Pressure Valves in Pneumatics

Import 05/08/2014Úkolem této práce je vypracovat přehled prvků pro řízení tlaku vzduchu, popis jejich konstrukce a charakteristiky. Následuje přehled aplikací a zapojení tlakových ventilů v pneumatických obvodech. Praktickou část práce tvoří návrh experimentu a provedení měření obvodu, ve kterém redukční ventil slouží jako prvek pro úsporu stlačeného vzduchu. Všechny dosažené výsledky v měření úspory vzduchu jsou nadále zpracovány a vyhodnoceny tak, že porovnáváme spotřebu vzduchu na pneumatickém obvodu bez redukčního ventilu a s redukčním ventilem nastaveným na dvě různé hodnoty tlaku.The goal of this work is to develop a set of elements for controlling air pressure, a description of their structure and characteristics. The following is a list of applications and the involvement of pressure valves in pneumatic circuits. The practical part consists of experimental design and the measurement circuit, in which a pressure reducing valve is used as an element for saving the compressed air. All the results obtained in the measurement of air savings are still processed and evaluated by comparing the consumption of air to the pneumatic circuit without reducing valve and pressure reducing valve set at two different pressure levels.338 - Katedra hydromechaniky a hydraulických zařízenívýborn

Elusive extremal graphs

We study the uniqueness of optimal solutions to extremal graph theory problems. Lovasz conjectured that every finite feasible set of subgraph density constraints can be extended further by a finite set of density constraints so that the resulting set is satisfied by an asymptotically unique graph. This statement is often referred to as saying that `every extremal graph theory problem has a finitely forcible optimum'. We present a counterexample to the conjecture. Our techniques also extend to a more general setting involving other types of constraints

A superlinear bound on the number of perfect matchings in cubic bridgeless graphs

Lovasz and Plummer conjectured in the 1970's that cubic bridgeless graphs have exponentially many perfect matchings. This conjecture has been verified for bipartite graphs by Voorhoeve in 1979, and for planar graphs by Chudnovsky and Seymour in 2008, but in general only linear bounds are known. In this paper, we provide the first superlinear bound in the general case.Comment: 54 pages v2: a short (missing) proof of Lemma 10 was adde

The step Sidorenko property and non-norming edge-transitive graphs

Sidorenko's Conjecture asserts that every bipartite graph H has the Sidorenko property, i.e., a quasirandom graph minimizes the density of H among all graphs with the same edge density. We study a stronger property, which requires that a quasirandom multipartite graph minimizes the density of H among all graphs with the same edge densities between its parts; this property is called the step Sidorenko property. We show that many bipartite graphs fail to have the step Sidorenko property and use our results to show the existence of a bipartite edge-transitive graph that is not weakly norming; this answers a question of Hatami [Israel J. Math. 175 (2010), 125-150].Comment: Minor correction on page

Quasirandom forcing orientations of cycles

An oriented graph $H$ is quasirandom-forcing if the limit (homomorphic) density of $H$ in a sequence of tournaments is $2^{-\|H\|}$ if and only if the sequence is quasirandom. We study generalizations of the following result: the cyclic orientation of a cycle of length $\ell$ is quasirandom-forcing if and only if $\ell\equiv 2$ mod $4$. We show that no orientation of an odd cycle is quasirandom-forcing. In the case of even cycles, we find sufficient conditions on an orientation to be quasirandom-forcing, which we complement by identifying necessary conditions. Using our general results and spectral techniques used to obtain them, we classify which orientations of cycles of length up to $10$ are quasirandom-forcing