Showing papers by "Lund University published in 1997"

First-principles calculations of the electronic structure and spectra of strongly correlated systems: the LDA+ U method

Abstract: The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.

System analysis via integral quadratic constraints

Abstract: This paper introduces a unified approach to robustness analysis with respect to nonlinearities, time variations, and uncertain parameters. From an original idea by Yakubovich (1967), the approach has been developed under a combination of influences from the Western and Russian traditions of control theory. It is shown how a complex system can be described, using integral quadratic constraints (IQC) for its elementary components. A stability theorem for systems described by IQCs is presented that covers classical passivity/dissipativity arguments but simplifies the use of multipliers and the treatment of causality. A systematic computational approach is described, and relations to other methods of stability analysis are discussed. Last, but not least, the paper contains a summarizing list of IQCs for important types of system components.

Apoptosis and proliferation of dentate gyrus neurons after single and intermittent limbic seizures

Abstract: Neuronal apoptosis was observed in the rat dentate gyrus in two experimental models of human limbic epilepsy. Five hours after one hippocampal kindling stimulation, a marked increase of in situ terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL) of fragmented DNA was observed in nuclei located within and on the hilar border of the granule cell layer and in the polymorphic region. Forty kindling stimulations with 5-min interval produced higher numbers of labeled nuclei compared with one stimulation. The increase of TUNEL-positive nuclei was prevented by the protein synthesis inhibitor cycloheximide but not affected by the N-methyl-d-aspartate receptor antagonist MK-801. Kainic acid-induced seizures lead to a pattern of labeling in the hippocampal formation identical to that evoked by kindling. A large proportion of cells displaying TUNEL-positive nuclei was double-labeled by the neuron-specific antigen NeuN, demonstrating the neuronal identity of apoptotic cells. Either 1 or 40 kindling stimulations also gave rise to a marked increase of the number of cells double-labeled with the mitotic marker bromodeoxyuridine and NeuN in the subgranular zone and on the hilar border of the dentate granule cell layer. The present data show that single and intermittent, brief seizures induce both apoptotic death and proliferation of dentate gyrus neurons. We hypothesize that these processes, occurring early during epileptogenesis, are primary events in the development of hippocampal pathology in animals and possibly also in patients suffering from temporal lobe epilepsy.

Comparative pharmacology of human adenosine receptor subtypes – characterization of stably transfected receptors in CHO cells

Abstract: Four adenosine receptor subtypes of the family of G protein-coupled receptors, designated A1, A2A, A2B and A3 are currently known. In this study all human subtypes were stably transfected into Chinese hamster ovary (CHO) cells in order to be able to study their pharmacological profile in an identical cellular background utilizing radioligand binding studies (A1, A2A, A3) or adenylyl cyclase activity assays (A2B). The A1 subtype showed the typical pharmacological profile with 2-chloro-N6-cyclopentyladenosine (CCPA) as the agonist with the highest affinity and a marked stereoselectivity for the N6-phenylisopropyladenosine (PIA) diastereomers. In competition with antagonist radioligand biphasic curves were observed for agonists. In the presence of GTP all receptors were converted to a single low affinity state indicating functional coupling to endogenous G proteins. For A2A adenosine receptors CGS 21680 (2-[p-(2-carboxyethyl)phenylethylamino]-5'-N-ethylcarboxamidoadeno sine) and N-ethylcarboxamidoadenosine (NECA) were found to be the most potent agonists followed by R- and S-PIA with minor stereoselectivity. The relative potencies of agonists for the A2B adenosine receptor could only be tested by measurement of receptor-stimulated adenylyl cyclase activity. NECA was the most potent agonist with an EC50-value of 2.3 microM whereas all other compounds tested were active at concentrations in the high micromolar range. Inhibition of NECA-stimulated adenylyl cyclase identified xanthine amino congener (XAC; 8-[4-[[[[(2-aminoethyl)amino]-carbonyl]methyl]oxy]phenyl]-1,3-dipropylxa nthine) as the most potent antagonist at this receptor subtype. The A3 receptor was characterized utilizing the nonselective agonist [3H]NECA. The N6-benzyl substituted derivatives of adenosine-5'-N-methyluronamide (MECA) turned out to be the most potent agonists. The notion of xanthine-insensitivity of the A3 receptor should be dropped at least for the human receptor as xanthines with submicromolar affinity were found. Overall, the pharmacological characteristics of the human receptors are similar to other species with some species-specific characteristics. In this study we present for the first time the comparative pharmacology of all known human adenosine receptor subtypes. The CHO cells with stably transfected adenosine receptors provide an identical cellular background for such a pharmacological characterization. These cells are valuable systems for further characterization of specific receptor subtypes and for the development of new ligands.

Capital and income breeding as alternative tactics of resource use in reproduction

Abstract: In order to compensate for the resource demands of reproduction, organisms usually increase the amount of total food resources available. This may be achieved by different tactics of resource use that also include foraging decisions. Two such general tactics are discussed in this paper under the concepts of capital and income breeding. These are defined mainly from the temporal distribution of resource acquisition relative to resource use. A capital breeder acquires its resources in advance and store them endogenously or exogenously until they are needed to supply aspects of offspring production. An income breeder, on the other hand, adjusts its food intake concurrently with breeding, without reliance on stores. In a perfectly predictable environment without limited resources, income breeding is the best option since capital breeders may have to pay a number of energetic and demographic costs for their stored resources. However, under unpredictable food conditions, food/time limitations, and risky foraging conditions, capital breeding offers many benefits. The costing systems (pre- or postbreeding costs) induced by capital and income breeding will largely influence the opportunity for these energetic tactics to evolve. While capital and income breeders may potentially experience both pre- and postbreeding costs, capital breeders may be more exposed to prebreeding costs due to predation in connection with acquisition and carriage of stores.

UV-B as an environmental factor in plant life: stress and regulation.

Abstract: Recent studies indicate that increasing solar UV-B is not merely an environmental stress for plants. Solar UV-B can cause plant morphogenetic effects, which can, in turn, modify the architecture of plants and the structure of a vegetation, In addition, UV-B radiation affect the production of various secondary metabolites (such as flavonoids, tannins and lignin) with important physiological and ecological consequences.

Estimation and Prediction for Stochastic Blockmodels for Graphs with Latent Block Structure

Abstract: A statistical approach to a posteriori blockmodeling for graphs is proposed. The model assumes that the vertices of the graph are partitioned into two unknown blocks and that the probability of an edge between two vertices depends only on the blocks to which they belong. Statistical procedures are derived for estimating the probabilities of edges and for predicting the block structure from observations of the edge pattern only. ML estimators can be computed using the EM algorithm, but this strategy is practical only for small graphs. A Bayesian estimator, based on Gibbs sampling, is proposed. This estimator is practical also for large graphs. When ML estimators are used, the block structure can be predicted based on predictive likelihood. When Gibbs sampling is used, the block structure can be predicted from posterior predictive probabilities. A side result is that when the number of vertices tends to infinity while the probabilities remain constant, the block structure can be recovered correctly with probability tending to 1. (Less)

A breakpoint map of recurrent chromosomal rearrangements in human neoplasia.

Abstract: Cytogenetic studies over the past few decades have revealed clonal chromosomal aberrations in almost 27,000 human neoplasms. Many of these neoplasia-associated chromosomal abnormalities have been characterised at the molecular level, revealing previously unknown genes that are closely associated with the tumorigenic process. Information on chromosome changes in neoplasia is growing rapidly, making it difficult to identify all recurrent chromosomal aberrations. We have developed a computer program to ascertain, for the first time, all recurrent structural abnormalities in all haematological malignancies and solid tumours published up to June 1996. Out of 26,523 cases, a total of 215 balanced and 1,588 unbalanced recurrent aberrations were identified among 75 different neoplastic disorders. Our compilation of all recurrent balanced and unbalanced neoplasia-associated rearrangements should help in directing future efforts aimed at identifying the molecular mechanisms involved in tumorigenesis.

Rapid reversible changes in organ size as a component of adaptive behaviour

Abstract: Organ structures and correlated metabolic features (e.g. metabolic rate) have often taken as fixed attributes of fully grown individual vertebrates. When measurements of these attributes became available they were often used as representative values for the species, disregarding the specific conditions during which the mesurement were made. Evidence is accumulating that the functional size of organs and aspects of the metabolic physiology of an individual may show great flexibility over timescales of weeks and even days depending on physiological status, environmental conditions and behavioural goals. This flexibility is a way for animals to cope successfully with a much wider range of conditions occurring during various life-cycle events than fixed metabolic machinery would allow. Such phenotypic flexibility is likely to be a common adaptive syndrome, typical of vertebrates living in variable environments.

Theoretical Foundations of Phenomenography.

Abstract: In this article the concepts of research tradition, research programme, research tool and research orientation are used to clarify the character of phenomenography. Phenomenography is said to be fundamentally a research orientation and to be characterised by the delimitation of an aim in relation to a kind of object. The aim is to describe and the kind of object is a conception. Phenomenographic research also has common characteristics of method of a general kind related to the orientation and these are called a research approach. The orientation and approach together are said to represent a research specialisation. The historical roots and the ontological, epistemological and methodological assumptions of this research specialisation are described and summarised. Lastly, phenomenography is described as a reaction against and an alternative to dominant positivistic, behaviouristic and quantitative research and as making its own ontological, epistemological and methodological assumptions with insp...

Deregulation of the platelet-derived growth factor B-chain gene via fusion with collagen gene COL1A1 in dermatofibrosarcoma protuberans and giant-cell fibroblastoma

Abstract: Dermatofibrosarcoma protuberans (DP), an infiltrative skin tumour of intermediate malignancy, presents specific features such as reciprocal translocations t(17;22)(q22;q13) and supernumerary ring chromosomes derived from the t(17;22). In this report, the breakpoints from translocations and rings in DP and its juvenile form, giant cell fibroblastoma (GCF), were characterised on the genomic and RNA level. These rearrangements fuse the platelet-derived growth factor B-chain (PDGFB, c-sis proto-oncogene) and the collagen type I alpha 1 (COL1A1) genes. PDGFB has transforming activity and is a potent mitogen for a number of cell types, but its role in oncogenic processes is not fully understood. COL1A1 is a major constituent of the connective tissue matrix. Neither PDGFB nor COL1A1 have so far been implicated in any tumour translocations. These gene fusions delete exon 1 of PDGFB, and release this growth factor from its normal regulation.

Learning Deficit in BDNF Mutant Mice

Abstract: Brain-derived neurotrophic factor (BDNF) has been implicated in the regulation of high-frequency synaptic transmission and long-term potentiation in the hippocampus, processes that are also thought to be involved in the learning of spatial tasks such as the Morris water maze. In order to determine whether BDNF is required for normal spatial learning, mice carrying a deletion in one copy of the BDNF gene were subjected to the Morris water maze task. Young adult BDNF mutant mice were significantly impaired compared with wild-type mice, requiring twice the number of days to reach full performance. Aged wild-type mice performed significantly worse than young wild-type mice and the effect was even more pronounced in the BDNF mutant mice, which did not learn at all. Although there was no difference in mean swimming speed between BDNF mutant and wild-type mice, we cannot exclude the possibility that developmental or peripheral deficits also contribute to the learning deficits in these mice. In situ hybridization and RNase protection analysis revealed that BDNF mRNA expression was indeed decreased in BDNF mutant mice. Furthermore, a pronounced effect of age on BDNF mRNA expression was seen, displayed as both a reduced level of mRNA expression and a reduced or entirely absent layer-specific expression pattern in the cerebral cortex of aged animals. Thus, our data suggest that BDNF expression may be linked to learning.

Chromosomal Imbalance Maps of Malignant Solid Tumors: A Cytogenetic Survey of 3185 Neoplasms

Abstract: To assess the distribution of gains and losses of genetic material in malignant solid neoplasms, 11 tumor types for which at least 100 short-term cultured cases with clonal chromosome aberrations had been reported in the literature were selected. The study was based on cytogenetic information from 508 breast carcinomas, 447 malignant neuroglial tumors, 435 kidney carcinomas, 333 colon carcinomas, 304 ovarian carcinomas, 303 lung carcinomas, 209 testicular germ cell tumors, 206 head and neck carcinomas, 172 malignant melanomas, 142 Wilms' tumors, and 126 neuroblastomas. In each case, the net imbalances were calculated for each chromosome band. The profiles of gains and losses revealed that all tumor types display unique combinations of imbalances. However, there is also considerable overlap among the profiles of the different diagnostic entities, indicating that similar molecular mechanisms may be operative in the development of many types of neoplasia. Deletions were more common than gains in all tumor types, with chromosomes X, Y, 4, 10, 13-15, 18, and 22 and chromosome segments 1p22-pter, 3p13-pter, 6q14-qter, 8p, 9p, and 11p being particularly often deleted in the majority of tumors. To better delineate critical lost segments, deletion profiles based only on structural rearrangements were made for chromosomes 1, 3-12, and 17, which all had on average at least four registered deletions per band. The relative distribution of losses indicated that different bands/regions are affected in different tumor types and that, often, several distinct candidate tumor suppressor gene loci can be discerned within the same chromosome arm, e.g., 1p12-13, 1p22, 1p34, and 1p36 on the short arm of chromosome 1 and 7q22, 7q32, and 7q36 on the long arm of chromosome 7. The only chromosomes or chromosome segments more often gained than deleted were chromosomes 7 and 20 and the long arms of chromosomes 1 and 12, suggesting the presence there of dominantly acting growth-regulatory genes. The data presented in this study should be valuable as a guide for molecular genetic studies on allelic imbalances and for the interpretation of results from studies using comparative genomic hybridization.

Poly(ethylene oxide)/poly(propylene oxide) block copolymer surfactants

Abstract: Block copolymers consisting of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) can self-assemble in water and water/oil mixtures (where water is a selective solvent for PEO and oil a selective solvent for PPO) to form thermodynamically stable spherical micelles as well as an array of lyotropic liquid crystalline mesophases of varying morphology. Significant advances have been made over the past year on the identification of different morphologies, the delineation of the composition-temperature ranges where they occur, and the structural characterization of the morphologies using primarily small angle scattering techniques. Important new findings on the copolymer micellization in water as affected by cosolutes, and on the time-dependency of the surface activity have also been reported.

Capillary Electrochromatography with Predetermined Selectivity Obtained through Molecular Imprinting

Abstract: This article presents a novel approach to capillary electrochromatography by which predetermined selectivity is achieved. A simple and quick method for the in situ preparation of monolithic molecularly imprinted flow-through polymers inside fused silica capillaries is described. The superporous structure of the polymers permits rapid solvent and electrolyte exchange, as well as easy regeneration of the capillaries by hydrodynamic pumping. Chiral stationary phases were prepared by molecular imprinting of the β-adrenergic antagonists propranolol and metoprolol. The separation systems were operational within 3 h of the start of capillary preparation. Chiral separations with baseline resolution could be carried out in less than 120 s.

The xanthophyll cycle, its regulation and components

Abstract: During the last few years much interest has been focused on the photoprotective role of zeaxanthin. In excessive light zeaxanthin is rapidly formed in the xanthophyll cycle from violaxanthin, via the intermediate antheraxanthin, a reaction reversed in the dark. The role of zeaxanthin and the xanthophyll cycle in photoprotection, is based on fluorescence quenching measurements, and in many studies a good correlation to the amount of zeaxanthin (and antheraxanthin) has been found. Other suggested roles for the xanthophylls involve, protection against oxidative stress of lipids, participation in the blue light response, modulation of the membrane fluidity and regulation of abscisic acid synthesis. The enzyme violaxanthin de-epoxidase has recently been purified from spinach and lettuce as a 43-kDa protein. It was found as 1 molecule per 20-100 electron-transport chains. The gene has been cloned and sequenced from Lactuca sativa, Nicotiana tabacum and Arabidopsis thaliana. The transit peptide was characteristic of nuclear-encoded and lumen-localized proteins. The activity of violaxanthin de-epoxidase is controlled by the lumen pH. Thus, below pH 6.6 the enzyme binds to the thylakoid membrane. In addition ascorbate becomes protonated to ascorbic acid (pKa= 4.2) the true substrate (Km= 0.1 mM) for the violaxanthin de-epoxidase. We present arguments for an ascorbate transporter in the thylakoid membrane. The enzyme zeaxanthin epoxidase requires FAD as a cofactor and appears to use ferredoxin rather than NADPH as a reductant. The zeaxanthin epoxidase has not been isolated but the gene has been sequenced and a functional protein of 72.5 kDa has been expressed. The xanthophyll cycle pigments are almost evenly distributed in the thylakoid membrane and at least part of the pigments appears to be free in the lipid matrix where we conclude that the conversion by violaxanthin de-epoxidase occurs.

Image enhancement based on a nonlinear multiscale method

Abstract: An image enhancement method that reduces speckle noise and preserves edges is introduced. The method is based on a new nonlinear multiscale reconstruction scheme that is obtained by successively combining each coarser scale image with the corresponding modified interscale image. Simulation results are included to demonstrate the performance of the proposed method.

Piecewise Linear Quadratic Optimal Control

Abstract: The use of piecewise quadratic cost functions is extended from stability analysis of piecewise linear systems to performance analysis and optimal control. Lower bounds on the optimal control cost are obtained by semidefinite programming based on the Bellman inequality. This also gives an approximation to the optimal control law. An upper bound to the optimal cost is obtained by another convex optimization problem using the given control law. A compact matrix notation is introduced to support the calculations and it is proved that the framework of piecewise linear systems can be used to analyze smooth nonlinear dynamics with arbitrary accuracy.

Short‐ and long‐term survival and function of unilateral intrastriatal dopaminergic grafts in Parkinson's disease

Abstract: Six patients with Parkinson's disease were followed for 10 to 72 months after human embryonic mesencephalic tissue from four to seven donors was grafted unilaterally into the putamen (4 patients) or putamen plus caudate (2 patients). After 8 to 12 months, positron emission tomography showed a 68% increase of 6-L-[18F]-fluorodopa uptake in the grafted putamen, no change in the grafted caudate, and minor decreases in nongrafted striatal regions. There was therapeutically valuable improvement in 4 patients, but only modest changes in the other 2, both of whom developed atypical features. Patient 4 was without L-dopa from 32 months and had normal fluorodopa uptake in the grafted putamen at 72 months. Overall, the L-dopa dose was reduced by a mean of 10 and 20%, "off" time was reduced by 34 and 44%, and the "off" phase Unified Parkinson's Disease Rating Scale motor score by 18 and 26%, and the duration of the response to a single L-dopa dose increased by 45 and 58% during the first and second years after surgery, respectively. Rigidity and hypokinesia improved bilaterally, but mainly contralateral to the implant. No consistent changes in dyskinesias were observed. We conclude that transplantation of embryonic mesencephalic tissue leads to highly reproducible survival of dopaminergic neurons, inducing clinically valuable improvements in most recipients.

Computational Atomic Structure: An MCHF Approach

Abstract: Preface Acknowledgments Introduction Angular Momentum Theory Hartree-Fock Calculations Multiconfiguration Hartree-Fock Wavefunctions Two-Electron Systems Correlation in Many-Electron Calculations Relativistic Effects Isotope and Hyperfine Effects Allowed and Forbidden Transitions MCHF Continuum Wavefunctions

Search for neutral heavy leptons produced in Z decays

Abstract: Weak isosinglet Neutral Heavy Leptons (m) have been searched for using data collected by the DELPHI detector corresponding to 3:3 106 hadronic Z0 decays at LEP1. Four separate searches have been performed, for short-lived m production giving monojet or acollinear jet topologies, and for long-lived m giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio BR(Z0 ! m) of about 1:310−6 at 95% confidence level for m masses between 3.5 and 50 GeV/c2. Outside this range the limit weakens rapidly with the m mass. The results are also interpreted in terms of limits for the single production of excited neutrinos.

The Preboreal oscillation around the Nordic Seas : Terrestrial and lacustrine responses

Abstract: The occurrence of an early Preboreal climatic cooling/oscillation (PBO) in lacustrine and glacial records from northwest Europe, Iceland and Greenland is reviewed and documented. The often subtle response of the proxy records to this oscillation, in combination with its short duration, make it difficult to detect. Owing to its chronostratigraphic position between the 10 000-9900 and 9600-9500 14 C plateaux (c. 11 300-11 150 calendar yr BP) it is also difficult to 14 C date with precision. We find that the vegetation response to the PBO varies between sites and regions. In contrast to the pioneer vegetation in Iceland and southern Sweden, the expanding birch-pine forest in Germany-Denmark was more susceptible to deteriorating growing conditions. The combined lacustrine, tree-ring and glacial records imply that the PBO was characterised by cool and humid conditions throughout northwestern and central Europe. This is documented by vegetation changes, decreased aquatic production, increased soil erosion, increased 2 H and 13 C content in tree-rings, readvances or stillstands of the ice sheet in Norway and Finland, and ingression of brackish water into the Baltic. Icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous Preboreal period, but not as extreme as during the Younger Dryas. Greenland records suggest that the early Preboreal was characterised by ice readvances, as an effect of cool climate and increased precipitation (in relation to the Younger Dryas). It was not until the end of the PBO that climate was warm enough to melt the land-based ice sheet. This Preboreal oscillation, found on both sides of the Nordic Seas, is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the Nordic Seas, which is implied by a simultaneous and distinct rise in the atmospheric 14 C/ 12 C ratio. A slow-down of the thermohaline circulation may tempor- arily have pushed the Polar Front further south. © 1997 by John Wiley & Sons, Ltd. Preboreal oscillation; thermohaline circulation; lacustrine records; glacial records; chronology.

Molecularly imprinted polymers : useful materials for analytical chemistry ?

Abstract: Molecular imprinting is a technique for producing chemically selective binding sites, which recognize a particular molecule, in a macroporous polymer matrix. This paper reviews recent advances in imprinting methodology, particularly emphasizing some recently introduced functional monomers and methods which directly yield polymeric material suitable for chromatography. Following this, attempts to incorporate imprinted polymers into a range of analytical methodologies are critically discussed, with some pointers to likely directions for future research.