3-D vision and range finding techniques

The introduction of third generation robots in automated systems is impeded by the absence of 3-D sensors collecting panoramic range data at medium distance (0–10 meters) in a large volume (up to 100 m³). The work described in the present paper offers a certain number of solutions to this general problem. Our system is built around a 2-D passive machine vision connected to various cameras (VIDICON and CCD). The host computer (HP 1000) pilots numerous sorts of range finders (acoustic and optical).

The concept of multisensory range finders is introduced to allow the best use of each type (active methods). This 3-D vision has been tested in two fields of application:

• -in robotics for the absolute of a mobile robot;

• -in audiovisual for fixing objects or actors in a 3-D synthetic scene.

In some cases the absolute location problem is solved with an opto-electronic remote tracking measurement system. It is the last part of our 3-D machine vision.     

Thermodynamics of solid surfaces

In contrast to the thermodynamics of fluid surfaces, the thermodynamics of solid surfaces was not elaborated in detail by Gibbs and other founders of surface thermodynamics. During recent decades, significant progress in this field has been achieved in both the understanding of old notions, like chemical potentials, and in formulating new areas. Applying to solid surfaces, basic relationships of classical theory of capillarity, such as the Laplace equation, the Young equation, the Gibbs adsorption equation, the Gibbs-Curie principle, the Wulff theorem and the Dupré rule, were reformulated and generalized. The thermodynamics of self-dispersion of solids and the thermodynamics of contact line phenomena were developed as well. This review provides a fresh insight into the modern state of the thermodynamics of solid surfaces. Not only a solid surface itself, both in a macroscopic body and in the system of fine particles, but also the interaction of solid surfaces with fluid phases, such as wetting phenomenon, will be analyzed. As the development of surface thermodynamics has given a powerful impetus to the creation of new experimental methods, some of these will be described as examples.     

Influence of oxygen on the track etch rate along light ion trajectories in CR-39

The role of oxygen for stabilising radicals to form permanent damages in irradiated samples which are basically important for the etching process of track detectors has been studied. Samples of CR-39 were irradiated with 4 MeV -particles with a fluence of 30 000 particles per cm². The irradiations were performed in three different regimes:

• variation of out-gassing time in vacuum before irradiation;

• no out-gassing time but varied post-irradiation storage times in vacuum;

• variation of both storage times in vacuum before and after irradiation.

Generally, the absence of dissolved oxygen in the irradiated sample results in a decreased detection sensitivity in comparison with the detection properties and track parameters of samples irradiated in air. To determine the sensitivity the depth dependence of the track etch rate v_T(x) along the particle trajectory has been measured. From the observation of the dependence of the decreasing sensitivity on the post-irradiation storage time in vacuum, a lifetime of free radicals of 30 min could be derived. The amount of permanent damages responsible for the etching mechanism is related to the concentration profile of back-diffused oxygen and the REL-dependent radical concentration. This confirms previous results that the detection sensitivity is not a simple function of REL but depends on both REL and x the stronger the deeper within the irradiated sample.     

Accurate double many-body expansion potential energy surface of HS_2(A~2A') by scaling the external correlation

A globally accurate single-sheeted double many-body expansion potential energy surface is reported for the first excited state of HS_2 by fitting the accurate ab initio energies, which are calculated at the multireference configuration interaction level with the aug-cc-pVQZ basis set. By using the double many-body expansion-scaled external correlation method,such calculated ab initio energies are then slightly corrected by scaling their dynamical correlation. A grid of 2767 ab initio energies is used in the least-square fitting procedure with the total root-mean square deviation being 1.406 kcal · mol~(-1).The topographical features of the HS_2(A_2A') global potential energy surface are examined in detail. The attributes of the stationary points are presented and compared with the corresponding ab initio results as well as experimental and other theoretical data, showing good agreement. The resulting potential energy surface of HS_2(A_2A') can be used as a building block for constructing the global potential energy surfaces of larger S/H molecular systems and recommended for dynamic studies on the title molecular system.     

On Lie supergroups and superbundles defined via the Baker-Campbell-Hausdorff formula

The Baker-Campbell-Hausdorff formula is extended to the class of Lie superalgebras and then is used to define a class of objects, which are called Lie supergroups. Such Lie supergroups turn out to be either Lie groups (then the Jacobi Z₂-identity is simultaneously the usual Jacobi identity) or some sets provided with a partially associative multiplication. Thus they are different objects from supergroups in the sense of Kostant, Berezin or A. Rogers. In particular no Grassman algebra is used in the paper. Examples of

1. 1) some matrix Lie superalgebras,

2. 2) certain superalgebras of the super-Poincaré algebra

3. 3) the special Lie superalgebras D(2, 1, ) and their superalgebras are presented.

Furthermore, cocycles of functions taking values in the Lie supergroups are defined and their partially associative multiplicative relations are considered. Some fibre bundles, whose transition functions determine such cocycles, are distinguished.     

Interaction of oxygen with the Pt(1 1 1) surface in wide conditions range. A DFT-based thermodynamical simulation

We present the results of ab initio calculations of oxygen atomic adsorption in a wide range of coverage on Pt(1 1 1). At θ = 0.25 ML, the O adsorption at fcc hollow site is clearly favoured over the hcp site. At θ = 0.5 ML, the O adsorption energy decreases but the same site is favoured. When experimental or theoretical previously reported data are available, the calculated adsorption energies and site preferences are in good agreement. Among the various configurations and coverages investigated in the present work, no adsorption is stable beyond θ = 0.5 ML, except by occupation of a subsurface tetrahedral site. In that case, a total O coverage of 0.75 ML could be achieved, which is only slightly less stable than the θ = 0.5 ML configuration.

The use of thermodynamics permitted to explore the temperature–pressure stability domain corresponding to 0.25 ML, 0.5 ML and 0.75 ML. From this, we conclude that subsurface O species could be stable at temperatures lower than 700 K, with O₂ pressures of 1 bar or less.     

The Rashba-effect at metallic surfaces

Surface states, that show a k-dependent splitting resulting from spin-orbit coupling, show wide similarities to a two-dimensional electron gas in semiconductor heterostructures, where the Rashba-effect lifts the spin-degeneracy of the bands and allows spin-manipulation by an electric field. We discuss the conditions for such a Rashba-effect at metallic surfaces by comparing ab initio calculations for Au(1 1 1), Ag(1 1 1), and Lu(0 0 0 1) and investigate the influence of electric and magnetic (exchange) fields on these surface states.     

Studies on the iodine complexes of pyridine picolines and aminopyridine by constant activity method

The iodine complexes of pyridine, -, β-, γ- picolines, 2-aminopyridine and 2,2′-bipyridine in cyclohexane were studied by the constant activity method, their spectral characteristics and thermodynamic parameters were determined. The equilibrium constants, molar extinction coefficients of the charge-transfer band maxima, _CT, at 25°C and heats of complexation, ΔH°, are respectively as follows:

1. (a) pyridine-iodine, 107 dm³mol⁻¹ 24200 dm³mol⁻¹m⁻¹ and 31 KJ/mol;

2. (b) -picoline-iodine, 172 dm³mol⁻¹m⁻¹, 49700 dm³mol⁻¹m⁻¹ and 33 KJ/mol;

3. (c) β-picoline-iodine, 243 dm³mol⁻¹, 50300 dm³mol⁻¹m⁻¹ and 35 KJ/mol;

4. (d) γ-picoline-iodine, 342 dm³mol⁻¹, 55900 dm³mol⁻¹m⁻¹ and 41 KJ/m;

5. (e) 2-aminopyridine-iodine, 427 dm³mol⁻¹, 60800 dm³mol⁻¹m⁻¹ and 47 KJ/mol;

6. (f) 2,2′-bipyridine-iodine, 6.0 dm³mol⁻¹,−, 21 KJ/mol.

The values of the blue shifted iodine band maxima of the above mentioned donors and their molar extinction coefficients are, 420 nm (1450 dm³mol⁻¹m⁻¹), 419 nm (1470 dm³mol⁻¹m⁻¹), 418 nm (1640 dm³mol⁻¹m⁻¹), 417 nm (1570 dm³mol⁻¹m⁻¹), 410 nm (1574 dm³mol⁻¹m⁻¹) and 452 nm (1370 dm³mol⁻¹m⁻¹) respectively. The oscillator strengths and transition dipole moments of the blue-shifted iodine bands are characterised.     

Surface oxides of the oxygen-copper system: Precursors to the bulk oxide phase?

To gain an initial understanding of the copper-based catalysts in commercially important chemical reactions such as the oxygen-assisted water-gas shift reaction, we performed density-functional theory calculations, investigating the interaction of oxygen and copper, focusing on the relative stability of surface oxides and oxide surfaces of the O/Cu system. By employing the technique of “ab initio atomistic thermodynamics”, we show that surface oxides are only metastable at relevant pressures and temperatures of technical catalysis, with no stable chemisorption phase observed even at very low coverage. Although exhibiting only metastability, these surface oxides resemble the bulk oxide material both geometrically and electronically, and may serve as a precursor phase before onset of the bulk oxide phase. Having identified the bulk oxide as the most stable phase under realistic catalytic conditions, we show that a Cu₂O(1 1 1) surface with Cu vacancies has a lower free energy than the stoichiometric surface for the considered range of oxygen chemical potential and could be catalytically relevant.     

First-principles atomistic thermodynamics for oxidation catalysis: surface phase diagrams and catalytically interesting regions

Present knowledge of the function of materials is largely based on studies (experimental and theoretical) that are performed at low temperatures and ultralow pressures. However, the majority of everyday applications, like, e.g., catalysis, operate at atmospheric pressures and temperatures at or higher than 300 K. Here we employ ab initio, atomistic thermodynamics to construct a phase diagram of surface structures in the (T,p) space from ultrahigh vacuum to technically relevant pressures and temperatures. We emphasize the value of such phase diagrams as well as the importance of the reaction kinetics that may be crucial, e.g., close to phase boundaries.     

Ab initio investigation of the Renner-Teller effect in tetra-atomic molecules

A method for theoretical ab initio treatment of the Renner-Teller effect in tetra-atomic molecules is described. It is based on the model developed in 1972 by Petelin and Kiselev, but instead perturbationally, as in the original work, the vibronic problem is solved by a variational approach. The reliability of the approximations on which the model is based is discussed in detail and checked by the explicit ab initio computations carried out at various levels of sophistication. The model is extended to take into account the interplay between the vibronic, spin-orbit and magnetic hyperfine couplings. The results of ab initio investigations of the structure of spectra involving the ground states, X²Π_u of C₂H⁺₂ and B₂H⁺₂ are reviewed.     

Ab Initio Thermodynamics Calculation of Beta Decay Rates

Beta-decay half-lives for the free neutron, for ⁶He and ⁸He, and for ⁸Li are calculated ab initio from geometrical thermodynamics arguments, independently of any quantum mechanics. Half-lives for the decay of ⁸Be to two alphas and for the disintegration of the tetraneutron are also calculated. The calculated values are close to those experimentally observed.     

Surface structure of cubic diamond nanowires

Presented are results of our ab initio study of the surface reconstruction and relaxation of (1 0 0) surfaces on diamond nanowires. We have used a density function theory within the generalized-gradient approximation using the Vienna ab initio simulation package, to consider dehydrogenated and hydrogenated surfaces. Edges of nanowires offer a new challenge in the determination of surface structure. We have applied the methodology for stepped diamond (1 0 0) surfaces to this problem, and consider it useful in describing diamond nanowire edges to first approximation. We have found that dimer lengths and atomic layer depths of the C(1 0 0)(2 × 1) and C(1 0 0)(2 × 1):H nanowire surfaces differ slightly from those of bulk diamond and nanodiamond surfaces. The aim of this study is provide a better understanding of the effects of nano-scale surfaces on the stability of diamond nanostructures.     

The virtual chemistry lab for reactions at surfaces: Is it possible? Will it be useful?

Ab initio total-energy calculations based on electronic structure theory have tremendously enlarged our knowledge about the geometrical and electronic structure of clean and adsorbate-covered low-index surfaces and reactions on these surfaces. In technological applications, however, extended flat surfaces are very rarely used. Hence the applicability of the theoretical results for the technological surfaces are indeed questionable. In this review I will reflect on the question whether ab initio calculations of reactions at surfaces can contribute to the development of, e.g., better catalysts. Simulations alone will not be able to lead to new products but it will be demonstrated that they can contribute enormously to the development process. Thus the virtual chemistry lab is indeed possible and helpful.     

Surface relaxation and surface stress of 4d transition metals

Using the density functional theory formulated within the framework of the exact muffin-tin orbitals method, we present a systematic study of the top layer relaxation and surface stress of 4d transition metals. Our calculations predict layer contractions for most surfaces. We also find that the relaxations of the close packed surfaces decrease with increasing atomic number through the 4d series. We propose that the relaxation is mainly due to the reduction of the number of sp electrons in the surface layer relative to bulk. The surface stress is found to be very sensitive to the relaxation and, therefore, an accurate determination of the layer relaxation is necessary for obtaining reliable values for the surface stress. Comparing the top layer relaxations for the close packed surfaces, we see essential deviations between data derived in different ab initio calculations. At the same time, the overall trend for the present surface stress of 4d metals is in reasonable agreement with recent full-potential data.     

Equilibrium ordering properties of Au–Pd alloys and nanoalloys

Equilibrium configurations of bulk and surface Au–Pd alloys as well as of nanoalloy clusters are studied using Metropolis Monte Carlo importance sampling and the embedded atom method. The clusters contain about 1000 atoms. Three ordered bulk phases are predicted at low temperature, centred on compositions around 25%, 50%, and 75% Pd. The predicted order–disorder transition temperatures partially disagree with the available experimental results, but they are in good agreement with ab initio calculations. Surface enrichment in Au is systematically predicted, accompanied by partial subsurface enrichment in Pd, best enhanced around the equiatomic overall composition. The subsurface enrichment in Pd is suggested to play a decoupling role between surface and bulk conditions and, subsequently, ordered surface structures not induced by the order in the bulk are predicted at low temperatures. Clusters display similar segregation and ordering properties as flat infinite surfaces. However, the stability of the ordering at cluster surfaces is not globally characterized. The order–disorder transitions in the clusters occur at temperatures between 50 and 100 K lower than in the bulk. The disorder appears at the surface and proceeds to the core as the temperature is increased.     

The atomic and electronic structure of the TiO2- and BaO-terminated BaTiO3(0 0 1) surfaces in a paraelectric phase

Relaxation and rumpling of BaTiO₃(0 0 1) surface with two different terminations have been investigated from ab initio local density approximation calculations. Large displacements of ions deviated from their crystalline sites have been obtained. These kinds of displacements lead to the formation the surface rumpling, dipole moments and electric field in the near-surface region. Band structures, density of states, bond population and electronic density redistributions have been obtained. Considerable enhancement of Ti–O chemical bond covalency nearby the surface, especially for the TiO₂ termination surface, has been found.     

Thermodynamics of the Apparent Horizon in FRW Universe with Massive Gravity

Applying Clausius relation with energy-supply defined by the unified first law of thermodynamics formalism to the apparent horizon of a massive gravity model in cosmology proposed lately, the corrected entropic formula of the apparent horizon is obtained with the help of the modified Friedmann equations. This entropy-area relation, together with the identified Misner-Sharp internal energy, verifies the first law of thermodynamics for the apparent horizon with a volume change term for consistency. On the other hand, by means of the corrected entropy-area formula and the Clausius relation δQ=T dS, where the heat flow δQ is the energy-supply of pure matter projecting on the vector ζ tangent to the apparent horizon and should be looked on as the amount of energy crossing the apparent horizon during the time interval dt and the temperature of the apparent horizon for energy crossing during the same interval is 1/2πrA, the modified Friedmann equations governing the dynamical evolution of the universe are reproduced with the known energy density and pressure of massive graviton. The integration constant is found to correspond to a cosmological term which could be absorbed into the energy density of matter. Having established the correspondence of massive cosmology with the unified first law of thermodynamics on the apparent horizon, the validity of the generalized second law of thermodynamics is also discussed by assuming the thermal equilibrium between the apparent horizon and the matter field bounded by the apparent horizon. It is found that, in the limit H_c→0, which recovers the Minkowski reference metric solution in the flat case, the generalized second law of thermodynamics holds if α₃+4α₄<0. Without this condition, even for the simplest model of dRGT massive cosmology with α₃=α₄=0, the generalized second law of thermodynamics could be violated.     

Stability and electronic properties of the O-terminated Cu2O(111) surfaces: First-principles investigation

The effect of different vacancies on the morphology of the O-terminated Cu₂O(111) surface has been studied through the first-principles calculations. Our results show that Cu and O vacancies trigger large relaxations and formation of two different facets. Our emulated STM images are in consistent with the experimental STM patterns. A sizeable magnetic moment (∼1.0 μ_B) was found for surfaces with either Cu or O vacancies. The calculated formation energies of surface vacancies indicate that the deficient surfaces are more stable than the stoichiometric O-terminated (1×1) surface, which is also in line with our results obtained from ab initio atomistic thermodynamics studies.