Frontal Features Research Articles

Characterizing behavioral and cognitive dysexecutive changes in progressive supranuclear palsy

Frontal lobe dysfunction is a prominent feature of many neurological disorders. Early diagnosis may be enhanced by establishing a profile of cognitive, behavioral, and emotional change. Traditional psychometric assessment focuses on cognitive dysfunction and fails to identify behavioral changes, particularly those associated with orbitofrontal dysfunction. We examined progressive supranuclear palsy (PSP), a prototypical subcortical dementia with frontal features, using commonly available neuropsychological measures and a modification of the Katz Adjustment Scale-Relatives (KAS-R), an instrument first developed to assess dysexecutive changes in head-injured patients. Executive tests identified deficits in reasoning, planning, set shifting, verbal fluency, information processing speed, and response initiation. On the KAS-R, changes in apathy, social withdrawal, and independence were observed, with little change in belligerence, social irresponsibility, uncooperativeness, obstreperousness, anxiety, and depression. The results show the potential utility of this instrument in characterizing behavioral and emotional changes associated with frontal lobe dysfunction in neurodegenerative disease.

Summary of Convective Storm Initiation and Evolution during IHOP: Observational and Modeling Perspective

Abstract The data-rich International H2O Project (IHOP_2002) experiment is used to study convective storm initiation and subsequent evolution for all days of the experiment. Initiation episodes were almost evenly divided between those triggered along surface-based convergence lines and elevated initiation episodes that showed no associated surface convergence. The elevated episodes occurred mostly at night, and the surface-based episodes occurred during the afternoon and evening. Surface-based initiations were mostly associated with synoptic fronts and gust fronts and less so with drylines and bores. Elevated initiations were frequently associated with observable convergent or confluent features in the Rapid Update Cycle (RUC) wind analysis fields between 900 and 600 hPa. The RUC10 3-h forecast of the precipitation initiation episodes were correct 44% of the time, allowing a tolerance of 250 km in space and for the forecast being early by one period. However, the accuracy was closely tied to the scale of the initiation mechanism, being highest for synoptic frontal features and lowest for gust fronts. Gust fronts were a primary feature influencing the evolution of the initiated storms. Almost one-half of the storm complexes associated with initiation episodes did not produce surface gust fronts. Storm systems that did not produce gust fronts most often lived 2–6 h while those that did frequently lived at least 8 h. The largest and longest-lived storm complexes had well-developed intense gust fronts that influenced the propagation of the storm system. The RUC10 was generally not successful in forecasting the evolution and motion of the larger, more intense storm complexes; presumably this was because it did not produce strong gust fronts. Implications for forecasting convective storm initiation and evolution are discussed.

Transition of a synoptic system to a polar low via interaction with the orography of Greenland

A case study of a polar low that occurred over the Labrador Sea from December 29–31, 1997 was performed using the Penn State—NCAR Mesoscale Model version 5 (MM5). The polar low was imaged by the synthetic aperture radar (SAR) on the RADARSAT-1 satellite and as a result, unique high resolution information on the polar low’s surface expression is available. This low is also of interest as it formed from a synoptic-scale low pressure system that underwent a bifurcation through an interaction with the topography of Greenland. Our model results showthat the polar lowachieved a minimum central pressure of 954 hPa with maximum 10 m wind speeds in excess of 30 ms−1. Coincident SSM/I data are in agreement with the model surface wind speed field. Sensitivity studies showed that the genesis of the low was relatively insensitive to air—sea fluxes of sensible and latent heat. The model precipitation field indicates the presence of features reminiscent of rainbands observed to occur in association with tropical cyclones, as well as frontal features typically seen in mid-latitude baroclinic systems. In addition, our model results indicate that precipitation as well as the surface wind contributes to the polar low’s surface expression as imaged by SAR.

Trophodynamics of selected mesozooplankton in the west-Indian sector of the Polar Frontal Zone, Southern Ocean

Mesozooplankton community structure and grazing impact were investigated at 15 stations in the west-Indian sector of the Polar Frontal Zone during the third dynamics of Eddie impacts on Marion’s ecosystem cruise, conducted during April 2004. An intense frontal feature, likely the convergence of the Sub-Antarctic and Antarctic Polar Fronts, was identified running in a north-eastward direction across the survey area. Total integrated chlorophyll-a (chl-a) biomass ranged from 4.15 mg m−2 to 22.81 mg m−2 and was dominated by picophytoplankton at all stations. Mesozooplankton abundances ranged from 163.84 ind m−2 to 2,478.08 ind m−2 and biomass between 6.70 mg Dwt. m−2 and 23.40 mg Dwt. m−2. The mesozooplankton community was dominated almost entirely by copepods, which contributed between 35% and 79% (mean=63%; SD=±12%) of the total numbers. The pteropoda, Limacina retroversa, contributed up to 30% (mean=10%; SD=± 8%) of the total numbers. Numerical analysis identified two distinct mesozooplankton communities separated by the intense frontal feature, namely the Antarctic and the Sub-Antarctic Zone Groups. Ingestion rates of the four numerically dominant copepod species (Calanus simillimus, Clausocalanus spp., Ctenocalanus spp. and Oithona similis) and the pteropod, L. retroversa, were estimated using the gut fluorescence technique. Total grazing impact ranged from 0.156 mg (pigm) m−2 to 2.958 mg (pigm) m−2 or between 1% and 29% of the available chl-a per day. The four copepods contributed approximately 36% of the total daily grazing impact, while the pteropod contributed to a mean of 64%, indicating that this zooplankton group may play an important role in the Southern Ocean carbon cycle. In general, the highest daily grazing impact was exhibited in the Antarctic Zone Group (mean=12% phytoplankton standing stock per day).

Processes controlling the position of frontal systems in Shark Bay, Western Australia

Shark Bay is a large inverse estuary on the west coast of Australia. Analytical and numerical approaches were used to predict the locations and causes of fronts in Shark Bay, and the results were compared with Sea Surface Temperature and field data. The study first applies an analytical theory, widely used in studies of traditional estuaries, to predict the location of fronts, and then applies a 3-D, baroclinic hydrodynamic model to analyze advection of temperature and salinity, and their ultimate influence on density fronts within the Bay. Analytical theory defines a front as a transitional region between mixed and stratified conditions, and it postulates that the location of fronts may be predicted through the balance of stratifying and de-stratifying energy input to the water column, ‘the stratification parameter’. In Shark Bay, fronts are predicted where the stratification parameter, S = 3.0. Furthermore, the distribution of the mean tidal velocity magnitude was determined to correlate to regions of high bathymetric gradients, showing that changes in water depth influence the local tidal currents, the value of the stratification parameter and by extension, the location of the fronts. However, calculation of the balance of all major energy inputs reveals a balance between evaporation-driven gravitational flow and tidal mixing in Shark Bay. A numerical model was then used to investigate the hydrodynamic processes contributing to frontal dynamics in Shark Bay. Predicted residual velocities revealed a two-layer flow regime and temperature and salinity simulations accurately reproduced the major frontal features observed at the entrances of the Bay using only tidal forcing and gravitational circulation. However, it was found that wind forcing clearly influenced the distribution of salinity, defining the shape of the major frontal feature inside the Bay.

Image-Based 3D Face Modeling System

This paper describes an automatic system for 3D face modeling using frontal and profile images taken by an ordinary digital camera. The system consists of four subsystems including frontal feature detection, profile feature detection, shape deformation, and texture generation modules. The frontal and profile feature detection modules automatically extract the facial parts such as the eye, nose, mouth, and ear. The shape deformation module utilizes the detected features to deform the generic head mesh model such that the deformed model coincides with the detected features. A texture is created by combining the facial textures augmented from the input images and the synthesized texture and mapped onto the deformed generic head model. This paper provides a practical system for 3D face modeling, which is highly automated by aggregating, customizing, and optimizing a bunch of individual computer vision algorithms. The experimental results show a highly automated process of modeling, which is sufficiently robust to various imaging conditions. The whole model creation including all the optional manual corrections takes only 2 3 minutes.

Application of an edge detection method to satellite images for distinguishing sea surface temperature fronts near the Japanese coast

This study applies an edge detection method to satellite sea surface temperature (SST) images in order to distinguish SST fronts frequently occurring near the Japanese coast. First, we develop a new set of edge detection algorithms. The method is based on an entropic approach using Jensen–Shannon divergence, which is certified as a robust technique for detecting edge pixel candidates. Additionally, we incorporate ridge-line extraction morphological filter to obtain edge pixels, which is suited to delineate intricate frontal features. The methodology allows us to detect reasonable amount of possible fronts to the fullest extent according to the original image resolution. Therefore, it enables us to analyze finer-scale fronts near the coast as well as larger-scale fronts associated with major currents. Then, we present four case study examples of SST fronts near the Japanese coast by applying the method to Advanced Very High Resolution Radiometer (AVHRR) SST images with a grid size of 0.01°. We describe the configuration and seasonal variability of the SST frontal systems from the viewpoint of occurrence probability, SST gradient magnitude, and orientation to the local bathymetry as compared with the previous observational studies. Consequently, it is demonstrated that application of the method can derive new views of finer-scale and highly variable SST fronts. Moreover, this study first verifies the capability of comprehensive and statistical description of SST front configurations and variations near the Japanese coast by applying edge detection method to sequences of satellite SST images.

Seasonal variability of near‐surface hydrography and frontal features in the northern Gulf of Alaska and Prince William Sound

The meridional structure and seasonal cycles of near‐surface hydrography and frontal features in the northern Gulf of Alaska and Prince William Sound are described from high‐resolution measurements of near‐surface temperature and salinity acquired by a vessel‐mounted thermosalinograph. Near‐surface temperature exhibits a well‐defined seasonal cycle with little variation between basin and shelf waters. Near‐surface salinity exhibits a well‐defined seasonal cycle that is confined largely to the shelf waters reflecting the influence of coastal freshwater inputs. Prominent near‐surface fronts at the shelf break, at the entrance to Prince William Sound, and in northern Prince William Sound intensify and weaken following the seasonal cycles of freshwater discharges into the northern Gulf of Alaska. These respective fronts are maintained by freshwater from the Alaska Coastal Current, the Copper River, and the snowfields and glaciers of northern Prince William Sound.

Predicting the distribution of crabeater seals Lobodon carcinophaga off east Antarctica during the breeding season

Predictive species-environment models have numerous ecological and management applications, and can provide insight into the functional relationships between a species and its envi- ronment. Generalised linear models were used to develop predictive models of crabeater seal Lobo- don carcinophaga distribution during the breeding season in relation to physical-oceanographic and ice-cover variables. Models were constructed from data collected on shipboard surveys in the pack- ice off east Antarctica between 50 and 115° E from 1985 to 1987, and were tested from surveys in the same region from 1995 to 1997. Models of presence selected ocean depth as the only significant phys- ical-oceanographic predictor variable for both breeding and non-breeding seals. Seals were most likely to be present on the ice at moderate ocean depths of approximately 2500 m. Unlike non-breed- ing seals, breeding seals were all but absent on the ice associated with depths of >4000 m. The pre- dicted distribution of presence comprised a band delineated by the shelf-break to the south and extending northwards for 1.5 to 5° latitude, with non-breeding seals having a more northerly limit than breeding seals. This band is coincident with the known distribution of the crabeater seals' pri- mary food source (Antarctic krill), and also coincides with frontal features such as the Antarctic slope front and the southern boundary of the Antarctic Circumpolar Current, which are considered to be areas of enhanced primary and secondary productivity. The presence-depth models were improved by the inclusion of ice-cover variables. Breeding seals may avoid areas with a high proportion of all ice as floes <20 m in size, because the chance of successfully weaning a pup in such areas is low.

Physical and biological variables affecting seabird distributions during the upwelling season of the northern California Current

Abstract As a part of the GLOBEC-Northeast Pacific project, we investigated variation in the abundance of marine birds in the context of biological and physical habitat conditions in the northern portion of the California Current System (CCS) during cruises during the upwelling season 2000. Continuous surveys of seabirds were conducted simultaneously in June (onset of upwelling) and August (mature phase of upwelling) with ocean properties quantified using a towed, undulating vehicle and a multi-frequency bioacoustic instrument (38–420 kHz). Twelve species of seabirds contributed 99% of the total community density and biomass. Species composition and densities were similar to those recorded elsewhere in the CCS during earlier studies of the upwelling season. At a scale of 2–4 km, physical and biological oceanographic variables explained an average of 25% of the variation in the distributions and abundance of the 12 species. The most important explanatory variables (among 14 initially included in each multiple regression model) were distance to upwelling-derived frontal features (center and edge of coastal jet, and an abrupt, inshore temperature gradient), sea-surface salinity, acoustic backscatter representing various sizes of prey (smaller seabird species were associated with smaller prey and the reverse for larger seabird species), and chlorophyll concentration. We discuss the importance of these variables in the context of what factors seabirds may use to find food. The high seabird density in the Heceta Bank and Cape Blanco areas indicates them to be refuges contrasting the low seabird densities currently found in most other parts of the CCS, following decline during the recent warm regime of the Pacific Decadal Oscillation.

Atmospheric front over the East China Sea studied by multisensor satellite and in situ data

A frontal feature visible on a synthetic aperture radar (SAR) image acquired by the Radarsat satellite over the East China Sea on 19 November 2000 is analyzed in conjunction with data acquired by Quikscat, TOPEX/Poseidon, Tropical Rain Measurement Mission (TRMM), Defense Meteorological Satellite Program (DMSP), and National Oceanic and Atmospheric Administration (NOAA) satellites, and with data obtained from ship measurements. Although this frontal feature is located close to the Kuroshio front, it is demonstrated that it is not a sea surface manifestation of an oceanic front, but rather of an atmospheric front extending over 800 km from an area of the Pacific Ocean northeast of Taiwan to the southern coast of Korea. It is a cold front moving in the southeast direction with a speed of approximately 45–50 km/hour and associated with a 40‐km‐wide rainband trailing the front. The Radarsat image, which has a resolution of 50 m, reveals fine‐scale structures of the atmospheric front, in particular small‐scale convective rain cells embedded in the front. Conclusion is drawn that accurate interpretation of frontal features in SAR images requires use of additional meteorological and remote sensing data and information.

Acoustic Mode Coupling by Nonlinear Internal Wave Packets in a Shelfbreak Front Area

A computational case study of coupled-mode 400-Hz acoustic propagation over the distance 27 km on the continental shelf is presented. The mode coupling reported here is caused by lateral gradients of sound-speed within packets of nonlinear internal waves, often referred to as solitary wave packets. In a waveguide having unequal attenuation of modes, directional exchange of energy between low- and high-loss modes, via mode coupling, can become time dependent by the movement of waves and can cause temporally variable loss of acoustic energy into the bottom. Here, that bottom interaction effect is shown to be sensitive to stratification conditions, which determine waveguide properties and, in turn, determine modal attenuation coefficients. In particular, time-dependent energy loss due to the presence of moving internal wave packets is compared for waveguides with and without a frontal feature similar to that found at the shelfbreak south of New England. The mean and variability of acoustic energy level 27 km distant from a source are shown to be altered in a first order way by the presence of the frontal feature. The effects of the front are also shown to be functions of source depth.

On the CO2 exchange between the atmosphere and the biosphere: the role of synoptic and mesoscale processes

Estimating global carbon fluxes by inverting atmospheric CO2 through the use of atmospheric transport models has shown the importance of the covariance between biospheric fluxes and atmospheric transport on the carbon budget. This covariance or coupling occurs on many time scales. This study examines the coupling of the biosphere and the atmosphere on the meso- and synoptic scales using a coupled atmosphere—biosphere regional model covering Canada. The results are compared with surface and light aircraft measurement campaigns at two boreal forest sites in Canada (Fraserdale and BERMS).Associated with cold and warm frontal features, the model results showed that the biospheric fluxes are strongly coupled to the atmosphere through radiative forcing. The presence of cloud near frontal regions usually results in reduced photosynthetic uptake, producing CO2 concentration gradients across the frontal regions on the order of 10 parts per million (ppm). Away from the frontal region, the biosphere is coupled to the mesoscale variations in similar ways, resulting in mesoscale variations in CO2 concentrations of about 5 ppm.The CO2 field is also coupled strongly to the atmospheric dynamics. In the presence of frontal circulation, the CO2 near the surface can be transported to the mid to upper troposphere. Mesoscale circulation also plays a significant part in transporting the CO2 from the planetary boundary layer (PBL) to the mid-troposphere. In the absence of significant mesoscale or synoptic scale circulation, the CO2in the PBL has minimal exchange with the free troposphere, leading to strong gradients across the top of the PBL. We speculate that the ubiquity of the common synoptic and mesoscale processes in the atmosphere may contribute significantly to the rectifier effect and hence CO2 inversion calculations.

On the role of biological dynamics in plankton patchiness at the mesoscale: An example from the eastern North Atlantic Ocean

In situations where the direct physical forcing of biological processes, through nutrient supply or light limitation of phytoplankton, does not show significant spatial variability, it is demonstrated that the effects of the mesoscale circulation and population dynamics on plankton patchiness are in principle, separable. In this case, the physical stirring and mixing control the size and shape of structures seen in plankton distributions, whilst the biological dynamics controls the size of the populations within those structures. This is demonstrated using field observations and a simple process model. The field data, which come from mesoscale surveys of a region (16 -20W, 46 - 49N) in the eastern North Atlantic during April-May 1997, provide simultaneous continuous measurements of hydrography, phytoplankton and three size classes of zooplankton with the same spatiotemporal resolution and sampling. The lack of significant spatial variability in the physical forcing arises due to the absence of any strong frontal features in the area and to the fact that storm mixing maintained nutrient levels above limiting values throughout the surveys. When the observed biological parameters are plotted in phase space, a close relationship between constituents of the ecosystem is revealed that is missed by other data analysis techniques. In particular, this approach provides an explanation of how zooplankton and phytoplankton can be simultaneously positively and negatively correlated at different sites in a region and yet still tightly coupled. It is further demonstrated that the much-maligned standard feature of surveying plankton patchiness at the mesoscale - asynopticity in sampling - actually assists in the extraction of the phase space relationships.

Nonconvulsive status epilepticus with frontal features: quantitating severity of subclinical epileptiform discharges provides a marker for treatment efficacy, recurrence and outcome

Nonconvulsive status epilepticus (NCSE) is difficult to diagnose but is an important cause of cognitive impairment. Electroencephalogram (EEG) monitoring is required for diagnosis and treatment. Little is known regarding the stability of subclinical epileptiform discharges (SEDs) preceding NCSE nor what strategies may optimize patient outcomes. We report extended follow-up of patients with recurrent frontal SEDs, integrating EEG and cognitive findings before and following treatment of NCSE, and show that quantitating SED severity provides an objective marker of treatment efficacy and recurrence.

Spatial Processing of Range-Bin ADCP Data to Resolve Small-Scale Frontal Features

Abstract A new approach is proposed for the processing of acoustic Doppler current profiler (ADCP) data that has the potential to better resolve the structure of small-scale dynamical features such as strongly convergent current fronts. The essence of this approach is to assign each range bin of radial velocity and backscatter data an x, y, and z position, and then to spatially average the bin data relative to the feature of interest. The approach is illustrated by an analysis of surface-towed ADCP data collected across the Connecticut River plume front. Results using an across-front averaging length of 5 m show that the frontal morphology and circulation (gravity-current head structure, shallow inflow layer, strong sinking motion) are consistently resolved, while 1-m averaging appears additionally to resolve flow instabilities occurring along the frontal interface. Other possible applications are briefly discussed.

Satellite observations of bloom events in the Strait of Ombai: Relationships to monsoons and ENSO

Persistent phytoplankton bloom events, surface cooling, and associated fronts in the Strait of Ombai were seen by Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS), Advanced Very High Resolution Radiometer (AVHRR), and Synthetic Aperture Radar (SAR) imagery. It is suggested that the cooling events were caused by variable flow through the strait and its interaction with complex bathymetry. During the strongest cooling events a sharp, midstrait frontal feature was seen with a cross‐front gradient in sea surface temperature (SST) of the order of 4°C and a gradient in chlorophyll concentration of over 1 mg/m3. The frontal feature, associated with increased ocean color signal, extended, during major events, 100s of kilometers downstream of the strait and at times influenced nearly all of the Savu Sea. We show that variability in the bloom events can be tied to seasonal monsoons, ENSO, and their effect on thermocline depth.

Salp/krill interactions in the Southern Ocean: spatial segregation and implications for the carbon flux

Available data on the spatial distribution and feeding ecophysiology of Antarctic krill, Euphausia superba, and the tunicate, Salpa thompsoni, in the Southern Ocean are summarized in this study. Antarctic krill and salps generally display pronounced spatial segregation at all spatial scales. This appears to be the result of a clear biotopical separation of these key species in the Antarctic pelagic food web. Krill and salps are found in different water masses or water mass modifications, which are separated by primary or secondary frontal features. On the small-scale (o100 km), Antarctic krill and salps are usually restricted to the specific water parcels, or are well segregated vertically. Krill and salp grazing rates estimated using the in situ gut fluorescence technique are among the highest recorded in the Antarctic pelagic food web. Although krill and salps at times may remove the entire daily primary production, generally their grazing impact is moderate (p50% of primary production). The regional ecological consequences of years of high salp densities may be dramatic. If the warming trend, which is observed around the Antarctic Peninsula and in the Southern Ocean, continues, salps may become a more prominent player in the trophic structure of the Antarctic marine ecosystem. This likely would be coupled with a dramatic decrease in krill productivity, because of a parallel decrease in the spatial extension of the krill biotope. The high Antarctic regions, particularly the Marginal Ice Zone, have, however, effective physiological mechanisms that may provide protection against the salp invasion. r 2002 Elsevier Science Ltd. All rights reserved.

Hybrid Classification for Face Recognition with Virtual Samples and Ensemble Neural Networks

Abstract This paper presents a novel hybrid classifier with artificially generated virtual training samples for face recognition. Our approach obtains a synergy effect by combining the results of two heterogeneous classifiers, and utilizes the nearest neighbor approach in feature angle space and a connectionist model. The first is a classifier called the nearest feature angle (NFA) based on angular information, which finds the most similar to the query from a given training set. The second is a classifier based on the recall of stored frontal projection of input features using a frontal recall network (FRN) that finds the most similar frontal one among the stored frontal feature set. For FRN, we used an ensemble neural network consisting of multiple MultiLayer Perceptrons (MLPs), each of which is trained independently to enhance generalization capability. Further, both classifiers used a virtual training set generated adaptively according to the spatial distribution of each person’s training samples. Fina...

Phytoplankton and microzooplankton variability between the Subtropical and Polar Fronts south of Australia: Thriving under regenerative and new production in late summer

Phytoplankton, microzooplankton were studied along a 42°–55°S, 141°–143°E transect in March 1998 and compared with production‐related parameters (carbon biomass, chlorophyll a, nitrogen and carbon uptake, and ƒ ratios). The transect crossed the Subtropical Front (STF), the Subantarctic Front (SAF), and the Polar Front (PF). Phytoplankton assemblages were dominated by nano‐ and pico‐sized flagellates; their peak numbers (nanoflagellates: 8.2×105 cells L−1) occurred in the areas of STF and within the Subantarctic Zone (SAZ). North of the SAF, dinoflagellates were next in abundance. Diatoms exceeded dinoflagellates in the PF area (maximum 1.26×105 cells L−1). Dinoflagellates were dominated by nano‐sized gymnodinioid forms with microplanktonic species increasing in numbers in SAZ and STF. Diatoms contained mainly Fragilariopsis pseudonana and Pseudonitzschia lineola; several abundant species exibited a latitudinally restricted distribution. Phytoplankton carbon biomass was dominated by dinoflagellates (including &gt;20 μm heterotrophs) representing 48 to 84% of total cell carbon. Maxima of 18–26 μg C L−1 occured both at STF and PF. Heterotrophic dinoflagellates and ciliates showed similar distributions. Their peaks of cell densities and carbon in STF and SAZ were associated with phytoplankton maxima. Microzooplankton cell distribution and biomass suggest they are major grazers and contributors to carbon flow. Phytoplankton assemblages represented at least three stages with different relative contributions of regenerative and new production. Production related parameters (e.g., low ƒ ratio and high NH4+ uptake) point to the presence of regenerative community at the STF. It attracted the highest concentration of microzooplankton. The phytoplankton community associated with a frontal feature (46°–47°S) within the SAZ, thrived under increased new production (e.g., relatively higher ƒ ratio and NO3− uptake). The community along 47°–55°S was characterized by intermediate ƒ ratios, with slight predominance of regenerated production. Southward of 47°S, the relative contribution of new production increased.