1,019 research outputs found
AdS flowing black funnels: Stationary AdS black holes with non-Killing horizons and heat transport in the dual CFT
We construct stationary non-equilibrium black funnels locally asymptotic to
global AdS4 in vacuum Einstein-Hilbert gravity with negative cosmological
constant. These are non-compactly-generated black holes in which a single
connected bulk horizon extends to meet the conformal boundary. Thus the induced
(conformal) boundary metric has smooth horizons as well. In our examples, the
boundary spacetime contains a pair of black holes connected through the bulk by
a tubular bulk horizon. Taking one boundary black hole to be hotter than the
other () prohibits equilibrium. The result is a so-called
flowing funnel, a stationary bulk black hole with a non-Killing horizon that
may be said to transport heat toward the cooler boundary black hole. While
generators of the bulk future horizon evolve toward zero expansion in the far
future, they begin at finite affine parameter with infinite expansion on a
singular past horizon characterized by power-law divergences with universal
exponents. We explore both the horizon generators and the boundary stress
tensor in detail. While most of our results are numerical, a semi-analytic
fluid/gravity description can be obtained by passing to a one-parameter
generalization of the above boundary conditions. The new parameter detunes the
temperatures and of the bulk and boundary black
holes, and we may then take \alpha =
and \Delta T small to control the accuracy of the fluid-gravity approximation.
In the small \alpha, \Delta T regime we find excellent agreement with our
numerical solutions. For our cases the agreement also remains quite good even
for . In terms of a dual CFT, our \alpha = 1 solutions
describe heat transport via a large N version of Hawking radiation through a
deconfined plasma that couples efficiently to both boundary black holes
Lin-Kernighan Heuristic Adaptations for the Generalized Traveling Salesman Problem
The Lin-Kernighan heuristic is known to be one of the most successful
heuristics for the Traveling Salesman Problem (TSP). It has also proven its
efficiency in application to some other problems. In this paper we discuss
possible adaptations of TSP heuristics for the Generalized Traveling Salesman
Problem (GTSP) and focus on the case of the Lin-Kernighan algorithm. At first,
we provide an easy-to-understand description of the original Lin-Kernighan
heuristic. Then we propose several adaptations, both trivial and complicated.
Finally, we conduct a fair competition between all the variations of the
Lin-Kernighan adaptation and some other GTSP heuristics. It appears that our
adaptation of the Lin-Kernighan algorithm for the GTSP reproduces the success
of the original heuristic. Different variations of our adaptation outperform
all other heuristics in a wide range of trade-offs between solution quality and
running time, making Lin-Kernighan the state-of-the-art GTSP local search.Comment: 25 page
Theory of Interfacial Plasmon-Phonon Scattering in Supported Graphene
One of the factors limiting electron mobility in supported graphene is remote
phonon scattering. We formulate the theory of the coupling between graphene
plasmon and substrate surface polar phonon (SPP) modes, and find that it leads
to the formation of interfacial plasmon-phonon (IPP) modes, from which the
phenomena of dynamic anti-screening and screening of remote phonons emerge. The
remote phonon-limited mobilities for SiO, HfO, h-BN and
AlO substrates are computed using our theory. We find that h-BN
yields the highest peak mobility, but in the practically useful high-density
range the mobility in HfO-supported graphene is high, despite the fact
that HfO is a high- dielectric with low-frequency modes. Our
theory predicts that the strong temperature dependence of the total mobility
effectively vanishes at very high carrier concentrations. The effects of
polycrystallinity on IPP scattering are also discussed.Comment: 33 pages, 7 figure
Physical activities and enjoyment during the lockdown: Effect of home-based supervised training among children and adolescents
Enjoyment during physical and sport activities is an essential and well recognized component that has been
also related to motor ability in children. During the period of home confinement due to Covid-19 lockdown,
the Italian version of the Physical Activity Enjoyment Scale (PACES-It) was used to evaluate the level of
enjoyment in physical and sports activities. The beginning stem of the questionnaire was modified by asking
subjects âDuring the lockdown, when I am physically activeâŠâ. Data were collected on a sample of 140
among children and adolescents (60 aged 6-11 and 80 aged 12-15, 66% males and 34% females). About
90% of subjects followed online school classes and 83% also received indications from their Sports
Associations about physical home-exercises and other forms of guided distance learning. Results from
PACES showed that subjects liked the home physical activities with a mean value of 65.2 11.8 with higher
values from those who received online support from their regular instructors; moreover, higher values from
PACES were obtained by middle school children respect to primary school children and high school
adolescents. Despite the mandatory confinement, a positive feedback regarding the enjoyment was reported
by children and adolescents for the home distance modality
The role of electron-electron scattering in spin transport
We investigate spin transport in quasi 2DEG formed by III-V semiconductor
heterojunctions using the Monte Carlo method. The results obtained with and
without electron-electron scattering are compared and appreciable difference
between the two is found. The electron-electron scattering leads to suppression
of Dyakonov-Perel mechanism (DP) and enhancement of Elliott-Yafet mechanism
(EY). Finally, spin transport in InSb and GaAs heterostructures is investigated
considering both DP and EY mechanisms. While DP mechanism dominates spin
decoherence in GaAs, EY mechanism is found to dominate in high mobility InSb.
Our simulations predict a lower spin relaxation/decoherence rate in wide gap
semiconductors which is desirable for spin transport.Comment: to appear in Journal of Applied Physic
The new Dutch timetable: The OR revolution
In December 2006, Netherlands Railways introduced a completely new timetable. Its objective was to facilitate the growth of passenger and freight transport on a highly utilized railway network, and improve the robustness of the timetable resulting in less train delays in the operation. Further adjusting the existing timetable constructed in 1970 was not option anymore, because further growth would then require significant investments in the rail infrastructure. Constructing a railway timetable from scratch for about 5,500 daily trains was a complex problem. To support this process, we generated several timetables using sophisticated operations research techniques, and finally selected and implemented one of these timetables. Furthermore, because rolling-stock and crew costs are principal components of the cost of a passenger railway operator, we used innovative operations research tools to devise efficient schedules for these two resources. The new resource schedules and the increased number of passengers resulted in an additional annual profit of 40 million euros (105 million) annually in the coming years. However, the benefits of the new timetable for the Dutch society as a whole are much greater: more trains are transporting more passengers on the same railway infrastructure, and these trains are arriving and departing on schedule more than they ever have in the past. In addition, the rail transport system will be able to handle future transportation demand growth and thus allow cities to remain accessible. Therefore, people can switch from car transport to rail transport, which will reduce the emission of greenhouse gases.
Branching on multi-aggregated variables
open5siopenGamrath, Gerald; Melchiori, Anna; Berthold, Timo; Gleixner, Ambros M.; Salvagnin, DomenicoGamrath, Gerald; Melchiori, Anna; Berthold, Timo; Gleixner, Ambros M.; Salvagnin, Domenic
Crew Scheduling for Netherlands Railways: "destination: customer"
: In this paper we describe the use of a set covering model with additional constraints for scheduling train drivers and conductors for the Dutch railway operator NS Reizigers. The schedules were generated according to new rules originating from the project "Destination: Customer" ("Bestemming: Klant" in Dutch). This project is carried out by NS Reizigers in order to increase the quality and the punctuality of its train services. With respect to the scheduling of drivers and conductors, this project involves the generation of efficient and acceptable duties with a high robustness against the transfer of delays of trains. A key issue for the acceptability of the duties is the included amount of variation per duty. The applied set covering model is solved by dynamic column generation techniques, Lagrangean relaxation and powerful heuristics. The model and the solution techniques are part of the TURNI system, which is currently used by NS Reizigers for carrying out several analyses concerning the required capacities of the depots. The latter are strongly influenced by the new rules
Using phage Lytic Enzymes to Control Pathogenic Bacteria
Our laboratory has developed phage lytic enzymes to prevent infection by specifically destroying disease bacteria on mucous membranes and in blood. Enzymes specific for S. pneumoniae and S. pyogenes have been developed to be used nasally and orally to control these organisms in environments such as hospitals and nursing homes to prevent or markedly reduce serious infections by these pathogens. In addition, a B. anthracis-specific enzyme was developed to kill the vegetative forms of these bacteria in the blood of infected individuals. In animal studies, >80% of mice colonized mucosally or infected intravenously with pathogenic bacteria were decolonized or survived after a single enzyme treatment delivered to the same site of colonization or infection
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