FROM THE RESEARCH LABORATORIES
Studies On The Nucleation And Growth Of Crystals
Absract. Crystallization is occurring frequently in nature (and already in the antiquity has been used for production of cooking salt).
As science and technology developed the crystallization to the current status, it has become one of the basic processes in a number of large-scale industries. This mini review describes some novel achievements in the research on the nucleation and growth of crystals. The thermodynamics and kinetics of these processes are considered, with a special focus on the Bulgarian contribution to the science of the crystallization. The relation between the sizes of the critical nucleus and the stable nucleus (which dissolution probability is zero) is calculated. Considered is the logistic functional dependence of the nucleation kinetics and its consequences for the crystal size distribution (CSD) of the grown crystals. Calculation of the crystal nuclei number per unit volume as a function of both nucleation time and supersaturation is enabled by recently devised formula. It has been shown that the polydispersity of the crystals occurs already at the stage of their nucleation (and the initial enlargement of the nucleated crystals) and is amplified during their subsequent growth to macroscopic dimensions. Pointed are two (gravity instigated) effects which amplify crystal polydispersity during the crystal growth in unstirred solutions. Special attention is paid to the growth of crystals in solutions with a preset concentration. In doing so, it is shown that the average size of the crystals reached at any time is reversely-proportional to the root third of the number of crystals in a unit volume. The review ends with practical intructions for achieving the desired characteristics of the crystallizing product.
Christo N. Nanev
Rostislaw Kaischew Institute of Physical Chemistr; Bulgarian Academy of Sciences
On the Structure and Evolution of Two-dimensional Soap Foam,
Enclosed between Glass Sheets
Abstract. Liquid foams are objects of great practical significance – they appear in firefighting mixtures, soaps, alcoholic drinks, etc. However, our knowledge about them is extremely limited due to their complexity. This investigation, based on the first problem of the International Young Naturalists Tournament (IYNT) 2019, aims to fill some of the gaps in our understanding of foams in general and of soap foams, enclosed between heavy sheets in particular. This article describes the main parameters of such a foam, the basic qualitative theory that governs its structure and an extensive experimental investigation concerning the evolution with time of this structure. Relevant parameters (e.g. concentration of the soap solution, distance between the glass plates) have been varied in order to find how the distribution of bubbles by size and other quantities behave.
Keywords: soap foam; structure; evolution; experimental investigation; IYNT
Yavor Yordanov
National High School of Mathematics and Science – Sofia (Bulgaria)
Applied Sampling Methodology and Analysis of Nonlinear Acoustic Properties in Solids of Revolution
Abstract. The main focus of this work is the research of the resulting sound caused by a constant airflow through the open end of a bottle by varying the relevant parameters. For a more in depth analysis, additional experiments with test tubes are carried out. The study aims to describe and document the influence of the parameters experimentally and with the help of theoretical apparatus, some of which are: Form, shape and material of the bottle, properties of the gas, filling agent. The aforementioned variables are defined and sorted on the basis of their effect on the process. Unpredicted acoustic properties emerge when the shape of the bottle is varied significantly. New methods for physical data collection such as an AFS (Acoustic Feedback System) and SRP (Solids of Revolution Parameterization) are introduced and compared to the already existing ones, in order to better equate for the emergent acoustic properties. For a holistic evaluation various samples and relations from the well-described acoustic properties are tested against their contemporary physical description for their predictive power. Similar methods are introduced to the analysis of the previously undescribed acoustic phenomena and presented with a multi-layered approach for full comparison.
Keywords: acoustic feedback system; airflow system; solid of revolution; resonance; Helmholtz resonance; standing wave
G.I. Ivanov
Sofia High School of Mathematics (Bulgaria)
Measuring the Collision Time of a Ball with High Coefficient
Abstract. The purpose of this paper is to measure the collision time of a ball with a high coefficient of restitution (SuperBall) with a hard surface. The manuscript discusses the theoretical model of the collision and approximations used; the direct methods for measuring the collision time – shooting with a high speed camera from the side; shooting with a high speed camera from below; verification of the theoretical model; measuring the voltage of a photodiode, and the non-direct methods used – component frequency analysis of the collision sound; measuring the spot left from the falling ball. Results and conclusions are highlighted.
Keywords: collision; coefficient of restitution; time; theoretical model; surface
Vasil Nikolov
First Private Mathematics High School – Sofia (Bulgaria)
NEW APPROACHES
Multiple Perspectives on Academic Laboratory Safety Course in
College Science Education
Abstract. There has been comparable neglect of safety aspects and impacts in science and engineering curriculum design and development. It should become an integral part of the higher science education ecosystem. The academic scenario will be much greener if laboratory safety learning content is prescribed at college levels. It should address a multitude of laboratory safety issues in academic institutions, from laboratory design to technology, from conducting an academic audit to developing a sustainable safety culture. The right steps, such as proper coordination, monitoring by conducting inspections at regular intervals, and a robust accountability mechanism in implementing a safety training program, will ensure progress with favorable results. Developing the safety culture and focusing more on a deeper understanding of the risks is essential for efficient safety management. A practical and meaningful laboratory safety course in educational planning and management, promoted by proper motivation, academic guidance, and administrative support, is crucial. Commitment to safety and proper safety precautions based on knowledge, skill, and attitude would have a substantial impact on preventing many unnecessary accidental injuries due to carelessness or oversight. This article looks at the multiple perspectives on academic lab safety in a changing world. It highlights the recent resurgence of interest in the safety to give an idea of the subject’s enormous scope and various safety-related topics.
Keywords: academic laboratory safety; curriculum design; lab accidents; loss prevention; safety culture
B.H.S. Thimmappa
Manipal Institute of Technology, Manipal Academy of Higher Education (India)
Development Of The Cognitive Interest In Physics And Astronomy Through Non-Formal Education
Absract. The text presents the experience gained in non-formal education in physics and astronomy – organizing and conducting educational activities with students attending the Municipal Center for Extracurricular Activities – “green schools”, summer camps. Shown is the effect for development of cognitive interest and the effect on positive attitude towards these activities.
Keywords: non-formal education; extracurricular activities; cognitive interest
Ivo Jokin
Municipal Center for Extracurricular Activities
INTERDISCIPLINARY
Theater Of Physics Or Physics In Theater?
Absract. In the STEAM – science, technology, engineering, arts and mathematics approach, science education is done through artistic experiences. STEAM training is an incredible opportunity to get boring for some science students. In one lesson, this may not happen, but in a project research activity, the result can be presented precisely through artistic experience. Project-based learning blends in well with STEAM education.
Keywords: project-based training; art; natural sciences; artistic experience
Radka Kostadinova
“Ivan Vazov” High School
Varshetz, Bulgaria
