67 research outputs found

    Arbitrary distribution and nonlinear modal interaction in coupled nanomechanical resonators

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    We propose a general one-dimensional {\em continuous} formulation to analyze the vibrational modes of antenna-like nanomechanical resonators consisting of two symmetric arrays of cantilevers affixed to a central nano-beam. The cantilever arrays can have arbitrary density and length profile along the beam. We obtain the secular equation that allows for the determination of their frequency spectrum and illustrate the results on the particular examples of structures with constant or alternating cantilever length profiles. We show that our analytical results capture the vibration spectrum of such resonators and elucidate key relationships that could prove advantageous for experimental device performance. Furthermore, using a perturbative approach to treat the nonlinear and dissipative dynamics of driven structures, we analyze the anharmonic coupling between two specific widely spaced modes of the coupled-element device, with direct application to experiments.Comment: 8 pages, 5 figures, additional info can be found at http://nano.bu.ed

    Генеративне розмноження Adenium obesum (Forssk.) Roem. et Schult. в умовах інтродукції

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    There have been studied the phenology and morphological features of the generative organs of Adenium obesum (Forssk.) Roem. et Schult. under the introduction conditions to identify the factors which hamper the artificial cross-pollination and production of viable seeds. It has been found that the budding of plants lasts nearly 90 days, flowering – 30–35 days, fruit ripening – 110–120 days. The flowering of one flower lasts for 5 days, but the pollination is possible only in the first two days, because the link between a flower style and carpers is broken further. Moreover, the high pollen fertility is observed within 3–4 days of blooming. At artificial pollination, mature fruits produce (80 ± 30) seeds. The germination of freshly harvested seeds is 96 %. The procedures at artificial pollination of flowers of A. obesum have been proposed.Досліджено фенологію та морфологічні особливості генеративних органів Adenium obesum (Forssk.) Roem. et Schult. в умовах інтродукції для виявлення чинників, як перешкоджають штучному перехресному запиленню та отриманню життєздатного насіння. Встановлено, що бутонізація у рослин триває майже 90 діб, цвітіння – 30–35 діб, достигання плодів – близько 110–120 діб. Цвітіння однієї квітки триває 5 діб, але запилення можливе лише в перші дві доби, оскільки потім порушується зв’язок між стовпчиком квітки і плодолистками. Висока фертильність пилку спостерігається протягом 3–4 діб цвітіння. При штучному запиленні зрілі плоди містять у середньому (80 ± 30) насінин. Схожість свіжозібраного насіння становить 96 %. Запропоновано послідовність дій при штучному запиленні квіток A. obesum

    Returns Management Practices in Swiss Online Apparel Retailing: A Multiple Case Study Approach

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    Product returns are a critical, costly task for online retailers; yet the process of managing and avoiding returns is neither actively coordinated nor investigated. Based on a multiple case study approach, six in-depth interviews with top- and middle-level apparel industry managers were conducted to explore and describe practices of managing product returns in online apparel retailing. Our findings revealed returns management practices implemented in online apparel retailing and identified several applications to reduce the environmental footprint of product returns and improving the company’s performance, based on five facets of returns management: (1) the interplay of return policy, product category, and preventive actions; (2) the application of avoidance practices; (3) the management of returns in omnichannel retail; (4) the potential of artificial intelligence to reduce return rates; and (5) the role of sustainability in consumer behaviour. To reduce product returns and enhance a company’s performance, we propose to map the practices against different phases of the return journey

    Анатомо-морфологічні особливості стебла Cissus tuberosa Moc. et Sesse ex DC. (Vitaceae) при підготовці до періоду спокою

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    This article describes a way of succulent plant Cissus tuberosa Moc. еt Sesse ex DC. (Vitaceae) natural asexual reproduction and gives the results of an anatomical and morphological investigation of this plant’s tigellum while preparing for a dry season.Описано спосіб природного вегетативного розмноження сукулентної рослини – Cissus tuberosa Moc. еt Sesse ex DC. (Vitaceae) і наведено результати анатомо-морфологічних досліджень стебел цієї рослини при підготовці до посушливого періоду

    Metamorphosis differences of caudiciform plants as an adaptation to arid conditions

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    In the course of evolution, the formation of succulent variations in the underground and surface parts of plants in different taxa could occur simultaneously under the influence of similar abiotic factors, in particular as an adaptation to arid conditions, and similar structural features even in distant families are a manifestation of convergent evolution. Along with this, the development of such adaptive structures in ontogeny can occur in different ways in different taxa. Studying the anatomical and morphological features of the vegetative organs of Fockea edulis (Asclepiadoideae, Apocynaceae) at the early stages of ontogenesis and comparing them with those of other plants will improve the understanding of the features of growth and development of caudex-like plants. The research was conducted on seedlings, juvenile and immature plants of F. edulis. When comparing the features of the development of vegetative parts of three representatives of the Apocynaceae family, we found that the strategy of succulent traits development in F. edulis at the organ level is characterized by the active development of the hypocotyl already at the seedling stage, similar to Adenium obesum, and the subsequent formation of an expanded basal part of the stem due to the combined cortex-pith thickening and radish-like root due to the growth of xylem parenchyma. However, Petopentia natalensis is characterized by a mesophytic seedling. It was established that secondary thickening in the basal part of the stem occurs in two individual ways: in Adenium obesum, the cambium generates solid rings of phloem and parenchymatized xylem; in P. natalensis and F. edulis, the bundle type of conducting elements is preserved. The thickening of the tap root in F. edulis is similar to that in A. obesum

    Quantum Friction in Nanomechanical Oscillators at Millikelvin Temperatures

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    We report low-temperature measurements of dissipation in megahertz-range, suspended, single-crystal nanomechanical oscillators. At millikelvin temperatures, both dissipation (inverse quality factor) and shift in the resonance frequency display reproducible features, similar to those observed in sound attenuation experiments in disordered glasses and consistent with measurements in larger micromechanical oscillators fabricated from single-crystal silicon. Dissipation in our single-crystal nanomechanical structures is dominated by internal quantum friction due to an estimated number of roughly 50 two-level systems, which represent both dangling bonds on the surface and bulk defects.Comment: 5 pages, two-column format. Related papers available at http://nano.bu.ed
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