Coloring intersection graphs of arc-connected sets in the plane

A family of sets in the plane is simple if the intersection of its any subfamily is arc-connected, and it is pierced by a line $L$ if the intersection of its any member with $L$ is a nonempty segment. It is proved that the intersection graphs of simple families of compact arc-connected sets in the plane pierced by a common line have chromatic number bounded by a function of their clique number.Comment: Minor changes + some additional references not included in the journal versio

Mechanism of anchoring proteins on the cell envelope

Surface proteins, essential structural components of bacterial cell wall, are synthesized as precursors equipped with specific functional domains. The N-terminal signal module enables translocation across the plasma membrane via Sec or Tat pathways, while sorting motif, located in the C-terminus, is responsible for protein attachment to the cell wall peptidoglycan. Only exception are lipoproteins which lipoylated cysteinyl residue connected with bacterial membrane is in N-terminal part of protein. Most of surface proteins, as surface (S-) layer proteins, internalins or autolysins, are linked to the different structures of cell wall through non covalent forces. From the other hand, molecules with LPXTG motif, which attachment involves sortase activity, are linked to the peptidoglycan by covalent bond. Due to structural, chemical and physicochemical properties, surface proteins are attractive components of diverse industrial or medical systems. Knowledge about mechanism of anchoring proteins to the cell envelope will open new possibility of their applications

Effect of changes in soil moisture on agriculture soils: response of microbial community, enzymatic and physiological diversity

Global warming-induced drought stress and the duration of changes in soil moisture content may reshape or complicate these ecological relations. Biological activity could be affected severely by the impact of drought on agricultural ecosystems. In this study, 4 agricultural different soils were collected, and analyzed at each time gradient (0, 1, 2, 4, 8th week) to determine the physicochemical parameters, microbial abundance, enzyme activities (dehydrogenases (DH), phosphatases (acid ACP and alkaline ALP) and urease (UR)), and physiological diversity. We found that soil physicochemical properties fluctuated within the time gradient in all sites, but significantly decreased in total organic carbon, available phosphorus (P2O5 Olsena), nitrate (NO3-), ammonium (NH4+) (except for S site) and calcium carbonate (CaCO3) content (except for L site). Overall, ALP activity was higher compared to ACP activity. The DH activity was highest at sampling day (high moisture content) in G and N sites, and at 2nd week for L and S sites, but significantly decreased at the end of the experiment. The UR activity decreased significantly in G, L and N sites but increased in S site at the end of our experiment compared to the sampling day. Overall, the physiological diversity of the microbial community was strongly affected by water stress in the utilization of carbohydrates, carboxylic and acetic acids, amino acids, polymers, and amines, in all sites. Our findings highlighted that the short-term duration of drought stress had a significant influence on soil biological activity. This may improve the understanding of impact of soil moisture changes on soil nutrient cycling and biological activities in agricultural ecosystems

Tree-width and dimension

Over the last 30 years, researchers have investigated connections between dimension for posets and planarity for graphs. Here we extend this line of research to the structural graph theory parameter tree-width by proving that the dimension of a finite poset is bounded in terms of its height and the tree-width of its cover graph.Comment: Updates on solutions of problems and on bibliograph

Effect of a skin-deep surface zone on formation of two-dimensional electron gas at a semiconductor surface

Two dimensional electron gases (2DEGs) at surfaces and interfaces of semiconductors are described straightforwardly with a 1D self-consistent Poisson-Schr\"{o}dinger scheme. However, their band energies have not been modeled correctly in this way. Using angle-resolved photoelectron spectroscopy we study the band structures of 2DEGs formed at sulfur-passivated surfaces of InAs(001) as a model system. Electronic properties of these surfaces are tuned by changing the S coverage, while keeping a high-quality interface, free of defects and with a constant doping density. In contrast to earlier studies we show that the Poisson-Schr\"{o}dinger scheme predicts the 2DEG bands energies correctly but it is indispensable to take into account the existence of the physical surface. The surface substantially influences the band energies beyond simple electrostatics, by setting nontrivial boundary conditions for 2DEG wavefunctions.Comment: 9 pages, 7 figures, 2 table

Triangle-free geometric intersection graphs with large chromatic number

Several classical constructions illustrate the fact that the chromatic number of a graph can be arbitrarily large compared to its clique number. However, until very recently, no such construction was known for intersection graphs of geometric objects in the plane. We provide a general construction that for any arc-connected compact set $X$ in $\mathbb{R}^2$ that is not an axis-aligned rectangle and for any positive integer $k$ produces a family $\mathcal{F}$ of sets, each obtained by an independent horizontal and vertical scaling and translation of $X$, such that no three sets in $\mathcal{F}$ pairwise intersect and $\chi(\mathcal{F})>k$. This provides a negative answer to a question of Gyarfas and Lehel for L-shapes. With extra conditions, we also show how to construct a triangle-free family of homothetic (uniformly scaled) copies of a set with arbitrarily large chromatic number. This applies to many common shapes, like circles, square boundaries, and equilateral L-shapes. Additionally, we reveal a surprising connection between coloring geometric objects in the plane and on-line coloring of intervals on the line.Comment: Small corrections, bibliography updat

Cliquewidth and dimension

We prove that every poset with bounded cliquewidth and with sufficiently large dimension contains the standard example of dimension $k$ as a subposet. This applies in particular to posets whose cover graphs have bounded treewidth, as the cliquewidth of a poset is bounded in terms of the treewidth of the cover graph. For the latter posets, we prove a stronger statement: every such poset with sufficiently large dimension contains the Kelly example of dimension $k$ as a subposet. Using this result, we obtain a full characterization of the minor-closed graph classes $\mathcal{C}$ such that posets with cover graphs in $\mathcal{C}$ have bounded dimension: they are exactly the classes excluding the cover graph of some Kelly example. Finally, we consider a variant of poset dimension called Boolean dimension, and we prove that posets with bounded cliquewidth have bounded Boolean dimension. The proofs rely on Colcombet's deterministic version of Simon's factorization theorem, which is a fundamental tool in formal language and automata theory, and which we believe deserves a wider recognition in structural and algorithmic graph theory

Selection of Thermotolerant Corynebacterium glutamicum Strains for Organic Acid Biosynthesis

U novije se vrijeme sojevi bakterije Corynebacterium glutamicum koriste kao proizvođači mnogih vrijednih kemijskih spojeva, među kojima su najznačajnije organske kiseline, poput L-mliječne i sukcinske kiseline. Poznato je da divlji tip bakterije C. glutamicum uspješno raste pri temperaturama od 25 do 37 °C. Pri temperaturama višim od 40 °C porast biomase obično naglo prestaje, no bakterija ostaje metabolički aktivna. Visoke temperature utječu na metaboličku aktivnost stanica bakterije C. glutamicum i uzrokuju promjene u sastavu i količini produkata fermentacije. Stoga smo u nizu selektivnih koraka iz kulture auksotrofa C. glutamicum ATCC 13287 koji raste na podlozi što sadržava homoserin sintetizirali prototrof, koji može rasti i pri 44 °C. Tijekom selekcije upotrijebljene su kompleksne i mineralne podloge s dodatkom jantarne i limunske kiselinu. Dobiveno je 47 klonova koji mogu rasti pri povišenim temperaturama, a optimalna je temperatura rasta bila 40 °C ili više. U uvjetima nedostatka kisika sojevi bakterije C. glutamicum proizvode organske kiseline, i to najviše L-mliječne kiseline, bez obzira na ispitani klon. Njezina je koncentracija bila najveća u kulturi uzgojenoj pri 44 °C. Povišene temperature također utjecale su i na biosintezu drugih organskih kiselina. U usporedbi s roditeljskim sojem, u kulturama termotolerantnih sojeva koncentracija se octene kiseline povećala, a jantarne smanjila. Soj RCG44.3 imao je zanimljiva svojstva: proizveo je 27,1 g/L L-mliječne kiseline, uz prinos od 0,57 g/g tijekom 24 h pri 44 °C.In recent years, Corynebacterium glutamicum has been considered as producer of many valuable chemical compounds. Among them, organic acids such as l-lactic and succinic acids are the most important ones. It is known that the wild-type C. glutamicum grows well in the temperature range between 25 and 37 °C. Above 40 °C, the biomass growth usually abruptly stops; however, the bacteria remain metabolically active. High temperature affects the metabolic activity of C. glutamicum cells and can lead to changes in the composition and quantity of the fermentation products. Therefore, in a series of subsequent selection steps, we tried to obtain prototrophic strains capable of growing at 44 °C from the culture of homoserine auxotroph C. glutamicum ATCC 13287. During selection, we used complex and mineral media containing succinic and citric acids. As a result, we obtained 47 clones able to grow at elevated temperature. Moreover, the estimated optimal growth temperature for several of them was about 40 °C or higher. Under oxygen limitation conditions, C. glutamicum strains produce organic acids. Regardless of the tested clone, l-lactic acid was the main product. However, its concentration was the highest in the cultures performed at 44 °C. The elevated temperature also affected the biosynthesis of other organic acids. Compared to the parental strain, the concentration of acetic acid increased, and of succinic acid decreased in the cultures of thermotolerant strains. Strain RCG44.3 exhibited interesting properties; it was able to synthesise 27.1 g/L l-lactic acid, with production yield of 0.57 g/g, during 24 h of fermentation at 44 °C