts. Three-terminal spectroscopy allows us to identify the coupling to the N contacts as the origin of the Andreev resonance (AR) linewidths and to determine the critical coupling strengths to S, for which a ground state transition S-QD systems can occur. We ascribe replicas of the lowest-energy ABS resonance to transitions between the ABS and odd-parity excited QD states, a process called excited state ABS resonances. In the conductance between the two N contacts we find a characteristic pattern of positive and negative differential subgap conductance, which we explain by considering two nonlocal processes, the creation of Cooper pairs in S by electrons from both N terminals, and a novel mechanism called resonant ABS tunneling. In the latter, electrons are transferred via the ABS without creating Cooper pairs in S. The three-terminal geometry also allows spectroscopy experiments with different boundary conditions, for example by leaving S floating. Surprisingly, we find that, depending on the boundary conditions, the experiments either show single-particle Coulomb blockade resonances, ABS characteristics, or both in the same measurements, seemingly contradicting the notion of ABSs replacing the single particle states as eigenstates of the QD. We qualitatively explain these results as originating from the finite time scale required for the coherent oscillations between the superposition states after a single electron tunneling event. These experiments demonstrate that three-terminal experiments on a single complex quantum object can also be useful to investigate charge dynamics otherwise not accessible due to the very high frequencies.Comment: 15 pages, 16 figure

Resonant and inelastic Andreev tunneling observed on a carbon nanotube quantum dot

We report the observation of two fundamental sub-gap transport processes through a quantum dot (QD) with a superconducting contact. The device consists of a carbon nanotube contacted by a Nb superconducting and a normal metal contact. First, we find a single resonance with position, shape and amplitude consistent with the theoretically predicted resonant Andreev tunneling (AT) through a single QD level. Second, we observe a series of discrete replicas of resonant AT at a separation of $\sim145\,\mu$eV, with a gate, bias and temperature dependence characteristic for boson-assisted, inelastic AT, in which energy is exchanged between a bosonic bath and the electrons. The magnetic field dependence of the replica's amplitudes and energies suggest that two different bosons couple to the tunnel process.Comment: 5 pages + 9 pages supplementary materia

Does More Generous Student Aid Increase Enrolment Rates into Higher Education?: Evaluating the German Student Aid Reform of 2001

Students from low-income families are eligible to student aid under the federal students' financial assistance scheme (BAfoeG) in Germany. We evaluate the effectiveness of a recent reform of student aid that substantially increased the amount received by eligible students to raise enrolment rates into tertiary education. We view this reform as a 'natural experiment' and apply the difference-in-difference methodology using a discrete-time hazard rate model to estimate the causal effect on enrolment rates into higher education. We find that the reform had a small positive but statistically insignificant effect on enrolment rates.Educational transitions, educational finance, natural experiment and difference-indifference estimation

Enrolment into Higher Education and Changes in Repayment Obligations of Student Aid – Microeconometric Evidence for Germany.

We evaluate the effect of the federal students’ financial assistance scheme (BAfoeG) on enrolment rates into higher education by exploiting the exogenous variation introduced through a discrete shift in the repayment regulations. Supported students had to repay the full loan until 1990. Thereafter, 50 percent of the student aid has been offered as a non-repayable grant. Our results from simple difference-in- difference estimates suggest that student aid is ineffective in raising enrolment rates. Our findings may have important implications for the current debate on the reform of financing higher education in Germany and elsewhere.educational decision, educational finance, higher education, difference-in-difference, discrete-choice

Semiparametric Multinomial Logit Models for Analysing Consumer Choice Behaviour

The multinomial logit model (MNL) is one of the most frequently used statistical models in marketing applications. It allows to relate an unordered categorical response variable, for example representing the choice of a brand, to a vector of covariates such as the price of the brand or variables characterising the consumer. In its classical form, all covariates enter in strictly parametric, linear form into the utility function of the MNL model. In this paper, we introduce semiparametric extensions, where smooth effects of continuous covariates are modelled by penalised splines. A mixed model representation of these penalised splines is employed to obtain estimates of the corresponding smoothing parameters, leading to a fully automated estimation procedure. To validate semiparametric models against parametric models, we utilise proper scoring rules and compare parametric and semiparametric approaches for a number of brand choice data sets

Turning Unemployment into Self-Employment: Effectiveness and Efficiency of Two Start-Up Programmes

Turning unemployment into self-employment has become a major focus of German active labour market policy (ALMP) in recent years. If effective, this would not only reduce Germany's persistently high unemployment rate, but also increase its notoriously low self-employment rate. Empirical evidence on the effectiveness of such programmes is scarce. The contribution of the present paper is twofold: first, we evaluate the effectiveness of two start-up programmes for the unemployed. Our outcome variables include the probability of being employed, the probability of being unemployed, and personal income. Second, based on the results of this analysis, we conduct an efficiency analysis, i.e., we estimate whether the Federal Employment Agency has saved money by placing unemployed individuals in these programmes. Our results show that at the end of the observation period, both programmes are effective and one is also efficient. The considerable positive effects present a stark contrast to findings from evaluations of other German ALMP programmes in recent years. Hence, ALMP programmes aimed at moving the unemployed into self-employment may prove to be among the most effective, both in Germany and elsewhereStart-up subsidies, evaluation, effectiveness, efficiency, self-employment

Design study of a regenerative pump using one-dimensional and three-dimensional numerical techniques

Regenerative pumps are low cost, compact, able to deliver high heads at low flow rates. Furthermore with stable performance characteristics they can operate with very small NPSH. The complexity of the flow field is a serious challenge for any kind of mathematical modelling. This paper compares an analytical and numerical technique of resolving the performance for a new regenerative pump design. The performance characteristics computed by a CFD approach and a new one-dimensional model are compared and matched to experimental test results. The approaches of both modelling techniques are assessed as potential design tools. The approaches are shown to not only successfully resolve the complex flow field within the pump; the CFD is also capable of resolving local flow properties to conduct further refinements. The flow field is represented by the CFD as it has never been before. A new design process is suggested. The new regenerative pump design is considered with a comparable duty centrifugal pump, proving that for many high head low flow rate applications the regenerative pump is a better choice

Design study of a novel regenerative pump using experimental and numerical techniques

This paper presents a numerical and experimental analysis of a new regenerative pump design. The complex flow-field within regenerative pumps represents a significant challenge to previous published mathematical models. The new pump design incorporates a new axial inlet and outlet port. The experimental and numerical results demonstrate that it is not only possible to resolve the flowfield for this pump type but also demonstrates this pump as a viable alternative to other kinetic rotodynamic machines. The use of the latest rapid manufacturing techniques have enabled the production of the complex geometry of the axial ports required for the new configuration