Browsing by Subject "Network"

Now showing 1 - 8 of 8

Open Access
60 GHz wireless data center networks: A survey
(Elsevier BV * North-Holland, 2021-02-11) Terzi, Çağlar; Körpeoğlu, İbrahim
Data centers (DCs) became an important part of computing today. A lot of services in Internet are run on DCs. Meanwhile a lot of research is done to tackle the challenges of high-performance and energy-efficient data center networking (DCN). Hot node congestion, cabling complexity/cost, and cooling cost are some of the important issues about data centers that need further investigation. Static and rigid topology in wired DCNs is an other issue that hinders flexibility. Use of wireless links for DCNs to eliminate these disadvantages is proposed and is an important research topic. In this paper, we review research studies in literature about the design of radio frequency (RF) based wireless data center networks. RF wireless DCNs can be grouped into two as hybrid (wireless and wired) and completely wireless data centers. We investigate both. We also compare wireless DCN solutions in the literature with respect to various aspects. Open areas and research ideas are also discussed.
Open Access
Beyond hierarchies: emerging organizational structures that are non-hierarchical
(1995) Karpuzoğlu, Gürhan
Open Access
Design of an interactive sequential graphic system on cyber-space
(2000) Atasoy, Berke
The aim of this study is to explore and discuss the possibility of an interactive sequential system on World Wide Web. It is an attempt to formulate a definition for a system, which utilises different mediums like text, image and audio in the standards of World Wide Web with a motive for generating a sequential art product in the cyber-space. The study discusses a software model, which offers a set of actions in which the user can participate in the development process of the system by creating and combining different media.
Open Access
Group-level ranking-based hubness analysis of human brain connectome reveals significant interhemispheric asymmetry and intraparcel heterogeneities
(Frontiers Media S.A., 2021-12-21) Hanalioğlu, Ş; Bahadır, S.; Işıkay, İ.; Çeltikçi, P.; Çeltikçi, E.; Yeh, F.-C.; Karlı Oğuz, Keder; Khaniyev, Taghi
Objective: Graph theory applications are commonly used in connectomics research to better understand connectivity architecture and characterize its role in cognition, behavior and disease conditions. One of the numerous open questions in the field is how to represent inter-individual differences with graph theoretical methods to make inferences for the population. Here, we proposed and tested a simple intuitive method that is based on finding the correlation between the rank-ordering of nodes within each connectome with respect to a given metric to quantify the differences/similarities between different connectomes. Methods: We used the diffusion imaging data of the entire HCP-1065 dataset of the Human Connectome Project (HCP) (n = 1,065 subjects). A customized cortical subparcellation of HCP-MMP atlas (360 parcels) (yielding a total of 1,598 ROIs) was used to generate connectivity matrices. Six graph measures including degree, strength, coreness, betweenness, closeness, and an overall “hubness” measure combining all five were studied. Group-level ranking-based aggregation method (“measure-then-aggregate”) was used to investigate network properties on population level. Results: Measure-then-aggregate technique was shown to represent population better than commonly used aggregate-then-measure technique (overall rs: 0.7 vs 0.5). Hubness measure was shown to highly correlate with all five graph measures (rs: 0.88–0.99). Minimum sample size required for optimal representation of population was found to be 50 to 100 subjects. Network analysis revealed a widely distributed set of cortical hubs on both hemispheres. Although highly-connected hub clusters had similar distribution between two hemispheres, average ranking values of homologous parcels of two hemispheres were significantly different in 71% of all cortical parcels on group-level. Conclusion: In this study, we provided experimental evidence for the robustness, limits and applicability of a novel group-level ranking-based hubness analysis technique. Graph-based analysis of large HCP dataset using this new technique revealed striking hemispheric asymmetry and intraparcel heterogeneities in the structural connectivity of the human brain.
Open Access
High-frequency return and volatility spillovers among cryptocurrencies
(Routledge, 2021-03-22) Şensoy, Ahmet; Silva, T. C.; Corbet, S.; Tabak, B. M.
We examine the high-frequency return and volatility of major cryptocurrencies and reveal that spillovers among them exist. Our analysis shows that return and volatility clustering structures are distinct among different cryptocurrencies, suggesting that return and volatility might have different spillover patterns. Further investigation via minimal spanning trees points out that BTC, LTC and ETH are the most relevant cryptocurrencies in general, serving as connection hubs for linking many other cryptocurrencies. However, their role is challenged lately, potentially due to the increased usage of other cryptocurrencies in time.
Open Access
Intrinsic oscillations of auditory networks in schizophrenia and bipolar disorder
(Yerküre Tanıtım ve Yayıncılık Hizmetleri A. Ş., 2019) Atagün, M. İ.; Akın, B.; Algın, Oktay; Sıkoğlu, E. M.; Can, S. S.; Kaymak, S. U.; Çayköylü, A.; Moore, C.; Phillips, M.; Ongur, D.
Objective: Several types of evidence have shown that auditory networks are dysfunctional in schizophrenia (Sch) and bipolar disorders (BD). Auditory cortices show abnormalities in hallucinations or during remission. This study aimed to assess resting-state connectivity of auditory cortices in Sch and BD. Method: Patients with BD-1 (n=28), BD-2 (n=21), Sch (n=30), and healthy controls (HC, n=30) were enrolled into the study. A 3 Tesla whole-body magnetic resonance imaging (MRI) system with a 32-channel phase-array head coil was used to acquire the MRI data. T1-weighted anatomical and gradient-echo based Echoplanar Imaging sequences were used. MATLAB and Freesurfer software packages were used for data analyses. Connectivity alterations within the auditory network guided our further seedbased connectivity analysis. Results: The left angular gyrus volume was decreased in Sch and BD-2 groups. The supramarginal gyrus had hyperconnectivity with the medial prefrontal cortices and decreased connectivity with the medial superior temporal gyrus (STG) in the BD-1 and BD-2 groups. The left superior temporal sulcus (STS) had increased connectivity with the bilateral posterior cingulate cortex in BD-1 and BD-2 and increased connectivity with the dorsal prefrontal cortices in the Sch group. The STS had increased connectivity with the medial STG in the BD-1 and Sch groups, whereas connectivity decreased in the BD-2 group. Conclusion: These findings suggest that functional connectivity of resting-state networks are altered in BD and Sch. Auditory network alterations may predispose to dysfunctional auditory information processing. Further studies are needed to determine the relationship between symptoms and auditory network dysfunction.
Open Access
Multistage optical interconnection architectures with the least possible growth of system size
(Optical Society of America, 1993) Özaktaş, Haldun M.; Mendlovic, D.
Multistage interconnection architectures can provide an arbitrary pattern of one-to-one connections between N input and N output channels. We show that bitonic multistage architectures, such as the Banyan architecture, result in the fundamentally least possible growth of system size with increasing N.
Open Access
A review of network location theory and models
(2004) Erdoğan, Damla Selin
In this study, we review the existing literature on network location problems. The study has a broad scope that includes problems featuring desirable and undesirable facilities, point facilities and extensive facilities, monopolistic and competitive markets, and single or multiple objectives. Deterministic and stochastic models as well as robust models are covered. Demand data aggregation is also discussed. More than 500 papers in this area are reviewed and critical issues, research directions, and problem extensions are emphasized.