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61.
We study a two-dimensional Bose-Hubbad model at a zero temperature with random local potentials in the presence of either uniform or binary disorder. Many low-energy metastable configurations are found with virtually the same energy as the ground state. These are characterized by the same blotchy pattern of the, in principle, complex nonzero local-order parameter as the ground state. Yet, unlike the ground state, each island exhibits an overall random independent phase. The different phases in different coherent islands could provide a further explanation for the lack of coherence observed in experiments on Bose glasses. 相似文献
62.
Elena Bertozzini Luca Galluzzi Fabio Ricci Antonella Penna Mauro Magnani 《Applied biochemistry and biotechnology》2013,170(7):1624-1636
Microalgae are one of the most promising biodiesel feedstocks due to their efficiency in CO2 fixation and high neutral lipid productivity. Nutrient–stress conditions, including nitrogen starvation, enhance neutral lipid content, but at the same time lead to a reduction of biomass. To maximize lipid production in the diatom Skeletonema marinoi, we investigated two different nitrogen starvation approaches. In the first experimental approach, inocula were effectuated in modified f/2 media with decreasing nitrogen concentration, while in the second experiment, nitrate concentration was gradually reduced through a collection/resuspension system in which the culture was periodically collected and resuspended in culture medium with a lower nitrate concentration. In the first approach, the neutral lipid accumulation was accompanied by a strong biomass reduction, as was expected, whereas the second experiment generated cultures with significantly higher neutral lipid content without affecting biomass production. The total proteins and total carbohydrates, which were also quantified in both experiments, suggest that in S. marinoi, neutral lipid accumulation during nutrient starvation did not derive from a new carbon partition of accumulated carbohydrates. 相似文献
63.
An Iterated Local Search heuristic for the Heterogeneous Fleet Vehicle Routing Problem 总被引:1,自引:0,他引:1
This paper deals with the Heterogeneous Fleet Vehicle Routing Problem (HFVRP). The HFVRP is $\mathcal{NP}$ -hard since it is a generalization of the classical Vehicle Routing Problem (VRP), in which clients are served by a heterogeneous fleet of vehicles with distinct capacities and costs. The objective is to design a set of routes in such a way that the sum of the costs is minimized. The proposed algorithm is based on the Iterated Local Search (ILS) metaheuristic which uses a Variable Neighborhood Descent procedure, with a random neighborhood ordering (RVND), in the local search phase. To the best of our knowledge, this is the first ILS approach for the HFVRP. The developed heuristic was tested on well-known benchmark instances involving 20, 50, 75 and 100 customers. These test-problems also include dependent and/or fixed costs according to the vehicle type. The results obtained are quite competitive when compared to other algorithms found in the literature. 相似文献
64.
P. Buonsante S. M. Giampaolo F. Illuminati V. Penna A. Vezzani 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):427-433
We consider strongly interacting boson-boson mixtures on one-dimensional lattices and, by adopting a qualitative mean-field
approach, investigate their quantum phases as the interspecies repulsion is increased. In particular, we analyze the low-energy
quantum emulsion metastable states occurring at large values of the interspecies interaction, which are expected to prevent the system from
reaching its true ground state. We argue a significant decrease in the visibility of the time-of-flight images in the case
of these spontaneously disordered states. 相似文献
65.
Paolo Penna 《International Journal of Game Theory》2018,47(3):839-855
Logit-response dynamics (Alós-Ferrer and Netzer in Games Econ Behav 68(2):413–427, 2010) are a rich and natural class of noisy best-response dynamics. In this work we revise the price of anarchy and the price of stability by considering the quality of long-run equilibria in these dynamics. Our results show that prior studies on simpler dynamics of this type can strongly depend on a sequential schedule of the players’ moves. In particular, a small noise by itself is not enough to improve the quality of equilibria as soon as other very natural schedules are used. 相似文献
66.
Penna M Márquez R Bosch J Crespo EG 《The Journal of the Acoustical Society of America》2006,119(2):1227-1237
This study compares the efficiency of transmission of the advertisement calls of two species of midwife toads, Alytes cisternasii and A. obstetricans, in both native and non-native habitats in the Iberian Peninsula. Recorded calls of both species and pure tones were broadcast at ten sites native to either the relatively small A. cisternasii or the larger A. obstetricans. A large variation in the patterns of excess attenuation between localities was observed for calls measured at distances of 0.5 to 8 m from a loudspeaker. However, attenuation rates were higher for calls of both species in habitats of A. obstetricans relative to habitats of A. cisternasii. The calls of A. obstetricans experienced lower attenuation rates than those of A. cisternasii in both conspecific and heterospecific localities. Thus, although A. cisternasii occupies habitats more favorable for sound transmission, its advertisement call spectrum is not optimized for these habitats; the calls of A. obstetricans suffer less attenuation in A. cisternasii habitats. This result argues against the notion that spectral features of the calls are adapted to enhance transmission efficiency in natural habitats, and suggests that differences in call dominant frequency between the two species result from constraints imposed by selection on body size. 相似文献
67.
The zero temperature phase diagram for ultracold bosons in a random 1D potential is obtained through a site decoupling mean-field scheme performed over a Bose-Hubbard (BH) Hamiltonian, whose hopping term is considered as a random variable. As for the model with random on-site potential, the presence of disorder leads to the appearance of a Bose glass phase. The different phases—i.e., Mott insulator, superfluid, and Bose glass—are characterized in terms of condensate fraction and superfluid fraction. Furthermore, the boundary of the Mott lobes is related to an off-diagonal Anderson model featuring the same disorder distribution as the original BH Hamiltonian. 相似文献
68.
A bit-string model for biological aging 总被引:1,自引:0,他引:1
T. J. P. Penna 《Journal of statistical physics》1995,78(5-6):1629-1633
We present a simple model for biological aging. We study it through computer simulations and fint it to reflect some features of real populations. 相似文献
69.
Thereza Christina Vessoni Penna Irene A. Machoshvili Marina Ishii 《Applied biochemistry and biotechnology》2003,106(1-3):287-294
The interference of eight components in the yield of sporulation and thermal resistance to moist heat (121°C) of Bacillus stearothermophilus spores suspended in 0.02 M calcium acetate solution and inoculated on paper strips previously treated with calcium acetate/calcium hydroxide was studied.
The spore yield of 1.0×108/mL was developed at 62°C in 17 media containing different concentrations of d-glucose, sodium chloride, l-glutamic acid, yeast extract, peptone, manganese sulfate, potassium phosphate, and ammonium phosphate. The combined effects
of yeast extract, peptone, and glucose contributed positively to the spore yield and to the stability of the thermal resistance
of both spores in suspension and on strips. 相似文献
70.
We investigated the spatial phase separation of the two components forming a bosonic mixture distributed in a four-well lattice with a ring geometry. We studied the ground state of this system, described by means of a binary Bose–Hubbard Hamiltonian, by implementing a well-known coherent-state picture which allowed us to find the semi-classical equations determining the distribution of boson components in the ring lattice. Their fully analytic solutions, in the limit of large boson numbers, provide the boson populations at each well as a function of the interspecies interaction and of other significant model parameters, while allowing to reconstruct the non-trivial architecture of the ground-state four-well phase diagram. The comparison with the L-well () phase diagrams highlights how increasing the number of wells considerably modifies the phase diagram structure and the transition mechanism from the full-mixing to the full-demixing phase controlled by the interspecies interaction. Despite the fact that the phase diagrams for share various general properties, we show that, unlike attractive binary mixtures, repulsive mixtures do not feature a transition mechanism which can be extended to an arbitrary lattice of size L. 相似文献