Studies of stabilization of non-aqueous polymer dispersions with diblock copolymers

A diblock copolymer of Poly (Styrene-b- [ethylene-co-propylene]) has been used as a stabilizer in non-aqueous dispersion polymerizations of methyl methacrylate and vinyl acetate in n-heptane. The particles thus produced were stabilized by well defined surface layers of ethylene-propylene copolymer chains. The dependence of the particle size on the stabilizer, monomer and initiator concentrations was studied. Both seeded and one-shot polymerization techniques were investigated. Polymer particles were characterized by transmission electron microscopy to determine particle shape and size. The long term stability of both types of polymer particles suggests that the anchoring efficiency in both systems was good. Rheological studies confirmed the sphericity of the particles and showed the particles to be non-flocculated under shear. The thickness of the surface layer was determined from viscosity studies of the dispersions at 298, 308 and 318K. Solution viscosities dispersions at of a narrow distribution standard of ethylene-propylene copolymer in n-heptane and in a binary liquid mixture of n-heptane and n-propanol (79:21, v/v) at 298, 308 and 318K were obtained in order to estimate the root-mean-square end-to-end distance of free ethylene-propylene copolymer chains. The thickness of the surface layer was observed to increase on raising the temperature and to decrease on changing the solvency of the dispersion medium from a good solvent to almost a theta solvent for the ethylene-propylene copolymer chains. The dimensions of the surface layer were slightly larger than the dimensions of the free ethylene-propylene copolymer chains in solution suggesting that long ethylene-propylene chains terminally anchored at the interface are only slightly extended over random coil dimensions. Calculations of the mean separation distance between adjacent stabilizing ethylene-propylene copolymer chains indicated close-packing of ethylene-propylene copolymer chains at the particle-liquid interface which may contribute to the slight extension of the ethylene-propylene copolymer chain conformation. The theta-conditions for ethylene-propylene copolymer in a mixture of n-heptane and n-propanol were determined using samples obtained by hydrogenating polyisoprene standards. The solvency of the dispersion medium for the stabilizing ethylene-propylene copolymer chain on the polymer particles was reduced until flocculation occurred, and this was achieved by cooling the dispersion system to find the critical flocculation temperature or by adding a non-solvent (n-propanol) for the ethylene-propylene copolymer chains at constant temperature to find the critical flocculation volume. The polymer dispersions just retained stability at theta conditions and started to lose stability when the dispersion medium was changed to slightly worse than a theta system for the ethylene-propylene chains. The close correspondence of the flocculation conditions to the theta conditions for free ethylene-propylene copolymer chains confirms that the steric stabilization mechanism is operative for these dispersions

How to Solve the Fronthaul Traffic Congestion Problem in H-CRAN?

The design of efficient wireless fronthaul connections for future heterogeneous networks incorporating emerging paradigms such as heterogeneous cloud radio access network (H-CRAN) has become a challenging task that requires the most effective utilization of fronthaul network resources. In this paper, we propose and analyze possible solutions to facilitate the fronthaul traffic congestion in the scenario of Coordinated Multi-Point (CoMP) for 5G cellular traffic which is expected to reach ZetaByte by 2017. In particular, we propose to use distributed compression to reduce the fronthaul traffic for H-CRAN. Unlike the conventional approach where each coordinating point quantizes and forwards its own observation to the processing centre, these observations are compressed before forwarding. At the processing centre, the decompression of the observations and the decoding of the user messages are conducted in a joint manner. Our results reveal that, in both dense and ultra-dense urban small cell deployment scenarios, the usage of distributed compression can efficiently reduce the required fronthaul rate by more than 50% via joint operation

On the traffic offloading in Wi-Fi supported heterogeneous wireless networks

Heterogeneous small cell networks (HetSNet) comprise several low power, low cost (SBSa), (D2D) enabled links wireless-fidelity (Wi-Fi) access points (APs) to support the existing macrocell infrastructure, decrease over the air signaling and energy consumption, and increase network capacity, data rate and coverage. This paper presents an active user dependent path loss (PL) based traffic offloading (TO) strategy for HetSNets and a comparative study on two techniques to offload the traffic from macrocell to (SBSs) for indoor environments: PL and signal-to-interference ratio (SIR) based strategies. To quantify the improvements, the PL based strategy against the SIR based strategy is compared while considering various macrocell and (SBS) coverage areas and traffic–types. On the other hand, offloading in a dense urban setting may result in overcrowding the (SBSs). Therefore, hybrid traffic–type driven offloading technologies such as (WiFi) and (D2D) were proposed to en route the delay tolerant applications through (WiFi) (APs) and (D2D) links. It is necessary to illustrate the impact of daily user traffic profile, (SBSs) access schemes and traffic–type while deciding how much of the traffic should be offloaded to (SBSs). In this context, (AUPF) is introduced to account for the population of active small cells which depends on the variable traffic load due to the active users

Spectral Efficiency Improvements in HetNets by Exploiting Device-to-Device Communications

Next generation cellular networks require huge capacity, ubiquitous coverage and maximum energy efficiency. In order to meet these targets, Device-to-device (D2D) communication is being considered for future heterogeneous networks (HetNets). In this paper, we consider a three tier hierarchical HetNet by exploiting D2D communication in traditional HetNet. D2D communication is deployed within the HetNet where closely located mobile users are engaged in direct communication without routing the traffic through cellular access network. The proposed configuration mandates to reduce the interference offered by the resultant HetNet by reducing the transmitter-receiver distance and ensuring that the mobile users are transmitting with adaptive power subject to maintaining their desired link quality. In this context, we analyzed and compared the spectral efficiency improvements in hierarchical HetNet against traditional HetNet. Simulation results show that D2D communication offers much higher spectral efficiency as compared to traditional HetNet

Flow injection analysis for the photometric determination of promethazine-HCl in pure and pharmaceutical preparation via oxidation by persulphate using Ayah 3SX3-3D solar micro photometer

The first flow injection spectrophotometric method is characterized by its speed and sensitivity which have been developed for the determination of promethazine-HCl in pure and pharmaceutical preparation. It is based on the in situ detection of colored cationic radicals formed via oxidation of the drug with sodium persulphate to pinkish-red species and the same species was determined by using homemade Ayah 3SX3-3D solar flow injection photometer. Optimum conditions were obtained by using the high intensive green light emitted diode as a source. Linear dynamic range for the absorbance versus promethazine-HCl concentration was 0-7 mmol.L-1, with the correlation coefficient (r) was 0.9904 while the percentage linearity (r2%) was 98.09%. the L.O.Q was 3.97 µg/sample, while L.O.D (S/N=3) = 0.2407µg/sample (5 µmol.L-1) from the stepwise dilution for the minimum concentration of lowest concentration in the linear dynamic range of the calibration graph. The R.S.D% at 2 mmol.L-1 promethazine-HCl is less than 1% (eight replicates) using 150 µL sample volume. Throughput 30 sample.hr-1. The method was applied successfully for the determination of promethazine-HCl in pharmaceutical preparation. By using paired t-test it was shown that there was no significant difference between the proposed method and official method and on that basis the new method can be accepted as an alternative analytical method

Approximation of Entire Function of Slow Growth in Several Complex Variables

In the present paper, we study the polynomial approximation of entire function in Banach space ace, Hardy space and Bergman space). The coefficient characterizations of generalized type of entire function of slow growth in several complex variables have been obtained in terms of the approximation errors. Keyword: Entire function, generalized order, generalized type, approximation error

A new four-dimensional hyper-chaotic system for image encryption

Currently, images are very important with the rapid growth of communication networks. Therefore, image encryption is a process to provide security for private information and prevent unwanted access to sensitive data by unauthorized individuals. Chaos systems provide an important role for key generation, with high randomization properties and accurate performance. In this study, a new four-dimensional hyper-chaotic system has been suggested that is used in the keys generation, which are utilized in the image encryption process to achieve permutation and substitution operations. Firstly, color bands are permuted using the index of the chaotic sequences to remove the high correlation among neighboring pixels. Secondly, dynamic S-boxes achieve the principle of substitution, which are utilized to diffuse the pixel values of the color image. The efficiency of the proposed method is tested by the key space, histogram, and so on. Security analysis shows that the proposed method for encrypting images is secure and resistant to different attacks. It contains a big key space of (2627) and a high sensitivity to a slight change in the secret key, a fairly uniform histogram, and entropy values nearby to the best value of 8. Moreover, it consumes a very short time for encryption and decryption