Cryptocurrency Mining Games with Economic Discount and Decreasing Rewards

In the consensus protocols used in most cryptocurrencies, participants called miners must find valid blocks of transactions and append them to a shared tree-like data structure. Ideally, the rules of the protocol should ensure that miners maximize their gains if they follow a default strategy, which consists on appending blocks only to the longest branch of the tree, called the blockchain. Our goal is to understand under which circumstances are miners encouraged to follow the default strategy. Unfortunately, most of the existing models work with simplified payoff functions, without considering the possibility that rewards decrease over time because of the game rules (like in Bitcoin), nor integrating the fact that a miner naturally prefers to be paid earlier than later (the economic concept of discount). In order to integrate these factors, we consider a more general model where issues such as economic discount and decreasing rewards can be set as parameters of an infinite stochastic game. In this model, we study the limit situation in which a miner does not receive a full reward for a block if it stops being in the blockchain. We show that if rewards are not decreasing, then miners do not have incentives to create new branches, no matter how high their computational power is. On the other hand, when working with decreasing rewards similar to those in Bitcoin, we show that miners have an incentive to create such branches. Nevertheless, this incentive only occurs when a miner controls a proportion of the computational power which is close to half of the computational power of the entire network

An MS-CASPT2 Study of the Photodecomposition of 4- Methoxyphenyl Azide. Role of Internal Conversion and Intersystem Crossing

Aryl azides photochemistry is strongly dependent on the substituent relative position, as has been studied by time resolved resonant Raman (TR3) spectroscopy for 4-methoxyphenyl azide and its isomer 3-methoxyphenyl azide. When irradiated at 266 nm, the former results in 4,4’-dimethoxyazobenzene whereas the latter forms 1,2-didehydroazepine. It is proposed that the key step of the reactions is the formation of a nitrene derivative. Recently, it has been proposed by us that nitrenes might have a relevant role in the Surface-Enhanced Raman Scattering (SERS) of p-aminothiophenol, however, the molecular mechanism is not well known in neither of these cases. Therefore, we studied the photodecomposition of 4-methoxyphenyl azide using multiconfigurational self-consistent field methods (MC-SCF) with the CAS-SCF and MS-CASPT2 approximations and calculated the resonant Raman spectra of the relevant species using a multi-state version of Albrecht’s vibronic theory. The results propose that the reaction follows a two steps sequence after irradiation at 266 nm: an intersystem crossing 21A’/23A’’ which decays through a 21A’/21A’’ conical intersection producing molecular nitrogen and triplet 4-methoxyphenyl nitrene in its ground state.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Modeling the effect of the electrode potential in SERS by electronic structure calculations.

Surface Enhanced Raman Spectroscopy (SERS), due to the ability of greatly intensify the weak Raman signal of molecules adsorbed to metal surfaces, has proven to be a very useful tool to investigate changes in the electronic structure of metal-molecule surface complex. A deep knowledge of the electronic structure of these metal-molecule hybrid systems is key in electrochemistry, catalysis, plasmonics, molecular electronics, and in the development of selective and ultra-sensitive analytical sensors. The origin of this huge enhancement in SERS is due to two contributions: the electromagnetic (EM), related to surface plasmons, and the chemical mechanism, due to resonant charge transfer (CT) process between the adsorbate and the metal (CTSERS). Unfortunately, the SERS implies very complex phenomena where the molecule and the metal nanoparticle are involved. This fact makes challenging to build realistic theoretical models that take into account both the metal and the molecule at quantum level. We propose a methodology, based on DFT and ab initio electronic calculations, to simulate the effect of the electrode potential on the absorption, on the charge transfer states energies, and on the electronic excitations in metal-molecule hybrid systems from a microscopic point of view. This methodology consists on the prediction of Raman intensities from ab initio calculations of the geometries or the energy gradients at the excited states Franck-Condon point, bringing the possibility to predict the intensities in CTSERS as well as in resonance Raman without the need to know the excited state geometries, not always feasible to compute. The microscopic model adopted to mimic the effect of the interphase electric potential consist in a molecule adsorbed to a linear silver cluster [Agn-Adsorbate]q, were n is the number of silver atoms, and the total charge of the system (q) is zero for n=2 and q=±1 for n=1, 3 and 7.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

La concentración de empresas industriales en España

Tesis Univ. de Madrid. Dirigida por Rafael Martínez Cortina.Fac. de Ciencias Económicas y EmpresarialesTRUEProQuestpu

Local Government, Taxes, and Guns: Successful Policy Innovation in Three Colombian Cities

This paper evaluates transformative policy innovations with respect to security and taxation in the three main Colombian cities: Bogotá, Medellín, and Cali. In the first two, such policies were associated with huge success. Elsewhere we (Gutiérrez et al. 2009) have tagged these transformation processes as ‘urban/metropolitan miracles’. The term comes from the fact that both common citizens and pundits considered these to be extremely unlikely, that they were fast, and that they were large-scale. We argue, that the success of Bogotá and Medellín was the result of a set of institutional underpinnings basically related to the 1991 constitution; the opening of a window of opportunity for new political actors; and, as a result, the formation of a new government coalition and ‘governance formula’. Anti-particularism was a language related to political demands— linked organically with the pro-1991 constitution movement—which became effective .../urban security, state building, public policies

Monitorización de una excavación arqueológica usando fotogrametría y modelos digitales del terreno (MDT). El caso de estudio de Barranco León, Orce (Granada, España)

In this paper, we describe and discuss emergent digital technologies employed for monitoring the excavations at the archaeological site of Barranco León (Granada, Spain) between 2017 and 2020. The method entails the following material requirements: a total station, a conventional camera, a computer and a software that integrates photogrammetry algorithms; in terms of human resources, the presence of an engineer for the first day of the excavation to set up the methodological process and trained excavation staff to perform said method on a daily basis is necessary. Here we present the daily workflow for monitoring archaeological excavations introduced at the site, followed by an estimation of the costs and a summary of the results obtained. The method introduced here is based on the height difference of Digital Elevation Models (DEMs) computed on successive days using photogrammetric techniques. It is a non-invasive method, which requires less than 8% of the economic resources of the excavation and can be carried out in less than 15 minutes. This allows the excavation director to have an accurate and visual idea of the excavation process in order to make appropriate decisions. In addition, from the results obtained in the method (differences in DEM of every two days), other derived results can be obtained such as the exact location of the archaeological remains extracted based on their size. These features highlight the relevance and applicability of this approach to a wide range of archaeological sites.En este artículo, describimos y discutimos las tecnologías digitales emergentes utilizadas para la monitorización de las excavaciones del yacimiento arqueológico de Barranco León (Granada, España) entre las campañas de 2017 y 2020. El método implica el uso de los siguientes recursos materiales: una estación total, una cámara de fotos convencional, un ordenador y un programa que integre algoritmos de fotogrametría; referente a los recursos humanos, es necesaria la presencia de un ingeniero durante el primer día de la excavación para establecer el proceso metodológico y un excavador entrenado para llevar a cabo dicho método diariamente. Aquí, presentamos un flujo de trabajo diario para la monitorización de la excavación de un yacimiento arqueológico, seguido de una estimación de los costos y un resumen de los resultados obtenidos. El método presentado se basa en la diferencia de altura de los modelos digitales del terreno (MDT) calculados en sucesivos días utilizando técnicas fotogramétricas. Es un método no invasivo, que requiere menos del 8% del coste total de la excavación y se puede llevar a cabo en menos de 15 minutos. Esto permite que el director de la excavación tenga una visión precisa y una idea visual del proceso de excavación para tomar las decisiones adecuadas. Además, a partir de los resultados obtenidos en el método (diferencias en MDT de cada dos días), se pueden obtener otros resultados derivados como la ubicación exacta de los restos arqueológicos extraídos en función de su tamaño.Junta de Andalucia BC.03.032/17FEDER 2020 Operative Program Research Project A-HUM-016-UGR1

Surface-Enhanced Raman spectroscopy of thiobenzoic acid on metal nanoparticles

Molecules adsorbed on some metal surfaces such as silver, copper and gold, can exhibit enormous Surface-enhanced Raman Scattering (SERS). The SERS effect has historically been associated with substrate roughness on two characteristic length scales [1,2]. Surface roughness on the 10 to 100 nm length scale supports the electromagnetic resonances which are the dominant mechanism of enhancement. A second mechanism often thought to require atomic scale roughness, is referred to as the chemical enhancement mechanism. This second mechanism involves the creation of new electronic excited states which result from adsorbate–substrate chemical interactions. These two mechanisms operate simultaneously making it difficult to isolate the role and magnitude of each one. In this work the SERS spectra of thiobenzoic acid (TBA) adsorbed on several silver colloids are recorded by using different excitation wavelengths. Taking advantage of the fact that SERS spectroscopy is both, surface selective and highly sensitive, we have attempted to determine the molecular structure of the surface complex once TBA is adsorbed on the metal. The analysis of the vibrational wavenumbers of the Raman and SERS spectra suggests that this molecule shows unidentate coordination to the silver surface through the sulphur atom. In order to confirm this conclusion DFT calculations have been carried out for different TBA-silver complexes concluding that the unidentate coordination is the most likely interaction of TBA on the metal surface. Wavelength-scanned SERS excitation spectroscopy involves the measurement of SERS signal by using several excitation wavelengths and it was recognized as a useful tool for checking the mechanisms responsible for the SERS enhancement [3]. We have studied the effect of the wavelength within the SERS spectra of TBA on silver colloid prepared by different methods and we have analyzed the intensity of the 8a vibrational mode of TBA recorded at about 1590 cm-1. The intensity of this mode is noticeably higher in the spectrum recorded with the 514.5 nm line (Fig. 1). This result is attributed to the presence of a resonant Raman effect associated to a photoinduced charge-transfer process when using the most energetic excitation line. Finally, it is important to mention the high affinity of TBA for the silver surfaces what allows for a detection limit estimated to be 0.01 microM.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Raman, SERS and DFT study of chemically-adsorbed thiobenzoic acid on silver nanoparticles

Thiocarboxylic acids are organosulphur compounds with general formula RC(O)SH. They are related to carboxylic acids by the replacement of one oxygen by sulphur. Two tautomers are possible, written as RC(S)OH and RC(O)SH. The second one is the majority species in solid state and solution of thiobenzoic acid (TBA) at room temperature [1], but derivatives from both tautomers are known so that the SERS spectrum can be originated by either one. Taking advantage of the fact that SERS spectroscopy is both surface selective and highly sensitive we have attempted to determine the molecular structure of TBA once it is adsorbed on the metal surface. To accomplish this SERS spectra of TBA have been recorded on different silver colloids. A combination of layer-by-layer method with spin-coating deposition of silver nanoparticles have been used to prepare SERS active substrates on which the homogeneity of the SERS signal of TBA has been analyzed. Fig. 1 (I) shows the Raman spectra of TBA in the neat liquid (a), 1 M aqueous solution at pH 14 (b), SERS spectrum of a 5x10-4 M silver colloid prepared by reduction of silver nitrate with sodium borohydride at pH 7 (c) and SERS spectrum of a 5x10-4 M silver colloid prepared by reduction of silver nitrate with hydroxylamine hydrochloride (d). The assignment of the Raman spectra has been based on the present work as well as on previous studies [2-4]. The two bands recorded at 1662 and 2572 cm-1 in Fig.1a, are assigned to (C=O) and (SH) modes, what confirms that the Raman spectrum in the neat liquid is due to the thiolic specie of TBA, RC(O)SH. In the Raman spectrum of the solution (Fig. 1b) a significant redshift of (C=O) mode of 52 cm-1 and the absence of the (SH) band are detected in agreement with the behavior observed in the SERS spectrum (Fig. 1c). The latter confirms that the thiol tautomer of thiobenzoate anion, RC(O)S-, is adsorbed on silver nanoparticles. Other important SERS enhancements have been registered for the following vibrational modes: 8a;ring, (C=O) and (CS) recorded at 1592, 1554 and 928 cm-1 in Fig. 1c and 1d, respectively. The last two modes, (C=O) and (CS), undergo wavenumber shifts of +40 and -40 cm-1 respectively, which are closely related with the coordination of thiobenzoate anion to the metal surface [5]. The analysis of the vibrational wavenumber of these modes suggests that this molecule shows unidentate coordination through the sulphur atom to the metal surface. In order to confirm this fact DFT calculations have been carried out for different silver complexes: I) bridging bidentate ligand, (II) chelating ligand and (III and IV) unidentate ligand (Fig. 2). Theoretical wavenumber of representative bands of these compounds have been compared to the experimental one concluding that the behavior of the unidentate ligand (III) is the most probably coordination type of TBA on the metal surface. In order to confirm these conclusions the SERS spectra of TBA on silver colloid prepared by reduction of silver nitrate with hydroxylamine hydrochloride at different concentration of analyte have been recorded as well (Fig. 1 (II)). It is well known that the SERS enhancement factor depends strongly on different factors and in particular on the adsorption properties of the probe and the analyte concentration on the surface coverage. In this sense TBA has shown a very good detection level for this particular silver colloid it being a highly SERS active molecule. The detection limit is estimated to be 0.01 molar. Finally, Fig. 3 shows a representative Raman mapping of TBA adsorbed on a silver substrate prepared by spin-coating. Generally speaking, the image represents a fairly homogeneous distribution of the SERS intensity highlighting some points where the intensity is stronger as is expected in areas with heterogeneous coverage. The reproducibility of this type of substrate is under study focusing their application as reproducible and ultrasensitive sensing assemblies by using TBA as the target molecule due its good SERS sensitivity.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Histoire et recherche pour la paix. Expériences autour de la Méditerranée

Ce travail aborde une série d’apports théoriques et méthodologiques que nous considérons intéressants pour la recherche historique. Parmi les premiers, il convient de souligner un tournant ontologique et épistémologique qui permet de situer la paix au cœur de notre recherche. Parmi les seconds, la proposition d’une matrice unitaire et compréhensible composée de cinq axes reliés : une théorie générale des conflits ; la réflexion autour d’une paix imparfaite ; la déconstruction de la violence ; la distinction entre les médiations et les interactions systémiques entre conflits, paix et violence ; et l’empowerment pacifiste. Suivant cette approche, nous abordons trois aspects du présent : l’évolution de l’Indice de Développement Humain, les mouvements des indignés et le printemps arabe et la participation au sein de la plateforme Avaaz.org. Les résultats indiquent que maintenant, et malgré les violences générées, la Méditerranée est une réalité historique plus pacifique qu’il y a trente-cinq ans.In this paper, we focus on a set of theoretical and methodological approaches that we consider relevant for History. From a theoretical point of view we emphasize the necessity of an ontological and epistemological turn which permit us to place peace in the core of our research. From the methodological one, we propose a comprehensive and integrative matrix shaped by five intertwined focuses: a general theory of conflicts; a reflection on an imperfect system of peace; a deconstruction of all forms of violence; a distinction between power of mediations and systemic interactions between conflicts, peace and violence; and pacifistic empowerment. Following this approach, we make a preliminary analysis of three aspects of contemporary Mediterranean: the evolution of the Human Development Index, the social movements known as indignados (indignants) and Arab Spring, and the participation in Avaaz.org. Our results show that in spite of the multiple violences generated through the Mediterranean Sea, this historical region is more pacific now than it was 35 years ago

Charge Transport in Trap-Sensitized Infrared PbS Quantum-Dot-Based Photoconductors: Pros and Cons

Control of quantum-dot (QD) surface chemistry offers a direct approach for the tuning of charge-carrier dynamics in photoconductors based on strongly coupled QD solids. We investigate the effects of altering the surface chemistry of PbS QDs in such QD solids via ligand exchange using 3-mercaptopropionic acid (MPA) and tetrabutylammonium iodide (TBAI). The roll-to-roll compatible doctor-blade technique was used for the fabrication of the QD solid films as the photoactive component in photoconductors and field-effect phototransistors. The ligand exchange of the QD solid film with MPA yields superior device performance with higher photosensitivity and detectivity, which is due to less dark current and lower noise level as compared to ligand exchange with TBAI. In both cases, the mechanism responsible for photoconductivity is related to trap sensitization of the QD solid, in which traps are responsible of high photoconductive gain values, but slow response times under very low incident optical power (100 pW), where traps are filled, both MPA- and TBAI-treated photodevices exhibit similar behavior, characterized by lower responsivity and faster response time, as limited by the mobility in the QD solid