A Technique for Frequency Synchronization in Multi-Band OFDM in Realistic UWB Channel

This paper presents a highly accurate frequency offset estimation algorithm for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for realistic ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier frequency offsets and different channel responses in different bands to keep the analysis and simulation compatible for practical multi-band UWB scenario. Performance of the proposed algorithm is studied by means of bit error rate (BER) performance of MB-OFDM system. In order to compare the variance of the synchronizer to that of the theoretical optimum, we derive the Cramer–Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1–CM4. Next, we modify the estimation algorithm by proposing a multi-band averaging frequency offset synchronization (MBAFS) scheme. We establish superior BER performance with MBAFS compared to our first scheme. We calculate modified CRLB for MBAFS and compare it with simulation results for CM1–CM4. Both analysis and simulation show that MBAFS algorithm can estimate the carrier frequency offset effectively and precisely in UWB fading channels for MB-OFDM applications. We also analyze the computational complexity of both the proposed algorithms in order to verify their feasibility of implementation in practical UWB receiver design.     

Evolution of the Horizons for Dark Energy Universe

Recent observational evidences of accelerating phase of the universe strongly demand that the dominating matter in the universe is in the form of dark energy. In this work, we study the evolution of the apparent and event horizons for various dark energy models and examine their behavior across phantom barrier line.     

Isolation,structural elucidation and in vitro antioxidant activity of compounds from chloroform extract of Cedrus deodara (Roxb.) Loud.

This study was designed to isolate, characterise and explore in vitro antioxidant potential of compounds from the chloroform extract of Cedrus deodara wood belonging to Pinacae family. We have investigated the in vitro free radical scavenging activity of isolated compounds by measuring total antioxidant capacity (TAC) and reducing power ability. From the chloroform extract five sesquiterpenes namely atlantone, himaphenolone, atlantolone, deodardione and atlantone-2,3-diol were identified. Himaphenolone and deodardione from the chloroform extract of this plant have been isolated for the first time. A marked dose-dependent reducing power and strong TAC were found in favour of himaphenolone and atlantone-2,3-diol, respectively. Moreover, deodardione and atlantolone also exhibit good antioxidant potentials. However, atlantone has showed least antioxidant activity. In conclusion, the chloroform extract of C. deodara exhibited significant antioxidant potential mainly due to the presence of sesquiterpenes which may be responsible for various pharmacological activities of this plant.     

Dispersive solid-phase extraction for in-sorbent Fourier-transform infrared detection and identification of nerve agent simulants in analysis for verification of chemical weapon convention

The combination of dispersive solid-phase extraction (DSPE) and Fourier-transform infrared (FTIR) spectroscopy is presented for detection and quantification of markers and simulants of nerve agents. Hydrophilic–lipophilic balance (HLB) sorbent was used for extraction and enrichment of organophosphonates from water. When the extraction efficiency of DSPE was compared with that of conventional solid-phase extraction (SPE), DSPE was more efficient. Extraction conditions such as extraction time, and type and quantity of sorbent material were optimized. In DSPE, extracted analytes are detected and quantified on the sorbent using FTIR as analytical technique. Absorbance in FTIR due to P–O–C stretching was used for detection and quantification. Infrared absorbance of different analytes were compared by determining their molar absorptivities (ε _max). Quantitative analyses were performed employing modified Beer’s law, and relative standard deviations (RSDs) for intraday repeatability and interday reproducibility were found to be in the range 0.30–0.90% and 0.10–0.80% respectively. The limit of detection (LOD) was 5–10 μg mL⁻¹. The applicability of the method was tested with an unknown sample prepared by mimicking the sample obtained in an international official proficiency test.     

Effects of Rapid Thermal Annealing on the Device Characteristics of Quantum Well Infrared Photodetectors

The effect of rapid thermal annealing (RTA) on important detector characteristics such as dark current, absolute response, noise, and detectivity is investigated for quantum-well infrared photodetectors (QWIP) operating in the 8–12 μm wavelength regime. A comprehensive set of experiments is conducted on QWIPs fabricated from both as-grown and annealed multiple-quantum-well structures. RTA is done at an anneal temperature of 850°C for 30 s using an SiO₂ encapsulant. In general, a decrease in performance is observed for RTA QWIPs when compared to the as-grown detectors. The peak absolute response of the annealed QWIPs is lower by almost a factor of four, which results in a factor of four decrease in quantum efficiency. In addition, a degraded noise performance results in a detectivity which is five times lower than that of QWIPs using asgrown structures. Theoretical calculations of the absorption coefficient spectrum are in excellent agreement with the experimental data.     

Equivalent-circuit interconnect modeling based on the fifth-order differential quadrature methods

This paper introduces an efficient and passive discrete modeling technique for estimating signal propagation delays through on-chip long interconnects that are represented as distributed RLC transmission lines. The proposed delay model is based on a less frequently used numerical approximation technique, called the differential quadrature method (DQM). The DQM can compute the partial derivative of a function at any arbitrary point located within a prespecified closed domain of the function by quickly estimating the weighted linear sum of values of the function at a relatively small set of well-chosen grid points within the domain. By using the fifth-order DQM, a new approximation framework is constructed in this paper for discretizing the distributed RLC interconnect and thereafter modeling its delay. Due to high efficiency of DQM approximation, the proposed framework requires only few grid points to achieve good accuracy. The presented equivalent-circuit model appears like the ones derived by the finite difference (FD) method. However, it has higher accuracy and less internal nodes than generated by the FD-based modeling. The fifth-order DQM modeling technique is shown to preserve passivity. It has linear forms that are compatible with the passive order-reduction algorithm for linear network. Numerical experiments show that the proposed modeling approach leads to high accuracy as well as high efficiency.     

In vivo antitussive potentiality of Lagerstroemia parviflora flower extract using a cough model induced by sulfur dioxide in mice

The methanol extract of the flowers of Lagerstroemia parviflora Roxb (Family: Lythraceae) was investigated for its effect on a cough model induced by sulphur dioxide gas in mice. It exhibited significant antitussive activity when compared with the control in a dose-dependent manner. The extract (100, 200, 300 mg kg(-1)) showed maximum inhibition of cough reflex at 90 min after drug administration and the antitussive activity was comparable to that of codeine phosphate, a standard antitussive agent.     

Assessment of the dilute approximation for the prediction of combined heat and mass transfer rates in multi-component systems

Use of the Fick’s law of diffusion is inappropriate in multi-component systems comprised of more than two species since it results in local violation of overall mass conservation. One approach that is often used to circumvent this problem is the dilute approximation, in which the conservation of the diluent is not enforced. It is generally believed that if the mass fraction of the diluent is “large” and it is a non-reacting species, the dilute approximation yields accurate results. In this study, the accuracy of the dilute approximation is quantitatively assessed by comparing its predictions against a rigorous multi-component diffusion formulation, derived from the Stefan–Maxwell equation. Both mass and heat flux errors are computed for a 1D pure diffusion problem. It is found that even for quite dilute mixtures with mass fraction of the diluent exceeding 70%, the errors are ∼15% for mass fluxes and as high as 35% for heat fluxes. In addition, the errors are found to be strongly dependent on the type of species in the mixture, implying that the validity of the dilute approximation cannot be judged a priori. Additional results are presented to show that in systems with combined heat and mass diffusion, net heat transfer can occur against the imposed temperature gradient. A Second Law analysis is presented and performed to corroborate these non-intuitive results.     

Influence of oxygen plasma treatment on boron carbon nitride film composition

Variations in the composition and bonds of boron carbon nitride (BCN) film caused due to an oxygen (O₂) plasma ashing process are investigated for a low dielectric constant (low-k) insulating film for next generation LSI devices. The O₂ plasma treatment is preformed for BCN samples with various C compositions. The etching rate of BCN films with an O₂ plasma decreases with increasing C composition. The reaction of O atoms is suppressed in the BCN film with a high C composition. B-N and B-C bonds with lower bond energies are easily broken by the O₂ plasma and replaced by the generation of B-O, N-O, and C-O bonds. The B-atom concentration for all samples is decreased significantly by the O₂ plasma treatment. Ion bombardment may play a more dominant role than the O-atom reaction in the etching of the BCN film. The existence of C-N bonds with a high bonding energy may suppress etching and incorporation of O atoms.