Submonolayer growth with decorated island edges

We study the dynamics of island nucleation in the presence of adsorbates using kinetic Monte Carlo simulations of a two-species growth model. Adatoms (A-atoms) and impurities (B-atoms) are codeposited, diffuse and aggregate subject to attractive AA- and AB-interactions. Activated exchange of adatoms with impurities is identified as the key process to maintain decoration of island edges by impurities during growth. While the presence of impurities strongly increases the island density, a change in the scaling of island density with flux, predicted by a rate equation theory for attachment-limited growth [D. Kandel, Phys. Rev. Lett. 78, 499 (1997)], is not observed. We argue that, within the present model, even completely covered island edges do not provide efficient barriers to attachment.Comment: 7 pages, 2 postscript figure

Micromechanical Analysis of Cement Paste with Carbon Nanotubes

Carbon nanotubes (CNT) are an attractive reinforcement material for several composites, due to their inherently high strength and high modulus of elasticity. There are controversial results for cement paste with admixed CNT up to 500 µm in length. Some results show an increase in flexural or compressive strength, while others showing a decrease in the values. Our experiments produced results that showed a small increase in fracture energy and tensile strength. Micromechanical simulations on a CNT-reinforced cement paste 50×50 µm proved that CNT clustering is the crucial factor for an increasein fracture energy and for an improvement in tensile strength

SIZE EFFECT ON THE ULTIMATE DRYING SHRINKAGE OF CEMENT MORTAR: 1-YEAR EXPERIMENT AND NUMERICAL MODELING

The magnitude and time evolution of shrinkage are influenced by numerous factors which are implemented in the design codes often in a different way. The time-dependent behavior of concrete in structures sensitive to creep and shrinkage should be verified by means of short-term laboratory measurements. Extrapolation of drying shrinkage from short-term measurements is an illposed problem. The process is extremely slow but can be accelerated by reducing the specimen size. The knowledge of the size-effect on drying shrinkage is a necessity to establish the transition from the laboratory to the structural size. In the literature, the experimental data on such size-effect are insufficient. For this reason a new experiment was developed to study this phenomenon on small-scale specimens made of cement mortar and the results from the first year are summarized in this paper. The measured data are validated by coupled FEM hygro-mechanical simulations

Determination of step--edge barriers to interlayer transport from surface morphology during the initial stages of homoepitaxial growth

We use analytic formulae obtained from a simple model of crystal growth by molecular--beam epitaxy to determine step--edge barriers to interlayer transport. The method is based on information about the surface morphology at the onset of nucleation on top of first--layer islands in the submonolayer coverage regime of homoepitaxial growth. The formulae are tested using kinetic Monte Carlo simulations of a solid--on--solid model and applied to estimate step--edge barriers from scanning--tunneling microscopy data on initial stages of Fe(001), Pt(111), and Ag(111) homoepitaxy.Comment: 4 pages, a Postscript file, uuencoded and compressed. Physical Review B, Rapid Communications, in press

Analytical solution of generalized Burton--Cabrera--Frank equations for growth and post--growth equilibration on vicinal surfaces

We investigate growth on vicinal surfaces by molecular beam epitaxy making use of a generalized Burton--Cabrera--Frank model. Our primary aim is to propose and implement a novel analytical program based on a perturbative solution of the non--linear equations describing the coupled adatom and dimer kinetics. These equations are considered as originating from a fully microscopic description that allows the step boundary conditions to be directly formulated in terms of the sticking coefficients at each step. As an example, we study the importance of diffusion barriers for adatoms hopping down descending steps (Schwoebel effect) during growth and post-growth equilibration of the surface.Comment: 16 pages, REVTeX 3.0, IC-DDV-94-00

Modular Document Supply System

Článek projednává o modulárním Document Delivery systému vyvíjeném v STK. Vývoj byl podpořen projekty LI200028 (VPK) a LI01018 (portál STM). Tento systém staví na zkušenostech získaných vývojem a provozem Virtuální polytechnické knihovny. Je implementován v jazyce Java, z důvodů snadné přenositelnosti. Systém neobsahuje katalog dokumentů, požadovaný dokument musí být vyhledán mimo tento systém a je možné předat metadata o vyhledaném dokumentu a jeho umístění v OpenURL adrese při zadání objednávky. Účastnící sytému musí být registrování a mají v systému svůj finanční účet. Objednávku na digitalizaci dokumentu a zprostředkování výtisku kopie si zadává účastník systému samoobslužně web browserem. Objednávka je uložena v databázi čekajících objednávek, a periodicky dotazována digitalizačními místy. Pro toto je digitalizační pracoviště vybaveno zvláštním komunikačním a digitalizačním programem. Digitalizační pracoviště dokument zdigitalizuje a uloží do souboru .pdf a předá zpět do databáze. Tento soubor .pdf je určený pouze k tisku a je chráněn proti změně. Uživatel si ho stáhne ze své www stránky chráněné heslem a vytiskne na své lokální tiskárně. Současně s těmito procesy probíhá účtování ceny zakázky, která je odečtena z konta uživatele a přičtena na konto knihovny, která pořídila kopii dokumentu. Systém se nazývá modulární, protože umožňuje komunikaci s jiným instalacemi téhož systému a tak předávat objednávky do jiných knihoven vybavených tímto systémem (obdoba požadavku MVS). Objednávky a data se předávají pomocí standardizovaných XML souborů. Cílem je dosáhnout kompatibility i mezi heterogenními systémy DDS