Showing papers by "Matej Bel University published in 2013"
TL;DR: In this article, the authors examined the habitats of Natura 2000 Sites by a set of landscape metrics for habitat area, size, density, and shape, such as Number of patches (NP), Patch density (PD), Mean patch size (MPS), Patch size standard deviation (PSSD), and Mean shape index (MSI).
Abstract: The Sitno Natura 2000 Site covers an area of 935,56 hectares. The Sitno region is significant due to the number of rare and endangered species of plants, and as a result is considered a location of great importance to the maintenance of floral gene pools. The study area suffers human impacts in the form of tourism. The main purpose of this study is to the measure landscape elements, determine the ecological significance of habitats within the Sitno area, and from this data, organize the study area into conservation zones. The results of this landscape quantification are numerical values that can be used to interpret the quality of ongoing ecological processes within individual landscape types. Interpretation of this quantified data can be used to determine the ecological significance of landscapes in other study areas. This research examines the habitats of Natura 2000 Sites by a set of landscape metrics for habitat area, size, density, and shape, such as Number of patches (NP), Patch density (PD), Mean patch size (MPS), Patch size standard deviation (PSSD) and Mean shape index (MSI). The classification of land cover patches is based on the Annex Code system.
65 citations
TL;DR: In this paper, the authors analyse the take-up by firms of internationally recognized standards such as ISO 9000 and ISO 14000, and conclude that the probability of standard certification increases with firm size, is greatest in large cities and in manufacturing industries.
62 citations
Journal Article•
TL;DR: In this article, the adsorptive properties of natural bentonite from Lieskovec (Slovakia) for the removal of Pb and Cu ions from aqueous solutions were studied in a batch adsorption system.
Abstract: The adsorptive properties of natural bentonite from Lieskovec (Slovakia) for the removal of Pb and Cu ions from aqueous solutions were studied in a batch adsorption system. It was found that the amount of adsorption of metal ion increased with the initial solution pH, metal ion concentration, and contact time, but decreased with the amount of adsorbent. The experimental data were analyzed by both the Freundlich and Langmuir isotherms. The maximum adsorption capacity of the adsorbent for Pb and Cu ions was calculated from the Langmuir isotherm and found to be 32.68 and 11.34 mg·g, respectively. The kinetic adsorption experimental results were analyzed using pseudo-first order and pseudo-second order kinetic models. The adsorption kinetic was found to follow a pseudo-second order kinetic model.
56 citations
TL;DR: Three aromatic sulfonamides show different activities for the isoenzymes studied with lowest affinity against isoenzyme hCA XII, with nanomolar half maximal inhibitory concentration ranging from 58 to 740 nmol/L.
Abstract: 4-Sulfamoyl-N-(3-morpholinopropyl)benzamide (I-1), N-(3-morpholinopropyl)benzene-1,4-disulfonamide (I-2) and N-(4-diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide (I-3), were prepared and assayed as inhibitors of four carbonic anhydrase (CA) isoenzymes hCA I, hCA II, hCA IV and hCA XII. These compounds exhibited nanomolar half maximal inhibitory concentration (IC50) ranging from 58 to 740 nmol/L. All three aromatic sulfonamides show different activities for the isoenzymes studied with lowest affinity against isoenzyme hCA XII.
55 citations
TL;DR: In this paper, the authors investigated the rainfall-groundwater relationship in a large deep-seated landslide near Ľubietova (Western Carpathians) catastrophically reactivated at the end of February 1977.
Abstract: It is a widely accepted idea that hydrologically triggered deep-seated landslides are initiated by an increase in pore-water pressure on potential slip surface induced by rising groundwater level after prolonged period of intense rainfall although the process is not fully understood. In order to contribute to better understanding, the rainfall–groundwater relationships, hydrogeological monitoring and repeated geoelectrical imaging were carried out from March 2007 to April 2011 in large deep-seated landslide near Ľubietova (Western Carpathians) catastrophically reactivated at the end of February 1977. Based on our observations, groundwater level (GWL) response to precipitation differs considerably with respect to both overall hydrological conditions and GWL mean depth. While the rate of GWL increase up to 25 cm/day were measured after some rainfall events during wet periods, noticeably lower recharge rate (up to 1–2 cm/day) and delayed GWL response to rainfall (usually from 2 weeks to 2–4 months) were observed at the beginning of the wet season after considerable depression of GWLs due to previous effective rainfall deficit. Likewise, slow GWL fluctuations without short-term oscillations are typical for deeper GWLs. Thus, long-term (several seasons to several years) hydrological conditions affect markedly groundwater response to rainfall events in the studied landslide and can be crucial for its behaviour. Comparison of hydrological conditions characterising the analysed period with those that accompanied the landslide reactivation in 1977 allow us to assume that slightly above-average rainy season following the prolonged wet period can be far more responsible for movement acceleration (and possibly failure initiation) in deep landslides than the isolated season of extreme precipitation following a longer dry period. This is true especially for landslides in regions with significant seasonal temperature changes where potential effective precipitation (PEP), calculated as excess of precipitation (P) over potential evapotranspiration (PET), may be efficiently used for estimation of slope saturation condition.
41 citations
TL;DR: Borschevsky et al. as discussed by the authors used relativistic Hartree-Fock and density functional theory to study the nuclear spin-dependent parity violating effects of heavy diatomic molecules.
Abstract: Nuclear-spin-dependent (NSD) parity violating effects are studied for a number of diatomic molecules using relativistic Hartree-Fock and density functional theory and accounting for core polarization effects. Heavy diatomic molecules are good candidates for the successful measurement of the nuclear anapole moment, which is the dominant NSD parity violation term in heavy elements. Improved results for the molecules studied in our previous publication [Borschevsky et al., Phys. Rev. A 85, 052509 (2012)] are presented along with the calculations for a number of new promising candidates for the nuclear anapole measurements.
35 citations
TL;DR: The use of magnetic-field dependent London atomic orbitals is known to be an efficient choice for accurate non-relativistic calculations of magnetisabilities as mentioned in this paper, and the appropriate formulas were extended and implemented in the framework of the four component relativistic linear response method at the self-consistent field single reference level.
Abstract: The use of magnetic-field dependent London atomic orbitals, also called gauge including atomic orbitals, is known to be an efficient choice for accurate non-relativistic calculations of magnetisabilities. In this work, the appropriate formulas were extended and implemented in the framework of the four-component relativistic linear response method at the self-consistent field single reference level. Benefits of employing the London atomic orbitals in relativistic calculations are illustrated with Hartree-Fock wave functions on the XF3 (X = N, P, As, Sb, Bi) series of molecules. Significantly better convergence of magnetisabilities with respect to the basis set size is observed compared to calculations employing a common gauge origin. In fact, it is mandatory to use London atomic orbitals unless you want to use ridiculously large basis sets. Relativistic effects on magnetisabilities are found to be quite small (<5%) for this particular set of molecules, but should be investigated on a larger set of molecules. We emphasise the breakdown of the connection between the paramagnetic contribution to magnetisabilities and rotational g tensors in the relativistic domain and discuss its origin. Finally, we visualise the magnetisability density which shows markedly atomic features evocative of Pascal's rules.
28 citations
TL;DR: In this paper, positive and negative time delays in various processes of classical and quantum physics are discussed, and an interpretation of the Hartmann paradox is suggested for the quantum tunneling and the three-dimensional scattering problem on a central potential.
Abstract: This article reviews positive and negative time delays in various processes of classical and quantum physics. In the beginning, we demonstrate how a time-shifted response of a system to an external perturbation appears in classical mechanics and classical electrodynamics. Then we quantify durations of various quantum mechanical processes. The duration of the quantum tunneling is studied, and an interpretation of the Hartmann paradox is suggested. Time delays and advances appearing in the three-dimensional scattering problem on a central potential are considered. We then discuss delays and advances appearing in quantum field theory and after that we focus on the issue of time delays and advancements in quantum kinetics. We discuss problems of the application of generalized kinetic equations in simulations of the system relaxation toward equilibrium and analyze the kinetic entropy flow. Possible measurements of time delays and advancements in experiments similar to the recent OPERA neutrino experiment are also discussed.
27 citations
TL;DR: A construction of canonical extension valid for all bounded lattices, which is shown to be functorial, with the property that the canonical extension functor decomposes as the composite of two functors, each of which acts on morphisms by composition, in the manner of hom-functors.
Abstract: This paper presents a novel treatment of the canonical extension of a bounded lattice, in the spirit of the theory of natural dualities. At the level of objects, this can be achieved by exploiting the topological representation due to M. Ploscica, and the canonical extension can be obtained in the same manner as can be done in the distributive case by exploiting Priestley duality. To encompass both objects and morphisms the Ploscica representation is replaced by a duality due to Allwein and Hartonas, recast in the style of Ploscica’s paper. This leads to a construction of canonical extension valid for all bounded lattices, which is shown to be functorial, with the property that the canonical extension functor decomposes as the composite of two functors, each of which acts on morphisms by composition, in the manner of hom-functors.
21 citations
TL;DR: In this article, an integrative framework including the relationships among the determinants of customers' behavioral intentions has been proposed and examined on a sample of grocery retail customers in Serbia, with maximum likelihood as the method of parameter estimation.
Abstract: The aim of the study is to investigate the relationships among atmospherics, service quality, customer satisfaction and their impact on behavioural intentions in a retail setting in an emerging economy. Based on a comprehensive literature review, an integrative framework including the relationships among the determinants of customers' behavioural intentions has been proposed and examined on a sample of grocery retail customers in Serbia. Structural equation modelling, with maximum likelihood as the method of parameter estimation, has been applied to test hypothesised relationships. The results of the study point to the indirect relatedness of service quality to customers' behavioural intentions, mediated via satisfaction. Although the dimensions of atmospherics do not impact behavioural intentions directly, perceptions of atmospherics significantly shape customers' evaluation of service quality. Implications of the study have been discussed and limitations and suggestions for future research have been hig...
20 citations
Journal Article•
TL;DR: In this paper, the authors investigate the relationship between contracting performance and quality of contract management in public sector services and find that although competitive selection is the key determining success, noncompetitive selection of suppliers prevails in Slovakia.
Abstract: Contracting out is the prevalent types of alternative
service-delivery arrangements in public sector. The literature
suggests that if the contracting is properly imlemented, then
it will improve cost-effectiveness, delivery quality, and
expenditure control. Using new Slovak data, we explain wha
constracting does not always produce the expected positive
results. We seek to dtermine the factores that account for
success in contracting for public sector services, by testing
for a link between contracting performance and quality of
contract management. This study uses a quantitative approach to
analyse our original survey data. The findings are not
positive, because although competitive selection is the key
factor determining success, non-competitive selection of
suppliers prevails in Slovakia.
TL;DR: The experiments show that the majority of cultivable mesophilic bacteria from the guano of bats belong to the S. nepalensis species, and the results indicate that the Guano accumulated near or directly in human dwellings and buildings may represent a significant risk for human health.
Posted Content•
TL;DR: In this article, the canonical extension of a bounded lattice has been studied in the spirit of the theory of natural duality, where the topological representation due to M. Ploscica is replaced by a duality due to Allwein and Hartonas.
Abstract: This paper presents a novel treatment of the canonical extension of a bounded lattice, in the spirit of thetheory of natural dualities. At the level of objects, this can be achieved by exploiting the topological representation due to M. Ploscica, and the canonical extension can be obtained in the same manner as can be done in the distributive case by exploiting Priestley duality. To encompass both objects and morphismsthe Ploscica representation is replaced by a duality due to Allwein and Hartonas, recast in the style of Ploscica's paper. This leads to a construction of canonical extension valid for all bounded lattices,which is shown to be functorial, with the property that the canonical extension functor decomposes asthe composite of two functors, each of which acts on morphisms by composition, in the manner of hom-functors.
TL;DR: In this article, the impact of long-term pollution by fluoride and heavy metals in two soils (PS1 and PS2) near an aluminium smelter in Slovakia, on soil microbial biomass C (MBC), basal respiration, metabolic quotient (qCO2) water-soluble organic C (WSOC) and enzymes activities involved in the C, N and P biogeochemical cycles was assessed.
Abstract: The aim of this research was to assess the impact caused by a long-term pollution by fluoride and heavy metals in two soils (PS1 and PS2) near an aluminium smelter in Slovakia, on soil microbial biomass C (MBC), basal respiration, metabolic quotient (qCO2) water-soluble organic C (WSOC) and enzymes activities involved in the C, N and P biogeochemical cycles. An unpolluted soil was used as control (C0). Results obtained for soil fluoride content reflected a gradient of fluoride exposure in topsoils of contaminated sites. Decreases in microbial and enzymatic activities and in MBC to organic C ratio were found in PS2 site, which is closer to the smelter and exhibited the highest fluoride content. PS1-soil showed an extreme alkaline pH caused by leaching of waste effluents from the smelter dumping site, higher contents of Zn, Cu, Pb and Cd, significantly larger MBC, qCO2 and catalase and urease activities, and much larger basal respiration and dehydrogenase activity than PS2 and C0-soil. Phosphatase, β-glucosidase and BAA-protease were negatively correlated with WSOC, basal respiration and dehydrogenase activity, and showed some degree of inhibition in polluted sites. These results may indicate different responses of microbial communities to ecosystem disturbances, caused by the drastic changes in soil's physicochemical properties as result of the long-term emissions of fly ash with high levels of contaminants that are still affecting soil microbial and enzymatic activities.
TL;DR: In this article, a syntaxonmical revision of azonal forest vegetation with dominance of Alnus glutinosa and A. incana was done along a latitudinal transect of Slovakia.
Abstract: Syntaxonmical revision of azonal forest vegetation with dominance of Alnus glutinosa and A. incana was done along a latitudinal transect of Slovakia. A data matrix consisting of 240 phytosociological releves was obtained in accordance with the standard Zurich-Montpellier approach. Detrended correspondence analysis was used to clarify the relationships between the vegetation composition and environmental variables, whereas one-way ANOVA was applied to quantify the differences in site requirements of particular vegetation types. The unsupervised numerical classification resulted in identification of five clusters corresponding to the traditionally described and ecologically interpretable associations within the Euro-Siberian alder carr forests of Alnion glutinosae and the European broad-leaved floodplain forests of A lnion incanae : Carici elongatae-Alnetum glutinosae Schwickerath 1933 (alder carr forests on permanently waterlogged soils), Stellario-Alnetum glutinosae Lohmeyer 1957 (riparian alder vegetation on mesic to humid sites along small brooks), Piceo-Alnetum Mraz 1959 (submontane and montane oligotrophic spruce-alder forests on waterlogged habitats), Cardamino amarae-Alnetum incanae Somsak 1961 (grey alder vegetation in spring fed areas) and Alnetum incanae Ludi 1921 (submontane and montane streamside grey alder forests on mesic sites). They significantly ( P < 0.05) differed in the Ellenberg's indicator values for nutrients, moisture, temperature and altitude. These environmental variables were also established by DCA analysis as underlying sources of variation in alder-dominated forest composition. Special attention was given to discussion of their syntaxonomy, nomenclature, floristic structure, ecological features and distribution.
01 Jan 2013
TL;DR: This chapter presents a survey of implication functions generated using an appropriate function of one variable including f-implications and g- Implications introduced by Yager, h-generated implications introduced by Jayaram, and their generalizations introduced by Massanet and Torrens.
Abstract: This chapter presents a survey of implication functions generated using an appropriate function of one variable including f-implications and g-implications introduced by Yager, h-generated implications introduced by Jayaram, h-implications and their generalizations introduced by Massanet and Torrens, I f and I g implications introduced by Smutna-Hliněna, and Biba.
TL;DR: This work considers the @a-cuts of an IF-set A as crisp sets consisting of those elements x for which the truth value of the statement ''x belongs to A and it is not true that x does not belong to A'' is at least @a.
TL;DR: The recurrence rate and determinism are expressed in terms of the correlation sum, and strong laws of large numbers are given for them.
Abstract: The recurrence rate and determinism are two of the basic complexity measures studied in the recurrence quantification analysis. In this paper, the recurrence rate and determinism are expressed in terms of the correlation sums, and strong laws of large numbers are given for them.
TL;DR: This work studies the class of those two variable aggregation operators that preserve quasiconvexity on a bounded lattice, i.e. A(@m,@n) is quasIconvex for quasiconsvex lattice valued fuzzy sets @m, @n.
TL;DR: The hypothesis of the influence of site conditions and heavy metals on the habitus of the plant and its development is supported.
Abstract: This study compared morphological characteristics and seed germinative capabilities of the metallophyte Arabidopsis arenosa grown at a copper mining heap with individuals of the same species grown at a reference site. We observed the height of the plant, the width of rosette leaves at ground level, the width and length of the lowest stem leaf, the number of seeds per silique, the below-ground biomass weight and the above-ground biomass weight. We found that the pH and the Eh of soil taken from the root sphere of A. arenosa were similar on both sites, and the pH ranged from 5.87 on the heap to 7.03 on the reference site. The measured morphological attributes and the number of seeds produced were significantly reduced (p < 0.01) in plants from the metalliferous site. The biggest difference was in leaf length, where plants from the heap were almost 2.5-times smaller. The mean germinative capacity of seeds ranged from 87% to 93%, and was not different between sites. The length of roots of germinated seeds from the heap (9.14 mm) was significantly longer than those from the reference site (8.27 mm). Results support the hypothesis of the influence of site conditions and heavy metals on the habitus of the plant and its development.
TL;DR: Surprisingly, ITS sequence variability within F. fomentarius was significantly lower compared to the variability of efa sequences, questioning the discriminatory power of ITS sequences for fungal species identification.
Abstract: The existence of two cryptic species within strains of the wood-decaying fungus Fomes fomentarius was revealed recently based on the internal transcribed spacer (ITS) sequence variability. In this study for the first time the sequences of another molecular markers, partial translation elongation factor 1-α (efa) region and partial 25S large subunit ribosomal RNA gene were obtained and used to evaluate genetic variability of F. fomentarius. Congruent phylogeny was observed for all three markers used confirming the presence of two cryptic species within F. fomentarius. Surprisingly, ITS sequence variability within F. fomentarius was significantly lower compared to the variability of efa sequences (0.023 versus 0.036 nucleotide substitutions per site) questioning the discriminatory power of ITS sequences for fungal species identification.
TL;DR: In this article, the recurrence rate and determinism are expressed in terms of the correlation sum, and strong laws of large numbers are given for them, which is the same as the strong laws for determinism.
Abstract: The recurrence rate and determinism are two of the basic complexity measures studied in the recurrence quantification analysis. In this paper, the recurrence rate and determinism are expressed in terms of the correlation sum, and strong laws of large numbers are given for them.
TL;DR: An algorithm is proposed and implemented to construct a grid of off-center s-type Gaussian functions surrounding the molecule; substituting the presence of atom-centered diffuse basis functions.
Abstract: Proper description of noncovalent interactions requires, among other things, the use of diffuse atomic orbital (AO) basis sets. However, the presence of diffuse functions, especially in extended molecular systems, can lead to linear dependent AO basis sets. This in turn results, for example, in molecular orbital optimization problems or, when dependencies are removed in unpredictable and possibly geometry-dependent accuracy fluctuations. In this work, an alternative approach is proposed which suffers no linear dependence problems and delivers comparably accurate noncovalent interaction energies. An algorithm is proposed and implemented to construct a grid of off-center s-type Gaussian functions surrounding the molecule; substituting the presence of atom-centered diffuse basis functions. While the number of basis functions in the grid is comparable to the number of diffuse basis functions in aug-cc-pVXZ (for each cardinality number “X”) basis sets for small molecular systems, the ratio becomes more favorab...
TL;DR: This work clarifies for which fuzzy intersections and unions, based on continuous triangular norms and conorms, the principle of inclusion and exclusion holds.
TL;DR: In this paper, the authors focused on the evaluation of the hydric potential of six river basins in Slovakia and assessed the most relevant landscape attributes in relation to the protection of water resources.
Abstract: Landscape attributes affect the quantity, quality, distribution and accessibility of water resources. Except for fixed and hardly impacted environmental characteristics affecting the hydric potential of the landscape, it is possible by optimal land use planning and management to modify its ability to infiltrate and detain precipitation. The use of landscape characteristics as an efficient tool in river basin management can improve disturbed conditions in catchments. In this paper, we have focused on the evaluation of the hydric potential of six river basins in Slovakia. Assessing the most relevant landscape attributes in relation to the protection of water resources, we have identified areas with various landscape hydric potentials (LHPs), which should be taken into consideration when developing a river basin management plan. The spatial distribution of LHP categories undermines the customary view that the landscape's ability to infiltrate and retain water is affected by only some of the physical–geographic attributes (frequently presented as hydrogeological bedrock and soil characteristics). The LHP distribution in model catchments is explained through specific combinations of factors having the greatest influence.
TL;DR: In this paper, the authors present the process of development of two models based on linear programming which describe situations production companies have to face in terms of resource allocation, and the most important parameters in models are of financial nature.
Abstract: Article deals with the topic of Linear Programming application on tasks of allocating limited resources in production companies. These restrictions come from both inside of company and market conditions. There is usually limited amount of resource available on market. Moreover the purchase price is also an important decisive factor when estimating the optimal amount of resource needed. The objective of article is to present the process of development of two models based on linear programming which describe situations production companies have to face in terms of resource allocation. We chose to look into this problem from financial point of view. Therefore most important parameters in models are of financial nature. We look into resource allocation in terms of possible costs and revenues. These two models describe the two possible optimization problems – the minimizing tasks and the maximizing tasks. Examples of such tasks from managerial practice are also included.
TL;DR: In this article, the root biomass has the most significant share in the total biomass of grasslands (49.9-54.2 %), followed by tillering zone (33.3-36.0 %) and with the lowest share of aboveground biomass (11.9 -16.8 %).
Abstract: Aim of the work was to determine the effect of different doses of mineral fertilization on belowground and aboveground plant biomass production of three different types of grasslands, to state R:S ratio (root:shoot) and turnover period of belowground plant biomass of grasslands. In the contribution, we assess production of underground biomass, tillering zone and aboveground biomass on three types of grasslands - permanent grassland (PG), over-sown grassland (OSG) and temporary grassland (TG) in sub-mountain area of central Slovakia. There were applied four levels of mineral nutrition in each grassland (non-fertilized variant, var. 30 kg.ha-1P and 60 kg.ha-1 K. var. 90 kg.ha-1 N + P30K60, var. 180 kg.ha-1 N + P30K60). The root biomass has the most significant share in the total biomass of grasslands (49.9-54.2 %), followed by tillering zone (33.3-36.0 %) and with the lowest share of aboveground biomass (11.9-16.8 %). A dominant share of root biomass and tillering zone ensure significant extra-productive functions of grasslands that contribute to the stability of agriculture landscape. We recorded the lowest amounts of root mass on TG (7.31 t.ha-1) and OSG (7.76 t.ha-1), the highest amounts on PG (8.52 t.ha-1). The specific nitrogen stimulating influence on root biomass production has been proven. Production of tillering zone was lower on OSG and TG (5.11 or 5.42 t.ha-1), significantly higher on PG (5.72 t.ha-1). We observed a significantly higher production of tillering zone with variants which were fertilized with nitrogen than on non-fertilized and PK fertilized. The lowest harvests of aboveground biomass were noticed on TG (5.80 t.ha-1), significantly higher on PG and OSG (6.35 or 6.54 t.ha-1). Mineral nutrition had a significant impact on production of aboveground biomass.R:S ratio of the assessed grasslands achieved the values from 4.02 to 5.16. Higher values on PG (5.16) are indicating its higher resistance to drought. Turnover time of root biomass was the longest on PG 3.5-5.0 years, on OSG and TG 2.5-3.5 years. Based on achieved results, we recommend using the fodder plants cultivation system on PG or OSG. Permanent grasslands are proved as ecologically more stable and more resistant to drought than temporary grasslands; they can together with optimal mineral nutrition provide adequate production of root biomass (8.5 t.ha-1) and a harvest of aboveground biomass (6.3 t.ha-1).
01 Jan 2013
TL;DR: In this article, the authors examined the relationship between higher education service quality and student satisfaction and their relatedness to students' behavioral intentions and found that satisfaction mediates the effect of service quality, and exerts more significant impact on behavioural intentions.
Abstract: This study aims to examine relationships among higher education service quality and student satisfaction and their relatedness to students’ behavioural intentions. Slovak higher education setting has provided a framework to this study. Structural equation modelling, using LISREL 8.80, has been performed on student survey data and indicated that both higher education service quality and satisfaction are important determinants of students’ behavioural intentions. However satisfaction mediates the effect of service quality and exerts more significant impact on behavioural intentions. Findings of this study indicate that university administrators should pay special attention to satisfying existing students in order to motivate them to recommend the institution to prospective students and enrol higher levels of study within the same faculty. Implications of the study, limitations and directions for future research have been discussed.
TL;DR: In this paper, the authors present a theoretical study of the two-dimensional spiral antiferromagnet in the presence of an external magnetic field, and employ a suitable nonlinear model to calculate the $T=0$ phase diagram and the associated low-energy spin dynamics for arbitrary canted magnetic fields, in general agreement with experiment.
Abstract: We present a theoretical study of the two-dimensional spiral antiferromagnet ${\mathrm{Ba}}_{2}{\mathrm{CuGe}}_{2}{\mathrm{O}}_{7}$ in the presence of an external magnetic field. We employ a suitable nonlinear $\ensuremath{\sigma}$ model to calculate the $T=0$ phase diagram and the associated low-energy spin dynamics for arbitrary canted magnetic fields, in general agreement with experiment. In particular, when the field is applied parallel to the $c$ axis, a previously anticipated Dzyaloshinskii-type incommensurate-to-commensurate phase transition is actually mediated by an intermediate phase, in agreement with our earlier theoretical prediction confirmed by the recent observation of the so-called double-$k$ structure. The sudden $\ensuremath{\pi}/2$ rotations of the magnetic structures observed in experiment are accounted for by a weakly broken $U(1)$ symmetry of our model. Finally, our analysis suggests a nonzero weak-ferromagnetic component in the underlying Dzyaloshinskii-Moriya anisotropy, which is important for quantitative agreement with experiment.