Hydrogen induced Si surface segregation on Ge-covered Si(001)

Journal ArticleUsing Fourier transform infrared-attenuated total reflectance spectroscopy in conjunction with hydrogen adsorption to probe surface layer composition, we observe a reversible place exchange between Ge and Si on Ge-covered Si(001) when the surface is dosed with atomic H at elevated temperatures. First-principles calculations confirm a thermodynamic driving force for this place exchange. To explain the intriguing kinetics of the place exchange, which shows no time dependence, we propose a dimer-vacancy diffusion-assisted mechanism limited by vacancy interactions

Locational Marginal Pricing of Natural Gas subject to Engineering Constraints

We derive a price formation mechanism to maximize social welfare for a pipeline network that delivers natural gas from suppliers to consumers. The system is modeled as a metric graph subject to physical balance laws for steady-state hydraulic flow on edges and mass balance at nodes. The pricing mechanism incorporates engineering constraints on local pressures and energy applied by gas compressors. Optimality conditions yield expressions for locational marginal prices for gas (gLMPs) and a decomposition of gLMPs into components corresponding to energy, compression, and two types of congestion. We demonstrate that price and pressure differentials between nodes have the opposite sign, so that price cannot decline in the direction of flow, and prove that the pricing mechanism is revenue adequate. We also present computational examples of congestion pricing for a small test network and a large-scale case study

The Impact of Extreme Weather Events on Planning for Resource Adequacy

Resource Adequacy in the electric power industry has historically focused on sufficient capacity (MW) to serve load on what was forecast to be the worst demand day of the year. The incorporation of intermittent resources both in front of and behind the meter, common mode events and the realization that the metric for reliability should focus on the loss to consumers is refocusing resource adequacy on probabilistic approaches to measurement and analysis. In this paper we focus on planning for resource adequacy given an increasingly stochastic environment in which extreme events caused in large part by changing weather patterns are having increasingly devastating impacts on consumers. These events can no longer be perceived and as being independent (the outage of a generating unit or a line) but are correlated, statistically in both space and time. We argue that there is a need for the definition of probabilistic metrics and methodologies that, over space and time can be used to incorporate the stochastics of common mode and high impact supply disruption

Shift factor-based SCOPF topology control MIP formulations with substation configurations

Topology control (TC) is an effective tool for managing congestion, contingency events, and overload control. The majority of TC research has focused on line and transformer switching. Substation reconfiguration is an additional TC action, which consists of opening or closing breakers not in series with lines or transformers. Some reconfiguration actions can be simpler to implement than branch opening, seen as a less invasive action. This paper introduces two formulations that incorporate substation reconfiguration with branch opening in a unified TC framework. The first method starts from a topology with all candidate breakers open, and breaker closing is emulated and optimized using virtual transactions. The second method takes the opposite approach, starting from a fully closed topology and optimizing breaker openings. We provide a theoretical framework for both methods and formulate security-constrained shift factor MIP TC formulations that incorporate both breaker and branch switching. By maintaining the shift factor formulation, we take advantage of its compactness, especially in the context of contingency constraints, and by focusing on reconfiguring substations, we hope to provide system operators additional flexibility in their TC decision processes. Simulation results on a subarea of PJM illustrate the application of the two formulations to realistic systems.The work was supported in part by the Advanced Research Projects Agency-Energy, U.S. Department of Energy, under Grant DE-AR0000223 and in part by the U.S. National Science Foundation Emerging Frontiers in Research and Innovation under Grant 1038230. Paper no. TPWRS-01497-2015. (DE-AR0000223 - Advanced Research Projects Agency-Energy, U.S. Department of Energy; 1038230 - U.S. National Science Foundation Emerging Frontiers in Research and Innovation)http://buprimo.hosted.exlibrisgroup.com/primo_library/libweb/action/openurl?date=2017&issue=2&isSerivcesPage=true&spage=1179&dscnt=2&url_ctx_fmt=null&vid=BU&volume=32&institution=bosu&issn=0885-8950&id=doi:10.1109/TPWRS.2016.2574324&dstmp=1522778516872&fromLogin=truePublished versio

Nodal Project Evaluation Applied to Large-Scale Renewable Energy Procurment: A case analysis of Massachusetts clean energy initiative

Abstract Evaluating a large number of renewable energy project proposals received in response to a single Request for Proposals (RFP) in a consistent manner independent of size and technology and fully cognizant of location and timing is a significant challenge. The current paper presents a methodology and set of tools for preparing a comparative quantitative evaluation of the economic and environmental benefits and costs of the renewable project proposals over a 25-year time horizon. The paper presents a case study of the large-scale renewable energy procurements undertaken in 2018 to comply with Massachusetts energy diversity and greenhouse gas (GHG) emission reduction goals mandated under its “Green Communities Act” of 2008 and Global Warming Solutions Act” of 2008. Section 83D of the Green Communities Act requires Massachusetts electric distribution companies (EDCs) to acquire 9,450 gigawatt hours per year of cost-effective renewable energy. The quantitative evaluation of each proposed renewable project is based on a scenario analysis approach in which a simulation modeling tool calculates energy costs and GHG emissions in the Northeast region (New England and New York) over the evaluation period for a “but for” case without any of the proposed renewable projects and for individual cases for each proposed renewable project. Working from a single database structure, the simulation modeling tool moves from a 30-year, annual resource adequacy module, to an hourly, nodal, 20-year plus SCUC / SCD, to a detailed capacity market valuation model. The simulation modeling system (ENELYTIX) operates with cloud-based technology utilizing user-friendly Excel interfacing with complex data / information transfer from an OLAP cube on the cloud to users’ workstations

Ein selbstassoziierender difunktioneller Rezeptor

Durch Komplexierung eines Na+ ‐Ions „einschalten”︁ läßt sich die Fähigkeit des Kationenrezeptors 1, eines Calixarens, Wasserstoffbrückenbindungen zwischen der Diamidopyridingruppe und einer komplementären Gruppe wie Thymin zu bilden. Ist diese ihrerseits an einen Anionenrezeptor (z.B. ein metalliertes Porphyrin) gebunden, erhält man einen nichtkovalent zusammengesetzten, difunktionellen Rezeptor, in dem Kation und Anion eines anorganischen Salzes wie NaSCN gleichzeitig komplexiert vorliegen

Evaluating Benefits of Rolling Horizon Model Predictive Control for Intraday Scheduling of a Natural Gas Pipeline Market

This paper analyzes a mechanism for clearing a physical market for intra-day schedules of receipts and deliveries of a natural gas pipeline. The Gas Balancing Market (GBM) is implemented to trade deviations from previously confirmed ratable nominations by solving a rolling horizon model predictive control (MPC) optimization formulation. The GBM mechanism operates by accepting quantity/price offers and bids from sellers and buyers of gas and producing an economically optimal schedule while guaranteeing its physical feasibility. The GBM’s solution engine is based on a strict mathematical representation of engineering factors of transient pipeline hydraulics and compressor station operations. The GBM’s settlement of cleared transactions is based on Locational Trade Values (LTVs) of natural gas that are fully consistent with the physics of energy flow. In this paper we provide numerical results of simulating a hypothetical GBM market operation using historical SCADA data for an actual pipeline system operation during the Polar Vortex period of February – March 2014. Based on these simulations, we quantify the potential deliverability and economic benefits of the GBM utilizing transient optimization of pipeline operations

Market Based Intraday Coordination of Electric and Natural Gas System Operation

This paper outlines the design of an intraday market-based mechanism for coordinated scheduling of gas-fired electric generation, intra-day natural gas purchases, sales and deliveries, and underlying pipeline operation. The mechanism is based on an exchange of physical and pricing data between participants in each market, with price formation in both markets being fully consistent with the physics of energy flow. In organized nodal electricity markets, prices are consistent with the physical flow of electric energy in the power grid because the economic optimization used to clear the market accounts for the physics of power flows. In the gas system, the proposed physical operation and pricing will be based on the transient optimization approach that accounts for physical and engineering factors of pipeline hydraulics and compressor station operations. The paper provides theoretical foundations for the market mechanism