Search

Background and Objective: Long-chain polyunsaturated fatty acids (LCPUFA) play an important role in the regulation of fat metabolism in the placenta and fetus. Changes in placental function in pre-eclampsia affect the transport of fatty acids and affect fetal nutrition. The aim of the study was to compare LCPUFA levels in blood, placenta and cord blood of pregnant women with or without pre-eclampsia. Methods: The blood, placenta and umbilical cord blood of pregnant women (n = 30 each) who were normotensive and with pre-eclampsia were collected. The levels of fatty acids in maternal blood, placenta and umbilical cord blood were determined by the quartz capillary gas chromatography technique. Results: The average age of normal pregnant women was 27.0±4.5 years and that of pre-eclampsia pregnant women was 30±4.0 years (P > 0.05). The levels of total fatty acids, arachidonic acid (AA) and docosahexaenoic acid (DHA) were higher in pregnant women with pre-eclampsia than in normal women. The level of linoleic acid in cord blood and placenta was significantly higher in pre-eclampsia group than in the normal pregnant women while linoleic acid content in maternal blood being lower in pre-eclampsia group compared to the normal maternal group. Conclusion: The changes of LCPUFA in blood, placenta and umbilical blood of pre-eclampsia may be related to the changes of LCPUFA in placenta. These changes may be involved in the pathophysiological process of pre-eclampsia. Maternal supplement of LCPUFA, such as DHA, in early gestation may be helpful in improving morbidity associated with maternal eclampsia. How to Cite This: Weili Z. Comparative Long-chain polyunsaturated fatty acids levels in blood, placenta and cord blood of pregnant women with or without pre-eclampsia. Biomedica. 2020; 36 (4): 379-83.Doi: https://doi.org/10.51441/BioMedica/5-83.

NLNet has been considered as one milestone in the study of capturing long-range dependencies. Many recent studies modify the internal structure of NLNet directly and apply them to video object detection and semantic segmentation tasks. The dependencies between local and global features have been well developed, but the dependencies between global features of different convolution layers are rarely considered. Convolution is a local operation, so the global features of different convolution layers cannot be directly related, resulting in the loss of dependencies between global features. Given the vulnerability, this study designs a network that can efficiently capture the dependencies between the global features of different convolution layers, potentially further improving the accuracy. Furthermore, for the calculation of the dependency matrix, based on the Dot-product used in NLNet, we propose RELU-Dot-product, which can achieve higher accuracy. We evaluate the proposed method on image classification and object detection tasks. The data sets involved are CIFAR10, CIFAR100, Tiny-imagenet, VOC2007, VOC2012 and MS COCO. Experiments show that our method can significantly improve network performance by introducing a few parameters.

The electron beam evaporation deposition method was employed to prepare scandium oxide(Sc2O3) films with substrate temperatures varying from 50 to 350 ℃. A spectrophotometer, a glancing incidence X-ray diffraction spectrometer and a WYKO optical profilograph were employed to investigate the optical, microstructure properties and surface roughness of the Sc2O3 films. The refractive index and the extinction coefficient were calculated from the transmittance and reflectance spectra with the help of the Essential Macleod. The laser induced damage threshold(LIDT) of the Sc2O3 films was characterized by a pulsed Nd:YAG laser system at 355 nm with a pulse duration of 8 ns. A maximum value of 2.6 J/cm2 was derived, and t

Very deep zero-order metallic grating structures are processed to study the transmission properties of THz radiation pulses. The experiments have been performed with two samples. The delay of the THz pulses and the corresponding resonantly enhanced transmission spectra through the samples are observed. To explain the extraordinary transmission we have treated the samples as Fabry–Perot resonators through resonant excitation of the coupled surface plasmon polaritons filled in the cavities between the metal slats. The experimental results are in reasonable agreement with the numerical simulation. Our results show that THz-time-domain spectroscopy may be an effective technique for studying the optical properties of various THz microstructured devices.

The N = 3 femtosecond solitonlike pulses are observed directly in a self-mode-locked Ti:sapphire laser as well as even higher-order solitonlike pulses for the first time. When the laser is operating in a stable train of mode-locked pulses, the periodic pulse train appears by only varying the intracavity dispersion. The soliton period with N = 3 corresponds to a cavity round trip number of 164.

The role of gain aperture in self-mode-locked Ti:sapphire laser was verified in our experiments. The observation of self-Q switching of self-mode-locked Ti:sapphire laser is reported. And tuning pulse duration from 50 fs to 14.5 ps was achieved.

Through analyzing the properties of vehicle GPS navigation system signal’s observation gross error and random noise, this paper presents a new dynamic filter algorithm, which based on stationary wavelet transformation (SWT). Firstly, the algorithm decomposes the vehicle GPS navigation signal with stationary wavelet function. Then, the algorithm detects, eliminates and corrects the signal’s observation gross error at different resolution levels with statistic theory, and the signal’s random noise is de-noised at different resolution levels with improved soft-threshold de-noising method. Finally, the algorithm provides precise positioning information for the vehicle GPS navigation system through reconstructing the de-noised SWT coefficients. The simulation result shows that the algorithm is better than Kalman filter, and is available for the vehicle GPS navigation system.

It is difficult to establish a precise mathematical model in Extended Kalman Filter (EKF) data fusion algorithm for GPS/DR integrated vehicle navigation system, a novel data fusion algorithm is put forward, which based on wavelet packet analysis. Firstly, the algorithm chooses best wavelet packet group for GPS, odometer and gyroscope signals with least cost principle, and does dynamic pre-filtering for the signals by high frequency coefficients de-noising threshold method based on Stein's Unbiased Risk Estimation?SURE?. Finally, the algorithm provides precise positioning information for the GPS/DR integrated vehicle navigation system through doing EKF data fusion. The simulation results show that the algorithm is better than EKF data fusion algorithm, and improve data fusion effect for the GPS/DR integrated vehicle navigation system.

This paper presents an improved image compression algorithm to make up a deficiency arising when the Embedded Zerotree Wavelet encoding (EZW) is employed to uniformly scan the low and high frequency coefficients. According to the feature of the wavelet transform's energy distribution, the scalar quantization is used to quantify sub-band coefficients of high frequency in order to reduce the IZ(Isolated Zero); the threshold sequence is then adjusted in the process of the successive approximation quantization to minimize distortion when recovering images in this paper. Simulation results show that this improved coding scheme is superior to the EZW algorithm in PSNR as well as image reconstruction quality.

Dielectric metamaterials based on high-impedance silicon were designed for controlling the amplitude and phase of the terahertz waves. Here, the basic unit cells of the dielectric metamaterials are subwavelength silicon pillars, they have lower loss and thus have higher efficiency compared with the metal based metamaterials. As different silicon pillars with different geometric parameters and orientation angles will have different transmission amplitude and phase when the terahertz wave passes through them, nearly arbitrary spatial amplitude and phase distributions can be achieved by designing the geometric parameters and orientation angles of the silicon pillars at different positions, which allows to fully control the shape of the transmitted terahertz wavefront. In experiment, three different meta-gratings were designed using the silicon based structures in which the diffractive orders and their numbers can be arbitrarily controlled. Such dielectric metamaterials are very easy to design and fabricate, making them very promising in developing low-loss terahertz functional devices.

Recently, terahertz radiation has been a branch of cutting-edge science and technology involving many fields such as public security, military defense and national economy. In the past, far-field measurements were widely carried out based on terahertz time-domain spectroscopy. But the spatial resolution is limited by far-field diffraction effect. In order to break diffraction limit and gain sub-wavelength spatial resolution in terahertz frequency region, a series of near-field detection methods came into being, such as confocal microscopy, using an aperture, guided mode, scattering, direct detection in the near-field, etc. Each method has its own advantages and disadvantages. Using the photoconductive-antenna tip is one of the direct detection methods and it delivers the possibility of near-field measurements of terahertz waves. In this method, the photoconductive-antenna tip is a tapered photoconductive tip probe. So it can be close enough to the sample surface and receive the near-field signal on the basis of principle of photoconductivity. In this way, high spatial resolution can be gained. In this article, we introduce our recent progress of near-field and far- field scanning terahertz spectroscopy system with photoconductive-antenna in detail. Firstly, we analyze and summarize the near-field detection methods that have been developed in these years. And then, using the femtosecond laser whose center wavelength is 800 nm and the photoconductive-antenna tip detector coupled with fiber, we construct fiber near-field/ far-field scanning terahertz spectroscopy (N/F-STS). The frequency bandwidth is in a range from 0.2 THz to 1.5 THz and the terahertz spot is circular and uniform indicated by performance test. Also the amplitude and phase of the terahertz field are recorded simultaneously. It has the ability to perform three-dimension scan in various experiment conditions conveniently. Finally, we introduce the real applications in our laboratory. N/F-STS can be used to scan spatial electric distribution in three dimensions and test the spectral properties in terahertz range like other traditional far-field methods. Nevertheless, the most importantly, N/F-STS is used to scan the terahertz near-field of samples, such as terahertz surface plasmon polaritons, etc. The presented method thus is useful in some application areas, such as metamaterials, graphene, surface plasmons, waveguide transmission, near-field imaging, biological test, and chip inspection.

Subwavelength arrays of dipole-bowtie antennas are designed and characterized using terahertz time-domain spectroscopy (THz-TDS) and finite element method (FEM) simulations. Two different substrates, silicon and mylar with an order of magnitude difference between their thickness values are used to study the resonance properties of the antennas. The 640-μm thick silicon substrate supports a sharper fundamental mode resonance. We discover that higher-order Fabry—Perot resonances can be excited only in 24-μm thin mylar substrates and show much higher sensitivity to dielectric changes in the environment and the geometrical parameters of the antennas than the fundamental dipole resonance.

Chirped mirrors (CMs) are designed and manufactured. The optimized CM provides a group delay dispersion (GDD) of around –60 fs2 and average reflectivity of 99.4% with bandwidth 200 nm at a central wavelength of 800 nm. The CM structure consists of 52 layers of alternating high refractive index Ta2O5 and low refractive index SiO2. Measurement results show that the control of CM manufacturing accuracy can meet our requirement through time control with ion beam sputtering. Because the GDD of CMs is highly sensitive to small discrepancies between the layer thickness of calculated design and those of the manufactured mirror, we analyze the error sources which result in thickness errors and refractive index inhomogeneities in film manufacture.

Noncollinear parametric superfluorescence (NPS) is obtained in the visible regio n by pumping a type-Ⅰ phase-matched BBO crystal with the second harmonic of an amplified Ti:sapphire laser at 1kHz repetition rate. The variation of the noncol linear angle and the wavelength at the peak intensity of the NPS with the phase- matched angle is studied, and the variations of the group velocity mismatch (GVM ) with the noncollinear angle and the phase-matched angle in the three-wave inte raction is calculated theoretically. The results indicate that the type-Ⅰ phase -matched NPS ring is centrosymmetric with respect to the pump beam on the observ ation screen. Along the NPS direction at the peak intensity, the GVM is minimal and the effective interaction length is maximal for the three waves. The angular distribution of the NPS intensity is ascribed to phase velocity and group veloc ity self-matching among interacting pulses. The theory and the experiment provid e an ideal geometrical model for reducing the GVM between three waves, and provi de a theoretical guidance and experimental verification for obtaining parametric pulses with higher gain and shorter duration in femtosecond optical parametric amplification.

The model of the pulse front tilted by a folded reflecting telescope used as a beam expander in the chirped pulse amplification system is developed, and the relationship between the pulse front aberrance and the parameters of the telesco pe is discussed. It is found that the effect of pulse front aberrance on the bea m is too strong to be ignored when the pulse duration is less than 100fs. An e ffective method is presented to overcome this problem.

Birefringent microstructure fibers are shown to allow efficient gereration of anti-Stokes line emission as a result of four-wave-mixing in higher mode by using unamplified femtosecond Ti:sapphire laser pulses.Intense blue-shifted lines with different central wavelength were generated in the high-delta (i.e.high-air filling in the cladding) microstructure fiber with axis sizes 50 and 46 μm by femtosecond laser pulses with 35-fs in duration,820nm in central wavelength and 4nJ in energy per pulse.The experimental result shows that phase-matched four-wa ve mixing in higher-order modes of microstructure fibers allows unprecedentedly high efficiencies of anti-Stokes frequency conversion to be achieved for subnano joule femtosecond laser pulses.The dependence factor of the four waves mixing in birefringent microstructure fiber is compared and analyzed.Good agreement betwe en the theory and experiment is achieved.

For femtosecond optical parametric amplification (OPA) pumped with a 400nm blue laser, limited by phase-matched condition and nonlinear crystal transparent range, the tuning range of the output parametric laser is restricted, and the blue and the near UV lasers with wavelength less than 460nm are difficult to obtain. In our experiment, we adopted the second harmonic of a Ti:sapphire nine-pass chirp pulse amplifier at 1kHz repetition rate as the pump beam, and the white- light supercontinuum as the seed beam; thus, by a type-Ⅰ noncollinear phase-mat ched broad bandwidth β-BaB2O4 (BBO) OPA, with certain exp erimental paramete rs, the amplified signal beam from 530nm to 810nm and the idler beam from 81 0nm to 17μm were obtained; at the same time, the idler second harmonic fr om 410nm to 700nm was obtained also. The idler second harmonic was cascaded with the idler beam, its pulse energy was 26μJ and the conversion efficienc y was greater than 5%. Therefore, femtosecond pulses tuned continuously from 410 nm to 810nm can be obtained by the BBO OPA with a single crystal only, there by a useful source is provided for more investigations and applications. In this paper, we also have theoretically analyzed the generation condition of the idle r second harmonic for femtosecond OPA.

The dispersion in a chirped pulse amplifier (CPA) with a Martinez stretcher is analyzed theoretically based on ray_tracing. The method of mutual compensation th at introduced properly the negative third_order dispersion to balance the fifth_ order dispersion is presented. A shorter pulse near the transform_limit can be g enerated by this method rather than by the traditional approach that zeros the s econd and the third order dispersion successively in the CPA system.

In this letter, we systematically investigated the temporal and spectral characteristic of ultra-broad band Ti:sapphire oscillator in femtosecond regime. Pulse formation in temporal regime was observed while the spectral shape evolved fro m hyperbolic secant shape into multi-peak one and the bandwidth increased from 40 to 180nm. Experimental results showed that pulse shortening mainly occurred n ot at its bottom part but at its central section while the spectrum was broadene d, and at the same time the relative energy at the bottom part increased.

For avoiding adverse effect arising from group velocity mismatching in parametri c amplification, a new method is presented, in which we combine pulse front slan t and noncollinear phase matching to completely compensate group velocity mismat ching of three pulses, in femtosecond optical parametric amplification (OPA). Th e change of the phase matching angle, the pulse front slant angle and the noncol linear angle with the signal wavelength are calculated, when group velocity matc hing of three pulses is achieved in BBO crystal type_Ⅰ and typeⅡ phase matching configurations. The effect of group velocity matching of three pulses on the spatial walk_off length, the parametric gain and the parametric bandwidth is analyzed. The results indicate that, using this method can make matching of gro up velocities of three pulses, when tuned continuously in both BBO type_I and Ⅱ phase matching femtosecond OPA, and thus the effective interaction length of th ree pulses is increased considerably. This calculation method and the analysis r esults provided a theoretical guidance for obtaining parametric pulses with high er gain and shorter duration.

A method that compensates completely the group velocity mismatch between three w aves for femtosecond optical parametric amplification (OPA) in BBO type-I phase- matched configuration is presented by combining noncollinear configuration with tilting pump wave front. When the group velocities of the three waves are matche d, the variations of the noncollinear angle, the phase-matched angle and the pum p wave front tilt angle with the signal wavelength are calculated theoretically, and the effects of the pump beam size and the spatial walk-off length are analy zed. The results indicate that this method not only can achieve maximal parametr ic bandwidth, but also can match completely the group velocities between three w aves for femtosecond OPA. In addition, with increasing parametric gain, it is ve ry importance to appropriately choose the pump beam size and the nonlinear cryst al length.

In this paper the spatial chirp and the angular dispersion for femtosecond optical parametric oscillation(OPO) are calculated theoretically and analysed. The analytical expression of the spatial chirp in the nonlinear crystal(BBO) is presented. And the analytical expressions of second-and third-order dispersions including angular dispersion of the nonlinear crystal for the noncollinearly phase-matched femtosecond BBO OPO in type-Ⅰ configuration with angle tuning. Moreover, variations of second- and third-order dispersions with the angular dispersion are calculated exactly.

In this paper, we report the photoluminescence from high-quality nanocrystalline ZnO thin films. The high-quality nanocrystalline ZnO thin films are prepared by thermal oxidation of ZnS films at 800℃, which are deposited by low-pressure metal-organic chemical vapor deposition technique. X-ray diffraction indicated that the nanocrystalline ZnO thin films have a polycrystalline hexagonal wurtzite structure. A strong ultraviolet emission peak at 3.26 eV was observed and the deep-level emission band was barely observable at room temperature. The strength (ΓLO) of the exciton-longitudinal-optical (LO)-phonon coupling is deduced from the temperature dependence of the full width at half maximum of the fundamental excitonic peak. ΓLO is reduced greatly due to the quantum confinement effect.

The characteristics of supercontinuum in various nonlinear materials has been investigated with high-gain, Low-dispersion femtosecond amplifier. The wide-band femtosecond laser supercon-tinuum has been obtained.

This paper gives a detailed theoretical investigation on phase conjugation induced by nearly degenerate four-wave mixing in single mode vertical-cavity surface-emitting lasers (VCSELs) with weak optical injection. Considering VCSELs that can work in linearly polarized or elliptically polarized states, it derives the theoretical expression of the conjugated field by small signal analysis based on the vectoral rate equations?the spin-flip model. For linearly polarized state, VCSELs show similar conjugate spectra to edge-emitting semiconductor lasers. For the elliptically polarized state, dichroism and birefringence parameters as well as the spin-flip rate can change the conjugate spectra. Especially, when frequency detuning of the probe and pump waves is between the positive and negative relaxation oscillation frequency, changes are evident. For specific values of parameters, conjugate efficiency between 20dB to 40dB are obtained.

In this letter, we investigated random lasing phenomenon in ZnO powder using the pump_probe technique. Under 267nm laser pumping, supernarrow single_mode emission and multi_mode emission were observed by precisely controlling the pumping intensity and the excitation beam size on the sample. The supernarrow emission peaks are much narrower than the normal luminescence and ASE spectra. The time_resolved pump_probe measurement shows that the lifetime of the emission state above the lasing threshold is only a few picoseconds which demonstrates that the formation of supernarrow random lasing bandwidth is due to stimulated emission.