Small Cells in Cellular Networks: Challenges of Future HetNets

Due to their low cost and easy deployment, small cells provide a viable and cost-effective way of improving the cellular coverage and capacity both for homes and enterprises, both in metropolitan and rural areas. Stimulated by their attractive features and advantages, the ongoing development and deployment of small cells by manufacturers and mobile network operators have seen a surge in recent years. Together with macro-cells, they form, what are called Heterogeneous Networks or HetNets. However, the successful rollout and operation of small cells are still facing significan issues. In this paper the need for, challenges and solutions of small cell deployments are analyzed. This analysis is conducted with respect to self-organizing features, interference coordination, energy efficiency and spectrum efficiency. The analysis is complemented with numerical results based on system simulations in Macro-only and HetNet scenarios and also on real measurements performed on an mobile operator network. Results show the clear improvement that a HetNet brings in term of user throughput and also the amunt of spectrum waste that is present in nowadays’ operator networks.     

Variable Cross-Section Cylinder-Type Corona and Combined Corona–Dielectric Barrier Discharge Precipitators for Fly-Ash Particles

This article is aimed at evaluating three designs of cylindrical-type electrostatic precipitators that might be installed at the output of household boilers in order to reduce the pollution due to burning wood or fossil fuels. The first design is the “standard” precipitator, which consists in a thin copper wire (0.16 mm in diameter), coaxial with a cylindrical aluminum cylinder, 345 mm in length, of constant radius (20 mm). The second and third designs, equipped with a similar wire electrode, are characterized by the same global length, but are divided into three sections, two having the same cross-section as the “standard” precipitator, while the third section, 20 mm in length and located between them, has a smaller radius (11.5 mm). The reduction of the diameter in this central section of the precipitator is done by introducing an aluminum ring, covered by a sleeve made of either aluminum (design #2) or polyvinyl chloride (design #3). Together with the modification of the conditions for mechanical collection of particles, the more intense corona (design #2) or dielectric barrier discharges (design #3) generated in these sections of reduced diameter contribute to a significant increase of precipitation efficiency.     

Super‐Resolution Nonlinear Photothermal Microscopy

Super‐resolution fluorescence microscopy enables imaging of fluorescent structures beyond the diffraction limit. However, this technique cannot be applied to weakly fluorescent cellular components or labels. As an alternative, photothermal microscopy based on nonradiative transformation of absorbed energy into heat has demonstrated imaging of nonfluorescent structures including single molecules and ~1‐nm gold nanoparticles. However, previously photothermal imaging has been performed with a diffraction‐limited resolution only. Herein, super‐resolution, far‐field photothermal microscopy based on nonlinear signal dependence on the laser energy is introduced. Among various nonlinear phenomena, including absorption saturation, multiphoton absorption, and signal temperature dependence, signal amplification by laser‐induced nanobubbles around overheated nano‐objects is explored. A Gaussian laser beam profile is used to demonstrate the image spatial sharpening for calibrated 260‐nm metal strips, resolving of a plasmonic nanoassembly, visualization of 10‐nm gold nanoparticles in graphene, and hemoglobin nanoclusters in live erythrocytes with resolution down to 50 nm. These nonlinear phenomena can be used for 3D imaging with improved lateral and axial resolution in most photothermal methods, including photoacoustic microscopy.     

Chirality-enriched semiconducting carbon nanotubes synthesized on high surface area MgO-supported catalyst

Single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution were synthesized by radio frequency-Catalytic Chemical Vapor Deposition (RF-CCVD) through the pyrolysis of CH4. Fe-Co bimetallic catalytic nanoclusters were supported on high-surface area MgO nanopowders and used in the nanotube synthesis process. Nanolog absorption fluorescence analysis was used to characterize the chiralities of the as-produced SWCNTs over this nanostructural catalyst. In the final SWCNT sample, the (7,5) semiconducting carbon nanotube species were found to be dominant, with a low chirality variation.     

Automated imaging, identification, and counting of similar cells from digital hologram reconstructions

This paper presents our method, which simultaneously combines automatic imaging, identification, and counting with the acquisition of morphological information for at least 1000 blood cells from several three-dimensional images of the same sample. We started with seeking parameters to differentiate between red blood cells that are similar but different with respect to their development stage, i.e., mature or immature. We highlight that these cells have different diffractive patterns with complementary central intensity distribution in a given plane along the propagation axis. We use the Fresnel approximation to simulate propagation through cells modeled as spheroid-shaped phase objects and to find the cell property that has the dominant influence on this behavior. Starting with images obtained in the reconstruction step of the digital holographic microscopy technique, we developed a code for automated simultaneous individual cell image separation, identification, and counting, even when the cells are partially overlapped on a slide, and accurate measuring of their morphological features. To find the centroids of each cell, we propose a method based on analytical functions applied at threshold intervals. Our procedure separates the mature from the immature red blood cells and from the white blood cells through a decision based on gradient and radius values.     

Mesoporous silica directly modified by incorporation or impregnation of some heteropolyacids: Synthesis and structural characterization

The synthesis of heteropolyacids-mesoporous silica composites was carried out in acidic media by impregnation and/or by direct incorporation of active phase. The effect of incorporation of heteropolyacids (HPAs) species into organized mesoporous silica was studied by using non-ionic and cationic surfactants. A comparison between direct incorporation of HPAs into mesoporous silica and impregnation of HPAs on mesoporous silica was done. The structure and texture of H₃PMo₁₂O₄₀ and H₄PVMo₁₁O₄₀ included on mesoporous silica were studied by XRD, SEM-EDS, FT-IR and Raman spectroscopies and BET and pore size distribution. Thermal stability was determined by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). FT-IR and Raman studies showed that HPAs anions preserved their Keggin structure after incorporation or impregnation on mesoporous silica support.     

Nanoparticles from a Gold Complex with Sulfite Ion as Ligand: Preparation and Characterization

Gold colloidal nanoparticles (GNPs) were prepared by reducing a complex of Au⁺. Na₃Au(SO₃)₂ with sodium citrate. The procedure provides control of the dimension of nanoparticles produced, which is a function of reaction time and concentration of reactants. The nanoparticles were separated by centrifugation and their characteristics and dimensions were studied using UV-Vis and IR spectroscopy and transmission electronic microscopy (TEM).     

Fluorescent solar concentrators. Experimental results

A physical characterization is presented for classes of selected fluorescent substances, with special emphasis on their concentration in the support. The influence of climatic factors was analyzed from two points of view: spectral and structural. Two types of geometrical models of fluorescent solar concentrators have been obtained : plates and cylinders.     

On the electrical conduction in the interpolysilicon dielectriclayers

To reduce the low-field electrical conductivity of interpolysilicon dielectrics used in electrically erasable programmable read-only (EEPROM) memories devices, the roughness of the poly-SiO₂ interface until now has been decreased in two ways: (1) by increasing the temperature of oxidation and doping of polysilicon combined with low-pressure chemical vapor deposition (LPCVD) of silicon (undoped or in-situ doped) in the amorphous phase, or (2) by the use of LPCVD high-temperature oxide (HTO) deposited over polycrystalline silicon. The advantages of both methods are combined, and electrical conduction results for an interpoly structure based on LPCVD smooth surface polysilicon and LPCVD HTO SiO₂ are presented. The data are interpreted in terms of the Fowler-Nordheim mechanism     

Carbon Nanotube Growth on Calcium Carbonate Supported Molybdenum-Transition Bimetal Catalysts

A comparison of different catalyst systems (Fe–Mo, Co–Mo or Ni–Mo nanoparticles supported on calcium carbonate) has been performed in order to optimize the carbon nanotube (CNT) growth. The influences of the reaction temperature, metal loading and carbon source on the synthesis of CNTs were investigated. Dense CNT networks have been synthesized by thermal chemical vapor deposition (CVD) of acetylene at 720 °C using the Co–Mo/CaCO₃ catalyst. The dependence of the CNT growth on the most important parameters was discussed exemplarily on the Co catalyst system. Based on the experimental observations, a phenomenological growth model for CVD synthesis of CNTs was proposed. The synergy effect of Mo and active metals was also discussed.