31,697 research outputs found
Integrability and chemical potential in the (3+1)-dimensional Skyrme model
Using a remarkable mapping from the original (3+1)dimensional Skyrme model to
the Sine-Gordon model, we construct the first analytic examples of Skyrmions as
well as of Skyrmions--anti-Skyrmions bound states within a finite box in 3+1
dimensional flat space-time. An analytic upper bound on the number of these
Skyrmions--anti-Skyrmions bound states is derived. We compute the critical
isospin chemical potential beyond which these Skyrmions cease to exist. With
these tools, we also construct topologically protected time-crystals:
time-periodic configurations whose time-dependence is protected by their
non-trivial winding number. These are striking realizations of the ideas of
Shapere and Wilczek. The critical isospin chemical potential for these
time-crystals is determined.Comment: 15 pages; 1 figure; a discussion on the closeness to the topological
bound as well as some clarifying comments on the semi-classical quantization
have been included. Relevant references have been added. Version accepted for
publication on Physics Letters
Competition between noise and coupling in the induction of synchronisation.
We apply a Fokker-Planck analysis to investigate the relative influences of coupling strength and noise on the synchronisation of two phase oscillators. We go beyond earlier studies of noise-induced synchronisation (without couplings) and coupling-induced synchronisation (without common noise) to consider both effects together, and we obtain a result that is very different from a straightforward superposition of the effects of each agent acting alone: two regimes are possible depending on which agent is inducing the synchronisation. In each regime, one agent induces and the other hinders the synchronisation. In particular we show that, counterintuitively, coupling can sometimes inhibit synchronisation
An innovative tool to evaluate and optimize GHG emissions in the food supply
Food systems’ contribution to GHG emissions is estimated to be around 30% of the total emissions. Heating and cooling technologies in food supply chains are highly important in maintaining the safety and quality of perishable food, but these operations are also energy-intensive and GHG emitters.
Simulation tools can be essential for the evaluation of the efficiency and sustainability of food supply chains.
Such tools can help in identifying critical points in those chains where efforts should be concentrated to reduce energy consumption and emissions. The software tool presented in this paper can perform a detailed analysis of the food supply chains with a focus on quality, energy consumption, and CO2 emissions. Based on a tool previously developed in the European FRISBEE project about refrigeration technologies, the software is extended to the simulation of non-perishable foods, heating processes, use of renewable energy sources, and use of heat recovery. This simulation tool will suggest possible improvements of simulated chains to reduce GHG emissions, based on roadmaps developed in ENOUGH European project
Duality in Non-Trivially Compactified Heterotic Strings
We study the implications of duality symmetry on the analyticity properties
of the partition function as it depends upon the compactification length. In
order to obtain non-trivial compactifications, we give a physical prescription
to get the Helmholtz free energy for any heterotic string supersymmetric or
not. After proving that the free energy is always invariant under the duality
transformation and getting the zero temperature
theory whose partition function corresponds to the Helmholtz potential, we show
that the self-dual point is a generic singularity
as the Hagedorn one. The main difference between these two critical
compactification radii is that the term producing the singularity at the
self-dual point is finite for any . We see that this behavior at
actually implies a loss of degrees of freedom below that point.Comment: (Preprint No. FTUAM-92/12) 17 page
Thermodynamic modeling of phase separation in manganites
We present a phenomenological model based on the thermodynamics of the phase
separated state of manganites, accounting for its static and dynamic
properties. Through calorimetric measurements on LaPrCaMnO the low temperature free energies of the coexisting
ferromagnetic and charge ordered phases are evaluated. The phase separated
state is modeled by free energy densities uniformly spread over the sample
volume. The calculations contemplate the out of equilibrium features of the
coexisting phase regime, to allow a comparison between magnetic measurements
and the predictions of the model. A phase diagram including the static and
dynamic properties of the system is constructed, showing the existence of
blocked and unblocked regimes which are characteristics of the phase separated
state in manganites.Comment: 7 pages, 5 figures, Submitted to Phys. Rev.
Conflict-Free Coloring of Planar Graphs
A conflict-free k-coloring of a graph assigns one of k different colors to
some of the vertices such that, for every vertex v, there is a color that is
assigned to exactly one vertex among v and v's neighbors. Such colorings have
applications in wireless networking, robotics, and geometry, and are
well-studied in graph theory. Here we study the natural problem of the
conflict-free chromatic number chi_CF(G) (the smallest k for which
conflict-free k-colorings exist). We provide results both for closed
neighborhoods N[v], for which a vertex v is a member of its neighborhood, and
for open neighborhoods N(v), for which vertex v is not a member of its
neighborhood.
For closed neighborhoods, we prove the conflict-free variant of the famous
Hadwiger Conjecture: If an arbitrary graph G does not contain K_{k+1} as a
minor, then chi_CF(G) <= k. For planar graphs, we obtain a tight worst-case
bound: three colors are sometimes necessary and always sufficient. We also give
a complete characterization of the computational complexity of conflict-free
coloring. Deciding whether chi_CF(G)<= 1 is NP-complete for planar graphs G,
but polynomial for outerplanar graphs. Furthermore, deciding whether
chi_CF(G)<= 2 is NP-complete for planar graphs G, but always true for
outerplanar graphs. For the bicriteria problem of minimizing the number of
colored vertices subject to a given bound k on the number of colors, we give a
full algorithmic characterization in terms of complexity and approximation for
outerplanar and planar graphs.
For open neighborhoods, we show that every planar bipartite graph has a
conflict-free coloring with at most four colors; on the other hand, we prove
that for k in {1,2,3}, it is NP-complete to decide whether a planar bipartite
graph has a conflict-free k-coloring. Moreover, we establish that any general}
planar graph has a conflict-free coloring with at most eight colors.Comment: 30 pages, 17 figures; full version (to appear in SIAM Journal on
Discrete Mathematics) of extended abstract that appears in Proceeedings of
the Twenty-Eighth Annual ACM-SIAM Symposium on Discrete Algorithms (SODA
2017), pp. 1951-196
CSU FIRE 2 cirrus field experiment: Description of field deployment phase
The Colorado State University (CSU) surface observing systems are described. These systems were deployed at the Parsons, Kansas site during the FIRE 2 Cirrus Special Observing Period (SOP) from 13 Nov. - 7 Dec. 1991. The geographical coordinates of the site containing most of the CSU instrumentation are 37 deg. 18 min N. latitude and 96 deg. 30 min. W. longitude; site elevation was 269 meters. In addition, one surface meteorological and broadband flux observing site was maintained at the Tri City Airport which is approximately 18 miles due west of Parsons (37 deg. 20 min. N. latitude, 95 deg. 30 min. 30 sec. W. longitude). A map of the locations of the CSU deployment sites is presented. At the main Parsons site, the instrumentation was located directly adjacent to and north of a lake. Under most cirrus observing conditions, when the wing had a significant southernly component, the lake was upwind of the observing site. The measurements and observations collected during the experiment are listed. These measurements may be grouped into five categories: surface meteorology; infrared spectral and broadband measurements; solar spectral and broadband measurements; upper air measurements; and cloud measurements. A summary of observations collected at the Parsons site during the SOP are presented. The wind profiler, laser ceilometer, surface meteorology and surface broadband radiation instrumentation were operated on a continuous basis. All other systems were operated on an 'on demand' basis when cloud conditions merited the collection of data
The Equivalence Principle in the Non-baryonic Regime
We consider the empirical validity of the equivalence principle for
non-baryonic matter. Working in the context of the TH\epsilon\mu formalism, we
evaluate the constraints experiments place on parameters associated with
violation of the equivalence principle (EVPs) over as wide a sector of the
standard model as possible. Specific examples include new parameter constraints
which arise from torsion balance experiments, gravitational red shift,
variation of the fine structure constant, time-dilation measurements, and
matter/antimatter experiments. We find several new bounds on EVPs in the
leptonic and kaon sectors.Comment: 22 pages, late
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