Clock Performance Research Articles

Excited-Band Coherent Delocalization for Improved Optical Lattice Clock Performance.

We implement coherent delocalization as a tool for improving the two primary metrics of atomic clock performance: systematic uncertainty and instability. By decreasing atomic density with coherent delocalization, we suppress cold-collision shifts and two-body losses. Atom loss attributed to Landau-Zener tunneling in the ground lattice band would compromise coherent delocalization at low trap depths for our ^{171}Yb atoms; hence, we implement for the first time delocalization in excited lattice bands. Doing so increases the spatial distribution of atoms trapped in the vertically oriented optical lattice by ∼7 times. At the same time, we observe a reduction of the cold-collision shift by 6.5(8) times, while also making inelastic two-body loss negligible. With these advantages, we measure the trap-light-induced quenching rate and natural lifetime of the ^{3}P_{0} excited state as 5.7(7)×10^{-4} E_{r}^{-1} s^{-1} and 19(2)s, respectively.

Tick-Tock Goes the Biological Clock: Challenges Facing Elite Scandinavian Mother-Athletes

Challenges facing mother-athletes (MAs) have aroused research and media attention in recent years, with an increasing number of sportswomen attempting to successfully combine pregnancy and motherhood with an elite athletic career. The aims of this study were to explore how MA-specific challenges manifest in elite cross-country skiing in Scandinavia and to better understand how female athletes balance their priorities as they initiate, maintain, and/or discontinue their role as a MA. Qualitative data were collected through semistructured interviews with 13 female cross-country skiers from Norway and Sweden. Thematic analyses revealed four MA-specific challenges facing the athletes: (a) Biological clock versus peak performance, (b) Maintaining fitness versus training safely, (c) Receiving support versus facing deselection, and (d) Balancing competing MA demands. Many of the athletes felt pressured into prioritizing either motherhood or athletic excellence, particularly in their early to mid-30s when the window of opportunity for building a family was considered limited. Further, maintaining fitness and training safely during pregnancy were perceived as a challenge, as was balancing the MA role after childbirth. In many cases, athletes felt uncertain about whether they would receive support from their team or federation. Moreover, there were expectations of incompatibility surrounding the MA role. More research and educational efforts to promote MA-specific knowledge, as well as developing structured processes and providing policies to support female athletes, are identified as vital future steps. These measures may prolong athletic careers and enhance well-being for elite female athletes.

Epigenetic Age Acceleration in Hematological Malignancies: Beyond Chronological Age, Clinical Implications, and Therapeutic Perspectives

Background: Age is important in prognosticating hematological malignancies. Biological based on DNA methylome changes offers new insights into the complex interplay between epigenetics, genetics, environment, and cancer. DNA methylation levels at specific CpG sites evolve in a predictable fashion with aging and can be used to develop biomarkers that estimate the epigenetic age (EA) of a tissue. Such biomarkers are called epigenetic clocks (Fig 1-B). Based on the EA, we can determine Epigenetic Age Acceleration (EAA), a tool to identify patients aging faster biologically than their chronological age. We sought to build a blood-based clock to predict epigenetic age in healthy young and old adults and subsequently assess the degree of EAA in AML patients. Finally, among multiple planned downstream applications, we propose to use EAA as a biomarker for monitoring treatment responses in targeted therapies (Fig 1-A). Methods: We used ClockBase and NCBI's Gene Expression Omnibus (GEO) repositories to collect methylation data based on Illumina's 450k array for healthy adults and patients with AML/MDS. Pre-processing was done using the minifi BioConductor package. We used a cohort of healthy young adults (YA, aged 18-30 ys.) to train our epigenetic clock and calibrate it with three well-studied epigenetic clocks: Horvath clock (HC), Hannum clock (HAC), and PhenoAge (PA). We hypothesized that EA and chronological ages (CA) should approximate each other in younger patients as they do not generally carry comorbidities or have a higher CHIP prevalence which could influence EA. We compared our clock's performance to known epigenetic clocks, and after fine-tuning, all 4 models were validated in a cohort of healthy older adults (OA, aged 70-85 ys.) with a higher risk of CHIP. Then, we tested our clock in an AML patient cohort and illustrated how EAA can predict therapy responses in AML patients treated with IDH1/2 inhibitors (Published methylation data from Wang et al 2021, Nat Comm.) Results: We designed the clock using an Elastic-Net regression scheme. We screened 130,000 patient samples from GEO and 1,813 eligible samples were divided into 3 cohorts: 800 healthy younger adults (aged 18-30 ys.), 800 healthy elderly adults (aged 70-85 ys.), and 213 patients with AML. To train and test our clock, we used the YA cohort (n=800) with a median age of 20 ys. (SD 3.168 ys) and our epigenetic clock predicted a median EA (MEA) of 19.1 ys. (SD 3.4 ys). HC, HAC and PA predicted MEA of 21.6 ys. (SD 3.9 ys.), 19.4 ys. (SD 4.1 ys.) and 21.5 ys. (SD 3.9 ys.). After fine-tuning of weights, we tested our clock in OA cohort (n=800) with a median age of 78 ys. (SD 4.8 ys.). Our clock predicted a MEA of 82.3 ys. (SD 4.9 ys.). HC, HAC and PA predicted a MEA of 83.7 ys. (SD 5.7 ys.), 85.2 ys. (SD 6.0 ys.) and 84.9 ys. (SD of 5.1 ys.) resp. The AML cohort (n=213) had a median age of 80.9 ys. (SD 2.5 ys.). We expected a significantly higher EA due to the mutation burden along with genomic and epigenomic changes induced by the disease, our clock predicted a MEA of 84.7 ys. (SD 3.0 ys.). EAA was calculated from the difference between EA and CA. YA cohort had a median EAA of 0.9 ys. (SD 1.8 ys.) and our clock predicted a median EAA of 1.1 ys. (SD 2.0 ys.). HC, HAC, and PA predicted a median EAA of 1.4 ys. (SD 2.3 ys.), 1.4 ys. (SD 2.9 ys.), and 1.5 ys. (SD 2.4 ys.). In the OA cohort, we expected higher EAA due to age-associated cardiometabolic disease and CHIP; our clock predicted a median EAA of 4.2 (SD 2.1). HC, HAC, and PA predicted a median EAA of 6.0 ys. (SD 2.7), 5.6 ys. (SD 3.0 ys.), and 5.1 ys. (SD 2.2 ys.). For the AML cohort, our clock predicted a median EAA of 8.0 ys. (SD 5.6). We then applied our clock to a cohort of 60 AML patients treated with IDH inhibitors to predict whether a patient cleared the IDH clone after therapy. We discovered that patients who failed to clear the IDH-clone (n=14) had a higher EAA (3.23 vs 7.91 ys., p=0.012) and shorter RFS compared to patients who cleared the IDH-clone (n=7) [RFS 20.6 vs 6.1 mo., p=0.0086]. Conclusion: We built an epigenetic clock that outperforms three standard clocks in predicting epigenetic age and applied it to AML patients demonstrating a significant increase in epigenetic age. We also illustrated how EAA can be used as a biomarker for targeted therapies. Ongoing work at Karmanos Cancer Center is focused on improving the underlying regression model for more sensitive epigenetic age predictions and implementing novel pace-of-aging algorithms for EAA calculations.

Status quo and improvements of timekeeping in GNSSs

A time offset of 1 microsecond could lead to 300-meter positioning offset for a global navigational satellite system (GNSS). Therefore, appropriately evaluating and improving the clock performance onboard GNSS satellites are critical. The research methods and conclusions of papers written in distinct periods about their contemporary satellites clocks are chronologically synthesized. The satellites clocks among the same and different GNSSs are compared, with the time primarily centered around the launching and development of BeiDou-2 and BeiDou-3. It is found that passive hydrogen maser (PHM) and rubidium atomic frequency standard (RAFS) have a better performance than cesium (Cs) clocks, and PHM are among the best clock onboard satellites so more attention may be given to its development. Two major factors affecting timekeeping precision are the selection of clock manufacturers and clock types. The European manufacturing technique is pioneering, but the RAFS and PHM independently developed by China in recent years indicate a good performance. To improve navigation service, an accurate evaluation of satellites performance should be conducted, and the results can be used to assign the weight of satellite differently in computing navigation information.

Advances in satellite atomic clock technologies for the GNSS

Abstract High-precision time frequency lays a foundation for the normal operation and accurate service of the global navigation satellite system (GNSS). The satellite clock, a payload vital to GNSS operation, has become a hot topic in GNSS technology research. This paper gives a systematic introduction to the operation features and principles of satellite clock, and an overview of its research status and current development. On this basis, several techniques that deserve attention of the satellite clocks are categorized in terms of precise orbit determination and clock estimation, performance assessment and characteristic analysis, and clock offset prediction. On this basis, a comprehensive description and analysis is given separately. In the end, this paper gives some prospects over the development trend of techniques of the satellite clock based on the current research achievements and development of the GNSS.

Advancing Precise Orbit Determination and Precise Point Positioning of BDS-3 Satellites from B1IB3I to B1CB2a: Comparison and Analysis

The third generation of the Chinese BeiDou Navigation Satellite System (BDS-3) broadcasts new signals, i.e., B1C, B2a, and B2b, along with the legacy signals of BDS-2 B1I and B3I. The novel signals are demonstrated to show adequate upgraded performance, due to the restrictions on the ground tracking network for the BDS-3 satellites in new frequency bands, and in order to maintain the consistency of the hybrid BDS-2 and BDS-3 orbit/clock products using the common B1IB3I data, the use of B1CB2a observations is not sufficient for both precise orbit determination (POD) and precise point positioning (PPP) applications. In this study, one-year data of 2022 from the International GNSS Service (IGS) and the International GNSS Monitoring and Assessment System (iGMAS) are used in the precise orbit and clock determination for BDS-3 satellites based on the two sets of observations (i.e., B1IB3I and B1CB2a), and the orbit and clock accuracy along with the PPP ambiguity resolution (AR) performance are investigated. In general, the validations demonstrate that clear improvement can be achieved for the B1CB2a-based solution for both POD and PPP. In comparison to the B1IB3I, using BDS-3 B1CB2a observations can help to improve orbit consistency by around 25% as indicated by orbit boundary discontinuities (OBDs), and this use can further reduce the bias and enhance the orbit accuracy as revealed by satellite laser ranging (SLR) residuals. Similar improvement was also identified in the satellite clock performance. The B1CB2a-based solution obtains decreased Allan deviation (ADEV) values in comparison with the B1IB3I-based solution by 6~12%. Regarding the PPP-AR performance, the advantage of B1CB2a observations is evidently reflected through the estimates of wide-lane/narrow-lane fractional cycle bias (FCB), convergence time, and positioning accuracy, in which a significant reduction over 10 min is found in the PPP convergence time.

The effect of 24-hour sleep deprivation and anaerobic exercise on the expression of BAX, BCL2, BMAL1 and CCAR2 genes in peripheral blood mononuclear cells after L-arginine supplementation

Sleep deprivation disrupt the circadian clock and exercise performance. Defective oxidative stress caused by sleep deprivation may affect the expression of genes involved in cell apoptosis. Since a number of studies have shown the anti-apoptotic effect of L-arginine, so the aim of this study was to evaluate the effect of eight weeks of L-arginine supplementation on the expression of brain and muscle ARNT-like protein 1 (BMAL1), cell cycle and apoptosis regulator 2 (CCAR2), and BAX and BCL2 genes during sleep deprivation and acute anaerobic exercise. Participants included 20 healthy men age 26–35 years, randomized into the L-arginine intervention group (n = 10) and a placebo control (n = 10). The running-based anaerobic sprint test (RAST) was used for anaerobic exercise. Intervention subjects took one 1000 mg L-arginine tablet daily for 8 weeks. The Real-Time PCR method was used to determine apoptosis gene expression in peripheral blood mononuclear cells (PBMCs). Acute anaerobic exercise and sleep deprivation both increased the expression of BAX and CCAR2 genes, and decreased the expression of BCL2 and BMAL1 genes (p < 0.05 for all). L-arginine supplementation increased the expression of BMAL1 and BCL2 genes and decreased the expression of BAX and CCAR2 genes relative to control (p < 0.05). L-Arginine controlled the increase in expression of BAX and CCAR2 genes and the decrease in expression of BCL2 and BMAL1 genes in response to sleep deprivation and acute anaerobic exercise (p < 0.05). Our results showed that 24-hour sleep deprivation and acute anaerobic exercise increased the expression of pro-apoptotic genes (BAX and CCAR2) and decreased the expression of anti-apoptotic genes (BCL2 and BMAL1), although the effect of sleep deprivation is greater. In this situation, L-arginine supplementation may balance the apoptotic state of peripheral blood mononuclear cells. However, any recommendation about this needs further research.

Evaluating Optical Clock Performance for GNSS Positioning.

Atomic clocks are highly precise timing devices used in numerous Positioning, Navigation, and Timing (PNT) applications on the ground and in outer space. In recent years, however, more precise timing solutions based on optical technology have been introduced as current technology capabilities advance. State-of-the-art optical clocks-predicted to be the next level of their predecessor atomic clocks-have achieved ultimate uncertainty of 1 × 10-18 and beyond, which exceeds the best atomic clock's performance by two orders of magnitude. Hence, the successful development of optical clocks has drawn significant attention in academia and industry to exploit many more opportunities. This paper first provides an overview of the emerging optical clock technology, its current development, and characteristics, followed by a clock stability analysis of some of the successfully developed optical clocks against current Global Navigation Satellite System (GNSS) satellite clocks to discuss the optical clock potentiality in GNSS positioning. The overlapping Allan Deviation (ADEV) method is applied to estimate the satellite clock stability from International GNSS Service (IGS) clock products, whereas the optical clock details are sourced from the existing literature. The findings are (a) the optical clocks are more stable than that of atomic clocks onboard GNSS satellites, though they may require further technological maturity to meet spacecraft payload requirements, and (b) in GNSS positioning, optical clocks could potentially offer less than a 1 mm range error (clock-related) in 30 s and at least 10 times better timing performance after 900 s in contrast to the Galileo satellite atomic clocks-which is determined in this study as the most stable GNSS atomic clock type used in satellite positioning.

High-precision clock research based on comparator delay characteristics with temperature

Accuracy is an important index in the design of clock circuits. The clock performance is affected by the fact that the delay time of the comparator in the circuit is strongly influenced by the temperature. This paper presents a principal analysis of this phenomenon and proposes a specific method for optimizing clock accuracy. By changing the comparator’s reference voltage, the clock accuracy is improved to meet the high-precision clock requirements. The high-precision clock frequency designed in this paper is 24 MHz, with temperature stability of ±1%.

A Real-Time Linear Prediction Algorithm for Detecting Abnormal BDS-2/BDS-3 Satellite Clock Offsets

Due to space environment interference, imperfect data processing model, and the performance of atomic clocks, real-time satellite clock products often contain outliers or irregular biases. We propose a real-time linear moving short-term prediction algorithm to predict clock offsets and detect abnormalities. The proposed algorithm mainly includes phase/frequency anomaly detection and real-time prediction part. Both the phase and frequency domains are used to detect abnormal clock offsets with previous epochs for building the clock prediction model accurately. The real-time moving prediction module utilizes the high short-term prediction performance to check the clock abnormality. The performance of the algorithm is then evaluated for all satellites with real-time estimated satellite clock offsets. To verify the feasibility and effectiveness of the proposed linear moving model and algorithm, the results of the grey model GM(1,1) and the ARIMA model are also compared. The experimental results indicated that the algorithm can detect clock outliers, frequency modulation, and phase jumps, and the linear model has a better clock performance improvement. After the abnormalities are removed with the proposed algorithm, the average STD accuracy of the real-time clock offsets for all satellites is improved by 15.5%, compared to an improvement of 11.4% by the GM(1,1) model and 11.5% by the ARIMA model. The PPP results demonstrate that the proposed clock prediction algorithm improves the positioning accuracy by 8.1%, 13.3%, and 16.9% in the east, north, and up components, respectively.

Characteristics of the IGS receiver clock performance from multi-GNSS PPP solutions

Global navigation satellite system (GNSS) receivers belonging to the International GNSS Service (IGS) are equipped with different types of clocks, such as internal crystal quartz clocks, rubidium and cesium atomic clocks, as well as hydrogen masers. These clocks are characterized by different phase and frequency accuracies and stabilities, resulting in different systematic clock time series patterns. We analyze the clock offsets between different GNSS systems, provide noise characteristics of the undifferenced and differenced clock parameters, and detect systematic patterns of the clocks. The time series of the receiver clocks are dominated by the diurnal, semidiurnal, and sometimes terdiurnal signals with amplitudes up to several meters. Hydrogen masers provide the highest clock stability, and the lowest is by internal clocks. However, there are also groups of very stable internal clocks that perform similarly to low-performing hydrogen masers and rubidium clocks. The interquartile ranges for epoch-differenced clock parameters fall between 3 and 250 mm for the best hydrogen masers and the worst internal clocks, respectively.

Clock-offset computation method of space network aided by satellite clock prediction

A novel network clock-offset resolution method for space network is proposed in the paper. In the process of clock-offset resolution based on the network inter-node measurement data, the prediction of satellite clock result is used as the priori information. A double weighted control is made with the consideration of the point clock performance and the measurement performance, and better measurement error suppression effect is achieved. The results of simulation experiment indicated that network clock-offset resolution result with better stability and accuracy is achieved compared with the traditional Least Squares method in different scenarios.

Applying Variational Autoencoder to Explore Changes in Clock Drawing With Hip Fracture Surgery

AbstractBackgroundOlder adults with acute hip fractures are particularly vulnerable to delirium and postoperative cognitive decline. Hospital staff, however, do not screen preoperative cognition or systematically monitor for delirium in these at‐risk individuals. Using the clock drawing test (CDT) our team demonstrated the potential for semi‐supervised deep learning using Variational Autoencoder (VAE) to extract clock drawing anomalies predictive of dementia (Bandyopadhyay, in review). We applied the VAE technique to assess preoperative to postoperative changes in CDTs in patients with acute hip fractures.MethodsPost‐injury, pre‐operative hip fracture patients completed screening including the CDT to command and copy, and a baseline delirium assessment with the Confusion Assessment Method for the Intensive Care Unit (CAM‐ICU). Postoperatively, delirium was assessed twice daily. Post‐surgery CDTs were collected after two consecutive negative CAM‐ICUs. A VAE with two latent dimensions was trained using 13,580 unlabeled clocks in an unsupervised manner to create a parsimonious 2D latent space to encode the constructional aspects of the CDT. This latent space was operationalized using a k‐Nearest Neighbor Classifier on a classification dataset consisting of 71 Dementia and 80 Control samples using 3‐fold cross validation. This separated the latent space into the “Red” and “Blue” areas corresponding to “Dementia” and “Control” groups, respectively. We projected the pre and postoperative hip fracture dataset CDTs onto this latent space to investigate changes in CDT relative constructional features post‐surgery for those with and without postoperative delirium.Result27 participants completed our study (age 82.96 ± 9.28; education 13.19 ± 2.90; 85% female). 2 were delirious preoperatively and excluded from analysis, and 4 developed delirium postoperatively (16%). All preoperative command and copy clocks were in the “Dementia” region of the VAE latent space. Copy, but not command clocks moved further into the “Dementia” region. Error type changed in the post‐operative command condition to resemble the copy condition more closely. Trends suggest preoperative copy clock performance may predict delirium risk after surgery.ConclusionSemi‐supervised deep learning with VAE applied to the CDT, particularly the copy condition, shows promise for automated preoperative cognitive screening and postoperative monitoring in at‐risk hip fracture patients. Future studies are needed with larger participant samples.

μ POP Clock: A Microcell Atomic Clock Based on a Double-Resonance Ramsey Scheme

We demonstrate and study a microcell microwave atomic clock based on optical-microwave double resonance (DR) interrogation operated in a pulsed Ramsey scheme, called the \ensuremath{\mu}POP clock, based on a microfabricated Rb vapor cell and a micro-loop-gap microwave resonator. For the mm-scale dimensions of this cell, the population and coherence relaxation rates of the Rb clock transition are on the order of 4--5 kHz, which puts constraints on the useful Ramsey times and overall pulse sequence in view of optimized clock performance. Our proof-of-principle demonstration of the \ensuremath{\mu}POP clock shows that the pulsed DR approach is nevertheless feasible and results in a short-term clock stability of 1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}11}$ \ensuremath{\tau}${}^{\ensuremath{-}1/2}$ and reaching the \ensuremath{\le}2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}12}$ level at timescales of 1000 s to one day. The short-term instability budget established for the \ensuremath{\mu}POP clock shows that the main limitation to the short-term stability arises from the detection noise. Thanks to the pulsed Ramsey scheme, light-shift effects are strongly reduced in the \ensuremath{\mu}POP clock, which opens perspectives for further improvements of long-term clock stability, in view of future generations of miniature vapor-cell clocks with enhanced performances based on the DR scheme.

Prenatal and birth associations of epigenetic gestational age acceleration in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) cohort

ABSTRACT Gestational age (GA) is an important determinant of child health and disease risk. Two epigenetic GA clocks have been developed using DNA methylation (DNAm) patterns in cord blood. We investigate the accuracy of GA clocks and determinants of epigenetic GA acceleration (GAA), a biomarker of biological ageing. We hypothesize that prenatal and birth characteristics are associated with altered GAA, thereby disrupting foetal biological ageing. We examined 372 mother-child pairs from the Center for the Health Assessment of Mothers and Children of Salinas study of primarily Latino farmworkers in California. Chronological GA was robustly correlated with epigenetic GA (DNAm GA) estimated by the Knight (r = 0.48, p < 2.2x10−16) and Bohlin clocks (r = 0.67, p < 2.2x10−16) using the Illumina 450K array in cord blood samples collected at birth. GA clock performance was robust, though slightly lower, using DNAm profiles from the Illumina EPIC array in a smaller subsample (Knight: r = 0.39, p < 3.5x10−5; Bohlin: r = 0.60, p < 7.7x10−12). After adjusting for confounders, high maternal serum triglyceride levels (Bohlin: β = −0.01 days per mg/dL, p = 0.03), high maternal serum lipid levels (Bohlin: β = −4.31x10−3 days per mg/dL, p = 0.04), preterm delivery (Bohlin: β = −4.03 days, p = 9.64x10−4), greater maternal parity (Knight: β = −4.07 days, p = 0.01; Bohlin: β = −2.43 days, p = 0.01), and male infant sex (Knight: β = −3.15 days, p = 3.10x10−3) were associated with decreased GAA.Prenatal and birth characteristics affect GAA in newborns. Understanding factors that accelerate or delay biological ageing at birth may identify early-life targets for disease prevention and improve ageing across the life-course. Future research should test the impact of altered GAA on the long-term burden of age-related diseases.

Differential clock comparisons with a multiplexed optical lattice clock.

Rapid progress in optical atomic clock performance has advanced the frontiers of timekeeping, metrology and quantum science1-3. Despite considerable efforts, the instabilities of most optical clocks remain limited by the local oscillator rather than the atoms themselves4,5. Here we implement a 'multiplexed' one-dimensional optical lattice clock, in which spatially resolved strontium atom ensembles are trapped in the same optical lattice, interrogated simultaneously by a shared clock laser and read-out in parallel. In synchronous Ramsey interrogations of ensemble pairs we observe atom-atom coherence times of 26 s, a 270-fold improvement over the measured atom-laser coherence time, demonstrate a relative instability of [Formula: see text] (where τ is the averaging time) and reach a relative statistical uncertainty of 8.9 × 10-20 after 3.3 h of averaging. These results demonstrate that applications involving optical clock comparisons need not be limited by the instability of the local oscillator. We further realize a miniaturized clock network consisting of 6 atomic ensembles and 15 simultaneous pairwise comparisons with relative instabilities below [Formula: see text], and prepare spatially resolved, heterogeneous ensemble pairs of all four stable strontium isotopes. These results pave the way for multiplexed precision isotope shift measurements, spatially resolved characterization of limiting clock systematics, the development of clock-based gravitational wave and dark matter detectors6-12 and new tests of relativity in the lab13-16.

BeiDou intra-system bias using different precise orbit and clock products

An intra-system bias (ISB) is a necessary parameter in the BeiDou Navigation Satellite System (BDS)-2 and BDS-3 integrated precise point positioning (PPP); however, its influence in BDS-2/BDS-3 combined processing remains unclear. This paper investigates the ISB effects on the combined PPP using different precise orbit and clock products. Considering an increasing number of BDS products, a comprehensive evaluation of the products is undertaken before validating with PPP tests. Results indicate that BDS-2 Wuhan University (WUM) orbital differences outweigh Centre National d’Etudes Spatiales (CNT), Shanghai Observatory (SHA), and Information and Analysis Center (IAC) orbits. Moreover, BDS-3 constellation registers better clock performance than BDS-2 using any MGEX product. Furthermore, introducing the ISB into the combined processing of BDS-2 and BDS-3 improves both the positioning performance and convergence time for all products. The best improvement in positioning performance is achieved when Deutsches GeoForschungsZentrum (GBM) product is employed. Finally, it is found that considering the ISB in the PPP model affects the code more than the phase observations.

Continuous multi-step pumping of the optical clock transition in alkaline-earth atoms with minimal perturbation.

A suitable scheme to continuously create inversion on an optical clock transition with negligible perturbation is a key missing ingredient required to build an active optical atomic clock. Repumping of the atoms on the narrow transition typically needs several pump lasers in a multi step process involving several auxiliary levels. In general this creates large effective level shifts and a line broadening, strongly limiting clock accuracy. Here we present an extensive theoretical study for a realistic multi-level implementation in search of parameter regimes where a sufficient inversion can be achieved with minimal perturbations. Fortunately we are able to identify a useful operating regime, where the frequency shifts remain small and controllable, only weakly perturbing the clock transition for useful pumping rates. For practical estimates of the corresponding clock performance, we introduce a straightforward mapping of the multilevel pump scheme to an effective energy shift and broadening of parameters for the reduced two-level laser model system. This allows us to evaluate the resulting laser power and spectrum using well-known methods.

Метод аппаратной реализации сверточной нейронной сети на основе системы остаточных классов

Convolutional Neural Networks (CNN) show high accuracy in pattern recognition solving problem but have high computational complexity, which leads to slow data processing. To increase the speed of CNN, we propose a hardware implementation method with calculations in the residue number system with moduli of a special type and . A hardware simulation of the proposed method on Field-Programmable Gate Array for LeNet-5 CNN is trained with the MNIST, FMNIST, and CIFAR-10 image databases. It has shown that the proposed approach can increase the clock frequency and performance of the device by 11%-12%, compared with the traditional approach based on the positional number system.

Frequency Noise Characterization of Diode Lasers for Vapor-Cell Clock Applications

The knowledge of the frequency noise spectrum of a diode laser is of interest in several high-resolution experiments. Specifically, in laser-pumped vapor cell clocks, it is well established that the laser frequency noise plays a role in affecting clock performances. It is then relevant to characterize the frequency noise of a diode laser since such measurements are rarely found in the literature and hardly ever provided by vendors. In this paper, we describe a technique based on a frequency-to-voltage converter that transforms the laser frequency fluctuations into voltage fluctuations. In this way, it is possible to characterize the laser frequency noise power spectral density in a wide range of Fourier frequencies, as required in cell clock applications.