Heat flux measurements for use in physiological and clothing research

Scientists use passive heat flow meters to measure body heat exchanges with the environment. In recent years, several such sensors have been developed and concerns about their proper calibration have been addressed. However, calibration methods have differed in the geometry of the heated device as well as in the heat transfer mechanism. Therefore, a comparison of calibration methods is needed in order to understand the obtained differences in calibration lines. We chose three commercially available heat flux sensors and placed them on four different heated devices: a hot plate, double hot plate, nude cylinder and a cylinder covered with a spacer material. We found differences between the calibration line of the manufacturer and our own measurements, especially when forced convection was involved as the main heat transfer mechanism. The results showed clearly that the calibration method should be chosen according to the intended purpose of use. In addition, we recommend use a thin, light heat flux sensor with good thermal conduction in human subject studies.     

Calibration of a Hall effect displacement measurement system for complex motion analysis using a neural network

Biomechanics studies often require the analysis of position and orientation. Although a variety of transducer and camera systems can be utilized, a common inexpensive alternative is the Hall effect sensor. Hall effect sensors have been used extensively for one-dimensional position analysis but their non-linear behavior and cross-talk effects make them difficult to calibrate for effective and accurate two- and three-dimensional position and orientation analysis. The aim of this study was to develop and calibrate a displacement measurement system for a hydraulic-actuation joystick used for repetitive motion analysis of heavy equipment operators. The system utilizes an array of four Hall effect sensors that are all active during any joystick movement. This built-in redundancy allows the calibration to utilize fully connected feed forward neural networks in conjunction with a Microscribe 3D digitizer. A fully connected feed forward neural network with one hidden layer containing five neurons was developed. Results indicate that the ability of the neural network to accurately predict the x, y and z coordinates of the joystick handle was good with r(2) values of 0.98 and higher. The calibration technique was found to be equally as accurate when used on data collected 5 days after the initial calibration, indicating the system is robust and stable enough to not require calibration every time the joystick is used. This calibration system allowed an infinite number of joystick orientations and positions to be found within the range of joystick motion.     

Fabrication of a sensing module using micromachined biosensors

Micromachining is a powerful tool in constructing micro biosensors and micro systems which incorporate them. A sensing module for blood components was fabricated using the technology. The analytes include glucose, urea, uric acid, creatine, and creatinine. Transducers used to construct the corresponding sensors were a Severinghaus-type carbon dioxide electrode for the urea sensor and a Clark-type oxygen electrode for the other analytes. In these electrodes, detecting electrode patterns were formed on a glass substrate by photolithography and the micro container for the internal electrolyte solution was formed on a silicon substrate by anisotropic etching. A through-hole was formed in the sensitive area, where a silicone gas-permeable membrane was formed and an enzyme was immobilized. The sensors were characterized in terms of pH and temperature dependence and calibration curves along with detection limits. Furthermore, the sensors were incorporated in an acrylate flow cell. Simultaneous operation of these sensors was successfully conducted and distinct and stable responses were observed for respective sensors.     

FRET measurements of intracellular cAMP concentrations and cAMP analog permeability in intact cells

Real-time measurements of second messengers in living cells, such as cAMP, are usually performed by ratiometric fluorescence resonance energy transfer (FRET) imaging. However, correct calibration of FRET ratios, accurate calculations of absolute cAMP levels and actual permeabilities of different cAMP analogs have been challenging. Here we present a protocol that allows precise measurements of cAMP concentrations and kinetics by expressing FRET-based cAMP sensors in cells and modulating them with an inhibitor of adenylyl cyclase activity and a cell-permeable cAMP analog that fully inhibits and activates the sensors, respectively. Using this protocol, we observed different basal cAMP levels in primary mouse cardiomyocytes, thyroid cells and in 293A cells. The protocol can be generally applied for calibration of second messenger or metabolite concentrations measured by FRET, and for studying kinetics and pharmacological properties of their membrane-permeable analogs. The complete procedure, including cell preparation and FRET measurements, takes 3-6 d.     

Process adapted calibration improves fluorometric pH sensor precision in sophisticated fermentation processes

Miniaturization and automation have become increasingly popular in bioprocess development in recent years, enabling rapid high‐throughput screening and optimization of process conditions. In addition, advances in the bioprocessing industry have led to increasingly complex process designs, such as pH and temperature shifts, in microbial fed‐batch fermentations for optimal soluble protein expression in a range of hosts. However, in order to develop an accurate scale‐down model for bioprocess screening and optimization, small‐scale bioreactors must be able to accurately reproduce these complex process designs. Monitoring methods, such as fluorometric‐based pH sensors, provide elegant solutions for the miniaturization of bioreactors, however, previous research suggests that the intrinsic fluorescence of biomass alters the sigmoidal calibration curve of fluorometric pH sensors, leading to inaccurate pH control. In this article, we present results investigating the impact of biomass on the accuracy of a commercially available fluorometric pH sensor. Subsequently, we present our calibration methodology for more precise online measurement and provide recommendations for improved pH control in sophisticated fermentation processes.     

Calibration of avian molecular clocks

Molecular clocks can be calibrated using fossils within the group under study (internal calibration) or outside of the group (external calibration). Both types of calibration have their advantages and disadvantages. An internal calibration may reduce extrapolation error but may not be from the best fossil record, raising the issue of nonindependence. An external calibration may be more independent but also may have a greater extrapolation error. Here, we used the advantages of both methods by applying a sequential calibration to avian molecular clocks. We estimated a basal divergence within birds, the split between fowl (Galliformes) and ducks (Anseriformes), to be 89.8 +/- 6.97 MYA using an external calibration and 12 rate-constant nuclear genes. In turn, this time estimate was used as an internal calibration for three species-rich avian molecular data sets: mtDNA, DNA-DNA hybridization, and transferrin immunological distances. The resulting time estimates indicate that many major clades of modern birds had their origins within the Cretaceous. This supports earlier studies that identified large gaps in the avian fossil record and suggests that modern birds may have coexisted with other avian lineages for an extended period during the Cretaceous. The new time estimates are concordant with a continental breakup model for the origin of ratites.     

Fluorescent europium-modified polymer nanoparticles for rapid and sensitive anthrax sensors

Novel fluorescent polyacrylonitrile nanoparticles were synthesized by microemulsion polymerization and Schiff base modification. By further modification with europium, the polyacrylonitrile nanoparticles could be used as a highly sensitive and rapid sensor for Bacillus anthracis spore detection in aqueous solution. The europium-modified polyacrylonitrile nanoparticles were readily combined with dipicolinic acid as a unique biomarker of B. anthracis, leading to high fluorescence emission. These nanoparticles enabled ratiometric detection without instrument-specific calibration due to the internal fluorescence reference. Additionally, the europium-modified polyacrylonitrile nanoparticle sensors exhibited a remarkable limit of detection (10pM) for dipicolinic acid and outstanding selectivity (160×) over aromatic ligands in aqueous solution. The ultrafine nanoparticle sensor showed a high capability for detecting anthrax due to the increased surface area-to-volume ratio and enhanced dispersibility.     

Calibration-curve-free quantitative PCR: a quantitative method for specific nucleic acid sequences without using calibration curves

We have developed a simple quantitative method for specific nucleic acid sequences without using calibration curves. This method is based on the combined use of competitive polymerase chain reaction (PCR) and fluorescence quenching. We amplified a gene of interest (target) from DNA samples and an internal standard (competitor) with a sequence-specific fluorescent probe using PCR and measured the fluorescence intensities before and after PCR. The fluorescence of the probe is quenched on hybridization with the target by guanine bases, whereas the fluorescence is not quenched on hybridization with the competitor. Therefore, quench rate (i.e., fluorescence intensity after PCR divided by fluorescence intensity before PCR) is always proportional to the ratio of the target to the competitor. Consequently, we can calculate the ratio from quench rate without using a calibration curve and then calculate the initial copy number of the target from the ratio and the initial copy number of the competitor. We successfully quantified the copy number of a recombinant DNA of genetically modified (GM) soybean and estimated the GM soybean contents. This method will be particularly useful for rapid field tests of the specific gene contamination in samples.     

Multimedia information retrieval and environmental monitoring: Shared perspectives on data fusion

Computer-based remote monitoring of our environment is increasingly based on combining data derived from in-situ-sensors with data derived from remote sources, such as satellite images or CCTV. In such deployments it is necessary to continuously monitor the accuracy of each of the sensor data streams so that we can account for sudden failures of sensors, or errors due to calibration drive or biofouling. In multimedia information retrieval (MMIR), we search through archives of multimedia artefacts like video programs, by implementing several independent retrieval systems or agents, and we combine the outputs of each retrieval agent in order to generate an overall ranking. In this paper we draw parallels between these seemingly very different applications and show how they share several similarities. In the case of environmental monitoring we also need some mechanism by which we can establish the trust and reputation of each contributing sensor, though this is something we do not need in MMIR. In this paper we present an outline of a trust and reputation framework we have developed and deployed for monitoring the performance of sensors in a heterogeneous sensor network.     

Telomere length measurement in mouse chromosomes by a modified Q-FISH method

Telomeres are physical ends of mammalian chromosomes that dynamically change during the lifetime of a cell or organism. In order to understand mechanisms responsible for telomere dynamics, it is necessary to develop methods for accurate telomere length measurement. The most sensitive method for measuring telomere length in mouse chromosomes is quantitative fluorescence in situ hybridization (Q-FISH). The usual protocol for Q-FISH requires plasmids with variable numbers of telomeric repeats and fluorescence beads as calibration standards. Here, we describe a Q-FISH protocol in which two mouse lymphoma cell lines with well-defined telomere lengths are used as calibration standards. Using this protocol we demonstrate that reproducible results can be obtained in a set of four different mouse cell lines. This method can be adapted so that any pair of mammalian cell lines can serve as an internal calibration standard.     

Measuring clinically relevant knee motion with a self-calibrated wearable sensor

Low-cost sensors provide a unique opportunity to continuously monitor patient progress during rehabilitation; however, these sensors have yet to demonstrate the fidelity and lack the calibration paradigms necessary to be viable tools for clinical research. The purpose of this study was to validate a low-cost wearable sensor that accurately measured peak knee extension during clinical exercises and needed no additional equipment for calibration. Sagittal plane knee motion was quantified using a 9-axis motion sensor and directly compared to motion capture data. The motion sensor measured the field strength of a strong earth magnet secured to the distal femur, which was correlated with knee angle during a simple calibration process. Peak knee motions and kinematic patterns were compared with motion capture data using paired t-tests and cross correlation, respectively. Peak extension values during seated knee extensions were accurate within 5 degrees across all subjects (root mean square error: 2.6 degrees, P = 0.29). Knee flexion during gait strongly correlated (0.84 ≤ r_xy ≤ 0.99) with motion capture measurements but demonstrated peak flexion errors of 10 degrees. In this study, we present a low-cost sensor (≈$ 35 US) that accurately determines knee extension angle following a calibration procedure that did not require any other equipment. Our findings demonstrate that this sensor paradigm is a feasible tool to monitor patient progress throughout physical therapy. However, dynamic motions that are associated with soft-tissue artifact may limit the accuracy of this type of wearable sensor.     

Reversible and repeatable linear local cell force response under large stretches

Large stretching and un-stretching force response of adherent fibroblasts is measured by micromachined mechanical force sensors. The force sensors are composed of a probe and flexible beams. The probe, functionalized by fibronectin, is used to contact the cells. The flexible beams are the sensing element. The sensors are made of single crystal silicon and fabricated by the SCREAM process. The maximum cell stretch reached is approximately 50 microm, which is about twice of the cell initial size, and the time delay between two consecutive stretching/un-stretching steps is 75 s unless otherwise stated. We find that the force response of the cells is strongly linear, reversible, and repeatable, with a small stiffening at the initial deformation stage. Force response of single cells measured before and after cytochalasin D treatment suggests that actin filaments take almost all the cell internal forces due to stretch. These findings may shed light on the increasing understanding on the mechanical behavior of cells and provide clues for making new classes of biological materials having uncommon properties.     

Lifespan of subcutaneous glucose sensors and their performances during dynamic glycaemia changes in rats

Performances of a glucose sensor have been investigated during dynamic variations of plasma glucose levels. Subcutaneous glucose concentrations measured by the sensors were calculated by a one-point calibration, performed in basal conditions. A first group of sensors were chronically implanted in the subcutaneous tissue of normal rats. The animals were submitted to glucagon and insulin injection, in order to induce rapid modifications of their glycaemia. This test was repeated at different days after implantation in order to investigate the lifespan and the performance of the sensors. All the sensors were working 1 or 2 days after implantation, and 70% adequately responded to glycaemia variations at day 3 or 4. The quality of the sensors' performance remained constant as a function of the time. With a second group of sensors, we demonstrated that an efficient sterilization procedure did not alter the sensors' characteristics. At the day of implantation, the sterilized sensors' performance, during dynamic variations of plasma glucose levels, was closely similar to that of the non-sterilized sensors. The animals bearing the sterilized devices were rendered diabetic by steptozotocin (STZ) injection. Once the rats had developed a severe hyperglycaemia (1–3 days after STZ), they were injected with intravenous insulin. The subcutaneously implanted glucose sensors correctly followed the decline in plasma glucose levels. We therefore conclude that our sensor could represent a useful tool for short-term continuous blood monitoring.     

Simplified off-gas analyses in animal cell cultures for process monitoring and control purposes

Batch-to-batch reproducibility of animal cell cultures can significantly be enhanced using process control procedures. Most informative signals for advanced process control can be derived from the volume fractions of oxygen and carbon dioxide in the vent line of the reactors. Here we employed simple low-cost sensors, previously not considered for off-gas analysis at a laboratory-scale cell cultures, and compared them with a simultaneously used quadrupole mass spectrometer, i.e., the standard equipment. A decisive advantage is that the sensors did not need any calibration and are easy to use. We show that monitoring and advanced control of cell cultures can significantly be simplified using the devices tested here and that the same batch-to-batch reproducibility can be obtained with much less effort than before.     

高分一号宽幅多光谱影像辐射定标偏差及其植被指数影响

自2013年4月在轨运行以来,高分一号(GF-1)宽幅(WFV)多光谱相机已实现持续对地观测,为包括生态学在内的相关研究领域与行业应用提供了丰富的数据源。当前场地定标频次偏低以及定标参数更新、发布滞后的现状,一定程度上影响了GF-1 WFV多光谱数据的定量应用。然而,现有文献仅在数据预处理流程中谈及对GF-1 WFV影像的辐射定标处理,很少讨论定标参数选取不当甚至误用产生的可能影响。基于已公布的辐射定标参数(2014—2021年)和4景GF-1 WFV Level1A级影像产品数据,重点围绕辐射定标偏差及其对多光谱波段星上反射率和常用植被指数的影响等展开模型分析和讨论。结果显示：即使两个相邻年份间,在多数情况下误用辐射定标参数会导致不可忽视的波段星上反射率相对偏差;进而给不同类型植被指数的实际应用带来不同程度的挑战。因辐射定标偏差的影响,常用的两波段归一化型植被指数在监测稀疏植被覆盖区时会存在明显的误差;而对高植被覆盖区的监测时采用两波段简单比值型植被指数将面临更大的挑战。针对存档GF-1 WFV Level1A数据的应用需求,提出利用时间距离加权的线性内插法来修正基于公开定标参数的辐...     

Real-time dissolved carbon dioxide monitoring I: Application of a novel in situ sensor for CO2 monitoring and control

Dissolved carbon dioxide (dCO₂) is a well-known critical parameter in bioprocesses due to its significant impact on cell metabolism and on product quality attributes. Processes run at small-scale faces many challenges due to limited options for modular sensors for online monitoring and control. Traditional sensors are bulky, costly, and invasive in nature and do not fit in small-scale systems. In this study, we present the implementation of a novel, rate-based technique for real-time monitoring of dCO₂ in bioprocesses. A silicone sampling probe that allows the diffusion of CO₂ through its wall was inserted inside a shake flask/bioreactor and then flushed with air to remove the CO₂ that had diffused into the probe from the culture broth (sensor was calibrated using air as zero-point calibration). The gas inside the probe was then allowed to recirculate through gas-impermeable tubing to a CO₂ monitor. We have shown that by measuring the initial diffusion rate of CO₂ into the sampling probe we were able to determine the partial pressure of the dCO₂ in the culture. This technique can be readily automated, and measurements can be made in minutes. Demonstration experiments conducted with baker's yeast and Yarrowia lipolytica yeast cells in both shake flasks and mini bioreactors showed that it can monitor dCO₂ in real-time. Using the proposed sensor, we successfully implemented a dCO₂-based control scheme, which resulted in significant improvement in process performance.     

A simple and rapid method for electromagnetic field distortion correction when using two Fastrak sensors for biomechanical studies

The article presents a simple and rapid method for the correction of electromagnetic distortions when using electromagnetic Fastrak (Polhemus, USA) sensors. It is based on the minimization of objective functions composed of derivative polynomial functions, hence estimating the distortion of the electromagnetic field. The polynomial functions composing the objective function each contain 35 deformation coefficients. These coefficients are then used to correct the electromagnetic measures in position and orientation. Preliminary results on the efficacy of the method are presented for two subjects who walked on a treadmill, and for whom relative movement of the lower leg with respect to the thigh was recorded using two Fastrak sensors. The corrected Fastrak measurements were compared with optoelectronic measurements (Vicon, USA), which are not affected by distortions as electromagnetic sensors are. Results showed that after 3 min of calibrating a volume of approximately 1m(3), the method proved to be efficient in correcting errors in orientation (56% (2.72-1.12 degrees ), 78% (4.4-0.89 degrees ), and 56% (2.25-0.90 degrees ) of error reduction in the respective flexion/extension, ab/adduction and tibial internal/external rotation) and position (53% (18.9-8.9 mm), 21% (6.6-4.6mm), and 48% (15.9-8.1mm) of error reduction in the respective medial/lateral, anterior/posterior and proximal/distal translations) (values are overall means for two subjects and four calibration procedures). That amount of correction compared favorably with values presented in the literature.     

Real-time update of calibration model for better monitoring of batch processes using spectroscopy

In order to reduce the large calibration matrix usually required for calibrating multiwavelength optical sensors, a simple algorithm based on the addition in process of new standards is proposed. A small calibration model, based on 14 standards, is periodically updated by spectra collected on-line during fermentation operation. Concentrations related to these spectra are reconciled into best-estimated values, by considering carbon and oxygen balances. Using this method, fructose, acetate, and gluconacetan were monitored during batch fermentations of Gluconacetobacter xylinus 12281 using mid-infrared spectroscopy. It is shown that this algorithm compensates for noncalibrated events such as production or consumption of by-products. The standard error of prediction (SEP) values were 0.99, 0.10, and 0.90 g/L for fructose, acetate, and gluconacetan, respectively. By contrast, without an updating of the calibration model, the SEP values were 2.46, 0.92, and 1.04 g/L for fructose, acetate, and gluconacetan, respectively. Using only 14 standards, it was therefore possible to approach the performance of an 88-standard-based calibration model having SEP values of 1.11, 0.37, and 0.79 g/L for fructose, acetate, and gluconacetan, respectively. Therefore, the proposed algorithm is a valuable approach to reduce the calibration time of multiwavelength optical sensors.     

Biosensors for real-time in vivo measurements

The current status of sensors capable of continuous measurement of analytes in biological media is reviewed. This review containing 173 references deals with devices whose use in single cells, tissue slices, animal models and humans has been demonstrated. In addition to sensors specific for glucose, lactate, glutamate, pyruvate, choline and acetylcholine, insights obtained from monitoring nitric oxide, Na(+), K(+), Ca(2+), and dopamine are presented. Performance criteria for sensor performance are described as is the subject of biosensor calibration. Biocompatibility issues are dealt with in some detail as is the status of continuous blood glucose monitoring in humans.