Formation mechanism of the O-induced added-row reconstruction on Ag(110): A low-temperature STM study

The formation of the O-induced added-row reconstruction on Ag(110) was studied by scanning tunneling microscopy at 190 K. At this temperature critical surface processes are slow enough to be followed on the atomic scale. Ag atoms, which are required for the formation of the reconstruction, detach from steps in a row-wise fashion, starting from kink sites. The growth rate of the added rows is constant and controlled by the detachment rate of Ag atoms from the steps. The data provide evidence for a reconstruction mechanism in which the release of the metal atoms from the steps and the formation of lateral oxygen metal bonds are independent processes

Diffusion and Atomic Hopping of N Atoms on Ru(0001) Studied by Scanning Tunneling Microscopy

The dynamic behavior of N atoms adsorbed on a Ru(0001) surface was studied by scanning tunneling microscopy. N atoms formed by dissociation of NO molecules show an initial sharp concentration profile at atomic steps. Its decay was followed as a function of time, providing a quasicontinuum diffusion constant; the activation energy is 0.94 eV and the prefactor is 2×10−2cm2s−1. The diffusion constant was determined also at equilibrium, from statistical jumps of individual N atoms in a uniform overlayer, and is found to be identical to the Fickian value

Adsorbate-adsorbate interactions from statistical analysis of STM images: N/Ru(0001)

Atomic nitrogen on Ru(0001) was prepared by dissociative chemisorption of N2 and studied by scanning tunneling microscopy (STM) at 300 K. Nitrogen occupies the hcp threefold hollow site and is imaged as a depression with a diameter of about 5 Å. Interactions between the adsorbed nitrogen atoms were obtained by statistical analysis of STM images, by extraction of the two-dimensional pair distribution function from the arrangement of the N atoms. Since the nearest-neighbor separations could be identified with atomic precision, the pair distribution function g and hence the potential of mean force Veff were obtained as a function of the discrete neighbor sites j up to the tenth nearest neighbor. A comparison with Monte Carlo calculations for balls with a hard-sphere potential provides information about the pair potential Vpair(j): The nearest-neighbor site is strongly repulsive, the second-neighbor site is weakly repulsive, and the third-neighbor site is weakly attractive. These findings rationalize the absence of island formation and of a well-ordered 2×2 phase for the N/Ru(0001) system: At temperatures ≥300 K the attractive interaction on the third-neighbor site is too weak, while at lower temperatures the diffusion barrier of 0.9 eV represents a kinetic obstacle. The fact that the range of the interaction is identical to the diameter of the N-atom features in the STM topographs is taken as evidence that the interaction is caused by substrate-mediated electronic forces

Direct observation of mobility and interactions of oxygen molecules chemisorbed on the Ag(110) surface

The energetics of thermal motions and interactions of oxygen molecules chemisorbed on a Ag(110) surface were investigated by scanning tunneling microscopy at 60–100 K. Surface mobility is anisotropic, preferably in the [1̅10] direction with an activation energy of 0.22±0.05 eV and a preexponential factor of 1×1013±3 s−1. Along the [1̅10] direction a repulsive interaction between nearest neighbors of about 0.02 eV and an attraction of 0.04±0.01 eV between next nearest neighbors were derived. Along [001] appreciable repulsion exists between nearest neighbors, while a ''diagonal'' arrangement of molecules is associated with an attraction of 0.02±0.01 eV. The data are indicative for the operation of indirect, substrate-mediated molecule-molecule interactions

Learning kinematic structure correspondences using multi-order similarities

We present a novel framework for finding the kinematic structure correspondences between two articulated objects in videos via hypergraph matching. In contrast to appearance and graph alignment based matching methods, which have been applied among two similar static images, the proposed method finds correspondences between two dynamic kinematic structures of heterogeneous objects in videos. Thus our method allows matching the structure of objects which have similar topologies or motions, or a combination of the two. Our main contributions are summarised as follows: (i)casting the kinematic structure correspondence problem into a hypergraph matching problem by incorporating multi-order similarities with normalising weights, (ii)introducing a structural topology similarity measure by aggregating topology constrained subgraph isomorphisms, (iii)measuring kinematic correlations between pairwise nodes, and (iv)proposing a combinatorial local motion similarity measure using geodesic distance on the Riemannian manifold. We demonstrate the robustness and accuracy of our method through a number of experiments on synthetic and real data, showing that various other recent and state of the art methods are outperformed. Our method is not limited to a specific application nor sensor, and can be used as building block in applications such as action recognition, human motion retargeting to robots, and articulated object manipulation

Finite temperature theory of the scissors mode in a Bose gas using the moment method

We use a generalized Gross-Pitaevskii equation for the condensate and a semi-classical kinetic equation for the noncondensate atoms to discuss the scissors mode in a trapped Bose-condensed gas at finite temperatures. Both equations include the effect of $C_{12}$ collisions between the condensate and noncondensate atoms. We solve the coupled moment equations describing oscillations of the quadrupole moments of the condensate and noncondensate components to find the collective mode frequencies and collisional damping rates as a function of temperature. Our calculations extend those of Gu\'ery-Odelin and Stringari at T=0 and in the normal phase. They complement the numerical results of Jackson and Zaremba, although Landau damping is left out of our approach. Our results are also used to calculate the quadrupole response function, which is related to the moment of inertia. It is shown explicitly that the moment of inertia of a trapped Bose gas at finite temperatures involves a sum of an irrotational component from the condensate and a rotational component from the thermal cloud atoms.Comment: 18 pages, 8 figure

Towards Anchoring Self-Learned Representations to Those of Other Agents

In the future, robots will support humans in their every day activities. One particular challenge that robots will face is understanding and reasoning about the actions of other agents in order to cooperate effectively with humans. We propose to tackle this using a developmental framework, where the robot incrementally acquires knowledge, and in particular 1) self-learns a mapping between motor commands and sensory consequences, 2) rapidly acquires primitives and complex actions by verbal descriptions and instructions from a human partner, 3) discovers correspondences between the robots body and other articulated objects and agents, and 4) employs these correspondences to transfer the knowledge acquired from the robots point of view to the viewpoint of the other agent. We show that our approach requires very little a-priori knowledge to achieve imitation learning, to find correspondent body parts of humans, and allows taking the perspective of another agent. This represents a step towards the emergence of a mirror neuron like system based on self-learned representations

Size-Selective Personal Air Sampling: A New Approach Using Porous Foams

Simultaneous sampling of three dust fractions (inhalable, thoracic, respirable) has been achieved using porous polyurethane foams, which serve both as selecting and sampling media. The particle penetration was measured in laboratory tests. Foam geometries were predicted using a semi-empirical model. Prototype samplers were constructed based on the IOM and GSP inhalable personal samplers. Weighing and chemical analysis procedures were checked for the foam

Gain of 20q11.21 in human pluripotent stem cells impairs TGF-β-dependent neuroectodermal commitment

Gain of 20q11.21 is one of the most common recurrent genomic aberrations in human pluripotent stem cells. Although it is known that overexpression of the antiapoptotic gene Bcl-xL confers a survival advantage to the abnormal cells, their differentiation capacity has not been fully investigated. RNA sequencing of mutant and control hESC lines, and a line transgenically overexpressing Bcl-xL, shows that overexpression of Bcl-xL is sufficient to cause most transcriptional changes induced by the gain of 20q11.21. Moreover, the differentially expressed genes in mutant and Bcl-xL overexpressing lines are enriched for genes involved in TGF-beta- and SMAD-mediated signaling, and neuron differentiation. Finally, we show that this altered signaling has a dramatic negative effect on neuroectodermal differentiation, while the cells maintain their ability to differentiate to mesendoderm derivatives. These findings stress the importance of thorough genetic testing of the lines before their use in research or the clinic