纳米微粒对低温保护剂溶液结晶性质的影响

为了研究纳米微粒对低温保护剂溶液结晶性质的影响,实验利用差示扫描量热仪(DSC)测量了加入不同粒径、不同质量分数的HA纳米微粒的乙二醇(EG)低温保护剂溶液的成核温度和结晶焓。实验结果表明:纳米微粒加入EG溶液后,成核温度明显升高,并且随着纳米微粒粒径的和质量浓度的增大而升高显著;加入一定质量浓度(>0.2%)的纳米微粒后,同浓度的低温保护剂溶液的结晶焓稳定地升高。成核温度与结晶焓的升高说明,纳米微粒能够促进低温保护剂溶液的结晶。     

纳米微粒对多元醇水溶液过冷度和水合性质的影响

利用差示扫描量热仪(Pyrid-Diamond DSC),研究乙二醇(EG)和丙三醇水溶液加入0.1%、0.5%质量分数,20nm、40nm、60nm粒径的HA纳米微粒后的过冷度、水合性质,分析HA纳米微粒对线性多元醇水溶液这些特性的影响。实验表明,纳米微粒加入后,线性多元醇水溶液过冷度显著降低,并随纳米微粒粒径增大而减小。水合实验的结果表明,HA纳米微粒对多元醇水溶液的水合性质影响显著,与未加入HA纳米微粒的线性多元醇溶液相比,纳米低温保护剂结晶焓降低,结合水含量增大。     

HA纳米微粒对PEG-600低温保护剂反玻璃化结晶的影响

为了研究羟基磷灰石HA纳米微粒对低温保护剂反玻璃化结晶的影响,本文利用DSC和低温显微镜研究了含有不同粒径(20nm、40nm、60nm)和不同质量浓度(0.1%、0.2%、0.4%、0.8%)HA纳米微粒的PEG-600(50%,w/w)溶液反玻璃化过程中的结晶现象.试验结果表明:与未添加纳米微粒的PEG-600溶液相比,加入40nm、0.4%纳米微粒的HA-PEG600溶液的反玻璃化温度升高了7℃;加入20nm、0.4%和40nm、0.8%纳米微粒的HA-PEG600溶液的冰晶生长速率分别降低了35%和提高了50%;纳米低温保护剂溶液的冰晶形貌从大圆形变成了小圆形、枝晶或小圆形中夹带枝晶.     

三元溶液共晶DSC实验研究

抑制共晶产生对低温保存非常重要。本文利用差示扫描量热法研究了加低温保护剂(DMSO、乙二醇、 1,2丙二醇、甘油和1,3丁二醇)的NaCl水溶液的共晶行为。得到以5％、10％、15％NaCl水溶液为母液的五种保护剂溶液热流曲线图。研究发现,溶液共晶是过冷、随机过程。低温保护剂有抑制NaCl水溶液共晶的作用。低温保护剂浓度越高, 共晶焓越小,对共晶的抑制作用越大。不同种类保护剂的抑制共晶的能力从强到弱依次是甘油、乙二醇、 DMSO、 1,2 丙二醇和1,3丁二醇。升温过程中,溶液发生共晶反玻璃化现象和玻璃化现象。     

冷冻速率对蚕豆热物性变化规律影响的实验研究

研究了不同冷冻速率下蚕豆热物性的变化规律。利用Hot Disk得到蚕豆在-30～30℃下的热导率变化曲线;通过DSC和低温冷冻实验台,冷冻速率在5～80℃/min条件下将蚕豆切片进行冷冻实验,得到了不同冷冻条件下冻结点、结晶点及比热容的变化规律。测试结果表明:蚕豆热导率随着温度的降低先减小再增大;冻结点随着降温速率的增大而增大;蚕豆的结晶点在降温速率小于20℃/min时出现浮动,但总体上,结晶点随着降温速率的增大而降低。在不同降温速率下,比热容随温度的变化规律基本相同,但在冷冻相变过程中发生剧烈变化。通过对冷冻过程中蚕豆热物性的实验研究,为冷冻干燥种子的传热传质分析提供了实验数据的支撑。     

纳米微粒对PVP低温保护剂比热的影响

为了研究纳米微粒对低温保护剂热力学性质的影响,本实验利用差示扫描量热仪(DSC)测量了加入不同质量分数的HA纳米微粒的PVP低温保护剂溶液的比热值.实验结果表明:纳米微粒加入PVP溶液后比热值明显减小,而且HA纳米微粒质量浓度越高,溶液的比热值越小.由于比热容与热扩算系数成反比关系,比热的降低能提高溶液的传热效率,进一...     

纳米微粒对低温保护剂溶液玻璃化性质的影响

利用差示扫描量热仪(DSC)研究了加入羟基磷灰石(HA)纳米微粒对低温保护剂溶液玻璃化的影响,实验得到了不同粒径和不同质量浓度的HA纳米微粒加入PVP溶液的玻璃化转变温度与反玻璃化温度.实验结果表明加入纳米微粒能显著的影响低温保护剂溶液的玻璃化性质.且随着纳米微粒质量分数的增加,溶液的玻璃化转变温度与反玻璃化温度均显著...     

乙醛（CH3CHO）水溶液的荧光特性

通过实验研究了乙醛（ＣＨ３ＣＨＯ）水溶液的荧光特性，测定了室温下乙醛１０％水溶液的吸收谱、在λ＝３５５ｎｍ处的表观吸收截面σ以及该溶液在不同浓度和不同温度下的荧光谱。实验发现，当激光的激励强度大于１０２３光子数／ｃｍ２ｓ时，乙醛水溶液的相对荧光效率渐趋饱和。     

纳米低温保护剂水合及玻璃化性质的DSC研究

利用差示扫描量热仪（DSC）研究了羟基磷灰石（HA）纳米微粒对丙三醇溶液冻结过程中水合性质及玻璃化性质的影响．实验结果表明在中高浓度HA纳米颗粒对溶液水合性质影响显著．与未加纳米颗粒的溶液相比,溶液结晶量减少,未冻水含量增大．在较低浓度溶液中,加入纳米颗粒后玻璃化温度变化不明显,但反玻璃化温度明显升高;当溶液浓度达到6...     

明胶水溶液的超声性质

用频率为11.4兆赫兹的超声波研究了明胶水溶液的超声性质。超声吸收的浓度曲线表明,一直到重量百分比浓度c=8.5％时超声吸收也没达到饱和值。当溶液浓度大于1.5％时,在室温下它们都可以转变成冻胶,而且在整个转化过程中超声吸收值不变。当溶液的温度下降到接近冻点时,溶液的粘滞系数随时间逐渐增大,从而使声吸收的经典理论值可能超过实验值几个数量级;但当溶液温度适当高于冻点时,经典声吸收理论值可能小于实验值而处于同一数量级。浓溶液(c=6.4％)超声速度的温度极大值与纯水中声速温度极大值没有什么明显的不同。文中对所有被观测到的这些现象进行了讨论。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.