Showing papers by "Tallinn University of Technology published in 2012"

A review on the thermal stability of calcium apatites

Abstract: High temperature processing is essential for the preparation of apatites for biomaterials, lighting, waste removal and other applications. This requires a good understanding of the thermal stability and transitions upon heating. The most widely used is hydroxyapatite (HAp), but increasing interest is being directed to fluorapatite (FAp) and chlorapatite (ClAp). The structural modifications for substitutions are discussed to understand the temperature processing range for the different apatites. This is based on a review of the literature from the past few decades, together with recent research results. Apatite thermal stability is mainly determined by the stoichiometry (Ca/P ratio and structural substitutions) and the gas composition during heating. Thermal stability is lowered the most by a substitution of calcium and phosphate, leading to loss in phase stability at temperatures less than 900 °C. The anions in the hexagonal axis, OH in HAp, F in FAp and Cl in ClAp are the last to leave upon heating, and prevention of the loss of these groups ensures high temperature stability. The information discussed here will assist in understanding the changes of apatites during heating in calcination, sintering, hydrothermal processing, plasma spraying, flame pyrolysis, and other high-temperature processes.

Step-Up DC/DC Converters With Cascaded Quasi-Z-Source Network

Abstract: This paper is devoted to the step-up dc/dc converter family with a cascaded quasi-Z-source network (qZS-network). The cascaded (two-stage) qZS-network could be derived by the adding of one diode, one inductor, and two capacitors to the traditional quasi-Z-source inverter (qZSI). The proposed cascaded qZSI inherits all the advantages of the traditional solution (voltage boost and buck functions in a single stage, continuous input current, and improved reliability). Moreover, as compared to the conventional qZSI, the proposed solution reduces the shoot-through duty cycle by over 30% at the same voltage boost factor. Theoretical analysis of the two-stage qZSI in the shoot-through and non-shoot-through operating modes is described. The proposed and traditional qZS-networks are compared. A prototype of a step-up dc/dc converter with the cascaded qZS-network was built to verify the theoretical assumptions. The experimental results are presented and analyzed. Finally, a further optimization method of the cascaded qZS-network is proposed, and some practical design issues are discussed.

Communities of Arbuscular Mycorrhizal Fungi Detected in Forest Soil Are Spatially Heterogeneous but Do Not Vary throughout the Growing Season

Abstract: Despite the important ecosystem role played by arbuscular mycorrhizal fungi (AMF), little is known about spatial and temporal variation in soil AMF communities. We used pyrosequencing to characterise AMF communities in soil samples (n = 44) from a natural forest ecosystem. Fungal taxa were identified by BLAST matching of reads against the MaarjAM database of AMF SSU rRNA gene diversity. Sub-sampling within our dataset and experimental shortening of a set of long reads indicated that our approaches to taxonomic identification and diversity analysis were robust to variations in pyrosequencing read length and numbers of reads per sample. Different forest plots (each 10×10 m and separated from one another by 30 m) contained significantly different soil AMF communities, and the pairwise similarity of communities decreased with distance up to 50 m. However, there were no significant changes in community composition between different time points in the growing season (May-September). Spatial structure in soil AMF communities may be related to the heterogeneous vegetation of the natural forest study system, while the temporal stability of communities suggests that AMF in soil represent a fairly constant local species pool from which mycorrhizae form and disband during the season.

Battle of the Water Calibration Networks

Abstract: Calibration is a process of comparing model results with field data and making the appropriate adjustments so that both results agree. Calibration methods can involve formal optimization methods or manual methods in which the modeler informally examines alternative model parameters. The development of a calibration framework typically involves the following: (1) definition of the model variables, coefficients, and equations; (2) selection of an objective function to measure the quality of the calibration; (3) selection of the set of data to be used for the calibration process; and (4) selection of an optimization/manual scheme for altering the coefficient values in the direction of reducing the objective function. Hydraulic calibration usually involves the modification of system demands, fine-tuning the roughness values of pipes, altering pump operation characteristics, and adjusting other model attributes that affect simulation results, in particular those that have significant uncertainty assoc...

Human superoxide dismutase 1 (hSOD1) maturation through interaction with human copper chaperone for SOD1 (hCCS).

Abstract: Copper chaperone for superoxide dismutase 1 (SOD1), CCS, is the physiological partner for the complex mechanism of SOD1 maturation. We report an in vitro model for human CCS-dependent SOD1 maturation based on the study of the interactions of human SOD1 (hSOD1) with full-length WT human CCS (hCCS), as well as with hCCS mutants and various truncated constructs comprising one or two of the protein’s three domains. The synergy between electrospray ionization mass spectrometry (ESI-MS) and NMR is fully exploited. This is an in vitro study of this process at the molecular level. Domain 1 of hCCS is necessary to load hSOD1 with Cu(I), requiring the heterodimeric complex formation with hSOD1 fostered by the interaction with domain 2. Domain 3 is responsible for the catalytic formation of the hSOD1 Cys-57–Cys-146 disulfide bond, which involves both hCCS Cys-244 and Cys-246 via disulfide transfer.

Comparing reconstructed past variations and future projections of the Baltic Sea ecosystem—first results from multi-model ensemble simulations

Abstract: Multi-model ensemble simulations for the marine biogeochemistry and food web of the Baltic Sea were performed for the period 1850‐2098, and projected changes in the future climate were compared with the past climate environment. For the past period 1850‐2006, atmospheric, hydrological and nutrient forcings were reconstructed, based on historical measurements. For the future period 1961‐2098, scenario simulations were driven by

Hydrodynamic pressure sensing with an artificial lateral line in steady and unsteady flows

Abstract: With the overall goal being a better understanding of the sensing environment from the local perspective of a situated agent, we studied uniform flows and Karman vortex streets in a frame of reference relevant to a fish or swimming robot. We visualized each flow regime with digital particle image velocimetry and then took local measurements using a rigid body with laterally distributed parallel pressure sensor arrays. Time and frequency domain methods were used to characterize hydrodynamically relevant scenarios in steady and unsteady flows for control applications. Here we report that a distributed pressure sensing mechanism has the capability to discriminate Karman vortex streets from uniform flows, and determine the orientation and position of the platform with respect to the incoming flow and the centre axis of the Karman vortex street. It also enables the computation of hydrodynamic features which may be relevant for a robot while interacting with the flow, such as vortex shedding frequency, vortex travelling speed and downstream distance between vortices. A Karman vortex street was distinguished in this study from uniform flows by analysing the magnitude of fluctuations present in the sensor measurements and the number of sensors detecting the same dominant frequency. In the Karman vortex street the turbulence intensity was 30% higher than that in the uniform flow and the sensors collectively sensed the vortex shedding frequency as the dominant frequency. The position and orientation of the sensor platform were determined via a comparative analysis between laterally distributed sensor arrays; the vortex travelling speed was estimated via a cross-correlation analysis among the sensors.

Plant species richness belowground: higher richness and new patterns revealed by next‐generation sequencing

Abstract: Variation in plant species richness has been described using only abovegroundvegetation. The species richness of roots and rhizomes has never been compared withaboveground richness in natural plant communities. We made direct comparisons ofgrassland plant richness in identical volumes (0.1 · 0.1 · 0.1 m) above and below the soilsurface, using conventional species identification to measure aboveground richness and454 sequencing of the chloroplast trnL(UAA) intron to measure belowground richness.We described above- and belowground richness at multiple spatial scales (from aneighbourhood scale of centimetres to a community scale of hundreds of metres), andrelated variation in richness to soil fertility. Tests using reference material indicated that454 sequencing captured patterns of species composition and abundance with acceptableaccuracy. At neighbourhood scales, belowground richness was up to two times greaterthan aboveground richness. The relationship between above- and belowground richnesswas significantly different from linear: beyond a certain level of belowground richness,aboveground richness did not increase further. Belowground richness also exceeded thatof aboveground at the community scale, indicating that some species are temporarilydormant and absent aboveground. Similar to other grassland studies, abovegroundrichness declined with increasing soil fertility; in contrast, the number of species foundonly belowground increased significantly with fertility. These results indicate thatconventional aboveground studies of plant richness may overlook many coexistingspecies, and that belowground richness becomes relatively more important in conditionswhere aboveground richness decreases. Measuring plant belowground richness canconsiderably alter perceptions of biodiversity and its responses to natural andanthropogenic factors.Keywords: 454 sequencing, DNA barcoding, plant richness, root identification, speciescoexistence, trnL (UAA)Received 1 July 2011; revision received 7 October 2011; accepted 19 October 2011

Maize multiple archesporial cells 1 (mac1), an ortholog of rice TDL1A, modulates cell proliferation and identity in early anther development

Abstract: To ensure fertility, complex somatic and germinal cell proliferation and differentiation programs must be executed in flowers. Loss-of-function of the maize multiple archesporial cells 1 (mac1) gene increases the meiotically competent population and ablates specification of somatic wall layers in anthers. We report the cloning of mac1, which is the ortholog of rice TDL1A. Contrary to prior studies in rice and Arabidopsis in which mac1-like genes were inferred to act late to suppress trans-differentiation of somatic tapetal cells into meiocytes, we find that mac1 anthers contain excess archesporial (AR) cells that proliferate at least twofold more rapidly than normal prior to tapetal specification, suggesting that MAC1 regulates cell proliferation. mac1 transcript is abundant in immature anthers and roots. By immunolocalization, MAC1 protein accumulates preferentially in AR cells with a declining radial gradient that could result from diffusion. By transient expression in onion epidermis, we demonstrate experimentally that MAC1 is secreted, confirming that the predicted signal peptide domain in MAC1 leads to secretion. Insights from cytology and double-mutant studies with ameiotic1 and absence of first division1 mutants confirm that MAC1 does not affect meiotic cell fate; it also operates independently of an epidermal, Ocl4-dependent pathway that regulates proliferation of subepidermal cells. MAC1 both suppresses excess AR proliferation and is responsible for triggering periclinal division of subepidermal cells. We discuss how MAC1 can coordinate the temporal and spatial pattern of cell proliferation in maize anthers.

Acetylated microfibrillated cellulose as a toughening agent in poly(lactic acid)

Abstract: Composites from poly(lactic acid) (PLA) and acetylated microfibrillated cellulose (MFC) were prepared by a solvent casting technique. MFC, mechanically isolated from never-dried bleached birch Kraft pulp, was used as a reinforcement. The acetylation reaction was carried out at 105°C in toluene and proved to be an effective way of increasing the dispersion of MFC in a nonpolar solution of PLA in chloroform. The maximum acetyl content (10.3%) was achieved after 30 min of reaction time. This could be translated to a degree of substitution (DS) of 0.43. The acetylation was confirmed by Fourier transform infrared spectroscopy. MFC with a higher DS exhibited a more pronounced effect on the properties of PLA. Mechanical testing showed that Young's modulus increased by approximately 70% and the tensile strength increased by approximately 60% at a fiber weight fraction of 20%. At an MFC loading of 10 wt %, the strain at break and toughness, expressed as the work of fracture, increased by around 500%. The Young's modulus increased by approximately 15%, whereas the tensile strength remained the same. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012

Advanced chromium carbide-based hardfacings

Abstract: Ceramic metal composite powders are widely used in thermal spray technologies; however, application of such hardphases in cladding systems has not been strongly developed yet. In the present study, two different hardfacings produced by the plasma transferred arc (PTA) process were analysed and compared to reveal differences between NiCrBSi coatings reinforced with standard chromium carbide and chromium-based cermet powders. The coatings were produced from a mixture of hardphases (Cr3C2 or Cr3C2–Ni) and nickel based powder with a ratio of 40/60 vol.%. The coatings' thickness was set to 2–2.5 mm on an austenite substrate. Hardfacings were characterised in terms of their microstructures, mechanical properties and impact–abrasion wear resistance at room and elevated temperatures. The manufactured Cr3C2–Ni reinforced hardfacing alloy has shown promising microstructural features with a low level of carbide dissolution and high temperature wear performance.

Pitt–Hopkins syndrome-associated mutations in TCF4 lead to variable impairment of the transcription factor function ranging from hypomorphic to dominant-negative effects

Abstract: Transcription factor TCF4 (alias ITF2, SEF2 or E2-2) is a broadly expressed basic helix–loop–helix (bHLH) protein that functions as a homo- or heterodimer. Missense, nonsense, frame-shift and splice-site mutations as well as translocations and large deletions encompassing TCF4 gene cause Pitt –H opkins syndrome (PTHS), a rare developmental disorder characterized by severe motor and mental retardation, typical facial features and breathing anomalies. Irrespective of the mutation, TCF4 haploinsufficiency has been proposed as an underlying mechanism for PTHS. We have recently demonstrated that human TCF4 gene is transcribed using numerous 5 ′ exons. Here, we re-evaluated the impact of all the published PTHS-associated mutations, taking into account the diversity of TCF4 isoforms, and assessed how the reading frame elongating and missense mutations affect TCF4 functions. Our analysis revealed that not all deletions and truncating mutations in TCF4 result in complete loss-of-function and the impact of reading frame elongating and missense mutations ranges from subtle deficiencies to dominant-negative effects. We show that (i) missense mutations in TCF4 bHLH domain and the reading frame elongating mutation damage DNA-binding and transactivation ability in a manner dependent on dimer context (homodimer versus heterodimer with ASCL1 or NEUROD2); (ii) the elongating mutation and the missense mutation at the dimer interface of the HLH domain destabilize the protein; and (iii) missense mutations outside of the bHLH domain cause no major functional deficiencies. We conclude that different PTHS-associated mutations impair the functions of TCF4 by diverse mechanisms and to a varying extent, possibly contributing to the phenotypic variability of PTHS patients.

Detection and genetic characterization of relapsing fever spirochete Borrelia miyamotoi in Estonian ticks.

Abstract: During the years 2008–2010 I ricinus and I persulcatus ticks were collected from 64 sites in mainland Estonia and on the island Saaremaa Presence of B miyamotoi was found in 09% (23/2622) of ticks The prevalence in I persulcatus and I ricinus ticks differed significantly, 27% (15/561) and 04% (8/2061), respectively The highest prevalence rates were in found South-Eastern Estonia in an area of I persulcatus and I ricinus sympatry and varied from 14% (1/73) to 28% (5/178) Co-infections with B burgdorferi sl group spirochetes and tick-borne encephalitis virus were also revealed Genetic characterization of partial 16S rRNA, p66 and glpQ genes demonstrated that Estonian sequences belong to two types of B miyamotoi and cluster with sequences from Europe and the European part of Russia, as well as with sequences from Siberia, Asia and Japan, here designated as European and Asian types, respectively Estonian sequences of the European type were obtained from I ricinus ticks only, whereas the Asian type of B miyamotoi was shown for both tick species in the sympatric regions

Linking landscape history and dispersal traits in grassland plant communities

Abstract: Dispersal limitation and long-term persistence are known to delay plant species’ responses to habitat fragmentation, but it is still unclear to what extent landscape history may explain the distribution of dispersal traits in present-day plant communities. We used quantitative data on long-distance seed dispersal potential by wind and grazing cattle (epi- and endozoochory), and on persistence (adult plant longevity and seed bank persistence) to quantify the linkages between dispersal and persistence traits in grassland plant communities and current and past landscape configurations. The long-distance dispersal potential of present-day communities was positively associated with the amounts of grassland in the historical (1835, 1938) landscape, and with a long continuity of grazing management—but was not associated with the properties of the current landscape. The study emphasises the role of history as a determinant of the dispersal potential of present-day grassland plant communities. The importance of long-distance dispersal processes has declined in the increasingly fragmented modern landscape, and long-term persistent species are expected to play a more dominant role in grassland communities in the future. However, even within highly fragmented landscapes, long-distance dispersed species may persist locally—delaying the repayment of the extinction debt.

Highly Enantio‐ and Diastereoselective Generation of Two Quaternary Centers in Spirocyclopropanation of Oxindole Derivatives.

Abstract: Spirocyclopropanes: only one out of eight possible stereoisomers was obtained in the asymmetric cascade cyclopropanation of alkylidene oxindoles with ethyl 2-chloroacetoacetate. Improved catalyst design ensured that spirocyclopropyl oxindoles featuring two quaternary centers were synthesized in high yield and high enantio-and diastereoselectivity.

Innovation: a factor explaining e-government success in Estonia

Abstract: Estonia is seen as a remarkable success story in the context of e-government. Several studies that have mapped the major factors affecting the evolution of e-government in Estonia are mainly grounded in information systems theory; even if public-private partnerships are examined, their treatment remains too general. The current article argues for the importance of public procurement for innovation. Several risks were avoided due to the high competencies of local suppliers, a lack of legacy infrastructure, and a supportive environment for ‘ethical hackers’. The importance of the framework and the success factors is illustrated by a case study on e-voting.

Myosins XI-K, XI-1, and XI-2 are required for development of pavement cells, trichomes, and stigmatic papillae in Arabidopsis

Abstract: The positioning and dynamics of vesicles and organelles, and thus the growth of plant cells, is mediated by the acto-myosin system. In Arabidopsis there are 13 class XI myosins which mediate vesicle and organelle transport in different cell types. So far the involvement of five class XI myosins in cell expansion during the shoot and root development has been shown, three of which, XI-1, XI-2, and XI-K, are essential for organelle transport. Simultaneous depletion of Arabidopsis class XI myosins XI-K, XI-1, and XI-2 in double and triple mutant plants affected the growth of several types of epidermal cells. The size and shape of trichomes, leaf pavement cells and the elongation of the stigmatic papillae of double and triple mutant plants were affected to different extent. Reduced cell size led to significant size reduction of shoot organs in the case of triple mutant, affecting bolt formation, flowering time and fertility. Phenotype analysis revealed that the reduced fertility of triple mutant plants was caused by delayed or insufficient development of pistils. We conclude that the class XI myosins XI-K, XI-1 and XI-2 have partially redundant roles in the growth of shoot epidermis. Myosin XI-K plays more important role whereas myosins XI-1 and XI-2 have minor roles in the determination of size and shape of epidermal cells, because the absence of these two myosins is compensated by XI-K. Co-operation between myosins XI-K and XI-2 appears to play an important role in these processes.

Numerical and Experimental Investigation on the Collision Resistance of the X-core Structure

Abstract: This paper analyses the collision resistance of the X-core structure. The analysis includes a detailed investigation of the non-linear plate and laser weld material behaviour using optical, full-field strain measurements. The resulting material relationships are implemented into the finite element model. Furthermore, the finite element model includes the influence of the ship motions to accurately predict the collision resistance. The verification of the numerical results is done by a comparison of the experimental and numerical force versus penetration curves and by a comparison of the deformed geometries. The latter is achieved through a digitised three-dimensional model of the post-experimental X-core structure. As a result, the accuracy of the collision simulations is presented and discussed.

Structural Changes of Starch during Baking and Staling of Rye Bread

Abstract: Rye sourdough breads go stale more slowly than wheat breads. To understand the peculiarities of bread staling, rye sourdough bread, wheat bread, and a number of starches were studied using wide-angle X-ray diffraction, nuclear magnetic resonance ((13)C CP MAS NMR, (1)H NMR, (31)P NMR), polarized light microscopy, rheological methods, microcalorimetry, and measurement of water activity. The degree of crystallinity of starch in breads decreased with hydration and baking to 3% and increased during 11 days of storage to 21% in rye sourdough bread and to 26% in wheat bread. (13)C NMR spectra show that the chemical structures of rye and wheat amylopectin and amylose contents are very similar; differences were found in the starch phospholipid fraction characterized by (31)P NMR. The (13)C CP MAS NMR spectra demonstrate that starch in rye sourdough breads crystallize in different forms than in wheat bread. It is proposed that different proportions of water incorporation into the crystalline structure of starch during staling and changes in starch fine structure cause the different rates of staling of rye and wheat bread.

RNA-Seq Analysis Reveals Different Dynamics of Differentiation of Human Dermis- and Adipose-Derived Stromal Stem Cells

Abstract: Background Tissue regeneration and recovery in the adult body depends on self-renewal and differentiation of stem and progenitor cells. Mesenchymal stem cells (MSCs) that have the ability to differentiate into various cell types, have been isolated from the stromal fraction of virtually all tissues. However, little is known about the true identity of MSCs. MSC populations exhibit great tissue-, location- and patient-specific variation in gene expression and are heterogeneous in cell composition. Methodology/principal findings Our aim was to analyze the dynamics of differentiation of two closely related stromal cell types, adipose tissue-derived MSCs (AdMSCs) and dermal fibroblasts (FBs) along adipogenic, osteogenic and chondrogenic lineages using multiplex RNA-seq technology. We found that undifferentiated donor-matched AdMSCs and FBs are distinct populations that stay different upon differentiation into adipocytes, osteoblasts and chondrocytes. The changes in lineage-specific gene expression occur early in differentiation and persist over time in both AdMSCs and FBs. Further, AdMSCs and FBs exhibit similar dynamics of adipogenic and osteogenic differentiation but different dynamics of chondrogenic differentiation. Conclusions/significance Our findings suggest that stromal stem cells including AdMSCs and dermal FBs exploit different molecular mechanisms of differentiation to reach a common cell fate. The early mechanisms of differentiation are lineage-specific and are similar for adipogenic and osteogenic differentiation but are distinct for chondrogenic differentiation between AdMSCs and FBs.

Innovation systems and policy: not only for the rich?

Abstract: This article argues that the conditions for innovation by and for the poor have changed considerably in the last four decades in ways that can be related to the paradigm shift in technology and to the resulting changes in behaviour of the major corporations. It suggests that innovation studies and evolutionary economics should consciously and constantly pursue an understanding of such changes by fully incorporating history in the interdisciplinary mix. In essence it holds that evolutionary thinking needs to strike an appropriate balance between universal and changing truths, especially when studying innovation with a view to making policy recommendations.

Catalogue of rogue waves reported in media in 2006–2010

Abstract: The data of rogue wave accidents reported in mass media during 2006–2010 years are collected and analysed. The collection includes 106 events, which are classified by their validity as true (78) and possible (28) and by the location of their occurrence: we distinguish deep, shallow and coastal rogue waves, which occurred in deep/shallow waters or at the coast. The validity of the event has been estimated by the rogue wave height, which should be twice larger than the significant wave height (significant wave height has been taken from satellite data), and/or by the associated hazard. It is shown that rogue waves cause especially high damage in shallow waters and at the coast.