Abstract: After the laser trapping and cooling, the cold atoms in a cesium fountain clock undergo a short period of upward acceleration and uniform motion due to the frequency detuning of the upward and the downward lasers. Then, with the cooling laser shut down, the cold atoms keep going up to the apex under the gravity and then fall down to the detection area to be detected by the detection laser. The height of cold atoms throw-up is the distance from the MOT center to the apex. Previous calculations ignored the acceleration and uniform upward movement of the cold atoms, resulting in a systematic error. This paper corrects for the error by considering three different movement processes of the cold atoms and accurately calculates the height of the cold atoms throw-up from the experimental data of the time-of-flight signal.
Abstract: Digital twins are widely used in medical and health fields. This paper introduces the basics of digital twins, the development status, and their applications in medical and health fields, including real-time acquisition of patient conditions, provision of safe environments, construction of an all-round service platform for innovation, etc. This paper points out two development trends of digital twins in medical and health fields and raises the problems that may arise in the use of digital twins in those fields.
Abstract: Cold-atom systems provide a nearly static measurement medium with almost no interaction between the atoms for quantum precision measurement processes, thereby avoiding the frequency shift and broadening existing in the working medium of hot atoms, making the measurement results more accurate. However, the atomic cooling part of current quantum precision measurement systems is bulky and complex, which is not conducive to miniaturization of distributable quantum measurement standard systems. In order to make a less complex magneto-optical trap system, we adopted the scheme to combine the diffraction grating chip and the atomic cooling technique. The wavefront of a single incident light was phase modulated through the linear grating, and the atoms were successfully trapped on a chip scale. The preparation of the core chip of a miniaturized magneto-optical trap and the realization of the magneto-optical trap system with a simple optical structure can lay a solid foundation for further miniaturization of the overall system of a magneto-optical trap in the future.
Abstract: Nuclear clocks, the high-precision optical clocks based on nuclear energy level transitions, are deemed to have better timing accuracy than atomic clocks, the current gold timekeeping standard. Related research has great scientific and strategic significance for the development of our society. The development of ultra-precision thorium nuclear clocks since 2003 is investigated using the bibliometric method. Scientific knowledge maps are used to show the current macro (national-level), meso (institutional-level), and micro (personnel-level) distributions of research forces, main research topics, and main funding agencies in the field of nuclear clocks.
Abstract: The range coefficient in the range method for standard uncertainty evaluation is simulated based on Monte Carlo simulation. The reference values of the range coefficients are given for the uncertainty evaluation by the range method under the condition that the overall input quantities obey different distributions. The accuracy of the calculated coefficients is verified by comparing them with the experimental standard deviations calculated by the Bessel formula. It is also found that the experimental standard deviations can be calculated easily and accurately by substituting the corresponding reference values of the range coefficients into the range method when the overall distribution of the input quantities is known. Finally, the differences of the range deviation coefficients under different distributions are compared, and the relationship between the number of measurements, the probability distribution function and the choice of range deviation coefficients is given.ice of range deviation coefficients is given.evaluation. In the end, by analyzing the difference of range coefficients calculated under the different population distributions, the relationship among the number of measurements, probability distribution, and the selection of range coefficient is demonstrated.
Abstract: Surface tension is one of the most important basic properties of liquid. Accurate measurement of surface tension plays an important role in industrial production and scientific research. At present, calibration of surface tensiometers in China lacks foundation due to the lack of detailed research on evaluation of measurement uncertainty of surface tension. This paper studies the measurement uncertainty in the error of indication of surface tensiometers based on the platinum plate method and the platinum ring method. The results showed that the main uncertainty components come from the measurement repeatability and the reference value. The uncertainty of reference value mainly comes from the probe size. The uncertainty caused by the special weights and the gravity acceleration is less than that caused by the probe size. For the same level of measurement repeatability, the uncertainty in the error of indication of a surface tensiometer based on the platinum plate method is greater than that of a surface tensiometer based on the platinum ring method.
Abstract: An exchangeable distributor was calibrated using the standard source method with a multi-functional calibration source, a digital multimeter, and a precision DC resistance box and the measurement uncertainty was evaluated. The linearity of the distributor was calculated considering that the linearity may affect the performance of the distributor.
Abstract: 68Ge-68Ga phantoms are mainly used in PET/CT image uniformity adjustment and SUV value correction. In order to produce a 68Ge-68Ga phantom, an epoxy resin modified by polysulfide rubber was used as the substrate and the carrier solution of 68Ge-68Ga was used to simulate 68Ge-68Ga radioactive solution. The homogeneous mixture of carrier solution, epoxy resin, and curing agent was filled in a shell of high density polyethylene (HDPE). After the mixture was solidified completely, a non-radioactive phantom with hard texture, color transparent and non-bubble was prepared. Inductively coupled plasma-optical emission spectrometer (ICP-OES) was used to detect the concentration of Ge and Ga elements in the phantom. The results of uniformity analysis showed that there was no significant difference in the concentration distribution of Ge and Ga in the phantom, and the relative standard deviations were 2.20% and 3.65%, respectively, which were equivalent to similar imported products. It was indicated that the process described in this paper can be used for the preparation of 68Ge-68Ga phantom.
Abstract: Nine samples of test dust in the wide particle size range of 1.7～19.4 μm ( D50) with cumulative particle size distribution percentages of up to 50% were prepared by applying grinding, sieving, sedimentation separation to the Arizona (ISO12103-A2) test dust. The Malvern laser particle size analyzer was used to characterize the particle size distribution of the samples. Repeatability tests showed that the developed Arizona test dust in each particle size range is reproducible.
Abstract: This paper proposes acceptance limits for the nosie dose ratio of noise dosimeters. The ratio of the noise dose of a sound burst signal to the noise dose of the steady-state signal under the same amplitude, frequency, measurement duration and judgment standard sound level, i.e. the noise dose ratio, of a noise dosimeter is studied. The dependence of the noise dose ratio on the time average sound level (i.e. equivalent continuous sound level), repetitive tone burst response, repetition time, and the duration of a single tone burst is also studied. The acceptance limits were used as criteria to evaluate the performance of several noise dosimeters and the test results lay within the limits.
Abstract: Temperature gradient of the side stirred constant thermostatic bath above 100 mm has been studied experimentally. The research shows that the temperature gradient of the upper temperature field of the thermostat bath (30~100) mm can meet the requirements of the general industrial thermometers such as liquid-in-glass thermometer for working and industrial platinum resistance thermometer between 50 ℃ and 200 ℃. According the experiment, the influence of insertion depth on the sensor measurement results depends on the thermal conductivity of the sensor material. The smaller the thermal conductivity is, the smaller the influence will be. For temperature sensors of the same material, the influence of the insertion depth on the measured result depends on the depth-to-diameter ratio. It could be inferred from the experiment that when calibrating the shorter temperature sensor, the axial heat transfer is the main source of measurement errors. As the calibration temperature increases, the insertion depth has a greater influence on the measurement results.
Abstract: Dynamic force sensors measure force dynamically, which plays an important role in industrial manufacture. It is important to calibrate the sensors as their accuracy directly affect the production. In this paper, the calibration principle for impact dynamic force sensors is studied. An existing impact acceleration standard device was modified to calibrate dynamic force sensors. A design scheme based on LabVIEW for the software and hardware of the calibration device for impact dynamic force sensors is proposed, with which a highly integrated and automatic calibration device was developed. Test results showed that the maximum deviation from the reference dynamic sensitivity was 0.81%, which met the design requirements.
Abstract: This paper mainly introduces the functions and implementation of the measurement and control system in a gas flow standard device of the 20000l mixed bell jar type as well as the device's working principles. It presents the hardware design of the lower computer and the software development for the upper computer. It also describes the way of realizing three working modes, based on the static volumetric method, the dynamic volumetric method, and the standard meter method, simultaneously in a single device, which greatly enhances the flexibility and mobility of the device. The upper computer of the device adopts VB.NET. The lower computer adopts the integrated module of measurement control cabinet. The configuration and control flow of the measurement control cabinet module and the realization process and functions of the upper computer are described in detail.
Abstract: A calibration device for indoor hand-held laser distance meters was developed according to JJG 966-2010 Verification Regulation of Hand-held Laser Distance Meters. The principle, calibration method, and uncertainty analysis are introduced. The experimental results showed that the device meets the verification requirements of JJG 966-2010 and can be used to calibrate hand-held laser distance meters in an indoor environment.
Abstract: A water flow standard device based on the static weighing method was built. The device can be used for calibration of electromagnetic flow meters for high flow rates. This paper briefly introduces the structure of the device and the design scheme for the main sub-systems.