Stvaranje ultrafino zrnate (UFZ) strukture i mehanička svojstva sa intenzivnom plastičnom deformacijom (IPD)

Commercial pure cooper (99,9% Cu) was deformed by equal channel angular pressing (ECAP) using up to 10 passes, route C. The evolution of microstructure and fracture character were observed by OM, SEM and TEM. The mean grain size decreased with increasing deformation, after 10 passes to 100 – 300 nm. TEM analysis suggested the possible nanostructure formation mechanism by the formation of cellular structure in grains, forming of subgrains and then forming of high angle nanograins with random orientation. Fractures of ECAP Cu material after 10 passes had transcrystalline ductile character with dimple morphology.Trgovački čisti bakar (99,9%) deformiran je kanalnim kutnim prešanjem (KKP) do 10 provlaka-putanje. C. Razvitak mikrostrukture i karakter loma praćeno je sa OM, SEM i TEM. Veličina zrna se smanjuje povećanjem deformacije poslije 10 provlaka na 100-300 nm. TEM analiza ukazuje mogućnost nastajanja mehanizma nanostrukture stvaranjem celularne strukture u zrnima, nastanak subzrna i zatim obrazovanje nanozrna pod visokim kutem sa slučajnom orjentacijom. Lomovi KKP Cu materijala poslije 10 provlaka imali su transkristalni duktilni karakter sa jamičastom morfologijom

Hitting all Maximal Independent Sets of a Bipartite Graph

We prove that given a bipartite graph G with vertex set V and an integer k, deciding whether there exists a subset of V of size k hitting all maximal independent sets of G is complete for the class Sigma_2^P.Comment: v3: minor chang

List coloring in the absence of a linear forest.

The k-Coloring problem is to decide whether a graph can be colored with at most k colors such that no two adjacent vertices receive the same color. The Listk-Coloring problem requires in addition that every vertex u must receive a color from some given set L(u)⊆{1,…,k}. Let Pn denote the path on n vertices, and G+H and rH the disjoint union of two graphs G and H and r copies of H, respectively. For any two fixed integers k and r, we show that Listk-Coloring can be solved in polynomial time for graphs with no induced rP1+P5, hereby extending the result of Hoàng, Kamiński, Lozin, Sawada and Shu for graphs with no induced P5. Our result is tight; we prove that for any graph H that is a supergraph of P1+P5 with at least 5 edges, already List 5-Coloring is NP-complete for graphs with no induced H

Utjecaj uvjeta zagrijavanja i hlađenja na strukturu i mehanička svojstva C-Mn-Si čelika

The paper deals with structure and properties development of AHSS (advance high-strength steel) and UHSS (ultra high-strength steel) steel grades for various groups of automotive parts. C-Mn-Si type steel properties are evaluated based on the results of laboratory controlled rolling and cooling. The important influence on mechanical and plastic properties, amount of residual austenite (RA) and final structural type has, except for cooling rate, also starting temperature of intensive cooling (TIC) which follows after hot plastic deformations. If TIC is from interval of 620-760°C the final structure predominantly consists of ferrite with RA. Mostly acicular ferrite with RA, as well as bainite with RA was obtained when TIC was kept in the range of 760-850°C.Utjecaj uvjeta zagrijavanja i hlađenja na strukturu i mehanička svojstva C-Mn-Si čelika. Članak daje razvitak strukture i svojstava NVČČ (napredno visoko čvrstih čelika) i UVČČ (ultra visoko čvrsti čelici) za raznolike skupine dijelova automobila. Svojstva čelika C-Mn-Si su utvrđena na temelju laboratorijskog kontroliranog valjanja i hlađenja. Najveći utjecaj na mehanička i plastična svojstva uz zaostali austenit (ZA) i završni tip strukture, ima osim brzine hlađenja i početna temperatura intenzivnog hlađenja (Tpo) koja je nastavak vruće plastične deformacije. Ako je Tpo u intervalu 620-760°C, završna struktura se sastoji od ferita sa ZA. Pretežito acikularni ferit sa ZA, također bainit sa ZA je uočen kad je Tpo bila u intervalu 760-850°C

The nonperturbative functional renormalization group and its applications

The renormalization group plays an essential role in many areas of physics, both conceptually and as a practical tool to determine the long-distance low-energy properties of many systems on the one hand and on the other hand search for viable ultraviolet completions in fundamental physics. It provides us with a natural framework to study theoretical models where degrees of freedom are correlated over long distances and that may exhibit very distinct behavior on different energy scales. The nonperturbative functional renormalization-group (FRG) approach is a modern implementation of Wilson's RG, which allows one to set up nonperturbative approximation schemes that go beyond the standard perturbative RG approaches. The FRG is based on an exact functional flow equation of a coarse-grained effective action (or Gibbs free energy in the language of statistical mechanics). We review the main approximation schemes that are commonly used to solve this flow equation and discuss applications in equilibrium and out-of-equilibrium statistical physics, quantum many-particle systems, high-energy physics and quantum gravity.Comment: v2) Review article, 93 pages + bibliography, 35 figure

A new characterization of P6-free graphs.

We study P 6-free graphs, i.e., graphs that do not contain an induced path on six vertices. Our main result is a new characterization of this graph class: a graph G is P 6-free if and only if each connected induced subgraph of G on more than one vertex contains a dominating induced cycle on six vertices or a dominating (not necessarily induced) complete bipartite subgraph. This characterization is minimal in the sense that there exists an infinite family of P 6-free graphs for which a smallest connected dominating subgraph is a (not induced) complete bipartite graph. Our characterization of P 6-free graphs strengthens results of Liu and Zhou, and of Liu, Peng and Zhao. Our proof has the extra advantage of being constructive: we present an algorithm that finds such a dominating subgraph of a connected P 6-free graph in polynomial time. This enables us to solve the Hypergraph 2-Colorability problem in polynomial time for the class of hypergraphs with P 6-free incidence graphs