Cluster Lifetime Research Articles

Energy-efficient data-gathering rendezvous algorithms with mobile sinks for wireless sensor networks

Energy conservation or energy balance in the process of data gathering has always been a crucial issue for prolonging the lifetime of wireless sensor networks (WSNs), especially on the premise of the introduction of mobile elements to cope with the phenomenon of hot spots or energy holes. In this paper, we propose optimal cluster-based mechanisms by a modified multi-hop layered model for load balancing with multiple mobile sinks for these problems. Furthermore, under the condition of a delay-tolerant application, rendezvous points (RPs) and rendezvous nodes (RNs) are utilised to realise the goal of optimal/suboptimal energy consumption in the sense of energy transmission model through a heuristic algorithm in a geometrical way. To further reduce the consumption of network energy, quantisation technologies are exploited. As a result, we analyse the cluster lifetimes in different situations and achieve balance to save significant energy.

Cluster Lifetime Analysis for Cooperative Beamforming in Wireless Sensor Networks

Cooperative multiple input multiple outputs (MIMO) or its variation cooperative multiple input single outputs (MISO) is becoming a potential technique to minimize the energy consumption and prolong lifetime in wireless sensor networks. For cluster based wireless sensor networks, cluster lifetime for cooperative beamforming (CBF) based cooperative MISO scheme is studied in this paper.We first establish the energy model of a cluster with cooperative MISO scheme based on CBF. Based on the energy consumption model, the effects of cluster size and distance between cluster and sink node on the performance of cluster lifetime are discussed, an joint optimization to maximize cluster lifetime by finding the optimal modulation parameter and number of cooperative nodes is proposed. Numerical results show that CBF based cooperative MISO scheme can achieve longer cluster lifetime compare with STBC and the joint optimization can further improve the cluster lifetime.

Super-resolution imaging of fluorescently labeled, endogenous RNA Polymerase II in living cells with CRISPR/Cas9-mediated gene editing.

Live cell imaging of mammalian RNA polymerase II (Pol II) has previously relied on random insertions of exogenous, mutant Pol II coupled with the degradation of endogenous Pol II using a toxin, α-amanitin. Therefore, it has been unclear whether over-expression of labeled Pol II under an exogenous promoter may have played a role in reported Pol II dynamics in vivo. Here we label the endogenous Pol II in mouse embryonic fibroblast (MEF) cells using the CRISPR/Cas9 gene editing system. Using single-molecule based super-resolution imaging in the living cells, we captured endogenous Pol II clusters. Consistent with previous studies, we observed that Pol II clusters were short-lived (cluster lifetime ~8 s) in living cells. Moreover, dynamic responses to serum-stimulation, and drug-mediated transcription inhibition were all in agreement with previous observations in the exogenous Pol II MEF cell line. Our findings suggest that previous exogenously tagged Pol II faithfully recapitulated the endogenous polymerase clustering dynamics in living cells, and our approach may in principle be used to directly label transcription factors for live cell imaging.

How multiple supernovae overlap to form superbubbles

We explore the formation of superbubbles through energy deposition by multiple supernovae (SNe) in a uniform medium. We use total energy conserving, 3-D hydrodynamic simulations to study how SNe correlated in space and time create superbubbles. While isolated SNe fizzle out completely by $\sim 1$ Myr due to radiative losses, for a realistic cluster size it is likely that subsequent SNe go off within the hot/dilute bubble and sustain the shock till the cluster lifetime. For realistic cluster sizes, we find that the bubble remains overpressured only if, for a given $n_{g0}$, $N_{\rm OB}$ is sufficiently large. While most of the input energy is still lost radiatively, superbubbles can retain up to $\sim 5-10\%$ of the input energy in form of kinetic+thermal energy till 10 Myr for ISM density $n_{g0} \approx 1$ cm$^{-3}$. We find that the mechanical efficiency decreases for higher densities ($\eta_{\rm mech} \propto n_{g0}^{-2/3}$). We compare the radii and velocities of simulated supershells with observations and the classical adiabatic model. Our simulations show that the superbubbles retain only $\lesssim 10\%$ of the injected energy, thereby explaining the observed smaller size and slower expansion of supershells. We also confirm that a sufficiently large ($\gtrsim 10^4$) number of SNe is required to go off in order to create a steady wind with a stable termination shock within the superbubble. We show that the mechanical efficiency increases with increasing resolution, and that explicit diffusion is required to obtain converged results.

A viscoelastic-stochastic model of the effects of cytoskeleton remodelling on cell adhesion.

Cells can adapt their mechanical properties through cytoskeleton remodelling in response to external stimuli when the cells adhere to the extracellular matrix (ECM). Many studies have investigated the effects of cell and ECM elasticity on cell adhesion. However, experiments determined that cells are viscoelastic and exhibiting stress relaxation, and the mechanism behind the effect of cellular viscoelasticity on the cell adhesion behaviour remains unclear. Therefore, we propose a theoretical model of a cluster of ligand–receptor bonds between two dissimilar viscoelastic media subjected to an applied tensile load. In this model, the distribution of interfacial traction is assumed to follow classical continuum viscoelastic equations, whereas the rupture and rebinding of individual molecular bonds are governed by stochastic equations. On the basis of this model, we determined that viscosity can significantly increase the lifetime, stability and dynamic strength of the adhesion cluster of molecular bonds, because deformation relaxation attributed to the viscoelastic property can increase the rebinding probability of each open bond and reduce the stress concentration in the adhesion area.

Birth of NaCl Crystals: Insights from Molecular Simulations.

Molecular dynamics simulations are used to investigate the factors that influence the nucleation of NaCl crystals in a supersaturated aqueous solution. We describe a methodology for detecting solidlike NaCl clusters (potential nuclei) and following their evolution in time until they achieve nucleation (which is very rare) or dissolve back into solution. Through an analysis of cluster lifetimes and multiple nucleation events, we demonstrate that cluster size is not the only property that influences cluster stability and the probability of achieving nucleation. We introduce a parameter called cluster crystallinity, which is a measure of the solidlike order in a particular cluster. We show that cluster order (as measured by this parameter) has a strong influence on the lifetime and nucleation probability of clusters of equal sizes, with the lifetime and probability of nucleation increasing with increasing crystallinity. These observations remain true for clusters as small as six ions, showing that the structural factors are important even at the earliest stages of crystal birth.

A Cognitive Self-Organising Clustering Algorithm for Urban Scenarios

Cooperative communications based on data sharing and relaying have been gaining huge interest lately, due to the increase in the number of mobile devices and the advancement in their capabilities. Research on green communications, location based services and mobile social networking have fueled research on this topic. Vehicular technology have also fostered this cooperative approach as a means to provide scalability and privacy preserving mechanisms. In these scenarios, a commonly suggested approach to benefit from cooperation is the formation of virtual groups of mobile terminals, usually referred to as clusters. Mobility-aware clustering algorithms are commonly proposed to form such clusters based on the mobility characteristics of the mobile devices. However, these solutions are limited by the unpredictable nature of mobility behavior that leads to frequent disconnections of nodes from clusters; hence reducing the time availability of cooperative relationships. In this paper, we go beyond existing research on clustering by including a cognitive perspective. We propose data mining and cooperative optimization in order to deduce mobility pattern information in conjunction with the clustering process. We propose a low complexity algorithm that can dynamically adapt to different mobility characteristics of an urban scenario, more importantly without the need for previous configuration/information. The proposed technique achieves considerable gains in terms of stability in urban scenarios. Additionally, the paper presents a comprehensive analytical evaluation of the problem and the proposed solution, and provides extended simulation results in both matlab and ns2. Results show an outstanding gain up to 150 % in cluster lifetime and 250 % in residence time of nodes within clusters and reduces the overhead for clustering maintenance in 70 %.

CACONET: Ant Colony Optimization (ACO) Based Clustering Algorithm for VANET.

A vehicular ad hoc network (VANET) is a wirelessly connected network of vehicular nodes. A number of techniques, such as message ferrying, data aggregation, and vehicular node clustering aim to improve communication efficiency in VANETs. Cluster heads (CHs), selected in the process of clustering, manage inter-cluster and intra-cluster communication. The lifetime of clusters and number of CHs determines the efficiency of network. In this paper a Clustering algorithm based on Ant Colony Optimization (ACO) for VANETs (CACONET) is proposed. CACONET forms optimized clusters for robust communication. CACONET is compared empirically with state-of-the-art baseline techniques like Multi-Objective Particle Swarm Optimization (MOPSO) and Comprehensive Learning Particle Swarm Optimization (CLPSO). Experiments varying the grid size of the network, the transmission range of nodes, and number of nodes in the network were performed to evaluate the comparative effectiveness of these algorithms. For optimized clustering, the parameters considered are the transmission range, direction and speed of the nodes. The results indicate that CACONET significantly outperforms MOPSO and CLPSO.

RNA Polymerase II cluster dynamics predict mRNA output in living cells.

Protein clustering is a hallmark of genome regulation in mammalian cells. However, the dynamic molecular processes involved make it difficult to correlate clustering with functional consequences in vivo. We developed a live-cell super-resolution approach to uncover the correlation between mRNA synthesis and the dynamics of RNA Polymerase II (Pol II) clusters at a gene locus. For endogenous β-actin genes in mouse embryonic fibroblasts, we observe that short-lived (~8 s) Pol II clusters correlate with basal mRNA output. During serum stimulation, a stereotyped increase in Pol II cluster lifetime correlates with a proportionate increase in the number of mRNAs synthesized. Our findings suggest that transient clustering of Pol II may constitute a pre-transcriptional regulatory event that predictably modulates nascent mRNA output.

The temporal evolution of a long‐lived contrail cirrus cluster: Simulations with a global climate model

AbstractThe representation of contrail cirrus in climate models has advanced in the last years tremendously. Nevertheless, uncertainties in particular regarding the representation of contrail microphysics still remain. Properties of young contrail cirrus differ from those of natural cirrus due to the large ice crystal number concentration common in contrails. Consequently, microphysical process rates in contrail cirrus, which control its lifetime, can be very different to those in natural cirrus. We extend a contrail cirrus scheme within a climate model by implementing a microphysical two‐moment scheme and study the life cycle of a contrail cirrus cluster. In an idealized experiment we study the properties and microphysical process rates of a contrail cirrus cluster in a large and long‐lived ice supersaturated region. We find that at flight level contrail cirrus display their typical high ice crystal number concentration (of about 10–100 cm−3) for a few hours with far lower densities in lower levels caused by sedimentation. After about 7 h contrail cirrus have spread considerably so that even at flight level associated ice crystal number concentrations have dropped to values that prohibit fast relaxation of ice supersaturation. The reduced ice crystal number and the resulting limited water uptake in the contrail cirrus limit the lifetime of the contrail cirrus cluster to about 10 h even though surrounding conditions would be still favorable for contrail cirrus persistence. In our case studies, contrail cirrus resembles natural cirrus regarding their ice crystal number concentration and size after 5–7 h.

INTERRUPTED BINARY MASS TRANSFER IN STAR CLUSTERS

ABSTRACT Binary mass transfer (MT) is at the forefront of some of the most exciting puzzles of modern astrophysics, including SNe Ia, gamma-ray bursts, and the formation of most observed exotic stellar populations. Typically, the evolution is assumed to proceed in isolation, even in dense stellar environments such as star clusters. In this paper, we test the validity of this assumption via the analysis of a large grid of binary evolution models simulated with the SeBa code. For every binary, we calculate analytically the mean time until another single or binary star comes within the mean separation of the mass-transferring binary, and compare this timescale to the mean time for stable MT to occur. We then derive the probability for each respective binary to experience a direct dynamical interruption. The resulting probability distribution can be integrated to give an estimate for the fraction of binaries undergoing MT that are expected to be disrupted as a function of the host cluster properties. We find that for lower-mass clusters ( ≲ 10 4 ?> M ⊙ ?> ), on the order of a few to a few tens of percent of binaries undergoing MT are expected to be interrupted by an interloping single, or more often binary, star, over the course of the cluster lifetime, whereas in more massive globular clusters we expect ≪ 1 % ?> to be interrupted. Furthermore, using numerical scattering experiments performed with the FEWBODY code, we show that the probability of interruption increases if perturbative fly-bys are considered as well, by a factor ∼2.

Predictability and Control of Gene Bursting in Live Mammalian Cells

Transcriptional bursting is a hallmark for cellular variability across species. Whether predictability and output control exist within the stochastic bursting process is unknown. Here, we advance that collective behaviors from transient bio-molecular interactions help confer gene expression control in mammalian cells. We developed a live cell super-resolution approach to uncover the correlation between mRNA synthesis and the dynamics of RNA Polymerase II (Pol II) clusters at a gene locus. For endogenous β-actin genes in mouse embryonic fibroblasts, we observe that short (∼8 s) Pol II clusters correlate with basal mRNA output. With serum stimulation, a stereotyped increase in Pol II cluster lifetime correlates with the proportionate increase in mRNAs synthesized minutes later. An additional burst of mRNA synthesis can be induced, at will, with a drug that stalls then releases Pol II clustering. Our findings reveal that transient clustering of Pol II constitutes a pre-transcriptional regulatory event which dynamically controls gene expression output.

Dynamical Evolution of Stellar Systems

Dynamical simulations have become a powerful tool to study the evolution of star clusters due to hardware and software progresses in recent years. Here, I review the state of the art of N-body and other simulation techniques and show what we have learned from these simulations about the dynamical evolution of star clusters. Special attention is given to the results on the lifetimes of star clusters as a function of their environment, the internal changes of the mass functions, the influence of primordial gas expulsion on the ratio of first to second generation stars in globular clusters, and the possible presence of intermediate-mass black holes in star clusters.

Fault-tolerant multi-path routing protocol for WSN based on HEED

To solve the network performance deterioration caused by network nodes failure according to unexpected and unforeseen environmental changes in wireless sensor network WSN, a high fault-tolerant and energy-efficient multipath routing protocol based on the idea of hybrid, energy-efficient distributed HEED clustering protocol, called HEED fault tolerant HEED-FT is proposed in this paper. To improve the routing reliability and energy balance between cluster heads, the HEED-FT algorithm first introduces the non-probability waiting time, residue energy and centres to improve the cluster lifetime. Then multiple clustering parameters are applied with different hierarchy which can control the ideal topology distribution of the cluster heads. Finally, a multiple trees Gabriel graph MTGG model is put forward to get a reliable communication link with multiple clustering parameters which can ensure the nodes in an ideal cluster topology distribution. The simulation results show that HEED-FT has less energy consumption, higher reliability and longer network survival than the traditional algorithms.

Acoustic spectroscopy of magnetic fluids based on transformer oil

The structural changes in transformer oil–based magnetic fluids with magnetite nanoparticles, FeO·Fe2O3, of different diameters upon the effect of an external magnetic field were studied by acoustic spectroscopy. The corresponding changes of the acoustic wave attenuation as a function of magnetic field were measured. Over the linear increasing magnetic field, the interaction between the magnetic field and the magnetic moments of the nanoparticles led to the aggregation of magnetic nanoparticles and following chain or cluster formation. These structures enlarged with the magnetic field and this process had the influence on the value of the acoustic attenuation. The remarkable changes in the acoustic attenuation were also observed in the magnetic fluid subjected to a jumped magnetic field observed for a given time. After the back change of magnetic field to zero, the attenuation drastically decreases because the lifetime of big clusters is in this case small. The anisotropy of the acoustic attenuation in external magnetic field was measured and analyzed at various temperatures, and the cluster radius, the number density of the colloidal nanoparticles, and some other parameters of magnetic nanoparticles could be determined from experimental results.

Periodic and quasiperiodic motions of many particles falling in a viscous fluid.

The dynamics of regular clusters of many nontouching particles falling under gravity in a viscous fluid at low Reynolds number are analyzed within the point-particle model. The evolution of two families of particle configurations is determined: two or four regular horizontal polygons (called "rings") centered above or below each other. Two rings fall together and periodically oscillate. Four rings usually separate from each other with chaotic scattering. For hundreds of thousands of initial configurations, a map of the cluster lifetime is evaluated in which the long-lasting clusters are centered around periodic solutions for the relative motions, and they are surrounded by regions of chaotic scattering in a similar way to what was observed by Janosi et al. [Phys. Rev. E. 56, 2858 (1997)] for three particles only. These findings suggest that we should consider the existence of periodic orbits as a possible physical mechanism of the existence of unstable clusters of particles falling under gravity in a viscous fluid.

Clustering and sensing with decentralized detection in vehicular ad hoc networks

In the near future, vehicles will be more and more advanced sensing platforms: for instance, at least one smartphone (with several on-board sensors) is likely to be inside each vehicle. Smartphone-based inter-vehicle communications thus support the creation of vehicular sensor networks (VSNs). In this paper, we analyze the performance of clustered VSNs, where (hierarchical) decentralized detection schemes are used to estimate the status of an observed spatially constant phenomenon of interest. Clustering makes processing efficient and the architecture scalable. Our approach consists of the creation, during a downlink phase, of a clustered VSN topology through fast broadcast of control messages, started from a remote sink (e.g., in the cloud), through a novel clustering protocol, denoted as cluster-head election irresponsible forwarding (CEIF). This clustered VSN topology is then exploited, during an uplink phase, to collect sensed data from the vehicles and perform distributed detection. The performance of the proposed scheme is investigated considering mostly IEEE 802.11b (smartphone-based) as well as IEEE 802.11p (inter-vehicle) communications in both highway-like and urban-like scenarios. Our results highlight the existing trade-off between decision delay and energy efficiency. The proposed VSN-based distributed detection schemes have to cope with the “ephemeral” nature of clusters. Therefore, proper cluster maintenance strategies are needed to prolong the cluster lifetime and, as a consequence, the maximum amount of data which can be collected before clusters break. This leads to the concept of decentralized detection “on the move.”

Ag2 and Ag3 clusters: synthesis, characterization, and interaction with DNA.

Subnanometric samples, containing exclusively Ag2 and Ag3 clusters, were synthesized for the first time by kinetic control using an electrochemical technique without the use of surfactants or capping agents. By combination of thermodynamic and kinetic measurements and theoretical calculations, we show herein that Ag3 clusters interact with DNA through intercalation, inducing significant structural distortion to the DNA. The lifetime of Ag3 clusters in the intercalated position is two to three orders of magnitude longer than for classical organic intercalators, such as ethidium bromide or proflavine.

Ag2 and Ag3 Clusters: Synthesis, Characterization, and Interaction with DNA

AbstractSubnanometric samples, containing exclusively Ag2 and Ag3 clusters, were synthesized for the first time by kinetic control using an electrochemical technique without the use of surfactants or capping agents. By combination of thermodynamic and kinetic measurements and theoretical calculations, we show herein that Ag3 clusters interact with DNA through intercalation, inducing significant structural distortion to the DNA. The lifetime of Ag3 clusters in the intercalated position is two to three orders of magnitude longer than for classical organic intercalators, such as ethidium bromide or proflavine.

Rough Set Based Fuzzy Scheme for Clustering and Cluster Head Selection in VANET

In Vehicular Ad hoc Network (VANET), clustering helps vehicles to communicate with other vehicles and to the nearby Road Side Unit (RSU). Conventional clustering methods follow precise clustering which degrades the stability of cluster formation. To stabilize the formation of clusters, the vehicles in the boundary region of more than one cluster should be uniquely added to the proper cluster. Fuzzy set representation of clusters makes this possible by assigning a membership value to all the vehicles and supports the formation of clusters based on this membership value. Since the cluster lifetime is very minimal in vehicular network, fuzzy based clustering is too descriptive to interpret the clustering results. In this paper, the rough set based fuzzy clustering is employed for formation of clusters in a VANET. Using this scheme, a vehicle in the transmission range of more than one cluster namely, the boundary vehicles are assigned with a membership value. Based on the fuzzy rule base, the vehicles are assigned to the appropriate cluster. Theoretical analysis and experimental results show that rough set based fuzzy scheme obtains 10 % to 20 % more average cluster lifetime and 20 % to 25 % more cluster head lifetime when compared to existing approaches.DOI: http://dx.doi.org/10.5755/j01.eee.21.1.7729