Four wave mixing nonlinearity effect in wavelength division multiplexing radio over fiber system

The integration of wireless and optical networks is a potential solution for the increasing capacity and mobility as well as decreasing costs in the access networks. Optical networks are fast, robust and error free, however, there are nonlinearity obstacles preventing them from being perfect media. The performance of wavelength division multiplexing (WDM) in radio over fiber (RoF) systems is found to be strongly influenced by nonlinearity characteristics in side the fiber. The effect of four wave mixing (FWM) as one of the influential factors in the WDM for RoF has been studied here using Optisystem and Matlab. From the results obtained, it is found that the FWM effects have become significant at high optical power levels and have become even more significant when the capacity of the optical transmission line is increased, which has been done by either increasing the channel bit rate, and decreasing the channel spacing, or by the combination of both process. It is found that when the channel spacing is 0.1 nm, 0.2 nm and 0.5 nm the FWM power is respectively, becomes about -59 dBm, -61 dBm and -79 dBm. This result confirms that the fiber nonlinearities play decisive role in the WDM for RoF system. The simulation results obtained here are in reasonable agreement as compared with other numerical simulation results obtained, elsewhere, using different simulation tools

The living aortic valve: From molecules to function.

The aortic valve lies in a unique hemodynamic environment, one characterized by a range of stresses (shear stress, bending forces, loading forces and strain) that vary in intensity and direction throughout the cardiac cycle. Yet, despite its changing environment, the aortic valve opens and closes over 100,000 times a day and, in the majority of human beings, will function normally over a lifespan of 70-90 years. Until relatively recently heart valves were considered passive structures that play no active role in the functioning of a valve, or in the maintenance of its integrity and durability. However, through clinical experience and basic research the aortic valve can now be characterized as a living, dynamic organ with the capacity to adapt to its complex mechanical and biomechanical environment through active and passive communication between its constituent parts. The clinical relevance of a living valve substitute in patients requiring aortic valve replacement has been confirmed. This highlights the importance of using tissue engineering to develop heart valve substitutes containing living cells which have the ability to assume the complex functioning of the native valve

The role of MR diffusion in differentiation of malignant and benign hepatic focal lesions

AbstractAimTo determine if focal liver masses could be differentiated as benign or malignant by DWI and ADC maps.Methods and materialsSixty focal liver lesions were scanned using 1.5T MRI. DWI was performed with b 0, b 500 and b 1000 gradients with ADC measurements. Comparison of mean ADC values between each benign and malignant lesion was done. Reference standard of diagnosis was obtained by correlating DWI with histopathologic findings and imaging follow-up. The accuracies of DWI and ADC values were assessed with the Student’s t test, and cut-off values were determined with receiver operating characteristic curve analysis.ResultsWhen ADC value of 1.0×10−3mm2/s was used as a threshold value for differentiation of malignant tumors from benign lesions, sensitivity was 90.3%, specificity 78.57% and accuracy 86.7%. The best result was obtained with the use of ADC cut off value (at b 500) of 1.5×10−3mm2/s and ADC cut off value (at b 1000) of 1.0×10−3mm2/s, with 90.3% sensitivity, 92.86% specificity, 91.1% accuracy, 96.6% positive predictive value and 81.3% negative predictive value.ConclusionDWI and ADC map is a useful tool in differential diagnosis of malignant from benign liver lesions

Disposition kinetics, in vitro plasma protein binding and tissue residues of tilmicosin in healthy and experimentally (CRD) infected broiler chickens

Background: Several studies assayed the pharmacokinetics of tilmicosin in broilers at a dosage of (25mg/kg.b.wt.). The aim of this study was to investigate the pharmacokinetics and tissue residues of tilmicosin following single and repeated oral administrations (25mg/kg.b.wt.) once daily for 5 consecutive days in healthy and experimentally Mycoplasma gallisepticum and E. coli infected broilers.Methods: After oral administrations of tilmicosin (25 mg/kg.b.wt.) one ml blood was collected from the right wing vein and tissues samples for determination of tilmicosin concentrations and the disposition kinetics of it by the microbiological assay method using Bacillus subtilis (ATCC 6633) as a test organism.Results: In this study, the plasma concentration time graph was characteristic of a two-compartments open model. Following a single oral administration, tilmicosin was rapidly absorbed in both healthy and experimentally infected broilers with an absorption half-life of (t0.5(ab)) 0.45 and 0.52h, maximum serum concentration (Cmax) was 1.06 and 0.69μg/ml at (tmax) about 2.56 and 2.81h, (t0.5(el)) was 21.86 and 22.91h and (MRT) was 32.15 and 33.71h, respectively; indicating the slow elimination of tilmicosin in chickens. The in-vitro protein binding was 9.72±0.83%. Serum concentrations of tilmicosin following repeated oral administration once daily for five consecutive days, almost peaked 2h after each dose with lower significant values recorded in experimentally infected broiler chickens than in healthy ones.Conclusions: This study showed that tilmicosin was cleared rapidly from tissues. The highest residue values were recorded in the lung followed by liver and kidneys while the lowest values were recorded in spleen, fat and thigh muscles. Five days for withdrawal period of tilmicosin suggested in broilers

Relay based thermal aware and mobility support routing protocol for wireless body sensor networks

The evolvement of wireless technologies has enabled revolutionizing the health-care industry by monitor patient health condition requiring early diagnosis and interfering when a chronic situation is taking place. In this regard, miniaturized biosensors have been manufactured to cover various medical applications forming therefore a Wireless Body Sensor Network (WBSN). A WBSN is comprised of several small and low power devices capable of sensing vital signs such as heart rate, blood glucose, body temperature etc.. Although WBSN main purpose is to provide the most convenient wireless setting for the networking of human body sensors, there are still a great number of technical challenges to resolve such as: power source miniaturization, low power transceivers, biocompatibility, secure data transfer, minimum transmission delay and high quality of service. These challenges have to be taken into consideration when creating a new routing protocol for WBSNs. This paper proposes a new Relay based Thermal aware and Mobile Routing Protocol (RTM-RP) for Wireless Body Sensor Networks tackling the problem of high energy consumption and high temperature increase where the mobility is a crucial constraint to handle

Model electrodes for the electrooxidation of simple alcohols : a DEMS study

Pt is considered as a model for fuel cell electrocatalysts. In the present thesis, I stud-ied the electrooxidation mechanisms of methanol (chapter 3) and ethanol (chapter 4) on different Pt surfaces, using a dual thin-layer flow through cell combined with the mass spectrometer. In chapter 5, Ru quasi single crystal films on different bead Pt surfaces were formed using the resistive heating in a stream of nitrogen. The Ru films were exam-ined by cyclic voltammetry in sulfuric acid and by structure-sensitive underpotential deposition of Cu. Finally, in chapter 6, in order to use bead single crystal in the right ar-rangement (hanging meniscus) on DEMS, a new DEMS flow cell was manufactured and improved for that purpose. The electrooxidation of methanol proceeds via the dual pathway mechanism. The path involving the formation of soluble intermediates such as formaldehyde and formic acid is the direct pathway, while the dehydrogenation of methanol to adsorbed CO fol-lowed by its oxidation to CO2 is referred to as indirect pathway. Methylformate is one of the volatile products formed during the electrooxidation of methanol at Pt surfaces. In all previous articles it is assumed that methylformate formation results from the reaction of formic acid and the excess of methanol, i.e. the detection of methylformate is an indirect way to determine the amount of formic acid produced during the oxidation reaction. However, the probability of esterification reaction is very small because the fast diffusion of the soluble products away from DEMS cell under effect of continuous electrolyte flow. A simple kinetic study of methanol esterification and methylformate hydrolysis in acid media was performed since literature data for the rate of this esterification reaction were not available. The reaction rate constant of methylformate formation was found to be far too low (τ ≈ 40 h at 0.1 mol L-1 methanol), while the time constant of dual-thin layer flow through cell at 1.6 µL s-1 is 5 s. Methylformate therefore is directly formed during oxida-tion of methanol at the electrode surface and not in the solution phase as believed before, with a current efficiency about 1%. The suggested mechanism for methylformate formation, is the nucleophilic attack of adsorbed methanol with another methanol molecule from the solu-tion; note that the nucleophilic power of the oxygen in methanol is higher than that in the water molecule. The current efficiency with respect to CO2 and the surface coverage with methanol adsorbate (COad) have been shown to be independent of the electrolyte flow rate (from 1.6–30 µL s-1); this confirms the parallel pathway mechanism. Poisoning of the catalyst with adsorbed CO is one of the main problems in fuel cells. Ru as a catalyst with Pt promotes the electrooxidation of adsorbed CO according to bi-functional and the electronic mechanism. On such bimetallic surfaces, Ru is preferentially deposited at steps. Using deliberately stepped Pt surfaces as model electrodes, it could be shown that the complete coverage of the step sites with Ru has an inhibiting effect for methanol and ethanol oxidation due to the blockage of the most active sites, i.e. the free step sites are necessary for the first step of C1 and C2 alcohols adsorption and oxidation. For ethanol, the cleavage of C–C bond is the most difficult step in the complete oxi-dation of ethanol to CO2. Also ethanol electrooxidation at Pt surfaces occurs according to different pathways depending on the surface structure. During the electrooxidation under controlled convection, where there is no further oxidation of soluble products at the sur-face, acetaldehyde is the main product at polycrystalline Pt and Pt stepped single crystal surfaces vicinal to the (100) plane. Acetaldehyde is formed at these surfaces over the po-tential range with a current efficiency close to 100%. At Pt stepped single crystals vicinal to the (111) plane, the formation of acetic acid proceeds at lower potentials than that of acetaldehyde production due to the direct reac-tion between adsorbed ethanol and adsorbed hydroxide species. At higher potentials, due the blockage of the surface with adsorbed anions, e.g. acetate and sulfate, only the dehydrogenation of ethanol takes place at (111) planes to produce acetaldehyde. In practical applications, the formation of acetic acid should be avoided because of its inertness whereas, in principle, acetaldehyde can be oxidized to CO2. Therefore, it might be advantageous to use nanoparticles without a large degree of (111) facets as electro-catalyst in fuel cells. Another kind of model electrode would be Ru single crystals modified by Pt. How-ever, since Ru is oxidized by atmospheric oxygen very fast, the usual flame annealing method in air does not work. Attard and co-workers developed a new method for Ru quasi single crystal preparation by forced deposition of Ru multilayer on Pt single crystals followed by resistive heating in a nitrogen atmosphere. In order to characterize this Ru film on different Pt single crystals, Cu UPD is the suitable technique. For Pt(100), the charge density of Cu UPD stripping from Ru quasi-single-crystal electrode is in agreement with the charge density of Cu UPD stripping from clean Pt(100); this suggests the formation of an epitaxial Ru film on the Pt(100) electrode. For the Ru films formed on Pt(111) and Pt(110) surfaces, Cu UPD deposition is inhibited due to strongly adsorbed oxygen species. For Ru films deposited on stepped Pt single crystal vicinal to the (100) plane, it was found that: Because the characteristic Cu UPD stripping peak related to the free Pt sites is absent, the stepped Pt single crystal surfaces are completely covered with Ru film. The charge density for the peak at 185 mV related to Cu UPD stripping from (100) terrace sites decreases linearly with increasing the step density of the Pt single crystal substrate, which confirms the formation of epitaxial Ru films on the Pt surfaces. Preliminary results show that the deposition of a Pt sub-monolayer on the Ru film is pos-sible by galvanic replacement of Cu UPD. In order to be able to use bead single crystals in the hanging meniscus configuration, a new DEMS cell was constructed. The recorded cyclic voltammogrames for different bead Pt single crystals in supporting electrolyte, under hanging meniscus arrangement and at constant flow of electrolyte, are in agreement with literature profiles. This and the calibration constant and corresponding ionic signals for organic molecules oxidation sug-gest that this new cell is well suited for bead single crystals. Compared with the dual thin layer flow through cell, it has the advantage that cleanliness is easier achieved and that less expensive single crystals can be used. The K* values are reproducible and typical to that of the dual thin layer flow through cell under the same experimental conditions. For the electrooxidation of bulk methanol at polycrystalline Pt in the new flow cell, the current efficiency with respect to CO2 is high-er than that in the previous cell design. The reason might be the further oxidation of the soluble intermediates because of a less efficient electrolyte flow in the thin layer between the electrode surface and the glass capillary. Also, the ionic signal of methylformate is not detected under the same experimental conditions due to the small surface area of the working electrode resulting in a small amount of product.</p

Study of MAC Protocols for Mobile Wireless Body Sensor Networks

Wireless Body Area Networks (WBAN) also referred to as a body sensor network (BSN), is a wireless network of wearable computing devices. It has emerged as a key technology to provide real-time health monitoring of a patient and diagnose many life threatening diseases. WBAN operates in close vicinity to, on, or inside a human body and supports a variety of medical and non-medical applications. The design of a medium access control is a challenge due to the characteristics of wireless channel and the need to fulfill both requirements of mobility support and energy efficiency.  This paper presents a comparative study of IEEE 802.15.6, IEEE 804.15.4 and T-MAC in order to analyze the performance of each standard in terms of delay, throughput and energy consumption. Keywords: Biomedical, IEEE 802.15.6; T-MAC, IEEE 802.15.4, mobility, low-power communication, wireless body sensor networks, implantable sensors, healthcare applications, biosensors