Compressible flows through micro-channels with sharp edged turns and bifurcations

Bends and bifurcations connecting straight channels are common features in micro-channel networks. We apply our recently extended Hele-Shaw asymptotic scheme to study the viscous compressible gas flow through a shallow bend (whose depth is small relative to all other characteristic dimensions). By the use of analytic-function theory, we obtain closed-form solutions for arbitrary values of the turn angle and the ratio between the upstream- and downstream- channel widths, respectively. The viscous resistance is thereby evaluated in terms of the geometrical parameters characterizing the bend. The linearity of the problem in terms of an appropriately defined quadratic form of the pressure allows us to briefly consider the role of bifurcations in the viscous resistance of tree-like micro-channel networks.     

Noninvertibility, chaotic coding, and chaotic multiplexity of synaptically modulated neural firing

Widely accepted neural firing and synaptic potentiation rules specify a cross-dependence of the two processes, which, evolving on different timescales, have been separated for analytic purposes, concealing essential dynamics. Here, the morphology of the firing rates process, modulated by synaptic potentiation, is shown to be described by a discrete iteration map in the form of a thresholded polynomial. Given initial synaptic weights, a firing activity is triggered by conductance. Elementary dynamic modes are defined by fixed points, cycles, and saddles of the map, building blocks of the underlying firing code. Showing parameter-dependent multiplicity of real polynomial roots, the map is proved to be noninvertible. The incidence of chaos is then implied by the parameter-dependent existence of snap-back repellers. The highly patterned geometric and statistical structures of the associated chaotic attractors suggest that these attractors are an integral part of the neural code. It further suggests the chaotic attractor as a natural mechanism for statistical encoding and temporal multiplexing of neural information. The analytic findings are supported by simulation.     

Engineering interchain disulfide bonds into conserved framework regions of Fv fragments: improved biochemical characteristics of recombinant immunotoxins containing disulfide-stabilized Fv

Using molecular modeling technology, we have recently identifiedtwo positions in conserved framework regions of antibody Fvfragments (Fvs) that are distant from CDRs, and potentiallycan be used to make recombinant Fv fragments in which the unstableV_H and V_L heterodimer is stabilized by an interchain disulfidebond inserted between structurally conserved framework positions.A disulfide bond has been introduced at one of these positions,V_H44-V_L105, and shown to stabilize various Fvs that retain fullbinding and specificity. Recombinant immunotoxias, e.g. B3(dsFv)-PE38KDELin which this disulfide-stabilized Fv moiety is connected toa truncated form of Pseudomonas exotoxin (PE; PE38KDEL) whichcontains the translocation and ADP ribosylation domains, areindistinguishable in binding and specificity from its single-chainimmunotoxin counterparts. We have now analyzed the alternativeposition, (V_H111-V_L48), predicted by the modeling methodology,for disulfide stabilization of mAb B3(Fv) by producing a recombinantimmunotoxin with such disulfide-stabilized (ds) Fv. This immunotoxinwas also very active and retained full specificity to B3 antigen-positivecells. However, it was 2- to 3-fold less active than the V_H44-V_L105dsFv-molecule. We also tested various biochemical features ofV_H44-V_L105 and V_H111-V_L48 dsFv immunotoxins and compared themwith the corresponding single-chain immunotoxin. We found thedsFv immunotoxins were more stable in human serum and more resistantto thermal and chemical denaturation than the single chain (sc)Fv immunotoxin. Because dsFv immunotoxins and dsFvs have fullactivity and specificity and improved stability, they may bemore useful than scFv immunotoxins as therapeutic and diagnosticagents.     

Performance characterization of III-V power devices

The power performance of GaAs/AlGaAs pseudomorphic high electron mobility transistors (PHEMTs) has been modeled by using the statistical Design of Experiment approach. Empirical models for the small signal gain, output power and power added efficiency have been developed. The “walk-out/in” phenomenon has been observed in the devices as a result of power measurements. The evolution of surface photovoltage spectra after RF power stress indicates accumulation of positive electrical charge in the buffer and the surface layer of the devices.     

Heart-surface reconstruction and ECG electrodes localization using fluoroscopy, epipolar geometry and stereovision: application to noninvasive imaging of cardiac electrical activity

To date there is no imaging modality for cardiac arrhythmias which remain the leading cause of sudden death in the United States (> 300000/yr.). Electrocardiographic imaging (ECGI), a noninvasive modality that images cardiac arrhythmias from body surface potentials, requires the geometrical relationship between the heart surface and the positions of body surface ECG electrodes. A photographic method was validated in a mannequin and used to determine the three-dimensional coordinates of body surface ECG electrodes to within 1 mm of their actual positions. Since fluoroscopy is available in the cardiac electrophysiology (EP) laboratory where diagnosis and treatment of cardiac arrhythmias is conducted, a fluoroscopic method to determine the heart surface geometry was developed based on projective geometry, epipolar geometry, point reconstruction, b-spline interpolation and visualization. Fluoroscopy-reconstructed hearts in a phantom and a human subject were validated using high-resolution computed tomography (CT) imaging. The mean absolute distance error for the fluoroscopy-reconstructed heart relative to the CT heart was 4 mm (phantom) and 10 mm (human). In the human, ECGI images of normal cardiac electrical activity on the fluoroscopy-reconstructed heart showed close correlation with those obtained on the CT heart. Results demonstrate the feasibility of this approach for clinical noninvasive imaging of cardiac arrhythmias in the interventional EP laboratory.     

Specific impact of radio and television on children's story comprehension.

A cross-media comparison of TV and radio elucidated the specific strengths of each medium for transmitting explicit and implicit story content. 48 elementary school children in 2 age groups (6.5–8 yrs and 9–10.5 yrs) were exposed to an animated audiovisual (TV) and an audio (radio) story. A narration of the original story text served as the common soundtrack. The design was counterbalanced for story-medium combinations and orders. Except for the inclusion of characters, recall of the explicit story content was equivalent across media. However, recall of details from the story was improved with a TV presentation. Recognition of expressive language was facilitated by a radio story, whereas picture sequencing was augmented by a TV story. The radio story also elevated the use of knowledge unrelated to the story for inferences by younger Ss and verbal sources for both ages, whereas the TV story enhanced inferences based on actions. Findings emphasize the need to consider the differential impact of media for conveying explicit and implicit content. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Total nitrogen analysis in water, soil and plant material with persulphate oxidation

A method for the determination of total (Kjeldahl) nitrogen in soil and water samples is presented. The sample is digested with a potassium persulphate solution in an autoclave. Subsequently, nitrates and nitrites are reduced to ammonium with Devarda alloy and ammonium determined colorimetrically. The method was found to be accurate, reproducible and efficient.     

Accurate determination of plasmonic fields in molecular junctions by current rectification at optical frequencies

Current rectification, i.e., induction of dc current by oscillating electromagnetic fields, is demonstrated in molecular junctions at an optical frequency. The magnitude of rectification is used to accurately determine the effective oscillating potentials in the junctions induced by the irradiating laser. Since the gap size of the junctions used in this study is precisely determined by the length of the embedded molecules, the oscillating potential can be used to calculate the plasmonic enhancement of the electromagnetic field in the junctions. With a set of junctions based on alkyl thiolated molecules with identical HOMO-LUMO gap and different lengths, an exponential dependence of the plasmonic field enhancement on gap size is observed.     

The onset of flows and instabilities in a thermosyphon with parallel loops

A theoretical study is presented for the stability of various steady flows in a thermosyphon with multiple vertical channels. The main interest is in the onset of motion from a rest state or in a stagnant branch, therefore laminar flow is considered and a one-dimensional model is used to describe the flow and temperature fields. The steady state solutions include a state of no flow (rest) in the whole system and two basic flow configurations: a single loop between two channels while the others are stagnant and a symmetric flow. For a three-channel system the latter consists of an upward velocity, u, in one branch and downward velocities, , in the other two. The mirror image of these basic flows are also steady state solutions.A critical modified number, R_c = 6, is found to be the stability margin for the onset of motion from a rest state in the entire system. This result was obtained both by a study of the steady state solution (no steady solution for R < R_c) and by the stability analysis. The steady flow with a stagnant loop is always unstable while the symmetric flow solution in the system considered here is always stable.