In the last few years, complex networks have become an increasingly relevant research topic due to the large number of fields of application. Particularly, complex networks are especially significant in the area of modern online social networks (OSNs). OSNs are actually a challenge for complex network analysis, as they present some characteristics that hinder topology processing. Concretely, social networks’ volume is exceedingly big, as they have a high number of nodes and links. One of the most popular and influential OSNs is Twitter. In this paper, we present a model to describe the growth of scale-free networks. This model is applied to Twitter after checking that it can be considered a “scale-free” complex network fulfilling the small world property. Checking this property involves the calculation of the shortest path between any two nodes of the network. Given the difficulty of this computation for large networks, a new heuristic method is also proposed to find the upper bounds of the path lengths instead of computing the exact length.

Context. Ice photodesorption has been the topic of recent studies that aim to interpret the abundances of gas-phase molecules, in particular CO, toward cold interstellar regions. But little is known about the effect of the ice’s physical properties on the photodesorption rate. The linear decrease observed in the photodesorption rate, as a function of increasing CO ice deposition temperature, was provisionally attributed to a more compact CO ice structure.Aims. The goal of this work is to monitor the physical properties of solid CO as a function of ice deposition temperature. Then, we evaluate the possible link between the structure of ice and the ice’s photodesorption rate.Methods. Infrared spectroscopy is an efficient tool to monitor the structural evolution of pure ices during warm-up or irradiation. The infrared absorption bands of molecular ice components observed toward various space environments allow for the detection of H2O, CO, CO2, CH3OH, NH3, etc. Typically, a pure ice that is composed of one of these species displays significant changes in their mid-infrared band profiles as a result of warm-up. But, at most, only very subtle changes appear in the narrow CO ice infrared absorption band as the result of warm-up. We, therefore, also used vacuum-ultraviolet spectroscopy of CO ice to monitor the effect of temperature in the physical properties of the ice. Finally, temperature-programmed desorption and photo-desorption experiments for different CO ice deposition temperatures were performed.Results. Mid-infrared and vacuum-ultraviolet spectroscopy showed that warm-up of CO ice that is deposited at 8 K did not lead to structural changes. Only CO ice samples deposited at temperatures above 20 K displayed different spectroscopic properties compared to lower deposition temperatures. The observed gradual and linear drop in the photodesorption rate of CO ice, as a function of increasing ice deposition temperature in the 7 to 20 K range, is, therefore, not due to a gradual re-structuring toward a more compact and crystalline ice, which is only triggered above 20 K and increases for higher deposition temperatures.Conclusions. We suggest that this decrease of the photodesorption rate is related to the disorder of CO dipole molecules within the amorphous or glassy state, which influences the necessary transfer of photon energy from the first excited molecule to the desorbing molecule on the ice surface. The photodesorption yield of CO deposited at 20 K is about four times lower than at 7 K. Dust models should adopt CO photodesorption yields that are compatible with the thermal history of the cloud.

This paper presents the results of a thorough microstructural characterisation of a set of cement mortars\ud (made with three w/b ratios and five different cement types), degraded by the ammonium nitrate\ud method. Both destructive and ultrasonic non-destructive techniques were used to characterise the samples.\ud The initial calcium content of the samples plays a dominant role in both the advance of the degradation\ud process and the degradation grade of the samples. In addition, the decalcification process kinetics\ud and the degradation grade are modelled, using Fick’s second law of diffusion and the shrinking unreacted-\ud core model. Two parametric equations are presented and used to estimate the decalcification process\ud kinetics and the degradation grade using accessible microstructural parameters of the native\ud mortars, such as the initial CaO content, the open porosity, and the cementitious matrix volume fraction.\ud Furthermore, the degraded depth in the samples is measured using ultrasonic testing with an average\ud error of about 10%

This paper proposes a method for merging Bluetooth and WLAN technologies to face the problem of indoor positioning. Firstly, using Bluetooth measurements the zone where the target object is located is enclosed. Afterwards, processing WiFi measurements the RSS readings are compared only against the fingerprints of the points within the previously determined zone for the precise determination of the object position. In a recent work, we approached this problem by constructing simulated Bluetooth and WLAN maps and assuming that Bluetooth measurements determine precisely the zone where the object is located. Here we present a new algorithm to cope with erroneous identification of the preselected region. The performance of this method has been tested experimentally and the comparison between the localization results obtained using both technologies and using only WiFi is presented.

This paper deals with the study of damage produced during freeze-thaw (F-T) cycles using two non-destructive measurement approaches—the first approach devoted to continuous monitoring using embedded sensors during the cycles, and the second one, performing ultrasonic imaging before and after the cycles. Both methodologies have been tested in two different types of concrete specimens, with and without air-entraining agents. Using the first measurement approach, the size and distribution of pores were estimated using a thermoporometrical model and continuous measurements of temperature and ultrasonic velocity along cycles. These estimates have been compared with the results obtained using mercury porosimetry testing. In the second approach, the damage due to F-T cycles has been evaluated by automated ultrasonic transmission and pulse-echo inspections made before and after the cycles. With these inspections the variations in the dimensions, velocity and attenuation caused by the accelerated F-T cycles were determined.