Computer Clock Research Articles

Wireless optically pumped magnetometer MEG

The current magnetoencephalography (MEG) systems, which rely on cables for control and signal transmission, do not fully realize the potential of wearable optically pumped magnetometers (OPM). This study presents a significant advancement in wireless OPM-MEG by reducing magnetization in the electronics and developing a tailored wireless communication protocol. Our protocol effectively eliminates electromagnetic interference, particularly in the critical frequency bands of MEG signals, and accurately synchronizes the acquisition and stimulation channels with the host computer's clock. We have successfully achieved single-channel wireless OPM-MEG measurement and demonstrated its reliability by replicating three well-established experiments: The alpha rhythm, auditory evoked field, and steady-state visual evoked field in the human brain. Our prototype wireless OPM-MEG system not only streamlines the measurement process but also represents a major step forward in the development of wearable OPM-MEG applications in both neuroscience and clinical research.

Assessment of an NTP service calibration over a Local Area Network

Nowadays, timekeeping is an essential component in modern computing. The Network Time Protocol (NTP) is a distributed service based on a hierarchical network protocol used to synchronize computer clocks over a network in an easy and scalable manner. Currently, this protocol is the main mechanism used on the internet to provide a common notion of time to all computers. The Real Instituto y Observatorio de la Armada (ROA) realizes Spanish legal time and disseminates it via the internet from two publicly accessible NTP time servers. In this study, it is assessed the implementation and characterization of two NTP time servers over a Local Area Network in client-to-server and server-to-server modes from the side of NTP protocol and all its functionalities. These measurements aim to analyze the client-to-server mode operation, forcing the polling interval at different values, and to verify the consistency of the results by employing the ppstest tool to compare one pulse‐per‐second from the UTC (ROA) with the client time offset. This comparison corroborates the proper operation of the NTP time server configured as stratum 1 and referred directly to UTC (ROA), and shows how a real deployment can be professionally deployed with the aim of distributing time over a public service using NTP.

Origin of biased noise in one-time readout temporal single pixel imaging

One-time readout temporal ghost imaging is a viable time-analog of single pixel imaging using a sluggish light receiver haunted by memory effects, which can be utilized to eliminate the need for steady watch and as such save computer clocks for data capturing and processing. Although the as-retrieved ghost image of a temporal object is modulated in proportion to the time-reversed impulse response function of the light receiver, it can be easily corrected by division. Nevertheless, inhomogeneously distributed noise plagues the images wildly, depending on the transmittance profile of an intensity-only object, which puzzles us. A coherent explanation is attempted for such apparently inconsistent behavior of the biased noise that develops even in simulation.

Optimal Parking Path Planning and Parking Space Selection Based on the Entropy Power Method and Bayesian Network: A Case Study in an Indoor Parking Lot

According to the vehicle dynamics model and the requirements of reliable safety and minimal time, the path planning problem of parking in different types of parking spaces is solved by obstacle avoidance analysis and motion analysis in the case of the optimal solution, and the parking trajectory from the initial position to the designated parking space is obtained. In the static situation, different parking spaces in the parking space are occupied; analyze the parking space type, parking space left and right occupancy situation, and the distance between the vacant parking space and the starting point location of unoccupied cars; and establish the attribute information matrix R0 of the vacant parking space and calculate the KMO value of the matrix R0. This is completed to determine the weak correlation between the attributes of the vacant parking space and use the matrix R0 as the original evaluation matrix of the entropy weight method, using the entropy weight method to calculate the three attributes of parking space type, parking space left and right occupancy situation, and distance between starting point and parking space. These results are weighted in the optimal parking space selection process, the difficulty score of the vacant parking space is determined, and the optimal parking space is determined through the ranking of the scores. In the dynamic case, the number of parking spaces and parking space usage will change over time, with the help of the Bayesian network, the existing parking spaces and number of spaces in the parking lot at the previous moment are learned according to the computer clock, which can be used to reason about the number of parking spaces and parking space availability in the parking lot at the next moment. The weights of the three attributes of parking space type, parking space left and right situation, and distance between the starting point and parking space are updated in the case of a dynamic change of parking space, and then the parking difficulty score of a new vacant parking space using the entropy weight method is used to select the optimal parking space in the dynamic situation. The optimized parking path planning and parking space selection method could contribute to enhancing parking efficiency for the sustainable management of indoor parking lots.

Demonstration and Comparison of Different Entanglement Fabrication Approaches

Quantum entanglement is the most representative feature of quantum mechanics to classical mechanics. It is the delocalization, non-classical strong correlation among multiple quantum system. It has been developed for nearly one hundred years and a lot of methods of production and applications have been proposed. Aiming at the generation mode of quantum entanglement, this study presents two general preparation methods of quantum entanglement sources, including spontaneous parametric down-conversion (SPDC) and the preparation of quantum entanglement sources based on the four-wave mixing (FWM) effect. The principle, advantages and disadvantages of quantum entanglement sources are analyzed respectively. Finally, the research and application direction of the preparation method of quantum entanglement source are prospected. With the ability of preparation of quantum entanglement source, the application of quantum entanglement developed quickly, (e.g., quantum teleportation, entanglement swapping, quantum key distribution and quantum dense coding in the area of communication), and other area such as quantum computer, quantum imaging, quantum ranging and quantum clock synchronization. These results shed light on guiding further exploration of entanglement fabrication.

A Security Enhancement of the Precision Time Protocol Using a Trusted Supervisor Node.

The Precision Time Protocol (PTP) as described in IEEE 1588–2019 provides a sophisticated mechanism to achieve microsecond or even sub-microsecond synchronization of computer clocks in a well-designed and managed network, therefore meeting the needs of even the most time-sensitive industrial and financial applications. However, PTP is prone to many security threats that impact on a correct clock synchronization, leading to potentially devastating consequences. Here, the most vicious attacks are internal attacks, where a threat actor has full access to the infrastructure including any cryptographic keys used. This paper builds on existing research on the impact of internal attack strategies on PTP networks. It shows limitations of existing security approaches to tackle internal attacks and proposes a new security approach using a trusted supervisor node (TSN), in line with prong D as specified in IEEE 1588–2019. A TSN collects and analyzes delay and offset outputs of monitored slaves, as well as timestamps embedded in PTP synchronization messages, allowing it to detect abnormal patterns that point to an attack. The paper distinguishes between two types of TSN with different capabilities and proposes two different detection algorithms. Experiments show the ability of the proposed method to detect all internal PTP attacks, while outlining its limitations.

ПОКРИТТЯ ЗОРІ АСТЕРОЇДОМ (853) НАНСЕНІЯ 8 КВІТНЯ 2021 р.

Observations of occultations of stars by asteroids provide useful information about the shape and size of asteroids. Ground-based multisite observations are especially valuable in that regard. To this end, on the joint initiative of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine and Astronomical Observatory of Taras Shevchenko National University of Kyiv, the development of Ukrainian network of stellar occultation observing stations is currently underway. Asteroids vary greatly in size with small asteroids being dominating. Occultations by small asteroids are visible across a rather narrow path. In such a case, it will not be feasible to make use of the entire network. Moreover, it is not always possible to conduct observations using telescopes with the required primary mirror diameter and light-gathering power or those equipped with special high-speed cameras. First of all, it applies to asteroids small in diameter for which the shadow tracks may run far from stationary telescopes. If this is the case, amateur telescopes or movable systems are employed. The aperture of such telescopes does not enable to acquire observations of occultations of faint stars with short exposure times. However, any observations are useful as they may help to determine the limits of asteroid diameter directly using techniques typical for the photometry of stellar occultations. This paper presents the results of observations of the star UCAC4 516-047388 occultation by the asteroid (853) Nansenia on 8 April 2021 performed at the Kryzhanovka observation station of Odessa I.I. Mechnikov National University. This observing station will become a part of the network of stellar occultation observers which is currently being set up. A Schmidt telescope(D = 271.25 mm, F = 440 mm) and Videoscan-415-2001 CCD camera were used to carry out observations. The ICX415AL chip (with the number of effective pixels 782 (H) x 582 (V) and unit cell size of 8.3 μm x 8.3 μm) serves as an interline image sensor for the specified CCD camera. The spectral sensitivity of the CCD camera approximately corresponds to the visible range. The NTP based PC system clock was used for the frame time-stamping. A GPS receiver with a specialised application running in the background was used to set (synchronise) the imaging system computer clock. The exposure duration for the occultation recording was chosen to be 5 seconds in order to acquire an image of the star adequate for photometric measurements, on the one hand, but to minimise the exposure time thus improving temporal resolution, on the other hand. The star UCAC4 516-047388 has a low brightness of 14.2 m which provides another reason for a long exposure time of 5 seconds to be used. This exposure time exceeds the maximum duration of occultation of 2.8 sec. An approach that enables us to draw a conclusion that the occultation has taken place and also to estimate the duration of such a phenomenon is adopted to construe the photometric (light) curve. Our calculations yield the duration of occultation τ = 2.0 ± 1.2 sec, which corresponds to the predicted value within the error. This paper also provides a description of the custom software, designed to process observations of occultations in the form of a series of graphic (image) files, which was employed for the stellar occultation by the asteroid (853) Nansenia. This software application can also be used to process observations of amateurs who will become involved in observing stellar occultations.

Half-life of 67Cu

The half-life of 67Cu was determined through serial gamma-ray spectrometry measurements of the dominant gamma emission (E γ : 184.6 keV; branching ratio: 48.7%) produced following β- decay. Data were collected consecutively for 1000 s per measurement, with a total of 3063 measurements over the duration of 36 days. The incidence rate for the 184.6 keV gamma-ray was determined from the spectral peak area and duration of each measurement. This rate was then corrected to account for detector dead-time, radioactive decay during each acquisition and drift in the computer clock in comparison to NIST nuclear clock. Least-squares regression analysis was performed to determine the half-life of 67Cu. The result was 61.761 ± 0.004 h, which is the highest precision measurement to date, and marks a 24-fold precision improvement over the current Nuclear Data Sheets value.

Traceability of network time service to UTC(NIM): online calibration

Network time service provided by Network Time Protocol (NTP) servers is widely used to synchronize the clocks of computers and other networked equipment. With the rapid development of smart devices and their applications, more NTP servers as time sources need to be calibrated to a legal time reference. This work proposes using a low-cost and convenient calibration method to investigate the time service capability of ten NTP servers located at different cities in China. The uncertainties (k = 2) of the time offsets between Coordinated Universal Time (National Institute of Metrology) and network time from NTP servers for a single measurement are generally less than 150 ms, and the uncertainties (k = 2) of the mean time offsets for 24 h are less than 85 ms. Calibration results were found at the same level when applying the two time references, which were maintained a time offset less than 10 ns and located more than 1000 km apart.

Stealthy and Robust Glitch Injection Attack on Deep Learning Accelerator for Target With Variational Viewpoint

Deep neural network (DNN) accelerators overcome the power and memory walls for executing neural-net models locally on edge-computing devices to support sophisticated AI applications. The advocacy of “model once, run optimized anywhere” paradigm introduces potential new security threat to edge intelligence that is methodologically different from the well-known adversarial examples. Existing adversarial examples modify the input samples presented to an AI application either digitally or physically to cause a misclassification. Nevertheless, these input-based perturbations are not robust or surreptitious on multi-view target. To generate a good adversarial example for misclassifying a real-world target of variational viewing angle, lighting and distance, a decent number of target’s samples are required to extract the rare anomalies that can cross the decision boundary. The feasible perturbations are substantial and visually perceptible. In this paper, we propose a new glitch injection attack on DNN accelerator that is capable of misclassifying a target under variational viewpoints. The glitches injected into the computation clock signal induce transitory but disruptive errors in the intermediate results of the multiply-and-accumulate (MAC) operations. The attack pattern for each target of interest consists of sparse instantaneous glitches, which can be derived from just one sample of the target. Two modes of attack patterns are derived, and their effectiveness are demonstrated on four representative ImageNet models implemented on the Deep-learning Processing Unit (DPU) of FPGA edge and its DNN development toolchain. The attack success rates are evaluated on 118 objects in 61 diverse sensing conditions, including 25 viewing angles (−60° to 60°), 24 illumination directions and 12 color temperatures. In the covert mode, the success rates of our attack exceed existing stealthy adversarial examples by more than 16.3%, with only two glitches injected into ten thousands to a million cycles for one complete inference. In the robust mode, the attack success rates on all four DNNs are more than 96.2% with an average glitch intensity of 1.4% and a maximum glitch intensity of 10.2%.

Pd-parser: A tool for Matching Photodiode Deflection Events to Time-Stamped Events.

SummaryPrecise synchronization of events displayed on a monitor to recordings of time series data is critical for applications such as vision or psychophysics research. To achieve this, researchers often use a photodiode to convert the luminance on a monitor over time into a voltage time course, which is what is recorded. pd-parser matches photodiode deflection events to time-stamped events; it is particularly useful when the photodiode signal is corrupted or there is drift between the clock of the computer controlling the monitor and the data acquisition computer clock.

Cyber Attacks on Precision Time Protocol Networks—A Case Study

The IEEE 1588 precision time protocol (PTP) is used by many time-sensitive applications and systems, as it achieves sub-microsecond time synchronization between computer clocks. However, a PTP network is vulnerable to cyber-attacks that can reduce the protocol accuracy to unacceptable levels for some or all clocks in a network with potentially devastating consequences. Of particular concern are advanced persistent threats (APT), where an actor infiltrates a network and operates stealthily and over extended periods of time before being discovered. This paper investigates the impact of the most important APT strategies on a PTP network, i.e., the delay attack, packet modification or transparent clock attack, and time reference attack, using a fully programable and customizable man in the middle device, thereby considering the two most popular PTP slave daemons PTPd and PTP4l. In doing so, it determines suitable attack patterns and parameters to compromise the time synchronization covertly.

The Statistics of Computer Clocks and the Design of Synchronization Algorithms.

In this study, I used standard statistical tools (such as the various forms of the two-sample Allan variance) to characterize the clocks in computers, and I show how the results of this study are used to design algorithms to synchronize the computer clocks. These synchronization algorithms can be used to synchronize the time of a computer to a local reference clock or to a remote server. The algorithms by themselves are not intended to be a simple replacement for software that implements the Network Time Protocol (NTP) or any other similar application. Instead, they describe the statistical principles that should be used to design an algorithm to synchronize any computer clock by using data from any external reference received in any format. These algorithms have been used to synchronize the clocks of the computers that support the Internet Time Service operated by the National Institute of Standards and Technology (NIST), and I illustrate the performance of the algorithm with real-time data from these servers. In addition to presenting the design principles of the algorithm, I illustrate the principles with two specific examples: synchronizing a computer clock to a local reference signal, and the design of a synchronization process that is based on time-difference data received from a remote server over the public Internet. The message exchange between the local system and the remote server in this configuration is realized in NTP format, but that is not a fundamental requirement.

Single-Phase Grid-Connected Inverters With Simplified SPWM Control

The conventional grid-connected inverters require a sophisticated digital signal processor to generate the demanded reference signal as a feedforward signal for the sinusoidal pulse width modulation (SPWM) control. However, the reference signal needs to be re-calculated to maintain the demanded power control as the ac mains varies. It increases the computation burden of the controller and has become a major obstacle of the grid connected energy storage system with demanded power flow control. Therefore, a simplified approach to reduce the computation burden of the controller is proposed in this paper. With the proposed simplified equation for the power flow control, the usage of a low cost microcontroller unit becomes possible. In additional, no additional sensors or circuitries are needed. Meanwhile, the performance of desired power flow control by using the simplified control is almost unaffected. The proposed simplified algorithm is validated via mathematical calculations, computer simulation and experimental results. By using the proposed simplified control, 52.3% of the computational clock cycles can be reduced. Different operation scenarios were tested to validate the performance of the proposed simplified control via the MATLAB/Simulink simulations and the 1kVA prototype experiments.

Time Drift Considerations When Using GPS and Accelerometers

Purpose: To investigate potential time drift between devices when using Global Positioning Systems (GPS) and accelerometers in field-based research. Methods: Six Qstarz BT-Q1000XT GPS trackers, activPAL3 accelerometers, and ActiGraph GT3X+ and GT3X accelerometers were tested over 1–3 waves, each lasting 9–14 days. Once per day an event marker was created on each pair of devices concurrently. The difference in seconds between the time stamps for each event marker were calculated between each pair of GPS and activPAL devices and GPS and ActiGraph devices. Mixed-effects linear regression tested time drift across days and waves and between two rooms/locations (in an inner room vs. on a windowsill in an outer room). Results: The GPS trackers remained within one second of the computer clock across days and waves and between rooms. The activPAL devices drifted an average of 8.38 seconds behind the GPS devices over 14 days (p < .001). The ActiGraph GT3X+ devices drifted an average of 11.67 seconds ahead of the GPS devices over 14 days (p < .001). The ActiGraph GT3X devices drifted an average of 28.83 seconds behind the GPS devices over 9 days (p < .001). Time drift did not differ across waves but did differ between rooms and across devices. Conclusions: Time drift between the GPS and accelerometer models tested was minimal and is unlikely to be problematic when addressing many common research questions. However, studies that require high levels of precision when matching short (e.g., 1-second) time intervals may benefit from consideration of time drift and potential adjustments.

TimeStream: Exploiting video streams for clock synchronization

Network Time Protocol (NTP) is the most commonly used protocol for clock synchronization on the Internet.In the wake of frequent news about attacks that use Network Time Protocol (NTP), we propose a TimeStream algorithm, which – in its plain version (without any extra settings) – successfully synchronizes computer clocks up to seconds, by processing data found in video streams that use HTTP Live Streaming (also known as HLS) protocol. Further increase of precision is possible with a proper setup of the origin video servers.TimeStream provides secure time synchronization without requiring new ports, new hardware, or expensive cryptography, and uses information which – currently – is already making at least 70% of all Internet traffic.We observe that some intrinsic properties of video streaming over HTTP and congestion control of TCP yield some useful properties that facilitate good performance of the proposed method even in adverse network conditions. These make TimeStream to be robust against packet delay manipulation attack in which, an attacker adds specifically crafted delays to packets carrying time information.To the best of our knowledge, TimeStream may be one of the first methods of its kind that uses structure and core features of video streams and underlying network transportation protocol, to extract information about time and opens a new line of research on almost real-time extraction of useful information from video content.

The Computational Efficiency of Monte Carlo Breakage of Articles using Serial and Parallel Processing: A Comparison

This paper presents a GPU-based parallelized and a CPU-based serial Monte-Carlo method for breakage of a particle. We compare the efficiency of the graphic card’s graphics processing unit (GPU) and the general-purpose central processing unit (CPU), in a simulation using Monte Carlo (MC) methods for processing the particle breakage. Three applications are used to compare the computational performance times, clock cycles and speedup factors, to find which platform is faster under which conditions. The architecture of the GPU is becoming increasingly programmable; it represents a potential speedup for many applications compared to the modern CPU. The objective of the paper is to compare the performance of the GPU and Intel Core i7-4790 multicore CPU. The implementation for the CPU was written in the C programming language, and the GPU implemented the kernel using Nvidia’s CUDA (Compute Unified Device Architecture). This paper compares the computational times, clock cycles and the speedup factor for a GPU and a CPU, with various simulation settings such as the number of simulation entries (SEs), for a better understanding of the GPU and CPU computational efficiency. It has been found that the number of SEs directly affects the speedup factor.

Design and Digital Implementation of Fast and Recursive DCT II–IV Algorithms

Using the proposed factorizations of discrete cosine transform (DCT) matrices, fast and recursive algorithms are stated. In this paper, signal flow graphs for the n-point DCT II and DCT IV algorithms are introduced. The proposed algorithms yield exactly the same results as with standard DCT algorithms but are faster. The arithmetic complexity and stability of the algorithms are explored, and improvements of these algorithms are compared with previously existing fast and stable DCT algorithms. A parallel hardware computing architecture for the DCT II algorithm is proposed. The computing architecture is first designed, simulated, and prototyped using a 40-nm Xilinx Virtex-6 FPGA and thereafter mapped to custom integrated circuit technology using 0.18- $$\upmu $$ m CMOS standard cells from Austria Micro Systems. The performance trade-off exists between computational precision, chip area, clock speed, and power consumption. This trade-off is explored in both FPGA and custom CMOS implementation spaces. An example FPGA implementation operates at clock frequencies in excess of 230 MHz for several values of system word size leading to real-time throughput levels better than 230 million 16-point DCTs per second. Custom CMOS-based results are subject to synthesis and place-and-route steps of the design flow. Physical silicon fabrication was not conducted due to prohibitive cost.

Improving mechanical sensor performance through larger damping.

Mechanical resonances are used in a wide variety of devices, from smartphone accelerometers to computer clocks and from wireless filters to atomic force microscopes. Frequency stability, a critical performance metric, is generally assumed to be tantamount to resonance quality factor (the inverse of the linewidth and of the damping). We show that the frequency stability of resonant nanomechanical sensors can be improved by lowering the quality factor. At high bandwidths, quality-factor reduction is completely mitigated by increases in signal-to-noise ratio. At low bandwidths, notably, increased damping leads to better stability and sensor resolution, with improvement proportional to damping. We confirm the findings by demonstrating temperature resolution of 60 microkelvin at 300-hertz bandwidth. These results open the door to high-performance ultrasensitive resonators in gaseous or liquid environments, single-cell nanocalorimetry, nanoscale gas chromatography, atmospheric-pressure nanoscale mass spectrometry, and new approaches in crystal oscillator stability.

How to build time-lock encryption

Time-lock encryption is a method to encrypt a message such that it can only be decrypted after a certain deadline has passed. We propose a novel time-lock encryption scheme, whose main advantage over prior constructions is that even receivers with relatively weak computational resources should immediately be able to decrypt after the deadline, without any interaction with the sender, other receivers, or a trusted third party. We build our time-lock encryption on top of the new concept of computational reference clocks and an extractable witness encryption scheme. We explain how to construct a computational reference clock based on Bitcoin. We show how to achieve constant level of multilinearity for witness encryption by using SNARKs. We propose a new construction of a witness encryption scheme which is of independent interest: our scheme, based on Subset-Sum, achieves extractable security without relying on obfuscation. The scheme employs multilinear maps of arbitrary order and is independent of the implementations of multilinear maps.