Product beamforming and nested array in tandem for enhanced sonar performance

Multidimensional Systems and Signal Processing - High-performance sonar systems mostly combine a large sensor array and an efficient beamformer for enhancing the overall detection capabilities and...     

On spacing policies for highway vehicle automation

This paper develops a framework for the design and evaluation of spacing policies for adaptive cruise control. Spacing policies are evaluated from the point of view of string stability, traffic flow stability and traffic flow capacity. The standard constant time-gap spacing policy can guarantee string stability but is shown to suffer from poor traffic capacity and traffic flow instability. An "ideal" spacing policy is proposed that evolves naturally from the evaluation framework. The proposed spacing policy is a nonlinear function of speed. It provides string stability and traffic flow stability as well as a higher traffic flow capacity compared to the standard time-gap controller. An associated result proved in the paper is that traffic flow stability implies string stability for flow volumes up to a described maximum value.     

Numerical modeling and experimental study of thermally induced residual stress in the direct diode laser heat treatment of dual-phase 980 steel

The direct diode laser application has been found useful in the localized heat treatment of metal parts because of its wider beam and more uniform energy distribution with respect to other lasers with Gaussian-like energy distribution. In this study, an uncoupled thermomechanical finite element model is developed to study the temperature field and thermally induced stress evolution in high-strength dual phase (DP) 980 steel during its direct diode laser heat treatment. Thermal analysis results are experimentally validated through thermocouples and then input into a mechanical model as transient temperature loading in order to acquire the thermally induced stresses and strains. The effect of martensite phase transformation on residual stress distribution in heat-treated DP980 steel is considered. An X-ray diffraction technique is used to measure the residual stress distribution at the top surface of the heat-treated coupons of DP980 steel. The numerical results show that compressive stresses are located at the laser–material interaction zone. After heat treatment, tensile stresses are retained at the heat-treated DP980 steel coupons. There is qualitative agreement between the numerically predicted and experimentally measured residual stresses. The effect of the overlapping ratio on the residual stress and hardness of the heat-treated DP980 steel is also experimentally and numerically investigated.     

Key issues and challenges in device level fabrication of MEMS acoustic sensors using piezo thin films doped with strontium and lanthanum

The development of next-generation piezoelectric micro-electro-mechanical systems (piezo-MEMS) demands reliable and reproducible processes to fulfil the ever-growing requirements. Research on doped PZT thin films with improved ferroelectric and piezoelectric thin films is on the rise; however, most of them mainly discuss the fabrication process flows and results. This paper attempts to present an overview of some of the key issues and challenges encountered in the device level fabrication of piezo-MEMS acoustic sensors using PZT thin films doped with Strontium and Lanthanum for underwater applications. A recipe on the technical challenges would have saved more time and cost for the researchers as several unsuccessful fabrications and damages were encountered. This paper discusses the issues starting from fabrication of sputtering target to deposition, annealing, patterning and isolation of device layers, electrical contacts, packaging as per the application requirements, etc. in detail.

     

Emission characteristics of a CI engine using preheated CNSL oil & diesel blends and ethanol fumigation

ABSTRACT

In this study, emission level under different load conditions at constant speed was tested for a one-cylinder Compression ignition engine using preheated cnsl oil & diesel blends and ethanol fumigation. According to the emission characteristics and performance of the engine, the temperature of 80°C is considered to be excellent at preheated state. The various blends are [(Preheated CNSL20?+?D80) +E fumigation], [(Preheated CNSL40?+?D60) +E fumigation], [(Preheated CNSL60?+?D40) +E fumigation), (Preheated CNSL80?+?D20) +E fumigation], [(Preheated CNSL100) +E fumigation] are being examined at 80° C. The outputs comprehension is done with pure diesel.     

Hardness prediction in multi-pass direct diode laser heat treatment by on-line surface temperature monitoring

This study was attempted to develop a process model, using the temperature values measured by the coupled infrared temperature measurement system (pyrometer and camera) correlated with the measured values of case depth hardness of the tool steel AISI S7 (hypo-eutectoid steel) for the specified multi-pass laser heat treatment conditions (1000–2500 J). A number of heat treatment experiments by changing the laser power (1400–1800 W), scanning speed (15–25 mm/s), size of overlap (1–6 mm), and the length of scan (10–30 mm) on the tool steel AISI S7 were carried out by using a 2-kW direct diode laser. The results indicated that the loss of case depth hardness uniformity was highly influenced by the tempering temperature and the change of cooling rate. The combination of higher laser power, lower scanning speed, smaller size of overlap, and the longer length of scan were influenced the formation of mixture of phases (martensite, bainite, ferrite, and pearlite) which in turn affected the case depth hardness uniformity. The process model can be used as a handy tool for the process engineers to configure the processing conditions in order to obtain the desired case depth hardness for the hypo-eutectoid steels.     

Synthesis of coumarin derivatives by palladium complex catalyzed intramolecular Heck reaction: Preparation of a 1,2-cyclobutadiene-substituted CpCoCb diphosphine chelated palladium complex

A cobalt-sandwich diphosphine chelated palladium complex 2, [(η⁵-cyclopentadienyl)(η⁴-1,2-diphenyl-3,4-bis(diphenylphosphino-κP)cyclobutadiene)cobalt(I)]palladium(II)dichloride, was prepared from the reaction of a cyclobutadiene-substituted CpCoCb diphosphine 1, (η⁵-cyclopentadienyl) (η⁴-1,2-diphenyl-3,4-bis-diphenylphosphinocyclobutadiene)cobalt(I), with one molar equivalent of Pd(COD)Cl₂. Both compounds were characterized by spectroscopic means as well as single-crystal X-ray diffraction methods. Application of purified 2 as the catalytic precursor in intramolecular Heck cyclization reaction on 4-hydroxycoumarin resulted in the formation of several derivatives with intensity enhanced fluorescence property.     

Fringe Formation in an In-Plane Displacement Measurement Configuration with Twofold Increase in Sensitivity: Theory and experiment

A fringe-formation theory for a dual-beam illumination configuration that leads to a twofold increase in sensitivity for the measurement of in-plane displacement is described. Here we have taken into account all four beams simultaneously that are generated at the image plane owing to two-beam illumination and their cross-interference terms for fringe formation. We show that the sensitivity obtainable is the usual interferometric sensitivity when we take into account all four beams simultaneously and doubles only when the retroreflected beams are observed. A detailed theory and an experimental demonstration of the method are presented.     

Valuing flexibilities in the design of urban water management systems

Climate change and rapid urbanization requires decision-makers to develop a long-term forward assessment on sustainable urban water management projects. This is further complicated by the difficulties of assessing sustainable designs and various design scenarios from an economic standpoint. A conventional valuation approach for urban water management projects, like Discounted Cash Flow (DCF) analysis, fails to incorporate uncertainties, such as amount of rainfall, unit cost of water, and other uncertainties associated with future changes in technological domains. Such approach also fails to include the value of flexibility, which enables managers to adapt and reconfigure systems over time as uncertainty unfolds.     

Modeling of temperature field and grain growth of a dual phase steel DP980 in direct diode laser heat treatment

The temperature field due to heating from a high-powered direct diode laser is calculated first by using an experiment-based finite element model. The Monte Carlo method is applied, which uses the calculated temperature history as thermal loading to obtain the grain growth in the heat-affected zone (HAZ) of dual phase steel DP980. The martensite decomposition in the heat treatment is considered to be a function of the scanning speed. Numerical results demonstrate that the increased scanning speed of the laser beam under laser power of 2 kW decreases the temperature gradient in the HAZ, resulting in finer martensite grains and a smaller percentage of martensite decomposition in the HAZ. This is in good agreement with the experimental data.