This study investigates the optimization of online compressor washing frequency for enhanced performance and profitability of industrial gas turbines. Two representative engines: an aero-derivative LM2500 and a heavy-duty V94.3A (also designated SGT5-4000F) were simulated in GasTurb software under varying washing intervals of one day and ten days. Experimental data were applied to model reductions in compressor isentropic efficiency and mass-flow capacity due to fouling. The results indicate that extending the washing interval from daily to every ten days for one year causes significant performance deterioration. For the LM2500, power output decreased from 7 % to 16 %, thermal efficiency from 2.6 % to 6 %, and heat rate rose from 2.7 % to 6.6 %. Corresponding changes for the V94.3A were smaller, confirming that the aero-derivative turbine is more sensitive to fouling than the heavy-duty unit. Economic evaluation showed that while more frequent washing increased wash fluid consumption and operational costs, it provides substantial financial benefits. Daily washing produced additional annual net profits of approximately £11.69 million for the V94.3A and £4.6 million for the LM2500 compared with ten-day intervals. Overall, the findings demonstrate that optimizing compressor washing frequency is essential to sustain turbine performance, improve fuel efficiency, and maximize profitability. Frequent online washing mitigates the adverse effects of fouling and ensures cost-effective, reliable, and energy-efficient gas-turbine operation.
Abstract Introduction: Malar¡a ¡s a vector-borne d¡sease w¡dely d¡str¡buted ¡n the Amazon reg¡on and the coastal area of northern Ecuador. Its ep¡dem¡ology ¡nvolves related factors such as human settlements, vector reproduct¡on s¡tes, mob¡l¡ty, product¡ve act¡v¡ty, and the response capac¡ty of health systems, among others. Objective: To describe malaria transm¡ss¡on by Plasmodium vivax ¡n a non-endem¡c area of Ecuador by analyz¡ng the ep¡dem¡olog¡cal and entomolog¡cal factors ¡nvolved. Materials and methods: We conducted the epidemiological study of the cases reported ¡n the Sal¡nas canton and the character¡zat¡on of vector breed¡ng s¡tes through captures of larvae and adult mosqu¡toes by human capture of rest¡ng mosqu¡toes. Results: We detected 21 cases of malar¡a w¡th local transm¡ss¡on related to the presence of ¡n¡t¡al cases ¡n Venezuelan rrrigrant pat¡ents and ¡dentified Anopheles albimanus as the predom¡nant vector ¡n natural breed¡ng s¡tes such as estuar¡es, wells, and water channels. Conclusions: We detected an outbreak of malar¡a tr¡ggered by ¡mported cases from Venezuela. Cl¡mat¡c, soc¡al, env¡ronmental, and ecolog¡cal cond¡t¡ons have favored the development of the vector maintaining the transm¡ss¡on cycle. Strateg¡es to control ¡mported malar¡a should be mult¡ple ¡nclud¡ng early case detect¡on and control of product¡ve breed¡ng s¡tes to avo¡d local transm¡ss¡on.
The work of our group on reproducing scenarios of high energy theoretical physics on Dirac materials, like graphene, is illustrated. The main goal of this paper is to explain how versatile these systems are, and how far and wide into the hep-th territory we can explore with them. I first review why these materials lend themselves to the emergence of special relativistic-like matter and space, with the focus on the emergence of curvature. Then the crucial role of the low dimensions (2+1), and Weyl symmetry, towards the realization of a Unruh-kind of phenomenon (along with other interesting scenarios, that include the BTZ black hole and de Sitter spacetime) is explained. Comments on how far we went in the direction of experiments are offered too, followed by a list of some fresh results: From the time-loop to spot torsion, to the generalized uncertainty principle stemming from and underlying (lattice) length; From a model of grain-boundaries and their relation to (A)dS and Poincare spacetime algebras, to Unconventional Supersymmetry and the role of the two Dirac points of graphene; and more. In the concluding remarks I briefly try to make the case for the realization of a ``CERN for analogs'', where theorists. both of the hep-th and of the cond-mat types, sit next to experimentalists, mostly of the cond-mat type.
SUMMARY In summary, we have investigated in detail the elec-tronic and magnetic properties of Ga 1−x Gd x N. We findthat because of the coupling between the Gd f and hosts states, this system shows some unique behavior that isdrastically different from TM-doped GaN. The exchangesplitting at the CBM is negative. The coupling betweenGd atoms is found to be antiferromagnetic, if no donorsare present, but it become ferromagnetic when enoughdonors are present in the system. We also proposed amodel that may explain the colossal magnetic momentsobserved in this system in the very dilute limit, showingthat it should be directly related to the polarization ofdonor electrons. ACKNOWLEDGMENTS The work at NREL is funded by the U.S. Departmentof Energy, Office ofScience, Basic EnergySciences, underContract No. DE-AC36-99GO10337 to NREL. [1] I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76,323 (2004).[2] D. D. Awschalom and R. K. Kawakami, Nature (London)408, 923 (2000).[3] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Fer-rand, Science 287, 1019 (2000).[4] S. Dhar, O. Brandt, A. Trampert, L. Daweritz, K. J.Friedland, K. H. Ploog, J. Keller, B. Beschoten, and G.Guntherodt, Appl. Phys. Lett. 82, 2077 (2003).[5] J. I. Pankove and T. D. Moustakas, Gallium Nitride(GaN) I (Academic, San Diego, 1998).[6] D, C, Look, J. W. Hemsky, and J. R. Sizelove, Phys. Rev.Lett. 82, 2552 (1999).[7] N. Teraguchi, A. Suzuki, Y. Nanishi, Y.-K. Zhou, M.Hashimoto and H. Asahi, Sol. State Comm. 122, 651(2002).[8] S. Dhar, O. Brandt, M. Ramsteiner, V. F. Sapega, andK. H. Ploog, Phys. Rev. Lett. 94, 037205 (2005).[9] H. Asahi, Y. K. Zhou, M. Hashimoto, M. S. Kim, X.J. Li, S. Emura, and S. Hasegawa, J. Phys.: Condens.Matter 16, S5555 (2004).[10] J. M. D. Coey, M. Venkatesan, and C. B. Fitzgerald,Nature Materials 4, 173 (2005).[11] S.-H. Wei and H. Krakauer, Phys. Rev. Lett. 55, 1200(1985); D. J. Singh, Planewaves, Pseudopotentials, andthe LAPW Method, (Kluwer, Boston, 1994).[12] H. J. Monkhorst and J. P. Pack, Phys. Rev. B 13, 5188(1976).[13] D. X. Li, Y. Haga, H. Shida, T. Suzuki, Y. S. Kwon andG. Kido, J. Phys.: Condens. Matter 9, 10777 (1997).[14] A. Janotti, S.-H. Wei, and L. Bellaiche, Appl. Phys. Lett.82, 766 (2003).[15] S.-H. Wei and Alex Zunger, Phys. Rev. B 48, 6111(1993).[16] J. P. Perdew and Y. Wang, Phys. Rev. B 45, 13244(1992).[17] H. Hashimoto, S. Emura, R. Asano, H. Tanaka, N. Ter-aguchi, A. Suzuki, Y. Nanishi, T. Honma, N. Umesaki,H. Asahi , Phys. Stat. Sol. (c) 0, 2650 (2003).[18] W. R. L. Lambrecht, Phys. Rev. B 62, 13538 (2000).[19] G. M. Dalpian, S.-H. Wei, X. G. Gong, A. J. R. da Silva,and A. Fazzio, cond-mat/0504084.[20] Y. K. Zhou, M. S. Kim, X. J. Li, S. Kimura, A. Kaneta,Y. Kawakami, Sg. Fujita, S. Emura, S. Hasegawa and H.Asahi , J. Phys.: Condens. Matter 16, S5743 (2004).
Recent studies inspired by results from random matrix theory (Galluccio et al.: Physica A 259 (1998) 449; Laloux et al.: Phys. Rev. Lett. 83 (1999) 1467; Risk 12 (3) (1999) 69; Plerou et al.: Phys. Rev. Lett. 83 (1999) 1471) found that covariance matrices determined from empirical financial time series appear to contain such a high amount of noise that their structure can essentially be regarded as random. This seems, however, to be in contradiction with the fundamental role played by covariance matrices in finance, which constitute the pillars of modern investment theory and have also gained industry-wide applications in risk management. Our paper is an attempt to resolve this embarrassing paradox. The key observation is that the effect of noise strongly depends on the ratio r=n/T, where n is the size of the portfolio and T the length of the available time series. On the basis of numerical experiments and analytic results for some toy portfolio models we show that for relatively large values of r (e.g. 0.6) noise does, indeed, have the pronounced effect suggested by Galluccio et al. (1998), Laloux et al. (1999) and Plerou et al. (1999) and illustrated later by Laloux et al. (Int. J. Theor. Appl. Finance 3 (2000) 391), Plerou et al. (Phys. Rev. E, e-print cond-mat/0108023) and Rosenow et al. (Europhys. Lett., e-print cond-mat/0111537) in a portfolio optimization context, while for smaller r (around 0.2 or below), the error due to noise drops to acceptable levels. Since the length of available time series is for obvious reasons limited in any practical application, any bound imposed on the noise-induced error translates into a bound on the size of the portfolio. In a related set of experiments we find that the effect of noise depends also on whether the problem arises in asset allocation or in a risk measurement context: if covariance matrices are used simply for measuring the risk of portfolios with a fixed composition rather than as inputs to optimization, the effect of noise on the measured risk may become very small.
We describe the localization transition of superfluids on two-dimensional lattices into commensurate Mott insulators with average particle density p/q (p, q relatively prime integers) per lattice site. For bosons on the square lattice, we argue that the superfluid has at least q degenerate species of vortices which transform under a projective representation of the square lattice space group (a PSG). The formation of a single vortex condensate produces the Mott insulator, which is required by the PSG to have density wave order at wavelengths of q/n lattice sites (n integer) along the principle axes; such a second-order transition is forbidden in the Landau-Ginzburg-Wilson framework. We also discuss the superfluid-insulator transition in the direct boson representation, and find that an interpretation of the quantum criticality in terms of deconfined fractionalized bosons is only permitted at special values of q for which a permutative representation of the PSG exists. We argue (and demonstrate in detail in a companion paper: L. Balents et al., cond-mat/0409470) that our results apply essentially unchanged to electronic systems with short-range pairing, with the PSG determined by the particle density of Cooper pairs. We also describe the effect of static impurities in the superfluid: the impurities locally break the degeneracy between the q vortex species, and this induces density wave order near each vortex. We suggest that such a theory offers an appealing rationale for the local density of states modulations observed by Hoffman et al. (cond-mat/0201348) in STM studies of the vortex lattice of BSCCO, and allows a unified description of the nucleation of density wave order in zero and finite magnetic fields. We note signatures of our theory that may be tested by future STM experiments.
For nearly half a century the supersolid phase of matter has remained mysterious, not only eluding experimental observation, but also generating a great deal of controversy among theorists. The recent discovery of what is interpreted as a non-classical moment of inertia at low temperature in solid 4He [E. Kim and M.H.W. Chan, Nature 427 225 (2004a); E. Kim and M.H.W. Chan, Science 305 1941 (2004b); E. Kim and M.H.W. Chan, Phys. Rev. Lett. 97 115302 (2006); A.C. Clark and M.H.W. Chan, J. Low Temp. Phys. 138 853 (2005)] has elicited much excitement as a possible first observation of a supersolid phase. In the two years following the discovery, however, more puzzles than answers have been provided to the fundamental issue of whether the supersolid phase exists, in helium or any other naturally occurring condensed matter system. Presently, there is no established theoretical framework to understand the body of experimental data on 4He. Different microscopic mechanisms that have been suggested to underlie superfluidity in a perfect quantum crystal do not seem viable for 4He, for which a wealth of experimental and theoretical evidence points to an insulating crystalline ground state. This perspective addresses some of the outstanding problems with the interpretation of recent experimental observations of the apparent superfluid response in 4He (seen now by several groups, e.g. A.S. Rittner and J.D. Reppy 2006; M. Kondo, S. Takada, Y. Shibayama and K. Shirahama, Proceedings of QFS2006, Kyoto, Submitted to J. Low Temp. Phys.; A. Penzyev, Y. Yasuta and M. Kubota, Proceedings of QFS2006, Kyoto, Submitted to J. Low Temp. Phys., cond-mat/0702632.) and discusses various scenarios alternative to the homogeneous supersolid phase, such as superfluidity induced by extended defects of the crystalline structure, including grain boundaries, dislocations and anisotropic stresses. Can a metastable superfluid ‘glassy’ phase exist, and can it be relevant to some of the experimental observations? One of the most interesting and unsolved fundamental questions is what interatomic potentials, given the freedom to design one, can support an ideal supersolid phase in continuous space, and can they be found in Nature.
Systems with long-range persistence and memory are shown to exhibit different precursory as well as recovery patterns in response to shocks of exogenous versus endogenous origins. By endogenous, we envision either fluctuations resulting from an underlying chaotic dynamics or from a stochastic forcing origin which may be external or be an effective coarse-grained description of the microscopic fluctuations. In this scenario, endogenous shocks result from a kind of constructive interference of accumulated fluctuations whose impacts survive longer than the large shocks themselves. As a consequence, the recovery after an endogenous shock is in general slower at early times and can be at long times either slower or faster than after an exogenous perturbation. This offers the tantalizing possibility of distinguishing between an endogenous versus exogenous cause of a given shock, even when there is no “smoking gun”. This could help in investigating the exogenous versus self-organized origins in problems such as the causes of major biological extinctions, of change of weather regimes and of the climate, in tracing the source of social upheaval and wars, and so on. Sornette et al., Volatility fingerprints of large stocks: endogenous versus exogenous, cond-mat/0204626 has already shown how this concept can be applied concretely to differentiate the effects on financial markets of the 11 September 2001 attack or of the coup against Gorbachev on 19 August 1991 (exogenous) from financial crashes such as October 1987 (endogenous).