Thermodynamic interactions of branched polyethylene in polar and nonpolar systems

The thermodynamic properties of polymer solutions are frequently described in terms of the Flory-Huggins equation. This equation includes a parameter χ, which depends upon the intermolecular forces acting between the molecules in a solution. The experimental determination of χ was performed by an improved microtechnique and extended to a wide range of polar and nonpolar diluents of polyethylene. Careful correlations are prescribed for calculating χ from pure-component properties; they are based on an extension of the Hildebrand-Scatchard theory of solutions and on the theory of intermolecular forces. Polar (τ) and nonpolar (δ) solubility parameters are presented for a variety of solvents. For polyethylene—nonpolar solvent systems we have emphasized the factor deciding the sign of heat of mixing, while for polyethylene-polar solvent systems we have determined the contribution of dipole-induced dipole interactions ψ (δτ) in interchange-energy density B and, hence, χ.     

Space–Time/Space–Frequency/Space–Time–Frequency Block Coded MIMO-OFDM System with Equalizers in Quasi Static Mobile Radio Channels Using Higher Tap Order

In 4G broadband wireless communications, multiple transmit and receive antennas are used to form multiple input multiple output (MIMO) channels to increase the capacity (by a factor of the minimum number of transmit and receive antennas) and data rate. In this paper, the combination of MIMO technology and orthogonal frequency division multiplexing (OFDM) systems is analyzed for wideband transmission which mitigates the intersymbol interference and hence enhances system capacity. In MIMO-OFDM systems, the coding is done over space, time, and frequency domains to provide reliable and robust transmission in harsh wireless environment. Also, the performance of space time frequency (STF) coded MIMO-OFDM is analyzed with space time and space frequency coding as special cases. The maximum achievable diversity of STF coded MIMO-OFDM is analyzed and bit error rate performance improvement is verified by simulation results. Simulations are carried out in harsh wireless environment, whose effect is mitigated by using higher tap order channels. The complexity is resolved by employing sphere decoder at the receiver.     

Performance improvement of 60‐GHz wireless optical systems with reverse‐parallel hybrid modulation scheme

This paper improves the performance of 60‐GHz wireless optical system including radio over fibre (RoF) and radio over free space optics (RoFSO), based on novel reverse‐parallel (RP) hybrid modulation scheme. This scheme combines the chromatic dispersion compensation technique of parallel modulation with energy efficiency manipulation technique of reverse modulation. Superior functioning of RoFSO is provided with reverse modulation compared with normal modulation. Comparative investigations are performed by loading 60‐GHz RF signal with 2.5 and 10‐Gbps data and modulating it with both reverse and hybrid modulators. Hybrid modulation performed better with improved BER of 10^?23 at distance of 51 km for 2.5‐Gbps data compared with reverse modulation with BER of 10^?7.     

Suppression of random dopant-induced threshold voltage fluctuationsin sub-0.1-μm MOSFET's with epitaxial and δ-doped channels

A detailed three-dimensional (3-D) statistical “atomistic” simulation study of fluctuation-resistant sub 0.1-μm MOSFET architectures with epitaxial channels and delta doping is presented. The need for enhancing the fluctuation resistance of the sub-0.1-μm generation transistors is highlighted by presenting summarized results from atomistic simulations of a wide range of conventional devices with uniformly doped channels. According to our atomistic results, the doping concentration dependence of the random dopant-induced threshold voltage fluctuations in conventional devices is stronger than the analytically predicted fourth-root dependence. As a result of this, the scaling of such devices will be restricted by the “intrinsic” random dopant-induced fluctuations earlier than anticipated. Our atomistic simulations confirm that the introduction of a thin epitaxial layer in the MOSFET's channel can efficiently suppress the random dopant-induced threshold voltage fluctuations in sub-0.1-μm devices. For the first time, we observe an “anomalous” reduction in the threshold voltage fluctuations with an increase in the doping concentration behind the epitaxial channel, which we attribute to screening effects. Also, for the first time we study the effect of a delta doping, positioned behind the epitaxial layer, on the intrinsic threshold voltage fluctuations. Above a certain thickness of epitaxial layer, we observe a pronounced anomalous decrease in the threshold voltage fluctuation with the increase of the delta doping. This phenomenon, which is also associated with screening, enhances the importance of the delta doping in the design of properly scaled fluctuation-resistant sub-0.1-μm MOSFET's     

Fair Single Code and Multi Code Designs for 3G and Beyond CDMA Systems

Multimedia rates are handled in 3G and beyond CDMA networks using orthogonal variable spreading factor (OVSF) codes. Multimedia rates can have non uniform distribution of real time and non real time users. The paper describes fair single code and multi code designs to handle these rates. The single code design is for quantized rates and divides the OVSF code tree capacity according to the arrival distribution. The change in the distribution is dynamically reflected in the division of the code tree capacity for different rates. The multi code design is preferred for the system dominated by non quantized rates. Simulation results are presented to show the superiority of the proposed designs with its existing counterparts.     

A Broadband Dual Circularly Polarized Compact Printed Monopole Antenna

Wireless Personal Communications - Now-a-days the most common pretentious disease is the lung cancer, which has become more prevalent in the world that primarily infects the pulmonary nodules of...     

Equivalent refractive index of MQW waveguides

In this paper, we have proposed some new numerical and semi-analytical methods for developing an equivalent three-layer model of an MQW waveguide. The waveguiding properties like effective index, field distribution, and fractional power within the core of the waveguide of these equivalent structures are compared with those of previously reported equivalent methods. These results are also compared with the results obtained from the exact multilayer analysis of the MQW waveguide. The waveguiding properties are accurately predicted by the semi-analytical method using variational analysis, and the computational effort is significantly reduced. The use of the three-layer equivalent is illustrated in obtaining an estimation of the waveguide losses and is used to study the effect of nonlinearity     

Heat rejection limits of air cooled plane fin heat sinks for computer cooling

Current desktop computers typically use fan-heat sinks for cooling the CPU, referred to as active heat sinks. This work seeks to determine the heat rejection limits for such fan-heat sinks, within specific fan and heat sink space limits. A fixed volume, 80 /spl times/ 60 /spl times/ 50 mm is chosen as the limiting dimensions, which includes the fan volume. The present work addresses plane fin heat sinks, on which a typical 60 mm fan is mounted. Both duct flow and impinging flow are considered. Analytically based models are used to predict the optimum geometry (minimum convection resistance) for plane fins with duct and impinging flow configurations. Also assessed are the effects of increased fan speed (up to 25%) and heat sink base size (33% increase) on air-cooling limits in duct and impinging flow. Tests on fan-heat sinks are done to validate the predictions. Optimization is also done for an enhanced (offset-strip) fin geometry in duct flow. The plane fin is found to outperform the enhanced geometry.