Supply Function Competition in Electricity Markets with Flexible, Inflexible, and Variable Generation

In this paper we study the supply function competition between power-generation firms with different levels of flexibility. Inflexible firms produce power at a constant rate over an operating horizon, while flexible firms can adjust their output to meet the fluctuations in electricity demand. Both types of firms compete in an electricity market by submitting supply functions to a system operator, who solves an optimal dispatch problem to determine the production level for each firm and the corresponding market price. We study how firms’ (in)flexibility affects their equilibrium behavior and the market price. We also analyze the impact of variable generation (such as wind and solar power) on the equilibrium, with the focus on the effects of the amount of variable generation, its priority in dispatch, and the production- based subsidies. We find that the classic supply function equilibrium model overestimates the intensity of the market competition, and even more so as more variable generation is introduced into the system. The policy of economically curtailing variable generation intensifies the market competition, reduces price volatility, and improves the system’s overall efficiency. Moreover, we show that these benefits are most significant in the absence of the production-based subsidies.http://deepblue.lib.umich.edu/bitstream/2027.42/102571/1/2014Jan28OWu.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102571/4/1218_Wu_Apr14.pd

Depressive Disorders: Focally Altered Cerebral Perfusion Measured with Arterial Spin-labeling MR Imaging

Purpose: To assess focal cerebral perfusion in patients with refractory depressive disorder (RDD), patients with nonrefractory depressive disorder (NDD), and healthy control subjects by using arterial spin-labeling (ASL) magnetic resonance (MR) imaging. Materials and Methods: This study was approved by the local ethical committee, and written informed consent was obtained from all participants. Twenty-four patients with RDD, 37 patients with NDD, and 42 healthy control subjects were included. From February 2006 to July 2007, all participants were imaged with a 3-T MR system. ASL and echo-planar images were subtracted and averaged to give perfusion-weighted images. Voxel-based analysis was performed. Region-of-interest analysis was applied to the bilateral hippocampi, thalami, and lentiform nuclei. Results: Patients with NDD showed reduced perfusion in the left prefrontal cortex versus control subjects and increased perfusion mainly in the limbic- striatal areas (P < .05). In contrast, patients with RDD had decreased perfusion predominantly in the bilateral frontal and bilateral thalamic regions (P < .05). Compared with patients with RDD, patients with NDD showed higher perfusion mainly in the limbic- striatal areas (P < .05). In region-of-interest analysis, the NDD group showed higher regional cerebral blood flow than both RDD and control groups in the left hippocampus (P < .045), right hippocampus (P < .001), and right lentiform nucleus (P < .049). Conclusion: This study revealed alterations of regional perfusion in the brains of patients with RDD that differed from those in patients with NDD. These results are consistent with the concept that RDD is associated with decreased activity of the bilateral prefrontal areas; and NDD, with decreased activity of left frontal areas in conjunction with overactivity of the bilateral limbic system.Purpose: To assess focal cerebral perfusion in patients with refractory depressive disorder (RDD), patients with nonrefractory depressive disorder (NDD), and healthy control subjects by using arterial spin-labeling (ASL) magnetic resonance (MR) imaging

Analysis of Multi-Server Queues with Station and Server Vacations

In this paper, we consider GI=M=c queues with two classes of vacation mechanisms: Station vacation and server vacation. In the first one, all the servers take vacation simultaneously whenever the system becomes empty, and they also return to the system at the same time, i.e., station vacation is group vacation for all servers. This phenomenon occurs in practice, for example, when the system consists of a set of machines monitored by a single operator, or the system consists of inseparable interconnected parallel machines. In such situations the whole station has to be treated as a single entity for vacation when the system is utilized for a secondary task. For the second class of vacation mechanisms, each server takes its own vacation whenever it completes a service and finds no customers waiting in the queue, which occurs, for instance in the post office, when each server is a relatively independent working unit, and can itself be used for other purposes. For both models, we derive steady state probabilities that have matrix geometric form, and develop computational algorithms to obtain numerical solutions. We also analyze and make comparisons of these models based on numerical observations. 1 Keywords: Queueing, embedded Markov chains, server and station vacations, Hessenberg matrix, matrix geometric solutions. 1

Potential effects of climate change on geographic distribution of the Tertiary relict tree species Davidia involucrata in China

18 p., fot. col., mapas, tablas -- El artículo está sujeto a una licencia Creative Commons Attribution 4.0 International License.This study, using species distribution modeling (involving a new approach that allows for uncertainty), predicts the distribution of climatically suitable areas prevailing during the mid-Holocene, the Last Glacial Maximum (LGM), and at present, and estimates the potential formation of new habitats in 2070 of the endangered and rare Tertiary relict tree Davidia involucrata Baill. The results regarding the mid-Holocene and the LGM demonstrate that south-central and southwestern China have been long-term stable refugia, and that the current distribution is limited to the prehistoric refugia. Given future distribution under six possible climate scenarios, only some parts of the current range of D. involucrata in the mid-high mountains of south-central and southwestern China would be maintained, while some shift west into higher mountains would occur. Our results show that the predicted suitable area offering high probability (0.5‒1) accounts for an average of only 29.2% among the models predicted for the future (2070), making D. involucrata highly vulnerable. We assess and propose priority protected areas in light of climate change. The information provided will also be relevant in planning conservation of other paleoendemic species having ecological traits and distribution ranges comparable to those of D. involucrata.This study received financial support from the Pro Natura Foundation-Japan (2014), the Environmental Research and Technology Development Fund (S-14) of the Ministry of the Environment, Japan, the “Proyecto Intramural Especial, PIE” (grant no. 201630I024) from the CSIC, Spain, and the National Natural Science Foundation of China (NSFC 31300349).Peer reviewe

Understanding How Generation Flexibility and Renewable Energy Affect Power Market Competition

We study supply function competition among conventional power generators with different levels of flexibility and the impact of intermittent renewable power generation on the competition. Inflexible generators commit production before uncertainties are realized, whereas flexible generators can adjust their production after uncertainties are realized. Both types of generators compete in an electricity market by submitting supply functions to a system operator, who solves a two-stage stochastic program to determine the production level for each generator and the corresponding market prices. We aim to gain an understanding of how conventional generators’ (in)flexibility and renewable energy’s intermittency affect the supply function competition and the market price. We find that the classic supply function equilibrium model overestimates the intensity of the market competition, and even more so when more intermittent generation is introduced into the system. The policy of economically curtailing intermittent generation intensifies the market competition, reduces price volatility, and improves the system’s overall efficiency. Furthermore, these benefits of economic curtailment are most significant when the production-based subsidies for renewable energy are absent. </jats:p

Preparation of Layer-by-Layer Nanofiltration Membranes by Dynamic Deposition and Crosslinking

In recent decades, the advancements in layer-by-layer (LBL) assembly technology have provoked increasing interest in the preparation of multilayer polyelectrolyte membranes with excellent performance. In the current study, a novel nanofiltration (NF) membrane was prepared by pressure-driven layer-by-layer (LBL) assembly of polyethylenimine (PEI) and polyacrylicacid (PAA) on a porous substrate with chemical crosslinking. The effect of deposition pressure on separation performance of the prepared membranes was studied. The surface morphology, hydrophilicity and the charge property of the dynamically-deposited membranes were compared with those prepared by static adsorption. The characterization results showed that dynamic deposition process resulted in a smoother membrane surface with improved hydrophilicity. The mechanism of water-path formation was proposed to interpret the effect of pressure on the membrane performance. Glutaraldehyde (GA) was used as a crosslinker to reduce the number of polyelectrolyte bilayers for obtaining good separation performance. The rejections of different inorganic salts of the dynamically-deposited NF membrane were also investigated