What determines the mobility of charge carriers in conjugated polymers?

In a conjugated polymer, the mobility of charge carriers is not a well-defined coefficient of a particular material as it is in an inorganic crystalline semiconductor but depends on the time domain of detection. On a time-scale of typically 100 fs, the on-chain mobility is ultra-high and controlled by the electronic band width of the polymer chain. When a carrier hits a chain imperfection, subsequent mesoscopic on-chain motion is retarded and controlled by intrachain disorder to which the chain environment contributes. Macroscopic transport commences after a time when interchain carrier jumps become rate limiting. It is routinely probed by time-of-flight experiments and can be rationalized in terms of random walk within a rough energy landscape. Experimental signatures of the various modes of transport are discussed.     

Modifying the surface charge of single track-etched conical nanopores in polyimide

Chemical modification of nanopore surfaces is of great interest as it means that the surface composition is no longer fixed by the choice of substrate material, even to the point where large biomolecules can be attached to the pore walls. Controlling nanopore transport characteristics is one important application of surface modification which is very relevant given the significant interest in sensors based on the transport of ions and molecules through nanopores. Reported here is a method to change the surface charge polarity of single track-etched conical nanopores in polyimide, which also has the potential to attach more complex molecules to the carboxyl groups on the nanopore walls. These carboxyl groups were converted into terminal amino groups, first by activation with N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) followed by the covalent coupling of ethylenediamine. This results in a changed surface charge polarity. Regeneration of a carboxyl-terminated surface was also possible, by reaction of the amino groups with succinic anhydride. The success of these reactions was confirmed by measurements of the pore's pH sensitive current-voltage (I-V) characteristics before and after the chemical modification, which depend on surface charge. The?permselectivity of the pores also changed accordingly with the modification.     

Investigation of charge and current dynamics in PVA–KOH gel electrolyte-based supercapacitor

Journal of Materials Science: Materials in Electronics - Poly-vinyl alcohol (PVA)-based electrolytes can play a vital role in the development of supercapacitors by providing a desirable charge...     

Theoretical aspects of charge correlations in θ-(BEDT-TTF)2X

Abstract

A review is given on the theoretical studies of charge correlations in θ-(BEDT-TTF)₂X. Various studies show that within a purely electronic model on the θ-type lattice with on-site U and nearest neighbor V_p and V_c interactions, the diagonal stripe, c-axis three-fold, and the vertical stripe charge correlations are favored in the regime V_p<V_c, V_p～V_c, and V_p>V_c, respectively. In the realistic parameter regime of V_p～V_c, there is competition between the c-axis three fold state and diagonal stripe state. Since these are different from the experimentally observed a-axis three fold and the horizontal stripe charge correlations, additional effects have to be included in order to understand the experiments. The electron–lattice coupling, which tends to distort the lattice into the θ_d-type, is found to favor the horizontal stripe state, suggesting that the occurrence of this stripe ordering in the actual materials may not be of purely electronic origin. On the other hand, distant electron–electron interactions have to be considered in order to understand the a-axis three fold correlation, whose wave vector is close to the nesting vector of the Fermi surface. These studies seem to suggest that the minimal model to understand the charge correlation in θ-(BEDT-TTF)₂X may be more complicated than expected. Future problems regarding the competition between different types of charge correlations are discussed.     

The increasing dominance of science in the economy: Which nations are successful?

Scientometrics - We analyzed breakthrough patents that serve as the basis of emerging technological trajectories and paradigm over 25-years. The results showed that although technological fields...     

Aqua regia extracted metals in sediments from the industrial area and surroundings of Pančevo, Serbia

Surface and buried sediments were analyzed for Ba, Ca, Cd, Co, Cr, Cu, Mn, Ni, Pb, Zn and V, as well as for total carbon and hydrogen to assess the distribution of sediment pollution due to the vicinity of the petrochemical complex. The samples, collected from 20 locations within the petrochemical complex and from 16 locations outside the complex, were aqua regia extracted and analyzed by ICP/OES. Metals were determined with an acceptable accuracy for certified metals of 82-113%. The precision for the aqua regia extraction was satisfactory, less than 20%, except for Cd where it was 28%. Comparison of the data from the petrochemical with those from the non-petrochemical areas showed different distributions of the metals. Metals that exceeded the baseline range; Ba, Cd, Cu, Zn and Pb, were detected in higher concentrations in sediments that were under the influence of the chlor-alkali plant within the petrochemical complex. Comparison with data from the petrochemical complex and its surroundings and their distribution demonstrated that the metal compositions of the sediments were modified by anthropogenic activities.     

An EU without the UK: mapping the UK’s changing roles in the EU scientific research

In science, technology and innovation, the consequences of Britain’s exit (Brexit) for both Britain and the Europe Union (EU) are still uncertain. However, there is no doubt that in the years to come, the UK will need to re-calibrate its scientific collaborations with other EU countries. In this research, we aim to identify which EU countries would suffer the greatest loss and which research fields would be most affected by Brexit. Based on the scientific output of each EU country, as indexed by the Web of Science, we demonstrate that international scientific collaboration frequently involves the UK. We also define four types of roles according to the UK’s performance in production and collaboration; these roles are of great significance to our understanding of the status of the UK in the EU. In this sense, the UK acted as a leader in health sciences, a pioneer in social sciences, an assistant in physical sciences, and a participant in engineering.     

Status of India in science and technology as reflected in its publication output in the Scopus international database, 1996–2006

This paper seeks to provide current indicators on Indian science and technology for measuring the country’s progress in research. The study uses for the purpose 11 years publications data on India and top 20 productive countries as drawn from the Scopus database for the period 1996 to 2006. The study examines country performance on several measures including country publication share in the world research output, country publication share in various subjects in the national context and in the global context, patterns of research communication in core Indian domestic and international journals, geographical distribution of publications, share of international collaborative papers at the national level as well as across subjects and characteristics of high productivity institutions, scientists and cited papers. The paper also compares the similarity of Indian research profile with top 20 productive countries. The findings of the study should be of special significance to the planners & policy-makers as they have implications for the long term S&T planning of the country.     

Effect of doping- and field-induced charge carrier density on the electron transport in nanocrystalline ZnO

The charge transport properties of thin films of sol-gel processed undoped and Al-doped zinc oxide nanoparticles with variable doping level between 0.8 and 10?at.% were investigated. The x-ray diffraction studies revealed a decrease of the average crystallite sizes in highly doped samples. We provide estimates of the conductivity and the resulting charge carrier densities with respect to the doping level. The increase of charge carrier density due to extrinsic doping was compared to the accumulation of charge carriers in field effect transistor structures. This allowed us to assess the scattering effects due to extrinsic doping on the electron mobility. The latter decreases from 4.6 × 10(-3) to 4.5 × 10(-4)?cm(2)?V(-1)?s(-1) with increasing doping density. In contrast, the accumulation leads to an increasing mobility up to 1.5 × 10(-2)?cm(2)?V(-1)?s(-1). The potential barrier heights related to grain boundaries between the crystallites were derived from temperature dependent mobility measurements. The extrinsic doping initially leads to a grain boundary barrier height lowering, followed by an increase due to doping-induced structural defects. We conclude that the conductivity of sol-gel processed nanocrystalline ZnO:Al is governed by an interplay of the enhanced charge carrier density and the doping-induced charge carrier scattering effects, achieving a maximum at 0.8?at.% in our case.     

Uncertainty in macroeconomic policy-making: art or science?

Uncertainty is pervasive in economic policy-making. Modern economies share similarities with other complex systems in their unpredictability. But economic systems also differ from those in the natural sciences because outcomes are affected by the state of beliefs of the systems' participants. The dynamics of beliefs and how they interact with economic outcomes can be rich and unpredictable. This paper relates these ideas to the recent crisis, which has reminded us that we need a financial system that is resilient in the face of the unpredictable and extreme. It also highlights how such uncertainty puts a premium on sound communication strategies by policy-makers. This creates challenges in informing others about the uncertainties in the economy, and how policy is set in the face of those uncertainties. We show how the Bank of England tries to deal with some of these challenges in its communications about monetary policy.     

Introduction—Up,down, round and round: Verticalities in the history of science

History of science's spatial turn has focused on the horizontal dimension, leaving the role of the vertical mostly unexplored as both a condition and object of scientific knowledge production. This special issue seeks to contribute to a burgeoning discussion on the role of verticality in modern sciences, building upon a wider interdisciplinary debate about the importance of the vertical and the volumetric in the making of modern lifeworlds. In this essay and in the contributions that follow, verticality appears as a condition of knowledge production—a set of movements and mobilities, technical challenges, political negotiations, and bodily hardships—and an object of scientific inquiry, requiring new techniques of mapping and visualisation and generative of new insights into physical processes and temporal change. By foregrounding the vertical, historians of science can gain new insights and tell new stories about how science is done in the field, the observatory, and the laboratory, and about how those sciences have helped build a modern, three-dimensional world.     

Does faculty disciplinary background play a role in the publication pattern of an interdisciplinary research area? The case of science education in Brazil

Scientometrics - Research in the Social Sciences and Humanities is published in a variety of formats and types of documents. Local journals are relevant for these fields, particularly in...     

Is the United States losing ground in science? A global perspective on the world science system

Based on the Science Citation Index-Expanded web-version, the USA is still by far the strongest nation in terms of scientific performance. Its relative decline in percentage share of publications is largely due to the emergence of China and other Asian nations. In 2006, China has become the second largest nation in terms of the number of publications within this database. In terms of citations, the competitive advantage of the American “domestic market” is diminished, while the European Union (EU) is profiting more from the enlargement of the database over time than the USA. However, the USA is still outperforming all other countries in terms of highly cited papers and citation/publication ratios, and it is more successful than the EU in coordinating its research efforts in strategic priority areas like nanotechnology. In this field, the People’s Republic of China (PRC) has become second largest nation in both numbers of papers published and citations behind the USA.     

Influence of the international collaboration in the field of metric studies of science and technology: the case of Mexico (1971–2018)

Scientometrics - We perform a bibliometric analysis of the research production and impact of Mexican scholars involved in the area of metric studies of science and technology in the period...     

Crystal design of organic pigments — a prototype discipline of materials science

The significance of crystal properties for the product performance of organic pigments has always required special efforts to analyze, to control and to design these materials. In this article recent developments and the modern scientific facets of pigments research (e.g. crystal structure prediction and polymorphism, electronic structures of molecular crystals, and crystal morphology determination) will be discussed. The broad interest in these topics is shared with many other areas of scientific and industrial research on molecular solids.     

Relationship among research collaboration, number of documents and number of citations: a case study in Spanish computer science production in 2000–2009

This paper analyzes the relationship among research collaboration, number of documents and number of citations of computer science research activity. It analyzes the number of documents and citations and how they vary by number of authors. They are also analyzed (according to author set cardinality) under different circumstances, that is, when documents are written in different types of collaboration, when documents are published in different document types, when documents are published in different computer science subdisciplines, and, finally, when documents are published by journals with different impact factor quartiles. To investigate the above relationships, this paper analyzes the publications listed in the Web of Science and produced by active Spanish university professors between 2000 and 2009, working in the computer science field. Analyzing all documents, we show that the highest percentage of documents are published by three authors, whereas single-authored documents account for the lowest percentage. By number of citations, there is no positive association between the author cardinality and citation impact. Statistical tests show that documents written by two authors receive more citations per document and year than documents published by more authors. In contrast, results do not show statistically significant differences between documents published by two authors and one author. The research findings suggest that international collaboration results on average in publications with higher citation rates than national and institutional collaborations. We also find differences regarding citation rates between journals and conferences, across different computer science subdisciplines and journal quartiles as expected. Finally, our impression is that the collaborative level (number of authors per document) will increase in the coming years, and documents published by three or four authors will be the trend in computer science literature.     

The state of science and technology in Africa (2000–2004): A scientometric assessment

This article reports for first time the state of science and technology in the African Continent on the basis of two scientometric indicators — number of research publications and number of patents awarded. Our analysis shows that Africa produced 68,945 publications over the 2000–2004 period or 1.8% of the World’s publications. In comparison India produced 2.4% and Latin America 3.5% of the World’s research. More detailed analysis reveals that research in Africa is concentrated in just two countries — South Africa and Egypt. These two counties produce just above 50% of the Continent’s publications and the top eight countries produce above 80% of the Continent’s research. Disciplinary analysis reveals that few African countries have the minimum number of scientists required for the functioning of a scientific discipline. Examination of the Continent’s inventive profile, as manifested in patents, indicates that Africa produces less than one thousand of the world’s inventions. Furthermore 88% of the Continent’s inventive activity is concentrated in South Africa. The article recommends that the African Governments should pay particular attention in developing their national research systems.     

When disasters strike environmental science: a case–control study of changes in scientific collaboration networks

Scientometrics - Studies of scientific collaboration networks reveal the social structure of scientific disciplines. Most of these studies assume scientists work under conditions of institutional...