2,925 research outputs found
General Model for Infrastructure Multi-channel Wireless LANs
In this paper we develop an integrated model for request mechanism and data
transmission in multi-channel wireless local area networks. We calculated the
performance parameters for single and multi-channel wireless networks when the
channel is noisy. The proposed model is general it can be applied to different
wireless networks such as IEEE802.11x, IEEE802.16, CDMA operated networks and
Hiperlan\2.Comment: 11 Pages, IJCN
WebWave: Globally Load Balanced Fully Distributed Caching of Hot Published Documents
Document publication service over such a large network as the Internet challenges us to harness available server and network resources to meet fast growing demand. In this paper, we show that large-scale dynamic caching can be employed to globally minimize server idle time, and hence maximize the aggregate server throughput of the whole service. To be efficient, scalable and robust, a successful caching mechanism must have three properties: (1) maximize the global throughput of the system, (2) find cache copies without recourse to a directory service, or to a discovery protocol, and (3) be completely distributed in the sense of operating only on the basis of local information.
In this paper, we develop a precise definition, which we call tree load-balance (TLB), of what it means for a mechanism to satisfy these three goals. We present an algorithm that computes TLB off-line, and a distributed protocol that induces a load distribution that converges quickly to a TLB one. Both algorithms place cache copies of immutable documents, on the routing tree that connects the cached document's home server to its clients, thus enabling requests to stumble on cache copies en route to the home server.Harvard University; The Saudi Cultural Mission to the U.S.A
Exploring how a third housing sector initiative can contribute to the challenge of housing affordability in Oslo
Rising housing prices have been challenging to certain groups in the population of Oslo. Research has shown that the increase in wages has not been able to keep up with the increase in housing prices in Norway, especially in Oslo, the city with the highest increase in housing prices compared to other cities in Norway. This study aims to determine if initiatives of the third housing sector, such as OsloBolig, can help with the challenge of housing affordability for certain criteria of people in Oslo called the in-betweeners. Based on the review of secondary data, this research is a case study about OsloBolig in Oslo, focusing on in-betweeners that are first-time buyers. Thus, the secondary data is from Oslo Municipality’s website on their initiative of OsloBolig, and articles that focus on housing affordability. The results indicate that there is an urgent need for projects with a higher number of housing units launched through OsloBolig. This research has illustrated how OsloBolig can contribute to the challenge of housing affordability for in-betweeners that are first-time buyers through discussion of the project Østensjøporten and through highlighting the importance of developing and innovating the third housing sector initiatives.B-D
Converting relational databases into object relational databases
This paper proposes an approach for migrating existing Relational DataBases (RDBs) into Object-Relational DataBases (ORDBs). The approach is superior to existing proposals as it can generate not only the target schema but also the data instances. The solution takes an existing RDB as input, enriches its metadata representation with required semantics, and generates an enhanced canonical data model, which captures essential characteristics of the target ORDB, and is suitable for migration. A prototype has been developed, which migrates successfully RDBs into ORDBs (Oracle 11g) based on the canonical model. The experimental results were very encouraging, demonstrating that the proposed approach is feasible, efficient and correct
Cluster Reconstruction from Combined Strong and Weak Lensing
The lensing information provided by multiple images, arclets, and statistical
distortions can all be formulated as linear constraints on the arrival-time
surface, and hence on the mass distribution. This reduces cluster lens
reconstruction from combined strong and weak lensing to a standard type of
inversion problem. Moreover, the mass sheet degeneracy is broken if there are
sources at different redshifts.Comment: 8 pages incl 6 figures. Invited talk at "Gravitational Lensing:
Recent Progress and Future Goals", Boston University, MA, July 1999, eds.
T.G. Brainerd and C.S. Kochane
Large gap magnetic suspension system
The design of a large gap magnetic suspension system is discussed. Some of the topics covered include: the system configuration, permanent magnet material, levitation magnet system, superconducting magnets, resistive magnets, superconducting levitation coils, resistive levitation coils, levitation magnet system, and the nitrogen cooled magnet system
Non-parametric Reconstruction of Cluster Mass Distribution from Strong Lensing: Modelling Abell 370
We describe a new non-parametric technique for reconstructing the mass
distribution in galaxy clusters with strong lensing, i.e., from multiple images
of background galaxies. The observed positions and redshifts of the images are
considered as rigid constraints and through the lens (ray-trace) equation they
provide us with linear constraint equations. These constraints confine the mass
distribution to some allowed region, which is then found by linear programming.
Within this allowed region we study in detail the mass distribution with
minimum mass-to-light variation; also some others, such as the smoothest mass
distribution. The method is applied to the extensively studied cluster Abell
370, which hosts a giant luminous arc and several other multiply imaged
background galaxies. Our mass maps are constrained by the observed positions
and redshifts (spectroscopic or model-inferred by previous authors) of the
giant arc and multiple image systems. The reconstructed maps obtained for \a370
reveal a detailed mass distribution, with substructure quite different from the
light distribution. The method predicts the bimodal nature of the cluster and
that the projected mass distribution is indeed elongated along the axis defined
by the two dominant cD galaxies. But the peaks in the mass distribution appear
to be offset from the centres of the cDs. We also present an estimate for the
total mass of the central region of the cluster. This is in good agreement with
previous mass determinations. The total mass of the central region is
M=(2.0-2.7) 10^14 Msun/h50, depending on the solution chosen.Comment: 14 pages(19 postscript figures), minor corrections, MNRAS in pres
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