Joint time and frequency transfer through one International Telecommunication Union 100 GHz wavelength division multiplexing channel with commercial devices.

We proposed a joint time and frequency transfer scheme over a single International Telecommunication Union 100 GHz wavelength division multiplexing (WDM) channel using a normal commercial WDM device and commercial offset WDM device. A standard 100 GHz WDM channel is divided into three sub-channels with a frequency interval of more than 20 GHz for a time and frequency transfer, which could help to avoid the interference among time, frequency, and data signals in other WDM channels. A joint high-precision time and frequency transfer is, therefore, able to be performed with data transmission over WDM optical communication links without extra requirements on devices. A joint time and frequency transfer in a single 100 GHz WDM channel is experimentally demonstrated over a 60 km fiber link with the communication data transmission in the adjacent channels. The stability of the time transfer can be better than 15 ps at 1 s, and the stability of the frequency transfer can be better than 2.7×10-14 at 1 s, while the bit error rates of the adjacent channels are at the same level as the separate transmission.

Optically synchronized unidirectional optical amplifier-based coherent optical fiber links.

We report on the realization of a unidirectional transmission-based bidirectional erbium-doped fiber amplifier (UTB-EDFA) for the coherent optical fiber links. By applying an optical phase-locked loop (OPLL) between the two unidirectional EDFA (Ui-EDFA) paths, the annoying uncorrelated phase noise between the two paths can be largely suppressed. Promisingly, we can independently optimize the gains of the UTB-EDFAs for bidirectional transmissions, resulting in higher net gain acquired compared with the conventional single-path bidirectional EDFA (SPBA)-based ones. We demonstrate that the fractional frequency instability of the UTB-EDFA-based scheme can be decreased by 26.3% over the most asymmetrical 100 km two-way optical frequency comparison (TWC) system compared with the SPBA-based ones and, more importantly, can acquire higher net gain for unevenly distributed sub-links over ultra-long fiber links, such as 1000 km, by independently optimizing the gains. This technique paves the way for the applications of large-scale fiber networks.

Pulsed microwave photonic vector network analyzer based on direct sampling.

Pulsed VNAs enabling large dynamic measurement at a low pulse duty cycle are necessary for the characterization of active devices due to the overheating damage risk under continuous wave stimulation. In this paper, we proposed a pulsed microwave photonic vector network analyzer (p-MPVNA) based on direct sampling. With the broad system bandwidth of the p-MPVNA and undersampling technique, pulsed signals are received thru asynchronous wideband detection, and pulsed S-parameters are calculated thru vector superposition. In asynchronous wideband detection, the continuous spectrum of the pulsed signal is discretized into multiple frequency components. A low repetition rate optical pulse train undersamples the pulsed signal, and the discretized frequency components are aliased. The frequency components in the main lobe including most energy of the pulse signal are vector superimposed to calculate the pulsed S-parameter. The proposed p-MPVNA has a dynamic range decreases rate of 10log(duty cycle) when pulse duty cycle is below 10% , which is much slower than that of 20log(duty cycle) for classical narrowband detection. An experimental p-MPVNA is established for validation. A 6 to 18 GHz microwave amplifier is measured with continuous and pulsed power supply and the measured gain curves are consistent with the results from a commercial VNA. The system dynamic range decrease with pulse duty cycle is verified by the pulsed S-parameter measurement of a 10 GHz low pass filter under continuous and pulsed stimulation.

Photonic millimeter-wave transfer with balanced dual-heterodyne phase noise detection and cancellation.

We report on the realization of long-haul and high-precision millimeter-wave (mm-wave) transfer through a fiber-optic link based on balanced dual-heterodyne phase noise detection. The balanced dual-heterodyne detection is achieved by detecting the fiber phase noise superimposed two intermediate frequency (IF) signals without requiring a local synchronization signal and its output is used to compensate the fiber-induced phase noise by actuating the frequency of the one optical carrier. The proposed scheme can effectively get rid of the effect of the local reference, largely simplifying the configuration at the local site. Additionally, we model and experimentally study the noise contribution coming from the out-of-band, which can be effectively suppressed to the below of the system noise floor with a fractional frequency instability of 1.9 × 10-17 at 10,000 s by designing and implementing a high-precision temperature control module with a peak-to-peak temperature fluctuation of no more than 0.002 K. We experimentally demonstrate that a 100 GHz mm-wave signal to be transmitted over a 150 km fiber-optic link can achieve the fractional frequency instabilities of less than 3.4 × 10-14 at 1 s and 3.5 × 10-17 at 10,000 s.

Log odds of positive lymph nodes as a novel prognostic predictor for gastric cancer: a systematic review and meta-analysis.

BACKGROUND: We conducted a systematic review and meta-analysis to summarize the predictive and prognostic ability of the log odds of positive lymph nodes (LODDS) staging system and compare it with pathological N (pN) classification and the ratio-based lymph node system (rN) for the overall survival (OS) of gastric cancer (GC). METHODS: Through a systematic review till March 7, 2022, we identified population-based studies that reported the prognostic effects of LODDS in patients with GC. We compare the predictive effectiveness of the LODDS staging system with that of the rN and pN classification systems for the OS of GC. RESULTS: Twelve studies comprising 20,312 patients were included in this systematic review and meta-analysis. The results showed that LODDS1, LODDS2, LODDS3, and LODDS4 in GC patients were correlated with poor OS compared with LODDS0 (LODDS1 vs. LODDS0: HR = 1.62, 95% CI (1.42, 1.85); LODDS2 vs. LODDS0: HR = 2.47, 95% CI (2.02, 3.03); LODDS3 vs. LODDS0: HR = 3.15, 95% CI (2.50, 3.97); LODDS4 vs. LODDS0: HR = 4.55, 95% CI (3.29, 6.29)). Additionally, significant differences in survival were observed among patients with different LODDS classifications (all P-values were < 0.001) with the same rN and pN classifications. Meanwhile, for patients with different pN or rN classifications with the same LODDS classification, prognosis was highly similar. CONCLUSION: The findings show that LODDS is correlated with the prognosis of GC patients and is superior to the pN and rN classifications for prognostic assessment.

Abortion storm of Yili horses is associated with Equus caballus papillomavirus 2 variant infection.

Nine different species of Equus caballus papillomavirus (EcPV) and three bovine papillomaviruses (BPVs) have been reported to infect horses. However, there are few descriptions of such infections in China. In our pioneer study on Chinese horses, we identified EcPV-2 in the nasal swabs (4/230, 1.7%) of Yili horses, and the semen (3/18, 16.7%) of thoroughbred horses. This indicated that EcPV is indeed hosted by horses in China, and that EcPV-2 might be transmitted though breeding. Further detection of EcPVs in the lung tissues of aborted fetuses of Yili horses, which were originally negative for equid herpes viruses, demonstrated EcPV-2 positivity in 19 of 50 samples, thereby indicating that EcPV-2 may be a new pathogen responsible for causing abortion. Thereafter, sequence analyses of the L1 genes of 26 EcPV-2 in China were performed, indicating that EcPV-2, which primarily infects horses in China, shared 98.3-99.9% nt identity with the published sequences for EcPV-2. These observations indicated that EcPV-2 identified in the current study were highly similar variants of the previously identified strains of EcPV-2. Phylogenetic analysis based on L1 gene sequences from GenBank showed that the EcPV-2 found in Chinese horses was closely related to and clustered together with an already known EcPV-2a lineage. Our study provides the first evidence related to EcPV-2 infection in Chinese horses, which can serve as a causative agent for Yili horse abortions, and may thus lay the foundation for a systematic and detailed epidemiological study of this infection in Chinese horses.

[Ketogenic diet improves low temperature tolerance in mice by up-regulating PPARα in the liver and brown adipose tissue].

The aim of the present study was to investigate the effects of short-term ketogenic diet on the low temperature tolerance of mice and the involvement of peroxisome proliferator-activated receptor α (PPARα). C57BL/6J mice were divided into two groups: normal diet (WT+ND) group and ketogenic diet (WT+KD) group. After being fed with normal or ketogenic diet at room temperature for 2 d, the mice were exposed to 4 °C low temperature for 12 h. The changes in core temperature, blood glucose, blood pressure of mice under low temperature condition were detected, and the protein expression levels of PPARα and mitochondrial uncoupling protein 1 (UCP1) were detected by Western blot. PPARα knockout mice were divided into normal diet (PPARα-/-+ND) group and ketogenic diet (PPARα-/-+KD) group. After being fed with the normal or ketogenic diet at room temperature for 2 d, the mice were exposed to 4 °C low temperature for 12 h. The above indicators were also detected. The results showed that, at room temperature, the protein expression levels of PPARα and UCP1 in liver and brown adipose tissue of WT+KD group were significantly up-regulated, compared with those of WT+ND group. Under low temperature condition, compared with WT+ND, the core temperature and blood glucose of WT+KD group were increased, while mean arterial pressure was decreased; The ketogenic diet up-regulated PPARα protein expression in brown adipose tissue, as well as UCP1 protein expression in liver and brown adipose tissue of WT+KD group. Under low temperature condition, compared to WT+ND group, PPARα-/-+ND group exhibited decreased core temperature and down-regulated PPARα and UCP1 protein expression levels in liver, skeletal muscle, white and brown adipose tissue. Compared to the PPARα-/-+ND group, the PPARα-/-+KD group exhibited decreased core temperature and did not show any difference in the protein expression of UCP1 in liver, skeletal muscle, white and brown adipose tissue. These results suggest that the ketogenic diet promotes UCP1 expression by up-regulating PPARα, thus improving low temperature tolerance of mice. Therefore, short-term ketogenic diet can be used as a potential intervention to improve the low temperature tolerance.

Fast and on-line link optimization for the long-distance two-way fiber-optic time and frequency transfer.

The performance of long-distance two-way fiber-optic time and frequency (T/F) transfer is directly affected by link parameters. In this paper, a fast on-line scheme to maximize the signal-to-noise ratio at the T/F transfer link ends (denoted by SNRW and SNRE) is proposed by optimizing the gains of bidirectional Erbium-doped fiber amplifiers (Bi-EDFAs). The dedicatedly defined objective optimization functions, ln(1/SNRW + 1/SNRE) for microwave and time transfer, and ln(1/SNRW) for optical frequency transfer, are proven to be a convex function and enable the computation time to be reduced significantly by employing the fast and mature convex optimization algorithm. The linear equations about the objective optimization function and the fiber parameters required by optimization are constructed, and then the fiber parameters are proposed to be on-line obtained accordingly by measuring the concerned SNR at the link end under different EDFA gain configurations and solving the linear equations. The transmission matrixes for the proposed optimization scheme are further derived, which can simplify the implementation in the long-distance multiple EDFAs links. The simulation shows that the proposed algorithm can obtain the optimal parameters consistent with the reported experimental results, and can reduce the computation time by more than four orders compared with the scanning optimization method for a link with more than 6 Bi-EDFAs.

Multiple-access relay stations for long-haul fiber-optic radio frequency transfer.

We report on the realization of a long-haul radio frequency (RF) transfer scheme by using multiple-access relay stations (MARSs). The proposed scheme with independent link noise compensation for each fiber sub-link effectively solves the limitation of compensation bandwidth for long-haul transfer. The MARS can have the capability to share the same modulated optical signal for the front and rear fiber sub-links, simplifying the configuration at the repeater station and enabling the transfer system to have the multiple-access capability. At the same time, we for the first time theoretically model the effect of the MARS position on the fractional frequency instability of the fiber-optic RF transfer, demonstrating that the MARS position has little effect on system's performance when the ratio of the front and rear fiber sub-links is around 1:1. We experimentally demonstrate a 1 GHz signal transfer by using one MARS connecting 260 and 280 km fiber links with the fractional frequency instabilities of less than 5.9 × 10-14 at 1 s and 8.5 × 10-17 at 10,000 s at the remote site and of 5.6 × 10-14 and 6.6 × 10-17 at the integration times of 1 s and 10,000 s at the MARS. The proposed scalable technique can arbitrarily add the same MARSs in the fiber link, which has great potential in realizing ultra-long-haul RF transfer.

Fiber-optic joint time and frequency transmission with enhanced time precision.

We propose a high-precision joint time and frequency transmission scheme based on bidirectional wavelength division multiplexing transmission over an optical fiber link. The time signal is generated based on the phase-stable frequency signal with employment of a dedicated designed low-jitter event generator. Time synchronization is realized by eliminating the time difference between the time signals of the master and slave stations, which is determined by accurate two-way time comparison. In this way, thanks to the high stability of the frequency transmission, low jitter of the dedicated designed event generator, and the high accuracy of the two-way time comparison, a high precision time signal with enhanced time stability and accuracy can be obtained at the slave station, which is synchronized to the master station. Experimentally, a joint time and frequency transmission system is demonstrated over a 62-km urban fiber link. The results show a time stability in terms of time deviation (TDEV) of 3.5 ps/s and 430 fs/10,000 s, and an accuracy of better than 20 ps can be realized.

Log odds of positive lymph nodes as a novel prognostic predictor for colorectal cancer: a systematic review and meta-analysis.

BACKGROUND: Colorectal cancer (CRC) is the third most prevalent cancer in the world, which remains one of the leading causes of cancer-related deaths. Accurate prognosis prediction of CRC is pivotal to reduce the mortality and disease burden. Lymph node (LN) metastasis is one of the most commonly used criteria to predict prognosis in CRC patients. However, inaccurate surgical dissection and pathological evaluation may lead to inaccurate nodal staging, affecting the effectiveness of pathological N (pN) classification in survival prediction among patients with CRC. In this meta-analysis, we aimed to estimate the prognostic value of the log odds of positive lymph nodes (LODDS) in patients with CRC. METHODS: PubMed, Medline, Embase, Web of Science and the Cochrane Library were systematically searched for relevant studies from inception to July 3, 2021. Statistical analyses were performed on Stata statistical software Version 16.0 software. To statistically assess the prognostic effects of LODDS, we extracted the hazard ratio (HR) and 95% confidence interval (CI) of overall survival (OS) and disease-free survival (DFS) from the included studies. RESULTS: Ten eligible articles published in English involving 3523 cases were analyzed in this study. The results showed that LODDS1 and LODDS2 in CRC patients was correlated with poor OS compared with LODDS0 (LODDS1 vs. LODDS0: HR = 1.77, 95% CI (1.38, 2.28); LODDS2 vs. LODDS0: HR = 3.49, 95% CI (2.88, 4.23)). Meanwhile, LODDS1 and LODDS2 in CRC patients was correlated with poor DFS compared with LODDS0 (LODDS1 vs. LODDS0: HR = 1.82, 95% CI (1.23, 2.68); LODDS2 vs. LODDS0: HR =3.30, 95% CI (1.74, 6.27)). CONCLUSIONS: The results demonstrated that the LODDS stage was associated with prognosis of CRC patients and could accurately predict the prognosis of patients with CRC.

Molecular characteristics and pathogenicity of an equid alphaherpesvirus 1 strain isolated in China.

Equid alphaherpesvirus 1 (EHV-1) is prevalent in China, and causes notable economic damage to the equine industry. However, there is no information regarding the molecular characteristics and pathogenicity of the Chinese strains. Therefore, an EHV-1 strain, named YM2019, was isolated from the lung tissue of an aborted horse fetus in Xinjiang, China, and its genome and pathogenicity were analyzed. The full genome of the isolate was 150,267 base pairs in length, with 56.7% G + C content. Genetic and phylogenetic analysis showed that strain YM2019 (GenBank: MT063054) belonged to the ORF30 N752 genotype but displayed a high level of similarity with strain Ab4 (ORF30 D752, GenBank: AY665713) isolated in Britain. Fourteen unique amino acid mutations were found when comparing strain YM2019 with the reference strains Ab4 and V592 (ORF30 N752, GenBank: AY464052). Syrian hamsters infected with strain YM2019 exhibited severe respiratory and neurological clinical signs and died. Infection with strain YM2019 in Yili horses caused rhinopneumonitis, viremia, and neurological clinical signs such as hind limb lameness, prostration, and reduced movement. Here, we describe the features of an EHV-1 strain discovered in China, together with the complete genome sequence, and reveal that a nonneurovirulent strain (ORF30 N752) can also cause neurological signs in horses. The data will be useful in providing some reference for further research into the relationship between viral genotypes and pathogenicity.

Interference and frequency-to-time mapping based high anti-jamming and anti-interception frequency hopping receiving.

We have proposed an interference and frequency-to-time mapping based high anti-jamming and anti-interception frequency hopping receiving scheme. By changing the delay difference between the interference arms through high-speed switchable delay lines and using electrooptical sampling, fast and large-range frequency hopping signals can be received. Benefited from the high shaping resolution for using the interference as the spectral shaping method, more receiving passbands in high frequency bands can be available to enhance the anti-jamming and anti-interception performance. By fast pulse shaping through switchable delay lines, the bandwidth of the electric end, the sampling rate, and the number of frequencies in the frequency hopping pattern are decoupled, and the bandwidth of the electric end can be reduced to improve the receiving selectivity. In experiments, the signal hopping from 15.2 GHz to 35.4 GHz with the switching time up to that of the used optical switch is received. Utilizing a switchable delay line in the interference arm with the tuning step of 2.5 ps, eight available receiving passbands within 25 GHz to 42 GHz are generated. The receiving selectivity is also improved from 18.3 to 43.7 in terms of Q factor by decreasing the electric end's bandwidth in experiments.

Fast and large-range frequency hopping receiving based on simultaneous photonic filtering and digitizing.

We propose a frequency hopping receiving method that can receive signals with a large frequency hopping range and rapid hopping speed simultaneously. It is based on simultaneous photonic filtering and digitizing, and the reception frequency is tuned by changing the temporal shape of the sampling optical pulse. The proposed receiving method is verified by an experimental verification scheme. In the verification scheme, the optical pulse from a mode-locked laser is shaped to obtain several sub-pulses with different temporal shapes by spectral shaping and frequency-to-time mapping. The reception of the frequency hopping signal is performed by introducing certain delay through a switchable delay line to select different sub-pulses as the optical sampling pulse. The frequency hopping speed and range of the verification scheme are limited mainly by the speed of the optical switches and the bandwidth of electro-optic modulators, respectively. In experiments, with available devices, frequency hopping signals with a switching time of 250 ns and signals whose carrier frequency hops from 13.35 GHz to 39.30 GHz are successfully received.

All-passive multiple-place optical phase noise cancellation.

We report on the realization of delivering coherent optical frequency to multiple places based on passive phase noise cancellation over a bus topology fiber network. This technique mitigates any active servo controller on the main fiber link and at arbitrary access places as opposed to the conventional technique, in which an active phase compensation circuit has to be adopted to stabilize the main fiber link. Although the residual fiber phase noise power spectral density in the proposed technique turns out to be a factor of seven higher than that of in the conventional multiple-access technique when the access place is close to the end of the fiber link, it could largely suppress the phase noise introduced by the servo bumps, improve the response speed and phase recovery time, and minimize hardware overhead in systems with many stations and connections without the need for active servo circuits including phase discriminators and active compensators. The proposed technique could considerably simplify future efforts to make precise optical frequency signals available to many users, as required by some large-scale science experiments.

Passive optical phase noise cancellation.

We report on the realization of an optical phase noise cancellation technique by passively embedding the optical phase noise information into a radio frequency signal and creating a copy of the optical frequency signal, which is pre-corrected by the amount of phase noise introduced by optical phase perturbations. Neither phase discrimination nor an active servo controller is required due to the open-loop design, mitigating some technical problems, such as the limited compensation speed and finite phase/timing jitter, in conventional phase noise cancellation. We experimentally demonstrate that this technique maintains the same delay-limited bandwidth and phase noise suppression capability as in conventional techniques, but significantly shortens the response speed and phase recovery time. Passive decoupling optical phase perturbation represents a powerful technique in the domains of optical frequency standard comparisons and tools for future optical atomic clocks, which are now under investigation for a potential redefinition of the International Time Scale.

High-speed and broadband digital receiver based on optical sampling pulse waveform matching.

In this Letter, we propose a high-speed, broadband photonic digital receiver that can realize the matched filtering of the digital signal through shaping the optical sampling pulse according to the specific waveform of the transmitted digital signal. The receiver's filtering response is matched with the spectrum of the digital signal's specific waveform, and the instantaneous signal-to-average-noise ratio of the filtered signal is maximized at the sampling points. The principle of proposed receiver is theoretically analyzed and experimentally verified. The weak digital signals with different signal-to-noise ratio are detected and correctly distinguished in the experiments.

Prognostic value of circulating tumor cells detected with the CellSearch system in esophageal cancer patients: a systematic review and meta-analysis.

BACKGROUND: Esophageal carcinoma (EC) is the seventh-most prevalent tumor in the world, which is still one of the primary causes of tumor-related death. Identifying noteworthy biomarkers for EC is particularly significant in guiding effective treatment. Recently, circulating tumor cells (CTCs) in peripheral blood (PB) were intensively discussed as prognostic markers in patients with EC. However, an ongoing controversy still exists regarding the prognostic significance of CTCs determined by the CellSearch system in EC sufferers. This meta-analysis was designed to approach this topic. METHODS: We systematically conducted searches using PubMed, Medline, Web of Science and the Cochrane Library for relevant studies, which were published through February 20, 2020. Using the random-effects model, our study was performed in Review Manager software, with odds ratios (ORs), risk ratios (RRs), hazard ratios (HRs) and 95% confidence intervals (CIs) as the effect values. RESULTS: Totally 7 articles were finally included in this study. For clinicopathological characteristics, the pooled results on TNM stage indicated that the III/IV group had higher rate of CTCs compared with the I/II group (OR = 1.36, 95% CI: 0.68-2.71, I2 = 0%). Incidence of CTCs was higher in patients with T3/T4 stage (OR = 2.92, 95% CI: 1.31-6.51, I2 = 0%) and distant metastasis group (OR = 5.18, 95% CI: 2.38-11.25, I2 = 0%) compared to patients with T1/T2 stage or non-metastatic group. The pooled analysis revealed that CTC positivity detected in EC patients was correlated with poor overall survival (OS) (HR = 2.83, 95% CI:1.99-4.03, I2 = 0%) and relapse-free survival (RFS) (HR = 4.71, 95% CI:2.73-8.13, I2 = 0%). When pooling the estimated RR, a poor therapeutic response to chemoradiotherapy was discovered in patients with CTC positivity (RR = 1.99, 95% CI:1.73-2.29, I2 = 60%). CONCLUSIONS: In summary, our meta-analysis demonstrated that CTCs positivity determined by the CellSearch system are correlated with the prognosis of EC patients and might indicate a poor therapeutic response to chemotherapy in EC patients.

Photonic compressive receiver for multiple microwave frequency measurement.

We present a photonic compressive receiver, where the frequency information of the captured signal is directly mapped to the time intervals between compressed pulses for multiple microwave frequency measurement. The theoretical measurement error, multiple-frequency resolution and effective measurement range are derived. The effects of dispersion deviation and the electrical bandwidth are also discussed. The theoretical results are verified by the measured pulse waveforms and frequency-time mapping relationship. A photonic compressive receiver with an effective measurement range of 42 GHz, a multiple-frequency resolution of 1.2 GHz, a measurement accuracy of 88 MHz and a signal interception period of 27 ns is experimentally obtained.

Time transfer through the optical supervisory channel in wavelength division multiplexing systems.

We present an optical fiber time transfer scheme through the optical supervisory channel (OSC) in wavelength division multiplexing (WDM) systems. A sub-band of the standard OSC band is used to transmit time signals by only adding sub-OSC filters in commercial WDM systems. The transmission of the existing communication data service is not affected. The wavelengths of bidirectional time transmission in the same sub-band can be very close, or even the same, to maximize the bidirectional propagation symmetry and improve the precision of time transfer. Combined time, optical supervisory signal, and communication data transmission is experimentally demonstrated along a single 100 km optical fiber in a WDM system in laboratory.