Silicon Waveguides and Ring Resonators at 5.5 {\mu}m

We demonstrate low loss ridge waveguides and the first ring resonators for the mid-infrared, for wavelengths ranging from 5.4 to 5.6 {\mu}m. Structures were fabricated using electron-beam lithography on the silicon-on-sapphire material system. Waveguide losses of 4.0 +/- 0.7 dB/cm are achieved, as well as Q-values of 3.0 k.Comment: 4 pages, 4 figures, includes supplemental material

When does the Lorenz 1963 model exhibit the signal-to-noise paradox?

Seasonal prediction systems based on Earth System Models exhibit a lower proportion of predictable signal to unpredictable noise than the actual world. This puzzling phenomena has been widely referred to as the signal-to-noise paradox (SNP). Here, we investigate the SNP in a conceptual framework of a seasonal prediction system based on the Lorenz, 1963 Model (L63). We show that the SNP is not apparent in L63, if the uncertainty assumed for the initialization of the ensemble is equal to the uncertainty in the starting conditions. However, if the uncertainty in the initialization overestimates the uncertainty in the starting conditions, the SNP is apparent. In these experiments the metric used to quantify the SNP also shows a clear lead-time dependency on subseasonal timescales. We therefore, formulate the alternative hypothesis to previous studies that the SNP could also be related to the magnitude of the initial ensemble spread. Plain Language Summary Comprehensive Earth System Models seem to be better at predicting the real observed climate system than expected based on their ability to predict their own modelled climate system. This puzzling phenomena is known as the signal-to-noise paradox (SNP) and its origin is still under intensive scientific debate with some studies pointing to deficiencies in the model formulation. In this study we investigate under which conditions the SNP can be obtained using a simple conceptual framework for a climate prediction system based on a simple dynamical model. Our results show that the SNP can be reproduced in the absence of model deficiencies if the model overestimates the observational uncertainty. We also investigate the development of the SNP on subseasonal timescales and find a clear dependency on the lead-time of the prediction. Our results lead us to formulate an alternative hypothesis to previous studies on the origin of the SNP

Testrun results from prototype fiber detectors for high rate particle tracking

A fiber detector concept has been realized allowing to registrate particles within less than 100 nsec with a space point precision of about 0.1 mm at low occupancy. Three full size prototypes have been build by different producers and tested at a 3 GeV electron beam at DESY. After 3 m of light guides 8-10 photoelectrons were registrated by multichannel photomultipliers providing an efficiency of more than 99%. Using all available data a resolution of 0.086 mm was measured.Comment: 18 pages, 17 figure

CMOS compatible athermal silicon microring resonators

Silicon photonics promises to alleviate the bandwidth bottleneck of modern day computing systems. But silicon photonic devices have the fundamental problem of being highly sensitive to ambient temperature fluctuations due to the high thermo-optic (TO) coefficient of silicon. Most of the approaches proposed to date to overcome this problem either require significant power consumption or incorporate materials which are not CMOS-compatible. Here we demonstrate a new class of optical devices which are passively temperature compensated, based on tailoring the optical mode confinement in silicon waveguides. We demonstrate the operation of a silicon photonic resonator over very wide temperature range of greater than 80 degrees. The fundamental principle behind this work can be extended to other photonic structures such as modulators, routers, switches and filters.Comment: 9 pages, 4 figure

The present and future system for measuring the Atlantic meridional overturning circulation and heat transport

of the global combined atmosphere-ocean heat flux and so is important for the mean climate of the Atlantic sector of the Northern Hemisphere. This meridional heat flux is accomplished by both the Atlantic Meridional Overturning Circulation (AMOC) and by basin-wide horizontal gyre circulations. In the North Atlantic subtropical latitudes the AMOC dominates the meridional heat flux, while in subpolar latitudes and in the subtropical South Atlantic the gyre circulations are also important. Climate models suggest the AMOC will slow over the coming decades as the earth warms, causing widespread cooling in the Northern hemisphere and additional sea-level rise. Monitoring systems for selected components of the AMOC have been in place in some areas for decades, nevertheless the present observational network provides only a partial view of the AMOC, and does not unambiguously resolve the full variability of the circulation. Additional observations, building on existing measurements, are required to more completely quantify the Atlantic meridional heat transport. A basin-wide monitoring array along 26.5°N has been continuously measuring the strength and vertical structure of the AMOC and meridional heat transport since March 31, 2004. The array has demonstrated its ability to observe the AMOC variability at that latitude and also a variety of surprising variability that will require substantially longer time series to understand fully. Here we propose monitoring the Atlantic meridional heat transport throughout the Atlantic at selected critical latitudes that have already been identified as regions of interest for the study of deep water formation and the strength of the subpolar gyre, transport variability of the Deep Western Boundary Current (DWBC) as well as the upper limb of the AMOC, and inter-ocean and intrabasin exchanges with the ultimate goal of determining regional and global controls for the AMOC in the North and South Atlantic Oceans. These new arrays will continuously measure the full depth, basin-wide or choke-point circulation and heat transport at a number of latitudes, to establish the dynamics and variability at each latitude and then their meridional connectivity. Modeling studies indicate that adaptations of the 26.5°N type of array may provide successful AMOC monitoring at other latitudes. However, further analysis and the development of new technologies will be needed to optimize cost effective systems for providing long term monitoring and data recovery at climate time scales. These arrays will provide benchmark observations of the AMOC that are fundamental for assimilation, initialization, and the verification of coupled hindcast/forecast climate models

Flow Phase Diagram for the Helium Superfluids

The flow phase diagram for He II and $^3$He-B is established and discussed based on available experimental data and the theory of Volovik [JETP Letters {\bf{78}} (2003) 553]. The effective temperature - dependent but scale - independent Reynolds number $Re_{eff}=1/q=(1+\alpha')/\alpha$, where $\alpha$ and $\alpha'$ are the mutual friction parameters and the superfluid Reynolds number characterizing the circulation of the superfluid component in units of the circulation quantum are used as the dynamic parameters. In particular, the flow diagram allows identification of experimentally observed turbulent states I and II in counterflowing He II with the turbulent regimes suggested by Volovik.Comment: 2 figure

The effect of magnetic dipolar interactions on the interchain spin wave dispersion in CsNiF_3

Inelastic neutron scattering measurements were performed on the ferromagnetic chain system CsNiF_3 in the collinear antiferromagnetic ordered state below T_N = 2.67K. The measured spin wave dispersion was found to be in good agreement with linear spin wave theory including dipolar interactions. The additional dipole tensor in the Hamiltonian was essential to explain some striking phenomena in the measured spin wave spectrum: a peculiar feature of the dispersion relation is a jump at the zone center, caused by strong dipolar interactions in this system. The interchain exchange coupling constant and the planar anisotropy energy were determined within the present model to be J'/k_B = -0.0247(12)K and A/k_B = 3.3(1)K. This gives a ratio J/J' \approx 500, using the previously determined intrachain coupling constant J/k_B = 11.8$. The small exchange energy J' is of the same order as the dipolar energy, which implies a strong competition between the both interactions.Comment: 18 pages, TeX type, 7 Postscript figures included. To be published in Phys. Rev.