9,707 research outputs found

    Second harmonic generating (SHG) nanoprobes for in vivo imaging

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    Fluorescence microscopy has profoundly changed cell and molecular biology studies by permitting tagged gene products to be followed as they function and interact. The ability of a fluorescent dye to absorb and emit light of different wavelengths allows it to generate startling contrast that, in the best cases, can permit single molecule detection and tracking. However, in many experimental settings, fluorescent probes fall short of their potential due to dye bleaching, dye signal saturation, and tissue autofluorescence. Here, we demonstrate that second harmonic generating (SHG) nanoprobes can be used for in vivo imaging, circumventing many of the limitations of classical fluorescence probes. Under intense illumination, such as at the focus of a laser-scanning microscope, these SHG nanocrystals convert two photons into one photon of half the wavelength; thus, when imaged by conventional two-photon microscopy, SHG nanoprobes appear to generate a signal with an inverse Stokes shift like a fluorescent dye, but with a narrower emission. Unlike commonly used fluorescent probes, SHG nanoprobes neither bleach nor blink, and the signal they generate does not saturate with increasing illumination intensity. The resulting contrast and detectability of SHG nanoprobes provide unique advantages for molecular imaging of living cells and tissues

    Perspective, Convention and Compromise

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    What is special about picturing according to the rules of perspectival drawing systems? My answer is at once both radical and conciliatory. I think that depiction essentially involves a distinctive experience, an experience of resemblance. More precisely, the picture must be seen as preserving what Thomas Reid (Enquiry 1764) called the "visible figure" of what is represented. It follows from this, and from some other plausible premises, that if a picture is to depict detailed spatial arrangements, rather than simply to represent them in some other, non-pictorial, way, it must conform to perspectival rules. Hence the radicalism. Perspective does not provide uniquely accurate or realistic ways to depict things, but, for certain aspects of the world, the only way to depict them at all. What of the conciliatory aspect of my view? My account of depiction in no way implies that only perspectival pictures can depict anything at all. Indeed, it is quite consistent with a good deal of variation in the marks which might, in the right context, depict a given content. But better still, the factors determining what we see a picture as resembling, and hence partially determining what it depicts, are just those factors emphasized by those who take perspective to be a matter of convention. They include, for instance, the nature of the subject's perceptual environment, and the sorts of pictures to which he has previously been exposed. Thus, even given the radical claim, the variety in ways of depicting a given thing is neither incomprehensible nor indicative of some kind of failure. We can understand perspective's special status without denigrating the alternatives

    Variants Of Array-Rewriting P Systems For Generating Picture Arrays

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    Bidang pengkomputeran membran dimulakan sekitar tahun 2000, berinspirasikan struktur dan fungsi sel-sel hidup. Model teori pengkomputeran membran ini dipanggil sistem P dan variannya dan penggunaan model ini dalam pelbagai masalah telah disiasat secara intensif sejak itu. Sistem P tatasusunan menghubungkan tatabahasa tatasusunan bahasa formal dengan sistem P. Dalam teori bahasa formal, salah satu kajian utama adalah terhadap keupayaan tatabahasa untuk menjana bahasa, yang disebut sebagai keupayaan generatif, yang bergantung kepada jenis-jenis peraturan yang digunakan. Kami menyiasat keupayaan generatif sistem P tatasusunan dengan memperkenalkan dalam peraturan sistem ciri-ciri benar, tatabahasa dengan penulisan semula selari dan kaedah mengumpul peraturan. Di sini dengan mengaitkan simbol benar dalam kaedah sistem P tatasusunan, kami memperkenalkan varian baru, yang dinamakan sebagai sistem P tatasusunan dengan ciri-ciri benar. Kami membuktikan bahawa jumlah membran yang digunakan dalam pembinaan itu dapat dikurangkan berbanding sistem P tatasusunan. Kami menggabungkan penulisan semula selari dalam sistem P rentetan di dalam sistem P tatasusuan, dengan itu memperkenalkan satu lagi varian baru dalam sistem P tatasusunan dan dinamakan sebagai sistem P tatasusunan selari. Inspired by the structure and functioning of the living cells, the field of membrane computing was initiated around the year 2000. Since then the theoretical model introduced in this area, called P system has been intensively investigated for properties and applications. One such P system known as array-rewriting P systems provides a link between two dimensional formal language theory and membrane computing. In formal language theory, one of the main studies is on the language generating capability of the grammars, referred to as the generative capacity, which depends on the types of rules. Also a standard technique to increase the generative capacity is to endow the rules with additional features. Here the array-rewriting P system is investigated by endowing the grammatical rules of the system with three such features, namely, permitting symbols, parallel rewriting and grouping of rules. Thus this thesis introduces and develops three such variants of the array-rewriting P system and brings out their advantages

    Introducing the Concept of Activation and Blocking of Rules in the General Framework for Regulated Rewriting in Sequential Grammars

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    We introduce new possibilities to control the application of rules based on the preceding application of rules which can be de ned for a general model of sequential grammars and we show some similarities to other control mechanisms as graph-controlled grammars and matrix grammars with and without applicability checking as well as gram- mars with random context conditions and ordered grammars. Using both activation and blocking of rules, in the string and in the multiset case we can show computational com- pleteness of context-free grammars equipped with the control mechanism of activation and blocking of rules even when using only two nonterminal symbols

    Satellite remote sensing facility for oceanograhic applications

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    The project organization, design process, and construction of a Remote Sensing Facility at Scripps Institution of Oceanography at LaJolla, California are described. The facility is capable of receiving, processing, and displaying oceanographic data received from satellites. Data are primarily imaging data representing the multispectral ocean emissions and reflectances, and are accumulated during 8 to 10 minute satellite passes over the California coast. The most important feature of the facility is the reception and processing of satellite data in real time, allowing investigators to direct ships to areas of interest for on-site verifications and experiments

    Recent Contributions of Theory to Our Understanding of the Atlantic Meridional Overturning Circulation

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    Revolutionary observational arrays, together with a new generation of ocean and climate models, have provided new and intriguing insights into the Atlantic Meridional Overturning Circulation (AMOC) over the last two decades. Theoretical models have also changed our view of the AMOC, providing a dynamical framework for understanding the new observations and the results of complex models. In this paper we review recent advances in conceptual understanding of the processes maintaining the AMOC. We discuss recent theoretical models that address issues such as the interplay between surface buoyancy and wind forcing, the extent to which the AMOC is adiabatic, the importance of mesoscale eddies, the interaction between the middepth North Atlantic Deep Water cell and the abyssal Antarctic Bottom Water cell, the role of basin geometry and bathymetry, and the importance of a three‐dimensional multiple‐basin perspective. We review new paradigms for deep water formation in the high‐latitude North Atlantic and the impact of diapycnal mixing on vertical motion in the ocean interior. And we discuss advances in our understanding of the AMOC's stability and its scaling with large‐scale meridional density gradients. Along with reviewing theories for the mean AMOC, we consider models of AMOC variability and discuss what we have learned from theory about the detection and meridional propagation of AMOC anomalies. Simple theoretical models remain a vital and powerful tool for articulating our understanding of the AMOC and identifying the processes that are most critical to represent accurately in the next generation of numerical ocean and climate models

    SOFIA: A Stratospheric Observatory for Infrared Astronomy

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    SOFIA is described as it was originally (May 1988) for the Space and Earth Sciences Advisory Committee (SESAC). The format and questions were provided by SESAC as a standard for judging the merit of potential U.S. space science projects. This version deletes Section IIF, which addressed development costs of the SOFIA facility. SOFIA's unique astronomical potential is described and it is shown how it complements and supports existing and planned facilities

    Low energy high angular resolution neutral atom detection by means of micro-shuttering techniques: the BepiColombo SERENA/ELENA sensor

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    The neutral sensor ELENA (Emitted Low-Energy Neutral Atoms) for the ESA cornerstone BepiColombo mission to Mercury (in the SERENA instrument package) is a new kind of low energetic neutral atoms instrument, mostly devoted to sputtering emission from planetary surfaces, from E ~20 eV up to E~5 keV, within 1-D (2x76 deg). ELENA is a Time-of-Flight (TOF) system, based on oscillating shutter (operated at frequencies up to a 100 kHz) and mechanical gratings: the incoming neutral particles directly impinge upon the entrance with a definite timing (START) and arrive to a STOP detector after a flight path. After a brief dissertation on the achievable scientific objectives, this paper describes the instrument, with the new design techniques approached for the neutral particles identification and the nano-techniques used for designing and manufacturing the nano-structure shuttering core of the ELENA sensor. The expected count-rates, based on the Hermean environment features, are shortly presented and discussed. Such design technologies could be fruitfully exported to different applications for planetary exploration.Comment: 11 page

    Vector quantization

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    During the past ten years Vector Quantization (VQ) has developed from a theoretical possibility promised by Shannon's source coding theorems into a powerful and competitive technique for speech and image coding and compression at medium to low bit rates. In this survey, the basic ideas behind the design of vector quantizers are sketched and some comments made on the state-of-the-art and current research efforts

    Master\u27s Project: Impacts to Natural Resources and the Natural Environment from Large-Scale Solar Facilities in Vermont: An Analysis of Public Utilities Commission Documents

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    Renewable energy deployment and conserving biodiversity are both related to mitigating and preventing the worst effects of climate change. These issues require careful consideration of land use and the consequences associated with land use choices. Large-scale ground-mounted photovoltaic solar energy is a promising clean energy technology, as it can be flexibly deployed, produces low lifecycle carbon emissions compared to other energy sources, and is cost competitive. However, questions remain about how large-scale solar will affect ecological functionality of the Vermont landscape. This report evaluates how the Vermont Public Utility Commission, the Vermont Agency of Natural Resources, and other parties to siting ground-mounted solar evaluate the ecological impacts from large-scale solar energy. It includes interviews with experts involved in solar siting issues, a review quantifying stipulations issued by regulators to avoid undue adverse impacts on protected natural resources, and an analysis reviewing common stipulations across all large-scale solar installations sited in Vermont. The analysis reveals a pattern of development favoring farmland and areas with no zoning designation near populated areas. Incentives to deploy 2.2 MW or smaller arrays appeared to have fewer natural resource concerns compared to larger installations. Impacts to grassland bird habitats, abutting forest blocks, soil erosion, and rare, threatened, or endangered species were commonly raised across developments. To improve solar siting and mitigate impacts to environmental resources, increased monitoring requirements and improved coordination between state and local governments solar should be considered by the state to facilitate low-impact developments at the local level
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