The Levi-Civita spacetime as a limiting case of the Gamma spacetime

It is shown that the Levi-Civita metric can be obtained from a family of the Weyl metric, the Gamma metric, by taking the limit when the length of its Newtonian image source tends to infinity. In this process a relationship appears between two fundamental parameters of both metrics.Comment: LaTeX2e 17 page

Functionalization of CNTS with maleic anhydride

The outstanding properties of carbon nanotubes (CNTs) [1] are mainly related with their unique structural features. However, the high π-π staking between the tubes is a major drawback for their manipulation and interaction with other materials. Chemical functionalization has been used as a convenient tool to improve their performance in various applications [2]. The work reports the functionalization of multi-wall carbon nanotubes (MWCNTs) with maleic anhydride via a Diels-Alder addition reaction, performed in dimethyl sulfoxide (190 ºC) or 2-chorotoluene (150 ºC) for 24 hours. The product was characterized by thermogravimetric analysis (TGA) and the weight loss at 800 ºC was 11.9 and 3.7 % respectively. Potentiometric titration suggests that CNTs modified at 190 ºC remain predominantly in the anhydride form, while for CNTs modified at 150 ºC, the extent of hydrolysis is approximately 40 %. Maleic anhydride was also reacted with a model compound (anthracene) in dimethyl sulfoxide (190 ºC) and the hydrolysis of the product (0.025 mmol in 650 µL of DMSO-d6) was followed by 1H RMN upon addition of 0.166 mmol of DCl (40 % weight in D2O) (graphic in figure). The anhydride 1 was easily regenerated from the dicarboxylic acid 2 when this compound was heated at 185 ºC for 10 minutes. A similar behavior is expected for the modified CNTs.Fundação para a Ciência e Tecnologi

HEI teaching mobility: looking for dynamics in a seven-year period

Higher Education Institutions are currently embracing mobility as an imperative goal, particularly and most impressively in the European Union countries where programs such as Erasmus+ strongly encourage students and staff to participate. This exploratory research aims to characterize teaching mobility in one university, identify facilitators, determine outcomes of repeated mobility, and provide clues on mobility dynamics over time. Qualitative and quantitative data were collected from application forms and final reports submitted by 107 outgoing and 58 incoming teachers in one university between 2009 and 2016. It was observed that teaching mobility covers diversified profiles (e.g., gender, seniority, and fields of study). 23 out of 71 outgoing teachers participated in more than one mobility program during that period. A deeper analysis on the mobility champions reveals both individual and team initiatives. The results provide some interesting data on facilitators and consequences of teaching mobility.publishe

Insights into the expectations of mobility students: the impact of Erasmus in their future professional careers

[EN] At the celebration of its 30th anniversary, Erasmus is recognised as the most successful exchange program ever implemented. The prospects of attaining a common European consciousness challenged the program's ability to blend together knowledge, attitudes and skills in a winning combination. It is no longer sufficient to communicate and integrate: mobility should actively foster skills to support students's professional career at national and international levels. Although literature on mobility is vast and interesting, studies on the impact of the mobility experience in the students' future employability profile rarely provide first-hand data on their expectations in this regard. This exploratory research comprises a qualitative focus group approach with Erasmus students during their exchange period in a Portuguese university and collected some insightful data on how students consider their mobility in terms of new learning outcomes, the professional value of the experience and the development of new skills. Results indicate that students seem to be quite aware of the positive implications of mobility in their professional careers and of the set of skills developed during that period. Overall, this article contributes to demonstrating the importance of assessing skills development during Erasmus mobility experiences. Managerial implications and suggestions for future research are provided.This work is financially supported by National Funds through FCT – Fundação para a Ciência e a Tecnologia, I.P., under the project UID/CED/00194/2013.Simões, D.; Pinheiro, MM.; Santos, C.; Filipe, S.; Barbosa, B.; Dias, GP. (2017). Insights into the expectations of mobility students: the impact of Erasmus in their future professional careers. En Proceedings of the 3rd International Conference on Higher Education Advances. Editorial Universitat Politècnica de València. 696-704. https://doi.org/10.4995/HEAD17.2017.536069670

Between promises and pitfalls: the impact of mobility on the internationalization of higher education

The study presented in this article aims at understanding the relevance of mobility initiatives to the internationalization efforts of Higher Education Institutions (HEIs). By building upon relevant literature, 17 propositions related to this contribution were identified. Empirical evidence from a concrete case of a European university was then used to evaluate those propositions. Data was collected from individual interviews to 19 outgoing faculty and from focus groups with 32 incoming students, resulting in the identification of the promises and pitfalls of mobility. The study concludes that HEIs must define clear strategies and carefully manage their mobility activities to maximize the potential benefits for internationalization. Based on this main implication, it presents a set of managerial recommendations that may be relevant for those involved in administering or promoting international mobility programmes at universities, governments or international organizations, and for researchers in higher education.publishe

Comportamento voltamétrico de perilenos bismides modificados em GCE e SPE

Uma das necessidades mais emergentes no planeta é a deteção e quantificação de diversos analitos prejudiciais aos seres vivos, presentes no meio ambiente, de uma forma rápida, com baixo custo e com elevada seletividade. Os screen printed electrodes (SPE) têm sido usados extensivamente como transdutores de sensores químicos para vários analitos importantes. A modificação da superfície dos SPEs com moléculas capazes de fazer o reconhecimento de diversos analitos traduz-se no aumento da seletividade do elétrodo, devido às interações entre as duas espécies [1]. Entre as técnicas de imobilização (covalente e não covalente) de moléculas na superfície dos SPE, destacamos a modificação não covalente, visto este ser um método rápido, com elevada reprodutibilidade, de baixo custo, e sem a necessidade de reações violentas para a superfície do sensor para formar a ligação covalente. A utilização de moléculas com estruturas capazes de formar ligações π com nanoestruturas de carbono [2] é uma vantagem, pois permite a adsorção de espécies que irão fazer o reconhecimento de analitos sem danificar a superfície da matriz principal mantendo assim as excelentes características das nanoestruras de carbono, como os nanotubos de carbono e as folhas de grafeno. (...

On the Levi-Civita solutions with cosmological constant

The main properties of the Levi-Civita solutions with the cosmological constant are studied. In particular, it is found that some of the solutions need to be extended beyond certain hypersurfaces in order to have geodesically complete spacetimes. Some extensions are considered and found to give rise to black hole structure but with plane symmetry. All the spacetimes that are not geodesically complete are Petrov type D, while in general the spacetimes are Petrov type I.Comment: Typed in Revtex, including two figures. To appear in Phys. Rev.

Non-covalent modification of voltammetric SPE sensors

Screen printed electrodes (SPE) are highly attractive as transducers of chemical sensors for the screening of a number of important analytes. The surface modification of these electrodes is easily carried out in order to achieve higher sensitivity. Carbon nanostructures have been extensively used for this purpose, as the number of active sites can be greatly increased. On the other hand, the immobilization of adequate functional groups is usually carried out to increase sensors selectivity through specific interactions between the immobilised chemical moieties and the analyte of interest. Among the techniques used to functionalize electrodes surface, non-covalent modification offer advantages related to the simplicity of the process and the reproducibility of the sensor operation. Recently a dopamine sensor based a perylene tetracarboxylic acid functionalized graphene sheets was developed [1]. In this work, voltammetric response of SPEs modified with CNTs functionalized by noncovalent bond using perylene modified using amino acids such as L-Tryptophan, L-Tyrosine and L-Cysteine is presented. The effect of the concentration ratio of CNT and perylene modified is studied analysing the response of model compounds, such as ascorbic acid and hydroquinone. The performance of these sensors is characterized regarding their catalytic activity

Simple strategies for stable aqueous suspensions of carbon nanotubes

Carbon nanotubes (CNT) are attractive nanoparticles for biological applications due to their broad absorption of light in the UV-Vis-NIR, NIR photoluminescence, unique Raman signature, photothermal response, and large surface area for the covalent and non-covalent conjugation of contrast agents and drugs, DNA/RNA. However, pristine CNT are highly hydrophobic and not biocompatible, requiring functionalization with hydrophilic molecules in order to form stable aqueous suspensions. Here, simple functionalization methods of perylene bisimides and pyrene, to render these polyaromatic molecules amphiphilic, will be presented. Bolaamphiphilic perylene bisimides (PBI) were prepared by the reaction of perylenetetracarboxylic dianhydride with -amino acids in good yield, using a simple protocol and avoiding complex purification methods. [1] Pyrene was modified by nitration followed by amination, and further reacted with maleic anhydride yielding carboxylic acid-functionalized pyrene. The CNT aqueous suspensions were studied by absorption and emission spectroscopy. Theoretical calculations were used to support the experimental observations. The possibility of CNT double functionalization (covalent and non-covalent) will be discussed based on CNT solubility studies in surfactant aqueous solutions. Pristine and covalently functionalized CNT, at different functionalization yields, were compared. The CNT were functionalized by the 1,3-dipolar cycloaddition of azomethine ylides. [2] The ability of CNT to adsorb surfactant molecules was reduced by the covalent functionalization. Nevertheless, depending on the extent of covalent functionalization, a high concentration of CNT in water could be attained, in comparison to that of pristine CNT.Fundação para a Ciência e a Tecnologia (FCT

Formation of graphene nanoribbons in solution

Recently, the formation of graphene by exfoliation of carbon nanotubes (CNT) has shown increasing interest. This process originates graphene nanoribbons (GNR) that are expected to present excellent electrical properties, depending on their width and on their edge shape [1]. Several methods for the unzipping of graphene from CNT were proposed along the past few years [2-6]. These methods often present some limitation, such as low yield of GNR, or extensively oxidized GNR without electrical conductivity. Recently, the formation of GNR was observed “in situ” by unzipping of carbon nanotubes under ultra-high vacuum scanning tunneling microscopy (UHV STM) [7]. The CNT under observation were functionalized by the 1,3-dipolar cycloaddition reaction [8]. This particular functionalization route seems to be responsible for the unzipping of the CNT under STM imaging conditions. The present work demonstrates the formation of GNR in solution by unzipping of functionalized CNT, in different solvents. The GNR thus formed were analyzed by UV-vis and Raman spectroscopy, and by transmission electron spectroscopy. GNR bundles were deposited from an ethanol solution and observed by TEM.Institute for Nanostructures, Nanomodelling and Nanofabrication (I3N