1,761 research outputs found
Luttinger liquid fixed point for a 2D flat Fermi surface
We consider a system of 2D interacting fermions with a flat Fermi surface.
The apparent conflict between Luttinger and non Luttinger liquid behavior found
through different approximations is resolved by showing the existence of a line
of non trivial fixed points, for the RG flow, corresponding to Luttinger liquid
behavior; the presence of marginally relevant operators can cause flow away
from the fixed point. The analysis is non-perturbative and based on the
implementation, at each RG iteration, of Ward Identities obtained from local
phase transformations depending on the Fermi surface side, implying the partial
vanishing of the Beta function
Energy-Efficient Algorithms
We initiate the systematic study of the energy complexity of algorithms (in
addition to time and space complexity) based on Landauer's Principle in
physics, which gives a lower bound on the amount of energy a system must
dissipate if it destroys information. We propose energy-aware variations of
three standard models of computation: circuit RAM, word RAM, and
transdichotomous RAM. On top of these models, we build familiar high-level
primitives such as control logic, memory allocation, and garbage collection
with zero energy complexity and only constant-factor overheads in space and
time complexity, enabling simple expression of energy-efficient algorithms. We
analyze several classic algorithms in our models and develop low-energy
variations: comparison sort, insertion sort, counting sort, breadth-first
search, Bellman-Ford, Floyd-Warshall, matrix all-pairs shortest paths, AVL
trees, binary heaps, and dynamic arrays. We explore the time/space/energy
trade-off and develop several general techniques for analyzing algorithms and
reducing their energy complexity. These results lay a theoretical foundation
for a new field of semi-reversible computing and provide a new framework for
the investigation of algorithms.Comment: 40 pages, 8 pdf figures, full version of work published in ITCS 201
Ward Identities and chiral anomalies for coupled fermionic chains
Coupled fermionic chains are usually described by an effective model written
in terms of bonding and anti-bonding spinless fields with linear dispersion in
the vicinities of the respective Fermi points. We derive for the first time
exact Ward Identities (WI) for this model, proving the existence of chiral
anomalies which verify the Adler-Bardeen non-renormalization property. Such WI
are expected to play a crucial role in the understanding of the thermodynamic
properties of the system. Our results are non-perturbative and are obtained
analyzing Grassmann functional integrals by means of Constructive Quantum Field
Theory methods.Comment: TeX file, 26 pages, 7 figures. Published version, new section added
to answer referee remarks and derive the Ward Identites, no modifications in
the main resul
The scaling limit of the energy correlations in non integrable Ising models
We obtain an explicit expression for the multipoint energy correlations of a
non solvable two-dimensional Ising models with nearest neighbor ferromagnetic
interactions plus a weak finite range interaction of strength , in a
scaling limit in which we send the lattice spacing to zero and the temperature
to the critical one. Our analysis is based on an exact mapping of the model
into an interacting lattice fermionic theory, which generalizes the one
originally used by Schultz, Mattis and Lieb for the nearest neighbor Ising
model. The interacting model is then analyzed by a multiscale method first
proposed by Pinson and Spencer. If the lattice spacing is finite, then the
correlations cannot be computed in closed form: rather, they are expressed in
terms of infinite, convergent, power series in . In the scaling limit,
these infinite expansions radically simplify and reduce to the limiting energy
correlations of the integrable Ising model, up to a finite renormalization of
the parameters. Explicit bounds on the speed of convergence to the scaling
limit are derived.Comment: 75 pages, 11 figure
Demonstrating a smart controller in a hospital integrated energy system
Integrated energy systems have recently gained primary importance in clean energy transition. The combination of the electricity, heating and gas sectors can improve the overall system efficiency and integration of renewables by exploiting the synergies among the energy vectors. In particular, real-time optimization tools based on Model Predictive Control (MPC) can considerably improve the performance of systems with several conversion units and distribution networks by automatically coordinating all interacting technologies. Despite the relevance of several simulation studies on the topic, however, it is significantly harder to have an experimental demonstration of this improvement. This work presents a methodology for the real-world implementation of a novel smart control strategy for integrated energy systems, based on two coordinated MPC levels, which optimize the operation of all conversion units and all energy vectors in the short- and long-term, respectively, to account also for economic incentives on critical units. The strategy that was previously developed and evaluated in a simulation environment has now been implemented, as a supervisory controller, in the integrated energy system of a hospital in Italy. The optimal control logic is easily actuated by dynamically communicating the optimal set-points to the existing Building Management System, without having to alter the system configuration. Field data collected over a two-year period, firstly when it was business as usual and when the new operation was introduced, show that the MPC increased the economic margin and revenues from yearly incentives and lowered the amount of electricity purchased, reducing dependency on the power grid
An autonomous ground mobile unit for the precision physical weed control.
In this paper the design, the main characteristics and the automation systems of innovative
autonomous ground mobile units (GMU) for physical weed control (PWC) in maize are
described. The machine will be created within the activities of the European Project RHEA
(Robot fleets for Highly Effective Agriculture and forestry management), that aims to produce
different prototypes of autonomous terrestrial and aerial robot able to perform several
activities related to the general crop protection in different agricultural scenarios. The first
autonomous ground unit machine was designed in order to perform a mechanical and
thermal treatment removing weeds from the inter-row crop space and applying in-row
selective and precision flaming by means of two crossed LPG rod burners. By means of
some modifications of the tools it will be possible to realize also an autonomous unit for the
precision broadcast flaming application. In this case the design involves a replacement of the
mechanical tools working in the inter-row space with 50 cm wide burners able to perform
flaming at different intensities according to weed cover detected by the perception system of
the robot. The working width of both the PWC machines will be of 4.5 m, thus covering five
entire maize inter-row spaces of 0.75 m each and 2 half inter-row space of 0.375 m each.
The correct position of the tools (mechanical and thermal) will be guaranteed by an
automatic precision guidance system connected and supervised to an image based row
detection system. Each working elements will be provided by two crossed 0.25 m wide rod
burners, hitting one side of each crop row. The flame should hit the weeds growing in the “inrow”
space (a 0.25 m wide strip of soil with the maize plant in the middle). Regarding the
control of the weed emerged in the “inter-row” space each working unit of the will be provided
with rigid tools (one central foot-goose and two side “L” shaped sweeps). The mechanical
treatment will be performed, independently from the weed presence, as hoeing is a very
important agronomical practice. On the contrary, broadcast flaming in the inter-row space will
be performed after weed detection, using three different LPG pressures and doses according
to weed cover (no weed cover-no treatment, weed cover between 0 and 25%-flaming at 0.3
MPa, weed cover higher than 25%-flaming at 0.4 MPa). This very innovative application of
precision PWC in maize could represent not only a good opportunity for farmers in term of
herbicide use reduction, but also an environmental friendly and energy saving application of
flaming in organic farming
Development of an algorithm for assessing canopy volumes with terrestrial LiDAR to implement precision spraying in vineyards
Received: February 13th, 2021 ; Accepted: November 28th, 2021 ; Published: December 3rd, 2021 ; Correspondence: [email protected] spraying is one of the techniques for the reduction of pesticides use and it
can help achieve the new European Green Deal standards. The aim of such technique is to apply
the right amount of pesticides according to the target characteristics. The precision spraying
implementation requires target volume assessment, which can be carried out by LiDAR sensors.
Such technique requires complex and time-consuming procedures of canopy characteristics
computing through post-processing points cloud reconstruction. The present work aimed to
develop and test an algorithm through the use of a tractor-coupled with terrestrial LiDAR and
GNSS technology in order to simplify the process. With the aim to evaluate the algorithm the
LiDAR-based volume was correlated with two manual measurements of canopy volume (Tree
Row Volume and Point Net Cloud). The results showed good correlations between manual and
LiDAR measures both for total canopy volumes (R
2 = 0.67 and 0.56) and for partial canopy
volume (R
2 = 0.74). In conclusion, although the LiDAR-based algorithm works in automatic
mode, the canopy volumes approximation seems acceptable to estimate the canopy volumes, with
the advantages of a swifter procedure and less laborious post-processing computations
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