Double-groove, two-depth grating coupler for light guides

A double-groove, two-depth dielectric grating structure for high-efficiency light coupling into a light guide is introduced. We show computationally that the optimized gratings can couple a monochromatic TE- or TM-polarized light beam with nearly 100% efficiency. For an unpolarized light beam 90% efficiency can be reached. In all cases the highest achieved coupling efficiencies require that the refractive index of the grating material be greater than 1.7. The illumination and fabrication tolerances of the couplers are also analyzed.     

Healable,Stable and Stiff Hydrogels: Combining Conflicting Properties Using Dynamic and Selective Three‐Component Recognition with Reinforcing Cellulose Nanorods

Nanocomposite hydrogels are prepared combining polymer brush‐modified ‘hard’ cellulose nanocrystals (CNC) and ‘soft’ polymeric domains, and bound together by cucurbit[8]uril (CB[8]) supramolecular crosslinks, which allow dynamic host–guest interactions as well as selective and simultaneous binding of two guests, i.e., methyl viologen (the first guest) and naphthyl units (the second guest). CNCs are mechanically strong colloidal rods with nanometer‐scale lateral dimensions, which are functionalized by surface‐initiated atom transfer radical polymerization to yield a dense set of methacrylate polymer brushes bearing naphthyl units. They can then be non‐covalently cross‐linked through simple addition of poly(vinyl alcohol) polymers containing pendant viologen units as well as CB[8]s in aqueous media. The resulting supramolecular nanocomposite hydrogels combine three important criteria: high storage modulus (G′ > 10 kPa), rapid sol–gel transition (<6 s), and rapid self‐healing even upon aging for several months, as driven by balanced colloidal reinforcement as well as the selectivity and dynamics of the CB[8] three‐component supramolecular interactions. Such a new combination of properties for stiff and self‐healing hydrogel materials suggests new approaches for advanced dynamic materials from renewable sources.     

Reliability of 80 μm pitch flip chip attachment on flex

The interest toward flip chip technology has increased rapidly during last decade. Compared to the traditional packages and assembly technologies flip chip has several benefits, like less parasitics, the small package size and the weight. These properties emphasize especially when flip chip component is mounted direct to the flexible printed board. In this paper flip chip components with Kelvin four point probe and daisy chain test structure were bonded to the polyimide flex with two different types of anisotropically conductive adhesive films and one anisotropically conductive adhesive paste. The reliability of small pitch flip chip on flex interconnections (pitch 80 μm) was tested in 85°C/85% RH environmental test and −40↔+125°C thermal shock test. According to the results it is possible to achieve reliable and stable ohmic contact, even in small pitch flip chip on flex applications.     

Determining relevance of imprecise temporal intervals for cultural heritage information retrieval

Time is an essential concept in cultural heritage applications. Instances of temporal concepts such as time intervals are used for the annotation of cultural objects and also for querying datasets containing information about these objects. Hence it is important to match query and annotation intervals by examining their similarity or closeness. One of the problems is that in many cases time intervals are imprecise. For example, the boundaries of the “Pre-Roman age” and the “Roman age” are inherently imprecise and it may be difficult to distinguish them with clear-cut intervals. In this paper we apply the fuzzy set theory to model imprecise time intervals in order to determine relevance of the relationship between two time intervals. We present a method for matching query and annotation intervals based on their weighted mutual overlapping and closeness. We present (1) methods for calculating these weights to produce a combined measure and (2) results of comparing the combined measure with human evaluators as a case study. The case study takes into consideration archaeological temporal information, which is in most cases inherently fuzzy, and therefore offers a particularly complex and challenging scenario. The results show that our new combined measure that utilizes different weighted measures together in rankings, performs the best in terms of precision and recall. It should be used when ranking annotation intervals according to a given query interval in cultural heritage information retrieval. Our approach intends to be generalizable: overlapping and closeness may be calculated between any two fuzzy temporal intervals. The presented procedure of using user evaluation results as a basis for assigning weights for overlapping and closeness could potentially be used to reveal weights in other domains and purposes as well.     

A feedforward–feedback controller for infinite‐dimensional systems and regulation of bounded uniformly continuous signals

We design a controller for infinite‐dimensional linear systems (with bounded control, observation and feedthrough operators) which, under certain assumptions, achieves asymptotic tracking of arbitrary bounded uniformly continuous reference signals in the presence of disturbances. The proposed controller is of feedforward–feedback type: The dynamic feedback part is used to stabilize the closed‐loop system consisting of the plant and the controller, whereas the feedforward part is tuned using the regulator equations to achieve the regulation of desired signals. We also completely solve the regulator equations for SISO systems, and we discuss robustness properties of the proposed controller. A useful feature in our design is that the feedforward part of the controller can be designed independently of the feedback part. This automatically leads to a degree of robustness in the stabilizing part of the controller, which is not present in the existing state feedback controllers solving the same output regulation problem. Copyright © 2006 John Wiley & Sons, Ltd.     

MRI quality assurance based on 3D FLAIR brain images

Objective

Quality assurance (QA) of magnetic resonance imaging (MRI) often relies on imaging phantoms with suitable structures and uniform regions. However, the connection between phantom measurements and actual clinical image quality is ambiguous. Thus, it is desirable to measure objective image quality directly from clinical images.

Materials and methods

In this work, four measurements suitable for clinical image QA were presented: image resolution, contrast-to-noise ratio, quality index and bias index. The methods were applied to a large cohort of clinical 3D FLAIR volumes over a test period of 9.5 months. The results were compared with phantom QA. Additionally, the effect of patient movement on the presented measures was studied.

Results

A connection between the presented clinical QA methods and scanner performance was observed: the values reacted to MRI equipment breakdowns that occurred during the study period. No apparent correlation with phantom QA results was found. The patient movement was found to have a significant effect on the resolution and contrast-to-noise ratio values.

Discussion

QA based on clinical images provides a direct method for following MRI scanner performance. The methods could be used to detect problems, and potentially reduce scanner downtime. Furthermore, with the presented methodologies comparisons could be made between different sequences and imaging settings. In the future, an online QA system could recognize insufficient image quality and suggest an immediate re-scan.

     

Factors influencing the reaction between phlogopite and CaSo4·2H2O plus CaO mixtures

According to earlier studies phlogopite reacts with CaSO₄.2H₂O and a mixture of CaSO₄.2H₂O and CaO exchanging 40–80% of its potassium with calcium. The same reactions occur only poorly in the case of muscovite. The structural difference between phlogopite and muscovite is small so that some unknown factors must effect the exchange reaction. In the present work the factors influencing the reaction between phlogopite and a CaSO₄.2H₂O/CaO mixture have been studied by means of X-ray diffraction and an electron microscope. A rod mill has been employed in the separation of the solid phases produced during the reaction. The results have been calculated and drawn by computer programs created for the study. The effects of gypsum, calcium oxide, iron, aluminium and magnesium have been treated in the exchange reaction. Also the poor reactivity of muscovite in the reaction conditions used has been discussed.     

Motives to restructure industries: Finnish evidence of cross-border and domestic mergers and acquisitions

Abstract.  We estimate a multilogit model for the probabilities that a firm will acquire or become a target in different M&A categories, which are defined according to the location of an acquiring firm with respect to a target. We find that certain firm characteristics of an acquiring firm regarded as indicative of having a high capability of monitoring a target – or internalising the potential synergies of M&A – increase the probability of distant M&As at the expense of close M&As. Factors which ease the monitoring of the target firm's value increase the probability that such a firm becomes a target located far from an acquiring firm.