69 research outputs found

    Improvement of the Specification of the Asphalt Concrete Overlay by Using Polypropylene

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    يهدف البحث إلى إعداد خلطة إسفلتية عالية الأداء تتمتع بمواصفات جيده لاستخدامها في طبقة التقوية تستطيع مقاومة المشاكل والعيوب التي تتعرض لها وتزيد من عمرها الخدمي. حيث استخدمت حبيبات البولي بروبلين كماده مضافة للرابط الإسفلتي نوع. ((AC 60-70بسته نسب (1, 2, 3, 4, 5, 7) % من وزن النسبة المثلى للإسفلت مع استخدام ركام ذو المقاس الأعظم 19 ملم. تم دراسة تأثير هذه الإضافات على الخصائص الحجمية والميكانيكية وتقييم أداء الخلطة باستخدام فحص مارشال وبأخذ ما لا يقل عن 3 نماذج لكل نسبة. بينت الدراسة ان استخدام 4% من حبيبات البولي بروبلين من وزن الإسفلت المثلى أعطت التحسين الأمثل بالاداء مقارنة مع الخلطة المرجعية غير المعالجة حيث زاد ثبات مارشال بنسبة 47% ونقص مقدار الانسياب بمقدار 17% مقارنه بالخلطة المرجعية. كما بينت النتائج ان اضافة مثل هكذا نسبة اعطت خلطة ذات مواصفات حجمية ضمن حدود المواصفة.The research aims to prepare high-performance asphalt concrete with good specifications for using in asphalt concrete overlay can resist deformations and problems faced and increase its age service. Used all of polypropylene particles as an additive to  the asphalt concrete type (AC 60-70) by six ratios (1, 2, 3, 4, 5 and 7) % of optimum asphalt content weight,  as an  additive for asphalt mixture with a maximum size of the aggregate (19mm). Study the effect of these additions on the volumetric and the mechanical properties of the asphalt concrete and evaluate its performance through Marshall Method test by take at least three specimens of ratio tested. The results showed that the use of polypropylene particles improve the performance and specifications of asphalt concrete and increase the ability to  resist deformations that are exposed, where  it was concluded that the addition of ratio (4%) of the weight of the asphalt of  polypropylene gives optimum improvement of the performance of the asphalt  concrete overlay, where Marshall stability is increased by 47% and flow decreased by 17% compared to untreated mixtures respectively, with volumetric properties within limitations of the specifications

    Vortex nucleation limited mobility of free electron bubbles in the Gross-Pitaevskii model of a superfluid

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    We study the motion of an electron bubble in the zero-temperature limit where neither phonons nor rotons provide a significant contribution to the drag exerted on an ion moving within the superfluid. By using the Gross-Clark model, in which a Gross-Pitaevskii equation for the superfluid wave function is coupled to a Schrödinger equation for the electron wave function, we study how vortex nucleation affects the measured drift velocity of the ion. We use parameters that give realistic values of the ratio of the radius of the bubble with respect to the healing length in superfluid 4He at a pressure of one bar. By performing fully three-dimensional spatiotemporal simulations of the superfluid coupled to an electron, that is modeled within an adiabatic approximation and moving under the influence of an applied electric field, we are able to recover the key dynamics of the ion-vortex interactions that arise and the subsequent ion-vortex complexes that can form. Using the numerically computed drift velocity of the ion as a function of the applied electric field, we determine the vortex nucleation limited mobility of the ion to recover values in good agreement with measured data

    Entropy of Negative Temperature States for a Point Vortex Gas

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    We study the dynamics and statistical mechanical equilibria of a neutral two-dimensional point vortex gas with Coulomb-like interactions confined in a squared and a rectangular domain. Using a punctuated Hamiltonian model in which we model the process of vortex-antivortex annihilation in superfluids by removing vortex dipoles, we show that this leads to evaporative heating of the system. Consequently, the vortex gas enters the negative temperature regime and subsequently relaxes to a maximum entropy configuration. We demonstrate that the large scale flows that emerge in this regime can be explained by using an equilibrium statistical mechanical mean field theory of point vortices based on a Poisson-Boltzmann (PB) equation. In particular, we observe that the emergent large scale flows in our point vortex simulations in the squared domain give rise to a spontaneous acquisition of angular momentum whereas the flows in the rectangular domain prefers a state with zero angular momentum. In addition to the observed qualitative agreement between the dynamical simulations and the theory that we demonstrate for the two geometries, we also present an approach that allows us to accurately compute a coarse-grained vorticity field, and henceforth recover the entropy from our dynamical runs. This allows us to perform a quantitative comparison between the dynamical point vortex simulations and the statistical mechanical predictions of the mean field theory thereby allowing us to clearly assert the validity of the assumptions of the statistical approaches as applied to this system with long-range interactions

    Approximating Steady States in Equilibrium and Nonequilibrium Condensates

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    We obtain approximations for the time-independent Gross-Pitaevskii (GP) and complex GP equation in two and three spatial dimensions by generalizing the divergence-free WKB method. The results include an explicit expression of a uniformly valid approximation for the condensate density of an ultracold Bose gas confined in a harmonic trap that extends into the classically forbidden region. This provides an accurate approximation of the condensate density that includes healing effects at leading order that are missing in the widely adopted Thomas-Fermi approximation. The results presented herein allow us to formulate useful approximations to a range of experimental systems including the equilibrium properties of a finite temperature Bose gas and the steady-state properties of a 2D nonequilibrium condensate. Comparisons between our asymptotic and numerical results for the conservative and forced-dissipative forms of the GP equations as applied to these systems show excellent agreement between the two sets of solutions thereby illustrating the accuracy of these approximations.Comment: 5 pages, 1 figur

    A vortex filament tracking method for the Gross–Pitaevskii model of a superfluid

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    We present an accurate and robust numerical method to track quantized vortex lines in a superfluid described by the Gross--Pitaevskii equation. By utilizing the pseudo-vorticity field of the associated complex scalar order parameter of the superfluid, we are able to track the topological defects of the superfluid and reconstruct the vortex lines which correspond to zeros of the field. Throughout, we assume our field is periodic to allow us to make extensive use of the Fourier representation of the field and its derivatives in order to retain spectral accuracy. We present several case studies to test the precision of the method which include the evaluation of the curvature and torsion of a torus vortex knot, and the measurement of the Kelvin wave spectrum of a vortex line and a vortex ring. The method we present makes no a-priori assumptions on the geometry of the vortices and is therefore applicable to a wide range of systems such as a superfluid in a turbulent state that is characterised by many vortex rings coexisting with sound waves. This allows us to track the positions of the vortex filaments in a dense turbulent vortex tangle and extract statistical information about the distribution of the size of the vortex rings and the inter-vortex separations. In principle, the method can be extended to track similar topological defects arising in other physical systems

    Breathers on quantized superfluid vortices

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    We consider the propagation of breathers along a quantized superfluid vortex. Using the correspondence between the local induction approximation (LIA) and the nonlinear Schrödinger equation, we identify a set of initial conditions corresponding to breather solutions of vortex motion governed by the LIA. These initial conditions, which give rise to a long-wavelength modulational instability, result in the emergence of large amplitude perturbations that are localized in both space and time. The emergent structures on the vortex filament are analogous to loop solitons but arise from the dual action of bending and twisting of the vortex. Although the breather solutions we study are exact solutions of the LIA equations, we demonstrate through full numerical simulations that their key emergent attributes carry over to vortex dynamics governed by the Biot-Savart law and to quantized vortices described by the Gross-Pitaevskii equation. The breather excitations can lead to self-reconnections, a mechanism that can play an important role within the crossover range of scales in superfluid turbulence. Moreover, the observation of breather solutions on vortices in a field model suggests that these solutions are expected to arise in a wide range of other physical contexts from classical vortices to cosmological strings

    Classical vs Quantum Annealing and Manifold Reduction in Soft-Spin Minimizers of Ising Hamiltonians

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    We investigate the minimization of the Ising Hamiltonians, comparing the dynamics of semi-classical soft-spin models with quantum annealing. We systematically analyze how the energy landscape for the circulant couplings of a Mobius graph evolves with increased annealing parameters. Our findings indicate that these semi-classical models face challenges due to a widening dimensionality landscape. To counteract this issue, we introduce the `manifold reduction' method, which restricts the soft-spin amplitudes to a defined phase space region. Concurrently, quantum annealing demonstrates a natural capability to navigate the Ising Hamiltonian's energy landscape due to its operation within the comprehensive Hilbert space. Our study indicates that physics-inspired or physics-enhanced optimizers will likely benefit from a blend of classical and quantum annealing techniques.Comment: 10 pages, 7 figure

    Microscopic theory of Bose–Einstein condensation of magnons at room temperature

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    A quantised spin wave – magnon – in magnetic films can undergo Bose- Einstein condensation into two energetically degenerate lowest-energy quan- tum states with non-zero wave vectors ±kBEC. This corresponds to two in- terfering condensates forming spontaneously in momentum space. Brillouin Light Scattering studies for a microwave-pumped film with sub-micrometer spatial resolution experimentally confirm the existence of the two wave- functions and show that their interference results in a non-uniform ground state of the condensate with the density oscillating in space. Moreover, fork dislocations in the density fringes provide direct experimental evidence for the formation of pinned half quantum vortices in the magnon condensate. The measured amplitude of the density oscillation implies the formation of a non-symmetric state that corresponds to non equal occupation of two en- ergy minima. We discuss the experimental findings and consider the theory of magnon condensates which includes, to leading order, the contribution from the non-condensed magnons. The e↵ect of the non-condensed magnon cloud is to increase the contrast of the asymmetric state and to bring about the experimental measurements

    Leapfrogging Kelvin waves

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    Two vortex rings can form a localized configuration whereby they continually pass through one another in an alternating fashion. This phenomenon is called leapfrogging. Using parameters suitable for superfluid helium-4, we describe a recurrence phenomenon that is similar to leapfrogging, which occurs for two coaxial straight vortex filaments with the same Kelvin wave mode. For small-amplitude Kelvin waves we demonstrate that our full Biot-Savart simulations closely follow predictions obtained from a simplified model that provides an analytical approximation developed for nearly parallel vortices. Our results are also relevant to thin-cored helical vortices in classical fluids
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