12,354 research outputs found
MobiCacher: Mobility-Aware Content Caching in Small-Cell Networks
Small-cell networks have been proposed to meet the demand of ever growing
mobile data traffic. One of the prominent challenges faced by small-cell
networks is the lack of sufficient backhaul capacity to connect small-cell base
stations (small-BSs) to the core network. We exploit the effective application
layer semantics of both spatial and temporal locality to reduce the backhaul
traffic. Specifically, small-BSs are equipped with storage facility to cache
contents requested by users. As the {\em cache hit ratio} increases, most of
the users' requests can be satisfied locally without incurring traffic over the
backhaul. To make informed caching decisions, the mobility patterns of users
must be carefully considered as users might frequently migrate from one small
cell to another. We study the issue of mobility-aware content caching, which is
formulated into an optimization problem with the objective to maximize the
caching utility. As the problem is NP-complete, we develop a polynomial-time
heuristic solution termed {\em MobiCacher} with bounded approximation ratio. We
also conduct trace-based simulations to evaluate the performance of {\em
MobiCacher}, which show that {\em MobiCacher} yields better caching utility
than existing solutions.Comment: Accepted by Globecom 201
Spin Transfer Torque for Continuously Variable Magnetization
We report quantum and semi-classical calculations of spin current and
spin-transfer torque in a free-electron Stoner model for systems where the
magnetization varies continuously in one dimension.Analytic results are
obtained for an infinite spin spiral and numerical results are obtained for
realistic domain wall profiles. The adiabatic limit describes conduction
electron spins that follow the sum of the exchange field and an effective,
velocity-dependent field produced by the gradient of the magnetization in the
wall. Non-adiabatic effects arise for short domain walls but their magnitude
decreases exponentially as the wall width increases. Our results cast doubt on
the existence of a recently proposed non-adiabatic contribution to the
spin-transfer torque due to spin flip scattering.Comment: 11 pages, 9 figure
Platinum-Bismuth Bimetallic Catalysts: Synthesis, Characterization and Applications
Bimetallic catalysts have been explored and shown to exhibit unique characteristics which are not present in monometallic catalysts. Platinum is well known as an effective catalyst for oxidation and reduction reactions, and it can be made more effective when bismuth is introduced as a promotor. Thus, the effectiveness of the Pt-Bi catalyst was demonstrated in prior work. What is not clear, however, is the mechanism behind the catalyst function; why addition of bismuth to platinum decreases deactivation and increases selectivity, and how effective would the Pt-Bi catalyst be in deoxygenation reactions? In this work, the effectiveness of different variations of the Pt-Bi catalyst was explored for the deoxygenation of guaiacol. Methane was selected as the model reductant. Two Pt-Bi catalysts with different metal ratios were prepared, tested and characterized to reveal the catalyst’s structure. Methods used in characterization included SEM, TEM and BET measurements. Representative catalysts were then tested in a fixed-bed reactor for performance
A Novel Approach for Designing Omnidirectional Slotted-Waveguide Antenna Array
This paper presents a novel design of a high-gain omnidirectional slotted-waveguide antenna array for 5G mm-wave applications. The structure is based on a circular waveguide filled with teflon for manipulating its dimension. It provides 12,1 dBi gain and omnidirectional coverage in the azimuth plane with only 1.3 dB deviation, which is ensured by making use of a twisting technique for proper placing the slots into the waveguide walls. A bandwidth of 1.61 GHz centered at 26.2 GHz has been numerically demonstrated
Physicochemical Characterization and Aerosol Dispersion Performance of Organic Solution Advanced Spray-Dried Cyclosporine A Multifunctional Particles for Dry Powder Inhalation Aerosol Delivery
In this systematic and comprehensive study, inhalation powders of the polypeptide immunosuppressant drug - cyclosporine A - for lung delivery as dry powder inhalers (DPIs) were successfully designed, developed, and optimized. Several spray drying pump rates were rationally chosen. Comprehensive physicochemical characterization and imaging was carried out using scanning electron microscopy, hot-stage microscopy, differential scanning calorimetry, powder X-ray diffraction, Karl Fischer titration, laser size diffraction, and gravimetric vapor sorption. Aerosol dispersion performance was conducted using a next generation impactor with a Food and Drug Administration-approved DPI device. These DPIs displayed excellent aerosol dispersion performance with high values in emitted dose, respirable fraction, and fine particle fraction. In addition, novel multifunctional inhalation aerosol powder formulations of cyclosporine A with lung surfactant-mimic phospholipids were also successfully designed and developed by advanced organic solution cospray drying in closed mode. The lung surfactantmimic phospholipids were 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-snglycero- 3-(phosphor-rac-1-glycerol). These cyclosporine A lung surfactant-mimic aerosol powder formulations were comprehensively characterized. Powder X-ray diffraction and differential scanning calorimetry confirmed that the phospholipid bilayer structure in the solid state was preserved following advanced organic solution spray drying in closed mode. These novel multifunctional inhalation powders were optimized for DPI delivery with excellent aerosol dispersion performance and high aerosol performance parameters
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