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Papers by Tomasz Kowalewski

Advanced Optical Materials, Apr 21, 2020

The stability of the P(NIPAm-co-NIPMAm) /GNR samples after a prolonged storage time in water was ... more The stability of the P(NIPAm-co-NIPMAm) /GNR samples after a prolonged storage time in water was verified by performing a detailed characterization of the morphological and optical properties. Four identical samples (see Materials and methods for technical details) were fully immersed in distilled water and investigated at t= 0 days, t= 1 day, t= 30 days, t= 45 days by a: i) field emission scanning electron microscope (FE-SEM); ii) UV-Vis spectrophotometer; iii) pump-probe optical setup. More details on these techniques are reported in the Experimental section. Figure S1. FE-SEM analysis of the samples at different hydration times: t= 0 days (a), t=1 day (b), t=30 days (c), t=45 days (d).

Advanced Materials Interfaces, May 4, 2020

Advanced Materials Interfaces, Jun 1, 2020

Using high speed video camera and numerical processing of the digital images transient descriptio... more Using high speed video camera and numerical processing of the digital images transient description of the geometry and the interface velocity for vapour bubble growing at the heated surface in subcooled liquid is achieved. Particle Image Velocimetry and Thermometry are applied to obtain details about velocity and temperature in the surrounding flow field. Experimental results are compared with the results of calculations based on a simple mathematical model.

The paper contains our attempts to estimate diffusion parameters of nanofibers actually applied a... more The paper contains our attempts to estimate diffusion parameters of nanofibers actually applied as protective mats for neurosurgery. Measurements of concentration profiles of fluorophore released from stained nanofibres are performed. The two release systems are investigated: solid nanofibres and core-shell nanofibres with targeted drug simulator encapsulated inside nanofibres. The gathered information allows us to estimate parameters necessary for controlling drug release profiles.

Acta Neurobiologiae Experimentalis, 2011

The current task of contemporary fluid mechanics evidently moves from modeling large scale turbul... more The current task of contemporary fluid mechanics evidently moves from modeling large scale turbulence to lower, molecular scale limit, where assumption of a continuous and deterministic description becomes questionable again. Once the scaling length of flow becomes comparable with structure dimensions, transport phenomena are strongly modulated by molecular interactions and its proper interpretation needs involvement of deeper physics. New experimental tools largely help in understanding transport phenomena at nanoscales. In the following review we give few examples of problems appealing for new theoretical and numerical models embracing continuous flow modeling with molecular scale phenomena. environment is based on “stochastic” transport phenomena. Molecular diffusion becomes very efficient at short distances. Whereas typical biomolecule needs hours to be transported by diffusion for distances of centimeter, such transport takes less than 1 s at subcellular distances. Hence, random walk of nano-objects driven by intermolecular interactions initiates all living processes, whereas hydrodynamic interactions play mainly role of a drag force, modifying species mobility. Physics of nanoscale mechanics can be more or less completely described using quantum mechanics. The methods, called ab initio, are rigorous but limited by present-day computers to systems containing a few hundred atoms at most. To determine the properties of larger ensembles of atoms the Molecular Dynamics method is commonly used, enabling studies of billions of atoms with effective interatomic potentials. Still its practical applications are limited by time and space scales to first nanoseconds of the analyzed phenomena and several nanometers in space. Hence, modelling fluid flow in microand nano-scales needs specific technique, which is based on assumption that fluid particle can be represented as a cluster of atoms. Effective clustering can be built using the so-called Voronoi tessellation, describing a special kind of decomposition of the flow domain (Czerwińska 2004). Such coarse grained modelling is useful for general flow description, but needs predefined interactions if we approach molecular distances to interpret specific phenomenon. Despite of all technical and physical problems with direct experimental analysis of nano/micro scale flows, physical experiment appears to be the only way to validate simplified assumptions, which by definition have to be incorporated to theoretical

The proposed benchmark configuration concerns steady-state natural convection of water in the dif... more The proposed benchmark configuration concerns steady-state natural convection of water in the differentially heated cube-shaped cavity for temperatures close to the freezing point. Strongly non-linear buoyancy term allowed for thoughtful testing of several numerical approaches. After selecting the best performing one a new, very restrictive verification procedure is proposed. The verified numerical code is used to simulate the “real world” of an experimental configuration.

The report treats on computing cluster in the IPPT. The first part of the report is a user manual... more The report treats on computing cluster in the IPPT. The first part of the report is a user manual of the cluster. In the following, we described chosen applications concerning applications of numerical methods in the computational biology, tectonophysics and fluid mechanics. Finally, we depicted a few selected computer programs that are implemented on the cluster. GRAFEN – IPPT PAN COMPUTER OF BIOCENTRUM OCHOTA GRID Pod redakcją: Eligiusza Postka i Tomasza A. Kowalewskiego Instytut Podstawowych Problemów Techniki Polskiej Akademii Nauk Streszczenie Praca traktuje o sposobie użytkowania klastra obliczeniowego znajdującego się w IPPT. Praca zawiera podręcznik użytkownika. W dalszym ciągu zostały opisane wybrane aplikacje dotyczące zastosowań metod numerycznych w problemach biologii obliczeniowej, tektonofizyki i mechaniki płynów. Na zakończenie podane zostały przykłady wybranych implementowanych programów komputerowych wraz z ich krótkimi opisami.

2. Wybór konfiguracji geometrycznej ścianek kanału prowadzącej do destabilizacji przepływu.......... more 2. Wybór konfiguracji geometrycznej ścianek kanału prowadzącej do destabilizacji przepływu.............................................................................................................................. 6 3. Analiza teoretyczna i numeryczna wpływu orientacji kierunku pofalowania względem gradientu ciśnienia............................................................................................. 11 4. Analiza wpływu ścian bocznych na opory przepływu........................................................ 12 5. Wpływ ścian bocznych na stateczność przepływu w pofalowanym kanale........................ 13 6. Badanie nieliniowej saturacji zaburzenia przy pomocy modelu niskowymiarowego......... 14 7. Lagranżowska symulacja procesów mieszania................................................................... 16 8. Analiza struktury przepływu w geometrii uproszczonej..................................................... 21 9. Symulacja DNS przepływu cieczy w kanale z poprze...

Proceedings of the Sixth International Symposium On Turbulence, Heat and Mass Transfer, 2009

Generation of vortices enhances heat transfer by swirl, flow destabilization and development of v... more Generation of vortices enhances heat transfer by swirl, flow destabilization and development of viscous layers. They may increase heat transfer by several hundred percent. Prior to the use of vortices to influence heat transfer it must be known how different vortices are generated and controlled, and how they interact with the base flow and temperature field. To select the most appropriate vortex generators (VG) for a given task it is necessary to know the heat transfer and flow losses associated with the generation of a specific vortex system. The aim of the paper is to asses the state of art and to encourage exploration of heat transfer control by vortices. Flow visualization and heat transfer experiments were conducted using an open low-speed wind tunnel equipped with Liquid Crystals Thermography (LCT) and Particle Image Velocimetry (PIV). In this work we consider five types of transverse vortex generators (TVGs) which where brought to required temperatures by the hot film method. Heat transfer measurements were carried out by LCT.

A fast discrete model for the simulations of thin charged jets produced during the electrospinnin... more A fast discrete model for the simulations of thin charged jets produced during the electrospinning process is derived, based on an efficient implementation of the boundary element method for the computation of electrostatic interactions of the jet with itself and with the electrodes. Short-range electrostatic forces are evaluated with slender-body analytical approximations, whereas a hierarchical force evaluation algorithm is used for long-range interactions. Qualitative comparisons with experiments is discussed.

Archive of Mechanical Engineering, 2011

ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B, 2006

Turbulent flow of water in a narrow gap of an emulsifier is investigated experimentally using mic... more Turbulent flow of water in a narrow gap of an emulsifier is investigated experimentally using micro-PIV (micro Particle Image Velocimetry) technique and compared with numerical predictions performed using the commercial code Fluent. The purpose of the investigations is to develop a procedure for well-controlled generation of mono-disperse suspension of micro droplets. These droplets will form a matrix for collection of nano-particles into well-structured configuration [1]. The micro-flow measurements are based on epi-fluorescence illumination and high-speed imaging. The experimental data are compared with the numerical results obtained using both turbulent and laminar flow models. It was found that, due to small channel dimensions and very small flow development length, the turbulent energy dissipation takes place mainly in the gap and shortly behind it. Very low amount of oil-phase fraction in investigated emulsions justifies us to use mean energy dissipation estimated for pure wat...

Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2014

Drug delivery systems based on nanofibrous mats appear to be a promising healing practice for pre... more Drug delivery systems based on nanofibrous mats appear to be a promising healing practice for preventing brain neurodegeneration after surgery. One of the problems encountered during planning and constructing optimal delivery system based on nanofibrous mats is the estimation of parameters crucial for predicting drug release dynamics. This study describes our experimental setup allowing for spatial and temporary evaluation of drug release from nanofibrous polymers to obtain data necessary to validate appropriate numerical models. We applied laser light sheet method to illuminate released fluorescent drug analog and CCD camera for imaging selected cross-section of the investigated volume. Transparent hydrogel was used as a brain tissue phantom. The proposed setup allows for continuous observation of drug analog (fluorescent dye) diffusion for time span of several weeks. Images captured at selected time intervals were processed to determine concentration profiles and drug release kinetics. We used presented method to evaluate drug release from several polymers to validate numerical model used for optimizing nanofiber system for neuroprotective dressing. V