Instytut Podstawowych Problemów Techniki
Polskiej Akademii Nauk


dr Paweł Sznajder

Zakład Biosystemów i Miękkiej Materii (ZBiMM)
Pracownia Fizyki Płynów Złożonych (PFPZ)
stanowisko: specjalista badawczo-techniczny
telefon: (+48) 22 826 12 81 wewn.: 421
pokój: 322
ORCID: 0000-0002-6916-0884

2019-12-09 Stan stacjonarny sedymentującej zawiesiny przy małej liczbie Reynoldsa i dużej liczbie Pecleta  (Uniwersytet Warszawski)
promotor -- prof. dr Bogdan Cichocki, UW

Ostatnie publikacje
1.  Słowicka A.M., Xue N., Sznajder P., Nunes J.K., Stone H.A., Ekiel-Jeżewska M.L., Buckling of elastic fibers in a shear flow, NEW JOURNAL OF PHYSICS, ISSN: 1367-2630, DOI: 10.1088/1367-2630/ac43eb, Vol.24, pp.013013-1-16, 2022

Three-dimensional dynamics of flexible fibers in shear flow are studied numerically, with a qualitative comparison to experiments. Initially, the fibers are straight, with different orientations with respect to the flow. By changing the rotation speed of a shear rheometer, we change the ratio A of bending to shear forces. We observe fibers in the flow-vorticity plane, which gives insight into the motion out of the shear plane. The numerical simulations of moderately flexible fibers show that they rotate along effective Jeffery orbits, and therefore the fiber orientation rapidly becomes very close to the flow-vorticity plane, on average close to the flow direction, and the fiber remains in an almost straight configuration for a long time. This ``ordering'' of fibers is temporary since they alternately bend and straighten out while tumbling. We observe numerically and experimentally that if the fibers are initially in the compressional region of the shear flow, they can undergo a compressional buckling, with a pronounced deformation of shape along their whole length during a short time, which is in contrast to the typical local bending that originates over a long time from the fiber ends. We identify differences between local and compressional bending and discuss their competition, which depends on the initial orientation of the fiber and the bending stiffness ratio A. There are two main finding. First, the compressional buckling is limited to a certain small range of the initial orientations, excluding those from the flow-vorticity plane. Second, since fibers straighten out in the flow-vorticity plane while tumbling, the compressional buckling is transient - it does not appear for times longer than 1/4 of the Jeffery period. For larger times, bending of fibers is always driven by their ends.

Słowa kluczowe:
Stokes flow, flexible fibers, bending, buckling, orientational order

Afiliacje autorów:
Słowicka A.M. - IPPT PAN
Xue N. - inna afiliacja
Sznajder P. - IPPT PAN
Nunes J.K. - inna afiliacja
Stone H.A. - Princeton University (US)
Ekiel-Jeżewska M.L. - IPPT PAN
2.  Sznajder P., Cichocki B., Ekiel-Jeżewska M., Lack of Plasma-like Screening Mechanism in Sedimentation of a Non-Brownian Suspension, SYMMETRY, ISSN: 2073-8994, DOI: 10.3390/sym14010063, Vol.14, No.1, pp.63-1-10, 2022

We investigate qualitatively a uniform non-Brownian sedimenting suspension in a stationary state. As a base of our analysis we take the BBGKY hierarchy derived from the Liouville equation. We then show that assumption of the plasma-like screening relations can cancel some long-range terms in the hierarchy but it does not provide integrable solutions for correlation functions. This suggests breaking the translational symmetry of the system. Therefore a non-uniform structure can develop to suppress velocity fluctuations and make the range of correlations finite.

Słowa kluczowe:
non-Brownian sedimentation, stability, BBGKY hierarchy, hydrodynamic screening, correlation functions, low-Reynolds-number hydrodynamics

Afiliacje autorów:
Sznajder P. - IPPT PAN
Cichocki B. - Uniwersytet Warszawski (PL)
Ekiel-Jeżewska M. - IPPT PAN
3.  Szczytko J., Vaupotic N., Madrak K., Sznajder P., Górecka E., Magnetic moment of a single metal nanoparticle determined from the Faraday effect, PHYSICAL REVIEW E, ISSN: 1539-3755, DOI: 10.1103/PhysRevE.87.033201, Vol.87, No.3, pp.033201-1-6, 2013

Optical properties of a composite material made of ferromagnetic metal nanoparticles embedded in a dielectric host are studied. We constructed an effective dielectric tensor of the composite material taking into account the orientational distribution of nanoparticle magnetic moments in external magnetic field. A nonlinear dependence of the optical rotation on magnetic field resulting from the reorientation of nanoparticles is demonstrated. The theoretical findings were applied to the magneto-optical experimental data of cobalt ferromagnetic nanoparticles embedded in a dielectric liquid host. The dependence of the Faraday rotation on Co-based ferromagnetic nanoparticles was measured as a function of the external magnetic field, varying the size of nanoparticles and the wavelength of light. The proposed approach enables quantitative determination of the magnetic moment and the plasma frequency of a single nanoparticle, and from this the size of the nonmagnetic shell of magnetic nanoparticles.

Afiliacje autorów:
Szczytko J. - inna afiliacja
Vaupotic N. - inna afiliacja
Madrak K. - inna afiliacja
Sznajder P. - inna afiliacja
Górecka E. - inna afiliacja
4.  Serafin K., Oracz J., Grzybowski M., Koperski M., Sznajder P., Zinkiewicz Ł., Wasylczyk P., Measurement of the mass of an object hanging from a spring-revisited, European Journal of Physics, ISSN: 0143-0807, DOI: 10.1088/0143-0807/33/1/011, Vol.33, pp.129-134, 2012

In an open competition, students were to determine the mass of a metal cylinder hanging on a spring inside a transparent enclosure. With the time for experiments limited to 24 h due to the unexpectedly large number of participants, a few surprisingly accurate results were submitted, the best of them differing by no more than 0.5% from the true value with a relative uncertainty of less than 1%.

Afiliacje autorów:
Serafin K. - inna afiliacja
Oracz J. - inna afiliacja
Grzybowski M. - inna afiliacja
Koperski M. - inna afiliacja
Sznajder P. - inna afiliacja
Zinkiewicz Ł. - inna afiliacja
Wasylczyk P. - inna afiliacja
5.  Sznajder P., Piętka B., Szczytko J., Łusakowski J., Bardyszewski W., Resonant plasmon response of a periodically modulated two-dimensional electron gas, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.122.1090, Vol.122, No.6, pp.1090-1092, 2012

We report the theoretical study of the optical response of a periodically modulated two-dimensional electron gas. The density of states is calculated within the first order of the perturbation theory and the effects of the short-range disorder are explained and discussed. We demonstrate that the magnetic field values corresponding to the characteristic narrowing of the density of states width are given by the zeros of the subsequent Laguerre polynomials. The observed increase of the density of states at the edges are interpreted as van Hove singularities. The broadening effects are shown to modify and smear out the observed effects with increasing temperature above 2 K. The plasmon dispersion relation is discussed in terms of the random phase approximation. Small changes in plasmon dispersion relation related to the periodic modulation were predicted.

Afiliacje autorów:
Sznajder P. - inna afiliacja
Piętka B. - inna afiliacja
Szczytko J. - inna afiliacja
Łusakowski J. - inna afiliacja
Bardyszewski W. - inna afiliacja

Abstrakty konferencyjne
1.  Ekiel-Jeżewska M.L., Słowicka A.M., Xue N., Sznajder P., Nunes J., Stone H.A., Buckling and temporal order of flexible fibers in shear flows, Bulletin of the American Physical Society, ISSN: 0003-0503, Vol.66, pp.M27.9, 2021

Numer/data zgłoszenia patentowego
Ogłoszenie o zgłoszeniu patentowym
Kraj i Nazwa uprawnionego z patentu
Numer patentu
Ogłoszenie o udzieleniu patentu
BUP 13/2014
Szczytko J., Górecka E., Vaupotic N., Madrak K., Sznajder P., Osewski P., Turski H., Pociecha D.
Sposób wyznaczania wartości namagnesowania nanocząstek magnetycznych oraz urządzenie do wyznaczania wartości namagnesowania nanocząstek magnetycznych
PL, Uniwersytet Warszawski
WUP 07/2016

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