Results 1 - 10 of 1395
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[en] Theoretical calculations of the director distribution in a Grandjean–Cano wedge in relation to the anchoring strength and mutual orientation of the easy axes at the wedge surfaces are performed for various model surface anchoring potentials. Comparison of the theory and experiment allows one to propose the socalled model D-potential, quadratic in angle of director deviation from the easy axes, as the best one in fitting the experiment in the angular range of performed measurements. To satisfy general requirements on the wedge surface, a modified D-potential is proposed. The optimal conditions of the experiment aimed at restoring the potential in the whole range of its definition (in particular, nonparallel orientation of the easy axes at the wedge surfaces) are formulated.
[en] We have studied the surface potential decays (SPD) of a variety of dielectric materials, and found that the SPD data of the samples with high charge retensions are well fitted by Tsallis q-exponential functions.
[en] The electrocardiographic (ECG) inverse problem is ill-posed and usually solved by regularization schemes. These regularization methods, such as the Tikhonov method, are often based on the L2-norm data and constraint terms. However, L2-norm-based methods inherently provide smoothed inverse solutions that are sensitive to measurement errors, and also lack the capability of localizing and distinguishing multiple proximal cardiac electrical sources. This paper presents alternative regularization schemes employing the L1-norm data term for the reconstruction of epicardial potentials (EPs) from measured body surface potentials (BSPs). During numerical implementation, the iteratively reweighted norm algorithm was applied to solve the L1-norm-related schemes, and measurement noises were considered in the BSP data. The proposed L1-norm data term-based regularization schemes (with L1 and L2 penalty terms of the normal derivative constraint (labelled as L1TV and L1L2)) were compared with the L2-norm data terms (Tikhonov with zero-order and normal derivative constraints, labelled as ZOT and FOT, and the total variation method labelled as L2TV). The studies demonstrated that, with averaged measurement noise, the inverse solutions provided by the L1L2 and FOT algorithms have less relative error values. However, when larger noise occurred in some electrodes (for example, signal lost during measurement), the L1TV and L1L2 methods can obtain more accurate EPs in a robust manner. Therefore the L1-norm data term-based solutions are generally less perturbed by measurement noises, suggesting that the new regularization scheme is promising for providing practical ECG inverse solutions.
[en] Force concepts in condensed systems have progressed significantly in recent years. In the context of bimetallic interfaces we consider the Pauli-Hellman-Feynman theorem, use it to check the variational calculations of interfacial energies and estimate the force constants. (author). 13 refs, 2 figs, 2 tabs
[en] In this paper, automatic parameter extraction techniques of Agilent's IC-CAP modeling package are presented to extract our explicit compact model parameters. This model is developed based on a surface potential model and coded in Verilog-A. The model has been adapted to Trigate MOSFETs, includes short channel effects (SCEs) and allows accurate simulations of the device characteristics. The parameter extraction routines provide an effective way to extract the model parameters. The techniques minimize the discrepancy and error between the simulation results and the available experimental data for more accurate parameter values and reliable circuit simulation. Behavior of the second derivative of the drain current is also verified and proves to be accurate and continuous through the different operating regimes. The results show good agreement with measured transistor characteristics under different conditions and through all operating regimes. (paper)
[en] The binding sites and diffusion pathways of Si adatoms on a c(4x2) reconstructed Si(001) surface are investigated by a tight-binding method with an environment-dependent silicon potential in conjunction with ab initio calculations using the Car--Parrinello method. A new diffusion pathway along the trough edge driven by dimer flipping is found with a barrier of 0.74 eV, comparable to that of 0.68 eV along the top of the dimer rows
[en] This paper presents an overview of the roles played by incoming and outgoing electrons in spacecraft surface and stresses the importance of surface conditions for spacecraft charging. The balance between the incoming electron current from the ambient plasma and the outgoing currents of secondary electrons, backscattered electrons, and photoelectrons from the surfaces determines the surface potential. Since surface conditions significantly affect the outgoing currents, the critical temperature and the surface potential are also significantly affected. As a corollary, high level differential charging of adjacent surfaces with very different surface conditions is a space hazard. (author)
[en] This paper is devoted to the asymptotics of the density of surfacic states near the spectral edges for a discrete surfacic Anderson model. Two types of spectral edges have to be considered: fluctuating edges and stable edges. Each type has its own type of asymptotics. In the case of fluctuating edges, one obtains Lifshitz tails the parameters of which are given by the initial operator suitably 'reduced' to the surface. For stable edges, the surface density of states behaves like the surface density of states of a constant (equal to the expectation of the random potential) surface potential. Among the tools used to establish this are the asymptotics of the surface density of states for constant surface potentials
[en] Oxygen adsorption on Pt(111) and Pt(100) was investigated using a Kelvin probe to measure adsorbate induced work function changes. The variation of Δphi with theta was linear (p = 0.103 D/atom) on Pt(111) even up to theta/sub max/approx.7 x 1014 atoms cm-2. On Pt(100), there was an abrupt increase in Δphi at low coverage (<1 x 1014 atom cm-2) which was presumed to be adsorption at defect sites (p = 0.62 D/atom). Sticking coefficients were calculated from the rate of change of the work function with time. For room temperature adsorption on Pt(111), the sticking coefficient followed the functional form S0(1-theta)2, theta = theta/theta/sub max/, and S0 = 0.038. On Pt(100) the functional dependence was more complex with an initial increase in S (from S0 = 0.042) to a theta of approx.0.1, then an approximately quadratic decrease as the coverage increased to saturation. The maximum coverage observed in room temperatue dosing of either surface was approx.3 x 1014. However, dosing at 200--300 0C at 10-5--10-4 Torr induced coverages as high as (7--9) x 1014 on both surfaces. The isosteric heat of adsorption was measured from equilibrium isotherms and found to be 232 +- 36 kJ mol-1 with a coverage dependence less than the experimental precision. For Pt(111), it is postulated that population of the high coverage state proceeds via the activated process of direct dissociation, whereas the unactivated room temperature process is via a molecularly adsorbed precursor. For Pt(100), population of the high coverage state involves activated transitions in the Pt surface structure which require further study