Measuring and mitigating behavioural segregation using Call Detail Records

The overwhelming amounts of data we generate in our daily routine and in social networks has been crucial for the understanding of various social and economic factors. The use of this data represents a low-cost alternative source of information in parallel to census data and surveys. Here, we advocate for such an approach to assess and alleviate the segregation of Syrian refugees in Turkey. Using a large dataset of mobile phone records provided by Turkey's largest mobile phone service operator, Türk Telekom, in the frame of the Data 4 Refugees project, we define, analyse and optimise inter-group integration as it relates to the communication patterns of two segregated populations: refugees living in Turkey and the local Turkish population. Our main hypothesis is that making these two communities more similar (in our case, in terms of behaviour) may increase the level of positive exposure between them, due to the well-known sociological principle of homophily. To achieve this, working from the records of call and SMS origins and destinations between and among both populations, we develop an extensible, statistically-solid, and reliable framework to measure the differences between the communication patterns of two groups. In order to show the applicability of our framework, we assess how house mixing strategies, in combination with public and private investment, may help to overcome segregation. We first identify the districts of the Istanbul province where refugees and local population communication patterns differ in order to then utilise our framework to improve the situation. Our results show potential in this regard, as we observe a significant reduction of segregation while limiting, in turn, the consequences in terms of rent increase

Thermomechanical response of HTPB-based composite beams subjected to near-resonant inertial excitation

At this time, there is a pressing need to develop new technologies capable of detecting, identifying, and potentially neutralizing energetic materials, preferably from a stand-off distance. To address this need, an improved understanding of the mechanics of energetic materials, prior to detonation or deflagration, must be developed. In light of this, the present effort seeks to characterize the thermomechanical response of a polymer-based composite material, which is a mechanical surrogate for a traditional composite explosive or propellant. This research focus is motivated by the fact that many polymer-based materials demonstrate significant self-heating when subjected to dynamic loading, due to the combination of appreciable internal dissipation and poor thermal diffusion. Such self-heating has the potential to enhance existing stand-off, vapor-based detection systems, due to the temperature sensitivity of vapor pressure attendant to many polymer-based energetic materials. In this effort, a thermomechanical model of a polymer-based composite beam is developed. The composite is modeled as a homogenized linear viscoelastic material and the mechanical response is determined using Euler–Bernoulli beam theory in conjunction with a harmonic base excitation. The system is excited near its first resonant frequency to elicit large mechanical responses and, thus, maximum heating. The heat generation resulting from the harmonic loading is derived using the hysteretic characteristics of the system. The Fourier Law of Conduction is then used in conjunction with the derived heat source, as well as numerical solvers, to obtain the thermal response. In addition to the aforementioned modeling efforts, experiments were conducted using a HTPB-based beam with embedded ammonium chloride (NH4Cl) crystals. The sample was subjected to harmonic base excitation and the thermal and mechanical responses were recorded using infrared thermography and scanning laser Doppler vibrometry, respectively. Direct comparisons of the results obtained through theory and experiments are presented for several distinct forcing levels. The acquired results show a strong dependence of the temperature distribution on the stress and strain fields produced by the mechanical loading. The effect of convection at the surfaces is also evident in the thermal response. Close agreement between the model predictions and experimental results is observed. In conclusion, by adopting a unified research approach, the authors hope to build upon recent research efforts related to explosives detection by bridging the substantial gap that exists between theory and experiments. The authors also hope that this effort will advance the worldwide research effort aimed at detecting and defeating hidden explosive materials

Use of Evanescent Plane Waves for Low-Frequency Energy Transmission Across Material Interfaces

The transmission of sound across high-impedance difference interfaces, such as an air-water interface, is of significant interest for a number of applications. Sonic booms, for instance, may affect marine life, if incident on the ocean surface, or impact the integrity of existing structures, if incident on the ground surface. Reflection and refraction at the material interface, and the critical angle criteria, generally limit energy transmission into higher-impedance materials. However, in contrast with classical propagating waves, spatially decaying incident waves may transmit energy beyond the critical angle. The inclusion of a decaying component in the incident trace wavenumber yields a nonzero propagating component of the transmitted surface normal wavenumber, so energy propagates below the interface for all oblique incident angles. With the goal of investigating energy transmission using incident evanescent waves, a model for transmission across fluid-fluid and fluid-solid interfaces has been developed. Numerical results are shown for the air-water interface and for common air-solid interfaces. The effects of the incident wave parameters and interface material properties are also considered. For the air-solid interfaces, conditions can be found such that no reflected wave is generated, due to impedance matching among the incident and transmitted waves, which yields significant transmission increases over classical incident waves

On The Use Of Evanescent Plane Waves For Low-Frequency Energy Transmission Across Material Interfaces

The transmission of airborne sound into high-impedance media is of interest in several applications. For example, sonic booms in the atmosphere may impact marine life when incident on the ocean surface, or affect the integrity of existing structures when incident on the ground. Transmission across high impedance-difference interfaces is generally limited by reflection and refraction at the surface, and by the critical angle criterion. However, spatially decaying incident waves, i.e., inhomogeneous or evanescent plane waves, may transmit energy above the critical angle, unlike homogeneous plane waves. The introduction of a decaying component to the incident trace wavenumber creates a nonzero propagating component of the transmitted normal wavenumber, so energy can be transmitted across the interface. A model of evanescent plane waves and their transmission across fluid-fluid and fluid-solid interfaces is developed here. Results are presented for both air-water and air-solid interfaces. The effects of the incident wave parameters (including the frequency, decay rate, and incidence angle) and the interfacial properties are investigated. Conditions for which there is no reflection at the air-solid interface, due to impedance matching between the incident and transmitted waves, are also considered and are found to yield substantial transmission increases over homogeneous incident waves

The Construction of Acoustic Waveforms from Plane Wave Components to Enhance Energy Transmission into Solid Media

The transmission of acoustic energy into solid materials is of interest in a wide range of applications, including ultrasonic imaging and nondestructive testing. However, the large impedance mismatch at the solid interface generally limits the transmission of incident acoustic energy. With the goal of improving the fraction of the energy transmitted into solid materials, the use of various bounded spatial profiles, including commonly-employed forms, such as Gaussian distributions, as well as newly-constructed profiles, has been investigated. The spatial profile is specified as the pressure amplitude distribution of the incident wave. Bounded acoustic beams are represented here as sums of harmonic plane waves, and results obtained for the optimal parameters of incident plane wave components are used to inform the construction of bounded wave profiles. The effect of the form of the spatial profile is investigated, with the total energy carried by the incident wave held constant as the profile is varied, and the relationship with the plane wave components which superimpose to form the bounded wave is discussed. Direct comparisons are made for the efficiency of the energy transmission of different profiles. The results reveal that, by tuning the form of the profile, substantial improvements in the total energy transmission can be achieved as compared to Gaussian and square waveforms

Thermal And Mechanical Response Of Particulate Composite Plates Under Inertial Excitation

The thermal and mechanical, near-resonant responses of particulate composite plates formed from hydroxyl-terminated polybutadiene (HTPB) binder and varying volume ratios of ammonium chloride (NH4Cl) particles (50, 65, 75%) are investigated. Each test specimen is clamped and forced with three levels of band-limited, white noise inertial excitation (10–1000 Hz at 1.00, 1.86 and 2.44 g RMS). The mechanical response of each plate is recorded via scanning laser Doppler vibrometry. The plates are then excited at a single resonant frequency and the thermal response is recorded via infrared thermography. Comparisons are made between the mechanical operational deflection shapes of each plate and spatial temperature distributions, with correlation seen between the observed level of strain, as visualized by strain energy density, and heat generation. The effect of particle/binder ratio on both the thermal and mechanical responses is discussed. Acquired results are also compared to an analytical model of the system. The observed thermomechanical effects render an improved understanding of the thermomechanics of plastic-bonded composites, an essential step in support of the development of new technologies for the vapor-based detection of hidden explosives

Low-Frequency Energy Transmission across Material Interfaces using Incident Evanescent Waves

Transmission of airborne sound into higher-impedance materials is of interest in a range of applications. Sonic booms, for example, may adversely affect marine life, if incident on the ocean surface, or may produce underground pressure waves potentially capable of impacting the integrity of existing structures, if incident on the ground surface. Energy transmission into higher-impedance materials is generally limited by significant reflection and refraction at the material interface, and by the critical angle criteria. However, unlike classical waves, spatially-decaying, or evanescent, incident waves can transmit energy at angles beyond the critical angle. When a decaying component is introduced into the incident trace wavenumber, the interaction at the interface produces a nonzero propagating component of the transmitted surface normal wavenumber, so energy is transmitted across the interface for all oblique incident angles. With the aim of investigating energy transmission using incident evanescent waves, a model for pressure and intensity transmission across the fluid-fluid and fluid-solid interfaces has been developed. Numerical results are given for common interfaces that include the air-water interface and typical air-solid interfaces, where the effects of the incident wave parameters and interface material properties are considered as well. For the air-solid interfaces, conditions can be tuned such that no reflected wave is generated at the interface, owing to impedance matching between the incident and transmitted waves, which yields considerable transmission increases over classical incident waves