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Abstract: Cohumulone and colupulone are representatives of - and -acids, respectively. These compounds are important antimicrobial hop (Humulus lupulus) constituents, where cohumulone is an important source of the bitter taste of beer. In this study, we examined the pH dependence of UV/Vis spectra of both compounds while CD spectra of cohumulone were also measured at various wavelengths. This facilitated the examination of the protolytic equilibrium of both compounds, where the second p value of cohumulone was determined for the first time. Additionally, comparing experimental spectra with spectra calculated using time-dependent density functional theory (TD-DFT) enabled the determination of the most likely deprotonation positions and corresponding species most likely present in the aqueous solution at various pH values. Last but not least, comparing calculated and experimental CD spectra of cohumulone facilitated the determination of the absolute stereoconfiguration of cohumulone.
Keywords: cohumulone, colupulone, UV/Vis spectrum, CD-spektrum, absolute configuration
Published in DKUM: 29.08.2024; Views: 77; Downloads: 0

Abstract: This paper presents a comprehensive study of winter temperatures in Norway and northern Sweden, covering a period of 50 to 70 years. The analysis utilizes Singular Spectrum Analysis (SSA) to investigate temperature trends at six selected locations. The results demonstrate an overall long-term rise in temperatures, which can be attributed to global warming. However, when investigating variations in highest, lowest, and average temperatures for December, January, and February, 50% of the cases exhibit a significant decrease in recent years, indicating colder winters, especially in December. The study also explores the variations in Atlantic Meridional Overturning Circulation (AMOC) variations as a crucial climate factor over the last 15 years, estimating a possible 20% decrease/slowdown within the first half of the 21st century. Subsequently, the study investigates potential similarities between winter AMOC and winter temperatures in the mid to high latitudes over the chosen locations. Additionally, the study examines another important climatic index, the North Atlantic Oscillation (NAO), and explores possible similarities between the winter NAO index and winter temperatures. The findings reveal a moderate observed lagged correlation for AMOC-smoothed temperatures, particularly in December, along the coastal areas of Norway. Conversely, a stronger lagged correlation is observed between the winter NAO index and temperatures in northwest Sweden and coastal areas of Norway. Thus, NAO may influence both AMOC and winter temperatures (NAO drives both AMOC and temperatures). Furthermore, the paper investigates the impact of colder winters, whether caused by AMOC, NAO, or other factors like winds or sea ice changes, on electrical power and energy systems, highlighting potential challenges such as reduced electricity generation, increased electricity consumption, and the vulnerability of power grids to winter storms. The study concludes by emphasizing the importance of enhancing the knowledge of electrical engineering researchers regarding important climate indices, AMOC and NAO, the possible associations between them and winter temperatures, and addressing the challenges posed by the likelihood of colder winters in power systems.
Keywords: winter temperatures, biogas, Atlantic Meridional Overturning Circulation, AMOC, weaking, NAO, North Atlantic Oscillation, SSA, Singular Spectrum Analysis, electrical power and energy systems
Published in DKUM: 15.02.2024; Views: 311; Downloads: 29
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Abstract: We present the expanded boundary integral method for solving the planar Helmholtz problem, which combines the ideas of the boundary integral method and the scaling method and is applicable to arbitrary shapes. We apply the method to a chaotic billiard with unidirectional transport, where we demonstrate the existence of doublets of chaotic eigenstates, which are quasi-degenerate due to time-reversal symmetry, and a very particular level spacing distribution that attains a chaotic Shnirelman peak at short energy ranges and exhibits Gaussian Unitary Ensemble (GUE) like statistics for large energy ranges. We show that, as a consequence of such particular level statistics or algebraic tunnelling between disjoint chaotic components connected by time-reversal operation, the system exhibits quantum current reversals.
Keywords: 2D Helmholtz equation, energy spectrum, quantum billiard
Published in DKUM: 03.07.2017; Views: 1811; Downloads: 203
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Keywords: matematika, teorija operatorjev, linearni operatorji, spekter, mathematics, operator theory, stiffness operator, damping operator, essential spectrum, semigroup generator
Published in DKUM: 10.07.2015; Views: 1043; Downloads: 21
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Abstract: Semigroups of normal complex square matrices having a finite spectrum are studied. It is shown that every mamber ▫$A$▫ of such a semigroup satisfies the condition ▫$A^ast = A^n$▫, where ▫$n$▫ does not depend on the matrix ▫$A$▫. Further, it is shown that such a semigroup is completely reducible, and each irreducible contraction consists of a group of unitary matrices and, aventually, the zero matrix.
Keywords: mathematics, matrix theory, normal matrices, spectrum, semigroups, reducability
Published in DKUM: 01.06.2012; Views: 2337; Downloads: 92
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