229 research outputs found
Film Thickness Changes in EHD Sliding Contacts Lubricated by a Fatty Alcohol
This paper describes the appearance of abnormal film thickness features
formed in elastohydrodynamic contacts lubricated by a fatty alcohol.
Experiments were conducted by varying the slide to roll ratio between a steel
ball and a glass disk in a ball-on-disk type device. Lauric alcohol was used as
lubricant and film thickness was measured in the contact area by optical
interferometry. Experimental results showed that the film thickness
distributions under pure rolling conditions remained classical whereas the film
shape changed when the slide to roll ratio was increased. The thickness in the
central contact area increased and in the same time inlet and exit film
thicknesses were modified. In addition, the film shapes observed when the ball
surface was moving faster than the disk one and those obtained in the opposite
case were different, i.e. when opposite signs but equal absolute values of the
slide to roll ratio were applied
Simplicial Homology for Future Cellular Networks
Simplicial homology is a tool that provides a mathematical way to compute the
connectivity and the coverage of a cellular network without any node location
information. In this article, we use simplicial homology in order to not only
compute the topology of a cellular network, but also to discover the clusters
of nodes still with no location information. We propose three algorithms for
the management of future cellular networks. The first one is a frequency
auto-planning algorithm for the self-configuration of future cellular networks.
It aims at minimizing the number of planned frequencies while maximizing the
usage of each one. Then, our energy conservation algorithm falls into the
self-optimization feature of future cellular networks. It optimizes the energy
consumption of the cellular network during off-peak hours while taking into
account both coverage and user traffic. Finally, we present and discuss the
performance of a disaster recovery algorithm using determinantal point
processes to patch coverage holes
Homology-based Distributed Coverage Hole Detection in Wireless Sensor Networks
Homology theory provides new and powerful solutions to address the coverage
problems in wireless sensor networks (WSNs). They are based on algebraic
objects, such as Cech complex and Rips complex. Cech complex gives accurate
information about coverage quality but requires a precise knowledge of the
relative locations of nodes. This assumption is rather strong and hard to
implement in practical deployments. Rips complex provides an approximation of
Cech complex. It is easier to build and does not require any knowledge of nodes
location. This simplicity is at the expense of accuracy. Rips complex can not
always detect all coverage holes. It is then necessary to evaluate its
accuracy. This work proposes to use the proportion of the area of undiscovered
coverage holes as performance criteria. Investigations show that it depends on
the ratio between communication and sensing radii of a sensor. Closed-form
expressions for lower and upper bounds of the accuracy are also derived. For
those coverage holes which can be discovered by Rips complex, a homology-based
distributed algorithm is proposed to detect them. Simulation results are
consistent with the proposed analytical lower bound, with a maximum difference
of 0.5%. Upper bound performance depends on the ratio of communication and
sensing radii. Simulations also show that the algorithm can localize about 99%
coverage holes in about 99% cases
Construction of the generalized Cech complex
In this paper, we introduce an algorithm which constructs the generalized
Cech complex. The generalized Cech complex represents the topology of a
wireless network whose cells are different in size. This complex is often used
in many application to locate the boundary holes or to save energy consumption
in wireless networks. The complexity of a construction of the Cech complex to
analyze the coverage structure is found to be a polynomial time
Bitcoin and the Rise of Decentralized Autonomous Organizations
Bitcoin represents the first real-world implementation of a “decentralized autonomous organization” (DAO) and offers a new paradigm for organization design. Imagine working for a global business organization whose routine tasks are powered by a software protocol instead of being governed by managers and employees. Task assignments and rewards are randomized by the algorithm. Information is not channelled through a hierarchy but recorded transparently and securely on an immutable public ledger called “blockchain”. Further, the organization decides on design and strategy changes through a democratic voting process involving a previously unseen class of stakeholders called “miners”. Agreements need to be reached at the organizational level for any proposed protocol changes to be approved and activated. How do DAOs solve the universal problem of organizing with such novel solutions? What are the implications? We use Bitcoin as an example to shed light on how a DAO works in the cryptocurrency industry, where it provides a peer-to-peer, decentralized and disintermediated payment system that can compete against traditional financial institutions. We also invite commentaries from renowned organization scholars to share their views on this intriguing phenomenon
A case study on regularity in cellular network deployment
This paper aims to validate the -Ginibre point process as a model for
the distribution of base station locations in a cellular network. The
-Ginibre is a repulsive point process in which repulsion is controlled
by the parameter. When tends to zero, the point process
converges in law towards a Poisson point process. If equals to one it
becomes a Ginibre point process. Simulations on real data collected in Paris
(France) show that base station locations can be fitted with a -Ginibre
point process. Moreover we prove that their superposition tends to a Poisson
point process as it can be seen from real data. Qualitative interpretations on
deployment strategies are derived from the model fitting of the raw data
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