Gas identification with tin oxide sensor array and self-organizing maps: adaptive correction of sensor drifts

Low-cost tin oxide gas sensors are inherently nonspecific. In addition, they have several undesirable characteristics such as slow response, nonlinearities, and long-term drifts. This paper shows that the combination of a gas-sensor array together with self-organizing maps (SOM's) permit success in gas classification problems. The system is able to determine the gas present in an atmosphere with error rates lower than 3%. Correction of the sensor's drift with an adaptive SOM has also been investigated

Bulk-plasmon dispersion relations in metals

Using an extended-random-phase-approximation sum-rule technique, we have investigated the bulk-plasmon dispersion relation, incorporating in a simple way exchange and correlation effects within the jellium model. The results obtained are compared with recent experimental findings. The key role played by exchange and correlation effects in improving the agreement between theory and experiment is stressed. The static polarizability has also been calculated as a function of q. The formulas can be easily modified to incorporate band-structure effects (through an intraband electron effective mass) and core-polarization effects (through a static dielectric constant).

Multipole surface-plasmon modes on simple metals

The average multipole surface-plasmon energy for simple metals, as well as that of ordinary surface and bulk plasmons, is obtained using energy-weighted moments of the electronic response to sufficiently general external perturbations. A local approximation of exchange and correlation effects is used within a jellium model. Band-structure effects are incorporated through an effective electronic mass. Taking advantage of the transparency of the method, we analyze under what circumstances such modes might be observable. It is shown that due to an interplay between Coulomb and kinetic energies, the multipole modes become unobservable for increasing values of the transferred momentum (q) parallel to the surface. The value of q at which the multipole mode becomes unobservable is much smaller than the cutoff value for Landau damping. The effect of the electronic surface diffuseness is also analyzed. We compare our results with previous density-functional calculations and with recent experimental data for Na, K, and Cs.

Comment on "Reappraisal of experimental values of third-order elastic constants of some cubic semiconductors and metals"

In a recent paper A. S. Johal and D. J. Dunstan [Phys. Rev. B 73, 024106 (2006)] have applied multivariate linear regression analysis to the published data of the change in ultrasonic velocity with applied stress. The aim is to obtain the best estimates for the third-order elastic constants in cubic materials. From such an analysis they conclude that uniaxial stress data on metals turns out to be nearly useless by itself. The purpose of this comment is to point out that by a proper analysis of uniaxial stress data it is possible to obtain reliable values of third-order elastic constants in cubic metals and alloys. Cu-based shape memory alloys are used as an illustrative example.

Characterization of nano-oxide layers fabricated by ion beam oxidation

In this paper, a remote O2 ion source is used for the formation of nano-oxide layers. The oxidation efficiency was measured in CoFe-oxide films, and a decrease of the oxide layer with the pan angle and the oxidation pressure is observed. For the same oxidation pressure, the oxidation efficiency depends on the O2 content in the Ar-O2 plasma. These results were applied in optimizing the fabrication of Al2O3 barrier for tunnel junctions. This method was also used to fabricate junctions with Fe-oxide layers inserted at the Al2O3-CoFe interface. TEM and magnetization data indicate that after anneal at 385°C, a homogeneous ferromagnetic Fe-oxide layer (Fe3O4?) is formed.

Static and dynamic structure of liquid metals: Role of the different parts of the interaction potential

The influence of different parts of the interaction potential on the microscopic behavior of simple liquid metals is investigated by molecular dynamics simulation. The role of the soft-core repulsive, short-range attractive, and long-range oscillatory forces on the properties of liquid lithium close to the triple point is analyzed by comparing the results from simulations of identical systems but truncating the potential at different distances. Special attention is paid to dynamic collective properties such as the dynamic structure factors, transverse current correlation functions, and transport coefficients. It is observed that, in general, the effects of the short-range attractive forces are important. On the contrary, the influence of the oscillatory long-range interactions is considerably less, being the most pronounced for the dynamic structure factor at long wavelengths. The results of this work suggest that the influence of the attractive forces becomes less significant when temperature and density increase.

Dynamic properties of Lennard Jones fluids and liquid metals

The dependence of the dynamic properties of liquid metals and Lennard-Jones fluids on the characteristics of the interaction potentials is analyzed. Molecular-dynamics simulations of liquids in analogous conditions but assuming that their particles interact either through a Lennard-Jones or a liquid-metal potential were carried out. The Lennard-Jones potentials were chosen so that both the effective size of the particles and the depth of the potential well were very close to those of the liquid-metal potentials. In order to investigate the extent to which the dynamic properties of liquids depend on the short-range attractive interactions as well as on the softness of the potential cores, molecular-dynamics simulations of the same systems but assuming purely repulsive interactions with the same potential cores were also performed. The study includes both singleparticle dynamic properties, such as the velocity autocorrelation functions, and collective dynamic properties, such as the intermediate scattering funcfunctions, and collective dynamic properties, such as the intermediate scattering functions, the dynamic structure factors, the longitudinal and transverse current correlations, and the transport coefficients.

Unconventional magnetic behavior of iron-oxide nanoparticles in polymeric matrices

We report the results of magnetization and 57Fe Mössbauer spectroscopy measurements performed in the temperature range 5-300 K on composites containing iron¿oxide nanoparticles encased in polystyrene type resins. After carrying out a suitable field treatment in order to decouple the particles from the matrix, a fraction of the particles freely rotate in response to an applied magnetic field

Structural and magnetic characterization of the lithiated iron oxide LixFe3O4

The Rietveld profile‐analysis method is used to investigate the x‐ray diffraction pattern of lithiated Fe3O4. It is shown that, after exposure to air, pure magnetite coexists with a lithium‐inserted LixFe3O4 phase. The Mössbauer spectra at 300 and 4.2 K have been used to estimate the lithium content of the sample, the pure magnetite concentration, and the iron distribution over the available 16c and 16d sites of the spinel structure. Magnetization measurements from 4.2 to 120 K with an external magnetic field up to 150 kOe have been used to obtain the saturation magnetic moment, the magnetic anisotropy constants, and the susceptibility. It is concluded that a noncollinear spin structure should be present in Li0.5Fe3O4. These results indicate that there is no room‐temperature extrusion of iron even for x→2.0, but that on exposure to air LixFe3O4 samples with x>0.5 are oxidized at room temperature by delithiation.

Structural disorder in two-dimensional random magnets: Very thin films of rare earths and transition metals

The low-temperature isothermal magnetization curves, M(H), of SmCo4 and Fe3Tb thin films are studied according to the two-dimensional correlated spin-glass model of Chudnovsky. We have calculated the magnetization law in approach to saturation and shown that the M(H) data fit well the theory at high and low fields. In our fit procedure we have used three different correlation functions. The Gaussian decay correlation function fits well the experimental data for both samples.

Nitric oxide synthase (NOS) inhibition for one week improves renal sodium and water excretion in cirrhotic rats with ascites

Normalization of the increased vascular nitric oxide (NO) generation with low doses of NG-nitro-L-arginine methyl ester (L-NAME) corrects the hemodynamic abnormalities of cirrhotic rats with ascites. We have undertaken this study to investigate the effect of the normalization of vascular NO production, as estimated by aortic cyclic guanosine monophosphate (cGMP) concentration and endothelial nitric oxide synthase (eNOS) protein expression in the aorta and mesenteric artery, on sodium and water excretion. Rats with carbon tetrachloride-induced cirrhosis and ascites were investigated using balance studies. The cirrhotic rats were separated into two groups, one receiving 0.5 mg/kg per day of L-NAME (CIR-NAME) during 7 d, whereas the other group (CIR) was administrated the same volume of vehicle. Two other groups of rats were used as controls, one group treated with L-NAME and another group receiving the same volume of vehicle. Sodium and water excretion was measured on days 0 and 7. On day 8, blood samples were collected for electrolyte and hormone measurements, and aorta and mesenteric arteries were harvested for cGMP determination and nitric oxide synthase (NOS) immunoblotting. Aortic cGMP and eNOS protein expression in the aorta and mesenteric artery were increased in CIR as compared with CIR-NAME. Both cirrhotic groups had a similar decrease in sodium excretion on day 0 (0.7 versus 0.6 mmol per day, NS) and a positive sodium balance (+0.9 versus +1.2 mmol per day, NS). On day 7, CIR-NAME rats had an increase in sodium excretion as compared with the CIR rats (sodium excretion: 2.4 versus 0.7 mmol per day, P < 0.001) and a negative sodium balance (-0.5 versus +0.8 mmol per day, P < 0.001). The excretion of a water load was also increased after L-NAME administration (from 28+/-5% to 65+/-7, P < 0.05). Plasma renin activity, aldosterone and arginine vasopressin were also significantly decreased in the CIR-NAME, as compared with the CIR rats. The results thus indicate that normalization of aortic cGMP and eNOS protein expression in vascular tissue is associated with increased sodium and water excretion in cirrhotic rats with ascites.

Growth rate of fractal copper electrodeposits: Potential and concentration effects

Experiments are reported on fractal copper electrodeposits. An electrochemical cell was designed in order to obtain a potentiostatic control on the quasi-two-dimensional electrodeposition process. The aim was focused on the analysis of the growth rate of the electrodeposited phase, in particular its dependence on the electrode potential and electrolyte concentration.

Further insights on dynamic morphological transitions in quasi-two-dimensional electrodeposition

Dynamic morphological transitions in thin-layer electrodeposits obtained from copper sulphate solutions have been studied. The chemical composition of the electrodeposits indicates that they appear as a consequence of the competition between copper and cuprous oxide formation. In addition, the Ohmic control of the process is verified at initial stages of the deposit growth. At higher deposit developments, gravity-induced convection currents play a role in the control of the whole process and affect the position of these transitions.

Chemisorption of group-III metals on the Si(111) and Ge(111) surfaces: An ab initio study

Chemisorption of group-III metal adatoms on Si(111) and Ge(111) has been studied through the ab initio Hartree-Fock method including nonempirical pseudopotentials and using cluster models to simulate the surface. Three different high-symmetry sites (atop, eclipsed, and open) have been considered by using X4H9, X4H7, and X6H9 (X=Si,Ge) cluster models. In a first step, ideal surface geometries have been used. Metal-induced reconstruction upon chemisorption has also been taken into account. Equilibrium distances, binding energies, and vibrational frequencies have been obtained and compared with available experimental data. From binding-energy considerations, the atop and eclipsed sites seem to be the most favorable ones and thus a coadsorption picture may be suggested. Group-III metals exhibit a similar behavior and the same is true for Si(111) and Ge(111) surfaces when chemisorption is considered.