33,976 research outputs found

    Self-Supervised Learning to Prove Equivalence Between Straight-Line Programs via Rewrite Rules

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    We target the problem of automatically synthesizing proofs of semantic equivalence between two programs made of sequences of statements. We represent programs using abstract syntax trees (AST), where a given set of semantics-preserving rewrite rules can be applied on a specific AST pattern to generate a transformed and semantically equivalent program. In our system, two programs are equivalent if there exists a sequence of application of these rewrite rules that leads to rewriting one program into the other. We propose a neural network architecture based on a transformer model to generate proofs of equivalence between program pairs. The system outputs a sequence of rewrites, and the validity of the sequence is simply checked by verifying it can be applied. If no valid sequence is produced by the neural network, the system reports the programs as non-equivalent, ensuring by design no programs may be incorrectly reported as equivalent. Our system is fully implemented for a given grammar which can represent straight-line programs with function calls and multiple types. To efficiently train the system to generate such sequences, we develop an original incremental training technique, named self-supervised sample selection. We extensively study the effectiveness of this novel training approach on proofs of increasing complexity and length. Our system, S4Eq, achieves 97% proof success on a curated dataset of 10,000 pairs of equivalent programsComment: 30 pages including appendi

    Chiral active fluids: Odd viscosity, active turbulence, and directed flows of hydrodynamic microrotors

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    While the number of publications on rotating active matter has rapidly increased in recent years, studies on purely hydrodynamically interacting rotors on the microscale are still rare, especially from the perspective of particle based hydrodynamic simulations. The work presented here targets to fill this gap. By means of high-performance computer simulations, performed in a highly parallelised fashion on graphics processing units, the dynamics of ensembles of up to 70,000 rotating colloids immersed in an explicit mesoscopic solvent consisting out of up to 30 million fluid particles, are investigated. Some of the results presented in this thesis have been worked out in collaboration with experimentalists, such that the theoretical considerations developed in this thesis are supported by experiments, and vice versa. The studied system, modelled in order to resemble the essential physics of the experimentally realisable system, consists out of rotating magnetic colloidal particles, i.e., (micro-)rotors, rotating in sync to an externally applied magnetic field, where the rotors solely interact via hydrodynamic and steric interactions. Overall, the agreement between simulations and experiments is very good, proving that hydrodynamic interactions play a key role in this and related systems. While already an isolated rotating colloid is driven out of equilibrium, only collections of two or more rotors have experimentally shown to be able to convert the rotational energy input into translational dynamics in an orbital rotating fashion. The rotating colloids inject circular flows into the fluid, such that detailed balance is broken, and it is not a priori known whether equilibrium properties of colloids can be extended to isolated rotating colloids. A joint theoretical and experimental analysis of isolated, pairs, and small groups of hydrodynamically interacting rotors is given in chapter 2. While the translational dynamics of isolated rotors effectively resemble the dynamics of non-rotating colloids, the orbital rotation of pairs of rotors can be described with leading order hydrodynamics and a two-dimensional analogy of Fax├ęnÔÇÖs law is derived. In chapter 3, a homogeneously distributed ensemble of rotors (bulk) as a realisation of a chiral active fluid is studied and it is explicitly shown computationally and experimentally that it carries odd viscosity. The mutual orbital translation of rotors and an increase of the effective solvent viscosity with rotor density lead to a non-monotonous behaviour of the average translational velocity. Meanwhile, the rotor suspension bears a finite osmotic compressibility resulting from the long-ranged nature of hydrody- namic interactions such that rotational and odd stresses are transmitted through the solvent also at small and intermediate rotor densities. Consequently, density inhomogeneities predicted for chiral active fluids with odd viscosity can be found and allow for an explicit measurement of odd viscosity in simulations and experiments. At intermediate densities, the collective dynamics shows the emergence of multi-scale vortices and chaotic motion which is identified as active turbulence with a self-similar power-law decay in the energy spectrum, showing that the injected energy on the rotor scale is transported to larger scales, similar to the inverse energy cascade of clas- sical two-dimensional turbulence. While either odd viscosity or active turbulence have been reported in chiral active matter previously, the system studied here shows that the emergence of both simultaneously is possible resulting from the osmotic compressibility and hydrodynamic mediation of odd and active stresses. The collective dynamics of colloids rotating out of phase, i.e., where a constant torque instead of a constant angular velocity is applied, is shown to be qualitatively very similar. However, at smaller densities, local density inhomogeneities imply position dependent angular velocities of the rotors resulting from inter-rotor friction. While the friction of a quasi-2D layer of active colloids with the substrate is often not easily modifiable in experiments, the incorporation of substrate friction into the simulation models typically implies a considerable increase in computational effort. In chapter 4, a very efficient way of incorporating the friction with a substrate into a two-dimensional multiparticle collision dynamics solvent is introduced, allowing for an explicit investigation of the influences of substrate on active dynamics. For the rotor fluid, it is explicitly shown that the influence of the substrate friction results in a cutoff of the hydrodynamic interaction length, such that the maximum size of the formed vortices is controlled by the substrate friction, also resulting in a cutoff in the energy spectrum, because energy is taken out of the system at the respective length. These findings are in agreement with the experiments. Since active particles in confinement are known to organise in states of collective dynamics, ensembles of rotationally actuated colloids are studied in circular confinement and in the presence of periodic obstacle lattices in chapters 5 and 6, respectively. The results show that the chaotic active turbulent transport of rotors in suspension can be enhanced and guided resulting from edge flows generated at the boundaries, as has recently been reported for a related chiral active system. The consequent collective rotor dynamics can be regarded as a superposition of active turbulent and imposed flows, leading to on average stationary flows. In contrast to the bulk dynamics, the imposed flows inject additional energy into the system on the long length scales, and the same scaling behaviour of the energy spectrum as in bulk is only obtained if the energy injection scales, due to the mutual generation of rotor translational dynamics throughout the system and the edge flows, are well separated. The combination of edge flow and entropic layering at the boundaries leads to oscillating hydrodynamic stresses and consequently to an oscillating vorticity profile. In the presence of odd viscosity, this consequently leads to non-trivial steady-state density modulations at the boundary, resulting from a balance of osmotic pressure and odd stresses. Relevant for the efficient dispersion and mixing of inert particles on the mesoscale by means of active turbulent mixing powered by rotors, a study of the dynamics of a binary mixture consisting out of rotors and passive particles is presented in chapter 7. Because the rotors are not self-propelled, but the translational dynamics is induced by the surrounding rotors, the passive particles, which do not inject further energy into the system, are transported according to the same mechanism as the rotors. The collective dynamics thus resembles the pure rotor bulk dynamics at the respective density of only rotors. However, since no odd stresses act between the passive particles, only mutual rotor interactions lead to odd stresses leading to the accumulation of rotors in the regions of positive vorticity. This density increase is associated with a pressure increase, which balances the odd stresses acting on the rotors. However, the passive particles are only subject to the accumulation induced pressure increase such that these particles are transported into the areas of low rotor concentration, i.e., the regions of negative vorticity. Under conditions of sustained vortex flow, this results in segregation of both particle types. Since local symmetry breaking can convert injected rotational into translational energy, microswimmers can be constructed out of rotor materials when a suitable breaking of symmetry is kept in the vicinity of a rotor. One hypothetical realisation, i.e., a coupled rotor pair consisting out of two rotors of opposite angular velocity and of fixed distance, termed a birotor, are studied in chapter 8. The birotor pumps the fluid into one direction and consequently translates into the opposite direction, and creates a flow field reminiscent of a source doublet, or sliplet flow field. Fixed in space the birotor might be an interesting realisation of a microfluidic pump. The trans- lational dynamics of a birotor can be mapped onto the active Brownian particle model for single swimmers. However, due to the hydrodynamic interactions among the rotors, the birotor ensemble dynamics do not show the emergence of stable motility induced clustering. The reason for this is the flow created by birotor in small aggregates which effectively pushes further arriving birotors away from small aggregates, which eventually are all dispersed by thermal fluctuations

    Articulación de la cadena de valor sostenible de la crianza de cuyes en el distrito de Huachis mediante el análisis de medios de vida

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    Desde el a├▒o 2013, todos los segundos viernes de octubre se celebra el d├şa nacional del cuy, patrimonio natural de la naci├│n, una especie con valor significativo a nivel hist├│rico, cultural y religioso en el Per├║, pues este roedor form├│ parte de la vida de los incas, no solo en su alimentaci├│n sino tambi├ęn en sus sacrificios religiosos. El cuy cumple un rol importante en la alimentaci├│n saludable del ser humano, pues estudios confirman el elevado contenido de prote├şnas y bajo porcentaje de grasas de dicho roedor. De hecho, con la pandemia originado por el virus SARS-CoV-2, especialistas como la Lic. Pilco recomend├│ el consumo de dicho roedor para ayudar en la regeneraci├│n de los tejidos da├▒ados por el Covid.19 Tambi├ęn es importante se├▒alar su rol en el combate contra la anemia y la desnutrici├│n en el Per├║. Respecto a la crianza de este animal, los sistemas m├ís empleados son el familiar, comercial y el familiar-comercial, siendo el primero el m├ís com├║n en las zonas rurales del Per├║. Desde hace varios a├▒os, el gobierno ha ido estimulando la crianza de cuyes como una forma comercial para impulsar la erradicaci├│n de la pobreza de las familias en el sector rural. Lamentablemente estos esfuerzos no han sido suficientes, ya que existen escasos programas que otorguen fondos para mejorar los sistemas de crianza tradicionales y elevar el nivel de vida de la poblaci├│n vulnerable mencionada. Sumado a ello, existen miles de personas que no conocen los grandes beneficios del consumo de la carne de cuy ni el impacto positivo de su crianza. Por ello, la presente tesis se centra en mejorar la calidad de los medios de vida e impulsar la crianza y comercializaci├│n de cuyes de una de las zonas rurales m├ís pobres del Per├║, la cual es el Centro Poblado de Huachis, ubicado en el distrito del propio nombre, provincia de Huari y departamento de Ancash, mediante la articulaci├│n de la cadena de valor del cuy usando el concepto de Value Links. Value links es un m├ętodo que consiste, en primer lugar, en realizar un an├ílisis de medios de vida de la comunidad de estudio a trav├ęs de una serie de indicadores de cinco activos: humano, social, natural, f├şsico y financiero. En segundo lugar, se centra en la caracterizaci├│n de la cadena de valor actual, siendo la del cuy de Huachis para el presente proyecto. A partir de ello, se plantear├í un FODA por cada eslab├│n de la cadena con el prop├│sito de mapear los principales problemas de dicha cadena y conocer las limitaciones y bondades m├ís importantes para la comercializaci├│n del producto final. Ello impulsar├í al planteamiento de estrategias de soluci├│n con apoyo de una matriz de enfrentamiento y la creaci├│n de una propuesta de cadena de valor mejorada. Finalmente, en base a dicha propuesta y una estimaci├│n de la oferta y demanda del cuy se crear├í un plan estrat├ęgico a partir del cual se realizar├í un cronograma de actividades para el an├ílisis de resultados final. En la investigaci├│n, se encontr├│ que el capital humano, financiero y f├şsico son los activos con mayor vulnerabilidad, sumado a ello que la cadena actual de valor del cuy no es sostenible para la poblaci├│n, ya que solo los primeros eslabones est├ín parcialmente desarrollados siendo los de mayor vulnerabilidad los de producci├│n y comercializaci├│n, pues el producto final en la mayor├şa de casos es el cuy vivo o muerto y su mercado se limita a los miembros del centro poblado estudiado y en ciertas oportunidades a las comunidades aleda├▒as. Finalmente, el resultado esperado del presente trabajo se basa en obtener una calidad de vida sostenible para los pobladores de Huachis, el cual se reflejar├í en el impacto positivo de cada indicador de los activos: humano, social, natural, f├şsico y financiero, ello a trav├ęs de la comercializaci├│n de nuevos productos, siendo el principal el empaquetado de cuy al vac├şo y como secundario los derivados de este

    An Introduction to the Unpublished Book "Reflections on a Tube" by Mitchell J. Feigenbaum

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    This paper is an adaptation of the introduction to a book project by the late Mitchell J. Feigenbaum (1944-2019). While Feigenbaum is certainly mostly known for his theory of period doubling cascades, he had a lifelong interest in optics. His book project is an extremely original discussion of the apparently very simple study of anamorphs, that is, the reflections of images on a cylindrical mirror. He observed that there are \emph{two images} to be seen in the tube, and discovered that the brain preferentially chooses one of them. I edited and wrote an introduction to this planned book. As the book is still not published, I have now adapted my introduction as a standalone version, so that some of Feigenbaum's remarkable work will be accessible to a larger audience

    Scalar spectral functions from the spectral fRG

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    We compute non-perturbative spectral functions in a scalar ¤Ľ4\phi^4-theory in three spacetime dimensions via the spectral functional renormalisation group. This approach allows for the direct, manifestly Lorentz covariant computation of correlation functions in Minkowski spacetime, including a physical on-shell renormalisation. We present numerical results for the spectral functions of the two- and four-point correlation functions for different values of the coupling parameter. These results agree very well with those obtained from another functional real-time approach, the spectral Dyson-Schwinger equation.Comment: 22 pages, 13 figure

    Examples of works to practice staccato technique in clarinet instrument

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    Klarnetin staccato tekni─čini g├╝├žlendirme a┼čamalar─▒ eser ├žal─▒┼čmalar─▒yla uygulanm─▒┼čt─▒r. Staccato ge├ži┼člerini h─▒zland─▒racak ritim ve n├╝ans ├žal─▒┼čmalar─▒na yer verilmi┼čtir. ├çal─▒┼čman─▒n en ├Ânemli amac─▒ sadece staccato ├žal─▒┼čmas─▒ de─čil parmak-dilin e┼č zamanl─▒ uyumunun hassasiyeti ├╝zerinde de durulmas─▒d─▒r. Staccato ├žal─▒┼čmalar─▒n─▒ daha verimli hale getirmek i├žin eser ├žal─▒┼čmas─▒n─▒n i├žinde et├╝t ├žal─▒┼čmas─▒na da yer verilmi┼čtir. ├çal─▒┼čmalar─▒n ├╝zerinde titizlikle durulmas─▒ staccato ├žal─▒┼čmas─▒n─▒n ilham verici etkisi ile m├╝zikal kimli─če yeni bir boyut kazand─▒rm─▒┼čt─▒r. Sekiz ├Âzg├╝n eser ├žal─▒┼čmas─▒n─▒n her a┼čamas─▒ anlat─▒lm─▒┼čt─▒r. Her a┼čaman─▒n bir sonraki performans ve tekni─či g├╝├žlendirmesi esas al─▒nm─▒┼čt─▒r. Bu ├žal─▒┼čmada staccato tekni─činin hangi alanlarda kullan─▒ld─▒─č─▒, nas─▒l sonu├žlar elde edildi─či bilgisine yer verilmi┼čtir. Notalar─▒n parmak ve dil uyumu ile nas─▒l ┼čekillenece─či ve nas─▒l bir ├žal─▒┼čma disiplini i├žinde ger├žekle┼čece─či planlanm─▒┼čt─▒r. Kam─▒┼č-nota-diyafram-parmak-dil-n├╝ans ve disiplin kavramlar─▒n─▒n staccato tekni─činde ayr─▒lmaz bir b├╝t├╝n oldu─ču saptanm─▒┼čt─▒r. Ara┼čt─▒rmada literat├╝r taramas─▒ yap─▒larak staccato ile ilgili ├žal─▒┼čmalar taranm─▒┼čt─▒r. Tarama sonucunda klarnet tekni─čin de kullan─▒lan staccato eser ├žal─▒┼čmas─▒n─▒n az oldu─ču tespit edilmi┼čtir. Metot taramas─▒nda da et├╝t ├žal─▒┼čmas─▒n─▒n daha ├žok oldu─ču saptanm─▒┼čt─▒r. B├Âylelikle klarnetin staccato tekni─čini h─▒zland─▒rma ve g├╝├žlendirme ├žal─▒┼čmalar─▒ sunulmu┼čtur. Staccato et├╝t ├žal─▒┼čmalar─▒ yap─▒l─▒rken, araya eser ├žal─▒┼čmas─▒n─▒n girmesi beyni rahatlatt─▒─č─▒ ve isteklili─či daha artt─▒rd─▒─č─▒ g├Âzlemlenmi┼čtir. Staccato ├žal─▒┼čmas─▒n─▒ yaparken do─čru bir kam─▒┼č se├žimi ├╝zerinde de durulmu┼čtur. Staccato tekni─čini do─čru ├žal─▒┼čmak i├žin do─čru bir kam─▒┼č─▒n dil h─▒z─▒n─▒ artt─▒rd─▒─č─▒ saptanm─▒┼čt─▒r. Do─čru bir kam─▒┼č se├žimi kam─▒┼čtan rahat ses ├ž─▒kmas─▒na ba─čl─▒d─▒r. Kam─▒┼č, dil atma g├╝c├╝n├╝ vermiyorsa daha do─čru bir kam─▒┼č se├žiminin yap─▒lmas─▒ gereklili─či vurgulanm─▒┼čt─▒r. Staccato ├žal─▒┼čmalar─▒nda ba┼čtan sona bir eseri yorumlamak zor olabilir. Bu a├ž─▒dan ├žal─▒┼čma, verilen m├╝zikal n├╝anslara uyman─▒n, dil at─▒┼č performans─▒n─▒ rahatlatt─▒─č─▒n─▒ ortaya koymu┼čtur. Gelecek nesillere edinilen bilgi ve birikimlerin aktar─▒lmas─▒ ve geli┼čtirici olmas─▒ te┼čvik edilmi┼čtir. ├ç─▒kacak eserlerin nas─▒l ├ž├Âz├╝lece─či, staccato tekni─činin nas─▒l ├╝stesinden gelinebilece─či anlat─▒lm─▒┼čt─▒r. Staccato tekni─činin daha k─▒sa s├╝rede ├ž├Âz├╝me kavu┼čturulmas─▒ ama├ž edinilmi┼čtir. Parmaklar─▒n yerlerini ├Â─čretti─čimiz kadar belle─čimize de ├žal─▒┼čmalar─▒n kaydedilmesi ├Ânemlidir. G├Âsterilen azmin ve sabr─▒n sonucu olarak ortaya ├ž─▒kan yap─▒t ba┼čar─▒y─▒ daha da yukar─▒ seviyelere ├ž─▒karacakt─▒r

    Alphaviruses Detected in Mosquitoes in the North-Eastern Regions of South Africa, 2014 to 2018

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    The prevalence and distribution of African alphaviruses such as chikungunya have increased in recent years. Therefore, a better understanding of the local distribution of alphaviruses in vectors across the African continent is important. Here, entomological surveillance was performed from 2014 to 2018 at selected sites in north-eastern parts of South Africa where alphaviruses have been identified during outbreaks in humans and animals in the past. Mosquitoes were collected using a net, CDC-light, and BG-traps. An alphavirus genus-specific nested RT-PCR was used for screening, and positive pools were confirmed by sequencing and phylogenetic analysis. We collected 64,603 mosquitoes from 11 genera, of which 39,035 females were tested. Overall, 1462 mosquito pools were tested, of which 21 were positive for alphaviruses. Sindbis (61.9%, N = 13) and Middelburg (28.6%, N = 6) viruses were the most prevalent. Ndumu virus was detected in two pools (9.5%, N = 2). No chikungunya positive pools were identified. Arboviral activity was concentrated in peri-urban, rural, and conservation areas. A range of Culicidae species, including Culex univittatus, Cx. pipiens s.l., Aedes durbanensis, and the Ae. dentatus group, were identified as potential vectors. These findings confirm the active circulation and distribution of alphaviruses in regions where human or animal infections were identified in South Africa.publishersversionpublishe

    Magnetic braking with MESA evolutionary models in the single star and LMXB regimes

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    Magnetic braking has a prominent role in driving the evolution of close low mass binary systems and heavily influences the rotation rates of low mass F- and later type stars with convective envelopes. Several possible prescriptions that describe magnetic braking in the context of 1D stellar evolution models currently exist. We test four magnetic braking prescriptions against both low mass X-ray binary orbital periods from the Milky Way and single star rotation periods observed in open clusters. We find that data favors a magnetic braking prescription that follows a rapid transition from fast to slow rotation rates, exhibits saturated (inefficient) magnetic braking below a critical Rossby number, and that is sufficiently strong to reproduce ultra compact X-ray binary systems. Of the four prescriptions tested, these conditions are satisfied by a braking prescription that incorporates the effect of high order magnetic field topology on angular momentum loss. None of the braking prescriptions tested are able to replicate the stalled spin down observed in open cluster stars aged 700 - 1000 Myr or so, with masses Ôë▓\lesssim 0.8 MÔŐÖ\rm M_{\odot}.Comment: 20 pages, 5 figure

    Antiferromagnet-mediated interlayer exchange: hybridization versus proximity effect

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    We investigate the interlayer coupling between two thin ferromagnetic (F) films mediated by an antiferromagnetic (AF) spacer in F*/AF/F trilayers and show how it transitions between different regimes on changing the AF thickness. Employing layer-selective Kerr magnetometry and ferromagnetic-resonance techniques in a complementary manner enables us to distinguish between three functionally distinct regimes of such ferromagnetic interlayer coupling. The F layers are found to be individually and independently exchange-biased for thick FeMn spacers - the first regime of no interlayer F-F* coupling. F-F* coupling appears on decreasing the FeMn thickness below 9 nm. In this second regime found in structures with 6.0-9.0 nm thick FeMn spacers, the interlayer coupling exists only in a finite temperature interval just below the effective N\'eel temperature of the spacer, which is due to magnon-mediated exchange through the thermally softened antiferromagnetic spacer, vanishing at lower temperatures. The third regime, with FeMn thinner than 4 nm, is characterized by a much stronger interlayer coupling in the entire temperature interval, which is attributed to a magnetic-proximity induced ferromagnetic exchange. These experimental results, spanning the key geometrical parameters and thermal regimes of the F*/AF/F nanostructure, complemented by a comprehensive theoretical analysis, should broaden the understanding of the interlayer exchange in magnetic multilayers and potentially be useful for applications in spin-thermionics.Comment: 14 pages, 9 figure
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