arXiv subjects

Vladimir Zakharov

Publications and source records attributed to Vladimir Zakharov.

At least 19 recordsLinked to original sources

arXiv2026

Compile-Time Java Stream Fusion via mapMulti

The Java Stream API, introduced in Java 8, makes data processing more expressive and concise compared to imperative loops. However, this abstraction can come with significant performance overhead, often due to the creation of multiple intermediate objects during pipeline execution. In functional languages such as Haskell, this problem is addressed through stream fusion, a compile-time optimization that eliminates unnecessary intermediate structures. Inspired by this idea, Streamliner was the first tool to perform ahead-of-time, bytecode-to-bytecode stream optimization for Java by unrolling stream pipelines into imperative loops. In this paper, we introduce an open-source optimizer that takes a different approach. Instead of unrolling streams into loops, it merges consecutive map() and filter() operations into a single mapMulti() call, available since Java 16. Our method avoids several limitations of Streamliner, including its sensitivity to escaping objects in lambda expressions and its restrictions on assigning or passing streams as variables. We evaluated our optimizer on nine benchmarks and observed superior performance in two cases and comparable results in most others. We also applied it to the bytecode of Apache Kafka, successfully executing all 31,799 unit tests without failures.

cs.PL↗

arXiv2024

Embracing Objects Over Statics: An Analysis of Method Preferences in Open Source Java Frameworks

In today's software development landscape, the extent to which Java applications utilize object-oriented programming paradigm remains a subject of interest. Although some researches point to the considerable overhead associated with object orientation, one might logically assume that modern Java applications would lean towards a procedural style to boost performance, favoring static over instance method calls. In order to validate this assumption, this study scrutinizes the runtime behavior of 28 open-source Java frameworks using the YourKit profiler. Contrary to expectations, our findings reveal a predominant use of instance methods and constructors over static methods. This suggests that developers still favor an object-oriented approach, despite its potential drawbacks.

cs.SE↗

arXiv2024

A patchy CO$_2$ exosphere on Ganymede revealed by the James Webb Space Telescope

Jupiter's icy moon Ganymede has a tenuous exosphere produced by sputtering and possibly sublimation of water ice. To date, only atomic hydrogen and oxygen have been directly detected in this exosphere. Here, we present observations of Ganymede's CO$_2$ exosphere obtained with the James Webb Space Telescope. CO$_2$ gas is observed over different terrain types, mainly over those exposed to intense Jovian plasma irradiation, as well as over some bright or dark terrains. Despite warm surface temperatures, the CO$_2$ abundance over equatorial subsolar regions is low. CO$_2$ vapor has the highest abundance over the north polar cap of the leading hemisphere, reaching a surface pressure of 1 pbar. From modeling we show that the local enhancement observed near 12 h local time in this region can be explained by the presence of cold traps enabling CO$_2$ adsorption. However, whether the release mechanism in this high-latitude region is sputtering or sublimation remains unclear. The north polar cap of the leading hemisphere also has unique surface-ice properties, probably linked to the presence of the large atmospheric CO2 excess over this region. These CO2 molecules might have been initially released in the atmosphere after the radiolysis of CO$_2$ precursors, or from the sputtering of CO$_2$ embedded in the H$_2$O ice bedrock. Dark terrains (regiones), more widespread on the north versus south polar regions, possibly harbor CO$_2$ precursors. CO$_2$ molecules would then be redistributed via cold trapping on ice-rich terrains of the polar cap and be diurnally released and redeposited on these terrains. Ganymede's CO$_2$ exosphere highlights the complexity of surface-atmosphere interactions on Jupiter's icy Galilean moons.

astro-ph.EP↗

arXiv2022

Determining the dust environment of an unknown comet for a spacecraft fly-by: The case of ESA's Comet Interceptor mission

We present a statistical approach to assess the dust environment for a yet unknown comet (or when its parameters are known only with large uncertainty). This is of particular importance for missions such as ESA's Comet Interceptor mission to a dynamically new comet. We find that the lack of knowledge of any particular comet results in very large uncertainties (~3 orders of magnitude) for the dust densities within the coma. The most sensitive parameters affecting the dust densities are the dust size distribution, the dust production rate and coma brightness, often quantified by Af$ρ$. Further, the conversion of a coma's brightness (Af$ρ$) to a dust production rate is poorly constrained. The dust production rate can only be estimated down to an uncertainty of ~0.5 orders of magnitude if the dust size distribution is known in addition to the Af$ρ$. To accurately predict the dust environment of a poorly known comet, a statistical approach as we propose here needs to be taken to properly reflect the uncertainties. This can be done by calculating an ensemble of comae covering all possible combinations within parameter space as shown in this work.

astro-ph.EP↗

arXiv2022

Lump interactions with plane solitons

We analyse the detail of interactions of two-dimensional solitary waves called lumps and one-dimensional line solitons within the framework of the Kadomtsev-Petviashvili equation describing wave processes in media with positive dispersion. We show that line solitons can emit or absorb lumps or periodic chains of lumps; they can interact with each other by means of lumps. Within a certain time interval, lumps or lump chains can emerge between two line solitons and disappear then due to absorption by one of the solitons. This phenomenon resembles the appearance of rogue waves in the oceans. The results obtained are graphically illustrated and can be applicable to the description of physical processes occurring in plasma, fluids, solids, nonlinear optical media, and other fields.

nlin.PS↗

arXiv2021

Dynamics of irregularly-shaped cometary particles subjected to outflowing gas and solar radiative forces and torques

The dynamics of irregularly-shaped particles subjected to the combined effect of gas drag and radiative forces and torques in a cometary environment is investigated. The equations of motion are integrated over distances from the nucleus surface up to distances where the gas drag is negligible. The aerodynamic forces and torques are computed assuming a spherically symmetric expanding gas. The calculations are limited to particle sizes in the geometric optics limit, which is the range of validity of our radiative torque calculations. The dynamical behaviour of irregular particles is quite different to those exhibited by non-spherical but symmetric particles such as spheroids. An application of the dynamical model to comet 67P/Churyumov-Gerasimenko, the target of the Rosetta mission, is made. We found that, for particle sizes larger than about 10 micrometer, the radiative torques are negligible in comparison with the gas-driven torques up to a distance of about 100 km from the nucleus surface. The rotation frequencies of the particles depend on their size, shape, and the heliocentric distance, while the terminal velocities, being also dependent on size and heliocentric distance, show only a very weak dependence on particle shape. The ratio of the sum of the particles projected areas in the sun-to-comet direction to that of the sum of the particles projected areas in any direction perpendicular to it is nearly unity, indicating that the interpretation of the observed u-shaped scattering phase function by Rosetta/OSIRIS on comet 67P coma cannot be linked to mechanical alignment of the particles.

astro-ph.EP↗

arXiv2021

Lump chains in the KP-I equation

We construct a broad class of solutions of the KP-I equation by using a reduced version of the Grammian form of the $τ$-function. The basic solution is a linear periodic chain of lumps propagating with distinct group and wave velocities. More generally, our solutions are evolving linear arrangements of lump chains, and can be viewed as the KP-I analogues of the family of line-soliton solutions of KP-II. However, the linear arrangements that we construct for KP-I are more general, and allow degenerate configurations such as parallel or superimposed lump chains. We also construct solutions describing interactions between lump chains and individual lumps, and discuss the relationship between the solutions obtained using the reduced and regular Grammian forms.

nlin.SI↗

arXiv2020

Ghost interaction of breathers

Mutual interaction of localized nonlinear waves, e.g. solitons and modulation instability patterns, is a fascinating and intensively-studied topic of nonlinear science. In this research report, we report on the observation of a novel type of breather interaction in telecommunication optical fibers, in which two identical breathers propagate with opposite group velocities. Under certain conditions, neither amplification nor annihilation occur at the collision point and most interestingly, its amplitude is almost equal to another maximum of either oscillating breather. This ghost-like breather interaction dynamics can be fully described by the N-breather solution of the nonlinear Schrödinger equation.

nlin.PS↗

arXiv2019

Generalized primitive potentials

In our previous work, we introduced a new class of bounded potentials of the one-dimensional Schrödinger operator on the real axis, and a corresponding family of solutions of the KdV hierarchy. These potentials, which we call primitive, are obtained as limits of rapidly decreasing reflectionless potentials, or multisoliton solutions of KdV. In this note, we introduce generalized primitive potentials, which are obtained as limits of all rapidly decreasing potentials of the Schrödinger operator. These potentials are constructed by solving a contour problem, and are determined by a pair of positive functions on a finite interval and a functional parameter on the real axis.

nlin.SI↗

arXiv2019

Bound state soliton gas dynamics underlying the noise-induced modulational instability

We investigate theoretically the fundamental phenomenon of the spontaneous, noise-induced modulational instability (MI) of a plane wave. The long-term statistical properties of the noise-induced MI have been previously observed in experiments and in simulations but have not been explained so far. In the framework of inverse scattering transform (IST), we propose a model of the asymptotic stage of the noise-induced MI based on $N$-soliton solutions ($N$-SS) of the integrable focusing one-dimensional nonlinear Schrödinger equation (1D-NLSE). These $N$-SS are bound states of strongly interacting solitons having a specific distribution of the IST eigenvalues together with random phases. We use a special approach to construct ensembles of multi-soliton solutions with statistically large number of solitons $N\sim100$. Our investigation demonstrates complete agreement in spectral (Fourier) and statistical properties between the long-term evolution of the condensate perturbed by noise and the constructed multi-soliton bound states. Our results can be generalised to a broad class of integrable turbulence problems in the cases when the wave field dynamics is strongly nonlinear and driven by solitons.

nlin.SI↗

arXiv2019

Nonlinear Ocean Waves Amplification in Straits

We study deep water ocean wind-driven waves in strait, with wind directed orthogonally to the shore, through exact Hasselmann equation. Despite of "dissipative" shores - we do not include any reflection from the coast lines - we show that the wave turbulence evolution can be split in time into two different regimes. During the first wave propagate along the wind, and the wind-driven sea can be described by the self-similar solution of the Hasselmann equation like in the open sea. The second regime starts later in time, after significant enough wave energy accumulation at the down-wind boundary. Since this moment the ensemble of waves propagating against the wind starts its formation. Also, the waves, propagation along the strait start to appear. The wave system eventually reaches asymptotic stationary state in time, consisting of two co-existing states: the first, self-similar wave ensemble, propagating with the wind, and the second, quasi-monochromatic waves, propagating almost orthogonal to the wind direction and tending to slant against the wind at the angle of 15 degrees closer to the wave turbulence origination shore line. These "secondary waves" appear only due to intensive nonlinear wave interaction. The total wave energy exceeds its "expected value" approximately by the factor of two, with respect to estimated in the absence of the shores. It is expected that in the reflective shores presence this amplification will grow essentially. We propose to call this laser-like Nonlinear Ocean Waves Amplification mechanism by the acronym NOWA.

physics.ao-ph↗

arXiv2018

On symmetric primitive potentials

The concept of a primitive potential for the Schroedinger operator on the line was introduced in [2,3,4]. Such a potential is determined by a pair of positive functions on a finite interval, called the dressing functions, which are not uniquely determined by the potential. The potential is constructed by solving a contour problem on the complex plane. In this paper, we consider a reduction where the dressing functions are equal. We show that in this case, the resulting potential is symmetric, and describe how to analytically compute the potential as a power series. In addition, we establish that if the dressing functions are both equal to one, then the resulting primitive potential is the elliptic one-gap potential.

nlin.SI↗

arXiv2018

Models of Rosetta/OSIRIS 67P dust coma phase function

The phase function of the dust coma of comet 67P has been determined from Rosetta/OSIRIS images \citep{Bertini17}. This function show a deep minimum at phase angles near 100$^\circ$, and a strong backscattering enhancement. These two properties cannot be reproduced by regular models of cometary dust, most of them based on wavelength-sized and randomly-oriented aggregate particles. We show, however, that an ensamble of oriented elongated particles of a wide variety of aspect ratios, with radii $r \gtrsim$10 $μ$m, and whose long axes are perpendicular to the direction of the solar radiation, are capable of reproducing the observed phase function. These particles must be absorbing, with an imaginary part of the refractive index of about 0.1 to match the expected geometric albedo, and with porosity in the 60-70\% range.

astro-ph.EP↗

arXiv2016

On ZRP wind input term consistency in Hasselmann equation

The new ZRP wind input source term (Zakharov et al. 2012) is checked for its consistency via numerical simulation of Hasselmann equation. The results are compared to field experimental data, collected at different sites around the world, and theoretical predictions of self-similarity analysis. Good agreement is obtained for limited fetch and time domain statements

physics.ao-ph↗

arXiv2016

Free-Surface Hydrodynamics in Conformal Variables: Are Equations of Free-Surface Hydrodynamics on Deep Water Integrable?

The hypothesis on complete integrability of equations describing the potential motion of incompressible ideal fluid with free surface in 2-D space in presence and absence of gravity was formulated by Dyachenko and Zakharov in 1994 [1]. Later on, the same authors found that these equations have indefinite number of additional motion constants [2] that was an argument in support of the integrability hypothesis. In this article we formulate another argument in favor of this conjecture. It is known [3] that the free-surface equations have an exotic solution that keeps the surface flat but describes the compression of the whole mass of fluid. In this article we show that the free-surface hydrodynamic is integrable if the motion can be treated as a finite amplitude perturbation of the compressed fluid solution. Integrability makes possible to construct an indefinite number of exact solutions of the Euler equations with free surface.

math-ph↗

arXiv2015

Non-periodic one-gap potentials in quantum mechanics

We describe a broad class of bounded non-periodic potentials in one-dimensional stationary quantum mechanics having the same spectral properties as periodic potentials. The spectrum of the corresponding Schroedinger operator consists of a finite or infinite number of allowed bands separated by gaps. In this letter we consider the simplest class of potentials, whose spectra consist of an interval on the negative semiaxis and the entire positive axis. The potentials are reflectionless, and a particle with positive energy moves freely in both directions. The potential is constructed as a limit of Bargmann potentials and is determined by a Riemann-Hilbert problem, which is equivalent to a pair of singular integral equations that can be efficiently solved using numerical techniques.

nlin.SI↗

arXiv2014

Transparency of Strong Gravitational Waves

This paper studies diagonal spacetime metrics. It is shown that the overdetermined Einstein vacuum equations are compatible if one Killing vector exists. The stability of plane gravitational waves of the Robinson type is studied. This stability problem bares a fantastic mathematical resemblance to the stability of the Schwarzschild black hole studied by Regge and Wheeler. Just like for the Schwarzschild black hole, the Robinson gravitational waves are proven to be stable with respect to small perturbations. We conjecture that a bigger class of vacuum solutions are stable, among which are all gravitational solitons. Moreover, the stability analysis reveals a surprising fact: a wave barrier will be transparent to the Robinson waves, which therefore passes through the barrier freely. This is a hint of integrability of the 1+2 vacuum Einstein equations for diagonal metrics.

gr-qc↗

arXiv2013

Rogue waves statistics in the framework of one-dimensional Generalized Nonlinear Schrodinger Equation

We measure evolution of spectra, spatial correlation functions and probability density functions (PDFs) of waves appearance for a set of one-dimensional NLS-like equations of focusing type, namely for the classical integrable Nonlinear Schrodinger equation (1), nonintegrable NLS equation accounting for dumping (linear dissipation, two- and three-photon absorption) and pumping terms (2) and generalized NLS equation accounting for six-wave interactions, dumping and pumping terms (3). All additional terms beyond the classical NLS equation are small. As initial conditions we choose seeded by noise modulationally unstable solutions of the considered systems in the form of (a) condensate for systems (1)-(3) and (b) cnoidal wave for the classical NLS equation (1). We observe 'strange' results for the classical NLS equation (1) with condensate initial condition including peak at zeroth harmonic in averaged over ensemble spectra, non-decaying spacial correlation functions and a 'breathing' region on the PDFs for medium waves amplitudes where frequency of waves appearance oscillates with time, while the far-tails of the PDFs remain Rayleigh ones. Addition of small dumping and pumping terms in model (2) breaks integrability that results in absence of the peak at zeroth harmonic in spectra, spacial correlation functions decaying to zero level and strictly Rayleigh PDFs for waves amplitudes. For the classical NLS equation (1) with cnoidal wave initial condition PDFs turn out to be significantly different from Rayleigh ones with 'fat tails' in the region of large amplitudes where higher waves appear more frequently, while for generalized NLS equation with six-wave interactions, dumping and pumping terms (3) we demonstrate absence of non-Rayleigh addition to the PDFs for zeroth six-wave interactions coefficient and increase of non-Rayleigh addition with six-wave interactions term.

physics.optics↗