CiteULike: Author Horváth

Cyclic Pattern Kernels Revisited

Tamás Horváth — 2008-07-30T08:35:07-00:00

Advances in Knowledge Discovery and Data Mining (2005), pp. 791-801.

The cyclic pattern kernel (CPK) is a powerful graph kernel based on patterns formed by simple cycles of labeled graphs. In a recent work, we proposed a method for computing CPK which is restricted to graphs containing polynomial number of simple cycles. In this work, we present two approaches relaxing this limitation. We first show that for graphs of bounded treewidth, CPK can be computed in time polynomial in the number of cyclic patterns, which in turn can be exponentially smaller than that of simple cycles. We then propose an alternative CPK based on the set of relevant cycles which is known to be enumerable with polynomial delay and its cardinality is typically only cubic in the number of vertices. Empirical results on the NCI-HIV dataset indicate that there is no significant difference in predictive performance between CPK based on simple cycles and that based on relevant cycles.

Measurement of ammonia exchange over grassland in the Hungarian Great Plain

László Horváth — 2008-06-01T17:23:04-00:00

Agricultural and Forest Meteorology, Vol. 130, No. 3-4. (30 June 2005), pp. 282-298.

The net dry flux of ammonia gas was measured between the atmosphere and a semi-natural grassland with low nitrogen input in Hungary, during the years of 2000 and 2001. A continuous flow denuder system was used to detect the ammonia concentrations at three levels (0.5, 1.0 and 2.0 m above the vegetation). Fluxes were calculated by the aerodynamic gradient method. According to the measurements, the net dry ammonia flux in the vegetation period is 0.37 kg N ha-1 (emission) and -5.0 kg N ha-1 (deposition) in the dormant season. For comparison the total atmospheric (dry + wet) input is -9.2 kg N ha-1 year-1 including all nitrogen forms and excluding ammonia. Net emission was observed only at daytime during the vegetation period when the canopy concentration exceeded the atmospheric ammonia concentration, due to an elevated stomatal compensation point. In all other times (night-time, outside the vegetation period) net deposition flux was observed. A sudden increase of N-input (application of 100 kg N ha-1 fertiliser) resulted in a large enhancement in emission during daytime, which lasted for 2-week period after the application of fertiliser, when the accumulated N-loss (emission factor) of fertiliser was amounted to approximately 1.3%. During night-time week deposition was detected from the fertilised sector suggesting that ammonia is emitted mainly by the plant through stomata in daytime, rather than from the soil. Measured fluxes have been compared to the prediction of a single layer compensation point model. The agreement is good, but some challenges remain for the selection of the parameterisation for individual model parameters.

Anomalous density dependence of static friction in sand

Viktor Horváth — 2008-05-03T00:04:28-00:00

Physical Review E, Vol. 54, No. 2. (1996), 2005.

Imaging polarimetry of forest canopies: how the azimuth direction of the sun, occluded by vegetation, can be assessed from the polarization pattern of the sunlit foliage

Ramón Hegedüs — 2008-03-27T09:45:50-00:00

Appl. Opt., Vol. 46, No. 23. (2007), pp. 6019-6032.

Radiance, color, and polarization of the light in forests combine to create complex optical patterns. Earlier sporadic polarimetric studies in forests were limited by the narrow fields of view of the polarimeters used in such studies. Since polarization patterns in the entire upper hemisphere of the visual environment of forests could be important for forest-inhabiting animals that make use of linearly polarized light for orientation, we measured 180° field-of-view polarization distributions in Finnish forests. From a hot air balloon we also measured the polarization patterns of Hungarian grasslands lit by the rising sun. We found that the pattern of the angle of polarization α of sunlit grasslands and sunlit tree canopies was qualitatively the same as that of the sky. We show here that contrary to an earlier assumption, the α -pattern characteristic of the sky always remains visible underneath overhead vegetation, independently of the solar elevation and the sky conditions (clear or partly cloudy with visible sun's disc), provided the foliage is sunlit and not only when large patches of the clear sky are visible through the vegetation. Since the mirror symmetry axis of the α -pattern of the sunlit foliage is the solar-antisolar meridian, the azimuth direction of the sun, occluded by vegetation, can be assessed in forests from this polarization pattern. Possible consequences of this robust polarization feature of the optical environment in forests are briefly discussed with regard to polarization-based animal navigation.

Determination of absolute configuration of ketamine enantiomers by HPLC-CD-UV technique.

A Gergely — 2008-03-01T00:43:07-00:00

Chirality, Vol. 11, No. 10. (1999), pp. 741-744.

Recognizing that the stereochemical structure of NMDA receptor antagonist ketamine provides valuable data about the relationship between its conformation and absolute configuration by CD-UV analysis, a method for the identification of ketamine enantiomers is proposed which avoids the need for authentic samples of the enantiomers. The ketamine enantiomers were separated by HPLC using Chiralcel OJ stationary phase. The in situ registration of CD and UV spectra, together with the application of the octant rule for cyclohexanone derivatives, makes possible the direct assignment of the eluted ketamine enantiomers.

[Novel chiroptical methods in pharmaceutical analysis]

A Gergely — 2008-03-01T00:42:29-00:00

Acta Pharm Hung, Vol. 69, No. 3. (June 1999), pp. 128-134.

Chiroptical spectroscopy, and its double and triple hyphenated combinations with UV-VIS spectroscopy and/or separation techniques constitute great progress in pharmaceutical analysis, of which five recently developed methods are surveyed here, as follows: The determination of enantiomeric purity by double, CD/UV detection without, and with the latter one provides enhanced sensitivity and selectivity. The determination of chromatographic peak homogeneity, by double detection, and peak slicing by recording. The separation, identification and four stereoisomers of doubly chiral compounds, by HPLC separation on chiral column, and optical-chiroptical detection.

Membranes: a meeting point for lipids, proteins and therapies.

Pablo V Escribáa — 2008-02-14T10:30:07-00:00

J Cell Mol Med (8 February 2008)

Membranes constitute a meeting point for lipids and proteins. Not only do they define the entity of cells and cytosolic organelles but they also display a wide variety of important functions previously ascribed to the activity of proteins alone. Indeed, lipids have commonly been considered a mere support for the transient or permanent association of membrane proteins, while acting as a selective cell/organelle barrier. However, mounting evidence demonstrates that lipids themselves regulate the location and activity of many membrane proteins, as well as defining membrane microdomains that serve as spatio-temporal platforms for interacting signaling proteins. Membrane lipids are crucial in the fission and fusion of lipid bilayers and they also act as sensors to control environmental or physiological conditions. Lipids and lipid structures participate directly as messengers or regulators of signal transduction. Moreover, their alteration has been associated with the development of numerous diseases. Proteins can interact with membranes through lipid co/post-translational modifications, and electrostatic and hydrophobic interactions, Van der Waals forces and hydrogen bonding are all involved in the associations between membrane proteins and lipids. The present study reviews these interactions from the molecular and biomedical point of view, and the effects of their modulation on the physiological activity of cells, the etiology of human diseases and the design of clinical drugs. In fact, the influence of lipids on protein function is reflected in the possibility to use these molecular species as targets for therapies against cancer, obesity, neurodegenerative disorders, cardiovascular pathologies, and other diseases, using a new approach called membrane-lipid therapy.

High-frequency network oscillation in the hippocampus.

G Buzsáki — 2008-01-09T13:17:12-00:00

Science, Vol. 256, No. 5059. (15 May 1992), pp. 1025-1027.

Pyramidal cells in the CA1 hippocampal region displayed transient network oscillations (200 hertz) during behavioral immobility, consummatory behaviors, and slow-wave sleep. Simultaneous, multisite recordings revealed temporal and spatial coherence of neuronal activity during population oscillations. Participating pyramidal cells discharged at a rate lower than the frequency of the population oscillation, and their action potentials were phase locked to the negative phase of the simultaneously recorded oscillatory field potentials. In contrast, interneurons discharged at population frequency during the field oscillations. Thus, synchronous output of cooperating CA1 pyramidal cells may serve to induce synaptic enhancement in target structures of the hippocampus.

Limit Theorems in Change-Point Analysis (Wiley Series in Probability & Statistics)

Miklós Csörgö — 2007-10-24T14:33:59-00:00

(05 January 1998)

Change-point problems arise in a variety of experimental and mathematical sciences, as well as in engineering and health sciences. This rigorously researched text provides a comprehensive review of recent probabilistic methods for detecting various types of possible changes in the distribution of chronologically ordered observations. Further developing the already well-established theory of weighted approximations and weak convergence, the authors provide a thorough survey of parametric and non-parametric methods, regression and time series models together with sequential methods. All but the most basic models are carefully developed with detailed proofs, and illustrated by using a number of data sets. Contains a thorough survey of:<P> <LI>The Likelihood Approach <LI>Non-Parametric Methods <LI>Linear Models <LI>Dependent Observations <P>This book is undoubtedly of interest to all probabilists and statisticians, experimental and health scientists, engineers, and essential for those working on quality control and surveillance problems. <P>Foreword by David Kendall

Altered calcium handling is an early sign of streptozotocin-induced diabetic cardiomyopathy.

L Ligeti — 2007-09-11T21:46:24-00:00

Int J Mol Med, Vol. 17, No. 6. (June 2006), pp. 1035-1043.

The main objective of the present study was to determine alterations of calcium handling in the diabetic rat heart during the transition from adaptive to maladaptive phase of cardiomyopathy. By inhibiting the nuclear enzyme poly(ADP-ribose) polymerase (PARP), we also investigated the possible role of this enzyme in the sequence of pathological events. Six weeks after induction of type I diabetes by injection of streptozotocin in rats, the hearts were perfused according to Langendorff. Intracellular-free calcium (Ca(2+)(i)) levels were measured by surface fluorometry using Indo-1 AM. Cyclic changes in Ca(2+)(i) concentrations and hemodynamic parameters were measured simultaneously. The hearts were challenged by infusion of isoproterenol. Six weeks of diabetes resulted in reduced inotropy and lusitropy. The diabetic hearts (DM) expressed a significantly elevated end-diastolic Ca(2+)(i) level (control, 111-/+20 vs DM, 221-/+35 nM). The maximal transport capacity of SERCA2a and conductance of RyR2 were reduced. These changes were not accompanied by major alterations in the tissue content of SERCA2a, RyR2, phospholamban and Na(+)/Ca(2+) exchanger. In response to beta-adrenergic activation, SERCA2a transport capacity and RyR2 conductance were stunted in the DM hearts. Inhibition of PARP induced minor changes in the mechanical function and calcium handling of the DM hearts. In conclusion, the observed changes in contractility and in Ca(2+)(i) handling are most likely attributable to functional disturbances of SERCA2a and RyR2 in this transitional phase of diabetes. At this stage of diabetes, PARP does not appear to play a significant pathogenetic role in the alterations in contractile function and calcium handling.

Magnetic dimer motion effects in a rotating magnetic field (A qualitative model of magnetoviscosity and permittivity in magnetorheological suspensions)

D Horváth — 2007-08-10T18:46:45-00:00

Czechoslovak Journal of Physics, Vol. 43, No. 6. (1 June 1993), pp. 671-681.

The motion of a pair of uniform interacting spherical mesoscopic particles situated in a viscous fluid under the influence of a rotating magnetic field was studied. The coupling interactions between the particles were chosen as a superposition of steric and dipolar pair potentials (for the dipoles parallel to the external field). The model dynamics consisting of particular rotation and vibration modes is the result of the interplay of viscous and interaction forces. The transition from the synchronous to the asynchronous regime of dimer rotation has been found. The results were discussed from a synergetic point of view. A qualitative picture of behaviour of the effective magnetoviscosity and permittivity for dimerized magnetorheological suspension has been given.

Dynamics of water droplets on a window pane

Imre Jánosi — 2007-08-06T07:53:06-00:00

Physical Review A, Vol. 40, No. 9. (1 November 1989), 5232.

We performed experiments and computer simulations in order to investigate whether the rain drops on a window pane are in a ‘‘self-organized critical state;’’ as proposed by Bak; Tang; and Wiesenfeld [Phys. Rev. Lett. 59 ; 381 (1987); Phys. Rev. A 38 ; 364 (1988); J. Stat. Phys. 51 ; 797 (1988)]; and Tang and Bak [Phys. Rev. Lett. 60 ; 2347 (1988)]. In contrast to the expected behavior; we found that the coverage fluctuations exhibit an f -2 power spectrum; and the characteristic distribution functions of the elementary events have no power-law dependence.

Multiple cyclin-dependent kinase complexes and phosphatases control G2/M progression in alfalfa cells.

T Mészáros — 2006-08-22T13:47:04-00:00

Plant Mol Biol, Vol. 43, No. 5-6. (August 2000), pp. 595-605.

Reversible phosphorylation of proteins by kinases and phosphatases plays a key regulatory role in several eukaryotic cellular functions including the control of the division cycle. Increasing numbers of sequence and biochemical data show the involvement of cyclin-dependent kinases (CDKs) and cyclins in regulation of the cell cycle progression in higher plants. The complexity represented by different types of CDKs and cyclins in a single species such as alfalfa, indicates that multicomponent regulatory pathways control G2/M transition. A set of cdc2-related genes (cdc2Ms A, B, D and F) was expressed in G2 and M cells. Phosphorylation assays also revealed that at least three kinase complexes (Cdc2Ms A/B, D and F) were successively active in G2/M cells after synchronization. Interaction between alfalfa mitotic cyclin (Medsa;CycB2;1) and a kinase partner has been reported previously. The present yeast two-hybrid analyses showed differential interaction between defined D-type cyclins and Cdc2Ms kinases functioning in G2/M phases. Localization of Cdc2Ms F kinase to the preprophase band (PPB), the perinuclear ring in early prophase, the mitotic spindle and the phragmoplast indicated a pivotal role for this kinase in mitotic plant cells. So far limited research efforts have been devoted to the functions of phosphatases in the control of plant cell division. A homologue of dual phosphatase, cdc25, has not been cloned yet from alfalfa; however tyrosine phosphorylation was indicated in the case of Cdc2Ms A kinase and the p(13suc1)-bound kinase activity was increased by treatment of this complex with recombinant Drosophila Cdc25. The potential role of serine/threonine phosphatases can be concluded from inhibitor studies based on okadaic acid or endothall. Endothall elevated the kinase activity of p(13suc1)-bound fractions in G2-phase alfalfa cells. These biochemical data are in accordance with observed cytological abnormalities. The present overview with selected original data outlines a conclusion that emphasizes the complexity of G2/M regulatory events in flowering plants.

MRI-assessed volume of left and right hippocampi in females correlates with the relative length of the second and fourth fingers (the 2D:4D ratio).

J Kallai — 2006-07-25T11:31:36-00:00

Psychiatry Res, Vol. 140, No. 2. (30 November 2005), pp. 199-210.

Atrophy of the left or right side of the hippocampus has been related to cognitive deficits and psychiatric disease. In this study, we examined the correlation between the hippocampal volume laterality index and the relative lengths of the second (index finger) and fourth (ring finger) digits (2D:4D) in healthy female subjects. The 2D:4D ratio is fixed in utero, and the ratio is higher in women than in men. There is evidence that this ratio is an indicator of the intrauterine concentration of testosterone, which influences the development of different regions of the brain. Assessing the volume of different parts of the brain of 40 healthy adult female students by magnetic resonance imaging (MRI), we found that the 2D:4D ratio was associated with an asymmetry in the hippocampal sub-regions. Smaller volume on the left side was found in the posterior part of the hippocampus in females with a low (masculine type) 2D:4D ratio. On the other hand, smaller volume on the left side was found in the middle part of the hippocampus in females with a high (female type) 2D:4D ratio. Thus, the development of the middle and posterior regions of the hippocampal formation may respond in opposite ways to prenatal levels of testosterone. Other brain regions such as the amygdala, the cerebral cortex, the total volume hippocampus, and the head of the hippocampus did not show such a difference.

Why do red and dark-coloured cars lure aquatic insects? The attraction of water insects to car paintwork explained by reflection-polarization signals.

G Kriska — 2006-06-22T22:46:28-00:00

Proc Biol Sci, Vol. 273, No. 1594. (7 July 2006), pp. 1667-1671.

We reveal here the visual ecological reasons for the phenomenon that aquatic insects often land on red, black and dark-coloured cars. Monitoring the numbers of aquatic beetles and bugs attracted to shiny black, white, red and yellow horizontal plastic sheets, we found that red and black reflectors are equally highly attractive to water insects, while yellow and white reflectors are unattractive. The reflection-polarization patterns of black, white, red and yellow cars were measured in the red, green and blue parts of the spectrum. In the blue and green, the degree of linear polarization p of light reflected from red and black cars is high and the direction of polarization of light reflected from red and black car roofs, bonnets and boots is nearly horizontal. Thus, the horizontal surfaces of red and black cars are highly attractive to red-blind polarotactic water insects. The p of light reflected from the horizontal surfaces of yellow and white cars is low and its direction of polarization is usually not horizontal. Consequently, yellow and white cars are unattractive to polarotactic water insects. The visual deception of aquatic insects by cars can be explained solely by the reflection-polarizational characteristics of the car paintwork.

Application of Different Learning Methods to Hungarian Part-of-speech Tagging

Tamás Horváth — 2005-10-09T10:17:27-00:00

. From the point of view of computational linguistics, Hungarian is a difficult language due to its complex grammar and rich morphology. This means that even a common task such as part-of-speech tagging presents a new challenge for learning when looked at for the Hungarian language, especially given the fact that this language has fairly free word order. In this paper we therefore present a case study designed to illustrate the potential and limits of current ILP and non-ILP algorithms...