408 research outputs found
Statistical Laws in Urban Mobility from microscopic GPS data in the area of Florence
The application of Statistical Physics to social systems is mainly related to
the search for macroscopic laws, that can be derived from experimental data
averaged in time or space,assuming the system in a steady state. One of the
major goals would be to find a connection between the statistical laws to the
microscopic properties: for example to understand the nature of the microscopic
interactions or to point out the existence of interaction networks. The
probability theory suggests the existence of few classes of stationary
distributions in the thermodynamics limit, so that the question is if a
statistical physics approach could be able to enroll the complex nature of the
social systems. We have analyzed a large GPS data base for single vehicle
mobility in the Florence urban area, obtaining statistical laws for path
lengths, for activity downtimes and for activity degrees. We show also that
simple generic assumptions on the microscopic behavior could explain the
existence of stationary macroscopic laws, with an universal function describing
the distribution. Our conclusion is that understanding the system complexity
requires dynamical data-base for the microscopic evolution, that allow to solve
both small space and time scales in order to study the transients.Comment: 17 pages, 14 figures .jpg, use imsart.cl
Assessing the Quality of QM/MM Approaches to Describe Vacuo-to-water Solvatochromic Shifts
The performance of different Quantum Mechanics/Molecular Mechanics embedding
models to compute vacuo-to-water solvatochromic shifts are investigated. In
particular, both non-polarizable and polarizable approaches are analyzed and
computed results as compared to reference experimental data. We show that none
of the approaches outperforms the others and that errors strongly depend on the
nature of the molecular transition. Thus, we prove that the best choice of
embedding model highly depends on the molecular system, and that the use a
specific approach as a black-box can lead to significant errors and sometimes
totally wrong predictions.Comment: 12 pages, 6 figure
Graphene Plasmonics: a Novel Fully Atomistic Approach for Realistic Structures
We demonstrate that the plasmonic properties of realistic graphene and
graphene-based materials can effectively and accurately be modeled by a novel,
fully atomistic, yet classical, approach, named FQ. Such model is able
to reproduce all plasmonic features of these materials, and their dependence on
shape, dimension and fundamental physical parameters (Fermi energy, relaxation
time and two-dimensional electron density). Remarkably, FQ is able to
accurately reproduce experimental data for realistic structures of hundreds of
nanometers ( 370.000 atoms), which cannot be afforded by any
\emph{ab-initio} method. Also, the atomistic nature of FQ permits the
investigation of complex shapes, which can hardly be dealt with by exploiting
widespread continuum approaches.Comment: 20 pages, 4 figure
QM/Classical Modeling of Surface Enhanced Raman Scattering Based on Atomistic Electromagnetic Models
We present quantum mechanics (QM)/frequency dependent fluctuating charge (QM/ωFQ) and fluctuating dipoles (QM/ωFQFμ) multiscale approaches to model surface-enhanced Raman scattering spectra of molecular systems adsorbed on plasmonic nanostructures. The methods are based on a QM/classical partitioning of the system, where the plasmonic substrate is treated by means of the atomistic electromagnetic models ωFQ and ωFQFμ, which are able to describe in a unique fashion and at the same level of accuracy the plasmonic properties of noble metal nanostructures and graphene-based materials. Such methods are based on classical physics, i.e. Drude conduction theory, classical electrodynamics, and atomistic polarizability to account for interband transitions, by also including an ad-hoc phenomenological correction to describe quantum tunneling. QM/ωFQ and QM/ωFQFμ are thus applied to selected test cases, for which computed results are compared with available experiments, showing the robustness and reliability of both approaches
Fully Atomistic Modeling of Plasmonic Bimetallic Nanoparticles: Nanoalloys and Core-Shell Systems
The recently developed ωFQFμ model (ACS Photonics, 9, 3,025–3,034) is extended to bimetallic nanoparticles, such as nanoalloys and core-shell systems. The method finds its grounds in basic physical concepts, such as Drude conduction theory, electrostatics, interband transitions, and quantum tunneling. The approach, which is parametrized on ab initio simulations of Ag-Au nanoalloys, is challenged against complex Ag-Au nanostructures (spheres, nanorods, and core-shell nanoparticles). Remarkable agreement with available experimental data is found, thus demonstrating the reliability of the newly developed approach
An End-to-End Solution for Enabling Urban Cyclability: The Bike2Work Experience
Mobility plays a fundamental role in modern cities. How citizens experience
the city, access its core services, and participate in city life, strongly
depends on its mobility organization and efficiency. The challenges that
municipalities face are very ambitious: on the one hand, administrators must
guarantee their citizens the right to mobility and to easily access local
services; on the other hand, they need to minimize the economic, social, and
environmental costs of the mobility system. Municipalities are increasingly
facing problems of traffic congestion, road safety, energy dependency and air
pollution, and therefore encouraging a shift towards sustainable mobility
habits based on active mobility is of central importance. Active modes, such as
cycling, should be particularly encouraged, especially for local recurrent
journeys (i.e., home-to-school, home-to-work). In this context, addressing and
mitigating commuter-generated traffic requires engaging public and private
stakeholders through innovative and collaborative approaches that focus not
only on supply (e.g., roads and vehicles) but also on transportation demand
management. In this paper, we propose an end-to-end solution for enabling urban
cyclability. It supports the companies' Mobility Managers (MMs) acting on the
promotion of active mobility for home-to-work commuting, helps the city
administrators to understand the needed urban planning interventions, and
motivates the citizens to sustainable mobility. To evaluate the effectiveness
of the proposed solution we developed two analyses: the first to accurately
analyze the user experience and any behaviour change related to the BIKE2WORK
initiative, and the second to demonstrate how exploiting the collected data we
can inform and possible guide the involved municipality (i.e., Ferrara, a city
in Northern Italy) in improving the urban cyclability.Comment: 12 pages, 11 figure
Fully Polarizable QM/Fluctuating Charge Approach to Two-Photon Absorption of Aqueous Solutions
We present the extension of the quantum/classical polarizable fluctuating
charge model to the calculation of single residues of quadratic response
functions, as required for the computational modeling of two-photon absorption
cross-sections. By virtue of a variational formulation of the quantum/classical
polarizable coupling, we are able to exploit an atomic orbital-based
quasienergy formalism to derive the additional coupling terms in the response
equations. Our formalism can be extended to the calculation of arbitrary order
response functions and their residues. The approach has been applied to the
challenging problem of one- and two-photon spectra of rhodamine 6G (R6G) in
aqueous solution. Solvent effects on one- and two-photon spectra of R6G in
aqueous solution have been analyzed by considering three different approaches,
from a continuum (QM/PCM) to two QM/MM models (non-polarizable QM/TIP3P and
polarizable QM/FQ). Both QM/TIP3P and QM/FQ simulated OPA and TPA spectra show
that the inclusion of discrete water solvent molecules is essential to increase
the agreement between theory and experiment. QM/FQ has been shown to give the
best agreement with experiments
Arbuscular Mycorrhizal Fungi and Associated Microbiota as Plant Biostimulants: Research Strategies for the Selection of the Best Performing Inocula
Arbuscular mycorrhizal fungi (AMF) are beneficial soil microorganisms establishing mutualistic symbioses with the roots of the most important food crops and playing key roles in the maintenance of long-term soil fertility and health. The great inter- and intra-specific AMF diversity can be fully exploited by selecting AMF inocula on the basis of their colonization ability and efficiency, which are aaffected by fungal and plant genotypes and diverse environmental variables. The multiple services provided by AMF are the result of the synergistic activities of the bacterial communities living in the mycorrhizosphere, encompassing nitrogen fixation, P solubilization, and the production of phytohormones, siderophores, and antibiotics. The tripartite association among host plants, mycorrhizal symbionts, and associated bacteria show beneficial emerging properties which could be efficiently exploited in sustainable agriculture. Further in-depth studies, both in microcosms and in the field, performed on different AMF species and isolates, should evaluate their colonization ability, efficiency, and resilience. Transcriptomic studies can reveal the expression levels of nutrient transporter genes in fungal absorbing hyphae in the presence of selected bacterial strains. Eventually, newly designed multifunctional microbial consortia can be utilized as biofertilizers and biostimulants in sustainable and innovative production systems
Chemical composition of the essential oils from leaves and flowers of Passiflor sexocellata and Passiflora trifasciata
The chemical composition of the essential oils of Passiflora sexocellata and Passiflora trifasciata (Passifloraceae, subgenus Decaloba) were
studied for the first time. Essential oils were obtained by steam distillation of fresh leaves and flowers. The chemical composition
was assessed by using GC/FID and GC/MS. For P. sexocellata leaves, the optimized analytical procedure allowed the identification
of 33 compounds (75% of the total oil composition) and 29 (74% of the total oil composition) in flowers. Regarding P. trifasciata,
35 compounds (76% of the total oil composition) were detected in leaves and 32 (71% of the total oil composition) in flowers.
Terpenes and mono unsaturated hydrocarbons were quantified as major constituents of the volatile fraction in flowers (17.0 to
52.6%) and (13.7 to 20.0%). Organic acids were detected in both leaves and flowers with a percentage ranging from 3.3% to 32.0%.
Aldehydes were also detected in leaves (12.6 to 41.4%) and in flowers (1.4 to 5.1%). The GC/MS analyzes allowed alcohols to be
detected in leaves (20.6 to 42.9%) and in flowers (8.2 to 18.1%). These compounds represent the most important feature of the
large Passiflora family. Moreover, a critical role in the coevolved mechanisms of pollinators' interaction has been investigated
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