Optimization of InP APDs for high-speed lightwave systems

Calculations based on a rigorous analytical model are carried out to optimize the width of the indium phosphide avalanche region in high-speed direct-detection avalanche photodiode-based optical receivers. The model includes the effects of intersymbol interference (ISI), tunneling current, avalanche noise, and its correlation with the stochastic avalanche duration, as well as dead space. A minimum receiver sensitivity of -28 dBm is predicted at an optimal width of 0.18 mu m and an optimal gain of approximately 13, for a 10 Gb/s communication system, assuming a Johnson noise level of 629 noise electrons per bit. The interplay among the factors controlling the optimum sensitivity is confirmed. Results show that for a given transmission speed, as the device width decreases below an optimum value, increased tunneling current outweighs avalanche noise reduction due to dead space, resulting in an increase in receiver sensitivity. As the device width increases above its optimum value, the receiver sensitivity increases as device bandwidth decreases, causing ISI to dominate avalanche noise and tunneling current shot noise

New hydrogen-like potentials

Using the modified factorization method introduced by Mielnik, we construct a new class of radial potentials whose spectrum for l=0 coincides exactly with that of the hydrogen atom. A limiting case of our family coincides with the potentials previously derived by Abraham and MosesComment: 6 pages, latex, 2 Postscript figure

Preserving the Ocean Circulation: Implications for Climate Policy

Climate modelers have recognized the possibility of abrupt climate changes caused by a reorganization of the North Atlantic's current pattern (technically known as a thermohaline circulation collapse). This circulation system now warms north-western Europe and transports carbon dioxide to the deep oceans. The posited collapse of this system could produce severe cooling in north-western Europe, even when general global warming is in progress. In this paper we use a simple integrated assessment model to investigate the optimal policy response to this risk. Adding the constraint of avoiding a thermohaline circulation collapse would significantly reduce the allowable greenhouse gas emissions in the long run along an optimal path. Our analysis implies that relatively small damages associated with a collapse (less than 1 % of gross world product) would justify a considerable reduction of future carbon dioxide emissions.

Versatile spectral imaging with an algorithm-based spectrometer using highly tuneable quantum dot infrared photodetectors

We report on the implementation of an algorithm-based spectrometer capable of reconstructing the spectral shape of materials in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) wavelengths using only experimental photocurrent measurements from quantum dot infrared photodetectors (QDIPs). The theory and implementation of the algorithm will be described, followed by an investigation into this algorithmic spectrometer's performance. Compared to the QDIPs utilized in an earlier implementation, the ones used here have highly varying spectral shapes and four spectral peaks across the MWIR and LWIR wavelengths. It has been found that the spectrometer is capable of reconstructing broad spectral features of a range of bandpass infrared filters between wavelengths of 4 and 12 mu m as well as identifying absorption features as narrow as 0.3 mu m in the IR spectrum of a polyethylene sheet

Pengaruh lama pemeraman berbeda terhadap kualitas fisik dan pH silase sorgum varietas Samurai 2 Ratun ke satu

Salah satu cara untuk mengatasi keterbatasan penyediaan hijauan pakan dapat dilakukan upaya pengawetan hijauan pakan diantaranya penerapan teknologi fermentasi melalui proses ensilase untuk menghasilkan silase. Penelitian ini bertujuan untuk mengetahui pengaruh lama pemeraman yang berbeda terhadap kualitas fisik dan pH silase sorgum.  Menggunakan Rancangan Acak Lengkap (RAL) dengan 5 perlakuan dan 4 ulangan.  Perlakuan yaitu lama pemeraman terdiri atas, P1: 7 hari, P2: 14 hari, P3: 21 hari, P4: 28 hari, dan P5: 35 hari. Variabel yang diukur yaitu: kandungan bahan kering, pH dan kualitas fisik dilihat dari warna, tekstur, bau/aroma. Hasil analisis keragaman menunjukkan bahwa perlakuan lama pemeraman memberikan pengaruh yang berbeda sangat nyata (P<0,01) terhadap kandungan bahan kering, warna, tekstur, bau dan pH silase. Hasil uji BNJ menunjukkan bahwa lama pemeraman 28 hari menghasilkan kandungan bahan kering yang sangat nyata (P<0,01) lebih tinggi dari lama pemeraman 7 hari dan 14 hari,  tetapi memberikan pengaruh yang berbeda tidak nyata (P>0,05) dengan lama pemeraman 21 hari dan 35 hari. Uji BNJ menunjukkan bahwa lama pemeraman 7 hari (P1) menghasilkan warna, bau, tekstur dan pH yang sangat nyata (P<0,01) lebih tinggi dari lama pemeraman 35 hari, tetapi memberikan pengaruh yang berbeda tidak nyata (P>0,05) dengan lama pemeraman 14 hari, 21 hari dan 28 hari.  Berdasarkan hasil penelitian ini dapat disimpulkan bahwa lama pemeraman 28 hari silase sorgum varietas samurai 2 ratun ke 1  menghasilkan silase yang berkualitas baik berdasarkan kandungan bahan kering, pH dan kualitas  fisik  (warna, bau, tekstur).Kata Kunci : sorgum, lama pemeraman, bahan kering, kualitas fisi

Sedimentology and chemostratigraphy of Carboniferous red beds in the western Moncton Basin, Sussex area, New Brunswick, Canada: possible evidence for a middle Mabou Group unconformity

The area around Penobsquis, east of Sussex, New Brunswick, Canada, is an important location of natural resources for the province. The McCully gas field produces from strata of the Mississippian Horton Group whereas younger strata of the Windsor Group are host to major potash and rocksalt deposits. Overlying these units are over 1 km of poorly understood red beds currently assigned to the Mississippian Mabou Group. To date, this latter unit lacks significant marker beds and has had no useful biostratigraphic recovery, despite recent extraction of close to 5 km of drill core. Research on this core broadly identifies siltstone and sandstone at the base of the Mabou Group that gradually coarsen up into conglomerate. The succession is considered the result of alluvial-fan progradation from the northeast. Within this succession, in several of the cores, is a single interval of localized, horizontally laminated to cross-stratified, bluish-grey sandstone, containing carbonaceous plant fragments and siltstone intraclasts. To assess the importance of this interval in the context of the red bed succession, a total of 131 samples of core from three boreholes have been analyzed using Inductively Coupled Plasma and spectroscopic techniques to determine chemostratigraphy. Study of various elemental ratios can delineate two packages, one that corresponds to the grey interval and overlying red beds, and the other to the underlying red beds. Changes in the elemental ratios are interpreted to mark a broader population of mineral species related to greater variation of provenance and diagenesis in the upper sediment package. The reduced horizons and rip-up clasts may have been produced by sediment reworking along a boundary that represents an unconformity (in core, a disconformity) at a stratigraphic level near to where one has been inferred by other workers

Students' decisions to use an eLearning system: a structural equation modelling analysis

This research investigates and identifies some of the major factors affecting studentsâ?? adoption of an e-learning system at Arab Open University in Jordan. E-learning adoption is approached from the information systems acceptance point of view. An extended version of the Technology Acceptance Model (TAM) was developed to investigate the underlying factors that influence studentsâ?? decisions to use an e-learning system. The proposed model uses the actual use of an e-learning system. It is different from most of the prior TAM studies, which only used a single dependent variable (intention to use). The model was estimated using Structural Equation Modelling (SEM). The final models derived from this study indicated that beliefs of usefulness and ease of use partially mediate the relationship between external factors and intention to use and actual use of e-learning systems

The impact of freight transport capacity limitations on supply chain dynamics

We investigate how capacity limitations in the transportation system affect the dynamic behaviour of supply chains. We are interested in the more recently defined, 'backlash' effect. Using a system dynamics simulation approach, we replicate the well-known Beer Game supply chain for different transport capacity management scenarios. The results indicate that transport capacity limitations negatively impact on inventory and backlog costs, although there is a positive impact on the 'backlash' effect. We show that it is possible for both backlog and inventory to simultaneous occur, a situation which does not arise with the uncapacitated scenario. A vertical collaborative approach to transport provision is able to overcome such a trade-off. © 2013 Taylor & Francis

A model of context-dependent component connectors

Recent approaches to component-based software engineering employ coordinat- ing connectors to compose components into software systems. For maximum flexibility and reuse, such connectors can themselves be composed, resulting in an expressive calculus of connectors whose semantics encompasses complex combinations of synchronisation, mutual exclusion, non-deterministic choice and state-dependent behaviour. A more expressive notion of connector includes also context-dependent behaviour, namely, whenever the choices a connector can take change non-monotonically as the context, given by the pending activity on its ports, changes. Context dependency can express notions of priority and inhi- bition. Capturing context-dependent behaviour in formal models is non-trivial, as it is unclear how to propagate context information through composition. In this paper we present an intuitive automata-based formal model of context- dependent connectors, and argue that it is superior to previous attempts at such a model for the coordination language Reo