Fabricating Janus membranes via physicochemical selective chemical vapor deposition

Membranes with asymmetric wettability-Janus membranes-have recently received considerable attention for a variety of critical applications. Here, we report on a simple approach to introduce asymmetric wettability into hydrophilic porous domains. Our approach is based on the physicochemical-selective deposition of polytetrafluoroethylene (PTFE) on hydrophilic polymeric substrates. To achieve selective deposition of PTFE, we inhibit the polymerization reaction within the porous domain. We prefill the substrates with glycerol, containing a known amount of free radical inhibitor, and utilize initiated chemical vapor deposition (iCVD) for the polymerization of PTFE. We show that the glycerol/inhibitor mixture hinders the deposition of PTFE within the membrane pores. As a result, the surface of the substrates remains open and porous. The fabricated Janus membranes show stable wetting-resistant properties, evaluated through sessile drop contact angle measurements and direct contact membrane distillation (DCMD).     

Dynamic compensation and decoupling for systems of uniform index 2

The design of ann-dimensional dynamic compensator for arbitrary pole placement for systems of dimension2nand uniform controllability and observability indexes 2 is considered in state space representation and frequency domain.     

Finite element analysis of gradient coil deformation and vibration in NMR microscopy

Resolution degradation due to gradient coil deformation and vibration in NMR microscopy is investigated using finite element analysis. From the analysis, deformations due to the Lorentz force can be as large as 1-10 mum depending on the gradient strength and coil frame material. Thus, these deformations can be one of the major resolution limiting factors in NMR microscopy. Coil vibration, which depends on the input current waveform and resolution degradation due to time-variant deformation and time-invariant deformation are investigated by numerical simulations.     

A new framework for soft decision equalization in frequency selective MIMO channels

We introduce a novel framework for soft-input, soft-output (SISO) equalization in frequency selective multipleinput multiple-output (MIMO) channels based on the well-known belief propagation (BP) algorithm. As in the BP equalizer, we model the multipath channels using factor graphs (FGs) where the transmitted and received signals are represented by the function and variable nodes respectively. The edges connecting the function and variable nodes illustrate the dependencies of the multipath channel and soft decisions are developed by exchanging information on these edges iteratively. We incorporate powerful techniques such as groupwise iterative multiuser detection (IMUD), probabilistic data association (PDA) and sphere decoding (SD) in order to reduce the computational complexity of BP equalizer with relatively small degradation in performance. The computational complexity of this new reduced-complexity BP (RCBP) equalizer grows linearly with block size and memory length of the channel. The proposed framework has a flexible structure that allows for parallel as well as serial detection. We will illustrate through simulations that the RCBP equalizer can even handle overloaded scenarios where the channel matrix is rank deficient, and it can achieve excellent performance by applying iterative equalization using the low-density parity check codes (LDPC).     

Hydrodynamics of three-phase fluidized bed containing cylindrical hydrotreating catalysts

Experiments were performed to study the hydrodynamic characteristics of a cocurrent, gas-liquid-solid fluidized bed containing cylindrical hydrotreating catalysts under conditions of high gas holdup. These conditions were established using an aqueous t-pentanol (0.5 wt. %) solution as the liquid phase in an attempt to simulate reaction conditions for hydrotreating of residual oils and coal liquefaction. Separate three-phase experiments were performed with air and water to investigate the effect of surface tension on hydrodynamic behavior. A mathematical model was developed to describe the minimum fluidization velocity behavior. Bed voidage, gas holdup and terminal velocity of the particles were analyzed and correlated empirically to investigate the effect of particle shape and liquid surface tension. A bubble-wakes interaction coefficient defined by Jean and Fan (1987) was determined for cylindrical particles.     

Reduced-Complexity Belief Propagation for System-Wide MUD in the Uplink of Cellular Networks

System-wide multiuser detection (MUD), in which all base stations (BSs) of a cellular system cooperate to detect the data of all mobile stations (MSs), has much promise. However, little is known at present about practical techniques or their performance. An attractive method is belief propagation (BP), with message exchange between nearby cooperating BSs over a backbone landline network, but its performance is known only for a greatly simplified network model and its computation load grows exponentially with the number of interfering MS symbols at each BS. In this paper, we present a reduced complexity variation of BP (RCBP) and show that its performance is close to or identical to that of BP in the simplified network. We also observe excellent performance by iterative multiuser detection and decoding of low-density parity check codes (LDPC). Furthermore, we examine RCBP performance in a realistic wireless network model, with path loss, shadowing, fading and power control. These results, though poorer than those of the simplified network, show that system-wide MUD with cooperating BSs provides great improvement compared with conventional systems.     

An iterative groupwise multiuser detector for overloaded MIMO applications

We consider a narrowband multiuser system in which several transmitting users are received through a synchronous, flat fading channel at an antenna array. The paper introduces a multiuser detection technique that combines group wise detection with iteration. It is well suited to overloaded conditions, where there are more transmitter antennas than receive antennas. The soft decisions it uses internally also make it suitable as a detector in a concatenated structure. Its performance and computation can be traded off through selection of group size. A variant of the algorithm achieves further computation reduction by incorporating a soft sphere detection core     

Analysis of the convergence properties of topology preservingneural networks

The authors provide a rigorous treatment of the convergence of the topology preserving neural networks proposed by Kohonen for the one-dimensional case. The approach extends the original work by Kohonen on the convergence properties of such networks in several respects. First, the authors investigate the convergence of the neuron weights directly as compared to Kohonen's treatment of the dynamic behavior of the expectation values of the weights. Second, the problem is formulated for a more general case of selecting the neighborhood amplitude of interaction rather than the uniform amplitude. Third, the proof of convergence is based on the well-known Gladyshev theorem which uses Lyapunov's function method. The authors provide a step-by-step constructive proof which establishes the asymptotic convergence to a unique solution. This proof also provides the relation between the boundary neurons' weight vectors and the number of neurons in the network. The approach is then extended to the two-dimensional case and the result is stated in a theorem.     

Mathematical modeling and steady-state analysis of a proton-conducting solid oxide fuel cell

This paper presents a study of mathematical modeling and steady-state analysis of a proton-conducting solid oxide fuel cell (SOFC). The SOFC has a SrCe_0.95Yb_0.05O_3?α (SCY) electrolyte and two platinum electrodes. A mathematical model of the SOFC is first developed. The model captures electrochemical processes as well as the transport phenomena. The existence of steady-state multiplicity in the cell under three modes of constant ohmic load, potentiostatic and galvanostatic operations is studied. Simulation results show that a multiple steady-states region exists at low inlet fuel and air temperatures under constant ohmic load and potentiostatic operations. The occurrence of ignition and extinction in the cell solid (electrolyte, anode and cathode) temperature is reported. This result is in agreement with those for oxygen ion-conducting solid oxide fuel cells in which the existence of steady-state multiplicity has been attributed to the dependence of the electrolyte oxygen-ion conductivity on temperature. This work shows that concentration and temperature multiplicities coexist.