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Learned lossy image compression has demonstrated impressive progress via end-to-end neural network training. However, this end-to-end training belies the fact that lossy compression is inherently not differentiable, due to the necessity of quantisation. To overcome this difficulty in training, researchers have used various approximations to the quantisation step. However, little work has studied the mechanism of quantisation approximation itself. We ad-dress this issue, identifying three gaps arising in the quantisation approximation problem. These gaps are visualised, and show the effect of applying different quantisation approximation methods. Following this analysis, we propose a Soft-STE quantisation approximation method, which closes these gaps and demonstrates better performance than other quantisation approaches on the Kodak dataset.

The interaction process and loss problem of gyro-devices are theoretically investigated. The analysis of interaction process is self-consistently divided into two parts, namely the wave equation and the beam motion. To take the effect of finite wall conductivity into consideration, a perturbation method is utilized to model the losses, in which the propagation constant is modified as a complex number. Based on the nonlinear theory and losses modeling, both frequency-domain single-mode and time-domain multi-mode simulation schemes are proposed, which provides an effective way to optimize the gyrotron operation and instruct the practical design. Using the proposed tools and multiphysics analysis, controllable thermal tuning scheme of a gyrotron is testified by combining the cavity expansion with frequency shift. The results indicate that the thermal-frequency tuning approach has the advantage of high interaction efficiency compared with the conventional voltage and magnetic tuning methods.

High power and frequency stability of electromagnetic wave input are required in the DNP-NMR system. It is necessary to monitor the electromagnetic wave energy in the transmission line in real-time to judge the magnitude and stability of the energy transmitted to the NMR spectrometer. However, the energy in the transmission system is too large to be directly measured in the transmission line. A part of the energy must be extracted to facilitate the measurement. We design a directional coupler by placing a wire array in the middle of the three-port circular corrugated waveguide for real-time extraction of transmitted energy. In the frequency range of 290 – 360 GHz, 0.05% energy can be stably coupled to port 3, so it is convenient for the energy detection. The S 11 parameter of the designed directional coupler can below −20dB from 290 to 360 GHz, and even −41dB at the operating frequency of 330 GHz.

Spatio-temporal information is valuable as a discriminative cue for presentation attack detection, where the temporal texture changes and fine-grained motions (such as eye blinking) can be indicative of some types of spoofing attacks. In this paper, we propose a novel spatio-temporal feature, based on motion history, which can offer an efficient way to encapsulate temporal texture changes. Patterns of motion history are used as primary features followed by secondary feature extraction using Local Binary Patterns and Convolutional Neural Networks, and evaluated using the Replay Attack and CASIA-FASD datasets, demonstrating the effectiveness of the proposed approach.

Objectives Researched the event data recorder and applied to vehicle quality judicial identification. Methods Extensive investigated the application of event data recorder at home and abroad, researched the parameter of event data recorder to apply to accident reconstruction, reappeared the vehicle running condition in the event, and combined with system working theory and design principle to analysis whether there is any fault, and used two cases to illustrate the application of event data recorder. Results The application of event data recorder provided a new identification method for judicial identification. Conclusion The application of event data recorder played an important role in judicial identification and enhanced the science level of judicial identification science.

A preliminary design of a 1-THz gyrotron based on the forth harmonic operation is presented. The cylindrical-waveguide TE 4,8 mode is selected as the operating mode. Considering the weak beam-wave coupling strength in a 4th-harmonic open-cavity interaction circuit at the frequency of 1 THz, this paper proposes applying low-temperature cooling, for example applying liquid nitrogen, to increase the limit of the Q factor and extend the effective length of the cavity resulting in a significant enhancement of the interaction efficiency and suppression of ohmic losses. Applying multi-mode time-domain theory in the simulation, it was found that although the competing third-harmonic TE 3,6 mode was excited first, the fourth-harmonic TE 4,8 mode finally dominates in the steady state regime.

A method to generate coherent terahertz (THz) radiation into free space via Brillouin zone overlapping is introduced in this paper. When the free electron bunch passes over the metallic grating, the spoof surface plasmon (SSP) is stimulated and confined in the surface. By loading a rod array above the grating, the Brillouin zones of the rod array and grating overlap. In this way, part of the dispersion curves of the SSP wave lies in the radiative region, achieving the transformation from SSP to radiation wave into the free space. Moreover, the field intensity of the coherent THz radiation shows an enhancement about 20 times compared with that of ordinary Smith-Purcell radiation (SPR) generated from the rod array. This method is promising for developing compact and efficient THz radiation source.

A multi-color coherent terahertz (THz) Smith-Purcell radiation based on compound grating is introduced in this paper. The periodically modulated depth in the compound grating is beneficial to decreasing the coupling strength of adj acent grooves and constructing a series of spoof surface plasmon (SPP) cavities. Owing to the weak coupling between two adjacent cavities, the multi-color coherent Smith-Purcell radiation in specific directions is induced by the excitation of free electron beam. This kind of Smith-Purcell radiation is promising for the development of THz radiation sources and THz communication.

We are currently investigating about demonstrating gyrotron with the capability of super broadband operation in THz band. A strong-field pulse magnet is applied to provide a time-varying magnetic field, and the cyclotron frequency of the electron beam in the cavity changes accordingly. The electron beam efficiently excites a backward wave in a specially designed pre-bunching cavity. A broadband quasioptical converter and a Brewster window are installed in the tube to radiate out the broadband power. Theoretical study reveals that the gyrotron is potential to radiate peak power about 1 kW around 0.33 THz and a frequency tuning range about 10 GHz in each pulse. Further study predicts that when high-order whispering gallery modes are employed as the operation modes, this broadband mini-gyrotron is capable of sequentially jumping from one mode to another and finally radiates power covering the range of 350 GHz - 410 GHz.

A scheme of a second harmonic gyrotron operating in CW regime is presented. This tube is designed to provide output power about several tens of watts at 330 GHz. - Whispering-gallery mode is selected as the operating mode. The performance of the candidate TE82 and $\mathbf{TE}_{\pmb{92}}$ mode is evaluated by nonlinear code. It is confirmed that TE92 mode can suppress the competing modes successfully. The fabricating key components of this tube is presented.

Gyrotron backward-wave oscillators (gyro-BWOs) extending to the terahertz (THz) band require high-order modes to improve the power-handling capability. Here we investigate a THz high-order whispering-gallery mode (WGM) gyro-BWO equipped with a cathode-end output circuit. The segment-tapered circuit contributes to uplifting the start-oscillation currents of the near-cutoff competing mode and reclaiming the dominance of operating mode. The scheme is applicable to other high-order mode gyro-BWOs with broadband tuning.

In this paper, we investigate the robust power allocation issue in orthogonal frequency division multiplexing-based cognitive radio networks (CRNs) with unavoidable uncertainties (channel perturbations and variable environment). In this case, to control the performance degradation due to the uncertainties, we maximize the data rate of secondary users (SUs) by considering maximum allowable interference constraints and total power budget of SUs. To solve this problem, we design a controller for a switched affine system with state constraint. This system is based on a distributed projected dynamic system in accordance with the classical distributed convex optimization model for the power allocation and dynamic property of the Nash equilibrium. The robust controller design is on the basis of Lyapunov stability theory and linear matrix inequality to better realize the original power allocation from the control perspective. To the best of our knowledge, we are the first to solve the aforementioned problem by this kind of approach under the control frame, which is more practical for the realization in CRNs. Simulation results are provided to show the validation of the effectiveness of this approach in comparison with iterative water filling algorithm and the worst-case method.

A high harmonic THz Terahertz frequency multiplier based on metallic grating is presented in this paper. The interaction between electron beam and the Spoof Surface Plasmon (SSP) is studied widely in recent years. Compared with the previous interactions operating at the fundamental frequency of the electron beam, the frequency multiplier operates at much higher harmonics, and a 10th harmonic frequency multiplier has been achieved in this paper. And the radiation frequency is greatly increased, accordingly. This system achieves a radiation power 5 W at 0.5 THz with 20kV/400mA electron beam bunches.

A 330 GHz pulse gyrotron has been developed in theory and experiment. The compact magnet and pre-bunched cavity interaction circuit bring about the advantages of system miniaturization and broadband tuning capability. Here the start-oscillation dominance of operating TE 6,2+ mode and the dynamic beam-wave interaction process are analyzed based on the measured magnetic field profile. We are currently carrying out the proof-of-principle experiment.

This paper proposes an electronic-tuning frequency stabilization scheme with power tuning for a Watt-level terahertz gyrotron oscillator in gyro-BWO state. The intrinsic positive relationship between electron-beam pitch factor $a$ and accelerating voltage $V$ in electron gun contributes to Doppler shift compensation during electronic tuning. When the pitch factor $a$ varies from 1.1 to 1.9, the prototype three-sectioned gyrotron oscillator can be fixed at 253.98 GHz with 10 MHz level error. The output power is tuned by 40% from maximum. This approach is of importance for heat-effect-oriented applications in biomedicines and material processing.

This paper introduces the small force measurement system at micronewton level at Center for Measurement Standards, Industrial Technology Research Institute (CMS/ITRI). The construction of the system started in 2009 and completed in 2014. The force measurement system consists of three main parts: a monolithic flexure stage, a three planar electrodes capacitor and a digital controller. The three planar electrodes capacitor is utilized simultaneously as a position sensor and an electrostatic force generator. Accurate electrostatic force is generated by constantly adjusting and maintaining gap distances between three planar electrodes. The lowest force uncertainty was evaluated to be 4.7 nN. The previous results show that the relative standard uncertainty at $10\ \mu \mathrm{N}$ and $100\ \mu \mathrm{N}$ are $2.3\times 10^{-4}$ and $7.4\times 10^{-5}$ , respectively. At current stage, the mass of mg level realized by this system has a slightly larger uncertainty than that obtained from traditional subdivision method. We discuss future works to further improve this system.

In this paper, a metallic grating structure with varying depth is presented for beam-wave interaction. The DC electron beam flies above the structure and backward spoof surface plasmon mode is excited. When the electromagnetic power flow reaches the left-hand of grating structure, it is trapped down and reflected to propagate forwardly due to rainbow trapped storage of terahertz wave. With energy reflecting and transmitting at both ends of this structure, a regenerate feedback is realized and a THz pulse is amplified repeatedly. This system achieved the maximum output power over 1.5 W after four times of reflections at 1 THz with a 3 kV/20mA electron beam.

The high-order operating modes in gyrotrons are always converted into Gaussian beam for transmission. However, the Gaussian beam radiated from the gyrotrons is frequently non-ideal, which may result in poor coupling to the fundamental HE 11 mode in corrugated waveguides and high attenuation in the transmission line. Therefore, a back-to-back corrugated horn structure is designed in this paper for Gaussian mode filtering This structure is capable of enhancing the coupling coefficient from 82% to nearly 98%. Besides, the high coupling coefficient maintains during a broadband frequency range of $\mathbf{200 GHz }\leq J \leq 240$ GHz.

The robust power allocation problem is often solved by different optimization approaches under a convex optimization model. But in this study, we use a distributed projected dynamic system (PDS) to describe this model and realize power allocation by designing a stable controller using Lyapunov function and linear matrix inequality (LMI) for the PDS. The controller can follow our defined target SINR and keeps the quality of service (QoS) required by primary user (PU) under the channel and the interference uncertainties (including feedback error). The simulation results illustrate that our proposed controller can realize power allocation with better performance compared with iterative waterfilling algorithm (IWFA).

This paper is concerned with biometrie spoofing detection using the dynamics of natural facial movements as a feature. Facial muscle movement information can be extracted from video sequences and encoded using the Facial Action Coding System (FACS). The proposed feature constructs a Facial Action Units Histogram (FAUH) to encapsulate this information for the detection of biometric presentation attacks without the need for active user cooperation. The performance of the proposed system was tested on two datasets: CASIA-FASD and Replay Attack and produced encouraging results. Further improvements may be possible by integrating this source of information with other indicators for further protecting biometric systems from subversion.

For many terahertz applications, the waveguide mode, due to severe dispersion and attenuation in free space, is always converted into Gaussian beam as the final shape of electromagnetic waves. However, the mode converter with manufacture tolerance cannot generate ideal Gaussian beam from waveguide modes, particularly from the high-order modes. Mode filtering and beam shaping is necessary to be conducted to improve the purity of Gaussian beam for effective transmission and focusing. Here a terahertz transmission system, composed of an improved overmoded corrugated waveguide transmission line and a back-to-back corrugated beam-shaping horn, is proposed. The loss in the transmission line with corner-filleted grooves decreases to 0.00184 dB/m. The purity of Gaussian mode is obtained nearly 98% in the 0.22 THz beam-shaping horn. This terahertz transmission system is potential to be employed in DNP-NMR spectrometer based on continuous wave gyrotron.

A broadband quasi-optical mode converter that could function at three segment-continuous frequencies in three different waveguide modes is investigated. The three modes and frequencies are TE 11,2 mode at 351–361 GHz, TE 12,2 mode at 375–385 GHz and TE 13,2 mode at 398–410 GHz. The mode converter consists of a Vlasov launcher, three reflecting mirrors and an output window. It converts rotating high-order waveguide modes into free-space Gaussian beams. The key to manage broad bandwidths at different modes is to select proper center frequencies corresponding with waveguide modes. Moreover, another crucial part to realize broad bandwidths is a relatively large radius of the Vlasov launcher. From the calculation of a program code called Gyrotron Quasi-optical Mode Converter (GQMC) that is developed, it shows that the mode converter could generate well-shaped Gaussian beam with efficiency higher that 77.3% at different modes and frequencies. This mode converter could be used in step-tunable multi-mode gyrotrons which could achieve continuous broadband radiation in different modes.

This paper reports our progress of developing a 0.33-THz gyrotron which is based on a compact pulse magnet and can generate broadband coherent THz radiation with bandwidth exceeding 10 GHz and peak power about 2 kW. The design and fabrication of the key components are addressed in detail, including strong-field magnet, pre-bunched cavity, broadband Quasi-Optical mode converter, and Brewster window. The terahertz gyrotron with kilowatt level high power, broadband capability, and compact configuration is the key to high-power terahertz research.

This paper presents a broadband quasi-optical (QO) mode converter antenna system, which can transfer a waveguide TE62 mode into free-space Gaussian beam around 330 GHz. The converter contains a Vlasov launcher and three reflector mirrors. Special considerations, including a reasonably large aperture of the Vlasov launcher and the optimized combination of two elliptic reflectors and a bifocal parabolic reflector, are the keys to achieve broadband mode converting. The optimized converter is well compatible with the gyrotron electron-optical system and generates Gaussian beam with efficiency higher than 80% in a broadband range between 310–340 GHz. The principle of the broadband converter can also be applied to gyrotron amplifiers, even other gyrotron devices.

The shear force sensor is one of the key elements in future robotic industries; it is of great importance in applications where robotic arms are required to delicately interact with objects to be handled. This paper presents the development of a capacitive shear force capable of sensing shear forces in two degrees of freedom. The fabrication of the sensor is based on the PCB fabrication process, a well-known and mature technology. We adopt the capacitance sensing scheme for its high sensitivity and easy implementation. For sensor characterization, we used a force gauge and an optical interferometer to measure sensor's parameters including its sensitivity and resolution. The dimension of our prototype shear force sensor including the metal housing is 26 mm × 13 mm × 58 mm suitable for the integration with commercial robotic grippers. For sensor performance, we achieved a shear force sensitivity of 126 fF/N and a resolution of smaller than 6 mN.

This paper introduces the torsion pendulum experiment at center for measurement standards, industrial technology research institute (CMS/ITRI). The torsion pendulum experiment aims at SI traceable measurement and generation of force at nano/subnano-newton scale. Three force generation mechanisms, namely optical force, electrostatic force and universal gravitation are implemented in the experiment. Recent progress on gravitation measurement is reported in this article.

In this paper, we describe the experiment of using radiation pressure to actively damp a strip torsion pendulum. The radiation source is a 1.5 W Nd:YAG laser with an actively controlled variable attenuator. By controlling the power of the laser, force of nano-newton scale can be generated and used to damp the resonant oscillation of the pendulum. We also quantitatively measured the force due to the radiation pressure. The result is in good agreement with the theoretical prediction.

This article illustrates the clinical and environmental researches of intermittent contact mode atomic force microscopy, utilizing AFM imaging of canine renal epithelial cell and influenza viruses. The images include topography, amplitude, and phase. In the AFM images of canine renal epithelial cell, not only the structure of single cell surface, but also the granules and the hole on the cell surface are shown, and the structure of glycocalyx on the cell membrane is obtained. In the AFM images of influenza viruses, the virus is obtained, and the glycoprotein protrusions on the virus surface are shown. The information from AFM images is helpful to understand the functions of biological sample surface structures.

A method to fabricate optical fiber probe nano-tips by combination of heated micro-pulling and static chemical etching has been developed. Firstly, electric arc heating and micro-pulling process is used to change the configuration of fiber cladding, thus to obtain semi-finished fiber probes with desirable shape. Then the dimension of probe tip is further reduced by hydrofluoric (HF) acid static chemical etching. Probe tips with dimension less than 100nm and cone angle 430 have been achieved by this method. Compared with traditional static chemical etching, fiber probes fabricated by this method have a larger cone angle and shorter taper length. The transmission efficiency of fiber probe is improved either. Using arc heating instead of traditional laser heating, the equipment requirement for probe fabrication has been greatly simplified. Micro-pulling process decreases the etching volume of the fiber cladding, which greatly reduces the etching time. The advancement of fabrication technique of optical fiber probe may further support the development of near-field imaging, biochemical sensing and nanofabrication fields.

We present our experimental progress in using atomic probes to continuously scan atomic surfaces, in developing picometer laser metrology, and in picometer real-time motion control for our scheme towards new definition of the kilogram.

For possible new definition of the kilogram, we propose to use picometer metrology and AFM to continuously scan with atomic resolution a surface strip of about 2 nm/spl times/10 mm area on a single silicon crystal in a 2/spl times/10/sup -11/ torr vacuum chamber to measure silicon lattice spacings to 0.1-1 ppb. >

Summary form only given. Optical heterodyne interferometry is widely used in the measurements of surface topography. In this paper, a novel polarized optical heterodyne interferometer associated with a differential amplifier is proposed. A surface topography of a holographic grating is successfully scanned.

Summary form only given.The optical configuration of the experimental setup is shown. An air cooled argon ion laser was used in the experiment. The laser output power was 40 mW, and the wavelength was set at 488 nm in this arrangement. A 50 cm-long PMMA plastic fiber having a diameter of 1000 /spl mu/m was adopted as the light guide that propagated the laser beam. The fluorescence was collected by a photomultiplier (PMT) set beside the fiber. In order to separate the pumping beam (488 nm) from the fluorescence signal, a narrow band interference filter having a center frequency of 520 nm and the a bandwidth of 10 nm was fixed in front of the PMT.