Showing papers by "University of Warsaw published in 2002"

Global air pollution crossroads over the Mediterranean

Abstract: The Mediterranean Intensive Oxidant Study, performed in the summer of 2001, uncovered air pollution layers from the surface to an altitude of 15 kilometers. In the boundary layer, air pollution standards are exceeded throughout the region, caused by West and East European pollution from the north. Aerosol particles also reduce solar radiation penetration to the surface, which can suppress precipitation. In the middle troposphere, Asian and to a lesser extent North American pollution is transported from the west. Additional Asian pollution from the east, transported from the monsoon in the upper troposphere, crosses the Mediterranean tropopause, which pollutes the lower stratosphere at middle latitudes.

Master of the cosmic microwave background anisotropy power spectrum: a fast method for statistical analysis of large and complex cosmic microwave background data sets

Abstract: We describe a fast and accurate method for estimation of the cosmic microwave background (CMB) anisotropy angular power spectrum—Monte Carlo Apodized Spherical Transform Estimator (MASTER). Originally devised for use in the interpretation of the BOOMERANG experimental data, MASTER is both a computationally efficient method suitable for use with the currently available CMB data sets (already large in size, despite covering small fractions of the sky, and affected by inhomogeneous and correlated noise) and a very promising application for the analysis of very large future CMB satellite mission products.

Mutations in SUFU predispose to medulloblastoma

Abstract: The sonic hedgehog (SHH) signaling pathway directs the embryonic development of diverse organisms and is disrupted in a variety of malignancies. Pathway activation is triggered by binding of hedgehog proteins to the multipass Patched-1 (PTCH) receptor, which in the absence of hedgehog suppresses the activity of the seven-pass membrane protein Smoothened (SMOH). De-repression of SMOH culminates in the activation of one or more of the GLI transcription factors that regulate the transcription of downstream targets. Individuals with germline mutations of the SHH receptor gene PTCH are at high risk of developmental anomalies and of basal-cell carcinomas, medulloblastomas and other cancers (a pattern consistent with nevoid basal-cell carcinoma syndrome, NBCCS). In keeping with the role of PTCH as a tumor-suppressor gene, somatic mutations of this gene occur in sporadic basal-cell carcinomas and medulloblastomas. We report here that a subset of children with medulloblastoma carry germline and somatic mutations in SUFU (encoding the human suppressor of fused) of the SHH pathway, accompanied by loss of heterozygosity of the wildtype allele. Several of these mutations encode truncated proteins that are unable to export the GLI transcription factor from nucleus to cytoplasm, resulting in the activation of SHH signaling. SUFU is a newly identified tumor-suppressor gene that predisposes individuals to medulloblastoma by modulating the SHH signaling pathway through a newly identified mechanism.

The snowmass Points and slopes: benchmarks for SUSY searches

Abstract: The ”Snowmass Points and Slopes” (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present and future experiments. This set of benchmarks was agreed upon at the 2001 ”Snowmass Workshop on the Future of Particle Physics” as a consensus based on different existing proposals.

A balanced view of scale in spatial statistical analysis

Abstract: Concepts of spatial scale, such as extent, grain, resolution, range, footprint, support and cartographic ratio are not interchangeable. Because of the potential confusion among the definitions of these terms, we suggest that authors avoid the term "scale" and instead refer to specific concepts. In particular, we are careful to discriminate between observation scales, scales of ecological phenomena and scales used in spatial statistical analysis. When scales of observation or analysis change, that is, when the unit size, shape, spacing or extent are altered, statistical results are expected to change. The kinds of results that may change include estimates of the population mean and variance, the strength and character of spatial autocorrelation and spatial anisotropy, patch and gap sizes and multivariate relationships, The First three of these results (precision of the mean, variance and spatial autocorrelation) can sometimes be estimated using geostatistical support-effect models. We present four case studies of organism abundance and cover illustrating some of these changes and how conclusions about ecological phenomena (process and structure) may be affected. We identify the influence of observational scale on statistical results as a subset of what geographers call the Modifiable Area Unit Problem (MAUP). The way to avoid the MAUP is by careful construction of sampling design and analysis. We recommend a set of considerations for sampling design to allow useful tests for specific scales of a phenomenon under study. We further recommend that ecological studies completely report all components of observation and analysis scales to increase the possibility of cross-study comparisons.

Energy dependence of pion and kaon production in central Pb+Pb collisions

Abstract: Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80, and 158 A GeV are presented. These are compared with data at lower and higher energies as well as with results from $p+p$ interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with ${s}_{\mathrm{NN}}^{1/4}$ with a change of slope starting in the region 15--40 A GeV. The change from pion suppression with respect to $p+p$ interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40A GeV. A nonmonotonic energy dependence of the ratio of ${K}^{+}$ to ${\ensuremath{\pi}}^{+}$ yields is observed, with a maximum close to 40A GeV and an indication of a nearly constant value at higher energies. The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.

Illustrations and guidelines for selecting statistical methods for quantifying spatial pattern in ecological data

Abstract: This paper aims to provide guidance to ecologists with limited experience in spatial analysis to help in their choice of techniques. It uses examples to compare methods of spatial analysis for ecological field data. A taxonomy of different data types is presented, including point- and area-referenced data, with and without attributes. Spatially and non-spatially explicit data are distinguished. The effects of sampling and other transformations that convert one data type to another are discussed; the possible loss of spatial information is considered. Techniques for analyzing spatial pattern, developed in plant ecology, animal ecology, landscape ecology, geostatistics and applied statistics are reviewed briefly and their overlap in methodology and philosophy noted. The techniques are categorized according to their output and the inferences that may be drawn from them, in a discursive style without formulae. Methods are compared for four case studies with field data covering a range of types. These are: 1) percentage cover of three shrubs along a line transect; 2) locations and volume of a desert plant in a 1 ha area; 3) a remotely-sensed spectral index and elevation from 105 km2 of a mountainous region; and 4) land cover from three rangeland types within 800 km2 of a coastal region. Initial approaches utilize mapping, frequency distributions and variance-mean indices. Analysis techniques we compare include: local quadrat variance, block quadrat variance, correlograms, variograms, angular correlation, directional variograms, wavelets, SADIE, nearest neighbour methods, Ripley's (t), and various landscape ecology metrics. Our advice to ecologists is to use simple visualization techniques for initial analysis, and subsequently to select methods that are appropriate for the data type and that answer their specific questions of interest. It is usually prudent to employ several different techniques.

Collective vibrational modes in biological molecules investigated by terahertz time-domain spectroscopy

Abstract: We present well-resolved absorption spectra of biological molecules in the far-IR (FIR) spectral region recorded by terahertz time-domain spectroscopy (THz- TDS). As an illustrative example we discuss the absorption spectra of benzoic acid, its monosubstitutes salicylic acid (2-hydroxy-benzoic acid), 3- and 4-hydroxybenzoic acid, and aspirin (acetylsalicylic acid) in the spectral region between 18 and 150 cm 1 . The spectra exhibit distinct features originating from low-frequency vibrational modes caused by intra- or intermolecular collective motion and lattice modes. Due to the collective origin of the observed modes the absorption spectra are highly sensitive to the overall structure and configuration of the molecules, as well as their environment. The THz-TDS procedure can provide a direct fingerprint of the molecular structure or conformational state of a compound. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospec- troscopy) 67: 310 -313, 2002

Crystal structure and spiral magnetic ordering of BiFeO 3 doped with manganese

Abstract: Neutron powder diffraction has been performed on polycrystalline BiMnxFe1-xO3 (x=0, 0.1 and 0.2). The structures of the doped compounds are described by the space group R3c of ferroelectric BiFeO3. Refined structure parameters are presented. Mn doping generates microstructural changes manifested by broadening in the diffraction patterns. The lattice parameters show a non-linear behaviour from 4 K to 630 K. Mn doping results in a transformation of the long-range spiral spin modulation of BiFeO3 to a collinear antiferromagnetic structure with spins along c. The average magnetic moments and the ordering temperatures decrease with increasing Mn concentration.

Dual-Primal FETI Methods for Three-dimensional Elliptic Problems with Heterogeneous Coefficients

Abstract: In this paper, certain iterative substructuring methods with Lagrange multipliers are considered for elliptic problems in three dimensions. The algorithms belong to the family of dual-primal finite element tearing and interconnecting (FETI) methods which recently have been introduced and analyzed successfully for elliptic problems in the plane. The family of algorithms for three dimensions is extended and a full analysis is provided for the new algorithms. Particular attention is paid to finding algorithms with a small primal subspace since that subspace represents the only global part of the dual-primal preconditioner. It is shown that the condition numbers of several of the dual-primal FETI methods can be bounded polylogarithmically as a function of the dimension of the individual subregion problems and that the bounds are otherwise independent of the number of subdomains, the mesh size, and jumps in the coefficients. These results closely parallel those of other successful iterative substructuring methods of primal as well as dual type.

Geometry of Generic Isolated Horizons

Abstract: Geometrical structures intrinsic to non-expanding, weakly-isolated and isolated horizons are analysed and compared with structures which arise in other contexts within general relativity, e.g. at null infinity. In particular, we address in detail the issue of singling out the preferred normals to these horizons required in various applications. This study provides powerful tools to extract invariant, physical information from numerical simulations of the near-horizon, strong-field geometry. While it complements the previous analysis of laws governing the mechanics of weakly-isolated horizons, prior knowledge of those results is not assumed.

Measurements of aerosol vertical profiles and optical properties during INDOEX 1999 using micropulse lidars

Abstract: Micro-pulse lidar systems (MPL) were used to measure aerosol properties during the Indian Ocean Experiment (INDOEX) 1999 field phase. Measurements were made from two platforms: the NOAA ship RN Ronald H. Brown, and the Kaashidhoo Climate Observatory (KCO) in the Maldives. Sunphotometers were used to provide aerosol optical depths (AOD) needed to calibrate the MPL. This study focuses on the height distribution and optical properties (at 523 nm) of aerosols observed during the campaign. The height of the highest aerosols (top height) was calculated and found to be below 4 km for most of the cruise. The marine boundary layer (MBL) top was calculated and found to be less than 1 km. MPL results were combined with air mass trajectories, radiosonde profiles of temperature and humidity, and aerosol concentration and optical measurements. Humidity varied from approximately 80% near the surface to 50% near the top height during the entire cruise. The average value and standard deviation of aerosol optical parameters were determined for characteristic air mass regimes. Marine aerosols in the absence of any continental influence were found to have an AOD of 0.05 +/- 0.03, an extinction-to-backscatter ratio (S-ratio) of 33 +/- 6 sr, and peak extinction values around 0.05/km (near the MBL top). The marine results are shown to be in agreement with previously measured and expected values. Polluted marine areas over the Indian Ocean, influenced by continental aerosols, had AOD values in excess of 0.2, S-ratios well above 40 sr, and peak extinction values approximately 0.20/km (near the MBL top). The polluted marine results are shown to be similar to previously published values for continental aerosols. Comparisons between MPL derived extinction near the ship (75 m) and extinction calculated at ship-level using scattering measured by a nephelometer and absorption using a PSAP were conducted. The comparisons indicated that the MPL algorithm (using a constant S-ratio throughout the lower troposphere) calculates extinction near the surface in agreement with the ship-level measurements only when the MBL aerosols are well mixed with aerosols above. Finally, a review of the MPL extinction profiles showed that the model of aerosol vertical extinction developed during an earlier INDOEX field campaign (at the Maldives) did not correctly describe the true vertical distribution over the greater Indian Ocean region. Using the average extinction profile and AOD obtained during marine conditions, a new model of aerosol vertical extinction was determined for marine atmospheres over the Indian Ocean. A new model of aerosol vertical extinction for polluted marine atmospheres was also developed using the average extinction profile and AOD obtained during marine conditions influenced by continental aerosols.

Empirical relationships between protein structure and carboxyl pKa values in proteins

Abstract: Relationships between protein structure and ionization of carboxyl groups were investigated in 24 proteins of known structure and for which 115 aspartate and 97 glutamate pK a values are known. Mean pK a values for aspartates and glutamates are ≤ 3.4 (′1.0) and 4.1 (′0.8), respectively. For aspartates, mean pK a values are 3.9 (′1.0) and 3.1 (′0.9) in acidic (pI 8) proteins, respectively, while mean pK a values for glutamates are approximately 4.2 for acidic and basic proteins. Burial of carboxyl groups leads to dispersion in pK a values: pK a values for solvent-exposed groups show narrow distributions while values for buried groups range from 5.5 and most are found in active sites or ligand-binding sites. These carboxyl groups are buried and usually accept no more than one hydrogen bond. Aspartates and glutamates at the N-termini of helices have mean pK a values of 2.8 (′0.5) and 3.4 (′0.6), respectively, about 0.6 units less than the overall mean values.

Higher-Order Pushdown Trees Are Easy

Abstract: We show that the monadic second-order theory of an infinite tree recognized by a higher-order pushdown automaton of any level is decidable. We also show that trees recognized by pushdown automata of level n coincide with trees generated by safe higher-order grammars of level n. Our decidability result extends the result of Courcelle on algebraic(pushdo wn of level 1) trees and our own result on trees of level 2.

First evidence for the two-proton decay of 45 Fe

Abstract: Decays of five 45Fe atoms have been observed at the fragment separator of GSI. Whereas one event is consistent with the β-decay of 45Fe accompanied by the emission of a 10 MeV proton, four decays are consistent with the emission of particle(s) of total energy 1.1±0.1 MeV. This observation represents the first evidence for two-proton ground-state radioactivity, a decay mode predicted for 45Fe. The time distribution of the observed decay events corresponds to a half-life of 3.2+2.6 -1.0 ms.

Two-proton radioactivity of 45Fe.

Abstract: In an experiment at the SISSI-LISE3 facility of GANIL, the decay of the proton drip line nucleus $^{\mathrm{45}}\mathrm{F}\mathrm{e}$ has been studied. Fragment-implantation events have been correlated with radioactive decay events in a $16\ifmmode\times\else\texttimes\fi{}16$ pixel silicon-strip detector. The decay-energy spectrum of $^{\mathrm{45}}\mathrm{F}\mathrm{e}$ implants shows a distinct peak at $(1.14\ifmmode\pm\else\textpm\fi{}0.04)\text{ }\text{ }\mathrm{M}\mathrm{e}\mathrm{V}$ with a half-life of ${T}_{1/2}=({4.7}_{\ensuremath{-}1.4}^{+3.4})\text{ }\text{ }\mathrm{m}\mathrm{s}$. None of the events in this peak is in coincidence with $\ensuremath{\beta}$ particles. For a longer correlation interval, daughter decays of the two-proton daughter $^{\mathrm{43}}\mathrm{C}\mathrm{r}$ can be observed after $^{\mathrm{45}}\mathrm{F}\mathrm{e}$ implantation. The decay energy for $^{\mathrm{45}}\mathrm{F}\mathrm{e}$ agrees nicely with several theoretical predictions for two-proton radioactivity.

Gamow Shell-Model Description of Neutron-Rich Nuclei

Abstract: This work presents the first continuum shell-model study of weakly bound neutron-rich nuclei involving multiconfiguration mixing. For the single-particle basis, the complex-energy Berggren ensemble representing the bound single-particle states, narrow resonances, and the nonresonant continuum background is taken. Our shell-model Hamiltonian consists of a one-body finite potential and a zero-range residual two-body interaction. It is demonstrated that the residual interaction coupling to the particle continuum is important; in some cases, it can give rise to the binding of a nucleus.

Structure prediction and phylogenetic analysis of a functionally diverse family of proteins homologous to the MT-A70 subunit of the human mRNA:m(6)A methyltransferase.

Abstract: MT-A70 is the S-adenosylmethionine-binding subunit of human mRNA:m(6)A methyl-transferase (MTase), an enzyme that sequence-specifically methylates adenines in pre-mRNAs. The physiological importance yet limited understanding of MT-A70 and its apparent lack of similarity to other known RNA MTases combined to make this protein an attractive target for bioinformatic analysis. The sequence of MT-A70 was subjected to extensive in silico analysis to identify orthologous and paralogous polypeptides. This analysis revealed that the MT-A70 family comprises four subfamilies with varying degrees of interrelatedness. One subfamily is a small group of bacterial DNA:m(6)A MTases. The other three subfamilies are paralogous eukaryotic lineages, two of which have not been associated with MTase activity but include proteins having substantial regulatory effects. Multiple sequence alignments and structure prediction for members of all four subfamilies indicated a high probability that a consensus MTase fold domain is present. Significantly, this consensus fold shows the permuted topology characteristic of the b class of MTases, which to date has only been known to include DNA MTases.

Synthesis of aligned carbon nanotubes

Abstract: Carbon nanomaterials seem to be most attractive because of their fascinating features. Carbon nanotubes emerged recently as unique nanostructures with remarkable mechanical and electronic properties. Future applications will require a fabrication method capable of producing uniform carbon nanotubes with well-defined and controllable reproducibility of their properties. In this review, recent results addressing rational and efficient methods to obtain aligned arrays of these one-dimensional carbon nanomaterials will be discussed.

Values, Economics, and Proenvironmental Attitudes in 22 Societies

Abstract: Using data provided by the 1993 International Social Survey Programme, the authors examine the relationship between economic factors, values, and environmental attitudes both at the societal level and the individual level. They tested the hypothesis derived from Inglehart that postmaterialist values mediate the relationship between economics and support for the environment. In a multilevel analysis, they also explored whether the relationship between individuals’ income and their attitudes toward the environment varies as a function of societal-level indicators. Results demonstrate that economic factors predicted proenvironmental attitudes at the societal level and less so at the individual level, but at neither level was the influence of economic factors mediated through postmaterialist values. Further, a society’s recent economic growth, but not current levels of economic development, predicted to what extent individuals’ proenvironmental views were linked to their personal economic resources.

Application of Lempel-Ziv Factorization to the Approximation of Grammar-Based Compression

Abstract: We present almost linear time (O(n?log |?|) time) O(log n)- ratio approximation of minimal grammar-based compression of a given string of length n over an alphabet ? and O(k ? log n) time transformation of LZ77 encoding of size k into a grammar-based encoding of size O(k ? log n). Computing exact size of the minimal grammar-based compression is known to be NP-complete. The basic novel tool is the AVL-grammar.

Discrete stages in the solvation and ionization of hydrogen chloride adsorbed on ice particles

Abstract: Ionization and dissociation reactions play a fundamental role in aqueous chemistry. A basic and well-understood example is the reaction between hydrogen chloride (HCl) and water to form chloride ions (Cl(-)) and hydrated protons (H(3)O(+) or H(5)O(2)(+)). This acid ionization process also occurs in small water clusters and on ice surfaces, and recent attention has focused on the mechanism of this reaction in confined-water media and the extent of solvation needed for it to proceed. In fact, the transformation of HCl adsorbed on ice surfaces from a predominantly molecular form to ionic species during heating from 50 to 140 K has been observed. But the molecular details of this process remain poorly understood. Here we report infrared transmission spectroscopic signatures of distinct stages in the solvation and ionization of HCl adsorbed on ice nanoparticles kept at progressively higher temperatures. By using Monte Carlo and ab initio simulations to interpret the spectra, we are able to identify slightly stretched HCl molecules, strongly stretched molecules on the verge of ionization, contact ion pairs comprising H(3)O(+) and Cl(-), and an ionic surface phase rich in Zundel ions, H(5)O(2)(+).

All-sky astrophysical component separation with Fast Independent Component Analysis (FastICA)

Abstract: We present a new, fast, algorithm for the separation of astrophysical components superposed in maps of the sky. The algorithm, based on the Independent Component Analysis (ICA) technique, is aimed at recovering both the spatial pattern and the frequency scalings of the emissions from statistically independent astrophysical processes, present along the line-of-sight, from multi-frequency observations, without any a priori assumption on properties of the components to be separated, except that all of them, but at most one, must have non-Gaussian distributions. The analysis starts from very simple toy-models of the sky emission in order to assess the quality of the reconstruction when inputs are well known and controlled. In particular we study the dependence of the results of separation conducted on and off the Galactic plane independently, showing that optimal separation is achieved for sky regions where components are smoothly distributed. Then we move to more realistic applications on simulated observations of the microwave sky with angular resolution and instrumental noise at the mean nominal levels for the Planck satellite. We consider several Planck observation channels containing the most important known diffuse signals: the Cosmic Microwave Background (CMB), Galactic synchrotron, dust and free-free emissions. A method for calibrating the reconstructed maps of each component at each frequency has been devised. The spatial pattern of all the components have been recovered on all scales probed by the instrument. In particular, the CMB angular power spectra is recovered at the percent level up to lmax ≃ 2000. Frequency scalings and normalization have been recovered with better than 1% precision for all the components at frequencies and in sky regions where their signalto-noise ratio > ∼ 1.5; the error increases at ∼ 10% level for signal-to-noise ratios ≃ 1.

Light and electric field control of ferromagnetism in magnetic quantum structures.

Abstract: A strong influence of illumination and electric bias on the Curie temperature and saturation value of the magnetization is demonstrated for semiconductor structures containing a modulation-doped p-type ${\mathrm{Cd}}_{0.96}{\mathrm{Mn}}_{0.04}\mathrm{Te}$ quantum well placed in various built-in electric fields. It is shown that both light beam and bias voltage generate an isothermal and reversible crossover between the paramagnetic and ferromagnetic phases, in the way that is predetermined by the structure design. The observed behavior is in quantitative agreement with the expectations for systems, in which ferromagnetic interactions are mediated by the weakly disordered two-dimensional hole liquid.