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Wrap-up Day 2 & Closing sessionCryogenic Safety - HSE seminar
http://cds.cern.ch/record/2220692
Wrap-up Day 2 & Closing sessionCERN. GenevaFri, 30 Sep 2016 07:10:47 GMT2016-09-22http://cds.cern.ch/record/2220692['']The world of particles
http://cds.cern.ch/record/2220687
What is our Universe made of? Where does it come from? Why does it behave as it does? We do not have all the answers to these questions but in recent years we have uncovered a lot of information about the Universe which surrounds us. This search has revealed that, beyond the evidence of our eyes, there is a seething world of tiny particles and messengers which pass between them...Boixader, GeorgesSouthworth, BrianFri, 30 Sep 2016 06:15:50 GMThttp://cds.cern.ch/record/2220687['']Additive manufacturing of titanium alloys: state of the art, challenges and opportunities
http://cds.cern.ch/record/2220686
Additive Manufacturing of Titanium Alloys: State of the Art, Challenges and Opportunities provides alternative methods to the conventional approach for the fabrication of the majority of titanium components produced via the cast and wrought technique, a process which involves a considerable amount of expensive machining. In contrast, the Additive Manufacturing (AM) approach allows very close to final part configuration to be directly fabricated minimizing machining cost, while achieving mechanical properties at least at cast and wrought levels. In addition, the book offers the benefit of significant savings through better material utilization for parts with high buy-to-fly ratios (ratio of initial stock mass to final part mass before and after manufacturing). As titanium additive manufacturing has attracted considerable attention from both academicians and technologists, and has already led to many applications in aerospace and terrestrial systems, as well as in the medical industry, this book explores the unique shape making capabilities and attractive mechanical properties which make titanium an ideal material for the additive manufacturing industry.Froes, Francis HDutta, BhaskarFri, 30 Sep 2016 06:06:06 GMThttp://cds.cern.ch/record/2220686['']Vibronic spectroscopy of sympathetically cooled CaH$^+$
http://cds.cern.ch/record/2220685
We report the measurement of the 1$^{1}\Sigma\longrightarrow$ 2$^{1}\Sigma$ transition of CaH$^+$ by resonance-enhanced photodissociation of CaH$^+$ that is co-trapped with laser-cooled Ca$^+$ . We observe four resonances that we assign to transitions from the vibrational $v$=0 ground state to the $v'$=1-4 excited states based on theoretical predictions. A simple theoretical model that assumes instantaneous dissociation after resonant excitation yield results in good agreement with the observed spectral features except for the unobserved $v'$=0 peak. The resolution of our experiment is limited by the mode-locked excitation laser, but this survey spectroscopy enables future rotationally resolved studies with applications in astrochemistry and precision measurement.Rugango, ReneCalvin, Aaron TJanardan, SmithaShu, GangBrown, Kenneth RFri, 30 Sep 2016 05:41:51 GMT29 Sep 2016arXiv:1609.09478http://cds.cern.ch/record/2220685['arXiv:1609.09478']arXiv:1609.09478Direct observation of chiral currents and magnetic reflection in atomic flux lattices
http://cds.cern.ch/record/2220684
The prospect of studying topologically nontrivial phases with the precision and control of atomic physics has driven the development of many techniques for engineering artificial magnetic fields and spin-orbit interactions in atomic gases. Recently, the idea of engineering nontrivial topology through the use of discrete internal (or external) atomic states as effective "artificial dimensions" has garnered attraction for its versatility and promise of immunity from sources of heating. Here, we directly engineer tunable artificial gauge fields through the local control of tunneling phases in an effectively two-dimensional manifold of discrete atomic momentum states. We demonstrate the ability to engineer homogeneous artificial gauge fields of arbitrary value, directly imaging the site-resolved dynamics of induced chiral currents. We furthermore engineer the first inhomogeneous artificial gauge fields for cold atoms, enabling the observation of magnetic reflection of atoms incident upon a step-like variation of an artificial vector potential. These results open up new possibilities for the study of topological phases and localization phenomena in cold atomic gases.An, Fangzhao AlexMeier, Eric JGadway, BryceFri, 30 Sep 2016 05:41:51 GMT29 Sep 2016arXiv:1609.09467http://cds.cern.ch/record/2220684['arXiv:1609.09467']arXiv:1609.09467Field-based observations confirm linear scaling of sand flux with wind stress
http://cds.cern.ch/record/2220683
Wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. However, it remains unclear how the sand flux scales with wind speed, largely because models do not agree on how particle speed changes with wind shear velocity. Here, we present comprehensive measurements from three new field sites and three published studies, showing that characteristic saltation layer heights, and thus particle speeds, remain approximately constant with shear velocity. This result implies a linear dependence of saltation flux on wind shear stress, which contrasts with the nonlinear 3/2 scaling used in most aeolian process predictions. We confirm the linear flux law with direct measurements of the stress-flux relationship occurring at each site. Models for dust generation, dune migration, and other processes driven by wind-blown sand on Earth, Mars, and several other planetary surfaces should be modified to account for linear stress-flux scaling.Martin, Raleigh LKok, Jasper FFri, 30 Sep 2016 05:41:51 GMT29 Sep 2016arXiv:1609.09458http://cds.cern.ch/record/2220683['arXiv:1609.09458']arXiv:1609.09458From arteries to boreholes: Steady-state response of a poroelastic cylinder to fluid injection
http://cds.cern.ch/record/2220682
The radially outward flow of fluid into a porous medium occurs in many practical problems, from transport across vascular walls to the pressurisation of boreholes. As the driving pressure becomes non-negligible relative to the stiffness of the solid structure, the poromechanical coupling between the fluid and the solid has an increasingly strong impact on the flow. For very large pressures or very soft materials, as is the case for hydraulic fracturing and arterial flows, this coupling can lead to large deformations and, hence, to strong deviations from a classical, linear-poroelastic response. Here, we study this problem by analysing the steady-state response of a poroelastic cylinder to fluid injection. We consider the qualitative and quantitative impacts of kinematic and constitutive nonlinearity, highlighting the strong impact of deformation-dependent permeability. We show that the wall thickness (thick vs. thin) and the outer boundary condition (free vs. constrained) play a central role in controlling the mechanics.Auton, Lucy CMacMinn, Christopher WFri, 30 Sep 2016 05:41:51 GMT29 Sep 2016arXiv:1609.09457http://cds.cern.ch/record/2220682['arXiv:1609.09457']arXiv:1609.09457Tables of experimental branching ratios of Auger-type post collisional ionization of rare gases
http://cds.cern.ch/record/2220681
When an electron is emitted from a sub-valence shell, a vacancy is created and there is a not-null probability for different post collisional ionization (PCI) processes giving rise to a higher target charge state. It is reasonable to consider that PCI is a time-delayed electron emission and, therefore, independent of the projectile. We include the tables of the branching ratios of $0-6$ post-collisionally emitted electrons after single ionization of Ne, Ar, Kr and Xe in different inner shells. These values have already been employed with good results in previous calculations of multiple ionization of rare gases by electrons, positron, protons, antiprotons and different positive ions (see the text and references therein). These tables and explanation is included in [Montanari C C and Miraglia J E 2014, \textit{J. Phys. B: At. Mol. Opt. Phys.} {\bf 45}, 105203].Montanari, C CMiraglia, J EFri, 30 Sep 2016 05:41:51 GMT29 Sep 2016arXiv:1609.09445http://cds.cern.ch/record/2220681['arXiv:1609.09445']arXiv:1609.09445On the statistical properties of viral misinformation in online social media
http://cds.cern.ch/record/2220680
The massive diffusion of online social media allows for the rapid and uncontrolled spreading of conspiracy theories, hoaxes, unsubstantiated claims, and false news. Such an impressive amount of misinformation can influence policy preferences and encourage behaviors strongly divergent from recommended practices. In this paper, we study the statistical properties of viral misinformation in online social media. By means of methods belonging to Extreme Value Theory, we show that the number of extremely viral posts over time follows a homogeneous Poisson process, and that the interarrival times between such posts are independent and identically distributed, following an exponential distribution. Moreover, we characterize the uncertainty around the rate parameter of the Poisson process through Bayesian methods. Finally, we are able to derive the predictive posterior probability distribution of the number of posts exceeding a certain threshold of shares over a finite interval of time.Bessi, AlessandroFri, 30 Sep 2016 05:41:51 GMT29 Sep 2016arXiv:1609.09435http://cds.cern.ch/record/2220680['arXiv:1609.09435']arXiv:1609.09435Infrequent social interaction can accelerate the spread of a persuasive idea
http://cds.cern.ch/record/2220679
We study the spread of a persuasive new idea through a population of continuous time random walkers in one dimension. The idea spreads via social gatherings involving groups of nearby walkers who act according to a biased "majority rule": After each gathering, the group takes on the new idea if more than a critical fraction $\frac{1-\varepsilon}{2} < \frac{1}{2}$ of them already hold it; otherwise they all reject it. The boundary of a domain where the new idea has taken hold expands as a travelling wave in the density of new idea holders. Our walkers move by L\'{e}vy Motion, and we compute the wave velocity analytically as a function of the frequency of social gatherings and the exponent of the jump distribution. When this distribution is sufficiently heavy tailed then, counter to intuition, the idea can propagate faster if social gatherings are held less frequently. When jumps are truncated, a critical gathering frequency can emerge which maximizes propagation velocity. We explore our model by simulation, confirming our analytical results.Burridge, JamesGnacik, MichalFri, 30 Sep 2016 05:41:50 GMT29 Sep 2016arXiv:1609.09418http://cds.cern.ch/record/2220679['arXiv:1609.09418']arXiv:1609.09418Clean up or mess up: the effect of sampling biases on measurements of degree distributions in mobile phone datasets
http://cds.cern.ch/record/2220678
Mobile phone data have been extensively used in the recent years to study social behavior. However, most of these studies are based on only partial data whose coverage is limited both in space and time. In this paper, we point to an observation that the bias due to the limited coverage in time may have an important influence on the results of the analyses performed. In particular, we observe significant differences, both qualitatively and quantitatively, in the degree distribution of the network, depending on the way the dataset is pre-processed and we present a possible explanation for the emergence of Double Pareto LogNormal (DPLN) degree distributions in temporal data.Decuyper, AdelineBrowet, ArnaudTraag, VincentBlondel, Vincent DDelvenne, Jean-CharlesFri, 30 Sep 2016 05:41:50 GMT29 Sep 2016arXiv:1609.09413http://cds.cern.ch/record/2220678['arXiv:1609.09413']arXiv:1609.09413Experimental Measurement of the Berry Curvature from Anomalous Transport
http://cds.cern.ch/record/2220677
Geometrical properties of energy bands underlie fascinating phenomena in a wide-range of systems, including solid-state materials, ultracold gases and photonics. Most famously, local geometrical characteristics like the Berry curvature can be related to global topological invariants such as those classifying quantum Hall states or topological insulators. Regardless of the band topology, however, any non-zero Berry curvature can have important consequences, such as in the semi-classical evolution of a wave packet. Here, we experimentally demonstrate for the first time that wave packet dynamics can be used to directly map out the Berry curvature. To this end, we use optical pulses in two coupled fibre loops to study the discrete time-evolution of a wave packet in a 1D geometrical "charge" pump, where the Berry curvature leads to an anomalous displacement of the wave packet under pumping. This is both the first direct observation of Berry curvature effects in an optical system, and, more generally, the proof-of-principle demonstration that semi-classical dynamics can serve as a high-resolution tool for mapping out geometrical properties.Wimmer, MartinPrice, Hannah MCarusotto, IacopoPeschel, UlfFri, 30 Sep 2016 05:41:50 GMT29 Sep 2016arXiv:1609.09412http://cds.cern.ch/record/2220677['arXiv:1609.09412']arXiv:1609.09412Seismic collapse prediction of frame structures by means of genetic algorithms
http://cds.cern.ch/record/2220676
This paper presents an automatic approach for the evaluation of the plastic load and failure modes of planar frames. The method is based on the generation of elementary collapse mechanisms and on their linear combination aimed at minimizing the collapse load factor. The minimization procedure is efficiently performed by means of genetic algorithms which allow to compute an approximate collapse load factor, and the correspondent failure mode, with sufficient accuracy in a very short computing time. A user-friendly original software in the agent-based programming language Netlogo, here employed for the first time with structural engineering purposes, has been developed showing its great versatility and advantages. Many applications have been performed both with reference to the classical plastic analysis approach, in which all the loads increase proportionally, and with a seismic point of view considering a system of horizontal forces whose magnitude increases while the vertical loads are assumed to be constant. In this latter case a parametric study has been performed aiming at evaluating the influence of some geometric, mechanical and load distribution parameters on the ultimate collapse load of planar frames.Greco, ACannizzaro, FPluchino, AFri, 30 Sep 2016 05:41:50 GMT29 Sep 2016arXiv:1609.09411http://cds.cern.ch/record/2220676['arXiv:1609.09411']arXiv:1609.09411Energy conversion by surface-tension driven charge separation
http://cds.cern.ch/record/2220675
In this work, the shear-induced electrokinetic streaming potential present in free-surface electrolytic flows subjected to a gradient in surface tension is assessed. Firstly, for a Couette flow with fully resolved electric double layer (EDL), the streaming potential per surface stress as a function of the Debye parameter and surface potential is analyzed. By contrast to the Smoluchowski limit in pressure-driven channel flow, the shear-induced streaming potential vanishes for increasing Debye parameter (infinitely thin EDL), unless the free surface contains (induced) surface charge or the flow at the charged, solid wall is permitted to slip. Secondly, a technical realization of surface-tension induced streaming is proposed, with surface stress acting on the free (slipping) surfaces of a micro-structured, superhydrophobic wall. The streaming potential is analyzed with respect to the slip parameter and surface charge. Finally, the surface tension is assumed to vary with temperature (thermocapillarity) or with surfactant concentration (destillocapillarity). The maximal thermal efficiency is derived and compared to the Carnot efficiency. For large thermal Marangoni number, the efficiency is severely limited by the large heat capacity of aqueous solvents. By contrast, destillocapillary flows may reach conversion efficiencies similar to pressure-driven flow.Pini, CesareBaier, TobiasDietzel, MathiasFri, 30 Sep 2016 05:41:50 GMT29 Sep 2016arXiv:1609.09404http://cds.cern.ch/record/2220675['arXiv:1609.09404']arXiv:1609.09404The Theory of SERS on Dielectrics and Semiconductors
http://cds.cern.ch/record/2220674
It is demonstrated that the reason of SERS on dielectric and semiconductor substrates is the enhancement of the electric field in the regions of the tops of the surface roughness with very small radius, or a very large curvature. The enhancement depends on the dielectric constant of the substrate and is stronger for a larger dielectric constant. It is indicated that the enhancement on dielectrics and semiconductors is stronger than on metals with the same modulus of the dielectric constant. The result obtained is confirmed by experimental data on the enhancement coefficients obtained for various semiconductor and dielectric substrates.Polubotko, V P Chelibanov A MFri, 30 Sep 2016 05:41:50 GMT29 Sep 2016arXiv:1609.09403http://cds.cern.ch/record/2220674['arXiv:1609.09403']arXiv:1609.09403Parametric Landau damping of space charge modes
http://cds.cern.ch/record/2220673
Landau damping is the mechanism of plasma and beam stabilization; it is caused by energy transfer from collective modes to incoherent motion of resonant particles. Normally this resonance requires the wave frequency in the particle frame to match the resonant particles frequency. Using the Synergia modeling package to study transverse coherent modes of bunched beams with space charge, we have identified a new kind of damping mechanism, parametric Landau damping, driven by the modulation of the wave-particle interaction.Macridin, AlexandruBurov, AlexeyStern, EricAmundson, JamesSpentzouris, PanagiotisFri, 30 Sep 2016 05:41:50 GMT23 Sep 2016arXiv:1609.09393http://cds.cern.ch/record/2220673['arXiv:1609.09393']arXiv:1609.09393Numerical and analytical approaches to an advection-diffusion problem at small Reynolds number and large P\'eclet number
http://cds.cern.ch/record/2220672
Obtaining a detailed understanding of the physical interactions between a cell and its environment often requires information about the flow of fluid surrounding the cell. Cells must be able to effectively absorb and discard material in order to survive. Strategies for nutrient acquisition and toxin disposal, which have been evolutionarily selected for their efficacy, should reflect knowledge of the physics underlying this mass transport problem. Motivated by these considerations, in this paper we consider a two-dimensional advection-diffusion problem at small Reynolds number and large P\'eclet number. We discuss the problem of mass transport for a circular cell in a uniform far-field flow. We approach the problem numerically, and also analytically through a rescaling of the concentration boundary layer. A biophysically motivated first-passage problem for the absorption of material by the cell demonstrates quantitative agreement between the numerical and analytical approaches.Fuller, Nathaniel JLicata, Nicholas AFri, 30 Sep 2016 05:41:50 GMT29 Sep 2016arXiv:1609.09366http://cds.cern.ch/record/2220672['arXiv:1609.09366']arXiv:1609.09366Lost chapter of Physical Chemistry means convergence between Fisher Kolmogorov equation and tunnel effect
http://cds.cern.ch/record/2220671
In this work we show that the dynamics of chemical reactions of order zero, one and two have a representation through logistics probability. This probability is robust, stable and complies systemically with the differential equation of Fisher Kolmogorov (F K). It is robust, because in theorem 1 and theorem 3 differential equations of diffusion and heat transfer are obtained, where the temperature plays a key role. Also, the Eikonal equation of wave mechanics allows us to construct the heat equation. In Lemma 2, Fick diffusion equation is demonstrated. It is stable, because probability convergence when t converge infinitum, gives us new ways to analyze the kinetics of a reaction integrally, in Corollary 5. Finally, the theoretically and experimentally obtained algorithms and results support the convergence in probability of the quantum tunnel effect and chemical reactions for: hydrogen production at ultra low temperature and catalytic cracking of asphalt at high temperature.Edward, JimenezHector, MosqueraMarco, CortezJimenez, EstebanAyala, Carlos EGustavo, LopezUllrich, StahlFri, 30 Sep 2016 05:41:49 GMT27 Sep 2016arXiv:1609.09351http://cds.cern.ch/record/2220671['arXiv:1609.09351']arXiv:1609.09351Dynamics of fragmentation and multiple vacancy generation in irradiated single-walled carbon nanotubes
http://cds.cern.ch/record/2220670
The results from mass spectrometry of clusters sputtered from Cs+ irradiated single-walled carbon nano-tubes (SWCNTs) as a function of energy and dose identify the nature of the resulting damage in the form of multiple vacancy generation. For pristine SWCNTs at all Cs+ energies, C2 is the most dominant species, followed by C3, C4 and C1. The experiments were performed in three stages: in the first stage, Cs+ energy E(Cs+) was varied. During the second stage, the nanotubes were irradiated continuously at E(Cs+) = 5 keV for 1,800 s. Afterwards, the entire sequence of irradiation energies was repeated to differentiate between the fragmentation patterns of the pristine and of heavily irradiated SWCNTs. The sputtering and normalized yields identify the quantitative and relative extent of the ion-induced damage by creating double, triple and quadruple vacancies; the single vacancies are least favored. Sputtering from the heavily irradiated SWCNTs occurs not only from the damaged and fragmented nanotubes, but also from the inter-nanotube structures that are grown due to the accumulation of the sputtered clusters. Similar irradiation experiments were performed with the multi-walled carbon nanotubes; the results confirmed the dominant C2 followed by C3, C4 and C1.Javeed, SumeraZeeshan, SumairaAhmad, ShoaibFri, 30 Sep 2016 05:41:49 GMT23 Sep 2016arXiv:1609.09347http://cds.cern.ch/record/2220670['arXiv:1609.09347']arXiv:1609.09347Scattering problems in elastodynamics
http://cds.cern.ch/record/2220669
In electromagnetism, acoustics, and quantum mechanics, scattering problems can routinely be solved numerically by virtue of perfectly matched layers (PMLs) at simulation domain boundaries. Unfortunately, the same has not been possible for general elastodynamic wave problems in continuum mechanics. In this paper, we introduce a corresponding scattered-field formulation for the Navier equation. We derive PMLs based on complex-valued coordinate transformations leading to Cosserat elasticity-tensor distributions not obeying the minor symmetries. These layers are shown to work in two dimensions, for all polarizations, and all directions. By adaptative choice of the decay length, the deep subwavelength PMLs can be used all the way to the quasi-static regime. As demanding examples, we study the effectiveness of cylindrical elastodynamic cloaks of the Cosserat type and approximations thereof.Diatta, AndreKadic, MuamerWegener, MartinGuenneau, SebastienFri, 30 Sep 2016 05:41:49 GMT22 Sep 2016arXiv:1609.09346http://cds.cern.ch/record/2220669['arXiv:1609.09346']arXiv:1609.09346An Unsupervised Method for Quantifying the Behavior of Interacting Individuals
http://cds.cern.ch/record/2220668
Social behaviors involving the interaction of multiple individuals are complex and frequently crucial for an animal's survival. These interactions, ranging across sensory modalities, length scales, and time scales, are often subtle and difficult to quantify. Contextual effects on the frequency of behaviors become even more difficult to quantify when physical interaction between animals interferes with conventional data analysis, e.g. due to visual occlusion. We introduce a method for quantifying behavior in courting fruit flies that combines high-throughput video acquisition and tracking of individuals with recent unsupervised methods for capturing an animal's entire behavioral repertoire. We find behavioral differences in paired and solitary flies of both sexes, identifying specific behaviors that are affected by social and spatial context. Our pipeline allows for a comprehensive description of the interaction between multiple individuals using unsupervised machine learning methods, and will be used to answer questions about the depth of complexity and variance in fruit fly courtship.Klibaite, UgneBerman, Gordon JCande, JessicaStern, David LShaevitz, Joshua WFri, 30 Sep 2016 05:41:49 GMT29 Sep 2016arXiv:1609.09345http://cds.cern.ch/record/2220668['arXiv:1609.09345']arXiv:1609.09345Linking Behavior in the PER Coauthorship Network
http://cds.cern.ch/record/2220667
There is considerable long-term interest in understanding the dynamics of collaboration networks, and how these networks form and evolve over time. Most of the work done on the dynamics of social networks focuses on well-established communities. Work examining emerging social networks is rarer, simply because data is difficult to obtain in real time. In this paper, we use thirty years of data from an emerging scientific community to look at that crucial early stage in the development of a social network. We show that when the field is very young, islands of individual researchers labored in relative isolation, and the co authorship network is disconnected. Thirty years later, rather than a cluster of individuals, we find a true collaborative community, bound together by a robust collaboration network. However, this change did not take place gradually -- the network remained a loose assortment of isolated individuals until the mid-2000s, when those smaller parts suddenly knit themselves together into a single whole. In the rest of this paper, we consider the role of three factors in these observed structural changes: growth, changes in social norms, and the introduction of institutions such as field-specific conferences and journals. We have data from the very earliest years of the field, and thus are able to observe the introduction of two different institutions: the first field-specific conference, and the first field-specific journals. We also identify two relevant behavioral shifts: a discrete increase in co authorship coincident with the first conference, and a shift among established authors away from collaborating with outsiders, towards collaborating with each other. The interaction of these factors gives us insight into the formation of collaboration networks more broadly.Anderson, Katharine ACrespi, MatthewSayre, Eleanor CFri, 30 Sep 2016 05:41:49 GMT28 Sep 2016arXiv:1609.09339http://cds.cern.ch/record/2220667['arXiv:1609.09339']arXiv:1609.09339Consistency of detrended fluctuation analysis
http://cds.cern.ch/record/2220666
The scaling function $F(s)$ in detrended fluctuation analysis (DFA) scales as $F(s)\sim s^{H}$ for stochastic processes with Hurst exponents $H$. We prove this scaling law for both stationary stochastic processes with $0<H<1$, and non-stationary stochastic processes with $1<H<2$. For $H<0.5$ we observe that using the asymptotic (power-law) auto-correlation function (ACF) yield $F(s)\sim s^{1/2}$. We also show that the fluctuation function in DFA is equal in expectation to: i) A weighted sum of the ACF ii) A weighted sum of the second order structure function. These results enable us to compute the exact finite-size bias for signals that are scaling, as well as studying DFA for signals that do not have power-law statistics. We illustrate this with examples, where we find that a previous suggested modified DFA will increase the bias for signals with Hurst exponents $H>1$. As a final application of the new theory, we present an estimator $\hat F(s)$ that can handle missing data in regularly sampled time series without the need for interpolation schemes. Under mild regularity conditions, $\hat F(s)$ is equal in expectation to the fluctuation function $F(s)$ in the gap-free case.Løvsletten, OlaFri, 30 Sep 2016 05:41:49 GMT29 Sep 2016arXiv:1609.09331http://cds.cern.ch/record/2220666['arXiv:1609.09331']arXiv:1609.09331Variational symmetries as the existence of ignorable coordinates
http://cds.cern.ch/record/2220665
It is shown that given a Lagrangian for a system with a finite number of degrees of freedom, the existence of a variational symmetry is equivalent to the existence of coordinates in the extended configuration space such that one of the coordinates is ignorable.del Castillo, G F TorresGarcía, I RubalcavaFri, 30 Sep 2016 05:41:49 GMT15 Sep 2016arXiv:1609.09330http://cds.cern.ch/record/2220665['arXiv:1609.09330']arXiv:1609.09330When the clock strikes: Modeling the relation between circadian rhythms and cardiac arrhythmias
http://cds.cern.ch/record/2220664
It has recently been observed that the occurrence of sudden cardiac death has a close statistical relationship with the time of day, viz., ventricular fibrillation is most likely to occur between 12 am-6 am, with 6 pm-12 am being the next most likely period. Consequently there has been significant interest in understanding how cardiac activity is influenced by the circadian clock, i.e., temporal oscillations in physiological activity with a period close to 24 hours and synchronized with the day-night cycle. Although studies have identified the genetic basis of circadian rhythms at the intracellular level, the mechanisms by which they influence cardiac pathologies are not yet fully understood. Evidence has suggested that diurnal variations in the conductance properties of ion channel proteins that govern the excitation dynamics of cardiac cells may provide the crucial link. In this paper, we investigate the relationship between the circadian rhythm as manifested in modulations of ion channel properties and the susceptibility to cardiac arrhythmias by using a mathematical model that describes electrical activity in ventricular tissue. We show that changes in the channel conductance that lead to extreme values for the duration of action potentials in cardiac cells can result either in abnormally high-frequency reentrant activity or spontaneous conduction block of excitation waves. Both phenomena increase the likelihood of wavebreaks that are known to initiate potentially life-threatening arrhythmias. Thus, disruptive cardiac excitation dynamics are most likely to occur in time-intervals of the day-night cycle during which the channel properties are closest to these extreme values, providing an intriguing relation between circadian rhythms and cardiac pathologies.Seenivasan, PavithraaMenon, Shakti NSridhar, SSinha, SitabhraFri, 30 Sep 2016 05:41:49 GMT29 Sep 2016arXiv:1609.09326http://cds.cern.ch/record/2220664['arXiv:1609.09326']arXiv:1609.09326