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1.
Compression of triangulated solids’ surfaces by Decimating Reconstructable Triangles
Blaž Repnik, Borut Žalik, Krista Rizman Žalik, 2025, izvirni znanstveni članek

Opis: This paper introduces a new programming solution for reducing the size of files needed to store 3D geometric solids, whose surfaces are interpolated by watertight irregular triangle meshes. Unlike other approaches, the software does not introduce any special storage data format, but, instead, utilises popular CAD formats such as STL, OBJ, or PLY. This increases the software’s interoperability significantly. The software comprises an encoder and a decoder. The encoder estimates which facets may be removed in such a way that they can later be reconstructed unambiguously by the decoder. The decoder also ensures that the reconstructed triangles are oriented correctly. The encoder and the decoder are straightforward to understand and to implement. They are asymmetric, making any potential programming error easier to identify and correct.
Ključne besede: data compression, geometric modelling, computer-aided design, boundary representation, topology, watertightness
Objavljeno v DKUM: 30.05.2025; Ogledov: 0; Prenosov: 1
.pdf Celotno besedilo (2,71 MB)

2.
An algorithm for voxelised solids representation using chain codes
Blaž Repnik, Libor Váša, Borut Žalik, 2025, izvirni znanstveni članek

Opis: The paper introduces a new method to describe the surfaces of voxelised solids. It operates in three stages: a hierarchical linked list of chain code sequences is created first; the linked lists are pruned; and, finally, the content of the data structure is stored. The method uses chain codes from either a three- or nine-symbols alphabet. In the first case, two chain code symbols are needed to access the next face, while, in the second case, this is done by one symbol. The pair of chain codes from the three-symbols alphabet, or the individual symbol from the nine-symbols alphabet are considered as tokens. The sets of tokens are, in both cases, extended by two tokens, indicating the beginning and ending of the list. The method processes solids of any shape, including those containing holes, cavities, or multiple components existing in the same voxel space. Edge-connectivity is permitted. The method was compared against the method proposed by Lemus et al., which is designed for solids without holes. Although supporting a broader set of voxelised solids, the proposed method generates sequences of tokens that are, on average, up to 10% shorter. Since the information entropy of the sequences of tokens produced by the proposed method is also smaller, the obtained sequences are more compressible, as confirmed by applying gzip and bzip2 data compressors.
Ključne besede: voxels, chain code, data structures, pruning, information entropy, data compression
Objavljeno v DKUM: 19.05.2025; Ogledov: 0; Prenosov: 1
.pdf Celotno besedilo (11,28 MB)

3.
Morphological, mechanical, and in-vitro bioactivity of gelatine/collagen/hydroxyapatite based scaffolds prepared by unidirectional freeze-casting
Yasir Beeran Potta Thara, Tomaž Vuherer, Uroš Maver, Vanja Kokol, 2021, izvirni znanstveni članek

Opis: The fabrication of biomaterials to be used in segmental bone defects, mimicking the bone's organic-inorganic architecture and mechanical properties to induce osteogenesis, persists as a key challenge. The purpose of this study was to elucidate the effect of a lightweight, morphologically graded, and multiphase self-standing scaffold structure prepared from a combination of gelatine (Gel), collagen type 1 (Col) and/or hydroxyapatite (HAP) nanoparticles by a unidirectional freeze-casting process at different temperatures (−20, −40, −60 °C), followed by carbodiimide induced cross-linking, on their in-vitro mechanical stability and bioactive properties. In addition, the rheological study of differently formulated Gel solutions has been performed to determine the effect of Col and HAP content on their microstructural arrangement, which, together with the freezing kinetic, affects Gel/Col orientation and cross-linking, and, thus, the scaffold's mechanical strength and stability. A bone-like anisotropic, interconnected, and graded porosity (from 120 to a few μm) scaffold structure with up to 30% total porosity and ~61 μm average pores' diameter is obtained by using a higher Col content (Col: Gel = 2:5) and freezing temperature (−20 °C) while forming a few μm thick close-to-parallel lamellae, separated with a 10–100 μm space when prepared at −60 °C. Such a structure influenced in-vitro stability strongly (lower swelling without weight loss), being accompanied with a ~76% increase of compression strength (to 37 kPa) and ~67% decrease of elastic modulus (to 17 kPa) when prepared with HAP and incubated in HBSS for 7 days. On the other hand, a significant reduction of both strength (~78%, to 15 kPa) and elasticity (~95%, to 5 kPa) was noted for a scaffold prepared with HAP at −60 °C, being related to faster degradation and the formation of a highly opened structure on the bottom, required to stimulate the bone ingrowth, while a more closed network structure on the top to adhere with the surrounding soft tissue. None of the scaffolds induced cytotoxicity to human bone-derived osteoblasts, even after 19 days of incubation, but rather improved their viability while promoting cells' adhesions, proliferation, and differentiation, being supported with an increased alkaline phosphatase activity and rod-like CaP formation.
Ključne besede: biomimetic scaffolds, rheology, unidirectional freeze-casting, morphology, compression properties, bioactivity
Objavljeno v DKUM: 10.03.2025; Ogledov: 0; Prenosov: 3
.pdf Celotno besedilo (22,97 MB)
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4.
Survey of inter-prediction methods for time-varying mesh compression
Jan Dvořák, Filip Hácha, Gerasimos Arvanitis, David Podgorelec, Konstantinos Moustakas, Libor Váša, 2025, izvirni znanstveni članek

Opis: Time-varying meshes (TVMs), that is mesh sequences with varying connectivity, are a greatly versatile representation of shapesevolving in time, as they allow a surface topology to change or details to appear or disappear at any time during the sequence.This, however, comes at the cost of large storage size. Since 2003, there have been attempts to compress such data efficiently. Whilethe problem may seem trivial at first sight, considering the strong temporal coherence of shapes represented by the individualframes, it turns out that the varying connectivity and the absence of implicit correspondence information that stems from itmakes it rather difficult to exploit the redundancies present in the data. Therefore, efficient and general TVM compression is stillconsidered an open problem. We describe and categorize existing approaches while pointing out the current challenges in thefield and hint at some related techniques that might be helpful in addressing them. We also provide an overview of the reportedperformance of the discussed methods and a list of datasets that are publicly available for experiments. Finally, we also discusspotential future trends in the field.
Ključne besede: compression algorithms, data compression, modelling, polygonal mesh reduction
Objavljeno v DKUM: 07.02.2025; Ogledov: 0; Prenosov: 2
.pdf Celotno besedilo (3,11 MB)

5.
State-of-the-art trends in data compression : COMPROMISE case study
David Podgorelec, Damjan Strnad, Ivana Kolingerová, Borut Žalik, 2024, izvirni znanstveni članek

Opis: After a boom that coincided with the advent of the internet, digital cameras, digital video and audio storage and playback devices, the research on data compression has rested on its laurels for a quarter of a century. Domain-dependent lossy algorithms of the time, such as JPEG, AVC, MP3 and others, achieved remarkable compression ratios and encoding and decoding speeds with acceptable data quality, which has kept them in common use to this day. However, recent computing paradigms such as cloud computing, edge computing, the Internet of Things (IoT), and digital preservation have gradually posed new challenges, and, as a consequence, development trends in data compression are focusing on concepts that were not previously in the spotlight. In this article, we try to critically evaluate the most prominent of these trends and to explore their parallels, complementarities, and differences. Digital data restoration mimics the human ability to omit memorising information that is satisfactorily retrievable from the context. Feature-based data compression introduces a two-level data representation with higher-level semantic features and with residuals that correct the feature-restored (predicted) data. The integration of the advantages of individual domain-specific data compression methods into a general approach is also challenging. To the best of our knowledge, a method that addresses all these trends does not exist yet. Our methodology, COMPROMISE, has been developed exactly to make as many solutions to these challenges as possible inter-operable. It incorporates features and digital restoration. Furthermore, it is largely domain-independent (general), asymmetric, and universal. The latter refers to the ability to compress data in a common framework in a lossy, lossless, and near-lossless mode. COMPROMISE may also be considered an umbrella that links many existing domain-dependent and independent methods, supports hybrid lossless–lossy techniques, and encourages the development of new data compression algorithms
Ključne besede: data compression, data resoration, universal algorithm, feature, residual
Objavljeno v DKUM: 04.02.2025; Ogledov: 0; Prenosov: 13
.pdf Celotno besedilo (1,13 MB)

6.
Recent advances in ejector-enhanced vapor compression heat pump and refrigeration systems : a review
Sven Gruber, Klemen Rola, Danijela Urbancl, Darko Goričanec, 2024, izvirni znanstveni članek

Opis: The incorporation of ejectors into heat pump and refrigeration cycles has been the subject of growing interest, largely due to their simple structure, high reliability, and cost-effectiveness. This paper investigates the recent advancements in novel design concepts of ejector-enhanced vapor compression heat pump and refrigeration cycles. An overview of novel single-stage and twostage compression cycles utilizing a single or multiple ejectors is provided. First, the system setup, operational principles, description, and figures of the existing schemes are provided. Second, the main results, such as the coefficient of performance (COP), volumetric heating capacity and exergy destruction, are discussed. In conclusion, the paper presents a coherent summary of the current developments, future prospects, and the current knowledge gap. A plethora of research is present in developing theoretical systems with high efficiency. However, experimental tests for real-life implementations are limited. This review aims to provide the reader with an overview of recent theoretical and experimental studies.
Ključne besede: ejector, heat pump, refrigeration, vapor compression system, review
Objavljeno v DKUM: 03.09.2024; Ogledov: 51; Prenosov: 20
.pdf Celotno besedilo (10,04 MB)

7.
Kolmogorov compression complexity may differentiate different schools of Orthodox iconography
Daniel Peptenatu, Ion Andronache, Helmut Ahammer, Richard Taylor, Ioannis Liritzis, Marko Radulovic, Bogdan Ciobanu, Marin Burcea, Matjaž Perc, Tuan D. Pham, 2022, izvirni znanstveni članek

Opis: The complexity in the styles of 1200 Byzantine icons painted between 13th and 16th from Greece, Russia and Romania was investigated through the Kolmogorov algorithmic information theory. The aim was to identify specific quantitative patterns which define the key characteristics of the three different painting schools. Our novel approach using the artificial surface images generated with Inverse FFT and the Midpoint Displacement (MD) algorithms, was validated by comparison of results with eight fractal and non-fractal indices. From the analyzes performed, normalized Kolmogorov compression complexity (KC) proved to be the best solution because it had the best complexity pattern differentiations, is not sensitive to the image size and the least affected by noise. We conclude that normalized KC methodology does offer capability to differentiate the icons within a School and amongst the three Schools.
Ključne besede: iconography, complexity, Kolmogorov compression, art, physics
Objavljeno v DKUM: 15.07.2024; Ogledov: 117; Prenosov: 17
.pdf Celotno besedilo (6,05 MB)
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8.
High strain rate hardening of metallic cellular metamaterials
Nejc Novak, Matej Vesenjak, Zoran Ren, 2024, izvirni znanstveni članek

Opis: Strain rate hardening caused by the changed deformation mode is a fascinating phenomenon in cellular metamaterials where the material’s stiffness and energy absorption capabilities increase as the strain rate increases. This unique behaviour is attributed to a combination of micro-inertia effects, base material’s strain rate hardening and inertia effects. At high strain rates, the metamaterial’s inertia influences its deformation response, which changes to shock mode. This work briefly presents the geometry and fabrication of different metallic metamaterials. Then, it evaluates their mechanical response at different strain rates, ranging from quasi-static to intermediate dynamic and shock, determined by experimental and computational investigation. The three deformation modes can be separated into two critical loading velocities, unique for each metamaterial, which are also presented and compared in this work for various metamaterials. The investigations show that the deformation mode change in metallic metamaterials depends on their porosity. The critical velocities separating the deformation modes decrease with increasing porosity, i.e., decreased density of the metamaterial results in reduced critical loading velocities. The shock deformation mode in cellular metamaterials is thus attainable at much lower loading velocities than in homogeneous (nonporous) materials.
Ključne besede: metamaterials, cellular structures, high strain rate, experimental testing, computational modelling, compression loading, mechanical properties
Objavljeno v DKUM: 22.05.2024; Ogledov: 204; Prenosov: 27
.pdf Celotno besedilo (3,42 MB)
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9.
10.
Lossless Compression of High-frequency Intervals in Digital Audio : bachelor's thesis
Ivan Benc, 2022, diplomsko delo

Opis: In this Thesis, an algorithm for lossless audio compression in a time domain is developed and implemented. The algorithm is designed to estimate the signal frequency based on the number of local extremes, and adapts the encoding to the estimated high or low- frequency intervals. As possible adaptations, fitting line segments, quadratic Bézier curves to the signal, and dictionary compression are examined. Residuals are encoded with delta encoding and compressed with binary adaptive sequential coding. The difference in the proportions of line segments and curves used in the high and low-frequency intervals have been detected, but this is not significant enough for this kind of interval discrimination to be meaningful in the current design of the algorithm.
Ključne besede: lossless audio compression, delta encoding, binary adaptive sequential coding, greedy method
Objavljeno v DKUM: 07.11.2022; Ogledov: 672; Prenosov: 54
.pdf Celotno besedilo (1,90 MB)

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