Indirect Measurement Approaches Research Articles

Indirect measurement method for high frequency response of complex structure based on statistical energy analysis

The harsh working environments often make it difficult to measure high frequency responses of complex structures in the fields such as aerospace and aeronautic, which severely hinders the evaluation of structural performance and safety. An indirect measurement method is proposed to estimate the high frequency responses of non-measurable subsystems using a statistical energy analysis (SEA) framework. Whether or not the non-measurable subsystem includes input load, two indirect measurement approaches are developed by constructing an overdetermined problem and a well-posed problem respectively. Both utilize only the power flow balance equations of unexcited subsystems to solve the problems and thus do not require solving for input loads. The approaches are validated numerically and experimentally through case study of a rocket engine structure. Furthermore, the interval error analyses indicate that the approaches are robust against SEA modeling errors and response measuring errors.

Abortion incidence and safety in Niger in 2021: Findings from a nationally representative cross-sectional survey of reproductive-aged women using direct and indirect measurement approaches.

Niger is a country in which legal restrictions and a dearth of research has long limited our understanding of the extent and safety of induced abortion. The current study is the first national study of induced abortion in Niger. It uses direct (self-report) and indirect (best friend method) to provide nationally representative estimates of induced abortion incidence and safety and evaluates the performance of the indirect measurement approach. We used cross-sectional, representative survey data on women aged 15-49 in Niger collected between January and May 2022; final sample included 3,696 women. The survey included questions on respondents' and their closest female friends' experience with abortion, including methods and sources used. We calculated one-year abortion incidence and the proportion of abortions involving non-recommended methods and/or sources to determine safety separately for respondents and friends, overall and by background characteristics. The fully adjusted one-year friend abortion rate was 6.7 abortions per 1,000 women in 2021, which was substantially higher than the corresponding respondent rate of 0.4 per 1,000 women. Confidence intervals were wide, but friend estimates suggest higher abortion rates among women in their 20s, those with secondary or higher education, and those with no children. Nearly all abortions were unsafe (97% respondents, 100% friends), involving non-recommended methods and/or sources. While abortion numbers were small, unsafe abortion appeared more common among older women, married women, those with children, and those residing in rural areas. Our findings indicate that, despite legal restrictions, some women undergo abortions in Niger at great risk to their physical safety. Ensuring adequate access to quality voluntary family planning services to prevent unintended pregnancy and postabortion care to treat complications is essential to reducing the risk of unsafe abortion in the country.

Closer than they look at first glance: A systematic review and a research agenda regarding measurement practices for policy learning

Learning is a cognitive and social dynamic through which diverse types of actors involved in policy processes acquire, translate and disseminate new information and knowledge about public problems and solutions. In turn, they maintain, strengthen or revise their policy beliefs and preferences. Despite the conceptual and theoretical developments over the last years, concerns about the measurement of policy learning remain persistent. Based on the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) approach, this article reports the results of a systematic review of the existing practices for measuring policy learning in the public administration and policy research. In addition to operationalizations, data sources, methods of analysis and levels of analysis, we examine how the reviewed articles deal with the processual nature of policy learning. We show that the existing measurement practices transcend the research streams on policy learning for the most part, which extends the argument developed by Dunlop and Radaelli (2018) that policy learning is an analytical framework of the policy process. Based on these results, we argue for more transparent operationalizations, discuss the strengths and weaknesses of direct and indirect measurement approaches, and call for more creativity in designing measurement methods that recognize the multilevel nature of policy learning.

Data assimilation of uncalibrated soil moisture measurements from frequency-domain reflectometry

Accurate measurements of soil moisture are essential for hydrological, agricultural and environmental sciences. Among many indirect measurement approaches, Frequency-Domain Reflectometry (FDR) soil moisture sensors are popular but are prone to be affected by many factors (e.g., temperature, bulk density, texture, mineralogy) at different installation sites. To avoid the enormous effort required for site-specific FDR calibration, we propose a calibration-free framework, in which a linear calibration model (that links FDR observation and true soil moisture) is incorporated. Based on the classical bias-blind methods using the ensemble Kalman filter (EnKF) and the iterative ensemble smoother (IES), two such bias-aware data assimilation methods are developed to simultaneously identify the unknown hydraulic and the linear calibration parameters based on uncalibrated FDR observations as well as meteorological data. We thoroughly discuss the effects of various factors (i.e., observation noise and number of observations, ensemble size, number of unknown parameters and two potential model errors) on their performances in the synthetic cases and make an application in a real-world case, besides comparing them with their previous versions simultaneously. In particular, the linear calibration model coupled with IES is more favored. From a pragmatic point of view, we demonstrate the usefulness of the proposed approaches in calibrating the FDR data in an online manner with easily-accessible meteorological data.

A review of principles of MEMS pressure sensing with its aerospace applications

PurposePressure, being one of the key variables investigated in scientific and engineering research, requires critical and accurate measurement techniques. With the advancements in materials and machining technologies, there is a large leap in the measurement techniques including the development of micro electromechanical systems (MEMS) sensors. These sensors are one to two orders smaller in magnitude than traditional sensors and combine electrical and mechanical components that are fabricated using integrated circuit batch-processing technologies. MEMS are finding enormous applications in many industrial fields ranging from medical to automotive, communication to electronics, chemical to aviation and many more with a potential market of billions of dollars. MEMS pressure sensors are now widely used devices owing to their intrinsic properties of small size, light weight, low cost, ease of batch fabrication and integration with an electronic circuit. This paper aims to identify and analyze the common pressure sensing techniques and discuss their uses and advantages. As per our understanding, usage of MEMS pressure sensors in the aerospace industry is quite limited due to cost constraints and indirect measurement approaches owing to the inability to locate sensors in harsh environments. The purpose of this study is to summarize the published literature for application of MEMS pressure sensors in the said field. Five broad application areas have been investigated including: propulsion/turbomachinery applications, turbulent flow diagnosis, experimentalaerodynamics, micro-flow control and unmanned aerial vehicle (UAV)/micro aerial vehicle (MAV) applications.Design/methodology/approachThe first part of the paper deals with an introduction to MEMS pressure sensors and mathematical relations for its fabrication. The second part covers pressure sensing principles followed by the application of MEMS pressure sensors in five major fields of aerospace industry.FindingsIn this paper, various pressure sensing principles in MEMS and applications of MEMS technology in the aerospace industry have been reviewed. Five application fields have been investigated including: Propulsion/Turbomachinery applications, turbulent flow diagnosis, experimental aerodynamics, micro-flow control and UAV/MAV applications. Applications of MEMS sensors in the aerospace industry are quite limited due to requirements of very high accuracy, high reliability and harsh environment survivability. However, the potential for growth of this technology is foreseen due to inherent features of MEMS sensors’ being light weight, low cost, ease of batch fabrication and capability of integration with electric circuits. All these advantages are very relevant to the aerospace industry. This work is an endeavor to present a comprehensive review of such MEMS pressure sensors, which are used in the aerospace industry and have been reported in recent literature.Originality/valueAs per the author’s understanding, usage of MEMS pressure sensors in the aerospace industry is quite limited due to cost constraints and indirect measurement approaches owing to the inability to locate sensors in harsh environments. Present work is a prime effort in summarizing the published literature for application of MEMS pressure sensors in the said field. Five broad application areas have been investigated including: propulsion/turbomachinery applications, turbulent flow diagnosis, experimental aerodynamics, micro-flow control and UAV/MAV applications.

Generalizability of gene expression programming and random forest methodologies in estimating cropland and grassland leaf area index

Leaf Area Index (LAI) is a very important structural attribute of ecosystems which affects the energy, water and carbon exchanges between the land surface and atmosphere. Direct measurement of LAI is costly and time consuming so indirect measurement approaches have been developed for determining its magnitude. The present paper aimed at modeling LAI in cropland and grassland sites using the available meteorological data through two heuristic data driven techniques, namely, gene expression programming (GEP) and random forest (RF). Different data set organizations were designed using local (temporal) and external (spatial) norms to provide a thoroughgoing data scanning strategy. The results showed that the external GEP and RF models (EGEP and ERF) might be suitable approaches for modeling LAI by average scatter index (SI) values of 0.275 and 0.270 (for cropland) and 0.273 and 0.279 (for grassland) when compared to the local GEP and RF models with average SI values of 0.207 and 0.204 (cropland), and 0.249 and 0.204 (grassland), respectively. The presented methodology allowed the evaluation in each site of models developed (trained) using local patterns and the models developed using the exogenous data (patterns from ancillary sites).

A system for measuring local radial strains in triaxial apparatus

The importance of local measurement of small strains is well recognised. Without such measurements, accurate stiffness determination is not possible and can result in overestimations of strains resulting from stress changes in the ground. Axial strain is often considered to be the primary strain to be measured under triaxial conditions and there has been a focus on its measurement. Radial strain is also important, for example for determining Poisson's ratio and bulk modulus, or maintaining K0 conditions during consolidation. There are a number of devices available that enable its determination, using both direct and indirect measurement approaches. This note describes a system for measuring radial strains directly using linear variable differential transformers. It is shown to be simple, reliable, accurate and robust.

Soil Moisture Data for the Validation of Permafrost Models Using Direct and Indirect Measurement Approaches at Three Alpine Sites

In regions affected by seasonal and permanently frozen conditions soil moisture influences the thermal regime of the ground as well as its ice content, which is one of the main factors controlling the sensitivity of mountain permafrost to climate changes. In this study, several well established soil moisture monitoring techniques were combined with data from geophysical measurements to assess the spatial distribution and temporal evolution of soil moisture at three high elevation sites with different ground properties and thermal regimes. The observed temporal evolution of measured soil moisture is characteristic for sites with seasonal freeze/thaw cycles and consistent with the respective site-specific properties, demonstrating the general applicability of continuous monitoring of soil moisture at high elevation areas. The obtained soil moisture data were then used for the calibration and validation of two different model approaches in permafrost research in order to characterize the lateral and vertical distribution of ice content in the ground. Calibration of the geophysically based four-phase model (4PM) with spatially distributed soil moisture data yielded satisfactory two dimensional distributions of water-, ice- and air content. Similarly, soil moisture time series significantly improved the calibration of the one-dimensional heat and mass transfer model COUP, yielding physically consistent soil moisture and temperature data matching observations at different depths.

The Size of Underground Economy in Albania

The main purpose of this paper is to assess the size of the underground sector of the economy in Albania by using the Indirect Approach - Currency Demand Approach. A few studies have tried estimate the size of the informal economy in Albania in the previous years and there’s no evidence of recent estimates of informality. Also, there are some other available studies which give some point assessments of informality in Albania but without information on its development over time. Using indirect measurement approaches we found that the size of the underground economy still accounts for a large share to GDP, but there is a decrease in size on the last years. This may be the result of vast reforms and a formalization process undertaken by the Albanian governments over time. Despite these results, it’s important to highlight the fact that the average ratio of the underground economy to GDP presents a declining trend over the period 1998 – 2013. DOI: 10.5901/ajis.2014.v3n4p503

Informal Economy in Albania

The main purpose of this paper is to assess the size of the informal sector of the economy in Albania by using indirect approaches: national accounts discrepancies, simple currency ratio, electrical energy consumption and some evidence by the labor market developments. A few studies have attempted to estimate the size of the informal economy in Albania in the previous years and there’s no evidence of recent estimates of informality (at least they are not publicly available), especially after 2007. Also, there are some other available studies which give some point assessments of informality in Albania but without information on its development over time. Using indirect measurement approaches we found that informality still accounts for a large share to GDP, but, differently from findings in other studies we found lower figures. This may be the result of vast reforms and a formalization process undertaken by the Albanian governments over time. Despite these results, it’s important to highlight the fact that the average ratio of the informal sector of the economy to GDP presents a declining trend over the period 1996-2012.

Informal Economy in Albania

The main purpose of this paper is to assess the size of the informal sector of the economy in Albania by using indirect approaches: national accounts discrepancies, simple currency ratio, electrical energy consumption and some evidence by the labor market developments. A few studies have attempted to estimate the size of the informal economy in Albania in the previous years and there’s no evidence of recent estimates of informality (at least they are not publicly available), especially after 2007. Also, there are some other available studies which give some point assessments of informality in Albania but without information on its development over time. Using indirect measurement approaches we found that informality still accounts for a large share to GDP, but, differently from findings in other studies we found lower figures. This may be the result of vast reforms and a formalization process undertaken by the Albanian governments over time. Despite these results, it’s important to highlight the fact that the average ratio of the informal sector of the economy to GDP presents a declining trend over the period 1996 – 2012. DOI: 10.5901/ajis.2013.v2n8p212

Silicon chips detect intracellular pressure changes in living cells

The ability to measure pressure changes inside different components of a living cell is important, because it offers an alternative way to study fundamental processes that involve cell deformation. Most current techniques such as pipette aspiration, optical interferometry or external pressure probes use either indirect measurement methods or approaches that can damage the cell membrane. Here we show that a silicon chip small enough to be internalized into a living cell can be used to detect pressure changes inside the cell. The chip, which consists of two membranes separated by a vacuum gap to form a Fabry-Pérot resonator, detects pressure changes that can be quantified from the intensity of the reflected light. Using this chip, we show that extracellular hydrostatic pressure is transmitted into HeLa cells and that these cells can endure hypo-osmotic stress without significantly increasing their intracellular hydrostatic pressure.

Harsh Environment Silicon Carbide Sensors for Health and Performance Monitoring of Aerospace Systems: A Review

The recent increase in transportation costs and the push for cleaner emissions demands advancements in aerospace technology. The current instrumentation used in aerospace applications is costly, and indirect measurement approaches are often employed due to the inability to locate sensors in harsh environments. Health monitoring technologies for the development of a distributed sensor network can be utilized to improve engine efficiencies and reduce emissions while maintaining safety. This paper reviews the recent advancements in silicon carbide (SiC) process technologies and demonstrations of SiC sensors and electronic circuits in hostile environments, which supports the use of SiC technology for health and performance monitoring of aerospace systems. Further development of this technology can ultimately improve the performance, reliability, and emissions of aerospace systems. However, challenges still remain for the realization of a distributed sensor network for harsh environment applications such as aerospace.

Competition and efficiency in the Dutch life insurance industry†

The lack of available prices in the Dutch life insurance industry makes competition an elusive concept that defies direct observation. Therefore, this article investigates competition by analysing several factors which may affect the competitive nature of a market and various indirect measurement approaches. After discussing various supply and demand factors which may constitute a so-called tight oligopoly, we establish the existence of scale economies and the importance of cost X-inefficiency, since severe competition would force firms to exploit available scale economies and to reduce X-inefficiencies. Both scale economies and X-inefficiencies turn out to be substantial, although more or less comparable to those found for insurers in other countries and to other financial institutions. Further, we apply the Boone indicator, a novel approach to measuring the effects of competition. This indicator points to limited competition in comparison to other sectors in the Netherlands. Further investigations of submarkets should reveal where policy measures in order to promote competition might be appropriate. †The views expressed in this article are personal and do not necessarily reflect those of CPB or DNB

Global synthesis of leaf area index observations: implications for ecological and remote sensing studies

ABSTRACTAim We present the first global synthesis of plant canopy leaf area index (LAI) measurements from more than 1000 published estimates representing ∼400 unique field sites. LAI is a key variable for regional and global models of biosphere‐atmosphere exchanges of energy, carbon dioxide, water vapour, and other materials.Location The location is global, geographically distributed.Results Biomes with LAI values well represented in the literature included croplands, forests and plantations. Biomes not well represented were deserts, shrublands, tundra and wetlands. Nearly 40% of the records in the database were published in the past 10 years (1991–2000), with a further 20% collected between 1981 and 1990. Mean (± SD) LAI, distributed between 15 biome classes, ranged from 1.3 ± 0.9 for deserts to 8.7 ± 4.3 for tree plantations, with temperate evergreen forests (needleleaf and broadleaf) displaying the highest average LAI (5.1–6.7) among the natural terrestrial vegetation classes. Following a statistical outlier analysis, the global mean (± SD) LAI decreased from 5.2 (4.1) to 4.5 (2.5), with a maximum LAI of 18. Biomes with the highest LAI values were plantations > temperate evergreen forests > wetlands. Those with the lowest LAI values were deserts < grasslands < tundra. Mean LAI values for all biomes did not differ statistically by the methodology employed. Direct and indirect measurement approaches produced similar LAI results. Mean LAI values for all biomes combined decreased significantly in the 1990s, a period of substantially more studies and improved methodologies.Main conclusions Applications of the LAI database span a wide range of ecological, biogeochemical, physical, and climate research areas. The data provide input to terrestrial ecosystem and land‐surface models, for evaluation of global remote sensing products, for comparisons to field studies, and other applications. Example uses of the database for global plant productivity, fractional energy absorption, and remote sensing studies are highlighted.