4,200 research outputs found
Development of durable “green” concrete exposed to deicing chemicals via synergistic use of locally available recycled materials and multi-scale modifiers
From the economic and social perspectives, the use of waste materials would not be attractive until their costs and quality can satisfy the construction requirements. In this study, a pure fly ash paste (PFAP) was developed in place of ordinary Portland cement paste (OPCP). This PFAP was prepared at room temperature and without direct alkali activation. The samples were prepared using only the as-received class C coal fly ash, water, and a very small amount of borax (Na2B4O7). On average, the PFAP featured 28-d compressive strength of about 36 MPa, and micro-nano hardness and elastic modulus 29% and 5%, higher than the OPCP, respectively. These mechanical and other properties of the PFAP make it a viable “green” construction binder suitable for a host of structural and non-structural applications. Advanced characterization of the raw material and PFAP pastes was employed to elucidate the hydration mechanisms of this “green” binder. The obtained knowledge sheds light on the role of class C CFA in the hydration process and may benefit the expanded use of various CFAs in cementitious materials
A Framework for Life Cycle Sustainability Assessment of Road Salt Used in Winter Maintenance Operations
It is important to assess from a holistic perspective the sustainability of road salt widely used in winter road maintenance (WRM) operations. The importance becomes increasingly apparent in light of competing priorities faced by roadway agencies, the need for collaborative decision-making, and growing concerns over the risks that road salt poses for motor vehicles, transportation infrastructure, and the natural environment. This project introduces the concept of Life Cycle Sustainability Assessment (LCSA), which combines Life Cycle Costing, Environmental Life Cycle Assessment, and Social Life Cycle Assessment. The combination captures the features of three pillars in sustainability: economic development, environmental preservation, and social progress. With this framework, it is possible to enable more informed and balanced decisions by considering the entire life cycle of road salt and accounting for the indirect impacts of applying road salt for snow and ice control. This project proposes a LCSA framework of road salt, which examines the three branches of LCSA, their relationships in the integrated framework, and the complexities and caveats in the LCSA. While this framework is a first step in the right direction, we envision that it will be improved and enriched by continued research and may serve as a template for the LCSA of other WRM products, technologies, and practices
Optimal Pilot Symbols Ratio in terms of Spectrum and Energy Efficiency in Uplink CoMP Networks
In wireless networks, Spectrum Efficiency (SE) and Energy Efficiency (EE) can
be affected by the channel estimation that needs to be well designed in
practice. In this paper, considering channel estimation error and non-ideal
backhaul links, we optimize the pilot symbols ratio in terms of SE and EE in
uplink Coordinated Multi-point (CoMP) networks. Modeling the channel estimation
error, we formulate the SE and EE maximization problems by analyzing the system
capacity with imperfect channel estimation. The maximal system capacity in SE
optimization and the minimal transmit power in EE optimization, which both have
the closed-form expressions, are derived by some reasonable approximations to
reduce the complexity of solving complicated equations. Simulations are carried
out to validate the superiority of our scheme, verify the accuracy of our
approximation, and show the effect of pilot symbols ratio.Comment: 5 pages, 3 figures, 2017 IEEE 85th Vehicular Technology Conference
(VTC Spring
Energy-Efficient User Access Control and Resource Allocation in HCNs with Non-Ideal Circuitry
In this paper, we study the energy-efficient user access control (UAC) based
on resource allocation (RA) in heterogeneous cellular networks (HCNs) with the
required downlink data rate under non-ideal power amplifiers (PAs) and circuit
power. It is proved that the energy consumption minimization is achieved when
the typical user accesses only one base station (BS), while the other BSs
remain in idle mode on the transmission resource allocated to this user. For
this purpose, we reformulate the original non-convex optimization problem into
a series of convex optimization problems where, in each case, the transmit
power and duration of the accessed BS are determined. Then, the BS with the
minimal energy consumption is selected for transmission. Considering the
approximate situation, it is showed that the optimal transmit duration of the
accessed BS can be estimated in closed form. The benefits of our proposed UAC
and RA schemes are validated using numerical simulations, which also
characterize the effect that non-ideal PAs have on the total energy consumption
of different transmission schemes.Comment: 6 pages, 4 figures, 2017 9th International Conference on Wireless
Communications and Signal Processing (WCSP
Bifurcation and Chaotic Behavior of a Discrete-Time SIS Model
The discrete-time epidemic model is investigated, which is obtained using the Euler method. It is verified that there exist some dynamical behaviors in this model, such as transcritical bifurcation, flip bifurcation, Hopf bifurcation, and chaos. The numerical simulations, including bifurcation diagrams and computation of Lyapunov exponents, not only show the consistence with the theoretical analysis but also exhibit the rich and complex dynamical behaviors
Casimir Energy Stabilization of Standard Model Landscape in Dark Dimension
In this paper we present a realization of dark dimension. We consider the 5D
standard model coupling to gravity with one dimension compactified on an
orbifold, which is seen as dark dimension of size R. We stabilize the radion by
casimir effect wrapping around compact dimension and recover the neutrino mass
and 4D cosmological constant with the observed value. Orbifold can lead to a
natural resolution of chirality problem in 5D at low energy, which we briefly
discussed in the paper. Although we found that the radion mass is too light to
survive under solar system tests of GR, several screening mechanisms might give
us a solution, for example, Chameleon mechanism
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