Abstractive chemisorption of O2 on Al(111)

We present experimental evidence that abstraction is a common mechanism (approximately 50%) in the dissociative chemisorption of oxygen on Al(111) at a translational energy of 0.5 eV. As a result of this mechanism, individual isolated O-atoms are observed in scanning tunneling microscopy (STM). At this translational energy ordinary dissociative chemisorption processes also occur, resulting in pairs of adatoms. The ejected O-atoms originating from the abstraction reaction are detected in the gas phase using laser spectrometry. Together, these observations provide compelling evidence for the abstraction mechanism.     

Scattering of O2 from AL111

Experimental results are presented for the scattering of well-defined beams of molecular oxygen incident on clean Al(111). The data consist of scattered angular distributions measured as a function of incident angle, and for fixed incident angle, the dependence on surface temperature of the angular distributions. The measurements are interpreted in terms of a scattering theory that treats the exchange of energy between the translational and rotational motions of the molecule and the phonons of the surface using classical dynamics. The dependence of the measured angular distributions on incident beam angle and temperature is well explained by the theory. Rotational excitation and quantum excitation of the O(2) internal stretching mode are briefly discussed.     

How can self-regulated learning support the problem solving of third-grade students with mathematics anxiety?

The study compares 140 third-grade Israeli students (lower and higher achievers) who were either exposed to self-regulated learning (SRL) supported by metacognitive questioning (the MS group) or received no direct SRL support (the N_MS group). We investigated: (a) mathematical problem solving performance; (b) metacognitive strategy use in three phases of the problem-solving process; and (c) mathematics anxiety. Findings indicated that the MS students showed greater gains in mathematical problem solving performance than the N_MS students. They reported using metacognitive strategies more often, and showed a greater reduction in anxiety. In particular, the lower MS achievers showed these gains in the basic and complex tasks, in strategy use during the on-action phase of the problem solving process and a decrease in negative thoughts. The higher achievers showed greater improvement in transfer tasks and an increase in positive thoughts towards mathematics. Both the theoretical and practical implications of this study are discussed.     

New Aqueous Gel Based on Soluble Cyclodextrin/Vitamin A Inclusion Complex

Rameb (randomized dimethyl--cyclodextrin) was mixed with vitamin A propionate (PVA) (molar ratio 10/1 in water) and a water soluble complex was formed and studied by HPLC and NMR (structure, concentration and stability of PVA). Then solution was used to form an aqueous gel. The skin absorption of PVA through stratum corneum, epidermis and dermis of human skin (on modified Franz cells) was assayed by HPLC and was compared to that of a reference gel (or oil) without cyclodextrin. The solution obtained contains a maximum of 10 mg/mL PVA (if saturated with Rameb) and the PVA can remain stable up to 90 days in solution, and up to 1 year if freeze-dried (storage at 4 °C, in the dark). The results of the different experiments of skin distribution were statistically analyzed and show that when complexed with Rameb, the amount of PVA that penetrates each skin layer is significantly higher than pure PVA. The results also show that PVA cannot pass through the dermis and enter the circulation.     

Direct investigation of the vectorization properties of amphiphilic cyclodextrins in phospholipid films

Recently, new cyclodextrin derivatives were synthesized and shown to exhibit strong amphiphilic properties. In this paper, we study the action of these new amphiphilic cyclodextrins on phospholipids. Mixed phospholipid/cyclodextrin derivative films were prepared and studied using X-ray reflectivity for various phospholipid/cyclodextrin ratios. A molar ratio of 3 provides a highly stable film the molecular structure of which has been investigated in detail. The cholesterol tail of the cyclodextrin molecule was found to be anchored into the phospholipid film. The cyclodextrin moieties exposed to the aqueous medium are prone to the addition of the guest molecule Dosulepin, making them of high interest for drug delivery. For this purpose and as an example of a potential application, this cyclodextrin molecular carrier property is also addressed to this complex film architecture.     

Flow conditions in the vicinity of microstructured interfaces studied by holography and implications for the assembly of artificial actin networks

Microstructured fluidic devices have successfully been used for the assembly of free standing actin networks as mechanical model systems on the top of micropillars. The assembly occurs spontaneously at the pillar heads when preformed filaments are injected into the channel. In order to reveal the driving mechanism of this localization, we studied the properties of the flow profile by holographic tracking. Despite the strong optical disturbances originating from the pillar field, 2 μm particles were traced with digital in-line holographic microscopy (DIHM). Trajectories in the pillar free region and local alterations of the flow profile induced by the channel structure in the pillar decorated region can be distinguished. Velocity histograms at different z-positions reveal that the laminar flow profile across the channel shows a difference between the minimum in the z-component of the velocity field and the maximum of the overall velocity. This minimum drag in vertical direction is present at the top of the pillars and explains why biopolymer networks readily assemble in this region instead of forming a homogeneous three-dimensional network in between the pillars. On the basis of the observations we propose a new mechanism for actin network formation on top of the microstructures.     

Theory of microwave absorption by the spin-1/2 Heisenberg-Ising magnet

We analyze the problem of microwave absorption by the Heisenberg-Ising magnet in terms of shifted moments of the imaginary part of the dynamical susceptibility. When both the Zeeman field and the wave vector of the incident microwave are parallel to the anisotropy axis, the first four moments determine the shift of the resonance frequency and the linewidth in a situation where the frequency is varied for fixed Zeeman field. For the one-dimensional model we can calculate the moments exactly. This provides exact data for the resonance shift and the linewidth at arbitrary temperatures and magnetic fields. In current ESR experiments the Zeeman field is varied for fixed frequency. We show how in this situation the moments give perturbative results for the resonance shift and for the integrated intensity at small anisotropy as well as an explicit formula connecting the linewidth with the anisotropy parameter in the high-temperature limit.     

Evidence for oxygen abstraction from NO<Subscript>2</Subscript> upon thermal scattering from an Al(111) surface

Evidence is presented for the existence of a non-adiabatic reaction channel, namely the abstraction of an oxygen atom from a nitrogen dioxide molecule upon scattering from an aluminium(111) surface. This reaction channel was studied by exposing the sample to an NO₂ molecular beam and subsequently analysing the scattered flux using REMPI spectroscopy. In these experiments, a considerable amount of NO emitted from the surface was detected. The emitted NO has a rotational temperature of ca. 260 K that increases only slowly with surface temperature. In summary, these results provide first evidence for the abstraction reaction NO_2(g)NO_(g)+O_(a) upon NO₂/Al(111) scattering, which may arise when two electrons are rapidly transferred to the incoming molecule while it is unfavourably oriented for concurrent adsorption of both fragments. PACS 82.65.+r; 68.43.-h     

Microfibrillated cellulose foams obtained by a straightforward freeze–thawing–drying procedure

Microfibrillated cellulose (MFC) is continuously gaining attention due to its outstanding mechanical properties, in particular high strength-to-weight ratio. Recently, more and more studies target the production of porous materials, such as foams, out of this natural resource. Commonly, an energy-consuming freeze–drying method is utilized for producing pure MFC porous structures from water-based suspensions, which renders these products particularly unattractive for industry. Although alternatives for foam production have been proposed, using either modified MFC or with various additives, the freeze–drying step is still one of the most critical bottle-neck of MFC foam production upscaling. A novel straightforward freeze–thawing–drying procedure assisted by the common additive urea was herein proposed. Such method allows the production of mechanically stable, lightweight MFC structures under low-cost ambient conditions drying. The influence of the cellulose fibril characteristics, the suspension formulation and the process parameters on the final foam properties have been studied in terms of porosity, density and mechanical properties.