Lembit Nei

The proposed method comprises a small-scale production of fuelwood from felled and delimbed tree trunks in private households by slicing them into roundwood discs. The time consumption of this method was compared to that of the traditional method, which consists of cutting roundwood into log sections that are subsequently split into split billets. Production of fuelwood by the novel method was 2.2 times faster compared to the traditional method. The reason for the higher productivity of the novel method is the smaller number of operations. The application of this pioneering approach resulted in a 25 % lower fuelwood production cost, if compared to the commonly applied practice.

The valuation of publicly traded software-as-a-service firms depends on how revenue expansion translates into profitability and enterprise value, making the growth–profitability trade-off important for corporate finance, investment analysis, and market valuation. Existing research offers limited evidence on whether the Rule of 40 has the same valuation relevance across development stages when its growth and profitability components are examined separately. This study assesses how revenue growth and earnings before interest, taxes, depreciation, and amortization margin, independently and jointly, are associated with annual enterprise value growth across revenue-defined groups and whether the Rule of 40 provides a consistent valuation-related indicator. The analysis uses a balanced panel of 30 software-as-a-service companies publicly traded on the United States capital market, with source data covering 2018–2024 and 180 firm-year observations analyzed for 2019–2024; firms are assigned to three fixed groups according to 2018 revenue. The empirical design combines Pearson correlations, pooled and group-specific linear regressions, interaction modelling, median-based growth–profitability profiling, Rule-of-40 quartiles, a binary comparison based on the conventional 40-point benchmark, and 1st/99th percentile winsorization of enterprise value growth. Firm-clustered standard errors with finite-sample correction are used for the principal full-sample regressions. Revenue growth showed a positive descriptive correlation with enterprise value growth (r = 0.165) and was statistically significant in the baseline firm-clustered regression (β = 0.847, SE = 0.295, p = 0.008; R² = 0.027; adjusted R² = 0.022), after adding EBITDA margin (β = 0.837, p = 0.013), and in the interaction specification (β = 0.791, p = 0.014). EBITDA margin (β = −0.043, p = 0.783), the revenue-growth–EBITDA interaction (β = −0.011, p = 0.287), and the stand-alone Rule of 40 (β = 0.154, p = 0.428) were insignificant. Formal pooled interaction tests did not identify significant cross-group slope differences for revenue growth (F(2, 29) = 1.281, p = 0.293), EBITDA margin (F(2, 29) = 0.251, p = 0.780), or the Rule of 40 (F(2, 29) = 1.325, p = 0.282). Among lower-revenue firms, high growth combined with a high margin was associated with median enterprise value growth of 28.8%, versus 15.9% for high growth with a low margin and −7.0% for low growth with a low margin; in the full sample, the third Rule-of-40 quartile recorded the highest median enterprise value growth of 31.6%, compared with 18.4% in the highest quartile. A direct comparison of observations with the Rule of 40 ≥ 40 versus < 40 produced no significant valuation difference (β = −4.445, p = 0.424). These findings indicate that revenue growth has the clearest contemporaneous association with enterprise-value dynamics, whereas the Rule of 40 is better interpreted as a contextual descriptive indicator than as a universal valuation threshold.

The suitability of reed- and straw-bale houses for the temperate climate zone was assessed. The influence of indoor climate indicators (relative humidity, internal humidity load of the borders, CO₂, temperature, mould index) and the microbial community was evaluated on air quality in the bedrooms. No similar studies on indoor air quality have been reported previously. The current study involved (1) indoor air quality indicators (relative humidity, CO₂, and temperature) in air and at two different heights in the walls were measured; (2) air quality was tested in the bedrooms of the studied houses, and the microbial species in air and walls were determined; (3) the impact of microbial communities on the air quality in the bedrooms of straw- and reed-bale buildings was assessed. Internal moisture was higher in the reed-bale buildings. The indoor air of the straw-bale and reed-bale buildings included more colonies than the outside air, but this did not affect indoor air quality.

The suitability of reed- and straw-bale houses for the temperate climate zone was assessed. The influence of indoor climate indicators (relative humidity, internal humidity load of the borders, CO2, temperature, mould index) and the microbial community was evaluated on air quality in the bedrooms. No similar studies on indoor air quality have been reported previously. In order to fulfil the set aim: (1) indoor air quality parameters (relative humidity, CO2, and temperature) in air and at two different heights in the walls were measured; (2) air quality was tested in the bedrooms of the studied houses, and the microbial species in air and walls were determined; (3) it was determined how the microbial communities of indoor air in the straw and reed-bale buildings influence indoor air quality in bedrooms. Internal moisture was higher in the reed-bale buildings (from 0.46 g m–3 to 3.42 g m–3 in summer and from 0.62 g m–3 to 2.73 g m–3 in winter). Microbial species in the air and walls of the studied houses were determined. Moulds belonging to four different genera were identified during this study (Alternaria, Aspergillus, Penicillium, and Cladosporium) in the bedrooms. Higher colony-forming unit (CFU) values were registered. The indoor air of the straw-bale and reed-bale build-ings included more colonies than the outside air, but this did not affect indoor air quality.

Instead of using paint, it is possible to manufacture white paper plaster by adding chalk to its ingredients. The moisture buffer values (MBVs) of paper plaster mixtures with chalk ranged from 1.8 to 2.9. The higher the chalk content was, the lower the MBV of the paper plaster was. Only the mix with the highest chalk content, where the percentage of chalk was 90, had a moisture buffering capacity below 2.0, i.e., not excellent (MBV > 2.0).

The objective of this study was to determine mould resistance of the plaster made from waste paper. To study the plaster quality, two laboratory tests were conducted. First, mould resistance of a dry plaster was studied, and second, mould resistance of a wet plaster was tested. Since wet plaster mix must be used for plastering, the resulting surfaces are extremely wet. The plaster placed on the wall would dry for at least two weeks under favourable conditions (sufficient ventilation and temperature). During this period, there is a great risk that the plaster might become mouldy. Another risk of becoming mouldy occurs when an already plastered wall receives moisture (e.g., water damage). The experiments carried out under laboratory conditions showed that in an environment with high relative humidity the plaster did not become mouldy.

This article deals with the reuse of wastepaper. Three components were used to make traditional paper plaster: wastepaper, glue, and water. Whether the glues used to make paper plaster and the quantities of those glues have an impact on the moisture buffering value (MBV) of paper plaster was studied. The scope of the Nordtest method is to evaluate the MBV for materials exposed to indoor air. The test intended to simulate daily variations with relative humidity between 75 % during 8 hours and 33 % during 16 hours. The test specimen was made according to the recipe which contained the following: waste-paper (newspaper paper), three different types of glue (potato starch (Amylum Solani) C₆H₁₀O₅, wallpaper glue Metylan Universal Premium (produced by Henkel), and methylcellulose C₆H₇O₂(OH)_x(OCH₃)_y, and water. Different percentages of glue were used in the specimens. Potato starch (Amylum Solani) C₆H₁₀O₅ clearly increased the moisture buffering ability. The tests performed showed that the composition and quantity of glue affected the MBV of paper plaster. The MBV of all the specimens remained in the range of 2.08–2.48 [g/(m²·%RH)@8/16h]. The largest MBV was 2.48[g/(m²·%RH)@8/16h], and it was registered in the case of a mixture that had a glue made from 100 g of potato starch (Amylum Solani) C₆H₁₀O₅ per litre of water and the smallest MBV was 2.08[g/(m²·%RH)@8/16h], and it contained glue mixture made of 20 g methylcellulose per litre of water. As a result of the current study, an environmentally friendly plaster with high moisture buffer value using wastepaper as a component of this material was developed.

Global deficit of fertilizers is evident and as a result of the war in Ukraine the situation is worsening. At the same time, not all the possible major resources of nutrients have found appropriate application in agriculture, as for example sewage and its sludge, which are among the most promising sources of P, N and organic matter. Sewage sludge (SS) usage as an agricultural fertilizer has a number of limitations. Amongst them persistent organic pollutants (POPs) have a special role due to their ability to affect living organisms. Ongoing work directed to eliminating POPs present in SS is widely reported, but due to the complexity of these compounds no universal success has been achieved. In the case of several undesired residual compounds promising results have been gained using SS composting with different bulking agents. The current study was concentrated on the degradation of some widely used persistent POPs that are present in SS, namely carbamazepine (CBZ) and triclosan (TCS). Peat alone as a bulking agent widely used in the mixture with sewage sludge in Estonia is not suitable for initiating the process of composting. Additions of carbon-rich matter, as for example draff, might provide the relevant conditions needed for launching this process.

The scope of the Nordtest method is to evaluate the moisture buffer value (MBV) of materials exposed to indoor air. The test is intended to simulate daily variations with relative humidity (RH) between 75 % during 8 hours and 33 % during 16 hours. The specimens follow a recipe that consists of waste paper, glue and water. Specimens made of paper plaster were covered with different colours. The results of the experiment showed that the type of paint used and the number of layers applied affected the MBV. Natural colours have a better moisture permeability than chemical paints, but the number of natural colour layers affects the MBV. The higher the number of layers, the lower the MBV.