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Out of vocabulary (OOV), which is a word that does not exist in a predefined vocabulary. How to deal with OOV is an important research topic in the field of natural language processing. The existence of OOV directly affects the performance of many NLP systems. For example, in some common scenarios such as machine translation, sentiment analysis, and intelligent question answering, the existence of OOV can greatly affect the key performance of the system. In recent years, with the advent of the word vector algorithm word2vec based on the principle of word morphology, the word embedding path of the NLP system has improved significantly. We combine LSTM with NLM, taking the morphemes of words as the basic processing unit, while taking into account the global context information. The results obtained are better than the existing OOV processing strategies, and the performance of commonly used NLP systems is generally improved. Finally, it is experimentally proved that our model is generally better than the existing models in the problem of unregistered word processing.

Recently a MeV quasi-monochromatic compact gamma-ray source with high peak spectral density based on the inverse Compton scattering (ICS) has been proposed in the Department of Engineering Physics, Tsinghua University. This type compact gamma-ray source will be used for advanced X/gamma-ray imaging application based on the nuclear resonance Fluorescence (NRF) [1]. The machine size and the peak spectral density of scattered photons are the most important parameters for such applications. In order to make the source compact enough, a compact commercial narrow bandwidth Nd: Yag laser system with ~50 fs FWHM duration and ~1.5 J maximum energy per pulse is selected as the scattering laser, and the linac is proposed to combine a photo-injector and an X-band main linac to obtain high quality 250 MeV maximum energy electron beam with high charge (~ 200 pC) and low transverse and longitudinal emittance. In ICS, the properties of the generated photons are determined by the parameters of the incident laser and electron beam, and also their interaction geometry. In this paper, we will present the optimization of the linac design. We systematically simulate and optimize the linac design with Matlab, Astra [2] and Cain [3]. In the simulations and optimizations, we use differential evolution algorithm for simultaneous optimization of multiple parameters. Three possible types of photo-injector, S-band photocathode RF(radio frequency) gun with S-band booster, C-band photocathode RF gun with C-band booster, X-band photocathode RF gun with X-band booster, are systematically optimized and compared. We also analyzed wakefield effect on the electron beam quality.

In this paper, we present a versatile methodology to accomplish the non-contact monitoring of heart rate signals in unconstrained environments, by combining the convolutional neural network (CNN) skin detection and the camera-based remote photoplethysmography (rPPG) methods. Compared to the widely-used three-step skin detection method (i.e., face detection, face tracking, and skin classification), the CNN method used here could enhance the monitoring robustness by achieving the skin detection in a single step. The proposed CNN-rPPG method has been tested in an unconstrained office environment to validate its applicability. Combined with the subsequent rPPG heart rate monitoring based on a low-cost camera, the method presented here is of practical interests for the large-scale deployment of the non-contact heart rate monitoring technologies.

High peak power, narrow band THz radiation can be generated by an ultrarelativistic electron beam passing through slow wave structure. In this paper we will review a series of recent experiments at Tsinghua University Accelerator Laboratory where a 31 MeV electron beam compressed to a sub-picosecond duration had been transported through dielectric loaded waveguide structures of various dimensions. Such high peak current electron beam generates wakefield, - a mix of TM0,N modes in the slow wave structure. This radiation is extracted from the slow wave structure and is characterized with interferometer. Narrowband signals in the range from 0.3 - 1.5 THz were measured with typical duration of few tens of picoseconds and few microjoules energy per pulse.

We report the first operation of a widely-tunable 8-period undulator at terahertz (THz) frequencies in the Tsinghua University beamline. We observed the coherent undulator radiation from sub-picosecond electron bunches of 30MeV. The measured radiation curve shows clearly that the radiation energy is proportional to the charge square, and the THz frequency can be changed from 0.4 THz to 10 THz with narrow-band spectrums. Our results demonstrate a high power and tunable coherent THz source, which could be useful for many applications in the future.

We report the experimental design and initial experimental results on high power RF generation at W-band based on coherent wakefield from the metallic periodic structure of 91 GHz, excited by intense electron beam at the Argonne Wakefield Accelerator (AWA) facility. The recently output RF power is 0.7 MW, with 67 MeV, 1.4 nano-column (nC) single electron beam go through the 12cm structure. The RF pulse is 3.4 nano-second (ns). We measure the energy loss of electron beam in the experiment. Next run is to increase the output RF power with higher charge in the driven beam and to excite higher gradient of wakefield with electron bunch train.

Femtosecond X-ray pulses could be generated by Thomson scattering between subpicosecond relativistic electron bunches and ultrashort infrared terra watt laser pulses. To ensure the stability and quality of the X-ray pulses, laser pulse must be synchronized to electron bunch generated by the photocathode RF gun. Here we demonstrate the design and implementation of the Laser-RF Synchronization system in Tsinghua University Thomson Scatter X-ray Source. Preliminary measurement shows 350 fs time jitter.

In this paper, the characteristics of terahertz coherent transition radiation are analyzed by the three-dimensional simulations. The results of field distributions are in agreement with the simulation.

A photocathode RF gun system was built to develop the electron source for the Thomson scattering X-ray source at Accelerator laboratory of Tsinghua University. The system consists of a BNL/ATF type 1.6 cell S-band RF cavity, a solenoid for emittance compensation, a laser system and some simple equipments for beam diagnosis. The status of the system is introduced in this paper, and the first beam measurements of the photocathode RF gun, including the dark current, transverse beam profile, charge and quantum efficiency is also reported.

In this paper we report the preliminary design and considerations on a multi-discipline ultra-fast source, which is capable of providing the user community with femtosecond electron bunch and light pulses with the wavelength ranging from IR to X-ray. The facility is based on photocathode RF gun driven by a Ti:Sapphire laser system. The low emittance subpicosecond electron bunch at the gun exit can be used in femtosecond electron diffraction setup to visualize the ultrafast structural dynamics. After acceleration and compression, the electron beam with the energy of 50 MeV is further used to provide high peak brightness X-ray by inverse Compton scattering with TW laser. We also consider the possibility and reliability of storing the electron beam in a compact storage ring and the laser pulse in a super-cavity Operating in this scheme may increase the average flux of the X-ray photons by orders of magnitude.

The ultrashort ultraviolet (UV) laser system and the optical transport line for driving the photocathode RF gun at Accelerator Laboratory of Tsinghua University are introduced in the article. Temporal profile of the UV pulse was measured by non-colinear difference frequency generation (DFG) between the UV pulse itself and the jitter-free residual IR laser pulse after third harmonic generation (THG) process. Experiments to measure the dependence of quantum efficiency (QE) on laser polarization state are also performed. Results show that in our case the ratio of QE between p- and s- polarization is more than 2.6.

There are growing interests in generation, preservation and applications of high brightness electron beam. With the rapid development in the techniques for emittance compensation, laser shaping and generation of ellipsoidal beam, we are approaching the limit--the uncorrelated thermal emittance. In this paper, we describe the design of the angle-resolved photoemission spectroscopy for measurements of thermal emittance for Cu and Mg. The measurement is conducted in a field-free region. The energy spectrum and angular distribution of the electrons will be measured immediately after its emission and further used to reconstruct the initial phase space and the corresponding thermal emittance. We also show how cathode surface roughness and laser incidence angle as well as its polarization state affect the quantum efficiency and thermal emittance.

Deflecting cavities are proposed for ALS at LBNL to generate sub-picosecond X-ray pulses. A 2-cell structure has been simulated to achieve required deflecting voltage and damping waveguide is attached on beam pipe to get low impedance. To demonstrate the simulation, we made an aluminum cold test model. Detailed configuration of the experiments measuring the field distribution and Qs with/without waveguide loaded are presented. Calculated (R/Q)s and waveguide damping are compared with simulation.

A new method for low energy electron beam profile measurement is advanced, which presents a full 2-D beam profile distribution other than the traditional 2-D beam profile distribution given by 1-D vertical and horizontal beam profiles. The method is based on the CT (Computer Tomography) algorithm. Multiple sets of 1-D beam profile projection data are obtained by rotating the multi-wire scanner. Then a 2-D beam profile is reconstructed from these projections with CT algorithm. The principle of this method is presented. An experimental setup was designed and the experimental results are analyzed in detail.

Summary form only given. Ferroelectric cathodes have the advantages of high luminance, high current density and low emittance. But the high current experiments show fast deterioration of the emission properties. We found that the emission current density is lower (

X-band electron linacs are an excellent choice for portable accelerators. In this pager we present an X-band disk-and-washer standing wave structure is studied in this paper for a low energy accelerating tube. The DAW cavities are optimized to obtain the largest shunt impedance and quality for the TM020 mode. A set of differential equations is used to describe the optimizing process. The optimized results of a DAW structure working at 9300 MHz are given using SUPERFISH and MAFIA400. Four radial stem supports are adopted. The modes near to the working frequency are given with and without supports. The electromagnetic field building process was analyzed with T3 of MAFIA400. OFC model DAW cavities are built and the first test results are described.