On the Reliability of LTE Random Access: Performance Bounds for Machine-to-Machine Burst Resolution Time

Random Access Channel (RACH) has been identified as one of the major bottlenecks for accommodating massive number of machine-to-machine (M2M) users in LTE networks, especially for the case of burst arrival of connection requests. As a consequence, the burst resolution problem has sparked a large number of works in the area, analyzing and optimizing the average performance of RACH. However, the understanding of what are the probabilistic performance limits of RACH is still missing. To address this limitation, in the paper, we investigate the reliability of RACH with access class barring (ACB). We model RACH as a queuing system, and apply stochastic network calculus to derive probabilistic performance bounds for burst resolution time, i.e., the worst case time it takes to connect a burst of M2M devices to the base station. We illustrate the accuracy of the proposed methodology and its potential applications in performance assessment and system dimensioning.Comment: Presented at IEEE International Conference on Communications (ICC), 201

Statistical Delay Bound for WirelessHART Networks

In this paper we provide a performance analysis framework for wireless industrial networks by deriving a service curve and a bound on the delay violation probability. For this purpose we use the (min,x) stochastic network calculus as well as a recently presented recursive formula for an end-to-end delay bound of wireless heterogeneous networks. The derived results are mapped to WirelessHART networks used in process automation and were validated via simulations. In addition to WirelessHART, our results can be applied to any wireless network whose physical layer conforms the IEEE 802.15.4 standard, while its MAC protocol incorporates TDMA and channel hopping, like e.g. ISA100.11a or TSCH-based networks. The provided delay analysis is especially useful during the network design phase, offering further research potential towards optimal routing and power management in QoS-constrained wireless industrial networks.Comment: Accepted at PE-WASUN 201

Searching for the statistically equilibrated systems formed in heavy ion collisions

Further improvements and refinements are brought to the microcanonical multifragmentation model [Al. H. Raduta and Ad. R. Raduta, Phys. Rev. C {\bf 55}, 1344 (1997); {\it ibid.} {\bf 61}, 034611 (2000)]. The new version of the model is tested on the recently published experimental data concerning the Xe+Sn at 32 MeV/u and Gd+U at 36 MeV/u reactions. A remarkable good simultaneous reproduction of fragment size observables and kinematic observables is to be noticed. It is shown that the equilibrated source can be unambiguously identified.Comment: Physical Review C, in pres

HP1 reshapes nucleosome core to promote phase separation of heterochromatin

Heterochromatin affects genome function at many levels. It enables heritable gene repression, maintains chromosome integrity and provides mechanical rigidity to the nucleus1,2. These diverse functions are proposed to arise in part from compaction of the underlying chromatin2. A major type of heterochromatin contains at its core the complex formed between HP1 proteins and chromatin that is methylated on histone H3, lysine 9 (H3K9me). HP1 is proposed to use oligomerization to compact chromatin into phase-separated condensates3-6. Yet, how HP1-mediated phase separation relates to chromatin compaction remains unclear. Here we show that chromatin compaction by the Schizosaccharomyces pombe HP1 protein Swi6 results in phase-separated liquid condensates. Unexpectedly, we find that Swi6 substantially increases the accessibility and dynamics of buried histone residues within a nucleosome. Restraining these dynamics impairs compaction of chromatin into liquid droplets by Swi6. Our results indicate that Swi6 couples its oligomerization to the phase separation of chromatin by a counterintuitive mechanism, namely the dynamic exposure of buried nucleosomal regions. We propose that such reshaping of the octamer core by Swi6 increases opportunities for multivalent interactions between nucleosomes, thereby promoting phase separation. This mechanism may more generally drive chromatin organization beyond heterochromatin