Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of ...Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of n-type Si C/graphene,while a comprehensive understanding of the quantum resistance metrology behavior of graphene with different doping types is lacking.Here,we fabricated both n-and p-type Si C/graphene devices via polymer-assisted molecular adsorption and conducted systematic magneto-transport measurements in a wide parameter space of carrier density and temperature.It is demonstrated that n-type devices show greater potential for development of quantum resistance metrology compared with p-type devices,as evidenced by their higher carrier mobility,lower critical magnetic field for entering quantized Hall plateaus,and higher robustness of the quantum Hall effect against thermal degeneration.These discrepancies can be reasonably attributed to the weaker scattering from molecular dopants for n-type devices,which is further supported by the analyses on the quantum interference effect in multiple devices.These results enrich our understanding of the charged impurity on electronic transport performance of graphene and,more importantly,provide a useful reference for future development of graphene-based quantum resistance metrology.展开更多
A lead-shielded HPGe detector and offlineγ-ray spectra of the residual product were used to measure the cross section(CS)and ratios of isomeric CS(σm/σg)in^(134)Xe(n,2n)^(133m),gXe reactions at different energies(1...A lead-shielded HPGe detector and offlineγ-ray spectra of the residual product were used to measure the cross section(CS)and ratios of isomeric CS(σm/σg)in^(134)Xe(n,2n)^(133m),gXe reactions at different energies(13.5 MeV,13.8 MeV,14.1 MeV,14.4 MeV,14.8 MeV)relative to the^(93)Nb(n,2n)^(92)mNb reaction CS.The target was high-purity natural Xe gas under high pressure.The T(d,n)4He reaction produces neutrons.TALYS code(version 1.95)for nuclear reactions was used for calculations,with default parameters and nuclear level density models.The uncertainties in the measured CS data were thoroughly analyzed using the covariance analysis method.The results were compared with theoretical values,evaluation data,and previous experimental findings.CS data of the 134Xe(n,2n)133mXe and 134Xe(n,2n)133gXe reactions and the corresponding isomeric CS ratios at 13.5 MeV,13.8 MeV,and 14.1 MeV neutron energies are reported for the first time.This research advances our knowledge of pre-equilibrium emission in the(n,2n)reaction channel by resolving inconsistencies in the Xe data.展开更多
An absolute gravimeter is a precision instrument for measuring gravitational acceleration, which plays an important role in earthquake monitoring, crustal deformation, national defense construction, etc. The frequency...An absolute gravimeter is a precision instrument for measuring gravitational acceleration, which plays an important role in earthquake monitoring, crustal deformation, national defense construction, etc. The frequency of laser interference fringes of an absolute gravimeter gradually increases with the fall time. Data are sparse in the early stage and dense in the late stage. The fitting accuracy of gravitational acceleration will be affected by least-squares fitting according to the fixed number of zero-crossing groups. In response to this problem, a method based on Fourier series fitting is proposed in this paper to calculate the zero-crossing point. The whole falling process is divided into five frequency bands using the Hilbert transformation. The multiplicative auto-regressive moving average model is then trained according to the number of optimal zero-crossing groups obtained by the honey badger algorithm. Through this model, the number of optimal zero-crossing groups determined in each segment is predicted by the least-squares fitting. The mean value of gravitational acceleration in each segment is then obtained. The method can improve the accuracy of gravitational measurement by more than 25% compared to the fixed zero-crossing groups method. It provides a new way to improve the measuring accuracy of an absolute gravimeter.展开更多
With the advancement in X-ray astronomical detection technology,various celestial polarization detection projects have been initiated.To meet the calibration requirements of polarimeters on the ground,a polarized X-ra...With the advancement in X-ray astronomical detection technology,various celestial polarization detection projects have been initiated.To meet the calibration requirements of polarimeters on the ground,a polarized X-ray radiation facility was designed for this study.The design was based on the principle that X-rays incident at 45°on a crystal produce polarized X-rays,and a second crystal was used to measure the polarization of the X-rays produced by the facility after rotation.The effects of different diaphragm sizes on the degree of polarization were compared,and the facility produced X-rays with polarization degrees of up to 99.55±0.96%using LiF200 and LiF220 crystals.This result revealed that the polarization of incident X-rays is one of the factors affecting the diffraction efficiency of crystals.The replacement of different crystals can satisfy the calibration requirements of polarized X-ray detectors with more energy points in the energy range(4-10)keV.In the future,the facility should be placed in a vacuum environment to meet the calibration requirements at lower energies.展开更多
The strength of microwave(MW)electric field can be observed with high precision by using the standard electromagnetically induced transparency and Aulter–Towns(EIT-AT)technique,when its frequency is resonant or nearl...The strength of microwave(MW)electric field can be observed with high precision by using the standard electromagnetically induced transparency and Aulter–Towns(EIT-AT)technique,when its frequency is resonant or nearly-resonant with the Rydberg transition frequency.As the detuning of MW field increases,one of the transmission peaks(single peak)is easier to measure due to its increased amplitude.It can be found that the central symmetry point of the two transmission peaks f_(1/2)is only related to the detuning of MW field△_(MW)and central symmetry point f_(0)of resonant MW field,satisfying the relation f_(1/2)=△_(MW)/2+f_(0).Thus,we demonstrate a single transmission peak method that the MW E-field can be determined by interval between the position of single peak and f_(1/2).We use this method to measure continuous frequencies in a band from-200 MHz to 200 MHz of the MW field.The experimental results and theoretical analysis are presented to describe the effectiveness of this method.For 50 MHz<△_(MW)<200 MHz,this method solves the problem that the AT splitting cannot be measured by using the standard EIT-AT techniques or multiple atomic-level Rydberg atom schemes.展开更多
A redundant-subspace-weighting(RSW)-based approach is proposed to enhance the frequency stability on a time scale of a clock ensemble.In this method,multiple overlapping subspaces are constructed in the clock ensemble...A redundant-subspace-weighting(RSW)-based approach is proposed to enhance the frequency stability on a time scale of a clock ensemble.In this method,multiple overlapping subspaces are constructed in the clock ensemble,and the weight of each clock in this ensemble is defined by using the spatial covariance matrix.The superimposition average of covariances in different subspaces reduces the correlations between clocks in the same laboratory to some extent.After optimizing the parameters of this weighting procedure,the frequency stabilities of virtual clock ensembles are significantly improved in most cases.展开更多
An optical lattice clock based on 87Sr is built at National Institute of Metrology (NIM) of China. The systematic frequency shifts of the clock are evaluated with a total uncertainty of 2.3×10-16. To measure it...An optical lattice clock based on 87Sr is built at National Institute of Metrology (NIM) of China. The systematic frequency shifts of the clock are evaluated with a total uncertainty of 2.3×10-16. To measure its absolute frequency with respect to NIM's cesium fountain clock NIM5, the frequency of a flywheel H-maser of NIM5 is transferred to the Sr laboratory through a 50-kin-long fiber. reference frequency of this H-maser, is used for the optical this Sr clock is measured to be 429228004229873.7(1.4)Hz. A fiber optical frequency comb, phase-locked to the frequency measurement. The absolute frequency of展开更多
Ultra-stable optical cavities are widely used for laser frequency stabilization. In these experiments the laser performance relies on the length stability of the Fabry-Perot cavities. Vibration-induced deformation is ...Ultra-stable optical cavities are widely used for laser frequency stabilization. In these experiments the laser performance relies on the length stability of the Fabry-Perot cavities. Vibration-induced deformation is one of the dominant factors that affect the stability of ultra-stable optical cavities. We have quantitatively analysed the elastic deformation of Fabry-Perot cavities with various shapes and mounting configurations. Our numerical result facilitates a novel approach for the design of ultra-stable cavities that are insensitive to vibrational perturbations. This approach can be applied to many experiments such as laser frequency stabilization, high-precision laser spectroscopy, and optical frequency standards.展开更多
到还原剂的最大的障碍之一 Avogadro 经常的 NA 的无常是以便将有氧化物一个硅范围的表面上的层。这层的厚度被修改分光镜的 ellipsometer 测量,它能消除弄弯的表面的影响,并且结果被 X 光反射率校准。在硅范围的表面上将近一致地散...到还原剂的最大的障碍之一 Avogadro 经常的 NA 的无常是以便将有氧化物一个硅范围的表面上的层。这层的厚度被修改分光镜的 ellipsometer 测量,它能消除弄弯的表面的影响,并且结果被 X 光反射率校准。在硅范围的表面上将近一致地散布的五十个位置被测量两次。全面氧化物层的吝啬的厚度是有 0.21 nm 的标准无常的 3.75 nm 的结果表演,意味着由于这层的 NA 的相对无常部件能被归结为 1.2 x 10, ?] 8。[从作者抽象]展开更多
Space scientific exploration is rapidly becoming the primary battlefield for humankind to explore the universe.Countries worldwide have launched numerous space exploration satellites.Accurate calibration of the detect...Space scientific exploration is rapidly becoming the primary battlefield for humankind to explore the universe.Countries worldwide have launched numerous space exploration satellites.Accurate calibration of the detectors on the ground is a crucial element for space science satellites to obtain observational results.For the purpose of providing calibration for various satellite-borne detectors,multiple monochromatic X-rays facilities have been built at the National Institute of Metrology,P.R.China(NIM).These facilities mainly pertain to grating diffraction and Bragg diffraction,and the energy range of the produced monochromatic X-rays is 0.218–301 ke V.These facilities have a high performance in terms of energy stability,monochromaticity,and flux stability.The monochromaticity was greater than 3.0%.The energy stability of the facility is 0.02%at 25 ke V over 8 h,and the flux stability was within 1.0%at 25 ke V over 8 h.Calibration experiments on the properties of satellite-borne detectors,such as energy linearity,energy resolution,detection efficiency,and temperature response,can be conducted at the facilities.Thus far,the calibration of two satellites has been completed by the authors,and the work on three other satellites is in progress.This study will contribute to the advancement of X-ray astronomy the development of Chinese space science.展开更多
A triplexer is fabricated based on SOI arrayed waveguide gratings (AWGs). Three wavelengths of the triplexer operate at different diffraction orders of an arrayed waveguide grating. The signals of 1490nm and 1550nm,...A triplexer is fabricated based on SOI arrayed waveguide gratings (AWGs). Three wavelengths of the triplexer operate at different diffraction orders of an arrayed waveguide grating. The signals of 1490nm and 1550nm, which are input from central input waveguide of an AWG, are demultiplexed and the signal of 131Onto, which is input from central output waveguide of an AWG, is uploaded. The tested results show that the downloaded and uploaded signals have fiat-top response. The insertion loss is 9 dB on chip, the nonadjacent crosstalk is less than -30 dB for 1490nm and 1301 nm, and is less than -25 dB for 1550nm, the 3dB bandwidth equates that of the input light source.展开更多
Polycrystalline powder samples of dysprosium doped Zn(BO2)2 phosphors were prepared by solid state reaction in air at high temperature and characterized by X-ray powder diffraction. The IR, Photoluminescence (PL),...Polycrystalline powder samples of dysprosium doped Zn(BO2)2 phosphors were prepared by solid state reaction in air at high temperature and characterized by X-ray powder diffraction. The IR, Photoluminescence (PL), diffuse reflectance and three-dimensional (3D) thermoluminescence (TL) emission spectrum after 60^Co gamma ray irradiation were investigated. The characteristic 3D TL emission bands at about 425, 481 and 573 um with a main emission band of around 573 um were attributed to the host emission, 4^F9/2→6H15/2 and F9/2→6^H13/2 f-f transitions of Dy^3+ ions. No emission from Dy^2+ ions was observed in the measurement wavelength range. The TL-dose response of the Zn(BO2)2:Dy polycrystalline powder sample to gamma ray radiation in the range from 1 to 100 Gy at clinical dose levels was almost linear. The experimental results showed that Zn(BO2)2:Dy had potential use as the materials of gamma-ray thermoluminescence dosimeter (TLD) for clinical dosimetry.展开更多
Femtosecond optical frequency combs correlate the microwave and optical frequencies accurately and coherently.Therefore,any optical frequency in visible to near-infrared region can be directly traced to a microwave fr...Femtosecond optical frequency combs correlate the microwave and optical frequencies accurately and coherently.Therefore,any optical frequency in visible to near-infrared region can be directly traced to a microwave frequency.As a result,the length unit“meter”is directly related to the time unit“second”.This paper validates the capability of the national wavelength standards based on a home-made Er-doped fiber femtosecond optical frequency comb to measure the laser frequencies ranging from visible to near-infrared region.Optical frequency conversion in the femtosecond optical frequency comb is achieved by combining spectral broadening in a highly nonlinear fiber with a single-point frequencydoubling scheme.The signal-to-noise ratio of the beat notes between the femtosecond optical frequency comb and the lasers at 633,698,729,780,1064,and 1542 nm is better than 30 d B.The frequency instability of the above lasers is evaluated by using a hydrogen clock signal with a instability of better than 1×10^(-13)at 1-s averaging time.The measurement is further validated by measuring the absolute optical frequency of an iodine-stabilized 532-nm laser and an acetylenestabilized 1542-nm laser.The results are within the uncertainty range of the international recommended values.Our results demonstrate the accurate optical frequency measurement of lasers at different frequencies using the femtosecond optical frequency comb,which is not only important for the precise and accurate traceability and calibration of the laser frequencies,but also provides technical support for establishing the national wavelength standards based on the femtosecond optical frequency comb.展开更多
NIM-Sr2 optical lattice clock has been developed on the Changping campus of National Institute of Metrology(NIM).Considering the limitations in NIM-Sr1,several improved parts have been designed including a differentia...NIM-Sr2 optical lattice clock has been developed on the Changping campus of National Institute of Metrology(NIM).Considering the limitations in NIM-Sr1,several improved parts have been designed including a differential pumping stage in the vacuum system,a permanent magnet Zeeman slower,water-cooled anti-Helmholtz coils,an extended viewport for Zeeman slower,etc.A clock laser with a short-time stability better than 3×10^(-16)is realized based on a self-designed 30-cm-long ultra-low expansion cavity.The systematic frequency shift has been evaluated to an uncertainty of 7.2×10^(-18),with the uncertainty of BBR shift and the collisional frequency shift being an order of magnitude lower than the last evaluation of NIM-Sr1.展开更多
The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology(NIM) of China. The device consists of...The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology(NIM) of China. The device consists of four junction arrays, each of which has 1200 3-stacked Nb/NbxSi1-x/Nb junctions and an on-chip superconducting microwave circuit which is mainly a power divider enabling each Josephson array being loaded with an equal amount of microwave power. A direct current(dc) quantum voltage of about 0.5 V with a ~1-mA current margin of the 1 st quantum voltage step is obtained.To further prove the quality of NIM device, a comparison between the NIM device with the National Institute of Standards and Technology(NIST) programmable Josephson voltage standard(PJVS) system device is conducted. The difference of the reproduced 0.5-V quantum voltage between the two devices is about 0.55 nV, which indicates good agreement between the two devices. With the homemade device, we have realized a precise and applicable 0.5-V applicable-level quantum voltage.展开更多
Optical coherence tomography(OCT)has been widely applied to the diagnosis of eye diseasesduring the past two decades.However,valid evaluation methods are stil not available for theclinical OCT devices.In order to asse...Optical coherence tomography(OCT)has been widely applied to the diagnosis of eye diseasesduring the past two decades.However,valid evaluation methods are stil not available for theclinical OCT devices.In order to assess the axial resolution of the OCT system,standard modeleyes with micro-scale multilayer structure have been designed and manufactured in this study.Mimicking a natural human eye,proper Titanium dioxide(TiO_(2))materials of particles withdifferent concentrations were selected by testing the scattering coefficient of PDMS phantoms.The artificial retinas with multilayer films were fabricated with the thicknesses from 9.5 to 30 micrometers using spin coating technology,Subsequently,standard OCT model eyes were ac-complished by embedding the retina phantoms into the artificial frames of eyes.For ease ofmeasurement processing,a series of model eyes were prepared,and each contained flms withthree kinds of thicknesses.Considering the traceability and accuracy of the key parameters of the standard model eyes,the thicknesses of multilayer structures were verfed using ThicknessMonitoring System.Through the experiment with three different OCT devices,it demonstratedthe model eyes fabricated in this study can provide an effective evaluation method for the axialresolution of an ophthalmic OCT device.展开更多
Posttranslational modifications of antibody products affect their stability,charge distribution,and drug activity and are thus a critical quality attribute.The comprehensive mapping of antibody modifications and diffe...Posttranslational modifications of antibody products affect their stability,charge distribution,and drug activity and are thus a critical quality attribute.The comprehensive mapping of antibody modifications and different charge isomers(CIs)is of utmost importance,but is challenging.We intended to quantitatively characterize the posttranslational modification status of CIs of antibody drugs and explore the impact of posttranslational modifications on charge heterogeneity.The CIs of antibodies were fractionated by strong cation exchange chromatography and verified by capillary isoelectric focusing-whole column imaging detection,followed by stepwise structural characterization at three levels.First,the differences between CIs were explored at the intact protein level using a top-down mass spectrometry approach;this showed differences in glycoforms and deamidation status.Second,at the peptide level,common modifications of oxidation,deamidation,and glycosylation were identified.Peptide mapping showed nonuniform deamidation and glycoform distribution among CIs.In total,10 N-glycoforms were detected by peptide mapping.Finally,an in-depth analysis of glycan variants of CIs was performed through the detection of enriched glycopeptides.Qualitative and quantitative analyses demonstrated the dynamics of 24 N-glycoforms.The results revealed that sialic acid modification is a critical factor accounting for charge heterogeneity,which is otherwise missed in peptide mapping and intact molecular weight analyses.This study demonstrated the importance of the comprehensive analyses of antibody CIs and provides a reference method for the quality control of biopharmaceutical analysis.展开更多
A trajectory generator based on vehicle kinematics model was presented and an integrated navigation simulation system was designed.Considering that the tight relation between vehicle motion and topography,a new trajec...A trajectory generator based on vehicle kinematics model was presented and an integrated navigation simulation system was designed.Considering that the tight relation between vehicle motion and topography,a new trajectory generator for vehicle was proposed for more actual simulation.Firstly,a vehicle kinematics model was built based on conversion of attitude vector in different coordinate systems.Then,the principle of common trajectory generators was analyzed.Besides,combining the vehicle kinematics model with the principle of dead reckoning,a new vehicle trajectory generator was presented,which can provide process parameters of carrier anytime and achieve simulation of typical actions of running vehicle.Moreover,IMU(inertial measurement unit) elements were simulated,including accelerometer and gyroscope.After setting up the simulation conditions,the integrated navigation simulation system was verified by final performance test.The result proves the validity and flexibility of this design.展开更多
Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. Th...Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. The three-dimensional trajectories and the supporting forces of water spider legs during walking forward were achieved. Results showed that the leg movement could be divided into three phases: slap, stroke, and retrieve. Employing an effective strategy to improving walking efficiency, the sculling legs supported most of its body weight while other legs were lifted to reduce the lateral water resistance, which was similar to the strategy of water striders. These findings could help guiding the design of water walking robots with high efficiency.展开更多
基金supported by the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-046)the National Natural Science Foundation of China(Grant Nos.92165201,11974324,12104435)+4 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)Hefei Science Center CAS(Grant No.2020HSC-UE014)the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000013 and WK2310000104)supported by USTC Tang Scholar。
文摘Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of n-type Si C/graphene,while a comprehensive understanding of the quantum resistance metrology behavior of graphene with different doping types is lacking.Here,we fabricated both n-and p-type Si C/graphene devices via polymer-assisted molecular adsorption and conducted systematic magneto-transport measurements in a wide parameter space of carrier density and temperature.It is demonstrated that n-type devices show greater potential for development of quantum resistance metrology compared with p-type devices,as evidenced by their higher carrier mobility,lower critical magnetic field for entering quantized Hall plateaus,and higher robustness of the quantum Hall effect against thermal degeneration.These discrepancies can be reasonably attributed to the weaker scattering from molecular dopants for n-type devices,which is further supported by the analyses on the quantum interference effect in multiple devices.These results enrich our understanding of the charged impurity on electronic transport performance of graphene and,more importantly,provide a useful reference for future development of graphene-based quantum resistance metrology.
基金supported by the National Natural science Foundation of China(Nos.11875016,12165006).
文摘A lead-shielded HPGe detector and offlineγ-ray spectra of the residual product were used to measure the cross section(CS)and ratios of isomeric CS(σm/σg)in^(134)Xe(n,2n)^(133m),gXe reactions at different energies(13.5 MeV,13.8 MeV,14.1 MeV,14.4 MeV,14.8 MeV)relative to the^(93)Nb(n,2n)^(92)mNb reaction CS.The target was high-purity natural Xe gas under high pressure.The T(d,n)4He reaction produces neutrons.TALYS code(version 1.95)for nuclear reactions was used for calculations,with default parameters and nuclear level density models.The uncertainties in the measured CS data were thoroughly analyzed using the covariance analysis method.The results were compared with theoretical values,evaluation data,and previous experimental findings.CS data of the 134Xe(n,2n)133mXe and 134Xe(n,2n)133gXe reactions and the corresponding isomeric CS ratios at 13.5 MeV,13.8 MeV,and 14.1 MeV neutron energies are reported for the first time.This research advances our knowledge of pre-equilibrium emission in the(n,2n)reaction channel by resolving inconsistencies in the Xe data.
基金Project supported by the National Key R&D Program of China (Grant No. 2022YFF0607504)。
文摘An absolute gravimeter is a precision instrument for measuring gravitational acceleration, which plays an important role in earthquake monitoring, crustal deformation, national defense construction, etc. The frequency of laser interference fringes of an absolute gravimeter gradually increases with the fall time. Data are sparse in the early stage and dense in the late stage. The fitting accuracy of gravitational acceleration will be affected by least-squares fitting according to the fixed number of zero-crossing groups. In response to this problem, a method based on Fourier series fitting is proposed in this paper to calculate the zero-crossing point. The whole falling process is divided into five frequency bands using the Hilbert transformation. The multiplicative auto-regressive moving average model is then trained according to the number of optimal zero-crossing groups obtained by the honey badger algorithm. Through this model, the number of optimal zero-crossing groups determined in each segment is predicted by the least-squares fitting. The mean value of gravitational acceleration in each segment is then obtained. The method can improve the accuracy of gravitational measurement by more than 25% compared to the fixed zero-crossing groups method. It provides a new way to improve the measuring accuracy of an absolute gravimeter.
基金supported by the National Natural Science Foundation of China(No.12205289).
文摘With the advancement in X-ray astronomical detection technology,various celestial polarization detection projects have been initiated.To meet the calibration requirements of polarimeters on the ground,a polarized X-ray radiation facility was designed for this study.The design was based on the principle that X-rays incident at 45°on a crystal produce polarized X-rays,and a second crystal was used to measure the polarization of the X-rays produced by the facility after rotation.The effects of different diaphragm sizes on the degree of polarization were compared,and the facility produced X-rays with polarization degrees of up to 99.55±0.96%using LiF200 and LiF220 crystals.This result revealed that the polarization of incident X-rays is one of the factors affecting the diffraction efficiency of crystals.The replacement of different crystals can satisfy the calibration requirements of polarized X-ray detectors with more energy points in the energy range(4-10)keV.In the future,the facility should be placed in a vacuum environment to meet the calibration requirements at lower energies.
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFF0603704)the National Natural Science Foundation of China(Grant No.62071443)。
文摘The strength of microwave(MW)electric field can be observed with high precision by using the standard electromagnetically induced transparency and Aulter–Towns(EIT-AT)technique,when its frequency is resonant or nearly-resonant with the Rydberg transition frequency.As the detuning of MW field increases,one of the transmission peaks(single peak)is easier to measure due to its increased amplitude.It can be found that the central symmetry point of the two transmission peaks f_(1/2)is only related to the detuning of MW field△_(MW)and central symmetry point f_(0)of resonant MW field,satisfying the relation f_(1/2)=△_(MW)/2+f_(0).Thus,we demonstrate a single transmission peak method that the MW E-field can be determined by interval between the position of single peak and f_(1/2).We use this method to measure continuous frequencies in a band from-200 MHz to 200 MHz of the MW field.The experimental results and theoretical analysis are presented to describe the effectiveness of this method.For 50 MHz<△_(MW)<200 MHz,this method solves the problem that the AT splitting cannot be measured by using the standard EIT-AT techniques or multiple atomic-level Rydberg atom schemes.
基金Project supported by the National Key Research and Development Program of China (Grant No.2021YFB3900701)the Science and Technology Plan Project of the State Administration for Market Regulation of China (Grant No.2023MK178)the National Natural Science Foundation of China (Grant No.42227802)。
文摘A redundant-subspace-weighting(RSW)-based approach is proposed to enhance the frequency stability on a time scale of a clock ensemble.In this method,multiple overlapping subspaces are constructed in the clock ensemble,and the weight of each clock in this ensemble is defined by using the spatial covariance matrix.The superimposition average of covariances in different subspaces reduces the correlations between clocks in the same laboratory to some extent.After optimizing the parameters of this weighting procedure,the frequency stabilities of virtual clock ensembles are significantly improved in most cases.
基金Supported by the National Natural Science Foundation of China under Grant Nos 91336212 and 91436104
文摘An optical lattice clock based on 87Sr is built at National Institute of Metrology (NIM) of China. The systematic frequency shifts of the clock are evaluated with a total uncertainty of 2.3×10-16. To measure its absolute frequency with respect to NIM's cesium fountain clock NIM5, the frequency of a flywheel H-maser of NIM5 is transferred to the Sr laboratory through a 50-kin-long fiber. reference frequency of this H-maser, is used for the optical this Sr clock is measured to be 429228004229873.7(1.4)Hz. A fiber optical frequency comb, phase-locked to the frequency measurement. The absolute frequency of
文摘Ultra-stable optical cavities are widely used for laser frequency stabilization. In these experiments the laser performance relies on the length stability of the Fabry-Perot cavities. Vibration-induced deformation is one of the dominant factors that affect the stability of ultra-stable optical cavities. We have quantitatively analysed the elastic deformation of Fabry-Perot cavities with various shapes and mounting configurations. Our numerical result facilitates a novel approach for the design of ultra-stable cavities that are insensitive to vibrational perturbations. This approach can be applied to many experiments such as laser frequency stabilization, high-precision laser spectroscopy, and optical frequency standards.
基金upported by the National Key R&D Plan of China(2016YFF0200802)Establishment of a standard device for air kerma in mammography X-rays(ANL1902)。
文摘Space scientific exploration is rapidly becoming the primary battlefield for humankind to explore the universe.Countries worldwide have launched numerous space exploration satellites.Accurate calibration of the detectors on the ground is a crucial element for space science satellites to obtain observational results.For the purpose of providing calibration for various satellite-borne detectors,multiple monochromatic X-rays facilities have been built at the National Institute of Metrology,P.R.China(NIM).These facilities mainly pertain to grating diffraction and Bragg diffraction,and the energy range of the produced monochromatic X-rays is 0.218–301 ke V.These facilities have a high performance in terms of energy stability,monochromaticity,and flux stability.The monochromaticity was greater than 3.0%.The energy stability of the facility is 0.02%at 25 ke V over 8 h,and the flux stability was within 1.0%at 25 ke V over 8 h.Calibration experiments on the properties of satellite-borne detectors,such as energy linearity,energy resolution,detection efficiency,and temperature response,can be conducted at the facilities.Thus far,the calibration of two satellites has been completed by the authors,and the work on three other satellites is in progress.This study will contribute to the advancement of X-ray astronomy the development of Chinese space science.
基金Supported by the National High-Tech Development Program of China under Grant Nos 2006AA03Z420 and 2007AA03Z420, and the National Natural Science Foundation of China under Grant No 60776057.
文摘A triplexer is fabricated based on SOI arrayed waveguide gratings (AWGs). Three wavelengths of the triplexer operate at different diffraction orders of an arrayed waveguide grating. The signals of 1490nm and 1550nm, which are input from central input waveguide of an AWG, are demultiplexed and the signal of 131Onto, which is input from central output waveguide of an AWG, is uploaded. The tested results show that the downloaded and uploaded signals have fiat-top response. The insertion loss is 9 dB on chip, the nonadjacent crosstalk is less than -30 dB for 1490nm and 1301 nm, and is less than -25 dB for 1550nm, the 3dB bandwidth equates that of the input light source.
基金the National Key Project of Basic Research of China (G1998061312)Science and Technology Project of Jilin Province (200505264)the Foundation of Doctoral Subject of Beihua University
文摘Polycrystalline powder samples of dysprosium doped Zn(BO2)2 phosphors were prepared by solid state reaction in air at high temperature and characterized by X-ray powder diffraction. The IR, Photoluminescence (PL), diffuse reflectance and three-dimensional (3D) thermoluminescence (TL) emission spectrum after 60^Co gamma ray irradiation were investigated. The characteristic 3D TL emission bands at about 425, 481 and 573 um with a main emission band of around 573 um were attributed to the host emission, 4^F9/2→6H15/2 and F9/2→6^H13/2 f-f transitions of Dy^3+ ions. No emission from Dy^2+ ions was observed in the measurement wavelength range. The TL-dose response of the Zn(BO2)2:Dy polycrystalline powder sample to gamma ray radiation in the range from 1 to 100 Gy at clinical dose levels was almost linear. The experimental results showed that Zn(BO2)2:Dy had potential use as the materials of gamma-ray thermoluminescence dosimeter (TLD) for clinical dosimetry.
基金the National Key Research and Development Program of China(Grant No.2016YFF0200204)。
文摘Femtosecond optical frequency combs correlate the microwave and optical frequencies accurately and coherently.Therefore,any optical frequency in visible to near-infrared region can be directly traced to a microwave frequency.As a result,the length unit“meter”is directly related to the time unit“second”.This paper validates the capability of the national wavelength standards based on a home-made Er-doped fiber femtosecond optical frequency comb to measure the laser frequencies ranging from visible to near-infrared region.Optical frequency conversion in the femtosecond optical frequency comb is achieved by combining spectral broadening in a highly nonlinear fiber with a single-point frequencydoubling scheme.The signal-to-noise ratio of the beat notes between the femtosecond optical frequency comb and the lasers at 633,698,729,780,1064,and 1542 nm is better than 30 d B.The frequency instability of the above lasers is evaluated by using a hydrogen clock signal with a instability of better than 1×10^(-13)at 1-s averaging time.The measurement is further validated by measuring the absolute optical frequency of an iodine-stabilized 532-nm laser and an acetylenestabilized 1542-nm laser.The results are within the uncertainty range of the international recommended values.Our results demonstrate the accurate optical frequency measurement of lasers at different frequencies using the femtosecond optical frequency comb,which is not only important for the precise and accurate traceability and calibration of the laser frequencies,but also provides technical support for establishing the national wavelength standards based on the femtosecond optical frequency comb.
基金supported by the National Key R&D Program of China(Grant Nos.2021YFF0603802 and 2016YFF0200201)。
文摘NIM-Sr2 optical lattice clock has been developed on the Changping campus of National Institute of Metrology(NIM).Considering the limitations in NIM-Sr1,several improved parts have been designed including a differential pumping stage in the vacuum system,a permanent magnet Zeeman slower,water-cooled anti-Helmholtz coils,an extended viewport for Zeeman slower,etc.A clock laser with a short-time stability better than 3×10^(-16)is realized based on a self-designed 30-cm-long ultra-low expansion cavity.The systematic frequency shift has been evaluated to an uncertainty of 7.2×10^(-18),with the uncertainty of BBR shift and the collisional frequency shift being an order of magnitude lower than the last evaluation of NIM-Sr1.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFF02000402)
文摘The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology(NIM) of China. The device consists of four junction arrays, each of which has 1200 3-stacked Nb/NbxSi1-x/Nb junctions and an on-chip superconducting microwave circuit which is mainly a power divider enabling each Josephson array being loaded with an equal amount of microwave power. A direct current(dc) quantum voltage of about 0.5 V with a ~1-mA current margin of the 1 st quantum voltage step is obtained.To further prove the quality of NIM device, a comparison between the NIM device with the National Institute of Standards and Technology(NIST) programmable Josephson voltage standard(PJVS) system device is conducted. The difference of the reproduced 0.5-V quantum voltage between the two devices is about 0.55 nV, which indicates good agreement between the two devices. With the homemade device, we have realized a precise and applicable 0.5-V applicable-level quantum voltage.
基金supported by the National Key Research and Development Program of China(2016YFF0201005).
文摘Optical coherence tomography(OCT)has been widely applied to the diagnosis of eye diseasesduring the past two decades.However,valid evaluation methods are stil not available for theclinical OCT devices.In order to assess the axial resolution of the OCT system,standard modeleyes with micro-scale multilayer structure have been designed and manufactured in this study.Mimicking a natural human eye,proper Titanium dioxide(TiO_(2))materials of particles withdifferent concentrations were selected by testing the scattering coefficient of PDMS phantoms.The artificial retinas with multilayer films were fabricated with the thicknesses from 9.5 to 30 micrometers using spin coating technology,Subsequently,standard OCT model eyes were ac-complished by embedding the retina phantoms into the artificial frames of eyes.For ease ofmeasurement processing,a series of model eyes were prepared,and each contained flms withthree kinds of thicknesses.Considering the traceability and accuracy of the key parameters of the standard model eyes,the thicknesses of multilayer structures were verfed using ThicknessMonitoring System.Through the experiment with three different OCT devices,it demonstratedthe model eyes fabricated in this study can provide an effective evaluation method for the axialresolution of an ophthalmic OCT device.
基金the financial support from the National Key Program for Basic Research of China(Grant Nos.:2018YFC0910302 and 2017YFF0205400)the National Natural Science Foundation of China(Grant No.:81530021)Innovation Foundation of Medicine(Grant Nos.:BWS14J052 and 16CXZ027)
文摘Posttranslational modifications of antibody products affect their stability,charge distribution,and drug activity and are thus a critical quality attribute.The comprehensive mapping of antibody modifications and different charge isomers(CIs)is of utmost importance,but is challenging.We intended to quantitatively characterize the posttranslational modification status of CIs of antibody drugs and explore the impact of posttranslational modifications on charge heterogeneity.The CIs of antibodies were fractionated by strong cation exchange chromatography and verified by capillary isoelectric focusing-whole column imaging detection,followed by stepwise structural characterization at three levels.First,the differences between CIs were explored at the intact protein level using a top-down mass spectrometry approach;this showed differences in glycoforms and deamidation status.Second,at the peptide level,common modifications of oxidation,deamidation,and glycosylation were identified.Peptide mapping showed nonuniform deamidation and glycoform distribution among CIs.In total,10 N-glycoforms were detected by peptide mapping.Finally,an in-depth analysis of glycan variants of CIs was performed through the detection of enriched glycopeptides.Qualitative and quantitative analyses demonstrated the dynamics of 24 N-glycoforms.The results revealed that sialic acid modification is a critical factor accounting for charge heterogeneity,which is otherwise missed in peptide mapping and intact molecular weight analyses.This study demonstrated the importance of the comprehensive analyses of antibody CIs and provides a reference method for the quality control of biopharmaceutical analysis.
基金Projects(90820302, 60805027, 61175064) supported by the National Natural Science Foundation of ChinaProject(2011ssxt231) supported by the Master Degree Thesis Innovation Project Foundation of Central South University, China+1 种基金Project(200805330005) supported by the Research Fund for the Doctoral Program of Higher Education, ChinaProject(2011FJ4043) supported by the Academician Foundation of Hunan Province, China
文摘A trajectory generator based on vehicle kinematics model was presented and an integrated navigation simulation system was designed.Considering that the tight relation between vehicle motion and topography,a new trajectory generator for vehicle was proposed for more actual simulation.Firstly,a vehicle kinematics model was built based on conversion of attitude vector in different coordinate systems.Then,the principle of common trajectory generators was analyzed.Besides,combining the vehicle kinematics model with the principle of dead reckoning,a new vehicle trajectory generator was presented,which can provide process parameters of carrier anytime and achieve simulation of typical actions of running vehicle.Moreover,IMU(inertial measurement unit) elements were simulated,including accelerometer and gyroscope.After setting up the simulation conditions,the integrated navigation simulation system was verified by final performance test.The result proves the validity and flexibility of this design.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51323006 and 51425502)the Tribology Science Fund of State Key Laboratory of Tribology(Grant No.SKLTKF17B18)
文摘Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. The three-dimensional trajectories and the supporting forces of water spider legs during walking forward were achieved. Results showed that the leg movement could be divided into three phases: slap, stroke, and retrieve. Employing an effective strategy to improving walking efficiency, the sculling legs supported most of its body weight while other legs were lifted to reduce the lateral water resistance, which was similar to the strategy of water striders. These findings could help guiding the design of water walking robots with high efficiency.