29 research outputs found
On the origin of X-ray spectra in luminous blazars
Gamma-ray luminosities of some quasar-associated blazars imply jet powers
reaching values comparable to the accretion power even if assuming very strong
Doppler boosting and very high efficiency of gamma-ray production. With much
lower radiative efficiencies of protons than of electrons, and the recent
reports of very strong coupling of electrons with shock-heated protons
indicated by Particle-in-Cell (PIC) simulations, the leptonic models seem to be
strongly favored over the hadronic ones. However, the electron-proton coupling
combined with the ERC (External-Radiation-Compton) models of gamma-ray
production in leptonic models predict extremely hard X-ray spectra, with energy
indices about 0. This is inconsistent with the observed 2-10 keV slopes of
blazars, which cluster around an index value of 0.6. This problem can be
resolved by assuming that electrons can be cooled down radiatively to
non-relativistic energies, or that blazar spectra are entirely dominated by the
SSC (Synchrotron-Self Compton) component up to at least 10 keV. Here, we show
that the required cooling can be sufficiently efficient only at distances r <
0.03pc. SSC spectra, on the other hand, can be produced roughly co-spatially
with the observed synchrotron and ERC components, which are most likely located
roughly at a parsec scale. We show that the dominant SSC component can also be
produced much further than the dominant synchrotron and ERC components, at
distances larger than 10 parsecs. Hence, depending on the spatial distribution
of the energy dissipation along the jet, one may expect to see
gamma-ray/optical events with either correlated or uncorrelated X-rays. In all
cases the number of electron-positron pairs per proton is predicted to be very
low. The direct verification of the proposed SSC scenario requires sensitive
observations in the hard X-ray band which is now possible with the NuSTAR
satellite.Comment: 19 pages, 1 figure, accepted for publication in Ap
Neighbourhood Properties in Some Single Processor Scheduling Problem with Variable Efficiency and Additional Resources
In the paper, we consider a problem of scheduling a set of tasks on a single processor. Each task must be preprocessed before it can be started on a processor. The efficiency of preprocessing is variable, i.e., the rate of the task preprocessing depends on the amount of continuously divisible resource allotted to this task. This dependency is given by concave, continuous, non-negative and strictly increasing function of the resource amount. The total consumption of resource at each moment is upper bounded. The objective is to minimize the maximum task completion time. The considered problem is NP-hard. Such a problem appears, e.g., in steel mill systems, where ingots (before hot rolling on the blooming mill) have to achieve the required temperature in the preheating process in soaking pits. Some new properties of the problem are proved. These properties are used to construct the procedure for evaluation of the neighbourhood. The procedure is proposed to improve the efficiency of algorithms based on the neighbourhood concept, such as metaheuristics. The computational experiment is conducted to examine the efficiency of the proposed procedure. The described approach can be easily used in the other discrete-continuous scheduling problems
MONTE CARLO SIMULATIONS FOR THE CHERENKOV TELESCOPE ARRAY OBSERVATORY USING PL-GRID E-INFRASTRUCTURE
The paper presents Monte Carlo simulations carried out during the preparatory phase of the Cherenkov Telescope Array project. The aim of the project is to build the next generation observatory of very high energy gamma rays. During the preparatory phase there is a need to optimize and verify design concepts for various elements of the array. In this paper we describe the main components of the software being used for that purpose, their functions and requirements. Preliminary results of the optimization of the small telescope – one of the several kinds intended for the array, are presented
Neighbourhood properties in some single processor scheduling problem with variable efficiency and additional resources
Tyt. z nagłówka.Bibliogr. s. 16-17.In the paper, we consider a problem of scheduling a set of tasks on a single processor. Each task must be preprocessed before it can be started on a processor. The efficiency of preprocessing is variable, i.e., the rate of the task preprocessing depends on the amount of continuously divisible resource allotted to this task. This dependency is given by concave, continuous, non-negative and strictly increasing function of the resource amount. The total consumption of resource at each moment is upper bounded. The objective is to minimize the maximum task completion time. The considered problem is NP-hard. Such a problem appears, e.g., in steel mill systems, where ingots (before hot rolling on the blooming mill) have to achieve the required temperature in the preheating process in soaking pits. Some new properties of the problem are proved. These properties are used to construct the procedure for evaluation of the neighbourhood. The procedure is proposed to improve the efficiency of algorithms based on the neighbourhood concept, such as metaheuristics. The computational experiment is conducted to examine the efficiency of the proposed procedure. The described approach can be easily used in the other discrete-continuous scheduling problems.Dostępny również w wersji drukowanej.KEYWORDS: scheduling, optimization, resource allocation, neighbourhood
Resource level minimization in the discrete-continuous scheduling
A discrete-continuous problem of non-preemptive task scheduling on identical parallel processors is considered. Tasks are described by means of a dynamic model, in which the speed of the task performance depends on the amount of a single continuously divisible renewable resource allotted to this task over time. An upper bound on the completion time of all the tasks is given. The criterion is to minimize the maximum resource consumption at each time instant, i.e., the resource level. This problem has been observed in many industrial applications, where a continuously divisible resource such as gas, fuel, electric, hydraulic or pneumatic power, etc., has to be distributed among the processing units over time, and it affects their productivity. The problem consists of two interrelated subproblems: task sequencing on processors (discrete subproblem) and resource allocation among the tasks (continuous subproblem). An optimal resource allocation algorithm for a given sequence of tasks is presented and computationally tested. Furthermore, approximation algorithms are proposed, and their theoretical and experimental worst-case performances are analyzed. Computer experiments confirmed the efficiency of all the algorithms.Scheduling Discrete-continuous scheduling
Towards energy neutrality of wastewater treatment plants via deammonification process
Energy neutrality of wastewater treatment plants is possible with constant and consistent optimization and implementation of new technologies. In recent years new process called deammonification has been discovered and implemented in treatment of side streams rich in nitrogen. With its implementation on wastewater treatment plants it is possible to remove nearly all nitrogen from side stream (even 30% of overall nitrogen load) in less energy consuming way. Additionally, thanks to lower nitrogen load to main stream reactors it is possible to optimize them to further lower energy consumption. This article presents simulation studies of deammonification implementation and main stream reactor optimization in case of medium Polish WWTP (115 000 p.e.). With removal of 20% of nitrogen in side stream via deammonification and subsequent main line optimization it is possible to save 5000 euro/year by lowering sludge retention time, oxygen concentration in main stream reactors. When additional COD is precipitated in primary clarifiers with iron coagulants, 55 000 euro/year can be saved in case of energy costs which states for most of the energy costs. However, when coagulant and disposal costs are included savings are on the level of 25 000 euro/year