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1.
Pulsed laser deposited (PLD) Y-doped BaZrO3 thin films (BaZr1-xYxO3-y/2, x = 0.2, y > 0), were investigated as to their viability for reliable humidity microsensors with long-term stability at high operating temperatures (T > 500 °C) as required for in situ point of source emissions control as used in power plant combustion processes. Defect chemistry based models and initial experimental results in recent humidity sensor literature [1] and [2]. indicate that bulk Y-doped BaZrO3 could be suitable for use in highly selective, high temperature compatible humidity sensors. In order to accomplish faster response and leverage low cost batch microfabrication technologies we have developed thin film deposition processes, characterized layer properties, fabricated and tested high temperature humidity micro sensors using these thin films. Previously published results on sputtering Y-doped BaZrO3 thin films have confirmed the principle validity of our approach [3]. However, the difficulty in controlling the stoichiometry of the films and their electrical properties as well as mud flat cracking of the films occurring either at films thicker than 400 nm or at annealing temperature above 800 °C have rendered sputtering a difficult process for the fabrication of reproducible and reliable thin film high temperature humidity microsensors, leading to the evaluation of PLD as alternative deposition method for these films.X-ray Photoelectron Spectroscopy (XPS) data was collected from as deposited samples at the sample surface as well as after 4 min of Ar+ etching. PLD samples were close to the desired stoichiometry. X-ray diffraction (XRD) spectra from all as deposited BaZrO3:Y films show that the material is polycrystalline when deposited at substrate temperatures of 800 °C. AFM results revealed that PLD samples have a particle size between 32 nm and 72 nm and root mean square (RMS) roughness between 0.2 nm and 1.2 nm. The film conductivity increases as a function of temperature (from 200 °C to 650 °C) and upon exposure to a humid atmosphere, supporting our hypothesis of a proton conduction based conduction and sensing mechanism. Humidity measurements are presented for 200–500 nm thick films from 500 °C to 650 °C at vapor pressures of between 0.05 and 0.5 atm, with 0.03–2% error in repeatability and 1.2–15.7% error in hysteresis during cycling for over 2 h. Sensitivities of up to 7.5 atm−1 for 200 nm thick PLD samples at 0.058 atm partial pressure of water were measured.  相似文献   

2.
Abstract— Terbium-doped ZnS and Y2O3 nanocrystalline phosphors were prepared using room-temperature organometallic synthesis and modified sol-gel processing. The photoluminescent and photoluminescent-excitation spectra of these materials reveal characteristic Tb3+ emission (d5−f7 transition). The intensities of the Tb3+ emission in standard terbium-doped LaOBr phosphor and terbium-doped nanocrystalline yttria phosphor are compared. To date, the best photoluminescent efficiency of the nanocrystalline phosphors excited at 254 nm is about 50% of that of the standard phosphor.  相似文献   

3.
Let f(xθ) = αθαx−(α+1)I(x>θ) be the pdf of a Pareto distribution with known shape parameter α>0, and unknown scale parameter θ. Let {(Xi, θi)} be a sequence of independent random pairs, where Xi's are independent with pdf f(xαi), and θi are iid according to an unknown distribution G in a class of distributions whose supports are included in an interval (0, m), where m is a positive finite number. Under some assumption on the class and squared error loss, at (n + 1)th stage we construct a sequence of empirical Bayes estimators of θn+1 based on the past n independent observations X1,…, Xn and the present observation Xn+1. This empirical Bayes estimator is shown to be asymptotically optimal with rate of convergence O(n−1/2). It is also exhibited that this convergence rate cannot be improved beyond n−1/2 for the priors in class .  相似文献   

4.
We consider a class of two-sided stochastic control problems. For each continuous process πt = πt+ − πt with bounded variation, the state process (xt) is defined by xt = Bt + f0t I(xs - a)dπs+f0t I(xs a)dπs, where a is a positive constant and (Bt) is a standard Brownian motion. We show the existence of an optimal policy so as to minimize the cost function J(π) = E [f0 e−αsXs2 ds], with discount rate α > 0, associated with π.  相似文献   

5.
This work proposes the amperometric determination of hydrogen peroxide reduction and oxidation as a tool for the characterization of La1−xAxMnO3 perovskites dispersed in a graphite composite electrode (carbon paste electrode, CPE). The catalytic activity of perovskites towards the oxidation and reduction of hydrogen peroxide is highly dependent on the nature of the A cation and on the temperature and time of calcination employed during the synthesis. Therefore, the selection of the optimal synthesis conditions to obtain the best catalytic activity towards hydrogen peroxide can be performed from amperometric determinations.We also report the analytical application of the perovskite modified CPE through the quantification of hydrogen peroxide in two real samples. Some preliminary results about the usefulness of La0.66Sr0.33MnO3–CPE to develop a glucose biosensor by incorporation of the enzyme glucose oxidase (GOx) within the electrode are also reported. The difference in sensitivity to glucose at CPE–GOx and CPE–La0.66Sr0.33MnO3–GOx (11.9 μA mol−1 L and 158.1 μA mol−1 L, respectively), clearly demonstrate the advantages of the association of the biocatalytic activity of GOx and the catalytic activity of perovskites towards hydrogen peroxide oxidation/reduction, and opens the doors to the development of new sensors for other important bioanalytes.  相似文献   

6.
It is shown that the doping of Zn and Sn can improve the gas sensitivity of α-Fe2O3-based sensing material to CO. X-ray photo-electron spectroscopy analysis suggests that this is mainly due to the fact that the simultaneous doping of Zn and Sn can increase the S and hence SO42− contents in the α-Fe2O3(SO42−, Sn, Zn) sensing material. The results also suggest that under a given condition, the gas sensitivity of α-Fe2O3(SO42−, Sn, Zn) to CO can be optimised by properly adjusting the doped Zn content.  相似文献   

7.
Numerous computer programs have been written to compute sets of points which approximate Julia sets [4]. Usually, no error estimations are added so that it remains unclear, how good such approximations are. Furthermore, high precision pictures are unreliable because of rounding errors, since the realizing computer programs use fixed length floating point numbers. Computable error estimation w.r.t. the Hausdorff metric dH means that the set is recursive [10]. Many Julia sets J are recursive [11]. Recursive compact subsets of the Euclidean plane have a computable Turing machine time complexity [10]. In this paper we prove that the Julia set of a complex function f(z) = z2 + c for c < 1/4 can be computed locally in time O(k2M(k)) (where M(k) is a time bound for multiplication of k-bit integers). Roughly speaking, the local time complexity is the number of Turing machine steps to decide for a single point whether it belongs to a grid Kk (2−k · )2 such that dH(Kk,J) ≤ = 2k.  相似文献   

8.
In many problems, modular exponentiation |xb|m is a basic computation, often responsible for the overall time performance, as in some cryptosystems, since its implementation requires a large number of multiplications.It is known that |xb|m=|x|b|(m)|m for any x in [1,m−1] if m is prime; in this case the number of multiplications depends on (m) instead of depending on b. It was also stated that previous relation holds in the case m=pq, with p and q prime; this case occurs in the RSA method.In this paper it is proved that such a relation holds in general for any x in [1,m−1] when m is a product of any number n of distinct primes and that it does not hold in the other cases for the whole range [1,m−1].Moreover, a general method is given to compute |xb|m without any hypothesis on m, for any x in [1,m−1], with a number of modular multiplications not exceeding those required when m is a product of primes.Next, it is shown that representing x in a residue number system (RNS) with proper moduli mi allows to compute |xb|m by n modular exponentiations |xib|mi in parallel and, in turn, to replace b by |b|(mi) in the worst case, thus executing a very low number of multiplications, namely log2mi for each residue digit.A general architecture is also proposed and evaluated, as a possible implementation of the proposed method for the modular exponentiation.  相似文献   

9.
An electrochemical sensor for hydroperoxides determination was investigated. The sensor was based on the electrocatalytic reduction of hydroperoxides on Prussian blue (PB)-modified glassy carbon electrode. The modified electrode possesses a high electrocatalytic effect towards all studied peroxides with the highest effect obtained with H2O2 followed by tert-butyl hydroperoxide (TBH), cumene hydroperoxide (CH) and linoleic acid hydroperoxide (LAH). In addition, the modified electrode showed a good stability and a fast response time (<20 s). The lower detection limits of H2O2, TBH, CH and LAH were found to be 10−7 mol L−1, 2 × 10−7 mol L−1, 3.5 × 10−7 mol L−1 and 4 × 10−7 mol L−1, respectively. The electrochemical sensor was then applied for amperometric determination of peroxide value (PV) in edible oil at an applied potential of 50 mV (vs. Ag/AgCl (1 M KCl)). A good linearity has been found in the range 0.02–1.0 mequiv. O2/kg, with a detection limit (S/N = 3) of 0.001 mequiv. O2/kg. The precision of the method (R.S.D., n = 9) for within and between-days is better than 1.9% and 2.7%, respectively at 0.1 mequiv. O2/kg. The method was successfully applied to the determination of PV in real edible oil samples with an excellent agreement with results obtained with the official standard procedure. The proposed method is accurate, simple, cheap and could be used to control edible oil rancidity with a high sample throughputs (more than 120 samples/h).  相似文献   

10.
We consider the problem of finding the extrema of a distributed multiset in a ring, that is, of determining the minimum and the maximum values,xminandxmax, of a multisetX= {x0,x2, ...,xn−1} whose elements are drawn from a totally ordered universeUand stored at thenentities of a ring network. This problem is unsolvable if the ring size is not known to the entities, and it has complexity Θ(n2) in the case of asynchronous rings of known size. We show that, in synchronous rings of known size, this problem can always be solved inO((c+ logn) ·n) bits andO(n·c·x1/c) time for any integerc> 0, wherex= Max{|xmin|, |xmax|}. The previous solutions requiredO(n2) bits and the same amount of time. Based on these results, we also present a bit-optimal solution to the problem of finding the multiplicity of the extrema.  相似文献   

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