10,722 research outputs found
One-dimensional Ising ferromagnet frustrated by long-range interactions at finite temperatures
We consider a one-dimensional lattice of Ising-type variables where the
ferromagnetic exchange interaction J between neighboring sites is frustrated by
a long-ranged anti-ferromagnetic interaction of strength g between the sites i
and j, decaying as |i-j|^-alpha, with alpha>1. For alpha smaller than a certain
threshold alpha_0, which is larger than 2 and depends on the ratio J/g, the
ground state consists of an ordered sequence of segments with equal length and
alternating magnetization. The width of the segments depends on both alpha and
the ratio J/g. Our Monte Carlo study shows that the on-site magnetization
vanishes at finite temperatures and finds no indication of any phase
transition. Yet, the modulation present in the ground state is recovered at
finite temperatures in the two-point correlation function, which oscillates in
space with a characteristic spatial period: The latter depends on alpha and J/g
and decreases smoothly from the ground-state value as the temperature is
increased. Such an oscillation of the correlation function is exponentially
damped over a characteristic spatial scale, the correlation length, which
asymptotically diverges roughly as the inverse of the temperature as T=0 is
approached. This suggests that the long-range interaction causes the Ising
chain to fall into a universality class consistent with an underlying
continuous symmetry. The e^(Delta/T)-temperature dependence of the correlation
length and the uniform ferromagnetic ground state, characteristic of the g=0
discrete Ising symmetry, are recovered for alpha > alpha_0.Comment: 12 pages, 7 figure
Two-dimensional quantum spin-1/2 Heisenberg model with competing interactions
We study the quantum spin-1/2 Heisenberg model in two dimensions, interacting
through a nearest-neighbor antiferromagnetic exchange () and a ferromagnetic
dipolar-like interaction (), using double-time Green's function, decoupled
within the random phase approximation (RPA). We obtain the dependence of as a function of frustration parameter , where is the
ferromagnetic (F) transition temperature and is the ratio between the
strengths of the exchange and dipolar interaction (i.e., ). The
transition temperature between the F and paramagnetic phases decreases with
, as expected, but goes to zero at a finite value of this parameter,
namely . At T=0 (quantum phase transition), we
analyze the critical parameter for the general case of an
exchange interaction in the form , where ferromagnetic
and antiferromagnetic phases are present.Comment: 4 pages, 1 figur
Giant reversible barocaloric response of (MnNiSi)(1-x)(FeCoGe)(x) (x=0.39, 0.40, 0.41)
MnNiSi-based alloys and isostructural systems have traditionally demonstrated impressive magnetocaloric properties near room temperature associated with a highly tunable first-order magnetostructural transition that involves large latent heat. However, these materials are limited by a small field-sensitivity of the transition, preventing significant reversible effects usable for cooling applications. Instead, the concomitant large transition volume changes prompt a high pressure-sensitivity, and therefore, promise substantial barocaloric performances, but they have been sparsely studied in these materials. Here, we study the barocaloric response in a series of composition-related (MnNiSi)1-x(FeCoGe)x (x = 0.39, 0.40, 0.41) alloys that span continuously over a wide temperature range around ambient. We report on giant reversible effects of ~40 J K-1 kg-1 and up to ~4 K upon application of ~2 kbar and find a degradation of the first-order transition properties with pressure that limits the barocaloric effects at high pressures. Our results confirm the potential of this type of alloys for barocaloric applications, where multicaloric and composite possibilities, along with the high density and relatively high thermal conductivity, constructively add to the magnitude of the caloric effects.Peer ReviewedPostprint (published version
Formation of stripes and slabs near the ferromagnetic transition
We consider Ising models in d=2 and d=3 dimensions with nearest neighbor
ferromagnetic and long-range antiferromagnetic interactions, the latter
decaying as (distance)^(-p), p>2d, at large distances. If the strength J of the
ferromagnetic interaction is larger than a critical value J_c, then the ground
state is homogeneous. It has been conjectured that when J is smaller than but
close to J_c the ground state is periodic and striped, with stripes of constant
width h=h(J), and h tends to infinity as J tends to J_c from below. (In d=3
stripes mean slabs, not columns.) Here we rigorously prove that, if we
normalize the energy in such a way that the energy of the homogeneous state is
zero, then the ratio e_0(J)/e_S(J) tends to 1 as J tends to J_c from below,
with e_S(J) being the energy per site of the optimal periodic striped/slabbed
state and e_0(J) the actual ground state energy per site of the system. Our
proof comes with explicit bounds on the difference e_0(J)-e_S(J) at small but
finite J_c-J, and also shows that in this parameter range the ground state is
striped/slabbed in a certain sense: namely, if one looks at a randomly chosen
window, of suitable size l (very large compared to the optimal stripe size
h(J)), one finds a striped/slabbed state with high probability.Comment: 23 pages, 2 figures. We discovered that our analysis works in 3D as
well as in 2D. We revised the paper and the title to reflect this. Our 2D
stripes become 3D slabs. Some references adde
Aging dynamics of +-J Edwards-Anderson spin glasses
We analyze by means of extensive computer simulations the out of equilibrium
dynamics of Edwards-Anderson spin glasses in d=4 and d=6 dimensions with +-J
interactions. In particular, we focus our analysis on the scaling properties of
the two-time autocorrelation function in a range of temperatures from T=0.07
T_c to T=0.75 T_c in both systems. We observe that the aging dynamics of the
+-J models is different from that observed in the corresponding Gaussian
models. In both the 4d and 6d models at very low temperatures we study the
effects of discretization of energy levels. Strong interrupted aging behaviors
are found. We argue that this is because in the times accessible to our
simulations the systems are only able to probe activated dynamics through the
lowest discrete energy levels and remain trapped around nearly flat regions of
the energy landscape. For temperatures T >= 0.5 T_c in 4d we find logarithmic
scalings that are compatible with dynamical ultrametricity, while in 6d the
relaxation can also be described by super-aging scalings.Comment: 7 pages, 10 figure
Opinion dynamics and synchronization in a network of scientific collaborations
In this paper we discuss opinion dynamics in the Opinion Changing Rate (OCR)
model, recently proposed (A.Pluchino, V.Latora and A.Rapisarda Int. J. Mod.
Phys. C, 16, No.4, 515-531 (2005)). The OCR model allows to study whether and
how a group of social agents, with a different intrinsic tendency rate to
change opinion, finds agreement. In particular, we implement the OCR model on a
small graph describing the topology of a real social system. The nodes of the
graph are scientists partecipating to the Tepoztlan conference, celebrating
Alberto Robledo's 60th birthday, and the links are based on coauthorship in
scientific papers. We study how opinions evolve in time according to the
frequency rates of the nodes, to the coupling term, and also to the presence of
group structures.Comment: 15 pages, 4 figures, Physica A (2006) in pres
Stability as a natural selection mechanism on interacting networks
Biological networks of interacting agents exhibit similar topological
properties for a wide range of scales, from cellular to ecological levels,
suggesting the existence of a common evolutionary origin. A general
evolutionary mechanism based on global stability has been proposed recently [J
I Perotti, O V Billoni, F A Tamarit, D R Chialvo, S A Cannas, Phys. Rev. Lett.
103, 108701 (2009)]. This mechanism is incorporated into a model of a growing
network of interacting agents in which each new agent's membership in the
network is determined by the agent's effect on the network's global stability.
We show that, out of this stability constraint, several topological properties
observed in biological networks emerge in a self organized manner. The
influence of the stability selection mechanism on the dynamics associated to
the resulting network is analyzed as well.Comment: 10 pages, 9 figure
Realization of stripes and slabs in two and three dimensions
We consider Ising models in two and three dimensions with nearest neighbor
ferromagnetic interactions and long range, power law decaying,
antiferromagnetic interactions. If the strength of the ferromagnetic coupling J
is larger than a critical value J_c, then the ground state is homogeneous and
ferromagnetic. As the critical value is approached from smaller values of J, it
is believed that the ground state consists of a periodic array of stripes (d=2)
or slabs (d=3), all of the same size and alternating magnetization. Here we
prove rigorously that the ground state energy per site converges to that of the
optimal periodic striped/slabbed state, in the limit that J tends to the
ferromagnetic transition point. While this theorem does not prove rigorously
that the ground state is precisely striped/slabbed, it does prove that in any
suitably large box the ground state is striped/slabbed with high probability.Comment: 4 pages, 1 figur
ReverCSP: Time-Travelling in CSP Computations
[EN] This paper presents reverCSP, a tool to animate both forward and backward CSP computations. This ability to reverse computations can be done step by step or backtracking to a given desired state of interest. reverCSP allows us to reverse computations exactly in the same order in which they happened, or also in a causally-consistent way. Therefore, reverCSP is a tool that can be especially useful to comprehend, analyze, and debug computations. reverCSP is an open-source project publicly available for the community. We describe the tool and its functionality, and we provide implementation details so that it can be reimplemented for other languages.This work has been partially supported by the EU (FEDER)
and the Spanish MCI/AEI under grants TIN2016-76843-C4-1-R and PID2019-
104735RB-C41, and by the Generalitat Valenciana under grant Prometeo/2019/098
(DeepTrust).Galindo-Jiménez, CS.; Nishida, N.; Silva, J.; Tamarit, S. (2020). ReverCSP: Time-Travelling in CSP Computations. Springer. 239-245. https://doi.org/10.1007/978-3-030-52482-1_14S239245Bernadet, A., Lanese, I.: A modular formalization of reversibility for concurrent models and languages. In: Proceedings of ICE 2016, EPTCS (2016)Brown, G., Sabry, A.: Reversible communicating processes. Electron. Proc. Theor. Comput. Sci. 203, 45–59 (2016)Conserva Filhoa, M., Oliveira, M., Sampaio, A., Cavalcanti, A.: Compositional and local livelock analysis for CSP. Inf. Process. Lett 133, 21–25 (2018)Danos, V., Krivine, J.: Reversible communicating systems. In: Gardner, P., Yoshida, N. (eds.) CONCUR 2004. LNCS, vol. 3170, pp. 292–307. Springer, Heidelberg (2004). https://doi.org/10.1007/978-3-540-28644-8_19Elnozahy, E.N.M., Alvisi, L., Wang, Y.-M., Johnson, D.B.: A survey of rollback- recovery protocols in message-passing systems. ACM Comput. Surv. 34(3), 375–408 (2002)Fang, Y., Zhu, H., Zeyda, F., Fei, Y.: Modeling and analysis of the disruptor framework in csp. In: Proceedings of CCWC 2018. IEEE Computer Society (2018)Ladkin, P.B., Simons, B.B.: Static deadlock analysis for CSP-type communications. In: Fussell, D.S., Malek, M. (eds.) Responsive Computer Systems: Steps Toward Fault-Tolerant Real-Time Systems. The Springer International Series in Engineering and Computer Science, vol. 297, pp. 89–102. Springer, Boston (1995). https://doi.org/10.1007/978-1-4615-2271-3_5Landauer, R.: Irreversibility and heat generation in the computing process. IBM J. Res. Dev. 5, 183–191 (1961)Lanese, I., Antares Mezzina, C., Tiezzi, F.: Causal-consistent reversibility. Bull. EATCS 114, 17 (2014)Lanese, I., Nishida, N., Palacios, A., Vidal, G.: CauDEr: a causal-consistent reversible debugger for erlang. In: Gallagher, J.P., Sulzmann, M. (eds.) FLOPS 2018. LNCS, vol. 10818, pp. 247–263. Springer, Cham (2018). https://doi.org/10.1007/978-3-319-90686-7_16Lanese, I., Palacios, A., Vidal, G.: Causal-consistent replay debugging for message passing programs. In: Pérez, J.A., Yoshida, N. (eds.) FORTE 2019. LNCS, vol. 11535, pp. 167–184. Springer, Cham (2019). https://doi.org/10.1007/978-3-030-21759-4_10Llorens, M., Oliver, J., Silva, J., Tamarit, S.: Dynamic slicing of concurrent specification languages. Parallel Comput. 53, 1–22 (2016)Llorens, M., Oliver, J., Silva, J., Tamarit, S.: Tracking CSP computations. J. Log. Algebr. Meth. Program. 102, 138–175 (2019)Perera, R., Garg, D., Cheney, J.: Causally consistent dynamic slicing. In Proceedings of CONCUR 2016, LIPIcs, vol. 59, pp. 18:1–18:15 (2016)Phillips, I., Ulidowski, I., Yuen, S.: A reversible process calculus and the modelling of the ERK signalling pathway. In: Glück, R., Yokoyama, T. (eds.) RC 2012. LNCS, vol. 7581, pp. 218–232. Springer, Heidelberg (2013). https://doi.org/10.1007/978-3-642-36315-3_18Roscoe, A.W.: The Theory and Practice of Concurrency. Prentice Hall PTR, Upper Saddle River (1997)Zhao, H., Zhu, H., Yucheng, F., Xiao, L.: Modeling and verifying storm using CSP. In: Proceedings of HASE 2019. IEEE Computer Society (2019
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