Concave Face Research Articles

Precision cylindrical face grinding

The mathematical models and experimental validations of precision cylindrical face grinding using a narrow ring superabrasive wheel are presented. The high pressure seal in diesel engine fuel systems demands the μm-scale form tolerance specifications and has driven the development of precision face grinding using the superabrasive wheel. Two mathematical models were developed: one was applied to predict the convex or concave face profile and another was used to simulate the abrasive trajectories, which become the cross-hatch grinding marks on the ground face. Cylindrical face grinding experiments were conducted. Experimental measurements of face profile and abrasive trajectories were used to validate the theoretical results. For high-pressure sealing surfaces, the height of face profile and grinding trajectories were two critical characteristics for design and manufacturing. Two design tools, a linear approximate solution for the profile height and an atlas for grinding trajectories, were developed to assist the selection of process parameters for the machine setup.

Costs and gains of porcelain crab suspension feeding in different flow conditions

Porcellana longicornis is a filter feeder that changes its feeding mechanism in relation to water flow conditions. In still water and slow flow, it actively sweeps the water with its maxillipeds. As flow speed increases, it switches from active suspension feeding to passive feeding. In low frequency oscillating flow, the crabs rhythmically reorient their suspension feeding fans so that both cup-shaped maxillipeds are upstream. In high frequency oscillating flow, the crabs perform alternate movements of left and right feeding fans, so that 1 fan is extended and the concave face is directed upstream, while the other is withdrawn. In the present study, we estimated the clearance rate and energy absorption of P. longicornis in the different flow regimes. The average clearance rate for active feeding, in slow unidirectional flow, was 0.267 l crab(-1) h(-1), while in passive feeding, in fast unidirectional now, the clearance rate was 0.1421 crab(-1) h(-1). In oscillating flow at 0.5 Hz, the clearance rate was 0.1581 crab(-1) h(-1), while at 0.1 Hz it was 0.201 l crab(-1) h(-1). Using the algal concentrations and the energy conversion factor we calculated the amount of energy gained by the crabs during the different feeding behaviors. The energy absorbed was computed and presented as J crab(-1) h-(1.) Using the dry weight of the crabs, this was converted to energy absorbed by a `standard' crab of 25 mg. The oxygen consumption of crabs was estimated as 1.122 pmol O-2 (25 mg dry wt)(-1) h(-1) for active feeding; 1.640 mu mol O-2 (25 mg dry wt)(-1) h(-1) for passive feeding; 0.921 pmol O-2 (25 mg dry wt)(-1) h(-1) for low frequency oscillating current; and 0.829 mu mol O-2 (25 mg dry wt)(-1) h(-1) for high frequency oscillating flow. However there was no significant difference between oxygen consumption during the different flow conditions. The average heat production for all the experiments was 0.5454 +/- 0.3096 J crab(-1) h(-1) or 0.5353 +/- 0.3734 J (25 mg dry wt)(-1) h(-1). The energy budget of P. longicornis during the different behaviors was computed, and it was found that the highest energy gain is during active feeding. The higher energy input is contributed by grazing, and not by low heat production. It is suggested that this behavior is an adaptation to life under stones where flow is limited and particulate organic matter is supplied by the activity of the crabs.

Concave Conical Gear.

PURPOSE:To increase the strength of the toothed surface of a concave conical gear by providing a concave conical gear where a concave toothed surface is selected. CONSTITUTION:Considering the normal toothed surface No of a conical gear, a group of generating lines ui (i=0, 1,...) of an involute helicoid and a group of curved lines vi (i=0, 1,...) serving as the loci of contact points on the toothed surface No exist on it while forming a network together. When the mounting positions of a pair of gears are decided, the loci of the contact points become only one curved line among the group of loci vi. So it is a curved line v0: ie. in the immediate neighborhood of the locus v0 of the contact point on toothed surfaces which mate with each other, the surface agrees with the involute helicoid which is the toothed surface of the conical gear, while in other parts such a concave face that may become a curved fact where the contact between the toothed surfaces approximates a line contact, ie. a concave toothed surface Co is selected.

Angioarchitectural structure and functional distributive pattern of the filiform papillae on the meso-dorsal surface of the rabbit tongue

The angioarchitectural classification and distributive patterns were investigated in the filiform papillae (FiP) on the meso-dorsal surface of the rabbit tongue by using microvascular cast specimens (MVCS) and the scanning electron microscope (SEM). The author examined the microvascular network structures, which consisted of ascending and descending branches entering the FiP. They inclined in a posterior (pharynx) direction, and densely and geometrically covered the meso-dorsal surface, directing the spoon-like concave face in an anterior direction. FiPs could be classified into three types: a small filiform papilla (SfP) covering on the meso-dorsal surface except for the marginal part of the intermolar eminence (MIME) and the intermolar eminence itself (IME): a spoon-like concave structure facing in an anterior (apex) direction with an arrowhead-like top: a middle filiform papilla (MfP) on the MIME, made up of a long triangle-like concave structure with a sharp arrowhead-like top and inclined at right angles to the IME. A large filiform papilla (LfP) on the whole swelling dorsal area of the IME was formed by a long triangle-like concave structure with a sharper arrowhead-like top. LfPs are longer and larger than MfPs and inclined towards the pharynx.

The lipase/colipase complex is activated by a micelle: neutron crystallographic evidence

The catalytic activity of most lipases depends on the aggregation state of their substrates. It is supposed that lipase activation requires the unmasking and structuring of the enzyme's active site through conformational changes involving the presence of oil-in-water droplets. This phenomenon has been called interfacial activation. Here, we report the crystal structure of the pancreatic activated lipase/colipase/micelle complex as determined using the D 2O/H 2O contrast variation low resolution neutron diffraction method. We find that a disk-shaped micelle interacts extensively with the concave face of colipase (CL) and the distal tip of the C-terminal domain of lipase away from the active site of the enzyme. Such interaction appears to help stabilizing the lipase–CL interaction. Consequently, we conclude that lipase activation is not interfacial but occurs in the aqueous phase and it is mediated by CL and a micelle.

The crystal structure of an intramolecular trans-sialidase with a NeuAc alpha2-->3Gal specificity.

Intramolecular trans-sialidase from leech (Macrobdella decora) is a unique enzyme which cleaves the terminal neuraminic acid (NeuAc) residue from sialoglycoconjugates, releasing 2, 7-anhydro-neuraminic acid (2,7-anhydro-NeuAc). It is the first enzyme found to exhibit strictly specific cleavage of NeuAc alpha2-->3Gal linkages in sialoglycoconjugates. The release of 2,7-anhydro-NeuAc instead of NeuAc implies a unique mechanism, in which the sialosyl linkage is transferred within the sialoglycoconjugate rather than hydrolyzed. The aims of the structural study were to gain structural insight into the strict specificity and unique mechanism of this unusual enzyme. . The 2.0 A crystal structure of recombinant leech intramolecular trans-sialidase has been solved by multiple isomorphous replacement. The 1.8 A structure of the enzyme in complex with 2-deoxy-2, 3-didehydro-NeuAc was also solved. The refined model comprising residues 81-769 has a catalytic beta-propeller domain (C), a N-terminal lectin-like domain (II) and an irregular beta-stranded domain (III) inserted into the catalytic domain. The structure reveals several possible carbohydrate-binding features: domain II has a concave face, like that of other sialidases, and there is a suitable surface charge distribution at the domain III-C interface. Structural comparisons showed closer evolutionary relationships to bacterial sialidases than to viral neuraminidases. Mainchain and sidechain atoms around Thr593 make the glycerol-binding pocket incapable of accommodating an extended equatorial 6-glycerol group, implying that the 6-glycerol group of the reaction intermediate may occupy an axial position, which is also required by the catalytic mechanism. The steric hindrance introduced by the bulky sidechain of Trp734 above the 2-carboxylate group may explain the lack of water involvement in the cleavage reaction and the substrate specificity.

The helix-hinge-helix structural motif in human apolipoprotein A-I determined by NMR spectroscopy.

The conformation of a synthetic peptide of 46 residues from apoA-I was investigated by fluorescence, CD, and 2D NMR spectroscopies in lipid-mimetic environments. ApoA-I(142-187) is mainly unstructured in water but helical in SDS or dodecylphosphocholine (DPC), although the peptide only associates with DPC at approximately the critical micellar concentration. Solution structures of apoA-I(142-187) were determined by distance geometry calculations based on 450 (in DPC-d38) or 397 (in SDS-d25) NOE-derived distance restraints, respectively. Backbone RMSDs for superimposing the two helical regions 146-162 and 168-182 are 0.98 +/- 0.22 (2.38 +/- 0.20) and 1.99 +/- 0.42 (2.02 +/- 0.21) A in DPC (SDS), respectively. No interhelical NOE was found, suggesting that helix-helix interactions between the two helical domains in apoA-I(142-187) are unlikely. Similar average, curved helix-hinge-helix structures were found in both SDS and DPC micelles with the hydrophobic residues occupying the concave face, indicating that hydrophobic interactions dominate. Intermolecular NOESY experiments, performed in the presence of 50% protonated SDS, confirm that the two amphipathic helices and Y166 in the hinge all interact with the micelle. The involvement of Y166 in lipid binding is supported by fluorescence spectroscopy as well. On the basis of all the data above, we propose a model for the peptide-lipid complexes wherein the curved amphipathic helix-hinge-helix structural motif straddles the micelle. The peptide-aided signal assignment achieved for apoA-I(122-187) (66mer) and apoA-I suggests that such a structural motif is retained in the longer peptide and most likely in the intact protein.

Neutron crystallographic evidence of lipase-colipase complex activation by a micelle.

The concept of lipase interfacial activation stems from the finding that the catalytic activity of most lipases depends on the aggregation state of their substrates. It is thought that activation involves the unmasking and structuring of the enzyme's active site through conformational changes requiring the presence of oil-in-water droplets. Here, we present the neutron structure of the activated lipase-colipase-micelle complex as determined using the D2O/H2O contrast variation low resolution diffraction method. In the ternary complex, the disk-shaped micelle interacts extensively with the concave face of colipase and the distal tip of the C-terminal domain of lipase. Since the micelle- and substrate-binding sites concern different regions of the protein complex, we conclude that lipase activation is not interfacial but occurs in the aqueous phase and is mediated by colipase and a micelle.

Structure of translation factor eIF4E bound to m7GDP and interaction with 4E-binding protein.

eIF4E, the mRNA cap binding protein, is a master switch that controls eukaryotic translation. To be active, it must bind eIF4G and form the eIF4F complex, which also contains eIF4A. Translation is downregulated by association of eIF4E with 4E-BP, which occupies the eIF4G binding site. Signalling events acting on 4E-BP cause it to dissociate from eIF4E, and eIF4E is then free to bind eIF4G to form the active eIF4F complex. We have solved the structure of the yeast eIF4E/m7Gpp complex in a CHAPS micelle. We determined the position of the second nucleotide in a complex with m7GpppA, and identified the 4E-BP binding site. eIF4E has a curved eight-stranded antiparallel beta-sheet, decorated with three helices on the convex face and three smaller helices inserted in connecting loops. The m7G of the cap is intercalated into a stack of tryptophans in the concave face. The 4E-BP binding site is located in a region encompassing one edge of the beta-sheet, the adjacent helix a2 and several regions of non-regular secondary structure. It is adjacent to, but does not overlap the cap-binding site.

The knowledge used in vision and where it comes from

Knowledge is often thought to be something brought from outside to act upon the visual messages received from the eye in a 'top-down' fashion, but this is a misleadingly narrow view. First, the visual system is a multilevel heterarchy with connections acting in all directions so it has no 'top'; and second, knowledge is provided through innately determined structure and by analysis of the redundancy in sensory messages themselves, as well as from outside. This paper gives evidence about mechanisms analysing sensory redundancy in biological vision. Automatic gain controls for luminance and contrast depend upon feedback from the input, and there are strong indications that the autocorrelation function, and other associations between input variables, affect the contrast sensitivity function and our subjective experience of the world. The associative structure of sensory message can provide much knowledge about the world we live in, and neural mechanisms that discount established associative structure in the input messages by recoding them can improve survival by making new structure more easily detectable. These mechanisms may be responsible for illusions, such as those produced by a concave face-mask, that are classically attributed to top-down influences.

Structural features of membrane fusion between influenza virus and liposome as revealed by quick-freezing electron microscopy.

The structure of membrane fusion intermediates between the A/PR/8(H1N1) strain of influenza virus and a liposome composed of egg phosphatidylcholine, cholesterol, and glycophorin was studied using quick-freezing electron microscopy. Fusion by viral hemagglutinin protein was induced at pH 5.0 and 23 degrees C. After a 19-s incubation under these conditions, small protrusions with a diameter of 10-20 nm were found on the fractured convex faces of the liposomal membranes, and small pits complementary to the protrusions were found on the concave faces. The protrusions and pits corresponded to fractured parts of outward bendings of the lipid bilayer or "microprotrusions of the lipid bilayer." At the loci of the protrusions and pits, liposomal membranes had local contacts with viral membranes. In many cases both the protrusions and the pits were aligned in regular polygonal arrangements, which were thought to reflect the array of hemagglutinin spikes on the viral surface. These structures were induced only when the medium was acidic with the virus present. Based on these observations, it was concluded that the microprotrusions of the lipid bilayer are induced by hemagglutinin protein. Furthermore, morphological evidence for the formation of the "initial fusion pore" at the microprotrusion was obtained. The protrusion on the convex face sometimes had a tiny hole with a diameter of <4 nm in the center. The pits transformed into narrow membrane connections <10 nm in width, bridging viruses and liposomes. The structures of the fusion pore and fusion neck with larger sizes were also observed, indicating growth of the protrusions and pits to distinct fusion sites. We propose that the microprotrusion of the lipid bilayer is a fusion intermediate induced by hemagglutinin protein, and suggest that the extraordinarily high curvature of this membrane structure is a clue to the onset of fusion. The possible architecture of the fusion intermediate is discussed with regard to the localization of intramembrane particles at the microprotrusion.

Structural transitions of a GG-platinated DNA duplex induced by pH, temperature and box A of high-mobility-group protein 1.

[1H, 15N] and 1H NMR, and CD spectroscopy are used to show that the duplex d(A-T-A-C-A-T-Pt 7G-Pt7G-T-A-C-A-T-A).d(T-A-T-G-T-A-C-C-A-T-G-T-A-T), where Pt7G is platinated guanine, containing the cis-[Pt(NH3)2]2+ adduct, undergoes reversible temperature-induced (T0.5 310 K) and pH-induced (pKa approximately 4.8) transitions between kinked-duplex and distorted forms, with the latter forms predominating at high temperature and low pH. A related pH-induced structural change was observed for the unplatinated duplex (pKa 4.69, Hill coefficient n = 1.4) but was less cooperative than for the platinated duplex (n = 2). The pH-induced transition is attributed to protonation of cytosine residues and has wider implications, since many reported NMR studies of DNA are carried out near pH 5 to minimize NH-exchange rates. The [Pt(en)]2+ (where en is 1,2-ethanediamine) GG chelate of the same duplex is shown to exist in kinked and distorted forms, and the [1H,15N]-NMR shifts for the kinked form are indicative of the presence of highly stereospecific interactions with the Pt-NH protons. On binding of the duplex platinated with [Pt(NH3)2]2+ to high-mobility-group protein 1 (HMG1) box A, similar changes in shifts of the Pt-NH3 resonances to those induced by raising the temperature or lowering the pH were observed. The specific changes in 1H-NMR chemical shifts of HMG1 box A are consistent with binding of the platinated duplex (intermediate exchange rate on the 1H-NMR time-scale) to the concave face of the protein via helices I and II and the intervening loop.

Stabilization of Atomic Nitrogen Inside C60

The concave inner face of C60 is so inert with respect to the formation of covalent bonds, that even atomic nitrogen in the quartet ground state is stable as an encapsulated guest (shown on the right). Semiempirical calculations and ESR investigations offer an explanation for this unprecedented behavior.

Binding to phosphatidyl serine membranes causes a conformational change in the concave face of annexin I

Recent studies have revealed that binding of annexin I to phospholipids induces the formation of a second phospholipid binding site. It is shown that the N terminus on the concave side of membrane-bound annexin I is cleaved much faster by trypsin or cathepsin than the N terminus of the free protein. The reactivity of the unique disulfide bond located near the concave face was similarly increased by membrane binding. These results demonstrate that Ca(2+)-dependent membrane binding induces a conformational change on the concave side of the annexin I molecule and support the notion that this face of the molecule may contribute to the formation of the secondary membrane-binding site.

Angioarchitectural comparison of the filiform papillae of the cat and rabbit using scanning electron microscopic specimens

Since the precise reasons for the functional and morphological relationship of the filiform papillae (FP) in microvascular cast specimens (MVCS) between the cat and rabbit tongue are as yet not clear, the functional and morphological characteristics of FP on the anterior dorsal surface of these tongues were studied and compared by scanning electron microscopy (SEM). In both species, numerous FP are usually inclined toward the pharynx. In the cat, in particular, there were five types of FP in which types I-III contained a main process (MP) and many accessory processes (AP), and the concave network aspect of their spoon-like and complex MP faced toward the posterior part of the tongue. In the rabbit, numerous FP showed the same type but without AP. The concave network aspect of their arrow-head-like and loose tips faced in an anterior direction, which was the opposite direction to those in the cat FP. These results suggest that the directional difference in the concave network face of MP on FP in both species i.e., the cat and the rabbit, is due to the difference in feeding habits.

Synthesis of bis-γ-butyrolactones containing conformationally constrained (S)- and (R)-diacylglycerol structures

The synthesis of two sets of rigid diacylglycerol (DAG) analogues with either the (S)-DAG or (R)-DAG enantiomer embedded into a bis-γ-butyrolactone template was accomplished stereoselectively from di-O-isopropylidene-α-d-apiose. The key step in both syntheses was the assemblage of the bicyclic perhydrofuro[3,4-b]furan ring system via a radical exo-dig intramolecular cyclization. A lipophilic undecanyl alkyl chain attached at C-3 of the fully assembled perhydrofuro[3,4-b]furan-2,4-dione (bis-γ-butyrolactone) template can adopt two orientations with the one directed away from the concave face of the bicyclic system favored by a 4 to 1 ratio in each case. Evaluation of the final target pairs of enantiomers as PK-Cα ligands revealed that the template containing an embedded (R)-DAG structure was more effective. The difference in binding affinity was also modulated by the direction of the alkyl chain.

The development of dual bluff body vortex flowmeters

If a bluff body is placed in the path of a fluid, vortex shedding occurs: the frequency of vortex shedding is proportional to the fluid velocity. A mechanism has been proposed by Gerrard to describe the formation of vortices downstream of a single bluff body. Because vortex shedding is a natural phenomenon, which is affected by random flow turbulence, vortex flowmeters have limited repeatability. Previous investigations have shown that this repeatability is improved by using certain optimum combinations of two rectangular bluff bodies in series. Visualisation studies on these dual combinations show that the vortex shedding mechanism is quite different to that proposed by Gerrard. This mechanism suggests that further improvements may be obtained: 1. (a) By having a gap in the shape of a double wedge. 2. (b) By having a downstrean bluff body with a concave or convex rear face. This means that a dual combination of triangular shaped rather than rectangular bluff bodies may give enhanced repeatability. This paper describes the results of a wind tunnel evaluation of ten dual combinations which have the above features. The tests were carried out at a fixed flow velocity and turbulence level, and for a range of bluff body separations. The paper presents results for percentage frequency standard deviation for the combinations tested. The results confirm that some combinations show significant improvements in repeatability.

Conformations of human apolipoprotein E(263-286) and E(267-289) in aqueous solutions of sodium dodecyl sulfate by CD and 1H NMR.

Structures of apoE(263-286) and apoE(267-289) have been determined in aqueous solution containing 90-fold molar excess of perdeuterated sodium dodecyl sulfate by CD and 1H NMR. Conformations were calculated by distance geometry based on 370 and 276 NOE distance restraints, respectively. RMSD for superimposing the region 265-284 from an ensemble of 41 structures for apoE(263-286) is 0.64 +/- 0.17 A for backbone atoms (N, C alpha, C = O) and 1.51 +/- 0.13 A for all atoms. The backbone RMSD for an ensemble of 37 structures for apoE(267-289) is 0.74 +/- 0.21 A for the region 268-275 and 0.34 +/- 0.10 A for the region 276-286. A two-domain structure was found for apoE(267-289) with the C-terminal half adopting a very well defined helix and the N-terminal segment 268-275 a less well defined helix, suggesting that the N-terminus may weakly bind to SDS. For apoE(263-286), an amphipathic helix-bend-helix structural motif was found with all hydrophobic side chains on the concave face. The existence of a bend around residues Q273 to G278 is consistent with their temperature coefficients of amide protons as well as secondary shifts of alpha-protons. Comparison of the structures of the two peptides revealed that the enhanced binding of apoE(263-286) to lipid could be attributed to the formation of a hydrophobic cluster consisting of residues W264, F265, L268, and V269. Aromatic side chains are proposed to be especially important in anchoring apolipoprotein fragments to micelles.

Interaction of soluble cellooligosaccharides with the N-terminal cellulose-binding domain of Cellulomonas fimi CenC 2. NMR and ultraviolet absorption spectroscopy.

The N-terminal cellulose-binding domain (CBDN1) from Cellulomonas fimi beta-1,4-glucanase CenC binds amorphous but not crystalline cellulose. To investigate the structural and thermodynamic bases of cellulose binding, NMR and difference ultraviolet absorbance spectroscopy were used in parallel with calorimetry (Tomme, P., Creagh, A. L., Kilburn, D. G., & Haynes, C. A., (1996) Biochemistry 35, 13885-13894) to characterize the interaction of soluble cellooligosaccharides with CBDN1. Association constants, determined from the dependence of the amide 1H and 15N chemical shifts of CBDN1 upon added sugar, increase from 180 +/- 60 M-1 for cellotriose to 4,200 +/- 720 M-1 for cellotetraose, 34,000 +/- 7,600 M-1 for cellopentaose, and an estimate of 50,000 M-1 for cellohexaose. This implies that the CBDN1 cellulose-binding site spans approximately five glucosyl units. On the basis of the observed patterns of amide chemical shift changes, the cellooligosaccharides bind along a five-stranded beta-sheet that forms a concave face of the jelly-roll beta-sandwich structure of CBDN1. This beta-sheet contains a strip of hydrophobic side chains flanked on both sides by polar residues. NMR and difference ultraviolet absorbance measurements also demonstrate that tyrosine, but not tryptophan, side chains may be involved in oligosaccharide binding. These results lead to a model in which CBDN1 interacts with soluble cellooligosaccharides and, by inference, with single polysaccharide chains in regions of amorphous cellulose, primarily through hydrogen bonding to the equatorial hydroxyl groups of the pyranose rings. Van der Waals stacking of the sugar rings against the apolar side chains may augment binding. CBDN1 stands in marked contrast to previously characterized CBDs that absorb to crystalline cellulose via a flat binding surface dominated by exposed aromatic rings.

Synthesis and structure determination by NMR of a putative vacuolar targeting peptide and model of a proteinase inhibitor from Nicotiana alata.

NA-proPI is a 40.3-kDa multidomain precursor protein found in the stigma of the ornamental tobacco Nicotiana alata. It is selectively targeted to the vacuole and, as the plant matures, is processed to produce a series of five 6-kDa proteinase inhibitors (one chymotrypsin and four trypsin reactive sites) which are thought to play a vital role in plant protection against insect pests. A putative sixth domain with a chymotrypsin reactive site is likely to be formed by three disulfide bridges linking the N- and C-terminal fragments of NA-proPI. This domain contains two distinct structural elements: a 54-residue sequence with high identity to each of the five repeated PI domains, and a nonrepeated 25-residue sequence at the C-terminus which is proposed to contain a vacuolar targeting peptide. The structure of the putative sixth domain was predicted using a combination of secondary structure prediction and homology modeling based on the known structure of one of the intact domains. A 26-residue peptide corresponding to the nonrepeated C-terminal sequence and encompassing the putative vacuolar targeting sequence was synthesized and its structure determined using 1H NMR spectroscopy and simulated annealing calculations. The peptide was found to adopt an amphipathic helical structure. The calculations based on NOE data suggested that the helix is curved, with a hydrophobic concave face and a hydrophilic convex face. This curvature is consistent with an observed periodicity in backbone NH chemical shifts. The structure of the entire sixth domain was modeled by combining the experimentally determined structure of the putative vacuolar targeting peptide with the homology model of the PI domain. In this model the alpha-helix of the putative targeting peptide protrudes from the otherwise compact PI domain. This observation is consistent with the requirement for targeting sequences to be relatively exposed for recognition by the sorting apparatus. As there is no consensus on the structure of vacuolar targeting sequences, this study provides a valuable insight into their potential mechanism of interaction with the cellular sorting apparatus.