34 research outputs found
Tilings of Rectangular Regions by Rectangular Tiles: Counts Derived from Transfer Matrices
Step by step completion of a left-to-right tiling of a rectangular floor with
tiles of a single shape starts from one edge of the floor, considers the
possible ways of inserting a tile at the leftmost uncovered square, passes
through a sequence of rugged shapes of the front line between covered and
uncovered regions of the floor, and finishes with a straight front line at the
opposite edge. We count the tilings by mapping the front shapes to nodes in a
digraph, then counting closed walks on that digraph with the transfer matrix
method.
Generating functions are detailed for tiles of shape 1 x 3, 1 x 4 and 2 x 3
and modestly wide floors. Equivalent results are shown for the 3-dimensional
analog of filling bricks of shape 1x 1 x 2, 1 x 1 x 3, 1 x 1 x 4, 1 x 2 x 2 or
1 x 2 x 3 into rectangular containers of small cross sections.Comment: 21 pages, 21 figure
Monomer-dimer tatami tilings of square regions
We prove that the number of monomer-dimer tilings of an square
grid, with monomers in which no four tiles meet at any point is
, when and have the same parity. In addition, we
present a new proof of the result that there are such tilings with
monomers, which divides the tilings into classes of size . The
sum of these tilings over all monomer counts has the closed form
and, curiously, this is equal to the sum of the squares of
all parts in all compositions of . We also describe two algorithms and a
Gray code ordering for generating the tilings with monomers,
which are both based on our new proof.Comment: Expanded conference proceedings: A. Erickson, M. Schurch, Enumerating
tatami mat arrangements of square grids, in: 22nd International Workshop on
Combinatorial Al- gorithms (IWOCA), volume 7056 of Lecture Notes in Computer
Science (LNCS), Springer Berlin / Heidelberg, 2011, p. 12 pages. More on
Tatami tilings at
http://alejandroerickson.com/joomla/tatami-blog/collected-resource
Structurally and magnetically complex materials: a magneto-caloric, a multiferroic skyrmion host and a ferrimagnetic semiconductor
The study of structural subtleties and complications in novel materials is often neglected and instead their physical functionality is investigated directly. When this is done however, details in the crystal structure can be missed which have significant consequences for the physical properties of the material. This thesis aims to prove this with the use of investigations of three separate inorganic systems which have very different atomic and magnetic structure, and therefore functionality, from each other. These investigations include the synthesis of polycrystalline and single crystal samples, followed by characterisation with the use of diffraction, magnetisation
and transport experiments, which are all introduced in Chapter 2. The most important concepts needed in the analysis of the collected data are explained in Chapter 3.
Chapter 4 re-examines the structure of incommensurate composite ferrimagnetic semiconductor Ba1âpCr2Se4âp, finding that a single crystal sample has a modulation vector of q = (0,0,0.24144) partly characterised by crenel occupational modulations, creating Se2â dimers. It also has large disorder in its sixfold channel which is modulated in its basal plane with q â (1/3,1/3,0), although chemical composition is found to vary greatly between samples. The magnetic structure has been determined to have P6/m symmetry with k = (0,0,0) with a total moment
of 0.413 ÎŒB/Cr3+. There is uniaxial negative thermal expansion along the c axis and a previously undiscovered structural transition at 135 K is observed. It is also determined that Ba1âpCr2Se4âp
is a p-type semiconductor with a high resistivity owed to hopping of the charge carriers but with very low thermal conductivity.
Chapter 5 aims to ascertain the cause of the phase coexistence in the lacunar spinel GaMo4Se8 below its Jahn-Teller transition. It is found that the strain of the dominant R3m phase is large and so is relieved by a partial distortion to the metastable Imm2 phase, which is determined to likely be insulating with charge-ordering of ions, in contrast to the R3m phase which is likely itinerant
and charge-disordered. Single domain crystals are grown, on which magnetisation measurements determine the critical behaviour at the Curie temperature, with critical exponents of ÎČ = 0.22(4), Îł = 1.19(1) and ÎŽ = 6.42(1) not belonging to any one universality class. Magnetoentropic mapping confirms the existence of at least three different non-collinear magnetic phases below the Curie temperature, including a NĂ©el-type skyrmion lattice.
Chapter 6 scrutinises the PbFCl-like structure and disorder of magneto-caloric candidate material MnZnSb. In some powder diffraction patterns, there are unusual, asymmetric peak shapes that are fit with a reduction of symmetry to a triclinic cell. In another sample, it is apparent that Rietveld refinements are greatly improved with the inclusion of a partially occupied, Zn containing interstitial site. In variable temperature data, the cell volume changes significantly at the near room temperature magnetic transition, which is identified as a big contributor to the large change in entropy there. It is also theorised that due to differences in diffraction data and results from magneto-caloric calculations, that samples first exist in a metastable triclinic state which then becomes the tetragonal state over time
Surface micro-discharge (SMD)
There is an urgent need for an efficient technology of disinfection and sterilization
in view of the alarming dimensions health care-associated infections (HAIs) have
reached. Cold atmospheric pressure plasma (CAP) can be utilized for hygienic and
medical purposes, in particular in surface decontamination applications, and provides
a promising alternative to the conventionally used sterilization techniques. Surface
Micro-Discharge (SMD) offers a technology for generating CAP that can be applied to
wide areas.
In the present work, I investigate the plasma chemistry involved in the inactivation
of microorganisms by application of the SMD in order to optimize the antimicrobial
effect. For this purpose, different strains of vegetative bacteria and bacterial
endospores are exposed to the SMD with experimental parameters such as the gas
composition, power input, treatment duration and humidity varied. At the same time,
the concentration of ozone produced by the SMD is monitored, and its correlation with
the antimicrobial efficacy is investigated.
I demonstrate that the bactericidal effect of the SMD on both the Gram-negative
Escherichia coli and Gram-positive Enterococcus mundtii is similar and strongly correlates
with the ozone concentration. The sporicidal effect on Geobacillus stearothermophilus
is crucially affected by the humidity, whereas the ozone concentration appears to have
no influence. In addition, I investigate the dynamic behavior of ozone produced by
the SMD by varying the geometry and the time interval for the plasma generation and
by igniting the plasma in two subsequent phases with different frequencies. Possible
explanations for the obtained results are provided.
This work fortifies the role of SMD as an efficient sterilization method and discloses
diverse possibilities for optimizing the antimicrobial effect.Die HĂ€ufigkeit der Krankenhausinfektionen und ihre Auswirkung haben alarmierende AusmaĂe angenommen. Angesichts dessen besteht ein akuter Bedarf an einer effizienten Technologie fĂŒr Desinfektion und Sterilisation. Die Anwendung von kaltem atmosphĂ€rischen Plasma (englisch: cold atmospheric plasma, CAP) fĂŒr die Hygiene und Medizin, insbesondere fĂŒr die OberflĂ€chendekon-tamination, stellt einen Versuch dar, eine schnelle und effektive Sterilisationstechnik zu schaffen.
Die OberflĂ€chenentladung (englisch: Surface Micro-Discharge, SMD) bietet eine Technologie fĂŒr die Erzeugung und Anwendung von CAP. In der vorliegenden Arbeit analysiere ich die antimikrobiellen Eigenschaften der SMD, um die Inaktivierungsmechnismen besser zu verstehen und den antimikrobiellen Effekt zu optimieren. Hierzu werden unterschiedliche StĂ€mme von vegetativen Bakterien und bakteriellen Endosporen unter unterschiedlichen Bedingungen, inklusive der Gaszusammensetzung, der Eingangsleistung, der Behandlungsdauer und der Luftfeuchtigkeit, dem SMD-Plasma ausgesetzt. Gleichzeitig wird die Konzentration des im SMD-Plasma erzeugten Ozons gemessen, um den Zusammenhang mit dem antimikrobiellen Effekt zu untersuchen.
Ich zeige in der vorliegenden Arbeit, dass eine SMD-Behandlung auf die gramnegative Escherichia coli und den grampositiven Enterococcus mundtii eine Àhnliche Wirkung erzielt. Zudem hÀngt die bakterizide Wirkung der SMD stark von der Ozonkonzentration ab. Die Luftfeuchtigkeit spielt eine erhebliche Rolle bei der sporiziden Wirkung der SMD auf Geobacillus stearothermophilus, wobei hier die Ozonkonzentration keine Rolle zu spielen scheint.
DarĂŒber hinaus untersuche ich die Dynamik der Konzentration des im SMD-Plasma erzeugten Ozons, indem die Geometrie und das Zeitintervall fĂŒr die Erzeugung der Entladung variiert werden, und indem die Entladung in zwei aufeinander folgenden Phasen mit verschiedenen Frequenzen gezĂŒndet wird. Mögliche ErklĂ€rungen fĂŒr die beobachteten Ergebnisse werden vorgeschlagen.
Die vorliegende Arbeit untermauert die Rolle der SMD als eine effiziente Sterilisationstechnik und offenbart unterschiedliche Möglichkeiten fĂŒr die Optimierung des antimikrobiellen Effekts der SMD. Jedoch konnte im Rahmen dieser Arbeit nicht fĂŒr alle Beobachtungen eine zufriedenstellende ErklĂ€rung geliefert werden. WeiterfĂŒhrende Forschungsarbeiten werden daher nahegelegt
Surface micro-discharge (SMD)
There is an urgent need for an efficient technology of disinfection and sterilization
in view of the alarming dimensions health care-associated infections (HAIs) have
reached. Cold atmospheric pressure plasma (CAP) can be utilized for hygienic and
medical purposes, in particular in surface decontamination applications, and provides
a promising alternative to the conventionally used sterilization techniques. Surface
Micro-Discharge (SMD) offers a technology for generating CAP that can be applied to
wide areas.
In the present work, I investigate the plasma chemistry involved in the inactivation
of microorganisms by application of the SMD in order to optimize the antimicrobial
effect. For this purpose, different strains of vegetative bacteria and bacterial
endospores are exposed to the SMD with experimental parameters such as the gas
composition, power input, treatment duration and humidity varied. At the same time,
the concentration of ozone produced by the SMD is monitored, and its correlation with
the antimicrobial efficacy is investigated.
I demonstrate that the bactericidal effect of the SMD on both the Gram-negative
Escherichia coli and Gram-positive Enterococcus mundtii is similar and strongly correlates
with the ozone concentration. The sporicidal effect on Geobacillus stearothermophilus
is crucially affected by the humidity, whereas the ozone concentration appears to have
no influence. In addition, I investigate the dynamic behavior of ozone produced by
the SMD by varying the geometry and the time interval for the plasma generation and
by igniting the plasma in two subsequent phases with different frequencies. Possible
explanations for the obtained results are provided.
This work fortifies the role of SMD as an efficient sterilization method and discloses
diverse possibilities for optimizing the antimicrobial effect.Die HĂ€ufigkeit der Krankenhausinfektionen und ihre Auswirkung haben alarmierende AusmaĂe angenommen. Angesichts dessen besteht ein akuter Bedarf an einer effizienten Technologie fĂŒr Desinfektion und Sterilisation. Die Anwendung von kaltem atmosphĂ€rischen Plasma (englisch: cold atmospheric plasma, CAP) fĂŒr die Hygiene und Medizin, insbesondere fĂŒr die OberflĂ€chendekon-tamination, stellt einen Versuch dar, eine schnelle und effektive Sterilisationstechnik zu schaffen.
Die OberflĂ€chenentladung (englisch: Surface Micro-Discharge, SMD) bietet eine Technologie fĂŒr die Erzeugung und Anwendung von CAP. In der vorliegenden Arbeit analysiere ich die antimikrobiellen Eigenschaften der SMD, um die Inaktivierungsmechnismen besser zu verstehen und den antimikrobiellen Effekt zu optimieren. Hierzu werden unterschiedliche StĂ€mme von vegetativen Bakterien und bakteriellen Endosporen unter unterschiedlichen Bedingungen, inklusive der Gaszusammensetzung, der Eingangsleistung, der Behandlungsdauer und der Luftfeuchtigkeit, dem SMD-Plasma ausgesetzt. Gleichzeitig wird die Konzentration des im SMD-Plasma erzeugten Ozons gemessen, um den Zusammenhang mit dem antimikrobiellen Effekt zu untersuchen.
Ich zeige in der vorliegenden Arbeit, dass eine SMD-Behandlung auf die gramnegative Escherichia coli und den grampositiven Enterococcus mundtii eine Àhnliche Wirkung erzielt. Zudem hÀngt die bakterizide Wirkung der SMD stark von der Ozonkonzentration ab. Die Luftfeuchtigkeit spielt eine erhebliche Rolle bei der sporiziden Wirkung der SMD auf Geobacillus stearothermophilus, wobei hier die Ozonkonzentration keine Rolle zu spielen scheint.
DarĂŒber hinaus untersuche ich die Dynamik der Konzentration des im SMD-Plasma erzeugten Ozons, indem die Geometrie und das Zeitintervall fĂŒr die Erzeugung der Entladung variiert werden, und indem die Entladung in zwei aufeinander folgenden Phasen mit verschiedenen Frequenzen gezĂŒndet wird. Mögliche ErklĂ€rungen fĂŒr die beobachteten Ergebnisse werden vorgeschlagen.
Die vorliegende Arbeit untermauert die Rolle der SMD als eine effiziente Sterilisationstechnik und offenbart unterschiedliche Möglichkeiten fĂŒr die Optimierung des antimikrobiellen Effekts der SMD. Jedoch konnte im Rahmen dieser Arbeit nicht fĂŒr alle Beobachtungen eine zufriedenstellende ErklĂ€rung geliefert werden. WeiterfĂŒhrende Forschungsarbeiten werden daher nahegelegt