Euler-Poincare reduction for discrete field theories

In this note, we develop a theory of Euler-Poincare reduction for discrete Lagrangian field theories. We introduce the concept of Euler-Poincare equations for discrete field theories, as well as a natural extension of the Moser-Veselov scheme, and show that both are equivalent. The resulting discrete field equations are interpreted in terms of discrete differential geometry. An application to the theory of discrete harmonic mappings is also briefly discussed.Comment: 24 pages, 3 figures (v2: simplified treatment

A 160Gb/s (4x40) WDM O-band Tx subassembly using a 4-ch array of silicon rings co-packaged with a SiGe BiCMOS IC driver

We present a 400 (8×50) Gb/s-capable RM-based Si-photonic WDM O-band TxRx with 1.17nm channel spacing for high-speed optical interconnects and demonstrate successful 50Gb/s-NRZ TxRx operation achieving a ~4.5dB Tx extinction ratio under 2.15Vpp drive

Description of the fluctuating colloid-polymer interface

To describe the full spectrum of surface fluctuations of the interface between phase-separated colloid-polymer mixtures from low scattering vector q (classical capillary wave theory) to high q (bulk-like fluctuations), one must take account of the interface's bending rigidity. We find that the bending rigidity is negative and that on approach to the critical point it vanishes proportionally to the interfacial tension. Both features are in agreement with Monte Carlo simulations.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Phys. Rev. Let

Simulation and experimental verification of W-band finite frequency selective surfaces on infinite background with 3D full wave solver NSPWMLFMA

We present the design, processing and testing of a W-band finite by infinite and a finite by finite Grounded Frequency Selective Surfaces (FSSs) on infinite background. The 3D full wave solver Nondirective Stable Plane Wave Multilevel Fast Multipole Algorithm (NSPWMLFMA) is used to simulate the FSSs. As NSPWMLFMA solver improves the complexity matrix-vector product in an iterative solver from O(N(2)) to O(N log N) which enables the solver to simulate finite arrays with faster execution time and manageable memory requirements. The simulation results were verified by comparing them with the experimental results. The comparisons demonstrate the accuracy of the NSPWMLFMA solver. We fabricated the corresponding FSS arrays on quartz substrate with photolithographic etching techniques and characterized the vector S-parameters with a free space Millimeter Wave Vector Network Analyzer (MVNA)

Privacy and Security in the Cloud: Some Realism About Technical Solutions to Transnational Surveillance in the Post-Snowden Era

Since June 2013, the leak of thousands of classified documents regarding highly sensitive U.S. surveillance activities by former National Security Agency (NSA) contractor Edward Snowden has greatly intensified discussions of privacy, trust, and freedom in relation to the use of global computing and communication services. This is happening during a period of ongoing transition to cloud computing services by organizations, businesses, and individuals. There has always been a question of inherent in this transition: are cloud services sufficiently able to guarantee the security of their customers’ data as well s the proper restrictions on access by third parties, including governments? While worries over government access to data in the cloud is a predominate part of the ongoing debate over the use of cloud serives, the Snowden revelations highlight that intelligence agency operations pose a unique threat to the ability of services to keep their customers’ data out of the hands of domestic as well as foreign governments. The search for a proper response is ongoing, from the perspective of market players, governments, and civil society. At the technical and organizational level, industry players are responding with the wider and more sophisticated deployment of encryption as well as a new emphasis on the use of privacy enhancing technologies and innovative architectures for securing their services. These responses are the focus of this Article, which contributes to the discussion of transnational surveillance by looking at the interaction between the relevant legal frameworks on the one hand, and the possible technical and organizational responses of cloud service providers to such surveillance on the other. While the Article’s aim is to contribute to the debate about government surveillance with respect to cloud services in particular, much of the discussion is relevant for Internet services more broadly

Transthyretin levels in the vitreous correlate with change in visual acuity after vitrectomy

Background/aim: Little is known about biochemical markers related to change in visual acuity after vitrectomy. The potential use of transthyretin (TTR), a carrier of the retinol/retinol-binding protein, as a biochemical marker protein, was investigated. Methods: TTR was measured using immunonephelometry in a group of patients (n = 77) in longstanding (> 1 week) retinal detachment (n = 29), fresh (< 1 week) retinal detachment (n = 17), macular holes (n = 20) or diabetic retinopathy (n = 11). Vitreous samples were taken at the start of every vitrectomy procedure. For reference values, cadaver specimens (n = 73) were used. Results: Reference values for vitreous TTR (median 18 mg/l; IQR 4 to 24 mg/l) comprised 2.2% of reference values for vitreous protein levels (median 538 mg/l; IQR 269 to 987 mg/l). Vitreous TTR values of patients were comparable in all disorders. Vitreous TTR values were higher in phakic (median 22.5 mg/l; IQR 10 to 27 mg/l) than in pseudophakic patients (median 12 mg/l; IQR 8 to 19 mg/l; p = 0.06). Postoperative change in visual acuity correlated well with vitreous TTR values found peroperatively (r(s) = 0.408; p = 0.012). Both change in visual acuity and lens status were the only variables which proved to explain the variance of TTR (multiple correlation coefficient: 0.494; phakic status: t = 2.767; p = 0.0084; and change in visual acuity t = 2.924: p = 0.0056). Conclusion: Vitreous fluid concentrations of TTR can be regarded as a biochemical marker for retinal function