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At least 127 records · Page 7Linked to original sources
PubMed2006

Enhancement of molecular-shape selectivity in high-performance liquid chromatography through multi-anchoring of comb-shaped polymer on silica.

Poly(octadecylacrylate) having plural trimethoxysilyl groups in the side chain (co-ODA(n)) was newly synthesized and immobilized onto silica through these groups. The liquid chromatographic behavior of silica-supported co-ODA(n) (Sil-co-ODA(n)) was investigated and compared with that of Sil-ODA(n), in which poly(octadecylacrylate) was immobilized through a terminal trimethoxy group at one side of the polymer main chain. Sil-co-ODA(n) showed higher selectivity for molecular shape, especially molecular planarity of PAHs than Sil-ODA(n).

Acrylates↗
PubMed2004

Shaping up: the genetic control of leaf shape.

Leaf initiation at the shoot apical meristem involves a balance between cell proliferation and commitment to make primordia. Several genes, such as CLAVATA1, CLAVATA3, WUSCHEL, KNOTTED1, and PHANTASTICA, play key roles in these processes. When expressed in the leaf primordium, however, these 'meristem' genes can profoundly affect leaf shape and size, possibly by regulating hormone gradients and transport. The KNOTTED1-like genes are involved in regulating changes in hormonal levels. Recent studies have elaborated on the role that hormones, such as auxin, play in releasing biophysical constraints on leaf initiation and growth. Final leaf form is elaborated by a coordination of these hormonally regulated processes, cell division and cellular differentiation.

Cell Division↗
PubMed2002

Why are rod-shaped bacteria rod shaped?

Generally speaking, bacteria grow and divide indefinitely, and as long as the growth conditions are maintained they retain constant dimensions and shapes with little variation. How they do this is a question that I have been considering for three decades. Here, I discuss two hypothetical mechanisms, one for Gram-positive rods and the other for Gram-negative rods. These mechanisms are consistent with what is known, but make some unproven assumptions.

Bacillus subtilis↗
PubMed1999

Molecular Shape and Solvation of the Lacunar, Saddle-Shaped, and Planar Metal Cyclidene Complexes: Molecular Dynamics Studies.

Molecular dynamics simulations have been used to study the three-dimensional distribution of methanol solvent molecules around three cobalt(II) cyclidene complexes differing in details of their ligand structures. The ligands are a planar unbridged 14-membered macrocycle in Co([14]Cyc), a saddle-shaped unbridged 16-membered macrocycle in Co([16]Cyc), and a lacunar bridged 16-membered macrocycle in Co(C6[16]Cyc). All three complexes contain five-coordinate cobalt(II) with the metal ion bound to four nitrogen donor atoms from the macrocycle and one nitrogen donor from an axial methylimidazole. Distinctly different solvation patterns are exemplified for the three complexes by the positions of the maximum in the Co-O pair distribution function (at r(Co-O) = 2.5, 3.7, and 4.5 Å for Co([14]Cyc), Co([16]Cyc), and Co(C6[16]Cyc), respectively) and by the number of methanol molecules within the macrocyclic cleft (1.5, 0.7, and 0.4 molecules at a Co-O distance of 5.25 Å in the "cavity", respectively). Analysis of the anisotropic solvent structure reveals the presence of a methanol molecule directly above the cobalt(II) center, at a distance of ca. 2.5 Å, for planar Co([14]Cyc), and the absence of solvent from such close proximity to the metal ion for the remaining complexes. The bridge further protects the sides of the cavity from the solvent. The width of an empty cavity of Co(C6[16]Cyc) shrinks by 0.3 Å in methanol solution, as compared to vacuum simulations. These results confirm the experimentally based (decrease in absolute value of enthalpies and entropies of dioxygen binding) suggestion that extensive solvation of the cobalt(II) center reduces its accessibility to incoming small molecules.

Journal Article↗
PubMed1999

Shape differences in the cervical and upper thoracic vertebrae in rats (Rattus norvegicus) and bats (Pteropus poiocephalus): can we see shape patterns derived from position in column and species membership?

The shapes of cervical (C1-C7) and upper thoracic (T1, T2) vertebrae from the rat and the grey-headed flying fox have been analysed by Fourier analysis to investigate the types of variation present and to try to isolate bones according to position along the vertebral column and species. It was found that the T2 vertebrae of the rat are very different from all others in the study, that C2 and C6 vertebrae are very similar and that the remaining vertebrae split according to species.

Animals↗
PubMed2006

Shape versus inverse-shape selective adsorption of alkane isomers in carbon nanotubes.

Simulation results are reported for the adsorption of pure pentane (C5) isomers and their ternary mixture in a series of open-ended armchair-type (m,m) single-walled carbon nanotubes (SWNTs). Inverse-shape selective adsorption occurs in the order of nC5 or=iC5>neoC5 as a result of the configurational entropy effect. In smaller SWNTs, depending on the diameter, only nC5 adsorbs, or no adsorption at all occurs. The entropy effects are found to lead to a large adsorptive separation among the C5 isomers from their mixture. Using the ideal-adsorbed-solution theory with data on the adsorption of only the pure isomers, we predict mixture adsorption. The agreement between predictions and simulations deteriorates with decreasing diameter of the SWNT.

Journal Article↗
PubMed1986

Experimental modification of PC12 neurite shape with the microtubule-depolymerizing drug Nocodazole: a serial electron microscopic study of neurite shape control.

The microtubule-depolymerizing drug Nocodazole has been used to experimentally manipulate the form of PC12 neurites. Both time-lapse photography and serial electron microscopy demonstrate that microtubule depolymerization leads to varicosity formation due to a clustering of membranous organelles in young neurites (nerve growth factor activated within 7 d). Neurites that have been nerve growth factor activated 7 or more d before Nocodazole application are resistant to microtubule depolymerization. These data and data from previous papers has been combined in an attempt to predict quantitatively the volume and the shape of a neurite. The relationship is described mathematically by Vn = 4.52 Vo + 0.0054 MTl, where Vn is local neurite volume, Vo is organelle volume, and MTl is MT length (the constant, 0.0054 is micron2), and 4.52 is the obligatory volume constant derived from serial electron microscopic studies. The equation predicts the total volume of neurites despite alterations of morphology due to Nocodazole and despite changes in morphology during development.

Animals↗
PubMed1974

Microtubule biogenesis and cell shape in Ochromonas. 3. Effects of herbicidal mitotic inhibitor isopropyl N-phenylcarbamate on shape and flagellum regeneration.

The role of microtubules and microtubule nucleating sites in the unicell, Ochromonas has been examined through the use of two mitotic inhibitors, isopropyl N-phenylcarbamate (IPC) and isopropyl N-3-chlorophenyl carbamate (CIPC). Although IPC and CIPC have little or no effect on intact microtubules, the assembly of three separate sets of microtubules in Ochromonas has been found to be differentially affected by IPC and CIPC. The assembly of flagellar microtubules after mechanical deflagellation is partially inhibited; the reassembly of rhizoplast microtubules after pressure depolymerization is totally inhibited (however, macrotubules may form at the sites of microtubule initiation or elsewhere); and, the reassembly of the beak set of microtubules after pressure depolymerization may be unaffected although similar concentrations of IPC and CICP completely inhibit microtubule regeneration on the rhizoplast. These effects on microtubule assembly, either inhibitory or macrotubule inducing, are fully reversible. The kinetics of inhibition and reversal are found to be generally similar for both flagellar and cell shape regeneration. Incorporation data suggest that neither IPC nor CIPC has significant effects on protein synthesis in short term experiments. Conversely, inhibiting protein synthesis with cycloheximide has little effect on microtubule regeneration when IPC or CIPC is removed. Although the exact target for IPC and CIPC action remains uncertain, the available evidence suggests that the microtubule protein pool or the microtubule nucleating sites are specifically and reversibly affected. Comparative experiments using the mitotic inhibitor colchicine indicate some similarities and differences in its mode of action with respect to that of IPC and CIPC on assembly and disassembly of microtubules in these cells.

Amino Acids↗
PubMed2001

Surface shape resonances and surface plasmon polariton excitations in bottle-shaped metallic gratings.

We study surface plasmon polariton excitations and surface shape resonances in a lossy metallic grating with bivalued cavities. The modal formalism is used to solve the diffraction problem for the infinite grating and the homogeneous problem for a single cavity in a plane surface. Both polarization modes are considered. We provide curves of reflected efficiency versus wavelength as well as near-field plots. The resonances are identified as dips in the reflected efficiency, which imply significant power absorptions. Results for various depths of the cavities and for several angles of incidence are shown, where the different types of resonant behavior can be appreciated. Particular attention is paid to the changes introduced by the finite conductivity of the metal in relation to the results obtained for a perfect conductor.

Journal Article↗
PubMed2006

Comparative study on the shaping ability and cleaning efficiency of rotary Mtwo instruments. Part 2. Cleaning effectiveness and shaping ability in severely curved root canals of extracted teeth.

AIM: To compare the cleaning effectiveness and shaping ability of Mtwo, K3, and RaCe nickel-titanium rotary instruments during the preparation of curved root canals in extracted human teeth. METHODOLOGY: A total of 60 root canals of mandibular and maxillary molars with curvatures ranging between 25 degrees and 35 degrees were divided into three groups of 20 canals. Based on radiographs taken prior to instrumentation with the initial instrument inserted into the canal, the groups were balanced with respect to the angle and the radius of canal curvature. Canals were prepared using a low-torque control motor. Using pre- and post-instrumentation radiographs, straightening of the canal curvatures was determined with a computer image analysis program. The amount of debris and smear layer was quantified on the basis of a numerical evaluation scale. The data established for scoring the debris and the smear layer was separately recorded and analysed statistically using the Kruskal-Wallis test. RESULTS: During preparation no instrument separated. Completely clean root canals were never observed. For debris removal Mtwo instruments achieved significantly better results (P < 0.001) than K3 and RaCe instruments. The results for remaining smear layer were similar and not significantly different (P > 0.05). Mtwo instruments maintained the original canal curvature significantly better (P < 0.05) than the other instruments. Instrumentation with Mtwo files was significantly faster than with K3 or RaCe instruments (P < 0.05). CONCLUSIONS: Under the conditions of this study, Mtwo instruments resulted in good cleaning and maintained the original curvature significantly better than K3 or RaCe files.

Analysis of Variance↗
PubMed2005

Exposure to the mass media, body shape concerns, and use of supplements to improve weight and shape among male and female adolescents.

OBJECTIVE: To assess the prevalence and correlates of products used to improve weight and shape among male and female adolescents. METHODS: A cross-sectional study was conducted of 6212 girls and 4237 boys who were 12 to 18 years of age and enrolled in the ongoing Growing Up Today Study. The outcome measure was at least weekly use of any of the following products to improve appearance, muscle mass, or strength: protein powder or shakes, creatine, amino acids/hydroxy methylbutyrate (HMB), dehydroepiandrosterone, growth hormone, or anabolic/injectable steroids. RESULTS: Approximately 4.7% of the boys and 1.6% of the girls used protein powder or shakes, creatine, amino acids/HMB, dehydroepiandrosterone, growth hormone, or anabolic/injectable steroids at least weekly to improve appearance or strength. In multivariate models, boys and girls who thought a lot about wanting more defined muscles (boys: odds ratio [OR]: 1.6; 95% confidence interval [CI]: 1.1-2.2; girls: OR: 2.3; 95% CI: 1.2-3.2) or were trying to gain weight (boys: OR: 3.0; 95% CI: 2.0-4.6; girls: OR: 4.3; 95% CI: 1.6-11.4) were more likely than their peers to use these products. In addition, boys who read men's, fashion, or health/fitness magazines (OR: 2.3; 95% CI: 1.1-4.9) and girls who were trying to look like women in the media (OR: 2.9; 95% CI: 1.4-4.0) were significantly more likely than their peers to use products to improve appearance or strength, but hours per week watching television, watching sports on television, and participation in team sports were not independently associated with using products to improve appearance or muscle mass. CONCLUSIONS: Girls and boys who frequently thought about wanting toned or well-defined muscles were at increased risk for using potentially unhealthful products to enhance their physique. These results suggest that just as girls may resort to unhealthful means to achieve a low body weight, girls and boys may also resort to unhealthful means to achieve other desired physiques.

Adolescent↗
PubMed1992

[A case of brain dead patient with a spinal pathology of preserved marginal white matter and pencil-shaped softening--a theory for pathogenesis of pencil-shaped softening].

We reported a case of brain death which had been caused by massive cerebral hemorrhage. The spinal pathology showed preserved marginal parts of spinal white matter in the segments of C7 to T5 and S1 to S3, and the other parts showed necrosis. We found pencil-shaped softening (PS)-like lesion in the segment C8 to T2, but the lesion was more preserved than the surrounding tissue. The intraspinal structure of C5 was distorted by the necrotic cerebellar tissue in the subarachnoid space of the segment and the posterior column area was decreased. The posterior column in C5 and PS showed the same severe pathology. Because the pia mater of the spinal cord is not so easily torn, and has some elasticity, swollen spinal necrotic tissue has no place to move but in a longitudinal direction; that circumstance may cause the PS. In this case the subarachnoid cerebellar tissue restricted the expansion of the spinal cord in C5, which might have helped cause PS. So we suggest that the subarachnoidal cerebellar tissue and changes of antero-posterior diameter in the spinal column, when the spine is flexed or extended, may contribute to the pathogenesis of PS. In this case the pathology of the PS was reversed as compared to the usual PS, because the PS was relatively preserved while the surrounding tissue was necrotic. There have been only a few reports which show preserved marginal white matter of the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Shape discrimination and the judgement of perfect symmetry: dissociation of shape from size.

We measured the accuracy with which subjects judged that a square or circle was perfectly symmetrical i.e. that aspect ratio (a/b) was exactly unity (where a and b were, respectively, the vertical and horizontal dimensions). Errors were remarkably small, ranging from 0.7 to 0.4% for the judgement of squareness and from 1.4 to < 0.1% for the judgement of circularity. Precision in judging aspect ratio was measured by requiring subjects to judge whether the aspect ratio (a/b)TEST of a test rectangle was greater or less than the aspect ratio (a/b)REF of a reference rectangle. Similar measurements were made for elliptical targets. To ensure that subjects based judgements on aspect ratio rather than a, b or (a-b), the area of each successive presentation was varied randomly. The just-discriminable percentage change of aspect ratio was as low as 1.6% at (a/b)REF = 1.0 (i.e. for a square or circular reference), and rose progressively as (a/b)REF was made progressively larger or smaller than 1.0. Aspect ratio discrimination threshold was independent of mean area over a sixteen-fold range of 0.25-4.0 deg2. For both rectangles and ellipses, the best value of aspect ratio discrimination threshold corresponded to a precision of encoding a and b of 14 sec arc or better. In further experiments, the method of constant stimuli was used to measure an aspect ratio aftereffect produced by adapting separately to rectangles of (a/b)ADAPT equal to 1.5, 1.0 and (1/1.5). Similar aftereffects were obtained whether the area of the test stimulus was fixed or varied randomly from trial to trial, and whether the test stimulus was rectangular or elliptical. The aftereffect could not be explained in terms of fatigue of neurons sensitive to linear dimension a or b. Nor could the aftereffect be explained in terms of the "contour repulsion" hypothesis, or in terms of orientation discrimination. We conclude (1) that the same neural mechanism determines aspect ratio discrimination threshold for rectangles and ellipses and (2) that this mechanism is sensitive to aspect ratio independently of linear dimensions. We propose that aspect ratio perception is determined by the balance of excitation of two pools of neurons that are selectively sensitive to different, but overlapping ranges of (a/b). One pool prefers aspect ratios > 1.0 and the others prefer aspect ratios < 1.0. We suppose that the two pools respond identically to changes in area (a * b).(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗