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Space rays can cause serious damage to the vital organs of astronauts. To assess the radiation safety of astronauts in the space environment, the most direct and effective way is to send radiation equivalent phantoms equipped with various radiation sensors into space through the spacecraft, and collect relevant radiation data. The phantom will be subjected to a large impact load during the lift-off of spacecraft, leading the various layers of the phantom to be dislocated or crushed, which will affect the collection of radiation data. Based on the Chengdu Dosimetric Phantom (CDP) and according to the distribution and installation requirements of radiation sensors, the phantom is sliced in multiple layers and connected by a center rod to obtain a model for space radiation dose collection, called Radiation Dosimetric Model (RDM). According to the mechanical parameters of the spacecraft during lift-off, we use Ansys Workbench Software to conduct Statics, Modal and Response Spectrum analysis of the RDM. Under a static load of 6.5g, we calculate the stress and deformation of the layers and the center rod of the RDM, as well as their size and distribution, carry out modal analysis, and calculate the maximum response of the RDM under a given acceleration spectrum with a load peak value of 6.5g. The result shows that under the dynamic and static load of 6.5g, the layers and the center rod will not be dislocated, crushed, etc. This ensures the safety of Radiation Dosimetric Model during the lift-off process, and has important theoretical significance and practical value.

We performed 3D simulations of the temperature field and velocity field in the Czochralski (Cz) process by using computational fluid dynamics (CFD) analysis software. With the obtained velocity field and temperature field in the Cz process, we showed the relative intensity of natural convection and forced convection under different rotation speeds of the growth process based on the Boussinesq approximation and by considering the conduction, convection, and radiation of heat. We simultaneously simulated the change of natural convection and forced convection due to the fall of the liquid surface level in the crucible used for Cz growth. The results will help guide Nd:YAG Cz growth with large diameters and high quality.

Some students of our colleges and universities at this stage are not enthusiastic about learning and their learning attitude is not correct, which has aroused due attention among higher education institutes, families and the society. With the problem getting worse, a direct impact on the overall quality of college graduates has been resulted. Therefore, it is of much value to analyze the reasons for the weariness of students toward their study and to explore practical measures to foster interest on student learning so that their learning interest and ability could be fostered and their awareness of innovation could be improved.

In order to obtain deflection device having wide bandwidth,small dispersion and high deflection sensitivity,a kind of traveling wave deflector is designed.Using commercial electromagnetic simulation software CST finite element method,bandwidth of traveling wave deflector in streak camera is studied,and the travelling wave deflector characteristics of dispersion curves,characteristic impedance changing with frequency and electron beam deflecting function are studied numerically using finite integration method.The comparison of deflecting sensitivity between traveling wave deflector and traditional plating deflector is made.Moreover,the electric field distribution in traveling wave deflector with sinewave scanning voltage signal is simulated.The results show that bandwidth of sharp top deflector is bigger than that of round top deflector and that bandwidth becomes smaller when legs of deflector become longer,with the biggest bandwidth of 7GHz;phase velocity and group velocity decrease with the increasing of frequency;when frequency increases,apeak value exists for characteristic impedance;under the same dimensions,the deflecting sensitivity of travelling wave detector is two times higher than that of plating deflector;the electric field produced by sinewave scanning voltage appears periodic;the designed traveling wave deflector has wide bandwidth,of which dispersion is small in wide frequency range,and it can effectively make electron beam deflect.

Rail is a main part of railway track. Its reliability relates to the national economy and people's livelihood. The fracture of rail will lead to disastrous consequences. This article mainly introduces the residual stress of rail detection and regulation technology, completes the relevant tensile experiments and rail experiments, analyses the results and the function of regulation. Eventually, an effective way to detect and reduce the residual stress of rail is found.

The compression of electron pulses in the temporal domain is a core technique to improve the temporal resolution of ultrafast diagnosis instruments,such as streak cameras and ultrafast electron diffraction systems.In this paper,a time focusing technique is adopted to potentially improve the physical temporal resolutions of streak cameras and ultrafast electron diffraction systems.This method uses a time-dependent acceleration field to greatly compensate the temporal dispersion between photocathode and anode to accelerate the slow electrons and decelerate the fast electrons,relatively.As a result,the temperal dispersion due to an initial energy spread can be compensated to a large extent at the output of time focusing region.Tracing and simulating a large number of photoelectrons through Monte-Carlo and finite difference methods shows that the electron pulse with a 300 fs can be compressed to 50 fs,which lays a powerful foundation for developing the streak cameras and ultrafast electron diffraction systems with better than 100 fs temporal resolution.

High resolution and high sensitive low light level imaging sensors are crucial in many applications such as astronomical observation, high energy physics, night vision and remote sensing. The electron bombarded complementary metal oxide semiconductor (EBCMOS) sensor is a novel imager in which very high gain can be produced by hitting the semiconductor with high voltage without any noise generation. In addition, it can process high-definition image with kHz frame rate. These advatages make the EBCMOS an ideal device for ultrafast single-photon imgaing. In this article, we present an EBCMOS sensor working in the ultraviolet range by combing the technology of vacuum photocathode and back illuminated CMOS together. This EBCMOS sensor can realize very high resolution in 40 mlx light illumination environment. The achieved spatial resolution is 25 lp/mm (line paris per millimeter) when the electric field intensity is 5000 V/mm. The liner relation between electric field intensity and the resolution indicates that much better perofromance can be achieved if the electric field intensity increases to a much higher value. The EBCMOS sensor developed in this paper can be directly applied to UV weak light detection, moreover it will provide a good reference for further developing the visible and near infrared sensitive EBCMOS sensors.

The streak tube imaging lidar (STIL) community requires the streak tube with characteristics of small-size, high edge spatial resolution, high luminance gain, and large working area. In this work, with the aid of the computer simulation technology software, a streak camera with high edge spatial resolution and high luminance gain is designed, in which there are adopted 1) a spherical photocathode and screen to increase the edge spatial resolution and detection area, further enlarging the field of view for the STIL; 2) a slit accelerating electrode instead of the mesh one favorable for improving the electrical resistance and reliability for streak camera; 3) a streak tube with lower magnification combining with -15 kV working voltage to be able to achieve high luminance gain, thus further increasing the detection distance for STIL. Some static and dynamic properties of the tube are analyzed by observing different electron trajectories emitted from a number of different points on the photocathode. As for the spatial resolution, spatial modulation transfer function method is used to evaluate the spatial resolution characteristics of the streak tube. The 36.9 lp/mm at MTF=5% in static mode and 23 lp/mm at MTF=5% in dynamic mode of the high resolution across the 16 mm long slit on the photocathode can be obtained. As for the temporal resolution, three electron pulses at intervals of 54.6 ps can be well resolved by the streak tube in the dynamic mode. Thus, the temporal resolution of the streak tube is better than 54.6 ps. Furthermore, the influence of shape of the photocathode and screen on spatial resolution are analyzed. Compared with the P-streak tube (streak tube with plane photocathode and plane screen), S-streak tube (steak tube with spherical photocathode and spherical screen) can greatly improve the spatial resolution. The slit image of the spherical and plane photocathode are simulated. The spatial dispersion of the off-axis 8 mm slit image along the scanning direction is analyzed. The experimental results demonstrate that the spatial resolution of the small-size streak tube is 29.3 lp/mm at MTF=5% over the whole working area 16 mm2 mm, and the luminance gain is higher than 39.4. The static spatial resolution of the small-size streak tube is much higher than 15 lp/mm at CTF = 11.64%; the dynamic spatial resolution is higher than 9.8 lp/mm at CTF=5.51%; the temporal resolution is higher than 54.6 ps at Tscreen=4.3 ns and has good consistency on the whole photocathode, and the dynamic range is 345:1 at 54.6 ps. The streak camera contains 6 scanning levels for different depth of field and detection accuracy to achieve ultrafast signal diagnosis at different scanning speeds. The streak tube has a smaller dimension of 40 mm140 mm. It is of great significance in unmanned aerial and spaceborne laser imaging lidar detection.

The prognosis of dominant left circumflex artery (LCx) occlusion-related inferior acute myocardial infarction (AMI) patients is poor, but the electrocardiographic (ECG) characteristics of this AMI entity have not been described.One hundred thirty-five patients with first dominant right coronary artery (RCA) or dominant LCx-related inferior AMI were included. The characteristics of ECG obtained on admission for 55 patients with culprit lesions proximal to the first major right ventricular (RV) branch of dominant RCA (group proximal dominant RCA), 62 patients with culprit lesions distal to the first major RV branch of dominant RCA (group distal dominant RCA), and 18 patients with culprit lesions in dominant LCx (group dominant LCx) were compared.There were no significant differences among the 3 groups in the prevalence regarding an S/R ratio greater than 1:3 in aVL, ST elevation in aVR (ST upward arrow(aVR)), ST depression in aVR (ST downward arrow(aVR)) of 1 mm or more, and atrioventricular block. Greater ST elevation in lead III than in II and greater ST depression in aVL than I showed specificity of 17% and 44% to identify dominant RCA as culprit lesion, respectively. All 3 groups could be distinguished on the basis of ST upward arrow(V4R), ST downward arrow(V4R), ST downward arrow(V3)/ST upward arrow(III) of 1.2 or less, and ST downward arrow(V3)/ST upward arrow(III) of more than 1.2.Greater ST elevation in lead III than in II, greater ST depression in aVL than I, and an S/R ratio of greater than 1:3 in aVL were not useful to discriminate between dominant RCA and dominant LCx occlusion-related inferior AMI. ST-segment deviation in lead V(4)R and the ratio of ST downward arrow(V3)/ST upward arrow(III) were useful in predicting the dominant artery occlusion-related inferior AMI.

We propose the hybrid optical burst switching (HOBS), and investigate the HOBS-based ring topology with numerical simulation. Results indicate that the packet loss ratio in HOBS is much less than that in optical burst switching(OBS) and its performance depends on some parameters such as the packet proportion, the electronic buffer size and the processing speed in the node.

Scannerless (flash) lidar system based on streak camera is able to realize three-dimensional (3D) multi-spectral fluorescence imaging and 3D imaging polarimetry. Compared with conventional lidar system, the flash lidar system overcomes image distortions caused by the motion between the target and the sensor platform. Other advantages of the flash lidar system are higher image update rates and the potential for creating a miniaturized lidar system. To meet the requirements for developing this new technology, a super small-sized, large photocathode area and meshless streak tube with spherical cathode and screen is designed with the aid of computer simulation technology (CST) software. The tube with nearly 28 mm wide photocathode work area contains two electrostatic focusing lens, a pair of deflection plates, and a 50 mm diameter output screen. The external dimension of the tube is merely 50 mm100 mm. And its electromagnetic fields are calculated in the CST Particle Studio based on the finite integration theory. Some dynamic properties of the tube are analyzed via observing different electron trajectories launched from a number of different points on the cathode. The influences of the deflector position on deflection sensitivity and spatial resolution are analyzed. Increasing the distance between the deflector and the anode pin hole leads to a worse deflection sensitivity but a better spatial resolution. As for the temporal resolution, three electron pulses separated by 30 ps can be well resolved by the streak tube in the dynamic mode. Thus, the dynamic temporal resolution of the streak tube is better than 30 ps. And a 10 lp/mm spatial resolution across the 28 mm long slit on the photocathode can be obtained by estimating modulation transfer functions of the electron trajectories. Temporal distortions at the entire photocathode working area are evaluated, and the data reveal that the larger the photocathode working area, the bigger the temporal distortions are. Also, the temporal distortion is present mainly in the photocathode-to-deflection plates region. In addition, the slit image of the streak tube working in the dynamic mode is simulated and presented. The phenomenon that the slit image is curved due to the temporal distortion is analyzed. Two rectangular electron pulses separated by 50 ps are well resolved by the streak tube. Therefore, the temporal resolution of this small-size steak tube is better than 50 ps with a rectangular slit dimension of 30 mm50 m on the photocathode, and its electron-optic magnification is 1.2.

Streak cameras applied to inertial confinement fusion research and flashless imaging lidar require large working areas. However, the larger the working area, the bigger the temporal distortion is. And the temporal distortion has a great influence on the detecting precision of the streak camera, resulting in an image distortion on the screen. Yet previous streak camera design work emphasized shorter time resolution and higher special resolution with paying less attention to the temporal distortion extent. Key factors that may affect the temporal distortion are thoroughly analyzed in this paper. We calculate the electric field of a small-size streak tube with the aid of the Computer Simulation Technology Particle Studio software which is a three-dimensional electromagnetic simulation software based on finite integration technology. Axial electric field distributions at different distances to the axis of the small-size streak tube are displayed. The electron trajectories launched from different points on photocathode of the streak tube are tracked through interpolating pre-calculated electromagnetic field to the particle position. It is known that curved photocathode can reduce the temporal distortion, so we calculate the temporal distortions of streak tubes whose radii of curvature of the photocathode are 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, and 55 mm respectively to ascertain how the curvature influences the temporal distortion. The results show that the temporal distortion is mainly produced in the photocathode-to-deflector region, and it is negligible in the equipotential region. Also, bigger radius of curvature of the photocathode leads to a positive temporal distortion, and smaller one leads to a negative temporal distortion. And the absolute value of the temporal distortion increases with the increase of the slit length. The small-size streak tube whose radius of curvature of the photocathode is 40 mm owns the smallest temporal distortion. We also calculate the temporal distortions of electrons launched from the different positions of the photocathode with different initial energies, and the initial energy has little influence on the temporal distortion. To sum up, the dominating factor that produces the temporal distortion is the curvature of the photocathode. The slit image under a ramp sweeping voltage on screen is curved due to the temporal distortion. And the bigger the temporal distortion, the greater the curvature of the slit image is. Besides, a linear relation between the temporal distortion and deflection of the slit image is displayed. The spatial resolutions of the streak tubes with the radii of curvature of the photocathode 30 mm, 40 mm, 50 mm are calculated respectively. And the small-size streak tube whose radius of curvature of the photocathode is 30 mm has the highest spatial resolution. The radius of curvature of the streak tube photocathode should be carefully selected according to actual requirements for the streak camera. Through the analysis we provide a significant guidance for streak tube design.

This paper describes a Computer-Aided Diagnosis (CAD) system for automatic pulmonary nodules detection on serial CT scans based on shape features. The system recognizes nodules by 3D geometric information through the process of interpolation, segmentation, suspicious area searching and recognition. Firstly, the serial CT images are interpolated to equal scales in X, Y and Z dimensions, in order to recover the original 3D shape of nodules. Secondly, pretreatment is implemented to segment the lung parenchyma region. Thirdly, detect objects called regions of interest (ROIs) as potential nodules by threshold of gray level and region growing. Finally, distinguish ROIs to find real nodules using moment invariants. The experimental results from CT scans data sets demonstrate that the proposed method yields a good performance of nodule detection. The system recognizes all the nodules of the data sets with a reasonable false positive (FP) 1/serial scans.

This paper analyses methods of the transmission and execution of the temporary speed restriction in CTCS-0/1, CTCS-2, CTCS-3, compares with their characteristics, points out the security risks exist in CTCS-0/1’s method, and proposes a new system based on data radio transceiver wireless data transmission which is suitable for CTCS-0/1. The system realizes closed-loop confirmation between the onboard and ground system of the transmission of temporary speed restriction, equipment automatic execution and supervision of CTC, improves the reliability of the temporary speed restriction information transmission and execution. Furthermore, this paper discusses the composition, working principle and key technologies of the system, and analyses its reliability and security.

Spray cooling is a well known, environmentally benign technology that can be employed for producing a comfortable condition in outdoor environment. It introduces the processes of heat and mass transfer, where air and water are the working fluid. The water droplets evaporate in the air stream to reduce the air temperature. A kind of spray cooling system of two phases flow by low pressure atomization was developed in this paper. The system possesses the advantage of additional heat removal that is thought to be due to the high latent heat of water droplets and the evaporation cooling in surroundings. The experimental studies of evaporative cooling of fine water mist in outdoor environment were presented. Cooling up to 6.7 ? was attainable in the measurement of temperature. The numerical simulation of influence of natural wind on temperature and relative humidity distribution was proposed.

The mechanisms of the so-called extensive anterior acute myocardial infarction including ST-segment elevation in leads V(1) (ST upward arrow(V1)) through V(6) (ST upward arrow(V6)) are not clear. This report is focused on the electrocardiographic (ECG) changes in 2 cases with anterior AMI. In case 1, the ECG showed complete right bundle-branch block, left anterior fascicular block, and ST upward arrow(V2) through ST upward arrow(V6) on admission, but 5 minutes later, after the disappearance of complete right bundle-branch block and left anterior fascicular block, a striking ST depression in V6 (ST downward arrow(V6)) and ST upward arrow(V1) occurred. In case 2, the ECG showed ST upward arrow(V1) through ST upward arrow(V6). The physiopathologic mechanisms of these ECG findings are discussed.

The correlation between ST-segment elevation (ST upward arrow) in lead V(3)R (ST upward arrow(V3R)), lead V(1) (ST upward arrow(V1)), and lead aVR (ST upward arrow(aVR)) during anterior wall acute myocardial infarction (AMI) and the culprit lesion site in the left anterior descending (LAD) coronary artery and the nature of the conal branch of the right coronary artery has not been thoroughly described.One hundred forty-two patients with first anterior wall AMI were included. The 15-lead electrocardiogram with the standard 12 leads plus leads V(3)R through V(5)R showing the most pronounced ST-segment deviation before initiation of reperfusion therapy was evaluated and correlated with the exact LAD occlusion site in relation to the first septal perforator (S1) and the nature of the conal branch of the right coronary artery as determined by coronary angiography.ST-segment elevation in lead aVR, ST upward arrow(V1) of at least 2 mm, and ST upward arrow(V3R) of at least 1 mm were more prevalent among patients with occlusions proximal to S1 than patients with occlusions distal to S1 (41.7% vs 4.9%, P.01; 30.0% vs 7.3%, P.01; and 91.7% vs 4.9%, P.01, respectively). Of the 60 patients with occlusions proximal to S1, 20 patients had a small conal branch (18 patients with ST upward arrow(aVR) and 15 patients with ST upward arrow(V1)or=2 mm), and 24 patients had a large conal branch (all patients with non-ST upward arrow(aVR) and ST upward arrow(V1)2 mm; P.01). The sensitivity of ST upward arrow(V1) of more than 1 mm, of at least 2 mm, ST upward arrow(V3R) of at least 1.5 mm, and ST upward arrow(aVR) for detecting a small conal branch was 65.1%, 81.8%, 84.0%, and 90%, respectively; the specificity was 68.5%, 64%, 66.7%, and 64.9%, respectively.In patients with anterior wall AMI, ST upward arrow(V3R) of at least 1 mm combined with ST upward arrow in leads V(2) through V(4) were strongly predictive of LAD occlusion proximal to S1; furthermore, ST upward arrow(aVR) and ST upward arrow(V1) of at least 2 mm were found to be useful in identifying LAD occlusion proximal to S1. ST upward arrow(aVR), ST upward arrow(V3R) of at least 1.5 mm, and ST upward arrow(V1) of at least 2.0 mm were also associated with the presence of a small conal branch not reaching the intraventricular septum during anterior wall AMI.

Chromatic stability and purity cannot be acquired easily in the top-emitting white organic light-emitting diode (TWOLED) due to its special device structure with metal film as both anode and cathode. Blue/red/blue emission layers are utilized to optimize the chromaticity and to improve the stability. Then step-doping is introduced into the red emission layer to further improve the device stability. In order to explain the mechanism of the improvement in chromaticity stability, effects of step-doping on the device performances are analyzed in detail. Experimental results refleal that the built-in electric field induced by the step-doping changes the carrier drifting and exciton recombination in emission layers. When the doping concentration gradually increases from the anode side to the cathode side (increasing step-doping), the built-in electric field is facilitated to suppress the electron drafting and the exciton diffusing, which helps control the exciton recombination zone. Color stability can be improved in the TWOLED with increasing step-doping. Additionally, as an important factor influencing the emission spectra of TWOLEDs, microcavity resonance is calculated and used to explain the variation of spectra induced by device structural changes.

In order to detect the weaker on greater span of light signals, the dynamic range, spatial resolution, and the signal to noise ratio of the streak camera need to be improved to meet further diagnostic requireflents in scientific area of materials, biology, information, semiconductor physics and energy, etc. Therefore, we design a streak camera with a larger dynamic range based on electron-bombarded CCD. Using the rectangle-framed electrode and electric quadruple lens in the streak camera can reduce its space charge effect and shorten the space charge interaction time by improving electron accelerating voltage to minimize the electron transit time. Using a back-illuminated CCD, which is based on the electron bombardment readout technology as image device to replace the traditional intensified CCD can shorten the chain of image conversion and greatly reduce the image degradation in the conversion of ultrafast diagnostic equipment. The signal to noise ratio, spatial resolution and dynamic range of the streak camera may gain improvement. Experimental results show that the static spatial resolution is better than 35 lp/mm and the dynamic spatial resolution is up to 20 lp/mm. Deflection sensitivity is 60.76 mm/kV and dynamic range reaches 2094: 1. Nonlinear scanning speed is 5.04%. EBS gain of the streak camera can be over 3000.

The primary requirement and the characteristics of the channel mode using wireless communication to transmit the control data of a high speed train is analyzed specifically. Some methods are presented for improving the transmission reliability and satisfying real time quality simultaneously. With a railway line as the background, the primary framework of the transmission system is designed. The reliability model is built and the reliability is computed using a Markov process.

In this paper, a kind of optimizing parameter method for vector control AC drive system is presented. This method optimizes parameters of the system by experiment, eliminating parameter errors in theoretical calculation and accumulative parameter errors resulting from unit errors. The experiment result indicates that the method is accurate for parameter recognition, simple to operate and easy to realize.

All optical solid state streak camera is to carry out the process of deflecting and scanning of the signal light which is coupled into the core of the waveguide, with spatially-modulated pump pulse exciting the light deflector, through precisely controlling the time delay between signal light and pump light. Not only can it solve the problems existing in the traditional photoelectron streak camera such as the decrease of the dynamic range caused by space charge effect and incapability of detecting the infrared light signal for photoelectric cathode, but also it has the advantages of simple structure, systemic stability. And the theoretical temporal resolution can reach up to picosecond scale even sub picosecond scale. For the AlxGa1-xAs/GaAs/AlxGa1-xAs planar waveguide light deflector, we discuss in detail the change of the refractive index of the GaAs with time under the common influences of band filling, band gap shrinkage and free carrier absorption effect; when the change of the refractive index is on the order of 0.01 and the ratio of the signal spot size to the width of the waveguide p=0.5, the theoretical temporal resolution can reach 2 ps; finally, the theoretical spatial resolution is calculated to be 17 lp/mm according to the condition of static experiment, while the experimental results show that spatial resolution is 9 lp/mm.

Owing to the excellent feature of ultrahigh temporal resolution, the streak image tube has been the indispensable scientific instrument for the application to measurement of ultrafast phenomena on subpicosecond time scale. In this paper, a new femtosecond streak image tube with both high temporal and spatial resolution is designed. To improve its integrated performance, a pair of traveling wave deflectors is located before a magnetic solenoid lens in the tube, which minimizes the electron transit time from anode to deflection plates and therefore reduces time dispersion and space charge effects. Using CST microwave studio finite element method, bandwidth and deflection sensitivity of traveling wave deflector have been studied numerically. The result shows that the wide bandwidth of the traveling wave deflectors designed is beneficial to slow down the electrical deflecting pulse to match the beam velocity in a wide frequency range, which can improve the deflection sensitivity. After tracing the trajectory of electrons and calculating the modulation transform function, we get temporal resolution of 220 fs and spatial resolution above 100 lp/mm. Based on the aberration theory, the aberration formulas of electron trajectory are deduced, which systematically evaluate the imaging quality of streak image tube with modulation transfer function. Finally, static experiment is carried out, and the result shows that the static spatial resolution is better than 35 lp/mm.

In this paper, we propose a new cellular automaton model for studying the temporary bottleneck induced by a special accident. The difference in driver behavior between before and after the accident occurrences is taken into account to investigate the effect of the bottleneck on driving character. Simulation results show that the new model can reproduce some complicated traffic phenomena, such as the asymmetrically lane-changing and grabbing the entrance on the bottleneck, and a reasonable asymmetrically gear-alternating control regulation can enhance the outflow of the bottleneck.

The powder jetting performance and the jetting rate were analyzed, and the jetting pressure was studied under different amount of explosion suppressant agent, different length and number of high pressure nozzles as well. The technical parameters of active explosion suppression system were tested and verified. The results showed that the suppression barrier forming rate was 0.024m/ms, the roadway of 6.25m2 section area could be filled in 100ms after the system was triggered. The longer the side distance was, the quicker the jetting pressure released. The formulation was obtained to calculate the amount of explosion suppressant agent for the unit area. The jetting rate was higher than 90% which can enssure a satisfied explosion suppression effect.

Ultrafast electron diffraction is an important technique to study the ultrafast phenomenon in physical, chemical and biological processes. This paper introduces a femtosecond electron diffractometer. The diameter of electron beam and deflection sensitivity of X-Y deflection plates are reported. We also demonstrate the static diffraction pattern of a 300 nm thick gold film taken by the femtosecond electron diffractometer.