Screening of charged singularities of random fields

Many types of point singularity have a topological index, or 'charge', associated with them. For example the phase of a complex field depending on two variables can either increase or decrease on making a clockwise circuit around a simple zero, enabling the zeros to be assigned charges of plus or minus one. In random fields we can define a correlation function for the charge-weighted density of singularities. In many types of random fields, this correlation function satisfies an identity which shows that the singularities 'screen' each other perfectly: a positive singularity is surrounded by an excess of concentration of negatives which exactly cancel its charge, and vice-versa. This paper gives a simple and widely applicable derivation of this result. A counterexample where screening is incomplete is also exhibited.Comment: 12 pages, no figures. Minor revision of manuscript submitted to J. Phys. A, August 200

An alternative field theory for the Kosterlitz-Thouless transition

We extend a Gaussian model for the internal electrical potential of a two-dimensional Coulomb gas by a non-Gaussian measure term, which singles out the physically relevant configurations of the potential. The resulting Hamiltonian, expressed as a functional of the internal potential, has a surprising large-scale limit: The additional term simply counts the number of maxima and minima of the potential. The model allows for a transparent derivation of the divergence of the correlation length upon lowering the temperature down to the Kosterlitz-Thouless transition point.Comment: final version, extended discussion, appendix added, 8 pages, no figure, uses IOP documentclass iopar

An examination of state and local government pension underfunding –Implications and guidance for governance and regulation

State and local government pension underfunding has become a major focus of public policy debate due in large part to recent Governmental Accounting Standards Board (GASB) actions that have brought national attention to the issue. The extent of these plans underfunding has been debated, along with the necessity for state government intervention and the level of regulatory actions that should be enacted by state legislatures. State and local public pension plans do not fall under the enumerated powers of the federal government in the Constitution and are therefore left to each individual state to regulate. The amount of plan underfunding and enacted public policy by state varies greatly. Additionally, in contrast to numerous state balanced-budget laws, legal directives for fully funding public pensions are virtually non- existent. This paper analyzes the state and local public pension crisis, examines current and long-term risk, studies public employee fiscal conditions, considers the societal impacts of these plans, considers the strengths and weakness of pension plan types, recommends public policy and regulation, and offers strategies for managers, board members, and public officials to adopt

NATURAL GAS HYDRATE INHIBITION USING METASTABLE STATES BETWEEN COMPETING CLATHRATE PHASES

This work summarizes the current understanding of formation and stability of natural gas hydrates - clathrates of methane encaged in crystalline lattice of water - with emphasis on their role as a hazard in natural gas pipelines. A novel method of hydrate formation inhibition is proposed that is based on creation of a metastable state between structure I and II clathrates by changing partial pressures of methane and ethane in natural gas flow. The work encourages future experiments that would look at the range of partial pressures of ethane added to methane gas that would lead to clathrate formation suppression

Microscopic mechanism for the 1/8 magnetization plateau in SrCu_2(BO_3)_2

The frustrated quantum magnet SrCu_2(BO_3)_2 shows a remarkably rich phase diagram in an external magnetic field including a sequence of magnetization plateaux. The by far experimentally most studied and most prominent magnetization plateau is the 1/8 plateau. Theoretically, one expects that this material is well described by the Shastry-Sutherland model. But recent microscopic calculations indicate that the 1/8 plateau is energetically not favored. Here we report on a very simple microscopic mechanism which naturally leads to a 1/8 plateau for realistic values of the magnetic exchange constants. We show that the 1/8 plateau with a diamond unit cell benefits most compared to other plateau structures from quantum fluctuations which to a large part are induced by Dzyaloshinskii-Moriya interactions. Physically, such couplings result in kinetic terms in an effective hardcore boson description leading to a renormalization of the energy of the different plateaux structures which we treat in this work on the mean-field level. The stability of the resulting plateaux are discussed. Furthermore, our results indicate a series of stripe structures above 1/8 and a stable magnetization plateau at 1/6. Most qualitative aspects of our microscopic theory agree well with a recently formulated phenomenological theory for the experimental data of SrCu_2(BO_3)_2. Interestingly, our calculations point to a rather large ratio of the magnetic couplings in the Shastry-Sutherland model such that non-perturbative effects become essential for the understanding of the frustrated quantum magnet SrCu_2(BO_3)_2.Comment: 24 pages, 24 figure

Increase supply chain resilience by applying early warning signals within big-data analysis

Purpose: The current environment of globally interconnected supply chains, the dynamics of changes and potential threats significantly reduce the time for a possible response. At the same time, there is a growing demand for information necessary to mitigate the consequences. To minimise the damage and increase the resilience of supply chains, it is necessary to identify sources of threats promptly, the extent of possible damage and the possibility of preventing or minimising their impact. The aim of the paper is to structure supply chain threats and search for appropriate datasets for prevention. Methodology: The paper analyses the state-of-the-art through a comprehensive literature review and demonstrates secondary data about how free-access business data can be used as Early Warning Signals to forecast supply chain disruptive events, with a particular focus on international maritime transportation. Results: It was confirmed that companies can access many open datasets, and collecting and aggregating these data can improve their preparedness for future disruptive events. As the most important issue, the authors defined the selection of proper datasets and interpreting results with foresight. Conclusions: Identifying and analysing the relevant Early Warning Signals by companies to prevent supply chain disruptions are essential for keeping their supply chains sustainable and their resilience on a sufficient level. It was proved that general business indicators (PMI delivery time, container capacity, inflation rate, etc.) can help to signal the increasing possibility of maritime traffic problems in ports and container unavailability as usual supply chain disruption types in recent years. Therefore, the companies in the supply chains need to find, collect and analyse the appropriate data, which are, in some cases, free and available. However, it is a substantial task for data analysts to identify the most relevant data and work out the analytical methodology which can be applied as Early Warning Systems (EWS)

Population dynamics studies of the western corn rootworm - experiments in isolation cages

Versuche zur Populationsdynamik des Westlichen Maiswurzelbohrers in Isolationskäfige