Two Modes Near-zero Dispersion Flattened Photonic-crystal Fiber

Through massive computer simulation, a photonic-crystal fiber with seven air-hole defects as fiber core is proposed by using the software CUDOS based on the multipole method. In the given fiber parameters, the photonic-crystal fiber’s fundamental and second modes are dispersion flattened simultaneously in the communication O wave band, S wave band and C wave band. It is important in the relative application of multi-mode dispersion flattened photonic-crystal fiber

Phase Errors Simulation Analysis for GNSS Antenna in Multipath Environment

High-precision GNSS application requires the exact phase center calibration of antenna. Various methods are published to determine the locations of the phase center. In the outfield, when the phase errors that arose by multipath exceed the phase center variations (PCV) tolerance, the calibration values may be not useful. The objective of this paper is thus to evaluate the phase errors that arose by multipath signals. An improved model of antenna receiving signal is presented. The model consists of three main components: (1) an antenna model created by combination of right hand circular polarization (RHCP) and left hand circular polarization (LHCP), (2) a multipath signals model including amplitude, phase, and polarization, and (3) a ground reflection model applying to circular polarization signals. Based on the model, two kinds of novel up-to-down (U/D) ratios are presented. The performance of the model is assessed against the impact of up-to-down ratio of antenna on phase errors

A positioning method of BDS receiver under weak signal circumstances based on Compressed Fractional-Step

U ovom se radu predlaže sažeta metoda frakcijskog koraka koja se odnosi na pozicioniranje BDS prijemnika u uvjetima slabog signala. Zatim se analiziraju karakteristike BDS konstelacije i poboljšava originalni algoritam zasnovan na dinamičkim uvjetima miješane konstelacije raznih satelita. U odnosu na neodređenost decimale tisućinke sekunde nastale zbog greške sata prijemnika pri izračunu, ovaj rad razvija način obrade proširenja dimenzija pretrage i korištenja metode frakcijskog koraka implicirane informacije o elevaciji prijemnika koja se zatim substituira u jednadžbu kao promatrana količina kako bi se smanjila izračunata količina neodređenosti. U zaključku se kaže da u najnepovoljnijim uvjetima ova metoda može smanjiti gotovo polovicu količine izračuna čitave druge fuzzy pretrage vremena emisije signala. U radu se također predlaže metoda skraćenja proračuna kako bi se smanjio raspon između približnog položaja i greške na satu zasnovana na karakateristici da je dinamika ne-MEO satelita među BDS satelitima mala. Uključujući ne-MEO satelite u računanje, sateliti mogu smanjiti potrebe za točnošću lokalnog sata prijemnika. Teorijski, računanje uporabom čistih GEO satelita može proširiti potrebu od 187,5 s na 1500 s. Imajući u vidu rezultate simulacije, proizlazi da kada je informacija o elevaciji poznata i točna, prvim se korakom računanja frakcijskog koraka može zadovoljiti potreba za pozicioniranjem. Inače, drugim se korakom računanja može dobiti točno pozicioniranje i postići rapidno pozicioniranje u uvjetima slabog signala.This article puts forward the compression fractional-step method which applies to the positioning of BDS receivers under weak signal circumstances. It then analyses the features of BDS constellation and improves the original algorithm based on various satellites’ dynamic conditions of mixed constellation. With respect to the ambiguity of the decimal of milliseconds arising from the clock error of receivers in the process of calculation, this article advances a processing mode of extending search dimension and a fractional-step method of employing the implied elevation information of receivers which is then substituted into the equation as the observed quantity to reduce the calculation amount of ambiguity. It concludes that in the most adverse circumstances this method can reduce nearly half of the calculation amount of the whole second fuzzy search of signals’ emission time. This article also brings forward the compression calculation method to compress the range between the approximate position and clock error based on the feature that the dynamic of non-MEO satellites among BDS satellites is small. Taking non-MEO satellites as calculation, satellites can reduce the accuracy requirements of the local clock of receivers. In theory, calculation through using pure GEO satellites can broaden the requirement from 187,5 s to 1500 s. In the light of simulation results, it turns out that when the elevation information is known and precise, the first step of fractional-step calculation is capable of meeting the requirement of positioning. Otherwise, the second step of calculation can obtain the accurate positioning and achieve the rapid positioning under weak signal circumstances

A positioning method of BDS receiver under weak signal circumstances based on Compressed Fractional-Step

U ovom se radu predlaže sažeta metoda frakcijskog koraka koja se odnosi na pozicioniranje BDS prijemnika u uvjetima slabog signala. Zatim se analiziraju karakteristike BDS konstelacije i poboljšava originalni algoritam zasnovan na dinamičkim uvjetima miješane konstelacije raznih satelita. U odnosu na neodređenost decimale tisućinke sekunde nastale zbog greške sata prijemnika pri izračunu, ovaj rad razvija način obrade proširenja dimenzija pretrage i korištenja metode frakcijskog koraka implicirane informacije o elevaciji prijemnika koja se zatim substituira u jednadžbu kao promatrana količina kako bi se smanjila izračunata količina neodređenosti. U zaključku se kaže da u najnepovoljnijim uvjetima ova metoda može smanjiti gotovo polovicu količine izračuna čitave druge fuzzy pretrage vremena emisije signala. U radu se također predlaže metoda skraćenja proračuna kako bi se smanjio raspon između približnog položaja i greške na satu zasnovana na karakateristici da je dinamika ne-MEO satelita među BDS satelitima mala. Uključujući ne-MEO satelite u računanje, sateliti mogu smanjiti potrebe za točnošću lokalnog sata prijemnika. Teorijski, računanje uporabom čistih GEO satelita može proširiti potrebu od 187,5 s na 1500 s. Imajući u vidu rezultate simulacije, proizlazi da kada je informacija o elevaciji poznata i točna, prvim se korakom računanja frakcijskog koraka može zadovoljiti potreba za pozicioniranjem. Inače, drugim se korakom računanja može dobiti točno pozicioniranje i postići rapidno pozicioniranje u uvjetima slabog signala.This article puts forward the compression fractional-step method which applies to the positioning of BDS receivers under weak signal circumstances. It then analyses the features of BDS constellation and improves the original algorithm based on various satellites’ dynamic conditions of mixed constellation. With respect to the ambiguity of the decimal of milliseconds arising from the clock error of receivers in the process of calculation, this article advances a processing mode of extending search dimension and a fractional-step method of employing the implied elevation information of receivers which is then substituted into the equation as the observed quantity to reduce the calculation amount of ambiguity. It concludes that in the most adverse circumstances this method can reduce nearly half of the calculation amount of the whole second fuzzy search of signals’ emission time. This article also brings forward the compression calculation method to compress the range between the approximate position and clock error based on the feature that the dynamic of non-MEO satellites among BDS satellites is small. Taking non-MEO satellites as calculation, satellites can reduce the accuracy requirements of the local clock of receivers. In theory, calculation through using pure GEO satellites can broaden the requirement from 187,5 s to 1500 s. In the light of simulation results, it turns out that when the elevation information is known and precise, the first step of fractional-step calculation is capable of meeting the requirement of positioning. Otherwise, the second step of calculation can obtain the accurate positioning and achieve the rapid positioning under weak signal circumstances

Anticancer effect of a combination of cisplatin and matrine on cervical cancer U14 cells and U14 tumor-bearing mice, and possible mechanism of action involved

Purpose: To investigate the anticancer effects of cisplatin (DDP) in combination with matrine on cervical cancer U14 cell tumor-bearing mice. Methods: The cell proliferation of cervical cancer U14 cells treated with DDP (25, 20, 15, 10 and 5 μg/mL); matrine (2.5, 2.0, 1.5, 1.0 and 0.5 mg/mL); or DDP (15 μg/mL) + matrine (2.5, 2.0, 1.5, 1.0 and 0.5 mg/mL) was determined with MTT assay. The anticancer effect of DDP + matrine in U14 tumor-bearing mice was also investigated, based on expression of tumor suppressor lung cancer 1 (TSLC1) using quantitative real time-polymerase chain reaction (qRT-PCR) and immunohistochemistry. Results: The inhibition of proliferation of U14 cells ranged from 26.68–70.25, 10.20–61.73, and 51.89–89.75 % for DDP, matrine and DDP + matrine, respectively. In mice with U14 solid tumors, the DDP group had 12.3 % weight loss (p < 0.05). Treatment with DDP, matrine, and DDP + matrine reduced tumor growth by 64.56, 42.22–56.67, and 67.78–81.11 %, respectively (p < 0.01). Results from RT-qPCR and immunohistochemistry showed corresponding increases in expression levels of TSLC1. Conclusion: These results indicate that the anticancer activity of DDP + matrine is higher than that of a single treatment with either DPP or matrine. The likely mechanism of action might be related to promotion of TSLC1 expression. This finding provides a potential strategy for the management of cervical cancer

A Quick Location Method for High Dynamic GNSS Receiver Based on Time Assistance

Traditional A-GPS positioning method when quickly calculate a position, need a condition that the approximate position must not exceed 150km, otherwise the calculation will be very complex. This paper proposes a time-assisted fast positioning method for high dynamic GNSS receiver, effectively solving the problem of large search calculation in traditional method, even if exact position is unknown after the signal is recaptured. According to the known auxiliary time information and implied  elevation information, this paper put forwards a custom coordinate system for building twodimensional search space, which could reduce the number of search-dimensions. It proposes a search method based on receiver clock calculated by analyzing the influence of time auxiliary accuracy. By using GPS ephemeris data provided by the IGS, it builds a simulation environment and analyzes the influence of different preferred satellites based on the custom coordinate system on the calculation, and thus puts forward a principle for choosing the preferred satellites. Simulation examples show that through the rational combination of satellites to create a custom coordinate system, and when time auxiliary accuracy is less than 60us, the calculation can 100% guarantee to restore a complete satellite signal emission time and obtain an accurate position

The positioning method of BDS receiver with auxiliary clock under the weak signal circumstance

Tradicionalni algoritam za pronalaženje vremena odašiljanja ne može se primijeniti u praksi zbog drastičnog povećanja izračuna kada je nepoznat približan položaj prijemnika. U ovom se radu predlaže metoda za određivanje položaja prijemnika temeljena na pomoćnom satu, koja se može primijeniti kada je približan položaj prijemnika nepoznat. Kako bi se odredilo područje traženja, u radu se koriste dva GEO satelita za dobivanje polarnih koordinata, i reduciraju se nepoznati brojevi pretraživanja na osnovu informacija o dometu elevacije uključenih u prijemniku. Nadalje, prema ograničenjima područja pokrivenog satelitskim signalom, preporučuje se izabrati dva najudaljenija GEO satelita za stvaranje uobičajenog koordinatnog sustava te dodati bilo koji broj satelita zbog verifikacije i selekcije, da bi se vrijeme prijenosa signala uspjelo vratiti do tisućinke sekunde. Ta se metoda provjerava simulacijskom analizom, točnije, statistička analiza točnosti algoritma pomoćnog sata provodi se jedino u uvjetima GEO konstelacije u Kini i susjednim područjima. U zaključku se pokazuje da kada je greška na pomoćnom satu ispod 100 us, a broj satelita za provjeru je dovoljan, prijemnik se može brzo pozicionirati u uvjetima slabog signala čak i kada mu je približni položaj nepoznat.The traditional time-of-transmission recovery algorithm cannot be applied to practice due to a drastic calculation increase when the approximate position of receiver is unknown. This paper puts forward a receiver positioning method based on auxiliary clock, which can be used when the receiver’s approximate position is unknown. To determine search scope, the paper makes use of double GEO satellites to build custom polar coordinates, and reduces unknown searching numbers on the basis of elevation range information implied in the receiver. Furthermore, according to the restraints of satellite signal coverage scope, it is advocated to choose two farthest GEO satellites to build the custom coordinate system, and add any validation satellites for verification and selection, so as to realize the restoration of millisecond integer of signal transmission time. This method is verified through simulation analysis. To be specific, statistical analysis of the algorithm’s precision requirements of auxiliary clock is made under the application circumstance of only GEO constellation in China and neighbouring areas. The conclusion shows that, when the auxiliary clock error is below 100 us and the number of validation satellites is enough, the receiver can be rapidly positioned under the weak signal circumstance even when the approximate position is unknown

Impact of ambiguity resolution on phase center offsets and hardware delay estimation for BDS-3 inter-satellite links

The Chinese BeiDou navigation satellite system (BDS) has already completed its three phases and developed into a global navigation satellite system for open positioning, navigation, and timing services. The BDS-3 satellites feature the inter-satellite link (ISL). The ISL observation-related error model and ambiguity resolution for L-band observation are the crucial factors in precise data processing. In this study, we present for the first time the impact of ambiguity resolution on phase center offsets (PCOs) and hardware delay estimation of BDS-3 inter-satellite links. Two weeks’ L-band observations from 99 globally distributed ground stations and Ka-band ISL observations are collected for experimental validation and analysis. First, network solutions with and without ISL observations are conducted to investigate the role of ISL observation in ambiguity resolution. Afterward, ISL observation-related errors, mainly PCOs and hardware delays, are estimated by processing L-band with ISL observations with and without ambiguity resolution to analyze the impact of ambiguity resolution on these two factors. Finally, orbit accuracy in the network solution is assessed to further validate the effectiveness of the estimated PCOs and hardware delays in our experiment. The result indicates that introducing the ISL can slightly improve the fixing rate compared to only L-band observations from 83.7% to 84.3%. Furthermore, ambiguity resolution has a positive influence on the stability of estimated PCOs and hardware delays in turn, although the root mean square (RMS) values basically remain unchanged. The standard deviation (STD) of the x-offset is reduced from 0.021 m to 0.012 m, a significant improvement of about 43%, and 0.022 m–0.016 m, with an improvement of about 27%, for the y-offset. There is a slight improvement of about 8% for z-offset. Similarly, around 10% improvement in the STD for hardware delays can be achieved while the RMS values almost stay the same except for C40. Orbit determination from network solutions shows high accuracy compared to the public products for the satellite with good geometry configuration, which further validates our estimates for ISL PCOs and hardware delays

Dysfunction of Cerebrovascular Endothelial Cells: Prelude to Vascular Dementia

Vascular dementia (VaD) is the second most common type of dementia after Alzheimer’s disease (AD), characterized by progressive cognitive impairment, memory loss, and thinking or speech problems. VaD is usually caused by cerebrovascular disease, during which, cerebrovascular endothelial cells (CECs) are vulnerable. CEC dysfunction occurs before the onset of VaD and can eventually lead to dysregulation of cerebral blood flow and blood–brain barrier damage, followed by the activation of glia and inflammatory environment in the brain. White matter, neuronal axons, and synapses are compromised in this process, leading to cognitive impairment. The present review summarizes the mechanisms underlying CEC impairment during hypoperfusion and pathological role of CECs in VaD. Through the comprehensive examination and summarization, endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling pathway, Ras homolog gene family member A (RhoA) signaling pathway, and CEC-derived caveolin-1 (CAV-1) are proposed to serve as targets of new drugs for the treatment of VaD