Non-planar Shape Research Articles

987-104 Flexible Annuloplasty Support Preserves Physiological Annular Movement and Non-planar Shape: A 3-Dimenslonal Intraoperative Echocardiographlc Study

Mitral annular motion and nonplanar shape has been shown to be important to normal valve dynamics and left ventricular systolic function. We evaluated the effect of a new flexible annuloplasty ring on the morphology and motion of the mitral annulus in patients undergoing mitral repair. The mitral valve was imaged over one complete cardiac cycle at ≈10° rotations using a multiplane transesophageal probe in 4 patients intraoperatively after mitral repair. Two had data pre and post repair for a total of 6 reconstructions. The data were digitized off-line and annular insertion points and ring location (post-op) were identified for each frame of data over the cardiac cycle (≈ 1000 points per reconstruction). The data were reconstructed in 3-D, and a least-square plane was fit. The following measures were obtained: A) annular area as projected onto the least-squares plane B) Atrio-ventricular motion of the annulus C) non-planarity of the annulus (mean-square- deviation from the least-squares fit plane). All the patients maintained the non-planarity with a maximal deviation from the plane of 8.6 mm. The mean atrio-ventricular motion was 2.6 mm and the % change in area during the cardiac cycle was 14.7%. For the 2 patients with pre and post repair data, there was a reduction in total area of 59%, an increase of 18% in non-planarity and a reduction of maximal excursion of 47%. This preliminary study shows that annuloplasty repair with a flexible ring preserves annular motion and nonplanarity while allowing significant reduction in annular area.

Reactivity of β-lactams and phosphonamidates and reactions with β-lactamase

Abstract

A Molecular Modeling Approach to In vivo Efficacy of Triclabendazole

The structural and electronic features of a narrow-spectrum benzimidazole anthelmintic triclabendazole (TCZ, 6-chloro-5-[2,3-dichlorophenoxy]-2-methylthio-benzimidazole) and its 2 main metabolites triclabendazole sulfoxide (TCZ sulfoxide, 6-chloro-5-[2,3-dichlorophenoxyl]-2-methylsulfonyl-benzimidazole) and triclabendazole sulfone (TCZ sulfone, 6-chloro-5-[2,3-dichlorophenoxy]-2-methylsulfonyl-benzimidazole) have been determined using a combination of quantum mechanics, molecular graphics, and molecular modeling techniques. Using conformational analyses and quantum mechanics, 2 important differences were found between TCZ sulfoxide, the purported active species, and the broad-spectrum benzimidazole anthelmintics. The first distinguishing feature is the shape of the molecule; the substituent at the 2 position of TCZ sulfoxide is nonplanar. All other broad-spectrum benzimidazole anthelmintics, regardless of substituent at the 2 position (methyl carbamate or thiazolyl group), are flat. The second distinguishing feature is the net atomic charge on the substituent at the 2 position of TCZ sulfoxide; it is an order of magnitude larger than the net atomic charges on the other anthelmintics. Thus the nonplanar shape of the methysulfinyl group at the 2 position of TCZ sulfoxide is different (as is its net charge), suggesting that this may be the origin of its narrow spectrum of activity.

Reductions in induced drag by the use of aft swept wing tips

SummaryRecent experimental and computational studies have indicated that rearward curvature of a wing can reduce the induced drag factor to values less than that obtained from the unswept elliptical wing considered optimal in classical wing theory. Wake non-planarity associated with a wing with aft swept tips has been suggested as a reason for this behaviour. This paper provides a systematic examination of the wake non-planarities induced by a variety of wing planforms and quantifies the induced drag reductions which may be expected. Results suggest a dependence of induced drag factor upon angle of attack, and therefore upon lift coefficient. The crescent wing is identified as the planform to derive the most benefit from its non-planar wake shape, typically a 4% reduction in induced drag factor at moderate angle of attack.

Structure of cyclooctatetraene at 129 K

CsH s, Mr= 104.2, orthorhombic, Aba2, a = 7.664 (6), b = 7.650 (3), c = 10.688 (6) A, V= 627 (1)/~3, T= 129 K, Z = 4, D x = 1.10 Mg m -3, F(000) = 224, 2(Mo Ka) = 0.71069 A, /~= 0.06 mm -1, final R = 0.036 (wR = 0.043) for 529 observed reflections (I> 2o(/)) (4525 (+h, +k, +l) measured, 597 averaged reflections (Rint 0.05) and 52 refined parameters). The molecular structure of COT in the solid state confirms earlier electron-diffraction results for the title compound suggesting a boat conformation. This is in accordance with recent structural investigations of COT derivatives. Introduction. Cyclooctatetraene (COT) ring systems are capable of three structural changes, which involve ring inversion, bond shifting and valence isomerization (Paquette, 1975). Whereas the first process requires a planar transition state only, all bond-shifting mechan- isms involve additionally an equalization of bond lengths, and consequently slightly higher energy barriers are found for the latter. As a ligand to transi- tion metals, COT usually adopts a boat form or a twisted boat conformation (Brauer & Krfiger, 1976); frequently the ligand shows fluxionality (Mann, 1982). As a dianionic ligand the COT skeleton is planar (Streitwieser et al., 1973; R6sch & Streitwieser, 1978). For free, non-substituted COT a non-planar ring shape was found by electron diffraction (Bastiansen, Hedberg & Hedberg, 1957; Tr~etteberg, 1966); preliminary results of a crystal structure analysis of COT have been quoted in the literature (Bordener, Parker & Stanford, 1972). A low-temperature X-ray diffraction study of COT was undertaken to reveal basic structural data for this important compound in the solid state.

Isoflavonoid feeding deterrents forCostelytra zealandica Structure ? Activity relationships

A number of naturally occurring isoflavonoids of differing substitution patterns and oxidation states have been tested for feeding deterrent activity in a bioassay with larvae ofCostelytra zealandica White. The most active deterrents, which reduced feeding significantly at 0.2-1.0 μg/g, are those compounds containing a ring B-fused cycloprenoid moiety. The least active compounds were highly oxidized coumestans and isoflavones. The ring B-fused cyclic isoprenoid moiety and the presence of a 2'-oxy function appear to be structural features important for high activity. It is suggested that the feeding deterrent activity of isoflavonoids relates to their stereochemistry and that the most active compounds have or can adopt a similar nonplanar molecular shape with a similar arrangement of polar and lipophilic groups.

Short Communication

Abstract For low-pressure premixed hydrocarbon-air flames on a circular porous plug burner,we have observed three nonplanar modes of propagation. Our interpretation of the present data suggests that these modes correspond to : (I) a radial mode, in which the flame front periodically changes its spatial extent on the burner, (2) a circular mode, in which the flame front moves in a circular path, and (3) a nonplanar mode, in which the flame front assumes a nonplanar shape. Similar modes of propagation have been predicted in recent theoretical studies of freely. propagating flames in channels.

Bedform Spacing and Flow Resistance

Experimental work, using rigid bedforms modeled on ripple and dune bedforms developed in sand, shows that the natural spacing of bedforms is that which, for their shape, causes maximum resistance to flow. This result supports a more general hypothesis, developed earlier from existing bedform, armored bed and meander data, that the equilibrium nonplanar shape of a deformable boundary is that which offers maximum resistance to flow past it. This principle, which may reflect some general principle of energy dissipation, should eventually allow bedform spacing to be predicted from bedform shape. In order to predict resistance to flow, however, bedform size relative to flow depth must be known. The maximum resistance principle cannot define bedform size, which must therefore result from the action of some further process that halts bedform growth.

A simple quadrilateral shell element

The paper describes a new four-noded quadrilateral shell element, called QUAD4, which is based on isoparametric principles with modifications which relax excessive constraints. The modifications include reduced order integration for shear terms, enforcement of curvature compatibility, and the augmentation of transverse shear flexibility to account for a deficiency in the bending strain energy. Practical features are discussed, including conversion to a nonplanar shape, coupling between bending and stretching, mass properties, and geometric stiffness. Experimental results are described which illustrate the accuracy and economy claimed for the element.

Shape of Two-Dimensional Solidification Interface During Directional Solidification by Continuous Casting

An analysis was made of the two-dimensional solidification of an ingot being cooled and withdrawn vertically downward from a mold consisting of parallel walls of finite length. In some metallurgical solidification processes the liquid metal is maintained superheated so that it transfers heat into the solidification interface as a means of controlling the metal structure during solidification. This energy plus the latent heat of fusion is removed by the coolant along the sides of the ingot. Increasing the ingot withdrawal rate or the heat addition at the solidification interface causes the interface to move downward within the mold and have a nonplanar shape as a result of the curved paths for heat flow into the coolant. This distortion of the interface in the case of directional solidification leads to an undesirable metallic structure. The present heat transfer analysis shows how the flatness of the interface is related to the ingot thickness, the withdrawal rate, the heat addition from the superheated liquid metal, and the temperature difference available for cooling. This provides an understanding of the conditions that will yield a maximum rate of casting while achieving the desired flatness of the interface. The results are interpreted with respect to the conditions for obtaining an aligned eutectic structure by directional solidification. In this process an additional constraint must be included that relates the ingot withdrawal rate and the heat transfer rate from the liquid metal to the solidification interface.

Spectroscopic evidence for a continuous change in molecular and crystal structure: deformation of biphenyl in the low temperature solid

A Raman temperature study of biphenyl- h 10 and biphenyl- d 10 crystals reveals an unusual spectral change over a wide temperature region. Many internal and external infrared-active modes appear gradually as the temperature is lowered from about 75 to 15°K. We interpret this as a mild and gradual change in both crystal and molecular structure: a loss of center of inversion, probably involving the partial return of the molecule to its non-planar shape (D 2) in the vapor phase.