University of Bremen

About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Context (language use). The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

Tamed Transparency: How Information Disclosure under the Global Reporting Initiative Fails to Empower

Abstract: In this contribution, we explore the tensions that seem inherent in the claim that transparency policies “empower” the users of disclosed information vis-avis those who are asked to provide the information. Since these tensions are particularly relevant in relation to voluntary disclosure, our analysis focuses on the Global Reporting Initiative (GRI) as the world's leading voluntary corporate non-financial reporting scheme. Corporate sustainability reporting is often hailed as a powerful instrument to improve the environmental performance of business and to empower societal groups, including consumers, in their relations with the corporate world. Yet, our analysis illustrates that the relationship between transparency and empowerment is conflictual at all four levels of activity examined in this article: in the rhetoric and policies of the GRI as well as in the actual reporting practice and in the activities of intermediaries in response to the organization's disclosure standard.

Direct observation of correlations between individual photon emission events of a microcavity laser

Abstract: Coherent light emission in lasers is reflected in a change of the photon statistics. Here Wiersig et al. demonstrate a streak camera technique with sufficient time resolution to probe the dynamical evolution of correlations between individual photon emission events. This work may lead to novel quantum optical studies addressing the dynamics of correlation functions of light. Lasers are recognized for coherent light emission, the onset of which is reflected in a change in photon statistics; but, until now, attempts to directly measure correlations in the individual photon emission events of semiconductor lasers have been unsuccessful. By using a streak camera technique with sufficient time resolution, the dynamical evolution of correlations between individual photon emission events is now demonstrated. Lasers are recognized for coherent light emission, the onset of which is reflected in a change in the photon statistics1. For many years, attempts have been made to directly measure correlations in the individual photon emission events of semiconductor lasers2,3. Previously, the temporal decay of these correlations below or at the lasing threshold was considerably faster than could be measured with the time resolution provided by the Hanbury Brown/Twiss measurement set-up4 used. Here we demonstrate a measurement technique using a streak camera that overcomes this limitation and provides a record of the arrival times of individual photons. This allows us to investigate the dynamical evolution of correlations between the individual photon emission events. We apply our studies to micropillar lasers5 with semiconductor quantum dots2,3,6,7,8 as the active material, operating in the regime of cavity quantum electrodynamics9. For laser resonators with a low cavity quality factor, Q, a smooth transition from photon bunching to uncorrelated emission with increasing pumping is observed; for high-Q resonators, we see a non-monotonic dependence around the threshold where quantum light emission can occur. We identify regimes of dynamical anti-bunching of photons in agreement with the predictions of a microscopic theory that includes semiconductor-specific effects.

Ballast, sinking velocity, and apparent diffusivity within marine snow and zooplankton fecal pellets: Implications for substrate turnover by attached bacteria

Abstract: We analyzed size-specific dry mass, sinking velocity, and apparent diffusivity in field-sampled marine snow, laboratory-made aggregates formed by diatoms or coccolithophorids, and small and large zooplankton fecal pellets with naturally varying content of ballast materials. Apparent diffusivity was measured directly inside aggregates and large (millimeter-long) fecal pellets using microsensors. Large fecal pellets, collected in the coastal upwelling off Cape Blanc, Mauritania, showed the highest volume-specific dry mass and sinking velocities because of a high content of opal, carbonate, and lithogenic material (mostly Saharan dust), which together comprised ,80% of the dry mass. The average solid matter density within these large fecal pellets was 1.7 g cm23, whereas their excess density was 0.25 6 0.07 g cm23. Volume-specific dry mass of all sources of aggregates and fecal pellets ranged from 3.8 to 960 m gm m 23, and average sinking velocities varied between 51 and 732 m d21. Porosity was .0.43 and .0.96 within fecal pellets and phytoplankton-derived aggregates, respectively. Averaged values of apparent diffusivity of gases within large fecal pellets and aggregates were 0.74 and 0.95 times that of the free diffusion coefficient in sea water, respectively. Ballast increases sinking velocity and, thus, also potential O2 fluxes to sedimenting aggregates and fecal pellets. Hence, ballast minerals limit the residence time of aggregates in the water column by increasing sinking velocity, but apparent diffusivity and potential oxygen supply within aggregates are high, whereby a large fraction of labile organic carbon can be respired during sedimentation.

Synthesis of quantum circuits for linear nearest neighbor architectures

Abstract: While a couple of impressive quantum technologies have been proposed, they have several intrinsic limitations which must be considered by circuit designers to produce realizable circuits. Limited interaction distance between gate qubits is one of the most common limitations. In this paper, we suggest extensions of the existing synthesis flow aimed to realize circuits for quantum architectures with linear nearest neighbor interaction. To this end, a template matching optimization, an exact synthesis approach, and two reordering strategies are introduced. The proposed methods are combined as an integrated synthesis flow. Experiments show that by using the suggested flow, quantum cost can be improved by more than 50% on average.

Silicon nanowire band gap modification.

Abstract: Band gap modification for small-diameter (∼1 nm) silicon nanowires resulting from the use of different species for surface termination is investigated by density functional theory calculations. Because of quantum confinement, small-diameter wires exhibit a direct band gap that increases as the wire diameter narrows, irrespective of surface termination. This effect has been observed in previous experimental and theoretical studies for hydrogenated wires. For a fixed cross-section, the functional group used to saturate the silicon surface significantly modifies the band gap, resulting in relative energy shifts of up to an electronvolt. The band gap shifts are traced to details of the hybridization between the silicon valence band and the frontier orbitals of the terminating group, which is in competition with quantum confinement.