Foehn Winds of Southern California

One of the characteristic weather phenomena of southern California is a wind of the foehn type known locally as the Santa Ana. Unseasonably high temperatures and very low humidities are associated with its occurence. The maximum effects of this wind are felt in the region south of Cajon Pass at the eastern extremity of the Los Angeles Basin. The latter area, extending eastward from the sea to the San Bernardino Mountains, is ordinarily protected from continental influences by the rather high San Gabriel Mountains to the north. Cajon Pass, trending roughly north and south between the San Gabriel Mountains to the west and the San Bernardino Mountains to the east, opens to the north upon the Mohave Desert and to the south upon the alluvial plain of the Los Angeles Basin

Proposed shunt rounding technique for large-scale security constrained loss minimization

The official published version can be obtained from the link below - Copyright @ 2010 IEEE.Optimal reactive power flow applications often model large numbers of discrete shunt devices as continuous variables, which are rounded to their nearest discrete value at the final iteration. This can degrade optimality. This paper presents novel methods based on probabilistic and adaptive threshold approaches that can extend existing security constrained optimal reactive power flow methods to effectively solve large-scale network problems involving discrete shunt devices. Loss reduction solutions from the proposed techniques were compared to solutions from the mixed integer nonlinear mathematical programming algorithm (MINLP) using modified IEEE standard networks up to 118 buses. The proposed techniques were also applied to practical large-scale network models of Great Britain. The results show that the proposed techniques can achieve improved loss minimization solutions when compared to the standard rounding method.This work was supported in part by the National Grid and in part by the EPSRC. Paper no. TPWRS-00653-2009

The Stable Roommates problem with short lists

We consider two variants of the classical Stable Roommates problem with Incomplete (but strictly ordered) preference lists SRI that are degree constrained, i.e., preference lists are of bounded length. The first variant, EGAL d-SRI, involves finding an egalitarian stable matching in solvable instances of SRI with preference lists of length at most d. We show that this problem is NP-hard even if d=3. On the positive side we give a (2d+3)/7-approximation algorithm for d={3,4,5} which improves on the known bound of 2 for the unbounded preference list case. In the second variant of SRI, called d-SRTI, preference lists can include ties and are of length at most d. We show that the problem of deciding whether an instance of d-SRTI admits a stable matching is NP-complete even if d=3. We also consider the "most stable" version of this problem and prove a strong inapproximability bound for the d=3 case. However for d=2 we show that the latter problem can be solved in polynomial time.Comment: short version appeared at SAGT 201

Modeling Stable Matching Problems with Answer Set Programming

The Stable Marriage Problem (SMP) is a well-known matching problem first introduced and solved by Gale and Shapley (1962). Several variants and extensions to this problem have since been investigated to cover a wider set of applications. Each time a new variant is considered, however, a new algorithm needs to be developed and implemented. As an alternative, in this paper we propose an encoding of the SMP using Answer Set Programming (ASP). Our encoding can easily be extended and adapted to the needs of specific applications. As an illustration we show how stable matchings can be found when individuals may designate unacceptable partners and ties between preferences are allowed. Subsequently, we show how our ASP based encoding naturally allows us to select specific stable matchings which are optimal according to a given criterion. Each time, we can rely on generic and efficient off-the-shelf answer set solvers to find (optimal) stable matchings.Comment: 26 page

Foehn Winds of Southern California

One of the characteristic weather phenomena of southern California is a wind of the foehn type known locally as the Santa Ana. Unseasonably high temperatures and very low humidities are associated with its occurence. The maximum effects of this wind are felt in the region south of Cajon Pass at the eastern extremity of the Los Angeles Basin. The latter area, extending eastward from the sea to the San Bernardino Mountains, is ordinarily protected from continental influences by the rather high San Gabriel Mountains to the north. Cajon Pass, trending roughly north and south between the San Gabriel Mountains to the west and the San Bernardino Mountains to the east, opens to the north upon the Mohave Desert and to the south upon the alluvial plain of the Los Angeles Basin

Foehn Wind Cyclo-Genesis

According to modern theories regions of cyclo-genesis arise where convergent flow occurs between air masses of different characteristics, provided significant temperature differences exist. Such a flow tends to form a discontinuity surface or front between the masses and to produce large amounts of potential energy of mass distribution along the frontal zone. If the conditions for stable equilibrium are not rigidly maintained along the front, the colder mass may move forward into the warmer current or vice versa. In any case there occurs a compensating flow in the adjacent mass, the whole process giving rise to the genesis of a cyclonic disturbance. The kinetic energy of the resulting cyclone is provided to a large measure by the initial potential energy of mass distribution; although, of course, the heat of condensation liberated in the event that the warm mass is particularly moist furnishes a minor portion. A detailed discussion of the formation, maintenance, occlusion and final death of the cyclone is beyond the scope of the present paper. I merely wish to emphasize at this point the importance of convergent flow in constrasting air masses for furnishing the potential energy necessary for the genesis and subsequent maintenance of the extra-tropical cyclone

Distributed monitoring and control of future power systems via grid computing

It is now widely accepted within the electrical power supply industry that future power systems operates with significantly larger numbers of small-scale highly dispersed generation units that use renewable energy sources and also reduce carbon dioxide emissions. In order to operate such future power systems securely and efficiently it will be necessary to monitor and control output levels and scheduling when connecting such generation to a power system especially when it is typically embedded at the distribution level. Traditional monitoring and control technology that is currently employed at the transmission level is highly centralized and not scalable to include such significant increases in distributed and embedded generation. However, this paper proposes and demonstrates the adoption of a relatively new technology 'grid computing' that can provide both a scalable and universally adoptable solution to the problems associated with the distributed monitoring and control of future power systems