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1.
Recent developments on Oka manifolds
Franc Forstnerič, 2023, pregledni znanstveni članek

Povzetek: In this paper we present the main developments in Oka theory since the publication of my book "Stein Manifolds and Holomorphic Mappings (The Homotopy Principle in Complex Analysis)", 2nd ed., Springer, 2017. We also give several new results, examples and constructions of Oka domains in Euclidean and projective spaces. Furthermore, we show that for $n > 1$ the fibre $\mathbb C^n$ in a Stein family can degenerate to a non-Oka fibre, thereby answering a question of Takeo Ohsawa. Several open problems are discussed.
Ključne besede: Oka manifold, Oka map, Stein manifold, elliptic manifold, algebraically subelliptic manifold, Calabi–Yau manifold, density property
Objavljeno v DiRROS: 14.03.2024; Ogledov: 58; Prenosov: 32
.pdf Celotno besedilo (1014,41 KB)
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2.
Oka domains in Euclidean spaces
Franc Forstnerič, Erlend Fornæss Wold, 2024, izvirni znanstveni članek

Povzetek: In this paper, we find surprisingly small Oka domains in Euclidean spaces $\mathbb C^n$ of dimension $n>1$ at the very limit of what is possible. Under a mild geometric assumption on a closed unbounded convex set $E$ in $\mathbb C^n$, we show that $\mathbb C^n\setminus E$ is an Oka domain. In particular, there are Oka domains only slightly bigger than a halfspace, the latter being neither Oka nor hyperbolic. This gives smooth families of real hypersurfaces $\Sigma_t \subset \mathbb C^n$ for $t \in \mathbb R$ dividing $\mathbb C^n$ in an unbounded hyperbolic domain and an Oka domain such that at $t=0$, $\Sigma_0$ is a hyperplane and the character of the two sides gets reversed. More generally, we show that if $E$ is a closed set in $\mathbb C^n$ for $n>1$ whose projective closure $\overline E \subset \mathbb{CP}^n$ avoids a hyperplane $\Lambda \subset \mathbb{CP}^n$ and is polynomially convex in $\mathbb{CP}^n\setminus \Lambda\cong\mathbb C^n$, then $\mathbb C^n\setminus E$ is an Oka domain.
Ključne besede: Oka manifold, hyperbolic manifolds, density property, projectively convex sets
Objavljeno v DiRROS: 19.02.2024; Ogledov: 133; Prenosov: 48
.pdf Celotno besedilo (278,96 KB)
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3.
Complete nonsingular holomorphic foliations on Stein manifolds
Antonio Alarcón, Franc Forstnerič, 2024, izvirni znanstveni članek

Povzetek: Let $X$ be a Stein manifold of complex dimension $n \ge 1$ endowed with a Riemannian metric ${\mathfrak g}$. We show that for every integer $k$ with $\left[\frac{n}{2}\right] \le k \le n-1$ there is a nonsingular holomorphic foliation of dimension $k$ on $X$ all of whose leaves are topologically closed and ${\mathfrak g}$-complete. The same is true if $1\le k \left[\frac{n}{2}\right]$ provided that there is a complex vector bundle epimorphism $TX\to X \times \mathbb{C}^{n-k}$. We also show that if $\mathcal{F}$ is a proper holomorphic foliation on $\mathbb{C}^n$ $(n > 1)$ then for any Riemannian metric ${\mathfrak g}$ on $\mathbb{C}^n$ there is a holomorphic automorphism $\Phi$ of $\mathbb{C}^n$ such that the image foliation $\Phi_*\mathcal{F}$ is ${\mathfrak g}$-complete. The analogous result is obtained on every Stein manifold with Varolin's density property.
Ključne besede: Stein manifolds, complete holomorphic foliations, density property
Objavljeno v DiRROS: 19.02.2024; Ogledov: 138; Prenosov: 46
.pdf Celotno besedilo (433,06 KB)
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4.
Mechanical properties of high carbon low-density steels
Jiri Hajek, Zbyšek Nový, Ludmila Kucerova, Hana Jirková, Črtomir Donik, Zdeňek Jansa, 2023, izvirni znanstveni članek

Ključne besede: low density steels, heat treatment, tensile test
Objavljeno v DiRROS: 02.02.2024; Ogledov: 101; Prenosov: 50
.pdf Celotno besedilo (10,85 MB)
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5.
Selective glucose oxidation to glucaric acid using bimetallic catalysts : lattice expansion or electronic structure effect?
Žan Lavrič, Janvit Teržan, Ana Kroflič, Janez Zavašnik, Joanna E. Olszówka, Štefan Vajda, Matej Huš, Miha Grilc, Blaž Likozar, 2024, izvirni znanstveni članek

Povzetek: Our study presents a comprehensive approach for the selective oxidation of glucose to glucaric acid (GA) by heterogeneous catalysis. We have synthesized and characterized Au/ZrO2, AuCu/ZrO2 and AuPt/ZrO2 catalysts using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and oxygen pulse chemisorption (OPS) techniques. Combining experimental observations with in-depth density functional theory (DFT) studies, we found that bimetallic catalysts form alloys, which exhibit different characteristics than monometallic counterparts for the given reaction. We performed batch reactions, varying temperature and oxygen pressure, and used the data to construct a predictive microkinetic model. As it turned out, AuPt/ZrO2 showed the highest selectivity, yielding 32 % of GA at 100 °C and 30 barg O2. Our results provide valuable insights for the developing of efficient catalysts and point out the bottlenecks for the oxidation of glucose to GA.
Ključne besede: glucaric acid, glucose oxidation, catalyst characterization, density functional theory, microkinetic modelling
Objavljeno v DiRROS: 06.12.2023; Ogledov: 182; Prenosov: 99
.pdf Celotno besedilo (2,73 MB)
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6.
Quality-assurance of heat-flow data: the new structure and evaluation scheme of the IHFC Global Heat Flow Database
Sven Fuchs, Ben Norden, Florian Neumann, Norbert Kaul, Akiko Tanaka, Ilmo T. Kukkonen, Christophe Pascal, Rodolfo Christiansen, Gianluca Gola, Dušan Rajver, 2023, izvirni znanstveni članek

Povzetek: Since 1963, the International Heat Flow Commission has been fostering the compilation of the Global Heat Flow Database to provide reliable heat-flow data. Over time, techniques and methodologies evolved, calling for a reorganization of the database structure and for a reassessment of stored heat-flow data. Here, we provide the results of a collaborative, community-driven approach to set-up a new, quality-approved global heat-flow database. We present background information on how heat-flow is determined and how this important thermal parameter could be systematically evaluated. The latter requires appropriate documentation of metadata to allow the application of a consistent evaluation scheme. The knowledge of basic data (name and coordinates of the site, depth range of temperature measurements, etc.), details on temperature and thermal-conductivity data and possible perturbing effects need to be given. The proposed heat-flow quality evaluation scheme can discriminate between different quality aspects affecting heat flow: numerical uncertainties, methodological uncertainties, and environmental effects. The resulting quality codes allow the evaluation of every stored heat-flow data entry. If mandatory basic data are missing, the entry is marked accordingly. In cases where more than one heat-flow determination is presented for one specific site, and all of them are considered for the site, the poorest evaluation score is inherited to the site level. The required data and the proposed scheme are presented in this paper. Due to the requirements of the newly developed evaluation scheme, the database structure as presented in 2021 has been updated and is available in the appendix of this paper. The new quality scheme will allow a comprehensible evaluation of the stored heat-flow data for the first time.
Ključne besede: heat-flow density, quality scheme, thermal geophysics, global heat flow database (GHFD), thermal parameter, data information system, International Heat Flow Commission (IHFC)
Objavljeno v DiRROS: 09.08.2023; Ogledov: 305; Prenosov: 114
.pdf Celotno besedilo (4,78 MB)

7.
Inter-person differences in isometric coactivations of triceps surae and tibialis anterior decrease in young, but not in older adults after 14 days of bed rest
Matjaž Divjak, Gašper Sedej, Nina Murks, Mitja Gerževič, Uroš Marušič, Rado Pišot, Boštjan Šimunič, Aleš Holobar, 2022, izvirni znanstveni članek

Povzetek: We examined activation patterns of the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), soleus (SO), and tibialis anterior (TA) muscles in eight older (58.4 ± 3.3 years) and seven young (23.1 ± 2.9 years) participants, before and after 14 days of horizontal bed rest. Visual feedback on the exerted muscle torque was provided to the participants. The discharge patterns of individual motor units (MUs) were studied in three repetitions of isometric plantar flexion at 30 and 60% of Maximum Voluntary Contraction (MVC), before, and 1 day after the 14-day bed rest, respectively. In the GL and GM muscles, the older participants demonstrated higher MU discharge rates than the young, regardless of the contraction level, both before and after the bed rest. In the TA and SO muscles, the differences between the older and young participants were less consistent. Detailed analysis revealed person-specific changes in the MU discharge rates after the bed rest. To quantify the coactivation patterns we calculated the correlation coefficients between the cumulative spike trains of identified MUs from each muscle, and measured the root mean square difference of the correlation coefficients between the trials of the same session (intra-session variability) and between different sessions (inter-session variability) in each participant (intra-person comparison) and across participants (inter-person comparison). In the intra-person comparison, the inter-session variability was higher than the intra-session variability, either before or after the bed rest. At 60% MVC torque, the young demonstrated higher inter-person variability of coactivation than the older participants, but this variability decreased significantly after the bed rest. In older participants, inter-person variability was consistently lower at 60% than at 30% MVC torque. In young participants, inter-person variability became lower at 60% than at 30% MVC torque only after the bed rest. Precaution is required when analyzing the MU discharge and coactivation patterns, as individual persons demonstrate individual adaptations to aging or bed rest.
Ključne besede: high density electromyography, muscle disuse, motor units, discharge rate, aging
Objavljeno v DiRROS: 05.09.2022; Ogledov: 574; Prenosov: 323
.pdf Celotno besedilo (4,31 MB)
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8.
Exploring the Density Improvement Mechanism of (K,Na)NbO3
Mahdi Feizpour, Hadi Barzegar Bafrooei, Darja Feizpour, 2021, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: piezoelectric ceramics, potassium sodium niobate, solid-state synthesis and sintering, bulk density
Objavljeno v DiRROS: 06.05.2022; Ogledov: 481; Prenosov: 109
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9.
Relationships between wood-anatomical features and resistance drilling density in Norway spruce and European beech
Domen Arnič, Luka Krajnc, Jožica Gričar, Peter Prislan, 2022, izvirni znanstveni članek

Povzetek: Environmental conditions affect tree-ring width (TRW), wood structure, and, consequently, wood density, which is one of the main wood quality indicators. Although studies on inter- and intra-annual variability in tree-ring features or density exist, studies demonstrating a clear link between wood structure on a cellular level and its effect on wood density on a macroscopic level are rare. Norway spruce with its simple coniferous structure and European beech, a diffuse-porous angiosperm species were selected to analyze these relationships. Increment cores were collected from both species at four sites in Slovenia. In total, 24 European beech and 17 Norway spruce trees were sampled. In addition, resistance drilling measurements were performed just a few centimeters above the increment core sampling. TRW and quantitative wood anatomy measurements were performed on the collected cores. Resistance drilling density values, tree-ring (TRW, earlywood width–EWW, transition-TWW, and latewood width–LWW) and wood-anatomical features (vessel/tracheid area and diameter, cell density, relative conductive area, and cell wall thickness) were then averaged for the first 7 cm of measurements. We observed significant relationships between tree-ring and wood-anatomical features in both spruce and beech. In spruce, the highest correlation values were found between TRW and LWW. In beech, the highest correlations were observed between TRW and cell density. There were no significant relationships between wood-anatomical features and resistance drilling density in beech. However, in spruce, a significant negative correlation was found between resistance drilling density and tangential tracheid diameter, and a positive correlation between resistance drilling density and both TWW + LWW and LWW. Our findings suggest that resistance drilling measurements can be used to evaluate differences in density within and between species, but they should be improved in resolution to be able to detect changes in wood anatomy.
Ključne besede: wood structure, Fagus sylvatica, Picea abies, quantitative wood anatomy, xylem anatomy, wood density, increment borer
Objavljeno v DiRROS: 08.04.2022; Ogledov: 573; Prenosov: 424
.pdf Celotno besedilo (3,23 MB)
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