Data Acquisition Interval Research Articles

An efficient numerical and experimental system identification approach for a flexible manipulator

Purpose – The purpose of this paper is to propose an efficient and straightforward approach for system identification of a rotating single link flexible manipulator (RSLFM). Also, the achieved results are experimentally validated through identification procedure. Design/methodology/approach – The proposed system identification approach is applied to a RSLFM with a tip mass. At first, the dynamic model of the system is derived using Lagrange method. Then, an efficient method is developed for identification of such a system. This method facilitates the nonlinear complicated identification problem of the RSLFM to a simplified root finding problem. Findings – The main advantage of the developed method is to convert a complicated system identification process to a simple nonlinear equation solution. This approach uses small-size input/output data set and requires a short-time interval of data acquisition, which gives important advantages in lower computational load and lower execution time. The investigated approach is studied on experimental system identification of a single link flexible manipulator. To demonstrate this fact, the developed method is successfully applied in identification of two other mechanical systems; the inverted pendulum on a cart and the ball and beam apparatus. Originality/value – In this work, the proposed identification approach has been originally applied to a RSLFM and two other mechanical examples. All obtained identification results show the performance and applicability of the developed method clearly. This approach is not restricted in using state space or transfer function. It has significant superiority in comparison with other known approaches including autoregressive with exogenous input (ARX) and Box-Jenkins (BJ).

Role of time scales for the non-Gaussianity of the Brownian motion combined with intermittent adsorption

Single-molecule tracking data near solid surfaces contain information on diffusion that is potentially affected by adsorption. However, molecular adsorption can occur in an intermittent manner, and the overall phenomenon is regarded as slower yet normal diffusion if the time scale of each adsorption event is sufficiently shorter than the interval of data acquisition. We compare simple numerical model systems that vary in the time scale of adsorption event while sharing the same diffusion coefficient, and show that the shape of the displacement distribution depends on the time resolution. We also evaluate the characteristics by statistical quantities related to the large deviation principle. We show that the characteristic time scale of the intermittent phenomena is elucidated when the time resolution of the observation is sufficiently fine and the amount of data is sufficiently large to evaluate the intermittency.

Estimation and Compensation of Phase Shifts in SAR Focusing of Spotlight Data Acquired With Discrete Antenna Steering

Modern spaceborne synthetic aperture radar sensors are able to operate the spotlight mode to achieve very high resolution images at microwave frequencies. This mode is characterized by antenna steering to increase the illumination interval. The steering is carried out by beam switching on bursts during the data acquisition interval. In addition to an unavoidable spectrum modulation in azimuth, phase shifts can occur from burst to burst. In this letter, we describe the problem and a procedure able to estimate the phase shifts based on the image contrast maximization technique for subsequent compensation at the data focusing stage. Results on real data acquired by the COSMO-SkyMed sensor demonstrate the effectiveness of the proposed solution.

Strategies for improved 3D small‐tip fast recovery imaging

PurposeSmall‐tip fast recovery (STFR) imaging is a recently proposed steady‐state sequence that has similar image contrast as balanced steady‐state free precession but has the potential to simultaneously remove banding artifacts and transient fluctuation. STFR relies on a “tip‐up” radiofrequency (RF) pulse tailored to the accumulated phase during the free precession (data acquisition) interval, designed to bring spins back to the longitudinal axis, thereby preserving transverse magnetization as longitudinal magnetization for the next pulse repetition time. We recently proposed an RF‐spoiled STFR sequence suitable for thin slab imaging, however, in many applications, e.g., functional magnetic resonance imaging or isotropic‐resolution structural imaging, three‐dimensional (3D) steady‐state imaging is desirable. Unfortunately, 3D STFR imaging is challenging due to the need for 3D tailored RF pulses. Here, we propose new strategies for improved 3D STFR imaging, based on (i) unspoiled imaging, and (ii) joint design of nonslice‐selective tip‐down/tip‐up RF pulses.Theory and MethodsWe derive an analytic signal model for the proposed unspoiled STFR sequence, and propose two strategies for designing the 3D tailored tip‐down/tip‐up RF pulses. We validate the analytic results using phantom and in vivo imaging experiments.ResultsOur analytic model and imaging experiments demonstrate that the proposed unspoiled STFR sequence is less sensitive to tip‐up excitation error compared to the corresponding spoiled sequence, and may, therefore, be an attractive candidate for 3D imaging. The proposed “joint” RF pulse design method, in which we formulate the tip‐down/tip‐up RF pulse design task as a magnitude least squares problem, produces modest improvement over a simpler “Separate” design approach. Using the proposed unspoiled sequence and joint RF pulse design, we demonstrate proof‐of‐principle 3D STFR brain images with balanced steady‐state free precession‐like signal properties but with reduced banding.ConclusionUsing the proposed unspoiled sequence and joint RF pulse design, STFR brain images in a 3D region of interest with balanced steady‐state free precession‐like signal properties but with reduced banding can be obtained. Magn Reson Med 72:389–398, 2014. © 2013 Wiley Periodicals, Inc.

Characteristics of Displacement Data Due to Time Scale for the Combination of Brownian Motion with Intermittent Adsorption

Single-molecule tracking data near solid surfaces contains information on diffusion that is potentially affected by adsorption. However, molecular adsorption can occur in an intermittent manner, and the overall phenomenon is regarded as slower yet normal diffusion if the time scale of each adsorption event is sufficiently shorter than the interval of data acquisition. We compare simple numerical model systems that vary in the time scale of adsorption event while sharing the same diffusion coefficient, and show that the shape of the displacement distribution depends on the time resolution. We also evaluate the characteristics by statistical quantities related to the large deviation principle.

Strategies for improved 3D small-tip fast recovery imaging.

Small-tip fast recovery (STFR) imaging is a recently proposed steady-state sequence that has similar image contrast as balanced steady-state free precession but has the potential to simultaneously remove banding artifacts and transient fluctuation. STFR relies on a "tip-up" radiofrequency (RF) pulse tailored to the accumulated phase during the free precession (data acquisition) interval, designed to bring spins back to the longitudinal axis, thereby preserving transverse magnetization as longitudinal magnetization for the next pulse repetition time. We recently proposed an RF-spoiled STFR sequence suitable for thin slab imaging, however, in many applications, e.g., functional magnetic resonance imaging or isotropic-resolution structural imaging, three-dimensional (3D) steady-state imaging is desirable. Unfortunately, 3D STFR imaging is challenging due to the need for 3D tailored RF pulses. Here, we propose new strategies for improved 3D STFR imaging, based on (i) unspoiled imaging, and (ii) joint design of nonslice-selective tip-down/tip-up RF pulses. We derive an analytic signal model for the proposed unspoiled STFR sequence, and propose two strategies for designing the 3D tailored tip-down/tip-up RF pulses. We validate the analytic results using phantom and in vivo imaging experiments. Our analytic model and imaging experiments demonstrate that the proposed unspoiled STFR sequence is less sensitive to tip-up excitation error compared to the corresponding spoiled sequence, and may, therefore, be an attractive candidate for 3D imaging. The proposed "joint" RF pulse design method, in which we formulate the tip-down/tip-up RF pulse design task as a magnitude least squares problem, produces modest improvement over a simpler "Separate" design approach. Using the proposed unspoiled sequence and joint RF pulse design, we demonstrate proof-of-principle 3D STFR brain images with balanced steady-state free precession-like signal properties but with reduced banding. Using the proposed unspoiled sequence and joint RF pulse design, STFR brain images in a 3D region of interest with balanced steady-state free precession-like signal properties but with reduced banding can be obtained.

The Pattern and Pace of Hyperacute Hemorrhage Expansion

Intracerebral hemorrhage (ICH) expansion is common during the first 24h after onset, but the pattern and pace of hyperacute hemorrhage growth have not been described because serial imaging is typically performed over the course of hours and days, not minutes. The purpose of this study is to elucidate the spatial and temporal characteristics of hyperacute hemorrhage expansion within minutes of ICH onset. An 86-year-old man with probable cerebral amyloid angiopathy developed an ICH while in the MRI scanner. Hyperacute hemorrhage growth was captured at three time points over a 14-min interval of MRI data acquisition and at fourth time point with CT 22h later. MRI and CT datasets were spatially coregistered, and three-dimensional models of ICH expansion were generated. Longitudinal analysis revealed that the spatial pattern of ICH growth was asymmetric at each time point. Maximal expansion occurred along the anterior-posterior plane during the first 4min but along the superior-inferior plane during the next 10min. The temporal pace of ICH expansion was also non-uniform, as growth along the anterior-posterior plane outpaced medial-lateral growth during the first 4min (2.8 vs. 2.5cm), but medial-lateral growth outpaced anterior-posterior growth over the next 10min (1.0 vs. 0.2cm). We provide evidence for asymmetric, non-uniform expansion of a hyperacute hemorrhage. These serial imaging observations suggest that hemorrhage expansion may be caused by local cascades of secondary vessel rupture as opposed to ongoing bleeding from a single ruptured vessel.

Time spatial labeling inversion pulse cerebral MR angiography without subtraction by use of dual inversion recovery background suppression

Time-spatial labeling inversion pulse (time-SLIP), which is a technique of nonenhanced magnetic resonance angiography (MRA) based on arterial spin labeling (ASL), is used in various situations. Although subtraction between the images obtained with and without ASL is usually employed in cerebral time-SLIP MRA, to reduce the imaging time, dual inversion recovery (IR) has been applied for suppression of the background signals in this study. Appropriate timings for the 1st IR, 2nd IR, and the interval of data acquisition were investigated using computer simulation and a phantom experiment. With a short interval of data acquisition, the visibility of the simulated vessel was inadequate because replacement of the suppressed flow was insufficient. With a long interval of data acquisition, the contrast between the vessel and background was reduced. The reasons for this appeared to be the following: the longitudinal magnetization of the replaced flow is reduced because of the prolonged 2nd inversion time, causing a mismatch of the null point between the calculated and the actual values to become prominent. As a result, 3-4 s seemed to be an appropriate interval for data acquisition. Sufficient angiographic information could be obtained by use of dual IR background suppression in a volunteer study. With this technique, cerebral time-SLIP MRA can be performed in half of the imaging time required with the conventional subtraction technique.

Analysis of influence of measurement conditions on repeatable results of thermal diffusivity of ceramic moulds designed for manufacturing the superalloys castings

The article presents the study results concerning development of methodology for measuring thermal diffusivity with the laser-flash method with special attention being paid to their repeatability. The first stage involved the literature review of the problem determining an influence of variable measurement parameters including presence of graphite coating, error correction methods and laser power. The main part of the study includes evaluation of the sample structure influence. A real ceramic mould of specific porosity and green compacts made after its grinding were examined. Influence of sample thickness and interval between individual laser shots were also determined. The analysis was performed by using the Netzsch LFA 427 instrument designed for direct measurement of thermal diffusivity with the laser-flash method. The material analysed included different types of ceramic moulds designed for manufacturing the elements made of nickel based superalloys. The preliminary study performed showed that the main factor that has an influence on obtaining correct and repeatable results of thermal diffusivity study is proper preparation of samples i.e. using them in a form of directly cut out from the mould, selection of data acquisition time and interval between individual shots. It is especially important in the case of measurements taken at high temperature when radiation mechanism of heat transfer is of basic significance.

124I PET-Based 3D-RD Dosimetry for a Pediatric Thyroid Cancer Patient: Real-Time Treatment Planning and Methodologic Comparison

Patient-specific 3-dimensional radiobiologic dosimetry (3D-RD) was used for (131)I treatment planning for an 11-y-old girl with differentiated papillary thyroid cancer, heavy lung involvement, and cerebral metastases. (124)I PET was used for pharmacokinetics. Calculation of the recommended administered activity, based on lung toxicity constraints, was performed in real time (i.e., during the data-acquisition interval). The results were available to the physician in time to influence treatment; these estimates were compared with conventional dosimetry methodologies. In subsequent, retrospective analyses, the 3D-RD calculations were expanded to include additional tumor dose estimates, and the conventional methodologies were reexamined to reveal the causes of the differences observed. A higher recommended administered activity than by an S-value-based method with a favorable clinical outcome was obtained. This approach permitted more aggressive treatment while adhering to patient-specific lung toxicity constraints. A retrospective analysis of the conventional methodologies with appropriate corrections yielded absorbed dose estimates consistent with 3D-RD.

Measuring Storm Surge with an Airborne Wide-Swath Radar Altimeter

Abstract Over the years, hurricane track forecasts and storm surge models, as well the digital terrain and bathymetry data they depend on, have improved significantly. Strides have also been made in the knowledge of the detailed variation of the surface wind field driving the surge. The area of least improvement has been in obtaining data on the temporal/spatial evolution of the mound of water that the hurricane wind and waves push against the shore to evaluate the performance of the numerical models. Tide gauges in the vicinity of the landfall are frequently destroyed by the surge. Survey crews dispatched after the event provide no temporal information and only indirect indications of the maximum water level over land. The landfall of Hurricane Bonnie on 26 August 1998, with a surge less than 2 m, provided an excellent opportunity to demonstrate the potential benefits of direct airborne measurement of the temporal/spatial evolution of the water level over a large area. Despite a 160-m variation in aircraft altitude, an 11.5-m variation in the elevation of the mean sea surface relative to the ellipsoid over the flight track, and the tidal variation over the 5-h data acquisition interval, a survey-quality global positioning system (GPS) aircraft trajectory allowed the NASA scanning radar altimeter carried by a NOAA hurricane research aircraft to demonstrate that an airborne wide-swath radar altimeter could produce targeted measurements of storm surge that would provide an absolute standard for assessing the accuracy of numerical storm surge models.

Line-Source Based X-Ray Tomography

Current computed tomography (CT) scanners, including micro-CT scanners, utilize a point x-ray source. As we target higher and higher spatial resolutions, the reduced x-ray focal spot size limits the temporal and contrast resolutions achievable. To overcome this limitation, in this paper we propose to use a line-shaped x-ray source so that many more photons can be generated, given a data acquisition interval. In reference to the simultaneous algebraic reconstruction technique (SART) algorithm for image reconstruction from projection data generated by an x-ray point source, here we develop a generalized SART algorithm for image reconstruction from projection data generated by an x-ray line source. Our numerical simulation results demonstrate the feasibility of our novel line-source based x-ray CT approach and the proposed generalized SART algorithm.

Radiation surveillance using an unmanned aerial vehicle

Radiation surveillance equipment was mounted in a small unmanned aerial vehicle. The equipment consists of a commercial CsI detector for count rate measurement and a specially designed sampling unit for airborne radioactive particles. Field and flight tests were performed for the CsI detector in the area where 137Cs fallout from the Chernobyl accident is 23–45 kBq m −2. A 3-GBq 137Cs point source could be detected at the altitude of 50 m using a flight speed of 70 km h −1 and data acquisition interval of 1 s. Respective response for 192Ir point source is 1 GBq. During the flight, the detector reacts fast to ambient external dose rate rise of 0.1 μSv h −1, which gives for the activity concentration of 131I less than 1 kBq m −3. Operation of the sampler equipped with different type of filters was investigated using wind-tunnel experiments and field tests with the aid of radon progeny. Air flow rate through the sampler is 0.2–0.7 m 3 h −1 at a flight speed of 70 km h −1 depending on the filter type in question. The tests showed that the sampler is able to collect airborne radioactive particles. Minimum detectable concentration for transuranium nuclides, such as 239Pu, is of the order of 0.2 Bq m −3 or less when alpha spectrometry with no radiochemical sample processing is used for activity determination immediately after the flight. When a gamma-ray spectrometer is used, minimum detectable concentrations for several fission products such as 137Cs and 131I are of the order of 1 Bq m −3.

A data acquisition and control system for high-speed gamma-ray tomography

A data acquisition and control system (DACS) for high-speed gamma-ray tomography based on the USB (Universal Serial Bus) and Ethernet communication protocols has been designed and implemented. The high-speed gamma-ray tomograph comprises five 500 mCi 241Am gamma-ray sources, each at a principal energy of 59.5 keV, which corresponds to five detector modules, each consisting of 17 CdZnTe detectors. The DACS design is based on Microchip's PIC18F4550 and PIC18F4620 microcontrollers, which facilitates an USB 2.0 interface protocol and an Ethernet (IEEE 802.3) interface protocol, respectively. By implementing the USB- and Ethernet-based DACS, a sufficiently high data acquisition rate is obtained and no dedicated hardware installation is required for the data acquisition computer, assuming that it is already equipped with a standard USB and/or Ethernet port. The API (Application Programming Interface) for the DACS is founded on the National Instrument's LabVIEW® graphical development tool, which provides a simple and robust foundation for further application software developments for the tomograph. The data acquisition interval, i.e. the integration time, of the high-speed gamma-ray tomograph is user selectable and is a function of the statistical measurement accuracy required for the specific application. The bandwidth of the DACS is 85 kBytes s−1 for the USB communication protocol and 28 kBytes s−1 for the Ethernet protocol. When using the iterative least square technique reconstruction algorithm with a 1 ms integration time, the USB-based DACS provides an online image update rate of 38 Hz, i.e. 38 frames per second, whereas 31 Hz for the Ethernet-based DACS. The off-line image update rate (storage to disk) for the USB-based DACS is 278 Hz using a 1 ms integration time. Initial characterization of the high-speed gamma-ray tomograph using the DACS on polypropylene phantoms is presented in the paper.

ADM1 application for tuning and performance analysis of a multi-model observer-based estimator

Anaerobic digestion model no.1 (ADM1) was used for tuning and performance analysis of the multi-model observer based estimator (mmOBE). The mmOBE was based on the variable structure model (VSM) of the anaerobic digestion model, which consists of several local submodels, each of which describes a typical process state. Depending on the hydraulic retention time, ADM1 simulated the methanogenic, organic overload, and acidogenic states of the process. These simulations allowed for optimising tunable parameters of the mmOBE. Owing to relatively slow process dynamics, a data acquisition interval as large as one day was sufficient to obtain acceptable accuracy. The simulations of mmOBE performance showed excellent rate of mmOBE convergence to ADM1 outputs. Moreover, mmOBE successfully estimated key kinetic parameters, such as maximal transformation rates of CODs, VFAs, and methane. These estimations can be used in the development of the advanced knowledge-based process system, which uses both available measurements and estimations of key kinetic parameters for extended diagnosis of failures and process trend analysis.

A Task Model to Reduce Control Delays

Industrial control applications are usually developed in two phases: control design and real-time system implementation. In the control design stage a regulator is obtained and later it is translated into an algorithm in the implementation phase. Traditionally, these two phases have been developed in separate ways. Recently, some works have pointed out the necessity of the integration of the control design and its implementation. One of these works reduce the delay variance of control tasks (defined as the control action interval (CAI) and data acquisition interval (DAI) parameters) splitting every task into three parts. The CAI reduction method highly reduces the delay variance and improves the control performance. This work shows how to evaluate these delays under static and dynamic scheduling policies. A new task model is proposed in order to reduce the CAI and DAI parameters, which implies an improvement in the control performance. The new task model will be implemented in a real process, and the experimental measurements will show how, effectively, the control performance is highly improved with the methods presented in this paper.

INFERRING SUBSURFACE MORPHOLOGY FROM TRANSIENT SOIL MOISTURE PATTERNS USING ELECTRICAL CONDUCTIVITY

A non–intrusive survey method was developed that examined the relationships among spatial and temporal variations of soil water content, soil texture, and bulk electrical conductivity (ECa) in a 7.5 ha research watershed in southwestern Tennessee. Our goal was to identify areas that may exhibit rapid movement of subsurface moisture, as this is a precursor of offsite agrochemical migration. The survey protocol identified similar and dissimilar temporal variations in ECa patterns. Repeated spatial measurements of ECa, starting at near field capacity and then progressing through the draining and drying process, supplied visually shifting ECa patterns that correspond to dynamic soil moisture variations and subsurface morphology transitions. We noted that spatial ECa patterns for a field remained somewhat analogous across data gathering events, shifting in relative amplitude along with seasonal moisture levels. For this study, we considered soil morphology constant over the short data acquisition interval, with short–term subsurface moisture variations as the parameter primarily influencing ECa changes. We inferred soil morphology as the major factor for ECa pattern similarity across time. Follow–up soil coring analysis along two separate low–to–high ECa transects supported this assumption for this site.

Appropriate 3-Dimensional Echocardiography Data Acquisition Interval for Left Ventricular Volume Quantification: Implications for Clinical Application

Volume-rendered 3-dimensional echocardiography (3DE) acquired with small imaging intervals has been validated for accurate left ventricular (LV) volume measurement. However, its clinical application is often impeded by the lengthy acquisition time. The aim of this study was to examine the accuracy of LV volume measurement from 3DE data acquired at different intervals. Methods: Transthoracic 3DE LV data sets were acquired at intervals of 2°, 6°, 9°, 12°, 15°, 18°, and 20° in 10 human subjects with various cardiac shapes and function. The LV end-diastolic volume and end-systolic volume were measured from each 3DE data set with the “summation of disks” method. Interobserver and intraobserver variability were also examined. Measurements obtained from data acquired at 2° intervals were used as references for comparison. Results: From 10 subjects a total of 70 3DE data sets were obtained. Data acquisition time decreased from 189 ± 143 seconds at intervals of 2° to 19 ± 6 minutes at 20°. No statistically significant difference was found among the measurements derived from data obtained at various intervals. Excellent agreement was obtained between interobserver and intraobserver measurements. Conclusion: Data acquired at 12° and 15° intervals remained accurate for LV volume measurement and saved over 80% of time in comparison with data acquired at 2° intervals. A further increase in imaging intervals tended to underestimate LV volumes without significant acceleration of the procedure. (J Am Soc Echocardiogr 1999;12:1053-7.)

Transcutaneous renal function monitor: precision during unsteady hemodynamics.

Hospital acquired renal dysfunction, most commonly caused by renal hypoperfusion, dramatically increases mortality in intensive care patients. Glomerular filtration rate (GFR) is rapidly altered during renal hypoperfusion, and a more rapid means of GFR measurement may prompt institution of renal-specific therapy. We hypothesized that a transcutaneous renal function monitor can rapidly and accurately assess acute changes in GFR within a time frame much shorter than the 2-4 hours currently available. The study design was a prospective determination of the capability to measure GFR transcutaneously. In three different studies, concurrent transcutaneous measurement of GFR, using the rate of disappearance of 99mTc-diethylenetriaminepentaacetic acid (DTPA), was compared by correlation and standard deviation (SD) to reference standards of DTPA plasma clearance, serum inulin clearance, or serum creatinine. Continuous transcutaneous clearance (TC) measurement correlated with standard DTPA plasma clearance techniques (r = 0.93). Acute pharmacologically induced changes in GFR are detectable by TC measurement within 12-20 min, a time interval significantly affected by the data acquisition interval. Excess patient movement in the ICU patients created clearance artifacts in 50% of clearance traces. Retrospective analysis of ICU patient data reveal TC measurements are 93% specific and 92% sensitive for serum creatinine levels in critically ill patients. TC monitoring provides prompt indication of directional changes in GFR and may provide the clinician warning of inadequate resuscitation. Prospective analysis of the specificity, sensitivity, and TC guided renal-specific resuscitation is needed.

RARE spiral T2‐weighted imaging

Spiral imaging has a number of advantages for fast imaging, including an efficient use of gradient hardware. However, inhomogeneity -induced blurring is proportional to the data acquisition duration. In this paper, we combine spiral data acquisition with a RARE echo train. This allows a long data acquisition interval per excitation, while limiting the effects of inhomogeneity. Long spiral k-space trajectories are partitioned into smaller, annular ring trajectories. Each of these annular rings is acquired during echoes of a RARE echo train. The RARE refocusing RF pulses periodically refocus off-resonant spins while building a long data acquisition. We describe both T2-weighted single excitation and interleaved RARE spiral sequences. A typical sequence acquires a complete data set in three excitations (32 cm FOV, 192 x 192 matrix). At a TR = 2000 ms, we can average two acquisitions in an easy breath-hold interval. A multifrequency reconstruction algorithm minimizes the effects of any off-resonant spins. Though this algorithm needs a field map, we demonstrate how signal averaging can provide the necessary phase data while increasing SNR. The field map creation causes no scan time penalty and essentially no loss in SNR efficiency. Multiple slice, 14-s breath-hold scans acquired on a conventional gradient system demonstrate the performance.