Dynamics of Gaseous Uptake in the Lungs: The Concentration and Second Gas Effects

A one-compartment, continuous-time model is proposed for the investigation of dynamic gas exchange in the lungs. The dynamics of the alveolar gas concentrations (state variables, xi) are demonstrated to be critically determined by, among other things, the blood-gas partition coefficients and the inspired concentrations (inputs, ui) of the component gases. The model has a bilinear structure which, when sibjected to a step input, can be exactly linearized. It is shown that the eigenvalues of the system are all real and negative, and can be simultaneously maximized if the most soluble gas of the inspirate alone is inhaled (i. e., the system becoming minimally stable). The normalized state response (xg/uj) corresponding to this input exhibits the greatest steady-state excursion, albeit with the slowest kinetics, so that the response xi/Ui rises most rapidly. Furthermore, this input-dependent effect extends also to the uptake kinetics of all other gases in the inspirate. Our investigations suggest that it can be ascribed primarily to an increase in the ratio of inspired-to-expired ventilation. These analytical predictions are further supported by simulation studies, and correspond closely with independent experimental observations. These results are consistent with, and provide a quantitative account for, the experimental observations generally known as the concentration and second gas effects.     

Real-time textural edge detection by incoherent spatial Gaussianbandpass filtering

A technique for textural edge detection using an acoustooptic two-pupil heterodyne scanning system is proposed. A textural region is modeled as a frequency-modulated tonal domain. Boundary extraction between two textures is discussed based on an extension of tonal edge detection by bandpass filtering in the frequency domain. The textural edge detection can be achieved optically by using two offset Gaussian pupils in the two-pupil scanning system. Its performance is discussed along with the experimental results     

Chemical Short-Range-Ordering Effect on Structural Relaxation in Metallic Glasses

A model is proposed to address chemical effects on structural relaxation in metallic glasses. The atomic short range ordering (SRO) is described under the quasi-chemical approximation (QCA). Local chemical deviations from the ideal SRO are considered as an excess enthalpy. The simplified analysis of a disordered region’s evolution is based on the notion of the collective bond exchange between neighboring atoms. The approach suggests a bimolecular mechanism with possibly large apparent activation energy for structural relaxation near the glass transitions. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Characterization of the elastin binding domain in the cell-surface 25-kDa elastin-binding protein of staphylococcus aureus (EbpS)

Our previous studies have established that a cell-surface 25-kDa elastin-binding protein of Staphylococcus aureus (EbpS) mediates binding of this pathogen to the extracellular matrix protein elastin. Results from binding assays examining the activity of various EbpS fragments suggested that the elastin recognition domain is contained within the first 59 amino acids. In this report, we have used functional analyses with synthetic peptides and recombinant truncated forms of EbpS to localize the elastin binding domain to a 21-amino acid region contained within residues 14-34 of EbpS. Further evidence for the importance of this domain was obtained by demonstrating that the inhibitory activity of anti-EbpS antibodies on staphylococcal elastin binding was neutralized when these antibodies were pre-absorbed with a truncated recombinant EbpS construct containing residues 1-34. Overlapping synthetic peptides corresponding to EbpS residues 14-36 were then generated and tested for elastin binding activity to define further the elastin binding domain, and results from these studies showed that sequences spanning amino acids Gln14-Asp23, Asp17-Asp23, and Thr18-Glu34 inhibit binding of Staphylococcus aureus to elastin. Our analyses indicate that the hexameric sequence Thr18-Asn-Ser-His-Gln-Asp23 is the minimal sequence common to all active synthetic peptides, proteolytic fragments, and recombinant constructs of EbpS. Furthermore, substitution of Asp23 with Asn abrogated the blocking activity of the synthetic peptides, demonstrating the requirement for a charged amino acid at this location. The composite data indicate that staphylococcal elastin binding is mediated by a discrete domain defined by short peptide sequences in the amino-terminal extracellular region of EbpS.     

A novel emitter-sharpened double-gate race-track-shaped fieldemitter structure

In this paper, a new emitter-sharpened double-gate race-track-shaped field emitter structure is reported. The race-track-shaped edge emission with double-gate control is used to provide high uniformity FEAs over a large area without the need of expensive submicron technology. In order to minimize the gate current, which is detrimental to the field emitter performance, an emitter-sharpened structure is used. Experimental results show that the turn-on voltage of the emitter-sharpened double-gate structure is 45 V, which is 60% smaller than that of the single-gate structure (110 V). Furthermore, the gate current of the emitter-sharpened double-gate structure is 7 times and 15 times smaller than that of the nonemitter-sharpened double-gate structure and the single-gate structure, respectively     

Increased sialylation of polymeric immunoglobulin A1: mechanism of selective glomerular deposition in immunoglobulin A nephropathy?

Monoclonal antibodies which recognize antigenic determinants expressed by T-cells and Ig-bearing cells, respectively, allowed lymphocyte subpopulations involved in allograft rejection of muscle transplants to be identified in the teleost fish Dicentrarchus labrax (L.). The monoclonal antibody DLT15 first allowed recognizing T-cells involved in an in vivo antigen-driven cellular response in teleosts. Immunohistochemical studies showed a high density of lymphocytes in allografts and provided evidence of predominance of T-cells. The heterogeneity of the cell populations recognized by the antibodies was evidenced by the different size, cytology, and staining patterns of T-cells and Ig-bearing cells.     

Effects of the E177K mutation in D-amino acid transaminase. Studies on an essential coenzyme anchoring group that contributes to stereochemical fidelity

D-Amino acid transaminase is a bacterial enzyme that uses pyridoxal phosphate (PLP) as a cofactor to catalyze the conversion of D-amino acids into their corresponding alpha-keto acids. This enzyme has already been established as a target for novel antibacterial agents through suicide inactivation by a number of compounds. To improve their potency and specificity, the detailed enzyme mechanism, especially the role of its PLP cofactor, is under investigation. Many PLP-dependent transaminases have a negatively charged amino acid residue forming a salt-bridge with the pyridine nitrogen of its cofactor that promotes its protonation to stabilize the formation of a ketimine intermediate, which is subsequently hydrolyzed in the normal transaminase reaction pathway. However, alanine racemase has a positively charged arginine held rigidly in place by an extensive hydrogen bond network that may destabilize the ketimine intermediate, and make it too short-lived for a transaminase type of hydrolysis to occur. To test this hypothesis, we changed Glu-177 into a titratable, positively charged lysine (E177K). The crystal structure of this mutant shows that the positive charge of the newly introduced lysine side chain points away from the nitrogen of the cofactor, which may be due to electrostatic repulsions not being overcome by a hydrogen bond network such as found in alanine racemase. This mutation makes the active site more accessible, as exemplified by both biochemical and crystallographic data: CD measurements indicated a change in the microenvironment of the protein, some SH groups become more easily titratable, and at pH 9.0 the PMP peak appeared around 315 nm rather than at 330 nm. The ability of this mutant to convert L-alanine into D-alanine increased about 10-fold compared to wild-type and to about the same extent as found with other active site mutants. On the other hand, the specific activity of the E177K mutant decreased more than 1000-fold compared to wild-type. Furthermore, titration with L-alanine resulted in the appearance of an enzyme-substrate quinonoid intermediate absorbing around 500 nm, which is not observed with usual substrates or with the wild-type enzyme in the presence of L-alanine. The results overall indicate the importance of charged amino acid side chains relative to the coenzyme to maintain high catalytic efficiency.     

A robust state observer scheme

This note proposes a new approach to robust state observer construction. The scheme is derived by including an extra term and adopting the Lyapunov stability theorem, and requires the solution of an algebraic Riccati equation. The scheme is implemented in a gas-fired furnace system example. Satisfactory results have been obtained, though in general special attention need be paid to some numerical issues in implementing the scheme     

Business environment and internet commerce benefit—a small business perspective

Anecdotal evidence shows that the internet can enable a start up company to globalise and achieve multi-million dollar turnover in a couple of years. Beyond this handful of examples, small businesses find that this is not always true. It seems that certain pre-conditions need to be in place before this is possible. We studied the business environment of a small business including its suppliers, customers, partner firms and competitors focusing on internet commerce adoption and usage. Among a sample of small firms in the non-manufacturing sector, the impression of competitive advantage and information support relates positively to internet commerce benefit. Also, customer participation in internet commerce is critical to success. We therefore suggest that the nature of the business environment bears an effect on the benefit small businesses can gain from internet commerce.