2,374 research outputs found
The Kovacs effect in the one-dimensional Ising model: a linear response analysis
We analyze the so-called Kovacs effect in the one-dimensional Ising model
with Glauber dynamics. We consider small enough temperature jumps, for which a
linear response theory has been recently derived. Within this theory, the
Kovacs hump is directly related to the monotonic relaxation function of the
energy. The analytical results are compared with extensive Monte Carlo
simulations, and an excellent agreement is found. Remarkably, the position of
the maximum in the Kovacs hump depends on the fact that the true asymptotic
behavior of the relaxation function is different from the stretched exponential
describing the relevant part of the relaxation at low temperatures.Comment: accepted for publication in Phys. Rev.
Bifurcation analysis and phase diagram of a spin-string model with buckled states
We analyze a one-dimensional spin-string model, in which string oscillators
are linearly coupled to their two nearest neighbors and to Ising spins
representing internal degrees of freedom. String-spin coupling induces a
long-range ferromagnetic interaction among spins that competes with a spin-spin
antiferromagnetic coupling. As a consequence, the complex phase diagram of the
system exhibits different flat rippled and buckled states, with first or second
order transition lines between states. The two-dimensional version of the model
has a similar phase diagram, which has been recently used to explain the
rippled to buckled transition observed in scanning tunnelling microscopy
experiments with suspended graphene sheets. Here we describe in detail the
phase diagram of the simpler one-dimensional model and phase stability using
bifurcation theory. This gives additional insight into the physical mechanisms
underlying the different phases and the behavior observed in experiments.Comment: 15 pages, 7 figure
Understanding the dependence on the pulling speed of the unfolding pathway of proteins
The dependence of the unfolding pathway of proteins on the pulling speed is
investigated. This is done by introducing a simple one-dimensional chain
comprising units, with different characteristic bistable free energies.
These units represent either each of the modules in a modular protein or each
of the intermediate "unfoldons" in a protein domain, which can be either folded
or unfolded. The system is pulled by applying a force to the last unit of the
chain, and the units unravel following a preferred sequence. We show that the
unfolding sequence strongly depends on the pulling velocity . In the
simplest situation, there appears a critical pulling speed : for pulling
speeds
it is the pulled unit that unfolds first. By means of a perturbative expansion,
we find quite an accurate expression for this critical velocity.Comment: accepted for publication in JSTA
Memory effects in vibrated granular systems
Granular materials present memory effects when submitted to tapping
processes. These effects have been observed experimentally and are discussed
here in the context of a general kind of model systems for compaction
formulated at a mesoscopic level. The theoretical predictions qualitatively
agree with the experimental results. As an example, a particular simple model
is used for detailed calculations.Comment: 12 pages, 5 figures; to appear in Journal of Physics: Condensed
Matter (Special Issue: Proceedings of ESF SPHINX Workshop on ``Glassy
behaviour of kinetically constrained models.''
Scaling and aging in the homogeneous cooling state of a granular fluid of hard particles
The presence of the aging phenomenon in the homogeneous cooling state (HCS)
of a granular fluid composed of inelastic hard spheres or disks is
investigated. As a consequence of the scaling property of the -particle
distribution function, it is obtained that the decay of the normalized two-time
correlation functions slows down as the time elapsed since the beginning of the
measurement increases. This result is confirmed by molecular dynamics
simulations for the particular case of the total energy of the system. The
agreement is also quantitative in the low density limit, for which an explicit
analytical form of the time correlation function has been derived. The reported
results also provide support for the existence of the HCS as a solution of the
N-particle Liouville equation.Comment: 17 pages, 3 figures; v3 revised version (minor changes, corrected
typos, v2=v1 due to a submission error)accepted for publication in J. Phys.
A: Math. Theo
Optimized LTE Data Transmission Procedures for IoT: Device Side Energy Consumption Analysis
The efficient deployment of Internet of Things (IoT) over cellular networks,
such as Long Term Evolution (LTE) or the next generation 5G, entails several
challenges. For massive IoT, reducing the energy consumption on the device side
becomes essential. One of the main characteristics of massive IoT is small data
transmissions. To improve the support of them, the 3GPP has included two novel
optimizations in LTE: one of them based on the Control Plane (CP), and the
other on the User Plane (UP). In this paper, we analyze the average energy
consumption per data packet using these two optimizations compared to
conventional LTE Service Request procedure. We propose an analytical model to
calculate the energy consumption for each procedure based on a Markov chain. In
the considered scenario, for large and small Inter-Arrival Times (IATs), the
results of the three procedures are similar. While for medium IATs CP reduces
the energy consumption per packet up to 87% due to its connection release
optimization
- …