8,401 research outputs found
Online Popularity and Topical Interests through the Lens of Instagram
Online socio-technical systems can be studied as proxy of the real world to
investigate human behavior and social interactions at scale. Here we focus on
Instagram, a media-sharing online platform whose popularity has been rising up
to gathering hundred millions users. Instagram exhibits a mixture of features
including social structure, social tagging and media sharing. The network of
social interactions among users models various dynamics including
follower/followee relations and users' communication by means of
posts/comments. Users can upload and tag media such as photos and pictures, and
they can "like" and comment each piece of information on the platform. In this
work we investigate three major aspects on our Instagram dataset: (i) the
structural characteristics of its network of heterogeneous interactions, to
unveil the emergence of self organization and topically-induced community
structure; (ii) the dynamics of content production and consumption, to
understand how global trends and popular users emerge; (iii) the behavior of
users labeling media with tags, to determine how they devote their attention
and to explore the variety of their topical interests. Our analysis provides
clues to understand human behavior dynamics on socio-technical systems,
specifically users and content popularity, the mechanisms of users'
interactions in online environments and how collective trends emerge from
individuals' topical interests.Comment: 11 pages, 11 figures, Proceedings of ACM Hypertext 201
Suppression of Brillouin oscillation in transparent free-standing diamond thin films in picosecond ultrasound
Brillouin oscillation appears in picosecond ultrasonics for a transparent specimen because of backward light scattering by moving strain pulse. Its amplitude is comparable with those of other responses, such as pulse-echo signals and through-thickness resonance, obscuring these non-Brillouin-oscillation responses. We here find that Brillouin oscillation can be suppressed in a transparent free-standing film by coating both sides with a metallic thin film of appropriate thickness and that this peculiar behavior is caused by strain pulses generated on both sides with a slight phase difference. This phenomenon allowed us to fabricate a Brillouin-oscillation-free diamond free-standing film, which showed a high capability for sensor applications.H. K. Weng, A. Nagakubo, H. Watanabe, and H. Ogi, "Suppression of Brillouin oscillation in transparent free-standing diamond thin films in picosecond ultrasound", Appl. Phys. Lett. 120, 112203 (2022) https://doi.org/10.1063/5.0087648
Recent Developments in Nonregular Fractional Factorial Designs
Nonregular fractional factorial designs such as Plackett-Burman designs and
other orthogonal arrays are widely used in various screening experiments for
their run size economy and flexibility. The traditional analysis focuses on
main effects only. Hamada and Wu (1992) went beyond the traditional approach
and proposed an analysis strategy to demonstrate that some interactions could
be entertained and estimated beyond a few significant main effects. Their
groundbreaking work stimulated much of the recent developments in design
criterion creation, construction and analysis of nonregular designs. This paper
reviews important developments in optimality criteria and comparison, including
projection properties, generalized resolution, various generalized minimum
aberration criteria, optimality results, construction methods and analysis
strategies for nonregular designs.Comment: Submitted to the Statistics Surveys (http://www.i-journals.org/ss/)
by the Institute of Mathematical Statistics (http://www.imstat.org
Particle dynamics of a cartoon dune
The spatio-temporal evolution of a downsized model for a desert dune is
observed experimentally in a narrow water flow channel. A particle tracking
method reveals that the migration speed of the model dune is one order of
magnitude smaller than that of individual grains. In particular, the erosion
rate consists of comparable contributions from creeping (low energy) and
saltating (high energy) particles. The saltation flow rate is slightly larger,
whereas the number of saltating particles is one order of magnitude lower than
that of the creeping ones. The velocity field of the saltating particles is
comparable to the velocity field of the driving fluid. It can be observed that
the spatial profile of the shear stress reaches its maximum value upstream of
the crest, while its minimum lies at the downstream foot of the dune. The
particle tracking method reveals that the deposition of entrained particles
occurs primarily in the region between these two extrema of the shear stress.
Moreover, it is demonstrated that the initial triangular heap evolves to a
steady state with constant mass, shape, velocity, and packing fraction after
one turnover time has elapsed. Within that time the mean distance between
particles initially in contact reaches a value of approximately one quarter of
the dune basis length
Minimal size of a barchan dune
Barchans are dunes of high mobility which have a crescent shape and propagate
under conditions of unidirectional wind. However, sand dunes only appear above
a critical size, which scales with the saturation distance of the sand flux [P.
Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. {\bf{89,}} 264301 (2002);
B. Andreotti, P. Claudin, and S. Douady, Eur. Phys. J. B {\bf{28,}} 321 (2002);
G. Sauermann, K. Kroy, and H. J. Herrmann, Phys. Rev. E {\bf{64,}} 31305
(2001)]. It has been suggested by P. Hersen, S. Douady, and B. Andreotti, Phys.
Rev. Lett. {\bf{89,}} 264301 (2002) that this flux fetch distance is itself
constant. Indeed, this could not explain the proto size of barchan dunes, which
often occur in coastal areas of high litoral drift, and the scale of dunes on
Mars. In the present work, we show from three dimensional calculations of sand
transport that the size and the shape of the minimal barchan dune depend on the
wind friction speed and the sand flux on the area between dunes in a field. Our
results explain the common appearance of barchans a few tens of centimeter high
which are observed along coasts. Furthermore, we find that the rate at which
grains enter saltation on Mars is one order of magnitude higher than on Earth,
and is relevant to correctly obtain the minimal dune size on Mars.Comment: 11 pages, 10 figure
O Serviço Social numa Comissão Social de Freguesia: uma abordagem preliminar deste novo espaço sócio ocupacional
Aprofundar o conhecimento do Serviço Social no âmbito das Comissões Sociais de Freguesia, refletindo sobre a prática do Serviço Social, nomeadamente na Comissão Social de Freguesia da Guia, é o objetivo deste relatório. O processo de criação e implementação do Programa Rede Social, como política social baseada nos fundamentos da descentralização de poderes e responsabilidades do Estado e a sua intensificação em parcerias entre o setor público e o setor privado, assentam numa lógica de desenho de políticas sociais neoliberais. O Serviço Social revela ser um importante recurso profissional para as autarquias, nomeadamente para as freguesias, desempenhando um trabalho de proximidade com as populações, facilitando-lhes o acesso a alguns direitos sociais e executando os seus deveres cívicos. No entanto, esta atuação de natureza assistencialista, pretende a resolução emergencial da situação de pobreza e das desigualdades sociais da população de determinada freguesia. Ora, estes fenómenos não estão circunscritos a uma pequena área territorial, são problemas estruturais e universais, como tal não podem ser tratados apenas como locais. Tendo como ponto de partida, a experiência vivenciada pela assistente social que fez parte da organização da Comissão Social de Freguesia da Guia e que desenhou o seu modelo de intervenção social, é feita uma análise a este novo espaço. Conclui-se, atestando que para a efetivação como espaço sócio profissional e que legitime a profissão, a política social que define as CSF terá que sofrer algumas alterações e melhorias, partindo ao encontro do projeto profissional do Serviço Social, ao mesmo tempo que potencia o enfrentamento à pobreza e desigualdades sociais ao nível local
Immunohistochemical evidence: testicular and scented glandular androgen synthesis in muskrats (Ondatra zibethicus) during the breeding season
In order to elucidate the relationship between androgens and the function of the muskrat (Ondatra zibethicus) scented glands during the breeding season, we investigated immunolocalization of steroidogenic enzymes P450scc, 3βHSD and P450c17 in the muskrat testes and scented glands. Nine adult muskrats were obtained in March (n=3), May (n=3) and July (n=3) 2010. Steroidogenic enzymes were immunolocalized using polyclonal antisera raised against bovine adrenal P450scc, human placental 3βHSD and porcine testicular P450c17. Histologically, all types of spermatogenic cells including mature-phase spermatozoa in seminiferous tubules were observed in all testes. Glandular cells, interstitial cells, epithelial cells and excretory tubules were identified in scented glands during the breeding season. P450scc, 3βHSD and P450c17 were only identified in Leydig cells during the breeding season; P450scc and P450c17 were observed in glandular cells of scented glands, however, 3βHSD was not found in scented glands during the breeding season. These novel findings provide the first evidence showing that scented glands of the muskrats are capable of locally synthesizing androgens and androgens acting via an endocrine, autocrine or paracrine manner may play an important role in scented gland function during the breeding season
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