Theory and simulation of a thermally matched micromachined thermopile in a wearable energy harvester

In this paper, a new theoretical concept in the thermoelectric theory is discussed, which is important for design optimization of a thermoelectric energy harvester. The general conditions are defined, which are required to make a thermoelectric converter effective in energy harvester application. The necessity of the work has been prompted by the fact that while modeling the harvesters neither a constant temperature difference nor a constant heat flow can be assumed. It is shown that the proposed equations allow thermal optimization of energy harvesters to reach their top performance characteristics. The example of thermal optimization in case of MEMS thermopiles is discussed then. It is shown that the knowledge of thermal properties of the environment, i.e., those of a heat source and a heat sink, play the key role in the optimization procedure.     

Analysis of the selective behavior of multilayer structures with adielectric grating

The potential use as dichroic surfaces in the millimeter frequency band of multilayer dielectric structures with a grating in one of the layers is examined. It is shown that the selectivity of the structure may be increased by using a convenient array of dielectric sections in the characteristic cell of the periodic layer. It is also shown how the selective behavior of the structure depends on the angle of incidence of the wave that excites the structure and on the height-periodicity ratio of the periodic layer. In addition, for an unloaded periodic layer, an approximate procedure is described to predict how many times and at which frequencies maximum reflection occurs. The effect of loading the periodic layer with increasing number of dielectric layers is examined with the conclusion that the number of frequencies where maximum reflection occurs may be increased     

Surface Engineered Carboxymethylchitosan/Poly(amidoamine) Dendrimer Nanoparticles for Intracellular Targeting

Novel highly branched biodegradable macromolecular systems have been developed by grafting carboxymethylchitosan (CMCht) onto low generation poly(amidoamine) (PAMAM) dendrimers. Such structures organize into sphere‐like nanoparticles that are proposed to be used as carriers to deliver bioactive molecules aimed at controlling the behavior of stem cells, namely their proliferation and differentiation. The nanoparticles did not exhibit significant cytotoxicity in the range of concentrations below 1 mg mL^?1, and fluorescent probe labeled nanoparticles were found to be internalized with highly efficiency by both human osteoblast‐like cells and rat bone marrow stromal cells, under fluorescence‐activated cell sorting and fluorescence microscopy analyses. Dexamethasone (Dex) has been incorporated into CMCht/PAMAM dendrimer nanoparticles and release rates were determined by high performance liquid chromatography. Moreover, the biochemical data demonstrates that the Dex‐loaded CMCht/PAMAM dendrimer nanoparticles promote the osteogenic differentiation of rat bone marrow stromal cells, in vitro. The nanoparticles exhibit interesting physicochemical and biological properties and have great potential to be used in fundamental cell biology studies as well as in a variety of biomedical applications, including tissue engineering and regenerative medicine.     

Analysis of the Effect of the I/Q Base-Band Filter Mismatch in an OFDM Modem

In digital communication modems in which a very high rate system clock is used, it is necessary to use analog base-band shaping filters in the inphase (I) and quadrature (Q) paths of the modulator. However, this type of implementation inherently produces a mismatch of the I and Q paths. In the present paper, results of the analysis of the transmitter (TX) I/Q mismatch in an Orthogonal Frequency Division Multiplexing (OFDM) system with Differential Coherent Quadrature Phase Shift Keying (DQPSK) modulation is presented. Theoretical analysis shows that the Signal-to-Noise (SNR) degradation due to the I/Q mismatch can be represented by a mismatch transfer function on the basis of which one can compute the maximum affordable amplitude and phase mismatch of the TX filters transfer functions.     

New Decision Support Tool for Treatment Intensity Choice in Childhood Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL), the most common cancer in childhood, has its treatment modulated by the risk of relapse. An appropriate estimation of this risk is the most important factor for the definition of treatment strategy. In this paper, we build up a new decision support tool to improve treatment intensity choice in childhood ALL. Our procedure was applied to a significant cohort of Brazilian children with ALL, the majority of the cases treated in the last decade in the two main University Hospitals of Rio de Janeiro. Some intrinsically difficulties of this dataset introduce an assortment of challenges, among those the need of a proper selection of features, clinical and laboratorial data. We apply a mutual information-based methodology for this purpose and a Neural Network to estimate the risk. Among the relapsed patients, 98.2% would have been identified as high-risk by the proposed methodology. The proposed procedure showed significantly better results when compared to the BFM95, a widely used classification protocol.     

Which differintegration? [fractional calculus]

Despite the great advances in the theory and applications of fractional calculus, some topics remain unclear, making a systematic use difficult. In this paper, the fractional differintegration definition problem is studied from a systems point of view. Both local (Grunwald-Letnikov) and global (convolutional) definitions are considered. It is shown that the Cauchy formulation should be adopted since it is coherent with usual practice in signal processing and control applications.     

Analysis of microstrip antennas on circular-cylindrical substrateswith a dielectric overlay

The use of dyadic Green's functions and the moment method is explored for the solution of microstrip antenna problems on circular cylindrical substrates. The dyadic Green's functions of the electric type are obtained for a medium consisting of three cylindrical dielectric layers concentric with a perfectly conducting cylinder, and integral equations are developed for the evaluation of the electromagnetic fields. The effect of a dielectric overlay on the resonant frequency of a cylindrical-rectangular microstrip antenna is analyzed. The patch is directly fed by means of a microstripline printed along the cylinder axial direction. The results show that the effect of the dielectric overlay is substantial when its relative permittivity and thickness are increased, such that this effect has to be very carefully considered in the design of microstrip antennas     

A Novel Control Method for Piezoelectric-Transformer Based Power Supplies Assuring Zero-Voltage-Switching Operation

In this paper, a new control strategy that allows zero-voltage-switching (ZVS) operation of power converters using piezoelectric transformers (PTs) is proposed. The control circuit operates in a closed loop by measuring the phase between the PTs resonant current and the switching pattern and adjusting the switching frequency to the optimum value so that ZVS operation is assured. An innovative nonlinear regulator based on an analog multiplexer is presented. The regulator automatically swaps the signs of the sensed signal and the reference signal to allow generation of the adequate control action. A laboratory prototype for a 6 W resonant inverter was tested; obtained experimental results are also shown.     

Analysis of Optical Losses in a Photoelectrochemical Cell: A Tool for Precise Absorptance Estimation

Optical losses in a photoelectrochemical (PEC) cell account for a substantial part of solar‐to‐hydrogen conversion losses, but limited attention is paid to the detailed investigation of optical losses in PEC cells. In this work, an optical model of combined coherent and incoherent light propagation in all layers of the PEC cell based on spectroscopic measurements is presented. Specifically, photoelectrodes using transparent conductive substrates such as F:SnO₂ coated with thin absorber films are focused. The optical model is verified for hematite photoanodes fabricated by atomic layer deposition and successfully used to determine wavelength‐dependent reflection, transmission, layer absorptances, and charge generation rates. Furthermore, the calculated absorptances enable 20–30% more accurate calculations of the absorbed photon‐to‐current efficiency of PEC cells. Our optical model is a powerful tool for the optimization of the optical performance of PEC cells focusing on single absorber or tandem configurations and represents a cornerstone of a complete (optical and electrical) model for PEC water splitting cells.     

Self‐Assembled Conjugated Thiophene‐Based Rotaxane Architectures: Structural,Computational, and Spectroscopic Insights into Molecular Aggregation

A comparative study of the self‐assembly at a variety of surfaces of a dithiophene rotaxane 1 ?β‐CD and its corresponding dumbbell, 1, by means of atomic force microscopy (AFM) imaging and scanning tunneling microscopy (STM) imaging on the micrometer and nanometer scale, respectively. The dumbbell is found to have a greater propensity to form ordered supramolecular assemblies, as a result of π–π interactions between dithiophenes belonging to adjacent molecules, which are hindered in the rotaxane. The fine molecular structure determined by STM was compared to that obtained by molecular modelling. The optical properties of both rotaxane and dumbbell in the solid state were investigated by steady‐state and time‐resolved photoluminescence (PL) experiments on spin‐cast films and diluted solutions. The comparison between the optical features of the threaded and unthreaded systems reveals an effective role of encapsulation in reducing aggregation and exciton migration for the rotaxanes with respect to the dumbbells, thus leading to higher PL quantum efficiency and preserved single‐molecule photophysics for longer times after excitation in the threaded oligomers.