Raman spectroscopy in Group IV nanowires and nanowire axial heterostructures

The control of the SiGe NW composition is fundamental for the fabrication of high quality heterostructures. Raman spectroscopy has been used to analyse the composition of SiGe alloys. We present a study of the Raman spectrum of SiGe nanowires and SiGe/Si heterostructures. The inhomogeneity of the Ge composition deduced from the Raman spectrum is explained by the existence of a Ge-rich outer shell and by the interaction of the NW with the electromagnetic field associated with the laser beam.

The influence of axial microgravity on the breakage of axisymmetric slender liquid bridges

The dynamics of inviscid, axisymmetric liquid bridges permits a simplified treatment if the bridge is long enough. Under such condition the evolution of the liquid zone is satisfactorily explained through a non-linear one-dimensional model. In the case of breaking, the one-dimensional model fails when the neck radius of the liquid column is close to zero; however, the model allows the calculation of the time variation of the liquid-bridge interface as well as of the fluid velocity field and, because the last part of the evolution is not needed, the overall results such as the breaking time and the volume of each of the two drops resulting after breakage can be calculated. In this paper numerical results concerning the behavior of clinical liquid bridges subjected to a small axial gravitational field are presented.

Minimum volume stability limits for axisymmetric liquid bridges subject to steady axial acceleration

In this paper the influence of an axial microgravity on the minimum volume stability limit of axisymmetric liquid bridges between unequal disks is analyzed both theoretically and experimentally. The results here presented extend the knowledge of the static behaviour of liquid bridges to fluid configurations different from those studied up to now (almost equal disks). Experimental results, obtained by simulating microgravity conditions by the neutral buoyancy technique, are also presented and are shown to be in complete agreement with theoretical ones.

Análisis interferométrico de la influencia de un campo magnético axial sobre una estructura cilíndrica de cristal líquido

En el estudio de la propagación transversal de una radiación luminosa a través de un capilar con cristal líquido nemático, y cuyas moléculas se encuentran orientadas homeotrópicamente con respecto a las paredes internas de dicho capilar es necesario conocer de forma exacta la distribución espacial del director de cada una de las moléculas contenidas en el mismo. Esta distribución ha sido obtenida de forma empírica por Scudieri interpretando los resultados mediante la suposición de "lente delgada". Experimentalmente, mediante técnicas interferométricas, se obtienen dos grupos de franjas correspondiendo uno al índice de refraccción ordinario y siendo el otro función del ordinario y del extraordinario. El análisis de estas franjas es de una gran importancia a la hora de aplicar estructuras como la presente en Optica Integrada, ya que de ellas se puede inferir cuál es la respuesta de las moléculas de cristal líquido frente a campos externos, conocidos los valores del índice de refracción.

Na,K-ATPase transport from endoplasmic reticulum to Golgi requires the Golgi spectrin–ankyrin G119 skeleton in Madin Darby canine kidney cells

Spectrin (βIΣ∗) and ankyrin (AnkG119) associate with Golgi membranes and the dynactin complex, but their role in vesicle trafficking remains uncertain. We find that the actin-binding domain and membrane-association domain 1 (MAD1) of βI spectrin together form a constitutive Golgi targeting signal in transfected MDCK cells. Expression of this signal in transfected cells disrupts the endogenous Golgi spectrin skeleton and blocks transport of α- and β-Na,K-ATPase and vesicular stomatitis virus-G protein from the endoplasmic reticulum (ER) but does not disrupt the formation of Golgi stacks, the distribution of β-COP, or the transport and surface display of E-cadherin. The Golgi spectrin skeleton is thus required for the transport of a subset of membrane proteins from the ER to the Golgi. We postulate that together with polyfunctional adapter proteins such as AnkG119, Golgi spectrin forms a docking complex that acts prior to the cis-Golgi, presumably with vesicular–tubular clusters (VTCs or ERGIC), to sequester specific membrane proteins into vesicles transiting between the ER and Golgi, and subsequently (probably involving other isoforms of spectrin and ankyrin) to mediate cargo transport within the Golgi and to other membrane compartments. We hypothesize that this vesicular spectrin–ankyrin adapter-protein trafficking (or tethering) system (SAATS) mediates the capture and transport of many membrane proteins and acts in conjunction with vesicle-targeting molecules to effect the efficient transport of cargo proteins.

Segregation of Two Spectrin Isoforms: Polarized Membrane-binding Sites Direct Polarized Membrane Skeleton Assembly

Spectrin isoforms are often segregated within specialized plasma membrane subdomains where they are thought to contribute to the development of cell surface polarity. It was previously shown that ankyrin and β spectrin are recruited to sites of cell–cell contact in Drosophila S2 cells expressing the homophilic adhesion molecule neuroglian. Here, we show that neuroglian has no apparent effect on a second spectrin isoform (αβH), which is constitutively associated with the plasma membrane in S2 cells. Another membrane marker, the Na,K-ATPase, codistributes with ankyrin and αβ spectrin at sites of neuroglian-mediated contact. The distributions of these markers in epithelial cells in vivo are consistent with the order of events observed in S2 cells. Neuroglian, ankyrin, αβ spectrin, and the Na,K-ATPase colocalize at the lateral domain of salivary gland cells. In contrast, αβH spectrin is sorted to the apical domain of salivary gland and somatic follicle cells. Thus, the two spectrin isoforms respond independently to positional cues at the cell surface: in one case an apically sorted receptor and in the other case a locally activated cell–cell adhesion molecule. The results support a model in which the membrane skeleton behaves as a transducer of positional information within cells.

Metabolism to a response pathway selective retinoid ligand during axial pattern formation

We report identification of 9-cis-4-oxo-retinoic acid (9-cis-4-oxo-RA) as an in vivo retinoid metabolite in Xenopus embryos. 9-Cis-4-oxo-RA bound receptors (RARs) α, β, and γ as well as retinoid X receptors (RXRs) α, β, and γ in vitro. However, this retinoid displayed differential RXR activation depending on the response pathway used. Although it failed to activate RXRs in RXR homodimers, it activated RXRs and RARs synergistically in RAR-RXR heterodimers. 9-Cis-4-oxo-RA thus acted as a dimer-specific agonist. Considering that RAR-RXR heterodimers are major functional units involved in transducing retinoid signals during embryogenesis and that 9-cis-4-oxo-RA displayed high potency for modulating axial pattern formation in Xenopus, metabolism to 9-cis-4-oxo-RA may provide a mechanism to target retinoid action to this and other RAR-RXR heterodimer-mediated processes.

Endogenous Msx1 antisense transcript: In vivo and in vitro evidences, structure, and potential involvement in skeleton development in mammals

Msx1 is a key factor for the development of tooth and craniofacial skeleton and has been proposed to play a pivotal role in terminal cell differentiation. In this paper, we demonstrated the presence of an endogenous Msx1 antisense RNA (Msx1-AS RNA) in mice, rats, and humans. In situ analysis revealed that this RNA is expressed only in differentiated dental and bone cells with an inverse correlation with Msx1 protein. These in vivo data and overexpression of Msx1 sense and AS RNA in an odontoblastic cell line (MO6-G3) showed that the balance between the levels of the two Msx1 RNAs is related to the expression of Msx1 protein. To analyze the impact of this balance in the Msx-Dlx homeoprotein pathway, we analyzed the effect of Msx1, Msx2, and Dlx5 overexpression on proteins involved in skeletal differentiation. We showed that the Msx1-AS RNA is involved in crosstalk between the Msx-Dlx pathways because its expression was abolished by Dlx5. Msx1 was shown to down-regulate a master gene of skeletal cells differentiation, Cbfa1. All these data strongly suggest that the ratio between Msx1 sense and antisense RNAs is a very important factor in the control of skeletal terminal differentiation. Finally, the initiation site for Msx1-AS RNA transcription was located by primer extension in both mouse and human in an identical region, including a consensus TATA box, suggesting an evolutionary conservation of the AS RNA-mediated regulation of Msx1 gene expression.

Studies on the biosynthesis of taxol: the taxane carbon skeleton is not of mevalonoid origin.

A cell culture of Taxus chinensis was established to produce the diterpene 2alpha,5alpha,10beta,14beta-tetra-acetoxy4 ++ +(20),11-taxadiene (taxuyunnanine C) in 2.6% (dry weight) yield. The incorporation of [U-13C6]glucose, [1-13C]glucose, and [1,2-13C2]acetate into this diterpene was analyzed by NMR spectroscopy. Label from [1,2-13C2]acetate was diverted to the four acetyl groups of taxuyunnanine C, but not to the taxane ring system. Label from [1-13C]glucose and [U-13C6]glucose was efficiently incorporated into both the taxane ring system and the acetyl groups. The four isoprenoid moieties of the diterpene showed identical labeling patterns. The analysis of long-range 13C13C couplings in taxuyunnanine C obtained from an experiment with [U-13C6]glucose documents the involvement of an intramolecular rearrangement in the biosynthesis of the isoprenoid precursor. The labeling patterns are inconsistent with the mevalonate pathway. The taxoid data share important features with the alternative pathway of isoprenoid biosynthesis operating in certain eubacteria Rohmer, M., Knani, M., Simonin, P., Sutter, B. & Sahm, H. (1993) Biochem. J. 295, 517-524].

Estudo da topologia de motores de fluxo axial de excitação híbrida com foco na utilização em tração elétrica.

Os motores de corrente contínua convencionais são muito bem conhecidos pela sua robustez e pelo seu alto nível de controlabilidade, alem do fato de possibilitarem a operação na região de enfraquecimento de campo (modo motor), quando esta situação se fizer necessária. Por estas características, as máquinas de corrente contínua ainda são empregadas nos dias atuais em nichos específicos de utilização. Não obstante, a máquina c.c. apresenta algumas desvantagens, principalmente a intensiva e dispendiosa manutenção eletromecânica necessária para sua operação. Como opção de sanar este problema, surgiram na década de 60, as máquinas elétricas de corrente contínua sem escovas (brushless) com excitação por ímãs permanentes de fluxo trapezoidal. O problema destas máquinas se deve justamente a impossibilidade da variação de fluxo de excitação uma vez que são produzidos puramente pelos ímãs. Sendo assim, este trabalho tem como propósito, o estudo de topologias diferenciadas da máquina elétrica, através de um circuito magnético não convencional para aplicação e utilização em sistemas de tração elétrica para operação na região de enfraquecimento de campo através da variação do fluxo resultante no entreferro. Como objeto de estudo, foi focada a topologia de fluxo axial com excitação híbrida, ou seja, dupla excitação (excitação a ímãs permanentes e excitação elétrica). Para o projeto da topologia proposta, nesta tese, adicionalmente ao método analítico, foram realizadas simulações computacionais para a comparação e refinamento dos resultados das grandezas eletromagnéticas da máquina.

Modelagem estocástica da dispersão axial: aplicação em um reator tubular de polimerização.

Reatores tubulares de polimerização podem apresentar um perfil de velocidade bastante distorcido. Partindo desta observação, um modelo estocástico baseado no modelo de dispersão axial foi proposto para a representação matemática da fluidodinâmica de um reator tubular para produção de poliestireno. A equação diferencial foi obtida inserindo a aleatoriedade no parâmetro de dispersão, resultando na adição de um termo estocástico ao modelo capaz de simular as oscilações observadas experimentalmente. A equação diferencial estocástica foi discretizada e resolvida pelo método Euler-Maruyama de forma satisfatória. Uma função estimadora foi desenvolvida para a obtenção do parâmetro do termo estocástico e o parâmetro do termo determinístico foi calculado pelo método dos mínimos quadrados. Uma análise de convergência foi conduzida para determinar o número de elementos da discretização e o modelo foi validado através da comparação de trajetórias e de intervalos de confiança computacionais com dados experimentais. O resultado obtido foi satisfatório, o que auxilia na compreensão do comportamento fluidodinâmico complexo do reator estudado.

Choroidal Thickness And Volume In Healthy Young Whites And Their Relationship With Axial Length, Ammetropy And Sex

Purpose: To evaluate choroidal thickness in young subjects using Enhanced Depth Imaging Spectral Domain Optical Coherence Tomography (EDI SD-OCT) describing volume differences between all the defined areas of the Early Treatment Diabetic Retinopathy Study (ETDRS). Design: Prospective, clinical study. Methods: Seventy-nine eyes of 95 healthy, young (23.8±3.2years), adult volunteers were prospectively enrolled. Manual choroidal segmentation on a 25-raster horizontal scan protocol was performed. The measurements of the nine subfields defined by the ETDRS were evaluated. Results: Mean subfoveal choroidal thickness was 345.67±81.80μm and mean total choroidal volume was 8.99±1.88mm3. Choroidal thickness and volume were higher at the superior and temporal areas compared to inferior and nasal sectors of the same diameter respectively. Strong correlations between subfoveal choroidal thickness and axial length (AL) and myopic refractive error were obtained, r = -0.649, p<0.001 and r = 0.473, p<0.001 respectively. Emmetropic eyes tended to have thicker subfoveal choroidal thickness (381.94±79.88μm versus 307.04±64.91μm) and higher total choroidal volume than myopic eyes (9.80± 1.87mm3 versus 8.14±1.48mm3). The estimation of the variation of the subfoveal choroidal thickness with the AL was-43.84μm/mm. In the myopic group, the variation of the subfoveal choroidal thickness with the myopic refractive error was -10.45μm/D. Conclusions: This study establishes for the first time a normal database for choroidal thickness and volume in young adults. Axial length, and myopic ammetropy are highly associated with choroidal parameters in healthy subjects. EDI SD-OCT exhibited a high degree of intraobserver and interobserver repeatability.

Relationship among Corneal Biomechanics, Refractive Error, and Axial Length

Purpose: To evaluate the relationship between different ocular and corneal biomechanical parameters in emmetropic and ametropic healthy white children. Methods: This study included 293 eyes of 293 healthy Spanish children (135 boys and 158 girls), ranging in age from 6 to 17 years. Subjects were divided according to the refractive error: control (emmetropia, 99 children), myopia (100 children), and hyperopia (94 children) groups. In all cases, corneal hysteresis (CH) and corneal resistance factor (CRF) were evaluated with the Ocular Response Analyzer system. Axial length (AL) and mean corneal power were also measured by partial coherence interferometry (IOLMaster), and central corneal thickness (CCT) and anterior chamber depth were measured by anterior segment optical coherence tomography (Visante). Results: Mean (±SD) CH and CRF were 12.12 (±1.71) and 12.30 (±1.89) mm Hg, respectively. Mean (±SD) CCT was 542.68 (±37.20) μm and mean (±SD) spherical equivalent was +0.14 (±3.41) diopters. A positive correlation was found between CH and CRF (p < 0.001), and both correlated as well with CCT (p < 0.0001). Corneal resistance factor was found to decrease with increasing age (p = 0.01). Lower levels of CH were associated with longer AL and more myopia (p < 0.001 and p = 0.001, respectively). Higher values of CH were associated with increasing hyperopia. Significant differences in CH were found between emmetropic and myopic groups (p < 0.001) and between myopic and hyperopic groups (p = 0.011). There were also significant differences in CRF between emmetropic and myopic groups (p = 0.02). Multiple linear regression analysis showed that lower CH and CRF significantly associated with thinner CCT, longer AL, and flatter corneal curvature. Conclusions: The Ocular Response Analyzer corneal biomechanical properties seem to be compromised in myopia from an early age, especially in high myopia.

Mounted skeleton of Homalodotherium / by Elmer S. Riggs --

v.6:no.17(1937)