Analysis and control of transient spectra using time-dependent density functional theory.

215 p.

Effect of graphene substrate on the SERS Spectra of Aromatic bifunctional molecules on metal nanoparticles

The design of molecular sensors plays a very important role within nanotechnology and especially in the development of different devices for biomedical applications. Biosensors can be classified according to various criteria such as the type of interaction established between the recognition element and the analyte or the type of signal detection from the analyte (transduction). When Raman spectroscopy is used as an optical transduction technique the variations in the Raman signal due to the physical or chemical interaction between the analyte and the recognition element has to be detected. Therefore any significant improvement in the amplification of the optical sensor signal represents a breakthrough in the design of molecular sensors. In this sense, Surface-Enhanced Raman Spectroscopy (SERS) involves an enormous enhancement of the Raman signal from a molecule in the vicinity of a metal surface. The main objective of this work is to evaluate the effect of a monolayer of graphene oxide (GO) on the distribution of metal nanoparticles (NPs) and on the global SERS enhancement of paminothiophenol (pATP) and 4-mercaptobenzoic acid (4MBA) adsorbed on this substrate. These aromatic bifunctional molecules are able to interact to metal NPs and also they offer the possibility to link with biomolecules. Additionally by decorating Au or Ag NPs on graphene sheets, a coupled EM effect caused by the aggregation of the NPs and strong electronic interactions between Au or Ag NPs and the graphene sheets are considered to be responsible for the significantly enhanced Raman signal of the analytes [1-2]. Since there are increasing needs for methods to conduct reproducible and sensitive Raman measurements, Grapheneenhanced Raman Scattering (GERS) is emerging as an important method [3].

Determinação eletroanalítica de ácido salicílico em produto dermatológico com eletrodos de nanotubos de carbono e nanopartículas de óxido de ferro

Dissertação (mestrado)—Universidade de Brasília, Instituto de Química, Programa de Pós-Graduação em Tecnologias Química e Biológica, 2016.

Wave impedance selection for passivity-based bilateral teleoperation

When a task must be executed in a remote or dangerous environment, teleoperation systems may be employed to extend the influence of the human operator. In the case of manipulation tasks, haptic feedback of the forces experienced by the remote (slave) system is often highly useful in improving an operator's ability to perform effectively. In many of these cases (especially teleoperation over the internet and ground-to-space teleoperation), substantial communication latency exists in the control loop and has the strong tendency to cause instability of the system. The first viable solution to this problem in the literature was based on a scattering/wave transformation from transmission line theory. This wave transformation requires the designer to select a wave impedance parameter appropriate to the teleoperation system. It is widely recognized that a small value of wave impedance is well suited to free motion and a large value is preferable for contact tasks. Beyond this basic observation, however, very little guidance exists in the literature regarding the selection of an appropriate value. Moreover, prior research on impedance selection generally fails to account for the fact that in any realistic contact task there will simultaneously exist contact considerations (perpendicular to the surface of contact) and quasi-free-motion considerations (parallel to the surface of contact). The primary contribution of the present work is to introduce an approximate linearized optimum for the choice of wave impedance and to apply this quasi-optimal choice to the Cartesian reality of such a contact task, in which it cannot be expected that a given joint will be either perfectly normal to or perfectly parallel to the motion constraint. The proposed scheme selects a wave impedance matrix that is appropriate to the conditions encountered by the manipulator. This choice may be implemented as a static wave impedance value or as a time-varying choice updated according to the instantaneous conditions encountered. A Lyapunov-like analysis is presented demonstrating that time variation in wave impedance will not violate the passivity of the system. Experimental trials, both in simulation and on a haptic feedback device, are presented validating the technique. Consideration is also given to the case of an uncertain environment, in which an a priori impedance choice may not be possible.

Voltage and current spectra for matrix power converters

Matrix power converters are used for transforming one alternating-current power supply to another, with different peak voltage and frequency. There are three input lines, with sinusoidally varying voltages which are 120◦ out of phase one from another, and the output is to be delivered as a similar three-phase supply. The matrix converter switches rapidly, to connect each output line in sequence to each of the input lines in an attempt to synthesize the prescribed output voltages. The switching is carried out at high frequency and it is of practical importance to know the frequency spectra of the output voltages and of the input and output currents. We determine in this paper these spectra using a new method, which has significant advantages over the prior default method (a multiple Fourier series technique), leading to a considerably more direct calculation. In particular, the determination of the input current spectrum is feasible here, whereas it would be a significantly more daunting procedure using the prior method instead.

Transmission Spectra of Rb 87 atoms near an Optical Nanofiber.

We present measurements of the transmission spectra of 87Rb atoms at 780 nm in the vicinity of a nanofiber. A uniform distribution of fixed atoms around a nanofiber should produce a spectrum that is broadened towards the red due to shifts from the van der Waals potential. If the atoms are free, this also produces an attractive force that accelerates them until they collide with the fiber which depletes the steady-state density of near-surface atoms. It is for this reason that measurements of the van der Waals interaction are sparse. We confirm this by measuring the spectrum cold atoms from a magneto-optical trap around the fiber, revealing a symmetric line shape with nearly the natural linewidth of the transition. When we use an auxiliary 750 nm laser we are able to controllably desorb a steady flux of atoms from the fiber that reside near the surface (less than 50 nm) long enough to feel the van der Walls interaction and produce an asymmetric spectrum. We quantify the spectral asymmetry as a function of 750 nm laser power and find a maximum. Our model, which that takes into account the change in the density distribution, qualitatively explains the observations. In the future this can be used as a tool to more comprehensively study atom-surface interactions.

Truncated projective spaces, Brown–Gitler spectra and indecomposable A(1)-modules

MSC 19L41; 55S10.

Bioelectric Impedance Analysis in the Diagnosis of Vesicoureteral Reflux

Background: Vesicoureteral reflux (VUR) is a common abnormality of the urinary tract in childhood. Objectives: As urine enters the ureters and renal pelvis during voiding in vesicoureteral reflux (VUR), we hypothesized that change in body water composition before and after voiding may be less different in children with VUR. Patients and Methods: Patients were grouped as those with VUR (Group 1) and without VUR (Group 2). Bioelectric impedance analysis was performed before and after voiding, and third space fluid (TSF) (L), percent of total body fluid (TBF%), extracellular fluid (ECF%), and intracellular fluid (ICF%) were recorded. After change of TSF, TBF, ECF, ICF (ΔTSF, ΔTBF%, ΔECF%, ΔICF%), urine volume (mL), and urine volume/body weight (mL/kg) were calculated. Groups 1 and 2 were compared for these parameters. In addition, pre- and post-voiding body fluid values were compared in each group. Results: TBF%, ECF%, ICF%, and TSF in both pre- and post-voiding states and ΔTBF%, ΔECF%, ΔICF%, and ΔTSF after voiding were not different between groups. However, while post-voiding TBF%, ECF% was significantly decreased in Group 1 (64.5 ± 8.1 vs 63.7 ± 7.2, P = 0.013 for TBF%), there was not post-voiding change in TSF in the same group. On the other hand, there was also a significant TSF decrease in Group 2. Conclusions: Bladder and ureter can be considered as the third space. Thus, we think that BIA has been useful in discriminating children with VUR as there was no decreased in patients with VUR, although there was decreased TSF in patients without VUR. However, further studies are needed to increase the accuracy of this hypothesis.

Body composition changes assessed by bioelectrical impedance and their associations with functional class deterioration in stable heart failure patients

Background: Heart failure (HF) patients develop important changes in body composition, but only a small number of studies have evaluated the associations between these changes and functional class deterioration in a prospective manner. Objective: The aim of this study was to evaluate whether changes in bioimpedance parameters were associated with NYHA functional class deterioration over six months. Methods: A total of 275 chronic stable HF patients confirmed by echocardiography were recruited. Body composition measurements were obtained by whole body bioelectrical impedance with multiple frequency equipment (BodyStat QuadScan 4000). We evaluated functional class using the New York Heart Association (NYHA) classification at baseline and after six months. Results: According to our results, 66 (24%) subjects exhibited functional class deterioration, while 209 improved or exhibited no change. A greater proportion of patients exhibited higher extracellular water (> 5%), and these patients developed hypervolemia, according to location on the resistance/reactance graph. A 5% decrease in resistance/height was associated with functional class deterioration with an OR of 1.42 (95% CI 1.01-2.0, p = 0.04). Conclusions: Body composition assessment through bioelectrical impedance exhibited a valuable performance as a marker of functional class deterioration in stable HF patients.

A microelectrode impedance method to measure interaction of cells

An impedance method was developed to determine how immune system cells (hemocyte) interact with intruder cells (parasites). When the hemocyte cells interact with the parasites, they cause a defensive reaction and the parasites start to aggregate in clusters. The level of aggregation is a measure of the host-parasite interaction, and provides information about the efficiency of the immune system response. The cell aggregation is monitored using a set of microelectrodes. The impedance spectrum is measured between each individual microelectrode and a large reference electrode. As the cells starts to aggregate and settle down towards the microelectrode array the impedance of the system is changed. It is shown that the system impedance is very sensitive to the level of cell aggregation and can be used to monitor in real time the interaction between hemocyte cells and parasites.

USE OF AN ELECTRICAL IMPEDANCE TOMOGRAPHY METHOD TO DETECT AND TRACK FRACTURES IN A GELATIN MEDIUM

Electrical impedance tomography is applied to the problem of detecting, locating, and tracking fractures in ballistics gelatin. The hardware developed is intended to be physically robust and based on off-the-shelf hardware. Fractures were created in two separate ways: by shooting a .22 caliber bullet into the gelatin and by injecting saline solution into the gelatin. The .22 caliber bullet created an air gap, which was seen as an increase in resistivity. The saline solution created a fluid filled gap, which was seen as a decrease in resistivity. A double linear array was used to take data for each of the fracture mechanisms and a two dimensional cross section was inverted from the data. The results were validated by visually inspecting the samples during the fracture event. It was found that although there were reconstruction errors present, it was possible to reconstruct a representation of the resistive cross section. Simulations were performed to better understand the reconstructed cross-sections and to demonstrate the ability of a ring array, which was not experimentally tested.

Online impedance spectroscopy estimation of a battery

Electrochemical impedance spectroscopy (EIS) is a helpful tool to understand how a battery is behaving and how it degrades. One of the disadvantages is that it is typically an 'off-line' process. This paper investigates an alternative method of looking at impedance spectroscopy of a battery system while it is on-line and operational by manipulating the switching pattern of the dc-dc converter to generate low frequency harmonics in conjunction with the normal high frequency switching pattern to determine impedance in real time. However, this adds extra ripple on the inductor which needs to be included in the design calculations. The paper describes the methodology and presents some experimental results in conjunction with EIS results to illustrate the concept.

An Islanding Detection Method based on Impedance Estimation and Grid Identification for Grid-Tie Distributed Power Generation Systems

Power system policies are broadly on track to escalate the use of renewable energy resources in electric power generation. Integration of dispersed generation to the utility network not only intensifies the benefits of renewable generation but also introduces further advantages such as power quality enhancement and freedom of power generation for the consumers. However, issues arise from the integration of distributed generators to the existing utility grid are as significant as its benefits. The issues are aggravated as the number of grid-connected distributed generators increases. Therefore, power quality demands become stricter to ensure a safe and proper advancement towards the emerging smart grid. In this regard, system protection is the area that is highly affected as the grid-connected distributed generation share in electricity generation increases. Islanding detection, amongst all protection issues, is the most important concern for a power system with high penetration of distributed sources. Islanding occurs when a portion of the distribution network which includes one or more distributed generation units and local loads is disconnected from the remaining portion of the grid. Upon formation of a power island, it remains energized due to the presence of one or more distributed sources. This thesis introduces a new islanding detection technique based on an enhanced multi-layer scheme that shows superior performance over the existing techniques. It provides improved solutions for safety and protection of power systems and distributed sources that are capable of operating in grid-connected mode. The proposed active method offers negligible non-detection zone. It is applicable to micro-grids with a number of distributed generation sources without sacrificing the dynamic response of the system. In addition, the information obtained from the proposed scheme allows for smooth transition to stand-alone operation if required. The proposed technique paves the path towards a comprehensive protection solution for future power networks. The proposed method is converter-resident and all power conversion systems that are operating based on power electronics converters can benefit from this method. The theoretical analysis is presented, and extensive simulation results confirm the validity of the analytical work.

Analysis of size spectra off northwest Africa: a useful indicator in tropical areas?

Changes in the size spectra of demersal fish communities off Cape Verde (1988, 1994), Guinea (1985-1995), and Mauritania (1987-2001) were studied. Intercepts and slopes showed opposite trends for Guinea and Mauritania, but were relatively stable in spite of a strong increase in landings per unit area. For Cape Verde, there were marked changes in size structure, seemingly inconsistent with the more moderate fishing pressure there. Changes in size structure do not seem to be suitable indicators of the effects of fishing in areas characterized by faster growth rates, small sizes, high species diversity, and complex interrelationships, such as the tropics. (c) 2005 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.

Uncertainty evaluation of multivariate quantities: A case study on electrical impedance

The paper discusses the evaluation of the uncertainty of a multivariate quantity using the Law of Propagation of Uncertainty defined in the Guide to the Expression of Uncertainty in Measurement (GUM) and a Monte Carlo method according to the GUM’s Supplement 2. The quantity analysed is the electrical impedance, which is not a scalar but a complex quantity. The used measuring method allows the evaluation of the impedance and of its uncertainty in different ways and the corresponding results are presented, compared and discussed. For comparison purposes, results of the impedance uncertainty obtained using the NIST Uncertainty Machine are also presented.