This article summarizes the comparison between the preparation, structure and mechanical properties of long fiber reinforced thermoplastics （LFT） and short fiber reinforced thermoplastics （SFT）. Both of the experi...This article summarizes the comparison between the preparation, structure and mechanical properties of long fiber reinforced thermoplastics （LFT） and short fiber reinforced thermoplastics （SFT）. Both of the experiment and theory results showed that the mechanical properties of long glass fiber reinforced thermoplastics pellets （LGFRT） have been enhanced better than that of short glass fiber reinforced thermoplastics pellets （SGFRT） manufactured by molding procession. After regulation of the relative humidity by 50 % , the mechanical properties of 30 % （ weight percent） short glass fiber content in SFT （ SFT-PA6-SGF30 ） are similar to that of 40 % long glass fiber content in LFT. Howev- er, the density of the latter is about 17 % lower than that of the former. Thus, the corresponding weight of products is reduced by 13 % ;output rate is increased by 21% , and the cost is therefore significantly lowered. And it has the fol- lowing advantages： impact strength is increased by 87 % ; the proportion is reduced by 20 % ; molding cycle is short- ened by 10 % ;materials cost is saved by 20 % -30 % and the final total cost is saved by 30 % -40 %. So LFT （LFT-PP-LGF40） can replace SFT （SFT-PA6-SGF30） with the similar basic mechanical properties under normal tem- perature or 160 ℃ lower.展开更多
The precursor sol of alumina was prepared by sol-gel method with aluminum nitrate and malic acid as raw materials.The effects of content of malic acid and polyvinylpyrrolidone （PVP） on sol spinnability were explored...The precursor sol of alumina was prepared by sol-gel method with aluminum nitrate and malic acid as raw materials.The effects of content of malic acid and polyvinylpyrrolidone （PVP） on sol spinnability were explored.The gel fibers with above 80 cm in length were obtained by mixing aluminum nitrate,malic acid and PVP on mass ratio of 10 3 1.5.Thermogravimetry-differential scanning calorimetry （TG-DSC）,Fourier transform infrared （FTIR） spectrum,X-ray diffractometry （XRD）,and scanning electron microscopy （SEM） were used to characterize the properties of the gel and ceramic fibers.The alumina fibers with a smooth surface and about 20μm in diameter were obtained by sintering at 1 200℃,and their main phase was indentified to be α-Al2O3.展开更多
A high sensitive long period fiber grating（LPFG） sensor for the detection of nitrite is proposed, which is realized by coating multiple poly（sodium 4-styrensulfonate）（PSS） and poly（diallyldimethylammonium） chl...A high sensitive long period fiber grating（LPFG） sensor for the detection of nitrite is proposed, which is realized by coating multiple poly（sodium 4-styrensulfonate）（PSS） and poly（diallyldimethylammonium） chloride （PDDA） layers on the fiber grating surface. The sensitivity of this LPFG sensor is maximum when the number of assembled layers is 70. Under this condition, a nitrite concentration of 3×10^-3 mol/L, which is lower than the National Food Additive Standard, 4.2×10^-3 mol/L, can be distinguished. The sensitivity is further increased by 30% when nitrite was determined in the sucrose solution with a concentration of 65%, which provides a new solution for the best refraction index approaching matched index of the fiber cladding. Compared with chemical methods, this nitrite detection technology offers some advantages, such as high accuracy, non toxicity, high speed, low cost, without chemical reagent, and is suitable for foodstuff security detection.展开更多
We demonstrate experimentally fabrication of CO2 laser written long-period fiber gratings （LPFGs） in single-mode fiber （SMF） under tension. New transmission dips can be generated due to the frozen-in stress in the...We demonstrate experimentally fabrication of CO2 laser written long-period fiber gratings （LPFGs） in single-mode fiber （SMF） under tension. New transmission dips can be generated due to the frozen-in stress in the fiber under tension. Dynamics analysis of laser writing process is performed to study the mechanism of the grating inscription. Experimental results show that the wavelength shift of new generated resonance dips can shift towards the longer or shorter wavelength with the increase of laser scanning cycles for gratings with different pitches.展开更多
Long-term potentiation(LTP) of C-fiber evoked field potentials in spinal dorsal horn is first reported in 1995.Since then,the mechanisms underlying the long-lasting enhancement in synaptic transmission between primary...Long-term potentiation(LTP) of C-fiber evoked field potentials in spinal dorsal horn is first reported in 1995.Since then,the mechanisms underlying the long-lasting enhancement in synaptic transmission between primary afferent C-fibers and neurons in spinal dorsal horn have been investigated by different laboratories.In this article,the related data were summarized and discussed.展开更多
The coupled-mode equations for fiber Bragg grating （FBG） and long period fiber grating （LPFG） undergoing linear and quadratic temperature change were given. The effects of temperature gradient and quadratic temper...The coupled-mode equations for fiber Bragg grating （FBG） and long period fiber grating （LPFG） undergoing linear and quadratic temperature change were given. The effects of temperature gradient and quadratic temperature change on the reflectivity spectrum of fiber Braggs grating and the transmission spectrum of long period fiber grating were investigated using the numerical simulation, and the dependence relationships of the central wavelength shift, the full-width-athalf-maximum, and the peak intensity upon temperature gradient were also obtained. These relationships may be used to design a novel fiber optical sensor which can simultaneously measure the temperature and temperature gradient.展开更多
Time synchronization techniques, especially on the pulse per second(PPS) temporal basis, have attracted growing research interests in recent years. In this paper, we have proposed and experimentally demonstrated a hig...Time synchronization techniques, especially on the pulse per second(PPS) temporal basis, have attracted growing research interests in recent years. In this paper, we have proposed and experimentally demonstrated a high-precision two-way time transfer(TWTT) system to realize long-distance dissemination of 1 PPS signal generated by a hydrogen maser. A dense-wavelength-division-multiplexing(DWDM) system and bi-directional erbium-doped fiber amplifiers(Bi-EDFAs) have also been adopted to suppress the impact of Rayleigh backscattering and optimize the signal to noise ratio(SNR) as well. We have theoretically analyzed the systematic delay in detail. The ultimate root mean square(RMS) variation of time synchronization accuracy is sub-26 ps and the time deviation can be reduced to as low as 1.2 ps at 100 s and 0.253 ps at 12 000 s, respectively.展开更多
Long period fiber gratings are emerging as a potential candidate in the list of surrounding refractive index optical fiber sensors. Their sensitivity can be enhanced greatly if the grating period, fiber dimensions and...Long period fiber gratings are emerging as a potential candidate in the list of surrounding refractive index optical fiber sensors. Their sensitivity can be enhanced greatly if the grating period, fiber dimensions and surrounding refractive index are optimized in a way to operate at a point called turn around point on phase matching curves of these gratings. Turn around point LPFGs are well known for their ultrahigh sensitivity to external parameters. Potential of operating LPFG at or near turn around point has been investigated by many researchers in various applications including physical parameter sensing, adulteration detection, radiation dose, etc. Since TAP LPFGs are in investigation phase therefore a lot of rigorous & efficient work in finding techniques for optimizing their potential as sensor in chemical, biochemical, structural health monitoring is still to be carried out. A brief review of work carried out in this domain till now is presented here and key findings from literature review are highlighted.展开更多
We propose an approach of long-term stabilization of optical fiber phase by controlling a piezo-based phase modulator and a Peltier component attached to the fiber via a phase-locked loop( PLL) circuit w ith dual prop...We propose an approach of long-term stabilization of optical fiber phase by controlling a piezo-based phase modulator and a Peltier component attached to the fiber via a phase-locked loop( PLL) circuit w ith dual proportional-integral- derivative( PID) adjustment. With this approach,we can suppress the fast disturbance and slow drifting of optical fiber to satisfy the requirements of optical phase long-term locking. In theory,a mathematical model of an optical fiber phase control system is established. The disturbance term induced by environment influence is considered into the PLL model. The monotonous and continuous changing environment disturbance w ill cause a steady-state error in this theory model. The experimental results accords w ell w ith the theory. The steady-state performance,adjusting time,and overshoot can be improved by using the dual PID control. As a result,the long-term,highly stable and low noise fiber phase locking is realized experimentally.展开更多
Stochastic noises of fiber optic gyroscope （FOG） mainly contain white noise and fractal noise whose long-term dependent component causes FOG a rather slow drift. In order to eliminate this component, a two-step filt...Stochastic noises of fiber optic gyroscope （FOG） mainly contain white noise and fractal noise whose long-term dependent component causes FOG a rather slow drift. In order to eliminate this component, a two-step filtering methodology is proposed. Firstly, fractional differencing （FD） method is introduced to trans-form fractal noise into fractional white noise based on the estima-tion of Hurst exponent for long-term dependent fractal process, which together with the existing white noise make up of a gener-alized white noise. Further, an improved denoising algorithm of wavelet maxima is developed to suppress the generalized white noise. Experimental results show that the basic noise terms of FOG greatly decrease, and especially the slow drift is restrained effectively. The proposed methodology provides a promising ap-proach for filtering long-term dependent fractal noise.展开更多
In this paper, we report a high power long-pulse single-frequency all-fiber amplifier at 1064 nm with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). By applyi...In this paper, we report a high power long-pulse single-frequency all-fiber amplifier at 1064 nm with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). By applying square wave pulse modulation to the diodes, with a frequency of 50 Hz and a pulse width of 668 μs, the peak power of the output laser reached 257 W with an average power of 8.65 W, linewidth of 10.6 kHz and M<sup>2</sup> < 1.5. .展开更多
This paper focuses on the investigation of modal characteristics and sensing properties of long period grating photonic crystal fibers (LPG-PCFs). An improved effective index method is employed with an objective to st...This paper focuses on the investigation of modal characteristics and sensing properties of long period grating photonic crystal fibers (LPG-PCFs). An improved effective index method is employed with an objective to study its limitations for various designs of LPG-PCFs. Results so obtained with the above method are compared with the corresponding values of multiple multipole (MMP) method results which points the range of validity and applicability of the improved effective index method to LPG-PCFs. It is shown that this method is excellent when the surrounding media is assumed to be air. However, it becomes less accurate when the fiber is immersed into a liquid with a refractive index close to that of the cladding.展开更多
文摘This article summarizes the comparison between the preparation, structure and mechanical properties of long fiber reinforced thermoplastics （LFT） and short fiber reinforced thermoplastics （SFT）. Both of the experiment and theory results showed that the mechanical properties of long glass fiber reinforced thermoplastics pellets （LGFRT） have been enhanced better than that of short glass fiber reinforced thermoplastics pellets （SGFRT） manufactured by molding procession. After regulation of the relative humidity by 50 % , the mechanical properties of 30 % （ weight percent） short glass fiber content in SFT （ SFT-PA6-SGF30 ） are similar to that of 40 % long glass fiber content in LFT. Howev- er, the density of the latter is about 17 % lower than that of the former. Thus, the corresponding weight of products is reduced by 13 % ;output rate is increased by 21% , and the cost is therefore significantly lowered. And it has the fol- lowing advantages： impact strength is increased by 87 % ; the proportion is reduced by 20 % ; molding cycle is short- ened by 10 % ;materials cost is saved by 20 % -30 % and the final total cost is saved by 30 % -40 %. So LFT （LFT-PP-LGF40） can replace SFT （SFT-PA6-SGF30） with the similar basic mechanical properties under normal tem- perature or 160 ℃ lower.
基金Project(2010K10-21) supported by the Natural Science Foundation of Shaanxi Province,China
文摘The precursor sol of alumina was prepared by sol-gel method with aluminum nitrate and malic acid as raw materials.The effects of content of malic acid and polyvinylpyrrolidone （PVP） on sol spinnability were explored.The gel fibers with above 80 cm in length were obtained by mixing aluminum nitrate,malic acid and PVP on mass ratio of 10 3 1.5.Thermogravimetry-differential scanning calorimetry （TG-DSC）,Fourier transform infrared （FTIR） spectrum,X-ray diffractometry （XRD）,and scanning electron microscopy （SEM） were used to characterize the properties of the gel and ceramic fibers.The alumina fibers with a smooth surface and about 20μm in diameter were obtained by sintering at 1 200℃,and their main phase was indentified to be α-Al2O3.
基金Supported by the National Natural Science Foundation of China(Nos.60707016 and 60807030)
文摘A high sensitive long period fiber grating（LPFG） sensor for the detection of nitrite is proposed, which is realized by coating multiple poly（sodium 4-styrensulfonate）（PSS） and poly（diallyldimethylammonium） chloride （PDDA） layers on the fiber grating surface. The sensitivity of this LPFG sensor is maximum when the number of assembled layers is 70. Under this condition, a nitrite concentration of 3×10^-3 mol/L, which is lower than the National Food Additive Standard, 4.2×10^-3 mol/L, can be distinguished. The sensitivity is further increased by 30% when nitrite was determined in the sucrose solution with a concentration of 65%, which provides a new solution for the best refraction index approaching matched index of the fiber cladding. Compared with chemical methods, this nitrite detection technology offers some advantages, such as high accuracy, non toxicity, high speed, low cost, without chemical reagent, and is suitable for foodstuff security detection.
基金Project supported by the Shanghai Pujiang Program (Grant No.09PJ1404600)the New Century Excellent Talents in University, Ministry of Education of China (Grant No.NCET-10-0082)+1 种基金the Shanghai Shuguang Program (Grant No.08SG40)the Shanghai Leading Academic Discipline Project (Grant No.S30108)
文摘We demonstrate experimentally fabrication of CO2 laser written long-period fiber gratings （LPFGs） in single-mode fiber （SMF） under tension. New transmission dips can be generated due to the frozen-in stress in the fiber under tension. Dynamics analysis of laser writing process is performed to study the mechanism of the grating inscription. Experimental results show that the wavelength shift of new generated resonance dips can shift towards the longer or shorter wavelength with the increase of laser scanning cycles for gratings with different pitches.
基金the National Natural Science Foundation of China(No.30200076,30370474,30570599)Department of Science and Technology of Guangdong Province,China(No.2005A30801002)
文摘Long-term potentiation(LTP) of C-fiber evoked field potentials in spinal dorsal horn is first reported in 1995.Since then,the mechanisms underlying the long-lasting enhancement in synaptic transmission between primary afferent C-fibers and neurons in spinal dorsal horn have been investigated by different laboratories.In this article,the related data were summarized and discussed.
基金Funded by the Natural Science Foundation of Wuhan University of Technology (471-38650024)the National Natural Science Foundation of China (No. 50802069)
文摘The coupled-mode equations for fiber Bragg grating （FBG） and long period fiber grating （LPFG） undergoing linear and quadratic temperature change were given. The effects of temperature gradient and quadratic temperature change on the reflectivity spectrum of fiber Braggs grating and the transmission spectrum of long period fiber grating were investigated using the numerical simulation, and the dependence relationships of the central wavelength shift, the full-width-athalf-maximum, and the peak intensity upon temperature gradient were also obtained. These relationships may be used to design a novel fiber optical sensor which can simultaneously measure the temperature and temperature gradient.
基金supported by the National Natural Science Foundation of China(Nos.61571244 and 61501262)the Science and Technology Project of Tianjin(No.16YFZCSF00540)the Natural Science Foundation of Tianjin(No.15JCYBJC51600)
文摘Time synchronization techniques, especially on the pulse per second(PPS) temporal basis, have attracted growing research interests in recent years. In this paper, we have proposed and experimentally demonstrated a high-precision two-way time transfer(TWTT) system to realize long-distance dissemination of 1 PPS signal generated by a hydrogen maser. A dense-wavelength-division-multiplexing(DWDM) system and bi-directional erbium-doped fiber amplifiers(Bi-EDFAs) have also been adopted to suppress the impact of Rayleigh backscattering and optimize the signal to noise ratio(SNR) as well. We have theoretically analyzed the systematic delay in detail. The ultimate root mean square(RMS) variation of time synchronization accuracy is sub-26 ps and the time deviation can be reduced to as low as 1.2 ps at 100 s and 0.253 ps at 12 000 s, respectively.
文摘Long period fiber gratings are emerging as a potential candidate in the list of surrounding refractive index optical fiber sensors. Their sensitivity can be enhanced greatly if the grating period, fiber dimensions and surrounding refractive index are optimized in a way to operate at a point called turn around point on phase matching curves of these gratings. Turn around point LPFGs are well known for their ultrahigh sensitivity to external parameters. Potential of operating LPFG at or near turn around point has been investigated by many researchers in various applications including physical parameter sensing, adulteration detection, radiation dose, etc. Since TAP LPFGs are in investigation phase therefore a lot of rigorous & efficient work in finding techniques for optimizing their potential as sensor in chemical, biochemical, structural health monitoring is still to be carried out. A brief review of work carried out in this domain till now is presented here and key findings from literature review are highlighted.
基金supported by the National Natural Science Foundation of China(Grant No.91436103)Research Programme of National University of Defense Technology(Grant No.JC15-02-03)
文摘We propose an approach of long-term stabilization of optical fiber phase by controlling a piezo-based phase modulator and a Peltier component attached to the fiber via a phase-locked loop( PLL) circuit w ith dual proportional-integral- derivative( PID) adjustment. With this approach,we can suppress the fast disturbance and slow drifting of optical fiber to satisfy the requirements of optical phase long-term locking. In theory,a mathematical model of an optical fiber phase control system is established. The disturbance term induced by environment influence is considered into the PLL model. The monotonous and continuous changing environment disturbance w ill cause a steady-state error in this theory model. The experimental results accords w ell w ith the theory. The steady-state performance,adjusting time,and overshoot can be improved by using the dual PID control. As a result,the long-term,highly stable and low noise fiber phase locking is realized experimentally.
基金supported by Aviation Science Foundation(20070851011).
文摘Stochastic noises of fiber optic gyroscope （FOG） mainly contain white noise and fractal noise whose long-term dependent component causes FOG a rather slow drift. In order to eliminate this component, a two-step filtering methodology is proposed. Firstly, fractional differencing （FD） method is introduced to trans-form fractal noise into fractional white noise based on the estima-tion of Hurst exponent for long-term dependent fractal process, which together with the existing white noise make up of a gener-alized white noise. Further, an improved denoising algorithm of wavelet maxima is developed to suppress the generalized white noise. Experimental results show that the basic noise terms of FOG greatly decrease, and especially the slow drift is restrained effectively. The proposed methodology provides a promising ap-proach for filtering long-term dependent fractal noise.
文摘In this paper, we report a high power long-pulse single-frequency all-fiber amplifier at 1064 nm with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). By applying square wave pulse modulation to the diodes, with a frequency of 50 Hz and a pulse width of 668 μs, the peak power of the output laser reached 257 W with an average power of 8.65 W, linewidth of 10.6 kHz and M<sup>2</sup> < 1.5. .
文摘This paper focuses on the investigation of modal characteristics and sensing properties of long period grating photonic crystal fibers (LPG-PCFs). An improved effective index method is employed with an objective to study its limitations for various designs of LPG-PCFs. Results so obtained with the above method are compared with the corresponding values of multiple multipole (MMP) method results which points the range of validity and applicability of the improved effective index method to LPG-PCFs. It is shown that this method is excellent when the surrounding media is assumed to be air. However, it becomes less accurate when the fiber is immersed into a liquid with a refractive index close to that of the cladding.
