A general method for unsteady stagnation region heat transfer and results for model turbine flows

Recent experiments suggest that the heat-transfer characteristics of stator blades are influenced by the frequency of passing of upstream rotor blades. The calculation of these effects requires that the movement of the stagnation point with variations in freestream velocity is properly represented together with the possible effects of turbulence characteristics on the thin leading-edge boundary layer. A procedure to permit the achievement of these purposes is described for laminar flows in this paper together with results of its application to two model problems which demonstrate its abilities and quantify the influence of wake characteristics on fluid-dynamic and heat-transfer properties of the flow and their effects on surface heat transfer

Characterization of Hamamatsu 64-channel TSV SiPMs

The Hamamatsu UV-light enhanced 64-channel SiPM array of the newest generation (S13361-3050AS-08) has been examined for the purpose of being used for the Silicon Elementary Cell Add-on (SiECA) of the EUSO-SPB balloon experiment. Characterization measurements have been performed with the newly installed Single Photon Calibration Stand at KIT (SPOCK). The results of the characterization measurements including the breakdown voltage, the gain, the PDE, the dark-count rate and the crosstalk probability of all 64 SiPM channels are presented. Additional measurements of the SiPM sensitivity to photons with wavelengths lower than 400nm show an improved PDE for small wavelengths compared to the SiPM array S12642-0808PA-50, which was also investigated for comparison. The response dynamics have been investigated for low numbers of incoming photons. Temperature dependent measurements of the gain, the PDE, the dark-count rate and the crosstalk probability have been performed for one channel of the SiPM array.Comment: Accepted for publication in Nuclear Instruments and Methods

Tunable X-ray source by Thomson scattering during laser-wakefield acceleration

We report results on all-optical Thomson scattering intercepting the acceleration process in a laser wakefield accelerator. We show that the pulse collision position can be detected using transverse shadowgraphy which also facilitates alignment. As the electron beam energy is evolving inside the accelerator, the emitted spectrum changes with the scattering position. Such a configuration could be employed as accelerator diagnostic as well as reliable setup to generate x-rays with tunable energy

A Quantum Repeater Node with Trapped Ions: A Realistic Case Example

We evaluate the feasibility of the implementation of two quantum repeater protocols with an existing experimental platform based on a $^{40}$Ca$^+$-ion in a segmented micro trap, and a third one that requires small changes to the platform. A fiber cavity serves as an ion-light interface. Its small mode volume allows for a large coupling strength of $g_c = 2 \pi 20$ MHz despite comparatively large losses $\kappa = 2 \pi 36.6$ MHz. With a fiber diameter of 125 mu m, the cavity is integrated into the microstructured ion trap, which in turn is used to transport single ions in and out of the interaction zone in the fiber cavity. We evaluate the entanglement generation rate for a given fidelity using parameters from the experimental setup. The DLCZ protocol (Duan et al, Nature, 2001, 414, 413-418) and the hybrid protocol (van Loock et al, Phys. Rev. Lett., 2006, 96, 240501) outperform the EPR protocol (Sanguard et al, New J. Phys., 2013, 15, 085004). We calculate rates of more than than 35 s$^{-1}$ for non-local Bell state fidelities larger than 0.9 with the existing platform. We identify parameters which mainly limit the attainable rates, and conclude that entanglement generation rates of 740 s$^{-1}$ at fidelities of 0.9 are within reach with current technology.Comment: 21 pages, 14 figure

A single ion as a shot noise limited magnetic field gradient probe

It is expected that ion trap quantum computing can be made scalable through protocols that make use of transport of ion qubits between sub-regions within the ion trap. In this scenario, any magnetic field inhomogeneity the ion experiences during the transport, may lead to dephasing and loss of fidelity. Here we demonstrate how to measure, and compensate for, magnetic field gradients inside a segmented ion trap, by transporting a single ion over variable distances. We attain a relative magnetic field sensitivity of \Delta B/B_0 ~ 5*10^{-7} over a test distance of 140 \micro m, which can be extended to the mm range, still with sub \micro m resolution. A fast experimental sequence is presented, facilitating its use as a magnetic field gradient calibration routine, and it is demonstrated that the main limitation is the quantum shot noise.Comment: 5 pages, 3 figure

The Economic Costs of Mass Surveillance: Insights from Stasi Spying in East Germany

Based on official records from the former East German Ministry for State Security, we quantify the long-term costs of state surveillance on social capital and economic performance. Using county-level variation in the spy density in the 1980s, we exploit discontinuities at state borders to show that higher levels of Stasi surveillance led to lower levels of social capital as measured by interpersonal and institutional trust in post-reunification Germany. We estimate the economic costs of spying by applying a second identification strategy that accounts for county fixed effects. We find that a higher spy density caused lower self-employment rates, fewer patents per capita, higher unemployment rates and larger population losses throughout the 1990s and 2000s. Overall, our results suggest that the social and economic costs of state surveillance are large and persistent

Structural labor supply models and wage exogeneity

There is still considerable dispute about the magnitude of labor supply elasticities. While differences in micro and macro estimates are recently attributed to frictions and adjustment costs, we show that relatively low labor supply elasticities derived from microeconometric models can also be explained by modeling assumptions with respect to wages. Specifically, we estimate 3,456 structural labor supply models each representing a plausible combination of frequently made choices. While most model assumptions do not systematically affect labor supply elasticities, our analysis shows that the results are very sensitive to the treatment of wages. In particular, the often-made but highly restrictive independence assumption between preferences and wages is key. To overcome this restriction, we propose a flexible estimation strategy that nests commonly used models. We show that loosening the exogeneity assumption leads to labor supply elasticities that are much higher

The long-term costs of government surveillance: Insights from Stasi spying in East Germany

Despite the prevalence of government surveillance systems around the world, causal evidence on their social and economic consequences is lacking. Using county-level variation in the number of Stasi informers within Socialist East Germany during the 1980s and accounting for potential endogeneity, we show that more intense regional surveillance led to lower levels of trust and reduced social activity in post-reunification Germany. We also find substantial and long-lasting economic effects of Stasi spying, resulting in lower self-employment, higher unemployment and larger out-migration throughout the 1990s and 2000s. We further show that these effects are due to surveillance and not alternative mechanisms. We argue that our findings have important implications for contemporary surveillance systems

The Long-Term Costs of Government Surveillance: Insights from Stasi Spying in East Germany

Based on official records from the former East German Ministry for State Security, we quantify the long-term costs of state surveillance on social capital and economic performance. Using county-level variation in the number of spies in the 1980s, we exploit discontinuities at state borders to show that higher levels of government surveillance led to lower levels of interpersonal and institutional trust in post-reunification Germany. Based on a second identification strategy that accounts for county fixed effects we further estimate the economic costs of spying. We find that a more intense surveillance caused lower self-employment rates, fewer patents per capita, higher unemployment rates and larger population losses throughout the 1990s and 2000s. Overall, our results suggest that the social and economic costs of East German state surveillance are large and persistent