Simulation of a high-speed demultiplexer based on two-photon absorption in semiconductor devices

In this paper, we present a theoretical model of an all-optical demultiplexer based on two-photon absorption in a specially designed semiconductor micro-cavity for use in an optical time division multiplexed system. We show that it is possible to achieve error-free demultiplexing of a 250 Gbit/s OTDM signal (25 × 10 Gbit/s channels) using a control-to-signal peak pulse power ratios of around 30:1 with a device bandwidth of approximately 30 GHz

Dispersion monitoring for high-speed WDM networks via two-photon absorption in a semiconductor microcavity

Due to the continued demand for bandwidth, network operators have to increase the data rates at which individual wavelengths operate at. As these data rates will exceed 100 Gbit/s in the next 5-10 years, it will be crucial to be able to monitor and compensate for the amount of chromatic dispersion encountered by individual wavelength channels. This paper will focus on the use of the novel nonlinear optical-to-electrical conversion process of two-photon absorption (TPA) for dispersion monitoring. By incorporating a specially designed semiconductor microcavity, the TPA response becomes wavelength dependent, thus allowing simultaneous channel selection and monitoring without the need for external wavelength filterin

Urban form and air quality in U.S. metropolitan and megapolitan areas

The spatial form, or morphology, of urban areas may significantly affect the anthropogenic production of air pollutants. This dissertation explores the relationships between air quality and urban form at the metropolitan and megapolitan (multi-metropolitan) scale. Urban form was quantified for 86 metropolitan and 19 megapolitan areas using both pre-existing sprawl indices and multiple spatial metrics derived from remotely sensed landcover data. Air quality was assessed by measuring several key air pollutants, including the ambient concentration of ozone (O3), the non-point source emissions of the two O3 precursors nitrogen oxides (NOx) and volatile organic compounds (VOCs), the ambient concentration and non-point source emissions of fine particulate matter (PM2.5) and coarse particulate matter (PM10), and the mobile emissions of carbon dioxide (CO2). The ambient concentrations of air pollutants were averaged over the 5-year period 1998 to 2002. While controlling for industrial emissions, climate, population and geographic area, multiple linear regression was used to evaluate the degree of association between measures of urban form and air quality. The results suggest that urban form has a measurable impact on both the non-point source emission and ambient concentration of air pollution. Urban areas that exhibited more "sprawl-like" urban forms (i.e. lower residential density, less street network connectivity, less contiguous urban development) generally had higher non-point source emissions and/ or ambient concentrations of air pollution. Pre-existing sprawl indices were most significantly associated with ambient concentrations, while two spatial-metrics based measures of urban structure, urban "continuity" and urban "shape complexity," were most significantly associated with non-point source emissions. The relationships between measures of urban form calculated using spatial metrics and air pollution were most significant at the metropolitan scale. The extent of the urban area (i.e. high versus low urban threshold), however, did not significantly affect the associations between urban form, as assessed using spatial metrics, and air pollution. Understanding the relationships between urban form and air quality is an important step in identifying effective urban land use configurations and developing healthier cities

Modeling nutrient attenuation by riparian buffer zones along headwater streams

"In this study I propose a statistical model, the Riparian Nutrient Attenuation Model (RNAM), designed to quickly and accurately access the nutrient attenuation capability of riparian buffer zones. This information may help land managers evaluate riparian systems in terms of their capacity to retain nutrients. Developed using data available in the literature, RNAM uses three physical properties of the riparian, including vegetation type, slope, and width, to estimate the retention of total N, NO3- and P. Three RNAM sub-models, RNAM-nitrogen, RNAM-nitrate and RNAM-phosphorus, were developed to handle each of the three nutrients. In developing RNAM, the relationships between the predictor variables and nutrient retention were examined. A preliminary test of RNAM indicated that each of the sub-models is capable of producing reasonably accurate estimations of percent nutrient reduction. RNAM-nitrogen, however, produced inconsistent estimates of nitrogen reduction at higher levels. More data is needed to calibrate and validate RNAM."--Abstract from author supplied metadat

All-optical sampling utilising two-photon absorption in semiconductor microcavity

A highly-efficient optical sampling system based on Two-Photon Absorption in a semiconductor micro-cavity is presented. The sensitivity of the sampling system is calculated to be 0.1mW² with a temporal resolution of 2ps

A Closed Class of Hydrodynamical Solutions for the Collective Excitations of a Bose-Einstein Condensate

A trajectory approach is taken to the hydrodynamical treatment of collective excitations of a Bose-Einstein condensate in a harmonic trap. The excitations induced by linear deformations of the trap are shown to constitute a broad class of solutions that can be fully described by a simple nonlinear matrix equation. An exact closed-form expression is obtained for the solution describing the mode {n=0, m=2} in a cylindrically symmetric trap, and the calculated amplitude-dependent frequency shift shows good agreement with the experimental results of the JILA group.Comment: RevTex, 4 pages, 1 eps figure, identical to the published versio

Weak force detection using a double Bose-Einstein condensate

A Bose-Einstein condensate may be used to make precise measurements of weak forces, utilizing the macroscopic occupation of a single quantum state. We present a scheme which uses a condensate in a double well potential to do this. The required initial state of the condensate is discussed, and the limitations on the sensitivity due to atom collisions and external coupling are analyzed.Comment: 12 pages, 2 figures, Eq.(41) has been correcte

An assessment of a three-beam Doppler lidar wind profiling method for use in urban areas

Currently there are few observations of the urban wind field at heights other than rooftop level. Remote sensing instruments such as Doppler lidars provide wind speed data at many heights, which would be useful in determining wind loadings of tall buildings, and predicting local air quality. Studies comparing remote sensing with traditional anemometers carried out in flat, homogeneous terrain often use scan patterns which take several minutes. In an urban context the flow changes quickly in space and time, so faster scans are required to ensure little change in the flow over the scan period. We compare 3993 h of wind speed data collected using a three-beam Doppler lidar wind profiling method with data from a sonic anemometer (190 m). Both instruments are located in central London, UK; a highly built-up area. Based on wind profile measurements every 2 min, the uncertainty in the hourly mean wind speed due to the sampling frequency is 0.05–0.11 m s−1. The lidar tended to overestimate the wind speed by ≈0.5 m s−1 for wind speeds below 20 m s−1. Accuracy may be improved by increasing the scanning frequency of the lidar. This method is considered suitable for use in urban areas

Bayesian inference of population expansions in domestic bovines

The past population dynamics of four domestic and one wild species of bovine were estimated using Bayesian skyline plots, a coalescent Markov chain Monte Carlo method that does not require an assumed parametric model of demographic history. Four domestic species share a recent rapid population expansion not visible in the wild African buffalo (Syncerus caffer). The estimated timings of the expansions are consistent with the archaeological records of domestication

Non-destructive, dynamic detectors for Bose-Einstein condensates

We propose and analyze a series of non-destructive, dynamic detectors for Bose-Einstein condensates based on photo-detectors operating at the shot noise limit. These detectors are compatible with real time feedback to the condensate. The signal to noise ratio of different detection schemes are compared subject to the constraint of minimal heating due to photon absorption and spontaneous emission. This constraint leads to different optimal operating points for interference-based schemes. We find the somewhat counter-intuitive result that without the presence of a cavity, interferometry causes as much destruction as absorption for optically thin clouds. For optically thick clouds, cavity-free interferometry is superior to absorption, but it still cannot be made arbitrarily non-destructive . We propose a cavity-based measurement of atomic density which can in principle be made arbitrarily non-destructive for a given signal to noise ratio