Who uses Transport Network Companies?: Characterization of Demand and its Relationship with Public Transit in Medellín

Transport Network Companies (TNCs) have become a popular alternative for mobility due to their ability to provide on-demand flexible mobility services. By offering smartphone-based, ride-hailing services capable of satisfying specific travel needs, these modes have transformed urban mobility worldwide. However, to-date, few studies have examined the impacts in the Latin American context. This analysis is a critical first step in developing policies to promote efficient and sustainable transport systems in the Latin-American region. This research examines the factors affecting the adoption of on-demand ride services in Medellín, Colombia. It also explores whether these are substituting or competing with public transit. First, it provides a descriptive analysis in which we relate the usage of platform-based services with neighborhood characteristics, socioeconomic information of individuals and families, and trip-level details. Next, factors contributing to the election of platform-based services modeled using discrete choice models. The results show that wealthy and highly educated families with low vehicle availability are more likely to use TNCs compared to other groups in Medellín. Evidence also points at gender effects, with being female significantly increasing the probability of using a TNC service. Finally, we observe both transit complementary and substitution patterns of use, depending on the context and by whom the service is requested

Superconductivity-Induced Transfer of In-Plane Spectral Weight in Bi2Sr2CaCu2O8: Resolving a Controversy

We present a detailed analysis of the superconductivity-induced redistribution of optical spectral weight in Bi2Sr2CaCu2O8 near optimal doping. It confirms the previous conclusion by Molegraaf et al. (Science 66, 2239 (2002)), that the integrated low-frequency spectral weight shows an extra increase below Tc. Since the region, where the change of the integrated spectral weight is not compensated, extends well above 2.5 eV, this transfer is caused by the transfer of spectral weight from interband to intraband region and only partially by the narrowing of the intraband peak. We show that the opposite assertion by Boris et al. (Science 304, 708 (2004)) regarding this compound, is unlikely the consequence of any obvious discrepancies between the actual experimental data.Comment: ReVTeX, 9 pages, 8 encapsulated postscript figures, several typo's correcte

Electroreflectance spectroscopy in self-assembled quantum dots: lens symmetry

Modulated electroreflectance spectroscopy $\Delta R/R$ of semiconductor self-assembled quantum dots is investigated. The structure is modeled as dots with lens shape geometry and circular cross section. A microscopic description of the electroreflectance spectrum and optical response in terms of an external electric field (${\bf F}$) and lens geometry have been considered. The field and lens symmetry dependence of all experimental parameters involved in the $\Delta R/R$ spectrum have been considered. Using the effective mass formalism the energies and the electronic states as a function of ${\bf F}$ and dot parameters are calculated. Also, in the framework of the strongly confined regime general expressions for the excitonic binding energies are reported. Optical selection rules are derived in the cases of the light wave vector perpendicular and parallel to $$. Detailed calculation of the Seraphin coefficients and electroreflectance spectrum are performed for the InAs and CdSe nanostructures. Calculations show good agreement with measurements recently performed on CdSe/ZnSe when statistical distribution on size is considered, explaining the main observed characteristic in the electroreflectance spectra

Surface anisotropy and particle size influence on hysteresis loops in La2/3Ca1/3MnO3 nanoparticles : A simulation approach

Thermal and hysteretic magnetic properties of La2/3Ca1/3MnO3 nanoparticles were studied using Monte Carlo simulations, with emphasis on the influence of anisotropy. In this work, several nanoparticle sizes ranging from 2.32 to 11.58 nm were analyzed and their properties were compared to those of the bulk material. The magnetic behavior of the material was modeled using the three dimensional Heisenberg model with nearest neighbor interactions. Furthermore, both uniaxial and Néel anisotropies were considered for core and surface magnetic sites respectively. Deviations in the critical temperature and coercive field were observed for nanoparticles when compared with those of the bulk material. In addition to these properties, the special spin configurations that arise from the competition between the exchange, anisotropy and external magnetic field were also studied. All these effects are interpreted in terms of the surface properties such as the Néel anisotropy and the decrease in the coordination number

Far-infrared and submillimeter-wave conductivity in electron-doped cuprate La_{2-x}Ce_xCuO_4

We performed far-infrared and submillimeter-wave conductivity experiments in the electron-doped cuprate La_{2-x}Ce_xCuO_4 with x = 0.081 (underdoped regime, T_c = 25 K). The onset of the absorption in the superconducting state is gradual in frequency and is inconsistent with the isotropic s-wave gap. Instead, a narrow quasiparticle peak is observed at zero frequency and a second peak at finite frequencies, clear fingerprints of the conductivity in a d-wave superconductor. A far-infrared conductivity peak can be attributed to 4Delta_0, or to 2Delta_0 + Delta_spin, where Delta_spin is the resonance frequency of the spin-fluctuations. The infrared conductivity as well as the suppression of the quasiparticle scattering rate below T_c are qualitatively similar to the results in the hole-doped cuprates.Comment: 5 pages, 4 figures include

Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations

A comprehensive study of the electronic properties of monoclinic MoO2 from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations. For the latter, the new full-potential augmented spherical wave (ASW) method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional hole-like surfaces centered around the Z- and B-point could be resolved; these surfaces were an artefact of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of MoO2 and the neighbouring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of VO2 and NbO2, which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.Comment: 17 pages, 21 figures, more information at http://www.physik.uni-augsburg.de/~eyert

Strain in InP/ZnSe, S core/shell quantum dots from lattice mismatch and shell thickness : material stiffness influence

We investigate the buildup of strain in InP quantum dots with the addition of shells of the lower-lattice constant materials ZnSe and ZnS by Raman spectroscopy. Both materials induce compressive strain in the core, which increases with increasing shell volume. We observe a difference in the shell behavior between the two materials: the thickness-dependence points toward an influence of the material stiffness. ZnS has a larger Young's modulus and requires less material to develop stress on the InP lattice at the interface, while ZnSe requires several layers to form a stress-inducing lattice at the interface. This hints at the material stiffness being an additional parameter of relevance for designing strained core/shell quantum dots