Effective diffusion constant in a two dimensional medium of charged point scatterers

We obtain exact results for the effective diffusion constant of a two dimensional Langevin tracer particle in the force field generated by charged point scatterers with quenched positions. We show that if the point scatterers have a screened Coulomb (Yukawa) potential and are uniformly and independently distributed then the effective diffusion constant obeys the Volgel-Fulcher-Tammann law where it vanishes. Exact results are also obtained for pure Coulomb scatterers frozen in an equilibrium configuration of the same temperature as that of the tracer.Comment: 9 pages IOP LaTex, no figure

Phonons in potassium doped graphene: the effects of electron-phonon interactions, dimensionality and ad-atom ordering

Graphene phonons are measured as a function of electron doping via the addition of potassium adatoms. In the low doping regime, the in-plane carbon G-peak hardens and narrows with increasing doping, analogous to the trend seen in graphene doped via the field-effect. At high dopings, beyond those accessible by the field-effect, the G-peak strongly softens and broadens. This is interpreted as a dynamic, non-adiabatic renormalization of the phonon self-energy. At dopings between the light and heavily doped regimes, we find a robust inhomogeneous phase where the potassium coverage is segregated into regions of high and low density. The phonon energies, linewidths and tunability are remarkably similar for 1-4 layer graphene, but significantly different to doped bulk graphite.Comment: Accepted in Phys. Rev. B as a Rapid Communication. 5 pages, 3 figures, revised text with additional dat

Tapping Thermodynamics of the One Dimensional Ising Model

We analyse the steady state regime of a one dimensional Ising model under a tapping dynamics recently introduced by analogy with the dynamics of mechanically perturbed granular media. The idea that the steady state regime may be described by a flat measure over metastable states of fixed energy is tested by comparing various steady state time averaged quantities in extensive numerical simulations with the corresponding ensemble averages computed analytically with this flat measure. The agreement between the two averages is excellent in all the cases examined, showing that a static approach is capable of predicting certain measurable properties of the steady state regime.Comment: 11 pages, 5 figure

Personalized Ranking for Context-Aware Venue Suggestion

Making personalized and context-aware suggestions of venues to the users is very crucial in venue recommendation. These suggestions are often based on matching the venues' features with the users' preferences, which can be collected from previously visited locations. In this paper we present a novel user-modeling approach which relies on a set of scoring functions for making personalized suggestions of venues based on venues content and reviews as well as users context. Our experiments, conducted on the dataset of the TREC Contextual Suggestion Track, prove that our methodology outperforms state-of-the-art approaches by a significant margin.Comment: The 32nd ACM SIGAPP Symposium On Applied Computing (SAC), Marrakech, Morocco, April 4-6, 201

On the Complexity of List Ranking in the Parallel External Memory Model

We study the problem of list ranking in the parallel external memory (PEM) model. We observe an interesting dual nature for the hardness of the problem due to limited information exchange among the processors about the structure of the list, on the one hand, and its close relationship to the problem of permuting data, which is known to be hard for the external memory models, on the other hand. By carefully defining the power of the computational model, we prove a permuting lower bound in the PEM model. Furthermore, we present a stronger \Omega(log^2 N) lower bound for a special variant of the problem and for a specific range of the model parameters, which takes us a step closer toward proving a non-trivial lower bound for the list ranking problem in the bulk-synchronous parallel (BSP) and MapReduce models. Finally, we also present an algorithm that is tight for a larger range of parameters of the model than in prior work

Multilayer and conformal antennas using synthetic dielectric substrates

This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available

CHARACTERISTICS OF NATURE-BASED TOURISM ENTERPRISES IN NORTH DAKOTA

Recreational activities related to North Dakota's wealth of natural resources are well-established in North Dakota. In recent years, North Dakota's abundant resources have attracted visitors from around the country and the world. In addition to providing recreational activities for residents and visitors alike, natural resource-based tourism is a basic sector that may have considerable potential for creating economic opportunities in rural areas. Recognition of the potential importance of resource-based tourism to rural economies is well-advanced in other parts of the United States. However, little attention has historically been paid to tourism in North Dakota. While much anecdotal evidence exists suggesting that natural resource-based tourism is growing in North Dakota, no basic research on the sector has to date been completed. The goal of this study is to identify and analyze existing agricultural and natural resource-based tourism enterprises in North Dakota.nature-based tourism, outdoor recreation, enterprise characteristics, rural businesses, economic development, Resource /Energy Economics and Policy,

RURAL ECONOMIC EFFECTS OF THE CONSERVATION RESERVE PROGRAM IN NORTH DAKOTA

The Conservation Reserve Program (CRP), enacted in 1985, provides conservation benefits and agricultural supply control through voluntary, long-term retirement of crop land. Large-scale, long-term land retirement programs produce, in varying degrees, negative effects on those businesses and economic sectors that provide agricultural inputs and services. While the effects of the CRP on agriculture are well understood, economic assessments of the market-value of conservation benefits from the program accruing to rural economies remains largely undocumented. One of the conservation benefits of the program is wildlife habitat, which has bolstered upland bird, waterfowl, and big game populations. Growing wildlife populations have contributed to increased consumptive and non-consumptive wildlife-based recreation. This study addressed the net economic effects of decreased agricultural activity and increased recreational activity associated with the CRP in six rural areas of North Dakota from 1996 through 2000. The negative effects of the CRP on agricultural revenues were based on the level of economic activity that would have occurred in the absence of the program. The net change in revenues from CRP land returning to agricultural production in the six study areas was estimated at $76 million or about$56 per CRP-acre. However, returning CRP lands to agricultural production was estimated to lower commodity prices and reduce agricultural revenues on non-CRP lands by $25.9 million. The combined effect was estimated at$50.2 million annually or $37 per CRP-acre in the study areas. The CRP affects many types of outdoor recreation; however, hunting was identified as the most influenced type of recreation in North Dakota. Recreational impacts were determined by comparing pheasant, waterfowl, and deer hunter numbers before and after the CRP, assigning the relative role the CRP has played in the change in hunter numbers, allocating a percentage of the change in hunter numbers to each study area, and applying seasonal hunter expenditure patterns to the change in hunter numbers. Average annual CRP-related hunter expenditures in the six study areas were estimated at$12.8 million or $9.45 per CRP-acre. Overall, recreational revenues averaged 26 percent of the agricultural losses. The degree to which CRP-based hunting revenues in rural areas offset agricultural losses varied throughout the state. In several cases, hunting expenditures offset a substantial portion of the agricultural losses, while in other areas, the net economic loss from the program remains high. The net economic effects of the program in western and central North Dakota were the most favorable, whereas the effects were least favorable in eastern areas of the state. In North Dakota, the net economic effect of losses in agricultural revenues and gains in hunting-based recreational expenditures indicated that several areas of the state are not as economically burdened by the CRP as previous research has suggested.Conservation Reserve Program, Economic Impacts, Rural Economies, Land Economics/Use,

PERCEPTIONS OF LEAFY SPURGE AND EVALUATION OF THE TEAM LEAFY SPURGE PROJECT, BY PUBLIC LAND MANAGERS, LOCAL DECISION MAKERS, AND RANCH OPERATORS

Leafy spurge is an exotic, noxious, perennial weed which is widely established in the north central United States and is an especially serious problem in the northern Great Plains (Bangsund et al. 1999). In 1997, the Agriculture Research Service and Animal Plant Health Inspection Service, U.S. Department of Agriculture, initiated a major Integrated Pest Management (IPM) research and demonstration project to develop and demonstrate ecologically based IPM strategies that can produce effective, affordable leafy spurge control. In 1998 and 1999, a survey of ranchers and public land managers was conducted to evaluate managerial, institutional, and social factors that might affect the rate and extent of implementation of various control strategies. In 2001, a second survey of the same ranchers and public land managers was conducted to (1) assess any changes in land managers' perceptions of weed problems, control alternatives, and related issues, and (2) evaluate the impact of the TEAM Leafy Spurge project on the respondent's weed control practices. The impacts of noxious weeds on grazing operations, specifically leafy spurge, are not abating, and ranchers seem more aware than ever of the severity of the problem. A slightly larger percentage of respondents in 2001 view leafy spurge as a major problem and the most serious problem for grazing operations than in 1998 and 1999. Heightened awareness among landowners may also be linked to TEAM Leafy Spurge's efforts to inform landowners of the problem and offer affordable, effective weed management techniques. While the use of biological control methods, specifically flea beetles, has grown, herbicides continue to be the control practice of choice. While slightly fewer respondents reported using herbicides in 2001 than in 1998 and 1999, the vast majority of landowners plan to continue to use herbicides. Over 50 percent of respondents are using biological control, and over 76 percent of respondents indicated flea beetles were either somewhat or very effective in controlling leafy spurge. Nearly half of the respondents had heard of TEAM Leafy Spurge, and all TEAM Leafy Spurge demonstration sites, events, and publications were favorably rated. A large majority of the respondents agreed that the program had been effective in demonstrating and communicating leafy spurge treatment and control options. Based on the results of the 2001 survey, it would appear that the program has indeed made progress in communicating the type of information landowners need to address what continues to be a significant issue for grazing operations in the Midwest.leafy spurge, noxious weeds, weed management, rancher opinion, Land Economics/Use,