Modulated thermogravimetry in analysis of decomposition kinetics

Optimal constants in physicochemical models describing decomposition kinetics are searched for from thermogravimetric information by the method of nonlinear regression. The method requires an iterative numerical solution of differential equations for non-isothermal kinetics. The technique of conjugate functions is used to provide a fast quadratic convergence of the iterations.The method is described in detail for the cases where input information represents either derivatives of mass loss or perturbations of these derivatives caused by sinusoidal modulation of linear temperature-time relationships. In both cases two-stage decomposition with two parallel (independent) reactions is considered as a numerical example. The discussion is mainly focused on the analysis of the perturbations (modulations).In the case of modulated thermogravimetry, a relative error in the calculated activation energy is approximately equal to a relative error in the approximation of the perturbations. That is why activation energy can be calculated with high accuracy. Moreover, the conclusion about the adequacy of evaluated models can be made immediately after a visual verification of the approximation error.Two-stage decomposition of cotton is used as an experimental example. The only curve of the perturbations measured at one heating rate is used for calculating the kinetic constants. This curve contains information about mass loss in the hidden form. Nevertheless, one can ensure that the used mathematical models with the obtained kinetic constants are able to approximate not only the curve of mass loss subjected to the handling but also a curve measured at another heating rate. The high predictive force of modulated thermal analysis promises to be an obvious alternative to the classical technique. The weak sensitivity of predictions made by modulated thermogravimetry to a form of models used is a very important distinction for the wide application of this analysis in different fields of chemical engineering.     

Performance of a Cantilever Retaining Wall

Earth pressure cells, tiltmeters, strain gauges, inclinometer casings, and survey reflectors were installed during construction of a reinforced concrete cantilever retaining wall. A data acquisition system with remote access monitored some 60 sensors on a continual basis. Analyses of the data indicated development of the active condition after translation of about 0.1% of the backfill height. The wall rotated into the backfill as a rigid body, but the top of the stem deflected away from the backfill, approximately equal in magnitude and opposite in direction to the displacement from rigid body rotation. Loading on the wall back-calculated from strain gauge readings was consistent with active earth pressure. The maximum lateral force, about the same as the design value, occurred during compaction of the backfill. Observations that differed from standard assumptions included the passive earth pressure in front of the shear key being less than 10% of the design value and vertical stress below the heel being greater than the toe. Compaction-induced lateral stresses on the stem were sometimes twice the vertical stress.     

Experimental validation of a model of an uncontrolled bicycle

In this paper, an experimental validation of some modelling aspects of an uncontrolled bicycle is presented. In numerical models, many physical aspects of the real bicycle are considered negligible, such as the flexibility of the frame and wheels, play in the bearings, and precise tire characteristics. The admissibility of these assumptions has been checked by comparing experimental results with numerical simulation results. The numerical simulations were performed on a three-degree-of-freedom benchmarked bicycle model. For the validation we considered the linearized equations of motion for small perturbations of the upright steady forward motion. The most dubious assumption that was validated in this model was the replacement of the tires by knife-edge wheels rolling without slipping (non-holonomic constraints). The experimental system consisted of an instrumented bicycle without rider. Sensors were present for measuring the roll rate, yaw rate, steering angle, and rear wheel rotation. Measurements were recorded for the case in which the bicycle coasted freely on a level surface. From these measured data, eigenvalues were extracted by means of curve fitting. These eigenvalues were then compared with the results from the linearized equations of motion of the model. As a result, the model appeared to be fairly accurate for the low-speed low-frequency behaviour.     

Impact attrition of brittle structured particles at low velocities: rigorous use of a laboratory vibrational impact tester

Brittle particle impact attrition was measured over three orders of magnitude of impact velocity by use of both single- and multiple-impact testers. The multiple-impact tester was a resonant cantilever impactor with dynamic amplitude control and small-gap cavities, designed to ensure operation near the transition between the bouncing and resonant impact regimes. For this impactor, a novel technique using a trajectory simulation was developed to elucidate average impact velocities, effective particle restitution behavior, and average losses per impact from a set of nominal attrition rates (loss/time). This allowed direct comparison of data from the single-impact and multiple-impact testers.Results were obtained for three brittle, porous pharmaceutical particles with significantly-different, well-characterized internal structures. Results reveal a relatively unexplored mode of attrition that is distinguished by lack of gross fragmentation at low velocities, with a steep velocity dependence. This regime is expected for any brittle particle for which simple chipping is not seen—such as rounded solid particles and many agglomerates. At higher impact velocity, gross particle fragmentation is observed. The transition between these attrition regimes appears connected to particle structure, such as the size of attrition-resistant primary particles in an agglomerate or the point at which dominant flaws (that lead to fragmentation) are no longer critically active. The ranking of particles according to damage in high-velocity impacts was not predictive of damage in low-velocity impacts, because the particle attrition did not necessarily exhibit the same velocity-dependence in the two regimes. Such differences are critical for predicting performance in operations such as pneumatic conveying or fluidized beds, respectively.     

BIT: Biosignal Igniter Toolkit

The study of biosignals has had a transforming role in multiple aspects of our society, which go well beyond the health sciences domains to which they were traditionally associated with. While biomedical engineering is a classical discipline where the topic is amply covered, today biosignals are a matter of interest for students, researchers and hobbyists in areas including computer science, informatics, electrical engineering, among others. Regardless of the context, the use of biosignals in experimental activities and practical projects is heavily bounded by the cost, and limited access to adequate support materials. In this paper we present an accessible, albeit versatile toolkit, composed of low-cost hardware and software, which was created to reinforce the engagement of different people in the field of biosignals. The hardware consists of a modular wireless biosignal acquisition system that can be used to support classroom activities, interface with other devices, or perform rapid prototyping of end-user applications. The software comprehends a set of programming APIs, a biosignal processing toolbox, and a framework for real time data acquisition and postprocessing.     

土-钢组合铁路桥的动力响应

对长跨钢涵洞铁路桥进行实际动力响应研究。桥为土-钢组合结构,长11m。通过测量不同车速下桥的应变和位移,对桥进行试验,同时,对垂直道床振动以及制动力的影响也进行了测量。研究显示:车速对位移、推力和力矩的影响较大;所测的动态位移与推力比超出相应静态响应的20%,远大于桥设计规范所规定的值;力矩到1/4点时,动荷系数高达1·45,高于关键点的值。鉴于从强迫振动试验中测得了高的阻尼值,与普通桥相比这种桥的类型对共振并不敏感。     

Effect of asymmetric actuator and detector position on Coriolis flowmeter and measured phase shift

Coriolis flowmeters (CFM) are forced to vibrate by a periodic excitation usually applied midpipe through an electromagnetic actuator. From hands-on experience with industrial CFMs it appears, that the electromagnetic actuator has to be located as symmetric as possible. For CFM design and trouble-shooting it is of relevance to know how and if imperfections, related to the excitation location, influence the dynamic behavior of the vibrating fluid-conveying pipes employed in CFMs. A simple model of an imperfectly excited, simply supported, straight, single pipe CFM is investigated using a multiple time scaling perturbation analysis. The result is a simple analytical expression for the approximated phase shift, which offers a direct insight into how the location of the actuator influences the phase shift. It appears, that asymmetrical forcing combined with fluctuating pipe damping could be a factor contributing to lack of zero shift stability observed with some industrial CFMs. Tests of the approximated solution against results obtained by pure numerical analysis using Galerkin expansion show very good agreement. The effect of asymmetric detector positions is also investigated. Any asymmetry in the detectors position, e.g. due to manufacturing variations or improper handling of the CFM, induces a phase shift that leads to changes of the meter’s sensitivity, and could therefore result into erroneous measurements of the mass flow. This phase shift depends on the mass flow and does not contribute to a lacking zero-point stability. The validity of the hypotheses, which are assumed to be basically similar for more complicated geometries, e.g. bended and/or dual pipe CFMs, with or without multiple actuators, is suggested to be tested using laboratory experiments with purpose built non-ideal CFMs.     

Design and Commissioning of a Friction Welding Machine

An experimental lightweight linear friction welding machine was designed and commissioned. The machine was designed to explore higher frequencies of oscillation (up to 1 kHz) than those commercially available, for a number of different amplitudes of oscillation. During the commissioning stage problems related to rig stiffening were recognized and the operating envelope of the machine was identified. Important friction welding process parameters like stress and temperature are monitored to evaluate process development and weld integrity.     

A low cost instrumentation system to analyze different types of milk adulteration

In this paper, the design of a complete instrumentation system to detect different types of milk adulteration has been reported. A simple to use indicator type readout device is reported which can be used by milk community people. A low cost microcontroller based automatic sensing system is also reported to detect ‘synthetic milk’, which has been reconstructed after adulterating the milk with ‘liquid-whey’.     

仪表控制系统干扰分析与抗干扰措施

在自动控制系统中,干扰存在于整个控制过程中。经现场测量仪表、导线传输、二次仪表或DCS,完成控制运算等功能,然后输出至气动或电动执行机构,干扰将影响整个仪表控制系统的测量准确性。干扰产生的原因按引入的途径主要分为静电感应、电磁感应等。对DCS信号传输系统的干扰包括对进出DCS系统的信号电缆产生的信号干扰和对DCS系统内部通讯电缆产生的信号干扰。不同的生产装置及所在区域,干扰的来源、类型、强度、分布是不同的,所涉仪表设备要求也不完全相同。因此,应有针对性地选用正确合理的抗干扰措施,对不同的对象和环境,采取不同的抗干扰措施。仪表信号传输过程中常见的抗干扰措施有:隔离、屏蔽、对绞、抑制共模干扰的生成与转化及正确接地等。DCS系统中主要是同轴电缆(通讯电缆)的干扰和CRT安装场所的磁场干扰,霍尼韦尔(HONEYWELL)公司提供了针对DCS系统的抗干扰措施。