Growth of oxide thin films for optical gas sensor applications

Tungsten trioxide and titanium dioxide thin films were synthesised by pulsed laser deposition. We used for irradiations of oxide targets an UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser source, at 2 J/cm² incident fluence value. The experiments were performed in low oxygen pressure. The (0 0 1) SiO₂ substrates were heated during the thin film deposition process at temperature values within the 300-500 °C range. The structure and crystalline status of the obtained oxide thin films were investigated by high resolution transmission electron microscopy. Our analyses show that the films are composed by nanoparticles with average diameters from a few to a few tens of nm. Moreover, the films deposited at substrate temperatures higher than 300 °C are crystalline. The tungsten trioxide films consist of a mixture of triclinic and monoclinic phases, while the titanium dioxide films structure corresponds to the tetragonal anatase phase. The oxide films average transmittance in the visible-infrared spectral range is higher than 80%, which makes them suitable for sensor applications.     

湍流燃烧二阶矩模型的大涡模拟验证

对美国Sandia国家实验室测量的甲烷-空气湍流射流火焰进行了三维大涡模拟(LES),其统计的时均量以及脉动量符合实验测量值,且和RANS代数二阶矩湍流燃烧模型模拟结果大致符合。LES统计得到的化学反应率系数脉动和甲烷浓度脉动的互关联与对应的时均量梯度的乘积分布趋势相同,大小幅值的位置也相对应,与二阶矩湍流燃烧模型的封闭假设相符,验证了二阶矩代数燃烧模型的合理性。     

Multi‐dimensional combustion waves for Lewis number close to one

This paper is devoted to the study of multi‐dimensional travelling wave solution for a thermo‐diffusive model, describing the propagation of curved flames in an infinite cylinder. The linear dependence of the components of the reaction rate together with the existence of an ignition temperature ensure that the corresponding linearized operator does not satisfy the Fredholm property. A direct consequence is that solvability conditions for the linearized operator are not known and classical methods of nonlinear analysis cannot be directly applied. We prove in this paper existence results of such travelling waves, by first introducing a suitable re‐formulation of the equations and then by choosing suitable weighted spaces that allows us to move the essential spectrum away from zero. Copyright © 2006 John Wiley & Sons, Ltd.     

A testbench for the nested dipole hypothesis of Kosterlitz and Thouless

We consider the two-dimensional one-component plasma without a background and confined to a half-plane near a metal wall. The particles are also subjected to an external potential acting perpendicular to the wall with an inverse-power-law Boltzmann factor. The model has a known solvable isotherm which exhibits a Kosterlitz-Thouless-type transition from a conductive to an insulator phase as the power law is varied. This allows predictions of theoretical methods of analyzing the Kosterlitz-Thouless transition to be compared with the exact solution. In particular, we calculate the asymptotic density profile by resumming its low-fugacity expansion near the zero-density critical coupling in the insulator phase, and solving a mean-field equation deduced from the first BGY equation. Agreement with the exact solution is obtained. As the former calculation makes essential use of the nested dipole hypothesis of Kosterlitz and Thouless, the validity of this hypothesis is explicitly verified.     

Nd2O3掺杂对SnO2气敏性质的影响

SnO_2是目前应用最广的一种气敏材料。我们曾经报道掺入La_2O_3,CeO_2,Pr_6O_(11),和Nd_2O_3后可使半导体元件的灵敏度提高,尤以对乙醇、乙醚、丙酮为显著。掺Nd_2O_3元件对乙炔的灵敏度也有提高。本文考察了SnO_2粒度和被测气氛的物化性质对掺Nd_2O_3元件灵敏度的影响。SnO_2采用水解SnCl_4法制备,纯度经光谱分析测定合格,试样用标准筛分目。在SnO_2中加1wt%Nd_2O_3(光谱纯)和适量水及甲基纤维素,混磨15分钟。将制成的悬浊液滴在一对铂     

Comments on “power-law falloff in the Kosterlitz-Thouless phase of a two-dimensional lattice Coulomb gas”

A simple argument is presented by which one can show that the critical inverse temperature _c of a two-dimensional Coulomb gas (standard or hard-core) with activityz satisfies , where in the low-activity limit. Previous results yield .     

Superdegenerate point in FCC phase diagram: CVM and Monte Carlo investigations

We investigate the topology of the phase diagram of binary alloys on the fee lattice with first-neighbor antiferromagnetic interactions around the superdegenerate point, where the L1₀ and L1₂ phases meet. We treat the system as a hard-constraint lattice gas, following a procedure previously described by Lebowitzet al. We perform cluster variation method calculations in theT0 limit and Monte Carlo simulations directly atT=0 K on the ground states of the superdegenerate point. We find that: (i) there is no disordered phase in the neighborhood of this point; (ii) a phase L for which two of the four cubic sublattices have the same average occupancy and each of the two others are different appears between L1₀ and L1₂; (iii) the transition L/L1₂ is of first order.     

Vicious random walkers in the limit of a large number of walkers

The vicious random walker problem on a line is studied in the limit of a large number of walkers. The multidimensional integral representing the probability that thep walkers will survive a timet (denotedP _t ^(p) ) is shown to be analogous to the partition function of a particular one-component Coulomb gas. By assuming the existence of the thermodynamic limit for the Coulomb gas, one can deduce asymptotic formulas forP _t ^(p) in the large-p, large-t limit. A straightforward analysis gives rigorous asymptotic formulas for the probability that after a timet the walkers are in their initial configuration (this event is termed a reunion). Consequently, asymptotic formulas for the conditional probability of a reunion, given that all walkers survive, are derived. Also, an asymptotic formula for the conditional probability density that any walker will arrive at a particular point in timet, given that allp walkers survive, is calculated in the limittp.