Showing papers by "Hungarian Academy of Sciences published in 1994"

The Trithorax-like gene encodes the Drosophila GAGA factor

Abstract: LITTLE is known about the way higher-order chromatin structure influences gene expression and chromosome topology in general. Genetic analysis in Drosophila has led to the discovery of two classes of genes, the regulators of homeotic genes and the modifiers of position-effect variegation, which seem to be good candidates for encoding some of the factors regulating chromatin functions1,2. The Trithorax-like gene we describe here is required for the normal expression of the homeotic genes and is a modifier of position-effect variegation. We found that Trithorax-like encodes the GAGA factor which is involved in the formation of an accessible chromatin structure at promoter sequences3. Our genetic analysis suggests that the chromatin modelling function of the GAGA factor is not restricted to promoter regions.

Effects of benthivorous bream (Abramis brama) and carp (Cyprinus carpio) on sediment resuspension and concentrations of nutrients and chlorophyll a

Abstract: SUMMARY 1. The effect of benthivorous bream and carp on sediment resuspension and the concentrations of nutrients and chlorophyll a were studied in sixteen experimental ponds (mean depth 1m, mean area 0.1 ha, sandy clay/clay sediment), stocked with bream or carp at densities varying from 0 to 500 kg ha−1. Planktivorous perch (Perca fluviatilis L.) were added to some ponds to suppress zooplankton. 2. Suspended sediment concentrations increased linearly with biomass of benthivorous fish. Bream caused an increase of 46 g sediment m−2 day−1 per 100kg bream ha−1 and a reduction of 0.38m−1 in reciprocal Secchi disc depth, corresponding to an increase in the extinction coefficient of 0.34m−1. 3. No relationship was found between size of fish and amount of resuspension, but the effect of bream was twice as great as that of carp. Benthivorous feeding was reduced in May because alternative food (zooplankton) was available. 4. Assuming a linear relationship, chlorophyll a level increased by 9.0 μgI−1, total P by 0.03mgl−1 and Kjeldahl-N by 0.48mgl−1 per 100kg bream ha−1. Silicate, chlorophyll a, total P and total N were all positively correlated with fish biomass, but orthophosphate showed no correlation.

Molecular interpretation of the absorption-induced optical reorientation of nematic liquid crystals.

Abstract: A molecular mechanism is proposed to explain the anomalous optical reorientation observed in nematic guest-host systems. According to the model, light-induced reorientation in these systems is due to the interaction between the excited dye molecules and the nematic host. The model justifies a phenomenological description given earlier. Numerical results, based on the present model, are in agreement with the observed order of magnitude of the effect.

Is the Broido-Shafizadeh model for cellulose pyrolysis true?

Abstract: The widely accepted Broido-Shafizadeh model describes cellulose pyrolysis kinetics in terms of two parallel (competing) reactions preceded by an initiation step. In spite of the fact that many recent experimental results seem to contradict the predictions of the model, its validity has not been seriously questioned. In this paper we report thermogravimetric analyses of Avicel cellulose involving prolonged thermal pretreatments of small samples (0.5-3 mg). The weight loss curves were simulated by modern numerical techniques using the Broido-Shafizadeh and other related models. Results were not consistent with the presence of an initiation reaction, but they did strongly confirm the role of parallel reactions in the decomposition chemistry. A subsequent, high-temperature (370{degrees}C), pyrolytic degradation of solid intermediates formed below 300{degrees}C was also detected. In the absence of a prolonged thermal pretreatment, only one of the two parallel reactions can be observed. This reaction is first order, irreversible, and manifests a high activation energy (238 kJ/mol). The kinetic parameters of this reaction are not influenced by the large quantity of solid intermediates formed during prolonged, low-temperature thermal pretreatments, indicating that chemical processes are much more significant than the physical structure of the sample during pyrolysis.

The L3 silicon microvertex detector

Abstract: The design and construction of the silicon strip microvertex detector (SMD) of the L3 experiment at LEP are described. We present the sensors, readout electronics, data acquisition system, mechanical assembly and support, displacement monitoring systems and radiation monitoring system of the recently installed double-sided, double-layered SMD. This detector utilizes novel and sophisticated techniques for its readout.

Spectroscopic properties of aromatic dicarboximides. Part1.—N—H and N-methyl-substituted naphthalimides

Abstract: The photophysical properties of the N—H and N-methyl derivatives of 1,2-, 2,3- and 1,8-naphthalimides have been studied. The shift of the fluorescence emission position as a function of the solvent polarity indicates only a weak variation of dipole moment for the excited state compared with the corresponding value in the ground state (5.7 D for 2b, 2.8 D for 3b and <2 D for 4b, 1 D ≈ 3.335 64 × 10–30 C m, and 2b, 3b and 4b are N-methyl-1,2- naphthalimide, N-methyl-2,3-napthalimide and N-methyl-1,8-naphthalimide). However, important modifications of the photophysical properties are observed which depend on the relative position of the dicarboximide moiety on the naphthalene ring: the intersystem crossing rate constant of 4b increases dramatically by three orders of magnitude compared with that of 2b; simultaneously, the fluorescence quantum yield decreases from 0.77 to 0.03, although the corresponding rate constant, kf, increases. This difference is found to arise from the energy gap between the lowest1(π, π*) singlet excited state and the upper 3(n,π*) triplet state, which is of the order of 9 kcal mol–1 for 2b and less than 2 kcal mol–1 for 4b in acetonitrile solution. Protic solvents increase the energy difference between the n,π* and π,π* states thus decreasing the mixing of the two levels; as a consequence, the lifetime of 4b is increased, i.e. from <60 ps in hexane to 2.1 ns in trifluoroethanol. A triplet–triplet annihilation process occurs with the N-methyl derivatives 3b and 4b which leads to a monomer delayed fluorescence with the former, and mainly to a delayed excimer emission with the latter.

Contribution of membrane lipids to the ability of the photosynthetic machinery to tolerate temperature stress.

Abstract: The contribution of the unsaturation of membrane lipids to the ability of the photosynthetic machinery to tolerate temperature stress was studied in a transgenic cyanobacterium. Anacystis nidulans R2-SPc was transformed with the desA gene, which encodes the Delta12-desaturase that desaturates the fatty acids of membrane lipids in Synechocystis PCC6803. The transformant acquired the ability to introduce a second double bond into palmitoleic and oleic acids. The transformation enhanced the tolerance of the photosynthetic machinery to chilling stress but it had no detectable effect on the ability to tolerate heat stress. The transformation itself did not have any effect on photosynthetic activity. These results imply that an increase in the unsaturation of membrane lipids enhances the tolerance of the photosynthetic machinery toward chilling stress but not toward heat stress and that such an increase does not affect photosynthesis within the range of physiological temperatures.

Pocket Machining Based on Contour-Parallel Tool Paths Generated by Means of Proximity Maps

Abstract: A fundamental NC-machining problem is the clearing of areas within specified boundaries from material. The paper presents an efficient algorithm for generating largely optimal tool paths to solve this pocket-machining problem for multiply connected planar pocket areas bounded by curvilinear boundaries. Using certain concepts of computational geometry, i.e. Voronoi diagrams and monotonic pouches, offsets of a pocket boundary are efficiently generated. Further, it is explained how the tool path can be optimized with respect to several criteria arising from technological requirements. The concepts presented have been implemented, and they form the basis of the pocketing package lark .

Density functional study of nitrogen oxides

Abstract: Equilibrium geometries, bond dissociation energies, dipole moments, harmonic vibrational frequencies, and infrared intensities were calculated for a set of ten neutral nitrogen oxides (NO, NO2, NO3, N2O, sym N2O2, asym N2O3, sym N2O3, sym N2O4, asym N2O4, and N2O5) by applying one local and two gradient‐corrected nonlocal functionals in a Gaussian‐type‐orbital density functional method. Comparison with available experimental data shows that, except for the bond dissociation energies, the local functional gives very accurate molecular properties. Nonlocal functionals considerably improve the bond dissociation energies, but the results still overestimate the experimental values by about 10 kcal/mol on average. For the other properties, the results obtained with nonlocal functionals are not necessarily superior to those calculated with the local functional. The properties of two molecules (sym N2O3 and asym N2O4) are predicted for the first time and several reassignments are proposed in the vibrational spect...

Channel capacity for a given decoding metric

Abstract: For discrete memoryless channels {W: X/spl rarr/Y} we consider decoders, possibly suboptimal, which minimize a metric defined additively by a given function d(x, y)/spl ges/0. The largest rate achievable by codes with such a decoder is called the d-capacity C/sub d/(W). The choice d(x, y)=0 if and only if (iff) W(y|x)>0 makes C/sub d/(W) equal to the "zero undetected error" or "erasures-only" capacity C/sub eo/(W). The graph-theoretic concepts of Shannon capacity (1956, 1974) and Sperner capacity are also special cases of d-capacity, viz. for a noiseless channel with a suitable {0, 1}-valued function d. We show that the lower bound on d-capacity given previously by Csiszar and Korner (1980), and Hui (1983), is not tight in general, but C/sub d/(W)>0 iff this bound is positive. The "product space" improvement of the lower bound is considered,and a "product space characterization" of C/sub eo/(W) is obtained. We also determine the erasures-only (e.o.) capacity of a deterministic arbitrarily varying channel defined by a bipartite graph, and show that it equals capacity. We conclude with a list of challenging open problems. >

Singlet oxygen production in thylakoid membranes during photoinhibition as detected by EPR spectroscopy.

Abstract: Exposure of isolated spinach thylakoids to high intensity illumination (photoinhibition) results in the well-characterized impairment of Photosystem II electron transport, followed by degradation of the D1 reaction centre protein. In the present study we demonstrate that this process is accompanied by singlet oxygen production. Singlet oxygen was detected by EPR spectroscopy, following the formation of stable nitroxide radicals from the trapping of singlet oxygen with a sterically hindered amine TEMP (2,2,6,6-tetramethylpiperidine). There was no detectable singlet oxygen production during anaerob photoinhibition or in the presence of sodium-azide. Comparing the kinetics of the loss of PS II function and D1 protein with that of singlet oxygen trapping suggests that singlet oxygen itself or its radical product initiates the degradation of D1.

Mcp and Fab-7: molecular analysis of putative boundaries of cis-regulatory domains in the bithorax complex of Drosophila melanogaster

Abstract: A very large cis-regulatory region of approximately 300 kb is responsible for the complex patterns of expression of the three homeotic genes of the bithorax complex Ubx, abd-A and Abd-B. This region can be subdivided in nine parasegment-specific regulatory subunits. Recent genetic and molecular analysis has revealed the existence of two novel cis-regulatory elements Mcp and Fab-7. Mcp is located between iab-4 and iab-5, the parasegment-specific regulatory subunits which direct Abd-B in parasegments 9 and 10. Similarly, Fab-7 is located between iab-6 and iab-7, the parasegment 11 and 12-specific regulatory units. Mcp and Fab-7 appear to function as domain boundaries that separate adjacent cis-regulatory units. We report the analysis of two new Mcp mutant deletions (McpH27 and McpB116) that allow us to localize sequences essential for boundary function to a approximately 0.4 kb DNA segment. These essential sequences closely coincide to a approximately 0.3 kb nuclease hypersensitive region in chromatin. We also show that sequences contributing to the Fab-7 boundary appear to be spread over a larger stretch of DNA, but like Mcp have an unusual chromatin structure.

Catalytic reaction of methane with carbon dioxide over supported palladium

Abstract: The reforming of methane with carbon dioxide has been investigated at 673–773 K on supported palladium catalysts in a fixed-bed continuous-flow reactor. In addition, the dissociation of carbon dioxide and methane, and the reactivity of the surface carbon formed have also been examined. The dissociation of carbon dioxide, detected by infrared spectroscopy, occurred at the lowest temperature, 373 K, on Pd/TiO2. It was greatly promoted by the presence of methane. The decomposition of methane at the temperature of the CH4 + CO2 reaction (ca. 773 K) proceeded initially at a high rate yielding hydrogen and small amounts of ethane and ethene. The deposition of surface carbon was also observed, which was hydrogenated only above 720 K. The reaction between carbon dioxide and methane occurred rapidly above 673 K to give carbon monoxide and hydrogen with a ratio of 1.3–1.7. Very little carbon was deposited during the reaction of a stoichiometric gas mixture. Kinetic parameters of the reaction were determined and a possible reaction mechanism is proposed. kw|carbon dioxide hydrogenation; kinetics; methane reforming; palladium

Topological Cliques in Graphs

Abstract: This note contains a refinement of our paper [8], leading to an alternative proof of a conjecture of Mader and of Erdős and Hajnal recently proved by Bollobas and Thomason.

Direct solution analysis by glow discharge: electrolyte-cathode discharge spectrometry

Abstract: A new glow discharge atomic emission source was developed for the direct determination of metals in aqueous solutions by applying an atmospheric glow discharge in the air gap (2–6 mm) between an electrolyte solution cathode and a W-rod anode. Cathode sputtering of the solution surface and subsequent excitations occur when the pH of the solution is below 2.5. The spectrum emitted contains the basic atomic lines of the dissolved metals from K 769.9 to Zn 213.8 nm, ion lines of Mg and Ca and strong OH, NH and N2 bands. Boiling of the cathode pole can be avoided by use of a flow-through technique. The electron temperature was found to be around 5000 K. The calibration curves of line intensities versus metal concentrations were linear in the 1–50 ppm range and showed strong positive dependence on the discharge current and on the hydrogen ion concentration of the solution. Pulse modulated operation with time-resolved signal processing promises a substantial increase in the signal-to-background ratio. The flow-through electrolyte acts as a continuously renewed cathode pole, thereby enabling the continuous direct multi-metal assay of solutions. This report is the first discussion on the analytical characteristics of electrolyte-cathode discharge (ELCAD). spectrometry as a new technique for metal monitoring in aqueous solutions.

Gonadal hormone regulation of glial fibrillary acidic protein immunoreactivity and glial ultrastructure in the rat neuroendocrine hypothalamus

Abstract: The influence of gonadal steroids on the ultrastructure of glial cells and on the immunoreactivity for the specific astrocytic marker glial fibrillary acidic protein (GFAP) has been assessed in the neuroendocrine hypothalamus. The following parameters were analyzed in the arcuate nucleus of adult female rats: the number and the surface density of cells immunoreactive for GFAP, the number of glial profiles showing bundles of glial filaments, the size of the bundles of glial filaments, and the proportion of neuronal perikaryal membrane apposed by glial processes. These parameters were studied during the different phases of the estrous cycle, after ovariectomy, and after the administration of estradiol or progesterone to ovariectomized rats. No significant differences were detected in the number of GFAP-immunoreactive cells among the different experimental groups. The surface density of GFAP-immunoreactive material, the number of glial profiles in the neuropil, and the proportion of neuronal perikaryal membrane covered by glia were increased in the afternoon of proestrus and in the morning of estrus compared with other phases of the estrous cycle or to ovariectomized rats and showed a rapid (5 h) and reversible increase in ovariectomized rats injected with 17 beta estradiol, with a maximal effect by 24 h after the administration of the hormone. In contrast, the size of the bundles of glial filaments was decreased in the afternoon of proestrus, in the morning of estrus, and by the administration of estradiol to ovariectomized rats. The parameters studied were not affected by the administration of progesterone. However, progesterone (300 micrograms/rat) blocked the effects of 17 beta estradiol (1, 10, and 300 micrograms). The results suggest that glial cells may be actively involved in the modulation of neuroendocrine events by the hypothalamus.

Structural modifications in Rhizobium meliloti Nod factors influence their stability against hydrolysis by root chitinases

Abstract: Summary Acylated chitooligosaccharide signals (Nod factors) trigger the development of root nodules on leguminous plants and play an important role in determining host specificity in the Rhizobium-plant symbiosis Here, the ability of plant chitinases to hydrolyze different Nod factors and the potential significance of the structural modifications of Nod factors in stabilizing them against enzymatic inactivation were investigated Incubation of the sulfated Nod factors of Rhizobium meliloti, NodRm-IV(S) and NodRm-V(S), as well as their desulfated derivatives NodRm-IV and NodRm-V, with purified chitinases from the roots of the host plant Medicago and the nonhost plant Vicia resulted in the release of the acylated lipotrisaccharide NodRm-III from NodRm-V, NodRm-IV and NodRm-V(S), whereas NodRm-IV(S) was completely resistant to digestion by both chitinases Kinetic analysis showed that the structural parameters determining host specificity, the length of the oligosaccharide chain, the acylation at the nonreducing end and the sulfatation at the reducing end of the lipooligosaccharide, influence the stability of the molecule against degradation by chitinases When the Nod factors were incubated in the presence of intact roots of Medicago, as well as of Vicia, the acylated lipotrisaccharide was similarly released in vivo from all Nod factors except NodRm-IV(S) In addition, a dimer-forming activity was observed in intact roots which also cleaved NodRm-IV(S) This activity was much greater in Medicago than in Vicia and increased upon incubation The initial overall degradation rate of the Nod factors on Medicago was inversely correlated with their biological activities on Medicago roots These results open the possibility that the activity of Nod factors on Medicago may partly be determined by the action of chitinases

Oxidative damage and recovery of silicone rubber surfaces. I. X‐ray photoelectron spectroscopic study

Abstract: The oxidative degradation of silicone rubber surfaces in air plasmas obtained by RF or corona discharges and the subsequent recovery process were studied by X-ray photoelectron spectroscopy (XPS or ESCA). Using relatively short treatment times (5 min), the surface oxygen content was found to increase and that of carbon to decrease. Within 1 day some recovery toward the original composition was observed, but it was far from being complete. Angle-dependent measurements have shown an almost total recovery in the topmost layer. The degree of surface degradation of a solvent-extracted sample was much higher while its recovery was much smaller than the corresponding features of the nonextracted sample. According to GC and GC–MS analyses the extract contained a mixture of cyclic, and, in a minor quantity, linear dimethylsiloxane oligomers. Based on the above results the following steps were proposed for the oxidative damage and the subsequent recovery processes on silicone rubber surfaces: first the majority of surface methyl groups is removed and an oxidized layer containing Si atoms bound to 3 or 4 oxygens appears. The surface is later covered by a very thin (2–3 nm thick) “silicone oil” layer due to migration of low-molecular-weight components from the bulk. This diffusion-controlled migration step plays a more important role in the recovery process than the eventual reorientation of the newly formed polar groups from the surface toward the bulk. The proposed model is discussed in the light of published data. © 1994 John Wiley & Sons, Inc.

Principal cells are the postsynaptic targets of supramammillary afferents in the hippocampus of the rat.

Abstract: Neurons of the supramammillary nucleus are known to fire phase-locked to hippocampal theta rhythm. Stimulation of this area induces theta activity in the hippocampus via the medial septum and facilitates perforant pathway stimulation-evoked population spikes in the dentate gyrus even if the medial septum is inactivated. This latter effect was suggested to be due to a direct inhibitory input from the supramammilary nucleus to hippocampal nonpyramidal cells resulting in disinhibition. In the present study, using anterograde tracing with Phaseolus vulgaris leucoagglutinin, we aimed to identify the types of neurons innervated by the supramammillary projection in the dentate gyrus and Ammons horn, with particular attention to the presumed postsynaptic inhibitory neurons, which may mediate the proposed disinhibitory action. Double-immunostaining for the tracer and different neuropeptides (somatostatin, cholecystokinin, neuropeptide Y) or calcium binding proteins (calretinin, parvalbumin, calbindin D28K) present in different subpopulations of interneurons revealed no multiple contacts between supramammillary afferents and labeled inhibitory cells at the light microscopic level. Furthermore, postembedding immunostaining of electron microscopic sections for GABA demonstrated that none of the 68 PHAL-labeled supramammillary boutons examined and none of their postsynaptic targets were immunoreactive for the inhibitory neurotransmitter. We conclude, therefore, that most if not all postsynaptic targets of the supramammillary projection are principal cells both in the dentate gyrus and in the CA2-CA3a subfields. This suggests that a mechanism other than disinhibition is responsible for the facilitatory effect of this pathway on hippocampal evoked activity.

Cell and Molecular Biology of Rhizobium-Plant

Abstract: Publisher Summary This chapter discusses the Cell and molecular biology of Rhizobium -plant interactions. Soil bacteria, referred to as rhizobia belonging to the genera Rhizobium , Bradyrhizobium , and Azorhizobium , have the unique ability to induce nitrogen-fixing nodules on the roots or stems of leguminous plants. Nodule development consists of several stages determined by different sets of genes both in the host and symbiont. At least at the very early steps of symbiosis, the bacterial and plant genes are activated consecutively by signal exchanges between the symbiotic partners. First, flavonoid signal molecules exuded by the host plant root induce the expression of nodulation ( nod, nol ) genes in Rhizobium in conjunction with the bacterial activator NodD protein. Then, in the second step, lipooligosaccharide Nod factors with various host-specific structural modifications are produced by the bacterial Nod proteins. The Nod factors induce various plant reactions, such as root hair deformation, initiation of nodule meristems, and induction of early nodulin genes, leading to nodule formation. Other classes of bacterial genes are required for successful infection and for nitrogen fixation. This chapter includes only the early events of communication between rhizobia and their host plants, that is, the perception of flavonoid signals by the bacteria, the production of Nod signals by rhizobia, and the early plant responses to the bacteria.

Infrared spectroscopic study of the photoinduced activation of CO2 on TiO2 and Rh/TiO2 Catalysts

Abstract: The effect of illumination on the activation of CO[sub 2] was investigated at 190 K on oxidized, evacuated, and reduced TiO[sub 2] and Rh/TiO[sub 2] by means of Fourier transform infrared spectroscopy. The main effect observed for pure titania was an enhancement of the intensity of bands at 1640 and 1219 cm[sup [minus]1] due to bent CO[sub 2]. On Rh/TiO[sub 2] the photoinduced dissociation of CO[sub 2] also occurred, as indicated by the development of CO bands at 2020-2040 cm[sup [minus]1]. It is assumed that the CO[sub 2] on Rh/TiO[sub 2] is bonded to the surface with both C (linked to a Rh atoms) and one of the O atoms (linked to the oxygen vacancy of titania), and an extended charge transfer induced by illumination leads to the cleavage of a C-O bond. 44 refs., 5 figs., 1 tab.

Self-consistent localized KKR scheme for surfaces and interfaces

Abstract: A Green's-function technique is presented that describes the electronic properties of surfaces and interfaces in the framework of multiple-scattering theory as based on localized structure constants Results of self-consistent calculations are presented for the Cu (111), (110), and (100) surfaces The obtained surface densities of states and work functions are in good agreement with previous calculations

Specialized vectors for gene tagging and expression studies

Abstract: A genetic approach for the functional identification of genes involves mutagenizing the genome with a known, unique DNA sequence that provides both phenotypic and molecular markers for the isolation and mapping of gene mutations, and the cloning of corresponding genes. The efficiency of a DNA tag as a mutagen is primarily determined by the frequency and randomness by which it can be introduced into the genome of a target organism, and to a lesser extent by its physical or genetic properties that may be modified by genetic engineering. In contrast to base pair exchanges and deletions induced by chemical and physical mutagens that may not result in a complete loss of gene function, insertional mutagens are believed to cause only null mutations by a structural interruption of genes. However, this view is not entirely correct, because insertions in promoters are known either to positively or negatively affect gene expression, whereas insertions in coding regions may also result in gene fusions encoding truncated, but still functional, proteins. In addition, mutations induced by insertion elements frequently cause polar effects enhancing or reducing the transcription of genes located in the vicinity of insertions. It is therefore not by chance that gene tagging by insertion elements is one of the most powerful methods in the molecular analysis of gene expression[1].

A survey of blending methods that use parametric surfaces

Abstract: The paper discusses the blending problem in geometric modelling, and it provides a comprehensive review of solutions that use parametric surfaces. A terminology and a classification are presented to help clarify the nature of blending, and the relationships between various parametric blending methods. Several geometric techniques are evaluated, highlighting concepts which the authors feel to be important. Topological issues are also discussed. In conclusion, the applicability and efficiency of parametric techniques for general blending situations are emphasized, and open questions for future research are presented. An up-to-date list of publications on blending, including parametric-surface methods and other methods, is provided as a key to the literature.