Fiber optic sensors

A survey of the developments in the field of fiber optics sensor technology is presented along with a discussion of the advantages of optical measuring instruments as compared with electronic sensors. The two primary types of fiber optics sensors, specifically those with multiwave fibers and those with monowave fibers, are described. Examples of each major sensor type are presented and discussed. Multiwave detectors include external and internal fiber optics sensors. Among the monowave detectors are Mach-Zender interferometers, Michelson interferometers, Sagnac interferometers (optical gyroscopes), waveguide resonators, and polarimeter sensors. Integrated optical sensors and their application in spectroscopy are briefly discussed

Conjugacy in Baumslag's group, generic case complexity, and division in power circuits

The conjugacy problem belongs to algorithmic group theory. It is the following question: given two words x, y over generators of a fixed group G, decide whether x and y are conjugated, i.e., whether there exists some z such that zxz^{-1} = y in G. The conjugacy problem is more difficult than the word problem, in general. We investigate the complexity of the conjugacy problem for two prominent groups: the Baumslag-Solitar group BS(1,2) and the Baumslag(-Gersten) group G(1,2). The conjugacy problem in BS(1,2) is TC^0-complete. To the best of our knowledge BS(1,2) is the first natural infinite non-commutative group where such a precise and low complexity is shown. The Baumslag group G(1,2) is an HNN-extension of BS(1,2). We show that the conjugacy problem is decidable (which has been known before); but our results go far beyond decidability. In particular, we are able to show that conjugacy in G(1,2) can be solved in polynomial time in a strongly generic setting. This means that essentially for all inputs conjugacy in G(1,2) can be decided efficiently. In contrast, we show that under a plausible assumption the average case complexity of the same problem is non-elementary. Moreover, we provide a lower bound for the conjugacy problem in G(1,2) by reducing the division problem in power circuits to the conjugacy problem in G(1,2). The complexity of the division problem in power circuits is an open and interesting problem in integer arithmetic.Comment: Section 5 added: We show that an HNN extension G = < H, b | bab^-1 = {\phi}(a), a \in A > has a non-amenable Schreier graph with respect to the base group H if and only if A \neq H \neq

Complexity confers stability: Climate variability, vegetation response and sand transport on longitudinal sand dunes in Australia’s deserts

Abstract The relationship between antecedent precipitation, vegetation cover and sand movement on sand dunes in the Simpson and Strzelecki Deserts was investigated by repeated (up to four) surveys of dune crest plots (≈25 × 25 m) over a drought cycle (2002–2012) in both winter (low wind) and spring (high wind). Vegetation varied dramatically between surveys on vegetated and active dune crests. Indices of sand movement had significant correlations with vegetation cover: the depth of loose sand has a strong inverse relationship with crust (cyanobacterial and/or physical) while the area covered by ripples has a strong inverse relationship with the areal cover of vascular plants. However, the relationship between antecedent rainfall and vegetation cover was found to be complex. We tentatively identify two thresholds; (1) &gt;10 mm of rainfall in the preceding 90 days leads to rapid and near total cover of crust and/or small plants &lt;50 cm tall, and (2) &gt;400 mm of rainfall in the preceding three years leads to higher cover of persistent and longer-lived plants &gt;50 cm tall. These thresholds were used to predict days of low vegetation cover on dune crests. The combination of seasonality of predicted bare-crest days, potential sand drift and resultant sand drift direction explains observed patterns of sand drift on these dunes. The complex vegetation and highly variable rainfall regime confer meta-stability on the dunes through the range of responses to different intervals of antecedent rainfall and non-linear growth responses. This suggests that the geomorphic response of dunes to climate variation is complex and non-linear.Abstract The relationship between antecedent precipitation, vegetation cover and sand movement on sand dunes in the Simpson and Strzelecki Deserts was investigated by repeated (up to four) surveys of dune crest plots (≈25 × 25 m) over a drought cycle (2002–2012) in both winter (low wind) and spring (high wind). Vegetation varied dramatically between surveys on vegetated and active dune crests. Indices of sand movement had significant correlations with vegetation cover: the depth of loose sand has a strong inverse relationship with crust (cyanobacterial and/or physical) while the area covered by ripples has a strong inverse relationship with the areal cover of vascular plants. However, the relationship between antecedent rainfall and vegetation cover was found to be complex. We tentatively identify two thresholds; (1) &gt;10 mm of rainfall in the preceding 90 days leads to rapid and near total cover of crust and/or small plants &lt;50 cm tall, and (2) &gt;400 mm of rainfall in the preceding three years leads to higher cover of persistent and longer-lived plants &gt;50 cm tall. These thresholds were used to predict days of low vegetation cover on dune crests. The combination of seasonality of predicted bare-crest days, potential sand drift and resultant sand drift direction explains observed patterns of sand drift on these dunes. The complex vegetation and highly variable rainfall regime confer meta-stability on the dunes through the range of responses to different intervals of antecedent rainfall and non-linear growth responses. This suggests that the geomorphic response of dunes to climate variation is complex and non-linear

Cross-Sectional Analysis of Sediment and Organic Matter from Transects Across the Lower Unchannelized Missouri River

The United States Army Corps of Engineers, U.S. Geological Survey, and Nebraska Game and Parks Commission cooperated in 1989 to obtain physical data from cross-section transects along the unchannelized Missouri River in northeastern Nebraska. Bed-sediment samples were collected from locations along these transects and taken to the laboratory. Mean particle-size and standard deviation were determined by weighing material retained on seven U.S. Standard sieves after being on a sieve shaker for six minutes. Organic matter content of each sample was obtained by ashing an aliquot in a muffle furnace to remove the organic portion. A new system for coding sediment mixtures was developed, and coded sediment and organic matter content were compared with depth and velocity in a regression analysis. The most common mean particle-size was determined to be medium sand; however, some samples were as coarse as fine gravel. Organic-matter content was less then 3% for the most part; however, it was measured as high as 20%. Sediment and organic matter were related to depth and velocity; however, r-square values were low, suggesting that other factors contribute to the observed variability in the sediment mixtures and organic matter content

Cross-Sectional Analysis of Sediment and Organic Matter from Transects Across the Lower Unchannelized Missouri River

The United States Army Corps of Engineers, U.S. Geological Survey, and Nebraska Game and Parks Commission cooperated in 1989 to obtain physical data from cross-section transects along the unchannelized Missouri River in northeastern Nebraska. Bed-sediment samples were collected from locations along these transects and taken to the laboratory. Mean particle-size and standard deviation were determined by weighing material retained on seven U.S. Standard sieves after being on a sieve shaker for six minutes. Organic matter content of each sample was obtained by ashing an aliquot in a muffle furnace to remove the organic portion. A new system for coding sediment mixtures was developed, and coded sediment and organic matter content were compared with depth and velocity in a regression analysis. The most common mean particle-size was determined to be medium sand; however, some samples were as coarse as fine gravel. Organic-matter content was less then 3% for the most part; however, it was measured as high as 20%. Sediment and organic matter were related to depth and velocity; however, r-square values were low, suggesting that other factors contribute to the observed variability in the sediment mixtures and organic matter content

In Vitro Studies of Encrustations on Catheters, a Model of Infection Stone Formation

Deposition of infection-induced stone material on urinary catheters is a common problem in urological patients. Therefore, a crystallization model was developed in order to form this material in a reproducible manner. Furthermore, the dissolving potency of two solutions (Suby-G® and Solution-R®) was investigated with this model. The encrustations were examined by infrared (IR) spectroscopy, chemical encrustation analysis , scanning electron microscopy (SEM) and X-ray microanalysis. In addition, the encrustations were calculated from the results of the urine analysis, before and after each experiment, as contents remaining in each artificial bladder. The model conditions changed during the experiment and led to supersaturation for struvite. The encrustation analysis resulted in 73 .5 % (IR spectroscopy) and 78.5 % struvite (chemical encrustation analysis) respectively. The calculated encrustation by urinary losses of stone forming contents resulted in 79.3% struvite. SEM showed that after the experiment, the catheters carried large amounts of mineral deposition and bacterial biofilm on their inner and outer surface. During the experiment, the catheters lost their homogeneous surface; cracks appeared and material was lost. X-ray microanalysis showed peaks for Mg, P and Ca (infection-induced stone material), Si (catheter material), Al (sample carrier) and Ag (conductive material) and supported the encrustation analysis. The solutions tested showed high dissolving capacities for infection stone material. After irrigation of the bladder with both solutions tested, 70 % and 85 % respectively, of struvite was dissolved

Structured cooperation in computer based collaborative Learning

Es wird der Frage nachgegangen, inwieweit hochstrukturierte kooperative Lernmethoden zur Förderung computerunterstützten kollaborativen Lernens genutzt werden können. Solche Methoden geben Regeln für das Dialogverhalten vor und haben sich in traditionellen face-to-face-Gruppen bewährt. In einer experimentellen Untersuchung wurde in einem telematischen Setting eine Kooperationsstruktur vorgegeben, die mittels Kommunikationsschnittstelle das Dialogverhalten kooperativer Paare gemäß dem Prinzip des gegenseitigen Erklärens regelt. Teilnehmer waren 30 Studenten verschiedener Fachrichtungen. Es zeigte sich im Vergleich zu einer Kontrollgruppe von ebenfalls 30 Studenten ein geringerer Koordinationsaufwand bei der gemeinsamen Aufgabenbearbeitung und ein effektiveres Dialogverhalten im Sinne eines geringeren Anteils an Aussagen zur Dialogsteuerung. Außerdem ergab sich eine Verbesserung der Problemlöseperformanz und des Wissenserwerbs aufgrund der gemeinsamen Aufgabenbearbeitung. (DIPF/Orig.

Characterization of queen specific components of the fluid released by fighting honey bee queens

Swarming honey bee (Apis mellifera L.) colonies rear supernumerary young queens that compete for the limited resources (workers) necessary for founding a new colony. Young queens often fight to death. Queens show several adaptations to fight and conflict, such as short developmental time and early onset of venom production. During fights, queens often release rectal fluid with a strong smell of wine grapes, after which they temporarily stop fighting. This potentially reduces individual overall risk of deadly injury. The fluid and one of its components, ortho-aminoacetophenone, were previously found to have a pheromonal effect on workers, but the evidence is equivocal. Recently, it has been suggested that the effects of this substance may be context- or concentration-specific. We performed semi-quantitative gas-chromatography mass spectrometry (GC/MS) analysis of the fluid (1) released by queens during their first fight, (2) released during a subsequent fight, and (3) obtained by dissecting the hindgut of queens and (4) of workers. Following preliminary results by Page et al. 1988 (Experientia 44: 270-271), we scored presence / absence of eight substances. Five substances (ortho-aminoacetophenone, decanoic acid, dodecanoic acid, octyl decanoate, and decyl decanoate) were characteristic of queens only. ortho-Aminoacetophenone was detected in all queen and in none of the worker samples, in agreement with previous findings that worker faeces do not have any pheromonal effect. The fluid released by queens on their second fight also contained ortho-aminoacetophenone, but in smaller quantities. These data substantiate previous bioassay results, and provide estimates of ortho-aminoacetophenone concentration as required to design experiments addressing the function and adaptive significance of this behaviour

Multiple steady states in exchange flows across faults and the dissolution of CO2

We develop a model of the steady exchange flows which may develop between two aquifers at different levels in the geological strata and across which there is an unstable density stratification, as a result of their connection through a series of fractures. We show that in general there are multiple steady exchange flows which can develop, depending on the initial conditions, and which may involve a net upwards or downwards volume flux. We also show that there is a family of equilibrium exchange flows with zero net volume flux, each characterised by a different interlayer flux of buoyancy. We present experiments which confirm our simplified model of the exchange flow. Such exchange flows may supply unsaturated water from a deep aquifer to drive dissolution of a structurally trapped pool of geologically stored $\text{CO}_{2}$, once the water in the aquifer containing the trapped pool of $\text{CO}_{2}$ has become saturated in $\text{CO}_{2}$, and hence relatively dense. Such exchange flows may also lead to cross-contamination of aquifer fluids, which may be of relevance in assessing risks of geological storage systems.This is the author accepted manuscript. The final version is available from CUP via http://journals.cambridge.org/download.php?file=%2FFLM%2FFLM769%2FS0022112015001007a.pdf&code=58f6f56d3a1302266ca4bcf617ba24df