Influencia de la forma del corte apical y de la posición de la estaca, en la producción de raiz en yuca (Manihot utilissima polh)

Con el objeto de determinar si la posición y el corte en el extremo apical, influían en el rendimiento de la raíz de yuca, se hizo un ensayo en el cual se utilizaron tres posiciones diferentes: a) Horizontal, b) Inolinada y c) Vertical; con tres cortes diferentes en el extremo apical enterrado: 1) Redondo, 2) Chaflan y 3) Punta de lápiz. Se uso el diseño experimental de bloques completos al azar con arreglo de parcelas sub-divididas, empleándose seis repeticiones. La cosecha se hizo a los siente meses de la siembra, obteniéndose la mayor producción con la interacción posición inclinada corte chaflan, la cual mostró diferencia significativa para uno por ciento de error. La posición de siembra influyo significativamente sobre el rendimiento de raíz de yuca; observándose que la posición inclinada fue la que facilito mas el cultivo. Se hizo dos labores de limpia en todo el periodo de ensayo. El porcentaje de enraizamiento de plantas, altura de plantas numero de raíces, tamaño de raíces y no mostraron diferencias estadísticas significativas. Este ensayo se realizo en los campos de la Escuela Nacional de Agricultura y Ganadería (ENAG), durante el periodo de julio de 1968 a febrero de 1969. La variedad empleada fue la Cubana, cortándose para este estacas de cuarenta a cuarenta y cinco centímetros de longitud de todo el tallo, con excepción de la parte muy cerca de la raíz y la muy tierna cerca del extremo a pical.

Adenylate Cyclase Toxin Promotes Internalisation of Integrins and Raft Components and Decreases Macrophage Adhesion Capacity

10 p.

Regeneration of Giant Salvinia from Apical and Axillary Buds following Desiccation or Physical Damage

Can a new giant salvinia infestation occur even if most of the mat is destroyed except for the protected buds? From this study, we are able to conclude that buds can produce new growth under certain stressful conditions. They must be greater than 0.2 cm in length and they must possess greater than 30% moisture content to survive.

Evaluation of the Interfacial Adhesion between Brittle Coating and Ductile Substrate by Cross-Secitional Indention

The cross-sectional indentation method is extended to evaluate the interfacial adhesion between brittle coating and ductile substrate. The experimental results on electroplated chromium coating/steel substrate show that the interfacial separation occurs due to the edge chipping of brittle coating. The corresponding models are established to elucidate interfacial separation processes. This work further highlights the advantages and potential of this novel indentation method

Molecular Dynamics Simulation of the Bio-Adhesion in Molecular Motors

Molecular dynamics (MD) simulation is employed to study the bio-adhesion in F1 ATP molecular motor. Histidine-peptide is widely used as linkage in micro systems because of its strong binding strength to metals. This paper focuses on the adhesion between a synthetic peptide containing 6xHis-tag (Gly-Gly-Lys-Gly-Gly-Lys-Gly-Gly-His-His-His-His-His-His) and metal substrate, which is used to define the position of the F1 ATP molecular motor on the metal substrate. It is shown that the binding strength between histidine and nickel substrate is the strongest, while that of copper is smaller and that of gold substrate is the smallest. From the result of simulation, we find that the stability of adhesion between histidine and the metal substate result of the ringed structure in histidine.

A special method to evaluate the strong adhesion between brittle coating and ductile substrate

The evaluation of the interfacial adhesion of coating system has always been a rough task. In this paper, a special testing method of cross-sectional indentation is applied on a model coating system, i.e. electroplated chromium on a steel substrate which is generally regarded as an example of materials pair with strong adhesion. Based on fractography analysis with SEM and interfacial stress simulation with FEM, it is found that interfacial shear stress may induce coating spalling. More interestingly, spalling location is sensitive to substrate pretreatment process. This shows the feasibility of cross-sectional indentation to distinguish interfacial strength at a high level.

Molecular dynamics simulation of adhesion forces in a dipalmitoylphosphatidylcholine membrane

Adhesion forces of Dipalmitoylphosphatidylcholine ( DPPC) membrane in the gel phase are investigated by molecular dynamics ( MD) simulation. In the simulations, individual DPPC molecules are pulled out of DPPC membranes with different rates and we get the maximum adhesion forces of DPPC membrane. We find that the maximum adhesion forces increase with pull rate, from about 400 to 700 pN when pull rates are from 0.001 to 0.03 nm/ps. We analyze the relationship between pull rate and adhesion forces of different origins using Brownian dynamics and notice that viscosity of solvent plays an important role in adhesion forces. Then we simulate the motion of a single DPPC molecule in solvent and it elucidates that the maximum drag force is almost linear with respect to the pull rate. We use Stokes' relation to describe the motion of a single DPPC molecule and deduce the effective length of a DPPC molecule. Conformational analyses indicate that the free energy variation of a DPPC molecule inside and outside of the DPPC membrane is an essential part of adhesion energy.

Candida albicans Increases Tumor Cell Adhesion to Endothelial Cells In Vitro: Intraspecific Differences and Importance of the Mannose Receptor

The dimorphic fungus Candida albicans is able to trigger a cytokine-mediated pro-inflammatory response that increases tumor cell adhesion to hepatic endothelium and metastasis. To check the intraspecific differences in this effect, we used an in vitro murine model of hepatic response against C. albicans, which made clear that tumor cells adhered more to endothelium incubated with blastoconidia, both live and killed, than germ tubes. This finding was related to the higher carbohydrate/protein ratio found in blastoconidia. In fact, destruction of mannose ligand residues on the cell surface by metaperiodate treatment significantly reduced tumor cell adhesion induced. Moreover, we also noticed that the effect of clinical strains was greater than that of the reference one. This finding could not be explained by the carbohydrate/protein data, but to explain these differences between strains, we analyzed the expression level of ten genes (ADH1, APE3, IDH2, ENO1, FBA1, ILV5, PDI1, PGK1, QCR2 and TUF1) that code for the proteins identified previously in a mannoprotein-enriched pro-metastatic fraction of C. albicans. The results corroborated that their expression was higher in clinical strains than the reference one. To confirm the importance of the mannoprotein fraction, we also demonstrate that blocking the mannose receptor decreases the effect of C. albicans and its mannoproteins, inhibiting IL-18 synthesis and tumor cell adhesion increase by around 60%. These findings could be the first step towards a new treatment for solid organ cancers based on the role of the mannose receptor in C. albicans-induced tumor progression and metastasis.

Vascular endothelial growth factor regulates melanoma cell adhesion and growth in the bone marrow microenvironment via tumor cyclooxygenase-2

Background: Human melanoma frequently colonizes bone marrow (BM) since its earliest stage of systemic dissemination, prior to clinical metastasis occurrence. However, how melanoma cell adhesion and proliferation mechanisms are regulated within bone marrow stromal cell (BMSC) microenvironment remain unclear. Consistent with the prometastatic role of inflammatory and angiogenic factors, several studies have reported elevated levels of cyclooxygenase-2 (COX-2) in melanoma although its pathogenic role in bone marrow melanoma metastasis is unknown. Methods: Herein we analyzed the effect of cyclooxygenase-2 (COX-2) inhibitor celecoxib in a model of generalized BM dissemination of left cardiac ventricle-injected B16 melanoma (B16M) cells into healthy and bacterial endotoxin lipopolysaccharide (LPS)-pretreated mice to induce inflammation. In addition, B16M and human A375 melanoma (A375M) cells were exposed to conditioned media from basal and LPS-treated primary cultured murine and human BMSCs, and the contribution of COX-2 to the adhesion and proliferation of melanoma cells was also studied. Results: Mice given one single intravenous injection of LPS 6 hour prior to cancer cells significantly increased B16M metastasis in BM compared to untreated mice; however, administration of oral celecoxib reduced BM metastasis incidence and volume in healthy mice, and almost completely abrogated LPS-dependent melanoma metastases. In vitro, untreated and LPS-treated murine and human BMSC-conditioned medium (CM) increased VCAM-1-dependent BMSC adherence and proliferation of B16M and A375M cells, respectively, as compared to basal medium-treated melanoma cells. Addition of celecoxib to both B16M and A375M cells abolished adhesion and proliferation increments induced by BMSC-CM. TNF alpha and VEGF secretion increased in the supernatant of LPS-treated BMSCs; however, anti-VEGF neutralizing antibodies added to B16M and A375M cells prior to LPS-treated BMSC-CM resulted in a complete abrogation of both adhesion-and proliferation-stimulating effect of BMSC on melanoma cells. Conversely, recombinant VEGF increased adherence to BMSC and proliferation of both B16M and A375M cells, compared to basal medium-treated cells, while addition of celecoxib neutralized VEGF effects on melanoma. Recombinant TNFa induced B16M production of VEGF via COX-2-dependent mechanism. Moreover, exogenous PGE2 also increased B16M cell adhesion to immobilized recombinant VCAM-1. Conclusions: We demonstrate the contribution of VEGF-induced tumor COX-2 to the regulation of adhesion-and proliferation-stimulating effects of TNFa, from endotoxin-activated bone marrow stromal cells, on VLA-4-expressing

Orientation-Dependent Adhesion Strength Of A Rigid Cylinder In Non-Slipping Contact With A Transversely Isotropic Half-Space

Recently, Chen and Gao [Chen, S., Gao, H., 2007. Bio-inspired mechanics of reversible adhesion: orientation-dependent adhesion strength for non-slipping adhesive contact with transversely isotropic elastic materials. J. Mech. Phys. solids 55, 1001-1015] studied the problem of a rigid cylinder in non-slipping adhesive contact with a transversely isotropic solid subjected to an inclined pulling force. An implicit assumption made in their study was that the contact region remains symmetric with respect to the center of the cylinder. This assumption is, however, not self-consistent because the resulting energy release rates at two contact edges, which are supposed to be identical, actually differ from each other. Here we revisit the original problem of Chen and Gao and derive the correct solution by removing this problematic assumption. The corrected solution provides a proper insight into the concept of orientation-dependent adhesion strength in anisotropic elastic solids. (c) 2008 Elsevier Ltd. All rights reserved.

Stabilizing to disruptive transition of focal adhesion response to mechanical forces

Strong mechanical forces can, obviously, disrupt cell-cell and cell-matrix adhesions, e.g., cyclic uniaxial stretch induces instability of cell adhesion, which then causes the reorientation of cells away from the stretching direction. However, recent experiments also demonstrated the existence of force dependent adhesion growth (rather than dissociation). To provide a quantitative explanation for the two seemingly contradictory phenomena, a microscopic model that includes both integrin-integrin interaction and integrin-ligand interaction is developed at molecular level by treating the focal adhesion as an adhesion cluster. The integrin clustering dynamics and integrin-ligand binding dynamics are then simulated within one unified theoretical frame with Monte Carlo simulation. We find that the focal adhesion will grow when the traction force is higher than a relative small threshold value, and the growth is dominated by the reduction of local chemical potential energy by the traction force. In contrast, the focal adhesion will rupture when the traction force exceeds a second threshold value, and the rupture is dominated by the breaking of integrin-ligand bonds. Consistent with the experiments, these results suggest a force map for various responses of cell adhesion to different scales of mechanical force. PMID: 20542514

EVALUATION OF FILM-SUBSTRATE ADHESION VIA IMPACT USING COATED BULLETS

A method was devised to evaluate the adhesion between a film and a substrate. A front-end coated bullet is accelerated by a gas gun and hits the substrate of the specimen under test. The impact generates a compressive stress pulse that propagates toward the film. After transmission through the interface, part of the pulse is reflected on the free surface of the film, and tensile stress arises at the film-substrate interface, possibly inducing debonding of the film. This dynamic process was demonstrated analytically and simulated numerically by the finite element method. The results validate the initial concept and lay the foundation for further optimization of this method.

On a novel method of impact by a front-end-coated bullet to evaluate the interface adhesion between film and substrate

A preliminary experiment was carried out to validate the feasibility of the method of impact by a front-end-coated bullet to evaluate the interface adhesion between film and substrate. The theoretical description of the initiation, propagation and evolution of the stress pulse during impact was generalized and formulized. The effects of the crucial parameters on the interface stress were further investigated with FEM. The results found the promising prospect of the application of such a method and provided useful guidance for experimental design.

Influência da associação de catalisadores químicos na cimentação de pinos pré-fabricados de fibra de vidro

O objetivo deste estudo foi avaliar a Influência da associação de catalisadores químicos junto a diferentes sistemas adesivos autocondicionantes e cimentos resinosos de dupla polimerização, na cimentação de pinos pré-fabricados de fibra de vidro, quanto a sua resistência ao cisalhamento por extrusão - push out, seu grau de conversão e nanoinfiltração. Foram utilizadas trinta raízes bovinas extraídas, que tiveram seus canais obturados com guta-percha termoplastificada, divididas em três grupos: G1 - Adper SE Plus /Rely X ARC; G2- Adper SE Plus / Catalisador Scotchbond + Rely X ARC ; G3- Clearfil SE Bond / ED Primer + Panavia F. Após a cimentação dos pinos foram obtidas fatias das raízes, com 1mm de espessura, dos terços cervical (C), médio (M) e apical (A). O ensaio de resistência ao cisalhamento por extrusão foi realizado em máquina de ensaio universal EMIC D500 com carga de 100KN à velocidade de 1,0 mm/min, até o deslocamento do pino. Os dados obtidos no ensaio foram tabulados e submetidos à análise estatística. A análise de variância a dois critérios mostrou que apenas os fatores grupo e profundidade foram significativos, não sendo significativa a sua interação. O resultado do teste de Tukey (ρ≥0,05), para o fator grupo, mostrou que a menor média de resistência ao cisalhamento por extrusão foi obtida pelo grupo 3, que apresentou diferença estatística significativa para os grupos 1 e 2 que não diferiram entre si. Para o fator Profundidade a maior média foi obtida no terço cervical que apresentou diferença estatística significativa para os terços médio e apical que não diferiram entre si: A análise do grau de conversão foi feita após vinte e quatro horas e os fatores estudados foram os cimentos resinosos Panavia F e Rely X ARC e os catalisadores químicos ED Primer e Catalisador Scotchbond, na forma incorporada ou aplicada superficialmente aos cimentos, formando 10 grupos experimentais. Para o grau de conversão, o teste de Tukey mostrou que o catalisador químico não aumentou o grau de conversão do RelyX ARC, já para o Panavia F, este aumentou significativamente seu grau de conversão. Quanto a análise em MEV da nanoinfiltração para o fator grupo, o resultado do teste de Tukey (ρ≥0,05) mostrou que a maior média foi obtida pelo grupo 3 que apresentou diferença estatística significativa para os grupos 1 e 2, que não diferiram entre si. Para o fator Profundidade a maior média foi obtida no terço apical que apresentou diferença estatística significativa para o terço cervical, que não diferiu do terço médio. Conclusões: 1- A associação de catalisadores químicos não aumentou a resistência ao cisalhamento por extrusão dos pinos de fibra de vidro. 2- O cimento Panavia F é dependente de catalisador aumentar o grau de conversão. 3- A associação de catalisadores químicos não foi capaz de alterar o padrão da camada híbrida, representado pela nanoinfiltração. 4- A nanoinfiltração está associada inversamente ao grau de conversão dos sistemas de cimentação, o que contribui negativamente para a resistência adesiva de pinos de fibra de vidro.