共查询到20条相似文献,搜索用时 31 毫秒
1.
Results are presented from experimental studies of a pulsating discharge produced by a dc power source in subsonic and supersonic cold (T = 150–300 K) air flows at static air pressures in the flow of 40–760 Torr. Two modes of pulsating discharge were implemented experimentally: without and with (from one to five) intermediate breakdowns. The discharge pulsation frequency, the maximum attainable voltage across the discharge gap, the length of the plasma channel, and the electric field in the discharge plasma were studied as functions of the air flow velocity and discharge current. 相似文献
2.
A semi-empirical model of apparent blood viscosity as a function of vessel diameter and discharge hematocrit 总被引:1,自引:0,他引:1
A semi-empirical model is developed to describe the dependence of apparent viscosity of blood on vessel diameter (2.7 to 500 microns) and vessel discharge hematocrit (5% to 60%). The blood flow is modeled as a cell-rich core and a cell-free marginal layer in the larger vessels and an axial-train in the smaller vessels. Laminar (Poiseuille) flow is assumed in all cases. An equation is derived in which apparent viscosity is a function of vessel diameter, core viscosity, and width of marginal layer. This is then complemented by empirical equations in which core viscosity varies exponentially with discharge hematocrit while the width of marginal layer varies linearly with discharge hematocrit. The model correlates well with several sets of experimental data and behaves according to the Fahraeus-Lindqvist effect. Predicted apparent viscosity tends to the expected finite value for large vessel diameters. Dependence of apparent viscosity on vessel diameter is realistically smooth in the whole diameter range. 相似文献
3.
A. Abu-Hashem M. A. Abd Al-Halim M. A. Hassouba M. M. Masoud 《Plasma Physics Reports》2010,36(3):271-278
A dc cylindrical coaxial glow discharge with an inner grid anode has been studied. The region between the two electrodes is
seen dark, while a brightly glowing region forms inside the grid anode up to the center. The current-voltage characteristic
of a dc cylindrical glow discharge in nitrogen is similar to that of a normal glow discharge, while the normal glow discharge
voltage decreases with increasing pressure. The minimum plasma potentials are observed in the hollow cathode region due to
the accumulation of electrons at the back of the grid anode. At the center, some of the passed electrons are converged, so
their potential is decreased. These electrons have a sufficient time to be redistributed to form one group with a Maxwellian
electron energy distribution function. The electron temperature measured by electric probes varies from 1.6 to 3.6 eV, while
the plasma density varies from 3.9 × 1016 to 7 × 1013 m−3, depending on the discharge current and probe position. The plasma density increases as the electrons move radially from
the grid toward the central region, while their temperature decreases. 相似文献
4.
K. K. Trusov 《Plasma Physics Reports》2014,40(9):739-753
Experimental results and model concepts concerning the relation between the index K of the interelectrode gap filling with spark channels and the peak current I peak of a single-pulse submicrosecond multichannel complete sliding discharge on an alumina ceramic surface are discussed. The spatial structure of an incomplete discharge at the threshold for the surface spark breakdown of gas is considered. The experiments were performed with three gases, Ne, Ar, and Xe, at pressures of 30 and 100 kPa and opposite polarities of the discharge voltage, with two discharge chambers differing in the geometry of the discharge gap and the thickness of the ceramic plate. It is shown that, although the structure of the incomplete discharge at the threshold for spark breakdown varies from diffuse homogeneous to pronounced filamentary, the dependence \(K\left( {\sqrt[6]{{I_{peak} }}} \right)\) for a complete discharge is close to linear and can be qualitatively explained by the earlier proposed semiempirical model of the time evolution of the structure of a multichannel discharge. In particular, the estimated steepness of the dependence \(K\left( {\sqrt[6]{{I_{peak} }}} \right)\) agrees best with the experimental results when the local density of free electrons at the threshold for spark breakdown is 1016 cm?3 or higher. 相似文献
5.
N. A. Popov 《Plasma Physics Reports》2006,32(3):237-245
A one-dimensional axisymmetric time-dependent model of a discharge in a gas flow is developed. The model includes a fairly complete set of plasmochemical reactions and describes the heating and gasdynamic expansion of a plasma channel in air. The processes governing the distribution of nitrogen molecules in the N2(C 3Πu, v) state over vibrational levels are considered. The parameters of a longitudinal glow discharge in a hot (T 0 = 1500?3000 K) air flow at atmospheric pressure are calculated. It is found that gas preheating considerably influences the parameters of the discharge channel. The results of calculations are compared with the experimental data. 相似文献
6.
The time evolution of the electric field in the leader channel and other characteristics of the leader plasma in long air gaps are simulated. Calculations are performed in the one-dimensional time-dependent model with allowance for the time-varying energy deposition in the channel, the channel expansion, and the nonequilibrium ionization kinetics in the leader plasma. The calculations show that, at a gas temperature of 4500–6000 K, associative ionization becomes a dominant ionization mechanism in the leader channel; as a result, the electric field decreases to 100–200 V/cm in 10?4–10?3 s under the conditions typical of the leader discharge. The calculated electric field agrees well with the data from the experimental modeling of long leaders by a spark discharge in short gaps. 相似文献
7.
The conversion of ethylene (C2H4) at concentrations of 400 and 930 ppm in an air flow at a temperature of 295 K is simulated. Ethylene is added to air either upstream of the discharge chamber or in the reaction tube, downstream of a pulsed corona discharge. It is taken into account that the distribution of the gas components in the discharge zone is nonuniform due to the streamer nature of the discharge. In the reaction tube, all of the components are assumed to be uniform. Simulation results agree with the experiments carried out at voltage pulse amplitudes of 30 and 40 kV, a gas flow rate of 2–10 l/min, and a specific energy deposition of up to 0.15 J/cm3. It is shown that the ozone produced plays a governing role in the C2H4 conversion. It is found that it is possible to minimize the energy spent on conversion by choosing the optimum pulse repetition rate and the specific energy deposited per pulse. The presence of water vapor impedes the ethylene conversion and increases the concentration of formaldehyde and methane. 相似文献
8.
Bieberich MT Van Duren AP 《Biomedical instrumentation & technology / Association for the Advancement of Medical Instrumentation》2003,37(2):103-112
The process of warming liquids for intravenous infusion presents several technical challenges for the engineer: Typical liquid inlet temperatures can range from 5 degrees C to 20 degrees C, flow requirements can vary from essentially zero ("Keep Vein Open," or K.V.O.) to 30 L/h, and desired outlet temperature is fixed at a maximum threshold of 41 degrees C to minimize the risk of thermally mediated hemolysis. The primary challenge is developing a control technique that can tailor the energy introduced to the liquid in response to a randomly variable flow in order to achieve, but not exceed, a fixed temperature. The most difficult aspect of this challenge is preventing the transient infusate temperature from exceeding 43 degrees C, even when the power requirement varies by orders of magnitude, such as occurs when the flow suddenly decreases from maximum to zero. Many current-generation fluid warmers are optimized for operation at either low or high flow rates; we believed that it was possible to design an easy-to-use device that could achieve good performance across the entire range of flow rates. This article describes some of the methods that were used successfully to meet these challenges in the design of the Augustine Medical Ranger blood fluid warmer. 相似文献
9.
V. A. Ivanov M. E. Konyzhev A. M. Zimin V. I. Troinov T. I. Kamolova A. A. Letunov 《Plasma Physics Reports》2013,39(13):1114-1121
Results are presented from experimental studies of the emission spectra of microplasma discharges excited on a titanium surface by a pulsed plasma flow. The excited discharges are maintained by current pulses with an amplitude of 200 A and a duration of 20 ms. Analysis of more than 100 spectral lines of titanium atoms and ions in the wavelength range of 350–800 nm shows that the electron temperature of a microplasma discharge is in the range of 0.2–1.3 eV. 相似文献
10.
Under conditions of a programmable discharge (a surface microwave discharge combined with a dc discharge), plasma-enhanced combustion of alcohol injected into a subsonic (M = 0.3?C0.9) airflow in the drop (spray) phase is stabilized. It is shown that the appearance of the discharge, its current-voltage characteristic, the emission spectrum, the total emission intensity, the heat flux, the electron density, the hydroxyl emission intensity, and the time dependences of the discharge current and especially discharge voltage change substantially during the transition from the airflow discharge to stabilized combustion of the liquid hydrocarbon fuel. After combustion stabilization, more than 80% of liquid alcohol can burn out, depending on the input power, and the flame temperature reaches ??2000 K. 相似文献
11.
K. S. Volodin I. M. Minaev A. A. Rukhadze K. Z. Rukhadze K. F. Sergeichev 《Plasma Physics Reports》2009,35(1):50-53
The possibility of controlling the directional pattern of a multislot waveguide antenna with the help of a gas-discharge tube placed inside the waveguide was studied experimentally. Since the dielectric parameters of the waveguide depend on the plasma density in the discharge column, they can be controlled by varying the discharge current. The high efficiency of such plasma control was demonstrated experimentally: as the discharge current was varied from 0 to 200 mA, the antenna directional pattern turned by ~17°. 相似文献
12.
Yu. S. Akishev G. I. Aponin M. E. Grushin V. B. Karal’nik M. V. Pan’kin A. V. Petryakov N. I. Trushkin 《Plasma Physics Reports》2008,34(4):312-324
The electric and spectral characteristics of a nonsteady discharge in an atmospheric air flow blown through a point-plane interelectrode gap were investigated experimentally. The discharge was produced by applying a constant positive voltage to the point electrode, the amplitude of the applied voltage being much higher than the corona ignition voltage. The nonsteady character of the discharge is due to the spontaneously repeating streamer-spark breakdown, followed by the formation of either a diffuse ultracorona or a filamentary glow discharge. In the latter case, the length of the plasma column increases progressively, being blown off by the gas flow from the discharge gap. The extinction of a filamentary discharge is unrelated to the break of the current channel: the discharge decays abruptly when the filament length reaches its critical value. The distribution of active particles (O, OH, and N*2) carried out from the discharge gap is determined from the data of spectral measurements. 相似文献
13.
A. L. Aleksandrov 《Plasma Physics Reports》2011,37(9):755-761
Results of two-dimensional hydrodynamic simulations of a surface glow discharge operating at pressures of 0.2–0.5 Torr in
a nitrogen flow propagating with a velocity of 1000 m/s in the presence of external ionization are presented. The effect of
the external ionization rate on discharge operation is analyzed. The current-voltage characteristics of the discharge are
calculated for different intensities of external ionization in both the presence and absence of secondary electron emission
from the cathode. The discharge structure and plasma parameters in the vicinity of the loaded electrode are considered. It
is shown that, when the discharge operates at the expense of secondary emission from the cathode, the discharge current and
cathode sheath configuration are insensitive to external ionization. It is also demonstrated that, even at a high rate of
external ionization, the discharge operates due to secondary emission from the cathode. 相似文献
14.
Myong-Kyun Roh Md. Salim Uddin Byung-Soo Chun 《Biotechnology and Bioprocess Engineering》2008,13(6):724-729
Extraction of brown seaweed (Undaria pinnatifida) oil was carried out by using supercritical carbon dioxide (SCO2) and ethanol as co-solvent. The flow rate of ethanol was 3.0% (v/v) as compared to that of SCO2. Experiments were performed in a semi-batch flow apparatus on dried samples at temperatures from 303 to 333 K and pressures
from 80 to 300 bar. Fucoxanthin and polyphenol were quantitatively analyzed by using HPLC and UV-spectrometer. The highest
yields of fucoxanthin and polyphenol were shown at 200 bar, 323 K and 250 bar, 333 K, respectively. The solubility of fucoxanthin
in SCO2 agreed well with the Chrastil model. 相似文献
15.
The excitation of oscillations in a discharge with negative differential conductivity is studied experimentally. The possibility is demonstrated of amplifying oscillations in the cathode dark space at frequencies close to the electron plasma frequency of the positive-column plasma. The phase velocities of waves at these frequencies are determined. When the waves pass from the cathode dark space to the discharge positive column, their phase velocities decrease; the closer the frequency is to the electron plasma frequency, the more pronounced the decrease in the phase velocity. As the intensity of oscillations increases, the discharge becomes non-steady-state. This is confirmed by the time evolution of the current-voltage characteristic. The shape of the current-voltage characteristic, its splitting, and the rate at which it varies depend on the input RF power. The decrease in the cathode dark space indicates that the ionization processes in the discharge are strongly influenced by electron plasma oscillations excited due to the collective interaction of the electron beam formed at the cathode with the discharge plasma. It is these processes that determine the maximum values of both the frequency of the excited oscillations and the power that can be withdrawn from the discharge. 相似文献
16.
Rapid rainfall events can be responsible for a large proportion of annual nutrient and carbon loading from a watershed. The bioavailability of organic matter during these rapid loading events increases, suggesting that storms play a relevant role in the mobilization of potentially labile terrestrial carbon. A high correlation between river discharge rates and dissolved and particulate nutrient and carbon concentrations during autumn and winter storms was observed in several temperate Pacific Northwest rivers. Dissolved and particulate lignin concentrations also increased with river discharge; for example, in October 2009 dissolved lignin concentrations increased roughly 240% with a 200% increase in river discharge. During these storms a unique phenolic composition was observed for dissolved lignin that was rapidly mobilized from surface soils relative to the base flow of dissolved lignin. The observed increase in Ad/Al ratios with discharge indicates that rapidly mobilized dissolved lignin is more degraded than the base flow of dissolved lignin. Similarly, a marked increase in C/V ratios and decrease in the S/V ratio of dissolved lignin phenols with increasing river discharge was observed. These results may indicate a difference in source between mobilized and base flow pools, or, more likely, preferential degradation and mobilization/retention of specific lignin phenols. The cumulative results from this year-long data set indicate that a shallow nutrient-rich pool of particulate and dissolved organic matter accumulates in watersheds during periods of soil-saturation deficiency (summer). Autumn and winter storms mobilize this pool of accumulated nutrients from surface soils, which is exhausted with successive winter storms. 相似文献
17.
Catherine E. Vrentas Justin J. Greenlee Gregory H. Foster James West Marianna M. Jahnke Mark T. Schmidt Eric M. Nicholson 《BMC research notes》2017,10(1):759
Objective
The most common hereditary prion disease is human Creutzfeldt-Jakob disease (CJD), associated with a mutation in the prion gene resulting in a glutamic acid to lysine substitution at position 200 (E200K) in the prion protein. Models of E200K CJD in transgenic mice have proven interesting but have limitations including inconsistencies in disease presentation, requirement for mixed species chimeric protein constructs, and the relatively short life span and time to disease onset in rodents. These factors limit research on the mechanism by which the mutation drives disease development. Therefore, our objective was to provide the first assessment of cattle carrying the homologous mutation, E211K, as a system for investigating longer-term disease mechanisms. The E211K substitution was associated with a case of bovine spongiform encephalopathy from 2006.Results
We assessed the molecular properties of bovine E211K prion protein, characterized the molecular genetics of a population of cattle E211K carriers (offspring of the original EK211 cow) in relation to findings in humans, and generated preliminary evidence that the impacts of copper-induced oxidative stress may be different in cattle as compared to observations in transgenic mouse models. The cattle E211K system provides the opportunity for future analysis of physiological changes over time.18.
The parameters of the plasma of a microwave electrode discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–80 W are measured by the so-called “relative intensity” method. The method allows one to determine the electron density and electric field in plasma by measuring the relative intensities of the Hα, Hβ, and 763.5-nm Ar line emission and calculating the electron-impact rate constants from the homogeneous Boltzmann equation. The measurements show that there are regions in the discharge where the electron density is higher (a bright electrode sheath) and lower (a spherical region) than the critical density for the frequency 2.45 GHz (ncr~7×1010 cm?3). Inside the spherical region, the electric field varies slightly over the radius and the electron density increases as the discharge boundary is approached. The observed discharge structure can be attributed to the presence of a self-sustained discharge zone (electrode sheath); a non-self-sustained discharge zone (spherical region); and a decaying plasma region, which is separated from the active discharge zone by an electric double layer. 相似文献
19.
Ionic selectivity, saturation, and block in a K+-selective channel from sarcoplasmic reticulum 总被引:18,自引:11,他引:7
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The open-channel conductance properties of a voltage-gated channel from sarcoplasmic reticulum were studied in planar phospholipid membranes. The channel is ideally selective for K+ over Cl- and for K+ over Ca++. In symmetrical 1 M solutions, the single-channel conductance (in pmho) falls in the order: K+ (214) > NH4+ (157) > Rb+ (125) > Na+ (72) > La+ (8.1) > Cs+ (< 3). In neutral bilayers, the channel conductance saturates with ion activity according to a rectangular hyperbolic relation, with half-saturation activities of 54 mM for K+ and 34 mM for Na+. Under symmetrical salt conditions, the K+:Na+ channel conductance ratio increases with salt activity, but the permeability ratio, measured by single-channel bi-ionic potentials, is constant between 20 mM and 2.5 M salt; the permeability ratio is equal to the conductance ratio in the limit of low-salt concentration. The channel conductance varies < 5% in the voltage range -100 to +70 mV. The maximum conductance varies K+ and Na+ is only weakly temperature dependent (delta H++ = 4.6 and 5.3 kcal/mol, respectively), but that of Li+ varies strongly with temperature (delta H++ = 13 kcal/mol). The channel's K+ conductance is blocked asymmetrically by Cs+, and this block is competitive with K+. The results are consistent with an Eyring-type barriers as it permeates the channel. The data conform to Lüger's (1973. Biochem. Biophys. Acta. 311:423-441) predictions for a "pure" single-ion channel. 相似文献
20.
A growing body of research suggests that different land use activities may alter both the quantity and quality of dissolved organic carbon (DOC) exported from terrestrial landscapes. However, little is known about DOC from mixed-use landscapes where hydrology varies seasonally. This study examined how DOC and chemical properties of stream water were related to land use, drainage area, and streamflow in mixed-use landscape in the Willamette River Basin, Oregon. Stream water samples were collected at roughly monthly intervals over three water years from 21 sites whose drainage areas ranged from 1 to?>?11,000 km2 and included pasture, forest, and developed land uses. DOC properties were characterized using PARAFAC (parallel factor) analyses of 3-D excitation and emission matrices (EEMs). We used the Cory-McKnight (CM) model, and we also developed a model unique to our samples. Thirteen components were identified using the CM model, and these were highly correlated with, and similar with respect to excitation and emission to the three components identified in our site-specific model. Fluorescent components of DOC were related to discharge and land cover, but not to drainage area. In our model, one component (C1) appeared to be associated with terrestrial detritus and was greater in streamflow from sites with forest/developed cover than from sites with high pasture cover. A second component (C2) was greater in streamflow from high-pasture sites than from high-forest sites. C2 was strongly correlated with a protein component identified in the CM model, and therefore we attributed this second component to more microbially-processed DOC. C1 increased significantly with discharge for both land covers, suggesting that periods of high flow produce less microbially-processed DOC from more surficial flow. C2 decreased significantly with discharge for both land covers, suggesting that deeper hydrologic flow paths produce more soil-associated, microbially processed DOC. SUVA254, often used as an index of chemical quality and aromaticity of DOC, was related only to streamflow but not land use, suggesting that while the chemistry of DOC differed among land use types as detected by EEMs analysis, the aromaticity of the DOC did not differ. The CM model and our site-specific model provided consistent results: those components that were highest in high pasture sites were also highest at low flow and appeared to be more microbially processed; components that were highest in low pasture sites were also greatest at high flow and appeared to reflect less microbially processed DOC. Taken together, these findings are consistent with a conceptual model of how differences in DOC chemistry among landscape types reflect differences in plant litter input chemistry, hydrologic connectivity, and degree of microbial processing. Such changes in DOC quality with land-use change can affect foodweb dynamics in receiving waters and change the balance between carbon storage and carbon flux to the atmosphere, and they imply that even non-intensive agricultural land use can have significant effects on terrestrial-aquatic carbon processes. 相似文献