One-way Time Research Articles

Accessibility of methadone treatment via public transit for syringe services program participants in Miami-Dade County, Florida.

Methadone is an opioid receptor agonist medication used in the treatment of opioid use disorder (OUD). Geographic distance to opioid treatment programs (OTPs) is a major barrier to treatment, given requirements for direct observation of dosing and periodic drug screens, and 'methadone treatment deserts' are defined as a public transit threshold of 30 minutes. The purpose of this study was to examine public transit access to methadone treatment for participants of a syringe services program (SSP) in Miami-Dade County, Florida. Public transit times were calculated using the R library r5r, which facilitates multi-modal transportation network routing. General Transit Feed Specification data was combined with street network data from OpenStreetMap for Miami-Dade County. Transit times were estimated from the population-weighted centroid of each zip code (n=79) with participants of Miami's only SSP (n=1597) to the nearest OTP (n=4) using 10 departure windows aligned with OTP service hours. The mean one-way transit time from zip codes with SSP participants in Miami-Dade County to the nearest OTP was 80 minutes. 75 of the 79 (95%) zip codes with SSP participants in Miami-Dade County have a mean transit time to the closest OTP greater than 30 minutes. Transit times differ substantially between zip codes with different numbers of SSP participants, but not between departure windows. Nearly all zip codes with SSP participants in Miami-Dade County can be classified as 'methadone treatment deserts'. Geographic isolation of methadone treatment from public transit routes represents a significant barrier to equitable OUD treatment.

Method to determine the optimal impedance profile of nonuniform transmission lines used for pulsed power accelerators

Nonuniform transmission lines (NTLs) are widely used in pulsed power accelerators because they provide an efficient way to achieve impedance matching and pulse shaping. Since designing and constructing these accelerators typically demands substantial effort, finding the optimal impedance profile to maximize the power transmission efficiencies of the NTLs is important. In this paper, a convenient numerical method to determine the optimal impedance profile is proposed. First, the output of the NTL with arbitrary parameters is theoretically analyzed under arbitrary input conditions. It was found that only four factors affect the power transmission efficiency: the ratio of output impedance to input impedance, the ratio of input pulse width to the NTL’s one-way transit time, the normalized impedance profile, and the normalized input pulse. Based on these findings, a method designed to minimize the reflected component within the working frequency range is proposed. Using this method, an impedance profile demonstrating superior power transmission efficiency compared to the traditional exponential profile is identified. This work can provide a rapid and effective method to determine the impedance profile of the NTL, undoubtedly benefiting the design process of pulsed power accelerators. Published by the American Physical Society 2024

A new PPP one-way timing approach via BDS-3 PPP-B2b and short-message communication service

In the realm of time-frequency, precise point positioning (PPP) technology has been widely used, the current PPP time transfer or timing necessitates network communication for data transmission, which consequently leads to a reduction in the reliability of PPP timing. Based on the BDS-3 PPP service (PPP-B2b) and the global short message communication (GSMC) service, this study proposes a novel PPP one-way timing method that is not subject to distance limitations or the requirements of network communication. Users can directly obtain the difference with UTC(k). Then, the proposed PPP timing method was validated using four stations equipped with external high-performance atomic clocks, based on a dataset of eight days. According to the findings, the suggested PPP one-way timing technique might reach a timing accuracy of roughly 0.5 ns in environments without a network. In terms of frequency stability, the proposed PPP timing method exhibits a stability of approximately 1.4 × 10−13 at 960 s and a stability of about 3 × 10−14 at 15360 s. Further, even under GSMC communication delays of 1 min, 5 min, and 10 min, the proposed PPP one-way timing accuracy can still achieve better than 0.5 ns.

Modeling and assessment of Galileo PPP one-way timing with RT-product

Precise point positioning (PPP) technology is widely used in positioning, navigation, and timing. In order to meet the needs of users for real-time high-precision time information, a real-time Galileo PPP one-way timing model based on existing real-time (RT) products (CAS, CNES, GMV, and WHU) was established and applied for the timing field. Experiments were designed with 8 GNSS stations with an external H-MASER clock to research Galileo PPP timing with 25 day observations. For the modified Allan deviation (MDEV) of Galileo PPP timing solutions, similar to the timing solutions of GPS, the MDEV of Galileo PPP with CAS and CNES shows worse short-term frequency stability, with 1 to 2 × 10−13 at 960 s stability, and indicates similar long-term frequency stability, with about 5–6 × 10−15 at 61 440 s stability. For Galileo PPP time transfer, the standard deviation values are about 0.01–0.49 ns for all time-links with different products. For the stability of Galileo time transfer, the similar characteristic of Galileo time transfer is comparable to that of GPS. For short-term stability, the MDEV of all time-links from Galileo PPP ranges from 2 × 10−14 to 3 × 10−14 at 960 s. For long-term stability, 1 to 2 × 10−15 levels can be reached at 61 440 s for all time-links, except for that of CNES.

A Bad Commute: Travel Time to Work Predicts Teacher Turnover and Other Workplace Outcomes

Research suggests that longer commute times may increase employee turnover probabilities by increasing stress and reducing job attachment and embeddedness. Using administrative data from a midsized urban school district, we test whether teachers with longer commute times are more likely to transfer schools or exit the district. Both descriptively and in regression results employing multiple fixed effects, we find that teachers with longer commutes are more likely to transfer schools within the district. Regression results show that each 5-minute increase in one-way commute time predicts an increase in transfer probability of 0.8 to 1.0 percentage points over most of the commute time distribution. We also find evidence that teachers with the longest commutes (i.e., 40+ minutes each way) have higher district exit probabilities. Moreover, teachers with longer commute times are absent from work more frequently and receive lower observation ratings. We discuss potential implications for local human resources policy and practice.

Groundwater Responses of Foundation Subjected to Water Level Fluctuation of Reservoir Considering Variability of Layered Structure

The effect of the variability in a layered structure, characterized by the spatial variability of the saturated hydraulic conductivity, on the distribution of a pressure head p in a foundation subjected to water level fluctuation in a reservoir is investigated with the aid of the random field theory, Karhunen–Loève (K-L) expansion, first-order moment approach, and cross-correlation analysis. The results show that the variability in the foundation structure has significant impacts on the groundwater response to the reservoir’s water level fluctuations. Regions with relatively large uncertainties of the p and σp values in the foundation are those around the initial water level at the reservoir side, and those at the distal end away from the reservoir. In addition, there is a larger variance of Ks, denoted as σlnKs2, a larger correlation scale in the horizontal direction λh, a larger correlation scale in the vertical direction λv, and a larger one-way time consumption of fluctuations T to a larger uncertainty in p. Moreover, the four factors (σlnKs2, λh, λv, and T) all have positive correlations with σp. σlnKs2 has the largest impact on σp in the foundation, λv has the second largest impact, and λh has the smallest impact. A foundation with small Ks values around the initial water level at the reservoir side and large Ks values around the highest water level at the reservoir side may produce larger p values in the foundation. These results yield useful insight into the effect of the variability in a layered structure on the distribution of the pressure head in a foundation subjected to water level fluctuation in a reservoir.

Sub-Nanosecond UTC Dissemination Based on BDS-3 PPP-B2b Service

The BeiDou-3 system (BDS-3) broadcasts PPP-B2b signals to provide real-time PPP service. Compared with the traditional PPP technique, the PPP-B2b service broadcasts corrections through satellite links, covers a wide area, and is independent of the internet. With the PPP-B2b service, users can obtain high-precision positioning information through the real-time PPP. Many studies have been conducted to evaluate the positioning performance of PPP-B2b. In theory, high-precision timing information could also be obtained through PPP-B2b. With the development of science and technology, the need for highly accurate time measurement, even at the sub-nanosecond level, is experiencing significant growth. However, the GNSS standard timing service can hardly meet these requirements. This contribution analyzes the timing performance of the PPP-B2b service and proposes a sub-nanosecond precise timing method of Coordinated Universal Time (UTC) based on the PPP-B2b service. BDS-3 and GPS observations from nine tracking stations and real-time collected PPP-B2b corrections over 516 days were used to analyze the performance of the proposed timing method. The results show that: (1) The difference between the PPP-B2b-restored UTC, which was realized by one-way timing with the UTC offsets in broadcast ephemeris, and UTC (NTSC), fluctuates within a few ns. (2) The timing uncertainty of the zero baseline based on the proposed method is better than 0.2 ns. (3) Compared with the post-processed PPP time transfer, the UTC dissemination uncertainty of the short and long baseline with the proposed method is better than 0.7 ns. The experiment results verified the feasibility of the proposed sub-nanosecond level precise UTC dissemination method based on the PPP-B2b service.

Demonstration of 75 km-fiber quantum clock synchronization in quantum entanglement distribution network

The quantum entanglement distribution network, serviced as the communication infrastructure which distributes quantum information among remote users, enables many applications beyond the reach of classical networks. Recently, the applications such as quantum key distribution and quantum secure direct communication, have been successfully demonstrated in the quantum entanglement distribution network. In this article, we propose a multi-user round-trip quantum clock synchronization (QCS) scheme in the quantum network, which can be implemented with one single entangled photon source located at the server. The server distributes the entangled photons to remote multiple users with the wavelength division multiplexing strategy, and each user feeds partial received photons back to the server. The clock difference between the server and each user is calculated from the one-way and round-trip propagation times, which are determined according to the time correlation of entangled photons. Afterwards, the demonstration has been conducted between the server and a user over a 75-km-long fiber link, where the measured clock difference uncertainty is 4.45 ps, and the time deviation is 426 fs with an average time of 4000 s. Furthermore, the proposed QCS scheme is linearly scalable to many users, with respect to user hardware and number of deployed fibers.

Deadline-Constrained Multi-Agent Collaborative Transmission for Delay-Sensitive Applications

Delay-sensitive applications impose the strict deadline-constrained latency requirement for end-to-end transmission. However, due to the high dynamics of link status and the limited network resources, it is still challenging to ensure deterministic end-to-end latency for deadline-constrained flows. To this end, we propose a deadline-constrained multi-agent collaborative transmission mechanism (DMCT). Specially, DMCT is featured by combining dynamic routing and packet active dropping control to avoid additional end-to-end latency. Firstly, we design a specific packet structure to detect network status and aware the deadline of each flow. Secondly, to enhance the precision of routing decision, we further formulate deadline-constrained flow scheduling as a joint minimization problem that considers the deadline of flows, queuing delay, and network status. Then, we propose a multi-agent collaborative routing algorithm to find the solution to the joint minimization problem. Finally, we propose a local-agent deadline-constrained active queue management algorithm for packet active dropping control and routing adjustment. Simulation results show that the proposed DMCT outperforms the state-of-the-art solutions, e.g., graph convolutional network-based deep reinforcement learning (GCNL) and delay-based shortest path first (D-SPF), in terms of one-way round-trip time, drop rate, and queue length.

Assisted-GNSS positioning algorithm based on one-way fuzzy time information

In order to solve the problem that the accuracy of approximate position and approximate time information is limited by the traditional auxiliary positioning algorithm, this paper analyzes the problem that the calculation amount may increase and fail when these auxiliary information exceeds the precision requirement range and puts forward a positioning algorithm based on one-way fuzzy time assistance that is suitable for the positioning solution of GNSS satellite navigation receivers under the condition of fuzzy time information, such as the rotation condition. Methods using the reference information in the ephemeris information, the relatively accurate approximate time information can be reasonably searched and verified so as to achieve the effect of obtaining the positioning result with less calculation. The experimental results show that this method can accurately calculate the exact position even if there is an error in the approximate position information under the condition of one-way time assistance, which not only solves the problem that it cannot be positioned under the conditions of rotation but also does not increase the additional calculation amount and has practical engineering value.

Two networked predictive control methods for output tracking of networked systems with plant-model mismatch

This paper addresses the output tracking control problem for networked systems with plant-model mismatch, where two-channel random network delays are considered. According to the different ways of obtaining future control commands, two networked predictive control (NPC) methods are designed. One is the NPC method using one-way time delays, called ONPC, and the other is the NPC method using round-trip time delays, called RNPC. Furthermore, they are compared in terms of the way of compensation for two-channel delays, prediction process, and communication load, respectively. Then, the closed-loop stability conditions of the RNPC system and the ONPC system for the plant-model mismatch and match cases are derived, and their output tracking performance is also theoretically analysed. Finally, the results of the theoretical analysis are verified through numerical simulation that illustrates the effectiveness of the proposed two NPC methods as well as their separate advantages.

Communication quality affects performance of astronauts and support teams through increased workload: Insights from the AMADEE-20 analog Mars mission

Astronaut crews and ground control support teams are highly interdependent teams that need to communicate effectively to achieve a safe mission - despite being separated by large distances. Team communication quality with its facets clarity of objectives and information flow, is a key coordination process to achieve high team performance and task satisfaction. Especially in interdependent teams working in extreme environments with time-delayed communications, the team's success is threatened if communication is ineffective. In this study, we hypothesized that communication quality affects two key team outcomes, performance and task satisfaction, and that these effects can be explained by increases in workload (effort and frustration). Hypotheses were tested during the AMADEE-20 analog Mars mission hosted by the Austrian Space Forum. The analog astronauts (AA) were supported by an On-Site-Support (OSS) team and a remote Mission-Support-Centre (MSC) team. The MSC was the only contact line for both AA and OSS, and the communication between them had a one-way time delay of 10 min. Our study consisted of three runs in which members across the three different multiteam systems had to exchange information to solve an interdependent task. We measured communication quality, effort and frustration, task satisfaction, and team performance. Results show that clarity of objectives and information flow positively impacted multiteam system performance. Furthermore, clarity of objectives reduced experienced effort and this in turn enhances team performance. High levels of information flow reduced experienced frustration, which in turn enhanced task satisfaction. Our findings show that these facets of communication quality are essential for multiteam systems that work separated from each other by a distance. We stress that specific (team) communication training for astronauts and support personnel will be key to effective teamwork during future Mars missions, and thus to overall mission success.

Long-Term Performance Evaluation of BeiDou PPP-B2b Products and Its Application in Time Service

Precise Point Positioning (PPP) is an official service of the BeiDou Global Navigation Satellite System (BDS-3) through the PPP-B2b signal. In this paper, we mainly focus on the long-term performance evaluation of BDS-3 PPP-B2b products and their application in time service. Since the PPP-B2b product is only available in and around China area, the arcs of PPP-B2b products are about several hours. We propose to evaluate the time datum stability by using all available satellites. Then, 557 day PPP-B2b products are collected for this experiment. The results show that there are large jumps in the GPS satellite clock time datum series. However, the BDS-3 satellite clock datum stability is almost at the same level with current Space State Representation (SSR) corrections from the International Global navigation satellite system Service (IGS). The difference between PPP-B2b GPS and BDS-3 satellite clock time datum will be absorbed into the Inter System Bias (ISB) parameter. Thus, it should be specially noted that the ISB parameter cannot be estimated as constant values if users use PPP-B2b products. In addition, the accuracy of the BDS-3 satellite clock is significantly better than that of the GPS for both the Root Mean Square Error (RMSE) and standard deviation (STD). The average Signal in Space Range Errors (SISREs) is 0.22 ns and 0.13 ns for GPS and BDS-3, respectively. The one-way timing experiment shows BDS-3 timing stability is 2.9 × 10−14@104 s. In addition, 10 baselines from 13 km to 4494 km are formed for time synchronization evaluation by using PPP-B2b products. The average RMSEs of time synchronization is from 0.46 ns to 1.58 ns and from 0.66 ns to 1.19 ns for GPS and BDS-3, respectively. As for STD, the average values are from 0.27 ns to 0.74 ns and from 0.27 ns to 0.47 ns for GPS and BDS-3, respectively. Overall, the results show that the time datum stability, accuracy, and service performance of BDS-3 PPP-B2b products has been stable over the past two years.

Research on Time Synchronization between Shore and Ship based on Two-way Time-frequeny Transmission

The purpose is to study the application of two-way time comparison method for time synchronization on motion platforms such as ships. Firstly, the one-way time comparison method and the two-way time comparison method are analyzed, and the characteristics of the two methods are compared. Combined with the influence of the motion platform on the time synchronization during movement, an improved two-way comparison time synchronization method suitable for the motion platform is proposed. The time synchronization technique of bidirectional comparison based on carrier ranging principle is discussed, and the conclusion of two-station time synchronization based on carrier bidirectional time comparison under weak relative motion is obtained.

Delay Compensated One-Way Time Synchronization in Distributed Wireless Sensor Networks

Wireless sensor networks require accurate time synchronization to perform collaborative tasks on multiple distributed sensor nodes. However, the performance is greatly affected by the unpredictability of message delays in the synchronization process, which causes cumulative error and challenges to clock parameter estimations. We propose a delay compensated consensus Kalman-based time synchronization (DCCKTS) protocol to estimate the fluctuated delay effectively. We propose an algorithm to update all parameters in a one-way message exchange while maintaining time synchronization accuracy and energy consumption. The performance of the proposed algorithm is compared with traditional algorithms. Simulation results demonstrate that the algorithm performs better than conventional algorithms under an unknown Gaussian delay model.

On the satellite clock datum stability of RT-PPP product and its application in one-way timing and time synchronization

On the satellite clock datum stability of RT-PPP product and its application in one-way timing and time synchronization

Inequalities of extreme commuting across Canada

There is growing body of research and practice assessing transportation equity and justice. Commuting is an especially important dimension to study since such frequent, non-discretionary travel, can come at the expense of time for other activities and therefore negatively impact mental health and well-being. An ”extreme commuter” is a worker who has a particularly burdensome commute, and has previously been defined based on one-way commute times above 60 or 90 minutes. In this paper, we examine the social and geographic inequalities of extreme commuting in Canada. We use a 25% sample of all commuters in Canada in 2016 (n = 4,543,417) and our analysis consists of descriptive statistics and logistic regression models. The average one-way commute time in 2016 across Canada was 26 minutes, but over 9.7% of the workforce had commute times exceeding 60 minutes. However, this rate of extreme commuting was 11.5% for low-income households, 13.5% for immigrants, and 13.4% among non-white Canadians, reaching as high as 18.6% for Black Canadians and 14.7% for Latin American Canadians specifically. We find that these inequalities persist even after controlling for household factors, commute mode, occupation, and built environment characteristics. The persistently significant effects of race in our models point to factors like housing and employment discrimination as possible contributors to extreme commuting. These results highlight commuting disparities at a national scale prior to the COVID-19 pandemic, and represents clear evidence of structural marginalization contributing to racialized inequalities in the critical metric of daily commute times seldom recognized by Canadian scholars and planners.

Preliminary Analysis and Evaluation of BDS-3 RDSS Timing Performance

Radio determination satellite service (RDSS) is one of the characteristic services of Beidou navigation satellite system (BDS), and also distinguishes with other GNSS systems. BDS-3 RDSS adopts new signals, which is compatible with BDS-2 RDSS signals in order to guarantee the services of old users. Moreover, the new signals also separate civil signals and military signals which are modulated on different carriers to improve their isolation and RDSS service performance. Timing is an important part of RDSS service, which has been widely used in the field of the power, transportation, marine and others. Therefore, the timing accuracy, availability and continuity is an important guarantee for RDSS service. This paper summarizes the principle of one-way and two-way timing, and provides the evaluation method of RDSS timing accuracy, availability and continuity. Based on BDS-3 RDSS signal measurements of system, the performance of one-way timing and two-way timing is analyzed and evaluated for the first time. The results show that: (1) the accuracy of one-way timing and two-way timing is better than 30 ns and 8 ns respectively, which are better than the official claimed accuracy; (2) the RMS of one-way timing accuracy is 5.45 ns, which is 20% smaller than BDS-2, and the availability and continuity are 100%; (3) the RMS of two-way timing accuracy is 3.59 ns, which is 34% smaller than one-way timing, and both of the availability and continuity are 100%; (4) the orbit maneuver of GEO satellite make the one-way timing has 7.68 h recovery, but has no affection on the two-way timing.

Performance Evaluation of VoIP Codecs over Network Coding in Wireless Mesh Networks

Voice over Internet protocol (VoIP) is used for transmitting voice signals in a packet-switched Internet protocol (IP) networks in real time. For transmitting voice over a wireless mesh networks (WMNs), the analog voice signal has to be digitalized, encoded, and packetized. Codecs based on different Quality of Service (QoS) requirements are used. One of the main QoS requirements is that packets are transmitted through the network in real time; one-way transmission time or End-to-End (ETE) packet delay, and packet delay variation or jitter have to be lower than thresholds. ETE delay depends on various parameters; among them is also network delay. Various mechanisms are used to lower the network delay in WMNs. A promising mechanism, for improving the performance of streaming services such as the case also in VoIP, is network coding. In this paper, we evaluate the benefits of using wireless network coding for VoIP in WMNs. Network coding procedure in combination with various VoIP codecs is used to observe the impact on network delay and jitter of the VoIP application. The simulation results show that network coding can decrease network delay and jitter. Moreover, results show that network coding benefits are codec dependent.

Optimized continuous-thrust round-trip trajectories to ultra-low Δv ISRU targets

We present the results and implications of our optimized round-trip trajectories to thousands of synthetic but realistic ultra-low Δv (≲ 8 ​km ​s−1) asteroids for the purpose of in-space resource utilization (ISRU) of water extracted from the targets. We show that our carpe diem mission scenario works — ISRU missions utilizing ‘hibernating’ spacecraft on loosely-bound orbits in cis-lunar space can begin soon after targets are discovered if the asteroids are rapidly characterized with accurate and precise orbits. Our algorithm identified ultra-low Δv round-trip mission trajectories for 100% of the ISRU targets that approach to within 0.05 au of Earth. The median minimum distance between the targets and Earth during the rendezvous/mining phase is ∼ 0.23 au (∼ 115 light-seconds) while the maximum one-way communication time is ​≲ ​4 ​min. The return-trip missions have a median Δv ∼ 2.9 ​km ​s−1 so that the typical mission returns about 50% of the extracted H2O to cis-lunar space. We estimate a steady-state rate of about 2 water-mining missions per year returning about 100 tonne yr−1 to the Earth-Moon system. Converting the water to LOX/LH2 is ∼ 93% efficient, suggesting that asteroid H2O mining could provide ∼ 93 tonne of bipropellant to cis-lunar space on an annual basis. We applied our mission optimization algorithm to 168 known near-Earth objects (NEO) with orbital elements similar to our synthetic ultra-low Δv population and estimate that almost 95% of the population of ultra-low Δv NEOs remain to be discovered.