The influence of piezoceramic stack location on nonlinear behavior of langevin transducers

Power ultrasonic applications such as cutting, welding, and sonochemistry often use Langevin transducers to generate power ultrasound. Traditionally, it has been proposed that the piezoceramic stack of a Langevin transducer should be located in the nodal plane of the longitudinal mode of vibration, ensuring that the piezoceramic elements are positioned under a uniform stress during transducer operation, maximizing element efficiency and minimizing piezoceramic aging. However, this general design rule is often partially broken during the design phase if features such as a support flange or multiple piezoceramic stacks are incorporated into the transducer architecture. Meanwhile, it has also been well documented in the literature that power ultrasonic devices driven at high excitation levels exhibit nonlinear behaviors similar to those observed in Duffing-type systems, such as resonant frequency shifts, the jump phenomenon, and hysteretic regions. This study investigates three Langevin transducers with different piezoceramic stack locations by characterizing their linear and nonlinear vibrational responses to understand how the stack location influences nonlinear behavior

Tratamento da doença de Chagas pelo Nifurtimox (Bayer 2502)

Foram tratados 77 pacientes com doença de Chagas pelo nifurtimox, subdivididos em quatro grupos. Grupo I, com 30 pacientes na fase aguda. Somente oito doentes usaram a droga durante 120 dias, na dose inicial de 15 mg/kg de peso corporal e posteriormente de 10 mg. Vinte e dois pacientes tomaram dose insuficiente. Em quatro doentes (50%) o xenodiagnóstico tornou-se negativo pós-tratamento; destes, três fizeram reação de Machado Guerreiro, a qual estava negativa. Houve um óbito por insuficiência cardíaca no 59 dia de tratamento. Seis pacientes apresentaram polineuropatia periférica. Grupo II, com 15 pacientes na fase crônica, tratados em ambulatório. Oito abandonaram o tratamento, mas cinco em dez que tomaram placebo fizeram o mesmo. Dos seis que tomaram a droga durante 120 dias e fizeram pelo menos um xenodiagnóstico pós-tratamento, havia quatro que estavam com os exames negativos. O tratamento não alterou o eletrocardiograma, a área cardíaca ou a radiografia do esôfago dos doentes e não evitou que um paciente viesse a desenvolver insuficiência cardíaca e um outro arritmia. Grupo III, com 15 pacientes na fase crônica, tratados com 10 mg/kg, durante 120 dias. Fizeram 12 xenodiagnósticos mensalmente, cada um com oito caixas contendo 10 T. infestans após o tratamento e somente 28,5% dos pacientes apresentaram todos os exames negativos. Houve acentuada redução da parasitemia, mesmo nos doentes não curados. O número de xenos positivos passou de 43% antes do tratamento para 24,4% após o mesmo e o número de caixas positivas caiu de 29,6% para 7%. Grupo IV, com 17 pacientes na fase crônica, tratados com 8 mg/kg ao dia, sendo que em oito durante 120 dias, em cinco durante 100 dias e em quatro durante 60 dias. A percentagem de doentes com os 12 xenos negativos pós-tratamento foi de 56,25. Também neste grupo houve redução de parasitemia, caindo a percentagem de xenos positivos de 76,5 antes do tratamento para 10,3 e a de caixas positivas de 28,6 para 3,1. Não há vantagem em se prolongar o uso do nifurtimox por mais de dois meses. As percentagens de cura são bem inferiores as obtidas na Argentina, Chile e Rio Grande do Sul. A droga produz muitas reações, sendo a mais importante a polineuropatia periférica.Seventy seven patientes with Chagas disease were treated with nifurtimox. They were divided into 4 groups. Group I consisted of 30 patients in the acute phase of the disease. Twenty two patients took an insufficient dose. Only 8 patients used the drug for 120 days in an initial daity dose of 15 mg/kilogram body weight for up to 2 weeks and later in a daily dose of 10 mg/kilo body weight. In 4 patients (50%) the xenodiagnosis became negativa after treatment and in 3 the Machado Guerreiro test became negative. One patient died with acute cardiac failure on the 5th day of treatment. Six patients developed evidence of sensory peripheral neuritis while on treatment. Group II consisted of 15 outpatients in the chronic phase. They also took the drug for 120 days in a variable dosage of 5-15 mg/kilo body weight. They had at least one xenodiagnosis performedafter treatment in four patients xenodiagnosis became negative. The treatment had no effect on the electrocardiogram, degree of cardiomegaly, or appearance on barium swallow. Treatment did not prevent one patient from developing an arrhythmia and another cardiac failure. Group III also contained 15 patients in the chronic phase with positive xenodiagnosis treated with 10 mg/kilo body weight for 120 days. Twelve serial monthly xenodiagnosis were done after treatment using 80 T. infestans (10 to a box) for each examination. In only 28.5% of the patients were all these xenodiagnoses negative. The frequency of parasitemia was decreased in the other patients but not eradicated. The number of xenodiagnoses positive before treatment was 43% and afterwards 24.4%. The number of positive boxes diminished from 29.6% to 7%. Group IV consisted of 17 patients in the chronic phase with positive xenodiagnosis treated with 8 mg/kg per day. Eight were treated with this dose for 120 days, 5 for 100 days and 4 for 60 days. The percentage of patients with 12 serial xenodiagnoses negative after treatment was 56.25%. A reduction in the incidence of positive xenodiagnoses from 76.5 to 10.3% also ocurred in this group and the number of positive boxes diminished from 28.6 to 3.1%. There is no advantage in prolonging treatment beyond 2 months. The percentage of cure is much less than that obtained in Argentina, Chile or Rio Grande do Sul (Brazil). The drug produces many side effects especially a peripheral neuritis

Characterisation of La0.6Sr0.4Co0.2Fe0.8O3-\u3b4- Ba0.5Sr0.5Co0.8Fe0.2O3-\u3b4composite as cathode for solid oxide fuel cells

Mixture of La0.6Sr0.4Co0.2Fe0.8O3-\u3b4 and Ba0.5Sr0.5Co0.8Fe0.2O3-\u3b4, was investigated as promising cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The two perovskites possess high catalytic activity for the oxygen reduction (ORR), although some problems related to their chemical and structural stability have still to be overcome in view of improving durability of the cell performance. The achievement of a stable and high-performing composite material is the aim of this study. In principle, chemical equilibrium at the LSCF-BSCF interface may be reached through ions interdiffusion during the sintering process, resulting in the chemical stabilization of the material. The composite-cathode deposited on Ce0.8Sm0.2O2-\u3b4 electrolyte was then investigated by Electrochemical Impedance Spectroscopy (EIS) as a function of temperature, overpotential and time. The results exhibited an interesting electrochemical behavior of the electrode toward oxygen reduction reaction. XRD analysis was performed to detect structural modification during thermal or operation stages and it was found that after the sintering the two starting perovskites were no longer present; a new phase with a rhombohedral La0,4Sr0,6FeO3-type structure (LSF) is formed. An improvement in composite cathode durability has been detected under the considered operating conditions (200 mAcm-2, 700 \ub0C) in comparison with the pure BSCF electrode. The results confirmed this new electrode as promising system for further investigation as IT-SOFC cathode

Quantum-classical correspondence in spin-boson equilibrium states at arbitrary coupling

It is known that the equilibrium properties of nanoscale systems can deviate significantly from standard thermodynamics due to their coupling to an environment. For the generalized $\theta$-angled spin-boson model, here we derive an explicit form of the classical mean force equilibrium state. Taking the large spin limit of the quantum spin-boson model, we demonstrate that the quantum-classical correspondence is maintained at arbitrary coupling strength. This correspondence gives insight into the conditions for a quantum system to be well-approximated by its classical counterpart. We further demonstrate that, counterintuitively, previously identified environment-induced 'coherences' in the equilibrium state of weakly coupled quantum spins, do not disappear in the classical case. Finally, we categorise various coupling regimes, from ultra-weak to ultra-strong, and find that the same value of coupling strength can either be 'weak' or 'strong', depending on whether the system is quantum or classical. Our results shed light on the interplay of quantum and mean force corrections in equilibrium states of the spin-boson model, and will help draw the quantum to classical boundary in a range of fields, such as magnetism and exciton dynamics

Application of electro-fenton process for the treatment of methylene blue

The electrochemical removal of an aqueous solution containing 0.25 mM of methylene blue (MB), one of the most important thiazine dye, has been investigated by electro-Fenton process using a graphite-felt cathode to electrogenerate in situ hydrogen peroxide and regenerate ferrous ions as catalyst. The effect of operating conditions such as applied current, catalyst concentration, and initial dye content on MB degradation has been studied. MB removal and mineralization were monitored during the electrolysis by UV\u2013Vis analysis and TOC measurements. The experimental results showed that MB was completely removed by the reaction with \u2022OH radicals generated from electrochemically assisted Fenton\u2019s reaction, and in any conditions the decay kinetic always follows a pseudo-first-order reaction. The faster MB oxidation rate was obtained applying a current of 300 mA, with 0.3 mM Fe2+at T=35 \ub0C. In these conditions, 0.25 mM MB was completely removed in 45 min and the initial TOC was removed in 90 min of electrolysis, meaning the almost complete mineralization of the organic content of the treated solution

Quantum–classical correspondence in spin–boson equilibrium states at arbitrary coupling

The equilibrium properties of nanoscale systems can deviate significantly from standard thermodynamics due to their coupling to an environment. We investigate this here for the θ-angled spin–boson model, where we first derive a compact and general form of the classical equilibrium state including environmental corrections to all orders. Secondly, for the quantum spin–boson model we prove, by carefully taking a large spin limit, that Bohr’s quantum–classical correspondence persists at all coupling strengths. This shows, for the first time, the validity of the quantum–classical correspondence for an open system and gives insight into the regimes where the quantum system is well-approximated by a classical one. Finally, we provide the first classification of the coupling parameter regimes for the spin–boson model, from weak to ultrastrong, both for the quantum case and the classical setting. Our results shed light on the interplay of quantum and mean force corrections in equilibrium states of the spin–boson model, and will help draw the quantum to classical boundary in a range of fields, such as magnetism and exciton dynamics

A Comprehensive Approach to Improve Performance and Stability of State-of-the- Art Air Electrodes for Intermediate Temperature Reversible Cells: An Impedance Spectroscopy Analysis

Solid oxide fuel cells (SOFC) are devices for the transformation of chemical energy in electrical energy. SOFC appear very promising for their very high efficiency, in addition to the capability to work in reverse mode, which makes them suitable for integration in production units powered with renewables. Research efforts are currently addressed to find chemically and structurally stable materials, in order to improve performance stability during long-term operation. In this work, we examine different approaches for improving stability of two state-of-the-art perovskite materials, La0.6Sr0.4Co0.2Fe0.8O3-\uf064 (LSCF) and Ba0.5Sr0.5Co0.8Fe0.2O3-\uf064 (BSCF), very promising as air electrodes. Two different systems are considered: (i) LSCF and BSCF porous electrodes impregnated by a nano-sized La0.8Sr0.2MnO3-\uf064 layer and (ii) LSCF-BSCF composites with the two phases in different volume proportions. The study considers the results obtained by electrochemical impedance spectroscopy investigation, observing the polarisation resistance (Rp) of each system to evaluate performance in typical SOFC operating conditions. Furthermore, the behaviour of polarisation resistance under the effect of a net current load (cathodic) circulating for hundreds of hours is examined, as parameter to evaluate long-term performance stability