Instrumentation and Measurement Science

The present article describes VAS Generator (www.vasgenerator.net), a free Web service for creating a wide
range of visual analogue scales that can be used as measurement devices in Web surveys and Web experimentation, as well as for local computerized assessment. A step-by-step example for creating and implementing a visual analogue scale with visual feedback is given. VAS Generator and the scales it generates work independently of platforms and use the underlying languages HTML and JavaScript. Results from a validation study with 355 participants are reported and show that the scales generated with VAS Generator approximate an interval-scale level. In light of previous research on visual analogue versus categorical (e.g., radio button) scales in Internet-based research, we conclude that categorical scales only reach ordinal-scale level, and thus visual analogue scales are to be preferred whenever possible.

Using a network analyzer, several experiments for the frequency-domain characterization of the indoor radio channel in the 0.9-1.1-GHz band are performed. In the experiments, the frequency response measurements are taken at spatially distributed locations throughout the test area by fixing the receiver in a central location and moving the transmitter to different locations. The experiments were performed in a high-rise office building and a three-story building with offices and laboratories. For each experiment, the exponent of the power-distance relationship and the statistics of the 3-dB width of the frequency correlation function are determined from the frequency-domain data. The approximation to the impulse response of the channel is obtained from the inverse Fourier transform of the frequency response. An empirical exponential relationship between the 3-dB width of the frequency correlation function and the inverse of the rms delay spread of the impulse response is derived.

Modern mobile phones, featuring high performance microprocessors, rich set of sensors and internet connectivity are largely diffused all over the world and are ideal devices for the development of low-cost sensing systems, in particular for low-income developing countries and rural areas that lack the access to diagnostic laboratories and expensive instrumentation. In the design of a smartphone based sensing system different elements must be taken in consideration such as sensors performance, acquisition rate and privacy preserving strategies when personal data must be shared in the cloud. In this paper a sensor-centric survey on smartphone based sensing systems is presented, covering different fields of application. Two different development approaches will be discussed: 1) the exploitation of the large number of sensors embedded in modern smartphones (high-resolution camera, microphone, accelerometer, gyroscope, magnetometer, GPS); 2) the interfacing with external sensors that communicate with the smartphone by the embedded wireless or wired communication technology.

In social economic researches we often need to measure non-observable, latent variables. For this we use special research
instruments, with uni and multi dimensional scales designed for measuring the constructs of interest. Validity and reliability of
these scales are crucial and special tests have been developed in this respect. Reliability concerns often arise, due to external
factors that can influence the power and significance of such tests. Even for standardized instruments variations are possible, and
they could seriously affect research results. The purpose of the present study is to investigate if and how external factors could
influence a largely used reliability estimator - Cronbach Alpha. Several scales commonly used in marketing researches were
tested, using a bootstrapping technique. Results show that important differences in the values of Cronbach Alpha are possible due
to indirect influence from external factors - respondents’ age, gender, level of study, religiousness, rural/urban living, survey type and relevance of the research subject for the participants to the survey.

Wireless sensor network nodes and mobile devices are normally powered by batteries that, when depleted, must be recharged or replaced. This poses important problems, in particular for sensor nodes that are placed in inaccessible areas or biomedical sensors implanted in the human body where the battery replacement is very impractical. Moreover, the depleted battery must be properly disposed of in accordance with national and international regulations to prevent envi-ronmental pollution. A very interesting alternative to power mobile devices is energy harvesting where energy sources naturally present in the environment (such as sunlight, thermal gradients and vibrations) are scavenged to provide the power supply for sensor nodes and mobile systems. Since the presence of these energy sources is discontinuous in nature, electronic systems powered by energy harvesting must include a power management system and a storage device to store the scavenged energy. In this paper, the main strategies to design a wireless mobile sensor system powered by energy harvesting are reviewed and different sensor systems powered by such energy sources are presented.

Free and open-source hardware (FOSH) is rapidly gaining momentum because it provides customized research hardware with over 90% savings compared to the costs of proprietary tools. However, the focused skill sets of researchers who aim to facilitate their own research limit FOSH complexity. The most expensive research equipment normally requires an interdisciplinary team. To overcome this complexity barrier and obtain large returns on investment for research funders by replacing the most expensive research equipment with FOSH, new development funding mechanisms are needed. To guide such research policy, this paper provides the first analysis of the strategic national benefit of applying the FOSH approach to major research equipment for any nation. The results of an example analysis for a single nation indicate Finland's science funders could save between 2.84-27.7m€/year directly on scientific equipment purchases if research hardware is converted to FOSH and the nation would likely garner the well-established concomitant benefits of increased research innovation within their economy. Finally, a detailed generalized model for determining national research policy in hardware development is derived and research policy mechanisms for accelerating FOSH deployment and greater accessibility to research equipment are discussed.

Incremental training is commonly applied to training recurrent neural networks (RNNs) for applications involving prognosis. As the number of prognostic time-step increases, the accuracy of prognosis generally decreases, as often seen in long-term prognosis. Revision of the training techniques is therefore necessary to improve the accuracy in long-term prognosis. This paper presents a competitive learning-based approach to long-term prognosis of machine health status. Specifically, vibration signals from a defect-seeded rolling bearing are preprocessed using continuous wavelet transform (CWT). Statistical parameters computed from both the raw data and the preprocessed data are then utilized as candidate inputs to an RNN. Based on the principle of competitive learning, input data were clustered for effective representation of similar stages of defect propagation of the bearing being monitored. Analysis has shown that the developed technique is more accurate in predicting bearing defect progression than the incremental training technique.

The sound of a working vehicle provides an important clue to the vehicle type. In this paper, we introduce the "eigenfaces method," originally used in human face recognition, to model the sound frequency distribution features. We show that it can be a simple and reliable acoustic identification method if the training samples can be properly chosen and categorized. We treat the frequency spectrum in a 200 ms time interval (a "frame") as a vector in a high-dimensional frequency feature space. In this space, we study the vector distribution for each kind of vehicle sound produced under similar working conditions. A collection of typical sound samples is used as the training data set. The mean vector and the most important principal component eigenvectors of the covariance matrix of the zero-mean-adjusted samples together characterize its sound signature. When a new zero-mean-adjusted sample is projected into the principal component eigenvector directions, a small residual vector indicates that the unknown vehicle sound can be well characterized in terms of the training data set.

The oscillation-test strategy is a low cost and robust test method for mixed-signal integrated circuits. Being a vectorless test method, it allows one to eliminate the analog test vector generator. Furthermore, as the oscillation frequency is considered to be digital, it can be precisely analyzed using pure digital circuitry and can be easily interfaced to test techniques dedicated to the digital part of the circuit under test (CUT). This paper describes the design for testability (DFT) of active analog filters based on oscillation-test methodology. Active filters are transformed to oscillators using very simple techniques.

This paper details a framework developed at the National Institute of Standards and Technology (NIST) that highlights the standardization efforts going on within the various levels of an Internet-based distributed measurement and control (DMC) system. The framework highlights state-of-the-art hardware and software techniques used at NIST to design, implement, and deploy next-generation Internet-based DMC applications and systems. The framework targets three important areas of standardization including transducer interfaces, open network communication, and distributed application development. An implementation of a DMC application on the Internet based on the NIST framework is also described. The paper concludes with a brief introduction to other research activities at NIST culminating from this core Internet-based DMC research.

This paper presents a new triaxial accelerometer calibration method using a mathematical model of six calibration parameters: three gain factors and three biases. The fundamental principle of the proposed calibration method is that the sum of the triaxial accelerometer outputs is equal to the gravity vector when the accelerometer is stationary. The proposed method requires the triaxial accelerometer to be placed in six different tilt angles to estimate the six calibration parameters. Since the mathematical model of the calibration parameters is nonlinear, an iterative method is used. The results are verified via simulations by comparing the estimated gain factors and biases with the true gain factors and biases. The simulation results confirm that the proposed method is applicable in extreme cases where the gain factor is 1000 V/(m/s 2 ) and the bias is ±100 V, as well as the cases where the gain factor is 0.001 V/(m/s 2 ) and the bias is 0 V. The proposed calibration method is also experimentally tested with two different triaxial accelerometers, and the results are validated using a mechanical inclinometer. The experimental results show that the proposed method can accurately estimate gain factors and biases even when the initial guesses are not close to the true values. In addition, the proposed method has a low computational cost because the calculation is simple, and the iterative method usually converges within three iteration steps. The error sources of the experiments are discussed in this paper.

We present an algorithm for the online detection of rotor bar breakage in induction motors through the use of wavelet packet decomposition (WPD) and neural networks. The system provides a feature representation of multiple frequency resolutions for faulty modes and accurately differentiates between healthy and faulty conditions, and its main applicability is to dynamic time-variant signals experienced in induction motors

We propose a multidimensional instrument to assess the degree of presence of marketing capabilities a firm possesses, at three levels of abstraction. We first present the theoretical framework for marketing capabilities and discuss the main scales proposed by Vorhies et al. Then, we detail the steps required to develop and validate our third-order formative instrument. We assess the convergent and discriminant validity of the proposed instrument via partial least squares path modelling (PLS-PM) applied to a sample of 199 French small- and medium-sized enterprises (SMEs). Finally, we check the nomological validity of our instrument by testing the positive effect of marketing capabilities on organisational performance.

In this article, we advance research on transparency by developing and validating a measure based on recent theoretical insights about its dimensionality. We find that transparency—defined as the perceived quality of information—is a three-dimensional construct consisting of perceived information disclosure, clarity, and accuracy. Evidence shows items associated with these dimensions can be aggregated into a single transparency construct. We also find that transparency (as an aggregate construct) is distinct from neighboring constructs such as informational justice and capable of predicting perceptions of the source’s trustworthiness (ability, benevolence, and integrity). Finally, we find evidence of measurement invariance between two commonly used referents of analysis, yielding confidence in the application of the proposed measure across research settings. We discuss implications of the new measure for research on transparency, the extension of the new measure to related research traditions, and the practical application of the new measure for managers interested in constructing and appraising transparent messages.

Multi-frequency electrical impedance tomography (EIT) systems require stable voltage controlled current generators that will work over a wide frequency range and with a large variation in load impedance. In this paper we compare the performance of two commonly used designs: the first is a modified Howland circuit whilst the second is based on a current mirror. The output current and the output impedance of both circuits were determined through PSPICE simulation and through measurement. Both circuits were stable over the frequency ranges 1 kHz to 1 MHz. The maximum variation of output current with frequency for the modified Howland circuit was 2.0% and for the circuit based on a current mirror 1.6%. The output impedance for both circuits was greater than 100 k for frequencies up to 100 kHz. However, neither circuit achieved this output impedance at 1 MHz. Comparing the results from the two circuits suggests that there is little to choose between them in terms of a practical implementation.

This study provides designs for a low-cost, easily replicable open-source lab-grade digital scale that can be used as a precision balance. The design is such that it can be manufactured for use in most labs throughout the world with open-source RepRap-class material extrusion-based 3-D printers for the mechanical components and readily available open-source electronics including the Arduino Nano. Several versions of the design were fabricated and tested for precision and accuracy for a range of load cells. The results showed the open-source scale was found to be repeatable within 0.05 g with multiple load cells, with even better precision (0.005 g) depending on load cell range and style. The scale tracks linearly with proprietary lab-grade scales, meeting the performance specified in the load cell data sheets, indicating that it is accurate across the range of the load cell installed. The smallest load cell tested (100 g) offers precision on the order of a commercial digital mass balance. The scale can be produced at significant cost savings compared to scales of comparable range and precision when serial capability is present. The cost savings increase significantly as the range of the scale increases and are particularly well-suited for resource-constrained medical and scientific facilities.

The Technological, Pedagogical, and Content Knowledge (TPACK) framework – a framework which proposes a set of knowledge domains that are essential for effective teaching with technology – has gained considerable attention in the domain of education and technology. With the efforts to conceptualize these knowledge domains comes the question to what extent they can be distinguished empirically. Hence, the present study examines a measure that assesses pre-service teachers' self-efficacy in the technology-related TPACK dimensions (“T-dimensions”). In pursuit of crafting a validity argument, we investigated its factor structure and tested it for measurement invariance across gender and educational tracks, two subgroups that may indicate considerable differences. By means of multi-group confirmatory factor analysis, the data of N = 665 pre-service teachers in 18 teacher training institutions in Flanders (Belgium) revealed a nested factor structure of the TPACK measure, which comprised a general factor and a specific factor of pre-service teachers’ technological knowledge. This factor structure was fully invariant across gender and educational tracks. Mean differences between educational tracks did not occur; yet, substantial differences were found across gender in favor of male pre-service teachers. This study sheds light on critical aspects of crafting a validity argument for the measurement of the T-dimensions in the TPACK framework and reports relevant subgroup differences.

Este artículo presenta una arquitectura para el diseño conceptual de vehículos subacuáticos operados remotamente (ROV). La arquitectura propuesta está basada en una revisión extensa de literatura y la experiencia obtenida durante 20 años con el desarrollo de tres sistemas ROV diseñados para misiones de inspección subacuática. El ROV se divide en cinco subsistemas: vehículo, estación en superficie, interfaz superficie/vehículo, sistema de control y software. Para cada uno de estos subsistemas se definen funciones y tareas, se enuncian componentes, se establecen interrelaciones con otros subsistemas y se plantean alternativas comúnmente utilizadas. La delimitación de los subsistemas desde el diseño conceptual busca evitar problemas en las fases avanzadas del desarrollo del sistema robótico de exploración.

Background: The Hospital Survey on Patient Safety Culture (HSOPSC) is widely utilized in multiple languages across the world. Despite culture and language variations, research studies from Latin America use the Spanish language HSOPSC validated for Spain and the United States. Yet, these studies fail to report the translation method, cultural adaptation process, and the equivalence assessment strategy. As such, the psychometric properties of the HSOPSC are not well demonstrated for cross-cultural research in Latin America, including Peru. The purpose of this study was to develop a target-language HSOPSC for cross-cultural research in Peru that asks the same questions, in the same manner, with the same intended meaning, as the source instrument. Methods: This study used a mixed-methods approach adapted from the translation guideline recommended by Agency for Healthcare Research and Quality. The 3-phase, 7-step process incorporated translation techniques, pilot testing, cognitive interviews, clinical participant review, and subject matter expert evaluation. Results: The instrument was translated and evaluated in 3 rounds of cognitive interview (CI). There were 37 problem items identified in round 1 (14 clarity, 12 cultural, 11 mixed); and resolved to 4 problems by round 3. The pilot-testing language clarity inter-rater reliability was S-CVI/Avg = 0.97 and S-CVI/UA = 0.86; and S-CVI/Avg = 0.96 and S-CVI/UA = 0.83 for cultural relevance. Subject matter expert agreement in matching items to the correct dimensions was substantially equivalent (Kappa = 0.72). Only 1 of 12 dimensions had a low Kappa (0.39), borderline fair to moderate. The remaining dimensions performed well (7 = almost perfect, 2 = substantial, and 2 = moderate).

Both the free and open source software (FOSS) as well as the distributed digital manufacturing of free and open source hardware (FOSH) has shown particular promise among scientists for developing custom scientific tools. Early research found substantial economic savings for these technologies, but as the open source design paradigm has grown by orders of magnitude it is possible that the savings observed in the early work was isolated to special cases. Today there are examples of open source technology for science in the vast majority of disciplines and several resources dedicated specifically to publishing them. Do the tremendous economic savings observed earlier hold today? To answer that question, this study evaluates free and open source technologies in the two repositories compared to proprietary functionally-equivalent tools as a function of their use of Arduino-based electronics, RepRap-class 3-D printing, as well as the combination of the two. The results of the review find overwhelming evidence for a wide range of scientific tools, that open source technologies provide economic savings of 87% compared to equivalent or lesser proprietary tools. These economic savings increased slightly to 89% for those that used Arduino technology and even more to 92% for those that used RepRap-class 3-D printing. Combining both Arduino and 3-D printing the savings averaged 94% for free and open source tools over commercial equivalents. The results provide strong evidence for financial support of open source hardware and software development for the sciences. Given the overwhelming economic advantages of free and open source technologies, it appears financially responsible to divert funding of proprietary scientific tools and their development in favor of FOSH. Policies were outlined that provide nations with a template for strategically harvesting the opportunities provided by the free and open source paradigm.

This paper explores the confrontation of physical and contextual factors involved in the emergence of the subject of color measurement, which stabilized in essentially its present form during the interwar period. The contentions surrounding the specialty had both a national and a disciplinary dimension. German dominance was curtailed by American and British contributions after World War I. Particularly in America, communities of physicists and psychologists had different commitments to divergent views of nature and human perception. They therefore had to negotiate a compromise between their desire for a quantitative system of description and the perceived complexity and human-centeredness of color judgement. These debates were played out not in the laboratory but rather in institutionalized encounters on standards committees. Groups such as this constitute a relatively unexplored historiographic and social site of investigation. The heterogeneity of such committees, and their products, highlight the problems of identifying and following such ephemeral historical 'actors'.

Experimental investigations of the nonlinear properties of superconducting niobium coplanar waveguide resonators are reported. The nonlinearity due to a current dependent kinetic inductance of the center conductor is strong enough to realize bifurcation of the nonlinear oscillator. When driven with two frequencies near the threshold for bifurcation, parametric amplification with a gain of +22.4 dB is observed.

Internet-Based Distributed Measurement and Control Applications ndustries that develop and use distributed measurement-and-control (DMC) systems are migrating away from proprietary hardware and software platforms in fa-\'or of open systems and standardized apprmches. Some of the key components of ' 1 DMC system are sensors, actuators, controllers, and control networks. Large DMC systems often consist of many sensors and actuators from various manufacturers and multiple sensors or control networks supplied by differellt \renders. Component interfacing and system integration are major issues that require significant efforts from multiple dxsciplines with technical backgrounds. Thus, standardized trmsclucer (sc'I1sc)r and actuator) interfaces,

Today, many commercial and private cloud computing providers offer resources for leasing under the infrastructure as a service (IaaS) paradigm. Although an abundance of mechanisms already facilitate the lease and use of single infrastructure resources, to complete multi-job workloads IaaS users still need to select adequate provisioning and allocation policies to instantiate resources and map computational jobs to them. While such policies have been studied in the past, no experimental investigation in the context of clouds currently exists that considers them jointly. In this paper we present a comprehensive and empirical performance-cost analysis of provisioning and allocation policies in IaaS clouds. We first introduce a taxonomy of both types of policies, based on the type of information used in the decision process, and map to this taxonomy eight provisioning and four allocation policies. Then, we analyze the performance and cost of these policies through experimentation in three clouds, including Amazon EC2. We show that policies that dynamically provision and/or allocate resources can achieve better performance and cost. Finally, we also look at the interplay between provisioning and allocation, for which we show preliminary results.

Scanning tunneling microscopes (STM) and atomic force microscopes (AFM) are used to study biological materials. These methods, often capable of achieving atomic resolutions, reveal fascinating information regarding the inner workings of these materials. However, both STM and AFM require physical contact to the specimen. In the case of STM the specimen needs to be conducting as well. Here we introduce a new method for imaging biological materials through air or a suitable liquid using decaying or evanescent fields at the tip of a properly designed microwave resonator. This novel method involves the use of an evanescent microwave probe (EMP) and it is capable of imaging a variety of nonuniformities in biological materials including conductivity, permittivity, and density variations. EMP is a noncontact and nondestructive sensor and it does not require conducting specimens. Its spatial resolution is currently around 0.4 m at 1 GHz. We have used this probe to map nonuniformities in a variety of materials including metals, semiconductors, insulators, and biological and botanical samples. Here we discuss applications of EMP imaging in bone, teeth, botanical, and agricultural specimens.

An Emergency Response (ER) Cyber-Physical System (CPS) to avoid landslides and survey areas located on or near slopes is introduced that handles two problems: electronic waste disposal, and environmental disasters. Uncomplicated detection circuits using salvaged components can pinpoint floods in impoverished regions. CPSs simplify hazard prediction and mitigation in disaster supervision. Nonetheless, few green practices and efforts have been accomplished in this regard. Recent technical advances help landslides studies and the evaluation of suitable risk alleviation measures. This work addresses in situ meters, and cameras to observe ground movements more accurately. The ER-CPS identifies and can help mitigate landslides using techniques based on motion detection that can productively predict and monitor the zone conditions to classify it, and the landslide-related data can be transmitted to inspecting stations to lessen the erosion/sedimentation likelihood while increasing security.

This study presents an entirely open-source, low-cost power monitoring system capable of many types of measurements including both loads and supplies such as solar photovoltaic systems. In addition, the system can be fabricated using only open source software and hardware. The design revolves around the Digital Universal Energy Logger (DUEL) Node, which is responsible for reading and properly scaling the voltage and current of a particular load, and then serializing it via an on-board ATTiny85 chip. The configuration of the DUEL node allows for custom sensitivity ranges, and can handle up to 50 A and 300 V. Up to 127 DUEL nodes communicate via Inter-Integrated Circuit (I2C) on a bus, which can be monitored and logged through an Arduino UNO, or other compatible microcontroller. Using accessible equipment, the DUEL node can be calibrated to a desirable accuracy and error. The DUEL nodes are also completely customizable, making them fit for any input range, where all commercially-available products are fixed range. The open source solution out performs commercial solutions as the price per measurement ($18.25) is significantly smaller, while the number of serviceable channels (127) is significantly higher.

Soybeans are an important crop for global food security. Every year, soybean yields are reduced by numerous soybean diseases, particularly the soybean cyst nematode (SCN). It is difficult to visually identify the presence of SCN in the field, let alone its population densities or numbers, as there are no obvious aboveground disease symptoms. The only definitive way to assess SCN population densities is to directly extract the SCN cysts from soil and then extract the eggs from cysts and count them. Extraction is typically conducted in commercial soil analysis laboratories and university plant diagnostic clinics and involves repeated steps of sieving, washing, collecting, grinding, and cleaning. Here we present a robotic instrument to reproduce and automate the functions of the conventional methods to extract nematode cysts from soil and subsequently extract eggs from the recovered nematode cysts. We incorporated mechanisms to actuate the stage system, manipulate positions of individual sieves using the gripper, recover cysts and cyst-sized objects from soil suspended in water, and grind the cysts to release their eggs. All system functions are controlled and operated by a touchscreen interface software. The performance of the robotic instrument is evaluated using soil samples infested with SCN from two farms at different locations and results were comparable to the conventional technique. Our new technology brings the benefits of automation to SCN soil diagnostics, a step towards long-term integrated pest management of this serious soybean pest.

Most of automatic blood pressure measurement devices on the market implement an oscillometric method. This paper highlights the need for standardized calibration procedures for these devices in order to reduce logistical difficulties, timeconsuming processes, and high costs involved in clinical validations. A critical overview of researchers' and manufacturers' proposals to answer this need is presented as a contribution to the IEEE P1721 project for a new standard on Objective Measurement of Systemic Arterial Blood Pressure in Humans.

Open-source technology not only has facilitated the expansion of the greater research community, but by lowering costs it has encouraged innovation and customizable design. The field of automated microscopy has continued to be a challenge in accessibility due the expense and inflexible, non-interchangeable stages. This paper presents a low-cost, open source microscope 3-D stage. A RepRap 3-D printer was converted to an optical microscope equipped with a customized, 3-D printed holder for a USB microscope. Precision measurements were determined to have an average error of 10 μm at the maximum speed and 27 μm at the minimum recorded speed. Accuracy tests yielded an error of 0.15%. The machine is a true 3-D stage and thus able to operate with USB microscopes or conventional desktop microscopes. It is larger than all commercial alternatives, and is thus capable of high depth images over unprecedented areas and complex geometries. The repeatibility is below 2-D microscope stages, but testing shows that it is adequate for the majority of scientific applications. The open source microscope stage costs less than 3% to 9% of the closest proprietary commercial stages. This extreme affordability vastly improves accessibility for 3-D microscopy throughout the world.

This paper presents a new RF built-in self-test (BIST) measurement and a new automatic-performance-compensation network for a system-on-chip (SoC) transceiver. We built a 5-GHz low noise amplifier (LNA) with an on-chip BIST circuit using 0.18-µm SiGe technology. The BIST-measurement circuit contains a test amplifier and RF peak detectors. The complete measurement setup contains an LNA with a BIST circuit, an external RF source, RF relays, 50-Ω load impedance, and a dc voltmeter. The proposed BIST circuit measures input impedance, gain, noise figure, input return loss, and output signal-to-noise ratio of the LNA. The test technique utilizes the output dc-voltage measurements, and these measured values are translated to the LNA specifications such as the gain through the developed equations. The performance of the LNA was improved by using the new automatic compensation network (ACN) that adjusts the performance of the LNA with the processor in the SoC transceiver.

A low-cost data logging platform is presented that provides long-term operation in remote or submerged environments. Three premade " breakout boards " from the open-source Arduino ecosystem are assembled into the core of the data logger. Power optimization techniques are presented which extend the operational life of this module-based design to >1 year on three alkaline AA batteries. Robust underwater housings are constructed for these loggers using PVC fittings. Both the logging platform and the enclosures, are easy to build and modify without specialized tools or a significant background in electronics. This combination turns the Cave Pearl data logger into a generalized prototyping system and this design flexibility is demonstrated with two field studies recording drip rates in a cave and water flow in a flooded cave system. This paper describes a complete DIY solution, suitable for a wide range of challenging deployment conditions.

Complementary single-and split-post dielectricresonator techniques were used for contactless absolute resistivity measurements of semiconductor wafers and for onwafer resistivity mapping in the range of 10 −5 to 10 5 Ω • cm. Uncertainties of the resistivity measurements employing both techniques are in the range of 2%-4%. Permittivities of high-resistivity semiconductors were measured with uncertainties of approximately 0.5%. Several Silicon, GaAs, and SiC wafers were tested at room and at elevating temperatures, showing excellent repeatability of measurements.

The power consumption of a streaming-media server can be obtained in real time by using the virtual-instrumentation software described in this paper without using an additional hardware meter. We have built a model to estimate the power consumption from the observation of experimental data that consists of tracking the CPU utilization and detecting the operation parameters of the measured servers. When calculated in real time, the CPU utilization can respond to the dynamic change of the power consumption of the measured servers. The operation parameters represent the hardware configuration of the measured servers. We also propose three methods to obtain these parameters: filledmanually, hardware-revised, and software-revised parameter estimating. We have constructed the virtual-instrumentation software according to this power model to measure the power consumption of the streaming-media server. To facilitate the measurement process, we have also designed a suitable graphic-user interface for it. Our virtual-instrumentation software with three parameterestimating methods has been tested by way of comparison with measurement results obtained by a power meter. The average power values of the hardware-revised method are found to yield mean errors of the estimate within 3%. The mean error of the software-revised method is within 6%. However, the filledmanually method may underestimate the power consumption by as much as 11%.

The combination of open-source software and hardware provide technically feasible methods to create low-cost, highly-customized scientific research equipment. Open-source 3-D printers have proven useful for fabricating scientific tools. Here the capabilities of an open-source 3-D printer are expanded to become a highly-flexible scientific platform. An automated low-cost 3-D motion control platform is presented having the capacity to perform scientific applications including: i) 3-D printing of scientific hardware, ii) laboratory auto-stirring, measuring and probing, iii) automated fluid handling and iv) shaking and mixing. The open-source 3-D platform not only facilities routine research while radically reducing the cost, but it also inspires the creation of a diverse array of custom instruments that can be shared and replicated digitally throughout the world to drive down the cost of research and education further.

This paper describes an ultrasonic ranging system (URS) that can be used to measure vibratory displacements in structures. A pair of ultrasonic transducers is used in a transmit-receive mode to acquire the motion of a point on a flexible structure. The structure's oscillating motion modulates the phase angle between the transmitted and received acoustic signals. A simple phase detector and low-pass filter combination demodulate the phase signal, thus extracting information about the motion of the point on the structure. The results reported here concentrate on some design issues of the URS and its use as a potential displacement measuring device for flexible structures. The URS accurately distinguished four vibration frequencies of a simple cantilevered aluminum beam, the highest frequency being near 50 Hz. A 3-D version of the system will be an effective, simple, and low-cost vibration sensor to be used in flexible structures' feedback control schemes.

A robust feedback linearizing control strategy, based on sliding mode compensation, is proposed for the operation of a grid-connected photovoltaic inverter system under grid faults, characterized by unbalanced voltages, to meet low-voltage ride through requirements. Under normal grid condition, the control system is developed for maximum power transfer from the photo-voltaic source to the grid by maximum power point tracking operation of the dc–dc converter, and regulation of the dc-link voltage and the current at the inverter-grid side. Under grid fault, which is unbalanced grid voltage due to voltage dips, the active power is regulated to reduce the current excess and the reactive power is injected to avoid the inverter damage or disconnection, while the dc-link voltage is controlled via the dc–dc converter. A sliding mode compensator is injected into the control system to enhance its robustness to uncertainties. The feedback linearizing control schemes are developed from the grid model at the inverter side and the dc-link model at the dc–dc converter side. The proposed control strategies are experimentally validated on a three-phase grid-connected photovoltaic inverter system and experimental results show that the control system is effective in terms of voltage and power control with smooth transitions between the modes.

With increasing terrorist threats of different types, explosives detection for various types and forms of explosives is of growing interest. This paper reviews the broad array of possible methods of explosives detection, using both nuclear- and nonnuclear-based instruments, with their advantages and disadvantages for different scenarios. An explanation of the fundamental physics for each approach is accompanied by its general applicability and citations to the relevant scientific literature.

Flash-type analog-to-digital converters (ADC's) presenting a nonlinear behavior, i.e., having nonequally spaced threshold levels, may introduce harmonic distortion that can be reduced by employing large-amplitude dither-based conversion techniques. However, large-scale dithering is difficult to implement and, in addition, severely reduces the ADC input dynamic range. In this paper, a new ADC architecture is presented based on ordinary flash conversion and dynamic element matching, that strongly reduces nonlinear distortion. It eliminates the need for large-scale dither signals by randomizing the resistor positions in the resistor string used to generate the voltage references. Some properties of this architecture are analyzed and simulation results that validate the theoretical assumptions are presented.

This paper presents the development of an inertial measurement data acquisition system intended for use in sailboats. The variables of interest are three-axis acceleration, three-axis rotation, Global Positioning System (GPS) position/velocity, magnetic compass bearing, and wind speed/direction. The design focus is on low-cost microelectromechanical systems-based technology and demonstrating the validity of these technologies in a scientific application. A prototype is constructed and submitted to a series of tests to demonstrate functionality and soundness of the design. Contributions of this paper include the novel application of inertial measurement unit technology to a sailboat racing application, the integration of all instrumentation, creative ruggedized packaging, and emphasizing the use of low-cost commercial off-the-shelf technology.

Real-world IP applications such as Peer-to-Peer filesharing are now able to benefit from network and location awareness. It is therefore crucial to understand the relation between underlay and overlay networks and to characterize the behavior of real users with regard to the Internet. For this purpose, we have designed and implemented MULTIPROBE, a framework for large-scale P2P file-sharing measurements. Using this framework, we have performed measurements of BitTorrent, which is currently the P2P file sharing network with the largest amount of Internet traffic. We analyze and correlate these measurements to provide new insights into the topology, the connectivity, and the path characteristics of the Internet parts underlying P2P networks, as well as to present unique information on the BitTorrent throughput and connectivity.