bluuebunny/crossref_metadata_2025 huggingface dataset:
A spectroscopic study of the interaction of isoflavones with human serum albumin
Authors: Mahesha H. G. , Singh Sridevi Annapurna , Srinivasan N. , Rao A. G. Appu
Published: January 2006

Genistein and daidzein, the major isoflavones present in soybeans, possess a wide spectrum of physiological and pharmacological functions. The binding of genistein to human serum albumin (HSA) has been investigated by equilibrium dialysis, fluorescence measurements, CD and molecular visualization. One mole of genistein is bound per mole of HSA with a binding constant of 1.5 ± 0.2 × 105 m−1. Binding of genistein to HSA precludes the attachment of daidzein. The ability of HSA to bind genistein is found to be lost when the tryptophan residue of albumin is modified with N‐bromosuccinimide. At 27 °C (pH 7.4), van't Hoff's enthalpy, entropy and free energy changes that accompany the binding are found to be −13.16 kcal·mol−1, −21 cal·mol−1K−1 and −6.86 kcal·mol−1, respectively. Temperature and ionic strength dependence and competitive binding measurements of genistein with HSA in the presence of fatty acids and 8‐anilino‐1‐naphthalene sulfonic acid have suggested the involvement of both hydrophobic and ionic interactions in the genistein–HSA binding. Binding measurements of genistein with BSA and HSA, and those in the presence of warfarin and 2,3,5‐tri‐iodobenzoic acid and Förster energy transfer measurements have been used for deducing the binding pocket on HSA. Fluorescence anisotropy measurements of daidzein bound and then displaced with warfarin, 2,3,5‐tri‐iodobenzoic acid or diazepam confirm the binding of daidzein and genistein to subdomain IIA of HSA. The ability of HSA to form ternery complexes with other neutral molecules such as warfarin, which also binds within the subdomain IIA pocket, increases our understanding of the binding dynamics of exogenous drugs to HSA.
Endo/exo mechanism and processivity of family 18 chitinases produced by Serratia marcescens
Authors: Horn Svein Jarle , Sørbotten Audun , Synstad Bjørnar , Sikorski Pawel , Sørlie Morten , Vårum Kjell M. , Eijsink Vincent G. H.
Published: January 2006

We present a comparative study of ChiA, ChiB, and ChiC, the three family 18 chitinases produced by Serratia marcescens. All three enzymes eventually converted chitin to N‐acetylglucosamine dimers (GlcNAc2) and a minor fraction of monomers. ChiC differed from ChiA and ChiB in that it initially produced longer oligosaccharides from chitin and had lower activity towards an oligomeric substrate, GlcNAc6. ChiA and ChiB could convert GlcNAc6 directly to three dimers, whereas ChiC produced equal amounts of tetramers and dimers, suggesting that the former two enzymes can act processively. Further insight was obtained by studying degradation of the soluble, partly deacetylated chitin‐derivative chitosan. Because there exist nonproductive binding modes for this substrate, it was possible to discriminate between independent binding events and processive binding events. In reactions with ChiA and ChiB the polymer disappeared very slowly, while the initially produced oligomers almost exclusively had even‐numbered chain lengths in the 2–12 range. This demonstrates a processive mode of action in which the substrate chain moves by two sugar units at a time, regardless of whether complexes formed along the way are productive. In contrast, reactions with ChiC showed rapid disappearance of the polymer and production of a continuum of odd‐ and even‐numbered oligomers. These results are discussed in the light of recent literature data on directionality and synergistic effects of ChiA, ChiB and ChiC, leading to the conclusion that ChiA and ChiB are processive chitinases that degrade chitin chains in opposite directions, while ChiC is a nonprocessive endochitinase.
Gene duplication and separation of functions in αB‐crystallin from zebrafish (Danio rerio)
Authors: Smith Amber A. , Wyatt Keith , Vacha Jennifer , Vihtelic Thomas S. , Samuel Zigler J. , Wistow Graeme J. , Posner Mason
Published: January 2006

We previously reported that zebrafish αB‐crystallin is not constitutively expressed in nervous or muscular tissue and has reduced chaperone‐like activity compared with its human ortholog. Here we characterize the tissue expression pattern and chaperone‐like activity of a second zebrafish αB‐crystallin. Expressed sequence tag analysis of adult zebrafish lens revealed the presence of a novel α‐crystallin transcript designatedcryab2and the resulting protein αB2‐crystallin. The deduced protein sequence was 58.2% and 50.3% identical with human αB‐crystallin and zebrafish αB1‐crystallin, respectively. RT‐PCR showed that αB2‐crystallin is expressed predominantly in lens but, reminiscent of mammalian αB‐crystallin, also has lower constitutive expression in heart, brain, skeletal muscle and liver. The chaperone‐like activity of purified recombinant αB2 protein was assayed by measuring its ability to prevent the chemically induced aggregation of α‐lactalbumin and lysozyme. At 25 °C and 30 °C, zebrafish αB2 showed greater chaperone‐like activity than human αB‐crystallin, and at 35 °C and 40 °C, the human protein provided greater protection against aggregation. 2D gel electrophoresis indicated that αB2‐crystallin makes up ≈ 0.16% of total zebrafish lens protein. Zebrafish is the first species known to express two different αB‐crystallins. Differences in primary structure, expression and chaperone‐like activity suggest that the two zebrafish αB‐crystallins perform divergent physiological roles. After gene duplication, zebrafish αB2 maintained the widespread protective role also found in mammalian αB‐crystallin, while zebrafish αB1 adopted a more restricted, nonchaperone role in the lens. Gene duplication may have allowed these functions to separate, providing a unique model for studying structure–function relationships and the regulation of tissue‐specific expression patterns.
Tryptophan 243 affects interprotein contacts, cofactor binding and stability in D‐amino acid oxidase from Rhodotorula gracilis
Authors: Caldinelli Laura , Molla Gianluca , Pilone Mirella S. , Pollegioni Loredano
Published: January 2006

The flavoenzyme d‐amino acid oxidase from Rhodotorula gracilis is a homodimeric protein whose dimeric state has been proposed to occur as a result of (a) the electrostatic interactions between positively charged residues of the βF5–βF6 loop of one monomer and negatively charged residues belonging to the α‐helices I3′ and I3′′ of the other monomer, and (b) the interaction of residues (e.g. Trp243) belonging to the two monomers at the mixed interface region. The role of Trp243 was investigated by substituting it with either tyrosine or isoleucine: both substitutions were nondisruptive, as confirmed by the absence of significant changes in catalytic activity, but altered the tertiary structure (yielding a looser conformation) and decreased the stability towards temperature and denaturants. The change in conformation interferes both with the interaction of the coenzyme to the apoprotein moiety (although the kinetics of the apoprotein–FAD complex reconstitution process are similar between wild‐type and mutant d‐amino acid oxidases) and with the interaction between monomers. Our results indicate that, in the folded holoenzyme, Trp243 is situated at a position optimal for increasing the interactions between monomers by maximizing van der Waals interactions and by efficiently excluding solvent.
Secretion of proteases in serglycin transfected Madin–Darby canine kidney cells
Authors: Zernichow Lillian , Dalen Knut T. , Prydz Kristian , Winberg Jan‐Olof , Kolset Svein O.
Published: January 2006

Madin–Darby canine kidney (MDCK) cells, which do not normally express the proteoglycan (PG) serglycin, were stably transfected with cDNA for human serglycin fused to a polyhistidine tag (His‐tag). Clones with different levels of serglycin mRNA expression were generated. One clone with lower and one with higher serglycin mRNA expression were selected for this study. 35S‐labelled serglycin in cell fractions and conditioned media was isolated using HisTrap affinity chromatography. Serglycin could also be detected in conditioned media using western blotting. To investigate the possible importance of serglycin linked to protease secretion, enzyme activities using chromogenic substrates and zymography were measured in cell fractions and serum‐free conditioned media of the different clones. Cells were cultured in both the absence and presence of phorbol 12‐myristate 13‐acetate (PMA). In general, enzyme secretion was strongly enhanced by treatment with PMA. Our analyses revealed that the clone with the highest serglycin mRNA expression, level of HisTrap isolated 35S‐labelled serglycin, and amount of serglycin core protein as detected by western blotting, also showed the highest secretion of proteases. Transfection of serglycin into MDCK cells clearly leads to changes in secretion levels of secreted endogenous proteases, and could provide further insight into the biosynthesis and secretion of serglycin and potential partner molecules.
Prohibitin attenuates insulin‐stimulated glucose and fatty acid oxidation in adipose tissue by inhibition of pyruvate carboxylase
Authors: Vessal Mahmood , Mishra Suresh , Moulik Saby , Murphy Liam J.
Published: January 2006

Prohibitin (PHB‐1) is a highly conserved protein involved in mitochondrial biogenesis and function. It is secreted in lipid droplets from adipocytes and is present in the circulation. In adipose tissue it functions as a membrane receptor and can target binding partners to the mitochondria. Here we report that PHB‐1 has a hitherto undescribed role as an inhibitor of pyruvate carboxylase (PC). As a consequence, it can modulate insulin‐stimulated glucose and fatty acid oxidation. It had no effect on insulin‐stimulated 2‐deoxglucose uptake by isolated adipocytes but inhibited insulin‐stimulated oxidation of [14C]glucose with a half‐maximal concentration of ≈ 4 nm. It also inhibited oleic acid oxidation in glucose‐depleted adipocytes via depletion of oxaloacetate. In vitro experiments using broken‐cell assays confirmed that PHB‐1 inhibited PC. MALDI‐TOF analysis of proteins identified by cross‐linking of PHB‐1 to adipocyte membranes indicated that PHB‐1 is closely associated with PC and EH domain 2 (EHD2). On the basis of these data, we propose that PHB‐1 is recycled between the extracellular space and the mitochondria by a mechanism involving lipid rafts and EHD2 and can modulate mitochondrial fuel metabolism by inhibition of PC.
Major phosphorylation of SF1 on adjacent Ser‐Pro motifs enhances interaction with U2AF65
Authors: Manceau Valérie , Swenson Matthew , Le Caer Jean‐Pierre , Sobel André , Kielkopf Clara L. , Maucuer Alexandre
Published: January 2006

Protein phosphorylation ensures the accurate and controlled expression of the genome, for instance by regulating the activities of pre‐mRNA splicing factors. Here we report that splicing factor 1 (SF1), which is involved in an early step of intronic sequence recognition, is highly phosphorylated in mammalian cells on two serines within an SPSP motif at the junction between its U2AF65 and RNA binding domains. We show that SF1 interacts in vitro with the protein kinase KIS, which possesses a ‘U2AF homology motif’ (UHM) domain. The UHM domain of KIS is required for KIS and SF1 to interact, and for KIS to efficiently phosphorylate SF1 on the SPSP motif. Importantly, SPSP phosphorylation by KIS increases binding of SF1 to U2AF65, and enhances formation of the ternary SF1–U2AF65–RNA complex. These results further suggest that this phosphorylation event has an important role for the function of SF1, and possibly for the structural rearrangements associated with spliceosome assembly and function.
Solution NMR structure of an immunodominant epitope of myelin basic protein
Authors: Farès Christophe , Libich David S. , Harauz George
Published: January 2006

Using solution NMR spectroscopy, three‐dimensional structures have been obtained for an 18‐residue synthetic polypeptide fragment of 18.5 kDa myelin basic protein (MBP, human residues Q81–T98) under three conditions emulating the protein's natural environment in the myelin membrane to varying degrees: (a) an aqueous solution (100 mm KCl pH 6.5), (b) a mixture of trifluoroethanol (TFE‐d2) and water (30 : 70% v/v), and (c) a dispersion of 100 mm dodecylphosphocholine (DPC‐d38, 1 : 100 protein/lipid molar ratio) micelles. This polypeptide sequence is highly conserved in MBP from mammals, amphibians, and birds, and comprises a major immunodominant epitope (human residues N83–T92) in the autoimmune disease multiple sclerosis. In the polypeptide fragment, this epitope forms a stable, amphipathic, α helix under organic and membrane‐mimetic conditions, but has only a partially helical conformation in aqueous solution. These results are consistent with recent molecular dynamics simulations that showed this segment to have a propensity to form a transient α helix in aqueous solution, and with electron paramagnetic resonance (EPR) experiments that suggested a α‐helical structure when bound to a membrane [I. R. Bates, J. B. Feix, J. M. Boggs & G. Harauz (2004) J Biol Chem, 279, 5757–5764]. The high sensitivity of the epitope structure to its environment is characteristic of intrinsically unstructured proteins, like MBP, and reflects its association with diverse ligands such as lipids and other proteins.
Effects of mechanosensitive ion channels on ventricular electrophysiology: experimental and theoretical models
Authors: Kohl Peter , Bollensdorff Christian , Garny Alan
Published: January 2006

The heart is an electrically driven mechanical pump, somewhat like an electric motor. Interestingly, like an electric motor in ‘dynamo mode’, the heart can also convert mechanical stimuli into electrical signals. This feedback from cardiac mechanics to electrical activity involves mechanosensitive ion channels, whose properties and pathophysiological relevance are reviewed in the context of experimental and theoretical modelling of ventricular beat‐by‐beat electromechanical function.
Dopamine‐dependent non‐linear correlation between subthalamic rhythms in Parkinson's disease
Authors: Marceglia S. , Foffani G. , Bianchi A. M. , Baselli G. , Tamma F. , Egidi M. , Priori A.
Published: January 2006

The basic information architecture in the basal ganglia circuit is under debate. Whereas anatomical studies quantify extensive convergence/divergence patterns in the circuit, suggesting an information sharing scheme, neurophysiological studies report an absence of linear correlation between single neurones in normal animals, suggesting a segregated parallel processing scheme. In 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐treated monkeys and in parkinsonian patients single neurones become linearly correlated, thus leading to a loss of segregation between neurones. Here we propose a possible integrative solution to this debate, by extending the concept of functional segregation from the cellular level to the network level. To this end, we recorded local field potentials (LFPs) from electrodes implanted for deep brain stimulation (DBS) in the subthalamic nucleus (STN) of parkinsonian patients. By applying bispectral analysis, we found that in the absence of dopamine stimulation STN LFP rhythms became non‐linearly correlated, thus leading to a loss of segregation between rhythms. Non‐linear correlation was particularly consistent between the low‐beta rhythm (13–20 Hz) and the high‐beta rhythm (20–35 Hz). Levodopa administration significantly decreased these non‐linear correlations, therefore increasing segregation between rhythms. These results suggest that the extensive convergence/divergence in the basal ganglia circuit is physiologically necessary to sustain LFP rhythms distributed in large ensembles of neurones, but is not sufficient to induce correlated firing between neurone pairs. Conversely, loss of dopamine generates pathological linear correlation between neurone pairs, alters the patterns within LFP rhythms, and induces non‐linear correlation between LFP rhythms operating at different frequencies. The pathophysiology of information processing in the human basal ganglia therefore involves not only activities of individual rhythms, but also interactions between rhythms.
Intracellular activity of cortical and thalamic neurones during high‐voltage rhythmic spike discharge in Long‐Evans rats in vivo
Authors: Polack Pierre‐Olivier , Charpier Stéphane
Published: January 2006

Spontaneous high‐voltage rhythmic spike (HVRS) discharges at 6–12 Hz have been widely described in the electrocorticogram (EcoG) of Long‐Evans rats. These ECoG oscillations have been proposed to reflect a state of attentive immobility allowing the optimization of sensory integration within the corticothalamic pathway. This hypothesis has been challenged by recent studies emphasizing similarities between HVRS discharges and spike‐and‐wave discharges (SWDs) in well‐established rat genetic models of absence epilepsy. Here, we made in vivo intracellular recordings to determine, for the first time, the cellular mechanisms responsible for the synchronized oscillations in the corticothalamic loop during HVRS discharges in the Long‐Evans rats. We show that HVRS discharges are associated in corticothalamic neurones with rhythmic suprathreshold synaptic depolarizations superimposed on a tonic hyperpolarization, likely due to a process of synaptic disfacilitation. Simultaneously, thalamocortical neurones exhibit a large‐amplitude ‘croissant’‐shaped membrane hyperpolarization with a voltage sensitivity suggesting a potassium‐dependent mechanism. This thalamic hyperpolarizing envelope was associated with a membrane oscillation resulting from interactions between excitatory synaptic inputs, a chloride‐dependent inhibitory conductance and voltage‐gated intrinsic currents. These cortical and thalamic cellular mechanisms underlying HVRS activity in Long‐Evans rats are remarkably similar to those previously described in the thalamocortical networks during SWDs. Thus, the present study provides an additional support to the hypothesis that HVRS activity in Long‐Evans rats is an absence‐like seizure activity.
Cardiac system bioenergetics: metabolic basis of the Frank‐Starling law
Authors: Saks Valdur , Dzeja Petras , Schlattner Uwe , Vendelin Marko , Terzic Andre , Wallimann Theo
Published: January 2006

The fundamental principle of cardiac behaviour is described by the Frank‐Starling law relating force of contraction during systole with end‐diastolic volume. While both work and respiration rates increase linearly with imposed load, the basis of mechano‐energetic coupling in heart muscle has remained a long‐standing enigma. Here, we highlight advances made in understanding of complex cellular and molecular mechanisms that orchestrate coupling of mitochondrial oxidative phosphorylation with ATP utilization for muscle contraction. Cardiac system bioenergetics critically depends on an interrelated metabolic infrastructure regulating mitochondrial respiration and energy fluxes throughout cellular compartments. The data reviewed indicate the significance of two interrelated systems regulating mitochondrial respiration and energy fluxes in cells: (1) the creatine kinase, adenylate kinase and glycolytic pathways that communicate flux changes generated by cellular ATPases within structurally organized enzymatic modules and networks; and (2) a secondary system based on mitochondrial participation in cellular calcium cycle, which adjusts substrate oxidation and energy‐transducing processes to meet increasing cellular energy demands. By conveying energetic signals to metabolic sensors, coupled phosphotransfer reactions provide a high‐fidelity regulation of the excitation–contraction cycle. Such integration of energetics with calcium signalling systems provides the basis for ‘metabolic pacing’, synchronizing the cellular electrical and mechanical activities with energy supply processes.
Temporal facilitation of spastic stretch reflexes following human spinal cord injury
Authors: Hornby T. George , Kahn Jennifer H. , Wu Ming , Schmit Brian D.
Published: January 2006

Recent evidence suggests that alterations in ionic conductances in spinal motoneurones, specifically the manifestation of persistent inward currents, may be partly responsible for the appearance of hyperexcitable reflexes following spinal cord injury (SCI). We hypothesized that such alterations would manifest as temporal facilitation of stretch reflexes in human SCI. Controlled, triangular wave, ankle joint rotations applied at variable velocities (30–120 deg s−1) and intervals between stretches (0.25–5.0 s) were performed on 14 SCI subjects with velocity‐dependent, hyperexcitable plantarflexors. Repeated stretch elicited significant increases in plantarflexion torques and electromyographic (EMG) activity from the soleus (SOL) and medial gastrocnemius (MG). At higher velocities (≥ 90 deg s−1), reflex torques declined initially, but subsequently increased to levels exceeding the initial response, while mean EMG responses increased throughout the joint perturbations. At lower velocities (≤ 60 deg s−1), both joint torques and EMGs increased gradually. Throughout a range of angular velocities, reflex responses increased significantly only at intervals ≤ 1 s between stretches and following at least four rotations. Ramp‐and‐hold perturbations used to elicit tonic stretch reflexes revealed significantly prolonged EMG responses following one or two triangular stretches, as compared to single ramp‐and‐hold excursions. Post hoc analyses revealed reduced reflex facilitation in subjects using baclofen to control spastic behaviours. Evidence of stretch reflex facilitation post‐SCI may reflect changes in underlying neuronal properties and provide insight into the mechanisms underlying spastic reflexes.
Src family kinases play multiple roles in differentiation of trophoblasts from human term placenta
Authors: Daoud Georges , Rassart Éric , Masse André , Lafond Julie
Published: January 2006

Tyrosine phosphorylation plays a major role in controlling many biological processes in different cell types. Src family kinases (SFKs) are one of the most studied groups of tyrosine kinases and can mediate a variety of signalling pathways. However, little is known about the expression of SFKs in human term placenta and their implication in trophoblast differentiation. Therefore, we examined the expression profile of SFK members over time in culture and their implication in differentiation. In vitro, freshly isolated cytotrophoblast cells, cultured in 10% fetal bovine serum (FBS), spontaneously aggregate and fuse to form multinucleated cells that resemble phenotypically mature syncytiotrophoblasts, that concomitantly produce human chorionic gonadotropin (hCG) and human placental lactogen (hPL). In this study, we showed that trophoblasts expressed all SFK members and some of them are expressed as different splice variants. Moreover, using real‐time PCR, this study showed two different expression profiles of SFKs in human trophoblasts during culture. In addition, the protein level and phosphorylation status of Src were evaluated using specific antibodies. Src was rapidly phosphorylated at Tyr‐416 and dephosphorylated at Tyr‐527 after FBS addition. Surprisingly, inhibition of SFKs by 4‐amino‐5‐(4‐chlorophenyl)‐7‐(t‐butyl) pyrazolo[3,4‐d] pyrimidine (PP2) or herbimycin A had different effects on trophoblast differentiation. While herbimycin A inhibited morphological and hormonal differentiation, PP2 stimulated hormonal differentiation and inhibited cell adhesion and spreading with no effect on cell fusion. In summary, this study showed that SFKs play different roles in trophoblast differentiation, probably depending on SFK members activated. Thus, this study increases our knowledge and understanding of pathology related to impaired trophoblast differentiation such as pre‐eclampsia and trophoblast neoplasm.
Classification of longissimus lumborum muscle spindle afferents in the anaesthetized cat
Authors: Durbaba R. , Taylor A. , Ellaway P. H. , Rawlinson S.
Published: January 2006

Recordings have been made from 127 single muscle spindle afferents from the longissimus lumborum muscles of anaesthetized cats. They have been characterized by their responses to passive muscle stretch and the effects of succinylcholine (SCh) and by their sensitivity to vibration. The use of SCh permitted the assessment for each afferent of the influence of bag1 (b1) and bag2 (b2) intrafusal muscle fibres. From this, on the assumption that all afferents were affected by chain (c) fibres, they were classified in four groups: b1b2c (41.9%), b2c (51.4%), b1c (1.3%) and c (5.4%). All the afferents with b1 influence were able to respond one to one to vibration at frequencies above 100 Hz and were considered to belong to primary endings. On the basis of the vibration test, 64% of the b2c type afferents appeared to be primaries and 36% secondaries. Of the units classified as primaries, 41% were designated as b2c and would not therefore be able to respond to dynamic fusimotor activity. The significance of this relatively high proportion of b2c‐type spindle primary afferents is discussed in relation to the specialized postural function of the back muscles.
Dynamic regulation of glycinergic input to spinal dorsal horn neurones by muscarinic receptor subtypes in rats
Authors: Wang Xiu‐Li , Zhang Hong‐Mei , Li De‐Pei , Chen Shao‐Rui , Pan Hui‐Lin
Published: January 2006

Activation of spinal muscarinic acetylcholine receptors (mAChRs) inhibits nociception. However, the cellular mechanisms of this action are not fully known. In this study, we determined the role of mAChR subtypes in regulation of synaptic glycine release in the spinal cord. Whole‐cell voltage‐clamp recordings were performed on lamina II neurones in the rat spinal cord slices. The mAChR agonist oxotremorine‐M significantly increased the frequency of glycinergic sIPSCs but not mIPSCs. Surprisingly, the effect of oxotremorine‐M on sIPSCs was largely attenuated at a higher concentration. On the other hand, 1–10 μmoxotremorine‐M dose‐dependently increased the frequency of sIPSCs in rats pretreated with intrathecal pertussis toxin. Furthermore, oxotremorine‐M also dose‐dependently increased the frequency of sIPSCs in the presence of himbacine (an M2/M4mAChR antagonist) or AF‐DX116 (an M2mAChR antagonist). The M3mAChR antagonist 4‐DAMP abolished the stimulatory effect of oxotremorine‐M on sIPSCs. Interestingly, the GABABreceptor antagonist CGP55845 potentiated the stimulatory effect of oxotremorine‐M on sIPSCs. In the presence of CGP55845, both himbacine and AF‐DX116 similarly reduced the potentiating effect of oxotremorine‐M on sIPSCs. Collectively, these data suggest that the M3subtype is present on the somatodendritic site of glycinergic neurones and is mainly responsible for muscarinic potentiation of glycinergic input to spinal dorsal horn neurones. Concurrent stimulation of mAChRs on adjacent GABAergic interneurones attenuates synaptic glycine release through presynaptic GABABreceptors on glycinergic interneurones. This study illustrates a complex dynamic interaction between GABAergic and glycinergic synapses in the spinal cord dorsal horn.
Cardiovascular consequences of life‐long exposure to dietary isoflavones in the rat
Authors: Douglas G. , Armitage J. A. , Taylor P. D. , Lawson J. R. , Mann G. E. , Poston L.
Published: January 2006

Dietary soy intake in man is proposed to provide cardiovascular protection, but it is not established whether this property is attributable to the soy protein per se or to associated dietary isoflavones. This investigation aimed to establish whether the dietary isoflavones in soy protein affect cardiovascular function. Ten days prior to mating, male and female Wistar rats were habituated to either a soy based isoflavone rich diet (plasma concentration 1.87 μmol l−1 isoflavones) or the same diet after isoflavone elution (plasma isoflavone not detectable). Offspring were weaned onto and maintained on the same diet as their dam and sire for 6 months. Blood pressure, and constrictor and dilator responses in the aorta and mesenteric resistance arteries were assessed at 3 and 6 months of age. There was no effect of isoflavone removal from the diet on blood pressure, heart rate, aortic function or mesenteric artery contractile function, at either 3 or 6 months of age. Resistance mesenteric arteries from 6‐month‐old female rats fed the isoflavone rich diet demonstrated a modest increase in arterial distensibility compared with those fed the depleted diet, and mesenteric arteries from male and female rats fed the isoflavone rich diet showed increased sensitivity to acetylcholine. In summary, the isoflavone content of soy protein has no influence on blood pressure in healthy rats fed a diet based on soy protein, but influences small artery function.
Cross Relations Between the Planar Elastic Moduli of Perforated Structures
Authors: Vigdergauz Shmuel
Published: January 2006

The effective compliance moduli of a plate with a doubly periodic set of traction-free holes are considered. Attention is drawn to the perturbation form in which they are expressed by applying the complex variable methods in two-dimensional elasticity. This permits one to derive specific dimensionless combinations of the effective moduli, which are independent of the solid Poisson ratio. Using them saves computations of the structure moduli by FEM-like methods and helps one to evaluate their practical accuracy. Thus far, the only result of this kind has been observed numerically by Day, Snyder, Garboczi, and Thorpe (J. Mech. Phys. Solids. 40, pp. 1031–1051, 1992) and later proved by Cherkaev, Lurie, and Milton (Proc. R. Soc. London, Ser. A 458, pp. 519–529, 1992).
Large Eddy Simulation of Rotating Finite Source Convection
Authors: Kimmel-Klotzkin Shari J. , Deek Fadi P.
Published: January 2006

Numerical simulations of turbulent convection under the influence of rotation will help understand mixing in oceanic flows. Though direct numerical simulations (DNS) can accurately model rotating convective flows, this method is limited to small scale and low speed flows. A large eddy simulation (LES) with the Smagorinsky subgrid scale model is used to compute the time evolution of a rotating convection flow generated by a buoyancy source of finite size at a relatively high Rayleigh number. Large eddy simulations with eddy viscosity models have been used successfully for other rotating convective flows, so the Smagorinsky model is a reasonable starting point. These results demonstrate that a LES can be used to model larger scale rotating flows, and the resulting flow structure is in good agreement with DNS and experimental results. These results also demonstrate that the qualitative behavior of vorticies which form under the source depend on the geometry of the flow. For source diameters that are small compared to the size of the domain, the vortices propagate away from the source. On the other hand, if the ratio of source diameter to domain size is relatively large, the vortices are constrained beneath the source. Though the results are qualitatively similar to a direct numerical simulation (DNS) and other LES, in this simulation the flow remains laminar much longer than the DNS predicts. This particular flow is complicated by the turbulence transition between the convective plume and the quiescent ambient fluid, and an eddy viscosity model is inadequate to accurately model this type of flow. In addition, the Smagorinsky model is not consistent in a noninertial reference frame. Thus the Smagorinsky model is not the optimal choice for this type of flow. In particular, the estimation model has demonstrated better results for other types of rotating flows and is the recommended subgrid scale model for future work.
Fluid Flows Through Some Geological Discontinuities
Authors: Ingham D. B. , Al-Hadhrami A. K. , Elliott L. , Wen X.
Published: January 2006

In this paper the fluid flow through some composite channels has been investigated in the physical parameter ranges appropriate to some flows in geological applications. In particular, we have considered the fluid flow through a composite channel that has undergone a vertical fracture. The vertical connecting channel is also composed of a composite material. In such physical situations, the materials undergo several orders of magnitude changes in their Darcy numbers. This results in very large changes in the pressure in the vicinity of the interfaces between these materials. Therefore it is necessary to develop mathematical and numerical techniques to deal with such situations and in this paper an approach is presented.
Modeling of Heat Transfer in a Moving Packed Bed: Case of the Preheater in Nickel Carbonyl Process
Authors: Henda Redhouane , Falcioni Daniel J.
Published: January 2006

Heat transfer in a two-dimensional moving packed bed consisting of pellets surrounded by a gaseous atmosphere is numerically investigated. The governing equations are formulated based on the volume averaging method. A two-equation model, representing the solid and gas phases separately, and a one-equation model, representing both the solid and gas phases, are considered. The models take the form of partial differential equations with a set of boundary conditions, some of which were determined experimentally, and design parameters in addition to the operating conditions. We examine and discuss the parameters in order to reduce temperature differences from pellet to pellet. The calculation results show that by adopting a constant temperature along the preheater outer wall and decreasing the velocity of the pellets in the preheater, the difference in temperature from pellet to pellet is reduced from ∼120°C to ∼55°C, and the thermal efficiency of the preheater is tremendously improved.
Magnetohydrodynamics-Mixed Convection From Radiate Vertical Isothermal Surface Embedded in a Saturated Porous Media
Authors: Damseh Rebhi A.
Published: January 2006

The magnetohydrodynamics-mixed convection heat transfer problem from a vertical surface embedded in a porous media is studied. The effects of transverse magnetic field and radiation heat transfer are examined. Both cases of the mixed convection heat transfer problem, namely: the buoyancy aiding flow and the buoyancy opposing flow are investigated. It is found that three dimensionless groups can describe the problem under consideration, the mixed convection parameter ζ, the radiation-conduction parameter Rd, and the magnetic field number Hax2∕Rex. Different velocity profiles, temperature profiles, and the local Nusselt number variations are also drawn.
Upscaling Fractured Heterogeneous Media: Permeability and Mass Exchange Coefficient
Authors: Kfoury Moussa , Ababou Rachid , Noetinger Benoît , Quintard Michel
Published: January 2006

In order to optimize oil recuperation, to secure waste storage, CO2 sequestration and describe more precisely many environmental problems in the underground, we need to improve some homogenization methods that calculate petrophysical parameters. In this paper, we discuss the upscaling of fluid transport equations in fractured heterogeneous media consisting of the fractures themselves and a heterogeneous porous matrix. Our goal is to estimate precisely the fluid flow parameters like permeability and fracture/matrix exchange coefficient at large scale. Two approaches are possible. The first approach consists in calculating the large-scale equivalent properties in one upscaling step, starting with a single continuum flow model at the local scale. The second approach is to perform upscaling in two sequential steps: first, calculate the equivalent properties at an intermediate scale called the ”unit scale,” and, second, average the flow equations up to the large scale. We have implemented the two approaches and applied them to randomly distributed fractured systems. The results allowed us to obtain valuable information in terms of sizes of representative elementary volume associated to a given fracture distribution.
Second Law Analysis in a Partly Porous Double Pipe Heat Exchanger
Authors: Allouache Nadia , Chikh Salah
Published: January 2006

A combination of the first and second laws of thermodynamics has been utilized in analyzing the performance of a double pipe heat exchanger with a porous medium attached over the inner pipe. The goal of this work is to find the best conditions that allow the lowest rate of entropy generation due to fluid friction and heat transfer with respect to the considered parameters. Results show that the minimization of the rate of entropy generation depends on the porous layer thickness, its permeability, the inlet temperature difference between the two fluids, and the effective thermal conductivity of the porous substrate. An increase in the effective thermal conductivity of the porous medium seems to be thermodynamically advantageous. Unexpectedly, the fully porous annular gap yields the best results in terms of the rate of total entropy generation.
Thermal and Concentrational Maragoni Convection at Liquid∕Air Bubble Interface
Authors: Kostarev Konstantin , Viviani Antonio , Zuev Andrew
Published: January 2006

The paper presents the experimental study of thermo- and solutocapillary Marangoni convection around a gas bubble in an inhomogeneous fluid with a vertical thermal or surfactant concentration gradient. The stationary bubble in the form of a short horizontal cylinder with a free lateral surface was placed into a vertically oriented thin liquid layer (Hele-Shaw cell). The evolution of thermal and concentration fields and fluid flows was studied applying the interferometric method. In contrast to a thermocapillary convection representing a stationary flow and stable temperature distribution, the periodic concentration disturbances around the bubble were observed in the solutocapillary case. The regularities of the discovered effect were revealed, and its interpretation was proposed.
Numerical Investigation of the Natural Convection Flows for Low-Prandtl Fluids in Vertical Parallel-Plates Channels
Authors: Campo Antonio , Manca Oronzio , Morrone Biagio
Published: January 2006

Laminar natural convection of metallic fluids (Pr⪡1) between vertical parallel plate channels with isoflux heating is investigated numerically in this work. The full elliptic Navier-Stokes and energy equations have been solved with the combination of the stream function and vorticity method and the finite-volume technique. An enlarged computational domain is employed to take into account the flow and thermal diffusion effects. Results are presented in terms of velocity and temperature profiles. The investigation also focuses on the flow and thermal development inside the channel; the outcomes show that fully developed flow is attained up to Ra=103, whereas the thermal fully developed condition is attained up to Ra=104. Further, correlation equations for the dimensionless induced flow rate, maximum dimensionless wall temperatures, and average Nusselt numbers as functions of the descriptive geometrical and thermal parameters covering the collection of channel Grashof numbers 1.32×103⩽Gr∕A⩽5.0×106 and aspect ratios 5⩽A⩽15. Comparison with experimental measurements has been presented to assess the validity of the numerical computational procedure.
Numerical Analysis of Thermal-Solutal Convection in Heterogeneous Porous Media
Authors: Jiang Charles-Guobing , Saghir M. Ziad , Kawaji M.
Published: January 2006

Thermal diffusion, or Soret effect, in porous media is mathematically modeled with the Firoozabadi model based on non-equilibrium thermodynamics. The Soret effect in a binary mixture is investigated in a vertical cavity with heterogeneous permeability, where natural convection can occur. The thermo solutal convection with heterogeneous permeability was studied in terms of flow pattern, concentration distribution, component separation ratio, and Soret coefficient distribution. A consistent analysis was conducted and it is concluded that the Soret coefficient of thermal diffusion in porous media strongly depends on the heterogeneity of permeability.
Motion of a Sphere Suspended in a Vibrating Liquid-Filled Container
Authors: Hassan Samer , Lyubimova Tatyana P. , Lyubimov Dmitry V. , Kawaji Masahiro
Published: January 2006

The effects of small vibrations on the motion of a solid particle suspended in a fluid cell were investigated theoretically and experimentally. An inviscid model was developed to predict the amplitude of a solid particle suspended by a thin wire in the fluid cell which was vibrated horizontally. Both the model and experimental data showed that the particle amplitude is linearly proportional to the cell amplitude, and the existence of a resonance frequency. At higher cell vibration frequencies well above the resonance frequency, both the model and experiments showed that the particle amplitude becomes constant and independent of the wire length.
The Soret Effect: A Review of Recent Experimental Results
Authors: Platten Jean K.
Published: January 2006

In the first part of the paper, we recall what the Soret effect is, together with its applications in science and industry. We emphasize the need to have a reliable data base for the Soret coefficient. Next we review the different techniques to measure the Soret coefficient (elementary Soret cell, beam deflection technique, thermal diffusion forced Rayleigh scattering technique, convective coupling and, in particular, the onset of convection in horizontal layers and the thermogravitational method). Results are provided for several systems, with both negative and positive Soret coefficients, and comparison between several laboratories are made for the same systems. We end with “benchmark” values of the Soret coefficient for some organic liquid mixtures of interest in the oil industry and to which all future new techniques should refer before gaining confidence. We conclude that correct values of the Soret coefficient can be obtained in earth conditions and we deny the need to go to microgravity.
Natural Convection of a Two-Component Fluid in Porous Media Bounded by Tall Concentric Vertical Cylinders
Authors: Bahloul A. , Yahiaoui M. A. , Vasseur P. , Bennacer R. , Beji H.
Published: January 2006

This paper reports an analytical and numerical study of the behavior of a binary mixture saturating a vertical annular porous medium. Uniform heat fluxes are applied to the vertical walls while the horizontal walls are impermeable and adiabatic. Solutal gradients are assumed to be induced either by the imposition of constant gradients of concentration on the vertical walls (double diffusive convection, a=0) or by the Soret effect (a=1). Governing parameters of the problem under study are the thermal Rayleigh RT, buoyancy ratio φ, Lewis number Le, aspect ratio A, constant a, and curvature η. An analytical solution, valid for tall enclosures (A⪢1), is derived on the basis of the parallel flow approximation. In the range of the governing parameters considered in this study, a good agreement is found between the analytical predictions and the numerical results obtained by solving the full governing equations. For large Rayleigh numbers (RT⪢1), an approximate solution valid in the limit of the boundary layer regime is obtained.
Natural Steady Convection in a Space Annulus Between Two Elliptic Confocal Ducts: Influence of the Slope Angle
Authors: Djezzar Mahfoud , Daguenet Michel
Published: January 2006

The authors express the Boussinesq equations of the laminar thermal and natural convection, in the case of permanent and bidimensional flow, in an annular space between two confocal elliptic cylinders. The latter is oriented at an arbitrary angle α with respect to the gravity force, using the elliptic coordinates system. A new calculation code using the finite volumes with the primitive functions (velocity-pressure formulation) is proposed. The Prandtl number is fixed at 0.7 (case of the air) with varying the Rayleigh number. The effect of the system inclination is examined.
Numerical Determination of Moment Lyapunov Exponents of Two-Dimensional Systems
Authors: Xie Wei-Chau , So Ronald M. C.
Published: January 2006

The pth moment Lyapunov exponent of an n-dimensional linear stochastic system is the principal eigenvalue of a second-order partial differential eigenvalue problem, which can be established using the theory of stochastic dynamical system. An analytical-numerical approach for the determination of the pth moment Lyapunov exponents, for all values of p, is presented. The approach is illustrated through a two-dimensional system under bounded noise or real noise parametric excitation. Series expansions of the eigenfunctions using orthogonal functions are employed to transform the partial differential eigenvalue problems to linear algebraic eigenvalue problems, which are then solved numerically. The numerical values obtained are compared with approximate analytical results with weak noise amplitudes.
The Load Capacity of a Kagome Based High Authority Shape Morphing Structure
Authors: dos Santos e Lucato S. L. , Evans A. G.
Published: January 2006

A protocol for optimizing a high authority shape morphing plate is described. The design incorporates an active Kagome back-plane capable of changing the shape of a solid face by transmitting loads through a tetrahedral truss core. The optimization assesses the required geometric dimensions and actuator specifications in order to maximize the permissible shape changes and load capacity. The critical external loads for all failure mechanisms of the individual components are calculated and used as constraints in the optimization. Resistance of the structure to actuation is presented as an additional constraint. The ensuing relations are subsequently used to choose the best material for a given application. Numerical examples of the procedure are given for a defined structure.
Periodic Antiplane Cracks in Graded Coatings Under Static or Transient Loading
Authors: Wang B. L. , Mai Y.-W.
Published: January 2006

A periodic array of cracks in a functionally graded coating bonded to a homogeneous substrate is considered. The medium is subjected to transient or static mechanical loads. The problem is formulated in terms of a singular integral equation with the crack face displacement as the unknown variable. In addition to the time-varied stresses and stress intensity factors for various parameters of the problem, the effect of periodic cracking on the relaxation of the transient stress on the coating surface is discussed. Also included is the influence of the material gradient (material nonhomogeneity) on the crack tip intensity factors and stresses. Solutions for a single graded layer and a graded coating bonded to an infinite substrate are given.
Modeling Flow of a Biviscous Fluid From Borehole Into Rock Fracture
Authors: Lavrov A.
Published: January 2006

Flow of bi-viscous fluid, i.e., non-Newtonian fluid with the shear stress versus shear rate function composed of two straight segments, from a borehole into a nonpropagating deformable horizontal fracture of circular shape was modeled within the lubrication approximation. The volume of the fluid lost into the fracture was found to be an almost-linearly decreasing function of the fluid yield stress and a linearly increasing function of the borehole pressure, under assumption of linear fracture deformation law. The model developed serves as a first approximation of mud loss during drilling of low-permeability naturally fractured rocks.
Quasi-One-Dimensional Periodic Structure with Locally Resonant Band Gap
Authors: Wang Gang , Wen Xisen , Wen Jihong , Liu Yaozong
Published: January 2006

The propagation of longitudinal elastic waves in quasi one-dimensional structure consisting of harmonic oscillators periodically jointed on a slender beam is studied. Sub-frequency locally resonant band gap with highly asymmetric attenuation is observed in both theoretical and experimental results, and both results match well. The stiffness and mass ratios are found analytically as two factors that influence the actual attenuation in the band gap of the locally resonant phononic crystals. The study on the weights of the two factors shows that the stiffness ratio is the key one. Thus, the reason for the mismatch between the regions of the sharp attenuation and the theoretical band gap in the locally resonant phononic crystals is discovered.