Konfigurasi Nat Ns 300
Time-resolved and ultrafast hard X-ray imaging, scattering and spectroscopy are powerful tools for elucidating the temporal and spatial evolution of complexity in materials. However, their temporal resolution has been limited by the storage-ring timing patterns and X-ray pulse width at synchrotron sources. Here we demonstrate that dynamic X-ray optics based on micro-electro-mechanical-system resonators can manipulate hard X-ray pulses on time scales down to 300 ps, comparable to the X-ray pulse width from typical synchrotron sources. This is achieved by timing the resonators with the storage ring to diffract X-ray pulses through the narrow Bragg peak of the single-crystalline material. Angular velocities exceeding 10 7 degrees s −1 are reached while maintaining the maximum linear velocity well below the sonic speed and material breakdown limit.
As the time scale of the devices shortens, the devices promise to spatially disperse the temporal width of X-rays, thus generating a temporal resolution below the pulse-width limit. Materials with nanoscopic-to-mesoscopic structures have taken center stage in advancing science and technology. There have been major efforts in establishing the structure-function relationship of materials on these length scales employing a variety of physical and chemical probes, and hard X-ray tools have played an important role to this effort,. However, a deeper understanding of energy conversion, storage, transmission, and utilization requires a complete mapping of the spatiotemporal behavior of relevant processes in, for example, solar and thermoelectric conversion, fuels cells and batteries, and efficient and clean combustion,. These processes include carrier dynamics, phonon transport, ionic conduction, multicomponent diffusion, phase transformation, interfacial diffusion, multiphase fluid flow, strain propagation, and soot formation on the temporal scales of microseconds and less,. Spatiotemporal X-ray probes with similar time resolution and spatial resolution—from picometers to mesoscopic scales—are essential to meeting this challenge.
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While X-ray free-electron lasers (XFELs) with a femtosecond pulse width are extremely effective in probing dynamics on ultrashort time scales, synchrotron-based X-ray sources are well suited for revealing the spatiotemporal evolution of mesoscopic details in materials. However, temporal resolution at synchrotron sources is generally limited by the X-ray pulse duration in the range of 10–100 s of picoseconds. Accessing shorter time scales, for example a few picoseconds, requires complex and costly modification of the storage ring, at the expense of other source characteristics such as intensity and brightness.On the other hand, photonic devices based on microelectromechanical systems (MEMS) technology have been implemented in a wide range of applications and scientific research. The ability to manipulate light dynamically in a compact package is highly desirable in many scientific and technological applications. In addition, favorable scaling laws for miniaturization result in capabilities not possible with macro-scale devices. In the MEMS photonics community, the wavelengths of interest have been mainly in the visible to infrared regions for a wide range of imaging and telecommunication applications.
Previously, we showed that a MEMS oscillator, asynchronous to the X-ray source, can create and preserve the spatial, temporal, and spectral correlation of the X-rays on a time scale of several nanoseconds.In this work, we demonstrate that a MEMS-based X-ray dynamic optics, oscillating with a frequency matched to a synchrotron storage ring with a 1.1-km circumference, can control and manipulate hard X-ray pulses significantly below one nanosecond at 300 ps. With this exceptional time scale, we are now one step closer to achieving pulse streaking and pulse slicing that would allow us to access information at a sub-pulse temporal scale. MEMS devices as dynamic X-ray opticsThe concept of using a MEMS device in the X-ray wavelength range as a dynamic diffractive optics for a monochromatic beam is shown schematically in Fig. A thin, single-crystal silicon MEMS can diffract or transmit X-rays just by a change in its orientation relative to the incident X-ray beam (Fig. ). When the Bragg condition is fulfilled, the diffractive beam intensity as a function of the incident angle, θ, can be described by a rocking curve, illustrated in Fig., around the Bragg angle, θ B. As the MEMS crystal rapidly oscillates in the vicinity of θ B, a diffractive time window (DTW, as shown in Fig. ) opens during that time period. There are three schemes for utilization of MEMS devices: First, when the DTW is wider than the individual synchrotron X-ray pulses, but narrower than the pulse interval, the MEMS device can be employed as an X-ray pulse-picking chopper, as shown in Fig.
Second, if the DTW is narrower than the X-ray pulse width (as shown in Fig. ), the MEMS device will generate X-ray pulses shorter than the incident pulses, which enables time-resolved experiments to be performed with a temporal resolution higher than that given by the incident pulse duration. Parenthetically, this scheme also applies to continuous X-ray beams such as lab sources. Third, when the DTW is comparable to or slightly narrower than the width of the X-ray pulse (as seen in Fig. ), an X-ray streaking theme can be envisioned, completely in the optical domain, without sacrificing the detection efficiency, a problem suffered by other photonic devices such as X-ray streak cameras.
The conversion from X-ray pulse in the time domain to a streaked signal in the spatial domain is illustrated in Fig., where a high-resolution, position-sensitive detector accomplishes the conversion. This could lead to information in the single-pulse duration with sub-pulse temporal resolution. To make possible the applications of MEMS devices as dynamic X-ray optics, the MEMS DTW has to be sufficiently narrow. A high-frequency device is essential for pulse-picking, while a minimum DTW is more critical for pulse-slicing and streaking applications. Manipulation of hard X-ray pulses using a microelectromechanical-system (MEMS)-based oscillator. A Schematic of a rapidly oscillating single-crystal micromirror in a torsional MEMS device that diffracts monochromatic X-rays at its Bragg angle. B Static crystal rocking curve around Bragg angle θ B with a full-width-at-half-maximum (FWHM) of Δ θ B, typically several milli-degrees.
C Around the instance that the single-crystal element rotates through the Bragg angle, the crystal rocking curve converts to a temporally dispersed diffractive time window (DTW) with a FWHM of Δ t w. D When the DTW width is much wider than the X-ray pulse, but narrower than the pulse-to-pulse spacing, the MEMS can be utilized as an ultrafast pulse-picking device. E When the DTW is narrower than the X-ray pulse, the device creates X-ray pulses shorter than the incident pulse width in a form of pulse slicing in the time domain. F Dispersion/streaking of the X-ray pulse is possible, when the MEMS DTW is close to the incoming pulse width. G In the dispersion/streaking mode using a position-sensitive detector (PSD), the oscillating MEMS converts the X-ray pulse in the time domain to a spatially dispersed signal that contains time-resolved, sub-pulse information.
Since MEMS devices are based on single-crystal silicon (see Methods), X-ray diffraction occurs at the Bragg angle, θ B, at which the incident X-rays satisfy the Bragg condition. Due to the dynamical diffraction process, the angular width of the diffraction condition is not zero, but has a finite value (Δ θ B, or rocking curve width), as illustrated in Fig. As the MEMS device oscillates around θ B (Fig. ), the single-crystal element will diffract the X-rays for the short amount of time in which the Bragg condition is satisfied, and the element will transmit and absorb the X-rays over the rest of the cycle.
The oscillatory device transforms the static rocking curve into a dynamic one in the time domain, i.e., DTW (Fig. ). The maximum angular speed of the MEMS device determines the width of the DTW over which the Bragg condition is fulfilled. For use as a monochromatic X-ray optic, the width of the DTW, Δ t w, is given. (1)where f and α are the MEMS oscillation frequency and amplitude, respectively.
In order to interact with X-ray pulses while preserving their spatiotemporal correlation, a MEMS device must perform as an X-ray diffractive element with the highest reflectivity while maintaining this performance at high speeds without introducing any distortion to the incident X-ray wavefront. Tuning the MEMS resonant frequency to match the storage-ring frequencyTo be a dynamic optics for pulsed X-rays in an efficient way, the oscillation must be in synchrony or frequency-matched with the X-ray source.
Since MEMS resonators with a quality factor (Q) exceeding 10 3 have an extremely narrow resonance bandwidth, it is virtually impossible for an as-fabricated MEMS device to have a resonant frequency that coincides with the storage-ring frequency. An asynchronous device cannot be an effective X-ray optics at a light source that produces periodic pulses. In order to tune the frequency of the MEMS devices to be commensurate with the frequency of the synchrotron ring, we developed a highly precise frequency trimming process based on focused ion beam (FIB) techniques (see Methods and Supplementary Note ). The tuning process started with an as-fabricated MEMS with a resonance frequency of 65.8 kHz, about 2 kHz lower than the desired frequency of 67.889 kHz (one-fourth of the Advanced Photon Source APS operation frequency of P0 = 271.555 kHz).As can be seen in Fig., the MEMS device we used is a torsional oscillating silicon crystal that is 25 µm in thickness and 250 × 250 µm in area, actuated with in-plane comb-drive actuators. The sinusoidal oscillation of the silicon crystal is excited by a square-wave voltage signal with a frequency twice that of the resonant frequency of MEMS devices at 135.777 kHz, or P0/2. Tuning the resonance frequency of the device was performed using the FIB tool to remove mass from the oscillating crystal, thus reducing its moment of inertia and increasing its resonance frequency (Fig. ). Removal of a 5 × 5 × 25-µm 3 volume of the crystal results in an 80-Hz increase in the driving frequency of applied excitation voltage.
The tuning curves (shown in Fig. As a function of the driving frequency) have the characteristic waveform of a nonlinear resonator, with a sharp edge on the low-frequency side. The peak frequency of the tuning curves showed linear shifts with respect to removed volume at the outer edges of the silicon crystal (Supplementary Note and Supplementary Figure ).
With careful calculations and control of the FIB micromachining, the frequency response of the device (at a 45-V driving voltage) was shifted to the range from 135.75 to 135.81 kHz, which overlaps with the desired frequency of 135.777 kHz or P0/2 (Fig. ). Hence, after the tuning process, this group of MEMS are denoted as P0/2 devices. We also note here that the method of FIB fine-tuning, together with the design flexibility of MEMS devices, allows us to deploy them at different synchrotron facilities worldwide (see Methods). Tuning the resonance frequency of a MEMS oscillator using focused ion beam (FIB). A b Scanning electron microscopy images of the MEMS device as fabricated and after multiple rounds of FIB micromachining, respectively. Note these FIB machined devices still have the phosphorous dopant-induced strained layers, which was reported in our previous work (more detail in the Supplementary Note ).
C Tuning curves of the MEMS device measured with 45-V (peak-to-valley) square pulses after each FIB micromachining. Note that the frequency denoted in the X-axis is the frequency of excitation voltage signal, or twice the resonance frequency of MEMS devices. A total of eight micromachining processes were performed to tune the device to 135.777 kHz (P0/2). Reducing diffractive time window by increasing excitation voltagesPer Eq., to achieve a narrow window with a MEMS device of fixed resonance frequency, the most direct and effective method is to increase the oscillation amplitude, α, by applying a higher excitation voltage.
This promises to provide a flexible DTW width from a few nanoseconds (as demonstrated previously ) to sub-nanosecond, as described below.After FIB micromachining, and at a 45-V excitation voltage, the target frequency (P0/2) falls to almost the middle of the tuning curve. This ensures that the MEMS device can oscillate with an amplitude close to the peak values over a wide range of excitation voltage. In Fig., the tuning curves of the device are shown as the excitation voltage is varied from 50 to 100 V, above its onset voltage of about 40 V. Note that the mechanical deflecting angle is the physical angle that the MEMS crystal element oscillates around its flexure from the rest position, which is one-fourth of the MEMS optical scan angle, the widely used figure-of-merit in the MEMS scanner community. Around the onset voltage, a typical vertical comb-drive MEMS actuator has its oscillation angle proportional to the square of voltage.
Our measurement here covers the medium-to-high voltage region, where the peak amplitude increases almost linearly up to about 80 V, and deviates from the straight line at higher voltages (inset to Fig. ). The MEMS oscillation amplitude at P0/2 is measured precisely by the APS X-ray pulse (using 8-keV photons), as shown in Fig. The measurement was performed with closely packed synchrotron pulses (324-bunch mode at the APS with a bunch interval of 11.37 ns), which is discussed in detail in Methods and Supplementary Note. The angle vs.
Time plots during one cycle of the 7.365-µs oscillation reveal extremely precise oscillation amplitudes of 14.57° at 90 V, indicating the responsiveness of the MEMS oscillation to the excitation voltage. Parenthetically, this angle corresponds to an astonishing 58.3° optical scan angle at 135.777 kHz, while the peak optical scan angle can be close to 80°, as indicated by Fig. Reaching sub-nanosecond diffractive time window by applying high excitation voltage. A Tuning curves of the P0/2 MEMS at excitation voltages from 50 to 100 V in the vicinity of P0/2, or half the Advanced Photon Source storage-ring frequency.
Inset to a shows the peak amplitude as a function of the excitation voltage. B Precise measurement of oscillation amplitude using the X-ray pulses while the MEMS device is excited exactly at a frequency of P0/2.
We note that the delay time covered only a fraction of the MEMS oscillation period near null delay time, where the oscillation amplitude measurement is extremely sensitive and more accurate than any optical and electrical methods available to date. T is the oscillation period equal to 2/P0, or 7.365 μs. C DTW measured by 8-keV X-ray time-delay scans when the excitation voltages increased from 60 to 90 V, at which time the DTW width drops to below 0.5 ns. The curve denoted as 45 V is from an as-fabricated device in our previous work that is not frequency-matched to X-ray pulses. The arrow pointing upward marks the direction of increasing oscillation amplitude.
D Comparison between the expected and measured DTW as a function of the excitation voltage at 135.777 kHz. The expected DTW is calculated using Eq. And the amplitude values from b, which have a linear relationship with the excitation voltage, shown as the blue symbols (data) and line (linear fit).
Konfigurasi Nat Ns 300 2017
The shaded areas indicate sub-nanosecond DTW where it becomes impractical to use a higher voltage to achieve narrower DTW in P0/2 MEMS devices. With the frequency-commensurate MEMS device, the determination of the DTW can be efficiently done by means of delay scans with a single, 100-ps-wide synchrotron X-ray pulse, given that the pulse width is narrower than the DTW. The description of the delay scan is given in Methods and Supplementary Note. Briefly, by varying the phase of the device oscillation with respect to a fixed timing signal from the accelerator, an X-ray pulse samples through the Bragg peak in controlled delay steps so that the window profile is measured with an accuracy of 20 ps.
Such delay scans can also be understood as the creation of the dynamic rocking curve of the MEMS element as illustrated in Fig. With the increase in oscillation amplitude by increasing excitation voltage, the DTW widths decrease steadily, from several ns to just below 0.5 ns at 90 V, reaching almost an order of magnitude decrease (Fig. ). This remarkable result is summarized in Fig., where the plots show the measured DTW widths match the values predicted by Eq. Extremely well, down to 0.49 ns at the highest voltage. We demonstrated that the MEMS element can effectively manipulate hard X-ray pulses on a 500-ps time scale, well below the shortest bunch interval at any synchrotron source, which is typically between 2 and 10 ns.To evaluate the quality of the diffracted X-ray pulses by the MEMS element, we measured the diffracted beam spatial profiles in the diffraction plane when the MEMS devices were static or oscillating, as they are compared with the incident beam spatial profile.
The result is documented in detail in Supplementary Note. We report here that the quality of the spatial profile of the diffracted beam remains high. While the diffraction efficiency is about 95% (with over 10 sampling points), the dynamic diffracted beam was broadened spatially by only about 20% compared to when the MEMS element is static (off). This degradation of diffracted beam quality is expected to be mitigated by the MEMS without the surface doping produced in future dedicated MEMS fabrication runs. In addition, with monochromatic X-ray beams, beam heating effect on the diffracted beam quality is negligible, as discussed in detail in Supplementary Note.In Fig., the MEMS deflection angle at 135.777 kHz increases linearly with the excitation voltage. Using a higher excitation voltage alone to achieve a narrow DTW, however, has its limitations.
With planar comb drives, the maximum oscillation amplitude is set by a pull-in phenomenon where the rate of electrostatic force starts to exceed the mechanical restoring torque, leading to unstable oscillation. In the pull-in-free region, we can estimate the maximum angle based on the geometry of the MEMS device. In our case, the maximum angle is 20.3°. As shown in Fig., the amplitude has already exceeded 15° at 90 V (blue shaded area in Fig. ), hence there is little room for further improvement. The calculated limit agrees well with the experiment as the measured amplitude saturates around 20° above 100 V. We have also estimated the mechanical limit of our MEMS device where a large oscillation amplitude leads to fracture failure of the device (Supplementary Note ).
The mechanical limit is about 40° (substantially beyond our measurement range) thanks to the excellent mechanical properties of silicon. In addition to a limited oscillation amplitude, at the high excitation voltages the tuning curve becomes significantly broadened, indicating lower Q factors (Fig. ) and higher energy dissipation. Therefore, it becomes impractical to rely on exciting the MEMS using a higher voltage (power) to achieve even narrower DTW (yellow shaded area in Fig. ).As seen in Eq., the most challenging technical requirements in developing dynamic X-ray optics are simultaneously achieving large-amplitude and high-frequency operation using the MEMS torsional oscillators, as well as retaining the X-ray diffraction quality of the MEMS crystal. MEMS devices have demonstrated frequencies of 100 MHz to 10 GHz in timing applications where the oscillation amplitude is not a part of the design merit. On the other hand, large deflecting angular amplitude devices have been developed for displays, optical scanners, and other beam steering applications.
Most of these applications are limited by the requirements of other essential parameters, which do not require high oscillation frequency. Our devices require simultaneous optimization of both parameters: frequency and amplitude of the torsional devices.
In addition to reducing DTW of the X-ray MEMS devices, higher resonant frequency, f, also improves the efficiency of X-ray delivery since the synchronized high-frequency devices have a greater duty cycle. Higher-frequency MEMS oscillators operated in vacuum environmentWe designed MEMS devices with higher frequency and addressed the challenge to maintain a large oscillation amplitude. These MEMS devices, after FIB-based tuning, operate at the higher frequency of 271.555 kHz, the same as the APS storage-ring frequency, P0. We denote these as P0 devices. However, when operating in air, they have a much higher onset excitation voltage of 70 V, compared to lower-frequency devices (e.g., 40 V for the P0/2 devices). To obtain an oscillation amplitude above 10°, the excitation voltage must be as high as 110 V (as shown in Fig. ) with very high-level power consumption. The requirement of higher excitation voltage is due to the increased stiffness of the torsional flexure and significant fluid dynamic damping by the presence of air surrounding the rapidly oscillating devices whose angular velocity is close to 10 7 degrees s −1.
The interaction of the surrounding fluid (air) with the vibrating structure leads to energy dissipation, adversely affecting the oscillation amplitude and Q factor.
National Service ( NS) is the national policy in mandated by statutory law that requires all male Singaporean citizens and second-generation permanent residents to serve a period of in the uniformed services. Contents.HistoryThe NS (Amendment) act was passed on 15 March 1967, making National Service (NS) compulsory for all 18-year-old male Singapore citizens and permanent residents. The felt that it was necessary to build a substantial military force to defend itself.
The country had only about 1,000 soldiers at independence. In the late 1960s, the had decided to withdraw its troops and bases from the, including troops stationed in Singapore. That prompted the government to implement a conscription program for the country's defence needs. It adopted a conscription model drawing on elements from the and national conscription schemes. Some 9,000 male youths born between 1 January and 30 June 1949 became the first batch of young men to be called up for NS. Singapore had sought assistance through official diplomacy from other countries, but their refusal to provide help prompted Israeli diplomats to extend a helping hand to the new sovereign nation in the establishment of the Singapore armed forces.The stated rationale behind conscription is twofold.
Firstly, because Singapore has a population of about five and a half million (as of 2014), an army solely of would not be practical to defend the country. See also:was a national footballer who signed a professional contract with (FC) in 2017 and was offered a second professional contract to Davis in 2018. As Davis is due to serve National Service in 2019, he applied for an application to defer NS to play for Fulham FC and was rejected. He then signed the contract on 29 June 2018.In a Parliament session in August 2018, it was explained that the deferment for Davis to play for Fulham Football Club (FC) was not granted as there was no commitment to serve Singapore or our national interests. As of 11 January 2019. MINDEF had not received further appeals for deferment from Davis.Public opinion was divided on his deferment over MINDEF's rigidity and the Ministry's position.Davis was issued with an Enlistment Notice in September 2018 and is scheduled due enlistment for NS in February 2019.Since as of 18 February 2019, Mr Benjamin Davis is a National Service (NS) defaulter.
He failed to report for NS as required. He is also staying overseas without a valid Exit Permit.In a MINDEF official press release on 18 February 2019, Mr Davis has committed offences under the Enlistment Act, and is liable upon conviction to a fine of up to $10,000 and/or imprisonment of up to 3 years.
See also:On 22 August 2018, Mindef revealed that the author of the novel which was adapted into a, is wanted for defaulting on his NS obligations. Kwan in an interview implied that he returned to Singapore on a few occasions and was not arrested despite being wanted. The clarified there were no records of him entering Singapore after the year 2000. Ekawit TangtrakarnOn 28 August 2018, 24-year-old Thai national Ekawit Tangtrakarn pleaded guilty to breaching the Enlistment Act. On 18 September 2018, Ekawit was sentenced to a $6,000 fine. District Judge John Ng acknowledged that Ekawit was 'first and foremost a Thai national' and that there was 'there was nothing to show that he had intentionally placed his personal pursuits above his obligations or chose to do his NS at his convenience'. This was different from other cases where individuals wanted to take on citizenship in other countries without fulfilling their NS obligations.In 2006, Deputy Prime Minister and then Defence Minister stated that 'only those who have emigrated at a young age and have not enjoyed substantial socio-economic benefits are allowed to renounce their citizenship without serving national service.'
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Panasonic Kx Ns300 Wiring
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