Sustainable tourism development : a critique

Sustainable tourism has become an increasingly popular field of research since the late 1980s. However, the sustainable tourism debate is patchy, disjointed and often flawed with false assumptions and arguments. This paper is a brief critique of some of the weaknesses in the sustainable tourism literature. In particular, it explores six issues that are often overlooked but must be addressed in research: the role of tourism demand, the nature of tourism resources, the imperative of intra-generational equity, the role of tourism in promoting sociocultural progress, the measurement of sustainability, and forms of sustainable development. Finally, it is argued that in order to transform research on sustainable tourism to a more scientific level, a systems perspective and an interdisciplinary approach are indispensable

Harnessing Flexible and Reliable Demand Response Under Customer Uncertainties

Demand response (DR) is a cost-effective and environmentally friendly approach for mitigating the uncertainties in renewable energy integration by taking advantage of the flexibility of customers' demands. However, existing DR programs suffer from either low participation due to strict commitment requirements or not being reliable in voluntary programs. In addition, the capacity planning for energy storage/reserves is traditionally done separately from the demand response program design, which incurs inefficiencies. Moreover, customers often face high uncertainties in their costs in providing demand response, which is not well studied in literature. This paper first models the problem of joint capacity planning and demand response program design by a stochastic optimization problem, which incorporates the uncertainties from renewable energy generation, customer power demands, as well as the customers' costs in providing DR. We propose online DR control policies based on the optimal structures of the offline solution. A distributed algorithm is then developed for implementing the control policies without efficiency loss. We further offer enhanced policy design by allowing flexibilities into the commitment level. We perform real world trace based numerical simulations. Results demonstrate that the proposed algorithms can achieve near optimal social costs, and significant social cost savings compared to baseline methods

Incentivizing Reliable Demand Response with Customers' Uncertainties and Capacity Planning

One of the major issues with the integration of renewable energy sources into the power grid is the increased uncertainty and variability that they bring. If this uncertainty is not sufficiently addressed, it will limit the further penetration of renewables into the grid and even result in blackouts. Compared to energy storage, Demand Response (DR) has advantages to provide reserves to the load serving entities (LSEs) in a cost-effective and environmentally friendly way. DR programs work by changing customers' loads when the power grid experiences a contingency such as a mismatch between supply and demand. Uncertainties from both the customer-side and LSE-side make designing algorithms for DR a major challenge. This paper makes the following main contributions: (i) We propose DR control policies based on the optimal structures of the offline solution. (ii) A distributed algorithm is developed for implementing the control policies without efficiency loss. (iii) We further offer an enhanced policy design by allowing flexibilities into the commitment level. (iv) We perform real world trace based numerical simulations which demonstrate that the proposed algorithms can achieve near optimal social cost. Details can be found in our extended version.Comment: arXiv admin note: substantial text overlap with arXiv:1704.0453

On a conjecture of Almgren: area-minimizing surfaces with fractal singularities

For any integer $n\ge 2,$ $0\le j\le n-2,$ any sequence of (not necessarily connected) smooth orientable compact Riemannian manifolds $N_j$ of dimension $j,$ and any closed compact subsets $K_j$ in $N_j$, we construct a smooth compact Riemannian manifold $M^{2n-k+1}$, with a smooth calibration $\phi$ and a calibrated irreducible homologically area minimizing surface $T^n$ in $M$. ($k$ is the smallest number with $K_k$ nonempty.) The singular set of $T$ is the disjoint union of $K_0,\cdots,K_{n-2},$ and the $j$-symmetric part of the $j$-th strata in the Almgren stratification of the singular set of $T$ is precisely $K_j.$ As a corollary, area-minimizing integral currents can have fractal singular sets. Thus, we settle a conjecture by Almgren and the answer is sharp dimension-wise. As a by-product, we also obtain similar conclusions for mod $p$ area-minimizing surfaces and stable minimal surfaces