1,723,017 research outputs found
Energy storage in Chlamydomonas reinhardtii measured with photoacoustic techniques
No full textThe energy storage efficiencies of the reaction centers in the intact cells of Chlamydomonas reinhardtii wild type cell, PSI-less mutants and PSII-less mutants in microsecond time window were determined using pulsed, time-resolved photoacoustic techniques. The heat emission from the photochemical reaction can result in the positive thermal expansion photoacoustic signal, opposing the negative thylokoid volume contraction signal caused by electrostriction during the charge separation. In this present research, we observed that PSI differed strongly from PSII, both in thermal expansion and volume contraction. Similar to the bacterial reaction centre, PSI is marked with the large volume contraction but small thermal expansion, in contrast to the large thermal expansion but small volume contraction in PSII. For wild type, the volume contraction signal is dominant over the thermal expansion signal upon low pulse energy illumination at room temperature. In microsecond time scale, the energy storage efficiencies were estimated to be 36%, 80±5%, and 50±14% per trap in wild type, PSI and PSII, respectively. The different energy conversion efficiencies are probably attributed to the escape of the bound counterions from the particle surface in PSI and rapid electron transfer in PSII. In the present work, we conducted the photoacoustic experiments to study the energy storage in different photosystem with the intact cells of PSI-less and PSII-less mutants, instead of using either specific wavelength excitation light or PSII inhibitors (e. g. DCMU), which were commonly applied in the previous studies. We also proved photoacoustic techniques’ usefulness and convenience in the photosynthesis research, especially in electron transfer and some related thermodynamics studies.M.S.Includes bibliographical references (p. 22-27)by Chengyi Ya
Resilience, Complexity and Cooperation in Socio-ecological System
No full textAdvances in experimental technologies, both in the laboratory and in the field, are generating an increasing volume of ecologically and sociologically relevant data, spanning a wide range of scales, revealing recurrent emergence of patterns in these systems. This "data explosion"' is both a challenge (inventing new tools for their analysis) and an opportunity (identifying rules driving the functioning of complex systems). However, data alone do not necessarily lead to an understanding of the systems of interest. At present, we are in a situation where in front of a rich (but common to many systems) phenomenology we have innumerable models for very specific cases that call for a general vision. This challenge is very fascinating for physicists, that have in their veins the search for general principles of apparently different phenomena.
In particular, a very important property that seems to be shared by most of the socio-ecological systems is their ability to respond to perturbations, i.e. the system resilience. Cell biology, ecology, environmental science, and food security are just some of the many areas of investigation on the mechanisms increasing the system resilience. Nevertheless, not all socio-ecological systems display high resilience. In food security, the intensification of international food trade and local shocks in food production led to global food crises, and for example Suweis develops a framework to investigate the coupled global food-population dynamics and finds that the global food system is losing resilience (increasingly unstable and susceptible to conditions of crisis); In ecology, the concept of resilience has evolved considerably since Holling's (1973) seminal paper to describe the persistence of natural systems in the face of changes in ecosystem variables due to natural or anthropogenic causes. It has been suggested that in many ecosystems we are facing a lost of resilience and consequent loss of biodiversity. Therefore an important challenge is to understand what are the main drivers ruling the resilience of ecological communities, so that proper ecosystem management strategy can be developed.
From data is emerging that one of the key feature of socio-ecological system resilience may lie in the architecture of the interaction networks. The topology of the interaction network may actually represent the "parameter" that system somehow self-tunes so that the system's responses to stimuli is optimized with respect to some feature (e.g. stability). In inanimate matter, spins or particles always have their mutual interactions turned on (with an intensity decaying with their relative distance) and the network describing their interaction is dense, with most of the connections present. In contrast, if we consider for instance an ecosystem, species interact selectively even if they coexist at short distances, and the species interaction network is sparse, that is, most of the interactions are turned off. At the same time, the interactions that are turned on form non-random evolving structures that are the result of some optimization process under adaptive/evolution pressure. Thanks to massive databases now easy available, characteristics similar to those just mentioned for ecological networks, have been observed also in gene-interaction network, in neuronal networks and even in social networks. These networks are very different and yet share a crucial aspect: they all have undergone biological/social evolution that has driven their incremental complexity.
One particular long-standing question regards the relationship between stability (resilience) and complexity in ecological system. Many of the population dynamics modeling frameworks proposed in the literature cannot elude the celebrated May's theorem. This theorem, recently refined by Allesina and Tang states that the stability of the system depends on the product [SC], where [S] is the number of species and [C] is the fraction of non-zero pairwise interactions between species. This result leads to the so-called stability and complexity paradox debate: a system in order to be stable cannot be too large ([S] large) or too connected (large [C]). The paradox lies in the fact that empirically, ecosystems with a large number of species seem to be very stable. Moreover, recently it has been suggested that because of this stability paradox, in microbial ecosystems competition may play a much important roles than what expected until now. In fact in these models, competition has a stabilizing role in ecosystem dynamics, contrarily to cooperation that decreases the ecosystem resilience.
During my Ph.D. I have used a physicists approach based on complex networks and statistical physics, to study the resilience in Socio-Ecological systems, how it is related to the system complexity and what is the role of cooperation in the ecosystem dynamics. I have used a comprehensive approach that includes data mining, theoretical modeling (both computational and analytical) and statistical analyses. In particular, I have investigated the efficiency of a recently proposed framework to study the resilience of complex interacting systems, what the role of cooperation and competition in the universal patterns theoretically predicted by the model, and its validation with data. I have then focused on the long-standing open question of the relation between complexity and resilience in ecosystems, by specifically focusing on how the architecture of interaction networks may confer to living systems their ability to promptly react to to perturbations (e.g. increase resilience). To do that we have developed a stochastic population dynamics model, generalizing an interacting non-equilibrium model known as the voter model, and I have also studied the effect of cooperation on the ecosystem resilience. The results of my work suggest a novel picture on the relation between complexity, cooperation and resilience, challenging previous results in the literature
The role of environmental factors in the spatial distribution of Japanese encephalitis in mainland China
No full textAbstract not availableLiya Wang, Wenbiao Hu, Ricardo J. Soares Magalhaes, Peng Bi, Fan Ding, Hailong Sun, Shenlong Li, Wenwu Yin, Lan Wei, Qiyong Liu, Ubydul Haque, Yansong Sun, Liuyu Huang, Shilu Tong, Archie C.A. Clements, Wenyi Zhang, Chengyi L
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A data driven network approach to rank countries production diversity and food specialization
No full textThe easy access to large data sets has allowed for leveraging methodology in network physics and complexity science to disentangle patterns and processes directly from the data, leading to key insights in the behavior of systems. Here we use country specific food production data to study binary and weighted topological properties of the bipartite country-food production matrix. This country-food production matrix can be: 1) transformed into overlap matrices which embed information regarding shared production of products among countries, and or shared countries for individual products, 2) identify subsets of countries which produce similar commodities or subsets of commodities shared by a given country allowing for visualization of correlations in large networks, and 3) used to rank country fitness (the ability to produce a diverse array of products weighted on the type of food commodities) and food specialization (quantified on the number of countries producing a specific food product weighted on their fitness). Our results show that, on average, countries with high fitness produce both low and high specializion food commodities, whereas nations with low fitness tend to produce a small basket of diverse food products, typically comprised of low specializion food commodities
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