Invariant solutions to the Strominger system and the heterotic equations of motion

We construct many new invariant solutions to the Strominger system with respect to a 2-parameter family of metric connections $\nabla^{\varepsilon,\rho}$ in the anomaly cancellation equation. The ansatz $\nabla^{\varepsilon,\rho}$ is a natural extension of the canonical 1-parameter family of Hermitian connections found by Gauduchon, as one recovers the Chern connection $\nabla^{c}$ for $({\varepsilon,\rho})=(0,\frac12)$, and the Bismut connection $\nabla^{+}$ for $({\varepsilon,\rho})=(\frac12,0)$. In particular, explicit invariant solutions to the Strominger system with respect to the Chern connection, with non-flat instanton and positive $\alpha'$ are obtained. Furthermore, we give invariant solutions to the heterotic equations of motion with respect to the Bismut connection. Our solutions live on three different compact non-K\"ahler homogeneous spaces, obtained as the quotient by a lattice of maximal rank of a nilpotent Lie group, the semisimple group SL(2,$\mathbb{C}$) and a solvable Lie group. To our knowledge, these are the only known invariant solutions to the heterotic equations of motion, and we conjecture that there is no other such homogeneous space admitting an invariant solution to the heterotic equations of motion with respect to a connection in the ansatz $\nabla^{\varepsilon,\rho}$.Comment: 27 pages, 3 figure

The ascending central series of nilpotent Lie algebras with complex structure

We obtain several restrictions on the terms of the ascending central series of a nilpotent Lie algebra $\mathfrak g$ under the presence of a complex structure $J$. In particular, we find a bound for the dimension of the center of $\mathfrak g$ when it does not contain any non-trivial $J$-invariant ideal. Thanks to these results, we provide a structural theorem describing the ascending central series of 8-dimensional nilpotent Lie algebras $\mathfrak g$ admitting this particular type of complex structures $J$. Since our method is constructive, it allows us to describe the complex structure equations that parametrize all such pairs $(\mathfrak g, J)$.Comment: 28 pages, 1 figure. To appear in Trans. Amer. Math. So

Influencia de las diferentes alturas de tacón en la marcha. Estudio goniométrico

En este estudio se ha pretendido analizar las variaciones goniométricas en las articulaciones de la cadera, rodilla y tobillo, caminando descalzo y con tacón de 2 y 4 centímetros de altura, en dos grupos de mujeres sin patología y con edades comprendidas entre los 20 y 24 años: el primero acostumbradas a caminar con zapato de tacón alto (9 casos) y el segundo acostumbrado a caminar con calzado plano (21 casos). Para ello se ha utilizado un sistema telemétrico de medida: «Sistema Telemétrico Biológico de MIE Medical Rechearch LTD». Se ha comprobado que existen diferencias importantes en la forma individual de llevar zapato de tacón alto, que varían con la experiencia. La máxima flexión de cadera, que se produce en la fase de oscilación, disminuye conforme aumenta la altura del tacón en las personas acostumbradas al mismo, mientras que aumenta en las no acostumbradas. La extensión máxima de la rodilla disminuye conforme aumenta el tacón en todas las personas estudiadas, es decir, tanto si tienen experiencia como si no la tienen, mientras que la flexión máxima se mantiene. A nivel del tobillo, la adaptación al tacón se produce de forma muy dispar aunque llama la atención la exageración de la flexión del mismo, en las personas acostumbradas a llevar tacón, cuando caminan descalzas

On the real homotopy type of generalized complex nilmanifolds

We prove that for any n = 4, there are infinitely many real homotopy types of 2n-dimensional nilmanifolds admitting generalized complex structures of every type k, for 0 = k = n

Cytotoxic gold(I) complexes with amidophosphine ligands containing thiophene moieties

A new phosphine ligand bearing a thiophene moiety, C 4 H 3 SNHCOCH 2 CH 2 PPh 2 (L), has been prepared by reaction of the aminophosphine Ph 2 PCH 2 CH 2 NH 2 with thiophenecarbonylchloride in the presence of triethylamine. The coordination behavior towards gold(I), gold(III) and silver(I) species has been studied and several metal compounds of different stoichiometry have been achieved, such as [AuL 2 ]OTf, [AuXL] (X = Cl, C 6 F 5 ), [Au(C 6 F 5 ) 3 L], [AgL 2 ]OTf or [Ag(OTf)L]. Additionally, the reactivity of the chloride gold(I) species with biologically relevant thiolates was explored, thus obtaining the neutral thiolate compounds [AuL(SR)] (SR = 2-thiocitosine, 2-thiolpyridine, 2-thiouracil, 2-thionicotinic acid, 2, 3, 4, 6-tetra-6-acetyl-1-thiol-ß-D-glucopyranosato or thiopurine). The antitumor activity of the compounds was measured by the MTT method in several cancer cells and the complexes exhibit excellent cytotoxic activity

Are orchid bees useful indicators of the impacts of human disturbance?

Biodiversity and ecosystem functions are threatened by human disturbance, and tropical forests are one the most vulnerable habitats. Monitoring the impacts of disturbance and the success of conservation projects is crucial, and to do this effectively it is important to identify suitable measures that are sensitive to ecosystem disturbance. Orchid bees (Euglossini) are a specialist group with mutualistic relationships with many plant species and can fly long distances, making them important pollinators of widely dispersed plant species. A loss of specialist pollinators such as these could have severe consequences for the plants that rely on their services. We therefore aimed to answer the following question: are orchid bees useful indicators of the impacts of human disturbance? If so, what measures of orchid bee diversity are most sensitive? And do orchid bees provide any indication of changes in pollination services along a disturbance gradient? Orchid bees were collected from 18 sites across a gradient of disturbance in a tropical forest region in southeast Peru. Alpha diversity across the gradient was compared using Hills numbers. Beta diversity was assessed using community composition, species contributions to beta diversity, beta diversity partitioning and novel measures of redundancy and representativeness. The potential pollination services available at each site were measured using artificial flowers and counts of pollinator visits. Alpha diversity of orchid bees showed low sensitivity to disturbance. Beta diversity measures were more informative, with disturbed sites found to be highly redundant in the ecosystem compared to the less disturbed sites. However, the most sensitive measure across the gradient was abundance – there was a significant decrease in the number of bees caught as disturbance increased, with likely consequences for pollination services. These results suggest that orchid bees may be useful indicators of the impacts of human disturbance, but alpha diversity is a poor metric for this purpose. In order to understand how human disturbance is affecting biodiversity, multiple diversity indices should be considered, and in the case of orchid bees, redundancy and abundance could be useful for detecting sensitive responses to forest disturbance. © 2019 Elsevier Lt

Twisted One-Dimensional Charge Transfer and Related Y-Shaped Chromophores with a 4 H-Pyranylidene Donor: Synthesis and Optical Properties

Three series of push-pull derivatives bearing 4H-pyranylidene as electron donor group and a variety of acceptors were designed. On one hand, one-dimensional chromophores with a thiophene ring (series 1H) or 5-dimethylaminothiophene moiety (series 1N) as an auxiliary donor, non-coplanar with the p-conjugated system, were synthesized. On the other hand, related two-dimensional (2D) Y-shaped chromophores (series 2) were also prepared to compare how the diverse architectures affect the electrochemical, linear, and second-order nonlinear optical (NLO) properties. The presence of the 5-dimethylaminothiophene moiety in the exocyclic C= C bond of the pyranylidene unit gives rise to oxidation potentials rarely low, and the protonation (with an excess of trifluoroacetic acid) of its derivatives results in the apparition of a new blue-shifted band in the UV-visible spectra. The analysis of the properties of derivatives with and without the additional thiophene ring shows that this auxiliary donor leads to a higher NLO response, accompanied by an enhanced transparency. Y-shaped chromophores of series 2 present a blue-shifted absorption, higher molar extinction coefficients, and higher Eox values compared to their linear twisted counterparts. As concerns NLO properties, 2D Y-shaped architecture gives rise to somewhat lower µß values (except for thiobarbiturate derivatives)

Modelling TiO2 photoanodes for PEC water splitting: Decoupling the influence of intrinsic material properties and film thickness

Semiconductor metal oxides are intensively studied in electrodes for photoelectrochemical (PEC) water splitting. On a series of nanoparticulate TiO2 photoanodes, we analyze specific fabrication variables by means of data fitting. First, the experimental outcome is gathered using PEC characterization techniques, mostly cyclic voltammetry and transient photocurrent measurements. Subsequently, we apply models to gain insights into the involved charge trapping and transfer phenomena. We find that capacitance coefficients and the switch-on transient kinetics depend on the TiO2 layer thickness, respectively indicating surface mechanisms and stationary regimes that are mediated by light accessibility. On the contrary, exponential factors of capacitance are independent of thickness, but reflect changes in the density of electron states with different sintering atmospheres. Also, the transfer resistance in the electrolyte side is indirectly influenced by sintering. Through meticulous quantitative analysis of trends, we stablish simple mathematical relationships that connect thickness-dependent parameters. This knowledge delves into fundamental mechanisms governing the TiO2 photoelectrode behaviour, and aims to facilitate further improvements in the efficiency of materials and electrodes for green hydrogen production

Alicante Coastal Management for Sustainable Development

Human intervention on the coast has been intense, due to the source of wealth that the coastal areas represent, especially in the form of tourism, which has resulted in a rapid erosion of its beaches. This paper discusses the current state of beach management in the various competent public administrations on the Costa Blanca (SE Spanish-Mediterranean), in relation to urban development and regression on the waterfront. To this end, an analysis has been carried out of the responses to a survey of those responsible for managing each of the 19 coastal municipalities of the Alicante coast, covering 244 km of coastline, 91 beaches and their personnel. Also, an investigation has been conducted as to whether this management’s aim is to protect the coastline and maintain the flora and fauna or just to manage recreation as the main economic activity is tourism. The analysis shows that the beach is simply regarded as a product or service offered to the user thereof. However, local authorities have not detected problems, possibly for two reasons: they do not have sufficient knowledge and this is understandable, given their lack of responsibilities in this area. This causes many beaches to have a high occupancy rate and there is a shift of users towards natural beaches. The study gives us information about the complex administrative process in the coastal system that often proves ineffective on this narrow strip of land