Spatial Sensitivity Distribution Research Articles

Spatial filtering characteristics of electrostatic sensor matrix for local velocity measurement of pneumatically conveyed particles

The accuracy of local particle mean velocity measurement with spatial filtering method based on an electrostatic sensor matrix (ESM) is closely related to its sensitivity and spatial filtering characteristics. In this paper, the three-dimensional electrostatic field generated by a point charge in the sensing zone of the ESM is solved by using a finite element method to obtain the spatial sensitivity distributions of the ESM. Further a dimensionless calculation model for the sensitivity of the ESM is suggested based on a Cosine function. The numerical results demonstrate that the spatial sensitivity has a periodic distribution along the axial direction and its spatial periodicity is determined by the axial spacing between two adjacent electrodes. The sensitivity over the central cross-section is localized. The spatial filtering characteristics of the ESM are also investigated and verified by experiments on a gravity-fed rig. These results provide a basis for the optimized design of the ESM.

Identifying Model Inaccuracies and Solution Uncertainties in Noninvasive Activation-Based Imaging of Cardiac Excitation Using Convex Relaxation

Noninvasive imaging of cardiac electrical function has begun to move towards clinical adoption. Here, we consider one common formulation of the problem, in which the goal is to estimate the spatial distribution of electrical activation times during a cardiac cycle. We address the challenge of understanding the robustness and uncertainty of solutions to this formulation. This formulation poses a nonconvex, nonlinear least squares optimization problem. We show that it can be relaxed to be convex, at the cost of some degree of physiological realism of the solution set, and that this relaxation can be used as a framework to study model inaccuracy and solution uncertainty. We present two examples, one using data from a healthy human subject and the other synthesized with the ECGSIM software package. In the first case, we consider uncertainty in the initial guess and regularization parameter. In the second case, we mimic the presence of an ischemic zone in the heart in a way which violates a model assumption. We show that the convex relaxation allows understanding of spatial distribution of parameter sensitivity in the first case, and identification of model violation in the second.

Investigation into Spatial Sensitivity of Probe-Type Electrostatic Sensors for On-Line Condition Monitoring of Heat Engines

Probe-type electrostatic sensors provide a novel and applicable way to realize on-line condition monitoring of heat engines. However, researches on this type of electrostatic sensors are still scanty, especially needs more detailed studies for the sensors sensing characteristics. In this paper, a simulative 3-D model with high fidelity was established using COMSOL, by which a detailed research on probe-type electrostatic sensors spatial sensitivity was conducted, the whole spatial sensitivity distribution on the centre section and conclusions about the influencing factors of spatial sensitivity were acquired. The simulative results were confirmed by experiments, and can be used for optimal design of probe-type electrostatic sensors.

Characteristics analysis and experiment verification of electrostatic sensor for aero-engine exhaust gas monitoring

An electrostatic sensor is a critical component of the electrostatic monitoring system for an aero-engine gas path. In this paper, the basic principles of the electrostatic sensor are described and the materials selection process for sensor electrodes and an isolation medium is introduced. The finite element method was adopted to calculate the sensitivity distribution, and the influence of relevant structural parameters on the sensitivity distribution characteristic is analyzed. The data fitting method was employed to acquire the unified spatial sensitivity distribution functions for a given structure sensor, which provides a useful reference for the sensor’s installation location. Based on the unified function, the sensitivity distribution function along the particle moving direction and the frequency characteristic of the electrostatic sensor were acquired. Then the corresponding influence factors of the frequency properties were analyzed. An experiment platform was established to verify the model and the theoretical analysis results. Then, simulated experiments were applied to verify the feasibility and validity of the electrostatic sensor, and the experiment results provided a useful reference for the identification of abnormal particles as a characteristic of aero-engine faults.

Study on the spatial filtering and sensitivity characteristic of inserted electrostatic sensors for the measurement of gas–solid two-phase flow parameters

A velocity measuring method using an inserted electrostatic sensor with spatial filtering effects is obtained using the point charge mathematical model established in this paper. Employing the established mathematical model helps determine the spatial filtering and spatial sensitivity characteristics of the probe. The spatial sensitivity distribution is obtained by simulating the point charge mathematical model, and when the point charge is near the probe (a>0), the sensitivity of the probe is higher and the spatial sensitivity of the probe has symmetry. The relation between the probe length L inserted into a pipe and the charge induced on the probe can also be obtained using simulation, where the longer the probe length L is, the larger the signal amplitude is. However, the signal amplitude is almost invariant when the probe length L is larger than the radius of the pipe. Experiments prove that the spatial filtering and sensitivity characteristics of the probe are consistent with the simulation results. When the free fall velocity of particles is the same, the probe has a low-pass characteristic for the measured signals. It is proven that the fluid velocity measurement method using spatial filtering effects can completely measure the fluid velocity using the spatial filtering characteristic experiments of the probe. The spatial filtering measurement velocity method is also feasible when measuring continuous objects.

Sensing characteristics of conductance sensor for measuring the volume fraction and axial velocity in oil-water pipe flow

The output response characteristics, spatial sensitivity distribution, spatial filtering effect and frequency response characteristics are important parameters influencing the accuracy of conductance sensor for measuring the volume fraction and axial velocity in oil-water pipe flow. In this paper, the mathematical model of conductance sensor was established, and using the finite element analysis software ANSYS the finite element model was obtained. The analysis of output response characteristics of the sensor was performed with reference to different non-uniform mediums. The spatial sensitivity distribution was also investigated, and its spatial filtering effect was analysed quantitatively. On this basis the frequency response characteristics function was derived. With the optimised six-electrode conductance sensor, a two-phase flow measurement system was designed for oil well logging; and the experiments were performed. The results indicate that the measurement error of water volume fraction is ±3%, and the flow axial velocity can resolve the flowrate difference with 2 m3/d.

Three‐Dimensional Sensitivity Distribution and Sample Volume of Low‐Induction‐Number Electromagnetic‐Induction Instruments

There is an ongoing effort to improve the understanding of the correlation of soil properties with apparent soil electrical conductivity as measured by low‐induction‐number electromagnetic‐induction (LIN FEM) instruments. At a minimum, the dimensions of LIN FEM instruments' sample volume, the spatial distribution of sensitivity within that volume, and implications for surveying and analyses must be clearly defined and discussed. Therefore, a series of numerical simulations was done in which a conductive perturbation was moved systematically through homogeneous soil to elucidate the three‐dimensional sample volume of LIN FEM instruments. For a small perturbation with electrical conductivity similar to that of the soil, instrument response is a measure of local sensitivity (LS). Our results indicate that LS depends strongly on the orientation of the instrument's transmitter and receiver coils and includes regions of both positive and negative LS. Integration of the absolute value of LS from highest to lowest was used to contour cumulative sensitivity (CS). The 90% CS contour was used to define the sample volume. For both horizontal and vertical coplanar coil orientations, the longest dimension of the sample volume was at the surface along the main instrument axis with a length of about four times the intercoil spacing (s) with maximum thicknesses of about 1 and 0.3 s, respectively. The imaged distribution of spatial sensitivity within the sample volume is highly complex and should be considered in conjunction with the expected scale of heterogeneity before the use and interpretation of LIN FEM for mapping and profiling.

関東地方における夏季地表オゾン濃度のNO_x, VOC排出量に対する感度の地理分布 : 第II報 光化学指標の実測に基づく推定

関東地方における夏季地表オゾン濃度のNO_x, VOC排出量に対する感度の地理分布 : 第II報 光化学指標の実測に基づく推定

関東地方における夏季地表オゾン濃度のNO_x, VOC排出量に対する感度の地理分布 : 第I報 大小2種類の植物起源VOC排出量推定値を入力した場合の数値シミュレーションによる推定

関東地方における夏季地表オゾン濃度のNO_x, VOC排出量に対する感度の地理分布 : 第I報 大小2種類の植物起源VOC排出量推定値を入力した場合の数値シミュレーションによる推定

Experimental investigation of NIRS spatial sensitivity

Near infrared spectroscopy (NIRS) is regarded as a potential medical diagnostic technique for investigation of hemodynamic changes. However, uncertainties pertaining to the origin of NIRS signals have hampered its clinical interpretation. The uncertainities in NIRS measurements especially in case of living tissues are due to lack of rigorous combined theoretical-experimental studies resulting in clear understanding of the origin of NIRS signals. For their reliable interpretation it is important to understand the relationship between spatial changes in optical properties and corresponding changes in the NIRS signal. We investigated spatial sensitivity of near infrared optical measurements using an experimental approach. It uses a liquid optical phantom as tissue equivalent, which is explored under robot-control by a small, approximately point like perturbation of desired optical properties, and a NIRS instrument for trans-illumination/reflection measurements. The experimentally obtained sensitivity has been analyzed and compared with numerical simulations. In preliminary experiments we investigated the influence of various optical properties of the medium and of source/detector distances on the spatial sensitivity distribution. The acquired sensitivity maps can be used to define characteristic parameters. As an example, we used a 25% threshold to define a penetration depth measure which provides values in good accordance with published ones. To the best of our knowledge this is the first experimental study of NIRS spatial sensitivity. The presented method will allow in depth experimental investigation of the influence of various conditions pertaining to medium such as optical properties of tissue (scattering and absorption) and of the source/detector configuration.

Evaluation of the Performance of Small Diode Pumped UV Solid State (DPSS) Nd:YAG Lasers as New Radiation Sources for Atmospheric Pressure Laser Ionization Mass Spectrometry (APLI-MS)

The performance of a KrF* bench top excimer laser and a compact diode pumped UV solid state (DPSS) Nd:YAG laser as photo-ionizing source in LC-APLI MS is compared. The commonly applied bench-top excimer laser, operating at 248 nm, provides power densities of the order of low MW/cm(2) on an illuminated area of 0.5 cm(2) (8 mJ/pulse, 5 ns pulse duration, beam waist area 0.5 cm(2), 3 MW/cm(2)). The DPSS laser, operating at 266 nm, provides higher power densities, however, on a two orders of magnitude smaller illuminated area (60 μJ/pulse, 1 ns pulse duration, beam waist area 2 × 10(-3) cm(2), 30 MW/cm(2)). In a common LC-APLI MS setup with direct infusion of a 10 nM pyrene solution, the DPSS laser yields a significantly smaller ion signal (0.9%) and signal to noise ratio (1.4%) compared with the excimer laser. With respect to the determined low detection limits (LODs) for PAHs of 0.1 fmol using an excimer laser, LODs in DPSS laser LC-APLI MS in the low pmol regime are expected. The advantages of the DPSS laser with respect to applicability (size, cost, simplicity) may render this light source the preferred one for APLI applications not focusing on ultimately high sensitivities. Furthermore, the impact of adjustable ion source parameters on the performance of both laser systems is discussed in terms of the spatial sensitivity distribution described by the distribution of ion acceptance (DIA) measurements. Perspectives concerning the impact on future APLI-MS applications are given.

Quantitative conductivity and permittivity imaging of the human brain using electric properties tomography

The electric properties of human tissue can potentially be used as an additional diagnostic parameter, e.g., in tumor diagnosis. In the framework of radiofrequency safety, the electric conductivity of tissue is needed to correctly estimate the local specific absorption rate distribution during MR measurements. In this study, a recently developed approach, called electric properties tomography (EPT) is adapted for and applied to in vivo imaging. It derives the patient's electric conductivity and permittivity from the spatial sensitivity distributions of the applied radiofrequency coils. In contrast to other methods to measure the patient's electric properties, EPT does not apply externally mounted electrodes, currents, or radiofrequency probes, which enhances the practicability of the approach. This work shows that conductivity distributions can be reconstructed from phase images and permittivity distributions can be reconstructed from magnitude images of the radiofrequency transmit field. Corresponding numerical simulations using finite-difference time-domain methods support the feasibility of this phase-based conductivity imaging and magnitude-based permittivity imaging. Using this approximation, three-dimensional in vivo conductivity and permittivity maps of the human brain are obtained in 5 and 13 min, respectively, which can be considered a step toward clinical feasibility for EPT.

Spatial sensitivity of acousto-optic and optical near-infrared spectroscopy sensing measurements

Near-infrared spectroscopy (NIRS) is a popular sensing technique to measure tissue oxygenation noninvasively. However, the region of interest (ROI) is often beneath a superficial layer, which affects its accuracy. By applying focused ultrasound in the ROI, acousto-optic (AO) techniques can potentially minimize the effect of physiological changes in the superficial layer. Using absorption perturbation experiments in both transmission and reflection modes, we investigated the spatial sensitivity distributions and mean penetration depths of an AO system based on a digital correlator and two popular NIRS systems based on i. intensity measurements using a single source and detector configuration, and ii. spatially resolved spectroscopy. Our results show that for both transmission and reflection modes, the peak relative sensitivities of the two NIRS systems are near to the superficial regions, whereas those of the AO technique are near to the ROIs. In the reflection mode, when the ROI is deeper than 14 mm, the AO technique has a higher absolute mean sensitivity than the two NIRS techniques. As the focused ultrasound is moved deeper into the turbid medium, the mean penetration depth increases accordingly. The focused ultrasound can shift the peak relative sensitivity of the AO measurement toward its focused region.

Distribution of optokinetic sensitivity across the retina of mice in relation to eye orientation

We examined the effects of stimulus size and location on the mouse optokinetic response (OKR). To this end, we recorded initial OKRs elicited by a brief presentation of horizontally moving grating patterns of different vertical widths and locations in the visual field. Large-field stimuli generated large sustained OKRs, whereas visual stimuli of narrower vertical widths elicited weaker sustained responses at the later period (400–500 ms after the onset of stimulus motion). However, even stimuli of only 5° vertical width elicited detectable transient responses at the initial open-loop period (100–200 ms after the onset of stimulus motion). Presenting 5°-width stimuli at different vertical locations (−10° to +35° relative to the horizon) revealed the spatial distribution of optokinetic sensitivity across the retina. The most sensitive part of the visual field was located at +25°. In addition, we examined the vertical orientation of the eye under our stereotaxic set-up. We observed the optic disc using a hand-held fundus camera and determined the ocular orientation. All eye orientations were distributed in the range of +20–30° relative to the horizon (25.2±2.5°). Thus, the direction of the most sensitive visual field matched the angle of eye orientation. These findings indicate that the spatial distribution of visual field sensitivity to optokinetic stimuli coincides with the distribution of retinal ganglion cell density.

Determination of Electric Conductivity and Local SAR Via B1 Mapping

The electric conductivity can potentially be used as an additional diagnostic parameter, e.g., in tumor diagnosis. Moreover, the electric conductivity, in connection with the electric field, can be used to estimate the local SAR distribution during MR measurements. In this study, a new approach, called electric properties tomography (EPT) is presented. It derives the patient's electric conductivity, along with the corresponding electric fields, from the spatial sensitivity distributions of the applied RF coils, which are measured via MRI. Corresponding numerical simulations and initial experiments on a standard clinical MRI system underline the principal feasibility of EPT to determine the electric conductivity and the local SAR. In contrast to previous methods to measure the patient's electric properties, EPT does not apply externally mounted electrodes, currents, or RF probes, thus enhancing the practicality of the approach. Furthermore, in contrast to previous methods, EPT circumvents the solution of an inverse problem, which might lead to significantly higher spatial image resolution.

Investigation of detection limits for diffuse optical tomography systems: I. Theory and experiment

We present a statistical test using simulated photon migration data and a noise model derived from the hardware of a particular diffuse optical tomography system to predict its detection limits. Our method allows us to assess the spatial distribution of the detection sensitivity of arbitrary geometries and noise without requiring phantom measurements and reconstructions. We determine the minimal detectable lesion size at selected lesion positions and compare the predicted results with phantom measurements carried out in a cup geometry.

Spinal cord functional MRI at 3 T: Gradient echo echo-planar imaging versus turbo spin echo

The purpose of this study was to evaluate and compare turbo spin echo (TSE) with gradient echo echo-planar imaging (GE-EPI) pulse sequences for functional magnetic resonance imaging (fMRI) of spinal cord activation at 3 T field strength. Healthy volunteers underwent TSE and GE-EPI spinal fMRI. The activation paradigm comprised the temporal alternation of finger motion and rest. Pulse sequences were optimized to obtain sufficient image quality and optimal sensitivity to small T 2 or T 2⁎ relaxation time changes. Spinal cord activation measured by the two pulse sequences was evaluated with respect to spatial distribution of activation, signal sensitivity, and reproducibility. For the GE-EPI sequence, fMRI activation was maximal in the spinal cord segments at the levels of the fifth cervical down to the first thoracic vertebra. For the TSE sequence, fMRI measurements showed no distinct location with maximal activation. Percentage signal change and number of activated voxels were approximately twice as high for GE-EPI compared to TSE fMRI. Reproducibility of the signal changes was much better for GE-EPI than for TSE imaging. To conclude, multi-subjects averaged GE-EPI is more location specific for blood-oxygen-level-dependent (BOLD) activation, more sensitive, and is suggested to be more reproducible than TSE fMRI.

Study on the spatial differences and its time lag effect on climatic factors of the vegetation in the Longitudinal Range-Gorge Region

This article analyzes the correlation of NDVI and two meteorological data including temperature and precipitation, and probes the spatial pattern of responding sensitivity of the vegetation to temperature and precipitation change. By constructing the NDVIr index, the relation between vegetation cover and land use in the Longitudinal Range-Gorge Region (LRGR) is revealed. The conclusion is as follows: (1) The time lag effect that vegetation responds to temperature and precipitation change is proven. Different regions have different delay time corresponding to maximum correlation coefficient. According to response time of precipitation and temperature combination, three kinds of temperature-precipitation forms are defined, namely, precipitation and temperature in the same time, precipitation prior to temperature and temperature prior to precipitation. (2) The spatial distribution of sensitivity, of which vegetation responses to temperature, is characterized by several high and low scattered correlation centers. Different from temperature, two insensitive regions and two sensitive belts are formed to present the response of vegetation to precipitation. (3) The NDVIr is constructed, which can perfectly reflect the corresponding relationship between meteorological factors and land use condition in the LRGR.

Parallel Magnetic Resonance Imaging

Parallel MRI started with the introduction of coil arrays in improving radiofrequency (RF) acquisition (what is called parallel imaging) and continued with an analogous development for RF transmission (parallel transmission). Based on differences in the spatial sensitivity distributions of the involved array elements, both techniques try to shorten the respective k-space trajectory. Parallel imaging refers to the acquisition of k-space data, whereas parallel transmission is dealing with the deposition of RF energy packages in the excitation k-space. However, parallel transmission is not simply the reciprocal of parallel imaging. The main goal of parallel imaging is the shortening of the acquisition time. The main goal of parallel transmission is the shortening of the pulse duration of spatially selective RF pulses. The present article describes the basic concept, the state of the art, and the similarities and differences of both technologies.

Quantifying energy savings in daylight responsive systems: The role of dimming electronic ballasts

The application of lighting control technologies with photosensors has led to an increase in public interest. Although these technologies have been promoted during the last years their successful use in buildings has been accomplished in a small percentage of new projects. One reason is the difficulty in quantifying the energy savings and thus the subsequent payback period. Daylight responsive dimming systems consist of three basic components: photosensor, controller, and dimming unit. Electronic dimming ballast (EDB) is one substantial component of these lighting control systems which can adjust the light output due to the transferred signal from the photosensor and lighting controller. The aim of this study is to quantify energy savings among different EDBs. Eighteen commercial EDBs were selected and various sets of electrical and illuminance measurements were taken for different dimming levels, in order to develop polynomial functions between light output and consumed power. Using the measured data, a set of simulations were performed for a photosensor with an ideal cosine spatial sensitivity distribution installed in a typical office room using two control algorithms, closed loop and integral reset, trying to quantify the relative differences in energy savings.