High Ka Research Articles

Anti-hemostatic Effects of a Serpin from the Saliva of the Tick Ixodes ricinus

Serpins (serine protease inhibitors) are a large family of structurally related proteins found in a wide variety of organisms, including hematophagous arthropods. Protein analyses revealed that Iris, previously described as an immunomodulator secreted in the tick saliva, is related to the leukocyte elastase inhibitor and possesses serpin motifs, including the reactive center loop (RCL), which is involved in the interaction between serpins and serine proteases. Only serine proteases were inhibited by purified recombinant Iris (rIris), whereas mutants L339A and A332P were found devoid of any protease inhibitory activity. The highest Ka was observed with human leukocyte-elastase, suggesting that elastase-like proteases are the natural targets of Iris. In addition, mutation M340R completely changed both Iris substrate specificity and affinity. This likely identified Met-340 as amino acid P1 in the RCL. The effects of rIris and its mutants were also tested on primary hemostasis, blood clotting, and fibrinolysis. rIris increased platelet adhesion, the contact phase-activated pathway of coagulation, and fibrinolysis times in a dose-dependent manner, whereas rIris mutant L339A affected only platelet adhesion. Taken together, these results indicate that Iris disrupts coagulation and fibrinolysis via the anti-proteolytic RCL domain. One or more other domains could be responsible for primary hemostasis inhibition. To our knowledge, this is the first ectoparasite serpin that interferes with both hemostasis and the immune response.

Multiple Active Site Conformers in the Carbon Monoxide Complexes of Trematode Hemoglobins

Sequence alignment of hemoglobins of the trematodes Paramphistomum epiclitum and Gastrothylax crumenifer with myoglobin suggests the presence of an unusual active site structure in which two tyrosine residues occupy the E7 and B10 helical positions. In the crystal structure of P. epiclitum hemoglobin, such an E7-B10 tyrosine pair at the putative helical positions has been observed, although the E7 Tyr is displaced toward CD region of the polypeptide. Resonance Raman data on both P. epiclitum and G. crumenifer hemoglobins show that interactions of heme-bound ligands with neighboring amino acid residues are unusual. Multiple conformers in the CO complex, termed the C, O, and N conformers, are observed. The conformers are separated by a large difference (approximately 60 cm(-1)) in the frequencies of their Fe-CO stretching modes. In the C conformer the Fe-CO stretching frequency is very high, 539 and 535 cm(-1), for the P. epiclitum and G. crumenifer hemoglobins, respectively. The Fe-CO stretching of the N conformer appears at an unusually low frequency, 479 and 476 cm(-1), respectively, for the two globins. A population of an O conformer is seen in both hemoglobins, at 496 and 492 cm(-1), respectively. The C conformer is stabilized by a strong polar interaction of the CO with the distal B10 tyrosine residue. The O conformer is similar to the ones typically seen in mutant myoglobins in which there are no strong interactions between the CO and residues in the distal pocket. The N conformer possesses an unusual configuration in which a negatively charged group, assigned as the oxygen atom of the B10 Tyr side chain, interacts with the CO. In this conformer, the B10 Tyr assumes an alternative conformation consistent with one of the conformers seen the crystal structure. Implications of the multiple configurations on the ligand kinetics are discussed.

EFFECT OF P-GLYCOPROTEIN ON INTESTINAL ABSORPTION AND BRAIN PENETRATION OF ANTIALLERGIC AGENT BEPOTASTINE BESILATE

The antiallergic agent bepotastine besilate is a nonsedating, second-generation H1-antagonist with high oral absorption and negligible distribution into brain. To clarify the role of P-glycoprotein (P-gp) in the pharmacokinetics of bepotastine, intestinal absorption and brain penetration studies were performed. [(14)C]Bepotastine transport in P-gp-overexpressed LLC-PK1 cells indicated that bepotastine was a substrate of P-gp. The affinity of bepotastine to P-gp estimated by ATPase activity assay was low, with a K(m) value of 1.25 mM. After i.v. administration, the brain/plasma free concentration ratio in mdr1-knockout mice was 3 times higher than that in wild-type mice. The in situ intestinal absorption studies of [(14)C]bepotastine in rats showed a clear regional difference, showing highest permeability at the upper part of small intestine with a decreasing permeability in the descending part of small intestine. The apparent absorption rate constant (ka) of [(14)C]bepotastine in the small intestine was greatly increased by cyclosporin A and verapamil, especially in the distal portion, and the site-specific absorption of [(14)C]bepotastine disappeared. The concentration dependence of ka of [(14)C]bepotastine was observed with a higher ka at higher concentration (20 mM) compared with that at lower concentration (1 microM). In conclusion, bepotastine is a substrate for P-gp, and P-gp clearly limited the brain distribution of bepotastine, whereas the effect of P-gp on intestinal absorption of bepotastine was minimal, presumably because of high membrane permeability at the upper region of small intestine where P-gp is less expressed. Such intestinal absorption property of bepotastine is distinctly different from the low membrane-permeable P-gp substrate fexofenadine.

High resolution ro-vibrational analysis of the ν2 spectral region of chlorine nitrate

A thorough ro-vibrational analysis of the hybrid (A- and B-type) ν2 bands of 35ClONO2 and 37ClONO2 has been carried out using a high-resolution (0.0009 cm−1) Fourier transform spectrum recorded at 190 K. Unlike previously studied infrared bands, weak pP- and rR-branch series were observed. From these transitions, very high Ka upper-state energy levels were obtained which permitted a satisfactory modelling of the strong Q-branch at ≈1292.5 cm−1. Accurate upper-state constants have been derived for all bands including the following band centres: ν0 (ν2) = 1292.83690(40) cm−1 and ν0 (ν2) = 1293.20801(50) cm−1 for the 35Cl and 37Cl isotopomers respectively.

Absorption kinetics and pharmacodynamics of two oral dosage forms of flecainide in patients with an episode of paroxysmal atrial fibrillation

The objectives were to study the absorption kinetics and pharmacodynamics of two oral formulations of flecainide in patients with atrial fibrillation (AF) and to assess the relationship between pharmacokinetic parameters and the efficacy in restoring sinus rhythm. The data of 54 patients included in a randomised, open, parallel-group study were used. Patients received an oral solution containing 300 mg flecainide and 20 mg cisapride or three tablets each containing 100 mg flecainide. The pharmacokinetic profile of flecainide was fitted using a one-compartment model with lag-time and first-order absorption. The tablets gave a maximum concentration (C (max\ fit)) of 0.43+/-0.14 mg/l at 2.37+/-1.20 h. The oral solution resulted in a much faster peak concentration at 1.05+/-0.71 h (P<0.0001). The C (max\ fit) of the oral solution of 0.60+/-0.17 mg/l was higher (P=0.0002) than that of the tablets, and interindividual variabilities of C (max\ fit) were 28% and 33%, respectively. The absorption rate constant (ka) of the oral solution was twofold larger (P<0.0001). A higher ka (P=0.04) and a duration of AF less than 24 h (P=0.006) increased the probability of cardioversion. If atrial fibrillation lasted less than 24 h, only ka (P=0.016) was obtained as a significant variable in multivariate analysis. The linear models of QRS interval changes versus flecainide concentrations of both formulations had similar slopes with similar interindividual variabilities. The probability of cardioversion after an oral loading dose of flecainide in patients with AF is dependent on ka. Rapid loading of the effect compartment, i.e. the atria, appears to be critical to reach cardioversion. Higher flecainide serum concentrations and a more rapid absorption does not increase interindividual variability of pharmacokinetics and pharmacodynamics, which is important when safety is considered.

Newly exposed immunochemically cross-reactive epitopes in sperm-specific LDH after glucosylation and gossypol interaction.

In a previous study, mouse lactate dehydrogenase-C4 (LDH-C4) after chemical modifications with gossypol (Gossy-LDH-C4) and glucosylation with lactose (Glu-LDH-C4) was found to induce high immunological infertility in allogenic mice. In the present study, the characterization of antibodies and cross reactivity of the antisera produced against Gossy- and Glu-LDH-C4 with purified somatic isozymes are being reported. Allo-antisera generated in Balb/c mice (i.r. route) against one primary (50 microg) and two secondary doses (30 x 2 microg) in Al(OH)3 were tested for cross-reactivity by ELISA and antibody avidity using Scatchard plot and Sip's plot. Results suggested that IgG against native LDH-C4 failed to recognize somatic isozyme, while antisera against chemically modified LDH-C4 consistently reacted with purified LDH from kidney and placenta. Scatchard plots and antibody saturation curves of native and complexed LDH supported the presence of heterogenous antibodies with a mean association constant (Ka) of the order of 10(6)-10(7) M(-1), whereas diversity of heterogeneity, defined by diversity constant (a), ranged between 0.89 and 1.23. In general, anti-Glu-LDH-C4 antiserum and native LDH-C4. reacted with higher Ka (low affinity) with a diversity constant of 0.89 compared with interaction between native LDH-C4 and it's antibodies. It is concluded that LDH-C4 is not an immunochemically sperm-specific protein, in which crossreactive epitopes are hidden within its conformation. Due to the large intake of cotton seed (a source of gossypol) by cattle, its unrefined oil by humans in various parts of the world, and the prevelance of diabetic state all the world over, the present study warns of immunological consequences in situ following gossypol interaction and glucosylation of LDH and conformationally related proteins in circulation.

Real-Time Measurements of the Interactions between Fluorescent Speract and Its Sperm Receptor

Lytechinus pictus sea urchin sperm express receptors for speract, a sperm-activating peptide derived from the homologous egg jelly coat. We found that the fluorescence of fluorophore-labeled, active, speract analogs is quenched upon receptor binding. This property allowed us to perform real-time measurements of speract–receptor interactions using intact sperm and to determine, for the first time, their association (kon) and dissociation (koff) rate constants. The high kon (2.4 × 107 M−1 s−1) and low koff (4.4 × 10−6 s−1 (95%) and 3.7 × 10−4 s−1 (5%)) can account for the sperm response to picomolar concentrations of speract. We also examined the influence of extracellular ions on speract–receptor interactions using the fluorescence quenching method described in this study. The association rate of speract to the receptor is dramatically reduced in Na+-free seawater (NaFSW), divalent cation-free seawater (DCFSW), and high-K+ seawater (HKSW). In seawater speract induces an increase in intracellular pH (pHi), while it is unable to do so in either NaFSW or HKSW. To test if the lack of this pHi change causes the reduction in the speract association rate, pHi was increased with NH4Cl (10 mM) at the time labeled speract was added. Interestingly, this procedure completely (in HKSW) or partially (in NaFSW and DCFSW) restored the speract association rate to its receptor. These findings indicate that an increase in sperm pHi positively affects the receptor binding activity for this peptide and may partially explain the positive binding cooperativity displayed by the speract receptor.

The Rotational Spectrum of SO2 and the Determination of the Hyperfine Constants and Nuclear Magnetic Shielding Tensors of 33SO2 and SO17O

Precise frequencies for the 111–202 transition of 33SO2 and SO17O in natural isotopic abundance have been obtained near 12 GHz by microwave Fourier transform spectroscopy in order to yield improved hyperfine constants. Nuclear spin–rotation coupling constants have been determined experimentally for 33SO2 for the first time. The spin–rotation constants have been used to derive nuclear magnetic shielding parameters. These parameters are compared with values for the isoelectronic O3 molecule. The transition mentioned above was also measured for 32SO2, 34SO2, SO18O, and vibrationally excited (v2 = 1) 32SO2. For 33SO2, some transitions with large hyperfine splitting were also recorded in the millimeter-wave region. Continuing our investigations of the rotational spectra of SO2 in the submillimeter region, several transitions of SO17O have been recorded with the Cologne terahertz spectrometer between 540 and 840 GHz with J and Ka up to 63 and 16, respectively. Transitions with high Ka, up to 28, have been recorded with the JPL laser sideband spectrometer between 1.8 and 3.2 THz.

High-Resolution Fourier Transform Infrared Spectroscopy of Vinyl Alcohol: Rotational Analysis of the ν13 CH2 Wagging Fundamental at 817 cm−1

The first high-resolution infrared spectra of the unstable molecule vinyl alcohol are reported. The spectra have been obtained using a new precursor, 2-chloroethanol, which when pyrolyzed at 1050°C gives strong infrared spectra of vinyl alcohol free of interfering hydrocarbon absorption bands. In this work, we have analyzed the strong ν13 fundamental at 817 cm−1 and substantially improved the ground state rotational constants by a simultaneous fitting of previous microwave data and a large number of infrared combination differences. The 131 upper state was found to be perturbed by the 152 “dark” state at 775.7 cm−1, and a complete analysis of the perturbed rotational structure has been achieved using an interacting two-state model. Further small perturbations at high Ka and J have been identified as interactions with the ν10 and ν12 fundamentals at 948 and 960 cm−1, respectively.

Application of the Bjerrum Association Model to Electrolyte Solutions. IV. Apparent Molar Heat Capacities and Compressibilities in Water and Aprotic Solvents

The Bjerrum association model, which has already been applied successfully to volumes and enthalpies of dilution of electrolyte solutions, has now been extended to apparent molar heat capacities and compressibilities of these systems. The proposed method of calculation, which takes into account the relaxation effect observed in second derivatives of the excess Gibbs free energy, can be used to extrapolate to infinite dilution the experimental data for systems showing a wide range of association constants in acetonitrile, propylene carbonate, and water. The concentration dependence of the thermodynamic properties can be reproduced quantitatively by the addition of one or two virial coefficients. Literature data for CP,2,ψ and KS,2,ψ of electrolytes in aprotic solvents were refitted with this equation. For dissociated or slightly associated systems (KA < 10), the standarY2od infinite dilution quantities () are in excellent agreement with literature values. For systems with high KA, Y2o obtained by the model are systematically lower than those reported in the literature. This is not surprising, since the traditional method of extrapolation using the Debye–Huckel limiting law or the Pitzer equation does not take association into account. A computer software that performs the calculations for the application of the Bjerrum model to thermodynamic properties has been designed and is presented in the appendix.

Abstracts of literature

Abstracts of literature

Reversible phosphorylation control of skeletal muscle pyruvate kinase and phosphofructokinase during estivation in the spadefoot toad, Scaphiopus couchii.

Both pyruvate kinase (PK) and phosphofructokinase (PFK) occur in two different forms, separable by isoelectric focusing (IEF), in skeletal muscle of the spadefoot toad Scaphiopus couchii. During estivation (aerobic dormancy) the proportions of the two forms changed compared with controls; in both cases the amount of enzyme in Peak I (pI = 5.3-5.4) decreased whereas activity in Peak II (isoelectric point = 6.2-6.4) increased. In vitro incubation of crude muscle extracts with 32P-ATP under conditions that promoted the activity of cAMP-dependent protein kinase led to strong radiolabeling associated with Peak I, but not Peak II, and reverse phase HPLC confirmed that 32P was associated with the subunits of both PK and PFK found in Peak I. Specific radiolabeling of Peak I PK and PFK by protein kinase A was further confirmed using immunoprecipitation. In total, this information allowed identification of the Peaks I and II enzymes as the phosphorylated and dephosphorylated forms, respectively, and the effect of estivation was to increase the proportion of dephosphorylated PK and PFK in muscle. Analysis of the kinetic properties of partially purified PK and PFK revealed significant kinetic differences between the two forms of each enzyme. For PK, the Peak II (low phosphate) enzyme showed a 1.6-fold higher Km for phosphoenolpyruvate and a 2.4-fold higher Ka for fructose-1,6-bisphosphate than did the Peak I (high phosphate) form. These kinetic properties suggest that Peak II PK is the less active form, and coupled with the shift to predominantly the Peak II form during estivation (87% Peak II vs. 13% Peak I), are consistent with a suppression of PK activity in estivating muscle, as part of the overall metabolic rate depression of the estivating state. A similar shift to predominantly the Peak II, low phosphate, form of PFK (75% Peak II, 25% Peak I) in muscle of estivating animals is also consistent with metabolic suppression since phosphorylation of vertebrate skeletal muscle PFK is typically stimulated during exercise to enhance enzyme binding to myofibrils in active muscle. Peak II PFK also showed reduced sensitivity to inhibition by Mg:ATP (I50 50% higher) compared with the Peak I form suggesting that the enzyme in estivating muscle is less tightly regulated by cellular adenylate status than in awake toads. The data indicate that reversible phosphorylation control over the activity states of enzymes of intermediary metabolism is an important mechanism for regulating transitions between dormant and active states in estivating species.

A Polymorphic Cluster in the 5′ Region of the Human Coagulation Factor VII Gene: Detection, Frequency, and Linkage Disequilibrium

Human coagulation factor VII (FVII) gene contains in the proximal part of the promoter three polymorphisms: two nucleotide substitutions (at position −122, −401) and a decanucleotide insertion (at position −323) [ 1 Pollak ES, Hung HL, Godin W, Overton GC, High KA. Functional characterization of the human factor VII 5′-flanking region. J Biol Chem 1996;271:1738–47. Google Scholar , 2 Marchetti G, Patracchini P, Papacchini M, Ferrati M, Bernardi F. A polymorphism in the 5′ region of coagulation factor VII gene (F7) caused by an inserted decanucleotide. Hum Genet 1993;90:575–6. Google Scholar ].

Follitropin action on the transferrin gene in Sertoli cells is mediated by cAMP-responsive-element-binding-protein and antagonized by chicken ovalbumin-upstream-promoter-transcription factor.

The transcription of the transferrin (Tf) gene is induced by follitropin via cAMP in rat Sertoli cells. We previously demonstrated that the cAMP-responsive-element-binding protein (CREB) interacts on the proximal region II (PRII) of the human Tf promoter (Suire et al., 1995). The PRII region is identified as essential for cAMP inducibility of the Tf promoter and contains a CCAAT box. This unexpected result led us to study the relation that exists between CREB and the PRII site. In the liver, CCAAT/enhancer-binding (C/EBP) proteins act at the PRII site. Although these factors are absent in Sertoli cells, their overexpression in Sertoli cells disturbs basal and induced transcription. C/EBP alpha and delta were able to stimulate the basal transcription driven by the -100 to +39 region, placed upstream of the chloramphenicol acetyltransferase (CAT) gene. However, only C/EBP alpha allowed the cAMP-inducible expression. The Ka of CREB bZIP (254-327), a deleted form of CREB, for the CRE site (3.92 x 10(8)M-1) and for the PRII site (1.38 x 10(8)M-1) were determined using the surface plasmon resonance (SPR) method. The Ka values were similar, although the derived kinetics were different: higher ka and kd of CREB for the PRII site were found compared with the CRE site. Since we observed important dissociation kinetics, we hypothesized that the binding of CREB to the PRII site is stabilized by CREB-binding protein (CBP) or by chicken-ovalbumin-upstream-promoter transcription factor (COUP-TF) binding to PRI site near to PRII. However, we observed that the overexpression of CBP in Sertoli cells did not potentiate the basal and cAMP-stimulated activity of CREB of the -100 to +39Tf-CAT construct. In basal and cAMP-stimulated conditions, COUP-TF appeared to repress the transcription driven by the -100 to +39 region in a specific manner. These results demonstrate a direct action of CREB on hTf promoter, which is antagonized by COUP-TF and may explain the transcriptional regulation of Tf by follitropin, via cAMP.

Determination of the molecular constants of interacting bright and dark states: Analysis of the high-resolution infrared spectrum of the S–O stretching fundamental of thionylimide, HNSO

The S–O stretching fundamental, ν2, of thionylimide has been recorded at high resolution and rotationally analyzed for the first time. This strong A-type band with origin at 1257.5808 cm−1 is extensively perturbed by the 5161 state at 1206.58 cm−1 through a- and b-axis Coriolis interactions. Even though no ν5+ν6 band transitions could be found, a complete analysis of the perturbed rotational structure has been achieved. Accurate molecular constants for the ‘‘bright’’ 21 state and the ‘‘dark’’ 5161 state have been obtained, using a Hamiltonian that includes both types of Coriolis interactions. Further small perturbations at high Ka and J have been identified as higher-order interactions with the ν3 band at much lower energy.

Determination of the spectroscopic constants of a dark vibrational state: Fermi and Coriolis perturbations in the ν2 band of formyl chloride

The ν2 infrared fundamental of the transient molecule formyl chloride, HCOCl, has been recorded at high resolution. Detailed assignments of the rotational structure have been made for both HCO 35Cl and HCO 37Cl. The ν2 band, whose origin is at 1784.1377 cm−1 in HCO 35Cl, is predominantly A type with a very weak B-type component. Numerous excited state perturbations occur throughout the band, caused mainly by ‖ΔKa‖=2 Fermi resonance and ‖ΔKa‖=1 Coriolis interactions with the 3151 vibrational state. Even though no ‘‘extra’’ lines resulting from the perturbations could be assigned, a complete analysis of the perturbed rotational structure has been possible. Accurate molecular constants for both the ‘‘bright’’ perturbed 21 state and the ‘‘dark’’ 3151 perturbing state have been obtained, using a Hamiltonian which includes both the Fermi and Coriolis interactions; only two interaction parameters are needed, one for each mechanism. Further perturbations at high Ka are assigned to Coriolis interactions with the 5261 level.

Nonlinear protein binding and enzyme heterogeneity: Effects on hepatic drug removal

The kinetics of substrate removal by the liver and the resulting nonlinear changes in unbound fraction along the flow path at varying input drug concentrations were examined by a model simulation study. Specifically, we varied the binding association constant, KA, and the Michaelis-Menten constants (Km and Vmax) to examine the steady state drug removal (expressed as hepatic extraction ratio E) and changes in drug binding for (i) unienzyme systems and (ii) simple, parallel metabolic pathways; zonal metabolic heterogeneity was also added as a variable. At low KA, E declined with increasing input drug concentration, due primarily to saturation of enzymes; only small differences in binding were present across the liver. At high KA, a parabolic profile for E with concentration was observed; changes in unbound fraction between the inlet and the outlet of the liver followed in parallel fashion. Protein binding was the rate-determining step at low input drug concentrations, whereas enzyme saturation was the rate-controlling factor at high input drug concentration. Heterogeneous enzymic distribution modulated changes in unbound fraction within the liver and at the outlet. Despite marked changes in unbound fraction occurring within the liver for different enzymic distributions, the overall transhepatic differences were relatively small. We then investigated the logarithmic average unbound concentration and the length averaged concentration as estimates of substrate concentration in liver in the presence of nonlinear drug binding. Fitting of simulated data, with and without assigned random error (10%), to the Michaelis-Menten equation was performed; fitting was repeated for simulated data obtained with presence of a specific inhibitor of the high-affinity, anteriorly distributed pathway. Results were similar for both concentration terms: accurate estimates were obtained for anterior, high affinity pathways; an overestimation of parameters was observed for the lower affinity posteriorly distributed pathways. Improved estimations were found for posteriorly distributed pathways upon inhibition with specific inhibitors; with added random error, however, the improvement was much decreased. We applied the method for fitting of several sets of metabolic data obtained from rat liver perfusion studies performed with salicylamide (SAM) (i) without and (ii) with the presence of 2,6-dichloro-4-nitrophenol (DCNP), a SAM sulfation inhibitor. The fitted results showed that SAM sulfation was a high-affinity high-capacity pathway; SAM glucuronidation was of lower affinity but comparable capacity as the sulfation pathway, whereas SAM hydroxylation was of lower affinity and lower capacity.

Characterization of gonadotropin-releasing hormone receptors in goldfish ovary: variation during follicular development

Gonadotropin-releasing hormone (GnRH) receptors were characterized in the goldfish ovary using an analogue of salmon GnRH ([D-Arg6,Trp7,Leu8,Pro9-NEt]GnRH; sGn-RH-A) as a labeled ligand. Binding of sGnRH-A to goldfish follicular membrane preparation was found to be saturable, reversible, and dependent on time, temperature, tissue concentration, and pH. Addition of unlabeled sGnRH-A displaced the bound 125I-labeled sGnRH-A in a dose-related manner. Hill plot as well as Scatchard analysis indicated the presence of two classes of binding sites, a high-affinity/low-capacity site and a low-affinity/high-capacity site, in the fully mature and less mature goldfish ovary. However, immature goldfish ovary contained only a single class of low-affinity binding sites. The equilibrium association constants (Ka) of the low-affinity sites were found to be similar in all follicular groups. However, there was a tendency for a higher Ka value of the high-affinity sites in the less mature follicles (0.5-0.95 mm) compared with the fully mature follicles (1.11-1.48 mm), although the differences were not statistically significant. Bound 125I-sGnRH-A was also found to be displaceable by sGnRH ([Trp7,Leu8]GnRH) and chicken GnRH-II (cGnRH-II; [His5,Trp7,Tyr8]GnRH), which occur naturally in the goldfish brain. sGnRH-A and cGnRH-II were found to bind with greater affinity than sGnRH to the goldfish ovarian GnRH binding sites.

Experimental simulation of premixed turbulent combustion using aqueous autocatalytic reactions

Aqueous autocatalytic reactions which produce propagating chemical fronts, analogous to premixed flame-fronts, are used to simulate premixed turbulent combustion in “laminar-flamelet” and “distributed-combustion” regimes. The characteristics of these chemical fronts more nearly match those assumed by current theories of turbulent combustion than do gaseous flames. In this work, proper chemical solutions for this simulation are identified and applied using a Taylor-Couette flow. The effect of the velocity disturbance intensity ( u′ ) normalized by the laminar burning velocity ( S L ) on the front propagation velocity ( S T ) are obtained at values of U≡u′/S L at least 200 times higher than those attainable in gas combustion experiments. At modest U, U T ≡S T /S L data collapse onto a single curve, regardless of S L , indicating stretch-free conditions; these data agree with an approximate theoretical model. Effects of the velocity spectrum are described. At higher U, U T deviates away from this curve, indicating stretch effects which are characterized by a turbulent Karlovitz number (Ka). At high Ka, behavior suggesting distributed-combustion is observed; in this regime U T data are fairly consistent with Damköhler's hypothesis. No quenching is observed, even at Ka≈900, suggesting that the commonly-held view that the quenching of flames in intense turbulence results from mass extinction of flamelets may require reconsideration. It is proposed that instead, heat-loss could be an important factor in extinction.

New approaches to the use of acoustic radiation forces in the calibration of high-frequency transducers.

A drop (of radius a) of one liquid acoustically levitated in another ‘‘host’’ liquid can be displaced from its equilibrium position by the imposition of the acoustic field of a transducer. The displacement is related to the radiation force which, in turn, can allow one to compute the acoustic pressure and thus absolutely calibrate the transducer. This approach is a variation of the sphere radiometer technique. For high-frequency calibration, however, the form function of the acoustic radiation force varies rapidly with frequency for ka≳1, where k is the wave number in the host liquid; therefore, the properties of drop and host must be known very accurately if the inversion process is to yield good estimates. If, however, the drop material is nearly impedance matched with the host, although the densities and sound velocities individually differ, the ‘‘resonances’’ in the form function are pushed to a much higher ka, and unambiguous inversion of the data over a wider frequency range to give accurate pressures is possible. Theoretical and experimental results will be presented, as will other possible acoustic radiation force configurations that overcome some of the limitations of levitation and sphere radiometry techniques. [Work supported, in part, by a U.S. National Institutes of Health Grant No. 5-RO1-CA-39374.]