Electrically Activated Paper Actuators

This paper describes the design and fabrication of electrically controlled paper actuators that operate based on the dimensional changes that occur in paper when the moisture absorbed on the surface of the cellulose fibers changes. These actuators are called “Hygroexpansive Electrothermal Paper Actuators” (HEPAs). The actuators are made from paper, conducting polymer, and adhesive tape. They are lightweight, inexpensive, and can be fabricated using simple printing techniques. The central element of the HEPAs is a porous conducting path (used to provide electrothermal heating) that changes the moisture content of the paper and causes actuation. This conducting path is made by embedding a conducting polymer (PEDOT:PSS) within the paper, and thus making a paper/polymer composite that retains the porosity and hydrophilicity of paper. Different types of HEPAs (straight, precurved, and creased) achieved different types of motions (e.g., bending motion, accordion type motion). A theoretical model for their behavior is proposed. These actuators have been used for the manipulation of liquids and for the fabrication of an optical shutter.     

Self-switching in Mach-Zehnder interferometers with SOA phase shifters

A self-switching mechanism in Mach-Zehnder interferometers (MZIs) is described. The input light signal is distributed unequally over the interferometer arms using an multimode interference (MMI) coupler. In the arms, semiconductor optical amplifiers are placed as nonlinear phase shifters. Unequal intensities yield a nonlinear phase shift. The signals from the two arms are then recombined in an output MMI coupler. If an obtained nonlinear phase shift in the arms can compensate the coupler-induced phase difference between the arms, the signals are in phase at the output port. Choosing an appropriate output coupler, 2/spl times/1 and 2/spl times/2 devices can be obtained. The 2/spl times/2 and 2/spl times/1 MZIs can be used as pattern effect compensators and 2R-regenerators or low-loss combiner circuits, respectively. An active-passive integration technique is applied in order to realize the interferometric structures. Fabrication, simulation, and characterization of these devices are presented in this letter.     

Normally Oriented Adhesion versus Friction Forces in Bacterial Adhesion to Polymer‐Brush Functionalized Surfaces Under Fluid Flow

Bacterial adhesion is problematic in many diverse applications. Coatings of hydrophilic polymer chains in a brush configuration reduce bacterial adhesion by orders of magnitude, but not to zero. Here, the mechanism by which polymer‐brush functionalized surfaces reduce bacterial adhesion from a flowing carrier fluid by relating bacterial adhesion with normally oriented adhesion and friction forces on polymer (PEG)‐brush coatings of different softness is studied. Softer brush coatings deform more than rigid ones, which yields extensive bond‐maturation and strong, normally oriented adhesion forces, accompanied by irreversible adhesion of bacteria. On rigid brushes, normally oriented adhesion forces remain small, allowing desorption and accordingly lower numbers of adhering bacteria result. Friction forces, generated by fluid flow and normally oriented adhesion forces, are required to oppose fluid shear forces and cause immobile adhesion. Summarizing, inclusion of friction forces and substratum softness provides a more complete mechanism of bacterial adhesion from flowing carrier fluids than available hitherto.     

An Organoid for Woven Bone

Bone formation (osteogenesis) is a complex process in which cellular differentiation and the generation of a mineralized organic matrix are synchronized to produce a hybrid hierarchical architecture. To study the mechanisms of osteogenesis in health and disease, there is a great need for functional model systems that capture in parallel, both cellular and matrix formation processes. Stem cell-based organoids are promising as functional, self-organizing 3D in vitro models for studying the physiology and pathology of various tissues. However, for human bone, no such functional model system is yet available. This study reports the in vitro differentiation of human bone marrow stromal cells into a functional 3D self-organizing co-culture of osteoblasts and osteocytes, creating an organoid for early stage bone (woven bone) formation. It demonstrates the formation of an organoid where osteocytes are embedded within the collagen matrix that is produced by the osteoblasts and mineralized under biological control. Alike in in vivo osteocytes, the embedded osteocytes show network formation and communication via expression of sclerostin. The current system forms the most complete 3D living in vitro model system to investigate osteogenesis, both in physiological and pathological situations, as well as under the influence of external triggers (mechanical stimulation, drug administration).     

A 3D Cell-Free Bone Model Shows Collagen Mineralization is Driven and Controlled by the Matrix

Osteons, the main organizational components of human compact bone, are cylindrical structures composed of layers of mineralized collagen fibrils, called lamellae. These lamellae have different orientations, different degrees of organization, and different degrees of mineralization where the intrafibrillar and extrafibrillar minerals are intergrown into one continuous network of oriented crystals. While cellular activity is clearly the source of the organic matrix, recent in vitro studies call into question whether the cells are also involved in matrix mineralization and suggest that this process could be simply driven by the interactions of the mineral with extracellular matrix. Through the remineralization of demineralized bone matrix, the complete multiscale reconstruction of the 3D structure and composition of the osteon without cellular involvement are demonstrated. Then, this cell-free in vitro system is explored as a realistic, functional model for the in situ investigation of matrix-controlled mineralization processes. Combined Raman and electron microscopy indicate that glycosaminoglycans (GAGs) play a more prominent role than generally assumed in the matrix–mineral interactions. The experiments also show that the organization of the collagen is in part a result of its interaction with the developing mineral.     

Validity of the Parabolic Effective Mass Approximation in Silicon and Germanium n-MOSFETs With Different Crystal Orientations

This paper investigates the validity of the parabolic effective mass approximation (EMA), which is almost universally used to describe the size and bias-induced quantization in n-MOSFETs. In particular, we compare the EMA results with a full-band quantization approach based on the linear combination of bulk bands (LCBB) and study the most relevant quantities for the modeling of the mobility and of the on-current of the devices, namely, the minima of the 2-D subbands, the transport masses, and the electron density of states. Our study deals with both silicon and germanium n-MOSFETs with different crystal orientations and shows that, in most cases, the validity of the EMA is quite satisfactory. The LCBB approach is then used to calculate the values of the effective masses that help improve the EMA accuracy. There are crystal orientations, however, where the 2-D energy dispersion obtained by the LCBB method exhibits features that are difficult to reproduce with the EMA model.     

Complementary integrated circuits on plastic foil using inkjet printed n- and p-type organic semiconductors: Fabrication,characterization, and circuit analysis

Complementary thin-film transistor circuits composed of 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS–PEN) and a rylene carboxylic diimide derivative for p- and n-channel thin-film transistors (TFTs) were fabricated on flexible foils. The so-called staggered TFT configuration is used, meaning that the semiconductors layers are deposited last. The work-function of the injecting gold electrodes were modified using several self-assembled monolayers (SAMs). For optimized contacts the mobility of the n- and p-channel TFTs was 0.5 cm²/Vs and 0.2 cm²/Vs, respectively. Strongly degraded performance is obtained when the n-channel material was printed on contacts optimized for the p-channel TFT, and vice versa. This illustrates that for CMOS circuits we need careful work-function engineering to allow proper injection for both electrons and holes. We show for the first time that by using a bimolecular mixture for the SAM we can systematically vary the work function, and demonstrate how this affects the performance of discrete n-type and p-type transistors, as well as CMOS inverters and ring oscillators. Under optimal processing conditions we realized complementary 19-stage ring oscillators with 10 μs stage delay operating at 20 V.     

Noise Analysis of Regenerative Comparators for Reconfigurable ADC Architectures

The need for highly integrable and programmable analog-to-digital converters (ADCs) is pushing towards the use of dynamic regenerative comparators to maximize speed, power efficiency and reconfigurability. Comparator thermal noise is, however, a limiting factor for the achievable resolution of several ADC architectures with scaled supply voltages. While mismatch in these comparators can be compensated for by calibration, noise can irreparably hinder performance and is less straightforward to be accounted for at design time. This paper presents a method to estimate the input referred noise in fully dynamic regenerative comparators leveraging a reference architecture. A time-domain analysis is proposed that accounts for the time varying nature of the circuit exploiting some basic results from the solution of stochastic differential equations. The resulting symbolic expressions allow focusing designers' attention on the most influential noise contributors. Analysis results are validated by comparison with electrical simulations and measurement results from two ADC prototypes based on the reference comparator architecture, implemented in 0.18- $mu{hbox {m}}$ and 90-nm CMOS technologies.      

Ontogenesis of peripheral electromagnetic receptors in hornets

This article traces the ontogenesis of peripheral electromagnetic receptors (PER) in the cuticle of the Oriental hornet (Vespa orientalis). In the abdominal cuticle of adult hornets, the PERs are densely distributed throughout, but there are even more than 30 at the margins of the segments. These organelles develop as a network in the hornet cuticle immediately upon its completion. Briefly, from each basic cell of a PER grows a bulge towards the exterior, that is, towards the illuminated region of the cuticle. This bulge develops rapidly and as it grows it starts to push out and lift up the various layers of the cuticle, the while pressing them together. By a spiraling movement, the bulge insinuates itself between the layers, whereupon it dissolves and punctures its way through all the layers of the hypocuticle, via the endocuticle up to the exocuticle. The only cuticular layer that remains intact is the epicuticle, but even that undergoes change, assuming the shape of a smooth surface with a depression at its center. The indented part in the epicuticle is circular, approximately 2.5 microm in diameter and enables the entry of radiation (illumination) from the outside into the PER, which is located half-way down the cuticle, with the distance from the exterior to the base of the PER being approximately 25 microm. The numerous lamellae of the cuticle run parallel to one another, but in the region of the bulge they are either perpendicular or directed upwards. This ontogeny of the PERs lends the cuticle a sandwich-like shape, being radically perforated by the PERs bulges, yet covered at the top by the epicuticle and at the bottom by basal cells. The PERs also extend shoots into the cuticular layer and these further perforate the cuticle but also interlink the various PERs. From all the above, it is clear that the cuticle forms first and only subsequently does the network of PERs develop and interpenetrate its various layers.     

Amplitude-modulation detection in single-stage negative-feedback amplifiers due to interfering out-of-band signals

The electromagnetic-interference effects of out-of-band signals on negative-feedback amplifiers are investigated. It is assumed that the interfering signals picked up at the input of the amplifier are dominant. Due to the nonlinear behavior of the active devices in the amplifier, unwanted dc shifts and amplitude-modulation (AM) detection may occur. Describing these effects is usually done by using the Volterra series. Although providing good results when used for analysis, methods to use the Volterra series for the design process are not yet mature enough. A simple procedure for calculating AM detection is presented. An equivalent source at the input of the amplifier is introduced that accounts for the nonlinear effects. Because the characteristics of this source are computed as a function of design parameters, this procedure facilitates a synthesis approach for designing amplifiers with a lower susceptibility to AM detection. It is shown that the root locus of the amplifier transfer function has a large influence on the amount of AM detection and, therefore, on the electromagnetic compatibility. Measurements made on a single-stage negative-feedback amplifier support the presented procedure.