1,830 research outputs found
Maximal partial Latin cubes
We prove that each maximal partial Latin cube must have more than 29.289% of its cells filled and show by construction that this is a nearly tight bound. We also prove upper and lower bounds on the number of cells containing a fixed symbol in maximal partial Latin cubes and hypercubes, and we use these bounds to determine for small orders n the numbers k for which there exists a maximal partial Latin cube of order n with exactly k entries. Finally, we prove that maximal partial Latin cubes of order n exist of each size from approximately half-full (n3/2 for even n ⼠10 and (n3 + n)/2 for odd n âĽ21) to completely full, except for when either precisely 1 or 2 cells are empty
Temperature dependence of the ``0.7'' 2(e^2)/h quasi plateau in strongly confined quantum point contacts
We present new results of the ``0.7'' 2(e^2)/h structure or quasi plateau in
some of the most strongly confined point contacts so far reported. This strong
confinement is obtained by a combination of shallow etching and metal gate
deposition on modulation doped GaAs/GaAlAs heterostructures. The resulting
subband separations are up to 20 meV, and as a consequence the quantized
conductance can be followed at temperatures up to 30 K, an order of magnitude
higher than in conventional split gate devices. We observe pronounced quasi
plateaus at several of the lowest conductance steps all the way from their
formation around 1 K to 30 K, where the entire conductance quantization is
smeared out thermally. We study the deviation of the conductance from ideal
integer quantization as a function of temperature, and we find an activated
behavior, exp(-T_a/T), with a density dependent activation temperature T_a of
the order of 2 K. We analyze our results in terms of a simple theoretical model
involving scattering against plasmons in the constriction.Comment: RevTex (4 pages) including 2 postscript figures. To appear in Physica
B, 199
Interspecific Bacterial Interactions are Reflected in Multispecies Biofilm Spatial Organization
Interspecies interactions are essential for the persistence and development of any kind of complex community, and microbial biofilms are no exception. Multispecies biofilms are structured and spatially defined communities that have received much attention due to their omnipresence in natural environments. Species residing in these complex bacterial communities usually interact both intra- and interspecifically. Such interactions are considered to not only be fundamental in shaping overall biomass and the spatial distribution of cells residing in multispecies biofilms, but also to result in coordinated regulation of gene expression in the different species present. These communal interactions often lead to emergent properties in biofilms, such as enhanced tolerance against antibiotics, host immune responses and other stresses, which have been shown to provide benefits to all biofilm members not only the enabling sub-populations. However, the specific molecular mechanisms of cellular processes affecting spatial organization, and vice versa, are poorly understood and very complex to unravel. Therefore, detailed description of the spatial organization of individual bacterial cells in multispecies communities can be an alternative strategy to reveal the nature of interspecies interactions of constituent species. Closing the gap between visual observation and biological processes may become crucial for resolving biofilm related problems, which is of utmost importance to environmental, industrial, and clinical implications. This review briefly presents the state of the art of studying interspecies interactions and spatial organization of multispecies communities, aiming to support theoretical and practical arguments for further advancement of this field
Using remote substituents to control solution structure and anion binding in lanthanide complexes.
A study of the anion-binding properties of three structurally related lanthanide complexes, which all contain chemically identical anion-binding motifs, has revealed dramatic differences in their anion affinity. These arise as a consequence of changes in the substitution pattern on the periphery of the molecule, at a substantial distance from the binding pocket. Herein, we explore these remote substituent effects and explain the observed behaviour through discussion of the way in which remote substituents can influence and control the global structure of a molecule through their demands upon conformational space. Peripheral modifications to a binuclear lanthanide motif derived from Îą,Îąâ˛-bis(DO3âAyl)-m-xylene are shown to result in dramatic changes to the binding constant for isophthalate. In this system, the parent compound displays considerable conformational flexibility, yet can be assumed to bind to isophthalate through a well-defined conformer. Addition of steric bulk remote from the binding site restricts conformational mobility, giving rise to an increase in binding constant on entropic grounds as long as the ideal binding conformation is not excluded from the available range of conformers
Effects of grade, smiley, and text on Danish and Finnish consumersâ perceptions of food safety inspection reports
Publicly accessible food safety inspection reports are a standard procedure to inform consumers on restaurants' food safety levels in many countries. This study examined how different formats of food safety inspection report are associated with consumer perceptions related to food safety, as well as other perceptions about the restaurant. The study was conducted in Denmark and Finland with similar inspection grade systems but differences in the distribution of awarded grades. We conducted a population-based survey experiment with a between-subjects design on nationally representative samples of the 18-70 years old Danish (n = 978) and Finnish (n = 907) populations. Respondents received one of six food safety inspection reports with different combinations of inspection grade with a smiley and/or text. According to the results, both Danish and Finnish consumers' food safety perceptions of the same grade were more positive when the report included a smiley, and more negative when the report included a text. Finnish respondents perceived a good food safety inspection grade more positively than Danish respondents but there were no country differences when the grade was poor. In addition, food safety inspection results elicited perceptions that were not related to food safety in both countries. The results suggest that if the grade is poor, the inclusion of text is effective in eliciting perceptions of increased food safety risk. If the grade is good, a standalone smiley may be most effective in eliciting positive perceptions of a high food safety level. Moreover, these results indicate the importance of carefully evaluating how to develop public accessible inspection grades to ensure they are correctly interpreted by consumers in different countries.Peer reviewe
Directed geometrical worm algorithm applied to the quantum rotor model
We discuss the implementation of a directed geometrical worm algorithm for
the study of quantum link-current models. In this algorithm Monte Carlo updates
are made through the biased reptation of a worm through the lattice. A directed
algorithm is an algorithm where, during the construction of the worm, the
probability for erasing the immediately preceding part of the worm, when adding
a new part,is minimal. We introduce a simple numerical procedure for minimizing
this probability. The procedure only depends on appropriately defined local
probabilities and should be generally applicable. Furthermore we show how
correlation functions, C(r,tau) can be straightforwardly obtained from the
probability of a worm to reach a site (r,tau) away from its starting point
independent of whether or not a directed version of the algorithm is used.
Detailed analytical proofs of the validity of the Monte Carlo algorithms are
presented for both the directed and un-directed geometrical worm algorithms.
Results for auto-correlation times and Green functions are presented for the
quantum rotor model.Comment: 11 pages, 9 figures, v2 : Additional results and data calculated at
an incorrect chemical potential replaced. Conclusions unchange
Bias and temperature dependence of the 0.7 conductance anomaly in Quantum Point Contacts
The 0.7 (2e^2/h) conductance anomaly is studied in strongly confined, etched
GaAs/GaAlAs quantum point contacts, by measuring the differential conductance
as a function of source-drain and gate bias as well as a function of
temperature. We investigate in detail how, for a given gate voltage, the
differential conductance depends on the finite bias voltage and find a
so-called self-gating effect, which we correct for. The 0.7 anomaly at zero
bias is found to evolve smoothly into a conductance plateau at 0.85 (2e^2/h) at
finite bias. Varying the gate voltage the transition between the 1.0 and the
0.85 (2e^2/h) plateaus occurs for definite bias voltages, which defines a gate
voltage dependent energy difference . This energy difference is
compared with the activation temperature T_a extracted from the experimentally
observed activated behavior of the 0.7 anomaly at low bias. We find \Delta =
k_B T_a which lends support to the idea that the conductance anomaly is due to
transmission through two conduction channels, of which the one with its subband
edge \Delta below the chemical potential becomes thermally depopulated as the
temperature is increased.Comment: 9 pages (RevTex) with 9 figures (some in low resolution
Nanoparticle metrology of silica colloids and super-resolution studies using the ADOTA fluorophore
We describe how a new fluorescent dye, methyl ADOTA (N-methyl-azadioxatriangulenium tetrafluoroborate), is an improvement on dyes reported previously for measuring silica nanoparticle size in sols using the decay of fluorescence anisotropy. Me(thyl)-ADOTA possesses the unusual combination of having a red emission and a long fluorescence lifetime of ~ 20 ns, leaving it better-placed to reveal particle sizes at the upper end of the 1-10 nm measurement range. For stable LUDOX colloids, Me-ADOTA is shown to offer higher measurement precision in ⤠1/30th of the measurement time required for dyes previously used. In measurement times of only ~ 20 mins nanoparticle radii for LUDOX SM-AS, AM and AS-40 of 4.6 Âą 0.3 nm, 5.9 Âą 0.2 nm and 11.1 Âą 1.1 nm, are in good agreement with two of the manufacturerâs values of 3.5 nm, 6 nm and 11 nm respectively. Unlike the Si-ADOTA (N-(4-(triethoxysilylethyl)urea-phenyl-) ADOTA tetrafluoroborate) derivative containing a reactive trimetoxysilane group, Me-ADOTA is shown to not induce aggregation of colloidal silica. Measurements on nanoparticles growing in an acidic silica hydrogel at pH 0.94, prior to the gel time of ~ 50 hr, reveals an average nanoparticle size up to ~ 6.3 nm, significantly larger than the 4.5 nm reported previously. The difference is most certainly due to the longer fluorescence lifetime of Me-ADOTA (~ 20 ns) revealing the presence of larger particles. Studies of growing silica clusters in an alcogel of tetraethyl orthosilicate (TEOS) were able to resolve a monotonically increasing average radius of 1.42 Âą 0.10 nm to 1.81 Âą 0.14 nm over a period of 48 hr. We have also assessed a carboxylic acid derivative of ADOTA (N-(3-carboxypropylene)-ADOTA tetrafluoroborate - Acid-ADOTA) using dSTORM super-resolution microscopy. Although demonstrating high photochemical stability and blinking, its lower brightness and relative propensity to aggregate limits Acid-ADOTAâs use for dSTORM
Three-body recombination rates near a Feshbach resonance within a two-channel contact interaction model
We calculate the three-body recombination rate into a shallow dimer in a gas
of cold bosonic atoms near a Feshbach resonance using a two-channel contact
interaction model. The two-channel model naturally describes the variation of
the scattering length through the Feshbach resonance and has a finite effective
range. We confront the theory with the available experimental data and show
that the two-channel model is able to quantitatively describe the existing
data. The finite effective range leads to a reduction of the scaling factor
between the recombination minima from the universal value of 22.7. The
reduction is larger for larger effective ranges or, correspondingly, for
narrower Feshbach resonances.Comment: 9 pages, 7 figure
Two-body correlations in N-body boson systems
We formulate a method to study two-body correlations in a system of N
identical bosons interacting via central two-body potentials. We use the
adiabatic hyperspherical approach and assume a Faddeev-like decomposition of
the wave function. For a fixed hyperradius we derive variationally an optimal
integro-differential equation for hyperangular eigenvalue and wave function.
This equation reduces substantially by assuming the interaction range much
smaller than the size of the N-body system. At most one-dimensional integrals
then remain. We view a Bose-Einstein condensate pictorially as a structure in
the landscape of the potential given as a function of the one-dimensional
hyperradial coordinate. The quantum states of the condensate can be located in
one of the two potential minima. We derive and discuss properties of the
solutions and illustrate with numerical results. The correlations lower the
interaction energy substantially. The new multi-body Efimov states are
solutions independent of details of the two-body potential. We compare with
mean-field results and available experimental data.Comment: 19 pages (RevTeX4), 13 figures (latex). Journal-link:
http://pra.aps.org
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