Precision Of Length Measurements Research Articles

Thermally induced refractive index fluctuations in transmissive optical components and their influence on the sensitivity of Einstein telescope

With a relative length measurement precision of better than 10−23, gravitational wave interferometers are the most precise instruments that have ever been built. With this enormous sensitivity many noise sources potentially effect gravitational wave detector sensitivity, each of which must be investigated to ensure confidence in design sensitivity. We present calculations of photoelastic noise as well as thermo refractive noise in the beam splitter and the input test masses in Einstein telescope (ET). It turns out that the amplitude of the photoelastic noise in the ET low-frequency detector is about five orders of magnitude below the maximum design sensitivity and five orders of magnitude below that of the ET high-frequency detector, whereas thermo refractive noise impairs the design sensitivity by approximately 20%.

A comparison of calibration methods and system configurations of underwater stereo-video systems for applications in marine ecology

Stereo-video systems are used by marine ecologists to count and measure the size of aquatic organisms.Most marine ecologists are not experts in underwater photogrammetry and are not necessarily aware of someof the key design and implementation issues that influence the accuracy and precision of the measurements.Two factors that can influence the measurement accuracy and precision of a stereo-video system are the cali-bration strategy and the physical orientation of the system. We compare the accuracy and precision of lengthmeasurements made by systems calibrated using two regularly used calibration approaches. We also comparelength measurements recorded from cameras with base separations of 150 mm, 400 mm, and 800 mm. Athree-dimensional (3D), network calibration method using a purpose built calibration cube was used to deter-mine key calibration and camera orientation parameters (e.g., base separation, focal length, and lens distor-tions) with much improved precision in comparison to a two-dimensional method using either an A3 or A4planar calibration pattern. As a result, measurements made with a 3D cube displayed improved accuracy andprecision compared to either the A3 or A4 planar calibration pattern across a range of typical operational dis-tances. The distance between the cameras on the base bar (base separation) affects the accuracy and precisionof measurements with the 800 mm system producing length estimates of improved accuracy and precisionthan the systems with narrower baselines. The 150 mm system resulted in measurements with poor precisionand accuracy, especially for measurements made at distances greater than six meters.

Coordinate measuring method with two operation modes based on the adjustable articulated arms

A coordinate measuring method with two operation modes, based on the adjustable articulated arms, is proposed to keep measurement capability in global space and improve the measurement precision in local space. The adjustable articulated arm coordinate measuring machine (AACMM) with an electromagnetic locking device can automatically switch between the all-free articulated arms operation mode and the partially bound articulated arms operation mode. In the former mode, three arms and six articulations can freely move and measure the coordinates of any point in global space. In the latter mode, the front two articulations are locked to improve the measurement precision by decreasing the importation of angle errors in the local space. A prototype of the adjustable AACMM has also been designed and developed. A mathematical model for the adjustable AACMM has been built. Theoretical analysis and numerical simulation show that the partially bound AACMM performed much better than the all-free AACMM in single point repeatability and length measurement precision in the local space. Therefore, the proposed coordinate measuring method based on the adjustable articulated arms is verified as being effective.

Porównanie trójwymiarowej i dwuwymiarowej analizy ilościowej tętnic wieńcowych w odniesieniu do pomiaru długości segmentów wieńcowych u pacjentów poddawanych diagnostycznej koronarografii

Aim: To determine if three-dimensional quantitative coronary angiographic analysis (3D QCA) provides an advantage over twodimensional (2D QCA) by increasing accuracy and precision of length measurements through compensating for foreshortening inherent to 2D images. Material and methods: A total of 800 inter-marker length measurements were performed (8 per wire, 5-40 mm) with novel 3D software and standard 2D software and compared with the true lengths of the inter-marker distances on the wire in coronary vessels of 21 patients recruited. Results: 2D QCA generally underestimated true length in comparison to 3D, and the discrepancy increased with absolute length. In contrast, 3D QCA showed a minimal difference from true length over the examined range of lengths. Conclusions: 3D QCA minimizes errors in length measurements associated with foreshortening, shows minimal difference from true length, and performs significantly better in comparison to 2D QCA. The advantage of 3D QCA is more pronounced at longer lengths.

Errors Analysis and Calibration on Measuring Mechanical Arm for EVA Spacesuit Ergonomics Research

A combined coordinate measuring mechanical arm (CCMMA) was developed to test the operational ability of astronaut in the EVA spacesuit. The equipment measures the space region coordinates of the astronaut’s hand-reach while forces act on a handle. The homogeneous transformation equations of CCMMA are established based on Modified Denavit-Hartenberg (MDH). Measurement error was analyzed and distance error model of CCMMA was set up to improve measurement precision. The improved genetic algorithm is applied to the identification of CCMMA structure parameters. The calibration experiment of CCMMA was carried out using such model and algorithm. The result showed that with identification, the repeatability and length measurement precision were improved by 5.38 and 3.11 times respectively.

Laparoscopic Instruments Marking Improve Length Measurement Precision

Introduction: Bariatric surgery has increased the demand for accurate laparoscopic bowel length measurement. Measures to achieve such precision are scarce in the medical literature. Our study investigates the effect of instruments marking on measurement precision. Methods: Eight consultants and fourteen senior trainees with laparoscopic experience were asked to estimate 150 cm on a piece of string fixed within a standard laparoscopic training stack. Each candidate carried out three pairs of measurement using standard laparoscopic instruments without marking, with 10 cm and with 5 cm mark. Each measurement was timed separately. Candidates were result blinded to prevent any self-correction. Data were analyzed using Bland-Altman plots along with ANOVA tests. Results: Greater accuracy was achieved via marked instrumentation, the differences being statistically significant (P < 0.01). The improvement was significant regardless of candidates' level or initial length judgment. Time was almost doubled for the marked measurement. No statistically significance differences were found between the 5 or 10 cm instrument markings for measurement or time. Conclusions: Marked laparoscopic instrument is a simple and effective way of enhancing length measurement precision regardless of surgeons' experience.

The deformation-DIA: A new apparatus for high temperature triaxial deformation to pressures up to 15 GPa

A new deformation apparatus has been developed, based on the widely used cubic-anvil apparatus known as the DIA. Two differential rams, introduced in the upper and lower guide blocks, allow independent control of the differential strain and stress field under high confining pressure. Testing experiments with synchrotron x rays have demonstrated that this deformation DIA (D-DIA) is capable of generating up to 30% axial strain on a 1–2 mm long sample under confining pressures up to 15 GPa at simultaneous high temperatures. Various compressional strain rates from 10−3 to about 5×10−6 s−1 have been achieved. Extensional experiments have also been carried out successfully. Strains are measured by x-ray imaging of the sample which has a length measurement precision of ∼0.1 μm; pressures are monitored using standard materials with well established equations of state. X-ray transparent anvils made of sintered polycrystalline cubic boron nitride have been successfully tested, with a two-dimensional x-ray charge coupled device detector. Distortions in the diffraction lines due to differential stress can be measured with a precision of about 20 MPa.

Estimation for restriction sites observed by optical mapping using reversible-jump Markov Chain Monte Carlo.

A fundamentally new molecular-biology approach in constructing restriction maps, Optical Mapping, has been developed by Schwartz et al. (1993). Using this method restriction maps are constructed by measuring the relevant fluorescence intensity and length measurements. However, it is difficult to directly estimate the restriction site locations of single DNA molecules based on these optical mapping data because of the precision of length measurements and the unknown number of true restriction sites in the data. We propose the use of a hierarchical Bayes model based on a mixture model with normals and random noise. In this model we explicitly consider the missing observation structure of the data, such as the orientations of molecules, the allocations of cutting sites to restriction sites, and the indicator variables of whether observed cut sites are true or false. Because of the complexity of the model, the large number of missing data, and the unknown number of restriction sites, we use Reversible-Jump Markov Chain Monte Carlo (MCMC) to estimate the number and the locations of the restriction sites. Since there exists a high multimodality due to unknown orientations of molecules, we also use a combination of our MCMC approach and the flipping algorithm suggested by Dancík and Waterman (1997). The study is highly computer-intensive and the development of an efficient algorithm is required.

Dual energy X-ray absorptiometry is also an accurate and precise method to measure the dimensions of human long bones.

The accuracy, as well as the in vitro and in vivo precision of width and length measurements of human humerus and femur from dual energy X-ray absorptiometry (DXA) images, was investigated. The measurement was based on the bone area inside a specified region determined by the bone edge detection software of the scanner. The accuracy and in vitro precision studies were performed using a bone-simulating aluminum phantom embedded in different amounts of water. The in vivo precision was determined by measuring both limbs twice in 10 subjects (for humerus) and in 9 subjects (for femur). The accuracy was not significantly affected by the amount of water, and varied from 0.6 to 1.2%. Similarly, the in vitro precision varied from 0.4 to 0.6%. The average in vivo precision of the width measurement ranged from 0.4% (humeral and femoral midshaft) to 0.9% (proximal humerus), not depending on the size of the measured bone. The precision of the length measurement was 0.3% for the humerus and 3.7% for the femoral neck. In conclusion, the standard DXA technique provides a reliable measurement of the width and length in human humerus and femur in vivo, and thus may be useful in evaluating the properties of these bones in conjunction with the standard bone mineral measurements. Specifically, studies evaluating the effects of various types of mechanical loading (exercise) on bone may greatly benefit from this possibility because not only the bone mineral content and density but also the bone geometry change due to loading.

An evaluation of water vapor radiometer data for calibration of the wet path delay in very long baseline interferometry experiments

The internal consistency of the baseline length measurements derived from analysis of several independent very long baseline interferometry (VLBI) experiments is an estimate of the measurement precision. In this paper we investigate whether the inclusion of water vapor radiometer (WVR) data as an absolute calibration of the propagation delay due to water vapor improves the precision of VLBI baseline length measurements. We analyzed 28 International Radio Interferometric Surveying runs between June 1988 and January 1989; WVR measurements were made at the G. R. Agassiz Station of the Harvard College Observatory in Ft. Davis, Texas, during each session. We found that the addition of WVR data decreased the scatter of the length measurements of Ft. Davis baselines by 5–10%. The observed reduction in the scatter of the baseline lengths is less than what we would expect from the behavior of the formal errors, which suggest that the baseline length measurement precision should improve 10–20% if WVR data at Ft. Davis are included in the analysis. The discrepancy between the formal errors and the baseline length results could be explained as the consequence of systematic errors in the dry‐mapping function parameters, instrumental biases in the WVR and Ft. Davis barometer, or both.

Time resolution in a neon-helium streamer chamber

The most probable length of streamers which form along the track of an ionising particle in a streamer chamber is shown to vary with the pulse delay in a way which can be predicted by theory. The precision of length measurements are such that the arrival time of particles in the chamber may be resolved to better than 5 μs in the range 0–20 μs. Measurements of these lengths have also been used to determine the streamer extension velocity which, for a streamer 0.74 cm long, is found to be (3.2±0.7) × 10 8 cm/s.