Temporal Data Series Research Articles

A statistical study of wave propagation in coronal holes

Aims. To find evidence for propagating magnetoacoustic waves in equatorial and polar coronal hole locations Methods. Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we study oscillations found in radiant flux and velocity measurements from transition region (O! 629) and coronal lines (Mg 624, Si # # 520). We use Fourier techniques to measure phase delays between flux (‘intensity’) oscillations and between velocity oscillations of di! erent transition region‐corona and corona‐corona line pairs. We also measure the phase delays between flux and velocity oscillations (I‐V) in the three spectral lines investigated. Results. We find outwardly propagating slow magnetoacoustic waves in both of the coronal hole regions studied. The propagation speeds are found to be lower than those found in o! -limb locations. We find evidence for a resonant cavity or ‘Doppler’ e! ect, whereby the measured phases are present at fixed integer intervals of f/4 (90 of phase) and 3f/8 (135 of phase) instead of the expected interval of f or 360 . We find, in addition, from the I‐V phases, evidence for standing waves at coronal temperatures in the lines of Mg 624 and Si # # 520. Correlations are found between the locations where the phases are measured and localised brightenings in both equatorial and polar coronal holes. This suggests that the slow magnetoacoustic waves are originating preferentially from bright areas within the coronal holes which we take to be the locations of concentrated magnetic field (loops, bright points). Finally, we find evidence that in these bright regions along the slit, the measured phases tend to occur at a spectrum of frequencies, perhaps suggesting the presence of discrete propagating wave packets. Conclusions. We conclude that propagating slow magnetoacoustic waves are present in equatorial and polar coronal hole locations and that they occur preferentially in bright regions that are associated with magnetic field concentrations in the form of loops or bright points. In addition, we conclude that some resonant cavity e! ect is a! ecting the propagating waves, perhaps resulting in the standing waves that are found at coronal temperatures.

Magnetoacoustic wave propagation in off-limb polar regions

Aims. To find evidence of magnetoacoustic waves in off-limb polar regions. Methods. Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we study oscillations found in radiant flux and velocity measurements from transition region and coronal spectral lines. We use Fourier techniques to measure phase delays between flux (“intensity”) oscillations and between velocity oscillations of different transition region-corona and corona-corona line pairs. We also measure the phase delays between flux and velocity oscillations (I − V). Results. The phase delays measured between different line pairs, when plotted over a –180 ◦ to +180 ◦ range, line up along diagonal lines corresponding to measurable and fixed time delays. The slopes of these diagonal lines suggest the outward propagation of waves. Using the measured time delays, we estimate propagation speeds for the different line pairs that indicate that the waves producing the observed phase delays are magnetoacoustic waves propagating at speeds close to the sound speed. In addition, we find that the phases occur at fixed integer frequencies of f / 4( 90 ◦ )a nd 3f /16 (67.5 ◦ ), instead of the expected interval of f (360 ◦ ), indicating that a “Doppler effect” is acting on the waves. Conclusions. From I − V measurements, we find evidence for fast magnetoacoustic waves to be predominantly present at coronal temperatures, while at transition region temperatures slow magnetoacoustic waves are more common. We find strong evidence for outwardly propagating slow magnetoacostic waves in off-limb polar regions and an indication that these propagating waves are influenced by some form of resonant cavity through which they pass.

Subtractive Transcriptomics: Establishing Polarity Drives In vitro Human Endothelial Morphogenesis

Although investigations of mature normal and tumor-derived capillaries have resulted in characterization of these structures at the phenotypic level, less is known regarding the initial molecular cues for cellular assembly of endothelial cells into human capillaries. Here, we employ a novel combination of microenvironmental manipulation and microarray data filtration over narrowly delineated temporal data series to identify the morphogenesis component apart from the proliferation component, as pooled human microvascular-derived endothelial cells are induced to form capillary-like structures in vitro in a murine tumor-derived matrix. The 217 morphogenesis-specific genes identified using this subtractive transcriptomics approach are mostly independent of the angiogenic proteins currently used as therapeutic targets for aberrant angiogenesis. Quantitative real-time PCR was used to validate 20% of these transcripts. Immunofluorescent analysis of proliferating and tube-forming cells validates at the protein level the morphogenesis-specific expression pattern of 16 of the 217 gene products identified. The transcripts that are selectively up-regulated in tube-forming endothelial cells reveal a temporal expression pattern of genes primarily associated with intracellular trafficking, guided migration, cytoskeletal reorganization, cellular adhesion, and proliferation inhibition. These data show that a sequential up-regulation of genes that establish and maintain polarity occurs during migration and morphogenesis of in vitro human endothelial cells undergoing tubulogenesis; some of which may well be effective as novel antiangiogenic drug targets.

A fish-based index of large river quality for French Guiana (South America): method and preliminary results

Growing pressures from development activities, on aquatic environments in South American countries, have created an urgent need for tools to measure the quality of aquatic systems. The index of biotic integrity, based on fish assemblages, elaborated in North America, constitutes a basis for the development of these tools. However, its direct application is problematic in regions having a rich and diverse ichthyofauna and where the knowledge of fish species ecology is incomplete. The response of taxonomic or trophic groups is often unknown and the selection of fish assemblage metrics cannot be based on previous knowledge, as in intensely studied regions. This work proposes a method, similar to the approach recently pursued in Europe, based on comparing the variability of fish assemblages in reference situations with their variability influenced by human-induced perturbations. The method was developed from 53 samples of 27 reaches in 7 hydrographic basins of French Guiana. For each of 28 fish assemblage descriptors, stepwise multiple linear regressions with 28 habitat variables were carried out. The residuals of the models obtained were used as candidate metrics independent of natural environmental factors. Nine metrics showing significant differences between reference and disturbed samples were selected to constitute the index. The index was validated by analysing a temporal data series obtained from a reach disturbed by dam construction.

A QUESTÃO CLIMÁTICA DO NORDESTE BRASILEIRO E OS PROCESSOS DE DESERTIFICAÇÃO

O presente trabalho discute os processos de desertificação na região Nordestedo Brasil, nas áreas de clima Semi-árido, a partir da utilização do métododas séries temporais. O quadro geral da análise indicou 49,7% das sériesapresentando tendência crescente nas médias pluviométricas, configurandouma distribuição geográfica indiferenciada, apresentando, contudo,incidência maior no Rio Grande do Norte, Paraíba e Pernambuco, sobretudono espaço compreendido entre o reverso continental da Borborema e chapadado Apodi e seus prolongamentos meridionais. Tal constatação indicaque a precipitação em nível regional acompanha a tendência de elevação damédia pluviométrica que vem sendo registrada nas últimas décadas, presumivelmenteassociada ao agravamento do efeito de estufa. Por outro lado,50,3% revelaram tendência estável ou decrescente, as primeiras, com distribuiçãogeográfica mal caracterizada, ao passo que as segundas agruparam-se em quatro manchas, sinalizadoras de indícios de desertificação localizada.

WE‐D‐T‐6C‐03: Development of Image Software Tools for Radiation Therapy Assessment

There has been extensive recent interest in the potential power of emerging imaging tools for early prediction of therapy effectiveness, both related to tumor control and normal tissue damage. These prognostic indicators are the results of combining improved imaging hardware, specialized scanning protocols, and advanced image processing and analysis paradigms. In order to study and eventually use these tools routinely in the radiotherapy process, serious consideration needs to be given to the software environment necessary for proper data collection and analysis ties to individual patients' treatments. Imaging for therapy assessment (IAT) presents a multidimensional information environment, requiring data from different imaging modalities and acquisition methods, as well as handling temporal data series, combined over short (breathing, dynamic contrast) and long (temporal changes over weeks of treatment) time periods. The information needed for relating these data sets for analysis (non‐rigid transformations, proper labeling of studies to measurement states) exceeds the capacities of existing DICOM standards. The extraction of analyzed information and relation to regional (radiation) dose should be multidimensional, and not restricted to voxel‐specific regions. Examples of imaging studies underway for therapy assessment will be presented. Software requirements will be demonstrated through an example system currently in use to support clinical trials at the University of Michigan. This system was designed around the unique needs of IAT, and is able to combine information from multiple sources (e.g., MRI, MRS, CT, PET, radiation dose) and time periods in an intuitive interface. This system has been used for studies of blood flow and volume, regional venous perfusion, vascular permeability, water diffusion, metabolite, and local contrast enhancement for high dose radiotherapy trials in the brain, lung, and liver to date.Educational Objectives:1. Understanding the unique needs related to imaging for assessment of radiation therapy.2. Understanding the required tools beyond those found in a typical treatment planning system3. Understanding a common ground needed for combining efforts of imaging physicists, radiation physicists, physicians and statisticians.4. Understanding opportunities for novel paradigm and algorithm development

Assessing environmental quality: a novel approach

A new approach to assess environmental integrity based on PRC analysis was proposed, tested, validated and developed. Environmental health assessment and community studies usually result in complex biological data sets. In order to find ecologically relevant patterns and tendencies from such sets of data it is necessary to reduce all the information to a summarised and simplified form, which might be more easily interpreted by ecologists, politicians, end-users and the population in general. However, several multivariate ordination methods currently used (e.g. redundancy analy- sis, principal component analysis, or multi-dimensional scaling) produce complex diagrams for the non-ecologist, which do not allow changes in biological communities over time to be easily under- stood. Here, we propose a recently developed method, principal response curves (PRC) analysis, to overcome these issues. This method has advantages over traditional ordination techniques, or any biotic index, in that it provides a powerful statistical analysis of temporal data series along spatial gra- dients. The PRC technique can make use of non-disturbed or unpolluted areas as reference sites with which other areas are compared, making it possible to assess changes in species composition between different areas over time. Moreover, individual species responses to stress agents can be inferred from the PRC curves. As well as providing insights into the behaviour of natural ecosys- tems — in particular, how ecosystem integrity changes over time — this new approach can potentially provide a practical tool for monitoring and implementing environmental policy instruments.

Sar monitoring of progressive and seasonal ground deformation using the permanent scatterers technique

Spaceborne differential radar interferometry has proven a remarkable potential for mapping ground deformation phenomena (e.g., urban subsidence, volcano dynamics, coseismic and postseismic displacements along faults, as well as slope instability). However, a full operational capability has not been achieved yet due to atmospheric disturbances and phase decorrelation phenomena. These drawbacks can often be-at least partially-overcome by carrying out measurements on a subset of image pixels corresponding to natural or artificial stable reflectors [permanent scatterers (PS)] and exploiting long temporal series of interferometric data. This approach allows one to push the measurement precision very close to its theoretical limit (in the order of /spl sim/1 mm for C-band European Remote Sensing (ERS)-like sensors). In this paper, the detection of both time-uniform and seasonal deformation phenomena is addressed, and a first assessment of the precision achievable by means of the PS Technique is discussed. Results highlighting deformation phenomena occurring in two test sites in California are reported (Fremont in the Southern Bay Area and San Jose in the Santa Clara Valley).

Monitoring landslides and tectonic motions with the Permanent Scatterers Technique

Spaceborne differential synthetic aperture radar interferometry (DInSAR) has already proven its potential for mapping ground deformation phenomena, e.g. volcano dynamics. However, atmospheric disturbances as well as phase decorrelation have prevented hitherto this technique from achieving full operational capability. These drawbacks are overcome by carrying out measurements on a subset of image pixels corresponding to pointwise stable reflectors (Permanent Scatterers, PS) and exploiting long temporal series of interferometric data. Results obtained by processing 55 images acquired by the European Space Agency (ESA) ERS SAR sensors over Southern California show that the PS approach pushes measurement accuracy very close to its theoretical limit (about 1 mm), allowing the description of millimetric deformation phenomena occurring in a complex fault system. A comparison with corresponding displacement time series relative to permanent GPS stations of the Southern California Integrated GPS network (SCIGN) is carried out. Moreover, the pixel-by-pixel character of the PS analysis allows the exploitation of individual phase stable radar targets in low-coherence areas. This makes spaceborne interferometric measurements possible in vegetated areas, as long as a sufficient spatial density of individual isolated man-made structures or exposed rocks is available. The evolution of the Ancona landslide (central Italy) was analysed by processing 61 ERS images acquired in the time span between June 1992 and December 2000. The results have been compared with deformation values detected during optical levelling campaigns ordered by the Municipality of Ancona. The characteristics of PS, GPS and optical levelling surveying are to some extent complementary: a synergistic use of the three techniques could strongly enhance quality and reliability of ground deformation monitoring.

Moon cycles and violent behaviours: myth or fact?

We formulated the hypothesis that lunar phases, identified by the fraction of the illuminated visible surface of the moon, have a relationship with the frequency of victims of aggression seen in an emergency department. If such a relationship exists, an increase in the frequency of incidents with the phases of full moon or new moon would be expected. In order to test this hypothesis, the daily frequency of victims of violent behaviour seen in the emergency department was used to create a temporal series of data. This was then correlated with a temporal series of lunar luminosity data from the same time period. Crossed correlations in the delay range -7 to +7 days showed coefficient values ranging between -0.102 and +0.034, demonstrating weak correlations without statistical significance. Despite the attractiveness of the popular belief that the moon influences human behaviour, the analysis of our data does not support an association between lunar phases and frequency of violent behaviour. That is, we cannot predict the frequency of cases from a knowledge of lunar luminosity, at least in the period over which our study was performed.

Rescuing Rhythms from Noise: A New Method of Analysis

The analysis of a temporal series usually begins with a visual inspection of the raw data, from which a proper method for the detection of periodicities is chosen. Some of the methods currently used, as circular statistics, Cosinor, or spectral analyses, are useful when it comes to ascertain the existence of some periods, expected ‘a priori’ or to detect unknown frequencies. Even though some of the methods allow a wide scanning of possibilities, difficulties arise when signals are weak and concealed in larger amplitude noise. The register of the activity of a cave cricket, Strinatia brevipennis, under constant conditions, showed an intricate pattern of small peaks, interspersed with rare ones of much higher amplitudes. Attempts to analyse these data with the usual methods gave inconsistent results and sometimes did not detect rhythms. The results are mostly biased by the large amplitude components which hamper the detection of rhythms from weak signals. Schimmel and Paulssen (1997) proposed a noise-reduction method, which detects weak but coherent signals. This new tool was developed for the analysis of seismic data, being afterwards adapted to the analysis of temporal series of biological data. The method is called phase weighted stack (PWS) and performs a weighted summation of temporal series according to their coherence. The results are stacked time series which are cleaned up from incoherent noise, allowing the detection of weak signals that otherwise would be undistinguishable from noises. The method also enables the identification of the time (hour) of every periodic signal. The use of PWS in the analysis of cricketsÕ activity data cleared out frequencies, exposing a circadian component in all records.

EFFECTS OF 'SEEING' ON VECTOR MAGNETOGRAPH MEASUREMENTS

We present a study of the effects of atmospheric seeing on quantities derived from observations of solar polarized light – specifically, the vector magnetic flux and quantities derived from its magnitude and direction. Data from the Imaging Vector Magnetograph (‘IVM’) at the U. Hawaii/Mees Solar Observatory, are degraded by various degrees by applying a blur function to the ‘incoming light’, simulating a range of seeing conditions. A quantitative study of the resulting effects on derived quantities including total magnetic flux, vertical electric current density and magnetic shear angles, are discussed as a function of the imposed degradation. The generality of the seeing effects is explored by comparing the results from two different active regions; we find that the results are comparable for those quantities directly computed from the magnetic flux vector (e.g., summed, as in total flux) but less so for those quantities involving higher-order calculations (e.g., derivatives, as in vertical currents). We suggest that for temporal series data from any instrument, a method such as that which we outline here, be applied in order to model the uncertainties imposed on the data (in addition to instrumental uncertainties, etc.) due to seeing variations.

Initial effects of the toxic waste spill (Aznalcóllar mine accident) on the aquatic macrofauna of the Guadalquivir Estuary

The initial effects of the toxic waste spill in April 1998 at the Aznalcóllar mine (SW Spain) on the nektonic community of the Guadalquivir Estuary were examined at three sampling sites using univariate and multivariate techniques. Since studied communities showed a considerable seasonal trend, only seasonally homogenous periods were compared to analyse effects of the spill: May–August 1997 (before spill) and May–August 1998 (after spill). Results of both techniques (two-way nested ANOVA and ANOSIM tests, P>0.05) indicated that there was no significant difference between the nektonic community of the estuary before and after the spill (monthly number of species, abundance, biomass and similarity among samples). Conversely, an unusually high density was observed at the outer sampling site immediately after the spill for species typical of more stagnant estuarine habitats. This feature seems to indicate that the fauna in the estuarine area through which the untreated water penetrated into the main course may have been disturbed. Results also suggest that this initial sudden input of fresh water to the estuary could have enhanced the effects of an increased river flow (a drop in the salinity). Nevertheless, longer temporal series of data, especially for permanent estuarine inhabitants, are recommended before conclusions can be drawn on the effects of the toxic waste spill on estuarine communities.

Measurements of the Effects of Gravity Waves in the Middle Atmosphere Using Parametric Models of Density Fluctuations. Part I: Vertical Wavenumber and Temporal Spectra

Parametric models of spectral analysis offer several distinct advantages over statistical methods such as the correlogram analysis. These advantages include higher spectral resolution and the ability, in principle, to separate correlated (i.e., wave) behavior from noise-driven (i.e., turbulent) behavior in the measurements. Here parametric models are used to highlight the spatial and temporal intermittency of the gravity wave spectrum. In Part II of this series the spatial and temporal spectrum are used to calculate energy dissipation and the eddy diffusion coefficient. The spectra are computed from measurements of density fluctuations obtained using a large power-aperture product lidar during a 6-h period on 30 August 1994. It is shown that parametric models provide an excellent representation of the temporal and spatial data series. One difficulty of parametric models is selecting the model order, an analogous situation to determining the proper lag in the correlogram procedure or the window length in the periodogram method. Extensive experimentation has shown that the ratio of the data matrix eigenvalues to the photon noise eigenvalues is an excellent indicator for the selection of the model order. The underlying spectral form found using the parametric models is similar to the standard correlogram method, that is, nominal underlying spatial and temporal spectral slopes between −2 and −4 and −1.25 and −2, respectively, with variability outside this range. The spatial–temporal behavior of the spectra is highly variable with numerous intermittent and intense features rising well above the photon noise floor. The vertical wavenumber spectra on this night may show a variation of spectral slope with height; however, the slope is both extremely sensitive to the noise level of the data, steepening as the signal-to-noise level increases, and highly variable in time. The temporal spectra also show considerable variation with height, both in magnitude and slope.

Statistical analysis of facies clustering in submarine-fan turbidite successions

ABSTRACT The Hurst statistic, converted easily into a fractal dimension, quantifies the degree of clustering of high and low values in spatial or temporal series of data. In an effort to better understand the stratigraphic organization of submarine-fan deposits, the Hurst statistic was calculated for nineteen turbidite sections that span a wide range of geological time, tectonic settings, facies characteristics, and depositional environments. Three bed-by-bed variables were considered: coarse-division thickness (i.e., net thickness, in a single bed, of conglomerate + sandstone + siltstone), grain size, and coarse-division thickness percentage (relative to thickness of overlying mudstone caps). Sixteen of the 19 turbidite sections analyzed (84.2%) show the Hurst phenomenon, i.e., irregular, long-term clustering of high and low values of the three bed-by-bed variables. This clustering is related to stratigraphic changes of sedimentary facies caused by lateral shifting of sub-environments on a submarine-fan surface. There is no evidence that the clustering is controlled by sea-level fluctuations. The strength of the clustering, inferred from Hurst K values, holds promise as an index to distinguish submarine-fan sub-environments. Preliminary results suggest that channel-levee deposits tend to have strong clustering; lobe-interlobe deposits tend to display moderate clustering; and basin-floor sheet-sand systems tend to have weak clustering. Combining facies characteristics with these statistical results provides more reliable criteria for the identification of submarine-fan sub-environments than are available from recently discredited models based on asymmetric cycles of bed thickness or grain size.

Phytoplankton bloom and the vertical thermal structure of the upper ocean

Local heating rate within the oceanic mixed layer (ML) depends not only on the amount of solar radiation incident on the sea surface, but also on the vertical distribution of the irradiance in the water column. We have evaluated the effect of a phytoplankton bloom on mixed layer depth and temperature at a high latitude site near Iceland. The level 21~ version of the Mellor-Yamada (1982) turbulence scheme has been modified to include the vertical distribution of irradiance. This has allowed the investigation of the ML temperature and stability structure resulting from both physical and biological effects. An important part of the model is the parameterization of pigment-dependence which affects the spectral attenuation coefficient for downwelling irradiance as proposed by Morel (1988). Concurrent, high temporal resolution time series of physical and bio-optical data were used for the model. These data were acquired using a mooring deployed during the spring of 1989. We have estimated that the Increase of phytoplankton abundance induced an increase of the sea surface temperature by about 0.2”C at the mooring site. This led to stronger near-surface thermal stratification and shallower mixed layers. The dependence of the upper layer thermal structure on biology is more important when vertical mixing is weaker and when phytoplankton concentrations are higher.