326,590 research outputs found
Virtual private network design over the first Chvátal closure
Get PDFIn this paper we consider the virtual private network (VPN) design problem. Given upper bounds on the amount of traf- fic that an endpoint could send or receive, the problem needs to reserve enough capacities in such a way that any demand matrix that respects the upper bound could be routed without exceeding the reserved ca- pacities and the total reservation cost is minimized. In [A. Moradi, A. Lodi and S.M. Hashemi. Networks 63 (2014) 327–333.] it is argued that the computational investigation on exact mathematical program- ming approaches for VPN needs to be revised after that challenging instances have been exposed. To that end, we consider the VPN design problem over the first Chva ́tal closure and demonstrate that tight so- lutions could be found for the VPN design problem only by optimizing over the closure. First, we perform theoretical investigation on adding rank-1 Chva ́tal–Gomory cuts to the problem. Along the way, an im- portant property for such cuts is proved that omits a large number of redundant rank-1 cuts. We then provide interesting insights about the problem and reduce the existing MIP formulations to a binary one. On the computational side, we investigate the idea of adding rank-1 cuts more aggressively in order to computationally evaluate tightness of the first Chva ́tal closure for the VPN design problem. Here, the binary re- duction plays an important role allowing the use of special cuts of the first closure, namely the zero-half cuts. We show that, almost all the success of the first Chv ́atal closure of the VPN design problem in rais- ing dual bound is due to zero-half cuts. Our experiments on the bench- mark instances in [A. Moradi, A. Lodi and S.M. Hashemi. Networks 63 (2014) 327–333.] show that a state-of-the-art IP solver without using zero-half cuts could not even hit the challenging benchmarks. As a re- sults a cut-and-branch framework that aggressively adds such cuts at the root could solve the challenging VPN instances to the extent of zero or small integrality gap in a reasonable amount of time
Directional time-distance probing of model sunspot atmospheres
No full textA crucial feature not widely accounted for in local helioseismology is that surface magnetic regions actually open a window from the interior into the solar atmosphere, and that the seismic waves leak through this window, reflect high in the atmosphere, and then re-enter the interior to rejoin the seismic wave field normally confined there. In a series of recent numerical studies using translation invariant atmospheres, we utilized a ‘directional time–distance helioseismology’ measurement scheme to study the implications of the returning fast and Alfvén waves higher up in the solar atmosphere on the seismology at the photosphere (Cally & Moradi 2013; Moradi & Cally 2014). In this study, we extend our directional time–distance analysis to more realistic sunspot-like atmospheres to better understand the direct effects of the magnetic field on helioseismic travel-time measurements in sunspots. In line with our previous findings, we uncover a distinct frequency-dependent directional behaviour in the travel-time measurements, consistent with the signatures of magnetohydrodynamic mode conversion. We found this to be the case regardless of the sunspot field strength or depth of its Wilson depression. We also isolated and analysed the direct contribution from purely thermal perturbations to the measured travel times, finding that waves propagating in the umbra are much more sensitive to the underlying thermal effects of the sunspot
An agent-based DDM for high level architecture
No full textThe Data Distribution Management (DDM) service is one of the six services provided in the Runtime Infrastructure (RTI) of High Level Architecture (HLA). Its purpose is to perform data filtering and reduce irrelevant data communicated between federates. The two DDM schemes proposed for RTI, region based and grid based DDM, are oriented to send as little irrelevant data to subscribers as possible, but only manage to filter part of this information and some irrelevant data is still being communicated. Previously (G. Tan et al., 2000), we employed intelligent agents to perform data filtering in HLA, implemented an agent based DDM in RTI (ARTI) and compared it with the other two filtering mechanisms. The paper reports on additional experiments, results and analysis using two scenarios: the AWACS sensing aircraft simulation and the air traffic control simulation scenario. Experimental results show that compared with other mechanisms, the agent based approach communicates only relevant data and minimizes network communication, and is also comparable in terms of time efficiency. Some guidelines on when the agent based scheme can be used are also give
Aktivitas Digital Marketing di PT Moradi (Retail Orang Tua Group)
Get PDFPraktik kerja magang merupakan salah satu kesempatan mahasiswa untuk mendapatkan pengalaman pada bidang Ilmu Komunikasi di lapangan kerja, dan dapat menerapkan ilmu teoritis yang diperoleh di perkuliahan. Pemagang mengambil kesempatan melakukan praktik kerja magang sebagai Digital Marketing Intern di Retail Orang Tua Group, yakni MOR (PT Moradi). Pemagang bertanggung jawab atas media sosial MOR dan dua sub-brandnya, Gorenc dan T'Endang. Tujuan dari praktik kerja magang ini adalah demi memperoleh pengalaman dalam Social Media and Mobile Marketing Strategy terhadap kenaikan brand awareness, memperoleh pengetahuan dan pengembangan soft skill berupa pencarian konten yang sedang tren, content planning, content execution, video editing, serta mengetahui dan mencari Key Opinion Leader (KOL) yang sesuai dengan brand. Tugas utama pemagang adalah content planning dan creation, melakukan kerja sama dengan KOL, dan membuat monthly report content untuk insights konten. Selama melakukan praktik kerja magang, pemagang menyadari bahwa digital marketing memegang peran penting dalam menaikan brand awareness. Hal ini dapat dilihat dari kenaikan followers, account reach, dan account engagement pada media sosial PT Moradi, yang membuat nama brand brand PT Moradi semakin dikenal
Germination and seedling growth responses of zygophyllum fabago, salsola kali l. And atriplex canescens to peg-induced drought stress
No full textIn arid and semi-arid regions, planting drought-tolerant species is the most useful strategy in the reclamation of degraded soils. In the present study, we evaluated the effect of simulated drought by polyethylene glycol (PEG-6000) on seed germination and seedling growth of three desert plants such as Atriplex canescens, Salsola kali and Zygophyllum fabago. Seeds were subjected to water stress to drought stress by PEG at five stress levels (0, −1, −4, −8, −12, −14 bars). Germination of Z. fabago was completely inhibited at an osmotic potential of −8, −10 and −12 bars and the germination of A. canescens was inhibited only at −14 bar. In contrast, S. kali responded positively to high levels of stress and our results showed the highest final germination percent (71.75, 54 and 18.25%) under three-drought stress −8, −12 and −14 bars, respectively. In addition, increasing PEG concentration adversely affected the germination rate and seedling vigor index as well as the root and shoot length of species. Under high stress levels, S. kali achieved a higher germination rate and seedling vigor index compared to Z. fabago and A. canescens. Among species, S. kali was the only one able to develop roots and shoots at −14 bar. Therefore, S. kali could be considered as a promising plant for the rehabilitation of degraded soils at risk of desertification
Influence of elevation on the species–area relationship
Get PDFAim: Species–area relationships (SARs) are among the best investigated patterns in ecology, yet the shape of the function that should describe SARs and the biological meaning of the function parameters are disputed. Elevational gradients offer the opportunity of investigating how biodiversity responds to large variations in environmental characteristics within small geographical areas. We asked which function describes SARs at different elevations and explored how variations in environmental characteristics influence SAR shape. Location: Alborz Mountains (Iran). Taxon: Vascular plants. Methods: We used sets of nested plots (0.001 to 100 m2) placed at 100 m intervals from 2,000 to 4,500 m elevation to construct series of nested SARs as species accumulation curves. Then, we used these curves to assess the appropriateness of different SAR functions at different elevations. We investigated how parameters of the power function varied along the elevational gradient in response to variation in environmental parameters (ruggedness, temperature, precipitation, exposed rock, percentages of soil sand and total nitrogen, and productivity, expressed by the normalized difference vegetation index). Results: The most frequently observed best fit model was the power function, which is controlled by two parameters: z (the velocity in species accumulation with sampled area) and c (the species richness per unit area). z was positively influenced by temperature and soil nitrogen, decreasing with elevation. c was positively influenced by temperature and soil nitrogen, and negatively by rock cover, decreasing with elevation. Main conclusions: The decrease in c-values with elevation is consistent with the altitudinal decrease in species richness and is explained by the increase in bare rock. By contrast, c was positively influenced by temperature and total nitrogen, which are two factors promoting plant growth. Similarly, z-values decreased with elevation, thus indicating a decrease in beta diversity
On the difficulty of virtual private network instances
No full textThe virtual private network design problem has attracted an impressive number of theoretical contributions but, surprisingly, very little computational attempts. This might be due to the fact that the compact formulation proposed in [Altın et al. Networks 49 (2007), 100–115] turned out to be very tight, that is, showing very little or no integrality gap in the computational experiments. In this short note, we first confirm the observations in [Altın et al. Networks 49 (2007), 100–115] by analyzing in detail the behavior of the compact formulation on a larger but similar testbed, and then we provide a set of difficult instances exposing large integrality gaps. This new insight is likely to reinvigorate efforts to develop effective exact computational approaches
Spin-particles entanglement in Robertson-Walker spacetime
No full textWe study the entanglement between two modes of Dirac field in an expanding spacetime characterized by the Robertson-Walker metric. This spacetime model turns out to be asymptotically (in the remote past and far future regions) Minkowskian. Then, on the one hand we show entanglement creation between particles and antiparticles when passing from remote past to far future. On the other hand, we show that particles entanglement in the remote past degrades into the far future. These effects are traced back to particle creation. In our analysis we highlight the role of spin (polarization) of particles and compare the results with those obtainable without accounting for it
Optimization of a solar air heater with phase change materials: Experimental and numerical study
Get PDFIn this paper, a solar air heater (SAH) with phase change material (PCM)-based energy storage is investigated. Paraffin was placed underneath the absorber plate as the PCM. A transient two-dimensional laminar model was used in the Ansys Fluent 17 software to study the effects of different parameters on the performance of the SAH, such as the air mass flow rate, the amount of paraffin, and the thermal conductivity of the paraffin. The performance of the SAH was optimized by considering two objectives simultaneously: thermal energy efficiency and maximum nocturnal temperature difference between the inlet and the outlet of the SAH. To validate the numerical model, a SAH with a 2-cm paraffin layer and the same dimensions as the numerical model was built and tested. The results of the simulation showed good agreement with the experimental results.
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