Packing Returning Secretaries

We study online secretary problems with returns in combinatorial packing domains with $n$ candidates that arrive sequentially over time in random order. The goal is to accept a feasible packing of candidates of maximum total value. In the first variant, each candidate arrives exactly twice. All $2n$ arrivals occur in random order. We propose a simple 0.5-competitive algorithm that can be combined with arbitrary approximation algorithms for the packing domain, even when the total value of candidates is a subadditive function. For bipartite matching, we obtain an algorithm with competitive ratio at least $0.5721 - o(1)$ for growing $n$, and an algorithm with ratio at least $0.5459$ for all $n \ge 1$. We extend all algorithms and ratios to $k \ge 2$ arrivals per candidate. In the second variant, there is a pool of undecided candidates. In each round, a random candidate from the pool arrives. Upon arrival a candidate can be either decided (accept/reject) or postponed (returned into the pool). We mainly focus on minimizing the expected number of postponements when computing an optimal solution. An expected number of $\Theta(n \log n)$ is always sufficient. For matroids, we show that the expected number can be reduced to $O(r \log (n/r))$, where $r \le n/2$ is the minimum of the ranks of matroid and dual matroid. For bipartite matching, we show a bound of $O(r \log n)$, where $r$ is the size of the optimum matching. For general packing, we show a lower bound of $\Omega(n \log \log n)$, even when the size of the optimum is $r = \Theta(\log n)$.Comment: 23 pages, 5 figure

To relate surface properties and surface elemental composition - Application of XPS in soil science

Soil particles always are coated by thin layers (nm to µm) of predominantly organic compounds that form the interface between particle and pore space and govern soil functioning (e.g. liquid transport, sorption, respiration). Chemical modification of the surface layer can change surface properties such as wettability (quantified in terms of contact angle CA) with implications for e.g. liquid distribution and sorption capacity. This points to the importance to specifically analyze the coating's chemical composition in order to better understand soil functioning. The shallow analysis depth (max. 10 nm) indicates X ray photoelectron spectroscopy (XPS) as a suitable tool. Here, all elements with Z ≥ 3 will be identified by the binding energy of the photoelectrons emitted after irradiation of the surface by X rays. In sensu stricto only applicable to flat and smooth surfaces our results so far prove applicability of XPS as well to rough surfaces such as soil particles. For XPS no sample pre-treatment is needed, i.e. the surfaces analyzed are those governing e.g. CA and sorption. The relation between surface elemental composition and CA could be demonstrated within a soil chronosequence where the changes of surface element contents due to an increasing coating of the particles by organic compounds and microorganisms were correlated to increasing CA. The surface O/C ratio could be identified as a general parameter linking surface chemical composition and CA for a wide range of different materials including hydrophobized glass slides while the amount of non-polar C species was indicated to define CA. Artificially induced modifications of surface properties became visible by changes in the surface elemental composition. Gentle crushing of soil microaggregates (SMA) resulted in slightly increased N contents hinting on a preferred location of N compounds within SMA. Exposition to HCl gas to decrease soil pH or cleaning of quartz sand by HCl treatment resulted in addition of Cl and removal of Fe, respectively. However, due to its high surface sensitivity XPS measures the presence of C species on all surfaces exposed to the environment (adventitious carbon AC). AC was found to complicate the verification of sorption of small amounts of organic acids to montmorillonite, pointing on the necessity to estimate the influence of AC in certain cases. On the other hand, detection of AC indicates AC as a factor to be considered when discussing surface properties

Observation of Nonspreading Wave Packets in an Imaginary Potential

We propose and experimentally demonstrate a method to prepare a nonspreading atomic wave packet. Our technique relies on a spatially modulated absorption constantly chiseling away from an initially broad de Broglie wave. The resulting contraction is balanced by dispersion due to Heisenberg's uncertainty principle. This quantum evolution results in the formation of a nonspreading wave packet of Gaussian form with a spatially quadratic phase. Experimentally, we confirm these predictions by observing the evolution of the momentum distribution. Moreover, by employing interferometric techniques, we measure the predicted quadratic phase across the wave packet. Nonspreading wave packets of this kind also exist in two space dimensions and we can control their amplitude and phase using optical elements.Comment: 4 figure

Анализ современных технологий заводнения при разработке нефтяных месторождений

Объектом исследования являются системы заводнения применяемые на месторождениях России Цель работы – анализ современных технологий заводнения при разработке нефтяных месторождений, а также обоснование применения технологий заводнения с целью увеличения темпов отбора, коэффициента нефтеизвлечения, технико-экономических показателей. В выпускной квалификационной работе приведены сведения о современных технологиях заводнения, применяемых на месторождениях России. Проведены расчеты экономической эффективности при внедрении нестационарного метода заводнения. Проанализирован процесс работы методов заводнения в условиях месторождений России. Бакалаврская работа выполнена в текстовом редакторе Microsoft Word, и Microsoft Excel.The object of the study are the waterflooding systems used in the fields of Russia The aim of the work is the analysis of modern flooding technologies in the development of oil fields, as well as the rationale for using flooding technologies to increase the rate of selection, the oil recovery factor, and the technical and economic indicators. In the final qualification work information on modern water flooding technologies used in the fields of Russia is given. Calculations of economic efficiency are implemented in the introduction of the non-stationary flooding method. The process of work of flooding methods in the conditions of Russian deposits is analyzed. Bachelor's work is executed in the text editor Microsoft Word, and Microsoft Excel

Einfluss von atmosphärischer Deposition auf das räumliche Muster von Benetzungshemmungen in Ober- und Unterböden eines grundwasserfernen Buchenwaldbestands

Der verstärkte Stofftransport mit dem Stammabfluss begünstigt die Versauerung des Bodens in unmittelbarer Nähe zu Bäumen. Veränderungen chemischer Bodenparameter wie pH-Wert oder C/N Verhältnis können dabei einen Einfluss auf die Benetzbarkeit des Bodens haben. Das Ziel dieser Studie war zu untersuchen, ob sich der Stammabstand auf die Benetzbarkeit (gemessen als Kontaktwinkel, KW) und die chemischen Parameter von Ober- und Unterböden entlang zweier Transekte (Länge ca. 50 m, Probenahmetiefe 0.1-0.2 m) auswirkt. Die Untersuchungsfläche ist ein 100 Jahre alter Buchenbestand (Fagus sylvatica L.), Bodentyp ist eine gut drainierte podsolierte Braunerde. Die Transekte hatten einen mittleren Abstand von etwa 50 m zueinander, Probenahmezeitpunkte waren Juli 2013 und Juli 2015, beprobt wurde im Abstand von 1 m. Drei kürzere Transekte (Länge 3 m) wurden zusätzlich im Juni 2013 deutlich tiefer beprobt (6 Tiefen zwischen 0.1-2 m). Die Datenauswertung mit statistischen Standardverfahren ergab keine signifikante Beziehung zwischen Stammabstand und Benetzbarkeit oder chemischen Parametern. Spektralanalytische Analysen zeigten jedoch, dass der Stammabstand bei beiden Transekten oberflächennah einen starken Einfluss sowohl auf chemische Parameter (oxalatlösliches Al, pH) als auch auf den KW in Form einer periodischen Schwingung hat (2013: mittlerer KW=40°±12°; 2015: mittlerer KW=110°±14°). Bei den kürzeren (und tiefer beprobten) 3 m-Transekten war der KW direkt am Baum i.d.R < 90°, und zeigte keine deutliche Abhängigkeit zum Stammabstand mehr. Daraus lässt sich schließen, dass der Stammabfluss nur relativ oberflächennah einen Einfluss auf die Benetzbarkeit hat. Analysen der chemischen Oberflächenstruktur der Bodenpartikel mittels Röntgenphotoelektronenspektroskopie (XPS) zeigten dabei einen klaren Zusammenhang zwischen chemischer Veränderung der Partikeloberflächen und Benetzbarkeit, etwa durch Korrelation von elementarem O/C-Verhältnis und KW (r2=0.78), dem Anteil nicht-polarer Kohlenstoffspezies und KW (r2=0.77). Ebenso gab es einen Zusammenhang zwischen Alo-Gehalt und KW (r2=0.87). Für das C/N-Verhältnis und sulfat- oder oxalatlösliches Fe gab es keine entsprechenden Zusammenhänge. Die Ergebnisse weisen auf einen engen Zusammenhang zwischen chemischen und zentralen physikalischen Parametern wie Benetzungshemmung hin und haben damit einen Einfluss auf physikalische Standorteigenschaftenwie die Wasserspeicherleistung von Waldböden

Colossal topological Hall effect at the transition between isolated and lattice-phase interfacial skyrmions

The topological Hall effect is used extensively to study chiral spin textures in various materials. However, the factors controlling its magnitude in technologically-relevant thin films remain uncertain. Using variable-temperature magnetotransport and real-space magnetic imaging in a series of Ir/Fe/Co/Pt heterostructures, here we report that the chiral spin fluctuations at the phase boundary between isolated skyrmions and a disordered skyrmion lattice result in a power-law enhancement of the topological Hall resistivity by up to three orders of magnitude. Our work reveals the dominant role of skyrmion stability and configuration in determining the magnitude of the topological Hall effect

Silica material variation for the Mn_xO_y-Na₂WO₄/SiO₂

The oxidative coupling of methane (OCM) is one of the best methods for the direct conversion of methane.Among the known OCM catalysts, MnxOy-Na2WO4/SiO2 is a promising candidate for an industrial appli-cation, showing a high methane conversion and C2 selectivity, with a good stability during long-termcatalytic activity tests. In the present study, some results have been already published and discussedbriefly in our previous short communication. However, we herein investigated comprehensively theinfluence of various silica support materials on the performance of the MnxOy-Na2WO4/SiO2 systemin the OCM by means of ex situ and in situ XRD, BET, SEM and TEM characterization methods andshowed new results to reveal possible support effects on the catalyst. The catalytic performance of most MnxOy-Na2WO4/SiO2 catalysts supported by different silica support materials did not differ substan-tially. However, the performance of the SBA-15 supported catalyst was outstanding and the methaneconversion was nearly twofold higher in comparison to the other silica supported catalysts at similar C2 selectivity as shown before in the communication. The reason of this substantial increase in performancecould be the ordered mesoporous structure of the SBA-15 support material, homogeneous dispersion ofactive components and high number of active sites responsible for the OCM

Shift towards pro-inflammatory intestinal bacteria aggravates acute murine colitis via Toll-like receptors 2 and 4.

BACKGROUND: Gut bacteria trigger colitis in animal models and are suspected to aggravate inflammatory bowel diseases. We have recently reported that Escherichia coli accumulates in murine ileitis and exacerbates small intestinal inflammation via Toll-like receptor (TLR) signaling. METHODOLOGY AND PRINCIPAL FINDINGS: Because knowledge on shifts in the intestinal microflora during colitis is limited, we performed a global survey of the colon flora of C57BL/10 wild-type (wt), TLR2(-/-), TLR4(-/-), and TLR2/4(-/-) mice treated for seven days with 3.5% dextrane-sulfate-sodium (DSS). As compared to wt animals, TLR2(-/-), TLR4(-/-), and TLR2/4(-/-) mice displayed reduced macroscopic signs of acute colitis and the amelioration of inflammation was associated with reduced IFN-gamma levels in mesenteric lymph nodes, lower amounts of neutrophils, and less FOXP3-positive T-cells in the colon in situ. During acute colitis E. coli increased in wt and TLR-deficient mice (P<0.05), but the final numbers reached were significantly lower in TLR2(-/-), TLR4(-/-) and TLR2/4(-/-) animals, as compared to wt controls (P<0.01). Concentrations of Bacteroides/ Prevotella spp., and enterococci did not increase during colitis, but their numbers were significantly reduced in the colon of DSS-treated TLR2/4(-/-) animals (P<0.01). Numbers of lactobacilli and clostridia remained unaffected by colitis, irrespective of the TLR-genotype of mice. Culture-independent molecular analyses confirmed the microflora shifts towards enterobacteria during colitis and showed that the gut flora composition was similar in both, healthy wt and TLR-deficient animals. CONCLUSIONS AND SIGNIFICANCE: DSS-induced colitis is characterized by a shift in the intestinal microflora towards pro-inflammatory Gram-negative bacteria. Bacterial products exacerbate acute inflammation via TLR2- and TLR4-signaling and direct the recruitment of neutrophils and regulatory T-cells to intestinal sites. E. coli may serve as a biomarker for colitis severity and DSS-induced barrier damage seems to be a valuable model to further identify bacterial factors involved in maintaining intestinal homeostasis and to test therapeutic interventions based upon anti-TLR strategies

Dyscalculia from a developmental and differential perspective

Developmental dyscalculia (DD) and its treatment are receiving increasing research attention. A PsychInfo search for peer-reviewed articles with dyscalculia as a title word reveals 31 papers published from 1991–2001, versus 74 papers published from 2002–2012. Still, these small counts reflect the paucity of research on DD compared to dyslexia, despite the prevalence of mathematical difficulties. In the UK, 22% of adults have mathematical difficulties sufficient to impose severe practical and occupational restrictions (Bynner and Parsons, 1997; National Center for Education Statistics, 2011). It is unlikely that all of these individuals with mathematical difficulties have DD, but criteria for defining and diagnosing dyscalculia remain ambiguous (Mazzocco and Myers, 2003). What is treated as DD in one study may be conceptualized as another form of mathematical impairment in another study. Furthermore, DD is frequently—but, we believe, mistakenly- considered a largely homogeneous disorder. Here we advocate a differential and developmental perspective on DD focused on identifying behavioral, cognitive, and neural sources of individual differences that contribute to our understanding of what DD is and what it is not