Stability and robustness of time‐delay systems

Abstract

Using some properties of matrix measures and matrix's spectral radius, a new stability criterion for a linear time‐delay system is derived. This result is also extended to interval time‐delay systems.     

Implication of Size-Controlled Graphite Nanosheets as Building Blocks for Thermal Conductive Three-Dimensional Framework Architecture of Nanocarbons

Preparation of three-dimensional (3D) networks has received significant attention as an effective approach for applications involving transport phenomena, such as thermal management materials, and several nanomaterials have been examined as potential building blocks of 3D networks for the improvement of heat conduction in polymer nanocomposites. For that purpose, nanocarbons such as graphene and graphite nanoplatelets have been spotlighted as suitable filler materials because of their excellent thermal conductivities (ca. 10²–10³ W·(m·K)^?1 along their lateral axes) and morphological merits. However, the implications of morphological features such as the lateral length and thickness of graphene or graphene-like materials have not yet been identified. In this study, a controlled dissociation of bulk graphite to graphite nanosheets (GNSs) using a low-cost, ecofriendly bead mill process was extensively examined and, when configured in a 3D framework architecture formation, the size-controlled GNSs demonstrated that the thermal conductivities of a 3D interconnected framework of GNSs and the corresponding polymer nanocomposite were intimately correlated with the size of the GNSs, thus demonstrating the successful preparation of an efficient thermal management material without highly sophisticated efforts. The capability of controlling the lateral size and thickness of the GNSs as well as the use of a 3D interconnected framework architecture should greatly assist the commercialization of high-quality graphene-based thermal management materials in a scalable production process.     

Ontogeny of the testicular excurrent duct system of male Japanese quail (Coturnix japonica): A histological,ultrastructural, and histometric study

The testicular excurrent duct system undergoes several physiological and morphological changes during the reproductive stage or breeding season in mammals, birds, and reptiles. Studies on normal age-related histomorphological changes in the excurrent duct system of Japanese quails (Coturnix japonica) remain unreported, despite the extensive use of this bird as an avian model in research studies. The current study investigated the histological, ultrastructural, and histometric changes in the testicular excurrent duct system of the Japanese quail during three reproductive stages, namely prepubertal, pubertal, and adult. Simple squamous to low cuboidal cells formed the epithelia of the rete testis in prepubertal and pubertal birds, while in adult birds the lining was low cuboidal to cuboidal. In pubertal and adult birds, the nonciliated Type I epithelial cells of the proximal efferent duct displayed a subapical endocytotic apparatus comprising coated pits, coated apical tubules, and endosomes. There was a significant increase (p ≤ .001) in epithelial heights of all ducts of the excurrent duct system in the mature, sexually active, adult birds when compared to the other age groups. The luminal and tubular diameters, and the cross-sectional areas of efferent ducts and the epididymal duct unit increased significantly (p ≤ .001) with age. It is concluded that the morphology and morphometry of the excurrent ducts of the testis of the Japanese quail change as birds mature.     

An Empirical Study on Factors Influencing Consumers' Initial Trust in Wearable Commerce

This paper focuses on the factors influencing consumers' initial trust in wearable commerce. Specifically, a conceptual model for wearable commerce is created and hypotheses are developed to study the initial trust. Through a survey of 266 valid questionnaires, we carry out an empirical analysis via Structure Equation Modeling method. The results show that five proposed factors (privacy concern, trust propensity, performance expectancy, facilitating conditions, hedonic motivation) all have significant effects on initial trust in wearable commerce. The conclusion is valuable to future research on wearable commerce. Theoretical and practical implications are also presented.     

Megasonic agitation for enhanced electrodeposition of copper

In this paper we propose an agitation method based on megasonic acoustic streaming to overcome the limitations in plating rate and uniformity of the metal deposits during the electroplating process. Megasonic agitation at a frequency of 1 MHz allows the reduction of the thickness of the Nernst diffusion layer to less than 600 nm. Two applications that demonstrate the benefits of megasonic acoustic streaming are presented: the formation of uniform ultra-fine pitch flip-chip bumps and the metallisation of high aspect ratio microvias. For the latter application, a multi-physics based numerical simulation is implemented to describe the hydrodynamics introduced by the acoustic waves as they travel inside the deep microvias.     

Some microwave applications of BaSrTiO3 and high temperature superconductors

Abstract

The group at the University of Colorado has been working on the applications of BaSrTiO₃ and high temperature superconductors to microwave circuits and systems with support from Superconducting Core Technologies, NASA and ONR. This work has included the development of a voltage tunable oscillator, a phase shifter, and a voltage tunable phased array antenna system. An important aspect of this program is the lattice match between the high temperature superconductor and the ferroelectric materials which enables us to grow thin films of either material on each other. By choosing the appropriate barium stronium ratio we are able to obtain changes in the dielectric constant of 5 to 1 in bulk capacitors at 77 K, the liquid nitrogen boiling temperature. Phase shifts of a little less than 126° at 10 Ghz have been obtained by applying 5 volts on a one centimeter coplanar line. The proposed phased array systems should enable us to point the beam radiated from the antenna in an arbitrary direction using two control voltages of less than 50 volts. We believe this approach leads to the possibility of inexpensive electronically scannable antenna systems which could be used for mobile communications with satellites and cellular systems.     

Project affinity: the role of emotional attachment in construction projects

Although a wide range of human and organizational factors have been found to be important in the operation of projects, those determined by cultural variables are less well defined. One such influence concerns the notion of ‘project affinity’, the commitment and attachment by stakeholders and participants to projects and their outcomes. The temporal nature and transient involvement context provided by construction projects arguably presents a climate in which many participants are less likely to display commitment to its goals. This note is concerned with the issue of whether an attachment to a project's goals or to the completed product can lead to improved commitment among those involved. The concept of project affinity was developed in the course of a case study investigation in which operatives' attitudes towards the construction of a cancer research facility were explored. Because of the contribution of the facility to the future care of cancer sufferers, the concept of project affinity proved helpful in understanding a factor that appeared to be influencing the commitment of those involved. The results suggest a complementary concept to that of ‘project chemistry’ (c.f. Nicolini, 2002 Nicolini, D. 2002. In search of ‘project chemistry’.. Construction Management and Economics, 20: 167–77.  ).     

Structural frame selection: case studies of hybrid concrete frames

Hybrid concrete construction (HCC) uses a combination of in-situ and precast concrete and is an example of ‘mixed’ construction, which is the term for an innovative combination of different materials or framing methods. Examples of HCC exist in many countries to fulfil varying structural requirements, so it is not clear why HCC is not better used in the UK. Research was undertaken to gain a better understanding of the selection and use of HCC. Two case study projects were investigated to explore decision-making criteria, the roles of project participants and the challenges particular to HCC. The findings suggest that HCC is selected when measurable cost or programme advantages are not the most important criteria, but where other factors such as satisfying architectural requirements (finish, colour, etc.) or operational demands (such as internal comfort or maintenance) are critical. In both cases, clients and architects were found to be the most influential team members in the frame-selection process.

La construction en béton hybride (HCC) utilise une combinaison de béton in situ et de béton précoulé; c'est un exemple de ‘construction mixte’; cette expression définit une combinaison innovante de différents matériaux et méthodes de coffrage. Il existe des exemples de HCC dans de nombreux pays qui répondent à différentes exigences structurales; on peut donc difficilement expliquer pourquoi la HCC n'est pas mieux utilisée au Royaume-Uni. Des recherches ont été entreprises pour mieux comprendre les choix et les usages de la HCC. Deux études de cas ont été engagées, l'objectif étant d'explorer les critères décisionnels, le rôle des participants à ces projets et les défis particuliers propres à la HCC. Les résultats laissent à penser que la HCC est retenue lorsque le coût mesurable ou les avantages du programme ne sont pas les critères les plus importants et lorsque d'autres facteurs comme la réponse aux exigences architecturales (finition, couleur, etc.) ou d'autres exigences opérationnelles (comme le confort intérieur ou la maintenance) sont critiques. Dans les deux cas, les clients et les architectes sont apparus comme les membres les plus influents des équipes lors du processus de sélection du cadre.

Mots clés: processus de conception, construction en béton hybride, construction mixte, critères de performances, cadre structural     

Multifunctional coatings created using an antimicrobial polymer as a platform for titania precipitation on cotton

Titania precipitation on cotton has been achieved using a commercially available antimicrobial polymer, Reputex 20. The cotton swatches precipitated with titania retain antimicrobial activity, and we have also shown the ability to encapsulate diisopropylfluorophosphatase (DFPase), an enzyme capable of breaking down organofluorophosphates. Cotton swatches are easily prepared and precipitation occurs at room temperature in aqueous solutions at neutral pH. Both the antimicrobial properties of Reputex 20 and the hydrolytic activity of the DFPase enzyme are retained after titania precipitation, generating a cotton material exhibiting multifunctional properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43199.