One-sided surface charring of beech wood (
Fagus sylvatica
L.) was analyzed. Specimens were charred on one surface using contact heating system with a hot plate, at a temperature of 220 °C and ...atmospheric pressure for 15 or 40 min. Surface charring was applied on the radial or tangential surface. Spectrophotometric chemical analysis was carried out to determine the total amount of soluble carbohydrates and phenolic compounds beneath the surface in order to evaluate the depth (within 1, 2, 3 and 4 mm) of the degradation affected by the charring. Specimens of dimensions 14 × 14 × 14 mm were used to determine the moisture behavior of charred specimens. The equilibrium moisture content (EMC) of specimens was calculated at a temperature of 20 °C and 65% relative humidity. Water absorption (WA) was recorded during the water immersion for 240 h at various intervals. Finally, the three-point bending tests were undertaken and modulus of rupture (MOR) and modulus of elasticity were calculated. Degradation of the main wood compounds due to chemical changes occurred during the surface charring is closely associated with a mass loss (3.5–5.5%) and further related to the severity of process and orientation of specimens to heat flow. Application of surface charring resulted in the significant reduction in EMC (~ 20%) as a result of a decrease in hydroxyl groups, an increase in cellulose crystallinity as well as further cross-linking of lignin. Furthermore, the WA of one-sided surface-charred wood considerably decreased (15%) when compared to that of the control specimens. A significant increase in soluble carbohydrates as well as phenolic compounds was found, and it can be stated that one-sided charring affected wood properties to depth 2–3 mm from the surface. Significant differences (14–24%) of bending strength MOR results are most likely due to improved sorption behavior of wood. The results show that beech wood charring improved moisture-related characteristics and consequently led to better mechanical behavior, but more studies are needed to exploit the potential of surface charring method for future use.
The use of linking or glottalization contributes to the characteristic sound pattern of a language, and the use of one in place of the other may affect a speaker’s comprehensibility and fluency in ...certain contexts. In this study, native speakers of Czech, a language that is associated with a frequent use of glottalization in vowel-initial word onsets, are examined in the second language (L2) context of three Romance languages that predominantly employ linking between words (Spanish, Italian and Portuguese). In total, 29 native speakers and 51 non-native learners were asked to read a short text in the respective language. The learners were divided into two groups based on their experience with the target language. A number of other factors were examined in a mixed-effects logistic regression model (segmental context, lexical stress, prosodic breaks, and the semantic status of the words). The main results show that, regardless of the target language, the more experienced (ME) learners displayed significantly lower rates of glottalization than the less experienced (LE) learners, but significantly higher rates than native speakers. The pedagogical implications of the results are discussed.
Magnetoelastic hybrid excitations in CeAuAl3 Čermák, Petr; Schneidewind, Astrid; Liu, Benqiong ...
Proceedings of the National Academy of Sciences - PNAS,
04/2019, Letnik:
116, Številka:
14
Journal Article
Recenzirano
Odprti dostop
Nearly a century of research has established the Born–Oppenheimer approximation as a cornerstone of condensed-matter systems, stating that the motion of the atomic nuclei and electrons may be treated ...separately. Interactions beyond the Born–Oppenheimer approximation are at the heart of magneto-elastic functionalities and instabilities. We report comprehensive neutron spectroscopy and ab initio phonon calculations of the coupling between phonons, CEF-split localized 4f electron states, and conduction electrons in the paramagnetic regime of CeAuAl3, an archetypal Kondo lattice compound. We identify two distinct magneto-elastic hybrid excitations that form even though all coupling constants are small. First, we find a CEF–phonon bound state reminiscent of the vibronic bound state (VBS) observed in other materials. However, in contrast to an abundance of optical phonons, so far believed to be essential for a VBS, the VBS in CeAuAl3 arises from a comparatively low density of states of acoustic phonons. Second, we find a pronounced anticrossing of the CEF excitations with acoustic phonons at zero magnetic field not observed before. Remarkably, both magneto-elastic excitations are well developed despite considerable damping of the CEFs that arises dominantly by the conduction electrons. Taking together the weak coupling with the simultaneous existence of a distinct VBS and anticrossing in the same material in the presence of damping suggests strongly that similarly well-developed magneto-elastic hybrid excitations must be abundant in a wide range of materials. In turn, our study of the excitation spectra of CeAuAl3 identifies a tractable point of reference in the search for magneto-elastic functionalities and instabilities.
Surface charring of wood is a one-sided thermal modification process that can be used to create a hydrophobic, durable surface to exterior claddings. Spruce (
L.) wood samples were charred with a hot ...plate and several time-temperature combinations while using simultaneous surface compression. Temperature profile, water sorption, cupping after water exposure and density profile were measured. Furthermore, changes in the microstructure and surface functional groups were investigated by scanning electron microscopy and photoacoustic FT-IR spectroscopy. Results show that surface charring notably improves the hydrophobicity measured by contact angle, water floating and dynamic vapour sorption. Increased holding time during charring reduced the sorption but at the same time increased the dimensional instability measured by cupping. The density profile showed a shifting density peak with more severe modification regimes, indicating a more porous surface. The PAS-FTIR showed increased aromaticity of the surface that was also present in the pyrolysis zone beneath the surface in samples modified with longer holding time. Higher modification temperature affected the sorption as well as cupping positively but it is possible similar results can be obtained with lower temperature and longer holding time.
In ethnically divided societies and political systems organized according to the principles of consociationalism, demography plays a crucial role as a powerful tool for promoting ethno-political ...interests. The aim of this article is to evaluate to what extent the first post-war 2013 census in Bosnia and Herzegovina became a hostage to the principle of ethno-politics. This study is grounded in Horowitz’s analysis of censuses in deeply divided societies, which assumes that ethnic identity in fragmented societies provides an explanation of who people vote for, and the reverse. We use the data on ethnic voting in 2014 as an indirect estimate of the ethnic structure of the population to verify the 2013 census findings. To do so, we determine the extent to which people enumerated as residents in the 2013 census actually live at the places they were counted, as required by the census law. Although we found that the indirect estimate of ethnic demography based on ethnic voting is largely in line with the census results, we also identified specific structural discrepancies between census results and voting patterns that indicate possible flaws in the census data in general. The method we used revealed significant territorial discrepancies, bringing into question the validity of the census data about the presence of Bosniak and Croat returnees in the Republika Srpska, and especially for Croats across Bosnia and Herzegovina. We argue that these discrepancies may have significant political consequences for the fragile Bosnian powersharing system based on ethnic quotas and proportionality.
Norway spruce (Picea abies (L.) Karst.) stands in certain areas of Central Europe have experienced substantial dieback since the 1970s. Understanding the reasons for this decline and reexamining the ...response of forests to acid deposition reduction remains challenging because of a lack of long and well-replicated tree-ring width chronologies. Here, spruce from a subalpine area heavily affected by acid deposition (from both sulfur and nitrogen compounds) is evaluated. Tree-ring width measurements from 98 trees between 1000 and 1350m above sea level (a.s.l.) reflected significant May–July temperature signals. Since the 1970s, acid deposition has reduced the growth–climate relationship. Efficient pollution control together with a warmer but not drier climate most likely caused the increased growth of spruce stands in this region, the so-called “Black Triangle,” in the 1990s.
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•Long-term growth changes of Norway spruce are evaluated for the “Black Triangle.”•The ring width variations of Norway spruce reflect May–July temperatures.•Acid deposition reduced the growth–temperature relationships of Norway spruce.•This study suggests a complex interplay of multiple factors on forest decline.•Our results prove a recovery of forest growth in the 1990s.
The traditional Japanese method of wood surface charring was studied. To perform the surface charring, three sawn Norway spruce and Silver fir wood boards of dimension 190 × 24 × 4000 mm3 were tied ...together to act as a chimney and charred in a short time (3–4 min) with open flame at a temperature above 500 °C. Temperature inside the chimney was recorded on the three different positions during the charring process. Surface temperature of spruce increased from 0 °C to 500 °C in approx. 120–300 s while fir increased in approx. 100–250 s. The thickness of the charred layer and the resulting cupping effect were investigated at the different heights of the chimney to evaluate its variability. Temperature achieved during the charring process was sufficient to get a significant charred layer of 2.5 and 4.5 mm on average for spruce and fir samples, respectively. The analyzed samples showed a significant cupping effect to the charred side with no difference between the annual ring orientation of sawn boards. Spruce exhibit a more significant cupping effect when compared to fir, i.e., 3.2–6 mm and 2.2–4.5 mm, respectively. Furthermore, the pH values of charred samples increased significantly, which could be an indication of improved resistance against wood-decay fungi. For better insight into the traditional charring method, further studies should be carried out to execute the charring process in a consistent quality and therefore fully exploit its potential.
The high portion of secondary Norway spruce in Central European forests constitutes a major problem because a significant part of these forests is moving further away from their original bioclimatic ...envelope. The precise evaluation and prediction of climatic suitability are needed for the implementation of forest adaptation strategies. We evaluated climatic suitability for the cultivation of Norway spruce in the Czech Republic forests, making use of the Random Forest combined learning statistical method. The evaluation presented was based on a comparison with the climatic normal period 1961–1990; change analysis was carried out for the period 1991–2014 and projected for 2021–2040 and 2041–2060. We found that suitable conditions for Norway spruce will remain only in 11.3% by area of Czech forests in the period 2041–2060 vs. 46.0% in the period 1961–1990. We also compared tree cover loss data (using Global Forest Watch) from 2001 to 2020 with statistics on salvage logging. In the period, the cover loss affected 19.5% of the area with more than 30% Norway spruce. The relationships between relative tree cover loss and the percentage of salvage logging caused by insects were conclusive and statistically significant.
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