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Time Patterns (time + pattern)
Selected AbstractsThe creation of an asymmetric hydraulic fracture as a result of driving stress gradientsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009T. Fischer SUMMARY Hydraulic fracture stimulation is frequently performed in hydrocarbon reservoirs and geothermal systems to increase the permeability of the rock formation. These hydraulic fractures are often mapped by hypocentres of induced microearthquakes. In some cases microseismicity exhibits asymmetry relative to the injection well, which can be interpreted by unequal conditions for fracture growth at opposite sides of the well or by observation effects. Here we investigate the role of the lateral change of the minimum compressive stress. We use a simple model to describe the relation among the lateral stress gradient, the mean viscous pressure gradients in the fracture wings, the fracture geometry, and the net pressure in the fracture. Our model predicts a faster fracture growth in the direction of decreasing stress and a limited growth in the opposite direction. We derive a simple relationship to estimate the lateral stress gradient from the injection pressure and the shape of the seismic hypocentre cloud. The model is tested by microseismic data obtained during stimulation of a Canyon Sands gas field in West Texas. Using a maximum likelihood method we fit the parameters of the asymmetric fracture model to the space,time pattern of hypocentres. The estimated stress gradients per metre are in the range from 0.008 to 0.010 times the bottom-hole injection overpressure (8,10 kPa m,1 assuming the net pressure of 1 MPa). Such large horizontal gradients in the order of the hydrostatic gradient could be caused by the inhomogeneous extraction of gas resulting in a lateral change of the effective normal stress acting normal to the fracture wall. [source] The Sahelian standardized rainfall index revisitedINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2009Abdou Ali Abstract The Standardized Precipitation Index (SPI) is usually defined as the arithmetic mean of the normalized precipitation recorded at several stations over a region of interest where the standard deviation computed at each station over a period of reference is used as the normalizing factor. It is common to use this index in order to diagnose whether the Sahelian region can be considered as wet or dry for a given year. There are several key factors interfering with the relevance of the SPI as a measure of how rainy is a season over the Sahel. The strong spatial variability of the Sahelian rainfall at the annual scale, the uneven distribution of the raingauge network and the mean interannual climatological gradients across the region are the most important of these factors, and their influence is studied in detail here. Using an optimal interpolation algorithm to compute the SPI, the effects of various sampling schemes are first studied showing that the SPI computed as a single mean value over the whole Sahelian region is relatively robust with respect to these effects. However, the central key question remains that computing a single mean SPI over the Sahelian region hides the strong underlying spatial variability of this index. For instance, 2006 was a significantly dry season over the Sahel as a whole, but working at the 0.5° × 0.5° resolution shows that in fact only 28% of the area was significantly dry, while 15% of the Sahel was significantly wet. From conditional empirical distributions a distribution function is proposed to determine the spatial distributions of the 0.5° × 0.5° SPI values for a given mean regional SPI value. Studying in detail the space,time pattern of the SPI over the 1950,2006 period, also shows that recent years are characterized by a greater interannual variability than the previous 40 years, and by a contrast between the western Sahel remaining dry and the eastern Sahel returning to wetter conditions. Copyright © 2008 Royal Meteorological Society [source] Social security pensionable ages in OECD countries: 1949-2035INTERNATIONAL SOCIAL SECURITY REVIEW, Issue 1 2007John Turner This paper examines the pensionable or early retirement age in social security in 23 OECD countries over the years 1949-2035. The policies for future years are those in current law, with some not being fully effective until 2035. The paper documents a pattern of decreasing pensionable ages that reversed in the 1990s, with many countries raising pensionable ages since the beginning of that decade, though generally with future effective dates. Pensionable-age policy provides insight into broader issues in social policy, such as whether social policies across countries have converged over time. The paper also examines the time pattern in the movement toward gender equality in social programmes. [source] Topographic pharmaco-EEG mapping of the effects of the South American psychoactive beverage ayahuasca in healthy volunteersBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 6 2002Jordi Riba Aims,Ayahuasca is a traditional South American psychoactive beverage used in Amazonian shamanism, and in the religious ceremonies of Brazilian-based syncretic religious groups with followers in the US and several European countries. This tea contains measurable amounts of the psychotropic indole N,N -dimethyltryptamine (DMT), and ,-carboline alkaloids with MAO-inhibiting properties. In a previous report we described a profile of stimulant and psychedelic effects for ayahuasca as measured by subjective report self-assessment instruments. In the present study the cerebral bioavailability and time-course of effects of ayahuasca were assessed in humans by means of topographic quantitative-electroencephalography (q-EEG), a noninvasive method measuring drug-induced variations in brain electrical activity. Methods, Two doses (one low and one high) of encapsulated freeze-dried ayahuasca, equivalent to 0.6 and 0.85 mg DMT kg,1 body weight, were administered to 18 healthy volunteers with previous experience in psychedelic drug use in a double-blind crossover placebo-controlled clinical trial. Nineteen-lead recordings were undertaken from baseline to 8 h after administration. Subjective effects were measured by means of the Hallucinogen Rating Scale (HRS). Results,Ayahuasca induced a pattern of psychoactive effects which resulted in significant dose-dependent increases in all subscales of the HRS, and in significant and dose-dependent modifications of brain electrical activity. Absolute power decreased in all frequency bands, most prominently in the theta band. Mean absolute power decreases (95% CI) at a representative lead (P3) 90 min after the high dose were ,20.20±15.23 µV2 and ,2.70±2.21 µV2 for total power and theta power, respectively. Relative power decreased in the delta (,1.20±1.31% after 120 min at P3) and theta (,3.30±2.59% after 120 min at P3) bands, and increased in the beta band, most prominently in the faster beta-3 (1.00±0.88% after 90 min at P3) and beta-4 (0.30±0.24% after 90 min at P3) subbands. Finally, an increase was also seen for the centroid of the total activity and its deviation. EEG modifications began as early as 15,30 min, reached a peak between 45 and 120 min and decreased thereafter to return to baseline levels at 4,6 h after administration. Conclusions, The central effects of ayahuasca could be objectively measured by means of q-EEG, showing a time pattern which closely paralleled that of previously reported subjective effects. The modifications seen for the individual q-EEG variables were in line with those previously described for other serotonergic psychedelics and share some features with the profile of effects shown by pro-serotonergic and pro-dopaminergic drugs. The q-EEG profile supports the role of 5-HT2 and dopamine D2 -receptor agonism in mediating the effects of ayahuasca on the central nervous system. [source] Age,period,cohort models and disease mappingENVIRONMETRICS, Issue 5 2003Corrado Lagazio Abstract Joint modelling of space and time variation of the risk of disease is an important topic in descriptive epidemiology. Most of the proposals in this field deal with at most two time scales (age,period or age,cohort). We propose a hierarchical Bayesian model that can be used as a general framework to jointly study the evolution in time and the spatial pattern of the risk of disease. The rates are modelled as a function of purely spatial terms (local effects of risk factors that do not vary in time), time effects (on the three time axes: age, calendar period and birth cohort) and space,time interactions that describe area specific time patterns. Copyright © 2003 John Wiley & Sons, Ltd. [source] Spatiotemporal properties of cytoplasmic cyclic AMP gradients can alter the turning behaviour of neuronal growth conesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2004Sebastian Munck Abstract Growth cones, the terminal structures of elongating neurites, use extracellular guidance information in order to navigate to appropriate target cells. The directional information of guidance cues is transduced to a cytoplasmic gradient of messenger molecules across the growth cone leading to rearrangements of the cytoskeleton. One messenger molecule regulating growth cone turning is cAMP, which is also known to be sufficient to direct growth cone attraction. Cytoplasmic cAMP gradients have been generated in the present study by photolysing caged cAMP with UV light focused on one side of growth cones of chick sensory neurons. Using this method we show that only specific time patterns of pulsed cAMP release are capable of inducing growth cone turning whereas others, which release the same amount of cAMP, are ineffective. Theoretical calculations show that diverse time patterns produce different intracellular gradients, which were visualized directly in HeLa cells expressing cAMP-sensitive ion channels as a reporter system. Together these data indicate that the spatiotemporal properties of the intracellular gradient are crucial for growth cone turning. [source] What are the high risk periods for incident substance use and transitions to abuse and dependence?INTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue S1 2008Implications for early intervention, prevention Abstract Background: For a better understanding of the evolution of addictive disorders and the timely initiation of early intervention and prevention, we have to learn when and how quickly the critical transitions from first substance use (SU) to regular use and from first SU and regular SU to abuse and dependence occur. Little data are currently available on the transitions to substance use disorders (SUDs) across the spectrum of legal and illegal drugs taking into account gender differences. It is the aim of this paper to describe the high density incidence and transition periods of SU and SUD for alcohol, nicotine, cannabis and other illicit drugs for young males and females. Methods: A sample of (N = 3021) community subjects aged 14,24 at baseline were followed-up prospectively over 10-years. SU and SUD were assessed using the DSM-IV/M-CIDI. Results: Ages 10,16 are the high risk period for first alcohol and nicotine use (up to 38% of subjects start before age 14). Onset of illegal SU occurs later. Substantial proportions of transitions to regular SU and SUD occur in the first three years after SU onset. Only few gender differences were found for time patterns of SU/SUD incidence and transition. Conclusion: Except for alcohol the time windows for targeted intervention to prevent progression to malignant patterns in adolescence are critically small, leaving little time for targeted intervention to prevent transition. The fast transitions to abuse and dependence in adolescence may be indicative for the increased vulnerability to substance effects in this time period. Basic research on the determinants of transitions should thus target this period in adolescence. Copyright © 2008 John Wiley & Sons, Ltd. [source] Space,time patterns of co-variation of biodiversity and primary production in phytoplankton guilds of coastal marine environmentsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2003Maria Rosaria Vadrucci Abstract 1.The relevance of biodiversity to ecosystem processes is a major topic in ecology. Here, we analyse the relationship between biodiversity and productivity of the nano- and micro-phytoplankton guilds in coastal marine ecosystems. 2.The patterns of variation of species richness, diversity and primary productivity (as 14C assimilation) were studied in two marine areas: a eutrophic,mesotrophic area beside the River Po delta (northern Adriatic) and an oligotrophic area around the Salento peninsula (southern Adriatic,Ionian). The study was carried out at 23 sites in the northern area and at 45 sites in the southern area. Sites were arranged on expected spatial and temporal gradients of primary productivity variation, according to distance from the coast, optical depths and seasonal period. 3.167 taxa were identified in the northern area and 153 taxa in the southern area. In both areas, the taxonomic composition of the nano- and micro-phytoplankton guilds exhibited greater temporal than spatial variation. The latter was much higher in the southern area than in the northern area (average dissimilarity between stations being 70.7±0.8% and 44.7±4.2% respectively). 4.Primary productivity varied in space and time on the gradients considered. Phytoplankton species richness and diversity exhibited significant patterns of variation in space and time; overall, these were inversely related to the primary productivity patterns in the northern area, whereas they were directly related in the southern area. 5.The small individual size and the high turnover rate of phytoplankton are likely to underlie the observed relationships, which emphasized a threshold response to nutrient enrichment in agreement with the ,paradox of enrichment'. Under resource enrichment conditions, the high turnover of producers leads to hierarchical partitioning of the available resources with an increasing dominance of a few species. Therefore, the relationship observed here seems likely to be explained by the complementarity hypothesis. Copyright © 2003 John Wiley & Sons, Ltd. [source] CAPACITY EXPANSION IN MARKETS WITH INTER-TEMPORAL CONSUMPTION EXTERNALITIESAUSTRALIAN ECONOMIC PAPERS, Issue 2 2010Article first published online: 20 MAY 2010, HIROSHI KITAMURA This paper analyses market capacity expansion in the presence of inter-temporal consumption externalities such as consumer learning, networks and bandwagon effects. An externality leads to an endogenous shift of market demand that responds to past market capacity. Whereas market capacity grows in waves, its magnitude depends on the degree of market concentration. The competitive environment contributes to S-shaped time patterns of market capacity expansion. On the other hand, using a low introductory price, a monopolist plans an initially larger amount of market cultivation than a competitive market capacity expansion. [source] Bioanalysis of pentoxifylline and related metabolites in plasma samples through LC-MS/MSBIOMEDICAL CHROMATOGRAPHY, Issue 6 2010Daniela Iuliana Sora Abstract Analytical aspects related to the assay of pentoxifylline (PTX), lisofylline (M1) and carboxypropyl dimethylxanthine (M5) metabolites are discussed through comparison of two alternative analytical methods based on liquid chromatography separation and atmospheric pressure electrospray ionization tandem mass spectrometry detection. One method is based on a ,pure' reversed-phase liquid chromatography mechanism, while the second one uses the additional polar interactions with embedded amide spacers linking octadecyl moieties to the silicagel surface (C-18 Aqua stationary phase). In both cases, elution is isocratic. Both methods are equally selective and allows separation of unknowns (four species associated to PTX, two species associated to M1) detected through specific mass transitions of the parent compounds and owning respective structural confirmation. Plasma concentration,time patterns of these compounds follow typical metabolic profiles. It has been advanced that in-vivo formation of conjugates of PTX and M1 is possible, such compounds being cleaved back to the parent ones within the ion source. The first method was associated with a sample preparation procedure based on plasma protein precipitation by strong organic acid addition. The second method used protein precipitation by addition of a water miscible organic solvent. Both analytical methods were fully validated and used to assess bioequivalence between a prolonged release generic formulation and the reference product, under multidose and single dose approaches. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||