共查询到20条相似文献,搜索用时 15 毫秒
1.
The positions and intensities of all vibrational transitions in the (ν 1, 2ν 2) Fermi doublet region of (CO 2) 2 dimers are obtained by means of variational method. The collision-induced absorption in compressed carbon dioxide is shown to be mainly due to dimeric absorption. Assignment of ν 1 and 2ν 2 vibrational bands in isolated CO 2 molecule is performed by consideration of the symmetries and intensities of dimeric vibrations. 相似文献
2.
We have obtained fifteen percent average internal power conversion efficiency for second harmonic generation in CdGeAs 2 of radiation from a TEA CO 2 laser operating at 10.6 μm. This is the highest reported doubling efficiency for a CO 2 laser. We have also observed cw difference frequency mixing in CdGeAs 2 at wavelengths between 11.4 and 16.8 μm using grating-tuned CO and CO 2 lasers. The CdGeAs 2 crystals are significantly improved in size and optical quality over those previously available. 相似文献
3.
The O 3 absorption coefficients for the rotational lines P(12)–P(28) of the 9.4 μm emission band of the CO 2 laser are presented. Measurements were made in O 3–air dilute mixtures (20–600 ppm) at 25°C and a total pressure of 1013.25 h Pa using a frequency stabilized cw CO 2 laser and values have been determined with greater precision than in previously reported studies. 相似文献
4.
We study the adsorption and reaction of CO 2 as a function of temperature between 100 and 700 K in the presence of Na on a Pd(111) surface using high resolution electron energy loss spectroscopy. While CO 2 does not react with a clean Pd(111) surface, we find various reaction channels on the Na precovered Pd(111) surface depending on the Na coverage. At intermediate coverage a bent CO 28− species with characteristic vibrational bands can be unambiguously identified. This species is stable up to 200 K, and dissociates into CO and oxygen similar to its behaviour on other surfaces, and as reported in a previous photoemission study [Wambach et al., Surface Sci. 209 (1989) 159]. In case the surface has been oxygen contaminated before Na and CO 2 exposure surface carbonates can be observed. 相似文献
5.
We present the discovery and frequency measurement of a new FIR laser line from CH 2F 2 optically pumped by a waveguide CO 2 laser. This new line has the same CO 2 laser pump line (9R32), offset (+5 MHz) and relative polarization of the strongest FIR laser line of CH 2F 2, namely the 184.3μm. The frequency is only 19,454 MHz apart from that of this line. We got a frequency measurement of 1,646,196.6 (10) MHz, which corresponds to a wavelength of 182.112 μm. 相似文献
6.
超低密度的SiO2气凝胶是一种经典的三维网状纳米多孔材料,已经广泛应用于如保温隔热、吸附等多种领域。以四甲氧基硅烷(TMOS)为硅源,采用酸碱两步法,利用乙醇超临界干燥技术制备了超低密度的SiO2气凝胶,分别利用SEM\TEM\BET等表征手段对该气凝胶进行了一系列的研究,发现当其密度为0.6 mg/cm3时,气凝胶拥有最佳的综合性能。该种气凝胶具有超低密度、高比表面积、加工成型性好、制备周期短等优点,有望在激光惯性约束聚变实验中作为冷冻靶发挥巨大的作用。 相似文献
7.
大气散射效应作为CO 2反演的主要误差源,严重影响了大气CO 2卫星测量的反演精度。氧气在大气中含量稳定,大气CO 2反演方法中常利用氧气的这一特性进行散射校正,其中典型的有光子概率密度函数(PPDF)方法。然而,O 2 A吸收带的光辐射中存在的植物叶绿素荧光会在不同程度上影响PPDF因子的反演,进而限制了CO 2反演精度。由于植被荧光信号较弱,在以往CO 2反演中没有引起足够重视。在调研全球植被荧光分布的基础上,模拟分析了荧光对大气CO 2柱含量(XCO 2)的影响。模拟计算无气溶胶条件下,以及气溶胶和地表反照率两者综合条件下荧光的影响,结果显示,当不考虑气溶胶的影响,荧光强度从0.1增加到1.8(mW·m-2·sr-1·nm-1),会给CO 2的反演结果造成0.1~2 (10-6)的偏差;考虑气溶胶与地表反射率的影响时,会给CO 2的反演结果造成(0.1~3)×10-6的偏差。此研究表明,对于具有高精度需求的CO 2反演,植物叶绿素荧光是一个不可忽略的影响因素。 相似文献
8.
In this paper, the effects of amplification of diffraction-limited pulsed CO 2 laser radiation over several meters of amplification length on beam quality and pointing stability are documented. Millijoule pulses are amplified up to 3 J. Generation and amplification of the 10 μm wavelength pulses were performed in the discharge volume of an e-beam sustained CO 2 laser. Beam quality is measured according to the ISO/DIS 11146 standard in terms of the beam quality factor M2. Fluence distributions were recorded with a beam analysing system of 100 μm spatial resolution. M2 parameter values ranged up to 1.55 for amplified pulse energies of 3 J. The necessity of beam-quality restoring techniques is inferred for the multijoule pulse energy regime. 相似文献
9.
Molecular CO 2 adsorption is observed on an Fe(111) surface at 85 K. For the main fraction of molecules the relative binding energies of the valence ion states as determined by ARUPS are consistent with those in the gas as well as in the condensed phase, and indicate that the electronic structure of that fraction of adsorbed molecules is only slightly distorted upon adsorption. There is a fraction of adsorbed molecules at 85 K that can be identified as bent, anionic CO 2− species. While the weakly adsorbed, linear CO 2 molecules desorb at low temperature, the CO 2− species is stable up to 160–180 K. The latter is proposed to be a precursor to dissociation. Above this temperature adsorbed carbon monoxide and oxygen are observed on the surface, and at room temperature the CO 2− signals have disappeared. Heating above room temperature dissociates the CO molecules into carbon and oxygen. 相似文献
10.
The reaction of CO 2 and H 2O to form bicarbonate (HCO −3) was examined on the nearly perfect and vacuum annealed surfaces of TiO 2(110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometry (HREELS). The vacuum annealed TiO 2(110) surface possesses oxygen vacancy sites that are manifested in electronic EELS by a loss feature at 0.75 V. These oxygen vacancy sites bind CO 2 only slightly more strongly (TPD peak at 166 K) than do the five-coordinated Ti 4+ sites (TPD peak at 137 K) typical of the nearly perfect TiO 2(110) surface. Vibrational HREELS indicates that CO 2 is linearly bound at the latter sites with a νa(OCO) frequency similar to the gas phase value. In contrast, oxygen vacancies dissociate H 2O to bridging OH groups which recombine to liberate H 2O in TPD at 490 K. No evidence for a reaction between CO 2 and H 2O is detected on the nearly perfect surface. In sequentially dosed experiments on the vacuum annealed surface at 110 K, CO 2 adsorption is blocked by the presence of preadsorbed H 2O, adsorbed CO 2 is displaced by postdosed H 2O, and there is little or no evidence for bicarbonate formation in either case. However, when CO 2 and H 2O are simultaneously dosed, a new CO 2 TPD state is observed at 213 K, and the 166 K state associated with CO 2 at the vacancies is absent. SSIMS was used to tentatively assign the 213 K CO 2 TPD state to a bicarbonate species. The 213 K CO 2 TPD state is not formed if the vacancy sites are filled with OH groups prior to simultaneous CO 2+H 2O exposure. Sticking coefficient measurements suggest that CO 2 adsorption at 110 K is precursor-mediated, as is known to be the case for H 2O adsorption on TiO 2(110). A model explaining the circumstances under which the proposed bicarbonate species is formed involves the surface catalyzed conversion of a precursor-bound H 2O–CO 2 van der Waals complex to carbonic acid, which then reacts at unoccupied oxygen vacancies to generate bicarbonate, but falls apart to CO 2 and H 2O in the absence of these sites. This model is consistent with the conditions under which bicarbonate is formed on powdered TiO 2, and is similar to the mechanism by which water catalyzes carbonic acid formation in aqueous solution. 相似文献
11.
The electrical conductivity of Cr 2O 3 nominally doped with 2 mol% MgO has been studied by the four point a.c. technique as a function of the oxygen activity (O 2 + Ar, CO + CO 2 and H 2 + H 2O) in the temperature range 400–1200 °C. It is concluded that Cr 2O 3 doped with MgO is an extrinsic conductor and that the dissolved Mg-dopant is compensated by the formation of electron holes at near atmospheric oxygen pressures and by oxygen vacancies (or possibly interstitial chromium ions) at highly reduced oxygen activities (in CO + CO 2 and H 2 + H 2O gas mixtures). In H 2 + H 2O mixtures Mg-doped chromia also dissolves hydrogen as protons and significantly affects the defect structure and electrical conductivity. The defect structure of the oxide under various conditions is discussed. 相似文献
12.
The temperature dependence of the upper critical fields, both perpendicular Hc2 and parallel Hc2 to layer planes of ferromagnet/superconductor bi- and multilayers, is theoretically investigated. The secular equation of the superconducting order parameter for determining the phase diagram ( H, T) is obtained by solving exactly the linearized Usadel equations in the multimode method taking into account the material parameter values. For the bilayers system, the influence of the boundary resistivity on the critical fields, and the dimensional crossover behavior of Hc2( T) are studied in details. For the multilayered structure, the effects of the π-phase state on both the superconducting transition temperature Tc and the upper critical fields ( Hc2, and Hc2) are also considered. The nonmonotonic Tc behaviors are predicted. The interplay between 0- and π-phases leading to the strong oscillations of Tc as well as the temperature dependence of the zero temperature critical fields on the ferromagnetic layer thickness are investigated theoretically. 相似文献
13.
The stability of SiC coating in helium with a low concentration of O 2, CO 2, and H 2O is a key factor for their application in improvement of oxidation resistance of graphite for high temperature gas-cooled reactors (HTGRs). Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC is partial pressure of active gas in helium; the critical temperature of passive oxidation for SiC increases with the partial pressure of O 2, CO 2, and H 2O, SiC is prone to undergo active oxidation in He–CO 2 and He–H 2O system. SiO 2/SiC multilayer coating can improve the oxidation resistance of graphite at higher temperature than SiC coating does under normal operation condition for HTGRs. 相似文献
14.
The appearance of ferromagnetism in Y(Co 1−xAl x) 2 is discussed in terms of a d band model. The approximate d bands for YCo 2 and Y(Co 1−x) 2 are calculated and the decrease in the electronic energy due to magnetization of the spin of estimated. The energy decrease is the largest in YCo 2, and it gradually decreases as the Al content increases, if the lattice constant is fixed, while this energy decrease increases if the lattice constant increases with increasing Al content. These results of calculations give a good account of the appearance of ferromagnetism in Y(Co 1−xAl x) 2 around x = 0.15. The ferromagnetism in Sc(CO 1−xAl x) 2 is also discussed, leading to the appearance of ferromagnetism between x = 0.15 and 0.30. 相似文献
15.
纳米孔隙内气体流动的理论预测对气体微流控器件的设计和制造具有重要的理论指导作用,文章采用分子动力学方法研究了氮气、氧气和二氧化碳混合气体在平行壁纳米孔隙内的剪切流动特性和边界滑移特性.研究结果表明:随着加入二氧化碳比例的不断增加,混合气体滑移速度不断增大,并且当二氧化碳的比例低于20%时,混合气体流动速度沿孔隙宽度方向呈线性分布;而当比例达到40%后,其速度轮廓将呈现非线性趋势.当二氧化碳所占比例为20%时,随着孔隙宽度的增加,混合气体的整体边界滑移随之减小.探究了混合气体密度和气-固耦合强度对混合气体流动及边界滑移的影响机理.发现随着混合气体密度的减小,气流边界滑移增大;随着气-固界面耦合强度的增强,边界气体分子易被吸附而出现黏滑运动,气体分子在边界处的积聚现象增强,剪切应变率增大,边界滑移减小. 相似文献
16.
We have investigated the reversible mixed-state magnetization M of three lanthanum substituted Bi 1.95Sr 2.05−xLa xCuO y (Bi-2201) ceramic samples having different critical temperatures Tc ranging from 20.0 to 35.5 K. As for the Bi 2Sr 2CaCu 2O 8+δ (Bi-2212) phase, we found that anisotropy of Bi-2201 is large. A manifestation of this anisotropy is the field independent magnetization M* observed at a temperature T*. In the framework of the London model, and including thermal fluctuations of vortices, we found for the temperature dependence of the penetration depth λ ab( T) = λ ab(0)[1 − ( T/ Tc0) n] −1/2, with n 1.7 and λ ab ( T = 0) 4000 Å. The estimated upper critical fields μ 0Hc2,c are of the order of 10 T. We observe a peculiar negative slope M/ T at low temperature and sufficiently high external magnetic field. This feature seems to be a characteristic of the Bi-2201 phase. However, we do not know whether it is associated with the superconducting mixed-state. A small amount of magnetic impurities could also be responsible for this behavior. Finally, the behavior of the reversible magnetization of the Bi-2201 samples investigated, which are situated at the optimal and in the overdoped region, did not indicate any unusual temperature dependence for the upper critical field Hc2,c. 相似文献
17.
The adsorption of oxygen and carbon dioxide on cesium-reconstructed Ag(1 1 0) surface has been studied with scanning tunneling microscopy (STM) and temperature programmed desorption (TPD). At 0.1 ML Cs coverage the whole surface exhibits a mixture of (1 × 2) and (1 × 3) reconstructed structures, indicating that Cs atoms exert a cooperative effect on the surface structures. Real-time STM observation shows that silver atoms on the Cs-covered surface are highly mobile on the nanometer scale at 300 K. The Cs-reconstructed Ag(1 1 0) surface alters the structure formed by dissociative adsorption of oxygen from p(2 × 1) or c(6 × 2) to a p(3 × 5) structure which incorporates 1/3 ML Ag atoms, resulting in the formation of nanometer-sized (10–20 nm) islands. The Cs-induced reconstruction facilitates the adsorption of CO 2, which does not adsorb on unreconstructed, clean Ag(1 1 0). CO 2 adsorption leads to the formation of locally ordered (2 × 1) structures and linear (2 × 2) structures distributed inhomogeneously on the surface. Adsorbed CO 2 desorbs from the Cs-covered surface without accompanied O 2 desorption, ruling out carbonate as an intermediate. As a possible alternative, an oxalate-type surface complex [OOC–COO] is suggested, supported by the occurrence of extensive isotope exchange between oxygen atoms among CO 2(a). Direct interaction between CO 2 and Cs may become significant at higher Cs coverage (>0.3 ML). 相似文献
18.
The data on the resistance and magnetoresistance (MR) as well as measurements of the linear and nonlinear susceptibilities are presented for a Nd 0.75Ba 0.25MnO 3 single crystal with the Curie temperature TC≈129 K. Although this compound remains insulating in the ferromagnetic state, its resistance has an anomaly near TC and it reveals the colossal magnetoresistance. The data on the magnetic response are well described by the dynamic scaling theory for 3D isotropic ferromagnets in the paramagnetic critical region at τ>τ *≈0.11, τ=( T− TC)/ TC. Below τ * an anomalous critical behavior is found that suggests the coexistence of two magnetic phases. This behavior is discussed in terms of a phase separation which can occur in the moderately doped manganites exhibiting an orbital ordering. 相似文献
19.
Of all the types of lasers now available, the CO 2 laser is particularly suitable for materials working. It has a very high efficiency (15–20%) and a high out-put power (up to several kW). When the laser light is focused by means of a lens or a mirror, a c.w. power density of more than 10 9 W cm -2 can be attained. The laser need not be used in vacuum. The CO2 laser is a suitable cutting tool for numerous materials. These include metals such as titanium or steel; combustible materials such as paper, textiles and wood; and plastics. The CO2 laser can also cut hard and brittle materials such as aluminum oxide and silicon carbide. If metals are cut in an oxidizing atmosphere, the cutting speed may be increased. The cutting width, however, is determined by the size of the laser spot. Another important field of application is the growth of single crystals. Experiments are reported in which the CO2 laser was used for welding steel, titanium, plastics, quartz, and glass. The advantages of the laser for this application are discussed. A comparative study of laser and electron beam techniques is included. 相似文献
20.
The magnetic behavior of rapidly solidified FePrB was investigated in the composition range Fe 77+χPr 15B 8−χ (0 ≤ χ ≤ 4). Furthermore, the magnetic and microstructural properties of Fe(NdPr)B were analyzed in the range Fe 78(Nd χPr 1−χ) 15B 7 (0 ≤ χ ≤ 1). The temperature dependence of the critical field was analyzed with a modified form of Brown's expression for the nucleation field. From this analysis the values for the microstructural parameters, K and Neff, were determined which describe the deteriorating effects of the non-ideal microstructure on the coercivity. 相似文献
|