Neutral Lipid Characterization of Non-Water-Soluble Fractions of <Emphasis Type=Italic>Carica Papaya</Emphasis> Latex

The non-water-soluble fraction of Carica papaya latex (CPL) constitutes a waste material from papain production; very little information exists regarding its chemical composition. The non-water-soluble fraction of CPL was fractionated by liquid chromatography into neutral lipids, glycolipids and phospholipids. The most abundant compounds were found to be the polar lipids, accounting for 79.2% (w/w) of the total extractible matter, while the total amount of neutral lipids was only around 20%. It was composed of free fatty acids, sterols and triterpenic alcohols, but no glycerides were detected. A high content of saturated fatty acids was measured; these saturated fatty acids were represented by very long chains with C24:0, C26:0 and C28:0 accounting for 6.3, 11.0 and 6.3%, respectively, in the total extractible matter and 7.3, 9.0 and 3.9% in the FFA fraction. The monounsaturated fatty acids were about 23–25% in both samples, with oleic acid (C18:1) being the most abundant. The polyunsaturated fatty acids that were 25.1% in the total matter and 21.6% in the FFA fraction were mainly represented by linoleic acid (C18:2n-6). Finally, a very interesting characteristic of the FA composition of this latex concerns the presence of odd-numbered fatty acids in significant amounts (around 22% in the total extract and 24.3% in the FFA fraction).     

An investigation of soft-core potentials for the simulation of mesogenic molecules and molecules composed of rigid and flexible segments

The phase behaviour of three soft core spherocylinder models is investigated with a view to producing an effective potential for use in coarse-grained simulations of liquid crystal phases and polymers composed of rigid and flexible segments. Provided potentials are not made too soft, two of the soft core models are found to work well in terms of successfully reproducing mesophases and in providing considerable improvements in computational speed over other commonly used coarse-grained models. In Monte Carlo simulations a soft-core spherocylinder model in which a cut and shifted Lennard-Jones potential is truncated with a linear tangential potential is found to be particularly effective; while for molecular dynamics a better model is provided by a DPD-like quadratic potential. Here, computational speed-ups of 20-30× are seen in equilibration times in comparison to the well-known soft repulsive spherocylinder (SRS) model. The quadratic potential is used in an additional set of coarse-grained simulations of a liquid crystal with a flexible chain, which exhibits spontaneous formation of a nematic phase. The use of different types of interaction sites is also illustrated by the simulation of a spherocylinder with two “tails” formed from spheres. Here, varying the hardness of the sphere-spherocylinder interaction potential allows the formation of a smectic-A phase which exhibits microphase separation.     

Average probability of packet error with diversity reception over arbitrarily correlated fading channels

Closed form expressions for the average probability of packet error (PPE) are presented for no diversity, maximum ratio combining (MRC), selection combining (SC) and switch and stay combining (SSC) diversity schemes. The average PPE for the no diversity case is obtained in two alternative expressions assuming arbitrarily correlated Nakagami and Rician fading channels. For the MRC case, L diversity branches are considered and the channel samples are assumed to follow Nakagami distribution and to be arbitrarily correlated in both time and space. For the SC diversity scheme with L diversity branches, two bounds on the average PPE are derived for both slow and fast fading channels. The average PPE in this case is obtained in an infinite integral form for Nakagami channels while it is reduced to a closed form expression for the Rayleigh case. The average PPE is also derived in the case of SSC diversity with dual branches for both slow and fast Rayleigh fading channels. The new formulas are applicable for all modulation schemes where the conditional probability of error has an exponential dependence on the signal‐to‐noise ratio. The average PPE is then used to obtain a modified expression for the throughput for network protocols. In general, the diversity gain exhibits a little diminishing effect as the number of diversity branches increases. In addition, the system is found to be more sensitive to the space correlation than to the time correlation. The effects of different system parameters and diversity schemes are studied and discussed. Specific figures about the system performance are also provided. Copyright © 2004 John Wiley & Sons, Ltd.     

Route selection in IEEE 802.11 wireless mesh networks

This paper addresses the problem of route selection in IEEE 802.11 based Wireless Mesh Networks (WMNs). Traditional routing protocols choose the shortest path between two routers. However, recent research reveals that there can be enormous differences between links in terms of quality (link loss ratio, interference, noise etc) and therefore selecting the shortest path (hop count metric) is a poor choice. We propose a novel routing metric—Expected Link Performance (ELP) metric for wireless mesh networks which takes into consideration multiple factors pertaining to quality (link loss ratio, link capacity and link interference) to select the best end-to-end route. Simulation based performance evaluation of ELP against contemporary routing metrics shows an improvement in terms of throughput and delay. Moreover, we propose an extension of the metric called ELP-Gateway Selection (ELP-GS) which is an extension meant for traffic specifically oriented towards the gateway nodes in the mesh network. We also propose a gateway discovery protocol which facilitates the dissemination of ELP-GS in the network. Simulation results for ELP-GS show substantial improvement in performance.     

Wireless Communications Transmitter Performance Enhancement Using Advanced Signal Processing Algorithms Running in a Hybrid DSP/FPGA Platform

This paper deals with digital base band signal processing algorithms, which are seen as enabling technologies for software-enabled radios, that are intended for the correction of the analog front end. In particular, this paper focuses on the design, optimization and testability of predistortion functions suitable for the linearization of narrowband and wideband transmitters developed with a hybrid DSP/FPGA platform. To select the best algorithm for the identification of the predistortion function, singular value decomposition, recursive least squares (RLS), and QR-RLS algorithms are implemented on the same digital signal processor; and, the computation complexity, time, accuracy and the required resources are studied. The hardware implementation of the predistortion function is then carefully performed, in order to meet the real time execution requirements.     

Performance of generalized selection combining over Weibull fading channels

The literature is relatively sparse in performance analysis of diversity combining schemes over Weibull fading channels, despite the fact that the Weibull distribution is often found to be suitably fit for empirical fading channel measurements. In this paper, we capitalize on some interesting results due to Lieblein on the order statistics of Weibull random variables to derive exact closed‐form expressions for the combined average signal‐to‐noise ratio (SNR) as well as amount of fading (AF) at a generalized selection combining (GSC) output over Weibull fading channels. We also use some simple AF‐based mappings between the fading parameters of the Weibull distribution and those of the Nakagami, Rice, and Hoyt distributions to obtain the approximate but accurate average SNR and AF of GSC over these types of channels. The mathematical equations are validated and illustrated by some numerical examples for scenarios of practical interest. Copyright © 2006 John Wiley & Sons, Ltd.     

A theoretical model for analyzing the dynamic behavior of a misaligned rotor with active magnetic bearings

The dynamic response of a misaligned rotor, mounted in two identical active magnetic bearings (AMBs) was numerically investigated in this work. Three simplified models of current biased radial active magnetic bearings were presented, where four, six and eight electromagnets were powered by the bias current i₀ and respective control current. The magnetic forces acting on the rotor, the coil currents and the displacement of the rotor were obtained through an electromagnetic theory. The AMBs’ dynamics support parameters were modelled by linearised direct cross axes stiffness and damping coefficients. These are strongly dependent on the air gap between the stator and the shaft. A spatial model of a misaligned rotor with two degrees of freedom was presented. The motion equations were established for the rotor bearing system and simulated with Newmark method. Simulations results were carried out to survey the dynamic behavior of spatial misaligned rotor mounted in AMBs. The angular misalignment was such that the 2× and 4× running speed components are predominant. Their magnitudes varied with the number of magnets in the bearing and with the air gap between the stator and the shaft.     

Is laparoscopic surgical practice "factual" (evidence based)? Results of a prospective regional survey

OBJECTIVE: Evidence-based medicine is a growing paradigm in health care. We conducted a prospective study to determine whether laparoscopic surgery is truly evidence-based in everyday practice. METHODS: A prospective regional survey was performed in 11 French hospitals (one university and 10 district hospitals) to ascertain how general laparoscopic surgery was conducted during the last 3 months of 1997. We also searched the electronic databases for original articles on laparoscopic procedures. The methodology of randomized trials was analyzed and procedures were classed by level of evidence. We assumed that an evidence-based procedure was which had been validated by well-designed randomized controlled or prospective trials giving homogeneous results. RESULTS: One half of the procedures performed had been evaluated by randomized controlled trials. Among the 428 laparoscopic procedures, 334 (78%) were found to be evidence-based (CI 74.1-81.9%). Twelve of the 18 indications for laparoscopy (67%) were evidence based (CI: 62.5%-71.5). There was no difference between university teaching hospitals and general district hospitals. CONCLUSION: Contrary to initial criticisms, the practice of laparoscopic surgery appears to be truly evidence-based in the majority of cases.