bluuebunny/crossref_metadata_2025_split huggingface dataset:
Motion Artifact Reducing Reconstruction of 4D CT Image Data for the Analysis of Respiratory Dynamics
Authors: Ehrhardt J. , Frenzel T. , Säring D. , Lu W. , Low D. , Handels H. , Werner R. 
Published: May 2007

Summary

Objectives:
Respiratory motion represents a major problem in radiotherapy of thoracic and abdominal tumors. Methods for compensation require comprehensive knowledge of underlying dynamics. Therefore, 4D (= 3D + t) CT data can be helpful. But modern CT scanners cannot scan a large region of interest simultaneously. So patients have to be scanned in segments. Commonly used approaches for reconstructing the data segments into 4D CT images cause motion artifacts. In orderto reduce the artifacts, a new method for 4D CT reconstruction is presented. The resulting data sets are used to analyze respiratory motion.

Methods:
Spatiotemporal CT image sequences of lung cancer patients were acquired using a multi-slice CT in cine mode during free breathing. 4D CT reconstruction was done by optical flow based temporal interpolation. The resulting 4D image data were compared with data generated bythe commonly used nearest neighbor reconstruction. Subsequent motion analysis is mainly concerned with tumor mobility.

Results:
The presented optical flow-based method enables the reconstruction of 3D CT images at arbitrarily chosen points of the patient’s breathing cycle. A considerable reduction of motion artifacts has been proven in eight patient data sets. Motion analysis showed that tumor mobility differs strongly between the patients.

Conclusions:
Due to the proved reduction of motion artifacts, the optical flow-based 4D CT reconstruction offers the possibility of high-quality motion analysis. Because the method is based on an interpolation scheme, it additionally has the potential to enable the reconstruction of 4D CT data from a lesser number of scans.
Statistical Image Reconstruction for Inconsistent CT Projection Data
Authors: Oehler M. , Buzug T. M. 
Published: May 2007

Summary

Objectives:
The filtered backprojection is not able to cope with metal-induced inconsistencies in the Radon space which leads to artifacts in reconstructed CT images. A new algorithm is presented that reduces the drawbacks of existing artifact reduction strategies.

Methods:
Inconsistent projection data are bridged by directed interpolation. These projections are reconstructed using a weighted maximum likelihood algorithm (λ-MLEM). The correlation coefficient between images of a torso phantom marked with steel markers reconstructed with λ-MLEM and images of the same torso slice without markers quantifies the quality achieved. For clinical data, entropy maximization is presented to obtain appropriate weightings.

Results:
Different interpolation strategies have been applied. The quality of reconstruction sensitively depends on the complexity of interpolation. A directional interpolation gives best results. However, the quality of the images can be further improved byan appropriate weighing within λ-MLEM. This has been demonstrated with data from a torso phantom, a jaw with amalgam fillings and a hip prosthesis.

Conclusions:
λ-MLEM image reconstruction using data from directional Radon space interpolation is a new approach for metal artifact reduction. The weighting in this statistical approach is used to reduce the influence of residual inconsistencies in a way that optimal artifact suppression is obtained by optimizing a compromise between residual inconsistencies and void data. The image quality is superior compared with other artifact reduction strategies.
Interactive Diffusion-based Smoothing and Segmentation of Volumetric Datasets on Graphics Hardware
Authors: Langer C. , Fritz L. , Hadwiger M. , Wolfsberger S. , Bühler K. , Beyer J. 
Published: May 2007

Summary

Objective
: Volume segmentation with concurrent visualization is becoming an increasingly important part of medical diagnostics. This is due to the fact that the immediate visual feedback speeds up evaluation of the segmentation process, hence enhances segmentation quality. Therefore, our aim was to develop a method for volume segmentation and smoothing which achieves interactive performance on standard PCs and is useful in clinical practice (i.e. fast and of high quality).

Methods
: Our application is based on seeded region growing and nonlinear isotropic as well as anisotropic diffusion. We use current GPUs (graphics processing units) to speed up the computation of the diffusion process and use hardware-accelerated interactive volume rendering.

Results
: Using our approach the user can observe the diffusion process in real-time, change parameters interactively and view the result in a high-quality 3D direct volume rendering (DVR).

Conclusion
: The interactive nature of our algorithm and simultaneous visualization improved the usability of our segmentation and smoothing algorithm and proved useful in the clinical workflow. Using our application we were able to speed up the (an)isotropic diffusion process to achieve interactive performance.
Interactions between Simulated Tropical Cyclones and an Environment with a Variable Coriolis Parameter
Authors: Ritchie Elizabeth A. , Frank William M. 
Published: May 2007

Abstract
Numerical simulations of tropical cyclones are performed to examine the effects of a variable Coriolis parameter on the structure and intensity of hurricanes. The simulations are performed using the nonhydrostatic fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model using a 5-km fine mesh and fully explicit representation of moist processes. When a variable Conolis parameter ( f ) environment is applied to a mature tropical cyclone, a persistent north-northwesterly shear develops over the storm center as a result of an interaction between the primary circulation of the storm and the gradient in absolute vorticity. As a result, the variable-f storm quickly develops a persistent wavenumber-1 asymmetry in its inner-core structure with upward motion and rainfall concentrated on the left side of the shear looking downshear, in agreement with earlier studies. In comparison, the constant-f storm develops weak transient asymmetries in structure that are only partially related to a weak vertical wind shear. As a result, it is found that the tropical cyclone with variable f intensifies slightly more slowly than that with constant f, and reaches a final intensity that is about 5 mb weaker. It is argued that this “beta shear” is not adequately represented in large-scale analyses and so does not figure into calculations of environmental shear. Although the effect of the beta shear on the tropical cyclone intensity seems small by itself, when combined with the environmental shear it can produce a large net shear or it can reduce an environmental shear below the apparent threshold to impact storm intensity. If this result proves to be generally true, then the presence of an additional overlooked beta shear may well explain differences in the response of tropical cyclone intensification to westerly versus easterly shear regimes.
Kinematic Observations of Misocyclones along Boundaries during IHOP
Authors: Marquis James N. , Richardson Yvette P. , Wurman Joshua M. 
Published: May 2007

Abstract
During the International H2O Project, mobile radars collected high-resolution data of several 0.5–2-km-wide vertically oriented vortices (or misocyclones) along at least five mesoscale airmass boundaries. This study analyzes the properties of the misocyclones in three of these datasets—3, 10, and 19 June 2002—to verify findings from finescale numerical models and other past observations of misocyclones and to further the understanding of the role that they play in the initiation of deep moist convection and nonsupercell tornadoes. Misocyclones inflect or disjoint the swath of low-level convergence along each boundary to varying degrees depending on the size of their circulations. When several relatively large misocyclones are next to each other, the shape of low-level convergence along each boundary is arranged into a staircase pattern. Mergers of misocyclones are an important process in the evolution of the vorticity field, as a population of small vortices consolidates into a smaller number of larger ones. Additionally, merging misocyclones may affect the mixing of thermodynamic fields in their vicinity when the merger axis is perpendicular to the boundary. Misocyclones interact with linear and cellular structures in the planetary boundary layers (PBLs) of the air masses adjacent to each boundary. Cyclonic low-level vertical vorticity generated by both types of structures makes contact with each boundary and sometimes is incorporated into preexisting misocyclones. Intersections of either type of PBL structure with the boundary result in strengthened pockets of low-level convergence and, typically, strengthened misocyclones.
Comparison of 10-m Wind Forecasts from a Regional Area Model and QuikSCAT Scatterometer Wind Observations over the Mediterranean Sea
Authors: Accadia Christophe , Zecchetto Stefano , Lavagnini Alfredo , Speranza Antonio 
Published: May 2007

AbstractSurface wind forecasts from a limited-area model [the Quadrics Bologna Limited-Area Model (QBOLAM)] covering the entire Mediterranean area at 0.1° grid spacing are verified against Quick Scatterometer (QuikSCAT) wind observations. Only forecasts within the first 24 h in coincidence with satellite overpasses are used. Two years of data, from 1 October 2000 to 31 October 2002, have been considered, allowing for an adequate statistical assessment under different wind conditions. This has been carried out by analyzing the fields of the mean wind vectors, wind speed bias, correlation, difference standard deviation, steadiness, gustiness, and mean wind direction difference, in order to investigate spatial variability. Statistics have been computed on a seasonal basis. A comparison of satellite and forecast winds with measurements from three buoys was also performed. Some critical areas of the Mediterranean Sea where wind forecast quality is lower than average have been identified. Such areas correspond to semienclosed basins surrounded by important orography and to small regions at the lee side of the main islands. In open-sea regions the model underestimates wind strength from about 0.5 m s−1 in spring and summer to 1.0 m s−1 in winter, as evidenced by the existing biases against scatterometer data. Also, a wind direction bias (scatterometer minus model) generally between 5° and 15° exists. A survey of the identified and likely sources of forecast error is performed, indicating that orography representation plays an important role. Numerical damping is identified as a likely factor reducing forecast wind strength. The need for a correction scheme is envisaged to provide more accurate forcing for numerical sea state forecasting models, wind energy evaluation, and latent and/or sensible heat exchanges.
Urban Canopy Modeling of the New York City Metropolitan Area: A Comparison and Validation of Single- and Multilayer Parameterizations
Authors: Holt Teddy , Pullen Julie 
Published: May 2007

Abstract
High-resolution numerical simulations are conducted using the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS)1 with two different urban canopy parameterizations for a 23-day period in August 2005 for the New York City (NYC) metropolitan area. The control COAMPS simulations use the single-layer Weather Research and Forecasting (WRF) Urban Canopy Model (W-UCM) and sensitivity simulations use a multilayer urban parameterization based on Brown and Williams (BW-UCM). Both simulations use surface forcing from the WRF land surface model, Noah, and hourly sea surface temperature fields from the New York Harbor and Ocean Prediction System model hindcast. Mean statistics are computed for the 23-day period from 5 to 27 August (540-hourly observations) at five Meteorological Aviation Report stations for a nested 0.444-km horizontal resolution grid centered over the NYC metropolitan area. Both simulations show a cold mean urban canopy air temperature bias primarily due to an underestimation of nighttime temperatures. The mean bias is significantly reduced using the W-UCM (−0.10°C for W-UCM versus −0.82°C for BW-UCM) due to the development of a stronger nocturnal urban heat island (UHI; mean value of 2.2°C for the W-UCM versus 1.9°C for the BW-UCM). Results from a 24-h case study (12 August 2005) indicate that the W-UCM parameterization better maintains the UHI through increased nocturnal warming due to wall and road effects. The ground heat flux for the W-UCM is much larger during the daytime than for the BW-UCM (peak ∼300 versus 100 W m−2), effectively shifting the period of positive sensible flux later into the early evening. This helps to maintain the near-surface mixed layer at night in the W-UCM simulation and sustains the nocturnal UHI. In contrast, the BW-UCM simulation develops a strong nocturnal stable surface layer extending to approximately 50–75-m depth. Subsequently, the nocturnal BW-UCM wind speeds are a factor of 3–4 less than W-UCM with reduced nighttime turbulent kinetic energy (average &lt; 0.1 m2 s−2). For the densely urbanized area of Manhattan, BW-UCM winds show more dependence on urbanization than W-UCM. The decrease in urban wind speed is most prominent for BW-UCM both in the day- and nighttime over lower Manhattan, with the daytime decrease generally over the region of tallest building heights while the nighttime decrease is influenced by both building height as well as urban fraction. In contrast, the W-UCM winds show less horizontal variation over Manhattan, particularly during the daytime. These results stress the importance of properly characterizing the urban morphology in urban parameterizations at high resolutions to improve the model’s predictive capability.
Short-Range Probabilistic Quantitative Precipitation Forecasts over the Southwest United States by the RSM Ensemble System
Authors: Yuan Huiling , Mullen Steven L. , Gao Xiaogang , Sorooshian Soroosh , Du Jun , Juang Hann-Ming Henry 
Published: May 2007

Abstract
The National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) is used to produce twice-daily (0000 and 1200 UTC), high-resolution ensemble forecasts to 24 h. The forecasts are performed at an equivalent horizontal grid spacing of 12 km for the period 1 November 2002 to 31 March 2003 over the southwest United States. The performance of 6-h accumulated precipitation is assessed for 32 U.S. Geological Survey hydrologic catchments. Multiple accuracy and skill measures are used to evaluate probabilistic quantitative precipitation forecasts. NCEP stage-IV precipitation analyses are used as “truth,” with verification performed on the stage-IV 4-km grid. The RSM ensemble exhibits a ubiquitous wet bias. The bias manifests itself in areal coverage, frequency of occurrence, and total accumulated precipitation over every region and during every 6-h period. The biases become particularly acute starting with the 1800–0000 UTC interval, which leads to a spurious diurnal cycle and the 1200 UTC cycle being more adversely affected than the 0000 UTC cycle. Forecast quality and value exhibit marked variability over different hydrologic regions. The forecasts are highly skillful along coastal California and the windward slopes of the Sierra Nevada Mountains, but they generally lack skill over the Great Basin and the Colorado basin except over mountain peaks. The RSM ensemble is able to discriminate precipitation events and provide useful guidance to a wide range of users over most regions of California, which suggests that mitigation of the conditional biases through statistical postprocessing would produce major improvements in skill.
High-Resolution Observations of the Trowal–Warm-Frontal Region of Two Continental Winter Cyclones
Authors: Grim Joseph A. , Rauber Robert M. , Ramamurthy Mohan K. , Jewett Brian F. , Han Mei 
Published: May 2007

Abstract
This paper compares the structure of the trough of warm air aloft (trowal)–warm-frontal region of two continental wintertime cyclones. The cyclones were observed over the central Great Lakes region during the Lake-Induced Convection Experiment/Snowband Dynamics Project field campaign. The cyclones had different origins, with the first forming east of the Colorado Rockies and the second forming over the Gulf of Mexico. They were associated with different upper-level flow regimes, one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet. Both storms produced heavy swaths of snow across the states of Illinois, Wisconsin, and Michigan. High-resolution observations of frontal structure were made during flights of the National Center for Atmospheric Research Electra aircraft using dropsondes and the Electra Doppler Radar tail radar system. The high-resolution observations suggest a different arrangement of air masses in the trowal region compared with the classical occlusion model, where the trowal axis forms at the intersection of a warm front and a cold front that has overtaken and subsequently ascended the warm front. In both cyclones dry air intruded over the warm front, isolating the warm, moist airflow within the trowal airstream. Very sharp moisture gradients were present at the leading edge of the dry air in both cyclones. In each case, relative humidity differences of over 50% were observed over distances of 10–20 km. The thermal gradient near the leading edge of the dry air in one cyclone was diffuse, so that the moist–dry boundary could best be characterized as an upper-level humidity front. In the other cyclone, the thermal gradient was sharper and aligned with the moisture boundary and was best characterized as a cold front aloft. The analyses suggest that the classical conceptual model of the trowal, at least in some cyclones such as the two illustrated here, needs to be revised to include the possibility that the warm moist airstream aloft may sometimes be bounded on its south side by an upper-level front rather than a surface-based cold front. Since the two cyclones discussed here had different origins, tracks, and flow regimes, the similarity of their structure suggests that these features may be common.
Further Results on the Sensitivity of Simulated Storm Precipitation Efficiency to Environmental Temperature
Authors: Cohen Charles , McCaul Eugene W. 
Published: May 2007

Abstract
A method is devised for diagnosing the condensation rate in simulations using the Regional Atmospheric Modeling System (RAMS) model, where ice-liquid water potential temperature is a prognostic variable and an iterative procedure must be used to diagnose the temperature and water vapor mixing ratio from ice-liquid water potential temperature. The condensation rate is then used to compute the microphysical precipitation efficiency (PE), which is defined as the ratio of the precipitation rate at the ground to the sum of the condensation and deposition rates. Precipitation efficiency is compared for pairs of numerical simulations, initialized with soundings having all key environmental parameters identical except for their temperature. The authors’ previous study showed that with a colder initial sounding, the conversion of cloud water to precipitation is relatively inefficient, but updrafts are stronger and there is relatively less evaporation of precipitation, with the net result being a larger climatological PE in the colder environment. Here, the authors consider the time lag between condensation and precipitation and demonstrate that in calculating a properly lagged microphysical PE, the combined effect of the decreased production of precipitation and the decreased evaporation is that the temperature of the initial soundings has no significant influence on the microphysical PE. To the authors’ knowledge, this is the first time that the lag has been used to compute PE. These results concerning PE are relevant only to deep convection.
Numerical Simulations of the Effects of Coastlines on the Evolution of Strong, Long-Lived Squall Lines
Authors: Lericos Todd P. , Fuelberg Henry E. , Weisman Morris L. , Watson Andrew I. 
Published: May 2007

Abstract
This study develops conceptual models of how a land–water interface affects the strength and structure of squall lines. Two-dimensional numerical simulations using the Advanced Regional Prediction System model are employed. Five sets of simulations are performed, each testing eight wind shear profiles of varying strength and depth. The first set of simulations contains a squall line but no surface or radiation physics. The second and third sets do not contain a squall line but include surface and radiation physics with a land surface on the right and a water surface on the left of the domain. The land is either warmer or cooler than the sea surface. These three simulations provide a control for later simulations. Finally, the remaining two simulation sets examine squall-line interaction with a relatively cool or warm land surface. The simulations document the thermodynamic and shear characteristics of squall lines interacting with the coastline. Results show that the inclusion of a land surface did not sufficiently affect the thermodynamic properties ahead of the squall line to change its overall structure. Investigation of ambient shear ahead of the squall line revealed that the addition of either warm or cool land reduced the strength of the net circulation in the inflow layer as measured by ambient shear. The amount of reduction in shear was found to be directly proportional to the depth and strength of the original shear layer. For stronger and deeper shears, the reduction in shear is sufficiently great that the buoyancy gradient circulation at the leading edge of the cold pool is no longer in balance with the shear circulation leading to changes in squall-line updraft structure. The authors hypothesize two ways by which a squall line might respond to passing from water to land. The weaker and more shallow the ambient shear, the greater likelihood that the squall-line structure remains unaffected by this transition. Conversely, the stronger and deeper the shear, the greater likelihood that the squall line changes updraft structure from upright/downshear to upshear tilted.
A Convective Line with Leading Stratiform Precipitation from BAMEX
Authors: Storm Brandon A. , Parker Matthew D. , Jorgensen David P. 
Published: May 2007

Abstract
On 31 May 2003, a front-fed convective line with leading stratiform precipitation (FFLS) was observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). The high-resolution BAMEX measurements provided one of the first opportunities to thoroughly observe the characteristics of an FFLS system. The 31 May system had an overturning updraft during its early stages, and produced leading stratiform precipitation. As the system matured, a jump updraft developed and the system began to produce trailing stratiform precipitation. It appears that this transition was facilitated by a local decrease in the low-level line-perpendicular vertical wind shear over time, as well as an increase in the surface cold pool’s strength. The BAMEX data further help to address the question of how FFLS systems can be long lived when their inflow passes through the line-leading precipitation: preline soundings suggest a destabilization mechanism resulting from the vertical profile of cooling within the leading stratiform precipitation. This destabilization also helps to explain the 31 May convective system’s persistence in an environment with very low CAPE.