首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The dependence of the CO2 concentration on the discharge conditions and the mixture composition in a CO laser is studied experimentally. The experimental data are compared with the calculated results. A scheme of the reactions that govern the concentration of CO2 molecules under the experimental conditions in question is constructed. It is shown that, in a gas-discharge plasma, an admixture of Xe in a mixture containing CO molecules gives rise to a new mechanism for the dissociation of CO2 molecules by metastable xenon atoms. Under conditions close to the operating conditions of sealed-off CO lasers, the dissociation of CO2 molecules in collisions with metastable. Xe(3P2) atoms becomes the dominant dissociation mechanism in a He: CO mixture because it proceeds at a fast rate. This explains the observed decrease in the CO2 concentration in a xenon-containing He: CO mixture.  相似文献   

2.
The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is ± 5 parts in 107. Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH2F2, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO2 pump laser, and strength.  相似文献   

3.
Fiber‐supercapacitors (FSCs) are promising energy storage devices that can complement or even replace microbatteries in miniaturized portable and wearable electronics. Currently, a major challenge for FSCs is achieving ultrahigh volumetric energy and power densities simultaneously, especially when the charge/discharge rates exceed 1 V s?1. Herein, an Au‐nanoparticle‐doped‐MnOx@CoNi‐alloy@carbon‐nanotube (Au–MnOx@CoNi@CNT) core/shell nanocomposite fiber electrode is designed, aiming to boost its charge/discharge rate by taking advantage of the superconductive CoNi alloy network and the greatly enhanced conductivity of the Au doped MnOx active materials. An all‐solid‐state coaxial asymmetric FSC (CAFSC) prototype device made by wrapping this fiber with a holey graphene paper (HGP) exhibits excellent performance at rates up to 10 V s?1, which is the highest charge rate demonstrated so far for FSCs based on pseudocapacitive materials. Furthermore, our fully packaged CAFSC delivers a volumetric energy density of ≈15.1 mW h cm?3, while simultaneously maintaining a high power density of 7.28 W cm?3 as well as a long cycle life (90% retention after 10 000 cycles). This value is the highest among all reported FSCs, even better than that of a typical 4 V/500 µA h thin‐film lithium battery.  相似文献   

4.
CO dehydrogenase (CODH) is an environmentally crucial bacterial enzyme that oxidizes CO to CO2 at a Mo–Cu active site. Despite the close to atomic resolution structure (1.1 Å), significant uncertainties have remained with regard to the protonation state of the water-derived equatorial ligand coordinated at the Mo-center, as well as the nature of intermediates formed during the catalytic cycle. To address the protonation state of the equatorial ligand, we have developed a realistic in silico QM model (~179 atoms) containing structurally essential residues surrounding the active site. Using our QM model, we examined each plausible combination of redox states (MoVI–CuI, MoV–CuII, MoV–CuI, and MoIV–CuI) and Mo-coordinated equatorial ligands (O2?, OH?, H2O), as well as the effects of second-sphere residues surrounding the active site. Herein, we present a refined computational model for the Mo(VI) state in which Glu763 acts as an active site base, leading to a MoO2-like core and a protonated Glu763. Calculated structural and spectroscopic data (hyperfine couplings) are in support of a MoO2-like core in agreement with XRD data. The calculated two-electron reduction potential (E = ?467 mV vs. SHE) is in reasonable agreement with the experimental value (E = ?558 mV vs. SHE) for the redox couple comprising an equatorial oxo ligand and protonated Glu763 in the MoVI–CuI state and an equatorial water in the MoIV–CuI state. We also suggest a potential role of second-sphere residues (e.g., Glu763, Phe390) based on geometric changes observed upon exclusion of these residues in the most plausible oxidized states.  相似文献   

5.
A one-dimensional hydrodynamic model of a dielectric-barrier discharge (DBD) in pure chlorine is developed, and the properties of the discharge are modeled. The discharge is excited in an 8-mm-long discharge gap between 2-mm-thick dielectric quartz layers covering metal electrodes. The DBD spatiotemporal characteristics at gas pressures of 15–100 Torr are modeled for the case in which a 100-kHz harmonic voltage with an amplitude of 8 kV is applied to the electrodes. The average power density deposited in the discharge over one voltage period is 2.5–5.8 W/cm3. It is shown that ions and electrons absorb about 95 and 5% of the discharge power, respectively. In this case, from 67 to 97% of the power absorbed by electrons is spent on the dissociation and ionization of Cl2 molecules. Two phases can be distinguished in the discharge dynamics: the active (multispike) phase, which follows the breakdown of the discharge gap, and the passive phase. The active phase is characterized by the presence of multiple current spikes, a relatively high current, small surface charge density on the dielectrics, and large voltage drop across the discharge gap. The passive phase (with no current spikes) is characterized by a low current, large surface charge density on the dielectrics, and small voltage drop across the discharge gap. The peak current density in the spikes at all pressures is about 4 mA/cm2. In the multispike phase, there are distinct space charge sheaths with thicknesses of 1.5–1.8 mm and a mean electron energy of 4.3–7 eV and the central region of quasineutral plasma with a weak electric field and a mean electron energy of 0.8–3 eV. The degree of ionization of chlorine molecules in the discharge is ~0.02% at a pressure of 15 Torr and ~0.01% at 100 Torr. The DBD plasma is electronegative due to the fast attachment of electrons to chlorine atoms: e + Cl2 → Cl + Cl. The most abundant charged particles are Cl 2 + and Cl? ions, and the degree of ionization during current spikes in the active phase is (4.1–5.5) × 10–7. The mechanism of discharge sustainment is analyzed. The appearance of a series of current spikes in the active phase of the discharge is explained.  相似文献   

6.
The traditional Zn/MnO2 battery has attracted great interest due to its low cost, high safety, high output voltage, and environmental friendliness. However, it remains a big challenge to achieve long‐term stability, mainly owing to the poor reversibility of the cathode reaction. Different from previous studies where the cathode redox reaction of MnO2/MnOOH is in solid state with limited reversibility, here a new aqueous rechargeable Zn/MnO2 flow battery is constructed with dissolution–precipitation reactions in both cathodes (Mn2+/MnO2) and anodes (Zn2+/Zn), which allow mixing of anolyte and catholyte into only one electrolyte and remove the requirement for an ion selective membrane for cost reduction. Impressively, this new battery exhibits a high discharge voltage of ≈1.78 V, good rate capability (10C discharge), and excellent cycling stability (1000 cycles without decay) at the areal capacity ranging from 0.5 to 2 mAh cm‐2. More importantly, this battery can be readily enlarged to a bench scale flow cell of 1.2 Ah with good capacity retention of 89.7% at the 500th cycle, displaying great potential for large‐scale energy storage.  相似文献   

7.
Fibre bundles or whole muscles from Xenopus laevis, ranging in size from 0.5-60g, were studied. Maximum power output of predominantly fast (sartorius) and slow (adductor magnus) muscles was measured at cycle frequencies between 0.5 and 20Hz, using the work loop technique. Power output was highly dependent on cycle frequency, and in 50-60g adults was maximal at 6 Hz for fast fibres (65 Wkg-1), and 2 Hz for slow fibres (14 Wkg-1). The cycle frequency for maximum power output was dependent on body mass (Mb), and decreased as a function of Mb-0.07 in fast fibres, and Mb-0.23 in slow fibres. The functional significance of these differences is discussed.  相似文献   

8.
Layered niobium phosphates have been considered very promising energy storage materials because of their high theoretical operating voltage window and the rich oxidation states of niobium. However, their development has been stymied by the phase‐controlled synthesis due to the insolubility of niobium sources except in concentrated hydrofluoric (HF) acid systems. Herein, a new avenue is opened for layered acid niobium phosphate (2NbOPO4·H3PO4·H2O) synthesis in a mild oxalic acid system. Taking advantage of this strategy, in situ growth of sub‐5 nm 2NbOPO4·H3PO4·H2O nanosheet (NPene) arrays on conductive carbon fiber cloth (CFC) substrates is achieved as self‐standing electrodes for solid‐state supercapacitors. Interestingly, the NPene@CFC electrode exhibits a typical cation (H+ or Li+)‐intercalation kinetics with a wide potential window of 0–1.0 V in aqueous electrolytes. Given the wide potential window and highly exposed active surface, the solid‐state asymmetric supercapacitors constructed from such a NPenes@CFC electrode display a high working potential of 2.0 V, energy density of 122.2 W h kg?1 at a power density of 589.7 W kg?1, cycle stability with a capacitance retention of 94.2% after 10 000 cycles, and also outstanding flexible and wearable characteristics.  相似文献   

9.
Two-dimensional numerical simulations of a dc discharge in a CH4/H2/N2 mixture in the regime of deposition of nanostructured carbon films are carried out with account of the cathode electron beam effects. The distributions of the gas temperature and species number densities are calculated, and the main plasmachemical kinetic processes governing the distribution of methyl radicals above the substrate are analyzed. It is shown that the number density of methyl radicals above the substrate is several orders of magnitude higher than the number densities of other hydrocarbon radicals, which indicates that the former play a dominant role in the growth of nanostructured carbon films. The model is verified by comparing the measured optical emission profiles of the H(n ≡ 3), C 2 * , CH*, and CN* species and the calculated number densities of excited species, as well as the measured and calculated values of the discharge voltage and heat fluxes onto the electrodes and reactor walls. The key role of ion–electron recombination and dissociative excitation of H2, C2H2, CH4, and HCN molecules in the generation of emitting species (first of all, in the cold regions adjacent to the electrodes) is revealed.  相似文献   

10.
Development of life cycle inventories for electricity grid mixes in Japan   总被引:2,自引:0,他引:2  
Since most industrial processes consume electricity, it is quite important to develop reliable inventory data for electricity. There is, however, a problem that only a few figures concerning emissions related to electricity have been reported. In this work, process models of power plants were developed for the Japanese situation which simulate the mass flows and estimate the missing figures of emissions dependent on technical parameters of the plants and fuels. In Japan, electricity is supplied to the various regions by 10 electric companies. Therefore, life cycle inventories for the electricity grid mixes of the 10 electric companies in 1997 were developed. The functional unit is 1 kWh of electricity distributed to electricity users in each region. The emission of CO2, SO2, NOk, CH4, CO, non-methane volatile organic compound (NMVOC), dust (all particulates) and heavy metals (Ni, V, As, Cd, Cr, Hg, Pb, Zn) from power stations as well as those from fuel production and transport were investigated. Other pollutants into air, emissions to water, solid wastes, radiation and radioactive emissions from atomic power stations were not included due to a limitation of the available data. Direct CO2 emissions related to 1 kWh of electricity distributed by companies ranged from 0.21 to 1.0 kg/kWh (average value: 0.38 kg/kWh). Direct emissions of SO2 and NOx from power stations related to 1 kWh of electricity are 2.5* 10-4 and 2.2* 10-4 kg/kWh on the average, respectively. SO2 emissions calculated in this work were somehow large compared with those reported by electric companies. Detailed information concerning total sulfur content in oil consumed in each oil-fired power station are required for an exact calculation of SO2 emissions from oil-fired power stations. In addition, the ratio of sulfur that goes into slag in combustion must be investigated further. The average amounts of CO, CH4, NMVOC and dust emissions were 5.0*10-5, 8.2*10-6, 1.8*10-5 and 6.8 * 10-6 kg/kWh, respectively. Heavy metal emissions from power stations were on the order of 10-9 to 10-8 kg/kWh. Detailed information concerning heavy metal content in oil and coals consumed in fossil fuel power stations are further required for an improved assessment of heavy metal emissions. Contribution of fuel production and transport to total CO2 emission was relatively small. On the other hand, contributions of fuel production and transport to total SO2 and NOx emissions were relatively large. In the case of CO, NMVOC and dust, emissions in fuel production and transport were predominant to total emissions. Heavy metal emissions into air during production and transport of fuels were on the order of 10/-8 to 10-9 kg/kWh.  相似文献   

11.
Lasers, sources of coherent UV and vacuum UV radiation, plasmachemical reactors, reactors for cleaning fouled gases, etc., can be classified as devices the working medium of which is plasma formed as a result of the interaction of a high-current relativistic electronic beam with gas. Efficiency of such devices which are united under the common name “systems of injection gas electronics” (SIGE) depends mainly on the efficiency of energy transfer from a beam to gas (ηg = W g /W b ) and that of the transform of the energy transferred to gas into the energy of the ultimate product W inin = W in/W g ). As a special case of SIGE, an experimental bench laser is considered. The new efficient method of pumping is supposed to be implemented on this laser to optimize the energy contribution η g and useful output ηin.  相似文献   

12.
13.
Undoped and Er-doped NaY(WO4)2 disordered single crystals have been grown by the Czochralski technique. The specific heat and thermal conductivity (κ) of these crystals have been characterized from T = 4 K to 700 K and 360 K, respectively. It is shown that κ exhibits anisotropy characteristic of single crystals as well as a κ(T) behavior observed in glasses, with a saturation mean free phonon path of 3.6 Å and 4.5 Å for propagation along a and c crystal axes, respectively. The relative energy positions and irreducible representations of Stark Er3+ levels up to 4G7/2 multiplet have been determined by the combination of experimental low (<10 K) temperature optical absorption and photoluminescence measurements and simulations with a single-electron Hamiltonian including both free-ion and crystal field interactions. Absorption, emission and gain cross sections of the 4I13/24I15/2 laser related transition have been determined at 77 K. The 4I13/2 Er3+ lifetime (τ) was measured in the temperature range of 77–300 K, and was found to change from τ (77K) ≈ 4.5 ms to τ (300K) ≈ 3.5 ms. Laser operation is demonstrated at 77 K and 300 K by resonantly pumping the 4I13/2 multiplet at λ≈1500 nm with a broadband (FWHM≈20 nm) diode laser source perfectly matching the 77 K crystal 4I15/24I13/2 absorption profile. At 77 K as much as 5.5 W of output power were obtained in π-polarized configuration with a slope efficiency versus absorbed pump power of 57%, the free running laser wavelength in air was λ≈1611 nm with the laser output bandwidth of 3.5 nm. The laser emission was tunable over 30.7 nm, from 1590.7 nm to 1621.4 nm, for the same π-polarized configuration.  相似文献   

14.
Summary Oxygen consumption of an in-pericardium heart preparation from the spiny dogfish (Squalus acanthias) was linearly related to cardiac power output. Basal oxygen consumption, predicted from the regression, was 0.127 l · s-1 · g ventricle mass-1 and increased by 0.189 l · s-1 · g ventricle mass-1 per milliwatt of power generated. From the relationship between cardiac power output and mechanical efficiency, mechanical efficiency was predicted to increase with cardiac power output to a maximum of 21 %. Mechanical efficiency was measured during volume loading and pressure loading at two power outputs (50% and 72% of maximum power output). At 50% of maximum power output, mechanical efficiency increased significantly by 2.87%, from 11.9±0.3% to 14.8±0.5% (n=7), when flow was halved and output pressure doubled to achieve the same power output. Similarly, at 72% of maximum power output, mechanical efficiency increased from 14.74±0.92% to 17.61±0.84% (n=6) when flow was halved and output pressure doubled to generate the same higher level of power output. The increased mechanical efficiency at higher output pressures is believed to result from cardiac myocytes working within a length range where they are able to generate the most tension during contraction and are most efficient. We speculate that the loss of mechanical efficiency associated with large changes in sarcomere length, when stroke volume is large, is a driving force behind the use of frequency as the principal means of increasing cardiac output as observed in more active fishes, birds and mammals.Abbreviations BM body mass - CO cardiac output - HR heart rate - P i mean cardiac input pressure - P o mean cardiac output pressure - PO partial pressure of oxygen - SV stroke volume of heart - VM ventricle mass  相似文献   

15.
《Inorganica chimica acta》1986,120(2):135-143
As known, on hydrated alumina support the Ru3(CO)12 cluster quickly decomposes into monometallic subcarbonyls. By FT-IR spectroscopy combined with data handling procedures, the structure and thermal behaviour of the bimetallic systems of Fe2Ru(CO)12/ Al2O3 and H2FeRu3(CO)13 together with that of Ru3(CO)12 have been studied. At the end of an interaction with the hydrated alumina surface, iron ruthenium bimetallic clusters decompose into identical ruthenium anchored surface species RuA  RuIII(CO)2, RuBRuII(CO)2 and RuCRu0(CO)2, like pure ruthenium clusters, and no CO bonded to iron has been detected RuB and RuC are stable in a wide temperature range (300–500 K) and they can be interconverted by oxidation and reduction. RuA is less stable (300–400 K). These main molecule-like species, anchored onto uniform sites of the surface, are accompanied by mobile subcarbonyls and stable monocarbonylic species, which occupy a large variety of different sites.  相似文献   

16.
Addition of KCN to Helix pomatia β-hemocyanin fully saturated with either O2 or CO results in a decrease of the spectroscopic properties of the protein (absorbance at 340 nm and luminescence at 550 nm) due to the displacement of the gaseous ligands (O2 or CO) from the active site. The anionic form of cyanide (CN?) is supposed to bind to the active site; its intrinsic affinity for the protein, as calculated from independent O2 and CO displacement experiments, is between 2 and 6 × 106M?1. The replacement of O2 or CO shows some differences which may be correlated with the different modes of binding at the active site. Thus, while displacement of oxygen by cyanide is hyperbolic, addition of cyanide to carbonylated hemocyanin shows a lag phase. This finding suggests the formation of a mixed liganded complex at the active site. The simultaneous presence of CO and CN? at the active site of hemocyanin is also supported by the experiment in which addition of small amounts of KCN to hemocyanin partially saturated with O2 and CO gives rise to an increase of emission intensity and a concomitant decrease of the O2 absorption band. The mixed-liganded species displays luminescence properties similar to those of CO-saturated hemocyanin, and the formation of the complex is reversible on dialysis or oxygenation.  相似文献   

17.
Results from studies of the parameters of a novel type of plasma source—a hollow cathode magnetron—are presented. The magnetron operates at a gas pressure of 5–20 mTorr, the discharge power being in the range of 0.5–4 kW. At discharge powers exceeding 2 kW, a plasma flow with a density of higher than 1011 cm?3 and length of up to 30 cm forms at the magnetron output. Using a grid quartz crystal microbalance, the ionized copper flux fraction was measured as a function of the gas pressure, discharge power, and distance from the target. At gas pressures of higher than 15 mTorr, the degree of ionization at a distance of 31 cm exceeds 50%.  相似文献   

18.
Printed batteries are an emerging solution for integrated energy storage using low‐cost, high accuracy fabrication techniques. While several printed batteries have been previously shown, few have designed a battery that can be incorporated into an integrated device. Specifically, a fully printed battery with a small active electrode area (<1 cm2) achieving high areal capacities (>10 mAh cm?2) at high current densities (1–10 mA cm?2) has not been demonstrated, which represents the minimum form‐factor and performance requirements for many low‐power device applications. This work addresses these challenges by investigating the scaling limits of a fully printed Zn–Ag2O battery and determining the electrochemical limitations for a mm2‐scale battery. Processed entirely in air, Zn–Ag2O batteries are well suited for integration in typical semiconductor packaging flows compared to lithium‐based chemistries. Printed cells with electrodes as small as 1 mm2 maintain steady operating voltages above (>1.4 V) at high current densities (1–12 mA cm?2) and achieve the highest reported areal capacity for a fully printed battery at 11 mAh cm?2. The findings represent the first demonstration of a small, packaged, fully printed Zn–Ag2O battery with high areal capacities at high current densities, a crucial step toward realizing chip‐scale energy storage for integrated electronic systems.  相似文献   

19.
A metalorganic gaseous doping approach for constructing nitrogen‐doped carbon polyhedron catalysts embedded with single Fe atoms is reported. The resulting catalysts are characterized using scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, and X‐ray absorption spectroscopy; for the optimal sample, calculated densities of Fe–Nx sites and active N sites reach 1.75812 × 1013 and 1.93693 × 1014 sites cm‐2, respectively. Its oxygen reduction reaction half‐wave potential (0.864 V) is 50 mV higher than that of 20 wt% Pt/C catalyst in an alkaline medium and comparable to the latter (0.78 V vs 0.84 V) in an acidic medium, along with outstanding durability. More importantly, when used as a hydrogen–oxygen polymer electrolyte membrane fuel cell (PEMFC) cathode catalyst with a catalyst loading as low as 1 mg cm‐2 (compared with a conventional loading of 4 mg cm‐2), it exhibits a current density of 1100 mA cm‐2 at 0.6 V and 637 mA cm‐2 at 0.7 V, with a power density of 775 mW cm‐2, or 0.775 kW g–1 of catalyst. In a hydrogen–air PEMFC, current density reaches 650 mA cm‐2 at 0.6 V and 350 mA cm‐2 at 0.7 V, and the maximum power density is 463 mW cm‐2, which makes it a promising candidate for cathode catalyst toward high‐performance PEMFCs.  相似文献   

20.
Herein, we report on unique bimetallic PtPb/Pt core/shell nanodisks consisting of structurally ordered PtPb hexagonal nanoplates as the core and the well‐organized Pt as the shell, as extremely active and selective catalysts towards CH3OH reformation. We found that the created Pt‐Pb nanodisks/C show the composition‐dependent activity with the optimized PtPb0.56 nanodisks/C being the most active for the CH3OH reformation to H2, 5.1 times higher than those of the commercial Pt/C. Significantly, only very limited carbon monoxide (CO) is produced during the CH3OH reformation, which is crucial for the practical application in fuel cells. The PtPb0.56 nanodisks/C is also more active for CH3OH reformation than PtPb hexagonal nanoplates/C and PtPb0.58 nanoparticles/C. X‐ray photoelectron spectroscopy (XPS) results reveal that the high ratio of Pt (0) to Pt (II) in Pt‐Pb nanodisks/C enhances the CH3OH reformation to H2, while the high content of Pb (0) is beneficial for decrease the CO production. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) of CO adsorption shows that Pt‐Pb nanodisks can promote the activation of CO molecules by forming the carboxylate (CO2δ?) intermediates, leading to the low CO production.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号