Precision and sensitivity optimization of quantitative measurements in solid state NMR

This work presents a methodology for optimizing the precision, accuracy and sensitivity of quantitative solid state NMR measurements based on the external reference method. It is shown that the sample must be exclusively located within and completely span the coil region where the NMR response is directly proportional to the sample amount. We describe two methods to determine this "quantitative" coil volume, based on whether the probe is equipped or not with a gradient coil. In addition, to improve the sensitivity and the accuracy, an optimum rotor packing design is described, which allows the sample volume of the rotor to be matched to the quantitative coil volume. Experiments conducted on adamantane and NaCl, which are representative of a soft and hard material, respectively, show that one order of magnitude increase in experimental precision can be achieved with this methodology. Interestingly, the precision can be further improved by using the ERETIC method in order to compensate for most instrumental instabilities.     

The variability of acoustic reflex threshold measurements

Repeated measurements of the acoustic reflex threshold for various stimuli were obtained in normal subjects following a procedure similar to that commonly used in clinical audiological work, and also using a recording method with a well-defined criterion for determining the threshold value. The variability of measurements was estimated for each technique using a statistical model approach. The standard deviations of repeated measurements for a given stimulus were 2·8 and 2·5 dB, respectively, for the two methods. When the apparatus was refitted to the subject between measurements, the variability was increased. The small gain in repeatability resulting from the recording method is unlikely to be of practical significance in the clinical situation but may be of importance in research work where greater precision is desirable.     

碳氢化合物/HFC227ea二元系的PVTx实验研究

对定容式 ＰＶＴｘ实验装置的恒温、测温和测压系统进行了改进，温度和压力基本测量精度提高到±５ｍＫ和±０．４ ｋＰａ．对 ＨＣ１２７０／ＨＦＣ２２７ｅａ、ＨＣ２９０／ＨＦＣ２２７ｅａ和 ＨＣ１７０／ＨＦＣ２２７ｅａ二元物系进行了 ＰＶＴｘ实验研究．     

A continuous stream flash evaporator for the calibration of an IR cavity ring-down spectrometer for the isotopic analysis of water

A new technique for high-resolution simultaneous isotopic analysis of δ1?O and δD in liquid water is presented. A continuous stream flash evaporator has been designed that is able to vapourise a stream of liquid water in a continuous mode and deliver a stable and finely controlled water vapour sample to a commercially available infrared cavity ring-down spectrometer. Injection of sub-microlitre amounts of the liquid water is achieved by pumping liquid water sample through a fused silica capillary and instantaneously vapourising it with 100% efficiency in a home-made oven at a temperature of 170 °C. The system's simplicity, low power consumption and low dead volume together with the possibility for automated unattended operation provides a solution for the calibration of laser instruments performing isotopic analysis of water vapour. Our work is mainly driven by the possibility to perform high-resolution online water isotopic analysis on continuous-flow analysis (CFA) systems typically used to analyse the chemical composition of ice cores drilled in polar regions. In the following, we describe the system's precision and stability and sensitivity to varying levels of sample size and we assess the observed memory effects. A test run with standard waters of different isotopic compositions is presented, demonstrating the ability to calibrate the spectrometer's measurements on a VSMOW scale with a relatively simple and fast procedure.     

Gravitational redshift experiments with the high-resolution Mössbauer resonance in67Zn

A gravitational tedshift (GRS) experiment using the high-resolution Mössbauer resonance in⁶⁷Zn is described. The tiny Doppler motion of the source can be checked by a dc-SQUID based displacement sensor. The results on the GRS strongly indicate that solid-state effects, which are difficult to control experimentally, finally limit the accuracy that Mössbauer measurements can provide in determining the GRS. We argue that for this reason conventional Mössbauer experiments most probably will not be able to compete with other methods in future GRS measurements of very high precision.     

A Solid Phase Extraction Application of Hybrid Nano B_2O_3/ZrO_2 for Separation and Determination of Trace Indium in Environmental Samples

Hybrid nanomaterials have attracted considerable interest in environmental science, analytical chemistry and atomic spectroscopy. In the present study, a column solid phase extractioo procedure was developed for the separation and preconcentration of indium in various matrixes by using hybrid nanomaterial B₂O₃/ZrO₂ (HNMBZ). Various experimental and analytical parameters such as sample solution pH, sample solution volume, flow rate of sample solution and eluent, volume and concentration of eluent aod amount of HNMBZ, effect of common matrix ions and capacity of sorbent were investigated. The adsorbed metal ions on HNMBZ were eluted with 6 mL of 1 mol·L-1 HNO₃ solutions and their concentrations were determined by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS). Under the optimized conditions, detection limits for indium for 3 pixels and 5 pixels were found as 0.20 and 0.16 μg·L-1, respectively. The accuracy of the procedure was checked by spiked water samples. The developed procedure was successfully applied to real samples for the separation and determination of indium.     

A continuous stream flash evaporator for the calibration of an IR cavity ring-down spectrometer for the isotopic analysis of water

A new technique for high-resolution simultaneous isotopic analysis of δ¹⁸O and δD in liquid water is presented. A continuous stream flash evaporator has been designed that is able to vapourise a stream of liquid water in a continuous mode and deliver a stable and finely controlled water vapour sample to a commercially available infrared cavity ring-down spectrometer. Injection of sub-microlitre amounts of the liquid water is achieved by pumping liquid water sample through a fused silica capillary and instantaneously vapourising it with 100% efficiency in a home-made oven at a temperature of 170?°C. The system's simplicity, low power consumption and low dead volume together with the possibility for automated unattended operation provides a solution for the calibration of laser instruments performing isotopic analysis of water vapour. Our work is mainly driven by the possibility to perform high-resolution online water isotopic analysis on continuous-flow analysis (CFA) systems typically used to analyse the chemical composition of ice cores drilled in polar regions. In the following, we describe the system's precision and stability and sensitivity to varying levels of sample size and we assess the observed memory effects. A test run with standard waters of different isotopic compositions is presented, demonstrating the ability to calibrate the spectrometer's measurements on a VSMOW scale with a relatively simple and fast procedure.     

Precision test of mass-ratio variations with lattice-confined ultracold molecules

We propose a precision measurement of time variations of the proton-electron mass ratio using ultracold molecules in an optical lattice. Vibrational energy intervals are sensitive to changes of the mass ratio. In contrast to measurements that use hyperfine-interval-based atomic clocks, the scheme discussed here is model independent and does not require separation of time variations of different physical constants. The possibility of applying the zero-differential-Stark-shift optical lattice technique is explored to measure vibrational transitions at high accuracy.     

等时性质量谱仪中N=Z核质量测量的方法探索

N=Z核的质量数据对于研究rp-和νp-过程至关重要。此外,N=Z原子核的质量数据将会帮助我们解决与核结构有关的许多关键问题。结合碎片分离器的等时性质谱仪（Isochronous mass spectrometry,IMS）是十分快速有效而且高分辨的质量测量工具。由于N=Z核的m/q值非常接近,目前国际上的储存环质量谱仪CSRe/IMP和ESR/GSI还无法实现对N=Z核运用飞行时间谱进行鉴别,因而无法对它们进行质量测量。在日本理化学研究所的仁科加速器中心新建了专用的等时性质谱仪（IMS）,即稀有放射性同位素储存环"Rare-RI Ring"（R3）,以确定短寿命的放射性原子核的质量,其目标质量相对精度为10-6。R3质谱仪与高分辨的碎片分离器BigRIPS的组合,运用束流线的高分辨的离子鉴别,使得R3上的IMS方法对N=Z核进行质量测量成为可能。本文设计了专用的等时性束流光学设置,模拟了124Xe的主束经过碎裂反应产生的N=Z核在束流线中穿过各焦平面的径迹、能量、速度等信息,同时检验了这些次级束在环内的飞行时间相对于动量的变化关系。模拟的结果表明:当储存环的等时性光学设置在某一个N=Z核时,所有其它N=Z核在环内的回旋时间也与动量弥散无关,说明了这些核也满足等时性条件。基于N=Z核的这种等时性的特点,本文对R3上刻度N=Z核的方法也进行了讨论。     

Application of acoustic methods for a non-destructive evaluation of the elastic properties of several typologies of materials

In solid phase materials, differently from what happens in the fluid phase, elastic waves propagate both through longitudinal and transverse waves. From the speed of propagation of longitudinal and transverse waves, it is possible to evaluate important elastic properties of the solids under study, namely the Young’s modulus, the Poisson’s coefficient, the bulk modulus and the shear modulus. This work suggests an accurate method for measuring wave propagation speeds in homogeneous and non-homogeneous materials with the purpose to evaluate their mechanical properties and the associated uncertainty.First of all, to assess the performance of the proposed methodology, based on the “pulse-echo” technique, in terms of accuracy and precision, measurements of wave propagation speeds have been carried out, in atmospheric conditions, in well-known homogeneous and isotropic materials, such as copper, aluminum, stainless steel and also polymethyl methacrylate (Plexiglas®), Teflon® and optical glass BK7. These results were compared with the values reported in literature (if present), showing how published speed of sound data are very disperse and not so reliable owing to the lack of a precise uncertainty evaluation and of the temperature value associated to the measurement. Then, the same experimental apparatus was used for measuring speed of sound as a function of temperature (from 274.15 to 313.15 K) for 304 stainless steel and oxygen free copper, showing a good accuracy of the results also for temperature conditions far from ambient. Finally, the same procedure was applied to a non-homogeneous solid, obtaining some very preliminary results in typical mediterranean building material, as Carrara marble.     

Reproducibility of the quantitative assessment of cartilage morphology and trabecular bone structure with magnetic resonance imaging at 7 T

To assess the reproducibility of quantitative measurements of cartilage morphology and trabecular bone structure of the knee at 7 T, high-resolution sagittal spoiled gradient-echo images and high-resolution axial fully refocused steady-state free-precession (SSFP) images from six healthy volunteers were acquired with a 7-T scanner. The subjects were repositioned between repeated scans to test the reproducibility of the measurements. The reproducibility of each measurement was evaluated using the coefficient(s) of variation (CV). The computed CV were 1.13% and 1.55% for cartilage thickness and cartilage volume, respectively, and were 2.86%, 1.07%, 2.27% and 3.30% for apparent bone volume over total volume fraction (app.BV/TV), apparent trabecular number (app.Tb.N), apparent trabecular separation (app.Tb.Sp) and apparent trabecular thickness (app.Tb.Th), respectively. The results demonstrate that quantitative assessment of cartilage morphology and trabecular bone structure is reproducible at 7 T and motivates future musculoskeletal applications seeking the high-field strength's superior signal-to-noise ratio.     

Accuracy and precision for measurements of the mass ratio 30/28 in dinitrogen from air samples and its application to the investigation of N losses from soil by denitrification

Abstract In the 1950s Hauck introduced a special version of the (15)N dilution technique ((15)N flux method) for the determination of N losses from the soil by denitrification. Although this method is very useful and reliable its application has been rather infrequent up to now. This is mainly due to the need to measure the m/z 30 in addition to the usually measured m/z 28 and 29 for dinitrogen, because the (15)N in the enriched air sample taken from an enclosure (cover box) at the soil surface is nonrandom. The signal from the m/z 30 is very low and difficult to measure with sufficient precision because other species (e.g. NO) also having the m/z 30 often interfere with its measurement. In this study the accuracy and precision of an easy to use CF-IRMS with sample batch operation to measure the ratio 30/28 was investigated. The relative standard deviation (RSD = precision) from natural abundance up to 2 at.% was always <1%. After correction of the mass ratio 30/28 (R30), by means of a formula obtained by linear regression of theoretical R30 against measured R30, the accuracy of the abundance calculated from this corrected R30 was very high. From the achieved precision and assuming a cover box height of 10 cm (headspace volume of 7 1), and a collection time of 2 h, a limit of detection for N(2) losses by denitrification equivalent to 16 g N/ha*d or 6 kg N/ha*a can be estimated. The performance of the (15)N dilution method using the equipment and procedure described is demonstrated by means of results from an incubation experiment with [(15)N]nitrate-amended soils.     

Thermal signatures of the Kondo volume collapse in cerium

X-ray diffraction measurements of cerium in the vicinity of the isostructural gamma-alpha transition have been performed with high precision and accuracy from room temperature to almost 800 K. The disputed location of the critical point has been found to occur at 1.5+/-0.1 GPa and 480+/-10 K. The data are well fit by the Kondo volume collapse model plus a quasiharmonic representation of the phonons. The resultant free energy is validated against data for the thermodynamic Grüneisen parameter and, beyond the dominant spin-fluctuation contribution, indicates a dramatic change in the lattice Grüneisen parameter across the transition.     

Polynomial fitting of DT-MRI fiber tracts allows accurate estimation of muscle architectural parameters

Fiber curvature is a functionally significant muscle structural property, but its estimation from diffusion-tensor magnetic resonance imaging fiber tracking data may be confounded by noise. The purpose of this study was to investigate the use of polynomial fitting of fiber tracts for improving the accuracy and precision of fiber curvature (κ) measurements. Simulated image data sets were created in order to provide data with known values for κ and pennation angle (θ). Simulations were designed to test the effects of increasing inherent fiber curvature (3.8, 7.9, 11.8 and 15.3 m(-1)), signal-to-noise ratio (50, 75, 100 and 150) and voxel geometry (13.8- and 27.0-mm(3) voxel volume with isotropic resolution; 13.5-mm(3) volume with an aspect ratio of 4.0) on κ and θ measurements. In the originally reconstructed tracts, θ was estimated accurately under most curvature and all imaging conditions studied; however, the estimates of κ were imprecise and inaccurate. Fitting the tracts to second-order polynomial functions provided accurate and precise estimates of κ for all conditions except very high curvature (κ=15.3 m(-1)), while preserving the accuracy of the θ estimates. Similarly, polynomial fitting of in vivo fiber tracking data reduced the κ values of fitted tracts from those of unfitted tracts and did not change the θ values. Polynomial fitting of fiber tracts allows accurate estimation of physiologically reasonable values of κ, while preserving the accuracy of θ estimation.     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

Precise atomic mass difference determinations between some stable isotopes of Ge,As and Se

The 1 m radius, high-resolution mass spectrometer at the University of Manitoba (“Manitoba II”) has been used to determine 11 atomic mass differences between some stable isotopes of Ge, As and Se. These values are of greater accuracy and precision than existing data. Their consistency has been checked by a major least-squares adjustment involving relevant data in the region. Results include improved S_2n values for several nuclides and the energies available for the ββ decays of ⁷⁶Ge and ⁷⁴Se, respectively.     

T(1) fast acquisition relaxation mapping (T(1)-FARM): optimized data acquisition

A theoretical procedure for estimating the precision of the T(1) Fast Acquisition Relaxation Mapping sequence as a function of a number of acquisition parameters has been validated by both simulations and experimental results. These results have clarified the selection of sequence parameters to give optimal accuracy and precision in the R(1)* measurements. There is excellent agreement between theory, simulation, and experiment except for flip angles greater than 9 degrees, at which point slice profile imperfections significantly degrade the precision of the technique. The experimental results indicate that over a range of T(1)s that would be seen in a bolus tracking experiment (25-1200 ms), T(1) Fast Acquisition Relaxation Mapping can be used to obtain 64 x 128 R(1)* maps at a rate of 1 map/s, with a precision of 10% or better.     

Modelling and design of a novel air-spring for a suspension seat

Air-springs used in conjunction with auxiliary volumes provide both spring stiffness and damping. The damping is introduced through the flow restriction connecting the two air volumes. This article presents a simplified model of an air-spring with an auxiliary volume derived from first principles for simulation and design of an air-spring coupled to an auxiliary volume for a suspension seat. Tests were performed on an experimental apparatus to validate the model. The simulation model of the air-spring and auxiliary volume followed the trend predicted by the literature but showed approximately 27% lower transmissibility amplitude and 21% lower system natural frequency than that obtained by tests when using large diameter flow restrictions. This inaccuracy is assumed to be introduced by the simplified mass transfer equations defining the flow restriction between air-spring and auxiliary volume. The model showed closer correlation to the experimental results when the auxiliary volume size was decreased by two-thirds of the volume actually used for the experiment. A procedure, using the developed simulation model, for the design of a prototype air-spring and auxiliary volume, is presented for application in a typical articulated or rigid frame dump truck. The goal of the study was to design a suspension seat for this application and to obtain a SEAT value below 1.1. The design was optimised by varying auxiliary volume size and flow restriction diameters for different loads. A SEAT value of less than 0.9 was achieved, clearly indicating the effectiveness of using an auxiliary volume with an air-spring as seat suspension.     

低温汽液相平衡实验系统的研制与验证

本文介绍了一套汽液相平衡(VLE)实验系统的设计、搭建和验证工作.该实验系统具有测试温区大(140 K＜T＜300 K),压力范围广(O＜P＜7 MPa),精度高等优点,并对C2H6 C3H8的二元混合物以及C3H8的饱和蒸汽压进行了实验,对比参考文献提供的数据,具有很高的精度.