Microsecond Level Research Articles

The Research of IEEE 1588 Interface Module Based on LXI Instrument

LXI, which is generally recognized as the new generation of instrument bus technology, not only has developed rapidly in the field of test and measurement, but also has a vast potential for future development. At present, the LXI trigger requires the clock synchronization precision to reach a sub microsecond level or even higher one. Therefore, in order to meet this accuracy requirement, a scheme based on the embedded Linux and IEEE 1588 protocol is proposed in this paper on the basis of studying LXI so as to realize high accurate clock synchronization. This scheme acquires hardware timestamp by utilizing PHY chip DP83640 and realizes PTP hardware clock driving based on Linux. A synchronization test with Agilent B LXI trigger box under the current condition is conducted and about 100ns of synchronization precision can be reached when connected with cable directly. The result demonstrates the feasibility of the scheme and that the clock synchronization precision can reach a nanosecond level.

The Detection Methods of Non-Level Road Based on OPCODE

The research of vehicle dynamics performance on the flat road has been more perfect at present. Around the world ,for lack of simulation environment, the analysis of vehicle driving and handling performance on non-level road is on an explorative stage. The paper established tire road detection model by using of open source code OPCODE. The ray given off from the wheel center intersects with the road model, and obtains the precise contact point and the road normal vector. Then wrote computer program based on the established detection model and embedded it into the complex vehicle model to simulate on longitudinal and lateral slope road. The simulation results show that: each detection time reach microsecond level and in the 1ms vehicle dynamics calculation step, road detection model meet the real-time simulation, and also the detection accuracy satisfy the requirements of the whole vehicle simulation.

Testing GPS generated 1PPS against a rubidium standard

GPS receivers are often used in time-keeping applications, due to their availability, low price and high accuracy. We tested the capability of the GPS receiver to deliver a time-keeping accuracy needed for the time-critical applications, such as astrometry measurements, when a microsecond or better level of accuracy is needed in real-time. We tested a geodetic class GPS receiver against a rubidium standard, over a 24 hours period. In the overall view, the accuracy corresponds to the nominal values. However, we experienced outliers with the certain regularity that we could not explain with cycle-slips or the experiment set-up.

Fast distributed multi-hop relative time synchronization protocol and estimators for wireless sensor networks

The challenging problem of time synchronization in wireless sensor networks is considered in this paper, where a new distributed protocol is proposed for both local and multi-hop synchronization. The receiver-to-receiver paradigm is used, which has the advantage of reducing the time-critical-path and thus improving the accuracy compared to common sender-to-receiver protocols. The protocol is fully distributed and does not rely on any fixed reference. The role of the reference is divided amongst all nodes, while timestamp exchange is integrated with synchronization signals (beacons). This enables fast acquisition of timestamps that are used as samples to estimate relative synchronization parameters. An appropriate model is used to derive maximum likelihood estimators (MLE) and the Cramer-Rao lower bounds (CRLB) for both the offset-only, and the joint offset/skew estimation. The model permits to directly estimating relative parameters without using or referring to a reference’ clock. The proposed protocol is extended to multi-hop environment, where local synchronization is performed proactively and the resulted estimates are transferred to the intermediate/end-point nodes on-demand, i.e. as soon as a multi-hop communication that needs synchronization is initiated. On-demand synchronization is targeted for multi-hop synchronization instead of the always-on global synchronization model, which avoids periodic and continuous propagation of synchronization signals beyond a single-hop. Extension of local MLE estimators is proposed to derive relative multi-hop estimators. The protocol is compared by simulation to some state-of-the-art protocols, and results show much faster convergence of the proposed protocol. The difference has been on the order of more than twice compared to CS-MNS, more than ten times compared to RBS, and more than twenty times compared to TPSN. Results also show scalability of the proposed protocol concerning the multi-hop synchronization. The error does not exceed few microseconds for as much as 10 hops in R4Syn, while in CS-MNS, and TPSN, it reaches few tens of microseconds. Implementation and tests of the protocol on real sensor motes confirm microsecond level precision even in multi-hop scenarios, and high stability (long lifetime) of the skew/offset model.

Microsecond molecular dynamics simulation of Aβ42 and identification of a novel dual inhibitor of Aβ42 aggregation and BACE1 activity

To study the conformational changes of Aβ42 and discover novel inhibitors of both Aβ42 aggregation and β-secretase (BACE1). A molecular dynamics (MD) simulation at a microsecond level was performed to explore stable conformations of Aβ42 monomer in aqueous solution. Subsequently, structure-based virtual screening was used to search for inhibitors of both Aβ42 aggregation and BACE1. Protein purification and in vitro activity assays were performed to validate the inhibition of the compounds identified via virtual screening. The initial α-helical conformation of Aβ42, which was unstable in aqueous solution, turned into a β-sheet mixed with a coil structure through a transient and fully random coil. The conformation of Aβ42 mainly comprising β-sheets and coils structure was used for further virtual screening. Five compounds were identified as inhibitors for Aβ42 aggregation, and one of them, AE-848, was discovered to be a dual inhibitor of both Aβ42 aggregation and BACE1, with IC50 values of 36.95 μmol/L and 22.70 μmol/L, respectively. A helical to β-sheet conformational change in Aβ42 occurred in a 1.8 microsecond MD simulation. The resulting β-sheet structure of the peptide is an appropriate conformation for the virtual screening of inhibitors against Aβ42 aggregation. Five compounds were identified as inhibitors of Aβ42 aggregation by in vitro activity assays. It was particularly interesting to discover a dual inhibitor that targets both Aβ42 aggregation and BACE1, the two crucial players in the pathogenesis of Alzheimer's disease.

Olivine-Type Nanosheets for Lithium Ion Battery Cathodes

Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li(+) to diffuse over a [010]-thickness of <5 nm (L) was calculated to be less than 25, 2.5, and 250 μs for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L(2)/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets).

The Design of Millimeter-Level Ultrasonic Distance Measurement Circuit

By analyzing the causes of ultrasonic distance measurement error, through the use of temperature compensation, and increasing the measured time interval to the microsecond level, ultrasonic ranging circuit can achieve the millimeter level. After the circuit design and construction, the ultrasonic range finder was calibrated from 1cm to 21cm. The measurement results show that in the scope of work, the linearity reached 0.999623; the measurement of the ultrasonic range finder achieved the millimeter level.

Synthesis, structure and photophysical properties of 2-benzhydryl-4-methyl-6-(aryliminomethyl)phenol ligands and the zinc complexes thereof

The Schiff-base ligands 2-benzhydryl-4-methyl-6-((phenylimino)methyl)phenol (L1–L5), and their corresponding zinc complexes (C1–C5), were prepared and fully characterized. The UV–Vis absorption and fluorescence spectra of the ligands and their Zn(II) complexes were measured in solvents such as methanol, dichloromethane, THF, or toluene, respectively. The results showed that the fluorescence intensity of the ligands was very weak, but upon coordination with Zn2+, the fluorescence intensity was greatly enhanced, and the fluorescent quantum yield ratio of C5 (0.46) to L5 (0.0004) in methanol increased by around 1150 times. The enhanced fluorescence of the zinc complexes is due to the intramolecular charge transfer (ICT) and the stronger geometrical rigidity of the delocalized bonding planes in these molecules. Transient absorption spectrum bands with peaks at about 310 and 460nm were attributed to triplet state absorptions and absorption dynamic curve fitting showed that lifetimes were of microsecond level scale. There was no time-resolved property observed for the bleaching spectral bands at 350nm and at ca. 460nm. This spectral property, like the Stokes shift, can be attributed to the typical behavior of nanosecond transient absorption of the compounds with the excited-state intramolecular proton transfer (ESIPT).

Long lifetime air plasma channel generated by femtosecond laser pulse sequence

Lifetime of laser plasma channel is significantly prolonged using femtosecond laser pulse sequence, which is generated from a chirped pulse amplification laser system with pure multi-pass amplification chain. Time-resolved fluorescence images and electrical conductivity measurement are used to characterize the lifetime of the plasma channel. Prolongation of plasma channel lifetime up to microsecond level is observed using the pulse sequence.

Development of Time Measuring Technique to Measure the Shock Speed during the Propagation in the Free Atmosphere

In the study of wave propagation in the free atmosphere, it is desirable to obtain time measurements to an accuracy of microsecond level. An experiment has been conducted to measure the wave speed during the propagation in the free atmosphere by the present technique. Due to sudden rupture of the diaphragm for the chamber pressure of 4.2 kg/cm2 and a wave generating in a shock tube travels with subsonic speed and the measured incident wave Mach number is 0.8 which leaves the shock tube in the free atmosphere. The measured travelling time of the incident wave to travel 61.5 cm distance in the shock tube is 2200 μsec and the same technique can apply to measure the shock wave speed. Several trigger points are installed at the exit of the shock tube in the open atmosphere to measure the strength of the wave propagation. It is observed that the wave strength decreases during the wave propagation in free atmosphere. Due to spherical expansion behind the wave, the pressure across the wave decreases. A numerical simulation is also conducted on supersonic shock wave to determine the shock speed and the travelling time in the free atmosphere. The pressures across shock wave at different locations of the shock wave are determined by solving the Euler equations and the simulation results indicate that the shock speed decreases during the propagation in the free atmosphere. In both experimental and numerical results, it is observed that the strength of the wave propagation in the free atmosphere decreases continuously due to spherical expansion. The present technique can also be used to measure the supersonic jet velocity, the velocity of bullet and any particle velocity in subsonic or supersonic ranges.

GPU-Enabled stochastic Spatiotemporal Model of Rat Ventricular Myocyte Calcium Dynamics

The dysfunction of the normal calcium dynamics is a major factor in certain types of cardiac arrhythmias. These cardiac arrhythmias are thought to result from Ca2+ waves which occur when Ca2+ release propagates from one release site to another outside of the normal time during systole resulting in depolarization of the cell's outer membrane. Experimental results suggest that the elementary event underlying calcium release at these sites is the Ca2+ spark and the summation of these Ca2+ sparks result in the global [Ca2+]i transient that causes contraction. We have developed a model of the cardiac myocyte that includes the spatial organization and microsecond level resolution of clusters of ryanodine receptor (RyR) that are Ca2+ release channels responsible for the generation of Ca2+ sparks. We use this model to explore how Ca2+ overload, RyR Ca2+ sensitivity, RyR coupling, and other factors that affect the propagation of Ca2+ release between release sites. We will utilize our newly developed Ultrafast Markov chain Monte Carlo method which allows the rapid simulation of a whole-cell model containing 20,000 release sites, each containing 7 L-type Ca2+ channels and 50 RyRs. This algorithm greatly reduces computation time by using adaptive time step approach and a compact representation of the Markov chain state space. Hence, this novel method provides a powerful tool for performing stochastic cellular simulation with realistic Ca2+ dynamics. Also, with the availability of the next generation graphics processing units (GPU) computing architecture - codename Fermi from NVIDIA - model solution is greatly accelerated allowing the implementation of such a detailed model for the first time.

Synchronization of Thomson scattering measurements on MAST using an FPGA based “Smart” trigger unit

The MAST Thomson scattering diagnostic has recently been upgraded to make electron density and temperature measurements at 130 points across the 1.5 m diameter of the plasma. The new system is able to take 240 measurements per second using eight Nd:YAG lasers, each running at 30 Hz. The exact firing time of these lasers is adjusted with 100 ns precision using a field programmable gate array based trigger unit. Trigger pulses are produced to fire the lamps of all lasers and the Q switches with the appropriate delay depending on the warm-up status. The lasers may be fired in rapid bursts so as to achieve a high temporal resolution over eight points separated down to the microsecond level. This trigger unit receives optical trigger events and signals from external sources, allowing the trigger sequences to be resynchronized to the start of the plasma pulse and further events during the shot such as the entry of a fuelling pellet or randomly occurring plasma events. This resynchronization of the laser firing sequence allows accurate and reproducible measurements of fast plasma phenomena.

DORIS/Jason-2: Better than 10 cm on-board orbits available for Near-Real-Time Altimetry

DIODE (DORIS Immediate Orbit on-board Determination) is a real-time on-board orbit determination software, embedded in the DORIS receiver. The purpose of this paper is to focus on DIODE performances. After a description of the recent DORIS evolutions, we detail how compliance with specifications are verified during extensive ground tests before the launch, then during the in-flight commissioning phase just after the launch, and how well they are met in the routine phase and today. Future improvements are also discussed for Jason-2 as well as for the next missions. The complete DORIS ground validation using DORIS simulator and new DORIS test equipments has shown prior to the Jason-2 flight that every functional requirement was fulfilled, and also that better than 10 cm real-time DIODE orbits would be achieved on-board Jason-2. The first year of Jason-2 confirmed this, and after correction of a slowly evolving polar motion error at the end of the commissioning phase, the DIODE on-board orbits are indeed better than the 10 cm specification: in the beginning of the routine phase, the discrepancy was already 7.7 cm Root-Mean-Square (RMS) in the radial component as compared to the final Precise Orbit Ephemerides (POE) orbit. Since the first day of Jason-2 cycle 1, the real-time DIODE orbits have been delivered in the altimetry fast delivery products. Their accuracy and their 100% availability make them a key input to fairly precise Near-Real-Time Altimetry processing. Time-tagging is at the microsecond level. In parallel, a few corrections (quaternion problem) and improvements have been gathered in an enhanced version of DIODE, which is already implemented and validated. With this new version, a 5 cm radial accuracy is achieved during ground validation over more than Jason-2 first year (cycles 1–43, from July 12th, 2008 to September 11th, 2009). The Seattle Ocean Surface Topography Science Team Meeting (OSTST) has recommended an upload of this v4.02 version on-board Jason-2 in order to take benefit from more accurate real-time orbits. For the future, perhaps the most important point of this work is that a 9 mm consistency is observed on-ground between simulated and adjusted orbits, proving that the DORIS measurement is very precisely and properly modelled in the DIODE navigation software. This implies that improvement of DIODE accuracy is still possible and should be driven by enhancement of the physical models: forces and perturbations of the satellite movement, Radio/Frequency phenomena perturbing measurements. A 2-cm accuracy is possible with future versions, if analysis and model improvements continue to progress.

Folding Simulations of a De Novo Designed Protein with a βαβ Fold

βαβ structural motifs are commonly used building blocks in protein structures containing parallel β-sheets. However, to our knowledge, no stand-alone βαβ structure has been observed in nature to date. Recently, for the first time that we know of, a small protein with an independent βαβ structure (DS119) was successfully designed in our laboratory. To understand the folding mechanism of DS119, in the study described here, we carried out all-atom molecular dynamics and coarse-grained simulations to investigate its folding pathways and energy landscape. From all-atom simulations, we successfully observed the folding event and got a stable folded structure with a minimal root mean-square deviation of 2.6 Å with respect to the NMR structure. The folding process can be described as a fast collapse phase followed by rapid formation of the central helix, and then slow formation of a parallel β-sheet. By using a native-centric Gō-like model, the cooperativity of the system was characterized in terms of the calorimetric criterion, sigmoidal transitions, conformation distribution shifts, and free-energy profiles. DS119 was found to be an incipient downhill folder that folds more cooperatively than a downhill folder, but less cooperatively than a two-state folder. This may reflect the balance between the two structural elements of DS119: the rapidly formed α-helix and the slowly formed parallel β-sheet. Folding times estimated from both the all-atom simulations and the coarse-grained model were at microsecond level, making DS119 another fast folder. Compared to fast folders reported previously, DS119 is, to the best of our knowledge, the first that exhibits a parallel β-sheet.

Spectral and defect analysis of Cu-doped combustion synthesized new SrAl 4O 7 phosphor

A simple solution combustion synthesis route for preparation of Cu-doped SrAl 4O 7 has been described. Average particle size of 33 nm and platelet-like morphology has been observed. ESR studies confirm the presence of Cu in polycrystalline SrAl 4O 7. Bright-green luminescence under near-UV irradiation arising due to transition between Cu + levels with microsecond level decay time makes it suitable for application in phosphor converted light emitting diode (LED). TL measurements show broad glow peaks which when deconvoluted indicate activation energies in the range of 0.6–1.1 eV and elucidate the trapping dynamics.

Pulsar timing for theFermigamma-ray space telescope

We describe a comprehensive pulsar monitoring campaign for the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The detection and study of pulsars in gamma rays give insights into the populations of neutron stars and supernova rates in the Galaxy, into particle acceleration mechanisms in neutron star magnetospheres, and into the “engines” driving pulsar wind nebulae. LAT's unprecedented sensitivity between 20 MeV and 300 GeV together with its 2.4 sr field-of-view makes detection of many gamma-ray pulsars likely, justifying the monitoring of over two hundred pulsars with large spin-down powers. To search for gamma-ray pulsations from most of these pulsars requires a set of phase-connected timing solutions spanning a year or more to properly align the sparse photon arrival times. We describe the choice of pulsars and the instruments involved in the campaign. Attention is paid to verifications of the LAT pulsar software, using for example giant radio pulses from the Crab and from PSR B1937+21 recorded at Nançay, and using X-ray data on PSR J0218+4232 from XMM-Newton. We demonstrate accuracy of the pulsar phase calculations at the microsecond level.

LHC Collimators Low Level Control System

The low level control system (LLCS) of the LHC collimators is responsible for accurate synchronization of 500 axes of motion at microsecond level. Stepping motors are used in open loop ensuring a high level of repeatability of the position. In addition, a position survey system based on Resolver and LVDT sensors and operating at approximately 100 Hz, verifies in real-time the position of each axis with some tens of micrometers accuracy with respect to the expected position. The LLCS is characterized by several challenging requirements such as high reliability, redundancy, strict timing constraints and compactness of the low level hardware because of the limited space available in the racks underground. The National Instruments PXI platform has been proposed and evaluated as real-time low level hardware. In this paper the architecture of the LHC collimators LLCS is presented. The solution adopted for implementing motion control and positioning sensors reading on the PXI platform are detailed.

Effects of finite emission height in precision pulsar timing

Precision timing is the key ingredient of ongoing pulsar-based gravitational wave searches and tests of general relativity using binary pulsars. The conventional approach to timing explicitly assumes that the radio emitting region is located at the center of the pulsar, while polarimetric observations suggest that radio emission is in fact produced at altitudes ranging from tens to thousands of kilometers above the neutron star surface. Here we present a calculation of the effects of finite emission height on the timing of binary pulsars using a simple model for the emitting region geometry. A finite height of emission $h$ changes the propagation path of radio photons through the binary and gives rise to a large spin velocity of the emission region corotating with the neutron star. Under favorable conditions these two effects introduce corrections to the conventional time delays at the microsecond level (for a millisecond pulsar in a double neutron star binary with a period of several hours and assuming $h=100\text{ }\text{ }\mathrm{km}$). Exploiting the dependence of the emission height on frequency (radius-to-frequency mapping) and using multifrequency observations one should be able to detect these timing corrections even though they are formally degenerate with conventional time delays. Although even in the most accurately timed systems the magnitude of the finite emission height effects is currently somewhat below timing precision, longer-term observations and future facilities like SKA will make measurement of these effects possible, providing an independent check of existing emission height estimates.

Wombat: The high-intensity powder diffractometer at the OPAL reactor

The Wombat powder diffractometer will be located on the TG1 thermal guide at the OPAL reactor. A variable vertically focusing monochromator will provide a flux of up to ≈10 8 ns −1 cm −2 at the sample position. A compact curved 2D position sensitive detector will allow simultaneous acquisition of 120 ° in 2 θ, with ≈10 6 s −1 count rate capability and time resolution down to the microsecond level. Wombat is designed for experiments requiring rapid real time acquisition (time-resolved environmental or kinetics experiments) or very good signal to noise (experiments with difficult sample environments or small sample volumes).

Analysis of the optical layout of the OZIRIS stellar interferometer

This paper presents an analysis of the optical layout and some aberrational calculations for the OZIRIS stellar arcmeter-interferometer, developed under contract with the Russian Space Agency. The device is intended to measure the arc between celestial bodies at a microsecond level of accuracy. The layout provides that the bases of two interferometers coincide and that the image of a stellar point source in the beams formed by the optical elements is spatially filtered to form aberration-free wave fronts of the interfering beams. The optical elements of the telescopes of each arm of the interferometers, which form beams diffracted at spatial filters, are used to aim the telescopes at the object to be measured.