CERN Document Server: Preprints
https://cds.cern.ch/collection/Preprints
CERN Document Server latest documents in PreprintsenSat, 28 Nov 2015 23:50:04 GMTInvenio 1.1.3.1106-62468cds.support@cern.ch360760770125https://cds.cern.ch/img/site_logo_rss.pngCERN Document Server
https://cds.cern.ch
Search Search this site:p
https://cds.cern.ch/search
Small pitch pixel sensors\\ for the CMS Phase II upgrade
https://cds.cern.ch/record/2108949
The CMS experiment intends to exchange the pixel detector for the high luminosity phase of the Large Hadron Collider (HL-LHC).
Therefore, a large R\&D; effort has been started in order to develop sensors capable of withstanding the expected extremely high radiation damage.
The targeted integrated luminosity of 3000 fb$^{-1}$, estimated for 10 years of operation at the design center-of-mass energy of 14 TeV, translates into an equivalent NIEL (Non-Ionizing Energy Loss) of 2$\times{10}^{16}$ neq cm$^{-2}$ and
an IEL (Ionizing Energy Loss) dose in the SiO$_{2}$ of 5 MGy at the expected position of the innermost pixel detector layer. \\%
The CMS collaboration has undertaken two sensor R\&D; programs on thin n-in-p planar and 3D silicon sensor technologies.
To cope with the increase in instantaneous luminosity, the pixel area has to be reduced to approximately 2500 $\mu$m$^{2}$ to keep the occupancy at the percent level. Suggested pixel cell geometries
to match this requirement are
{50$\times$50 }$\mu$m$^2$
or 25$\times$100 $\mu$m$^2$, leaving little space for design choices and a possible biasing scheme.
Monte Carlo studies comparing the hit resolution for these two scenarios are presented.
\\%
CMS has initiated the production of test-sensors with the envisaged pixel geometries. Status, progress, and prospects of this effort are discussed.Steinbrueck, GeorgFri, 27 Nov 2015 13:36:38 GMT20 Nov 2015CMS-CR-2015-312https://cds.cern.ch/record/21089492015312CMS overview
https://cds.cern.ch/record/2108320
Most recent CMS data related to the high-density QCD are presented for pp and PbPb collisions at 2.76 TeV and pPb collisions at 5.02 TeV. The PbPb collision is essential to understand collective behavior and the final-state effects for the detailed characteristics of hot, dense partonic matter, whereas the pPb collision provides the critical information on the initial-state effects including the modification of the parton distribution function in cold nuclei. This paper highlights some of recent heavy-ion related results from CMS.Hong, ByungsikThu, 26 Nov 2015 09:55:58 GMT19 Nov 2015CMS-CR-2015-310https://cds.cern.ch/record/21083202015310Flow and correlations results from CMS
https://cds.cern.ch/record/2108296
The observation of long-range two-particle correlations in high energy heavy ion collisions opens the opportunities of exploring novel QCD dynamics in quark gluon plasma (QGP), the hot dense matter created in heavy ion collisions. In particular, such correlations are sensitive to the degree of thermalization in the system. We present selected results from non-identified and identified two-particle and multi-particle correlations in PbPb collisions, as well as in lighter systems.Devetak, DamirThu, 26 Nov 2015 08:44:24 GMT02 Oct 2015CMS-CR-2015-209https://cds.cern.ch/record/21082962015209Search for the Standard Model Higgs boson produced in association with a vector boson and decaying into a tau pair in pp collisions at $\sqrt(s) = 8$ TeV with the ATLAS detector
https://cds.cern.ch/record/2108290
A search for the Standard Model Higgs boson produced in association with a vector boson with the decay $H\rightarrow \tau\tau$ is presented. The data correspond to 20.3 fb$^{-1}$ of integrated luminosity from proton-proton collisions at $\sqrt{s} = 8$ TeV recorded by the ATLAS experiment at the LHC during 2012. The data agree with the background expectation, and 95% confidence-level upper limits are placed on the cross section of this process. The observed (expected) limit, expressed in terms of the signal strength $\mu = \sigma/\sigma_{\mathrm{SM}}$ for $m_\mathrm{H} = 125 GeV$, is $\mu <$ 5.6 (3.7). The measured value of the signal strength is $\mu = 2.3\pm1.6$.ATLAS CollaborationThu, 26 Nov 2015 07:24:16 GMT26 Nov 2015CERN-PH-EP-2015-226https://cds.cern.ch/record/21082902015226Reaching Quantum Supremacy with a Boson Sampling Experiment
https://cds.cern.ch/record/2108276
Boson Sampling represents a promising witness of the supremacy of quantum systems as a resource for the solution of computational problems. The classical hardness of Boson Sampling has been related to the so called Permanent-of-Gaussians Conjecture and has been extended to some generalizations such as scattershot Boson Sampling, approximate and lossy sampling under some reasonable constraints. However, it is still unclear how demanding these bounds are for a quantum experimental sampler. Starting from a state of the art analysis and focusing on the foreseeable practical conditions needed to reach quantum supremacy, we look at different techniques and present a more general and effective solution. We apply our approach to both the experimental suggestions presented to date and we eventually find in both cases a new threshold that is less error sensitive and experimentally more feasible.Latmiral, LudovicoThu, 26 Nov 2015 06:40:36 GMT25 Nov 2015arXiv:1511.08161https://cds.cern.ch/record/2108276['arXiv:1511.08161']arXiv:1511.08161The stability of polarisation singularities in disordered photonic crystal waveguides
https://cds.cern.ch/record/2108275
The effects of short range disorder on the polarisation characteristics of light in photonic crystal waveguides were investigated using finite difference time domain simulations with a view to investigating the stability of polarisation singularities. It was found that points of local circular polarisation (C-points) and contours of linear polarisation (L-lines) continued to appear even in the presence of high levels of disorder, and that they remained close to their positions in the ordered crystal. These results are a promising indication that devices exploiting polarisation in these structures are viable given current fabrication standards.Lang, BenBeggs, Daryl MYoung, Andrew BRarity, John GOulton, RuthThu, 26 Nov 2015 06:40:36 GMT25 Nov 2015arXiv:1511.08159https://cds.cern.ch/record/2108275['arXiv:1511.08159']arXiv:1511.08159Linked Coupled Cluster Monte Carlo
https://cds.cern.ch/record/2108273
We consider a new formulation of the stochastic coupled cluster method in terms of the similarity transformed Hamiltonian. We show that improvement in the granularity with which the wavefunction is represented results in a reduction in the critical population required to correctly sample the wavefunction for a range of systems and excitation levels and hence leads to a substantial reduction in the computational cost. This development has the potential to substantially extend the range of the method, enabling it to be used to treat larger systems with excitation levels not easily accessible with conventional deterministic methods.Franklin, Ruth S TSpencer, James SZoccante, AlbertoThom, Alex J WThu, 26 Nov 2015 06:40:36 GMT25 Nov 2015arXiv:1511.08129https://cds.cern.ch/record/2108273['arXiv:1511.08129']arXiv:1511.08129Efficient Dielectric Metasurface Collimating Lenses for Mid-Infrared Quantum Cascade Lasers
https://cds.cern.ch/record/2108272
Light emitted from single-mode semiconductor lasers generally has large divergence angles, and high numerical aperture lenses are required for beam collimation. Visible and near infrared lasers are collimated using aspheric glass or plastic lenses, yet collimation of mid-infrared quantum cascade lasers typically requires more costly aspheric lenses made of germanium, chalcogenide compounds, or other infrared-transparent materials. Here we report mid-infrared dielectric metasurface flat lenses that efficiently collimate the output beam of single-mode quantum cascade lasers. The metasurface lenses are composed of amorphous silicon posts on a flat sapphire substrate and can be fabricated at low cost using a single step conventional UV binary lithography. Mid-infrared radiation from a 4.8 $\mu$m distributed-feedback quantum cascade laser is collimated using a polarization insensitive metasurface lens with 0.86 numerical aperture and 79% transmission efficiency. The collimated beam has a half divergence angle of 0.36$^\circ$ and beam quality factor of $M^2$=1.02.Arbabi, AmirBriggs, Ryan MHorie, YuBagheri, MahmoodFaraon, AndreiThu, 26 Nov 2015 06:40:36 GMT25 Nov 2015arXiv:1511.08127https://cds.cern.ch/record/2108272['arXiv:1511.08127']arXiv:1511.08127Circular orbit spacecraft control at the L4 point using Lyapunov functions
https://cds.cern.ch/record/2108271
The objective of this work is to demonstrate the utility of Lyapunov functions in control synthesis for the purpose of maintaining and stabilizing a spacecraft in a circular orbit around the L4 point in the circular restricted three body problem (CRTBP). Incorporating the requirements of a fixed radius orbit and a desired angular momentum, a Lyapunov function is constructed and the requisite analysis is performed to obtain a controller. Asymptotic stability is proved in a defined region around the L4 point using LaSalle's principle.Agrawal, RachanaBanavar, Ravi NThu, 26 Nov 2015 06:40:36 GMT25 Nov 2015arXiv:1511.08121https://cds.cern.ch/record/2108271['arXiv:1511.08121']arXiv:1511.08121Non-reciprocal nonlinear optic induced transparency and frequency conversion on a chip
https://cds.cern.ch/record/2108270
Developments in photonic chips have spurred photon based classical and quantum information processing, attributing to the high stability and scalability of integrated photonic devices [1, 2]. Optical nonlinearity [3] is indispensable in these complex photonic circuits, because it allows for classical and quantum light sources, all-optical switch, modulation, and non-reciprocity in ambient environments. It is commonly known that nonlinear interactions are often greatly enhanced in the microcavities [4]. However, the manifestations of coherent photon-photon interaction in a cavity, analogous to the electromagnetically induced transparency [5], have never been reported on an integrated platform. Here, we present an experimental demonstration of the coherent photon-photon interaction induced by second order optical nonlinearity (\chi^{(2)} ) on an aluminum nitride photonic chip. The non-reciprocal nonlinear optic induced transparency is demonstrated as a result of the coherent interference between photons with different colors: ones in the visible wavelength band and ones in the telecom wavelength band. Furthermore, a wide-band frequency conversion with an almost unit internal (0.14 external) efficiency and a bandwidth up to 0.76\,\mathrm{GHz} is demonstrated.Guo, XiangZou, Chang-LingJung, HojoongTang, Hong XThu, 26 Nov 2015 06:40:36 GMT25 Nov 2015arXiv:1511.08112https://cds.cern.ch/record/2108270['arXiv:1511.08112']arXiv:1511.08112What is the Brillouin Zone of an Anisotropic Photonic Crystal?
https://cds.cern.ch/record/2108269
The concept of the Brillouin zone (BZ) in relation to a photonic crystal fabricated in an optically anisotropic material is explored both experimentally and theoretically. In experiment, we used femtosecond laser pulses to excite THz polaritons and image their propagation in lithium niobate and lithium tantalate photonic crystal (PhC) slabs. We directly measured the dispersion relation inside PhCs and observed that the lowest bandgap expected to form at the BZ boundary forms inside the BZ in the anisotropic lithium niobate PhC. Our analysis shows that in an anisotropic material the BZ - defined as the Wigner-Seitz cell in the reciprocal lattice - is no longer bounded by Bragg planes and thus does not conform to the original definition of the BZ by Brillouin. We construct an alternative Brillouin zone defined by Bragg planes and show its utility in identifying features of the dispersion bands. We show that for an anisotropic 2D PhC without dispersion, the Bragg plane BZ can be constructed by applying the Wigner-Seitz method to a stretched or compressed reciprocal lattice. We also show that in the presence of the dispersion in the underlying material or in a slab waveguide, the Bragg planes are generally represented by curved surfaces rather than planes. The concept of constructing a BZ with Bragg planes should prove useful in understanding the formation of dispersion bands in anisotropic PhCs and in selectively tailoring their optical properties.Sivarajah, PMaznev, A AOfori-Okai, B KNelson, K AThu, 26 Nov 2015 06:40:35 GMT25 Nov 2015arXiv:1511.08109https://cds.cern.ch/record/2108269['arXiv:1511.08109']arXiv:1511.08109Formation and stability of a hollow electron beam in the presence of a plasma wake field driven by an ultra-short electron bunch
https://cds.cern.ch/record/2108268
A numerical investigation on the spatiotemporal evolution of an electron beam, externally injected in a plasma in the presence of a plasma wake field, is carried out. The latter is driven by an ultra-short relativistic axially-symmetric femtosecond electron bunch. We first derive a novel Poisson-like equation for the wake potential where the driving term is the ultra-short bunch density, taking suitably into account the interplay between the sharpness and high energy of the bunch. Then, we show that a channel is formed longitudinally, through the externally injected beam while experiencing the effects of the bunch-driven plasma wake field, within the context of thermal wave model. The formation of the channel seems to be a final stage of the 3D evolution of the beam. This involves the appearance of small filaments and bubbles around the longitudinal axis. The bubbles coalesce forming a relatively stable axially-symmetric hollow beam structure.Tanjia, FFedele, RDe Nicola, SAkhter, TJovanovic, DThu, 26 Nov 2015 06:40:35 GMT25 Nov 2015arXiv:1511.08107https://cds.cern.ch/record/2108268['arXiv:1511.08107']arXiv:1511.08107Phase Coherent Link of an Atomic Clock to a Self-Referenced Microresonator Frequency Comb
https://cds.cern.ch/record/2108267
The counting and control of optical cycles of light has become common with modelocked laser frequency combs. But even with advances in laser technology, modelocked laser combs remain bulk-component devices that are hand-assembled. In contrast, a frequency comb based on the Kerr-nonlinearity in a dielectric microresonator will enable frequency comb functionality in a micro-fabricated and chip-integrated package suitable for use in a wide-range of environments. Such an advance will significantly impact fields ranging from spectroscopy and trace gas sensing, to astronomy, communications, atomic time keeping and photonic data processing. Yet in spite of the remarkable progress shown over the past years, microresonator frequency combs ("microcombs") have still been without the key function of direct f-2f self-referencing and phase-coherent frequency control that will be critical for enabling their full potential. Here we realize these missing elements using a low-noise 16.4 GHz silicon chip microcomb that is coherently broadened from its initial 1550 nm wavelength and subsequently f-2f self-referenced and phase-stabilized to an atomic clock. With this advance, we not only realize the highest repetition rate octave-span frequency comb ever achieved, but we highlight the low-noise microcomb properties that support highest atomic clock limited frequency stability.Del'Haye, PascalCoillet, AurelienFortier, TaraBeha, KatjaCole, Daniel CYang, Ki YoulLee, HansuekVahala, Kerry JPapp, Scott BDiddams, Scott AThu, 26 Nov 2015 06:40:35 GMT25 Nov 2015arXiv:1511.08103https://cds.cern.ch/record/2108267['arXiv:1511.08103']arXiv:1511.08103The organization of the interbank network and how ECB unconventional measures affected the e-MID overnight market
https://cds.cern.ch/record/2108264
The properties of the interbank market have been discussed widely in the literature. However a proper model selection between alternative organizations of the network in a small number of blocks, for example bipartite, core-periphery, and modular, has not been performed. In this paper, by inferring a Stochastic Block Model on the e-MID interbank market in the period 2010-2014, we show that in normal conditions the network is organized either as a bipartite structure or as a three community structure, where a group of intermediaries mediates between borrowers and lenders. In exceptional conditions, such as after LTRO, one of the most important unconventional measure by ECB at the beginning of 2012, the most likely structure becomes a random one and only in 2014 the e-MID market went back to a normal bipartite organization. By investigating the strategy of individual banks, we show that the disappearance of many lending banks and the strategy switch of a very small set of banks from borrower to lender is likely at the origin of this structural change.Barucca, PaoloLillo, FabrizioThu, 26 Nov 2015 06:40:35 GMT25 Nov 2015arXiv:1511.08068https://cds.cern.ch/record/2108264['arXiv:1511.08068']arXiv:1511.08068Curvature-induced dissipation
https://cds.cern.ch/record/2108263
By inspecting the effect of curvature on a moving fluid, we find that local sources of curvature not only exert inertial forces on the flow, but also generate viscous stresses as a result of the departure of streamlines from the idealized geodesic motion. The curvature-induced viscous forces are shown to cause an indirect and yet appreciable energy dissipation. As a consequence, the flow converges to a stationary equilibrium state solely by virtue of curvature-induced dissipation. In addition, we show that flow through randomly-curved media satisfies a non-linear transport law, resembling Darcy-Forchheimer's law, due to the viscous forces generated by the spatial curvature. It is further shown that the permeability can be characterized in terms of the average metric perturbation.Debus, J -DMendoza, MSucci, SHerrmann, H JThu, 26 Nov 2015 06:40:35 GMT25 Nov 2015arXiv:1511.08031https://cds.cern.ch/record/2108263['arXiv:1511.08031']arXiv:1511.08031Numerical reconstruction of pulsatile blood flow from 4D computer tomography angiography data
https://cds.cern.ch/record/2108262
We present a novel numerical algorithm developed to reconstuct pulsatile blood flow from ECG-gated CT angiography data. A block-based optimization method was constructed to solve the inverse problem corresponding to the Riccati-type ordinary differential equation that can be deduced from conservation principles and Hooke's law. Local flow rate for 5 patients was computed in 10cm long aorta segments that are located 1cm below the heart. The wave form of the local flow rate curves seems to be realistic. Our approach is suitable for estimating characteristics of pulsatile blood flow in aorta based on ECG gated CT scan thereby contributing to more accurate description of several cardiovascular lesions.Lovas, AttilaNagy, RóbertCsobo, ElekSzilágyi, BrigittaSótonyi, PéterThu, 26 Nov 2015 06:40:35 GMT25 Nov 2015arXiv:1511.08021https://cds.cern.ch/record/2108262['arXiv:1511.08021']arXiv:1511.08021A general framework for microscopically reversible processes with memory
https://cds.cern.ch/record/2108261
Statistical Mechanics deals with ensembles of microstates that are compatible with fixed constraints and that on average define a thermodynamic macrostate. The evolution of a small system is normally subjected to changing constraints and involve a stochastic dependence on previous events. Here, we develop a theory for reversible processes with memory that comprises equilibrium statistics and that converge to the same physics in the limit of independent events. This framework is based on the characterization of single phase-space pathways and is used to derive ensemble-average dynamics in stochastic systems driven by a protocol in the limit of no friction. We show that the state of a system depends on its history to the extent of attaining a one-to-one correspondence between states and pathways when memory covers all the previous events. Equilibrium appears as the consequence of exploring all pathways that connect two states by all procedures. This theory is useful to interpret single-molecule experiments in Biophysics and other fields in Nanoscience and an adequate platform for a general theory of irreversible processes.Arias-Gonzalez, J RicardoThu, 26 Nov 2015 06:40:35 GMT25 Nov 2015arXiv:1511.08017https://cds.cern.ch/record/2108261['arXiv:1511.08017']arXiv:1511.08017Unsteady flow and particle migration in dense, non-Brownian suspensions
https://cds.cern.ch/record/2108260
We present experimental results on dense corn-starch suspensions as examples of non-Brownian, nearly-hard particles that undergo continuous and discontinuous shear thickening (CST and DST) at intermediate and high densities respectively. Our results offer strong support for recent theories involving a stress-dependent effective contact friction among particles. We show however that in the DST regime, where theory might lead one to expect steady-state shear bands oriented layerwise along the vorticity axis, the real flow is unsteady. To explain this, we argue that steady-state banding is generically ruled out by the requirement that, for hard non-Brownian particles, the solvent pressure and the normal-normal component of the particle stress must balance separately across the interface between bands. (Otherwise there is an unbalanced migration flux.) However, long-lived transient shear-bands remain possible.Hermes, MichielGuy, Ben MPoy, GuilhemCates, Michael EWyart, MatthieuPoon, Wilson C KThu, 26 Nov 2015 06:40:35 GMT25 Nov 2015arXiv:1511.08011https://cds.cern.ch/record/2108260['arXiv:1511.08011']arXiv:1511.08011Singly excited S-states of compressed two-electron ions
https://cds.cern.ch/record/2108257
A detailed analysis on the effect of spherical impenetrable confinement on the structural properties of two-electron ions in S-states have been done. The energy values of 1sns [n = 2-4] (3Se) states of helium-like ions (Z = 2-5) are estimated within the framework of Ritz variational method by using explicitly correlated Hylleraas-type basis sets. The correlated wave functions used here are consistent with the finite boundary conditions due to spherical confinement. A comparative study between the singlet and triplet states originating from a particular electronic configuration shows incidental degeneracy and the subsequent level-crossing phenomena. The thermodynamic pressure felt by the ion inside the sphere pushes the energy levels towards continuum. Critical pressures for the transition to strong confinement regime (where the singly excited two-electron energy levels cross the corresponding one-electron threshold) as well as for the complete destabilization are also estimated.Saha, J KBhattacharyya, SMukherjee, T KThu, 26 Nov 2015 06:40:34 GMT25 Nov 2015arXiv:1511.07980https://cds.cern.ch/record/2108257['arXiv:1511.07980']arXiv:1511.07980Collisional-Radiative Model for the visible spectrum of $W^{26+}$ ions
https://cds.cern.ch/record/2108256
Plasma diagnostics in magnetic confinement fusion plasmas by using visible spectrum strongly depends on the knowledge of fundamental atomic properties. A detailed collisional-radiative model of W$^{26+}$ ions has been constructed by considering radiative and electron excitation processes, in which the necessary atomic data had been calculated by relativistic configuration interaction method with the implementation of Flexible Atomic Code. The visible spectrum observed at an electron beam ion trap (EBIT) in Shanghai in the range of 332 nm to 392 nm was reproduced by present calculations. Some transition pairs of which the intensity ratio are sensitive to the electron density were selected as potential candidate of plasma diagnostics. Their electron density dependence are theoretically evaluated for the cases of EBIT plasmas and magnetic confinement fusion plasmas.Ding, XiaobinLiu, JiaxinKoike, FumihiroMurakami, IzumiKato, DaijiSakaue, Hiroyuki ANakamura, NobuyukiDong, ChenzhongThu, 26 Nov 2015 06:40:34 GMT25 Nov 2015arXiv:1511.07976https://cds.cern.ch/record/2108256['arXiv:1511.07976']arXiv:1511.07976Direct Optical Probing of Transverse Electric Mode in Graphene
https://cds.cern.ch/record/2108255
Unique electrodynamic response of graphene implies a manifestation of an unusual propagating and localised transverse-electric (TE) mode near the spectral onset of interband transitions. However, excitation and further detection of the TE mode supported by graphene is considered to be a challenge for it is extremely sensitive to excitation environment and phase matching condition adherence. Here for the first time, we experimentally prove an existence of the TE mode by its direct optical probing, demonstrating significant coupling to an incident wave in electrically doped multilayer graphene sheet at room temperature. We believe that proposed technique of careful phase matching and obtained access to graphene TE excitation would stimulate further studies of this unique phenomenon, and enable its potential employing in various fields of photonics as well as for characterization of graphene.Menabde, SergeyMason, DanielKornev, EvgenyLee, ChangheePark, NamkyooThu, 26 Nov 2015 06:40:34 GMT25 Nov 2015arXiv:1511.07968https://cds.cern.ch/record/2108255['arXiv:1511.07968']arXiv:1511.07968A bandgap phenomenon in non-periodic plasmonic waveguides
https://cds.cern.ch/record/2108254
The phenomenon of a dispersion bandgap opening between low-loss spectral windows of odd and even plasmonic modes in a layered insulator-metal-insulator plasmonic waveguide is introduced. Beginning with a three layer plasmonic dispersion relation, we explain and numerically confirm the existence of the plasmonic bandgap, and investigate its properties at a very broad spectrum range from ultraviolet to far infrared. The nature of the observed bandgap opening is explained in terms of the near-zero value of an effective permittivity for plasmonic modes in the waveguide. The adjustment of the plasmonic bandgap spectrum is demonstrated with the structural modification of the plasmonic waveguide. As an application example, we illustrate a new concept of coupling control between surface plasmons and free-space excitation waves, by employing a tapered non-adiabatic insulator-metal-insulator waveguide.Shaidiuk, ViacheslavMenabde, SergeyPark, NamkyooThu, 26 Nov 2015 06:40:34 GMT25 Nov 2015arXiv:1511.07964https://cds.cern.ch/record/2108254['arXiv:1511.07964']arXiv:1511.07964Conditional Generation Scheme for Entangled Vacuum Evacuated Coherent States by Mixing Two Coherent Beams with a Squeezed Vacuum State
https://cds.cern.ch/record/2108253
Conditions to generate high-purity entangled vacuum-evacuated coherent states ($|0>|\alpha>^0 - |-\alpha>^0 |0>$ were studied for two cascade-placed beam splitters, with one squeezed state input and two coherent state inputs whenever a single photon is detected. Controlling the amplitudes and the phases of the beams allows for various amplitudes of the vacuum-evacuated coherent states ($|\alpha>^ 0 = |\alpha> -e^{-|\alpha|^2} |0> $) up to $\alpha = 2.160$ to be manipulated with high-purity.Youn, Sun-HyunThu, 26 Nov 2015 06:40:34 GMT25 Nov 2015arXiv:1511.07956https://cds.cern.ch/record/2108253['arXiv:1511.07956']arXiv:1511.07956On well-posedness of variational models of charged drops
https://cds.cern.ch/record/2108252
Electrified liquids are well known to be prone to a variety of interfacial instabilities that result in the onset of apparent interfacial singularities and liquid fragmentation. In the case of electrically conducting liquids, one of the basic models describing the equilibrium interfacial configurations and the onset of instability assumes the liquid to be equipotential and interprets those configurations as local minimizers of the energy consisting of the sum of the surface energy and the electrostatic energy. Here we show that, surprisingly, this classical geometric variational model is mathematically ill-posed irrespectively of the degree to which the liquid is electrified. Specifically, we demonstrate that an isolated spherical droplet is never a local minimizer, no matter how small is the total charge on the droplet, since the energy can always be lowered by a smooth, arbitrarily small distortion of the droplet's surface. This is in sharp contrast with the experimental observations that a critical amount of charge is needed in order to destabilize a spherical droplet. We discuss several possible regularization mechanisms for the considered free boundary problem and argue that well-posedness can be restored by the inclusion of the entropic effects resulting in finite screening of free charges.Muratov, Cyrill BNovaga, MatteoThu, 26 Nov 2015 06:40:34 GMT25 Nov 2015arXiv:1511.07952https://cds.cern.ch/record/2108252['arXiv:1511.07952']arXiv:1511.07952Two-timing Hypothesis, Distinguished Limits, Drifts, and Vibrodiffusion for Oscillating Flows
https://cds.cern.ch/record/2108251
In this paper we develop and use the two-timing method for a systematic study of a scalar advection caused by a general oscillating velocity field. Mathematically, we study and classify the multiplicity of distinguished limits and asymptotic solutions produced in the two-timing framework. Our calculations go far beyond the usual ones, performed by the two-timing method. We do not use any additional assumptions, hence our study can be seen as a test for the validity and sufficiency of the two-timing hypothesis. Physically, we derive the averaged equations in their maximum generality (and up to high orders in small parameters) and obtain qualitatively new results. Our results are: (i) the dimensionless advection equation contains \emph{two independent dimensionless small parameters}: the ratio of two time-scales and the spatial amplitudes of oscillations; (ii) we identify a sequence of \emph{distinguished limit solutions} which correspond to the successive degenerations of a \emph{drift velocity}; (iii) for a general oscillating velocity field we derive the averaged equations for the first \emph{four distinguished limit solutions}; (iv) we show, that \emph{each distinguish limit solution} produces an infinite number of \emph{parametric solutions} with a Strouhal number as the only large parameter; those solutions differ from each other by the slow time-scale and the velocity amplitude; (v) the striking outcome of our calculations is the inevitable appearance of \emph{vibrodiffusion}, which represents a Lie derivative of the averaged tensor of quadratic displacements; (vi) our main methodological result is the introduction of a logical order/classification of the solutions; we hope that it opens the gate for applications of the same ideas to more complex systems; (vii) five types of oscillating flows are presented as examples of different drifts and vibrodiffusion.Vladimirov, Vladimir AThu, 26 Nov 2015 06:40:34 GMT24 Nov 2015arXiv:1511.07941https://cds.cern.ch/record/2108251['arXiv:1511.07941']arXiv:1511.07941