170,800 research outputs found
Subsidization Competition: Vitalizing the Neutral Internet
Unlike telephone operators, which pay termination fees to reach the users of
another network, Internet Content Providers (CPs) do not pay the Internet
Service Providers (ISPs) of users they reach. While the consequent cross
subsidization to CPs has nurtured content innovations at the edge of the
Internet, it reduces the investment incentives for the access ISPs to expand
capacity. As potential charges for terminating CPs' traffic are criticized
under the net neutrality debate, we propose to allow CPs to voluntarily
subsidize the usagebased fees induced by their content traffic for end-users.
We model the regulated subsidization competition among CPs under a neutral
network and show how deregulation of subsidization could increase an access
ISP's utilization and revenue, strengthening its investment incentives.
Although the competition might harm certain CPs, we find that the main cause
comes from high access prices rather than the existence of subsidization. Our
results suggest that subsidization competition will increase the
competitiveness and welfare of the Internet content market; however, regulators
might need to regulate access prices if the access ISP market is not
competitive enough. We envision that subsidization competition could become a
viable model for the future Internet
Paid Peering, Settlement-Free Peering, or Both?
With the rapid growth of congestion-sensitive and data-intensive
applications, traditional settlement-free peering agreements with best-effort
delivery often do not meet the QoS requirements of content providers (CPs).
Meanwhile, Internet access providers (IAPs) feel that revenues from end-users
are not sufficient to recoup the upgrade costs of network infrastructures.
Consequently, some IAPs have begun to offer CPs a new type of peering
agreement, called paid peering, under which they provide CPs with better data
delivery quality for a fee. In this paper, we model a network platform where an
IAP makes decisions on the peering types offered to CPs and the prices charged
to CPs and end-users. We study the optimal peering schemes for the IAP, i.e.,
to offer CPs both the paid and settlement-free peering to choose from or only
one of them, as the objective is profit or welfare maximization. Our results
show that 1) the IAP should always offer the paid and settlement-free peering
under the profit-optimal and welfare-optimal schemes, respectively, 2) whether
to simultaneously offer the other peering type is largely driven by the type of
data traffic, e.g., text or video, and 3) regulators might want to encourage
the IAP to allocate more network capacity to the settlement-free peering for
increasing user welfare
A Cosmic Microwave Background Radiation Polarimeter Using Superconducting Bearings
Measurements of the polarization of the cosmic microwave background (CMB)
radiation are expected to significantly increase our understanding of the early
universe. We present a design for a CMB polarimeter in which a cryogenically
cooled half wave plate rotates by means of a high-temperature superconducting
(HTS) bearing. The design is optimized for implementation in MAXIPOL, a
balloon-borne CMB polarimeter. A prototype bearing, consisting of commercially
available ring-shaped permanent magnet and an array of YBCO bulk HTS material,
has been constructed. We measured the coefficient of friction as a function of
several parameters including temperature between 15 and 80 K, rotation
frequency between 0.3 and 3.5 Hz, levitation distance between 6 and 10 mm, and
ambient pressure between 10^{-7} and 1 torr. The low rotational drag of the HTS
bearing allows rotations for long periods of time with minimal input power and
negligible wear and tear thus making this technology suitable for a future
satellite mission.Comment: 6 pages, IEEE-Transactions of Applied Superconductivity, 2003, Vol.
13, in pres
Heavy quarkonium 2S states in light-front quark model
We study the charmonium 2S states and , and the bottomonium
2S states and , using the light-front quark model and the
2S state wave function of harmonic oscillator as the approximation of the 2S
quarkonium wave function. The decay constants, transition form factors and
masses of these mesons are calculated and compared with experimental data.
Predictions of quantities such as Br are made. The
2S wave function may help us learn more about the structure of these heavy
quarkonia.Comment: 5 latex pages, final version for journal publicatio
Axial vector form factor of nucleons in a light-cone diquark model
The nucleon axial vector form factor is investigated in a light-cone quark
spectator diquark model, in which Melosh rotations are applied to both the
quark and vector diquark. It is found that this model gives a very good
description of available experimental data and the results have very little
dependence on the parameters of the model. The relation between the nucleon
axial constant and the anomalous magnetic moment of nucleons is also discussed.Comment: 8 pages, Revtex4, 1 figure, version to be published in Phys. Rev.
On Optimal Service Differentiation in Congested Network Markets
As Internet applications have become more diverse in recent years, users
having heavy demand for online video services are more willing to pay higher
prices for better services than light users that mainly use e-mails and instant
messages. This encourages the Internet Service Providers (ISPs) to explore
service differentiations so as to optimize their profits and allocation of
network resources. Much prior work has focused on the viability of network
service differentiation by comparing with the case of a single-class service.
However, the optimal service differentiation for an ISP subject to resource
constraints has remained unsolved. In this work, we establish an optimal
control framework to derive the analytical solution to an ISP's optimal service
differentiation, i.e. the optimal service qualities and associated prices. By
analyzing the structures of the solution, we reveal how an ISP should adjust
the service qualities and prices in order to meet varying capacity constraints
and users' characteristics. We also obtain the conditions under which ISPs have
strong incentives to implement service differentiation and whether regulators
should encourage such practices
Sampling Online Social Networks via Heterogeneous Statistics
Most sampling techniques for online social networks (OSNs) are based on a
particular sampling method on a single graph, which is referred to as a
statistics. However, various realizing methods on different graphs could
possibly be used in the same OSN, and they may lead to different sampling
efficiencies, i.e., asymptotic variances. To utilize multiple statistics for
accurate measurements, we formulate a mixture sampling problem, through which
we construct a mixture unbiased estimator which minimizes asymptotic variance.
Given fixed sampling budgets for different statistics, we derive the optimal
weights to combine the individual estimators; given fixed total budget, we show
that a greedy allocation towards the most efficient statistics is optimal. In
practice, the sampling efficiencies of statistics can be quite different for
various targets and are unknown before sampling. To solve this problem, we
design a two-stage framework which adaptively spends a partial budget to test
different statistics and allocates the remaining budget to the inferred best
statistics. We show that our two-stage framework is a generalization of 1)
randomly choosing a statistics and 2) evenly allocating the total budget among
all available statistics, and our adaptive algorithm achieves higher efficiency
than these benchmark strategies in theory and experiment
An integrated wind risk warning model for urban rail transport in Shanghai, China
The integrated wind risk warning model for rail transport presented has four elements:
Background wind data, a wind field model, a vulnerability model, and a risk model. Background
wind data uses observations in this study. Using the wind field model with effective surface
roughness lengths, the background wind data are interpolated to a 30-m resolution grid. In the
vulnerability model, the aerodynamic characteristics of railway vehicles are analyzed with CFD
(Computational Fluid Dynamics) modelling. In the risk model, the maximum value of three
aerodynamic forces is used as the criteria to evaluate rail safety and to quantify the risk level under
extremely windy weather. The full model is tested for the Shanghai Metro Line 16 using wind
conditions during Typhoon Chan-hom. The proposed approach enables quick quantification of real-
time safety risk levels during typhoon landfall, providing sophisticated warning information for
rail vehicle operation safety
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