1,391 research outputs found
A New Two-Parameter Family of Potentials with a Tunable Ground State
In a previous paper we solved a countably infinite family of one-dimensional
Schr\"odinger equations by showing that they were supersymmetric partner
potentials of the standard quantum harmonic oscillator. In this work we extend
these results to find the complete set of real partner potentials of the
harmonic oscillator, showing that these depend upon two continuous parameters.
Their spectra are identical to that of the harmonic oscillator, except that the
ground state energy becomes a tunable parameter. We finally use these
potentials to analyse the physical problem of Bose-Einstein condensation in an
atomic gas trapped in a dimple potential.Comment: 15 pages, 5 figure
Unbinding of giant vortices in states of competing order
Funding: EPSRC (UK) via Grants No. EP/I031014/1 and No. EP/H049584/1.We consider a two-dimensional system with two order parameters, one with O(2) symmetry and one with O(M), near a point in parameter space where they couple to become a single O(2+M) order. While the O(2) sector supports vortex excitations, these vortices must somehow disappear as the high symmetry point is approached. We develop a variational argument which shows that the size of the vortex cores diverges as 1/root Delta and the Berezinskii-Kosterlitz-Thouless transition temperature of the O(2) order vanishes as 1/1n(1/Delta), where Delta denotes the distance from the high-symmetry point. Our physical picture is confirmed by a renormalization group analysis which gives further logarithmic corrections, and demonstrates full symmetry restoration within the cores.Publisher PDFPeer reviewe
Team morale and leadership styles of project managers in China construction projects
W112 Culture in Construction: Paper ID: 779The relationships of project team morale and the supervisory styles of project leaders are examined in this paper based on P-M theories which assume dichotomous styles of performance-oriented and maintenance-oriented leadership. In P-M theories, leadership affects motivational arousal directly through a combination of pressure and support where the work structuring aspects of leadership, which affect motivation by clarifying paths to goals, are less central. Generally, previous research supported both P- and M-oriented leadership styles being consistently and positively related to organisational performance measures, although the M-oriented style of leadership was found to be more effective in functional organisations and P-oriented leadership was more effective in the engineering project field of temporary organisations. Situational contingencies in this study are assumed to affect subordinates’ interpretations of leadership primarily, i.e. the leadership styles reported by subordinates are assumed not to reflect the objective level of leadership behaviour. Instead, those measures reflect the amount of a leadership function that subordinates experience given their own personalities, cultural background and the situational contingencies that they face. The subjects in an exploratory study of joint venture projects in China reported in this paper reflect the influence of leadership styles on the level of team morale and project time performance in given sets of situational contingencies.postprintThe 2010 World Congress of CIB on Building a Better World, University of Salford, Salford, U.K., 10-14 May 2010. In Proceedings: TG59 and W112 - Special Track 18th CIB World Building Congress, 2010, p. 180-19
Fluctuation spectroscopy as a probe of granular superconducting diamond films
We present resistance versus temperature data for a series of boron-doped
nanocrystalline diamond films whose grain size is varied by changing the film
thickness. Upon extracting the fluctuation conductivity near to the critical
temperature we observe three distinct scaling regions -- 3D intragrain,
quasi-0D, and 3D intergrain -- in confirmation of the prediction of Lerner,
Varlamov and Vinokur. The location of the dimensional crossovers between these
scaling regions allows us to determine the tunnelling energy and the Thouless
energy for each film. This is a demonstration of the use of \emph{fluctuation
spectroscopy} to determine the properties of a superconducting granular system
Observation of a superconducting glass state in granular superconducting diamond
The magnetic field dependence of the superconductivity in nanocrystalline
boron doped diamond thin films is reported. Evidence of a glass state in the
phase diagram is presented, as demonstrated by electrical resistance and
magnetic relaxation measurements. The position of the phase boundary in the H-T
plane is determined from resistance data by detailed fitting to
zero-dimensional fluctuation conductivity theory. This allows determination of
the boundary between resistive and non-resistive behavior to be made with
greater precision than the standard ad hoc onset/midpoint/offset criterion
Expanding the expressive power of Monadic Second-Order logic on restricted graph classes
We combine integer linear programming and recent advances in Monadic
Second-Order model checking to obtain two new algorithmic meta-theorems for
graphs of bounded vertex-cover. The first shows that cardMSO1, an extension of
the well-known Monadic Second-Order logic by the addition of cardinality
constraints, can be solved in FPT time parameterized by vertex cover. The
second meta-theorem shows that the MSO partitioning problems introduced by Rao
can also be solved in FPT time with the same parameter. The significance of our
contribution stems from the fact that these formalisms can describe problems
which are W[1]-hard and even NP-hard on graphs of bounded tree-width.
Additionally, our algorithms have only an elementary dependence on the
parameter and formula. We also show that both results are easily extended from
vertex cover to neighborhood diversity.Comment: Accepted for IWOCA 201
The effect of cultural and environmental factors on potato seed tuber morphology and subsequent sprout and stem development
Seed crops of the variety Estima were grown in each of 2 years using two planting dates, two harvest dates, two plant densities and two irrigation regimes to produce seed tubers which had experienced different cultural and environmental conditions. The effects of these treatments on tuber characteristics, sprout production and stem development in the ware crop were then determined in subsequent experiments using storage regimes of 3 and 10 °C. Time of planting the seed crop affected numbers of eyes, sprouts and above ground stems in the subsequent ware crop because environmental conditions around the time of tuber initiation appeared to alter tuber shape. Cooler, wetter conditions in the 7 days after tuber initiation were associated with tubers which were longer, heavier and had more eyes, sprouts and above ground stems. In contrast, the time of harvesting the seed crop did not affect tuber shape or numbers of above ground stems and there was no interaction with tuber size. The density of the seed crop had no effect on any character measured and irrigation well after tuber initiation did not affect tuber shape, numbers of sprouts or numbers of stems. Seed production treatments, which resulted in earlier dormancy break, were associated with tubers that produced more sprouts and above ground stems, in contrast to the conventional understanding of apical dominance. Storage at 3 °C gave fewer sprouts, a lower proportion of eyes with sprouts and fewer stems than storage at 10 °C. The major effects on stem production appear to result from environmental conditions at the time of tuber initiation of the seed crop and sprouting temperature
Letter graphs and geometric grid classes of permutations: characterization and recognition
In this paper, we reveal an intriguing relationship between two seemingly
unrelated notions: letter graphs and geometric grid classes of permutations. An
important property common for both of them is well-quasi-orderability,
implying, in a non-constructive way, a polynomial-time recognition of geometric
grid classes of permutations and -letter graphs for a fixed . However,
constructive algorithms are available only for . In this paper, we present
the first constructive polynomial-time algorithm for the recognition of
-letter graphs. It is based on a structural characterization of graphs in
this class.Comment: arXiv admin note: text overlap with arXiv:1108.6319 by other author
Polynomial Kernels for Weighted Problems
Kernelization is a formalization of efficient preprocessing for NP-hard
problems using the framework of parameterized complexity. Among open problems
in kernelization it has been asked many times whether there are deterministic
polynomial kernelizations for Subset Sum and Knapsack when parameterized by the
number of items.
We answer both questions affirmatively by using an algorithm for compressing
numbers due to Frank and Tardos (Combinatorica 1987). This result had been
first used by Marx and V\'egh (ICALP 2013) in the context of kernelization. We
further illustrate its applicability by giving polynomial kernels also for
weighted versions of several well-studied parameterized problems. Furthermore,
when parameterized by the different item sizes we obtain a polynomial
kernelization for Subset Sum and an exponential kernelization for Knapsack.
Finally, we also obtain kernelization results for polynomial integer programs
Development of numerical model for the determination of crack opening and closure loads, for long cracks
​A two-dimensional Finite Element (FE) model has been developed for determining crack opening and closure stresses, with the eventual aim of investigating plasticity induced closure effects on crack growth under variable amplitude loading. An issue with model verification is obtaining accurate experimental values of crack opening and closure loads. Validation was therefore carried out using experimental data from constant amplitude loading tests, recently obtained by the authors1, 2 where there was good confidence in the accuracy of the opening and closing loads. Elastic-perfect plastic and work hardening material properties were investigated to determine the effect they had on crack growth. The modelling considered long cracks by dividing the crack into consecutive small lengths. For this purpose, the restart capability included in the ABAQUS code was employed. In addition, a mesh refinement strategy was optimised to reduce the memory requirements for the thousands of cycles analysed. This enabled both long crack lengths and small element sizes to be studied which has not been done in the literature before. The FE results were in good agreement with most of the experimental results and possible reasons are given for some of the minor discrepancies observed
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