MODELING OF COMPETITIVE ADSORPTION OF NITROGEN SPECIES IN HYDRODESULFURIZATION

Previously, we developed a simple, one-parameter model reproducing the observed inhibiting effect of nitrogen species in the hydrodesulfurization (HDS) of hindered sulfur heterocycles. The model owes its simplicity to some nontrivial assumptions. Here we develop a full model by relaxing these assumptions, which gives a more quantitative picture of how sulfur, nitrogen, and catalyst surface interact on many widely disparate time scales. Computational results build a strong case for the accuracy of the previous one-parameter theory. As such, the theory should be applicable to reaction systems in which catalyst poisoning is driven by nonequilibrium adsorption. Some of the complexities and subtleties in modeling the competitive adsorption effects in distillate HDS are discussed, giving special attention to the design of robust catalyst-deactivation-compensation operating strategies.     

Partial-band jamming rejection of FFH/BFSK with product combiningreceiver over a Rayleigh-fading channel

An exact closed-form expression of the characteristic function is derived for a fast frequency-hopping (FFH) binary orthogonal frequency-shift-keying (FSK) spread-spectrum (SS) communication system. The FFH system employs a product combining receiver over a Rayleigh-fading channel with partial-band jamming and additive white Gaussian noise (AWGN). The derived characteristic function is then used to obtain a compact bit error rate (BER) expression for different diversity levels. Our study shows that there exists an optimum diversity level under certain channel conditions     

Specific antiviral activity demonstrated by TGTP, a member of a new family of interferon-induced GTPases

The GTPase superfamily includes a diversity of molecules whose functions are regulated through the binding and hydrolysis of GTP. This superfamily can be segregated into families of functionally related molecules that typically share amino acid sequence similarity within and around the nucleotide-binding domains. A new family of putative GTPases, including IRG-47, LRG-47, IGTP, and TGTP/Mg21, has recently emerged that share significant sequence identity (25-40%). Expression of these molecules has been shown to be selectively induced by IFN-gamma and in some cases by IFN-alpha beta or bacterial LPS. This induction pattern implicates these putative GTPases as part of the innate defense of cells to infection, but their role in such defense has not yet been defined. We have previously described the cloning of TGTP and now confirm its intrinsic activity as a GTPase. We found that TGTP is strongly induced by endogenous IFN-alpha beta produced in response to standard lipofection of plasmid DNA or polyinosinic polycytidylic acid. The ability of endogenously produced IFN-alpha beta to efficiently induce expression of TGTP under these conditions suggested that TGTP might participate in defense against viral infection. This proposal was borne out when TGTP-transfected L cells displayed relative resistance to plaque formation by vesicular stomatitis virus but not herpes simplex virus. This observation places TGTP among a small family of innate antiviral agents and has implications for the functions of other members of this family of GTPases.     

Power Doppler ultrasound evaluation of the shear rate and shearstress dependences of red blood cell aggregation

The use of power Doppler ultrasound at 10 MHz is evaluated as a method to study the shear rate and the shear stress dependences of red blood cell aggregation. This evaluation was based on 6 in vitro experiments conducted in a 1.27-cm diameter tube under steady flow conditions. Porcine whole blood was circulated in the flow model at flow rates ranging between 125 to 1500 ml/min (mean shear rate across the tube ranging between 6 and 74 s^-1). For each flow condition, the variation of the Doppler power across the tube and the velocity profile were measured by moving the Doppler sample volume across the tube diameter. For each radial position, the shear rate within the Doppler sample volume was also determined by considering the radial power pattern of the ultrasound beam. To estimate the shear stress within the Doppler sample volume, the apparent viscosity of blood samples withdrawn from the flow model was measured for each experiment. The variation of the Doppler power as a function of the shear rate within the sample volume showed a rapid reduction of the power between 1 and 5 s^-1, a transition region between 5 and 10 s^-1, and a very slow reduction beyond 10 s^-1. Little variation of the Doppler power was measured for shear stress higher than 2 dyn/cm. The maximum Doppler power for all flow rates was usually found near the center of the tube. Based on the ultrasonic scattering models, which predict that the Doppler power is related to the volume square of the scatterers, the method described in the present study showed a very high sensitivity to the presence of red blood cell aggregation for shear rates below 10 s^-1     

Improved tolerance in optical directional couplers

Tolerance requirements in conventional synchronous-mode directional couplers are examined. It is proposed that the tolerance situation can be improved considerably by tapering one, or both, of the propagation coefficients, so that they intersect at one position. This model is examined numerically, and suggestions are made for the practical realisation of a device.     

A method for the identification of crack-front location during fatigue fracture in polymers

An attempt has been made to accurately locate the crack-front position at intervals during fatigue cycling of low density polyethylene specimens by means of markers. Scanning electron microscopy has been used to inspect the fracture surfaces and the markers have been identified by means of the X-ray image produced by the signal from a fully focusing crystal spectrometer.     

Further development of the uniqueness criteria of the steady state via the contraction mapping principle

Uniqueness criteria of the steady state in porous catalysts are derived by using the contraction mapping principle with different norms. Among the norms considered, the one involving the gradient of the steady state yields the strongest result. The criteria developed in the present study bear some resemblance to those developed by other methods     

An achievable rate region of cooperative multiple-access channels with hybrid CF and DF cooperation

In this letter, we derive an achievable rate region of a two-user cooperative multiple-access (CMA) channel where one user performs decode-and-forward (DF) cooperation and the other user performs Wyner-Ziv-type compress-and-forward (CF) cooperation. The proposed rate region is achieved using a communication scheme that applies block Markov coding at each user and backward decoding at destination. Numerical results show that for some channel scenarios, the proposed hybrid CF and DF cooperation scheme enlarges the rate region achieved by the pure DF-based cooperation scheme.     

Design of adaptive supply voltage for sub-threshold logic based on sub-1 V bandgap reference circuit

This paper presents the design methodology to produce an adaptive supply voltage, which is used to drive digital sub-threshold logic system. Design guidelines to maintain constant speed and power via adaptive V_DD regulation are presented first. Then the paper discusses modification of sub-1 V bandgap reference (BGR) circuits using dynamic threshold MOSFET technique to provide the necessary adaptive reference voltage. Another well-known sub-1 V BGR circuit using current mode technique is also fabricated and compared. Both circuits are implemented in CMOS 0.18 μm technology. Empirical data from SPICE simulation and first order approximation techniques are used to derive analytical design models used inside BGR circuit. Measurement results of both the fabricated circuits show reference voltage output of 500 mV range; which are in good match of SPICE simulation.