Multi-user multiple-input multiple-output (MU-MIMO) using a large number of spatially distributed antennas (DAs) is a promising technique to achieve high link capacity uniformly over a macro-cell area. To reduce the computational complexity of MU-MIMO processing, the UE clustering can be used. However, this produces the inter-cluster interference (ICI) and degrades the link capacity of a user equipment (UE) especially near the cluster boundary. In this paper, to solve the ICI problem, we propose a dynamic UE clustering in which UEs in a macro-cell area are grouped into non-overlapped UE cluster-sets and they are activated in a time-division manner. We evaluate, by computer simulation, the UE link capacity of OFDM downlink achievable by the use of the proposed dynamic UE clustering.

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In this paper, we study the degrees of freedom (DoF) of a multiple-input multiple-output (MIMO) multiway relay channel (mRC) with two relays, two clusters and K (K≥3) users per cluster. We consider a clustered full data exchange model, i.e., each user in a cluster sends a multicast (common) message to all other users in the same cluster and desires to acquire all messages from them. The DoF results of the mRC with the single relay have been reported. However, the DoF achievability of the mRC with multiple relays is still an open problem. Furthermore, we consider a more practical scenario where no channel state information at the transmitter (CSIT) is available to each user. We first give a DoF cut-set upper bound of the considered mRC. Then, we propose a distributed interference neutralization and retransmission scheme (DINR) to approach the DoF cut-set upper bound. In the absence of user cooperation, this method focuses on the beamforming matrix design at each relay. By investigating channel state information (CSI) acquisition, we show that the DINR scheme can be performed by distributed processing. Theoretical analyses and numerical simulations show that the DoF cut-set upper bound can be attained by the DINR scheme. It is shown that the DINR scheme can provide significant DoF gain over the conventional time division multiple access (TDMA) scheme. In addition, we show that the DINR scheme is superior to the existing single relay schemes for the considered mRC.

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Traditional cellular networks suffer the so-called “cell-edge problem” in which the user throughput is deteriorated because of pathloss and inter-cell (co-channel) interference. Recently, Base Station Cooperation (BSC) was proposed as a solution to the cell-edge problem by alleviating the interference and improving diversity and multiplexing gains at the cell-edge. However, it has minimal impact on cell-inner users and increases the complexity of the network. Moreover, static clustering, which fixes the cooperating cells, suffers from inter-cluster interference at the -. In this paper, dynamic fractional cooperation is proposed to realize dynamic clustering in a shared RRU network. In the proposed algorithm, base station cooperation is performed dynamically at cell edges for throughput improvement of users located in these areas. To realize such base station cooperation in large scale cellular networks, coordinated scheduling and distributed dynamic cooperation are introduced. The introduction of coordinated scheduling in BSC multi-user MIMO not only maximizes the performance of BSC for cell-edge users but also reduces computational complexity by performing simple single-cell MIMO for cell-inner users. Furthermore, the proposed dynamic clustering employing shared RRU network realizes efficient transmission at all cell edges by forming cooperative cells dynamically with minimal network complexity. Owing to the combinations of the proposed algorithms, dynamic fractional cooperation achieves high network performance at all areas in the cellular network. Simulation results show that the cell-average and the 5% cell-edge user throughput can be significantly increased in practical cellular network scenarios.

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The growth of gold on top of a n-alkane monolayer, which consists of lamellar assemblies with close-packed flat-lying chains, is observed by using scanning tunneling microscopy. The n-alkane monolayer sustains gold atoms,and penetration of the atoms into the monolayer is inhibited. The molecular conformation is unaffected and the arrangement is only slightly changed upon deposition of the gold atoms. Two-dimensional clusters are grown and a smooth monolayer is finally obtained. [DOI: 10.1380/ejssnt.2015.209]

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It is well known that nuclear pressure vessel steel shows embrittlement under thermal aging and strong neutron irradiation. We focus on nanoscale copper-rich precipitates and try to clarify the effect of the nanoscale copper-rich precipitates on embrittlement of reactor pressure vessel steels. Our final goal is to evaluate such embrittlement from microscopic viewpoint based on atomistic simulation. In this study, we simulate interaction between motion of an edge dislocation and copper clusters using Molecular Dynamics method with a PBC, where uniform shear strain is applied to the boundaries parallel to the slip plane (1 1 2) in the system. As the results, we clarify the effects of size, distance and pinning of the copper clusters on dislocation motion.

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Reflection high-energy electron diffraction (RHEED) method is one of the powerful techniques for a surface structural analysis and is conventionally used for an atomically flat crystal surface. In the case of nano crystal islands such as nano clusters or nano dots on a flat substrate, transmission pattern is observed especially on a grazing incident condition. Morphology of such nano clusters influences the spot shape of the transmission electron diffraction due to the effects of refraction and Laue function. It is shown that the chevron shape of the diffraction spots observed from Ge hut clusters grown on Si(001) substrate can be reproduced well by kinematic calculation. Relation between the spot shape and the cluster's morphology is summarized. It has been confirmed that the diffraction spots are shifted to downward normal to the facets where electrons enter or exit and their intensity distributions are prolonged by the effect of Laue function for the 's region where electrons can transmit.

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Coordinated multi-point (CoMP) transmission and reception is a promising technique for interference mitigation in cellular systems. The scheduling algorithm for CoMP has a significant impact on the network processing complexity and performance. Performing exhaustive search permits centralized scheduling and thus the optimal global solution; however, it incurs a high level of computational complexity and may be impractical or lead to high cost as well as network instability. In order to provide a more realistic scheduling method while balancing performance and complexity, we propose a low complexity centralized scheduling scheme that adaptively selects users for single-cell transmission or different CoMP scheme transmission to maximize the system weighted sum capacity. We evaluate the computational complexity and system-level simulation performance in this paper. Compared to the optimal scheduling method with exhaustive search, the proposed scheme has a much lower complexity level and achieves near optimal performance.

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　大気との気－液平衡では説明しきれない濃度のCFCsが諏訪湖湖水から検出された。本研究では，その原因を探るため，諏訪湖の集水域において，河川水および地下水の調査を行った。諏訪湖流入河川のうち，2つの河川（河川Cと河川F）で極めて高い濃度のCFCsが検出され，これらは諏訪湖の主要なCFCs流入源と考えられた。河川Cでは，高濃度のCFCsによって汚染された地下水の流入が確認された。工業活動にともなう地下水のCFCs汚染が，諏訪湖のCFCs汚染の主要な原因と考えられた。

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The cluster model calculations using the discrete variational (DV)-Xα molecular orbital method have been employed to investigate the electronic structure of the silicon nitride surface. It is found that, even though the small silicon nitride cluster is used, the hydrogen termination of edge Si atoms can successfully eliminate the edge effect and give the reasonable electronic structure.

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Coordinated Multi-point (CoMP) transmission has long been known for its ability to improve cell edge throughput. However, in a CoMP cellular network, fixed CoMP clustering results in cluster edges where system performance degrades due to non-coordinated clusters. To solve this problem, conventional studies proposed dynamic clustering schemes. However, such schemes require a complex backhaul topology and are infeasible with current network technologies. In this paper, small power base stations (BSs) are introduced instead of dynamic clustering to solve the problem in CoMP cellular networks. This new cell topology is called the diamond cellular network since the resultant cell structure looks like a diamond pattern. In our novel cell topology, we derive the optimal locations of small power base stations and the optimal resource allocation between the CoMP base station and small power base stations to maximize the proportional fair utility function. By using the proposed architecture, in the case of perfect user scheduling, a more than 150% improvement in 5% outage throughput is achieved, and in the case of successive proportional fair user scheduling, nearly 100% improvement of 5% outage throughput is achieved compared with conventional single cell networks.

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The mechanism of ferromagnetism stability in sandwich clusters V_n(C₆H₆)_n+1 has been studied by first-principles calculation and model analysis. It is found that each of the three types of bonds between V and benzene (Bz) plays different roles. V 3d_z² orbital, extending along the molecular axis, is weakly hybridized with Bz’s HOMO−1 orbital to form the σ-bond. It is quite localized and singly occupied, which contributes 1 μ_B to the magnetic moment but little to the magnetic coupling between neighboring V magnetic moments. The in-plane d_x²−y², d_xy orbitals are hybridized with the LUMO of Bz and constitute the δ-bond. This hybridization is medium and crucial to the magnetic coupling though the δ states have no net contribution to the total magnetic moment. d_xz, d_yz, and HOMO of Bz form a quite strong π-bond to hold the molecular structure but they are inactive in magnetism because their energy levels are far away from the Fermi level. Based on the results of first-principles calculation, we point out that the ferromagnetism stability is closely related with the mechanism proposed by Kanamori and Terakura [J. Phys. Soc. Jpn. 70 (2001) 1433]. However, the presence of edge Bzs in the cluster introduces an important modification and suppresses significantly the ferromagnetism stability. A simple model is constructed to explain the essence of the physical picture.

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Base station (BS) cooperation is a promising technique to suppress co-channel interference for cellular networks. However, practical limitations constrain the scale of cooperation, thus the network is divided into small disjoint BS cooperation groups, namely clusters. A decentralized scheme for BS cluster formation is proposed based on efficient BS negotiations, of which the feedback overhead per user is nearly irrelevant to the network size, and the number of iteration rounds scales very slowly with the network size. Simulations show that our decentralized scheme provides significant sum-rate gain over static clustering and performs almost the same as the existing centralized approach. The proposed scheme is well suited for large-scale cellular networks due to its low overhead and complexity.

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The interfacial shear strength (IFSS) between a bamboo fiber bundle and maleic anhydride polypropylene (MAPP) was examined for various kinds of surface treatments in conjunction with ultrasonic washing. Bamboo fiber bundles were extracted from Chinese bamboo by either mechanical scratching or steam explosion. The effect of fiber bundle diameter on IFSS was measured by using the micro-droplet test. The test results showed that higher IFSS was observed for bundles having smaller diameter. Isocyanate silane treatment improved IFSS in the case of raw bamboo fibers while it was less effective to improve IFSS for steam exploded fibers. The highest tensile strength of bamboo fiber reinforced polypropylene was obtained when steam exploded bamboo fibers were used as the reinforcement.

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In this letter, we propose a novel precoding scheme for base station (BS) cooperation in downlink cellular networks that allow overlapped clusters. The proposed precoding scheme is designed to mitigate the overlapping-BS interference by maximizing the so-called clustered virtual signal-to-interference-plus-noise ratio (CVSINR). Simulations show that with the proposed scheme, overlapped clustering provides substantial throughput gain over the traditional non-overlapped clustering methods, and user fairness is also improved.

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Nanoclusters of Ge, such as hut clusters and pyramidal clusters, were grown on Si(001) substrates and evaluated by surface electron diffraction methods such as reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED). Observations of the same sample by both RHEED and LEED were carried out for the first time. The diffraction spots had a characteristic shape and intensity distribution depending on the morphology of the clusters. The spot shapes in RHEED and LEED were simulated by kinematic calculations, which reproduced the experimental results fairly well. It was confirmed that the characteristic spot shapes can be explained by refraction effects and Laue function of diffraction intensity. [DOI: 10.1380/ejssnt.2012.18]

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Accuracy of the adsorption energy on a quasicrystal surface calculated with the density functional theory and cluster models were discussed. Two types of cluster models of various sizes were tested to represent a fivefold surface of the Ag–In–Yb quasicrystal. Some cylindrical clusters caused unnaturally rippled potential energy surfaces regardless of the cluster thickness. However, it was confirmed that the ripples are disappeared with a cluster radius of 1.4 nm or larger. A similar trend was observed even in the hemispherical clusters, and also confirmed in their root mean square errors. It was concluded that both cluster models with a certain size are expected to give relative adsorption energy within an error of 0.15 eV.

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Engineering objects often exhibit symmetries on their surfaces for functionality or aesthetics. Detecting such symmetries from their scanned meshes enables advanced applications, such as feature-based CAD model reconstruction or mesh size reduction for efficient CAE. In this paper, we propose a new method for detecting a common class of symmetries in engineering, such as translation, rotation and reflection, from scanned meshes of a variety of objects ranging from mechanical parts to aesthetic products. Major advantages of our proposed method over conventional ones are considerable robustness for scanner noise and exhaustive detection of multiple symmetries from a mesh. We demonstrate its effectiveness from various experiments on scanned meshes acquired by laser or CT scanners. We also show that surface distortions or deformations on the object surfaces can be evaluated using symmetries quantitatively.

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To cope with ever growing mobile data traffic, we recently proposed a concept of cellular ultra-dense radio access network (RAN). In the cellular ultra-dense RAN, a number of distributed antennas are deployed in the base station (BS) coverage area (cell) and user-clusters are formed to perform small-scale distributed multiuser multi-input multi-output (MU-MIMO) transmission and reception in each user-cluster in parallel using the same frequency resource. We also proposed a decentralized interference coordination (IC) framework to effectively mitigate both intra-cell and inter-cell interferences caused in the cellular ultra-dense RAN. The inter-cell IC adopted in this framework is the fractional frequency reuse (FFR), realized by applying the channel segregation (CS) algorithm, and is called CS-FFR in this paper. CS-FFR divides the available bandwidth into several sub-bands and allocates multiple sub-bands to different cells. In this paper, focusing on the optimization of the CS-FFR, we find by computer simulation the optimum bandwidth division number and the sub-band allocation ratio to maximize the link capacity. We also discuss the convergence speed of CS-FFR in a cellular ultra-dense RAN.

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背景:われわれは組織学的に確定診断が得られた乳腺管状癌3例を経験したので, その摘出腫瘤穿刺細胞標本の細胞像を中心に報告する.
症例:患者は乳房腫瘤を主訴とする41歳から48歳の女性で, 組織学的腫瘍径は全例が10mm以下であった. 細胞像はすべての症例の背景に少数の紡錘形裸核細胞がみられた. 腫瘍細胞は結合性が強く, 筋上皮細胞との二相性を認めない管状あるいはシート状集団として出現し, 細胞異型は軽度であった. また, 集塊の核密度は高く, 全例に腺管の太さが核3個程度で明瞭な内腔を有する小腺管や, 先端部の尖った管状集団, および集塊最外層の細胞の核が辺縁に対して直角に並ぶ管状集団が観察された.
結語:細胞異型に乏しい管状癌の診断では, 筋上皮細胞との二相性の欠如を前提とした,(1) 核密度が高い細胞集団の出現 (2) 集団の太さが核3個程度の明瞭な管腔を有する小腺管, および先端部が尖った管状集団.(3) 集塊最外層の核が辺縁に対して直角に並ぶ管状集団などの標本中にみられる管状集団の構造異型, あるいは出現性の異常に着目して総合的判定することが必要であると思われた.

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