Effect of temperature and frequency on the dielectric properties of cellulose nanofibers from cotton

The present work has been carried out to evaluate the dielectric properties and ac-electrical conductivity of cellulose nanofibers. The cellulose nanofibers (CNF) described in this work are the ones extracted from cotton via a simple acid hydrolysis method and are characterized with X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and UV–Visible diffuse reflectance spectroscopy. The optical band gap of CNF found out using the Kubelka–Munk plot is 3.30 eV. The dielectric constant, dielectric loss, and ac-electrical conductivity of the prepared CNF have been investigated in the temperature range from 30 °C to 300 °C and in the frequency range from 50 Hz to 5 MHz. The synthesized system exhibits a higher dielectric constant value for all temperatures in the low-frequency (0.1 kHz) region and a frequency-independent behavior above 10 kHz. In the high-frequency region, the dielectric constant is independent of temperature. Also, the study shows that the conductivity increases with increasing frequency and temperature. The maximum values of ac-conductivity at room temperature (30 °C) and high temperature (300 °C) are found to be 4.58?×?10^–5 S/cm and 2.26?×?10^–4 S/cm, respectively. In brief, the studies point to the application potential of CNF for future flexible electronics.

     

Bulk production of porous TiO2 nanowires by unique solvo-plasma oxidation approach for combating biotic and abiotic water contaminants

Pure, porous titania nanowires (TiO₂-pNW) are produced in bulk amount (~?250 kg/day, reaction time scale?<?1 min) using a unique solvo-plasma oxidation method utilizing microwave plasma with the potential of easy scale up. The prepared nanowire is found to be efficient towards both biotic disinfection and destruction of various abiotic contaminants in wastewaters. In terms of organic contaminants, the TiO₂-pNW is tested for destruction of Rhodamine B (RhB) dye, tetracycline (TC) antibiotic, and diclofenac (DFC) and caffeine (CAF) drugs. In the case of biotic contaminants, the disinfection of E. coli bacteria is demonstrated. In all of the studies, the photocatalytic performance of anatase TiO₂-pNW is compared to that of commercially available P25 nanoparticles (TiO₂-P25), both in the presence and absence of ozone. The excellent photoactivity exhibited by TiO₂-pNW is a result of low recombination rate of electron–hole pair owing to the spatial separation of electrons and holes within the photoexcited nanowires. Moreover, the scavenger experiments and experiments involving ozone reveal that electron transfer and/or presence of dissolved oxygen are the major limiting factors for both porous titania nanowires and P25 spherical powder under UV exposure with photocatalytic activity towards pollutant degradation.

     

Self-Strengthening Adhesive Force Promotes Cell Mechanotransduction

The extracellular matrix (ECM) undergoes dynamic remodeling and progressive stiffening during tissue regeneration and disease progression. However, most of the artificial ECMs and in vitro disease models are mechanically static. Here, a self-strengthening polymer coating mimicking the dynamic nature of native ECM is designed to study the cellular response to dynamic biophysical cues and promote cell mechanical sensitive response. Spiropyran (SP) is utilized as dynamic anchor group to regulate the strength of cell adhesive peptide ligands. Benefiting from spontaneous thermal merocyanine-to-spiropyran (MC–SP) isomerization, the resulting self-responsive coating displays dynamic self-strengthening of interfacial interactions. Comparing with the static and all of the previous dynamic artificial ECMs, cells on this self-responsive surface remodel the weakly bonded MC-based coatings to activate α5β1 integrin and Rac signaling in the early adhesion stage. The subsequent MC-to-SP conversion strengthens the ligand–integrin interaction to further activate αvβ3 integrin and RhoA/ROCK signaling in the latter stage. This sequential process enhances cellular mechanotransduction as well as the osteogenic differentiation of mesenchymal stem cells (MSCs). It is worth emphasizing that the self-strengthening occurs spontaneously in the absence of any stimulus, making it especially useful for implanted scaffolds in regenerative medicine.     

EGO: A personalized multimedia management and retrieval tool

The problems of content‐based image retrieval (CBIR) systems can be attributed to the semantic gap between the low‐level data representation and the high‐level concepts the user associates with images, on the one hand, and the time‐varying and often vague nature of the underlying information need, on the other. These problems can be addressed by improving the interaction between the user and the system. In this article, we sketch the development of CBIR interfaces and introduce our view on how to solve some of the problems these interfaces present. To address the semantic gap and long‐term multifaceted information needs, we propose a “retrieval in context” system, EGO. EGO is a tool for the management of image collections, supporting the user through personalization and adaptation. We will describe how it learns from the user's personal organization, allowing it to recommend relevant images to the user. The recommendation algorithm is described, which is based on relevance feedback techniques. Additionally, we provide results of a performance analysis of the recommendation system and of a preliminary user study. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 725–745, 2006.     

Monitoring the cellular surface display of recombinant proteins by cysteine labeling and flow cytometry

A general method is described that allows one to follow the surface display of recombinant proteins in Escherichia coli without having to use specific antibodies or enzymatic reactions. The method is based on cysteine-specific labeling through Michael addition to the double bond of maleimide and its derivatives, and takes advantage of the fact that naturally occurring surface proteins in E. coli contain no accessible cysteine residues. The method is easy to perform and could be simply applied to different analytic procedures including Western blot, spectral photometry, and flow cytometry. By using this new labeling method, single cells bearing a distinct protein at the surface could be selected by fluorescence-activated cell sorting. The data were obtained by using autodisplay, an efficient surface display system established for E. coli, but the method presented here represents rather a general solution for analyzing the surface display of recombinant proteins, independent of the cellular system used.     

Determination of refractive indices of quarter-wavelength Bragg reflectors by reflectance measurements in wavelength and angular domains

We show that all the structural properties of periodic dielectric multilayers can be accurately determined by a combined measurement of the transmission as a function of the wavelength and of the reflection as a function of the angle of incidence when the wavelength of the incident light is fixed. This method is applied to determine the structural properties of two commercial dielectric mirrors, and the results obtained are compared with a measurement of the same structural parameters by use of another technique based on the more standard optical guiding method.     

Linear scanning array with bulk ferroelectric-integrated feed network

Variable ferroelectric delay line technology has been utilized to implement a proof-of-concept, continuous scanning, ferroelectric integrated phased array antenna system. S₂₁ phase shifts of up to 157° have been achieved from the phase shifter itself via analogous variation of a DC bias. When integrated into a phased array, beam scanning of at least ±12° is achieved prior to any optimization. Some of the key material requirements, fabrication procedures, characterization, and assembly of the ferroelectric material are revealed. The design, integration, and performance of the array system using such phased shifters are presented     

Dual Grid: A New Approach for Robust Spatial Algebra Implementation

Systems of spatial data types and operations, or spatial algebras, are fundamental for the implementation of spatial database systems. Several designs of such algebras have been proposed in the last decade, and recently commercial DBMS offer such algebras in the form of extension packages (e.g., data blades). However, actual implementations are generally severely restricted when compared to designs in the literature. A main reason is that at the implementation level one cannot further ignore the problems of robustness and topological correctness arising from the discrete number representations used in computers. Therefore, implemented packages either avoid problematic operations, or accept inconsistencies and topological errors in the answers of queries due to rounding effects.The ROSE algebra [12], proposed and implemented earlier, goes a long way towards avoiding such problems, since it was defined from scratch with robustness problems in mind. It is founded on a discrete geometric basis called a realm. The ROSE algebra guarantees a correct behavior of operations and has an entirely robust implementation. Unfortunately, the realm concept and its interaction with DBMS are difficult to implement, and certain kinds of topological problems still remain.In this paper we introduce the concept of dual grid, which provides a new approach for the representation of spatial information that avoids any robustness and topological correctness problem and allows a less restrictive implementation of spatial algebras. As an example, we show how can it be used for implementing the ROSE algebra without realms, and show that such an implementation does not suffer from the side effects and disadvantages of the original realm-based one.     

Data-driven construction of Convex Region Surrogate models

With the increasing trend of solving more complex and integrated optimization problems, there is a need for developing process models that are sufficiently accurate as well as computationally efficient. In this work, we develop an algorithm for the data-driven construction of a type of surrogate model that can be formulated as a set of mixed-integer linear constraints, yet still provide good approximations of nonlinearities and nonconvexities. In such a surrogate model, which we refer to as Convex Region Surrogate (CRS), the feasible region is given by the union of convex regions in the form of polytopes, and for each region, the corresponding cost function can be approximated by a linear function. The general problem is as follows: given a set of data points in the parameter space and a scalar cost value associated with each data point, find a CRS model that approximates the feasible region and cost function indicated by the given data points. We present a two-phase algorithm to solve this problem and demonstrate its effectiveness with an extensive computational study as well as a real-world case study.