Who Contributes to the Knowledge Sharing Economy?

Information sharing dynamics of social networks rely on a small set of influencers to effectively reach a large audience. Our recent results and observations demonstrate that the shape and identity of this elite, especially those contributing \emph{original} content, is difficult to predict. Information acquisition is often cited as an example of a public good. However, this emerging and powerful theory has yet to provably offer qualitative insights on how specialization of users into active and passive participants occurs. This paper bridges, for the first time, the theory of public goods and the analysis of diffusion in social media. We introduce a non-linear model of \emph{perishable} public goods, leveraging new observations about sharing of media sources. The primary contribution of this work is to show that \emph{shelf time}, which characterizes the rate at which content get renewed, is a critical factor in audience participation. Our model proves a fundamental \emph{dichotomy} in information diffusion: While short-lived content has simple and predictable diffusion, long-lived content has complex specialization. This occurs even when all information seekers are \emph{ex ante} identical and could be a contributing factor to the difficulty of predicting social network participation and evolution.Comment: 15 pages in ACM Conference on Online Social Networks 201

Evidence for Lysosomal Enzymes in Acanthamoeba and Their Activity Changes During Encystment

Author Institution: Graduate Program in Zoology and Department of Microbiology, The Ohio State UniversityAssays on cell-free homogenates of Acanthamoeba castellanii reveal that the three hydrolases, acid phosphatase (APase), acid deoxyribonuclease, and acid ribonuclease (RNase), possess pH optima of 5.0, 4.8, and 5.2, respectively. These enzymes exhibit an enhanced sedimentation at 20,000 x g when sucrose is in the homogenizing buffer. Treatment of homogenates with Triton X-100 increases total enzyme activity. These results suggest that the enzymes are particle-bound in lysosomes. During encystment there is a differential decrease in the activity per cell of all three enzymes, with RNase decreasing most rapidly and APase least rapidly. The specific activity of APase increases during encystment even though its activity per cell gradually decreases

Visualisation Tools for Multi-Perspective, Cross-Sector, Long-Term Infrastructure Performance Evaluation

Across different infrastructure sectors there are systems that help to monitor the current and near-future operation and performance of a particular system. Whilst Supervisory Control and Data Acquisition (SCADA) systems are critical to maintaining acceptable levels of functionality, they do not provide insights over the longer timescales across which strategic investment decisions play out. To understand how individual or multiple, interdependent, infrastructure sectors perform over longer timescales, capacity/demand modelling is required. However, the outputs of such models are often a complex high-dimensionality result-set, and this complexity is further compounded when crosssector evaluation is required. To maximise utility of such models, tools are required that can process and present key outputs. In this paper we describe the development of prototype tools for infrastructure performance evaluation in relation to different strategic decisions and the complex outputs generated from capacity and demand models of five infrastructure sectors (energy, water, waste water, solid waste, transport) investigated within the UK Infrastructure Transitions Research Consortium (ITRC). By constructing tools that expose various dimensions of the model outputs, a user is able to take greater control over the knowledge discovery process

Noether symmetries, energy-momentum tensors and conformal invariance in classical field theory

In the framework of classical field theory, we first review the Noether theory of symmetries, with simple rederivations of its essential results, with special emphasis given to the Noether identities for gauge theories. Will this baggage on board, we next discuss in detail, for Poincar\'e invariant theories in flat spacetime, the differences between the Belinfante energy-momentum tensor and a family of Hilbert energy-momentum tensors. All these tensors coincide on shell but they split their duties in the following sense: Belinfante's tensor is the one to use in order to obtain the generators of Poincar\'e symmetries and it is a basic ingredient of the generators of other eventual spacetime symmetries which may happen to exist. Instead, Hilbert tensors are the means to test whether a theory contains other spacetime symmetries beyond Poincar\'e. We discuss at length the case of scale and conformal symmetry, of which we give some examples. We show, for Poincar\'e invariant Lagrangians, that the realization of scale invariance selects a unique Hilbert tensor which allows for an easy test as to whether conformal invariance is also realized. Finally we make some basic remarks on metric generally covariant theories and classical field theory in a fixed curved bakground.Comment: 31 pa

Development of boron calibration via hybrid comparator method in prompt gamma activation analysis

The prompt gamma activation analysis (PGAA) facility at the Nuclear Engineering Teaching Laboratory at The University of Texas at Austin was utilized to quantify boron concentrations in boron carbide semiconductor films deposited on silicon substrates. Calibration was complicated by the unique and varying sample geometries analyzed. In addition, there was a dearth of solid materials available with quantified boron concentrations having comparable or readily modifiable dimensions to exploit for calibration purposes. Therefore, a novel hybrid comparator method was developed for the quantification of boron utilizing aluminum as an inexpensive and easily machinable reference material. Aluminum samples were manufactured with high tolerances to match the geometry of each sample of interest. Each boron carbide film sample and its congruent aluminum sample were measured in the PGAA system. The measured aluminum responses and relevant nuclear parameters were used to standardize the measurements. A boron standard was created using a procedure derived from a similar approach used by the National Institute of Standards and Technology. Quality control measurements using this standard show that the method provided accuracy to within 5% for boron quantification

Theory of a Scanning Tunneling Microscope with a Two-Protrusion Tip

We consider a scanning tunneling microscope (STM) such that tunneling occurs through two atomically sharp protrusions on its tip. When the two protrusions are separated by at least several atomic spacings, the differential conductance of this STM depends on the electronic transport in the sample between the protrusions. Furthermore two-protrusion tips commonly occur during STM tip preparation. We explore possible applications to probing dynamical impurity potentials on a metallic surface and local transport in an anisotropic superconductor.Comment: revtex, 11 pages, 6 figures upon reques

Mechanisation Developments Within the New Zealand Forest Industry: The Human Factors.

The ergonomic benefits of mechanisation for the forest worker focus around the removal of the worker from the majority of the hazards and severe physical workloads inherent in the forest workplace. However, the characteristics of the current New Zealand forest industry workforce, the lack of trained operators, lack of appropriate training and selection programmes, and the high level of turnover in the New Zealand forest industry, are current obstacles to the full achievement of mechanisation's ergonomic benefits. In order for the New Zealand forest industry to maximise the economic and ergonomic benefits of mechanisation, some formal preparation of machine operators is essential

Strong spin relaxation length dependence on electric field gradients

We discuss the influence of electrical effects on spin transport, and in particular the propagation and relaxation of spin polarized electrons in the presence of inhomogeneous electric fields. We show that the spin relaxation length strongly depends on electric field gradients, and that significant suppression of electron spin polarization can occur as a result thereof. A discussion in terms of a drift-diffusion picture, and self-consistent numerical calculations based on a Boltzmann-Poisson approach shows that the spin relaxation length in fact can be of the order of the charge screening length.Comment: 4 pages, 3 figures, to be presented at PASPSI

State Regulation of Franchising: The Washington Experience Revisited

Thirty-six years ago, and one year after Washington became the second state in the nation to enact a statute regulating franchise relationships, Professor Donald S. Chisum wrote the seminal article on franchising in Washington, State Regulation of Franchising: The Washington Experience. Professor Chisum\u27s article has been one of the few reference sources for Washington franchise law, and it has been the primary source relied on by courts addressing claims under Washington\u27s Franchise Investment Protection Act (FIPA). Since Professor Chisum originally published his article, the Federal Trade Commission (FTC) has promulgated and amended regulations governing the sale of franchises nationally, and two different groups have drafted uniform franchise acts. In Washington, the legislature significantly amended FIPA in 1991, and courts have addressed some of the unresolved issues under the statute. This Article assesses the changed state of franchise law in Washington. Part II considers the economic impact of franchising and the need for a review of franchising in Washington. Part III reviews the historical foundation for Washington\u27s current franchise laws, the context in which they were created, and the changes to franchise law that drive our modem understanding of FIPA today. Part IV addresses the current regulatory scheme in Washington, including practical considerations such as franchise registration, disclosure, and state enforcement powers. Finally, Part V addresses civil liability for violations of FIPA\u27s registration, disclosure, and relationship provisions

Evidence for a superfluid density in t--J ladders

Applying three independent techniques, we give numerical evidence for a finite superfluid density in isotropic hole-doped t--J ladders: We show the existence of anomalous flux quantization, emphasising the contrasting behaviour to that found in the `Luttinger liquid' regime stabilised at low electron densities; We consider the nature of the low-lying excitation modes, finding the 1-D analog of the superconducting state; And using a density matrix renormalization group approach, we find long range pairing correlations and exponentially decaying spin-spin correlations.Comment: 4 pages, revtex, postscript figs included, submitted to PR