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1.
V 1−x−yW xSi yO 2 films for uncooled thermal detectors were coated on sodium-free glass slides with sol–gel process, followed by the calcination under a reducing atmosphere (Ar/H 2 5%). The V 1−x−yW xSi yO 2 films as prepared inherit various phase transition temperatures ranging from 20 to 70 °C depending on the dopant concentrations and the fabrication conditions. Compared to the hysteresis loop of plain VO 2 films, a rather steep loop was obtained with the addition of tungsten components, while a relaxed hysteresis loop with the tight bandwidth was contributed by Si dopants. Furthermore, the films with switching temperature close to room temperature were fabricated to one-element bolometers to characterize their figures of merit. Results showed that the V 0.905W 0.02Si 0.075O 2 film presented a satisfactory responsivity of 2600 V/W and detectivity of 9 × 10 6 cm Hz 1/2/W with chopper frequencies ranging from 30 to 60 Hz at room temperature. It was proposed that with appropriate amount of silicon and tungsten dopants mixed in the VO 2, the film would characterize both a relaxed hysteresis loop and a fair TCR value, which effectively reduced the magnitude of noise equivalent power without compromising its performance in detectivity and responsivity. 相似文献
2.
The {SBA/PSS} n/PDDA films modified electrode was prepared by layer-by-layer (LBL) assembly with mesoporous SiO 2 (SBA), poly(sodium 4-styrene-sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) in this paper. SBA is a large pore-size mesoporous material with highly ordered hexagonally arranged mesochannels and high thermal stability etc. The electrochemical characteristics of the {SBA/PSS} n/PDDA films have been studied by electrochemical impedance spectroscopy in 0.1 M KCl solution containing 5.0 mM Fe(CN) 63−/Fe(CN) 64− at the formal potential of 0.230 V. The ultratrace nitroaromatic compounds (NACs) such as TNT, TNB, DNT and DNB were determined by differential pulse voltammetry (DPV) measurement. The sensitivities for NACs determination with {SBA/PSS} n/PDDA modified electrode were dependent on the number of layers, pH and ionic strength of electrolyte, based on which a set of optimized conditions for film fabrication was inferred. The current responses were linear with NACs ranging from 10 −9 to 10 −7 mol/l. The results showed that the {SBA/PSS} n/PDDA modified electrode established a new way for fast, simple and sensitive analysis of NACs. 相似文献
3.
The preparation method and the sensing properties (sensitivity and selectivity to interfering gases) towards carbon monoxide of the new ternary compound Sn 1-xFe xO y deposited in the form of thin films, are presented in this paper. The metal of the VIIIB group is introduced with concentrations in the range 0< x<25 at %. Thin films are sputtered using the RGTO (rhotaxial growth and thermal oxidation) technique. This technique consists of metal deposition onto a substrate maintained at a temperature higher than the metal melting point and metal oxidation by means of an annealing cycle in pure oxygen. Particular emphasis is given to the relations between some preparation parameters of the material, namely the atomic percentage ofiron or the annealing cycle, and to the sensor sensitivity towards CO and other interfering gases like C 2H 5OH, H 2 and NO x diluted in dry air. A sensitivity S= (Ggas- Gair)/ Gair=3.5 towards 10 ppm of CO has been measured: the kinetic characteristics of the sensors are also presented, together with the working mechanism. 相似文献
4.
The aim of this paper is double. First, we point out that the hypothesis D( t1) D( t2) = D( t2) D( t1) imposed in [1] can be removed. Second, a constructive method for obtaining analytic-numerical solutions with a prefixed accuracy in a bounded domain Ω( t0, t1) = [0, p] × [ t0, t1], for mixed problems of the type ut( x, t) − D( t) uxx( x, t) = 0, 0 < x < p, t> 0, subject to u(0, t) = u( p, t) = 0 and u( x,0) = F( x) is proposed. Here, u( x, t) and F( x) are r-component vectors, D( t) is a Cr × r valued analytic function and there exists a positive number δ such that every eigenvalue z of (1/2) ( D( t) + D( t) H) is bigger than δ. An illustrative example is included. 相似文献
5.
In this paper we study the behavior of the beta-spline functions in the case the parameter β 2( i) is negative. We prove that a negative value
exists so that if
, the beta-spline functions Ni( u) are positive. Moreover, if the control vertices are such that x0 xm−1, we have proved that the design curve keeps the properties already proved in the case β 2( i) 0. 相似文献
6.
It is pointed out in this brief paper that the l1 optimization problem min Q ε lqp1 | H − U * Q * V | 1, H ε lmn1, U ε lmq1, V ε lpn1 can be solved in one step rather than two. The solution of the dual problem is obviated by the direct solution of the primal problem via linear programming. The method here is applicable to finite-dimensional problems or approximating finite-dimensional problems, in the general case. 相似文献
7.
Undoped and Eu 3+, Ce 3+ and Tb 3+-doped YVO 4 YPO 4, LaPO 4 and YV xP 1−xO 4 were prepared in H 2O by the recently introduced hydrolyzed colloid reaction (HCR) technique working at low temperature (<100°C) and atmospheric pressure. Two intermediate — partially hydrophobic — complex colloidal mixtures with metastable characteristics can transform into the stable orthovanadate–orthophosphate phase due to intensive hydrolysis. In contrast with the other low temperature reacting processes — like the sol-gel technique, which makes an amorphous structure — the HCR method can produce crystalline structures in nanometer size ranges. The reaction, morphology, incorporation of activators and different luminescent characteristics are surveyed in this letter-type paper selected from our previous results. 相似文献
8.
This paper describes some new techniques for the rapid evaluation and fitting of radial basic functions. The techniques are based on the hierarchical and multipole expansions recently introduced by several authors for the calculation of many-body potentials. Consider in particular the N term thin-plate spline, s( x) = Σ j=1N djφ( x− xj), where φ( u) = | u| 2log| u|, in 2-dimensions. The direct evaluation of s at a single extra point requires an extra O( N) operations. This paper shows that, with judicious use of series expansions, the incremental cost of evaluating s( x) to within precision ε, can be cut to O(1+|log ε|) operations. In particular, if A is the interpolation matrix, ai,j = φ( xi− xj, the technique allows computation of the matrix-vector product Ad in O( N), rather than the previously required O( N2) operations, and using only O( N) storage. Fast, storage-efficient, computation of this matrix-vector product makes pre-conditioned conjugate-gradient methods very attractive as solvers of the interpolation equations, Ad = y, when N is large. 相似文献
9.
Oxide semiconductors have been examined to develop NO x sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al 3+, Sc 3+, Ga 3+ or In 3+, has a good sensitivity and selectivity to NO between 450 and 550 °C, and shows rapid response. A sensor probe for monitoring exhaust NO x has been fabricated. Many kinds of interference gases, such as C 3H 6, CO and SO 2, have been found to have only a slight influence on the sensor response to NO. The influence of O 2 and H 2O is also negligible, except for the cases of 0% H 2O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactority in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases. 相似文献
10.
NO 2 sensing properties of SnO 2-based varistor-type sensors have been investigated in the temperature range of 400-650°C and in the NO 2 concentration range of 15–30 ppm. Pure SnO 2 exhibited a weak nonlinear I– V characteristic in air, but clear nonlinearity in NO 2 at 450°C. The breakdown voltage of SnO 2 shifted to a high electric field upon exposure to NO 2 and the magnitude of the shift was well correlated with NO 2 concentration. Thus, SnO 2 exhibited some sensitivity to NO 2 as a varistor-type sensor. When SnO 2 particles coated with a SiO 2 thin film were used as a raw material for fabricating a varistor, the breakdown voltage in air was approximately the double that of pure SnO 2 and the sensitivity to 15 ppm NO 2 was enhanced slightly. However, the sensitivity to 30 ppm NO 2 decreased. The Cr 2O 3-loading on SnO 2 also led to an increase in the breakdown voltage in air, but the Cr 2O 3 addition was not effective for promoting the NO 2 sensitivity under the present experimental conditions. 相似文献
11.
To approach a simple game Δ 2 of P and E = {E1, E2} with no a priori evaders' role assignment and the payoff equal to the distance to one evader at an instant of catching another, we introduce a concept of casting and study the games Δ 1,2 and Δ 2,1 for preassigned and Δ p2 for open-loop casting procedures. Since Δ p2 is reduced to Δ 1,2 or Δ 2,1 which, in turn, are distinguished only by their notations, we focus attention mainly on Δ 1,2. According to the tenet of transition, Δ 1,2 is divided into a concatenation of Δ 1,2b (basic) and Δ 1,2a (auxiliary) games that model the problem before and after the first instant of E1 capture. The games Δ1,2a, Δ 1,2b, Δ 1,2 are studied one after another with use of the Isaacs' approach extended by Berkowitz, Breakwell, Bernhard et al. 相似文献
12.
Pt-loaded metal oxides [WO 3/ZrO 2, MO x/TiO 2 (MO x = WO 3, MoO 3, V 2O 5), WO 3 and TiO 2] equipped with interdigital Au electrodes have been tested as a NO x (NO and NO 2) gas sensor at 500 °C. The impedance value at 4 Hz was used as a sensing signal. Among the samples tested, Pt-WO 3/TiO 2 showed the highest sensor response magnitude to NO. The sensor was found to respond consistently and rapidly to change in concentration of NO and NO 2 in the oxygen rich and moist gas mixture at 500 °C. The 90% response and 90% recovery times were as short as less than 5–10 s. The impedance at 4 Hz of the present device was found to vary almost linearly with the logarithm of NO x (NO or NO 2) concentration from 10 to 570 ppm. Pt-WO 3/TiO 2 showed responses to NO and NO 2 of the same algebraic sign and nearly the same magnitude, while Pt/WO 3 and WO 3/TiO 2 showed higher response to NO than NO 2. The impedance at 4 Hz in the presence of NO for Pt-WO 3/TiO 2 was almost equal at any O 2 concentration examined (1–99%), while in the case of Pt/WO 3 and WO 3/TiO 2 the impedance increased with the oxygen concentration. The features of Pt-WO 3/TiO 2 are favorable as a NO x sensor that can monitor and control the NO x concentration in automotive exhaust. The effect of WO 3 loading of Pt-WO 3/ZrO 2-based sensor is studied to discuss the role of surface W-OH sites on the NO x sensing. 相似文献
13.
This paper presents an efficient algorithm for enumerating all minimal a- b separators separating given non-adjacent vertices a and b in an undirected connected simple graph G = ( V, E), Our algorithm requires O( n3Rab) time, which improves the known result of O( n4Rab) time for solving this problem, where ¦ V¦= n and Rab is the number of minimal a- b separators. The algorithm can be generalized for enumerating all minimal A- B separators that separate non-adjacent vertex sets A, B < V, and it requires O( n2( n − nA − nb) RAB) time in this case, where na = ¦ A¦, nB = ¦ B¦ and rAB is the number of all minimal A− B separators. Using the algorithm above as a routine, an efficient algorithm for enumerating all minimal separators of G separating G into at least two connected components is constructed. The algorithm runs in time O( n3R+Σ + n4RΣ), which improves the known result of O( n6RΣ) time, where Rσ is the number of all minimal separators of G and RΣR+Σ = ∑ 1i, v j) ER vivj (n( n − 1)/2 − m) RΣ. Efficient parallelization of these algorithms is also discussed. It is shown that the first algorithm requires at most O(( n/ log n) Rab) time and the second one runs in time O(( n/ log n) R+Σ+ n log nRΣ) on a CREW PRAM with O( n3) processors. 相似文献
14.
A subdivision scheme for constructing smooth surfaces interpolating scattered data in R 3 is proposed. It is also possible to impose derivative constraints in these points. In the case of functional data, i.e., data are given in a properly triangulated set of points {( xi, yi)} i=1N from which none of the pairs ( xi, yi) and ( xj, yj) with i≠ j coincide, it is proved that the resulting surface (function) is C1. The method is based on the construction of a sequence of continuous splines of degree 3. Another subdivision method, based on constructing a sequence of splines of degree 5 which are once differentiable, yields a function which is C2 if the data are not ‘too irregular’. Finally the approximation properties of the methods are investigated. 相似文献
15.
For an ordered set W = { w1, w2,…, wk} of vertices and a vertex v in a connected graph G, the (metric) representation of v with respect to W is the k-vector r( v | W) = ( d( v, w1), d( v, w2),…, d( v, wk)), where d( x, y) represents the distance between the vertices x and y. The set W is a resolving set for G if distinct vertices of G have distinct representations. A new sharp lower bound for the dimension of a graph G in terms of its maximum degree is presented. A resolving set of minimum cardinality is a basis for G and the number of vertices in a basis is its (metric) dimension dim(G). A resolving set S of G is a minimal resolving set if no proper subset of S is a resolving set. The maximum cardinality of a minimal resolving set is the upper dimension dim+(G). The resolving number res(G) of a connected graph G is the minimum k such that every k-set W of vertices of G is also a resolving set of G. Then 1 ≤ dim(G) ≤ dim+(G) ≤ res(G) ≤ n − 1 for every nontrivial connected graph G of order n. It is shown that dim+(G) = res(G) = n − 1 if and only if G = Kn, while dim+(G) = res(G) = 2 if and only if G is a path of order at least 4 or an odd cycle. The resolving numbers and upper dimensions of some well-known graphs are determined. It is shown that for every pair a, b of integers with 2 ≤ a ≤ b, there exists a connected graph G with dim(G) = dim+(G) = a and res(G) = b. Also, for every positive integer N, there exists a connected graph G with res(G) − dim+(G) ≥ N and dim+(G) − dim(G) ≥ N. 相似文献
16.
Na 1+xZr 2Si xP 3−xO 12 are ceramic materials which are fast ionic conductors by Na +. The present work concerns the characterizations of such materials in the range x = 1.4–3.0 for their use as ion sensitive membranes. Samples were prepared by sol-gel route to obtain pellets with a high density. Characteristics, such as lattice parameters and bulk conductivity are given. Results on detection limit and selectivity of such membranes used in ISE devices are presented. The effect of the stoichiometry on electrochemical characteristics is discussed. The best performances are obtained for x = 2.0–2.2, with samples sintered at 1200°C. No influence of sintering temperature is noticeable for the selectivity, excepted for proton which is less interfering after sintering at 1200°C. 相似文献
17.
In this paper, we consider coupled semi-infinite diffusion problems of the form ut( x, t)− A2 uxx( x, t) = 0, x> 0, t> 0, subject to u(0, t)= B and u( x,0)=0, where A is a matrix in
, and u( x, t), and B are vectors in
. Using the Fourier sine transform, an explicit exact solution of the problem is proposed. Given an admissible error and a domain D( x0, t0)={( x, t);0≤ x≤ x0, t≥ t0 > 0, an analytic approximate solution is constructed so that the error with respect to the exact solution is uniformly upper bounded by in D( x0, t0). 相似文献
18.
The relative stabilities of L1 2, D0 22, D0 23, 21, and 3 structures in the Pd 3V, Pt 3V, Rh 3V, and Pt 3Ti compounds are investigated employing the Vienna ab initio simulation package. In the pseudobinary Pd 3xRh 3(1−x)V, Pt 3xRh 3(1−x)V, and Pt 3V xTi (1−x) alloys, the energy differences from L1 2 of D0 22, D0 23, 21, and 3 structures are assumed to be linear as function of the number of electrons per atom. At T=0K, the resulting energy diagram shows that the equilibrium between the limiting binary phases is the most stable state. At high temperature, the Gibbs energy curves are computed assuming a Bragg and Williams entropy of mixing in the pseudobinary sections. The D0 23 and 21 structures are stabilized in the pseudobinary Pd 3xRh 3(1−x)V, Pt 3xRh 3(1−x)V, and Pt 3V xTi (1−x) alloys. The phase diagram between the various structures is calculated in each pseudobinary section and compared with the experimental one. 相似文献
19.
We formulate a class of difference schemes for stiff initial-value problems, with a small parameter ε multiplying the first derivative. We derive necessary conditions for uniform convergence with respect to the small parameter ε, that is the solution of the difference scheme uih satisfies | uih− u( xi)| Ch, where C is independent of h and ε. We also derive sufficient conditions for uniform convergence and show that a subclass of schemes is also optimal in the sense that | uih− u( xi)| C min ( h, ε). Finally, we show that this class contains higher-order schemes. 相似文献
20.
In this work we study the structural properties and mechanical stress of silicon oxynitride (SiO xN y) films obtained by plasma enhanced chemical vapor deposition (PECVD) technique at low temperatures (320 °C) and report the feasibility of using this material for the fabrication of large area self-sustained grids. The films were obtained at different deposition conditions, varying the gas flow ratio between the precursor gases (N 2O and SiH 4) and maintaining all the other deposition parameters constant. The films were characterized by ellipsometry, by Fourier transform infrared (FT-IR) spectroscopy and by optically levered laser technique to measure the total mechanical stress. The results demonstrate that for appropriated deposition conditions, it is possible to obtain SiO xN y with very low mechanical stress, a necessary condition for the fabrication of mechanically stable thick films (up to 10 μm). Since this material (SiO xN y) is very resistant to KOH wet chemical etching it can be utilized to fabricate, by silicon substrate bulk micromachining, very large self-sustained grids and membranes, with areas up to 1 cm 2 and with thickness in the 2–6 μm range. These results allied with the compatibility of the PECVD SiO xN y films deposition with the standard silicon based microelectronic processing technology makes this material promising for micro electro mechanical system (MEMS) fabrication. 相似文献
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