1,360 research outputs found
Divergence of the Thermal Conductivity in Uniaxially Strained Graphene
We investigate the effect of strain and isotopic disorder on thermal
transport in suspended graphene by equilibrium molecular dynamics simulations.
We show that the thermal conductivity of unstrained graphene, calculated from
the fluctuations of the heat current at equilibrium is finite and converges
with size at finite temperature. In contrast, the thermal conductivity of
strained graphene diverges logarithmically with the size of the models, when
strain exceeds a relatively large threshold value of 2%. An analysis of phonon
populations and lifetimes explains the divergence of the thermal conductivity
as a consequence of changes in the occupation of low-frequency out-of-plane
phonons and an increase in their lifetimes due to strain.Comment: 6 pages, 7 figures. Accepted for publication in Physical Review
Mechanical Tuning of Thermal Transport in a Molecular Junction
Understanding and controlling heat transport in molecular junctions would
provide new routes to design nanoscale coupled electronic and phononic devices.
Using first principles full quantum calculations, we tune thermal conductance
of a molecular junction by mechanically compressing and extending a short
alkane chain connected to graphene leads. We find that the thermal conductance
of the compressed junction drops by half in comparison to the extended
junction, making it possible to turn on and off the heat current. The low
conductance of the off state does not vary by further approaching the leads and
stems from the suppression of the transmission of the in--plane transverse and
longitudinal channels. Furthermore, we show that misalignment of the leads does
not reduce the conductance ratio. These results also contribute to the general
understanding of thermal transport in molecular junctions.Comment: 12 pages, 6 figure
Microscopic Mechanism and Kinetics of Ice Formation at Complex Interfaces: Zooming in on Kaolinite
Most ice in nature forms thanks to impurities which boost the exceedingly low
nucleation rate of pure supercooled water. However, the microscopic details of
ice nucleation on these substances remain largely unknown. Here, we have
unraveled the molecular mechanism and the kinetics of ice formation on
kaolinite, a clay mineral playing a key role in climate science. We find that
the formation of ice at strong supercooling in the presence of this clay is
twenty orders of magnitude faster than homogeneous freezing. The critical
nucleus is substantially smaller than that found for homogeneous nucleation
and, in contrast to the predictions of classical nucleation theory (CNT), it
has a strong 2D character. Nonetheless, we show that CNT describes correctly
the formation of ice at this complex interface. Kaolinite also promotes the
exclusive nucleation of hexagonal ice, as opposed to homogeneous freezing where
a mixture of cubic and hexagonal polytypes is observed
Infrastructure Exposure, Extreme Weather Events & Climate Change - SF Bay - Napoli
Big Data analysis and computer modeling to compare the Mediterranean-type climate coastlands of San Francisco Bay, California (USA), and Naples Bay, southern Italy, prone to extreme weather events, sea storms and tsunami, climate change and sea level rise
Canonical sampling through velocity-rescaling
We present a new molecular dynamics algorithm for sampling the canonical
distribution. In this approach the velocities of all the particles are rescaled
by a properly chosen random factor. The algorithm is formally justified and it
is shown that, in spite of its stochastic nature, a quantity can still be
defined that remains constant during the evolution. In numerical applications
this quantity can be used to measure the accuracy of the sampling. We
illustrate the properties of this new method on Lennard-Jones and TIP4P water
models in the solid and liquid phases. Its performance is excellent and largely
independent on the thermostat parameter also with regard to the dynamic
properties
Assetto geomorfologico dell’area marina di Sinuessa ed ipotesi di fruizione sostenibile
Studio geomorfologico dell’area costiera di Sinuessa (Golfo di Gaeta) che ha consentito di individuare l’approdo di epoca romana di Sinuessa; la ricostruzione dell’evoluzione geomorfologica e tettonica recente dell’area ha reso possibile l’individuazione delle cause della sommersione dell’approdo. L’intenso sviluppo insediativo che oggi caratterizza il tratto di litorale prospiciente l’area spinge a sviluppare un sistema di gestione integrato volto alla valorizzazione dell’area
High-resolution lightning detection and possible relationship with rainfall events over the Central Mediterranean area
Lightning activity is usually associated with precipitations events and represents a possible indicator of climate change, even contributing to its increase with the production of NOx gases. The study of lightning activity on long temporal periods is crucial for fields related to atmospheric phenomena from intense rain-related hazard processes to long-term climate changes. This study focuses on 19 years of lightning-activity data, recorded from Italian Lightning Detection Network SIRF, part of the European network EUCLID (European Cooperation for Lightning Detection). Preliminary analysis was dedicated to the spatial and temporal assessment of lightning through detection in the Central Mediterranean area, focusing on yearly and monthly data. Temporal and spatial features have been analyzed, measuring clustering through the application of global Moran’s I statistics and spatial local autocorrelation; a Mann–Kendall trend test was performed on monthly series aggregating the original data on a 5 × 5 km cell. A local statistically significant trend emerged from the analysis, suggesting a possible linkage between surface warming and lightning activity
Environmental Regeneration Integrating Soft Mobility and Green Street Networks: A Case Study in the Metropolitan Periphery of Naples
Public space and street networks form a significant and central determinant of urban quality. The advent of the COVID-19 pandemic has focused their crucial importance in the reorganisation of places that are “safe” because they allow movement through cities with minimal risk of contagion. While addressing the need for social distancing, open-air exercise, and mobility without the use of public transport, these measures resulted in other environmental and social benefits. Living with the coronavirus pandemic has produced a series of adaptative actions, such as barring or limiting automobile traffic, thereby expanding street space for pedestrians and bicyclists, whose impact is, as yet, difficult to fathom because of their contingent, temporary nature. In this context, this case study proposes a sustainable bicycle network to inform the future, permanent street redesign. Based on topographic, morphologic, and climatic data, it evaluates a series of contiguous road sections, defining redesign capacities and critical conditions to implement sustainable interventions to manage urban runoff, mitigate of extreme heat events, expand pedestrian paths and provide a bicycle network. This holistic approach to sustainable urban design evaluation, supported by reproducible
data and parameters, serves as a replicable model for the sustainable redesign of roads in other urban settings. The extent, integration, and complexity of the study engaged an interdisciplinary framework, facilitating detailed planning and design and quantified assessments of the environmental outcomes
Development and implementation of a smart greenhouse
A smart greenhouse was developed at Laboratorio de Informatica Aplicada with the department of Agronomic Engineering at the University of Rio Negro, it must provide real-time measurements of parameters such as humidity, temperature and luminosity; it also must allow manual and automatic control for actuators such as heaters, sprinklers and fans based on user input. In order to fulfill the aforementioned requirements the following actions were performed: (a) Design and implementation of a webpage to communicate with and control the greenhouse and, (b) Development: at first a model using Object Oriented Programming was implemented in an Arduino Mega board equipped with an ethernet shield; posteriorly, given that Arduino could not fulfill the necessary tasks, it was decided to develop a second prototype using a Raspberry Pi 2 Model B+ board along with completely new software programmed in Python 3.X Workshop Procesamiento de Señales y Sistemas de Tiempo Real.Red de Universidades con Carreras en Informátic
Development and implementation of a smart greenhouse
A smart greenhouse was developed at Laboratorio de Informatica Aplicada with the department of Agronomic Engineering at the University of Rio Negro, it must provide real-time measurements of parameters such as humidity, temperature and luminosity; it also must allow manual and automatic control for actuators such as heaters, sprinklers and fans based on user input. In order to fulfill the aforementioned requirements the following actions were performed: (a) Design and implementation of a webpage to communicate with and control the greenhouse and, (b) Development: at first a model using Object Oriented Programming was implemented in an Arduino Mega board equipped with an ethernet shield; posteriorly, given that Arduino could not fulfill the necessary tasks, it was decided to develop a second prototype using a Raspberry Pi 2 Model B+ board along with completely new software programmed in Python 3.X Workshop Procesamiento de Señales y Sistemas de Tiempo Real.Red de Universidades con Carreras en Informátic
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